Motor control device, method of estimating initial position of magnetic pole of rotor, and image forming apparatus

A method of estimating an initial position of a magnetic pole of a rotor of a motor that is of a sensorless type, the method comprising:

• continuously or intermittently applying a voltage to each of a plurality of phases of a stator winding at each of a plurality of energization angles while sequentially changing the energization angles, and at a voltage value and for an energization time period, the voltage value and the energization time period being set such that the rotor does not rotate;
• at each of the energization angles, converting peak values of currents flowing through the phases of the stator winding into a first current component having an electrical angle that is equal to a corresponding one of the energization angles and a second current component that is different in electrical angle by 90 degrees from the first current component;
• and
• estimating the initial position of the magnetic pole of the rotor based on a phase angle of a trigonometric function curve, the phase angle being obtained when a variation of the first current component with respect to each of the energization angles is approximated by the trigonometric function curve, wherein
• the trigonometric function curve has a cycle equal to one electrical cycle of the motor.

An image forming apparatus comprising:

• a plurality of rollers that each convey a sheet of paper from a paper feed cassette;
• a printer that forms an image on the sheet of paper that is conveyed;
• and
• a motor control device that controls a motor that drives at least one of the rollers, the motor being of a sensorless type, wherein
• the motor control device includes:
• a drive circuit that applies a voltage to each of a plurality of phases of a stator winding of the motor, and
• a controller that controls the drive circuit,
• when the controller estimates an initial magnetic pole position of a rotor of the motor in an inductive sensing scheme, the controller:
• (i) causes the drive circuit to continuously or intermittently apply a voltage to the stator winding at each of a plurality of energization angles while sequentially changing the energization angles, and at a voltage value and for an energization time period, the voltage value and the energization time period being set such that the rotor does not rotate;
• (ii) converts peak values of currents flowing through the phases of the stator winding into a first current component having an electrical angle that is equal to a corresponding one of the energization angles and a second current component that is different in electrical angle by 90 degrees from the first current component, each of the peak values being obtained at a corresponding one of the energization angles;
• and
• (iii) estimates the initial magnetic pole position of the rotor based on a phase angle of a trigonometric function curve, the phase angle being obtained when a variation of the first current component with respect to each of the energization angles is approximated by the trigonometric function curve, and
• the trigonometric function curve has a cycle equal to one electrical cycle of the motor.