Design And Control Research Of A New Type Flexible Joint With Variable Stiffness

The variable stiffness joint,for its adjustable stiffness characteristics,has greater environmental adaptability than traditional rigid joints and simple flexible joints,especially suitable for human-mechanism interaction occasion.But the variable stiffness also brings problems to system such as more complex construction and worse stability.Furthermore,in the existing variable stiffness mechanism,stiffness tend to be nonlinear with multiple parameters,making the joint stiffness identification and stiffness dynamic adjustment more difficult.Aiming at these problems,we design a new variable stiffness structure by using geometric relationships between its structures.On this basis,the design of the set-point control system with dynamic stiffness adjustment are completed.Firstly,aiming at the non-linear problem in the principle of variable stiffness model,this paper proposes a kind of crank-slider like mechanism,which uses the geometric relation between the structure to change the preload of spring and finally realize the approximate linear relation between stiffness and the offset of fulcrum.The introduction of the fulcrum-slider-bearing form in this scheme solves the friction,gap and instability problem in existing fulcrum-chute structures.Besides,the planetary wheel also makes the structure more compact.On this basis,several functional modules of the project are divided and designed,including the stiffness adjustment module,the variable stiffness mechanical drive module,the main drive module and other functional module used for joint measurement.Secondly,according to the non-linearity of the joint stiffness model,the relation between the stiffness and the offset of fulcrum is used to solve the problem in Taylor expansion and parameters decoupling process,after that,stiffness curve can be fitted.On the basis of this,the given value control mode based on trajectory generator is designed for dynamic control of output stiffness,and the mapping between demand stiffness and position is realized.Then,the hardware and software of the control algorithm are studied,and the hardware circuit with command processing,CAN communication,RS485 serial communication,voltage conversion and status indication is designed for the requirements of system communication,power supply and circuit integration.According to the algorithm,the software part is programmed and optimized,and the transmission and feedback from the control command to the lower computer and the motion adjustment module are completed,thus the overall design of the control system is realized.Finally,based on the structure and control system mentioned above,a single joint experiment platform is created.After that,in order to verify the joint stiffness characteristic and position characteristic,we design static stiffness identification experiment,dynamic stiffness following experiment and position tracking experiment under various load,stiffness and demand signals.The experimental results show that the controller designed in this project can realize the continuous adjustment of stiffness and position in qualified range.