Xiaoqin Zhou

Development of pseudo-random diamond turning method for fabricating freeform optics with scattering homogenization

In this paper, a novel pseudo-random diamond turning (PRDT) method is proposed for the fabrication of freeform optics with scattering homogenization by means of actively eliminating the inherent periodicity of the residual tool marks. The strategy for accurately determining the spiral toolpath with pseudo-random vibration modulation is deliberately explained. Spatial geometric calculation method is employed to determine the toolpath in consideration of cutting tool geometries, and an iteration algorithm is further introduced to enhance the computation efficiency. Moreover, a novel two degree of freedom fast tool servo (2-DOF FTS) system with decoupled motions is developed to implement the PRDT method. Taking advantage of a novel surface topography generation algorithm, theoretical surfaces generated by using the calculated toolpaths are obtained, the accuracy of the toolpath generation and the efficiency of the PRDT method for breaking up the inherent periodicity of tool marks are examined. A series of preliminary cutting experiments are carried out to verify the efficiency of the proposed PRDT method, the experimental results obtained are in good agreement with the results obtained by numerical simulation. In addition, the results of scattering experiments indicate that the proposed PRDT method will be a very promising technique to achieve the scattering homogenization of machined surfaces with complicated shapes.

A novel hybrid control strategy for trajectory tracking of fast tool servo

By integrating the fractional order PID (FPID) with repetitive control (RC), a hybrid control strategy is proposed for fast tool servo (FTS) to improve the trajectory tracking performances. A differential evolution algorithm is used to determine the optimal parameters of FPID controller. The control performances of conventional PID (CPID) and FPID controllers are compared by numerical simulation based on the response time and tracking accuracy, the results verify that FPID controller is of more excellent control performance. In order to improve the tracking performance of FTS on periodical command signals, RC is further integrated into the FPID control system. The feasibility and availability of the proposed hybrid controller has been examined by tracking control of a sinusoidal command, the results show that the tracking error of the hybrid controller is 1/11.7 and 1/4.5 times of CPID and FPID, respectively, and it is suitable for the trajectory tracking control of FTS.

Notice of Retraction A review on mathematical description and decomposition algorithms of freeform optical surfaces in diamond turning

There is an ever-increasing demand for freeform optical surfaces in various industrial fields. The fast tool servo (FTS) based diamond turning has been recognized as a high-efficiency, high-precision and cost-effective machining process of generating freeform optical surfaces. In order to implement the FTS based diamond turning, the freeform optical surface should be decomposed into a rotationally symmetric component and a non-rotationally symmetric residual. The mathematical description of freeform optical surfaces used in optical design is systematically summarized, and the decomposition algorithms of freeform optical surfaces used in optical manufacturing are presented in this paper.