A Novel Robotic Variable Stiffness Mechanism Based on Helically Wound Structured Electrostatic Layer Jamming

TL;DR

The paper tackles the challenge of achieving rapid and substantial variable stiffness in compact robotic joints by introducing the Helically Wound Structured Electrostatic Layer Jamming (HWS-ELJ). It couples a helically wound electrode geometry with electrostatic adhesion, predicting an exponential increase in interfacial friction—and thus stiffness—as a function of winding angle, modeled via the Serret–Frenet framework and an Euler belt friction approach. Experimental validation on prototypes demonstrates voltage-driven stiffness modulation within a small footprint, including a robotic finger integration that shows measurable increases in stiffness with applied voltage and preload conditions. The work offers a promising avenue for miniaturized, safe, and adaptable joints in advanced robotics and wearables, while noting high-voltage insulation needs and localized pressure effects as avenues for future improvement.

Abstract

This paper introduces a novel variable stiffness mechanism termed Helically Wound Structured Electrostatic Layer Jamming (HWS-ELJ) and systematically investigates its potential applications in variable stiffness robotic finger design. The proposed method utilizes electrostatic attraction to enhance interlayer friction, thereby suppressing relative sliding and enabling tunable stiffness. Compared with conventional planar ELJ, the helical configuration of HWS-ELJ provides exponentially increasing stiffness adjustment with winding angle, achieving significantly greater stiffness enhancement for the same electrode contact area while reducing the required footprint under equivalent stiffness conditions. Considering the practical advantage of voltage-based control, a series of experimental tests under different initial force conditions were conducted to evaluate the stiffness modulation characteristics of HWS-ELJ. The results demonstrated its rational design and efficacy, with outcomes following the deduced theoretical trends. Furthermore, a robotic finger prototype integrating HWS-ELJ was developed, demonstrating voltage-driven stiffness modulation and confirming the feasibility of the proposed robotic variable stiffness mechanism.

Figures (7)

• Figure 1: Structural schematic diagram of HWS-ELJ. a) Main structure: two electrode sheets with PI films attached. b) Principle of variable stiffness of the HWS-ELJ. c) Force on a unit electrode during relative sliding. d) Diagram of force analysis on an infinitesimal section of the wound electrode.
• Figure 2: Schematic of the Geometric Parameters of the HWS-ELJ
• Figure 3: Fabrication process of the prototype. Step I: Attach the dielectric film to the flexible electrode 1. Step II: Attach the flexible electrode 1 coated with dielectric film to the cylinder with helical grooves. Step III: Wrap the flexible electrode 2 coated with dielectric film around the cylinder with helical grooves.
• Figure 4: A tensile test of uniform relative sliding under a series of voltages. a) Validation experiment setup. b) Schematic diagram of force acquisition with a 6-axis force sensor. c) Relationship between the force sensor output and the end tension.
• Figure 5: Comparison of Output Force vs. Voltage Under Various Loads for the HWS-ELJ.