A Comprehensive Experimental Characterization of Mechanical Layer Jamming Systems

TL;DR

This paper addresses how to design mechanical layer jamming systems with tooth-like interlocks to modulate stiffness under bending and torsion. It presents a systematic experimental protocol on 27 geometries built from dual materials and actuated by vacuum, evaluating bending, twisting, and interlayer separation. The results show that the jammed state can achieve up to $5$-fold increases in bending stiffness and up to $3.2$-fold increases in torsional stiffness, with separation force increasing as gap decreases and height increases. The study provides principled design guidance for soft robotics and suggests avenues for extended 3D arrangements and rapid jam–unjam transitions.

Abstract

Organisms in nature, such as Cephalopods and Pachyderms, exploit stiffness modulation to achieve amazing dexterity in the control of their appendages. In this paper, we explore the phenomenon of layer jamming, which is a popular stiffness modulation mechanism that provides an equivalent capability for soft robots. More specifically, we focus on mechanical layer jamming, which we realise through two-layer multi material structure with tooth-like protrusions. We identify key design parameters for mechanical layer jamming systems, including the ability to modulate stiffness, and perform a variety of comprehensive tests placing the specimens under bending and torsional loads to understand the influence of our selected design parameters (mainly tooth geometry) on the performance of the jammed structures. We note the ability of these structures to produce a peak change in stiffness of 5 times in bending and 3.2 times in torsion. We also measure the force required to separate the two jammed layers, an often ignored parameter in the study of jamming-induced stiffness change. This study aims to shed light on the principled design of mechanical layer jammed systems and guide researchers in the selection of appropriate designs for their specific application domains.

Figures (9)

• Figure 1: Design of the layer jamming structure. (a) Showing the 3D printed structure with the teeth that enable mechanical layer jamming. (ab) Cross-sectional view through the teeth showing one layer and the geometric parameters. The gap is uniform along both the length and width axes. (bc) A composite layer without any teeth. The height is the only tunable parameter.
• Figure 2: Setup of the bending test (a) and the end position after a 15 mm displacement of the load (b). In this case the sample is unjammed.
• Figure 3: Setup of the twisting (a) and pulling (b) and (c) tests. The samples are glued to a support during the pulling test. The linear actuator and the load cell (b) is the same for the bending and the pulling tests.
• Figure 4: Force–displacement curves measured during the bending test at 1 mm/s for samples of different tooth heights. Opaque lines indicate the mean of the repetitions, and shaded areas represent one standard deviation.
• Figure 5: Stiffness values for samples measured at different velocities - for the jammed, unjammed and composite states (top) and the ratio of mean stiffness between jammed (j) and unjammed (u) states (bottom). The data were grouped by diameter to illustrate the increasing trend of stiffness with height and gap. Composite state varies only with the height and it is the same values over group diameter.