Research ArticleBIOMIMETICS

Insect-scale fast moving and ultrarobust soft robot

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Science Robotics  31 Jul 2019:
Vol. 4, Issue 32, eaax1594
DOI: 10.1126/scirobotics.aax1594
  • Fig. 1 The prototype and working mechanism.

    (A) Optical photo showing a robot connected with two electrical wires to the top and bottom electrodes, respectively, alongside a U.S. quarter coin. The inset SEM image shows the cross-sectional view of the prototype robot with different layers of materials. (B) Comparison of the wavelike running paths showing the movements of the COM of a cockroach (41) and a prototype robot (from movie S1). (C) Series of optical images recording the movements of a prototype robot in one driving cycle. (D) Applied driving signal (black line) and vertical (blue lines) and lateral displacements (red lines) of a prototype robot, where the bold solid lines are the average movements for 20 cycles. (E) Two-step cycles of the vertical displacement of the COM during cockroach running [red line for a period of 60 ms, (41)] compared with a prototype soft robot (blue line for a period of 100 ms).

  • Fig. 2 Locomotion gait analysis.

    (A to D) Optical photos from the high-speed camera (top), corresponding contracted configurations (middle), and corresponding expanded configurations (bottom) of a prototype robot showing different gaits in the cross-sectional views. (E) Simplified dynamic model based on two rigid bodies joined by a pin joint (both-touching posture as an example) with a torsional spring-damper system. (F) Duty cycles in different gaits of both experimental and simulation results for a 25-mm-long prototype robot driven at its fastest speed at resonance of 200 Hz. (G) Relationships between the vibration amplitude and moving speed as well as aerial duty cycle for driving frequencies of 170, 190, 200, 210, and 230 Hz. Error bars indicate mean ± 1 SD.

  • Fig. 3 Geometric parameter optimization and performance characterization.

    (A) Side view of a robot with the definitions of geometric parameters. (B) Experimental results (gray dots) for normalized running speeds from a 10-mm-long robot with different geometric combinations used to plot a color map as a function of relative leg position (λ/L) and relative leg angle (β/π). The color map is interpolated by the thin-plate spline interpolation scheme for surface fitting. Original data can be found in table S2. (C) Relative running speeds of robots versus the driving frequencies for robots with lengths of 10, 15, 20, 25, and 30 mm. Shaded bands represent 90% confidence limits. (D) Relative running speeds (under the resonant frequency) of robots versus the driving voltages for robots with lengths of 10, 15, 20, 25, and 30 mm. Error bars indicate mean ± 1 SD.

  • Fig. 4 Relative running speeds of some mammals, arthropods, soft robots, and actuators versus body mass.

    For animals including both mammals (purple) and arthropods (orange), relative speeds show a strong negative scaling law with respect to the body mass, showing that relative running speeds increase as body masses decrease. However, for soft robots, the relationship appears to be the opposite, where the relative running speeds decrease as the body mass decrease. The performances of the prototype robots (red stars with body lengths from 30 to 10 mm) follow a scaling law similar to that of living animals: Higher relative running speed was attained as the body mass decreased, with the fastest measured running speed at 20 BL/s among reported insect-scale robots and actuators (blue). For data, see table S3.

  • Fig. 5 Weight-bearing, slope-climbing, and load-carrying capabilities.

    (A to C) Soft robot can continue to function (one-half of the original speed) after being stepped on by an adult human (59.5 kg), a load about 1 million times its own body weight. Scale bars, 3 cm. A robot climbs a slope (D) of 7.5° with a relative speed of 7 BL/s and a slope (E) of 15.6° with a relative speed of 1 BL/s. Scale bars, 1 cm. (F and G) A robot (0.064 g) carries a peanut (0.406 g), which is six times its own body weight, to show the load-carrying capability. The speed with the peanut on top is about one-six of the original speed without the peanut. Scale bars, 1 cm.

  • Fig. 6 Galloping-like gait with the design of a two-legged robot.

    (A) Series of optical images (top) from the high-speed camera to show the galloping strides and their corresponding schematic diagrams (bottom). (B) Comparison of one-legged and two-legged robots in duty cycles in different operation postures. Error bars indicate mean ± 1 SD. See movie S9.

Supplementary Materials

  • robotics.sciencemag.org/cgi/content/full/4/32/eaax1594/DC1

    Section S1. Actuation mechanism of PVDF film and curved unimorph structure

    Section S2. Qualitative analysis of the locomotion mechanism

    Section S3. Simplified dynamic model for the robot’s locomotion

    Section S4. Resonant frequency evaluation

    Section S5. COT calculation

    Fig. S1. Actuating mechanism of PVDF film and curved unimorph structure.

    Fig. S2. Locomotion performances inside a tube.

    Fig. S3. Conceptual image of the free body diagram: A robot at a both-touching posture.

    Fig. S4. Velocity and force analysis for front-leg touchdown.

    Fig. S5. System configurations of the simplified dynamic model.

    Fig. S6. Gait statistics near fast speed.

    Fig. S7. The relationship between robot length and resonant frequency for FEM simulation results under different boundary conditions compared with that of experimental results.

    Fig. S8. Dynamic tests when the robot is clamped at one end.

    Fig. S9. Locomotion of a robot under low driving voltage.

    Fig. S10. Measurement of electrical parameters.

    Fig. S11. COT of select robots (circles) and insects (squares) plotted against their body masses.

    Fig. S12. Performance of a 3 cm–by–1.5 cm prototype robot after applying and removing different loads.

    Fig. S13. Fabrication processes of a prototype robot with the turning ability.

    Fig. S14. Direction control.

    Fig. S15. Main fabrication and assembly processes of a prototype robot.

    Table S1. Material parameters.

    Table S2. Data of 25 combinations of λ/L and β/π as well as their normalized speeds.

    Table S3. Data of relative speed versus mass of some animals as well as soft robots and actuators.

    Movie S1. Locomotion observation of prototype robot running at the fastest speed.

    Movie S2. Posture and position observation of prototype robot.

    Movie S3. Locomotion inside tube with different driving frequencies.

    Movie S4. Locomotion observation of prototype robot running at slower speeds.

    Movie S5. Locomotion of the simplified dynamic model in MATLAB simulation.

    Movie S6. Locomotion of prototype robot under low driving voltage.

    Movie S7. Robustness, climbing, and carrying loads.

    Movie S8. Galloping-like gaits of two-legged robot.

    Movie S9. Comparison of locomotion of one-legged robot and two-legged robot.

    Movie S10. Robot with two separate electrical domains for turning.

    References (6487)

  • Supplementary Materials

    The PDF file includes:

    • Section S1. Actuation mechanism of PVDF film and curved unimorph structure
    • Section S2. Qualitative analysis of the locomotion mechanism
    • Section S3. Simplified dynamic model for the robot’s locomotion
    • Section S4. Resonant frequency evaluation
    • Section S5. COT calculation
    • Fig. S1. Actuating mechanism of PVDF film and curved unimorph structure.
    • Fig. S2. Locomotion performances inside a tube.
    • Fig. S3. Conceptual image of the free body diagram: A robot at a both-touching posture.
    • Fig. S4. Velocity and force analysis for front-leg touchdown.
    • Fig. S5. System configurations of the simplified dynamic model.
    • Fig. S6. Gait statistics near fast speed.
    • Fig. S7. The relationship between robot length and resonant frequency for FEM simulation results under different boundary conditions compared with that of experimental results.
    • Fig. S8. Dynamic tests when the robot is clamped at one end.
    • Fig. S9. Locomotion of a robot under low driving voltage.
    • Fig. S10. Measurement of electrical parameters.
    • Fig. S11. COT of select robots (circles) and insects (squares) plotted against their body masses.
    • Fig. S12. Performance of a 3 cm–by–1.5 cm prototype robot after applying and removing different loads.
    • Fig. S13. Fabrication processes of a prototype robot with the turning ability.
    • Fig. S14. Direction control.
    • Fig. S15. Main fabrication and assembly processes of a prototype robot.
    • Table S1. Material parameters.
    • Table S2. Data of 25 combinations of λ/L and β/π as well as their normalized speeds.
    • Table S3. Data of relative speed versus mass of some animals as well as soft robots and actuators.
    • References (6487)

    Download PDF

    Other Supplementary Material for this manuscript includes the following:

    • Movie S1 (.mp4 format). Locomotion observation of prototype robot running at the fastest speed.
    • Movie S2 (.mp4 format). Posture and position observation of prototype robot.
    • Movie S3 (.mp4 format). Locomotion inside tube with different driving frequencies.
    • Movie S4 (.mp4 format). Locomotion observation of prototype robot running at slower speeds.
    • Movie S5 (.mp4 format). Locomotion of the simplified dynamic model in MATLAB simulation.
    • Movie S6 (.mp4 format). Locomotion of prototype robot under low driving voltage.
    • Movie S7 (.mp4 format). Robustness, climbing, and carrying loads.
    • Movie S8 (.mp4 format). Galloping-like gaits of two-legged robot.
    • Movie S9 (.mp4 format). Comparison of locomotion of one-legged robot and two-legged robot.
    • Movie S10 (.mp4 format). Robot with two separate electrical domains for turning.

    Files in this Data Supplement:

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