Experimental validation of a reduced model based tracking control of parallel robots

In this paper we present a basis for the development of model-based control of closed kinematic chain robots (parallel robots). The configuration of most parallel robots can be uniquely established only in terms of dependent sets of coordinates which therefore form the basis of most dynamics formulations. In order to establish stability properties for control, a reduced dynamics model in terms of actuated joint positions is preferable. This reduced model depends on a coordinate transformation from the independent (actuated) coordinates to the dependent coordinates. We review a reduced model based on such a transformation and then characterize a domain suitable for tracking control in which the existence of the coordinate transformation can be guaranteed and computed in real time. This provides the basis for devising provably stable control laws. We demonstrate the results with tracking experiments using the Rice Planar Delta Robot.