Uncertain Dynamic Parameters Research Articles

Experimental Comparison of Control Approaches on Trajectory Tracking Control of a 3-DOF Parallel Robot

In this paper, the effect of control approaches on improvement of trajectory tracking accuracy of a 3-degree-of-freedom (DOF) planar parallel robot is studied through the experimental evaluation of four controllers: proportional-integral (PI)-type synchronized control, adaptive synchronized (A-S) control, conventional proportional-integral-differential (PID) control and adaptive control. The adaptive control and A-S control are dynamic model-based while the PID and PI-type synchronized control are not. Given the closed-loop kinematic chain mechanism structure, tracking control of the planar parallel robot may be treated as a synchronization control problem; hence, use of the synchronized-type control approaches can substantially improve tracking accuracy of the robot end-effector compared with use of the nonsynchronized-type control approaches. Further, with uncertain dynamic parameters, use of the A-S control, a model-based synchronized control approach, can, thus, improve the tracking performance. Through experiments conducted on an experimental 3-DOF planar parallel robot, the previous claims are demonstrated.

Based on Hierarchical Strategy of Adaptive Tracking Control of Mobile Robots Using Backstepping Design

A hierarchical control architecture, divided into upper and lower control levels, for the trajectory tracking control of mobile robots is proposed in this paper. The objective of the upper control level is to navigate the mobile robot on the desired trajectories by means of the kinematic model. A control law based on backstepping techniques is synthesized to make the posture error asymptotically stable. On the lower control level, the dynamic model of the robot is adopted from practical viewpoint. In order to guarantee the global asymptotic stability and demanded performance, a time-varying adaptive tracking control is designed such that the generalized velocities can converge to the upper control level's inputs. A hybrid controller is developed to incorporate the kinematic controller into the dynamic controller to deal with uncertain dynamic parameters of the mobile robot. Simulation results are utilized to illustrate the effectiveness of the proposed control algorithm.

Adaptive output rejection of unmatched input disturbances

To adaptively reject the effect of certain unmatched input disturbances on the output of a linear time-invariant system, a transfer function matching condition is needed. A lemma which presents a novel basic property of linear systems is derived to characterize system conditions for such transfer function matching. An adaptive disturbance rejection control scheme is developed for such systems with uncertain dynamics parameters and disturbance parameters. This adaptive control technique is applicable to control of systems with actuator failures whose failure values, failure time instants, and failure patterns are unknown. A solution is presented to this adaptive actuator failure compensation problem, which ensures closed-loop stability and asymptotic output tracking, in the presence of any up to m−1 uncertain failures of the total m actuators. Desired adaptive system performance is verified by simulation results.