JP2007199641A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of suppressing such a failure that forcibly consumed toner is transferred to an intermediate transfer body, and then, removed by an intermediate transfer body cleaning means, and also, of suppressing up-sizing of the apparatus, the reduction of degree of layout freedom in the apparatus, and the increase of the cost of the apparatus. <P>SOLUTION: During the execution of a mode for forcibly consuming the toner, a primary transfer bias is controlled by an arithmetic processing part as a primary transfer bias control means so as to weaken a primary transfer field. Consequently, the failure that the forcibly consumed toner is transferred to the intermediate transfer body is suppressed without using a mechanical mechanism. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as a copying machine, a facsimile machine, or a printer, and more particularly to an image forming apparatus having a function of forcibly consuming toner for the purpose of suppressing deterioration in image quality due to toner deterioration. .

  As a method for developing an electrostatic latent image on an image carrier, a two-component development method in which development is performed with a two-component developer including toner and a carrier, and a single component in which development is performed with a one-component developer not including a carrier. Development methods are known. Of these, the one-component development method is advantageous over the two-component development method in terms of small size, simple mechanism, and maintainability. In addition, the one-component development method includes a contact development method in which development is performed by bringing a developer into contact with the electrostatic latent image on the photoconductor, and a developer is allowed to fly without contacting the electrostatic latent image on the photoconductor. There is a non-contact development method in which development is performed. Of these methods, the non-contact development method is advantageous for reasons such as the life of the photoconductor and the developing roller and the ability to perform superposition development.

In the one-component development method, the developer (hereinafter referred to as “toner” as appropriate) is subjected to various mechanical stresses in the developing device, so that the charging characteristics of the toner deteriorate with time. Examples of the mechanical stress include friction with a thinning blade and a developer supply roller, toner conveyance and stirring in the developing device, and the like. When the charging characteristics of the toner deteriorate in this way, the deteriorated residual toner remaining in the developing device may be charged with a reverse polarity. In this case, there is a problem that the residual toner adheres to the background portion where the electrostatic latent image on the photosensitive member is not formed and the phenomenon of background contamination occurs. In particular, when the non-contact development method is employed, the above-described toner deterioration causes a problem that the flying property to the photosensitive member is lowered and the image density is lowered.
In addition, problems due to toner deterioration can occur not only in one-component development but also in two-component development.

  The toner deterioration described above proceeds in proportion to the time during which mechanical stress is applied in the developing device, that is, the driving time of the developing device. Therefore, toner deterioration is progressing at the time of toner end, and the above-described problems are likely to occur. For this reason, conventionally, in an image forming apparatus that replenishes new toner after the toner in the developing device is used up, the driving time of the developing device between the time of toner replenishment and the end of the toner does not exceed a certain time. Ingenuity has been proposed.

  For example, in Patent Document 1, when a printing rate calculated for each sheet is smaller than a reference printing rate, a toner pattern is forcibly formed by forming a non-printing developer pattern before the next image formation. A consuming image forming apparatus is disclosed. The printing rate here can be printed on the image forming medium by the number of times of laser emission (number of pixels constituting the actual latent image) emitted to form a latent image on the image forming medium. Divided by the number of dots (total number of pixels that can form a latent image). In this apparatus, when the printing rate is small, the amount of toner corresponding to the calculated printing rate is forcibly consumed, so that the amount of toner actually consumed is approximately the same as the amount of toner consumed for the reference printing rate. . Thus, the number of printed sheets from the time of toner replenishment to the time of toner end is reduced to a certain number or less. Since the number of printed sheets is approximately proportional to the driving time of the developing device, according to the device disclosed in Patent Document 1, the driving time of the developing device can be suppressed within a certain time that does not cause problems due to toner deterioration. Is possible. As a result, it is possible to use up the toner before the degree of toner deterioration exceeds the allowable degree of deterioration.

  Further, there is known an intermediate transfer type image forming apparatus in which a process cartridge having an image carrier, developing means, and the like is disposed on an intermediate transfer body. This intermediate transfer type image forming apparatus forms a toner image on the image carrier by the developing means of the process cartridge, and acts by a primary transfer electric field between the image carrier and the intermediate transfer member formed by the primary transfer means. These toner images are primarily transferred onto an intermediate transfer member to form a toner image. The transfer residual toner adhering to the image carrier after the transfer is removed by the removing member of the image carrier cleaning means and is accommodated in the waste toner accommodating portion of the image carrier cleaning means. The toner image formed on the intermediate transfer member is transferred to the recording material by the secondary transfer unit and fixed by the fixing unit. The transfer residual toner adhering to the intermediate transfer body after the transfer is removed by the removing member of the intermediate transfer body cleaning unit, and stored in the waste toner storage unit of the intermediate transfer cleaning unit. In such an intermediate transfer type image forming apparatus, the forcibly consumed toner is electrostatically transferred to the intermediate transfer member by the primary transfer unit and then removed by the removal member of the intermediate transfer unit cleaning unit. Then, it is stored in the waste toner storage portion of the intermediate transfer cleaning means.

  By the way, the process cartridge is configured to be detachable from the apparatus main body, and the image forming apparatus can be replaced by replacing the process cartridge itself when the end of its life or when the toner in the developing unit runs out. Can be used continuously. Also, the intermediate transfer body, primary transfer means, intermediate transfer body cleaning means, etc. are integrally configured, and the transfer unit is configured to be detachable from the main body of the apparatus, and the transfer unit itself can be replaced when it reaches the end of its life. To be able to. Since the process cartridge is replaced whenever the toner in the developing unit runs out, the life of the process cartridge is shorter than that of the transfer unit.

  When the waste toner container of the intermediate transfer member cleaning unit becomes full, the waste toner overflows from the waste toner container and the waste toner adheres to the intermediate transfer member. For this reason, it is necessary to replace the transfer unit when the waste toner container is full.

  When the toner that is forcibly consumed as described above is removed by the intermediate transfer cleaning unit, the toner that is forcibly consumed in addition to the residual transfer toner is also stored in the waste toner storage unit of the intermediate transfer cleaning unit. . For this reason, the time when the waste toner container becomes full is advanced, and the frequency of replacement of the transfer unit is increased. In a color image forming apparatus including four process cartridges, the time when the waste toner container of the intermediate transfer member cleaning unit becomes full is further advanced, and the transfer unit replacement frequency is further increased. This is because the toner forcibly consumed by each process cartridge is accommodated in the waste toner accommodating portion of the intermediate transfer member cleaning means. Therefore, the waste toner container of the intermediate transfer member cleaning unit is enlarged so that the transfer unit can be replaced with the same time when the life of the intermediate transfer member and the like is reached and when the waste toner container is full of waste toner. It is conceivable to reduce the frequency. However, when the waste toner container is made larger, the space taken by the waste toner container in the apparatus increases, and the apparatus becomes larger and the degree of freedom of layout in the apparatus becomes lower. In a color image forming apparatus, if the time when the life of the intermediate transfer member comes to the same time as when the waste toner container becomes full, the waste toner container needs to be remarkably enlarged, and the size of the apparatus is increased. Becomes prominent.

  Japanese Patent Application Laid-Open No. 2004-228561 describes a device that provides a separating unit that separates the primary transfer unit from the image carrier, and separates the primary transfer unit from the image carrier when executing a forced toner consumption unit that forcibly consumes toner. ing. As a result, the forcibly consumed toner is removed by the image carrier cleaning means without being transferred to the intermediate transfer body by the primary transfer means. As a result, the amount of toner forcibly consumed by the intermediate transfer member cleaning unit can be reduced, and the time when the waste toner container of the intermediate transfer member cleaning unit becomes full can be extended. Thus, the transfer frequency of the transfer unit can be reduced. On the other hand, in the waste toner storage portion of the image carrier cleaning means, the toner that is forcibly consumed in addition to the transfer residual toner is also stored, so that the time when the waste toner storage portion becomes full is advanced. However, the life of the process cartridge is shorter than that of the transfer unit. Therefore, the number of times that the forced toner consumption means is executed before the end of the life of the process cartridge is smaller than the number of times that the toner forcible consumption means is executed before the end of the life of the transfer unit. As a result, the amount of toner forcibly consumed until the end of the life of the process cartridge is smaller than the amount of toner forcibly consumed until the end of the life of the transfer unit. Therefore, even if the waste toner container is designed so that the waste toner container of the image carrier cleaning means becomes full at the time of replacement of the process cartridge, it is possible to prevent the waste toner container from becoming extremely large. it can. Therefore, without increasing the replacement frequency of the process cartridge, it is possible to suppress an increase in the size of the apparatus and a reduction in the degree of freedom of layout in the apparatus.

Japanese Patent No. 3029648 JP-A-2005-43799

  However, in Patent Document 2, the separating unit that separates the primary transfer unit has a mechanical configuration. For this reason, it is necessary to secure a space in which the parts constituting the separating means are arranged, and there is a problem that the apparatus becomes large and the degree of freedom of layout in the apparatus decreases. There is also a problem that the cost of the apparatus increases.

  The present invention has been made in view of the above problems, and the objects thereof are as follows. In other words, forcibly consumed toner is transferred to the intermediate transfer member and is not removed by the intermediate transfer member cleaning means, and the size of the device is suppressed and the degree of freedom of layout in the device is reduced. An object of the present invention is to provide an image forming apparatus that can suppress the cost increase of the apparatus.

In order to achieve the above object, an invention according to claim 1 is directed to an image carrier, developing means for forming a toner image on the image carrier, a removing member for removing toner on the image carrier, and the removing member. And a process cartridge configured to be detachable from the apparatus main body and an intermediate to which a toner image on the image carrier is transferred. A transfer member, a primary transfer means for applying a primary transfer bias for forming a primary transfer electric field for electrostatically moving a toner image from the image carrier to the intermediate transfer member side, and removing toner on the intermediate transfer member And a transfer unit configured to be detachable from the apparatus main body, and a developing unit that moves the developing means. In the image forming apparatus, forcibly consuming the toner in the developing unit, forcibly adhering the toner in the developing unit to the image carrier and forcibly consuming the toner in the developing unit. The image forming apparatus is characterized by comprising transfer bias control means for controlling the primary transfer bias so that the primary transfer electric field at the time of execution of the means is weaker than the primary transfer electric field at the time of image formation.
According to a second aspect of the present invention, in the image forming apparatus of the first aspect, the absolute value of the primary transfer bias at the time of image formation is the absolute value of the primary transfer bias at the time of image formation. The primary transfer bias is controlled to be smaller than the value.
According to a third aspect of the present invention, in the image forming apparatus of the second aspect, the transfer bias control unit controls the primary transfer bias so that the primary transfer bias when the forced toner consumption unit is executed is OFF. It is characterized by.
According to a fourth aspect of the present invention, in the image forming apparatus of the first or second aspect, the transfer bias control means is configured such that the polarity of the primary transfer bias when the forced toner consumption means is executed is equal to the primary transfer bias when the image is formed. The primary transfer bias is controlled to be different from the polarity.
The invention according to claim 5 is the image forming apparatus according to claim 4, further comprising an intermediate transfer body cleaning means for removing toner on the intermediate transfer body, and when the toner forced consumption means is executed, the intermediate transfer body cleaning is performed. In this configuration, the toner on the intermediate transfer member is not removed by the means.
According to a sixth aspect of the present invention, in the image forming apparatus according to any one of the first to fifth aspects, the intermediate transfer member cleaning unit includes a waste toner storage unit that stores the toner removed from the intermediate transfer member. The replacement time of the waste toner container and the replacement time of the intermediate transfer belt are the same.
According to a seventh aspect of the present invention, in the image forming apparatus according to any one of the first to sixth aspects, a plurality of the process cartridges are provided.

According to the first to seventh aspects of the present invention, forcibly consumed toner can be obtained by making the primary transfer electric field at the time of executing the forced toner consumption means weaker than the primary transfer electric field at the time of image formation by controlling the primary transfer bias. Transfer to the intermediate transfer member can be suppressed. As a result, most of the toner forcibly consumed can be removed by the image carrier cleaning means, and the amount of toner forcibly consumed by the intermediate transfer body cleaning means can be reduced. The time when the waste toner container of the intermediate transfer member cleaning unit becomes full can be extended, and the replacement frequency of the transfer unit can be reduced.
Further, if a memory for storing a control program for controlling the primary transfer bias and an arithmetic means for executing the control program are provided, the primary transfer bias can be controlled. Therefore, it is possible to suppress the toner that is forcibly consumed by the control of the primary transfer bias without using a mechanical mechanism from being transferred to the intermediate transfer member. As a result, the following effects can be obtained as compared with those in which the primary transfer means is separated from the image carrier and the toner that is forcibly consumed is prevented from being transferred to the intermediate transfer member. That is, since it is not necessary to provide the components constituting the mechanical mechanism in the apparatus main body, an increase in the size of the apparatus can be suppressed, and a reduction in the degree of freedom of layout in the apparatus can be suppressed. Moreover, an increase in the number of parts of the apparatus can be suppressed, and an increase in cost can be suppressed.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic configuration diagram illustrating an example of a printer as an image forming apparatus according to the present embodiment. This printer is an electrophotographic tandem type image forming apparatus having a photosensitive drum as four image carriers.

  This printer has four process cartridges 1Y, 1M, 1M, 4M for forming toner images of yellow, magenta, cyan, and black (hereinafter referred to as Y, M, C, and K) above the intermediate transfer belt 15 in the vertical direction. C and K are provided. These use different colors of Y, M, C, and K toners as image forming substances, but the other configurations are the same, and there is no toner in the developing device, or parts that constitute a process cartridge. It will be replaced when the life of the battery is reached. These process cartridges are provided with photosensitive drums 1Y, 1C, 1M, and 1K. Here, the suffixes Y, C, M, and K of the symbols indicate yellow, cyan, magenta, and black, respectively. These photosensitive drums 1Y, 1C, 1M, and 1K are arranged such that their rotational axes are horizontal and face in the front-rear direction of the apparatus (the normal direction of the drawing in FIG. 2), and each rotational axis is on the same horizontal plane. Are arranged so as to be parallel to each other. In the present embodiment, each of the photosensitive drums 1Y, 1C, 1M, and 1K is set to be driven to rotate at a peripheral speed of 150 [mm / sec] in the direction of the arrow in the drawing.

  Around the photosensitive drums 1Y, 1C, 1M, and 1K, chargers 2Y, 2C, 2M, and 2K are provided as charging means for uniformly charging the surfaces thereof. This charger is a contact-type charging unit that makes contact with a charging roller that rotates along with the surface of the photosensitive drum and charges it. However, a non-contact type charging unit that uses a charging charger may be used. In the present embodiment, a DC bias or a bias obtained by superimposing an AC bias on the DC bias is applied to each of the chargers 2Y, 2C, 2M, and 2K by a high-voltage power source (not shown), and each of the photosensitive drums 1Y, 1C, 1M, and 1K is applied. It is charged so that the surface potential is uniformly −500 [V].

  Further, an exposure device (not shown) serving as a latent image forming unit is provided above the photosensitive drums 1Y, 1C, 1M, and 1K in the vertical direction. This exposure apparatus irradiates each photosensitive drum 1Y, 1C, 1M, 1K with light 3Y, 3C, 3M, 3K according to image information, and electrostatically for each color on each photosensitive drum. A latent image is formed. As this exposure apparatus, a laser beam scanner using a laser diode or the like can be used.

  A unit 30 having an endless intermediate transfer belt 15 is disposed below the process cartridges 10Y, 10M, 10C, and 10K in the vertical direction. In addition to the intermediate transfer belt 15, the transfer unit 30 includes a tension roller 20, four primary transfer bias rollers 5Y, 5M, 5C, and 5K, a secondary transfer counter roller 21, a belt cleaning device 33, and the like. The transfer unit 30 is configured to be detachable from the apparatus main body so that consumable parts can be replaced at a time.

  Further, around each of the photosensitive drums 1Y, 1C, 1M, and 1K, developing devices 4Y, 4C, 4M, and 4K are provided as developing means for developing the electrostatic latent image formed on the surface thereof. Yes. By applying a predetermined developing bias from a high voltage power source (not shown) to the developing roller as the developer carrying member of each developing device 4Y, 4C, 4M, 4K, the toner in the developer carried on the developing roller is removed. The photosensitive drums 1Y, 1C, 1M, and 1K are moved to electrostatic latent images, and toner is attached to the electrostatic latent images. As a result, toner images corresponding to the electrostatic latent images are formed on the photosensitive drums 1Y, 1C, 1M, and 1K. In the developing unit, 180 [g] of a one-component developer is accommodated at the initial stage of use.

  The respective color toner images on the photosensitive drums 1Y, 1C, 1M, and 1K developed by the developing units 4Y, 4C, 4M, and 4K are primarily transferred so as to overlap each other on the intermediate transfer belt 15 that is an intermediate transfer member. Is done. The intermediate transfer belt 15 is stretched around a support rotating body of a secondary transfer counter roller 21 constituting a secondary transfer unit, primary transfer bias rollers 5Y, 5M, 5C, 5K constituting a primary transfer unit, and a tension roller 20. Has been. In the present embodiment, a rotational driving force from a drive source (not shown) is transmitted to the secondary transfer counter roller 21, and the secondary transfer counter roller 21 rotates to move the intermediate transfer belt 15 endlessly in the direction of the arrow in the figure. . In other words, in the present embodiment, the secondary transfer counter roller 21 is a driving support rotating body of the intermediate transfer belt 15. Of course, another supporting rotating body may be used as the driving supporting rotating body. The secondary transfer counter roller 21 also functions as a belt cleaning counter roller. Each roller that stretches the intermediate transfer belt 15 is supported by a side plate of the transfer unit 30 (not shown).

Materials used for the intermediate transfer belt 15 include PVDF (vinylidene fluoride), ETFE (ethylene-tetrafluoroethylene copolymer), PI (polyimide), PC (polycarbonate), TPE (thermoplastic elastomer), and carbon black. A resin film-like endless belt in which a conductive material such as the above is dispersed can be used. In this example, a single-layer structure in which carbon black was added to PC (polycarbonate) with a thickness adjusted to 140 μm was used. Further, as the resistance of the intermediate transfer belt 15, the volume resistivity is 10 ⁸ to 10 ¹¹ [Ω · cm] and the surface resistivity is 10 ⁸ to 10 ¹¹ [Ω / □] in an environment of 22 [° C.] 55 [% RH]. It is desirable to be in the range. If the volume resistivity and surface resistivity of the intermediate transfer belt 15 exceed these ranges, it is necessary to increase the transfer bias, resulting in an increase in power supply cost. In addition, since the charging potential of the intermediate transfer belt 10 is increased by receiving the transfer bias and self-discharge becomes difficult, a static elimination mechanism for neutralizing the intermediate transfer belt 15 is required, leading to an increase in cost. On the other hand, if the volume resistivity and the surface resistivity are below the above-described ranges, the charge potential of the intermediate transfer belt 15 is attenuated quickly, which is advantageous for static elimination by self-discharge. Therefore, the toner scatters. Therefore, it is preferable that the volume resistivity and the surface resistivity of the intermediate transfer belt 15 are within the above-described ranges.
Note that the volume resistivity and surface resistivity of the intermediate transfer belt 15 were set to a high resistivity meter (Mitsubishi Chemical Corporation: Hiresta IP) with an HRS probe (inner electrode diameter 5.9 [mm], ring electrode inner diameter 11 [mm]. ] And a voltage of 500 [V] is applied to the front and back of the intermediate transfer belt 15 and the value after 10 seconds is used.

As the primary transfer bias rollers 5Y, 5M, 5C, and 5K, conductive blades, conductive sponge rollers, metal rollers, and the like can be used. In this embodiment, a conductive sponge roller of φ12 having a resistance value of 10 ⁶ to 10 ¹⁰ Ω is used. A predetermined primary transfer bias +500 to +800 [V] is commonly applied to the primary transfer rollers 5Y, 5M, 5C, and 5K by a primary transfer power source (not shown), thereby causing the intermediate transfer belt 15 and the photoreceptors 1Y, 1M, 1C, and 1K to be applied in common. A transfer electric field is formed between them and the toner image on the photosensitive member is electrostatically transferred to the intermediate transfer belt 15.
The resistance value of the primary transfer bias roller is such that the primary transfer bias roller is installed on a conductive metal plate and 4.9 [N] on one side at both ends of the core metal (total of 9.8 [N] on both sides). ) Is applied from the value of the current that flows when a voltage of 1000 [V] is applied between the metal core and the metal plate.

  Further, around each of the photosensitive drums 1Y, 1C, 1M, and 1K, photosensitive member cleaning as an image carrier cleaning unit for removing the transfer residual toner remaining on the photosensitive drum after the primary transfer, respectively. Units 2Y, 2C, 2M, and 2K are provided. The photosensitive member cleaning units 2Y, 2C, 2M, and 2K include cleaning blades 6Y, 6C, 6M, and 6K as removal members and waste toner storage portions 7Y, 7C, 7M, and 7K. The cleaning blades 6Y, 6C, 6M, and 6K are in contact with the surface of the photoreceptor, and scrape off and remove the transfer residual toner on the surface of the photoreceptor drum. The transfer residual toner removed by the cleaning blade is stored in a waste toner storage unit.

The toner image transferred onto the intermediate transfer belt 15 is a secondary transfer area between the belt portion wound around the secondary transfer counter roller 21 and the secondary transfer bias roller 25, and is conveyed to this area. Secondary transfer is performed on the material. A predetermined secondary transfer bias is applied to the secondary transfer bias roller 25 by a high voltage power source (not shown), thereby electrostatically transferring the toner image on the intermediate transfer belt 15 onto the recording material. The secondary transfer bias roller 25 is formed by coating a metal core such as SUS with an elastic layer such as urethane prepared to have a resistance value of 10 ⁶ to 10 ¹⁰ [Ω] with a conductive material. It is configured. If the resistance value of the secondary transfer bias roller 25 exceeds the above range, the transfer current becomes difficult to flow. Therefore, a higher voltage must be applied in order to obtain a required transfer property, resulting in an increase in power supply cost. . Further, as a result of the necessity of applying such a high voltage, discharge occurs in the gaps before and after the secondary transfer nip, and white spots are lost on the halftone image due to the discharge. On the other hand, if the resistance value of the secondary transfer bias roller 25 falls below the above range, good transferability can be achieved between an image portion where a plurality of color toner images on the same image overlap and a single color image portion. Disappear. This is because the resistance value of the secondary transfer bias roller 25 is low. Therefore, if the secondary transfer bias is set to a relatively low voltage at which an optimum transfer current can be obtained for a single color image portion, sufficient for a plurality of color image portions. If the transfer current cannot be obtained and the secondary transfer bias is set to a relatively high voltage that can obtain the optimum transfer current for the image portions of a plurality of colors, excessive transfer current flows for the image portion of the single color. This is because efficiency is reduced.
The resistance value of the secondary transfer bias roller 25 is such that the secondary transfer bias roller 21 is installed on a conductive metal plate and 4.9 [N] on one side at both ends of the core metal (total of 9.8 [on both sides]. N]), and is calculated from the current value that flows when a voltage of 1000 [V] is applied between the metal core and the metal plate.

  The recording material 22 is fed by a paper feeding / conveying roller 23 and a registration roller pair 24 at the timing when the leading edge of the toner image on the surface of the intermediate transfer belt 15 reaches the secondary transfer position, and a predetermined 2 is supplied by a high voltage power source (not shown). By applying the next transfer bias, the toner image on the intermediate transfer belt 15 is transferred to the recording material 22. The transfer material 22 is separated from the intermediate transfer belt 15 by the curvature of the secondary transfer counter roller 21, and the toner image transferred to the transfer material 22 is fixed by the fixing unit 26 and then discharged.

  Further, residual toner remaining on the intermediate transfer belt 15 after the secondary transfer is removed at a position facing the belt portion of the intermediate transfer belt 15 that is wound around the belt cleaning counter roller (secondary transfer counter roller) 21. For this purpose, a belt cleaning device 33 is provided as an intermediate transfer member cleaning means. The belt cleaning device 33 includes a cleaning blade 31 as a removing member and a toner storage portion 32. The cleaning blade 31 is in contact with the surface of the intermediate transfer belt 15 and scrapes off and removes transfer residual toner on the surface of the intermediate transfer belt. The transfer residual toner removed by the cleaning blade 31 is stored in the waste toner storage unit 32.

  In this embodiment, a single color mode for forming an image of any one color of yellow, magenta, cyan, and black, a two-color mode for forming an image of two colors of yellow, magenta, cyan, and black, and yellow , Magenta, cyan, and black, a three-color mode that forms an image with three colors superimposed, and a full-color mode that forms a four-color superimposed image as described above. These modes can be specified on the operation unit. is there.

Further, in this embodiment, the process speed at the time of fixing is changed depending on the type of the recording material 22. Specifically, when a recording material having a basis weight of 110 [g / m ² ] or more is used, the process speed is set to a half speed, and the recording material has a normal process speed at a fixing nip formed by a pair of fixing rollers. The toner image can be secured by passing through twice as long.

Next, the toner forced consumption means will be described. FIG. 2 is a functional block diagram showing the control unit 40 for controlling the toner forced consumption operation in the present embodiment. The control unit 40 actually controls the entire copying machine, but only functions relating to the forced toner consumption operation are displayed in the drawing.
As shown in the figure, the control unit 40 includes an arithmetic processing unit 41 and a pixel amount counter 42. The arithmetic processing unit 41 includes a ROM that stores various control programs, a RAM that is a working memory for executing the control programs, a CPU for executing the programs, and the like. Connected to the controller 40 is an external device 44, a charger 2, an exposure device 3, a developing device 4, and a primary transfer unit 11 including a primary transfer power source 12 and a primary transfer bias roller.
When a color image is printed by this printer, first, image information is received by the arithmetic processing unit 41 of the control unit 40 from an external device 44 such as a personal computer or a scanner. The arithmetic processing unit 41 performs control for a normal printing operation and stores the pixel amount Pi of the electrostatic latent image portion formed on the photosensitive drum 1 in the pixel amount counter 42. In addition, the arithmetic processing unit 41 receives the paper length data L from the external device 44 or an operation panel (not shown) and stores it in the internal memory of the control unit. Further, the arithmetic processing unit 41 uses the pixel amount P _i stored in the pixel amount counter 42, the paper length data L, and the predetermined reference pixel amount P ₀ per unit length to forcibly consume the toner. Calculate the forced consumption of. Then, after the printing operation, a latent image corresponding to the calculated pixel amount is formed in a non-image area on the photosensitive drum 1, and this is developed to execute a toner forced consumption mode in which toner is forcibly consumed. The latent image pattern formed when the toner is forcibly consumed may be any pattern such as a dot, a solid, or a line. In addition, the arithmetic processing unit 41 controls the primary transfer power source 12 so that the primary transfer electric field in the primary transfer region is weaker than the primary transfer electric field at the time of image formation when the forced toner consumption mode is executed.
The forced toner consumption is not necessarily performed for each printing operation determined to be small in the above-described determination of the arithmetic processing unit 21. For example, a pixel amount corresponding to the calculated shortage may be accumulated several times, and the accumulated toner may be forcibly consumed later.

FIG. 3 is a flowchart showing the flow of processing related to the toner forced consumption mode of the control unit 40 in the present embodiment. When the printing operation starts (S1), the arithmetic processing unit 41 of the control unit 40 functions as a forced consumption calculation unit, and forms on the photosensitive drum 1 based on image information sent from the external device 44. and calculates the pixel quantity P _i of the electrostatic latent image portion. Calculation pixel amount _{P i} that is stored in pixel amount counter 42 (S2). Next, the arithmetic processing unit 41 receives the paper length data L from the external device 44 or an operation panel (not shown), and stores it in the internal memory of the control unit 40 (S3). Then, it calculates a reference pixel amount P ₀ per unit length which is determined in advance, and the paper length data L, and forced consumption of toner is forcibly consumed from the pixel quantity P _i (S4). After calculating the forced toner consumption Pc (S4), the arithmetic processing unit 41 determines whether the calculated forced toner consumption Pc is greater than 0 (S5). If it is determined (S5 of NO) and small at this time, it means that this is the actual toner consumption related pixel amount P _i is the reference pixel amount (P ₀ × L) toner consumption amount or more relating to a toner There is no need to force consumption. Therefore, the process proceeds to the next image forming operation without forcibly consuming the toner. On the other hand, if it is determined (S5 YES) of greater above judgment, it means that the toner consumption of the actual pixel quantity P _i is less than the amount of toner consumption for the reference pixel amount (P ₀ × L), toner Need to be forcibly consumed. In this case, the arithmetic processing unit 41 of the control unit 40 functions as a transfer bias control unit and controls the primary transfer power source. That is, the arithmetic processing is performed so that the primary transfer bias V _t1 applied to the primary transfer bias roller 5 at the time of image formation is changed to a transfer bias V _t2 at which the primary transfer electric field in the primary transfer region becomes weaker than the primary transfer electric field at the time of image formation. The unit 41 controls the primary transfer power supply 12 (S6). Then, an electrostatic latent image corresponding to the pixel amount of the forced toner consumption Pc calculated in S4 is optically written on the surface of the photosensitive drum immediately after the trailing edge of the electrostatic latent image to be a printed image by an exposure device, and developed. Develop with device 4. Thereby, the toner consumption shortage of the actual pixel amount Pi with respect to the reference pixel amount (P ₀ × L) can be forcibly consumed (S7). Most of the toner image formed for the forced consumption of the toner is removed by the photoreceptor cleaning unit 8 without being electrostatically transferred to the intermediate transfer belt.
When the forced toner consumption mode ends, the pixel amount Pi and the paper length data L are reset. Further, the primary transfer bias V _t2 is changed to V _t1 .

Next, FIG. 4 shows the amount of waste toner stored in the waste toner storage portion 7 of the photoconductor cleaning unit 8 when the primary transfer bias V _t2 is changed when the forced toner consumption mode is executed, and the intermediate transfer body cleaning unit 33. 6 is a graph showing a relationship with the amount of waste toner stored in the waste toner storage unit 32. This graph is a graph obtained by conducting an experiment using this printer. In the experiment, the reference pixel amount (P ₀ × L) was set to a value corresponding to an image area ratio of 5 [%], and 5000 images with an image area ratio of 2 [%] were printed. That is, the experimental condition is set so that when the toner forced consumption mode is executed, the toner amount corresponding to the image area ratio of 3 [%] is forcibly consumed. Further, the primary transfer bias V _t1 during image formation was set to +600 [V]. In the conventional example in the figure, the primary transfer bias V _t2 at the time when the forced toner consumption mode is executed is set to +600 [V], which is the same as the primary transfer bias V _t1 at the time of image formation. In the first exemplary embodiment, the primary transfer bias V _t2 at the time of executing the forced toner consumption mode is set to +600 [V] and is set to a value half of the primary transfer bias V _t1 at the time of image formation. In the second embodiment, the primary transfer bias V _t2 when the forced toner consumption mode is executed is set to OFF. In the third embodiment, the primary transfer bias V _t2 at the execution of the toner forced consumption mode is set to −600 [V], and a polarity opposite to the polarity of the primary transfer bias V _t1 at the time of image formation is applied. In the fourth embodiment, the primary transfer bias V _t2 when the forced toner consumption mode is executed is set to −600 [V], and the cleaning blade 32 of the intermediate transfer member cleaning unit 33 is separated from the intermediate transfer belt when the forced toner consumption mode is executed. It has been made.

  As can be seen from the drawing, in the conventional example, the intermediate transfer member cleaning unit 33 is compared with the waste toner contained in the waste toner containing portions 7Y, C, M, K of the photoconductor cleaning units 8Y, C, M, K. It can be seen that the amount of waste toner stored in the waste toner storage section 32 is very large. This is because the toner forcibly consumed from the process cartridges 10Y, 10M, 10C, and 10K is transferred to the intermediate transfer belt and removed by the intermediate transfer body cleaning unit 33. Therefore, in the conventional example, the waste toner container 32 of the intermediate transfer member cleaning unit 33 is immediately filled with waste toner, and the replacement frequency of the transfer unit 30 is increased.

On the other hand, in the first embodiment in which the primary transfer bias V _t2 at the time of executing the forced toner consumption mode is set to a half value of the primary transfer bias V _t1 at the time of image formation, the waste toner of the intermediate transfer member cleaning unit 33 is compared with the conventional example. It can be seen that the amount of waste toner in the container is decreasing. This is presumably because the primary transfer electric field in the primary transfer region during execution of the forced toner consumption mode has weakened. That is, as a result of the weakening of the primary transfer electric field, most of the forcibly consumed toner adhering to the photoconductor no longer moves electrostatically to the intermediate transfer belt, so that it is forcibly removed by the intermediate transfer body cleaning unit. The consumed toner is considered to have decreased. Thereby, the time when the intermediate transfer member cleaning unit 33 becomes full can be extended, and the replacement frequency of the transfer unit 30 can be reduced.
Also, most of the toner that is forcibly consumed is removed by the respective photoconductor cleaning units 8Y, 8C, 8M, and 8K, and stored in the waste toner storage portions 7Y, 7C, 7M, and 7K of the photoconductor cleaning unit. . As a result, the total amount of waste toner stored in the four photosensitive member cleaning unit waste toner storage units 7Y, C, M, and K is larger than the waste toner stored in the waste toner storage unit 32 of the intermediate transfer member cleaning unit 33. Become more. However, the amount of waste toner stored in each photoconductor cleaning unit waste toner container 7Y, C, M, K is smaller than the waste toner stored in the waste toner container 32 of the intermediate transfer body cleaning unit. Therefore, it can be seen that each photosensitive member cleaning unit waste toner container 7Y, C, M, K has a higher margin for storing waste toner than the waste toner container 32 of the intermediate transfer member cleaning unit. Therefore, for example, when the toner in the developing devices 4Y, C, M, and K runs out, the photosensitive member cleaning unit waste toner storage portions 7Y, C, M, and K are replaced when the process cartridges 10Y, 10C, 10M, and 10K are replaced. Even if it is designed to be full, the waste toner container does not become extremely large. Further, since the process cartridges 10Y, C, M, and K have a shorter life than the transfer unit, they are forcibly consumed in the waste toner storage portions 7Y, C, M, and K of the photosensitive member cleaning unit. The amount of toner is also small. Therefore, even if the photosensitive member cleaning unit waste toner container 7Y, C, M, K is designed to become full when the process cartridges 10Y, C, M, K are replaced, the waste toner container is significantly enlarged. There is nothing. As a result, it is possible to suppress an increase in the size of the device and a decrease in the degree of freedom of layout in the device.

  Further, as in the second embodiment, when the forced toner consumption mode is executed, the primary transfer power source 12 is turned off so that no bias is applied to the primary transfer bias roller 6, and the primary transfer electric field is weakened compared to the first embodiment. The amount of waste toner stored in the waste toner storage unit 32 of the intermediate transfer member cleaning unit can be further reduced. Therefore, the replacement time of the transfer unit 30 can be extended.

Further, as in the third embodiment, the primary transfer bias V _t2 at the time of executing the forced toner consumption mode is set to the opposite polarity to the primary transfer bias V _t1 at the time of image formation, so that the toner is moved to the photoconductor side when the forced toner consumption mode is executed. The primary transfer electric field is such that it is moved. Therefore, the toner that adheres to the intermediate transfer belt 15 in the toner forced consumption mode is only the toner charged to the reverse polarity. Therefore, the amount of waste toner stored in the waste toner storage unit 32 of the cleaning unit can be further reduced, and the replacement time of the transfer unit 30 can be further extended.

Further, according to the fourth embodiment, the amount of waste toner stored in the waste toner storage unit 32 of the intermediate transfer body cleaning unit can be further reduced. However, in the case of the fourth embodiment, the forcibly consumed toner transferred to the intermediate transfer belt 15 is not removed by the cleaning unit 33 and therefore remains attached to the intermediate transfer belt 15. As a result, forcibly consumed toner may be transferred to the recording material during image formation. However, also in the fourth embodiment, as in the third embodiment, the primary transfer bias V _t2 at the time of executing the forced toner consumption mode is opposite in polarity to the primary transfer bias V _t1 at the time of image formation, so that the toner adhering to the intermediate transfer belt 15 Is a very small amount of reversely charged toner. Therefore, even if it is transferred to a recording material during image formation, the image quality is not significantly reduced.

  Although the color image forming apparatus has been described above, the same effect can be obtained by adopting the configuration of the present invention even in a monochromatic image forming apparatus having one process cartridge. That is, it is possible to reduce the replacement frequency of the transfer unit and to suppress the enlargement of the apparatus.

(1)
As described above, according to the image forming apparatus of this embodiment, the primary transfer bias is controlled so as to weaken the primary transfer electric field when the forced consumption mode as the toner forced consumption unit is executed, and the forcedly consumed toner is transferred to the intermediate transfer body as the intermediate transfer body. It is difficult to transfer to the belt. As a result, it is possible to reduce the amount of toner that is forcibly consumed by the intermediate transfer member cleaning unit, which is an intermediate transfer member cleaning unit, and to extend the time when the waste toner container of the intermediate transfer member cleaning unit becomes full. Can do. Thus, the transfer frequency of the transfer unit can be reduced. On the other hand, since the toner that is forcibly consumed in addition to the transfer residual toner is also stored in the toner storage portion of the photosensitive member cleaning unit that is an image carrier cleaning means, the time when the waste toner storage portion becomes full is advanced. However, since the process cartridge is replaced every time the toner in the developing device as developing means runs out, the life of the process cartridge is shorter than that of the transfer unit. Therefore, the number of times that the forced toner consumption mode, which is the forced toner consumption means, is executed before the end of the life of the process cartridge is smaller than the number of times that the transfer unit is executed before the end of the life of the transfer unit. As a result, the amount of toner forcibly consumed until the end of the life of the process cartridge is smaller than the amount of toner forcibly consumed until the end of the life of the transfer unit. Therefore, even if the waste toner container is designed so that the waste toner container of the photosensitive member cleaning unit becomes full at the time of replacement of the process cartridge, the waste toner container can be prevented from becoming extremely large. . Therefore, even if the toner forcibly consumed by the photosensitive member cleaning unit is removed, it is possible to suppress the enlargement of the apparatus and the degree of freedom of layout in the apparatus and to increase the frequency of replacement of the process cartridge. Can be prevented.
Further, since the primary transfer bias is controlled by the arithmetic processing unit 41 serving as the primary transfer bias control means to suppress the toner that is forcibly consumed from being transferred to the intermediate transfer body, the mechanical mechanism is not used. Forcibly consumed toner can be prevented from being transferred to the intermediate transfer member. As a result, since it is not necessary to provide a space for arranging mechanical components in the apparatus, it is possible to suppress an increase in the size of the apparatus and increase the degree of freedom of layout in the apparatus. Moreover, an increase in the number of parts of the apparatus can be suppressed, and an increase in cost can be suppressed.
(2)
Further, by making the absolute value of the primary transfer bias when the toner forced consumption mode is executed smaller than the absolute value of the primary transfer bias at the time of image formation, the primary transfer electric field is weakened, and the forcibly consumed toner on the photoconductor However, transfer to the intermediate transfer belt can be made difficult. Therefore, it is possible to reduce the toner adhering to the intermediate transfer belt.
(3)
Further, by turning OFF the primary transfer bias when the toner forced consumption mode is executed, the primary transfer electric field can be further weakened, and the toner that is forcibly consumed on the photoreceptor is more difficult to transfer to the intermediate transfer belt. be able to. Therefore, it is possible to further reduce the toner adhering to the intermediate transfer belt.
(4)
Further, by making the primary transfer bias polarity during execution of the toner forced consumption mode different from the polarity of the primary transfer bias during image formation, the electric field at the primary transfer position attracts the toner to the photoconductor side. It becomes an electric field. Thereby, only the toner charged to the reverse polarity can be used as the toner adhering to the intermediate transfer belt among the forcibly consumed toner. Therefore, it is possible to further reduce the forcibly consumed toner adhering to the intermediate transfer belt.
(5)
In the toner forced consumption means mode, the toner on the intermediate transfer member cleaning unit is not removed by the intermediate transfer member cleaning unit, so that the forcibly consumed toner is stored in the waste toner storage unit of the intermediate transfer member cleaning unit. Can be prevented. Therefore, it is possible to reduce the amount of waste toner stored in the waste toner storage unit of the intermediate transfer body cleaning unit when the transfer unit reaches the end of its life. As a result, the waste toner container of the intermediate transfer member cleaning unit can be further reduced, and the apparatus can be made compact.
(6)
Also, the replacement frequency of the transfer unit can be reduced by making the replacement timing of the waste toner container of the intermediate transfer body cleaning unit and the replacement timing of the intermediate transfer belt coincide.
(7)
In addition, a color image can be formed by providing a plurality of the process cartridges.

1 is a schematic configuration diagram illustrating a main part of a printer according to an embodiment. FIG. 3 is a functional block diagram showing a control unit for controlling a toner forced consumption mode of the printer. 6 is a flowchart showing a flow of processing relating to a forced toner consumption operation performed by a control unit of the printer. The amount of waste toner stored in the waste toner storage portion 7 of the photoconductor cleaning unit 8 when the primary transfer bias V _t2 is changed when the forced toner consumption mode is executed and the waste toner storage portion 32 of the intermediate transfer body cleaning unit 33 are changed. 6 is a graph showing the relationship with the amount of waste toner stored.

Explanation of symbols

1Y, M, C, K Photoconductor 5Y, M, C, K Primary transfer bias roller 7Y, M, C, K Waste toner storage unit 8Y, M, C, K Photoconductor cleaning unit 15 Intermediate transfer belt 32 Waste toner storage Part 33 Intermediate transfer member cleaning unit

Claims (7)

The image bearing member includes a developing unit that forms a toner image on the image bearing member, a removing member that removes toner on the image bearing member, and a waste toner container that stores toner removed by the removing member. A process cartridge comprising an image carrier cleaning means and configured to be detachable from the apparatus main body;
An intermediate transfer member to which a toner image on the image carrier is transferred, and a primary transfer bias for forming a primary transfer electric field for electrostatically moving the toner image from the image carrier to the intermediate transfer member side. An intermediate transfer body cleaning means comprising a transfer means, a removal member for removing toner on the intermediate transfer body, and a waste toner storage section for storing toner removed by the removal member is detachable from the apparatus main body. A transfer unit configured in
An image forming apparatus comprising: a toner forcible consumption unit that operates the developing unit to forcibly attach the toner in the developing unit to the image carrier and forcibly consumes the toner in the developing unit. ,
An image forming apparatus comprising: transfer bias control means for controlling the primary transfer bias so that the primary transfer electric field at the time of executing the forced toner consumption means is weaker than the primary transfer electric field at the time of image formation. The image forming apparatus according to claim 1.
The transfer bias control means controls the primary transfer bias so that the absolute value of the primary transfer bias at the time of execution of the forced toner consumption means is smaller than the absolute value of the primary transfer bias at the time of image formation. Forming equipment. The image forming apparatus according to claim 2.
The image forming apparatus, wherein the transfer bias control unit controls the primary transfer bias so that the primary transfer bias when the toner compulsory consumption unit is executed is OFF. The image forming apparatus according to claim 1 or 2,
The image forming apparatus, wherein the transfer bias control means controls the primary transfer bias so that the polarity of the primary transfer bias at the time of executing the forced toner consumption means is different from the polarity of the primary transfer bias at the time of image formation. The image forming apparatus according to claim 4.
An intermediate transfer member cleaning unit that removes toner on the intermediate transfer member is provided, and the toner on the intermediate transfer member is not removed by the intermediate transfer member cleaning unit when the toner forced consumption unit is executed. Image forming apparatus. The image forming apparatus according to claim 1,
The intermediate transfer member cleaning unit includes a waste toner storage portion that stores toner removed from the intermediate transfer member, and the replacement timing of the waste toner storage portion and the replacement timing of the intermediate transfer belt are at the same time. An image forming apparatus characterized by being configured as described above. The image forming apparatus according to claim 1.
An image forming apparatus comprising a plurality of the process cartridges.

Images