Abstract
The popularization level of the electric arm prosthesis in the present Japanese market is still very low due to the high cost and the lack of function, safety, etc. Our purpose is to know how to make cost-effective electric arm prosthesis. For that purpose, we first made a simple electric arm prosthesis and tried to drive the prosthesis by a surface myoelectric signal through our own made preamp, band-pass filter and a computer controller. After the driving experiment, we thought that the application of the myoelectric signal might be one of the reasons of the high-cost constitution. Myoelectric signal is originally generated by the brain. Therefore, we may generally believe that the myoelectric signal is the signal that we should use for driving the arm prosthesis. The real surface myoelectric signal is, however, an indirect signal that is measured an alternative muscle's activity through a skin. The signal strength is very weak, that is mV order level. Therefore, we have to prepare anti-noise measures. It leads to the cost up. So we searched the alternative information. We decided to apply a balloon shaped soft pressure sensors made of silicone rubber. This sensor was developed by us to measure the inner pressure distribution of the socket of the leg prosthesis. The basic structure is that a photo-reflector was installed in the center of the silicone rubber balloon, and if the balloon is deformed by the pressure, the deformation quantity of the balloon membrane is measured by the inner photo-reflector. We install this sensor on the jacket of the arm prosthesis and measured the tension and the projection of the muscle. The noise level of this sensor is very low and we can use it very stably to drive the electric arm prosthesis. We also succeeded to apply the sensor's signal to control the opening and closing speed and grasping force of the fingers.
