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.

A method for computer assisted kinematic calibration of a modular Gantry-Tau parallel robot is presented and tested in an experiment. A computer tool developed executes the first step of a kinematic calibration, the choice of appropriate measurement points, using a priori knowledge about kinematic parameters, e.g. obtained with a measuring tape. This step is performed by intersecting the robot's kinematic workspace and the area surveyable by the measurement device and overlaying it with a grid of a desired number of measurement points. A simulation determines automatically whether the choice leads to an accurate calibration and outputs a trajectory readable by a robot controller. In a calibration experiment it is shown that the method gives results with an accuracy comparable to that of manual calibration. The method allows non-experts to execute kinematic calibration of modular robots after reconfiguration thus making possible the use of modular robots in small size enterprises where such robots can answer the need for flexibility required with regularly changing tasks.

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.

Affordable and competitive industrial automation is of key importance for small and medium enterprises, in Europe and elsewhere. A key factor is the introduction of new robot automation concepts that ease fast deployment and extend available task repertoire. The Gantry-Tau manipulator is a new robot concept. In contrast to other parallel kinematic manipulators (PKMs), it has a large working range. The high stiffness makes it ideal for a wide range of tasks such as grinding, deburring, and cutting. An additional aspect of such a PKM is the modularity, which in this work has been studied in terms of possibilities for assembly and mechanical reconfiguration at the end-user site, integration of such a kinematically different robot with a standard industrial controller, and new needs for methods/tools to support simple (re)configuration. What is needed for fully utilizing the modularity of the concept in typical SME manufacturing scenarios? A range of software tools and methods were found to be useful and necessary for efficient engineering and integration. For experimental evaluation, a full-scale prototype robot was designed and built, the kinematic software was developed and integrated into the ABB kinematics software, robot CAD software was adapted to the configuration needs, and both simulations and physical experiments were carried out. Our findings make us believe that enhanced software tools should be integrated on a higher symbolic (or meta-) level to better support transformation of data and code generation, but also that the Gantry-Tau type of robot (with adequate software support) will bring a new dimension of flexibility into SME manufacturing.

In this article, a new kinematic and a dynamic model for a 3-degree-of-freedom Gantry-Tau parallel kinematic robot are presented. Similar to an earlier proposed kinematic model, the dynamic model is based on the assumption of parallel actuator axes and constant end-effector orientation. The new kinematic model takes into account rotations of actuator axes which do not affect the end-effector orientation. Results from a calibration experiment show an improved positioning accuracy of the new kinematic model. A more general model of the robot including possible geometric inaccuracies causing deviations from the model assumptions has been developed in the modeling language Modelica. In a simulation, the proposed dynamic model is tested as a feedforward term in a control application and is found to improve the tracking performance considerably.