Patent ID: 8333450

Claim:
A speed calculation device for a printing apparatus including inkjet recording heads that serve as plural image forming elements, the device comprising: a rotary encoder that generates a plurality of pulse signals with different phases in accordance with rotation of an image forming drum; a detection component that detects rises and falls of respective pulses of the plurality of pulse signals generated by the rotary encoder; a duration calculation component that, each time a rise or fall is detected by the detection component, calculates a total duration of a pre-specified first number of durations representing detection intervals of rises or falls detected prior to the rise or fall currently detected by the detection component; and a speed calculation component that includes a speed detection section that detects a speed relating to rotation of the image forming drum on the basis of the total duration and a rotation angle of the image forming drum that corresponds to one pulse of the pulse signals, and a speed calculation section that, after a pre-specified number of speeds have been detected by the speed detection section, calculates by estimation, on the basis of a pre-specified second number of the speeds relating to rotation of the image forming drum that have been detected by the speed detection section, the speed relating to rotation of the rotating body that is to be detected subsequent to the speed relating to rotation of the rotating body currently detected by the speed detection section, to output a clock signal whereby the image forming elements form dots that respectively constitute an image at a predetermined surface synchronously with the clock signal.