摘要

Calibration is one of the most important works for the parallel manipulator. The manufacturing and assembling errors will modify the designed parameters of the parallel mechanism, leading to the positioning errors. Calibration is an effective method for improving the accuracy of the parallel mechanism. It is vital to identify the parameters and calibrate the system aiming at improving the positioning accuracy. In order to build an object stage of the micro/nano operation system, a 3 degree-of-freedoms (DOFS) parallel mechanism has been designed and constructed, with combination of legs of the PRR type (the underline of the P represent the actuated joint), P and R representing prismatic and revolute pairs respectively (3PRR). Due to the space constraint, this 3PRR mechanism is built without the end-effector feedback, and must be calibrated for high accuracy positioning. The error model of the 3PRR mechanism has been derived and analyzed, and the error distribution mappings of the 3PRR mechanism are obtained. The calibration method based on the error model is investigated. Since some parameters are difficult to be identified by using the decoupling error model, the assistant measurements are proposed and utilized to compensate for this calibration method. Numerical simulations and experiments are carried out. The simulation results show that it is not enough to calibrate this system by using the calibration method based on error model only, and the experimental results demonstrate that the combined assistant measurements will achieve a better effect for calibration.