JP7180240B2 - image forming device - Google Patents

Description

The present invention relates to an image forming apparatus.

2. Description of the Related Art In a printer or the like that forms an image by electrophotography or the like, control is performed to control the image quality of the formed image.

For example, Patent Document 1 discloses a printer unit that forms an image on a recording sheet and a scanner unit that reads an image of a document and replaces it with image data. An apparatus is described which is provided with means for adjusting the image density based on the detection signal of the scumming detected portion.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an image forming apparatus that suppresses image density in non-image areas.

In order to solve the above problems, the invention according to claim 1 provides an image forming unit that forms an image on a recording medium based on image data using a plurality of developers of different colors; a density detection unit capable of detecting the image density of at least part of the above image for each color; and a density adjustment unit adjusting the density of the image formed by the image forming unit, wherein the density detection The density adjustment unit detects, for each color, the density of a non-image area, which is an area where no image is formed on the recording medium based on the image data, and the density adjustment unit detects at least the non-image area detected by the density detection unit. when the density of any one of the plurality of developer colors in the image area is equal to or higher than a predetermined threshold value, performing image density adjustment of the color whose density is equal to or higher than the predetermined threshold value; The image forming apparatus is characterized in that the threshold differs according to the type of the recording medium.

According to the present invention, it is possible to provide an image forming apparatus that suppresses image density in non-image areas.

2 is a hardware configuration diagram of an image forming apparatus; FIG. 3 is a hardware configuration diagram of a printer engine; FIG. 1 is a schematic configuration diagram of an image element; FIG. 2 is a cross-sectional view perpendicular to the main scanning direction of the density sensor; FIG. 1 is a first example of a perspective view of a concentration sensor; FIG. 1 is a first example of a perspective view of a concentration sensor; FIG. 3 is a functional block diagram of the image forming apparatus; FIG. It is an example of thresholds stored in a threshold storage unit. It is an example of density adjustment values stored in an adjustment value storage unit. FIG. 5 is a diagram for explaining a charging bias or a developing bias as a density adjustment value; FIG. 10 is a diagram illustrating printing speed as a density adjustment value; FIG. 10 is a diagram for explaining whether or not toner refresh is executed as a density adjustment value; 4 is a flow chart showing a first example of an image density adjustment flow; 9 is a flow chart showing a second example of the image density adjustment flow; 5 is a flow chart showing an example of a recording medium density detection flow; 4 is another example of a functional block diagram of the image forming apparatus; FIG. It is an example of an image misregistration correction pattern. It is an example of a gradation correction pattern. It is an example of a density deviation correction pattern.

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described below with reference to the accompanying drawings. In addition, in each drawing for explaining the embodiments of the present invention, constituent elements such as members and constituent parts having the same function or shape are denoted by the same reference numerals as much as possible, and will be described once. We omit the explanation.

The image forming apparatus 1 of the present embodiment has a copy function, a fax function, a printer function, a scanner function, and performs image processing on an input image (a document read by the scanner function, or an image input by the printer function or the facsimile function). It is a so-called MFP (Multi Function Peripheral), which has a combination of functions such as a function of storing and distributing an input image. In this embodiment, the "image" processed by the image forming apparatus 1 includes not only image data but also data that does not contain image data, that is, data that is only text information.

FIG. 1 is a hardware configuration diagram of the image forming apparatus 1. As shown in FIG. As shown in FIG. 1, the image forming apparatus 1 includes a CPU (Central Processing Unit) 10, a ROM (Read Only Memory) 20, a RAM (Random Access Memory) 30, and a HDD (Hard Disc). 40 , an external communication I/F 50 , an operation panel 60 , a density sensor 70 and a printer engine 100 . It also has a system bus 80 interconnecting them.

The CPU 10 controls operations of the image forming apparatus 1 . That is, the CPU 10 controls the overall operation of the image forming apparatus 1 by executing programs stored in the ROM 20 or the HDD 40 using the RAM 30 as a work area (work area), thereby performing the above-described copy function, scanner function, facsimile function, It realizes various functions such as a printer function.

The ROM 20 is a non-volatile semiconductor memory that can retain data even when power is turned off. The RAM 30 is a volatile semiconductor memory that temporarily stores programs and data.

The HDD 40 is a non-volatile memory that stores programs and data. The programs and data stored in the HDD 40 include an operating system (OS), which is basic software for controlling the entire image forming apparatus 1, various application programs that run on the OS, the above-described copy function, scanner function, facsimile function, There are operating conditions for various functions such as the printer function. Each operation executed by these various functions (hereinafter sometimes referred to as a job) can also be stored as the operation of the image forming apparatus 1 .

The external communication I/F 50 is an interface for connecting the image forming apparatus 1 to a network such as the Internet or a LAN (Local Area Network). The image forming apparatus 1 can receive print instructions, image data, and the like from an external device via the external communication I/F 50 .

The operation panel 60 accepts various inputs according to user's operations, and also displays various kinds of information (for example, information indicating the accepted operation, information indicating the operation status of the image forming apparatus 1, and setting state of the image forming apparatus 1). information, etc.). The operation panel 60 is configured by, for example, a liquid crystal display device (LCD: Liquid Crystal Display) equipped with a touch panel function, but is not limited to this. For example, it may be composed of an organic EL (Electro-Luminescence) display device equipped with a touch panel function. Furthermore, in addition to or instead of this, an operation unit such as hardware keys and a display unit such as a lamp may be provided. The operation panel 60 is controlled by the CPU 10

A printer engine 100, which is an image forming unit, is hardware for realizing a printer function, a copy function, a facsimile function, and the like. That is, hardware such as printers, copiers, facsimiles, and scanners. An electrophotographic method, an inkjet method, or the like can be applied to the printer function, but the present invention is not limited to this. Other specific options such as a finisher for sorting printed paper and an ADF (Auto Document Feeder) for automatically feeding documents can also be provided. The printer engine 100 is controlled by the CPU 10 .

The image forming apparatus 1 further has an external interface, through which external recording media such as CDs (Compact Discs), DVDs, SD (Secure Digital) memory cards, and USB (Universal Serial Bus) memories can be read and/or read. Writing may be performed.

The programs stored in the ROM 20 or HDD 40 are programs that can be processed by a computer. It may be installed in the ROM 20 or HDD 40 when the image forming apparatus 1 is manufactured or shipped, or may be installed after sale. As a method of installing after sale, a method of installing via an external storage medium drive using an external storage medium in which the program is stored, or a method of installing via a network using the external communication I/F 50 are possible.

FIG. 2 is a hardware configuration diagram of the printer engine 100. As shown in FIG. Note that the operation panel 60 and the density sensor 70 are also shown for explanation.

The printer engine 100 is provided inside the housing 90 and has an exposure section 101 , an image forming section 102 , a transfer section 103 and a fixing device 104 . An operation panel 60 is provided on the top of the housing 90 .

The imaging unit 102 has a yellow (Y) photoreceptor 120y, a black (K) photoreceptor 120k, a magenta (M) photoreceptor 120m, and a cyan (C) photoreceptor 120c, each of which is an image carrier. . The image forming unit 102 also has a yellow (Y) developing device 121y, a black (K) developing device 121k, a magenta (M) developing device 121m, and a cyan (C) developing device 121c, which are respectively developing units. . The image forming unit 102 further includes a yellow (Y) charger 122y, a black (K) charger 122k, a magenta (M) charger 122m, and a cyan (C) charger 122c, each of which is a charging unit. .

The transfer unit 103 also has an intermediate transfer belt 130, a secondary transfer belt 133, and the like. A fixing device 104, which is a fixing unit, has a fixing member 141, a discharge roller 142, and the like.

A function of forming an image on a recording medium based on image data will be described below as an example of the function of the printer engine 100, which is an image forming unit, with reference to FIG.

The exposure unit 101 exposes the photoreceptors 120y to 120c of the image forming unit 102 and emits writing light for writing a latent image on each photoreceptor according to image data. In other words, the light beam is selectively emitted at the writing position corresponding to the image pattern of the image data and the writing light amount corresponding to the image density. As the writing light, light from a laser light source or a light emitting dilde (LED) light source may be used. As an example, the case of using a laser light source having an LD (Laser Diode) will be described below.

First, a light beam BM emitted from a laser light source is deflected by a polygon mirror 110 and enters scanning lenses 111a and 111b each including an fθ lens. The configuration and operation of emitting the light beam BM from the laser light source will be described later.

The light beams are generated in numbers corresponding to the respective color images of yellow (Y), black (K), magenta (M), and cyan (C). Reflected by mirrors 112y-112c.

For example, a yellow light beam Y passes through the scanning lens 111a, is reflected by the reflecting mirror 112y, and enters the WTL lens 113y. The same is true for the light beams K, M, and C of black, magenta, and cyan, so the description thereof will be omitted.

The WTL lenses 113y to 113c shape the incident light beams Y to C, respectively, and then deflect the light beams Y to C toward the reflecting mirrors 114y to 114c. The light beams Y to C are further reflected by reflecting mirrors 115y to 115c, and irradiated onto the photoreceptors 120y to 120c as light beams Y to C used for exposure, respectively.

Irradiation of the light beams Y to C onto the photoreceptors 120y to 120c is synchronized in timing with respect to the main scanning direction and sub-scanning direction of the photoreceptors 120y to 120c. Note that the photoreceptor is, for example, in the shape of a drum elongated in the main scanning direction, and is also called a photoreceptor drum.

Hereinafter, the main scanning direction for the photoreceptors 120y to 120c is defined as the scanning direction of the light beam, and the sub-scanning direction is defined as the direction perpendicular to the main scanning direction, that is, the direction in which the photoreceptors 120y to 120c rotate. do.

Photoreceptors 120y-120c comprise a photoconductive layer comprising at least a charge generation layer and a charge transport layer on a conductive drum such as aluminum.

The photoconductive layers are provided corresponding to the photoreceptors 120y to 120c, respectively, and are charged by chargers 122y to 122c as charging units including a corotron charger, a scorotron charger, or a charging roller. A surface charge is imparted in response to the bias.

The electrostatic charges imparted to the photoreceptors 120y to 120c by the chargers 122y to 122c are respectively exposed to light beams Y to C as writing light according to image patterns, and the chargers 122y to 122c are scanned. An electrostatic latent image is formed on the surface.

The electrostatic latent images respectively formed on the scanned surfaces of the photoreceptors 120y to 120c are developed by developing devices 121y to 121c, which are developing units including a developing roller to which a developing bias is applied, a toner supply roller, and a regulating blade. It is developed to form a toner image on the surface to be scanned of the photosensitive members 120y to 120c.

Each developer carried on the surface to be scanned of the photoconductors 120y to 120c is transferred onto the intermediate transfer belt 130 moving in the direction of arrow D by the transport rollers 131a to 131c. 132y to 132c are primary transfer rollers for the photosensitive members 120y to 120c, respectively.

The intermediate transfer belt 130 as an image bearing member is conveyed to the secondary transfer position F while carrying the Y, K, M, and C developers transferred from the scanned surfaces of the photosensitive members 120y to 120c. be.

The secondary transfer belt 133 is stretched over conveying rollers 134a and 134b, and further conveyed in the direction of arrow E by the rotation of the conveying rollers 134a and 134b.

At the secondary transfer position F, a paper P, which is an image receiving material such as high-quality paper or a plastic sheet, is supplied from a paper container T such as a paper feed cassette by a conveying roller 135 . At the secondary transfer position F, a secondary transfer bias is applied to transfer the multicolor developer image carried on the intermediate transfer belt 130 onto the paper P attracted and held on the secondary transfer belt 133 . The paper P is conveyed in a direction orthogonal to the main scanning direction.

As the secondary transfer belt 133 is conveyed, the paper P is supplied to the fixing device 104 as a fixing unit.

The fixing device 104 includes a fixing member 141 such as a fixing roller containing silicone rubber, fluororubber, or the like. , is discharged to the outside of the fixing device 104 as a sheet of paper P' (hereinafter referred to as a sheet of paper P').

The density sensor 70 detects the image density of the image on the sheet P′ serving as the image carrier discharged from the fixing device 104 . Although details of the density sensor 70 will be described later, the density sensor 70 can detect the image density for each color corresponding to the toner color.

After transferring the multicolor developer image, the intermediate transfer belt 130 is supplied to the next image forming process after transfer residual developer is removed by a cleaning unit 139 including a cleaning blade.

In the operation of the printer engine 100, the rotation direction of the photoconductors 120y to 120c, which are image carriers, the conveying direction of the intermediate transfer belt 130, which is the image carrier, and the conveying direction of the paper P and the paper P' which are the image carriers. , are orthogonal to the main scanning direction and are the same as the sub-scanning direction.

Although the density sensor 70 is arranged after the fixing device in FIG. 2, it can also detect the image density of the image formed on the intermediate transfer belt 130 if it is installed near the conveying roller 131a, for example. .

As described above, the printer engine 100, which is an image forming unit, forms an image on a recording medium based on image data. As a result, an image area, which is an area with toner image density based on the image data, and a non-image area, which is an area without toner image density based on the image data, are formed on the recording medium.

On the other hand, due to a failure or malfunction of the printer engine 100, toner may adhere to the non-image area, and the image density due to the toner may be detected in the non-image area as well. The image density of such a non-image area is sometimes called scumming. The density sensor 70 can detect the presence or absence of image density in at least such non-image areas.

FIG. 3 is a schematic configuration diagram of an image element included in the density sensor 70. As shown in FIG. As shown in FIG. 3, the image element 71 has a shape extending in the main scanning direction, and small light receiving elements 72-0 to 72-n (hereinafter referred to as light receiving elements 72 when they do not need to be distinguished from each other). are arranged side by side in the main scanning direction. The range in which the light receiving elements 72 are arranged is the detection width of the density sensor 70 in the main scanning direction.

FIG. 4 is a cross-sectional view of the density sensor 70 perpendicular to the main scanning direction. As shown in FIG. 4, the density sensor 70 has therein the aforementioned image element 71, a light source 73, a lens array 74, and an output circuit 75. FIG. A dotted line represents light emitted from the light source 73 .

As the light source 73, a light emitting element provided at the end of a light guide, an LED array, or the like can be used. The light source 73 emits RGB light. A SELFOC (registered trademark) lens or the like is used as the lens array 74 .

Light emitted from the light source 73 is reflected on the paper P′ and formed into an image by the lens array 74 . The image element 71 receives the light imaged by the lens array 74 with each light receiving element 72 shown in FIG. 5, and outputs a signal corresponding to the received light. A CMOS sensor, a CCD sensor, or the like is used as the image element 71 .

The output circuit 75 is, for example, an ASIC (Application Specific Integrated Circuit), and outputs data indicating the image density corresponding to the position of the pattern on the paper P' based on the signals from the light receiving elements 72 on the image element 71. converted to and output. For example, 0 to 255 gradations represented by 8 bits are output.

Next, a configuration example of the density sensor 70 will be described with reference to FIG. FIG. 5 is a perspective view of the density sensor 70. FIG. The density sensor 70 has a shape elongated in the main scanning direction. It has an image element elongated in the main scanning direction inside, and is sometimes called a line sensor. The detection width of the density sensor 70 in the main scanning direction is the width indicated by the dotted line in the main scanning direction in FIG. Since this detection width is longer than the width of the paper P' in the main scanning direction, if the paper P' is conveyed so as to pass through the width indicated by the dotted line in the main scanning direction, the image density is obtained over the entire area of the paper P'. It is possible to detect That is, the density sensor 70 in FIG. 5 can also detect the density at the right edge, the left edge, the leading edge with respect to the transport direction, and the trailing edge with respect to the transport direction.

Next, another configuration example of the density sensor 70 will be described with reference to FIG. FIG. 6 is a perspective view of the density sensor 70. FIG. The detection width in the main scanning direction of the density sensor 70 shown in FIG. 6 is the width indicated by the dotted line in the main scanning direction. This detection width is the edge region of the paper P'. Assuming that the far side of the paper surface is the right end in FIG. 6, the left end may be used instead of the right end shown in FIG. good.

As described with reference to FIG. 2, the density sensor 70 should be able to detect the density of the non-image area. There is a high possibility that the peripheral portion of the image data is a margin, that is, the edge area of the paper P' is a non-image area or includes a non-image area. Therefore, the density sensor 70 shown in FIGS. 5 and 6 is provided at a position for detecting the edge of the paper. In this way, at least one of the edge areas, that is, the right edge, the left edge, the leading edge, and the trailing edge, which is an area with a high possibility of being a blank space, is detected. Therefore, the occurrence of scumming in the non-image area can be detected during normal printing without printing a recording medium on which no image has been formed, that is, a so-called blank sheet.

FIG. 7 is a functional block diagram of the image forming apparatus 1. As shown in FIG. The input reception unit 150 is realized by the operation panel 60, displays information necessary for operation to the user, and executes functions of receiving various inputs by the user. The input reception unit 150 is also implemented by the processing of the external communication I/F 50, and executes a function of receiving print instructions and setting changes from the user input from an external device via a LAN (Local Area Network) or the Internet.

Display control unit 160 is implemented by CPU 10 executing a program stored in ROM 20 or HDD 40 using RAM 30 as a work area, and performs a function of controlling a display screen displayed on input reception unit 150 .

The communication control unit 170 is realized by the processing of the external communication I/F 50, and transmits image information to the outside by e-mail, and when various setting information can be set from the external device, communicates with the external device via the network. perform the function to

The density detection control unit 180 is implemented by the CPU 10 executing a program stored in the ROM 20 or the HDD 40 using the RAM 30 as a work area, and executes control related to density detection. If the density sensor 70 has a control circuit equipped with a CPU, ROM, RAM, etc., it may be implemented by the CPU of the density sensor 70, or the CPU 10 and the CPU of the density sensor 70 may be implemented. It may be realized by cooperating.

The control unit 190 is implemented by the CPU 10 executing a program stored in the ROM 20 or the HDD 40 using the RAM 30 as a work area, and controls the overall functions of the image forming apparatus 1, such as a copy function, a scanner function, a printer function, a facsimile function, and a facsimile function. perform a function.

The control unit 190 has an image formation control unit 191 , a scumming determination unit 192 and a density adjustment unit 193 . The image forming control unit 191 performs a function of controlling the printer engine 100, which is an image forming unit. As an example, the image formation control unit 191 can execute image formation under image formation conditions according to the type of recording medium included in the print instruction by the user. The scumming determination unit 192 performs a function of determining the presence or absence of scumming based on the output of the density detection control unit 180 . The density adjustment section 193 executes a function of adjusting the density of image formation by the image formation control section 191 .

The read/write processing unit 200 is implemented by the CPU 10 executing a program stored in the ROM 20 or the HDD 40 using the RAM 30 as a work area, and stores various data in the storage unit 210 and reads various stored data. perform functions such as

The storage unit 210 is executed by processing of the ROM 2 or the HDD 40, and executes a function of storing programs, document data, image forming conditions and various setting information necessary for the operation of the image forming apparatus 1, operation logs of the image forming apparatus 1, and the like. do. Examples of image forming conditions include charging bias, developing bias, amount of light for optical writing, and transfer bias.

Various information stored in storage unit 210 may be set before shipment of image forming apparatus 1, or may be updated after sale. Depending on the stored information, the temporary storage function of the RAM 30 may be used.

The storage unit 210 has a threshold storage unit 211 and an adjustment value storage unit 212 . The threshold value storage unit 211 stores in advance a threshold value for determining scumming for each color. The adjustment value storage unit 212 stores adjustment values for adjusting the density of image formation in advance.

FIG. 8 shows an example of thresholds stored in the threshold storage unit 211. As shown in FIG. Density (C), density (M), density (Y), and density (K) are the density of each color (ground color density) in the ground color of a certain storage medium. Threshold (C), Threshold (M), Threshold (Y), and Threshold (M) are thresholds for determining background contamination when the difference between the image density of the non-image area and each color density is equal to or greater than the threshold. be.

In the threshold value storage unit 211, the background color density and the threshold value for each color are stored in advance according to types 1, 2, 3, . . . remembered. In FIG. 8, the threshold value is the difference between the density of the non-image area and the density of each color, but it is also possible to store only the threshold value of the density of the non-image area to be judged as scumming.

FIG. 9 shows an example of density adjustment values stored in the adjustment value storage unit 212. As shown in FIG. The density adjustment value is an adjustment value that is applied to adjust the image density for each value that is the image forming condition used by the printer engine 100 . Application includes at least overwrite, update, addition, subtraction, change, recalculation, and the like.

As an example of the density adjustment value, FIG. 9 stores a developing bias, a charging bias, a printing speed, and a flag for toner refresh. First, the charging biases Vc(C), Vc(M), Vc(Y), and Vc(K) are the charging applied when scumming is detected in cyan, magenta, yellow, and black, respectively. Bias. Developing biases Vd(C), Vd(M), Vd(Y), and Vd(K) are applied when background contamination is detected in cyan, magenta, yellow, and black, respectively. Bias. The printing speed is the printing speed that is applied when scumming is detected in any one of cyan, magenta, yellow, and black. As an example, the printing speed is represented by the number of printed sheets per unit time, but is not limited to this. Further, 1 is stored as a flag value indicating whether toner refresh is to be executed or not.

Different values can be applied to the charging bias and developing bias for each color, and only the density of that color can be adjusted. The printing speed is a density adjustment value that can adjust the density of all colors. The presence or absence of execution of toner refresh can be applied to each color, and is a density adjustment value capable of adjusting only the image density of that color. Any density adjustment value is a density adjustment value that can adjust at least the image density of any color when the image density of any color in the non-image area is equal to or higher than the threshold value.

In the adjustment value storage unit 212, each density adjustment value is stored in advance in association with the type of recording medium on which an image may be formed by the image forming apparatus 1, type 1, type 2, type 3, and so on. there is Therefore, different image density adjustments can be performed according to the type of storage medium.

FIG. 10 is a diagram for explaining charging bias or developing bias as a density adjustment value. Although the yellow color is described here, the same applies to other colors.

In the present embodiment, the surface potential of the surface of the photoreceptor 120y as a result of applying a charging bias by a charger 122y, which is a charging bias applying section, is called a charging potential. The potential of the electrostatic latent image after being exposed by the light beam BM emitted from the laser light source at 1 is called the exposed portion potential. Further, the surface potential of the developing roller surface resulting from the application of the developing bias by the developing roller provided in the developing device 121y is called development potential, and the difference between the development potential and the exposed portion potential is called development potential.

The toner has a charge amount corresponding to its state and environment, and the toner carried on the developing roller of the developing device 121y is formed on the photoreceptor 122y so as to cancel out the potential corresponding to this developing potential. the electrostatic latent image. Therefore, the amount of toner attached to the electrostatic latent image formed on the photoreceptor 122y changes depending on the charge amount of the toner and the development potential.

The difference between the charging potential and the developing potential is called the background potential. If the background potential is too small, the toner will adhere to other than the electrostatic latent image and cause scumming. Therefore, scumming can be improved by changing the image forming conditions so as to increase the background potential.

That is, in FIG. 10, the background potential can be increased by increasing the charging potential. Therefore, scumming can be improved by increasing the charging bias Vc (Y) indicated by the dashed line. Further, by reducing the developing bias Vd(Y) indicated by the chain double-dashed line, background contamination can be improved. Also, even if both the charging bias Vc(Y) and the developing bias Vd(Y) are changed to increase the difference between the charging potential and the developing potential, the background potential increases and the background contamination can be improved. can.

FIG. 11 is a diagram illustrating printing speed as an adjustment value for image density.

If the printing speed is increased, the time required to transfer the toner image to the recording medium is shortened, resulting in a lower transfer rate. In addition, if the image forming conditions at the start of printing remain unchanged due to changes in the state of the printer engine 100, for example, changes in the state of the developer, the transfer rate may increase excessively and scumming may occur. Therefore, in such a case, the scumming can be eliminated by increasing the printing speed and decreasing the transfer rate. FIG. 11 shows a situation in which relatively slight scumming (rank 4) occurs, and the scumming is completely eliminated when the printing speed vh is changed to about 230 mm/sec faster than the printing speed vl at that time. (Rank 5 = no occurrence) example is shown.

As described above, if the printing speed after density adjustment is faster than the printing speed before density adjustment is performed, the scumming before density adjustment can be improved.

FIG. 12 is a diagram for explaining whether or not toner refresh is performed as an adjustment value for image density.

FIG. 12 is an enlarged view of the developing device 121y of FIG. The developing device 121y has a developing roller 1211y whose peripheral surface is partly exposed through an opening provided in a casing. Into the developing device 121y, two conveying screws 1212y and 1213y agitate and convey the magnetic carrier and the negatively charged Y toner, thereby accelerating frictional electrification of the Y toner. Due to the magnetic force of the magnet roller, which is the magnetic field generating means, the toner is attracted to the surface of the rotating developing sleeve of the developing roller 1211y and is drawn up.

As the developing sleeve rotates, the layer thickness of the developing sleeve is regulated when it passes through the opposing position of the blade 1214y as a regulating member, and then it is transported to the developing position facing the photoreceptor 120y. At the development position, a development potential is formed on the surface of the development roller 1211y generated by the development bias applied to the development roller 1211y, and the electrostatic latent image on the photoreceptor 120y is developed with toner.

The developing device 121y also has a stored toner concentration sensor 1215y, which is a magnetic permeability sensor, for example. The contained toner concentration sensor 1215y, which is the toner concentration detecting means, outputs a voltage corresponding to the magnetic permeability of the Y developer contained in the developing device 121y. Since the magnetic permeability of the developer has a good correlation with the toner density of the developer, the stored toner density sensor 1215y outputs a voltage value corresponding to the toner density.

When the toner density measured by the stored toner density sensor 1215y is greater than the desired value, the toner in the developing device 121y is developed and discharged to the photoreceptor 120y by an electric field and consumed, thereby controlling the toner density to the desired value. . On the other hand, if the toner density measured by the toner density sensor 1215y is smaller than the desired value, the developing device 121y is replenished with toner to control the toner density to the desired value.

If the toner concentration in the developing device 121 is too high, the toner will adhere to areas other than the electrostatic latent image and cause scumming. By refreshing, scumming can be improved.

Further, when the toner is refreshed, the toner in the developing device 121y is developed on the photosensitive member 120y by an electric field and consumed, thereby discharging the deteriorated toner out of the developing device 121y. If scumming occurs due to toner deterioration, the scumming is eliminated by this toner refresh.

In order to forcibly consume the deteriorated toner in the developing device 121y, as an example, a consumption pattern is set in the area of the intermediate transfer belt 130 shown in FIG. create. The created consumption pattern is cleaned by the cleaning unit 139 shown in FIG. 2 without being transferred to the recording medium.

In this way, background staining caused by high image density in the developing device 121 can be improved by adjusting the image density in the developing device 121, that is, by lowering the toner density. As an example, executing toner refresh can reduce the toner density and improve scumming.

FIG. 13 is a first example of the image density adjustment flow. As an example, this flow starts when the image forming apparatus 1 receives a print command and starts operating.

First, the scumming determination unit 192 acquires the type of recording medium included in the print command to the printer engine 100 (S11). Next, the density detection control unit 180 sets the image density of the non-image area or the area including the non-image area acquired by the density sensor 70 with respect to the recording medium conveyed to the detection area of the density sensor 70 for each toner color. 190 (S12). The background stain determination unit 192 refers to the threshold value storage unit 211 and obtains the background color density and the threshold value corresponding to the type of the obtained storage medium (S13). Then, the background color density acquired in step S12 and the image density output by the density detection control unit 180 are compared, and it is determined whether the difference is less than a threshold (S14). If it is larger than the threshold value in step S14, the density adjustment unit 193 refers to the adjustment value storage unit 212, acquires the adjustment value (S15), and outputs it to the image formation control unit 191. FIG. As a non-image area or an area including a non-image area, the image density of at least one of the leading edge, trailing edge, right edge, and left edge of the recording medium may be detected. Moreover, among the results of detecting the image density of the entire surface of the recording medium, the image density of at least one of the leading edge, the trailing edge, the right edge, and the left edge may be output.

If it is less than the threshold in step S14, the process proceeds to step S16, and the scumming determining unit 192 determines whether the density of all colors has been determined (S16). If all colors have not been determined (No), the process returns to step S12. If it is determined that all colors have been determined in step S16 (Yes), the image formation control unit 191 continues printing under the image formation conditions at that time (S17). At this time, the image formation control unit 191 performs image formation under the conditions for adjusting the image density for the color obtained in step S15 and for which the image density of at least the non-image area is equal to or higher than a predetermined value.

As described above, in the present embodiment, the scumming color is detected, and the image forming conditions are adjusted so that the image density of the color becomes appropriate, thereby accurately and efficiently suppressing the scumming. can be done. In addition, since a threshold corresponding to the type of recording medium is used for determination of scumming, scumming can be detected with higher accuracy. For example, scumming can be determined even for highly yellowed paper or colored paper. Further, since a predetermined density adjustment value is used according to the type of print medium, density adjustment can be performed more precisely.

In step 13, the background color density and the threshold value are obtained, and the difference between the background color density and the image density is used as the threshold value. You may judge by comparing with the image density obtained.

FIG. 14 is a second example of the image density adjustment flow. As an example, this flow starts when the image forming apparatus 1 receives a print command and starts operating.

First, the scumming determination unit 192 acquires the type of recording medium included in the print command to the printer engine 100 (S21). The area is specified (S22) and output to the density detection control section 180. FIG. Next, the density detection control unit 180 detects the image detected by the density sensor 70 for each toner color in the non-image area extracted based on the image data, or the area including the non-image area, for the recording medium based on the image data. As an example, the density is output to the control section 190 (S23). Since steps S24 to S28 are the same as steps S13 to S17 in the flow of FIG.

In the flow of FIG. 14, the non-image area is extracted based on the image data, and the image density of the extracted non-image area is detected. Normally, there is a high possibility that the edges of the recording medium are non-image areas, but when printing on the entire surface of the recording medium, there is an image at the edges of the recording medium, and there is a possibility that non-image areas exist in other areas. The image density adjustment flow of FIG. 14 can perform image density detection corresponding to various image data in addition to the effect of the image density adjustment flow of FIG. Of the results of detecting the image density on the recording medium, based on the image data, the image density of only the detection result of a specific area may be output.

FIG. 15 is a flow chart showing an example of the recording medium density detection flow. As an example, this flow starts when the user designates a certain type of recording medium from the operation panel 60 and selects the background color density detection mode.

First, the image forming control unit 191 controls the printer engine 100, which is an image forming unit, to convey the recording medium without forming an image on the recording medium (S31). Next, the density detection control unit 180 outputs the density of a so-called blank recording medium that has reached the detection area of the density sensor 70 without image formation to the control unit 190 as an example. (S32). The image formation control unit 191 refers to the threshold storage unit 211 for the recording medium specified by the user, and determines whether it is the storage medium stored in the threshold storage unit 211 (S33). If the recording medium is stored in the threshold storage unit 211, the image formation control unit 191 stores the detected background color density in association with the corresponding recording medium already stored in the threshold storage unit 211. (S34). On the other hand, if the recording medium is not the recording medium stored in the threshold storage unit 211, a new recording medium and the detected background color density are stored in the threshold storage unit 211 in association with the new storage medium (S35). .

By detecting and storing the background color density in this way, the above-described image density detection flow can be executed even for recording media that are not stored in the threshold storage unit 211 in advance. Also, for the recording medium already stored in the threshold storage unit 211, by executing this detection flow and storing the detected background color density in association with the type of storage medium already stored, the specified The quality of image density detection can be improved when image density detection is unsuccessful for a recording medium.

A more specific example of the process of storing the detected background color density in step 34 in association with the corresponding recording medium already stored in the threshold storage unit 211 is This is a process of overwriting the background color density associated with the relevant recording medium that has been detected with the background color density detected in this flow.

After executing step S35 and ending this flow, a new threshold may be set for executing the image density detection flow, or the background color detected by the image density detection flow in the threshold storage unit 211 may be set. A threshold value associated with another background color density relatively close to the density may be used, or a predetermined threshold value for the background color density detected by the storage medium density detection flow may be used. Also, the density adjustment value in the adjustment value storage unit 212 may be newly set, or an adjustment value for another type of recording medium close to the background color density detected in the image density detection flow may be used.

FIG. 16 is another example of the functional blocks of this embodiment described in FIG. In FIG. 16, in addition to the functional blocks in FIG. 7, a positional deviation correction section 194, a gradation correction section 195, and a density deviation correction section 196 are provided.

The positional deviation correction unit 194 executes control for correcting the positional deviation when a positional deviation occurs in the transported storage medium. In other words, the misregistration correction unit 194 sends the image formation control unit 191 a condition for correcting the misregistration based on the detection result of the density sensor 70 detecting the misregistration correction pattern formed on the recording medium. Output. The conditions for correcting misalignment are, for example, correcting the writing position of the writing device to match the misalignment of the paper transport position, controlling the paper transport rollers to transport the paper so as to correct the transport misalignment, or displaying on the display panel For example, it is possible to display that there is a positional deviation, but the present invention is not limited to these.

For example, as shown in FIG. 17, there is an image misregistration correction pattern in which L-shaped detection marks are printed at the four corners of the paper. When the image misregistration correction pattern passes the density sensor 70, the four corners of the paper on which the image misregistration correction pattern is printed and the detection marks printed on the image misregistration correction pattern are detected. The amount of correction of the image position is calculated based on the coordinates of . There is also a method in which patterns for correcting image misregistration are printed on both sides (first and second sides) of a sheet, and front and back image misregistration correction is performed not only on the image position on the first side but also on the second side. Note that the image misalignment correction pattern is not necessarily limited to the L shape.

As described above, in the image forming apparatus 1 having the density sensor 70 for correcting the positional deviation, there is no need to newly provide a sensor for correcting the image density or change the layout for the newly provided sensor. , image density correction can be performed using the detection result of the density sensor 70 for misregistration correction only by changing the control, so that the cost can be reduced.

The gradation correction unit 195 executes control for correcting the gradation when an abnormality occurs in the gradation image formed on the storage medium. That is, the gradation correction unit 195 instructs the image formation control unit 191 to correct the gradation based on the detection result of the density sensor 70 detecting the gradation correction (calibration) pattern formed on the recording medium. output the conditions for The conditions for correcting the gradation include, but are not limited to, charging bias, developing bias, stored toner concentration, printing speed, and displaying on the display panel that there is an abnormality in gradation.

Gradation correction patterns include gradation patches of C, M, Y, and K respectively. As an example of the gradation correction pattern, for example, patch images of 10, 20, 30, 40, 50, 60, 70, 80, 90, and 100% for C, M, Y, and K are shown in FIG. Although some are formed, the formed gradation and layout are not limited to this.

Thus, in the image forming apparatus 1 having the density sensor 70 for gradation correction, there is no need to provide a new sensor for image density correction or change the layout for the newly provided sensor. , image density correction can be performed using the detection result of the density sensor 70 for gradation correction only by changing the control, so that the cost can be reduced.

A density deviation correction unit 196 executes control for correcting density deviation when density deviation occurs in an image formed on a recording medium. That is, the density deviation correction unit 196 outputs conditions for correcting the density deviation to the image formation control unit 191 based on the detection result of the density sensor 70 inspecting the density deviation correction pattern formed on the recording medium. do. The conditions for correcting the density deviation are, for example, charging bias, development bias, stored toner density, printing speed, or density deviation in the display panel that cancels out the image density deviation in the main scanning direction and the paper transport direction (sub-scanning direction). For example, it is possible to display what is occurring, but the present invention is not limited to these.

The density deviation correction pattern includes, for example, a pattern in which a uniform halftone image is printed on the entire surface as shown in FIG. 18(a). In addition, what is illustrated in FIG.14(b) and FIG.14(c) may be used. FIG. 14(b) shows an image density deviation correction pattern mainly intended to grasp and correct the image density deviation in the main scanning direction, and FIG. 14(c) shows a pattern for grasping and correcting the image density deviation in the sub-scanning direction. It is a pattern for image density deviation correction placed for the main purpose (the horizontal direction in the figure is the main scanning direction, the vertical direction is the sub-scanning direction), but is not limited to these, the number of gradations and the number of colors printed per sheet of paper etc. can be selected.

In this way, in the image forming apparatus 1 having the density sensor 70 for correcting the density deviation, there is no need to newly provide a sensor for correcting the image density or change the layout for the newly provided sensor. , image density correction can be performed using the detection result of the density sensor 70 for gradation correction only by changing the control, so that the cost can be reduced.

Although the image forming apparatus according to the embodiments has been described above, the present invention is not limited to the above embodiments, and various modifications and improvements are possible within the scope of the present invention.

1 Image forming apparatus 60 Operation panel 70 Density sensor (an example of a density detection unit)
100 printer engine 120c, 120m, 120k, 120y photoreceptor (an example of image carrier)
121c, 121m, 121k, 121y developing device (an example of developing section)
122c, 122m, 122k, 122y charger (an example of a charging unit)
180 density detection control unit 190 control unit 191 image formation control unit 192 scumming determination unit 193 density adjustment unit 194 positional deviation correction unit 195 gradation correction unit 196 density deviation correction unit 210 storage unit 211 threshold storage unit 212 adjustment value storage unit

Japanese Patent Laid-Open No. 06-03203

Claims (17)

an image forming unit that forms an image on a recording medium based on image data using a plurality of developers of different colors;
a density detection unit capable of detecting image density of at least a part of an image formed on the recording medium for each color;
a density adjusting unit that adjusts the density of the image formed by the image forming unit;
The density detection unit detects the density of each color of a non-image area, which is an area where no image is formed, on the recording medium based on the image data,
The density adjustment unit adjusts the density of the color of the plurality of developers in the non-image area detected by the density detection unit to be equal to or higher than a predetermined threshold value , at least when the density of the color of the developer is equal to or higher than the predetermined threshold value. Execute the image density adjustment for the color with the density of
The image forming apparatus, wherein the predetermined threshold differs according to the type of the recording medium. 2. The image forming apparatus according to claim 1, wherein said density detection section detects the image density of at least one of the leading edge, trailing edge, right edge and left edge of said recording medium as said non-image area. identifying the non-image area based on the image data;
3. The image forming apparatus according to claim 1, wherein the density detection unit detects the specified non-image area. The image forming unit
an image carrier on which a latent image is formed;
a charging unit that applies a charging bias to the image carrier to form a surface potential on the surface of the image carrier;
and a developer carrier for developing the latent image as a toner image to which a developing bias is applied, wherein the density adjusting section adjusts at least one of the charging bias and the developing bias. 3. The image forming apparatus according to any one of 3. The image forming unit
an image carrier on which a latent image is formed;
a developing unit that has toner inside and develops the latent image as a toner image;
4. The image forming apparatus according to claim 1, wherein the density adjusting section adjusts the toner density inside the developing section. The image forming unit
an image carrier on which a latent image is formed;
a developing unit that has toner inside and develops the latent image as a toner image;
4. The image forming apparatus according to claim 1, wherein the density adjusting section causes the developing section to consume the toner in the developing section without forming an image. 7. The image forming apparatus according to any one of claims 1 to 6, wherein said density adjusting section changes a printing speed of said image forming apparatus. 8. The image forming apparatus according to claim 7, wherein the printing speed after the density adjustment is faster than the printing speed before the density adjustment is performed by the density adjusting unit. 9. The image forming apparatus according to any one of claims 1 to 8, wherein the density adjustment section performs the image density adjustment with different content depending on the type of the recording medium. a threshold storage unit in which the background color density of the recording medium and the predetermined threshold are stored in advance;
conveying the recording medium without image formation by the image forming unit;
The density detection unit detects the density of a recording medium conveyed without image formation by the image forming unit,
If the recording medium conveyed without image formation by the image forming unit is not the recording medium stored in the threshold value storage unit, it is stored in the threshold value storage unit as a new storage medium,
10. The image forming apparatus according to any one of claims 1 to 9, wherein the detected density is stored in the threshold storage unit in association with the new storage medium as the background color density. When the recording medium conveyed without image formation by the image forming unit is the recording medium stored in the threshold storage unit, the detected density is used as the background color density corresponding to the stored storage medium. 11. The image forming apparatus according to claim 10, which is stored in said threshold storage unit. a misregistration correction unit that corrects misregistration of the image formed by the image forming unit;
12. The image forming method according to claim 1, wherein the positional deviation correcting section executes the positional deviation correction based on a result of detection of the positional deviation correction pattern formed by the image forming section by the density detecting section. Device. a gradation correction unit that corrects the gradation of the image formed by the image forming unit;
13. The image forming method according to claim 1, wherein the gradation correcting section executes gradation correction based on a result of detection of the gradation correction pattern formed by the image forming section by the density detecting section. Device. a density deviation correction section for correcting density deviation in at least one of the main scanning direction and the sub-scanning direction of the image formed by the image forming section;
14. The image forming method according to claim 1, wherein the density deviation correcting section executes density deviation correction based on a detection result of the density deviation correcting pattern formed by the image forming section detected by the density detecting section. Device. 15. The image forming apparatus according to claim 1, wherein the density detection unit is formed by arranging light receiving elements in a direction orthogonal to the conveying direction of the recording medium. 16. An image forming apparatus according to claim 15, wherein said light receiving element is formed so as to be longer than the width of said recording medium in a direction orthogonal to the conveying direction of said recording medium. 17. The image forming apparatus according to claim 15, wherein the density detection unit is capable of detecting the entire width of the recording medium through which the recording medium passes.

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