JPS6446776A - Printing device - Google Patents

Abstract

PURPOSE:To detect such a fault as a laser beam is not projected exactly due to a fault of a laser beam generator, etc., and to contrive to improve the reliability, by photodetecting a part of the laser beam, and comparing it with a font data. CONSTITUTION:By a memory access circuit 2, a data which is read out of a font memory 1 is converted from an electric signal to an optical signal by a laser beam generator 3, and projected as a laser beam on a photosensitive drum 4. A part of the laser beam is reflected by a reflecting plate 7, and thereafter, goes into a photodetecting part 8, and converted to an electric signal (b) by a light-electricity converting circuit 9. A comparing circuit 10 compares a signal (a) which is read out of the memory access circuit 2 and the signal (b) which is converted to the electric signal by the light-electricity converting circuit 9, and when a discrepancy is detected, an abnormality is informed to an external device by a signal (c). In such a way, such a fault as the laser beam is not projected normally can be detected.