JP3480065B2 - Image forming device - Google Patents

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 suitable for use in a copying machine.

[0002]

2. Description of the Related Art In an image forming apparatus such as a full-color copying machine, it is necessary to maintain the density characteristic of each primary color in order to ensure good color balance, and various techniques are known for this purpose. For example, JP-A-63-106672
In the technique disclosed in Japanese Patent Laid-Open No. 1-295281 and Japanese Patent Laid-Open No. 1-295281, a toner patch (toner image of a primary color having a predetermined target value density in an ideal state) is formed on each of the primary colors on the photoconductor or the transfer body. And the densities of these toner patches are measured by a density sensor. Then, the deviation between the measured density and the target value is obtained, and the value of the image forming condition such as the density characteristic in the image forming apparatus is set based on the result.

The timing at which the toner patch is formed and the image forming conditions are set may be when the power of the copying machine is turned on or during printing. In the latter case, a toner patch is automatically formed every time a predetermined number of sheets (for example, about several tens of sheets) are printed, and thereby the image forming conditions are reset.

[0004]

By the way, since the changes in temperature and humidity in the copying machine are relatively large for a while after the power supply of the copying machine is turned on, the fluctuation of the density is larger than that in the stable state. Is also big. Therefore, if the toner patch is formed and the image forming condition is reset within such a period, the variation amount of the image forming condition is inevitably large. However, if the image forming conditions are changed abruptly during printing, the density of the output image before and after the change is changed significantly, which causes a problem that the output image becomes unnatural. That is,
Even if the density after resetting is close to the target value, the user often does not want to suddenly change the density.

Further, the toner patch often has color unevenness, and the density measurement result inevitably has an error due to the characteristics of the toner density sensor. Therefore, if the image forming condition is immediately changed based on the density measurement result of the toner patch, there is a problem that the stability of the density characteristic is rather deteriorated. The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to provide an image forming apparatus capable of suppressing a rapid density change of an output image and obtaining a high-quality output image.

[0006]

In order to solve the above-mentioned problems, in the structure according to claim 1, the supplied image data
An image-based, and developing means for developing a test image having a predetermined reference density in an ideal state, the density of the test image was measured, and the concentration measuring means for outputting the result as a measurement concentration, more Each time the image data of is developed,
Step the range of the difference between the pre-assumed measured concentration and the reference concentration
From the divided steps, the reference concentration at the present time
And the difference between the measured concentration and
Revise up to one step change from the selected step
The measured concentration and the reference concentration
The range of difference was divided into stages and prepared in advance according to each stage
Image corresponding to the selected stage from the image forming conditions
Control means for using forming conditions for development by the developing means
It is characterized by having and .

Further, in the configuration according to claim 2,
In the ideal state, the first test image having the first reference density is developed when the power is turned on, and when the image data is supplied thereafter, an image based on the image data,
A developing device that develops a second test image having a second reference density in an ideal state, and a density that measures the densities of the first and second test images and outputs the result as the measured density. Measuring means and the power supply
Each step that divides the range of the difference between the measured concentration and the reference concentration
From among the first reference density and the first test image
Select the stage closest to the stage to which the difference from the measured concentration of
If the image data is supplied after that,
From the respective stages, the second reference concentration at the present time
And the difference between the measured density of the second test image and
The stage close to is changed from the currently selected stage by one stage.
Selection again with the limitation of
The range of the difference between the concentration and the reference concentration is divided into stages and
Selected from among the image forming conditions prepared in advance.
The image forming condition corresponding to the stage is developed by the developing means.
And a control means used for the above.

[0008]

In the structure of claim 1, the developing device is
The supplied image data and a test image having a predetermined reference density in an ideal state are developed. The density measuring means measures the density of the test image and outputs the result as the measured density. Further, the target value determining means determines a target value for any image forming condition value that determines the density of the test image such that the difference between the reference density and the measured density is small. Here, when a plurality of image data are developed, the control means gradually brings the value of the image forming condition closer to the target value along with this. As a result, the value of the image forming condition changes gently.

According to the second aspect of the invention, the developing device develops the first test image having the first reference density in the ideal state when the power is turned on. Next, the density of the first test image is measured by the density measuring means. Next, when the image data is supplied to the developing device, the developing device develops the image data and the second test image having the second reference density in the ideal state. Then this second
The density of the test image is measured by the density measuring means. The target value determining means determines a target value for the value of any of the image forming conditions that determines the densities of the first and second test images such that the difference between the reference density and the measured density is small. . Here, when the target value is determined based on the measured density of the first test image, the control means immediately sets the value of the image forming condition to the target value, while the second test image is displayed. When the target value is determined based on the measured density, the value of the image forming condition is gradually brought close to the target value. As a result, the value of the image forming condition fluctuates rapidly when the power is turned on, and fluctuates gently in other cases.

[0010]

EXAMPLES A. Configuration of Embodiments A full-color copying machine according to an embodiment of the present invention will be described below with reference to the drawings. In FIG. 1, the full-color copying machine according to the present embodiment includes a scanner unit 100, an image processing unit 200, a ROS optical system 300, and an image forming unit 400. In the scanner unit 100,
The original 109 is read, and its content is density data L ^* ,
It is output as a ^* and b ^* . Next, a color conversion unit 201 inside the image processing unit 200 converts the density data L ^* , a ^* , b ^* into image data represented by the density of the primary color YMCK. Then, this image data is output in order of Y, M, C, K for each page. Two
Reference numeral 02 denotes a gamma correction device, which performs gamma correction on this image data and outputs it.

The contents of gamma correction will be described below. First, the density of each primary color YMCK in the image data is 2
It is represented by 56 gradations (“0” to “255”). However, if the image data is simply output based on the image data, the fidelity is deteriorated when the density characteristic of the image forming unit 400 changes. Therefore, the gamma correction device 20
2 is provided, and the input image data is appropriately converted and output. In the gamma correction device 202,
Look-up tables of "7" types of LUT_1 to LUT_7 are provided, and one of them is selected, and the input / output characteristic is determined according to the selected look-up table.

The input / output characteristics corresponding to these LUT_1 to LUT_7 are shown in FIG. As shown, LUT_1-
When any one of LUT_3 is selected, the density of the image data before conversion becomes higher than that of the image data after conversion. On the other hand, when any one of LUT_5 to LUT_7 is selected, the density of the image data before conversion becomes lower than that of the image data after conversion. When LUT_4 is selected, the densities of the image data before and after the conversion are the same. The lookup tables adjacent to each other in FIG.
The toner patch densities are different by "0.1". Which lookup table is selected is determined according to the density of the toner patch, which will be described in detail later.

Returning to FIG. 1, reference numeral 203 denotes a D / A converter which converts gamma-corrected image data into an analog signal and outputs it. A triangular wave generator 204 outputs a triangular wave having a predetermined cycle. Reference numeral 206 denotes a triangular wave adjusting circuit, which appropriately adjusts the level of the triangular wave and outputs it. Two
Reference numeral 05 denotes a comparator, which detects the level of the analog signal output from the D / A converter 203 and the triangular wave adjusting circuit 206.
The level of the triangular wave output from is compared, and when the analog signal is equal to or higher than the triangular wave, the "0" signal is output, and in other cases, the "1" signal is output. Therefore, the comparator 205
The output signal is a pulse signal which becomes "1" or "0" as appropriate. The duty ratio of the pulse signal becomes smaller as the level of the analog signal becomes higher (the density becomes higher), and the gradation area ratio is determined by this.

Next, a toner patch signal generation circuit 207 supplies an analog signal (toner patch signal) of a level corresponding to a predetermined toner density to the comparator 205 at a timing corresponding to the developing position of the toner patch. . This analog signal is compared with the triangular wave similarly to the analog signal output from the D / A converter 203, and a pulse signal corresponding to the result is output from the comparator 205.

Further, inside the ROS optical system 300, a laser driving circuit 301 controls the laser 302 on / off in synchronization with the pulse signal output from the comparator 205. That is, when the pulse signal is "1", the laser 302 is turned on, while when it is "0", it is turned off. The laser light emitted from the laser 302 is converged via the polygon 303, the fθ lens 304, and the reflection mirror 305 in order.

Further, in the inside of the image forming section 400, 4
Reference numeral 11 denotes an arithmetic unit, which controls other components based on a control program described later. A charging device 402 uniformly negatively charges the photoconductor 401 under the control of the arithmetic device 411 and the charge amount varying device 409. The photoconductor 401 rotates clockwise in the figure, and after being charged by the charging device 402, the laser light is emitted. As a result, a latent image is formed on the photoconductor 401. Reference numeral 403 denotes a rotary developing device that attaches toner of each primary color to the photoconductor 401. Reference numeral 412 denotes a toner dispensing device, which supplies toner of each color to the rotary developing device 403 under the control of the arithmetic device 411. Here, the amount of toner supplied from the toner dispensing device 412 to the rotary developing device 403 is controlled by the arithmetic device 411 based on the measurement result of the toner density sensor 414.

A transfer device 406 transfers the toner adhering to the photosensitive member 401 onto a sheet. A cleaner device 404 removes the toner remaining on the photoconductor 401. Reference numeral 405 denotes a static elimination lamp, which eliminates static electricity from the photoconductor 401. An electrometer 410 measures the potential of the photoconductor 401 charged by the charging device 402. 413 is a humidity sensor, which is composed of an LED reflection type sensor,
The humidity around the photoconductor 401 is measured. A toner density sensor 414 measures the density of the toner developed on the photoconductor 401. Then, the electrometer 410 and the sensor 4
The measurement results of 13, 414 are supplied to the arithmetic unit 411.

B. Operation of Embodiment Next, the operation of this embodiment will be described with reference to FIG. In addition,
FIG. 2 is a flowchart of a control program in the arithmetic unit 411. This control program is started when the power of the full-color copying machine of this embodiment is turned on. When the process is started in the figure, the process proceeds to step SP1 and it is determined whether or not the current state is the state immediately after the power is turned on. If "YES" is determined here, the process proceeds to step SP2, a toner patch of each primary color (YMCK) is formed at a predetermined position on the photoconductor 401, the density measurement result is stored, and the measurement is performed. L based on the result
One of the lookup tables UT_1 to LUT_7 is selected.

In more detail, first, the photoconductor 40
The portion on which the toner patch is to be formed is the charging device 402.
This part is electrically charged when facing. Next, from the arithmetic unit 411 to the toner patch signal generation circuit 207,
A command indicating that a toner patch signal should be generated is transmitted. As a result, the toner patch signal generation circuit 207 supplies the toner patch signal to the comparator 205 for a predetermined period. On the other hand, the triangular wave is supplied to the comparator 205 via the triangular wave generator 204 and the triangular wave adjusting circuit 206, and the pulse signal is supplied from the comparator 205 to the laser drive circuit 301 based on the magnitude relationship between the toner patch signal and the triangular wave. It As a result, pulsed laser light is emitted from the laser 302, and the laser light is emitted from the polygon 30.
3 to a latent image of a toner patch is formed on the photoconductor 401 via the reflection mirror 305.

Here, the density of the toner patch to be formed will be described with reference to FIGS. FIG. 7 shows the degree of color unevenness of the toner patch with respect to the gradation area ratio Cin. As shown in the figure, the smaller the gradation area ratio Cin, the larger the color unevenness, but in the region where the gradation area ratio Cin is “50%” or more, the color unevenness is almost constant. Next, FIG.
Indicates the output level of the toner density sensor (LED reflection type sensor) 414 with respect to the gradation area ratio Cin. The sensor output is saturated at about "70%" for YMC colors and about "60%" for K colors. Therefore, the gradation area ratio Cin with less color unevenness and capable of density detection is "50.
.About.60% ", and in this embodiment, the gradation area ratio Cin of the toner patch is set in advance within this range.

When the latent image of the toner patch is formed on the photoconductor 401 and then the photoconductor 401 is slightly rotated, the previously formed latent image faces the rotary developing device 403. As a result, toner of a predetermined color (any one of YMC) is attached to the charged portion on the photoconductor 401, and the toner patch is developed. The photoconductor 401 rotates further,
When the toner patch faces the toner density sensor 414,
The toner density sensor 414 measures the density of the toner patch, and the result is stored in the arithmetic unit 411.
When the photoconductor 401 rotates further, the cleaner device 40
The toner of the toner patch is removed by 4 and the toner patch portion of the photoconductor 401 is destaticized by the static elimination lamp 405, and then the photoconductor 401 is recharged by the charging device 402. The above operation is performed for each primary color of YMC, and the calculation device 411 stores the density measurement result for each primary color of YMC.

Next, for each of the primary colors YMC, the target value is subtracted from the measured value of the toner patch density, and the average value (average density deviation value) of these subtraction results is obtained. The target value of the density of each toner patch is stored in the arithmetic unit 411 in advance. Next, when the processing proceeds to step SP3, the look-up table in the gamma correction device 202 is selected based on the following table 1 according to the density deviation average value (note that the decimal part of the density deviation average value is rounded off). Have been).

[0023]

[Table 1]

With the above, the processing of step SP2 is completed, and then the processing proceeds to step SP3. Step SP3
In the above, the amount of toner supplied from the toner dispensing device 412 to the rotary developing device 403 is controlled based on the previously detected density of the toner patch. This processing is a density correction method called "ADC method", which is well known in the art. Then, a copying operation similar to that of a general full color copying machine is performed. That is,
When the document is read by the scanner unit 100, the content is output as density data L ^* , a ^* , b ^{*, and} is output from the color conversion unit 201 in order of Y, M, C, K for each page. When this image data is supplied to the gamma correction device 202, the image data is converted based on the look-up table previously selected in step SP2.

Then, the laser drive circuit 301 is driven based on the converted image data, and the latent image processing and the development processing are performed on the photoconductor 401. On the other hand, the sheet is conveyed to the transfer device 406, and the developed toner is transferred to the sheet. Such a latent image, development and transfer process are performed for each primary color, and each toner is transferred to the paper. Thereafter, each toner is fixed on the paper and the paper is ejected.

Next, when the processing advances to step SP4, it is determined whether or not the present time is the toner patch preparation timing. Here, the toner patch creation timing is a timing that occurs each time a predetermined number of sheets (for example, several tens of sheets) are printed. Here, if it is determined to be "NO", the process returns to step SP3, and the toner amount is controlled again based on the density of the toner patch detected earlier,
The paper on which the image data is printed is ejected. The reason why the ADC type density correction in step SP3 is repeatedly executed will be described. In the ADC method, the result of the control does not appear until the toner is consumed by the image formation, and when a large amount of toner is supplied to the rotary developing device 403 at one time, "fog" occurs, so that only a small amount of toner can be supplied. Therefore, the responsiveness is slow. Therefore, it is necessary to repeatedly execute it as in the present embodiment.

As described above, when step SP3 is repeatedly executed through step SP4, the paper on which the image data is printed is sequentially ejected. When the process proceeds to step SP4 after the predetermined number of sheets are ejected, it is determined to be "YES" here, and the process proceeds to step SP5. In step SP5, a toner patch is generated as in step SP2, and its density is measured by the toner density sensor 414. However, step SP5 is different from step SP2 in the processing of selecting the lookup table based on the result. That is,
In step SP5, the next look-up table is selected with respect to the current look-up table within a limit of "± 1 step" in Table 1.

As an example, description will be made assuming that LUT_6 is currently selected and the average value of the density deviations is "-5". In such a case, according to Table 1, the appropriate lookup table is LUT_3, but since the current lookup table is LUT_6, the lookup table closest to LUT_3 within that “± 1 stage”, namely LUT_5. Is selected as the next lookup table. Next, the process is step SP6.
Proceeding to step 3, it is determined whether the power of the copying machine has been turned off. If it is determined to be "NO" here, the process returns to step SP3. When the loop of steps SP3 and SP4 is repeated, the toner amount is controlled by the ADC method, and the paper on which the image data is printed is sequentially ejected.

When the toner patch preparation timing comes again, the process proceeds to step SP5, a toner patch is generated, and its density is measured by the toner density sensor 414. Here, similarly to the previous time, if the average density deviation value is “−5”, the lookup table closest to LUT_3 within “± 1 step” of the current lookup table (LUT_5), that is, LUT_4.
Is selected as the next lookup table.

As described above, according to this embodiment, the lookup table selected first after the power is turned on is immediately determined according to the density of the toner patch (step SP).
2) On the other hand, the lookup table selected thereafter is
It is limited to those within “± 1 step” with respect to the current lookup table. Therefore, it is possible to suppress the density fluctuation of the output image before and after the change of the lookup table, and it is possible to perform stable image output.

Next, for reference, the characteristics of each part of the copying machine in various cases are shown in FIGS. In these figures, the power of the copying machine is in the ON state until the time just before the time t _{0 to} t ₃ and the copying operation is performed. And
At time t ₃ , the power is turned off / on, and it is assumed that the environment has changed significantly during that time (temperature before change: 20 ° C, humidity: 55%, temperature after change: 28 ° C, humidity: 80%). . That is, although these figures are continuous graphs on the time axis, there is actually a power-off period of about several tens of hours at time t ₃ .

First, FIG. 4A shows an example of density characteristics when density correction is performed only by the ADC method. According to this figure, if a significant environmental change occurs at time t ₃ ,
The density characteristic of the output image also deviates significantly from the target value. In addition, as described above, since the ADC system has a slow response, it takes a considerable time for the concentration to approach the target value.

Next, FIG. 8A shows the density characteristics when the ADC method and gamma correction are simply used together. It should be noted that such characteristics are obtained when it is assumed that the corresponding lookup table is immediately selected according to the density of the toner patch in step SP5 of the above embodiment. According to the figure, the density characteristic is made to follow the target value even though a rapid environmental change occurs at time t ₃ . However, the toner patch often has color unevenness, and an error necessarily occurs in the density measurement result. Due to this cause, a sharp concentration change occurs at times t ₁ and t ₄ . In particular, the density variation at the time t ₄ is large, which has a great adverse effect on the image quality. Here, the reason why the density fluctuation is particularly large is that the look-up table fluctuates by two steps at time t ₄ (see FIG. 7D).

Next, FIG. 6A shows the density characteristics according to this embodiment under the same conditions. Also in this embodiment, it is inevitable that the density deviates from the target value to some extent due to the color unevenness of the toner patch and the density measurement error. However, the fluctuation range of the density at time t ₄ is suppressed to be lower than that in FIG. This is at start-up (time t ₀ and t
Except for ₃ ), the fluctuation range of the lookup table is kept within “± 1 step”.

C. Modifications The present invention is not limited to the embodiments described above, and various modifications can be made, for example, as follows. In the above-described embodiment, the look-up table in the gamma correction device 202 is selected based on the density deviation average value, but the factor (image forming condition) that determines the density is not limited to the look-up table number.
Various other parameters may be selected. For example, the charging voltage (V _GRID ) in the charging device 402 may be selected based on the density deviation average value and Table 2 below. When adopting such a modified example, the maximum fluctuation range of the charging voltage (V _GRID ) is shown in Table 2 in the process corresponding to step SP5.
It should be suppressed within "± 1 step".

[0036]

[Table 2]

Similarly, the light amount of the laser 302 (LD light amount) and the rotary developing device 4 are calculated based on the average value of the density deviations.
The developing bias voltage of 03 may be selected. Further, as shown in Table 3 below, these plural parameters may be selected.

[0038]

[Table 3]

Although the LED reflection type sensor is used as the toner concentration sensor 414 in the above embodiment, an RGB color sensor or various other sensors may be used instead.

[0040]

As described above, according to the structure of the first aspect, the value of the image forming condition can be gently changed, so that the rapid density change of the output image can be suppressed and the high quality output image can be obtained. Can be obtained. Further, according to the second aspect of the present invention, the power can be rapidly changed when the power is turned on. Therefore, when the power is turned on after the operating environment of the image forming apparatus is changed, the environmental change can be quickly dealt with. It is possible.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an example.

FIG. 2 is a flowchart of a control program according to an embodiment.

3 is an input / output characteristic diagram of each look-up table in the gamma correction device 202. FIG.

FIG. 4 is a density fluctuation characteristic diagram in a conventional copying machine.

FIG. 5 is a density variation characteristic diagram when the ADC method and gamma correction are simply used together.

FIG. 6 is a concentration variation characteristic diagram in one example.

FIG. 7 is a characteristic diagram of density unevenness of a toner patch with respect to a gradation area ratio Cin.

FIG. 8 is a toner concentration sensor 4 for the gradation area ratio Cin.
14 is an output characteristic diagram of FIG.

[Explanation of symbols]

400 Image forming unit (developing device) 411 Computing device (target value determination means, control means) 414 Toner density sensor (density measuring means)

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI H04N 1/60 H04N 1/40 D (58) Fields investigated (Int.Cl. ⁷ , DB name) H04N 1/40-1 / 409 H04N 1/46-1/48 H04N 1/52 H04N 1/60

Claims (2)

(57) [Claims] 1. An image based on the supplied image data,
A developing means for developing a test image having a predetermined reference density in an ideal state, a density measuring means for measuring the density of the test image and outputting the result as a measured density, and a plurality of the image data Each time it is developed, it is assumed in advance
Each step with the range of the difference between the measured concentration and the reference concentration
From the floor, the reference concentration and the measurement concentration at the present time
The stage close to the stage to which the difference from the degree belongs is currently selected.
Select again from the stage of change from one stage to the next,
Note the range of the difference between the measured concentration and the reference concentration, which is assumed in advance.
Image forming conditions prepared in advance for each step
Image forming conditions corresponding to the selected stage
An image forming apparatus comprising: a control unit used for development by the developing unit. 2. A first test image having a first reference density in an ideal state is developed when the power is turned on, and when the image data is supplied after that, the image data is added to the image data .
A developing device for developing an image based on the image and a second test image having a second reference density in an ideal state; and measuring the densities of the first and second test images, and measuring the result. And the measured concentration and the reference concentration that are assumed in advance when the power is turned on.
From the respective stages in which the range of the difference of
The difference between the reference density and the measured density of the first test image belongs to
Select the step that is closest to
If data is supplied, the
The second reference density at the point and the second test image
The stage close to the stage where the difference from the measured concentration of
Re-selecting within the limit of one step from the
Of the difference between the previously assumed measured concentration and the reference concentration.
Images prepared in advance for each step of the range
Image formation corresponding to the selected stage from the forming conditions
An image forming apparatus comprising: a control unit that uses a condition for development by the developing unit.