Gravity Balancing Flexure Spring Mechanisms for Shoulder Support in
Assistive Orthoses
Abstract
Passive shoulder supports show large potential for a wide range of
applications, such as assisting activities of daily living and
supporting work-related tasks. The rigid architectures of currently
available devices, however, may pose an obstacle to finding designs that
offer low protrusion and close-to-the-body alignment. This study
explores the use of mechanisms that employ a flexible element which
connects the supported arm to an attachment at the back and acts as
energy storage, transmission and part of the load bearing structure.
Based on the synthesis method explained in this paper, we conducted a
large scope investigation into possible flexure-based mechanism
topologies. Many potential designs were discovered and are presented,
categorized and compared. Two promising designs were developed into
prototypes that were built and tested on a dedicated test bench. These
mechanisms reduce the necessary moment to lift the arm by more than 80
% throughout 85 % of the range of motion, while staying within 18 cm
and 10 cm distance from the body, respectively. Our study indicates
that, due to its lower protrusion and interface loads, a design with a
tapered flexure connecting the upper arm via a hinge to a spring loaded
slider at the back offers the most promising solution.