Photoreceptor motion sensor using a segmented photosensor array

A method for determining the velocity of a photoreceptor belt moving in a process direction, said photoreceptor belt characterized as having a series of apertures along an edge extending in a row which is parallel to said process direction, the method comprising the steps of:

• positioning an illumination source adjacent said photoreceptor belt so that a band of illumination is directed along said row of apertures, at least two of said apertures being simultaneously illuminated,
• placing a segmented position sensor on the side of the photoreceptor opposite that occupied by said illumination source, said position sensor aligned so that illumination from said illumination source is viewed over a group of sensor segments through at least two of said apertures as the photoreceptor belt moves therepast, said sensors producing output signals representing the light distribution intensity sensed by said group of sensor signals during a sampling period,
• calculating the centroid positions of said intensity distributions, and
• calculating the velocity of the belt using the centroid position information from at least two sampling periods.