MAXFAS: a mobile arm exoskeleton for firearm aim stabilization
Date
2013
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Publisher
University of Delaware
Abstract
Accurately aiming and firing a pistol requires a steady hand. While many devices can steady a shooter's arm or hand by restricting movement or degrees of freedom, few devices actively reduce involuntary tremors while allowing larger voluntary aiming movements. This paper details the design, fabrication, and experimental evaluation of an arm exoskeleton that can actively damp arm tremors while allowing voluntary aiming movements. The MAXFAS (Mobile Arm eXoskeleton for Firearm Aim Stabilization) device allows five degrees of freedom, controlling four degrees of freedom using thin steel cables. The cable-driven architecture allows the control motors to be mounted away from the arm, resulting in device that adds very little weight and inertia to the arm. The cables attach to braces that are mounted on the forearm and upper arm. Weight of MAXFAS is further reduced compared to conventional arm exoskeletons through the careful design and manufacture of the braces using stiff, lightweight carbon fiber composites. The initial design called for tremorous movement to be filtered out from voluntary motion, and an adaptive algorithm to provide a tremor-cancelling signal to the cable control motors. Experiments described in this paper involved a control method which used the motors to only actively allow voluntary motion, thus attempting to passively damp tremorous motion. The device was evaluated on subjects performing a pistol aiming task, using an airsoft pistol with a laser sight. Results indicate that this simpler control mode was effective at reducing the amplitude of motion in all five degrees of freedom. During a simulated shooting task, this control mode improved shooting performance both while subjects were wearing the device, as well as 5 minutes after removing the device. These results will be discussed, and future experiments will be suggested.