The stick-slip friction phenomenon is observed near zero relative velocity, during the transition from static to dynamic friction, when static friction is greater than dynamic friction. This nonlinear change in friction force over a small change in velocity results in difficulties in achieving accurate and repeatable position control. In some cases, the actuator position controller reaches a limit cycle (hunting effect). Friction compensation at low speeds has traditionally been approached through various control techniques. This paper proposes an alternative solution, namely, friction avoidance. By rotating the piston and rod, the Stribeck region of the friction-velocity curve is avoided and the axial friction opposing the piston movement is approximately linearized. Simulation and experimental results are presented to validate this approach.

The reduction of stick-slip friction in hydraulic actuators

Sliding Mode Controller Design with Optimized PID Sliding Surface Using Particle Swarm Algorithm

This paper presents the position tracking performance of an electro-hydraulic hydraulic servo (EHS) system using sliding mode control (SMC) with proportional-integral-derivative (PID) sliding surface. In modelling process, a mathematical model of the EHS system is developed by considering its nonlinearities as represented by a Lu-Gre friction model. The control strategy is derived from the developed dynamics equation and stability of the control system is theoretically proven by Lyapunov theorem. Simulation results show that the proposed controller has a better tracking performance compared to conventional PID controller.

Sliding Mode Control with PID Sliding Surface of an Electro-hydraulic Servo System for Position Tracking Control

This paper evaluates the position tracking performance of an electro-hydraulic hydraulic servo (EHS) system using sliding mode control (SMC). The EHS system is established in modelling process by consider its nonlinearities with a friction model. The control strategy is derived from developed dynamics equation and stability of the control system is theoretically proven by Lyapunov theorem. Simulation results demonstrate the proposed controller is highly robust and capable to cope with the uncertainties and disturbances occur during the position tracking control. It is also shows that the proposed controller can achieve better tracking performance compared with conventional PID controller.

Position tracking control of an electro-hydraulic servo system using sliding mode control

This paper presents a perfect tracking optimal control for discrete-time nonminimum phase of electrohydraulic actuator (EHA) system by adopting a combination of feedback and feedforward controller. A linear-quadratic regulator (LQR) is firstly designed as a feedback controller, and a feedforward controller is then proposed to eliminate the phase error emerged by the LQR controller during the tracking control. The feedforward controller is developed by implementing the zero phase error tracking control (ZPETC) technique in which the main difficulty arises from the nonminimum phase system with no stable inverse. Subsequently, the proposed controller is performed in simulation and experimental studies where the EHA system is represented in discrete-time model that has been obtained using system identification technique. It also shows that the controller offers better performance as compared to conventional PID controller in reducing phase and gain error that typically occurred in positioning or tracking systems.

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Simulation and experimental studies on perfect tracking optimal control of an electrohydraulic actuator system

This paper reports the results of an experimental study, which was conducted to evaluate the performance and implementation aspects of a generalized predictive control (GPC) technique to an electro-hydraulic positioning actuator. Poor dynamics and high nonlinearities form part of the difficulty in the control of hydraulic functions which make the application of adaptive controls an attractive solution. The applicability of GPC to the position control of hydraulic manipulator has been investigated through computer simulations in the literature. However, there is no experimental record of applying this technique to an actual hydraulic system. A suitable plant model is established and recursive U-D factorization technique is adopted for on-line estimation of time-varying plant parameters. Experimental results are obtained from a laboratory electrohydraulic actuator test stand. Various benchmark tests, comprising step and tracking inputs, demonstrate good performance and the promise of the technique. In spite of significant actuator dynamics (control voltage saturation, flow nonlinearity and dry frictional nonlinearity in the hydraulic actuator), successful control tests could be performed repetitively.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0263574798000307

G. Wu

Papers

Experimental evaluation of generalized predictive control applied to a hydraulic actuator