In this paper a force sensor is proposed which comprises a segmental photo-sensor facing a light source supported by an elastic frame, and in which measurements are taken of relative positions varying with an external force on the basis of output variations from each photo-sensor. The photo-sensor detects minute displacements of the light source with good reproducibility and high sensitivity, and gives a large output signal. Therefore, the amplifier may be a simple type and can be easily built in. Also, this force sensor has a simple structure. Thus, the force sensor in the present method is more compact and far less costly than a conventional force sensor which uses a strain gauge. In this work, studies were carried out on the basic structure for measuring displacements in three axial directions with one piece of quadri-segmental photo-sensor and, having established the principle, the team prepared a prototype tri-axial force sensor with a built-in amplifier. Experiments indicated that the prototype tri-axial force sensor was capable of measuring separate displacements with an accuracy of 0.4 standard deviation, even when forces were applied from different directions simultaneously.
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