JP4419791B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus using an electrophotographic system such as a copying machine or a printer.

  In an electrophotographic image forming apparatus, after an image carrier is charged, it is exposed according to image information to form an electrostatic latent image, and the toner in the developing means is applied to the image carrier according to the electrostatic latent image. The toner image is developed into a toner image, and the toner image is transferred onto a recording material such as a recording paper, an OHP sheet, or a cloth by a transfer unit, and then fixed by a fixing unit to obtain a recorded image.

  By the way, in the above-described image forming apparatus, when images with a low image printing rate and a small amount of toner consumption are continuously output, the development time is increased due to a long residence time of toner in the developing means. May adversely affect the transferability and transferability. In other words, the chargeability and fluidity of the toner are mainly imparted by the attached external additive. However, when the residence time is long, the external additive is easily detached due to the stress of stirring in the developing means. As a result, it becomes easy to release or bury the toner, and the developing property and the transfer property are adversely affected by a change in the charge amount of the toner and an increase in physical adhesion. If the toner charge amount or physical adhesion increases, the developability deteriorates or the image density decreases on the recording material due to transfer defects. If the charge amount decreases, fog, toner scattering, and development occur. Excessive image density on the recording material due to excess will occur.

  Therefore, conventionally, as described in Patent Document 1, for example, an amount of toner that will be consumed in an image is estimated from an image signal, and when the amount is smaller than a predetermined amount of toner, a certain amount of toner is set. It was forcibly consumed in advance on the image carrier.

  In addition, image formation is performed such that a toner image is formed on an image carrier, the toner image is primarily transferred to an intermediate transfer member, and then the toner image on the intermediate transfer member is secondarily transferred to a recording material to obtain a recorded image. The device is known. In such an apparatus, after a toner image is formed on the image carrier and a primary transfer process of the toner image to the intermediate transfer member is repeated, a color image composed of a plurality of colors is formed on the intermediate transfer member. The image can be secondarily transferred collectively to a recording material to obtain a color image, and is effective as a color image forming apparatus for obtaining a color image by sequentially laminating and transferring a plurality of color images. It is possible to obtain an image without misalignment (color misregistration).

In such a color image forming apparatus, it can be considered that the toner forcibly consumed on the image carrier is primarily transferred to the intermediate transfer member in the same manner as in normal image formation.
JP 2000-206744 A

  However, in the conventional example disclosed in Patent Document 1, the toner that is forcibly consumed is cleaned by the cleaning member of the image carrier, so that the load on the cleaning member of the image carrier increases. If the cleaning member is in the initial state, cleaning can be performed without any problem. However, if the cleaning member is worn by repeated use, the toner slips between the cleaning member and the image carrier. There is a technical problem that a defective cleaning due to the above occurs and a good image cannot be output.

  In the above-described color image forming apparatus, when the toner that is forcibly consumed is primarily transferred to the intermediate transfer member, the toner that is forcibly consumed is cleaned by the cleaning member for the intermediate transfer member. As a result, the load on the cleaning member of the intermediate transfer member increases. In particular, when the four color toners on the image carrier that have been forcibly consumed are sequentially transferred onto the intermediate transfer member, the four color toners are transferred to the intermediate transfer member in a superposed state. Thus, an excessive load is applied to the cleaning member of the intermediate transfer member. When cleaning is performed by the image bearing member cleaning member for each color without performing the primary transfer, the load on the intermediate transfer member cleaning member is reduced, but the load on the image bearing member cleaning member is increased, The same problem as in the conventional example occurs.

  An object of the present invention is to appropriately control the primary transfer amount of the toner on the image carrier that has been forcibly consumed to the intermediate transfer body based on the rubbing distance from the initial state of the cleaning member of the image carrier. Another object of the present invention is to provide an image forming apparatus capable of preventing poor cleaning of an image carrier and maintaining good image quality for a long period of time.

  The object of the present invention is achieved by the following configurations.

(Claim 1)
An image carrier on which an electrostatic latent image is formed, developing means for developing the electrostatic latent image with toner to form a toner image on the image carrier, an intermediate transfer member, and a toner image on the image carrier a primary transfer means for transferring the primary and then pressed to the intermediate transfer member, and a first cleaning member for cleaning the toner on the image carrier by rubbing the image bearing member on said image bearing member a secondary transfer unit that transfers the secondary bets toner image which is primarily transferred to the intermediate transfer member onto a recording material from the cleaning the toner on said intermediate transfer member rubs on the intermediate transfer member an image forming apparatus having a second cleaning member, the forced consumption mode execution means for executing a forced consumption mode for forcibly consuming the toner in the developing unit in the image bearing member, said first cleaning member The rubbing distance based on the initial state of the Counting means for bets, a pinch release means for crimping or crimped release the primary transfer means to the intermediate transfer member, in the forced consumption mode, rubbing distance counted by the counting means first predetermined value or less In this case, the primary transfer unit is released from pressure bonding, and cleaning is performed by the first cleaning member. When the rubbing distance exceeds a first predetermined value, the primary transfer unit is pressure bonded to An image forming apparatus comprising: a control unit that controls to perform cleaning with the second cleaning member .

(Claim 2)
When the forced consumption mode is executed , the control means is configured to force the upper surface of the image carrier to be forcibly consumed when the sliding distance exceeds a first predetermined value and the primary transfer means is pressure-bonded to the intermediate transfer body. When the rubbing distance counted by the counting means exceeds the second predetermined value larger than the first predetermined value , the primary transfer output in the primary transfer of the toner to the intermediate transfer member is: The image forming apparatus according to claim 1, wherein the image forming apparatus is larger than the first predetermined value and larger than the second predetermined value .

(Claim 3)
In the forced consumption mode, the control means outputs the primary transfer output in the primary transfer of the toner on the image carrier forcibly consumed to the intermediate transfer member, and the developed image carrier at the time of image formation. 3. The image forming apparatus according to claim 1, wherein the toner image is smaller than a primary transfer output in the primary transfer of the upper toner image to the intermediate transfer member.

  According to the first aspect of the present invention, in the forced consumption mode, selection of pressure bonding or pressure release of the primary transfer unit in the primary transfer of the toner on the image carrier that has been forcibly consumed to the intermediate transfer body is performed. Since the image bearing member is changed based on the rubbing distance from the initial state of the cleaning member of the image carrier, the intermediate transfer member for forcibly consumed toner based on the rubbing distance from the initial state of the cleaning member of the image carrier It is possible to change the amount of primary transfer toner to.

  In the region where the rubbing distance is short, the primary transfer means is released from pressure contact, and the primary transfer of the consumed toner to the intermediate transfer body is not performed. The secondary transfer means is pressure-bonded and the toner that is forcibly consumed is primarily transferred to the intermediate transfer member.

  As a result, when the cleaning member for the image carrier is close to the initial state, it is necessary to clean the toner forcibly consumed by the cleaning member for the intermediate transfer member by cleaning the forcibly consumed toner with the cleaning member for the image carrier. Since it disappears, the load can be reduced. Further, in a region where the rubbing distance is large, in a state where the cleaning member of the image carrier is worn, the primary transfer means is pressure-bonded to forcibly consume the consumed toner to the intermediate transfer member to perform primary transfer. The load on the cleaning member of the carrier can be reduced, the cleaning failure on the image carrier can be prevented, and good image quality can be maintained for a long time.

  According to invention of Claim 2, there exist the following effects. In the first aspect of the invention, in the region where the rubbing distance is large, the primary transfer means is pressure-bonded and the toner that is forcibly consumed is primarily transferred to the intermediate transfer member. By changing the next transfer output based on the rubbing distance from the initial state of the cleaning member of the image carrier, the primary transfer means is pressure-bonded based on the rubbing distance from the initial state of the cleaning member of the image carrier. In this state, the primary transfer toner amount can be changed.

  As the rubbing distance increases, the primary transfer output in a state where the primary transfer unit is pressure-bonded is increased, and the primary transfer toner amount is increased. As a result, in a state where the cleaning member is worn in a region where the sliding distance of the cleaning member of the image carrier is large, by increasing the amount of primary transfer toner, according to the wear state of the cleaning member of the image carrier, It is possible to reduce the load, prevent a cleaning failure on the image carrier, and maintain good image quality for a longer period.

  According to invention of Claim 3, there exist the following effects. Normally, during image formation, the primary transfer output in the primary transfer of the toner image developed on the image carrier to the intermediate transfer member is the transfer rate (with respect to the toner amount on the image carrier before the primary transfer). The ratio of the amount of toner on the intermediate transfer body after the primary transfer) is set to be almost 100%. When the primary transfer output in the primary transfer of the toner on the image bearing member that has been forcibly consumed to the intermediate transfer body is set to be the same as that during image formation, the toner is forcibly consumed particularly in a plurality of image forming units. When the toners are sequentially primary transferred to the intermediate transfer member, all of the toners are transferred to the intermediate transfer member in a superposed state, and the cleaning member for the intermediate transfer member is excessively large. It becomes a load.

  Therefore, in the forced consumption mode, the primary transfer output in the primary transfer of the toner on the image carrier that is forcibly consumed to the intermediate transfer member is the intermediate of the toner image developed on the image carrier at the time of image formation. By making the output smaller than the primary transfer output in the primary transfer to the transfer body, it is possible to reduce the amount of toner forcibly consumed in the primary transfer. Therefore, the cleaning load of the toner that is forcibly consumed can be distributed to the cleaning member of the image carrier and the cleaning member of the intermediate transfer member, and all of the toner that is forcibly consumed by the plurality of image forming units It is possible to prevent an excessive load on the cleaning member for the intermediate transfer member when the intermediate transfer member is transferred to the intermediate transfer member.

  Embodiments of the present invention will be described. FIG. 1 is a diagram showing a configuration of a color image forming apparatus which is an example of an image forming apparatus according to an embodiment of the present invention.

  The color image forming apparatus includes an image forming apparatus main body GH and an automatic document feeder JG installed on the image forming apparatus main body GH.

  The automatic document feeder JG conveys the documents d placed on the document feed table 31 one by one, passes the reading position, and discharges them to the document discharge table 32. The automatic document feeder JG can be opened and closed. By opening the automatic document feeder JG, a document can be placed on the document placement unit 45.

  Reference numeral 40 denotes an image reading unit, which includes a scanning unit 41 including a light source and a mirror for illuminating a document, a scanning unit 42 including two mirrors, an imaging lens 43, an image pickup device 44 including a CCD, and a document placement unit 45. .

  In document reading using the automatic document feeder JG, the scanning units 41 and 42 are set at the positions shown in the figure, and the automatic document feeder JG is set at the positions shown in the figure to convey the document d and to deliver a large number of documents d. Are continuously read. In document reading using the document placement unit 45, the automatic document feeder JG is opened, the document d is placed on the document placement unit 45, and the scanning units 41 and 42 are moved to scan the document d. Thus, the original is read. The automatic document feeder JG includes an automatic duplex document feeder. Image data read from the document is stored in a storage unit M2 of an image processing unit C2 (not shown), and image processing such as filter processing, gradation adjustment, and scaling processing is performed.

  The image forming apparatus main body GH includes four image forming units 10Y, 10M, 10C, and 10K, a control unit 100, a belt-shaped intermediate transfer body 6, a paper feeding / conveying unit, a fixing unit 24, and an operation input unit 9. (Not shown), and four image forming units 10Y, 10M, 10C, and 10K are arranged in parallel along the moving direction of the belt-shaped intermediate transfer body 6 that moves around in the direction of arrow AA in the drawing. This is a so-called tandem full-color image forming apparatus.

  The image forming unit 10Y that forms a yellow image includes a charging unit 2Y, an exposure unit 3Y, a developing unit 4Y, and a first cleaning unit 8Y disposed around a photoconductor 1Y that is an image carrier. The image forming unit 10M that forms a magenta image includes the photoconductor 1M, the charging unit 2M, the exposure unit 3M, the developing unit 4M, and the first cleaning unit 8M as described above. The image forming unit 10C that forms a cyan image includes the photoconductor 1C, the charging unit 2C, the exposure unit 3C, the developing unit 4C, and the first cleaning unit 8C as described above. The image forming unit 10K that forms a black image includes the photoconductor 1K, the charging unit 2K, the exposure unit 3K, the developing unit 4K, and the first cleaning unit 8K as described above. The charging unit 2Y and the exposure unit 3Y, the charging unit 2M and the exposure unit 3M, the charging unit 2C and the exposure unit 3C, and the charging unit 2K and the exposure unit 3K constitute an electrostatic latent image forming unit. 5Y, 5M, 5C, and 5K are toner containers containing yellow toner, magenta toner, cyan toner, and black toner, respectively, and these toner containers correspond to consumption in the developing units 4Y, 4M, 4C, and 4K. Toner is supplied.

  Each of the photoreceptors 1Y, 1M, 1C, and 1K is a negatively chargeable OPC photoreceptor in which an OPC photosensitive layer is formed on a metal drum. As the photoreceptors 1Y, 1M, 1C, and 1K, those other than the OPC photoreceptor such as an aSi photoreceptor can be used, and a positively charged photoreceptor can also be used. Each of the photoconductors 1Y, 1M, 1C, and 1K is provided with an encoder (not shown) that outputs a pulse for each rotation, and the control means 100 detects the output to thereby detect the photoconductor. The rotational speeds of 1Y, 1M, 1C, and 1K can be counted.

  As the charging means 2Y, 2M, 2C, and 2K, a corotron discharger or a scorotron discharger can be used, and a discharge wire type, a saw electrode type, or the like can be used.

  The exposure unit 3Y has a semiconductor laser as a light source, and performs dot exposure of the photoreceptor 1Y with a laser beam, and performs exposure based on yellow image data. Similarly, the exposure unit 3M exposes the photoconductor 1M based on the magenta image data, the exposure unit 3C exposes the photoconductor 1C based on the cyan image data, and the exposure unit 3K uses the black image data. To expose. As the exposure means 3Y, 3M, 3C, 3K, an exposure means other than a laser beam such as an LED array or a liquid crystal can be used, but those that perform dot exposure are preferable.

  In the forced consumption mode in which the toner is forcibly consumed, each color toner in the developing means 4Y, 4M, 4C, and 4K is forcibly received on the photoreceptors 1Y, 1M, 1C, and 1K in response to the output from the control means 100. The exposure means 3Y, 3M, 3C, 3K exposes a predetermined pattern to be consumed in detail.

  The developing means 4Y, 4M, 4C, and 4K form openings with respect to the photoreceptors 1Y, 1M, 1C, and 1K, and are rotatable cylindrical developer carriers 46Y, 46M, 46C, and 46K, and the developer. And a plurality of stirring screws 47Y, 47M, 47C, 47K for supplying the developer after stirring to the developer carriers 46Y, 46M, 46C, 46K. The toner replenished from the toner containers 5Y, 5M, 5C, and 5K is supplied to the developer carriers 46Y, 46M, 46C, and 46K while being stirred by the stirring screws 47Y, 47M, 47C, and 47K.

  As the developer, either a two-component developer containing a toner and a carrier or a one-component developer containing a toner and not containing a carrier may be used.

  Further, the developing means 4Y, 4M, 4C, and 4K may be either a reversal developing type that attaches toner to an exposed portion or a regular developing type that attaches toner to an unexposed portion, a contact developing method or a non-contact developing method. Either of these may be used. As described above, any known developing means can be used as the developing means 4Y, 4M, 4C, and 4K, but a reversal developing type developing means using a two-component developer is preferable.

  The first cleaning means 8Y, 8M, 8C, 8K are rubber cleaning blades 88Y, 88M, 88C, 88K as first cleaning members formed long in the longitudinal direction of the photoreceptors 1Y, 1M, 1C, 1K. Each. When the photoreceptors 1Y, 1M, 1C, and 1K are rotated with the edge portions of the cleaning blades 88Y, 88M, 88C, and 88K being in contact with the surfaces of the photoreceptors 1Y, 1M, 1C, and 1K, the photoreceptors 1Y, 1M, and 1K are rotated. The surfaces of 1C and 1K are rubbed to clean the toner. The cleaning blades 88Y, 88M, 88C, 88K are always in contact with the photoreceptors 1Y, 1M, 1C, 1K when the first cleaning means 8Y, 8M, 8C, 8K are installed. The rubbing distance corresponds to the rotation amount of the photoreceptors 1Y, 1M, 1C, and 1K.

  The control means 100 receives the output from the encoder that outputs a pulse every time the photoreceptors 1Y, 1M, 1C, and 1K make one rotation, with the initial state of the cleaning blades 88Y, 88M, 88C, and 88K being zero. Each time the photosensitive member 1 rotates, the number of rotations is counted and counted up to detect the frictional distance of each of the cleaning blades 88Y, 88M, 88C, 88K.

  The count value of each rubbing distance is set to zero when the apparatus is shipped from the factory. When the cleaning blades 88Y, 88M, 88C, and 88K are newly replaced, the count values are changed by the user or service person. Reset to zero. A means for detecting the replacement of the cleaning blades 88Y, 88M, 88C, 88K may be provided, and the count value may be reset by an output from the detecting means.

The intermediate transfer member 6 is a semiconductive endless belt having a resistance value of 10 ⁵ Ωcm to ^{10 10} Ωcm, is stretched by a plurality of rollers, and is supported so as to be able to move around. It moves around in response to a signal to a transfer member driving means (not shown).

  Each color image formed by the image forming units 10Y, 10M, 10C, and 10K is in a state where the primary transfer unit 7Y, 7M, 7C, and 7K are pressure-bonded to the intermediate transfer body 6 that is circulated and moved. , 7M, 7C, and 7K are applied with a primary transfer output having a polarity opposite to that of the toner to form a transfer electric field, whereby primary transfer is sequentially performed on the intermediate transfer body 6 to form a synthesized color image. The

  The primary transfer units 7Y, 7M, 7C, and 7K are basically released from the press release by the press release units 71Y, 71M, 71C, and 71K except for the time of image formation, and are separated from the intermediate transfer body 6 to form an image. Before the transferred toner image reaches the intermediate transfer position, the toner image is pressed against the intermediate transfer body 6 by the pressing release means 71Y, 71M, 71C, 71K. The selection of these crimping or crimping release is changed and controlled by the output from the control means 100 to the crimping releasing means 71Y, 71M, 71C, 71K.

  A primary transfer output is applied to the primary transfer units 71Y, 71M, 71C, and 71K from a power source that is a primary transfer output application unit (not shown). As a control method of the primary transfer output applied to the primary transfer unit, (1) a constant current method for setting a predetermined target current value and controlling the transfer current to be the target current value; (2) There is a constant voltage method in which a predetermined target voltage value is set and control is performed so that the transfer voltage becomes this target voltage value. In (1), the current value becomes the primary transfer output, and in (2), the voltage value becomes the primary transfer output. In this embodiment, the constant current control (1) is performed, and the current value is set as the primary transfer output. The control unit 100 controls the primary transfer output and the application timing, which are current values, for each of the primary transfer units 71Y, 71M, 71C, and 71K by a signal to the primary transfer output application unit. During normal image formation, the primary transfer output is set to 30 μA so that the transfer rate is approximately 100%.

As the primary transfer means, a semiconductive roller having a resistance value of 10 ⁵ Ωcm to ^{10 10} Ωcm is preferably used.

  The color toners remaining on the surfaces of the photoreceptors 1Y, 1M, 1C, and 1K after the toner is primarily transferred to the intermediate transfer member 6 are respectively cleaned by the cleaning blades 88Y, 88M, 88C, and 88K as the first cleaning members. To be cleaned. In the forced consumption mode, the toner that is forcibly consumed is also cleaned in the same manner, but the details will be described later.

  The sheet P, which is a recording material accommodated in the sheet feeding cassette 20 of the sheet feeding / conveying section, is fed by the sheet feeding means 21 of the sheet feeding / conveying section, and is fed by the sheet feeding rollers 22A, 22B, 22C, 22D, and the registration roller 23. And the like, and is conveyed to the secondary transfer means 7A, and the color images are batch-transferred onto the paper P collectively. The paper P on which the color image has been transferred is fixed by the fixing unit 24, is sandwiched between the paper discharge rollers 25, and is placed on a paper discharge tray 26 outside the apparatus.

  On the other hand, after transferring the color image to the paper P by the transfer means 7A, the intermediate transfer body 6 from which the paper P has been separated is made of rubber, which is a second cleaning member formed long in the width direction of the intermediate transfer body 6. Cleaning is performed by the second cleaning means 8A having the cleaning blade 89A.

  The cleaning blade 89A is always in pressure contact with the intermediate transfer member 6, and the intermediate transfer member 6 slidably rubs on the intermediate transfer member 6 by the driving means of the intermediate transfer member, whereby the toner is cleaned. The In the forced consumption mode, the toner that is forcibly consumed is also cleaned in the same manner, but the details will be described later.

  Further, in the state where the primary transfer means 71Y, 71M, 71C, 71K is released from being pressed onto the intermediate transfer body 6, the intermediate transfer body 6 is rotated by the output from the control means 100 to the drive means of the intermediate transfer body. The cleaning blade 89A is not rubbed without moving.

  In the photoreceptors 1Y, 1M, 1C, and 1K, in which residual toner is cleaned by the cleaning blades 88Y, 88M, 88C, and 88K, the charge remaining on the surface is erased by a neutralizing unit (not shown) in a neutralization process. Then, returning to the charging process again, the above-described series of image forming operations is repeated.

  Next, an operation for forcibly consuming toner in the forced consumption mode will be described. The operation for forcibly consuming the toner is executed for the image forming units 10Y, 10M, 10C, and 10K of the respective colors.

  Since the image forming section for each color has the same configuration except that the color of the image to be formed is different, the following indicates that the element belongs to the image forming section for each color unless otherwise distinguished. The letters Y, M, C, and K will be omitted and the description will be made comprehensively.

  When the above-described series of image forming operations are continuously performed, if an original with a relatively low printing rate, that is, an original with a low black solid ratio, which is a ratio of the image area to the total area of the original, is used, image formation is performed. This reduces the amount of toner consumed and replenished. Accordingly, the toner stays in the developing unit 4 for a long period of time, and the time during which the toner is stirred with the magnetic particle carrier becomes longer, and the stress applied to the toner increases. As a result, the deterioration of the toner such as separation of the external additive silica, penetration into the toner, and spheroidization of the toner is caused, and the charge amount and the adhesive force change. As a result, the developability and transferability of the toner change, the density of the image formed on the paper fluctuates, and the image quality is greatly reduced.

  Here, as a method of forcibly consuming the toner in the forced consumption mode, the toner is forcibly adhered on the photosensitive member 1 during a non-image forming period, that is, a period when the image forming operation is not performed.

  In this method, the toner is forcibly consumed during a period when the image forming operation is not performed, so that the toner can be forcibly adhered to almost the entire surface of the photoreceptor 1 without being limited to the non-image area. This is very effective when a document having a small printing rate is continuously used and a large amount of toner must be forcibly adhered.

  When a predetermined amount of toner is forcibly adhered, the amount of toner consumed in a series of image forming operations increases. That is, by forcibly using the toner so that the predetermined amount of toner is consumed in a series of image forming operations, the predetermined amount of toner is discharged out of the developing unit 4 and supplied. For this reason, toner retention in the developing unit 4 is reduced, and the toner in the developing unit 4 is always replaced. Therefore, stress applied to the toner is suppressed, and high-quality image formation without image density fluctuation is possible.

  Examples of the electrostatic latent image when toner is forcibly adhered to the surface of the photosensitive member 1 include a black solid image having a predetermined density or a black solid image having a predetermined area. In the case of an electrostatic latent image of a black solid image of a predetermined density, the toner consumption can be easily adjusted by changing the area of the black solid image by changing the irradiation area during exposure of the exposure means 3. On the other hand, in the case of an electrostatic latent image of a black solid image having a predetermined area, the density of the black solid can be changed and the toner consumption can be easily adjusted by changing the amount of irradiation light when the exposure means 3 is exposed. it can. The exposure amount, irradiation area, and exposure timing are controlled by the output from the control means 100.

  In the toner forced consumption mode described above, the amount of toner to be forcibly consumed, that is, the amount of toner attached to the surface of the photoreceptor 1 and the timing thereof are (1) the document printing rate and (2) the image is formed. And (3) conditions such as the magnification of the image to be formed. At this time, (2) and (3) are determined by the user's operation from the operation input means 9 and the detection result of the paper size detection unit (not shown), and (1) is detected by the control means 100. .

  In the present embodiment, the control means 100 calculates an average print rate for image data for a predetermined number of pages (100 in the present embodiment) set in advance, and the average print rate is a threshold value (this embodiment). In the case of 5% or less), a signal is output to the image forming unit to execute the forced consumption mode. The amount of toner consumed in one forced consumption mode is set to such an amount that the toner adheres to almost the entire surface of the photoreceptor 1.

  Specifically, every time one page of image data is image-exposed on the photosensitive member by the copying operation, the pixel number counting unit 99 of the control unit 100 stores one page stored in the storage unit M2 of the image processing unit C2. When the number of black pixels and white pixels in the image data is counted and counted up, and the cumulative number of black pixels and white pixels for 100 pages, which is the set value of the predetermined number, is counted, control is performed. The means 100 calculates the average printing rate per page from the accumulated black pixel count and white pixel count value for 100 pages.

  A binary image will be described as an example. For example, image data having 256 pixel values is processed by a density conversion circuit that performs luminance / density conversion, a spatial filter process, and a gradation correction circuit in the image processing unit C, and then binarized by an error diffusion circuit. Is done. The binarized image data is stored in the storage means M2, and then converted into a PWM signal in the PWM circuit. Independently of this, the pixel number counting means 99 counts the number of black pixels and the number of white pixels.

  The printing rate per page is the state where the image data for one page is completely filled with toner, with the printing rate of 0% in the printing area for one page, with the printing rate being 0%. Is defined as the ratio of the printing area to the non-printing area in the printing area. For example, an image with a white color has a printing rate of 0%, a solid image with a single color other than white for all regions has a printing rate of 100%, and half of the area within the printing region has no white portion and the rest is white. In the case of an image, the printing rate is 50%. Expressed by the formula, the printing rate is black pixel count / total pixel count (white pixel count + black pixel count) × 100.

  Next, forcibly consumed toner processing in the forced consumption mode will be described. Forcibly consumed toner processing is executed for the image forming units 10Y, 10M, 10C, and 10K of the respective colors. In the image forming apparatus of the present embodiment, the primary transfer method of the toner on the photosensitive member 1 that has been forcibly consumed to the intermediate transfer member 6 and the cleaning method associated therewith are the initial steps of the cleaning blade 88 of the photosensitive member 1. Change according to the rubbing distance from the state.

  In the image forming apparatus of the present embodiment, the limit rubbing distance of the cleaning blade 88 of the photosensitive member 1 with respect to the untransferred toner is 24 km to 32 km. From the running test (comparative example).

  Therefore, the control means 100 receives the output from the encoder of the photoconductor 1 and counts the rubbing distance from the initial state of the cleaning blade 88 of the photoconductor 1, and the rubbing distance is set to 24 km which is the first threshold value. Until reaching, the pressure cancellation of the primary transfer means 7 is selected. The control means 100 outputs a signal so that the intermediate transfer body 6 is not moved in a revolving manner to the intermediate transfer body drive means so as to release the pressure contact with the pressure release means 71 of the primary transfer means 7. In this case, since the primary transfer is not performed, the untransferred toner that has been forcibly consumed is cleaned by the cleaning blade 88 of the photoconductor. Further, since the intermediate transfer member 6 does not move around, the intermediate transfer member cleaning blade 89A is not rubbed.

  Further, until the rubbing distance exceeds 24 km and reaches the second threshold value of 56 km, the control means 100 selects the pressure bonding of the primary transfer means 7. The control means 100 causes the intermediate transfer body 6 to rotate around the intermediate transfer body drive means so that the primary transfer means 7 is pressed against the intermediate transfer body 6 by the press release means 71, and the primary transfer output. The application means outputs a signal so that the primary transfer current is zero, and the toner that is forcibly consumed is primarily transferred. In this case, 30 to 40% of the forcibly consumed toner on the photosensitive member 1 is primarily transferred to the intermediate transfer member 6 and cleaned by the intermediate transfer member cleaning blade 89A. The residual toner on the photoreceptor 1 after the primary transfer is cleaned by the cleaning blade 88 of the photoreceptor 1.

  Further, until the rubbing distance exceeds 56 km and reaches the third threshold value of 80 km, the control unit 100 selects the pressing of the primary transfer unit 7. The control means 100 causes the intermediate transfer body 6 to rotate around the intermediate transfer body drive means so that the primary transfer means 7 is pressed against the intermediate transfer body 6 by the press release means 71, and the primary transfer output. The applying means outputs a signal so that the primary transfer current is 10 μA, and the toner that is forcibly consumed is primarily transferred. In this case, 70 to 80% of the toner on the photosensitive member 1 that is forcibly consumed is primarily transferred to the intermediate transfer member 6 and cleaned by the cleaning blade 89A of the intermediate transfer member 6. The residual toner on the photoreceptor 1 after the primary transfer is cleaned by the cleaning blade 88 of the photoreceptor 1.

  As described above, the cleaning blade 88 of the photosensitive member 1 is worn due to repeated rubbing by gradually increasing the primary transfer toner amount from zero as the sliding distance of the cleaning blade 88 of the photosensitive member 1 increases. Reduces the load on and prevents poor cleaning. Further, when the primary transfer unit 7 is released and the primary transfer toner amount is set to zero, the intermediate transfer member 6 is not moved around so that the load on the cleaning blade 89A of the intermediate transfer member 6 can be reduced. .

  Further, in the forced consumption mode, the primary transfer output in the primary transfer of the toner on the photoreceptor 1 that is forcibly consumed to the intermediate transfer body 6 is 10 μA at the maximum, and the developed photosensitive material is used during image formation. The transfer rate was lowered by making the toner image on the body 1 smaller than 30 μA, which is the primary transfer output in the primary transfer to the intermediate transfer body, and all the untransferred toner images of a plurality of colors were superimposed. The excessive load on the cleaning blade 89A of the intermediate transfer body 6 in the case of moving to the intermediate transfer body in the state is prevented.

  FIG. 2 is a block diagram of the image forming apparatus of the present invention. A functional configuration of the image forming apparatus according to the present invention will be described with reference to FIG. The same components as those described in FIG. 1 are denoted by the same reference numerals, and the description thereof is omitted.

  A control unit 100 that performs overall control of the operation of the image forming apparatus includes a nonvolatile memory M1 that stores variable data, a ROM 602 that stores operation programs, a CPU (central processing circuit) (not shown), an arithmetic unit, a comparator, an input / output interface, and the like. It is a computer system composed of

  In addition, the control means 100 operates as the following means by operating according to the operation program.

  The page number counting means 305 counts the number of pages MZ for a series of copying operations.

  The cumulative page number counting means 405 counts the cumulative number of copied pages MX, and the count value MX is set to the set value 100 of the number of copied pages when calculating the average printing rate stored in the nonvolatile memory M1. When it reaches, it is reset.

  The pixel count unit 99 counts up every time the number of black pixels and white pixels of the image data for one page stored in the storage unit M2 of the image processing unit C2 is counted, and the above-mentioned set value is 100 pages. When the cumulative number of black pixels and white pixels are counted, the cumulative count value is output to the nonvolatile memory M1 and stored.

  The rubbing distance counting means 306 counts the rubbing distance from the initial state of the cleaning blade 88 in response to an output from an encoder that outputs a pulse each time the photosensitive member 1 rotates.

  Further, the nonvolatile memory M1 includes a setting value (100) for the number of copied pages when calculating the average printing rate, and a threshold value for the average printing rate for determining whether to perform the forced consumption mode (in this embodiment, the paper size Regardless of the threshold, the threshold value may be changed depending on the paper size), the image exposure area and exposure amount in the forced consumption mode, and the rubbing distance from the initial state of the cleaning blade 88 described above. A table defining the relationship between the primary transfer method of the consumed toner on the photosensitive member 1 to the intermediate transfer member 6 and the cleaning processing method associated therewith is stored in a rewritable state in advance.

  Further, every time the image forming apparatus is powered off, the control unit 100 downloads the values of the pixel number counting unit 99, the rubbing distance counting unit 306, and the cumulative page number counting unit 405 to the nonvolatile memory M1, and Each time the power of the forming apparatus is turned on, the value of the nonvolatile memory M1 is programmed to be uploaded to the black pixel number counting means 99, the rubbing distance counting means 306, and the cumulative page number counting means 405.

  The configuration controlled by the control unit 100 includes an image reading unit 40 that performs a function of reading a document image and taking in corresponding image data, and storing image data input from the image reading unit in the storage unit M2 for filtering, A toner image is formed on the photosensitive member based on the image data processed by the image processing unit C2 and the image processing unit C2 that performs image processing such as tone adjustment and scaling, and the toner image is intermediately transferred by the primary transfer unit 7. Image transfer unit 10 for primary transfer to transfer body 6, intermediate transfer body 6, intermediate transfer body cleaning means 8A, secondary transfer means 7A for secondary transfer of toner image on intermediate transfer body 6 to paper P, secondary transfer A paper feed / conveying section for supplying recording paper to the means 7A, a fixing means 24 for fixing the paper P on which the toner image has been transferred, and both display and input functions. Duplication star Made from the operation input unit 9, etc. for performing an instruction operation equal to the control unit 100.

(Embodiment)
An operation flow of the image forming apparatus according to the embodiment of the present invention will be described with reference to a flowchart of FIG. Here, a case where image data is read from a document for a predetermined page and printed (copied) will be described as an example. Since the operation is common to Y, M, C, and K, the symbols Y, M, C, and K of each part are omitted.

  In step S100, the power of the image forming apparatus is turned on, and the values of the black pixel count, white pixel count, rubbing distance count, and cumulative page count stored in the nonvolatile memory M1 are the pixel count counting means. 99, the friction distance counting means 306 and the cumulative page number counting means 405 are uploaded.

  In step S101, the copy start switch is turned on with the number of copies per page and the paper size set from the operation input means 9, and a predetermined number of pages of originals are read from the image reading unit 40, and image data is read. Is entered. The input image data for a predetermined number of pages is stored in the storage means M2 of the image processing unit C2, and is subjected to image processing.

  In step S102, the control means 100 calculates the total number of copied pages M from the number of pages of image data input in step S101 and the number of copied pages per document page.

  In step S103, the control unit 100 sets the count value MX of the accumulated page number counting unit 405 from the accumulated page number counting unit 405 to the set value of the number of copied pages when calculating the average printing rate (100 is set here). Are read from the nonvolatile memory M1, respectively, and it is determined whether or not the sum of MX and the total number of copied pages M calculated in step S102 is 100 or more. If it is 100 or more (YES in step S103), the process of step S104 is executed. If it is not 100 or more (NO in step S103), the process of step S118 is executed.

  In step S104, the image forming unit 10 charges the photoreceptor 1, exposes the image, and develops the toner, and then forms a toner image on the paper P and executes copying. The rubbing distance counting means 306 counts up based on the number of rotations of the photosensitive member 1.

  In step S105, the pixel count counting unit 99 of the control unit 100 analyzes the image data stored in the storage unit M2 of the image processing unit C for the image for one page image-exposed in step S104, and the black pixel The number and the number of white pixels are counted, and each counts up.

  In step S106, the control unit 100 increments the count value MZ of the page number counting unit 305 by one.

  In step S107, the control unit 100 increments the count value MX of the cumulative page number counting unit 405 by one.

  In step S108, the control unit 100 sets the count value MX of the accumulated page number counting unit 405 from the accumulated page number counting unit 405 to the set value of the number of copied pages (100 is set here) when calculating the average printing rate. Are read from the non-volatile memory M1, respectively, and it is determined whether or not the count value MX of the accumulated page number counting means 405 has reached the set value 100. If it has reached (YES in step S108), the process of step S109 is executed. If it has not reached (NO in step S108), the process of step S117 is executed.

  In step S109, the control unit 100 resets the count value MX of the accumulated page number counting unit 405 to 0. Further, the black pixel count value and the white pixel count value of the pixel count counting means 99 are stored in the nonvolatile memory M1, the black pixel count count value and the white pixel count count value of the pixel count counting means 99 are set to 0, and reset. To do.

  In step S110, the control unit 100 reads the average printing rate threshold (5%) for determining whether to perform the forced consumption mode from the nonvolatile memory M1, and stores the number of black pixels for 100 pages stored in the nonvolatile memory M1. An average printing rate per page is calculated from the count value and the white pixel count value, and it is determined whether the average printing rate is 5% or less. If it is 5% or less (YES in step S110), the process of step S111 is executed. If it is not 5% or less (NO in step S110), the process of step S117 is executed.

  In step S111, the copying operation is paused and the forced toner consumption mode is executed. The control unit 100 reads out conditions such as an exposure area and an exposure amount from the nonvolatile memory M1, outputs a signal to the image forming unit, is charged and solidly exposed on almost the entire surface of the photoconductor, and the toner is forced on the photoconductor. Is consumed. The rubbing distance counting means 306 counts up based on the number of rotations of the photosensitive member 1.

  In step S112, the control unit 100 performs the primary transfer method from the storage unit M1 to the intermediate transfer member 6 of the toner on the photosensitive member 1 forcibly consumed by the sliding distance from the initial state of the cleaning blade 88, and A table defining the relationship between the cleaning processing methods is read out, and it is determined whether or not the rubbing distance of the cleaning blade 88 counted by the rubbing distance counting means 306 is 24 km or less. If it is 24 km or less (YES in step S112), the process of step S113 is executed. If it is not 24 km or less (NO in step S112), the process of step S114 is executed.

  In step S 113, the pressure of the primary transfer unit 7 is released, and the forcibly consumed toner is not primarily transferred to the intermediate transfer member 6 but is cleaned by the cleaning blade 88 of the photosensitive member 1. At this time, the intermediate transfer member 6 does not move around and the intermediate transfer member 6 is not rubbed by the cleaning blade 89A. The rubbing distance counting means 306 counts up based on the number of rotations of the photosensitive member 1.

  In step S114, the control unit 100 performs a primary transfer method from the storage unit M1 to the intermediate transfer member 6 of the toner on the photosensitive member 1 and the rubbed distance from the initial state of the cleaning blade 88 and the forcibly consumed toner. Accordingly, a table defining the relationship of the cleaning processing method is read, and it is determined whether or not the rubbing distance of the cleaning blade 88 counted by the rubbing distance counting means 306 is 56 km or less. If it is 56 km or less (YES in step S114), the process of step S115 is executed. If it is not 56 km or less (NO in step S114), the process of step S116 is executed.

  In step S115, the primary transfer means 7 is pressure-bonded, and the forcibly consumed toner is primary-transferred to the intermediate transfer body 6 with the primary transfer current set to zero, and the intermediate transfer body 6 is cleaned 89A. It is cleaned by. The residual toner on the photoreceptor 1 after the primary transfer is cleaned by the cleaning blade 88 of the photoreceptor 1. The rubbing distance counting means 306 counts up based on the number of rotations of the photosensitive member 1.

  In step S116, the primary transfer means 7 is pressure-bonded, and the forcibly consumed toner is primary-transferred to the intermediate transfer body 6 with the primary transfer current set to 10 μA, and the intermediate transfer body 6 is cleaned 89A. It is cleaned by. The residual toner on the photoreceptor 1 after the primary transfer is cleaned by the cleaning blade 88 of the photoreceptor 1. The rubbing distance counting means 306 counts up based on the number of rotations of the photosensitive member 1.

  In step S117, the control unit 100 determines whether or not the number of copied pages MZ counted by the page number counting unit 305 has reached the total number of copied pages M calculated in step S102. If it has reached (YES in step S117), the process of step S123 is executed. If it has not reached (NO in step S117), the process of step S104 is executed.

  In step S118, the control unit 100 counts up the count value MX of the accumulated page number counting unit 405 as the new MX, which is the sum of the number of copied pages M calculated in step S103.

  In step S119, after the photosensitive member 1 is charged, image exposed, and developed with toner in the image forming unit A, a toner image is formed on the paper P, and copying is executed. The rubbing distance counting means 306 counts up based on the number of rotations of the photosensitive member 1.

  In step S120, the pixel count counting unit 99 of the control unit 100 analyzes the image data stored in the storage unit M2 of the image processing unit C for the image for one page image-exposed in step S119, and the black pixel The number and the number of white pixels are counted, and each counts up.

  In step S121, the control unit 100 increments the count value MZ of the page number counting unit 305 by 1.

  In step S122, the control unit 100 determines whether or not the number of copied pages MZ counted by the page number counting unit 305 has reached the number of copied pages M calculated in step S102. If it has reached (YES in step S122), the process of step S123 is executed. If it has not reached (NO in step S122), the process of step S119 is executed.

  In step S123, the control unit 100 resets the count value MZ of the page number counting unit 305 to zero.

  In step S124, a series of image forming processes is completed, and a standby operation is started.

  In this embodiment, the forced toner consumption mode is performed for each color image forming unit by the control unit 100. For example, at least one of four image forming units Y, M, C, and K is used. In one image forming unit, when the average printing rate of a predetermined number of pages is 5% or less, the forced consumption mode is simultaneously performed in all four image forming units to cause the photoreceptor 1 to forcibly consume toner. May be.

(1) Comparative Example A color image was formed under the following conditions using the color image forming apparatus shown in FIG.
Photoconductor: Drum-shaped OPC photoconductor having a diameter of 60 mm.
Photoconductor cleaning: Cleaning blade method.
Primary transfer means: sponge roller having a resistance of 10 ⁷ Ωcm and a diameter of 20 mm.
Transfer control of primary transfer: constant current control. The primary transfer current during normal image formation is 30 μA (transfer rate is almost 100%).
Intermediate transfer member cleaning: Cleaning blade method.

  Under the above conditions, a running test was performed from an initial state where the cleaning blade was not used to a copy of A4 size, 5 sheets intermittently 200,000 sheets with a Y, M, C, K color printing ratio of 5%. The following forced toner consumption mode was carried out for each sheet to check for the occurrence of defective cleaning.

A solid image of each color in the forced toner consumption modes Y, M, C, and K was developed on each color photoconductor in each image forming unit for 20 seconds. Thereafter, the photoreceptors of each color were rotated for 60 seconds in order to clean the toner on the photoreceptors of each color that was forcibly consumed by a cleaning blade of the photoreceptor. At this time, the primary transfer means was released from the pressure bonding, and the primary transfer was not performed. Further, the intermediate transfer member was not moved around, and the cleaning blade of the intermediate transfer member was not rubbed.

(2) Example When the rubbing distance of the cleaning blade of the photosensitive member is up to 24 km, the primary transfer means is not pressure-bonded (transfer rate 0%), and the primary transfer is not performed. The primary transfer means is pressure-bonded and primary transfer is performed at a primary transfer current of 0 μA (transfer rate of 30 to 40%). The primary transfer means is pressure-bonded to the primary transfer means until the sliding distance exceeds 56 km to 80 km. A running test was similarly performed under the same conditions as in the comparative example except that the primary transfer was performed at a transfer current of 10 μA (transfer rate was 70 to 80%). The primary transfer was sequentially performed on the Y, M, C, and K color toners, and the respective color toners were superimposed on the intermediate transfer member.

  Table 1 shows the relationship between the number of copies, the rubbing distance from the initial state of the cleaning blade of the photosensitive member, and the presence or absence of defective cleaning.

○: No cleaning failure occurred.
X: A cleaning failure occurred.

  In the example, no cleaning failure occurred from the beginning up to 200,000 sheets.

  In the comparative example, cleaning failure did not occur up to the first 60,000 sheets, but after 80,000 sheets, cleaning failure due to toner slipping occurred in the cleaning blade of the photoreceptor.

  As described above, in the embodiment, in the primary transfer of the toner that is forcibly consumed, the primary transfer unit is changed from the pressure-release to the pressure-bonding as the sliding distance of the cleaning blade of the photosensitive member increases, and the primary transfer is further performed. By increasing the amount of primary transfer toner by increasing the primary transfer current, which is an output, the load on the cleaning blade of the photoreceptor can be reduced, and defective cleaning can be prevented.

  In addition, by lowering the primary transfer current of the toner that has been forcibly consumed compared to the primary transfer current of the toner image during normal image formation, all four color toners are in an intermediate state in a superimposed state. Primary transfer to the transfer member is no longer performed, and an excessive load on the cleaning blade of the intermediate transfer member can be prevented.

1 is a diagram illustrating an overall configuration of a color image forming apparatus which is an example of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a block diagram of the image forming apparatus illustrated in FIG. 1. 3 is a flowchart showing an operation flow of the image forming apparatus shown in FIG. 1.

Explanation of symbols

10, 10Y, 10M, 10C, 10K Image forming unit 1, 1Y, 1M, 1C, 1K Photoconductor 8, 8Y, 8M, 8C, 8K Photoconductor cleaning means 7, 7Y, 7M, 7C, 7K Primary transfer means Reference Signs List 6 intermediate transfer member 8A intermediate transfer member cleaning unit 100 control unit 9 operation input unit 40 image reading unit C2 image processing unit 99 pixel number counting unit 305 page number counting unit 306 rubbing distance counting unit 405 cumulative page number counting unit

Claims (3)

An image carrier on which an electrostatic latent image is formed, developing means for developing the electrostatic latent image with toner to form a toner image on the image carrier, an intermediate transfer member, and a toner image on the image carrier a primary transfer means for transferring the primary and then pressed to the intermediate transfer member, and a first cleaning member for cleaning the toner on the image carrier by rubbing the image bearing member on said image bearing member a secondary transfer unit that transfers the secondary bets toner image which is primarily transferred to the intermediate transfer member onto a recording material from the cleaning the toner on said intermediate transfer member rubs on the intermediate transfer member An image forming apparatus having two cleaning members,
Count for counting the forced consumption mode execution means for executing a forced consumption mode for forcibly consumed in the image bearing member toner, the rubbing distance relative to the initial state of the first cleaning member in the developing unit means and a pinch release means for releasing crimped or crimped to the first transfer means to said intermediate transfer member, in the forced consumption mode, if rubbing distance counted by the counting means is equal to or less than a first predetermined value When the primary transfer means is released from pressure bonding and cleaned by the first cleaning member, and the rubbing distance exceeds a first predetermined value, the primary transfer means is pressure-bonded and the first and second An image forming apparatus comprising: a control unit that controls the cleaning member to perform cleaning . When the forced consumption mode is executed , the control means is configured to force the upper surface of the image carrier to be forcibly consumed when the sliding distance exceeds a first predetermined value and the primary transfer means is pressure-bonded to the intermediate transfer body. When the rubbing distance counted by the counting means exceeds the second predetermined value larger than the first predetermined value , the primary transfer output in the primary transfer of the toner to the intermediate transfer member is: The image forming apparatus according to claim 1, wherein the image forming apparatus is larger than the first predetermined value and larger than the second predetermined value . In the forced consumption mode, the control means outputs the primary transfer output in the primary transfer of the toner on the image carrier forcibly consumed to the intermediate transfer member, and the developed image carrier at the time of image formation. 3. The image forming apparatus according to claim 1, wherein the toner image is smaller than a primary transfer output in the primary transfer of the upper toner image to the intermediate transfer member.

Images