Damping effect of particle-jamming structure for soft actuators with 3D-printed particles

Significance 

Soft actuators have attracted significant research attention in the emerging field of robots. Unlike traditional conventional actuators, they are highly adaptive and compliant as they do not have rigid links and joints. Generally, soft actuators made of soft materials exhibit potential applications in numerous areas, including the design of grippers, surgical tools, and wearable devices because the soft materials can adapt to various unstructured environments. Unfortunately, soft actuators made of soft materials generate large vibrations in certain dynamic environments that deteriorate their damping performance and efficiency. Therefore, controlling the undesirable vibrations of soft actuators is very important.

Damping effects and stiffness are two critical mechanical properties in controlling vibrations of soft actuators. Whereas damping is mainly important for reducing vibrations in dynamic environments, stiffness is essential for load capacity. To date, significant research has been conducted to determine effective approaches for modulating these properties. Recently, particle jamming was identified as a promising solution for modulating the mechanical properties of soft actuators. The jamming system uses various types of particles like glass spheres and sands. For soft actuators, however, lightweight and reliable particles are preferred to maintain intrinsic properties. Nevertheless, fabricating particles with desirable properties and understanding the underlying mechanism of damping in the presence of a large number of particles has remained a great research challenge.

With the continuous advancement in technology, three-dimensional (3D) printing technology has been lately adapted to fabricate particles with desirable properties and strengthen their jamming effects. Consequently, it also provides insights into the damping mechanism by controlling the properties of the particles. Equipped with this knowledge, a team of researchers from the Northwestern Polytechnical University: Si-Qi An (PhD candidate), Dr. Hai-Lin Zou, Dr. Zi-Chen Deng, and Dong-Yun Guo (Ph.D. student) presented a new method for suppressing the undesirable vibrations and modulation of damping in soft actuators using 3D-printed particle-jamming systems. The main objective was to establish a lightweight and reliable approach to enhance the damping performance of soft actuators. Their research work is currently published in the journal, Smart Materials and Structures.

In their approach, the authors fabricated more lightweight and durable spherical particles with different diameters and surface topographies using 3D printing technology. Next, an analytical model for energy dissipation was established to identify the parameters affecting damping performance and to understand the underlying mechanism of energy dissipation. Finally, the particle-jamming method based on 3D printed particles was experimentally verified to determine its feasibility in suppressing undesirable vibration in soft actuators.

The authors observed that the particle-jamming system with 3D-printed particles was highly effective for suppressing the vibrations and improving the damping performance of soft actuators. Specifically, it achieved up to a six-fold increase in the damping ratio because the use of 3D technology enabled the customization of the particles to achieve distinct structures and desired properties. Moreover, the damping performance depended on various parameters, including pressure difference, the dimensions of the particle chamber, particle properties, and the soft material of the particle chamber. For instance, the damping ratio could be improved by increasing pressure level difference, increasing the coefficient of friction of the particle layer, decreasing the particle size, and increasing the height of the particle chamber.

In summary, the research team integrated the 3D-printed particles and particle-jamming mechanism to suppress vibrations of soft particles. It allowed customization of the weight and mechanical properties of the particles to control damping. A remarkable improvement in the damping ratio was reported. The presented analytical model for energy dissipation provided an understanding of the underlying mechanism, thus enabling the prediction of specific parameters affecting the damping performance. The experimental results were in good agreement with the theoretical analysis, thus verifying the method’s feasibility. In a statement to Advances in Engineering, the authors explained their study provided important insights into the design of soft actuators capable of suppressing undesirable vibrations in some dynamic environments.

Damping effect of particle-jamming structure for soft actuators with 3D-printed particles - Advances in Engineering
Fig. 1. The soft materials tend to induce large undesired vibrations. The damping performance of soft actuator can be tuned by the 3D-printed particles, resulting in effective damping responses. In this way, the soft actuator can improve its performance in dynamic environments.

About the author

Zi-Chen Deng, Professor at Northwestern Polytechnical University, currently the dean of school of aeronautics, and the director of MIIT Key Laboratory of Dynamics and Control of Complex Systems. Prof. Deng was appointed as the distinguished professor of the Yangtze River Scholar Award Program of the Ministry of Education (2009), and excellent teacher in Shaanxi Province (2014).  He currently serves as editorial board members on 9 journals, and is currently the chairman of Shaanxi Vibration Engineering Society, council member of Chinese Society for Vibration Engineering, member of Committee on Dynamics and Control of the Chinese Society of Mechanics, member of Committee on Dynamics and Control of the Chinese Society of Mechanics and member of Committee on Chinese Association of Computational Mechanics.

Prof. Deng’s research interest is in the broad area of dynamics and control, engineering mechanics, computational mechanics, applied mathematics and structural engineering. He has long been engaged in developing symplectic methodologies for Hamilton systems, and the related interdisciplinary research between computational mechanics and control theory. The methodologies have been successfully applied in various fields, including nonlinear dynamical systems, flexible multi-body systems, Dynamics of Aerospace Systems and Optimal design of composite materials. He has published more than 320 papers and 5 monographs. The research results won 5 provincial and ministerial science and technology awards.

About the author

Siqi An received his B.Eng. degree in engineering mechanics from Northwestern Polytechnical University, Xi’an, China, in 2017 and is pursuing his Ph.D. degree in general and fundamental mechanics from Northwestern Polytechnical University. His present research interests include soft robots and variable stiffness structures.

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About the author

Hai-Lin Zou, is currently Associate Professor at the department of engineering mechanics from Northwestern Polytechnical University. He received M.S. and Ph.D. from Xi’an Jiaotong University and the National University of Singapore in 2007 and 2012 respectively. He was Postdoctoral Fellow from 2012-2013 at The University of Tokyo. His main research interests focus on soft actuators with variable mechanical properties, dynamical analysis of soft machines, as well as nonlinear dynamics of coupled systems.

About the author

Dongyun Guo received his B.Eng. degree in engineering mechanics from Shijiazhuang Tiedao University, Shijiazhuang, China, in 2017 and is pursuing his Ph.D. degree in general and fundamental mechanics from Northwestern Polytechnical University. His present research interests include soft robots and magnetic structures.

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Reference

An, S., Zou, H., Deng, Z., & Guo, D. (2020). Damping effect of particle-jamming structure for soft actuators with 3D-printed particlesSmart Materials and Structures, 29(9), 095012.

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