直线超声电动机驱动的平面3-PRR并联平台视觉精密定位

提出一种直线超声电动机驱动的平面3-PRR并联平台，研究并联平台视觉精密定位技术。给出并联平台结构并采用矢量链法得到并联平台运动学模型。针对并联平台动平台位姿测量问题，利用视觉系统作为反馈单元，通过图像处理技术对动平台上的人工特征中心定位，实现对动平台位姿精确测量；针对传统PID关节控制器在实际控制中问题，采用基于扰动观测器的并联平台支链控制器模型。试验结果表明：对于目标位置为(20 mm,20 mm)，并联平台半闭环控制精度约为±500 µm，而通过视觉定位精度达到±5 µm。视觉定位较半闭环控制大幅提高了并联平台定位精度，能够满足并联平台大行程、高精度定位的需求。

Precision Positioning of a 3-PRR Planar Parallel Manipulator Driven by Linear Ultrasonic Motors Based on Machine Vision

A 3-PRR planar parallel manipulator actuated by liner ultrasonic motor is set up and investigated. The structure of the planar parallel manipulator (PPM) is presented, and then the kinematic model of the manipulator is developed based on vector chain method. To realize the global closed-loop feedback, charge coupled device camera is adopted to measure the output of the manipulator, namely the 3 degrees of freedom of the manipulator. By using the technologies of image processing, the center of the artificial features fixed on the moving platform is located to realize the pose measurement of the moving platform. A perturbation observer-based joint control is adopted to overcome the disadvantage of the traditional PID control in real time control. Experimental results show that the accuracy of the semi-closed loop control of the PPM is around 500 µm while the target position is (20 mm,20 mm), but after the procedure of the visual based closed loop control, the positioning accuracy is further improved to ±5 µm. Compared with the semi-closed loop control, the visual based positioning control provides a substantial increasing in positioning accuracy of the PPM, which could satisfy the positioning requirements of the PPM.