JP3622382B2 - Exposure control apparatus and recording apparatus having the same - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a high-precision exposure control apparatus that performs scanning exposure using a semiconductor laser and a recording apparatus including the exposure control apparatus.
[0002]
[Prior 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 explanatory drawings.
[0003]
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 the printer controller 802 via a communication line. The two-color original image 801 is generally 2-bit digital data per pixel. The printer controller 802 outputs 2-bit image data, that is, first color image data 210 and second color image data 211 in accordance with a pixel clock 804 from a two-color electrophotographic printing apparatus 803 serving as a recording apparatus. Output to the color electrophotographic printing apparatus 803.
[0004]
Here, it is assumed that 1-bit first color image data 210 representing a chromatic color is PicD1, and 1-bit second color image data 211 representing black 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 a sheet. .
[0005]
The two-color electrophotographic printing apparatus described in Japanese Patent Application Laid-Open No. 48-37148 and US Pat. No. 4,078,929 has a high potential (hereinafter referred to as a high potential) that does not expose after uniformly charging a photoconductor that forms an image with image data. The first color material is developed at a low potential (hereinafter referred to as a low potential) where the first color material is strongly exposed, and the second color material is developed at a low potential (hereinafter referred to as a low potential). In this case, neither color material is developed.
[0006]
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.
[0007]
A general semiconductor laser has a built-in photodetector for measuring the amount of emitted light, and the method for stably controlling the amount of emitted light is to cause the semiconductor laser to emit light at a certain drive current value until the photodetector has settled. A method of obtaining a target light emission amount by measuring the light emission amount of the laser with the photodetector, comparing it with a target value of the light emission amount, and feeding back the result to the drive current value.
[0008]
This control is generally performed outside the print area on the photoconductor because the color material may be developed when the photoconductor print area is exposed.
[0009]
[Problems to be solved by the invention]
In the above 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 equal to the high potential of the portion where the first color material is developed, The potential of the second color material must be set to a substantially intermediate potential with respect to the low potential of the developed portion.
[0010]
However, since the potential characteristics with respect to the exposure amount of the photosensitive member are not saturated at the intermediate potential, the potential greatly fluctuates even if the exposure amount is small, and the first color material or the second color material is slightly developed. Will come to be. Such unintended development is called fogging and is regarded as a problem as a phenomenon that significantly impairs image quality.
[0011]
On the other hand, the semiconductor laser tends to increase its internal temperature due to light emission and to decrease the amount of light emitted with respect to the drive current. In recent years, the amount of light emitted from a semiconductor laser tends to increase as the speed of the printing apparatus increases. Further, in the conventional two-color electrophotographic printing apparatus, in order to obtain a wide development potential difference, it is necessary to perform strong exposure, and the tendency for the amount of emitted light to decrease is more prominent.
[0012]
For this reason, in the exposure control of the semiconductor laser of the conventional two-color electrophotographic printing apparatus, the amount of emitted light is reduced and the surface potential is relatively high in the weakly exposed portion exposed immediately after the strongly exposed portion, and the surface potential is relatively high. In the weakly exposed portion that is exposed immediately after the light emission amount, the amount of emitted light increases, the surface potential becomes relatively low, and potential unevenness occurs. This unevenness of the potential causes the above-described fog.
[0013]
SUMMARY OF THE INVENTION An object of the present invention is to provide an exposure control apparatus that suppresses fluctuations in the amount of thermal light emitted from a semiconductor laser and reduces potential unevenness, and a recording apparatus having the exposure control apparatus.
[0014]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides: First control means for controlling a first laser drive current for switching the semiconductor laser with a first light emission amount; and second control means for controlling a second laser drive current for switching the semiconductor laser with a second light emission amount; And an optical system that scans and exposes a photosensitive member with a laser beam from the semiconductor laser. In exposure control equipment ,Previous Change point calculating means for obtaining a characteristic change point of the light emission characteristic of the semiconductor laser from the first laser drive current and the second laser drive current, and the characteristic change point From the amount of emitted light and the target bias emitted light amount for the current of For the first laser driving current and the second laser driving current Addition And bias current calculation means for calculating a bias drive current to be performed.
[0015]
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 preset first light emission amount target value, and the second control unit controls the second laser drive current. The 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.
[0016]
Another feature of the present invention is that the value of the bias drive current is set to a limit value at which the potential of the photoconductor does not drop.
[0017]
Another feature of the present invention resides in that the first light emission amount is a weak exposure light emission amount, and the second light emission amount is a strong exposure light emission amount.
[0019]
Another feature of the present invention is that a photoconductor for forming an image, a charger for charging the photoconductor, and an exposure control device for scanning and exposing the charged photoconductor with a semiconductor laser based on image data. And a transfer device that transfers the developed image to a recorded material. The exposure control device includes: an exposure optical unit including: a developing device that develops the scanned and exposed image area; Or claims 5 Any one of Record To be a device.
[0020]
According to the present invention, the first control means controls the first laser drive current so that the first light emission amount emitted from the semiconductor laser becomes a preset first light emission amount target value.
[0021]
The second control means controls the second laser drive current so that the second light emission amount becomes a preset second light emission amount target value.
[0022]
The change point calculation means obtains a characteristic change point of the light emission characteristic of the semiconductor laser from the first laser drive current and the second laser drive current. Bias current calculation means From the amount of emitted light and the target bias emitted light amount for the current of For the first laser drive current and the second laser drive current Addition The bias drive current to be calculated is calculated. And the bias drive current value , Feeling The limit is set so that the potential of the light body does not drop.
[0023]
In this way, by always setting the bias current value that flows to the semiconductor laser to the maximum in a range where the potential of the non-exposed portion of the photoreceptor does not drop, the amount of heat generated by the semiconductor laser during non-exposure is maximized, The temperature difference is reduced, fluctuations in the amount of emitted light are suppressed, and a high-quality image without fogging can be obtained.
[0024]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an exposure control apparatus and a recording apparatus including the same according to an embodiment of the present invention will be described with reference to the drawings.
[0025]
FIG. 2 shows a configuration of a recording apparatus according to an embodiment of the present invention.
As shown in FIG. 2, a two-color electrophotographic printing apparatus 800, which is one of recording apparatuses, sequentially includes a charger 202, an exposure optical unit 203 including an exposure control device, and a first around a photoconductor 201. The developing device 204, the second developing device 205, the recharging device 206, the transfer device 207, the cleaner 208, and the eraser 209 are arranged.
[0026]
The charger 202 uniformly charges the surface of the photoconductor 201 with, for example, -900 V, and the exposure optical unit 203 uses the exposure optical unit 203 to display the first color image data 210 representing a chromatic color and the second color image data representing black. Based on 211, the photosensitive member 201 is scanned and exposed.
[0027]
In this embodiment, if the first color material is positively charged and the second color material is negatively charged, the image area of the first color is not exposed, the surface potential is set to about −900 V, and the second color material is The image area is strongly exposed and the surface potential is about -100V, and the so-called white image area without any color material is weakly exposed and the surface potential is about -500V.
[0028]
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 develops the positively charged color material into the image area of the first color. In the second developing device 205, the negatively charged color material is developed into the image area of the second color.
[0029]
Thereafter, the recharger 206 aligns the charging polarities of the color materials, and the transfer device 207 transfers both color materials onto the paper 212 at once. The remaining color material is removed by the cleaner 208, the charge is uniformly eliminated by the eraser 209, and the initial charging is restored. On the other hand, the color material of the paper 212 is fixed on the paper by the fixing device 213.
[0030]
FIG. 3 shows a configuration of the exposure optical unit in FIG.
As shown in FIG. 3, the exposure optical unit 203 includes an exposure control device 301, a semiconductor laser 302, a rotary polygon mirror 303, and a beam detector 304.
[0031]
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 rotary polygon mirror 303 to scan and expose the photoconductor 201. At this time, in order to align the writing position, the beam immediately before writing is guided to the beam detector 304 to obtain the beam detection signal BDT.
[0032]
FIG. 1 shows the arrangement of an exposure control apparatus according to an embodiment of the present invention.
As shown in FIG. 1, the exposure control device 301 includes a microcomputer 101, a logic circuit unit (selector 102 and negation of logical sum 105), laser drive ICs 103 and 104, and an exposure mode generator 106.
[0033]
The beam detection signal BDT obtained by the beam detector 304 in FIG. 3 is input to the exposure mode generator 106.
[0034]
Here, FIG. 4 shows the configuration of the exposure mode generator 106. The beam detection signal BDT is input to the trigger terminals T of the three timers 901, 902, and 903. Timers 901, 902, and 903 are, for example, 74LS123, which is a TTL element.
[0035]
Timers 901, 902, and 903 output pulses Pa, Pb, and Pc in synchronization with the beam detection signal BDT, respectively. Their widths are Ta, Tb. It is set in advance by an external element so as to be Tc.
[0036]
Output pulses Pa, Pb, and Pc of the timers 901, 902, and 903 become 2-bit signals M0 and M1 through a logic circuit as shown in FIG. 4, and are input to the microcomputer 101 in FIG. Here, the timer is usually configured simply by counting a high-frequency clock with a counter and generating a signal (programmable timer) when a set numerical value is reached.
[0037]
FIG. 5 shows the timing of each pulse Pa, Pb, Pc and signals M1, M0. As described above, the beam detection signal BDT is generated at the position of the laser beam spot on the photoconductor 201 slightly on the left side (outside) from the left end of the photoconductor 201.
[0038]
When time Ta elapses 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 comes slightly to the right (outside) from the right end of the photosensitive member 201. Then, the beam detection signal BDT for the next line comes again.
[0039]
If the signals M1 and M0 are 2-bit signals, the exposure modes are numbered as shown in FIG. Here, the respective modes are set as mode 0, a weak exposure control mode, mode 1, a strong exposure control mode, mode 2, a bias light amount measurement mode, and mode 3, a print mode.
The above is the description of the exposure mode generator 106 in FIG.
[0040]
Returning to FIG. 1, the description of the exposure control apparatus 301 will be continued. The microcomputer 101 knows the exposure mode from the signals M1 and M0, and operates as follows for the logic circuits 102 and 105 for mode switching for each mode.
[0041]
First, the print mode (mode 3) will be described.
The selector 102 (a) selects the first color image data 210 (PicD1) and the selector 102 (b) selects the second color image data 211 (PicD2) according to the selection signal Sel from the microcomputer 101, and the laser driving IC 103. , 104 output a signal LasD1 and a signal LasD2, respectively.
[0042]
Here, LasD1 is a signal made from the logical sum (NOR) 105 of the outputs of the selectors 102 (a) and (b), and LasD2 is an output signal of the selector 102 (b). The image data (PicD1, PicD2, LasD1, LasD2) are all 1-bit binary signals.
[0043]
The selector 102 has a function of selecting and outputting one of two input signals according to the logic of the Sel terminal (for example, LS element LS157).
[0044]
FIG. 6 shows a general configuration of the laser driving IC 103. First, when a current detected by the photodiode PD of the semiconductor laser 302 shown in FIG. 1 and proportional to the amount of light emitted from the laser diode LD enters the terminal 701, it is amplified internally and becomes a voltage value Plasc from the terminal 702 to the microcomputer. 101 is output.
[0045]
Further, it has two current sources (current source 1 and current source b) inside, and control signals llasc1 and llasbb from the microcomputer 101 are connected to terminals 703 and 704, respectively. The two current sources 1 and b draw the current values llas1 and llasb in accordance with the voltage values of the control signals llas1 and llasb.
[0046]
A switch is connected to the current source 1, which is intermittently connected by the image data LasD 1 from the terminal 705. Here, it is assumed that the current llas1 is drawn when the signal LasD1 is 1, and is cut when the signal LasD1 is 0. These lass 1 and lasb are combined and connected from the terminal 706 to the laser diode LD of FIG.
[0047]
On the other hand, the laser drive IC 104 has the same configuration. However, in this embodiment, the amplification of the current Pla from the PD and the bias current source b are sufficient, so that the laser drive IC 104 does not use the amplification of the current Pla and the bias current source b as shown in FIG. . The laser drive IC 104 receives the image data LasD2 and the control signal Ilas2c, and draws a laser drive current llas2 corresponding to the input.
[0048]
FIG. 7 shows the relationship between the drive current llas of the semiconductor laser 302 and the laser emission output Plas.
In the image area where the second color material which is strongly exposed is developed, the light emission output Plas2 is obtained with the driving current llas2. In this case, the second color signal PicD2 is 1. In the white image region that is weakly exposed, the light emission amount Plas1 (<Plas2) is obtained with the driving current llas1 (<llas2). In this case, the first color signal PicD1 is 0 and the second color signal PicD2 is 0.
[0049]
In an image area where the second color material that is not exposed is developed, a drive current of 0 may be used. However, when the laser is switched at a high speed, a normally constant bias is used in order to reduce a light emission error due to a dull waveform of the drive current. A drive current llasb is allowed to flow. Of course, the photoconductor 201 is hardly exposed at the light emission amount Plasb, and the surface potential remains at -900V.
[0050]
As described above, in the white image area where neither the first color material nor the second color material is developed on the photosensitive member 201, the potential of the portion where both color materials are developed is substantially in the middle. The potential is set to (−500V). At an intermediate potential, the potential characteristic with respect to the exposure amount of the photosensitive member is not saturated. Therefore, even if a slight unevenness in the exposure amount occurs, the potential greatly fluctuates so that any one of the coloring materials is slightly developed. become.
Such unintended development is called fogging and is known as a phenomenon that significantly impairs image quality.
[0051]
On the other hand, the semiconductor laser tends to increase its internal temperature due to light emission and to decrease the amount of light emitted with respect to the drive current. In recent years, the amount of light emitted from a semiconductor laser tends to increase as the speed of the printing apparatus increases. Furthermore, in the conventional two-color electrophotographic printing apparatus, it is necessary to perform strong exposure in order to obtain a wide development potential difference, and the tendency for the amount of emitted light to decrease is more prominent.
[0052]
For this reason, in the conventional semiconductor laser exposure control of the two-color electrophotographic printing apparatus, the image area of the first color is intensely exposed, so that the internal temperature of the semiconductor laser rises during recording and the amount of emitted light decreases. To do.
[0053]
In the image area of the first color that is strongly exposed, the potential characteristic with respect to the exposure amount of the photosensitive member is saturated, so that the potential variation due to the decrease in the amount of emitted light is small and does not appear in the image. When the area comes, the potential characteristic with respect to the exposure amount is not saturated, so that the photoreceptor potential largely fluctuates in the negative (charging potential) direction due to the decrease in the amount of emitted light, so that the second color material is slightly developed. Become.
[0054]
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, when the white image area, that is, the weak exposure amount area comes immediately after this, the photoconductor potential is greatly changed in the 0 (ground potential) direction, and the second color material is slightly developed. .
[0055]
In this embodiment, in order to suppress such fluctuations in the amount of emitted light due to the heat of the semiconductor laser 302, the emitted light amount is controlled with high accuracy in the exposure mode described below.
[0056]
First, the weak exposure control mode (mode 0) will be described.
In FIG. 1, selectors 102 (a) and (b) select control signals S 1 and S 2 from the microcomputer 101 according to a selection signal Sel from the microcomputer 101, and a signal LasD 1 is sent to the laser drive ICs 103 and 104, respectively. 1 and the signal LasD2 are output to be 0.
[0057]
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, so that the drive current llas1 in FIG. 7 flows through the semiconductor laser LD. The light emission amount of the semiconductor laser LD is measured by the photodiode PD shown in FIG. 1 and returned to the microcomputer 101 as an analog voltage value Plasc1 corresponding to the light emission amount Plas1 through the laser driving IC 103.
[0058]
The microcomputer 101 compares the preset light exposure target value for weak exposure with the actual light emission amount value Plas1 and controls to increase the drive current llas1 when the light emission amount Plas1 is small.
[0059]
As a result, the light emission amount of the semiconductor laser LD becomes equal to the light emission target amount for weak exposure when the light emission amount is stabilized and the weak exposure control mode ends. In the present embodiment, the value of the driving current llas1 at this time is stored in a memory in the microcomputer 101.
As described above, the mode 0 control is the first control means for controlling the first (weak exposure) light emission amount.
[0060]
Next, the strong exposure control mode (mode 1) will be described.
In FIG. 1, selectors 102 (a) and (b) select an input signal from the microcomputer 101 based on a selection signal Sel from the microcomputer 101, and a signal LasD 1 is 0 and a signal to the laser driving ICs 103 and 104, respectively. Output so that LasD2 becomes 1.
[0061]
Since this is the same as the combination of signals at the time of strong exposure when recording the second color, the drive current llas2 in FIG. 7 flows through the semiconductor laser LD. The light emission amount of the semiconductor laser LD is measured by the photodiode PD of FIG. 1 and returned to the microcomputer 101 through the laser driving IC 103 as an analog voltage value Plasc2 of the light emission amount Plas2.
[0062]
The microcomputer 101 compares the preset light emission target value for strong exposure with the actual light amount value Plas2, and controls to increase the drive current llas2 when the light amount value Plas2 is small. As a result, the amount of light emitted from the semiconductor laser LD becomes equal to the target value of the amount of emitted light for strong exposure when the amount of emitted light is stabilized and the strong exposure control mode ends.
[0063]
At this time, since the laser beam in FIG. 3 crosses the beam detector 304, a stable beam detection signal BDT is obtained. In this embodiment, the value of the driving current llas2 at this time is stored in the memory in the microcomputer 101.
As described above, the control in mode 1 is the second control means for controlling the second (strong exposure) light emission amount.
[0064]
Next, the bias light quantity measurement mode (mode 2) will be described.
In FIG. 1, selectors 102 (a) and (b) select an input signal from the microcomputer 101 based on a selection signal Sel from the microcomputer 101, and a signal LasD 1 is 0 for each of the known laser driving ICs 103 and 104. And the signal LasD2 is output to be zero.
[0065]
This is the same as the combination of signals during 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).
[0066]
llas0 = (lllas1Plas2-llas2Plas1) / (Plas2-Plas1) ......... (Equation 1)
Here, the combination of the laser drive current for weak exposure and the amount of emitted light (llas1, Plas1) and the group for strong exposure (llas2, Plas2) are already stored in the memory in the microcomputer 101 as described above. ing.
[0067]
The calculation is performed by the microcomputer 101. As a result, as shown in FIG. 1, the bias drive current llas0 is guided to the laser drive IC 104 as an analog voltage value of the signal lasb1 as in the case of the signal lasc1. As a result, the bias drive current llas0 in FIG. 7 flows through the semiconductor laser LD.
[0068]
The physical meaning of the bias drive current llas0 will be described. As shown in FIG. 7, the light emission characteristics of the semiconductor laser 302 are generally divided into LED light emission having a gentle inclination and laser light emission having a steep inclination. 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, the characteristic change point of the laser emission characteristic is shown. Therefore, it can be said that the means for controlling the above is a change point calculation means for obtaining a characteristic change point of the laser emission characteristic.
[0069]
An example of a method for obtaining an appropriate bias drive current value after obtaining the drive current llas0 is disclosed in JP-A-3-139671. As described in Japanese Patent Application Laid-Open No. 3-139671, the laser is slightly emitted by this driving current llas0, and the potential of the charged photosensitive member 201 is slightly lowered. However, in the conventional electrophotographic printing apparatus, printing is performed. There was little effect on the results. Therefore, the amount of light is controlled on the characteristic line of stable laser emission (current value larger than llas0).
[0070]
However, in the above-described two-color electrophotographic printing apparatus, in order to obtain a wide development potential difference, there is a demand for intense exposure with a laser having a relatively large power, and for the non-exposed portion to not lower the charging potential at all. . Therefore, in practice, the amount of light is controlled on the characteristic line of unstable LED emission (current value smaller than llas0). Therefore, the bias drive current value cannot be set unless the means of the present embodiment as described below.
[0071]
The amount of light emitted from the semiconductor laser LD at this driving current llas0 is measured by the photodiode PD shown in FIG. 1, and the analog voltage value Plas of the signal Plas through the laser driving IC 103. 0 To the microcomputer 101. Thereafter, the microcomputer 101 executes the calculation by the following equation (Equation 2), and sets the result as a new bias drive current llasb.
[0072]
llasb = (llas0Plasb) / Plas0 (2)
Here, the bias light emission amount Plasb is the maximum laser light emission amount Plasb for which the photosensitive member 201 is hardly exposed and the surface potential remains approximately −900 V, and this is obtained in advance by experiments. . As shown in FIG. 1, the new bias drive current llasb is led to the current source b of the laser drive IC 103 as an analog voltage value llasbc of lasb.
[0073]
As a result, the bias drive current llasb in FIG. 7 flows through the semiconductor laser LD. As described above, since this apparatus uses a laser having a relatively high power, llasb is hardly larger than lllas0 in the equation (Equation 2). The bias current value may be determined by a conventional method as disclosed in Japanese Patent No. 3-139671.
[0074]
The above means is the characteristic change point of the laser emission characteristics. From the amount of emitted light and the target bias emitted light amount for the current of For the first laser driving current and the second laser driving current Addition Bias current calculating means for obtaining a bias driving current to be applied.
[0075]
In the present embodiment, since the light emission output Plas0 with respect to the drive current llas0 is measured again, the calculation accuracy near the drive current Ilas set in the present embodiment is high. After this, the print mode (mode 3) shown in FIG. 5 is returned again, and this cycle is repeated thereafter.
[0076]
FIG. 8 shows a summary of the above processing in a flowchart. First, in step 601, processing at startup is performed. The target values of the light emission amounts Plas1, Plas2, and Plasb at the time of strong exposure, weak exposure, and bias light emission are obtained from the outside or set in advance. The drive currents llas1, llas2, and llasb are initially set by predicting values at which a target value is likely to be realized at startup.
[0077]
The signal to the laser drive IC is initially set to the strong exposure setting. Thereafter, when the beam detection signal BDT is generated, the mode (0) to the mode (3) are repeated as described above.
[0078]
In mode 0, the first control means for controlling the weak exposure light emission amount is executed. In mode 1, the second control means for controlling the strong exposure light emission amount is executed. When the calculation means is executed and mode 3 is entered, the bias current calculation means for obtaining the bias drive current is executed, and exposure for two-color printing of one line is executed. After the exposure is completed, the process waits until the mode 0 is reached, and is repeated thereafter.
[0079]
In the conventional control of the amount of emitted light, the bias drive current is not controlled in units of scanning lines because no consideration is given as in this embodiment. Therefore, the above-described fogging due to thermal fluctuation has occurred, degrading the image quality.
[0080]
In this embodiment, since the bias drive current is controlled in units of scanning lines, the bias drive current can be set to a large value up to the limit at which the photosensitive member 201 drops in potential.
[0081]
As a result, the difference between the drive current llas1 at the time of strong exposure and the drive current llasb at the time of non-exposure is minimized, so that the difference in the amount of laser heat generated between the two is also minimized. For this reason, temperature fluctuation due to the recording signal of the semiconductor laser, and potential unevenness in the white image region are reduced, fogging does not occur, and high-quality image output can be obtained.
[0082]
In addition, the method of this embodiment is used for the method of obtaining the drive current llasb for the emitted light amount Plasb, without using the same light amount control method as that for obtaining the drive current llas1 for the emitted light amount Plas1 and the drive current llas2 for the emitted light amount Plas2. The reason for this is that, as shown in FIG. 7, in the LED light emission region, the change in the light emission amount Plas with respect to the drive current llas is small, so it is difficult to set the drive current llasb in a short time with the same light amount control method. This is because an error is added and the desired effect described above cannot be obtained.
[0083]
In the present embodiment, the maximum laser light emission amount Plasb for which the surface potential remains approximately −900 V may change 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 surface potential of the photosensitive member 201 in the non-exposed portion is measured by the surface potential meter 214 shown in FIG. 2, with or without the bias current llasb. Confirm that there is almost no difference.
[0084]
If there is a difference greater than a certain value with and without the bias drive current llasb due to deterioration of the photosensitive member 201, the light emission amount Plasb is decreased by a certain amount. As a result, even if the photoconductor 201 is deteriorated, the surface potential of the non-exposed portion of the photoconductor 201 is kept constant.
[0085]
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 semiconductor laser described above in an analog manner or in multiple stages is provided, and the light emission light amount at any two points of the continuous light emission amount is controlled by the laser drive current. If the drive current value for the light emission quantity at any two points can be obtained, the bias drive current can be controlled as in the embodiment of FIG. In this case, only the linear laser emission mode can be used in the characteristics of the semiconductor laser 302 shown in FIG. 7, and the calculation accuracy of the equations (Equation 1) and (Equation 2) can be improved.
[0086]
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, an ordinary silver halide photographic film is wound on a rotating drum, and the surface is scanned and exposed on the basis of image information with a semiconductor laser in the same manner as a photoreceptor of a two-color electrophotographic printing apparatus, and then developed to obtain an image. And a silver halide photographic recording apparatus. There is also a recording apparatus that uses a photocurable resin instead of a silver salt photographic film. In this case, etching is performed by scanning exposure to form hydrophobic and hydrophilic portions, which are used as a printing plate in a simple printing machine.
[0087]
【The invention's effect】
According to the present invention, it is possible to obtain a high-quality image without fogging by suppressing fluctuations in the amount of thermal light emitted from the semiconductor laser and reducing potential unevenness.
[Brief description of the drawings]
FIG. 1 is a block 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 block diagram of an exposure optical unit provided with the exposure control apparatus of FIG. 1. FIG.
4 is a block diagram of the exposure mode generator of FIG. 1. FIG.
5 is a diagram showing timings of respective modes of the exposure control apparatus of FIG. 1. FIG.
FIG. 6 is a configuration diagram of a laser driving IC.
FIG. 7 is a diagram showing a relationship between a laser driving current and a laser emission output.
FIG. 8 is a flowchart of exposure control processing.
FIG. 9 is a configuration diagram of a conventional two-color printing system.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 101 ... Microcomputer, 102 ... Selector, 103, 104 ... Laser drive IC, 105 ... Logical sum negation (NOR), 106 ... Exposure mode generator, 201 ... Photoconductor, 203 ... Exposure optical part, 210 ... 1st Color image data 211 ... Second color image data 301 ... Exposure control device 302 ... Semiconductor laser 800 ... 2-color electrophotographic printing device BDT ... Beam detection signal Sel ... Selection signal S1, S2 ... Control signal, Plas ... laser emission light quantity, lalas ... laser drive current, Plasb ... bias emission light quantity, lasb ... bias drive current

Claims (6)

First control means for controlling a first laser driving current for switching the semiconductor laser with a first light emission amount;
Second control means for controlling a second laser driving current for switching the semiconductor laser with a second light emission amount;
In an exposure control apparatus comprising an optical system that scans and exposes a photosensitive member with a laser beam from the semiconductor laser ,
From the the front Symbol first laser drive current second laser drive current, and the change point calculating means for determining a characteristic changing point of the emission characteristics of the semiconductor laser,
Bias current calculation means for calculating a bias drive current to be added to the first laser drive current and the second laser drive current from the emitted light quantity with respect to the current at the characteristic change point and the target bias emitted light quantity. Exposure control device. In Claim 1, the said 1st control means controls the said 1st laser drive current so that the said 1st emitted light quantity may turn into the preset 1st emitted light quantity target value,
The second control means controls the second laser drive current so that the second light emission amount becomes a preset second light emission amount target value. 2. The exposure control apparatus according to claim 1, wherein the bias drive current value is set to a limit value at which the photosensitive member does not drop in potential. 3. The exposure control apparatus according to claim 1, wherein the first light emission amount is a weak exposure light emission amount, and the second light emission amount is a strong exposure light emission amount. 2. The first control unit according to claim 1, wherein the first laser driving current controls a light emission amount at an arbitrary point of a continuous light emission amount obtained by modulating the laser driving current in an analog manner or in multiple stages. ,
The exposure control apparatus, wherein the second control means controls a light emission amount at another point of the continuous light emission amount with the second laser driving current. A photoconductor for forming an image; a charger for charging the photoconductor; an exposure optical unit including an exposure controller for scanning and exposing the charged photoconductor with a semiconductor laser based on image data; and the scanning In a recording apparatus having a developing machine for developing an exposed image area, and a transfer unit for transferring the developed image to a recorded material,
The recording apparatus according to claim 1, wherein the exposure control apparatus is the exposure control apparatus according to claim 1.

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