Study On Disturbance Observation And Compensation In Nonlinear Syetem With Backlash

Servo system,which is the most widely applied feedback system,occupies an important role in social production by virtue of its advantages of high speed,high accuracy and high performance.Due to the high speed of the control motor,the actuator cannot be directly controlled,so the transmission link is required for speed regulation.Gear transmission is the most common deceleration device in servo system.As the gears cannot be completely meshed during transmission process,backlash occurs.However,backlash nonlinearity is a nonlinear factor that exists in transmission link of servo system and is very difficult to eliminate in mechanical means.It would seriously affect stability and dynamic accuracy of the control system.A large number of experts,scholars and engineers in control field at home and abroad have made research on eliminating the nonlinear-effect of backlash.How to design effective control schemes anti-backlash is the main goal of current scientific research.In this paper,compensation problem for backlash in gear transmission is discussed.Combined with the advanced control algorithm,observer is designed to estimate unknown variables in closed-loop control system,so as to obtain better control scheme.Consulting a large number of domestic and foreign literature and considering that current digital controller mostly works in discrete time,control schemes in this paper are desiggned for discrete-time system.The main work of this article is as follows.(1)Firstly,a discrete-time feedback system with input backlash nonlinearity is studied,which contain uncertain functions and unkonwn external disturbance.Based on the backstepping mothed and active disturbance rejection control framework,a novel adaptive fuzzy control scheme is proposed.In this close-loop system,all of the total disturbance consists of unknown function approximation error and external unknown disturbance.Meanwhile,the discrete-time accurate disturbance observer proposed to compensate the total disturbance.Compared with traditional backlash compensation schemes,fuzzy backlash model is introduced to describe backlash with uncertain parameters directly and effectively.Then,the fuzzy backlash is defuzzified and approximated by the linear combination of a linear term and a disturbance-like term.The proposed controller maintains tracking error in an arbitrary small neighborhood of zero.Lyapunov theorem is utilized to prove stability of controller to ensure all signals are bounded.Simulation examples verify the feasibility of the proposed scheme at last.(2)Aiming at compensating backlash compensation in servo system,observer-based control schemes are proposed in this article.The observer is designed to estimate both system states and vibration torque.The feedback and feedforward signals of servo system are obtained by an improved extended state observer,and a sliding mode variable structure control scheme is proposed.The power function is selected instead of the sign function as the sliding film approach function,which eliminates the high frequency chattering phenomenon of the system caused by the sign function.Finally,extensive experiments are performed on a practical dual motor drive servo system with backlash nonlinearity and experimental results prove the feasibility of the proposed scheme.