Motor controlling devices well known in the art, such as that disclosed in Japanese Patent Application Publication No. 2001-61297, include detecting means for detecting the rotational speed of the motor; controlling means; and a motor driver for driving the motor based on commands from the controlling means.
This type of controlling device employs an FG (frequency generator) sensor as the detecting means for detecting the rotational speed of the motor and outputting an FG signal, and an ASIC as the controlling means for outputting an acceleration and deceleration signal based on the FG signal outputted from the FG sensor to the motor driver. By controlling the supply current provided by the motor driver to the motor, this construction can control the speed of the motor through feedback control.
However, the motor requires a large torque on startup and takes a predetermined time to achieve a target rotational speed. One conceivable method of minimizing this predetermined time is to perform feedback control at startup (when the rotational speed deviates most from the desired speed) using a large gain and to switch to a smaller gain when the rising rotational speed of the motor has a smaller deviation from the target value in order to quickly stabilize the motor rotation.