Abstract:Aiming to analyze the hysteresis characteristics between the air pressure and angle of four-bar elbow joint driven by pneumatic muscles. The Prandtl-Ishlinskii (PI) model of the hysteresis characteristics of elbow -joint was established, the required parameters of the model were identified by Levenberg-Marquardt method. The appropriate envelope fuction for the improved Play operator was selected, and the modified Prandtl-Ishlinskii (MPI) was designed to describe the asymmetric hysteresis, compared with the classical Prandtl-Ishlinskii (CPI) model, the results of the simulation showed that the MPI model had higher fitting degree for the asymmetric hysteresis curves. Based on the MPI model, a feed-forward integral inverse compensator was designed, an integral inverse compensation controller (MPI-I-I-PID) was formed with PID. The simulation of position control of MPI-I-I-PID, PID and CPI-I-I-PID controller was completed. The results of the simulation and root-mean-square error showed that MPI-I-IPID can reduce the tracking error and improve the tracking accuracy. Equal amplitude sinusoidal signals experiment on PID, CPI-I-I-PID and MPI-I-I-PID controller under different loads was completed, according to the compensation effect influenced by the load which was explosed in the experiment, and piecewise PID control was added in the compensator. The results of experiment and root-mean-square error showed that MPI-I-I-PID can reduce the dither amplitude and tracking error of elbow joint, improve the accuracy and stability of elbow joint position control, which proved the effectiveness of the proposed hysteresis compensator.
