Motor controller

A motor controller comprising:

• a frequency generator means for generating, in accordance with a rotation of a motor, a predetermined number of pulses every time the motor makes one rotation;
• a counter means for outputting a speed value of the motor by counting reference clocks between pulses supplied from the frequency generator means;
• speed error determining means for determining a speed error of the motor by subtracting the speed value from a predetermined value;
• storing means for storing the speed error at a predetermined address;
• filter means for filtering the speed error so that a speed error component, due to a magnetic error, is eliminated from the speed error;
• a servo means for controlling the motor based on an input speed error;
• control means for operating in three modes, a first mode being a mode in which, when the speed error exceeds a predetermined range, the control means deactivates the filter means and the storing means so that the speed error is directly fed to the servo means, a second mode being a mode in which, when the speed error is within the predetermined range, the control means activates both the filter means and the storing means so that the speed error is first subjected to filtering and then fed to the servo means, and a third mode being a mode in which, when the speed error is within the predetermined range and the speed value is a predetermined value, the control means deactivates the filter means and subtracts from the speed error a speed error that was previously stored in the storing means in the second mode so that a difference between the speed error and the stored speed error is fed to the servo means.