Development of a Finger Soft Pneumatic Bending Actuator

A growing research and development of soft manipulators that are able to mimic movements of human hand for prostheses and rehabilitation is one of the main streams in advanced robotics technologies. Soft compliant materials are overtaking the role of hard materials for this cause. This paper presents a model of soft pneumatic bending actuator (sPBA) to mimic the movements of a finger. The sPBA developed is composed of air chambers connected together with a common channel that bends symmetrically, achieving the bending characteristics of a finger joint. Three actuators which act as joints are connected to form a finger. Finite element method (FEM) is used to simulate the pressure and bending characteristics of the model prior to fabrication. The materials used in the model are the hyper elastic silicon rubbers; Dragon Skin 10 Medium (DS10M) and Elastosil M4601 (EM4601). The kinematic model of the planar movement of the actuator is based on the assumption of a rigid multiple-link hyper redundant structure. The inverse kinematics is solved using sequential quadratic programming algorithm (SQPA) as an optimization function in a numerical computing environment software. The constraint equation used in solving the joint angles is the forward kinematics equation. The derived least square polynomial equations are used to estimate the pressure. The cost functions are defined to minimize displacement error. In addition, a prototype was developed to validate the movement of the designed finger. The results present an acceptable maximum displacement error at low pressure of 3.4%. The bending was successfully achieved having the same pose as that of the FEM simulation and is also able to grip an object.