3D printing of smart materials for robotics with variable stiffness and position feedback

Abstract

This paper proposes a novel soft robotic design that possesses variable stiffness and position feedback. A gripper adopting this design is presented. Each finger in the gripper is based on a 3D printed substrate (driven by an air actuated soft actuator) composed of two smart materials: shape memory polymer (SMP) and conductive thermoplastic polyurethane (TPU). SMP's dramatic change of elastic modulus around its glass transition temperature (T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">g</sub> ) enables the finger to have variable stiffness. The conductive TPU acts as a heater to provide Joule heating for the SMP when a weakening of stiffness is needed. Furthermore, the deflection of the substrate can be estimated due to the conductive TPU's inherent piezo-resistive effect. Experiments regarding the finger's position estimation capability and variable stiffness property are conducted. A gripper is fabricated to perform grasping demonstration. The proposed robotic design has other potential applications such as metamorphic legged robots.