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Research Papers

Investigation of the State Transition and Moving Boundary in a Pneumatic–Hydraulic Coupled Dielectric Elastomer Actuator

[+] Author and Article Information
Liyuan Chen

State Key Laboratory of Fluid Power and
Mechatronic Systems,
Zhejiang University,
Hangzhou 310027, China;
Key Laboratory of Soft Machines and
Smart Devices of Zhejiang Province,
Zhejiang University,
Hangzhou 310027, China
e-mail: liyuanch@zju.edu.cn

Weijia Chen

State Key Laboratory of Fluid Power and
Mechatronic Systems,
Zhejiang University,
Hangzhou 310027, China;
Key Laboratory of Soft Machines and
Smart Devices of Zhejiang Province,
Zhejiang University,
Hangzhou 310027, China
e-mail: 3150105252@zju.edu.cn

Yaoting Xue

Key Laboratory of Soft Machines and
Smart Devices of Zhejiang Province,
Zhejiang University,
Hangzhou 310027, China
e-mail: 3160105511@zju.edu.cn

Mingqi Zhang

State Key Laboratory of Fluid Power and
Mechatronic Systems,
Zhejiang University,
Hangzhou 310027, China;
Department of Engineering Mechanics,
Zhejiang University,
38 Zheda Road,
Hangzhou 310027, China;
Key Laboratory of Soft Machines and
Smart Devices of Zhejiang Province,
Zhejiang University,
Hangzhou 310027, China
e-mail: zhangmq@zju.edu.cn

Xiangping Chen

State Key Laboratory of Fluid Power and
Mechatronic Systems,
Zhejiang University,
Hangzhou 310027, China;
Department of Engineering Mechanics,
Zhejiang University,
38 Zheda Road,
Hangzhou 310027, China;
Key Laboratory of Soft Machines and
Smart Devices of Zhejiang Province,
Zhejiang University,
Hangzhou 310027, China
e-mail: chenxiangping@zju.edu.cn

Xunuo Cao

State Key Laboratory of Fluid Power and
Mechatronic Systems,
Zhejiang University,
Hangzhou 310027, China;
Department of Engineering Mechanics,
Zhejiang University,
38 Zheda Road,
Hangzhou 310027, China;
Key Laboratory of Soft Machines and
Smart Devices of Zhejiang Province,
Zhejiang University,
Hangzhou 310027, China
e-mail: caoxn@zju.edu.cn

Zhen Zhang

State Key Laboratory of Fluid Power and
Mechatronic Systems,
Zhejiang University,
Hangzhou 310027, China;
Department of Engineering Mechanics,
Zhejiang University,
38 Zheda Road,
Hangzhou 310027, China;
Key Laboratory of Soft Machines and
Smart Devices of Zhejiang Province,
Zhejiang University,
Hangzhou 310027, China
e-mail: Zhangzhen105@zju.edu.cn

Guorui Li

State Key Laboratory of Fluid Power and
Mechatronic Systems,
Zhejiang University,
Hangzhou 310027, China;
Department of Engineering Mechanics,
Zhejiang University,
38 Zheda Road,
Hangzhou 310027, China;
Key Laboratory of Soft Machines and
Smart Devices of Zhejiang Province,
Zhejiang University,
Hangzhou 310027, China
e-mail: guoruili@zju.edu.cn

Tiefeng Li

State Key Laboratory of Fluid Power and
Mechatronic Systems,
Zhejiang University,
Hangzhou 310027, China;
Department of Engineering Mechanics,
Zhejiang University,
38 Zheda Road,
Hangzhou 310027, China;
Key Laboratory of Soft Machines and
Smart Devices of Zhejiang Province,
Zhejiang University,
Hangzhou 310027, China
e-mail: litiefeng@zju.edu.cn

1Corresponding author.

Manuscript received October 17, 2018; final manuscript received November 28, 2018; published online December 24, 2018. Assoc. Editor: Yong Zhu.

J. Appl. Mech 86(3), 031004 (Dec 24, 2018) (12 pages) Paper No: JAM-18-1590; doi: 10.1115/1.4042136 History: Received October 17, 2018; Revised November 28, 2018

Compared to robots and devices made of rigid components, soft robots and flexible devices driven by soft active materials possess various advantages including high adaptability under extreme environment and compatibility with a human. Dielectric elastomer (DE) membrane, which is commonly used in building soft actuators, can achieve large actuation by the combined loadings of voltage-induced Maxwell stress and fluidic pressures (pneumatic and hydraulic pressure). This paper proposes a pneumatic–hydraulic coupled electromechanical actuator (PHCEA), which exhibits strong coupling effect of electromechanical actuation (the Maxwell stress on DE membrane), pneumatic and hydraulic pressures. Considering the moving boundary and state transition, a computational model has been developed to investigate the coupling behaviors of the PHCEA. The numerical result by this model is in accordance with the experimental measurements. The combination of experimental data and the theoretical result indicates that the state transition and moving boundary separate the potential region of electrical breakdown and mechanical damage. This model can be utilized as a practical method to characterize the performance and guide the design of soft devices. The experimental setup and computational method of the PHCEA bring new insights into the fabrication and characterization of soft robots, adaptive optics, and flexible bio-medical devices. The PHCEA possesses wide applications in underwater robots, soft muscles, and microfluidics systems. It can serve as the gas bladder of soft swimming robots, the soft actuator of hydraulic–pneumatic coupling systems, and the gas–liquid valve of flexible microfluidics systems.

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Figures

Grahic Jump Location
Fig. 1

Sectional views (in the axial direction) of a PHCEA. A prestretched membrane is fixed between two hollow cylindrical chambers. The bottom surface of the membrane is coated with compliant electrode and is connected to a HVP supply. The upper chamber (hydraulic chamber) contains certain volume of water and the lower chamber (pneumatic chamber) is enclosed with a hole on the wall connected to an air pressure control system. (a) The membrane is in the prestretched state and mounted on the device. (b) Certain volume of water is poured into the hydraulic chamber which results in the downward deformation of the membrane. (c) The pneumatic chamber is pressurized by air and the membrane is deformed upward. (d) When the electric voltage is applied, the membrane moves upward again and protrudes out of the water in a high voltage.

Grahic Jump Location
Fig. 2

(a) Schematic of the experimental system. (b) Experimental setup consists of the PHCEA, a homemade pressure control system, a laser displacement measurement, and a HVP supply. (c) Simulation and experimental results of the relation between the voltage and the apical displacement of the membrane. (d) When the voltage is low (∼3.3 kV), the entire membrane is immersed in the water. (e) When the voltage increases (∼4.7 kV), the membrane moves upward and its apex touches the water surface. (f) When the voltage is high enough (∼5.3 kV), the membrane protrudes out of the water surface. The actuated and de-actuated regions are labeled by red and black dashed lines, respectively. The water surface is labeled by a white solid line.

Grahic Jump Location
Fig. 3

Different states in the description of the computational model. A certain material particle is labeled by the circular dot. The (a) reference, (b) prestretched, (c) hydraulic pressurized, (d) air pressurized, (e) low voltage actuated, and (f) high voltage actuated states of the PHCEA.

Grahic Jump Location
Fig. 4

The membrane's force equilibrium. (a) In the reference state, we select a ring-shaped band between two circular shape material particles R and R + dR. (b) In the deformed state, the flat band is deformed into an axisymmetric band in three dimensions where the hydraulic pressure, air pressure, and stresses on the band's edge are balanced. (c) For half of the band, the hydraulic pressure, air pressure, and the longitudinal and latitudinal stresses are balanced.

Grahic Jump Location
Fig. 6

(a) Relations between voltage and the apical displacement of the membrane. (b) Configurations of the DE membrane in different voltages with air pressure p=500 Pa. The membrane is deformed largely and protrudes out of the water surface at Φ/(Hμ/ε)=0.21. The de-actuated region of DE membrane is highlighted with the dashed curve. (c) Relations between voltage and the radius of the de-actuated area. (d) Relations between pressure and the apical displacement of the membrane. (e) Configurations of the DE membrane in small air pressures with electric voltage Φ=0. The membrane is concave when the pressure is low and is convex when the pressure is high. (f) Configurations of the DE membrane in big air pressures with electric voltage Φ=0.

Grahic Jump Location
Fig. 7

Details of the state transition point and electrical breakdown point. (a) Relation between voltage and apical displacement near the state transition point and the point is labeled by a circular dot. (b) Configuration of the DE membrane. (c) True electric field and latitudinal stretch distributions. (d) Relation between voltage and apical displacement near the electrical breakdown point and the point is labeled by a circular dot. (e) Configuration of the DE membrane. (f) True electric field and latitudinal stretch distributions.

Grahic Jump Location
Fig. 8

Field distributions in the membrane in different voltages: (a) true electrical field; (b) tangential angle; (c) longitudinal and (d) latitudinal stresses; and (e) longitudinal and (f) latitudinal stretches

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