This work is a continuation of previously published work on the application of fiber-based tools in precision polishing of optical components. Previous publications mainly focused on understanding how fiber-based tools remove material and the potential of such tools in reducing existing midspatial frequency errors on planar samples. In this work, an exemplary tool consisting of nylon 6/6 fibers is used in a five-axis computerized numerically controlled machine tool to evaluate the tool’s ability to polish nonplanar BK7 components. The five-axis system has an inline slurry feed system which is found to produce higher material removal rates than the nonrecirculatory slurry bath configuration used in earlier polishing tests. Polishing results obtained on planar and spherical surfaces in the five-axis system show close agreement with that predicted via convolution. A finite element model of the fiber’s interaction with a concave surface shows that the calculated local pressure distribution reflects that observed experimentally, thus further supporting the predictable behavior of fiber-based tools.
An optical positioning sensor is realized by combining optical projection and a virtual camera model. This technique provides a low cost and non-contact measurement and has the potential to provide real-time 6 DOF measurements of an object. The optical sensor first generates a projection pattern that is observable on the surrounding walls, cameras are used to track the motion of the projected optical pattern, and the motion of the optical sensor can thus be tracked indirectly. In this technique, the optical sensor itself is treated as a virtual pinhole camera. A virtual image is generated that carries the angular characteristics of the optical pattern. The virtual image and the images of the projected optical pattern on the walls taken by real cameras are then processed through a photogrammetry-based bundle adjustment to give a position and orientation estimate of the optical sensor. Experiment is performed to calibrate the angular information of the optical pattern. Monte-Carlo simulation is performed to analyse the measurement uncertainty. The simulation result has good agreement with the experimental result for 0.9 m translation test along a precision rail. The optical sensor with the virtual camera model solution is preferable to provide real time measurements for simple-to-complex environments.
Many advanced dimensional measurements exist that incorporate two-dimensional images of the object to be measured, such as structured-light measurements and photogrammetry. The measurements are quite complex and often suitable calibration artifacts are not available; consequently, a traceable uncertainty analysis is difficult. Advanced optical simulation packages can be used to assess important aspects of the uncertainty. These packages can simulate a virtual object to be measured, simulate a virtual camera, and trace rays as they leave a light source, scatter from the object, propagate through the camera, and arrive at the camera image plane. The result is a virtual image of the object whose dimensions are known. The virtual image(s) can then be processed as part of a dimensional measurement and the results compared to the known dimensions of the object. This allows different uncertainty aspects to be isolated and explored. It can be used to validate and understand the current methods of estimating measurement uncertainty, explore optimal measurement conditions, and/or test data analysis algorithms. These types of measurements involve a camera calibration process and the technique can also be used to check this step. This paper demonstrates the approach as applied to a photogrammetry measurement of a box.
In the 70's Leistner  demonstrated that PTFE (Teflon) coated substrates, when used instead of pitch coated substrates,
have the ability to produce polished surfaces with low surface roughness (<2A°) and high flatness (<&lgr;/100). Their PTFE
tool was made by painting and curing several layers of PTFE on a glass ceramic substrate, a time and labor intensive
process. Over the years there has been an increase in the number of formats in which PTFE can be purchased. One such
format is that of thin PTFE sheets with an adhesive backing. The potential of this user friendly PTFE format to replace
pitch was investigated. A thin sheet of PTFE was adhered to metal substrate and used to polish a glass workpiece.
Different polishing set-ups were investigated and the resulting surface finish measured. Best surface roughness values
obtained on optical glass polished with an alumina based slurry was R<sub>rms</sub> = 0.49nm (Zygo interferometer 50x). Under the
same conditions a pitch tool produced a surface roughness value of R<sub>rms</sub> >1.1 nm (Zygo interferometer 50x). The
material removal rate with pitch tooling was approximately five times greater than that achieved using the PTFE sheet.
While the results are not as good as that produced by Leistner, the work does illustrate the potential of an off the shelf
PTFE sheet as a polishing pad. Should the entire process be further optimized lower surface roughness values should be obtainable.
Nano-sized particles with well defined geometries and size distributions suitable for polishing glass and glass ceramics
are readily available. Understanding how effective these particles are at removing material and smoothening surfaces
during pitch polishing processes is essential for process optimization and achieving better surfaces. This paper details
work conducted to measure how effective sub-micron sized particles are at polishing and to isolate the influence of
process chemistry and slurry density on the material removal rate (MRR). The paper also details how modifying the
slurry pH affects the polishing coefficient of friction (CoF). Fused silica was polished on a synthetic pitch polishing tool
with a range of different polishing slurries. Slurries tested included 40nm diameter ceria based slurries with varying
density and pH, and both 20nm and 750nm diameter ceria based slurries with fixed density and pH values. Findings
include that a) the material removal rate decreases with particle size and decreasing slurry density, b) the surface finish is
not strongly dependent on particle size, c) slurries with a pH of 7 are most effective in removing material, while slurries
with a pH value of 4 have the lowest MRR, and finally that d) the polishing CoF is greatest at pH 4 and lowest at pH 10.
The results indicate that while process chemistry is very influential when polishing with submicron sized particles, the
actual nature of the interaction between the abrasive, the workpiece and the tool requires further investigation.
Different applications of aspheric optics and their related fabrication methods are firstly summarized and then discussed using Carl Zeiss examples. This is done in order to highlight the potential and challenges of fabricating aspheric optics. The need to stimulate new ideas for extending manufacturing capabilities, process improvements and new fabrication technologies will also be outlined.