Soft Electrohydraulic Bending Actuators for Untethered Underwater Robots
Abstract
:1. Introduction
2. Soft Electrohydraulic Bending Actuator
2.1. Actuator Design and Operating Principle
2.2. Simulations of the Actuator
2.3. Materials of the Actuator
2.4. Research and Testing of Parameters
2.4.1. Effect of Silicone Rubber Film Thickness on Actuator Bending Performance
2.4.2. Effect of Silicone Oil Volume on Actuator Bending Performance
2.5. Determination of Parameters
2.6. Fabrication of the Actuator
2.6.1. The Fabrication Process of 1.1 mm-Thick Silicone Rubber Film
2.6.2. The Fabrication Process of the Pressing Mold
2.6.3. The Fabrication Process of the Soft Electrodes Chamber
2.6.4. The Fabrication Process of the Silicone Oil Chamber
3. Untethered Underwater Robot
3.1. Structural Design of the Underwater Robot
3.2. Force Analysis
3.2.1. Static Force Analysis
3.2.2. Dynamic Force Analysis
3.3. Swimming Posture Design of the Underwater Robot
3.3.1. Static Suspension
3.3.2. Draining and Propelling
3.3.3. Decelerating and Drifting
3.3.4. Action Recovery
3.4. Design of Control Circuit
3.5. Production of the Underwater Robot
3.6. Underwater Robot Test Device
3.7. Swimming Test of the Underwater Robot
4. Conclusions
- (1)
- We designed a type of soft electrohydraulic bending actuators, mostly consisting of five layers. A 5-A silicone rubber film made up the first layer. In the second layer, there were soft electrodes made of black carbon paste. The third layer fully enclosed the soft electrodes with a 150 μm-thick PDMS film. The fourth layer consisted of a closed chamber filled with dimethyl silicone oil, which was the working liquid that achieved bending during the actuation process. This silicone oil also acted as an insulating medium to protect the silicone film at the edge of the electrode from being broken down by the electric field. The final layer of the construction was a 300 μm-thick PDMS film. Furthermore, we used an acrylic frame and a soft flipper to amplify the actuator’s bending motion. In order to create an electrostatic field and squeeze the silicone oil into motion, which allowed the actuator to bend, the soft electrode served as a positive electrode and the surrounding water as a ground electrode. When a square wave voltage was applied, the soft electrohydraulic bending actuator could generate continuous flapping motions.
- (2)
- Through electric field simulations and experiments, we determined the actuator’s basic parameters. We studied the effects of silicone rubber film thickness and silicone oil volume in the silicone oil chamber on the bending degree and output force of the actuator and obtained that the optimal silicone rubber film thickness was 1.1 mm and the optimal silicone oil volume was 0.8 mL. Combining the results of our research with the experimental data, we found that the highest input voltage for the actuator was 16 kV, and the maximum bending angle of the actuator was 16.7°. After that, we created a mold using a laser cutting machine and paired it with the mold pressing technique to produce an actuator prototype.
- (3)
- We created the primary construction of the underwater robot based on the swimming ways of Haliclystus auricula. This structure consisted of a body frame, six soft electrohydraulic bending actuators, and a box that housed lithium batteries and a control circuit. We constructed a mechanical model of the underwater robot, examined its force state when it was suspended and swimming underwater, obtained the mechanical equation that propelled the robot to swim, and used theoretical deduction to infer the underwater robot’s properties. It was concluded that there existed a positive correlation between the driving force and the maximum speed. When the driving force was stronger, the underwater robot could reach a faster maximum speed. The conclusions drawn from the analytical mechanics model provide a theoretical basis for robot swimming tests.
- (4)
- We designed the swimming action of the underwater robot based on the swimming posture of Haliclystus auricula, which mainly included four parts. In order to realize the untethered motions of the robot, we designed a high-voltage circuit board for driving and controlling the robot, with a built-in 7.4 V lithium battery for power supply. The circuit board could both receive control signals from smart phones to enable remote control and can output high-voltage square wave signals to drive the robot. For testing, we built an underwater robot prototype and fed it signals at various frequencies. The experiment results demonstrate that the horizontal movement speed of the underwater robot could reach its maximum value (7.3 mm/s) when the input signal frequency was 1 Hz. This is because the signal frequency of 1 Hz is closest to the natural frequency of the actuator when moving underwater, which can maximize the displacement of the actuator within a certain period of time.
Supplementary Materials
Author Contributions
Funding
Data Availability Statement
Conflicts of Interest
References
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Voltage (kV) | Bending Angle (°) When the Film Thickness (mm) Is: | ||||
---|---|---|---|---|---|
0.8 | 0.9 | 1.0 | 1.1 | 1.2 | |
0~3 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
4 | 3.5 | 3.0 | 2.5 | 2.0 | 1.0 |
5 | 4.9 | 4.0 | 3.5 | 3.0 | 2.3 |
… | … | … | … | … | … |
12 | 16.0 | 14.0 | 12.0 | 11.0 | 9.5 |
13 | Breakdown | 15.5 | 14.0 | 13.0 | 11.0 |
14 | Breakdown | Breakdown | 15.5 | 14.5 | 12.5 |
15 | Breakdown | Breakdown | 16.5 | 15.0 | 13.0 |
16 | Breakdown | Breakdown | Breakdown | 16.5 | 13.0 |
17 | Breakdown | Breakdown | Breakdown | Breakdown | 13.0 |
18 | Breakdown | Breakdown | Breakdown | Breakdown | 13.0 |
Parameter | Value | Unit |
---|---|---|
Shore hardness of silicone rubber film | 5 | A |
Length of the actuator | 64 | mm |
Layers of film structure | 3 | unit |
Number of chambers | 2 | unit |
Volume of silicone oil | 0.8 | mL |
Thickness of silicone rubber film | 1.1 | mm |
Soft electrode dimensional parameters | 36 × 8 | mm × mm |
Dimensional parameters of silicone oil chamber | 40 × 20 | mm × mm |
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Lin, H.; Chen, Y.; Tang, W. Soft Electrohydraulic Bending Actuators for Untethered Underwater Robots. Actuators 2024, 13, 214. https://doi.org/10.3390/act13060214
Lin H, Chen Y, Tang W. Soft Electrohydraulic Bending Actuators for Untethered Underwater Robots. Actuators. 2024; 13(6):214. https://doi.org/10.3390/act13060214
Chicago/Turabian StyleLin, Hao, Yihui Chen, and Wei Tang. 2024. "Soft Electrohydraulic Bending Actuators for Untethered Underwater Robots" Actuators 13, no. 6: 214. https://doi.org/10.3390/act13060214
APA StyleLin, H., Chen, Y., & Tang, W. (2024). Soft Electrohydraulic Bending Actuators for Untethered Underwater Robots. Actuators, 13(6), 214. https://doi.org/10.3390/act13060214