Design Of Series Elastic Actuator System For The Assistive Limb

In recent years, human assistive robot is widely used for the gait rehabilitation of the elderly and disabled and it can also reduce the energy consumption of soldiers and improve their combat capability. As one kind of interactive robots, human assistive robots have high requirement for the comfort and safety. Therefore, a kind of driver with the characteristic of flexibility and bionic-series elastic actuator was designed. Compared with the conventional motor-drive, an elastic element is introduced to the series elastic actuator. In this paper, performance analysis and system design were accomplished in the background of Assistive Limb.Firstly, an analysis for the advantages and constraints when elastic element is introduced to the system was performed with the method of theoretical derivation and Matlab numerical simulation. The result shows that the nature of the series elastic actuator is to get good mechanical properties, such as low mechanical impedance and enhanced impact resistance, at the expense of reduced closed-loop system bandwidth compared with the conventional motor drive.Secondly, a series elastic actuator system used for Assistive Limb was designed. Because of the characteristic of time-varying of the interactive system during motion, a PD feedback controller was designed with the linear quadratic optimal control theory. In addition, the feed-forward filter and disturbance observer were used to improve the robust stability of the system in the human-robot interaction process. As the control algorithm designed above does not involve any body structure parameter, it can be a good reference for the design of other interactive robots.Finally, the theoretical analysis and design of the system were verified through experimental study and simulation by SolidWorks, ADAMS and MATLAB/Simulink. The result shows that the control system can drive the load to move according to the desired motion trajectory by controlling the amount of deformation of the torsion spring. Also, it can restrain external interference to some degree. Meanwhile, the closed loop control system has the robust stability when used for different joints. The experiments also indicate that the nature of the series elastic actuator is to get good mechanical properties at the expense of reduced closed-loop system bandwidth through comparing with the conventional motor drive.