Tip position tracking of flexible-link manipulators based on online robust trajectory modification

Abstract

This paper presents a composite controller for tip position tracking of flexible link manipulators. In this regard, an inner/outer control structure is proposed. Opposed to previous conducted researches in this area, the desired reference trajectory is robustly modified (online) to minimize the tracking error of the tip utilizing the outer controller. The outer trajectory modifier is a synthesis based controller which modifies the reference trajectory of the inner loop in the uncertain situations. In the inner control loop a Lyapunov Redesign Feedback Linearization (LRFL) approach is applied to alleviate the degrading effects of uncertainties and nonlinearities presented in the dynamics of the flexible link. In the inner control loop, a conventional redefined output namely "close to the tip" is considered to avoid the difficulties associated with non-minimum phase behavior of the main output (tip). In conventional control strategies this choice leads to undesirable oscillations in tip. These oscillations are considerably minimized applying the outer trajectory modifier. Simulation results performed on a single-link flexible manipulator (with the parameters of an experimental setup) are presented to illustrate the significant improvements of performance over the conventional methods.

A Critical Review of Control Techniques for Flexible and Rigid Link Manipulators

“…100 A μ-synthesis-based controller was proposed to robustly modify the input trajectory and reduce the tip error of a single-FLM. 101 Another μ-synthesis robust controller was applied to damp the oscillations of a single-FLM with taking into consideration an external disturbance and model parameter variation; the μ-controller revealed better robustness in disturbance rejections, vibration suppression, and parameter variation than a H ∞ controller as verified experimentally in ref. [102].…”

Precise Positioning Control Using Online Modification of Reference Trajectory

“…But this is a method intended to satisfy constraints related to input and states, so that tracking the target trajectory remains a problem. A method in which a feedback control system outside the existing feedback control system is designed by μ synthesis [6] and a method of design using preview control [7,8] have also been proposed. However, Ref.…”

“…However, Ref. [6] considers a flexible link manipulator, and residual vibration is observable in the simulation results, so that positioning precision remains an issue. Refs.…”