Design method of DEMES rotary joint

Abstract

The dielectric elastomer minimum energy structure (DEMES) joint is a kind of soft rotary actuator that consists of a pre-stretched dielectric elastomer (DE) film and a flexible primary frame. The elastic energy stored in the DE film performs work on the frame, which makes the frame bend to a given angle. Applying a voltage on the DE film causes the DE film to relax and the frame can unfold. Removing the voltage causes the frame to bend again. From the perspective of energy conversion, it is proposed that the torque of the DE film on the frame is proportional to the volume of the DE film. This hypothesis was proved through theoretical derivation and was also verified by experiments in two popular types of DEMES rotary joint. Based on the hypothesis, we present a design method for DEMES joints and provide an application example. The proposed hypothesis provides a quantitative relationship between the torque of the DE film and its volume. This is of great significance for the application of DEMES joints in soft robots.

Dielectric elastomer actuators as artificial muscles for wearable robots

“…We also present some simplified dynamic models and compare the different configurations with natural muscle in terms of strain. It worth mentioning that the DEA configurations employ rigid or flexible structures as restrictions, like fibers (Lu et al, 2016), rods, springs (Pei et al, 2004), and frames (Wang et al, 2020a), to improve the desired output characteristics of the actuator, which can also limit its impact on the outside environment.…”

“…For this reason, DEMES are often referred as bi-stable. Wang et al (2020a) developed a design method for a rotational joint based on DEMES. Since human limbs are constituted by a high number of joints, DEMES might be a great type of actuator for orthoses and prostheses.…”

Design and Position Control of a Bionic Joint Actuated by Shape Memory Alloy Wires

“…Their primary objective is to mimic the rotational motion and flexibility inherent in human and animal joints through the integration of mechanical structures, actuators, transmission methods, sensors, and controllers. Bionic joints can be categorized into several groups based on their actuators: electric motors [1,2], hydraulic actuators [3][4][5], pneumatic actuators [6][7][8], and smart material actuators (such as piezoelectric actuators [9][10][11][12], electroactive polymer actuators [13][14][15], shape memory alloy (SMA) actuators [16][17][18][19][20], and twisted and coiled polymer actuators [20,21]).…”