DEVISING A ROBOTIC ARM MANIPULANDUM FOR NORMAL AND ALTERED REACHING MOVEMENTS TO INVESTIGATE BRAIN MECHANISMS OF MOTOR CONTROL

The objective of this work was to develop a manipulandum system capable of measuring a monkey's arm movements and applying extrinsic forces to the hand. The manipulandum (RANARM) was designed as a five-bar linkage mechanism in order to realize sufficient rigidity and efficient force transmission. In addition, RANARM's control enables it to cancel its own dynamics by calculating the inverse dynamics. We evaluated the performance of RANARM from the mechanism, control, and application points of view. From the mechanism point of view, RANARM was able to provide a sufficiently large workspace for experiments, where it exhibited high manipulability and the capacity to apply force perturbations of at least 12N under static conditions, and 5.3N under dynamic conditions. From the control point of view, we estimated the uncompensated dynamics of RANARM to be negligibly small. Finally, we evaluated the performance of a monkey operating RANARM, and observed that the hand speed profiles followed a natural bell shape, while the maximal speeds were high (i.e., 15-cm reaching within 500 ms). In conclusion, RANARM allows a monkey to execute rapid movement and it is an efficient apparatus for investigating brain mechanisms for generating voluntary movements.