A method of
processing signals in a
rotary encoder of the kind which comprises at least one annular track of encoding regions arranged as an alternating pattern of first encoding regions and second encoding regions, comprises providing a first
detector at a first
fixed position which is arranged to produce a first alternating output
signal as the track of encoding regions rotates about its axis past the
detector, the alternating
signal comprising a series of transitions between a first state corresponding to the
detector being aligned with a first encoding region and a second state corresponding to the detector being aligned with second encoding region;providing a second detector at a second
fixed position which is arranged to produce a first alternating output
signal as the track of encoding regions rotates about its axis past the detector, the alternating signal comprising a series of transitions between a first state corresponding to the detector being aligned with a first encoding region and a second state corresponding to the detector being aligned with second encoding region;identifying a
usable pair of transitions in the first and second signals comprising a transition of the first signal from the first state to the second state followed by a transition in the second signal from the first state to the second state without in the intervening period having changed from the second state to the first state; measuring the elapsed time between the transitions of the identified
usable pair, and determining the
angular velocity by combining the elapsed time with the spacing between the first and second detectors.