Research On Hybrid System Framework For Unified Impedance/Admittance And Force Tracking Control Of Collaborative Robot

Nowadays,robots outperform humans in terms of repetitive speed and precision tasks.However,with the expanding application of robots,more and more tasks require the robot to have dynamic interaction with the environment,which requires the robot to have compliance and puts forward new requirements for the control algorithm of robots.Therefore,this paper conducts research on active compliance control for collaborative robots.Firstly,based on Spong's hypothesis,the complete model and reduced model of the flexible joint robot are established using the Lagrangian method.Collision detection and identification of rigid robot and flexible joint robot are realized by establishing energy observer and generalized momentum observer.A sensor-less method for estimating the force of robot end-effector is given.Secondly,the hybrid system framework of rigid robot is studied to improve the performance of impedance-based control.Cartesian impedance control and admittance control algorithms are designed for rigid robots.Based on the complementary stability and performance characteristics of impedance control and admittance control,a hybrid impedance and admittance controller is designed by using the concept of switching system,and a hybrid system framework is established.By taking the duty cycle as a design parameter,the ratio of impedance control and admittance control to the total response of the system can be adjusted,and regulation of the impedance control performance of the hybrid controller is achieved.For environment with unknown time-varying stiffness,an adaptive strategy,consisting of a RLS algorithm and a piecewise function,has been proposed.The RLS algorithm is used to establish the environmental stiffness estimator.By designing the evaluation function of the controller's performance,the adaptation rate of the duty cycle to the environmental stiffness is obtained.Thirdly,in order to realize the robot's interaction with the outside world with a desired force,the force control algorithm of the flexible joint robot based on impedance control is studied.Based on the passivity theory,the joint space and Cartesian space impedance control algorithm of flexible joint robot are established respectively,and the passivity of the system is analyzed.For Cartesian impedance control,the contact equilibrium condition of the robot is analyzed,and the force tracking impedance control algorithm of rigid robot is deduced.Based on the passive impedance control framework,a force tracking impedance control algorithm for flexible joint robots is established.An energy tank is designed to preserve the passivity of the whole Robot-Environment interaction system.At the same time,an adaptive compensation rate is designed to ensure the force control performance of the algorithm.Finally,simulation analysis is performed using Matlab/Simulink and Adams.The simulation results show that the hybrid controller can make an interpolation of impedance control and admittance control performance by changing the value of the duty cycle.The adaptive hybrid controller can combine the robustness of impedance control in rigid contact with the accuracy of admittance control in free motion,and can always achieve excellent impedance performance in different unknown time-varying stiffness environments.The force tracking impedance control algorithm has excellent force control performance.In particular,the control algorithm with adaptive compensation term can adapt to various changes of the environment's surface and realize the tracking of the environmental surface with a small force tracking error.