Stress Estimation Using Clock Spring Modeling Techniques in Twist Capsule Design
Hale, Brian D.
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Twist Capsules are rotating electrical connections that are used when low noise electrical signals are required between a stationary connector and a mechanically oscillating one. Twist capsules are used throughout industry especially in areas that require exceptionally clean signals such as the space satellite industry and military applications. Due to the high cost of replacing parts on satellites launched into space and life-sustaining aspects of military applications, accurate modeling of these devices is essential to predict their behavior. Clock spring twist capsules use a flex tape, copper traces between two layers of Kapton, which rolls onto itself tightening against the shaft at one extreme and rolling out against the frame at the other extreme. This cyclic tightening and loosing can cause stresses on these flex tapes consequently, resulting in their failure due to fatigue. Therefore, it is imperative that some method be used to estimate the stresses in the flex tape in order that the optimal design parameters may be calculated. The natural progression from estimating the stresses is to predict the life of the twist capsule. Current techniques involve iteratively building physical models and heritage (what has worked in the past will work in the future) to build twist capsules. This methodology has been sufficient, but a large factor of safety is used during design to cover the lack of assurance in the method. This thesis proposes a new design method using clock spring equations to estimate the torque in twist capsules and the stresses induced into the flex tapes. This new design method accurately predicts operating range, torque, and stress in the normal operating range of the twist capsule sufficient enough for design purposes in a fraction of the amount of time it would normally take to design a twist capsule.
- Masters Theses