Patent ID: 6955412

Claim:
A print mechanism comprising: a print head assembly comprising a position detector and a marking device, said position detector comprising an imaging device for periodically forming an image of a portion of a print medium; an actuator for moving said print head assembly relative to said print medium in a predetermined direction; and a controller for comparing first and second images formed by said imaging device at first and second times, respectively, in a time interval in which said actuator has moved said print head assembly relative to said print medium and for determining a displacement of said print head assembly between said first and second times, said controller causing said marking device to mark said print medium at locations determined by said determined displacement while said print head assembly is moving relative to said print medium, wherein said actuator moves said print head assembly relative to said print medium at a speed that depends on an input signal to said actuator and wherein said input signal is varied in response to said determined displacement so as to reduce fluctuations in said speed.