Non-contact torque measurement using rolled single crystal-like Galfenol patches

Abstract

Galfenol is an iron-gallium alloy that exhibits magnetostrictive behavior up to approximately 350 ppm. It has been shown that Galfenol exhibits a linear response in strain that follows commercially available strain gauges when a magnetic bias field is placed near the Galfenol patch in a bending test. In this study we extend these results to use of a Galfenol patch for measuring torque. The benefits of Galfenol-based torque sensors over existing strain sensors for measuring torque are (1) the potential for use of stray magnetic fields for non-contact torque measurement; (2) ease of integration and/or retrofit of the proposed torque measuring capability into existing hardware; and (3) an inexpensive yet mechanically robust alternative to torque sensors that require slip rings or wireless signal transmission. This research will show that when placed on a circular shaft at ± 45o relative to the shaft axis, Galfenol will exhibit a linear response to shear strain produced when a torque is applied to the shaft. By showing that measurement of shear strain is possible it is evident that the torque on the shaft can also be determined. A Hall Effect sensor will be rigidly attached to a non-rotating component of the measurement frame supporting the shaft, and used to determine the change in the magnetic field above the patch. While the shaft is rotating the response from the Hall Effect sensor is monitored to determine the torque load on the shaft.