JP2005265969A - Image forming apparatus and its control method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of suppressing a change in image quality due to characteristic change of an image forming element after power source input. <P>SOLUTION: A correction amount is calculated on the basis of a difference ▵D between the characteristics of a recording material image of a prescribed pattern formed on an image carrier when powered up and previously stored reference characteristics, and an amount used (n) after power source input in the image forming apparatus (S24), and<SB>γ</SB>LUT data is corrected based on the calculated correction amount (S25). <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus and a control method thereof, and for example, relates to image control when forming a color image.

  As a method for adjusting image processing characteristics of an image forming apparatus such as a copying machine or a printer using electrophotographic technology (hereinafter referred to as “image control method”), the following method is known (for example, Patent Document 1). reference).

  That is, when the image forming apparatus is turned on (after the image forming apparatus is started and its warm-up operation is completed), an image having a specific pattern is formed on an image carrier such as a photosensitive drum. Then, the density of the formed pattern is read, and based on the read density value, the operation of a circuit for determining image forming conditions such as a gamma correction circuit is changed to stabilize the quality of the formed image. is there.

JP-A-4-343573

  In Patent Document 1, image control is executed when the power is turned on. However, when a general usage pattern is assumed, most of the power is turned on in the morning and left overnight after the power is turned off the night before. It is thought that there are many. In this case, due to the effect of being left for a long time, each element (image forming element) related to image formation such as a photoconductor and a developer is in a peculiar state, so image formation determined by performing image control at power-on The condition is determined based on the unique state of the imaging element. For this reason, when the image forming apparatus starts to be used, when the image forming element is in a steady state, or when the air conditioning of the room where the image forming apparatus is installed starts functioning, the image control is performed in a relatively short period of time. There is a problem that the characteristics of the image forming element change, and as a result, image quality fluctuations such as density and color appear. In order to suppress such image quality fluctuations, image control may be performed frequently, but there is a problem that productivity decreases.

  The present invention has been made in view of the above-described problems of the prior art, and mainly provides an image forming apparatus that can suppress image quality fluctuations after power-on by simple image control, and a control method therefor. Objective.

  An object of the present invention is to provide an image forming apparatus for forming a recording material image on an image carrier based on image data and recording material image forming conditions, and transferring and fixing the formed recording material image on a recording medium. Detecting means for detecting the characteristics of the recording material image having a predetermined pattern formed thereon, determining means for determining the recording material image forming condition based on the detected characteristics of the recording material image, and detecting means when the power is turned on The recording material image of the predetermined pattern detected when the power is turned on based on the characteristics of the recorded material image of the predetermined pattern, the reference characteristics stored in advance, and the usage amount since the power of the image forming apparatus is turned on. This is achieved by an image forming apparatus comprising correction means for correcting the recording material image forming conditions determined by the determining means based on the characteristics.

  The above-described object is a control method for an image forming apparatus that forms a recording material image on an image carrier based on image data and recording material image forming conditions, and transfers and fixes the formed recording material image to a recording medium. A detection process for detecting the characteristics of the recording material image of a predetermined pattern formed on the image carrier, a determination process for determining the recording material image forming conditions based on the detected characteristics of the recording material image, and turning on the power. The predetermined pattern detected at the time of power-on based on the characteristics of the recording material image of the predetermined pattern sometimes detected by the detecting means, the reference characteristics stored in advance, and the usage amount since the power-on of the image forming apparatus And a correction step of correcting the recording material image forming condition determined by the determining means based on the characteristics of the recording material image.

  With the above-described configuration, the image forming apparatus according to the present invention can suppress image quality fluctuations after power-on by simple image control.

Hereinafter, the present invention will be described in detail by way of preferred embodiments with reference to the drawings.
● (first embodiment)
[Constitution]
FIG. 1 is a diagram illustrating a schematic configuration example of a color copying machine as an example of an image forming apparatus according to an embodiment of the present invention. In the figure, the copying machine is formed of a reader unit A for reading a document and a printer unit B for outputting the document read by the reader unit A by an electrophotographic method.

Reader unit A document 101 placed on the document table glass 102 of the reader unit A is illuminated by a light source 103, and reflected light from the document 101 passes through an optical system 104 to an image sensor (CCD sensor in this embodiment) 105. To form an image. The CCD sensor 105 is composed of, for example, CCD line sensors arranged in three rows, and one line sensor generates one color component signal of red, green, and blue of reflected light, whereby three color component signals are generated. To get. The light source 103, the optical system 104, and the CCD sensor 105 are moved as a reading optical system unit in the direction of the arrow shown in FIG. 1 (radial scanning direction), and the image of the original 101 is sequentially converted into electrical signals (image signals) for each line. Convert.

  The white level of the positioning member 107 and the CCD sensor 105 that prevent one side of the original 101 from contacting one side of the original 101 is determined around the original platen glass 102, and shading correction in the thrust direction of the CCD sensor 105 is performed. For this purpose, a reference white plate 106 is disposed.

  The image signal for each line obtained by the CCD sensor 105 is subjected to image processing by the reader image processing unit 108 and then sent to the printer unit B, where it is processed by a printer control unit 109 described later.

FIG. 2 is a block diagram illustrating a configuration example of the reader image processing unit 108.
As shown in FIG. 2, the image signals R, G, and B output from the CCD sensor 105 are input to the analog signal processing circuit 201, and after the gain and offset are adjusted, the A / D converter 202 performs, for example, Each color is converted into 8-bit digital image signals R1, G1, and B1. The image signals R1, G1, and B1 are input to the shading correction circuit 203, subjected to known shading correction using the read signal of the reference white plate 106 for each color, and output as image signals R2, G2, and B2. .

  The clock generator 211 generates a clock CLK for each pixel. The address counter 212 counts CLK and generates and outputs a main scanning address signal for each line. The decoder 213 decodes the main scanning address signal, a line-unit CCD drive signal such as a shift pulse and a reset pulse, a signal VE representing an effective area in the image signal for one line output from the CCD sensor 105, and line synchronization. A signal HSYNC is generated. Note that the address counter 212 is cleared by HSYNC and starts counting the main scanning address of the next line.

  The line sensors constituting the CCD sensor 105 are arranged at a predetermined distance from each other in the sub-scanning direction. Therefore, the line delay 204 corrects a spatial shift (position shift) in the sub-scanning direction. Specifically, for example, by delaying the R and G signals in the sub-scanning direction with respect to the B signal, RGB signals R3, G3, and B3 obtained by reading the same line of the document can be obtained.

  The input masking circuit 205 converts a color space (reading color space) of an image signal determined by the spectral characteristics of the RGB filter used for each line sensor of the CCD sensor 105 into a predetermined color space (for example, sRGB) by matrix calculation of the following equation. Or the standard color space of NTSC) and output as image signals R4, G4, and B4.

  The LOG conversion circuit 206 includes a look-up table (LUT) ROM, and converts the image signals (luminance signals) R4, G4, and B4 from the input force masking circuit 205 into density signals of C0, M0, and Y0. The line delay memory 207 includes a line delay amount C0, M0 until a determination signal such as UCR (under color removal), FILTER, and SEN is generated and output from the R4, G4, and B4 image signals by a black character determination unit (not shown). And Y0 image signals are delayed and output as C1, M1, and Y1.

  The masking UCR circuit 208 extracts the black signal Bk from the input Y1, M1 and C1 primary color signals, and further performs an operation for correcting the color turbidity of the recording material of the printer unit B, and Y2 for each reading operation. , M2, C2, or Bk2 image signals are sequentially output with a predetermined bit width (for example, 8 bits). The gamma correction circuit 209 corrects the density of the image signal to match the ideal gradation characteristics of the printer unit B. The output filter 210 performs edge enhancement or smoothing processing on the image signal.

  The M4, C4, Y4, and Bk4 frame sequential image signals obtained by these processes are sent to the printer control unit 109 of the printer unit B, converted into pulse width modulated pulse signals, and density recording is performed.

  In FIG. 2, the CPU 214 uses the RAM 215 as a work memory and performs control and image processing of each component of the reader unit A including the reader image processing unit 108 in accordance with a program stored in the ROM 216. The operation unit 217 is a user interface provided in the reader unit A, for example, and the operator inputs instructions and processing conditions to the CPU 214 via the operation unit 217. The display 218 displays the operation state of the entire image forming apparatus including the reader unit A and the printer unit B, set processing conditions, and the like.

FIG. 3 is a timing chart of each signal in the reader image processing unit 108.
In FIG. 3, VSYNC is an image effective section signal in the sub-scanning direction. Image reading (scanning) is performed in a section of logic “1” (high level), and output signals of C, M, Y, and Bk are sequentially generated. Is done. VE is an image effective section signal in the main scanning direction, and the timing of the main scanning start position is taken in the section of logic “1”, and is mainly used for line count control of line delay. CLK is a pixel synchronization signal, and image data is transferred at the rising timing of “0” → “1”.

● Printer part B
Returning to FIG. 1, the configuration of the printer unit B will be described. The surface of the photosensitive drum 4 rotating in the direction of the arrow shown in the figure is uniformly charged by the primary charger 8. The printer control unit 109 includes a laser driver and outputs a pulse signal corresponding to the image data input from the reader unit A to the laser light source 110. The laser light source 110 outputs laser light corresponding to the pulse signal input from the printer control unit 109. The laser beam is reflected by the polygon mirror 1 and the mirror 2 and scans the surface of the charged photosensitive drum 4. An electrostatic latent image is formed on the surface of the photosensitive drum 4 by scanning with the laser beam.

  The electrostatic latent image formed in units of color components on the surface of the photosensitive drum 4 is developed with toner of each color for each color by the developing device 3. In this embodiment, two-component toner is used, and the developing devices of the respective colors are arranged around the photosensitive drum 4 in the order of black Bk, yellow Y, cyan C, and magenta M from the upstream. Then, a developing device having a developer corresponding to the color component of the electrostatic latent image approaches the photosensitive drum 4 to develop the electrostatic latent image, and forms a toner image on the photosensitive drum 4.

  The toner images of the respective colors formed on the photosensitive drum 4 are sequentially transferred onto the recording paper 6 wound around the transfer drum 5. The transfer drum 5 rotates once every time the toner image is transferred. When the toner image is rotated a total of four times, the four color toner images are transferred onto the recording paper 6 and superimposed. When the transfer is completed, the recording paper 6 is separated from the transfer drum 5 and the toner is fixed by the fixing roller pair 7 to complete a full-color image print.

  Further, around the photosensitive drum 4, a surface potential sensor 12 for measuring the surface potential of the photosensitive drum 4 on the upstream side of the developing device 3 (the arrow head side shown in the drawing is downstream) is not transferred on the photosensitive drum 4. A cleaner 9 for cleaning the remaining toner, and an LED light source 10 and a photodiode 11 for detecting the amount of reflected light from a toner patch (a predetermined pattern for image control) formed on the photosensitive drum 4 are arranged. ing.

FIG. 4 is a block diagram showing other constituent elements related to the configuration example of the printer control unit 109.
The printer control unit 109 includes a CPU 28, a pattern generator 29, a ROM 30, a RAM 32, a test pattern storage unit 31, a density conversion circuit 42, an LUT 25, a laser driver 26, and the like, and can communicate with the reader unit A and the printer engine 100. The CPU 28 controls the operation of the printer unit B, and controls the grid potential of the primary charger 8 and the developing bias of the developing device 3.

  The printer engine 100 includes the above-described photosensitive drum 4, the photosensor 40 including the LED 10 and the photodiode 11, the primary charger 8, the laser light source 110, the surface potential sensor 12, the developing device 3, and the like disposed around the photosensitive drum 4. Is done. Furthermore, the environmental sensor 33 which measures the moisture content (or temperature / humidity) in the air in an apparatus is provided.

Image Processing Operation The image processing operation of the printer control unit 109 will be further described with reference to FIG.
As described above, in the reader unit A, the luminance signals R, G, and B of the image obtained by the CCD sensor 105 are converted into the field sequential density signals C4, M4, Y4, and K4 by the reader image processing unit 108. . The converted density signal is a LUT (γLUT) so as to be a signal corresponding to the gamma (γ) characteristics of the printer unit B at the time of initial setting, that is, so that the density of the original image matches the density of the output image. 25.

  FIG. 6 is a quadrant illustrating the tone reproduction. The first quadrant is the reading characteristic of the reader unit A that converts the density of the original image into a density signal, the second quadrant is the conversion characteristic of the LUT 25 for converting the density signal into a laser output signal, and the third quadrant is the laser output. The recording characteristics of the printer unit B that converts the signal into the density of the output image, and the fourth quadrant indicates the relationship between the density of the original image and the density of the output image, that is, the tone reproduction characteristics of the entire image forming apparatus shown in FIG. . FIG. 6 shows a case where the number of gradations is 256, assuming that the document image density is processed by an 8-bit digital signal.

  In order to make the gradation characteristic of the entire image forming apparatus, that is, the gradation characteristic of the fourth quadrant linear, the non-linear printer characteristic shown in the third quadrant is corrected by the characteristic of the γLUT 25 shown in the second quadrant. The image signal whose tone characteristics are converted by the γLUT 25 is converted into a pulse signal corresponding to the dot width by a pulse width modulation (PWM) circuit 26 a of the laser driver 26, and an LD driver 26 b that controls on / off of the laser light source 110. Sent to. In this embodiment, a gradation reproduction method using pulse width modulation is used for all colors Y, M, C, and Bk.

  Then, an electrostatic latent image having a predetermined gradation characteristic in which the gradation is controlled by the change in the dot area is formed on the photosensitive drum 4 by the scanning of the laser light output from the laser light source 110. The gradation image is reproduced through the processes of development, transfer and fixing.

[First control system]
The image forming apparatus according to the present embodiment includes a first control system relating to stabilization of image reproduction characteristics of a system including both the reader unit A and the printer unit B, and an image reproduction characteristic of the printer unit B alone performed when the power is turned on. And a second control system for stabilization.

  First, here, as image control in a sequence different from normal image formation for forming an image on recording paper, a first control system relating to stabilization of image reproduction characteristics of a system including both the reader unit A and the printer unit B, Specifically, a control system for calibrating (image control) the printer unit B using the reader unit A will be described.

FIG. 7 is a flowchart showing an example of calibration processing by the first control system, which is realized by the cooperation of the CPU 214 that controls the reader unit A and the CPU 28 that controls the printer unit B.
When the operator presses a mode setting button “automatic gradation correction” provided on the operation unit 217, for example, the calibration process shown in FIG. 7 is started. In the present embodiment, the display 218 provided in the operation unit 217 is configured by a liquid crystal operation panel (touch panel display) with a touch sensor, as shown in FIGS.

  First, the start button 81 of the test print 1 shown in FIG. When the operator presses the “test print 1” button, the start button 81 is highlighted (FIG. 8C), and for example, the test print 1 having the format shown in FIG. 11 is printed out by the printer unit B (S51). When the start button 81 is pressed, the CPU 214 determines the presence or absence of a recording sheet for forming the test print 1, and displays a warning as shown in FIG. . Note that pattern data for forming a test print is stored in the test pattern storage unit 31.

  The initial value registered in advance is used as the contrast potential when the test print 1 is formed. In addition, the image forming apparatus according to the present embodiment includes a plurality of recording paper cassettes, and a plurality of types of recording paper sizes such as B4, A3, A4, and B5 can be selected. However, the recording paper used in this calibration process is a so-called large size paper, that is, B4, A3, 11 ″ × 17 ″ or LTR in order to avoid errors in the vertical reading and horizontal setting in the subsequent reading operation. The size is set to be used.

  The test pattern 1 shown in FIG. 11 includes a belt-like pattern (band pattern) 61 and patch patterns 62 of each color according to intermediate gradation densities for four colors Y, M, C, and Bk. By visually inspecting the pattern 61, it is confirmed that there are no streaky abnormal images, density unevenness, and color unevenness.

  Note that the sizes of the gradation patterns 71 and 72 included in the patch pattern 62 and the test pattern 2 (FIG. 12) described later are set so as to fall within the reading range of the CCD sensor 105 in the thrust direction.

  If an abnormality is recognized by visual inspection of the belt pattern 61, it is necessary to print the test print 1 again, and when an abnormality is recognized again, it is necessary to perform maintenance by calling a service man call, that is, a service man. It is also possible to read the belt pattern 61 with the reader unit A and automatically determine whether or not to perform subsequent control based on the density information in the thrust direction.

  On the other hand, the patch pattern 62 is a maximum density patch for each color of Y, M, C, and Bk, that is, a patch pattern corresponding to the density signal value 255.

  When the output of the test pattern 1 is completed, the CPU 214 displays a “read” button 91 and an operator operation guidance message on the display unit 218 so that the test print 1 is read by the reader A (FIG. 9A). In accordance with the message, the operator places the output test print 1 on the platen glass 102 as shown in FIG. 13, for example, and presses a “read” button 91.

  FIG. 13 is a diagram showing a state where the document table 102 on which the test print 1 is placed is viewed from above, and a wedge-shaped mark T at the upper left is a document alignment mark. Then, an operation guidance message is displayed on the display 218 so that the operator sets the test print 1 so that the band pattern 61 is arranged on the abutment mark T side and the front and back of the print are not mistaken ( FIG. 9A). In other words, the operation guidance has a purpose of preventing erroneous control due to the placement error of the test print 1.

  When the patch pattern 62 is read, the first density gap point is obtained at the corner of the belt pattern 61 (point A in FIGS. 11 and 13) by gradually scanning from the mark T. The relative position of each patch of the patch pattern 62 is determined from the coordinates of the density gap point A, and the density of the patch pattern 62 is read (S52). While the test print 1 is being read, the display as shown in FIG. 9B is performed, and when the test print 1 has an incorrect orientation and position and cannot be read, a message as shown in FIG. 9C is displayed. Then, the test print 1 is read again by causing the operator to correct the layout of the test print 1 and press the “read” key 91.

In order to convert the RGB value obtained from the patch pattern 62 into an optical density, the following equation is used. In order to make it the same value as a commercially available densitometer, it adjusts with correction coefficient km, kc, ky, kk. Alternatively, a separate LUT may be prepared, and RGB luminance information may be converted into MCYBk density information without performing calculations.
M = −km × log ₁₀ (G / 255)
C = −kc × log ₁₀ (R / 255)
Y = −ky × log ₁₀ (B / 255). . . (2)
Bk = −kk × log ₁₀ (G / 255)

Next, a method for correcting the maximum density from the obtained density information will be described.
FIG. 15 is a diagram showing the relationship between the relative drum surface potential of the photosensitive drum 4 and the image density obtained by the above-described calculation.
When the test print 1 is printed, the contrast potential (development bias potential and the photosensitive drum 4 exposed to the laser beam modulated with the maximum signal value (255 for 8 bits) after the photosensitive drum 4 is primarily charged). the difference between the surface potential) in a of FIG. 15, the image density obtained from patch pattern 62 printed with a concentration 255 is D _a.

In the maximum density region, the image density with respect to the relative drum surface potential is almost linear as shown by the solid line L in FIG. However, in the two-component development system, when the toner density occupying the developer in the developing device 3 decreases, the image density with respect to the relative drum surface potential becomes non-linear in the maximum density area as shown by the broken line N in FIG. There is. Accordingly, in the example of FIG. 15, the final maximum density target value is set to 1.6, but the control target value of the maximum density is set to 1.7 in consideration of a margin of 0.1. To decide. The contrast potential B corresponding to the control target maximum density is obtained from the following equation.
B = (A + Ka) × 1.7 / D _A. . . (3)
In equation (3), Ka is a correction coefficient, and it is preferable to optimize the value depending on the type of development method.

  Since the density of the original image and the output image does not match unless the contrast potential of the electrophotographic method is set according to the environment, for example, the output (that is, absolute moisture) of the environmental sensor 33 that monitors the moisture amount in the apparatus described above, for example. 16), the value of the contrast potential A is set as shown in FIG.

In order to correct the contrast potential A to the contrast potential B, a correction coefficient Vcont. The rate is stored in a backed up RAM (NVRAM) or the like.
Vcont. ratel = B / A

  The image forming apparatus according to the present embodiment monitors the amount of water in the environment by the environment sensor 33, for example, every 30 minutes. Each time the value of the contrast potential A is determined based on the detected amount of water, A × Vcont. The rate is calculated to obtain the contrast potential B.

  Next, a method for obtaining the grid potential and the developing bias potential from the contrast potential will be briefly described. FIG. 17 is a diagram showing the relationship between the grid potential and the surface potential of the photosensitive drum 4.

First, at the grid potential of −200 V, the surface potential V _L of the photosensitive drum 4 that is exposed with the laser light modulated with the minimum signal value, and the surface of the photosensitive drum 4 that is exposed with the laser light modulated with the maximum signal value. The potential V _H is measured by the surface potential sensor 12. Similarly, _VL and _VH are measured when the grid potential is -400V. Then, the relationship between the grid potential and the surface potential is obtained by interpolating and extrapolating -200V data and -400V data. Note that the control for obtaining the potential data is referred to as potential measurement control.

Next, the _{V L,} provided the difference in Vbg which toner fog is set so as not to generate (e.g. 100 V) to set the developing bias _{V DC} to the image. Contrast potential Vcont is a developing bias V _DC, the difference voltage potential V _H on the photosensitive drum which is photosensitive at a pulse signal corresponding to the maximum density, the maximum density as Vcont is large increases are as described above .

  The grid potential and the developing bias for obtaining the contrast potential B obtained by calculation can be obtained from the relationship shown in FIG. Therefore, the CPU 28 obtains the contrast potential so that the maximum density is 0.1 higher than the final target value, and determines the grid potential and the development bias potential so that the contrast potential can be obtained (S53).

Next, it is determined whether or not the determined contrast potential is within the control range (S54). If it is out of the range, it is determined that there is an abnormality in the developing device 3 or the like, and the developing device 3 of the corresponding color is determined. Set an error flag to be checked. The state of the error flag can be viewed by a serviceman in a predetermined service mode. Further, in the case of an abnormality, the contrast potential is corrected as close as possible within the control range, and the control is continued (S55).
The CPU 28 controls the grid potential and the developing bias so that the contrast potential set in this way is obtained (S56).

FIG. 27 shows the density conversion characteristics after the control. In the present embodiment, the printer characteristic in the third quadrant becomes a solid line J by the control for setting the maximum control density (1.7) higher than the final target value (1.6). If such control is not performed, there is a possibility that the printer characteristics such that the maximum control density does not reach the target density (1.6) as indicated by the broken line H may be obtained. When the printer characteristic is a broken line H, the maximum density cannot be increased by the LUT 25. Therefore, the density region between the density _DH and 1.6 cannot be reproduced regardless of how the LUT 25 is set. As shown by the solid line J, if the printer characteristic is slightly higher than the maximum density, the density reproduction range is guaranteed by the correction of the LUT 25 as shown in the total gradation characteristic of the fourth quadrant.

  When the setting of the grid potential and the developing bias is completed, as shown in FIG. 10A, a print start button 150 for the test print 2 (“test print 2” button) and an operation guidance message are displayed on the display 218. When the operator presses the “test print 2” button, the test print 2 shown in FIG. 12 is printed out (S57). During printing, the state of the display unit 218 is as shown in FIG.

  As shown in FIG. 12, the test print 2 includes a gradation patch group in which patches of 4 × 16 (for 64 gradations) are arranged for each color of Y, M, C, and Bk. The 64 gradations are selected by focusing on the gradations in the low density region from the 256 gradations, and by thinning out the gradations in the high density region. This is because the gradation characteristics particularly in the highlight portion are adjusted favorably.

  In FIG. 12, a patch pattern 71 is a patch group having a resolution of 200 lpi (line / inch), and a patch pattern 72 is a patch group having a resolution of 400 lpi. Image formation at each resolution is realized by preparing a plurality of periods of signals such as triangular waves used for comparison with the image signal to be processed in the pulse width modulation circuit 26a.

Note that the image forming apparatus of the present embodiment forms a gradation image such as a photographic image at 200 lpi and a binary image such as a character or line drawing at 400 lpi based on the output signal of the black character determination unit described above. Patterns with the same gradation level may be output at these two types of resolution, but if the difference in resolution greatly affects the gradation characteristics, it is preferable to output a pattern with gradation levels according to the resolution. .
The test print 2 is printed based on the image signal generated from the pattern generator 29 without operating the LUT 25.

  FIG. 14 is a diagram showing a state in which the document table 102 on which the test print 2 is placed is viewed from above, and a wedge-shaped mark T at the upper left is a document alignment mark. Then, an operation guidance message is displayed on the display 218 so that the operator sets the test print 2 so that the Bk patch pattern is placed on the contact mark T side and the front and back of the print are not mistaken ( FIG. 10 (c)). In other words, the operation guidance has a purpose of preventing erroneous control due to the placement error of the test print 1.

  When the patch patterns 71 and 72 are read, the first density gap point is obtained at the corner of the patch pattern 72 (point B in FIGS. 12 and 14) by gradually scanning from the contact mark T. The relative positions of the patches of the patch patterns 71 and 72 are determined from the coordinates of the density gap point B, and the densities of the patch patterns 71 and 72 are read (S58). During the reading of the test print 2, a display as shown in FIG.

  As shown in FIG. 18, the reading value of one patch (for example, patch 73 shown in FIG. 12) is 16 points inside the patch, and the average value of the values obtained by reading the 16 points is used. Note that the number of reading points for calculating the average value is preferably optimized in accordance with the reader and the printer unit.

  FIG. 19 is a diagram illustrating the relationship between the output density obtained by converting the RGB signal obtained from each patch into a density value by the optical density conversion method described above and the laser output level (image signal value). . Then, as shown by the vertical axis on the right side of FIG. 19, the background density (for example, 0.08) of the recording paper is set to 0 level, and the target value 1.60 of the maximum density is normalized to 255 level.

  If the density of the read patch is specifically high as shown by point C in FIG. 19 or specifically low as shown by point D, the stain on the platen glass 102 or the test pattern Possible failure. In that case, the slope between the adjacent output densities is corrected by a limiter so that the relationship between the output density and the laser output level is kept continuity. For example, if the slope between output densities exceeds 3, the slope is fixed at 3, and the data with a negative slope is set to the same value as that of one low density patch.

In order to correct such printer characteristics and make the gradation characteristics of the entire image forming apparatus linear, a conversion characteristic opposite to that shown in FIG. 19 may be set in the γLUT 25 (S59). That is, the density level (vertical axis in FIG. 19) may be set to the input level (density signal in FIG. 6), and the laser output level (horizontal axis in FIG. 19) may be set to the output level (laser output signal in FIG. 6). For levels that do not correspond to patches, values are obtained by interpolation. At this time, a condition is set so that a zero input level is a zero output level.
The contrast potential control and gamma conversion table creation by the first control system are thus completed, and the display as shown in FIG.

[Supplementary control of gradation]
Next, correction of gradation after control by the first control system will be described.
The image forming apparatus according to the present embodiment corrects the maximum density with respect to environmental fluctuations by contrast potential control using the first control system described above. Further, the image forming apparatus further performs tone correction (“tone control supplement control”). Call).

  Considering a case where an environmental change occurs in a state where the first control system is disabled, the ROM 30 includes a table of a plurality of types of LUTs 25 corresponding to the environment (for example, the amount of water) as shown in FIG. Data is stored.

Then, the control by the first control system is performed, and the table data (referred to as “LUT 1 ”) of the LUT 25 obtained as a result, and the moisture amount at that time are non-volatile such as the battery-backed area of the RAM 32 Save it in the storage area. The table data stored in the RAM 32 and corresponding to the amount of moisture in the ROM 30 is referred to as LUT A.

Thereafter, every time the environment changes, acquires table data in ROM30, corresponding to a water content of that time (referred to as "LUT B"), using a LUT A and LUT B, the LUT 1 as follows to correct. That is, by adding the difference between LUT B and LUT A corresponding to the change in moisture content to LUT 1 , it is possible to obtain the appropriate table data LUT present of LUT 25 without performing control by the first control system. .
LUTpresent = LUT 1 + (LUT B -LUT A). . (4)
By such supplementary control, the input / output characteristics of the image forming apparatus are linearly corrected. As a result, variations in density gradation characteristics among the apparatuses are suppressed, and the standard state can be easily set.

By releasing such supplementary control to the user of the image forming apparatus, the gradation control can be performed as necessary when it is determined that the gradation characteristics of the image forming apparatus have deteriorated. The gradation characteristics of the system including both of the above can be easily corrected.
Furthermore, the correction for the environmental variation as described above can be appropriately performed.

  Of course, since the service person can switch the validity / invalidity of the first control system, during the maintenance of the image forming apparatus, the first control system is invalidated and the state of the image forming apparatus is judged easily and in a short time. be able to. When the first control system is disabled, the standard contrast potential of the model and the table data of the LUT 25 are read from the ROM 30 and set in the CPU 28 and the LUT 25. Accordingly, during maintenance, the deviation of the characteristics from the standard state becomes obvious, and the optimum maintenance can be performed efficiently.

[Second control system]
Next, a second control system relating to the stabilization of the image reproduction characteristics of the printer unit B alone performed when the power is turned on, which is a feature of the present invention, will be described.
The second control system detects the density of the patch (recording material density) formed on the photosensitive drum 4 and corrects the LUT 25 to stabilize the image reproducibility. The density of the patch formed on the photosensitive drum 4 means the recording material density of an image formed by developing a predetermined electrostatic latent image.

  FIG. 21 is a block diagram illustrating a configuration related to processing of an output signal of the photosensor 40 including the LED 10 and the photodiode 11 in the image forming apparatus according to the present embodiment. In the photosensor 40, the reflected light (near infrared light) emitted from the LED 10 and input to the photodiode 11 is converted into an electric signal in the range of 0 to 5 V, for example, and output. This electric signal is converted into an 8-bit (0 to 255) digital signal by the A / D conversion circuit 41, and converted into density information by the density conversion circuit 42 having a table 42a for converting the digital signal value into the density value. .

  Note that the color toner used as the developing material in the image forming apparatus of the present embodiment is yellow, magenta, and cyan color toner, in which the color material of each color is dispersed using a styrene copolymer resin as a binder. The photosensitive drum 4 is an OPC drum having a reflectance of near infrared light (960 nm) of about 40%, but may be an amorphous silicon photosensitive drum or the like as long as the reflectance is approximately the same. Further, the photosensor 40 is configured to detect only regular reflection light from the photosensitive drum 4.

  FIG. 22 is a diagram showing the relationship between the output of the photosensor 40 and the density of the output image when the density of the patch formed on the photosensitive drum 4 is changed stepwise by the area gradation of each color. As shown in FIG. 22, in this embodiment, the output of the photosensor 40 in a state where the toner is not attached to the photosensitive drum 4 is set to 5 V, that is, 255 level. As shown in FIG. 22, the area coverage by each toner increases, the amount of reflected light decreases as the image density increases, and the output of the photosensor 40 decreases.

  From these characteristics, by preparing a table 42a (see FIG. 21) dedicated to each color and converting the sensor output to the density signal, the density can be read with high accuracy for each color.

  The second control system aims to suppress image quality fluctuations caused by fluctuations in image forming elements from the time the power is turned on and stabilize the image quality. Only the LUT 25 is corrected. This fixed period can be determined based on the time taken for an image forming element left overnight to be in a steady state after power-on, for example.

  The operation performed when the image forming apparatus of this embodiment is turned on will be described with reference to the flowchart of FIG. After the power is turned on and the warm-up operation of the image forming apparatus is completed (S11), Y, M, C, and Bk color patches are formed on the photosensitive drum 4, and the reflected light is read by the photosensor 40. It converts into density | concentration information by the structure (S12).

  In the present embodiment, a 128-level density signal is used for each color as a laser output when forming a patch. At this time, as the table data and contrast potential of the γLUT 25, values previously obtained by the first control system described above and recorded in the backup area of the RAM 32 are used.

FIG. 24 is a diagram showing a sequence for forming patches on the photosensitive drum 4.
In this embodiment, a photosensitive drum having a relatively large aperture is used, and in order to obtain density information accurately and efficiently in a short time, the eccentricity of the photosensitive drum 4 is taken into consideration and the point is symmetrical with respect to the axis of the photosensitive drum 4. Density information is obtained by forming patches of the same color at positions (positions facing each other on the circumference) and averaging a plurality of values obtained by measuring these patches. Further, patches of two colors are formed per circumference of the photosensitive drum 4 and, as shown in FIG. 24, the photosensitive drum 4 is rotated twice to obtain density information for four colors.

  The obtained density information is compared with the reference density information corresponding to the 128-level density signal stored in advance, and the difference ΔD is stored in the RAM 32 or the like (S13), and a transition is made to the standby state (S14). The 128-level density signal is corrected by the γLUT 25 so as to obtain the patch density 128 on the density scale obtained by normalizing the density 0 to 1.6 to 255.

  Based on ΔD, the second control system corrects the table data of the γLUT 25 created by the first control system for a certain period. The reason why the correction is performed for a certain period is that the main purpose of this control is to correct image quality fluctuations caused by fluctuations until an image forming element that is in a singular state at power-on reaches a steady state. This is because the image characteristics are stabilized in a steady state after a certain period. Therefore, ΔD is the difference between the singular state and the steady state, and the difference is reduced by using the device.

Therefore, in the present control system, the γLUT 25 is corrected by an amount α * ΔD obtained by multiplying ΔD by a function α depending on the usage status of the apparatus. The value of the function α is 1 for the first output immediately after power-on, and becomes 0 after a certain period. In the present embodiment, it is assumed that the image forming element reaches a steady state by outputting 20 sheets after turning on the power.
When α = 1 / n and n> 20, α = 0,
It was. In the present embodiment, α is a function of the number n of output sheets, but it may be a function of time or may be related to temperature / humidity or the like, and is preferably matched to the characteristics of the image forming element used by the image forming apparatus.

FIG. 25 is a flowchart for explaining output processing according to the number of output sheets from the time of power-on of the image forming apparatus according to the present embodiment.
First, when there is an output instruction, it is checked whether or not the cumulative number n of output since power-on exceeds 20 (S21). As described above, in this embodiment, α = 1 / n (S22) if the cumulative output number n since power-on is 20 or less, and α = 0 (S23) if n is greater than 20, power-on. A correction table for correcting the γLUT 25 by α * ΔD multiplied by ΔD obtained at times is created (S24). Then, the γLUT 25 is corrected using this correction table (S25), and image output is performed using the corrected γLUT 25 (S26). After the image is output, 1 is added to the cumulative output number n (S27), and it is checked whether or not the last page has been output (S28). When the output of the last page is finished, the process is finished.

  FIG. 26 is a diagram showing a general density signal correction table (γLUT correction table) when the density deviation detected from the patch formed using the 128-level density signal is ΔDx. Such a γLUT correction table is stored in advance in the ROM 30 or the like, and in the second control system, the γLUT correction table is normalized so that ΔDx becomes α * ΔD, and the characteristics of the standardized γLUT correction table are canceled. The LUT 25 is corrected by adding the table data to the table data of the LUT 25. In this embodiment, the γLUT 25 is not corrected when 20 sheets are output after the power is turned on.

  In the image control by the second control system in this embodiment, ΔD for four colors is detected and the γLUT correction of each color is performed. However, the image control by the second control system is performed after the power is turned on. Since it is a simple correction for a relatively short period until the formation element reaches a steady state, and the variation factor is not independent of each color, the γLUT correction table created from only one representative color patch is used for all colors. You may apply to. If this method is used, the time required for image control is shortened instead of a slight decrease in control accuracy.

  As described above, according to this embodiment, by correcting the γLUT 25 for a certain time from when the power is turned on until the image forming element reaches a steady state, the image forming element is left in a power-off state for a long time, for example. Even if it is in a singular state, appropriate correction is made in response to the characteristic change until the image forming element reaches the steady state, so that the density and color change after the power is turned on can be reduced without reducing productivity. It can be suppressed.

● (Second Embodiment)
The image forming apparatus according to the second embodiment of the present invention will be described below. In the present embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

  In the first embodiment, ΔD used in the control by the second control system is calculated using a 128-level density signal as a reference density signal. However, in this embodiment, the reference density determined by detecting image characteristics when the power is turned off. It calculates using a signal, It is characterized by the above-mentioned.

  To properly correct image quality variations caused by the difference between the singular state and the steady state when the image forming element is turned on (after being left for a long time in the power-off state), the characteristics between the singular state and the steady state It is important to accurately detect ΔD as a value representing the difference between the two. In the first embodiment, a specific density signal determined in advance is used as a reference density signal representing a steady state, and the status of each device is not taken into consideration. Therefore, in this embodiment, the power-off state is regarded as a steady state, and the image density at that time is detected to determine the reference density signal.

  The reference density signal determination process when the power is turned off will be described using the flowchart of FIG. This process is realized by the cooperation of the reader CPU 214 and the printer unit CPU 28 as in the other processes described above, and when it is detected that the power switch provided in the image forming apparatus is operated in the power-off state. Executed.

  First, a message “Preparing to turn off power” is displayed on the display 218 (liquid crystal operation panel), and Y, M, C, and Bk color patches are formed on the photosensitive drum 4 (S281). Next, the LED 10 of the photosensor 40 is caused to emit light, irradiate the patch on the photosensitive drum 4, and the reflected light is detected by the photodiode 11 and converted into density information (S282). The patch formation conditions, the reflected light detection method, and the method of converting the detected reflected light amount into density information may all be the same as in the first embodiment. Then, the laser output level corresponding to the obtained density information is stored as a reference density signal, for example, in the backup area of the RAM 32 (S283). Thereafter, the patch image is cleaned and a post-processing sequence at the time of normal power-off is performed (S284), the measurement of the standing time is started (S285), and then the power is turned off (S286). The measurement of the leaving time may be started, for example, by storing the date / time information at the time of power-off in the backup area of the RAM 32, or may be the time measurement start by a timer.

  When image quality control is performed by the second control system described above in the present embodiment, after the power-on process S11 in the first embodiment described in FIG. Append. This is because if the leaving time in the power-off state is not so long, the state of the image forming element has not reached the singular state, and it is considered that the image characteristics have not changed.

  In S291, the time left in the power-off state is acquired. The neglected time may be obtained from the date and time information at power-on and the date and time information at power-off stored in the backup area of the RAM 32 or may be obtained from a timer value.

  Next, it is determined whether or not the standing time is longer than a predetermined time (S292). In the present embodiment, if the standing time from power-off to power-on is less than 1 hour, it is determined that the image characteristics have not changed and image control is not performed. Therefore, if the leaving time is less than 1 hour, ΔD is not calculated, and the process proceeds to S14. If the leaving time is 1 hour or more, the process proceeds to S12, and ΔD calculation processing described in the first embodiment is performed. I do. If image quality control is not performed, the value of ΔD may be stored as 0, or a flag indicating that image quality control is not performed is stored, and the presence or absence of this flag is performed before performing the processing described with reference to FIG. May be detected to determine whether or not the γLUT 25 needs to be corrected.

  When calculating ΔD, as described in the first embodiment, each color patch of Y, M, C, and Bk is formed on the photosensitive drum 4, the reflected light is read by the photosensor 40, and the density is determined. Convert to information. Then, the obtained density information is compared with the reference density information determined when the power is turned off, and the difference ΔD is calculated and stored in the RAM 32 or the like. Thereafter, when a print instruction is issued, the γLUT 25 is corrected based on ΔD as described in the first embodiment.

  According to the second embodiment, it is possible to more accurately detect a characteristic difference between a singular state of an image forming element after being left for a long time in a power-off state such as when the power is turned on, and a normal steady state. Concentration and color stabilization can be performed. In addition, since the image quality control is performed only when necessary, the rise time of the apparatus (the time from when the power is turned on until the standby state is reached) can be shortened when the control is not necessary.

  Here, the configuration in which the neglected time is directly acquired by time information or measurement by a timer has been described. However, whether or not image control is performed is determined based on other arbitrary information that changes according to the length of the estimated time. Also good. For example, when the temperature of the fixing device is detected and the temperature is equal to or higher than a predetermined temperature, it is determined that the standing time is short enough that image control is unnecessary, or ΔD is always calculated when the power is turned on, and if the value of ΔD is less than the predetermined value It may be determined that it is not necessary to perform image control.

● (Other embodiments)
In the above-described embodiment, the case where the image control is applied to the γLUT table data has been described. However, the present invention can be similarly applied to various conditions such as a charging potential, a developing bias, laser power, or color misregistration correction. It is.

  In each of the above-described embodiments, the photosensitive drum is exemplified as an image carrier that carries an electrostatic latent image or a toner image. However, the photosensitive belt is a belt-like image carrier having a photosensitive layer on the surface. The present invention can also be applied to an image forming element using the above. The present invention is also applicable to an image forming apparatus having an intermediate transfer body to which a toner image is once transferred from a photosensitive drum in order to transfer a toner image to a recording medium such as recording paper or film. In these apparatuses, density information that is input information of the second control system may be acquired from a patch formed on a photosensitive belt or an intermediate transfer member.

  In the above-described embodiment, the configuration in which the present invention is applied to the image forming apparatus including the reader and the printer unit has been described. However, the present invention can also be applied to an image forming apparatus having no reader. In this case, the operation unit and the display unit are provided in the printer unit, and the processing related to the second control system described above is executed by the CPU 28 of the printer unit.

  In the above-described embodiment, the γLUT that is corrected by the second control system is generated by the first control system. However, the present invention also applies to an image forming apparatus that does not have the first control system. Is applicable. In this case, the γLUT prepared in advance by another method may be corrected.

  Furthermore, in the above-described embodiment, only the image forming apparatus configured by one device has been described, but an equivalent function may be realized by a system configured by a plurality of devices.

  A software program that realizes the functions of the above-described embodiments is supplied directly from a recording medium or to a system or apparatus having a computer that can execute the program using wired / wireless communication. The present invention includes a case where an equivalent function is achieved by a computer executing the supplied program.

  Accordingly, the program code itself supplied and installed in the computer in order to implement the functional processing of the present invention by the computer also realizes the present invention. That is, the computer program itself for realizing the functional processing of the present invention is also included in the present invention.

  In this case, the program may be in any form as long as it has a program function, such as an object code, a program executed by an interpreter, or script data supplied to the OS.

  As a recording medium for supplying the program, for example, a magnetic recording medium such as a flexible disk, a hard disk, a magnetic tape, MO, CD-ROM, CD-R, CD-RW, DVD-ROM, DVD-R, DVD- There are optical / magneto-optical storage media such as RW, and non-volatile semiconductor memory.

  As a program supply method using wired / wireless communication, a computer program forming the present invention on a server on a computer network, or a computer forming the present invention on a client computer such as a compressed file including an automatic installation function A method of storing a data file (program data file) that can be a program and downloading the program data file to a connected client computer can be used. In this case, the program data file can be divided into a plurality of segment files, and the segment files can be arranged on different servers.

  That is, the present invention includes a server device that allows a plurality of users to download a program data file for realizing the functional processing of the present invention on a computer.

  In addition, the program of the present invention is encrypted, stored in a storage medium such as a CD-ROM, distributed to the user, and key information for decrypting the encryption for the user who satisfies a predetermined condition is obtained via, for example, a homepage It is also possible to realize the program by downloading it from the computer and executing the encrypted program using the key information and installing it on the computer.

  In addition to the functions of the above-described embodiments being realized by the computer executing the read program, the OS running on the computer based on the instruction of the program is a part of the actual processing. Alternatively, the functions of the above-described embodiment can be realized by performing all of them and performing the processing.

  Furthermore, after the program read from the recording medium is written in a memory provided in a function expansion board inserted into the computer or a function expansion unit connected to the computer, the function expansion board or The CPU of the function expansion unit performs part or all of the actual processing, and the functions of the above-described embodiments can also be realized by the processing.

1 is a diagram illustrating a schematic configuration example of a color copying machine as an example of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a block diagram illustrating a configuration example of a reader image processing unit in an image forming apparatus according to an embodiment of the present invention. 3 is a timing chart of each signal in the reader image processing unit 108 in FIG. 2. FIG. 2 is a block diagram including other components related to the configuration example of the printer control unit 109 in FIG. 1. FIG. 3 is a block diagram illustrating a configuration example for obtaining a gradation image in the image forming apparatus according to the embodiment of the present invention. It is a quadrilateral diagram for explaining gradation reproduction. 5 is a flowchart illustrating an example of calibration processing by a first control system in the image forming apparatus according to the embodiment of the present invention. , , FIG. 4 is a diagram illustrating a display example of a display in the image forming apparatus according to the embodiment of the present invention. It is a figure which shows the example of the test print 1 in embodiment of this invention. It is a figure which shows the example of the test print 2 in embodiment of this invention. FIG. 3 is a diagram illustrating a state where a document table 102 on which a test print 1 is placed is viewed from above. FIG. 3 is a diagram illustrating a state where a document table 102 on which a test print 2 is placed is viewed from above. FIG. 6 is a diagram illustrating a relationship between a relative drum surface potential of the photosensitive drum 4 and an image density obtained by the above-described calculation. It is a figure which shows the relationship between absolute water content and contrast potential. FIG. 4 is a diagram illustrating a relationship between a grid potential and a surface potential of the photosensitive drum 4. It is a figure explaining the example of arrangement | positioning of the density reading point of a patch. It is a figure which shows the relationship between the output density which converted the RGB signal obtained from each patch into the density value, and the laser output level. It is a figure explaining the some LUT according to the moisture content. FIG. 3 is a block diagram illustrating a circuit configuration example for processing an output signal of a photosensor 40 in the image forming apparatus according to the embodiment of the present invention. It is a figure which shows the relationship between the output of the photosensor 40, and the density | concentration of an output image when the density | concentration of the patch formed on the photosensitive drum 4 is changed in steps by the area gradation of each color. 4 is a flowchart illustrating an example of an operation at power-on in the image forming apparatus according to the first exemplary embodiment of the present invention. FIG. 5 is a diagram illustrating a sequence for forming a patch on the photosensitive drum 4 in the image forming apparatus according to the embodiment of the present invention. 6 is a flowchart illustrating an example of a correction method for the γLUT 25 in the image forming apparatus according to the embodiment of the present invention. It is a figure which shows the example of a (gamma) LUT correction table. It is a figure which shows the density | concentration conversion characteristic after control. 10 is a flowchart illustrating an example of a power-off process in the image forming apparatus according to the second embodiment of the present invention. 10 is a flowchart illustrating an example of processing added to power-on processing in an image forming apparatus according to a second embodiment of the present invention.

Claims (6)

An image forming apparatus that forms a recording material image on an image carrier based on image data and recording material image forming conditions, and transfers and fixes the formed recording material image to a recording medium,
Detecting means for detecting characteristics of a recording material image having a predetermined pattern formed on the image carrier;
Determining means for determining the recording material image forming conditions based on the detected characteristics of the recording material image;
Based on the characteristics of the recording material image of the predetermined pattern detected by the detection means when the power is turned on, the reference characteristics stored in advance, and the usage amount of the image forming apparatus since the power is turned on. An image forming apparatus comprising: a correcting unit that corrects the recording material image forming condition determined by the determining unit based on the characteristics of the recording material image of the predetermined pattern detected at the time of loading.   2. The correction amount by the correction unit decreases as the usage amount of the image forming apparatus from the time of turning on the power increases, and becomes zero when the predetermined usage amount is reached. Image forming apparatus.   The image forming apparatus according to claim 1, wherein the reference characteristic stored in advance is a characteristic of the recording material image detected by the detection unit when the power is turned off. When the power is turned on, the apparatus further includes an idle time information acquisition unit that acquires information indicating the idle time that has elapsed since the last time the power was turned off.
2. The recording material image forming condition is not corrected when the correcting unit determines that the leaving time is equal to or less than a predetermined time based on the information indicating the leaving time. The image forming apparatus according to claim 3.   The image forming apparatus according to claim 1, wherein the image forming condition is a density correction characteristic of the image forming apparatus. A control method for an image forming apparatus for forming a recording material image on an image carrier based on image data and recording material image forming conditions, and transferring and fixing the formed recording material image to a recording medium,
A detection step of detecting characteristics of a recording material image having a predetermined pattern formed on the image carrier;
A determination step of determining the recording material image forming conditions based on the detected characteristics of the recording material image;
Based on the characteristics of the recording material image of the predetermined pattern detected by the detection means when the power is turned on, the reference characteristics stored in advance, and the usage amount of the image forming apparatus since the power is turned on. And a correction step of correcting the recording material image forming conditions determined by the determining means based on the characteristics of the recording material image of the predetermined pattern detected at the time of input.

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