| Lower limb exoskeleton is a kind of power assisted wearable device,which can provide the human body load-bearing,protection and assistance power functions.It can also help the human body to carry out proper rehabilitation training by planning gait.In view of the complexity of the technology of the lower extremity exoskeleton,the prototype is still in the stage of testing and testing,and commercial products have not yet been formed.This paper mainly studies the position following control strategy of the electro-hydraulic servo system for a lower limb exoskeleton.Due to the multi variable,nonlinear and complex model,the difficult control of the lower limb exoskeleton’s electro-hydraulic control system is increased.The conventional PID control method requires the exact mathematical model,while the analysis of the exoskeleton of the lower limb is more or less simplified,and there are some differences between its actual situation and model;Although the fuzzy PID control optimizes the PID algorithm,the fuzzy control reduces the precision of the control;and sliding mode fuzzy PID control is expected to overcome its shortcomings.This paper is supported by the scientific and technological research project of Anhui province "wearable lower limb exoskeleton robot"(item number:1604a0902125),and the mechanical structure,dynamics model,kinematics analysis,the design of the hydraulic drive system and the modeling of the electro-hydraulic servo system are studied,and the PID and fuzzy PID control method is used to control the electro-hydraulic servo system,and the sliding mode control is used to optimize the fuzzy PID control to make the motion state of lower limb exoskeleton consistent with the gait of the wearer.The main contents included,1.The structure,the form of movement and the range of movement of the joints of the lower limbs in normal walking is studied.According to the mechanical structure,the mathematical model of the lower extremity exoskeleton dynamics and kinematics is established.2.Due to the characteristics of lower limb exoskeleton robot,such as fast response,light weight and so on,the hydraulic system is used to drive the lower limb exoskeleton in this paper.According to the mechanical structure of the exoskeleton,completes the design of the hydraulic system and the selection of hydraulic components.The transfer function of the electro-hydraulic servo system is derived,and the geometric relationship between the output position of the electro-hydraulic servo system and the mechanical structure of the lower limb is analyzed.3.According to the mathematical model of the exoskeleton electro-hydraulic servo system,the effect of the lower limb exoskeleton following the human gait trajectory is studied with each joint angle as the input signal.By using PID algorithm,fuzzy PID algorithm and sliding mode fuzzy PID algorithm,the control system model is established and simulated in the Simulink software.The rationality of the control method is verified,and the sliding mode fuzzy PID is used to control the exoskeleton of the lower limb.The main innovation of this paper is based on the PID algorithm and the fuzzy control,combining with sliding mode control,designing sliding mode fuzzy PID controller and comparing with the conventional PID algorithm and fuzzy PID control algorithm which can effectively improve the accuracy of the exoskeleton position control,providing a reference for the lower extremity exoskeleton further study. |
