JPH08214526A - Motor fitted with rotational position detector - Google Patents

Abstract

PURPOSE: To enable stable record and reproduction of information by providing a field magnetic pole with a compensative magnetic pole which has a middle magnetic flux density between the magnetic flux density of a mark magnetic pole and the magnetic flux density of other field magnetic pole. CONSTITUTION: A rotor 1 holds a magnet 3, where a field magnetic pole for driving sixteen poles is provided, within a rotor yoke 2, and rotates in a body with a center hub for rotating a flexible magnetic pole disc, and a rotor. And, the driving magnet 13 has a nonmagnetized section 4a in a part of any of the field magnetic poles, whereby the magnetic density of this magnetic pole is made lower than that of other magnetic pole, thus it is constituted as a mark magnetic pole 3A. And, a compensative magnetic pole 3B, which has a magnetized section 4b so that it may has an intermediate strength between that of the magnetic pole 3A provided with a mark and that of the magnetic pole without a mark, is arranged in the next magnetic pole 3B of the rotor 1. As a result, stable record and reproduction can be made because the cogging by the compensative magnetic pole negates and reduces the cogging by the mark magnetic pole.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rotation reference signal such as a so-called index signal indicating the rotation reference timing of an FDD disk and a so-called PG signal indicating the rotation reference timing of the rotation of a cylinder equipped with a VTR rotary head. The present invention relates to a motor with a rotational position detecting device for outputting a rotation position detecting device that reduces cogging torque due to the influence of mark magnetic poles.

[0002]

2. Description of the Related Art The applicant of the present invention has disclosed a mark magnetic pole in which the peak magnetic flux density is lower in one pole of the field magnetic field than in the other magnetic poles in JP-A-2-10569 and Japanese Patent Application No. 5-297415. A technique relating to a motor provided with a rotational position detecting device, which is provided with a discrimination circuit that outputs a rotational reference position signal of a rotor in accordance with a detection voltage corresponding to the mark magnetic pole, has been proposed. According to these techniques, the discriminating operation of the rotation reference position signal is stable regardless of variations in the sensitivity of the magnetoelectric conversion element such as the Hall element and the detection voltage due to the temperature characteristic.

FIG. 8 is an exploded perspective view showing a schematic structure of a conventional motor with a rotational position detecting device in a radial gap type hole brushless motor having an iron core.

The rotor 1 holds a magnet 3 having field poles for driving 16 poles in a rotor yoke 2, and a center hub for rotating and driving a flexible magnetic disk (not shown) and a rotor shaft (both not shown). ) And rotate together.
This drive magnet 3 is provided with a part 4a in which a part of the one pole (for example, the N pole) in the field magnetic field (the part having the strongest magnetic force) is not magnetized or the magnetized part is weakened. The mark magnetic pole 3A is configured such that the magnetic flux density of this magnetic pole is lower than the magnetic flux density of other magnetic poles.

As shown in the figure, the portion having the strongest magnetic force is a substantially central portion near the outer circumference of the one magnetic pole 3A.

On the other hand, on the stator base 9, three-phase drive coils 7a, 7b and 7c are wound around 12 teeth of the stator iron core 5 provided so as to face the field magnetic poles, respectively, and are electrically connected. The three hall elements 6a, 6b, 6c for detecting the field magnetic poles arranged at an angle of 120 degrees are arranged, and the bearing 8 for rotatably supporting the rotor shaft is arranged at the center, and the stator portion Are configured. By directly supporting the rotor shaft on the bearing 8, a direct drive type spindle motor is constructed.

The rotor 1 is rotationally driven by the known rotation principle of the brushrel motor by the interaction of the field magnetic field of the magnet, the drive coil, the Hall element, and the brushless motor drive circuit (not shown). When the mark magnetic pole 3A provided in one pole of the field pole of the drive magnet 3 faces the Hall element, the amplitude of the output voltage is 6 times that of the other magnetic poles.
The magnetization is adjusted to be 5%, and the difference from the output amplitude of the other magnetic poles is discriminated by the discriminating circuit to output the rotation reference position signal.

[0008]

The field magnetic poles generate an attractive force with respect to the stator iron core, and this is what is called cogging torque. However, if the magnetic flux densities of the respective magnetic poles and the respective tooth shapes are uniform over the entire circumference, the phases of the cogging torques generated over the entire circumference are different, so that they are canceled out and become small as a whole. However, if the mark magnetic pole 3A having a portion where the peak magnetic flux density is lower than that of the other magnetic poles is provided in one pole of the field magnetic pole as described above, the condition of uniform all around is broken and the cancellation is performed. As a result of the incompleteness, a large fluctuation is repeated in a cycle corresponding to the number of teeth of the stator per one rotation of the rotor.

FIG. 9 shows the cogging torque of a conventional motor with a rotational position detecting device, and FIG. 10 shows the uneven rotation (W) when this motor is applied to a spindle motor of a flexible disk drive rotating at 300 rpm.
/ F) is a frequency analysis, and the 60 Hz component (300 rp), which is the uneven rotation component due to the cogging torque described above.
m × 12 cycles ÷ 60) is as large as 0.23%. As described above, the cogging torque causes uneven rotation in the rotation of the motor, which may cause a problem in stable recording or reproduction of information, and in turn, may reduce the reliability of the device.

[0010]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and includes a rotatable rotor provided with a magnet having a field magnetic field in which N poles and S poles alternate in the circumferential direction. A stator including an armature coil facing the magnet and a magnetoelectric conversion element that outputs a detection voltage according to the magnetic flux density of the field magnetic field; and a magnetic flux density of one magnetic pole of the field magnetic pole to another magnetic pole. In a motor with a rotational position detecting device comprising a lower mark magnetic pole and a discrimination circuit for outputting a rotational position reference signal of the rotor according to the detected voltage corresponding to the magnetic flux density of the mark magnetic pole, the field magnetic pole And a correction magnetic pole having a magnetic flux density intermediate between the magnetic flux density of the mark magnetic pole and the magnetic flux density of other field magnetic poles.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of a motor with a rotational position detecting device according to the present invention will be described in detail below with reference to FIGS.

FIG. 1 is an exploded perspective view showing a schematic structure of an embodiment of a motor with a rotational position detecting device of the present invention, FIG. 2 is a block diagram for driving the device of the present invention, and FIG. 3 is an operation of the circuit of FIG. 4 is a circuit diagram showing the contents of the block diagram of FIG. In FIG. 1, the same parts as those in the conventional example described above are designated by the same reference numerals.

Explaining it in an exploded perspective view of the motor shown in FIG. 1, the rotor 1 holds a magnet 3 having field poles for driving 16 poles in a rotor yoke 2, and a flexible magnetic disk (not shown). It rotates integrally with a center hub and a rotor shaft (both not shown) that rotate and drive. This drive magnet 3 is provided with a part 4a in which a part of the one pole (for example, the N pole) in the field magnetic field (the part having the strongest magnetic force) is not magnetized or the magnetized part is weakened. ,
The mark magnetic pole 3A is configured such that the magnetic flux density of this magnetic pole is lower than the magnetic flux density of the other magnetic poles. As shown in the figure, the portion having the strongest magnetic force is a substantially central portion near the outer circumference of the one magnetic pole 3A.

Then, in the direction of rotation of the rotor 1 indicated by the arrow, to the same pole 3B (N pole) next to the mark magnetic pole 3A,
A correction having a portion 4b in which the above-described mark is magnetized so that the strength of the magnetic pole 3A with the magnetic pole 4a is intermediate to the strength (magnetic flux density) of the magnetic pole without a mark (S pole). A magnetic pole 3B is provided. The magnetized portion 4b is also a substantially central portion near the outer circumference.

The output amplitude of the magnetic pole 3A serving as the mark magnetic pole when facing the Hall element is the magnetic pole 3 serving as the correction magnetic pole.
The magnetic pole strength excluding B is set to 65%, and the output amplitude when the magnetic pole 3B serving as the correction magnetic pole faces the Hall element is adjusted to 85% of that of the other magnetic poles. It has been given.

Here, as shown in FIGS. 2 to 4, from the Hall elements 6a, 6b, 6c to the brushless motor drive circuit 10.
Three-phase armature coils 7a to 7 according to the signals supplied to the
The rotor 1 rotates in the direction of the arrow by sequentially supplying a drive current to c.

Hall element (HG) accompanying rotation of the rotor 1
From 6a, 6b, 6c, sinusoidal voltages whose phases are shifted by 120 degrees as shown in a, b, c of FIG. 3 are output. This waveform has a small amplitude waveform when the mark magnetic pole 3A faces each Hall element once per one rotation of the drive magnet 3 and an intermediate amplitude waveform when the correction magnetic pole 3B faces each Hall element. Contains. In the figure, the portion indicated by the dotted line is a normal waveform when the mark magnetic pole 3A and the correction magnetic pole 3B are not operated.

The output of each Hall element (HG) 6a, 6b, 6c is supplied to the brushless motor drive circuit 9, and the output c of the Hall element 6c is also supplied to the amplifier circuit 11 shown in FIG. As a result, the waveform shown in FIG. That is, the Hall elements 6 connected in series in FIG.
a to 6c are biased, the output c of the Hall element 6c is appropriately amplified by an amplifier circuit 11 including transistors Q1 to Q10, resistors R3 to R5, diode D4, etc., and output from the emitter of the NPN transistor Q10. This output d is, as shown in FIG. 2, the inverting input terminal of the voltage comparison circuit 14, the peak hold circuit 12, and the shaping circuit 15.
Is supplied to each.

The peak hold circuit 12 detects and holds the maximum value of the input voltage and supplies the output of the waveform shown in FIG. 3e to the reference voltage generation circuit 13. That is, the peak hold circuit 12 is composed of the transistors Q11 to Q17 and the capacitor C1 in FIG. 4, and is output to the emitter of the NPN transistor Q17. The reference voltage generation circuit 13 divides the input voltage into 75% and supplies it as the reference voltage Vt to the non-inverting input terminal (Q18) of the voltage comparison circuit 14. The level of the reference voltage Vt is, as shown in FIG. 3D, the peak value when the Hall element faces the mark magnetic pole 3A and the correction magnetic pole 3
Since it is in the middle of the peak value when it faces B, the output of this voltage comparison circuit 14 is when the Hall element 6c faces the peak of the correction magnetic pole 3B other than the mark magnetic pole 4 as shown in f of FIG. It is "L" and "H" in other cases, and this output f is supplied to the discrimination circuit 15 as shown in FIG. That is, in FIG. 4, R6 and 7 are the reference voltage generating circuit 13
, Q18 to Q22 and the like constitute the voltage comparison circuit 14.

The shaping circuit 15 in FIG. 2 further amplifies the input signal and shapes it into a rectangular wave, and supplies a signal as shown in g of FIG. 3 to the discrimination circuit 16. In FIG. 4, Q23 to Q27 form the shaping circuit 15. The discrimination circuit as shown in FIG. 4 is set by the “L” logic of the output f of the voltage comparison circuit 14 and reset by the “L” logic of the output g of the shaping circuit 15, and the Q of the RS flip-flop (RS-FF). The output signal g of the shaping circuit 15 is supplied to the clock input terminal of the output, and the output signal g is composed of a D flip-flop triggered by the falling edge of this signal. As a result, the Q output terminal of the RS flip-flop outputs h of FIG. 3 and the Q reference terminal of the D flip-flop outputs the rotation reference position signal, so-called index signal i.

As described above, since the peak magnetic flux density of the correction magnetic pole 3B is in the middle of the peak magnetic flux density of the mark magnetic pole 3A, there is no influence on the detection operation of the rotation reference position signal.

Next, the relationship between the correction magnetic pole 3B and the cogging torque will be described. FIG. 5j shows the cogging torque due to the mark magnetic pole 3A, and the torque fluctuation of 12 cycles per rotation occurs as the drive magnet 3 rotates. Figure 5k
Is a cogging torque due to the correction magnetic pole 3B, and although the phase is different from the cogging torque j with the rotation of the drive magnet 3, a torque fluctuation of 12 cycles still occurs. The phase difference Dp is given by the equation (1) by the phase difference M between the mark magnetic pole 3A and the correction magnetic pole 3B and the number T of driving magnetic poles.

Dp = 2 × T × M / P (1) In order for the respective cogging torques to cancel each other, the fundamental waves of the cogging torque j and the cogging torque k are substantially π.
It is preferable to have a phase difference of, and the condition that Dp is N (where N is an odd number such as 1, 3, 5 ...) × π is obtained from formula (1), and formula (2) is obtained.

M = N × π × P / (2 × T) (2) By substituting P = 16 and T = 12 into this equation (2), the relationship shown in Table 1 is obtained.

[0025]

[Table 1]

Although it is possible to provide the correction magnetic poles 3B at the respective positions of M, positions such as 2π of N = 3 and 6π of N = 9 where N × P / (2 × T) is an integer are provided. It is easy to manufacture and can be said to be more preferable.

The phase difference between the mark magnetic pole 3A and the correction magnetic pole 3B in the drive magnet 3 of FIG. 1 is 2π, and N = 3.
Since the cogging torque j and the cogging torque k have opposite phases in the fundamental wave and substantially cancel each other out, they are as small as about 1/3 as shown by l in FIG.

FIG. 6 is a frequency analysis of the rotation unevenness (W / F) of the motor when the motor with the rotation position detecting device according to the present invention is applied to a spindle motor of a flexible disk drive rotating at 300 rpm.
The rotation unevenness component due to the aforementioned cogging torque is 60.
It is shown that the Hz component (300 rpm, 12 cycles, 60) was reduced to 0.08%, or about 1/3, by providing the correction magnetic pole. The cogging cancellation effect by the correction magnetic pole depends on the ratio of the strength of the mark magnetic pole and the correction magnetic pole. If the ratio is large, the cancellation effect is not lost, and if the ratio is small, the discrimination operation of the rotational position detection is hindered. It will come.

FIG. 7 shows the intensity of the correction magnetic pole as a ratio, with the intensity of the mark magnetic pole 3A being 100%, and shows the relationship between this ratio and the rotation unevenness (W / F) of the motor. In this example, the correction magnetic pole 3B is used. And the mark magnetic pole 3A is 65, and the ratio is 1
Although it is 30%, as shown in the figure, good rotation unevenness and characteristics are obtained at 150% or less. In order to obtain a stable rotational position detecting operation from now on, 115% or more is preferable, and in order to obtain a good rotational unevenness characteristic, the ratio of these is 115%.
The preferable range is from about 150%.

In the above description, the correction magnetic pole is set at one location, but a plurality of correction magnetic poles may be provided if the cancellation conditions are met.

[0031]

According to the motor with the rotational position detecting device of the present invention described in detail above, since the cogging caused by the mark magnetic pole is canceled out by the cogging caused by the correction magnetic pole, wah and flutter of the motor are excellent, and information recording / reproduction is performed. When used in a device or the like, there are effects such that stable recording and reproduction can be performed and the reliability of the device can be improved.

[Brief description of drawings]

FIG. 1 is a schematic exploded perspective view showing an embodiment of a motor with a rotational position detecting device according to the present invention.

FIG. 2 is a block diagram of a motor with a rotational position detecting device of the present invention.

FIG. 3 is a timing chart showing the operation of the circuit of FIG.

FIG. 4 is a circuit diagram showing the contents of the block diagram of FIG.

FIG. 5 is an explanatory diagram of cogging torque in the present invention.

FIG. 6 is a frequency analysis diagram of rotation unevenness in the device of the present invention.

FIG. 7 is a characteristic diagram showing corrected magnetic pole strength-rotational unevenness in the present invention.

FIG. 8 is a schematic exploded perspective view of a conventional motor with a rotational position detecting device.

FIG. 9 is an explanatory diagram of cogging torque of a conventional motor.

FIG. 10 is a frequency analysis diagram of conventional rotation unevenness.

[Explanation of symbols]

1 ... Rotor, 3 ... Magnet, 3A ... Mark magnetic pole, 3B
... correction magnetic poles, 6a, 6b, 6c ... Hall elements, 7a, 7
b, 7c ... Armature coil.

[Equation 1]

Claims (2)

[Claims] 1. A rotatable rotor provided with a magnet having a field magnetic field in which N poles and S poles alternate in the circumferential direction, an armature coil facing the magnet, and a magnetic flux density of the field magnetic field. A stator having a magnetoelectric conversion element that outputs a corresponding detection voltage; a mark magnetic pole in which the magnetic flux density of one magnetic pole of the field magnetic pole is lower than that of the other magnetic pole; and the detection corresponding to the magnetic flux density of the mark magnetic pole. In a motor with a rotation position detecting device that includes a discrimination circuit that outputs a rotation position reference signal of the rotor according to a voltage, in the field magnetic pole, the magnetic flux density of the mark magnetic pole and the magnetic flux density of another field magnetic pole A motor with a rotational position detecting device, comprising a correction magnetic pole having an intermediate magnetic flux density. 2. The motor with a rotational position detecting device according to claim 1, wherein the strength of the correction magnetic pole is 115% to 150% of the strength of the mark magnetic pole.