Patent ID: 7557822

Claim:
An image forming apparatus comprising: a controller which outputs image signals of plural colors corresponding to a received image forming command; and an engine which is provided with an image forming unit in correspondence to each of the plural colors, each of the image forming units operative to form a latent image on a latent image carrier by scanning a light beam, modulated according to the image signal of the corresponding color applied from the controller, in a main-scan direction by means of an oscillation mirror resonantly oscillating according to a drive signal, and to form a toner image by developing the latent image with a toner of the corresponding color, and which forms a color image by superimposing the toner images of the plural colors on a transfer medium, wherein the engine comprises in correspondence to each of the plural colors: a detector unit which detects a drive period of the oscillation mirror provided at the image forming unit for the corresponding color and outputs a drive period signal related to the drive period; a drive signal controlling section which outputs a drive signal for controlling the drive of the oscillation mirror; and a mirror controlling section which drives the oscillation minor into operation based on the drive signal outputted from the drive signal controlling section, wherein the controller generates a reference signal common to the plural colors and outputs the reference signal to the drive signal controlling sections for the plural colors at a time, wherein each of the plural drive signal controlling sections receives the drive period signal outputted from the corresponding detector unit and the reference signal from the controller, so as to control the drive signal in a manner to establish a predetermined relationship between a phase of the reference signal and a phase of the drive period signal, and wherein the resonant frequency of the oscillation mirror is matched with the frequency of the drive signal such that each oscillation mirror is driven at a common resonant frequency, before controlling the drive signal in a manner to establish the predetermined relationship between the phase of the reference signal and the phase of the drive period signal.