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Compensation of geometric and elastic errors in large manipulators with an application to a high accuracy medical system

Ph.  Drouet a1, S.  Dubowsky a2, S.  Zeghloul a1 and C.  Mavroidis a3
a1 Laboratoire de Mécanique des Solides, Université de Poitiers, 86960 Futuroscope (FRANCE)
a2 Massachusetts Institute of Technology, Department of Mechanical Engineering, Cambridge, MA (USA)
a3 Department of Mechanical and Aerospace Engineering, Rutgers University, Piscataway, NJ (USA)


A method is presented that compensates for manipulator end-point errors in order to achieve very high position accuracy. The measured end-point error is decomposed into generalized geometric and elastic error parameters that are used in an analytical model to calibrate the system as a function of its configuration and the task loads, including any payload weight. The method exploits the fundamental mechanics of serial manipulators to yield a non-iterative compensation process that only requires the identification of parameters that are function only of one variable. The resulting method is computationally simple and requires far less measured data than might be expected. The method is applied to a six degrees-of-freedom (DOF) medical robot that positions patients for cancer proton therapy to enable it to achieve very high accuracy. Experimental results show the effectiveness of the method.

(Received December 12 2001)

Key Words: Errors; Compensation; Large manipulators; Medical system; Accuracy.