Research On Haptic Interaction Of Cable Driven Parallel Robot Based On Admittance Control

With the continuous development of human-computer interaction and virtual reality,force sense simulation equipment is gradually developed.However,traditional force sense simulation equipment mostly adopts rigid link structure,which has small workspace,poor dynamic characteristics and weak immersion in the interaction process.In this paper,a kind of parallel mechanism with rope is proposed as the force sense simulation equipment.The rope has the characteristics of intrinsic safety,which can realize large space movement.The overall inertia of the mechanism is small,and the controllability is high.It can better realize the matching with people,which has important research significance.In this paper,according to the characteristics of force sense,the functions that can be realized when parallel mechanism is applied to force sense simulation are given.Firstly,according to the structure of winch and guide pulley,the relationship between motor angle and rope length is deduced.Secondly,the closed vector method is used to establish the inverse kinematics model considering the influence of the guide pulley movement on the rope length.Then,the forward kinematics model is established by Newton Raphson method.Finally,Newton Euler method is used to complete the dynamics modeling of the whole mechanism,including the dynamics of mobile platform,winch,guide pulley and elastic rope.It lays a theoretical foundation for motion control and calibration.On the basis of kinematics and dynamics,the motion control of the mechanism is realized.The closed form method is used to distribute the tension of the rope.Then,the control strategies based on joint space and task space are explored,and two solutions are proposed to solve the problems of loose rope and large confrontation: the position control based on the combination of inverse solution and rope elasticity and the position control based on internal force coordination;Finally,considering the influence of the installation error of hinge point and the accuracy of inverse solution,the motion control based on pose closed loop is analyzed.For the simulation of force sense,this paper adds admittance controller into the motion control framework of mobile platform,and analyzes the influence of various parameters of admittance controller.Due to the limitation of the space position of the mobile platform,the method of indirectly obtaining the external force by using the rope tension sensor is discussed,and the complete control framework of the rope parallel mechanism applied to the force sensing simulation is given.Through the experiment of the whole control frame,the feasibility of force sense simulation is further verified.Considering the influence of machining error and assembly error,the kinematic parameters of the actual test-bed are uncertain,which reduces the motion accuracy of the test-bed to a large extent.In this paper,the transfer models of structure error,joint error and pose error are derived,and the calibration methods based on forward kinematics and inverse kinematics are used for simulation analysis,which proves the feasibility of calibration for improving motion accuracy.