Source-Free Bistable Fluidic Gripper for Size-Selective and Stiffness-Adaptive Grasping

TL;DR

This paper tackles the portability limitations of conventional fluid-driven soft grippers by introducing a self-contained, fixed-size gripper that uses internal liquid redistribution among three interconnected bistable snap-through chambers. The actuation relies on volume-controlled hydraulic inflation triggered by the sensing contact chamber, eliminating the need for external pumps and enabling stable, size-selective grasping with passive stiffness adaptation. Finite element simulations and experiments show that a tilt angle of $\alpha=45^{\circ}$ yields robust bistability, while the system modulates internal pressure ($1$–$6$ kPa) in response to object stiffness, enabling gentle handling of fragile targets. The compact, source-free design supports on-board, untethered operation suitable for underwater and field deployments with potential applications in targeted sampling and autonomous manipulation.

Abstract

Conventional fluid-driven soft grippers typically depend on external sources, which limit portability and long-term autonomy. This work introduces a self-contained soft gripper with fixed size that operates solely through internal liquid redistribution among three interconnected bistable snap-through chambers. When the top sensing chamber deforms upon contact, the displaced liquid triggers snap-through expansion of the grasping chambers, enabling stable and size-selective grasping without continuous energy input. The internal hydraulic feedback further allows passive adaptation of gripping pressure to object stiffness. This source-free and compact design opens new possibilities for lightweight, stiffness-adaptive fluid-driven manipulation in soft robotics, providing a feasible approach for targeted size-specific sampling and operation in underwater and field environments.

Figures (9)

• Figure 1: The pictures showing the working mechanism of the self-sustaining fluid-driven gripper. (a) The original state and snap-through state of the fundamental unit of the self-sustaining fluid-driven gripper. (b) The complete gripper structure that utilizes a snap-through response to hold the fish oil bottle. (c) The data curves that illustrate the simulation curve of pressure-volume change along equilibrium path (Axissymm. Simulation), simulation curve of pressure-volume change under snap-through response (3D Simulation), and experimental curve of pressure-volume change under snap-through response (Experimental Data).
• Figure 2: Modeling and simulations. (a, c) 3D modeling of the contact chamber and gripping chamber. (b, d) Numerically obtained 3D deformation processes of the contact chamber and gripping chamber in general-static analysis.
• Figure 3: Pressure–volume response of the snap-through membranes with different tilt angles in gripping chambers along the equilibrium and snap-through paths. (a) Pressure–volume curves of snap-through membranes with various tilt angles along the equilibrium path. (b–f) Comparison of the pressure–volume curves between the equilibrium and snap-through paths for tilt angles of $45^{\circ}$, $40^{\circ}$, $35^{\circ}$, $30^{\circ}$, and $25^{\circ}$, respectively.
• Figure 4: Pressure–volume response of the snap-through membranes with a $45^{\circ}$ tilt angle in the gripping and contact chambers. (a) Effect of material variation on the pressure–volume response. (b) Pressure–volume response of the contact chamber along the equilibrium and snap-through paths.
• Figure 5: Design and experimental setup of the gripping module. (a–b) Schematic diagrams showing the overall configuration of the fixed-size gripping module. The three orange chambers correspond to the contact chamber and two gripping chambers; the green components represent clamping fixtures used to attach the module to supporting structures, and the blue component denotes a generic platform (e.g., robotic arm or mobile base) capable of carrying the module. (a) Grasping state; (b) initial undeformed state. (c) Photograph showing the gripping module mounted on the robotic arm for proof-of-concept experiments.