Research ArticleINDUSTRIAL ROBOTS

Inverted and vertical climbing of a quadrupedal microrobot using electroadhesion

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Science Robotics  19 Dec 2018:
Vol. 3, Issue 25, eaau3038
DOI: 10.1126/scirobotics.aau3038
  • Fig. 1 HAMR-E performing inverted locomotion.

    Manufactured using PC-MEMS techniques (23), HAMR-E is an insect-scale legged robot that combines electroadhesion and a highly articulated drive train to enable locomotion on inclines from 0° to 180°.

  • Fig. 2 Design modifications and evaluation.

    (A) An image of the HAMR-E including axes definitions. (B) Schematic representation of the electroadhesive pad and the three-DOF origami ankle with components labeled. Inset depicts a detailed view of the ankle’s center of rotation. (C) Experimental (mean ± SD, n = 5) and theoretical normal adhesion pressure as a function of applied electrical field for the highest-performing pad designs (see fig. S2 for measurement details).

  • Fig. 3 Modified tripedal crawl gait.

    (A) Schematic representation of the tripedal crawl gait with individual legs colored. Footfalls are spaced one-quarter cycle apart. (B) Electroadhesion input voltage for consecutive legs, characterized by the activation (EOn) and deactivation (EOff) timings. Note that the orange signal is artificially offset for clarity. (C) Swing input voltage for the newly designed gait with duty cycle (DC) and swing amplitude SA labeled. (D) Lift input voltage for the newly designed gait defined by the lift offset (LO), the lift amplitude (LA), reach (R), and push (P) parameters. (E) Schematics of HAMR-E’s pose and gait pattern visualizing the effects of the reach and push parameters during a quarter gait cycle.

  • Fig. 4 Experimental gait tuning results.

    (A) Drift in COM height versus cycles achieved for nine different combinations of reach and push parameters. Error bars represent ±1 SD (n = 5). The inset shows the modifications to the lift actuator inputs for the reach and push parameters. (B) Push force measurements during the tripedal crawl with (blue) and without (red) electroadhesion active. Shaded regions show ±1 SE (n = 5). (C to E) COM height during the gait cycle for different reach and push parameter combinations: R50/P50, R100/P50, and R100/P100 during inverted locomotion. Shaded regions represent ±1 SD (n = 3 trials with 6, 12, and 40 cycles, respectively). (F) COM height during vertical locomotion for the R100/P100 gait. Shaded region represents ±1 SD (n = 40).

  • Fig. 5 Locomotion performance on inverted and vertical surfaces, and during left and right maneuvers.

    Time-stamped images of HAMR-E performing inverted (A) and vertical (B) locomotion at a stride frequency of 0.2 Hz. (C) Average forward velocity (mean ± SD, n = 5) as a function of frequency during inverted (blue) and vertical (orange) locomotion. (D) Number of open-loop steps achieved (mean ± SD, n = 5) as a function of stride frequency. Pads failed to completely disengage from the substrate at frequencies higher than 1.6 Hz during vertical locomotion, resulting in sustained locomotion (marked by an asterisk). Time-stamped images from a left (E) and right (F) turn using the tripedal crawl gait with electroadhesion active on a horizontal conductive substrate.

  • Fig. 6 Inverted locomotion on the inner surface of a commercial jet engine.

    This environment exhibits moderate local curvature and high surface roughness.

  • Fig. 7 Experimental setup for electroadhesive force measurements, blocked force measurement, and tracking of HAMR-E.

    (A) Schematic of the experimental setup used to measure the shear force generated by individual pads and both the shear and normal force generated by the whole robot. Components are labeled, and a detailed image of the pad attached to the substrate is shown. (B) Schematic of the experimental setup used to measure the push force generated by the whole robot. Components are labeled, and a detailed image of the robot pushing on the force sensor is shown. (C) Schematic of the experimental setup used to track the robot during inverted, vertical, and horizontal locomotion with components labeled. Two orthogonal high-speed cameras are centered on HAMR-E. Three reflective markers were placed on the robot (shown in the inset) and tracked by using vision-based techniques.

  • Table 1 Climbing robots comparison.

    T, tethered; UT, untethered; N/A, not available.

    Climbing robotAdhesion strategyBL (mm)Robot mass (g)Maximum voltage (V)Incline range (°)Maximum velocity
    for given incline (BL s−1)
    HAMR-E, TElectroadhesion451.482500–1800°: 3.1
    90°: 0.026
    180°: 0.10
    Electroadhesive climbing robots
    Wang et al. (19), TElectroadhesion183491000–900°: 0.58
    90°: 0.56
    Wang et al. (51), TElectroadhesion173946000–9090°: 0.2
    Prahlad et al. (40), TElectroadhesion40018040000–9090°: 0.375
    Yamamoto et al. (39), TElectroadhesion30032715000–9090°: 0.022
    Liu et al. (20), UTElectroadhesion36070030000–9090°: <0.001
    Other legged climbing robots < 100 g
    Hawkes et al. (11), TDry adhesion120.02N/A0–90Not reported
    Hawkes et al. (11), UTDry adhesion3093.70–9090°: 0.6
    Greuter et al. (10), UTDry adhesion40103.70–9090°: 0.08
    Birkmeyer et al. (52), UTSpines100153.70–9090°: 1.5
    Breckwoldt et al. (12), UTDry adhesion47223.70–18090°: 1.6
    180°: 1.8
    Murphy et al. (7), UTDry adhesion9685N/A0–1800°: 0.5
    90°: 0.5
    180°: 0.5

Supplementary Materials

  • robotics.sciencemag.org/cgi/content/full/3/25/eaau3038/DC1

    Note S1. Cost of transport calculation.

    Note S2. Charge accumulation measurements.

    Fig. S1. Schematic of HAMR-E’s SFB transmission.

    Fig. S2. Electroadhesive force measurement details.

    Fig. S3. Electrode manufacturing methods.

    Fig. S4. Final swing and lift input waveforms.

    Fig. S5. System-level diagram of the open-loop controller.

    Fig. S6. Effective stride length during vertical locomotion.

    Fig. S7. Electroadhesive pad characteristics.

    Table S1. Tripedal crawl gait parameter values.

    Table S2. Cost of transport for HAMR-E.

    Movie S1. Inverted locomotion of HAMR-E.

    Movie S2. Vertical locomotion of HAMR-E.

    Movie S3. Inverted incline locomotion of HAMR-E.

    Movie S4. Role of ankle joint during locomotion with adhesion.

    Movie S5. Demonstration of inverted locomotion inside jet engine part.

    Movie S6. Failure of HAMR-E during inverted locomotion when using a standard tripedal crawl gait.

    Movie S7. Maneuverability of HAMR-E during locomotion with electroadhesion.

  • Supplementary Materials

    The PDF file includes:

    • Note S1. Cost of transport calculation.
    • Note S2. Charge accumulation measurements.
    • Fig. S1. Schematic of HAMR-E’s SFB transmission.
    • Fig. S2. Electroadhesive force measurement details.
    • Fig. S3. Electrode manufacturing methods.
    • Fig. S4. Final swing and lift input waveforms.
    • Fig. S5. System-level diagram of the open-loop controller.
    • Fig. S6. Effective stride length during vertical locomotion.
    • Fig. S7. Electroadhesive pad characteristics.
    • Table S1. Tripedal crawl gait parameter values.
    • Table S2. Cost of transport for HAMR-E.
    • Legends for movies S1 to S7

    Download PDF

    Other Supplementary Material for this manuscript includes the following:

    • Movie S1 (.mp4 format). Inverted locomotion of HAMR-E.
    • Movie S2 (.mp4 format). Vertical locomotion of HAMR-E.
    • Movie S3 (.mp4 format). Inverted incline locomotion of HAMR-E.
    • Movie S4 (.mp4 format). Role of ankle joint during locomotion with adhesion.
    • Movie S5 (.mp4 format). Demonstration of inverted locomotion inside jet engine part.
    • Movie S6 (.mp4 format). Failure of HAMR-E during inverted locomotion when using a standard tripedal crawl gait.
    • Movie S7 (.mp4 format). Maneuverability of HAMR-E during locomotion with electroadhesion.

    Files in this Data Supplement:

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