Shape Memory Alloy Wire for Force Sensing

Shape memory alloy (known dominantly as SMA actuator) which is well known for its actuation, is hereby proposed to be designed exclusively as a sensor. A principle of active force sensing using shape memory effect (SME) of SMA is evolved. SMA wire along with a passive bias (antagonistic) element performs sensing as an actuated sensor, by the variation in its electrical resistance for a contact force, in a linear elastic manner. The principle is validated on a measurement system, which resembles that of a standard load cell. The SMA-based sensor is able to provide an accurate static and dynamic force measurement. The variation in the electrical resistance of the SMA is a measure of the strain induced on the load cell for a contact force placed upon it. The objective of sensing is accomplished by overcoming the nonlinearity of the SMA with a passive biasing element. A prototype of the active force sensor is realized to evaluate its sensing ability for serving a motor. The measurement principle of the sensor and test on its static calibration are described; the experimental results demonstrate the validity and reliability of the sensor. The uniqueness of this contribution is that- a new dimension is added to SMA's functionality by the design of a linear active sensor for force measurement, though it is an inherently non-linear element.