A new thin pickup coil for magnetic head type torque sensors

A new thin pickup head is proposed for magnetic-head-type torque sensors. The new pickup head consists of a stacked pair of figure eight coils, in which one of the coils is rotated in the coil plane by 90 degrees from the other. The applied torque can be detected from the difference in self-inductances of a pair of the figure eight coils faced to the shaft through an air gap in a manner such that each figure eight coil sees the permeability of the shaft along either 45 degrees or -45 degrees from the axis. Unlike conventional pickup heads of 3-D structure, the proposed pickup head is thin, making it easy to build the torque sensor on a shaft. Experimental results using a magnetic yoke backing the pickup head show good linearity with small hysteresis. >