Ultra-Low-Impedance Robotic Gripper for High-Bandwidth and Transparent Physical Interaction

2026-08-10

AI Summary

This work addresses the limitations of conventional robotic grippers, which suffer from high friction, inertia, and mechanical impedance due to high gear reduction ratios and rely on external force sensors that increase system complexity. The authors propose a 9-degree-of-freedom, three-fingered differential direct-drive (DDD) gripper featuring a 1:2 low-reduction differential transmission and direct-drive motors. By concentrating actuator mass at the base, the design minimizes moving-part inertia, while dual-motor parallel coupling enhances flexion torque. This architecture achieves high torque output, dexterity, and low mechanical impedance without requiring external force sensors, enabling high-bandwidth physical interaction and seamless intrinsic force estimation. The prototype delivers a nominal grasping force of 18 N, fingertip force of 4.7 N, contributes only 0.236% to system inertia from its motors, and exhibits a maximum passive mechanical impedance of 50.1 N/m when unpowered.

Abstract

Conventional robotic grippers often use high-ratio transmissions to generate grasping torque and external force sensors to measure physical interaction. High-ratio transmissions increase friction, reflected inertia, and mechanical impedance, while external sensors add hardware complexity. To address these trade-offs, this study proposes a novel 9-DOF, three-fingered Differential Direct-Drive (DDD) gripper that combines DD motors with a low-ratio (1:2) differential transmission. The mechanism centralizes actuator mass at the base to minimize moving-link inertia, while the differential architecture couples two motors in parallel to amplify torque during flexion. Experiments show that the prototype delivers a nominal grasping force of approximately 18 N and a fingertip force of 4.7 N, while maintaining a low motor contribution to system inertia (0.236%) and low passive mechanical impedance, with a maximum measured value of 50.1 N/m when the motors are unpowered. The proposed hardware addresses the trade-offs among torque, physical transparency, and kinematic dexterity, providing a foundation for high-bandwidth interaction and sensorless proprioceptive force estimation.

Problem

• robotic gripper
• mechanical impedance
• high-bandwidth interaction
• physical transparency
• torque-dexterity trade-off

Innovation

• Differential Direct-Drive
• ultra-low impedance
• sensorless force estimation
• high-bandwidth interaction
• robotic gripper