JPH07131650A - Image forming device - Google Patents

Abstract

PURPOSE:To form high-gradation images by changing a correction amount to be applied to read image information corresponding to time from the fixing of a gradation test pattern to reading. CONSTITUTION:The gradation test patterns in all the colors are outputted according to the gradation test patterns registered on a test pattern storage area 211, at the same time, a timer 213 is started, and the elapse of time until the outputted gradation test pattern is next read from an original reading part 202 is measured. Then, a correction coefficient is multiplied corresponding to the lapse of time set to a correction coefficient table 214, and the read image density is corrected. Based on this corrected image density, a gamma-LUT 25 is set.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus.

[0002]

2. Description of the Related Art Conventionally, the following method has been known as a method for adjusting the image processing characteristics of an image forming apparatus such as a copying machine or a printer. That is, the image forming apparatus is activated to form one specific gradation test pattern on the recording material, and then the density of the gradation test pattern formed on the recording material is read by the image reading means, A method has been known in which, on the basis of image information, feedback is made to a means for determining an image forming condition such as a γ correction means. By this method, it was possible to stabilize the image quality according to the characteristic variation due to durability and the environmental condition variation.

[0003]

However, it is known that in conventional copying machines, printers, etc., the density of the output sample just after the fixing step is unstable. For example, immediately after thermal fixing, the temperature of the output toner image greatly changes, and the physical properties of the toner of the output sample also change, and the surface condition may change as the room temperature rises.

Further, it is well known that the surface of the roller is usually coated with silicone oil in order to improve the releasability so that the toner image does not adhere to the fixing roller. Immediately after fixing, the toner remains on the surface of the support and the toner layer, but is adsorbed on the support with the passage of time. This results in
The optical density was changed by causing phenomena such as gloss reduction and density reduction.

Further, in the case of the ink jet system, it is known that the optical density of the image also changes because the ink hit on the recording material gradually dries. As described above, even though the optical density of the gradation test pattern is changed, the optimum image is fed back to the means for determining the image forming condition such as the γ correction means based on the information. There was a drawback that it would not be obtained.

[0006]

SUMMARY OF THE INVENTION The present invention is intended to solve the above-mentioned problems, and as one means for solving the above-mentioned problems, the following structure is provided. That is, pattern forming means for forming a specific gradation test pattern, reading means for reading the gradation test pattern formed by the pattern forming means, and reading means for reading the gradation test pattern after the gradation test pattern is formed. A time measuring unit that measures the time until the gradation test pattern is read, a density correcting unit that corrects the density according to a correction coefficient according to the time measured by the time measuring unit, and the read unit that reads the density. Storage means for storing the position of the gradation test pattern and the density data density-corrected by the density correction means; and gradation correction means for gradation correction using the density data of each gradation level stored by the storage means. Have.

Further, an environment monitor means for monitoring an operating environment is provided, the density correction means sets a correction coefficient in accordance with the environment information detected by the environment monitor means, and the environment monitor means sets temperature and humidity, Alternatively, the type of recording material is detected. Further, the density correction means is provided with a correction coefficient table, and a correction coefficient is obtained from the correction coefficient table, and a fixing control means for controlling a fixing condition is provided, and the correction coefficient table is provided in the fixing condition control means. The correction coefficient is set according to the fixing condition controlled by the fixing condition control means, and the fixing condition control means controls the fixing temperature, the oil application amount, and the fixing speed.

[0008]

With the above configuration, the amount of correction given to the information during image formation is changed according to the time from the formation of the gradation test pattern to the reading of the gradation test pattern to form an image with excellent gradation. There is an effect that can be done. In addition, by performing gradation correction with the gradation test pattern described above regularly, the gradation is excellent over a long period of time.
An image with excellent color balance can be formed.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment according to the present invention will be described in detail below with reference to the drawings. <First Embodiment> FIG. 1 is a block diagram showing the schematic arrangement of a color copying machine according to this embodiment. In FIG. 1, reference numeral 201 denotes a printer control unit for controlling the entire copying machine, which includes a CPU 28 such as a microprocessor, a ROM 210 for storing a control program for the CPU 28 and various data, and a CPU 2.
The RAM 212 and the like used as work areas of 8 are provided. The ROM 210 includes a test pattern area 211 that stores a gradation test pattern described later.

Reference numeral 202 denotes a document reading unit, which includes a CCD 21 and the like, which will be described later, reads a document image and outputs the read image signal to the printer control unit 201.
The printer control unit 201 corrects the image signal from the document reading unit 202 with a look-up table (γ-LUT) 25 for γ correction, which will be described later, and converts it into data that matches the output characteristics of the printer engine unit 100. It is output to the printer engine unit 100. Reference numeral 100 denotes a printer engine unit, which has a configuration as a laser beam printer shown in FIG. 2 in this embodiment.

Reference numeral 213 is a timer, and 214 is a correction coefficient table in this embodiment, the details of which will be described later. FIG. 2 is a sectional view showing a schematic configuration of the printer engine unit 100 shown in FIG. 1. Hereinafter, the printer engine unit 100 in this embodiment will be described with reference to FIG.

The printer engine unit 100 of this embodiment shown in FIG. 1 forms an image on a recording sheet based on an image signal from the document reading unit 202. In FIG. 2, 201
Reference numerals 202 and 202 respectively denote the printer control unit and the document reading unit shown in FIG. The document reading unit 202 uses the light source 3
03, a color separation optical system 304, a CCD 21, and the like, and reads an image of the read original 301 placed on the original platen glass and converts it into a signal. Printer control unit 201
Converts the image signal read by the document reading unit 202 into a driving signal for the semiconductor laser 103 and outputs the driving signal to the laser driver 102.

The laser driver 102 is a semiconductor laser 10.
3 is a circuit for driving the semiconductor laser 3 and switches the semiconductor laser on / off in accordance with the input image signal. The laser light 104 is swung in the left-right direction by the rotary polygon mirror 105 and scans on the photosensitive drum 106. The photosensitive drum 106 on which the latent image is formed by the scanning of the laser light rotates in the direction of the arrow shown in the figure. By this rotation, development is performed for each color by the rotary developing device 112 (in FIG. 2, the development state with yellow toner is shown).

On the other hand, the recording paper is wound around the transfer drum 113 and developed by the rotary developing device 112 in order of Y (yellow), M (magenta), C (cyan) and Bk (black) every one rotation. After four rotations in total, four colors are transferred and color recording is completed. When the color transfer is completed in this way, the recording paper is separated from the transfer drum 113 and is fixed by the fixing roller pair 114 to complete the color image print.

A cut sheet is used as the recording paper, and the cassette recording paper is stored in a paper cassette mounted in the printer section 100, and is taken into the apparatus by the paper feed roller 109 and the conveyance rollers 110 and 111, and electrostatically charged. Drum 10
6 is supplied. An operation panel 300 is provided with various switches for operation, an LED display, and the like.

FIG. 3 shows the control unit 2 in the copying machine of this embodiment.
2 is a block diagram showing the configuration of an image signal processing unit provided in No. 01 for obtaining a gradation image. FIG. The configuration of the image signal processing unit shown in FIG. 3 will be described below. Reading unit 2
The brightness signal of the original image read by the CCD 21 in 02 is input to the A / D converter 22 and converted into a digital brightness signal. This digital luminance signal is sent to the shading unit 23, and shading correction is performed for uneven light amount due to sensitivity variations of individual elements of the CCD 21. By performing the shading correction, the measurement reproducibility of the CCD 21 is improved. The luminance signal corrected by the shading unit 23 is further LOG-converted by the LOG conversion unit 24. Subsequently, the LOG-converted signal is sent to the gamma look-up table (γ-LUT) 25, and the γ-LUT2
5, the image signal is converted so that the original image density at the time of initial setting of the printer engine unit 100 and the output image density processed according to the γ characteristic match. γ
The LUT 25 is created by the CPU 28 for each printer by the process described later.

The image signal thus converted becomes a signal whose pulse width is modulated by the pulse width modulation circuit 26 and is input to the laser driver 102, and the semiconductor laser 10 shown in FIG.
3 is driving. A pattern generator 29 generates various tone test patterns described later. In the present embodiment, a gradation reproducing means is used by a pulse width conversion process in which pixels are lined up in the sub-scanning direction for all colors, and an electrostatic latent image having gradation characteristics due to a dot area change on the photosensitive drum 106 by scanning laser light. An image is formed, and a gradation image is obtained through processes such as development, transfer and fixing.

Next, FIG. 4 shows a 4-limit chart showing characteristics for reproducing the density of the original image. In FIG. 4, the quadrant I shows the characteristic of the reading unit 202 for converting the document density into the density signal, and the quadrant II shows the characteristic of the γ-LUT 25 for converting the density signal into the laser output signal. The third quadrant shows the characteristics of the printer that converts the laser output signal to the printer output density, and the fourth quadrant shows the relationship between the document density and the printer output density, that is, the characteristics shown in the fourth quadrant are 3 shows the overall gradation characteristics of the copying machine of the embodiment.

In this embodiment, in order to make the gradation characteristics linear as shown in the fourth quadrant of FIG. 4, the distortion of the recording characteristics of the printer section shown in the third quadrant is shown in the second quadrant. It is corrected by the γ-LUT 25. Since the image signal is processed as an 8-bit digital signal in this embodiment, the number of gradations is 256.

In the present embodiment, the above-mentioned γ-LUT2
5 is set by the calculation result described below, but γ-L
The setting of the UT 25 is intended to correspond to the change in density with the passage of time after the image data is output to the printer.
FIG. 5 shows a specific example of the change in density over time after image data is output to the printer. In FIG. 5, the horizontal axis represents the elapsed time after the image data is output to the printer, and the vertical axis represents the optical density of the output image.

The density of the image data stabilizes in about 3 hours after output to the printer, but the amount of change in density is large especially in the first 30 minutes. Below, γ by the CPU 28 described above
The setting of the LUT 25 will be described. FIG. 6 is a flowchart showing the process of setting the γ-LUT 25 by the CPU 28 in this embodiment. First, step S31
Then, the control switch for creating the γ-LUT is turned on from the operation panel 300.

Then, in step S32, the printer controller 2 is operated by the pattern generator 29 shown in FIG.
01 test pattern storage area 211 in ROM 210
The gradation test patterns of all colors are output in accordance with the gradation test pattern registered in, and the timer 213 in the main body shown in FIG. 1 is started. An example of this gradation test pattern for all colors is shown in FIG.

When outputting the gradation test patterns of all the colors, as shown in FIG. 3, the γ-LUT 25 must be output without being operated. Then in step S33,
For example, the original document on which the gradation test pattern shown in FIG. 7 is output in step S32 is placed on the original platen glass 302 as the reading original document 301 shown in FIG. 1, illuminated by the light source 303, and then passed through the color separation optical system 304. CC
At D21, it is converted into a reflected light amount signal. Then, the reflected light amount signal is LOG-converted by the LOG converter 24 shown in FIG.
The CPU 28 takes in the read density data.

Next, in step S34, step S
The timer 213 started at 32 measures the time from the output of the gradation test pattern to the reading of the gradation test pattern by the document reading unit 202,
The correction coefficient is obtained from the correction coefficient table 214 having the characteristics shown in FIG. 8 according to the time, and the correction coefficient is multiplied by the density of the gradation test pattern read by the document reading unit 202 to perform the correction.

Subsequently, the process proceeds to step S35, and step S
The laser output level at the time of reading the gradation test pattern at 33 and the density value of the gradation test pattern read at step S34 are made to correspond by the coordinates of each gradation test pattern, and the relationship between the laser output level and the read density is obtained. Is stored in the RAM 212. Then, the process proceeds to step S35, and the printer characteristics shown in the third quadrant of FIG. 4 are obtained from the relationship between the laser output level and the read density obtained in step S34. By exchanging the input / output relations of the printer characteristics with each other, the characteristics of the γ correction of the printer shown in the second quadrant are determined for each density,
Set the γ-LUT 25.

In step S35, γ-LUT2
Since there is only the number of gradation patterns of the gradation test pattern when obtaining 5, 5 is insufficient in the middle so that the laser output level can correspond to all levels from 0 to 255 of the density signal. The existing data must be set by performing interpolation. As described above, the setting of the γ-LUT 25 in the present embodiment is completed, and a message such as “ready for copying” that informs the user that the printer is ready for copying is displayed on the operation panel 300 and the copy standby is set. .

Γ-L set as described above
By using the UT 25 in the image signal processing unit shown in FIG. 3 to perform γ correction, the stable density after the printer output and the density of the original document have a linear relationship as shown in the fourth quadrant of FIG. Is maintained. In this embodiment, the correction coefficient of the correction coefficient table 214 is calculated so that the stable density is reflected as the density to be controlled after a sufficient time has passed after the output. However, if it is desired to compensate the density immediately after the output. The correction coefficient may be set as such.

In the present embodiment, the same correction coefficient is applied to the entire area of the density signal, but the coefficient may be changed for each density area if necessary. As described above, according to this embodiment,
By setting the γ-LUT 25 according to the time from when the gradation test pattern is fixed to when it is set on the platen and read, the stable density after printer output becomes linear with the density of the original image, Good gradation can be obtained. Further, by performing the above control regularly, it is possible to form an image having excellent gradation and excellent color balance for a long period of time.

<Second Embodiment> The second embodiment according to the present invention will be described below. As described in the first embodiment, the output image density changes immediately after fixing in the printer or the like. The degree of change in the density of the output image varies depending on the temperature and humidity of the outside air, which is a level that cannot be ignored by an output machine that requires particularly strict density gradation characteristics.

The second embodiment is intended to eliminate the distortion of the density change of the output image due to the temperature and humidity of the outside air. FIG. 9 is a block diagram showing a schematic configuration of the printer device in the second embodiment. The same components as those in the block diagram of FIG. 1 according to the first embodiment described above are designated by the same reference numerals and the description thereof will be omitted.

The difference from the first embodiment described above is that the printer control unit 201 is provided with an environment sensor 215.
This is the place where the temperature and humidity of the outside air are monitored. Next, FIG. 10 shows the relationship between the output image density, the elapsed time after output, and the outside air temperature as described above. According to the characteristics as shown in FIG. 10, as shown in FIG. 11, the relationship between the post-output elapsed time, the correction coefficient, and the outside air temperature is set in advance in the correction coefficient table 214. Here, correction coefficient data for outside air temperatures of, for example, 10 ° C., 20 ° C., and 30 ° C. is set in the correction coefficient table 214, and the temperatures in between are corrected by interpolation.

With the above-described structure, the environment sensor 21 can detect the image density read by the document reading unit 202.
Density correction is performed by multiplying the correction coefficient obtained from the correction coefficient table 214 according to the temperature sensed in 5 and the elapsed time from reading the image. Or later,
The γ-LUT 25 is recreated as in the first embodiment, but in the second embodiment, the temperature sensed by the environment sensor 215 is also included in the correction condition in the process of step S34 of the first embodiment shown in FIG. This is the difference from the first embodiment.

In the second embodiment, among the parameters that can be detected by the environment sensor, the temperature has been described, but the present embodiment is not limited to this and is also effective in the following cases. For example, when the molecular weight of silicone oil is small and the output image density changes due to its volatilization, the humidity greatly influences as a factor causing the density change. Therefore, it is preferable to adopt humidity as an environmental parameter. Also, depending on the type of recording material,
Of course, since the density change characteristics are different, it is possible to use the recording material type as an environmental parameter.

As described above, it is desirable to optimize the detection parameter depending on the material used in the image forming apparatus, such as oil, ink, or recording material. As explained above,
In the second embodiment, even when the output image density changes due to environmental factors such as the temperature and humidity of the outside air, the stable density after the printer output becomes linear with respect to the density of the original image, and a good level is obtained. Tonality comes to be acquired. Further, by performing the above control regularly, it is possible to form an image having excellent gradation and excellent color balance for a long period of time.

<Third Embodiment> The third embodiment of the present invention will be described below. In a printer or the like, the tendency of change in output image density varies depending on the fixing conditions. For example, the higher the fixing temperature, the larger the variation range of the output image density.

The degree of change in the density of the output image cannot be ignored in an output machine that requires particularly strict density gradation characteristics. The third embodiment is intended to remove the distortion due to the fixing condition of the density change of the output image. 12
FIG. 9 is a block diagram showing a schematic configuration of a printer device in a third embodiment. The same components as those in the block diagram of FIG. 1 according to the first embodiment described above are designated by the same reference numerals and the description thereof will be omitted.

The difference from the first embodiment described above is that the printer control unit 201 is provided with a fixing temperature controller 216. The fixing temperature controller 216 controls the fixing temperature, and the fixing unit 1201 incorporated in the printer engine unit 100 is driven so that the fixing temperature is preset to the RAM 212.

The fixing temperature set in the RAM 212 can be changed depending on the type of recording material. For example, when the recording material is a thin paper of 80 g / m ² , the fixing temperature of 160 ° C. is optimum, and when the recording material is a thick paper of 125 g / m ² , the fixing temperature of 180 ° C. is optimum. Next, FIG. 13 shows the relationship between the output image density, the elapsed time after output, the recording material type, and the fixing temperature as described above for the density signal 255 level.

As shown in FIG. 13, 125 g / m ²
In the case of thick paper having a thickness of 80 g / m ² , the image density is slightly lower immediately after output than in the case of a thin paper having a weight of 80 g / m ^{2, and} the amount of change in image density is large in the initial stage after output, for example, about 10 minutes. According to the characteristics as shown in FIG. 13, as shown in FIG. 14, the relationship between the post-output elapsed time, the correction coefficient, and the fixing temperature is set in advance in the correction coefficient table 214. Here, correction coefficient data with fixing temperatures of, for example, 160 ° C. and 180 ° C. is set in the correction coefficient table 214, and the temperatures in between are corrected by interpolation.

With the above-mentioned configuration, the image density read by the original reading unit 202 is previously stored in the RAM 2 by the fixing temperature controller 216 as in the first embodiment.
The density correction is performed by multiplying the fixing temperature set to 12 and the correction coefficient obtained from the correction coefficient table 214 in accordance with the elapsed time after the image is read.

Thereafter, as in the first embodiment, the γ-LUT 25 is used.
Recreate. In the third embodiment, the fixing temperature and the thickness of the recording material among the fixing conditions have been described. However, the present invention is not limited to this. For example, a change in the amount of silicone oil applied and the fixing roller may be used. Rotation speed of
Further, since the density change characteristics also change depending on the type of recording material and the like, it is possible to output an image with more excellent gradation by setting a correction coefficient suitable for the density change characteristics.

As described above, in the third embodiment, even when the output image density changes depending on the fixing conditions, the stable density after the printer output becomes linear with the density of the original image, and the good density is obtained. Tonality comes to be acquired. Further, by performing the above control regularly, it is possible to form an image having excellent gradation and excellent color balance for a long period of time.

Although the laser beam printer has been mainly described in the above first to third embodiments, the present invention is not limited to these examples and the present invention can be applied to, for example, an ink jet printer or a dot matrix printer. Is also applicable. The present invention may be applied to a system including a plurality of devices or an apparatus including one device. Further, it goes without saying that the present invention can be applied to the case where it is achieved by supplying a program to a system or an apparatus.

[0044]

As described above, according to the present invention, the gradation amount is changed by changing the correction amount at the time of image formation according to the time from the formation of the gradation test pattern to the reading thereof. There is an effect that an excellent image can be formed. Further, by periodically performing the gradation correction using the gradation test pattern described above, it is possible to form an image having excellent gradation and excellent color balance for a long period of time.

[Brief description of drawings]

FIG. 1 is a block diagram showing a schematic configuration of a first embodiment according to the present invention.

FIG. 2 is a device configuration diagram in the present embodiment.

FIG. 3 is a block diagram showing a detailed configuration of an image processing unit in the present embodiment.

FIG. 4 is a fourth limit chart showing the gradation reproduction characteristics in the present embodiment.

FIG. 5 is a diagram showing a relationship between an elapsed time after output of a gradation test pattern and an image density in the present embodiment.

FIG. 6 is a flowchart of a γ-LUT update process in this embodiment.

FIG. 7 is a diagram showing an output example of a gradation test pattern in the present embodiment.

FIG. 8 is a diagram showing the relationship between the elapsed time after output of the gradation test pattern and the correction coefficient in the present embodiment.

FIG. 9 is a block diagram showing a schematic configuration of a second embodiment according to the present invention.

FIG. 10: The outside air temperature in the second embodiment is 10 ° C., 20
It is a figure which shows the relationship between the elapsed time after gradation test pattern output at 30 degreeC and 30 degreeC, and a gradation test pattern image density.

FIG. 11 is an outside air temperature of 10 ° C. and 20 in the second embodiment.
It is a figure which shows the relationship between the elapsed time after the gradation test pattern output and correction coefficient at 30 degreeC and 30 degreeC.

FIG. 12 is a block diagram showing a schematic configuration of a third embodiment according to the present invention.

FIG. 13 is a fixing temperature of 160 ° C. and 1 in the third embodiment.
It is a figure which shows the relationship between the elapsed time after the gradation test pattern output at 80 degreeC, and the gradation test pattern image density.

FIG. 14 is a fixing temperature of 160 ° C. and 1 in the third embodiment.
It is a figure which shows the relationship between the elapsed time after the gradation test pattern output at 80 degreeC, and a correction coefficient.

[Explanation of symbols]

 21 CCD 25 γ-LUT 28 CPU 29 Pattern Generator 100 Printer Unit 102 Semiconductor Laser 106 Photosensitive Drum 113 Transfer Drum 114 Fixing Roller Pair 201 Printer Control Unit 202 Document Reading Unit 210 ROM 211 Test Pattern Area 212 RAM 213 Timer 214 Correction Coefficient Table 300 Operation panel 301 Original document to be read 302 Original platen glass 303 Light source 304 Color separation optical system

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Claims (8)

[Claims] 1. A pattern forming means for forming a specific gradation test pattern, a reading means for reading the gradation test pattern formed by the pattern forming means, and a step of forming the gradation test pattern after the formation of the gradation test pattern. A time measuring unit that measures the time until the reading of the gradation test pattern by the reading unit, a density correcting unit that corrects the density according to a correction coefficient corresponding to the time measured by the time measuring unit, and a reading unit that reads the density. Storage means for storing the position of the gradation test pattern and the density data density-corrected by the density correction means, and gradation for gradation correction using the density data of each gradation level stored by the storage means An image forming apparatus comprising: a correction unit. 2. The image according to claim 1, further comprising environment monitor means for monitoring an operating environment, wherein the density correction means sets a correction coefficient in accordance with environment information detected by the environment monitor means. Forming equipment. 3. The image forming apparatus according to claim 2, wherein the environment monitor means detects temperature. 4. The image forming apparatus according to claim 2, wherein the environment monitoring unit detects humidity. 5. The image forming apparatus according to claim 2, wherein the environment monitor unit detects the type of recording material. 6. The image forming apparatus according to claim 1, wherein the density correction unit includes a correction coefficient table, and the correction coefficient is obtained from the correction coefficient table. 7. A fixing control means for controlling a fixing condition is provided, and the correction coefficient table sets a correction coefficient according to a fixing condition controlled by the fixing condition control means. Image forming apparatus. 8. The image forming apparatus according to claim 7, wherein the fixing condition control unit controls a fixing temperature, an oil application amount, and a fixing speed.