Patent ID: 7208902

Claim:
A closed-loop digital speed controlling apparatus that makes a sensor detect displacement of a movable body that is moved by digitally controlling a driving unit, and controls stop of the movable body, the digital speed controlling apparatus comprising: a displacement detector that obtains displacement of the movable body detected by the sensor, by an integral multiple of minimum unit displacement corresponding to a sampling cycle; a target speed calculator that calculates a target speed of the movable body based on the lapse of a sampling time; a current speed calculator that calculates a current speed of the movable body, based on displacement detected by the displacement detector and a difference of a sampling time for detecting the displacement; a target speed determining unit that determines whether a target speed calculated by the target speed calculator is smaller than a predetermined value; a speed corrector that replaces the current speed with a value set in advance, when the target speed determining unit determines that the target speed is smaller than the predetermined value and also when the current speed calculator calculates that the current speed is the minimum unit displacement per the sampling cycle; a speed error calculator that calculates an error between the set value to which the current speed is replaced by the speed corrector and the target speed; and a controller that controls the driving unit based on a speed error calculated by the speed error calculator.