Development of A Novel Pneumatic Bending-Type Actuator and An Assistive Glove, Composed of Multi-Materials

Abstract

Rapid aging of the modern society has led to growth of the number of the physically disabled suffering from many geriatric diseases such as stroke, joint diseases and so forth. the elderlies, stroke patients. Along with this, expansion of the application field of the robot beyond industrial robots activated the research on wearable assistive device. Though researches about wearable devices were already conducted before 21th centuries, traditional robots with rigid materials had limitations to become a successful assistive device because of their bulky and heavy structure. Meanwhile, in 2000s, biomimetic and biologically-inspired design have been emerging as a new way of mechanical design. Polymer, textile and other deformable materials were adopted to mimic the structure of living organisms. The research field about the robots made of these soft materials is called soft robotics or soft bodied robotics. Since these materials are relatively lightweight, safe and comfortable when interacting with human body, the soft robotics also suggested a new approach to the wearable device. Intrinsic compliance of the soft materials provide infinite degree of freedom(DOF) to the structure, and it makes hard to make an analytical model or algorithm to control all the DOF. Hence, under-actuation method was applied. It is an actuation method where the robot structure has redundant DOF relative to the number of the actuator, and the soft materials are suitable for this method since they can deform continuously, changing its shape to environment. It enables consequent robots to move adaptively to the surrounding environments while being actuated by simple driving part and control algorithm. In this research, a device was designed and fabricated with multi-materials including the soft and the rigid materials, to improve the motion of the soft wearable device. Soft assistive glove was chosen as the application since a hand has the largest number of the joints in relatively small space in a human body. Previous linkage-based assistive devices for a hand are too complicated and bulky for practical use. On the other hand, recently developed soft wearable gloves are not precise enough to realize various grasp motions of human hand. To improve the soft assistive glove, a pneumatic bending-type actuator(PBA) is developed in this research, using both soft and rigid materials. The soft materials form the main structure of the PBA so that the PBA has adaptability. The rigid parts are adopted to constrain the deformation of the soft materials partially, while making it possible to control position, angle and force of the bending motion by changing design parameters of them. Although the analytical model was not established, the effect of different design parameters of the rigid parts is anticipated and verified by experiments. Then PBAs with multi-joints is designed for human finger, in which the motions of each joints can be actuated separately. The PBAs for index, middle fingers and thumb are fabricated, and the rigid parts are designed regarding the requirements for the motion of the human finger. Finally an assistive was developed adopting the PBAs. By actuating each joint independently, various grasp postures including precision grasps are realized, which was not able to be realized by previously developed soft assistive gloves. The contribution of this research is that, a device which can be placed between rigid robot and soft robot is developed by using multi-materials. Consequent device actuator has less adaptability than fully-soft devices at where the rigid material is used, it enables to separates the motions of the each part of the robot, and therefore the device can make more various motions compared to the fully-soft devices. It is expected that designing multi-materials can make the motions of the soft wearable devices more precise. In addition, multi-materials can be also applied to general soft robots, to increase the efficiency and predictability of the motions by constraining unnecessary deformations.