Patent ID: 6154292
Filing Date: 2000-11-28
Classification: H04N

Abstract:
An apparatus for scanning with multiple beams emitted from a semiconductor laser by a polygonal mirror, wherein an image is written for each scanning line by each beam of the multiple beams, said apparatus comprising:an automatic light amount control circuit including: (i) a light amount detecting circuit to detect a light amount of each beam for each scanning line, and (ii) a sampling/holding circuit to sample and hold a control voltage corresponding to the detected light amount of each beam for each scanning line, wherein the sampling/holding circuit comprises a plurality of sample-hold circuits, each one being provided for a respective one of the multiple beams and holding the control voltage for the respective one of the multiple beams, said automatic light amount control circuit controlling the semiconductor laser based on the control voltage held by each of the plurality of sample-hold circuits so as to control the light amount of each beam to be a predetermined light amount for each scanning line; anda synchronization control circuit having an index sensor and a light receiving section on which each beam passes, said index sensor detecting a passage of each beam on the light receiving section and generating a passage signal for each beam, and said synchronization control circuit controlling each beam based on the passage signal so as to be synchronized with other beams for each scanning line;wherein the automatic light amount control circuit finishes controlling the light amount of each beam for each scanning line before each beam on each scanning line enters the light receiving section of the synchronization control section so that when each beam passes the light receiving section for each scanning line, each of the plurality of sample-hold circuits holds the control voltage for the respective one of the multiple beams and each beam has the predetermined light amount.