Active Handrest for precision manipulation and ergonomic support

People use handrests every day to complete dexterous activities as routine as providing a signature. However, the dexterous workspace of the hand is somewhat limited. To address this limit, we have developed an Active Handrest to aid in precision manipulation tasks by extending a user's dexterous work space while providing ergonomic support for reduced fatigue - ideally while maintaining or even improving upon the precision obtained from a fixed handrest. Such a device could be useful for performing precision tasks over large workspaces, such as surgery, machining, or pick-and-place tasks. Our current prototype Active Handrest is a planar, computer controlled support for the user's wrist and arm that allows the user complete control over a grasped tool or manipulation device. The device uses force input from the user's hand, position input from a grasped manipulandum, or a combination of both force and position inputs. The control algorithm of the device then interprets and converts the input(s) into handrest motions. Pilot studies were conducted to optimize the control strategy by investigating the effects of control mode and of velocity limits. Task precision and completion time were used as performance metrics. Pilot testing showed that the device provided the greatest task precision when its velocity was limited to 5 mm/s, while using force input for its control strategy. An experiment was then conducted to compare the Active Handrest to various fixed wrist and arm support conditions, as well as the unsupported condition. Use of the Active Handrest was found to reduce task error by 36.6%, compared to performing the tasks with an unsupported arm, and by 26.0% compared to task completion with a static wrist support. These results are statistically significant (p < 0.0001). While users generally completed experiments more slowly using the Active Handrest, performance with the Active Handrest shows lower sensitivity of task error relative to task completion time. Added experience with our drawing task leads to an increase in accuracy; however, the Active Handrest continues to outperform other hand support conditions (p < 0.0001).