Robert Brik

Mechanical/Design Engineer

Soft Pneumatic Gripper with Synthetic Fibrillar Adhesive

Softo Robot

Overview

  • The proposed gripper combined principles from the Suzumori and Pneu-net actuators to create fingers that flex and grip.
  • A hand was designed with three identical fingers, one of which was prototyped.
  • Each finger is made of an air chamber that is encompassed by ribs sitting on a strain limiting layer. The intent is to allows the finger to bend when air pressure is applied without the need to balloon significantly outward.
  • The tip of each finger has a piece of fibrillar adhesive attached in order to allow for better manipulation of flat objects.
Softo Robot

CAD & Modeling

  • The design was drawn in Solidworks and the movement was modeled with the assistance of Matlab.
  • A number of assumptions were made in order to create an estimate for the bending curvature:
    • Strain only occurs along the axis due to radial strain limiting bands.
    • The air chamber behaves in a Neo-Hookean fashion.
    • The strain limiting layer does not stretch due to its thickness and resilience.
  • As a result, a mathematical model was created to predict the deformation of the gripper at a given pressure.
Softo Robot

Fabrication

  • A multi-step fabrication method was developed to make each finger.
    • The strain layer was created by pouring ST-1060 Polyurethane into the base of a 3D-printed mold. Prior to the polyurethane fully curing, a comb like mold was used to insert 3D printed ribs into the rubber. The resulting strain limiting layer was highly resistant to strain along its axis, but easily bendable.
    • The strain layer was then inserted into a second 3D-printed ABS mold along with internal wax extrusions to form the air channels. F-25 polyurethane was poured to form the layer around the ribs and finally the tip of the finger was dipped in polyurethane to form an end-cap and seal the channels.
    • The completed finger was attached to a triangular base that included channels to supply air to the chambers.
Softo Robot

Results & Conclusion

  • Overall, when air pressure was applied, the finger bent successfully along the predicted axis without ballooning outward.
  • During initial testing, the finger could adapt to 3D geometry
  • Some leaks and bonding issues were found which necessitated a post-mold coating of polyurethane.
  • In the future, it would be interesting to include multiple air chambers in each finger or make the strain limiting layer non-homogenous.
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