Some robotic prosthetics currently in development are connected to the user via a socket which detects electrical signals from muscle movements. One challenge with this technology is maintaining an electrical connection to the muscle via sensors placed on the skin inside the socket. For example, this connection can be lost because of sweat, which can inhibit the prosthetic hand’s ability to function.Fabricating and calibrating the system for a user is also quite expensive.
The researchers’ prototype sensor system is said to avoid this pitfall by detecting mechanical signals, instead of electrical signals, from tiny vibrations produced by muscle fibres as they move when muscles flex.These vibrations can be sensed and passed to a robot hand to make it move in response.
The team caution that they have not yet carried out patient clinical trials with the technology. They still have a number of refinements to complete before the sensor and motion tracking system can be commercialised. However, they believe their work is a step forward in making robotic prosthetics more robust in their design, which could widen their usefulness for patients.
The team have carried out a preliminary demonstration of the system with Alex Lewis who lost his legs, his right arm and use of his left arm following a rare infection.
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’s 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 a three fingered pinch that could enable movements such as picking up a small object like a set of keys, and a power grip that could enable the prosthetic to grasp a larger object such as a glass of water.
Future refinements to the technology will include adding more sensors to increase the range of commands and isolating the range of vibration interference that may make the hand open or close unexpectedly. The team also plan to refine the device so that it is more portable and enables the user to self-calibrate.
Lewis said: “It is really exciting to be part of this project to test the robotic hand system. Current prosthetics can be very cumbersome, so any technology that can reduce the burden on users is an important step forward. I look forward to seeing this device developed further.”
In the future, the team predict that the sensor system could also be adapted so that it could be used to control other technologies and appliances around the home, to further benefit people living with disabilities.