JP2021162783A - Image forming apparatus - Google Patents

Abstract

To improve correction accuracy in density correction by increasing the accuracy of detecting toner density in an image forming apparatus.SOLUTION: An image forming apparatus has: an intermediate transfer belt that carries a formed image; an LED that irradiates the intermediate transfer belt with light; photo diodes that detect regularly reflected light and diffuse reflected light, respectively; a state detection unit that detects the state of the intermediate transfer belt from results of detection performed by the photo diodes; and control means that forms a first toner pattern or a second toner pattern on the intermediate transfer belt in accordance with a result of detection of the state of the intermediate transfer belt. The first toner pattern and the second toner pattern include at least two or more toner images different in density from each other, and a pattern of a difference in density between the toner images included in the first toner pattern and a pattern of a difference in density between the toner images included in the second toner pattern are different from each other.SELECTED DRAWING: Figure 14

Description

The present invention relates to an image forming apparatus that forms a toner image on a transfer medium such as a transfer belt.

The image forming apparatus has short-term fluctuations due to changes in the environment of the installation location and the environment inside the equipment, and long-term fluctuations due to factors such as changes over time or deterioration over time of the photoconductor and developer. Be exposed to the influence of. As a result, the density and density gradation in the output image of the image forming apparatus may differ from the desired density and gradation. For this reason, in the image forming apparatus, in order to adjust the density and gradation of the output image to the desired density and gradation, it is necessary to correct the image forming conditions at any time in consideration of various fluctuations due to the above-mentioned factors. be.

In some image forming devices, a toner image having a predetermined pattern is formed on a belt-shaped image carrier (hereinafter referred to as a transfer belt), and these toner images are read by an optical sensor including a light emitting element and a light receiving element. In such an image forming apparatus, there is known a method of appropriately correcting the toner density by comparing the toner density of the toner image read by the optical sensor with a density target value.

The optical sensor has a diffuse reflection light detection method that detects a change in the amount of diffuse reflection light reflected from the toner pattern and a normal reflection light detection method that detects a change in the amount of normal reflection light reflected from the image carrier. There is. Since the color toner image has a specular reflection component and a diffuse reflection component, a diffuse reflection light detection type optical sensor is generally used. However, since the diffuse reflection component of the black toner image is minute, a specular light detection method may be used.

However, in specular light detection, the detection value of the optical sensor fluctuates greatly when the shape or surface of the transfer belt changes. Therefore, if the gloss is lowered due to the continuous use of the transfer belt, or if the transfer belt is stagnant while being wound around the roller, the concentration may not be detected correctly.

Patent Document 1 discloses an image forming apparatus using a composite toner image formed by superimposing a black toner image on a color toner image on a density measurement patch image. By doing so, the black toner image is detected from the difference in reflectance between the color toner image and the black toner image. When a black toner image is superimposed on a color toner image, the detected reflected light is mainly diffuse reflected light from the underlying color toner image, so the reflected light intensity also changes according to the density of the black toner image. do. By holding these relationships in advance and using a conversion formula or conversion table based on the detected value of the reflected light, the toner concentration of the black toner image can be calculated more accurately.

Japanese Unexamined Patent Publication No. 9-34210

However, in the method described in Patent Document 1, since the color toner is used in addition to the black toner to be detected in the patch image, the toner consumption at the time of density correction becomes large. Further, it is not desirable to use such a method in which the toner consumption increases even when no abnormality occurs in the transfer belt, because the toner consumption increases.

On the other hand, by detecting the shape and surface condition of the transfer belt and appropriately selecting the black toner concentration detection mode according to the detection result, the black toner concentration is detected with high accuracy and the toner consumption is minimized. The method is also known. In this case, the specular reflection light sensor that measures the black toner formed on the transfer belt and the diffuse reflection light sensor that measures the black toner formed on the transfer belt and the cyan toner have the surface properties of the black toner base. Is different. Therefore, the output characteristics of the specular reflection sensor and the diffuse reflection sensor are also different.

Here, when the toner density is detected and the density correction is performed, the toner density can be detected with high accuracy and the correction accuracy in the density correction can be improved by using the toner pattern corresponding to the output characteristic of the sensor. However, when the same toner pattern is used for the positively reflected light and the diffusely reflected light, a toner pattern different from the sensor output characteristic is used for at least one of the positively reflected light sensor and the diffusely reflected light sensor. As a result, by using a toner pattern different from the sensor output characteristics, the detection accuracy of the toner density in the formed toner image may be lowered, and the correction accuracy in the density correction may also be lowered.

The present invention has been made in view of the above problems, and an object of the present invention is to improve the correction accuracy in density correction by increasing the detection accuracy of the toner density in the formed toner image.

The image forming apparatus of the present invention includes an image forming means for forming an image, an image carrier formed by the image forming means for carrying the image, an irradiation means for irradiating the image carrier with light, and the above. From the irradiation means detected by at least one of the first detecting means for detecting the positively reflected light of light, the second detecting means for detecting the diffusely reflected light of the light, and the first detecting means and the second detecting means. It has a control means for correcting the density of an image formed by the image forming means from the detection result of the reflected light of the irradiated light, and the control means has the first detection means and the second detection means. A first toner pattern or a second toner pattern is selected based on the detection result of the means, and the selected first toner pattern or the second toner pattern is formed on the image carrier by using the image forming means. The first toner pattern is formed by using the first toner, and the second toner pattern is formed by superimposing the second toner formed on the image carrier and the second toner. The second toner contains toner, the second toner is different from the first toner, and the number of toner images contained in the second toner pattern is larger than the number of toner images contained in the first toner pattern. It is characterized by.

According to the present invention, by increasing the detection accuracy of the toner density in the formed toner image, the correction accuracy in the density correction can be improved.

Schematic diagram of the image forming apparatus. Schematic block diagram of the concentration sensor. The block diagram of the control part of an image forming apparatus. (A) to (c) are explanatory views of a density detection pattern used for density correction. (A) to (c) are graphs showing the relationship between the toner concentration and the received signal value of the density sensor. Toner pattern for density correction target toner, optical sensor, and sensor characteristic explanatory diagram. Functional block diagram of the control unit. A flowchart showing the density correction table creation process of the correction unit. A graph showing the initial correction table. Graph using sequential correction table. Graph using a synthetic correction table. The graph which shows the relationship between the toner density and the received signal value of a density sensor. Explanatory drawing of toner pattern. A graph showing the relationship between the toner density when the gradation level of the toner pattern is changed and the received signal value of the density sensor. A flowchart showing the main processing executed by the image forming apparatus. The explanatory view of the toner pattern in 2nd Embodiment. The explanatory view of the toner pattern in 3rd Embodiment. The explanatory view of the toner pattern in the modification of 3rd Embodiment.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

First Embodiment In the first embodiment, the present invention will be described using an electrophotographic laser beam printer as an image forming apparatus. However, the present invention is not limited to the laser beam printer, and can be applied to any type of image forming apparatus such as an inkjet printer and a sublimation printer.

<Configuration of image processing device>
FIG. 1 is a schematic configuration diagram of the image forming apparatus of the first embodiment. The image forming apparatus 200 can be realized by a printer, a copying machine, a multifunction device, a facsimile, or the like that forms a color image by an electrophotographic method. The image forming apparatus 200 is a so-called intermediate transfer tandem type image forming apparatus in which four image forming portions Pa to Pd are arranged side by side on an intermediate transfer belt 7 as an image carrier. The recording material S such as a sheet on which an image is formed is loaded in the recording material storage 60, and the paper feed roller 61 adopting a friction separation method according to the timing of image formation by the image forming units Pa to Pd. Is fed by. The paper feed roller 61 conveys the recording material S to the resist roller 62 via the transfer path. The resist roller 62 corrects the skew of the recording material S, adjusts the timing, and conveys the recording material S to the secondary transfer unit T2.

The image forming apparatus 200 has a control unit 50, and images are formed by the image forming units Pa to Pd. The image forming units Pa to Pd include photoconductors 1a to 1d, chargers 2a to 2d, laser scanners 3a to 3d, developing units 100a to 100d, primary transfer units T1a to T1d, and photoconductor cleaners 6a to 6d. The chargers 2a to 2d uniformly charge the surfaces of the photoconductors 1a to 1d. The photoconductors 1a to 1d are rotationally driven, and are irradiated with light by the laser scanners 3a to 3d. The laser scanners 3a to 3d operate as an exposure device and irradiate the photoconductors 1a to 1d with light modulated according to the image information of the image to be formed. As a result, electrostatic latent images corresponding to the images are formed on the photoconductors 1a to 1d.

The developing devices 100a to 100d develop the electrostatic latent image formed on the photoconductors 1a to 1d with a developing agent. In this embodiment, toner is used as the developer. The developing devices 100a to 100d develop the image by adhering toner to the photoconductors 1a to 1d on which the electrostatic latent image is formed. Hereinafter, the image developed by adhering toner to the photoconductors 1a to 1d in this way will be referred to as a toner image. The primary transfer units T1a to T1d are given a predetermined pressure amount and electrostatic load bias, and transfer the toner image from the photoconductors 1a to 1d to the intermediate transfer belt 7. At this time, the toner images formed on each of the photoconductors 1a to 1d are transferred so as to be superimposed on the intermediate transfer belt 7.

The image forming unit Pa generates a yellow toner image. The image forming unit Pb generates a magenta toner image. The image forming unit Pc generates a cyan toner image. The image forming unit Pd generates a black toner image. The number of colors of the formed toner image is not limited to four. The developers 100a to 100d of the first embodiment contain a two-component developer in which a non-magnetic toner and a magnetic carrier are mixed, but may be a one-component developer containing only magnetic toner or non-magnetic toner.

A full-color toner image is formed by superimposing and transferring the toner images of each color of yellow, magenta, cyan, and black on the intermediate transfer belt 7. The toner remaining on the photoconductors 1a to 1d after the transfer is recovered by the photoconductor cleaners 6a to 6d. When the amount of toner contained in the developing units 100a to 100d is lower than a predetermined amount, toner is replenished from the toner bottles Ta to Td, which are replenishment containers for the developer.

The intermediate transfer belt 7 is an endless belt provided on an intermediate transfer belt frame (not shown) and stretched by a secondary transfer inner roller 8, a tension roller 17, and a secondary transfer upstream roller 18. The intermediate transfer belt 7 is rotationally driven in the direction of arrow R7 by the secondary transfer inner roller 8, the tension roller 17, and the secondary transfer upstream roller 18. The intermediate transfer belt 7 on which the full-color toner image is formed transfers the toner image to the secondary transfer unit T2 by rotating.

The toner images formed on the recording material S and the intermediate transfer belt 7 are conveyed by the secondary transfer unit T2 at matching timings. The secondary transfer portion T2 is a transfer nip portion formed by the secondary transfer inner roller 8 and the secondary transfer outer roller 9 arranged to face each other, and by applying a predetermined pressing force and electrostatic load bias. The toner image is adsorbed on the recording material S. In this way, the secondary transfer unit T2 transfers the toner image on the intermediate transfer belt 7 to the recording material S. The toner remaining on the intermediate transfer belt 7 after transfer is recovered by the transfer cleaner 11.

The recording material S on which the toner image is transferred is conveyed from the secondary transfer unit T2 to the fixing device 13 by the secondary transfer outer roller 9. The fixing device 13 applies a predetermined pressure and heat to the recording material S in the fixing nip formed by the opposing rollers to melt and fix the toner image on the recording material S. The fuser 13 includes a heater that serves as a heat source, and is controlled so that an optimum temperature is always maintained. The recording material S on which the toner image is fixed is discharged onto the paper ejection tray 63. In the case of double-sided image formation, the recording material S is inverted by the inversion transport mechanism and conveyed to the resist roller 62. A density sensor 70 for detecting the toner density is provided in the vicinity of the intermediate transfer belt 7. The density sensor 70 is arranged between the photoconductor 1d and the secondary transfer outer roller 9 in order to detect the toner pattern of each color formed on the intermediate transfer belt 7.

FIG. 2 is a schematic configuration diagram of the concentration sensor 70. The density sensor 70 is arranged opposite to the intermediate transfer belt 7 and detects the toner pattern 74 formed on the intermediate transfer belt 7. The density sensor 70 has a light emitting diode (hereinafter referred to as LED) 71 that irradiates the intermediate transfer belt 7 with infrared rays at an incident angle of 15 °. The density sensor 70 has an optical sensor, and the optical sensor has PD72 and PD73 which are photodiodes (PD). The PD 72 receives the reflected light of the light radiated from the LED 71 to the intermediate transfer belt 7 and the toner pattern 74 at the position of the specular reflection angle. The PD 73 receives the reflected light of the light radiated from the LED 71 to the intermediate transfer belt 7 and the toner pattern 74 at the position of the diffuse reflection angle. In this way, the PD 72 operates as a specular reflected light sensor, and the PD 73 operates as a diffuse reflected light sensor. Further, the concentration sensor 70 has an electric board (not shown) on which these PD72 and PD73 are mounted. These optical elements are mounted on an electric board (not shown) including a drive circuit that supplies a current to the LED 71 and a light receiving circuit having an IV conversion function that converts the current flowing according to the amount of light received by the PD 72 and PD 73. There is.

The density sensor 70 having the above configuration can measure both specularly reflected light and diffusely reflected light (or diffusely reflected light). The PD72 that receives specularly reflected light and the PD73 that receives diffusely reflected light measure the reflected light of the intermediate transfer belt and the toner pattern 74. Here, the concentration sensor 70 is not limited to the configuration shown in the present embodiment, and may be a configuration in which the PD72 or PD73 is arranged directly above or a configuration including a polarizing filter. In the present embodiment, a configuration in which the intermediate transfer belt is arranged so as to face the intermediate transfer belt will be described, but it is also possible to appropriately arrange the arrangement in another position such as on a photosensitive drum.

<Structure of control unit 50>
FIG. 3 is a functional configuration diagram of the control unit 50 of the image forming apparatus 200. The CPU 301 has a function of generating various instruction signals and executing arithmetic processing in order to operate various sensors and motors of the image forming apparatus 200 along the electrophotographic process. Further, a memory for storing data is built in the CPU 301. The image data generation unit 302 has a function of converting various image data into signals for laser control and sending control signals to the laser drive units 303a to 303d. The image data generation unit 302 also has a function of generating a toner pattern 74 for detecting the toner concentration.

The laser drive units 303a to 303d have a function of driving the laser elements of the laser scanners 3a to 3d based on the signal sent from the image data generation unit 302 to control the lighting and the amount of light of the laser. The concentration sensor drive circuit 304 controls ON / OFF and drive current of the LED 71 inside the concentration sensor 70 according to a command signal of the CPU 301. The concentration sensor detection circuit 305 amplifies the received voltage signal from the concentration sensor 70 and sends it to the CPU 301.

<Outline of toner pattern detected by density sensor>
4 (a) to 4 (c) are explanatory views of the first to third toner patterns for density detection used for density correction, which are formed on the intermediate transfer belt 7 and shown as the toner pattern 74 in FIG. .. All of these drawings show the toner image as viewed from the side of the toner pattern. Further, a toner patch for density detection formed on the intermediate transfer belt 7 is described as a toner image, and a toner image group composed of a plurality of toner images having different gradations is described as a toner pattern.

FIG. 4A shows a state in which a black toner image is formed on the intermediate transfer belt 7 as the first toner pattern, and FIG. 4B shows cyan on the intermediate transfer belt 7 as the second toner pattern. Indicates a state in which a toner image is formed. FIG. 4C shows a state in which a black toner image is superimposed on a cyan toner image on the intermediate transfer belt 7 as a third toner pattern. Each of the first to third toner patterns includes two or more toner images. As shown in FIG. 4A, the black toner image is divided into 10 images, and the density increases as the black toner image proceeds to the right in the drawing.

In FIG. 4B, the cyan toner image is divided into 10 images, and the density increases as the cyan toner image advances to the right in the drawing. In FIG. 4C, the density of the underlying cyan toner image is constant, while the black toner image is divided into 10 images, and the density increases as the drawing progresses to the right. .. The first toner pattern and the third toner pattern shown in FIGS. 4A and 4C show whether the black toner image is formed on the intermediate transfer belt 7 or the cyan toner image. Is different. Further, each of the first toner pattern and the third toner pattern has 10 toner images formed by black toner. However, as will be described later, in the first toner pattern, the density difference between adjacent toner images is constant, but in the third toner pattern, the density difference between adjacent toner images is not constant.

The second toner pattern shown in FIG. 4B is not limited to cyan toner, and targets chromatic toner such as yellow toner and magenta toner. Further, the third toner pattern shown in FIG. 4C is not limited to the configuration shown in the drawing. For example, the base color toner is not limited to cyan toner, and any chromatic color such as yellow toner or magenta toner may be used. Further, the toner pattern formed by superimposing on the color toner is not limited to black, and other colors may be used as long as they are achromatic.

Further, the method of forming the toner pattern at a desired density is not limited to the method of changing the dot density of the image data. For example, the amount of laser light of the laser scanners 3a to 3d can be changed, or the voltage value applied at the time of transferring the toner pattern can be changed. In this way, in order to form the toner pattern at a desired density, any image forming condition whose density can be controlled can be used.

5 (a) to 5 (c) are graphs showing the relationship between the light-receiving signal value measured by the PD72, which is a positively reflected light sensor, and the light-receiving signal value, which is measured by the PD73, which is a diffuse-reflected light sensor, and the toner concentration. Yes, the vertical axis represents the received signal value, and the horizontal axis represents the density.

5 (a) is the first toner pattern of FIG. 4 (a), FIG. 5 (b) is the second toner pattern of FIG. 4 (b), and FIG. 5 (c) is the first toner pattern of FIG. 4 (c). It corresponds to each of the three toner patterns. Further, in FIGS. 5A to 5C, the solid line shows the signal value output from the PD72, and the broken line shows the signal value output from the PD73.

As shown in FIG. 5A, in the first toner pattern, in the specular reflection light sensor, the signal value decreases as the toner concentration (Bk) increases, and the rate of change of the received signal value with respect to the toner concentration (Bk) changes. big. Therefore, when a specularly reflected light sensor is used, it is possible to obtain the toner concentration (Bk) with high accuracy from the received signal value. On the other hand, in the diffuse reflection light sensor, the signal value is small and the amount of change is small regardless of the density range, and it is shown that the rate of change of the received signal value with respect to the toner concentration (Bk) is small. Therefore, in the first toner pattern, when the toner concentration (Bk) is obtained from the received signal value of the diffuse reflected light sensor, the accuracy is lower than that when the specular reflected light sensor is used.

Explaining the specularly reflected light component, since the base of the intermediate transfer belt 7 has gloss, there are many specularly reflected light components when the toner image is not formed. On the other hand, as the amount of toner formed on the substrate increases, the substrate of the intermediate transfer belt 7 is hidden, so that the specularly reflected light component also decreases. Therefore, the rate of change of the received signal value with respect to the change of the toner concentration (Bk) becomes large. As for the diffuse reflection component, since both the base color of the intermediate transfer belt 7 and the black toner have low brightness, the diffuse reflection light is small regardless of whether or not a toner image is formed. Therefore, when the diffuse reflected light sensor is used, the rate of change of the received signal value with respect to the change in the toner concentration (Bk) is smaller than that when the specular reflected light sensor is used.

As shown in FIG. 5B, in the second toner pattern, in the specular reflection light sensor, the signal value decreases as the toner concentration (Cy) increases. On the other hand, in the diffuse reflection light sensor, the signal value increases as the toner concentration increases. The specularly reflected light component is the same as in FIG. 5 (a). Therefore, in both cases of specularly reflected light and diffusely reflected light, the rate of change of the received signal value with respect to the change of the toner concentration (Bk) is large. In the diffuse reflection component, the base color of the intermediate transfer belt 7 has a low brightness, and the cyan toner has a higher brightness than the intermediate transfer belt 7. Therefore, as the amount of cyan toner increases, the base of the intermediate transfer belt 7 is hidden and the diffuse reflection component increases.

As shown in FIG. 5C, in the third toner pattern, the signal value remains small in the specular reflected light sensor regardless of the density range of the toner concentration (Bk), and the change is small. On the other hand, in the diffuse reflection light sensor, the signal value decreases as the toner concentration increases, and the rate of change of the received signal value with respect to the toner concentration (Bk) increases. Therefore, when the diffuse reflected light sensor is used, the toner concentration (Bk) can be obtained with high accuracy from the received signal value. On the other hand, in the specular light sensor, the signal value is small and the rate of change is small regardless of the density range. That is, the rate of change of the received signal value with respect to the toner concentration (Bk) is small.

Therefore, in the third toner pattern, when the toner concentration (Bk) is obtained from the received signal value of the diffuse reflected light sensor, the accuracy is higher than that when the specular reflected light sensor is used. Explaining the specular light component, since cyan toner is formed as a base of the black toner, the specular light component is small regardless of whether or not the black toner is formed. On the other hand, in the diffuse reflection component, when the black toner is not formed, the diffuse reflection component due to the underlying cyan toner is large, but the brightness decreases as the amount of black toner increases. As a result, the diffuse reflection component is reduced.

FIG. 6 shows a combination of the first to third toner patterns, the optical sensor, and the sensor characteristics with respect to the toner color to be corrected for density. As shown in these figures, when the shape and surface of the intermediate transfer belt 7 are normal, the combination of the first toner pattern and the positively reflected light sensor is used for black toner detection, and the second toner toner detection is performed. Use a toner pattern and a diffuse sensor. With such a combination, it is possible to increase the rate of change of the received signal value with respect to the toner concentration and obtain the toner concentration with high accuracy.

On the other hand, if an abnormality occurs in the shape or surface of the intermediate transfer belt 7, the light-receiving signal value detected by the specularly reflected light sensor fluctuates greatly, so it is necessary to accurately obtain the toner concentration from the light-receiving signal value. It can be difficult. For this reason, a combination of the third toner pattern and the diffuse reflection light sensor is used to detect the black toner when an abnormality occurs in the shape or surface of the intermediate transfer belt 7. As a result, it is possible to increase the rate of change of the received signal value with respect to the toner concentration and obtain the toner concentration with high accuracy. Even if an abnormality occurs in the shape or surface of the intermediate transfer belt 7, the light receiving signal value detected by the diffuse reflection sensor has almost no effect. Therefore, the second toner is detected by the cyan toner as in the normal state. Use a pattern.

As described above, the first to third toner patterns suitable for detecting the toner concentration and the normal reflected light sensor and the diffuse reflected light sensor, which are optical sensors, are suitable for detecting the toner concentration depending on the toner color to be detected and the state of the intermediate transfer belt 7. The combination of is different. In addition, the sensor output characteristics with respect to the toner concentration also differ depending on the combination of these. As a result, the sensor output characteristics are also different, so that the sensor measurement accuracy changes depending on the toner concentration. Therefore, in the first embodiment, by selecting the optimum gradation level of the first to third toner patterns according to the output characteristics of each sensor, the toner density detection accuracy is improved and the density correction is performed with high accuracy. Do it properly.

<Functional configuration of control unit 50>
In the first embodiment, when the state of the intermediate transfer belt 7 is normal, the control unit 50 forms the first toner pattern shown in FIG. 4A by using black toner as the toner pattern 74. , A specularly reflected light sensor (PD72 in FIG. 2) is used as the optical sensor. On the other hand, if an abnormality occurs in the shape or surface of the intermediate transfer belt 7, or if it is determined that an abnormality may occur, the combination of the toner pattern formed on the intermediate transfer belt 7 and the optical sensor is changed. do. At this time, the control unit 50 forms the third toner pattern shown in FIG. 4 (c) using black toner and cyan toner as the toner pattern 74, and the diffuse reflection light sensor (PD73 in FIG. 2) as the optical sensor. Is used.

As described with reference to FIG. 2, the light receiving voltage signal received by the PD72, which is a specular reflection light sensor, and the PD73, which is a diffuse reflection light sensor, are input to the CPU 301 via the density sensor detection circuit 305, respectively. The CPU 301 corrects the density based on the received voltage signal.
In the first embodiment, the gradation level of the toner pattern formed from the plurality of black toner images is changed according to the output characteristics of the specular reflection light sensor and the diffuse reflection light sensor. Therefore, although the black toner image is used in both FIGS. 4 (a) and 4 (c), the toner patterns are different.

FIG. 7 shows a functional block diagram of the control unit 50 in the image forming apparatus 200 of the first embodiment. Each functional block is formed by the CPU 301 reading a program stored in the memory. The state detection unit 701 is a detection means for detecting the state of the intermediate transfer belt 7 which is an image carrier, for example, whether or not an abnormality may occur in the shape or surface.

The LED 71 of the density sensor 70 irradiates the intermediate transfer belt 7 in a state where the toner image is not formed based on the instruction from the CPU 301. The PD72, which is a specularly reflected light sensor, is provided at a position where it receives the specularly reflected light of the irradiated light, can detect the specularly reflected light, and generates a received voltage signal as the detection result. The PD 72 transmits a received voltage signal to the CPU 301 via the concentration sensor detection circuit 305. At this time, if an abnormality occurs in the shape or surface of the intermediate transfer belt 7, the received voltage signal value generated by the PD 72 that has received the specularly reflected light fluctuates greatly.

The CPU 301 holds in advance a received voltage signal (hereinafter, referred to as a reference signal) when there is no abnormality in the intermediate transfer belt 7. Then, the acquired received voltage signal and the reference signal are compared, and whether or not an abnormality has occurred in the intermediate transfer belt 7 is detected depending on whether or not the difference is equal to or greater than a certain value. The image forming unit 702 is a means for forming a toner pattern as shown in FIGS. 4A to 4C on the intermediate transfer belt 7. The image forming unit 702 selects a first toner pattern or a third toner pattern for the black toner image based on the detection result of the state detecting unit 701. Specifically, when the state detection unit 701 does not detect an abnormality in the intermediate transfer belt 7, a first toner pattern is formed, and when an abnormality is detected, a third toner pattern is formed. Details of the features of the image forming unit 702 will be described later.

The first density detection unit 703 is a means for detecting the density of each toner image of the first toner pattern by using specularly reflected light with respect to the first toner pattern formed by the image forming unit 702. The first density detection unit 703 uses the LED 71 of the density sensor 70 to irradiate the first toner pattern with light. The PD 72 receives the specularly reflected light of the toner pattern, generates a received voltage signal as the detection result, and sends the light reception voltage signal to the CPU 301 via the density sensor detection circuit 305.

The second density detection unit 704 is a means for detecting the density of each toner image of each toner pattern by using diffuse reflection light with respect to the second toner pattern and the third toner pattern formed by the image forming unit 702. The second density detection unit 704 causes the LED 71 of the density sensor 70 to irradiate the second and third toner patterns with light. The PD73 receives the diffuse reflected light of the toner pattern, generates a received voltage signal as a detection result, and sends the light receiving voltage signal to the CPU 301 via the density sensor detection circuit 305.

The correction unit 705 is a means for correcting the density of the image forming apparatus by using the received voltage signal acquired from the first density detection unit 703 and the second density detection unit 704. The correction unit 705 performs density conversion on each of the received voltage signals generated by the PD 72 and PD 73, and creates a density correction table by comparing with a preset target density. Hereinafter, the details of the correction unit 705 will be described.

<Details of correction unit 705>
As an image density correction control method executed by the correction unit 705, there is a method of detecting the density of a predetermined toner pattern formed on the recording material S and creating a density correction table. There is also a method of creating a density correction table by detecting a predetermined toner pattern formed on the intermediate transfer belt 7. The image density correction described in the present embodiment is a method using a toner pattern formed on the intermediate transfer belt 7, but in order to perform this image density correction, the intermediate transfer belt 7 is preliminarily used when the density is corrected on the recording material S. Get the concentration target on.

In the first embodiment, a method of creating a correction table executed by the correction unit 705 under the control of the CPU 301 will be described using three correction tables, an initial correction table, a sequential correction table, and a composite correction table. The initial correction table is a look-up table created in response to the case where the toner pattern is formed on the recording material S, and is created at the time of automatic gradation correction performed by the user at an arbitrary timing. At the time of this automatic gradation correction, the density target value for creating the sequential correction table is acquired. After that, a pattern for adjusting the image density is created on the intermediate transfer belt 7, the created pattern image is detected by the density sensor, and a sequential correction table is sequentially created based on the detection result. The composite correction table is a table obtained by multiplying two tables, an initial correction table and a sequential correction table. Density correction is performed on the input image data using the composite correction table. Immediately after the automatic gradation correction, the initial correction LUT and the composite correction LUT are the same.

Hereinafter, a method of creating each table will be described with reference to FIGS. 8A and 8B, FIGS. 9, 10 and 11. 8 (a) and 8 (b) are flowcharts showing the processes executed in the synthetic correction table creation process, respectively. In detail, FIG. 8A is a flowchart showing a correction table creation process in the case of forming a toner pattern on the recording material S which is an output paper, and FIG. 8B is a correction on the intermediate transfer belt. It is a flowchart which shows the table creation process. The process of FIG. 8A is performed by the user at an arbitrary timing, and the process of FIG. 8B is performed by the image forming apparatus 200 at a predetermined timing.

The correction table creation process on the recording material S will be described with reference to FIG. 8A. When the user executes the automatic gradation correction at an arbitrary timing, the image forming apparatus 200 forms a toner pattern for density correction based on the instruction from the CPU 301 and outputs the toner pattern on the paper (S801a). Unless otherwise specified, the following controls are executed under the control of the CPU 301.

Based on the instruction from the CPU 301, the image forming apparatus 200 reads the toner pattern output in S801a and detects the density (S802a). When the user inputs the execution of density detection by setting the recording material S in the reader unit and pressing the read button or the like, the image forming apparatus 200 detects the density of the toner pattern on the paper.

FIG. 9 is a graph showing the relationship between the signal value and the density of the toner pattern on paper. In the figure, the black dot (.) Indicates the density value detected in S802a, and the broken line indicates the density curve based on the density value. Here, for the sake of explanation, the input signal of the toner pattern has five gradations of 30H, 60H, 90H, C0H, and FFH. The concentration curve of the broken line is approximately generated from the detected concentration value, and a commonly used approximation method such as obtaining an approximation formula by connecting the detected concentrations of the five points is used. It can be arbitrarily generated by using.

After performing the density detection in S802a, the CPU 301 creates an initial correction table (S803a). The initial correction table is a look-up table created according to the gamma characteristic peculiar to the image forming apparatus so that the density acquired in S802 and the preset gradation target match. In FIG. 9, the gradation target curve is shown by a dotted line, and the curve generated by the initial correction table (initial correction table curve) is shown by a long chain line so that the density curve represented by the broken line and the gradation target curve match.

The CPU 301 creates a composite correction table (S804a). The composite correction table is created by multiplying the initial correction table and the sequential correction table. In S804a, the sequential correction table is a linear table, and the composite correction table has the same value as the initial correction table. Therefore, the initial correction table is used as it is as the composite correction table. The CPU 301 sets the created composite correction table as the density correction table of the image forming apparatus 200 (S805a).
Next, the CPU 301 forms a toner pattern on the intermediate transfer belt 7 (S806a), and detects the density using the density sensor 70 (S807a). As a result, the detected density value is acquired as the target density for the toner pattern on the intermediate transfer belt 7 (S808a). As described above, the combination of the first to third toner patterns and the specular reflection light sensor (PD72) and the diffuse reflection light sensor (PD73) of the density sensor 70 is set by the state detection unit 701. The concentration sensor 70 transmits the detected concentration information to the CPU 301 and sets it as a target concentration. As a result, the processing of each table shown in FIG. 8A is completed.

A correction table creation process in the case of forming a toner pattern on the intermediate transfer belt 7 will be described with reference to FIG. 8 (b). The image forming apparatus 200 forms a density correction toner pattern on the intermediate transfer belt 7 at a predetermined timing based on an instruction from the CPU 301 (S801b). This predetermined timing is a case where the control unit 50 determines that density correction is necessary, and examples thereof include a case where long-term jobs are continuous or a case where the image formation environment is changed.

Based on the instruction from the CPU 301, the image forming apparatus 200 reads and detects the toner pattern formed on the intermediate transfer belt 7 in S801b through the density sensor 70 (S802b). As described above, the combination of the first to third toner patterns and the specular reflection light sensor (PD72) and the diffuse reflection light sensor (PD73) of the density sensor 70 is set by the state detection unit 701. In FIG. 10, the concentration value acquired at this time is indicated by a circle, and the concentration curve generated based on the acquired concentration value is indicated by a long two-dot chain line.

The CPU 301 creates a sequential correction table so that the density obtained in S802b matches the target density with respect to the toner pattern on the intermediate transfer belt 7 set in S808a (S803b). In FIG. 10, the target density is shown by a dotted line, and the sequential correction table created so that the long two-dot chain line matches the target density is shown by a broken line. The density curve shown by the long two-dot chain line in FIG. 10 is inversely transformed so as to be the gradation target at the time of creating the initial correction table shown by the dotted line in FIG. 10, and the sequential correction table shown by the broken line in FIG. 10 is obtained. create.

The CPU 301 creates a composite correction table by multiplying the initial correction table and the sequential correction table (S804b). By multiplying these two tables, a density correction table is obtained in which the density characteristics of the image forming apparatus 200 are corrected so as to match the preset gradation target. In FIG. 11, the composite correction table curve is shown by a solid line. After that, the CPU 301 sets the created composite correction table as the density correction table of the image forming apparatus 200 (S805b), and ends the process. Since the process shown in FIG. 8B is executed at a predetermined timing, the density correction adjustment can be performed with the new composite correction table by multiplying the new sequential correction table with the initial correction table.

<Method of forming toner pattern in image forming part>
Hereinafter, a method of forming a toner pattern in the image forming unit 702 will be described. 12 (a) and 12 (b) show the toner concentration when the black toner pattern is formed on the intermediate transfer belt 7, and the received signal values detected by the PD72 which is a specular reflection light sensor and the PD73 which is a diffuse reflection light sensor. The relationship is shown.

FIG. 12 (a) is a received signal value of the front-reflective sensor with respect to the first toner pattern shown in FIG. 4 (a), which forms a black toner pattern directly on the intermediate transfer belt 7. FIG. 12B is a received signal value of the diffuse reflection light sensor for the third toner pattern shown in FIG. 4C, which is formed by superimposing cyan toner and black toner on the intermediate transfer belt 7. Although it was stated that the density difference between adjacent toner images of the third toner pattern is not constant, the third toner is shown in FIG. 12 (b) for comparison between FIGS. 12 (a) and 12 (b). The density difference between adjacent toner images of the pattern is made constant. That is, it is the same as the density interval between adjacent toner images in the first toner pattern. In these figures, the vertical axis represents the received light signal value corrected as follows, and the horizontal axis represents the density of the formed black toner image (represented as "concentration (Bk)" in the figure).

In order to obtain the received signal value of FIG. 12A, the specularly reflected light from the surface of the first toner pattern formed on the intermediate transfer belt 7 is measured in advance. FIG. 12A shows the correction by subtracting (taking a difference) the measured value obtained by measuring the surface of the intermediate transfer belt 7 from the measured value in a state where the black toner image is not formed. The indicated, corrected received signal value is obtained.

In order to obtain the received signal value of FIG. 12B, a cyan toner image is formed at the output immediately before the third toner pattern, and the density of the cyan toner image is measured in that state. The correction shown in FIG. 12B is performed by subtracting the measured value from the measured value obtained by measuring the specularly reflected light on the surface of the third toner pattern formed on the intermediate transfer belt 7. The received light signal value is obtained.

The plot points in FIGS. 12 (a) and 12 (b) show the average value when the above measurement is performed a plurality of times, and the error bar shows the variation of the measured received signal value at the same density. The difference in the surface properties of the base of the black toner image, that is, whether the black toner image is formed on the intermediate transfer belt 7 (FIG. 12 (a)) or on the cyan toner image (FIG. 12 (FIG. 12)). Depending on the difference in b)), the variation in the measured value of the received signal value also changes.

In the example of FIG. 12A, it is shown that the error bar is small and the variation in the measured values is relatively small. However, in the example of FIG. 12 (b), there is a tendency that the error bar is larger than that of the example of FIG. 12 (a), and therefore the variation in the measured values is also large. Further, in FIG. 12B, the error bar in the low concentration region is larger than that in the high concentration region.

The larger the error bar in the graph, the greater the effect of variation on the measured value, so the density correction value set using the measured value also increases. In FIG. 12A, the error bar is small and no special correlation is observed between the density and the size of the error bar. Therefore, in the first toner pattern, the density signal values are measured at regular intervals with respect to the density. Do it with.

However, in FIG. 12B, the error bars tend to be larger on the low density side. Due to such a correlation, if the density signal value of the first toner pattern is used in the third toner pattern, an appropriate density correction value may not be obtained. Therefore, in the first embodiment, the low concentration region, which is a region in which the measured values vary widely in FIG. 12B, is appropriately corrected. Specifically, in order to suppress the influence of variation in the measured value in the low concentration region, the concentration signal value is measured at fine concentration intervals to increase the number of measurement points. Further, as will be described later, it is possible to suppress the influence of variation in the measured values by increasing the number of measurements even if the concentration is the same. This is because as the number of measurements increases, the average of the measured values approaches the correct value.

The first toner pattern and the third toner pattern in the first embodiment are shown in FIG. As described above, the first toner pattern is formed only from black toner, and the third toner pattern is formed by superimposing black toner on cyan toner. Each of these toner patterns is composed of 10 toner images. In the first toner pattern, the density difference of the toner density in each adjacent toner image is made substantially equal, and the measurement is performed on average with respect to the density. On the other hand, in the third toner pattern, the density difference of the toner density in each adjacent toner image is made smaller as the density is lower, and the number of low density toner images is increased in 10 toner images. As a result, in the 10 toner images of the third toner pattern, the proportion of the toner images in the region where the measurement variation is large (in this example, the low density region) is increased as compared with the first toner pattern. As described above, in the first toner pattern, the density difference in the toner density between the adjacent toner images takes a constant value with respect to the density. On the other hand, in the third toner pattern, the density difference is not a constant value, and the lower the density, the smaller the density difference in the toner density between adjacent toner images.
The second toner pattern is formed by the cyan toner image on the intermediate transfer belt 7, and the density difference between adjacent toner images is constant as in the first toner pattern.

FIG. 14A shows the relationship between the toner concentration in the toner pattern (a) formed by superimposing the black toner image on the cyan toner image on the intermediate transfer belt 7 and the received signal value by the PD73 which is a diffuse reflection light sensor. Is shown.
FIG. 14B shows the relationship between the toner concentration in the toner pattern (b) formed by superimposing the black toner image on the cyan toner image on the intermediate transfer belt 7 and the received signal value by the PD73 which is a diffuse reflection light sensor. Is shown.
14 (a) and 14 (b) are the same in that a black toner image is superposed on the cyan toner image on the intermediate transfer belt 7, but the density difference between adjacent toner images is different. In FIG. 14A, the density difference between adjacent toner images is constant, but in FIG. 14B, the density difference between adjacent toner images is not constant, and the lower the density, the more adjacent toner images are located. The difference in toner concentration is small. The first toner pattern shown in FIGS. 4A and 13 is different from the toner pattern (a) in that a black toner image is formed on the intermediate transfer belt 7. However, the first toner pattern and the toner pattern (a) are common in other respects.
On the other hand, the toner pattern (b) is the same as the third toner pattern shown in FIGS. 4 (c) and 13.
In these figures, the vertical axis represents the received signal values of the toner patterns (a) and (b), and the horizontal axis represents the black toner concentration. In FIG. 14A, the density difference between adjacent toner images in the toner pattern (a) is substantially equal to that of the “first toner pattern” in FIG. 13A.
In FIG. 14 (b), the density difference between adjacent toner images of the toner pattern (b) takes different values as shown in the “third toner pattern” of FIG. 13 (b), and the density difference in the low density region. Is getting smaller.

The solid line in FIG. 14A corresponds to the gradation level of the toner pattern in FIG. 13A, and the toner pattern is measured on average with respect to the density, and the plot showing the measurement result is connected by a straight line. Is. In the figure, the horizontal axis represents the density of the black toner image, and it is shown that the intervals between the plots are the same and the density difference between the plots is the same. That is, with respect to the density, the density difference between adjacent toner images is constant. The broken line is a line graph showing the average value when the diffuse reflected light is measured a plurality of times by superimposing the cyan toner and the black toner on the intermediate transfer belt 7 shown by the solid line in FIG. 12 (b).

The solid line in FIG. 14B is a graph in which plots representing measurement results are connected by a straight line corresponding to the gradation level of the toner pattern in FIG. 13B. Further, this measurement is performed so that the measurement interval becomes narrower as the concentration becomes lower. In the figure, the horizontal axis represents the density of the black toner image, and the interval between plots is shorter as the density is lower and longer as the density is higher. This indicates that the density difference between the plots is not constant, and as the density increases, the density difference between adjacent toner images increases. That is, with respect to the density, the density difference between adjacent toner images is not constant, and in the low density region, which is a region where the variation in the measured values is large, the density difference between the adjacent toner images is small, and the measurement variation is small. The concentration difference is large in the high concentration region. Similar to FIG. 14A, the broken line in the figure is the average when cyan toner and black toner are superposed on the intermediate transfer belt 7 shown by the solid line in FIG. 12B and the diffuse reflection light is measured a plurality of times. Shows the value.

As shown in FIG. 14A, when the measurement interval is constant regardless of the concentration, the influence of the variation appears as it is in the low concentration region where the measurement variation is large. For example, in FIG. 14A, in the low concentration region, many plots are located away from the broken line representing the average value, and the portion where the straight line formed by connecting the plots and the curved line of the broken line do not overlap is small.

On the other hand, as shown in FIG. 14B, the lower the density, the narrower the detection interval of the density of the measured toner image, so that the plot interval becomes shorter on the horizontal axis representing the density in the low density region, and the measured value. The effect of variation in can be reduced. Further, since the error bar is small in the medium concentration to high concentration region as shown in FIG. 12B, even if the measurement interval is widened on the concentration axis, the influence of the variation in the measured values is compared with that in the low concentration region. Is small.

From the above, in the first embodiment, in the toner pattern in the diffuse reflection light measurement, the number of toner images in the low density region is relatively increased compared to the number of toner images in the high density region. As a result, the influence of the concentration fluctuation due to the measurement variation can be reduced and the concentration correction can be appropriately performed.

<Flowchart>
The main processing flow of the image forming apparatus 200 in the first embodiment will be described with reference to the flowchart of FIG. Unless otherwise specified, each process is executed under the control of the CPU 301.
The state detection unit 701 detects the state of the intermediate transfer belt 7 and determines whether or not there is an abnormality (S1501). When it is determined that there is no abnormality in the shape or surface of the intermediate transfer belt 7 (S1501: N), the image forming unit 702 forms a first toner pattern formed of black toner on the intermediate transfer belt 7 (S1502). ). After that, the first density detection unit 703 acquires the received signal value of the specularly reflected light of the first toner pattern (S1503), and executes the density correction (S1506).

On the other hand, when it is detected in S1501 that there is an abnormality in the shape or surface of the intermediate transfer belt 7 (S1501: Y), the image forming unit 702 displays a cyan toner image and a black toner image on the intermediate transfer belt 7. The formed third toner pattern is formed (S1504). After that, the second density detection unit 704 acquires the received signal value of the diffuse reflection light of the third toner pattern (S1505) and executes the density correction (S1506). In S1506, the correction unit 705 corrects the density based on the light receiving signal value acquired from the first density detection unit 703 or the second density detection unit 704, whereby the processing is completed.

As described above, in the first embodiment, when an abnormality occurs in the shape or surface of the intermediate transfer belt, or when it is determined that an abnormality may have occurred, the density is corrected on the intermediate transfer belt. Change the type of toner pattern to be formed and the type of density sensor to be used. Further, the gradation level of the toner pattern formed from the plurality of toner image regions is changed according to the output characteristics of the specular reflection light sensor and the diffuse reflection light sensor. As a result, even when an abnormality such as a curl of the intermediate transfer belt or a decrease in gloss is observed, appropriate density correction can be performed.

Further, in the first embodiment, as the toner density is lower in the received signal value, the detection interval of the density of the measured toner image is narrowed, and the number of toner images in the low density region in the toner pattern is increased. However, the present invention is not limited to this. For example, with respect to the density of the toner image, the variation in the measured value of the density may be small in the low density region and the high density region, and the variation in the measured value of the density may be large in the intermediate density. In this case, by increasing the number of intermediate density toner images in the toner pattern, the influence of variation in the intermediate density can be suppressed to a small value.

Further, not limited to this, regarding the density of the toner image, by increasing the number of toner images having a density included in the density range in which the variation becomes large in the toner pattern, the influence of the variation in the density range can be suppressed to be small. ..

2nd Embodiment In the 1st embodiment described above, in the 3rd toner pattern acquired by the diffuse reflection light sensor, the ratio of the toner image having a low density value is compared with the 1st toner pattern acquired by the specular reflection light sensor. By increasing the number, the accuracy of density correction is improved.

However, depending on the image forming apparatus, it is necessary to measure the toner image of a specific density regardless of the use of the specular reflection light sensor and the diffuse reflection light sensor, and the toner image of the specific density contained in the first toner pattern is deleted or deleted. It may not be desirable to change it.

Therefore, in the second embodiment, the third toner pattern of the black toner formed on the cyan toner image on the intermediate transfer belt 7 includes the toner image of the density value contained in the first toner pattern, and , A new toner image has been added. Since the configuration of the image forming apparatus of the second embodiment and its functional configuration are the same as those of the first embodiment, the description thereof will be omitted. On the other hand, in the second embodiment, the toner pattern formed by the image forming unit 702 is different from the toner pattern in the first embodiment, and this will be described.

FIG. 16 is an explanatory diagram of the fourth toner pattern used in the second embodiment. Since the first toner pattern is the same as that of the first embodiment, the description thereof will be omitted. In the fourth toner pattern, a toner image in a low density region (four toner images in the example of FIG. 16) is further added to ten toner images having the same density value as the first toner pattern. The four toner images in the added low density region are toner images having density values not included in the ten toner images in the first toner pattern shown in FIG. 4A. As described in the first embodiment, in the low concentration region of the diffuse reflection light sensor having a large measurement variation, the narrower the concentration interval for detection, the less the influence of the measurement variation can be reduced.

Therefore, in the fourth toner pattern used in the second embodiment, the toner concentration is increased by newly adding a toner image in a low density region in addition to the ten toner images having the same density as the first toner pattern. The measurement interval is narrowed to improve the accuracy of density correction. From this, the density difference between adjacent toner images in the low density region is smaller than the density difference between adjacent toner images in the high density region (or a region other than the low density region).

The density value of the toner image added to the low density region in the toner pattern as described above can be a density value not included in the first toner pattern. In this case, it is possible to improve the accuracy of the concentration correction by narrowing the measurement interval with respect to the concentration and increasing the number of measurement points in the low concentration region.

However, the density of the added toner image may be the same as the density of the toner image contained in the first toner pattern. In this case, although the measurement point at the density does not increase, the number of measurements of the toner image can be increased by performing the measurement a plurality of times on the toner image having the same density, and as a result, the influence of the measurement variation can be reduced. Further, when the measurement is performed a plurality of times at the same density, the density difference between the toner images becomes 0, so the measurement is performed with the density difference being 0.

In this way, it is possible to reduce the influence of measurement variation by increasing the number of measurements in the low concentration region, not limited to narrowing the measurement interval in the low concentration region. Further, it is of course possible to add a toner image having a density contained in other density regions in addition to the toner image having a density contained in the low density region. In addition, as a result of suppressing the influence of measurement variation in the low concentration region to a small value, the influence of measurement variation in other concentration regions may become relatively large. In such a case, the concentration contained in the other concentration region It is desirable to add a toner image of. In this way, the toner image may be added over the density of the entire region. Further, the number of toner images to be added can be arbitrarily determined from the viewpoint of toner consumption.

The fourth toner pattern formed by the image forming unit 702 in the second embodiment includes a toner image having the same density value as the first toner pattern, and a new toner image is added. The number of toner images included in the fourth toner pattern is larger than the number of toner images included in the first to third toner patterns. As a result, it is possible to reduce the measurement variation in the diffuse reflection light and improve the accuracy of the density correction while maintaining the toner image of the density that needs to be measured.

Third Embodiment In the second embodiment described above, both the specular reflection light sensor and the diffuse reflection light sensor have a toner image of the same density, and a new toner image is added to the diffuse reflection light sensor to reduce measurement variation. I'm letting you. Further, when the density of the toner image added to the fourth toner pattern is the same as the density of the toner image included in the first toner pattern, it is synonymous with increasing the number of times the toner image is measured.

In the third embodiment, in the third toner pattern that receives light by diffuse reflection light, a configuration will be described in which the number of measurements of each toner image is increased without adding the number of toner patterns and the measurement variation is reduced. Since the configuration of the image forming apparatus and its functional configuration in the third embodiment are the same as those in the first embodiment, the description thereof will be omitted. On the other hand, in the third embodiment, the toner pattern formed by the image forming unit 702 is different from the toner pattern in the first embodiment, and this will be described.

FIG. 17 is an explanatory diagram of the toner pattern in the third embodiment. Since the first toner pattern is the same as that of the first embodiment, the description thereof will be omitted. The toner images included in the fifth toner pattern have the same number and density as the toner images included in the first toner pattern. However, the fifth toner pattern used in the third embodiment is different in length and size of each toner image as compared with the first embodiment. Specifically, the length of the fifth toner pattern in the transport direction of the intermediate transfer belt 7 is longer than that of the first toner pattern, and as a result, the size is also large. The transport direction of the intermediate transfer belt 7 is a direction perpendicular to the scanning direction of the laser beam for reading the toner image, that is, a sub-scanning direction.

When the toner image is long in the transport direction of the intermediate transfer belt 7, the time for passing through the density sensor 70 increases, so that the number of times the density is measured for each toner image can be increased. Further, in the first embodiment, it has been explained that the specular reflection light sensor and the diffuse reflection light sensor tend to have a large measurement variation in the diffuse reflection light sensor with reference to FIG. Therefore, in the diffuse reflected light, if the measurement variation of the diffuse reflected light sensor is reduced by increasing the number of measurements of each toner image and taking the average value, the measurement is performed with the same accuracy as the normal reflected light sensor. It is possible.

Therefore, in the third embodiment, the fifth toner pattern formed by the image forming unit 702 compares at least one of the toner images included in the fifth toner pattern with the toner image of the first toner pattern in the diffuse reflection light sensor. Then, the intermediate transfer belt 7 is lengthened in the transport direction. As a result, the measurement variation generated when the diffuse reflected light sensor is acquired can be reduced, and the density correction can be appropriately performed.

Modification Example FIG. 18 shows a sixth toner pattern used in the modification. In the third embodiment described above, for all the toner images of the fifth toner pattern, the toner images are lengthened in the transport direction of the intermediate transfer belt 7, and as a result, all the toner images are oriented in the transport direction of the intermediate transfer belt 7. I made it longer. However, it is not always necessary to lengthen all the toner images in the transport direction of the intermediate transfer belt 7, and it is sufficient to lengthen at least one toner image.

In the modified example, the length of the toner image included in the first density region (the above-mentioned low density region) is set to the length of the toner image included in the second density region (the region having a higher density than the low density region) with respect to the sub-scanning direction. Make it longer than the length. Specifically, as shown in the figure, in the sixth toner pattern, the five toner images in the low density region are lengthened in the sub-scanning direction, and the other toner images are the same length as the first toner pattern. .. As a result, it is possible to increase the number of times the density is measured for the toner image in the low density region, which is a region in which the measured values vary widely in the density measurement. As a result, the area of the toner image included in the sixth toner pattern becomes smaller than that of the fifth toner pattern in which the toner image is lengthened in the transport direction of the intermediate transfer belt 7 in the entire density region. Therefore, it is possible to suppress the toner consumption required for detecting the received signal value, which is advantageous in terms of cost.
Further, in this example, a low density region is selected as a region for extending the toner image in the sub-scanning direction, but the region is not limited to this. Depending on the type of toner, it is conceivable that the variation in the measured value becomes large not only in the low concentration region but also in a specific concentration region. Therefore, by lengthening the toner image in the sub-scanning direction in the density region where the variation in the measured values is large, it is possible to suppress the variation in the measured values in the density region.

According to the present invention, it is possible to improve the detection accuracy of the toner density of the formed toner image and appropriately perform the density correction in the image forming apparatus. Further, in the above description, two toner patterns, a first toner pattern and a second toner pattern (or any of the third to sixth toner patterns), are selectively formed on the intermediate transfer belt 7.

In this case, it is assumed that the variation of the measured value in the concentration measurement in the second concentration region is larger than the variation of the measured value in the concentration measurement in the first concentration region. The first concentration region corresponds to the high concentration region in the first to third embodiments, and the second concentration region corresponds to the low concentration region in the first to third embodiments. By making the density difference between the toner images included in the second density region smaller than the density difference between the toner images included in the first density region, it is possible to suppress the influence of the variation in the measured values.

Claims (12)

Image forming means for forming an image and
An image carrier that supports the image formed by the image forming means, and an image carrier that supports the image.
An irradiation means for irradiating the image carrier with light,
The first detecting means for detecting the specularly reflected light of the light and
The second detecting means for detecting the diffusely reflected light of the light and
Control to correct the density of the image formed by the image forming means from the detection result of the reflected light of the light emitted from the irradiation means detected by at least one of the first detecting means and the second detecting means. With means,
The control means selects a first toner pattern or a second toner pattern based on the detection results of the first detection means and the second detection means, and uses the image forming means to select the selected first toner. A pattern or a second toner pattern is formed on the image carrier,
The first toner pattern is formed by using the first toner.
The second toner pattern includes a second toner formed on the image carrier and the first toner formed by superimposing on the second toner, and the second toner is different from the first toner. It is a thing
The number of toner images included in the second toner pattern is larger than the number of toner images included in the first toner pattern.
Image forming device. The first toner pattern and the second toner pattern each contain at least two toner images having different densities.
The image forming apparatus according to claim 1. The second toner pattern is characterized by including a toner image having the same density as the toner image contained in the first toner pattern and a toner image having a density different from that of the toner image contained in the first toner pattern. To,
The image forming apparatus according to claim 1. The second toner pattern is characterized by including a plurality of toner images having the same density as the toner images contained in the first toner pattern.
The image forming apparatus according to claim 1. The second toner pattern includes a plurality of toner images having a density included in the first density region and a plurality of toner images having a density included in the second density region, and the density in the second density region is included. Is lower than the first concentration region,
The density difference between the toner images included in the second density region is smaller than the density difference between the toner images included in the first density region.
The image forming apparatus according to any one of claims 1 to 4. The second toner pattern includes a plurality of toner images having a density included in the first density region and a plurality of toner images having a density included in the second density region, and the second toner pattern includes a plurality of toner images having a density included in the second density region. The variation of the measured value in the concentration measurement is larger than the variation of the measured value in the concentration measurement in the first concentration region.
The density difference between the toner images included in the second density region is smaller than the density difference between the toner images included in the first density region.
The image forming apparatus according to any one of claims 1 to 4. The first toner is an achromatic toner and is
The second toner is a chromatic toner.
The image forming apparatus according to any one of claims 1 to 6. The density difference between the toner images included in the first toner pattern takes a constant value, and the density difference between the toner images included in the second toner pattern is not a constant value.
The image forming apparatus according to any one of claims 1 to 7. Image forming means for forming an image and
An image carrier that supports the image formed by the image forming means, and an image carrier that supports the image.
An irradiation means for irradiating the image carrier with light,
A first detecting means for detecting the specularly reflected light of the light, a second detecting means for detecting the diffusely reflected light of the light, and a second detecting means.
Control to correct the density of the image formed by the image forming means from the detection result of the reflected light of the light emitted from the irradiation means detected by at least one of the first detecting means and the second detecting means. With means,
The control means selects a first toner pattern or a second toner pattern based on the detection results of the first detection means and the second detection means, and uses the image forming means to select the selected first toner. A pattern or a second toner pattern is formed on the image carrier,
The first toner pattern is formed by using the first toner.
The second toner pattern includes the first toner formed on the image carrier and the second toner formed by superimposing on the first toner and different from the first toner.
The first toner pattern and the second toner pattern each have a plurality of toner images.
The first detection means and the second detection means can detect the reflected light while the image carrier is being conveyed.
At least one of the toner images included in the second toner pattern has a length of the image carrier in the transport direction longer than the length of the toner image included in the first toner pattern in the transport direction. Characteristic,
Image forming device. The toner image included in the first density region of the second toner pattern is included in the second density region, which is a region having a lower density than the first concentration region as compared with the length of the carrier in the transport direction. The toner image is characterized in that the length of the carrier in the transport direction is relatively long.
The image forming apparatus according to claim 9. This is a region in which the measured value in the density measurement has a larger variation than the third density region in the transport direction of the carrier of the toner image included in the third density region of the second toner pattern. The length of the carrier of the toner image contained in the two-concentration region in the transport direction is relatively long.
The image forming apparatus according to claim 9. The number of toner images included in the second toner pattern is equal to the number of toner images included in the first toner pattern.
The image forming apparatus according to any one of claims 9 to 11.

Images