SPARK Hand: Scooping-Pinching Adaptive Robotic Hand with Kempe Mechanism for Vertical Passive Grasp in Environmental Constraints

TL;DR

Problem: robust grasping of objects with varying geometry, especially thin items on surfaces, under environmental constraints. Approach: a passive adaptive SPARK Finger uses a Kempe linkage for vertical straight-line fingertip motion and a parallelogram to maintain orientation, with a passive switch between pinching and scooping modes driven by a single linear actuator and springs. Contributions: mechanical design with a link-length ratio $L_1:L_2:L_3 = 4:2:1$, kinematic and grasp-force analyses, and experimental validation of pinching, symmetric scooping, and asymmetric scooping on thin/flat objects, aided by spacers to improve scooping angle. Significance: a simple, low-cost robotic hand capable of robust manipulation in constrained environments, reducing control complexity.

Abstract

This paper presents the SPARK finger, an innovative passive adaptive robotic finger capable of executing both parallel pinching and scooping grasps. The SPARK finger incorporates a multi-link mechanism with Kempe linkages to achieve a vertical linear fingertip trajectory. Furthermore, a parallelogram linkage ensures the fingertip maintains a fixed orientation relative to the base, facilitating precise and stable manipulation. By integrating these mechanisms with elastic elements, the design enables effective interaction with surfaces, such as tabletops, to handle challenging objects. The finger employs a passive switching mechanism that facilitates seamless transitions between pinching and scooping modes, adapting automatically to various object shapes and environmental constraints without additional actuators. To demonstrate its versatility, the SPARK Hand, equipped with two SPARK fingers, has been developed. This system exhibits enhanced grasping performance and stability for objects of diverse sizes and shapes, particularly thin and flat objects that are traditionally challenging for conventional grippers. Experimental results validate the effectiveness of the SPARK design, highlighting its potential for robotic manipulation in constrained and dynamic environments.

Figures (10)

• Figure 1: SPARK Hand
• Figure 2: Mechanism principle of the SPARK finger.
• Figure 3: Fingertip transition from pinching to scooping poses using stoppers.
• Figure 4: Mathematical model.
• Figure 5: Motion characteristic of the SPARK Hand.(a) Horizontal kinematic characteristic of the mechanism;(b) Vertical kinematic characteristic of the mechanism.