Variable-Sensitivity Force Sensor Utilizing Modified Cross-Sectional Shape

Abstract

Force sensors require different measurement ranges and sensitivities depending on the operating environment. Therefore, we developed a force sensor with both variable sensitivity and measurement range based on structural modification induced by simple bending. In our previous study, we changed the distance between the force application point and the detection area. However, it was necessary to change the position and direction of the measured force. Therefore, in the present study, we changed the cross-sectional shape of the sensor. First, we introduce the theoretical basis for the proposed force sensor. We then describe prototype sensors and the experimental methods used to determine their performance. We fabricated the prototypes by attaching a strain gauge to one side of shape-memory polymer plates, which can be deformed at temperatures above the glass transition temperature (T_g) by applying a small load and maintain their rigid shape after they have been cooled below T_g. We designed two types of sensor with different cross-sectional shapes (i.e., hollow cylinder and channel beam) and experimentally evaluated them. The results indicated that the sensitivity and measurement range of the sensor can be changed by modifying the cross-sectional shape. For example, for hollow cylinder and channel beam types of sensor, the maximum change in sensitivity before and after bending was 6.2 and 2.7 times, respectively. Although these values were smaller than that (12 times) obtained in our previous study, it was possible to change the sensitivity without changing the position or direction of the measured force.