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Hydraulically amplified self-healing electrostatic actuators with muscle-like performance

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Science  05 Jan 2018:
Vol. 359, Issue 6371, pp. 61-65
DOI: 10.1126/science.aao6139
  • Fig. 1 Basic components and fundamental physical principles of HASEL actuators.

    (A) Schematic of a HASEL actuator shown at three different applied voltages, where V1 < V2 < V3. (B) Typical actuation response of a HASEL actuator with geometry shown in (A). (C) The actuator deforms into a donut shape with application of voltage. This voltage-controlled deformation can be used to apply force F onto an external load. (D and E) Strain and force of actuation can be tuned by modifying the area of the electrode. The minimum electric field to trigger the pull-in transition was ~2.7 kV/mm; the maximum field applied was ~33 kV/mm. (F) The use of a liquid dielectric confers self-healing capabilities to HASEL actuators.

  • Fig. 2 Stacks of donut HASEL actuators operating as linear actuators and soft grippers.

    (A) Schematic depicting a stack of five donut HASEL actuators oriented such that adjacent electrodes are at the same electrical potential (cross-section view). (B) Demonstration of linear actuation with stacked-donut HASEL actuators. (C to G) A soft gripper fabricated from two modified stacks of donut HASEL actuators handled fragile objects such as a raspberry [(C) to (E)] and a raw egg [(F) and (G)].

  • Fig. 3 Design and performance of planar HASEL actuators.

    (A) For a given voltage, a circular planar HASEL actuator achieves larger area strain in comparison to a circular DE actuator. (B) Schematic of a planar HASEL actuator that functions as a linear actuator. The actuator is prestretched laterally and a load is applied in the direction perpendicular to the prestretch. (C) Demonstration of linear actuation with a single-unit planar HASEL actuator. (D) HASEL actuators can be readily scaled up to exert large forces.

  • Fig. 4 A self-sensing planar HASEL actuator powering a robotic arm.

    HASEL actuators simultaneously serve as strain sensors; measured capacitance is low when the arm is fully flexed (left; screenshot of movie S7 at 52.1 s) and capacitance is high when the arm is extended (right; at 52.6 s). The bottom plot shows details of the applied voltage signal (red) and measured relative capacitance (green, dashed), C/Co, where C is measured capacitance and Co is the minimum value for capacitance. Voltage and capacitance are ~90° out of phase, which is typical for a driven damped oscillator.

Supplementary Materials

  • Hydraulically amplified self-healing electrostatic actuators with muscle-like performance

    E. Acome, S. K. Mitchell, T. G. Morrissey, M. B. Emmett, C. Benjamin, M. King, M. Radakovitz, C. Keplinger

    Materials/Methods, Supplementary Text, Tables, Figures, and/or References

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    • Materials and Methods
    • Figs. S1 to S16
    • References
    • Captions for movies S1 to S8

    Images, Video, and Other Media

    Movie S1
    The experimental setup shown in Fig. S5 was used to demonstrate dielectric breakdown through a solid dielectric (PDMS) and through a liquid dielectric (Envirotemp FR3). One T-pin was connected to ground while the other was connected to the high voltage amplifier. Voltage was increased linearly at 0.5 kV/s until dielectric breakdown. Dielectric breakdown through the solid dielectric (PDMS) occurred at 34.3 kV which resulted in permanent damage to the material. Dielectric breakdown through the liquid dielectric (Envirotemp FR3) occurred at 14.7 kV which produced a gas bubble that quickly dissipated and the liquid dielectric returned to its initial insulating state
    Movie S2
    A single donut HASEL actuator made of Ecoflex 00-30 with an electrode diameter of 1.5 cm was actuated, until dielectric breakdown occurred, at which point the device self-healed and continued to operate. The actuator was activated with a 0.5 Hz reversing square wave with varying amplitudes. Sequences of three breakdown cycles are shown: Cycle 1 â€" 15 kV, 18 kV, breakdown, self-heal Cycle 2 - 15 kV, 17 kV, breakdown, self-heal Cycle 3 â€" 15 kV, 18 kV, 20 kV, 22 kV
    Movie S3
    A stack of five donut HASEL actuators with an electrode diameter of 2.5 cm was actuated with a 15 kV reversing square wave at 0.5, 5, 10, 15, and 20 Hz.
    Movie S4
    Two stacks of five donut HASEL actuators were used as a soft gripper which was capable of delicately grasping a fresh raspberry and a raw egg. Each donut HASEL actuator had an electrode diameter of 1.5 cm. Before picking up the raspberry, the HASEL actuators were driven with a 1 Hz, 18 kV reversing square wave to demonstrate the gripping actuation, while an 18 kV DC signal was applied to grip and then transport the raspberry. The HASEL actuators were driven with a 20 kV DC signal to lift the raw egg then voltage was turned off to drop the egg.
    Movie S5
    HASEL actuators were driven near their resonant frequency which amplified actuation response. A single-unit planar HASEL actuator lifted 250 g. The applied voltage signal was a 4.6 Hz sine wave with three different voltage amplitudes â€" 7, 10, and 13 kV. A twounit planar HASEL actuator lifted 700 g. The applied voltage signal was a 2.7 Hz sine wave with two different voltage amplitudes â€" 9.0 and 14.5 kV.
    Movie S6
    Six two-unit planar HASEL actuators were arranged in parallel to deliver large actuation force. The HASEL actuators lifted a gallon of water (~ 4 kg) which had been dyed with blue food coloring (McCormick) for visibility. The front view shows actuation of the device with a 2.5 Hz sine wave at an amplitude of 11.5 kV and 12.5 kV. The side view shows the six actuators operating at 2.7 Hz with an amplitude of 9.0 kV. Two planar HASEL actuators were mounted on a single clamp so that only three clamps were used, 45 which when viewed from the side, appears as though only three HASEL actuators were used.
    Movie S7
    Two self-sensing planar HASEL actuators powered a robotic arm. The ‘driving voltage’ (red plot) shows the combined actuation voltage signal and sensing voltage signal. The ‘sensing signal’ (green plot) is the capacitance measured from the HASEL actuators. The HASEL actuators were connected to ground on one side and to the high voltage amplifier on the other. With the actuation voltage turned off, the arm measured changes in capacitance from the external force of a handshake. A tennis ball (60 g) and baseball (125 g) were used to show a change in capacitance from different loads. The arm was then actuated while holding the baseball. The actuation voltage signal was 1 Hz sine wave. Voltage amplitude started at 12.5 kV, was decreased to 10 kV, then further decreased to 8 kV before being turned off.
    Movie S8
    Two self-sensing planar HASEL actuators powered a robotic arm. The ‘driving voltage’ (red plot) shows the combined actuation voltage signal and sensing voltage signal. The ‘sensing signal’ (green plot) is the capacitance measured from the HASEL actuators. The HASEL actuators were connected to ground on one side and to the HV amplifier on the other. With the actuation voltage turned off, the arm was manually moved and held at different positions. The change in capacitance from these movements is shown in the green plot.

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