JP2004240204A - Image control method and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image control method capable of stabilizing an image by an image stabilization control process which can be more accurately and frequently performed. <P>SOLUTION: At least one or more image patterns B are formed on an image carrier at the point when an image control by a first control system is finished, image information on the formed image pattern B is read by an optical detecting means, then, the image pattern B is formed in a non-image forming area on the image carrier based on the image information in the midst of a normal image forming operation, and then, the formed image pattern B is read by the optical detecting means, and then, the image forming condition corrected by the image control by the first control system is corrected again based on a difference between the read image information and the reference image information. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an image control method and an image forming apparatus for forming an image in a copying machine, a laser beam printer, and the like.
[0002]
[Prior art]
Conventionally, the following method is known as a method (image control method) for adjusting image processing characteristics of an image forming apparatus such as a copying machine or a printer.
[0003]
First, the image forming apparatus is started, and after the warm-up operation is completed, a specific pattern is formed on an image carrier such as a photosensitive drum. Then, the quality of the formed image is stabilized by reading the density of the formed pattern and changing the operation of a circuit for determining image forming conditions such as a γ correction circuit based on the read density value. ing.
Further, even when the gradation characteristic changes due to a change in environmental conditions, a specific pattern is formed on the image carrier again, read, and fed back to a circuit for determining image forming conditions such as a γ correction circuit. Accordingly, the image quality can be stabilized in accordance with the variation amount of the environmental condition.
Further, when the image forming apparatus has been used for a long period of time, the density of the pattern read on the image carrier may not match the density of the actually printed image. Therefore, there is also known a method of forming a specific pattern on a recording material and correcting an image forming condition based on the density value.
[0004]
[Problems to be solved by the invention]
However, in the above-mentioned conventional example, since control takes time and effort, control cannot be started frequently, and it cannot be said that the quality is sufficiently stabilized against the ever-changing image characteristics.
[0005]
Accordingly, an object of the present invention is to provide an image control method and an image forming apparatus capable of stabilizing an image by performing image stabilization control that can be performed more accurately and more frequently.
[0006]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides an image carrier, an image forming unit for forming an image on the image carrier, a transfer unit for transferring an image on the image carrier to a recording material, and the recording material. Fixing means for fixing the image transferred to the recording material to the recording material, optical detection means for detecting image information of the image on the image carrier, and reading means for reading image information of the image fixed to the recording material. And adjusting means for adjusting image forming conditions, and forming at least one or more image patterns A on the recording material for determining image characteristics in a sequence different from that during normal image formation. In an image forming apparatus having an image control method of reading an image pattern A by the reading means and controlling image forming conditions based on the read image information, when the image control is completed, At least one or more image patterns B are formed on the carrier, and the image information of the formed image patterns B is read by the optical detection means. Based on the image information, the image patterns B are formed during normal image formation. Is formed in a non-image forming area on the image carrier, the formed image pattern B is read by the optical detection means, and image forming conditions are controlled based on a difference between the read image information and the reference image information. It is characterized by the following.
In this case, based on the image information read from the image pattern B formed during the normal image formation, the image information of at least one or more image patterns A formed in a sequence different from the sequence at the time of the normal image formation is estimated. Based on the image information, the same image forming condition control as the control of the image forming condition in a sequence different from that during the normal image formation can be performed during the normal image formation.
Further, an image signal formed by the image forming means may be converted into an image signal in accordance with the correction information.
An image carrier, image forming means for forming an image on the image carrier, transfer means for transferring the image on the image carrier to a recording material, and recording the image transferred on the recording material. In an image forming apparatus including a fixing unit for fixing a material, image density adjustment and image gradation adjustment can be performed by the above-described image control method.
In this case, the image carrier is a drum-shaped photosensitive drum having a photosensitive layer on the surface, or a sheet-shaped photosensitive sheet having a photosensitive layer on the surface, or a belt-shaped photosensitive belt having a photosensitive layer on the surface, or The transfer member may be a transfer member on which the toner image is transferred from the photosensitive member, or an intermediate transfer member on which the toner image is transferred from the photosensitive member.
[0007]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0008]
<Embodiment 1>
FIG. 1 shows a configuration diagram of the present embodiment.
A full-color image forming method will be described.
A document 101 placed on a platen glass 102 is illuminated by a light source 103 and is imaged on a CCD sensor 105 via an optical system 104. The CCD sensor 105 generates red, green, and blue color component signals for each line sensor using a group of red, green, and blue CCD line sensors arranged in three rows. These reading optical system units scan the document in the direction of the arrow to convert the document into an electric signal data sequence for each line.
Also, an abutting member 107 for abutting the position of the original on the platen glass 102 to prevent the original from being skewed, and for determining the white level of the CCD sensor 105 on the platen glass surface, A reference white plate 106 for shading the CCD sensor 105 in the thrust direction is provided.
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.
Next, the image processing unit 108 will be described.
FIG. 2 is a block diagram showing a flow of an image signal in the image processing unit 108 of the reader unit A according to the present embodiment.
[0009]
As shown in FIG. 2, the image signal output from the CCD sensor 105 is input to an analog signal processing unit 201, where the image signal is subjected to gain adjustment and offset adjustment. Are converted into digital image signals R1, G1, and B1. Thereafter, the signal is input to the shading correction unit 203, and a known shading correction is performed for each color using a read signal of the reference white plate 106.
The clock generation unit 211 generates a clock for each pixel. The main scanning address counter 212 counts the clock from the clock generator 211 and generates a one-line pixel address output. Then, the decoder 213 decodes the main scanning address from the main scanning address counter 212, and outputs a line drive CCD drive signal such as a shift pulse or a reset pulse, or a VE indicating an effective area in a one-line read signal from the CCD. A signal and a line synchronization signal HSYNC are generated. The main scanning address counter 212 is cleared by the HSYNC signal, and starts counting the main scanning addresses of the next line.
Since the line sensors of the CCD sensor 105 are arranged at a predetermined distance from each other, the line delay circuit 204 in FIG. 2 corrects a spatial shift in the sub-scanning direction. Specifically, in the sub-scanning direction with respect to the B signal, each of the R and G signals is line-delayed in the sub-scanning direction to match the B signal.
The input masking unit 205 converts a read color space determined by the spectral characteristics of the R, G, and B filters of the CCD sensor into an NTSC standard color space, and performs a matrix operation as shown in the following equation.
The light amount / density conversion unit (LOG conversion unit) 206 is configured by 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 delays the C0, M0, and Y0 image signals by the line delay from the R4, G4, and B4 signals to the determination signals such as UCR, FILTER, and SEN in a black character determination unit (not shown). Let it.
The masking and UCR circuit 208 extracts a black signal (Bk) from the input three primary color signals of Y1, M1, and C1, and further performs an operation of correcting color turbidity of a recording color material in the printer unit B. The signals of Y2, M2, C2, and Bk2 are sequentially output at a predetermined bit width (8 bits) for each reading operation.
The γ correction circuit 209 performs density correction in the reader unit A so as to match the ideal gradation characteristics of the printer unit B. The spatial filter processing unit (output filter) 210 performs edge enhancement or smoothing processing.
The M4, C4, Y4, and Bk4 frame-sequential image signals thus processed are sent to the printer control unit 109, and the printer unit B performs density recording by PWM.
Reference numeral 214 denotes a CPU for controlling the inside of the reader unit, 215 denotes a RAM, and 216 denotes a ROM. An operation unit 217 has a display 218.
FIG. 3 is a diagram showing the timing of each control signal in the image processing unit 108 shown in FIG.
[0010]
In FIG. 3, a VSYNC signal is an image valid section signal in the sub-scanning direction, and performs image reading (scanning) in a section of logic "1" to sequentially perform (C), (M), (Y), (Bk) output signal is formed. The VE signal is an image effective section signal in the main scanning direction, takes the timing of the main scanning start position in the section of logic "1", and is mainly used for line counting control of line delay. The CLOCK signal is a pixel synchronization signal, and is used to transfer image data at the rising timing of “0” → “1”.
Next, the printer section B will be described.
In FIG. 1, the photosensitive drum 4 is uniformly charged by a primary charger 8.
The image data is converted into laser light via a laser driver and a laser light source 110 included in the printer image processing unit 109, and the laser light is reflected by the polygon mirror 1 and the mirror 2 and is uniformly charged. 4 is illuminated.
The photosensitive drum 4 on which the latent image has been formed by the scanning of the laser beam rotates in the direction of the arrow shown in the figure. Then, development for each color is sequentially performed by the developing device 3.
In the present embodiment, a two-component system is used as a developing method, and a developing device 3 of each color is provided around the photosensitive drum 4 with black (Bk), yellow (Y), cyan (C), The developing devices are arranged in the order of magenta (M) and perform a developing operation at a timing when a developing device corresponding to the image signal develops a latent image area formed on the photosensitive drum.
On the other hand, the transfer paper 6 is wound around the transfer drum 5 and rotates once in the order of M, C, Y, and Bk, and rotates four times in total, so that the toner images of each color are transferred onto the transfer paper 6 in a multiplex manner. .
When the transfer is completed, the transfer paper 6 is separated from the transfer drum 5, the toner image is fixed by the fixing roller pair 7, and a full-color image print is completed.
Further, a surface potential sensor 12 is arranged on the photosensitive drum 4 upstream of the developing device 3.
Further, a cleaner 9 for cleaning the transfer residual toner on the photosensitive drum 4, an LED light source 10 and a photodiode 11 for detecting a reflected light amount of a toner patch pattern formed on the photosensitive drum 4, which will be described later. Provided.
FIG. 4 is a block diagram illustrating a configuration of the image forming apparatus according to the present embodiment.
The printer image processing unit 109 includes the CPU 28, the ROM 30, the RAM 32, the test pattern storage unit 31, the density conversion circuit 42, and the LUT 25, and can communicate with the reader unit A and the printer engine unit 100.
The printer engine unit 100 controls the optical reading device 40 including the LED 10 and the photodiode 11 disposed around the photosensitive drum 4, the primary charger 8, the laser 101, the surface potential sensor 12, and the developing device 3. I have.
Further, an environment sensor 213 for measuring the amount of water in the air in the machine is provided.
The surface electronic sensor 12 is provided on the upstream side of the developing device 3, and the grid potential of the primary charger 8 and the developing bias of the developing device 3 are controlled by the CPU 28 as described later.
FIG. 5 shows an image signal processing circuit for obtaining a gradation image according to the present embodiment.
A luminance signal of the image is obtained by the CCD 105, and is converted into a frame-sequential image signal in the reader image processing unit 108. The density characteristic of this image signal is converted by the LUT 25 (γLUT) so that the original image density and the output image density are represented by the input image signal and the γ characteristic of the printer at the time of the initial setting. You.
FIG. 6 is a four-limit chart showing how the gradation is reproduced.
The first quadrant indicates the reading characteristics of the reader unit A for converting the document density into a density signal, the second quadrant indicates the conversion characteristics of the LUT 25 for converting the density signal into a laser output signal, and the third quadrant indicates the laser output. The recording characteristics of the printer unit B for converting a signal into an output density are shown, and the fourth quadrant shows the total tone reproduction characteristics of the image forming apparatus showing the relationship between the original density and the output density.
Since the number of gradations is processed by an 8-bit digital signal, there are 256 gradations.
In this image forming apparatus, in order to make the gradation characteristic of the IV quadrant linear, the printer characteristic of the III quadrant is corrected by the LUT 25 of the IV quadrant to the extent that the printer characteristic is not linear.
The LUT 25 is generated based on a calculation result described later.
After the density conversion by the LUT 25, the signal is converted into a signal corresponding to the dot width by a pulse width modulation (PWM) circuit 26, and sent to a laser driver 27 for controlling ON / OFF of the laser.
In the present embodiment, a tone reproduction method by pulse width modulation processing is used for all colors of Y, M, C, and K.
Then, a latent image having a predetermined gradation characteristic is formed on the photosensitive drum 4 by the change of the dot area by the scanning of the laser 110, and the gradation image is reproduced through processes of development, transfer and fixing.
(First control system: gradation control of system including both reader / printer)
Next, as image control in a sequence different from that during normal image formation in which an image pattern is formed on a recording material, first control relating to stabilization of image reproduction characteristics of a system including both the reader unit A and the printer unit B is performed. The system will be described.
[0011]
First, the calibration of the printer unit B using the reader unit A will be described with reference to the flowchart of FIG. This flow is realized by the CPU 214 controlling the reader unit A and the CPU 28 controlling the printer unit B.
[0012]
This control is started by pressing a mode setting button called automatic gradation correction provided on the operation unit 217. In the present embodiment, the display 218 is configured by a liquid crystal operation panel (touch panel display) with a push sensor as shown in FIGS.
[0013]
In S51, the print start button 81 of test print 1 appears on the display 218 (FIG. 8A), and by pressing it, the image of test print 1 shown in FIG. At this time, the CPU 214 determines whether or not there is a sheet for forming the test print 1, and if there is no sheet, a warning display as shown in FIG.
[0014]
When the test print 1 is formed, a contrast potential (to be described later) in a standard state according to the environment is registered as an initial value and used.
[0015]
Further, the image forming apparatus used in the present embodiment includes a plurality of paper cassettes, and can select a plurality of types of paper sizes such as B4, A3, A4, and B5.
[0016]
However, the printing paper used in this control uses large-size paper, which is generally referred to, in order to avoid an error due to a mistake in vertical or horizontal placement in a later reading operation. That is, it is set so that B4, A3, 11 × 17, and LGR are used.
[0017]
In the test pattern 1 shown in FIG. 11, a band-shaped pattern 61 having an intermediate gradation density for four colors of Y, M, C, and K is formed. By visually inspecting the pattern 61, it is confirmed that there are no streaky abnormal images, density unevenness, and color unevenness. In this pattern, the size of the CCD sensor 105 in the main scanning direction is set so as to cover the patch pattern 62 and the gradation patterns 71 and 72 (FIG. 12) in the thrust direction.
[0018]
If an abnormality is found, the test print 1 is printed again, and if an abnormality is found again, a serviceman call is made. It is also possible to read the band pattern 61 by the reader unit A and automatically determine whether or not to perform subsequent control based on the density information in the thrust direction.
[0019]
On the other hand, the pattern 62 is the maximum density patch of each color of Y, M, C, and Bk, and uses 255 levels of density signal values.
[0020]
In S52, the image of the test print 1 is placed on the platen glass 102 as shown in FIG. 13, and the reading start button 91 shown in FIG. 9A is pressed.
At this time, a guidance display for the operator shown in FIG. 9A appears.
[0021]
FIG. 13 is a view of the document table as viewed from above. The upper left wedge-shaped mark T is a mark for abutting the document on the document table, and the band pattern 61 is located on the butting mark T side. The message as described above is displayed on the operation panel so that the front and back sides are not mistaken (FIG. 9A). By doing so, a control error due to misplacement is prevented.
[0022]
When reading the pattern 62 by the reader unit A, the pattern 62 is gradually scanned from the abutment mark T, and the first density gap point A is obtained at the corner of the pattern 61. And the density value of the pattern 62 is read out.
[0023]
During the reading, the display shown in FIG. 9B is performed. When the orientation or position of the test print 1 is incorrect and the reading cannot be performed, the message shown in FIG. 9C is displayed. By pressing the key 92, reading is performed again.
[0024]
Alternatively, RGB luminance information may be converted into MCYBk density information using an LUT.
[0025]
Next, a method of correcting the maximum density from the obtained density information will be described.
[0026]
FIG. 15 shows the relationship between the relative drum surface potential and the image density obtained by the above calculation.
[0027]
The contrast potential used at that time, that is, the difference between the developing bias potential and the surface potential of the photosensitive drum when the maximum level was hit by using the laser beam after the primary charging, was the maximum obtained by setting A. In the case of the density DA, the image density mostly corresponds linearly to the relative drum surface potential as indicated by the solid line L in the maximum density range.
[0028]
However, in the two-component developing system, when the toner density in the developing device fluctuates and drops, nonlinear characteristics may occur in the maximum density range as shown by the broken line N.
[0029]
Therefore, in this case, the final target value of the maximum density is 1.6, but in consideration of a margin of 0.1, the control amount is determined by setting 1.7 as the target value of the control for adjusting the maximum density. I do.
[0030]
Here, the contrast potential B is obtained using the following equation (3).
[0031]
B = (A + Ka) × 1.7 / DA (3)
Here, Ka is a correction coefficient, and it is preferable to optimize the value according to the type of the developing method.
[0032]
Actually, in the electrophotographic method, depending on the environment, the setting of the contrast potential A does not match the image density unless it is changed in accordance with the environment. The settings are changed as shown in FIG.
[0033]
Therefore, as a method of correcting the contrast potential, the correction coefficient Vcont. The ratel is stored in the backed-up RAM.
[0034]
Vcont. ratel = B / A
The image forming apparatus monitors the transition of the environment (moisture content) every 30 minutes, and each time the value of A is determined based on the detection result, A × Vcont. The contrast potential is obtained by calculating the rate.
[0035]
A method for obtaining the grid potential and the developing bias potential from the contrast potential will be briefly described.
[0036]
FIG. 17 shows the relationship between the grid potential and the photosensitive drum.
[0037]
The grid potential is set to -200 V, and the surface potential VL when scanning is performed with the level of the laser beam at the minimum and the surface potential VH when the level is maximized are measured by the surface potential sensor 12.
[0038]
Similarly, VL and VH when the grid potential is -400 V are measured.
[0039]
By interpolating and extrapolating -200V data and -400V data, the relationship between grid potential and surface potential can be determined. Control for obtaining this potential data is called potential measurement control.
[0040]
The developing bias VDC is set by providing a difference of Vbg (here, set to 100 V) set so that fog toner does not adhere to the image from VL.
[0041]
The contrast potential Vcont is a difference voltage between the developing biases VDC and VH. As described above, the larger the Vcont, the larger the maximum density can be obtained.
[0042]
In order to obtain the calculated contrast potential B, from the relationship shown in FIG. 17, how many volts of the grid potential is required and how many volts of the developing bias potential are required can be obtained by calculation.
[0043]
In S53 of FIG. 7, the contrast potential is obtained so that the maximum density becomes 0.1 higher than the final target value, and the CPU 28 sets the grid potential and the developing bias potential so as to obtain this contrast potential.
[0044]
It is determined whether or not the contrast potential obtained in S54 is within the control range. If the contrast potential is out of the control range, it is determined that there is an abnormality in the developing device or the like, and the developing device of the corresponding color is checked. In this manner, an error flag is set so that the serviceman can recognize the error flag so that the serviceman can see the error flag in a predetermined service mode.
[0045]
Here, in the case of such an abnormality, a limit value is multiplied by a limiter to perform correction control (S55), and the control is continued.
[0046]
As described above, the grid potential and the developing bias potential are set by the CPU 28 so that the contrast potential obtained in S53 can be obtained.
[0047]
FIG. 28 shows a density conversion characteristic diagram. By the maximum density control for setting the maximum density higher than the final target value in the present embodiment, the printer characteristic diagram in the third quadrant is as shown by the solid line J.
[0048]
If such control is not performed, the printer characteristic may not reach 1.6 as indicated by the broken line H. In the case of the characteristic indicated by the broken line H, no matter how the LUT 25 is set, since the LUT 25 does not have the ability to increase the maximum density, the density between the density DH and 1.6 cannot be reproduced.
[0049]
If the setting slightly exceeds the maximum density as indicated by the solid line J, the density reproduction range can be reliably guaranteed with the total gradation characteristics of the fourth quadrant.
[0050]
Next, as shown in FIG. 10A, a print start button 150 for the image of the test print 2 appears on the operation panel, and when pressed, the image of the test print 2 in FIG. 12 is printed out (S56). During printing, the display is as shown in FIG.
[0051]
As shown in FIG. 12, the test print 2 is made up of a gradation group of 64 colors in total for each color of Y, M, C, and Bk, 4 columns and 16 rows. The laser output level is mainly assigned to the low density area of the 256 gradations, and the laser output level is thinned out in the high density area. This makes it possible to satisfactorily adjust the gradation characteristics particularly in the highlight portion.
[0052]
12, reference numeral 71 denotes a patch having a resolution of 200 lpi (lines / inch), and reference numeral 72 denotes a patch having a resolution of 400 lpi (lines / inch). To form an image of each resolution, the pulse width modulation circuit 26 can be realized by preparing a plurality of periods of the triangular wave used for comparison with the image data to be processed.
[0053]
In this image forming apparatus, a gradation image is created at a resolution of 200 lpi, and a line image such as a character is created at a resolution of 400 lpi. Although the same gradation level pattern is output at these two resolutions, if the gradation characteristics greatly differ due to the difference in resolution, it is more preferable to set the preceding gradation level according to the resolution. . The test print 2 is generated from the pattern generator 29 without operating the LUT 25.
[0054]
FIG. 14 is a schematic view of the output of the test print 2 viewed from above when the output is placed on the platen glass 102. The upper left wedge-shaped mark T is a mark for contacting the original on the platen. The message is displayed on the operation panel so that the pattern comes to the abutting mark T side and the front and back are not mistaken (FIG. 10C). By doing so, a control error due to misplacement is prevented.
[0055]
When the pattern is read by the reader unit A, the scanning is gradually performed from the abutting mark T, and the first density gap point B is obtained. From the coordinate point, the position of each color patch of the pattern is calculated by relative coordinates. (S57).
[0056]
As for the reading points per patch (73 in FIG. 12), as shown in FIG. 18, 16 reading points (x) are taken inside the patch, and the obtained signals are averaged. It is preferable that the number of points is optimized by the reading device and the image forming device.
[0057]
FIG. 19 shows the RGB signal obtained by averaging the values of 16 points for each patch, converted into a density value by the conversion method to the optical density described above, and plotting the laser output level on the horizontal axis with the output density as the output density. It is.
[0058]
Further, as shown on the right vertical axis, the base density of the paper, in this example, 0.08 is normalized to the 0 level, and 1.60, which is set as the maximum density of the image forming apparatus, is normalized to the 255 level.
[0059]
If the obtained data has a specific high density such as point C or a low density such as point D, the original platen glass 102 may be contaminated or the test pattern may be defective. In some cases, the inclination is limited by a limiter so that continuity is preserved in the data sequence. Here, specifically, when the inclination is 3 or more, it is fixed to 3, and when the inclination is a negative value, the density level is the same as the previous level.
[0060]
As described above, the contents of the LUT 25 can be easily obtained by simply changing the coordinates of the density level in FIG. 19 to the input level (density signal axis in FIG. 6) and the laser output level to the output level (laser output signal axis in FIG. 6). Can be created. For a density level that does not correspond to a patch, a value is obtained by interpolation. At this time, a limiting condition is set so that the output level becomes 0 level with respect to the input level 0 level.
[0061]
Then, the conversion contents created as described above are set in the LUT 25 in S58.
[0062]
As described above, the contrast potential control and the creation of the γ conversion table by the first control system using the reading device are completed. During the above-described processing, a display as shown in FIG. 10D is performed, and when it is completed, a display as shown in FIG. 10E is displayed.
[0063]
Next, supplementary control on the gradation after the control by the first control system is performed will be described.
[0064]
In the image forming apparatus used in the present embodiment, the maximum density can be corrected even if the environment fluctuates by the above-described contrast potential control, but the gradation is also corrected.
[0065]
The ROM 30 stores data of the LUT 25 shown in FIG. 20 for each environment in response to a change in the environment with the first control system disabled.
[0066]
The water content data when the control by the first control system is performed is stored, and the LUT. Ask for A.
[0067]
Thereafter, each time the environment changes, the LUT. B is obtained in advance, and the LUT. 1 is corrected by the following equation using (LUT.B-LUT.A).
[0068]
LUT. present = LUT. 1+ (LUT.B-LUT.A) (4)
With this control, the image forming apparatus is configured to have a linear characteristic with respect to the density signal. As a result, it is possible to suppress the density gradation characteristic variation for each machine, and to set the standard state. became.
[0069]
Also, by releasing this control to the general user, when it is determined that the gradation characteristics of the image forming apparatus have deteriorated, the control is applied as necessary, so that the gradation of the system including both the reader / printer is provided. Correction of characteristics can be easily performed.
[0070]
Further, the above-described correction for environmental fluctuation can be appropriately performed.
[0071]
The setting of the first control system is enabled / disabled by a serviceman, and disabled during service maintenance so that the state of the image forming apparatus can be determined.
[0072]
When invalidated, the standard contrast potential and the γLUT 25 of the image forming apparatus of this model are called from the ROM 30 and set. By doing so, it becomes clear how much the characteristic deviates from the standard state during service maintenance, and optimal maintenance can be performed efficiently.
(Second control system: printer gradation control)
Next, as image control performed during normal image formation, a second control system relating to stabilization of image reproduction characteristics of the printer unit B alone will be described.
[0073]
This control achieves image stabilization by detecting the patch pattern density on the photosensitive drum 4 and correcting the LUT 25 described above.
FIG. 21 shows a processing circuit for processing a signal from a photo sensor 40 including an LED 10 and a photodiode 11 facing the photosensitive drum 4.
[0074]
The near-infrared light from the photosensitive drum 4 incident on the photosensor 40 is converted into an electric signal by the photosensor 40, and the electric signal is output from an output voltage of 0 to 5 V by an A / D conversion circuit 41 to a level of 0 to 255. It is converted to a digital signal. Then, the density is converted into a density by the density conversion circuit 42.
The toner used in the present embodiment is a yellow, magenta, or cyan color toner, which is formed by dispersing a color material of each color using a styrene copolymer resin as a binder.
Further, the photosensitive drum 4 is an OPC drum, the reflectance of near infrared light (960 nm) is about 40%, and an amorphous silicon drum or the like may be used as long as the reflectance is almost the same.
[0075]
Further, the photo sensor 40 used in the present embodiment is configured to detect only the regular reflection light from the photosensitive drum 4.
[0076]
FIG. 22 shows the relationship between the output of the photosensor 40 and the output image density when the density on the photosensitive drum 4 is changed stepwise according to the area gradation of each color.
[0077]
The output of the photosensor 40 in a state where the toner did not adhere to the photosensitive drum 4 was set to 5 V, that is, 255 level.
[0078]
As can be seen from FIG. 22, as the area coverage of each toner increases and the image density increases, the output of the photosensor 40 becomes smaller than that of the photosensitive drum 4 alone.
[0079]
From these characteristics, by having a table 42a dedicated to each color and converting the sensor output signal into a density signal, the density signal can be read with high accuracy for each color.
Since the second control system aims at maintaining stable color reproducibility achieved by the first control system, the state immediately after the end of the control by the first control system is set as a target value. FIG. 23 shows a flow of the target value setting. When the control by the first control system is completed, a patch pattern for each color of Y, M, C, and Bk is formed on the photosensitive drum, and is detected by the photo sensor 40.
Here, the laser output of the patch uses a density signal (density signal axis in FIG. 6) of 128 levels for each color. At this time, the contents of the LUT 25 and the setting of the contrast potential use those obtained by the first control system.
A sequence for forming a patch on the photosensitive drum 4 was performed as shown in FIG.
In this embodiment, since the large-diameter photosensitive drum 4 is used, in order to obtain density data accurately and efficiently in a short period of time, the photosensitive drum is opposed to the photosensitive drum 180 degrees in consideration of the eccentricity of the photosensitive drum. A patch of the same color was formed at the position and measured, and a plurality of samplings were performed to obtain an average. By forming patches of different colors so as to sandwich the patch, data for two colors was obtained in one round.
In this way, data for four colors is obtained in two rounds, and a density value is obtained using the density conversion table 42a in FIG. The density value D128 at this time is set as a target value of the second control system and is backed up. The target value is updated each time control is performed by the first control system.
The second control system is a control for detecting a patch density formed in a non-image area during normal image formation, and correcting the γLUT obtained by the first control system as needed. In the present embodiment, since the position on the photosensitive drum corresponding to the joint portion of the transfer sheet on the transfer drum 5 is a non-image area, a patch is formed in that portion. A sequence for forming a patch on a non-image area on the photosensitive drum 4 during normal image formation was performed as shown in FIG. 25 when A4 paper was continuously output in full color. It is important that the laser output of the patch is the same as when the target value is set, and for each color, 128 levels are used for the density signal (density signal axis in FIG. 6). At this time, the contents of the LUT 25 and the setting of the contrast potential are the same as in the normal image formation at that time. That is, what is obtained by the first control system and corrected by the second control system up to the previous time is used.
The density signal 128 is controlled so that the patch output density becomes D128 on a density scale obtained by normalizing 1.6 to 255. However, the image characteristics of the printer are unstable, and there is a possibility that the density is constantly changed. Therefore, the measured result is not always D128, but may be shifted by ΔD. Based on this ΔD, the second control system corrects the LUT 25 (γLUT) created by the first control system.
FIG. 26 shows a γLUT correction table corresponding to a change in output density from general density signals 0 to 255 when the output density is shifted by ΔDx in the density signal 128 in the present embodiment. This is held in advance, and at the time of control, the γ correction table is normalized so that the value of the density signal 128 in the γ LUT correction table becomes ΔD, and the LUT 25 is corrected by adding the LUT formed so as to cancel this to the LUT 25. . The timing at which the LUT 25 is rewritten differs for each color. When the LUT 25 is ready for rewriting, the LUT 25 is rewritten by a TOP signal while laser writing of the color is not performed.
In the present embodiment, the second control system is activated during normal image formation when the non-image area can be developed. That is, in the case of continuous output of A4 size full color, the γLUT correction by this gradation control is performed once for each color for every two sheets output, or for each color in the case of intermittent sheets.
Since the first control system involves a human operation, it is difficult to assume that the first control system is frequently performed.
Therefore, the serviceman executes the first control system for the installation work of the image forming apparatus, and if there is no problem in the image, the second control system automatically maintains the characteristics for a short period of time. The first control system can perform the role of performing the calibration for those that have been gradually changed, and as a result, the gradation characteristics can be maintained until the life of the image forming apparatus.
[0080]
<Embodiment 2>
This embodiment is an embodiment in which the density signal of the patch is set to a low density range in the second control system in the first embodiment.
Hereinafter, the same parts as those in the first embodiment will be omitted, and only different parts will be described.
The object of the present invention is to stabilize the tint, and since it is generally said that the lower the density, the larger the color difference due to the density fluctuation becomes, the patch density used for control is set to a low density area, and the control accuracy in the low density area is increased. In this embodiment, image control for further suppressing color fluctuation is performed.
FIG. 27 shows the relationship between the density difference and the color difference in the copying machine used in the present embodiment.
From the sensor sensitivities shown in FIG. 27 and FIG. 22 and the sensitivities to the fluctuations that can be read from FIG. 26, the laser output of the patch in this embodiment is similar to the target value setting and the normal image formation in that the density signal ( Sixty-four levels (about 0.4 in terms of density) in the density signal axis of FIG. 6) were used.
When a low-density patch is detected by a density sensor, it is strongly affected by the state of the surface of the photosensitive drum serving as a base. Measurement is performed by a sensor, and the sensor output at the time of patch measurement is corrected based on the measured value.
Since the target value setting sequence includes the measurement of the base in addition to the first embodiment, the number of rotations of the drum only increases by one. The sequence of forming a patch on a non-image area on the photosensitive drum 4 during normal image formation is the same as in the first embodiment, but the background is measured at the time of pre-rotation at the start of each job.
In the present embodiment, sufficient stabilization is achieved in the vicinity of the density level at which the patch is formed, so that fluctuations in the low density range can be suppressed, and control can be performed to further suppress color fluctuations. <Embodiment 3>
This embodiment is an example in the case where a plurality of gradation patches are formed in the same non-image area where only one patch is formed in the second control system in the first embodiment. The same parts as those in the first embodiment are omitted, and only different parts will be described.
The laser output of the patch according to the present embodiment uses 64, 128, and 192 levels of the density signal (density signal axis in FIG. 6) for each color similarly to the target value setting and the normal image formation. In the sequence for setting the target value, the number of laps of the drum increases only because the number of patches in the first embodiment is tripled. A sequence for forming a patch on a non-image area on the photosensitive drum 4 during normal image formation was performed as shown in FIG.
From ΔD of each density signal obtained from three patches of each color, a density variation amount of the entire density signal is obtained by interpolation. As an interpolation method, spline interpolation, Lagrange interpolation, or the like is used. The density difference between the density signals 0 and 255 was 0. The obtained density change amount is the same as that obtained by standardizing the γ correction table in the first embodiment, and the LUT correction is performed using this.
In this case, in Embodiment 1, it is assumed that the form of the change in density is constant, but since the form of the change is read at that time, various changes can be handled. In addition, since sufficient stabilization is achieved at least at the density level where the patch is formed, it is possible to perform control appropriate for the purpose by increasing the number of important density areas, for example, low density patches that have an effect on color. become.
[0081]
【The invention's effect】
As described above, according to the present invention, it is possible to obtain an effect that image stabilization can be achieved by more accurate and more frequent image stabilization control.
[Brief description of the drawings]
FIG. 1 is a configuration sectional view of a first embodiment of the present invention.
FIG. 2 is a block diagram illustrating a configuration of a reader image processing unit according to the first embodiment of the present invention.
FIG. 3 is a diagram illustrating timings of a reader image processing unit according to the first embodiment of the present invention.
FIG. 4 is a control block diagram according to the first embodiment of the present invention.
FIG. 5 is a block diagram showing Embodiment 1 of the present invention.
FIG. 6 is a fourth-limit chart showing gradation reproduction characteristics.
FIG. 7 is a flowchart of a first control system.
FIG. 8 is a diagram showing display contents of a display device.
FIG. 9 is a diagram showing display contents of a display device.
FIG. 10 is a diagram showing display contents of a display device.
FIG. 11 is a diagram showing an example of test print 1.
FIG. 12 is a diagram illustrating an example of a test print 2.
FIG. 13 is a diagram showing how to place a test print 1 on a document table.
FIG. 14 is a diagram showing how to place a test print 2 on a document table.
FIG. 15 is a diagram showing a relationship between relative drum surface potential and image density.
FIG. 16 is a diagram showing a relationship between an absolute water content and a contrast potential.
FIG. 17 is a diagram showing a relationship between a grid potential and a surface potential.
FIG. 18 is a diagram showing read points of a patch pattern.
FIG. 19 is a diagram illustrating an example of reading a test print 2.
FIG. 20 is a diagram showing an LUT corresponding to each water content.
FIG. 21 is a flowchart from the photo sensor to the density conversion.
FIG. 22 is a diagram illustrating a relationship between a photosensor output and an image density.
FIG. 23 is a flowchart for setting a target value.
FIG. 24 is a diagram illustrating an example of detection by a second control system.
FIG. 25 is a sequence diagram of forming a patch in a non-image area.
FIG. 26 is a diagram showing a γLUT correction table.
FIG. 27 is a diagram illustrating a relationship between a density difference and a color difference.
FIG. 28 is a diagram illustrating density conversion characteristics.
FIG. 29 is a sequence diagram for forming a patch in a non-image area according to Embodiment 3 of the present invention.
[Explanation of symbols]
3 Developing device
4 Photosensitive drum
7 Fixing roller
8 Primary charger
10 LED
11 Photodiode
12 Surface potential sensor
25 γ-LUT
29 Pattern Generator
33 Environmental (moisture content) sensor
100 Printer Engine
105 CCD sensor
109 Printer control unit
110 semiconductor laser

Claims (12)

An image carrier, image forming means for forming an image on the image carrier, transfer means for transferring the image on the image carrier to a recording material, and fixing the image transferred to the recording material to the recording material Fixing means, optical detecting means for detecting image information of an image on the image carrier, reading means for reading image information of an image fixed on the recording material, and adjusting means for adjusting image forming conditions. At least one or more image patterns A for determining image characteristics in a sequence different from that during normal image formation are formed on the recording material, and the formed image patterns A are read by the reading unit and read. In an image forming apparatus having a first control system that controls image forming conditions based on image information,
At the end of the image control by the first control system, at least one or more image patterns B are formed on the image carrier, and the image information of the formed image patterns B is read by the optical detection means. On the basis of image information, during normal image formation, the image pattern B is formed in a non-image forming area on the image carrier, and the formed image pattern B is read by the optical detection means. An image control method, comprising: a second control system for further correcting an image forming condition corrected by image control by a first control system based on a difference between the first control system and reference image information. Based on image information read from an image pattern B formed during the normal image formation, image information of at least one or more image patterns A formed in a sequence different from that at the time of the normal image formation is estimated, and the image information And controlling the same image forming conditions during normal image formation in a sequence different from that for the normal image formation. An image carrier, an image forming unit for forming an image on the image carrier, a transfer unit for transferring the image on the image carrier to a recording material, and an image transferred to the recording material on the recording material. An image forming apparatus comprising: a fixing unit configured to perform image density adjustment and image gradation adjustment by the image control method according to claim 1. 2. The image control method according to claim 1, wherein the image forming condition is a [gamma] LUT. 2. The image control method according to claim 1, wherein said optical detection means is a regular reflection type sensor. 2. The image control method according to claim 1, wherein the image signal formed by the image forming unit is an image signal converted according to the correction information. The image control method according to claim 1, wherein the image carrier is a drum-shaped photosensitive drum having a photosensitive layer on a surface. The image control method according to claim 1, wherein the image carrier is a sheet-shaped photosensitive sheet having a photosensitive layer on a surface. 2. The image control method according to claim 1, wherein the image carrier is a belt-shaped photosensitive belt having a photosensitive layer on a surface. 2. The image control method according to claim 1, wherein the image carrier is a transfer body on which a toner image is transferred from the photoconductor. The image control method according to claim 10, wherein the transfer body is an intermediate transfer body. 2. The image control method according to claim 1, wherein the image forming condition includes a toner density in a developer.

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