JPH06237591A - Constant current drive circuit of dc motor - Google Patents

Abstract

PURPOSE:To make it possible to execute a constant current drive of a DC motor inexpensively by reducing high-speed switching elements needed for a constant current drive circuit of the motor and also by simplifying the construction of the drive circuit. CONSTITUTION:Based on a pulse signal outputted from a triangular wave generating circuit 39 for preparing the upper-side apex of a triangular wave and on a PWM signal, a sample hold circuit 44 holds a sample of a current detected by a current detector 32, and based on this current of which the sample is held and on an output from an arithmetic part 40, an amplifier 38 and a comparator 37 prepare the PWM signal so as to execute a constant current drive of a motor 45.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a constant current drive circuit for controlling the speed of a DC motor.

[0002]

2. Description of the Related Art Many electronic devices and control devices use a motor. Taking an electrophotographic copying machine (hereinafter referred to as a copying machine) as an example, a plurality of motors are used in one copying machine for driving a photosensitive drum, driving an optical scanning system, driving a fixing roller, and the like.

Although some of these motors may always rotate in a fixed direction, in the motor for driving the optical scanning system, the rotation direction of the motor is set in the forward movement for exposing and scanning the original and in the optical scanning. The optical scanning system is caused to reciprocate by rotating the motor in the opposite direction when returning to the reference position after exposure scanning of the system. For this reason, the motor for driving the optical scanning system is a motor capable of rotating in the forward and reverse directions. Further, since the optical scanning system needs to be moved at a constant speed when the original is exposed, speed control is performed. .

As a motor speed control method, an actual rotation speed of the motor is detected by an encoder, a pulse signal from this encoder is compared with a pulse signal corresponding to a target rotation speed, and PID (proportional, integral, differential) is compared. A method is known in which control is performed, and based on the result, the time for applying a constant voltage to the motor is changed by a PWM (pulse width modulation) method to adjust the current flowing in the motor to perform speed control.

By the way, only by such a speed control method in which the voltage application time is changed based on the actual rotation speed of the motor and the target rotation speed, for example, a load is applied to the power supply in addition to a constant voltage applied to the motor. If the voltage drops unexpectedly, the current flowing through the motor decreases even if the voltage application times are the same, and the rotation speed of the motor does not reach the target rotation speed.

Therefore, even if the applied voltage fluctuates, constant current driving is performed to detect and correct the current flowing in the motor so that the same current as the current that should flow when the voltage does not fluctuate. Control is taking place.

Here, FIG. 6 shows a circuit diagram of a drive driver of a conventional constant current drive circuit for a DC motor.

A DC voltage source 30 is applied to the motor M to rotate the motor M. F
The ETs 51, 52, 53, 54 are bridge-connected, and, for example, the FETs 52, 53 are turned off to set the FE
When the PWM signal is applied to T51 and T54, the FETs 51 and 54 are turned ON when the PWM signal is HIGH, and the point C,
Through point B, FET 51, point E, point F, motor M, point G, point H, FET 54, point K, point J, resistance r, point L,
Current flows from the voltage source 30 to ground. When the motor M is rotated in the reverse direction, the FETs 51 and 54 are turned off.
Then, when the PWM signal is applied to the FETs 52 and 53,
When the PWM signal is HIGH, the FETs 52 and 53 are turned on, and the point C, the point D, the FET 52, the point H, the point G, the motor M, the point F, the point E, the FET 53, the point I, the point J, the resistance r, the point L. A current flows from the voltage source 30 to the ground through.

In order to drive the motor M with a constant current, it is necessary to detect the current flowing through the motor M. In FIG.
The potential difference between the point L and the point L is detected, and the current flowing to M is detected from this potential difference. When the FETs 52 and 53 are turned off and a PWM signal is applied to the FETs 51 and 54, P
When the WM signal is HIGH, the FETs 51 and 54 are turned on, and the point C, the point B, the FET 51, the point E, the point F, the motor M, the point G, the point H, the FET 54, the point K, the point J, the resistance r, the point. A current flows from the voltage source 30 to the ground through L and the motor M starts to rotate. In this state, when the PWM signal becomes LOW, the FETs 51 and 54 are turned off and the motor M,
Point F, diode D1, point B, point C, path of voltage source 30, ground, point L, resistance r, point J, point K, diode D
4, current flows through the path of point G and motor M. That is, P
Regardless of whether the WM signal is HIGH or LOW, when the motor M is rotating, there is a current flowing through the resistor r. Therefore, the constant current drive of the motor M can be performed by detecting the current.

[0010]

However, in the drive driver of the conventional constant current drive circuit for the DC motor described with reference to FIG. 6, four FETs are required for accurate speed control.
51, 52, 53, 54 are all HI of the PWM signal
It is necessary to use an expensive high-speed switching element that turns ON / OFF in response to GH / LOW at high speed. For example, when a PWM signal is applied to the FETs 51 and 54, there is a switching timing difference between the FETs 51 and 54. I had to make sure it didn't, and I needed a predriver for this. Therefore, conventionally, the configuration of the constant current drive circuit of the motor is complicated and the cost is high.

The present invention has been made in view of the above points, and reduces the number of high-speed switching elements required for a constant current drive circuit of a motor and simplifies the configuration of the drive circuit to inexpensively drive a constant current of a DC motor. The purpose is to be able to.

[0012]

In order to achieve the above object, the present invention connects a motor on one diagonal of a bridge composed of four switching elements, and supplies a predetermined power source to both ends of the other diagonal. Is connected to the ground, and when the motor is rotated in one direction, only one of the switching elements on one side of the pair is turned on and the PWM signal is applied to the other to turn on O.
When the motor is turned N / OFF and the motor is rotated in the reverse direction, only one of the switching elements on the opposite side of the other pair is turned ON and a PWM signal is applied to the other to turn the motor ON / OFF to rotate the motor forward / reversely. A current detecting means for detecting a current flowing to the ground side of the motor driving means, a triangular wave generating means for generating a triangular wave for creating a PWM signal and a pulse signal located at an inflection point of the triangular wave, and The sample and hold means for sampling and holding the current detected by the current detecting means based on the pulse signal and the PWM signal output from the triangular wave generating means, and the current after the hold output output from the sample and hold means,
The constant current drive circuit of the DC motor is composed of the correction means for correcting the PWM signal so that it becomes equal to the current flowing through the motor when the voltage of the predetermined power source does not change.

[0013]

According to the present invention, with the above configuration, the sample hold means detects the current detected by the current detecting means on the basis of the pulse signal and the PWM signal for producing, for example, the upper vertex of the triangular wave output from the triangular wave generating means. Is sampled and held, and the correction means corrects the PWM signal applied to the motor based on the held current output from the sample and hold means, and the motor is driven with a constant current.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings.

FIG. 5 shows a schematic construction of a copying machine to which a constant current drive circuit for a DC motor according to the present invention is applied.

A control panel 10 provided on the upper surface of the main body of the copying machine.
When the copying is started by the copy start key on the operation panel 100 after the power button on 0 is turned on, the original 21 placed on the original table 1 is reciprocally moved to the illumination lamp 2 of the optical scanning system A.
The reflected light 20 (shown by a chain line) from the original 21 is reflected by the first mirror 3 and the fixed second mirror 4 and third mirror 5, which also constitute the optical scanning system A, and is reflected by the lens. After passing through 6, the light is reflected by the fourth mirror 7 and projected onto the photosensitive drum 8, and an electrostatic latent image of the original 21 is formed on the drum 8. On the other hand, the copy paper 12 is conveyed from the paper feed cassette 11 to the transfer position through the path indicated by the chain double-dashed line.

Around the drum 8, a charging electrode 9 for uniformly charging the photoconductor provided on the surface of the drum 8 is provided.
A developing device 10 for developing the electrostatic latent image formed on the photoconductor into a visible image (toner image), and a transfer electrode 13 for transferring the visible image to the copy paper P. , A separation electrode 14 for separating the copy paper P on which the visible image has been transferred from the drum 8, a charge eliminating electrode 15 for eliminating charges remaining on the photoconductor, and a toner remaining on the photoconductor after the charge elimination. And a cleaning device 16 for removing the above.

The electrostatic latent image formed on the photosensitive member is transferred onto the copy paper 12 by the transfer electrode 13, and after transfer, the copy paper 12 separated from the drum 8 by the separation electrode 14 is transferred to two points by the conveying roller 17. The fixing device 1 passes through the path indicated by the chain line.
Then, the toner on the copy paper 12 is melted by heat, fixed on the copy paper 12, and discharged to the discharge tray 19.

The constant current drive circuit of the DC motor according to the present invention can be applied to the drive motor of the optical scanning system A shown in FIG.

FIG. 1 is a circuit diagram of a constant current drive circuit for a DC motor according to the present invention.

Reference numeral 30 is a DC voltage source for applying to the motor 45, 31 is an encoder for detecting the rotation speed of the motor 45, and 40 is a rotation speed of the motor 45 detected by the encoder 31 and a predetermined target rotation speed. Based on this, it is a calculation unit that calculates the voltage to be applied to the motor 45. A current detector 32 detects a current flowing through the resistor r, and the detected current is input to the sample hold circuit 44.
The sample hold circuit 44 includes an FE 534, a capacitor 35, and an amplifier 36, and holds and outputs the detected current input from the current detector 32 based on the output of the OR circuit 33. Reference numeral 38 denotes an amplifier that combines the calculation result of the calculation unit 40 and the output of the sample hold circuit 44,
Based on the output of the amplifier 38 and the triangular wave from the triangular wave generation circuit 39, the comparator 37 outputs a PWM signal for controlling the speed of the motor 45. This PWM signal is applied to the drive driver of the motor 45 and the OR circuit 3
It is also input to 3. Further, the OR circuit 33 is supplied with a pulse signal from the triangular wave generating circuit 39 for creating the upper vertex of the triangular wave.

FIG. 2 is a circuit diagram of a drive driver of a constant current drive circuit for a DC motor according to the present invention.

A DC voltage source 30 is applied to the motor 45 to rotate the motor 45. The FETs 51, 52, 53, 54 are bridge-connected, and for example, the FETs 52, 53 are turned off and the FE is turned on.
When T51 is turned ON and the PWM signal is applied to the FET 54, the FET 54 is turned ON when the PWM signal is HIGH, and the point C, the point B, the FET 51, the point E, the point F, and the motor 4 are turned on.
5, the current flows from the voltage source 30 to the ground through the point G, the point H, the FET 54, the point K, the point J, the resistor r, and the point L.
When the motor 45 is rotated in the reverse direction, FET5
1,54 OFF, FET52 ON, FET5
When the PWM signal is applied to 3, the FET 53 is turned on when the PWM signal is HIGH, and the point C, the point D, and the FET 5
2, point H, point G, motor 45, point F, point E, FET5
3, the current flows from the voltage source 30 to the ground through the points I, J, the resistance r, and the point L.

By the way, in the drive driver of FIG.
Turn off T52 and 53, turn on FET51, and set F
When the PWM signal is applied to ET54, the PWM signal is H
When IGH, FET54 is turned on, and point C, point B,
FET 51, point E, point F, motor 45, point G, point H, F
A current flows from the voltage source 30 to the ground through the ET 54, the point K, the point J, the resistance r, and the point L, and the motor 45 starts to rotate. In this state, when the PWM signal becomes LOW, the FET 5
4 is turned off, motor 45, point G, diode D
2, the current flows through the path of the point D, the point C, the point B, the FET 51, the point E, the point F, and the motor 45. That is, the PWM signal is L
In the case of OW, there is no current flowing through the resistor r even though the motor 45 is rotating and current is flowing. Therefore, if the current flowing through the resistor r is simply detected and the constant current drive of the motor is performed, it is misunderstood that the current flowing in the motor 45 is 0 when the PWM signal is LOW, and the motor is unnecessarily driven. Because it will send an electric current to
The speed of the motor 45 cannot be controlled accurately. In the present invention, as a measure against this problem, by using the sample hold circuit 44 shown in FIG. 1, when the current flowing through the resistor r is 0 even though the motor 45 is rotating and the current is flowing, the current is reduced. The current just before it becomes 0 is held, and the motor 45 is driven with a constant current based on the held current.

FIG. 3 is an internal circuit diagram of the triangular wave generating circuit 39 shown in FIG.

Reference numeral 41 is a comparator, which creates a pulse at the upper vertex of the triangular wave, and this pulse is output to the flip-flop circuit 46 and the terminal M shown in FIG. Reference numeral 42 is a comparator, which creates a pulse at the lower apex of the triangular wave, and this pulse is output to the flip-flop circuit 46. The output of the flip-flop circuit 46 is input to the amplifier 43, and the amplifier 43 generates a triangular wave. This triangular wave is output to the comparator 41 and the comparator 42 and also to the terminal N shown in FIG.

Next, FIG. 4 shows waveforms of signals and the like at various points in the constant current drive circuit shown in FIG.

(A) shows the waveform of the triangular wave output from the triangular wave generating circuit 39. (B) shows the comparator 37
It is the waveform of the PWM signal output from. (C) is a waveform of a pulse for creating the upper vertex of the triangular wave output from the triangular wave generating circuit 39. (D) is the waveform of the signal output from the OR circuit 33 and obtained by ORing the PWM signal (b) and the pulse (c) for creating the upper vertex of the triangular wave. (E) is a sample hold circuit 4
4 is a waveform of a current output after being held from FIG.
(F) is the waveform of the current that actually flows through the motor 45. (G) is the waveform of the current that actually flows through the resistor r.

As described above, the FET shown in FIG.
When the PWM signal is applied only to 53 or 54, if the constant current drive of the motor 45 is used with the current actually flowing in the resistor r shown in FIG. 4, the PWM signal becomes L
When it is OW, the current becomes 0 as shown in FIG. 4 (g), and the constant current drive of the motor 45 cannot be performed.

According to the present invention, the signal shown in FIG.
At the timing of becoming W, the sample hold circuit 44 holds the current actually flowing in the resistor r, and the current close to the current actually flowing in the motor 45 shown in FIG.
(E)) is used to drive the motor 45 at a constant current.

[0031]

As described above, according to the present invention,
It is the FET that switches at the timing of the PWM signal
Since only 53 or 54 is required, only the two high-speed switching elements, FET 53 and 54 or FET 51 and 52, out of the four switching elements that make up the constant current drive circuit of the motor are necessary.
A pre-driver for eliminating the timing difference of switching between 51 and 54 is unnecessary, and the configuration of the drive circuit can be simplified.

Further, according to the present invention, the fast recovery diodes of the diodes D3 and D4 shown in FIG. 6 are also unnecessary. However, this diode may be used for a purpose other than the constant current drive of the motor (protection during abnormal operation of the circuit).

According to the present invention, a sample and hold circuit is required, but considering that only two high speed switching elements are required, the sample and hold circuit is inexpensive, so that the constant current drive circuit for a DC motor is inexpensive. Can be configured to.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a constant current drive circuit for a DC motor according to the present invention.

FIG. 2 is a circuit diagram of a drive driver of a constant current drive circuit for a DC motor according to the present invention.

FIG. 3 is an internal circuit diagram of a triangular wave generation circuit 39 shown in FIG.

4 shows waveforms of signals and the like in (a) to (g) of the constant current drive circuit of the DC motor shown in FIG.

FIG. 5 is a schematic configuration diagram of a copying machine to which a constant current drive circuit for a DC motor according to the present invention is applied.

FIG. 6 is a circuit diagram of a drive driver of a constant current drive circuit of a conventional DC motor.

[Explanation of symbols]

 30 DC voltage source 31 Encoder 32 Current detector 33 OR circuit 37 Comparator 38 Amplifier 39 Triangular wave generating circuit 40 Arithmetic unit 44 Sample hold circuit 45 Motor

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hiroyuki Watanabe 2970 Ishikawacho, Hachioji City, Tokyo Konica Stock Company

Claims (1)

[Claims] 1. A motor is connected to one diagonal of a bridge composed of four switching elements, and a predetermined power source and a ground are connected to both ends of the other diagonal to rotate the motor in one direction. Turn on only one of the switching elements on one side of the pair and apply the PWM signal to the other
When the motor is turned N / OFF and the motor is rotated in the reverse direction, only one of the switching elements on the opposite side of the other pair is turned ON, and a PWM signal is applied to the other to turn it ON / OFF to drive the motor in the forward / reverse direction. Means, current detecting means for detecting a current flowing to the ground side of the motor driving means, and triangular wave generating means for generating a triangular wave for creating the PWM signal and a pulse signal located at an inflection point of the triangular wave. The pulse signal output from the triangular wave generating means and the PW
The sample and hold means for sampling and holding the current detected by the current detection means based on the M signal, and the motor after the voltage of the predetermined power supply does not fluctuate between the held current output from the sample and hold means. A constant current drive circuit for a DC motor, comprising: a correction unit that corrects the PWM signal so as to be equal to the current flowing through the DC motor.