JP2007187859A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of preventing offset toner caused by paper dust adhering to the heating rotary body of a fixing device, with simple configuration. <P>SOLUTION: The image forming apparatus is provided with: a paper dust amount measuring means (60) which measures the amount of the paper dust adhering to a paper (3) supplied to an image forming device (11); and a control means (30) which performs control operation to change the paper supplied to the image forming device (11) from the paper storage sections (41 and 43) of a paper feeder (40) into the paper whose storage direction is different by 90 degrees and form a toner image formed by the image forming device (11), in such a state that the direction of the toner image is rotated by 90 degrees, according to the measurement results of the paper dust amount measuring means. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a printer, a copying machine, a facsimile machine, or a multi-function machine that forms an image made of dry toner (developer) on a sheet, and in particular, a toner in a fixing device that fixes a toner image transferred to a sheet. The present invention relates to an image forming apparatus having a new function for preventing the occurrence of offset.

  In an image forming apparatus such as a printer to which an electrophotographic method or an electrostatic recording method is applied, an image made of dry toner is generally formed on a sheet as follows.

  First, after a toner image based on image information is formed on an image carrier such as a photoconductor through a predetermined image forming process (charging, exposure and development process), the toner image is directly or intermediately transferred onto a predetermined sheet. Then, the sheet on which the toner image is transferred is heated and pressed by a fixing device to thermally fix the toner image on the sheet. In this case, as a fixing device, a sheet carrying an unfixed toner image is heated and pressed by passing it through a pressure contact area where a fixing (heating) rotating body having a heating source and a pressure member are pressed. Many heat-fixing types are used.

  However, in such an image forming apparatus, a phenomenon in which a part (toner) of the toner image on the paper passing during fixing is transferred to and adhered to the heating rotator of the fixing device, a so-called toner offset may occur. is there. When toner offset occurs in the fixing device, the toner offset to the heating rotator adheres to the paper passing through the pressure contact area for subsequent fixing, contaminates the paper, or disturbs the fixed image and induces image defects. There are problems such as.

  On the other hand, conventionally, as will be described below, there has been known an image forming apparatus in which measures against toner offset in such a fixing device are taken.

  For example, there is an image forming apparatus provided with a roller cleaning device for cleaning a roller of a fixing device (Patent Document 1). This is a roller cleaning device provided with a cleaning web impregnated with silicone oil in a nonwoven fabric, and the cleaning web is brought into contact with the peripheral surface of the heating rotator and gradually moved to update the contact portion with the peripheral surface. By doing so, the toner offset to the peripheral surface of the heating rotator is removed.

  In addition, there is an image forming apparatus configured to apply an offset prevention voltage to a fixing (heating) rotating body of a fixing device via a static elimination brush (Patent Document 2). By applying a voltage having the same polarity as the charging polarity of the toner that electrostatically adheres to the heating rotator as an offset prevention voltage, this prevents the toner from electrostatically adhering to the heating rotator. It is a thing.

JP 2003-76200 A Japanese Patent Laid-Open No. 8-16012

  However, this conventional image forming apparatus has the following problems.

  That is, in the former image forming apparatus, the toner after offset to the heating rotator can be removed by the roller cleaning device, but the occurrence of the toner offset itself cannot be prevented in advance. Further, depending on the amount of toner to be offset, there is a possibility that the roller cleaning device cannot sufficiently remove the toner.

  Further, in the latter image forming apparatus, it is possible to prevent toner offset of a type in which toner adheres to the heating rotator due to electrostatic factors, but to prevent toner offset caused by other factors. I couldn't.

  On the other hand, according to studies by the present inventors, one of the causes of toner offset is the presence of paper dust adhering to the heating rotator, and it has been found that the paper dust induces toner offset. It was done.

  In particular, when using recycled paper or low-cost paper, which is poor paper manufactured to reduce costs, as paper for image formation, paper that adheres to these papers in a detachable state. It has also been found that since the amount of powder is relatively large, a part of the paper powder tends to adhere to the heating rotator during fixing. It was also found that when there are many non-image parts on which the toner image is not formed on the paper, the paper part that becomes the non-image part tends to come into direct contact with the heating rotator and the paper powder tends to adhere. did.

  In this way, when paper dust adheres to the heating rotator (particularly strongly or abundantly), the toner of the toner image being fixed is easily transferred to the heating rotator by using the paper dust as a scratch. It is presumed that toner offset is induced. In addition, when a plurality of images having the same content are continuously formed, a large amount of paper dust tends to adhere to the same portion of the heating rotator, and accordingly, toner offset may be easily induced. The toner offset caused by such paper dust is caused by the charging polarity of the toner electrostatically adhering to the heating rotator as the offset preventing voltage in the latter image forming apparatus that applies the offset prevention voltage to the heating rotator. Therefore, the paper dust charged to the polarity opposite to the charging polarity of the toner is easily attached to the heating rotator by the offset prevention voltage. It cannot be sufficiently prevented because it is difficult to remove the paper dust adhering to the heating rotator due to the mechanical action.

  The present invention has been made in view of such problems, and mainly prevents toner offset caused by paper dust adhering to the heating rotator of the fixing device with a simple configuration. An image forming apparatus is provided.

  An image forming apparatus according to the present invention (first invention) includes a sheet storage unit that can store sheets of the same rectangular size in different directions rotated by 90 °, and a sheet feeding device that supplies sheets from the sheet storage unit. A paper information detecting means for detecting the size and orientation of the paper stored in the paper storage unit of the paper supply device, and forming a toner image based on the image information and storing the toner image in the paper storage device of the paper supply device An image forming apparatus for transferring to a sheet supplied from the section, a fixing apparatus having a heating rotator and a pressure member for performing heat fixing by heating and pressing the sheet on which the toner image is transferred by the image forming apparatus, Paper dust amount measuring means for measuring the amount of paper dust of the paper supplied to the image forming device, and from the paper container of the paper feeding device to the image forming device according to the measurement result of the paper dust amount measuring means. The paper to supply Description orientation is characterized in that a control means for controlling operation of forming a toner image its orientation is rotated 90 ° to form by said image forming apparatus together with change in 90 ° different paper.

  Here, prior to executing a control operation involving a change in the paper to be supplied and a change in the orientation of the toner image to be formed, the control means determines the same size in the required storage orientation from the detection result of the paper information detection means. It is confirmed whether or not a sheet exists in the sheet storage unit of the sheet feeding device. In other words, if there is no paper of the same size in the required storage orientation, a warning or notification is given so that the paper is stored in the required storage orientation in the predetermined paper storage section, and the required paper is present. The control operation is put in a wait state until it is confirmed. This also applies to the control means of the image forming apparatus according to the second aspect of the invention described later.

  In the image forming apparatus according to the first aspect of the present invention, the control means performs a control operation involving a change in the paper to be supplied and a change in the orientation of the toner image to be formed, and the amount of paper dust measured by the paper dust amount measuring means is a predetermined value. It is preferable that the setting is made so as to be executed at intervals of a relatively small number of image forming sheets when the number is larger than. In this case, the control operation is performed at a more appropriate time and at an interval, thereby preventing paper dust from adhering to the heating rotator more appropriately. Furthermore, it is more preferable that the control means in this case is set to be executed at intervals of a relatively large number of image forming sheets when the amount of paper dust is smaller than a predetermined value. In that case, in addition to the above effect, when the amount of paper dust is small, the interval of the control operation becomes long, so that the effect that the ratio of the direction of the sheet discharged after image formation is reduced is convenient.

  The image forming apparatus according to the present invention (the second invention) also includes a sheet storage unit that can store sheets of the same rectangular size in different directions rotated by 90 °, and a sheet feeding unit that supplies sheets from the sheet storage unit. A sheet information detecting means for detecting a size and a storing direction of a sheet stored in a sheet storing unit of the sheet feeding device, a toner image based on the image information, and the toner image of the sheet feeding device. Image forming apparatus for transferring to a sheet supplied from a sheet storage unit, and a fixing apparatus having a heating rotator and a pressure member for performing heat fixing by heating and pressing a sheet onto which a toner image has been transferred by the image forming apparatus And a non-image portion prediction means for predicting the amount of the non-image portion in the image forming device, and a supply from the sheet storage portion of the paper feeding device to the image forming device according to a prediction result of the non-image portion prediction means. Paper to be used And a control means for performing a control operation of changing the accommodation direction to a sheet having a 90 ° difference and rotating the direction of the toner image formed by the image forming device by 90 °. .

  Here, the non-image portion prediction means is not particularly limited as long as it can predict the amount of the non-image portion that affects the adhesion of paper dust to the heating rotator. For example, it can be configured as means for inferring from the value of the image density of the toner image formed on the paper.

  In the image forming apparatus according to the second aspect of the present invention, the control means performs a control operation involving a change in the paper to be supplied and a change in the orientation of the toner image to be formed, with a non-image part amount predicted by the non-image part prediction means being When the number is larger than the value, it may be set to execute at intervals of a relatively small number of image forming sheets. In this case, the control operation is performed at a more appropriate time and at an interval, thereby preventing paper dust from adhering to the heating rotator more appropriately. Further, it is more preferable that the control means in this case is set so as to be executed at intervals of a relatively large number of image forming sheets when the amount of the non-image portion is smaller than a predetermined value. In that case, in addition to the above effect, when the amount of the non-image portion is small, the interval of the control operation becomes long, so that the ratio of different orientations of the paper discharged after the image formation decreases, which is convenient. can get.

  According to the first invention, the control operation (image rotation output) of the control means accompanied by the change of the paper to be supplied and the change of the direction of the toner image to be formed is executed in a timely manner according to the paper dust amount measured by the paper dust amount measuring means. Is done. When this control operation is executed, after the same toner image rotated by 90 ° is formed on the paper supplied in a rotated state of 90 °, the rotated paper passes through the fixing device and is heated. Fixing will be performed. As a result, the paper dust adhering to the peripheral surface of the heating rotator of the fixing device before the control operation is performed adheres to the toner of the toner image portion whose position is shifted due to the rotation image output and is removed. It becomes like this. As a result, the paper dust does not continue to adhere to the same position of the heating rotator or does not adhere much.

  According to the second aspect of the present invention, the control operation of the control means (image rotation) accompanied by a change in the paper to be supplied and a change in the orientation of the toner image to be formed, depending on the amount of the non-image part predicted by the non-image part amount prediction means Output) is executed in a timely manner. When this control operation is executed, as in the case of the first invention, the same toner image rotated by 90 ° is formed on the paper supplied in a rotated state by 90 °, and then the paper is fixed. It will be heat-fixed through the device. As a result, the paper dust adhering to the peripheral surface of the heating rotator of the fixing device before the control operation is performed adheres to the toner in the toner image portion that has been displaced due to the execution of the rotation image formation. As a result, the paper dust does not continue to adhere to the same position of the heating rotator or does not adhere much.

  Therefore, in any of the image forming apparatuses of the present invention, the surface of the heating rotator of the fixing device is recovered (held) to a state where paper dust does not continue to adhere or to a state where a large amount does not adhere to a certain place. Therefore, it is possible to prevent toner offset induced by the presence of paper dust when performing subsequent image formation (fixing). This effect is beneficial because it can be obtained even when recycled paper or low-cost paper is used as the paper. Further, this image forming apparatus has a simple configuration because the rotation image output control operation only changes the supplied paper and the orientation of the toner image to be formed. This is advantageous in terms of cost without wasteful use.

[Embodiment 1]
FIG. 1 shows an outline of an image forming apparatus according to Embodiment 1 of the present invention.

  The image forming apparatus 1A accommodates an image output unit 10 that finally forms and outputs an image made of toner on a sheet 3 and a sheet 3 to be supplied to the image output unit 10 inside the apparatus main body 2. A paper section 40 is provided. In addition, the image forming apparatus 1A is installed or connected to the outside of the apparatus body 2 via a receiving unit 4 having a communication function, and is an external device 6 such as an image reading apparatus 5, a personal computer, or a reading apparatus for various memory media. In addition, an operation unit 7 for inputting, selecting, displaying, etc., information related to the operation of the image forming apparatus is connected.

  The image output unit 10 includes an image forming device 11 that forms a toner image based on image information and then transfers the toner image to the paper 3, a fixing device 20 that performs thermal fixing by passing the paper 3 on which the toner image is transferred, and an image The image output control unit 30 mainly controls the overall operation related to the output operation. A chain line with arrows in FIG. 1 and the like indicates a main conveyance path of the paper 3.

  The image forming apparatus 11 is capable of forming a toner image using, for example, a known electrophotographic method, and specifically includes a cylindrical photosensitive drum 12 that is rotationally driven in the direction of an arrow. A charging device 13 including a charging roll for uniformly charging the surface of the photosensitive drum 12 around the photosensitive drum 12, and an image based on image information (signal) on the surface of the photosensitive drum 12 after charging. An exposure device 14 including a laser scanning device that irradiates light to form a latent image having a potential difference, a developing device 15 that forms a toner image by transferring and attaching toner to the latent image, and feeding the toner image A transfer device 16 composed of a transfer roll or the like for transferring to the paper 3 supplied from the section 40 and a cleaning device 17 for removing toner remaining on the surface of the photosensitive drum 12 after the transfer are mainly disposed.

  The fixing device 20 includes a heating roll 21 that is driven to rotate in the direction of an arrow, and a pressure roll 22 that is pressed against and substantially rotated along the axial direction of the heating roll 21. A pressure contact region (fixing nip portion) through which the sheet 3 having the image transferred thereon is introduced and passed therethrough is formed. Of these, the heating roll 21 has a structure in which a release layer is formed on a cylindrical metal roll, and a heating source such as a halogen heater is installed in the roll so as to be heated to a predetermined temperature. . The pressure roll 22 has a structure in which an elastic layer or the like is formed on a metal roll base, and is supported so as to be pressed against the heating roll 21 with a predetermined pressure by a pressure mechanism.

  The image output control unit 30 includes an arithmetic processing circuit, a control circuit, a storage device, and the like, and is stored in the storage device by input of detection information from various sensors, commands from the external device 5 or the operation unit 7, and the like. An arithmetic processing circuit or the like is operated according to the control program and data that are being controlled, and controls each operation of the image output unit 10 and the paper feeding unit 30 related to image output. In addition, the image output unit 10 performs predetermined image processing on image information (signal) input from the external device 5 via the receiving unit 4 and image reading information (signal) from the image reading device 6. An image processing unit 32 that transmits the processed image signal to the exposure device 14 of the image forming device 11 as necessary is installed. The operation of the image processing unit 32 is also controlled by the image output control unit 30.

  The paper feed unit 40 is stacked and accommodated in the paper feed cassettes 41A, 41B, 41C, and 41D that are arranged in a plurality of stages in the vertical direction at the bottom of the apparatus main body 2 and are detachably attached. Feeding mechanism 42A, 42B, 42C, 42D that feeds the sheet 3 to be fed one by one, a manual sheet feed tray 43 that is mounted in a protruding state outside the apparatus main body 2, and sheets that are stacked and accommodated in the manual sheet feed tray 43 3 and a plurality of storage paper detection sensors 45A to 45E that individually detect the presence, size, and storage orientation of the paper 3 stored in each of the paper feed cassettes 41 and the manual paper feed tray 43. It is mainly composed of.

  As shown in FIG. 2, each of the paper feed cassettes 41 includes a slide-type side guide 41 a that aligns one end of the paper 3 in the feeding direction with the paper containing surface, and a rear end in the feeding direction of the containing paper 3. A slide-type end guide 41b for aligning the parts is provided. Each of the paper feed cassettes 41 has a rectangular fixed size (for example, A4 size, B5 size) by moving the side guide 41a and the end guide 41b by appropriate amounts along the slide grooves 41c, 41d and stopping and fixing them. When the paper 3 of the same size is accommodated in a direction in which it is fed out with its long side at the top (the paper accommodated in this orientation is referred to as the long side first feed paper 3L), the paper 3 of the same size is 90%. It is possible to store the paper in such a direction that it is rotated and sent out with its short side leading (the paper stored in this direction is referred to as short-side head feed paper 3S). When there are such a plurality of paper feed cassettes 41, it is possible to store the paper 3 of the same size in different paper feed cassettes with the feeding direction changed. In addition, the storage paper detection sensors 45A to 45D that detect information (particularly size and storage direction) of the paper 3 stored in the paper feed cassette 41 detect the position of the side guide 41a and the end guide 41b to detect information. Is configured to get. An arrow A in the figure indicates the sheet conveyance (feeding out) direction.

  On the other hand, the manual feed tray 43 is similarly equipped with the side guide (41a) as described above. The storage paper detection sensor 45E that detects information (particularly size and storage orientation) of the paper 3 stored in the manual paper feed tray 43 is a result of measuring the position of the side guide and the time required for delivery from the tray 43. It is comprised so that the information may be obtained by detecting or grasping. The above information may be configured to be grasped by the image output control unit 30 by inputting information from the operation unit 7 in advance and specifying the information of the paper stored in the tray 43 (in this case, the image output control unit). 30 performs the function of the accommodation paper detection sensor 45E).

  In FIG. 1 and the like, reference numeral R1 denotes a main paper feed path that conveys the paper 3 fed from each paper feed cassette 41 to the transfer unit (between the photosensitive drum 12 and the transfer device 16) of the image forming device 11, and includes a plurality of paper feed paths. The sheet transport roll pair 46, the resist roll pair 47, and a guide member (not shown). R2 is a discharge path that conveys the sheet 3 discharged from the fixing device 20 so as to be discharged to a discharge tray 50 that protrudes outside the apparatus main body 2, and includes a pair of sheet transport rolls 46, a discharge roll 47 and a guide member (not shown). R3 is a manual sheet feed path that conveys the sheet 3 fed from the manual sheet feed tray 43 to a junction point in the middle of the main sheet feed path R1, and includes a sheet feed roll and a guide member.

  In the image forming apparatus 1 </ b> A, a paper dust amount measuring device 60 that measures the amount of paper dust that adheres to the paper 3 supplied to the image forming device 11 in a detachable state is installed.

  In this example, the paper dust amount measuring device 60 is installed in the middle of the main paper feed path R1 (position passing through the junction of the main paper feed path R1 and the manual paper feed path R3). Further, as shown in FIGS. 3 to 5, the paper dust amount measuring device 60 includes a light-shielding casing 61 opened in a state where the measurement openings 62 and 63 face each other on the upper and lower surfaces, and the casing 61. , A light emitting element (LED) 64 and a light receiving element (photodiode) 65, a paper powder adsorption electrode plate 66 installed close to the upper opening 62 of the housing 60, and the paper powder adsorption The electrode plate 66 includes a power source 67 that applies a polar suction voltage for adsorbing paper dust to static electricity. Among these elements, the light emitting element 64 and the light receiving element 65 are installed in such a state that the light emitting optical path and the light receiving optical path (two dotted lines in FIG. 4) of the respective elements intersect with each other at substantially the center of the measurement opening 62. (FIG. 4). The paper dust amount measuring device 60 is fixedly installed in a state where the lower opening 63 is in the middle of the paper feed path R1 and faces the upper side of the paper feed path, and the measurement result (detection signal) ) Is input to the image output control unit 30 (FIGS. 1 and 4).

  In the measurement of the paper dust amount, the light receiving element 65 and the light receiving element 65 are brought into the light emitting and light receiving state in accordance with the paper conveyance (and detection) timing of the paper feed path R1, and the electrode plate. A suction voltage is applied to 66 from a power supply 67. As a result, the paper dust that removably adheres to the upper surface side of the paper 3 passing through the paper feed path R1 (actually temporarily stopped by the resist roll 47) is sucked up toward the electrode plate 66 by the electrostatic force. . The sucked-up paper powder enters the measurement space 61 (a space connecting the openings 62 and 63) 61a of the housing 61 from the lower opening 63 and is guided so as to stay temporarily (on the electrode plate 66). Hardly stick). At this time, the light emitted from the light emitting element 64 is irradiated with the paper powder moving in the measurement space 61 a to be scattered light, and the scattered light is received by the light receiving element 65. Further, as shown in FIG. 6, the amount of light received by the light receiving element 65 is substantially proportional to the amount of paper dust existing in the measurement space 61a, that is, the amount of paper dust sucked up from the paper 3. For this reason, the paper dust amount is appropriately associated depending on the amount of received light, and the image output control unit 30 uses the received light amount information (voltage signal) transmitted from the paper dust amount measuring device 30 as paper dust. We try to grasp it as a quantity.

  Further, in this image forming apparatus 1A, the image output control unit 30 performs image output including image rotation as described below according to the paper dust amount measured by the paper dust amount measuring device 60 during the image forming operation. It is configured to perform a control action to select and execute.

  That is, as shown in FIG. 7 and FIG. 9, the image output control unit 30 compares the measurement result of the paper dust amount measuring device 60 with a predetermined threshold when executing the image forming operation (image output). The paper 3L (3S) supplied to the image forming device 11 from the paper feed cassette 41 or the manual paper feed tray 43 of the paper feed unit 40 at a predetermined timing of the image forming operation scheduled to be executed according to the comparison result is stored in a 90 orientation. It is set to perform control to change the direction of the toner image formed by the image forming device 11 by 90 ° and to change to a different paper 3S (3L) of the same size. The direction of the toner image is changed by a known image rotation function (image conversion pattern for 90 ° rotation) provided in the image processing unit 32. By executing this control operation, as shown in FIGS. 8 and 10, image formation is performed in a state of being rotated by 90 ° together with the sheet 3 (this is referred to as “image output with image rotation”).

  In addition, when the image output control unit 30 executes the control operation to perform the image output with the image rotation, the paper orientation cassettes rotated by 90 ° and different sizes of the same size paper are fed into the paper feed cassette 41 of the paper feed unit 40. Alternatively, it is set to detect whether or not the manual feed tray 43 exists. In addition, if it does not exist, a warning message (information) that prompts the user to store the required paper 3 in the paper feed cassette 41 or the like is sent to the external device 5 for notification or operation. It is made to display on the part 7 (FIG. 8).

  Particularly in this example, as shown in FIG. 7 and FIG. 9, the control operation accompanied by the change of the paper to be supplied and the change of the orientation of the toner image to be formed is performed by the paper dust amount ( When A) exceeds a predetermined value (first threshold B, second threshold C), it is a relatively small interval for each number of formed images (hereinafter also referred to as “image rotation interval: N”). On the other hand, when the paper dust amount (A) is smaller than a predetermined value (especially the second threshold value C), it is set to execute at a relatively large interval (N) for each number of formed images. Further, the image rotation interval N is appropriately selected according to the information (somewhat) of the number of sheets on which image formation should be performed (image formation number: D) in addition to the measurement result of the paper dust amount. The image forming number D is a value transmitted and input together with image information from the external device 5 or a value input and set from the operation unit 7 before the operator starts an image forming operation.

  The control operation by the image output control unit 30 as described above is executed based on a control program and data stored in a storage unit (storage device) of the control unit 30.

  Next, each operation in the image forming apparatus 1A will be described.

  First, an operation when normal image output is executed will be described. First, an image formation command is input from the external device 4 or the operation unit 7 to the image output control unit 30.

  At this time, the type and size of the paper 3 used for the image output are selected. This selection is performed based on image information input from the external device 5 or the image reading device 6 or setting information input from the operation unit 7 by the operator.

  When the selection related to the paper 3 is confirmed, the paper 3 to be targeted is sequentially sent out one by one from the predetermined paper feed cassette 41 or the manual paper feed tray 43 of the paper feed unit 40 by the feed mechanisms 42 and 44, and The sheet is conveyed and supplied toward the transfer unit of the image forming apparatus 11 of the image output unit 10 through the sheet feeding path R1 or the manual sheet feeding path R3.

  Further, when the first sheet 3 of the image forming operation is transported through the main sheet feed path R1, the paper dust amount is measured by the paper dust amount measuring device 60 in the middle of the sheet feed path. That is, as described above, the paper dust adhering to the surface (upper surface) of the paper 3 conveyed through the main paper feed path R1 is located between the electrode plate 66 and the measurement space 61a of the housing 61 of the measuring device 60. In the measurement space 61a, the light emitted from the light emitting element 65 is irregularly reflected by the paper powder to become scattered light, which is received by the light receiving element 65. The received light amount (voltage signal) is sent to the image output control unit 30 as information on the amount of paper dust.

  On the other hand, based on the image signal output from the image processing unit 32 after the photosensitive drum 12 is rotated and charged by the charging device 13 in the image forming device 11 at the same time or before the paper feeding operation is started. Then, the photosensitive drum 12 charged from the exposure device 14 is scanned and exposed to form an electrostatic latent image. Subsequently, when the latent image passes through the developing device 15, the latent image is developed with toner to become a toner image, and then the toner image is sent at a predetermined timing by a resist roll 47 in a transfer portion facing the transfer device 16. It is transferred to the paper 3.

  The sheet 3 on which the toner image has been transferred is introduced and passed through a pressure contact area between the heating roll 21 and the pressure roll 22 of the fixing device 20 so that the toner image is thermally fixed to the sheet 3 by being heated and pressurized. Is done. Thereafter, the fixed sheet 3 is discharged to the discharge tray 50 through the discharge conveyance path R2 and stacked and accommodated. As a result, basic image formation on one sheet is completed. However, when there are a plurality of image forming sheets and it is necessary to perform them continuously, the above image forming operation is continuously repeated. .

  When such image output is repeated continuously, the paper dust adhering to the paper 3 is transferred and attached to the surface of the heating roll 21 of the fixing device 20, which is caused by the presence of the paper dust. Thus, the toner offset as described above is likely to occur.

  In the image forming apparatus 1 </ b> A, image output after image rotation is performed at a predetermined interval N by executing the control described later, and as a result, the paper dust adhering to the surface of the heating roll 21 is removed. And the position where the paper dust adheres is dispersed.

  Next, control operations relating to selection and execution of image output including image rotation will be described with reference to FIG.

First, as described above, the result (voltage signal relating to the amount of received light) measured by the paper dust amount measuring device 9 is input to the image output control unit 30 and the paper dust amount measurement value (A) is confirmed (step: S101). Thereafter, a first image rotation paper dust amount reference value (hereinafter referred to as “first threshold”) B for determining whether or not image rotation is necessary is confirmed. That is, a value corresponding to the first threshold value B (in this example, “7 mg / m ³ ”) is called from the control data (FIG. 9) stored in the image output control unit 30 (S102).

  Subsequently, the magnitude relationship between the confirmed paper dust amount measurement value (A) and the first threshold value (B) is compared (S103), and if the comparison result is “A> B”, the amount of paper dust is It is considered that there are relatively many cases, and an image rotation interval (N) corresponding to the result is selected (S104). The image rotation interval N is selected based on the control data (FIG. 9) stored in the image output control unit 30. In this example, since the measurement result of the amount of paper dust is relatively large, the image rotation interval N is set to “100 sheets” which is relatively small. In this case, the process proceeds to a control operation (FIG. 8) for performing image output including image rotation described later (S105).

If the comparison result is “A <B” in step S103, the second image rotation paper dust amount reference value (hereinafter referred to as “second threshold”) C is confirmed (S106), and the paper dust amount measurement value is determined. (A) is compared with the second threshold measurement value C (S107). The second threshold value in this example is “3 mg / m ³ ” (FIG. 9).

  If the comparison result at this time is “A> C”, the number of images to be continuously formed, that is, the number of image formation (D) is confirmed (S108), and the number of image rotation intervals (N) is determined according to the number of images. Is selected (S104). At this time, the number of image formations: 1 every "300 sheets" when D is 500 or less, every "250 sheets" when 500 to 1000 sheets, and every "150 sheets" when it is 1000 sheets or more. Image rotation is performed each time.

  On the other hand, if the comparison result is “A <C”, first, the number of formed images: D is confirmed (S109), and the image rotation reference number (hereinafter referred to as “number threshold”) E is confirmed (S110). Both are compared (S111). The sheet number threshold value E is called from the control data (FIG. 9) stored in the image output control unit 30, and is set to “1000 sheets” in this example.

  If the comparison result at this time is “D <E”, it is considered that image rotation is unnecessary because the number of formed images is relatively small, and setting for executing the image rotation is not performed (S112). ), It is determined to execute “normal image output” as described above (S113).

  On the other hand, if the comparison result in step S111 is “D> E”, after confirming the number of formed images: D (S108), the image rotation interval: N is selected according to the number (S104). Then, the process proceeds to a control operation (FIG. 8) for performing image output including image rotation described later (S105). At this time, image rotation is performed once every "500 sheets" when D is in the range of 1000 to 5000 sheets, and once every "250 sheets" when it is 5000 sheets or more. . The image rotation interval N at this time is set to a relatively small number of image forming sheets because the amount of paper dust is relatively small.

  Hereinafter, an operation when image output including image rotation will be described with reference to FIGS.

  First, confirmation of the number of formed images: D and confirmation of the selected image rotation interval: N are performed (S201, 202). Here, it is assumed that the image output is first performed using A4 size paper 3L in the long side leading direction (see the upper part of FIG. 10).

  Subsequently, it is determined whether or not there is a sheet 3L (A4 size) accommodated in the sheet feeding cassette 41 of the sheet feeding unit 40 or the manual sheet feeding tray 43 in the long side leading feed direction that is scheduled to be used initially. (S203). The determination at this time is made based on the detection information of the stored paper detection sensor 45 installed in the paper feed cassette 41 or the like.

  At this time, if the paper 3L to be used is stored, image output (the image forming operation described above) is started (S204). However, if the paper 3L to be used is not stored, a warning message for prompting the storage of the paper 3L to the predetermined paper feed cassette 41 or the like is transmitted or displayed as described above. It is confirmed that the sheet 3L is detected by the accommodation sheet detection sensor 45 (S205), and image output is started when the sheet 3L is confirmed (S204).

  When this image output is started, an output counter is added each time one sheet of paper 3L after image formation (after fixing) is output (discharged to the discharge tray 50), and the accumulated count (total paper passing) ) It is confirmed whether or not the number (F) of images has reached the number D of image formation (S206). If it has reached (F = D), the image output is terminated (S207).

  On the other hand, if the total number of sheets to be passed: F has not reached the number of images formed: D (F <D), the number of sheets to be passed (the count value after image rotation) X is set to the image rotation interval: N. It is determined whether or not the image has been reached (S208). If the number of image rotation intervals has not been reached (X <N), image output on the paper 3L is continued (S204).

  At this time, when the number of sheets to be passed: X reaches the image rotation interval: N (X = N), the head of the short side that is used for the image rotation output to the sheet feeding cassette 41 of the sheet feeding unit 40 or the like. It is determined whether or not there is a sheet 3S (A4 size) accommodated in the feeding direction (S203).

  At this time, if the paper 3S to be used is stored, the image formed by the image forming device 11 is formed in a state rotated by 90 ° (S210). The image formed at this time is rotated by forming a latent image by the exposure device 14. More specifically, the image processing unit 32 receives the image signal that forms the same image rotated by 90 ° from the image processing unit 32.

  Further, when the paper 3S to be used is not stored, a warning message for prompting the storage of the paper 3S to the predetermined paper feed cassette 41 or the like is transmitted or displayed, and the paper 3S is displayed. It is confirmed that the sheet detection sensor 45 has detected it (S211), and when the confirmation is made, an operation of forming an image rotated 90 ° is started (S210).

  When the operation of forming the image by rotating is started, the paper 3 supplied to the transfer unit of the image forming device 11 is changed from “paper 3L” to “paper 3S” (S212). Actually, the paper feed from the paper feed cassette 41 or the like in which the paper 3S is stored is switched. As a result, image output (image output after image rotation) is performed on the sheet 3S (S213). That is, as shown in FIG. 10, the image output for the previous paper 3L is switched to the image output for the paper 3S in a state rotated by 90 ° with respect to the paper 3L.

  When this image output is started, the output counter is incremented every time one sheet of paper 3S after the image formation is output, and the cumulative count (total number of sheets passed): F is the number of image formations D Is reached (S214), and if it is reached (F = D), the image output is terminated at that time (S207).

  On the contrary, when the total number of sheets passed: F has not reached the number of images formed: D (F <D), the number of sheets passed (cumulative count value after image rotation) X becomes the image rotation interval: N. It is determined whether or not the image has been reached (S215). If the number of image rotation intervals has not been reached (X <N), image output on the sheet 3S is continued (S213).

  At this time, when the number of sheets to be passed: X reaches the image rotation interval: N (X = N), the image formed by the image forming device 11 is formed by being rotated by 90 ° (S216). The paper 3 supplied to the transfer unit of the image forming device 11 is changed from “paper 3S” to “paper 3L” (S217). The image output of the image rotation at this time is eventually returned to the image output (S204) for the previous paper 3L. In other words, in this case, as shown in FIG. 10, the image output for the paper 3 </ b> S having undergone the previous image rotation is switched to the image output for the paper 3 </ b> L that is rotated 90 ° with respect to the paper 3 </ b> S.

  When image output including image rotation is executed in this way, image output is performed by rotating the image by 90 ° every time the image rotation interval N arrives while image formation is repeatedly performed by the number of image formations: D. Will be. Then, when the rotated image is output, the sheet 3L (3S) on which the image rotated by 90 ° is formed (vertically and horizontally changed) passes through the fixing device 20 alternately. It becomes like this. As a result, in the fixing device 20, the paper dust adhering to the peripheral surface of the heating roll 21 adheres to the toner of the toner image portion whose position is shifted due to the image rotation output and is appropriately removed to be in the same position on the heating roll 21. Paper dust does not continue to adhere locally or in large quantities, and toner offset caused by paper dust can be prevented beforehand.

  This is because, for example, when an image as illustrated in the upper part of FIG. 10 is formed on the sheet 3L facing the leading edge of the long side, the division position in the axial direction (of the heating roll 21) perpendicular to the transport direction A 1 to 10), if there is a blank paper portion (non-image portion: positions 2, 3, 4, 6, and 7 in the axial direction in the illustrated example) of the sheet 3L corresponding to the non-image increase portion. The surface portion is in direct contact with the heating roll 21, and the paper powder is likely to partially adhere to the heating roll 21. However, when image output with image rotation is executed, the same image is formed on the paper 3S in the short side leading direction as illustrated in the lower part of FIG. 10, and the paper 3S passes through the fixing nip. Therefore, the toner image comes into contact with the heating roll 21 that is in direct contact with the surface of the paper, and the paper dust is removed by the toner of the toner image. In this example, paper dust adhering to positions 3, 4, and 6 in the axial direction of the heating roll 21 is removed by the toner image formed on the paper 3S. Incidentally, the distance indicated by the symbol W in FIG. 10 is the circumference of the heating roll 21. In this example, the heating roll 21 having a diameter of 65 mm was used.

  In this image forming apparatus 1A, the image rotation interval: N is set to a relatively small value as the measured value of paper dust amount: A increases, and as the number of images formed at that time: D increases. It is set so that image output by rotation is frequently performed (FIG. 9). For this reason, it is possible to efficiently reduce the adhesion of paper dust to the heating roll 21 and more appropriately prevent the occurrence of toner offset.

[Embodiment 2]
11 to 14 show an image forming apparatus and the like according to the second embodiment of the present invention.

  The image forming apparatus 1B predicts the amount of a non-image portion where a toner image is not formed by the image forming device 11 instead of the paper dust amount measuring device 60, as a determination criterion when performing control for image rotation. The configuration is the same as that of the image forming apparatus 1A according to the first embodiment except that the image amount detection unit 35 is changed. For this reason, in FIGS. 11-14, the same code | symbol is attached | subjected to the part which is common in the case of Embodiment 1, and the description of the part is abbreviate | omitted except when it is required.

  The image amount detection unit 35 measures image density by a video (pixel) counter based on an image signal (digital signal) output after image information input at the time of image formation is processed by the image processing unit 32. . For example, when the image to be formed on the sheet 3 has the contents illustrated in the upper part of FIG. 12, the position (1) obtained by dividing the axial direction (main scanning direction) region into a plurality of sections. The image density for each of (-10 positions) is tabulated to obtain an image density (distribution) as shown in the lower part of FIG. When the image density is less than a predetermined value (part), the image density is set to be regarded as a non-image portion of the image to be formed.

  In the image forming apparatus 1B, the image output control unit 30 performs image output including image rotation as described below according to the image (density) amount measured by the image amount detection unit 35 during the image forming operation. The control operation is selected and executed.

  That is, as shown in FIGS. 13 and 14, the image output control unit 30 compares the measurement result of the image amount detection unit 35 with a predetermined threshold when performing an image forming operation (image output), and compares the measurement result. The sheet 3L (3S) supplied to the image forming device 11 from the sheet feed cassette 41 or the manual sheet feed tray 43 of the sheet feed unit 40 at a predetermined timing of the image forming operation scheduled to be executed according to the result is 90 ° in the accommodation direction. It is set to perform control for changing to a different sheet 3S (3L) of the same size and rotating the direction of the toner image formed by the image forming device 11 by 90 °. By executing this control operation, as in the case of the first embodiment, image formation is performed with the paper 3 rotated by 90 ° (referred to as “image output with image rotation”, FIG. 8 and FIG. 10). reference).

  Particularly in this example, as shown in FIG. 13 and FIG. 14, the control operation accompanied by the change of the supplied paper and the change of the direction of the toner image to be formed is measured by the image amount detection unit 35. When (A) exceeds a predetermined value (first threshold value B, second threshold value C), it is executed with a relatively small image rotation interval: N ”, while its paper dust amount: A is a predetermined value (especially the first threshold value). When the number is smaller than the two threshold values C), the interval is set to be N: every relatively large number of image forming sheets. Further, the image rotation interval N is appropriately selected according to the information (somewhat) of the number of sheets on which image formation should be performed (image formation number: D) in addition to the measurement result of the paper dust amount.

  Next, control operations related to selection and execution of image output including image rotation will be described with reference to FIG.

  First, as described above, the result (image density value) measured by the image amount detection unit 35 is input to the image output control unit 30, and the measured value (A) of the image density is confirmed (S301). Thereafter, a first image rotation image amount reference value (hereinafter referred to as “first threshold”) B for determining whether image rotation is necessary is confirmed. That is, a value corresponding to the first threshold value B (in this example, “20%”) is called from the control data (FIG. 14) stored in the image output control unit 30 (S302).

  Subsequently, the magnitude relationship between the confirmed image density measurement value: A and the first threshold value: B is compared (S303), and when the comparison result is “A> B”, the non-increasing portion is relatively It is considered that there are many cases, and an image rotation interval N corresponding to the result is selected (S304). The image rotation interval N is selected based on the control data (FIG. 14) stored in the image output control unit 30. In this example, since the measurement result of the image density (that is, the amount of the non-image portion) is relatively large, the image rotation interval N is set to “100 sheets” that is relatively small. In this case, the process proceeds to the control operation (FIG. 8) for executing the image output including the image rotation as described above (S305).

  If the comparison result is “A <B” in step S303, the second image rotation image amount reference value (hereinafter referred to as “second threshold”) C is confirmed (S306), and the image density measurement value: A Is compared with the second threshold value C (S307). The second threshold value in this example is “50%” (FIG. 14).

  If the comparison result at this time is “A <C”, the number of images to be continuously formed, that is, the number of image formation (D) is confirmed (S308), and the number of image rotation intervals: N is set according to the number of images. Select (S304). At this time, the number of image formations: 1 every "300 sheets" when D is 500 or less, every "250 sheets" when 500 to 1000 sheets, and every "150 sheets" when it is 1000 sheets or more. Image rotation is performed each time.

  On the other hand, if the comparison result is “A> C”, first, the number of formed images: D is confirmed (S309), the number threshold: E is confirmed (S310), and both are compared (S111). The sheet number threshold value E is called from the control data (FIG. 14) stored in the image output control unit 30 and is set to “1000 sheets” in this example.

  If the comparison result at this time is “D <E”, it is considered that image rotation is unnecessary because the number of images formed is relatively small, and no setting is made to execute the image rotation (S312). ), It is determined to execute “normal image output” as described above (S313).

  On the other hand, if the comparison result in step S311 is “D> E”, after confirming the number of formed images: D (S308), the image rotation interval: N is selected according to the number (S304). Then, the process proceeds to the control operation (FIG. 8) for executing the image output including the image rotation described above (S305). At this time, image rotation is performed once every "500 sheets" when D is in the range of 1000 to 5000 sheets, and once every "250 sheets" when it is 5000 sheets or more. . The image rotation interval N at this time is set to a relatively small number of image forming sheets because the image amount is relatively small (the amount of non-image portions is small).

  Hereinafter, when image output including image rotation is set, an image output operation that rotates the image is performed every time the image rotation interval N arrives, as in the case of the first embodiment (see FIG. 8 and FIG. 14).

  When image output including image rotation is executed according to the detection result of the image amount and the like in this way, the image rotation interval N arrives while image formation for only the number of image formations: D is repeatedly performed. Every time the image is rotated by 90 °, the image is output. When the rotated image is output, the sheet 3L (3S) on which the image rotated by 90 ° is formed alternately with respect to the fixing device 20, as in the first embodiment. To pass through. As a result, in the fixing device 20, the paper dust adhering to the peripheral surface of the heating roll 21 adheres to the toner of the toner image portion whose position is shifted due to the image rotation output and is appropriately removed to be in the same position on the heating roll 21. Paper dust does not continue to adhere locally or in large quantities, and toner offset caused by paper dust can be prevented beforehand.

  In this image forming apparatus 1B, as the measured value of image density: A is smaller (that is, the amount of the non-image portion is larger), and the number of images formed at that time: D is larger, the image rotation interval: N is relatively set. Therefore, it is set so as to frequently output an image by rotating the image (FIG. 14). For this reason, it is possible to efficiently reduce the adhesion of paper dust to the heating roll 21 and more appropriately prevent the occurrence of toner offset.

1 is a schematic diagram showing a main part of an image forming apparatus according to Embodiment 1. FIG. FIG. 4 is a schematic plan view showing a configuration of a paper feed cassette or the like that can store paper in a state rotated by 90 °. It is upper surface explanatory drawing which shows the structure of a paper dust amount measuring device. It is a plane schematic diagram which shows the state which removed the upper surface of the paper dust amount measuring device of FIG. It is a schematic sectional drawing of the QQ line of FIG. It is a graph which shows the relationship between the light reception amount of a paper dust amount measuring device, and paper dust amount. It is a flowchart which shows the control action regarding selection and execution of image output including image rotation. It is a flowchart which shows operation | movement when implementing the image output containing image rotation. 6 is a chart showing set values of image rotation intervals with respect to the amount of paper dust and the number of formed images. FIG. 9 is an explanatory plan view illustrating an example in which image formation is performed in a state where sheets of the same size are rotated by 90 °. 6 is a schematic diagram illustrating a main part of an image forming apparatus according to Embodiment 2. FIG. It is explanatory drawing which shows the structure regarding the measurement of image density. It is a flowchart which shows the control action regarding selection and execution of image output including image rotation. 6 is a chart showing set values of image rotation intervals with respect to image density and the number of formed images.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 3L, 3S ... Paper, 11 ... Image forming apparatus, 20 ... Fixing apparatus, 21 ... Heating roll (heating rotary body), 22 ... Pressure roll (pressing member), 40 ... Paper feed part ( Paper feeding device) 41... Paper cassette (paper storage unit) 43. Manual feed tray (paper storage unit) 45. Storage paper detection sensor (paper condition detection unit) 30. Image output control unit (control unit) 35... Image amount detection unit, 60.

Claims (4)

A paper storage unit capable of storing the same rectangular paper in different orientations rotated by 90 °, and a paper feeding device for supplying paper from the paper storage unit;
Paper information detection means for detecting the size and orientation of the paper stored in the paper storage unit of the paper supply device;
An image forming device that forms a toner image based on image information and transfers the toner image to a sheet supplied from a sheet storage unit of the sheet feeding device;
A fixing device having a heating rotator and a pressure member for performing heat fixing by heating and pressurizing a sheet onto which a toner image has been transferred by the image forming device;
Paper dust amount measuring means for measuring the amount of paper dust of the paper supplied to the image forming device;
According to the measurement result of the paper dust amount measuring means, the paper supplied from the paper storage unit of the paper supply device to the image forming device is changed to a paper whose storage direction is different by 90 ° and is formed by the image forming device. An image forming apparatus comprising: control means for performing a control operation for forming a toner image by rotating its direction by 90 °.   The control means performs a control operation accompanied by a change in the paper to be supplied and a change in the orientation of the toner image to be formed when the amount of paper dust measured by the paper dust amount measuring means is larger than a predetermined value and relatively small. The image forming apparatus according to claim 1, wherein the image forming apparatus is set to be executed at an interval for each number of image forming sheets. A paper storage unit capable of storing the same rectangular paper in different orientations rotated by 90 °, and a paper feeding device for supplying paper from the paper storage unit;
Paper information detection means for detecting the size and orientation of the paper stored in the paper storage unit of the paper supply device;
An image forming device that forms a toner image based on image information and transfers the toner image to a sheet supplied from a sheet storage unit of the sheet feeding device;
A fixing device having a heating rotator and a pressure member for performing heat fixing by heating and pressurizing a sheet onto which a toner image has been transferred by the image forming device;
Non-image part prediction means for predicting the amount of the non-image part in the image forming device;
In accordance with the prediction result of the non-image portion prediction means, the paper supplied from the paper storage unit of the paper supply device to the image forming device is changed to a paper whose storage direction differs by 90 ° and is formed by the image forming device. An image forming apparatus comprising: control means for performing a control operation for forming a toner image by rotating its direction by 90 °.   The control means performs a control operation involving a change in the supplied paper and a change in the orientation of the toner image to be formed when the non-image portion amount predicted by the non-image portion prediction means is larger than a predetermined value. The image forming apparatus according to claim 3, wherein the image forming apparatus is set to be executed at intervals of a small number of image forming sheets.

Images