Research ArticleBIOMIMETICS

Kirigami skins make a simple soft actuator crawl

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Science Robotics  21 Feb 2018:
Vol. 3, Issue 15, eaar7555
DOI: 10.1126/scirobotics.aar7555
  • Fig. 1 Kirigami-skinned soft crawlers.

    (A) We considered a fiber-reinforced elastomeric soft actuator that extends axially upon inflation. (B) A kirigami skin was fabricated by embedding an array of cuts into a thin plastic sheet. (C) A kirigami-skinned soft crawler was built by wrapping the kirigami skin around the actuator. (D) Cross-sectional view of a kirigami-skinned soft crawler. (E) Inflation of the actuator resulted in a buckling-induced pop-up texture similar to that of a snake’s skin. Inset: A typical volume-control actuation protocol with a maximum volume Vmax. (F) Close-up views of a kirigami skin with triangular cuts at a different level of supplied volume V (note that Vmax = 24 ml is the maximum supplied volume). (G) Snapshots showing the rectilinear gait of a female Dumeril’s boa (Acrantophis dumerili). The snake actively tilts the ventral scales to increase frictional anisotropy and enhance anchoring (video courtesy of H. Marvi and D. Hu).

  • Fig. 2 Characterization of kirigami-skinned soft crawlers.

    (A) Cut shapes considered in this study. (B) Elongation of the crawlers as a function of their volume. (C) Pressure normalized by the shear modulus of actuator μa versus axial strain for the kirigami-skinned crawlers. (D and E) Friction force Ffr measured in backward and forward directions at supplied volumes (D) V/Vmax = 0 and (E) V/Vmax = 1 (with a maximum volume Vmax = 24 ml). (F to I) Effective coefficients of friction versus inflation levels in forward (hollow symbols) and backward (filled symbols) directions with (F) linear, (G) triangular, (H) circular, and (I) trapezoidal cuts. Insets: 3D-scanned surface profiles of the skins at the supplied volume V/Vmax = 1.

  • Fig. 3 Crawler locomotion.

    (A) Initial and final position of the crawlers after six inflation cycles with V ∈ [0,24] ml. (B) Displacement of the center of mass (solid line), head (dashed line), and tail (dotted line) of the crawlers versus number of cycles. (C) Position of the anchor point during inflation and deflation. The markers denote the experimental data over six cycles. The solid lines denote the predictions given by Eq. 2 using the experimentally measured friction coefficients. (D) Measured (markers) and predicted (continuous lines) total displacement when a volume of 120 ml of air was supplied by cyclically inflating and deflating the actuators between Vmax = 24 ml and Vmin ∈ [0,Vmax]. (E) Elongation versus supplied volume for a kirigami-skinned crawler with triangular cuts. Results for elastic (yellow line) and plastically deformed (purple line) skins are compared. The inset shows the plastically deformed skin at V/Vmax = 0 and 1 (with Vmax = 24 ml). (F) Effective coefficients of friction versus supplied volume for the crawler with the plastically deformed skin. (G) Measured total displacement for the crawler with the plastically deformed skin when a volume of 120 ml of air was supplied by cyclically inflating and deflating it between 0 ml and Embedded Image, with Embedded Image ml. Error bars indicate SD of the measured anchor points during six inflation/deflation cycles.

  • Fig. 4 Untethered kirigami-skinned soft crawlers.

    (A) Fabrication of our untethered kirigami-skinned crawlers. (B) Untethered kirigami-skinned soft crawler with circular cuts moves over asphalt. (C) Untethered kirigami-skinned soft crawler with trapezoidal cuts climbs a concrete ramp.

Supplementary Materials

  • robotics.sciencemag.org/cgi/content/full/3/15/eaar7555/DC1

    Supplementary sections S1 to S4.

    Fig. S1. Fabrication of an extending fiber-reinforced actuator.

    Fig. S2. Kirigami patterns.

    Fig. S3. Fabrication and assembly of kirigami-skinned crawlers.

    Fig. S4. Untethered kirigami-skinned crawler.

    Fig. S5. Mechanical response of the actuator.

    Fig. S6. Mechanical response of kirigami sheets.

    Fig. S7. Mechanical response of kirigami-skinned crawlers.

    Fig. S8. Evolution of surface morphology for our kirigami-skinned crawlers.

    Fig. S9. Friction measurement setup.

    Fig. S10. Friction measurements.

    Fig. S11. Effective friction coefficients.

    Fig. S12. Frictional properties of a crawler with a plastically deformed skin.

    Fig. S13. Locomotion of our untethered kirigami-skinned crawler.

    Fig. S14. Relation between the location of the anchor point and the fraction coefficients.

    Fig. S15. Finite-element simulations of kirigami unit cells.

    Movie S1. Rectilinear gait of a female Dumeril’s boa.

    Movie S2. A fiber-reinforced extending actuator is placed over a rough surface and is subjected to cyclic inflation/deflation.

    Movie S3. Assembly of a kirigami-skinned soft crawler.

    Movie S4. Motion of the crawlers during six inflation cycles with V ∈ [0,24] ml.

    Movie S5. Motion of the crawlers when a total volume Vtot = 120 ml of air is supplied by cyclically inflating and deflating them between Vmax = 24 ml and Vmin ∈ [0,Vmax].

    Movie S6. Fully untethered kirigami skinned crawlers with triangular, circular, and trapezoidal kirigami skins.

    Movie S7. An untethered crawler with circular kirigami skin propels itself over asphalt.

    Movie S8. An untethered crawler with trapezoidal kirigami skin climbs a concrete ramp.

    Movie S9. An untethered crawler with triangular kirigami skin propels itself over rough stone.

    Movie S10. Motion of an untethered crawler with trapezoidal kirigami skin for Pmin = 1, 4, 8, and 12 kPa and Pmax = 16 kPa.

    References (3438)

  • Supplementary Materials

    Supplementary Material for:

    Kirigami skins make a simple soft actuator crawl

    Ahmad Rafsanjani, Yuerou Zhang, Bangyuan Liu, Shmuel M. Rubinstein, Katia Bertoldi*

    *Corresponding author. Email: bertoldi{at}seas.harvard.edu

    Published 21 February 2018, Sci. Robot. 3, eaar7555 (2018)
    DOI: 10.1126/scirobotics.aar7555

    This PDF file includes:

    • Supplementary sections S1 to S4.
    • Fig. S1. Fabrication of an extending fiber-reinforced actuator.
    • Fig. S2. Kirigami patterns.
    • Fig. S3. Fabrication and assembly of kirigami-skinned crawlers.
    • Fig. S4. Untethered kirigami-skinned crawler.
    • Fig. S5. Mechanical response of the actuator.
    • Fig. S6. Mechanical response of kirigami sheets.
    • Fig. S7. Mechanical response of kirigami-skinned crawlers.
    • Fig. S8. Evolution of surface morphology for our kirigami-skinned crawlers.
    • Fig. S9. Friction measurement setup.
    • Fig. S10. Friction measurements.
    • Fig. S11. Effective friction coefficients.
    • Fig. S12. Frictional properties of a crawler with a plastically deformed skin.
    • Fig. S13. Locomotion of our untethered kirigami-skinned crawler.
    • Fig. S14. Relation between the location of the anchor point and the fraction coefficients.
    • Fig. S15. Finite-element simulations of kirigami unit cells.
    • Legends for movies S1 to S10
    • References (3438)

    Download PDF

    Other Supplementary Material for this manuscript includes the following:

    • Movie S1 (.mp4 format). Rectilinear gait of a female Dumeril's boa.
    • Movie S2 (.mp4 format). A fiber-reinforced extending actuator is placed over a rough surface and is subjected to cyclic inflation/deflation.
    • Movie S3 (.mp4 format). Assembly of a kirigami-skinned soft crawler.
    • Movie S4 (.mp4 format). Motion of the crawlers during six inflation cycles with V ∈ 0,24 ml.
    • Movie S5 (.mp4 format). Motion of the crawlers when a total volume Vtot = 120 ml of air is supplied by cyclically inflating and deflating them between Vmax = 24 ml and Vmin ∈ 0,Vmax.
    • Movie S6 (.mp4 format). Fully untethered kirigami skinned crawlers with triangular, circular, and trapezoidal kirigami skins.
    • Movie S7 (.mp4 format). An untethered crawler with circular kirigami skin propels itself over asphalt.
    • Movie S8 (.mp4 format). An untethered crawler with trapezoidal kirigami skin climbs a concrete ramp.
    • Movie S9 (.mp4 format). An untethered crawler with triangular kirigami skin propels itself over rough stone.
    • Movie S10 (.mp4 format). Motion of an untethered crawler with trapezoidal kirigami skin for Pmin = 1, 4, 8, and 12 kPa and Pmax = 16 kPa.

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