Registration system for a moving substrate

摘要

A registration system is provided for maintaining accurate correspondence between an image on a moving substrate 14 and the action of an operating element 16 with respect to the substrate. A comparison optical device is mounted such that timing marks 22 on the substrate pass in correspondence with the comparison optical device when the substrate is moving. A detector senses the intensity of radiation reflected from the substrate through the comparison optical device and generates a firing signal based on the reflected radiation intensity. The firing signal is provided to the operating element to activate it in correspondence to the passage of the timing marks. The operating element may be an electrostatic write head in a colour printer. The comparison optical device may comprise a grating having a line spacing corresponding to the spacing of the timing marks. The grating may comprise two or four displaced grating sections or a single grating section having lines of two or four colours. Such a grating is usable to provide quadrature multiplication of the output of the detector. The timing marks extend along each edge of the substrate, and two detectors and comparison optical devices are used for skew detection. The skew signal is used to adjust the position of the operating element. Two longitudinal tracks 24 are sensed by optical detectors to provide signals for transverse positioning of the operating element.