Towards Pneumatic Spiral Grippers: Modeling and Design Considerations

Abstract

There are a number of instances in nature where long and slender objects are grasped by a continuum arm spirally twirling around the object, thereby increasing the area of contact and stability between the gripper and the object. This paper investigates the design and modeling of spiral grippers using pneumatic fiber-reinforced actuators. The paper proposes two reduced order models, a pure helical model, and a spatial Cosserat rod model to capture the deformed behavior of the gripper using the mechanics of fiber-reinforced actuators in the presence of self-weight. While the former model can yield closed form expressions that aid in design, the deformation parameters deviate by greater than 40% of its length for actuators longer than 200 mm. However, the Cosserat rod model deviates by less than 8% of its length for two different prototypes validated in this work. The deformation of the gripper is then correlated to the number of spiral turns achievable about the object, which determines the quality of the grip. Together, they enable a systematic framework where the gripper parameters can be designed for a given range of object sizes to be handled. This framework is experimentally validated by successful gripping of a range of slender objects that lie between a 20 mm diameter tubelight and a 60 mm diameter PVC pipe.

Design of Soft Continuum Manipulators Using Parallel Asymmetric Combination of Fiber Reinforced Elastomers

“…The deformation patterns are determined by fiber angles. The fabrication methodology of FREEs is detailed in the authors' previous publications [28], [31]. The BR 2 manipulator consists of three FREEs, one extending FREE denoted by B, and two rotating FREEs denoted by R (one rotating clockwise and the other counterclockwise).…”

“…2) Whole arm gripping: The BR 2 manipulator is capable of using its entire length to spirally wrap and grip long and slender objects. In our previous work [31] we have demonstrated a single spiral FREE to grip cylindrical objects of different radii. The BR 2 manipulator is also capable of spiral motion, because of it ability to generate simultaneous curvature and torsion.…”

“…Furthermore, the pitch of the spiral can be varied depending on the relative pressures in the rotating and bending FREEs. For successful gripping, the spiral must generate at least one complete turn along a cylindrical object to ensure force (or form) closure [31].…”

Pneumatic Coiling Actuator Inspired by the Awns of Erodium cicutarium

“…Hydrogel-based bimorph materials with uniformly distributed fibers or stripes could bend or twist in response to different ambient stimuli (Wan et al, 2018). However, their relatively simple reinforcing fibers are not sufficient to create coiling-a combination of twisting and bending-unless we add strainlimiting layers or a third fiber (Bishop-Moser and Kota, 2013;Uppalapati and Krishnan, 2018) to the standard helical fibers, or use multiple fluidic chambers (Martinez et al, 2013). These are not as simple and elegant as the tilted helix design in Erodium.…”

Characterization, Simulation and Control of a Soft Helical Pneumatic Implantable Robot for Tissue Regeneration

“…When used in soft robotic systems, they also provide increased dexterity, more efficient workspaces by using routed tendons [27], enhanced area of contact and stability when acting as a gripper [28]. Nevertheless, scarce attention has been put into their investigation.…”