SCAL for Pinch-Lifting: Complementary Rotational and Linear Prototypes for Environment-Adaptive Grasping

TL;DR

This paper introduces environment-adaptive pinch-lifting fingers based on a novel SCAL mechanism, enabling robust grasping of various objects with minimal sensing, through two complementary designs tested in diverse scenarios.

Contribution

It presents two new SCAL-based finger designs, SCAL-R and SCAL-L, that adaptively grasp objects by combining active and passive mechanisms for environment-aware manipulation.

Findings

Both designs achieve consistent grasps across multiple trials.

The fingers can handle small parts, boxes, jars, and tape rolls effectively.

A quasi-static analysis provides useful force models for design guidance.

Abstract

This paper presents environment-adaptive pinch-lifting built on a slot-constrained adaptive linkage (SCAL) and instantiated in two complementary fingers: SCAL-R, a rotational-drive design with an active fingertip that folds inward after contact to form an envelope, and SCAL-L, a linear-drive design that passively opens on contact to span wide or weak-feature objects. Both fingers convert surface following into an upward lifting branch while maintaining fingertip orientation, enabling thin or low-profile targets to be raised from supports with minimal sensing and control. Two-finger grippers are fabricated via PLA-based 3D printing. Experiments evaluate (i) contact-preserving sliding and pinch-lifting on tabletops, (ii) ramp negotiation followed by lift, and (iii) handling of bulky objects via active enveloping (SCAL-R) or contact-triggered passive opening (SCAL-L). Across dozens of trials on small parts, boxes, jars, and tape rolls, both designs achieve consistent grasps with limited tuning. A quasi-static analysis provides closed-form fingertip-force models for linear parallel pinching and two-point enveloping, offering geometry-aware guidance for design and operation. Overall, the results indicate complementary operating regimes and a practical path to robust, environment-adaptive grasping with simple actuation.