For prosthetic hand users, pressing buttons on a remote control, typing on a keyboard or braiding a child’s hair has remained elusive.
Users with existing myoelectric prosthetic hands can only carry out a single grasp function at a time even though advanced artificial hands can mechanically control all five digits individually.
First-of-its-kind research using haptic/touch sensation feedback, electromyogram (EMG) control and a pioneering wearable soft robotic armband could be a game-changer for users of prosthetic hands who have long-anticipated advances in dexterity.
The study’s findings could catalyze a paradigm shift in the way present-day and future prosthetic hands are regulated by people without a limb.
Scientists from Florida Atlantic University’s College of Engineering and Computer Science in collaboration with FAU’s Charles E. Schmidt College of Science examined if people could precisely regulate the grip forces applied to two different objects grasped concurrently with a dexterous prosthetic hand.
For the research, they also investigated the role played by visual feedback in this intricate multitasking model by methodically obstructing visual and haptic feedback in the experimental design. Furthermore, they investigated the potential for saving time in an instantaneous object transportation experiment compared to a one-at-a-time method.
To achieve these functions, they engineered a unique multichannel wearable soft robotic armband to transport simulated sensations of touch to the robotic hand users.
Results, reported in the journal Scientific Reports, demonstrated that many channels of haptic feedback allowed subjects to effectively grasp and carry two objects concurrently with the dexterous prosthetic hand without dropping or breaking them, even when their vision of the two objects was blocked.
Moreover, the simultaneous control method enhanced the time needed to convey and deliver both objects compared to a one-at-a-time method generally used in earlier studies. Notably, for clinical translation, scientists did not discover important differences between the limb-absent subject and the other subjects for the main performance metrics in the tasks.
Notably, subjects qualitatively rated haptic feedback as significantly more crucial than visual feedback even when vision was unobstructed because there was frequently little-to-no visually distinctive warning before grasped objects were dropped or broken.
Our study is the first to demonstrate the feasibility of this complex simultaneous control task while integrating multiple channels of haptic feedback noninvasively. None of our study participants had significant prior use of EMG-controlled artificial hands, yet they were able to learn to harness this multitasking functionality after two short training sessions.
Erik Engeberg, PhD., Corresponding Author and Professor, Department of Ocean and Mechanical Engineering, College of Engineering and Computer Science, Florida Atlantic University
Engeberg is also a member of FAU’s Center for Complex Systems and Brain Sciences, Charles E. Schmidt College of Science, and a member of I-SENSE and the FAU Stiles-Nicholson Brain Institute.
To deliver haptic feedback, Engeberg and the team focused on the EMG control and design of the custom-made multichannel bimodal soft robotic armband with Emmanuelle Tognoli, Ph.D., co-author, a research professor, FAU Department of Psychology and Center for Complex Systems and Brain Sciences, and a member of the FAU Stiles-Nicholson Brain Institute.
The armband was comprised of soft actuators to deliver a proportional sense of contact forces; vibrotactile stimulators were added to specify if the grasped object(s) had been damaged. The armband was engineered for haptic feedback at three locations corresponding to the thumb, index and little finger - an adequate number to transport the amplitudes of the forces applied to both objects clutched by the hand.
The armband consisted of three air chambers, each of which proportionally matches one of the three BioTacs fitted on the Shadow Hand fingertips. The armband also has three co-located vibrotactile actuators that would vibrate to warn the subject if the object(s) in the grasp(s) had been broken (if one or both force thresholds was/were surpassed).
Examples of multifunction control demonstrated in our study included the proportional control of a card being pinched between the index and middle fingers at the same time that the thumb and little finger were used to unscrew the lid of a water bottle. Another simultaneous control demonstration was with a ball that was grasped with three fingers while the little finger was simultaneously used to toggle a light switch.
Moaed A. Abd, Study First Author and PhD Student, Department of Ocean and Mechanical Engineering, Florida Atlantic University
Information gathered from the research could be applied in the future frameworks of extremely complex bimanual operations, such as those needed of guitarists and surgeons, with the goal of empowering upper limb-absent people to follow career paths and recreational pursuits that are presently unachievable for them.
Enabling refined dexterous control is a highly complex problem to solve and continues to be an active area of research because it necessitates not only the interpretation of human grasp control intentions, but also complementary haptic feedback of tactile sensations.
Stella Batalama, PhD., Dean, College of Engineering and Computer Science, Florida Atlantic University
“With this innovative study, our researchers are addressing the loss of tactile sensations, which is currently a major roadblock in preventing upper limb-absent people from multitasking or using the full dexterity of their prosthetic hands,” Batalama added.
The other study co-authors include Joseph Ingicco, a graduate of FAU’s College of Engineering and Computer Science and a member of the Biorobotics Lab within FAU’s Department of Ocean and Mechanical Engineering; and Douglas T. Hutchinson, M.D., an orthopedic hand surgeon affiliated with the University of Utah Hospitals and Clinics.
The study received support from the National Institute of Biomedical Imaging and Bioengineering of the National Institutes of Health (NIH); the National Institute of Aging of the NIH; the National Science Foundation; the United States Department of Energy; Burroughs Wellcome Fund, and seed grants from the FAU Stiles-Nicholson Brain Institute and FAU I-SENSE.
Research Footage of Novel Wearable Armband and Prosthetic Hand
Video Credit: Florida Atlantic University.
Abd, M. A., et al. (2022) Multichannel haptic feedback unlocks prosthetic hand dexterity. Scientific Reports. doi.org/10.1038/s41598-022-04953-1.