JP2003057887A - Image forming device and calibration method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make the time required to read a test pattern as short as possible in the case of reading the test pattern several times in the case of calibration of an image forming device. SOLUTION: Before outputting the test pattern in the calibration, the number of using times of an element exerting influence on image formation such as the cumulative number of drum using times is acquired (s101), and the number of sampling times in the case of reading the test pattern of every element is obtained in accordance with the number of using times (s102). Thereafter, the test pattern is outputted and read in accordance with the number of sampling times, and maximum density is adjusted and a gamma correction part is updated based on the read result (s103 to s123).

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 and a calibration method, and more particularly to reading a test pattern formed by calibration.

[0002]

2. Description of the Related Art Conventionally, printers and copying machines have been known as typical image forming apparatuses. For example, in a copying machine that forms a full-color image, a plurality of output color components C (cyan), M (magenta), Y (yellow), and K (black) form an image in a frame-sequential manner. An electrophotographic method using a laser beam is often used for the image formation, and in this method, the emission of the laser beam is controlled by a signal whose pulse width is modulated according to an image signal, thereby forming a dot By changing the size, halftone expression is possible.

In such an image forming apparatus, when the image forming operation is performed for a relatively long time, the characteristics of the elements constituting the apparatus such as the characteristics of latent image formation on the photosensitive drum and the development with toner are temperature and humidity. The quality of the image formed as a result may change due to changes and the like, or the quality may differ depending on the output time when the same image is output multiple times. In addition, such a change in characteristics also appears as a change with time of each of the above elements. It is known that calibration is conventionally performed in order to keep the image forming characteristic constant in order to cope with the change in the characteristic as described above.

In this calibration, generally, a predetermined test pattern is formed on an image bearing member such as a photosensitive drum or an intermediate transfer member or a medium such as recording paper, and the density of the predetermined pattern is measured by a sensor or a scanner. Is performed, and processing for making the output characteristics constant in image formation is performed based on the read result.

[0005]

By the way, as described above, even when the components of the image forming apparatus change with time, the influence on the image formation is reduced and a constant output characteristic is maintained. The calibration is performed as described above. One of the influences of this temporal change on the image formation is that the density and color are nonuniform.

[0006] For example, with the use of the apparatus, the performance of the photosensitive drum for forming a latent image and the developing device for development deteriorates, the toner as a developer becomes old, and the amount thereof decreases. The image forming characteristics may change due to changes such as the above. On the other hand, in addition to the calibration performed as described above, normally, when a certain period of time has passed or when the cumulative number of sheets of image output has reached a certain number, the photosensitive drum, toner, etc. Parts and consumables will be replaced with new ones.

However, even before the replacement of parts and consumables, if the degree of the above-mentioned change with time is relatively large, the effect does not appear as a uniform decrease in the density, but the density is reduced. In some cases, it may appear as non-uniform image deterioration such as color unevenness. Specifically, streaks as partial color fading or uneven density may appear in the image. In the calibration performed on the apparatus in such a state, the above-described color fading or streaks may occur in the test pattern formed for that purpose. As a result, the faint areas and streaks of this color may be read in by reading the test pattern, and the calibration based on the reading results
It may not correspond to the overall gradation characteristic at that time, but may correspond to a relatively biased characteristic. As a result, the gradation characteristics and the like in the subsequent image formation are not properly corrected by the calibration, and in an extreme case, they may be inferior to the state before the calibration.

On the other hand, in reading the test pattern, it has been conventionally proposed to increase the sampling number of read data and use the average of these data. For example, the read position is changed in each patch constituting the test pattern to obtain a plurality of sampling data, and the average of these is used as the read data of each patch. However, when the number of data samples is increased in this way, a problem arises in that reading for the sampling requires a relatively long time. In particular, in a mode in which calibration is performed during image formation, the time during which image formation is interrupted for calibration becomes long, which causes problems such as a decrease in throughput and inconvenience of the apparatus.

The present invention has been made to solve the above problems, and an object of the present invention is to reduce the time required for reading a test pattern a plurality of times during calibration. An object is to provide an image forming apparatus and a calibration method.

[0010]

Therefore, according to the present invention,
In an image forming apparatus for forming an image on a medium, a number-of-uses counting unit for counting the number of times the elements forming the image forming apparatus and affecting the image forming characteristic are used for image formation, and a constant image forming characteristic. The test pattern output means for image forming and outputting the test pattern during the calibration to obtain the test pattern and the number of times the test pattern output by the test pattern outputting means is counted by the use number counting means. And a reading means for reading.

Further, in a calibration method for making image forming characteristics of an image forming apparatus for forming an image on a medium constant, an image of an element that constitutes the image forming apparatus and affects the image forming characteristics There is a step of counting the number of times used for forming, performing image formation output of a test pattern when executing calibration, and reading the test pattern output by the image formation a number of times according to the counted number of times of use. It is characterized by having done.

According to the above configuration, when the calibration is executed, the test pattern is read a number of times corresponding to the number of times that it is used for the image formation, which is counted for the factors that affect the image forming characteristics.
It is possible to eliminate the influence of streak unevenness that appears in the test pattern, for example, which cannot be resolved by calibration, by multiple readings, and to change the number of readings depending on the degree of the possibility that streak unevenness may appear. It is possible to suppress unnecessary reading.

[0013]

DETAILED DESCRIPTION OF THE INVENTION Embodiments of the present invention will be described in detail below with reference to the drawings.

[Arrangement of Image Forming Apparatus] FIG. 1 is a view showing the outline of the internal arrangement of a copying machine which is an embodiment of the image forming apparatus of the present invention.

In the figure, reference numeral 201 denotes a platen glass on which a document 202 to be read is placed. Manuscript 20
2 is illuminated by an illumination 203, and its reflected light passes through mirrors 204, 205, 206 and forms an image on a CCD 208 by an optical system 207. In this configuration, the motor 209 is used as a power source to mechanically drive the first mirror unit 210 including the mirror 204 and the illumination 203 at the speed V, and the second mirror unit 211 including the mirrors 205 and 206 is moved at the speed V. By driving at 1/2 V, the entire surface of the original 202 is scanned and the original is read.

Reference numeral 212 denotes an image processing circuit section, which processes the image information read as described above as an electric signal, temporarily holds it in the image memory 108, and outputs it as a print signal.

The print signal output from the image processing circuit section 212 is sent to a laser driver (not shown) and similarly drives four semiconductor lasers (not shown). And 2
Reference numeral 13 denotes a polygon mirror, which receives each laser beam emitted from the four semiconductor lasers. By the predetermined rotation of the polygon mirror 213, one of the four laser beams scans the photosensitive drum 217 via the mirrors 214, 215 and 216, and the next one is the mirror 218.
The photosensitive drum 221 is scanned via 219 and 220, the next one is scanning the photosensitive drum 225 via mirrors 222, 223 and 224, and the next one is the mirror 22.
The photosensitive drum 229 is scanned via 6, 227 and 228.

On the other hand, reference numeral 230 denotes a developing device for supplying yellow (Y) toner, which develops the latent image formed on the photosensitive drum 217 by the above-mentioned laser light with yellow toner. Reference numeral 231 denotes a developing device that supplies magenta (M) toner, and similarly, the latent image formed on the photosensitive drum 221 by the laser light is developed by the magenta toner. Similarly, a developing device 232 that supplies cyan (C) toner forms a cyan toner image on the photosensitive drum 225, and a developing device 233 that supplies black (Bk) toner forms a magenta image on the photosensitive drum 229. To form a toner image.

The four colors formed as described above
The toner image of (Y, M, C, Bk) is transferred onto a sheet as an image forming medium, whereby a full-color output image can be obtained.

The paper fed from any of the paper cassettes 234 and 235 or the manual feed tray 236 is conveyed by the registration roller 237 at a predetermined timing, and then sent onto the transfer belt 238 at a predetermined timing. Then, by being attracted to the transfer belt 238 that is rotationally driven, the conveyance for image formation is performed. On the other hand, the toner images of the respective colors are formed in advance on the photosensitive drums 217, 221, 225, and 229 in synchronism with the above-described paper feeding timing, and as a result, the toner is conveyed as the paper is conveyed. The image is transferred to the paper. And
The sheet on which the toner images of the respective colors have been transferred is separated from the transfer belt and conveyed by the conveyor belt 239. During this conveyance, the fixing device 240 fixes the toner on the sheet and the sheet is ejected to the sheet ejection tray 241.

When images are formed on both sides of the paper,
In the same manner as described above, the paper fed from any of the paper cassettes 234 and 235 or the manual feed tray 236 is adsorbed to the transfer belt 238 via the registration roller 237 and conveyed. Then, similarly, in synchronization with the feeding timing, the photosensitive drums 217, 221 and 22 are previously synchronized.
Toner images of respective colors have been developed on Nos. 5 and 229, and as the paper is conveyed, an image is formed on the first surface of the paper,
Then, the toner is transferred to the paper. Then, the sheet on which the toner of each color is transferred is separated from the transfer belt, is conveyed by the conveying belt 239, and the toner is fixed on the sheet by the fixing device 240.

After that, the paper output vertical path 24 is output by the paper output deflector.
After passing 6, the sheet is conveyed to the double-sided reversing unit 245. Then, after a lapse of a predetermined time after the sheet passes through the reversing unit, the double-sided reversing unit entrance roller reversely rotates, the sheet is reversed and conveyed to the double-sided path pre-conveying unit 247, and then to the double-sided path 244.
By this conveyance, the upper side of the sheet on the double-sided path 244 is the first side on which an image has already been formed. When the sheets are conveyed to the double-sided path, the sheets are aligned and then immediately fed in the same manner as described above to form the image on the second side.
After passing 0, the paper is discharged to the paper discharge tray 241. When the double-sided operation is continuously performed on a plurality of sheets, re-feeding from the double-sided path and sheet-feeding from the sheet tray are alternately performed.

The four photosensitive drums 217, 221 and
The sheets 225 and 229 are arranged at equal intervals with a distance d, while the transfer belt 238 conveys the sheet at a constant speed v. Therefore, each of the four semiconductor lasers is driven in synchronization with the timing required from now on.

In the above-described image forming operation, Y (yellow) and M are printed every time image formation is performed on one sheet.
For each of (magenta), C (cyan), and Bk (black), there is a consumable part usage counter that indicates the number of times the photosensitive drum has been used, the number of times the developing device using toner has been used, and the number of times a developer that is toner has been used. Each is incremented by 1, and each count value is stored in the RAM (not shown). The value of the counter for each element for each of these colors is used to determine the number of samplings for reading the patch of the test pattern in the calibration process described later. In this embodiment, the count values of the photosensitive drum, the developing device, and the developer are incremented by 1 each time an image is formed on one sheet of paper, but the count values may be different for each element. Alternatively, it can be determined according to, for example, the manner of deterioration of each element.

The values of the respective counters are cleared to 0 when the corresponding elements, that is, the photosensitive drum, the developing device, and the toner of the respective colors are replaced with new ones. On the other hand, these elements are replaced with new ones when an image defect or the like occurs, or when the value of the consumable component usage count counter reaches a predetermined value.

In this embodiment, the photosensitive drum is used as the element for counting the number of times of use by the counter, but the element is not limited to these. For example, any device component such as a transfer drum that affects image forming characteristics can be counted, and the count value indicating the number of times of use is used when determining the number of times of sampling in calibration. You can also

[Flow of Image Signal] FIG. 2 is a block diagram showing the configuration of the image processing circuit section 212 of the copying machine described above, showing the processing of the image signal representing the image information obtained by reading the original. There is.

As shown in FIG. 2, the CC explained in FIG.
The D sensor 208 uses the read image information as red
It is output as a digital image signal for three color components of (R), green (G), and blue (B).

The image signals (R0, G0, B0) are converted into standard signals (R, G, B) in the masking circuit 112 by the calculation according to the following equation.

[0030]

[Equation 1]

Here, cij (i = 1,2,3 j = 1,2,3) is
It is a constant peculiar to the device in consideration of various characteristics such as the sensitivity characteristic of the CCD sensor and the spectral characteristic of the illumination lamp.

Next, the brightness / density conversion section 104 converts the brightness signal of the image signal converted as described above into a density signal. The brightness / density conversion unit 104 is composed of a look-up table of RAM or ROM, and this table performs conversion equivalent to the calculation of the following equation.

[0033]           C1 = -α × log10 (R / 255)           M1 = -α × log10 (G / 255) (2)           Y1 = -α × log10 (B / 255) (α is a constant)

Further, the output masking / UCR circuit 10
6, the density signals M1, C1, and Y1 are converted into signals corresponding to Y, M, C, and Bk which are the colors of the toner used for image formation in the copying machine of the present embodiment by the calculation of the following equation.

[0035]

[Equation 2]

Here, aij (i = 1, 2, 3, 4 j = 1, 2, 3,
4) is a constant peculiar to the apparatus in consideration of various characteristics such as the tint of the toner, and is obtained as Bk1 = min (C1, M1, Y1) ... (4).

Based on the above equations (2), (3) and (4), the C1, M1, Y1 and Bk1 signals based on the R, G and B signals read by the CCD sensor correspond to the spectral distribution characteristics of the toner. The converted C, M, Y and Bk signals are output.

On the other hand, the image signal output from the masking circuit 112 is also input to the character / line image detection circuit 105. The character / line drawing detection circuit 105 is a circuit that judges whether or not each pixel of an image obtained by reading a document is a part of a character or a line drawing and generates a judgment signal TEXT. A known method can be used for this determination, and the description thereof is omitted here.

The compression / expansion circuit 107 compresses the image signals (Y1, M1, C1) from the luminance / density conversion unit 104 and the signal TEXT from the character / line drawing determination circuit 105,
Stored in the memory 108 as data with reduced information amount,
Further, the data is read from the memory 108, and the data is expanded to obtain an image signal (Y1, M1, C1) and a character / line drawing determination signal TEXT. As the image compression / expansion circuit, a known one can be used, and a description thereof will be omitted here.

The gamma correction circuit 312 is composed of a look-up table (LUT), and has gradation characteristics for image formation by an image forming section including a photosensitive drum and toner of a developing device in the copying machine of this embodiment. Image signal conversion is performed to perform gamma correction.

[Image Formation in Copying] Image formation based on the read image information in the copying machine of the present embodiment having the above-described configuration will be described. The copying machine according to the present embodiment can also operate as a printer that forms an image based on image information from a host device such as a host computer, but here, it is read by the above-described reading configuration. Image formation when copying an original image will be described.

In the case of a copying operation, the read image information is output as an image signal from the CCD 208, passes through the masking circuit 112 and the brightness / density conversion unit 104, and is compressed / compressed.
After being compressed by the expansion circuit, it is written in the memory 108. The character / line drawing determination signal TEXT from the character / line drawing determination circuit 105 is also compressed by the compression / expansion circuit 107 and then written in the memory 108.

The data stored in the memory 108 is read out according to a predetermined image forming timing and expanded by the compression / expansion circuit 107, and the PW which will be described later with reference to FIG.
It is used to drive the laser driver via the M circuit.
As a result, the laser is driven in accordance with the image signal, and as described above, formation of a latent image, development with toner, transfer to a sheet and fixing are performed.

FIG. 3 is a timing chart showing the timing of writing and reading in the memory 108.

In FIG. 3, the image signal from the CCD 208 is transmitted through the masking circuit 112 at the timing 40.
1 is written in the memory 108. In addition, the memory 108
The data written in is read at timings 402, 403, 404 and 405 for each color. The relationship of these timings is such that the reading has an interval of time d / v as illustrated. Here, as described above, d is the distance between four drums arranged at equal intervals, and v is the speed of the sheet conveyed by the transfer belt.

[PWM Circuit] FIG. 4 is a block diagram showing the configuration of a PWM (pulse width modulation) circuit according to this embodiment. Note that FIG. 4 shows only one color signal, and the configuration shown in FIG. 4 is provided for each color of Y, M, C, and Bk.

In the figure, reference numeral 601 denotes a D / A converter, which converts the input digital image signal into an analog signal and sends the converted signal to a comparator 605.

Reference numeral 602 denotes a triangular wave generator corresponding to the case where an image to be formed emphasizes gradation, and generates a triangular wave having a two-pixel cycle. On the other hand, reference numeral 603 denotes a triangular wave generator for an image that places importance on resolution, and generates a triangular wave of one pixel period. Reference numeral 604 denotes a selector, which selects one of the triangular waves from the triangular wave generator 602 or 603 according to the above-described determination signal ТEXТ and outputs it to the comparator 605. That is, in the present embodiment, a laser beam is used to form an image on the photosensitive drum by a laser, in the case of forming an image whose gradation is important such as a photographic image and in the case of forming an image whose resolution is important such as characters and line drawings. To change the density (resolution) of the dots to be
As a result, an image can be formed that matches the characteristics of the type of image to be formed, and a high-quality printed image can be obtained.

Specifically, when the gradation is emphasized, a triangular wave having a lower dot density (resolution) is generated as compared with the case where the resolution is emphasized. That is, in the image to be printed, the determination signal ТEXТ is "1",
In the image area forming a character or a line drawing, the selector 6
Reference numeral 04 selects a triangular wave for an image output from the triangular wave generator 603, which emphasizes resolution, and a comparator 605
Compares the triangular wave with the analog image signal that has been D / A converted, and outputs as described later with reference to FIG. On the other hand, in an image area other than a character or a line drawing, the triangular wave for an image output from the triangular wave generator 602 which emphasizes gradation is compared with the analog image signal. Then, the output of the comparator 605 is input as a PWM signal to the laser driver 606 that drives the semiconductor laser element.

FIG. 5 is a diagram showing the state of pulse width modulation, and specifically shows the comparison in the comparator 605 and the output thereby.

The upper part of FIG. 5 shows the state of pulse width modulation in the case of forming an image with emphasis on gradation.
The image signal 801 from the D / A converter 601 is compared with the triangular wave 802 having a period of two pixels. By this comparison, P having a pulse width corresponding to the value (density value) of the image signal is obtained.
A WM signal 803 is obtained. On the other hand, the lower part of FIG. 5 shows a state of pulse width modulation in the case of forming an image in which resolution is important, and the image signal 804 from the D / A converter 601 is shown.
Is compared with a triangular wave 805 of one pixel period, and a PWM signal 806 is obtained in the same manner. By driving the laser driver 606 with the PWM signal obtained in this manner, dots having a size corresponding to the pulse width are formed on the photosensitive drum.

The PWM signal 803 and the PWM signal 80
6 is appropriately switched and output in accordance with the determination signal ТEXТ as described above, so that high-quality image formation is performed according to the characteristics of the image area in the image to be formed.

[Calibration] The copying machine according to the present embodiment described above calibrates the density and gradation in order to maintain constant output density and gradation in image formation. In this embodiment, calibration is performed for two characteristics relating to maximum density and gamma correction in image formation, and therefore two test patterns are formed and read.

FIG. 6 is a flow chart showing the control relating to the calibration of this embodiment. Also, FIG.
12 to 14 are views showing display examples on the operation panel of the copying machine.

When a predetermined key operation for instructing the start of calibration is performed on the operation panel, the control relating to the calibration shown in FIG. 6 is activated. Then, the screen shown in FIG. 7 is displayed on the operation panel, and the number of times the drum is used, the number of times the developing machine is used, the number of times the developing material is used for each color are calculated based on the count value of the number of times the consumable parts are used stored in the RAM. Get the usage count
(Step S101). For each number of times of use, a predetermined value is set which indicates the time to replace the part, and the value is stored in a RAM (not shown). That is, the value of each consumable part usage counter and the predetermined value can be displayed for each part, and the user or service person can know the replacement time. As will be described below, when each counter value is compared with a predetermined value for each acquisition of the number of times of use, when the counter value reaches the predetermined value, a predetermined display or the like is notified to the user or the like. You may

In the next step S102, the ratio of the number of times of use of the drum, the number of times of use of the developing device, and the number of times of use of the developer obtained above to the predetermined value indicating the replacement time is obtained, and in accordance with this ratio, The number of samplings for reading the test pattern in the calibration described below is determined. In the present embodiment, the number of samplings is determined within the range of 1 to 9 according to the ratio obtained above, and as described below, the higher the ratio, the greater the number of samplings. It is what is done. Specifically, Y, M, C,
For each Bk, the number of times of sampling is determined according to the maximum ratio among the ratios of the number of times of using the drum, developing device, and developer.

For example, when the count value indicating the number of times the Y photosensitive drum has been used is 10,000, while the predetermined value indicating the replacement time of the photosensitive drum is 100,000, the ratio of the Y drum is 10%. Become. Then, the ratio is similarly obtained for the Y developing device and the developing material, and the ratio is 10%.
When is the maximum, the number of times of sampling of the Y test pattern is determined according to the ratio. Similarly, when the count value indicating the number of times the drum of C is used is 90,000 times,
The ratio is 90% with respect to the predetermined value 100000 indicating the replacement time. Then, when this value is the maximum of the ratios obtained for other developing devices and developing materials, the number of samplings corresponding to this 90% is determined for the C test pattern.

Specifically, in the above example, since the photosensitive drum of Y has a low usage frequency of 10% after being replaced,
Since it is unlikely that the above-mentioned uneven color or uneven density occurs in the test pattern due to the deterioration of the Y photosensitive drum, 1
Sampling around the pattern is only once. On the other hand, since the usage frequency of the C drum has reached 90% after replacement, there is a high possibility that the unevenness of the photosensitive drum of C causes color unevenness and density unevenness. To 9 times. In this way, the number of sampling times for each color patch in the test pattern is determined based on the number of times each type of consumable part is used for each color.

The correspondence relationship between the above-mentioned ratio and the number of times of sampling may be different for each color, and of course, may be different for each device.

Next, when the "test print 1" key on the display screen shown in FIG. 7 is pressed, step S10 is performed.
The process shifts to 3. Here, first test pattern 1
The presence / absence of the paper required to form the
When it is determined that there is no paper, a warning is displayed. When forming the test pattern 1, the test pattern 1 is output using a standard contrast potential (described later) according to the environmental conditions of the copying machine as an initial value. Test pattern 1
As shown in FIG. 13, for each of the four colors Y, M, C, and BK, each band pattern is composed of patches of 64 levels of density from maximum density (density signal level 255) to halftone density. 901 (Y), 902 (M), 903
(C) and 904 (Bk). That is, this test pattern 1 is used for adjusting the maximum density in image formation as described later.

When the test pattern 1 is output, the display shown in FIG. 8 is displayed on the operation screen in the next step S104. Then, the test pattern 1 is the original platen glass 201.
When the "read" key is pressed after being placed on the top, the reading of the test pattern 1 is started. First, the certification lamp 203 is turned on and the mirror unit 211 moves forward to a predesignated position.
The pattern 1 is read by the CD 208. R, G, B of each pattern in the read test pattern 1
The data is converted into optical density by the LUT of the brightness density conversion unit 104. That is, L of the brightness density conversion unit 104
The UT is preset with a conversion relationship equivalent to the calculation of the above-mentioned formula (2). That is, the conversion relationship is adjusted so that the correction coefficient α of the equation (2) is obtained so as to obtain the optical density.

In the next step S105, it is determined based on the converted data whether or not what is placed on the platen glass 201 is the test pattern 1 or whether it is placed correctly. When it is determined that the test pattern 1 is not correctly placed, an error display (FIG. 11) is displayed (step S111), and then the process returns to step S104 to read again with the test pattern 1 properly placed. .

That is, in step S104, when the test pattern 1 is recognized, the mirror unit 211 is moved forward little by little and the CCD 208 continuously reads it. For reading, data of 4677 pixels is sampled at 400 DPI in the Y direction.

At this time, the sampling of each patch, that is, the reading of the patch density is performed in step S1.
The sampling is performed according to the sampling number determined in 02.
Specifically, when reading one patch a plurality of times, the reading is performed at different positions. As a result, even if the patch has uneven density or uneven color,
The averaging process performed on the results of multiple readings can reduce the effect of density unevenness on the results,
More accurate calibration can be performed.

FIG. 14 is a diagram for explaining an example of sampling, and is a diagram showing a part of the patch array of each color shown in FIG. In FIG. 14, black circles indicate sampling points. As is clear from this, yellow (Y)
Performs sampling once for one patch, and magenta (M) performs sampling four times by changing their positions. Similarly, cyan (C) changes its position and performs sampling 9 times in total. In this example, the usage ratio of at least one of the consumable parts related to yellow, that is, the photosensitive drum, the developing device, and the developing material, obtained in step S102 corresponds to one sampling number, and similarly, It shows that magenta is four times and cyan is nine times.

As described above, since cyan is highly likely to cause color unevenness and density unevenness during image formation, more sampling is performed, and when the possibility of color unevenness is small, the number of sampling times is increased accordingly. Also reduce. This makes it possible to minimize the number of sampling times for each color patch, reduce the effect of color unevenness and density unevenness in the test pattern reading, and increase the time required for sampling as much as possible. Can be suppressed.

A specific reading operation is as follows. First, in FIG. 14, sampling points located in the Y direction will be described with reference to FIG.
Reading is performed by the optical system described in the above. Figure 1
In the example shown in FIG. 4, reading is performed at one location for yellow, two locations for magenta, and three locations for cyan. Then, the mirror units 210 and 211 forming the above optical system are sequentially moved in the X direction in the drawing by a distance corresponding to the number of samplings to perform reading. Figure 1
In the example shown in FIG. 4, it is necessary to sample 9 points for each patch of cyan. Therefore, after moving the patch width by about 1/4 of the patch width in the X direction, two points of each patch are read only for cyan. Then, the same distance mirror unit is moved to read two and three spots of each patch for both magenta and cyan.

When the reading of all patches is completed, in step S106, the average of the read data for each patch is calculated by the number of samplings of the patch, and the average is stored in a predetermined RAM as the read density data.

Next, in step S107, the operation panel shown in FIG. 9 is displayed, and the test pattern 2 is output by operating the "test pattern 2" key. When the test pattern 2 is output, the correction function of the γ correction unit 312 is stopped, and no γ correction is performed in this process, or a γ table that outputs the input as is is selected. Output is made.

As shown in FIG. 15, the test pattern 2 includes M patch groups 1101 and 1105, Bk patch groups 1102 and 1106, and Y patch groups 1103 and 1.
107 and C patch groups 1104 and 1108, each consisting of a gradation patch group of 64 gradations in 4 rows and 16 columns. Different from the test pattern 1, the gradations of the low density region are assigned to these 64 gradation patches in a concentrated manner, out of all 256 gradations. This is because the test pattern 2 is used for calibrating the γ correction characteristic, specifically, for updating the contents of the gamma correction unit 312, as described later. This makes it possible to satisfactorily adjust the gradation characteristics especially in the highlight portion. The patch groups 1101, 1102, 1103, and 1104 have a resolution of 200 LPI (lines / in).
ch) patch, while the patch group 1105,
1106, 1107 and 1108 have a resolution of 400L
It is composed of PI patches. Note that patch groups having the same gradation pattern may be output at two resolutions. However, if the gradation characteristics are relatively different due to the difference in resolution, the gradation pattern according to the resolution as in the present embodiment. Is preferably set.

Next, the screen shown in FIG. 10 is displayed on the operation panel. When the test pattern 2 output in response to this is placed on the platen glass 201 and the "read" key is pressed, in step S108. The test pattern 2 is read. At this time, it is determined whether the test pattern 2 is placed or not correctly by the same procedure as the case of the test pattern 1 (S10).
9) If the test pattern 2 is not placed correctly, a warning message is displayed on the operation panel (S112) as shown in FIG.
After the document is set on the platen again, the reading of step S108 is performed again.

The reading is performed in the same manner as the reading of the test pattern 1, the number of samplings per patch of the test pattern 2 is according to the number of samplings calculated in advance, and in step S110, the sampled data are averaged. RA with location information of corresponding patch
Stored in M.

Next, in steps S120 to S123,
Based on the reading results (average values) of the test patterns 1 and 2 read as described above, the maximum density adjustment relating to the main calibration and the contents of the table of the gamma correction unit are updated as follows.

First, the adjustment of the maximum density will be described.

FIG. 16 shows the relative value of the surface potential of the photosensitive drum (hereinafter simply referred to as "surface potential") and the above step S.
It is a figure which shows the relationship with the density information obtained by 106.

The photosensitive drum, which is primarily charged by the contrast potential used for forming the test pattern 1, that is, the developing bias potential, is scanned by the laser beam output from the semiconductor laser element driven at the maximum emission level. The surface potential difference of the drum is Va, and the maximum density obtained at that time is Da. In this case, in a region near the maximum density, the density value with respect to the surface potential of the photosensitive drum almost always has a linear relationship as shown by the solid line L in FIG.

However, in the two-component developing system, when the toner density in the developing unit changes and decreases, as shown by the solid line N in FIG. 16, the surface potential of the photosensitive drum is particularly high near the maximum density. The concentration value for may be non-linear. Therefore, the final maximum density is set to a target value of 1.6 with a margin of 0.1 set, and 1.7 is set as the control target value of the maximum density to determine the control amount such as the contrast potential. Here, the contrast potential Vb can be obtained using the following equation (5), where Va is the surface potential detected when the density D is measured, and ka is the two-component development system. It is a correction coefficient according to the developing method such as.

That is, in step S120,
The correction coefficient ka in the equation (5) is determined according to the developing method of this embodiment. This makes it possible to obtain the corrected contrast potential Vb using the measured maximum density D and the surface potential Va at that time.

Vb = (Va + ka) × 1.7 / Da (5)

Next, in step S121, the grid potential and the developing bias potential are obtained based on the contrast potential Vb determined so that the maximum density target value 1.7 can be obtained as described above. FIG. 17 is a diagram showing an example of the relationship between the grid potential and the surface potential of the photosensitive drum.

The grid potential Vg is set to -300 V, the surface potential Vd1 when the light emission level of the semiconductor laser element is minimized and the photosensitive drum is scanned with the laser beam, and the light emission level of the semiconductor laser element is maximized to set the photosensitive drum to the maximum value. The surface potential Vl1 when scanned with a laser beam is measured by a surface potential meter 708 (see FIG. 18). Similarly, Vd2 and Vl when the grid potential Vg is set to -700V
Measure 2. And obtained -300V and -70
By interpolating between each data of 0V and extrapolating,
The relationship between the grid potential Vg and the surface potential of the photosensitive drum can be obtained. The control for obtaining this potential data is called “potential measurement control”.

Based on the relationship of the surface potential Vd (straight line shown in FIG. 17) with respect to the grid potential thus obtained, a predetermined potential difference Vback is generated so that so-called fog toner, which adheres to the image, does not occur. (Eg 150V)
Is set to obtain the relationship of the developing bias Vdc.
The contrast potential Vb is a difference voltage between the developing biases Vdc and Vl, and the larger Vb is, the larger the maximum density can be. That is, the grid potential Vg and the developing bias potential Vdc for obtaining the contrast potential Vb obtained by the above (5) can be obtained from the relationship between Vd and Vl shown in FIG.

Next, in steps S122 and S123,
The contents of the gamma correction unit 312 are updated based on the read result of the test pattern 2 described above. Before the description, the role of the gamma correction unit 312, which is the direct target of this calibration, and the gradation by the correction unit. A method of correcting the error will be described.

FIG. 19 is a characteristic conversion chart showing an example of density reproduction characteristics.

The first area I shown in FIG. 19 shows the image reading characteristic for converting the original image into the density signal, and the second area II is
The conversion characteristic of the gamma correction unit 312 that performs gamma correction on the density signal is shown. The third area III shows the gamma characteristic of the printer, which is the relationship between the laser output signal and the output image density that is actually realized. Area IV shows the relationship between the document density and the output image density. That is, the characteristics shown in the fourth region IV are
It represents the overall gradation characteristics of this copying machine.
In this embodiment, since 8-bit digital signals for each color are handled, the number of gradations for each color is 256.

By adjusting the maximum density by setting the above-mentioned target value of the maximum density to a higher value, the gamma characteristic of the third region becomes as shown by the solid line J in FIG. On the other hand, when the control for increasing the target value of the maximum density is not performed, the gamma characteristic of the printer has a target density of 1.
It may not reach 6. That is, in the case of a printer showing the characteristics of the solid line H, the maximum density cannot be increased by the correction of the gamma correction unit 312, no matter how the gamma correction unit 312 is set.
The concentrations between are not reproducible.

That is, the gamma correction unit 312 changes the gamma characteristic of the second region II according to the degree to which the gamma characteristic of the third region III is non-linear in order to make the comprehensive characteristic of the fourth region IV linear. The gamma correction is performed with the contents of the characteristics.

In the calibration for gamma correction, the gamma conversion characteristic of the gamma correction unit 312 is
Third region II obtained from the reading result of test pattern 2
It is obtained as an inverse function of the input / output relation of the gamma characteristic H of I and updated with the content. As a result, the characteristic of the image formed by the laser output signal obtained by the gamma correction after the calibration should be the gamma characteristic H, but the above-described maximum density adjustment is performed. It has the gamma characteristic J, and as a result, a linear relationship can be obtained in the fourth region.

Specifically, in step S122,
A new gamma conversion characteristic of the gamma correction unit 312 is obtained by obtaining the relationship between the laser output signal and the measured density, that is, the gamma characteristic H of the above-mentioned third region from the read result of the test pattern 2, and obtaining the inverse function thereof in step S123. To set. More specifically, the table of the gamma correction unit 312 is updated.

The data that can be used when obtaining the gamma conversion characteristics is only the gradation value data of the output signal in which the patch of the test pattern 2 is formed and the measurement data corresponding to the gradation value data. Insufficient data is compensated by interpolation so that the laser output level corresponds to all 256 levels from 0 to 255.

As described above, according to this embodiment, it is possible to control the image density and gradation reproducibility by calibration, and form a full-color image with stable image density and gradation reproducibility. At the same time, the number of times of sampling in reading the test pattern is changed according to the number of times of using the drum, and the like, so that it is possible to perform good calibration in which influences such as uneven streaks are arranged without decreasing throughput.

<Other Embodiments> The present invention is as described above.
It may be applied to a system composed of a plurality of devices (for example, a host computer, an interface device, a reader, a printer, etc.) or an apparatus composed of one device (for example, a copying machine, a facsimile machine).

Further, the functions of the above-described embodiment are realized by a computer in an apparatus or system connected to the various devices so as to operate the various devices so as to realize the functions of the above-described embodiment in FIG. The program of the software for supplying the program code is supplied, and the computer (CPU or MPU) of the system or the apparatus is operated by operating the various devices according to the stored program, which is also included in the scope of the present invention.

Further, in this case, the program code itself of the software realizes the functions of the above-described embodiments, and the program code itself and means for supplying the program code to the computer, for example, such program code The stored storage medium constitutes the present invention.

A storage medium for storing the program code is, for example, a floppy (registered trademark) disk, a hard disk, an optical disk, a magneto-optical disk, a CD-R.
An OM, a magnetic tape, a non-volatile memory card, a ROM or the like can be used.

Further, the computer executes the supplied program code so that not only the functions of the above-described embodiments are realized, but also the OS (operating system) in which the program code runs on the computer, or another Needless to say, the program code is also included in the embodiments of the present invention when the functions of the above-described embodiments are realized in cooperation with application software or the like.

Further, the supplied program code is stored in the memory provided in the function expansion board of the computer or the function expansion unit connected to the computer, and then the function expansion board or function expansion unit is instructed based on the instruction of the program code. Needless to say, the present invention also includes a case where the CPU or the like included in the above performs a part or all of the actual processing and the functions of the above-described embodiments are realized by the processing.

[0098]

As is apparent from the above description, according to the present invention, when calibration is executed, the factors affecting the image forming characteristics are counted, and the number of times used for the image forming is counted. Since the test pattern is read a number of times, it is possible to eliminate the influence of streak unevenness that appears in the test pattern, for example, which cannot be eliminated by calibration, by multiple times of the above-mentioned reading, and the streak unevenness may appear. The number of times of reading can be changed according to the degree, and useless reading can be suppressed.

As a result, it becomes possible to execute a good calibration in which influences such as stripe unevenness are arranged, without lowering the throughput.

[Brief description of drawings]

FIG. 1 is a diagram showing a mechanical configuration of a copying machine according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration of image processing in the copying machine.

FIG. 3 is a chart showing write and read timings of a compression / expansion circuit in the image processing configuration.

FIG. 4 is a circuit diagram showing a configuration of a PWM circuit in the copying machine.

FIG. 5 is a signal waveform diagram illustrating pulse width modulation in the PWM circuit.

FIG. 6 is a flowchart showing a control relating to calibration executed in the copying machine.

FIG. 7 is a diagram showing a display example of an operation panel when calibration is executed in the copying machine.

FIG. 8 is a diagram showing a display example of an operation panel when calibration is executed in the copying machine.

FIG. 9 is a diagram showing a display example of an operation panel when calibration is executed in the copying machine.

FIG. 10 is a diagram showing a display example of an operation panel when calibration is executed in the copying machine.

FIG. 11 is a diagram showing a display example of an operation panel when calibration is executed in the copying machine.

FIG. 12 is a diagram showing a display example of an operation panel when calibration is executed in the copying machine.

FIG. 13 is a diagram showing a test pattern output by the calibration.

FIG. 14 is a diagram illustrating sampling points in reading the test pattern.

FIG. 15 is a diagram showing another test pattern output by the calibration.

FIG. 16 is a diagram showing the relationship between the surface potential of the photosensitive drum and the image density relating to the maximum density in image formation.

FIG. 17 is a diagram for explaining the setting of the contrast potential and the like relating to the surface potential and the image density.

FIG. 18 is a diagram showing a detailed configuration of an image forming unit in the copying machine.

FIG. 19 is a characteristic conversion chart showing an example of density reproduction characteristics in the copying machine.

[Explanation of symbols]

104 Luminance density conversion circuit 105 character / line drawing detection circuit 106 Output masking / UCR circuit 107 compression / expansion circuit 108 memory 112 Masking circuit 208 CCD 212 image processing unit 312 γ (gamma) correction circuit

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) G03G 15/043 G03G 21/00 372 5C077 21/14 B41J 3/00 M 5C079 H04N 1/23 H04N 1/40 D 1/46 1/46 Z 1/60 F term (reference) 2C362 CA18 CA24 CA25 CA29 CA30 CB73 EA00 2H027 DA01 DA09 DA15 DA24 DA32 DA44 DA45 DB03 DE02 DE07 DE09 EA01 EA02 EA05 EB04 EC03 EC04 EC06 EC07 EC11 EC14 EC18 EC20 ED03 ED09 ED11 EE01 EE07 EE08 EF06 EF09 GA23 GA47 GA54 GB04 GB09 GB19 HA07 ZA07 2H030 AA02 AA03 AB02 AD02 AD13 AD17 BB02 BB13 BB16 BB34 BB36 2H076 AB05 AB06 DD08A02 DD01 A07 BB06 A08 DD07 A01 BB06 DA08 A08 DA02 DA04 A08 DA04 DA04 A08 DA08 DA04 A08 GG12 GG13 5C077 LL19 MM27 MP08 PP33 PP37 PP42 PP46 PQ17 RR18 TT06 5C079 HA18 HB03 KA04 LB00 MA10 NA21 PA02

Claims (12)

[Claims] 1. An image forming apparatus for forming an image on a medium, comprising: a number-of-uses counting means for counting the number of times an element constituting the image forming apparatus and affecting the image forming characteristic is used for image forming. The test pattern output means for forming and outputting a test pattern during calibration for making the image forming characteristics constant, and the test pattern output by the test pattern output means for forming an image are counted by the use number counting means. An image forming apparatus comprising: a reading unit that reads the number of times according to the number of times. 2. The image forming apparatus according to claim 1, wherein the reading unit reads the number of times according to the number of times of counting by changing the reading position. 3. The method according to claim 1, further comprising a calibration execution unit that performs calibration based on a result read by the reading unit.
The image forming apparatus according to item 1. 4. The image forming apparatus performs image formation using yellow, cyan, magenta, and black color materials, and the test pattern is output for each of the yellow, cyan, magenta, and black color materials. 4. The image forming apparatus according to claim 1, wherein the reading unit performs reading for each test pattern of each color material. 5. The image forming apparatus according to claim 1, wherein the calibration unit uses an average of a plurality of readings read by the reading unit as the reading result. 6. A calibration method for making an image forming characteristic of an image forming apparatus for forming an image on a medium constant, wherein an image of an element that constitutes the image forming apparatus and influences the image forming characteristic is formed. There is a step of counting the number of times used for forming, performing image forming output of a test pattern when performing calibration, and reading the image forming output test pattern as many times as the counted number of times of use. A calibration method characterized in that 7. The calibration method according to claim 6, wherein in the reading step, the number of times of reading corresponding to the number of times of counting is performed by changing the reading position. 8. The calibration method according to claim 6, further comprising a step of performing calibration based on a result read in the reading step. 9. The image forming apparatus forms an image using yellow, cyan, magenta, and black color materials, and the test pattern is output for each of the yellow, cyan, magenta, and black color materials. 9. The calibration method according to claim 6, wherein the reading step is performed for each test pattern of each color material. 10. The calibration method according to claim 6, wherein the calibration execution step uses an average of a plurality of readings read in the reading step as the reading result. 11. A program for executing calibration of an image forming apparatus for forming an image on a medium, wherein the processing executed by the program configures the image forming apparatus and influences the image forming characteristic. The number of times that the element is used for image formation is counted, the test pattern is image-formed and output when the calibration is executed, and the test pattern that is image-formed and output is read the number of times according to the counted number of times of use. A program having steps to perform. 12. A storage medium for storing a program for executing calibration of an image forming apparatus for forming an image on a medium, wherein the processing executed by the program constitutes the image forming apparatus, The number of times an element that influences the formation characteristics is used for image formation is counted, a test pattern is image-formed and output at the time of executing calibration, and the test pattern output by image formation is output according to the counted number of times of use. A program characterized by having a step of reading a predetermined number of times.