Elastomeric Prepregs Simplify Soft Robot Production

Significance 

Soft robotics is a specific subfield of robotics that deals with construction of robots from highly compliant materials termed soft materials, i.e., materials with Young’s moduli in the range of biological materials. This field heavily employs biomimicry, particularly with respect to movement. Typically, soft robots that are driven with compressed air consist of two parts which are bonded together, a top and a strain-limiting bottom part. During fabrication, the upper and lower parts are cast and then bonded together. However, if paper is used as a strain-limiting layer, it must be placed in the middle of the lower part. Alternatively, it can also be glued onto the cured underside. As such, the casting of the lower part, the integration of paper or fabric, and the bonding of both parts is a considerable amount of work and a source of possible leakage at the seam.

To this end, simplification of this tedious manufacturing process would save both time and cost. Recently, Hamburg University of Technology scientists Tristan Wienzek and Dr. Arthur Seibel from the Workgroup on System Technologies and Engineering Design Methodology in Germany developed textile semi-finished products pre-impregnated with liquid elastomer (prepregs) that can be stored at a low temperature without significant curing and then further used as the strain-limiting part of a soft robot. In their study, they focused on describing the possibility of simplifying the manufacturing process of a sealant using the aforementioned approach. Their work is currently published in the research journal Advanced Engineering Materials.

Briefly, the two researchers mixed samples of various silicone rubbers often used in soft robotics and stored the resultant mixture in a freezer at ‒25 °C for a period of 12 weeks. The mixture was monitored on a weekly basis with its viscosity being measured as it would aid establish extent of cross-linking. Subsequently, the impregnability of various textiles was evaluated and the applicability of prepregs tested on a state-of-the-art soft bending actuator.

The authors reported that by using elastomeric prepregs, the undesired casting process of the upper part of a soft actuator or robot could be avoided. Additionally, they pointed out that two elastomers, namely Elastosil M 4601 and Sylgard 184, could be stored at ‒25 °C for a period of 8.7 weeks (the former) to 12 weeks (the latter).

In summary, the cross-linking behavior of three different elastomers on the basis of the viscosity change under reduced temperature was determined with the aim of producing elastomeric prepregs. Tristan Wienzek and Arthur Seibel reported that various textiles could be impregnated with the two elastomers (Elastosil M 4601 and Sylgard 184) and were therefore suitable for production of prepregs. Prepregs were reported to facilitate and accelerate production. Overall, prepregs thus represent a first step toward the industrial production of soft robots.

Elastomeric Prepregs Simplify Soft Robot Production - Advances in Engineering
Figure: Fabrication steps of a soft bending actuator using a prepreg as the strain limiting bottom part: a) preparing the mold for the top part of the actuator, b) mixing of elastomer, c) casting the top part, d) extracting the cured top part from the mold, e) placing the top part of a prepreg, thus creating the soft bending actuator.

About the author

Arthur Seibel received the Diploma and Ph.D. degrees (both with distinction) in Mechanical Engineering from Hamburg University of Technology, Hamburg, Germany, in 2011 and 2015, respectively.

He is a Research Associate with Workgroup on System Technologies and Engineering Design Methodology, Hamburg University of Technology, Hamburg, Germany. His research interests include soft robotics, parallel robotics, and design methodology.

About the author

Tristan Wienzek received the Bachelor’s and Master’s (with distinction) degrees in Mechanical Engineering from Hamburg University of Technology, Hamburg, Germany, in 2017 and 2019, respectively. He was a student with Workgroup on System Technologies and Engineering Design Methodology, Hamburg University of Technology, Hamburg, Germany. His research focused on the production of soft robots.

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Reference

Tristan Wienzek, Arthur Seibel. Elastomeric Prepregs for Soft Robotics Applications. Advanced Engineering Materials 2019, volume 21, page 1801200.

Go To Advanced Engineering Materials

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