JP2011150182A - Toner concentration control method and image forming apparatus - Google Patents

Abstract

Even if a region corresponding to a toner pattern one round before a developing sleeve is a solid image, the toner pattern adhesion amount that was originally detected is corrected and fed back to toner density control so that it is always stable. Help maintain image quality.
An image area ratio of a region 504 corresponding to a toner pattern 512 before a developing sleeve round 503 (positioned in the past in the image forming order by the length of the circumference of the sleeve in the past) is acquired, and the acquired image area percentage is obtained. Accordingly, the toner adhesion amount of the toner pattern 512 calculated based on the detection data by the optical detection unit is corrected.
[Selection] Figure 5

Description

  The present invention relates to a toner density control method based on toner adhesion amount detection, a copier, a printer, a facsimile machine, a plotter having a function for carrying out the toner density control method, and a multifunction machine provided with at least one of these. The present invention relates to an image forming apparatus.

Conventionally, in an image forming apparatus such as an electrophotographic copying machine or a laser beam printer, a density detection toner patch is provided on an image carrier such as a photoconductor in order to always obtain a stable image density. (Hereinafter also referred to as “toner pattern”, “density pattern” or “density detection pattern”), the patch density is detected by optical detection means, and the development potential is changed based on the detection result (specifically Specifically, the LD power, the charging bias, and the developing bias are changed).
Also, in the case of the two-component development method in which the electrostatic latent image on the image carrier is visualized by a developing sleeve that carries and rotates the two-component developer, the toner density control target value in the developing device is changed. By doing so, image density control is performed such that the maximum target adhesion amount (adhesion amount for obtaining a target ID) becomes a target value.

As such a density detection patch detection means, a reflection type sensor in which an LED as a light emitting element (light emitting means) and a PD (photodiode) or PTr (phototransistor) as a light receiving element (light receiving means) is generally combined. Are known.
The sensor configuration includes a type that detects only specularly reflected light as shown in FIG. 9 (see Japanese Patent Laid-Open No. 2001-324840), and a type that detects only diffusely reflected light as shown in FIG. As shown in FIG. 11, there are three types of types (see Japanese Patent Laid-Open No. 2001-194443). 9, 10, and 11, reference numerals 50 </ b> A, 50 </ b> B, and 50 </ b> C are element holders, 51 is an LED, 52 is a regular reflection light receiving element, 53 is a detection target surface, and 54 is a toner patch on the detection target surface. , 55 denotes a diffuse reflection light receiving element.

In recent years, as shown in FIG. 12, a type in which a beam splitter is provided in the light path on the light emitting side and the light receiving side (refer to Japanese Patent No. 2729976, Japanese Patent Laid-Open No. 10-221902, Japanese Patent Laid-Open No. 2002-72612, etc.) Has also been used a lot.
In FIG. 12, reference numeral 56 denotes an LED, 57 and 58 denote beam splitters, 59 denotes a photodiode as a light receiving means for P wave light (regular reflection light), and 60 denotes a light receiving means for S wave light (diffuse reflected light). Each photodiode is shown.

In the two-component development method, as will be described later, the toner density after one round of the developing sleeve decreases during solid development.
For this reason, for example, in toner density control in which toner patches are formed by forming toner patches between paper (between recording media) and the toner density is controlled based on the detected toner adhesion quantity, a developing sleeve corresponding to the toner pattern is used. When the previous area is a solid image, the toner pattern adhesion amount is lower than when the solid image is not a solid image.
When the toner pattern adhesion amount is detected low, control is performed to increase the toner density, the image density becomes high, the density becomes unstable, and the image quality is lowered.

  The present invention has been made in view of such a current situation, and even if the area in front of the developing sleeve corresponding to the toner pattern is a solid image, it is corrected to the toner pattern adhesion amount originally desired to be detected, The object is to maintain stable image quality at all times by enabling feedback to toner density control.

  In order to achieve the above-mentioned object, the invention according to claim 1 detects a toner pattern formed by using a two-component developer between image forming regions on a detection target surface with an optical detection means, and In the toner concentration control method for calculating the toner adhesion amount of the toner pattern based on the detection data and controlling the toner concentration based on the calculated toner adhesion amount, an area before the developing sleeve corresponding to the toner pattern The image area ratio is acquired, and the calculated toner adhesion amount is corrected according to the acquired image area ratio.

According to a second aspect of the present invention, in the toner density control method according to the first aspect of the present invention, a relational data table between the image area ratio one round before the developing sleeve and the toner pattern adhesion amount decrease rate obtained in advance is provided. It is stored, and the toner adhesion amount is corrected using the data table.
According to a third aspect of the present invention, the image forming apparatus has a function of executing the toner density control method according to the first or second aspect.

  According to the present invention, even when an image with a high image area ratio such as a solid image is formed, it is possible to suppress a decrease in the accuracy of image density control due to a decrease in the amount of toner attached to the toner pattern, and it is possible to always maintain a stable image quality. Can be maintained.

It is a figure for demonstrating the mechanism in which a toner density falls at the time of development of a solid image. FIG. 6 is a schematic diagram illustrating a toner adhesion state in an inter-sheet toner pattern when a low image area ratio is passed. FIG. 6 is a schematic diagram illustrating a toner adhesion state in an inter-sheet toner pattern when a high image area ratio is passed. FIG. 4 is a schematic diagram showing a positional relationship between a toner pattern when a low image area ratio is passed and a region corresponding to the toner pattern one round before the developing sleeve. FIG. 6 is a schematic diagram showing a positional relationship between a toner pattern when a high image area rate is passed and a region corresponding to the toner pattern one round before the developing sleeve. It is a control block diagram. FIG. 6 is a characteristic diagram showing a relationship between an image area ratio in a region before the development sleeve and a reduction rate of the toner adhesion amount in the toner pattern. 1 is a schematic configuration diagram of a color laser printer as an image forming apparatus. It is a block diagram of the optical detection means of the type which detects only regular reflection light. It is a block diagram of the optical detection means of the type which detects only diffuse reflection light. It is a block diagram of the optical detection means of the type which detects a regular reflection light and diffuse reflection light simultaneously. FIG. 5 is a configuration diagram of an optical detection means using a beam splitter, which is a type that detects specular reflection light and diffuse reflection light simultaneously. 6 is a flowchart of a process control operation for optimizing the image density. FIG. 6 is a plan view showing a gradation pattern as a toner pattern. It is a schematic block diagram of a color image forming apparatus as another example of the image forming apparatus. It is a schematic block diagram of the color image forming apparatus as another example of an image forming apparatus.

Embodiments of the present invention will be described below with reference to the drawings.
First, a schematic configuration of a color laser printer of a 4-drum tandem direct transfer system as an image forming apparatus in the present embodiment will be described based on FIG.
The color laser printer has three paper feed trays, one manual feed tray 36, two paper feed cassettes 34 (first paper feed tray), and 34 (second paper feed tray). A transfer sheet (not shown) as a sheet-like recording medium that has been formed is separated one by one in order from the uppermost one by a paper feeding roller 37 and conveyed toward the registration roller pair 23.
The transfer sheets fed from the first sheet feed tray 34 or the second sheet feed tray 34 are separated one by one from the uppermost one by the sheet feed roller 35 and are transferred to the registration roller pair 23 via the transport roller pair 39. It is conveyed toward.
The fed transfer paper is temporarily stopped by the pair of registration rollers 23, the skew is corrected, and then the leading edge of the image formed on the photosensitive drum 14Y positioned at the uppermost stream described later and the transfer paper in the transport direction. At a timing coincident with the predetermined position, the sheet is conveyed toward the transfer belt 18 as a detection target surface by a rotation operation of the registration roller pair 23 by ON control of a registration clutch (not shown).
When the transfer paper passes through a paper suction nip composed of the transfer belt 18 and a paper suction roller 41 in contact with the transfer belt 18, the transfer paper is attracted to the transfer belt 18 by an electrostatic force by a bias applied to the paper suction roller 41. It is conveyed at a process linear velocity of 125 mm / sec.

The transfer paper adsorbed by the transfer belt 18 has toner transferred to the transfer brushes 21B, 21C, 21M, and 21Y disposed at positions facing the photosensitive drums 14B, 14C, 14M, and 14Y of the respective colors with the transfer belt 18 interposed therebetween. By applying a transfer bias (plus) opposite to the charging polarity (minus), the toner images of the respective colors formed on the photoconductor drums 14B, 14C, 14M, and 14Y are converted into yellow (Y) and magenta (M ), Cyan (C), and black (Bk).
The transfer paper that has undergone the transfer process of each color is separated from the transfer belt 18 by the downstream drive roller 19 and is conveyed to the fixing device 24.
By passing through a fixing nip formed by the fixing belt 25 and the pressure roller 26 in the fixing device 24, the toner image is fixed on the transfer paper by heat and pressure.
In the single-sided printing mode, the fixed transfer paper is discharged to an FD (face-down) tray 30 formed on the upper surface of the apparatus main body.
When the double-sided printing mode is selected in advance, the transfer paper that has exited the fixing device 24 is sent to a reversing unit (not shown), and the front and back sides are reversed by the unit, and then the double-sided transport unit positioned below the transfer unit. It is conveyed to 33.
The transfer paper is fed again from the double-sided conveyance unit 33 and conveyed to the registration roller pair 23 through the conveyance roller pair 39. Thereafter, it passes through the fixing device 24 through the same operation as in the single-sided printing mode, and is discharged to the FD tray 30.

Next, the configuration and image forming operation in the image forming unit of the color laser printer will be described in detail.
Since the image forming unit has the same configuration and operation for each color, the configuration and operation for forming a yellow image will be described as a representative.
An image forming unit 12Y having a charging roller 42Y and a cleaning unit 43Y, a developing unit 13Y, an optical writing unit 16, and the like are provided around the photosensitive drum 14Y positioned on the most upstream side in the transfer paper conveyance direction.
At the time of image formation, the photosensitive drum 14Y is rotated clockwise by a main motor (not shown), is neutralized by an AC bias (DC component is zero) applied to the charging roller 42Y, and its surface potential is a reference of approximately −50v. It becomes a potential.

Next, the photosensitive drum 14Y is uniformly charged to a potential approximately equal to the DC component by applying a DC bias with an AC bias superimposed on the charging roller 42Y, and the surface potential thereof is approximately −500 v to −700 v (target charging). The potential is determined by the process control unit).
Digital image information sent from a controller unit (not shown) as a print image is converted into a binarized LD light emission signal for each color, and a cylinder lens, a polygon motor, an fθ lens, first to third mirrors, and a WTL. Exposure light 16Y is irradiated onto the photosensitive drum 14Y by an optical writing unit 16 having a lens or the like.
The drum surface potential of the irradiated portion becomes approximately −50 v, and an electrostatic latent image corresponding to the image information is formed.

The electrostatic latent image corresponding to the yellow image information on the photosensitive drum 14Y is visualized by the developing unit 13Y.
By applying DC (-300 to -500v) with AC bias superimposed on the developing sleeve 44Y of the developing unit 13Y, toner (Q / M: -20 to -30 μC / g) is developed to form a toner image.
The formed toner images on the photosensitive drums 14B, 14C, 14M, and 14Y of the respective colors are transferred onto the transfer paper adsorbed on the transfer belt 18 by the transfer bias.

In the color laser printer according to the present embodiment, in addition to the image forming mode as described above, a process control operation (hereinafter referred to as “process control”) is performed in order to optimize the image density of each color when the power is turned on or after a predetermined number of sheets have passed. Abbreviated as “operation”). The flow of the process control operation is as shown in FIG.
A predetermined gradation pattern (= density detection pattern (toner pattern), hereinafter abbreviated as a P pattern) 70 shown in FIG. 14 is switched on the transfer belt 18 by sequentially switching the charging bias and the developing bias at appropriate timing for each color. An image is formed (STEP 2), and the output voltage of these P patterns is a density detection sensor (hereinafter abbreviated as “P sensor”) 40 as an optical detection means disposed outside the transfer belt 18 in the vicinity of the drive roller 19. (STEP 3), and the output voltage is converted by the adhesion amount conversion algorithm (powder adhesion amount conversion method) of the present invention (STEP 4 to 5) to represent the current development capability (development γ, development start) (Voltage Vk) is calculated (STEP 6), and the development bias value and the toner density control target value are changed based on the calculated value (STEP 6). ), And the calculated values (development γ, development start voltage Vk, sensitivity correction coefficients α, γ) are stored in the memory of the control means (which can also serve as the main controller of the color laser printer) described later (STEP 8). Is going.
Here, the predetermined gradation pattern means a normal density detection pattern having a predetermined number of patches. Hereinafter, it is also simply referred to as “gradation pattern”.

The configuration of the P sensor 40 is as shown in FIG. 11, and its specifications are as described above.
Here, PTr (phototransistor) is used as the light receiving element, but a light receiving element such as PD (photodiode) may be used.

  The main part of the present embodiment will be described below with reference to FIGS. Although not shown, a magnetic brush of a two-component developer used for visualizing the electrostatic latent image formed on the latent image carrier (photosensitive drum) is provided on the surface of the developing sleeve 44. The two-component developer on the surface of the developing sleeve positioned downstream of the main electrode with respect to the moving direction of the latent image carrier is conveyed in cooperation with the rotation of the developing sleeve. A transport electrode for returning the two-component developer to the developing case side is provided. In the following description, the developing sleeve 44 is simply abbreviated as “sleeve”.

As shown in FIG. 1, in the two-component development method, the toner density after one round of the sleeve is lowered by the mechanisms (1) to (4) during solid development.
(1) At the time of solid development, since the developing electric field is applied in the direction of the arrow, the toner concentration of the agent in the vicinity of the sleeve is reduced and the toner charge amount is increased.
(2) Since the toner after solid development has a high toner charge amount, the agent is not separated at the agent separation portion.
(3) The agent that has not separated the agent is mixed with the holding agent on the back of the doctor blade 45 that regulates the layer thickness of the developer on the sleeve, and is conveyed to the developing nip where the sleeve and the photoconductor face each other.
(4) Since the toner charge amount of the agent that has undergone (1) to (3) during solid development is higher than that of the background portion, the powder concentration (toner concentration) decreases after one round of the sleeve.

Therefore, a toner patch is formed between papers, the amount of toner adhesion is detected, and the toner density control (controlling the toner density (image density) based on this is detected. In this case, the toner adhesion amount of the toner pattern 512 (see FIG. 3) is lower than the toner adhesion amount of the toner pattern 511 when a sheet is passed when an image having a low image area ratio is formed (FIG. 2). There was a problem of reference).
This decrease in the toner adhesion amount is due to the mechanism described above. If the toner density control is executed based on the detection result, not the toner adhesion amount that is originally desired to be detected, the toner concentration is controlled to increase. Too much will be invited.
In FIG. 2, reference numeral 501 indicates a transfer sheet on which an image having a low image area ratio is transferred, and an arrow S indicates the transfer sheet conveyance direction, that is, the transfer belt 18 movement direction. In FIG. 3, reference numeral 502 indicates a transfer sheet onto which an image with a high image area ratio is transferred.
Speaking from the mechanisms (1) to (4), even if the entire surface is not solid, if the area corresponding to the toner pattern is a solid image before the entire circumference of the sleeve, the toner adhesion amount of the toner pattern 512 (see FIG. 5). Is lower than the toner adhesion amount of the toner pattern 511 when the low image area ratio is passed (see FIG. 4).

Therefore, in the present invention, when the toner adhesion amount of the toner pattern 512 is reduced when the toner image 512 is a solid image before the sleeve of the inter-sheet toner patch, the adhesion amount does not decrease. The amount of toner patch adhesion was corrected and fed back to toner density control.
Specifically, as shown in FIGS. 4 and 5, the image area ratio of the area 504 that is one round of the sleeve corresponding to the toner pattern between the sheets is obtained, and the image area ratio of the area 504 is a predetermined value (for example, FIG. 7). If the toner adhesion amount of the inter-paper toner pattern 512 is corrected to obtain the toner adhesion amount of the inter-paper toner pattern 511 when the low image area ratio is passed, what value is obtained? It was calculated.
“Sleeve circumference (= length of sleeve circumference)” indicated by reference numeral 503 indicates a position earlier (past) in time than the toner pattern in the image forming sequence.
As shown in FIG. 6, the image area ratio of the area 504 (the ratio of the image area to the area corresponding to the toner pattern) is acquired by the image area ratio acquisition means 601 which is a conventional image processing means.
The image area ratio of the region 504 may be calculated by the control means 600 as the toner density control means based on the image data from the image area ratio acquisition means 601.
The image area ratio acquisition unit 601 can acquire the image area ratio in units of pages and has a function of acquiring an image area ratio of a specific local area such as the area 504.

For the correction, a pre-measured “relation data table between the image area ratio of the sleeve one round before and the toner adhesion amount reduction rate of the toner pattern” is stored in a memory (for example, ROM 602 shown in FIG. 6). This data was used.
For example, in the case where the image area ratio x = 90% before the length of one full circumference of the sleeve, the amount of toner adhesion of the inter-paper toner pattern = 0.35 mg / cm ² and the data measured in advance have a relationship as shown in FIG. That is, y = f (90%) = 75%
Toner adhesion amount when passing through a low image area = (Toner adhesion amount when x = 90%) / f (90%)
= 0.35 / (75/100)
= 0.47 mg / cm ²
It was corrected as follows.
By feeding this correction value back to the toner density control when a high image area ratio is passed (when a solid image is passed), stable image quality can be maintained.

An outline of the configuration and operation of a tandem type color copying machine as another example of the image forming apparatus will be described with reference to FIG.
The color copying machine 1 has an image forming unit 1A located at the center of the apparatus main body, a paper feeding unit 1B located below the image forming unit 1A, and an image reading unit 1C located above the image forming unit 1A. is doing.
An intermediate transfer belt 2 as a transfer body having a transfer surface extending in the horizontal direction is disposed in the image forming unit 1A, and an image of a color complementary to the color separation color is disposed on the upper surface of the intermediate transfer belt 2. The structure for forming is provided. In this example, the intermediate transfer belt 2 is a detection target surface, and the P sensor 40 is disposed to face the intermediate transfer belt 2.
That is, the photosensitive drums 3Y, 3M, 3C, and 3B as image carriers capable of carrying an image of complementary color toners (yellow, magenta, cyan, and black) are arranged along the transfer surface of the intermediate transfer belt 2. It is juxtaposed.

Each of the photosensitive drums 3Y, 3M, 3C, and 3B is composed of a drum that can rotate in the same counterclockwise direction, and around the charging device 4 is a charging unit that performs image forming processing in the rotation process. , An optical writing device 5 as an exposure means for forming an electrostatic latent image having a potential VL on the basis of image information on each of the photosensitive drums 3Y, 3M, 3C, 3B. A developing device 6 as a developing means for developing the latent image with toner having the same polarity as that of the electrostatic latent image, a transfer bias roller 7 as a primary transfer means, an applied voltage member 15, and a cleaning device 8 are arranged.
The alphabets attached to the respective symbols correspond to the colors of the toner as in the photosensitive drum 3. Each developing device 6 accommodates each color toner.
The intermediate transfer belt 2 is configured to be wound around a plurality of rollers 2A to 2C and to move in the same direction at a position facing the photosensitive drums 3Y, 3M, 3C, and 3B.
A roller 2C, which is different from the rollers 2A and 2B that support the transfer surface, faces the secondary transfer device 9 with the intermediate transfer belt 2 interposed therebetween.
In FIG. 15, reference numeral 10 indicates a cleaning device for the intermediate transfer belt 2.

The surface of the photosensitive drum 3Y is uniformly charged by the charging device 4Y, and an electrostatic latent image is formed on the photosensitive drum 3Y based on the image information from the image reading unit 1C.
The electrostatic latent image is visualized as a toner image by a two-component (carrier and toner) developing device 6Y containing yellow toner, and the toner image is transferred onto the intermediate transfer belt 2 as a first transfer step. The image is attracted and transferred by the electric field generated by the voltage applied to the transfer bias roller 7Y.
The applied voltage member 15Y is provided on the upstream side of the transfer bias roller 7Y in the rotation direction of the photosensitive drum 3Y.
The applied voltage member 15Y applies a voltage to the intermediate transfer belt 2 that has the same polarity as the charging polarity of the photosensitive drum 3Y and has an absolute value that is greater than the solid VL. From the photosensitive drum 3Y before the toner image enters the transfer area. The toner is prevented from being transferred to the intermediate transfer belt 2, and the disturbance due to dust during the transfer of the toner from the photosensitive drum 3Y to the intermediate transfer belt 2 is prevented.

The other photoconductor drums 3M, 3C, and 3B also form similar images only with different toner colors, and the toner images of the respective colors are sequentially transferred onto the intermediate transfer belt 2 and superimposed.
The toner remaining on the photosensitive drum 3 after the transfer is removed by the cleaning device 8, and the potential of the photosensitive drum 3 is initialized by a neutralizing lamp (not shown) after the transfer to prepare for the next image forming process.
The secondary transfer device 9 includes a transfer belt 9 </ b> C that is wound around the charging drive roller 9 </ b> A and the driven roller 9 </ b> B and moves in the same direction as the intermediate transfer belt 2.
By charging the transfer belt 9C with the charging drive roller 9A, it is possible to transfer a multicolor image superimposed on the intermediate transfer belt 2 or a supported single color image onto a paper 28 as a sheet-like recording medium.

The paper 28 is fed from the paper feed unit 1B to the secondary transfer position.
The paper feed unit 1B has a plurality of paper feed cassettes 1B1 in which papers 28 are stacked and housed, and a paper feed roller 1B2 that separates and feeds the papers 28 contained in the paper feed cassette 1B1 one by one in order from the top. A pair of conveying rollers 1B3, a pair of registration rollers 1B4 positioned upstream of the secondary transfer position, and the like.
The paper 28 fed from the paper feed cassette 1B1 is temporarily stopped by the registration roller pair 1B4, and after correcting the oblique displacement and the like, the front end of the toner image on the intermediate transfer belt 2 and a predetermined position at the front end in the transport direction are set. Are sent to the secondary transfer position by the registration roller pair 1B4.
A manual feed tray 29 is provided on the right side of the apparatus main body so that it can be turned up and down, and the paper 28 accommodated in the manual feed tray 29 joins the paper feed path from the paper feed cassette 1B1 fed by the paper feed roller 31. The paper is sent toward the registration roller pair 1B4 by the conveying path.

In the optical writing device 5, writing light is controlled by image information from the image reading unit 1C or image information output from a computer (not shown), and the photosensitive drums 3Y, 3M, 3C, and 3B correspond to the image information. Writing light is emitted to form an electrostatic latent image.
The image reading unit 1C includes an automatic document feeder 1C1, a scanner 1C2 having a contact glass 80 as a document table, and the like.
The automatic document feeder 1C1 has a configuration capable of reversing the document fed on the contact glass 80, and can perform scanning on each surface of the document.
The electrostatic latent image formed on the photosensitive drum 3 formed by the optical writing device 5 is subjected to visible image processing by the developing device 6 and is primarily transferred to the intermediate transfer belt 2.
When the toner images for each color are superimposed and transferred onto the intermediate transfer belt 2, they are secondarily transferred onto the paper 28 by the secondary transfer device 9.
The second-transferred paper 28 is sent to the fixing device 11 where the unfixed image is fixed by heat and pressure.
Residual toner on the intermediate transfer belt 2 after the secondary transfer is removed by the cleaning device 10.

The paper 28 that has passed through the fixing device 11 is selectively guided to the conveyance path toward the paper discharge tray 27 and the reverse conveyance path RP by the conveyance path switching claw 12 provided on the downstream side of the fixing apparatus 11.
When the paper is conveyed toward the paper discharge tray 27, it is discharged onto the paper discharge tray 27 by the paper discharge roller pair 32 and stacked.
When guided to the reversal conveyance path RP, it is reversed by the reversing device 38 and sent again toward the registration roller pair 1B4.

With the above configuration, in the color copying machine 1, the photosensitive drum 3 that is uniformly charged is statically exposed by scanning the document placed on the contact glass 80 or by image information from the computer. An electrostatic latent image is formed, and the electrostatic latent image is subjected to visible image processing by the developing device 6, and then the toner image is primarily transferred to the intermediate transfer belt 2.
In the case of a single image, the toner image transferred to the intermediate transfer belt 2 is transferred as it is to the paper 28 fed out from the paper supply unit 1B.
In the case of a multi-color image, the images are superimposed by repeating primary transfer, and then secondary transferred onto the paper 28 at once.
After the secondary transfer, the paper 28 is fixed with an unfixed image by the fixing device 11 and then discharged to the paper discharge tray 27 or reversed and sent again toward the registration roller pair 1B4 for double-sided image formation. In this embodiment, the detection target surface is the intermediate transfer belt 2 as a transfer member, but each photosensitive drum may be a detection target surface.
In this case, the P sensor 40 is provided to face each photosensitive drum.

Further, each color toner image is formed by using one photosensitive drum and a revolver type developing device, and each toner image is transferred onto an intermediate transfer member, and then transferred onto a transfer sheet as a sheet-like recording medium. The same can be applied to the color image forming apparatus of the type.
An example is shown in FIG. In this example, the P pattern for density detection shown in FIG. 14 is formed on an intermediate transfer belt 426 as an intermediate transfer member, and this is detected by a P sensor 40 disposed in the vicinity of the drive roller 444. That is, in this example, the intermediate transfer belt 426 is the detection target surface.
The detection method and operation (handling of detection data, etc.) are the same as in the above embodiment.

An outline of the configuration of the color copying machine as the image forming apparatus shown in FIG. 16 will be described.
In a color copying machine, a writing optical unit 400 serving as an exposure unit converts color image data from the color scanner 200 into an optical signal and performs optical writing corresponding to a document image, on a photosensitive drum 402 serving as an image carrier. An electrostatic latent image is formed on the surface.
The writing optical unit 400 includes a laser diode 404, a polygon mirror 406, a rotation motor 408 thereof, an fθ lens 410, a reflection mirror 412, and the like.
The photosensitive drum 402 is rotated in the counterclockwise direction as indicated by an arrow, and the photosensitive drum cleaning unit 414, the charge eliminating lamp 416, the potential sensor 420, and the rotary developing device 422 are selected around the photosensitive drum 402. A developing device, a development density pattern detector 424, an intermediate transfer belt 426 as an intermediate transfer member, and the like are arranged.

The rotary developing device 422 includes a black developing unit 428, a cyan developing unit 430, a magenta developing unit 432, a yellow developing unit 434, and a rotation driving unit (not shown) that rotates each developing unit.
Each developing device is a so-called two-component developing type developer containing a mixed developer of carrier and toner, and has the same configuration as the developing device 4 shown in the above embodiment.
The conditions and specifications of the magnetic carrier are the same.
In the standby state, the rotary developing device 422 is set at the black development position. When the copying operation is started, the color scanner 200 starts reading the black image data at a predetermined timing. Based on the above, optical writing with a laser beam and formation of an electrostatic latent image (black latent image) are started.

In order to develop from the leading edge of the black latent image, before the leading edge of the latent image reaches the developing position of the black developing device 428, the developing sleeve is started to rotate and the black latent image is developed with black toner. A negative polarity toner is formed on the photosensitive drum 402.
Thereafter, the development operation of the black latent image area is continued, but when the trailing edge of the latent image passes the black development position, the rotary development is quickly performed from the development position for black to the development position for the next color. The device 422 rotates. This operation is completed at least before the leading edge of the latent image by the next image data arrives.
When the image forming cycle is started, first, the photosensitive drum 402 is rotated counterclockwise as indicated by an arrow, and the intermediate transfer belt 426 is rotated clockwise by a drive motor (not shown).
As the intermediate transfer belt 426 rotates, black toner image formation, cyan toner image formation, magenta toner image formation, and yellow toner image formation are performed. Finally, black (Bk), cyan (C), and magenta (M) are formed. , Yellow (Y) in this order (primary transfer) on the intermediate transfer belt 426 to form a toner image.

The intermediate transfer belt 426 includes a primary transfer electrode roller 450 that faces the photosensitive drum 402, a drive roller 444, a secondary transfer counter roller 446 that faces the secondary transfer roller 454, and a cleaning unit that cleans the surface of the intermediate transfer belt 426. It is stretched between the supporting members of the cleaning facing roller 448A facing the surface 452, and is driven and controlled by a driving motor (not shown).
The black, cyan, magenta, and yellow toner images sequentially formed on the photosensitive drum 402 are accurately and sequentially aligned on the intermediate transfer belt 426, thereby forming a four-color superimposed belt transfer image.
This belt transfer image is collectively transferred onto a sheet by a secondary transfer counter roller 446.

Each of the recording paper cassettes 458, 460, and 462 in the paper supply bank 456 contains various sizes of paper different from the size of the paper stored in the cassette 464 in the apparatus body. The designated paper is fed and conveyed in the direction of the registration roller pair 470 by the paper feed roller 466 from the size paper storage cassette.
In FIG. 16, reference numeral 468 denotes a manual paper feed tray for OHP paper, thick paper, and the like.
At the time when image formation is started, the paper is fed from the paper feed port of one of the above cassettes and waits at the nip portion of the registration roller pair 470.
Then, when the leading edge of the toner image on the intermediate transfer belt 426 approaches the secondary transfer counter roller 446, the registration roller pair 470 is driven so that the leading edge of the sheet exactly coincides with the leading edge of the image. Is done.

In this manner, the sheet is overlapped with the intermediate transfer belt 426 and passes under the secondary transfer counter roller 446 to which a voltage having the same polarity as the toner is applied. At this time, the toner image is transferred to the paper. Subsequently, the sheet is neutralized, peeled off from the intermediate transfer belt 426, and moved to the sheet conveying belt 472.
The sheet onto which the four-color superimposed toner images have been collectively transferred from the intermediate transfer belt 426 is conveyed to the belt fixing type fixing device 470 by the paper conveying belt 472, and the toner image is fixed by the fixing device 470 by heat and pressure.
The sheet that has been fixed is discharged out of the apparatus by the discharge roller pair 480 and stacked on a tray (not shown). Thereby, a full color copy is obtained.
In this embodiment, the detection target surface is the intermediate transfer belt 426 as a transfer body, but the photosensitive drum 402 may be the detection target surface. In this case, the P sensor 40 is provided facing the photosensitive drum 402, and the development density pattern detector 424 corresponds to this.

  In each of the above embodiments, the density control method using toner as the powder is exemplified, but the same detection function can be obtained by the same processing method in the density control method that handles powder other than the toner.

18 Transfer Belt as Detection Target Surface 44 Developing Sleeve 512 Toner Pattern

JP 2001-194443 A Japanese Patent No. 2729976 JP 2002-72612 A JP 2001-215850 A JP 2000-39746 A JP 2000-66463 A Japanese Patent Laid-Open No. 2000-227692 JP 2000-231254 A JP 2000-250286 A JP 2000-275167 A Japanese Patent Laid-Open No. 2001-34027 JP 2001-215762 A Japanese Patent Laid-Open No. 2001-312115 Japanese Patent Laid-Open No. 2002-40746 JP-A-8-123110 JP-A-8-21990 JP-A-8-271230 Japanese Patent Laid-Open No. 9-73215 JP-A-10-221902 JP-A-11-174753 JP 11-249373 A Japanese Patent No. 2577354 JP-A-5-249787

Claims (3)

A toner pattern formed by using a two-component developer between image forming areas on the detection target surface is detected by an optical detection means, and a toner adhesion amount of the toner pattern is calculated based on the detection data, and is calculated In the toner concentration control method for controlling the toner concentration based on the applied toner adhesion amount,
A toner density control method, comprising: acquiring an image area ratio of a region corresponding to the toner pattern one round before the developing sleeve, and correcting the calculated toner adhesion amount according to the acquired image area ratio. The toner concentration control method according to claim 1,
Storing a relational data table of an image area ratio that is obtained in advance of one round of the developing sleeve and a toner pattern adhesion amount reduction rate, which is obtained in advance, and correcting the toner adhesion amount using the data table; Toner density control method.   An image forming apparatus having a function of executing the toner density control method according to claim 1.

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