JP2006091351A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress paper wrinkle in accordance with an image which is formed. <P>SOLUTION: An image forming apparatus 100 is prestored with contents of image formation processing in which paper wrinkle is apt to occur. When image formation processing matching the stored contents of image formation processing is performed in image formation, image formation conditions are changed on the basis of predetermined alteration algorithm. For example, the image forming apparatus forms invisible toner in a region where toner density decreases on a recording material. Alternatively, the image forming apparatus 100 decreases the toner density in an area where the toner density increases on the recording material. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a technique for suppressing generation of wrinkles in an electrophotographic image forming apparatus.

  An electrophotographic image forming apparatus such as a color printer or a color copying machine forms a toner image on a sheet (recording material) through several steps of exposure, development, transfer, and fixing. The fixing device that performs fixing among these steps includes a pair of heating / pressurizing members disposed so as to face each other across the sheet conveyance path, and an area where these heating / pressurizing members are in contact with each other When the sheet passes through the (nip region), the toner is fixed to the sheet by applying heat and pressure to the sheet.

However, a paper wrinkling (wrinkle) may occur on the paper if the paper entry posture when entering the nip region is poor or the distribution of heat and moisture content in the paper is not uniform. When such a paper wrinkle is generated, the toner formed on the paper is distorted or a fixing failure occurs, so that the appearance of the paper on which the image is formed is significantly impaired.
For this reason, various techniques for suppressing paper wrinkles of paper have been proposed. For example, the technique described in Japanese Patent Application Laid-Open No. H10-260260 suppresses paper wrinkles generated on the paper by detecting the thickness of the paper and changing the fixing pressure in accordance with the thickness. Further, the technique described in Patent Document 2 suppresses paper wrinkles generated on a sheet by changing an adsorption force according to the thickness, size, material, and the like of the sheet in a conveyance unit that conveys the sheet while adsorbing the sheet. Is. That is, these techniques change control amounts such as fixing pressure and suction force according to the type of paper classified by thickness, size, and the like.

Japanese Patent Laid-Open No. 07-121052 Japanese Patent Laid-Open No. 10-035943

By the way, the occurrence of paper wrinkles is not limited to that caused by the type of paper as described above, and there are various other factors that cause paper wrinkles. For example, even with the same type of paper, it is considered that there is a difference in the likelihood of paper wrinkles depending on how the image is formed on the paper. However, the techniques of the above-mentioned Patent Documents 1 and 2 do not pay attention to such a point, and there is a problem that generation of paper wrinkles due to this difference cannot be suppressed.
The present invention has been made in view of such a background, and an object thereof is to provide a technique for suppressing the occurrence of paper wrinkles in accordance with an image to be formed.

In order to achieve the above-described object, the present invention includes an image forming unit that forms a toner image on a recording material in accordance with predetermined image forming conditions, a storage unit that previously stores the contents of a specific image forming process, When the content of the image forming process instructed to be executed by the image forming unit matches the content of the image forming process stored in the storage unit, the image forming condition to be followed by the image forming unit is determined. There is provided an image forming apparatus including a control unit configured to change based on a given change algorithm.
According to this image forming apparatus, the contents of a specific image forming process indicating conditions in which paper wrinkles are likely to occur are stored in advance, and paper wrinkles are more generated when an image forming process that matches this is performed. Since the image forming conditions are changed so as to be difficult, generation of paper wrinkles can be suppressed.

In a more preferred aspect of the image forming apparatus of the present invention, the storage means has a toner density difference between the first image area and the second image area on the recording material equal to or greater than a predetermined value. Are stored as the contents of the image forming process.
More preferably, the first image region is a region having the highest toner density among the plurality of image regions on the recording material, and the second image region is a plurality of the plurality of image regions on the recording material. This is an area where the toner density is lowest in the image area.
At the time of image formation, if the difference in toner density between the first image area and the second image area on the recording material exceeds a predetermined value, paper wrinkles are likely to occur. By doing so, it becomes possible to suppress the occurrence of paper wrinkles.

In a more preferred aspect of the image forming apparatus of the present invention, the control unit changes the image forming condition so that an image with invisible toner is formed in an area where the toner density is low on the recording material.
By doing so, the difference in dynamic frictional force between the area where the toner density is low and the area where the toner density is high on the recording material is reduced, so that the generation of paper wrinkles can be suppressed.

In a more preferred aspect of the image forming apparatus of the present invention, the control unit changes the image forming condition so as to reduce the toner density in a region where the toner density is high on the recording material.
Specifically, the control unit reduces the toner density in the region by changing the screen applied to the region where the toner density is high on the recording material to a screen having a low resolution.
Alternatively, the control unit reduces the toner density in the region by adjusting the exposure amount when forming an image in the region where the toner density is high on the recording material.
In this way, the toner density difference between the area where the toner density is low and the area where the toner density is high on the recording material is reduced, so the difference in dynamic friction force between these areas is reduced, and paper wrinkles occur. Can be suppressed.

In a more preferred aspect of the image forming apparatus according to the present invention, the control unit may be a region where the toner density is low on the recording material when an image forming mode in which image quality is emphasized is set as the image forming condition. When an image forming mode in which image quality is emphasized as an image forming condition is not set, an image with invisible toner is formed in a region where the toner density is low on the recording material, and recording is performed. The image forming conditions are changed so as to reduce the toner density in a region where the toner density is high on the material.
In this way, when an image forming mode in which image quality is emphasized is set, the image quality of an area where the toner density is high is not deteriorated, and when an image forming mode in which image quality is not so important is set. Thus, it is possible to more reliably suppress the occurrence of paper wrinkles.

(1) Principle of the present invention According to the investigation and research by the present inventors, it is clear that in an electrophotographic image forming apparatus, paper wrinkles are likely to occur when a specific image forming process is performed. It became. The image forming process is “to form an image having a large deviation in the toner distribution on the paper”. The reason why paper wrinkles are likely to occur in this case will be described below.

  As described above, in the fixing device inside the image forming apparatus, if the distribution of heat and moisture content in the paper when entering the nip area is not uniform, paper wrinkles may occur. This is because the local dynamic frictional force on the paper surface depends on the heat and moisture content at each location. If the dynamic friction force on the paper surface is locally changed, the slipperiness of the paper changes when it passes through the nip region. As a result, a speed difference locally occurs during paper conveyance, and this speed difference causes the generation of paper wrinkles.

The same applies to the toner on the paper. Naturally, the dynamic frictional force of the surface is different between the area where the toner is formed on the paper and the area where the toner is not. Here, if the color change of the image on the paper is gradual, the speed difference due to the difference in the dynamic friction force is negligible. However, if there is a portion on the paper where the color of the image changes abruptly, a speed difference that cannot be ignored occurs here, and paper wrinkles are generated. In particular, when a fixing device of a type that applies oil is used in the image forming apparatus or toner containing a lubricant such as oil or wax is used, the area where the toner is formed becomes more slippery. Therefore, paper wrinkles are more likely to occur.
In order to suppress paper wrinkles when an image having a large deviation in the toner distribution on the paper is formed as described above, the present inventors have devised an image forming apparatus described below. From here, the configuration and operation of the image forming apparatus will be described in detail.

(2) Configuration FIG. 1 is a diagram showing a configuration of an image forming apparatus 100 according to an embodiment of the present invention. As illustrated in FIG. 1, the image forming apparatus 100 includes an image forming unit 1, a paper feeding unit 2, an image reading unit 3, and an operation unit 4. This image forming apparatus 100 forms five types of toner images of invisible toner (i) on a sheet in addition to toners of four colors of yellow (Y), magenta (M), cyan (C), and black (K). can do. The invisible toner is used only when an instruction to form a toner image with the invisible toner is given in a paper wrinkle suppressing process described later.

  The image forming unit 1 is a photoconductor 10i, 10Y, 10M, 10C, 10K on which toner images of i, Y, M, C, K colors are formed while rotating in the direction of arrow a in the figure, and the photoconductor. Chargers 11i, 11Y, 11M, 11C, and 11K for uniformly charging 10i, 10Y, 10M, 10C, and 10K, and exposure light modulated based on image data of each color of iYMCK, and charged photoreceptors 10i, 10Y, Exposure units 12i, 12Y, 12M, 12C, and 12K that form electrostatic latent images of iYMCK colors by irradiating 10M, 10C, and 10K, and electrostatics formed on the photoreceptors 10i, 10Y, 10M, 10C, and 10K Developing units 13i, 13Y, 13M, 13C, and 13K that form toner images on the photoreceptors 10i, 10Y, 10M, 10C, and 10K by developing the latent image with toner; It is provided.

  The image forming unit 1 is stretched around a driving roll 17 and a backup roll 18 and is an intermediate transfer belt 14 that circulates and moves in the direction of arrow b in the drawing while being in contact with the photoreceptors 10i, 10Y, 10M, 10C, and 10K. A nip region is formed with the photoreceptors 10i, 10Y, 10M, 10C, and 10K across the intermediate transfer belt 14, and toner images on the peripheral surfaces of the photoreceptors 10i, 10Y, 10M, 10C, and 10K are transferred to the intermediate transfer belt in the nip region. A nip region is formed with the primary transfer rolls 15i, 15Y, 15M, 15C, and 15K to be transferred to 14 and the backup roll 18 across the intermediate transfer belt 14, and the toner image on the intermediate transfer belt 14 is secondarily transferred to a sheet. And a secondary transfer roll 16.

  Further, the image forming unit 1 includes a fixing device 19. The fixing device 19 includes a heating roll 191 and a pressure roll 192, and fixes the toner image transferred onto the paper in the nip region formed by these rolls by heating and pressing. The fixing device 19 also includes an oil supply device 193 that applies a lubricant such as oil to the surface of the pressure roll 192. When oil is applied to the surface of the pressure roll 192, the releasability of the toner with respect to the pressure roll 192 is improved, and image quality defects and stains on the surface of the pressure roll 192 due to toner separation on the paper surface can be prevented.

  The paper feed unit 2 stores papers of various sizes in a plurality of paper trays 20 and supplies papers of sizes corresponding to the images to be formed. The sheet is transported by a plurality of transport rolls 21, and a toner image is transferred in a nip region formed by the secondary transfer roll 17 and the backup roll 18.

  The image reading unit 3 is a so-called scanner, and includes a platen, a light source, an optical system, a light receiving element, and a signal processing unit (not shown). The light source irradiates light on a document placed on the platen, and the reflected light is optically reflected. The light receiving element receives light through the system and outputs an image signal. The signal processing unit performs various signal processing such as shading correction on the image signal, and supplies the signal to the image forming unit 1 as image data. .

  The operation unit 4 includes a liquid crystal display (not shown), various buttons, and the like, and accepts instructions from the user. The user can use the operation unit 4 to instruct execution of double-sided printing (form images on both sides of the paper) or change the image forming mode. The image forming apparatus 100 of the present embodiment has two types of image forming modes, “character mode” and “image mode”. The “character mode” is a mode for forming an image including many characters and diagrams at high speed. On the other hand, the “image mode” is a mode for forming an image including more natural images such as photographs than characters, and image processing (screen processing or the like) with higher resolution than that in the “character mode” is performed. Therefore, the “image mode” can form a higher-definition image than the “character mode”.

  FIG. 2 is a block diagram illustrating a functional configuration of the image forming apparatus 100. The control unit 50 includes an arithmetic device such as a CPU (Central Processing Unit) and various memories such as a ROM (Read Only Memory) and a RAM (Random Access Memory), and each unit described above by executing a control program. To control the operation. The storage unit 51 is a large-capacity nonvolatile storage device such as a hard disk and stores the above-described control program. An input / output IF (Interface) is connected to a computer (not shown) and receives a print job from the computer. Here, the print job includes image data on which an image is to be formed by the image forming apparatus 100 and print attribute information indicating image forming conditions at the time of image formation. The print attribute information includes, for example, information related to the image forming mode, the paper size, and the number of copies. That is, the image data supplied from the computer is printed by the image forming apparatus 100 in accordance with the conditions described in the print attribute information supplied together with the image data.

The storage unit 52 stores the contents of specific image forming processing in the image forming apparatus 100. The content of the image forming process is an image forming process in which paper wrinkles are likely to occur during image formation by the image forming apparatus 100. In the present embodiment, “a large image density difference in image data” is registered as the “specific image forming process”.
Here, “the image density difference in the image data is large” indicates, for example, image data as shown in FIG. The image data G in FIG. 3 is image data in which a black image having a toner density of 100% is formed in the image area G ₁ and no image is formed in the other image areas G ₂ . Therefore, here, “image data having a large image density difference” indicates “image data in which the toner density difference between one image region and another image region is equal to or greater than a predetermined threshold value”. The threshold value at this time is a value obtained experimentally or empirically. Hereinafter, the value of this threshold is “Th”.
In the following, the content of the specific image forming process stored in the storage unit 52 is referred to as “wrinkle generation condition”.

(3) Operation Based on the configuration described above, the image forming apparatus 100 of the present embodiment forms an image. Specifically, the image forming apparatus 100 forms toner images of each color of YMCK on the photoreceptors 10Y, 10M, 10C, and 10K according to the image data input from the image reading unit 3 or the input / output IF 53, and this toner. The image is transferred to the intermediate transfer belt 14, transferred again to the paper supplied by the paper feed unit 2 in the nip region formed by the secondary transfer roll 17 and the backup roll 18, and fixed on the paper by the fixing device 19. To form an image. Prior to this image formation, the control unit 5 of the image forming apparatus 100 performs an algorithm (hereinafter referred to as “paper wrinkle suppression processing”) for suppressing the occurrence of paper wrinkles in accordance with the “wrinkle generation condition” stored in advance. To change the image forming conditions. Hereinafter, the paper wrinkle suppressing process will be described.

  FIG. 4 is a flowchart showing the paper wrinkle suppressing process in the present embodiment. In this process, when image data is input, it is determined what kind of image the image data is and how it is formed, and image formation is performed according to the determination result. This is a process for forming an image by changing the conditions. The above determination is made based on the print attribute information supplied together with the image data or the user instruction input to the operation unit 4. The control unit 5 refers to the print attribute information when image data is supplied from the computer, and refers to the instruction content from the operation unit 4 when image data is supplied from the image reading unit 3. Hereinafter, the specific operation of the paper wrinkle suppressing process will be described along the flow of FIG.

  First, when image data is input (step S1), the control unit 5 of the image forming apparatus 100 determines whether the image data is image data having a large image density difference (step S2). If this determination is negative, the control unit 5 causes the image data to be formed on the sheet in accordance with predetermined image forming conditions (step S6).

  Here, a specific operation in the determination in step S2 will be described. As described above, “image data with a large difference in image density” refers to the above-described image data “with a large bias in the toner distribution on the paper”. Here, “image data having a large image density difference” is defined in more detail as “image data in which the toner density difference between one image region and another image region is equal to or greater than the threshold Th”. The “one image area” and the “other image area” are defined as follows here. Although two examples are shown below, the control part 5 should just judge by any one of these.

FIG. 5 shows a case where the image data G1 is divided into two image areas. In this case, the control unit 5 detects the toner density of the image areas G ₁₁ and G ₁₂ and calculates the difference d ₁₁ (toner density difference). If the difference d ₁₁ is equal to or greater than the threshold Th, the control unit 5 determines that “the image density difference is large”, and the determination in step S3 is positive.
FIG. 6 shows a case where the image data G2 is divided into three image areas. In this case, the control unit 5 first detects the toner density of the image areas G ₂₁ and G ₂₂ and calculates the difference d ₂₁ . Then, to calculate the toner density of the difference d ₂₃ of the toner density of the difference d ₂₂ of the image region G ₂₁ and G ₂₃ and in the same manner as this image area G ₂₂ and G _23. Then, if at least one of the differences d ₁₁ , d ₂₂ , and d ₂₃ is greater than or equal to the threshold Th, the control unit 5 determines that “the image density difference is large” and the determination in step S3 is affirmative.

If the determination in step S2 is affirmative, the control unit 5 subsequently determines whether or not the image forming mode for forming image data is “image mode” (step S3). If the image forming mode is not the “image mode” (step S3; NO), the control unit 5 forms the image so that the toner density of the high density area in the image data, that is, the image area where the toner density increases on the paper is lowered. The condition is changed (step S4). Specifically, the control unit 5 changes the screen applied to the high density region in the screen processing to a screen with a lower resolution.
As described above, if the screen applied to the high density region is changed to a screen having a lower resolution, the image quality deteriorates. Therefore, when the image forming mode is “image mode” (step S3; YES) ), The control unit 5 skips the process of step S5.

After performing the above processing, the control unit 5 instructs to form invisible toner in a low density area in the image data, that is, an image area where the toner density is low on the paper (step S5).
When these processes are completed, the control unit 5 forms the image data on the sheet according to the image forming conditions changed in steps S4 and S5 (step S6). At this time, in accordance with the instruction in step S5, the image forming unit 1 forms a toner image with invisible toner.

  By performing the above processing, in the image forming apparatus 100, when image formation is performed under conditions where paper wrinkles are likely to occur, the image formation conditions are changed so that paper wrinkles are less likely to occur. The Specifically, by reducing the toner density in the high density area, the difference in toner density between the image area having a high toner density and the image area having a low toner density is reduced, and as a result, paper wrinkles are less likely to occur. In addition, by forming a toner image with invisible toner in the low density area, the low density area is also covered with the toner, so that the difference in dynamic friction force with the high density area becomes small. Therefore, the difference in the sheet conveyance speed between the low density area and the high density area during toner fixing is reduced, and as a result, paper wrinkles are less likely to occur.

(4) Modifications The application of the present invention is not limited to the above-described embodiment, and various modifications can be made. An example is shown below.
The image forming apparatus 100 of the above-described embodiment is of a type in which the fixing device 19 applies a lubricant such as oil. However, the present invention is not limited to such an embodiment. For example, even when the toner contains a lubricant such as oil or wax, it is possible to satisfactorily suppress paper wrinkles by applying the present invention. In other words, if the dynamic friction force between the area where the toner image is formed and the area where the toner image is not different on the paper surface, the present invention can achieve a certain effect, and the difference between the dynamic friction forces is large. The greater the case, the greater the effect of the present invention.

  In the above-described embodiment, it is described that “the image density difference in the image data is large” is registered as the “wrinkle generation condition”, but the “wrinkle generation condition” is not limited to these. Absent. In addition to these conditions, if conditions that are likely to cause paper wrinkles during image formation are found experimentally or empirically, they may be registered as “wrinkle generation conditions”. For example, “wrinkle generation is performed” in which images are formed on both sides of a sheet can also be a “wrinkle generation condition” in the present invention.

  In the above-described embodiment, for ease of explanation, there are two types of image forming modes, “character mode” and “image mode”, and the process of step S5 is executed only in the “character mode”. Then explained. However, in an actual image forming apparatus, various image forming modes are generally prepared according to the user's application. In such a case, in any image forming mode, the determination in step S4 in the paper wrinkle suppression process is negative, and it becomes a problem whether the process in step S5 is performed. The process in step S5 is, for example, a process for changing the screen applied to the high density area to a lower resolution screen in the screen process. Therefore, this process is performed in an image forming mode in which image quality is emphasized. It turns out to be inconvenient. That is, the determination in step S4 is positive in the “image forming mode in which image quality is important”, and the determination in step S4 is negative in the “image forming mode in which image quality is not so important”. .

In the above-described embodiment, FIGS. 5 and 6 are shown as examples of determining that the image density difference is large in Step S3 of the paper wrinkle suppression process. However, the determination of the image density difference is not limited to these methods. An example will be described below.
FIG. 7 shows image data G3 divided into five image areas. In such a case, the control unit 5 calculates the toner density of each of the image areas G ₃₁ , G ₃₂ , G ₃₃ , G ₃₄ , and G ₃₅ , and determines the image area having the highest toner density among these image areas. An image area having the lowest toner density is specified, and each is set as G _MAX and G _MIN . Then, the control unit 5 calculates the difference d ₃ between the toner densities of the image regions G _MAX and G _MIN , and determines that “the image density difference is large” if the difference d ₃ is equal to or greater than the threshold Th, and the determination in step S3. Can be positive.

  Note that various methods are conceivable as a method of measuring the “toner density” in the above-described embodiment. For example, the toner weight per unit area of the toner image on the photoconductors 10Y to 10K or the intermediate transfer belt 14, that is, a so-called TMA (Toner Mass Area) may be used, or the toner image formed on the paper may be the paper. It may be a ratio of covering the surface. As a method for calculating the toner density in an image area, for example, the average value of the toner density in the entire image area may be used as the toner density in the image area, or the mode value of the toner density in the entire image area may be used as the image density. The toner density in the region may be used.

1 is a diagram illustrating a configuration of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a block diagram illustrating a functional configuration of the image forming apparatus according to the embodiment. It is the figure which showed an example of image data. It is the flowchart which showed the paper wrinkle suppression process in the same embodiment. It is the figure which showed the case where image data was divided | segmented into two image areas. It is the figure which showed the case where image data was divided | segmented into three image areas. It is the figure which showed the case where image data was divided | segmented into five image areas.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 ... Image forming apparatus, 1 ... Image forming part, 19 ... Fixing apparatus, 2 ... Paper feed part, 3 ... Image reading part, 4 ... Operation part, 50 ... Control part, 51 ... Memory | storage part.

Claims (8)

Image forming means for forming a toner image on a recording material in accordance with determined image forming conditions;
Storage means for storing in advance the contents of a specific image forming process;
When the content of the image forming process instructed to be executed by the image forming unit matches the content of the image forming process stored in the storage unit, the image forming condition to be followed by the image forming unit is set. An image forming apparatus comprising: a control unit configured to change based on a predetermined change algorithm. The storage unit stores, as the content of the image forming process, that the difference in toner density between the first image area and the second image area on the recording material is equal to or greater than a predetermined value. Image forming apparatus. The first image region is a region having the highest toner density among a plurality of image regions on the recording material,
The image forming apparatus according to claim 2, wherein the second image region is a region having a lowest toner density among a plurality of image regions on the recording material. The image forming apparatus according to claim 1, wherein the control unit changes the image forming condition so that an image with invisible toner is formed in a region where the toner density is low on the recording material. The image forming apparatus according to claim 1, wherein the control unit changes the image forming condition so as to reduce a toner density in a region where the toner density is high on the recording material. The image forming apparatus according to claim 5, wherein the control unit changes the screen applied to the region where the toner density is high on the recording material to a screen having a low resolution, thereby reducing the toner density in the region. The image forming apparatus according to claim 5, wherein the control unit reduces the toner density in the region by adjusting an exposure amount when forming an image in a region where the toner density is high on the recording material. The control means includes
When an image forming mode in which image quality is emphasized as the image forming condition is set, an image with invisible toner is formed on an area where the toner density is low on the recording material,
When an image forming mode in which image quality is emphasized is not set as the image forming condition, an image with an invisible toner is formed in an area where the toner density is low on the recording material, and an area where the toner density is high on the recording material The image forming apparatus according to claim 1, wherein the image forming condition is changed so as to reduce a toner density of the toner.

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