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A soft ring oscillator

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Science Robotics  26 Jun 2019:
Vol. 4, Issue 31, eaaw5496
DOI: 10.1126/scirobotics.aaw5496
  • Fig. 1 The soft ring oscillator composed of three elastomeric, pneumatic inverters.

    (A) The soft ring oscillator converts a constant input pressure to multiple temporally coordinated oscillating outputs. (B) The ring oscillator is composed of three inverters connected in a loop, resulting in a systematic instability (because no stable state exists); it is driven by a constant supply pressure, Psupp, and generates output pressures PA, PB, and PC. Side views of a single soft inverter show the internal tubes for airflow, with the upper tube kinked by the membrane in (C) and the lower tube kinked in (D) (top, photo; bottom, schematic; 2D schematic shown in fig. S8). The output pressure, Pout, is an inverted signal of the input pressure, Pin, with hysteresis due to the difference in the pressures required to snap the membrane from its initial state (Psnap-thru) and allow the membrane to return back to its initial state (Psnap-back); this behavior exemplifies an inverting Schmitt trigger (detailed characterization in fig. S11 and operation shown in movie S1).

  • Fig. 2 The two states of the ring oscillator: Inflation and deflation.

    The ring oscillator always contains either two adjacent unactuated inverters (A), in which case one of the inverters inflates, or two adjacent actuated inverters (B), in which case one of the inverters deflates. (C) The three-inverter ring oscillator generates three temporally coordinated output pressures, shown here as PA, PB, and PC, when a constant supply pressure, Psupp, is applied. Horizontal dashed gray lines indicate the supply pressure, Psupp; the snap-through pressure required to transition the internal membrane from its unactuated to its actuated state, Psnap-thru; and the snap-back pressure beneath which the internal membrane transitions from its actuated to its unactuated state, Psnap-back. The red and blue dashed arrows overlaid onto the plot indicate inflation and deflation, respectively.

  • Fig. 3 Response to variable supply pressure, pneumatic resistance, and pneumatic capacitance.

    (A) A constant supply pressure, Psupp, drives the system, which exhibits resistances and capacitances due to friction during airflow and pressurization of volumes of gas, respectively. We performed experimental parametric sweeps over multiple supply pressures (B), pneumatic resistances resulting from thin-diameter tubing added between inverters (C), and pneumatic capacitances provided by added volumes of gas (D). Error bars represent 95% confidence intervals of the means. (B to D) Predictions from the analytical RC circuit model are overlaid as dashed red curves.

  • Fig. 4 Translation of a spherical object.

    The soft ring oscillator rolls a ball on an elastomeric track. The track relies on sequential inflation of serially arranged elastomeric chambers to translate objects (A). A circular track can roll a ball indefinitely; the schematic illustrates a completely soft design of a circular track with 30 internal chambers (B), which we used in an experimental demonstration shown here (C) and in movie S3.

  • Fig. 5 Rolling soft robot driven by integrated ring oscillator.

    (A) A hexagonal roller with a soft foam frame relies on an integrated, onboard ring oscillator to inflate balloons attached to each face and to cause the hexagon to tilt as each of the balloons inflates sequentially. (B) Once the rolling angle reaches 30° because of inflation of a balloon, the hexagon tips onto its next face. This design uses double-balloon actuators (C), which exhibit a pressure-volume characteristic based on the interplay between the elastic, easy-to-stretch inner balloon and the stiff, difficult-to-stretch outer balloon (D). (E) These double-balloon actuators, mounted on each of the hexagon’s six faces, cause it to tip from one face to another during inflation and roll, with only a single, constant-pressure input required. Movie S4 shows this soft robot rolling.

  • Fig. 6 Separation of particles by size.

    The three temporally coordinated output pressures from the ring oscillator enable separation. (A) When a stage is mounted on three soft linear actuators and the actuators’ inputs are connected to the three pneumatic outputs of the ring oscillator (i.e., PA, PB, and PC), the stage tilts in a circularly undulating pattern. (B) This stage motion can separate particles of different sizes when a size-selective gate is placed on the side of the stage (complete separation shown in movie S5).

  • Fig. 7 Soft mechanotherapy device for the lower leg.

    The internal fabric chambers of the mechanotherapy device connect to the three pneumatic outputs of the ring oscillator [i.e., PA, PB, and PC; (A)], and the device sequentially contracts around a human user’s leg, “pumping” fluid up the leg for treatment of conditions such as lymphedema and chronic venous disease and for prevention of deep vein thrombosis. The device is easily applied to the lower leg with Velcro closures [top closure open (B); all closures closed (C)]. (D) We demonstrated propagation of a low-pressure region up the leg experimentally, using a pressure-sensitive mat placed between the mechanotherapy device and the leg; the low-pressure region corresponds to the region of fluid inside of the leg that is “pumped” upward, toward the torso (blue corresponds to a gauge pressure of 0 kPa, and red corresponds to about 50 kPa; 100 kPa ≈ 1 atm).

Supplementary Materials

  • robotics.sciencemag.org/cgi/content/full/4/31/eaaw5496/DC1

    Materials and Methods

    Text

    Fig. S1. Design of the molds for the tubing used inside the chambers of the inverter.

    Fig. S2. Assembly of the tubing used inside the chambers of the inverter.

    Fig. S3. Design of the molds for the inverter.

    Fig. S4. Assembly of the inverter.

    Fig. S5. Design of the molds, and assembly, for the ball roller (circular track).

    Fig. S6. Design of the molds, and assembly, for the rolling hexagonal frame.

    Fig. S7. Design and assembly of the soft, undulating stage.

    Fig. S8. Unactuated and actuated inverter schematics, with labels, alongside photographs.

    Fig. S9. Membrane snap-through hysteresis.

    Fig. S10. Experimental setup for characterization of the soft, pneumatic inverter.

    Fig. S11. Inverting Schmitt trigger–like behavior.

    Fig. S12. Psupp does not influence the critical pressures.

    Fig. S13. Pneumatic RC circuit analog.

    Fig. S14. A soft linear ball roller connected to the ring oscillator.

    Fig. S15. Soft stage mounted on three linear actuators connected to the ring oscillator.

    Fig. S16. The soft ring oscillator can control and meter fluid flows.

    Fig. S17. Experimental setup for the demonstration of metering of fluid.

    Data file S1. Zip file containing stereolithography (STL) files of 3D-printed molds used in this work.

    Movie S1. Single inverter demonstration: When the input is off (0), the output is on (1), and vice versa.

    Movie S2. High-strain deformation test: The ring oscillator is manually compressed to 25% of its initial size, after which it resumes operation.

    Movie S3. Translation of spherical object around a circular elastomeric track.

    Movie S4. Actuation of a rolling soft robot with an integrated soft ring oscillator.

    Movie S5. Separation using an elastomeric stage driven by the soft ring oscillator.

    Movie S6. Fluid-metering valves controlled by the soft ring oscillator.

    Reference (41)

  • Supplementary Materials

    The PDF file includes:

    • Materials and Methods
    • Text
    • Fig. S1. Design of the molds for the tubing used inside the chambers of the inverter.
    • Fig. S2. Assembly of the tubing used inside the chambers of the inverter.
    • Fig. S3. Design of the molds for the inverter.
    • Fig. S4. Assembly of the inverter.
    • Fig. S5. Design of the molds, and assembly, for the ball roller (circular track).
    • Fig. S6. Design of the molds, and assembly, for the rolling hexagonal frame.
    • Fig. S7. Design and assembly of the soft, undulating stage.
    • Fig. S8. Unactuated and actuated inverter schematics, with labels, alongside photographs.
    • Fig. S9. Membrane snap-through hysteresis.
    • Fig. S10. Experimental setup for characterization of the soft, pneumatic inverter.
    • Fig. S11. Inverting Schmitt trigger–like behavior.
    • Fig. S12. Psupp does not influence the critical pressures.
    • Fig. S13. Pneumatic RC circuit analog.
    • Fig. S14. A soft linear ball roller connected to the ring oscillator.
    • Fig. S15. Soft stage mounted on three linear actuators connected to the ring oscillator.
    • Fig. S16. The soft ring oscillator can control and meter fluid flows.
    • Fig. S17. Experimental setup for the demonstration of metering of fluid.
    • Legends for movies S1 to S6
    • Reference (41)

    Download PDF

    Other Supplementary Material for this manuscript includes the following:

    • Data file S1 (.zip format). Zip file containing stereolithography (STL) files of 3D-printed molds used in this work.
    • Movie S1 (.mp4 format). Single inverter demonstration: When the input is off (0), the output is on (1), and vice versa.
    • Movie S2 (.mp4 format). High-strain deformation test: The ring oscillator is manually compressed to 25% of its initial size, after which it resumes operation.
    • Movie S3 (.mp4 format). Translation of spherical object around a circular elastomeric track.
    • Movie S4 (.mp4 format). Actuation of a rolling soft robot with an integrated soft ring oscillator.
    • Movie S5 (.mp4 format). Separation using an elastomeric stage driven by the soft ring oscillator.
    • Movie S6 (.mp4 format). Fluid-metering valves controlled by the soft ring oscillator.

    Files in this Data Supplement:

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