Research ArticleSOFT ROBOTS

An untethered isoperimetric soft robot

See allHide authors and affiliations

Science Robotics  18 Mar 2020:
Vol. 5, Issue 40, eaaz0492
DOI: 10.1126/scirobotics.aaz0492
  • Fig. 1 An overview of the components and operating principle of the robot.

    (A) A large-scale inflated robot that does not require a tether. The robot is composed of a set of identical robotic roller modules that are mounted onto inflated fabric tubes that form the primary structure of the robot. (B) The rollers pinch the fabric tube between rollers, creating an effective joint that can be relocated by driving the rollers. (C) The roller modules actuate the robot by driving along the tube, simultaneously lengthening one edge while shortening another. The roller modules can connect to one another to construct 2D and 3D truss-like structures capable of shape change and locomotion. (D) The roller modules connect to each other at nodes using three-degree-of-freedom universal joints that are composed of a clevis joint that couples two rods, each free to spin about its axis. The arrows indicate how the joints can rotate. (E) The robot locomotes untethered outdoors using a punctuated rolling gait. One face of the robot is highlighted to illustrate the rolling motion.

  • Fig. 2 Demonstrations of two different 2D robots, each a collective of the same roller modules with different tube architectures, showing truss-like shape change.

    (A) A robot, formed from three separate tubes that are routed into triangles and connected together, inflates and springs into shape without intervention. (B) This three-tube robot can change to a variety of shapes. Casters under the roller modules allow motion. (C) A robot composed of a single inflated tube can markedly lengthen its edges, because each edge can exchange material with any other edge. The single-tube design also means that sometimes roller modules must run to pass material through the network, even if the edge lengths immediately connected to it are not changing length. (D) A single active roller module moves, causing one adjacent edge to shorten and the other to lengthen. (E) To lengthen and shorten the two edges adjacent to the passive module, all the active roller modules move in coordination. (F) The single-tube configuration is capable of much larger edge lengths because all other edges can shorten to accommodate the lengthening of two edges.

  • Fig. 3 A 3D untethered, octahedron truss robot capable of shape-morphing and locomotion.

    (A) The robot first inflates from a small package into an octahedron. The octahedron is composed of four individual triangles. (B) The robot can exhibit extreme shape change. A 186-cm-tall human and a 24-cm-diameter basketball are shown for size reference in some images. (C) The robot is also capable of a punctuated rolling gait, beginning with one of the four triangles as a bottom face (t = 0 s) and returning to this configuration (with a different triangle now at the bottom) after two rolling events (t = 28 s).

  • Fig. 4 Demonstration and characterization of the robot’s compliant behavior.

    (A) Overloading the robot causes the robot to collapse. After being restored to its initial configuration, the robot is again able to support the initial load. (B) Load displacement behavior of a single triangle in three different configurations. In all cases, there is a moderate initial stiffness until a critical load is reached and the beam buckles, at which point the force required to maintain a given level of deflection is much lower than the peak value, demonstrating a mechanical fuse–type behavior of the robot. (C) The robot moves a 6.8-kg load over a trajectory.

  • Fig. 5 Demonstration of the robot’s ability to use its inherent compliance to manipulate and interact with objects.

    (A) The robot grasps a basketball (diameter of 24 cm and mass of 580 g) by first engulfing it and then pinching it between two compliant edges. The robot then changes shape to lift the basketball into the air. (B) With the basketball secured between two edges, motion of the roller module closest to the basketball causes the basketball to spin. A coordinate frame has been added to allow visualization of how the orientation of the basketball changes. Between the second and third configurations, the basketball rotates about 135°. CW, clockwise; CCW, counterclockwise.

  • Fig. 6 Analysis of the effective joint formed by rollers pinching a tube.

    (A) The relationship between angle and torque with changing roller diameter (tube diameter is 7.32 cm). Model predictions are shown in solid lines, and experimental data are shown in dashed lines. The model slightly underpredicts the torque. The amount of torque increases substantially beyond the point where the model predicts self-interference. Torque increases with roller size, but interference also begins at larger angles. (B) Increasing torque with increasing tube diameters when the roller diameter is 1.14 cm. (C) Double roller configuration and the gear train that ensures all rollers move together from a single motor input. (D) Torque required to bend a tube with no rollers, with a single set of rollers, and with two sets of rollers as shown in (C) (roller diameters are 0.64 cm separated by 6.35 cm). Without rollers, the tube exhibits low stiffness, but large torque at a wide range of angles. The presence of one set of rollers markedly reduces the torque at low angles, but the torque rises quickly after self-interference begins. With two sets of rollers, the torque is low for small and large angles because the tube does not self-interfere.

  • Fig. 7 Exploration of the energetic cost to move along the tube.

    (A) Force required to move the tube through the rollers over a range of pressures and with three different roller diameters. The tube diameter is 7.32 cm. The force-pressure relationship is approximately linear, and increasing the roller diameter slightly increases the required force. (B) Force required to move the tube through the rollers over a range of pressures and with three different tube sizes. The roller diameter is 1.14 cm. The force-pressure relationship is approximately linear, and tubes with larger diameter require more force. (C) Force required to move a 10.1-cm tube at 30 kPa through two pairs of 0.76-cm rollers over a range of distances between the pairs. A single roller is included with gap distance equal to zero. The double roller cost to move when the separation is equal to the tube diameter is 80% of twice the single roller cost to move.

  • Fig. 8 Comparison of 2D triangular robot architectures.

    (A) Isoperimetric robot. (B) Truss robot with three linear actuators. (C) Truss robot with two linear actuators. (D) Workspaces and manipulability index, μ, of node 2 for each robot. The minimum edge length for all robots is 0.5 m, and the maximum length of linear actuators in robots B and C is 1 m. The total edge length of the isoperimetric robot is the maximum perimeter of the truss robots (3 m). The small black and red arrows indicate the direction of maximum velocity for node 2 of robot A and robots B and C, respectively. (E) Effect of frequency on the energy required to move node 2 between 50 waypoints within the shared workspace for robots A and C. With increased frequency, the isoperimetric robot becomes less efficient because of the coupled motion of nodes 2 and 3. (F) Required energy to move node 2 between waypoints when both robots A and C are driven by a specific electric motor and when robot C is driven by a microcompressor of comparable mass. The systems driven by an electric motor are faster than those driven by the microcompressor.

Supplementary Materials

  • robotics.sciencemag.org/cgi/content/full/5/40/eaaz0492/DC1

    Text

    Fig. S1. Experimental setup for measuring battery life.

    Fig. S2. Torque angle relationship for a beam between rollers.

    Fig. S3. Model predictions of the normal force between rollers.

    Fig. S4. Test apparatus to quantify cost of motion.

    Fig. S5. Deformation of an individual triangle.

    Fig. S6. Mechanical design of roller module.

    Fig. S7. Diagram of points used to define the kinematics of each roller module.

    Fig. S8. Details of the comparison with different truss robots.

    Movie S1. Motion of the roller module along an inflated tube.

    Movie S2. Inflation and shape change of a 2D robot.

    Movie S3. Operation of a single-tube 2D robot.

    Movie S4. Shape change of octahedron robot.

    Movie S5. Comparison of predicted and measured motion.

    Movie S6. Octahedron robot locomotes with a punctuated rolling gait.

    Movie S7. Compliance and interaction of the robot with people.

    Movie S8. Octahedron robot moving a payload.

    Movie S9. Simulated loading with payload.

    Movie S10. Self-recovery from buckling.

    Movie S11. Manipulation.

    Movie S12. Reachable workspace for a single triangle.

    References (5459)

  • Supplementary Materials

    The PDF file includes:

    • Text
    • Fig. S1. Experimental setup for measuring battery life.
    • Fig. S2. Torque angle relationship for a beam between rollers.
    • Fig. S3. Model predictions of the normal force between rollers.
    • Fig. S4. Test apparatus to quantify cost of motion.
    • Fig. S5. Deformation of an individual triangle.
    • Fig. S6. Mechanical design of roller module.
    • Fig. S7. Diagram of points used to define the kinematics of each roller module.
    • Fig. S8. Details of the comparison with different truss robots.
    • Legends for movies S1 to S12
    • References (5459)

    Download PDF

    Other Supplementary Material for this manuscript includes the following:

    • Movie S1 (.mp4 format). Motion of the roller module along an inflated tube.
    • Movie S2 (.mp4 format). Inflation and shape change of a 2D robot.
    • Movie S3 (.mp4 format). Operation of a single-tube 2D robot.
    • Movie S4 (.mp4 format). Shape change of octahedron robot.
    • Movie S5 (.mp4 format). Comparison of predicted and measured motion.
    • Movie S6 (.mp4 format). Octahedron robot locomotes with a punctuated rolling gait.
    • Movie S7 (.mp4 format). Compliance and interaction of the robot with people.
    • Movie S8 (.mp4 format). Octahedron robot moving a payload.
    • Movie S9 (.mp4 format). Simulated loading with payload.
    • Movie S10 (.mp4 format). Self-recovery from buckling.
    • Movie S11 (.mp4 format). Manipulation.
    • Movie S12 (.mp4 format). Reachable workspace for a single triangle.

    Files in this Data Supplement:

Stay Connected to Science Robotics

Navigate This Article