Scanning clock generating device for optical scanner

In an optical scanner of a type scanning a desired surface by a deflected light beam and without using an F-theta lens, a scanning clock generating device for generating an image scanning clock the frequency of which is continuously variable, comprising:

• an oscillator for oscillating a reference clock;
• a first frequency divider for dividing a frequency of the reference clock to produce a position control clock;
• an up-down counter for stepwisely varying a division ratio N which is assigned to said first frequency divider;
• a controller for, in the event of scanning a scanning range which is divided into K blocks BLi (i=1 to K), driving based on a predetermined finite series Mi (i=1, 2, . . ., K) said up-down counter responsive to every Mi pulses of the position control clock in an "i" block BLi (i=1 to K), thereby stepwisely switching over the division ratio N;
• and
• a phase locked loop for generating a scanning clock a frequency of which continuously varies responsive to the stepwise variation of the frequency of the position control clock.