Closed-Loop Manufacturing of Complex Micro Optics Project

On-machine measurement of micro optics is essential for producing complex high-precision optical components used in next generation imaging systems.  Standard test methods and traceable measurement artifacts are needed to allow users and manufacturers of ultra-precision turning centers equipped with on-machine part inspection systems to communicate measurement uncertainty clearly.  This project seeks to develop standard test methods, traceable measurement artifacts, and uncertainty budgets to enable the performance evaluation of non-contact measurement systems integrated with ultra-precision turning centers.

Objective:

Design, develop, evaluate and propose standard test methods and NIST traceable measurement artifacts for the performance evaluation of in-process measurements of diamond turned micro optics to enable closed-loop machining of complex micro optics with form tolerances in the order of tens of nanometers by 2014.

What is the new technical idea?

Efficiently generating micro optical features with complex form (e.g. aspheric lenses) and tolerances on the order of tens of nanometers is currently an unresolved problem by the optics manufacturing industry.  In-process measurements of machined surfaces, tool geometries, and tool locations with respect to part features provide potential solutions to this problem^[1],[2],[3].  For in-process measurements to be viable, the uncertainty in the measurement should, at a minimum, be four times better than the critical form tolerance.  Therefore the measurement uncertainty must be clearly understood.  Quantifying the measurement uncertainty of on-machine in-process measurements of diamond turned micro optics requires technical expertise in diamond turning, machine design, measurement of optical quality surfaces, machine tool metrology, measurement uncertainty, development of standardized test methods for performance evaluation, and modeling of machines, processes and instrumentation.  NIST has more than 20 years of experience in these technical areas.  This project will combine expertise from these technical areas and use it to synergistically develop standard test methods and traceable measurement artifacts for the performance evaluation of this type of on-machine measurement system.  One idea to be tested will be the development and implementation of "peel and stick" type reference marks on the part blank to establish relative position and orientation of the cutting tool and measuring probe with respect to the part at the nanometer level.

What is the research plan?

This work will be achieved by integrating a commercially available non-contact measurement system(s) with the existing Moore diamond turning machine and using the system(s) to evaluate proposed test methods, measurement artifacts, and uncertainty budgets.  In addition, a working group, led by NIST, consisting of members from imaging, machine tool, and measuring instrument industry as well as academia and other government agencies will be assembled to regularly discuss the technical approach and proposed solutions associated with this work.  Prior discussions with industry have already helped to identify several commercially available measurement instruments being considered for integration with commercially available ultra-precision turning centers.  These instruments include multi-wavelength interferometer probes, confocal probes, and Shack-Hartmann wave front sensors.  The discussions have also identified a technique where feature reference marks (fiducials) are added to the workpiece and used to establish relative position and orientation of the cutting tool with respect to the part feature.  Fiducials will be added to workpieces and measurement artifacts and evaluated for effects on feature accuracy and in-process measurement uncertainty.

The work will begin by first performing detailed measurement uncertainty analyses for the aforementioned measurement systems.  The results of the analyses will then be used to select the measurement system(s) for integration with the existing diamond turning machine.  After instrument(s) selection, a design for mechanically and electrically integrating the selected instrument(s) with the diamond turning machine will be created.  A comprehensive model of the machine and measurement system will then be developed and used to evaluate the compound effect of machine and instrument error on workpiece measurements.  Through simulation of the completed system and regular working group meetings, standard performance measurements and measurement artifacts will be designed, developed, and proposed.  The on-machine measurement system will then be evaluated using the proposed measurement methods and artifacts under open-loop and closed-loop control.  Results from the simulations and measurement tests will be used to help refine the proposed test methods and artifacts.  Upon completion, the evaluated methods and artifacts will be considered for submission to active standard committees for inclusion in national and international standards.

This work will also involve leading the development of a new standard for the performance evaluation of ultra-precision positioning systems.  Proposed test methods and instrumentation will be evaluated and recommendations will be provided to the standards working group.  Upon completion, a draft standard will be submitted to standard committees for inclusion in national and international standards.  Other possible paths for dissemination of the results from this project will include NISTIRs, peer reviewed journal articles, working group discussions and oral presentations at professional conferences, industrial meetings, and standards committee meetings.

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[1] Gill D.D, Claudet A.A., Southwell L.M., 2006, Development and analysis of an optical capability for the measurement of arrays, Proceedings of the 2006 ASPE Annual Meeting.

[2] Kim H.S., Lee K.I., Lee K.M., Bang Y.B., 2009, Fabrication of free-form surfaces using a long-stroke fast tool servo and corrective figuring with on-machine measurement, Int. J. of Machine Tools & Manufacture, V49, pp. 991-997.

[3] Jiang X., 2011, In situ real-time measurement for micro-structured surfaces, CIRP Annals, V60, pp. 563-566.

Recent Results: 

• Outcome:  Capability for ultra-precision machining of optics (using diamond turning) at NIST has been resurrected.
• Outcome:  An on-machine closed-loop measurement capability for diamond turning aluminum cylinders that are 40 mm in diameter and 180 mm long with straightness and diameter tolerances better than ± 100 nanometers has been established at NIST.
  
• Output: (Staff development) Operator training for the M18AG Moore diamond turning machine was completed.
• Output:  Measurement equipment, fixturing, data acquisition software, and analysis software for on-machine multi-probe inspection of diamond turned cylinders.
• Output:  Optical quality aluminum test cylinders for the new calculable capacitor being developed by NIST.
  
• Output:  Type B measurement uncertainty analyses and uncertainty templates/metrics for analytically evaluating the measuring performance of interferometric sensors and confocal pens integrated with ultra-precision turning centers were developed.
• Output:  An absolute multi-probe multi-wavelength interferometer measurement system was selected to be integrated with the NIST diamond turning machine and used for on-machine measurements of optical quality workpieces.
• Output:  A test specimen for a CIRP organized Interlaboratory Comparison was manufactured using the diamond turning machine and submitted to the CIRP collaborative working group on Micro Production Engineering.
• Outcome:  A web based meeting consisting of members from industry, academia, and government was held on May 2, 2012 to discuss the development of a new standard for the performance evaluation of ultra-precision positioning systems.  The need for a new standard was identified and a working group consisting of members from industry, government, and academia was established to develop a draft standard for the performance evaluation of ultra-precision positioning systems.
•  Output:  Fesperman R.R., Donmez M.A., Moylan S.P., Ultra-precision linear motion metrology of a commercially available translation stage, Proceedings of the 2011 ASPE Annual Meeting, Denver, CO, 2011.
• Output:  Fesperman R.R, Ultra-precision Linear Motion Metrology of a commercially available translation stage, Oral Presentation, 2011 ASPE Annual Meeting, Denver, CO, 2011.

Several additional outputs will be achieved before the end of FY2012

• Output:  Documentation including design descriptions and detailed engineering drawings for mechanically and electrically integrating the multi-probe multi-wavelength interferometer system with the NIST diamond turning machine will be generated.
• Output:  A NISTIR describing the uncertainty analyses, the selection process, and the measurement instrument selected for integration with the existing NIST diamond turning machine will be produced.
• Output:  A web based working group meeting consisting of members of industry, academia, and government will be held to discuss NIST’s work in closed-loop manufacturing of micro-optics.  The results from this meeting (e.g., industrial feedback) will be documented in an internal group report.
• Output:  A draft scope for a new standard for the performance evaluation of ultra-precision positioning systems will be generated and presented to the working group and a standard development organization.
  

Recognition of EL

• EL received a letter of appreciation from Aerotech Inc. for ELs work in ultra-precision motion metrology
  

Standards and Codes: 

The EL currently has leadership roles within both National (ASME B5-TC52) and International (ISO TC39/SC2) standard committees for machine tool performance testing.  This project is currently focused on two standards strategies. 

• EL is currently taking a leadership role in the development of standard test methods and traceable measurement artifacts for the performance evaluation of on-machine workpiece inspection systems used during the machining of micro optics.  The developed test methods and artifacts will be proposed for inclusion in ASME B5.57 (Performance evaluation of turning centers) and ISO 230 (Test code for machine tools) series of standards.
  
• EL is currently taking a leadership role in the development of a new standard for the performance evaluation of ultra-precision positioning systems.