Study On Compliant Control Methods For A Categories Of For Parallel Robots

When carrying out grinding,sorting,handling and other tasks,a robot is in direct contact with the environment(people or objects to be operated).However,excessive interaction force may easily damage the robot or do harm to the environment.Therefore,when interacting with the environment,the robot should need certain flexibility to avoid damage to the environment or itself,which means the compliance control is an important way to improve the flexibility.The impedance control law for a robot usually aims at achieving the desired linear spring-damping dynamics of the interaction force and the desired-trajectory tracking error,which is an important active compliance control method.While the series elastic actuator(SEA)brings in attractive features including low output impedance,tolerance to shocks and elasticities,energy efficiency,smooth force transmission,it is a popular passive compliance actuator.However,the uncertainties in the robot control model and the time-varying impedance parameters affect the stability of the impedance control.Also,control saturations induced by the introduction of SEAs cannot be neglected.Therefore,it is of great value to study adaptive impedance control and saturated control for SEA-driven robots.The main research work of this paper are summarized as follows:1)A neural approximation-based variable impedance controller for robots in robotenvironment interaction is proposed.Constraints on variable impedance parameters are given to ensure the exponential stability of the desired first-and second-order variable impedance dynamics.Adaptive neural network controllers are proposed to ensure the achievement of the desired first-and second-order variable impedance dynamics through convergence of variable impedance errors based on dead zone network regulation law.Theoretical analysis and simulation results validate the effectiveness of the proposed variable impedance control methods.2)A saturated nonlinear control strategy is proposed for regulation of SEA-driven robots which is based on Energy Shaping(ES).The ES-based saturated nonlinear controller is proposed by a saturated PD regulation control term plus a static gravity compensator.Satisfaction of the control saturation is guaranteed by introduction of the hyperbolic tangent function.Asymptotic stability of the closed-loop control systems is established based on the La Salle theorem.3)Base on singular perturbation method(SP),a saturated nonlinear control strategy is proposed for regulation of SEA-driven robots.The SP-based saturated controller is designed with two saturated control terms for cascaded two subsystems.A bounded proportional derivative(PD)control term plus a bounded adaptive gravitational torque compensator is designed for the slow-varying subsystem.A bounded derivative-type control term is designed for the fast actuator subsystem.The Hoppensteadts Theorem is applied to approve the semiglobal asymptotical control stability while satisfying the control saturations.