In conventional load sensors, a typical electrical sensor includes a pressure sensor (cord switch) 91, for example, illustrated in FIG. 9. The pressure sensor 91 detects the load by way of the internal conductors 92 contacting to each other upon the external load applied.
In other types of load sensor, there are generally used such a method that the load is sensed by an accelerator sensor or a strain gauge, or such a method that the load is sensed by the modulated intensity of light inside the optical fiber caused by the flexural loss and compression loss of the optical fiber.
In the above methods, as the used electrical processing circuits and the light sensing and emitting apparatus are complex, their detection accuracy and noise tolerance are low, and thus, there has never been a good solution for providing low-cost, downsized and high-precision sensors.
In addition to the above methods, there was provided such a load sensor using conducting rubbers that has a simple structure and operates with a simple principle.
Prior art related to the present invention is disclosed in JP 2769754 B, JP 63-290922 A, JP 3731475 B, and JP 3354506 B.