Design Methodology Of A Non-linear Stiffness Compliant Actuator For Shoulder Rehabilitation Robotics

In order to realize the flexible interaction between human and rehabilitation robots and avoid the bulky and complicated mechanical structure of variable stiffness actuators,the concept of “small load,low stiffness and large load,high stiffness” was presented in this thesis.Such concept can be applied not only to design the actuated joints of rehabilitation robots,but also to the joints of robotic manipulators in unstructured environments.According to this concept,a method of designing a novel compliant actuator whose stiffness matches the predefined deflection-torque trajectory was proposed.The simulation with finite element and experiment were implemented to verify the validity of the design.Torque control and impedance control were developed.The contents and achievements of this thesis were summarized as follows:Firstly,a new compliant topological structure which consists of a roller and an elastic element with customized curve profile was proposed innovatively.The elastic element includes elastic part and contact part.Take the contact part as rigid body,the effect of the elastic part can be equivalent to the common action of a linear spring and a torsion spring.The analysis of non-linear stiffness was carried out based on straight profile and curve profile of the contact part.Secondly,the size of the elastic part was optimized by ANSYS Workbench and then the curve profile of the contact part was designed by MATLAB with an iterative method.For matching the high precision requirement to stiffness characteristic,a method of error compensation was proposed by using a pseudo desired trajectory.An experiment was implemented to evaluate the efficacy of the proposed method of designing a non-linear stiffness compliant actuator.Finally,according to the dynamic model of the compliant actuator,the torque control system was established.The control system with disturbance observer introduced was analyzed by using MATLAB/SIMULINK.Internal torque-based impedance control was also implemented.The simulation results indicated that the proposed controller can improve the performance of the compliant actuator.