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Optimization and redesign of actuators for a medical device

Ooms, E.M.J. (2016) Optimization and redesign of actuators for a medical device.

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Abstract:Demcon is developing custom designed actuators for a medical company which are used in a therapeutic vest worn by patients who suffer from cystic fibrosis. The actuators create oscillating forces in a predetermined force profile on the patient’s thorax that helps to loosen the mucus in the lungs. This can be coughed up at a later stage. The current design of the actuator has magnets to create force with the current through the coil, and leaf springs that cause pretension and linear guidance of the back iron. A sensitivity analysis on the influence of variations in the actuator parameters on the therapy force is performed. These actuator parameters are: mass of the moveable body, stiffness of the springs that are used to connect the moveable body to the static part of the actuator, coil resistance, coil inductance, and the (position dependent) motor constant. This sensitivity analysis is done using simulations in Matlab/Simulink, and analytically using the Taylor series expansion. The Matlab/Simulink model is optimised and the tolerances of the parameters are determined. Results were used to optimise and improve the control system of the actuator. This decreased the dissipated power and improved the accuracy of the applied therapy force. After that, a redesign of the actuator is made in order to lower weight. A therapeutic vest contains eight actuators of 550 grams each, which makes the vest very heavy. The main goal of the redesign is to lower weight to 350 grams per actuator and keep the other functionalities of the actuator the same. The redesign contains a ball bearing which causes linear guidance of the back iron, and helical compression springs to generate the pretension of the back iron. The new actuator is easy to assemble and has a minimum amount of components. Furthermore, the actuator is 15% smaller in volume and weighs only 331 grams.
Item Type:Internship Report (Master)
DEMCON, the Netherlands
Faculty:ET: Engineering Technology
Subject:52 mechanical engineering
Programme:Mechanical Engineering MSc (60439)
Keywords:Demcon, cystic fibrosis, voice coil actuator, sensitivity analysis, design of an actuator
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