Bending Angle Effect of the Cross-Section Ratio for a Soft Pneumatic Actuator Jutamanee Auysakul, Nitipan Vittayaphadung, Sarawut Gonsrang, and Pruittikorn Smithmaitrie Department of Mechanical Engineering, Faculty of Engineering, Prince of Songkla University, Hat Yai, Songkhla 90112, Thailand Email: jutamanee.a@psu.ac.th, nitipan.v@psu.ac.th, gsarawut@eng.psu.ac.th and pruittikorn.s@psu.ac.th Abstract— A soft pneumatic actuator is a soft robotics part that significantly increases ability of a robotic arm to grasp an object in the automatic production line. To grip an object of various sizes and shapes, the bending angle of the actuator is a parameter that affects the grasping area and positioning of a robotic arm while applying air pressure. In this study, the actuator models with small and large cross- section ratios are compared by simulation using the finite element method. The simulation results show that increasing of the model cross-section ratio provides the wider bending angle than the reduced cross-section ratio model or the basic configuration model at the same input pressure. The proposed model still maintains the air surface area inside the actuator. Furthermore, it was found that the reduced cross-section ratio model has the most significant influence on the bending angle than the other models. Thus, the model comparison in term of the cross-section ratio is helpful to design the most effective gripper. Index Terms—soft pneumatic actuator, soft robotic gripper, mathematical modeling, soft robotics I. INTRODUCTION Soft robot research has become increasingly popular in the robotic field. One of the main reasons is that soft robots can perform unique actions such as grasping objects of various sizes and shapes safely, deliver high power and safely interact with human operators. Additionally, the technology is usually lightweight and cheap. In contrast, conventional robots have stiff designs. [1]. Therefore, soft actuators, which can execute fast, precise and strong operations, have been extensively used in automation, locomotion, and rehabilitation. Accordingly, soft actuators have evolved to behave like natural muscles [2]. Soft actuators that operate with air pressure are called soft pneumatic actuators (SPAs). Some use shape- memory alloy [3], [4] or hydraulics [5] to drive the peripheral components. SPAs are applied via a pneumatic network to generate bending action and movement that are inspired by animals; for example, a soft gripper like a human finger can play a digital keyboard [6]. A multi- gait quadruped is inspired by an octopus and can produce complex motions [7]. The simple structure of a SPA combines a hollow shape with a thin membrane made of Manuscript received April 10, 2019; revised December 4, 2019. silicone. This special polymer is flexible enough to be stretched while air pressure is being applied [8]-[11]. Polyether ketones and PVC coating films are used when the actuators require complex structures like zigzag origami [12], which is currently a trend in the robotic field. Furthermore, several fabrication techniques are used to produce SPAs using two-step molding technique [13], silicone 3D printer [14] or dissolvable core technique. The chamber geometry is a significant design parameter which affects the bending performance. Hu et al. [15] introduced an optimization approach that selected optimal parameters like the bottom layer thickness, gap size between adjacent chambers, wall thickness, and chamber cross section. The work also illustrated how the finite element method (FEM) is useful to optimize geometric variables and validated the findings via experimental methods. This work investigates cross- section ratios and parameters that influence bending performance. The optimized parameter in this study is the ratio between the size of the first and last chamber. The ratio is optimized by finite element analysis. This paper is organized in the following way. In Section II, the basic SPA configuration and the SPA designs are introduced and compared. Section III describes how FEM is used to simulate the models by comparing in terms of bending analysis. The simulation results of each model are shown in Section IV. Finally, Section V concludes this work. II. SPA DESIGN AND CONFIGURATION A. Basic Configuration of a SPA Figure 1. The basic configuration of a SPA. (a) basic model; (b) cross- sectional view; and (c) bending effect. The basic configuration of a SPA as shown in Fig. 1(a) composes of an upper layer and base layer. The configuration reveals of air chambers and air channels as shown in Fig. 1(b). The SPA actuation depends on 366 International Journal of Mechanical Engineering and Robotics Research Vol. 9, No. 3, March 2020 © 2020 Int. J. Mech. Eng. Rob. Res doi: 10.18178/ijmerr.9.3.366-370