JPH1076705A - Laser oscillator driving device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laser oscillator driving device capable of always obtaining a stable optical output of which optical quantity is not varied by temperature variation or a returning light and obtaining a high quality output image. SOLUTION: A voltage feedback type operational amplifier 51 executes a differential calculation between an optical modulation signal f01 inputted from a modulation circuit 34 and a reference voltage Vref from a reference voltage source 53 and outputs the calculated result as a voltage signal. A current driving transistor 54 converts the output voltage of the operational amplifier 51 to a laser driving current ID and drives a laser oscillator 31 in accordance with the laser driving current ID. A photodiode 42 detects a part of the laser light outputted from the laser oscillator 31 and converts it to a current signal. A feedback resistor 56 negatively feeds the current obtained by the photodiode 42 back to an inversion input terminal A to which the optical modulation signal f01 of the operational amplifier 51 is inputted.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser oscillator driving apparatus for driving a laser oscillator used as an exposure light source for forming an image on a photosensitive drum, and a digital copying machine using the same. The present invention relates to an image forming apparatus such as a laser printer and a facsimile.

[0002]

2. Description of the Related Art Recently, for example, a digital copying machine has been developed which forms an image by scanning exposure using a light beam and an electrophotographic process. In such a digital copying machine, a semiconductor laser oscillator is used as a light source for obtaining a light beam. As is well known, a laser oscillator emits light at a desired optical output by applying a predetermined drive current. However, an automatic optical output control (APC) is used to always obtain a constant optical output. : AUTO
POWER CONTROL).

In a conventional digital copying machine, automatic light output control of a laser oscillator is performed by detecting a light output after a previous scan by a light detecting element such as a monitor photodiode during a horizontal synchronizing signal detection period, and setting an arbitrary output level. The light output is set to the first position, and the light output of the light beam at the time of the next scanning is corrected.

[0004] For example, see Japanese Patent Application Laid-Open No. 5-128535.
In the optical disc device disclosed in Japanese Patent Application Laid-Open Publication No. H11-157, the automatic light output control of the laser oscillator for obtaining the beam light required for the reproduction, erasure, and recording is not limited to continuous emission during reproduction in order to realize high-density recording. Real-time APC operation by optical coupling is always performed for high-output continuous light emission at the time of erasing, high-frequency light emission at the time of recording, and the like, so that light output changes due to temperature changes and light output changes due to return light are corrected and suppressed.

[0005]

However, in the automatic light output control of the laser oscillator in the above-mentioned conventional digital copying machine, negative feedback control is not performed at the time of image formation at the next scanning. For this reason, when recording at high density or high gradation, 1
There is a problem that the influence of a temperature change during the scanning period is concerned.

In the above-described automatic optical output control of a laser oscillator in a conventional optical disk apparatus, when this is applied to an image forming apparatus such as a digital copying machine, negative feedback control cannot be performed when there is no light amount between dots. There is a problem that the operation becomes unstable.

Further, in the conventional automatic light output control, since a voltage feedback type operational amplifier (operational amplifier) is used in the basic circuit of the control circuit, it is difficult to obtain gradation by using the output waveform of the laser light. In addition, there is a problem that a change in the amount of negative feedback of the operational amplifier due to a difference in the output of the laser beam causes band limitation and peaking to occur, and a change in the output waveform deteriorates the gradation.

Accordingly, the present invention provides a laser oscillator driving apparatus and an image forming apparatus which can always obtain a stable light output without a change in light amount due to a temperature change or return light and can obtain a high quality output image. The purpose is to:

It is another object of the present invention to provide a laser oscillator driving apparatus and an image forming apparatus which can remove the influence of frequency change on gradation change due to increase or decrease of light output and can obtain a high quality output image. I do.

It is a further object of the present invention to provide a laser oscillator driving device and an image forming apparatus capable of stabilizing negative feedback control by optical output and obtaining a high-quality output image.

[0011]

SUMMARY OF THE INVENTION A laser oscillator driving apparatus according to the present invention comprises: an operational amplifier for performing an operation between an input optical modulation signal and a preset reference signal; and a laser oscillator in accordance with an output of the operational amplifier. , A light detecting means for detecting a part of the laser light output from the laser oscillator and converting it into an electric signal, and outputting an output of the light detecting means to a light modulation signal input side of the operational amplifier. Return means for returning.

Further, the laser oscillator driving device of the present invention comprises:
A voltage feedback type operational amplifier that performs a differential operation between an input optical modulation signal and a preset reference signal, and outputs a result of the differential operation as a voltage value, and a drive current that outputs an output voltage of the operational amplifier. And a drive element for driving a laser oscillator with the drive current, a photodetector element for detecting a part of the laser light output from the laser oscillator and converting it into a current signal, and a photodetector element. A feedback circuit for feeding the current back to the optical modulation signal input side of the operational amplifier.

Further, the laser oscillator driving device of the present invention comprises:
A current feedback type operational amplifier that performs a differential operation between an input optical modulation signal and a preset reference signal and outputs a result of the differential operation as a voltage value and has no frequency change with respect to a gain change; A drive element that converts the output voltage of the amplifier into a drive current, drives a laser oscillator with the drive current, and a photodetector that detects a part of the laser light output from the laser oscillator and converts it into a current signal, A feedback circuit for feeding back the current obtained by the photodetector to the optical modulation signal input side of the operational amplifier.

Further, the laser oscillator driving device of the present invention comprises:
An operational amplifier for performing an operation on an input optical modulation signal and a preset reference signal; driving means for driving a laser oscillator in accordance with the output of the operational amplifier; and a laser beam output from the laser oscillator A light detecting means for detecting the portion and converting the light into an electric signal; a first feedback means for feeding back the output of the light detecting means to a light modulation signal input side of the operational amplifier; and a driving current for the laser oscillator. Second feedback means for feeding back the voltage to the optical modulation signal input side of the operational amplifier; and clamp means for clamping the voltage fed back by the second feedback means in accordance with the drive current of the laser oscillator. ing.

Further, the laser oscillator driving device of the present invention comprises:
A voltage feedback type operational amplifier that performs a differential operation between an input optical modulation signal and a preset reference signal, and outputs a result of the differential operation as a voltage value, and a drive current that outputs an output voltage of the operational amplifier. And a drive element for driving a laser oscillator with the drive current, a photodetector element for detecting a part of the laser light output from the laser oscillator and converting it into a current signal, and a photodetector element. A first feedback circuit for feeding the current back to the optical modulation signal input side of the operational amplifier, a current-voltage conversion circuit for converting the drive current into a voltage value, and a voltage obtained by the current-voltage conversion circuit A second feedback circuit that feeds back to the optical modulation signal input side, and a clamp circuit that clamps a voltage fed back by the second feedback circuit by setting a predetermined voltage according to the drive current It is equipped with.

Further, the laser oscillator driving device of the present invention comprises:
A voltage feedback type operational amplifier that performs a differential operation between an input optical modulation signal and a preset reference signal, and outputs a result of the differential operation as a voltage value, and a drive current that outputs an output voltage of the operational amplifier. And a drive element for driving a laser oscillator with the drive current, a photodetector element for detecting a part of the laser light output from the laser oscillator and converting it into a current signal, and a photodetector element. A first feedback circuit for feeding the current back to the optical modulation signal input side of the operational amplifier, a current-voltage conversion circuit for converting the drive current into a voltage value, and a voltage obtained by the current-voltage conversion circuit A second feedback circuit that feeds back to the optical modulation signal input side, and a clamp circuit that clamps a voltage fed back by the second feedback circuit by setting a predetermined voltage according to the drive current , And a varying means for varying according to the voltage obtained by the predetermined voltage to be set by the clamping circuit in the current-voltage conversion circuit.

Further, the image forming apparatus of the present invention is an image forming apparatus for forming an image on the image carrier by scanning and exposing the image carrier with scanning light, wherein the laser oscillator outputs a laser beam; An optical system for generating scanning light based on laser light output from the laser oscillator, and image forming for forming an image on the image carrier by guiding the scanning light output from the optical system onto the image carrier Means,
An operational amplifier for calculating an optical modulation signal corresponding to an input formed image and a preset reference signal; driving means for driving the laser oscillator according to the output of the operational amplifier; and an output from the laser oscillator The optical amplifier includes a light detecting means for detecting a part of the laser light to be converted into an electric signal, and a feedback means for returning an output of the light detecting means to an optical modulation signal input side of the operational amplifier.

Further, the image forming apparatus of the present invention is an image forming apparatus for forming an image on the image carrier by scanning and exposing the image carrier with scanning light, wherein the laser oscillator outputs a laser beam; An optical system for generating scanning light based on laser light output from the laser oscillator, and image forming for forming an image on the image carrier by guiding the scanning light output from the optical system onto the image carrier Means,
A voltage feedback type operational amplifier that performs a differential operation between a light modulation signal according to an input formed image and a preset reference signal, and outputs a result of the differential operation as a voltage value;
A drive element that converts an output voltage of the operational amplifier into a drive current, and drives the laser oscillator with the drive current;
A photodetector that detects a part of the laser light output from the laser oscillator and converts it into a current signal; and a feedback circuit that feeds back the current obtained by the photodetector to the optical modulation signal input side of the operational amplifier. Is provided.

Further, the image forming apparatus of the present invention is an image forming apparatus for forming an image on the image carrier by scanning and exposing the image carrier with scanning light, wherein the laser oscillator outputs a laser beam; An optical system for generating scanning light based on laser light output from the laser oscillator, and image forming for forming an image on the image carrier by guiding the scanning light output from the optical system onto the image carrier Means,
Performs a differential operation between an optical modulation signal corresponding to an input formed image and a preset reference signal, and outputs a result of the differential operation as a voltage value. A current feedback type operation having no frequency change with respect to a gain change. An amplifier, an output voltage of the operational amplifier is converted into a drive current, a drive element that drives the laser oscillator by the drive current, and a part of laser light output from the laser oscillator is detected and converted into a current signal. And a feedback circuit for feeding a current obtained by the photodetector back to the optical modulation signal input side of the operational amplifier.

Further, the image forming apparatus of the present invention is an image forming apparatus for forming an image on the image carrier by scanning and exposing the image carrier with scanning light, wherein the laser oscillator outputs a laser beam; An optical system for generating scanning light based on laser light output from the laser oscillator, and image forming for forming an image on the image carrier by guiding the scanning light output from the optical system onto the image carrier Means,
An operational amplifier for calculating an optical modulation signal corresponding to an input formed image and a preset reference signal; driving means for driving the laser oscillator according to the output of the operational amplifier; and an output from the laser oscillator Light detection means for detecting a part of the laser light to be converted into an electric signal, first feedback means for feeding back the output of the light detection means to the light modulation signal input side of the operational amplifier, and the laser oscillator Second feedback means for feeding back a voltage corresponding to the driving current to the optical modulation signal input side of the operational amplifier, and clamping the voltage fed back by the second feedback means in accordance with the driving current of the laser oscillator. Clamp means.

Further, the image forming apparatus of the present invention is an image forming apparatus for forming an image on the image carrier by scanning and exposing the image carrier with scanning light, wherein the laser oscillator outputs a laser beam; An optical system for generating scanning light based on laser light output from the laser oscillator, and image forming for forming an image on the image carrier by guiding the scanning light output from the optical system onto the image carrier A voltage feedback type operational amplifier for performing a differential operation between an optical modulation signal according to an input formed image and a preset reference signal, and outputting a result of the differential operation as a voltage value; The output voltage of the operational amplifier is converted into a drive current, and a drive element that drives the laser oscillator with the drive current, and a part of the laser light output from the laser oscillator is detected to generate a current signal. A photodetector that converts the current, a first feedback circuit that feeds back a current obtained by the photodetector to the optical modulation signal input side of the operational amplifier, a current-voltage converter that converts the drive current into a voltage value, A second feedback means for feeding back the voltage obtained by the current-voltage conversion circuit to the optical modulation signal input side of the operational amplifier; and a voltage fed back by the second feedback means to a predetermined voltage according to the drive current. And a clamp circuit that clamps by setting.

According to the present invention, by always performing negative feedback control on the optical output of the laser oscillator regardless of the shape of the recording waveform or the like, an always stable optical output free from a change in light quantity due to a temperature change, return light or the like. And a high-quality output image can be obtained.

Further, according to the present invention, a current feedback type operational amplifier is used for a control circuit which always performs negative feedback control on the optical output of the laser oscillator regardless of the form of the recording waveform or the like. The influence of the frequency change on the gradation change due to the increase or decrease can be removed, and a high-quality output image can be obtained.

Further, according to the present invention, in a control circuit for always performing negative feedback control on the optical output of the laser oscillator regardless of the form of the recording waveform, etc. With the combined use, the continuous control of the drive current of the laser oscillator is performed regardless of the presence or absence of the light output, so that the negative feedback control by the light output is stabilized, and a high-quality output image is obtained.

[0025]

Embodiments of the present invention will be described below with reference to the drawings. First, a first embodiment will be described. FIG. 1 shows a configuration of a digital copying machine as an image forming apparatus to which the laser oscillator driving device according to the present embodiment is applied. That is, this digital copying machine is composed of, for example, a scanner unit 1 as an image reading unit and a printer unit 2 as an image forming unit.

First, the scanner section 1 will be described. The scanner unit 1 includes a first carriage 3 and a second carriage 4 movable in the direction of the arrow in the figure, an imaging lens 5, a CCD type line sensor 6 as a photoelectric conversion element, and the like.

That is, in FIG. 1, an original O is placed downward on an original plate 7 made of transparent glass.
The placement reference is centered on the right front side of the document table 7 in the lateral direction. The document O is pressed onto a document table 7 by a document fixing cover 8 provided to be freely opened and closed.

The original O on the original table 7 is illuminated by a light source 9 and its reflected light is reflected by mirrors 10, 11, 12 and
The light is condensed on the light receiving surface of the line sensor 6 via the imaging lens 5. Here, the first carriage 3 on which the light source 9 and the mirror 10 are mounted, the mirror 11,
The second carriage 4 mounted with 12 moves at a relative speed of 2: 1 so as to keep the optical path length constant.
The first carriage 3 and the second carriage 4 are moved from right to left by a carriage driving motor (not shown) in synchronization with a read timing signal.

As described above, the image of the original O placed on the original platen 7 is sequentially read line by line by the scanner unit 1, and the read output is shaded by an image processing unit (not shown). Is converted into an 8-bit digital image signal.

Next, the printer section 2 will be described. The printer unit 2 includes an optical system unit 13 as a light beam scanning device, and an image forming unit 14 in which an electrophotographic method capable of forming an image on a sheet P as an image forming medium is combined.
It is composed of

That is, in FIG. 1, an image signal read from a document O by a scanner unit 1 is processed by an image processing unit (not shown) and then outputted as a laser beam (hereinafter simply referred to as a beam). Is converted into an on / off modulation signal (optical modulation signal) of the semiconductor laser oscillator, and the optical modulation signal causes the semiconductor laser oscillator to emit pulse light.

Although the configuration of the optical system unit 13 will be described later in detail, the semiconductor laser oscillator provided in the unit emits light in accordance with a light modulation signal output from an image processing unit (not shown). The reflected beam light is reflected by a polygon mirror to become scanning light,
It is designed to be output outside the unit.

The beam light output from the optical system unit 13 is formed as a spot-like scanning light having a required resolution at a position of an exposure position X on a photosensitive drum 15 as an image carrier, and is scanned and exposed. You. As a result, an electrostatic latent image is formed on the photosensitive drum 15 according to the image signal (formed image).

Around the photosensitive drum 15, a charging charger 16 for charging the surface, a developing unit 17, a transfer charger 18, a peeling charger 19, and a cleaner 20 are provided.
And so on. The photosensitive drum 17 is driven to rotate at a predetermined peripheral speed by a drive motor (not shown),
The charging charger 16 provided opposite to the surface thereof
Charged by The beam light (scanning light) is spot-imaged at the position of the exposure position X on the charged photosensitive drum 15.

The electrostatic latent image formed on the photosensitive drum 15 is developed with a toner (developer) from a developing unit 17. Photoconductor drum 15 on which toner image is formed by development
Is transferred by the transfer charger 18 onto the sheet P supplied at a transfer position at a timing by the sheet feeding system.

The paper feeding system feeds the paper P in the paper feeding cassette 21 provided at the bottom portion to the paper feeding roller 22 and the separation roller 2.
3 and supply them one by one. Then, it is fed to the registration roller 24 and is supplied to the transfer position at a predetermined timing. On the downstream side of the transfer charger 18, a paper transport mechanism 25, a fixing device 26, and a paper discharge roller 27 for discharging the paper P on which an image has been formed are provided. As a result, the paper P on which the toner image has been transferred is fixed on the toner image by the fixing device 26, and then is discharged to an external discharge tray 28 via the discharge roller 27.

The photosensitive drum 15 after the transfer to the paper P is completed, the residual toner on the surface thereof is removed by the cleaner 20, and the photosensitive drum 15 returns to the initial state, and enters a standby state for the next image formation.

The image forming operation is continuously performed by repeating the above process operations. As described above, the document O placed on the document table 7 is
The read information is subjected to a series of processes in the printer unit 2 and then recorded on the paper P as a toner image.

Next, the optical system unit 13 will be described. FIG. 2 schematically shows the configuration of the optical system unit 13. In FIG. 2, a semiconductor laser oscillator (for example, a laser diode) 31 is driven by a laser drive circuit 32, which will be described in detail later, and outputs a light beam.
The laser drive circuit 32 drives the laser oscillator 31 in accordance with an optical modulation signal from a modulation circuit 34 provided in a main control unit 33 that controls the entire copying machine and an output of a photodiode 42 described later. It has become.

After the beam light output from the laser oscillator 31 passes through the collimator lens 35, the polarization beam splitter 36 as a spectral unit and the condenser lens 3
7 and a polygon mirror 38 as a polygon mirror.
Incident on. The light beam reflected by the polygon mirror 38 passes through the two fθ lenses 39 and 40 to form an image at the exposure position X on the photosensitive drum 15 as spot-like scanning light having a required resolution. , For scanning exposure.

A part of the light beam split by the polarization beam splitter 36 enters a pin photodiode 42 as a light detecting means (light detecting element) via a condenser lens 41 and is converted into an electric signal. It has become.

FIG. 3 shows the laser driving circuit 32 shown in FIG.
Is shown in detail. That is, the optical modulation signal f01 from the modulation circuit 34 is supplied to the inverting input terminal (-) of the voltage feedback type operational amplifier (op-amp) 51 via the resistor 52, and the non-inverting input terminal (+) is supplied to the non-inverting input terminal (+). Is the reference voltage source 5
3 is supplied with the reference voltage Vref.

The output terminal of the operational amplifier 51 is connected to a current driving transistor (NPN transistor) 5 as a driving element.
The collector of the transistor 54 is connected to a positive DC power supply + Vcc via the laser oscillator (laser diode) 31 with the polarity shown in the figure, and the emitter is grounded via a resistor 55. .

The photodiode 42 is connected between the inverting input terminal (-) of the operational amplifier 51 and the DC power supply + Vcc with the polarity shown in FIG. Here, the operational amplifier 51 is the core of the negative feedback control in the present laser drive circuit 32, is a voltage feedback operational amplifier in which the frequency characteristic is governed by the GB product affected by the gain, and is input. Performs differential amplification of two signals.

The transistor 54 converts a differential output voltage obtained from the output of the operational amplifier 51 into a laser drive current. The resistors 52 and 56 are voltage-dividing resistors that determine the amount of negative feedback. The resistor 52 is an input resistor, and the resistor 56 is a feedback resistor. The resistor 55 is a bias resistor of the transistor 54, and determines a laser drive current and contributes to stabilization of the transistor 54.

In such a configuration, when recording (image formation) is performed by an arbitrary image signal and a current waveform as shown in FIG. The potential of the inverting input terminal A of FIG. However, the inverting input terminal A of the operational amplifier 51 is controlled by the operational amplifier 51 so as to always have the same potential as the non-inverting input terminal B.

Therefore, a current such that the output current of the photodiode 42 cancels the current waveform a, that is, a voltage waveform as shown in FIG. The operational amplifier 51 outputs a voltage so that the optical output of the laser oscillator 31 is set.

Here, the return light enters the resonator in the laser oscillator 31 and the amount of light is reduced as shown in the waveform of FIG. In the case of the disturbance, the operational amplifier 51
Is output as shown in FIG. 4C, and as a result, the optical output waveform shines as shown by the solid line in FIG. 4C.

As described above, according to the first embodiment, in the digital copying machine, the light output of the laser oscillator 31 as the exposure means is constantly changed regardless of the shape of the recording waveform. By performing the negative feedback control, it is possible to obtain image exposure without a change in light amount due to a change in temperature or return light, and a high-quality copy image can be obtained.

Next, a second embodiment will be described. The difference between the second embodiment and the first embodiment is that, as shown in FIG. 5, instead of the voltage feedback type operational amplifier 51, a current feedback type operational amplifier 57 whose frequency characteristics are not affected by the gain is used. The other points are the same as those of the first embodiment, and the description is omitted.

In such a configuration, for example, FIG.
As shown in FIG. 6A, when an optical modulation signal f01 that changes the magnitude of the optical output is input, the voltage feedback type operational amplifier 51 is not affected by the GB product (see FIG. 6D). As a result, as shown in FIG. 6B, the frequency characteristic is deteriorated, and as a result, the gradation of the image formed on the photosensitive drum 15 is deteriorated.

On the other hand, in the case of the current feedback type operational amplifier 57, since there is no influence of the GB product (see FIG. 6E), the output current becomes as shown in FIG. As a result, the gradation of the image formed on the photosensitive drum 15 is maintained as intended.

As described above, according to the second embodiment, in the digital copying machine, the light output of the laser oscillator 31 as the exposure means is kept constant regardless of the shape of the recording waveform. By using a current feedback type operational amplifier in a control circuit for performing negative feedback control, it is possible to remove the influence of frequency change on gradation change due to increase or decrease of light output, and to obtain a high-quality copy image.

Next, a third embodiment will be described. In the third embodiment, for example, as shown in FIG. 7, in the second embodiment, one end of a clamp circuit 58 is connected to a connection point between the emitter of the transistor 54 and the resistor 55, and the clamp circuit 58 Is connected to the inverting input terminal A of the operational amplifier 57 via the feedback resistor 59, and the other configuration is the same as that of the second embodiment.

The clamp circuit 58 cuts off the negative feedback control by the feedback resistor 59 when the drive current of the laser oscillator 31 exceeds the dark current region and the laser oscillator 31 starts emitting light.

FIG. 8 shows the clamp circuit 58 in FIG. 7 in detail. That is, the emitter resistor 55 is divided into two resistors 55a and 55b, which are connected in series. The emitter of the transistor 54 and the resistor 55a
Is connected to the emitter of the NPN transistor 61, and the collector is connected to one end of the feedback resistor 59. A resistor 62 is connected between the base and the emitter of the transistor 61, and a series circuit of a resistor 63 and a backflow prevention diode 64 is connected between the base and the collector of the transistor 61.

The base of a PNP transistor 66 is connected via a bias resistor 65 to a connection point between the resistors 55a and 55b. Transistor 66 has its collector grounded and its emitter connected to the base of transistor 61.

Here, ID is a drive current of the laser oscillator 31. The resistances 55a and 55b are emitter resistances of the transistor 54, and supply the laser drive current ID with the voltage VE1.
(VE2), converted to VEO. The transistor 61 clamps negative feedback due to the feedback resistor 59. The diode 64 has an emitter voltage VE1 (VE2) which is equal to the reference voltage V
This is to prevent the current from flowing backward when ref is exceeded (when light output is generated).

The resistors 62 and 63 determine the emitter-collector voltage VEC of the transistor 61.
The emitter-collector voltage VEC is added to the current at the switching point of the laser drive current ID between the emission current and the dark current, that is, the difference voltage between the emitter voltage VE1 and the reference voltage Vref obtained when the emission threshold current IS is obtained. It is chosen at the ratio that you set. The transistor 66 changes the current IC3 flowing through the resistor 63 according to the increase or decrease of the voltage VEO.

In such a configuration, for example, when the optical output is desired as shown by PW1 in FIG. 9B, when the characteristic curve of the laser oscillator 31 is as shown by C in FIG. The current will increase due to the change,
By the automatic light output control, the current is directed to decrease in order to keep the light output constant, and the characteristic curve shifts as indicated by D in FIG. 9A.

In this case, the emitter voltage VE2 of the transistor 54 shifts to VE1 (see FIG. 9), but the emitter voltage VE2 is set to a voltage lower than the reference voltage Vref. Now, when the emitter-collector voltage VEC of the transistor 61 is maintained at Vref-VE1, and the emitter voltage VE2 shifts to VE1 by the operation of the automatic optical output control, the emitter-collector voltage VEC is fixed. For example, when the reference voltage Vref is about to decrease, the laser drive current ID increases and the laser oscillator 31 emits light continuously. However, when the emitter voltage VE2 shifts to VE1, that is, when the emitter voltage VE2 decreases, the connection point of the resistors 55a and 55b is connected. The voltage VEO also decreases, and the current IB3 flowing through the resistor 65 increases, so that the current IC3 increases.

For this reason, the voltage generated at both ends of the resistor 63 increases, the ratio of the voltage generated at both ends of the resistor 62 changes, and the emitter-collector voltage VEC of the transistor 61 increases. Therefore, the voltage difference between the emitter voltages VE2 and VE1 of the transistor 54 is canceled, and continuous emission of the laser oscillator 31 is prevented. In this case, the rate of increase and decrease of the emitter-collector voltage VEC of the transistor 61 and the emitter voltages VE1 and VE2 of the transistor 54
Are determined so that the rate of change becomes the same.

As described above, according to the third embodiment, in real-time automatic optical output control as exposure means, in addition to optical coupling of the negative feedback control circuit, negative feedback of a voltage by a resistor is used in combination. Thus, the continuous control of the laser drive current is performed regardless of the presence or absence of the light output, so that the negative feedback control based on the light output is stabilized, and a high-quality copy image is obtained.

[0064]

As described above in detail, according to the present invention, it is possible to always obtain a stable light output without a change in light amount due to a temperature change or return light, and to drive a laser oscillator capable of obtaining a high quality output image. An apparatus and an image forming apparatus can be provided.

Further, according to the present invention, it is possible to provide a laser oscillator driving apparatus and an image forming apparatus capable of removing the influence of a frequency change on a gradation change due to an increase or a decrease in light output, and obtaining a high quality output image. Furthermore, according to the present invention,
It is possible to provide a laser oscillator driving device and an image forming apparatus capable of stabilizing negative feedback control by light output and obtaining a high-quality output image.

[Brief description of the drawings]

FIG. 1 is a configuration diagram schematically showing a digital copying machine to which a laser oscillator driving device according to an embodiment of the present invention is applied.

FIG. 2 is a schematic diagram showing a configuration of an optical system unit.

FIG. 3 is a circuit diagram showing a configuration of a laser drive circuit according to the first embodiment.

FIG. 4 is a signal waveform diagram specifically showing the operation of the laser drive circuit.

FIG. 5 is a circuit diagram showing a configuration of a laser drive circuit according to a second embodiment.

FIG. 6 is a diagram showing characteristics of a voltage feedback type operational amplifier and a current feedback type operational amplifier.

FIG. 7 is a circuit diagram showing a configuration of a laser drive circuit according to a third embodiment.

FIG. 8 is a circuit diagram showing a configuration of a clamp circuit in the embodiment.

9A and 9B are diagrams for explaining the operation of automatic optical output control in the embodiment, in which FIG. 9A is a characteristic diagram showing a relationship between the output of the laser oscillator and current, and FIG. FIG. 3C is a diagram illustrating an example of a light emission waveform, and FIG. 3C is a characteristic diagram illustrating a relationship between an emitter current and an emitter voltage of a current driving transistor.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... scanner part, 2 ... printer part, 6 ... photoelectric conversion element, 7 ... platen, 9 ... light source, 13 ... optical system unit, 14 ... image forming part, 15 ... photosensitive drum (Image carrier), 16: charging charger, 17: developing device,
18 Transfer charger, 21 Paper cassette, 26
... Fixing device, 31 ... Semiconductor laser oscillator, 32 ... Laser drive circuit, 34 ... Modulation circuit, 36 ... Polarization beam splitter, 38 ... Polygon mirror (multi-plane rotating mirror), 42 ... Photo diode (light Detecting element, light detecting means), 51: voltage feedback type operational amplifier, 52: input resistance, 53: reference voltage source, 54: current driving transistor (driving element), 55: emitter resistance, 55a ...
... IV conversion resistance, 55b ... voltage detection resistance, 56 ...
Feedback resistor 57 57 Current feedback type operational amplifier 58
Clamp circuit, 59 Feedback resistor, 61 Clamping transistor, 66 Clamp voltage adjusting transistor.

Claims (13)

[Claims] 1. An operational amplifier for performing an operation between an input optical modulation signal and a preset reference signal, a driving unit for driving a laser oscillator in accordance with an output of the operational amplifier, and an output from the laser oscillator Light detecting means for detecting a part of the laser light to be converted into an electric signal, and feedback means for feeding back the output of the light detecting means to the light modulation signal input side of the operational amplifier. Laser oscillator driving device. 2. A voltage feedback type operational amplifier which performs a differential operation between an input optical modulation signal and a preset reference signal, and outputs a result of the differential operation as a voltage value. A drive element that converts an output voltage into a drive current and drives a laser oscillator with the drive current; a photodetector that detects part of the laser light output from the laser oscillator and converts the laser light into a current signal; A feedback circuit for feeding back the current obtained by the detection element to the optical modulation signal input side of the operational amplifier. 3. The laser oscillator driving device according to claim 1, wherein said operational amplifier is a current feedback type operational amplifier. 4. A current feedback type operation in which a differential operation is performed between an input optical modulation signal and a preset reference signal, and the result of the differential operation is output as a voltage value. An amplifier, an output voltage of the operational amplifier is converted into a drive current, a drive element that drives a laser oscillator with the drive current, and a part of laser light output from the laser oscillator is detected and converted into a current signal. A laser oscillator driving device comprising: a photodetector; and a feedback circuit for feeding back a current obtained by the photodetector to a light modulation signal input side of the operational amplifier. 5. An operational amplifier for performing an operation between an input optical modulation signal and a preset reference signal, driving means for driving a laser oscillator in accordance with an output of the operational amplifier, and an output from the laser oscillator. Light detecting means for detecting a part of the laser light and converting it to an electric signal; first feedback means for feeding back the output of the light detecting means to the light modulation signal input side of the operational amplifier; Second feedback means for feeding back a voltage corresponding to the drive current to the optical modulation signal input side of the operational amplifier; and a clamp for clamping the voltage fed back by the second feedback means in accordance with the drive current of the laser oscillator. Means for driving a laser oscillator. 6. The laser oscillator driving device according to claim 5, wherein said operational amplifier is a current feedback type operational amplifier. 7. A voltage feedback type operational amplifier for performing a differential operation between an input optical modulation signal and a preset reference signal, and outputting a result of the differential operation as a voltage value. A drive element that converts an output voltage into a drive current and drives a laser oscillator with the drive current; a photodetector that detects part of the laser light output from the laser oscillator and converts the laser light into a current signal; A first feedback circuit that feeds back the current obtained by the detection element to the optical modulation signal input side of the operational amplifier; a current-voltage conversion circuit that converts the drive current into a voltage value; and a voltage obtained by the current-voltage conversion circuit. A second feedback circuit that feeds back the voltage to the optical modulation signal input side of the operational amplifier, and clamps the voltage that is fed back by the second feedback circuit by setting a predetermined voltage according to the drive current. A laser oscillator driving device, comprising: 8. A voltage feedback type operational amplifier for performing a differential operation between an input optical modulation signal and a preset reference signal, and outputting a result of the differential operation as a voltage value; A drive element that converts an output voltage into a drive current and drives a laser oscillator with the drive current; a photodetector that detects part of the laser light output from the laser oscillator and converts the laser light into a current signal; A first feedback circuit that feeds back the current obtained by the detection element to the optical modulation signal input side of the operational amplifier; a current-voltage conversion circuit that converts the drive current into a voltage value; and a voltage obtained by the current-voltage conversion circuit. A second feedback circuit that feeds back the voltage to the optical modulation signal input side of the operational amplifier, and clamps the voltage that is fed back by the second feedback circuit by setting a predetermined voltage according to the drive current. And a variable means for varying the predetermined voltage set by the clamp circuit according to a voltage obtained by the current-voltage conversion circuit. 9. An image forming apparatus for forming an image on an image carrier by scanning and exposing the image carrier with scanning light, a laser oscillator for outputting a laser beam, and a laser output from the laser oscillator. An optical system that generates scanning light based on light; an image forming unit that forms an image on the image carrier by guiding the scanning light output from the optical system onto the image carrier; An operational amplifier that performs an operation of an optical modulation signal corresponding to the above and a preset reference signal; a driving unit that drives the laser oscillator according to an output of the operational amplifier; and a laser light output from the laser oscillator. Light detection means for detecting a part of the light and converting the light into an electric signal; and feedback means for returning an output of the light detection means to a light modulation signal input side of the operational amplifier. An image forming apparatus symptoms. 10. An image forming apparatus for forming an image on an image carrier by scanning and exposing the image carrier with scanning light, a laser oscillator for outputting a laser beam, and a laser output from the laser oscillator. An optical system that generates scanning light based on light; an image forming unit that forms an image on the image carrier by guiding the scanning light output from the optical system onto the image carrier; A voltage feedback type operational amplifier that performs a differential operation between an optical modulation signal corresponding to the above and a preset reference signal, and outputs the result of the differential operation as a voltage value, and a drive current A drive element that drives the laser oscillator with the drive current, and a photodetector that detects a part of the laser light output from the laser oscillator and converts it into a current signal. An image forming apparatus characterized by including a feedback circuit for feeding back a current obtained by the light detecting element to the optical modulation signal input of the operational amplifier, the. 11. An image forming apparatus for forming an image on an image carrier by scanning and exposing the image carrier with scanning light, a laser oscillator for outputting a laser beam, and a laser output from the laser oscillator. An optical system that generates scanning light based on light; an image forming unit that forms an image on the image carrier by guiding the scanning light output from the optical system onto the image carrier; A differential operation between an optical modulation signal corresponding to the above and a preset reference signal, and outputting a result of the differential operation as a voltage value. A drive element that converts an output voltage of the amplifier into a drive current, drives the laser oscillator with the drive current, and detects a part of laser light output from the laser oscillator to generate a current. An image forming apparatus comprising: a photodetector for converting a signal into a signal; and a feedback circuit for feeding back a current obtained by the photodetector to a light modulation signal input side of the operational amplifier. 12. An image forming apparatus for forming an image on an image carrier by scanning and exposing the image carrier with scanning light, a laser oscillator for outputting a laser beam, and a laser output from the laser oscillator. An optical system that generates scanning light based on light; an image forming unit that forms an image on the image carrier by guiding the scanning light output from the optical system onto the image carrier; An operational amplifier that performs an operation of an optical modulation signal corresponding to the above and a preset reference signal; a driving unit that drives the laser oscillator according to an output of the operational amplifier; and a laser light output from the laser oscillator. Light detecting means for detecting a part of the light and converting the light into an electric signal; first feedback means for feeding back the output of the light detecting means to an optical modulation signal input side of the operational amplifier; Second feedback means for feeding back a voltage corresponding to the drive current of the oscillator to the optical modulation signal input side of the operational amplifier; clamping the voltage fed back by the second feedback means in accordance with the drive current of the laser oscillator An image forming apparatus comprising: 13. An image forming apparatus for forming an image on an image carrier by scanning and exposing the image carrier with scanning light, a laser oscillator for outputting a laser beam, and a laser output from the laser oscillator. An optical system that generates scanning light based on light; an image forming unit that forms an image on the image carrier by guiding the scanning light output from the optical system onto the image carrier; A voltage feedback type operational amplifier that performs a differential operation between an optical modulation signal corresponding to the above and a preset reference signal, and outputs the result of the differential operation as a voltage value, and a drive current A drive element that drives the laser oscillator with the drive current, and a photodetector that detects a part of the laser light output from the laser oscillator and converts it into a current signal. A first feedback circuit that feeds back the current obtained by the photodetector to the optical modulation signal input side of the operational amplifier; a current-voltage conversion circuit that converts the drive current into a voltage value; Second feedback means for feeding back a voltage to the optical modulation signal input side of the operational amplifier; and a clamp for clamping a voltage fed back by the second feedback means by setting a predetermined voltage in accordance with the drive current. An image forming apparatus comprising: a circuit;