Photograph courtesy of FAU/Alex Dolce.
Results of a recent study showed that multiple channels of haptic feedback enabled participants to successfully grasp and transport two objects simultaneously with a dexterous artificial hand, even when their vision of both objects was obstructed.
The researchers, from Florida Atlantic University (FAU) College of Engineering and Computer Science in collaboration with FAU’s Charles E. Schmidt College of Science, studied haptic/touch sensation feedback, electromyogram (EMG) control, and an innovative wearable soft robotic armband. They also explored the role visual feedback played in the multitasking model by systematically blocking visual and haptic feedback, and the potential for time saving in a simultaneous object transportation experiment compared to a one-at-a-time approach. To accomplish these tasks, they designed a novel multichannel wearable soft robotic armband to convey artificial sensations of touch to the robotic hand users.
The simultaneous control approach improved the time required to transport and deliver both objects compared to a one-at-a-time approach commonly used in prior studies. Of note for clinical translation, the researchers did not find significant differences between the limb-absent subject and the other subjects for the key performance metrics in the tasks. Subjects qualitatively rated haptic feedback was considerably more important than visual feedback even when vision was available because there was often little to no visually perceptible warning before grasped objects were broken or dropped.
“Our study is the first to demonstrate the feasibility of this complex simultaneous control task while integrating multiple channels of haptic feedback noninvasively,” said Erik Engeberg, PhD, corresponding author and a professor in FAUs Department of Ocean and Mechanical Engineering and a member of FAU’s Center for Complex Systems and Brain Sciences. “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.”
To provide haptic feedback, Engeberg and the research team worked on the EMG control and design of the custom fabricated multichannel bimodal soft robotic armband with Emmanuelle Tognoli, PhD, a co-author and research professor in the FAU Department of Psychology and Center for Complex Systems and Brain Sciences.
The armband was fitted with soft actuators to convey a proportional sense of contact forces; vibrotactile stimulators were included to indicate if the grasped object(s) had been broken. The armband was designed for haptic feedback at three locations corresponding to the thumb, index, and little finger, a sufficient number to convey the amplitudes of the forces applied to both objects grasped by the hand, according to the researchers. The armband had three air chambers, each of which proportionally corresponded to one of the three sensors equipped on the prosthetic fingertips. The armband was also equipped with three co-located vibrotactile actuators that would vibrate to alert the subject if one or both force thresholds were exceeded, indicating the grasped object had been broken.
“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,” said Moaed A. Abd, first author and a PhD student in FAU’s Department of Ocean and Mechanical Engineering.
The results demonstrated that subjects were able to integrate multiple channels of haptic feedback into their motor control strategies to perform a complex simultaneous object grasp control task with an artificial limb, which could serve as a paradigm shift in the way prosthetic hands are operated, the researchers concluded.
To watch research footage, visit FAU’s YouTube page.
The open-access study, “Multichannel haptic feedback unlocks prosthetic hand dexterity,” was published in Scientific Reports.
Editor’s note: This story was adapted from materials provided by Florida Atlantic University.
