JPH0449837A - Detection of number of revolutions of brushless dc motor - Google Patents

Abstract

PURPOSE:To lower a signal frequency and eliminate fear of mistake in response of a control system even during high speed revolution by dividing a signal of a magnetoelectric converting element to 1/(n-2) to form a number-of- revolutions detecting signal. CONSTITUTION:A stator 4 winding a coil 3 for each phase is arranged at the inside of a rotor magnet 2 of rotatable rotor 1 and the coil 3 is commutated by a magnetoelectric converting element 6 such as a hall element for each phase provided to a printed circuit board 5. An output signal of the magnetoelectric converting element 6 for commutation is used as the signal for detecting the number of revolutions. Particularly, the number of poles of motor is reduced to 1/(n-2) so that one pulse signal is outputted for a single rotation in order to eliminate influence of fluctuation of magnetization pitch of the rotor magnet 2. Thereby, a control circuit can easily be formed in the high speed region without lowering the rotating accuracy and moreover effect of low cost may be obtained since the magnet for detecting the number of revolution and coil are no longer necessary.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for detecting the rotational speed of a brushless DC motor for a high-speed polygon scanner used in a laser beam printer (LBP), digital copying II (DPPC), etc.

[Conventional technology]

In this field, PLL speed control is the mainstream control method for obtaining a constant speed of the motor.

Since this motor requires high rotation accuracy without wow and flutter, the rotation speed detection method for this control generally uses a pulse signal for rotation speed detection of, for example, about 100 pulses/rotation.

FIG. 3 is a longitudinal cross-sectional view of a conventional example, in which a stator 4 having a winding vA3 wound for each phase is arranged inside a rotor magnet 2 of a freely rotatable rotor 1, and the winding 3 is V! of Hall elements etc. for each phase provided on the printed board 5! ! 1 is commutated by the conversion element 6. A rotation speed detection magnet 7 is arranged on the rotor 1, and a rotation speed detection coil 8 provided on the printed board 5
generate a pulse signal.

[Problem to be solved by the invention]

In high-speed LBP and high-speed DPPC, which have become mainstream in recent years, the signal frequency of the conventional rotational speed detection method described above is high, causing problems in control responsiveness.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for detecting the rotational speed of a direct current motor, which reduces the signal frequency and eliminates the risk of response errors in the control system even at high speeds.

[Means to solve the problem]

In order to solve the above problems, the rotation speed detection force method of the brushless DC motor of the present invention involves winding a winding for each phase, a stator, a rotor magnet facing the stator, and a fixed side. In the method for detecting the rotation speed of a bra coil DC motor with n≧4 poles comprising a magnetoelectric conversion element for commutation for each phase, the signal of the magnetoelectric conversion element is divided into 1/(n, /2). This is used as a rotation speed detection signal.

That is, we focus on the output signal of the Hall element, which captures changes in the magnetism of the motor's rotor magnet and uses it as a commutation signal for motor winding, and use this signal as the rotational speed detection signal.

[Effect]

By frequency-dividing the signal of the magneto-electric transducer for commutation by 1/(n/2), a rotation speed detection signal of one pulse per motor revolution can be obtained, ensuring control response even at high speeds of 10,000 revolutions or more. The circuit configuration of the control system is relatively simple. By the frequency division, variations in the @magnetic pitch of the rotor magnets are eliminated from the rotational speed detection signal.

Further, the possibility of a decrease in rotational accuracy such as wow and flutter due to the low frequency of the control signal is avoided because a high-inertia mirror is mounted and the mirror rotates at high speed.

〔Example〕

FIG. 1 is a cross-sectional view of the main part of the embodiment, showing the I-1 cross section in FIG. FIG. 2 is a longitudinal sectional view of FIG. 1. In the figure, a stator 4 is arranged inside a rotor magnet 2 of a rotor 1 which can freely rotate twice, and a stator 4 is wound with a Q-coil winding 3 for each phase.
The winding 3 is commutated by a magnetoelectric conversion element 6 such as a Hall element provided for each phase on a printed board 5. Then, the output signal of the commutation magnetoelectric conversion element 6 is used as a rotation speed detection signal. In particular, in order to eliminate the influence of variations in the magnetization pitch of the rotor magnets 2, the frequency is divided by 1/(n-2) of the number of motor poles (n) so that one pulse signal is output per rotation. This embodiment eliminates the need for the rotation speed detection magnet 7 and the rotation speed detection coil 8 shown in the conventional example.

〔Effect of the invention〕

This invention consists of a stator in which a winding is wound for each phase, a rotor magnet facing the stator, and a magnetoelectric conversion element provided on the stationary side for commutation for each phase with n≧4 poles. In the method for detecting the rotational speed of a brushless DC motor, the signal of the magnetoelectric conversion element is frequency-divided by 1/(n/2) and 7
Since the rotation speed detection signal is used as the rotation speed detection signal, the configuration of the control circuit can be simplified in the high speed range of 10,000 rotations or more without reducing rotation accuracy, and there is no need for a rotation speed detection magnet and coil. The effect of cost reduction can be achieved by reducing the cost.

[Brief explanation of drawings]

Fig. 1 is a cross-sectional view of the main part of the embodiment.
2 is a longitudinal sectional view of FIG. 1, and FIG. 3 is a longitudinal sectional view of a conventional example. 2... Rotor magnet, 3... Winding wire, 4... Stator,
6... Magnetoelectric conversion element, 7... Rotation speed detection magnet, 8
...Rotation speed detection coil.

Claims (1)

[Scope of Claims] 1) A stator having a winding wound for each phase, a rotor magnet facing the stator, and a magnetoelectric conversion element provided on the stationary side for commutation for each phase. In the method for detecting the rotation speed of a brushless DC motor with n≧4 poles, the signal of the magnetoelectric conversion element is frequency-divided by 1/(n/2) to obtain the rotation speed detection signal. Rotation speed detection method.