Slow Tool Servo Research Articles

Design and fabrication of a micro Alvarez lens array with a variable focal length

A 5 × 5 micro Alvarez lens array mold was fabricated using a 5-axis ultraprecision diamond machine and an Alvarez lens array was manufactured by injection molding process. Unlike conventional processes for asymmetrical element fabrication such as small tool grinding, this research demonstrates slow tool servo broaching process that allows the entire Alvarez lens array to be accurately machined on a metal mold in a single operation. To further reduce manufacturing cost, injection molding was used to fabricate the Alvarez lens arrays. The mold and molded lenses were both measured using an optical profiler. All measured profiles showed a good agreement with design and surface roughness also indicated an optical surface finish. The functionality of the molded polymeric lens arrays was achieved when the focal lengths were varied by laterally translating the molded Alvarez lens array pair. This research is a demonstration of the capability of fabricating complex optics using the same approach.

Diamond Turning Freeform Optics

Freeform optics fabrication has become one of the hottest topics in optics industry in recent years. Although it still remains a challenge, many have tried different ways of manufacturing it. Some have achieved degrees of success. By means of a Nanotech 350-FG five axis diamond turning machine, we too have successfully produced some prototype freeform optics and lens arrays with Slow Tool Servo and Milling method. The produced freeform optics are mainly for automobile LED headlamps and the lens arrays are for LED illumination. In order to produce the freeform optics, we developed our own DT Slow Tool Servo program which is capable of generating a DT program for diamond turning a universal/general 3D freeform surface. Slow Tool Servo technique and Diamond Milling technique were mainly employed to produce these freeform surfaces. The manufacturing process and machining parameter details will be given in the paper. The two main methods we used will be compared and discussed as well. In measuring the freeform surface, a 3D white light interferometer was used to scan and obtain the surface coordinates. The software made by ourselves enabled us to compare the measure results of the work piece with that of the design drawings. The deviation of our finished forms is within 5 um from that of the nominal. The surface quality Rq is about 10 nm. Measuring equipment and methodology will also be discussed in the paper.

Fabrication of precision 3D microstructures by use of a combination of ultraprecision diamond turning and reactive ion etching process

A novel 3D microstructure fabrication process using a combination of an ultraprecision machining process and reactive ion etching technique is described. Compared to the lithographic process, the conventional microstructuring technique, this new process can produce continuous 3D features on wafer substrates instead of the multi-level profiles created using the lithography-based method. Using ultraprecision single point diamond turning and slow tool servo control, true 3D microstructures were fabricated first on a thin SU-8 photoresist layer, and then the patterned 3D structures on the photoresist layer were transferred to the silicon substrate by precisely controlling the etch depth using the timed reactive ion etching technique. Specifically, a diffractive optical element and a sine wave grating were fabricated using this method on silicon and fused silica wafer substrates. The machined wafers were measured by using an optical profilometer, a scanning electron microscope and an atomic force microscope. All measured profiles showed good agreement with the original design. Finally, a diffractive optical pattern that was fabricated using this technique was successfully transferred to a glass optical surface by use of the compression molding process as a demonstration of possible industrial applications.

Fabrication of diffractive optics by use of slow tool servo diamond turning process

In recent years, it has become possible to fabricate complicated optical surfaces using multi-axis ultraprecision machines. Two diffractive optical designs were fabricated using an ultraprecision diamond turning machine equipped with four independent axes. Unlike the conventional clean-room-based micromachining process, this research demonstrates the development of two innovative diamond tool trajectories that allow the entire diffractive pattern to be machined in a single operation directly, without going through multiple steps, as commonly used in conventional lithography processes. The machined diffractive optical elements were measured for curve geometry and surface roughness. In addition, the optical performance was also evaluated. Finally, a simple welding test setup was utilized to test the 256-level diffractive optical elements (DOEs). Compared to conventional approaches where feature indexing is difficult and unreliable, the slow tool servo (STS) process can be utilized to produce DOEs with accurate geometry and optical surface finish; therefore, the process may be called non-clean-room or maskless micromachining. Unlike its predecessors, this micromachining process which is based on ultraprecision diamond machining can be used to produce true three-dimensional (3D) features in a single operation, thus making it a promising technology for micro-optical, electromechanical component fabrication. Moreover, the 3D micro features can be readily applied to a freeform substrate, making this process a unique approach for fabrication of complicated micro-optical devices.

Design and fabrication of a freeform phase plate for high-order ocular aberration correction

In recent years it has become possible to measure and in some instances to correct the high-order aberrations of human eyes. We have investigated the correction of wavefront error of human eyes by using phase plates designed to compensate for that error. The wavefront aberrations of the four eyes of two subjects were experimentally determined, and compensating phase plates were machined with an ultraprecision diamond-turning machine equipped with four independent axes. A slow-tool servo freeform trajectory was developed for the machine tool path. The machined phase-correction plates were measured and compared with the original design values to validate the process. The position of the phase-plate relative to the pupil is discussed. The practical utility of this mode of aberration correction was investigated with visual acuity testing. The results are consistent with the potential benefit of aberration correction but also underscore the critical positioning requirements of this mode of aberration correction. This process is described in detail from optical measurements, through machining process design and development, to final results.

Design and fabrication of a microlens array by use of a slow tool servo

In recent years it has become possible to fabricate free-form optics by use of multiaxis ultraprecision machines. Here a 5 x 5 microlens array is fabricated by using an ultraprecision diamond turning machine equipped with four independent axes. Unlike the conventional process where a single diamond tool is used to machine one lens at a time, this research demonstrates the development of an innovative diamond tool trajectory that allows the entire microlens array to be machined in a single operation. The machined microlens array is measured for both curve conformity and surface roughness. Compared to the conventional approach where indexing the workpiece is difficult and unreliable, this process can produce microlenses with accurate geometry and optical surface finish. This unique process is described in detail from optical measurement to machining process design and development to final results. This research also demonstrates the possibility of fabricating any arbitrary shape with the same approach.