Task-specific demonstration and practiced synergies for writing with the ACT hand

Muscle synergies are hypothesized as a way to reduce the control space of redundant biological neuromuscular control. Robotics researchers are starting to use grasping synergies to simplify the task of coordinating many joints for complex manipulators. This is especially useful for hand movement control as there are many joints and muscles to control to achieve even simple tasks. This paper uses the Anatomically Correct Testbed (ACT) Robotic Hand to understand how task-specific synergies may be formed and used for complex robotic manipulation tasks such as writing. A comparison is made between synergies formed from (1) general hand movements, (2) task-specific demonstration of generic writing, and (3) practice of writing a specific letter. Results showed that performance using task specific demonstration synergies outperforms performance using general-purpose synergies in terms of completion time, energy expenditure, and trajectory error. Performance using practiced synergy outperforms the performance using demonstration synergies in trajectory error, even though there was no statistical difference in completion time and energy expenditure. These results indicate that task specific synergies from demonstration and practice allow a robotic hand to write better than using more generic synergies that may work for other tasks. How general/specific these synergies should be to optimize the performance of different complex tasks without learning too many specific synergies is an interesting topic for the future.