Multi-Material Soft Strain Sensors with High Gauge Factors for Proprioceptive Sensing of Soft Bending Actuators

Highly stretchable strain sensors, with embedded microchannels filled with conductive liquid, have been widely used in various applications in soft robotics for detecting different types of deformation modes, when attached to human or robot bodies. One of recent applications that draws an attention is direct integration of soft sensors with soft actuators for proprioceptive feedback. However, it is not easy to obtain a high resolution in curvature sensing when combined with bending actuators in which curvature is indirectly measured from strain sensing, since the placement of soft sensors are limited to the location where the strain sensitivity is relatively small. Therefore, we propose a new design of high gauge factor strain sensors using a multi-material structure. By alternately arranging low and high stiffness elastomers, the structure experiences amplified strain changes on each of the low-stiffness regions. The gauge factor was significantly increased as high as over three times of a conventional single material sensor. In this paper, the design and fabrication of the proposed sensor are described with an analytical model. The sensor was tested while integrated with a PneuNet bending actuator for curvature detection as an application.