JP2021051206A - Image forming apparatus - Google Patents

Abstract

To stabilize an image density when the causes of variations in density including the film thickness and the temperature and humidity of a photoreceptor are changed, compared with a case where a plurality of test patterns having different patterns are formed to set an image forming condition.SOLUTION: An image forming apparatus comprises: image forming means that forms patch images on image holding means in a standard number of lines used for image formation and a low number of lines lower than the standard number of lines; detection means that detects the density of the patch images; storage means that stores the density of the patch images in the standard number of lines and the low number of lines detected by the detection means when the image holding means is in a reference state; and correction means that corrects an image forming condition for the image forming means, according to a result of comparison between the density stored in the storage means and the density of the patch images in the standard number of lines and the low number of lines detected by the detection means in a predetermined period after the start of use of the image holding means.SELECTED DRAWING: Figure 6

Description

The present invention relates to an image forming apparatus.

Conventionally, in an image forming apparatus, those disclosed in Patent Document 1 and the like have already been proposed as a technique for stabilizing the image density even when the density fluctuation factors such as the film thickness and temperature / humidity of the photoconductor change. There is.

Patent Document 1 forms a plurality of test patterns having different patterns on the surface of a photoconductor by a charging step, a laser beam scanning step, and a developing step, and is photosensitive based on the detection result of each reflection density of these test patterns. The image forming conditions to be formed on the body are set, and the image is formed on the surface of the photoconductor based on the print data according to the set image forming conditions.

Japanese Unexamined Patent Publication No. 11-78123

An object of the present invention is to stabilize the image density when density fluctuation factors such as the film thickness and temperature / humidity of the photoconductor change, as compared with the case where a plurality of test patterns having different patterns are formed and image formation conditions are set. To let you.

The invention according to claim 1 comprises an image forming means for forming a patch image with a standard number of lines used for image forming in the image holding means and a lower number of lines than the standard number of lines.
A detection means for detecting the density of the patch image and
A storage means for storing the density of the patch image of the standard number of lines and the low line number detected by the detection means when the image holding means is in the reference state, and a storage means.
Comparison result of the density of the patch image of the standard number of lines and the low line number detected by the detection means at a predetermined time after the start of use of the image holding means and the density stored in the storage means. A correction means for correcting the image formation conditions of the image forming means according to
It is an image forming apparatus provided with.

According to the second aspect of the present invention, the comparison between the density of the patch image having the standard number of lines and the low line number detected by the detecting means and the density stored in the storage means is the standard number of lines. Depending on whether or not the difference between the densities of the patch images is equal to or less than the predetermined first threshold value and the difference between the densities of the patch images having the low line number exceeds the predetermined second threshold value. The image forming apparatus according to claim 1.

According to the third aspect of the present invention, in the correction means, the difference between the densities of the patch image of the standard line number is equal to or less than a predetermined first threshold value, and the patch image of the low line number is used. The image according to claim 2, wherein when it is determined that the difference between the densities exceeds a predetermined second threshold value, the image formation condition is corrected after changing the density target value of the patch image having the standard number of lines. It is a forming device.

The invention according to claim 4 is the image forming apparatus according to claim 1, wherein the predetermined time after the start of use is when the image holding means operates for a predetermined operation time. is there.

The invention according to claim 5 is the case where the image holding means operates for a predetermined operation time and the cumulative rotation speed of the image holding means reaches a predetermined value. Item 4. The image forming apparatus according to item 4.

The invention according to claim 6 is the image forming apparatus according to claim 1, wherein the predetermined time after the start of use is when the environmental temperature changes by a specified value or more.

The invention according to claim 7 is the image forming apparatus according to claim 6, wherein when the environmental temperature changes by a specified value or more, the environmental temperature rises or falls over 10 ° C. or more.

According to the first aspect of the present invention, when the concentration fluctuation factors such as the film thickness and temperature / humidity of the photoconductor change as compared with the case where a plurality of test patterns having different patterns are formed and the image formation conditions are set. , The image density can be stabilized.

According to the invention described in claim 2, the density of the patch image having a low line number and the density of the patch image having a low line number is compared with the density of the patch image having a standard number of lines and a low line number detected by the detecting means and the density stored in the storage means. It is possible to detect a change in image density due to a change in the film thickness of the photoconductor, as compared with the case where the difference between the two is not exceeded depending on whether or not the difference exceeds a predetermined second threshold value.

According to the invention described in claim 3, the correction means is such that the difference between the densities of the patch images having a standard line number is equal to or less than a predetermined first threshold value, and the densities of the patch images having a low line number are different from each other. When it is determined that the difference exceeds a predetermined second threshold value, the image density can be stably maintained as compared with the case where the density target value of the patch image having a standard number of lines is not changed.

According to the fourth aspect of the present invention, the film thickness of the photoconductor as the image-holding means changes as compared with the case where the predetermined time after the start of use is not set based on the operating time of the image-holding means. Can be accommodated.

According to the fifth aspect of the present invention, when the image holding means operates for a predetermined operation time, the image holding means is used as an image holding means as compared with the case where the image holding means is not determined based on the cumulative rotation speed of the image holding means. It is possible to reliably detect a change in the film thickness of the photoconductor.

According to the sixth aspect of the present invention, as compared with the case where the predetermined time after the start of use is not set based on the change of the environmental temperature equal to or more than the specified value, the exposure as an image holding means due to the environmental change It is possible to respond to changes in the light receiving characteristics of the body.
According to the invention described in claim 7, the change in the environmental temperature is accompanied by the change in the environmental temperature, as compared with the case where the change in the environmental temperature is not determined based on the case where the environmental temperature rises or falls over 10 ° C. or higher. Changes in the light receiving characteristics of the photoconductor as an image holding means can be reliably detected.

It is a schematic block diagram which shows the image forming apparatus which concerns on Embodiment 1 of this invention. It is a block diagram which shows the screen structure. It is sectional drawing which shows the density sensor of the image forming apparatus which concerns on Embodiment 1 of this invention. It is a graph which shows the relationship between the light amount of an exposure apparatus and the electric potential of a photoconductor drum with changing the film thickness of a photoconductor drum. It is a schematic diagram which shows the standard patch and the check patch. It is a graph and schematic diagram which shows the latent image potential and the developed image of a standard patch and a check patch, respectively. It is a plan view which shows the standard patch and the check patch. It is a graph which shows the relationship between the film thickness of the photoconductor layer of a photoconductor drum, and the output of a density sensor. It is a graph which shows the relationship between the density | concentration of a patch, and the output of a density sensor. It is a block diagram which shows the control device of the image forming apparatus in Embodiment 1 of this invention. It is a flowchart which shows the operation of the image forming apparatus in Embodiment 1 of this invention. It is a flowchart which shows the subroutine of the detection operation of a standard patch and a check patch. It is a schematic block diagram which shows the image forming apparatus which concerns on Embodiment 2 of this invention. It is a flowchart which shows the operation of the image forming apparatus in Embodiment 2 of this invention. It is a graph which shows the relationship between the light amount of an exposure apparatus and the electric potential of a photoconductor drum with the change of an environmental condition.

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

[Embodiment 1]
FIG. 1 shows an image forming apparatus according to the first embodiment.

<Overall configuration of image forming apparatus>
The image forming apparatus 1 is a full-color printer that employs an electrophotographic method to finally form an image composed of toner on recording paper 9, which is an example of a recording medium, based on image information consisting of characters, photographs, figures, and the like. Is. As shown in FIG. 1, the image forming apparatus 1 includes an image forming apparatus 20 as an example of an image forming means for forming a toner image composed of toner as a developer, and a toner formed by the image forming apparatus 20. The intermediate transfer device 30 that holds the image by the primary transfer and then conveys it to the secondary transfer position that is secondarily transferred to the recording paper 9 and the recording paper 9 that is supplied to the secondary transfer position of the intermediate transfer device 30 are accommodated and supplied. A paper feeding device 40 and a fixing device 50 and the like for fixing the toner image secondarily transferred by the intermediate transfer device 30 to the recording paper 9 are arranged. The thick solid line shown in FIG. 1 is the main transport path of the recording paper 9.

The image forming apparatus 20 includes four image forming apparatus 20Y, 20M, which individually form four color developer (toner) images of yellow (Y), magenta (M), cyan (C), and black (K), respectively. It is configured using 20C and 20K. As shown in FIG. 1, each of the image forming devices 20 (Y, M, C, K) includes a photoconductor drum 21 as an example of an image holding means that is rotationally driven in the direction indicated by the arrow A. ing. A charging device 22, an exposure device 23, a developing device 24, a primary transfer device 25, a drum cleaning device 26, and the like are arranged around each photoconductor drum 21. The reference numerals of the photoconductor drum 21 and the members arranged around the photoconductor drum 21 are attached only to the black (K) image forming device 20K, and are omitted in the other image forming devices 20 (Y, M, C). ..

The photoconductor drum 21 has, for example, an image-forming surface (image-forming range) having a photodielectric layer (photoreceptor layer) made of a photosensitive material such as OPC on the peripheral surface of a cylindrical or columnar conductive base material to be grounded. ) Is a drum-shaped photoconductor. The photoconductor drum 21 is provided so as to receive power from a drive device (not shown) and rotationally drive in the direction indicated by the arrow A.

As the charging device 22, for example, a non-contact type charging device such as a scorotron that is arranged in a non-contact state on the image forming surface of the photoconductor drum 21 and is supplied with a required charging bias having a negative polarity is used. The charging device 22 is not limited to a non-contact type charging device such as a scorotron, and of course, a contact type charging device provided with a charging roll may be used.

The exposure device 23 is, for example, a non-scanning exposure device configured by using a light emitting diode and optical components, or a scanning exposure device configured by using optical components such as a semiconductor laser and a polygon mirror. is there. In the exposure device 23, image information input from the outside through a communication means, an image reading device, or the like or image information stored in an internal storage unit is yellowed (after being subjected to necessary processing by the image control unit 110). It is input as an image signal decomposed into each color component (Y, M, C, K) of Y), magenta (M), cyan (C), and black (K). The exposure device 23 performs exposure according to the input image signal.

The exposure apparatus 23 uses a screen capable of reproducing (forming) a halftone image when performing image exposure. As a screen, as shown in FIG. 2, a universal screen consisting of parallel lines in which straight lines in one direction are arranged at a uniform pitch (interval) (FIG. 2A) and a standard screen in which lines intersect at 45 degrees. A typical mesh screen ((b) in the figure), a special screen such as a wavy screen or a grain screen, and the like can be mentioned. In each case, the density of the electrostatic latent image of the screen changes depending on the density of the lines on the screen. The density of this screen is called the number of screen lines, or simply the number of lines, and is indicated by the number of lines per inch (lpi).

In the first embodiment, a 400-line universal screen is used when the image is exposed by the exposure apparatus 23. Further, in each of the yellow (Y), magenta (M), cyan (C), and black (K) image-forming devices 20 (Y, M, C, K), for example, at least one or more image-forming devices are desirable. At 20 (Y, M, C, K), the angle of the magenta screen is configured to be different from the others.

The developing device 24 is, for example, a developing device 24 (Y, M, C, K) that uses a two-component developer containing toner of any one of the four colors (Y, M, C, K) and a magnetic carrier. Is. Further, the developing apparatus 24 (Y, M, C, K) is used, for example, to charge the toner to a negative polarity to perform reverse development. Further, the developing apparatus 24 (Y, M, C, K) is a developing agent holding means that rotates so as to hold the two-component developing agent contained in the housing and convey it to the developing region facing the photoconductor drum 21. A developing roll 241 or the like is provided as an example. A development bias in which an AC component is superimposed on a DC component, for example, is supplied to the development roll 241 with the photoconductor drum 21.

The yellow (Y), magenta (M), cyan (C), and black (K) developing devices 24 (Y, M, C, K) are supplied from a toner cartridge 242 containing toner of the corresponding color. By rotationally driving the 243, toner of the corresponding color is supplied. The drive timing and drive time of each supply motor 243 are controlled by the drive control unit 120. The developing device 24 (Y, M, C, K) changes the toner concentration in the developing device 24 (Y, M, C, K) by appropriately supplying toner of the corresponding color from the toner cartridge 242.

The primary transfer device 25 is arranged so as to be in contact with, for example, an image forming surface portion to be the primary transfer position of the photoconductor drum 21 (via the intermediate transfer belt 31 described later) and to rotate in a driven manner, and is required. It is a contact type transfer device provided with a primary transfer roll to which a primary transfer bias is supplied.

The drum cleaning device 26 is arranged so as to come into contact with at least the image-forming surface portion of the photoconductor drum 21 after the primary transfer at the opening for cleaning work of the housing, and removes unnecessary substances such as residual toner on the image-forming surface. It is equipped with a cleaning member such as an elastic plate that is scraped off and removed.

The intermediate transfer device 30 is arranged at a position on the lower side of the four image drawing devices 20 (Y, M, C, K). The intermediate transfer device 30 is arranged so as to rotate in the direction indicated by the arrow B while passing through the primary transfer positions facing the primary transfer device 25 of the photoconductor drum 21 in the image drawing device 20 (Y, M, C, K). An intermediate transfer belt 31 is provided as an example of the intermediate transfer means (image holding means) to be performed.

The intermediate transfer belt 31 is formed into an endless belt having a required thickness and an electrical resistance value using a material obtained by dispersing a resistance adjusting agent such as carbon black on a base material such as a polyimide resin or a polyamide-imide resin. It is a thing.

Further, the intermediate transfer belt 31 is rotatably supported by being hung around a plurality of support rolls 32a to 32c. The support roll 32a is formed as a drive roll, and the support roll 32b is supported on the intermediate transfer belt 31 in a state where the intermediate transfer belt 31 is wound around the outer peripheral surface, and is formed on the intermediate transfer belt 31 by a concentration sensor 60 as an example of the detection means (first detection means). The support roll 32c is configured as a secondary transfer backup roll as a sensor roll for detecting a patch image as a density control image. The density sensor 60 is located at a position facing the surface of the intermediate transfer belt 31, and has four image forming devices 20 (Y, M,) of yellow (Y), magenta (M), cyan (C), and black (K). Of C and K), it is arranged on the downstream side of the black (K) image forming apparatus 20K arranged on the most downstream side along the moving direction of the intermediate transfer belt 31.

FIG. 3 is a configuration diagram showing an optical density sensor.

As shown in FIG. 3, the density sensor 60 includes a light emitting element 61 made of an LED or the like, a light shielding member 62 emitted from the light emitting element 61 and irradiating the light beam to an exposed position on the intermediate transfer belt 31, and an intermediate transfer. A condenser lens 63 that collects the positively reflected light from the patch formed on the belt 31, an ultraviolet light cut filter 64 that blocks the ultraviolet light, and a normal reflection from the patch P formed on the intermediate transfer belt 31. It includes a light receiving element 65 composed of a photodiode, a phototransistor, or the like that receives light through a condenser lens 63 and an ultraviolet light cut filter 64. The light emitting element 61 is set at an incident angle of 45 degrees with respect to the patch on the intermediate transfer belt 31, for example. Further, the light receiving element 65 is set to a light receiving angle of 45 degrees in order to receive the specularly reflected light from the patch P on the intermediate transfer belt 31. The detection signal from the density sensor 60 is input to the image control unit 110 as shown in FIG. The detection signal (sensor value) of the density sensor 60 decreases as the amount of toner in the patch P increases.

Further, the intermediate transfer device 30 includes a secondary transfer device 33 as an example of a transfer means for secondary transfer of the toner image transferred on the intermediate transfer belt 31 to the recording paper 9, and an image on the outer peripheral surface of the intermediate transfer belt 31. The belt cleaning device 34 and the like as an example of the cleaning means of the intermediate transfer device 30 for removing and cleaning unnecessary substances such as toner remaining on the holding surface are provided.

As shown in FIG. 1, the secondary transfer device 33 is arranged to rotate in contact with the image holding surface portion supported by the support roll 32c of the intermediate transfer belt 31, for example, during normal image formation. A contact-type transfer device equipped with a secondary transfer roll 331 is adopted. A secondary transfer voltage having the same polarity as or opposite to the charging polarity of the toner is applied to the support roll 32c or the secondary transfer roll 331 that supports the intermediate transfer belt 31 from the back surface by a power supply device (not shown). The support roll 32c or the secondary transfer roll 331 that supports the intermediate transfer belt 31 from the back surface is configured so that the secondary transfer roll 331 can come into contact with and separate from the intermediate transfer belt 31 by the contact / detachment means 35.

The belt cleaning device 34 is arranged so as to come into contact with at least the image holding surface portion of the intermediate transfer belt 31 after the secondary transfer at the opening for cleaning work of the housing, and unnecessary substances such as residual toner on the image holding surface. It is equipped with a cleaning member such as an elastic plate that scrapes and cleans.

The paper feeding device 40 is arranged at a position on the lower side of the intermediate transfer device 30. The paper feeding device 40 supplies a storage body 41 in which recording paper 9 of a required size, type, etc. is stacked on a loading plate (not shown) and a recording paper 9 from the storage body 41 one by one. It is provided with a delivery device 42 that sends the paper toward the paper transport path. The number of the housing 41 and the sending device 42 is increased or decreased as necessary.

The recording paper 9 can be applied as long as it is a recording medium that can be conveyed by a conveying path and can transfer and fix a toner image. Examples of the recording paper 9 include thin paper such as plain paper and tracing paper used in electrophotographic copiers and printers, and OHP sheets. In order to further improve the smoothness of the image surface after fixing, it is preferable that the surface of the recording paper 9 is as smooth as possible. For example, coated paper in which the surface of plain paper is coated with resin or the like, art paper for printing, or the like. So-called thick paper having a relatively large basis weight can also be preferably used.

The fixing device 50 is arranged on the lower side of the intermediate transfer device 30 near the secondary transfer position along the transport direction of the recording paper 9. The fixing device 50 includes a rotating body 52 for heating, which is in the form of a roll or a belt, which rotates inside the housing 51 in the direction indicated by an arrow and is heated by a heating means so that the surface temperature is maintained at a predetermined temperature. A pressurizing rotating body 53 having a roll form or a belt form that is in contact with a predetermined pressure and rotates drivenly in a state substantially along the axial direction of the heating rotating body 52 is installed. In the fixing device 50, the portion where the rotating body 52 for heating and the rotating body 53 for pressurization come into contact with each other is configured as a fixing process section in which the recording paper 9 for holding the toner image is introduced and the fixing process (heating and pressurization) is performed. Has been done.

Further, the image forming apparatus 1 has a supply transport path RT1 connecting the paper feed device 40 and the intermediate transfer device 30 as a main paper transport path for the recording paper 9, and a secondary transfer position of the intermediate transfer device 30. A relay transport path RT2 that connects the fixing device 50 and the discharge transport path RT3 that connects the fixing device 50 and a paper discharge port (not shown) are provided.

In the supply transport path RT1, a single or a plurality of paper transport roll pairs 43 for transporting the recording paper 9 supplied from the paper feed device 40 to the secondary transfer position, a transport guide (not shown), and the like are arranged. The paper transport roll pair 43 arranged adjacent to the upstream side of the secondary transfer position of the intermediate transfer belt 31 is configured as a resist roll that transports the recording paper 9 in synchronization with the image on the intermediate transfer belt 31. ..

<Basic image formation operation by the image forming device>
In this image forming apparatus 1, the basic image forming operation described below is performed. Here, an operation in the case of forming a full-color image composed by combining toner images of four colors (Y, M, C, K) will be described as an example.

First, as shown in FIG. 1, when the control device 100 receives a request command for an image forming operation from the outside or the like, the image forming apparatus 1 is used in the four image forming apparatus 20 (Y, M, C, K). Each photoconductor drum 21 is rotated in the direction indicated by the arrow A, and each charging device 22 receives a charging current to generate a corona discharge. As a result, the image-forming surface of each photoconductor drum 21 is charged to a required polarity (for example, negative polarity) and potential, respectively.

Subsequently, each exposure device 23 exposes the image-forming surface of each photoconductor drum 21 after charging according to the image signal decomposed into each color component (Y, M, C, K). As a result, an electrostatic latent image of each color component having a predetermined potential is formed on the image-forming surface of each photoconductor drum 21.

Subsequently, each developing device 24 (Y, M, C, K) supplies toner of each color (Y, M, C, K) charged to a predetermined polarity (minus polarity) from the developing roll 241. Due to the developing electric field formed between the developing roll 241 and the photoconductor drum 21 by receiving the supply of the developing bias, the electrostatic latent image portion of each color component on the image forming surface of the photoconductor drum 21 is electrostatically generated. Attach. As a result, toner images of the corresponding colors of the four colors (Y, M, C, K) are individually formed on the image-forming surface of each photoconductor drum 21.

Subsequently, each primary transfer device 25 receives the supply of the primary transfer current to form a primary transfer electric field with the photoconductor drum 21, so that the toner image on each photoconductor drum 21 is intermediated in the intermediate transfer device 30. The primary transfer is performed in order (in the order of Y, M, C, K) with respect to the image holding surface of the transfer belt 31. Further, the drum cleaning device 26 cleans the image forming surface of each photoconductor drum 21 after the primary transfer or the like to prepare for the next image forming operation on each photoconductor drum 21.

Next, in the intermediate transfer device 30, the intermediate transfer belt 31 rotates in the direction indicated by the arrow B, so that the unfixed toner image that is primarily transferred and held on the image holding surface faces the secondary transfer device 33. Transport to the next transfer position. On the other hand, in the paper feed device 40, after the paper feed device 42 feeds the recording paper 9 from the accommodating body 41 to the supply transport path RT1, the paper transport roll pair 43 supplies the paper to the secondary transfer position of the intermediate transfer device 30. Then, at the secondary transfer position, the secondary transfer device 33 receives the supply of the secondary transfer bias and forms a secondary transfer electric field with the intermediate transfer belt 31, so that the four colors on the intermediate transfer belt 31 are formed. The toner image of is secondarily transferred to one side of the recording paper 9.

Next, the recording paper 9 on which the unfixed toner image is secondarily transferred is transferred so as to be sent to the fixing device 50 via the relay transfer path RT2 after being peeled off from the intermediate transfer belt 31. In the fixing device 50, the recording paper 9 is heated and pressurized when it is introduced into a fixing processing portion which is a contact portion between the heating rotating body 52 and the pressing rotating body 53 and passes therethrough. As a result, the toner constituting the toner image is melted under pressure, and the toner image is fixed on the recording paper 9.

Subsequently, the recording paper 9 after the toner image is fixed is discharged from the housing 51 of the fixing device 50 and then transported via the discharge transport path RT3, and finally to the outside from a paper discharge port (not shown). It is discharged.

By performing the above operation, one sheet of recording paper 9 on which a full-color image is formed is output. Further, when a request command for a plurality of image forming operations is received, the above image forming operation is repeated in the same manner for the number of images.

In addition, in the image forming apparatus 1, in the above image forming operation, a monochromatic image is formed by operating any one of the four image forming apparatus 20 (Y, M, C, K), and 4 It is also possible to form a color image other than a full-color image by operating two or three of the image-forming devices 20 (Y, M, C, K) in combination.

<Structure of characteristic parts of image forming apparatus>
The image forming apparatus 1 configured as described above has individual differences for each individual image forming apparatus 1. More specifically, the individual image forming apparatus 1 describes the change with time of the photoconductor layer of the photoconductor drum 21 used in each image forming apparatus 20 (Y, M, C, K) and the developer used in the developing apparatus 24. The amount of toner in the image when the electrostatic latent image formed on the photoconductor drum 21 is developed due to environmental changes such as temperature and humidity, and the amount of toner transferred from the photoconductor drum 21 onto the intermediate transfer belt 31. The amount of toner in the image at the time of processing is different, and the density, color tone, etc. of the full-color image finally formed on the recording paper 9 are changed.

Therefore, in the image forming apparatus 1, a patch image as a density detecting image for detecting the image density is formed on the photoconductor drum 21 of each image forming apparatus 20 (Y, M, C, K), and each of them. The density of the patch image formed on the photoconductor drum 21 or the patch image primary transferred from each photoconductor drum 21 onto the intermediate transfer belt 31 is detected by the optical density sensor 60 to obtain the detection density of the patch image. Image formation conditions such as the charging bias of the charging device 22, the development bias of the developing device 24, the toner concentration in the developing device 24, the exposure amount of the exposure device 23, and the image area ratio are controlled accordingly, and finally the recording paper 9 is used. Fluctuations in density, color tone, etc. of full-color images formed in the image are suppressed.

By the way, the image forming apparatus 1 is a photoconductor drum in each of the yellow (Y), magenta (M), cyan (C) and black (K) image forming apparatus 20 (Y, M, C, K) over time. When the surface of the photoconductor 21 is worn and the film thickness of the photoconductor layer is reduced, as shown in FIG. 4, a dark attenuation curve (PIDC) showing the relationship of the exposed portion potential with respect to the exposure amount of the photoconductor drum 21 is formed in the photoconductor layer. As the film thickness decreases, it shifts to the low sensitivity side (right side in the figure). That is, in the image forming apparatus 1, when the film thickness of the photoconductor layer of the photoconductor drum 21 is reduced, the potential of the exposed portion of the photoconductor drum 21 is increased even if the exposure amount of the photoconductor drum 21 is constant. Compared with the case where the thickness of the photoconductor layer is relatively thick, it does not decrease but increases (absolute value increases). Therefore, the image forming apparatus 1 forms a patch image on the surface of the photoconductor drum 21, detects the density of the patch image on the intermediate transfer belt 31, and controls the image forming conditions based on the detected density of the patch image. In order to keep the latent image potential, which is the exposure portion potential of the photoconductor drum 21, constant and the density of the patch image constant, it is necessary to relatively increase the amount of light of the exposure apparatus 23.

At this time, as shown in FIG. 5A, the patch image is 1 dot using, for example, a multi-line screen having a high screen line number of 400 lines (lpi) of the exposure apparatus 23 used at the time of normal image formation. It is formed by a thin line like. Then, when the amount of light of the exposure device 23 is increased in order to make the latent image potential of the photoconductor drum 21 constant, a patch image formed on the surface of the photoconductor drum 21 as shown in FIG. 6A. The electrostatic latent image corresponding to the above has a clearer shape as compared with the case where the contrast of the exposed portion forming the patch image is relatively low in the amount of light of the exposure apparatus 23 (see the lower part of FIG. 6A). When the electrostatic latent image corresponding to this patch image is developed by the developing device 24, the toner in the developing agent adheres substantially faithfully to the profile of the exposed portion, and the toner layer of the developed image increases. As a result, the image density of the patch image increases.

However, as shown in FIG. 3, the optical density sensor 60 that detects the density of the patch image P depends on the toner area (density) of the patch image P, that is, the area of the toner adhering to each unit area. However, the output hardly changes with respect to the thickness (height) of the toner layer, and it is difficult to detect an increase in the toner layer of the patch image P as an increase in density.

Therefore, in the conventional image forming apparatus 1, when the surface of the photoconductor drum 21 is worn and the film thickness of the photoconductor layer decreases with time, the dark attenuation curve (PIDC) causes the film thickness of the photoconductor layer to decrease. In order to compensate for the shift to the low sensitivity side, it is difficult to detect the density change of the patch image formed by increasing the light intensity of the exposure device 23 as the density increase, and it is difficult to detect the gradation fluctuation of the image density and the full color. There is a risk that the image density will become unstable due to problems such as changes in the color tone of the image.

Therefore, in the image forming apparatus 1 according to the first embodiment, the photoconductor drum 21 is in a reference state (for example, when it is new), such as a decrease in the thickness of the photoconductor layer of the photoconductor drum 21 over time. It is configured to be able to detect the density change of the patch image P due to the change from the above, and to stabilize the image density even when the density fluctuation factors such as the film thickness of the photoconductor layer and the temperature and humidity change.

Here, the reference state of the photoconductor drum 21 refers to a state that serves as a reference for fluctuation factors such as a decrease in film thickness of the photoconductor layer over time. Specifically, for example, there is a case where the photoconductor drum 21 is new and is in an unused state. When the photoconductor drum 21 is in an unused state, not only when the image forming apparatus 1 is used for the first time, but also the photoconductor drum 21 itself and the image forming unit including the photoconductor drum 21 are replaced with new ones. Including the case where it was done.

The image forming apparatus 1 according to the first embodiment is yellow (Y) as an example of an image forming means for forming a patch image with a standard number of lines used for image forming in the image holding means and a low number of lines lower than the standard number of lines. , Magenta (M), Cyan (C) and Black (K) image forming devices 20 (Y, M, C, K), density sensor 60 for detecting the density of patch images, and each image forming device 20 (Y). , M, C, K) Photoreceptor drum 21 is a storage unit 104 as an example of a storage means for storing the density of the patch image of the standard line number and the low line number detected by the density sensor 60 when the photoconductor drum 21 is in the reference state. (See FIG. 10) and the standard number of lines and low lines detected by the density sensor 60 at a predetermined time after the start of use of the photoconductor drum 21 of each image forming apparatus 20 (Y, M, C, K). A control unit 101 (see FIG. 10) as an example of the correction means for correcting the image formation conditions of the image forming means according to the comparison result between the density of the number of patch images and the density stored in the storage unit 104 is provided. There is.

More specifically, in the image forming apparatus 1 according to the first embodiment, each of the yellow (Y), magenta (M), cyan (C), and black (K) image forming apparatus 20 (Y) of the image forming apparatus 1 , M, C, K) Photoreceptor drum 21 is new, that is, when the image forming apparatus 1 is in an unused state or starts to be used, by each image forming apparatus 20 (Y, M, C, K). A patch image is formed with a standard number of lines used at the time of image formation and a low number of lines lower than the standard number of lines. Here, when the image forming apparatus 1 is in an unused state, for example, the time when the image forming apparatus 1 is shipped from the factory can be mentioned. Further, the time when the image forming apparatus 1 starts to be used is when the image forming apparatus 1 is transported to the user and the service engineer or the like performs the installation work or the installation work is completed.

As shown in FIG. 5A, the patch image with a standard number of lines (hereinafter referred to as “standard patch”) 200 is, for example, a 400-line universal line, which is the standard number of lines used during normal image formation. Formed using a screen. FIG. 5A schematically shows a state in which a standard patch having an image density of 67% is formed using a 400-line vertical screen. Similarly, a patch image with a low line number lower than the standard line number (hereinafter referred to as “check patch”) 300 is used, for example, for normal image formation as shown in FIG. 5 (b). It is formed by using a 100-line universal screen having a number of lines lower than the standard number of 400 lines. FIG. 5B schematically shows a state in which a check patch having an image density of 67% is formed using a 100-line vertical screen. The standard patch is not limited to the case where it is formed by a 400-wire screen, and of course, it may have another number of lines such as 200 lines or 300 lines. Similarly, the check patch 300 is not limited to a 100-wire universal screen, and may have a lower number of lines than the standard patch. The screen forming the standard patch 200 and the check patch 300 is not limited to the universal screen, and a screen having another structure such as a mesh screen may be used. Further, the concentrations of the standard patch 200 and the check patch 300 are not limited to 67% of Cin, and of course, other values such as 33% of Cin and 50% of Cin may be used.

As shown in FIG. 7, the standard patch 200 and the check patch 300 formed on the photoconductor drum 21 of each image forming apparatus 20 (Y, M, C, K) of the image forming apparatus 1 are yellow (Y). ), Magenta (M), cyan (C), and black (K) are each primary transferred onto the intermediate transfer belt 31 as a pattern corresponding to a plurality of image densities. Then, the standard patch 200 and the check patch 300 that are primarily transferred onto the intermediate transfer belt 31 are imaged by the density sensor 60 on the downstream side of the black (K) image forming apparatus 20K along the moving direction of the intermediate transfer belt 31. The concentration is detected.

By the way, in the image forming apparatus 1 according to the first embodiment, in addition to the standard patch 200 having a standard line number, a check patch 300 having a low line number is formed and the image density of the check patch 300 is also detected. As a result, the photoconductor layer in the photoconductor drum 21 of any of the yellow (Y), magenta (M), cyan (C), and black (K) image forming devices 20 (Y, M, C, K) The reason why the density change of the patch image according to the film thickness change can be detected accurately is as follows.

When forming the standard patch 200 and the low-line number check patch 300, the exposed portion and the non-exposed portion (background portion) of the latent image potential formed by exposing the patch image to the surface of the photoconductor drum 21 by the exposure device 23. ) Is worse in the low line number check patch 300 than in the standard patch 200.

Further, the contrast (shading) between the exposed portion and the non-exposed portion (background portion) of the latent image potential is worse when the film thickness of the photoconductor layer of the photoconductor drum 21 is thick, and the contrast (shading) of the photoconductor layer of the photoconductor drum 21 is worse. It becomes better as the film thickness becomes thinner.

Further, the contrast (shading) between the exposed portion and the non-exposed portion (background portion) of the latent image potential is better when the amount of light of the exposure device 23 that forms the patch image on the surface of the photoconductor drum 21 is large.

Therefore, as shown in FIGS. 6 and 8, the low-line number check patch 300 is essentially a standard patch in which the contrast (shading) between the exposed portion and the non-exposed portion (background portion) of the latent image potential is the standard patch. Coupled with the fact that it is worse than 200, when the thickness of the photoconductor layer of the photoconductor drum 21 is thick, the contrast (shading) between the exposed portion and the non-exposed portion (background portion) of the latent image potential is poor. The density of the patch image is lower than that of the standard patch 200, and the output of the density sensor 60 is higher.

Further, in the low-line number check patch 300, as the film thickness of the photoconductor layer of the photoconductor drum 21 becomes thinner, the contrast (shading) between the exposed portion and the non-exposed portion (background portion) of the latent image potential becomes better. Due to the effect of increasing the amount of light of the exposure apparatus 23, the density of the patch image becomes higher than that of the standard patch 200, and the output of the density sensor 60 decreases.

As a result, in the low-line number check patch 300, the output of the density sensor 60 changes (decreases) linearly with a large gradient as compared with the standard patch 200 as the film thickness of the photoconductor layer of the photoconductor drum 21 changes. To do.

On the other hand, the standard patch 200 originally has a better contrast (shading) between the exposed portion and the non-exposed portion (background portion) of the latent image potential than the patch 300 for checking the low line number, and the photoconductor drum 21 has a better contrast. Even when the thickness of the photoconductor layer is thin, the density of the patch image becomes higher than that of the check patch, and the output of the density sensor 60 decreases.

Further, in the standard patch 200, the contrast (shading) between the exposed portion and the non-exposed portion (background portion) of the latent image potential hardly changes with the change in the film thickness of the photoconductor layer of the photoconductor drum 21, and the standard patch 200 is photosensitive. Even when the thickness of the photoconductor layer of the body drum 21 is thin, the density of the patch image is higher than that of the check patch, and the output of the density sensor 60 is reduced.

As a result, the output of the density sensor 60 of the standard patch 200 hardly changes as compared with the standard patch 200 even if the film thickness of the photoconductor layer of the photoconductor drum 21 changes, and maintains a substantially constant value.

Therefore, by detecting the image density of the check patch 300, the density of the check patch 300 increases due to the increase in the amount of light of the exposure apparatus 23 as the film thickness of the photoconductor layer of the photoconductor drum 21 decreases. It can be detected, and the image density can be stabilized by controlling the target value and the like when forming the standard patch 200 accordingly.

On the other hand, as shown in FIG. 9, the standard patch 200 has almost no density fluctuation due to a change in the thickness of the photoconductor layer of the photoconductor drum 21, but the thickness of the photoconductor layer of the photoconductor drum 21 is fixed. By changing the image density of the standard patch 200, the output change of the density sensor 60 due to the density change of the standard patch 200 is large.

Therefore, except when the film thickness of the photoconductor layer of the photoconductor drum 21 changes significantly, the standard patch is used during normal image formation in which the film thickness of the photoconductor layer of the photoconductor drum 21 can be regarded as substantially constant. By detecting the image density of 200 with the density sensor 60 and controlling the image formation conditions so that the image density of the standard patch 200 becomes a target value, it is possible to maintain good image density.

<Control device configuration>
FIG. 10 is a block diagram showing a control device of the image forming apparatus according to the first embodiment.

The control device 100 includes a control unit 101 as an example of the correction means, a timing generation unit 102, a patch generation unit 103, a storage unit 104 as an example of the storage means, and a calculation unit 105.

The control unit 101 comprehensively controls the operation of the image forming apparatus 1 including the image density control operation by executing the program stored in the storage unit 104. The control unit 101 includes a charging device 22, an exposure device 23, and a developing device in each of the yellow (Y), magenta (M), cyan (C), and black (K) image forming devices 20 (Y, M, C, K). By driving the apparatus 24, the primary transfer apparatus 25, the photoconductor driving means (not shown), and the transfer belt driving means, the formation operation of a color image or the like is executed.

Further, the control unit 101 executes an image density control operation via the timing generation unit 102, the patch generation unit 103, the storage unit 104, the calculation unit 105, and the like.

At that time, when the control unit 101 determines that it is the timing to execute the image density control operation, the timing generation unit 102 generates a timing signal for image density control. The timing at which the image density control operation should be executed is, for example, when the photoconductor drum 21 in each image forming device 20 (Y, M, C, K) of the image forming device 1 is new, each image forming device 20 ( This is a required time such as when the cumulative rotation speed of the photoconductor drum 21 in Y, M, C, K) reaches a predetermined value.

Further, when the timing signal for image density control is generated by the timing generation unit 102, the patch generation unit 103 outputs a patch generation signal for generating the standard patch 200 and the check patch 300, and yellow (Y). A standard patch 200 and a check patch 300 are formed in each of the magenta (M), cyan (C), and black (K) image-forming devices 20 (Y, M, C, K).

When the control unit 101 detects the densities of the standard patch 200 and the check patch 300 of each color of yellow (Y), magenta (M), cyan (C) and black (K) by the density sensor 60, the control unit 101 standardizes in the calculation unit 105. The image density of the patch 200 and the check patch 300 is calculated, and the charging device 22, the exposure device 23, the developing device 24, etc. of each image forming device 20 (Y, M, C, K) are controlled to control the image density. To execute.

<Operation of the characteristic part of the image forming device>
In the image forming apparatus 1 according to the first embodiment, as compared with the case where a plurality of test patterns having different patterns are formed and image forming conditions are set as follows, the film thickness, temperature and humidity of the photoconductor, etc. It is possible to stabilize the image density when the density fluctuation factor changes.

That is, in the image forming apparatus 1 according to the first embodiment, as shown in FIG. 11, the control unit 101 of the control apparatus 100 uses yellow (Y), magenta (M), cyan (C), and black (K). It is determined whether or not the photoconductor drum 21 of each image forming apparatus 20 (Y, M, C, K) of the above is new (step 101). Whether or not the photoconductor drum 21 of each image forming apparatus 20 (Y, M, C, K) is new is determined based on, for example, the count value of a counter that counts the cumulative number of rotation cycles of each photoconductor drum 21. It is determined. The number of rotation cycles of the photoconductor drum 21 at the start of use of the image forming apparatus 1 or when the photoconductor drum 21 of any of the image forming devices 20 (Y, M, C, K) is replaced with a new one. Since the count value of the counter that cumulatively counts is zero, it is determined that the photoconductor drum 21 is new.

In the image forming apparatus 1, the photoconductor drum 21 is not a single unit, but an image forming means such as a charging device 22 including the photoconductor drum 21 and a drum cleaning device 26 is integrally united as an image holder unit. There is. The image holder unit includes a memory as an example of a storage means for storing a value obtained by cumulatively counting the number of rotation cycles of the photoconductor drum 21. Therefore, in this case, it is possible to determine whether or not the photoconductor drum 21 is new by reading out the number of rotation cycles of the photoconductor drum 21 stored in the memory provided in the image formation unit.

Next, when the control device 100 determines that at least one or more photoconductor drums 21 are new, the control device 100 forms a standard patch 200 and a check patch 300 on the photoconductor drum 21 determined to be new. Then, the standard and check patch detection subroutines for detecting the image densities of the standard patch 200 and the check patch 300 are executed (step 102). At the start of use of the image forming apparatus 1, the photoconductors of the yellow (Y), magenta (M), cyan (C), and black (K) image forming apparatus 20 (Y, M, C, K) are started to be used. Since all the drums 21 are new, the standard and check patch detection subroutines for detecting the image densities of the standard patch 200 and the check patch 300 are executed.

In the standard and check patch detection subroutines, as shown in FIG. 12, the control unit 101 of the control device 100 creates a pattern of the standard patch 200 (step 201), and the image density of the pattern of the standard patch 200. _Is detected by the concentration sensor 60 and the output V std is calculated (step 202). After that, the control unit 101 creates a pattern of the check patch 300 (step 203), detects the image density of the pattern of the check patch 300 by the density sensor 60, _{and calculates the output V che} (step). 204), the operation of the standard and check patch detection subroutine is terminated.

_{After that, as shown in FIG. 11, the control device 100 determines the concentration detection values V std} , V _che of the standard patch 200 and the check patch 300 in any one or more photoconductor drums 21 determined to be new. _Is stored and stored in the storage unit 104 in the control device 100 as V std0 and V _{che0 (step 103).}
V _std0 = V _std
V _che0 = V _che

After that, the control unit 101 of the control device 100 changes the image formation conditions so that _{the detected value V std} of the standard patch 200 becomes the target value V _{std_tgt (step 104).} Here, the target value V _{std_tgt} of the standard patch 200 is stored in the storage unit 104 in advance.

Next, the control unit 101 of the control device 100 determines whether or not it is a print end (step 105), returns to step 101 if it is not a print end, and ends the operation if it is a print end.

On the other hand, when the control unit 101 of the control device 100 determines in step 101 that none of the photoconductor drums 21 is new, the number of cycles of the photoconductor drum 21 is predetermined as an example of a predetermined time after the start of use. It is determined whether or not it is equal to or more than the specified specified value (predetermined operating time) (step 106). Here, the predetermined predetermined value of the number of cycles of the photoconductor drum 21 is set to, for example, a value at which the film thickness of the photoconductor layer of the photoconductor drum 21 is reduced by 5 μm. That is, in step 106, it is determined whether or not the film thickness of the photoconductor layer of the photoconductor drum 21 has decreased by 5 μm from the previous time.

Then, when the control unit 101 of the control device 100 determines that the number of cycles of any one or more photoconductor drums 21 is not equal to or more than a predetermined predetermined value, the detection value of the standard patch 300 becomes the _{target value V std_tgt.} The image formation conditions are changed (step 104), and it is determined whether or not the image is a print end (step 105).

Further, when the control unit 101 of the control device 100 determines that the number of cycles of any one or more photoconductor drums 21 is equal to or more than a predetermined value, the operation of the above-mentioned standard and check patch detection subroutines Is executed (step 107).

In the standard and check patch detection subroutines, as shown in FIG. 12, the control unit 101 of the control device 100 creates a pattern of the standard patch 200 (step 201), and the image density of the pattern of the standard patch 200. _Is detected by the concentration sensor 60 and the output V std is calculated (step 202). After that, the control unit 101 creates a pattern of the check patch 300 (step 203), detects the image density of the pattern of the check patch 300 by the density sensor 60, _{and calculates the output V che} (step). 204), the operation of the standard and check patch detection subroutine is terminated.

In the standard and check patch detection subroutines executed at this time, the number of cycles of any one or more photoconductor drums 21 is equal to or more than a predetermined value, and the film of the photoconductor layer of the photoconductor drum 21 is formed. Since the thickness is reduced by about 5 μm, when the patterns of the standard patch 200 and the patch 300 are formed, as shown in FIG. 4, the exposure amount of the exposure apparatus 23 corresponds to the change in the film thickness of the photoconductor drum 21. The exposure portion potential of the standard patch 200 and the patch 300 is changed (increased) to be substantially constant.

After that, as shown in FIG. 11, the control unit 101 of the control device 100 _{determines that the absolute value of the difference between the concentration detection values V std0} and V _std of the standard patch 200 is equal to or less than a predetermined first threshold value. It is determined whether or not the difference between the density detection values V _che0 and V _che of the check patch 300 exceeds a predetermined second threshold value (step 108).

Here, it is determined that the thickness of the photoconductor drum 21 determines whether or not the absolute value of the difference between the density detection values V _std0 and V _{std of the standard patch 200 is equal to or less than a predetermined first threshold value.} Despite the change and increasing the light intensity of the exposure device 23, the increase in the light intensity of the exposure device 23 _{is not reflected in the density detection value V std} of the standard patch 200, that is, it cannot be detected. Means that.

On the other hand, _{it is determined whether or not the difference between the density detection values V che0} and V _che of the check patch 300 exceeds a predetermined second threshold value because the film thickness of the photoconductor drum 21 changes. The amount of light of the exposure device 23 is increased, which means that the increase in the amount of light of the exposure device 23 _{is reflected in the density detection value V che} of the check patch 300 and is actually detected.

That is, the absolute value of the difference between the density detection values V _std0 and V _std of the standard patch 200 is equal to or less than a predetermined first threshold value, and the difference between _{the concentration detection values V che0} and V _{che of the check patch 300.} When exceeds a predetermined second threshold value, the film thickness of the photoconductor drum 21 is reduced, and the amount of light of the exposure device 23 is increased as the film thickness of the photoconductor drum 21 is reduced. Moreover, the increase in the amount of light of the exposure apparatus 23 due to the decrease in the film thickness of the photoconductor drum 21 is detected by the check patch 300, but is not detected by the standard patch 200.

Then, the control unit 101 of the control device 100 detects _whether the absolute value of the difference between the density detection values V std0 and V _std of the standard patch 200 is not equal to or less than a predetermined first threshold value, or the density detection of the check patch 300. When it _{is determined that the difference between the values V che0} and V _che does not exceed a predetermined second threshold value, the image formation conditions are changed so that the detected value of the standard patch 200 becomes the target value (step 104). It is determined whether or not it is a print end (step 105).

On the other hand, the control unit 101 of the control device 100 detects the density of the check patch 300 while the absolute value of the difference between the _{density detection values V std0} and V _{std of the standard patch 200 is equal to or less than a predetermined first threshold value.} When it _{is determined that the difference between the values V che0} and V _che exceeds a predetermined second threshold value, the target value V _{std_tgt} for the standard patch is calculated based on the following equation (step 109).
V _{std_tgt} = V _{std_} reference + (V _che0 −V _che ) * Coefficient α

_{The target value V std_tgt} for the standard patch calculated here is the sum of the original V _{std_} reference and the (V _che0 −V _che0 ) * coefficient α, and is larger than _{the V std_ reference.} As shown in FIG. 9, the output of the density sensor 60 decreases as the image density of the standard patch 200 increases, so that the calculated target value V _{std_tgt} for the standard patch is larger than the original V _{std_ reference.} This is substantially equivalent to detecting a high image density of the standard patch 200.

Then, the control unit 101 of the control device 100 changes the image formation conditions so that _{the detected value V std} of the standard patch 200 becomes equal to the newly calculated target value V _{std_tgt (step 104).}

After that, the control device 100 determines whether or not it is a print end (step 105), returns to step 101 if it is not a print end, and ends the process if it is a print end.

As described above, the image forming apparatus 1 according to the first embodiment is the yellow (Y), magenta (M), cyan (C), and black (K) image forming apparatus 20 (Y, M, C, K). ) Is new or not corresponding to the reference state, and if it is determined that any one or more of the photoconductor drums 21 are also new, both the standard patch 200 and the check patch 300 are used. _{The values V std0} and V _che0 detected by the density sensor 60 for the image densities of the standard patch 200 and the check patch 300 are stored in the storage unit 104 of the control device 100.

After that, the cumulative number of cycles of the photoconductor drum 21 in each of the yellow (Y), magenta (M), cyan (C), and black (K) image forming devices 20 (Y, M, C, K) is predetermined. When it is determined whether or not the specified specified value has been exceeded and the cumulative number of cycles of the photoconductor drum 21 exceeds the predetermined specified value, the image densities of the standard patch 200 and the check patch 300 are adjusted. It is detected by the density sensor 60.

Then, the image densities of the detected standard patch 200 and the check patch 300, and the image densities of the standard patch 200 and the check patch 300 when the corresponding photoconductor drum 21 stored in the storage unit 104 is new, V _std0 , The difference from V _che0 is calculated, and if the difference from the image density satisfies a predetermined condition, the target value of the image density of the standard patch 200 at the time of image density control is changed.

Therefore, in the first embodiment, the image density of the standard patch 200 is increased as the light intensity of the exposure apparatus 23 is increased in order to keep the image density of the standard patch 200 constant as the film thickness of the photoconductor drum 21 decreases. It becomes possible to cope with the increase in the image density, and the image density in each image forming apparatus 20 (Y, M, C, K) can be stably maintained.

[Embodiment 2]
FIG. 13 shows an image forming apparatus according to the second embodiment. The image forming apparatus 1 according to the second embodiment is configured to stabilize the image density when environmental conditions such as temperature and humidity fluctuate.

That is, the second embodiment considers a case where environmental conditions such as temperature and humidity change as a concentration fluctuation factor, and the reference state of the photoconductor drum 21 as an example of the image holding means is an image forming apparatus. It means a case where at least one of the temperature and humidity in the environment in which 1 is installed, preferably both temperature and humidity, are normal temperature and / or normal humidity (25 ° C., relative humidity 50%).

In FIG. 13, reference numeral 70 indicates an environment sensor as an example of a second detection means for detecting environmental conditions such as temperature and humidity in the environment in which the image forming apparatus 1 is installed.

In the second embodiment, as shown in FIG. 14, at the time of shipment of the image forming apparatus 1, whether or not the detection temperature and humidity of the environment sensor 70 are in an environment of normal temperature and humidity (25 ° C., relative humidity 50%). (Step 301), and when it is determined that the installation environment of the image forming apparatus 1 is an environment of normal temperature and humidity (25 ° C., relative humidity 50%), yellow (Y), magenta (M), and cyanide are determined. Both the standard patch 200 and the check patch 300 are formed by using the image forming apparatus 20 (Y, M, C, K) of (C) and black (K), and these standard patch 200 and the check patch 300 are formed. the image density detected by the density sensor 60, the concentration detection value _V std of the standard patch 200 and the check patch _{300, V che} a _{V STD0} and _{V Che0} stored in the storage unit 104 of the control device 100 stores as ( Step 103).

Then, as shown in FIG. 14, the control unit 101 of the control device 100 determines whether or not the temperature of the environmental condition has changed by 10 ° C. or more (step 302).

Next, when the control unit 101 of the control device 100 determines that the temperature of the environmental condition has changed by 10 ° C. or more, it executes the operation of the standard and check patch detection subroutines (step 107).

In the standard and check patch detection subroutines, as shown in FIG. 12, the control unit 101 of the control device 100 creates a pattern of the standard patch 200 (step 201), and the image density of the pattern of the standard patch 200. _Is detected by the concentration sensor 60 and the output V std is calculated (step 202). After that, the control unit 101 creates a pattern of the check patch 300 (step 203), detects the image density of the pattern of the check patch 300 by the density sensor 60, _{and calculates the output V che} (step). 204), the operation of the standard and check patch detection subroutine is terminated.

In the standard and check patch detection subroutines executed at this time, since the temperature of the environmental conditions changed by 10 ° C. or more, exposure was performed as shown in FIG. 15 when forming the patterns of the standard patch 200 and the patch 300. The exposure amount of the device 23 is changed (increased) according to the change of the environmental conditions, and the exposure portion potentials of the standard patch 200 and the patch 300 are made substantially constant.

After that, as shown in FIG. 14, the control unit 101 of the control device 100 _{determines that the absolute value of the difference between the concentration detection values V std0} and V _std of the standard patch 200 is equal to or less than a predetermined first threshold value. It is determined whether or not the difference between the density detection values V _che0 and V _che of the check patch 300 exceeds a predetermined second threshold value (step 108).

Then, the control unit 101 of the control device 100 detects _whether the absolute value of the difference between the density detection values V std0 and V _std of the standard patch 200 is not equal to or less than a predetermined first threshold value, or the density detection of the check patch 300. When it _{is determined that the difference between the values V che0} and V _che does not exceed a predetermined second threshold value, the image formation conditions are changed so that the detected value of the standard patch 200 becomes the target value (step 104). It is determined whether or not it is a print end (step 105).

On the other hand, the control unit 101 of the control device 100 detects the density of the check patch 300 while the absolute value of the difference between the _{density detection values V std0} and V _{std of the standard patch 200 is equal to or less than a predetermined first threshold value.} When it _{is determined that the difference between the values V che0} and V _che exceeds a predetermined second threshold value, the target value V _{std_tgt} for the standard patch is calculated based on the following equation (step 109).
V _{std_tgt} = V _{std_reference} 2+ (V _che0 −V _che0 ) * Coefficient β

Here, V _{std_reference} 2 is a reference value of the standard patch 200 when temperature change as a change in environmental conditions is taken into consideration.

Since the following operation is the same as the flowchart shown in FIG. 11, the description thereof will be omitted.

As described above, in the second embodiment, in order to keep the image density of the standard patch 200 constant when the environmental conditions change, the image density of the standard patch 200 increases as the amount of light of the exposure apparatus 23 is increased. It becomes possible to stably maintain the image density in each image forming apparatus 20 (Y, M, C, K).

Since other configurations and operations are the same as those of the above-described embodiment, the description thereof will be omitted.

In the above embodiment, a full-color image forming apparatus having yellow (Y), magenta (M), cyan (C), and black (K) image forming apparatus 20 (Y, M, C, K) is provided. Although the image forming apparatus has been described, it goes without saying that the image forming apparatus can be similarly applied to a monochrome image forming apparatus having only a black (K) image forming apparatus.

1 ... Image forming device 20 ... Image forming device 21 ... Photoreceptor drum 23 ... Exposure device 24 ... Developing device 100 ... Control device 101 ... Control unit 200 ... Standard patch 300 ... Check patch

Claims (7)

An image forming means for forming a patch image with a standard number of lines used for image forming as an image holding means and a low number of lines lower than the standard number of lines, and an image forming means.
A detection means for detecting the density of the patch image and
A storage means for storing the density of the patch image of the standard number of lines and the low line number detected by the detection means when the image holding means is in the reference state, and a storage means.
Comparison result of the density of the patch image of the standard number of lines and the low line number detected by the detection means at a predetermined time after the start of use of the image holding means and the density stored in the storage means. A correction means for correcting the image formation conditions of the image forming means according to
An image forming apparatus comprising. In the comparison between the density of the patch image with the standard number of lines and the low line number detected by the detection means and the density stored in the storage means, the difference between the densities of the patch images with the standard number of lines is in advance. The image forming apparatus according to claim 1, wherein the image forming apparatus is performed depending on whether or not the difference between the densities of the patch images having the low line number is equal to or less than a predetermined first threshold value and exceeds a predetermined second threshold value. .. In the correction means, the difference between the densities of the patch images having the standard number of lines is equal to or less than a predetermined first threshold value, and the difference between the densities of the patch images having the low number of lines is predetermined. The image forming apparatus according to claim 2, wherein if it is determined that the threshold value of 2 is exceeded, the image forming condition is corrected after changing the density target value of the patch image having the standard number of lines. The image forming apparatus according to claim 1, wherein the predetermined time after the start of use is when the image holding means operates for a predetermined operating time. The image forming apparatus according to claim 4, wherein when the image holding means operates for a predetermined operation time, the cumulative rotation speed of the image holding means reaches a predetermined value. The image forming apparatus according to claim 1, wherein the predetermined time after the start of use is when the environmental temperature changes by a specified value or more. The image forming apparatus according to claim 6, wherein when the environmental temperature changes by a specified value or more, the environmental temperature rises or falls over 10 ° C. or higher.

Images