Contribution
  • Michael Benisch
  • Christian Vogt
  • Rolf Rascher
  • O. Fähnle
Octopus: A simple and effective tool for polishing slurry monitoring
  • 2020

DOI: 10.1117/12.2567952

The present paper shows a way for a cost-effective, integrated measurement of the density p of polishing suspensions. It is based on the principle of measuring the turbidity of a solution on the basis of the light transmitted through it, and of calculating back to the density on the basis of the turbidity. The tool is suitable for monitoring polishing agents and for detecting when the density of the polishing slurry leaves the permissible parameter space and can perspectively enable the automated monitoring and adjustment of polishing suspensions. The tool is named after an Octopus. These animals have amazing abilities, for example they can copy the behaviour of other sea animals or act with a plan. Their tentacles each have their own brain and can perform biochemical analyses.
JournalArticle
  • Armin Reif
  • P. Rinck
  • Sebastian Sitzberger
  • Rolf Rascher
  • M. Zäh
Zerspanung von Hochleistungswerkstoffen mit ultrasonisch modulierter Schnittgeschwindigkeit , vol115
  • 2020

DOI: 10.3139/104.112255

Die steigenden Anforderungen an die Festigkeit und die Qualität von Bauteilen und die damit verbundene Verwendung hochfester Materialien erfordert die Weiterentwicklung neuer wirtschaftlicher Zerspanungstechniken. Durch eine werkzeugseitige Schwingungsüberlagerung können bei der Bearbeitung von schwer zerspanbaren Werkstoffen die Zerspankräfte und der Werkzeugverschleiß reduziert sowie die Oberflächenqualität verbessert werden.
Contribution
  • Michael Benisch
  • O. Fähnle
  • Rolf Rascher
Application of a pressure measuring film for pressure observation in overarm polishing
  • 2020

DOI: 10.1051/epjconf/202023803003

In previous publications the inhomogeneous pressure transfer through the polishing tool onto a glass surface could be shown. This experiment shows polishing trials with different polishing materials and the differences in the homogeneity of the pressure transfer through them. Only the properties of the material will be discussed explicitly, the change of the tool constitution through the process will be part of further publications.
Contribution
  • Simon Killinger
  • Johannes Liebl
  • Rolf Rascher
Interferometric measurement with robot kinematics
  • 2020

DOI: 10.1117/12.2568348

Polishing precision optics is highly depending on the operator. Hence, a good result relies on a skilled optician who controls the process chain. This process chain consists of different manual steps such as loading, cleaning and calibrating different machines. To get more control over the process and to speed up the production we currently build an operator independent polishing cell using a single robot. Therefore, we positioned the robot in the middle of the production cell, which enables the robot to reach and manipulate different tools located around the kinematic. One major issues is the lower positioning accuracy and stiffness of an industrial robot in comparison to standard optic machines. Probably the most challenging step concerning accuracy in precision optics manufacturing is the interferometric measurement. In this paper, we present a method using an ESDI Intellium H2000 interferometer, designed for use in unsteady conditions. The robot positions the surface under test without the use of any additional mechanics to enhance the accuracy. The measurement position was manually teached in and approached several times for a statistically significant evaluation. The results show that the robot is sufficiently accurate and stable to perform interferometric measurements. This is a key element towards a completely operator-independent manufacturing cell for precision optics.
Contribution
  • Olga Kukso
  • Rolf Rascher
  • M. Pohl
  • R. Börret
On the metrology and analysis of MSF error
  • 2020

DOI: 10.1117/12.2566251

The aim of our research was to study middle spatial frequency errors (MSFE) on optical surfaces. We investigate the surfaces after manufacturing processes to find out the main affecting factors and to choose the proper processing parameters to minimize the size of the errors. To find an appropriate parameter window we have to be able not only to define the factors, which lead to MSFE, but also to analyze the change of the error after next following production steps.
Contribution
  • Michael Benisch
  • O. Fähnle
  • Rolf Rascher
  • Werner Bogner
Force and pressure analysis during overarm polishing
  • 2020

DOI: 10.1117/12.2564903

The Preston-equation implies, that, besides the relative speed υrel and a specific constant KP, the pressure p plays a significant role for the removal rate when polishing an optical component. This paper demonstrates a possibility for a qualitative evaluation of the pressure distribution before the polishing process. A pressure-sensitive foil is used as a gauge for pressure measurement. The effectiveness of this measuring method is explained. Specific weaknesses and limitations in the use of these foils are discussed. A method for an integrated evaluation of the pressure on different spots of the polishing pad is proposed at the end of the paper.
Contribution
  • Michael Benisch
  • O. Fähnle
  • Rolf Rascher
Observation of pressure distribution between tool and surface in different polishing situations
  • 2020

DOI: 10.1117/12.2567885

Pressure is a relevant parameter in the polishing of components according to the Preston equation.1, 2 Preliminary investigations have shown that the pressure can vary with inclined position and different polishing pads. It is not constant with regard to its distribution in the contact area between polishing pad and glass surface. In this publication, the pressure distribution during the polishing of glass components is analyzed. For the measurement of the pressure distribution a pressure sensitive foil is used.
Contribution
  • Sebastian Sitzberger
  • Johannes Liebl
  • Christian J. Trum
  • Rolf Rascher
Concept of a two-part clamping system for lenses in optical metrology
  • 2020

DOI: 10.1117/12.2566547

The developed concept represents a universally applicable clamping system designed to fit in any measuring machine with any measuring principle. The design ensures that, as long as the lens remains clamped, the measurement results are reproducible. Form errors due to tension remain constant across all measuring and processing steps. The version presented in this paper was developed especially for small lenses in the diameter range up to 40 mm. On the one hand, the design allows for fast measurement of loose lenses. On the other hand, the device can also be used for measurement comparisons, since lenses can also be mounted permanently. In the following, the concept and first results of measurement tests are presented.
Contribution
  • M. Pohl
  • R. Börret
  • Olga Kukso
  • Rolf Rascher
Mid spatial frequency error prevention strategies for the grinding process
  • 2020

DOI: 10.1117/12.2565261

This research is focused on the link between manufacturing parameters and the resulting mid-spatial frequency error in the manufacturing process of precision optics. The goal is to understand the generation mechanisms of mid-spatial frequency errors and avoid their appearance in the manufacturing process. Also, a simulation which is able to predict the resulting mid spatial frequency error from a manufacturing process is desired.
Contribution
  • Michael Benisch
  • Christian Vogt
  • Rolf Rascher
  • O. Fähnle
Octopus: A simple and effective tool for polishing slurry monitoring
  • 2020

DOI: 10.1117/12.2567952

The present paper shows a way for a cost-effective, integrated measurement of the density p of polishing suspensions. It is based on the principle of measuring the turbidity of a solution on the basis of the light transmitted through it, and of calculating back to the density on the basis of the turbidity. The tool is suitable for monitoring polishing agents and for detecting when the density of the polishing slurry leaves the permissible parameter space and can perspectively enable the automated monitoring and adjustment of polishing suspensions. The tool is named after an Octopus. These animals have amazing abilities, for example they can copy the behaviour of other sea animals or act with a plan. Their tentacles each have their own brain and can perform biochemical analyses.
JournalArticle
  • Armin Reif
  • P. Rinck
  • Sebastian Sitzberger
  • Rolf Rascher
  • M. Zäh
Zerspanung von Hochleistungswerkstoffen mit ultrasonisch modulierter Schnittgeschwindigkeit , vol115
  • 2020

DOI: 10.3139/104.112255

Die steigenden Anforderungen an die Festigkeit und die Qualität von Bauteilen und die damit verbundene Verwendung hochfester Materialien erfordert die Weiterentwicklung neuer wirtschaftlicher Zerspanungstechniken. Durch eine werkzeugseitige Schwingungsüberlagerung können bei der Bearbeitung von schwer zerspanbaren Werkstoffen die Zerspankräfte und der Werkzeugverschleiß reduziert sowie die Oberflächenqualität verbessert werden.
Contribution
  • Simon Killinger
  • Johannes Liebl
  • Rolf Rascher
First steps towards an automated polishing process chain using one robot
  • 2020

DOI: 10.1117/12.2564840

Manufacturing precision optics is a complex process chain, which requires many operations on different machines. This is combined with operator-dependent steps such as manual cleaning, loading and measuring. In order to realize this process chain on a smaller shop area and to achieve a higher level of automation we build an operator-independent polishing cell. In this cell, an ABB robot serves as the actuator handling the workpiece. We positioned the robot in the center of the polishing cell to operate several workstations, so the whole process chain works with one single actuator. This arrangement allows a smaller and cheaper system, since no additional handling is required.
Contribution
  • Michael Benisch
  • O. Fähnle
  • Rolf Rascher
Application of a pressure measuring film for pressure observation in overarm polishing
  • 2020

DOI: 10.1051/epjconf/202023803003

In previous publications the inhomogeneous pressure transfer through the polishing tool onto a glass surface could be shown. This experiment shows polishing trials with different polishing materials and the differences in the homogeneity of the pressure transfer through them. Only the properties of the material will be discussed explicitly, the change of the tool constitution through the process will be part of further publications.
Contribution
  • Armin Reif
  • Sebastian Sitzberger
  • Rolf Rascher
Cutting high-performance materials with ultrasonically modulated cutting speed
  • 2020

DOI: 10.1117/12.2565757

The continuing trend towards lightweight construction and the associated machining rates of up to 95 % lead to an increased use of high-performance materials. The ever growing demands on the strength and quality of components and the associated use of materials which are hard to machine require the further development of new, economical machining techniques. In ultrasonic-assisted machining, an additional high-frequency vibration is superimposed on the conventional machining process. The vibration of the tool is usually excited axially or longitudinally to the workpiece, i.e. vertical to the cutting direction. An additional vibration overlay around the rotation axis (torsional) of the tool is also possible. This generates a vibration overlay in the cutting direction. The vibration initiation causes vibration amplitudes in the range of a few micrometers at the tool cutting edge. This leads in turn to a high-frequency change in the cutting speed or feed rate. Overall, an additional torsional vibration overlap can further reduce cutting forces, increase tool life and improve workpiece quality. In order for a grinding tool to generate a torsional vibration, a special tool was required that had to be designed by simulation. The formation of a torsional vibration was achieved by helical slots in the sonotrode. Depending on the angle of rotation and the length of the slots, a part of the axial vibration is converted into a torsional vibration by an axial excitation of the sonotrode. The aim in designing the slots was to achieve the highest possible vibration amplitude. Following the simulation, the slots were inserted into the tool in the corresponding optimum geometric position. Afterwards, the specially designed grinding tool was validated by machining the brittle-hard glass-ceramic material Zerodur. The first test results with the torsionally vibrating tool are presented in the following.
Contribution
  • Armin Reif
  • Sebastian Sitzberger
  • Rolf Rascher
Cutting high-performance materials with ultrasonically modulated cutting speed
  • 2020

DOI: 10.1117/12.2565757

The continuing trend towards lightweight construction and the associated machining rates of up to 95 % lead to an increased use of high-performance materials. The ever growing demands on the strength and quality of components and the associated use of materials which are hard to machine require the further development of new, economical machining techniques. In ultrasonic-assisted machining, an additional high-frequency vibration is superimposed on the conventional machining process. The vibration of the tool is usually excited axially or longitudinally to the workpiece, i.e. vertical to the cutting direction. An additional vibration overlay around the rotation axis (torsional) of the tool is also possible. This generates a vibration overlay in the cutting direction. The vibration initiation causes vibration amplitudes in the range of a few micrometers at the tool cutting edge. This leads in turn to a high-frequency change in the cutting speed or feed rate. Overall, an additional torsional vibration overlap can further reduce cutting forces, increase tool life and improve workpiece quality. In order for a grinding tool to generate a torsional vibration, a special tool was required that had to be designed by simulation. The formation of a torsional vibration was achieved by helical slots in the sonotrode. Depending on the angle of rotation and the length of the slots, a part of the axial vibration is converted into a torsional vibration by an axial excitation of the sonotrode. The aim in designing the slots was to achieve the highest possible vibration amplitude. Following the simulation, the slots were inserted into the tool in the corresponding optimum geometric position. Afterwards, the specially designed grinding tool was validated by machining the brittle-hard glass-ceramic material Zerodur. The first test results with the torsionally vibrating tool are presented in the following.
Contribution
  • Michael Benisch
  • O. Fähnle
  • Rolf Rascher
  • Werner Bogner
Force and pressure analysis during overarm polishing
  • 2020

DOI: 10.1117/12.2564903

The Preston-equation implies, that, besides the relative speed υrel and a specific constant KP, the pressure p plays a significant role for the removal rate when polishing an optical component. This paper demonstrates a possibility for a qualitative evaluation of the pressure distribution before the polishing process. A pressure-sensitive foil is used as a gauge for pressure measurement. The effectiveness of this measuring method is explained. Specific weaknesses and limitations in the use of these foils are discussed. A method for an integrated evaluation of the pressure on different spots of the polishing pad is proposed at the end of the paper.
Contribution
  • M. Jung
  • Christian J. Trum
  • Beate Schmidbauer
  • E. Willenborg
  • Rolf Rascher
Non-ablative removal of sub surface damages in ground optical glass substrates by controlled melting of thin surface layers using CO2-laser radiation
  • 2020

DOI: 10.1117/12.2564801

The form generation of optical surfaces by grinding and mechanical polishing results in small sub surface damages in the form of micro cracks that conventionally have to be removed by further removal of the damaged surface layers. In order to reduce process time and material cost non-ablative methods for removal of micro cracks are desired. Utilising the low optical penetration depths of less than 10 μm for CO2-laser radiation in glass, the laser energy can be used to heat up and melt thin surface layers. Using a 1.5 kW CO2-laser, a quasi-line focus formed by a scanner unit and a constant feed speed, it is possible to close all micro cracks present in the rough grinded test surfaces (max. SSD-depth ~ 63 μm), while achieving a process time of less than 2 seconds for a Ø 30 mm N-BK7 lens, respectively 7.5 seconds for fused silica. With a Sa as low as 50 nm and low distortion from the original shape the surfaces can directly be conventionally polished, further reducing the process chain complexity.
Contribution
  • Michael Benisch
  • O. Fähnle
  • Rolf Rascher
Observation of pressure distribution between tool and surface in different polishing situations
  • 2020

DOI: 10.1117/12.2567885

Pressure is a relevant parameter in the polishing of components according to the Preston equation.1, 2 Preliminary investigations have shown that the pressure can vary with inclined position and different polishing pads. It is not constant with regard to its distribution in the contact area between polishing pad and glass surface. In this publication, the pressure distribution during the polishing of glass components is analyzed. For the measurement of the pressure distribution a pressure sensitive foil is used.
Contribution
  • Sebastian Sitzberger
  • Johannes Liebl
  • Christian J. Trum
  • Rolf Rascher
Concept of a two-part clamping system for lenses in optical metrology
  • 2020

DOI: 10.1117/12.2566547

The developed concept represents a universally applicable clamping system designed to fit in any measuring machine with any measuring principle. The design ensures that, as long as the lens remains clamped, the measurement results are reproducible. Form errors due to tension remain constant across all measuring and processing steps. The version presented in this paper was developed especially for small lenses in the diameter range up to 40 mm. On the one hand, the design allows for fast measurement of loose lenses. On the other hand, the device can also be used for measurement comparisons, since lenses can also be mounted permanently. In the following, the concept and first results of measurement tests are presented.
Contribution
  • Simon Killinger
  • Johannes Liebl
  • Rolf Rascher
First steps towards an automated polishing process chain using one robot
  • 2020

DOI: 10.1117/12.2564840

Manufacturing precision optics is a complex process chain, which requires many operations on different machines. This is combined with operator-dependent steps such as manual cleaning, loading and measuring. In order to realize this process chain on a smaller shop area and to achieve a higher level of automation we build an operator-independent polishing cell. In this cell, an ABB robot serves as the actuator handling the workpiece. We positioned the robot in the center of the polishing cell to operate several workstations, so the whole process chain works with one single actuator. This arrangement allows a smaller and cheaper system, since no additional handling is required.
Contribution
  • Christian J. Trum
  • M. Jung
  • Beate Schmidbauer
  • Sebastian Sitzberger
  • E. Willenborg
  • Rolf Rascher
Hybrid-process-chain for polishing optical glass lenses – HyoptO
  • 2020

DOI: 10.1117/12.2568400

A number of process steps that build on one another are required to manufacture optical components from glass. The polishing steps are the most time-consuming and therefore cost-intensive parts of the process chain. Low removal rates and the depth of the Sub Surface Damage (SSD) to be removed contribute to this. An alternative for the complete removal of the SSD-penetrated material using contactless polishing methods such as Ion Beam Figuring (IBF) is the healing of the SSD. Due to the induced energy during laser-polishing, the material is remelted at the defects and the SSD are closed. However, laser-polishing is also associated with disadvantages in terms of shape accuracy and surface quality. The project HyoptO is therefore devoted to the development of a hybrid-process-chain consisting of laser processing and conventional polishing. It is expected that the healing times of the SSD can significantly reduce the process times in the subsequent polishing steps. However, there are a few questions to be answered regarding the economic use of the hybrid-process-chain. These include:
Contribution
  • Simon Killinger
  • Johannes Liebl
  • Rolf Rascher
Interferometric measurement with robot kinematics
  • 2020

DOI: 10.1117/12.2568348

Polishing precision optics is highly depending on the operator. Hence, a good result relies on a skilled optician who controls the process chain. This process chain consists of different manual steps such as loading, cleaning and calibrating different machines. To get more control over the process and to speed up the production we currently build an operator independent polishing cell using a single robot. Therefore, we positioned the robot in the middle of the production cell, which enables the robot to reach and manipulate different tools located around the kinematic. One major issues is the lower positioning accuracy and stiffness of an industrial robot in comparison to standard optic machines. Probably the most challenging step concerning accuracy in precision optics manufacturing is the interferometric measurement. In this paper, we present a method using an ESDI Intellium H2000 interferometer, designed for use in unsteady conditions. The robot positions the surface under test without the use of any additional mechanics to enhance the accuracy. The measurement position was manually teached in and approached several times for a statistically significant evaluation. The results show that the robot is sufficiently accurate and stable to perform interferometric measurements. This is a key element towards a completely operator-independent manufacturing cell for precision optics.
Contribution
  • Olga Kukso
  • Rolf Rascher
  • M. Pohl
  • R. Börret
On the metrology and analysis of MSF error
  • 2020

DOI: 10.1117/12.2566251

The aim of our research was to study middle spatial frequency errors (MSFE) on optical surfaces. We investigate the surfaces after manufacturing processes to find out the main affecting factors and to choose the proper processing parameters to minimize the size of the errors. To find an appropriate parameter window we have to be able not only to define the factors, which lead to MSFE, but also to analyze the change of the error after next following production steps.
Contribution
  • M. Pohl
  • R. Börret
  • Olga Kukso
  • Rolf Rascher
Mid spatial frequency error prevention strategies for the grinding process
  • 2020

DOI: 10.1117/12.2565261

This research is focused on the link between manufacturing parameters and the resulting mid-spatial frequency error in the manufacturing process of precision optics. The goal is to understand the generation mechanisms of mid-spatial frequency errors and avoid their appearance in the manufacturing process. Also, a simulation which is able to predict the resulting mid spatial frequency error from a manufacturing process is desired.
Contribution
  • Christian J. Trum
  • M. Jung
  • Beate Schmidbauer
  • Sebastian Sitzberger
  • E. Willenborg
  • Rolf Rascher
Hybrid-process-chain for polishing optical glass lenses – HyoptO
  • 2020

DOI: 10.1117/12.2568400

A number of process steps that build on one another are required to manufacture optical components from glass. The polishing steps are the most time-consuming and therefore cost-intensive parts of the process chain. Low removal rates and the depth of the Sub Surface Damage (SSD) to be removed contribute to this. An alternative for the complete removal of the SSD-penetrated material using contactless polishing methods such as Ion Beam Figuring (IBF) is the healing of the SSD. Due to the induced energy during laser-polishing, the material is remelted at the defects and the SSD are closed. However, laser-polishing is also associated with disadvantages in terms of shape accuracy and surface quality. The project HyoptO is therefore devoted to the development of a hybrid-process-chain consisting of laser processing and conventional polishing. It is expected that the healing times of the SSD can significantly reduce the process times in the subsequent polishing steps. However, there are a few questions to be answered regarding the economic use of the hybrid-process-chain. These include:
Contribution
  • M. Jung
  • Christian J. Trum
  • Beate Schmidbauer
  • E. Willenborg
  • Rolf Rascher
Non-ablative removal of sub surface damages in ground optical glass substrates by controlled melting of thin surface layers using CO2-laser radiation
  • 2020

DOI: 10.1117/12.2564801

The form generation of optical surfaces by grinding and mechanical polishing results in small sub surface damages in the form of micro cracks that conventionally have to be removed by further removal of the damaged surface layers. In order to reduce process time and material cost non-ablative methods for removal of micro cracks are desired. Utilising the low optical penetration depths of less than 10 μm for CO2-laser radiation in glass, the laser energy can be used to heat up and melt thin surface layers. Using a 1.5 kW CO2-laser, a quasi-line focus formed by a scanner unit and a constant feed speed, it is possible to close all micro cracks present in the rough grinded test surfaces (max. SSD-depth ~ 63 μm), while achieving a process time of less than 2 seconds for a Ø 30 mm N-BK7 lens, respectively 7.5 seconds for fused silica. With a Sa as low as 50 nm and low distortion from the original shape the surfaces can directly be conventionally polished, further reducing the process chain complexity.
Contribution
  • Michael Benisch
  • Werner Bogner
  • Rolf Rascher
Using A Digital Temperature Sensor To Measure The Temperature Development During A Polishing Process
  • 2019
Lecture
  • Sebastian Sitzberger
  • J. Reitberger
  • Rolf Rascher
Clamping system for optical components for adaptation in optical production
  • 2019
Lecture
  • Sebastian Sitzberger
  • J. Reitberger
  • Rolf Rascher
Clamping system for optical components for adaptation in optical production
  • 2019
Lecture
  • Simon Killinger
  • Alexander Haberl
  • Rolf Rascher
Analysis of residual errors during computer controlled polishing
  • 2019
In computer controlled subapertur polishing the formation of mid spatial frequency errors (MSFE) needs special attention. In this work the formation of MSFE in feed direction is investigated using the ADAPT tool from Satisloh.
Contribution
  • M. Pohl
  • U. Bielke
  • R. Börret
  • Rolf Rascher
  • Olga Kukso
MSF-error prevention strategies for the grinding process
  • 2019

DOI: 10.1117/12.2526581

This research is focused on the link between manufacturing parameters and the resulting mid-spatial frequency error in the manufacturing process of precision optics. This third publication focuses on strategies of avoidance and generation mechanisms of the mid-spatial frequency errors from the grinding process. The Goal is to understand the generation mechanisms of the mid-spatial frequency errors and avoid their appearance in the manufacturing process.
Contribution
  • M. Pohl
  • U. Bielke
  • R. Börret
  • Rolf Rascher
  • Olga Kukso
MSF-error prevention strategies for the grinding process
  • 2019

DOI: 10.1117/12.2526581

This research is focused on the link between manufacturing parameters and the resulting mid-spatial frequency error in the manufacturing process of precision optics. This third publication focuses on strategies of avoidance and generation mechanisms of the mid-spatial frequency errors from the grinding process. The Goal is to understand the generation mechanisms of the mid-spatial frequency errors and avoid their appearance in the manufacturing process.
Contribution
  • Sebastian Sitzberger
  • Johannes Liebl
  • J. Reitberger
  • Rolf Rascher
Zero-point clamping systems in optical production
  • 2019

DOI: 10.1117/12.2528774

Zero point clamping systems are an integral part of the manufacturing industry. They have only yet to find their way into the optical industry. This article compares the hydraulic expansion holder, a clamping system currently used in the optical industry with a zero-point clamping system. The achievable accuracies of both systems are compared over several measurement series. In addition, the process capability evaluation is used for the comparison. Finally, the results are summarized to provide every researcher and practitioner with a foundation for assessing whether zero point clamping systems meet the requirements for the use in optical manufacturing.
Lecture
  • Sebastian Sitzberger
  • P. Rinck
  • A. Gueray
  • Rolf Rascher
Ultraschallunterstützte Zerspanung von Advanced Materials
  • 2019
Lecture
  • Simon Killinger
  • Alexander Haberl
  • Rolf Rascher
Analysis of residual errors during computer controlled polishing
  • 2019
In computer controlled subapertur polishing the formation of mid spatial frequency errors (MSFE) needs special attention. In this work the formation of MSFE in feed direction is investigated using the ADAPT tool from Satisloh.
Contribution
  • Simon Killinger
  • Johannes Liebl
  • Rolf Rascher
Mid-spatial frequency errors in feed direction occurring in ADAPT polishing
  • 2019

DOI: 10.1117/12.2528114

Previous work shows the effectiveness of computer controlled polishing (CCP) with the ADAPT tool by Satisloh for correcting form errors in optics manufacturing. This method however has a risk of producing residual errors in the range of mid spatial frequency errors (MSFE). In order to prevent these errors the residual in feed direction is investigated as well as the behavior at different parameters.
Lecture
  • Sebastian Sitzberger
  • P. Rinck
  • A. Gueray
  • Rolf Rascher
Ultraschallunterstützte Zerspanung von Advanced Materials
  • 2019
Contribution
  • Simon Killinger
  • Johannes Liebl
  • Rolf Rascher
Mid-spatial frequency errors in feed direction occurring in ADAPT polishing
  • 2019

DOI: 10.1117/12.2528114

Previous work shows the effectiveness of computer controlled polishing (CCP) with the ADAPT tool by Satisloh for correcting form errors in optics manufacturing. This method however has a risk of producing residual errors in the range of mid spatial frequency errors (MSFE). In order to prevent these errors the residual in feed direction is investigated as well as the behavior at different parameters.
Contribution
  • Michael Benisch
  • Werner Bogner
  • Rolf Rascher
Using A Digital Temperature Sensor To Measure The Temperature Development During A Polishing Process
  • 2019
Contribution
  • Sebastian Sitzberger
  • Johannes Liebl
  • J. Reitberger
  • Rolf Rascher
Zero-point clamping systems in optical production
  • 2019

DOI: 10.1117/12.2528774

Zero point clamping systems are an integral part of the manufacturing industry. They have only yet to find their way into the optical industry. This article compares the hydraulic expansion holder, a clamping system currently used in the optical industry with a zero-point clamping system. The achievable accuracies of both systems are compared over several measurement series. In addition, the process capability evaluation is used for the comparison. Finally, the results are summarized to provide every researcher and practitioner with a foundation for assessing whether zero point clamping systems meet the requirements for the use in optical manufacturing.
Contribution
  • Olga Kukso
  • Rolf Rascher
  • R. Börret
  • M. Pohl
On the metrology of the MSF errors
  • 2018

DOI: 10.1117/12.2318675

The aim of our research is to study middle spatial frequency errors (MSFE) on optical surfaces. We investigate the surfaces after all manufacturing processes to find out the main affecting factors and to choose the proper processing parameters to minimize the size of the errors. In this paper we describe some middle spatial frequency errors, which occur during grinding. As there are limited possibilities to measure ground surfaces, their analysis from the point of measurement is most difficult. Therefore, it is of utmost importance to optimally organize the measurement guaranteeing sufficient data for the reconstruction of the toolpath and avoidance of aliasing effects. In the paper discuss possible classifications and some difficulties during measuring of grinded surfaces.
Lecture
  • Rolf Rascher
Grinding and polishing of glass - Basis for a perfect coating
  • 2018
Contribution
  • Alexander Haberl
  • Johannes Liebl
  • Rolf Rascher
ABC-polishing
  • 2018

DOI: 10.1117/12.2318549

In the past, steadily increasing demands on the imaging properties of optics have led more and more precise spherical apertures. For a long time, these optical components have been produced in a satisfying quality using classic polishing methods such as pitch polishing. The advance of computer-controlled subaperture (SA) polishing techniques improved the accuracy of spheres. However, this new machine technology also made it possible to produce new lens geometries, such as aspheres. In contrast to classic polishing methods, the high determinism of SA polishing allows a very specific correction of the surface defect. The methods of magneto-rheological finishing (MRF) [1], [2] and ion beam figuring (IBF) [3], [4] stand out in particular because of the achievable shape accuracy. However, this leads to the fact that a principle of manufacturing "As exact as possible, as precise as necessary" [5] is often ignored. The optical surfaces often produced with unnecessary precision, result at least in increased processing times. The increasing interconnection of the production machines and the linking with databases already enables a consistent database to be established. It is possible to store measurements, process characteristics or tolerances for the individual production steps in a structured way. The difficulty, however, lies in the reasonable evaluation of the measurement data. This is where this publication comes in. The smart evaluation of the measurement data with the widespread Zernike polynomials should result in a classification, depending on the required manufacturing tolerance. In combination with the so-called ABC analysis, all surface defects can be categorized. In this way, an analytic breakdown of a - initially confusing - overall problem is made. With the aid of cost functions [6] an evaluation and consequently a deduction of actions is made possible. Thus, for example, the isolated processing of rotationally symmetrical errors in spiral mode, setup times and machining times can be reduced while avoiding mid spatial frequency errors (MSFE) at the same time.
Contribution
  • O. Fähnle
  • Christian Vogt
  • Rolf Rascher
Load controlled process window analysis of feed controlled CNC grinding
  • 2018

DOI: 10.1117/12.2315336

Contribution
  • Sebastian Sitzberger
  • Christian J. Trum
  • Rolf Rascher
  • M. Zaeh
Workpiece self-weight in precision optics manufacturing: compensation of workpiece deformations by a fluid bearing
  • 2018

DOI: 10.1117/12.2318577

The effects, the extent and the importance of workpiece deformations, particularly lenses, caused by the weight of the workpiece itself, were examined in a previous paper1 . The considered deformations are in the single-digit to two-digit nanometer range. The investigation was carried out by FEM calculations. The conclusion of the previous aper was that a full-surface support of a workpiece in the processing of one surface presumably produces the best results. Furthermore, it was found that if the second functional surface is not to be touched in the process, a full contact lens mounting on its circumference is advisable. An alternative method for fixing precision lenses is therefore desirable. This can be accomplished in two steps. As a first step, the lens must be gripped at its periphery so that none of the optically functional surfaces of the lens is compromised. However, the complete circumference has to be fixated gaplessly because a punctual fixation has the disadvantage of deforming the lens surface asymmetrically. As a second step, the freely hanging lens surface should be supported to minimize deformation. An approach had to be found that supports the surface like a solid bearing but at the same time does not touch it. Therefore, the usage of an incompressible fluid as a hydrostatic bearing for full-surface support is pursued. For this purpose, the bottom side of the lens has to be stored on water. The results of the FEM simulation showed that with a fluid bearing the resulting deformations can be drastically reduced in comparison to a freely hanging surface. Furthermore, under the right conditions, a resulting deformation comparable to a full surface solid support can be achieved. The content of this paper is a test series under laboratory conditions for a first validation of the theoretical results. Therefore, a prototype model to test a lens fixation with a fluid bearing was developed and manufactured. The resulting deformations were measured with an interferometer and the effects are discussed.
JournalArticle
  • O. Fähnle
  • Rolf Rascher
  • Christian Vogt
  • D.W. Kim
Closed-loop laser polishing using in-process surface finish metrology , vol57
  • 2018

DOI: 10.1364/AO.57.000834

This paper lays out the trail onto a closed-loop polishing process of optical elements enabling the application of the optimum polishing time needed. To that aim, an in-process testing method for monitoring an inclusive micro surface quality (e.g., comprising surface roughness and scratch-and-dig) within the polishing spot is analyzed and its applicability to closed-loop polishing for classical loose-abrasive full-aperture polishing as well as for computer controlled laser polishing is experimentally tested and verified. This enables the determination of the optimum local dwell time resulting in a stable and cost optimized polishing.
Contribution
  • O. Fähnle
  • O. Dambon
  • M. Doetz
  • F. Klocke
  • Christian Vogt
  • Rolf Rascher
Ductile grinding of tungsten carbide applying standard CNC machines: a process analysis
  • 2018

DOI: 10.1117/12.2315338

Contribution
  • Alexander Haberl
  • H. Harsch
  • Gerald Fütterer
  • Johannes Liebl
  • C. Pruß
  • Rolf Rascher
  • W. Osten
Model based error separation of power spectral density artefacts in wavefront measurement
  • 2018

DOI: 10.1117/12.2321106

Contribution
  • Olga Kukso
  • Rolf Rascher
  • R. Börret
  • M. Pohl
On the metrology of the MSF errors
  • 2018

DOI: 10.1117/12.2318675

The aim of our research is to study middle spatial frequency errors (MSFE) on optical surfaces. We investigate the surfaces after all manufacturing processes to find out the main affecting factors and to choose the proper processing parameters to minimize the size of the errors. In this paper we describe some middle spatial frequency errors, which occur during grinding. As there are limited possibilities to measure ground surfaces, their analysis from the point of measurement is most difficult. Therefore, it is of utmost importance to optimally organize the measurement guaranteeing sufficient data for the reconstruction of the toolpath and avoidance of aliasing effects. In the paper discuss possible classifications and some difficulties during measuring of grinded surfaces.
Lecture
  • Olga Kukso
  • Rolf Rascher
  • M. Pohl
  • R. Börret
EmmaV - Entstehungsmechanismen mittelfrequenter Fehler und deren aktive Vermeidung Posterpräsentation
  • 2018
Contribution
  • M. Pohl
  • R. Börret
  • Rolf Rascher
  • Olga Kukso
Simulation of MSF errors using Fourier transform
  • 2018

DOI: 10.1117/12.2317484

This research is focused on the link between manufacturing parameters and the resulting mid spatial frequency error in the manufacturing process of precision optics. This first publication focuses on the parameters of the grinding step. The Goal is to understand and avoid the appearance of the mid spatial frequency error and develop a simulation which is able to predict the resulting mid spatial frequency error for/of a manufacturing process.
Contribution
  • Christian Vogt
  • O. Fähnle
  • E. Langenbach
  • Rolf Rascher
In situ monitoring of laser polishing
  • 2018
Contribution
  • O. Fähnle
  • Christian Vogt
  • Rolf Rascher
  • M. Doetz
  • O. Dambon
  • F. Klocke
From turning to grinding: ductile machining with gPVA
  • 2018

DOI: 10.1117/12.2323246

Contribution
  • O. Fähnle
  • Christian Vogt
  • Rolf Rascher
  • M. Doetz
  • O. Dambon
  • F. Klocke
From turning to grinding: ductile machining with gPVA
  • 2018

DOI: 10.1117/12.2323246

Lecture
  • Christian J. Trum
  • Sebastian Sitzberger
  • Rolf Rascher
Improved performance of CMP processes through targeted adjustment of polishing slurry and polish pad
  • 2018
Lecture
  • Sebastian Sitzberger
  • Christian J. Trum
  • Rolf Rascher
  • M. Zaeh
Workpiece self-weight induced deformation in precision optics manufacturing Posterpräsentation
  • 2018
Contribution
  • M. Doetz
  • O. Dambon
  • Christian Vogt
  • Rolf Rascher
  • E. Langenbach
  • O. Fähnle
Enlarging process window of ductile mode machining of WC molds
  • 2018
Lecture
  • Rolf Rascher
Grinding and polishing of glass - Basis for a perfect coating
  • 2018
Contribution
  • Christian Vogt
  • O. Fähnle
  • Rolf Rascher
gPVA: a system for the classification of grinding tools
  • 2018

DOI: 10.1117/12.2318695

Contribution
  • Christian Vogt
  • O. Fähnle
  • E. Langenbach
  • Rolf Rascher
In situ monitoring of laser polishing
  • 2018
Contribution
  • O. Fähnle
  • Christian Vogt
  • Rolf Rascher
  • M. Doetz
  • O. Dambon
  • F. Klocke
Ductile grinding of tungsten carbide molds applying standard CNC machines
  • 2018

DOI: 10.1117/12.2323245

Contribution
  • M. Pohl
  • R. Börret
  • Rolf Rascher
  • Olga Kukso
Simulation of MSF errors using Fourier transform
  • 2018

DOI: 10.1117/12.2317484

This research is focused on the link between manufacturing parameters and the resulting mid spatial frequency error in the manufacturing process of precision optics. This first publication focuses on the parameters of the grinding step. The Goal is to understand and avoid the appearance of the mid spatial frequency error and develop a simulation which is able to predict the resulting mid spatial frequency error for/of a manufacturing process.
Contribution
  • Christian Vogt
  • Rolf Rascher
  • O. Fähnle
  • Dae Kim
Closed-loop next generation laser polishing
  • 2018

DOI: 10.1117/12.2318749

Contribution
  • Christian Vogt
  • M. Doetz
  • Rolf Rascher
  • O. Fähnle
Standardized evaluation of grinding tools for brittle and ductile mode grinding Invited Paper
  • 2018
Lecture
  • Rolf Rascher
  • Christian Vogt
  • O. Fähnle
  • E. Langenbach
Closed-loop laser polishing of glass
  • 2018
Lecture
  • Christian Schopf
  • Florian Schneider
  • Rolf Rascher
ArenA – Foi: Erprobung des ADAPT-Polierwerkzeugs Posterpräsentation
  • 2018
Contribution
  • Sebastian Sitzberger
  • Christian J. Trum
  • Rolf Rascher
  • M. Zaeh
Workpiece self-weight in precision optics manufacturing: compensation of workpiece deformations by a fluid bearing
  • 2018

DOI: 10.1117/12.2318577

The effects, the extent and the importance of workpiece deformations, particularly lenses, caused by the weight of the workpiece itself, were examined in a previous paper1 . The considered deformations are in the single-digit to two-digit nanometer range. The investigation was carried out by FEM calculations. The conclusion of the previous aper was that a full-surface support of a workpiece in the processing of one surface presumably produces the best results. Furthermore, it was found that if the second functional surface is not to be touched in the process, a full contact lens mounting on its circumference is advisable. An alternative method for fixing precision lenses is therefore desirable. This can be accomplished in two steps. As a first step, the lens must be gripped at its periphery so that none of the optically functional surfaces of the lens is compromised. However, the complete circumference has to be fixated gaplessly because a punctual fixation has the disadvantage of deforming the lens surface asymmetrically. As a second step, the freely hanging lens surface should be supported to minimize deformation. An approach had to be found that supports the surface like a solid bearing but at the same time does not touch it. Therefore, the usage of an incompressible fluid as a hydrostatic bearing for full-surface support is pursued. For this purpose, the bottom side of the lens has to be stored on water. The results of the FEM simulation showed that with a fluid bearing the resulting deformations can be drastically reduced in comparison to a freely hanging surface. Furthermore, under the right conditions, a resulting deformation comparable to a full surface solid support can be achieved. The content of this paper is a test series under laboratory conditions for a first validation of the theoretical results. Therefore, a prototype model to test a lens fixation with a fluid bearing was developed and manufactured. The resulting deformations were measured with an interferometer and the effects are discussed.
Contribution
  • Christian Vogt
  • Rolf Rascher
  • O. Fähnle
  • Dae Kim
Closed-loop next generation laser polishing
  • 2018

DOI: 10.1117/12.2318749

Contribution
  • O. Fähnle
  • Christian Vogt
  • Rolf Rascher
  • M. Doetz
  • O. Dambon
  • F. Klocke
Ductile grinding of tungsten carbide molds applying standard CNC machines
  • 2018

DOI: 10.1117/12.2323245

Contribution
  • M. Doetz
  • O. Dambon
  • Christian Vogt
  • Rolf Rascher
  • E. Langenbach
  • O. Fähnle
Enlarging process window of ductile mode machining of WC molds
  • 2018
Lecture
  • Christian Schopf
  • Florian Schneider
  • Rolf Rascher
ArenA – Foi: Erprobung des ADAPT-Polierwerkzeugs Posterpräsentation
  • 2018
Contribution
  • Christian J. Trum
  • Christian Vogt
  • Sebastian Sitzberger
  • Rolf Rascher
  • O. Fähnle
Filled-Up-Microscopy (FUM): a non-destructive method for approximating the depth of sub-surface damage on ground surfaces
  • 2018

DOI: 10.1117/12.2318576

Contribution
  • Christian J. Trum
  • Christian Vogt
  • O. Fähnle
  • Sebastian Sitzberger
  • Rolf Rascher
First experiences with Filled-Up-Microscopy (FUM) to evaluate the depth of sub-surface damages on ground surfaces
  • 2018
JournalArticle
  • O. Fähnle
  • Rolf Rascher
  • Christian Vogt
  • D.W. Kim
Closed-loop laser polishing using in-process surface finish metrology , vol57
  • 2018

DOI: 10.1364/AO.57.000834

This paper lays out the trail onto a closed-loop polishing process of optical elements enabling the application of the optimum polishing time needed. To that aim, an in-process testing method for monitoring an inclusive micro surface quality (e.g., comprising surface roughness and scratch-and-dig) within the polishing spot is analyzed and its applicability to closed-loop polishing for classical loose-abrasive full-aperture polishing as well as for computer controlled laser polishing is experimentally tested and verified. This enables the determination of the optimum local dwell time resulting in a stable and cost optimized polishing.
JournalArticle
  • Christian J. Trum
  • Rolf Rascher
  • M. Zäh
Effizientes chemisch-mechanisches Polieren (CMP)
  • 2018
JournalArticle
  • Christian J. Trum
  • Rolf Rascher
  • M. Zäh
Effizientes chemisch-mechanisches Polieren (CMP)
  • 2018
Lecture
  • Christian Vogt
  • O. Fähnle
  • E. Langenbach
  • Rolf Rascher
In situ laser monitoring of laser polishing
  • 2018
A novel fabrication parameter controlling method for laser polishing is presented, measuring within the footprint the smoothening process in real time. Recently, a new method for in situ measuring level of surface roughness has been developed [1] where a HeNe laser beam is being reflected from within the sample at the surface under test and the intensity of its reflected beam is being monitored.In this paper we report on an experimental study where this method has been applied to laser polishing. The internal local surface area under test is chosen to be located at the very spot where the laser polishing footprint is located from the outside of the sample melting its surface locally. Because fused silica is not transparent at the operating CO2 laser wavelength, the intensity of the reflected beam can be monitored enabling an in situ control of the laser polishing process. Consequently, the optimum dwell time can be determined, a footprint needs to stay at a certain point before moving further enabling a more stable and cost optimized polishing. [1] O.Fähnle,“In process monitoring of optics fabrication”, SPIEconference “PrecisionOptics Manufacturing”2017
Lecture
  • Christian Vogt
  • O. Fähnle
  • E. Langenbach
  • Rolf Rascher
In situ laser monitoring of laser polishing
  • 2018
A novel fabrication parameter controlling method for laser polishing is presented, measuring within the footprint the smoothening process in real time. Recently, a new method for in situ measuring level of surface roughness has been developed [1] where a HeNe laser beam is being reflected from within the sample at the surface under test and the intensity of its reflected beam is being monitored.In this paper we report on an experimental study where this method has been applied to laser polishing. The internal local surface area under test is chosen to be located at the very spot where the laser polishing footprint is located from the outside of the sample melting its surface locally. Because fused silica is not transparent at the operating CO2 laser wavelength, the intensity of the reflected beam can be monitored enabling an in situ control of the laser polishing process. Consequently, the optimum dwell time can be determined, a footprint needs to stay at a certain point before moving further enabling a more stable and cost optimized polishing. [1] O.Fähnle,“In process monitoring of optics fabrication”, SPIEconference “PrecisionOptics Manufacturing”2017
Lecture
  • Christian J. Trum
  • Sebastian Sitzberger
  • Rolf Rascher
Improved performance of CMP processes through targeted adjustment of polishing slurry and polish pad
  • 2018
Lecture
  • Rolf Rascher
  • Christian Vogt
  • O. Fähnle
  • E. Langenbach
Closed-loop laser polishing of glass
  • 2018
Contribution
  • O. Fähnle
  • M. Doetz
  • O. Dambon
  • F. Klocke
  • Christian Vogt
  • Rolf Rascher
Ductile mode single point diamond turning (SPDT) of binderless tungsten carbide molds
  • 2018

DOI: 10.1117/12.2323244

Lecture
  • Christian Vogt
  • Rolf Rascher
grinding Process Validation Approach (gPVA) Posterpräsentation
  • 2018
Lecture
  • Christian Vogt
  • Rolf Rascher
grinding Process Validation Approach (gPVA) Posterpräsentation
  • 2018
Contribution
  • Christian J. Trum
  • Christian Vogt
  • Sebastian Sitzberger
  • Rolf Rascher
  • O. Fähnle
Filled-Up-Microscopy (FUM): a non-destructive method for approximating the depth of sub-surface damage on ground surfaces
  • 2018

DOI: 10.1117/12.2318576

Contribution
  • O. Fähnle
  • Christian Vogt
  • Rolf Rascher
Load controlled process window analysis of feed controlled CNC grinding
  • 2018

DOI: 10.1117/12.2315336

Contribution
  • Christian J. Trum
  • Sebastian Sitzberger
  • Rolf Rascher
Improved performance of CMP processes through targeted adjustment of polishing slurry and polish pad
  • 2018

DOI: 10.1117/12.2321031

Chemical-mechanical polishing (CMP) of optical glasses is widespread and forms the basis for many high-precision polishing processes. The pads, slurries and glass materials used in polishing have many different properties. The effects of these properties on the process results are often unknown. The right choice and combination is therefore often a challenge. By means of a plan processing of N-BK7 and SF56 samples by a plan-polishing process, the influence on the process results, material removal rate (MRR), micro roughness and cleanliness caused by slurry and polishing pad is shown. It turns out that the type of polish pad has the biggest impact on the results. The easy-to-process material N-BK7 shows only little influence by the type of slurry used. The more challenging SF56, however, shows significant effects, especially in the area of the resulting micro roughness and the appearance of surface damages like orange peel. Especially the use of Auerpol® PZ500 shows clear advantages here. For a selection of three out of nine polishing pads, the effect of density variation of the slurry was also investigated. Lower particle concentrations lead to lower material removal rates. This applies to both materials. The more sensitive SF56 shows a reduction in micro roughness by the use of a less dense slurry. The correct selection of the polishing pad has a positive effect on the material removal rate and/or the micro roughness in all tested materials. An adaptation of the type and concentration of the slurry is especially important for more sensitive materials and in combination with the right polishing pad. In view of the development towards special materials and small lot sizes, the targeted and correct selection of polishing slurries and pads becomes more and more important. The information required for this purpose on the behavior of the pads and slurries available on the market must therefore first be determined in a targeted manner and clearly presented.
Contribution
  • Alexander Haberl
  • Johannes Liebl
  • Rolf Rascher
ABC-polishing
  • 2018

DOI: 10.1117/12.2318549

In the past, steadily increasing demands on the imaging properties of optics have led more and more precise spherical apertures. For a long time, these optical components have been produced in a satisfying quality using classic polishing methods such as pitch polishing. The advance of computer-controlled subaperture (SA) polishing techniques improved the accuracy of spheres. However, this new machine technology also made it possible to produce new lens geometries, such as aspheres. In contrast to classic polishing methods, the high determinism of SA polishing allows a very specific correction of the surface defect. The methods of magneto-rheological finishing (MRF) [1], [2] and ion beam figuring (IBF) [3], [4] stand out in particular because of the achievable shape accuracy. However, this leads to the fact that a principle of manufacturing "As exact as possible, as precise as necessary" [5] is often ignored. The optical surfaces often produced with unnecessary precision, result at least in increased processing times. The increasing interconnection of the production machines and the linking with databases already enables a consistent database to be established. It is possible to store measurements, process characteristics or tolerances for the individual production steps in a structured way. The difficulty, however, lies in the reasonable evaluation of the measurement data. This is where this publication comes in. The smart evaluation of the measurement data with the widespread Zernike polynomials should result in a classification, depending on the required manufacturing tolerance. In combination with the so-called ABC analysis, all surface defects can be categorized. In this way, an analytic breakdown of a - initially confusing - overall problem is made. With the aid of cost functions [6] an evaluation and consequently a deduction of actions is made possible. Thus, for example, the isolated processing of rotationally symmetrical errors in spiral mode, setup times and machining times can be reduced while avoiding mid spatial frequency errors (MSFE) at the same time.
Contribution
  • Christian J. Trum
  • Christian Vogt
  • O. Fähnle
  • Sebastian Sitzberger
  • Rolf Rascher
First experiences with Filled-Up-Microscopy (FUM) to evaluate the depth of sub-surface damages on ground surfaces
  • 2018
Contribution
  • Christian Vogt
  • O. Fähnle
  • Rolf Rascher
gPVA: a system for the classification of grinding tools
  • 2018

DOI: 10.1117/12.2318695

Contribution
  • O. Fähnle
  • M. Doetz
  • O. Dambon
  • F. Klocke
  • Christian Vogt
  • Rolf Rascher
Ductile mode single point diamond turning (SPDT) of binderless tungsten carbide molds
  • 2018

DOI: 10.1117/12.2323244

Lecture
  • Sebastian Sitzberger
  • Christian J. Trum
  • Rolf Rascher
  • M. Zaeh
Workpiece self-weight induced deformation in precision optics manufacturing Posterpräsentation
  • 2018
Lecture
  • Olga Kukso
  • Rolf Rascher
  • M. Pohl
  • R. Börret
EmmaV - Entstehungsmechanismen mittelfrequenter Fehler und deren aktive Vermeidung Posterpräsentation
  • 2018
Lecture
  • Alexander Haberl
  • H. Harsch
  • Gerald Fütterer
  • Johannes Liebl
  • C. Pruß
  • Rolf Rascher
  • W. Osten
Model based error separation of power spectral density artefacts in wavefront measurement
  • 2018
Contribution
  • Alexander Haberl
  • H. Harsch
  • Gerald Fütterer
  • Johannes Liebl
  • C. Pruß
  • Rolf Rascher
  • W. Osten
Model based error separation of power spectral density artefacts in wavefront measurement
  • 2018

DOI: 10.1117/12.2321106

Contribution
  • Christian Vogt
  • M. Doetz
  • Rolf Rascher
  • O. Fähnle
Standardized evaluation of grinding tools for brittle and ductile mode grinding Invited Paper
  • 2018
Contribution
  • Johannes Liebl
  • Christian Schopf
  • Rolf Rascher
DefGO
  • 2018

DOI: 10.1117/12.2318704

The manufacturing of optical lenses has various steps. Generally, the manufacturing can be split up into the following steps: the workpiece is pre-ground with a coarse tool; it is then fine-ground with a finer tool. As the final polishing is a demanding and time-consuming process that cannot manage large removal rations not can it equalise rough shape errors, the starting quality and surface quality needs to be as high as possible. According to the current state of technology, ground lenses must be measured with tactile measuring techniques in order to detect shape errors. This is timeconsuming and expensive, and only two dimensional profiles can be measured. DefGO’s project objective is to introduce deflectometry as a new, three dimensional lens measuring standard. A problem with the application of deflectometry is that the object to be measured has to reflect enough light, which is not the case for ground glass with rough surfaces. DefGO’s solution is to wet the lens with a fluid to create a closed reflecting surface.
Contribution
  • Christian J. Trum
  • Sebastian Sitzberger
  • Rolf Rascher
Improved performance of CMP processes through targeted adjustment of polishing slurry and polish pad
  • 2018

DOI: 10.1117/12.2321031

Chemical-mechanical polishing (CMP) of optical glasses is widespread and forms the basis for many high-precision polishing processes. The pads, slurries and glass materials used in polishing have many different properties. The effects of these properties on the process results are often unknown. The right choice and combination is therefore often a challenge. By means of a plan processing of N-BK7 and SF56 samples by a plan-polishing process, the influence on the process results, material removal rate (MRR), micro roughness and cleanliness caused by slurry and polishing pad is shown. It turns out that the type of polish pad has the biggest impact on the results. The easy-to-process material N-BK7 shows only little influence by the type of slurry used. The more challenging SF56, however, shows significant effects, especially in the area of the resulting micro roughness and the appearance of surface damages like orange peel. Especially the use of Auerpol® PZ500 shows clear advantages here. For a selection of three out of nine polishing pads, the effect of density variation of the slurry was also investigated. Lower particle concentrations lead to lower material removal rates. This applies to both materials. The more sensitive SF56 shows a reduction in micro roughness by the use of a less dense slurry. The correct selection of the polishing pad has a positive effect on the material removal rate and/or the micro roughness in all tested materials. An adaptation of the type and concentration of the slurry is especially important for more sensitive materials and in combination with the right polishing pad. In view of the development towards special materials and small lot sizes, the targeted and correct selection of polishing slurries and pads becomes more and more important. The information required for this purpose on the behavior of the pads and slurries available on the market must therefore first be determined in a targeted manner and clearly presented.
Contribution
  • Johannes Liebl
  • Christian Schopf
  • Rolf Rascher
DefGO
  • 2018

DOI: 10.1117/12.2318704

The manufacturing of optical lenses has various steps. Generally, the manufacturing can be split up into the following steps: the workpiece is pre-ground with a coarse tool; it is then fine-ground with a finer tool. As the final polishing is a demanding and time-consuming process that cannot manage large removal rations not can it equalise rough shape errors, the starting quality and surface quality needs to be as high as possible. According to the current state of technology, ground lenses must be measured with tactile measuring techniques in order to detect shape errors. This is timeconsuming and expensive, and only two dimensional profiles can be measured. DefGO’s project objective is to introduce deflectometry as a new, three dimensional lens measuring standard. A problem with the application of deflectometry is that the object to be measured has to reflect enough light, which is not the case for ground glass with rough surfaces. DefGO’s solution is to wet the lens with a fluid to create a closed reflecting surface.
Contribution
  • O. Fähnle
  • O. Dambon
  • M. Doetz
  • F. Klocke
  • Christian Vogt
  • Rolf Rascher
Ductile grinding of tungsten carbide applying standard CNC machines: a process analysis
  • 2018

DOI: 10.1117/12.2315338

Lecture
  • Alexander Haberl
  • H. Harsch
  • Gerald Fütterer
  • Johannes Liebl
  • C. Pruß
  • Rolf Rascher
  • W. Osten
Model based error separation of power spectral density artefacts in wavefront measurement
  • 2018
Contribution
  • Sebastian Sitzberger
  • Christian J. Trum
  • Rolf Rascher
Analysis of the influence of the workpiece self-weight in precision optics manufacturing using FEM simulation
  • 2017

DOI: 10.1117/12.2273023

Contribution
  • Robert Schneider
  • Alexander Haberl
  • Rolf Rascher
Parametrization of a Subaperture Polishing Tool - Analysis of the Path Tests , volPaper OM3B.2
  • 2017
Contribution
  • Engelbert Hofbauer
  • Rolf Rascher
  • Felix Friedke
  • R. Kometer
Resolution, measurement errors and uncertainties on deflectometric acquisition of large optical surfaces "DaOS"
  • 2017

DOI: 10.1117/12.2267513

Contribution
  • Rolf Rascher
  • Christian Vogt
  • C. Faehnle
In situ laser polishing optimization method: Control of LASer Surface Optimisation (C-Lasso)
  • 2017
Laser polishing is achieved by local absorption of laser power within the polishing spot causing the surface and its sub-surface region to melt and flow reducing surface roughness and removing sub-surface damage. In this paper we present a novel fabrication controlling method for laser polishing processes called C-Lasso (Control of LASer Surface Optimization, Patent Pending), monitoring in situ the surface smoothening process. It is possible to determine and control the minimum dwell time a footprint needs to stay at a certain point before moving further. C-Lasso enables to avoid unnecessarily long local dwell times. Besides the functioning principle, a proof of concept will be presented as well as experimental data demonstrating the in situ monitoring.
Contribution
  • Robert Schneider
  • Alexander Haberl
  • Rolf Rascher
Polishing tool and the resulting TIF for three variable machine parameters as input for the removal simulation
  • 2017

DOI: 10.1117/12.2267415

JournalArticle
  • Christian Vogt
  • C. Faehnle
  • Rolf Rascher
Grinding Process Validation Approach (gPVA) , vol7
  • 2017

DOI: 10.17265/2159-5348/2017.05.004

Contribution
  • Christian J. Trum
  • Sebastian Sitzberger
  • Rolf Rascher
Advanced method for the characterization of polishing suspensions
  • 2017

DOI: 10.1117/12.2272431

Contribution
  • Rolf Rascher
  • Christian Vogt
  • C. Faehnle
In situ laser polishing optimization method: Control of LASer Surface Optimisation (C-Lasso)
  • 2017
Laser polishing is achieved by local absorption of laser power within the polishing spot causing the surface and its sub-surface region to melt and flow reducing surface roughness and removing sub-surface damage. In this paper we present a novel fabrication controlling method for laser polishing processes called C-Lasso (Control of LASer Surface Optimization, Patent Pending), monitoring in situ the surface smoothening process. It is possible to determine and control the minimum dwell time a footprint needs to stay at a certain point before moving further. C-Lasso enables to avoid unnecessarily long local dwell times. Besides the functioning principle, a proof of concept will be presented as well as experimental data demonstrating the in situ monitoring.
Contribution
  • Christian Vogt
  • O. Fähnle
  • Rolf Rascher
Three wagons Approach Applied to Optimization of Industrial Grinding Processes
  • 2017

DOI: 10.1364/OFT.2017.OTu2B.2

Contribution
  • Christian Vogt
  • O. Fähnle
  • Rolf Rascher
Force-controlled analysis tool for optimization of precision CNC grinding processes
  • 2017

DOI: 10.1117/12.2272713

Contribution
  • Christian Vogt
  • O. Fähnle
  • Rolf Rascher
Three wagons Approach Applied to Optimization of Industrial Grinding Processes
  • 2017

DOI: 10.1364/OFT.2017.OTu2B.2

Contribution
  • Bin Dong
  • Christian Vogt
  • Rolf Rascher
Wear detection of brass bond diamond grinding wheel by spectral coherence of grinding forces
  • 2017
Contribution
  • Christian Schopf
  • Rolf Rascher
  • Johannes Liebl
Cheap and fast measuring roughness on big surfaces with an imprint method
  • 2017
Contribution
  • Christian Vogt
  • O. Fähnle
  • Rolf Rascher
Setting-up high-end cnc grinding processes: a Preston-based approach
  • 2017
The design of grinding processes is commonly based on the principle of trial and error. In most cases this will end up with a usable setup that delivers acceptable results. On the other hand this method is unlikely to reveal the process’s total potential. Allthough the principles of grinding and polishing are entirly different, the preston approach can be used to design grinding processes more intelligent and highly efficient. Carrying out a testing procedure for grinding tools reveals the tool’s removal properties on different materials. This allows to choose ideal sequences of pre and fine-grinding. Furthermore it is possible to choose the optimum machining parameters to optain a maximum output.
Contribution
  • Engelbert Hofbauer
  • Rolf Rascher
  • Felix Friedke
  • R. Kometer
Resolution, measurement errors and uncertainties on deflectometric acquisition of large optical surfaces "DaOS"
  • 2017

DOI: 10.1117/12.2267513

JournalArticle
  • Christian Vogt
  • C. Faehnle
  • Rolf Rascher
Grinding Process Validation Approach (gPVA) , vol7
  • 2017

DOI: 10.17265/2159-5348/2017.05.004

Contribution
  • Christian J. Trum
  • Sebastian Sitzberger
  • Rolf Rascher
Advanced method for the characterization of polishing suspensions
  • 2017

DOI: 10.1117/12.2272431

Contribution
  • Alexander Haberl
  • Rolf Rascher
Yet one more dwell time algorithm
  • 2017

DOI: 10.1117/12.2270540

Contribution
  • Robert Schneider
  • Alexander Haberl
  • Rolf Rascher
Parametrization of a Subaperture Polishing Tool - Analysis of the Path Tests , volPaper OM3B.2
  • 2017
Contribution
  • Alexander Haberl
  • Rolf Rascher
Yet one more dwell time algorithm
  • 2017

DOI: 10.1117/12.2270540

Contribution
  • Christian Vogt
  • O. Fähnle
  • Rolf Rascher
Setting-up high-end cnc grinding processes: a Preston-based approach
  • 2017
The design of grinding processes is commonly based on the principle of trial and error. In most cases this will end up with a usable setup that delivers acceptable results. On the other hand this method is unlikely to reveal the process’s total potential. Allthough the principles of grinding and polishing are entirly different, the preston approach can be used to design grinding processes more intelligent and highly efficient. Carrying out a testing procedure for grinding tools reveals the tool’s removal properties on different materials. This allows to choose ideal sequences of pre and fine-grinding. Furthermore it is possible to choose the optimum machining parameters to optain a maximum output.
Contribution
  • Christian Schopf
  • Rolf Rascher
  • Johannes Liebl
Cheap and fast measuring roughness on big surfaces with an imprint method
  • 2017
Contribution
  • Sebastian Sitzberger
  • Christian J. Trum
  • Rolf Rascher
Analysis of the influence of the workpiece self-weight in precision optics manufacturing using FEM simulation
  • 2017

DOI: 10.1117/12.2273023

Contribution
  • Bin Dong
  • Christian Vogt
  • Rolf Rascher
Wear detection of brass bond diamond grinding wheel by spectral coherence of grinding forces
  • 2017
Contribution
  • Robert Schneider
  • Alexander Haberl
  • Rolf Rascher
Polishing tool and the resulting TIF for three variable machine parameters as input for the removal simulation
  • 2017

DOI: 10.1117/12.2267415

Contribution
  • Christian Vogt
  • O. Fähnle
  • Rolf Rascher
Force-controlled analysis tool for optimization of precision CNC grinding processes
  • 2017

DOI: 10.1117/12.2272713

Lecture
  • Rolf Rascher
  • Christine Wünsche
  • Christian Schopf
Aspects in laser polishing of precision optical components
  • 2016
Contribution
  • Engelbert Hofbauer
  • Rolf Rascher
  • Manon Schilke
  • Johannes Liebl
  • J.-P. Richters
Deflectometric acquisition of large optical surfaces (DaOS) using a new physical measurement principle: vignetting field stop procedure
  • 2016

DOI: 10.1117/12.2236134

Lecture
  • Christian Schopf
  • Rolf Rascher
Reducing forces during drilling brittle hard materials by using ultrasonic and variation of coolant
  • 2016
Contribution
  • Christian Vogt
  • S. Sinzinger
  • Martin Rohrbacher
  • Rolf Rascher
Prediction of grinding tool wear and lifetime by using a test bench
  • 2016
Contribution
  • Christian J. Trum
  • Rolf Rascher
Improving efficiency of chemo-mechanical polishing processes by systematic selection and conditioning of the polishing suspension
  • 2016

DOI: 10.1117/12.2236000

During design of optical systems or individual components, customers and designers already predetermine the way through production and the necessary resources. They define the tolerances that are required for their application like shape, micro-roughness and cleanliness, as well as the glass material that is necessary for the targeted optical effect. By the tolerances, they have also an influence on the manufacturer and his decisions on the production environment, measurement technology and the process chain that in his opinion is necessary to meet the specification. In most cases the type of polishing suspension and its parameters are also predetermined by the use of central polishing supply systems. With this paper, the authors want to give a prospect of a currently running research with the aim of increasing the efficiency of chemo-mechanical polishing processes by a systematic selection and conditioning of the polishing suspension. They want to show that small amounts of well-conditioned and stabilized polishing suspension could be a tool to improve the efficiency in CMP processes under the influence of the global trend to products that are more individual and down to one piece flow production. Main parts of this research are the identification of influences of polishing suspensions on the quality criteria of optical components and the creation of a method to find well-working suspension parameters in a deterministic and reproducible way. © (2016) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
JournalArticle
  • Engelbert Hofbauer
  • Rolf Rascher
  • Manon Schilke
  • Johannes Liebl
  • J.-P. Richters
Deflectometric Acquisition of Large Optical Surfaces “DaOS” Using a New Physical Measurement Principle: Vignetting Field Stop (Reprinted from Proceedings of SPIE Volume 10009: Third European Seminar on Precision Optics Manufacturing, 100090Y [Teisnach, April 12th 2016] doi:10.1117/12.2236134)
  • 2016
The vignetting field stop procedure uses a deflectometric approach to acquire big Optical Surfaces – DaOS – and it offers the possibility to measure nearly any shape or form using a scanning routine. The basic physical measurement principle in DaOS is the vignettation of a quasi-parallel light beam emitted by an expanded light source in auto collimation arrangement with a reflecting element. Thereby nearly any curvature of the specimen, is measurable. Due to the fact, that even sign changes in the curvature can be detected, also aspheres and freeform surfaces of any size can be evaluated. In this publication the vignetting field stop procedure is discussed. Additionally the deflectometric setup is described. Because of some typical influences of beam deflection to the accuracy of angle measurement by using the vignetting principle, suitable methods of calibration for the sensor are examined and the results of these methods are presented. Furthermore, the technical principle of deflectometric measurements using an angle detecting device is explained inclusive of all random and systematic errors generated by the setup. The last part of this publication shows the actual result of test measurements with calculated absolute deviation of errors with a large lateral dimension as well as the determination of the maximal achievable lateral resolution by detecting mid frequent structures on flat and spherical test parts with a diameter of 300 mm. These measurements are compared critically to reference results which are recorded by interferometry and further scanning methods.
Lecture
  • Rolf Rascher
  • C. Weingarten
Hybridfertigung optischer Oberflächen
  • 2016
Lecture
  • Rolf Rascher
Innovationsentwicklung mit der Technischen Hochschule Deggendorf
  • 2016
Contribution
  • Christian Schopf
  • Rolf Rascher
Reducing forces during drilling brittle hard materials by using ultrasonic and variation of coolant
  • 2016

DOI: 10.1117/12.2257106

The process of ultrasonic machining is especially used for brittle hard materials as the additional ultrasonic vibration of the tool at high frequencies and low amplitudes acts like a hammer on the surface. With this technology it is possible to drill holes with lower forces, therefor the machining can be done faster and the worktime is much less than conventionally. A three-axis dynamometer was used to measure the forces, which act between the tool and the sample part. A focus is set on the sharpness of the tool. The results of a test series are based on the Sauer Ultrasonic Grinding Centre. On the same machine it is possible to drill holes in the conventional way. Additional to the ultasonic Input the type an concentration of coolant is important for the Drilling-force. In the test there were three different coolant and three different concentrations tested. The combination of ultrasonic vibration and the right coolant and concentration is the best way to reduce the Forces. Another positive effect is, that lower drilling-forces produce smaller chipping on the edge of the hole. The way to reduce the forces and chipping is the main issue of this paper.
Lecture
  • Rolf Rascher
Innovationsentwicklung mit der Technischen Hochschule Deggendorf
  • 2016
Lecture
  • Rolf Rascher
  • C. Weingarten
Hybridfertigung optischer Oberflächen
  • 2016
Contribution
  • Sebastian Sitzberger
  • Rolf Rascher
An investigation on the efficiency of the manufacturing of components in precision optics
  • 2016

DOI: 10.1117/12.2236137

By adaption and coordination of successive process steps the efficiency of producing optics can be improved. In the beginning of this investigation, the focus is on two crucial process steps of the optical manufacturing process. First, there is the optical and mechanical design of the optical part and system. In this context, it is important to consider what modifications compared to the current standard design are possible respectively useful. Thus, the modifications will only concentrate on parts of the optic that do not interfere with the optical functionality. Furthermore in this part of the study the main aspect is the clamping situation of the optical part in a holder or an optical system. It will be discussed, whether it is useful to add special clamping surfaces respectively a clamping flange in contrast to the standard design. The faultless functioning of the optics has always first priority. Second, the manufacturing process itself has a great number of single steps. Therefore, a main part of the research is the investigation of current clamping situations in optics manufacturing, with prospect to improve them in order to work perfectly with the design modifications, as mentioned above. This part of the investigation focuses on the clamping system for the lens on each machine necessary for manufacturing. In the scope of this paper the authors want to summarize characteristics and deficits of current clamping systems and workpiece mounts and give a prospect of the following course of action. © (2016) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Contribution
  • Johannes Liebl
  • Horst Linthe
  • Sebastian Sitzberger
  • Rolf Rascher
Interferometric measurement of highly accurate flat surfaces
  • 2016

DOI: 10.1117/12.2235525

The most important part in manufacturing precision optics is a reliable measurement procedure which provides results a few times more accurate than the quality to be produced. In general two specific values are important, the repeatability of several measurements which are done in a row and the absolute accuracy which is mostly defined by the systematical error of the measurement device. The repeatability can be improved relatively simple, by increasing the number of measurements and a following averaging step. To increase the absolute accuracy of a measurement device in the field of precision optics is far more challenging. In this paper several interferometer absolute testing methods to measure flat surfaces are compared. The main objective was to name a value for the achievable accuracy. Therefor four different methods were analyzed: 1. The three flat test, a method which is already used several decades to determine the quality of a flat surface. As a result, two absolute measured profiles, horizontal and vertical, can be calculated. 2. The multi rotation test, an extension of the classical three flat test. The big advantage of this method is a fully three dimensional map of the systematical error. 3. The systematical error calculated by the SSI-A. Hereby several subapertures are measured over the whole surface. The redundant information’s of the overlapping regions can be used to calculate the systematical error of the system. 4. The rotation of the transmission flat relatively to the interferometer. Thereby the rotation unsymmetrical errors can be calculated and subtracted. © (2016) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Lecture
  • Rolf Rascher
  • Christine Wünsche
  • Christian Schopf
Aspects in laser polishing of precision optical components
  • 2016
Contribution
  • Engelbert Hofbauer
  • Rolf Rascher
  • Manon Schilke
  • Johannes Liebl
  • J.-P. Richters
Deflectometric acquisition of large optical surfaces (DaOS) using a new physical measurement principle: vignetting field stop procedure
  • 2016

DOI: 10.1117/12.2236134

Contribution
  • Christian Vogt
  • S. Sinzinger
  • Martin Rohrbacher
  • Rolf Rascher
Prediction of grinding tool wear and lifetime by using a test bench
  • 2016
JournalArticle
  • Engelbert Hofbauer
  • Rolf Rascher
Deflectometric Acquisition of Large Optical Surfaces DaOS Using a new physical measurement principle: vignetting field stop procedure , vol11
  • 2016

DOI: 10.1002/opph.201600036

Contribution
  • Johannes Liebl
  • Horst Linthe
  • Sebastian Sitzberger
  • Rolf Rascher
Interferometric measurement of highly accurate flat surfaces
  • 2016

DOI: 10.1117/12.2235525

The most important part in manufacturing precision optics is a reliable measurement procedure which provides results a few times more accurate than the quality to be produced. In general two specific values are important, the repeatability of several measurements which are done in a row and the absolute accuracy which is mostly defined by the systematical error of the measurement device. The repeatability can be improved relatively simple, by increasing the number of measurements and a following averaging step. To increase the absolute accuracy of a measurement device in the field of precision optics is far more challenging. In this paper several interferometer absolute testing methods to measure flat surfaces are compared. The main objective was to name a value for the achievable accuracy. Therefor four different methods were analyzed: 1. The three flat test, a method which is already used several decades to determine the quality of a flat surface. As a result, two absolute measured profiles, horizontal and vertical, can be calculated. 2. The multi rotation test, an extension of the classical three flat test. The big advantage of this method is a fully three dimensional map of the systematical error. 3. The systematical error calculated by the SSI-A. Hereby several subapertures are measured over the whole surface. The redundant information’s of the overlapping regions can be used to calculate the systematical error of the system. 4. The rotation of the transmission flat relatively to the interferometer. Thereby the rotation unsymmetrical errors can be calculated and subtracted. © (2016) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Contribution
  • Christian Schopf
  • Rolf Rascher
Reducing forces during drilling brittle hard materials by using ultrasonic and variation of coolant
  • 2016

DOI: 10.1117/12.2257106

The process of ultrasonic machining is especially used for brittle hard materials as the additional ultrasonic vibration of the tool at high frequencies and low amplitudes acts like a hammer on the surface. With this technology it is possible to drill holes with lower forces, therefor the machining can be done faster and the worktime is much less than conventionally. A three-axis dynamometer was used to measure the forces, which act between the tool and the sample part. A focus is set on the sharpness of the tool. The results of a test series are based on the Sauer Ultrasonic Grinding Centre. On the same machine it is possible to drill holes in the conventional way. Additional to the ultasonic Input the type an concentration of coolant is important for the Drilling-force. In the test there were three different coolant and three different concentrations tested. The combination of ultrasonic vibration and the right coolant and concentration is the best way to reduce the Forces. Another positive effect is, that lower drilling-forces produce smaller chipping on the edge of the hole. The way to reduce the forces and chipping is the main issue of this paper.
Lecture
  • Christian Schopf
  • Rolf Rascher
Reducing forces during drilling brittle hard materials by using ultrasonic and variation of coolant
  • 2016
Contribution
  • Christian J. Trum
  • Rolf Rascher
Improving efficiency of chemo-mechanical polishing processes by systematic selection and conditioning of the polishing suspension
  • 2016

DOI: 10.1117/12.2236000

During design of optical systems or individual components, customers and designers already predetermine the way through production and the necessary resources. They define the tolerances that are required for their application like shape, micro-roughness and cleanliness, as well as the glass material that is necessary for the targeted optical effect. By the tolerances, they have also an influence on the manufacturer and his decisions on the production environment, measurement technology and the process chain that in his opinion is necessary to meet the specification. In most cases the type of polishing suspension and its parameters are also predetermined by the use of central polishing supply systems. With this paper, the authors want to give a prospect of a currently running research with the aim of increasing the efficiency of chemo-mechanical polishing processes by a systematic selection and conditioning of the polishing suspension. They want to show that small amounts of well-conditioned and stabilized polishing suspension could be a tool to improve the efficiency in CMP processes under the influence of the global trend to products that are more individual and down to one piece flow production. Main parts of this research are the identification of influences of polishing suspensions on the quality criteria of optical components and the creation of a method to find well-working suspension parameters in a deterministic and reproducible way. © (2016) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Contribution
  • Sebastian Sitzberger
  • Rolf Rascher
An investigation on the efficiency of the manufacturing of components in precision optics
  • 2016

DOI: 10.1117/12.2236137

By adaption and coordination of successive process steps the efficiency of producing optics can be improved. In the beginning of this investigation, the focus is on two crucial process steps of the optical manufacturing process. First, there is the optical and mechanical design of the optical part and system. In this context, it is important to consider what modifications compared to the current standard design are possible respectively useful. Thus, the modifications will only concentrate on parts of the optic that do not interfere with the optical functionality. Furthermore in this part of the study the main aspect is the clamping situation of the optical part in a holder or an optical system. It will be discussed, whether it is useful to add special clamping surfaces respectively a clamping flange in contrast to the standard design. The faultless functioning of the optics has always first priority. Second, the manufacturing process itself has a great number of single steps. Therefore, a main part of the research is the investigation of current clamping situations in optics manufacturing, with prospect to improve them in order to work perfectly with the design modifications, as mentioned above. This part of the investigation focuses on the clamping system for the lens on each machine necessary for manufacturing. In the scope of this paper the authors want to summarize characteristics and deficits of current clamping systems and workpiece mounts and give a prospect of the following course of action. © (2016) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
JournalArticle
  • Engelbert Hofbauer
  • Rolf Rascher
  • Manon Schilke
  • Johannes Liebl
  • J.-P. Richters
Deflectometric Acquisition of Large Optical Surfaces “DaOS” Using a New Physical Measurement Principle: Vignetting Field Stop (Reprinted from Proceedings of SPIE Volume 10009: Third European Seminar on Precision Optics Manufacturing, 100090Y [Teisnach, April 12th 2016] doi:10.1117/12.2236134)
  • 2016
The vignetting field stop procedure uses a deflectometric approach to acquire big Optical Surfaces – DaOS – and it offers the possibility to measure nearly any shape or form using a scanning routine. The basic physical measurement principle in DaOS is the vignettation of a quasi-parallel light beam emitted by an expanded light source in auto collimation arrangement with a reflecting element. Thereby nearly any curvature of the specimen, is measurable. Due to the fact, that even sign changes in the curvature can be detected, also aspheres and freeform surfaces of any size can be evaluated. In this publication the vignetting field stop procedure is discussed. Additionally the deflectometric setup is described. Because of some typical influences of beam deflection to the accuracy of angle measurement by using the vignetting principle, suitable methods of calibration for the sensor are examined and the results of these methods are presented. Furthermore, the technical principle of deflectometric measurements using an angle detecting device is explained inclusive of all random and systematic errors generated by the setup. The last part of this publication shows the actual result of test measurements with calculated absolute deviation of errors with a large lateral dimension as well as the determination of the maximal achievable lateral resolution by detecting mid frequent structures on flat and spherical test parts with a diameter of 300 mm. These measurements are compared critically to reference results which are recorded by interferometry and further scanning methods.
JournalArticle
  • Engelbert Hofbauer
  • Rolf Rascher
Deflectometric Acquisition of Large Optical Surfaces DaOS Using a new physical measurement principle: vignetting field stop procedure , vol11
  • 2016

DOI: 10.1002/opph.201600036

Contribution
  • Christian Vogt
  • Martin Rohrbacher
  • Rolf Rascher
  • S. Sinzinger
Dependency between removal characteristics and defined measurement categories of pellets
  • 2015

DOI: 10.1117/12.2189987

Contribution
  • Engelbert Hofbauer
  • Rolf Rascher
  • Felix Friedke
  • Thomas Stubenrauch
  • Johannes Liebl
  • J.-P. Richters
The vignetting field stop procedure: A new physical measurement principle for the Deflectometric acquisition of big Optical Surfaces - DaOS
  • 2015
JournalArticle
  • Heiko Biskup
  • Christian J. Trum
  • Rolf Rascher
Stabilität im Polierprozess
  • 2015
Lecture
  • Heiko Biskup
  • Christian Schopf
  • Rolf Rascher
Surface roughness testing below 0.5 nm Sq Measuring of Sub-Nanometer Surface Texture by White-Light Interferometry
  • 2015
Contribution
  • Christian Vogt
  • Martin Rohrbacher
  • Rolf Rascher
  • S. Sinzinger
Dependency between removal characteristics and defined measurement categories of pellets
  • 2015

DOI: 10.1117/12.2189987

JournalArticle
  • Heiko Biskup
  • Christian J. Trum
  • Rolf Rascher
Stabilität im Polierprozess
  • 2015
Contribution
  • Heiko Biskup
  • Alexander Haberl
  • Rolf Rascher
Surface errors in the course of machining precision optics
  • 2015

DOI: 10.1117/12.2189991

Precision optical components are usually machined by grinding and polishing in several steps with increasing accuracy. Spherical surfaces will be finished in a last step with large tools to smooth the surface. The requested surface accuracy of non-spherical surfaces only can be achieved with tools in point contact to the surface. So called mid-frequency errors (MSFE) can accumulate with zonal processes. This work is on the formation of surface errors from grinding to polishing by conducting an analysis of the surfaces in their machining steps by non-contact interferometric methods. The errors on the surface can be distinguished as described in DIN 4760 whereby 2nd to 3rd order errors are the so-called MSFE. By appropriate filtering of the measured data frequencies of errors can be suppressed in a manner that only defined spatial frequencies will be shown in the surface plot. It can be observed that some frequencies already may be formed in the early machining steps like grinding and main-polishing. Additionally it is known that MSFE can be produced by the process itself and other side effects. Beside a description of surface errors based on the limits of measurement technologies, different formation mechanisms for selected spatial frequencies are presented. A correction may be only possible by tools that have a lateral size below the wavelength of the error structure. The presented considerations may be used to develop proposals to handle surface errors. © (2015) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Contribution
  • Heiko Biskup
  • Alexander Haberl
  • Rolf Rascher
Surface errors in the course of machining precision optics
  • 2015

DOI: 10.1117/12.2189991

Precision optical components are usually machined by grinding and polishing in several steps with increasing accuracy. Spherical surfaces will be finished in a last step with large tools to smooth the surface. The requested surface accuracy of non-spherical surfaces only can be achieved with tools in point contact to the surface. So called mid-frequency errors (MSFE) can accumulate with zonal processes. This work is on the formation of surface errors from grinding to polishing by conducting an analysis of the surfaces in their machining steps by non-contact interferometric methods. The errors on the surface can be distinguished as described in DIN 4760 whereby 2nd to 3rd order errors are the so-called MSFE. By appropriate filtering of the measured data frequencies of errors can be suppressed in a manner that only defined spatial frequencies will be shown in the surface plot. It can be observed that some frequencies already may be formed in the early machining steps like grinding and main-polishing. Additionally it is known that MSFE can be produced by the process itself and other side effects. Beside a description of surface errors based on the limits of measurement technologies, different formation mechanisms for selected spatial frequencies are presented. A correction may be only possible by tools that have a lateral size below the wavelength of the error structure. The presented considerations may be used to develop proposals to handle surface errors. © (2015) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Lecture
  • Heiko Biskup
  • Christian Schopf
  • Rolf Rascher
Surface roughness testing below 0.5 nm Sq Measuring of Sub-Nanometer Surface Texture by White-Light Interferometry
  • 2015
Contribution
  • Patrick Schäfer
  • Christine Wünsche
  • Rolf Rascher
Quantification of synthetic lens surface characteristics by an optical measurement system as stylus instrument
  • 2015
Contribution
  • Patrick Schäfer
  • Christine Wünsche
  • Rolf Rascher
Quantification of synthetic lens surface characteristics by an optical measurement system as stylus instrument
  • 2015
Contribution
  • Engelbert Hofbauer
  • Rolf Rascher
  • Felix Friedke
  • Thomas Stubenrauch
  • Johannes Liebl
  • J.-P. Richters
The vignetting field stop procedure: A new physical measurement principle for the Deflectometric acquisition of big Optical Surfaces - DaOS
  • 2015
JournalArticle
  • Johannes Liebl
  • Heiko Biskup
  • S. Draxinger
  • Rolf Rascher
  • Christine Wünsche
Process developement fort the reproducible roughness measurement of optical surfaces using white light interferometry , vol5
  • 2014
Lecture
  • S. Draxinger
  • Christian J. Trum
  • Heiko Biskup
  • Christine Wünsche
  • Rolf Rascher
Active Fluid Jet Polishing - Behaviour on Different Materials
  • 2014
Lecture
  • Rolf Rascher
  • Johannes Liebl
  • Paul Schötz
  • P. Frieder
Automatische Kratzererkennung an hochpräzisen Drehteilen „Projekt KonoScan“
  • 2014
Lecture
  • S. Draxinger
  • Christian J. Trum
  • Heiko Biskup
  • Christine Wünsche
  • Rolf Rascher
Active Fluid Jet Polishing - Behaviour on Different Materials
  • 2014
Lecture
  • Thorsten Gerdes
  • K. Kyrgyzbayev
  • A. Rosin
  • A. Saberi
  • A. Füller
  • Rolf Rascher
  • Christine Wünsche
Aims for the development of new optical glass materials
  • 2014
Contribution
  • Christian Vogt
  • S. Sinzinger
  • Rolf Rascher
A Study on Elastic Grinding Tools
  • 2014

DOI: 10.1364/OFT.2014.OTu3B.3

This paper reports on results of testruns with experimental grinding tools. The ball shaped tools comprise of abrasive layers with diamond grits, on top of an elastic layer. The tool’s design allows dwell time based corrections on simple and complex shapes, such as spheres and parabolic shapes.
Lecture
  • Rolf Rascher
Technologies and results for the mirror production in Teisnach
  • 2014
Contribution
  • O. Fähnle
  • E. Langenbach
  • F. Frost
  • A. Schindler
  • Heiko Biskup
  • Johannes Liebl
  • Christine Wünsche
  • Rolf Rascher
Generation and field testing of roughness reference samples for industrial testing of surface roughness levels below 0.5nm Sq
  • 2014
Lecture
  • Rolf Rascher
Technologies and results for the mirror production in Teisnach
  • 2014
Contribution
  • O. Fähnle
  • E. Langenbach
  • F. Frost
  • A. Schindler
  • Heiko Biskup
  • Johannes Liebl
  • Christine Wünsche
  • Rolf Rascher
Generation and field testing of roughness reference samples for industrial testing of surface roughness levels below 0.5nm Sq
  • 2014
Lecture
  • Rolf Rascher
  • Johannes Liebl
  • Paul Schötz
  • P. Frieder
Automatische Kratzererkennung an hochpräzisen Drehteilen „Projekt KonoScan“
  • 2014
Lecture
  • Patrick Schäfer
  • Christine Wünsche
  • Rolf Rascher
Quantification of synthetic lens surface characteristics by an optical measurement system as stylus instrument
  • 2014
Contribution
  • Engelbert Hofbauer
  • Rolf Rascher
  • K. Wühr
  • Felix Friedke
  • Thomas Stubenrauch
  • B. Pastötter
  • S. Schleich
  • C. Zöcke
3D-optical measurement system using vignetting aperture procedure
  • 2014

DOI: 10.1117/12.2052631

Lecture
  • Thorsten Gerdes
  • K. Kyrgyzbayev
  • A. Rosin
  • A. Saberi
  • A. Füller
  • Rolf Rascher
  • Christine Wünsche
Aims for the development of new optical glass materials
  • 2014
Lecture
  • Patrick Schäfer
  • Christine Wünsche
  • Rolf Rascher
Quantification of synthetic lens surface characteristics by an optical measurement system as stylus instrument
  • 2014
Contribution
  • Christian Vogt
  • S. Sinzinger
  • Rolf Rascher
A Study on Elastic Grinding Tools
  • 2014

DOI: 10.1364/OFT.2014.OTu3B.3

This paper reports on results of testruns with experimental grinding tools. The ball shaped tools comprise of abrasive layers with diamond grits, on top of an elastic layer. The tool’s design allows dwell time based corrections on simple and complex shapes, such as spheres and parabolic shapes.
Contribution
  • Engelbert Hofbauer
  • Rolf Rascher
  • K. Wühr
  • Felix Friedke
  • Thomas Stubenrauch
  • B. Pastötter
  • S. Schleich
  • C. Zöcke
3D-optical measurement system using vignetting aperture procedure
  • 2014

DOI: 10.1117/12.2052631

Lecture
  • Christian Vogt
  • S. Sinzinger
  • Rolf Rascher
A study on elastic grinding tools
  • 2014
JournalArticle
  • Johannes Liebl
  • Heiko Biskup
  • S. Draxinger
  • Rolf Rascher
  • Christine Wünsche
Process developement fort the reproducible roughness measurement of optical surfaces using white light interferometry , vol5
  • 2014
Lecture
  • Christian Vogt
  • S. Sinzinger
  • Rolf Rascher
A study on elastic grinding tools
  • 2014
Lecture
  • S. Draxinger
  • Christine Wünsche
  • Rolf Rascher
Subaperture-polishing with variable spots
  • 2013
Lecture
  • M. Willert-Porada
  • Thorsten Gerdes
  • A. Rosin
  • A. Saberi
  • A. Füller
  • Rolf Rascher
  • Christine Wünsche
Flexiplant: schmelzebasierte kontinuierliche Herstellung von low TG-Glas-Preformen (mittels Minimeltertechnologie)
  • 2013
JournalArticle
  • Christian Schopf
  • Rolf Rascher
  • Christine Wünsche
Rauhigkeitsmessungen an großen und schwer zugänglichen Bauteilen
  • 2013
Contribution
  • Christian Vogt
  • Florian Schneider
  • Rolf Rascher
Grinding Processes for Silicon Carbide (CSiC) Materials , vol2
  • 2013
Lecture
  • M. Willert-Porada
  • Thorsten Gerdes
  • A. Rosin
  • A. Saberi
  • A. Füller
  • Rolf Rascher
  • Christine Wünsche
Flexiplant: schmelzebasierte kontinuierliche Herstellung von low TG-Glas-Preformen (mittels Minimeltertechnologie)
  • 2013
Contribution
  • Roland Maurer
  • Heiko Biskup
  • Christian J. Trum
  • Rolf Rascher
  • Christine Wünsche
Determination of a suitable parameter field for the active fluid jet polishing process
  • 2013

DOI: 10.1117/12.2028752

In 2012 a well-known company in the field of high precision optics assigned the University of Applied Sciences Deggendorf to determine a suitable parameter field for the active fluid jet polishing (AFJP) process in order to reach a surface accuracy of at least lambda / 5. The active fluid jet polishing is a relatively new and an affordable sub-aperture polishing process. For a fast and precise identification of the parameter field a considered design of experiment is necessary. The available control variables were the rotational speed of the nozzle, the distance between the test object and the jet, the feed rate, the material of the pin inside the nozzle and the material of the test object itself. In order to reach a significant data density on the one hand and to minimize the number of test runs on the other hand a meander shaped tool path was chosen. At each blank nine paths had been driven whereby at each path another parameter combination was picked. Thus with only one test object nine parameter settings may be evaluated. For the automatized analysis of the tracks a software tool was developed. The software evaluates ten sections which orthogonally intersect the nine tracks on the test-lens. The significant measurement parameters per section are the width and the height of each path as well as the surface roughness within the polished tracks. With the aid of these parameters and further statistical evaluations a suitable parameter field for the goal to find a constant and predictable removal spot was determined. Furthermore up to now over 60 test runs have been successfully finished with nine parameter combinations in each case. As a consequence a test evaluation by hand would be very time-consuming and the software facilitates it dramatically.
Lecture
  • Rolf Rascher
Fertigung präziser Optikflächen – schleifen und polieren oder pressen?
  • 2013
Contribution
  • Engelbert Hofbauer
  • Rolf Rascher
  • Thomas Stubenrauch
  • Johannes Liebl
  • Roland Maurer
  • et al.
Approach to the measurement of astronomical mirrors with new procedures
  • 2013
Lecture
  • Rolf Rascher
Fertigung präziser Optikflächen – schleifen und polieren oder pressen?
  • 2013
Contribution
  • Engelbert Hofbauer
  • Rolf Rascher
  • Thomas Stubenrauch
  • Johannes Liebl
  • Roland Maurer
  • et al.
Approach to the measurement of astronomical mirrors with new procedures
  • 2013
Contribution
  • Roland Maurer
  • Heiko Biskup
  • Christian J. Trum
  • Rolf Rascher
  • Christine Wünsche
Determination of a suitable parameter field for the active fluid jet polishing process
  • 2013

DOI: 10.1117/12.2028752

In 2012 a well-known company in the field of high precision optics assigned the University of Applied Sciences Deggendorf to determine a suitable parameter field for the active fluid jet polishing (AFJP) process in order to reach a surface accuracy of at least lambda / 5. The active fluid jet polishing is a relatively new and an affordable sub-aperture polishing process. For a fast and precise identification of the parameter field a considered design of experiment is necessary. The available control variables were the rotational speed of the nozzle, the distance between the test object and the jet, the feed rate, the material of the pin inside the nozzle and the material of the test object itself. In order to reach a significant data density on the one hand and to minimize the number of test runs on the other hand a meander shaped tool path was chosen. At each blank nine paths had been driven whereby at each path another parameter combination was picked. Thus with only one test object nine parameter settings may be evaluated. For the automatized analysis of the tracks a software tool was developed. The software evaluates ten sections which orthogonally intersect the nine tracks on the test-lens. The significant measurement parameters per section are the width and the height of each path as well as the surface roughness within the polished tracks. With the aid of these parameters and further statistical evaluations a suitable parameter field for the goal to find a constant and predictable removal spot was determined. Furthermore up to now over 60 test runs have been successfully finished with nine parameter combinations in each case. As a consequence a test evaluation by hand would be very time-consuming and the software facilitates it dramatically.
JournalArticle
  • Christian Schopf
  • Rolf Rascher
  • Christine Wünsche
Rauhigkeitsmessungen an großen und schwer zugänglichen Bauteilen
  • 2013
Lecture
  • S. Draxinger
  • Christine Wünsche
  • Rolf Rascher
Subaperture-polishing with variable spots
  • 2013
Lecture
Contribution
  • Roland Maurer
  • Florian Schneider
  • Christine Wünsche
  • Rolf Rascher
Calculation of the reference surface error by analyzing a multiple set of sub-measurements
  • 2013

DOI: 10.1117/12.2024003

In the field of precision optics the interferometry is the most applied measurement method to test spherical and flat objects. In principle, a standard interferometer setup is limited to these surface geometries, but interferometric systems may be modified with the aid of CGH’s or the stitching technology. As a consequence aspherical shapes and even freeform optics are measurable up to a certain extent. In an interferometric measurement the measured variable is the optical path difference (OPD) between the reference wave and the test wave. Based on the detected OPD the surface error of the test object is calculated by phase shifting methods for instance. It is evident, that the error from the reference surface affects the determination of the test object surface error. One option to face this problem is the calibration of the system prior to the measurement. For this the determination of the reference surface error may be realized with the aid of a two sphere test or a random ball test e.g. [1]. In the well-known SSI-technology from QED technologies the reference surface error is calculated on the basis of the sub-measurements. Due to the self-calibrating nature of the QED stitching principle [2-4] a calibration of the system prior to the measurement is not necessary. The University of Applied Sciences Deggendorf has implemented a similar algorithm to estimate the reference wave front error, or to be exact the error of the whole optical system, based on a multiple set of sub-measurements. This paper describes the applied algorithm in detail and discusses the results. To verify the implemented tool the results are compared to the outcomes of the QED stitching software. © (2013) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Contribution
  • Christian Vogt
  • Florian Schneider
  • Rolf Rascher
Grinding Processes for Silicon Carbide (CSiC) Materials , vol2
  • 2013
Contribution
  • Roland Maurer
  • Florian Schneider
  • Christine Wünsche
  • Rolf Rascher
Calculation of the reference surface error by analyzing a multiple set of sub-measurements
  • 2013

DOI: 10.1117/12.2024003

In the field of precision optics the interferometry is the most applied measurement method to test spherical and flat objects. In principle, a standard interferometer setup is limited to these surface geometries, but interferometric systems may be modified with the aid of CGH’s or the stitching technology. As a consequence aspherical shapes and even freeform optics are measurable up to a certain extent. In an interferometric measurement the measured variable is the optical path difference (OPD) between the reference wave and the test wave. Based on the detected OPD the surface error of the test object is calculated by phase shifting methods for instance. It is evident, that the error from the reference surface affects the determination of the test object surface error. One option to face this problem is the calibration of the system prior to the measurement. For this the determination of the reference surface error may be realized with the aid of a two sphere test or a random ball test e.g. [1]. In the well-known SSI-technology from QED technologies the reference surface error is calculated on the basis of the sub-measurements. Due to the self-calibrating nature of the QED stitching principle [2-4] a calibration of the system prior to the measurement is not necessary. The University of Applied Sciences Deggendorf has implemented a similar algorithm to estimate the reference wave front error, or to be exact the error of the whole optical system, based on a multiple set of sub-measurements. This paper describes the applied algorithm in detail and discusses the results. To verify the implemented tool the results are compared to the outcomes of the QED stitching software. © (2013) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Lecture
Lecture
  • Rolf Rascher
  • Johannes Liebl
  • et al.
Hochgenaue Optische Abstandssensoren in Messtechnik und Qualitätssicherung
  • 2012
Lecture
  • Heiko Biskup
  • Rolf Rascher
  • Christine Wünsche
Laserdiffraktometrie zur Charakterisierung von Korngrößen und deren Verteilung in Poliermitteln
  • 2012
Lecture
  • Heiko Biskup
  • Rolf Rascher
  • Christine Wünsche
Laserdiffraktometrie - Korngrößenverteilung in Poliermitteln Posterbeitrag
  • 2012
Contribution
  • M. Fuchs
  • Rolf Rascher
  • Alois Kasberger
  • Christian Wistl
Precision Glass Molding of lenses by using the nanotech molding process - a practical summary Joint Poster Session (JTu5A)
  • 2012
Lecture
  • Heiko Biskup
  • Rolf Rascher
  • Christine Wünsche
Laserdiffraktometrie zur Charakterisierung von Korngrößen und deren Verteilung in Poliermitteln
  • 2012
Lecture
  • Heiko Biskup
  • Rolf Rascher
  • Christine Wünsche
Poliermittelerprobung II
  • 2012
Contribution
  • M. Fuchs
  • Rolf Rascher
  • Alois Kasberger
  • Christian Wistl
Precision Glass Molding of lenses by using the nanotech molding process - a practical summary Joint Poster Session (JTu5A)