JP2010091600A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of detecting an image pattern with high accuracy without being affected by dispersion in the time when the image pattern on a transfer material arrives in a sensor detection area. <P>SOLUTION: The image forming apparatus includes: an image pattern forming means for forming and fixing the image pattern used in an image density control on the transfer material; an image pattern detecting means for detecting the image pattern formed and fixed on the transfer material; a storage means for storing output values of the image patterns detected over several times by the image pattern detecting means; an output value decision means for deciding representative output values corresponding to the respective image patterns based on changes in the output values of the image patterns stored in the storage means; and a control means for controlling operations of the image pattern detecting means, the storage means and the output value detecting means, and executing a density control of an output image based on the representative output values (S106) decided by the output value decision means. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as a color printer or a color copying machine, and more particularly to detection of an image pattern (toner patch) used for image density control.

In recent years, color image forming apparatuses such as color printers and color copiers are required to improve the output image quality. In particular, the gradation of density and its stability greatly affect the quality of the image.
However, in general, in an electrophotographic image forming apparatus, if there is a change in each part of the apparatus due to a change in environment or long-term use, the density of an obtained image will change. In particular, in the case of an electrophotographic color image forming apparatus, there is a possibility that the color balance may be lost even by a slight change in density, and therefore it is necessary to have means for always maintaining a constant density characteristic.

Therefore, a density detection toner patch is prepared on the intermediate transfer member, the photosensitive member or the transfer material carrier so that a constant density gradation characteristic can be obtained even if fluctuations in each part of the apparatus occur. A technique for stabilizing an image by detecting the density of an unfixed toner patch by a density detection sensor and performing density control by applying feedback to process conditions such as exposure amount and development bias based on the detection result is widely used. .
However, density control using the density sensor detects unfixed toner patches by forming them on an intermediate transfer member, a photosensitive member, or a transfer material carrier, and can deal with changes in transferability and fixability to transfer materials. Can not.

Therefore, the density of the patch image transferred and fixed on the transfer material can be adjusted to an original reading device such as an external flatbed scanner or a copier, There is a method in which density control is performed by detection using a sensor (hereinafter referred to as a color sensor) that detects the density and chromaticity of a toner patch on a transfer material provided separately from the density sensor.
Such an image density control method is disclosed in Patent Document 1, for example.
JP 2003-287934 A

However, the method of detecting the toner patch on the transfer material and controlling the image density has the following problems.
In order to measure a toner patch with a color sensor with high accuracy, it is necessary to detect a toner patch on a transfer material to be measured at an accurate timing.

However, there is a variation in the time when the toner patch on the transfer material arrives in the sensor detection area for the following two reasons.
First, it is difficult to estimate the timing when the leading toner patch reaches the sensor detection area.
In general, a sensor (fixing paper discharge sensor) for detecting a jam is prepared immediately after the fixing unit of the image forming apparatus. Therefore, if a color sensor is provided immediately after this sensor, the arrival timing of the transfer material can be accurately estimated. However, since the color sensor is composed of an optical element such as a lens and a resin member that holds the sensor, the color sensor needs to be disposed at a position sufficiently away from a heat source such as a fixing unit. It was necessary to provide.
Second, there is an effect of shrinkage of the transfer material size that occurs when the transfer material passes through the fixing device.
The shrinkage rate of the transfer material is difficult to predict because it varies depending on the fixing unit temperature, the type of transfer material, and the amount of moisture contained in the transfer material. For example, large-size paper (for example, A3 size) varies by several mm. It will occur.
Therefore, if the toner patch is detected at a fixed timing from a predetermined reference position (for example, a reference patch for position detection), there is a problem that a deviation occurs between the detection position and the toner patch, resulting in a decrease in detection accuracy. It was.

In order to solve the above problem, a method (for example, FIG. 16) that widens the margin of detection timing by increasing the size of the toner patch in the conveyance direction, or a reference patch for position detection is inserted at predetermined intervals, and the reference position is periodically set. Although there is a method of detecting and correcting the detection timing (for example, Bk in FIG. 15), there arises a problem that wasteful toner increases and economic efficiency decreases.
Further, since the number of patches that can be formed on one transfer material is reduced, there is a problem that the number of transfer materials on which patches are formed increases in order to provide feedback to various image forming process conditions.

  The present invention has been made under such circumstances, and can detect an image pattern with high accuracy without being affected by variations in time when the image pattern on the transfer material arrives in the sensor detection area. It is an object of the present invention to provide an image forming apparatus.

  In order to solve the above-described problems, in the present invention, an image forming apparatus is configured as described in (1) below.

(1) Image pattern forming means for forming and fixing an image pattern used for image density control on a transfer material;
An image pattern detecting means for detecting an image pattern formed and fixed on the transfer material;
Storage means for storing the output value of the image pattern detected multiple times by the image pattern detection means;
Output value determining means for determining a representative output value corresponding to each image pattern based on a change in the output value of the image pattern stored in the storage means;
Control means for controlling the operation of the image pattern detection means, the storage means and the output value determination means, and for controlling the density of the output image based on the representative output value determined by the output value determination means;
Image forming apparatus provided with

  In the present invention, it is possible to detect an image pattern with high accuracy without being affected by variations in time when the image pattern arrives in the sensor detection area.

  Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to an embodiment of a color image forming apparatus.

  A “color image forming apparatus” that is Embodiment 1 will be described. In this embodiment, a case where image gradation control is performed by a color sensor will be described.

  FIG. 1 is a cross-sectional view showing the overall configuration of the color image forming apparatus of this embodiment. As shown in the figure, this apparatus is an example of an electrophotographic color image forming apparatus, and is a tandem color image forming apparatus that employs an intermediate transfer member 27. The color image forming apparatus includes a control unit 10 and an image forming unit 20. The process speed of the image forming apparatus is 100 mm / s.

First, the operation of the image forming unit in the electrophotographic color image forming apparatus will be described with reference to FIG.
The image forming unit 20 forms an electrostatic latent image with exposure light that is turned on based on image information, develops the electrostatic latent image to form a single color toner image, and superimposes the single color toner image to create a multicolor image. A toner image is formed. Then, the multicolor toner image is transferred to the transfer material 11 and the multicolor toner image on the transfer material 11 is fixed. The image forming unit includes a sheet feeding unit 21, photosensitive drums 22Y, 22M, 22C, and 22K for each station arranged in parallel for the number of development colors, chargers 23Y, 23M, 23C, and 23K as primary charging units, a toner cartridge 25Y, 25M, 25C, 25K, developing units 26Y, 26M, 26C, 26K, intermediate transfer member 27, transfer roller 28, cleaner container 29, fixing unit 30, and color sensor 42 (corresponding to the image pattern detection means in the claims). It is configured.

The photosensitive drums (photoconductors) 22Y, 22M, 22C, and 22K are configured by applying an organic optical transmission layer to the outer periphery of an aluminum cylinder, and rotate by receiving a driving force of a driving motor (not shown). The drive motor rotates the photosensitive drums 22Y, 22M, 22C, and 22K in the counterclockwise direction according to the image forming operation.
The primary charging means includes four chargers 23Y, 23M, 23C, and 23K for charging the yellow (Y), magenta (M), cyan (C), and black (K) photoreceptors for each station. It is. Each charger is provided with sleeves 23YS, 23MS, 23CS, and 23KS.

  Exposure light to the photosensitive drums 22Y, 22M, 22C, and 22K is sent from the scanner units 24Y, 24M, 24C, and 24K, and the electrostatic latent images are selectively exposed by exposing the surfaces of the photosensitive drums 22Y, 22M, 22C, and 22K. An image is formed.

  As developing means, in order to visualize the electrostatic latent image, four developing devices 26Y, 26M for developing yellow (Y), magenta (M), cyan (C), and black (K) for each station, 26C and 26K. Each developing device is provided with sleeves 26YS, 26MS, 26CS, and 26KS. Each developing device is detachably attached.

  The intermediate transfer member 27 is in contact with the photosensitive drums 22Y, 22M, 22C, and 22K, and rotates clockwise when forming a color image. The intermediate transfer member 27 rotates in accordance with the rotation of the photosensitive drums 22Y, 22M, 22C, and 22K. The toner image is transferred. Thereafter, a transfer roller 28 to be described later comes into contact with the intermediate transfer member 27 to sandwich and transfer the transfer material 11, and the multicolor toner image on the intermediate transfer member 27 is transferred to the transfer material 11.

  The transfer roller 28 contacts the transfer material 11 at the position 28a while the multicolor toner image is transferred onto the transfer material 11, and is separated to the position 28b after the printing process.

The fixing unit 30 melts and fixes the transferred multi-color toner image while conveying the transfer material 11, and as shown in FIG. 1, the fixing roller 31 for heating the transfer material 11 and the transfer material 11 are fixed to the fixing roller. A pressure roller 32 is provided for pressure contact with 31. The fixing roller 31 and the pressure roller 32 are formed in a hollow shape, and heaters 33 and 34 are incorporated therein, respectively. That is, the transfer material 11 holding the multicolor toner image is conveyed by the fixing roller 31 and the pressure roller 32, and heat and pressure are applied to fix the toner on the surface.
After the toner image is fixed, the transfer material 11 is discharged to a discharge tray (not shown) by a discharge roller (not shown) and the image forming operation is finished.

  The cleaning means 29a cleans the toner remaining on the intermediate transfer member 27. After transferring the four-color multicolor toner image formed on the intermediate transfer member 27 onto the transfer material 11, the waste toner is removed from the cleaner. It is stored in the container 29b.

  The control unit 10 includes an arithmetic unit 12 such as a CPU and an MPU, a ROM 13 in which a program of the arithmetic unit is stored, and a RAM 14 in which work areas and various tables used during control execution are defined. Based on the output value from each sensor, feedback is given to a gradation correction unit such as a look-up table, and control is performed so as to produce a desired color on the transfer material. The control unit 10 corresponds to a control unit that performs density control of an output image in the claims.

  The color sensor 42 is arranged at the center position in the scanning direction of the scanner toward the image forming surface of the transfer material 11 downstream from the fixing unit 30, and the RGB output value for the toner patch after fixing formed on the transfer material 11. Is output to the control unit 10.

  FIG. 2A is a diagram showing the configuration of the color sensor 42. Here, the color sensor 42 includes a white LED 43 and a charge storage sensor 44 with an RGB on-chip filter. The white LED 43 is incident on the transfer material 11 on which the patch after fixing is formed at an angle of 45 degrees, and the intensity of diffuse reflected light in the 0 degree direction is detected by the charge storage sensor 44 with an RGB on-chip filter. The light receiving portion of the charge storage type sensor with RGB on-chip filter 44 is an independent RGB pixel as shown in FIG.

  The detected output value of the color sensor 42 is the maximum for both RGB in the absence of toner (white transfer material background), and the complementary color relationship increases as the color toner (C, M, Y toner) on the transfer material increases. The output value of a certain light receiving unit decreases. For example, if a large amount of C toner is used, the complementary color R output decreases. Similarly, G output corresponds to M toner, and B output corresponds to Y toner. That is, by detecting RGB output values, it is possible to detect the amount of toner of C, M, and Y (corresponding to a plurality of colors in the claims) toner. In the case of K toner, since all RGB output values decrease, any received light output value may be used. In this image forming apparatus, the amount of K toner is calculated from the G output.

  FIG. 3 is a diagram showing a toner patch pattern for chromaticity adjustment in Example 1, in which an image pattern of the same color is gradually changed in image print rate and density is changed. Corresponds to an “array so that the printing rate changes sequentially each time”). Specifically, the correspondence between each patch and the printing rate (gradation degree) is Y1, M1, C1, K1 = 12.5%, Y2, M2, C2, K2 = 25%, Y3, M3, C3, K3. = 37.5%, Y4, M4, C4, K4 = 50%, Y5, M5, C5, K5 = 62.5%, Y6, M6, C6, K6 = 75%, Y7, M7, C7, K7 = 87 .5%, Y8, M8, C8, K8 = 100%. One size of the toner patch pattern is 10 mm in the direction perpendicular to the transfer material conveyance direction and 6.5 mm in the transfer material conveyance direction, and there is a white portion between the toner patches. The chromaticity adjustment toner patch pattern corresponds to an image pattern used for image density control in the claims.

  Next, the detection process of the toner patch pattern on the transfer material, which is a feature of this embodiment, will be described with reference to the drawings. In this embodiment, the color sensor output is monitored, and when the output change amount falls within a predetermined range, the output is made to the RAM 14 to obtain the output value of the toner patch.

  FIG. 4 shows a state where the transfer material on which the toner patch pattern is fixed is conveyed to the color sensor position and conveyed while being irradiated by the white LED. S is a spot portion (diameter = 3 mm) of the white LED, and scans on the transfer material. The white portion length Lw between patch patterns is larger than the spot diameter.

FIG. 5 shows the time change of the B output value (complementary color of Y and the output value is large) output by the charge storage sensor 44 with an RGB on-chip filter when the color sensor scans Y1 at the head of the toner patch. Is shown. The vertical axis is a value obtained by inverting the AD value, and the higher the vertical axis, the higher the density.
FIG. 5 is a line connecting B output values every 10 ms. When the tip of the toner patch reaches the spot of the color sensor (B in FIGS. 4 and 5), the output gradually rises and the output waveform rises until the spot is completely covered with the toner patch. Exists. Thereafter, the output of the color sensor becomes stable, and the output decreases when the spot portion passes the trailing edge of the toner patch.

Next, a flow until the Y1 output value is determined from the output waveform of the color sensor will be described with reference to the flowchart of FIG. Processing of this flow is performed by the CPU 12.
First, after the toner patch pattern is transferred and fixed on the transfer material (corresponding to the image pattern forming means in the claims), the leading edge of the transfer material reaches the color sensor position. In step S101, it is determined whether the B output exceeds a threshold Th (corresponding to a first predetermined value in the claims), and if it exceeds, sampling is started (step S102). If the B output does not exceed the threshold Th, sampling is not performed. Here, the threshold value Th is the lowest output value assumed in the toner patch Y1, and is the lowest value expected due to environmental fluctuations and durability fluctuations in the image forming apparatus.
When the sampling is started, in step S103, the difference (AD value difference) from the previous B output value stored in the control unit (the difference between the current detection output and the previous detection output). The output change rate d is obtained. The output change rate d is a value for determining the degree of change, and a change value or the like can be used as a designation.
Next, in step S104, it is determined whether the output change rate d is smaller than a predetermined value (3 in this embodiment). In step S104, the description is made using the wording of the output change rate d, but the present invention is not limited to this. In this step S104, it may be determined whether or not the change value based on at least the current detection output and the previous detection output is smaller than a predetermined value in order to determine that the change in the detection result has decreased. . In this determination, the change value referred to by the CPU 12 may be a simple difference value between the previous detection result and the current detection result, or a change calculated based on the current detection result and a plurality of past detection results. It may be a value (average change).

If it is determined in step S104 that the output is small, it is determined that the output B has entered the stable region, and batch processing is started (step S105). The batch process is a process of saving the output value of the image pattern detected by the color sensor 42 a plurality of times in the RAM 14 as a storage unit. In other words, it is a process of collectively storing a plurality of sampling data in the RAM 14 which is a storage means. In order to prevent erroneous detection, it is preferable to move to step S105 after confirming the determination in step S104 about three times.
Conversely, if the output change rate d is greater than 3, it is determined that the rising portion is in the middle, and the calculation of the output change rate d is continued.

In step S106, the batch-processed data is calculated as an average value (representative output value) in the control unit 10, and then stored as a B output value of Y1 (corresponding to the output value determining means in the claims). The process ends (step S107).
Thereafter, in step S108, the sampling is terminated when the B output becomes smaller while determining whether the B output becomes smaller than the threshold Th (corresponding to the first predetermined value or less in the claims) (step S109).
The above processing is performed until an output value of other toner patches after Y2 is obtained (step S110).
Note that sampling and batch processing are performed for G output in M1 to M8, R output in C1 to C8, and G output in K1 to K8.

Next, the size of the toner patch in this embodiment will be described in comparison with a conventional example.
FIG. 16 is a diagram showing a conventional toner patch pattern for position detection. A toner patch for position detection is provided at the tip, and then the sensor output is read at a predetermined fixed timing. It is made larger considering the minutes.
The comparison was performed under the condition that 32 patches were formed with a constant size on a sheet of A3 size (length in transfer material conveyance direction = 420 mm). The sampling cycle is performed every 5 ms (length 0.5 mm), and the shrinkage rate of the transfer material [(length before fixing−length after fixing) / length before fixing] × 100) is 1%. Estimated by

  In the case of the conventional example, since the spot diameter is 3 mm, the sampling number is 5 points (the length of the toner patch is 4.0 mm), the margin is 1.5 mm, and the position variation at the rear end of the transfer material is about 4 mm, a total of 12 A length of 5 mm in the transfer material conveyance direction is required. Also, a toner patch of 5 mm is required for detecting the position of the transfer material tip. Here, the margin of 1.5 mm is a length for ensuring that the spot portion does not protrude from the toner patch.

  On the other hand, in this embodiment, the spot diameter is 3 mm, the sampling number is 5 points (the toner patch length is 4 mm), and the margin is 1.5 mm. The total length of the toner patches is 8.5 mm. That's fine. This sampling number of 5 points is an example of “the image pattern detection means samples the output value every time shorter than the time each image pattern passes through the image pattern detection means” in the claims. is there. Therefore, since the size of the toner patch can be reduced in the present embodiment as much as the shrinkage rate of the transfer material is not expected, the amount of toner to be used can be reduced. Further, in the conventional example, not all toner patches could be formed in A3 size paper, but in this embodiment, only one A3 size paper is required, and the amount of transfer material to be used can be reduced. .

  As a conventional toner patch pattern, there is a method of correcting the detection position by inserting black toner patches between toner patches at a predetermined interval as shown in FIG. The amount will increase.

  As described above, in this embodiment, instead of reading the output value of the color sensor at every predetermined timing as in the prior art, the output value of the toner patch is determined based on the output change of the color sensor. Therefore, it is possible to obtain an optimum toner patch output regardless of the position change of the toner patch due to the shrinkage of the transfer material. Accordingly, it is not necessary to increase the size of the toner patch or to insert a toner patch that becomes a reference position at a predetermined interval as in the conventional case, so that it is possible to suppress consumption of toner and transfer material.

A “color image forming apparatus” that is Embodiment 2 will be described. In this embodiment, when the RGB output of the color sensor becomes equal to or higher than a predetermined value, all batch processing is performed, and data optimum for each toner patch is extracted later.
Note that the overall configuration of the color image forming apparatus of this embodiment and the configuration of the color sensor are the same as those of the color image forming apparatus described in Embodiment 1, and a description thereof is omitted.
Further, the chromaticity adjusting toner patch pattern on the transfer material in the present embodiment is the same as that in the first embodiment, and the description thereof is omitted.

FIG. 7 shows the time change of the B output value output by the charge storage sensor 44 with the RGB on-chip filter when the color sensor scans the toner patches Y1 to Y8. The vertical axis is a value obtained by inverting the AD value, and the higher the vertical axis, the higher the density.
A flow for extracting an output value from the output waveform of the color sensor in this embodiment will be described with reference to FIG.
First, after the pattern of the chromaticity adjusting toner patch is transferred and fixed onto the transfer material, the leading edge of the transfer material reaches the color sensor position.
In step S201, it is determined whether the output B exceeds a threshold Th (corresponding to a second predetermined value in the claims), and if it exceeds, batch processing is started (step S202). Here, the threshold value Th is the lowest output value assumed for the toner patch with the lowest image printing rate (gradation degree).
In step S203, it is determined whether the B output is lower than the threshold value Th (corresponding to a second predetermined value in the claims).
The above operation is performed as many times as the number of toner patches formed on the transfer material (step S205).
Thereafter, the output value of each toner patch is obtained from the B output data stored in the output value table in order from the toner patch Y1 (step S206). In this embodiment, the average output value obtained from the three central points of each toner patch is used as the representative output value.

FIG. 9 is a table showing RGB output results and extraction areas stored in the output value table in order from the toner patch Y1. In this embodiment, the average value of the three central points of the sampling data (data area 1 to 100 in Y1) in each toner patch is calculated as an output value.
Similarly, batch processing and output calculation of G output are performed for M1 to M8, R output for C1 to C8, and G output for K1 to K8.

As described above, in this embodiment, the output value at the center of the toner patch can be extracted as compared with the first embodiment, so that it is possible to avoid the influence of the density variation at the edge portion.
In this embodiment, the median value of the output values exceeding the threshold value Th is shown. However, all data from the beginning to the end of the toner patch are sampled and batch-processed, stored in the storage means, and output later. It is also possible to calculate the rate of change, obtain the rise change point and the fall change point, and extract the median thereof.

A “color image forming apparatus” that is Embodiment 3 will be described. In the present embodiment, the order of the toner patches formed on the transfer material is formed so that the contrast of the adjacent toner patches is increased, and even when the number of toner patches formed on one transfer material is increased, the toner patch is suitable. This is an example in which an output value can be detected.
Note that the overall configuration of the color image forming apparatus of this embodiment and the configuration of the color sensor are the same as those of the color image forming apparatus described in Embodiment 1, and a description thereof is omitted.

FIG. 10 is a diagram showing a toner patch pattern for chromaticity adjustment in this embodiment, in which the image printing rate is changed and the chromaticity is changed. The correspondence between each patch and the printing rate (gradation degree) is the same as that of the toner patch pattern of the first embodiment, but the arrangement order is different.
For example, a yellow toner patch is arranged in the order of Y1, Y5, Y2, Y6, Y3, Y7, Y4, and Y8 from the top of the transfer material. Equivalent to “alternately changing”). The correspondence between each patch and the printing rate (gradation degree) is Y1 = 12.5%, Y2 = 25%, Y3 = 37.5%, Y4 = 50%, Y5 = 62.5%, Y6 = 75%, Y7 = 87.5% and Y8 = 100% are set. The other toner colors have the same arrangement.
That is, it is characterized in that toner patches are continuously formed (no white portion is provided), and an image is formed on a transfer material so as to obtain strength and weakness in output from a color sensor.

  FIG. 11 shows the time change of the B output value (AD value) output by the charge storage sensor 44 with the RGB on-chip filter when the color sensor 42 scans the yellow Y toner patch. The vertical axis is the value obtained by inverting the AD value.

Next, a method for extracting the output value of each toner patch from the output waveform of the color sensor 42 will be described with reference to the flowchart of FIG.
First, in step S301, it is determined whether the output B exceeds a threshold Th (corresponding to a third predetermined value in the claims), and if it exceeds, sampling is started (step S302). If the B output does not exceed the threshold Th, sampling is not performed. Here, the threshold Th is a minimum output value assumed in the toner patch Y1.
When sampling is started, in step S303, a difference (AD value difference) from the previous B output value stored in the control unit is obtained to obtain an output change rate d.
Next, in step S304, it is determined whether the absolute value of the output change rate d is smaller than a predetermined value (3 in the present embodiment). In step S304, the description has been made using the wording of the output change rate d, but the present invention is not limited to this. In this step S304, in order to determine that the change in the detection result has decreased, it is sufficient to determine whether or not the change value based on at least the current detection output and the previous detection output is smaller than a predetermined value. . In this determination, the change value referred to by the CPU 12 may be a simple difference value between the previous detection result and the current detection result, or a change calculated based on the current detection result and a plurality of past detection results. It may be a value (average change).

If it is determined in step S304 that the output is small, it is determined that the B output has entered the stable region, and batch processing is started (step S305). On the contrary, if the absolute value of the output change rate d is larger than a predetermined value (3 in this embodiment), it is determined that it is in the middle of the rising portion (or falling portion), and the calculation of the output change rate d is continued.
In step S306, the batch-processed data is calculated as an average value (representative output value) in the control unit 10, and then stored as a Y output value of Y1, and the batch processing is terminated (step S307).
Further, in step S308, it is determined whether batch processing for a predetermined number of toner patches has been performed. When the output values of all the toner patches have been obtained, sampling is terminated (step S309).
The above is also performed for toner patches of other colors. Note that sampling and batch processing are performed for G output in M1 to M8, R output in C1 to C8, and G output in K1 to K8.

  As described above, in this embodiment, the toner patch for chromaticity detection is formed on the transfer material so that the difference (contrast) between adjacent sensor output values becomes large. Therefore, when obtaining finer chromaticity information for color stability control of the color image forming apparatus, for example, even when the density change with respect to the printing rate is small and the output is difficult to detect, such as a solid part or a highlight part, There is an advantage that the output value can be detected with high accuracy.

A “color image forming apparatus” that is Embodiment 4 will be described. In the third embodiment, the case where the density of images having the same hue is sequentially changed as the toner patches continuously formed on the transfer material has been described. However, in this embodiment, toner patches having different hues are continuously formed. explain.
Note that the overall configuration of the color image forming apparatus of this embodiment and the configuration of the color sensor are the same as those of the color image forming apparatus described in Embodiment 1, and a description thereof is omitted.

  FIG. 13 is a diagram showing a toner patch pattern for chromaticity adjustment in this embodiment, and the hues are in the order of Y, M, and C. The printing rate is gradually increased. Since the correspondence between each patch and the printing rate is the same as that of the toner patch pattern of the first embodiment, description thereof is omitted.

FIG. 14 shows the time of the BGR output value (inverted AD value) output by the charge accumulation type sensor with RGB on-chip filter when the color sensor 42 scans the chromaticity adjustment toner patch pattern in this embodiment. It shows a change.
As described above, since the toner patches having different hues are continuously formed and arranged, the output values from the color sensor are spaced apart from the B output, G output, and R output until the toner patches of the same hue arrive. It becomes a waveform.

In this embodiment, when the Y color pattern passes through the color sensor 42, the output signal of the B output is read, when the M color pattern passes, the G output is read, and when the C color pattern passes, the output signal of the R output is read. The value is to be determined. The method for determining the output value is the same as in the first embodiment.
That is, first, after the toner patch pattern is transferred and fixed onto the transfer material, the leading edge of the transfer material reaches the color sensor position. It is determined whether the color sensor output exceeds a threshold Th (corresponding to a fourth predetermined value in the claims), and if it exceeds, sampling is started. If the color sensor output does not exceed the threshold Th, sampling is not performed. Here, the threshold value Th is the lowest output value assumed in the toner patch Y1, and is the lowest value expected due to environmental fluctuations and durability fluctuations in the image forming apparatus.
When sampling is started, the output change rate d is obtained by taking the difference (AD value difference) from the previous output value stored in the control unit.
Next, it is determined whether the output change rate d is smaller than a predetermined value. In addition, although it demonstrated using the word of the output change rate d here, it is not limited to this. Here, in order to determine that the change in the detection result has decreased, it is sufficient to determine whether or not the change value based on at least the current detection output and the previous detection output is smaller than a predetermined value. In this determination, the change value referred to by the CPU 12 may be a simple difference value between the previous detection result and the current detection result, or a change calculated based on the current detection result and a plurality of past detection results. It may be a value (average change). If it is smaller, it is determined that the output has entered the stable region, and batch processing is started. The batch process is a process for collectively storing a plurality of sampling data in the RAM 14 as a storage unit. On the contrary, if the output change rate d is larger than the predetermined value, it is determined that the rising portion is in the middle, and the calculation of the output change rate d is continued.

The batch-processed data is calculated as an average value (representative output value) in the control unit 10 and then stored as a Y output value of Y1, and the batch process is terminated.
Thereafter, the sampling is finished when the output of the color sensor becomes smaller than the threshold Th (when it is smaller than the fourth predetermined value in the claims).
The above processing is performed until output values of other toner patches after M1 are obtained.

As described above, in this embodiment, toner patches having different hues are continuously formed and arranged. Therefore, since the interval between sensor output values is widened, there is a merit that the output change becomes larger and the detection accuracy is improved as compared with the case where images of the same hue are continuously formed with the density gradually changed.
In addition, as the toner patches continuously formed and arranged on the transfer material, toner patches having different hues may be formed and arranged only in a highlight portion or a solid portion where the density change with respect to the printing rate is small. This corresponds to “the arrangement order is such that patterns of different hues are adjacent to each other for at least some of the image patterns” in the claims.

Sectional drawing which shows the whole structure of the color image forming apparatus which is Example 1. FIG. The figure which shows the structure of the color sensor 42 FIG. 5 is a diagram illustrating a toner patch pattern for chromaticity adjustment according to the first exemplary embodiment. The figure which shows the state which the transfer material with which the toner patch pattern was fixed is conveyed to a color sensor position, and is conveyed, irradiated with white LED. The figure which shows the time change of B output value output by the charge storage type sensor with a RGB on-chip filter. Flow chart showing the flow from determining the output value of the color sensor to determining the output value The figure which shows the time change of B output value when a color sensor scans the toner patches Y1-Y8. 7 is a flowchart showing a flow for extracting an output value from an output waveform of a color sensor in Embodiment 2. A table showing RGB output results and extraction areas stored in the output value table in order from the toner patch Y1. FIG. 10 is a diagram illustrating a toner patch pattern for chromaticity adjustment according to the third exemplary embodiment. The figure which shows the time change of B output value when a color sensor scans the toner patch of yellow Y A flowchart showing a flow of extracting the output value of each toner patch from the output waveform of the color sensor FIG. 10 is a diagram illustrating a chromaticity adjustment toner patch pattern according to a fourth exemplary embodiment. The figure which shows the time change of a BGR output value when a color sensor scans the toner patch pattern for chromaticity adjustment. FIG. 5 is a diagram illustrating a toner patch pattern used in a conventional method of inserting a position detection reference patch at predetermined intervals, periodically detecting the reference position, and correcting the detection timing. The figure which shows the toner patch pattern used with the method of enlarging the margin of a detection timing by enlarging the size of the conveyance direction of a toner patch conventionally.

Explanation of symbols

12 CPU
22 Photoconductor 30 Fixing section 42 Color sensor

Claims (10)

Image pattern forming means for forming and fixing an image pattern used for image density control on a transfer material;
An image pattern detecting means for detecting an image pattern formed and fixed on the transfer material;
Storage means for storing the output value of the image pattern detected multiple times by the image pattern detection means;
Output value determining means for determining a representative output value corresponding to each image pattern based on a change in the output value of the image pattern stored in the storage means;
Control means for controlling the operation of the image pattern detection means, the storage means and the output value determination means, and for controlling the density of the output image based on the representative output value determined by the output value determination means;
An image forming apparatus comprising: The image forming apparatus according to claim 1,
The image pattern is a pattern in which the printing rate is changed for a plurality of colors arranged in the transfer material conveyance direction, and the arrangement order is arranged so that the printing rate changes sequentially for the same hue. An image forming apparatus. The image forming apparatus according to claim 2.
The control means, when the detection output of the image pattern detection means exceeds a first predetermined value, and at least a change value based on the current detection output and the previous detection output is smaller than a predetermined value, An image forming apparatus that stores an output value of an image pattern in the storage unit, and terminates the storage of the output value when a detection output of the image pattern detection unit becomes less than the first predetermined value. . The image forming apparatus according to claim 2.
When the detection output of the image pattern detection means exceeds a second predetermined value, the control means stores the output value of the image pattern in the storage means, and when the output is less than the second predetermined value An image forming apparatus, which finishes storing an output value of an image pattern. The image forming apparatus according to claim 1,
The image pattern is a pattern in which the printing rate is changed for a plurality of colors arranged in the transfer material conveyance direction, and the arrangement order is arranged so that the printing rate changes alternately in magnitude for every same hue. An image forming apparatus. The image forming apparatus according to claim 5.
The control means has a detection output of the image pattern detection means exceeding a third predetermined value, and a change value based on at least the current detection output and the previous detection output of the image pattern detection means is greater than a predetermined value. An image forming apparatus, wherein an output value of an image pattern is stored in the storage means when it becomes smaller. The image forming apparatus according to claim 1,
The image pattern is a pattern in which the printing rate is changed for a plurality of colors arranged in the transfer material conveyance direction, and the arrangement order is arranged so that patterns of different hues are adjacent to at least some of the image patterns. An image forming apparatus. The image forming apparatus according to claim 7.
The control means, when the detection output of the image pattern detection means exceeds a fourth predetermined value, and when the change value based on at least the current detection output and the previous detection output is smaller than the predetermined value, An image forming apparatus, wherein an output value of an image pattern is stored in the storage means, and the storage of the image pattern is terminated when the output value is less than the fourth predetermined value. The image forming apparatus according to claim 1,
The image forming apparatus is characterized in that the image pattern detecting means samples the output value every time shorter than the time each image pattern passes through the image pattern detecting means. The image forming apparatus according to any one of claims 1 to 9,
The image forming apparatus according to claim 1, wherein the image pattern detecting unit includes a sensor that detects a color complementary to a color of the image pattern formed on the transfer material.

Images