Papers by Keyword: Precision Diamond Turning

Abstract: In recent years, micro lens arrays have played a crucial role in optical illumination systems. The function of micro lens arrays (MLAs) is to create a uniform light intensity or shape the light profile. Polymers that are commonly used as MLAs have several advantages, such as cost effectiveness, light weight, and easy formation. In general, the ultra-precision diamond-turning technique and plastic injection molding technique have been combined to fabricate MLAs with polymer materials. However, residual stress and non-balance injection pressure are produced on MLAs during injecting processing. Therefore, this paper presents the fabrication of MLAs using a direct molding method (DMM). The STAVAX with electroless nickel coating and PMMA were used as the mold and polymer preform, respectively. First, a mold of MLA with 100% filling factor was fabricated using the ultra-precision diamond-turning technique. A high filling factor can decrease the non-effective area of the MLA in an optical system. Subsequently, an MLA was formed on the PMMA surface using DMM processing. This paper shows the DMM process parameters, including molding temperature, molding force, and cooling rate. Moreover, the profile of the MLA was measured using a laser confocal microscope. Finally, a high filling factor MLA with a diameter of 11.5 mm, and lenses with a height of 8.5 μm and a radius of 470 μm were formed on PMMA.

Abstract: A novel fast tool servo driven by piezoelectric actuator for precision diamond turning is designed in this paper. To overcome the inherent hysteresis and drift nonlinearity effect of the piezoelectric actuator, a closed-loop control system is established using strain gauge integrated in the actuator for position feedback, which has compact structure and can avoid interference in the machining. Furthermore, a fuzzy PI control algorithm is presented. It has not only the advantages of agility and adaptability of fuzzy control, but the characteristics of high accuracy of PI arithmetic. At last, experiments are carried out and the results show that the fuzzy PI control provides significantly better tracking accuracy and robustness against hysteresis and drift effects.

Abstract: Precise and efficient tool setting technique and accurate tool shape monitoring are of essential importance in ultra-precision diamond turning operation. The traditional way of tool setting are typically laborious, inefficient and rely heavily on experience. A big part of the tool setting is done by using a contact probe such as LVDT. The contact tool setting station can normally, depending on the resolution of the probes, place the tool tip to within a 1~10μm positioning accuracy. However, it is running the risk of damage the delicate tool tip and has the ambiguity introduced by contact point of tool and touch probe. The optical/non-contact way of setting the tool do have the advantage of not having to touch the tool, but its resolution is limited by the optical diffraction limit and the resolution of the CCD device used (mm/pixel). A non-contact precision tool setting system is developed and built in this study using edge-detection image processing and sub-pixel dividing techniques in conjunction with CNC controller of the precision turning machine to improve the system presently available. Depending on the sampling distance of the images, the error band gets wider when the sampling step becomes larger. In the case of 0.1μm sampling distance the obtained error band was within ±0.1μm and the results showed that tools of different shapes namely round, half-round and sharp tool could all be positioned to within an error band of ±0.1μm by using the developed tool setting system.