Fine resolution smart force sensor based on lever arm mechanism using shape memory alloy spring

A novel force measurement technique using the variable resistance property of shape memory alloy (SMA) spring is presented. The unique abilities of SMA, a smart material make it a potential candidate to construct actuators and dampers and of late is added to the domain of sensing technology in the design of creative sensing systems. The sensing mechanism is realized using a lever arm made of less stiff acrylic material; one of the links of the lever arm is integrated with an SMA spring actuator that is connected perpendicular to the stationary base, and the unknown load is placed at the other link; the force due to the measurand and the transmitted force act on the arms of the lever. The displacement due to the application of force on one of the flexible arms causes a variation in the strain that leads to resistance variation of the Joule-heated SMA spring attached at the other arm. The active sensor possesses static and dynamic sensing capabilities and can detect force in the range of a few millinewtons, and the sensor design is validated from the experimental measurements and analytical results. The performance of the sensor is evaluated from its static and dynamic characteristics and depicts promising results. The design methodology of the sensor mechanism and selection of material suitable to offer flexible transformation of force leads to the development of a force sensor with fine resolution.