Force sensor utilizing stiffness change of shape-memory polymer based on temperature

In this study, we propose a force sensor using a shape-memory polymer (SMP) whose stiffness varies according to the temperature. An SMP can be deformed above its glass transition temperature (Tg) by applying a small load. A deformed SMP maintains its shape when cooled below Tg and returns to its predefined shape when subsequently heated above Tg. The reversible change in the elastic modulus between the glassy and rubbery states of an SMP can be on the order of several hundred-fold. The relationship between the applied force and the deformation of the SMP changes depending on the temperature. Our sensor consists of strain gauges bonded to an SMP bending beam and senses the applied force by measuring the strain. Therefore, the force measuring range and the sensitivity can be changed according to the temperature. In this study, we evaluate a prototype of the sensor using the SMP sheet with embedded electrical heating wire. Moreover, we improve the sensor by combining the SMP and a stainless steel plate. The enhanced versatility of SMP force sensors is demonstrated through a series of experiments conducted using the prototype.