Image forming device

Abstract

To reduce downtime while preventing deterioration of toner.SOLUTION: An image forming apparatus comprises: an image forming unit; an intermediate transfer body to which toner images carried on image carriers are transferred; cleaning members that are in contact with the intermediate transfer body to clean the intermediate transfer body; and a control unit that controls the image forming unit to, when executing an image forming job, form patch images for supplying toner to the cleaning members in a non-paper feed area of the intermediate transfer body after images for forming the toner images on a recording material. The control unit changes the density of the patch images based on the consumption of toner for the travel distance of developer carriers.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to an image forming apparatus equipped with a developing device that develops an electrostatic image formed on an image carrier. [Background technology]

[0002] The developing device includes a developing roller (developer carrier) that carries and conveys toner (developer) to develop an electrostatic image formed on a photosensitive member (image carrier). A technique is known for forcibly discharging toner when the amount of toner consumed per unit driving time of the developing roller is low (i.e., when the printing rate is low) (see Patent Document 1). The forcible toner discharging operation is an operation forcibly consuming toner by applying a bias to the developing roller to cause the toner carried by the developing roller to adhere to non-image forming areas on the photosensitive member. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2003-263027 Summary of the Invention [Problem to be solved by the invention]

[0004] By forcibly consuming toner through the forced toner discharge operation, fresh toner is replenished into the developing device, thereby suppressing deterioration of the toner circulating within the developing device. Therefore, in order to enhance the effect of suppressing deterioration of the toner circulating within the developing device, it is desirable to increase the amount of toner forcibly consumed through the forced toner discharge operation.

[0005] However, if the time interval between sheets of an image forming job is increased in order to perform the forced toner discharge operation, downtime occurs each time the forced toner discharge operation is performed. Therefore, if the frequency of the forced toner discharge operation is increased or the duration of the forced toner discharge operation is extended in order to increase the amount of toner forcibly consumed by the forced toner discharge operation, there is a risk that productivity will decrease.

[0006] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide an image forming apparatus that can reduce downtime while suppressing toner deterioration. [Means for solving the problem]

[0007] In order to achieve the above object, an image forming apparatus according to one aspect of the present invention has the following configuration: That is, the image forming apparatus has an image carrier on which an electrostatic image is formed, a developer container containing a developer including toner, and a rotatable developer carrier that carries the developer to develop the electrostatic image formed on the image carrier, and the image forming apparatus has an image forming section that forms a toner image on the image carrier, a movable intermediate transfer member to which the toner image formed on the image carrier by the image forming section is transferred, a cleaning member that is provided in contact with the intermediate transfer member and that cleans toner remaining on the intermediate transfer member, and a control section that controls the image forming section, and the control section is configured to: when a ratio of an amount of toner consumed in a continuous image forming job in which images are formed on a plurality of recording materials including a first recording material and a second recording material subsequent to the first recording material to a distance over which the developer carrier is rotated is higher than a predetermined threshold, the control section controls the image forming section to clean the toner each time a toner image for an image to be formed on one recording material is transferred to the intermediate transfer member; toand controlling the image forming unit to form a first toner supply image for supplying toner to the cleaning member during a predetermined period from when a toner image for an image formed on the first recording material is transferred to the intermediate transfer body until when a toner image for an image formed on the second recording material is transferred to the intermediate transfer body, and when the ratio is lower than the predetermined threshold value, controlling the image forming unit to form a first toner supply image for supplying toner to the cleaning member during a predetermined period from when a toner image for an image formed on one recording material is transferred to the intermediate transfer body. to During the specified period, the image forming unit is controlled to form a second toner supply image for supplying toner to the cleaning member, and the density of the second toner supply image is higher than the density of the first toner supply image. [Effects of the Invention]

[0008] According to the present invention, it is possible to reduce downtime while suppressing toner deterioration. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a schematic cross-sectional view of an image forming apparatus according to a first embodiment. [Figure 2] FIG. 2 is a block diagram of a controller according to the first embodiment. [Figure 3] FIG. 10 is a diagram for explaining an execution threshold value [1]:Ya of the low print mode according to the first embodiment. [Figure 4] 4 is a flowchart illustrating a control example according to the first embodiment. [Figure 5] FIG. 10 is a diagram for explaining a low-printing mode according to a second embodiment. [Figure 6] 10 is a flowchart illustrating an example of control according to the second embodiment. [Figure 7] 10 is a flowchart illustrating a control example according to the third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. Note that the following embodiments do not limit the scope of the present invention, and not all of the combinations of features described in the embodiments are necessarily essential to the solution of the present invention. The present invention can be implemented in a variety of applications, such as printers, various printing machines, copiers, fax machines, and multifunction machines.

[0011] First Embodiment [Configuration of image forming device] Before describing the characteristic features of this embodiment, the overall configuration of the image forming apparatus will be described.

[0012] 1 is a schematic diagram showing an example of the cross-sectional configuration of an image forming apparatus. Image forming apparatus 1 is an apparatus that forms an image in an image forming unit that uses an electrophotographic process, transfers the formed image to paper P, which is a recording material, in a transfer unit, and fixes the image to paper P by heating the paper P to which the image has been transferred in a fixing unit. The image forming apparatus described in this embodiment is a four-color full-color multifunction printer (color image forming apparatus) that uses an electrophotographic process. This will be described in detail below.

[0013] The image forming apparatus 1 includes a control unit 600 that controls each component within the apparatus. The control unit 600 functions as a control unit that performs various controls, and plays a role in executing image forming operations by comprehensively controlling each component within the apparatus based on input print information signals (e.g., image data, paper information, etc.). In other words, the image forming apparatus 1 can execute an image forming job that forms a toner image on a recording material.

[0014] The paper P used in this explanation is a recording material on whose surface an image is formed. Examples of paper P include plain paper, cardboard, transparency paper, coated paper, label paper, and perforated paper.

[0015] The image forming apparatus 1 forms multicolor images by overlaying four colors of developer (hereinafter referred to as toner): yellow (Y), magenta (M), cyan (C), and black (K). To this end, it includes image forming stations 10 (image forming units) that form toner images of each color. While the reference numerals in the figures are given the suffixes YMCK, the image forming stations 10 for each color have the same basic configuration. Therefore, in the specification, when a description applies to all image forming stations, the suffixes are omitted. The image forming station 10 includes a rotating photosensitive drum 11 (a rotatable image carrier) on which an image is formed. The image forming station 10 also includes a drum cleaning member 16 as a process means acting on the photosensitive drum 11, a charging roller 12 as a charging device, and a developing unit 14 as a developing device. The toner storage chamber (developer container) of the developing unit 14 contains toner (developer) of each color, which is basically negatively charged. The toner contained in the toner containing chamber is carried and transported by a developing roller (a rotatable developer carrier) provided in the developing unit 14. The toner carried by the developing roller then flies toward the photosensitive drum 11 due to the action of a bias applied to the developing roller, thereby developing the electrostatic latent image formed on the photosensitive drum 11.

[0016] A laser scanner unit 13 is disposed adjacent to the image forming station 10 as an exposure means for the photosensitive drum 11, and a cassette 2 for storing paper P is disposed below the image forming station 10. Furthermore, a transfer belt unit 20 (hereinafter referred to as a transfer unit) is provided above the image forming station 10.

[0017] The transfer unit 20 has an intermediate transfer belt 21 (intermediate transfer body) and a drive roller 22 that drives it. Furthermore, four primary transfer rollers 15 (first to fourth) that serve as primary transfer devices are arranged in parallel inside the intermediate transfer belt 21. Each primary transfer roller 15 is disposed opposite the photosensitive drum 11 of each image forming station.

[0018] The upper surface of the photosensitive drum 11 of each color in the image forming station 10 is in contact with the lower surface of the intermediate transfer belt 21 at the position of each primary transfer roller 15. This contact portion is called a primary transfer portion.

[0019] The drive roller 22 is a roller that drives the rotation of the intermediate transfer belt 21, and a secondary transfer roller 25, which serves as a secondary transfer device, is disposed outside the portion of the intermediate transfer belt 21 that is backed up by the drive roller 22. The intermediate transfer belt 21 contacts the secondary transfer roller 25, which serves as a transfer means, and this contact portion is called the secondary transfer nip portion T2. ​​An intermediate transfer belt cleaner 23 (cleaning member) is disposed outside the portion of the intermediate transfer belt 21 that is backed up by the tension roller. The intermediate transfer belt cleaner 23 is configured by pressing (contacting) a blade-shaped elastic body against (with) the intermediate transfer belt 21.

[0020] Toner remaining on the intermediate transfer belt 21 without being transferred to the paper P at the secondary transfer nip T2 is cleaned by an intermediate transfer belt cleaner 23 and collected in a main body collected toner box 24. Toner remaining on the photosensitive drum 11 is collected in a collected toner box 17 by a drum cleaning member 16.

[0021] The image forming apparatus 1 is equipped with a paper transport device. A paper transport path Q (indicated by a dashed line in the figure) is provided to transport paper P picked up from a cassette 2 upward. On the paper transport path Q, a feed roller 3, a pair of separation rollers 4, a pair of registration rollers 5, a paper jam detection mechanism J, a secondary transfer roller 25, a fixing unit 30, and a pair of discharge rollers are arranged in this order from upstream to downstream, and the paper P is transported to a discharge tray 9.

[0022] The fixing unit 30, which is a fixing device, is equipped with a pair of rollers that press against the paper P and a heater that heats the paper P, and by heating the paper P while pressing against it, the unfixed toner image on the paper P is melted and fixed to the paper P. A voltage is applied to the surface of the fixing unit 30, which electrically prevents the toner from adhering to the pair of fixing rollers.

[0023] The image forming apparatus 1 is equipped with an image reader 40. The image reader 40 has a function of reading an image of a document with an optical sensor and converting it into an image signal.

[0024] The image forming apparatus 1 also includes a UI (user interface) unit 50 that displays the status of the image forming apparatus 1 and receives input from the user.

[0025] [Configuration of image formation control unit] The controller 100 that controls the image forming apparatus 1 will be described in detail with reference to FIG. 2. The controller 100 is an electric circuit 101 that includes a calculation unit such as a CPU, a ROM 102, and a RAM 103. The controller 100 functions as a control unit that performs various controls by having the CPU circuit unit 101 read out programs stored in the ROM 102 and RAM 103. The controller 100 is also electrically connected to various components, such as an external information terminal such as a personal computer 200, an input device such as an image reader 40, and an operation panel 50, and is capable of exchanging signal information. The controller 100 performs overall control of various components within the apparatus to perform image forming operations based on print information signals (e.g., image data, paper information, etc.) input from the input devices.

[0026] 2 is a block diagram showing a schematic configuration of the controller 100. Note that the diagram focuses on the parts necessary for explaining the operation of this embodiment, and other parts known as image control are omitted.

[0027] 2, the controller 100 has a CPU circuit unit 101. The CPU circuit unit 101 has a built-in CPU, ROM 102, and RAM 103, and controls each block (104, 105, 106, 107, 108, 109) in an integrated manner using a control program stored in the ROM 102. The RAM 103 temporarily stores control data and is used as a work area for calculations associated with the control.

[0028] Next, the details of the control by the CPU circuit unit 101 will be explained for each block.

[0029] The document feed control unit 107 controls the operations of the document feed unit 41 related to the document feeding and transport operations. The image reader control unit 106 controls the operation of the reader scanner 43 and the operation related to conversion to an analog image signal. The image signal control unit 105 controls the image processing operation of the analog image signal converted by the reader scanner 43. Specifically, this involves converting the analog image signal into a digital image signal, performing image processing, and converting the processed digital signal into a video signal and outputting it to the image forming control unit 104. The image signal control unit 105 also controls the image processing operation of the digital image signal input from the computer 200 via the external I / F 109. The image forming control unit 104 controls the driving of components related to the image forming operation based on the input video signal. In the first embodiment, the toner consumption amount is calculated by detecting the remaining toner amount using a toner remaining amount detection sensor in the development unit 14, and the image forming control unit 104 calculates the toner consumption amount based on the detection result. On the other hand, there is also a method in which the image signal control unit 105 calculates the toner consumption amount from the image signal, and either method is acceptable in the present invention.

[0030] The operation and display unit control unit 108 exchanges information between the operation and display unit 50 and the CPU circuit unit 101. The operation and display unit 50 outputs key signals corresponding to the operation of each key to the CPU circuit unit 101, and displays corresponding information on the display unit based on the signal from the CPU circuit unit 101.

[0031] [Image formation sequence] When the image forming apparatus 1 performs an image forming operation, the image forming control unit 104 executes the following control for each component involved in the image forming operation, and forms a full-color image on the paper P.

[0032] First, the image formation control unit 104 starts to rotate the photosensitive drum 11 in the image forming station 10 and the drive roller 22 in the transfer unit 20 at a predetermined speed in accordance with the image formation timing. Specifically, the photosensitive drum 11 is rotated clockwise in the drawing, and the drive roller 22 is rotated in a direction (counterclockwise in the drawing) that rotates the intermediate transfer belt 21 forward relative to the rotation direction of the photosensitive drum 11.

[0033] Next, the image forming station 10 executes operational control to develop an image on the photosensitive drum 11 of each color. Specifically, first, the charging roller 12 uniformly charges the surface of the photosensitive drum 11 with a predetermined potential and polarity. Next, the laser scanner unit 13 scans and exposes the surface of the photosensitive drum 11 using a laser beam modulated according to the image information signal for each color of Y, M, C, and K, thereby forming an electrostatic latent image of each color. Next, the developing unit 14 electrostatically attaches toner to the formed electrostatic latent image, forming (developing) a toner image on the photosensitive drum 11.

[0034] Next, an operation control is performed to superimpose the toner images formed on the photosensitive drums 11 of each color onto the intermediate transfer belt 21. In detail, a predetermined potential is applied to the primary transfer rollers 15 that face the photosensitive drums 11 via the intermediate transfer belt 21, and the toner images on the photosensitive drums 11 are electrostatically transferred onto the intermediate transfer belt 21 at the primary transfer section. By performing this operation for each color, an unfixed toner image of full color (Y color + M color + C color + K color) is formed on the intermediate transfer belt 21. This unfixed toner image is carried to the secondary transfer section by the rotational drive of the drive roller 22. Note that toner that cannot be transferred onto the intermediate belt 21 at the primary transfer section and remains on the photosensitive drums 11 is collected into a collected toner box 17 by a drum cleaning member 16.

[0035] Meanwhile, an operation of feeding paper from cassette 2 is carried out in parallel with the operation of forming an unfixed toner image on intermediate transfer belt 21. More specifically, in synchronization with the image formation timing, paper P is fed one sheet at a time by feed roller 3 and separation roller pair 4 and transported to registration roller pair 5. Thereafter, in synchronization with the unfixed toner image on intermediate transfer belt 21, paper P is transported to the secondary transfer unit.

[0036] Next, operational control is executed to transfer the unfixed toner image on the intermediate transfer belt 21 onto the paper P. More specifically, at the timing when the unfixed toner image and the paper P are transported to the secondary transfer section, a secondary transfer bias of a polarity opposite to the normal charging polarity of the toner is applied to the secondary transfer roller 25, and the unfixed toner image is electrostatically transferred from the intermediate transfer belt 21 to the paper P (secondary transfer). In other words, as the paper P is nipped and transported in the secondary transfer section, the unfixed toner image is transferred to the entire surface of the paper P. Note that any toner remaining on the intermediate transfer belt 21 that was not transferred to the paper P at the secondary transfer section is cleaned by the belt cleaning member 23 and collected in the main body collected toner box 24.

[0037] Generally, in image forming apparatus 1, when a large proportion of documents with low print ratios are subjected to image formation processing, the proportion of toner transferred from the developing roller in developing unit 14 to photosensitive drum 11 decreases. If the developing roller in developing unit 14 continues to rotate for a long time under such conditions, the toner is stirred and transported within developing unit 14. Furthermore, external additives contained in the toner may peel off or become embedded in the toner surface due to stirring and rubbing by the stirring member that supplies toner to the developing roller, or due to rubbing with the regulating member that regulates the amount of developer on the developing roller, resulting in a decrease in charging performance and fluidity. As a result, if image formation processing of documents with low print ratios continues, the amount of toner with reduced charging performance and fluidity increases in the developer container of developing unit 14 and on the developing roller, which tends to make the toner more susceptible to scattering.

[0038] Therefore, in the first embodiment, a forced toner discharge operation is performed when the amount of toner consumed per unit drive time of the developing roller is low (i.e., when the print ratio is low). The forced toner discharge operation is an operation that forcibly consumes toner by applying a bias to the developing roller to cause the toner carried by the developing roller to adhere to non-image forming areas on the photosensitive drum 11. By forcibly consuming toner through the forced toner discharge operation, fresh toner is replenished into the developing unit 14, thereby suppressing deterioration of the toner circulating within the developing unit 14 and ultimately suppressing toner scattering. Therefore, to increase the effect of suppressing deterioration of the toner circulating within the developing unit 14, it is desirable to increase the amount of toner forcibly consumed through the forced toner discharge operation.

[0039] However, if the forced toner discharge operation is performed by widening the time interval between sheets of an image forming job, downtime occurs each time the forced toner discharge operation is performed. Therefore, if the frequency of the forced toner discharge operation is increased or the duration of the forced toner discharge operation is extended in order to increase the amount of toner forcibly consumed by the forced toner discharge operation, productivity may decrease. Therefore, the invention according to the first embodiment reduces downtime while suppressing toner degradation. Details of this are described below.

[0040] [Method for suppressing toner deterioration during low-volume printing] Here, a detailed description will be given of a method for suppressing toner deterioration during low-yield printing, which is a feature of the present invention.

[0041] First, the transition of toner consumption relative to the development travel distance during low-yield printing will be explained with reference to Figure 3. The development travel distance during low-yield printing refers to the distance traveled by the development roller of the development unit 14 while image formation is being performed at a low print ratio.

[0042] In the first embodiment, low print quality is defined as the area below Ya (Y=aX) of toner consumption when an image with a 1% image coverage is output on A4 paper size, and Ya is the execution threshold [1] for the low print quality mode. In the first embodiment, Ya is the threshold at which toner deterioration is accelerated, and when it falls below Ya, the low print quality mode is executed.

[0043] During normal printing, the image forming apparatus 1 according to the first embodiment suppresses cleaning failures of the intermediate transfer belt cleaner 23 for each page of image output. To achieve this, the image forming apparatus 1 according to the first embodiment forms a halftone patch image (main scanning: 220 mm, sub-scanning: 5 mm) with a longitudinal width equivalent to A4 paper, and sends toner to the intermediate transfer belt cleaner 23. The density of this halftone patch image is expressed as the area ratio of the toner to the total area of ​​the patch image (hereinafter referred to as the toner coverage ratio).

[0044] This halftone patch image itself is created on the intermediate transfer belt 21 after one page is created, and is a toner consumption means that does not reduce productivity. Furthermore, the recovered toner is also collected by the intermediate transfer belt cleaner 23 into the main body recovered toner box 24, which has a sufficient collection capacity on the main body side, so there is no problem of recovered toner overflowing.

[0045] In the first embodiment, the toner coverage rate of the halftone patch image is varied to suppress poor cleaning of the intermediate transfer belt cleaner 23, and this is also used as a means to promote toner consumption during low-volume printing.

[0046] When the toner consumption with respect to the development running distance is lower than the low-printing mode threshold: Ya, the low-printing mode is turned on. Then, a halftone patch image for suppressing cleaning defects (the width of the band is the same as that during normal printing) is formed with a toner coverage rate of j% (during normal printing, it is i% (i < j)), and toner is fed into the intermediate transfer belt cleaner 23. This increases the toner coverage rate of the halftone image for suppressing cleaning defects and also suppresses toner degradation in low-printing. In the first embodiment, when i = 4 during normal printing and j = 65 during low-printing, it was confirmed that it is possible to suppress toner degradation in low-printing along with cleaning defects.

[0047] The halftone patch image used in the low-printing mode has a toner consumption equivalent to an image printing rate of 1% with respect to A4. Therefore, when the toner consumption state of the developing unit 14 is lower than the low-printing mode execution threshold [1]: Ya at which toner degradation progresses, the toner consumption of the actual printed image is also added. And toner consumption of 1% or more with respect to A4 (since the printing rate of the actual image is added) can be performed. As a result, the degradation of the toner circulating in the developing container of the developing unit 14 can be suppressed, and thus toner scattering can be suppressed.

[0048] Subsequently, a control example of the low-printing mode according to the first embodiment will be described using the flowchart of FIG. 4. The control of FIG. 4 is executed by the CPU 110 reading out a control program stored in the ROM 102 or the RAM 103 and controlling various devices. Also, the control of FIG. 4 starts when the CPU 110 receives an instruction to execute the low-printing mode and the low-printing mode is entered.

[0049] When job data is sent from computer 200 and paper P is conveyed to registration roller pair 5, the development travel distance and toner consumption of development unit 14(Y) are confirmed (step 401). Next, image formation control unit 104 calculates the toner consumption amount relative to the development travel distance of development unit 14(Y) (step 402). It is confirmed whether the calculated value is equal to or less than low print mode threshold [1]:Ya (step 403). If it is equal to or less than Ya, a halftone patch image for preventing cleaning defects is set so that the toner coverage (the toner coverage rate relative to the area of ​​the patch image) is j% (step 404). Next, the toner coverage rate of the halftone patch image set for that job is stored in memory (step 405). One page is output (step 406), and a halftone patch image is created in the non-image area on intermediate transfer belt 21 (step 407). If there is a next page (step 408), the process returns to (step 406); if there is no next page (step 408), the toner coverage rate of the halftone patch image set in the job is cleared from memory (step 409), and printing (image formation) is terminated.

[0050] If the value is greater than the low-yield print mode threshold [1]:Ya (step 403), the halftone patch image is set so that the toner coverage (toner coverage relative to the area of ​​the patch image) is i% (the toner coverage during normal printing) (step 410). Next, the toner coverage of the halftone patch image set for the job is stored in memory (step 411). One page is output (step 412), and a halftone patch image is created in the non-image area on the intermediate transfer belt 21 (step 413). If there is a next page (step 414), the process returns to (step 412); if there is not a next page (step 414), the toner coverage of the halftone patch image set for the job is cleared from memory (step 415), and printing ends.

[0051] In this way, when a job arrives in a low-yield printing state below the low-yield printing mode threshold [1]: Ya, the toner coverage of the halftone patch image for preventing cleaning failures is set to j%. This makes it possible to consume more toner than the toner consumption transition: Ya when outputting an image with an image coverage rate of 1% on A4 paper, thereby suppressing toner degradation.

[0052] The halftone patch image for cleaning this time is itself created on the intermediate transfer belt 21 after one page is created, and is a toner consumption means that does not reduce productivity. Furthermore, the recovered toner is also collected by the intermediate transfer belt cleaner 23 in the main body recovered toner box on the main body side, and there is sufficient toner collection capacity, so the problem of recovered toner overflowing does not occur.

[0053] In this case, the halftone patch image for preventing cleaning failure is switched on a job-by-job basis. On the other hand, it is also possible to check for each page whether the low print state is below the low print mode threshold [1]:Ya, and switch the toner coverage of the halftone patch image based on the result.

[0054] In the first embodiment described above, when executing an image formation job, the controller 100 controls the image forming station 10 to form a halftone patch image in a non-paper passing area of ​​the intermediate transfer belt 21 after an image for forming a toner image on a recording material is formed. The halftone patch image refers to a patch image for supplying toner to the intermediate transfer belt cleaner 23. At this time, the controller 100 changes the density of the halftone patch image based on the toner consumption (pixel count) relative to the travel distance of the developing roller. Specifically, when the pixel count is a first consumption amount, the controller 100 controls the image forming station 10 to form a halftone patch image of a first density. On the other hand, when the pixel count is a second consumption amount less than the first consumption amount, the controller 100 controls the image forming station 10 to form a halftone patch image of a second density darker than the first density. This makes it possible to suppress toner degradation and reduce downtime.

[0055] <Second embodiment> In the second embodiment, only the parts that are different from the first embodiment will be described, and the other basic configurations are common to the first and second embodiments.

[0056] In the first embodiment described above, toner is consumed only by the first toner discharge means, which has the advantage of not reducing productivity, but the halftone patch image formed in the non-image area on the intermediate transfer belt 21 comes into contact with the secondary transfer roller 25. For this reason, the higher the density of the halftone patch image, the worse the contamination of the secondary transfer roller 25 becomes, leading to contamination of the back side of the paper P. Therefore, simply increasing the density of the halftone patch image may result in contamination of the secondary transfer roller 25.

[0057] The second embodiment has been made in consideration of the above-mentioned problems, and when used in a low printing state, two types of toner discharge means are used to consume toner equivalent to Ya (Y=aX) and suppress toner deterioration. Details will be explained below. In addition, unless otherwise specified, the same as in the first embodiment.

[0058] The difference from the first embodiment is that the toner coverage rate j% of the cleaning halftone patch image is reduced to k% (j>k), thereby minimizing contamination of the secondary transfer roller 25 by the patch image. This reduces toner consumption accordingly, and when the extremely low printing threshold [2]:Yb (Y=aX-b) in the second embodiment is reached, a forced toner discharge operation is performed to suppress toner degradation.

[0059] A toner coverage rate of j% for a cleaning halftone patch image can consume toner equivalent to an image printing rate of 1% for A4 paper, while a toner coverage rate of k% can consume toner equivalent to an image printing rate of 0.6%.

[0060] The forced toner ejection operation stops the image formation operation, separates the transfer unit 20 from the photosensitive drum 11 of each color in each image forming station 10, and forces the laser scanner unit 13 to light up over the entire area by the image formation control unit 104. This forms a solid image, and operates the image forming station 10 to form a toner image. The toner image formed on the photosensitive drum 11 is collected into the collected toner box 17 by the drum cleaning member 16.

[0061] The method of consuming toner by the toner discharging means in a low print state, which is a feature of the present invention, will be described in detail below.

[0062] First, the forced toner discharge execution threshold [2]:Yb in the extremely low print state according to the second embodiment will be described with reference to FIG. 5. The forced toner discharge execution threshold [2]:Yb is shifted downward by the toner consumption amount b for one forced toner discharge with the same slope a as the threshold [1]:Ya (Y=aX) for low print, using the same slope a as the threshold [1]. Also, let Y=aX-b be the forced toner discharge execution threshold [2]:Yb. If forced toner discharge is executed once when the development unit 14(Y) reaches the forced toner discharge execution threshold [2]:Yb, the state of the development unit 14 is returned to Ya.

[0063] As shown in FIG. 5, for a user who outputs a large number of images with extremely low printing (in the second embodiment, an image coverage rate of 0.3% or less for A4 is defined as extremely low printing), toner consumption transitions below the low printing mode execution threshold [1]:Ya, and the low printing mode is turned on. Also, the toner coverage rate of the halftone patch image for preventing cleaning failure, which is the first toner discharge means described in the first embodiment, changes from i% (the toner coverage rate during normal printing) to k%. In the second embodiment, to prevent contamination of the secondary transfer roller 25 by the patch image, the toner coverage rate of the patch image is reduced from j% to k% compared to the first embodiment. Therefore, if printing with extremely low printing continues, the forced toner discharge execution threshold [2]:Yb, which indicates the extremely low printing state, is reached, and forced toner discharge is executed. By performing forced toner discharge, the toner consumption returns to Ya, and if printing at extremely low print quality continues in the same manner, the forced toner discharge execution threshold [2]:Yb is reached and the forced toner discharge operation is performed.

[0064] After that, when the development rotation distance is c, normal printing (image coverage rate of 2% or more for A4) is resumed, and when the toner consumption amount for the development rotation distance is equal to or greater than the low-printing print mode execution threshold [1]: Ya, the low-printing print mode is turned off. Also, the first toner discharge means returns to the normal toner coverage rate of the halftone patch image for preventing cleaning failures to i%, and printing continues.

[0065] In the second embodiment, the toner coverage rate of the halftone image for preventing cleaning defects is increased to a level that does not cause contamination of the secondary transfer roller 25, thereby also preventing toner degradation during extremely low yield printing. Also, in the second embodiment, it was confirmed that by setting i=4 during normal printing and k=40 during low yield printing, it is possible to prevent toner degradation during extremely low yield printing as well as cleaning defects.

[0066] The amount of toner consumed for the development rotation distance used in the low print mode in the second embodiment is equivalent to the amount of toner consumed for an image printing rate of 1% for A4 paper. As a result, deterioration of the toner circulating in the development container of the development unit 14 can be suppressed, and ultimately toner scattering can be suppressed.

[0067] An example of control in the low print mode according to the second embodiment will be described with reference to the flowchart of Fig. 6. The control in Fig. 6 is executed by the CPU 110 reading out a control program stored in the ROM 102 or RAM 103 and controlling various devices.

[0068] When job data is sent from computer 200 and paper P is conveyed to registration roller pair 5, the development travel distance and toner consumption of development unit 14(Y) are confirmed (step 601). Next, image formation control unit 104 calculates the toner consumption amount relative to the development travel distance of development unit 14(Y) (step 602). It is confirmed whether the calculated value is equal to or less than low print mode threshold [1]:Ya (step 603). If it is equal to or less than Ya, the halftone patch image is set so that the toner coverage (the toner coverage rate relative to the area of ​​the patch image) is k% (step 604). Next, the toner coverage rate of the halftone patch image set for that job is stored in memory (step 605). Next, it is confirmed whether it is equal to or less than forced toner discharge execution threshold [2]:Yb, which is an extremely low print output (step 606). If it is equal to or less than Yb, forced toner discharge is promptly executed (step 607), and one page is output (step 608). If the toner consumption is greater than Yb, one page is output without forcibly discharging toner (step 608). After outputting one page (608), a halftone patch image is created in the non-image area on the intermediate transfer belt 21 (step 609). If there is a next page (step 610), the process returns to (step 601); if there is not a next page (step 610), the toner coverage rate of the halftone patch image set in the job is cleared from memory (step 611), and printing (image formation) ends.

[0069] If the value is greater than the low-yield print mode threshold [1]:Ya (step 603), the halftone patch image is set so that the toner coverage (toner coverage relative to the area of ​​the patch image) is i% (the toner coverage during normal printing) (step 612). Next, the toner coverage of the halftone patch image set for the job is stored in memory (step 613). Next, one page is output (step 608), and a halftone patch image is created in the non-image area on the intermediate transfer belt 21 (step 609). If there is a next page (step 610), the process returns to (step 601). If there is not a next page (step 610), the toner coverage of the halftone patch image set for the job is cleared from memory (step 611), and printing ends.

[0070] In this way, when a job arrives in a low-yield printing state below Ya, the toner coverage of the halftone patch image for preventing cleaning defects is set to k%. This makes it possible to consume the same amount of toner per page output as when outputting an image equivalent to 0.6% image coverage on A4 paper. Furthermore, by changing the toner coverage of the halftone patch image from j% to k% compared to the first embodiment, contamination of the secondary transfer roller 25 by the patch image can be reduced. Because toner consumption is reduced accordingly, when the forced toner discharge execution threshold [2] is reached, a forced toner discharge operation can be executed to bring toner consumption back to Ya, thereby suppressing toner degradation due to low-yield printing.

[0071] Although the forced toner ejection operation temporarily stops the image formation operation and thus affects productivity, it can reliably return toner consumption to the low print threshold while suppressing contamination of the secondary transfer roller 25 by halftone patch images for suppressing cleaning failures. This makes it possible to suppress toner degradation while suppressing contamination of the secondary transfer roller 25.

[0072] Furthermore, the halftone patch image for cleaning this time is created on the intermediate transfer belt 21 after one page is imaged, and is a toner consumption means that does not reduce productivity. Furthermore, the recovered toner is also collected by the intermediate transfer belt cleaner 23 in the main body recovered toner box on the main body side, and there is sufficient toner collection capacity, so the problem of recovered toner overflowing does not occur.

[0073] In this case, the halftone patch image for preventing cleaning failure is switched on a job-by-job basis. On the other hand, it is also possible to check for each page whether the low print state is below the low print mode threshold [1]:Ya, and switch the toner coverage of the halftone patch image based on the result.

[0074] <Third embodiment> In the third embodiment, only the parts that are different from the second embodiment will be described, and the other basic configurations are common to the second and third embodiments.

[0075] In the second embodiment described above, an example was described in which, when a forced ejection operation is required, the forced ejection operation is performed between sheets of paper in an image forming job. Meanwhile, in recent years, there has been a particular demand for improved productivity in image forming devices. To further improve productivity, it is necessary to narrow the time interval between sheets of paper, and in this case, the time required to perform the forced ejection operation becomes a constraint on improving productivity. Therefore, instead of performing the forced ejection operation between sheets of paper, a method of performing the forced ejection operation during post-rotation after the job is completed can be considered.

[0076] Generally, the image forming apparatus 1 is configured so that the image forming stations 10 for each color can be started and stopped as needed. For example, when forming a monochrome black image, the Y, M, and C image forming stations 10 are stopped, while when forming a full-color image, all of the Y, M, C, and K image forming stations 10 are started. The reason for stopping the image forming stations 10 other than K, which are not used in image formation, when forming a monochrome black image is as follows: by not driving the unused image forming stations 10, the lifespan of the developing devices 14, photosensitive drums 11, and the components that drive them can be extended, and unnecessary power consumption can be reduced.

[0077] Consider a case where a mixed job of full-color and monochrome images is performed in this configuration. While the full-color image is being formed, all of the Y, M, C, and K image forming stations 10 are activated to form the image. Then, when it's time to form a monochrome image, the Y, M, and C image forming stations 10 other than K are stopped. If the job ends and the system shifts to post-rotation in this state, the image forming stations 10 other than K will remain stopped. Even if a forced toner ejection operation for Y, M, and C is required, it cannot be performed while the image forming stations 10 are stopped.

[0078] The third embodiment has been made in consideration of the above-mentioned problems. In the third embodiment, when a forced toner discharge operation is required at the end of a job, if the image forming station 10 for that color is stopped, the image forming station 10 is started again in a post-job rotation, and the forced toner discharge operation is performed after the start.

[0079] Hereinafter, the density adjustment of halftone patch images and the forced toner ejection method in the low print state according to the third embodiment will be described in detail.

[0080] An example of control in the low print mode according to the third embodiment will be described with reference to the flowchart of Fig. 7. The control in Fig. 7 is executed by the CPU 110 reading out a control program stored in the ROM 102 or RAM 103 and controlling various devices.

[0081] When job data is sent from computer 200 and paper P is conveyed to registration roller pair 5, the development travel distance and toner consumption of development unit 14 for each color (Y, M, C, K) are confirmed (step 701). Next, image formation control unit 104 calculates the toner consumption for each color of development unit 14 relative to the development travel distance (step 702). It is confirmed whether the calculated value is equal to or less than low-yield print mode threshold [1]: Ya (step 703). If it is equal to or less than Ya, a halftone patch image for preventing cleaning defects is set so that the toner coverage is k% (step 704). Next, the toner coverage of the halftone patch image set for the job is stored in memory (step 705). On the other hand, if the value is greater than low-yield print mode threshold [1]: Ya (step 703), the halftone patch image for preventing cleaning defects is set so that the toner coverage is i% (step 716). Next, the toner coverage of the halftone patch image set for the job is stored in memory (step 717). Next, it is determined whether the transmitted job data is a monochrome job (step 706). If it is a monochrome job, the K image forming station 10 is started (step 707), while the image forming stations 10 other than K are stopped (step 708). If it is a color image in the determination of whether the job data is a monochrome job (step 706), all the color image forming stations 10 are started (step 718). One page is then output (step 709). After one page is output (step 709), a halftone patch image is created in the non-image area on the intermediate transfer belt 21 (step 710). If there is a next page (step 711), the process returns to step 701. If there is not a next page (step 711), the toner coverage of the halftone patch image set in the job is cleared from memory (step 712).

[0082] Next, each color is checked to see if it is below the forced toner discharge execution threshold [2]: Yb, which is the extremely low print output (step 713). If it is below the forced toner discharge execution threshold [2]: Yb, the image forming station 10 for the corresponding color that requires forced toner discharge is started (step 714), and after performing forced toner discharge (step 715), the job is terminated. If the toner consumption is greater than Yb (step 713, No), the job is terminated without performing forced toner discharge.

[0083] As described above, when the determination of whether or not the forced toner discharge operation is necessary is made during post-rotation, if the image forming station 10 of the color in question is in a stopped state, the image forming station 10 of the color in question that requires the forced toner discharge operation is started at this timing. Then, by performing the forced toner discharge operation after startup, downtime can be reduced.

[0084] <Other embodiments> The present invention is not limited to the above-described embodiments, and various modifications (including organic combinations of the respective embodiments) are possible based on the spirit of the present invention, and these are not excluded from the scope of the present invention.

[0085] In the above embodiment, an image forming apparatus configured to use an intermediate transfer belt 21 as shown in Fig. 1 has been described as an example, but the present invention is not limited to this. It is also possible to apply the present invention to an image forming apparatus configured to perform transfer by directly contacting the paper P with the photosensitive drums 11 in sequence.

[0086] In addition, in the above embodiment, an image forming apparatus configured to use a single-component development system has been described as an example, but the present invention is not limited to this. It is also possible to apply the present invention to an image forming apparatus configured to use a two-component development system. [Explanation of symbols]

[0087] 1. Image forming device 10 Image forming station 11 Photosensitive drum 13 Exposure means 14 Development unit 21 Intermediate transfer belt 23 Intermediate transfer belt cleaner 100 Controllers

Claims

1. an image forming section including an image carrier on which an electrostatic image is formed, a developer container containing a developer including toner, and a rotatable developer carrier that carries the developer to develop the electrostatic image formed on the image carrier, and that forms a toner image on the image carrier; a movable intermediate transfer body onto which a toner image formed on the image carrier by the image forming unit is transferred; a cleaning member provided in contact with the intermediate transfer body and configured to clean toner remaining on the intermediate transfer body; a control unit that controls the image forming unit; Equipped with The control unit when a ratio of an amount of toner consumed in a continuous image forming job to a distance over which the developer carrier is rotationally driven in the continuous image forming job for forming images on a plurality of recording materials including a first recording material and a second recording material following the first recording material is higher than a predetermined threshold value, each time a toner image for an image to be formed on one sheet of recording material is transferred to the intermediate transfer body, the image forming unit is controlled to form a first toner supply image for supplying toner to the cleaning member during a predetermined period from when a toner image for an image to be formed on the first recording material is transferred to the intermediate transfer body until when a toner image for an image to be formed on the second recording material is transferred to the intermediate transfer body, if the ratio is lower than the predetermined threshold value, controlling the image forming unit so as to form a second toner supply image for supplying toner to the cleaning member during the predetermined period every time a toner image for an image formed on one sheet of recording material is transferred to the intermediate transfer body; The density of the second toner-supplied image is higher than the density of the first toner-supplied image. An image forming apparatus characterized by:

2. an area of ​​the second toner supply image is the same as an area of ​​the first toner supply image; A toner coverage rate relative to the area of ​​the second toner supply image is higher than a toner coverage rate relative to the area of ​​the first toner supply image.

2. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

3. The length of the second toner supply image in the movement direction of the intermediate transfer body is the same as the length of the first toner supply image in the movement direction of the intermediate transfer body.

3. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

4. an image forming section including an image carrier on which an electrostatic image is formed, a developer container containing a developer including a toner, and a rotatable developer carrier that carries the developer to develop the electrostatic image formed on the image carrier, and that forms a toner image on the image carrier; a movable intermediate transfer body onto which a toner image formed on the image carrier by the image forming unit is transferred; a first cleaning member provided in contact with the intermediate transfer body and configured to clean toner remaining on the intermediate transfer body; a second cleaning member provided in contact with the image carrier and configured to clean toner remaining on the image carrier; a control unit that controls the image forming unit; Equipped with The control unit when a ratio of an amount of toner consumed in a continuous image forming job to a distance over which the developer carrier is rotationally driven in the continuous image forming job, which forms images on a plurality of recording materials including a first recording material and a second recording material following the first recording material, is higher than a first threshold value, the image forming unit is controlled to form a first toner supply image for supplying toner to the first cleaning member during a predetermined period from when a toner image for an image to be formed on the first recording material is transferred to the intermediate transfer body until when a toner image for an image to be formed on the second recording material is transferred to the intermediate transfer body; when the ratio is lower than the first threshold value and higher than a second threshold value lower than the first threshold value, controlling the image forming unit to form a second toner supply image for supplying toner to the first cleaning member during the predetermined period; If the ratio is lower than the second threshold value, the continuous image forming job is interrupted, and in a state in which the continuous image forming job is interrupted, the image forming unit is controlled to form a third toner supplying image for supplying toner to the second cleaning member; The density of the second toner-supplied image is higher than the density of the first toner-supplied image. An image forming apparatus characterized by:

5. an area of ​​the second toner supply image is the same as an area of ​​the first toner supply image; A toner coverage rate relative to the area of ​​the second toner supply image is higher than a toner coverage rate relative to the area of ​​the first toner supply image.

5. The image forming apparatus according to claim 4.

6. The length of the second toner supply image in the movement direction of the intermediate transfer body is the same as the length of the first toner supply image in the movement direction of the intermediate transfer body.

6. The image forming apparatus according to claim 4, wherein the image forming apparatus is a recording medium.

7. The control unit If the ratio is higher than the first threshold value, the image forming unit is controlled to form the first toner supply image during the predetermined period every time a toner image for an image formed on one sheet of recording material is transferred to the intermediate transfer body, When the ratio is lower than the first threshold value and higher than the second threshold value, the image forming unit is controlled so as to form the second toner supply image during the predetermined period every time a toner image for an image formed on one sheet of recording material is transferred to the intermediate transfer body.

7. The image forming apparatus according to claim 4, wherein the image forming apparatus is a recording medium.

8. the image forming unit has an exposure unit that exposes the image carrier to light in order to form an electrostatic image on the image carrier; The image forming unit forms a toner image for the third toner supply image on the image carrier by exposing the entire area of ​​the image carrier to light using the exposure unit.

8. The image forming apparatus according to claim 4, wherein the image forming apparatus is a recording medium.

9. When the ratio is lower than the second threshold value, the control unit interrupts the continuous image forming job, separates the image carrier from the intermediate transfer body, and controls the image forming unit to form the third toner supply image in a state in which the continuous image forming job is interrupted and the image carrier is separated from the intermediate transfer body.

9. The image forming apparatus according to claim 4, wherein the image forming apparatus is a recording medium.

Images