UltraForm Finishing (UFF) is a new deterministic subaperture computer numerically controlled (CNC) polisher.
Because UFF uses a compliant tool, the desired depth of removal is achieved by adjusting the tool crossfeed velocity.
Algorithms for determining an optimum crossfeed velocity profile that satisfies tool velocity and acceleration constraints
have been derived for flats, spheres, and mild aspheres. The solutions were validated experimentally. The removal
function that characterizes the interaction between a particular tool and part material is evaluated by making a removal
spot for one set of process parameters. Its variations, as a function of the process parameters, are predicted by using
Hertz contact theory and the Preston equation. Additional algorithms were developed for the evaluation of part and spot
metrology inputs and for tool path generation to prevent tool-part collisions.
UltraForm Finishing (UFF) is a new deterministic subaperture computer numerically controlled (CNC) polisher. Because UFF uses compliant tools with large contact patches, the depth of removal is prescribed by adjusting the tool crossfeed velocity. The equations for the depth of removal as the tool traverses an axisymmetric part are derived. The form correction problem consists in solving these equations by adjusting the tool crossfeed velocity to achieve a desired removal profile. The solution must satisfy constraints on the tool velocity and acceleration. Solutions for flats, spheres and aspheres are achieved by treating the problem as a constrained optimization after writing the depth of removal equations in matrix form. The solutions were validated experimentally. The removal function is evaluated by making a removal spot for one set of process parameters. Its variations, as a function of the process parameters, are predicted by using Hertz contact theory and the Preston equation. To prevent tool-part collisions and to analyze part and spot measurements, algorithms were developed for the tool path and evaluation of metrology inputs.
A new compliant sub-aperture optical finishing technique is being investigated for the removal of mid-spatial frequency artifacts and smoothing of hard polycrystalline infrared ceramics for aspheric applications and conformal shaped optics. The UltraForm concept was developed by OptiPro Systems, Ontario, NY, and is a joint process development effort with the Center for Optics Manufacturing (COM). The latest version of the UltraForm tool "V3" is of a belted design whereby a belt of finishing material is passed over a toroidal elastomeric wheel. Finishing materials used include a wide variety of pad materials and abrasive selections. Experimentation has been conducted using both slurry mixes and fixed abrasive bands. The toroidal wheel is rotated while the compliant tool is compressed into contact with the optical surface. Presented will be the current results in optical glasses and crystalline ceramics such as ALON, Spinel and Polycrystalline Alumina.
Contact mechanics was investigated for compliant tools being developed for UltraForm Finishing. Hertz contact theory predictions were compared with experimental measurements. A high speed camera was used to investigate the size and consistency of the contact spots. The contact pressure distributions were measured with a Tekscan tactile grid system. Preston's equation was used to derive a relation between the pressure distributions and the corresponding removal spots. Experimental results were used to estimate Preston's coefficient for this process.
A new generation of compliant tools and processes called UltraForm Finishing is under development at the Center for Optics Manufacturing (COM) and OptiPro Systems (Ontario, NY). The purpose is to achieve rapid, high quality finishing of hard materials. These compliant tools exhibit a large contact patch that can be up to 1 cm wide. A numerical model was developed to account for finite contact patch geometry on removal for a flat rotating axisymmetric workpiece. This model was used to determine the depth of removal as a function of radial position after the polishing tool has completely traversed the workpiece from its center to a given radial position. The depth of removal was investigated for circular and oval contact patches and a variety of removal functions. A constant removal depth is desired to minimize the induced figure error. Predicted results were compared to experimental measurements of induced figure error.