Research ArticleAPPLIED SCIENCES AND ENGINEERING

Electrically controlled liquid crystal elastomer–based soft tubular actuator with multimodal actuation

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Science Advances  11 Oct 2019:
Vol. 5, no. 10, eaax5746
DOI: 10.1126/sciadv.aax5746
  • Fig. 1 Design, fabrication, and operation principle of an LCE tubular actuator.

    (A) Fabrication steps of an LCE-based tubular actuator: (i) Three serpentine heating wires were sandwiched between two layers of loosely cross-linked LCE films. (ii) The sandwiched structure was compressed slightly to promote adhesion. (iii) A tube was made by rolling the thin film. (iv) An LCE tubular actuator was obtained by stretching and then exposing the actuator under UV irradiation. (B) Principle of operation of LCE tubular actuators. Bending motion can be realized by applying an electrical potential to one of the heating wires (colored red); homogeneous contraction can be obtained by applying an electrical potential to all heating wires (colored red).

  • Fig. 2 Thermomechanical characterizations of LCE artificial muscle film.

    (A) Optical images of reversible actuation of the artificial muscle: The film contracted by 40% of its initial length when an electrical potential of 3.0 V was applied. (B) Plot of actuation strain of LCE artificial muscle versus time with different applied electrical potential ranging from 1.0 to 3.0 V. For a given electrical potential, actuation strain increased and then reached a plateau value (steady state). When the electrical potential increased from 1.0 to 2.0 V, the actuation strain at steady state increased from 15 to 41%. As the electrical potential further increased from 2.0 to 3.0 V, the actuation strain of LCE artificial muscle at steady state remained the same, while the response time (time for reaching the steady state) decreased from 100 to 30 s. (C and D) Actuation stress of the artificial muscle film (with fixed length) versus time with different electrical potentials ranging from 1.0 to 3.0 V for 30 s. The actuation stress increased from 0.05 to 0.35 MPa as the electrical potential was increased from 1.0 to 3.0 V. (E) An LCE artificial muscle film could lift a load of 3.92 N (the stress was 0.312 MPa) by 38% of its initial length. (F) Actuation strain of the LCE artificial muscle film versus time under three different levels of applied stresses. As the load was increased, the time needed for the LCE film to contract was almost unchanged, while the time needed for it to recover to its original length decreased. Inset: Maximal work density of LCE artificial muscle under different applied stresses. Scale bars, 1 cm (A, C, and E). Photo credit: Qiguang He, University of California, San Diego.

  • Fig. 3 Multimodal actuation of an LCE-based tubular actuator.

    (A) Real and thermal images of an LCE tubular actuator during actuation: Activating one or two heating wires resulted in bending motion; activating all three heating wires resulted in homogeneous contraction. (B) Different actuation modes of the tubular actuator. Six directional bending were realized by activating one or two heating wires. Contraction was achieved by simultaneously activating all three heating wires. (C) Plot of bending angle of LCE tubular actuator versus time by applying electrical potentials from 1.0 to 3.0 V. The heating time was 30 s, and the cooling time was 270 s. Solid lines represent theoretical prediction, and dots represent experimental results. (D) Plot of contraction of LCE tubular actuator versus time through the activation of all three heating wires. The electrical potential was set to 3.0 V, and the time of electrical potential on was set to 30 s; the time of electrical potential off was set to 270 s. Solid lines represent theoretical prediction, and dots represent experimental results. Scale bars, 1 cm (A and B). Photo credit: Qiguang He, University of California, San Diego.

  • Fig. 4 A multifunctional soft gripper composed of three LCE tubular actuators.

    (A) Schematic of the assembly of the soft gripper. (B) Soft gripper twisting the cap of a vial. (C) Soft gripper grasping and lifting the vial (50 g). Scale bars, 1 cm (B and C). Photo credit: Qiguang He, University of California, San Diego.

  • Fig. 5 Electrically activated, untethered soft robot.

    (A) Schematic of the robot, mainly composed of a microcontroller, battery, and four LCE tubular actuators. (B) Frames from a video of the robot walking. Walking began from rest (all the actuators were in the deactivated state); then, a pair of diagonal tubular actuators was simultaneously activated for 17 s to bend forward. After that, the other pair of tubular actuators was activated simultaneously for 18 s. In the last step, the electrical potential to all actuators was turned off for 205 s, returning the actuators to their original states. (C) Frames from the video of the robot transporting an object on a plate of cardboard. During the operation, the two front actuators first bent forward for 45 s and then straightened without touching the top plate. During the straightening of the two front actuators, the two rear actuators bent forward for approximately 45 s; then, the electrical potential to all the actuators was turned off. Repeating this sequence enabled the robot to move the rigid plate and the weight on top forward about 5 cm within 15 min. (D) Plot of displacement of the untether robot (black curve) and displacement of the item on the top plate (red curve) versus time. Scale bars, 2 cm (B and C). Photo credit: Qiguang He, University of California, San Diego.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/5/10/eaax5746/DC1

    Fig. S1. Chemical component, fabrication process, and actuation performance of an LCE thin film.

    Fig. S2. Process of the fabrication of an LCE tubular actuator.

    Fig. S3. Design, fabrication, and morphology of heating wire.

    Fig. S4. Temperature change of the LCE artificial muscle film during contraction and recovery.

    Fig. S5. Cyclic actuation test of the LCE artificial muscle film with applied stress of 0.078 MPa.

    Fig. S6. Theoretical prediction of bending angle of LCE tubular actuator by using the actuation of LCE artificial muscle thin film.

    Fig. S7. Characterizations of LCE tubular actuators.

    Fig. S8. The actuation behavior of LCE tubular actuator with different voltage controls.

    Fig. S9. Cyclic test of LCE tubular actuator with different heating wires.

    Fig. S10. The reversible actuation (bending motion and contraction) of LCE tubular actuator in the water environment.

    Movie S1. Reversible actuation of LCE thin film actuator.

    Movie S2. Reversible bending actuation of LCE tubular actuator (activate one heating wire).

    Movie S3. Reversible bending actuation of LCE tubular actuator (activate two heating wires).

    Movie S4. Homogeneous contraction of LCE tubular actuator (activate three heating wires).

    Movie S5. Soft gripper grasps the vial.

    Movie S6. Soft gripper twists the cap.

    Movie S7. Untether soft robot walks on the ground.

    Movie S8. Untether soft robot manipulates the weight.

  • Supplementary Materials

    The PDF file includes:

    • Fig. S1. Chemical component, fabrication process, and actuation performance of an LCE thin film.
    • Fig. S2. Process of the fabrication of an LCE tubular actuator.
    • Fig. S3. Design, fabrication, and morphology of heating wire.
    • Fig. S4. Temperature change of the LCE artificial muscle film during contraction and recovery.
    • Fig. S5. Cyclic actuation test of the LCE artificial muscle film with applied stress of 0.078 MPa.
    • Fig. S6. Theoretical prediction of bending angle of LCE tubular actuator by using the actuation of LCE artificial muscle thin film.
    • Fig. S7. Characterizations of LCE tubular actuators.
    • Fig. S8. The actuation behavior of LCE tubular actuator with different voltage controls.
    • Fig. S9. Cyclic test of LCE tubular actuator with different heating wires.
    • Fig. S10. The reversible actuation (bending motion and contraction) of LCE tubular actuator in the water environment.

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    Other Supplementary Material for this manuscript includes the following:

    • Movie S1 (.mp4 format). Reversible actuation of LCE thin film actuator.
    • Movie S2 (.mp4 format). Reversible bending actuation of LCE tubular actuator (activate one heating wire).
    • Movie S3 (.mp4 format). Reversible bending actuation of LCE tubular actuator (activate two heating wires).
    • Movie S4 (.mp4 format). Homogeneous contraction of LCE tubular actuator (activate three heating wires).
    • Movie S5 (.mp4 format). Soft gripper grasps the vial.
    • Movie S6 (.mp4 format). Soft gripper twists the cap.
    • Movie S7 (.mp4 format). Untether soft robot walks on the ground.
    • Movie S8 (.mp4 format). Untether soft robot manipulates the weight.

    Files in this Data Supplement:

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