Research On Safety Evaluation And Control Strategy Of Cable-Driven Lower Limb Rehabilitation Robot

The reasonable rehabilitation trainings have a significant influence on the plasticity of the nervous system and the recovery of basic functions of patients with limb movement disorders.The safety performance of the rehabilitation training robot for training patients is a key issue to realize the rehabilitation treatment of patients.Due to the different training needs of different patients and the poor combination of patient initiative movement and control methods,it is difficult to evaluate the safety of the rehabilitation robot.The traditional motion control methods cannot solve the behaviors coordination and interaction between patients and rehabilitation robots in the dynamical rehabilitation treatment.Therefore,the rehabilitation robot cannot complete targeted rehabilitation treatment for different patients,resulting in the rehabilitation effect cannot meet the needs of clinical rehabilitation treatment.The rehabilitation effect cannot meet the needs of clinical rehabilitation treatment.In order to realize the safe and effective man-machine compatible rehabilitation training by cable-driven lower limb rehabilitation training robot(CDLR)system,the key scientific problems of human-machine compatibility,system safety evaluation,and compliance control are solved in this study.The rehabilitation needs and main tasks of different patients are analyzed at different rehabilitation stages.Combined with the clinical medicine theory and the analysis of the biological structure and movement of the lower limb,the training modes,rehabilitation training mechanism and design requirements of the CDLR are determined.The overall structure scheme and the cable-driven unit module of the CDLR are proposed based on these design requirements.The control scheme of the CDLR is determined based on the characteristics and use requirements of the rehabilitation robot.The dynamic models of the CDLR with and without bionic muscle cable are established in spatial comprehensive training mode and plane flexion/extension gait training mode.Four optimization algorithms of cable tension are analyzed,and the real-time evaluation index of the optimization algorithms is defined.The mechanical characteristics of the CDLR are analyzed through simulation calculation.The influences of the structural parameters of the elastic elements in the bionic muscle cable on the cable tension are analyzed.The safety evaluation problem of the CDLR is studied in different training modes.The system stiffness of the CDLR was studied.The safety performance factors,position performance factors,cable tension performance factors,and system stiffness performance factors,were defined.The stability evaluation method and index of the CDLR were proposed considering the above safety performance factors in different training modes.The distribution rule of the stability and the influence of the structural parameters of the elastic element in the bionic muscle cable on the stability of the rehabilitation robot system are analyzed by numerical calculation.The reasonable elastic element structural parameters are given in different workspace areas.Considering that different patients have different ability to withstand exercise intensity at different rehabilitation stage,combined with the speed of traction point and the speed fluctuation of the rigid branch-chain slider,the motion speed function was defined.The use safety evaluation index of the CDLR is defined based on the stability evaluation index in different training modes.The influence of motion speed of traction point on the use safety was analyzed through numerical calculations.Taking the CDLR in the spatial comprehensive training mode as the research object,a fuzzy sliding mode variable admittance(FSMVA)control strategy based on system safety evaluation and supervision was designed.The fuzzy sliding mode controller in the inner loop can realize the position control of the end-effector(i.e.traction point of lower limb)of the CDLR.Combined with the variable admittance controller of the outer loop,the compliance control of the CDLR can be realized in different rehabilitation stages and different training courses of different patients.The safety of the CDLR is calculated and supervised by the system safety evaluation and supervision module in real-time.In the variable admittance parameter adjustment algorithm,the safety of the CDLR and the needs of the targeted rehabilitation treatment plan formulated by the rehabilitation physiotherapist were comprehensively considered based on their own clinical experience.A virtual prototype experimental platform for the CDLR was built through ADAMS/MATLAB software,and the control performances of the FSMVA controller based on system safety evaluation and supervision are analyzed through virtual experiments.A CDLR test prototype that meets the requirements of different training modes was built.The safety experiments were carried out on the test prototype in the spatial comprehensive training mode and the plane flexion/extension gait training mode.The performance experiments of the control method of the CDLR were carried out on the test prototype in the spatial comprehensive training mode.The rationality of configuration and the safety evaluation index of the CDLR system,the general control performance of the control strategy of the CDLR are verified by test experiments and human-machine performance experiment,which further shows that the designed CDLR can assist patients to realize the lower limb rehabilitation training.