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Hybrid Gripper with Passive Pneumatic Soft Joints for Grasping Deformable Thin Objects

Ngoc-Duy Tran, Hoang-Hiep Ly, Xuan-Thuan Nguyen, Thi-Thoa Mac, Anh Nguyen, Tung D. Ta

Abstract

Grasping a variety of objects remains a key challenge in the development of versatile robotic systems. The human hand is remarkably dexterous, capable of grasping and manipulating objects with diverse shapes, mechanical properties, and textures. Inspired by how humans use two fingers to pick up thin and large objects such as fabric or sheets of paper, we aim to develop a gripper optimized for grasping such deformable objects. Observing how the soft and flexible fingertip joints of the hand approach and grasp thin materials, a hybrid gripper design that incorporates both soft and rigid components was proposed. The gripper utilizes a soft pneumatic ring wrapped around a rigid revolute joint to create a flexible two-fingered gripper. Experiments were conducted to characterize and evaluate the gripper performance in handling sheets of paper and other objects. Compared to rigid grippers, the proposed design improves grasping efficiency and reduces the gripping distance by up to eightfold.

Hybrid Gripper with Passive Pneumatic Soft Joints for Grasping Deformable Thin Objects

Abstract

Grasping a variety of objects remains a key challenge in the development of versatile robotic systems. The human hand is remarkably dexterous, capable of grasping and manipulating objects with diverse shapes, mechanical properties, and textures. Inspired by how humans use two fingers to pick up thin and large objects such as fabric or sheets of paper, we aim to develop a gripper optimized for grasping such deformable objects. Observing how the soft and flexible fingertip joints of the hand approach and grasp thin materials, a hybrid gripper design that incorporates both soft and rigid components was proposed. The gripper utilizes a soft pneumatic ring wrapped around a rigid revolute joint to create a flexible two-fingered gripper. Experiments were conducted to characterize and evaluate the gripper performance in handling sheets of paper and other objects. Compared to rigid grippers, the proposed design improves grasping efficiency and reduces the gripping distance by up to eightfold.
Paper Structure (19 sections, 7 equations, 10 figures)

This paper contains 19 sections, 7 equations, 10 figures.

Table of Contents

  1. INTRODUCTION
  2. Hybrid Gripper Design and Prototype
  3. Gripper fingers
  4. Soft pneumatic ring
  5. Gripper prototype
  6. Experiments
  7. Soft joint stiffness experiments
  8. Grasping experiments
  9. Thin-large object grasping experiment
  10. Grasping & manipulation of different objects
  11. Grasping paper experiment using hybrid and rigid gripper
  12. Experiment Results and Discussions
  13. Fundamental experiment results
  14. Grasping experiment results
  15. Thin-large object grasping experiment
  16. ...and 4 more sections

Figures (10)

  • Figure 1: Hybrid gripper with soft pneumatic rings is used to grasp deformable objects, thin objects, and a variety of other objects. (a) The way humans use finger hand to pick up a sheet of paper; the rest is our gripper grasping, (b) a sheet of paper, (c) a PET bottle, (d) a water-filled plastic cup, (e) a paper roll, (f) a plastic box, (g) a gum box, (h) a cylinder Box, (i) a mobile charger, (j) a glue stick.
  • Figure 2: Hybrid gripper design and prototype (a) Gripper including dimensions of two fingers in grasping operation and predetermined dimensions of the fingertip ($R_c=20mm$, $d_1=31mm$, $\beta=20.64°$) with $d$ standing for the distance between two contact points, $d_f$ standing for the distance between two fingers and $d_e$ standing for the extended distance of bending fingertip. (b) Exploded view of the finger including 7 components: finger body, fingertip adapter, fingertip, rivet-screw, M2 screws connecting all rigid parts, soft pneumatic ring consisting of soft core and silicone tube. (c) The drawing view shows the dimension of the finger. (d) The final finger after fabricating and assembling.
  • Figure 3: Soft pneumatic ring. (a) Three stages of fabricating soft core including Stage 1 Main body Casting, Stage 2 Cap Closing, and Stage 3 Silicone tube inserting. (b) The drawing view shows the dimension of the cross-section soft core. (c) The components of the final soft pneumatic ring consist of soft core, a layer of fabric, and plastic cables. (d) The final finger consists of hard links and a soft pneumatic ring.
  • Figure 4: Grasping experimental system using the hybrid gripper.
  • Figure 5: Soft joint stiffness experiment. (a) A picture of the actual system, (b) experiment devices and force applied on testing fingertip. $F_z \text{ and } F_y$ are the force exerted from the joint of the force sensor device, and $\uptau$ is the torque generated from the soft ring to the testing fingertip. Based on this, the torque is calculated by Eq. \ref{['eq: torque experiment 1']}.
  • ...and 5 more figures