Design, Development and Characterization of a Wrap Spring Clutch/Brake Mechanism As a Knee Joint for an Assistive Exoskeleton

Over the past decade, wearable robotics and exoskeletons have been gaining recognition in the field of medical, assistive and augmentative robotics and have led to numerous new innovative mechanisms and designs. Due to fast-paced research activities, the critical importance and performance of established mechanisms such as wrap spring clutch/brake, Wafer Disc Brakes have been overlooked or used ineffectively. This paper describes a practical design approach that will enable the designer to choose a mechanism based on the application of the device, which will promote overall growth in current technology. The Legged Anthropomorphic Robotic Rehabilitation Exoskeleton (LARRE) project used this approach to design, manufacture, and test the knee joint for ground-level walking. This paper provides the reasoning behind the selection of wrap spring clutch, its evaluation, and testing standards as the knee joint. A thorough literature review was conducted to understand the current state of the art. This project collected a rich set of biomechanical data to ensure that the mechanism will produce the right moments and range of motions during walking. To ensure that our mechanism meets the requirements, the mechanism was put through a wide range of stress tests. The paper establishes a methodology to choose a mechanism for an exoskeleton’s joint based on the desired requirements. The outcome of this paper is an analytical based design approach that can be used by other researchers to impart additional traits and weights, which will aid in the development of exoskeleton design.

Modeling and analysis of engagement behavior of one-way clutch with a variable rectangular cross-section torsional spring

This article presents a study on the transient dynamic responses of engagement process of one-way clutch using variable rectangular cross-section torsional spring, which is usually installed on the end of engine for preventing torque being transmitted back. A 2-degree-of-freedom torsional dynamic model is proposed in this article to study the engagement process of clutch under two conditions. Due to the variation of parameters, the torque transfer of the wrap–spring clutch during engagement is described by a multi-parameter equation. The torque transmitted by clutch during engagement process has been described by two phases, spring expanding and spring locking. Physical parameters of spring determining the torque during expanding are discussed. To verify the model, a dynamic experiment on clutch engagement is conducted.

Theoretical Analysis and Numerical Optimization of a Wearable Spring-Clutch Mechanism for Reducing Metabolic Energy Cost During Human Walking

There is a growing interest in assistive wearable devices for laden walking, with applications to civil hiking or military soldiers carrying heavy loads in outdoor rough terrains. While the solution of powered exoskeleton is known to be heavy and energy consuming, recent works presented wearable light-weight (semi-)passive elements based on elastic springs engaged by timed clutches. In this work, we theoretically study the dynamics of a five-link model of a human walker with point feet, using numerical simulations. We propose a novel mechanism of a spring and two triggered clutches, which enables locking the spring with stored energy while the device's length can change freely. For a given gait of joint angles trajectories, we numerically optimize the spring parameters and clutch timing for minimizing the metabolic energy cost. We show that a cleverly designed device can, in theory, lead to a drastic reduction in metabolic energy expenditure.