JPH09272222A - Optical printer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical printer which corresponds to increase of operating speed and maintains stable picture quality even when environment is fluctuated by modulating intensity of exposure and puls width as the exposure condition and also generating a patch to regulate the operating condition of the printer by its density. SOLUTION: A look-up table(LUT) selection part 501 selects a proper LUT from LUTs 502 conforming to the respective environmental conditions stored in a ROM 302 on the basis of output sent from a patch sensor. The proper LUT is set in a RAM 303 and referred in a data conversion part 503. Then, the conversion part 503 inputs image data from a color changeover part and converts image data into intensity of exposure and the signal of pulse width by LUT set in the RAM 303. On one side, in a patch signal generation part 504, intensity of exposure and the signal of pulse width which are used in the case of producing a patch from the ROM 302 are read and outputted. A changeover part 505 changes over output sent from the data conversion part 503 and output sent from the generation part 504 by information whether a changeover part 505 is a normal image formation mode or a patch production mode.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a copying machine, a printer, a facsimile, and the like, which uses electrophotography to print paper or OH.
The present invention relates to an optical printer that forms an image on a recording material such as P, and more particularly to an optical printer that generates a patch under a predetermined condition, detects the density of the patch, and adjusts printer operating conditions such as an exposure condition, a developing bias, and a charging bias.

[0002]

2. Description of the Related Art In a conventional optical printer such as a laser beam printer or an LED printer, a pulse width or an exposure intensity is modulated to form a halftone image.
However, in the case of the type in which the pulse width is modulated, there is a problem that the pulse width modulation must be accelerated in order to increase the speed of the printer.
On the other hand, in the case of the type that modulates the exposure intensity, there is a problem that the density of the output image is easily affected by the environmental change of the printer.

On the other hand, in the apparatus disclosed in US Pat. No. 5,371,524, the pulse width is determined by the upper 2 bits of the 8-bit digital image data given to each pixel, and the exposure intensity is determined by the lower 6 bits. By determining, both the pulse width and the exposure intensity are modulated. By doing this, speedup is possible and it is less susceptible to environmental changes.

[0004]

However, by simply allocating the high-order bit and the low-order bit to the pulse width and the intensity, an improvement can be made as compared with the type in which only the exposure intensity is modulated, but the output image is also affected by environmental fluctuations. There was still the problem of fluctuations.

The present invention has been made in view of these problems, and an object thereof is to provide an image forming apparatus capable of coping with speeding up and maintaining stable image quality even when the environment changes. It is to be.

[0006]

In order to solve the above problems, an optical printer according to the present invention develops a latent image obtained by irradiating a photosensitive member with light and develops it with a toner, and transfers it onto a recording material. An optical printer that obtains an output image with a normal image forming mode for forming an image based on image data given from outside the printer and a patch generating mode for adjusting the operating conditions of the printer are provided for each pixel. In the normal image forming mode, the exposure means for irradiating the photoreceptor with light according to the exposure conditions, the density measuring means for measuring the density of the patch formed in the patch generation mode, and the result of the density measurement by the density measuring means The exposure means includes an exposure condition and a control means for modulating an exposure intensity and a pulse width.

Further, in the optical printer of the present invention, the control means exposes the pixel data according to the result of the density measurement by the exposure control means and the density measuring means for modulating the exposure light according to the signal representing the exposure intensity and the pulse width. Determining means for determining a rule for converting into a combination of intensity and pulse width, and converting means for converting pixel data into a combination of exposure intensity and pulse width and outputting a first signal representing the combination according to the rule determined by the determining means. And a signal generating means for generating a second signal representing an exposure light intensity and a pulse width for forming a patch, a switching means for sending a first signal to the exposure control means in the normal image forming mode and a second signal in the patch generating mode. , And.

Further, in the optical printer of the present invention, the combination of the exposure intensity and the pulse width represented by the first signal when the image having the same density as that of the patch is output is the combination of the exposure intensity and the pulse width represented by the second signal. It is characterized by being different from.

In the optical printer of the present invention, when the image having the same density as that of the patch is output, the first image by the combination of the exposure intensity and the pulse width represented by the first signal and the exposure intensity represented by the second signal, The second image by the combination of the pulse widths, and the density fluctuation amounts ΔD1 and ΔD2 with respect to the predetermined temperature and humidity fluctuations of the respective images have a relationship of ΔD1 <ΔD2.

Further, the optical printer of the present invention is characterized in that at least one of the first signals corresponding to various pixel data has the same exposure intensity as the second signal and only a short pulse width.

Further, the optical printer of the present invention is characterized in that at least one of the first signals corresponding to various pixel data has the same pulse width as the second signal and only the exposure intensity is high.

Further, in the optical printer of the present invention, the converting means converts the pixel data into a combination of the exposure intensity, the pulse width and the pulse density according to the rule determined by the determining means, and the first converting according to the pulse density. At a frequency of, a conversion unit that outputs a first signal that represents the exposure intensity and the pulse width, and a second signal that represents the exposure intensity and the pulse width for forming a patch, and a second frequency that corresponds to a predetermined pulse density. And the first signal in the normal image forming mode,
The patch generation mode includes a switching unit that sends the second signal to the exposure unit, and the pulse density corresponding to the first frequency when outputting an image having the same density as the patch corresponds to the second frequency. It is characterized by being lower than the pulse density.

Further, the optical printer of the present invention comprises the second
The pulse density corresponding to the frequency of 1 is the same as the maximum density of the pulse density corresponding to the first frequency output from the converting means.

[0014]

FIG. 16A shows the output density when an image is formed while the intensity of the laser light is fixed and the pulse width is fixed.
/ 8 pixel, 2/8 pixel, ..., 8/8 (1) pixel width. As you can see from the figure, for example, density 0.8
Even if the pulse width is 8/8 and the intensity is 25%, the pulse width is 7/8 and the intensity is 32% and 6/8.
The same density of 0.8 can be output even with a combination of 48% for 5% and 82% for 5/8.

FIG. 16 (b) is a graph similar to FIG. 16 (a), but with the pulse width e of 5/8 and the pulse width h of 8/8, the output densities at the same time when the environment in which the device is placed are different are simultaneously measured. It is shown. In the combination of the pulse width of 5/8 and the intensity of 82%, which can output the density of 0.8, the output density changes by ΔDe = 0.03 when the environment changes from low temperature / low humidity to high temperature / high humidity. On the other hand, in the combination of the pulse width of 8/8 and the intensity of 25%, which was able to output the same density 0.8 as before, the density change becomes ΔDh = 0.3 when the temperature changes from low temperature / low humidity to high temperature / high humidity. In this way, the environmental fluctuation amount changes depending on the combination of the laser intensity and the pulse width.

The present invention takes advantage of this relationship, and provides a patch for adjusting printer operating conditions with a combination of intensity and pulse width with which environmental fluctuation becomes large (for example, the above-mentioned pulse width 8/8 and intensity 25).
% Combination) to improve the detection accuracy.
Further, by setting the image forming condition based on the detection result, it is possible to appropriately cope with a slight environmental change.
Furthermore, in actual image formation, by using a combination with a small environmental fluctuation (for example, the combination of the above-mentioned pulse width of 5/8 and intensity of 82%), environmental stability, especially in one screen where patch generation is not possible on the way It is possible to enhance the stability of concentration against environmental changes.

[0017]

1 is a main sectional view of an optical printer according to the present invention. Such an optical printer is roughly divided into an electrophotographic process unit 100 and an image processing unit 200 (described in FIG. 2) described later. The configuration of the electrophotographic process unit 100 and its image forming operation will be described with reference to FIG. The charging roller 102 charges the photoconductor 101 to a uniform certain potential (for example, -700 V). Exposure means 10
600 dpi (dot per) formed by
The laser beam having the resolution of (inch) is guided onto the photoreceptor 101 by the return mirror 104 to form an electrostatic latent image. Next, among the one-component contact type developing devices 105 that can be contacted and separated in the direction of the arrow in the figure, the yellow developing device 105Y is brought into contact with the other developing devices and the other developing devices are separated from each other. The toner is reversely developed and visualized on the photoconductor 101. The visualized yellow toner is dispersed on carbon in ETFE (ethylene tetrafluoroethylene copolymer) and is transferred to the primary transfer roller 107 on the intermediate transfer body 106 adjusted to have an appropriate resistance.
A bias having a polarity opposite to that of the toner is applied by the next transfer power source 108, and the toner is transferred by the action of the electric field. The transfer residual toner on the photoreceptor 101 is collected by a photoreceptor cleaner 109 which cleans the photoreceptor by bringing the blade into contact therewith, and then the photoreceptor potential is reset by a discharging lamp 110. By repeating the same operation for the magenta developing unit 105M, the cyan developing unit 105C, and the black developing unit 105K while synchronizing the position of the intermediate transfer member 106 and the light emission timing of the exposure unit 103, the toner of each color is formed on the intermediate transfer member 106. Are overlaid to form a full-color image. During this time,
Secondary transfer roller 116 and intermediate transfer body cleaner 11
Reference numeral 9 denotes a separated state. On the other hand, the recording material 113 such as paper or OHP is conveyed from the paper feeding cassette 112 to the registration roller pair 114 by the paper feeding means 111, and then is synchronized with the driving roller 115 in synchronization with the full color image on the intermediate transfer body 106. Secondary transfer roller 11 that can be moved toward and away from the direction of the middle arrow
It is conveyed to the secondary transfer portion formed at 6. In the secondary transfer portion, in synchronization with the recording material 113, the secondary transfer roller 116 contacts the intermediate transfer member 106 to form and press the nip portion, and to calculate the voltage obtained from the primary transfer power supply 108. The voltage determined by 121 is the power supply for secondary transfer 1
The transfer material 11 is controlled by a constant voltage by the action of the electric field.
3, a full-color toner image is formed. Thereafter, the recording material 113 is fixed by the fixing unit 120 and discharged out of the apparatus.

The electrophotographic process section 100 is further provided with a patch sensor 122 at a position facing the surface of the intermediate transfer member 106 downstream of the primary transfer roller. The patch sensor 122 is a sensor in which an LED and a photo sensor are combined, and the read value is A / D converted and then the image processing unit 20.
Sent to 0.

Further, the optical printer of this embodiment has a normal image forming mode and a patch generating mode as operation modes. In the normal image forming mode, an image is formed and output based on data sent from a host such as a personal computer outside the printer. In the patch generation mode, an image is formed based on the data inside the printer, and the formed image is not output to the outside of the printer, and the density is measured by the patch sensor 122 inside the printer.

Next, the processing performed by the image processing section 200 will be described. FIG. 2 shows an image processing unit 2 for data sent from a host such as a computer outside the printer.
It is a block diagram which shows the process performed by 00. Host 201
The data sent from is the code that controls the printer,
There are character codes, vector data, and image data.
The transmitted data is interpreted by the code interpretation unit 202 as any type of data, and is converted into a bit map if necessary. Image data and bitmap-converted image data are stored in the memory 203 as 8-bit RGB information.
Stored in. The stored data is read out for each pixel in synchronization with the printing operation, and the color conversion processing unit 204 performs CMY.
The data is converted into K data, converted into 5-bit data for each color by the multi-value processing unit 205, the developing device is selected by the color switching unit 206, and only the image data of the color being printed is sent to the modulation processing unit 207. Then, the signal is converted into a signal indicating the exposure intensity and the pulse width and sent to the laser driver 208.

FIG. 3 is a block diagram showing the configuration of the modulation processing unit 207. The modulation processing unit 207 is a CPU 301, CP
ROM302, R that can exchange data with U301
It is composed of an AM 303 and a peripheral circuit (not shown) for driving them. To the CPU 301, the monochromatic image data selected by the color switching unit 206, the mode signal of the normal image forming mode or the patch generation mode, and the detection signal from the patch sensor 122 via the A / D converter 304 are input, An intensity signal and a pulse width signal are output. In the optical printer of this embodiment, the image data input to the CPU 301 is 5 bits for each color, the intensity data output is 8 bits, and the pulse width data is 4 bits.

FIG. 4 is a block diagram showing the configuration of the laser driver 208. The laser driver 208 includes a laser power control circuit 402 for controlling the intensity of the semiconductor laser 401, a sensor 403 for monitoring the output of the semiconductor laser 401, and circuit portions 404 to 410 for generating a pulse corresponding to a pulse width signal. It is configured. The code converter 404 inputs the 4-bit pulse width signal output from the modulation processing unit 207 as an address and outputs two 4-bit signals. Each signal is data indicating the timing to start and stop the pulse in one pixel period. The respective data are held in the latches 405 and 406 for one pixel period.
The counter 410 counts a clock signal having a cycle of 1/8 hour of one pixel. The count signal is the comparator 40
7 and 408, and when the start timing held in the latch 405 is reached, the comparator 407 outputs and sets the flip-flop 409. When the counter output reaches the stop timing, the flip-flop 409 is reset by the output of the comparator 408. In this way, the output of the flip-flop 409 becomes a pulse having a width corresponding to the pulse width signal and is input to the laser power control circuit 402. By setting the start timing and the stop timing according to the pulse width in this way, the dots formed by the exposure pulse are aligned with the center position of each pixel.

The laser power control circuit 402 is
The signal obtained by D / A converting the input intensity signal and adjusting the level is compared with the signal returned from the sensor 403 to generate a laser drive current having a level corresponding to the exposure intensity signal. Further, the laser power control circuit 402
Turns on / off its output by the pulse output from the flip-flop 409. In this way, the laser 401 is driven by the signal in which both the exposure intensity and the pulse width are modulated.

In this embodiment, the circuit portion for generating the pulse corresponding to the pulse width signal uses the synchronous digital circuit as described above, but of course the pulse width signal is D / A converted. A pulse having a predetermined width may be generated by comparing the obtained level with the level of the reference triangular wave. Also, the laser power control circuit used was a type that can be turned on and off by inputting a pulse signal, but the one that can only perform power control was used. May be connected by an AND circuit. In order to modulate the exposure intensity, the method of changing the driving current of the semiconductor laser is used here, but this method can also be applied to the case of exposing with an LED. In addition to this method, it is also possible to adopt a method of changing the characteristics by providing an optical element capable of changing the transmittance in the optical path.

FIG. 5 is a block diagram showing the arrangement of processing performed by the modulation processing unit 207. The modulation processing unit 207 includes a look-up table (LUT) selection unit 501, a data conversion unit 503, a patch signal generation unit 504, and a switching unit 50.
5, which are all realized by software processing executed on a circuit including the CPU 301, the ROM 302, and the RAM 303 shown in FIG.

Look-up table (LUT) selector 5
01 indicates R based on the output from the patch sensor 122.
L that meets each environmental condition stored in OM302
An appropriate LUT is selected from the UT 502 and set in the RAM 303 referred to by the data conversion unit 503. The data conversion unit 503 inputs the image data from the color switching unit 206 and converts it into an exposure intensity and pulse width signal by the LUT set in the RAM 303. Patch signal generator 504
Then, the exposure intensity and pulse width data used when generating the patch is read from the ROM 302 and output. The switching unit 505 switches the output from the data conversion unit 503 and the output from the patch signal generation unit 504 according to the information on the normal image forming mode or the patch generation mode.

Since the patch signal generator 504 of this embodiment stores the patch data in a memory area different from that of the image data, the data being received and the patch data do not coexist and the memory management is easy. . Further, since this memory area can be managed by a CPU different from the CPU that receives and expands the image data from the host, the processing is performed in parallel and the speed can be increased.

Next, a method of switching to the patch generation mode will be described with reference to FIG. When the optical printer of this embodiment receives data from the host computer, the code analysis unit 202 analyzes the content and continues processing as it is in the case of character code or vector data, and patches it in the case of image data. Move to generation mode. In the case of image data, the amount of data is generally large and it takes time to communicate the data. Therefore, there is a certain amount of time from the start of receiving the data to the actual start of printing. By generating the patch during this period, the printer operating condition can be adjusted without increasing the time until the image is output. Further, since the target of image data is a natural image in many cases, reproduction of a halftone density portion is more important in terms of image quality than a line drawing such as a graph described by vector data. In the optical printer of this embodiment, the adjustment processing of the printer operating conditions is performed before the output of the image data, so that the halftone reproduction can be stabilized.

The patch generation mode is performed in three steps: a step of forming a patch on the intermediate transfer member 106, a step of reading the density of the patch, and a step of determining the LUT. The step of generating the patch is basically the same as the normal printing operation except that the image is not transferred to the transfer material. In order to stabilize the halftone level, which is important for tone reproduction, the patches form gradation patch groups of each color including low-density patches. In the optical printer of this embodiment, pulse widths are shown in Table 1 in order to generate patches corresponding to output densities of 0.15, 0.6, and 1.2 (referred to as A patch, B patch, and C patch, respectively). To generate a patch. When outputting the actual image,
To obtain these output densities, the combination used to generate this patch is not used, as described below.

[0030]

[Table 1]

For patch generation, for each color of YMCK, the modulation processing unit 207 reads out the data corresponding to the exposure conditions of Table 1 from the ROM 302 and sends it to the laser driver 208 via the switching unit 505, and the YMCK patches are transferred one after another. Formed on body 106. However, even if the four-color patches are formed, the sheet feeding unit 111 is not driven and the secondary transfer to the transfer material is not performed.

When four color gradation patches are formed on the intermediate transfer member 106, the process advances to the patch reading step. The intermediate transfer member 106 to which the K-color patch of the fourth color has been transferred at the primary transfer portion is sent as it is, and the patch sensor 122
To the opposite part of. The patch of each color is read by the patch sensor 122 in which the LED and the photo sensor are combined by sending the intermediate transfer member. The read value is A / D converted by the A / D converter 304, and the CPU of the image processing unit 200
Sent to 301.

After being read by the sensor 122, most of the patches on the intermediate transfer member 106 are reversely transferred to the photosensitive member 101 by applying a bias to the primary transfer roller 107 different from that at the time of transfer, and the rest is left. The cleaner 119 removes the intermediate transfer member 106.

The final step is to determine the LUT according to the patch value sent by the LUT selection unit 501. The LUT 502 described above, which associates the input image data with the parameter of the laser light modulation by the value, is selected.
Tables 2-4 show the selection method, concentration and LU to choose
It is a table showing correspondence of T. Table 2 is for A patch, Table 3 is for B
For patches, Table 4 is a correspondence table for C patches.

[0035]

[Table 2]

[0036]

[Table 3]

[0037]

[Table 4]

FIG. 12 shows the procedure of LUT selection. First, the density measurement result of the yellow (Y) A patch is compared with the index in Table 2 to find the closest index (S1). Then, the LUT number corresponding to the index is read from the table (S2). This is repeated for the B and C patches, and three LUT numbers are obtained from each of the A, B and C patches (S3). Next, these three LUT numbers are averaged, and the LUT having a number closest to the average value is selected as the Y LUT (S
4). Repeat the steps from S1 to S4 for the remaining colors (MCK)
Is repeated, and the LUT for each color is selected. The selected LUT is prepared for each color and stored in the ROM 302. The reason why the LUT is prepared for each color is that the output characteristics of the density with respect to the exposure condition are different for each color.

As described above, an appropriate LUT is selected and the patch generation mode is exited.

Next, the LUT 502 that determines the exposure condition will be described. The LUT is used by the data conversion unit 503 and outputs data corresponding to the exposure intensity and the pulse width with respect to the target image density represented by the image data. FIG. 7 is a graph showing the contents of the LUT 502 of this embodiment, in which the horizontal axis represents the image density that is the input of the LUT and the vertical axis represents the exposure intensity. This graph plots the exposure intensities in the combination of the exposure intensities and the pulse widths associated with each other by the LUT with respect to the image density represented by the input image data, and connects the lines having the same pulse width with a line. The solid line in the figure is the part of the combination that is actually set in the LUT,
The broken line portion is a portion that is not set in the LUT. For example, when an output target density of 1.0 is input, a combination of a pulse width of 7/8 and an intensity of 60% is set for the LUT, and a combination of 8/8 and 32% is set. Absent. In this LUT, when the output target density rises from the minimum density, the initial pulse width is 1/8 and the intensity is 62%.
The intensity starts to increase from 1/8 with the pulse width being 1/8, and when the intensity reaches 100% at the target concentration of 0.18, the pulse width is 2/8 intensity 57% for the next concentration of 0.184.
And the strength is increased again. In this way, the combination of the pulse width and the intensity is set as shown by the solid line in the figure for each density up to the maximum density of 1.46.

On the other hand, the exposure intensities and pulse widths for generating patches output from the patch signal generator shown in Table 1 are also plotted in the same manner as Pp1 to Pp in the figure.
p3.

As described above, the patch forms a density range output in the normal image forming mode, that is, a density range between 0.13 and 1.46. That is, an image having the same density as the patch is output in the normal image forming mode. However, the combination of the exposure intensity and the pulse width for outputting the same density is different between the patch generation and the normal image generation. Further, the graph of exposure intensity during image formation is above the graph during patch formation. That is, the exposure intensity when forming an image with the same density as the patch is higher than the exposure intensity used when generating the patch.

In FIG. 8, the horizontal axis is the same as that in FIG. 7, but the pulse width is plotted on the vertical axis. The graph of the pulse width during image formation is below the graph of the pulse width during patch generation represented by Pp1 to Pp3. That is, the pulse width when forming an image with the same density as the patch is narrower than the pulse width used when generating the patch.

L that can be switched as a result of patch density measurement
The UTs are, of course, different from each other, and if the same graphs as those in FIGS. 7 and 8 are drawn, the UTs may be slightly moved up and down, but the upper and lower relationships with the graphs at the time of patch formation are not interchanged.

FIG. 9 is a plot of combinations of exposure intensity and pulse width designated by the LUT 502.
The combination indicated by the solid line is usually used for image formation. On the other hand, the combination used for patch generation is the point Pp1 in the figure.
~ Pp3. As can be seen from this figure, the pulse width is 8/8 among the combinations normally used for image formation.
Although the pulse width is the same as that of the combination used for patch generation, the exposure intensity is 50% or more, and the exposure intensity is stronger than the combination of 41% or less used for patch generation. Among the combinations used for normal image formation, the exposure widths of 16%, 28%, and 41% have a pulse width of 1%.
/ 8, the pulse width used for patch generation is 8/8 and the exposure intensity is 16%, 28%, 41.
The exposure intensity is the same, but the pulse width is shorter than the one with%.

As described above, in the optical printer of this embodiment, when the same density as that of the patch is output at the time of image formation, the pulse width is narrower and stronger than that at the patch generation. With this configuration, when the patch is generated, the density greatly changes due to the environmental change, and the accuracy of detecting the environmental change by the patch density measurement is improved. Further, since the density fluctuation due to the environmental fluctuation is small during the image formation, the density fluctuation of the output image can be suppressed even if the environmental fluctuation occurs after the correction of the image forming condition by the patch density.

The reason for this will be described with reference to FIG. FIG.
0 (a) is a diagram showing the surface potential of the photoconductor after exposure with laser light having high intensity and short pulse width and light having low intensity and long pulse width, and FIG. 10 (b) is output density versus surface potential. It is a figure which shows the relationship ((gamma) characteristic) of. FIG. 10 (a)
As shown in, the potential distribution differs between the latent image formed by the laser light with high intensity and short pulse width and the one by light with low intensity and long pulse width. In the latent image with a narrow pulse width shown on the right side in FIG. 10A, the output density is saturated at the surface potential V2 at the pulse central portion as shown in FIG. 10B. When the environment fluctuates, the developing characteristics fluctuate as shown by the arrow in FIG. 10B, but at the potential V2 of the latent image with a narrow pulse width and high intensity, even if the environment fluctuates, the output density enters a saturated portion. Therefore, there is little environmental change. On the other hand, the potential V1 of the latent image with a wide pulse width and weak intensity is in the transient region of the γ characteristic.
Due to environmental changes, the concentration changes greatly from point A to point B in the figure. For this reason, the density variation amount due to the environment is different between the patch formation and the image formation.

As a method of creating an LUT in consideration of such environmental changes, a method of more directly measuring and creating environmental change characteristics can be used. The following embodiment is an example of an optical printer using the LUT thus created. The stability to the environment means how much the image density changes when the environment changes. Therefore, when the image density D is viewed as a function of the temperature T and the humidity H, dD =
It can be evaluated by the magnitude of (∂D / ∂T) dT + (∂D / ∂H) dH. The fact that the dD is large means that the density changes greatly when the environment changes. Therefore, this is referred to as the “environmental fluctuation degree”, and the exposure condition including the exposure intensity, the pulse width, and the pulse density is given. The environmental fluctuation degree can be calculated for each environment for each of the combinations.

In this example, the degree of environmental fluctuation was determined as follows. The exposure conditions include an exposure intensity of 0 to 255,
The pulse widths were used in combination from the range of 0-7. For each combination, change the temperature and humidity from 10 ℃ to 20% RH and the temperature to 5 ℃.
Image formation is performed in an environment in which the pitch and humidity are changed in steps of 20% RH up to 35 ° C. and 80% RH. The formed image density is read by a patch density sensor in the printer to obtain a density value, and the output image density is also measured separately. The degree of environmental variability of each combination with respect to each temperature / humidity environment is determined by adding the density differences between the output densities in the environment deviated by 5 ° C. and the environment deviated by 20% RH from the temperature / humidity environment.

FIG. 11 (a) was obtained in this way,
It is the figure which showed the relationship between the output density in a standard environment (20 degreeC60% RH), and the environmental variation degree for every combination of exposure intensity and pulse width, (b) is the same conditions as (a) but instead of output density. Is the density read by the patch sensor. The line group has the same pulse width but different intensities. Similar diagrams can be created for other environments.
The density of the patch sensor in (b) is higher than the output density in (a) because the patch is formed on the intermediate transfer member having a relatively low reflectance. Of course, if the characteristics of the patch sensor are adjusted or the reflectance of the intermediate transfer member is adjusted, the densities of (a) and (b) can be made substantially equal, but such adjustment was not performed here. Well, LUT
When creating, an exposure condition is selected by using this figure (a) so that the environmental fluctuation degree is the smallest among the combinations that can output the same density, and the LUT for that environment is created.
The portion indicated by the solid line in (a) is the portion registered in the actual LUT. On the other hand, for patch generation, the exposure condition is selected using (b) so that the environmental fluctuation degree is maximized. In this example, the exposure conditions were selected such as the combination of points d1 to d9 plotted in (b). The output densities under these exposure conditions correspond to e1 to e9 in (a). By doing so, the sum of the output density differences due to the environmental fluctuations of 5 ° C. and 20% RH is larger in the combination used in the patch generation mode than in the combination used in the normal image forming mode.

As the predetermined temperature and humidity fluctuation, the temperature is 5
A change in temperature and humidity of 20% RH was adopted, but the ratio of the amount of change in temperature and humidity is constant when the partial pressure of water vapor is constant with reference to the environmental change tendency in an office where a printer is usually used. It is also possible to determine the amount of change in humidity corresponding to the temperature under the condition. To make this easier, as a different environment, a high temperature and high humidity environment of 30 ° C 85% RH, 20 ° C
A standard environment of 50% RH and a low temperature and low humidity environment of 10 ° C. and 15% RH can also be used.

Although the values read by the patch sensor are used to obtain the combination for patch generation, the same result can be obtained by obtaining the combination using the output density.
However, if the value of the patch sensor is used, it is convenient to simultaneously obtain information used for the determination unit which LUT should be selected from the result of the patch measurement.

Now, in an optical printer, especially in a color optical printer, it is important to reproduce halftone as described above. Even in the optical printer described so far, a 5-bit (32-step) halftone can be expressed by combining intensity modulation and 4-bit (9-step) pulse width modulation. However, by increasing the pixel size, pulse-width modulation can be performed. The number can be increased to improve the reproduction of halftones. For example,
Up to now, there were 8 divisions per 600 dpi, so if the pixel has a width of three 600 dpi pixels,
The pulse width can be divided into 8 × 3 = 24 per pixel, and 25 steps of pulse width modulation can be performed. Hereinafter, an example of such an optical printer will be described.

In this embodiment, L used in the laser driver 208 and the modulation processing unit 207 in the image processing unit 200.
The configuration of the UT 502 is different from that of the previous embodiment. In addition,
The electrophotographic process section is the same as that in the above-mentioned embodiment, and therefore its explanation is omitted.

FIG. 13 is a block diagram showing the arrangement of the modulation processing section 207 of this embodiment. In this embodiment, the CPU 130
From 1 to the intensity signal and the pulse width signal, a 2-bit pulse density signal is output.

FIG. 14 shows a laser driver 208 of this embodiment.
FIG. 3 is a block diagram showing the configuration of FIG. Code converter 1404
Is supplied with a pulse width signal and a pulse density signal, and data indicating a pulse start timing, a stop timing and a pixel cycle is output. These timing data are held in the latches 1405, 1406, 1407, respectively. The counter 1411 is 1 for 1 pixel of 600 dpi.
A clock signal having a cycle of / 8 hours is counted, and the count signal is output to the comparators 1408, 1409 and 1410. When the count of the counter 1411 reaches the pulse start timing held in the latch 1405, the comparator 1408 outputs and sets the flip-flop 1412. When the count reaches the pulse stop timing of the latch 1406, the flip-flop 1412 is reset by the output of the comparator 1409. When the count reaches the pixel cycle timing of the latch 1407, the comparator 1410 outputs the counter 1411 and the latch 1
405 to 1407 are reset. In this way, a signal whose intensity and pulse width are modulated can be output to the semiconductor laser at a frequency corresponding to the pulse density signal.

Table 5 shows a part of the LUT 502 of this embodiment. The intensity, pulse width, and pulse density are set for the image data input to the data conversion unit 503. The data conversion unit 503 converts the image data according to this table.

[0058]

[Table 5]

The patch signal generator 504 has an intensity of 25%, a pulse width of 7/8 and a pulse density of 600 pulses / inch (pp
Generate the patch generation signal of i). This combination is a LUT
However, if the image is formed by this combination, the output density will be 0.6. When outputting an image with an output density of 0.6 in the normal image forming mode, the pulse density is 200 pulses / inch, and the pulse density of the patch is higher than the pulse density used for image formation. Further, the pulse density used for this patch generation is the highest density of the pulse density used for image formation.

FIG. 15 is a diagram similar to FIG. 10 showing the surface potential and γ characteristic of the latent image. When the pulse density is high, the electric potential V3 of the blank portion is located in the transient region of the development γ characteristic, and is susceptible to environmental changes. In this way, the environmental variability of the patch is made larger than the environmental variability of the normal image having the same density. In the above-described embodiment, the potential of the central portion of the latent image (see FIG.
Although the environmental fluctuation degree was increased by setting V2) of 0 to the transient region of the γ characteristic, the method of the present embodiment sets the potential of the blank portion to the transient region.

Further, the higher the pulse density, the larger the absolute value of V3 (moving downward in the figure (a)), and the greater the degree of environmental fluctuation. Therefore, it is better to generate the patch at the maximum pulse density of the printer.

Although it has been described that the density is detected, the brightness and the brightness may be detected. When using the luminance, there is an effect that the step of logarithmically converting the received light amount is unnecessary. When the lightness is used, the lightness corresponds to the human visual characteristics, and therefore, the effect of the error at the time of selecting the LUT can be visually minimized.

[0063]

According to the optical printer of claims 1 and 2, the exposure intensity and the pulse width are modulated as the exposure condition, and the operating condition of the printer is adjusted according to the density measurement result of the patch. Even if fluctuates, fluctuations in image quality can be suppressed.

Further, according to the optical printers of the third to eighth aspects, the density variation amount with respect to the environment differs depending on the exposure condition when the patch is generated and the exposure condition when the normal image is formed. The accuracy of concentration measurement is increased,
It is possible to detect and correct a slight environmental change, and further suppress the density change during normal image formation.

[Brief description of drawings]

FIG. 1 is a main sectional view of an optical printer according to the present invention.

FIG. 2 is a block diagram showing processing performed by an image processing unit 200 on data sent from a host such as a computer outside the printer.

FIG. 3 is a block diagram showing a configuration of a modulation processing unit 207.

FIG. 4 is a block diagram showing the configuration of a laser driver 208.

FIG. 5 is a block diagram showing a configuration of processing performed by a modulation processing unit 207.

FIG. 6 is a flowchart showing a method of switching to a patch generation mode.

FIG. 7 is a graph showing the contents of the LUT 502 of the embodiment.

FIG. 8 is a graph showing the contents of the LUT 502 of the embodiment.

FIG. 9 is a graph in which a combination of exposure intensity and pulse width designated by the LUT 502 is plotted.

FIG. 10 is a graph showing a surface potential of a photoconductor after exposure by a laser beam having a high intensity and a short pulse width, and a light having a low intensity and a long pulse width, and a relationship (γ characteristic) between an output density and a surface potential.

FIG. 11 is a graph showing the relationship between output density and environmental fluctuation degree for each combination of exposure intensity and pulse width.

FIG. 12 is a flowchart showing the procedure of LUT selection.

FIG. 13 is a block diagram showing a configuration of a modulation processing unit 207 according to an embodiment.

FIG. 14 is a block diagram showing the configuration of a laser driver 208 according to an embodiment.

FIG. 15 is a graph showing the surface potential and γ characteristic of a latent image.

FIG. 16 is a graph showing output density with respect to pulse width and intensity.

[Explanation of symbols]

100 Electrophotographic Process Unit 101 Photosensitive Member 102 Charging Roller 103 Exposure Means 104 Folding Mirror 105Y Yellow Developer 105M Magenta Developer 105C Cyan Developer 105K Black Developer 106 Intermediate Transfer Body 107 Primary Transfer Roller 108 Primary Transfer Power Supply 109 Photosensitive Body cleaner 110 Static elimination lamp 111 Paper feeding means 112 Paper feeding cassette 113 Transfer material 114 Registration roller pair 115 Driving roller 116 Secondary transfer roller 117 Secondary transfer power supply 118 Tension roller 119 Intermediate transfer body cleaner 120 Fixing means 121 Computing means 122 Patch Sensor 200 Image processing unit 201 Host 202 Code interpretation unit 203 Memory 204 Color conversion unit 205 Multi-value processing unit 206 Color switching unit 207 Modulation processing unit 208 Laser driver BA 301, 1301 CPU 302, 1302 ROM 303, 1303 RAM 304 A / D converter 401 Semiconductor laser 402 Laser power control circuit 403 Sensor 404 Code converter 405, 406, 1405, 1406, 1407 Latch, 407, 408, 1408, 1409, 1410 comparators 409, 1412 flip-flops 410, 1411 counters 501 LUT selection section 502 LUT 503 data conversion section 504 patch signal generation section 505 switching section

Claims (8)

[Claims] 1. An optical printer which obtains an output image by developing a latent image obtained by irradiating a photoreceptor with light and transferring the latent image onto a recording material, based on image data provided from the outside of the printer. Has a normal image forming mode for forming an image by means of a patch and a patch generation mode for adjusting the operating conditions of the printer, and an exposure means for irradiating the photoconductor with light according to the exposure condition given for each pixel, and a patch generation Density measuring means for measuring the density of the patch formed in the mode, and control means for modulating the exposure intensity and the pulse width as the exposure condition of the exposing means in the normal image forming mode based on the result of the density measurement by the density measuring means. An optical printer having: 2. The exposure control means for modulating the exposure light according to a signal representing the exposure intensity and the pulse width,
A determination unit that determines a rule for converting pixel data into a combination of exposure intensity and a pulse width based on the result of the density measurement by the density measurement unit, and a combination of the pixel intensity of the exposure intensity and the pulse width according to the rule determined by the determination unit. First converted to and representing it
A converting means for outputting a signal; a signal generating means for generating a second signal representing an exposure light intensity and a pulse width for forming a patch; a first signal in the normal image forming mode; and a second signal in the patch generating mode 2. The optical printer according to claim 1, further comprising switching means for sending to the control means. 3. A combination of the exposure intensity and the pulse width represented by the first signal when outputting an image having the same density as that of the patch,
3. The optical printer according to claim 2, wherein the combination of the exposure intensity and the pulse width represented by the second signal is different. 4. A first image based on a combination of exposure intensity and pulse width represented by a first signal when outputting an image having the same density as a patch, and a second image based on a combination of exposure intensity and pulse width represented by a second signal. Images, and the density fluctuation amounts ΔD1 and ΔD2 with respect to the predetermined temperature and humidity fluctuations of the respective images are ΔD1 <
4. The optical printer according to claim 3, wherein the relationship is ΔD2. 5. The optical printer according to claim 3, wherein at least one of the first signals corresponding to various pixel data has the same exposure intensity as the second signal and only a short pulse width. 6. The optical printer according to claim 3, wherein at least one of the first signals corresponding to various pixel data has the same pulse width as that of the second signal and only has high exposure intensity. 7. The converting means converts the pixel data into a combination of an exposure intensity, a pulse width and a pulse density according to the rule determined by the determining means, and outputs the exposure intensity at a first frequency according to the pulse density. Converting means for outputting a first signal representing the pulse width, and signal generating means for generating a second signal representing the exposure intensity and pulse width for forming the patch at a second frequency corresponding to a predetermined pulse density. , A switching means for sending the first signal to the exposure means in the normal image forming mode and a second signal in the patch generation mode, which corresponds to the first frequency when an image having the same density as the patch is output. 6. The optical printer according to claim 2, wherein the pulse density is lower than the pulse density corresponding to the second frequency. 8. The pulse density corresponding to the second frequency is the same as the maximum density of the pulse density corresponding to the first frequency output from the converting means. Optical printer.