Application Cases

Experiment Name: Material Testing of Flexible Crawling Robots

Research Direction:
The minimum energy structure of dielectric elastomers (DE) is a novel type of flexible actuator designed by combining the electrically induced deformation of DE materials with the deformation of flexible frames. The term "minimum energy" refers to the state where the overall system energy is minimized when the actuator is in equilibrium. When the system is subjected to an external voltage stimulus, it undergoes corresponding deformation. As the external voltage decreases or disappears, the entire system returns to its minimum energy state due to the removal of the stimulus. The fabrication method typically involves pre-stretching the DE film, fixing it onto a rigid frame, and then attaching the flexible frame to one or both sides of the film after cutting. When the rigid frame is removed, the external frame transitions from a simple planar structure to a complex saddle-shaped structure under the action of the DE's elastic restoring force. When voltage is applied to the DE film, the Maxwell stress within the film decreases due to electrical stress, causing the saddle-shaped structure to revert to its original planar form.

Experiment Objective:
To address the issue of insufficient energy in traditional saddle-shaped minimum energy structures, a novel DE actuator is proposed. This actuator consists of a spring and a dielectric elastomer capable of generating pure shear deformation upon voltage application. As described, pure shear deformation of the DE film enables reciprocating motion in a single direction with relatively high actuation strain. Therefore, pure shear deformation of DE films finds wide applications in dielectric elastomer actuators, bidirectional stabilizers, and flexible driving robots.

Testing Equipment:
ATA-7050 high-voltage amplifier, dielectric elastomer material, pressure sensor, displacement sensor, etc.

Experimental Process:
Among various dielectric elastomer materials, acrylic tape (as shown in Figure 3.1(a)) was selected for this experiment due to its large deformation capability, high energy density per unit condition, and relatively high dielectric constant. Additionally, this material is a common consumable, making it easily accessible and moderately priced. For the flexible electrode, carbon conductive grease 846-80G (as shown in Figure 3.1(b)) was chosen as the manufacturing material. For the high voltage required in the experiment, the ATA-7050 high-voltage power supply from Aigtek Electronics Technology Co., Ltd. (as shown in Figure 3.1(c)) was used. This power supply has a maximum output of 10 kV and provides various signals such as constant waves, triangular waves, sinusoidal waves, and square waves, with relatively high safety. The displacement sensor used was the BL-100NZ laser displacement sensor, with an accuracy of 0.075 mm. The pressure sensor was the LANRINAUMI type, with a measurement accuracy of 1 g and a range of 1 kg. Both the displacement sensor and pressure sensor could be connected to the host computer via data cables for real-time data acquisition. Other consumables are listed in Table 3.1.

Experimental Results:
Figures 4.2(a) and 4.2(b) show the physical setup for testing the elongation and driving force of the dielectric elastomer actuator. When measuring the relationship between voltage magnitude and the displacement of the DE actuator, one end of the actuator was fixed to a support, while the other end was left free to move. The specific steps were as follows:
(1) Fix the actuator at one end of the aluminum profile support and mount the laser displacement sensor at the other end, with the sensor's laser beam directed at the actuator's outer casing.
(2) Drive the DE actuator using a high-voltage generator.
(3) As the voltage applied to the actuator increases, the free end elongates until the dielectric elastomer film inside the actuator breaks down.
(4) During the elongation process, the displacement sensor continuously records data and uploads it to the host computer.
(5) Multiple actuator samples of the same size were tested, and the average of the measured data was taken.
The steps for measuring the actuator's driving force were similar:
(1) Fix the actuator and pressure sensor, ensuring that only one end of the actuator can move.
(2) Connect the DE actuator to the high-voltage generator.
(3) As the voltage increases, the pressure sensor records the readings and transmits them to the computer.
(4) Multiple samples were tested, and the average value was taken.

Before conducting the performance testing of the DE actuator, the spring's elasticity coefficient was tested. The spring was initially in an unloaded state, and the pressure sensor compressed the spring under the push of a motor. The experimental results are shown in Figure 4.3. Since the spring could not maintain perfect vertical compression during deformation (it might deform under elastic forces), the results were not a perfect straight line. However, because the spring installed in the casing was constrained by the casing, it maintained unidirectional compression and avoided such issues.

When the DE actuator is energized, it undergoes deformation, as shown in Figure 4.4. This figure compares the actuator in its stationary state and its actuated state after applying 4 kV voltage. The difference in length between the actuated state and the stationary state represents the elongation ΔL of the DE actuator. Due to the presence of the spring in the casing, the restoring force of the DE film and the elastic force of the spring maintain equilibrium in the driving direction, keeping the actuator stationary. When high voltage is applied to the DE film, the equilibrium is disrupted by the generation of Maxwell stress, causing the DE actuator to displace and reach a new equilibrium position. This state of the actuator is referred to as the actuated state.

When testing the static characteristics of the actuator, the voltage was kept constant at 4 kV, and a triangular wave with a rate of 200 V/s was used as the driving signal for the DE actuator. In the experiment, because the compression amount under the 200 V/s triangular wave was relatively small, the DE film could be considered quasi-static at each moment, meaning the output voltage of the generator remained relatively constant. Figure 4.5 shows the actuator's adhesion experiment, with the left side depicting the predicted model and the right side showing the experimental results. The comparison indicates that the experimental results align well with the predictions.

Recommended High-Voltage Amplifier: ATA-7050

Figure: Specifications of the ATA-7050 High-Voltage Amplifier