Making aspheres with Robotic Polishing
Aperture Optical Sciences Inc. applies two unique technologies, Zeeko robotic grinding and polishing and QED’s magnetorheological (MRF) polishing. Both technologies address the growing demand for high performance aspheric lenses and mirrors for industry and science. We offer MRF polishing through our partner Okamoto Optics and provide Zeeko Robotic polishing on optics up to 800 mm in diameter in our advanced fabrication facility in Central Connecticut.
Making optical mirrors with conic sectional form geometry or Freeform surfaces to nanometer scale tolerances requires programable precision technologies and fine control of material removal methods. Our process begins with precision CNC machining, followed by robotic fine grinding and polishing, high resolution interferometry, coating, and clean system assembly.
Robotic polishing addresses the fundamental problem in aspheric fabrication of surfaces by controlling both the tool contact geometry and the polishing tool motion over the aspheric surface to precisely correct for errors in surface form. This process is dependent on accurate measurement of the surface prior to polishing. Interferometric maps of the surface form are translated into machine instructions, which guide the corrective polishing process.
The Zeeko solution employs a seven-axis robotic platform, which traverses the surface of the workpiece with a user defined polishing tool and abrasive. The tool contact geometry, dwell time, and pressure may all be varied and serve as degrees of freedom to achieve a corrective solution to a user input error map obtained with mechanical or optical metrology. Calculation of a corrective solution also depends on the input of an accurate characterization of the “influence function”, or volumetric removal function over a defined geometry.
As a result of process instabilities, and possible errors in the inputs to the correction plan, 100% predictability of actual material volume is never fully achieved – requiring an iterative process of sequential measurements, calculations, and polishing runs.
A large element of the success or failure of robotic polishing (as well as any form of deterministic finishing) is the accuracy of the measurements made to the surface to be polished. It doesn’t take much to introduce nanometer scale wavefront errors into calibrations of the surface.
To overcome these error sources we employ the highest resolution interferometers available today and collect data with careful attention to thermal control, vibration, mounting errors and image distortion. We employ statistical methods to characterize random and systematic errors.
At AOS we’ve dedicated ourselves, our energy and talents toward perfecting the process of making precision optics.