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