The measurement of creep of elgiloy springs with a balanced interferometer

Elgiloy is a cobalt alloy that is commonly used as the material of analog clock springs. The rotational creep of loaded ‘clock’ springs made of elgiloy, as measured with a balanced interferometer, is described. For the measurements described here, the spiral clock springs are supported on a radial air bearing and wound up to support the nominal torque load required in the actual application. Two linear interferometers measure displacements of retroreflectors attached to the spring, and rotational creep is calculated by the ratio of the difference between the displacements and the distance between the retroreflectors. Environmental disturbances are nominally cancelled through the difference in the displacements measured by the interferometers at the same distance from the retroreflectors.