JP2010079290A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus equipped with a controller which precisely and easily detects a continuous grayscale pattern even when a temporal sensor output varies significantly owing to a surface property, etc., of an object of detection. <P>SOLUTION: A continuous grayscale toner pattern which is continuous in the rotating direction of a photoreceptor and formed under condition that the sticking amount of a head portion is maximum is used and outputs detected in a time T1-T0 from a point T0 of time after the lapse of a predetermined time after a detection threshold Vth of a sticking amount detecting means is detected to a point T1 of time right before the time that the toner patter passes from the detection threshold Vth. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an electrophotographic image forming apparatus applied to a copying machine, a facsimile, a printer, and the like.

Conventionally, a photosensitive member surface is uniformly charged to a predetermined potential by a charging unit, an electrostatic latent image is formed by an exposure unit, and the electrostatic latent image is developed by a developing unit using a two-component developer composed of at least a toner and a carrier. In an electrophotographic image forming apparatus that develops and forms a toner image, the image density varies depending on the toner density of the developer, the toner charge amount, and the temperature and humidity dependence of the mobility of the photoconductor photocarrier. Therefore, a predetermined toner pattern formed on the photoconductor is detected by an optical sensor on the photoconductor, on the intermediate transfer belt or on the secondary transfer roller, and depending on the detection result, image forming conditions, toner supply, etc. Control is in progress. As a result, even when the developing ability fluctuates, image density fluctuations are suppressed by optimizing the control parameters. Such control is referred to as image density control.
Since the image density control needs to form a predetermined toner pattern, the executable period is limited. In other words, image density control cannot be executed during copying, and can only be executed during times other than image formation. For this reason, it is necessary to execute it at the end of a print job, to stop and interrupt the output during job output, or to execute it in a standby state. Although it is possible to perform simple process control by forming a toner pattern between papers that are being output (so-called paper spacing), there is no time to change the bias condition between papers. In many cases, the toner supply amount is changed without changing the bias condition. Further, when an output command is received during image density control, the output cannot be started until the end of the control, so that a waiting time occurs. From the user's standpoint, it is preferable that the image density control has an operation time reduced as much as possible and an operation frequency is low.

In the image density control, in order to measure the developing ability at that time, a plurality of pieces of information on the development potential and the toner adhesion amount, which is the difference between the development bias and the post-exposure potential, are necessary. For this purpose, there is a method in which a development potential is changed to form a plurality of patterns of toner patches, and the plurality of toner patch patterns are read by an optical sensor. In this case, it is preferable to reduce the number of patterns from the standpoint of standby time and toner yield, but from the standpoint of accuracy, reliability, and robustness, it is preferable to have a plurality of patterns. Accordingly, attempts have been made to reduce the number of patch patterns while maintaining reliability.
In order to reduce the number of patch patterns, a method is known in which only one continuous tone pattern in which the toner adhesion amount is continuously changed is imaged to obtain a plurality of information from one continuous tone pattern. ing. In this case, the waiting time and toner yield can be reduced as compared with a plurality of patch patterns, and information for several tens of patterns can be obtained by reducing the sampling time. When a plurality of pieces of information are obtained with such a continuous tone pattern, a method for capturing the output of an optical sensor that is an adhesion amount detection means becomes a problem. With multiple patch patterns, one patch pattern is output under the same conditions, so even if there are mechanical variations in the pattern, the number of detections and the detection timing can be optimized to ensure accurate output. Can be obtained.

However, since the continuous tone pattern can obtain only one output under the same condition, it is inevitable that the accuracy of each condition is lowered. You may perform processing to select the detection output when the detection output fluctuates greatly or when it is not linear compared to the output before and after, but what value should be treated as a true value, etc. Judgment and selection processing methods become complicated. There is a concern that the load on the CPU (arithmetic element) increases due to the complicated control and causes a delay in processing. Therefore, there is a demand for a method of selecting detection outputs with high accuracy by a simple detection method.
In order to satisfy such a demand, as described in Patent Document 1, an erase lamp is disposed on the downstream side of the charging device in the moving direction of the photosensitive member, and the continuous charging pattern is detected by the charging device. The erase lamp is turned on at the same time as charging of the surface of the photoconductor is started, and the erase lamp is continuously turned on until exposure is started, thereby avoiding detection of unstable detection output until exposure is started. It has been proposed.
Further, Patent Document 2 discloses a method of feeding back to an image forming condition using, as a parameter, the time from when the output of the optical sensor crosses the threshold value Vth for the first time to the second time for the continuous tone pattern. ing.

In the one described in Patent Document 1, since the detection start point of the continuous tone pattern is set by the erase lamp disposed on the downstream side of the charging device in the moving direction of the photosensitive member, the erase lamp is necessary, Not only is the cost increased, but a space for erasing the lamp is required. The arrangement of the erase lamp needs to be performed in consideration of the incident optical path of exposure formed between the electric device and the developing device, and there is a problem that the arrangement becomes complicated.
Moreover, in the thing of patent document 2, since time is used as a parameter, the detection method is simple. However, when the adhesion amount of the continuous tone pattern decreases due to environmental fluctuations, the sensor output may not reach the output threshold Vth. Although it can be solved by setting the output threshold value Vth as the output value of the low adhesion amount region, it has now been clarified that variations occur at the time of the second intersection. This occurs because the optical sensor detection output is not stable, and the detection accuracy has deteriorated. Such a phenomenon becomes apparent when the fine scratches or surface properties of the detection target surface deteriorate.
In addition, when the detection target is on a belt such as an intermediate transfer belt or a paper conveyance belt, it has been clarified that the fluctuation of the belt due to the driving greatly affects. In other words, the distance and angle between the optical sensor for detecting the toner adhesion amount of the toner image and the detection target, and the surface property of the detection target greatly vary locally, so that the sensor output varies greatly and Vth contrary to the original intention. The detection accuracy was deteriorated by the earlier crossing point of.
In view of the above, the present invention includes a control device that detects a continuous tone pattern accurately and easily even when a temporary sensor output due to the surface property of a detection target greatly fluctuates. An object of the present invention is to provide an image forming apparatus.

In order to solve the above-described problems, the invention of claim 1 is directed to image data on an image carrier, a charging unit that uniformly charges the surface of the image carrier, and an image carrier charged by the charging unit. An exposure unit that forms an electrostatic latent image by irradiating an exposure based on the image, a developing unit that supplies toner to the electrostatic latent image formed by the exposure unit to form a toner image, and a toner adhesion amount of the toner image An adhesion amount detection means for detecting a toner adhesion amount of a predetermined toner pattern formed on the image carrier by the charging means, an exposure means and a development means by the adhesion amount detection means, and depending on the detection result And a control device for controlling the image forming conditions of the toner image, wherein the toner pattern has the toner adhesion amount gradually decreased from the head in the moving direction of the image carrier. When the adhesion amount detection unit detects the toner adhesion amount of the toner pattern, the control device detects the detection threshold value Vth of the adhesion amount detection unit and then detects the toner pattern of the toner pattern. The image forming condition is controlled based on output data of a toner adhesion amount detected from a time T0 when a predetermined time elapses until the head portion is detected to a time T1 when the final portion of the toner pattern is detected.
According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the control device is detected from the time point T0 to a time point T2 preset between the time point T0 and the time point T1. The output data of the toner adhesion amount is compared with the output data of the toner adhesion amount detected from the time T0 to the time T1, and based on the comparison result, either one of the output data is used to determine the image forming condition. It is characterized by controlling.

According to a third aspect of the present invention, in the image forming apparatus according to the first or second aspect, the image forming apparatus further includes a potential sensor that detects a surface potential between an exposure position and a development position on the image carrier, and the control device includes: When the toner pattern is formed on the image carrier, a final time of the toner pattern from the time T0 ′ after a predetermined time elapses from when the detection threshold value Vth ′ of the potential sensor is detected until the leading portion of the toner pattern is detected. Output data of the surface potential of the image carrier detected up to the time T1 ′ to detect the part and the time T2 ′ detected from the time T0 ′ to the time T0 ′ to the time T1 ′ The output data of the surface potential of the image carrier is compared, and the image forming condition is determined based on either one of the output data selected based on the comparison result and the output data of the used toner adhesion amount. It is characterized by controlling.
According to a fourth aspect of the present invention, in the image forming apparatus according to any one of the first to third aspects, the toner pattern is formed by continuously changing a light amount of the exposure unit. And
According to a fifth aspect of the present invention, in the image forming apparatus according to any one of the first to fourth aspects, the toner pattern includes a developing bias of the developing unit set by the previous image density control and the charging unit. It is formed based on the charging conditions in

  According to the present invention, the toner pattern is a continuous tone toner pattern in which the toner adhesion amount is gradually and continuously decreased from the top in the moving direction of the image carrier. When detecting the toner adhesion amount of the pattern, the final portion of the toner pattern is detected from the time T0 when a predetermined time elapses from when the detection threshold value Vth of the adhesion amount detection means is detected until the leading portion of the toner pattern is detected. By controlling the image forming conditions based on the output data of the toner adhesion amount detected up to the time point T1, the continuous tone level can be obtained even when the temporary sensor output greatly varies due to the surface property of the detection target. It is possible to provide an image forming apparatus including a control device that detects a pattern accurately and easily.

1 is a schematic configuration diagram of a copying machine as an image forming apparatus according to an embodiment of the present invention. FIG. 2 is an enlarged view of a black image forming unit in FIG. 1. FIG. 3 is a plan view of a continuous tone toner pattern used in the image forming apparatus according to an embodiment of the present invention. It is a block diagram for demonstrating the control apparatus used in the image forming apparatus which concerns on one Embodiment by this invention. It is sectional drawing of the photosensor used in the image forming apparatus which concerns on one Embodiment by this invention. FIG. 6 is a graph showing a change in detection output of a continuous tone toner pattern of K toner by a sensor used in an image forming apparatus according to an embodiment of the present invention, and FIG. , (B) are graphs showing changes with time of the output detected by the regular reflection light receiving element. FIG. 6 is a graph showing a change in detection output of a continuous tone toner pattern of C toner by a sensor used in an image forming apparatus according to an embodiment of the present invention, and FIG. (B) is a graph which shows the change accompanying the time passage of the output detected by the diffused light receiving element. FIG. 7A is a graph showing another detected output change of a continuous tone toner pattern of K toner by a sensor used in an image forming apparatus according to an embodiment of the present invention, and FIG. Graph (B) is a graph showing changes with time of the output detected by the regular reflection light receiving element. FIG. 6A is a graph showing another detected output change of a C toner continuous tone toner pattern by a sensor used in an image forming apparatus according to an embodiment of the present invention, and FIG. Graph (B) is a graph showing a change with time of the output detected by the diffused light receiving element.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
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 is provided with an intermediate transfer belt 10 formed of an endless belt at the center thereof. The intermediate transfer belt 10 is stretched around support rollers 14, 15, 16 as three support rotating bodies, and rotates in the clockwise direction in the drawing.
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 drawing among these three support rollers. Further, the belt portion stretched between the first support roller 14 and the second support roller 15 among the three support rollers has yellow (Y) along the belt moving direction as shown in FIG. ), Magenta (M), cyan (C), and black (K) four image forming units 18Y, 18M, 18C, and 18K that are arranged side by side are tandem image forming units 20 that are arranged to face each other. .
In the present embodiment, the third support roller 16 is a drive roller. Further, an exposure device 21 as an exposure unit is provided above the tandem image forming unit 20.

A secondary transfer device 22 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, which is an endless belt as a transfer sheet conveying member, is stretched between 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 after transferring the toner image from the intermediate transfer belt 10 to the transfer sheet S to the fixing device 25. 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 provide this sheet conveying function together. In the present embodiment, the transfer sheet S is inverted under such a secondary transfer device 22 and the fixing device 25 so as to record images on both sides of the transfer sheet S in parallel with the tandem image forming unit 20 described above. A sheet reversing device 28 is also provided.

When making a copy using the 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, and the automatic document feeder 400 is closed and pressed by it. 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.
On the other hand, 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 further reflects the reflected light from the document surface toward the second traveling body 34, and is reflected by the mirror of the second traveling body 34 and passes through the imaging lens 35. The document is placed in the reading sensor 36 and the original content is read.
In parallel with this document reading, the drive roller 16 is rotated 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 figure, 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 image carriers are rotated in the individual image forming units 18, and yellow, magenta, and the like are respectively formed on the photoconductors 40Y, 40M, 40C, and 40K. Then, each of the color information of cyan, black is exposed and developed to form a single color toner image (developed image).
Then, the toner images on the photoconductors 40Y, 40M, 40C, and 40K are sequentially transferred onto the intermediate transfer belt 10 so as to overlap each other, thereby forming a composite color toner image 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 selectively rotated, the transfer sheet S is fed out from one of the paper feed cassettes 44 provided in the paper bank 43 in multiple stages, and the separation roller The sheet is separated one by one at 45 and put into the sheet feeding path 46, conveyed by the conveying roller 47, led to the sheet feeding path in the copying machine main body 100, and abutted against the registration roller 49 and stopped. Alternatively, the sheet feeding roller 50 is rotated to feed the transfer sheet S on the manual feed tray 51, separated one by one by the separation roller 52, put into the manual sheet 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, and the transfer sheet S is sent between the intermediate transfer belt 10 and the secondary transfer device 22. The color toner image is transferred onto the transfer sheet S by transfer.
After transfer of the toner image, the transfer sheet S is conveyed by the secondary transfer belt 24 and sent to the fixing device 25. The fixing device 25 applies heat and pressure to the transfer toner image by the fixing belt 26 and the pressure roller 27. Is fixed by the switching claw 55, discharged by the discharge roller 56, and stacked on the discharge tray 57. Alternatively, it is switched by the switching claw 55 and 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 discharge tray 57 by the discharge roller 56.
The intermediate transfer belt 10 after the toner image transfer is removed by an intermediate transfer belt cleaning device 17 to remove residual toner remaining on the intermediate transfer belt 10 after the toner image is transferred, and the tandem image forming unit 20 forms an image again. Prepare. Here, the registration roller 49 is generally used while being grounded, but it is also possible to apply a bias for removing paper dust from the sheet.

Next, the image forming unit 18 of the tandem type image forming unit 20 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.
For example, as shown in FIG. 2, the image forming unit 18K includes a charging device 60K, a potential sensor 70K, a developing device 61K, a photoconductor cleaning device 63K, a static elimination device (not shown), and the like around a drum-shaped photoconductor 40K. ing.
At the time of image formation, the photoreceptor 40K is rotationally driven in the direction of arrow A by a drive motor (not shown). The surface of the photoreceptor 40K is uniformly charged by the charging device 60K, and then the image data of the above-described original document from the exposure device 21 is exposed by the writing exposure L 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 output to the exposure device 21 as an image signal of each color of K, Y, M, and C. . The exposure device 21 converts the K image signal from the image processing unit into an optical signal, and scans and exposes the surface of the uniformly charged photoreceptor 40K based on the optical signal, thereby exposing the electrostatic latent image. Form.

A developing bias is applied to the developing roller 61a which is a developing member of the developing device 61K, and a developing potential which 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.
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 according to the present embodiment includes a full color mode in which all the photoreceptors 40Y, 40M, 40C, and 40K are in contact with the surface of the intermediate transfer body 10 when the color of an image to be formed is full color, and black when the color is black. And a monochrome mode in which the other photoreceptors 40Y, 40M, and 40C are separated from the surface of the intermediate transfer member 10. 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) serving as a manual operation means so that the user can determine and input the mode.

Since the mode can be selected 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 are always separated from the intermediate transfer belt 10, so that the deterioration of the Y, M, and C photoconductors 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.
In this embodiment, a drum-shaped photoconductor is used as the image carrier. However, in addition to the drum-shaped photoconductor, an endless belt-shaped photoconductor can also be used appropriately. .
In the image forming apparatus of this embodiment, image density control for optimizing the image density of each color is executed when the power is turned on or every time a predetermined number of prints are performed. In this image density control, toner patches are formed on the photoreceptors 40Y, 40M, 40C, and 40K, respectively. As shown in FIG. 3, the toner patches formed on the respective photoconductors 40Y, 40M, 40C, and 40K are rotated in the pattern traveling direction (arrow B direction), that is, the photoconductors 40Y, 40M, 40C, and 40K. A continuous tone toner pattern P is formed in which the toner adhesion amount gradually decreases from the leading portion P1 toward the final portion P2 with respect to the (moving) direction.

In this embodiment, the continuous tone toner pattern is irradiated onto the surface of the uniformly charged photoreceptor 40 with the charging bias applied to the charging device 60 and the developing bias applied to the developing roller 61a fixed. It is formed by continuously changing the LD (laser diode) light quantity that is the exposure L from the exposure device 21. Here, “continuous” means that the step of changing the LD light quantity is sufficiently small, and the difference in the average value of the light quantity in the adjacent parts is smaller than the standard deviation of the light quantity in each part.
In this embodiment, a continuous tone toner pattern is formed with the charging bias and the development bias fixed, but in the present invention, it is only necessary that a continuous tone toner pattern can be formed. The image may be formed by continuously changing the conditions. Further, the area gradation may be continuously changed. However, when the linear speed at which the photosensitive member or the intermediate transfer belt rotates is faster than the response speed of the bias, it is preferable to change the LD light amount and the area gradation with a faster response speed.
A method for controlling the image density using the continuous tone toner pattern thus formed will be described. The continuous tone toner patterns on the photoconductors 40Y, 40M, 40C, and 40K of the respective colors formed as described above are transferred onto the intermediate transfer belt 10, and as shown in FIG. Detection is performed by an optical sensor 310 which is an optical toner adhesion amount detection means provided at an opposing position.

Next, the change in the toner adhesion amount with the lapse of time of the toner pattern P is calculated using the change in the detection value of the optical sensor 310 with the passage of time and the toner adhesion amount calculation algorithm. On the other hand, a potential sensor 70 provided between the charging device 60 and the developing device 61 and on the downstream side in the rotation direction of the photoconductor from the position where the exposure device 21 exposes the photoconductor is used when the toner pattern P is created. The photosensitive member surface potential with the passage of time is detected, and the developing potential with the passage of time is calculated from the relationship between the developing bias and the photosensitive member surface potential after exposure. At this time, both the toner adhesion amount and the development potential are calculated as linear functions with respect to time. That is, Y = aX + b is calculated (Y: toner adhesion amount or development potential, X: time t, a and b: proportional constant).
Then, using the relational expression between the toner adhesion amount and time and the relational expression between the development potential and time, the term of time is deleted to obtain the relation between the toner adhesion amount and the development potential. This slope is the developing ability (the slope when the development potential is the horizontal axis and the toner adhesion amount is the vertical axis), and the intercept is the development start voltage Vk (the intercept when the development potential is the horizontal axis and the toner adhesion amount is the vertical axis). ). Based on the obtained developing ability, image forming conditions such as exposure power (writing intensity), charging bias, and developing bias are adjusted and controlled so as to obtain a developing potential with an appropriate toner adhesion amount.
Such adjustment / control can be appropriately performed by using, for example, a control device 73 as shown in FIG. That is, the detection value detected by the optical sensor 310, the surface potential after exposure of the photosensitive member detected by the potential sensor 70, the developing bias value 71, and the charging bias value 72 are input to the control device 73, and As described above, the developing capability is obtained by the control device 73, and the developing bias, the charging bias, and the exposure power of the developing device 61, the charging device 60, and the exposure device 21 are adjusted based on this developing capability to obtain an appropriate image density. So as to adjust and control.
As described above, in the present invention, since the continuous tone toner pattern is used as the toner pattern, it is possible to obtain the developing capability with higher accuracy and to control the image density more appropriately.

Next, the configuration of the optical sensor 310 in the present embodiment will be described. FIG. 5 is a cross-sectional view showing a schematic configuration of the optical sensor 310 in the present embodiment. The optical sensor 310 in the present embodiment mainly receives a light emitting element 311 as a light emitting means, a regular reflection light receiving element 312 as a first light receiving means for receiving specular reflected light, and a diffuse reflected light. And a diffuse reflection light receiving element 313 as the second light receiving means. The specifications of each element are as follows.
Light emitting side element: GaAs infrared light emitting diode (peak emission wavelength: λp = 950 nm), top view type, diameter 3 mm, spot diameter: 1.0 mm diameter
Light receiving side element: Si phototransistor (peak spectral sensitivity wavelength: λp = 850 nm), top view type, diameter 3 mm, light receiving diameter: specular reflection light receiving side: diameter 1.0 mm, diffuse reflection light receiving side: main scanning direction: 3√2, sub-scanning direction: 3 mm, detection distance: 5 mm (distance from sensor top to detection target surface)
In this embodiment, the toner adhesion amount detection uses a regular reflection output for the K toner, and a diffuse reflection output for the color toner. Depending on each method, the detectable adhesion amount range is different.

Next, a method for performing density control using a continuous tone toner pattern in the present embodiment will be described.
First, as a first example, FIGS. 6 and 7 show the detection results of the present embodiment when the developing ability has increased from the previous image density control due to environmental fluctuations or the like.
When the developing ability is increased, the toner adhesion amount when a predetermined pattern is formed increases. When the optical sensor 310 has a high toner adhesion amount, the optical sensor output is saturated, and the detection error becomes large. Even in the case of a continuous tone pattern, it is necessary to calculate the developing ability in a pattern portion having a small detection error.
FIG. 6A is a graph showing changes in the photoreceptor surface potential over time when a continuous tone toner pattern of K toner is formed on the photoreceptor surface, and FIG. 6B shows the K toner. FIG. 6 is a graph showing a change with time of output detected by a regular reflection light receiving element among outputs detected by the optical sensor 310 of the continuous tone toner pattern of FIG.
FIG. 7A is a graph showing changes in the photoreceptor surface potential with time when a continuous tone toner pattern of C toner is formed on the photoreceptor surface. FIG. FIG. 6 is a graph showing a change with time of an output detected by a diffuse light receiving element among outputs detected by a photosensor 310 for a continuous tone toner pattern of C toner.
In the graphs of FIGS. 6 and 7, the time when the potential sensor and the toner adhesion amount detection sensor start detection is set to 0 second.

In the present embodiment, as shown in FIG. 6B, the K toner is detected from time T0 to time T1 after the output of the optical sensor becomes equal to or less than a predetermined threshold value Vth. Both time point T0 and time point T1 are the time points when a predetermined time has elapsed from the time point when the output of the optical sensor becomes equal to or less than the threshold value Vth, and time point T0 is the detection output of the toner adhesion amount detection sensor (optical sensor). Is set to the time at which The time point T1 is determined as the time from the Vth to the final part P2 just before the toner pattern P finishes passing. These values are determined by the length of the toner pattern P, the rotational speed of the photosensitive member, and the like, and are unique values for each image forming apparatus.
Further, a predetermined time T2 determined in advance between time T0 and time T1 is defined, and the output group detected in the time between T1-T0 and T1-T2 is sent to the storage device of the control device 73 shown in FIG. Store. The slope when time is taken on the horizontal axis and the detection output is taken on the vertical axis is calculated, and the slopes are compared between two output group sections between T1 and T0 and between T1 and T2.
As a result of comparing the slopes, if the difference in slope between the two output groups between T1 and T0 and T1 and T2 is 0.5 (V / s) or less, the output value between T1 and T0 is converted to the image density. Adopted as control data, and in the case of more than that, the output value between T1 and T2 is adopted. In this way, the difference between the slopes of the two output group sections between T1 and T0 and between T1 and T2 is calculated. If the difference exceeds a predetermined value, the sensor output is between T0 and T2. Judge that saturation is occurring.
In that case, the data of the output group section between T1 and T2 is adopted for image density control, and the image density is controlled by the control device 73 and adjusted.
In this way, even when the sensor output is saturated, the density control can be performed based on the output data corresponding to the change, and the density control can be performed with higher accuracy.
In addition, in FIG. 6B, the portion where the output suddenly fluctuates between T2 and T1 is a noise component. This phenomenon is caused by scratches on the surface of the intermediate transfer belt or flapping of the belt itself. In the case of a measurement method in which measurement is started from Vth and measurement is continued until the output rises to Vth again as in the above-mentioned patent document, before sufficient data can be obtained with such a large output fluctuation. Sometimes, the measurement ends. In this embodiment, since the measurement is performed for a predetermined time, it is a strong measurement method from a sudden output fluctuation factor such as a flaw to be detected.

Also in the potential sensor output, the surface potential after exposure of the photoconductor may fluctuate due to fluctuations in the characteristics of the photoconductor or the charging bias of the charging device, and a continuous tone pattern that is not suitable for image density control may be formed. is there. In other words, the exposure amount becomes too strong, and even if the intensity of the exposure amount is changed, a region where the change in the photoreceptor potential is small occurs. In the present embodiment, the above case can be handled.
That is, as shown in FIG. 6A, the head of the toner pattern P at which the detection output of the potential sensor becomes almost the lowest after a lapse of a predetermined time after the output of the potential sensor 70 becomes equal to or less than the predetermined threshold value Vth ′. Detection is started as a detection value used for image density control from time T0 ′ reaching the part P1, and detection is performed until time T1 ′ reaching the final part P2 just before the toner pattern P finishes passing. Here, since the time at which the toner pattern P passes differs for each sensor, T1 in FIG. 6B and T1 ′ in FIG. 6A are different time points, but from a predetermined threshold Vth (Vth ′). The time is the same. That is, the detection time is different, but the detection time is the same.
Further, a control device (not shown) that defines a predetermined time T2 ′ determined in advance between the time T0 ′ and the time T1 ′ and detects the output group detected during the time between T1 ′ and T0 ′ and between T1 ′ and T2 ′. 73 is stored in the storage device. Then, the slope when time is taken on the horizontal axis and the detection output is taken on the vertical axis is calculated, and the slopes are compared between the two output group sections between T1'-T0 'and T1'-T2'.
As a result of comparing the slopes, when the difference between the slopes of the two output group sections between T1'-T0 'and T1'-T2' is 100 (V / s) or less, the output value between T1-T0 is Employed as data for image density control, and output values between T1 and T2 are employed for more data.
In this way, as in the case of detecting the toner adhesion amount, the difference between the slopes of the two output group sections between T1′-T0 ′ and T1′-T2 ′ is calculated, and the difference is determined as predetermined. If it is within the value, it is determined that the output group between T1 ′ and T0 ′ may be used.
As described above, in the optical sensor and the potential sensor, which output group section data is used for image density control is determined. When the output group sections adopted by the optical sensor and the potential sensor are different, both employ the output group section between T1 and T2. In this embodiment, the sensor detects so as to eliminate noise such as saturation of the optical sensor output due to a high toner adhesion amount and a change in the photoreceptor potential due to fluctuations in characteristics of the photoreceptor due to aging and environmental fluctuations. Therefore, the concentration can be controlled with higher accuracy.

Next, the case of C toner as an example of color toner will be described with reference to FIG. The toner adhesion amount of C toner is detected by detecting the diffuse reflection output as shown in FIG.
The calculation process is the same as in the case of K toner, but C toner detects diffuse reflection output and has different output characteristics, so that the slope is different from the threshold value Vth. In the case of diffusion output, a toner pattern in which the detection output of the toner adhesion amount detection sensor (optical sensor) is almost the maximum after a predetermined time has elapsed since the adhesion amount detection sensor output (optical sensor output) exceeds the predetermined threshold Vth. Detection starts as a detection value used for image density control from time T0 when the head portion P1 of P is reached. The detection is performed until time T1 when the toner reaches the final part P2 just before the toner pattern has passed.
Further, a predetermined time point T2 determined in advance between the time point T0 and the time point T1 is defined, and the output group detected in the time between T1 and T0 and between T1 and T2 is stored in a storage device (not shown). The slope when taking the time on the horizontal axis and the detection output on the vertical axis is calculated, and the slopes are compared between the two output group sections. The value used for image density control is the output value between T1 and T0 when the difference between the two slopes is 0.4 (V / s) or less, and between T1 and T2 when the difference is more than that. The output value is adopted.

Further, as shown in FIG. 7A, the on-photoreceptor potential, which is the detection output of the potential sensor 70, is also applied to the image density by using the time of the classification adopted in the adhesion amount detection sensor as in FIG. Used for control. In the present embodiment, the results shown in FIG. 6 and FIG. 7 both show the case where image density control is performed using time segments T1-T2.
In this embodiment, the inclination threshold for each output is 0.5 (V / s) for regular reflected light output, 0.4 (V / s) for diffuse reflected light output, and 100 (V / s) for potential sensor output. Yes. However, these threshold values vary depending on the length of the toner pattern, the photosensitive member rotation speed, the sensor characteristics (response speed, output characteristics, etc.), the toner pattern adhesion amount, and the like. The slope threshold needs to be optimized.
In addition, the determination between T1 and T0 or between T1 and T2 may be made based on an inclination in which the horizontal axis is the adhesion amount and the vertical axis is the development potential, or the vertical axis is detected by the horizontal axis detection output. An axial development potential may be used, or other criteria may be used.

Next, FIG. 8 and FIG. 9 show the results when the variation in the developing ability is small from the previous image density control. FIG. 8A is a graph showing a change in the surface potential of the photoconductor over time when a continuous tone toner pattern of K toner is formed on the surface of the photoconductor. FIG. FIG. 6 is a graph showing a change with time of an output detected by a regular reflection light receiving element among outputs detected by a photosensor 310 for a continuous tone toner pattern.
FIG. 9A is a graph showing changes in the surface potential of the photoconductor over time when a continuous tone toner pattern of C toner is formed on the surface of the photoconductor. FIG. FIG. 6 is a graph showing a change with time of an output detected by a diffused light receiving element among outputs detected by a photosensor 310 of a continuous tone toner pattern of toner.
In the graphs of FIGS. 8 and 9, the time when the potential sensor and the toner adhesion amount detection sensor (optical sensor) start detection is set to 0 second.
Similar to the detection method of FIGS. 6 and 7, detection is started as a detection value used for image density control from a time T0 when a predetermined time has elapsed after the output of the optical sensor 310 becomes equal to or less than a predetermined threshold value Vth, and toner from Vth Detection is performed until time T1 immediately before the pattern has passed.
Further, a predetermined time point T2 determined in advance between the time point T0 and the time point T1 is defined, and an output group detected in the time between T1 and T0 and between T1 and T2 is stored in a storage device (not shown). The slope when taking the time on the horizontal axis and the detection output on the vertical axis is calculated, and the slopes are compared for each of the two output group sections. The value used for image density control is the output value between T1 and T0 when the difference between the two slopes is 0.5 (V / ms) or less, and between T1 and T2 when the difference is more than that. The output value at is adopted. Similarly, the on-photoreceptor potential that is the detection output of the potential sensor 70 also determines the value to be used for image density control from the slopes of the two output group sections. When the output group sections adopted by the optical sensor and the potential sensor are different, both employ the output group section between T1 and T2.

In both FIG. 8 and FIG. 9, since there is no change in the slope in either the section between T1 and T0 or between T1 and T2, the image density control is performed using the time section between T1 and T0. Of course, the longer the time used for image density control, the higher the accuracy. If the amount of adhesion can be detected in the entire continuous tone pattern, that is, if the change in the vertical axis detection output in the horizontal axis time is small in each time segment, the longer time segment is adopted. To do.
In the present embodiment, the values determined by the previous image density control are used as the bias conditions for forming the continuous tone pattern. When an image is formed every time under the same bias condition, the pattern adhesion amount varies greatly depending on the developing ability. That is, when the developing ability is high, only a short section can be adopted each time. On the other hand, when image formation is performed under the previous determination conditions, adjustment is made so that the optimum amount of adhesion can be formed when the development performance is the previous development capability. The nature is getting higher. Therefore, detection with higher accuracy is possible.
As described above, in this embodiment, a continuous tone toner pattern that is continuous in the rotation direction of the photoconductor and is imaged under the condition that the amount of adhesion at the head portion is maximum is used, and the detection of the amount of adhesion detection means is performed. Image forming conditions are controlled using outputs detected at a time T0 after a predetermined time from the detection of the threshold Vth and a time T1-T0 from the detection threshold Vth to a time T1 immediately before the toner pattern finishes passing. Therefore, even if there is no need for parts such as an erase lamp and there is a temporary fluctuation in the sensor output due to local flaws on the surface to be detected, the number of samples can be reduced by detecting for a predetermined time. Many can be set. As a result, variation in output data can be minimized, so that a continuous tone pattern can be detected accurately and easily.

In this embodiment, the output detected at T1-T0 is compared with the output detected at time T1-T2 from time T2 to time T1, which is predetermined between time T0 and time T1. Since either one of the outputs is used to control the imaging conditions, the output to be fed back to the imaging conditions is selected even if the sensor detection output becomes nonlinear in the high adhesion amount region. Therefore, it is possible to detect a continuous tone pattern easily and accurately.
Further, in the present embodiment, by detecting the potential sensor output on the photoconductor in the same manner as the adhesion amount detection output, it is possible to measure fluctuations in the post-exposure potential due to light fatigue and environmental fluctuations of the photoconductor. The development ability can be accurately measured.
In this embodiment, since the light quantity of the exposure unit is continuously changed as a condition for forming a continuous tone toner pattern, even if the process linear velocity is high, it is continuous without time limitation. Therefore, it is possible to change the toner adhesion amount, and it is possible to quickly form a continuous tone toner pattern.
In the present embodiment, the development bias as the condition for forming the continuous tone toner pattern and the charging condition of the charging unit are the conditions determined by the previous image density control. Can be prevented from being outside the detectable range, and a continuous tone pattern can be detected accurately and simply.

  10 intermediate transfer belt, 18Y, 18M, 18C, 18K image forming unit, 21 exposure device, 22 secondary transfer device, 25 fixing device, 40Y, 40M, 40C, 40K photoconductor, 60 charging device, 61 developing device, 61a development Roller, 62 Primary transfer device, 63 Cleaning device, 70 Potential sensor, 71 Development bias, 72 Charging bias, 73 Control device, 310 Photo sensor, 311 LED, 312 Regular reflection light receiving element, 313 Diffuse reflection light receiving element

Japanese Patent No. 3254235 Japanese Patent No. 3386231

Claims (5)

An image carrier, a charging unit that uniformly charges the surface of the image carrier, and an exposure unit that irradiates the image carrier charged by the charging unit with exposure based on image data to form an electrostatic latent image. A developing unit that supplies toner to the electrostatic latent image formed by the exposure unit to form a toner image, an adhesion amount detection unit that detects a toner adhesion amount of the toner image, the charging unit, and an exposure unit And a controller for detecting a toner adhesion amount of a predetermined toner pattern formed on the image carrier by the developing means by the adhesion amount detection means, and controlling an image forming condition of the toner image according to the detection result; In an image forming apparatus comprising:
The toner pattern is a continuous tone toner pattern in which the toner adhesion amount is gradually and continuously reduced from the top in the moving direction of the image carrier,
When the adhesion amount detection unit detects the toner adhesion amount of the toner pattern, the control device performs a predetermined period from detection of the detection threshold value Vth of the adhesion amount detection unit to detection of the leading portion of the toner pattern. An image forming apparatus, wherein the image forming condition is controlled based on output data of a toner adhesion amount detected from time T0 to time T1 when the final part of the toner pattern is detected. The image forming apparatus according to claim 1.
The control device outputs the toner adhesion amount output data detected from the time T0 to the time T2 preset between the time T0 and the time T1, and the toner detected from the time T0 to the time T1. An image forming apparatus that compares output data of an adhesion amount and controls the image forming condition using one of the output data based on the comparison result. The image forming apparatus according to claim 1 or 2,
A potential sensor that detects a surface potential between an exposure position and a development position on the image carrier;
When the toner pattern is formed on the image carrier, the control device starts from a time T0 ′ at which a predetermined time elapses from when the detection threshold Vth ′ of the potential sensor is detected until the leading portion of the toner pattern is detected. The output data of the surface potential of the image carrier detected by the time T1 ′ at which the final portion of the toner pattern is detected, and the time set in advance between the time T0 ′ and the time T0 ′ and the time T1 ′. The output data of the surface potential of the image carrier detected up to T2 ′ is compared, and either one of the output data selected based on the comparison result and the output data of the toner adhesion amount used are used. An image forming apparatus that controls image forming conditions. The image forming apparatus according to any one of claims 1 to 3,
The image forming apparatus, wherein the toner pattern is formed by continuously changing a light amount of the exposure unit. The image forming apparatus according to any one of claims 1 to 4, wherein:
The image forming apparatus according to claim 1, wherein the toner pattern is formed based on a developing bias of the developing unit set in a previous image density control and a charging condition in the charging unit.

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