Research ArticleACTUATORS

Actuation of untethered pneumatic artificial muscles and soft robots using magnetically induced liquid-to-gas phase transitions

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Science Robotics  15 Apr 2020:
Vol. 5, Issue 41, eaaz4239
DOI: 10.1126/scirobotics.aaz4239
  • Fig. 1 Fabricating a MITPAM.

    MNPs are first mixed with deionized water, and the resulting mixture is then added to the balloon. The open end of the balloon is then sealed with a knot. The braided carbon fiber sleeve is then jacketed on the balloon. Upon excitation with a high-frequency (150 kHz) magnetic field, steam bubbles form and generate a significant pressure, P. The braiding translates the generated pressure to an axial contractile strain and radial expansion, resulting in a change in the length of the balloon, ΔL.

  • Fig. 2 Characterization of the MNPs.

    (A) SEM image of the MNPs showing particle size variation between 100 and 300 nm. (Inset) Selected area electron diffraction patterns. (B) XRD analysis indicates that the MNPs are magnetite (Fe3O4). (C) DC magnetization of the magnetite MNPs. (D) For the specific absorption test, 197 mg of the magnetite sample was excited at an input power of 900 W.

  • Fig. 3 Force, strain, and temperature response of a MITPAM.

    (A) Photograph illustrating the pressure generated inside the balloon during excitation. The outer diameter of the copper coil is 38 mm. (B) Thermal images of the actuator in (A) before (left) and after (right) excitation. (C) Before (left) and after (right) excitation of a MITPAM actuator under a 2-kg load generating 20% strain. (D) Temperature profile of the sample during on-off cycles. (E) Strain curve for multiple cycles. The first cycles are still warming up, whereas the last cycles have reached a steady-state peak strain. (F) Temperature and blocking force profiles as a function of time for a sample under isometric conditions. (Inset) The force response to the increase in temperature.

  • Fig. 4 Thermodynamics of the MITPAM.

    (A) Illustration of force versus strain for the MITPAM excited at temperatures T1 and T2. (B) Change in the pressure as a function of the maximum temperature. (C) Normalized volume change as a function of the maximum temperature.

  • Fig. 5 Modeling and demonstration of robotic arm actuation.

    (A) Force-strain relationship through model and experimental data for two samples with different initial bias angles and mixture concentrations excited at two different temperatures. (B) Demonstration of locking strain or locking contraction after the first cycle with carbonated water. (C) Peak strain evolution through 50 successive excitations. (D to F) Before excitation (left) and after excitation (right) of the arm without any load (D), with a 250-g load (E), and with a 500-g load (F).

  • Fig. 6 Soft gripper demonstration.

    (A) Pulse width modulation control of a magnetothermally actuated soft gripper. The input power was pulse width–modulated to control the position of the gripper. In the first excitation cycle, the gripper was excited at 80% duty cycle, followed by a 10% duty cycle to prevent bursting. After 32 s of cooling, the gripper was excited with the same duty cycle pattern again. (B to D) DC excitation of a soft gripper: A cooked egg and a tennis ball were used as objects in experiments in (B) and (D). (C) The orange color object is a clamp that connects the actuator to the load. (D) The excitation time for this particular case was timed right before the bending of the gripper occurs. In all grippers, the mass of the connector is included in the mass of the gripper.

Supplementary Materials

  • robotics.sciencemag.org/cgi/content/full/5/41/eaaz4239/DC1

    Working mechanism

    Modeling

    Energy analysis

    Fig. S1. The hardware schematic for magnetically induced thermal soft robotic grippers.

    Fig. S2. The circuit diagram for MITPAM.

    Fig. S3. Measured data and simulation results for magnetic field strength inside the coil.

    Fig. S4. The specs for the molds used to fabricate the soft robotic grippers.

    Fig. S5. Illustration of the response of various types of magnetic particles under magnetic field.

    Fig. S6. Characterization of the MNPs based on their thermal response to various magnetic field strengths.

    Table S1. Heat parameters of the fluids used in this work.

    Movie S1. Magnetothermal actuation of a MITPAM demonstrating 20% strain under a 2-kg load excited at an input power of 900 W.

    Movie S2. MITPAM robotic arms under no load.

    Movie S3. MITPAM robotic arms under a 250-g load.

    Movie S4. MITPAM robotic arms under a 500-g load.

    Movie S5. Lifting an egg by magnetothermal actuation of a soft gripper.

    Movie S6. Lifting a ball by magnetothermal actuation of a soft gripper.

    Movie S7. Controlled magnetothermal actuation of a soft gripper.

    References (3841)

  • Supplementary Materials

    The PDF file includes:

    • Working mechanism
    • Modeling
    • Energy analysis
    • Fig. S1. The hardware schematic for magnetically induced thermal soft robotic grippers.
    • Fig. S2. The circuit diagram for MITPAM.
    • Fig. S3. Measured data and simulation results for magnetic field strength inside the coil.
    • Fig. S4. The specs for the molds used to fabricate the soft robotic grippers.
    • Fig. S5. Illustration of the response of various types of magnetic particles under magnetic field.
    • Fig. S6. Characterization of the MNPs based on their thermal response to various magnetic field strengths.
    • Table S1. Heat parameters of the fluids used in this work.
    • References (3841)

    Download PDF

    Other Supplementary Material for this manuscript includes the following:

    • Movie S1 (.mp4 format). Magnetothermal actuation of a MITPAM demonstrating 20% strain under a 2-kg load excited at an input power of 900 W.
    • Movie S2 (.mp4 format). MITPAM robotic arms under no load.
    • Movie S3 (.mp4 format). MITPAM robotic arms under a 250-g load.
    • Movie S4 (.mp4 format). MITPAM robotic arms under a 500-g load.
    • Movie S5 (.mp4 format). Lifting an egg by magnetothermal actuation of a soft gripper.
    • Movie S6 (.mp4 format). Lifting a ball by magnetothermal actuation of a soft gripper.
    • Movie S7 (.mp4 format). Controlled magnetothermal actuation of a soft gripper.

    Files in this Data Supplement:

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