Active Joint Mechanism Driven by Multiple Actuators Made of Flexible Bags: A Proposal of Dual Structural Actuator

Abstract

An actuator is required to change its speed and force depending on the situation. Using multiple actuators for one driving axis is one of the possible solutions; however, there is an associated problem of output power matching. This study proposes a new active joint mechanism using multiple actuators. Because the actuator is made of a flexible bag, it does not interfere with other actuators when it is depressurized. The proposed joint achieved coordinated motion of multiple actuators. This report also discusses a new actuator which has dual cylindrical structure. The cylinders are composed of flexible bags with different diameters. The joint torque is estimated based on the following factors: empirical formula for the flexible actuator torque, geometric relationship between the joint and the actuator, and the principle of virtual work. The prototype joint mechanism achieves coordinated motion of multiple actuators for one axis. With this motion, small inner actuator contributes high speed motion, whereas large outer actuator generates high torque. The performance of the prototype joint is examined by speed and torque measurements. The joint showed about 30% efficiency at 2.0 Nm load torque under 0.15 MPa air input.

Inflatable L-shaped prisms as soft actuators for soft exogloves

“…Tendon-actuated inflatable jointed actuators have been investigated for safe human-robot interaction in an elbowed robot [22,23], but these actuators rely on external motors for actuation. Folded inflatable tubes have been used to create the rotation of a rigid joint [24], as an inflatable member for stiffness control between the joints of a robotic arm [25], and as a rotary elastic chamber actuators to create an entirely soft robotic joint [26]. Pleated films have been used to realize bending and twisting actuators using the anisotropic expansion of the pleats [27][28][29], pouch motors consisting of inflatable flat rectangular pouches have been used to produce linear and bending motions using rigid constraints [30,31], and these pouch motors have been used as a gait rehabilitation device for rats [32].…”