Laser power control for cut-paper printer

Abstract

Electric-photosensitive printing is accomplished with an LD providing a laser scanning beam that is modulated to affect printing, and the power output of the LED is maintained constant through negative feedback by a holding voltage provided by a capacitor having its charge determined only during a non-printing portion of the printing period wherein a plurality of sheets are printed. During the non-printing period, contact of the scanning laser beam with the electro-photosensitive material is disabled while the laser beam is maintained on so that its power may be measured and compared with a reference level to provide a feedback signal for controlling the output of the laser beam, particularly the feedback signal being provided to the holding capacitor only during the non-printing portion of the period, and the holding capacitor being isolated from the feedback signal during the printing portion of the period. As a specific embodiment, a rectangular sheet of electric-photosensitive material is replaceable wound around a drum so that its opposite ends are spaced apart to provide a seam to affect the disablement of the laser beam from contracting the electro-photosensitive material during the non-printing portion of the period, and a separate light source used to detect this seam portion to determine the non-printing portion of the period.