JPH07222480A - Electric motor speed control device and office equipment including an electric motor controlled by the speed control device - Google Patents

Abstract

(57) [Summary] [Purpose] Stable control of the motor to the target rotation speed even if the load torque changes due to switching of the rotation speed or changes in the ambient temperature. When the load torque changes and the drive current changes, the current detection device 27 detects this and changes the operation reference voltage level given to the non-inverting input terminal of the operational amplifier 19 to assist the control of the motor drive voltage. As described above, the electric motor can be stably controlled to the target rotation speed even if the rotation speed is switched or the load changes due to the ambient temperature change.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a speed control device for an electric motor and an office machine equipped with an electric motor whose speed is controlled by the control device. In particular, there is a large change in load torque due to speed switching and changes in ambient temperature. Even so, it relates to speed control of an electric motor for stably maintaining a predetermined rotation speed.

[0002]

2. Description of the Related Art A speed control device for controlling the rotation speed of an electric motor includes phase comparison means for comparing the phases of a rotation speed detection signal of the electric motor and a speed reference signal and outputting a phase control signal, and a speed reference signal and a speed detection signal. Speed comparison means for comparing the signal periods and outputting a speed control signal; and drive control circuit means for controlling the motor drive voltage (current) with a control signal obtained by adding the phase control signal and the speed control signal. I have it.

When the magnitude of the load torque changes, the speed control device changes the voltage level of the phase control signal to increase or decrease the drive (load) current and absorb the change in the load torque. It acts to maintain the rotation speed at a predetermined value.

[0004]

By the way, in a motor in which the load torque has a small instantaneous fluctuation due to viscous friction loss and wind loss of the bearing, the gain of the control device is set as small as possible in order to reduce uneven rotation. In such a control device, when a change in the viscous friction load torque of the bearing due to a change in the ambient temperature or a change in the load torque such as a viscous friction load torque of the bearing, a hysteresis loss, and a wind loss due to the switching of the rotation speed occurs, the rotation unevenness occurs. However, there is a problem that the gain set to a small value for the purpose of reducing the torque cannot cope with the change of the load torque, the stable synchronous control state cannot be achieved, and the speed becomes out of synchronization and the stable speed control cannot be performed. It was

As described above, in the conventional speed control device for an electric motor, when the gain is set small for controlling the rotational speed of the electric motor, which is desired to rotate with a small rotational irregularity, the rotational speed is changed and the ambient temperature changes. Therefore, when the load torque of the electric motor changes, there is a problem that the rotation speed of the electric motor cannot be stably controlled to a target value.

An object of the present invention is to provide a speed control device for an electric motor and a speed control device for the electric motor, which can stably control the electric motor to a target rotational speed even if there is a change in load torque due to a change in rotational speed or a change in ambient temperature. It is to provide office equipment using an electric motor controlled by a device.

[0007]

According to the present invention, there is provided speed detecting means for generating a speed detecting signal having a frequency proportional to the rotation speed of an electric motor, reference signal generating means for generating a predetermined speed reference signal, and the speed reference. Phase comparison means for comparing the phases of the signal and the speed detection signal to generate a phase control signal, speed comparison means for comparing the periods of the speed reference signal and the speed detection signal to generate a speed control signal, and the phase control In a speed control device for a motor including drive control circuit means for controlling a motor drive voltage according to a signal and a speed control signal, a load current detection device for detecting a load current of the motor, and the load current detection device according to the detected amount thereof. The present invention is characterized in that load current correction means for preventing the synchronization of the phase comparison means by changing the operation reference voltage of the drive control circuit means is provided.

Further, the invention comprises a copying or printing section, a polygon mirror driving electric motor for driving a polygon mirror for sweeping laser light on the copying or printing section, and an electric motor control circuit for controlling the polygon mirror driving electric motor. In the office equipment, in the electric motor control circuit, speed detection means for generating a speed detection signal having a frequency proportional to the rotation speed of the electric motor, reference signal generation means for generating a predetermined speed reference signal, and the speed reference signal Phase comparison means for comparing the phases of the speed detection signals to generate a phase control signal; speed comparison means for comparing the periods of the speed reference signal and the speed detection signals to generate a speed control signal; Drive control circuit means for controlling an electric motor drive voltage according to a speed control signal; a load current detection device for detecting a load current of the electric motor; Characterized in that a load current compensation means for preventing the loss of synchronization the phase comparing means by changing the operation reference voltage of the drive control circuit means in response to the detected quantity.

[0009]

When the load torque of the electric motor increases, the electric motor becomes lower than the target rotation speed, and the speed control device increases the speed control signal and the phase control signal to increase the electric motor drive (load) current. Increase the drive voltage. The increased load current of the motor is detected by the load current detection device to change the operation reference voltage level of the drive control circuit means. When the rotation speed of the electric motor returns to the target rotation speed, the speed control signal returns to the original voltage level, and the operation reference voltage level also returns to a level close to the original voltage level.

[0010]

1 is a block diagram of a speed controller for a DC brushless motor to which a motor speed controller according to the present invention is applied. The permanent magnet rotor of this DC brushless motor is 8
It is magnetized to the pole.

In FIG. 1, magnetic detection elements 1, 2, 3
Detects the magnetic flux of the permanent magnets magnetized to the eight poles that form the rotor 4, and gives the distributor 5 a detection signal corresponding to the detected magnetic flux. The distributor 5 receives the detection signals from the magnetic detection elements 1 to 3 and gives a drive command signal to the drive device 6.
The drive device 6 supplies a drive voltage (current) from the power supply 7 to the drive coils 8, 9 and 10 according to the drive command signal given from the distributor 5.

The rotor 4 rotates by generating torque with the magnetic flux of the magnetized eight-pole permanent magnet and the magnetic field generated by the drive coils 8 to 10.

The speed sensor 11 responds to the change in the magnetic flux acting from the permanent magnet of the rotor 4 as the rotor 4 rotates, and detects the speed of the frequency proportional to the speed of the DC brushless motor. The signal 12 is generated and applied to the amplifier 13. The amplifier 13 gives a speed detection signal 14 obtained by amplifying the speed detection signal 12 to a control signal generator 15.

The control signal generator 15 includes a transmitter 16
A clock signal is supplied from the input terminal, and the input clock signal is internally divided to create a reference signal for speed control and phase control. Further, the control signal generator 15 is
A phase control circuit for comparing the phase difference between the reference signal and the speed detection signal 14 and outputting a phase control signal having a voltage level corresponding to the phase difference is built in. The output signal of the phase control circuit, that is, the phase control signal 24 is output to the output terminal P of the control signal generator 15. Further, the control signal generator 15 has a built-in speed control circuit for comparing the speed difference between the reference signal and the speed detection signal 14 and outputting a speed control signal having a voltage level corresponding to the speed difference. The output signal of the speed control circuit, that is, the speed control signal 25 is output to the output terminal F of the control signal generator 15.

One end of the resistor 17 is connected to the output terminal P, one end of the resistor 18 is connected to the output terminal F, and the other ends of the resistors 17 and 18 are commonly connected to the operational amplifier. 19 connected to the inverting input terminal.

A reference voltage is applied to the non-inverting input terminal of the operational amplifier 19 via a resistor 20, and a resistor 21 is connected between the output terminal and the inverting input terminal. And
The output terminal of the operational amplifier 19 is connected to the non-inverting input terminal of the comparator 22.

A triangular wave voltage, which is the output signal of the triangular wave generator 23, is applied to the inverting input terminal of the comparator 22, and as a result, the comparator 22 responds to the voltage level of the output signal of the operational amplifier 19. A rectangular wave signal voltage 26 having a duty is output.

The rectangular wave signal voltage 26 is applied to the drive unit 6, and the duty of the drive current flowing through the drive coils 8 to 10 is determined by the duty of the electric motor drive voltage controlled by the rectangular wave signal voltage 26.

On the other hand, the current detection device 27 detects the drive (load) current output from the drive device 6 and flowing to the drive coils 8 to 10, and lowers the potential at one end of the resistor 28 in proportion to the detected value. Let The other end of the resistor 28 is connected to the non-inverting input terminal of the operational amplifier 19.

As shown in FIG. 2, the control signal generator 15 D / A-converts the phase difference between the speed reference signal and the speed detection signal 14 and outputs it to the output terminal P. In addition, as shown in FIG. 3, the speed control signal 25 that functions to change linearly and is output to the output terminal F is
A fixed value of high (H) level is set in a region where the frequency of the speed detection signal 14 is a fixed value or less, a fixed value of low (L) level is set in a region of a fixed value or more, and D / A conversion is performed in a specific region It functions to change linearly.

FIG. 4 shows the rotational speed S-load (output) torque T-drive (load) current I curve of this DC brushless motor. The rotation speed S of the DC brushless electric motor has the maximum rotation speed N0 when the load torque T is 0, and decreases linearly as the load torque T increases, as the characteristic of the electric motor alone, as indicated by the broken line. . When the rotation speed of this DC brushless motor is controlled to Nf by the speed control device, the load torque T is Tm as shown by the solid line characteristic.
In the region where the rotation speed Nf is maintained until it becomes ax and the load torque T of Tmax or more is applied, the rotation speed decreases almost linearly like the characteristic of the single body. Further, it is necessary to flow a drive current approximately proportional to the load torque T into the DC brushless motor.

Here, in order to flow the drive current following the change of the load torque T so as to keep the rotation speed of the DC brushless motor at a target constant value, the control signal generator 15 is used.
Needs to change the value of the phase control signal 24 output from the output terminal P, and its load torque T-phase control signal voltage Vp (voltage of the phase control signal 24) characteristic is
As shown in FIG. 5, when the load torque T fluctuates from 0 to Tmax, the characteristic is that it changes greatly from L1 to H1.
Depending on the characteristics of the DC brushless motor and the characteristics of the control device, there is a risk that the phase control signal voltage Vp during the synchronous settling cannot be set between 0 and H and the rotation becomes unstable.

In order to prevent this, it is a general countermeasure to increase the gain. However, if the gain is excessively increased in the control device for the electric motor for driving the polygon mirror, which is required to have the characteristic of low rotation unevenness. Since a cyclical undulation occurs in the rotation speed to increase the rotation unevenness, this problem cannot be solved by simply increasing the gain.

FIG. 6 shows changes in the phase control signal voltage Vp of the speed control device according to the present invention, even when the load torque T varies from 0 to Tmax without setting a large gain. As described above, the operation is performed so that a small change in the range from L2 to H2 can be used.

This operation will be described with reference to the control system shown in FIG. 7, which is a part of FIG.

When the load torque T applied to the DC brushless motor increases and the drive current increases, the current detecting device 27
Detects this increase in drive current and lowers its output potential. This characteristic can be obtained by configuring the current detection device 27 with an inverting amplifier or the like. The output potential of the current detection device 27 is given to the resistor 28, but in the configuration of this embodiment, the output potential of the operational amplifier 19 decreases due to the decrease of the output potential of the current detection device 27, and the output voltage of this operational amplifier 19 is reduced. As a result, the duty of the motor drive voltage increases and the drive current increases. Therefore, the load torque T does not depend entirely on the change of the phase control signal voltage Vp.
Of the phase control signal voltage Vp when the load torque T fluctuates from 0 to Tmax without setting a large gain, as shown in FIG. As shown, a small change between L2 and H2 makes it possible to deal with it.

The speed control device according to the present invention can be controlled in the same manner even if the operational amplifier 19 connected to the subsequent stage of the control signal generation device 15 is modified to have non-inverting amplification characteristics instead of inverting amplification characteristics. The characteristics can be obtained.

FIG. 8 is a block diagram of this modified speed control device. The same components as those of the embodiment shown in FIG. 1 are designated by the same reference numerals, the description thereof will be omitted, and different points will be mainly described.

The resistor 17 connected to the output terminal P and the resistor 1 connected to the output terminal F of the control signal generator 15.
The other end of 8 is connected in common to the non-inverting input terminal of the operational amplifier 19. A reference voltage is applied to the inverting input terminal of the operational amplifier 19 via the resistor 20, and a resistor 21 is connected between the output terminal and the inverting input terminal. The current detection device 27 detects the drive current output from the drive device 6, applies a potential proportional to the detected value to one end of the resistor 28, and supplies the potential to the operational amplifier 19 via the resistor 28.
Change the potential applied to the inverting input terminal of.

The operation of this embodiment will be described with reference to the control system of FIG. 9 which is a part of FIG.

When the load torque T applied to the DC brushless motor increases and the drive current increases, the current detecting device 27
Detects an increase in its drive current and lowers its output potential. This characteristic can be obtained by configuring the current detection device 27 with an inverting amplifier or the like. The output potential of the current detection device 27 is given to the resistor 28.
Is an input resistance of the inverting amplifier when viewed from the current detection device 27, the output potential of the operational amplifier 19 rises as the output potential of the current detection device 27 decreases. This characteristic is that by changing the operation reference voltage according to the detected amount of the drive current, the drive current control corresponding to the variation of the load torque T can be realized without completely depending on the change of the phase control signal voltage Vp. And a change in the phase control signal voltage Vp when the load torque T changes from 0 to Tmax without setting a large gain, as shown in FIG.
A small change between 2 and H2 makes it possible to deal with it. In this embodiment, the operational amplifier 1
The drive device 6 is configured so that the drive current increases due to the change in the duty of the rectangular wave output signal voltage 26 of the comparator 22 due to the increase in the output potential of the comparator 9.

The speed control device of the present invention can also be applied to speed control of an electric motor with a DC brush. Figure 1
Reference numeral 0 is a block diagram of a speed controller for a DC brushless motor, and the same components as those of the DC brushless motor speed controller described with reference to FIG. Omit it.

One brush 30 of the electric motor 29 with a DC brush
Is connected to the power source 7, and the other brush 31 is connected to the driving device 3
2 are connected. The drive device 32 similarly controls the duty of the drive voltage applied to the electric motor 29 with a DC brush to control the drive current.

The speed control device according to the present invention includes the phase control signal voltage V output to the output terminal P of the control signal generator 15.
Since it is possible to cope with a large change in the load torque T even if the change in p is kept small, it is possible to perform speed switching that could not be realized unless the phase control signal voltage Vp is changed greatly.

FIG. 11 is a block diagram of a speed control device for a direct current brushless motor capable of switching the fourth speed according to the present invention. The same components as those in the embodiment shown in FIG. 1 are designated by the same reference numerals and the description thereof will be omitted.

The oscillator for generating the frequency that serves as the reference of the rotation speed is composed of the first oscillator 33, the second oscillator 34, the third oscillator 35 and the fourth oscillator 36, and the oscillator 3
The frequency of the clock signal output from 3 to 36 is proportional to the frequency of the speed detection signal 12 output from the speed sensor 11 at the four control target rotation speeds of the DC negative brush motor.

Each of the four oscillators 33 to 36 is connected so that its output signal is input to the selector 37, one of which is selected according to a command from the 2-bit speed command signal 38 and controlled as a clock signal. It is provided to the signal generator 15.

The control signal generator 15 generates a control signal for controlling the speed of the DC brushless motor in the same manner as in the above-described embodiment, with the oscillation frequency of the oscillator selected and given by the selector 37 as a reference.

FIG. 12 is a vertical cross-sectional side view of office equipment such as a printer, a facsimile or a copying machine, which drives a polygon mirror by using an electric motor controlled by the speed control device according to the present invention. System controller 39
Controls the blinking of the laser emission source 40,
The laser light generated from the above is deflected by the polygon mirror 42 which is rotationally driven by the polygon mirror electric motor 41 to expose the photosensitive drum 43. The print pattern formed on the photosensitive drum 43 by being exposed to the laser light is transferred to the transfer drum 44 and developed by the developing device 45 to form a visible image. The recording paper 47 placed on the paper feed tray 46 is
The transfer drum 4 is extracted and conveyed by the paper feed roller 48.
The visible image is transferred from No. 4, is conveyed by the paper feeding belt 49, is fixed by the fixing device 50, and is sent out of the device.

Although the above-mentioned embodiment has been described by using the PWM (pulse width modulation) system as the drive (load) current control of the electric motor, it can be similarly implemented by the PAM system (pulse amplitude modulation). .

[0041]

According to the present invention, when the load torque changes and the drive current changes, the operation reference voltage level of the drive control circuit means changes to assist the control of the motor drive voltage. Even if there is a change in load due to switching or a change in ambient temperature, the electric motor can be stably controlled at a target rotation speed.

[Brief description of drawings]

FIG. 1 is a block diagram of a speed control device for a DC brushless motor according to the present invention.

FIG. 2 is an output characteristic of a phase control signal in a speed control device for an electric motor.

FIG. 3 is an output characteristic of a speed control signal in a speed control device for an electric motor.

FIG. 4 is a correlation characteristic of rotation speed S of DC motor, load torque T, and drive current I.

FIG. 5 is a correlation characteristic of load torque T-phase control signal voltage Vp in the conventional speed control device.

FIG. 6 is a correlation characteristic of load torque T-phase control signal voltage Vp in the speed control device according to the present invention.

FIG. 7 is a block diagram for explaining the operation of the control system, in which a part of the speed control device shown in FIG. 1 is extracted.

FIG. 8 is a block diagram showing another embodiment of the speed control device for a DC brushless motor according to the present invention.

9 is a block diagram for explaining the operation of the control system, which is a part of the speed control device shown in FIG.

FIG. 10 is a block diagram of a speed control device for an electric motor with a DC brush according to the present invention.

FIG. 11 is a block diagram showing still another embodiment of the speed control device for a DC brushless motor according to the present invention.

FIG. 12 is a vertical cross-sectional side view of office equipment using an electric motor controlled by the speed control device according to the present invention.

[Explanation of symbols]

 1, 2 and 3 Magnetic detection element 4 Rotor 6 Drive device 8, 9 and 10 Drive coil 11 Speed sensor 12 and 14 Speed detection signal 15 Control signal generator 19 Operational amplifier 22 Comparator 23 Triangular wave generator 24 Phase control signal 25 Speed control signal 27 Current detector 28 Resistor

Claims (3)

[Claims] 1. A speed detection means for generating a speed detection signal having a frequency proportional to a rotation speed of an electric motor, a reference signal generation means for generating a predetermined speed reference signal, and a phase of the speed reference signal and the speed detection signal. Phase comparison means for comparing and generating a phase control signal, speed comparison means for comparing the periods of the speed reference signal and speed detection signal to generate a speed control signal, and depending on the phase control signal and the speed control signal A speed control device for an electric motor, comprising a drive control circuit means for controlling an electric motor drive voltage, wherein a load current detection device for detecting a load current of the electric motor,
A speed control device for an electric motor, comprising: load current correction means for preventing out-of-synchronization of the phase comparison means by changing an operation reference voltage of the drive control circuit means in accordance with the detected amount. 2. The speed control device for an electric motor according to claim 1, wherein the reference signal generating means switches the speed reference signal to switch the rotation speed of the electric motor. 3. An office machine comprising a copying or printing section, a polygon mirror driving electric motor for driving a polygon mirror for sweeping laser light on the copying or printing section, and an electric motor control circuit for controlling the polygon mirror driving electric motor. In the motor control circuit, the speed control means for generating a speed detection signal having a frequency proportional to the rotation speed of the motor, a reference signal generation means for generating a predetermined speed reference signal, the speed reference signal and the speed detection signal. Phase comparison means for generating a phase control signal by comparing the phases of the two, speed comparison means for generating a speed control signal by comparing the periods of the speed reference signal and the speed detection signal, the phase control signal and the speed control signal Drive control circuit means for controlling the motor drive voltage according to the above, a load current detection device for detecting the load current of the motor, and the additional current Load current correction means for preventing the phase comparison means from being out of synchronization by changing the operation reference voltage of the drive control circuit means in accordance with the detected amount of the load current detected by the output device. office supply.