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Design, Calibration, and Control of Compliant Force-sensing Gripping Pads for Humanoid Robots

Yuanfeng Han, Boren Jiang, Gregory S. Chirikjian

TL;DR

The paper tackles the challenge of enabling dual-arm manipulation for small, cost-constrained humanoid robots by developing lightweight, compliant force-sensing gripping pads that measure normal grip force and CoP. It introduces a calibration pipeline to improve CoP accuracy and a three-loop hybrid control framework that integrates force control, surface alignment, and CoP-based adjustments, guided by limit surface friction modeling to prevent slippage. Experimental validation on a NAO robot demonstrates stable grip, accurate force/CoP tracking, and reduced slipping compared to force-only control, even with misaligned or tilted box sides. The work offers a practical, low-cost solution with clear pathways for extension to more complex object shapes and rotations, broadening the applicability of small humanoids in manipulation tasks.

Abstract

This paper introduces a pair of low-cost, light-weight and compliant force-sensing gripping pads used for manipulating box-like objects with smaller-sized humanoid robots. These pads measure normal gripping forces and center of pressure (CoP). A calibration method is developed to improve the CoP measurement accuracy. A hybrid force-alignment-position control framework is proposed to regulate the gripping forces and to ensure the surface alignment between the grippers and the object. Limit surface theory is incorporated as a contact friction modeling approach to determine the magnitude of gripping forces for slippage avoidance. The integrated hardware and software system is demonstrated with a NAO humanoid robot. Experiments show the effectiveness of the overall approach.

Design, Calibration, and Control of Compliant Force-sensing Gripping Pads for Humanoid Robots

TL;DR

The paper tackles the challenge of enabling dual-arm manipulation for small, cost-constrained humanoid robots by developing lightweight, compliant force-sensing gripping pads that measure normal grip force and CoP. It introduces a calibration pipeline to improve CoP accuracy and a three-loop hybrid control framework that integrates force control, surface alignment, and CoP-based adjustments, guided by limit surface friction modeling to prevent slippage. Experimental validation on a NAO robot demonstrates stable grip, accurate force/CoP tracking, and reduced slipping compared to force-only control, even with misaligned or tilted box sides. The work offers a practical, low-cost solution with clear pathways for extension to more complex object shapes and rotations, broadening the applicability of small humanoids in manipulation tasks.

Abstract

This paper introduces a pair of low-cost, light-weight and compliant force-sensing gripping pads used for manipulating box-like objects with smaller-sized humanoid robots. These pads measure normal gripping forces and center of pressure (CoP). A calibration method is developed to improve the CoP measurement accuracy. A hybrid force-alignment-position control framework is proposed to regulate the gripping forces and to ensure the surface alignment between the grippers and the object. Limit surface theory is incorporated as a contact friction modeling approach to determine the magnitude of gripping forces for slippage avoidance. The integrated hardware and software system is demonstrated with a NAO humanoid robot. Experiments show the effectiveness of the overall approach.
Paper Structure (24 sections, 35 equations, 16 figures, 2 tables, 1 algorithm)

This paper contains 24 sections, 35 equations, 16 figures, 2 tables, 1 algorithm.

Table of Contents

  1. Introduction
  2. Gripping Pad Design
  3. Design Concept
  4. Mechanical Design
  5. Electronic Design
  6. Force-sensing Principle
  7. Gripping Pad Calibration and Evaluation
  8. Load Cell Calibration
  9. Measurement Evaluation
  10. CoP Calibration
  11. Contact Analysis
  12. Contact Mechanics
  13. Control
  14. Control System Overview
  15. Task Space Controller
  16. ...and 9 more sections

Figures (16)

  • Figure 1: Humanoid robot retrofitted with force-sensing gripping pads and associated electronics.
  • Figure 2: (a) Mechanical design of the gripping pad. (b) The universal joint formed using the 3-D printed parts. (c) Disassembled compliant mechanism of the gripping pad. (d) A snapshot of a NAO robot wearing a force-sensing gripping pad. (e) Electronic components of the force-sensing gripping pads.
  • Figure 3: Schematics of the measured normal force and CoP of the gripping pad.
  • Figure 4: (a) Load cell calibration. (b) Force-sensing gripping pad CoP calibration setup. (c) CoP calibration parameters.
  • Figure 5: (a) Normal force measurement precision of the force-sensing gripping pads, respectively. Left and right plots show the result for the left and right gripping pads. Black lines show the ground truth for measurement using 0.2, 0.5, 1.0 kg weights. Circles represent measurement using each weight at different calibration positions. (b) CoP measurements precision of the force-sensing grippers. Left and right plots show the left and right gripping pads. Gray, red and blue markers show CoP ground truth and CoP measurements before and after calibration. Circular, square and triangle markers show measurements using 0.2, 0.5, 1.0 kg weights. Black circles show the sensor locations.
  • ...and 11 more figures