JPH10147001A - Exposure control device and recording device equipped with exposure control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress fluctuations of thermal quantity of emitted light of a semiconductor laser and reduce irregularities of a potential. SOLUTION: This exposure control device is equipped with an exposure mode generating device 106 which divides a single line into at least, four exposure modes based on a beam detection signal from a semiconductor laser 302, a logical circuit part for switching the mode which causes the semiconductor laser 302 to emit a light respectively at a first quantity of emitted light, a second quantity of emitted light and a bias quantity of emitted light in response to the exposure mode or sets a drive current to O and a microcomputer 101 which calculates drive current values corresponding to the first quantity of emitted light and the second quantity of emitted light, a quantity of laser emitted light at the characteristic change point of the semiconductor laser 302 and a bias drive current based on the bias luminescent quantity of light. Thus it is possible to suppress the thermal fluctuations of quantity of emitted light of the semiconductor laser 302 and reduce the irregularities of a potential with the help of this exposure control device.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a high-precision exposure control apparatus for performing scanning exposure using a semiconductor laser and a recording apparatus having the same.

[0002]

2. Description of the Related Art Conventionally, a two-color image obtained by adding one chromatic color such as red, green, and blue as an accent color to a black image is often used in catalogs and illustrations.

FIG. 9 shows a configuration of a conventional two-color printing system. A two-color original image 801 created by a computer or the like (not shown) is temporarily stored in a printer controller 802 via a communication line. 2-color original image 8
01 is generally 2-bit digital data per pixel. The printer controller 802 converts 2-bit image data, that is, the first color image data 210 and the second color image data 211 into two in accordance with a pixel clock 804 from a two-color electrophotographic printing device 803 as a recording device. The image is output to the color electrophotographic printing device 803.

Here, the 1-bit first color image data 210 representing a chromatic color is represented by PicD1, and the 1-bit second color 1-bit image data representing black.
The color image data 211 is PicD2. The two-color electrophotographic printing apparatus 803 prints two colors based on the first-color image data 210 and the second-color image data 211 and forms an output image similar to the two-color original image 801 on paper. .

JP-A-48-37148 and US Pat.
The two-color electrophotographic printing apparatus described in JP 8929,
After uniformly charging the photoreceptor that forms an image based on image data,
The first color material is exposed to a high potential not exposed (hereinafter high potential), and the second color material is developed to a low potential exposed to strong exposure (hereinafter low potential). Neither color material is developed at a substantially intermediate potential (hereinafter referred to as an intermediate potential).

A compact semiconductor laser is used as the light source of the two-color electrophotographic printing apparatus, and a semiconductor laser driving IC is used for controlling the exposure of the semiconductor laser.

A general semiconductor laser has a built-in photodetector for measuring the amount of emitted light. A method for stably controlling the amount of emitted light is to emit the semiconductor laser at a certain drive current value until the photodetector settles. Let
A method has been adopted in which the light emission amount of the laser at that time is measured by the photodetector, the light emission amount is compared with a target light emission amount, and the result is fed back to the drive current value to obtain a target light emission amount.

This control is generally performed outside the printing area on the photoreceptor, since if the printing area of the photoreceptor is exposed, the coloring material may be developed.

[0009]

In the above-described conventional two-color electrophotographic printing apparatus, as described above, the intermediate potential of the portion where neither color material is developed on the photosensitive member is determined by the first color material being developed. It must be set to a potential approximately intermediate between the high potential of the portion to be developed and the low potential of the portion where the second color material is developed.

However, at the intermediate potential, since the potential characteristic with respect to the exposure amount of the photosensitive member is not saturated, the potential fluctuates greatly even with a slight unevenness in the exposure amount, and the first color material or the second color material becomes It becomes slightly developed. Such unintended development is called fog and is regarded as a problem as a phenomenon that significantly impairs image quality.

On the other hand, a semiconductor laser tends to increase its internal temperature due to light emission and decrease the amount of light emitted with respect to a drive current. In recent years, the light emission amount of the semiconductor laser tends to increase with the speeding up of the printing apparatus. Further, in the conventional two-color electrophotographic printing apparatus, in order to obtain a wide developing potential difference, it is necessary to perform strong exposure, and the tendency for the amount of emitted light to decrease is more remarkable.

For this reason, in the exposure control of the semiconductor laser of the conventional two-color electrophotographic printing apparatus, in the weakly exposed portion which is exposed immediately after the strongly exposed portion, the amount of emitted light is reduced and the surface potential is relatively increased. In a weakly exposed portion that is exposed immediately after a non-exposed portion, the amount of emitted light increases, the surface potential becomes relatively low, and potential unevenness occurs. Due to this potential unevenness, the above-mentioned fogging occurs.

SUMMARY OF THE INVENTION An object of the present invention is to provide an exposure control apparatus which suppresses fluctuations in the amount of thermal emission of a semiconductor laser and reduces potential unevenness, and a recording apparatus including the same.

[0014]

In order to achieve the above object, the present invention provides an exposure control apparatus for controlling the amount of light emitted by a semiconductor laser and performing scanning exposure on a photosensitive member, wherein First to emit light with the amount of light emitted
First control means for controlling a laser drive current, second control means for controlling a second laser drive current to cause the semiconductor laser to emit light with a second light emission amount, the first laser drive current and the second Change point calculating means for calculating a characteristic change point of the light emission characteristics of the semiconductor laser from the laser drive current;
A bias for calculating a bias drive current to be added to the first laser drive current and the second laser drive current such that a change point emission light amount of the semiconductor laser at the characteristic change point becomes a preset target bias emission light amount. And a current calculating means.

Another feature of the present invention is that the first control means controls the first laser driving current so that the first light emission amount becomes a first light emission amount target value set in advance. The second control means may control the second laser drive current so that the second light emission amount becomes a preset second light emission amount target value.

Another feature of the present invention resides in that the value of the bias drive current is set to a limit value at which the potential of the photosensitive member does not drop.

Further, another feature of the present invention is that the first light emission amount is a light exposure amount of weak exposure, and the second light emission amount is a light emission amount of strong exposure.

Another feature of the present invention is that in an exposure control apparatus for scanning and exposing a photoreceptor by using an amount of light emitted by a semiconductor laser, one of the lines is controlled based on a beam detection signal of the semiconductor laser. An exposure mode generating device that divides the semiconductor laser into at least four exposure modes;
A mode switching logic circuit section for emitting light with the amount of light emission and the amount of bias light emission, or for setting the drive current to 0, and a laser drive current value corresponding to the first light emission amount and the second light emission amount. A microcomputer for calculating a bias driving current from the laser light emission amount at the characteristic change point of the semiconductor laser and the bias light emission amount.

Another feature of the present invention is that a photosensitive member for forming an image, a charger for charging the photosensitive member, and scanning and exposure of the charged photosensitive member with a semiconductor laser based on image data. An exposure optical unit having an exposure control device, a developing device that develops the scan-exposed image area, and a recording device that has a transfer device that transfers the developed image to a recording material, wherein the exposure control device includes: An exposure control apparatus according to any one of claims 1 to 7.

According to the present invention, the first control means controls the first laser drive current such that the first light emission amount emitted by the semiconductor laser becomes the first light emission amount target value set in advance.

The second control means controls the second laser drive current so that the second light emission amount becomes a predetermined second light emission amount target value.

The change point calculating means obtains a characteristic change point of the light emission characteristics of the semiconductor laser from the first laser drive current and the second laser drive current. The bias current calculation means calculates a bias drive current to be added to the first laser drive current and the second laser drive current so that the change point emission light quantity of the semiconductor laser at the characteristic change point becomes a preset target bias emission light quantity. I do. Then, the value of the bias drive current is set to a limit value at which the potential of the photosensitive member does not drop.

As described above, the value of the bias current flowing through the semiconductor laser is always set to the maximum value in a range where the potential of the non-exposed portion of the photosensitive member does not drop, so that the heat generated by the semiconductor laser at the time of non-exposure is maximized. The temperature difference from the time of exposure is reduced, the fluctuation in the amount of emitted light is suppressed, and a high-quality image without fog can be obtained.

[0024]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an exposure control apparatus according to an embodiment of the present invention and a recording apparatus having the same will be described with reference to the drawings.

FIG. 2 shows the configuration of a recording apparatus according to one embodiment of the present invention. As shown in FIG. 2, a two-color electrophotographic printing apparatus 800, which is one of the recording apparatuses, includes, in order, around a photoconductor 201, a charger 202, an exposure optical unit 203 having an exposure control device, and a first optical unit 203. The configuration includes a developing device 204, a second developing device 205, a recharger 206, a transfer device 207, a cleaner 208, and an eraser 209.

The charger 202 uniformly charges the surface of the photosensitive member 201 at, for example, a surface potential of -900 V, and
Based on the first color image data 210 representing chromatic color and the second color image data 211 representing black, the photoconductor 201
The upper side is exposed by scanning.

In the present embodiment, assuming that the first color material is positively charged and the second color material is negatively charged, the image potential of the first color is not exposed, and the surface potential is set to about -900 V. The two-color image area is strongly exposed and the surface potential is about -100 V, and the so-called white image area without any color material is weakly exposed and the surface potential is about -500 V
And

Further, if the bias potential of the first developing device 204 is -700 V and the bias potential of the second developing device 205 is -300 V, the first developing device 204 is a device in which the positively charged color material is an image of the first color. In the second developing unit 205, the negatively charged coloring material is developed into the second color image area.

Thereafter, the charging polarity of the color materials is made uniform by the recharger 206, and both color materials are transferred onto the paper 212 at once by the transfer device 207. Remove the remaining coloring material with the cleaner 208,
The charge is uniformly removed by the eraser 209 to return to the initial charge. On the other hand, the color material of the paper 212 is fixed on the paper by the fixing device 213.

FIG. 3 shows the structure of the exposure optical unit shown in FIG.
As shown in FIG. 3, the exposure optical unit 203 includes an exposure control device 301, a semiconductor laser 302, a rotating polygon mirror 303, and a beam detector 304.

The exposure control device 301 supplies an appropriate drive current llas to the semiconductor laser 302 based on the first color image data 210 and the second color image data 211 during printing. The semiconductor laser 302 emits light based on the driving current llas, and the laser beam is deflected by the rotating polygon mirror 303 and the photosensitive member 2
01 is exposed by scanning. At this time, the beam immediately before the writing is guided to the beam detector 304 in order to align the writing position, and the beam detection signal BDT is obtained.

FIG. 1 shows the configuration of an exposure control apparatus according to one embodiment of the present invention. As shown in FIG. 1, the exposure control device 3
01 is a microcomputer 101, a logic circuit unit (selector 102 and negation of logical sum 105), laser drive I
C103, 104 and an exposure mode generator 106.

The beam detection signal BDT obtained by the beam detector 304 shown in FIG.
Is input to

FIG. 4 shows the exposure mode generator 106.
Is shown. The beam detection signal BDT has three timers 9
01, 902, and 903 are input to the trigger terminals T. Timers 901, 902, and 903 are, for example, 74LS1
It's like 23.

The timers 901, 902 and 903 respectively output pulses Pa, Pb and Pc in synchronization with the beam detection signal BDT. So that their width is Ta, Tb.Tc respectively
It is set in advance by an external element.

The output pulses Pa, Pb, Pc of the timers 901, 902, 903 become 2-bit signals M0, M1 through a logic circuit as shown in FIG. 4 and are inputted to the microcomputer 101 of FIG. Here, the timer normally counts a high frequency clock with a counter, and when it reaches the set value,
It is easily configured with a signal emitting device (programmable timer).

FIG. 5 shows each pulse Pa, Pb, Pc and signals M1, M0.
The timing of is shown. As described above, the beam detection signal BDT occurs when the position of the laser beam spot on the photoconductor 201 is slightly left (outside) of the left end of the photoconductor 201.

After a lapse of time Ta from the beam detection signal BDT, the beam spot comes to the recording start position on the photosensitive member 201. When the time Tb elapses from the beam detection signal BDT, the beam spot comes to the recording end position on the photosensitive member 201.
When the time Tc elapses from the beam detection signal BDT, the beam spot moves slightly to the right (outside) of the right end of the photoconductor 201.
I come to. Then, again, the beam detection signal BDT of the next line
Comes.

If the signals M1 and M0 are 2-bit signals, the exposure modes are numbered as shown in FIG. Here, each mode is set to mode 0, a weak exposure control mode, mode 1, a strong exposure control mode, mode 2, a bias light quantity measurement mode, and mode 3, a printing mode.
The above is the description of the exposure mode generator 106 in FIG.

Returning to FIG. 1, the description of the exposure control device 301 will be continued. The microcomputer 101 receives the signals M1, M
Based on 0, the exposure mode is known, and for each mode, the logic circuits 102 and 105 for mode switching operate as follows.

First, the print mode (mode 3) will be described. Selection signal S from microcomputer 101
The selector 102 (a) selects the image data 210 (PicD1) of the first color and the selector 102 (b) selects the image data 211 (PicD2) of the second color by e.
A signal LasD1 and a signal LasD2 are output to the ON / OFF control terminals 103 and 104, respectively.

Here, LasD1 is the selector 102 (a) and the selector 102 (a).
(B) is a signal generated from the logical NOT (NOR) 105 of the output, and LasD2 is an output signal of the selector 102 (b). The image data (PicD1, PicD2, LasD1, LasD2) is
All are 1-bit binary signals.

The selector 102 has a function of selecting and outputting one of the two input signals according to the logic of the Sel terminal (for example, a TTL element LS157).

FIG. 6 shows a general configuration of the laser driving IC 103. First, the laser diode is detected by the photodiode PD of the semiconductor laser 302 shown in FIG.
When a current proportional to the amount of light emitted from the LD enters the terminal 701, it is amplified internally and becomes a voltage value Plasc, which is output from the terminal 702 to the microcomputer 101.

Further, two current sources (current source 1 and current source b) are provided therein, and control signals llasc1 and llascb from the microcomputer 101 are connected to terminals 703 and 704, respectively. The two current sources 1, b draw current values llas1, llasb according to the voltage values of the control signals llasc1, llascb.

A switch is connected to the current source 1 and is interrupted by image data LasD1 from a terminal 705.
Here, when the signal LasD1 is 1, the current llas1 is drawn and 0
At the time of the cut. These llas1 and llasb are put together and connected from the terminal 706 to the laser diode LD of FIG.

On the other hand, the laser drive IC 104 has exactly the same configuration. However, in this embodiment, the current from the PD
Since only one Plas amplification and bias current source b is required,
As shown in the figure, the laser drive IC 104 does not use the amplification of the current Plas and the bias current source b. Laser drive IC
104 inputs the image data LasD2 and the control signal Ilas2c,
The corresponding laser drive current llas2 is drawn.

FIG. 7 shows the driving current ll of the semiconductor laser 302.
6 shows the relationship between as and the laser emission output Plas. In the image area where the second color material that is strongly exposed is developed, the emission current Plas2 is obtained with the drive current llas2. In this case, the signal PicD2 of the second color is 1. In a white image area where light exposure is performed, a light emission amount Plas1 (<Plas2) is obtained with a drive current llas1 (<llas2).
In this case, the signal PicD1 of the first color is 0 and the signal PicD2 of the second color is
Is 0.

The drive current may be 0 in the image area where the second color material which is not exposed is developed. However, when the laser is switched at high speed, the light emission error due to the blunted drive current waveform is reduced. A constant bias drive current llasb is passed. Of course, the photoconductor 201 is hardly exposed by the emitted light amount Plasb, and the surface potential remains at -900 V.

As described above, the first photoconductor 201
In the color image material, the second color material, and the white image region in which neither color material is developed, the potential is set to a substantially intermediate potential (−500 V) of the potential of the portion where both color materials are developed. At an intermediate potential, the potential characteristic with respect to the exposure amount of the photoreceptor is not saturated, so that even if a slight unevenness in the exposure amount occurs, the potential greatly fluctuates, and any of the coloring materials is slightly developed. become. Such unintended development is called fogging, and is known as a phenomenon that significantly deteriorates image quality.

On the other hand, a semiconductor laser tends to increase its internal temperature due to light emission, and to decrease the amount of light emitted with respect to a drive current. In recent years, the light emission amount of the semiconductor laser tends to increase with the speeding up of the printing apparatus. Further, in the conventional two-color electrophotographic printing apparatus, it is necessary to perform strong exposure in order to obtain a wide developing potential difference, and the tendency of the amount of emitted light to decrease is more remarkable.

For this reason, in the conventional exposure control of the semiconductor laser of the two-color electrophotographic printing apparatus, since the image area of the first color is strongly exposed, the internal temperature of the semiconductor laser rises during recording and light emission occurs. The amount of light decreases.

In the first color image area where the strong exposure is performed, the potential characteristic with respect to the exposure amount of the photosensitive member is saturated, so that the potential change due to the decrease in the light emission amount is small and does not appear in the image. When the weak light exposure area comes, the potential characteristic with respect to the light exposure is not saturated, so that the photoconductor potential fluctuates largely in the negative (charge potential) direction due to the decrease in the amount of emitted light, and the second color material is slightly developed. Become so.

On the contrary, since the image area of the second color is not exposed, the internal temperature of the semiconductor laser decreases during recording and the amount of emitted light increases. Therefore, if a white image area, that is, a weak exposure area comes immediately after this, the photoconductor potential will fluctuate greatly in the 0 (ground potential) direction, and the second color material will be developed slightly. .

In this embodiment, such a semiconductor laser 3
In order to suppress fluctuations in the amount of emitted light due to the heat of 02, highly accurate control of the amount of emitted light is performed in the following exposure mode.

First, the weak exposure control mode (mode 0) will be described. In FIG. 1, a microcomputer 1
01 (a) by the selection signal Sel from
And (b) are control signals S from the microcomputer 101
1 and S2 are selected and output to the laser driving ICs 103 and 104 so that the signal LasD1 becomes 1 and the signal LasD2 becomes 0, respectively.

Since this is the same as the combination of signals at the time of weak exposure when white is recorded, that is, when the color material is not developed, the driving current shown in FIG.
llas1 starts to flow. The amount of light emitted from the semiconductor laser LD is measured by the photodiode PD in FIG.
Is returned to.

The microcomputer 101 calculates a light emission target value for light exposure set in advance and an actual light emission light value.
In comparison with Plas1, if the amount of emitted light Plas1 is small, control is performed so as to increase the drive current llas1.

As a result, when the light emission amount becomes stable and the weak exposure control mode ends, the light emission amount of the semiconductor laser LD becomes
It becomes equal to the light emission target value of the weak exposure. In this embodiment,
The value of the drive current llas1 at this time is stored in a memory in the microcomputer 101. As described above, the control in mode 0 is the first control means for controlling the first (light exposure) light emission amount.

Next, the strong exposure control mode (mode 1) will be described. In FIG. 1, a microcomputer 1
01 (a) by the selection signal Sel from
And (b) select an input signal from the microcomputer 101, and the laser drive ICs 103 and 104
The signals LasD1 and 0 are output such that the signal LasD1 becomes 0 and the signal LasD2 becomes 1, respectively.

Since this is the same as the combination of signals at the time of strong exposure when recording the second color, the semiconductor laser
The drive current llas2 in FIG. 7 flows through the LD. The light emission amount of the semiconductor laser LD is measured by the photodiode PD in FIG. 1, and is returned to the microcomputer 101 through the laser drive IC 103 as the analog voltage value Plasc2 of the light emission amount Plas2.

The microcomputer 101 calculates the target value of the light emission amount of the strong exposure set in advance and the actual light emission amount value.
In comparison with Plas2, if the light emission amount value Plas2 is small, control is performed so as to increase the drive current llas2. As a result,
By the time the intensity of emitted light stabilizes and the strong exposure control mode ends,
The light emission amount of the semiconductor laser LD becomes equal to the light emission target value of the strong exposure.

At this time, since the laser beam in FIG. 3 crosses the beam detector 304, a stable beam detection signal B
DT is obtained. In the present embodiment, the value of the drive current llas2 at this time is stored in a memory in the microcomputer 101. As described above, the control in mode 1 is as follows.
The second control unit controls the second (strong exposure) light emission amount.

Next, the bias light quantity measurement mode (mode 2) will be described. In FIG. 1, a selector 1 is selected by a selection signal Sel from a microcomputer 101.
02 (a) and (b) select an input signal from the microcomputer 101, and the known laser driving ICs 103 and 10
4, the signals LasD1 and 0 are output such that the signal LasD1 becomes 0 and the signal LasD2 becomes 0, respectively.

This is the same as the combination of signals at the time of weak exposure when recording the second color. At this time, in this embodiment, the bias current value is first set to a value llas0 calculated by the following equation (Equation 1).

Llas0 = (llas1Plas2-llas2Plas1) / (Plas2-Plas1) (Equation 1) Here, a set (lla) of a laser drive current and a light emission amount for weak exposure.
s1, Plas1) and the set for strong exposure (llas2, Plas2) are already stored in the memory in the microcomputer 101 as described above.

The calculation is performed by the microcomputer 101. As a result, the bias driving current llas0 is
As shown in (1), similarly to the signal llasc1, the signal is guided to the laser drive IC 104 as an analog voltage value of the signal llasb. As a result, the bias drive current llas0 in FIG. 7 flows through the semiconductor laser LD.

The physical meaning of the bias drive current llas0 will be described. As shown in FIG.
The light emission characteristics of 02 are generally divided into LED light emission having a gentle inclination and laser light emission having a steep inclination. The current llas0 indicates the drive current at the intersection of the linear extension of the laser emission and the drive current llas axis. That is, it indicates a characteristic change point of the laser emission characteristics. Therefore, it can be said that the means for controlling the above is a change point calculating means for obtaining a characteristic change point of the laser emission characteristics.

An example of a method for obtaining an appropriate bias drive current value after obtaining the drive current llas0 is disclosed in
It is disclosed in 9671. As described in Japanese Patent Application Laid-Open No. H3-139671, with this drive current llas0, the laser slightly emits light, and the potential of the charged photoconductor 201 drops slightly. There was little effect on the results. Therefore, the light amount was controlled on the characteristic line of stable laser emission (current value larger than llas0).

However, in the above-described two-color electrophotographic printing apparatus, in order to obtain a wide developing potential difference, strong exposure is performed with a laser having a relatively large power, and the charging potential is not reduced at all in a non-exposed portion. There is a request. Therefore, in practice, the light amount is controlled on the characteristic line of the unstable LED light emission (current value smaller than llas0). Therefore, the bias drive current value cannot be set unless the means of this embodiment is used as described below.

The semiconductor laser LD with this driving current llas0
Is measured by the photodiode PD of FIG. 1 and is returned to the microcomputer 101 through the laser drive IC 103 as an analog voltage value Plasb of the signal Plas. After that, the microcomputer 101 executes the calculation according to the following equation (Equation 2), and uses the result as a new bias drive current llasb.

Llasb = (llas0Plasb) / Plas0 (Equation 2) Here, the bias emission light amount Plasb is the maximum value because the photoconductor 201 is hardly exposed and the surface potential remains almost −900 V. This is the laser emission light amount Plasb, which is obtained in advance by experiments. As shown in FIG. 1, the new bias drive current llasb has an analog voltage value of llasb.
It is led to the current source b of the laser drive IC 103 as llasbc.

As a result, the bias drive current llasb in FIG. 7 flows through the semiconductor laser LD. As described above, since a laser having a relatively large power is used in the present apparatus, llasb is hardly larger than llas0 in the equation (Equation 2). The bias current value may be determined by a conventional method as disclosed in Japanese Patent Application Laid-Open No. 3-139671.

The above means adds the first laser drive current and the second laser drive current so that the change point emission light quantity at the characteristic change point of the laser emission characteristic becomes a preset target bias emission light quantity. This is a bias current calculation means for obtaining a bias drive current to be performed.

In this embodiment, since the light emission output Plas0 with respect to the drive current llas0 is measured again, the calculation accuracy in the vicinity of the drive current Ilas set in this embodiment is high. Thereafter, the printing mode (mode 3) shown in FIG.
And this cycle is repeated thereafter.

FIG. 8 is a flowchart summarizing the above processing. First, a process at the time of startup is performed in step 601. The target values of the light emission amounts Plas1, Plas2, and Plasb at the time of the strong exposure, the weak exposure, and the bias emission are externally set or set in advance. Drive current llas1, llas2, llasb
At the time of startup, a value that is likely to achieve a target value is predicted and initialized.

The signal to the laser drive IC is initially set to a strong exposure. Thereafter, when the beam detection signal BDT is generated, the mode from the mode (0) to the mode (3) is repeated as described above.

In mode 0, the first control means for controlling the amount of light emitted from the weak exposure is executed. In mode 1, the second control means for controlling the amount of light emitted from the strong exposure is executed. The change point calculation means to be obtained is executed, and when the mode is set to 3, the bias current calculation means to obtain the bias drive current is executed, and the exposure for one-line two-color printing is executed. After the exposure is completed, the process waits until the mode becomes 0, and then the process is repeated.

In the conventional control of the amount of emitted light, the bias driving current is not controlled for each scanning line because the considerations as in this embodiment are not taken into account. Therefore, fogging due to the above-mentioned thermal fluctuation has occurred, deteriorating the image quality.

In this embodiment, since the bias drive current is controlled for each scanning line, the bias drive current can be set to a value as large as the potential of the photosensitive member 201 drops.

As a result, the difference between the driving current llas1 at the time of strong exposure and the driving current llasb at the time of non-exposure is minimized, so that the difference in laser heat generation between the two is also minimized. Therefore, the temperature fluctuation due to the recording signal of the semiconductor laser and the potential non-uniformity in the white image area are reduced, fog does not occur, and a high-quality image output can be obtained.

The driving current lla with respect to the emission light quantity Plasb
In the method of obtaining sb, the drive current lla for the emission light quantity Plas1 is
The reason for using the method of the present embodiment without using the same light amount control method as when obtaining the drive current llas2 for s1 and the light emission amount Plas2 is as shown in FIG. This is because, since the change in the emitted light amount Plas is small, it is difficult to stabilize the drive current llasb in a short time with the same light amount control method, and a large error occurs, and the above-described desired effect cannot be obtained.

In this embodiment, the surface potential is approximately -900 V
There is a possibility that the maximum amount of laser light emission Plasb to keep as it is is changed due to deterioration of the photoconductor 201 or the like. Therefore, a non-exposed portion for testing is provided every certain period during printing, and the photoconductor 2 in the non-exposed portion is measured by the surface voltmeter 214 shown in FIG.
01 The surface potential is measured, and it is confirmed that there is almost no difference between the case with and without the bias current llasb.

If there is a bias drive current llasb due to the deterioration of the photosensitive member 201 and there is a bias drive current llasb, and if there is a certain difference or more, the light emission amount Plasb is reduced by a fixed amount. As a result, even if the photoconductor 201 deteriorates, the surface potential of the photoconductor 201 in the non-exposed portion is kept constant.

Next, another embodiment of the present invention will be described. A means for obtaining a continuous light emission amount by modulating the drive current of the aforementioned semiconductor laser in an analog or multi-step manner is provided, and the light emission light amount at any two points in the continuous light emission amount is controlled by the laser drive current. If the drive current value for two arbitrary light emission amounts can be obtained, the bias drive current can be controlled as in the embodiment of FIG. In this case, in the characteristics of the semiconductor laser 302 shown in FIG. 7, only the linear laser emission mode can be used, and the calculation accuracy of the equations (1) and (2) can be improved.

The exposure control apparatus of the present invention can be similarly applied to other recording apparatuses that perform scanning exposure using a laser, other than the two-color electrophotographic printing apparatus of the above-described embodiment. For example, a normal silver halide photographic film is wound on a rotating drum, and the surface thereof is scanned and exposed with a semiconductor laser based on image information, and then developed to obtain an image, similarly to the photoreceptor of a two-color electrophotographic printing apparatus. Silver halide photographic recording apparatus. Some recording devices use a photocurable resin instead of a silver halide photographic film. In this case, the film is etched by scanning exposure to form hydrophobic and hydrophilic portions, and used as a printing plate by a simple printing machine.

[0087]

According to the present invention, fluctuations in the amount of thermal emission of a semiconductor laser are suppressed, and potential unevenness is reduced.
A high-quality image without fogging can be obtained.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an exposure control apparatus according to an embodiment of the present invention.

FIG. 2 is a configuration diagram of a recording apparatus according to an embodiment of the present invention.

3 is a configuration diagram of an exposure optical unit including the exposure control device of FIG.

FIG. 4 is a configuration diagram of the exposure mode generator of FIG. 1;

FIG. 5 is a diagram illustrating timings of respective modes of the exposure control device of FIG. 1;

FIG. 6 is a configuration diagram of a laser driving IC.

FIG. 7 is a diagram illustrating a relationship between a laser drive current and a laser emission output.

FIG. 8 is a flowchart of an exposure control process.

FIG. 9 is a configuration diagram of a conventional two-color printing system.

[Explanation of symbols]

101: microcomputer, 102: selector, 1
03, 104: Laser drive IC, 105: Negation of logical sum
(NOR), 106: Exposure mode generator, 201: Photoconductor, 203: Exposure optical unit, 210: Image data of the first color, 211: Image data of the second color, 301: Exposure control device, 302: Semiconductor Laser, 800: two-color electrophotographic printing apparatus, BDT: beam detection signal, Sel: selection signal, S1, S2 ...
Control signal, Plas: laser light emission amount, llas: laser drive current, Plasb: bias light emission amount, llasb: bias drive current

Claims (8)

[Claims] 1. An exposure control device for controlling the amount of light emitted by a semiconductor laser to scan and expose a photoreceptor, wherein a first laser drive current is controlled to cause the semiconductor laser to emit light at a first amount of light. 1 control means; second control means for controlling a second laser drive current to cause the semiconductor laser to emit light at a second light emission amount; and the semiconductor laser based on the first laser drive current and the second laser drive current. Change point calculating means for obtaining a characteristic change point of the laser emission characteristic; and the first laser drive current and the first laser drive current so that the change point emission light amount of the semiconductor laser at the characteristic change point becomes a preset target bias emission light amount. An exposure control device comprising: a bias current calculation unit configured to calculate a bias drive current to be added to the second laser drive current. 2. The method according to claim 1, wherein the first control means includes:
Controlling the first laser drive current so that the first light emission amount becomes a preset first light emission amount target value; and the second control means controls the second light emission amount to a predetermined second light emission amount. An exposure control device, wherein the second laser drive current is controlled so as to be a light amount target value. 3. The exposure control apparatus according to claim 1, wherein the value of the bias drive current is set to a limit value at which the potential of the photoconductor does not drop. 4. The exposure control according to claim 1, wherein the first light emission amount is a light exposure amount of weak exposure, and the second light emission amount is a light emission amount of strong exposure. apparatus. 5. The method according to claim 1, wherein said first control means comprises:
The first laser drive current controls the light emission amount at an arbitrary point in the continuous light emission amount obtained by modulating the laser drive current in an analog or multi-step manner. An exposure control device, wherein the amount of emitted light at another point of the amount of emitted light is controlled by the second laser drive current. 6. A measuring means according to claim 1, wherein said surface potential of said photosensitive member is measured at a non-exposure portion for testing on said photosensitive member when said bias drive current only emits bias light and when no current is applied. And an adjusting unit for adjusting the target bias light emission amount according to the potential difference between the bias light emission and the no-current time. 7. An exposure control apparatus for scanning and exposing a photoreceptor by using an amount of light emitted from a semiconductor laser, wherein an exposure is divided into at least four exposure modes in one line based on a beam detection signal of the semiconductor laser. A mode generation device, and a mode switching device for causing the semiconductor laser to emit light at a first light emission amount, a second light emission amount, a bias light emission amount, or a drive current of 0 corresponding to the exposure mode. A logic circuit unit, a laser drive current value corresponding to the first light emission amount and the second light emission amount, a laser emission light amount value at a characteristic change point of the semiconductor laser, and a bias drive current from the bias light emission amount. An exposure control device, comprising: a microcomputer for calculating. 8. An exposure optical system comprising: a photoreceptor for forming an image; a charger for charging the photoreceptor; and an exposure controller for scanning and exposing the charged photoreceptor with a semiconductor laser based on image data. And a developing device for developing the scanned and exposed image area, and a transfer device for transferring the developed image to a recording material. The exposure control device according to claim 1, wherein: A recording apparatus, which is the exposure control apparatus according to claim 1.