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Concept refinement
It looks like mechanomyography (MMG) is the right technology to use, since we have found a research group that has demonstrated its practicality. Jorge Silva, Winfried Haim, and Tom Chau of the PRISM Lab have made and tested a self-contained MMG controlled prosthesis1. Their device used three sensors, each consisting of a microphone to pick up muscle sounds and an accelerometer to detect external interference. The sensors were integrated into a soft silicone socket at the end of the user’s residual limb and placed 120 degrees apart. Their signals were interpreted by a microcontroller and converted into simulated EMG signals to control an Otto Bock hand. Their results were promising, and the devices performed with over 70% control accuracy. The prosthesis was difficult to control when the user was sustaining heavy loads with it, when the arm was held over the head, and when the user was walking. However, none of the usual problems with EMG electrode placement showed up. Active Living Magazine has published an article on the project.
It seems like major improvements can be made on this design if it were built from the ground up to be controlled by MMG signals. Better use might be made of the sensor data, the possible unreliability of the EMG control electronics could be eliminated, and the latency might be reduced from the paper’s average of 120ms.
1 Silva, J., Heim, W., & Chau, T. (2005).“A self-contained mechanomyography-driven externally powered prosthesis”, Archives of Physical Medicine and Rehabilitation, 86(10):2066-2070.
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