LASER HEAD EXPOSURE TIME CONTROL CIRCUIT

PURPOSE:To output serial print data which is not affected by variation in the rotating speed of a polygon mirror to a laser oscillator by using a signal read out of the rotation of the polygon mirror as the synchronizing clock for the transmission of the serial print data inputted to a data processing circuit. CONSTITUTION:A laser scanning photodetector 4 installed on the path of laser scanning light next to a photosensitive body 1 outputs a negative pulse signal the moment the laser scanning light passes the photodetector and a data processing circuit 6 outputs the serial print data from a host controller to the laser oscillator 7 while synchronizing the data with the signal from a magnetic head circuit 9 according to the leading edge of the pulse signal as the reference of a printing position. Therefore, when the rotating speed of the polygon mirror 8 becomes fast, the period of the signal outputted by the magnetic head circuit 9 becomes shorter correspondingly and the sending speed of the serial print data outputted by the data processing circuit 6 varies associatively with the rotating speed of the polygon mirror 8. Consequently, the position of a latent image recorded on the photosensitive body 1 is not affected by the variation in the rotating speed of the polygon mirror 8.