Application Cases

Experiment Name: Design and Performance Testing of Cylindrical Actuators

Research Direction:
Based on the working principle of dielectric elastomers, a cylindrical actuator was designed, and its theoretical analysis, structural design, manufacturing process, and specific applications were elaborated and analyzed. Using VHB4910 film as the dielectric elastomer material, hyperelastic models—the Yeoh model and the Ogden model—were employed to construct mathematical theoretical models for the electro-induced deformation process of the cylindrical actuator. The effects of factors such as pre-stretch ratio and applied voltage on the actuator's driving performance (axial stress, electro-induced deformation capability) were analyzed. Furthermore, to study the safe and reliable working range of the cylindrical actuator, numerical analysis of four failure modes during operation—electromechanical instability, electrical breakdown, tensile instability, and ultimate tensile fracture—was conducted based on the thermodynamic theory of the Helmholtz free energy function and the Ogden model. The effective working range of the actuator was determined, providing a theoretical basis for its design.

Experimental Objective:
An equivalent circuit model was established for the leakage current phenomenon during the operation of the cylindrical actuator. A measurement method for the parameters in the model was proposed, and the leakage current was experimentally measured to validate the designed cylindrical actuator. Theoretical data were verified through practical testing.

Test Equipment:
The test system consisted of high-voltage equipment, a displacement rangefinder, a tension-compression sensor, and a computer. The high-voltage equipment used Aigtek's ATA-7100 high-voltage amplifier, with a voltage adjustment range of ±10 kVp, a current output range of 0–2 mA, and a rated power of 20 W. It could be adjusted via the power supply itself or remotely controlled by a computer, with operational stability of less than 0.1% per hour. The electric vertical single-column test bench had a built-in sensor with an accuracy of ±0.5%, a maximum load of 100 N, a maximum displacement stroke of 580 mm, and a stretching speed of 0.5 mm/s. 

Figure: Experimental Test Setup

Experimental Process:
To better understand the leakage current phenomenon of the actuator, the current changes during the voltage application to the cylindrical actuator were monitored to study the leakage current. The schematic and experimental setup for leakage current detection are shown in Figure 2. During the experiment, a large resistor was connected in series with the actuator, and ramp voltages with different slopes were applied to the series circuit. The switch was turned on, and the voltage change across the series resistor R was measured using an oscilloscope. After conversion, this voltage change represented the current in the series circuit. The specific steps were as follows:

1. Fix the actuator on the test platform and slowly move the test platform, with each stretching distance being L.

2. After achieving positional balance, measure the capacitance value of the cylindrical actuator at the current position.

3. Apply a ramp voltage with a slope of 200 V to the actuator until the target voltage is reached, and maintain it for a period.

4. Use an oscilloscope to measure the voltage change U(t) across resistor R during the application of the ramp voltage and calculate the leakage current.

   
   

Figure 2: Schematic Diagram of Leakage Current Detection Experiment

Experimental Results:
During the experiment, the oscilloscope used had an analog bandwidth of 100 MHz and a sampling frequency of 1 GS/s, enabling fast sampling. A high-voltage probe with a ratio of 1000:1 was used to prevent damage to the oscilloscope from high voltage.

The target voltages were 1 kV, 3 kV, and 4.5 kV, respectively. The large resistor R in the series circuit was a high-resistance resistor with a value of 10 MΩ. During detection, the cylindrical actuator was maintained in a stationary state for a period (10 s), so the capacitance remained constant, with a measured value of C = 2.4 nF.

Figures 4-7, 4-8, and 4-9 show the leakage current detection results for target voltages of 1 kV, 3 kV, and 4.5 kV, respectively. The results indicate that the leakage current exhibited some fluctuations, which were attributed to minor structural changes in the actuator during axial elongation under voltage changes, as well as external environmental influences during the experiment. Although the applied voltages differed, the trend of leakage current change was consistent, indicating the presence of current leakage during voltage application to the actuator, with leakage current becoming more pronounced as the electric field strength increased.

The leakage current i can be calculated by multiplying the leakage current density j by the effective area A of the flexible electrode. The effective area A was approximately 2500 mm². The leakage current density j was calculated using the formula, typically with σ = 3.23 × 10⁻⁴ S/m and Ee = 40 MV/m. The theoretical leakage current calculated based on the theoretical formula is shown in the figures.

Recommended High-Voltage Amplifier: ATA-7100

Figure: ATA-7100 High-Voltage Amplifier Specifications

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