Patent ID: 7187400

Claim:
A method for compensating for image misalignment in a bi-directional electrophotographic image forming system, said method comprising: (a) providing a processing circuit and a memory circuit for controlling an image forming apparatus, said image forming apparatus having: (i) a light source that generates a moving light beam that scans across an imaging area of a photosensitive image forming surface, said imaging area having a first edge and a second, opposite edge in at least one scanning direction, and (ii) at least one light-detecting sensor that receives said moving light beam at a location other than at said image forming surface; (b) storing data in said memory circuit corresponding to a first nominal margin of said photosensitive image forming surface, in which said first nominal margin corresponds to a nominal power setting for said light source, and in which said first nominal margin is related to a first time interval between: (i) when a first electrical signal is output from said at least one light-detecting sensor as it is stimulated by said moving light beam traveling in a first scanning direction of said at least one scanning direction; and (ii) when said first edge of said imaging area is reached by said moving light beam, while traveling in said first scanning direction; (c) storing data in said memory circuit corresponding to a second nominal margin of said photosensitive image forming surface, in which said second nominal margin corresponds to said nominal power setting for said light source, and in which said second nominal margin is related to a second time interval between: (i) when a second electrical signal is output from said at least one light-detecting sensor as it is stimulated by said moving light beam, traveling in a second scanning direction of said at least one scanning direction, which is substantially opposite said first scanning direction; and (ii) when said second, opposite edge of said imaging area is reached by said moving light beam, while traveling in said second scanning direction; (d) determining compensating data to be used with said first and second nominal margins, when said light source is operating at a power setting other than said nominal power setting; and (e) when needed, applying said compensating data to said first nominal margin to generate a first corrected margin, and applying said compensating data to said second nominal margin to generate a second corrected margin.