气动肌肉肘关节MPI迟滞模型与补偿控制

Hysteresis Model Based on Modified PI Model and Compensation Control for Elbow Joint Driven by Pneumatic Muscles

摘要:

针对气动肌肉驱动的四连杆肘关节输入气压与输出角度间的迟滞进行分析。建立肘关节迟滞的Prandtl-Ishlinskii（PI）模型，采用Levenberg-Marquardt方法辨识模型参数；选择改进Play算子合适的包络函数，设计一种可描述非对称迟滞现象的改进PI（Modified PI, MPI）模型，相较于传统PI模型（Classical PI, CPI），MPI模型对非对称迟滞曲线拟合度更高。基于MPI模型，设计前馈积分逆补偿器，并与PID组成积分逆补偿控制器(MPI-I-I-PID)；完成了MPI-I-I-PID、PID与基于CPI模型的积分逆补偿PID控制器（CPI-I-I-PID）的位置控制仿真。仿真结果表明，MPI-I-I-PID可以减小跟踪误差，提高跟踪精度。在不同负载下进行了控制实验，实验结果表明，随着负载增加，补偿效果减弱，为此在补偿器中加入分段PID，MPI-I-I-pPID可减小抖动幅度，降低肘关节跟踪误差，提高位置控制精度和稳定性，验证了迟滞补偿器的有效性

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.