Smoothness-oriented path optimization for robotic milling processes

Industrial robots are increasingly used for five-axis machining operations, where the rotation of the end effector along the toolaxis direction is functionally redundant. This functional redundancy should be carefully resolved when planning the robot path according to the tool path generated by a computer-aided manufacturing(CAM) system. Improper planning of the redundancy may cause drastic variations of the joint motions, which could significantly decrease the machining efficiency as well as the machining accuracy. To tackle this problem, this paper presents a new optimization-based methodology to globally resolve the functional redundancy for the robotic milling process. Firstly, a global performance index concerning the smoothness of the robot path at the joint acceleration level is proposed. By minimizing the smoothness performance index while considering the avoidance of joint limits and the singularity and the constraint of the stiffness performance, the resolution of the redundancy is formulated as a constrained optimization problem. To efficiently solve the problem, the sequential linearization programming method is employed to improve the initial solution provided by the conventional graph-based method. Then, simulations for a given tool path are presented. Compared with the graph-based method, the proposed method can generate a smoother robot path in which a significant reduction of the magnitude of the maximum joint acceleration is obtained, resulting in a smoother tool-tip feedrate profile. Finally, the experiment on the robotic milling system is also presented. The results show that the optimized robot path of the proposed method obtains better surface quality and higher machining efficiency, which verifies the effectiveness of the proposed method.     

Reducing anchor loss In thin-film aluminum nitride-on-diamond contour mode MEMS resonators with support tethers based on phononic crystal strip and reflector

In this paper, we report on (1) the proposed support tether configuration based on phononic crystal (PnC) strip to reduce the anchor loss in the thin-film piezoelectric-on-diamond (TPoD) contour mode microelectromechanical systems (MEMS) resonators, namely the \(100^0\) oriented thin-film aluminum nitride (AlN)-on-diamond wine glass (WG) and width shear (WS) mode MEMS resonators, (2) impacts of the geometrical dimensions on the band gaps of the proposed PnC structure, (3) evaluation of the performance of the Q improvement between the proposed support tether configuration and the one based on the reflector presented by B P Harrington and R Abdolvand. The designed resonators operate at approximately 115 and 156 MHz corresponding with the WG and WS modes. The band gap width covering these two operating frequencies is 30.2 and 20.6 MHz, respectively. The maximum Q of the WG mode resonator with five-unit cell PnC strip based support tethers achieves up to 398.5 % over that of the same resonator with reflector based support tethers. Similar to the WS mode one with three-unit cell PnC strip based support tethers, this Q is up to 591.1 %. The average Q of the WG mode resonator with PnC strip based support tethers over the maximum Q of the same one with different reflectors is enhanced about 964.4, 952.9, 364.2 and 4599.5 %. For the WS mode resonator, these Q values are up to 2388.8, 1830.4, 528.2 and 2384.5 %. The finite element (FE) analysis in COMSOL Multiphysics software (COMSOL) is utilized to simulate the proposed PnC strip as well as the WG and WS mode resonators.