To unlock the potential of space, there is a push for better optical imaging, including for larger parabolic on and off-axis mirrors. Costs and lead times have prohibited many programs from scaling. To answer this call, Optimax is developing manufacturing capabilities using a Lean Cell approach, where generation, polishing, smoothing, final figuring, and core metrology are centrally located and tightly controlled. This approach, and its adaptability, will allow lead time reduction from 60+ weeks to eight weeks for 0.5 m optics. Because all components are contained in one cell, ownership of results is carefully monitored by engineers and technicians from start to finish, increasing the quality and decreasing the decision-making time between steps. Finally, advances in the coating capabilities allow for a variety of customized, 0.5 m optic size coating formulations to finish the process. Data from recent projects will be shared to highlight the process and capabilities.
Many optics applications, including x-ray synchrotron systems and space applications, require increasingly precise mirrors to enable diffraction limited focusing of x-ray beams. These mirrors require nanometer level form error and extremely tight tolerances in the mid-spatial frequency and surface roughness ranges. This talk will discuss efforts at Optimax to address this need through advancement of robotic smoothing platforms and processes. Specifically, process refinement results using a large robot, with up to a 1 meter reach, will be shared.
Over the past decade, Optimax has been developing a robotic platform for polishing and smoothing of optics. The robotic platform allows for flexibility and rapid adaptation to different geometries, and significant effort has been applied to improving process and determinism. The robotic platform will enable scaling production of large (up to 500 mm) freeform and aspheric optics much more easily than with commercial manufacturing machines, with improved flexibility to adapt to changing work requirements. This paper with review the robotic platform developments and step through the process of deterministic form correction and predictive smoothing on a simplified geometry.
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 (MSF) errors and surface roughness. Recognizing a gap in domestic production capability for this need, the United States Department of Energy funded Small Business Innovation Research contracts to improve US domestic manufacturing capabilities of these ultra-precision silicon mirrors. This paper will discuss efforts at Optimax to address this need through advancement of robotic smoothing platforms and processes. Flat test parts were ground then had a mirror surface fabricated through single point diamond turning (SPDT). The SPDT process leaves behind characteristic signatures in the surface texture which are detrimental to short wavelength applications. These parts were then smoothed using Optimax’s robotic smoothing platform to eliminate the SPDT signature. Multiple pad and slurry compositions were investigated to determine the optimal choice for each step in the process chain. Significant reduction in the MSF content was achieved, as well as sub- 0.3 nm rms surface roughness, meeting the specifications set out in the project solicitation. Ongoing work is being performed to improve the performance of the robotic smoothing process to address form error.
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.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.