Citation: Jing, X.; Chen, S.; Zhang, C.;
Xie, F. Increasing Bending
Performance of Soft Actuator by
Silicon Rubbers of Multiple Hardness.
Machines 2022, 10, 272. https://
doi.org/10.3390/machines10040272
Academic Editor: César M.
A. Vasques
Received: 16 February 2022
Accepted: 7 April 2022
Published: 11 April 2022
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Article
Increasing Bending Performance of Soft Actuator by Silicon
Rubbers of Multiple Hardness
Xishuang Jing
1,2
, Siyu Chen
1,2
, Chengyang Zhang
1,3,
* and Fubao Xie
2,3
1
School of Mechanical Engineering and Automation, Beihang University, Beijing 100191, China;
tom@buaa.edu.cn (X.J.); xavier_csy@buaa.edu.cn (S.C.)
2
Beihang Hangzhou Innovation Institute Yuhang, Hangzhou 311121, China; xiefb@buaa.edu.cn
3
Key Laboratory of Intelligent Manufacturing Technology for Aeronautics Advanced Equipment,
Ministry of Industry and Information Technology, Beihang University, Beijing 100191, China
* Correspondence: zhangchengyang@buaa.edu.cn
Abstract:
In this study, a method for fabricating actuators made of various silicone materials is
proposed to improve the flexural performance of soft-body actuators. Specifically, the redundant
deformation part of the soft actuator was replaced with a material with higher hardness to limit the
redundant deformation of the soft actuator. Materials with lower hardness were used to produce
the main deformation part of the soft actuator, so that the soft body actuator could perform greater
bending under the same air pressure and create a greater bending force. In addition, the fabricated
actuator was divided into three regions in this study: the periphery of the chamber, the chamber wall
(the main curved part), and the bottom surface of the actuator. The impact on the overall performance
of soft-body actuators when using silicone materials with different hardness in these three regions
was explored in this study. According to the idea of the multi-hardness silicone structure, an actuator
with seven chambers was fabricated, and the performance of the actuator was improved by 90.72%
compared with the uniform material actuator.
Keywords: soft robotics; bending performance; multiple hardness
1. Introduction
As soft robotic technology develops, soft robots are being applied to different fields
such as medical, sorting and transporting, and bio-inspired products owing to their out-
standing advantages such as strong adaptability, gentle man-machine interaction, simple
control, fast iteration of design, and biomimetic nature [
1
]. Nevertheless, current soft robots
made of flexible materials (polymers [
1
], elastomers [
1
], hydrogels [
2
], and particles [
3
])
still have some problems. Actually, many actuating pneumatic soft robots that adapt to air
as a power supply have difficulty sustaining a stable working state under high load or high
acceleration owing to the compressibility of air. Moreover, the energy efficiency of pneu-
matic soft robots is rather low because most energy is lost during redundant deformation
and inflation/deflation. In addition, the response speed of soft robots is lower than that of
traditional rigid robots, and hysteresis occurs during the actuation. Therefore, increasing
the response speed, bending performance, and tip capacity generated by bending has been
the focus of researchers in the field of soft robots.
Soft robots can be operated with several different drive modes including pneumatics,
shape-memory alloys and electrically powered methods, and their motions are divided into
fast (>1 Hz) and slow (<0.1 Hz) responses [
1
]. Using a shape memory alloy (SMA), a single
fast actuation (<100 ms) can be achieved [
4
], in which deformation occurs within 100 ms,
and a linear velocity of over 0.2 m/s is generated. The electrically powered methods can
offer several advantages, including high-speed actuation, high strain, silent operation, and
self-sensing, but they need to have a rigid frame and pre-stretch to successfully finish the
actuating task. The electro-hydraulic method is a newly developed electrically powered
Machines 2022, 10, 272. https://doi.org/10.3390/machines10040272 https://www.mdpi.com/journal/machines
