DYNAMIC BELT TRACKING USING SPECKLE METROLOGY
Original Publication Date: 1994-Aug-31
Included in the Prior Art Database: 2004-Apr-07
Xerox Disclosure Journal
Multicolor printing in an electrostatic printing machine necessitates that a photoconductive belt be accurately tracked in both the circumferential and lateral directions. The present process of tracking the photoconductive belt with timing marks and lateral low friction rolls impedes tracking ability when image on image transfer technology is desired. At least 40 percent of all image registration problems are related to the edge of the photoconductive belt. The edge profile is typically smooth at 400-500 microns, of which approximately 150 microns are desired for lateral tracking. Motion control, in the process direction requires a positional accuracy of 25 microns or less, creating a need to directly encode the photoconductive belt for servomechanism control. Specifically, the use of a laser and a matrix array detector is proposed to create and measure the speckle pattern (power intensity pattern) produced by the laser as the coherent laser light is reflected off an organic photoconductive belt surface. The detected speckle pattern is then used as a "fingerprint" of the belt position.