LITHE-joint: Variable Stiffness Compliant Spherical Contact Joint in an Under-Actuated System
Sanpoom Punapanont, Run Janna, Harn Sison, Poramate Manoonpong
Abstract
The concept of morphological computation (MC) is applied in the robotics field to improve the design and reduce the complexity of control systems. The MC uses mechanical intelligence, where stiffness properties play an important role as constraints to enhance system flexibility and to store elastic energy. This can reduce the number of required actuators. According to the MC principle, This work proposes LITHE-joint: variable stiffness compliant spherical contact joint in an under-actuated system. This compact design for a 2-degrees of freedom (DOF) compliant spherical contact joint with controllable stiffness uses a pneumatic artificial muscle (PAM). This joint requires only one PAM actuator to control stiffness in a 2-DOF system, achieving a stiffness of up to 0.38 Nm/rad with a bandwidth of 0.1967 Nm/rad. With its variable stiffness properties, the joint is able to adapt its bending behavior, enabling energy redistribution of torque and angle. The modulation of torque and bending angle is governed by joint stiffness and the passive body dynamics. The benefits of the passive, compliant joint with a variable stiffness property are demonstrated by using as the spine of an under-actuated robot, controlling the passive bending of the body and the robot’s walking direction using the adjustable stiffness.
BibTeX
@inproceedings{iros2025_lithejointvariab,
title = {LITHE-joint: Variable Stiffness Compliant Spherical Contact Joint in an Under-Actuated System},
author = {Sanpoom Punapanont and Run Janna and Harn Sison and Poramate Manoonpong},
booktitle = {IROS 2025},
year = {2025}
}