Researchers from Imperial College London, England, have developed technology that enables an upper-limb prosthesis user to control a robotic hand through arm movements and muscle vibrations. The prototype sensor system detects mechanical signals from small vibrations produced by muscle fibers when muscles flex. The vibrations are sensed and passed to the robotic hand to make it move in response to the user’s muscles. The technology also has a motion sensor system to detect arm movements that allow the user to control how the robotic hand grasps different sized objects through a simple sequence of muscle flexes and arm movements. The research team, part of the Department of Mechanical Engineering, noted that its technology avoids some pitfalls of robotic hands that rely on electrical signals, which can be lost when the user sweats, inhibiting the prosthetic hand’s function, and the greater fabrication and calibration expenses.
The team performed a preliminary demonstration of the system with Alex Lewis who has quadrilateral amputations. To operate the robotic hand, Lewis had a small arm band placed around his bicep, which has a muscle sensor and motion tracking electronics embedded into it. When he flexed his bicep the vibrations made were detected by the sensor, interpreted as signals, and transmitted to a computer. A program then executed a mathematical algorithm designed to isolate Lewis’ muscle signal and filter out other arm motions and sounds, converting it into a command for the robotic hand.
Lewis had the option of activating two different grip modes while the prosthesis was detached from his arm. The first was a three-fingered pinch that could enable movements such as picking up a small object like a set of keys. The other was a power grip that could enable the robotic hand to grasp a larger object such as a glass of water.
Future refinements to the technology will include isolating the range of vibration interference that may make the hand open or close unexpectedly. The team also plans to refine the device so that it is more portable and enables the user to self-calibrate, removing the need for engineers in the setup process. Adding more sensors would also expand the range of commands, so that the prosthesis can perform more complex grasping tasks.
“This technology takes us a step closer to providing prosthetics that are potentially more robust, accessible, and easier for patients to use in the future,” said Ravi Vaidyanathan, PhD, a senior lecturer in bio-mechatronics who conducted the research with Samuel Wilson, MEng, a research postgraduate.
Editor’s note: This story was adapted from materials provided by Imperial College London.