Adaptive-Twist Soft Finger Mechanism for Grasping by Wrapping
Hiroki Ishikawa, Kyosuke Ishibashi, Ko Yamamoto
AI summary
Problem
Soft fingers struggle to adapt to uneven gaps among densely packed objects while maintaining sufficient normal grasping force without complex multi-actuator systems.
Approach
The authors designed a soft finger with a 2-DOF joint unit containing a self-locking variable stiffness mechanism that activates passively as hydraulic pressure increases, enabling adaptive twisting and rigid wrapping with a single actuator.
Key results
- FEA and experiments validated a 2.5 mm design gap achieving ~1.2 Nm locking moment at 1.5 MPa
- Finger successfully twists adaptively in both in-plane and out-of-plane directions to navigate uneven gaps
- Demonstrated secure grasping-by-wrapping of various objects and a 1.5 kg target using only one hydraulic actuator
- Experimental tests confirmed the variable stiffness locking behavior aligns with simulations, showing stronger locking at lower pressures due to plate contact
Why it matters
Simplifies control and fabrication for soft robotic hands in agricultural and food automation by enabling robust, force-controlled grasping in cluttered environments with minimal hardware.
Abstract
This paper presents a soft robot finger capable of adaptive-twist deformation to grasp objects by wrapping them. For a soft hand to grasp and pick-up one object from densely contained multiple objects, a soft finger requires the adaptive- twist deformation function in both in-plane and out-of-plane directions. The function allows the finger to be inserted deeply into a limited gap among objects. Once inserted, the soft finger requires appropriate control of grasping force normal to contact surface, thereby maintaining the twisted deformation. In this paper, we refer to this type of grasping as grasping by wrapping. To achieve these two functions by a single actuation source, we propose a variable stiffness mechanism that can adaptively change the stiffness as the pressure is higher. We conduct a finite element analysis (FEA) on the proposed mechanism and determine its design parameter based on the FEA result. Using the developed soft finger, we report basic experimental results and demonstrations on grasping various objects.