Patent ID: 6396052
Filing Date: 2002-05-28
Classification: G01D

Abstract:
A method of determining a feed position of a print medium in an imaging apparatus, said method comprising the steps of:providing a feed roll with a central feed shaft, said feed roll carrying the print medium such that each of a plurality of rotational positions of said feed shaft has a predetermined relationship with the feed position of the print medium; connecting an encoder device to said feed shaft, said encoder device producing a first periodic signal and a second periodic signal, each said periodic signal being a function of said rotational position of said feed shaft, each period of each said signal corresponding to a predetermined rotational distance of said feed shaft, said two signals being approximately 90 degrees out of phase with each other; creating a modified first signal based upon said first periodic signal, a slope of said modified first signal having a same sign at each said rotational position of said feed shaft, a magnitude of said slope of said modified first signal being equal to a magnitude of a slope of said unmodified first signal at each said rotational position of said feed shaft; creating a modified second signal based upon said second periodic signal, a slope of said modified second signal having said same sign at each said rotational position of said feed shaft, a magnitude of said slope of said modified second signal being equal to a magnitude of a slope of said unmodified second signal at each said rotational position of said feed shaft; adding said modified first signal to said modified second signal to thereby create a summation signal, said summation signal having a plurality of local minimum values, a plurality of local maximum values, and a plurality of substantially linear segments, each said linear segment interconnecting a corresponding said local minimum value with an adjacent said local maximum value; creating a periodic modified summation signal by adding a corresponding constant value to each said linear segment to thereby create a plurality of shifted linear segments such that each said shifted linear segment extends between a substantially equal minimum value and a substantially equal maximum value, each said shifted linear segment representing one cycle of a plurality of cycles of said periodic modified summation signal; determining a value of said modified summation signal at a selected point in time; counting a number of completed said cycles of said modified summation signal at said value at said selected point in time; and calculating the feed position of the print medium based upon said number of completed cycles counted and said determined value of said modified summation signal.