Patent ID: 7073872

Claim:
An apparatus for driving a motor that includes a rotor having a field section generating field magnetic flux and plural phases of coils, the apparatus comprising: a power source that supplies a direct-current voltage; a power supply unit that includes a plurality of switching elements, and converts direct-current voltage from the power source into a desired alternating-current voltage to supply driving power to the motor; a position detector that detects a rotating position of the rotor of the motor and outputs the detection result as a position signal; a controller that controls switching action of the switching elements of the power supply unit based on the position signal; a frequency comparator that, during a period after brake control of the motor is started and before the motor speed reaches zero, compares frequencies of at least two consecutive periods in the position signal, detects a reversed state in which a frequency of the signal in a later output period becomes higher than a frequency of the signal in an earlier output period, and outputs a signal showing the detection result; a rotating state command generator that outputs a command signal for exciting and controlling the coil so as to apply normal torque or reverse torque to the rotor; and a brake changeover unit that selects, as a brake control of the motor, either a reverse torque brake control for braking the rotation of the rotor by applying a reverse torque to the rotor, or a short brake control for braking rotation of the rotor by short-circuiting the coil of the motor, and instructs the controller to implement the selected brake control, wherein the brake changeover unit selects the reverse torque brake control when the detection signal from the frequency comparator does not show the reversed state, or selects the short brake control when the detection signal shows the reversed state when the rotating state command generator is issuing a command signal for applying reverse torque, and then instructs the controller to implement the selected brake control.