JPH10186259A - Laser scanning recording device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laser scanning recording device with high stability and reliability by preventing plotting density from varying associated with variations in a reflectance of a reflection mirror and also preventing over-power and change in a laser power of a laser source. SOLUTION: Each laser light reflected by two or more reflection mirrors of a polygon mirror 4 is detected by an optical sensor 9, and their detected values are stored in a storage means (sample-hold circuit) SH1-SH6 respectively. When a certain reflection mirror is rotated up to a position where it scan the laser light for the next scanning, the detection value detected at a previous laser light scanning and stored in the storage means is read out and a correction voltage ΔVref is generated based on this detection value and a reference voltage Vref is corrected according to this correction voltage. A constant optical power about the laser light scanned to the exposure body is obtainable regardless of variations in the reflectance of two or more reflection mirrors of the polygon mirror 4 by controlling a luminescence output of laser diode LD based on this corrected reference voltage Vref'.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used in a laser printer or the like, and scans a photosensitive surface of a photosensitive member with a rotating polygonal mirror to record information by scanning a laser beam. More particularly, the present invention relates to an apparatus for adjusting the light intensity of a laser beam applied to a photosensitive surface.

[0002]

2. Description of the Related Art In a laser scanning recording apparatus of this type, a laser beam emitted from a laser light source is projected on a reflecting mirror of a polygon mirror driven by rotation, and the laser beam is reflected by the reflecting mirror as the polygon mirror rotates. A configuration is adopted in which laser light is scanned on the photosensitive surface of the photosensitive member while changing the reflection direction, and drawing is progressed in a line shape. In this case, in order to obtain a uniform image density on the photosensitive surface, the light intensity of the laser light emitted from the laser light source (hereinafter, the laser light intensity emitted from the laser light source is referred to as laser power) is set to a predetermined power. It is necessary to control the intensity of the laser beam emitted from the laser light source and control the laser power based on the detected value.
(Automatic output control) control is performed. FIG. 6 is a diagram showing the conceptual configuration, in which the light intensity of laser light emitted from the laser diode LD of the semiconductor laser 1 is detected by the monitoring photodiode PD, and the detected current is I / V.
(Current / Voltage) Converted to a detection voltage Vm by a converter 11 and then compared with a reference voltage Vref in a comparator 12.
Then, a comparison voltage Vo, which is a difference voltage between the detection voltage Vm and the reference voltage Vref obtained by the comparison in the comparator 12, is held in the sample and hold circuit 13, and the hold voltage, that is, the comparison voltage Vo is converted to V / I. The laser power is input to a laser drive circuit 14 having a (voltage / current) conversion function, and the laser drive circuit 14 controls the drive current of the laser diode LD, thereby controlling the laser power to a predetermined value.

[0003]

However, even when the laser power is controlled to a predetermined power, if the laser light intensity varies due to factors in the optical path from the laser light source to the photosensitive surface, the uniform image density is obtained. It becomes difficult. One of the factors is variation in the reflectance of each of the plurality of reflecting mirrors constituting the polygon mirror. That is, if the reflectivity of each reflector is different, the intensity of the laser beam reflected by each reflector will also vary, and the density of the scanning line by the laser beam reflected by each reflector will vary. There will be differences. Although these reflectors are formed to have the same reflectance, the reflectance of the mirror over time is increased due to collisions with dust in the air when the rotor is rotated at a high speed and fine scratches are generated on the surface. This causes a variation of about 3 to 4% in the reflectance of each reflecting mirror. This variation in reflectance has little problem in a binary image in which an image is formed by turning on and off a laser beam, but in a color printer or the like that requires a halftone, it is necessary to control the density of 256 tones or more. For that purpose, it is necessary to suppress the variation to 1% or less.

[0004] In order to eliminate such a variation in the reflectivity of each mirror surface of the polygon mirror, the detection of the laser beam intensity under the APC control is performed at a position downstream of the polygon mirror, preferably at the photosensitive surface. May be performed in the vicinity of. With this configuration, it is possible to detect the light intensity of the laser light actually reflected by the polygon mirror and control the laser power based on the detected light intensity, thereby making the laser light intensity on the photosensitive surface uniform. For example, JP-A-53-37029
Japanese Patent Application Laid-Open Publication No. H11-163873 proposes a beam recording apparatus that detects laser beam intensity at a position immediately before a laser beam scans a photosensitive surface of a photosensitive drum, and controls laser power based on the detected value. That is, in this technique, the light intensity output of the laser beam from the sensor disposed near the photosensitive drum is peak-held and fed back to the APC control circuit, and the AP
The C control circuit controls the modulator of laser light and the semiconductor laser generator as a laser light source based on the held sensor output.

However, according to the technique described in this publication, the laser power is controlled solely based on the laser light intensity detected by an optical sensor disposed immediately before the photosensitive drum. For example, before the laser light is projected onto the optical sensor as in the initial state, or when the laser scanning is shifted up and down and the laser light is not projected onto the optical sensor, the output of the optical sensor is close to zero. , The APC control circuit controls the laser power in the maximum direction. For this reason, especially in the latter case, the laser light source and the optical modulator are operated at the maximum output power of the laser power, and when the laser light source is continuously driven at the maximum output operation, the semiconductor laser generator is overdriven. The output may be destroyed. In the former case, the laser power changes such that the laser power is reduced from the maximum output state to a predetermined laser power, which is repeated, and the life of the semiconductor laser generator is shortened.

SUMMARY OF THE INVENTION An object of the present invention is to prevent a variation in drawing density due to a variation in the reflectance of a reflecting mirror, and to prevent an over-output and a variation in laser power in a laser light source, thereby providing a stable and highly reliable laser light source. It is to provide a laser scanning recording device.

[0007]

SUMMARY OF THE INVENTION The present invention relates to a laser scanning recording apparatus which scans a photosensitive member by reflecting a laser beam emitted from a laser light source by a rotating polygon mirror.
Means for detecting the light intensity of the laser light reflected by each of the reflecting mirrors of the polygonal mirror, and means for storing the detection output,
Next, means for reading the stored detection output when the laser beam is scanned by the reflection mirror whose reflectance has been measured, calculating a correction voltage corresponding to the read detection output, and It is characterized by comprising: means for correcting a reference voltage by a voltage; and light emission output control means for controlling the light emission output of the laser light source based on the corrected reference voltage.

A preferred embodiment of the present invention is a laser diode, a polygon mirror driven by rotation having a plurality of reflecting mirrors for scanning a laser beam emitted from the laser diode toward a photosensitive member, and a reflecting mirror. An optical sensor that detects the laser light reflected by the optical sensor, a storage unit that stores a voltage corresponding to the light intensity detected by the optical sensor for each reflecting mirror, and the reflecting mirror rotates to a scanning position in the next cycle. Means for reading a storage voltage from the storage means when being located; means for calculating a correction voltage from the read voltage; and means for correcting a reference voltage based on the correction voltage, and means for correcting the reference voltage based on the corrected reference voltage. And a laser output control circuit for controlling the emission output of the laser diode. In particular, the reference voltage correction means is provided by the same number as the number of the reflecting mirrors of the polygon mirror, and a sample and hold circuit for sampling and holding the detection output of the laser beam reflected by each reflecting mirror by the optical sensor, and the rotation of the polygon mirror. Write selection means for selecting one of the sample and hold circuits to perform a sample and hold operation in synchronization with the sample and hold circuit, which is one scan cycle ahead of the sample and hold circuit in synchronization with the rotation of the polygon mirror; Selecting means for selecting one and reading the held voltage; and calculating means for obtaining a correction voltage by calculating a difference between the voltage read from the read selecting means and a reference voltage, and correcting the reference voltage from the correction voltage. It is preferable to adopt a configuration including: Further, it is preferable that the laser output control circuit includes a selection means for selecting a reference voltage and a corrected correction voltage, and is configured to select the reference voltage during the first rotation of the polygon mirror.

[0009]

Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a conceptual configuration diagram showing an overall configuration of a laser scanning recording apparatus to which the present invention is applied. A collimator lens 2 that converts a laser beam into a parallel beam is provided on a laser beam emission optical path of a semiconductor laser 1 as a laser light source.
And a cylinder lens 3 for shaping the beam shape of the laser light
Are arranged, and the laser light beam-shaped by these is projected to a polygon mirror 4 which is a polygon mirror. Here, the polygon mirror 4 is formed in a hexagonal column shape, and reflection mirrors are provided on its six side surfaces, respectively, and is driven to rotate around the central axis at a high speed in a counterclockwise direction as illustrated. The laser light reflected by the polygon mirror 4 is transmitted through the fθ lens 5 while the reflection direction is deflected by the rotation of the polygon mirror 4, is reflected by the reflection mirror 6, and is projected on the photosensitive surface of the photosensitive drum 7. In the axial direction of the photosensitive drum 7,
That is, scanning is performed in the horizontal direction. The fθ lens 5 corrects the angular velocity of the reflected laser beam on the photosensitive drum 7 at a constant scanning speed. In addition, the photosensitive drum 7 is rotated around an axis, and scanning in the vertical direction is performed by this rotation. Further, a reflection mirror 8 is disposed outside the drawing area with respect to the photosensitive drum 7 and at a position near the photosensitive drum on the scanning start side of the laser light, and detects the laser light reflected by the reflection mirror 8 to perform scanning timing. An optical sensor 9 for obtaining a signal is provided.

On the other hand, the semiconductor laser 1 has a laser diode LD and a monitoring photodiode PD integrally formed as in the conventional example shown in FIG.
As shown in FIG. 3, three external leads 102 are provided on a base 101 of a semiconductor laser package 100, and the laser diode LD is supported on a stem 103 formed integrally with one of the external leads 102. . Further, a monitoring photodiode PD is fixed on the base 101 facing the laser diode LD. The laser diode LD and the photodiode PD are electrically connected to other external leads 102, respectively. The base 101 is provided with a cover 104 having a light transmitting member 105 on a part of the top surface thereof.
D and the monitoring photodiode PD are sealed.
Therefore, in the semiconductor laser 1, the light transmitting member 1
The laser light emitted from the laser light emitting surface of the laser diode LD disposed so as to face the laser light 05 passes through the light transmitting member 105 and is emitted outside the package 100. On the other hand, the laser diode LD emits a part of the laser light also from the side surface opposite to the laser light emission surface, and the laser light is received by the monitor photodiode PD as the monitor light, so that the laser diode L
The light intensity of the laser light emitted from D can be monitored.

As will be described in detail later, a laser output control circuit 10 based on a comparison between a reference voltage and a detection voltage obtained by detecting the light intensity of the laser light emitted from the laser diode LD by the monitoring photodiode PD. Is configured to control the light emission output of the laser diode LD. In this embodiment, the optical sensor 9 for obtaining the scanning timing signal is used as a detector of the light intensity of the laser beam reflected and scanned by each reflecting mirror of the polygon mirror 4. A reference voltage correction circuit 20 for correcting the reference voltage of the laser output control circuit 10 based on the detection output of the optical sensor 9 is provided.

FIG. 2 is a circuit diagram showing each circuit configuration of the laser output control circuit 10 and the reference voltage correction circuit 20.
The laser output control circuit 10 performs I / V conversion of a detection current based on the light intensity of the laser diode detected by the monitoring photodiode PD to obtain a detection voltage Vm.
V converter 11 and this detection voltage Vi is used as a reference voltage Vref
And a sample-and-hold circuit 13 that samples and holds a comparison voltage Vo, which is a difference voltage between the detection voltage Vm and the reference voltage Vref, as a comparison output of the error comparator 12 using an APC timing signal. A laser drive circuit 14 having a V / I conversion function of generating a drive current for the laser diode LD based on the held comparison voltage Vo; and an on / off signal for causing the laser diode LD to emit light.
And a drive switch 15 for supplying a current controlled by the laser drive circuit 14 after being turned off to the laser diode LD at a required timing. Here, a reference selection switch 16 for selecting the reference voltage Vref and the output of the reference voltage correction circuit 20 is connected to an output terminal of the reference voltage Vref, and a reference output from a central processing unit (not shown). It is configured to be switched by a selection signal. The APC timing signal and the on / off signal are output from the central processing unit in synchronization with the rotation of the polygon mirror 4.

The reference voltage correction circuit 20 includes an I / V converter 21 for converting the detection current Is detected by the optical sensor 9 into a voltage Vs, and the converted voltage to each of the reflecting mirrors of the polygon mirror. Correspondingly, six sample-and-hold circuits SH1 to SH6 for sample-and-hold, a selector 22 for selectively operating these sample-and-hold circuits, and a voltage held by each of the sample-and-hold circuits SH1 to SH6 are selected. And a multiplexer 23 for outputting. Here, the I / V converter 2
1 and the I / V converter 11 connected to the monitoring photodiode PD are connected to the laser diode L
The voltage Vm obtained from the detection current Im of the monitor photodiode PD when D emits a laser beam having the light intensity as a reference, and the voltage Vs obtained from the detection current Is similarly detected by the optical sensor 9 So that the current / voltage conversion rates R of the I / V converters 21 and 11 are equal to each other.
m and Rs are set. Generally, since Im <Is, Rm> Rs is set.

Further, a pulse generation circuit 24 for generating a pulse in synchronization with a scanning timing signal based on the detection voltage Vm detected by the optical sensor 9, And a read counter 26 for operating the multiplexer 23 as well. Here, each of the counters 25 and 26 is configured as a ring counter that circulates and counts the values of “1” to “6” in accordance with the order of rotation of the six reflecting mirrors of the polygon mirror 4. The read counter 26 is configured to always count a value that is advanced by “+1” from the write counter 25. further,
The multiplexer 23 is connected to an arithmetic circuit 27 that performs a required operation on the voltage selected and output by the multiplexer 23 to calculate a correction voltage, and further corrects the reference voltage Vref based on the correction voltage. Then, the corrected reference voltage Vref 'is output to the reference selection switch 16 of the laser output control circuit 10.

Next, the APC operation in the laser scanning recording apparatus having the above configuration will be described. An APC timing signal and an on / off signal are output from a central processing unit (not shown) in synchronization with the rotation cycle of the polygon mirror 4. The laser output control circuit 10 receives these signals, and
By turning on 5, the drive current from the laser drive circuit 14 is supplied to the laser diode LD, and the laser diode LD emits light. The light emitted by the laser diode LD is received by the monitoring photodiode PD, and the detection current of the light intensity is converted into a voltage Vm by the I / V converter 11, and the reference voltage Vr is output by the error comparator 12.
ef. Then, a comparison voltage Vo which is a difference voltage from the detection voltage Vm is obtained by comparison with the reference voltage Vref.
The comparison voltage Vo is output from the sample-and-hold circuit 13 at the time of APC by the APC timing signal.
, And the held comparison voltage Vo is input to the laser drive circuit 14, where it is V / I converted and output as a drive current. As described above, the drive current of the laser drive circuit 14 is controlled by the detection current of the monitoring photodiode PD,
The light emission output of the laser diode LD is feedback-controlled, and is controlled to a light intensity corresponding to the reference voltage Vref.

The laser light emitted from the laser diode LD is projected onto a reflecting mirror of a polygon mirror 4 which is rotated and positioned at a position facing the laser light, and is reflected there.
Scanning to the photosensitive drum 7 via the fθ lens 5 and the reflection mirror 6 is as described above. At this time, the laser beam reflected by each reflecting mirror of the polygon mirror 4 is reflected by the reflecting mirror 8 at a timing before scanning the photosensitive drum 7 and received by the optical sensor 9. Outputs a scanning timing signal. The scanning timing signal from the optical sensor 9 is used as a horizontal synchronizing signal serving as a reference for various timing signals from the central processing unit.

On the other hand, the detection current Is of the optical sensor 9 is I
The voltage is converted by the / V converter 21 into the voltage Vs. A part of the voltage Vs is input to the central processing unit to generate a horizontal synchronizing signal, and at the same time, is input to the pulse generation circuit 24 as an APC-controlled scanning timing signal, where a pulse synchronized with the scanning timing is generated. , Are input to the write counter 25 and the read counter 26, respectively. The write counter 25 counts this pulse,
The selector 22 sequentially selects the six sample-and-hold circuits SH1 to SH6 based on the counted values. The selected sample and hold circuit holds the converted voltage at that timing. Therefore,
The voltages corresponding to the light intensities of the laser beams reflected by the six reflecting mirrors sequentially rotated to the scanning position by the rotation of the polygon mirror 4 are sequentially applied to the sample and hold circuits SH1 to SH1.
SH6.

Since the read counter 26 counts a value larger by "+1" than the write counter 25, the voltages from the sample and hold circuits SH1 to SH6 corresponding to the counted value are sequentially sent from the multiplexer 23. Read out. As a result, the voltage detected by the optical sensor 9 for the reflecting mirror to be scanned next (hereinafter referred to as the next reflecting mirror) after the currently scanned reflecting mirror is read. That is, in the cycle before one rotation of the polygon mirror, light used when performing the APC control on the next reflecting mirror is detected by the optical sensor 9 and the voltage stored in the corresponding sample-and-hold circuit is equal to this voltage. The data is read out immediately before scanning by the next reflecting mirror. Then, the read voltage Vsh is applied to a difference ΔVref (= Vref−V) from the reference voltage Vref in the arithmetic circuit 27.
sh) is taken, and this difference ΔVref is calculated as a correction voltage. Further, by adding the correction voltage ΔVref to the reference voltage Vref, the corrected reference voltage Vr
ef ′ is output to the reference selection switch 16. That is, in the arithmetic circuit 27, 2 · Vref−V
The reference voltage Vref 'corrected by performing the calculation of sh
Is output.

The corrected reference voltage Vref 'is input as a reference voltage to the error comparator 12 through the reference selection switch 27 at a timing immediately before the scanning by the corresponding reflecting mirror is performed. Therefore, in the laser output control circuit 10, when the detection voltage Vm of the light intensity of the laser diode LD detected by the monitoring photodiode PD is constant, the voltage read from the sample hold circuits SH1 to SH6 through the multiplexer 23. Vs
If h is higher than the reference voltage Vref, this means that the reflectance of the corresponding reflecting mirror is high and the light intensity detected by the optical sensor 9 is high, and thus the correction voltage ΔVref is negative ( Minus), the reference voltage Vref ′ input to the comparator 12 decreases, and the comparison voltage Vo from the error comparator 12 decreases. Then, the next reflection mirror is rotated to the scanning position, and the comparison voltage Vo is sampled and held at the APC timing based on the scanning timing signal from the optical sensor 9 and input to the laser driving circuit 14 to drive the laser diode LD. The current is corrected in the decreasing direction. Accordingly, when the reflectance of the reflecting mirror moved to the scanning position is high, the light intensity of the laser light emitted from the laser diode LD is reduced, and as a result, the light intensity of the laser light reflected by the reflecting mirror becomes a predetermined value. Is held at the value of

Conversely, when the reflectance of the next reflecting mirror is low, the voltage Vsh read from the sample hold circuits SH1 to SH6 through the multiplexer 23 becomes the reference voltage Vsh.
ref, the correction voltage ΔVref becomes positive (plus), and the reference voltage Vre input to the comparator 12
f ′ increases, and the comparison voltage Vo from the error comparator 12 increases. Therefore, when the next reflecting mirror is rotated to the scanning position, the driving current of the laser diode LD is corrected in the increasing direction. Thereby, the light intensity of the laser diode LD with respect to the reflecting mirror moved to the scanning position is increased, and as a result, the light intensity of the laser light reflected by the reflecting mirror is maintained at a predetermined value.

FIG. 4 is a timing chart for explaining the above-described operation. The six reflecting mirrors of the polygon mirror 4 are denoted by 〜, and the scanning timing signal from the optical sensor 9 is represented by B.
D. Then, as for the first reflecting mirror, assuming that the scanning of the laser beam is performed by the first reflecting mirror of the polygon mirror at time t1, at the scanning time t0 of the first reflecting mirror one rotation before. The voltage detected by the optical sensor 9 is written to the sample and hold circuit. Then, at a time point t2 immediately before the time point t1, that is, when the first reflecting mirror is rotated to the next rotational position to be scanned, the voltage recorded at the time point t0 is read out from the sample and hold circuit. The APC control based on the voltage is performed immediately before the time point t1.
Further, from this operation, the voltage at the time point t0 stored in the sample-and-hold circuit is stored again in the sample-and-hold circuit and refreshed at the time point t1 when the scanning is performed by the APC control. This refreshed voltage is the APC in the next rotation.
It will be used for control. Therefore, since the voltage based on the reflection state of the reflecting mirror at the time of scanning one rotation before is always stored in the sample-and-hold circuit and APC control is performed, high-precision APC control that follows aging can be performed.

FIG. 5 shows an n-plane reflecting mirror among the six reflecting mirrors of the polygon mirror, and an n-1 plane and an n +
The reflectances R (n) and R (n−
1), R (n + 1) is R (n-1) <R (n + 1) <R
The case of (n) is shown. Therefore, n
The laser power of the laser diode at the time of scanning with the n-1 surface reflecting mirror is increased as compared with the laser output at the time of scanning with the +1 surface reflecting mirror, and the laser power of the laser diode at the time of scanning with the n surface reflecting mirror is increased. The laser power is reduced, and as a result, the light intensity of the laser light reflected by the reflecting mirror on each surface is controlled to a predetermined value.

As described above, the light intensity at the time of scanning at each reflecting mirror before one rotation of the polygon mirror is detected and stored in the sample and hold circuit. By performing the laser power control based on the stored light intensity, it is possible to control the light intensity of the laser light reflected by each reflecting mirror of the polygon mirror to a predetermined value. Irrespective of the variation in reflectance, the light intensity of the laser beam in each scanning line on the photosensitive drum can be controlled uniformly.
Thereby, the image density in each scanning line is made uniform, and high-quality drawing can be realized. FIG. 7 is a waveform diagram showing the state of laser power control in the APC control circuit shown in FIG.
Although the laser power at is controlled to be constant, due to the variation in the reflectivity of each of the reflecting mirrors of the polygon mirror 4,
The light intensity of the laser beam scanned on the photosensitive drum 7 has a variation in light intensity corresponding to the reflectance, and a variation in density occurs in each scanning line, making it difficult to draw at a uniform image density.

In the above-described embodiment, since the corrected reference voltage Vref 'cannot be obtained unless the scanning of the polygon mirror 4 is performed for at least one rotation, the above-described APC control cannot be performed at the time of starting. For this reason, in this embodiment, the reference selection switch 16 is switched to the reference voltage Vref by the reference signal during the first rotation of the polygon mirror, and the reference voltage Vr
The laser power is controlled based on ef. Therefore, even in such a case, it is ensured that an error voltage corresponding to the reference voltage is output from the comparator 12, so that the laser drive circuit 14 or the laser output control circuit 10 runs away and the laser diode LD There is no excessive output state.

In the above embodiment, the correction voltage is obtained by using the detection output of the optical sensor for obtaining the scanning timing signal. However, a dedicated optical sensor may be provided separately. The optical sensor 9 and the reflection mirror 8 do not detect the light intensity near the photosensitive drum shown in FIG. 1, but are indicated by reference numerals 9 ', 9 "and 8', 8" in FIG. As described above, it can be installed at an arbitrary position such as a position immediately after the polygon mirror 4 or a position immediately after the fθ lens 5. Further, the means for storing the detected voltage detected by the optical sensor is not limited to the sample-and-hold circuit, and may be configured, for example, to convert the detected voltage into a digital value and store it in a semiconductor memory. In this case, an address decoder or the like is used instead of the selector and the multiplexer of the above embodiment.

[0026]

As described above, the present invention detects the light intensity of a laser beam reflected by a polygon mirror that is driven to rotate a laser beam emitted from a laser light source, and stores the detected value. Reading the stored detection value when the laser beam is scanned by the reflector, calculating a correction voltage corresponding to the read detection value, and correcting a reference voltage for controlling the laser power. Therefore, even when the reflectance of each of the polygon mirrors varies, the light intensity of the laser beam reflected by each of the mirrors can be controlled to a predetermined level, and a plurality of scans on the photoconductor can be performed. Variations in light intensity at the lines are eliminated, image density is made uniform, and high-quality drawing can be realized. In addition, at the time of starting, APC control is performed based on the reference voltage, so that APC control of laser power is also ensured at that time, which prevents over-output of the laser diode and prevents destruction of the laser diode. In addition, stable and reliable laser power control can be realized.

[Brief description of the drawings]

FIG. 1 is a diagram showing a conceptual configuration of an embodiment of a laser scanning recording apparatus of the present invention.

FIG. 2 is a circuit diagram of an APC control circuit according to the present invention.

FIG. 3 is a sectional view of an example of a laser diode in which a monitoring photodiode is integrated.

FIG. 4 is a timing chart for explaining an APC control operation in the present invention.

FIG. 5 is a waveform chart for explaining an APC control operation in the present invention.

FIG. 6 is a circuit diagram showing an example of a conventional APC control circuit.

FIG. 7 is a waveform chart of an APC control operation in the APC control circuit of FIG. 6;

[Explanation of symbols]

 Reference Signs List 1 semiconductor laser 4 polygon mirror 5 fθ lens 7 photosensitive drum 9 optical sensor 10 laser output control circuit 11 I / V converter 12 comparator 13 sample hold circuit 14 laser drive circuit 16 reference changeover switch 20 reference voltage correction circuit 21 I / V Converter 22 Selector 23 Multiplexer 24 Pulse generation circuit 25 Write counter 26 Read counter 27 Arithmetic circuit LD Laser diode PD Monitor photodiode SH1 to SH6 Sample hold circuit

Claims (6)

[Claims] 1. A laser scanning and recording apparatus for scanning a photosensitive member by reflecting a laser beam emitted from a laser light source on a rotating polygon mirror and scanning the photosensitive member with the laser reflected on each of the polygon mirrors. Means for detecting the light intensity of light;
Means for individually storing these detection outputs, means for reading out the previously stored detection outputs when the laser beam is scanned by the reflector whose reflectance has been measured next time, A laser scanning recording apparatus, comprising: means for correcting a reference voltage in accordance with the detected output, and light emission output control means for controlling the light emission output of the laser light source based on the corrected reference voltage. . 2. A laser diode, a rotationally driven polygon mirror having a plurality of reflecting mirrors for scanning a laser beam emitted by the laser diode toward a photosensitive member, and a laser reflected by the reflecting mirror An optical sensor for detecting light, a storage unit for storing a voltage corresponding to the light intensity detected by the optical sensor for each reflecting mirror unit, and when the reflecting mirror is rotated to the scanning position in the next cycle. Means for reading the stored voltage from the storage means, calculating means for calculating a correction voltage from the read voltage and correcting the reference voltage based on the corrected voltage, and A laser output control circuit for controlling the light emission output of the laser diode. 3. The laser output control circuit selects a monitoring photodiode for detecting the light intensity of the laser light emitted from the laser diode, a reference voltage, and a corrected reference voltage from the reference voltage correction means. Means for comparing a detection output of the monitoring photodiode with the selected reference voltage, and outputting an error voltage thereof;
3. The laser scanning recording apparatus according to claim 2, further comprising: a laser driving circuit that controls a driving current supplied to the laser diode in accordance with the error voltage. 4. A reference voltage correcting means provided by the same number as the number of reflecting mirrors of the polygon mirror, and a sample and hold circuit for sampling and holding a detection output of a laser beam reflected by each reflecting mirror by an optical sensor, and a polygon mirror. Write selection means for selecting one of the sample and hold circuits to perform a sample and hold operation in synchronization with the rotation of the polygon mirror, and a sample which is advanced by one scan period from the sample and hold circuit in synchronization with the rotation of the polygon mirror Selecting means for selecting one of the hold circuits and reading the held voltage; obtaining a correction voltage from the voltage read from the read selecting means and a reference voltage; and correcting the reference voltage with the correction voltage 3. An arithmetic unit comprising:
Or the laser scanning recording device of 3. 5. The laser output control circuit according to claim 3, wherein the selection means for selecting the reference voltage and the corrected reference voltage is configured to select the reference voltage during the first rotation of the polygon mirror. Laser scanning recording device. 6. The laser scanning recording apparatus according to claim 2, wherein said optical sensor is an optical sensor for detecting a laser beam scanned by a polygon mirror and outputting a scanning timing signal.