Patent ID: 8466672
Filing Date: 2013-06-18
Classification: G01D,G01P

Abstract:
1. A method of processing signals in an encoder comprising the following steps: (a) providing a rotary encoder that includes at least one annular track having an axis and encoding regions arranged as an alternating pattern of first encoding regions and second encoding regions, said rotary encoder also including a first detector at a first fixed position which is arranged to produce a first alternating output signal as said annular track of encoding regions rotates about its axis past said first detector, said first alternating output signal comprising a series of transitions between a first state corresponding to said first detector being aligned with a first encoding region being one of said first encoding regions and a second state corresponding to said first detector being aligned with a second encoding region being one of said second encoding regions, said rotary encoder further including a second detector at a second fixed position which is arranged to produce a second alternating output signal as said annular track of encoding regions rotates about its axis past said second detector, said second alternating signal comprising a series of transitions between a first state corresponding to said second detector being aligned with a first encoding region being one of said first encoding regions and a second state corresponding to said second detector being aligned with a second encoding region being one of said second encoding regions; (b) identifying a sequence of four pairs of temporally adjacent transitions in said first and second alternating output signals with each pair of transitions comprising a transition of said first alternating output signal from said first state to said second state followed by a transition in said second alternating output signal from said first state to said second state without in an intervening period having changed from said second state to said first state, said four pairs including two usable pairs and two rejectable pairs; (c) determining a time lapse between transitions of said usable identified pair, (d) determining an angular velocity by combining said elapsed time with a spacing between said first and second detectors; (e) determining a time lapse between transitions of at least one of said rejectable pairs; (f) comparing a time lapse for said usable pair with each time lapse for said rejectable pairs so as to determine an elapsed time error value for each rejectable pair; and; (g) utilizing said elapsed time error value to produce a compensated position measurement for said rotary encoder.