JPS6087690A - Brushless dc motor - Google Patents

Abstract

PURPOSE:To obtain a uniform generating force proportional to a command signal by cancelling a positional variation in a field magnetic flux partly modulated from a current supplied to a coil. CONSTITUTION:3-phase coils 14-16 cross the magnetic flux generated from a field magnet 13 mounted on a rotor. The composite supplying currents to the coils 14-16 are detected by a current detector 20. A current signal having a magnitude in response to the output of the detector 20 is outputted from a current detector 22, and the current signal is modulated by a modulator 24 by a modulation signal in response to the rotor position from a modulation signal generator 23. The modulated current signal and the command signal from a command signal generator 21 are inputted to a current supplying unit 25, and the currents in response to both are supplied to the coils 14-16.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a brushless DC motor that generates force in response to a command signal.

Conventional Structure and Its Problems 7 According to Lemming's law, it is widely known that the force generated by a motor is determined by the product of the magnetic flux generated by the field magnet and the current supplied to the coil.

Generally, the magnetic flux generated by a field magnet varies depending on the location. Therefore, the generated force when a constant current is passed through the coil changes as the relative position of the magnet and the coil changes, causing unevenness in the generated force, which has been a problem.

In particular, in brushless DC motors widely used in audio and video equipment, it is desired to minimize the unevenness of the generated force in order to improve the performance of the equipment.

The present applicant has addressed this problem by filing a patent application filed in 1983-6.
No. 7671 proposes a motor with an iron core structure that generates uniform force. This proposal is extremely useful for motors with a slotted core structure. However, when using a smooth iron core without slots, such as in a slotless motor or coreless motor, it is extremely difficult to obtain a uniform generated force.

OBJECTS OF THE INVENTION The present invention has been made in consideration of the above points, and uses back electromotive force induced in the coil to partially modulate the current supplied to the coil, thereby suppressing local fluctuations in field magnetic flux. The purpose of the present invention is to provide a brushless DC motor that is capable of canceling out the force and generating a uniform force (with little unevenness) in proportion to the command signal.

Structure of the Invention The motor of the present invention includes a magnet attached to a rotor, a multiphase coil, and a current supply means having a plurality of drive transistors for controlling opening/closing of a current path to the coil.
current detection means for detecting the current supplied to the coil; current generation means for obtaining a current signal linked to the output of the current detection means; modulation signal generation means for obtaining a modulation signal according to the rotational position of the rotor; The current signal is provided with a modulation means for obtaining a modulated signal obtained by modulating the current signal, and a command signal generation means for obtaining a command signal, and the current supply means is responsive to both the command signal and the modulated signal. A current is supplied to the multiphase coils, and the modulation signal generating means is configured to generate the modulation signal by a composite signal of back electromotive voltages induced in the multiphase coils.

Description of examples Hereinafter, the present invention will be explained based on illustrated embodiments.

FIG. 1 is an electrical circuit diagram representing one embodiment of the present invention.

In Fig. 1, 11.12 is a DC power supply, 13 is a field magnet attached to the rotor, 14, 15.1
6 is a generator for the magnet 13, a three-phase coil interlinks with the bundle, 20 is a current detector that detects the combined supply current to the coil 14゜15.16, and 21 is a command signal that generates the command signal ■1. A generator 22 is a current generator 23 that obtains a current signal 11 of a magnitude corresponding to the output v3 of the current detector 20.
24 is a modulator that modulates the current signal 11 with the modulation signal V to obtain the modulated current signal i4; 25 is the command signal v1 and the modulated current; This is a current supply device that supplies current to the coil in response to both signals i4.

Next, its operation will be explained. Command signal generator 21
is composed of, for example, a frequency generator, a speed voltage converter, etc., and generates a voltage signal that changes depending on the rotational speed of the magnet 13 (rotor rotational speed), and when the speed is slow, the voltage value changes. is large (maximum about 0.6v) and becomes smaller as the speed approaches a predetermined value (minimum is oV). The command signal v1 is the current supply device 25
is input to the coil 1, and the current Ia corresponding to the voltage value is input to the coil 1.
Provided on 4.15.16. The current Ia supplied to the coil is detected as a voltage drop v3 across the resistor 69 of the current detector 20, and the voltage signal v3 is input to the current generator 22.

FIG. 2 shows a specific circuit example of the current generator 22. The command signal v3 becomes the voltage difference between the bases of the transistors 102 and 104, and the current I6 of the current source 101 changes depending on the magnitude of the voltage difference between the bases of the transistors 102 and 104.
is distributed to the collector sides of transistors 103 and 105. Collector current I7 and I are compared by the first current mirror (transistors 108 and 109) of the current generator, and when I7>I, the current 1 is compared by the second current mirror (transistors 110 and 111) of the current generator.
1 is output (attracted). The value of v3 is 0≦v3≦0.5
Since the current is quite small, the current 11 is approximately. Here, R1°6 is the value of the resistor 106, and R1°6 is the value of the resistor 106.
The values of 6 and 107 were assumed to be equal, and the emitter equivalent resistances of the transistors 102, 103, 104, and 105 were ignored as being small.

The output 11 of the current generator 22 is input to the modulator 24, and the modulation signal V() transistor 34.3 of the modulation signal generator 23 is inputted to the modulator 24.
A current i4 modulated according to the base-to-base voltage of 5 is obtained. The modulation signal generator 23 generates a modulation signal V synchronized with the rotation of the magnet 13 (the actual operation will be described later).
The current 11 is input to a differential circuit consisting of collector currents 6 and 37, and the current 11 is distributed to each collector current 12t13 according to its magnitude. Collector current 12 of transistor 34 is outputted via a current mirror circuit made up of transistors 40 and 41, and is supplied to current supply 26. That is, the current i4 is modulated according to the modulation signal ■, and when V-Max, i4 is 0; when V=o, it is 14=11/2; when V=Min (-4=-Max), it is Z
4 "4" 11.

The modulation signal generator 23 includes a three-phase coil 14, 15°1
The three-phase back electromotive force induced in the diode 87゜88
．． 89 to obtain a composite signal W having a frequency three times higher than the frequency of the back electromotive force.

The composite signal W is generated by resistors 90, 94, 95 and diodes 92.
93 and transistor 91, the DC level is shifted, and the AC component is taken out by capacitor 96.
A modulated signal V is produced.

The current supply device 25 includes drive transistors 51, 52, and 53 that supply current Ia to the three-phase coils 14, 15, and 16.
and a resistor 69 inserted in series in the current path between the coil and the power supply.
a combiner 56 that obtains a signal responsive to the modulated current i4 (voltage drop across the resistor 7o) and combines it with the output voltage v3 of the current detector 20; A controller 56 (see FIG. 3) that receives the output ■2 and the command signal ■1 and outputs a current i5 in response to both pressure signals, and Hall elements 61, 62, and 63 that detect the magnetic flux generated by the magnet 13. a position detector 57 consisting of a position detector 57, and a selector 58 consisting of differential transistors 66, 67, and 68 that selects the drive transistor (therefore, the coil) to be energized in response to the outputs of the Hall elements 61, 62, and 63. There is.

FIG. 3 shows a specific example of the configuration of the controller 56.

The command signal ■ and the output ■2 of the synthesizer 65 are input to the base sides of the differential transistors 122 and 124, and the current 2 I9 of the current source 121 is applied to the collector side of the transistors 123 and 125 according to the voltage difference v-■. to be distributed. Collector current I,. , Engineering 1. is the first controller
The current mirrors (transistors 126 and 127) are used to compare the current mirrors. 〉■11 (when ■1>■2), the difference ■10-111 is amplified by the transistor 128, and the current i5 is passed through the second current mirror (transistors 129, 130) of the controller. Output.

The output current i5 of the controller 66 is supplied to the differential transistors 66, . This results in a common emitter current of 67.68. The output voltages of the Hall elements 61, 62, 63 of the position detector 57 are applied to the base sides of the differential transistors 66, 67, and 68, and the output voltage of the transistor 6 is applied according to the base voltage.
6.67.68 distributes the emitter current i6 to the collector side. That is, the transistor with the lowest base voltage becomes the most active, and the other transistors become inactive. As a result, the transistor whose output from the position detector 57 is activated is selected.

The collector currents of the transistors 66, 67, and 68 become the base currents of the drive transistors 51, 52, and 53,
The current is amplified and supplied to the coils 14, 15, 16-. The currents supplied to the coils 14, 15, 16 (currents flowing through the drive transistors 51, 52, 53) are combined and detected by the current detector 20, and a signal corresponding to the output voltage v and the modulated current i4 is combined. and the composite signal v2 is input to the controller 56. The composite signal v2 is V27-R69-Ia+(R7o+R69)i4--
- (3). Here, R69' R7° is resistance 6
The value is 9.70, and Ia is the current supplied to the coil.

In this way, if a feedback loop is formed by the drive transistors 51, 52, 53, the current detector 20, the controller 56, etc., the hF between the drive transistors 51, 52, 53, etc.
The influence of phase-to-phase variations due to variations in E and the like is small, and switching of coils to be energized is performed smoothly.

In addition, 71 is a capacitor for phase compensation (oscillation prevention) of this feedback loop, and coils 14, 15, 1
A series circuit consisting of a capacitor 81.83.85 and a resistor 82.84.86 connected in parallel to 6 reduces the spike-like voltage caused by switching of the energized coil.

In this return loop, the composite signal v2 is the command signal V.

In the equilibrium state, ■=■ (4)1. Therefore, the current Ia supplied to the coil is as follows. That is, the current Ia supplied to the coil has a value responsive to both the command signal V 1 and the modulated current i4. Note that R7o is also made sufficiently larger than R69 (Ω to R7゜=1, R6
, = 0.560), i4 is made sufficiently smaller than Ia.

In this way, if the current Ia supplied to the coil is changed in response to a modulation signal synchronized with the rotation of the motor, a uniform generated force can be obtained. This will be explained with reference to the waveform diagram of FIG. 4 for explaining the operation. Figure 4 (-) shows the magnetic flux density generated by the magnet 13 applied to the coils 14.1j and 16, with the rotational position of the magnet 13 taken as the horizontal axis, and the magnetic flux density varies depending on the relative position of the coil and magnet. Changes periodically. In order to obtain continuous rotational force in the same direction, the brushless DC motor detects the rotational position with a position detector 57, selects the coil to be energized with a selector 58, and supplies current. There are 1. The energized section is shown at the bottom of FIG. 4(a). Now, if a constant current is supplied to the selected coil, according to Fleming's law, the generated force is proportional to the product of magnetic flux density and current, and as shown by the solid line in Figure 4 (, ), the generated force is proportional to the product of magnetic flux density and current. will fluctuate significantly. This variation in generated force is caused by local changes in magnetic flux density, so it is unique to the motor structure. Once the motor structure is determined, the waveform and rate of variation are also determined, and there is little variation during mass production. . Therefore, if the current Ia supplied to the coil is changed in accordance with a signal synchronized with the rotation of the magnet as in the present invention, a uniform generated force can be obtained.

Consider the case where the command signal v1 is constant [Fig. 4(b)].

When the magnet 13 begins to rotate at a predetermined speed (speed control state), a back electromotive voltage with an amplitude proportional to the rotational speed is induced in the three-phase coils 14, 15, and 16. According to Fleming's law, the back electromotive force is proportional to the magnetic flux density. Therefore, the waveform is similar to the waveform of the magnetic flux density in Figure 4 (-).
It becomes a phase AC voltage. Diode 8 of modulation signal generator 23
7.88.89 compares the respective terminal voltages of the coils 14, 15, and 16, selects the waveform of the maximum terminal voltage, and obtains the composite signal W. Therefore, the composite signal W is the coil 14, 15°1
The result is a composite of the three-phase back electromotive voltage waveforms occurring in each non-energized section of 6, as shown by the dashed dotted line in the upper part of FIG. 4(a). That is, the frequency of the composite signal W is three times the frequency of the back electromotive force of each phase, and its AC amplitude is a predetermined value depending on the rotational speed of the rotor. composite signal W
Since the alternating current component of is the modulation signal V, the modulation signal V becomes a synchronization signal that synchronizes with the rotation corresponding to fluctuations in magnetic flux density.

Therefore, the waveform of the modulation signal (2) generated between the bases of the transistors 34 and 35 of the modulator 24 is as shown in FIG. 4(e). The output current 14 of the modulator 24 modulated by the modulation signal ■ changes depending on the rotational position as shown in FIG. 4(d). In other words, when V=Max, 14=0, and as ■ becomes larger, i4 increases, and V
When =Min, i4 is equal to 11 and is approximately equal. Therefore, the supply current I to the coil based on equation (6)
a becomes as shown in FIG. 4(e). Generated force Ia [4th
(e)] and the magnetic flux density (solid line in Fig. 4 (a)), the generated force of the brushless DC motor of the present invention is the fourth
As shown in Figure (f), uniform generated force with little variation can be obtained. Furthermore, the frequency of unevenness in the generated force also increases.

This will be explained in more detail. Since the current proportional to the output v3 of the current detector 20 is modulated by the signal V to produce the modulated current i4, it responds to i 1J)V . Here, it may be considered that 14<<I a or 3 v3=R69·Ia. This v3 is (1
), it becomes . The gain of the modulator 24 due to the modulation signal ■ is q(v)
So, 14=9. (v)・11 ・・・・・・・・・・・・(7
) and when V = M a x , g(v) = O
, when V=Min, g(v)=1, Min<V(M
When ax, o<g(v)<1. (5)
From equations , (6) and (7), the current I supplied to the coil
The relationship between a and command signal ■1 is as follows. Therefore, the current Ia supplied to the coil is proportional to the command signal 1, and the conversion gain la/v1 changes depending on the value of the modulation signal V. That is, as shown in FIG. 4(e), a current Ia that changes depending on the rotational position is supplied to the coil selected by the output of the position detector 67. As a result, the command signal v1
A generated force proportional to the value of is obtained, and the unevenness of the generated force is significantly reduced. Also, the supply current I to the coil
The rate of change (minimum value/maximum value) of a is as follows, and since it is less affected by variations in the magnitude and waveform of the modulation signal (2), the performance during mass production is stable (the unevenness in the generated force is small).

To explain this, the magnitude and waveform of the modulation signal V vary considerably depending on the individual motor during mass production (for example, variations in magnet contact).

(affected by variations in coil shape, magnet temperature characteristics, etc.)

Therefore, if the supply current Ia of the coil is directly modulated by the modulation signal V, the current with the required rate of change cannot be stably obtained due to large variations during mass production. However, if the configuration is as in the above-mentioned embodiment, the waveform of the current Ia supplied to the coil is slightly affected by variations in the modulation signal V, but the rate of change hardly changes (the output current i4 of the modulator 24 The maximum is 11 and the minimum is 0).

The result is a high-performance motor that is sufficiently stable even during mass production, with little unevenness in generated force.

Furthermore, as shown in the embodiments described above, if the current supply device 26 is configured to include a feedback loop in the drive tractor to reduce the influence of variations in the hFE of the register, the unevenness in the generated force of the brushless DC motor of the present invention can be reduced. The reduction effect becomes stable.

In addition, in the above explanation, the command signal v1 was assumed to be constant, but
Actually, the brushless DC motor of this embodiment is subjected to speed control so that the rotational speed of the rotor is kept constant. Therefore, as the unevenness of the generated force becomes smaller, the fluctuation in the rotational speed becomes smaller, and as the frequency of the unevenness of the generated force becomes higher, the effect of motor inertia appears and the rotational speed becomes smaller.

Note that during the motor startup/acceleration stage, the back electromotive voltage is small and a sufficiently large modulation signal V cannot be obtained. Now, if v = o, then q (v) = X, and the current 1a proportional to the command signal V is
6 [see equation (8)], the rotor is immediately started and accelerated, and shifts to a steady speed control state. When the speed is controlled, a sufficiently large back electromotive force is generated, so the above-mentioned modulation operation is performed, and the unevenness of the generated force is reduced.

- Since the modulation signal V is still generated using the back electromotive force generated in the coils 14, 15, 16, no additional structural parts (sensors) are required, so no changes to the motor structure occur.

In the above embodiment, the modulated current i4 and the output v3 of the current detector 20 are combined, but the present invention is not limited to such a case.

FIG. 6 shows an electrical circuit diagram representing another embodiment of the present invention. In this embodiment, the output i4 of the modulator 24 is inverted by a current mirror consisting of transistors 303 and 304, and is supplied to a combiner 302 consisting of a resistor 301. The other configurations and operations are the same as those of the embodiment shown in FIG. 1, and their explanation will be omitted. Depending on the operation of the current supply device 25, v = v (13)
It becomes 3. Here, V3=R69-1a ・----=-・(14) V 6
= V 1-R301” 14” ” ” ” ” (
15), so by substituting it into equation (13) and rearranging it, we get I
a = '(-)'' (V, -R3o, -t4) -
---C1e)69. If R301=R7°+R69, (16)
The equation matches equation (5). Therefore, the current Ia and the generated force in this embodiment are the same as in the embodiment shown in FIG. 1 described above. In other words, the unevenness of the generated force is significantly reduced.

Note that the present invention is applicable not only to three-phase motors but also to base motors that generally have multi-phase coils. Further, the invention is not limited to motors that generate rotational force, but can also be applied to motors that generate linear force and move in a straight line. Other modifications can be made without changing the spirit of the invention.

Effects of the Invention The brushless DC motor of the present invention has the great advantage that the unevenness of the generated force Q can be significantly reduced. Therefore, if a brushless motor for a cylinder motor of audio/visual equipment is constructed based on the present invention, a stable and high performance device can be obtained.

[Brief explanation of the drawing]

Fig. 1 is an electric circuit diagram showing one embodiment of the present invention, Fig. 2 is a specific example of the configuration of the current generator, Fig. 3 is a specific example of the configuration of the controller, and Fig. 4 is the operation. The explanatory waveform diagram and FIG. 6 are electric circuit diagrams representing another embodiment of the present invention. 11.12...DC power supply, 13...Magnet, 14.15.16...Coil, 2o.
...Current detector, 21...Command signal generator, 2
2...Current generator, 23...Modulation signal generator, 24-...Modulator, 26...Current supply device, 6
1,62.63...drive transistor, 55,30
2...Synthesizer, 56...Controller, 57...
-Position detector, 5B.-Selector. Name of agent: Patent attorney Toshio Nakao and one other thief
Castle 1 Go Yare @Katai 0 Jin-gu9 緘(5 1S ＼-

Claims (1)

[Claims] A magnet attached to the rotor, a multiphase coil,
a current supply means having a plurality of drive transistors for controlling opening and closing of a current path to the coil; a current detection means for detecting the current supplied to the coil; and a current for obtaining a current signal linked to the output of the current detection means. a generating means; a modulating signal generating means for obtaining a modulating signal according to the rotational position of the rotor;
The current supply means is provided with a modulation means for obtaining a modulated signal obtained by modulating the current signal with the modulation signal, and a command signal generation means for obtaining a command signal, and the current supply means is responsive to both the command signal and the modulated current signal. a brushless direct current supplying a current to the multiphase coil, and the modulation signal generating means generating the modulation signal by a composite signal of reverse voltages induced in the multiphase coil. motor.