JP2005250230A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of stabilizing density and color tones from the first sheet of paper after turning on a power supply by minimizing image stabilization control time when the power supply is turned on. <P>SOLUTION: In the case of receiving a printing job during the warming-up of the image forming apparatus and outputting an image immediately after the end of warming-up, control for correcting the image forming conditions of all colors by using an image pattern of one gradation per color is performed. In the case of outputting an image immediately after the end of warming-up without receiving a printing job during the warming-up of the image forming apparatus, image forming conditions are corrected independently in respective colors by using image patterns equal to the number of colors each of which has one gradation. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an image processing apparatus, for example, image stabilization 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 (hereinafter referred to as “image control method”), the following method is known.

  After starting the image forming apparatus and completing the warm-up operation, 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.

  Furthermore, even when the gradation characteristics of the image forming apparatus change due to changes in environmental conditions, a specific pattern is again formed on the image carrier, read, and image forming conditions such as a gamma correction circuit are determined again. By feeding back to the circuit, the image quality can be stabilized according to the change in environmental conditions.

  In order to achieve further stabilization, a method is also known in which the above-described control is performed for each image forming operation or for each end of the image forming operation.

Further, when the image forming apparatus is used for a long period of time, there may occur a case where the density obtained by reading the pattern on the image carrier does not match the density of the image actually printed out. Therefore, a method is known in which a specific pattern is formed on a recording material and the image forming conditions are corrected by the density value. As an example, there is Patent Document 1 below.
JP 2003-167394 A

  Since the above method takes time and labor to control, if it is performed after the image forming apparatus has been warmed up, the time from when the apparatus is turned on until it becomes usable increases. Therefore, there is a method in which control is not performed after the warm-up but at the subsequent image forming operation or at the end of the image forming operation. However, in this case, there is a problem that the density and color of the first sheet after power-on cannot be guaranteed. there were.

  The present invention is to solve the above-described problems, and an image forming apparatus that minimizes the image stabilization adjustment time when power is turned on and stabilizes density and color from the first sheet after power is turned on. The purpose is to provide.

  In order to solve the above-described problems, the present invention has the following configuration.

  According to a first aspect of the present invention, there is provided an image processing apparatus for forming a color image on an image carrier based on image data, and detecting means for detecting image characteristics of an image pattern formed on the image carrier. Control means for independently correcting image forming conditions for each color based on the difference between the image characteristics of the image pattern detected by the detection means and reference information, and the control means receives a print job during warm-up. When an image is output immediately after the warm-up is completed, control for correcting the image forming conditions for all colors using one image pattern of one color and one gradation is performed after the warm-up is completed, and the image forming apparatus is warmed up. If a print job is not received and image output is not performed immediately after the warm-up is completed, the number of images equal to the number of colors for each gradation after the warm-up is completed. There is provided an image forming apparatus and performs control for correcting each color independently to the image forming conditions using the pattern.

  According to a second aspect of the present invention, there is provided an image forming apparatus, wherein the image carrier is a recording medium or an image carrier.

  According to a third aspect of the present invention, there is provided an image forming apparatus wherein the image forming condition is a density correction characteristic (γLUT) of the image data.

  According to a fourth aspect of the present invention, there is provided the image forming apparatus, wherein the correction unit adds up the differences and corrects the image forming conditions based on the integrated value of the differences in normal image formation. It is to provide.

  According to a fifth aspect of the present invention, when a print job is received during the warm-up of the image forming apparatus and an image is output immediately after the warm-up is completed, whether or not the control to be performed after the warm-up is completed It is an object of the present invention to provide an image processing apparatus which is performed from an operation unit of a forming apparatus.

  According to a sixth aspect of the present invention, when a print job is not received during the warm-up of the image forming apparatus and image output is not performed immediately after the warm-up is completed, When a print job is received during control for correcting the image formation conditions independently for each color using the same number of image patterns, control is canceled at that point or whether to cancel is selected on the operation unit. An image forming apparatus characterized by this is provided.

  According to a seventh aspect of the present invention, the control for correcting image forming conditions performed when a print job is not received during warm-up of the image forming apparatus and image output is not performed immediately after the warm-up is completed An image pattern for detecting image characteristics is formed on the recording medium by a sequence different from that at the time of formation, and image formation on the image carrier is performed based on the image characteristics of the image pattern detected by the detection means. It is an object of the present invention to provide an image forming apparatus characterized by correcting conditions independently for each color.

  According to an eighth aspect of the present invention, the control for correcting an image forming condition performed when a print job is not received during warm-up of the image forming apparatus and image output is not performed immediately after the warm-up is completed At the time of image formation, each color image pattern is formed outside the image forming area on the image carrier, and each color is independently imaged based on the difference between the image characteristics of the image pattern detected by the detection means and the reference information. The present invention provides an image forming apparatus characterized by correcting a forming condition.

  According to a ninth aspect of the present invention, when a print job is not received during the warm-up of the image forming apparatus and image output is not performed immediately after the warm-up is completed, In the control for correcting the image forming conditions independently for each color by using an equal number of image patterns, the image forming is characterized in that the end of the warm-up is not immediately after the end of the warm-up but after a certain time after the end of the warm-up. A device is provided.

  According to the present invention, when a print job is received during the warm-up of the image forming apparatus and an image is output immediately after the warm-up is completed, the image forming conditions for all colors are used using one image pattern of one color and one gradation. If the image forming apparatus does not receive a print job during the warm-up of the image forming apparatus and does not output an image immediately after the warm-up is finished, the number of image patterns equal to the number of colors of each gradation is used. To provide an image forming apparatus that stabilizes the density and color from the first sheet after power-on by correcting the image forming conditions independently for each color, thereby minimizing the image stabilization adjustment time when the power is turned on Can do.

  Hereinafter, an image processing apparatus according to an embodiment of the present invention will be described in detail with reference to the drawings.

(First embodiment)
FIG. 1 is a diagram illustrating an overview of an image processing apparatus according to an embodiment.

Reader Unit The document 101 placed on the document table glass 102 of the reader unit A is illuminated by the light source 103, and the reflected light from the document 101 forms an image on the CCD sensor 105 via the optical system 104. The CCD sensor 105 includes a group of red, green, and blue CCD line sensors arranged in three rows, and generates red, green, and blue color component signals for each line sensor. These reading optical system units are moved in the direction of the arrow shown in FIG. 1, and convert the image of the original 101 into electric signals for each line.

  On the original platen glass 102, one side of the original 101 is brought into contact with the positioning member 107 to prevent the oblique placement of the original 101, the white level of the CCD sensor 105 is determined, and shading correction in the thrust direction of the CCD sensor 105 is performed. The reference white plate 106 is arranged.

  The image signal obtained by the CCD sensor 105 is subjected to image processing by the reader image processing unit 108, sent to the printer unit B, and processed by the printer control unit 109.

  FIG. 2 is a block diagram showing the flow of image signals in the reader image processing unit 108.

  As shown in FIG. 2, the image signal output from the CCD sensor 105 is input to the analog signal processing circuit 201, and after the gain and the offset are adjusted, the A / D converter 202 performs an 8-bit digital image of each color. Converted to signals R1, G1 and B1. The image signals R1, G1, and B1 are input to the shading correction circuit 203, and known shading correction using a read signal of the reference white plate 106 is performed for each color.

  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 CCD drive signal in units of lines such as a shift pulse and a reset pulse, a signal VE indicating an effective area in a read signal for one line output from the CCD 105, and a line synchronization 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.

  Each line sensor of the CCD 105 is disposed at a predetermined distance from each other in the sub-scanning direction. For this reason, the spatial delay in the sub-scanning direction is corrected by the line delay 204. Specifically, the R and G signals are line-delayed in the sub-scanning direction with respect to the B signal, so that the spatial positions of the RGB signals are matched.

  The input masking circuit 205 converts the color space (reading color space) of the input image signal determined by the spectral characteristics of the RGB filter of the CCD 105 into a predetermined color space (for example, sRGB or NTSC standard color space) by matrix calculation of the following equation. Convert.

┌ ┐ ┌ ┐┌ ┐
│R4│ │a11 a12 a13││R3│
│G4│ = │a21 a22 a23││G3│ (1)
│B4│ │a31 a32 a33││B3│
└ ┘ └ ┘└ ┘

  The LOG conversion circuit 206 includes a look-up table ROM, and converts the luminance signals of R4, G4, and B4 into density signals of C0, M0, and Y0. The line delay memory 207 receives the C0, M0, and Y0 image signals corresponding to the line delay until a determination signal such as UCR, FILTER, and SEN is generated and output from the R4, G4, and B4 image signals by a black character determination unit (not shown). Delay.

  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 color material of the printer unit B, for each reading operation. Y2, 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.

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

  The CPU 214 controls the reader unit A and performs image processing according to a program stored in the ROM 216 using the RAM 215 as a work memory. The operator inputs instructions and processing conditions to the CPU 214 through the operation unit 217. A display 218 displays the operating state of the image processing apparatus, set processing conditions, and the like.

  FIG. 3 is a timing chart of each signal in the image processing unit 108.

  In FIG. 3, VSYNC is an image effective section signal in the sub-scanning direction, and image reading (scanning) is performed in the section of logic ‘1’, and output signals of C, M, Y, and Bk are sequentially generated. 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 Section In FIG. 1, 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 outputs a pulse signal corresponding to the image data input by the laser driver. The laser light source 110 outputs laser light corresponding to the input pulse signal. 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 on the surface of the photosensitive drum 4 is developed with toner of each color for each color by the developing device 3. In the embodiment, a two-component toner is used, and developing units of 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. A developing device corresponding to the image forming color approaches the photosensitive drum 4 and develops the electrostatic latent image.

  The recording paper 6 is wound around the transfer drum 5 that rotates once for each color component, and the toner images of the respective colors are transferred and superimposed on the recording paper 6 by a total of four rotations. 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 reflected light amount of the toner patch formed on the photosensitive drum 4 are disposed.

  FIG. 4 is a block diagram illustrating a configuration example of the printer unit B.

  The printer control unit 109 includes a CPU 28, 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 a photosensitive drum 4, a photo sensor 40 including an LED 10 and a photodiode 11, a primary charger 8, a laser light source 110, a surface potential sensor 12, a developing device 3, and the like disposed around the photosensitive drum 4. . Furthermore, the environmental sensor 33 which measures the moisture content (or temperature / humidity) in the air in an apparatus is provided.

Image Processing Configuration FIG. 5 is a block diagram showing a configuration example of an image processing unit for obtaining a gradation image.

  The luminance signal of the image obtained by the CCD 105 is converted into a frame sequential density signal in the image processing unit 108. The converted density signal is corrected by the LUT (γLUT) 25 so that the density signal of the original image matches the density of the output image so as to be a signal corresponding to the gamma characteristic of the printer at the initial setting. Is done.

  FIG. 6 is a quadrant chart showing how gradation is reproduced. 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, the fourth quadrant shows the relationship between the density of the original image and the density of the output image, respectively, and the total gradation reproduction of the image processing apparatus shown in FIG. Show properties. In the case of processing with an 8-bit digital signal, the number of gradation levels is 256.

  In order to make the gradation characteristics of the image processing apparatus total, that is, the gradation characteristics of the fourth quadrant linear, the non-linear printer characteristics of the third quadrant are corrected by the LUT 25 of the second quadrant. The image signal whose tone characteristics are converted by the LUT 25 is converted into a pulse signal corresponding to the dot width by a pulse width modulation (PWM) circuit 26a of the laser driver 26, and an LD driver for controlling on / off of the laser light source 110. 26b. In the embodiment, the tone 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]
Next, 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 will be described as image control in a sequence different from normal image formation for forming an image on recording paper. To do. First, a control system for calibrating the printer unit B using the reader unit A will be described.

  FIG. 7 is a flowchart showing an example of calibration, 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 shown in FIG. 7 is started. As shown in FIGS. 8 to 10, the display 218 includes a liquid crystal operation panel (touch panel display) with a touch sensor.

  First, the start button 81 of the test print 1 shown in FIG. When the operator presses the “test print 1” button, the test print 1 shown in FIG. 11 is printed out by the printer unit B (S51). The display during printing is as shown in FIG. At that time, the CPU 214 determines whether or not there is a recording sheet for forming the test print 1, and if not, displays a warning as shown in FIG. 8B on the display unit 218.

  As the contrast potential when forming the test print 1, a standard potential corresponding to the environment is registered as an initial value and used. The image processing apparatus 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 control uses so-called large-size paper, that is, B4, A3, 11 × 17, or LGR, in order to avoid errors in the vertical reading and horizontal setting in the subsequent reading operation. Is set.

  The test pattern 1 shown in FIG. 11 includes a belt-like pattern 61 having intermediate gradation densities for four colors Y, M, C, and Bk. By visually inspecting this pattern 61, it is confirmed that there are no streaky abnormal images, density unevenness, and color unevenness. The sizes of the patch pattern 62 and the gradation patterns 71 and 72 shown in FIG. 12 are set so as to fall within the reading range of the CCD sensor 105 in the thrust direction.

  If an abnormality is found by visual inspection, it is necessary to print 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.

  Next, the operator places the test print 1 on the platen glass 102 as shown in FIG. 13 and presses a “read” button 91 shown in FIG. At that time, as shown in FIG. 9A, the operator's operation guidance is displayed on the display 218.

  FIG. 13 is a view of the document table 102 as viewed from above, and a wedge-shaped mark T at the upper left is a document contact mark. An operation guidance message is displayed on the display 218 so that the belt pattern 61 is arranged on the contact mark T side and the print is not mistaken. 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-like pattern 61 (point A in FIG. 11) by gradually scanning from the contact 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 obtain the same value as a commercially available densitometer, adjustment is made with a correction coefficient k. Alternatively, a separate LUT may be prepared to convert RGB luminance information into MCYBk density information.

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.

Contrast potential at the time of printing the test print 1 (developing bias potential and photosensitive drum 4 that is photosensitive by 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 of) the in a of FIG. 15, the density obtained from patch pattern 62 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 in the developing device 3 fluctuates and decreases, the image density with respect to the relative drum surface potential may become non-linear in the maximum density area as indicated by the broken line N in FIG. is there. 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 here is obtained from the following equation.

B = (A + Ka) × 1.7 / DA (3)
In equation (3), Ka is a correction coefficient, and it is preferable to optimize the value depending on the type of development method.

  If the contrast potential of the electrophotographic system is not set according to the environment, the density of the original image and the output image will not match, and the output of the environmental sensor 33 that monitors the moisture content in the apparatus described above (that is, the absolute moisture content) will be used. Based on this, a contrast potential corresponding to the maximum density is set as shown in FIG.

  Therefore, in order to correct the contrast potential, the correction coefficient Vcont. The rate is stored in a backed-up RAM or the like.

Vcont. ratel = B / A
The image processing apparatus monitors the amount of water in the environment every 30 minutes, for example. Each time the value of A is determined based on the detection result of the moisture content, A × Vcont. The rate is calculated to obtain the contrast potential.

  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.

The grid potential is set to −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 photosensitive drum 4 that is exposed with the laser light modulated with the maximum signal value. The surface 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. The contrast potential Vcont is a differential voltage between the development biases V _DC and V _H , and as described above, the maximum density increases as Vcont increases.

  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).

  In order to obtain the contrast potential set in this way, the CPU 28 controls the grid potential and the developing bias (S56).

FIG. 28 is a diagram showing density conversion characteristics after control. In the embodiment, the printer characteristic in the third quadrant becomes a solid line J by the control for setting the maximum density higher than the final target value. If such control is not performed, there is a possibility that the printer characteristics such as the broken line H where the maximum density does not reach 1.6 will 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.

  Next, as shown in FIG. 10A, the print start button 150 for the test print 2 appears 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). The display during printing is as shown in FIG.

  As shown in FIG. 12, the test print 2 includes a gradation patch group of 4 × 16 (for 64 gradations) patches for each of the colors Y, M, C, and Bk. The 64 gradations are allotted to the low density area among the 256 gradations, and the high density area is thinned out. This is in order to adjust the gradation characteristics particularly in the highlight portion.

  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 processing apparatus according to the embodiment forms a gradation image such as a photographic image at 200 lpi and 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 view of the original table glass 102 on which the test print 2 is placed as viewed from above. A message is displayed on the display unit 218 so that the Bk patch pattern is on the abutment mark T side and the front and back sides are not mistaken (see FIG. 10C), and due to an arrangement error of the test print 2 Prevent control errors.

  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 FIG. 12) 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) takes 16 points inside the patch, and averages the values obtained by reading the 16 points. The number of reading points is preferably optimized by the reading device and the image forming apparatus.

  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 is The test pattern may be defective. In that case, in order to maintain the continuity of the data string, the inclination of the data string is limited and corrected. For example, when the slope of the data string exceeds 3, the slope is fixed to 3, and the data with a negative slope is set to the same value as that of the one low density patch.

  A conversion characteristic opposite to that shown in FIG. 19 may be set in the LUT 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 the creation of the gamma conversion table by the first control system are thus completed, and the display 218 displays as shown in FIG.

[Supplementary control of gradation]
Next, correction of gradation after control by the first control system will be described.

  The image processing apparatus according to the embodiment corrects the maximum density with respect to environmental fluctuations by the above contrast potential control, and further performs gradation correction (referred to as “gradation supplementary control”).

  Considering the case where an environmental change occurs in the state where the first control system is disabled, the ROM 30 stores the table data of the LUT 25 corresponding to the environment (for example, the amount of water) as shown in FIG. Has been.

  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 water amount at that time are stored in the battery-backed area of the RAM 32 or the like. Keep it. Note that the table data in the ROM 30 corresponding to the amount of water stored in the RAM 32 is referred to as LUT (A).

  Thereafter, whenever the environment changes, the table data in the ROM 30 (referred to as “LUT (B)”) corresponding to the water content at that time is acquired, and the following equation is obtained using the LUT (A) and LUT (B): The LUT (1) is corrected as follows. That is, by adding the difference between the LUT (B) and the LUT (A) corresponding to the change in the amount of water to the LUT (1), the table data of the appropriate LUT 25 can be obtained without performing control by the first control system. LUTpresent can be determined.

LUTpresent = LUT (1) + (LUT (B) −LUT (A)) (4)
By such supplementary control, the input / output characteristics of the image processing apparatus are linearly corrected. As a result, variations in the density gradation characteristics of each apparatus are suppressed, and the standard state can be easily set.

  By releasing such supplementary control to the user of the image processing apparatus, it is possible to perform gradation control as necessary when it is determined that the gradation characteristics of the image processing 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 processing apparatus, the first control system is invalidated and the state of the image processing apparatus is easily and quickly determined. 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 stabilization of image reproduction characteristics of the printer unit B alone, which is image control performed during normal image formation, will be described.

  The second control system stabilizes the image reproducibility by detecting the density of the patch formed on the photosensitive drum 4 and correcting the LUT 25.

  FIG. 21 is a block diagram illustrating a circuit configuration example for processing the output signal of the photosensor 40 described above. Reflected light (near infrared light) from the photosensitive drum 4 input to the photosensor 40 is converted into an electrical signal. The electric signal of 0 to 5 V is converted into an 8-bit digital signal by the A / D conversion circuit 41 and converted into density information by the density conversion circuit 42.

  The toners used in the embodiments are yellow, magenta, and cyan color toners in which color materials of each color are 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. Note that the output of the photosensor 40 in a state where no toner is 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, and the output of the photosensor 40 decreases as the image density increases.

  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 purpose of the second control system is to maintain the stability of color reproducibility achieved by the first control system, and the state immediately after the end of the control by the first control system is set as the target value. FIG. 23 is a flowchart showing an example of the target value setting process.

  When the control by the first control system 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 and converted into density information ( S12). Then, a target value for the second control system is set.

  It should be noted that a 128-level density signal is used for each color as a laser output when forming a patch. At this time, it goes without saying that the table data and contrast potential of the LUT 25 are obtained from the first control system.

  FIG. 24 is a diagram showing a sequence for forming patches on the photosensitive drum 4.

  In the 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, it is point-symmetric with respect to the center of the photosensitive drum 4 in consideration of the eccentricity of the photosensitive drum 4. Density information is obtained by forming patches of the same color at positions and averaging a plurality of values obtained by measuring the 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. Then, density information corresponding to the image density 128 is stored in the RAM 32 or the like as the target value of the second control system. This target value is updated every time control by the first control system is performed.

  The second control system is a control in which patches are formed in a non-image area during normal image formation, the density is detected, and the table data of the LUT 25 obtained by the first control system is corrected as needed. Since the area on the photosensitive drum 4 corresponding to the gap portion of the recording paper wound around the transfer drum 5 is a non-image area, a patch is formed in that area. FIG. 25 is a diagram showing a sequence for forming a patch in a non-image area on the photosensitive drum 4 during normal image formation, and is an example in the case of continuously outputting an A4 size full color image.

  It is important that the laser output at the time of patch formation is the same as that at the time of setting the target value, and a 128-level density signal is used for each color. At that time, the table data and the contrast potential of the LUT 25 are made equal to those at the time of normal image formation at that time. That is, as the gamma correction table, the result of correcting the table data of the LUT 25 obtained by the first control system by the control of the second control system until the previous time is used.

  The density signal of 128 level is corrected so that the density of the patch becomes 128 by the LUT 25 of the density scale obtained by normalizing the density 1.6 to 255. However, the image characteristics of the printer unit B are unstable and constantly changed. May cause. Therefore, the density of the measurement result is not 128. Based on the deviation ΔD between the concentration signal and the measurement result, the second control system corrects the table data of the LUT 25 created by the first control system.

  FIG. 26 is a diagram showing a general density signal correction table (γLUT correction table) when the patch density deviation is ΔDx with respect to the 128-level density signal. Such a γLUT correction table is stored in advance in the ROM 30 or the like, and the γLUT correction table is normalized so that ΔDx becomes ΔD during control by the second control system, 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.

  The timing at which the LUT 25 is rewritten (corrected) is different for each color. When the preparation for rewriting is completed, rewriting is performed based on the TOP signal during the period in which laser light scanning (photosensitization) of that color is not performed.

  ΔD is a deviation between the target value obtained from the patch formed previously using the LUT 25 by the second control system and the density obtained from the patch formed using the LUT 25 this time. However, since the LUT 25 corrected by the previous second control system is used for each patch formation, the deviation ΔDn between the read patch density and the target value is different from ΔD. Therefore, the integrated value of ΔDn is stored as ΔD.

  FIG. 29 is a flowchart showing a process for creating a γLUT correction table, which starts with the start of normal image formation.

  First, the table data of the LUT 25 is corrected by the γLUT correction table obtained by the previous second control system (S21), the correction result table data is set in the LUT 25 (S22), and an image is output using the LUT 25. (S23). At that time, a patch is formed on the photosensitive drum 4 and the density of the patch is read (S24). Then, ΔDn is calculated (S25), an integrated value ΔD = ΔD + ΔDn is obtained (S26), and a γLUT correction table is created (S27). Thereafter, it is determined whether or not to continue the print job (S28). If the job continues, the process returns to step S21, and if the job ends, the process ends.

  The second control system is activated whenever a patch can be formed in a non-image area during normal image formation. That is, when continuously outputting A4 size full color images, the LUT 25 is corrected once for each color when outputting two images, and when outputting only one image, the LUT 25 is corrected for each color.

[Third control system]
Next, a third control system that is performed when the power is turned on, which is a feature of the present invention, will be described.

  In the third control system, the LUT 25 is corrected as needed by the second control system to stabilize the density and color, but the first output from power-on is the γLUT created before power-off. Since the correction table is used, the control is performed to correct that a proper image cannot be obtained when the power-off period is long, for example, when the power-off period is left overnight.

  In this embodiment, when a print job is not received during warm-up of the image forming apparatus and image output is not performed immediately after the warm-up is completed, each color is independently used by using the same number of image patterns as the number of colors of each gradation. Then, control for correcting the image forming condition is performed. Specifically, after the warm-up is completed, control for correcting the LUT 25 performed during normal image formation described in the second control system is performed. The patch formation sequence is a target value setting process in the second control system. In the sequence for forming patches on the photosensitive drum 4 (FIG. 24), one patch for each color is performed, and density information for four colors is obtained in one drum rotation. If image output is not performed immediately after the warm-up is completed, there is no problem even if the apparatus operates for a while after the warm-up is completed.

  When a print job is received during the warm-up of the image forming apparatus and an image is output immediately after the warm-up is completed, the image formation conditions for all colors are corrected using one image pattern of one color and one gradation after the warm-up is completed. Control. Specifically, after the warm-up is completed, control for correcting the LUT 25 performed at the time of normal image formation described in the second control system is performed, but one patch is formed on the photosensitive drum. The LUT 25 for all colors is corrected using the difference ΔDn from the reference value obtained from the density information as ΔDn for all colors. This control, which is performed with one patch, cannot sufficiently correct the color tone, but this control corrects the influence of neglect, and the influence of neglect does not depend on the color, and it causes a uniform decrease or increase in density. The effect of the control is sufficient to cause it. As a result, even when the image is output immediately after the warm-up is completed, the time required for the control is read from the formation of one patch, and the time until the correction is sufficient, and the user can obtain an appropriate output image with a short waiting time. I can do it.

  FIG. 27 shows a control flow when the power is turned on in this embodiment. Means for determining whether a print job is received during warm-up (S31). If received, after warm-up is completed (S32), only one patch is formed on the photosensitive drum. The LUT 25 at this time is obtained by adding the γLUT correction table to the LUT 25 (S33) (S34), as in the normal image formation. In this embodiment, only one magenta patch is formed and detected (S35). This is because in this embodiment, the magenta development position is closest to the patch detection position, and the time required for control is the shortest. Magenta ΔDn is calculated from the detected density information (S36), and ΔDn is set to ΔDn of yellow, cyan, and black (S37). Thereafter, a ΔD and γLUT correction table for each color is created (S38) (S39), and the control ends, but a normal image forming sequence is performed in order to output the image received during the warm-up (S40). ). Naturally, the control shown in FIG. 29 is also performed during the image formation.

  If no print job is received during the warm-up, after one warm-up is completed (S41), one color patch is formed on the photosensitive drum and detected (S44). The LUT 25 at this time is obtained by adding a γLUT correction table to the LUT 25 (S42) (S43) as in the case of normal image formation. ΔDn for each color is calculated from the detected density information (S45), and then ΔD and γLUT correction tables for each color are created (S46) (S47), and the control ends.

  The first control system involves human work. For this reason, it is difficult to assume that the control by the first control system is frequently performed. Therefore, if the service person executes control by the first control system when the image processing apparatus is installed and no problem occurs in the output image, the gradation characteristic is maintained and gradually maintained during the period of control by the second control system. When the gradation characteristic changes, control (calibration) by the first control system can be performed. Further, the third control is used to maintain the gradation characteristics of the first image after the power is turned on. If gradation control is shared in this way, as a result, the gradation characteristics can be properly maintained in the minimum necessary time and effort until the image processing apparatus reaches the end of its life.

(Second Embodiment)
The image processing apparatus according to the second embodiment of the present invention will be described below. Note that in the present embodiment, the same reference numerals are given to substantially the same configurations as those in the first embodiment, and the detailed description thereof is omitted.

  In the second embodiment, in the control by the third control system described above, when a print job is received during warm-up and an image is output immediately after the warm-up is completed, control selection and control OFF performed after the warm-up is completed. A case where the operation can be performed from the operation unit of the image forming apparatus will be described.

  When a print job is received during warm-up and image output is performed immediately after the warm-up is completed, control using one patch is performed as in the first embodiment. However, a control-selectable message and button are displayed on the operation unit screen, and if another control is selected there, the control is performed. In this embodiment, the control with one patch in the first embodiment is “simple image correction”, the control with one patch for each color is “normal image correction”, and the no control is “no image correction”. Selectable from items.

  As a result, the user can select speed priority or image quality priority as necessary, and convenience is improved.

(Third embodiment)
The image processing apparatus according to the third embodiment of the present invention will be described below. Note that in the present embodiment, the same reference numerals are given to substantially the same configurations as those in the first embodiment, and the detailed description thereof is omitted.

  In the third embodiment, in the above-described control by the third control system, when the print job is not received during the warm-up of the image forming apparatus and the image output is not performed immediately after the warm-up is completed, the image is output immediately after the warm-up is completed. A case will be described in which the control is not performed for correcting the forming conditions, but is performed after a certain time from the end of warm-up.

  Immediately after the image forming apparatus is turned on, the frequency of use is often high, so even if a print job is not received during the warm-up, a rush job may occur immediately after the warm-up is completed. Immediate control can be a problem. For this reason, in this embodiment, control is activated when a print job is not received during warm-up and a print job does not arrive within a certain time after the warm-up is completed. Furthermore, the control is started under this condition, and if a print job comes during the control, the control is immediately stopped and printing is started. Thus, in this embodiment, the setting is focused on productivity for a while after the power is turned on, and the setting is focused on image quality when it is determined that the apparatus is not used for a while. It should be noted that whether or not to cancel the above may be displayed on the display unit to allow the operator to select.

(Other embodiments)
Note that the present invention can be applied to a system including a plurality of devices (for example, a host computer, an interface device, a reader, and a printer), and a device (for example, a copying machine and a facsimile device) including a single device. You may apply to. Another object of the present invention is to supply a storage medium (or recording medium) in which a program code of software that realizes the functions of the above-described embodiments is recorded to a system or apparatus, and the computer (or CPU or CPU) of the system or apparatus. Needless to say, this can also be achieved by the MPU) reading and executing the program code stored in the storage medium. In this case, the program code itself read from the storage medium realizes the functions of the above-described embodiments, and the storage medium storing the program code constitutes the present invention. Further, by executing the program code read by the computer, not only the functions of the above-described embodiments are realized, but also an operating system (OS) running on the computer based on the instruction of the program code. It goes without saying that a case where the function of the above-described embodiment is realized by performing part or all of the actual processing and the processing is included.

  Furthermore, after the program code read from the storage medium is written into a memory provided in a function expansion card inserted into the computer or a function expansion unit connected to the computer, the function is determined based on the instruction of the program code. It goes without saying that the CPU or the like provided in the expansion card or the function expansion unit performs part or all of the actual processing and the functions of the above-described embodiments are realized by the processing.

  When the present invention is applied to the storage medium, the storage medium stores program codes corresponding to the flowcharts described above.

  In each of the above-described embodiments, the photosensitive drum is taken as an example of the image carrier that carries the electrostatic latent image or the toner image. However, the photosensitive member is a belt-like image carrier having a photosensitive layer on the surface thereof. The present invention can also be applied to a belt. 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 and third control systems may be acquired from a patch formed on a photosensitive belt or an intermediate transfer member.

The figure which shows the external appearance of the image processing apparatus of embodiment Block diagram showing flow of image signal in reader image processing unit Timing chart of each signal in the image processor Block diagram showing a configuration example of the printer unit Block diagram showing a configuration example of an image processing unit for obtaining a gradation image A quadrant chart showing how gradation is reproduced Flow chart showing an example of calibration Figure showing a display example of the display unit Figure showing a display example of the display unit Figure showing a display example of the display unit The figure which shows the example of test print 1 The figure which shows the example of test print 2 The figure which shows a mode that the test print 1 is mounted in an original stand. The figure which shows a mode that the test print 2 is mounted on an original stand. The figure which shows the relationship between the relative drum surface potential of a photosensitive drum, and image density Diagram showing the relationship between absolute water content and contrast potential Diagram showing the relationship between grid potential and surface potential The figure explaining the density reading point of the patch The figure which shows the relationship between the density | concentration read from the test print 2, and a laser output level The figure explaining LUT according to moisture content A block diagram showing an example of a circuit configuration for processing an output signal of a photosensor The figure which shows the relationship between the output of the photo sensor and the density of the output image when changing the density of the patch stepwise Flow chart showing an example of target value setting processing The figure which shows the sequence which forms a patch on a photosensitive drum Diagram showing a sequence for forming patches in non-image areas on a photosensitive drum during normal image formation The figure which shows the gamma LUT correction table Flow chart showing processing at power-on Diagram showing density conversion characteristics after control Flow chart showing processing for creating a γLUT correction table

Explanation of symbols

A Reader B Printer 1 Polygon mirror 2 Mirror 3 Developer 4 Photosensitive drum 5 Transfer drum 6 Recording paper 7 Fixing roller pair 8 Primary charger 9 Cleaner 10 LED light source 11 Photo diode 12 Surface potential sensor 25 LUT
26 Laser driver 28 CPU
30 ROM
32 RAM
40 Photosensor 101 Document 102 Document platen glass 103 Light source 104 Optical system 105 CCD sensor 106 Reference white plate 107 Positioning member 108 Image processing unit 109 Printer control unit 110 Laser light source

Claims (9)

An image forming apparatus that forms a color image on an image carrier based on image data,
A detection unit that detects an image characteristic of an image pattern formed on the image carrier, and an image formation condition is corrected independently for each color based on a difference between the image characteristic of the image pattern detected by the detection unit and reference information Control means to
When the control unit receives a print job during warm-up and outputs an image immediately after the warm-up is completed, the image forming conditions for all colors are corrected using one image pattern of one color and one gradation after the warm-up is completed. When the image forming apparatus does not receive a print job during the warm-up of the image forming apparatus and does not output an image immediately after the warm-up is finished, the number of image patterns equal to the number of colors for each gradation is used after the warm-up is finished. An image forming apparatus that performs control to correct image forming conditions for each color independently.   The image forming apparatus according to claim 1, wherein the image carrier is a recording medium or an image carrier.   The image forming apparatus according to claim 1, wherein the image forming condition is a density correction characteristic (γLUT) of the image data.   The image forming apparatus according to claim 1, wherein the correction unit integrates the difference and corrects the image forming condition based on the integrated value of the difference in normal image formation.   When a print job is received during the warm-up of the image forming apparatus and an image is output immediately after the warm-up is completed, whether or not the control to be performed after the warm-up is completed is performed from the operation unit of the image forming apparatus. The image forming apparatus according to claim 1, wherein:   When a print job is not received during the warm-up of the image forming apparatus and image output is not performed immediately after the warm-up is completed, each color is independently used by using the same number of image patterns as the number of colors of one gradation after the warm-up is completed. The control unit according to claim 1, wherein when a print job is received during control for correcting image forming conditions, control is stopped at that time, or whether to cancel is selected on the operation unit. Image forming apparatus.   The control for correcting the image forming conditions performed when the image forming apparatus does not receive a print job during the warm-up and does not output an image immediately after the warm-up is completed is performed according to a sequence different from that during normal image formation. An image pattern for detecting the image is formed on the recording medium, and the image forming condition on the image carrier is corrected independently for each color based on the image characteristics of the image pattern detected by the detecting means. The image forming apparatus according to claim 1.   The control for correcting the image forming conditions performed when the print job is not received during the warm-up of the image forming apparatus and the image output is not performed immediately after the warm-up is completed. The image forming condition is corrected independently for each color based on the difference between the image characteristic of the image pattern and the reference information formed outside the image forming area on the image carrier and detected by the detecting means. The image forming apparatus according to claim 1.   When a print job is not received during the warm-up of the image forming apparatus and image output is not performed immediately after the warm-up is completed, each color is independently used by using the same number of image patterns as the number of colors of one gradation after the warm-up is completed. 9. The image according to claim 1, wherein in the control for correcting the image forming condition, the end of the warm-up is not immediately after the end of the warm-up but after a certain time after the end of the warm-up. Forming equipment.

Images