Geometric and elastic error calibration of a high accuracy patient positioning system

Important robotic tasks could be effectively performed by powerful and accurate manipulators. However, high accuracy is generally difficult to obtain in large manipulators capable of producing high forces due to system elastic and geometric distortions. In this work, a high-accuracy patient positioning system is calibrated, consisting of a six degree of freedom manipulator used to position cancer patients during proton therapy sessions. It is found that the original manipulator does not meet the required absolute accuracy due to both geometric and elastic deformation positioning errors. The experimentally identified errors are used to predict, and compensate for, end-point errors as a function of configuration and measured forces, improving the system absolute accuracy. Experimental results show that the adopted methodology is able to effectively correct for the system errors.