The MIME System

The Palo Alto VA MIME system, the mirror-image motion enabler for upper-extremity stroke therapy, clips a forearm trough, into which the user is strapped, onto the end of a PUMA-560 robot via a 6-axis force transducer and a breakaway overload sensor. In one mode, 12 personalized trajectories can be selected to provide assisted (passive on the part of the user), active-assisted (user initiates movement, and robot then guides the weak-side arm along the path), and active-constrained (user initiates path, and the robot provides a viscous resistance in the direction of movement and spring-like loads in all other directions) exercises. This system is being used for upper-extremity therapy for individuals who are hemiplegic as a result of a stroke. The force/torque sensor measures the force production by the user. A metric correlating performance with the functional (clinical) status of the user has been found to be the force produced in the direction of the trajectory divided by the total applied force, integrated over the trajectory. In the bilateral mode, a 6-axis position digitizer is clipped to the forearm trough on the subject's strong side and provides a target trajectory for the weak side to follow, thereby implementing a "master/slave" mode using both limbs. The force sensor measures the extent to which the person can make bilaterally-symmetric movements. Results indicate that this treatment is effective in returning bilateral function to the impaired limb of a person who has become hemiparetic as a result of a stroke.