Research ArticleACTUATORS

Addressable wireless actuation for multijoint folding robots and devices

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Science Robotics  19 Jul 2017:
Vol. 2, Issue 8, eaan1544
DOI: 10.1126/scirobotics.aan1544
  • Fig. 1 Illustration of the addressable wireless folding concept.

    A time-varying magnetic field [B(t)] is produced by passing current [I(t)] through a source coil. This field induces a voltage on the receiver coil(s) of the purely passive self-folding device/robot and initiates folding at desired joints. Folding at single joints selectively and collective folding at any combination of joints can be realized.

  • Fig. 2 Self-folding triangular devices at two scales.

    (A) Size comparison of the two devices and the close up view of the electronic components in the larger device. I, II, and III show the circuit parts indicated in Figure 3A. Inductors L1, L2, and L3 (shown in Fig. 3A) are implemented by using two inductors connected in parallel as shown in the inset to increase the current capacity. (B) Top view of the smaller device. (C) Bottom view of the smaller device. Inductors and capacitors are placed at the bottom of the device. The corresponding circuit diagram can be seen in Fig. 3B.

  • Fig. 3 Circuit diagrams of the wireless actuation electronics in the triangular folding devices.

    (A) The larger device. (B) The smaller device.

  • Fig. 4 Characterization of the frequency response of the circuits in the two triangular devices.

    (A) Square of the current through the resonators versus frequency for the circuit in the larger device. Solid lines show analytical calculations and dashed lines show experimental results. (B) Ratio of the square of the first maximum current to the square of the second maximum in the resonators as a measure of selectivity for the circuit in the larger device (as calculated using the circuit model shown in Fig. 3). (C) Square of the current through the resonators versus frequency for the circuit in the smaller device. Solid lines show analytical calculations, and dashed lines show experimental results. (D) Ratio of the square of the first maximum to the square of the second maximum current in the resonators as a measure of selectivity for the circuit in the smaller device.

  • Fig. 5 Folding structure design.

    (A) Three-dimensional rendering of the folding laminate: a, rigid sheet; b, adhesive; c, flexure film. (B) Folding joint with a coil SMA actuator with a moment arm that also serves as a fold stop.

  • Fig. 6 External magnetic field versus time.

    Frequency modulation is used to actuate multiple actuators simultaneously.

  • Fig. 7 Wireless folding.

    (A) Wireless folding of the large-scale prototype. Each actuator can be actuated or released individually or collectively. (B) Wireless folding of the small-scale structure. The complete device weighs 0.8 g.

  • Fig. 8 A battery-free microorigami robotic arm.

    (A) Simplified illustration of the kinematic design and components. (B) A working prototype on a glass wall with a permanent magnet for anchoring. The inset figure shows one of the coil SMA actuators attached at the side of the spherical six-bar folding pattern. Scale bar, 1 cm. (C) Sequential photos from a movie at various positions by single (left turn, right turn, and gripper open) and multiple actuations (left turn and gripper open together). (D) Pitching motion from a lateral perspective. (E) Sequential photos from a movie that shows the robotic arm picking up a sponge hanging above and dropping it to the right.

  • Table 1 Values of the components.
    L1C1Rtot,1L2C2Rtot,2L3C3Rtot,3
    Large scale232 μH100 nF12 ohms238 μH46 nF15 ohms252 μH20 nF16 ohms
    Small scale39 μH180 nF4.5 ohms42 μH98 nF4.6 ohms43 μH42 nF5.5 ohms
  • Table 2 Resonance frequencies and quality factors of the resonators.
    fres,1Q1fres,2Q2fres,3Q3
    Large
    scale
    33 kHz448 kHz4.871 kHz7
    Small
    scale
    60 kHz3.378 kHz4.5118 kHz5.8
  • Table 3 Characteristics of the flexure hinge.
    Large scaleSmall scale
    Torsional stiffness
    (mN·m/rad)
    81.3 × 10317.2 × 103
    Maximum required
    torque (mN·m)
    99 × 10321 × 103
  • Table 4 Coil SMA actuator design.
    Large scaleSmall scale
    Wire diameter (μm)200100
    Coil diameter (mm)1.61.1
    Number of turns63
    Maximum stroke (mm)156
    Maximum force (N)0.60.3

Supplementary Materials

  • robotics.sciencemag.org/cgi/content/full/2/8/eaan1544/DC1

    Fig. S1. Magnetic flux density of the source coil.

    Fig. S2. Magnetic flux density variation with distance from the coil center.

    Fig. S3. Folding structure design.

    Fig. S4. Robotic arm design.

    Fig. S5. Mechanism of the origami gripper.

    Fig. S6. Foldable ship in a bottle.

    Movie S1. Wireless folding of the large-scale prototype.

    Movie S2. Wireless folding of the small-scale prototype.

    Movie S3. A wireless robotic arm and gripper: capabilities.

    Movie S4. A wireless robotic arm and gripper: gripping an object and moving.

    Movie S5. Wireless ship in a bottle.

  • Supplementary Materials

    Supplementary Material for:

    Addressable wireless actuation for multijoint folding robots and devices

    Mustafa Boyvat,* Je-Sung Koh,* Robert J. Wood*

    *Corresponding author. Email: mboyvat{at}fas.harvard.edu (M.B.); jskoh{at}seas.harvard.edu (J.-s.K.); rjwood{at}seas.harvard.edu (R.J.W.)

    Published 19 July 2017, Sci. Robot. 2, eaan1544 (2017)
    DOI: 10.1126/scirobotics.aan1544

    This PDF file includes:

    • Fig. S1. Magnetic flux density of the source coil.
    • Fig. S2. Magnetic flux density variation with distance from the coil center.
    • Fig. S3. Folding structure design.
    • Fig. S4. Robotic arm design.
    • Fig. S5. Mechanism of the origami gripper.
    • Fig. S6. Foldable ship in a bottle.
    • Legends for movies S1 to S5

    Download PDF

    Other Supplementary Material for this manuscript includes the following:

    • Movie S1 (.mov format). Wireless folding of the large-scale prototype.
    • Movie S2 (.mov format). Wireless folding of the small-scale prototype.
    • Movie S3 (.mov format). A wireless robotic arm and gripper: capabilities.
    • Movie S4 (.mov format). A wireless robotic arm and gripper: gripping an object and moving.
    • Movie S5 (.mov format). Wireless ship in a bottle.

    Files in this Data Supplement:

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