An exploration of grip force regulation with a low-impedance myoelectric prosthesis featuring referred haptic feedback

Abstract

BackgroundHaptic display technologies are well suited to relay proprioceptive, force, and contact cues from a prosthetic terminal device back to the residual limb and thereby reduce reliance on visual feedback. The ease with which an amputee interprets these haptic cues, however, likely depends on whether their dynamic signal behavior corresponds to expected behaviors—behaviors consonant with a natural limb coupled to the environment. A highly geared motor in a terminal device along with the associated high back-drive impedance influences dynamic interactions with the environment, creating effects not encountered with a natural limb. Here we explore grasp and lift performance with a backdrivable (low backdrive impedance) terminal device placed under proportional myoelectric position control that features referred haptic feedback.MethodsWe fabricated a back-drivable terminal device that could be used by amputees and non-amputees alike and drove aperture (or grip force, when a stiff object was in its grasp) in proportion to a myoelectric signal drawn from a single muscle site in the forearm. In randomly ordered trials, we assessed the performance of N=10 participants (7 non-amputee, 3 amputee) attempting to grasp and lift an object using the terminal device under three feedback conditions (no feedback, vibrotactile feedback, and joint torque feedback), and two object weights that were indiscernible by vision.ResultsBoth non-amputee and amputee participants scaled their grip force according to the object weight. Our results showed only minor differences in grip force, grip/load force coordination, and slip as a function of sensory feedback condition, though the grip force at the point of lift-off for the heavier object was significantly greater for amputee participants in the presence of joint torque feedback. An examination of grip/load force phase plots revealed that our amputee participants used larger safety margins and demonstrated less coordination than our non-amputee participants.ConclusionsOur results suggest that a backdrivable terminal device may hold advantages over non-backdrivable devices by allowing grip/load force coordination consistent with behaviors observed in the natural limb. Likewise, the inconclusive effect of referred haptic feedback on grasp and lift performance suggests the need for additional testing that includes adequate training for participants.

Multichannel Electrotactile Feedback With Spatial and Mixed Coding for Closed-Loop Control of Grasping Force in Hand Prostheses

“…As explained before, the control interface seemed to be the main limiting factor in the routine grasping task, and therefore, implanted solutions can allow the user to benefit from the higher resolution feedback and thereby improve the control performance. Finally, novel prosthetic devices might be developed allowing fine force control, such as a low-impedance prosthesis presented in [42], which in combination with the better control can also have an important impact on the utility of the feedback.…”

Comparison of vibrotactile and joint-torque feedback in a myoelectric upper-limb prosthesis

“…Not all investigations of haptic feedback in prostheses have resulted in improved functionality. In previous work done by members of our research group, it was found that neither vibrotactile nor jointtorque feedback improved grasp and lift performance over vision with a myoelectric prosthesis [16]. Likewise, Saunders et al found that vibrotactile feedback was only useful in a grasp and lift task with a myoelectric prosthesis when feedforward uncertainty was present in the control loop [26].…”

“…Despite these findings, some investigations into the utility of haptic feedback have shown no benefit or improved functionality. In previous research from members of this research group, Brown et al found no significant improvement with either jointtorque feedback or vibrotactile feedback over no feedback in a grasp-and-lift task with a myoelectric prosthesis [16]. Similarly, no significant improvement in myoelectric control was found for a compensatory tracking task with pressure feedback over visual feedback [17].…”

“…The literature comparing joint-torque feedback and vibrotactile feedback is limited to research done previously by members of this research group. Brown et al found that there was no difference between joint-torque and vibrotactile feedback in a grasp and lift task using a myoelectric prosthesis [16]. Similarly, Brown et al found that there was no difference in kinesthetic feedback delivered to a different part of the body than the part used for exploration (non-colocated) and vibrotactile feedback in a single-DoF spring stiffness discrimination task [29].…”

Psychometric characterization of incidental feedback sources during grasping with a hand prosthesis

“…Intuitive methods to provide somatosensory feedback have been a research topic for several decades [8], and substantial progress was made in recent years [9][10][11][12]. However, a commercially available solution capable of improving the prosthesis performance in the activities of daily living is still unavailable [13,14]. There is a single commercial prosthesis (VINCENTevolution 2, Vincent Systems, DE) equipped with a simple vibratory feedback on the grasping force, but its clinical and functional utility has not been yet demonstrated.…”