Research ArticleSOFT ROBOTS

An origami-inspired, self-locking robotic arm that can be folded flat

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Science Robotics  14 Mar 2018:
Vol. 3, Issue 16, eaar2915
DOI: 10.1126/scirobotics.aar2915
  • Fig. 1 The foldable robotic arm enabled UAVs to perform tasks that could not be performed otherwise.

    (A) A UAV equipped with the self-locking foldable robotic arm was tested outdoors. (B) A foldable arm could be folded into a compact volume and deployed on command. The arm equipped with an adequate end effector could grasp an object or inspect inside a narrow, deep space. (C and D) Examples of tasks that could be performed with the foldable arm. The UAV could inspect locations that are difficult to access, such as underwater and spaces between branches. Furthermore, the foldable arm could allow the UAV to obtain samples from crevices in rugged terrain.

  • Fig. 2 Foldable module with locking mechanism.

    (A to C) Foldable structure using Sarrus linkage. (D to F) Locking mechanism by adjusting the shape of the Sarrus linkage and adding an extra facet. (A) Deployed state. The Sarrus linkage with four chains assumes a square column shape when deployed. (B) Transition state. (C) Folded state. The Sarrus linkage can be folded flat when the two links are of the same length. (D) In the locked mode, the fold line p to r cannot be folded because the lockers are in the locked position. The locking mechanism constrained the degrees of freedom of the foldable module and increased its stiffness. (E) Locker in the transitional position. (F) In the foldable mode, the lockers are in the unlocked position. The lockers were unlocked from the U1-B1 facet and overlapped with U2. Because all facets were in the same plane, the fold line p to r could be folded. Upper figures depict trimetric views of the module. The figure shows only the frontal two chains for simplicity. Lower figures depict a top view of the module.

  • Fig. 3 Tendon path design of the module.

    Tendon friction was minimized to increase force transmission and not to constrain antagonistic actuation. The folding process is in order of A to C. The deployment process follows the reverse order. (A) Tendon path when the module is deployed and the lockers are locked. (B) Locker in transitional position. When the tendon was pulled upward to fold the module, Fz and FL were applied to the module. (C) Tendon path when the module is being folded. During folding, the tendon moved along the slit from Bn to Cn (yellow double-headed arrow). During deployment, the tendon stayed at Cn owing to the bent slit. Upper figures depict trimetric views of the module. The figure shows only two frontal chains for simplicity. Lower figures depict a top view of the module.

  • Fig. 4 Types and directions of external forces on the module and coordination representing the movement of the locker.

    In the performance study, we analyzed the mechanical responses of the module according to the change of the design parameters in the compression direction and the bending direction shown in the figure. Because the relative motion of the lockers is an important factor in determining the mechanical response, a coordinate system shown in the figure is used to describe the motion of the lockers.

  • Fig. 5 Results of the performance study experiment: Compression (sample size: n = 5).

    (A) Compressive stiffness of the module when Embedded Image was changed. (B) Compressive stiffness of the module when Embedded Image was changed. (C) Compressive stiffness of the module when Embedded Image and Embedded Image were both changed. (D) Compressive stiffness of the module when Embedded Image was changed. (E) Maximum compressive load when Embedded Image was changed. (F) Maximum compressive load when Embedded Image was changed. (G) Maximum compressive load when Embedded Image and Embedded Image were both changed. (H) Maximum compressive load when Embedded Image was changed. Blue plots on the figures represent bending stiffness trend according to the general beam theory. Red plots on the figures represent the trend of results that are driven by least-squares methods. α and β are exponents of Embedded Image and Embedded Image, respectively. Whiskers are extended to 1.5 times of interquartile range (IQR) from the edge of the box; IQR is difference between upper and lower quartile. Asterisks indicate outliers that are beyond the whiskers.

  • Fig. 6 Results of the performance study experiment: Bending (sample size: n = 5).

    (A) Bending stiffness of the module when Embedded Image was changed. (B) Bending stiffness of the module when Embedded Image was changed. (C) Bending stiffness of the module when Embedded Image and Embedded Image were both changed. (D) Bending stiffness of the module when Embedded Image was changed. (E) Maximum bending load when Embedded Image was changed. (F) Maximum bending load when Embedded Image was changed. (G) Maximum bending load when Embedded Image and Embedded Image were both changed. (H) Maximum bending load when Embedded Image was changed. Blue lines on the figures represent expected bending stiffness trend according to the general beam theory. Red lines on the figures represent the trend of results that are driven by least-squares methods. α and β are exponents of Embedded Image and Embedded Image, respectively. Whiskers are extended to 1.5 times of IQR from the edge of the box; IQR is difference between upper and lower quartile. Asterisks indicate outliers that are beyond the whiskers.

  • Fig. 7 The foldable robotic arm with seven modules assembled in series.

    (A) Stills from a movie that shows folding process of the arm. (B) Foldable arm picking up objects with its gripper at the bottom of a 500-mm-deep ditch. (C) A camera and a gimbal were attached to the arm and filmed between branches.

  • Fig. 8 Steps in the fabrication process of the foldable module.

Supplementary Materials

  • robotics.sciencemag.org/cgi/content/full/3/16/eaar2915/DC1

    Text

    Fig. S1. Results of performance experiment: Bending (sample size: N = 5).

    Fig. S2. Results of performance experiment: Compression (sample size: N = 5).

    Fig. S3. Results of performance experiment: Tensile stiffness (sample size: N = 5).

    Fig. S4. Results of performance experiment: Robustness (sample size: N = 3).

    Fig. S5. Force-displacement graph under compressive and bending loads.

    Fig. S6. Experimental setup.

    Fig. S7. Experimental setup for repeatedly folding the module.

    Fig. S8. Origami-inspired pattern design of the foldable module.

    Fig. S9. Schematics of the foldable module for tendon friction modeling.

    Fig. S10. The lightweight and compact buckling gripper.

    Fig. S11. Fabricated samples with different variable sets.

    Table S1. Variables for the foldable module assuming [l, h, w] = [40, 100, 16] (mm).

    Table S2. Specifications for the foldable arm.

    Table S3. Tensile test results of ripstop fabric.

    Table S4. Parameters chosen for the buckling gripper.

    Table S5. Experimental results of performance study experiment: Compression.

    Table S6. Experimental results of performance study experiment: Bending.

    Table S7. Experimental results of application performance experiment.

    Movie S1. Tendon-driven foldable module.

    Movie S2. Foldable module with locking mechanism.

    Movie S3. Foldable arm indoor test.

    Movie S4. Foldable arm outdoor test.

    Movie S5. Lightweight and compact buckling gripper.

    Reference (40)

  • Supplementary Materials

    Supplementary Material for:

    An origami-inspired, self-locking robotic arm that can be folded flat

    Suk-Jun Kim, Dae-Young Lee, Gwang-Pil Jung, Kyu-Jin Cho*

    *Corresponding author. Email: kjcho{at}snu.ac.kr

    Published 14 March 2018, Sci. Robot. 3, eaar2915 (2018)
    DOI: 10.1126/scirobotics.aar2915

    This PDF file includes:

    • Text
    • Fig. S1. Results of performance experiment: Bending (sample size: N = 5).
    • Fig. S2. Results of performance experiment: Compression (sample size: N = 5).
    • Fig. S3. Results of performance experiment: Tensile stiffness (sample size: N = 5).
    • Fig. S4. Results of performance experiment: Robustness (sample size: N = 3).
    • Fig. S5. Force-displacement graph under compressive and bending loads.
    • Fig. S6. Experimental setup.
    • Fig. S7. Experimental setup for repeatedly folding the module.
    • Fig. S8. Origami-inspired pattern design of the foldable module.
    • Fig. S9. Schematics of the foldable module for tendon friction modeling.
    • Fig. S10. The lightweight and compact buckling gripper.
    • Fig. S11. Fabricated samples with different variable sets.
    • Table S1. Variables for the foldable module assuming l, h, w = 40, 100, 16 (mm).
    • Table S2. Specifications for the foldable arm.
    • Table S3. Tensile test results of ripstop fabric.
    • Table S4. Parameters chosen for the buckling gripper.
    • Table S5. Experimental results of performance study experiment: Compression.
    • Table S6. Experimental results of performance study experiment: Bending.
    • Table S7. Experimental results of application performance experiment.
    • Legends for movies S1 to S5
    • Reference (40)

    Download PDF

    Other Supplementary Material for this manuscript includes the following:

    • Movie S1 (.mp4 format). Tendon-driven foldable module.
    • Movie S2 (.mp4 format). Foldable module with locking mechanism.
    • Movie S3 (.mp4 format). Foldable arm indoor test.
    • Movie S4 (.mp4 format). Foldable arm outdoor test.
    • Movie S5 (.mp4 format). Lightweight and compact buckling gripper.

    Files in this Data Supplement:

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