Minimal Footprint Grasping Inspired by Ants

Ants are highly capable of grasping objects in clutter, and we have recently observed that this involves substantial use of their forelegs. The forelegs, more specifically the tarsi, have high friction microstructures (setal pads), are covered in hairs, and have a flexible under-actuated tip. Here we abstract these features to test their functional advantages for a novel low-cost gripper design, suitable for bin-picking applications. In our implementation, the gripper legs are long and slim, with high friction gripping pads, low friction hairs and single-segment tarsus-like structure to mimic the insect’s setal pads, hairs, and the tarsi’s interactive compliance. Experimental evaluation shows this design is highly robust for grasping a wide variety of individual consumer objects, with all grasp attempts successful. In addition, we demonstrate this design is effective for picking single objects from dense clutter, a task at which ants also show high competence. The work advances grasping technology and shed new light on the mechanical importance of hairy structures and tarsal flexibility in insects.

💡 Research Summary

This paper presents the design, analysis, and experimental validation of a novel robotic gripper inspired by the functional morphology of ant legs, specifically their tarsi (foot segments). The research addresses the challenge of grasping objects in cluttered environments, such as bin-picking, where a minimal gripper footprint is crucial to navigate between tightly packed items.

The core innovation lies in abstracting three key functional features observed in ant tarsi: 1) High-friction microstructures (setal pads), mimicked using a thin, elastic high-friction material (F80 resin). 2) A covering of hairs, reinterpreted here as low-friction, angled TPU filaments that initially separate the friction pads from the object during pre-grasp positioning in clutter, only to deflect and allow pad contact once grasping force is applied. 3) Interactive compliance, replicated through a flexible, single-segment, tarsus-like TPU structure at the tip of each leg that safely deforms upon contact.

The gripper embodiment consists of four long, slim legs (150mm length, 5mm diameter) made of polished stainless steel for low outer friction. The high-friction pad and low-friction hairs cover the lower 100mm of each leg. All legs are actuated by a single timing belt, providing one degree of freedom and inherent passive compliance. The design emphasizes a minimal footprint, quantified by metrics like maximum individual leg footprint area (afp = 35 mm²) and total gripper footprint area (Afp = 140 mm²).

A detailed cantilever beam stress analysis was conducted to ensure structural integrity. Under a worst-case scenario of a 50N total grasp force distributed among legs, with a 120mm moment arm, the maximum bending stress (163 MPa) was calculated to be safely below the yield strength of stainless steel (200 MPa). The analysis also predicted leg deflection (1.56mm) and slope at the tip (1.12°), which informed the design of an inward leg inclination to improve grip stability by pulling objects inward.

Experimental evaluation was performed in two parts. First, the gripper was tested on a diverse set of 18 common household objects (cylinders, boxes, irregular shapes, weights 45g-690g). Each object was grasped from a fixed position and subjected to a dynamic manipulation sequence involving lifting, shaking, and rotating. All grasp attempts on individual objects were successful, demonstrating high robustness. Second, the gripper’s capability for “clutter picking” was demonstrated by successfully extracting single items from a densely packed bin, highlighting the advantage of its slim leg profile.

The work concludes that by abstracting and combining the key functional principles of the ant tarsus—high friction, low-friction pre-contact elements, and terminal compliance—into a simple, low-cost, and single-DoF design, highly effective grasping in clutter can be achieved. This advances gripper technology for logistics and automation while also providing an engineering perspective on the mechanical roles of hairy structures and tarsal flexibility in insect locomotion and manipulation.