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A historical review of constrained robot modeling and control strategies is first introduced. Next, a design of a motion/force controller for a constrained servo-robot, which is based on a commonly known modeling structure, is proposed. The contact between the end-effector and the environment is subject to frictional features. Accordingly, the control plant is based on the LuGre friction closed-loop observer. Therefore, new nonlinear position and force input transforms, which are slightly different from classical computed torques, are proposed, combined with a new change of variable. The main purpose of this paper is to establish the stability condition by using the passivity of interconnected linear and nonlinear subplants. From then on, because of this formulation, the authors succeed in designing a full-order dynamic position feedback and an integral force controller that ensure exponential stabilization within an Hinfin multiobjective optimization. These conditions are expressed in terms of linear matrix inequalities. The performances are experimentally validated on a two-degrees-of-freedom robot manipulator acting on a horizontal worktable with friction. The LuGre model estimator exhibits a richer behavior in terms of friction compensation and positioning tracking when experimentally compared to the Karnopp friction compensation. The latter form exhibits poor modeling properties at zero crossings of the velocity

This paper addresses an extended output feedback positioning tracking of a servo-system with friction. It is based on LuGre friction observer dynamics with fixed model parameters. Our design features a global asymptotic stability of the tracking error while sustaining desired transient specifications using dual conditions of strictly positive real (SPR) one and exponential stability margin. These latter have to be fixed with respect to specific pole placement limiting fast controller dynamics. Our full-order dynamic output feedback controller is composed of two components: the first deals with the tracking context and the second represents a correction term in the observer from the position and velocity errors. The subsequent linear state space controller matrices are found by using the linear matrix inequality (LMI) approach. Simulation results illustrate the effectiveness of the proposed compensator.

This paper presents an approach to design an observer for a pneumatic cylinder system for which the connection port comprises a non-negligible restriction. The pressure chamber of this system is difficult to control because the servo valve and the connection port form a double restriction. Moreover, the pressure in the cylinder cannot be directly measured and cannot be expressed as an explicit function of the measurable pressure. A nonlinear observer is further designed to estimate the pressure in the chamber by using the measured pressure outside the cylinder. The linear matrix inequality (LMI) approach is used to calculate the observer gains which ensure the exponential stability of the estimation error. Simulation results show good performance of the proposed observer.