Adaptive Motion/Force Control For Rigid-Link Flexible-joint Manipulators With Time Delay

Recently,due to their attractive features,robotic manipulators enjoy great popularity in a variety of industrial applications and play a more and more important role in the areas of grinding,welding,assembling,as well as space exploration.The flexibility of the robot joint increases due to the harmonic drive and torque sensor integrated in the robot joint,which makes the control tasks of robotic system be a challenging issue and results in inevitable vibrations during the robot motion and residual vibrations upon the stopping of the motion.The flexibility of the joints should be taken into account in both modeling and control if high performance is to be achieved.In many industrial applications such as deburring,assembling and carving,the constraint force due to the contact with the constraint surfaces has to be taken into consideration.Time delay constitutes an important part of the whole robot system and may cause detrimental effects when neglected in the design procedure,especially in the cases of high speed movement.Therefore,the research of the constrained manipulators with jiont flexibility and time delay is of great significance.This paper takes a two-link flexible-joint manipulators as an example.The proposed control scheme can deal with the joint flexibility,time delay,as well as motion/force simultaneous tracking problem.The main work in this thesis is organized as follows:The mathematical model of the manipulators is established.This model includes kinematic model,dynamic model,the model of time delay and hysteresis loop.By introducing the coordinate transformation to reduce the dynamic model,a new reduced dynamic model suitable for motion and force control is derived.Based on the model of rigid-link flexible-joint manipulators with time delay,a design scheme of adaptive backstepping controller is given.Time delay is approximately regarded as first-order to design the controller.Meanwhile,the adaptive law updates the unknown parameters on line to deal with modeling uncertainties.The Lyapunov stability theory is utilized to prove the stability of system.Simulation results show that the manipulators can track the given position and force signals quickly and accurately.To deal with the motion/force control problem of rigid-link flexible-joint manipulators with hysteresis loop,an adaptive controller is given.Analyzing the properties of manipulators with hysteresis loop,a kind of differential equation is proposed to describe the characteristics of hysteresis.Then its severly limited characteristic are further studied.From control point of view,the model of the hysteresis loop is simplified and a robust control scheme is presented to overcome this problem.The adaptive law is utilized to deal with modeling uncertainties.The proposed control scheme can guarantee the stability of the systems,and simulation results demonstrate the effectiveness of the proposed method.