Development of Variable Chain Motor with Shape and Speed-Torque Characteristics Variability and Its Application to a Humanoid

Abstract

Various methods have been proposed to achieve high output torque and a wide output range for fast and high-load robotic motions. However, in robots composed of slender frames, such as humanoid robots, the limited space available for actuators and transmission components restricts the application of conventional methods. In this paper, we propose a Variable Chain Motor (VC Motor), an electric actuator that features both shape variability and speed-torque characteristics variability. Shape variability refers to the ability of the actuator to change its form during operation. This property enhances output torque by enabling a dense motor arrangement even under spatial constraints imposed by the frame structure. For example, the actuator can be placed across adjacent frames and deform according to joint rotation. Speed-torque characteristics variability allows switching output characteristics during operation using a dedicated electrical circuit. This enables an expanded range of output speed and torque without significantly increasing size or weight. We evaluated the performance of the developed VC Motor by measuring output torque and efficiency. Furthermore, by applying the VC Motor to the elbow joint of a humanoid robot, we demonstrated its capability for high-speed and high-load operations.