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Soft Rigid Hybrid Gripper with Inflatable Silicone Pockets for Tunable Frictional Grasping

Hoang Hiep Ly, Cong-Nhat Nguyen, Doan-Quang Tran, Quoc-Khanh Dang, Ngoc Duy Tran, Thi Thoa Mac, Anh Nguyen, Xuan-Thuan Nguyen, Tung D. Ta

Abstract

Grasping objects with diverse mechanical properties, such as heavy, slippery, or fragile items, remains a significant challenge in robotics. Conventional rigid grippers typically rely on increasing the normal forces to secure an object, however, this can cause damage to fragile objects due to excessive force. To address this limitation, we propose a soft rigid hybrid gripper finger that combines rigid structural shells with soft, inflatable silicone pockets, which could be integrated into a conventional gripper. The hybrid gripper can actively modulate its surface friction by varying the internal air pressure of the silicone pockets, enabling the gripper to securely grasp objects without increasing the gripping force. This is demonstrated by fundamental experimental results, in which an increase in internal pressure leads to a proportional increase in the effective coefficient of friction. The gripping experiments also show that the integrated gripper can stably lift heavy and slippery objects or fragile, deformable objects, such as eggs, tofu, fruits, and paper cups, with minimal damage by increasing friction rather than applying high force.

Soft Rigid Hybrid Gripper with Inflatable Silicone Pockets for Tunable Frictional Grasping

Abstract

Grasping objects with diverse mechanical properties, such as heavy, slippery, or fragile items, remains a significant challenge in robotics. Conventional rigid grippers typically rely on increasing the normal forces to secure an object, however, this can cause damage to fragile objects due to excessive force. To address this limitation, we propose a soft rigid hybrid gripper finger that combines rigid structural shells with soft, inflatable silicone pockets, which could be integrated into a conventional gripper. The hybrid gripper can actively modulate its surface friction by varying the internal air pressure of the silicone pockets, enabling the gripper to securely grasp objects without increasing the gripping force. This is demonstrated by fundamental experimental results, in which an increase in internal pressure leads to a proportional increase in the effective coefficient of friction. The gripping experiments also show that the integrated gripper can stably lift heavy and slippery objects or fragile, deformable objects, such as eggs, tofu, fruits, and paper cups, with minimal damage by increasing friction rather than applying high force.
Paper Structure (21 sections, 14 equations, 13 figures)

This paper contains 21 sections, 14 equations, 13 figures.

Table of Contents

  1. Introduction
  2. Methods and Materials
  3. Hybrid gripper finger in the context of contact theory
  4. Hybrid Gripper Finger Design
  5. Outer Shell
  6. Silicone Air Pocket
  7. Hybrid Gripper Prototype
  8. Experiments
  9. Fundamental Experiment
  10. Grasping Objects Experiments
  11. Grasping Heavy and Slippery Objects Experiments
  12. Grasping Deformable Objects Experiments
  13. Grasping Different Objects Experiments
  14. Experiment Results
  15. Fundamental Experiment Results
  16. ...and 6 more sections

Figures (13)

  • Figure 1: Hybrid robotic gripper for adaptive grasping using inflatable silicone pockets to grasp heavy and slippery objects, deformable objects, and various types of objects (a) egg, (b) tomato, (c) stainless steel weight, (d) tofu, (e) orange.
  • Figure 2: Modeling the contact mechanisms between a hybrid gripper finger and a target object. a) Contact in no pressure condition b) Contact in high pressure condition c) Contact in low pressure condition.
  • Figure 3: Inflation stages of the silicone air pocket at different pressure levels. (a) Total deflated, (b) Slightly inflated, (c) Inflated, (d) Fully inflated.
  • Figure 4: Design model of the outer shell. (a) Assembled view. (b) Front part with three grooves. (c) Back part with load-cell mount. Dimensions are in mm.
  • Figure 5: Fabrication of the silicone air pocket. (a) Female mold (Split in half for easy assembly and disassembly during molding) and Male mold. (b) The three stages of fabrication.
  • ...and 8 more figures