Isolde Dressler

Observer-based ILC Applied to the Gantry-Tau Parallel Kinematic Robot

Three approaches of iterative learning control (ILC) applied to a Gantry-Tau parallel kinematic robot are studied; ILC algorithms using 1) measured motor angles, 2) tool-position estimates, and for evaluation purposes, 3) measured tool position. The approaches are compared experimentally, with the tool performance evaluated using external sensors. It is concluded that the tool performance can be improved using tool-position estimates in the ILC algorithm, compared to when using motor-angle measurements. Applying ILC algorithms to a system following trajectories with so-called lead-in/lead-out is also considered in the paper.

Subspace-based identification of compliance dynamics of parallel kinematic manipulator

A high-bandwith robot-workpiece interaction requires a stiff robot without resonances in the frequency range of operation. In this article, the compliance dynamics of the Gantry-Tau parallel kinematic robot were identified using subspace-based identification and physical modeling. Measurements were performed both with a camera vision system developed and with a laser tracker. Although promising simulation results for another Gantry-Tau prototype exist, both vision and laser tracker experiments identified multiple resonances around 14 Hz, which can reduce force control performance.

A kinematic error model for a parallel Gantry-Tau manipulator

Parallel robots are generally said to be more accurate but to have a smaller workspace compared to serial robots. With the Gantry-Tau robot, a parallel robot with a large, reconfigurable workspace was presented. This article tries to identify the maximum achievable end-effector positioning accuracy of the Gantry-Tau robot. To this end, a couple of new kinematic error models are presented and evaluated. The sources of the remaining positioning errors (0.09 mm) are discussed.

Characterization of the Tau Parallel Kinematic Machine for Aerospace Application

A consortium of interested parties has conducted an experimental characterization of two Tau parallel kinematic machines which were built as a part of the EU-funded project, SMErobot1. Characteristics such as machine stiffness, work envelope, repeatability and accuracy were considered. This paper will present a brief history of the Tau parallel machine, the results of this testing and some comment on prospective application to the aerospace industry.

Closed-form calibration of the Gantry-Tau parallel robot

This paper addresses the kinematic calibration of the Gantry-Tau parallel kinematic manipulator. It offers two closed-form solutions to this problem, which do not need any initial guess, contrarily to most calibration methods that are based on non-linear least square minimization. This makes the proposed methods applicable by non expert users in a context of mechanical modularity of the robot. Experimental results validate the approach.