JPH1084690A - Brushless motor drive control circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase torque and prevent uneven rotation, by controlling the difference between the content of the third harmonic component and the content of the fifth harmonic component to a specified value or below. SOLUTION: Hall signals U and V are synthesized by a signal synthesizing means comprising an adder circuit 1 and a non-linear converting means 2, and the signal synthesizing means outputs a synthesized signal W. At this time, the driving magnetic pole waveform is of trapezoidal wave containing a third harmonic component and a fifth harmonic component; therefore, the synthesized signal W is obtained as triangular-wave-shaped signal. A triangular-wave-to-trapezoidal-wave conversion means 3 converts the synthesized signal W into a trapezoidal-wave-shaped conversion signal W', and supplies it to a drive circuit means 7. The stator coil 6 of the drive rotating means 7 produces rotating magnetic fields corresponding to the rotation of a rotor, and generates rotational driving force through interaction with driving magnetic poles. However, as the fifth harmonic component of the driving magnetic poles is eliminated and only the third harmonic component is increased, the trapezoidal waveform is distorted and uneven rotation results. To cope with this, the value obtained by subtracting the content of the third harmonic component is controlled to 16% or below.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a brushless motor drive control circuit suitable for a spindle motor of a VTR or a polygon mirror or a spindle motor of a disk type storage device.

[0002]

2. Description of the Related Art FIG. 1 is a sectional view of a brushless motor for directly driving the capstan shaft of a VTR, and FIG.
FIG. 2 is a plan view of a stator section of the brushless motor shown in FIG. The rotor 10 has a shaft 40 serving as a capstan shaft fixed at the center and rotatably supported by bearing means 90 and 100.
A drive magnet 50 having a sinusoidal drive magnetic pole is provided. An FG magnet 60 having 360 FG magnetic poles on the outer periphery is provided around the periphery.

[0003] A stator 20 is formed by laminating a copper foil on a soft magnetic steel sheet via an insulating layer and forming a circuit pattern by etching or the like on a stator substrate 70 (also serving as a wiring substrate). 6 of stator coil 80
It is arranged coaxially with the center of rotation at intervals of 0 degrees and fixed. These stator coils 80 are opposed to the above-described drive magnetic poles in a plane, and two pairs, one set facing each other across the rotation center, are connected in series, and three sets constitute a star-connected three-phase stator coil. I have.

[0004] At the center of these coils, two Hall elements 130 are provided at intervals of a mechanical angle of 120 degrees.
It is arranged to output Hall signals U and V having a phase difference of 20 degrees.

An MR type magnetic sensing element (not shown) is disposed on the stator 20 and faces the FG magnetic pole on the outer periphery of the FG magnet 60 provided on the rotor 10 with a gap of about 0.1 mm. Accordingly, an FG signal of 360 cycles per rotation is output. The FG signal is converted into a speed control signal for controlling the motor to a target rotation speed by the speed control means, and is supplied to a drive circuit built in the IC 140 so as to control the drive current.

The above-mentioned Hall signals U and V are summed and inverted by the signal synthesizing means and output as a synthesized signal W. At this time, if the drive magnetic poles are formed in a sine wave shape, the Hall signals U and V also become sine wave signals, and the composite signal W is obtained as a sine wave signal having the same amplitude. The Hall signals U and V and the composite signal W each constitute a three-phase position signal having a phase difference of 120 degrees and are supplied to a drive circuit. The drive circuit supplies a three-phase stator coil with a magnitude corresponding to the speed control signal described above. The current acts to control and flow at a ratio corresponding to the position signal. The driving current causes the stator coil 80 to generate a rotating magnetic field corresponding to the rotation of the rotor 10 and generate a rotational driving force by interaction with the magnetic field of the driving magnetic pole.

[0007]

In recent years, there has been a demand for miniaturization and improved efficiency of devices, and in such a brushless motor, it has been required to reduce the drive current and increase the torque. Increasing the total magnetic flux is considered to be effective, and attempts have been made to change the drive magnetic pole from a sine wave to a trapezoidal wave. When the driving magnetic pole is changed from a sine wave to a trapezoidal wave, the maximum magnetic flux density determined by the characteristics of the magnet is constant. Therefore, as shown in FIG. It has also been found that this also increases the torque. In other words, according to FIG. 4, for example, if the driving magnetic pole contains 10% of the third harmonic, the fundamental wave also increases by about 10%, and as a result, the torque also increases by 1%.
It can be seen that it increases by 0%.

However, the same applies to the portion that supplies the magnetic flux to the Hall element. The Hall signal also contains this third harmonic component, and when these signals are summed and inverted to generate a composite signal W, the waveform of the Hall signal becomes A waveform including a lot of distortion different from the above was generated, resulting in a difference in drive current between the stator coils of each phase, which resulted in torque unevenness, which worsened the rotation unevenness of the motor. These are shown in FIG.
As the content of the third harmonic of the driving magnetic pole increases, the rotation unevenness increases. In particular, when the content is 8% or more, the rotation unevenness exceeds 0.3% and becomes unusable. .
SUMMARY OF THE INVENTION The present invention has been made in view of such a conventional problem, and provides a brushless motor that increases torque and has good rotation unevenness by adopting the configuration described in the claims.

[0009]

In order to solve the above-mentioned problems, a brushless motor drive control circuit according to the present invention comprises: a rotor provided with a drive magnetic pole and rotatably held; and a three-phase rotor facing the drive magnetic pole. And two Hall elements that are supplied with a magnetic flux according to the rotation angle of the rotor and output Hall signals U and V having a phase difference of 120 degrees in electrical angle, and synthesize the Hall signals U and V. Signal combining means for outputting a combined signal W having a phase difference of 120 degrees in electrical angle with respect to the Hall signals U and V, and driving the stator coil according to the Hall signals U, V and the combined signal W In a brushless motor having a drive circuit for controlling and flowing an electric current, the signal synthesizing means is configured to include an addition circuit and a non-linear conversion means, and the signal synthesizing means is provided in accordance with a rotation angle of the rotor. The magnetic pole waveform of the portion that supplies the magnetic flux to the Hall element has the third harmonic component in phase with the fundamental wave and the fifth harmonic component.
And wherein the difference between the content of the third harmonic component and the content of the fifth harmonic component is 16% or less, and The drive circuit has a difference X between a signal corresponding to the Hall signal U and a signal according to the Hall signal V, a difference Y between a signal according to the Hall signal V and a signal according to the composite signal W, A difference Z between a signal corresponding to the composite signal W and a signal corresponding to the Hall signal U is generated, and a driving current flowing through the stator coil is controlled according to the differences X, Y, and Z. Further, the two Hall elements are arranged at an interval of 60 degrees or less in mechanical angle, or the Hall elements are GaAs type Hall elements.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The appearance of a brushless motor according to an embodiment of the present invention is substantially the same as that of the prior art described with reference to FIGS. It will be described using FIG.

The brushless motor according to the present invention is provided with a drive magnet 50 having a trapezoidal drive magnetic pole on the surface of the rotor 10 containing predetermined eight-pole third and fifth harmonic components. The stator 20 is based on a substrate on which a circuit pattern is formed in the same manner as in the prior art, and
The air core coils are arranged coaxially with the center of rotation at intervals of 60 degrees and fixed.

These coils are opposed to the above-described drive magnetic poles in a plane, and a pair of two coils facing each other across the center of rotation are connected in series, and three sets constitute a star-connected three-phase stator coil 80. doing. In addition, two Hall elements 130 are provided at the center of these coils in accordance with the magnetic flux density of a portion for supplying the magnetic pole to the Hall element of the driving magnetic pole.
It is arranged so as to output Hall signals U and V of a phase difference.

Further, similarly to the conventional example, an MR type magnetic sensing element is provided and outputs an FG signal. This FG signal is converted by a speed control means into a speed control signal for controlling the motor to a target rotation speed, and the drive current is controlled. Is supplied to the drive circuit means so as to control.

(First Embodiment) FIG. 3 is a block diagram showing the configuration of the first embodiment, and FIG. 6 is a diagram showing each waveform. This will be described below with reference to the drawings. The above-mentioned Hall signals U and V are summed and inverted by a signal synthesizing means comprising an adding circuit 1 and a non-linear conversion means 2 to output a synthesized signal W. At this time, the magnetic pole waveform of the portion of the drive magnetic pole that supplies the magnetic flux to the Hall element has a trapezoidal waveform including the third harmonic component and the fifth harmonic component, so that the Hall signals U and V are also shown in FIG. As shown in (a) and (b), the signal becomes a trapezoidal wave, and the combined signal W is obtained as a distorted triangular wave signal as shown in (c) of FIG.

The triangular-wave / trapezoidal-wave converting means 3 converts the input triangular-wave composite signal W into a trapezoidal-wave converted signal W 'as shown in FIG. 6 (d). High, the gain decreases as the amplitude of the input signal increases, and finally the output amplitude hardly increases even if the input amplitude increases. The relationship between the input amplitude and the output amplitude is triangular-trapezoidal. It has wave conversion characteristics.

Specifically, in the case of this embodiment, the input amplitude is set to 3
After the power of / 4, the signal is further converted from a triangular wave signal to a trapezoidal wave signal by using the logarithmic conversion characteristic of the differential amplifier. Conversion characteristics were obtained, and preferable triangular wave-trapezoidal wave conversion characteristics were obtained especially in the 乗 power to the ／ power.

Each of the Hall signals U and V and the conversion signal W 'constitutes a three-phase position signal having a phase difference of 120 degrees, and a drive circuit means 7 comprising a Hall amplifier 4, a differential distribution output circuit 5, and a stator coil 6. Supplied to The drive circuit means 7 acts to flow a current of a magnitude corresponding to the above-described speed control signal to the three-phase stator coil 6 at a ratio corresponding to the position signal.

The driving current causes the stator coil 6 to generate a rotating magnetic field corresponding to the rotation of the rotor, and generates a rotational driving force by interaction with the magnetic field of the driving magnetic pole. However, if the fifth harmonic of the driving magnetic pole is eliminated and only the third harmonic component is increased, the inclination of the triangular wave synthesized signal W near the zero cross becomes small as shown in FIG.
Even through the non-linear conversion means, the output becomes a distorted trapezoidal wave as shown in FIG.

In particular, when the content of the third harmonic exceeds 16%, the slope near the zero cross of the composite signal W is reversed as shown in FIG. 6G, and as shown in FIG. 6H. The output becomes extremely distorted, and a driving torque in the reverse direction is generated, which makes the device unusable.

When the fifth harmonic is included in the driving magnetic pole to solve this problem, the above-mentioned synthesized signal W has a good slope near the zero cross as shown in FIG. 6 also decreases as shown in FIG. 6 (j), and exhibits excellent rotation unevenness characteristics. For this reason, even if the content of the third harmonic exceeds 16%, the content of the third
If the difference obtained by subtracting the content of the second harmonic is 16% or less, the inclination of the synthesized signal W near the zero cross does not reverse, and no driving torque is generated in the reverse direction. If the difference in the content of the fifth harmonic is 12% or less, even better rotation unevenness characteristics are exhibited.

The above-mentioned problem is solved if the magnetic pole waveform of the portion of the driving magnetic pole that supplies the magnetic flux to the Hall element contains the third harmonic component and the fifth harmonic component as described above. Therefore, the same effect can be obtained even if the contents of other parts of the driving magnetic pole are different.

(Second Embodiment) As described in the first embodiment, the drive circuit means 7 supplies the three-phase stator coil 6 with a current having a magnitude corresponding to the speed control signal described above, If the Hall signals U and V and the conversion signal W ′ are trapezoidal waves, the change in the ratio of the currents of the three-phase stator coils becomes steep, because they act so as to flow in a controlled manner according to the size. There is a problem that the amount of generation of vibration, noise, and electromagnetic noise increases.

The differential X between the signal corresponding to the Hall signal U and the signal corresponding to the Hall signal V, the signal corresponding to the Hall signal V, and the signal corresponding to the converted signal W ' Is generated, and the difference Z between the signal corresponding to the converted signal W ′ and the signal corresponding to the Hall signal U is generated, the third harmonic signal cancels out the difference signal, and (k) and (k) in FIG. 1) and (m) have a substantially sinusoidal shape. By configuring the drive circuit means 7 so as to control and supply a drive current to the stator coil 6 in accordance with the substantially sinusoidal difference signals X, Y and Z, the drive magnetic pole has a trapezoidal wave to increase the torque. At the same time, the change in the current ratio of the three-phase stator tail 6 becomes slow, the amount of vibration, noise, and electromagnetic noise is reduced, and the above-mentioned problem is solved.

(Third Embodiment) Even if the rotor driving magnet is manufactured with care, surface runout remains on the surface facing the Hall element, and the magnetic flux density of the magnetic flux supplied to the Hall element changes due to the rotation of the rotor. . This effect is what is called AM modulation of one cycle per rotation in which a portion where the amplitude of the Hall element output increases and a portion where the amplitude of the Hall element output decreases alternately are repeated.

As an inherent problem of the circuit having the signal synthesizing means, if the arrangement of the two Hall elements is far apart, when the amplitude of one Hall element output is large, the output of the other Hall element becomes large. The amplitude becomes small, and the waveforms of the combined signal W and the converted signal W ′ change, causing an increase in rotation unevenness.

Therefore, as shown in FIG. 7, when the arrangement of the Hall elements in the mechanical angle is 30 °, the ratio of the rotation unevenness is about 0.15%. FIG. 9 shows the relationship between the distance between the Hall elements expressed in mechanical angles and the rotation unevenness in an experiment when the surface deflection of the surface of the drive magnet facing the Hall element is large. Is 6
0.25% at which the effect of increased rotation unevenness can be used below 0 degree
When the angle is 45 degrees or less, the influence of the increase in rotation unevenness is reduced to about 0.18%, which can be ignored.

(Fourth Embodiment) As an inherent problem of the circuit provided with the above-described nonlinear conversion circuit, when the sensitivity of the Hall element changes with temperature and the amplitude of the output of the Hall element changes, the output of the nonlinear conversion means is changed. There is a characteristic that the waveform changes, which may lead to an increase in rotation unevenness, and the usable temperature range is limited. In order to solve this problem, there is a method of changing the conversion characteristic of the non-linear conversion means according to the temperature and compensating the output waveform. However, another problem arises in that the circuit configuration becomes complicated.

For this reason, by using a GaAs type Hall element having good temperature characteristics as the Hall element, the amplitude of the output of the Hall element is less likely to change due to a temperature change, and the nonlinear conversion can be performed without complicating the circuit configuration. There is no change in the output waveform of the means, and there is obtained an effect that stable rotation unevenness with respect to temperature is obtained and the usable temperature range is expanded.

Although the present embodiment has been described with reference to a so-called axial gap type brushless motor, the present invention can be applied to a radial gap type motor and the same effects can be obtained. Furthermore, although the description has been given of the motor in which the driving magnetic poles are integrally provided on the same surface, a brushless motor in which the magnetic flux is supplied to the stator coil and the magnetic flux is supplied to the Hall element in a divided manner is also described. Various modifications are possible without being limited to the described embodiment, such as not departing from the invention.

[0030]

According to the present invention, in a drive circuit control device for a brushless motor for generating a synthesized signal W by synthesizing Hall signals U and V output from two Hall elements,
The signal synthesizing means includes a non-linear conversion means, and the driving magnetic pole has a third
Includes a fifth harmonic component and a fifth harmonic component, and by increasing the difference between the contents to 16% or less, torque can be increased, efficiency can be reduced, current consumption can be reduced, and rotation unevenness can be improved. The change of the current ratio becomes slow, the amount of vibration, noise, and electromagnetic noise is reduced, the effect of the drive magnet surface runout is reduced, the yield is improved, and a brushless motor with a wide usable temperature range is provided at low cost. It has the effect of being able to do things.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a brushless motor that directly drives a capstan shaft of a VTR.

FIG. 2 is a plan view of a brushless motor stator used in a brushless motor drive control circuit according to one embodiment of the present invention.

FIG. 3 is a block diagram showing a brushless motor drive circuit according to one embodiment of the present invention.

FIG. 4 is a diagram showing a torque increase rate depending on a content rate of a third harmonic.

FIG. 5 is a diagram showing a ratio of rotation unevenness depending on a content rate of a third harmonic.

FIG. 6 is a diagram showing waveforms of a hall signal, a composite signal, and a converted signal.

FIG. 7 is a plan view of another stator of the brushless motor used in the brushless motor drive control circuit according to one embodiment of the present invention.

FIG. 8 is a comparison diagram of drive magnetic pole waveforms.

FIG. 9 is a diagram illustrating a ratio of rotation unevenness depending on a distance between Hall elements.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Addition circuit 2 Nonlinear conversion means 3 Triangular wave-trapezoidal wave conversion means 4 Hall amplifier 5 Differential distribution & output synthesis means 6 Stator coil 7 Drive circuit means

Claims (4)

[Claims] 1. A rotor having a driving magnetic pole and rotatably held therein, a three-phase stator coil facing the driving magnetic pole, and a magnetic flux corresponding to a rotation angle of the rotor is supplied, and an electrical angle of 120 degrees is provided. Two Hall elements for outputting Hall signals U and V having a phase difference of
And the Hall signals U and V are converted into 1 electrical angle.
A brushless motor comprising: signal combining means for outputting a combined signal W having a phase difference of 20 degrees; and a drive circuit for controlling and flowing a drive current to the stator coil according to the Hall signals U and V and the combined signal W. In the above, the signal synthesizing means includes an adding circuit and a non-linear conversion means, and a third-order harmonic in which a magnetic pole waveform of a portion for supplying a magnetic flux to the Hall element according to a rotation angle of the rotor has the same phase as a fundamental wave. A wave component and a fifth harmonic component,
A brushless motor drive control circuit, wherein a difference between the content of the third harmonic component and the content of the fifth harmonic component is 16% or less. 2. The driving circuit according to claim 1, wherein a difference X between a signal corresponding to the Hall signal U and a signal corresponding to the Hall signal V, a signal corresponding to the Hall signal V, and a signal corresponding to the composite signal W. And a difference Z between a signal corresponding to the composite signal W and a signal corresponding to the Hall signal U, and controls a drive current flowing through the stator coil according to the differences X, Y, and Z. 2. The method according to claim 1, wherein
The brushless motor drive control circuit described in the above. 3. The brushless motor drive control circuit according to claim 1, wherein said two Hall elements are arranged at a mechanical angle of 60 degrees or less. 4. The brushless motor drive control circuit according to claim 1, wherein said Hall element is a GaAs type Hall element.