Adaptive Output Force Tracking Control of Hydraulic Cylinders With Applications to Robot Manipulators

Abstract

An adaptive output force control scheme for hydraulic cylinders is proposed by using direct output force measurement through loadcells. Due to the large and somewhat uncertain piston friction force, cylinder chamber pressure control with Coulomb-viscous friction prediction may not be sufficient enough to achieve a precise output force control. In the proposed approach, the output force error resulting from direct measurement is used not only for feedback control, but also to update the parameters of an appropriate friction model which includes the Coulomb-viscous friction force in sliding motion and the output force dependent friction force in presliding motion. The L2 and L∞ stability is guaranteed for both the pressure force error and the output force error. Under bounded desired output force and its derivative, asymptotic stability of both the pressure force error and the output force error is also guaranteed. The experimental results demonstrate that a good pressure force control system does not necessarily guarantee a good output force control, and that adaptive friction compensation is superior to fixed-parameter friction compensation. The output force control transfer functions of a robot joint driven by two hydraulic cylinders in pull–pull configuration are limited by ±1.5dB up to 20Hz, tested in free motion and in rigid constraint. The excellent output force (joint torque) control performance implies the dynamic equivalency between a hydraulic cylinder and an electrically-driven motor within the prespecified bandwidth. This allows to emulate an electrically-driven robot by a hydraulic robot.

Adaptive sliding mode control of electro-hydraulic system with nonlinear unknown parameters

“…Yao et al (1998Yao et al ( , 2000 applied nonlinear adaptive robust control in double-rod and single-rod cylinder hydraulic system based on backstepping techniques to compensate for the uncertainties from both parametric uncertainties and uncertain nonlinearities. Recently, some novel nonlinear adaptive control methods have been presented for the hydraulic system (Bu & Yao, 2001;Duraiswamy & Chiu, 2003;Liu & Yao, 2003;Shi, Gu, Lennox, & Ball, 2005;Zhu & Piedboeuf, 2005). These nonlinear adaptive control laws not only solved the control problem coming from uncertain nonlinear system successfully in some conditions but also demonstrated that nonlinear control schemes can achieve better performance than conventional linear controllers.…”

A new method for parameter identification for N-DOF hydraulic robots

“…In fact, even in recent papers on hydraulic robots and the other hydraulic systems [7], [2], [9], difficult parameters (the bulk modulus and the flow gain coefficients) are identified by trial and error [8], [1], [10], [3].…”

Trajectory control of an electro hydraulic actuator using an iterative backstepping control scheme

“…Control problems of conventional valve-controlled hydraulic systems face challenges of high nonlinearities and uncertainties due to the nonlinear dynamics of cylinder and uncertain fluid parameters. Hence, several nonlinear adaptive control techniques have been introduced based on back stepping control [6][7][8], sliding mode control [9][10], and adaptive control [11][12]. However, for the pump-controlled EHA systems the control problems are more challenging.…”