Technology

Our innovative Computer-Controlled Surface Forming (CSF) technology incorporated traditional pitch polishing processes onto a modern CNC (Computer Numeric Control) platform to achieve the deterministic surface figuring and yet yielding smoothly polished surface. The innovative way of applying polishing pressure and controlling of tool path enables the suppression and elimination of mid-spatial frequency surface irregularity. It offers the combination of the following features into one machine:

1. Deterministic Process resulting fast convergence of surface figure

The CSF machine has been constructed using a precision positioning system with commercially available yet customizable mechanical components. The polishing head is attached to a pressure-sensitive polishing arm that is mounted on gantry stages. A sub-aperture tool is moved across the optical surface radially, while the part is mounted on a spindle for circularly symmetric elements. The system is also capable of raster motion of the polishing head which allows for generating, polishing and correcting of rotationally asymmetric features.

The relative dwell time of the tool over a given position is calculated with a mathematical algorithm based on its deviation from nominal figure, the pressure of tool applied on the part, and other machine operating parameters are also controlled. By varying the amount of time the machine works on any region, a controlled amount of materials may be removed. The best tool configuration for any polishing/figuring operation is determined by use of computer modeling, while the proper operation parameters are obtained from experimentation.

 After testing of various polishing pressures and measuring resulted material removal rates and surface microroughness, the material removal rate data will be incorporated into a deterministic motion control calculation. Using suitable composition materials, customized design of polishing pad, and careful selection of polishing compounds, our process is optimized for the targeted surface polishing and figuring of a particular optics configuration. This technology has proven successful in meeting or exceeding surface figure and finishing specifications, while delivering on target of cost and schedule.

2. Fast material removal rate

The polishing tool provided a key element for manufacturing aspheric surfaces. Depending on the aspheric departure from its best-fit-sphere, the material’s hardness property and volume of material removal, the system uses different sub-aperture polishing materials as polishing pads, which is customized by comprising different combinations of suitable materials at a different iteration stage of the processes. The pad includes natural and man-made material to achieve the best material removal rate and polishing stabilities.

We have achieved fast material removal rate which allows us to economically aspherizing glass substrate with over 100micons of aspheric departure without using grinding compounds and roughen up the surface. It also had shown effectiveness at removing surface pits and scratches.

3. Smooth finish

CSF was designed to accommodate polishing pads of various shapes, sizes, and material. This ability of large selection coupled with design for easy interchangeability allows us to use the most appropriate polishing pads determined by substrate material, shape of aspheric surface, aspheric departure of surface, and most importantly the particular process stage the polisher is used. Especially the pitch pad, incorporated with a predication algorithm, e.g., enabled us to yield ultra-smooth surface without significant degradation of surface figure at the finish process stage.

4. No introduction of proprietary compounds

CSF technology uses conventional polishing compounds and achieves excellent results by tightly controlling its physical and chemical properties. However, this is done without introducing any non-conventional substances or chemicals, which might not be compatible with certain application environments. For example, we can incorporate well developed compounds and processes on flat and spherical optics for super-high power laser optics into our aspheric surface finishing, avoiding proprietary compounds containing particles which lower the damaging threshold of laser optics.

5. No limitation on substrate materials

It has been proven that CSF technology can be applied to many types of, reflective and diffractive, substrate materials, including all glass substrates, fused silica, Zerodur, single crystal silicon, calcium fluoride, etc. As a matter of fact, due to its ability of incorporating pitch and other types of polishing pad materials, CSF technology should be able to polish aspheric surfaces on any type of material as long as they can be conventionally polished into flat and spherical optics.

6. Maximum flexibility and manufacturing efficiencies

Kong Optics’ in-house developed polishing system with innovative technologies allows easy duplication of similar systems with high economic efficiency and maximum flexibility. This is essential in a volume production environment, where polishing is the bottle neck.