Abstract:
The measurement of instantaneous angular speed is being increasingly investigated for its use in a wide
range of condition monitoring and prognostic applications. Central to many measurement techniques are
incremental shaft encoders recording the arrival times of shaft angular increments. The conventional approach
to processing these signals assumes that the angular increments are equidistant. This assumption
is generally incorrect when working with toothed wheels and especially zebra tape encoders and has been
shown to introduce errors in the estimated shaft speed. There are some proposed methods in literature
that aim to compensate for this geometric irregularity. Some of the methods require the shaft speed to be
perfectly constant for calibration, something rarely achieved in practice. Other methods assume the shaft
speed to be nearly constant with minor deviations. Therefore existing methods cannot calibrate the entire
shaft encoder geometry for arbitrary shaft speeds.
The present article presents a method to calculate the shaft encoder geometry for arbitrary shaft speed
profiles. The method uses Bayesian linear regression to calculate the encoder increment distances. The
method is derived and then tested against simulated and laboratory experiments. The results indicate that
the proposed method is capable of accurately determining the shaft encoder geometry for any shaft speed
profile.
