Novel design and 3D printing of variable stiffness robotic fingers based on shape memory polymer

Abstract

In this study, a novel variable stiffness robotic finger composed of a soft pneumatic actuator and pin heaters embedded in a shape memory polymer (SMP) substrate is presented. The dramatic change in elastic modulus of SMP around its glass transition temperature Tg is used to realize soft finger's variable stiffness function, which can potentially be developed into variable stiffness grippers or hands. By selectively heating the SMP in three regions with pin heaters, the finger mimics the motion of a human index finger. The fabrication of the finger is obtained by combining fiber reinforced soft actuator and 3D printed SMP substrate using our in house developed SMP 3D printing process. In the experimental section, we characterize the prototype robotic finger in terms of heat dissipation rate, bending angle and stiffness. Experiments have shown that the controllable bending angle can be up to 84.5° under the air pressure of 125kPa when the SMP joints are heated to 65°C. Besides, the robotic finger's stiffness at 25°C is 5.76 times of the stiffness at 65°C when there is no air pressure in the finger's air chamber, and about 4.65 times when the air pressure is 100kPa.