Output Feedback High-Precision Position Control For Robot Manipulators

Robot manipulators have long been concerned and developed for their abilities to replace humans in high-intensity and high-hazard jobs.The position control of robot manipulators has been recognized as the most basic and simplest aim in the robotic control field.With the rapid development of modern science and technology and the continuous improvement of industrial automation,the requirement on the control accuracy of robot manipulators is higher and higher.In addition,robot manipulator is a typical highly nonlinear system with strong couplings between joints,which can serve as an interesting benchmark for the test of various novel control strategies.Therefore,the high-precision position control of robot manipulators is an active branch in robotics and industrial automation.On the other hand,despite the success of modern control theory,it has been recognized that the majority of controllers used in robot manipulators are still the PD and PID-type control.This is mainly due to the simple structure,explicit tuning procedures and ease of implementation of the PD/PID algorithms.Moreover,it is often impossible to obtain both the position and velocity information of the joint for a practical robotic system.Thus,based on the PD and PID-type control,the output feedback high-precision position control of robot manipulators has a significant theoretical and practical value.This dissertation proposes several easy-going output feedback nonlinear PD/PID controls for high-precision position control of robot manipulators.Advantages of the proposed controllers are the simple structure and the ease of implementation with high performance such as faster transient and higher steady-state precision.The main contents of this dissertation are as follows.First,recognizing the appealing advantages of finite-time convergence to the equilibrium and the high-precision performance of the finite-time control,an output feedback finite-time PD plus gravity compensation(PD+)is proposed for position control of robot manipulators.Using Lyapunov's stability theory and a geometric homogeneity technique,the proposed controller can ensure global finite-time stability of robot manipulators.The proposed finitetime controller can obtain a faster response and a better system performance.Second,in practice,the actuator cannot provide an unlimited power.Taking into account actuator constraints,a saturated output feedback finite-time PD+ controller is proposed for high-precision positioning of robot manipulators with bounded inputs.Using Lyapunov's stability theory and a geometric homogeneity technique,the global finite-time stability is proved.By properly introducing a nonlinear saturation function,the proposed controller has a clear and explicit upper bound.The actuator constraints are not breached by selecting control gains a priori,and thus meet the practical needs.The proposed finite-time saturated PD+ controller removes the possibility of actuator failure due to excessive torque input levels and obtains a faster convergence and a better system performance.Third,friction is an inevitable nonlinear phenomenon in robot manipulators.The nonlinear friction deteriorates the motion performance of robot manipulators.An output feedback nonlinear PD+ control method is proposed for high-precision positioning of friction robot manipulators.The proposed controller is proven to guarantee global asymptotic stability of the closed-loop system by using a strict Lyapunov function and Lyapunov's direct method.The proposed PD+ controller can reduce the undesirable behaviors of nonlinear friction to robotic system and gains a better control precision.Fourth,the implementations of the above-mentioned PD+ position controls rely heavily on the knowledge of gravity terms.It is not easy to obtain the accurate gravity terms of a complex robotic system.A model-free output feedback nonlinear PID position controller is proposed for friction robot manipulators.Using Lyapunov's direct method and Barbalat's lemma,the proposed controller can ensure global asymptotic stability.The appealing features of the proposed control are the absence of modeling parameters in the control law formulation and the control gains can be explicitly determined based on some well-known bounds extracted from the robot dynamics,and thus permits easy implementation.Moreover,the proposed control also obtains a much improved motion performance for friction robot manipulators.Finally,simulations and experimental results are carried out to verify the effectivenesses and the improved performances of all the proposed schemes.