Repositioning-Unit for very Fine and Accurate Displacements. Analysis and Design

Abstract

Displacement and orientation of work pieces in space are the typical tasks for which industrial robots are well suited. Nevertheless these robots, which consist generally of several rigid bodies connected sequentially by revolute or prismatic points, are mainly designed to perform large scale displacements. In the same way as they are built according to different coordinate structures (i.e. cartesian, cylindrical, spherical or articulated) the analysis of the task planning may be a criterion for the choice of the suitable robot architecture. The SCARA robot is a typical example of this choice. On the contrary, when task planning needs,eds small amplitude displacements, high positioning accuracy and high resolution, commercially available robots with classical architecture have not the required performance. For instance, the superposition of moving joints leads to several drawbacks such as cumulation of backlash, too much bulk and robot control tricky to carry out. For these reasons, in the last few years, several laboratories have designed three dimensional displacement units which are better suited to perform fine and very accurate displacements (figure 1). Such units with various geometrical architectures have been designed and built at LIMBO laboratory (1)