JP3449147B2 - Optical scanning device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser printer,
The present invention relates to an optical scanning device used in an electrophotographic digital image forming machine such as a laser copying machine, and more particularly to an optical scanning device that divides an exposure range and scans with a plurality of beams to form an image.

[0002]

2. Description of the Related Art An optical scanning device, which is generally used in an electrophotographic digital image forming machine such as a laser printer or a laser copying machine, which scans a photosensitive member with a laser beam to expose it, has a wide exposure range or a high speed. Various improvements have been made to achieve scan speeds . However, in this type of conventional optical scanning device, it is necessary to upsize the optical member such as the fθ lens in order to widen the exposure range.
Therefore, there is a problem that the optical scanning device itself becomes large.

[0003] or in order to speed up the scanning speed rotating polygon mirror for light deflection (hereinafter, referred to as a polygon mirror.) Or to increase the number of faces of, or the rotational speed of the motor itself which rotates the polygon mirror Need to raise. When increasing the number of faces of the polygon mirror, the size of the polygon mirror is increased in order to maintain the optical characteristics of the optical scanning device, so that the load on the motor that rotationally drives the polygon mirror is increased, and wind damage and vibration Occurrence becomes a problem. When increasing the rotation speed of the motor itself that rotates the polygon mirror, the increase in rotation speed poses a problem of vibration and requires a motor that can rotate at a high rotation speed, which is very expensive. There was a problem.

In order to solve the above problem, a plurality of laser light sources are made to enter the reflecting surface of the polygon mirror at different incident angles, the exposure range on the photosensitive member is divided, and the laser beam is scanned to widen the area. An optical scanning device that realizes an exposure range and a high scanning speed has been proposed (Japanese Patent Laid-Open No. 63-4).
7718). When such an optical scanning device is used, since the photosensitive member is scanned with a plurality of laser beams, if the light amounts at the joints of adjacent scanning beams are not equal, unlike a scanning beam using one laser light source, A streak pattern is generated at the joint between the adjacent scanning beams of the formed image, and the image becomes fragmentary, which may impair the image quality.

To solve this, Japanese Patent Laid-Open No. 58-127
In the optical scanning device described in Japanese Patent No. 912, an area where scanning beams are optically overlapped is provided at a joint position that causes an image to be fragmented, and the area is defined as a boundary area, and within the boundary area. The joints are set randomly so that the streak pattern at the joints that originally occurs is made inconspicuous.

Further, in the optical scanning device disclosed in Japanese Patent Laid-Open No. 3-98066, an area where the scanning beams optically overlap is provided, and the exposure energy of each scanning beam is reduced by one at the same rate and the other is reduced. By increasing it, the added exposure amount in the overlap area is set to an average value that is not much different from the exposure amounts in the other exposure ranges.

[0007]

SUMMARY OF THE INVENTION In the above-mentioned invention, as a method for correcting the image disturbance of the seams of the exposure range,
Although the joint position is changed and the light amount is averaged, when the image is formed on the photoconductor, considering the image data that actually modulates the laser beam, the joint position changing method is used. Since the eyes are different at random, there is a problem that the relationship between the exposure range to be scanned and the image data becomes complicated. If this method is performed periodically so that the relationship with the image data can be easily performed, image distortion occurs in that period.

Further, in the method of averaging the light amount to correct the disturbance of the image of the seam in the exposure range, the average light amount is good, but since the overlap area is written twice by the image data, the image itself is written. It becomes blurry and becomes fatal especially when the resolution is high.

This is common to both the method of changing the joint position and the method of averaging the light amount. When a semiconductor laser or the like is used as a light source of an optical scanning device, a plurality of divided exposure ranges are respectively divided. , Even if the light output of a plurality of semiconductor lasers to be scanned is constantly equal to each other, the semiconductor laser has droop characteristics, so that it is not possible to correct the transient light amount fluctuation that occurs at the joint of the divided exposure ranges. .

That is, the laser beams output from the two semiconductor lasers that scan the exposure ranges before and after the joint between the adjacent exposure ranges are the joints of the two adjacent exposure ranges in the main scanning direction. A laser beam that scans the exposure range located in front of the eye often has a steady light amount near the joint, but a laser beam that scans the exposure range behind the joint does not rise at the joint. Since the amount of transient light is generated, the amount of light of the laser beam inevitably increases due to the droop characteristic. For this reason, there is a problem that the image is disturbed or a streak pattern is generated even if the position of the joint is randomly changed or the light amount at the joint is averaged.

The present invention has been made in view of such circumstances, and it is possible to delicately correct the light amount at the joint of the exposure areas divided into a plurality of exposure beams by a plurality of exposure beams, and the image disturbance at the joint, Alternatively, it is an object of the present invention to provide an optical scanning device capable of preventing the generation of streak patterns.

[0012]

In order to achieve the above object, the invention according to claim 1 is such that a plurality of light source sections for generating light beams and a plurality of light source drives for driving the plurality of light source sections are provided. Means, scanning means for dividing the exposure range into a plurality in the main scanning direction and scanning each divided exposure range with each light beam, at least one scanning position detecting means for detecting a scanning position, and detection by the scanning position detecting means. A plurality of light amount detecting means for detecting the light amount by receiving the light beam from the light source part at a predetermined timing in synchronization with the output, and two adjacent exposure ranges based on the detection results of the plurality of light amount detecting means. Light source control means for controlling the plurality of light source driving means so that the light amounts of the two beams of the light source part for scanning the light source part are uniform in the vicinity of the joint between the two adjacent exposure ranges.
An optical scanning device having:
Is the light near the joint between the adjacent exposure ranges.
For controlling the light intensity of the source beam,
Exposure that is located in front of the seam in the main scanning direction
ON state of the light source when modulating with image data in the range
Based on the data indicating the active and off areas.
Cormorant be characterized.

[0013]

[0014] According to a second aspect of the invention, in the optical scanning apparatus <br/> claim 1, wherein the light source control means, the beam of the light source unit in the joints near the adjacent exposure range The light amount control is not performed when the image data is not continuous in the vicinity of the joint between the two adjacent exposure ranges.

In the optical scanning device having the above structure, a plurality of light source sections for generating a plurality of beams are driven by a plurality of light source driving means, and a plurality of beams are scanned in the exposure range divided into a plurality in the main scanning direction. Scanned by means . Amount of light is detected by receiving each in synchronization with the scanning position detecting means for detecting a run査position the beam from the light source unit by a plurality of light quantity detecting means at a predetermined timing. Further, based on the detection results of the plurality of light amount detecting means, the light source so that the light amounts of the two beams of the light source unit that scan the two adjacent exposure ranges are uniform near the joint between the two adjacent exposure ranges. The plurality of light source driving means are controlled by the control means. At this time, in the light source control means,
The VI of the light source section near the joint between the adjacent exposure areas
Control of the light intensity of the system
The exposure range is located on the front side of the joint with respect to the scanning direction.
Area of the light source in the ON state when modulated by image data
And data indicating the off-state area.

According to the first or second aspect of the present invention, it is possible to make uniform the light amounts of the two beams scanning the adjacent exposure ranges in the vicinity of the joint between the adjacent exposure ranges.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a schematic configuration of an optical scanning device to which the present invention is applied. This optical scanning device is an optical scanning device which makes laser beams from a plurality of light sources A22 and B23 incident on a polygon mirror 1 and divides an exposure range X for scanning. FIG. 1 shows a case where the structure of the optical scanning device is simplified and two light sources A22 and B23 are used and there is one polygon mirror. Of course, these may be plural. In the optical scanning device shown in FIG. 1, the light source B23
The scanning of the laser beam by (1) is started from the end P0 of the entire exposure range X, while the scanning of the laser beam by the light source A22 is started from the central part P1 of the entire exposure range X. The scanning start position is determined based on the detection output of the synchronization sensor 3 which receives the laser beam emitted from the light source B23 via the polygon mirror 1 and the reflecting mirror 2. As shown in the figure, the exposure range by the light source A is Xa, and the exposure range by the light source B is Xb. The light sources A22 and B23 are configured to include a laser diode, and the light amount control of the light sources A22 and B23 is performed by the control unit 4.

The scanning timing of the light sources A22 and B23 is shown in FIG. In the same figure, when the laser beam from the light source B23 is received by the synchronous sensor 3 at time t0,
At a time t1 after a lapse of a predetermined time from this point, the light source B23 starts scanning from the end portion P0 of the entire exposure range X, and at the same time, the light source A22 starts scanning from the central portion P1 of the entire exposure range X. At time t2, the scanning by the light source B is performed up to the central portion P1, the scanning by the light source A22 is performed up to the end portion P2, and the scanning for one line in each exposure range is completed. The shaded portion in the timing chart in the range from time t1 to t2 is the exposure range Xa and the light source B by the light source A22.
The total exposure range X which is a joint part with the exposure range Xb
The scanning timing in the vicinity of the central portion P1 of FIG. That is, the scanning range of the joint portion by the laser beam of the light source B23 is a portion near the scanning end point in the exposure range Xb, and the scanning range of the joint portion by the laser beam of the light source A22 is near the scanning start point in the exposure range Xa. It is a part. The streak pattern generated at the joint between the adjacent exposure ranges scanned by the laser beams of different light sources depends on the light amount at the timing near the scanning scanning end point on the photoconductor by the laser beam of the light source B23 and the laser beam of the light source A22. This occurs when there is a difference in the light amount at the timing near the scanning start point on the photoconductor.

It should be noted that even at times t3 to t5, times t0 to t0
Similar to t2, the light sources A22 and B23 scan the next line in the respective exposure ranges Xa and Xb.

Next, FIG. 3 shows a specific configuration of the control unit of the optical scanning device according to the embodiment of the present invention. In the figure, the control unit 4 of the optical scanning device has a control circuit 10. The control circuit 10 is a circuit that controls the entire optical scanning device, and the control circuit 10 controls the optical scanning device. Various data necessary for input / output are input and output, and control signals necessary for controlling each circuit unit are output. The control circuit 10 has image memories 11 and 12 built therein. The image memory 11 stores image data for forming an image on a photoconductor by scanning a laser beam from a light source A22.
2 stores image data for forming an image on the photoconductor by scanning the laser beam from the light source B23.

Synchronous sensor 13 as scanning position detecting means
Is the same as that shown in FIG. 1, and the detection signal of the synchronization sensor 13 is used to determine the scanning start position.
The detection signal of the synchronization sensor 13 is input to the control circuit 10 and the counter 14. In the control circuit 10, the synchronization sensor 13
The scanning start timing is determined based on the output timing of the detection signal of.

The counter 14 uses the detection signal of the synchronous sensor 13 as a reset signal and receives the enable signal output from the control circuit 10 to enable the counting operation. Reference numeral 15 is a clock used for light amount detection. The counter 14 counts the clock at the input timing of the enable signal, and the count output is the AND circuit 18,
It is used as a gate signal of 19 or a light amount detection timing signal of the light receiving circuits 24 and 25.

The digital image data read from the image memories 11 and 12 are processed by the PWM modulators 16 and 17, respectively.
It is pulse width modulated, converted into analog image data, and output to AND circuits 18 and 19, respectively. The AND circuits 18 and 19 convert the analog image data output from the PWM modulators 16 and 17 in pixel units into LD drive circuits 20 and 2, respectively.
It is a circuit for outputting to 1. Here, the PWM modulation refers to controlling the number of lighting pulses and the number of extinguishing pulses in one pixel by dividing one pixel into a plurality and turning on or off the pulse of the light source in units of the division.

The LD (laser diode) driving circuits 20 and 21 as the light source driving means are based on the analog image data of the PWM modulators 16 and 17, respectively, and are the light source A2.
2. A circuit for driving the light source B23 on and off. The light source A22 and the light source B23 are configured to include a laser diode. Light receiving circuits 24 and 25 as light amount detecting means
Is configured to include a photo diode, and detects the light amounts of the laser beams emitted from the light sources A22 and B23, respectively, based on the light amount detection timing signal output from the counter 14.

The arithmetic circuit 26 is a conversion circuit for converting the amount of light detected by the light receiving circuits 24 and 25 into a voltage, and the converted output is output to the control circuit 10 and the light source control circuit 30 as the light source control means .

The optical source control circuit 30, the pixel calculation circuit 3
1, a joint light amount calculation circuit 32, an offset correction circuit 33, and a correction cancel circuit 34.

The pixel arithmetic circuit 31 reads out image data for forming an image obtained by scanning the exposure range Xb in FIG. 1 with the laser beam of the light source B23 from the image memory 12, and PWMs the image data.
The number of lighting pulses and the number of extinguishing pulses per scanning line in the exposure range Xb at the time of modulation are counted, and the image state in one scanning line, that is, the light source in one scanning line is turned on, based on these counted values. An on / off ratio pixel (the definition of which will be described later) Pr indicating the ratio of the area to be turned on and the area to be turned off is calculated.

The joint light amount arithmetic circuit 32 is composed of the arithmetic circuit 26.
From the exposure range Xa and the exposure range Xb near the joint between the light source A22 and the light source B23, and the on / off ratio pixel Pr output from the pixel calculation circuit 31 from the exposure range Xa and the exposure range Xb. An offset light quantity value for correcting a transient light quantity change of the laser beams of the light sources A22 and B23 in the vicinity of the joint is calculated.

The offset correction circuit 33 includes a control circuit 10
An offset voltage value corresponding to the corrected light amount value is calculated from the light amount setting voltage Vref set by the light amount setting signal output from the output voltage value and the voltage value ΔV corresponding to the offset light amount value calculated by the joint light amount calculation circuit 32. A drive voltage Vref-ΔV / 2, Vref is applied to the LD drive circuits 20 and 21.
+ ΔV / 2 is supplied respectively. As a result, the light source A22 near the joint between the exposure range Xa and the exposure range Xb,
The light quantity of the laser beam of the light source B23 is corrected.

The correction cancel circuit 34 is provided in the image memory 1
Image data is read out from the light sources A22 and B2.
It is determined whether or not the image data in the vicinity of the joint between the exposure range Xa and the exposure range Xb scanned by the laser beam No. 3 has continuity, and if there is no continuity, the light source A2
Since it is not necessary to correct the light amounts of the laser beams of B2 and B23, a correction cancel signal for instructing the offset correction circuit 33 not to perform the correction corresponding to the offset light amount value is output. In this case, the offset correction circuit 33
Then, the drive voltage Vref is supplied to the LD drive circuits 20 and 21.

Here, the light amount adjustment of the optical scanning device will be specifically described. The light amount adjustment at the time of initial setting such as manufacturing of the optical scanning device is usually performed by a power meter or the like with a constant light amount such as when a laser light source such as a laser diode is continuously turned on at a position corresponding to the position of the photoconductor. The drive current value in the LD drive circuits 20 and 21 for driving the laser light source or the light receiving circuits 24 and 25 for receiving the laser beam and measuring the amount of light measured by a measuring device The gain and the conversion rate are adjusted to determine the relationship between the steady light amount on the photoconductor and the light amount setting voltage signal used in the LD drive circuits 20 and 21. The most general method is to monitor the amount of light with a photodiode that constitutes the light receiving circuits 24 and 25. In this method, a photodiode and a variable resistor are combined to adjust the resistance value of this variable resistor. By the constant light quantity and LD on the photoconductor
The relationship with the light amount setting voltage signal used in the drive circuits 20 and 21 is determined. After this adjustment, the set voltage value input to the LD drive circuit corresponding to the set light amount on the photoconductor, that is, the light amount set voltage is uniquely determined as the set light amount on the photoconductor. As a result, the amount of light required on the photoconductor is set to L
This can be performed by changing the value of the light amount setting voltage signal input to the D drive circuit. In the embodiment of the present invention shown in FIG. 3, the control circuit 10 sets the light amount setting voltage value corresponding to the target light amount desired to be set on the photoconductor to Vref by the control circuit 10 via the offset correction circuit 33 to drive the LD drive circuits 20, 21.
To set the amount of light on the photoconductor. In this case, FIG. 4 shows a change state of the light amount on the photoconductor in a steady state during scanning in which the light source is continuously turned on and the polygon mirror is rotationally driven. The light receiving circuit 2 is based on the light amount detection timing signal output from the counter 14 in order to obtain the light amount information of the initial value setting required for future light amount control.
Reference numerals 4 and 25 are the constant light amount on the photoconductor, PA (min),
PB (min) is detected, and a voltage signal corresponding to the above light quantity value is supplied to the joint light quantity calculation circuit 32 in the light source control circuit 30 via the calculation circuit 26. This steady light amount PA (mi
Since n) and PB (min) can be obtained by the pulse widths of the light amount setting voltage signal Vref and the light amount detection timing signal as is clear from the above-described light amount adjustment, they are held in the memory in the control circuit 10 as initial information in advance. You may leave it. The pulse width of the light amount detection timing signal output from the counter 14 naturally varies depending on the scanning speed. In the optical scanning device according to the embodiment of the present invention, for example, when photodiodes are used for the light receiving circuits 24 and 25 as one example, the pulse width of the light amount detection timing signal is set to 10 μsec. Further, in the case of an optical scanning device which requires a high scanning speed, the light receiving circuits 24 and 25 are provided with peak hold circuits and the pulse width of the light amount detection timing signal is set to 0.1 μsec, but it can be further shortened. is there. In FIG. 4, the timing of detecting the light quantity is set near the joint between the adjacent exposure ranges scanned by the laser beams of the light sources A22 and B23, respectively.
Since the light amount is in the steady state, the position to be detected may be anywhere within each adjacent exposure range. The light quantity values PA (min) and PB (min) held at this time are summarized as PB (min) = PA (min) = Vref, when summarized from the relationship with each light source.

Next, FIG. 5 shows a light quantity state when writing one scanning line such as a black print. As shown in the figure, the exposure range Xb scanned by the laser beam of the light source B23
Is near the scanning end point of the laser beam of the light source B23, and the joint part of the exposure range Xa scanned by the laser beam of the light source A22 is near the scanning start point of the laser beam of the light source A22. Therefore, when the laser diode is used as the light source even when the light amount is set by the light amount setting voltage, the light source B23 is located near the joint on the exposure range Xb side at the joint between the exposure ranges Xa and Xb due to the droop characteristic of the laser diode. The light amount of the laser beam becomes a steady light amount, and the light amount of the laser beam of the light source A22 becomes a transitional light amount in the vicinity of the joint of the exposure range Xa. Therefore, there is a step difference in the light amount at the joint portion of the exposure ranges Xa and Xb. Occurs. In order to detect a transient light quantity higher than the steady light quantity, the laser diode of the light source A22 is driven through the LD drive circuit 20 at the light quantity detection timing, and is monitored by the light receiving circuit 24.

[0033] Then the light source A22 in FIG. 6, B23 exposure range X a in the case where the laser diode pulsed lighting of,
The light amount state of the joint portion of Xb is shown. The light quantity detection necessarily exposure range X a case, it is not necessary to carry out the joint portion of Xb, exposure range if detected transient rise portion at the time of pulse lighting X a, but may be anywhere in Xb, the amount of light The pulse width of the detection timing signal must be the same as the light amount detection timing signal used when detecting the stationary light amount. In order to simplify the circuit configuration, the light amount detection timing signal used when detecting the stationary light amount may be used.

The light quantity values PA (max) and PB (max) of the transient rising portions of the light sources A22 and B23 detected by the light receiving circuits 24 and 25 at the time of pulse lighting are photoelectrically converted by the arithmetic circuit 26, Joint light intensity calculation circuit 3
2 is held as the initial light amount value. The joint light amount calculation circuit 32 uses the initial light amount values PA (max) and PB (m
ax), A (min), PB (min)
Circumference X a, it corrects the light amount of the joint portion of Xb. Exposure range
X a, which is when the amount of the joint portion of Xb is simply scanned one line to become the worst are shown in FIG. In this case, the light amount difference ΔV between the laser beam of the light source A22 and the laser beam of the light source B23 in the vicinity of the joint is ΔV = PA (max) −PB (min) (1). This light amount difference ΔV can be easily calculated from the initial light amount value. In this case, the correction is performed by setting the light amount value corresponding to ΔV / 2, which is a half of the light amount difference ΔV, as the offset amount, and the voltage ΔV / 2 corresponding to this offset amount with respect to the light amount setting voltage Vref. The offset correction circuit 33 supplies the drive voltage (Vref−ΔV / 2) to the LD drive circuit 20 and the drive voltage (Vref + ΔV / 2) to the LD drive circuit 21 so as to perform the correction. When performing this correction, the LD drive circuit 2 that drives either one of the light sources A22 and B23 so that the voltage corresponding to the light amount difference ΔV is corrected with respect to the light amount setting voltage Vref.
0 or a drive voltage may be supplied to the LD drive circuit 21. That is, in the case of correcting only the light amount of the laser beam of the light source B, the drive voltage (Vref + ΔV) for increasing the light amount corresponding to ΔV is supplied to the LD drive circuit 21 that drives the light source B23, and the light source A when correcting only the light quantity of the laser beam may be supplied to the driving voltage for reducing the amount equivalent ΔV (Vref-ΔV) with respect to the LD driving circuit 2 1 for driving the light source B. However, in order to suppress the light amount difference between the scanning lines in the sub-scanning direction to the minimum, the light amount to be corrected is set to the light source A22,
It is desirable to disperse B23 evenly. Although there are two light sources in the embodiment of the present invention,
When the number of light sources is three or more, the same light amount correction as described above is performed at the first joint of the exposure ranges adjacent from the scanning start side in the main scanning direction, and at the second and subsequent joints, the preceding joint is provided. It is only necessary to perform the light amount correction in consideration of the correction light amount difference between the adjacent exposure ranges in.

Next, during a normal operation for actually forming an image, the image state within one scanning line, that is, the region where the light source B23 is turned on and the region where the light source B23 is turned off within one scanning line. The ratio is calculated by the pixel calculation circuit 31, and the joint light amount calculation circuit 3 is calculated based on the calculation result.
In 2, the light amount of the light source that changes in the vicinity of the joint between the adjacent exposure ranges due to the droop characteristics of the laser diodes of the light sources A22 and B23 is predicted. Light source B23 in FIG.
The change state of the light amount when the image data output to is PWM-modulated is shown. As shown in the figure, when the off state of the light source B continues for a while, the droop characteristic, which is the thermal characteristic of the laser diode, is sufficient, and the laser diode cools down over time, and thus returns to the initial state. . As a result, the light quantity obtained by the pulse lighting immediately after that becomes equal to the light quantity in the initial state. State of various image data, that is, PW of each pixel within one scanning line in the exposure range Xb
Finally, the light amount of the laser diode of the light source B23 in the vicinity of the joint between the exposure ranges Xa and Xb is calculated by the pixel arithmetic circuit 31 and the joint light amount arithmetic circuit 32 from the on / off array during M modulation. From the light quantity PB (calc) obtained by the calculation and the initial light quantity PA (max) of the laser diode of the light source A22, the light quantity difference ΔV between the light source A22 and the light source B23 at the joint between the exposure ranges Xa and Xb is ΔV = PA (Max) -PB (calc) (2), and as in the example shown in FIG.
From the offset correction circuit 33 to the LD drive circuit 20, so that the light amount correction corresponding to V / 2 is performed by the light sources A22 and B23.
21 is a drive voltage (Vref−ΔV / 2),
(Vref + ΔV / 2) is output. Formula ( 1 ),
As is clear from (2), the cause of the light amount difference at the joint between the exposure ranges Xa and Xb is the initial light amount value PA (max). That is, when the laser beam of the laser diode of the light source A starts scanning based on the image data read from the image memory 11 from the joint between the exposure ranges Xa and Xb, a light amount difference occurs between the light source A22 and the light source B23. To do. However, even in this case, if the image data to be written by the laser beam of the laser diode of the light source B23 does not exist near the joint between the exposure ranges Xa and Xb on the photoconductor, the joint portion of the exposure ranges Xa and Xb is not detected. Image quality is light source A
The laser beam of the 22 laser diode does not influence the image state to be written. Therefore, an image formed in the exposure range Xb by the laser beam of the laser diode of the light source B23 and an image formed in the exposure range Xa by the laser beam of the laser diode of the light source A22 are near the joint between the exposure ranges Xa and Xb. When there is no continuity, specifically, the light source A22 or the light source B23 is exposed to the exposure range X.
When it is in the off state near the joint between a and Xb, it is not necessary to perform the light amount correction control of the light sources A22 and B23 at the joint between the exposure ranges Xa and Xb. Exposure range X
Whether or not the image has continuity near the joint between a and Xb is
Correction canceling circuit 34 reads out the image data from the image memory 1 1, 1 2, the exposure range Xa, can be easily determined by checking the image data corresponding to the joint near the Xb. When the image is not continuous in the vicinity of the joint between the exposure ranges Xa and Xb, the correction cancel circuit 34 outputs a correction cancel signal to the offset correction circuit 33 to stop the light amount correction operation of the offset correction circuit 33.

Next, the control operation of the light source control circuit 30 will be described with reference to FIG.
Will be described with reference to. In the processing flow of FIG. 10, the predicted light intensity PB by the laser beam of the laser diode of the light source B23 is mainly in the vicinity of the joint between the exposure ranges Xa and Xb.
The calculation of (calc) is shown. First, in step 41, initial value setting (1) is performed in the pixel calculation circuit 31. Here, the pixel clock counter that softly counts the pixel clock that is a parameter indicating one pixel unit is reset, and the predicted light amount PB
Initial values of various data necessary for the calculation of (calc) are set. As the initial value set here, the bit number n of PWM modulation indicating the number of divisions when dividing one pixel into a plurality of regions, the Heat coefficient α of the laser diode, the Cool coefficient β of the laser diode, and the one-part exposure Total number of pixels Q per range, initial light amount values PA (max), PB (ma
x), PA (min) and PB (min) are set.
Specifically, for example, n = 4, α = 1, β = 0.5, Q =
It is set to 2000. Regarding the Heat coefficient α and the Cool coefficient β of the laser diode, the Heat coefficient α is a coefficient for heating the laser diode when the laser diode is turned on and off because the droop characteristic of the laser diode is a thermal phenomenon. The Cool coefficient β is defined as a coefficient for cooling. Since these coefficients are determined by the structure of the laser diode, the composition of the constituent materials, etc., they are uniquely determined by the type and product type of the laser diode. Further, the Heat coefficient α and the Cool coefficient β may be defined and given as a ratio.

Next, at step 42, the pixel arithmetic circuit 3
In 1, the initial value setting (2) is performed. Here, the count content M of the on-counter that counts the number of lighting pulses in one pixel during PWM modulation of the image data read from the image memory 12 and the count content N of the off-counter that counts the number of light-off pulses in one pixel are reset. It Here, the on-counter and the off-counter are soft counters.

In step 43, the image data is read from the image memory 12 by the pixel arithmetic circuit 31, the on-counter and the off-counter start counting pixel by pixel for each division unit within one pixel, and a lighting pulse for one pixel is started. The number and the number of extinction pulses are counted.

In step 44, the pixel clock counter C
K is incremented. In the next step 45, the count content M of the on-counter that counts the number of ON pulses in one pixel during PWM modulation of the image data or the count content N of the off-counter that counts the number of OFF pulses in one pixel OFF is set in step 43. Only the amount counted in step is added.

Further, in step 46, the pixel arithmetic circuit 3
The on / off ratio pixel Pr is calculated from 1. Here, the on / off ratio pixel Pr can be expressed by the following equation.

Pr = M.alpha.-N.beta. (3) That is, the pixel arithmetic circuit 31 adds on-state and off-state per pixel from the image data read from the image memory 12 obtained in step 46. An on / off ratio pixel Pr obtained by multiplying the result by the Heat coefficient α and the Cool coefficient β of the laser diode is calculated.

In step 47, the pixel clock counter CK
Is determined whether CK ≧ Q, that is, whether the pixel clock has reached the total number Q of the 1-division exposure range. If CK <Q, then in step 48 it is determined whether the on / off ratio pixel Pr is Pr ≦ 0.

When Pr ≦ 0, the LD drive circuit 21
It is determined that the state of the laser diode of the light source B driven by is returned to the initial state, the process returns to step 42, and Pr> 0.
If it is determined that the condition is true, the process returns to step 43.

In step 47, the pixel clock counter CK
When it is determined that the count value CK of CK ≧ Q, the joint light amount calculation circuit 32 determines in step 49 in step 4
Based on the calculation result of the on / off ratio pixel Pr at 6, the predicted light amount PB (cal) by the laser beam of the laser diode of the light source B23 in the vicinity of the joint between the exposure ranges Xa and Xb
The calculation of c) is performed. This predicted light intensity PB (calc)
Is for calculating the offset light amount based on the droop characteristic of the laser diode from the calculation result of the on / off ratio pixel Pr which is the final thermal state of the laser diode of the light source B in the vicinity of the joint between the exposure ranges Xa and Xb. It is calculated using the defined droop characteristic function. As this droop characteristic function, a function defined based on the droop characteristic data of the laser diode actually used for the light source B of the optical scanning device may be used. As an example, the droop characteristic function may be approximated to dy / dx =- It may be defined as a function in which the slope is inversely proportional as α / (x + 1) (4). Here, as the boundary condition, the standard condition is x = 0, y = 1,
Droop 10% (x = xmax, y = 10/1
Solving as 1), PB (calc) = f (x) = y = −1 / [11 · ln {((2 to the power of n) −1) · Q · α}] · ln (x + 1) +1 (5 ). Here, x is the on / off ratio pixel Pr finally calculated by calculating up to the total number of pixels per one-division exposure range in equation (3), and y corresponds to the light amount of the laser diode of the light source B at that time. Further, xmax corresponds to the worst value when the laser diode is continuously lit, and xmax = Q · {(2 to the nth power) −1} · α (6). Where Q is the total number of pixels in the 1-division exposure range,
n is the number of bits of PWM modulation. FIG. 11 shows an example in which the droop characteristic function shown in Expression (5) is plotted.

Next, at step 50, the exposure ranges Xa, Xb
The light amount difference ΔV between the light source A22 and the light source B23 at the joint is calculated by the equation (2).

ΔV = PA (max) −PB (calc) (2) Since the light amount and the light amount setting voltage have a proportional relationship, the light amount difference ΔV
The voltage ΔV corresponding to can be easily obtained as Vref (1-y).

Next, at step 51, the light quantity setting voltage Vref set by the light quantity setting signal output from the control circuit 10 by the offset correction circuit 33 and the voltage corresponding to the offset light quantity value calculated by the joint light quantity calculation circuit 32. An offset voltage value corresponding to the corrected light amount value is calculated from the value ΔV, and the LD drive circuits 20 and 21 receive the drive voltage Vr.
ef−ΔV / 2 and Vref + ΔV / 2 are supplied, respectively.

In this way, by correcting the transient light quantity change due to the droop characteristic of the laser diode, the light quantity of different light sources in the vicinity of the joint between the adjacent exposure ranges can be made uniform, resulting in a streak pattern. It is possible to prevent the occurrence of a typical image quality defect.

[0049]

As described above, according to the invention described in claim 1 or 2 , by controlling the light amount based on the image information, the exposure range divided into a plurality of exposure beams by a plurality of exposure beams can be obtained. It is possible to delicately correct the amount of light at the joint, and it is possible to prevent the image disturbance or the generation of the streak pattern at the joint.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an optical scanning device according to an embodiment of the present invention.

FIG. 2 is a timing chart showing scanning timing by light sources A and B in FIG.

FIG. 3 is a block diagram showing a specific configuration of a control unit of the optical scanning device according to the embodiment of the present invention.

FIG. 4 is an explanatory diagram showing a change state of a light amount on a photosensitive member in a steady state during scanning with a light source continuously turned on.

FIG. 5 is an explanatory diagram showing a change state of the light amount on the photoconductor when actual line printing is performed by continuously turning on the light source.

FIG. 6 is an explanatory diagram showing a change state of a light amount at a joint portion between adjacent exposure ranges on a photoconductor when a light source is pulse-lighted.

FIG. 7 is an explanatory diagram showing a change state of the light amount on the photoconductor after light amount correction when actual line printing is performed by continuously turning on the light source.

FIG. 8 is an explanatory diagram showing a change state of a light amount on a photoconductor when an actual line printing is performed by turning on a light source of a pulse.

FIG. 9 is an explanatory diagram showing a change state of the light amount on the photoconductor after the light amount correction when actual line printing is performed by continuously turning on the light source.

10 is a flowchart showing a control operation of the light source control circuit shown in FIG.

FIG. 11 is a diagram showing a specific example of a droop characteristic function.

[Explanation of symbols]

1 polygon mirror 2 reflector 3 Synchronous sensor 4 control unit 10 Control circuit 11 Image memory 12 image memory 13 Synchronous sensor 14 counter 15 clock pulse generator 16 PWM modulator 17 PWM modulator 18 AND circuit 19 AND circuit 20 LD drive circuit 21 LD drive circuit 22 Light source A 23 Light source B 24 Light receiving circuit 25 Light receiving circuit 26 arithmetic circuit 30 Light source control circuit 31 pixel arithmetic circuit 32 Joint light intensity calculation circuit 33 Offset correction circuit 34 Correction cancellation circuit

Claims (2)

(57) [Claims] 1. A plurality of light source units for generating a light beam, a plurality of light source driving units for driving the plurality of light source units, an exposure range divided into a plurality in the main scanning direction, and each divided exposure range is divided into a plurality of divided exposure ranges. A scanning unit that scans with a light beam, at least one scanning position detecting unit that detects a scanning position, and a light beam from the light source unit is received at predetermined timings in synchronization with the detection output of the scanning position detecting unit. And a plurality of light amount detecting means for detecting the light amount, and the light amount of the two beams of the light source unit for scanning the two adjacent exposure ranges based on the detection results of the plurality of light amount detecting means are the two adjacent exposure ranges. having a light source control means for controlling the plurality of light source driving means so as to uniform joint near the
In the optical scanning device, the light source control means is arranged near the joint between the adjacent exposure ranges.
Adjacent the light quantity control of the beam of the light source unit
Before the joint in the main scanning direction of the two exposure ranges
When modulating with image data in the exposure range located on the side
Of the light source section of the
The optical scanning device is characterized in that it is carried out based on the data. 2. The light source control means is configured to perform the adjacent exposure.
Light intensity control of the beam of the light source unit in the vicinity of the range joint
Control in the vicinity of the joint between the two adjacent exposure areas.
If the image data is not continuous,
The optical scanning device according to claim 1, which is a characteristic.