JP2016177139A - Image formation device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image formation device that allows an adhesion amount of K toner in a monochrome mode to be properly calculated even when a relation of a distance and an angle between a sensor of an adhesion amount of toner and an intermediate transfer belt is deviated in a full color mode and monochrome mode.SOLUTION: An adhesion amount conversion table is changed over in accordance with a change in distance and angle between a sensor of an adhesion amount of toner and an intermediate transfer belt at a time of a full color mode and monochrome mode. That is, a calibration of the sensor of the adhesion amount of toner by an adjustment of an LED light emitting amount so as to obtain a prescribed amount of reflection light in the full color mode is configured to make adjustments to the light emitting amount again upon changing to the monochrome mode thereafter. Respective light emitting amounts are managed by an amount of current input to an LED of the sensor of the adhesion amount of toner, and an amount of change in an angle of incidence and reflection angle of the sensor of the adhesion amount of toner is obtained from a difference between the amounts of input current in the full color mode and monochrome mode.SELECTED DRAWING: Figure 6

Description

  The present invention relates to an electrophotographic image forming apparatus such as a copying machine, a printer, and a facsimile.

  Some image forming apparatuses that form a latent image on a photosensitive member, develop toner on the latent image, and then transfer the latent image to print paper to perform image quality adjustment operations. In this operation, first, a toner image is created as a gradation pattern while changing image forming conditions such as a developing bias, a charging bias, or an exposure condition outside the printing operation. The toner adhesion amount is acquired by using the toner adhesion amount sensor for the created toner image of the gradation pattern. Then, an optimum image forming condition is determined by obtaining the developing ability of the toner from the correlation between the developing potential (difference between the developing potential and the exposure potential) and the toner adhesion amount.

  As a method of converting the reflected light of the toner adhesion amount sensor into the adhesion amount of the toner image, the normalized value of the reflected light of the toner image portion is reflected by the reflected light of the background portion, and the toner adhesion amount that is experimentally obtained is normalized. There is a method of calculating the toner adhesion amount using an adhesion amount conversion table (hereinafter referred to as an adhesion amount conversion table) of value correlation (see, for example, Patent Document 1). Since the reverse transfer amount of the K (black) toner is different between the full color (FC) mode and the monochrome (BW) mode, a difference occurs in the toner adhesion amount on the print medium under the same image forming conditions. Therefore, it is desirable to determine the image forming conditions for each mode, and a method is disclosed in which a plurality of patches are created while switching the image forming conditions so that a reference toner density can be obtained in the monochrome mode, and the optimum image forming conditions are determined. (See, for example, Patent Document 2).

  By the way, in the toner adhesion amount detection using the optical toner adhesion amount sensor, the positional relationship between the sensor and the target toner image must always be fixed. However, in an image forming apparatus that has an intermediate transfer belt and switches between the full color mode and the monochrome mode with the contact and separation of the primary transfer roller, the tension of the intermediate transfer belt changes due to the contact and separation of the primary transfer roller. As a result, when the sensor facing member inside the intermediate transfer belt is distorted, the positional coordinate relationship between the toner density sensor and the toner image may change. In that case, a detection error occurs when an adhesion amount conversion table created experimentally (central condition) is referred to.

  FIG. 8 shows the difference in the adhesion amount conversion table between the tilt angle center state (full color mode) and the tilt angle variation (monochrome mode). In the monochrome mode, the amount of adhesion is detected higher than the normalized value. For this reason, the image forming condition and the toner replenishment condition are adjusted by adjusting the density so that the amount of adhesion is low, so that the amount of adhesion is low in the monochrome mode.

  In the adhesion amount conversion based on the reflected light of the toner adhesion amount sensor, the relationship between the position and angle of the toner adhesion amount sensor and the target toner image needs to be the same. However, due to the contact and separation of the primary transfer roller, the tension of the intermediate transfer belt changes, the curvature of the toner adhesion amount sensor facing member inside the intermediate transfer belt changes, and the relative position and angular relationship between the toner adhesion amount sensor and the toner image. May change. In that case, a detection error occurs when an adhesion amount conversion table created experimentally (central condition) is referred to.

  FIG. 7 shows a change in the adhesion amount conversion table when the tilt angle changes (monochrome mode) from the tilt angle center state (full color mode). The “tilting angle” referred to here is a change angle in the sub-operation direction of the optical axis of the adhesion amount sensor as shown in FIG. When the tilt angle changes, the adhesion amount is converted to be higher than the normalized value. For this reason, when image forming conditions are set so that a target adhesion amount can be obtained during the image quality adjustment operation, the obtained toner adhesion amount becomes lower.

  In the method disclosed in Patent Document 2 described above, the image forming conditions can be determined so that the detected adhesion amount of the toner adhesion amount sensor in the monochrome mode is the same as that in the full color mode. It cannot be dealt with when a detection error occurs.

  In the present invention, even when the relationship between the distance and angle between the toner adhesion amount sensor and the intermediate transfer belt is deviated in the full color mode and the monochrome mode, the monochrome mode K toner (black toner: hereinafter, abbreviated as “K toner” in this specification). It is an object to make it possible to calculate the adhesion amount of

An image forming apparatus according to the present invention includes an image carrier, a charging device that uniformly charges the image carrier, an exposure device that forms a latent image by exposing the uniformly charged image carrier, and The image forming apparatus includes a developing device that develops the latent image with toner and a transfer device that transfers the toner image formed on the image carrier onto the intermediate transfer member, and is formed on the intermediate transfer member. An optical density detecting means for detecting reflected light of the toner image by an optical means, and the amount of the reflected light detected by the optical density detecting means is converted into an adhesion amount of the toner image based on an adhesion amount conversion table; An image quality adjusting operation including an adhesion amount converting unit, forming a plurality of patches by the image forming device, detecting the toner adhesion amount of the plurality of patches by the optical density detecting unit, and determining an image forming condition; , Black single-color image creation mode and multi-color production In the image forming apparatus, the mode is switched, and the switching is accompanied by contact between the image carrier and the transfer device, and the black single-color image forming mode and the multi-color image forming mode are referred to respectively. Change the black adhesion amount conversion table,
It is characterized by that.

  According to the present invention, the variation amount of the tilt angle is predicted from the difference between the calibration amount of the calibration amount of the toner adhesion amount sensor in the full color mode and the monochrome mode, and the adhesion amount conversion LUT (look) is determined according to the tilt angle variation amount. By correcting the up table (hereinafter abbreviated as “LUT” in this specification), even if the relationship between the distance and the angle between the toner adhesion amount sensor and the intermediate transfer belt is shifted in the full color mode and the monochrome mode, the K in the monochrome mode is corrected. The toner adhesion amount can be calculated appropriately.

1 is a schematic configuration diagram of a copying machine as an image forming apparatus according to an embodiment of the present invention. It is a schematic block diagram of an example of a tandem type image forming part. FIG. 2 is a schematic configuration diagram of a single light emission and two light reception type sensor that can be used as a toner adhesion amount sensor. It is a block diagram which shows the structural example of an electric potential control apparatus and its peripheral device. It is a figure which shows the adhesion amount conversion table used at the time of K toner adhesion amount conversion. FIG. 5A is a diagram showing the positional relationship between the toner adhesion amount sensor and the opposing roller which is a supporting member of the detection surface in the full color mode, FIG. 5B is a diagram showing the positional relationship in the monochrome mode, and the tilt angle direction. It is a figure (c) shown. It is a figure which shows the change of the adhesion amount conversion table at the time of a tilt angle change (monochrome mode) from a tilt angle center state (full color mode). It is a figure which shows the difference in the adhesion amount conversion table in case a tilt angle fluctuates (monochrome mode) and a tilt angle center state (full color mode). FIG. 4 is a diagram illustrating an operation flow of the first embodiment. It is a figure which shows the example of the regular reflection output in each gradation. It is a figure which shows the correlation table of LED electric current value and tilt angle. It is a figure which shows the correlation table of tilt angle and (DELTA) forward current If. FIG. 10 is a diagram illustrating an operation flow of the second embodiment. It is a figure which shows the relationship between a tilt angle and a background part output. It is a figure which shows the relationship between a tilt angle and the variation | change_quantity of a background part output. It is a figure which shows the difference in the adhesion amount conversion table in case a tilt angle fluctuates (monochrome mode) and a tilt angle center state (full color mode).

<Outline of the present invention>
First, the outline of the present invention will be described.
In the present invention, the adhesion amount conversion table is switched in accordance with the distance and angle change between the toner adhesion amount sensor and the intermediate transfer belt in the full color mode and the monochrome mode. That is, when the toner adhesion amount sensor is calibrated by adjusting the LED light emission amount so that a predetermined amount of reflected light can be obtained in the full color mode, the light emission amount is adjusted again when the monochrome mode is subsequently switched. Each light emission amount is managed by an input current amount to the LED of the toner adhesion amount sensor, and a change amount of the incident angle and the reflection angle of the toner adhesion amount sensor is obtained from a difference between the input current amounts of the full color mode and the monochrome mode. Alternatively, the amount of reflected light in the monochrome mode may be acquired with the same amount of light emission as in the full color mode, and the incident angle and the amount of change in the reflection angle may be obtained from the difference between the amount of reflected light in the full color mode and the monochrome mode. Based on the amount of angle change acquired as described above, it is detected from a K pattern (image formation pattern using black toner: hereinafter abbreviated as “K pattern”) during image quality adjustment operations in the full color mode and the monochrome mode. Switching or correction of the adhesion amount conversion table used when converting the reflected light amount into the toner adhesion amount is performed.

  The correction amount of the adhesion amount conversion table is determined from the difference between the forward currents If. The LED current adjustment (forward current If adjustment) of the toner adhesion amount sensor is performed in each of the full color mode and the monochrome mode. Thereby, the change amount of the tilt angle is calculated from the change amount of the forward current If. The adhesion amount conversion table correction amount is calculated from the tilt angle change amount, or the adhesion amount conversion table is switched.

  Next, Vsg (voltage as a sensor output with respect to the amount of reflected light received when light is applied to a background portion where a gradation pattern image is not formed: hereinafter abbreviated as background portion output, or simply “ The correction amount of the adhesion amount conversion table is determined from the difference of “Vsg”. The background output, that is, Vsg is acquired from the toner adhesion amount sensor in each of the full color mode and the monochrome mode. Then, the tilt angle change amount is calculated from the Vsg change amount, and the adhesion amount conversion table correction amount is calculated from the tilt angle change amount, or the adhesion amount conversion table is switched. That is, the present invention switches the LUT between the monochrome mode and the full color mode. Select an appropriate LUT for each of the full color mode and monochrome mode.

  The image forming apparatus according to the present invention forms a latent image by exposing an image carrier uniformly charged by a charging device, and develops the latent image with toner by a developing device. Then, an image forming device for transferring the toner image formed on the image carrier onto the intermediate transfer member by the transfer device, and an optical density detection for detecting reflected light of the toner image formed on the intermediate transfer member by an optical means. And an adhesion amount conversion means for converting the detected light quantity into an adhesion amount based on the adhesion amount conversion table. In addition, a plurality of patches are formed by the image forming device, and the toner adhesion amount of the plurality of patches is detected by the optical density detecting means, and an image quality adjustment operation for determining the image forming conditions is executed. The switching between the black monochromatic image formation mode and the multiple color image formation mode involves the contact between the image carrier and the transfer device, and the black adhesion amount referred to in the black monochromatic image formation mode and the multicolor image formation mode, respectively. Change the conversion table. The amount of change in the tilt angle is predicted based on the difference between the light emission amount calibrated with the toner adhesion amount sensor in the full color mode and the monochrome mode. The adhesion amount conversion LUT is corrected according to the tilt angle change amount. This makes it possible to appropriately calculate the K toner adhesion amount in the monochrome mode even when the relationship between the distance and angle between the toner adhesion amount sensor and the intermediate transfer belt is shifted in the full color mode and the monochrome mode.

  The image forming apparatus according to the present invention determines the correction amount of the adhesion amount conversion LUT based on the difference in the amount of forward current If between the monochrome mode and the full color mode (in the monochrome mode and the full color mode during the image quality adjustment operation). Adjust the light intensity). The light intensity adjustment operation can be executed to adjust the amount of light emitted so that the regular reflection light from the image carrier of the optical density detection means is within a predetermined range (light intensity adjustment operation means). The image forming mode and the multi-color image forming mode are performed respectively. Then, the adhesion amount conversion table is switched depending on the difference between the light emission amount determined in the black single-color image formation mode and the light emission amount determined in the multi-color image formation mode. It is possible to appropriately calculate the K toner adhesion amount in the monochrome mode and set the optimum image forming conditions.

  In addition, the image forming apparatus according to the present invention determines the correction amount of the adhesion amount conversion LUT based on the difference between the forward current If light amounts of the monochrome mode and the full color mode. During the printing operation, the light amount adjustment is performed after the mode is switched in the full color mode and in the monochrome mode. That is, it has a light amount adjusting means for adjusting the light emission amount so that the regular reflection light from the image carrier of the optical density detecting means is within a predetermined range, in other words, a light amount adjusting function. The light amount adjustment operation is performed in the multi-color image forming mode during the image quality adjustment operation and when the black single color mode is switched during printing. Then, the adhesion amount conversion table is switched depending on the difference between the light emission amount determined in the black single-color image formation mode and the light emission amount determined in the multi-color image formation mode. By appropriately calculating the K toner adhesion amount in the monochrome mode, it is possible to set optimum image forming conditions.

  Furthermore, the image forming apparatus according to the present invention detects the Vsg in the monochrome mode and the full color mode during the image quality adjustment operation, and determines the correction amount of the adhesion amount conversion table based on the difference between the Vsg. The forward current If is not changed. That is, it has a non-toner image portion detection means from the intermediate transfer member by the optical density detection means. The detection is performed in the black single-color image forming mode and the multi-color image forming mode in the image quality adjustment operation. Then, the adhesion amount conversion table is switched depending on the difference between the reflected light amount detected in the black single-color image forming mode and the reflected light amount detected in the multi-color image forming mode. The amount of change in the tilt angle is predicted from the difference in the amount of reflected background light (Vsg) in the full color mode and the monochrome mode, and the adhesion amount conversion LUT is corrected according to the tilt angle change amount. As a result, even when the relationship between the distance and angle between the toner adhesion amount sensor and the intermediate transfer belt is deviated in the full color mode and the monochrome mode, the K toner adhesion amount in the monochrome mode can be calculated appropriately, and the optimum image forming conditions are obtained. Can be set.

  Furthermore, the image forming apparatus according to the present invention detects Vsg in the monochrome mode and the full color mode at the time of printing, and determines the correction amount of the adhesion amount conversion table based on the difference between the Vsg. The forward current If is not changed. That is, Vsg in monochrome mode and full color mode is detected during printing, and if Vsg is outside the predetermined range, the toner adhesion amount sensor is calibrated, and the correction amount in the adhesion amount conversion table is calculated from the change in LED current value. To decide. Accordingly, the non-toner image portion detection means from the intermediate transfer member by the optical density detection means is provided, and the detection is performed in the multi-color image formation mode during the image quality adjustment operation and in the single-color image formation mode during printing. Then, the adhesion amount conversion table is switched depending on the difference between the reflected light amount detected in the black single-color image forming mode and the reflected light amount detected in the multi-color image forming mode. Similarly, the K toner adhesion amount in the monochrome mode can be calculated appropriately, and the optimum image forming conditions can be set.

  Monochrome mode and full color mode Vsg are detected during printing. If Vsg is outside the specified range, the toner adhesion amount sensor is calibrated, and the correction amount of the adhesion amount conversion table is determined from the amount of change in the LED current value. To do. The forward current If is not changed and is detected during printing. That is, if the difference between the reflected light amount detected in the black single-color image forming mode and the reflected light amount detected in the multi-color image forming mode is outside the predetermined range, the optical density detection means from the image carrier. A light amount adjustment function is performed to adjust the light emission amount so that the regular reflection light is within a predetermined range. Then, the adhesion amount conversion table is switched depending on the difference between the light emission amount determined in the black single-color image formation mode and the light emission amount determined in the multi-color image formation mode. The toner adhesion amount sensor is calibrated only when the difference in the belt background reflected light amount (Vsg) between the full color mode and the monochrome mode is outside the predetermined range. This prevents an adhesion amount error due to abnormally small Vsg in monochrome mode, and if the Vsg is not small enough to be abnormal, it does not adjust the light amount, resulting in excessive `` waiting time '' Suppresses the occurrence.

<General Description of Image Forming Apparatus>
Next, a general description of the image forming apparatus will be given. FIG. 1 is a schematic configuration diagram of a copying machine as an image forming apparatus according to an embodiment of the present invention. In FIG. 1, reference numeral 100 denotes a copying machine main body, reference numeral 200 denotes a paper feed table on which the copying machine is placed, reference numeral 300 denotes a scanner mounted on the copying machine main body 100, and reference numeral 400 further denotes an automatic document transport mounted thereon. Device (ADF). This copier is a tandem type electrophotographic copier that employs an intermediate transfer (indirect transfer) system.

The copying machine main body 100 includes an intermediate transfer belt 10 formed of an endless belt at the center thereof. The intermediate transfer belt 10 is wound around three support rollers 14, 15, and 16 that are support rotating bodies, and moves in the clockwise direction in the drawing. The volume resistance of the intermediate transfer belt 10 used in this embodiment is 10 ¹⁰ [Ωcm ³ ]. If the volume resistance value is too low, for example, the bias applied to the optical sensor facing roller 311 leaks, causing an abnormal image. Similarly, when a leak occurs in the transfer roller, the image density is lowered due to insufficient transfer efficiency. On the other hand, when the volume resistance value is too high, an appropriate value exists because an image density drop at a low image area or an abnormal image due to discharge is generated.

  An intermediate transfer belt cleaning device 17 for removing residual toner remaining on the intermediate transfer belt 10 after image transfer is provided on the left side of the second support roller 15 in the figure among the three support rollers. Further, among the three support rollers, the belt portion stretched between the first support roller 14 and the second support roller 15 has a moving direction of the intermediate transfer belt 10 as shown in FIG. A tandem image forming unit 20 in which four image forming units 18Y, 18M, 18C, and 18K of yellow (Y), magenta (M), cyan (C), and black (K) are arranged side by side is arranged oppositely as an image forming unit. is there.

  In the embodiment of the present invention described later, the third support roller 16 is a drive roller. In addition, an exposure device 21 as an exposure unit is provided above the tandem image forming unit 20.

  A secondary transfer device 22 serving as a second transfer unit is provided on the opposite side of the tandem image forming unit 20 with the intermediate transfer belt 10 interposed therebetween. In the secondary transfer device 22, a secondary transfer belt 24 that is an endless belt as a transfer sheet conveying member is wound around two rollers 231 and 232. The secondary transfer belt 24 is provided so as to be pressed against the third support roller 16 via the intermediate transfer belt 10. The secondary transfer device 22 transfers the toner image on the intermediate transfer belt 10 to a transfer sheet S that is a transfer material.

  A fixing device 25 for fixing the toner image transferred onto the transfer sheet S is provided on the left side of the secondary transfer device 22 in the drawing. The fixing device 25 has a configuration in which a pressure roller 27 is pressed against a fixing belt 26 that is a heated endless belt.

  The secondary transfer device 22 described above also has a sheet conveyance function for conveying the transfer sheet S to the fixing device 25 after the toner image is transferred from the intermediate transfer belt 10 to the transfer sheet S. Of course, as the secondary transfer device 22, a transfer roller or a non-contact transfer charger may be used. In such a case, it is difficult to have this sheet conveying function together. In this embodiment, a sheet reversing device 28 for reversing the transfer sheet S is also provided below the secondary transfer device 22 and the fixing device 25. The sheet reversing device 28 is provided in parallel with the tandem image forming unit 20 described above in order to record images on both sides of the transfer sheet S.

  When making a copy using the above-described copying machine, a document is set on the document table 30 of the automatic document feeder 400. Alternatively, the automatic document feeder 400 is opened, a document is set on the contact glass 32 of the scanner 300, the automatic document feeder 400 is closed, and the document is pressed. Thereafter, when a start switch (not shown) is pressed, when the document is set on the automatic document feeder 400, the document is conveyed and moved onto the contact glass 32. When an original is set on the contact glass 32, the scanner 300 is immediately driven. Next, the first traveling body 33 and the second traveling body 34 are caused to travel. Then, the first traveling body 33 emits light from the light source, and the reflected light on the document surface is further reflected and directed to the second traveling body 34. This light is reflected by the mirror of the second traveling body 34 and is incident on the reading sensor 36 through the imaging lens 35, and the reading sensor 36 reads the document content.

  In parallel with this document reading, the drive roller 16 is rotationally driven by a drive motor which is a drive source (not shown). As a result, the intermediate transfer belt 10 moves in the clockwise direction in the drawing, and the remaining two support rollers (driven rollers) 14 and 15 rotate along with the movement. At the same time, the drum-shaped photoconductors 40Y, 40M, 40C, and 40K as the image carriers are rotated in the individual image forming units 18, and monochromatic toner images (development) are formed on the photoconductors 40Y, 40M, 40C, and 40K. Image). In this development, exposure development is performed using color-specific information of yellow (Y), magenta (M), cyan (C), and black (K). Then, the toner images on the respective photoconductors 40Y, 40M, 40C, and 40K are sequentially transferred onto the intermediate transfer belt 10 so as to overlap each other, and a composite color toner image is formed on the intermediate transfer belt 10.

  In parallel with such image formation, one of the paper feed rollers 42 of the paper feed table 200 is selected and rotated. Thus, the transfer sheet S is fed out from one of the paper cassettes 44 provided in the paper bank 43 in multiple stages. Even if a plurality of transfer sheets S are fed out, the transfer sheets S are separated one by one by the separation roller 45 and put into the paper feed path 46. Then, the transfer sheet S is transported by the transport roller 47 and guided to the paper feed path in the copying machine main body 100, and is abutted against the registration roller 49 and stopped. Alternatively, the transfer sheet S on the manual feed tray 51 is fed out by rotating the paper feed roller 50, separated one by one by the separation roller 52, put into the manual paper feed path 53, and abutted against the registration roller 49 and stopped.

  Then, the registration roller 49 is rotated in synchronization with the composite color toner image on the intermediate transfer belt 10. As a result, the transfer sheet S is sent between the intermediate transfer belt 10 and the secondary transfer device 22 and transferred by the secondary transfer device 22 to transfer the color toner image onto the transfer sheet S.

  The transfer sheet S after the toner image is transferred is conveyed by the secondary transfer belt 24 and sent to the fixing device 25. In the fixing device 25, heat and pressure are applied to the transfer sheet S by the fixing belt 26 and the pressure roller 27 to fix the transferred toner image. After that, the transfer claw 55 is switched by the switching claw 55, is discharged by the discharge roller 56, and is stacked on the discharge tray 57. Alternatively, the conveyance path is switched by the switching claw 55 and is put into the sheet reversing device 28, where it is reversed and guided again to the transfer position, and an image is recorded also on the back surface, and then discharged onto the paper discharge tray 57 by the discharge roller 56. .

  The intermediate transfer belt 10 after the toner image is transferred is prepared by removing the residual toner remaining after the toner image is transferred by the intermediate transfer belt cleaning device 17 and re-forming the image by the tandem image forming unit 20. In general, the registration roller 49 is often used while being grounded, but a bias can be applied to remove the paper dust of the transfer sheet S.

  When thick paper is selected and copied, the driving speed of the photoconductors 40Y, 40M, 40C, and 40K and the intermediate transfer belt 10 is halved. The order of driving is the same, but only the driving speed is half speed. Hereinafter, a mode in which the photoconductors 40Y, 40M, 40C, and 40K and the intermediate transfer belt 10 are driven at a half speed when copying thick paper is referred to as a half speed mode.

  Next, the image forming unit 18 of the tandem image forming unit 20 described above will be described with reference to FIG. Although the K color image forming unit 18K will be described here, the Y, M, and C image forming units have the same configuration.

  The image forming unit 18 includes, for example, a charging device 60K, a potential sensor 70K, a developing device 61K, a photoconductor cleaning device 63K, and a charge removal device (not shown) around the drum-shaped photoconductor 40K as in the image forming unit 18K shown in FIG. Equipment.

  At the time of image formation, the photoreceptor 40K is rotationally driven in the direction of arrow A by a drive motor (not shown). Then, after the surface of the photoreceptor 40K is uniformly charged by the charging device 60K, the image data of the original or the like is exposed by the writing exposure L from the exposure device 21 to form an electrostatic latent image. The The color image signal based on the image data from the scanner 300 is subjected to image processing such as color conversion processing by an image processing unit (not shown), and is converted into yellow (Y), magenta (M), cyan (C), and black (K). Each color image signal is output to the exposure device 21. The exposure device 21 converts the black (K) image signal from the image processing unit into an optical signal, and scans and exposes the surface of the uniformly charged photoconductor 40K based on the optical signal to perform static exposure. An electrostatic latent image is formed.

  A developing bias is applied to the developing roller 61a, which is a developing member of the developing device 61K, and a developing potential that is a potential difference is formed between the electrostatic latent image on the photoreceptor 40K and the developing roller 61a. The toner on the developing roller 61a is transferred from the developing roller 61a to the electrostatic latent image on the photoreceptor 40K by this developing potential, whereby the electrostatic latent image is developed and a toner image is formed. Further, a toner concentration sensor 312K is provided on the bottom surface of the developer conveying screw in the developing device, and the toner concentration can be detected at any time.

  The K toner image formed on the photoreceptor 40K is primarily transferred onto the intermediate transfer belt 10 by the primary transfer device 62K. After the toner image is transferred to the photoreceptor 40K, the residual toner is cleaned by the photoreceptor cleaning device 63K, and the charge is removed by a charge removal device (not shown) to prepare for the next image formation. Similarly, the image forming units 18Y, 18M, and 18C include a charging device, a potential sensor, a developing device, a photoconductor cleaning device, a static elimination device, and the like around the drum-shaped photoconductors 40Y, 40M, and 40C. Then, Y, M, and C toner images are formed on the photoreceptors 40Y, 40M, and 40C, and these are primarily transferred onto the intermediate transfer belt 10 while being superimposed.

  The image forming apparatus of this embodiment includes a full color mode and a monochrome mode. In the full color mode, when the color of an image to be formed is full color, all the photoreceptors 40Y, 40M, 40C, and 40K are kept in contact with the surface of the intermediate transfer belt 10. In the monochrome mode, the photosensitive members 40Y, 40M, and 40C other than black are separated from the surface of the intermediate transfer belt 10 when the color is black. The image forming apparatus of the present embodiment also includes an auto color change mode that detects whether a document image read by a scanner is a monochrome image or a color image and automatically switches between the monochrome mode and the full color mode. .

  In the monochrome mode, a first monochrome mode in which an image is formed with a photosensitive member other than the K color photosensitive member relatively spaced from the intermediate transfer belt, and a second monochrome mode in which the operation of the developing device other than the K color is stopped. There are two types. The second monochrome mode is a mode that is executed when the auto color change mode is selected. To switch between the monochrome mode, the full color mode, and the auto color change mode, an input unit is provided on an operation panel (not shown) that is a manual operation unit so that the user can determine and input the mode.

  By making the mode selectable by the user, there are the following advantages. For example, the original image is a color image, but when the user wants to make a monochrome image, the user can operate the operation panel to select the monochrome mode, and a monochrome image as desired by the user can be obtained. In addition, when the user selects the monochrome mode, the Y, M, and C photoconductors 40Y, 40M, and 40C are always separated from the intermediate transfer belt 10, so that deterioration of the photoconductors 40Y, 40M, and 40C can be suppressed. . When the color mode is selected by the user, the monochrome mode is not switched in the case of a monochrome image as in the auto color change mode. Therefore, the printing speed when continuously printing a plurality of originals in which color originals and monochrome originals are mixed is faster than in the automatic color change mode. As a result, when the user selects the color mode, the user can quickly obtain print images of a plurality of originals in which color and monochrome are mixed.

<Embodiment 1>
Embodiment 1 of the present invention will be described.
The image forming apparatus according to the present embodiment has a potential control device 401 as one of means for controlling the image density. The potential control device 401 can appropriately control by using information as shown in FIG. That is, the detection value detected by the toner adhesion amount sensor 310, the temperature / humidity detected by the toner concentration sensor 312, the temperature / humidity sensor (not shown) as an environmental sensor, the toner concentration, and the photosensitivity detected by the potential sensor 70. The surface potential after exposure of the body 40 and the developing bias are input. Then, the potential controller 401 outputs the charging device 60, the developing device 61, the charging bias of the exposure device 21, the developing bias, the exposure light amount, and the toner density control target value. A stable image density is provided by controlling each bias and toner supply in accordance with the optimum image forming conditions. Note that the toner adhesion amount sensor 310 of the present embodiment is a one-emission two-reception type sensor as shown in FIG. Black toner performs adhesion amount conversion based only on regular reflection light, and color toner performs adhesion amount conversion based on regular reflection light and diffuse reflection light.

  The first monochrome mode is adopted as the monochrome mode, and it is assumed that the image quality adjustment accompanied by the adjustment operation of the toner adhesion amount sensor 310 and the image quality adjustment pattern in each of the full color mode and the monochrome mode is performed during the image quality adjustment operation. The angle difference between the incident and reflection of the toner adhesion amount sensor 310 and the intermediate transfer belt 10 is detected from the difference in the adjusted light emission amount of the toner adhesion amount sensor 310 in each mode. The adhesion amount conversion table is switched based on the detected angle change amount.

  In an image forming apparatus in which the photosensitive member 40 and the primary transfer device (primary transfer roller) 62K are brought into contact with each other only when K is switched between the full color mode and the monochrome mode and C, M, and Y are not contacted, the full color mode and the monochrome mode are used. Thus, the tension of the intermediate transfer belt 10 changes. Since the tension in the monochrome mode is lower than that in the full color mode, the stress on the support member (the opposing roller 14 in this embodiment) on the detection surface of the toner adhesion amount sensor 310 also changes. That is, when the opposing roller 14 moves from the position shown in FIG. 6A in the full color mode to the outside in the monochrome mode as shown in FIG. 6B, the angular relationship between the toner adhesion amount sensor 310 and the detection surface changes.

  FIG. 5 shows an adhesion amount conversion table used when converting the adhesion amount of K toner. By using this, a value obtained by normalizing the reflected light of the K toner patch with the regular reflected light of the background portion of the intermediate transfer belt 10 can be converted into a toner adhesion amount (steps in the flow of FIG. 9 described later). Details are described in the explanation of S1-7). Generally, the adhesion amount conversion table is experimentally created in the full color mode. This adhesion amount conversion table changes as shown in FIG. 7 due to the tilt angle fluctuation in the monochrome mode. Therefore, even with the same reflected light, the toner adhesion amount is increased and detected in the monochrome mode. Therefore, when image quality adjustment operations are performed in each of the full color mode and the monochrome mode to set image forming conditions, a phenomenon occurs in which the toner adhesion amount becomes thin as shown in FIG. 8 in the monochrome mode.

  An object of the present embodiment is to suppress the difference in toner adhesion amount between the full color mode and the monochrome mode. The light emission amount of the toner adhesion amount sensor is adjusted in each of the full color mode and the monochrome mode, and the change amount of the tilt angle is obtained from the difference in the light emission amount. The toner adhesion amount in the monochrome mode can be maintained by changing the adhesion amount conversion table in the monochrome mode based on the change amount of the tilt angle.

Hereinafter, the operation flow of this embodiment will be specifically described with reference to FIG.
Step S1-1: Execute calibration of the toner adhesion amount sensor in the full color mode Here, the regular reflection light from the background portion of the intermediate transfer belt 10 is adjusted so that the light receiving element falls within the range of 4.0 ± 0.5 [V]. Adjust the current. LED current calibration is performed by binary search.
Step S1-2: Create gradation pattern latent image The gradation pattern of image density adjustment created here is as shown in FIG. The exposure portion potential is fixed, the charging bias is changed, and images are sequentially formed from the side with the lower development potential. In addition, an image is formed using the charging bias determined in the previous image quality adjustment operation. The image formation bias of the gradation pattern is changed stepwise by dividing the one determined in the previous image quality adjustment operation flow by the number of each color patch of the gradation pattern (5 patches in this embodiment). That is, the charging biases Vc (n) and Vb (n) for the nth patch are as follows.
The writing LD power used at this time is determined in the previous image quality adjustment operation flow.
Step S1-3: Gradation pattern latent image is detected. Thereafter, the patch pattern latent image is detected by a potential sensor to acquire the latent image potential.
Step S1-4: Calculation of development potential of gradation pattern Here, the gradation pattern latent image created in step S1-2 is detected by the potential sensor 70, and the latent image potential Vp is acquired. In addition, the latent image potential of the patch portion created using the previous image forming conditions is recorded as a solid portion potential VL and used in the subsequent flow. Further, the development potential is calculated from the gradation pattern latent image potential using Equation 3 below.
Step S1-5: Develop gradation pattern latent image Here, the gradation pattern latent image created in step S1-2 is imaged sequentially from the low development potential side while changing the development bias, and finally the last time The image is formed using the development bias of.
Step S1-6: Detect reflected light from gradation pattern Here, the gradation pattern is irradiated with LED light, and the reflected light is detected by a phototransistor (PTr). In this embodiment, the K pattern detects only regular reflection light, and the color pattern detects both regular reflection light and diffuse reflection light. This is because both reflected lights are used in the color toner adhesion amount conversion algorithm described later.
Step S1-7: Converting the sensor detection value into the toner adhesion amount The reflected light from the gradation pattern created in Step S1-3 is detected using the toner adhesion amount sensor 310 installed at the position shown in FIG. In this embodiment, a toner adhesion amount sensor 310 for detecting image density is installed at the center of the image, and this sensor detects gradation patterns of all four colors.

Here, the output value from the toner adhesion amount sensor 310 is converted into the toner adhesion amount. The toner adhesion amount conversion method of K toner will be described below.
Step 1: Data sampling and ΔVsp and ΔVsg calculation First, the difference from the offset voltage is calculated for each color point [n] for both the regular reflection light output and the diffuse light output. FIG. 10 shows an example of regular reflection output at each gradation. Here, Vsg_reg indicates the regular reflection output of the background, K in the legend indicates black toner, and C indicates Cyan toner. The processing formula is as follows.
However, when using an OP amplifier in which each offset output voltage value (Voffset_reg: 0.0621 V) when the LED is off is sufficiently small to a negligible level as in this embodiment, such difference processing is performed. Is no longer necessary.
Step 2: Calculation of the normalization value The normalization value is calculated based on the regular reflection light output of the background portion, the regular reflection light output of the toner portion, and the regular reflection output VminK of the toner portion having a sufficiently high adhesion amount. Here, Vsg_reg is a regular reflection output of the background portion. VminK is a value obtained by detecting the high adhesion amount toner patch by the toner adhesion amount sensor 310. The processing formula is as follows.
Step 3: Adhesion amount conversion using the adhesion amount conversion table If the relationship between the normalized value and the adhesion amount is experimentally determined in advance, this can be converted back or converted to a high adhesion amount region by referring to the conversion table. Quantity conversion is possible. Then, the normalized value is converted into an adhesion amount using the relationship of the table of FIG.

  By performing the processing as described above, even if the developing ability is reduced, the amount of emitted light of the toner adhesion amount sensor 310 is changed, or even when the toner adhesion amount sensor 310 is replaced, the adhesion amount conversion is accurately performed. It becomes possible. Since the toner adhesion amount conversion method for C, M, and Y is known (see, for example, Patent Document 3), description thereof is omitted.

The flow of FIG. 9 will be further described.
Step S1-8: Calculating the developing ability The developing ability is calculated by linearly approximating the two-dimensional arrangement of the developing potential (the difference between the developing potential and the exposure potential) of the latent image portion of the gradation pattern and the toner adhesion amount. Since this is also known (see, for example, Patent Document 3), description thereof is omitted.

Step S1-9: Calculate the optimum image forming conditions Based on the development ability calculated in Step S1-8, calculate the development potential when the target toner adhesion amount is obtained, and develop bias, charging bias, exposure light quantity Is calculated (see, for example, Patent Document 3).
Step S1-10: Switch to monochrome mode From the state in which all of the photoconductors K, C, M, and Y are relatively in contact with the intermediate transfer belt 10, the photoconductors 40 for colors other than K are intermediately transferred. The belt 10 is in a state of being relatively separated from the belt 10.
Step S1-11: The toner adhesion amount sensor 310 is calibrated in the monochrome mode. Here, the regular reflection light from the background portion of the intermediate transfer belt 10 is adjusted so that the light receiving element is within a range of 4.0 ± 0.5 [V]. Adjust the LED current.
Step S1-12: Change the adhesion amount conversion table in the monochrome mode The tilt angle is calculated based on the change amount of the LED current value of the toner adhesion amount sensor 310 in the full color mode and the monochrome mode. As shown in FIG. 11, the LED current value has a correlation with the tilt angle, and the LED current value increases as the tilt angle increases. That is, it is possible to calculate the amount of change in the tilt angle from the amount of change in the LED current value. The change amount of the LED current value (Δ forward current If) is calculated by the following equation (6).
In the formula, forward current If (FC): LED current value in full color mode Forward current If (BW): LED current value in monochrome mode Δ Forward current If: LED current value change amount.
Then, the tilt angle change amount is calculated using the correlation table between the tilt angle and the Δ forward current If shown in FIG. An adhesion amount conversion table as shown in FIG. 7 is selected from the tilt angle change amount calculated from this. The tilt angle change amount is rounded off to the first decimal place, and a matching adhesion amount conversion table is adopted.

The flow of FIG. 9 will be further described.
Steps S1-13 to S1-20: Perform the same contents as steps S1-1 to S1-9 in the monochrome mode. Since this flow is performed in the monochrome mode, the LED current value is the forward current If (BW). It is assumed that the adhesion amount conversion table used in the toner adhesion amount conversion is adopted in step S1-13.

  The improvement effects are as follows. FIG. 8 shows a change in the toner adhesion amount of the solid image portion before and after switching the print mode at the time of improvement. Since the image forming conditions in the monochrome mode can be calculated appropriately, it can be seen that there is no change in the toner adhesion amount before and after the print mode switching as shown in FIG.

<Embodiment 2>
A second embodiment of the present invention will be described.
In this embodiment, the amount of emitted light of the toner adhesion amount sensor in the full color mode and the monochrome mode at the time of image quality adjustment operation is made the same, and the tilt angle amount change in the monochrome mode is predicted from the difference in the background reflected light amount (Vsg). To correct. In the present embodiment, the first monochrome mode is adopted as the monochrome mode, and the adjustment operation of the toner adhesion amount sensor in each of the full color mode and the monochrome mode and the image quality adjustment accompanied with the formation of the gradation pattern are performed during the image quality adjustment operation. Assumption. Calibration of the toner adhesion amount sensor 310 is performed only in the full color mode. The amount of change in the angle of incidence and reflection of the toner adhesion amount sensor 310 to the intermediate transfer belt 10 is predicted from the difference between the reflected light amount (Vsg) of the background portion in the full color mode and the monochrome mode. The adhesion amount conversion table is switched based on the predicted angle change amount.

The flow of the second embodiment will be specifically described below with reference to FIG.
Steps S2-1 to S2-10: Since they are the same as steps S1-1 to S1-10 described in the first embodiment, description thereof is omitted.
Step S2-11: Obtaining Background Output in Monochrome Mode Here, the background output of the intermediate transfer belt is obtained. In addition, when the background part output has fallen significantly, it is good also as a flow which adjusts an LED electric current value like Embodiment 1, and selects an adhesion amount conversion table from the variation | change_quantity of LED electric current amount here.
Step S2-12: Change the adhesion amount conversion table in the monochrome mode. The tilt angle is calculated based on the change amount of the background portion output of the intermediate transfer belt acquired by the toner adhesion amount sensor in the full color mode and the monochrome mode. As shown in FIG. 14, the background portion output correlates with the tilt angle, and the background portion output decreases as the tilt angle increases. That is, it is possible to calculate the amount of change in the tilt angle from the amount of change in the background output. The change in background output (ΔVsg) is calculated from Equation 7 below.
In the formula
Vsg (FC): Full color mode background output
Vsg (BW): Background portion output in monochrome mode ΔVsg: Background portion output change amount. Then, the tilt angle change amount is calculated using the correlation table of the tilt angle and the background portion output change amount ΔVsg shown in FIG. An adhesion amount conversion table as shown in FIG. 7 is selected from the tilt angle change amount calculated from this. The tilt angle change amount is rounded off to the first decimal place, and a matching adhesion amount conversion table is adopted.
Steps S2-13 to S2-20: Since they are the same as steps S2-13 to S2-20 described in the first embodiment, description thereof is omitted.

  The improvement effects are as follows. FIG. 16 shows the toner adhesion amount transition of the solid image portion before and after switching the print mode at the time of improvement. Since the image forming conditions in the monochrome mode can be calculated appropriately, it can be seen that there is no change in the toner adhesion amount before and after the print mode switching as shown in FIG.

  In the first and second embodiments, the image forming conditions in both the full color mode and the monochrome mode are adjusted during the image quality adjustment operation. However, in an image forming apparatus that performs image quality adjustment operation only in full color, Δ forward current If may be calculated by calibrating the toner adhesion amount sensor immediately after switching to monochrome mode, and the adhesion amount conversion table may be switched. . In this case, there is an advantage that the toner adhesion amount can be accurately detected by a model in which an adjustment toner pattern is formed between printing media or both ends of the printing media during printing, and toner supply control and switching of image forming conditions are performed. The present invention is not limited to the embodiments described above, and many modifications can be made by those having ordinary knowledge in the art within the technical idea of the present invention.

10: intermediate transfer belt 18: image forming unit 20: tandem image forming unit 21: exposure device 22: secondary transfer device 24: secondary transfer belt 25: fixing device 26: fixing belt 40: photoconductor 60: charging device 61: Developing device 100: Copier main body 200: Paper feed table 300: Scanner 310: Toner adhesion amount sensor 311: Optical sensor facing roller 312: Toner density sensor 400: Automatic document feeder 401: Potential control device L: Write exposure S: Transfer sheet

JP 2010-266682 A JP 2002-244390 A JP 2006-139180 A

Claims (6)

An image carrier;
A charging device for uniformly charging the image carrier;
An exposure device that forms a latent image by exposing a uniformly charged image carrier; and
A developing device for developing the latent image with toner;
A transfer device that transfers the toner image formed on the image carrier onto the intermediate transfer member;
Optical density detecting means for detecting reflected light of the toner image formed on the intermediate transfer member by optical means;
An adhesion amount conversion means for converting the amount of reflected light detected by the optical density detection means into an adhesion amount of the toner image based on an adhesion amount conversion table;
A plurality of patches are formed by the image forming device, and an image density adjusting operation for determining an image forming condition by detecting a toner adhesion amount of the plurality of patches by the optical density detecting unit,
It has switching between black single color image formation mode and multiple color image formation mode,
In the image forming apparatus characterized in that the switching involves the contact between the image carrier and the transfer device.
Changing the black adhesion amount conversion table referenced in each of the black single-color image formation mode and the multiple-color image formation mode;
An image forming apparatus. The image forming apparatus according to claim 1.
A light amount adjustment operation means for adjusting the light emission amount so that the regular reflection light from the image carrier detected by the optical density detection means falls within a predetermined range;
The adjustment by the light amount adjustment operation means is performed in the black single color image formation mode and the multiple color image formation mode at the time of image quality adjustment operation,
Switching the adhesion amount conversion table according to the difference between the light emission amount determined in the black single-color image formation mode and the light emission amount determined in the multi-color image formation mode;
An image forming apparatus. The image forming apparatus according to claim 1, wherein
A light amount adjustment operation means for adjusting the light emission amount so that the regular reflection light from the image carrier detected by the optical density detection means falls within a predetermined range;
The adjustment by the light amount adjusting operation means is performed in the multi-color image forming mode at the time of image quality adjusting operation, and at the time of switching the black single-color image forming mode at the time of printing,
Switching the adhesion amount conversion table according to the difference between the light emission amount determined in the black single-color image formation mode and the light emission amount determined in the multi-color image formation mode;
An image forming apparatus. The image forming apparatus according to claim 1, wherein
A non-toner image portion detection means from above the intermediate transfer member by the optical density detection means;
Detection of the non-toner image portion by the non-toner image portion detection means is performed in the black single color image formation mode and the multiple color image formation mode at the time of image quality adjustment operation,
Switching the adhesion amount conversion table according to the difference between the reflected light amount detected in the black monochromatic image forming mode and the reflected light amount detected in the multiple color image forming mode;
An image forming apparatus. The image forming apparatus according to claim 1,
Non-toner image portion detection means on the intermediate transfer member by the optical density detection means, and detecting the non-toner image portion in the multi-color image formation mode during image quality adjustment operation and in the black single-color image formation mode during printing Carried out
Switching the adhesion amount conversion table according to the difference between the reflected light amount detected in the black monochromatic image forming mode and the reflected light amount detected in the multiple color image forming mode;
An image forming apparatus. The image forming apparatus according to any one of claims 1 to 5,
If the difference between the reflected light amount detected in the black single-color image forming mode and the reflected light amount detected in the multi-color image forming mode is outside a predetermined range, the optical density detection means from the image carrier is corrected. Implement a light amount adjustment function to adjust the amount of light emission so that the reflected light is within a predetermined range,
Switching the adhesion amount conversion table according to the difference between the light emission amount determined in the black single-color image formation mode and the light emission amount determined in the multi-color image formation mode;
An image forming apparatus.