Research ArticleACTUATORS

Untethered soft robotic matter with passive control of shape morphing and propulsion

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Science Robotics  21 Aug 2019:
Vol. 4, Issue 33, eaax7044
DOI: 10.1126/scirobotics.aax7044
  • Fig. 1 3D printing of soft robotic matter.

    (A) Active hinges were printed from oligomeric LCE inks, whose rigid mesogens aligned along the print path during HOT-DIW (left). Immediately upon printing, LCE ink cross-linking was photo-initiated to lock in the desired director alignment. Structural tiles were then printed from an ink composed of acrylate resin that chemically bonded to LCE hinges upon photo-initiated cross-linking (right). (B) The LCE hinges were printed in the form of 0°/90° and 90°/0° bilayers, which bend into mountain and valley folds, respectively, when actuated above TNI. A simple structure composed of two hinges, with mountain and valley folds, that interconnect three structural tiles is shown as printed (middle and top) and as actuated (middle and bottom). (C) A more complex, square-twist reconfigurable structure was printed (left) and actuated at 125°C (right). The LCE hinges that form the central square and the four LCE hinges that point toward the center of the structure (left) are mountain folds, whereas the other LCE hinges are valley folds. Scale bars, 1 cm.

  • Fig. 2 Untethered, sequential, and reversible folding of active hinges.

    (A) Chemical composition of the LTNI (blue) and HTNI (orange) oligomeric LCE inks (where n = 3 and 6, and m = 6 in the molecular structures). (B) Bending angle θ as a function of temperature for LTNI and HTNI LCE hinges with length of 10 mm, width of 4 mm, and thickness of 0.25 mm. (C) A printed structure composed of LTNI and HTNI LCE hinges with mountain folds that interconnect three structural tiles, which undergo sequential actuation when heated (left to center) and cooled (center to right). Scale bar, 1 cm. (D) Bending angle θ as a function of thickness, h, for LTNI and HTNI LCE hinges of fixed length of 10 mm and width of 3 mm. Their bending angle decreased with thickness. Other bilayer systems display inverse proportionality between curvature and thickness (5759). We plot this relationship, where c is a constant, for comparison. Both hinges exhibited a maximum bending angle of 180°, where panels contact one another. (E) Bending angle θ as a function of hinge width, w, for LTNI and HTNI LCE hinges of fixed length of 10 mm and thickness of 0.5 mm. Error bars indicate SD.

  • Fig. 3 Printed soft robotic matter with programmed sequential folding and deformation.

    (A) A triangulated polyhedron was printed in the form of a flat sheet composed of both LTNI hinges (top section) and HTNI hinges (bottom section) that interconnect the structural tiles. All diagonal LCE hinges are valley folds, whereas all vertical and horizontal LCE hinges are mountain folds. (B) The printed flat sheet was manually assembled into a 3D triangulated structure that exhibited sequential folding upon heating from (C) ambient temperature to (D) 100°C, where the LTNI LCE hinges actuated, and to (E) 150°C, where the HTNI LCE hinges actuated. Scale bars, 1 cm.

  • Fig. 4 Torque capacity of printed active hinges.

    (A) LTNI LCE hinge (10 mm by 4 mm by 1 mm) folds to a 75° bending angle while unbiased. (B) When a 10-g mass was suspended 1 cm away from the LCE hinge at room temperature, it deflected to −72°. The mass was lifted by about 1 cm when actuated above TNI. (C) Exerted torque as a function of hinge folding angle, θ, as defined by the inset. Hinge composition and thickness, h, are the primary factors that affect torque output. (D) LCE hinges (5 mm by 3 mm by 0.5 mm) undergo multiple actuation cycles with negligible changes in the torque output. Error bars indicate SD. Scale bars, 1 cm.

  • Fig. 5 Printed self-propelling structure.

    (A) Self-propelling rollbot is shown in its printed configuration. In the legend (inset), the blue (LTNI) and orange (HTNI) LCE hinges denote valley and mountain folds, respectively, and gray indicates structural tiles. (B) Printed structure in its rolling configuration, in which the LTNI LCE hinges induced folding into a pentagonal prism and the HTNI LCE hinges propelled the rollbot when heated above their actuation temperature. (C) Still images (from movie S4) of the rollbot that show its self-propelling locomotion when heated. The structure self-propels at least six times over the time sequence shown. [The heated surface was held at 200°C, and the average ambient temperature was 45°C. Scale bars, 1 cm.]

Supplementary Materials

  • robotics.sciencemag.org/cgi/content/full/4/33/eaax7044/DC1

    Text S1. Mechanics of thin nematic elastomer bilayers.

    Fig. S1. LCE and structural tile ink rheology.

    Fig. S2. DSC curves for the LCE inks.

    Fig. S3. LCE alignment.

    Fig. S4. Actuation response of unidirectional printed LCEs.

    Fig. S5. Bending angle as a function of temperature.

    Fig. S6. Bending angle as a function of hinge dimensions.

    Fig. S7. Valley fold bending angles.

    Fig. S8. Repeatable hinge folding.

    Fig. S9. Triangulated polyhedron actuation sequence at ambient temperature.

    Fig. S10. Free-body diagrams of self-propelling rollbot.

    Fig. S11. Torque requirements of hinges for self-propelling rollbot.

    Fig. S12. Torque measurement experimental setup.

    Fig. S13. Torque measurements for hinges of varied dimensions.

    Movie S1. Actuation of square twist origami unit.

    Movie S2. Reversible, sequential actuation of hinges.

    Movie S3. Actuation sequence of triangulated polyhedron.

    Movie S4. Passively controlled propulsion of soft robot.

  • Supplementary Materials

    The PDF file includes:

    • Text S1. Mechanics of thin nematic elastomer bilayers.
    • Fig. S1. LCE and structural tile ink rheology.
    • Fig. S2. DSC curves for the LCE inks.
    • Fig. S3. LCE alignment.
    • Fig. S4. Actuation response of unidirectional printed LCEs.
    • Fig. S5. Bending angle as a function of temperature.
    • Fig. S6. Bending angle as a function of hinge dimensions.
    • Fig. S7. Valley fold bending angles.
    • Fig. S8. Repeatable hinge folding.
    • Fig. S9. Triangulated polyhedron actuation sequence at ambient temperature.
    • Fig. S10. Free-body diagrams of self-propelling rollbot.
    • Fig. S11. Torque requirements of hinges for self-propelling rollbot.
    • Fig. S12. Torque measurement experimental setup.
    • Fig. S13. Torque measurements for hinges of varied dimensions.

    Download PDF

    Other Supplementary Material for this manuscript includes the following:

    • Movie S1 (.mp4 format). Actuation of square twist origami unit.
    • Movie S2 (.mp4 format). Reversible, sequential actuation of hinges.
    • Movie S3 (.mp4 format). Actuation sequence of triangulated polyhedron.
    • Movie S4 (.mp4 format). Passively controlled propulsion of soft robot.

    Files in this Data Supplement:

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