PENTAPOD: Calibration of parallel robots

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The possible applications of a parallel robot depend on several characteristic features, including in particular accuracy. In this context, a distinction is made between two parameters: repeatability and absolute accuracy.

Repeatability refers to the position and orientation deviations that occur when repeating the approach of learned layers. Absolute accuracy, on the other hand, is the distance between the target and actual positions. The latter is usually by an order of magnitude worse than the repeatability. The reasons for this are the inadequate internal control modeling of the robot. Since this modeling is a rigid-body model, the inaccuracies in the geometric parameters due to manufacturing tolerances and assembly errors are the main source of error. Accordingly, a procedure is necessary to correct the kinematic model stored in the controller and to identify the correct kinematic parameters. In this way, a significant reduction of the position and orientation deviation is achieved.

 

The Institute of Mechanism Theory, Machine Dynamics and Robotic has an optical measuring system from Metris with a measuring volume of 17 cubic meters, a measuring accuracy of 60 micrometer and a measuring frequency of 1,000 Hertz, which allows a fast and reliable identification of the kinematic parameters.