A Soft Variable Stiffness Hand With an Integrated Actuating–Cooling System

In this article, a new soft finger is presented to achieve a fast variable stiffness mechanism using polycaprolactone based on an integrated actuating–cooling system. First, the variable stiffness finger demonstrates a dramatic 15-fold stiffness variation from 10.2 × 10
⁴
to 0.67 × 10
⁴
N·mm
²
when the temperature is changed in a range from 20 °C to 60 °C. The cycle time of the variable stiffness based on the integrated actuating–cooling hydraulic system is approximately 505 s, which is much shorter than that of 3870 s based on the pneumatic method. Second, due to the varied weight of water in the chamber, Cosserat rod theory is used to model the bending shape of the soft finger instead of the constant curvature model. A feasible method to control the position and stiffness simultaneously based on the Cosserat model is presented. Finally, a three-fingered soft hand is fabricated based on the variable stiffness and self-locking method, which can hold objects up to 3560 g successfully, which is more than 5.2 times its own weight of 680 g.