Research On Dynamic Torque Control Of Magneto-Rheological Compliant Joint Based On Fractional Order PID Algorithm

Traditional rigid robots are widely used in modern society according to their precise control.However,it is impossible to achieve safer human-machine cooperation due to their lack of active stiffness.Therefore,more and more scholars have integrated new smart materials into rigid robot arms,expected to achieve the compliance of the robotic joint based on multimode sensing information fusion and complex control algorithms.Magneto-rheological Fluid(MRF)is a new type of smart material that has obvious rheological properties under the action of magnetic field and it has been widely used.The magneto-rheological fluid is integrated into the robot joint,and the controlled rheological properties of the magneto-rheological fluid can be used to make the robot joint have the active variable stiffness characteristic.This paper will focus on the problems of magneto-rheological fluids that are difficult to apply to robot joints to achieve active compliance of robot joints.A novel compliant joint coupler was designed based on MRF which as transmission medium.We integrate compliant joint coupler into the traditional rigid mechanical arm and call it as MRF compliant joint.The torque transmission test platform is designed for the compliant joint coupler and conduct related tests: The characteristics of zero-magnetic field with no-load,the characteristics of output torque-excitation circuit and the characteristics of constant torque output.The test results clearly show that the compliant joint coupler which proposed in this paper has good torque transfer characteristics.Analyzing the theory of torque transmission for MRF to establish the static model of the torque transfer of the compliant joint coupler combined with its Bingham-Plastic model.By analyzing the characteristics of MRF material itself with non-uniformity and easy precipitation,we found the dynamic model of torque transfer for compliant joint coupler under the autoregressive principle.We use System Identification toolbox of MATLAB to identify the transfer function model with a set of experimental data.Combined with the torque transfer theory of compliant joint coupler,we proposed a fractional-order PID control algorithm,and focuses on the theoretical basis of fractional calculus.The Oustaloup filter algorithm approximates the calculus operator of fractional-order PID to obtain its digitized form.In MATLAB/Simulink.A simulation model of fractional-order PID control strategy and integer-order PID control strategy is established respectively.The parameters of the fractional-order PID controller are designed based on the ideal Bode transfer function.Finally,the simulation results demonstrate that the closed-loop scheme of fractional-order PID on the compliant joint coupler is better than integer-order PID controller.Finally we built the experimental platform of the compliant joint coupler torque control system.The way how to design the hardware and software of the experimental platform is described in detail.In the LabVIEW environment,the program of the fractional-order PID and the integer-order PID were written.Based on this,the experimental study on torque transmission control of compliant joint couple was developed.The result shows that the static model of the compliant joint coupler is reasonable.The fractional-order PID and integer-order PID control strategies both have effectiveness on the torque transfer control of the compliant joint coupler,but the fractional order PID control strategy is better than integer-order PID control strategy.