JP2009186847A - Image forming apparatus and image density control method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus and an image density control method with which characteristic information such as development &gamma; is accurately obtained with a small number of toner patches when the development &gamma; is not largely varied from the previous value, and two or more toner patches are put within a detection range of an optical detection means by forming a gradation pattern once even when the development &gamma; is much larger than the previous value. <P>SOLUTION: One toner patch of the gradation pattern is formed with fixed developing bias determined in advance so that it may be sure to be within the detection range of an optical sensor in the variation range of the development &gamma;, and remaining toner patches are formed with developing bias set so that they are equally dispersed within the detection range of the optical sensor on the basis of the developing bias determined by previous process control. <P>COPYRIGHT: (C)2009,JPO&amp;INPIT

Description

  The present invention relates to an image forming apparatus and an image density control method.

  In an image forming apparatus such as a copying machine or a laser beam printer using an electrophotographic system, the following image density control is performed in order to always obtain a stable image density. That is, a gradation pattern composed of 10 to 17 density detection toner patches formed on different image forming conditions (development potentials) on an image carrier such as a photoconductor so as to have different toner adhesion amounts. . A toner adhesion amount (toner density) of each toner patch is calculated using a detection value obtained by detecting the toner patch by an optical sensor as an optical detection unit and a predetermined adhesion amount calculation algorithm. Then, after obtaining a linear equation y = ax + b from the relationship between the toner adhesion amount (toner density) of each toner patch and the image forming condition (development potential), development γ (development potential is represented on the horizontal axis and toner adhesion amount is represented on the vertical axis. The inclination a) with respect to the axis and the development start voltage Vk (intercept b with the development potential on the horizontal axis and the toner adhesion amount on the vertical axis) are obtained. Based on the obtained development γ and development start voltage Vk, the image forming conditions such as LD power, charging bias, and developing bias are adjusted so as to obtain a developing potential with an appropriate toner adhesion amount.

  An optical sensor as an optical detection means for detecting the toner patch is composed of a light emitting element such as an LED and a light receiving element such as a phototransistor, and the reflected light of the light emitting element is detected by the light receiving element. The optical sensor can detect the low adhesion side with high sensitivity, but the high adhesion side has a predetermined detection range depending on the detection sensitivity of the light receiving element. Therefore, in order to obtain the development γ and the development start voltage Vk, it is necessary that the adhesion amount of the toner patch is within the detection range of the optical sensor at least two points or more.

  In the above-described image density control, the image forming conditions of the toner patches are set so that the adhesion amount of the two or more toner patches always falls within the detection range of the optical sensor regardless of the development γ. By changing, 10 to 17 density detection toner patches are created. However, when the number of toner patches is increased, there is a problem that the image density control time becomes longer and the downtime of the apparatus becomes longer. There is also a problem that the amount of toner consumed for image density control increases.

  Patent Document 1 describes an image forming apparatus that performs the following image density control. That is, the development γ and the development start voltage Vk obtained based on the detection result obtained by detecting the gradation pattern with the optical sensor are stored in the storage unit. In the next image density control, each toner patch is uniformly distributed within the detection range of the sensor based on the development γ and development start voltage Vk stored in the storage means. The development bias for forming the patch is calculated for each. Then, a gradation pattern is created with the calculated development bias, and image density control is performed. Usually, the development γ does not vary greatly from the previous value. Therefore, if the gradation pattern is created with the development bias adjusted based on the development γ and development start voltage Vk obtained last time, a plurality of toner patches are within the detection range of the optical sensor even if the number of toner patches is small. Can be evenly distributed. Since the toner patches are evenly distributed within the detection range of the optical sensor, the development γ and the development start voltage Vk can be accurately calculated, and the image forming conditions can be adjusted. Further, since the number of toner patches can be reduced, the image density control time can be shortened, and the amount of toner consumed for image density control can be reduced.

JP 2006-106222 A

  However, when image density control is performed after abrupt environmental fluctuations or after leaving the apparatus for a long time, the development γ may be significantly different from the previous time.

  If it is significantly larger than the previous development γ, only the toner patch with the lowest density among the toner patches of the gradation pattern created with the development bias calculated based on the previous development γ and development start voltage Vk. The development γ cannot be calculated because it does not fall within the detection range of the optical sensor. In such a case, in the image forming apparatus described in Patent Document 1, a gradation pattern is created again by changing the developing bias or increasing the number of toner patches, and at least within the detection range of the optical sensor. Two toner patches are attached.

  However, creating the gradation pattern again causes a problem that the image density control time becomes long and the downtime of the apparatus becomes long. In addition, there is a problem that the amount of toner consumed for image density control increases.

It is also conceivable to detect an environment or the like that causes the development γ to fluctuate and determine the image forming conditions for all the toner patches of the gradation pattern based on the detection result. In this way, by determining the image forming conditions for all toner patches based on the environment, even if development γ is significantly different from the previous time due to sudden environmental changes, the toner patches are within the detection range of the optical sensor. It is thought that it can be evenly distributed.
However, if all the toner patches are formed by the image formation based on the environment without providing the toner patches created under the image formation conditions calculated based on the development γ and the development start voltage Vk obtained previously, the following is performed. Will cause trouble.
That is, for example, if the environment changes greatly from the previous execution of image density control and the environment becomes low temperature and low humidity, the toner is likely to be charged, and the development γ is reduced. However, due to factors other than the environment such as the state where the developer cannot be stirred well, in practice, the development γ does not fluctuate significantly, and conversely, the environment may be somewhat larger despite low temperature and low humidity. In such a case, if all the toner patches are created under image forming conditions based on the environment, there is a possibility that only one toner patch may be entered, and there is a possibility that the development γ cannot be calculated. There is.

  The present invention has been made in view of the above-described problems. The object of the present invention is to obtain characteristic information such as the development γ with a small number of toner patches when the development γ does not vary greatly from the previous value. An image that can be obtained with high accuracy and that allows two or more toner patches to be included within the detection range of the optical detection means by creating a gradation pattern once even when development γ is significantly larger than the previous time. A forming apparatus and an image density control method are provided.

In order to achieve the above object, a first aspect of the present invention provides a latent image carrier, charging means for charging the latent image carrier to a predetermined potential, and a latent image on the surface of the latent image carrier charged to a predetermined potential. And transferring the toner on the developer carrying body to a latent image on the latent image carrying body while applying a developing bias to the developer carrying body carrying a developer containing at least toner. Developing means for developing the latent image, transfer means for transferring the toner image obtained by the development from the latent image carrier to the transfer body, and the toner image on the transfer body or the latent image carrier An optical detection means for detecting reflected light from the toner image and a gradation pattern composed of a plurality of toner patches formed under image forming conditions having different adhesion amounts are formed and detected by the optical detection means. Adjust image forming conditions using detected values In the image forming apparatus including the control unit that executes the control, at least one toner patch of the gradation pattern is determined in advance so as to be always within the detection range of the optical detection unit within the variation range of the development γ. The remaining plurality of toner patches are formed under fixed image forming conditions, and the remaining toner patches are set to be evenly distributed within the detection range of the optical detection unit based on the previously adjusted image forming conditions. The control means is configured to be formed under conditions.
According to a second aspect of the present invention, there is provided a latent image carrier, a charging means for charging the latent image carrier to a predetermined potential, and a latent image formation for forming a latent image on the surface of the latent image carrier charged to a predetermined potential. And transferring the toner on the developer carrying member to a latent image on the latent image carrying member while applying a developing bias to the developer carrying member carrying the developer containing at least toner. Development means for developing, transfer means for transferring the toner image obtained by development from the latent image carrier to the transfer body, and reflected light from the toner image on the transfer body or the toner image on the latent image carrier A detection is performed by forming a gradation pattern composed of a plurality of toner patches formed under image forming conditions in which the amount of adhesion is different between the optical detection unit and the image forming unit. Adjust image forming conditions using values And at least one toner patch in the gradation pattern within a detection range of the optical detection unit based on a change with time of the environment and / or developer. The remaining plurality of toner patches are formed so as to be evenly distributed in the detection range of the optical detection unit based on the previously adjusted image formation conditions. The control means is configured so as to be formed under image forming conditions.
According to a third aspect of the present invention, in the image forming apparatus of the second aspect, when the environment is a high temperature / high humidity environment, the toner adhesion amount is reduced with respect to the image forming conditions when the environment is normal temperature / normal humidity. The control means is configured to change the image forming conditions.
According to a fourth aspect of the present invention, in the image forming apparatus of the second or third aspect, when the environment is a low temperature / low humidity environment, the toner adhesion amount increases with respect to the image forming conditions when the environment is normal temperature / normal humidity. The control means is configured to change the image forming conditions.
According to a fifth aspect of the present invention, in the image forming apparatus according to any one of the first to fourth aspects, the previously adjusted image forming condition based on forming the remaining toner patches is a previously adjusted developing bias. It is characterized by being.
According to a sixth aspect of the present invention, there is provided a step of forming a gradation pattern composed of a plurality of toner patches formed under image forming conditions having different adhesion amounts, and the gradation pattern is detected by an optical detection means. In the image density control method, comprising: adjusting the image density by adjusting an image forming condition using the detected detection value, at least one toner patch of the gradation pattern has a predetermined development In the case of γ, the image is formed under fixed image forming conditions determined in advance so as to be within the detection range of the optical detecting means, and the remaining toner patches are detected based on the previously adjusted image forming conditions. The image forming conditions are set so as to be evenly distributed in the detection range of the means.
According to a seventh aspect of the invention, there is provided a step of forming a gradation pattern composed of a plurality of toner patches formed under image forming conditions having different adhesion amounts, and the gradation pattern is detected by an optical detection means. In the image density control method, comprising: adjusting the image density by adjusting an image forming condition using the detected detection value, at least one toner patch of the gradation pattern is an environment or a development Based on the change with time of the agent, the image is formed under the set image forming conditions, and the remaining toner patches are evenly distributed in the detection range of the optical detection unit based on the previously adjusted image forming conditions. It is characterized in that the image is formed under the set image forming conditions.

According to the first aspect of the present invention, when the development γ does not fluctuate significantly with respect to the development γ at the previous adjustment of the image forming conditions, the image is formed under the image forming conditions based on the previously adjusted image forming conditions. The toner patches are evenly distributed within the detection range of the optical detection means. Thereby, even with a small number of toner patches, characteristic information such as development γ can be obtained with high accuracy, and image forming conditions can be adjusted with high accuracy.
In addition, even if the development γ is significantly larger than the development γ at the previous adjustment of the image formation conditions, the image is formed under the image formation conditions that surely fall within the detection range of the optical detection means within the fluctuation range of the development γ. The at least one or more toner patches that are applied are within the detection range of the optical detection means. As a result, the development γ greatly fluctuates with respect to the development γ at the time of adjusting the previous image formation conditions, and only one of the toner patches formed under the image formation conditions based on the previously adjusted image formation conditions. Even if it does not fall within the detection range of the optical detection means, two or more toner patches can enter the detection range of the scientific detection means, and development γ can be obtained and image forming conditions can be adjusted. . Therefore, even if the development γ fluctuates significantly with respect to the development γ at the previous adjustment of the image forming conditions, two or more toner patches can be included in the detection range of the optical detection unit. The image forming conditions can be adjusted by creating the gradation pattern. Therefore, it is not necessary to create a gradation pattern again, and it is possible to suppress the problem that the image density control time becomes longer and the downtime of the apparatus becomes longer. Further, it is possible to suppress a problem that the consumption amount of toner used for image density control increases.

In the second aspect of the invention, when the development γ does not vary significantly with respect to the development γ at the time of adjusting the previous image formation condition, the image formation condition based on the image formation condition adjusted last time is used. The formed toner patches are evenly distributed within the detection range of the optical detection means. Thereby, even with a small number of toner patches, characteristic information such as development γ can be obtained with high accuracy, and image forming conditions can be adjusted with high accuracy.
Also, if development γ changes significantly with respect to development γ at the time of the previous adjustment of the image forming conditions, the setting is made based on environmental fluctuations and / or changes over time of the developer that are a factor of development γ fluctuations. At least one or more toner patches formed under the image forming conditions set can be included in the detection range of the optical detection means. As a result, the development γ greatly fluctuates with respect to the development γ at the time of adjusting the previous image formation conditions, and only one of the toner patches formed under the image formation conditions based on the previously adjusted image formation conditions. Even if it does not fall within the detection range of the optical detection means, two or more toner patches can enter the detection range of the scientific detection means, and development γ can be obtained and image forming conditions can be adjusted. . Therefore, even if the development γ fluctuates significantly with respect to the development γ at the previous adjustment of the image forming conditions, two or more toner patches can be included in the detection range of the optical detection unit. The image forming conditions can be adjusted by creating the gradation pattern. Therefore, it is not necessary to create a gradation pattern again, and it is possible to suppress the problem that the image density control time becomes longer and the downtime of the apparatus becomes longer. Further, it is possible to suppress a problem that the consumption amount of toner used for image density control increases.
Rather than determining the image formation conditions for all toner patches in the gradation pattern based on changes in the environment and developer over time, the actual development γ may change due to environmental fluctuations and factors other than changes in developer over time. Even if the development γ is greatly different from the development γ predicted from the change with time of the developer, two or more toner patches can be included in the detection range of the optical detection means, and the development γ can be calculated.

Hereinafter, an electrophotographic copying machine as an image forming apparatus to which the present invention is applied will be described.
FIG. 1 is a schematic configuration diagram showing a copying machine according to the present embodiment. The copying machine includes a printer unit 1 that forms an image on recording paper, a paper feeding device 200 that supplies the recording paper P to the printer unit 1, a scanner 300 that reads a document image, and automatically feeds a document to the scanner 300. An automatic document feeder (hereinafter referred to as ADF) 400 is provided.

  The scanner 300 is placed on the contact glass 301 as the first traveling body 303 equipped with a document illumination light source or mirror and the second traveling body 304 equipped with a plurality of reflecting mirrors reciprocate. Scanning of a document (not shown) is performed. The scanning light sent out from the second traveling body 304 is condensed on the imaging surface of the reading sensor 306 installed behind the imaging lens 305 and then read as an image signal by the reading sensor 306.

  On the side surface of the housing of the printer unit 1, a manual feed tray 2 for manually placing the recording paper P to be fed into the housing, and a paper discharge tray 3 for stacking the recording paper P after image formation discharged from the housing. Is provided.

  FIG. 2 is an enlarged partial configuration diagram illustrating a part of the internal configuration of the printer unit (1). In the housing of the printer unit (1), there is disposed a transfer unit 50 as transfer means for stretching an endless intermediate transfer belt 51 as an image carrying belt by a plurality of stretching rollers. The intermediate transfer belt 51 is driven by a driving roller 52, a secondary transfer backup roller 53, a driven roller 54, and four primary transfer rollers 55Y, 55Y, 55K, which are driven to rotate clockwise in FIG. While being stretched, the drive roller 52 is rotated endlessly in the clockwise direction in the drawing. Note that the suffixes Y, C, M, and K attached to the ends of the symbols of the primary transfer roller indicate the members for yellow, cyan, magenta, and black. Hereinafter, the subscripts Y, C, M, and K attached to the ends of the symbols are the same.

  The intermediate transfer belt 51 is greatly curved at the portions where the intermediate transfer belt 51 is wound around the driving roller 52, the secondary transfer backup roller 53, and the driven roller 54, so that the intermediate transfer belt 51 is stretched in an inverted triangular posture with the bottom side directed vertically upward. ing. The belt upper stretch surface corresponding to the base of the inverted triangle extends in the horizontal direction. Above the belt upper stretch surface, four process units 10Y, 10C, 10M, and 10K are provided on the upper stretch surface. It arrange | positions so that it may align with a horizontal direction along the extending direction.

  In FIG. 1 described above, an optical writing unit 68 serving as a latent image forming unit is disposed above the four process units 10Y, 10C, 10M, and 10K. The optical writing unit 68 emits four writing lights L by driving four semiconductor lasers (not shown) by a control unit (not shown) based on the image information of the original read by the scanner 300. Then, the drum-shaped photoconductors 11Y, 11C, 11M, and 11K serving as latent image carriers of the process units 10Y, 10C, 10M, and 10K are scanned in the dark by the writing light L, respectively. , K, electrostatic latent images for Y, C, M, and K are written.

  In this embodiment, the optical writing unit 68 performs optical scanning by deflecting laser light emitted from a semiconductor laser by a polygon mirror (not shown) and reflecting the laser light by a reflection mirror (not shown) or passing through an optical lens. Is used. Instead of such a configuration, an LED array that performs optical scanning may be used.

  FIG. 3 is an enlarged configuration diagram showing the process units 10Y and 10 for Y and C together with the intermediate transfer belt 51. As shown in FIG. The Y process unit 10Y has a charging member 12Y as a charging means, a charge eliminating device 13Y, a drum cleaning device 14Y, a developing device 20Y as a developing means, and the like around a drum-shaped photoreceptor 11Y. And while these are hold | maintained with the casing which is a common holding body, it is attached and detached integrally as one unit with respect to a printer part.

  The charging member 12Y is a roller-like member that is rotatably supported by a bearing (not shown) while being in contact with the photoreceptor 11Y. The surface of the photoconductor 11Y is uniformly charged with, for example, the same polarity as that of Y toner by rotating in contact with the photoconductor 11Y while a charging bias is applied by a bias supply means (not shown). Instead of the charging member 12Y having such a configuration, a scorotron charger or the like that performs a uniform charging process in a non-contact manner on the photoconductor 11Y may be employed.

  A developing device 20Y in which a Y developer containing a magnetic carrier (not shown) and non-magnetic Y toner is contained in a casing 21Y has a developer conveying device 22Y and a developing unit 23Y. In the developing unit 23Y, a developing sleeve 24Y as a developer carrying member that is endlessly moved by being rotated by a driving unit (not shown) exposes a part of its peripheral surface to the outside through an opening provided in the casing 21Y. ing. As a result, a developing region is formed in which the photoconductor 11Y and the developing sleeve 24Y face each other with a predetermined gap.

  Inside the developing sleeve 24Y made of a non-magnetic hollow pipe-like member, a magnet roller (not shown) having a plurality of magnetic poles arranged in the circumferential direction is fixed so as not to rotate with the developing sleeve 24Y. The developing sleeve 24Y is driven to rotate while adsorbing the Y developer in the developer conveying device 22Y, which will be described later, to the surface by the magnetic force generated by the magnet roller, thereby pumping the Y developer from the developer conveying device 22Y. Then, the Y developer conveyed toward the developing area as the developing sleeve 24Y rotates, the doctor blade 25Y having the tip opposed to the surface of the developing sleeve 24Y with a predetermined gap, and the sleeve A doctor gap formed between the surface and the surface is entered. At this time, the layer thickness on the sleeve is regulated to substantially the same thickness as the doctor gap. When the developing sleeve 24Y is rotated and conveyed to the vicinity of the developing area facing the photoconductor 11Y, it receives a magnetic force of a developing magnetic pole (not shown) of the magnet roller and rises on the sleeve to become a magnetic brush. .

  For example, a developing bias having the same polarity as the charging polarity of the toner is applied to the developing sleeve 24Y by a bias supply unit (not shown). As a result, in the development region, non-development in which Y toner is electrostatically moved from the non-image portion side to the sleeve side between the surface of the development sleeve 24Y and the non-image portion (uniformly charged portion = background portion) of the photoreceptor 11Y. Potential acts. Further, a developing potential for electrostatically moving Y toner from the sleeve side toward the electrostatic latent image acts between the surface of the developing sleeve 24Y and the electrostatic latent image on the photoreceptor 11Y. The Y toner in the Y developer is transferred to the electrostatic latent image by the action of the developing potential, so that the electrostatic latent image on the photoreceptor 11Y is developed into the Y toner image.

  The Y developer that has passed through the developing area as the developing sleeve 24Y rotates is separated from the developing sleeve 24Y due to the influence of the repulsive magnetic field formed between the repelling magnetic poles provided in the magnet roller (not shown). The developer returns to the developer conveying device 22Y.

  The developer conveying device 22Y includes two first screw members 26Y, a second screw member 32Y, a partition wall interposed between the two screw members, a toner concentration detection sensor 45Y including a magnetic permeability sensor, and the like. The partition wall divides the first transport chamber, which is a developer transport section, in which the first screw member 26Y is accommodated, and the second transport chamber, which is a developer transport section in which the second screw member 32Y is accommodated. In the region facing both ends of the screw member in the axial direction, both transfer chambers are communicated with each other through an opening (not shown).

  The first screw member 26Y and the second screw member 32Y as the agitating / conveying members are respectively provided with a rod-like rotary shaft member whose both ends are rotatably supported by a bearing (not shown), and a spiral projection on the peripheral surface thereof. And a spiral blade. Then, as it is driven to rotate by a driving means (not shown), the Y developer is conveyed in the rotation axis direction by the spiral blade.

  In the first transport chamber in which the first screw member 26Y is accommodated, the Y developer is transported from the near side to the far side in the direction orthogonal to the drawing surface as the first screw member 26Y is driven to rotate. . And if it conveys to the edge part vicinity of the back | inner side of casing 21Y, it will approach into a 2nd conveyance chamber via the opening which is not provided in the partition wall.

  The above-described developing unit 23Y is formed above the second transfer chamber in which the second screw member 32Y is accommodated, and the second transfer chamber and the developing unit 23Y communicate with each other in the entire area of the opposing part. ing. As a result, the second screw member 32Y and the developing sleeve 24Y disposed obliquely above the second screw member 32Y face each other while maintaining a parallel relationship. In the second transport chamber, the Y developer is transported from the back side to the near side in the direction orthogonal to the drawing sheet as the second screw member 32Y is driven to rotate. In this transport process, the Y developer around the rotation direction of the second screw member 32Y is appropriately pumped up to the developing sleeve 24Y, and the developed Y developer is appropriately collected from the developing sleeve 24Y. Then, the Y developer transported to the vicinity of the near end of the second transport chamber in the drawing returns to the first transport chamber through an opening (not shown) provided in the partition wall.

A toner concentration detection sensor 45Y as a toner concentration detection means including a magnetic permeability sensor is fixed to the lower wall of the first conveyance chamber, and the toner concentration of the Y developer conveyed by the first screw member 26Y is lowered. And outputs a voltage according to the detection result. A control unit (not shown) has a difference value Tn of + (plus) based on a difference value Tn (= Vt _ref −Vt) between the output voltage value Vt from the toner density detection sensor 45Y and the toner density control reference value Vt _ref . In this case, it is determined that the toner density is sufficiently high and the toner is not replenished. When the difference value Tn is − (minus), the Y toner replenishing device (not shown) is set so that the output value Vt becomes the target output value Vt _ref. Is driven to supply an appropriate amount of Y toner into the first transfer chamber. As a result, the toner concentration of the Y developer, which has been lowered with the development, is recovered.

  The Y toner image formed on the photoreceptor 11Y is primarily transferred onto the intermediate transfer belt 51 at a Y primary transfer nip described later. The transfer residual toner that has not been primarily transferred onto the intermediate transfer belt 51 adheres to the surface of the photoreceptor 11Y after passing through the primary transfer process.

  The drum cleaning device 14Y cantilever-supports a cleaning blade 15Y made of, for example, polyurethane rubber, and the free end thereof is brought into contact with the surface of the photoreceptor 11Y. In addition, the brush tip side of the brush roller 16Y, which includes a rotating shaft member that is driven to rotate by a driving means (not shown) and an infinite number of conductive brushes erected on the peripheral surface thereof, is brought into contact with the photoreceptor 11Y. Yes. The transfer residual toner is scraped off from the surface of the photoreceptor 11Y by the cleaning blade 15Y and the brush roller 16Y. A cleaning bias is applied to the brush roller 16Y via a metal electric field roller 17Y that is in contact with the brush roller 16Y, and the tip of the scraper 18Y is pressed against the electric field roller 17Y. The transfer residual toner scraped off from the photoconductor 11Y by the cleaning blade 15Y and the brush roller 16Y passes through the brush roller 16Y and the electric field roller 17Y, and then is scraped off from the electric field roller 17Y by the scraper 18Y and is placed on the recovery screw 19Y. Fall. Then, after the recovery screw 19Y is driven to rotate, the recovery screw 19Y is discharged out of the casing, and then returned to the developer transport device 22Y via a toner recycling transport means (not shown).

  The surface of the photoreceptor 11Y from which the transfer residual toner has been cleaned by the drum cleaning device 14Y is neutralized by the neutralizing device 13Y including a neutralizing lamp and then uniformly charged again by the charging member 14Y.

  Although the Y process unit 10Y has been described in detail, the process units (10C, M, K) of other colors have the same configuration as that of Y except that the color of the toner to be used is different. .

  In FIG. 2 shown above, the photoconductors 11Y, 11C, 11M, and 11K of the process units 10Y, 10C, 10M, and 10K are in contact with the upper stretched surface of the intermediate transfer belt 51 that is moved endlessly in the clockwise direction. Rotating to form primary transfer nips for Y, C, M, and K. On the back side of the primary transfer nips for these Y, C, M, and K, the above-described primary transfer rollers 55Y, 55C, 55M, and 55K are in contact with the back surface of the intermediate transfer belt 51. A primary transfer bias having a polarity opposite to the charging polarity of the toner is applied to each of the primary transfer rollers 55Y, 55C, 55M, 55K by a bias supply unit (not shown). Due to this primary transfer bias, a primary transfer electric field is formed in the primary transfer nips for Y, C, M, and K to electrostatically move the toner from the photoreceptor side to the belt side. The Y, C, M, and K toner images formed on the photoreceptors 11Y, 11C, 11M, and 11K are primary for Y, C, M, and K as the photoreceptors 11Y, 11C, 11M, and 11K rotate. When entering the transfer nip, primary transfer is performed by sequentially superimposing on the intermediate transfer belt 51 by the action of the primary transfer electric field and nip pressure. As a result, a four-color superimposed toner image (hereinafter referred to as a four-color toner image) is formed on the front surface (loop outer peripheral surface) of the intermediate transfer belt 51. Instead of the primary transfer rollers 55Y, 55C, 55M, 55K, a conductive brush to which a primary transfer bias is applied, a non-contact type corona charger, or the like may be employed.

  A secondary transfer roller 56 as an abutting member is disposed below the intermediate transfer belt 51. The secondary transfer roller 56 is rotated counterclockwise in the drawing by a driving means (not shown) while the intermediate transfer belt 51 A secondary transfer nip is formed in contact with the front surface. A secondary transfer backup roller 53 wraps around the intermediate transfer belt 51 on the back side of the secondary transfer nip.

  A secondary transfer bias having the same polarity as the toner charging polarity is applied to the secondary transfer backup roller 53 by a secondary transfer power source (not shown). On the other hand, the secondary transfer roller 56 that is a contact member that is in contact with the front surface of the belt and forms a secondary transfer nip is grounded. As a result, a secondary transfer electric field is formed between the secondary transfer backup roller 53 and the secondary transfer roller 56. The four-color toner image formed on the front surface of the intermediate transfer belt 51 enters the secondary transfer nip as the intermediate transfer belt 51 moves endlessly.

  In FIG. 1 described above, the paper feeding device 200 is fed with a paper feeding cassette 201 for storing the recording paper P, and a paper feeding roller 202 for feeding the recording paper P stored in these paper feeding cassettes 201 out of the cassette. A plurality of separation roller pairs 203 for separating the recording paper P one by one, a plurality of conveyance roller pairs 205 for conveying the separated recording paper P along the delivery path 204, and the like are provided. The sheet feeding device 200 is disposed directly below the printer unit 1 as shown in the figure. The feeding path 204 of the paper feeding device 200 is connected to the paper feeding path 70 of the printer unit 1. As a result, the recording paper P delivered from the paper feed cassette 201 of the paper feed device 200 is sent into the paper feed path 70 of the printer unit 1 via the feed path 204.

  Near the end of the paper feed path 70 of the printer unit 1, a registration roller pair 71 is disposed as a feeding means, and the recording paper P sandwiched between the rollers is converted into a four-color toner image on the intermediate transfer belt 51. The sheet is fed into the secondary transfer nip at a timing that can be synchronized. In the secondary transfer nip, the four-color toner images on the intermediate transfer belt 51 are collectively transferred to the recording paper P due to the influence of the secondary transfer electric field and the nip pressure, and combined with the white color of the recording paper P, Become. The recording paper P on which the full-color image is formed in this way is separated from the intermediate transfer belt 51 when discharged from the secondary transfer nip.

  On the left side of the secondary transfer nip in the figure, a conveyor belt unit 75 is provided that moves the endless paper conveyor belt 76 endlessly in the counterclockwise direction in the figure while being stretched by a plurality of stretching rollers. . The recording paper P separated from the intermediate transfer belt 51 is transferred to the upper stretched surface of the paper conveying belt 76 and conveyed toward the fixing device 80.

  The recording paper P sent into the fixing device 80 is sandwiched in a fixing nip formed by a heating roller 81 containing a heat source such as a halogen lamp (not shown) and a pressure roller 82 pressed toward the heating roller 81. The full color image is sent to the outside of the fixing device 80 while being fixed on the surface by being heated while being pressurized.

  On the surface of the intermediate transfer belt 51 after passing through the secondary transfer nip, a slight amount of secondary transfer residual toner that has not been transferred to the recording paper P adheres. The secondary transfer residual toner is removed from the belt by a belt cleaning device 57 that is in contact with the front surface of the intermediate transfer belt 51.

  A switchback device 85 is disposed below the fixing device 80. When the recording paper P discharged from the fixing device 80 reaches the conveyance path switching position by the swingable switching claw 86, depending on the swing stop position of the switching claw 86, the paper discharge roller pair 87 or the switchback device. Sent to 85. When the paper is sent toward the paper discharge roller pair 87, the paper is discharged to the outside of the apparatus and then stacked in the form of the paper discharge tray 3.

  On the other hand, when it is sent toward the switchback device 85, it is turned upside down by the switchback conveyance by the switchback device 85 and then conveyed toward the registration roller pair 71 again. Then, it again enters the secondary transfer nip, and a full-color image is formed on the other side.

  The recording paper P manually fed onto the manual feed tray 2 provided on the side surface of the housing of the printer unit 1 passes through the manual feed roller 72 and the manual separation roller pair 73 and then toward the registration roller pair 71. Sent.

  When copying a document with the copying machine according to the present embodiment, first, the document is set on the document table 401 of the automatic document feeder 400. Alternatively, the automatic document feeder 400 is opened, a document is set on the contact glass 301 of the scanner 300, and the automatic document feeder 400 is closed and pressed. Thereafter, when a start switch (not shown) is pressed, when the document is set on the automatic document feeder 400, the document is sent into the contact glass 301. Then, the scanner 300 is driven and reading scanning by the first traveling body 303 and the second traveling body 304 is started. At substantially the same time, driving of the transfer unit 50 and each color process unit 10Y, C, M, K starts. Furthermore, the feeding of the recording paper P from the paper feeding device 200 is also started. When recording paper P not set in the paper feed cassette 201 is used, the recording paper P set on the manual feed tray 2 is sent out.

On the right side of the K process unit 10K in the drawing, an optical sensor 69 as optical detection means is disposed so as to face the front surface of the intermediate transfer belt 51 with a predetermined gap. .
FIG. 4 is a schematic sectional view of the optical sensor 69. As shown in the figure, the optical sensor 69 mainly receives a light emitting element 311 as a light emitting means, a regular reflection light receiving element 312 as a first light receiving means for receiving specular reflection light, and diffuse reflection light. And a diffuse reflection light receiving element 313 as a second light receiving means. Light emitted from the light emitting element 311 is emitted toward the surface of the intermediate transfer belt 51. Then, regular reflection light regularly reflected by the surface of the intermediate transfer belt 51 and the toner patch transferred to the surface is received by the regular reflection light receiving element 312, and a voltage corresponding to the amount of received light is output. Further, the diffuse reflection light diffusely reflected by the surface of the intermediate transfer belt 51 and the toner patch transferred to the surface is received by the diffuse reflection light receiving element 313, and a voltage corresponding to the amount of received light is output.

  FIG. 5 is a block diagram showing the main part of the electric circuit of the copying machine. In FIG. 1, a control unit 100 as a control means includes a CPU (Central Processing Unit) 101 as a calculation means, a nonvolatile RAM (Random Access Memory) 102 as a data storage means, a ROM (Read Only Memory) 103 as a data storage means, and the like. Have. The control unit 100 is electrically connected to process units 10Y, 10M, 10C, 10K, an optical writing unit 68, a transfer unit 50, an optical sensor unit 69, and the like. And the control part 100 controls these various apparatuses based on the control program memorize | stored in RAM102 or ROM103.

  The control unit 100 also controls image forming conditions for forming an image. Specifically, the control unit 100 performs control to individually apply a charging bias to each charging member in the process units 1Y, M, C, and K. As a result, the photoreceptors 2Y, 2M, 2C, and 2K of the respective colors are uniformly charged to the Y, M, C, and K drum charging potentials. The control unit 100 individually controls the powers of the four semiconductor lasers corresponding to the process units 1Y, M, C, and K of the optical writing unit 68. In addition, the control unit 100 performs control to apply the developing bias of the developing bias values for Y, M, C, and K to the developing rollers in the process units 1Y, M, C, and K. As a result, a developing potential for electrostatically moving the toner from the sleeve surface side to the photosensitive member side acts between the electrostatic latent images of the photosensitive members 2Y, 2M, 2C, and 2K and the developing sleeve. Develop.

In addition, the control unit 100 executes process control as image density control for optimizing the image density of each color when the power is turned on or every time a predetermined number of prints are performed.
FIG. 6 is a control flow chart of process control. Note that the process control flow of FIG. 6 is a process flow chart of process control when power is turned on.
First, when the power is turned on and the apparatus is started up (S1), the control unit 100 calibrates the optical sensor 69 (S2). Specifically, the light emission intensity of the light emitting element 311 is adjusted so that the output of the regular reflection light receiving element 312 of the optical sensor 69 becomes a predetermined value (4 V). The optical sensor 69 need not be calibrated.

  Next, the control unit 100 acquires the output value Vt of the toner density detection sensor 45 (S3), grasps the toner density in the developing device for each color, and then creates a gradation pattern as shown in FIG. Each color is automatically formed at a position on the intermediate transfer belt 51 facing each optical sensor 69 (S4). Each color gradation pattern is composed of about five toner patches with different toner adhesion amounts, and has a Bk color gradation pattern and a C color gradation pattern at 14.4 mm in the sub-scanning direction and a patch interval of 5.6 mm. , M color gradation pattern and Y color gradation pattern are formed on the intermediate transfer belt 51 in this order. In the gradation pattern, the charging and developing bias conditions are changed for each toner patch, and the exposure conditions are formed with a predetermined value (full exposure in which the photosensitive member is sufficiently discharged). The setting of the developing bias and charging bias of each toner patch of the gradation pattern will be described later. The gradation pattern of each color on the intermediate transfer belt is optically detected by the optical sensor 69 (S5).

Next, the toner adhesion amount using the output value obtained by detecting each toner patch of the gradation pattern of each color and the adhesion amount calculation algorithm constructed based on the relationship between the adhesion amount and the output value of the light receiving element Conversion to (image density) is performed.
In this embodiment, as described in Japanese Patent Application Laid-Open No. 2004-354623, the toner adhesion amount is calculated using regular reflection light regularly reflected by the toner patch and diffuse reflection light. By calculating the toner adhesion amount using the regular reflection light and the diffuse reflection light, the detection range of the high adhesion amount can be expanded as compared with the case where the toner adhesion amount is calculated using only the regular reflection light. Further, by using the toner adhesion amount calculation algorithm described in Japanese Patent Application Laid-Open No. 2004-354623, the output of the light emitting element and the light receiving element changes due to temperature change, deterioration with time, etc. Even if the output of the toner changes, an accurate toner adhesion amount can be obtained.
The toner adhesion amount calculation algorithm described in Japanese Patent Application Laid-Open No. 2004-354623 will be briefly described. First, from the output value of the regular reflection light receiving element 312 and the output value of the diffuse reflection light receiving element 313 when each toner patch is detected, A sensitivity correction coefficient α which is the minimum value of the ratio between the output value of the regular reflection light receiving element 312 and the output value of the diffuse reflection light receiving element 313 when each toner patch is detected is calculated. Next, the output value of the regular reflection light receiving element 312 is decomposed into a regular reflected light component and a diffuse reflected light component using the sensitivity correction coefficient α. Next, the ratio of the output value (background output value) when the surface of the intermediate transfer belt is detected and the regular reflection component is taken, and the regular reflection component is converted into a normalized value β from 0 to 1. Next, using the value obtained by multiplying the output value of the diffuse reflection light receiving element 313 by the normalized value β, the diffuse reflection light component from the surface of the intermediate transfer belt is removed from the output value of the diffuse reflection light receiving element 313, and the toner patch is obtained. The diffuse reflection light component from is extracted. Next, a sensitivity correction coefficient η for performing sensitivity correction of the output value of the diffuse reflection light receiving element 313 is calculated using the normalized value β and the diffuse reflection light component. The diffuse reflection light component from the toner extracted from the output value of the diffuse reflection light receiving element 313 is multiplied by the sensitivity correction coefficient η to correct (calibrate) the output value of the diffuse reflection light receiving element 313. Then, the toner adhesion amount of each toner patch is uniquely obtained from the output value of the diffuse reflection light receiving element 313 corrected (calibrated) with the sensitivity correction coefficient η.
Even if the output value of the light receiving element fluctuates due to a change in characteristics of the light emitting element or light receiving element due to temperature change, deterioration with time, etc., the output value of each light receiving element is corrected (calibrated) with the sensitivity correction coefficient α and sensitivity correction coefficient η Thus, the relationship between the output value of the light receiving element and the toner adhesion amount can be corrected to a unique relationship. Thereby, a good toner adhesion amount can be detected with the optical sensor over time.

  When the toner adhesion amount of each toner patch is detected using the above-described toner adhesion amount calculation algorithm, the relationship between the toner adhesion amount of each toner patch and each development potential when each toner patch is created is shown in FIG. Then, a linearly approximated development potential-toner adhesion amount straight line (y = ax + b) is obtained for each color. The development γ (slope a) and development start voltage Vk (intercept b) are calculated for each color from the development potential-toner adhesion amount straight line (S6).

Next, the control unit 100 specifies a development potential necessary for obtaining a predetermined target adhesion amount based on the development γ, and then calculates a development bias Vb that matches the development potential (S7). The target adhesion amount is determined by the degree of coloring of the toner pigment, but is generally 0.4 to 0.6 [mg / cm ² ]. Further, the control unit 100 determines the charging bias Vc based on the calculated developing bias Vb, and stores the developing bias Vb and the charging bias Vc in a nonvolatile storage unit such as the RAM 102. The charging bias Vc is generally set higher by about 100 to 200 [V] than the developing bias Vb. The developing bias Vb is set in the range of 350 to 700 [V]. That is, even if the calculated development bias is 1 [kV], the development bias Vb is set to 700 [V]. This is because if the setting value of the developing bias exceeds 700 [V], the capacity of the power supply may be exceeded, and the bias may not be stably maintained. If the setting value of the developing bias is less than 350 [V], the charging bias Since the set value becomes too low, the charging tends to be non-uniform, and an abnormal image called “afterimage” that may appear in the next image may occur.

After calculating the development bias Vb, the control unit 100 corrects the toner density control reference value Vt _ref using the development γ and the output value Vt of the toner density detection sensor 45 acquired in S3 (S8). First, a difference value Δγ (Δr = calculated development γ−target development γ) between the target development γ and the calculated development γ is calculated. The target development γ is, for example, 1.0 [(mg / cm ² ) / KV] (when the development start voltage Vk is 0 [V] and the development potential is 1 [kV], the toner adhesion amount is 1.0 [ mg / cm ² ] That is, if the development start voltage Vk = 0 V, the target adhesion amount is 0.5 [mg / cm ² ], and the photosensitive member potential Vl after exposure is 50 V, the target development is achieved. (The developing bias Vb calculated from γ is 550 V.)

When the calculated Δγ is outside the predetermined range, the calculated developing bias Vb may exceed the above-described setting range during the next developing bias adjustment, and therefore the toner density control reference value Vt _ref is calculated. Thus, the development γ is made closer to the target development γ until the next process control. If the toner density control reference value Vt _ref is corrected so that the development γ approaches the target development γ, the adhesion amount does not become the target adhesion amount even if an image is formed with the calculated development bias. Therefore, the toner replenishment control is performed so that the toner density in the developing device gradually becomes the target toner density, so that the development γ does not change suddenly. Therefore, even if the toner density control reference value Vt _ref is corrected, the target adhesion amount can be initially set with the calculated developing bias. Then, although gradually deviating from the target adhesion amount, the correction amount of the toner density control reference value Vt _ref is such that the adhesion amount greatly deviates from the target adhesion amount even when image formation is performed with the calculated development bias. Since the correction amount is not set, the image is not greatly deteriorated. However, the output value Vt of the gradation pattern creation of the toner density detection sensor 45 is, in a case where substantially different from the toner density control standard value Vt _ref, the results in the correction of the toner density control standard value Vt _ref, On the contrary, since there is a possibility of deviating from the target development γ, the output value Vt of the toner density detection sensor 45 at the time of gradation pattern creation and the output value Vt of the toner density detection sensor 45 at the time of gradation pattern creation are In consideration of the relationship, it is determined whether or not to correct the toner density control reference value Vtref.
As a specific example, when Δγ ≧ 0.30 [(mg / cm ² ) / kV] and Vt−V _tref ≧ −0.2V, the toner density control reference value V _tref is decreased by 0.2V. Thus, correction is performed to lower the toner density from the present time. Further, when Δγ ≦ −0.30 [(mg / cm ² ) / KV] and Vt−V _tref ≧ 0.2 V, the toner density control reference value V _tref is increased by 0.2 V, and compared with the present time. Perform correction to increase toner density. Further, when −0.30 [(mg / cm ² ) / KV] <Δγ <0.30 [(mg / cm ² ) / KV], the toner density control reference value V _tref is not corrected.
The above is the control flow of process control.

  Next, a developing bias and a charging bias when forming each toner patch of a gradation pattern will be described based on Examples 1 to 3.

ここで、べた部露光後電位：Ｖｌとは露光を行った後の感光体電位であり、感光体の特性に依存する値となる。 [Example 1]
First, a developing bias and a charging bias when forming each toner patch having a gradation pattern in the first embodiment will be described.
In the first embodiment, some of the toner patches of the gradation pattern are imaged with a predetermined developing bias, and the remaining toner patches are calculated based on the developing bias Vb determined by the previous process control. Create an image with the same development bias.
This will be specifically described below.
First, the development bias Vb obtained by executing the previous process control stored in a nonvolatile storage means such as a RAM is acquired. Next, the maximum development potential: PotMax is obtained from the obtained development bias from the following formula 1.

Here, the solid portion post-exposure potential: Vl is the photoconductor potential after exposure and is a value depending on the characteristics of the photoconductor.

ここで、ＶＰｂは階調パターンの各トナーパッチの現像バイアスを表し、ｎは、前回のプロセスコントロールを実行して得られた現像バイアスＶｂに基づいて作像されるトナーパッチの番数である。ｍは前回のプロセスコントロールを実行して得られた現像バイアスＶｂに基づいて作像されるトナーパッチ数である。階調パターンのトナーパッチのうち、４つが前回のプロセスコントロールを実行して得られた現像バイアスＶｂに基づいて作像される。 Next, the development bias of each toner patch imaged with the development bias based on the development bias Vb determined by the previous process control in the gradation pattern from the maximum development potential PotMax is calculated from Equation 2.

Here, VPb represents the development bias of each toner patch of the gradation pattern, and n is the number of toner patches that are formed based on the development bias Vb obtained by executing the previous process control. m is the number of toner patches formed based on the developing bias Vb obtained by executing the previous process control. Of the toner patches of the gradation pattern, four images are formed based on the developing bias Vb obtained by executing the previous process control.

ここで、ｋは、予め決められた現像バイアスで作像されるトナーパッチ番数である。ＶＰｂ初期値は、現像γが高い場合でも、トナー付着量が、先の図８に示すセンサの高感度領域、かつ、現像ポテンシャルと付着量との関係が直線関係にある領域に必ず入る現像バイアスであり、予め実験などにより求められた値であり、このＶＰｂ初期値は、ＲＡＭなどの不揮発性の記憶手段に記憶されている。 Further, the development bias of the toner patch formed with a predetermined development bias can be expressed as follows.

Here, k is the number of toner patches formed with a predetermined development bias. The initial value of VPb is a development bias in which the toner adhesion amount always enters the high sensitivity region of the sensor shown in FIG. 8 and the region where the relationship between the development potential and the adhesion amount has a linear relationship even when the development γ is high. The VPb initial value is stored in a non-volatile storage means such as a RAM.

上記地肌ポテンシャル係数、地肌ポテンシャルオフセットは、地汚れが生じないように、設定されるものである。 Next, by using the calculated developing bias VPb, a charging bias when forming each toner patch in the gradation pattern is calculated using the following formula.

The background potential coefficient and the background potential offset are set so as not to cause background contamination.

  The obtained development bias and charging bias are stored in a nonvolatile storage means such as a RAM. Then, a gradation pattern is created using this value.

Next, the effect of Example 1 is demonstrated concretely based on FIG. 9, FIG. FIG. 9 is a diagram for explaining the adhesion amount of the gradation pattern in Example 1 when there is not much difference between the development γ at the previous process control and the development γ at the current process control. . FIG. 10 is a diagram for explaining the adhesion amount of the gradation pattern in the embodiment 1 when the development γ at the current process control is significantly larger than the development γ at the previous process control. .
In FIG. 9 and FIG. 10, symbol ■ indicates a toner patch formed based on the developing bias determined in the previous process control, and symbol ◆ indicates a toner patch imaged with a predetermined developing bias. Is shown.
As shown by symbol ■ in FIG. 9, if there is not much difference between the development γ at the previous process control and the development γ at the current process control, the development based on the development bias Vb determined by the previous process control. Each toner pattern imaged with a bias can all fall within the valid data range. The effective data range is a high sensitivity region of the optical sensor and a region where the relationship between the development potential and the adhesion amount data is a straight line. Therefore, even with a small number of toner patches, the number of toner patches detected by the optical sensor increases, and characteristic information such as development γ can be obtained with high accuracy, and the development bias Vb and the like can be adjusted with high accuracy.

  However, in the case of each toner pattern imaged with the development bias based on the development bias Vb determined in the previous process control, the current development γ is significantly larger than the development γ in the previous process control. Of the toner patterns imaged with the developing bias based on the developing bias Vb determined in the previous process control, only the toner patch on the low adhesion amount side may fall within the valid data range. In particular, in an apparatus in which the capacity of the developer in the developing device is reduced for downsizing, the characteristics of the developer are likely to change and the development γ is likely to fluctuate significantly.

  However, in the first embodiment, as shown in FIG. 10, when the value of development γ at the current process control is significantly larger than the value of development γ at the previous process control, Of the toner patterns formed with the developing bias based on the developing bias Vb determined by the process control, only the toner pattern on the low adhesion amount side falls within the valid data range. On the other hand, as shown by the symbol ◆ in FIG. 10, the toner patch imaged with a predetermined development bias has the development γ value at the current process control changed to the development γ value at the previous process control. On the other hand, even if it is significantly large, it is within the range of valid data. Therefore, even if the value of development γ at the time of the current process control is significantly larger than the value of development γ at the time of the previous process control, two or more toner patches are included in the valid data range. be able to. As a result, even when the value of development γ at the current process control is significantly larger than the value of development γ at the previous process control, the development γ and the development start voltage Vk can be obtained. The developing bias Vb can be calculated.

  Further, as shown in FIG. 11, when the value of development γ at the current process control is significantly smaller than the value of development γ at the previous process control, each toner patch of the gradation pattern Will be concentrated on the low adhesion amount side. As described above, when the adhesion amount of each toner patch is concentrated, it becomes easy to be affected by variations in the toner adhesion amount, and the accuracy of the development γ may be deteriorated. For this reason, when the development γ is small, the number of toner patches that form an image with a fixed development bias that increases the toner adhesion amount (high density) may be increased.

  As shown in FIG. 12, as a toner patch produced with a predetermined fixed bias, when the development γ is large, the development bias Vpb (k1) is such that the toner patch adhesion amount falls within the valid data range. A toner patch to be imaged and a toner patch to be imaged with a developing bias Vpb (k2) such that when the development γ is small, the adhesion amount of the toner patch falls within the valid data range and becomes a high adhesion amount. As described above, the development bias Vb can be calculated even when the development γ becomes significantly larger than that in the previous process control, and as shown in FIG. When γ is significantly smaller than that of the previous process control, one toner patch in the gradation pattern is applied to the high adhesion amount in the effective data range. It can be. Therefore, the influence of variation in the toner adhesion amount can be reduced, and deterioration in accuracy of the development γ can be suppressed.

Next, a specific example of Example 1 will be described.
Number of toner patches in gradation pattern: 5, number of toner patches formed with a predetermined development bias: k = 1, development bias Vb: 550 V as a result of the previous process control, solid portion exposure potential: Vl = 50 When [V] and VPb initial value (k) = 520 [V], the maximum development potential: PotMax = 550−50 = 500 [V].

Further, the development biases of the toner patches formed based on the development bias Vb obtained by executing the previous process control are as follows.
VPb (1) = PotMax × 1/4 + Vl = 500 × 1/4 + 50 = 175 [V]
VPb (2) = PotMax × 2/4 + Vl = 500 × 2/4 + 50 = 300 [V]
VPb (3) = PotMax × 3/4 + Vl = 500 × 3/4 + 50 = 425 [V]
VPb (4) = PotMax × 4/4 + Vl = 500 × 4/4 + 50 = 550 [V]

When the background potential coefficient is 0 and the background potential offset is 200 V, each charging bias when forming a toner patch formed based on the development bias Vb obtained by executing the previous process control is ,
VPc (1) = 175 + 200 = 375 [V]
VPc (2) = 300 + 200 = 500 [V]
VPc (3) = 425 + 200 = 625 [V]
VPc (4) = 550 + 200 = 750 [V]
It becomes.

In addition, the charging bias when forming a toner patch formed with a predetermined developing bias is:
VPc (k) = 520 + 200 = 720 [V]

A gradation pattern was created with the above development bias and charging bias, and development γ was calculated. Development γ = 0.86 [(mg / cm ² ) / kV] Development start voltage Vk = 0.046 [kV] ] Was requested. Further, the maximum development potential is obtained using the following formula.

When the target adhesion amount is 0.45 [mg / cm ² ] and the development γ obtained from the process control result and the development start voltage Vk are substituted, the maximum image potential = 0.567. From development bias: Vb = maximum development potential + solid part post-exposure potential: Vl, development bias Vb = 617 [V] is obtained.

In this specific example, when the development γ deviates significantly from the target development γ, the toner density in the developing device is adjusted so that the development γ approaches the target development γ. Therefore, the initial value (k) of VPb, which is a development bias that always falls within the detection range of the optical sensor within the fluctuation range of development γ, can be set high. In addition, since the upper limit value of the developing bias Vb is 700 V, even if the developing γ fluctuates significantly from the low side to the high side, the four images formed based on the developing bias Vb determined by the previous process control are used. Of the toner patches, at least two points can be included in the detection range of the optical sensor. This is because the development bias of the four toner patches is 175 V, 350 V, 525 V, and 700 V when the development bias Vb determined in the previous process control is the upper limit of 700 V, which is higher than the VPb initial value (k) 520 V. This is because there are two low development biases, so that the toner patch formed at 175V and 350V surely falls within the detection range of the optical sensor. Therefore, in this specific example, even if there is no VPb initial value, two points are surely entered in the detection range of the optical sensor, so that the development γ is calculated even if the development γ is significantly larger than the previous time. be able to. However, by providing a toner patch that forms an image with the initial value of VPb, the development γ can be within the detection range of the three optical sensors when the development γ is significantly larger than the previous time, and the development γ is accurately calculated. be able to.
In this specific example, the VPb initial value (k) is set to 520 [V], but may be smaller than this. However, by setting the VPb initial value (k) as high as possible, when the development γ greatly fluctuates from the high side to the low side, the toner pattern formed with the VPb initial value (k) Can be on the side.

[Example 2]
Next, the developing bias and the charging bias when forming each toner patch of the gradation pattern in the second embodiment will be described.
In the second embodiment, some of the gradation pattern toner patches are imaged with a development bias determined based on the environment (temperature and humidity), and the remaining toner patches are determined with the previous process control. Based on Vb, an image is formed with the calculated developing bias.

FIG. 13 is a diagram illustrating the relationship between the development potential and the toner adhesion amount in each environment.
Compared with the MM environment (standard environmental conditions: 23 [° C.], 50 [% RH]), the development γ is higher in the case of (high temperature and high humidity environment: 27 [° C.], 80 [% RH]). This is because the humidity in the developing device is high, so that there is a lot of moisture around the toner, and the charge of the toner is likely to be released due to the influence of the moisture. As a result, the toner charge amount decreases, and the development γ increases. On the other hand, in the case of the LL environment (low temperature and low humidity environment: 10 [° C.], 15 [% RH]), since the amount of water in the developing device is small, the toner charge is difficult to be released and the charge amount increases. Therefore, compared with the MM environment (standard environmental conditions: 23 [° C.], 50 [% RH]), the development γ becomes lower.
As described above, since development γ varies according to changes in the environment, if the environment at the time of the previous process control execution and the environment at the time of the current process control execution are significantly different, The development γ and the development γ when the process control is executed this time are significantly different. As a result, as described above, among the toner patches that are imaged with the developing bias calculated in the previous process control, only the toner patch on the low adhesion amount side falls within the effective data range, or the toner patch adhesion amount. Will concentrate on the low adhesion amount side.
Therefore, in the second embodiment, the development bias for forming at least one toner patch in the gradation pattern is determined based on the environment.

  In the same manner as in the first embodiment, the control unit 100 performs development for forming a toner patch formed with a development bias based on the development bias Vb obtained by executing the previous process control in the gradation pattern. The bias Vpb (n) and the charging bias Vpc (n) are determined.

環境補正係数は、取得した温湿度センサ１０４の値によって変化する係数であり、例えば、温湿度センサの出力値と環境補正係数とを対応させたＬＵＴ（ルックアップテーブル）をＲＡＭなどの不揮発性の記憶手段に記憶しておき、取得した温湿度センサ１０４の値とＬＵＴとに基づいて、計算に用いる環境補正係数を決定する。
また、環境補正係数を乗じずに、温湿度センサの出力値とこの出力値に対応させたＶｐｂ（ｅ）とからなるＬＵＴを設けて、温湿度センサの出力値から、計算せずに、現像バイアスＶｂｐ（ｅ）を決定してもよい。 Next, the control unit 100 acquires the value of the temperature / humidity sensor 104, and develops a bias voltage Vpb (e) for creating a toner patch imaged with a development bias based on the environment from the following equation. To decide.

The environmental correction coefficient is a coefficient that varies depending on the acquired value of the temperature / humidity sensor 104. For example, an LUT (look-up table) in which the output value of the temperature / humidity sensor and the environmental correction coefficient are associated with each other is a nonvolatile memory such as a RAM. Based on the acquired value of the temperature / humidity sensor 104 and the LUT, the environment correction coefficient used for the calculation is determined.
Further, an LUT composed of the output value of the temperature / humidity sensor and Vpb (e) corresponding to the output value is provided without multiplying the environmental correction coefficient, and development is performed without calculating from the output value of the temperature / humidity sensor. The bias Vbp (e) may be determined.

  When the control unit 100 determines the development bias Vpb (e) for forming the toner patch formed with the development bias based on the environment, the control unit 100 determines a predetermined value ( 100 to 200 [V]) is added to determine a charging bias Vpc (e) for forming a toner patch formed with a development bias based on the environment.

  When the environment is the LL environment (low temperature and low humidity environment: 10 [° C.], 15 [% RH]), the development γ moves in the direction of arrow M in FIG. Since the value of development γ is predicted to be smaller than γ, development bias Vpb for creating a toner patch imaged with a development bias based on the environment by increasing the value of the environmental correction coefficient. Increase (e). As a result, even if the value of development γ is significantly smaller than the previous value due to the environment, the toner adhesion amount of the toner patch formed with the development bias based on the environment becomes a high adhesion amount. Even if the toner patches formed based on the calculated development bias are concentrated on the low adhesion amount side, it is possible to suppress deterioration in accuracy of the development γ.

  Further, when the environment is an HH environment (27 [° C.], 80 [% RH]), the development γ moves in the direction of arrow N in FIG. 14 and is compared with the development γ when the previous process control is executed. Since the value of development γ is predicted to increase, the development bias Vpb (e) for forming a toner patch formed with a development bias based on the environment by reducing the value of the environmental correction coefficient. Make it smaller. As a result, even if the value of development γ is significantly smaller than the previous value depending on the environment, the amount of toner patch deposited with a development bias based on the environment can be kept within the effective data range. Therefore, even if only one of the toner patches formed based on the development bias calculated in the previous process control falls within the valid data range, the development γ can be calculated.

  In Example 1, in order to cope with the case where the development γ is significantly increased and the case where the development γ is significantly reduced, at least two fixed development biases determined in advance are used. Although it is necessary to set a toner patch for forming an image, in the second embodiment, one toner patch corresponds to both when the development γ is greatly increased and when the development γ is significantly decreased. be able to. Therefore, the number of toner patches can be reduced as compared with the first embodiment.

[Example 3]
Next, the developing bias and the charging bias when forming each toner patch of the gradation pattern in the embodiment 3 will be described.
In the third exemplary embodiment, some of the toner patches of the gradation pattern are imaged with a developing bias calculated based on the change with time of the developer, and the remaining toner patches are determined with the previous process control. Based on Vb, an image is formed with the calculated developing bias.

FIG. 15 is a diagram showing the relationship between the development potential using the developer when the developer is new and after the 250K sheet image is formed, and the toner adhesion amount.
As can be seen from the figure, the development γ is higher when the developer after forming 250K sheets of images is used compared to when a new developer is used. This is because the use of the toner over time causes the developer fluidity to deteriorate over time due to the removal of the external additive or the toner being embedded in the toner, or the charging ability of the toner itself may deteriorate over time. Due to such a change in the toner over time, the charge amount of the toner in the developing device decreases and the development γ increases. For this reason, when the development γ is significantly increased due to environmental fluctuations, the value of the development γ is greater for the developer that has changed with time than for the new developer. Therefore, in the case of Example 1 in which some of the toner patches of the gradation pattern are imaged with a predetermined fixed development bias, the development γ is further increased depending on the environment from the state where the development γ is high due to the change of the developer over time. If it becomes significantly large, there is a possibility that the adhesion amount of the toner patch formed with a predetermined fixed developing bias will not fall within the effective data range.

  Therefore, in the third embodiment, a developing bias for forming an image of at least one toner patch in the gradation pattern is determined based on a change with time of the developer.

  In the same manner as in the first embodiment, the control unit 100 performs development for forming a toner patch formed with a development bias based on the development bias Vb obtained by executing the previous process control in the gradation pattern. The bias Vpb (n) and the charging bias Vpc (n) are determined.

経時補正係数は、取得した感光体の回転数によって変化する係数であり、例えば、感光体の回転数と経時補正係数とを対応させたＬＵＴ（ルックアップテーブル）をＲＡＭなどの不揮発性の記憶手段に記憶しておき、取得した感光体の回転数とＬＵＴとに基づいて、計算に用いる経時補正係数を決定する。
また、経時補正係数を乗じずに、感光体の回転数とこの回転数に対応させたＶｐｂ（ｃ）とからなるＬＵＴを設けて、感光体の回転数から、計算せずに、現像バイアスＶｂｐ（ｃ）を決定してもよい。なお、上記では、感光体の回転数から現像剤の経時変化を把握しているが、画像形成枚数や、現像装置の稼動時間などから現像剤の経時変化を把握してもよい。 Next, the developing bias of the toner patch imaged with the developing bias based on the change with time is determined. The control unit 100 counts the number of rotations of the photoconductor, and stores the count value in a nonvolatile storage unit such as a RAM. When determining the developing bias of the toner patch imaged with the developing bias based on the change over time, the control unit 100 obtains the rotational speed of the photosensitive member from the nonvolatile storage unit, and from the equation shown below, A developing bias Vpb (c) for forming a toner patch formed with a developing bias based on a change with time of the developer is determined.

The temporal correction coefficient is a coefficient that varies depending on the obtained rotational speed of the photosensitive member. For example, a LUT (look-up table) that associates the rotational speed of the photosensitive member with the temporal correction coefficient is a non-volatile storage unit such as a RAM. The time-dependent correction coefficient used for the calculation is determined based on the acquired rotation number of the photosensitive member and the LUT.
Further, an LUT composed of the rotational speed of the photosensitive member and Vpb (c) corresponding to the rotational speed is provided without multiplying the time correction coefficient, and the developing bias Vbp is calculated without calculating from the rotational speed of the photosensitive member. (C) may be determined. In the above description, the change with time of the developer is ascertained from the number of rotations of the photosensitive member. However, the change with time of the developer may be ascertained from the number of images formed, the operation time of the developing device, and the like.

  When the control unit 100 determines the developing bias Vpb (c) for forming the toner patch formed with the developing bias based on the change with time of the developer, the control unit 100 determines the determined developing bias Vpb (c) in advance. A predetermined value (100 to 200 [V]) is added to determine a charging bias Vpc (e) for forming a toner patch formed with a developing bias based on a change with time of the developer.

  As the number of rotations of the photoreceptor increases, the value of the correction coefficient with time decreases, and the value of the developing bias Vpb (c) for forming a toner patch formed with the developing bias based on the change with time of the developer becomes smaller. Get smaller. As a result, even if the developer deteriorates and the development γ changes from a large value to a large change due to environmental changes, etc., the toner patches created with the development bias based on the changes over time of the developer are effective. Can fit within the range of data. Therefore, even if only one of the toner patches formed based on the development bias calculated in the previous process control falls within the valid data range, the development γ can be calculated.

  In addition, some of the toner patches of the gradation pattern are imaged with the development bias calculated based on the environment and the change over time of the developer, and the remaining toner patches are set to the development bias Vb determined by the previous process control. Based on this, an image may be formed with the calculated development bias.

As described above, according to the image forming apparatus of the present embodiment, the latent image is formed on the surface of the photosensitive member charged to the predetermined potential, the photosensitive member serving as the latent image carrier, the charging member serving as charging means for charging the photosensitive member to the predetermined potential. The toner on the developing sleeve is converted into a latent image on the photosensitive member while a developing bias is applied to the optical writing unit as a latent image forming means to be formed and the developing sleeve as a developer carrying member carrying a developer containing at least toner. A developing device as a developing means for developing a latent image by transferring, a transfer unit as a transferring means for transferring a toner image obtained by development from a photosensitive member to a transfer member, and an optical for detecting reflected light from the toner image Forming a gradation pattern consisting of a plurality of toner patches formed under image forming conditions such that the amount of adhesion is different from that of the optical unit serving as the detection means, and using the detection values detected by the optical sensor And a control means serving controller that executes control for adjusting the image forming conditions such as the image bias and the charging bias.
Further, the image forming apparatus of the present embodiment has a fixed image forming condition determined in advance so that at least one toner patch in the gradation pattern always falls within the detection range of the optical sensor at a predetermined development γ. The formed toner patches are formed under image forming conditions set so as to be evenly distributed within the detection range of the optical sensor based on the previously adjusted image forming conditions. According to such a configuration, if the development γ does not vary significantly with respect to the development γ at the time of adjusting the previous image formation conditions, the toner formed under the image formation conditions based on the image formation conditions adjusted last time Many of the patches fall within the detection range of the optical sensor. As a result, even with a small number of toner patches, the number of toner patches detected by the optical sensor increases, the development γ and the development start voltage can be obtained with high accuracy, and the image forming conditions can be adjusted with high accuracy.
Further, the development γ is significantly larger than the development γ at the time of adjusting the previous image formation condition, and only one of the toner patches formed under the image formation condition based on the previously adjusted image formation condition is optical. Even if it does not fall within the detection range of the sensor, at least one or more toner patches formed under image forming conditions that surely fall within the detection range of the optical sensor during such development γ are detected by the detection range of the optical sensor. Inside. As a result, even if the development γ changes significantly with respect to the development γ at the previous adjustment of the image forming conditions, two or more toner patches are included in the detection range of the optical sensor, and the development γ and the like are obtained. Image forming conditions can be adjusted. Therefore, even if the development γ fluctuates significantly with respect to the development γ at the previous adjustment of the image forming conditions, two or more toner patches can be included in the detection range of the optical sensor. The image forming conditions can be adjusted by creating a tone pattern. Therefore, it is not necessary to create a gradation pattern again, and it is possible to suppress the problem that the image density control time becomes longer and the downtime of the apparatus becomes longer. Further, it is possible to suppress a problem that the consumption amount of toner used for image density control increases.

  In addition, at least one toner patch in the gradation pattern is formed under the set image forming conditions based on changes in the environment and / or the developer over time, and the remaining toner patches are formed as previously adjusted images. You may form on the image formation conditions set so that it might disperse | distribute equally to the detection range of an optical sensor based on conditions. Even in this configuration, if the development γ does not vary greatly with respect to the development γ at the time of the previous adjustment of the image forming conditions, a large number of toner patches can be applied even if the number of gradation patterns is small. The image can be within the detection range of the optical sensor, the development γ and the development start voltage Vk can be obtained with high accuracy, and the image forming conditions can be adjusted with high accuracy. In addition, since at least one toner patch is formed taking into consideration the environment that is the variation factor of development γ and the change over time of the developer, even if development γ varies significantly compared to the previous adjustment, This toner patch can be placed in the detection range of the optical sensor. Therefore, even if the development γ fluctuates significantly with respect to the development γ at the time of adjusting the previous image forming conditions, two or more toner patches can be included in the detection range of the optical sensor, and one gradation can be obtained. Image formation conditions can be adjusted by creating a pattern.

  In addition, by changing the image forming conditions in a direction that reduces the amount of toner adhesion with respect to the image forming conditions at normal temperature and normal humidity when the development γ value fluctuates to a large value. The toner patch formed under the set image forming conditions can be put in the detection range of the optical sensor based on the environment and / or the change with time of the developer.

  In addition, by changing the image forming condition in the direction in which the toner adhesion amount increases with respect to the image forming condition at normal temperature and normal humidity in the low temperature / low humidity environment where the value of development γ fluctuates to a small value, Based on the change over time of the environment and / or developer, the toner adhesion amount of the toner patch formed under the set image forming conditions can be increased within the detection range of the optical sensor. As a result, when the value of development γ changes to a small value, even if toner patches formed under the image forming conditions based on the image forming conditions adjusted last time are concentrated on the low adhesion amount side, the environment and / or Alternatively, since the toner patch formed under the set image forming conditions based on the change of the developer over time is on the high adhesion amount side, the influence of variation in the toner adhesion amount can be reduced, and the accuracy of development γ Deterioration can be suppressed.

  Further, the previously adjusted image forming conditions based on the remaining toner patches are set to the previously adjusted developing bias, so that they can be evenly distributed within the detection range of the optical sensor.

1 is a schematic configuration diagram showing a copier according to an embodiment. FIG. 3 is a partially enlarged configuration diagram illustrating a part of an internal configuration of a printer unit in the copier. FIG. 3 is an enlarged configuration diagram showing a process unit for Y and C together with an intermediate transfer belt in the copier. The schematic sectional drawing of an optical sensor. The block diagram which shows the principal part of an electric circuit. Control flow diagram of process control. FIG. 4 is a schematic diagram showing a gradation pattern on an intermediate transfer belt. FIG. 6 is a diagram illustrating a relationship between a development potential and a toner adhesion amount. The figure explaining the adhesion amount of the gradation pattern in Example 1 when there is not much difference between development γ during the previous process control and development γ during the current process control. The figure explaining the adhesion amount of the gradation pattern in Example 1 when development (gamma) at the time of this process control becomes large largely with respect to development (gamma) at the time of the last process control. The figure explaining the adhesion amount of the gradation pattern in Example 1 when development (gamma) at the time of this process control becomes significantly small with respect to development (gamma) at the time of the last process control. The figure explaining the adhesion amount of the gradation pattern in the modification of Example 1 when development (gamma) at the time of this process control becomes significantly small with respect to development (gamma) at the time of the last process control. The figure which shows the relationship between the development potential and toner adhesion amount in each environment. FIG. 6 is a diagram illustrating a gradation pattern according to the second embodiment. The figure which shows the relationship between the developing potential using the developer at the time of a new developer and after 250K sheet image formation, and the toner adhesion amount.

Explanation of symbols

51: Intermediate transfer belt 69: Optical sensor 311: Light emitting element 312: Regular reflection light receiving element 313: Diffuse reflection light receiving element

Claims (7)

A latent image carrier;
Charging means for charging the latent image carrier to a predetermined potential;
A latent image forming means for forming a latent image on the surface of the latent image carrier charged to a predetermined potential;
Development in which the latent image is developed by transferring the toner on the developer carrying member to a latent image on the latent image carrying member while applying a developing bias to the developer carrying member carrying the developer containing at least toner. Means,
Transfer means for transferring a toner image obtained by development from the latent image carrier to a transfer member;
Optical detection means for detecting reflected light from the toner image on the transfer body or the toner image on the latent image carrier;
Control is performed to form a gradation pattern composed of a plurality of toner patches formed under image forming conditions with different adhesion amounts, and to adjust the image forming conditions using detection values detected by the optical detection means. And an image forming apparatus including a control unit.
Among the gradation patterns, at least one toner patch is formed under a fixed image forming condition determined in advance so as to always fall within the detection range of the optical detection means within the fluctuation range of development γ, and the remaining plurality of toner patches. The control unit is configured such that the toner patch is formed with the image forming condition set to be evenly distributed within the detection range of the optical detecting unit based on the previously adjusted image forming condition. An image forming apparatus. A latent image carrier;
Charging means for charging the latent image carrier to a predetermined potential;
A latent image forming means for forming a latent image on the surface of the latent image carrier charged to a predetermined potential;
Development in which the latent image is developed by transferring the toner on the developer carrying member to a latent image on the latent image carrying member while applying a developing bias to the developer carrying member carrying the developer containing at least toner. Means,
Transfer means for transferring a toner image obtained by development from the latent image carrier to a transfer member;
Optical detection means for detecting reflected light from the toner image on the transfer body or the toner image on the latent image carrier;
The image forming unit forms a gradation pattern composed of a plurality of toner patches formed under different image forming conditions so that the adhesion amounts are different from each other, and the image forming condition is adjusted using the detection value detected by the optical detecting unit. An image forming apparatus including a control unit that executes control to perform
Among the gradation patterns, at least one toner patch is formed under the image forming conditions set so as to fall within the detection range of the optical detection unit based on changes in the environment and / or developer over time, and the rest. The plurality of toner patches are configured so as to be formed with image forming conditions set so as to be evenly distributed in the detection range of the optical detecting unit based on the previously adjusted image forming conditions. An image forming apparatus. The image forming apparatus according to claim 2.
The control means is configured to change the image forming condition so that the amount of toner adhesion decreases with respect to the image forming condition at normal temperature and normal humidity when the environment is a high temperature / high humidity environment. An image forming apparatus. The image forming apparatus according to claim 2 or 3,
When the environment is a low temperature / low humidity environment, the control means is configured to change the image forming condition so that the toner adhesion amount increases with respect to the image forming condition at normal temperature / normal humidity. Image forming apparatus. The image forming apparatus according to claim 1,
The image forming apparatus according to claim 1, wherein the previously adjusted image forming condition based on forming the remaining toner patches is a previously adjusted developing bias. Forming a gradation pattern composed of a plurality of toner patches formed under image forming conditions such that the adhesion amounts are different from each other;
Detecting the gradation pattern with an optical detection means;
An image density control method comprising: controlling image density by adjusting image forming conditions using detected detection values;
Among the gradation patterns, at least one toner patch is formed under a fixed image forming condition determined in advance so as to always fall within the detection range of the optical detection means at a predetermined development γ, and the remaining toner patches Is formed under image forming conditions set so as to be evenly distributed in the detection range of the optical detecting unit based on the previously adjusted image forming conditions. Forming a gradation pattern composed of a plurality of toner patches formed under image forming conditions such that the adhesion amounts are different from each other;
Detecting the gradation pattern with an optical detection means;
An image density control method comprising: controlling image density by adjusting image forming conditions using detected detection values;
Among the gradation patterns, at least one toner patch is formed under a set image forming condition based on an environment or a change over time of a developer, and the remaining toner patches are based on a previously adjusted image forming condition. The image density control method is characterized in that the image density control method is formed under image forming conditions set so as to be evenly distributed in the detection range of the optical detection means.

Images