Research ArticleSPACE ROBOTS

A robotic device using gecko-inspired adhesives can grasp and manipulate large objects in microgravity

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Science Robotics  28 Jun 2017:
Vol. 2, Issue 7, eaan4545
DOI: 10.1126/scirobotics.aan4545
  • Fig. 1 Technologies in the integrated gripper:

    (A) Microscopic side views of the gecko-inspired controllable adhesive. (B) Flat gripper unit composed of two opposed adhesive tiles (36). (C) Curved unit of opposed, flexible adhesive films (37). (D) Load sharing using a pulley and tendon differential. (E) Applying moments with outriggers and in-riggers. (F) Wrist with nonlinear elements (in green) is stiff at light loads and compliant at larger loads. (G) Procedures for aligning, applying preload, applying forces and moments to manipulate, and releasing.

  • Fig. 2 Integrated gripper including eight flat gripper units and two curved gripper units.

    Servo motors control the pretensioning and release of gripping elements and SMA wrist wires.

  • Fig. 3 Load-sharing results.

    (A) Force profiles for four flat gripper units and five trials with and without pulley differential [adapted from (40)]. (B) Load sharing reduces variability and improves load sharing; friction gradually reduces tendon/pulley performance.

  • Fig. 4 Force limits and layout design.

    (A) Limit surface for a single flat gripper unit represents maximum pulling forces in each direction. (B) Two-dimensional force limit curve for flexible film on a curved surface. (C) Radial layout with 20 flat gripper units is limited by units in blue dashed ovals. Red shading represents percentage of each unit’s maximum load. (D) Rectangular layout: All units contribute equally and overall limit surface is isomorphic to (A). (E) Ellipsoidal fits to limit surfaces for radial and rectangular layouts. Dots correspond to the load limits for blue and cyan vectors in (C) and (D).

  • Fig. 5 Comparison of predicted and measured forces and moments.

    (A) Flat gripper array: measurements taken in one quadrant, assuming symmetry. Labeled vertices B to E correspond to loading scenarios in (B) to (E), respectively. (F) Curved gripper array: measurements taken in two quadrants, assuming symmetry. Labeled vertices G to J correspond to loading scenarios in (G) to (J). (K) The residuals between the model and data for all loading planes. Additional loading scenarios and limit surfaces are included in the Supplementary Materials.

  • Fig. 6 Nonlinear passive wrist.

    (A) Loading and unloading curves for pretensioned superelastic SMA wire; energy loss approximated by the shaded rectangular region. (B) One-DOF wrist joint and corresponding torque/deflection model. SMA wire is connected to stop bars and flexible tendon strings, which are slack when unloaded. This design prevents deadband about the center. (C) Nonlinear wrist performance in comparison to critically damped linear system. (D) Simulation of wrist behavior in comparison to the spring-damper system. Initial energy and maximum torque are set equal in both cases. (E) Comparison of critically damped and SMA single-axis joints for absorbing energy from collision with a metal ball.

  • Fig. 7 Typical loading cycles of the integrated gripper.

    (A) Attachment to a flat glass plate. (B) Attachment to a 1-m-diameter spherical vinyl surface. Preloading denotes a process where the gripper is pushed into the surface to engage the gripper. Contact sensors are disabled to bypass their effects. During pretensioning on flat surfaces, motors eliminate slack in pulleys and cables. During release, forces are internal with negligible disturbance to object.

  • Fig. 8 Demonstrations integrated system tests.

    (A and B) Tests aboard zero-gravity airplane grasping and releasing large flat and curved objects. (C) Astronaut testing spring-loaded gripper units aboard the ISS. (D) Integrated system tests on large floating platforms at JPL: master robot captured target by gripping flat solar panels. (E) Lemur robot with four-unit flat gripper climbed a solar panel with gravity off-load.

Supplementary Materials

  • robotics.sciencemag.org/cgi/content/full/2/7/eaan4545/DC1

    Materials

    Methods

    Movie S1. The force and moment limit surface of a four-unit flat gripper in the x-z (shear-normal) plane.

    Movie S2. The force and moment limit surface of a four-unit flat gripper in the y-z (shear-normal) plane.

    Movie S3. The force and moment limit surface of a four-unit flat gripper in the x-y (shear) plane.

    Movie S4. The force and moment limit surface of a two-unit curved gripper in the x-z (shear-normal) plane.

    Movie S5. The force and moment limit surface of a two-unit curved gripper in the y-z (shear-normal) plane.

    Movie S6. The force and moment limit surface of a two-unit curved gripper in the x-y shear plane.

    Movie S7. Demonstration of the 2D and 3D floating tests of the grippers.

    Reference (48)

  • Supplementary Materials

    Supplementary Material for:

    A robotic device using gecko-inspired adhesives can grasp and manipulate large objects in microgravity

    Hao Jiang,* Elliot. W. Hawkes, Christine Fuller, Matthew A. Estrada, Srinivasan A. Suresh, Neil Abcouwer, Amy K. Han, Shiquan Wang, Christopher J. Ploch, Aaron Parness, Mark R. Cutkosky

    *Corresponding author. Email: jianghao{at}stanford.edu

    Published 28 June 2017, Sci. Robot. 2, eaan4545 (2017)
    DOI: 10.1126/scirobotics.aan4545

    This PDF file includes:

    • Materials
    • Methods
    • Legends for movies S1 to S7
    • Reference (48)

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    Other Supplementary Material for this manuscript includes the following:

    • Movie S1 (mp4 format). The force and moment limit surface of a four-unit flat gripper in the x-z (shear-normal) plane.
    • Movie S2 (mp4 format). The force and moment limit surface of a four-unit flat gripper in the y-z (shear-normal) plane.
    • Movie S3 (mp4 format). The force and moment limit surface of a four-unit flat gripper in the x-y (shear) plane.
    • Movie S4 (mp4 format). The force and moment limit surface of a two-unit curved gripper in the x-z (shear-normal) plane.
    • Movie S5 (mp4 format). The force and moment limit surface of a two-unit curved gripper in the y-z (shear-normal) plane.
    • Movie S6 (mp4 format). The force and moment limit surface of a two-unit curved gripper in the x-y shear plane.
    • Movie S7 (mp4 format). Demonstration of the 2D and 3D floating tests of the grippers.

    Files in this Data Supplement:

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