This study aims to build a totally flexible mechanical system with hydraulic skeleton driving mechanism. The main components of this system are two types of flexible bags. One is a structural bag with constant inner pressure. The other is an actuator bag with controlled inner pressure. Such flexible system will provide various advantages, for example, safety, portability, lightweight and dealing with fragile objects. Efficiency is also an advantage because only actuator parts consume driving fluid with the proposed system. This paper deals with a flexible robotic arm as an example of the proposed mechanism. With geometric relationship, effective parts arrangement and driving force at the joint are discussed in this paper. Quantitative estimations of structural deformation and driving force of flexible bags are important for design of the proposed system. However, numerical analysis of flexible bags is difficult because of their large nonlinear deformation. This study tries to analyze large nonlinear deformations of flexible bags with the nonlinear finite element analysis software ABAQUS. From the analytical results, this paper discusses unique effects of structural deformation depending on the driving force. The validity of the analysis is verified by experimental results. Both results show that the effect of concave deformation of a structural bag at the joint is 10 times larger than normal cantilever deformation. Pick and place motion of a raw egg is also performed with a proposed robotic arm avoiding large concave deformation without complex control such as force sensing and so on.

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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.

Abstract-The present paper describes new flexible ciliary actuators made of thin urethane rubber, to imitate the hydraulic skeleton found in soft creatures, such as earthworms. Several trial actuators are manufactured while varying the number of fluid chambers from 1 to 3. These actuators are driven by fluid pressure and different methods of posture restoration. A new multiple two-way ciliary actuator sheet with an embedded multi-layered fluid circuit is proposed. A pipe inspection robot of 27 mm in height with ciliary actuator arrays moves at 5.4 mm/s. A new ciliary actuator with a z-shaped body is also discussed.

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