Yitbarek Kazentet2, Michael Palmer1, Dr. Dae Wook Kim1

1University of Arizona, Tucson, AZ ; 2Georgia Perimeter College, Clarkston, GA

Background

AbstractOptical surfacing consist of polishing and grinding of all/part of the surface of optical material (lenses or mirrors) to create adesired form/shape and finish. The traditional polishing involves moving a polishing lap over the entire surface to be polished insuch a way that eventually almost every portion of the optics will be rubbed by the polisher. Most traditional methods lack theprecision in creating aspherical smooth finish without damaging the desired details of the surface. The introduction of ComputerControlled Polishing (CCP) empowered the industry to overcome the disadvantages of traditional polishing. CCP uses acomputerized small tool which can rotate and travels on the intended work-pieces to create the parts of the optics. CCP enabledto create a more accurate and precise, controlled, fast, and various shapes. During polishing, the optics may be tested to confirmthat the anticipated surface shape/form is being produced. This test allows to determine the final shape of optics is within theacceptable precision. The deviation of an optical surface from the correct shape is typically expressed in fractions of a visiblewavelength of light. This project is aimed to develop a method to remove tool marks from various optical surfacing technologiessuch as diamond turning, and other machine manufacturing. To achieve this target, it is important to generate small strokepattern that will effectively grind down the tool marks without damaging the surface figure.

Conclusion

Results

The optics under investigation was measured consistently using five distinct reference points. This was important to truck information as well as to get asmany as possible measurements. The testing part of the project go through several experiments. It involved pressing out optical pitch on the surface of theoptics to minimize surface mismatch and identifying the proper polishing chemicals (liquids) such as olive oil, water, soapy water, and Indian ink. The Indianink showed the least effect in scratching the optics during polishing.

Methods

Michael Palmer1

UofA LOFT Group1

Dr. Dae Wook Kim1

Research in Optics (RiO)Korea Basic Science InstituteGrant # 1460723Dr. John KoshelMelissa Sarmiento Ayala, M.Ed.

Figure #2Initial Measurement of the Optics Under investigation.

Figure #3Intermediate Surface Measurement in 3D After Several Stroke Runs.

Figure #1ZYGO Interferometry Workstation. This is usedto take precise Surface Measurements.

Several parts were produced and assembled using nuts and bolts beforemounted to the CNC machine. In this process, we were able to learn thebasics of drilling and tapping holes. We also studied how the 3D printerworks and were able to work the software from formlabR who are thesuppliers of the machine. The most important part of the project hasbeen running successful stokes of different patterns using the CNCmachine. This was important since its success was crucial in proceedingor continuing to the next steps of the project. Different chemicalsincluding water were used until the safest liquid, Indian Ink wasdetermined. Indian Ink as a polishing chemical for the optic underinvestigation showed the least damaging/scratching effect.

Future Work

The results and the depth to which the project progressed should beused as a spring board to complete more successful runs of correctedpatterns. The new runs should use a strong and sharp material insteadof optical pitch in order to smooth out the mid-spatial errors.Measurement of the optics should be more consistent in terms ofrepeating the same exact measurement to avoid inaccuracy.Furthermore, increasing the number of points of measurement can givea better complete understanding of the optics. The analysis andreproducing of the new correction patterns will stay as the fundamentalobjective of the project.

Testing• Run the

generated stroke on CNC Machine

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Support References• DeGroote, Jessica E., “Better Polishing through Chemistry”., www.osa-open.org., (2008)• DeGroote, Jessica E., “Incorporating VIBE into the precision optics manufacturing process”., SPIE

Vol. 8126 812613-1., (2008)• Klinger, Charles., “Vibe: A New Process For High Speed Polishing Of Optical Elements”.,

www.optimaxsi.com., (2006)• Lyons, James J., http://www.nasatech.com/tsp., “Process for Polishing Bare Aluminum to High

Optical Quality”., (2007)• Schinhaer, Markus “Advanced techniques for computer-controlled polishing”. SPIE Vol. 7060

70600Q-1. (2008)

Mid-Spatial Frequency Optical Surface Error Control

Figure #6CNC Machine is used to test the pattern generated by MATLAB.

Measurement • Take Various

measurements and transfer Data

Interpret• Reread and

analyze the data

Preparation• Use the data to

develop an appropriate stroke pattern

Figure #5Stroke pattern on G CODE initiated to run on CNC Machine.

Figure #4A MATLAB output of a stroke pattern density ready to be sent to G CODE

One of the several partsmodelled usingAutodesk’s inventor. Thispart was printed andused to hold the opticswhile the CNC machinewas running the strokepatterns.

Several designed partswere printed using 3Dmachine and assembledto be mounted to theCNC machine. Nuts andbolts were used toassemble the partstogether.

The CNC Machine was guided by theassembled parts to make thecorrected stroke patterns. Differentpolishing chemicals were used to testuntil a constructive result was seenusing Indian Ink. Initial trials weremade on cardboard before it wasexperimented on the real optics. Inthe process, SAGUARO software wasmanipulated for different parametersof the stroke patterns: speed,duration, and length/size of thestrokes.

A typical optical surfacemeasurement taken fromZYGO. The measurementstaken from the ZYGOWhite LightInterferometry werecritical in determining thesurface smoothness of theoptic under investigation.

The ZYGO Interferometryenabled us to provide awide range of statisticaldata and images whichwere transferred andfurther analyzed usingMATLAB program togenerate correctionpatterns.

Courtesy to http://www.acmetools.com

Courtesy to http://www.directindustry.com