3D Printing of Piezoresistive Flex Sensors for Soft Robotic Grippers and Strain Sensing

Abstract

Flexible piezoresistive sensors also referred to as strain gauges or flex sensors are extensively used in soft robotics to detect strain due to their inherent flexibility. They change their resistance in response to strain. This change in resistance can be used to detect bending in soft robots. 3D printing based on filament extrusion (or Fused Filament Fabrication/ Fused Deposition Modeling) of conductive polymers proffers the ability to fabricate inexpensive flex sensors quickly. There seems to be a dearth of literature that characterizes FFF printed flex sensors by cyclic bending. The effect of fabrication parameters, substrate materials, and sensing element geometry on the cyclic bending response of the sensor needs to be assessed. In this thesis, a voltage divider circuit is used for data acquisition and characterization experiments are conducted to determine parameters for fabricating flex sensors with high repeatability (with a coefficient of variation less than 2% which is lower than any other literature reviewed), good sensitivity (with a gauge factor of over 6.5, more than three times higher than conventional metal strain gauges), and longevity greater than a hundred thousand cycles. The longevity of the flex sensor is experimentally demonstrated. The flex sensors manufactured are compared with additively manufactured strain sensors in literature. To demonstrate their applications the flex sensors are incorporated in a soft silicone robotic gripper and TPU finger in which they successfully detect the bending angle. The temperature sensitivity of the sensor is also demonstrated. These sensors may have a potential for sensing in several other soft structures that need flexibility as a prime factor