Patent ID: 7840372

Claim:
A method of calibrating a rotary encoder comprising a detectable portion having a plurality of detectable elements about a rotational axis of the encoder and a detector operable to detect the detectable elements and generate an output signal in response to movement of the detectable portion about the rotational axis of the encoder, the method comprising the steps of: (a) rotating the encoder to a selected first speed then allowing the encoder to freely decelerate to a selected second speed over a spindle-free response period; (b) during the spindle-free response period, receiving output signals from the detector, the signals including a plurality of data sets wherein each data set comprises the periods between sampling events occurring in one revolution of the encoder at an angular speed, each sampling event representing a transition between successive detectable elements of the encoder and each sampling event being spaced an angular distance apart from the preceding sampling event; (c) selecting a data set pair from the output signals, wherein the data set pair contains two linearly uncorrelated data sets; (d) defining a model of the angular distances between each sampling event occurring in one revolution of the encoder as a function of one or more damping coefficients and the periods between each sampling event as contained in the data set pair; (e) solving the model for the angular distances for the data set pair using circular closure and dynamic reversal techniques; and (f) establishing an encoder error map using the selected solved angular distances from the model.