Soft robots have great potential to realize machines that interact and coexist with humans. A key technology to realize soft robots is soft fluidic actuators. Previously, we developed a soft pump using the electrohydrodynamics (EHD) phenomenon. EHD is a flow phenomenon, which is generated by applying a high voltage to a dielectric fluid. In this study, we developed flexible high-power-density EHD pumps. First, a pump was fabricated by a simple design with interdigitated electrodes. Second, a mathematical model was used to analyze the pressure generated per length assuming that electric fields only act between neighboring electrodes in a flexible EHD pump with interdigitated electrodes. The results were used to optimize the gap between electrodes to maximize the pressure per length. Third, we used the optimized process to fabricate multiple flexible EHD pumps. The procedure produced pumps easily and reliably. Fourth, we compared the experimental values with the analytical solutions. The good agreement confirmed that the generated pressure per unit length can be approximated in a uniform electric field between neighboring electrodes. Because our flexible EHD pump can operate even when deformed, it has potential for wearable device applications.

1. [1] A. Minaminosono, H. Shigemune, Y. Okuno, T. Katsumata, N. Hosoya, and S. Maeda, “A deformable motor driven by dielectric elastomer actuators and flexible mechanisms,” Frontiers in Robotics and AI, Vol.6, No.1, pp. 1-12, doi: 10.3389/frobt.2019.00001, 2019.
2. [2] C. Jiang, K. Takagi, S. Hirano, T. Suzuki, S. Hosoe, K. Hashimoto, and A. Nozawa, “Flexible Parallel Link Mechanism Using Tube-Type Dielectric Elastomer Actuators,” J. Robot. Mechatron., Vol.27, No.5, pp. 504-512, doi: 10.20965/jrm.2015.p0504, 2015.
3. [3] Y. Okuno, H. Shigemune, Y. Kuwajima, and S. Maeda, “Stretchable Suction Cup with Electroadhesion,” Advanced Materials Technologies, Vol.4, No.1, 1800304, doi: 10.1002/admt.201800304, 2019.
4. [4] S. Maeda, T. Kato, Y. Otsuka, N. Hosoya, C. Matteo, and C. Laschi, “Large deformation of self-oscillating polymer gel,” Physical Review E, Vol.93, 010501, doi: 10.1103/PhysRevE.93.010501, 2016.
5. [5] Z. Mao, M. Kuroki, Y. Otsuka, and S. Maeda, “Contraction waves in self-oscillating polymer gels,” Extreme Mechanics Letters, Vol.39, 100830, doi: 10.1016/j.eml.2020.100830, 2020.
6. [6] S. Maeda and S. Hashimoto, “Volume oscillation of microphase-separated gel,” Macromolecular Chemistry & Physics, Vol.214, No.3, pp. 343-349, doi: 10.1002/macp.201200448, 2013.
7. [7] H. Nakagawa, Y. Hara, S. Maeda, and S. Hashimoto, “A Pendulum-Like Motion of Nanofiber Gel Actuator Synchronized with External Periodic pH Oscillation,” Polymers, Vol.3, No.1, pp. 405-412, doi: 10.3390/polym3010405, 2011.
8. [8] H. Shigemune, S. Maeda, V. Cacucciolo, Y. Iwata, E. Iwase, S. Hashimoto, and S. Sugano, “Printed paper robot driven by electrostatic actuator,” IEEE Robotics and Automation Letters, Vol.2, No.2, pp. 1001-1007, doi: 10.1109/LRA.2017.2658942, 2017.
9. [9] H. Shigemune, S. Maeda, Y. Hara, N. Hosoya, and S. Hashimoto, “Origami Robot: A Self-folding Paper Robot with an Electrothermal Actuator Created by Printing,” IEEE/ASME Trans. on Mechatronics, Vol.21, No.6, pp. 2746-2754, doi: 10.1109/TMECH.2016.2593912, 2016.
10. [10] K. Suzumori, S. Iikura, and H. Tanaka, “Development of flexible microactuator and its applications to robotic mechanisms,” IEEE Int. Conf. on Robotics and Automation, Vol.2, pp. 1622-1627, doi: 10.1109/ROBOT.1991.131850, 1991.
11. [11] S. Kurumaya, H. Nabae, G. Endo, and K. Suzumori, “Design of thin McKibben muscle and multifilament structure,” Sensors and Actuators A: Physical, Vol.261, No.1, pp. 66-74, doi: 10.1016/j.sna.2017.04.047, 2017.
12. [12] S. Wakimoto and K. Suzumori, “Fabrication and basic experiments of pneumatic multi-chamber rubber tube actuator for assisting colonoscope insertion,” IEEE Int. Conf. on Robotics and Automation, pp. 3260-3265, doi: 10.1109/ROBOT.2010.5509633, 2010.
13. [13] V. Cacucciolo, H. Shigemune. M. Cianchetti, C. Laschi, and S. Maeda, “Conduction Electrohydrodynamics with Mobile Electrodes: A Novel Actuation System for Untethered Robots,” Advanced Science, Vol.4, No.9, 1600495, doi: 10.1002/advs.201600495, 2017.
14. [14] Y. Kuwajima, H. Shigemune, V. Cacucciolo, M. Cianchetti, C. Laschi, and S. Maeda, “Active suction cup actuated by ElectroHydroDynamics phenomenon,” IEEE/RSJ Int. Conf. on Intelligent Robots and Systems, pp. 470-475, doi: 10.1109/IROS.2017.8202195, 2017.
15. [15] V. Cacucciolo, J. Shintake, Y. Kuwajima, S. Maeda, D. Floreano, and H. Shea, “Stretchable pumps for soft machines,” Nature, Vol.572, pp. 516-519, doi: 10.1038/s41586-019-1479-6, 2019.
16. [16] H. Shigemune, S. Sugano, H. Sawada, S. Hashimoto, Y. Kuwajima, Y. Matsushita, S. Maeda, V. Cacucciolo, M. Cianchetti, and C. Laschi, “Swinging paper actuator driven by conduction electrohydrodynamics,” IEEE Int. Conf. on Robotics and Biomimetics, pp. 379-384, doi: 10.1109/ROBIO.2017.8324447, 2017.
17. [17] S. Yokota, K. Kawamura, K. Takemura, and K. Edamura, “High-Integration Micromotor Using Electro-Conjugate Fluid (ECF),” J. Robot. Mechatron., Vol.17, No.2, pp. 142-148, doi: 10.20965/jrm.2005.p0142, 2005.
18. [18] K. Tokida, A. Yamaguchi, K. Takemura, S. Yokota, and K. Edamura, “A Bio-Inspired Robot Using Electro-Conjugate Fluid,” J. Robot. Mechatron, Vol.25, No.1, pp. 16-24, 2013.
19. [19] P. Atten and J. Seyed-Yagoobi, “Electrohydrodynamically induced dielectric liquid flow through pure conduction in point/plane geometry-theory,” IEEE Trans. on Dielectrics and Electrical Insulation, Vol.10, No.1, pp. 27-36, doi: 10.1109/TDEI.2003.1176555, 2003.
20. [20] A. Ramos, “Electrokinetics and Electrohydrodynamics in Microsystems,” Springer Science & Business Media, 2011.
21. [21] Z. Mao, K. Yoshida, and J.-W. Kim, “Developing O/O (oil-in-oil) droplet generators on a chip by using ECF (electro-conjugate fluid) micropumps,” Sensors and Actuators B: Chemical, Vol.296, No.1, 126669, doi: 10.1016/j.snb.2019.126669, 2019.
22. [22] Y. Kuwajima, S. Maeda, and H. Shigemune, “Analysis of EHD pump with planer electrodes using FEM simulation,” Int. Symp. on Micro-NanoMechatronics and Human Science, pp. 1-3, doi: 10.1109/MHS.2017.8305176, 2017.
23. [23] T. Sato, Y. Yamanishi, V. Cacucciolo, Y. Kuwajima, H. Shigemune, M. Cianchetti, C. Laschi, and S. Maeda, “Electrohydrodynamic Conduction Pump with Asymmetrical Electrode Structures in the Microchannels,” Chemistry Letters, Vol.46, No.7, pp. 950-952, doi: 10.1246/cl.170217, 2017.
24. [24] T. Sato, S. Maeda, and Y. Yamanishi, “Study of Low Energy Micro EHD Pump by Designed Electric Field,” Int. Symp. on Micro-NanoMechatronics and Human Science, pp. 1-3, doi: 10.1109/MHS.2018.8886968, 2018.
25. [25] K. Cherenack and L. V. Pieterson, “Smart textiles: Challenges and opportunities,” J. of Applied Physics, Vol.112, No.9, pp. 1536-1550, doi: 10.1063/1.4742728, 2012.
26. [26] P. Polygerinos, Z. Wang, K. C. Galloway, R. J. Wood, and C. J. Walsh, “Soft robotic glove for combined assistance and at-home rehabilitation,” Robotics and Autonomous Systems, Vol.73, pp. 135-143, doi: 10.1016/j.robot.2014.08.014, 2015.
27. [27] R. M. Fish and L. A. Geddes, “Conduction of electrical current to and through the human body: a review,” Eplasty, Vol.9, e44, 2009.
28. [28] R. Hinchet, V. Vechev, H. Shea, and O. Hilliges, “DextrES: Wearable Haptic Feedback for Grasping in VR via a Thin Form-Factor Electrostatic Brake,” UIST ’18: Proc. of the 31st Annual ACM Symp. on User Interface Software and Technology, pp. 901-912, doi: 10.1145/3242587.3242657, 2018.
29. [29] I. M. Koo, K. Jung, J. C. Koo, J. Nam, Y. K. Lee, and H. R. Choi, “Development of Soft-Actuator-Based Wearable Tactile Display,” IEEE Trans. on Robotics, Vol.24, No.3, pp. 549-558, doi: 10.1109/TRO.2008.921561, 2008.