When teaching physical skills, experts or robotic assistants commonly move a novice through a task. However, this guiding motion is only partially effective at portraying the full experience because the guided person is only performing the task passively and the guidance and task forces can become ambiguously intertwined. The interaction evaluated in this paper separates the task and guidance forces by guiding one hand so the user can actively recreate the motion with their other hand that receives task-related forces. This method is based on the ability of humans to easily move their hands through similar paths, such as drawing circles, compared to the difficulty of simultaneously drawing a square with one hand and a circle with the other. Several experiments were first performed to characterize the reference frames, interaction stiffnesses, and trajectories that humans can recreate. Visual Symmetry and Joint-Space Symmetry proved to be easier than Point Mirror Symmetry and participants' recreated motions typically lagged by approximately 50-100 ms. Based on these results, participants used bimanual guidance to identify the orientation of a hard rod embedded in a soft material. The results show that participants could identify the orientation of the rod equally well when working independently compared to being bimanually guided through a desired motion.

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Abstract-Bimanual rehabilitation devices show promise for use in low cost trainers for home use. To gain a better understanding of the symmetry modes and coupling stiffnesses that would be beneficial for home use bimanual trainers, we conducted a haptic tracking task. Participants used one hand to recreate the trajectory applied by a robot to the other hand using three bimanual symmetry modes. The participants recreated visual symmetry and joint space (mirror) symmetry more easily than point mirror symmetry. Joint space symmetry was the easiest mode when the trajectory was an increasing chirp frequency function. The stiffness between the robot and one hand affected the coordination between both hands and stiffnesses of 200 -700 N/m enabled better tracking than 50 N/m.

Coupled bimanual rehabilitation allows an individual with hemiparesis to use their sound arm to assist their impaired arm during rehabilitation. This method of self-rehabilitation could be used as a low-cost alternative for home rehabilitation, however, few studies have looked at the effects of coupling stiffness and symmetry mode on bimanual task performance. We have developed a compliant bimanual rehabilitation device (CBRD) that allows for the symmetry mode and stiffness of the coupling to be easily changed. Our results show the CBRD effectively couples the motions of two individuals in a task simulating hemiparesis, and that for some tasks, the symmetry mode and stiffness affect completion time. A stiffer coupling resulted in faster completion times and lower error. The device also reduced the completion time and error of bimanual tasks performed by healthy individuals.

Abstract-Bimanual rehabilitation allows an individual with hemiparesis to use their sound arm to help rehabilitate their impaired arm and shows promise as a means of low cost home use rehabilitation. However, few studies have attempted to determine the best combination of bimanual symmetry modes and coupling stiffnesses. To examine the effects of stiffness and symmetry type, we have developed a compliant bimanual rehabilitation device (CBRD) that allows the two hands to be coupled in a variety of symmetry modes and coupling stiffnesses so that their efficacy may be tested. Preliminary analysis has shown that the CBRD can couple the motions of two healthy individuals, which we are using to simulate an individual with a hemiparesis, and improves bimanual task performance of a single individual. The results also show that a higher coupling stiffness reduces the coupling error and that some tasks were easier to complete in visual symmetry.