Mechanical Performance of Actuators in an Active Orthosis for the Upper Extremities

Abstract

The aim of the project OrthoJacket is to develop a lightweight, portable, and active orthosis for the upper limps. The system consists of two special designed fluidic actuators which are used for supporting the elbow function and the internal rotation of the shoulder. A new design of flexible fluid actuator (FFA) is presented that enables more design options of attaching parts, as it is allowed by conventional actuators with a stationary centre of rotation. This advantage and the inherent flexibility and the low weight of this kind of actuator predestined them for the use in exoskeletons, orthoses, and prostheses. The actuator for the elbow generates a maximum torque of 32 Nm; the internal rotation is supported with 7 Nm. Both actuators support the movement with up to 100% of the necessary power. The shells for the arm and forearm are made of carbon reinforced structures in combination with inflatable cushions.

Towards compliant and wearable robotic orthoses: A review of current and emerging actuator technologies

“…It was found that important performance requirements are compliance [37,43,68] ; high specific power [38,42] and force [35,45] ; natural motion characteristics [33,36,63,64] ; infinitely variable backdrivability [15,48,64,75] ; ease of control [15,26,39,58] ; and efficiency [63] . Key physical requirements include low mass [47] , slim form [23,29,48,61,63] , low cost [14,40] , modularity [15,22,33,47] , environmental compatibility [28,68] , and quietness [40] . Lastly, significant safety requirements are sanitary cleanliness [68] ; safe exposed parts [33,38,46,52] ; and limited range of motion (ROM), speed, and force [43] .…”

“…As a guideline, for the orthosis to be comfortably worn all day, its total unsupported or unpowered mass (of which the actuator is only one part) located on the torso, each foot, or in each hand needs to be less than 15%, 1.25%, or 3.75% of the user's body weight respectively [80,81] . A slim actuator form is essential for an orthosis that does not impede its user's motion [61] and is able to be integrated with [47] or hidden under one's clothing. Users appreciate the unobtrusiveness of a slim form-fitting orthosis [48,82,83] .…”

“…Electric actuators' are limited by their need for transmission elements to convert their high-speed, low-torque output to the low speeds and high torques needed to drive orthoses [78,103] . These transmission elements may negatively affect the backdrivability [36,75,104] , efficiency, safety, size [37,48] , mass [105] , noise Compliance similar to human joint [44] Reduced control bandwidth due to compliance Backdrivable [46] Easily integrated with orthosis and user's clothing [47] Variable compliance through antagonistic actuation [68] Robust to wet and dirty environments Force output scales with actuator dimensions or operating pressure [43] [50] , cost [48] , and complexity of electric actuators. Battery technology does not necessarily limit electric orthoses' portability and operation times [10,48] .…”