In this paper, we propose a flexure spring based gravity compensation device which provides assistance to lift the forearm. Three different spring designs are obtained and evaluated. The synthesis method to obtain these is explained in detail and an experimental evaluation validates the desired gravity balancing properties. It is found that in comparison to a flexure spring with constant thickness, a variable thickness distribution along the spring leads to a drastic reduction of its width, which amounts to 81 % in the presented case, and offers an energy to weight ratio that is 94 % higher. Employing a nested spring design further increases the storable elastic energy of the variable thickness design by 145 % through utilization of the otherwise unused space within the original spring envelope. A proof-of-concept prototype is built to illustrate a practical implementation. The presented synthesis method provides a tool to obtain gravity balancing flexure springs that offer a promising solution for the design of assistive devices which aim to be both wearable and inconspicuous.Index Terms-Gravity balancing, wearable device, assistive orthosis, arm support, flexure spring.

A compact McKibben muscle based bending actuator for close-to-body application in assistive wearable robots Tschiersky, Martin; Hekman, Edsko E.G.; Brouwer, Dannis M.; Herder, Just L.; Suzumori, Koichi

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.

Upper-limb impairments are all-pervasive in Activities of Daily Living (ADLs). As a consequence, people affected by a loss of arm function must endure severe limitations. To compensate for the lack of a functional arm and hand, we developed a wearable system that combines different assistive technologies including sensing, haptics, orthotics and robotics. The result is a device that helps lifting the forearm by means of a passive exoskeleton and improves the grasping ability of the impaired hand by employing a wearable robotic supernumerary finger. A pilot study involving 3 patients, which was conducted to test the capability of the device to assist in performing ADLs, confirmed its usefulness and serves as a first step in the investigation of novel paradigms for robotic assistance.

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-link architecture used in currently available devices, however, may pose an obstacle to finding designs that offer low protrusion and close-to-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, a large scope investigation into possible flexure-based mechanism topologies is conducted. Thereby, many potential designs are discovered, which are presented, categorized and compared. Two promising designs are developed into prototypes, and are built and tested on a dedicated test bench. These two 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. The 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.