LASER REGISTRATION ALIGNMENT TECHNIQUE FOR MULTIPLE IMAGE PRINT BARS
Original Publication Date: 1994-Dec-31
Included in the Prior Art Database: 2004-Apr-07
Xerox Disclosure Journal
Electronic printers are known in the art wherein a plurality of LED print bars are positioned adjacent to photoreceptor surface and selectively energized to create successive scan lines to form color image exposures. The latent image exposures are developed and transferred to an output sheet. The print bars must be in exact alignment in the scan and cross-scan (process) directions in order that the successively formed color images are superimposed in exact registration. Figure 1 shows a LED printing system wherein 2 LED print bars, 4 and 6, are positioned adjacent to the surface of a photoreceptor belt 10 moving in the indicated direction. The print bars are pulsed by video image signals from a source not shown to lay down a series of modulated scan lines in the scan (Y) direction across the surface of the belt. Aligned aperture pairs 12, 14 and 16,18 are formed on opposite sides of the belt. Charge and development stations are omitted for purposes of clarity. Mounted at the end of print bars 4 and 6 is a solid state laser 20, 22, respectively (Figure 2). The output beam from lasers 20,22 pass through beam splitters 24,26, respectively. The beam from laser 20 is, thus, split, one beam passing through to strike a detector 30 mounted on print bar 6 while the second beam is directed downward and will impinge on detector 32 when aperture 18 passes there beneath. Detector 30 will provide an output (registration) signal when two reference pixels on bar 4 and 6 are detected as being in alignment. Additional print bars are registered by providing additional lasers and detectors in the same manner described above. The downwardly projecting beams which are detected by detectors 32, 34 beneath the belt are used to generate signals which set the registration between print bars in the process direction. Print bar 6 writes a line in response to the crossing of an aperture edge by laser 20 beam. Bar 4 also writes a line in response to the crossing of laser 22 to the scan edge.