Strain sensors for soft robotic applications

This chapter summarizes some recent developments in strain sensors for soft robotic applications including the different strain sensing mechanisms, fabrication approach, and key results. Resistive-type strain sensors are quite common and generally have good sensitivity. However, they often suffer from hysteresis and nonlinear electromechanical response. The performance of resistive-type strain sensors has been improved through the use of advanced nanomaterials, structural engineering, and fabrication approach. On the other hand, capacitive-type sensors offer excellent stretchability, linearity, and negligible hysteresis, but they have poor sensitivity. Further, as the interest in self-powered systems continues to rise, triboelectric-type strain sensors are gradually gaining attention. However, their sensitivity is still low when compared to the resistive-type strain sensors. For the application of strain sensors for robotic applications, a number of technical challenges which prevent its application for real-life application still exists. First, it is still challenging to realize a stretchable strain sensor that has the ability to measure decoupled multidirectional and multiplane deformations [3]. Solving this challenge will be a breakthrough for applications such as soft robotics, considering the stretchable and conformable nature of soft robots. Rather than the conventional architectures and materials, researches could strive to realize more advanced sensing architectures with 3D structures and metamaterials. Some other key novel features to introduce into the available strain sensors include, high sensitivity, nonlinearity, self-healing, and to adopt a more reliable system integration approach. Most strain sensors are also susceptible to unwanted pressure as well as variations in environmental conditions such as changes in temperature and humidity [3]. The solution to such environment challenges could come from the use of a more advanced packages.