Azobenzene-functionalized liquid crystalline materials can be operated by remote light stimuli without complicated circuits or parts and therefore attract a great deal of attention in areas such as human interfaces, haptic devices and miniaturized soft robots.
Previous studies showed light-induced movements of the soft robot and reported crawling and walking movements where a lot of friction was observed. Recently, rolling movements in cylindrical and spiral soft robots with multiple revolutions have been reported, which reduce friction by taking over the rolling resistance, similar to the wheel. However, rolling is not an effective strategy for climbing stairs as we experience it in everyday life.
The researchers went a step further and implemented a torsional movement of the helical soft robot with one revolution that maximized the spiral diameter per unit length, a factor closely related to the height of the obstacle a soft robot can overcome. In the case of a single-turn helix, the torsional soft robot rolling on the floor only comes into contact at one and two points, while a single end of the soft robot can reach over the obstacles. With these observations, it was clear that a single-turn helix would be an effective design that minimized rolling resistance while maximizing the soft robot’s height range.
To overcome obstacles, the torsion soft robot would have to lift its entire body at a single point of contact. Molecular engineering has made it possible for researchers to demonstrate step-climbing torsional soft robots and high speed per body length (0.15 BL / s) with a light body weight (0.2 mg). Seven different azobenzene-based molecular switches were studied to program the molecular alignment and crosslink density as liquid crystalline polymers. Most previous studies controlled the crosslink density of polymers through incomplete cure or the addition of non-crosslinkable monomers. However, these strategies increase dangling molecules that cannot transmit the photo-generated stress from molecular switches. By varying the molecular length of molecular switches, the researchers were able to control the crosslinking density without increasing the dangling chains. Thus, both a high modulus of elasticity (> 2 GPa) and a photo-generated stress (> 1 MPa) are achieved. This helps soft robots maintain a high coil height and allows them to lift the entire body with a point of contact on the substrate. The simulation of finite element analysis also helps to understand the locomotion mechanism of torsional soft robots.
In addition, the researchers optimized the temperature state of viscoelastic soft robots with regard to the glass transition temperature. In a glassy state, the speed of soft robots increases at higher temperatures because softer materials are easier to reconfigure. In a rubbery state, however, the opposite is observed. If the temperature is too high, soft robots cannot generate enough stress and reduce photo-generated stress, which illustrates the importance of viscoelasticity in polymer-based soft robots.
Through this work, a new torsional soft robot design can expand the potential of soft robot application in different areas where greater actuation or long reach is required, while at the same time providing our basic knowledge of the structure-property relationship for light-driven soft robots is expanded.
Watch these tubular robots roll up stairs, carry carts, and compete against each other
Jae Gwang Kim, Jisoo Jeon, Rajamanickam Sivakumar, Jonggeon Lee, Yun Ho Kim, Maenghyo Cho, Ji Ho Youk, Jeong Jae Wie, Light-Fueled Climbing of Monolithic Torsional Soft Robots via Molecular Engineering, Advanced intelligent systems (2021). DOI: 10.1002 / aisy.202100148
Quote: Lightly powered torsion soft robot that can climb stairs quickly (2021, October 25), accessed on October 25, 2021 from https://techxplore.com/news/2021-10-light-fueled-torsional-soft -robot-rapidly.html
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