Exposure control device for use in electrophotographic printing apparatus

An electrophotographic printing apparatus including:

• a photosensitive image carrier;
• charging means for uniformly electrifying a surface of said image carrier;
• exposing means for selectively exposing the electrified surface of said image carrier with a laser beam to form an electrostatic latent image on the electrified surface, and
• developing means for supplying said image carrier with a developer which selectively adheres to the electrostatic latent image, thereby developing the electrostatic latent image so as to be a visible developed image to be transferred to a sheet of paper, said apparatus comprising
• means for generating a laser beam;
• means for guiding the laser beam from said generating means to repeatedly scan a scanning range constituted by an exposure area and a non-exposure area external to the exposure area, thereby producing a latent image having any of available image densities;
• sensing means having a predetermined sensitivity range and responsive to a laser beam intensity falling within the predetermined sensitivity range, for sensing the laser beam directed to a reference position of the non-exposure area to provide a sense signal;
• means for controlling said generating means to synchronize a timing of a scanning start for the exposure area with the sense signal provided by said sensing means;
• means for energizing said generating means to generate the laser beam having a first laser power while said guiding means guides the laser beam to the exposure area, and having a second laser power while said guiding means guides the laser beam to the reference position of the non-exposure area;
• first setting means setting a first laser control signal serving as a reference for the first laser power which represents one of the available image densities of said latent image;
• second setting means for setting a second laser control signal serving as another reference for the second laser power which is independent of the first laser power, said second laser control signal corresponding to a value falling within the predetermined sensitivity range of said sensing means;
• and
• means for driving said generating means based on the first and second laser control signals set by said first and second setting means.

An apparatus having a scanning area to be exposed by a laser beam for image formation, said apparatus comprising:

• means for generating the laser beam having given intensities;
• means for scanning the scanning area with the laser beam generated by said generating means, said scanning area having an exposure area for image formation and a non-exposure area outside of the exposure area;
• sensing means located at the non-exposure area and responsive to the laser beam scanned by said scanning means, for sensing the laser beam directed to the non-exposure area to provide a sense signal;
• means for energizing the laser beam generated by said generating means in accordance with the sense signal provided by said sensing means, so as to form an image at the exposure area;
• first setting means for setting the laser beam generated by said generating means at one of the given intensities, said one of the given intensities corresponding to the density of the image forced at the exposure area by said energizing means;
• second setting means for setting, independently of the setting by said first setting means, the laser beam generated by said generating means at another intensity which can be sensed by said sensing means;
• and
• means for selecting the given intensities of the laser beam so that the laser beam has the one intensity set by said laser setting means when said scanning means scans the laser beam at the exposure area and that the laser beam has the other intensity set by said second setting means when said sensing means senses the laser beam at the non-exposure area.