JPH01214290A - Dc brushless motor for optical deflector - Google Patents

Abstract

PURPOSE:To prevent a noise from generating by combining PLL control means and PWM control means, and synchronizing these control frequencies. CONSTITUTION:A position signal detected by the rotor position detector 13 of a brushless motor 12 is processed by a rotor position detector and a speed detector 10. This speed signal is compared by a PLL controller 2 with the frequency of a crystal oscillator 1, stabilized for the variation of an AC power source 5 by a current amplifier 4 and a power detection shaft 9, and input to the positive side of a PWM comparator 16. The output of a sawtooth signal generator 15 synchronized with the clock of the controller 2 is input to the negative side. As a result, the PWM-modulated pulse signal is combined with the position signal by a logic circuit 17, thereby driving a coil switching transistor 11 in a pulse manner. Thus, since the transistor 11 completely performs a switching operation of ON and OFF, power can be suppressed to the minimum limit.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention provides a D
The present invention relates to a drive circuit for a C brushless motor.

(Prior Art) As shown in FIG. 3, this type of conventional drive circuit uses rotor position detectors 13, 13, and 13 to control the speed of a three-phase brushless motor 12 employed in an optical deflector. ..., the signals detected by the rotor position detection circuit and the speed detection circuit 10 are respectively made into pulse signals corresponding to the rotor position, the coil switching transistor 11 switches the current to the coil group 14 of the motor 12, and the rotation speed signal is generated. is compared with the frequency of the crystal oscillator 1 in the phase-locked loop control section 2 (hereinafter simply referred to as the PLL control section 2). The output analog signal drives the base of the power transistor 8 in a state stabilized against fluctuations in the AC power supply 5 by the current amplifier 4 and the current detection shunt 9. This power transistor 8 lowers the DC voltage which is converted into DC by the rectifier circuit 6 and the power supply filter 7 from the AC power supply 5 using a dropper type, and supplies it to the coil group 14 of the three-phase brushless motor 12 through the coil switching transistor 11. Ru.

That is, in order to control the rotation of the three-phase brushless motor 12, the rotation speed of the motor is controlled by changing the analog amount of voltage applied to the coil group 14 of the brushless motor 12.

(Problems to be solved by the invention) In the conventional DC brushless motor described above,
Since speed control is performed using a single dropper type, the power loss in the control circuit is very large, and as a result, the amount of heat generated is large, resulting in poor efficiency. Particularly in large DC brushless motors for optical deflectors, the heat generated has an adverse effect on the laser oscillation section and the like.

In addition, when control is performed simply by switching to suppress this heat generation, when the switching frequency is from several KH2 to several tens of KH2, the rotational frequency of the motor and the switching frequency of the pulse width control section (hereinafter simply referred to as PWM control section) Due to the difference between the two, the two devices interfere with each other, producing audible noise, or causing noise that adversely affects the operation of peripheral circuits.

(Means for Solving the Problems) Therefore, the present invention aims to solve the above problems, and as a means thereof, a PLL control means and a PWM control means are combined, and the control frequencies of these are combined. A drive circuit for a DC brushless motor configured to be synchronized is provided.

(Function) According to the present invention, the power control of the DC brushless motor is
By using the WM control means, there is no analog power loss in the control circuit, so there is only switching loss. Furthermore, by synchronizing the frequencies of the PLL control section and the PWM control section, it is possible to prevent the generation of undulation noise due to the difference between the rotational frequency of the motor and the frequency of the PWM control section.

(Example) Hereinafter, an example of the present invention will be described with reference to the accompanying drawings.

In FIG. 1, a position signal detected by a rotor position detector 13 of a brushless motor 12 is processed by a rotor position detection circuit and a speed detection circuit 10. Here, the speed signal is compared with the frequency of the crystal oscillator 1 in the PLL control section 2. The output analog signal is stabilized against fluctuations in the AC power supply 5 by a current amplifier 4 and a power detection shunt 9, and is stabilized by a pulse width control comparator 16 (hereinafter simply PW
6 is input to the ■ side of the M comparator), while PW
The output of a sawtooth signal generator 15 that generates a sawtooth signal synchronized with the clock of the PLL control section 2 is input to the θ side of the M comparator 16. As a result, the output of the PWM comparator 16 appears in the form of a sawtooth signal sliced from the output of the current amplifier 4, which is pulse width controlled (hereinafter referred to as PWM).
be done. This PWM pulse signal is transmitted to the logic circuit 1.
At 7, it is combined with the position signal processed by the rotor position detection circuit and the speed detection circuit IO to drive the base of the coil switching transistor 11 in a pulse manner.

As a result, the coil switching transistor 11 is connected to the AC power source 5.
The rectifier circuit 6 and the power supply filter pulse-width modulate the DC voltage converted into DC voltage, and supply it to the coil 14 of the three-phase brushless motor 12 in a form matched to the rotor position.

In this way, the coil switching transistor 11 is completely turned off.
Since the switching operation is performed between N and OFF, the power in this control circuit can be kept to a minimum.

Therefore, the operation when the PLL control frequency and PWM control frequency in the DC brushless motor circuit for an optical deflector according to the present invention are synchronized will be explained.

In FIG. 2, the PLL control frequency and the PWM control frequency are shown enlarged for easy understanding.

The sawtooth signal 18 of the PWM control circuit is sliced at the output level B of the PLL control circuit to form a PWM output 19. This signal is combined with the signals from the rotor position detection circuit and the speed detection circuit 10 in the logic circuit 17 and distributed to the respective coils 14. The state is shown in the energization signal 20 of the coil 14φA, the energization signal 21 of the coil 14φB, and the energization signal 22 of the coil 14φC. By synchronizing the P L L ltj control frequency and the PWM control frequency as shown in these signal waveforms, power is uniformly supplied to each coil. Further, even at the moment 23 of coil switching, since the switching can be performed at a timing when no current is applied, noise generation can be suppressed to a minimum.

Next, in order to clarify the operation of the drive circuit according to the present invention, in the drive circuit of the conventional example, PLL control frequency and PW
The operation when the M control frequency is not synchronized will be explained.

In FIG. 4, the frequencies mentioned above are shown enlarged for ease of understanding.

The sawtooth signal 24 of the PWM control circuit is sliced at the output level A of the PLL control circuit to form a PWM output 25. This signal is combined with the signals from the rotor position detection circuit and the speed detection circuit 10 in the logic circuit 7, and distributed to the respective coils 14. Coil 1
4φA′ energization signal 26, coil 14φBA electric signal 27,
In the conventional DC brushless motor, the PL
Since the L control frequency and the PWM control frequency are not synchronized, the waveforms applied to each coil are different, resulting in variations in the amount of electric power. As a result, many problems have arisen, such as torque fluctuations, abnormal noises, and even at the moment 29 of coil switching, since the current is switched while continuing to be energized, noise is likely to occur. However, as already explained, the drive circuit according to the present invention solves all of these problems.

(Effects of the Invention) As explained above, in the DC brushless motor drive circuit according to the present invention, heat generation is minimized by implementing PWM in the power control section, so the power element in the power control section is miniaturized. At the same time, the heat dissipation fins were also downsized accordingly, making the entire device more compact, and PWM
Since the switching frequency of the control section is synchronized with the rotation of the motor, variations in the amount of electricity and generation of undulation noise are prevented, so there is an advantage that the influence on external electronic circuits can be minimized.

[Brief explanation of the drawing]

FIG. 1 is a block circuit diagram of a DC brushless motor for an optical deflector according to the present invention. Figure 2 shows the PLL control frequency and PWM of the circuit according to the present invention.
FIG. 3 is a waveform diagram showing the relationship with control frequency. FIG. 3 is a block circuit diagram of a conventional DC brushless motor for an optical deflector. FIG. 4 is a waveform diagram showing the relationship between the PLL control frequency and the PWM control frequency of a conventional circuit. 1... Crystal oscillator, 2... PLL control section, 4...
Current amplifier, 5... AC power supply, 6... Rectifier circuit, 7
...Power supply filter, 8...Power transistor, 9
... Current detection shunt, 10... Rotor position detection circuit, speed detection circuit, 11... Coil switching transistor, 12... Three-phase brushless motor, 13... Rotor position detector, 14... Coil, 15... Sawtooth signal generator, 16... PWM comparator, 17... Logic circuit

Claims (2)

[Claims] 1. A drive circuit for a DC brushless motor for a rotating polygonal mirror optical deflector for scanning a beam, etc., includes a phase-locked loop control means and a pulse width control means, and controls the rotation speed of the motor by combining these means. A DC brushless motor for an optical deflector, which is characterized by: 2. 2. The DC brushless motor for an optical deflector according to claim 1, wherein the reference clock pulse signal of the phase-locked loop control means and the switching frequency of the pulse width control means are synchronized.