Automatic Tool Changer

The Problem

A humanoid robotics company needed interchangeable fingertips for their dexterous grippers—enabling the robot to swap between specialized tools for different manipulation tasks. The primary use case was fiber optic cable plugging, which requires precise positioning and significant insertion/extraction forces.

The interface needed to be small enough to integrate into an existing finger form factor (adding no more than ~25mm to finger length), robust enough to handle substantial loads during plugging operations, and purely mechanical—no pneumatics or active locking elements in the finger itself.

Design Constraints

The load case during cable plugging operations drove the mechanical requirements. The interface must resist substantial forces and moments while maintaining alignment precision tighter than what's needed for the cable plugging task itself.

• Purely mechanical, force-based attachment and removal
• No active electrical or pneumatic locking in the finger
• Insertion/removal forces applied by robot arm (no Z-axis leverage)
• Removal only occurs with deliberate removal action
• Must integrate with existing DH grippers and transfer to custom ADT gripper

Design Strategy

I developed a push-to-connect mechanism with a self-aligning taper that guides initial engagement, followed by a passive draw-in feature that pulls the finger the final 2mm into its seated position. This two-stage approach allows for generous approach tolerances while achieving precise final positioning.

The retention mechanism locks automatically once fully seated and requires a deliberate release action to disengage—preventing accidental detachment during the high forces encountered in cable manipulation tasks. The mechanism is entirely passive on the finger side, with all active elements contained in the gripper-side interface.

Mechanism Design

The self-aligning taper handles initial misalignment during approach, funneling the finger into position as the robot arm moves through the engagement trajectory. Once contact is established, the draw-in feature takes over—using the insertion force to drive the finger the final 2mm while the retention elements engage.

Load transfer through the interface was carefully analyzed to ensure the moment loads from cable manipulation (pinch forces at the fingertip creating moments about the interface) are reacted through the mechanical features rather than relying solely on friction.

Results

The design met all functional requirements while staying within the size envelope needed to integrate with the existing finger geometry. The two-stage engagement approach proved robust to the positioning variability inherent in humanoid arm movements, and the passive retention reliably held through worst-case cable manipulation loads.