This work presents a stability analysis and experimental assessment of a visual control algorithm applied to a redundant planar parallel robot under uncertainty in relation to camera orientation. The key feature of the analysis is a strict Lyapunov function that allows the conclusion of asymptotic stability without invoking the Barbashin-Krassovsky-LaSalle invariance theorem. The controller does not rely on velocity measurements and has a structure similar to a classic Proportional Derivative control algorithm. Experiments in a laboratory prototype show that uncertainty in camera orientation does not significantly degrade closed-loop performance.

This paper is concerned with the design and experimental assessment of, both, feedback linearization and sliding mode control techniques to the tracking trajectory problem of a flexible-joint robotic arm for a smooth rest to rest maneuver. The robust improvement of these controllers is analyzed by means of additional integral compensation, in which an alternative sliding surface was proposed for the control of the flexible arm. A feedback linearization of the nonlinear dynamic equation of the robot arm is computed in order to get a full-state non-linear feedback control law. On the other hand, it is proposed a second order sliding mode control with an integral term in the sliding surface, which improves the robustness of the controller sliding surface. Some experimental evaluations that include the addition of external unmodeled perturbations to test the enhancement of the robustness property show the improvements and effectiveness of the proposed control laws in disturbance rejection tasks. The controllers were implemented using exclusively position measurements and time derivatives approximations.

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In the present contribution, a methodology to solve the tracking control problem of robot manipulators through the use of a Proportional Retarded plus Gravity (PR+G) compensation scheme is presented. The main advantage of the proposal is to avoid the necessity of velocity measurements or their estimation, which is commonly used in most control schemes, such as the proportional derivative-type controllers or the computed torque control. The design of the PR+G controller is addressed via σ-stability analysis and its performance is tested in an experimental platform that consists of 2 degrees of the freedom robot manipulator. The proposed controller is compared with a classic proportional derivative plus gravity compensation scheme. The results are analyzed from a frequency perspective and measured by a quadratic error index. INDEX TERMS Manipulator robot, time-delay controller, trajectory tracking.

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