Image Number 5 for United States Patent #5208633.
In an imaging device having a belt supporting image on an image supporting surface and moving along an endless path in a process direction, an exposure device for forming images on the image supporting surface, an arrangement is provided to derive information about belt position with respect to the exposure device. The belt is provided with at least one fiducial opening or target at a belt edge, and a sensor is arranged with respect to the belt and the fiducial opening, to sense illumination directed through the fiducial opening. An illumination source is provided at a fixed position with respect to the exposure device and the sensor to directing illumination to the sensor, when the fiducial opening is aligned with the sensor, including at least two independently detectable illumination sources arranged along a cross process direction. Belt position with respect to the exposure device is then determined from the amount of occlusion of one of the first and second independently detectable illumination sources. Control of belt position may be split between image processing methods and mechanical methods.