Image forming device

Abstract

In an image forming device using a laser beam having light components of three wavelengths, a pair of photosensor units are provided at a point adjacent the start of the scan line to calibrate or adjust the focus of the component wavelengths at the same impact point prior to printing. Each of the two photosensor units has three phototransistors, one phototransistor sensitive to each wavelength. The first photosensor unit detects the laser beam components and sends a detection pulse that synchronizes the control circuits for each of the three component wavelengths and initiates a time delay in each circuit. The second photosensor is connected to a time delay circuit for each of the component wavelengths and is also connected to a LED associated with each component wavelength to indicate its strike on the appropriate phototransistor. When a pulse of each component wavelength, appropriately time delayed corresponding to a data position is emitted, the second sensor indicates proper positioning of the impact point by lighting the associated LED. Where the impact point of one or more of the component wavelength pulse does not strike the second sensor, the operator can focus the impact point using volume variable resistor, correct focus being indicated by a lighted LED, to obtain a focused impact point thereby establishing accurate timing delays for each component wavelength.