Ultra-Low-Impedance Robotic Gripper for High-Bandwidth and Transparent Physical Interaction
Joon Lee, Ari Choi, Seokhwan Jeong
Abstract
Conventional robotic grippers relying on external force sensors or high gear-ratio actuators suffer from high mechanical impedance and limited control bandwidth. To address these limitations, this study proposes a novel 9-DOF, three-fingered Direct-Drive Differential (DDD) gripper that integrates DD motors with an low gear ratio (1:2) differential transmission. This mechanism centralizes the actuator mass at the base to achieve an ultra-low inertia design, while the differential architecture couples motors in parallel to amplify torque for flexion movements. Performance evaluations demonstrate that the prototype delivers a nominal grasping force of 15 N and a fingertip force of 3.1 N, while maintaining a remarkably low system inertia (motor contribution of 0.236%) and mechanical impedance (<700 N/m) within the typical human manipulation frequency range. The proposed hardware successfully resolves the trade-offs among torque, transparency, and kinematics, establishing a robust foundation for highly responsive, sensorless proprioceptive force estimation in dynamic environments.