Research On Compliant Interactive Control Strategy Of Manipulator For Unstructured Environment

With the progress of industry and the development of control technology,traditional non-contact operation of manipulators is no longer adequate to meet the increasingly diverse requirements of compliant automation production.Manipulators compliant interaction control system has gradually been applied in industrial scenarios in order to adapt to the actual requirements of complex,intelligent,and compliant contact operation tasks of manipulators in unstructured environments.Compared with traditional position control,compliant interaction control has a wider range of application scenarios,better operational capability,and safer interaction methods,and can more effectively replace human work in dangerous,complex scenarios,and repetitive operations.It is one of the current hot topics in the field of manipulators control.This paper focuses on the research of manipulators compliant interaction with unstructured environments,aiming to achieve compliant completion of complex interaction tasks in unstructured space.The key issues of lack of adaptability and poor dynamic performance in compliant interaction process of manipulators have been given significant attention.An effective manipulator compliant interaction method is proposed by referring to the adaptive mechanism of sliding mode variable structure control and iterative learning control in admittance control framework.The main research content and contributions are as follows:1.The dynamic and steady-state performance of system can be improved by adjusting given values of mass,damping,and stiffness,which has been discovered through a comprehensive comparison of effects of different parameters of admittance control in interaction system of a manipulator in interactive environments ranging from simple to complex,and with expected interaction forces ranging from constant to dynamic.Dynamic changes in environmental position and complexity of task requirements have a greater impact on compliant interaction performance of system.Feasibility of optimizing interaction performance of a manipulator has been analyzed through adjustment of damping and stiffness coefficients using sliding mode variable structure control and iterative learning control.2.An interaction control strategy is proposed based on adaptive sliding mode mechanism,which addresses problem that constant force compensation mechanism lack adaptive capability for manipulator contact with unstructured environment.Adaptive and robust characteristics of sliding mode control are borrowed from proposed method.The proposed control strategy consists of force tracking outer loop and position control inner loop.Proposed control strategy consists of force tracking outer loop and position control inner loop.Force tracking error and sliding mode structure are used to adaptively update damping and stiffness coefficients of admittance controller online.Position tracking error and sliding mode control are used to design position controller to track desired position generated by admittance controller.Simulation experimental results show that proposed compliant interaction control method can ensure stable interaction during dynamic contact between manipulator and unstructured environment.Meanwhile,desired force tracking accuracy of manipulator in steady state is guaranteed.3.A compliant interaction strategy is proposed which draws on iterative learning control to continuously learn valid information from priori information to gradually improve learning mechanism of controller.Proposed method solves problems of long response time,high overshoot,large force error,external disturbance,and uncertainty of manipulator model during interaction between manipulator and unstructured environment.Proposed control strategy consists of force tracking outer loop and position control inner loop.Admittance control parameters are adaptively adjusted by PD-type iterative learning control,and forgetting factor is introduced to compensation to further improve dynamic performance.Sliding mode controller based on continuous hyperbolic tangent functions is used to design position controller to track desired position generated by admittance controller.Simulation experimental results show that proposed compliant interaction strategy can not only greatly reduce force overshoot at contact but also shorten system response time.