3D Gel Printing for Jellyfish-Mimic Robot

Abstract

Various kinds of underwater exploration techniques have been developed. For instance, submersible research vehicles and autonomous underwater vehicle (AUV) have been used for observation of underwater conditions, in addition to the technique of fixed-point observation. However, such research vehicles and conventional AUV are difficult to control, are expensive, and are usually made with non-biodegradable materials such as metals. In contrast, jellyfish is the most efficient swimmers, traveling for long distance with saving energy by drifting in the ocean, its body can be decomposed after death, and safe for surrounding creatures. Therefore, we are developing the jellyfish-mimic AUV using a hydrogel. For designing a Jellyfish-mimic AUV robot, it is preferable to introduce a soft actuator driven by water pressure, as it requires low electric power and it is eco-friendly. In this study, we prototyped a Jellyfish-AUV robot using a soft material and a soft actuator. While it is ideal to make a robot body with hydrogel it is difficult to make the actuator with hydrogel. Here, we report a silicone-based hydraulically-driven soft actuator that can make a bending motion of umbrella-shaped bell of artificial Jellyfish. We utilized the Pneunets Bending Actuator for designing the actuator, and the detailed information of this actuator is shown in the website of Soft Robotics Toolkit (see https://softroboticstoolkit.com/book/pneunets-bending-actuator). The actuator is composed of inflation parts, basis, and copy paper placed between them. We poured into the 3D printed mold made with polylactic acid (PLA) and preserved at room temperature for 4 h to cure the silicone parts (inflation parts and basis). Copy paper was sandwiched between inflation parts and basis. The size of copy paper was 30 mm × 5 mm. Then, we poured additional silicone resin to combine the parts. By inserting a toothpick into the mold, we made the insertion port of the silicon tube. Before curing, we removed the air bubbles for 20 minutes with a vacuum de-foaming device. Finally, we inserted a silicon tube into the fuselage and attached a syringe for air supply. The behavior of the actuator in salt water was evaluated by image analysis, and the shrinkage factors of gel robots were compared with that of real jellyfish. The results were obtained as shown in Figs.1, 2 and 3. The shrinkage ratio of the jellyfish robot was 46.4 % at the maximum in the case of air injection of 2.8 cm³. The ratio did not reach 56.3 % at the maximum shrinkage ratio of the real jellyfish. To achieve the 56.3 % shrinkage ratio, we have to improve the maximum volume of injection air. Consequently, we have concluded there is a possibility that this actuator can reproduce jellyfish movement.