The next generation of x-ray synchrotron systems require increasingly precise mirrors to enable diffraction limited focusing of x-ray beams. Due to the extremely short wavelength of the x-ray radiation, coated silicon mirrors must be used at grazing incidence to focus the x-ray beams. These mirrors need to be polished to nanometer level form error and are particularly susceptible to surface texture, including mid-spatial frequency errors and surface roughness. This talk will discuss efforts at Optimax to address this need through advancement of robotic smoothing platforms and processes.
Freeform optics have shown the ability to drastically increase optical design options, providing new solutions for space telescope and optics applications. Freeform optics manufacturing strives to provide designers this flexibility, but the requisite subaperture generation and polishing techniques often result in mid-spatial frequency (MSF) errors. Because these errors negatively impact final performance, they must be removed. However, mitigation options are costly and timeconsuming. The HERMES (High End Robotic MSF Elimination System) is a robotic platform that uses a machine learning algorithm and deflectometry data to smooth optics. This project has shown preliminary success, and began to forecast increases in form error to help balance smoothing time predictions. Other advancements are explored by the current work. First, the algorithm has been upgraded to include a force-controlled option that utilizes form data (from interferometry) to scale applied force during the smoothing process that is mapped to deviation data. This project also integrated an orthogonal (or raster) pattern of smoothing found in early human smoothing recordings. The various conditions were compared, and result metrics included the peak power spectral density (PSD) values of the frequency of interest as well as irregularity (form) error. All conditions decreased peak PSD values reliabilty, but irregularity data became more difficult to interpret. Findings and further work are discussed.
Freeform optics offer great flexibility in design parameters, but the subaperture techniques required for manufacture often result in mid-spatial frequency (MSF) errors that can impact final performance. These errors must be removed, but the options to do so, often requiring hand-smoothing by a skilled artisan, are costly and time-consuming. Optimax has developed the HERMES (High End Robotic MSF Elimination System) a robotic platform that uses a machine learning algorithm to smooth parts. Preliminary research indicated promising results, but the process had not yet been compared to the “gold standard” of human smoothing. Results indicate that HERMES fared well compared to smoothing results of a highly skilled artisan. Future directions for work are discussed.
There is a potential need for large (<500 mm diameter) conformal windows for use on air, space, and water craft. These windows need to fit the curvature of the vehicle, which results in extreme freeform geometries. “Extreme Freeforms” are a class of shapes that do not have rotational symmetry, must be polished using sub-aperture techniques, and whose deviation from a best-fit sphere is on the same order as the size of the part. This paper will discuss some of the challenges associated with manufacturing optics of this size and shape and how Optimax solved them. These challenges include: blank acquisition, a lack of viable commercially available polishing platforms for extreme freeform shapes, and metrology. A demonstrator optic was designed and manufactured from fused quartz. Final metrology data for both sides of the window will be shown and discussed.
With optical technology and design advances, larger freeform optics are increasingly sought after by consumers for an expanding number of applications. Many techniques have been developed to meet the challenges of producing these nonrotationally symmetric optics, which cannot be fabricated via traditional manufacturing and metrology processes. In the past, methods were established to create smaller freeforms. With demands for more and larger freeforms, manufacturers must scale up existing processes. This paper will present some of the challenges and solutions of extending freeform polishing capabilities from approximately 150 mm diameter parts to a component of over 500 mm in diameter. In fabricating the 500 mm freeform, Optimax has addressed many of the manufacturing and metrology challenges using some proprietary techniques as well as some novel methods. Some of the approaches explored in this paper include acquisition of a substrate blank of sufficient dimensions, material handling logistics, polishing strategies, and metrology. Earlier freeform polishing projects at Optimax utilized a smaller pick-and-place style, 6-axis robotic arm. The route to design, build, and program a scaled-up polishing robotic arm is discussed. Considerations for polishing path planning and metrology are explained. In addition, deflectometry, a non-interferometric measurement method using fringe reflection and ray tracing, has been developed in parallel to help measure mid-spatial frequency error on a part surface faster and more safely than traditional methods, as it can be done in-situ.
Freeform optical components are gaining popularity with designers due to their ability to improve optical and aerodynamic performance for many applications. The challenges involved with the manufacturing and metrology of these shapes, which have little or no symmetry, has been discussed at previous talks and conferences. This paper will focus on the challenges that Optimax faced as we scaled up our freeform polishing process from parts with approximately 150 mm diameters, to polishing components with diameters over 600 mm. The large format platform, designed, built, and programmed at Optimax, utilizes a pick-and-place style, 6-axis robotic arm for the polishing motion. In order to scale up the platform from our existing robotic polishers, a larger robotic arm was used. The associated challenges include: timing considerations for both the polishing and metrology, obtaining sufficient material removal for reliable measurements, and difficulties modelling robot joint positions for collision prevention. These issues have been investigated and mitigated through proprietary techniques and novel solutions, some of which will be explored in this paper. One such technique currently under development at Optimax is deflectometry; which is a noninterferometric method involving fringe reflection and ray tracing to calculate the mid-spatial frequency (MSF) error on a part surface. Deflectometry is able to measure MSF error two orders of magnitude faster than the current method, and has been implemented in-situ, mitigating another challenges involved with larger freeform optics: the logistics of moving them around a shop floor safely.
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