JP6083311B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus, and more particularly to operation control of an image forming apparatus capable of borderless image formation and double-sided image formation.

  In an image forming apparatus such as a copying machine, a printer, or a facsimile, a transfer member that transfers an image to transfer paper or the like, particularly a secondary transfer member in an intermediate transfer system, is in contact with a toner pattern or toner stain on the intermediate transfer member. Since toner may adhere to the surface of the next transfer member, a technique for providing a cleaning mechanism for removing the toner is disclosed in, for example, “Patent Document 1”. In particular, when a toner pattern is formed between sheets in order to control the toner density, the toner adheres to the surface of the intermediate transfer member, so that a cleaning mechanism is indispensable.

  As the above-described cleaning mechanism, brush cleaning and blade cleaning are generally used, but the secondary transfer member may be a roller member having a relatively small diameter in order to improve the paper separation performance. It is difficult to clean the surface of the member, and as a result, there is a problem in that the toner attached to the secondary transfer member adheres to the back surface of the conveyed paper and stains the back of the paper. Means for improving the cleaning performance include techniques such as coating the surface of the secondary transfer member with a material having good releasability, and applying a lubricant to the surface. Will lead to an increase in size.

  As a means for preventing this, a technique for preventing toner from adhering to a transfer member by applying a bias having a reverse polarity to the transfer bias in order to prevent the occurrence of stains on the back of the paper is disclosed in, for example, “Patent Document 2”. It is disclosed. Further, for example, “Patent Document 3” discloses a technique in which the toner once adhered to the secondary transfer member is returned to the intermediate transfer member by bias to perform cleaning. However, these techniques alone are insufficient to prevent toner adhesion due to a toner pattern formed between sheets. Therefore, a toner pattern is formed between sheets, which is used for density detection control during continuous image formation and prevention of image deterioration due to toner replacement, and the toner of the secondary transfer member without providing an expensive cleaning mechanism for the secondary transfer member. As a means for preventing contamination, a technique for separating a secondary transfer member from an intermediate transfer member between sheets when a toner pattern is formed between sheets is disclosed in, for example, “Patent Document 4”.

  On the other hand, in recent years, there is an increasing demand for borderless image formation. In the conventional borderless image formation, an image is formed on a sheet that is slightly larger than a standard size, and then the margin is removed. However, for the purpose of simplifying the operation, there is a need for borderless image formation. It is growing. As a technique for performing borderless image formation, a technique for forming an image up to the edge of a sheet to convey a sheet with high positional accuracy, or detecting a sheet conveyance position and adjusting an image forming area is disclosed in, for example, “Patent Document 5”. The disclosed technique and the technique disclosed in, for example, “Patent Document 6” in which an image is formed by protruding an image from a sheet on the assumption that a certain conveyance position varies.

  However, in the above-described technology, the control means for high-precision paper conveyance is accompanied by an increase in cost and an increase in the size of the apparatus. When the toner is formed so as to protrude from the sheet, there is a problem that the surface of the secondary transfer member becomes dirty due to the toner that protrudes, causing back contamination or edge contamination. In order to prevent this, it is necessary to clean the surface of the secondary transfer member. However, as described above, cleaning of the secondary transfer member with the cleaning member is technically difficult, and the cost is increased when performance is improved. In addition, there is a problem of affecting the enlargement of the apparatus.

  In addition, when image formation without a border is performed without a border at the leading edge of the paper, in the electrophotographic apparatus, a paper wraps around a fixing member at the fixing portion. Therefore, a margin is generally provided at the leading edge of the paper. Is. However, when double-sided image formation is performed when the rear end of the paper is formed without a border, the rear end on the front side becomes the front end on the back side, and enters the fixing unit with toner at the front end of the paper. Since the paper is wound around the member, it is difficult to perform borderless image formation and double-sided image formation at the same time.

  The present invention solves the above-described problems, and can achieve both borderless image formation and double-sided image formation while preventing the paper from being wound around the fixing member, and at the time of borderless image formation and toner pattern image formation between sheets. Small size that can prevent stains on the back of the paper with a simple and inexpensive configuration, reduce the user's workload by installing a borderless image formation mode, and obtain high image quality stability during continuous image formation by controlling the toner pattern between paper Another object is to provide a low-cost image forming apparatus.

  The invention according to claim 1 includes an image carrier on which a toner image is carried on a surface, and a transfer unit including a transfer member that transfers the toner image onto a recording sheet conveyed in a predetermined conveyance direction, Image forming apparatus capable of performing rear endless image formation for forming the toner image without providing a rear end margin on the recording sheet and double-sided image formation for forming an image on both sides of the recording sheet In this case, when the width of the toner image formed in the non-blank image area having no trailing edge margin in the direction perpendicular to the conveyance direction of the recording sheet is less than a predetermined value, double-sided image formation is permitted, If it exceeds the value, double-sided image formation is prohibited.

  According to the present invention, double-sided image formation is permitted when the width of the blank space image area having no trailing edge margin is less than a predetermined value, and double-sided image formation is prohibited when the width is equal to or greater than the predetermined value. Thus, it is possible to prevent the edge of the paper from being wound around the fixing member during the double-sided image formation, and it is possible to continuously perform good double-sided image formation.

1 is a schematic diagram of a color copying machine to which an embodiment of the present invention can be applied. 1 is a schematic diagram of a main part of an image forming unit of a color copying machine to which an embodiment of the present invention can be applied. It is a figure explaining the transfer part and contact / separation means used for one Embodiment of this invention. 1 is a schematic diagram illustrating a toner density adjustment mechanism of a color copying machine to which an embodiment of the present invention can be applied. It is the schematic which shows the state of the secondary transfer apparatus between the paper in the 1st Embodiment of this invention. It is a diagram which shows the evaluation result of the shock jitter in the 1st Embodiment of this invention. It is the schematic explaining the image formation without a trailing edge used for one Embodiment of this invention. 6 is a flowchart illustrating an image forming operation in the first embodiment of the present invention. 6 is a flowchart illustrating an image forming operation in the second embodiment of the present invention. 10 is a flowchart illustrating an image forming operation in the third embodiment of the present invention. 10 is a flowchart illustrating an image forming operation in the fourth embodiment of the present invention. It is a figure explaining each predetermined value used for the 4th Embodiment of this invention. 10 is a flowchart illustrating an image forming operation according to a fifth embodiment of the present invention. FIG. 10 is a schematic diagram illustrating switching of a secondary transfer bias between sheets when image formation without a trailing edge in the fifth embodiment of the present invention is not selected. FIG. 10 is a schematic diagram illustrating switching of a secondary transfer bias between sheets when image formation without a trailing edge is selected according to a fifth exemplary embodiment of the present invention. FIG. 3 is a schematic diagram illustrating an example of a toner image formed in a blank image area in the first embodiment of the present invention.

  FIG. 1 shows an image forming apparatus to which an embodiment of the present invention can be applied. In the figure, a color copying machine 100 as an image forming apparatus is a tandem type electrophotographic apparatus having an intermediate transfer belt 10, a sheet feeding table 2 at the bottom, an apparatus body 1 at the top, and a scanner at the top. 3 and an automatic document feeder (ADF) 4.

  A transfer device 20 including an intermediate transfer belt 10 as an image carrier, which is an endless belt, is disposed at a substantially central portion of the apparatus main body 1. The intermediate transfer belt 10 is stretched around a driving roller 9 and driven rollers 15 and 16, and is driven to rotate clockwise in FIG. 1 when the driving roller 9 is rotationally driven by a driving means (not shown). A cleaning device (not shown) is provided on the left side of the driven roller 15, and the toner remaining on the surface of the intermediate transfer belt 10 after the image transfer is removed by a cleaning device (not shown), and the transfer device 20 forms an image again. Prepared for.

  Above the linear intermediate transfer belt 10 stretched between the driving roller 9 and the driven roller 15, a drum constituting four image forming portions of yellow, magenta, cyan, and black along the moving direction. Shaped photoconductors 40Y, 40M, 40C, and 40K are juxtaposed. Each photoconductor 40 as an image carrier can be rotated counterclockwise. As shown in FIG. 2, a known charging device 60, developing device 61, primary transfer device 62, photoconductor cleaning device 63, and charge eliminating device 64 are arranged around each photoconductor 40. An exposure device 21 is disposed above.

  On the other hand, below the intermediate transfer belt 10, a secondary transfer device 22 as a transfer portion is disposed. The secondary transfer device 22 includes a secondary transfer roller 7 as a transfer member that can be brought into and out of contact with the driven roller 16 via the intermediate transfer belt 10, and a base member 8 that rotatably supports the secondary transfer roller 7 ( 3). The secondary transfer device 22 collectively transfers the toner images formed on the intermediate transfer belt 10 to a sheet as a recording sheet fed between the intermediate transfer belt 10. On the downstream side of the secondary transfer device 22 in the sheet conveyance direction, a fixing device 25 having an endless fixing belt 26 and a pressure roller 27 in pressure contact with the belt is fixed. Has been. The sheet that has passed through the secondary transfer device 22 is sent to the fixing device 25 by an endless conveying belt 24 that is stretched between a pair of rollers 23. A sheet reversing device 28 is disposed below the secondary transfer device 22 for reversing and conveying the sheet when images are formed on both the front and back surfaces of the sheet.

  When an image is formed in the color copying machine 100 having the above-described configuration, a document is usually set on the document table 30 of the ADF 4. However, when the ADF 4 is not used, the ADF 4 is opened, an original is set on the contact glass 32 of the scanner 3, the ADF 4 is closed, and the original is pressed against the contact glass 32.

  Next, when a start switch (not shown) is pressed, when the document is set on the document table 30, the document is automatically fed onto the contact glass 32. When the ADF 4 is not used, the scanner 3 is immediately activated. Then, the first traveling body 33 and the second traveling body 34 start traveling. Accordingly, light from the light source of the first traveling body 33 is emitted toward the document, and reflected light from the document surface is reflected in the direction of the second traveling body 34 by the mirror of the first traveling body 33. Further, the reflected light is changed by 180 degrees by the pair of mirrors of the second traveling body 34 and enters the reading sensor 36 through the imaging lens 35, and the content of the document is read.

  When the start switch is pressed, the intermediate transfer belt 10 starts running, and at the same time, each photoconductor 40 also starts rotating, and each monochrome image of yellow, magenta, cyan, and black is formed on each photoconductor 40. The Each formed single color image is superimposed and transferred onto the traveling intermediate transfer belt 10, thereby forming a full-color composite color toner image on the intermediate transfer belt 10.

  On the other hand, the paper feed roller 42 provided corresponding to the selected paper feed stage in the paper feed table 2 rotates, and the sheet is fed from the selected paper feed cassette 44 in the paper bank 43, and the separation roller 45 is separated into one sheet and fed to the sheet feeding path 46. The fed sheet is fed to the sheet feeding path 48 of the apparatus main body 1 by the conveying roller 47 and is brought into contact with the nip portion of the registration roller pair 49 and temporarily stopped. In the case of manual sheet feeding, the sheet set on the manual tray 51 is brought into contact with the nip portion of the registration roller pair 49 fed by the rotation of the sheet feeding roller 50 and temporarily stopped.

  In either case, the registration roller pair 49 starts rotating at a timing that matches the color image on the intermediate transfer belt 10, and feeds the temporarily stopped sheet between the intermediate transfer belt 10 and the secondary transfer device 22. A color image is transferred onto the sheet by the secondary transfer device 22. The sheet on which the color image has been transferred is conveyed to the fixing device 25 by the conveying belt 24, heated and pressed to fix the transferred image, guided to the discharge side by the switching claw 55, and discharged to the discharge tray by the discharge roller 56. 57 is discharged and stacked. When the double-sided image forming mode is selected, the sheet on which the image is formed on the front surface is guided to the sheet reversing device 28 side by the switching claw 55, and is reversed and guided again to the transfer position to be imaged on the back surface. Is discharged onto the discharge tray 57 by the discharge roller 56.

  When a black single color image is formed on the intermediate transfer belt 10, the driven rollers 15, 16 other than the driving roller 9 are moved so that the yellow, magenta, and cyan photoconductors 40Y, 40M, and 40C are transferred to the intermediate transfer belt. 10 so as to be separated from 10. In the so-called one-drum type image forming apparatus having only one photosensitive member instead of the tandem type shown in FIG. 1, it is common to first form black in order to increase the first print speed. After that, the remaining colors are imaged only when the document is in color.

In the above-described configuration, the registration roller pair 49 is usually used while being grounded, but it is also possible to apply a bias for removing paper dust from the sheet. For example, when a bias is applied using a conductive rubber roller having a diameter of 18 mm and a surface covered with a conductive NBR rubber having a thickness of 1 mm, the volume resistivity of the rubber material is about 10 ⁹ Ωcm. A voltage of about −800 V is applied to the front side of the sheet, which is the toner transfer side, and a voltage of about +200 V is applied to the back side of the sheet. In general, in the intermediate transfer system, it is difficult for paper dust to move to the photosensitive member, so there is little need to consider paper dust transfer, and it may be grounded. Further, although a DC bias is generally applied as the applied voltage, an AC voltage having a DC offset component may be applied in order to charge the sheet more uniformly. Thus, the sheet surface after passing through the pair of registration rollers 49 to which a bias is applied is slightly charged on the negative side. For this reason, in the transfer from the intermediate transfer belt 10 to the sheet, the transfer condition may be changed as compared with the case where no voltage is applied to the registration roller pair 49, and the transfer condition may be changed.

  Next, a first embodiment of the present invention using the above-described color copying machine 100 will be described. In the first embodiment, a foaming roller in which a foaming rubber is coated around a metal core roller is used as the secondary transfer roller 7. The material of the foamable rubber is not particularly limited, but in this embodiment, the NBR rubber is used and the formulation is adjusted so that the Asker C hardness is 40 degrees.

  In addition to the above configuration, a secondary transfer contact / separation mechanism 6 is provided as contact / separation means for contacting / separating the secondary transfer device 22 to / from the intermediate transfer belt 10. The schematic configuration of the secondary transfer contact / separation mechanism 6 is shown in FIG. 3, FIG. 3 (a) shows the state where the secondary transfer device 22 and the intermediate transfer belt 10 are in contact, and FIG. Each state is shown. The base member 8 is swingably supported by the apparatus main body 1 by a support shaft 8a, and below the base member 8 is a rotatable cam 11 disposed in contact with the base member 8 and a stepping motor that rotationally drives the cam 11. 12, a secondary transfer contact / separation mechanism 6 is provided. The secondary transfer contact / separation mechanism 6 selectively rotates the secondary transfer device 22 between the state shown in FIG. 3A and the state shown in FIG. 3B by rotating the cam 11 by a predetermined angle by the stepping motor 12. Position to.

  Further, in addition to the above-described configuration, a toner patch is formed on the intermediate transfer belt 10 corresponding to the space between the sheets, and the secondary transfer device 22 is separated from the intermediate transfer belt 10 by the secondary transfer contact / separation mechanism 6 between the sheets. . The secondary transfer device 22 is brought into contact with the intermediate transfer belt 10 before the next sheet reaches the secondary transfer device 22. The above-described toner patch is formed between sheets on the same principle as a normal toner image. Specifically, a toner image is formed by the photoreceptor 40, the charging device 60, and the developing device 61 shown in FIG. The

  The toner density control using this toner patch will be described. The toner adhesion amount sensor 5 shown in FIG. 4 detects the adhesion amount of the toner patch. Based on the detected value, the density adjustment control means 13 controls at least one of a toner replenishment motor, a developing bias, and a charging bias (not shown) to Adjust the density. When adjustment is performed by controlling the toner replenishment motor, the toner density is adjusted by adjusting toner replenishment to adjust the image density. When the adjustment is performed by controlling the developing bias and the charging bias, the image density is adjusted by adjusting the bias value. Although only the black image forming unit is shown in FIG. 4, the actual control is performed for all colors.

FIG. 5 shows the state of the secondary transfer device 22 between sheets in the first embodiment of the present invention. The secondary transfer device 22 performs contact / separation operation by the secondary transfer contact / separation mechanism 6 between sheets in the order of a to d described later.
a. After the trailing edge of the sheet passes through the contact portion between the secondary transfer device 22 and the intermediate transfer belt 10, the secondary transfer roller 7 starts to be separated from the intermediate transfer belt 10 by the secondary transfer contact / separation mechanism 6.
b. The separation is completed before the toner patch reaches the contact portion.
c. After the toner patch passes through the contact portion, the secondary transfer roller 7 starts to come into contact with the intermediate transfer belt 10 by the secondary transfer contact / separation mechanism 6.
d. The contact of the secondary transfer roller 7 with the intermediate transfer belt 10 is completed before the leading edge of the next sheet reaches the contact portion.

In the above-described configuration, the evaluation result of shock jitter (horizontal band-like image defect that occurs when the writing unit shakes due to obstruction of traveling of the intermediate transfer belt 10 or transmission of vibration when the paper enters the transfer portion) is shown. As shown in FIG. The evaluation is performed by visual rank evaluation in five stages. Rank 5 is the best evaluation without jitter, rank 1 is the worst, and allowable rank is 4 or more. The paper used for the evaluation test was a thick paper with a basis weight of 300 g / m ² , and it occurred when 10 evaluation papers were passed to evaluate the effects on primary transfer, development, and writing when the paper entered. Rated the worst jitter. Further, as the secondary transfer roller 7, in addition to the foaming roller having an Asker C hardness of 40 degrees used in the first embodiment, for comparison, a foaming roller having an Asker C hardness of 70 degrees, 60 degrees, 50 degrees, and 30 degrees and an 80 A solid rubber roller was also used.

  As shown in FIG. 6, the lower the hardness of the secondary transfer roller 7, the less likely to generate jitter. If the Asker C hardness is 60 degrees or less, it is within the allowable range, and if the Asker C hardness is 40 degrees or less, the jitter is It was found that the situation was improved even when it was not visible. However, the lower the roller hardness, the more easily the roller is deformed by repeatedly applying pressure, so it is not preferable to reduce the roller hardness more than necessary.

  As described above, by using a soft foam roller as the material of the secondary transfer roller 7, it is possible to suppress vibrations when the thick paper enters the secondary transfer device 22 and collides with the secondary transfer roller 7. As a result, the vibration can be prevented from propagating to the primary transfer device 62, the developing device 61, and the exposure device 21, and the occurrence of shock jitter can be prevented. In addition, since such a foaming roller is difficult to clean when toner adheres, the operation of the secondary transfer contact / separation mechanism 6 is controlled so that the secondary transfer roller 7 does not contact the intermediate transfer belt 10 between sheets. Yes. As a result, it is possible to prevent a problem that the toner on the surface of the intermediate transfer belt 10 moves to the secondary transfer roller 7 and stains the back surface of the paper.

  In addition, since the foam roller is difficult to clean at all times by a cleaning member such as a cleaning blade, the surface of the secondary transfer roller 7 is soiled by the toner protruding from the paper when borderless image formation is performed. The edge is dirty. However, by limiting the edgeless image formation to only the rear end, if the toner protruding from the sheet during image formation can be cleaned between the sheets, it is possible to prevent the occurrence of the sheet back surface contamination and the edge surface contamination.

  Next, image formation with a border, image formation without a border, and image formation without a trailing edge will be described. 7A shows image formation with a border, FIG. 7B shows image formation without a border, and FIG. 7C shows image formation without a trailing edge. When an image with a border is formed, the toner image is all contained in the sheet, and there are margins (upper margin, lower margin, left margin, right margin) on the top, bottom, left, and right of the sheet. At the time of borderless image formation, the toner image exists up to the edge of the paper, and there is no above-mentioned margin.

  At the time of image formation without a trailing edge, the toner image exists up to the lower end of the paper and there is no lower margin, and there are an upper margin, a left margin, and a right margin. In FIG. 7C, reference numeral 70 denotes a no-blank image area, which indicates an area having a length L from the edge of the trailing edge of the sheet. The no-margin image area 70 is a rear end area that should originally be a blank area, and is an area in which a toner image can be formed when an image without a rear end edge is formed. In the first embodiment of the present invention, the width W of the blank image area 70 in which the toner image is formed, that is, the length of the width W of the toner image formed in the area in the direction orthogonal to the paper transport direction. Thus, control for selecting whether or not to permit double-sided image formation is performed. This control is performed by a control unit 99 such as a CPU. A flowchart of this control is shown in FIG.

  In FIG. 8, when a start switch (not shown) of the color copying machine 100 is pressed, an image forming operation is started (ST01), and surface image formation is started (ST02). Judgment is made (ST03). If it is determined in step ST03 that the double-sided image formation is not performed, a single-sided image forming operation is performed (ST04), and the process ends.

  If it is determined in step ST03 that double-sided image formation is performed, it is determined whether or not the width W of the toner image formed in the blank image area 70 is less than a predetermined value A (ST05). In this case, the double-sided image forming operation is continued (ST06). If it is determined in step ST05 that the width W is greater than or equal to the predetermined value A, a single-sided image forming operation is performed (ST07), and the single-sided image forming operation is continued with the back side image as the second sheet (ST08) and is terminated. . The width W is the maximum value of pixels that are continuous in the direction orthogonal to the paper transport direction, and this is determined by a controller (not shown) provided in the main body during image reading or image input. FIG. 16 shows an example of a toner image formed in the blank image area 70. In FIG. 16A, the width of the toner image is W1, and in FIG. 16B, the width of the toner image is W2.

  If the toner image is present at the leading edge of the paper, an adhesion force is generated between the fixing member and the toner when the toner is melted at the fixing portion, and the paper is easily wound around the fixing member, causing jamming. This winding is likely to occur because the larger the toner image area at the front end of the paper, the stronger the adhesion between the paper and the fixing member. Conversely, if the toner image area is a certain amount or less, the sheet can be separated from the fixing member without causing winding even if there is no leading margin.

  In the first embodiment, when the width W of the toner image formed in the non-blank image area 70 having no trailing edge margin is less than the predetermined value A, double-sided image formation is permitted, and the width W is the predetermined value A. If this is the case, double-sided image formation is prohibited. Accordingly, it is possible to prevent the end of the paper from being wound around the fixing member during the double-sided image formation, and it is possible to continuously perform good double-sided image formation. The predetermined value A in the first embodiment varies depending on the area of the toner image, the type and thickness of the paper, the type of toner, environmental conditions, and the like. However, assuming that the toner image area is a 100% solid image, the width W is preferably about 20% of the paper width in the direction orthogonal to the paper transport direction.

  Next, a second embodiment of the present invention will be described using the flowchart shown in FIG. In the second embodiment, control is performed to increase a predetermined value that allows the width W of the toner image formed in the blank image area 70 in accordance with the pixel area of the blank image area 70.

  In FIG. 9, when a start switch (not shown) of the color copying machine 100 is pressed, an image forming operation is started (ST11), and surface image formation is started (ST12). Determination is made (ST13). If it is determined in step ST13 that double-sided image formation is not being performed, a single-sided image forming operation is performed (ST14), and the process ends.

  If it is determined in step ST13 that double-sided image formation is performed, it is determined whether or not the pixel area of the blank image area 70 is less than 100% (ST15). When it is determined that the pixel area is 100%, it is determined whether or not the width W of the toner image formed in the blank image area 70 is less than the predetermined value A, as in the first embodiment. (ST16) If it is less than the predetermined value A, the double-sided image forming operation is continued (ST17). If it is determined in step ST16 that the width W is greater than or equal to the predetermined value, a single-sided image forming operation is performed (ST18), and the single-sided image forming operation is continued with the back side image as the second sheet (ST19). The pixel area of the blank image area 70 is the sum of the pixels existing in the blank image area 70 shown in FIG. 7C, which is determined by a controller (not shown) provided in the main body at the time of image reading or image input. To do.

  If it is determined in step ST15 that the pixel area of the blank area image region 70 is less than 100%, the upper limit of the width W of the toner image formed in the blank area image region 70 is determined based on the determined pixel area. The predetermined value B is determined (ST20). The width W is defined such that the predetermined value A is about 20% of the paper width in the direction orthogonal to the paper transport direction when the toner image area, which is the pixel area, is 100%. Accordingly, the predetermined value B is, for example, about 25% of the paper width in the direction orthogonal to the paper conveyance direction when the pixel area is 80%, and the paper conveyance direction when the pixel area is 70%. The width W is defined to be about 28.6% of the width of the paper in the direction orthogonal to the direction.

  Then, it is determined whether or not the width W of the toner image formed in the blank image area 70 is less than the predetermined value B determined in step ST20 (ST21). The image forming operation is continued (ST17). If it is determined in step ST21 that the width W is greater than or equal to the predetermined value B, a single-sided image forming operation is performed (ST18), and the single-sided image forming operation is continued with the back side image as the second sheet (ST19). .

  The greater the amount of toner attached to the leading edge of the paper, the stronger the adhesive force between the toner and the fixing member. As a result, the adhesive force between the paper and the fixing member also increases, so that the paper is easily wound around the fixing member. Even if the toner image area is small, if the toner adhesion amount per unit area is large, the adhesive force becomes strong and wrapping is likely to occur. Conversely, even if the toner image area is large, if the toner adhesion amount per unit area is small, the wrapping will occur. Is less likely to occur.

  In the second embodiment, when the pixel area of the blank image area 70 having no trailing edge margin is less than 100%, the predetermined value B of the width W is set larger than the predetermined value A according to the pixel area. ing. When the width W is equal to or larger than the predetermined value B, the double-sided image formation is prohibited, so that the edge of the paper is wound around the fixing member at the time of double-sided image formation in more toner images than in the first embodiment. Can be prevented. Thereby, favorable double-sided image formation can be performed continuously.

  Next, a third embodiment of the present invention will be described using the flowchart shown in FIG. In the third embodiment, control is performed to increase a predetermined value that allows the width W of the toner image formed in the blank image area 70 in accordance with the thickness of the recording paper.

  In FIG. 10, when a start switch (not shown) of the color copying machine 100 is pressed, an image forming operation is started (ST41), and a front surface image is started (ST42). Determination is made (ST43). If it is determined that the double-sided image formation is not performed, the single-sided image forming operation is performed (ST44), and the process ends.

  If it is determined in step ST43 that double-sided image formation is performed, it is determined whether or not the recording paper has a thickness that allows double-sided image formation (ST45). If it is determined that the thickness is not such that double-sided image formation is possible, the process proceeds to step ST44 where the single-sided image forming operation is performed and the process ends. Here, if the thickness of the recording paper is greater than or equal to a reference value, it is difficult to enter the conveyance path for double-sided image formation due to the rigidity of the recording paper, which causes a recording paper conveyance jam. For this reason, it is common not to allow double-sided image formation for recording paper having a thickness greater than a reference value.

  If it is determined in step ST45 that the recording sheet is thick enough to form a double-sided image, it is determined whether the recording sheet is equal to or greater than a predetermined thickness (ST46). If it is determined that the thickness is less than the predetermined thickness, it is determined whether or not the width W of the toner image formed in the blank image area 70 is less than the predetermined value A as in the first embodiment (ST47). If the value is less than the predetermined value A, the double-sided image forming operation is continued (ST48). If it is determined in step ST47 that the width W is greater than or equal to the predetermined value, a single-sided image forming operation is performed (ST49), and the single-sided image forming operation is continued with the back side image as the second sheet (ST50), and the process ends. The pixel area of the blank image area 70 is the sum of the pixels existing in the blank image area 70 shown in FIG. 7C, which is determined by a controller (not shown) provided in the main body at the time of image reading or image input. To do.

When it is determined in step ST46 that the thickness of the recording paper is equal to or greater than the predetermined thickness, a predetermined value C that determines the upper limit of the width W of the toner image formed in the blank image area 70 based on the thickness of the recording paper is set. It is determined (ST51). For example, when the thickness of the recording paper is less than 120 g / m ² , the width W is defined so that the predetermined value A is about 20% of the width of the paper in a direction orthogonal to the recording paper conveyance direction. On the other hand, the predetermined value C is about 45% of the width of the paper in the direction orthogonal to the recording paper conveyance direction at 180 g / m ² , for example, and the recording paper conveyance direction at 240 g / m ^2. The width W is defined so as to be about 60% of the width of the sheet in the orthogonal direction.

  Next, it is determined whether or not the width W of the toner image formed in the blank image area 70 is less than the predetermined value C determined in step ST51 (ST52). Proceed to step 2 to continue the double-sided image forming operation. If it is determined in step ST52 that the width W is greater than or equal to the predetermined value C, the process proceeds to step ST49 to perform a single-sided image forming operation, and further proceeds to step ST50 to set the back side image as the second sheet and the single-sided image forming operation. Continues and ends.

  As described above, the greater the toner adhesion amount at the leading edge of the recording paper, the stronger the adhesion between the toner and the fixing member, and the stronger the adhesion between the recording paper and the fixing member. For this reason, the recording paper is easily wound around the fixing member. However, as the thickness of the recording paper increases, a force acts in the direction of peeling from the fixing member due to the rigidity of the recording paper. For this reason, the greater the recording paper thickness, the larger the predetermined value C for permitting double-sided image formation.

  In the third embodiment, when the thickness of the recording paper is equal to or greater than a predetermined thickness, the predetermined value C of the width L is set larger than the predetermined value A according to the thickness, and the width W is equal to or greater than the predetermined value C. In the case of, double-sided image forming operation is prohibited. As a result, jamming can be prevented in more toner images than in the first embodiment, and a good double-sided image forming operation can be continuously performed.

  Next, a fourth embodiment of the present invention will be described using the flowchart shown in FIG. In the fourth embodiment, a predetermined value that allows the length of the width W of the toner image formed in the blank image area 70 according to both the pixel area of the blank image area 70 and the thickness of the recording paper. The control is increased.

  In FIG. 11, when a start switch (not shown) of the color copying machine 100 is pressed, an image forming operation is started (ST61), and surface image formation is started (ST62). Determination is made (ST63). If it is determined that the double-sided image formation is not performed, the single-sided image forming operation is performed and the process ends (ST64).

  If it is determined in step ST63 that double-sided image formation is possible, it is determined whether or not the thickness of the recording paper is such that double-sided image formation is possible (ST65). It progresses to step ST64 and is complete | finished. Here, if the thickness of the recording paper is greater than or equal to a reference value, it is difficult to enter the conveyance path for double-sided image formation due to the rigidity of the recording paper, which causes a recording paper conveyance jam. For this reason, it is common not to allow double-sided image formation for recording paper having a thickness greater than a reference value.

  If it is determined in step ST65 that the recording paper is thick enough to form a double-sided image, it is determined whether or not the pixel area of the blank image area 70 is less than 100% or whether the recording paper is equal to or larger than a predetermined thickness. Judgment is made (ST66). When it is determined that none of the conditions is satisfied (the pixel area is 100% and the thickness of the recording paper is less than the predetermined thickness), the width W of the toner image formed in the blank image area 70 is less than the predetermined value A. Is determined (ST67). If it is less than the predetermined value A, the double-sided image forming operation is continued (ST68), and if it is equal to or greater than the predetermined value A, the single-sided image forming operation is performed (ST69). It is continued and finished (ST70). The pixel area of the blank image area 70 is the sum of the pixels existing in the blank image area 70 shown in FIG. 7C, which is determined by a controller (not shown) provided in the main body at the time of image reading or image input. To do.

  If it is determined in step ST66 that the pixel area of the blank image area 70 is less than 100% or the thickness of the recording paper is equal to or greater than a predetermined thickness, then whether or not the thickness of the recording paper is equal to or greater than the predetermined thickness is determined. Is determined (ST71). If the thickness is less than the predetermined thickness, a predetermined value B that determines the upper limit of the width W of the toner image formed in the blank image area 70 is determined based on the determined pixel area (ST72).

  Next, it is determined whether or not the width W of the toner image formed in the blank image area 70 is less than the predetermined value B determined in step ST72 (ST73). Proceed to step 2 to continue the double-sided image forming operation. If it is equal to or greater than the predetermined value B, the process proceeds to step ST69, where the single-sided image forming operation is performed, and further proceeds to step ST70, where the single-sided image forming operation is continued with the back side image as the second sheet.

  If it is determined in step ST71 that the thickness of the recording paper is equal to or greater than the predetermined thickness, it is next determined whether or not the pixel area of the blank image area 70 is less than 100% (ST74). When it is determined that the pixel area is 100%, a predetermined value C that determines the upper limit of the width W of the toner image formed in the blank image area 70 is determined based on the determined thickness of the recording paper. (ST75).

  Next, it is determined whether or not the width W of the toner image formed in the blank image area 70 is less than the predetermined value C determined in step ST75 (ST76). Proceed to step 2 to continue the double-sided image forming operation. If it is determined that the value is equal to or greater than the predetermined value C, the process proceeds to step ST69 where a single-sided image forming operation is performed, and further proceeds to step ST70 where the single-sided image forming operation is continued with the back side image as the second sheet.

  If it is determined in step ST74 that the pixel area of the blank image region 70 is less than 100%, the width of the toner image formed in the blank image region 70 based on the determined pixel area and the thickness of the recording paper. A predetermined value D for determining the upper limit of W is determined (ST77). Next, it is determined whether or not the width W of the toner image formed in the non-blank image area 70 is less than a predetermined value D (ST78). If it is less than the predetermined value D, the process proceeds to step ST68 and the double-sided image forming operation is performed. continue. If it is determined that the value is equal to or greater than the predetermined value D, the process proceeds to step ST69, where the single-sided image forming operation is performed, and further proceeds to step ST70, where the single-sided image forming operation is continued with the back side image as the second sheet.

  In the fourth embodiment described above, in order to determine whether double-sided image formation is permitted or prohibited, predetermined values for determining the upper limit of the width W of the toner image formed in the blank image area 70 are set to A, B, There are a plurality of C and D, and FIG. 12 shows a table for determining these. From FIG. 12, the predetermined values A, B, C, and D are determined as follows.

Predetermined value A: When the pixel area is 100% and the recording paper thickness is less than the predetermined value (120 g / m ² ), the predetermined value A is determined. For example, the value is 20%.
Predetermined value B: When the pixel area is less than 100% and the recording paper thickness is less than a predetermined value (120 g / m ² ), the determination is made with the predetermined value B. The value of the predetermined value B is determined based on the pixel area. For example, when the pixel area is less than 100% and 60% or more, B1 (for example, 25%), and when the pixel area is less than 60% and 30% or more, B2 (for example, 30). %) And B3 (for example, 35%) when the pixel area is less than 30%.
Predetermined value C: When the pixel area is 100% and the recording paper thickness is equal to or greater than the predetermined value (120 g / m ² ), the determination is made with the predetermined value C. The value of the predetermined value C is determined based on the thickness of the recording paper. For example, when the value is 120 g / m ² or more and less than 200 g / m ^2, C1 (for example, 40%), 200 g / m ² or more and less than 260 g / m ² Is C2 (for example, 60%). In the case of 260 g / m ² or more, double-sided image formation is not permitted.
Predetermined value D: When the pixel area is less than 100% and the recording paper thickness is greater than or equal to a predetermined value (120 g / m ² ), the predetermined value D is determined. The value of the predetermined value D is determined based on both the pixel area and the recording paper thickness. For example, D1 to D6 are determined based on the determination criteria shown in FIG. Here, D1 = 45%, D2 = 50%, D3 = 55%, D4 = 65%, D5 = 70%, and D6 = 75%. In this example, the predetermined value is determined from the range of the pixel area and the recording paper thickness according to the determined table. However, the predetermined value may be calculated from the area value and the thickness value.

  In the fourth embodiment, when the pixel area of the blank image area 70 is less than 100% and the recording paper thickness is equal to or larger than a predetermined thickness, the upper limit of the width W according to both the pixel area and the recording paper thickness. The predetermined value D is set to be larger than the predetermined value A. When the width W is equal to or larger than the predetermined value D, the double-sided image formation is prohibited, so that jamming is prevented and good double-sided image formation is performed on more toner images than in the first to third embodiments. Can be carried out continuously.

  Next, a fifth embodiment of the present invention will be described using the flowchart shown in FIG. In the fifth embodiment, when image formation without a trailing edge is performed, the distance between sheets is longer than that of normal image formation by at least one rotation of the secondary transfer roller 7. Then, it is lengthened by 1.2 rotations.

  First, after the trailing edge of the sheet has passed through the secondary transfer device 22 (ST31), the secondary transfer contact / separation mechanism 6 is operated to wait for a certain interval regardless of whether or not the image is formed without the trailing edge. The transfer roller 7 is separated from the intermediate transfer belt 10. Then, the secondary transfer bias is switched to a positive bias having a polarity opposite to that at the time of image formation (ST32). If the separation operation of the secondary transfer roller 7 is performed immediately after the trailing edge of the sheet, the secondary transfer roller 7 may be separated in a state where the sheet is still in the secondary transfer device 22 due to variations in sheet conveyance timing. is there. In this case, since there is a possibility that an image defect may occur, the present embodiment is configured to be spaced by a certain distance.

  When a predetermined time has elapsed after the toner pattern (toner patch) formed between the images passes through the secondary transfer device 22 (ST33), it is determined whether or not the image formation without the trailing edge is selected. (ST34). When the image formation without the trailing edge is selected, the secondary transfer contact / separation mechanism 6 is operated to start the contact operation of the secondary transfer roller 7 with respect to the intermediate transfer belt 10 (ST35). Then, after the contact operation is started, the operation of the image forming section of the image forming section is continued for an amount equivalent to 1.2 rotations of the secondary transfer roller 7 (ST36), and then the secondary transfer bias is switched to a minus bias for image formation. (ST37) to finish the operation. If the image formation without the trailing edge is not selected in step ST34, the contact operation of the secondary transfer roller 7 with respect to the intermediate transfer belt 10 is started (ST38), and the process proceeds to step ST37.

  In the fifth embodiment described above, FIG. 14 shows the switching of the secondary transfer bias between sheets when the trailing edgeless image formation is not selected. FIG. 14 shows the sheet when trailing edgeless image formation is selected. FIG. 15 shows the switching of the secondary transfer bias in between.

When the image formation without the trailing edge shown in FIG. 14 is not selected, the secondary transfer bias in the secondary transfer device 22 is switched in the following order from a to d.
a. After the trailing edge of the sheet passes through the contact portion between the secondary transfer roller 7 and the intermediate transfer belt 10, the secondary transfer bias is switched from minus to plus.
b. When the toner patch enters the contact portion, the switching is completed so that the secondary transfer bias is positive.
c. After the toner patch passes through the contact portion, the secondary transfer bias is switched from plus to minus.
d. The secondary transfer bias is set to the normal output before the leading edge of the next sheet is input to the contact portion.

Further, when the image formation without the trailing edge shown in FIG. 15 is selected, the secondary transfer bias in the secondary transfer device 22 is switched in the following order a to e.
a. After the trailing edge of the sheet passes through the contact portion between the secondary transfer roller 7 and the intermediate transfer belt 10, the secondary transfer bias is switched from minus to plus.
b. When the toner patch enters the contact portion, the switching is completed so that the secondary transfer bias is positive.
c. After the toner patch passes through the contact portion, the operation of the secondary transfer contact / separation mechanism 6 is controlled to start the contact operation of the secondary transfer roller 7 with respect to the intermediate transfer belt 10.
d. After the contact operation of the secondary transfer roller 7 is started, the secondary transfer bias is switched from plus to minus after waiting for a running time of 1.2 rotations of the secondary transfer roller 7.
e. The secondary transfer bias is set to the normal output before the leading edge of the next sheet is input to the contact portion.

  In the configuration described above, the switching of the secondary transfer bias after passing through the toner patch is delayed by 1.2 rotations of the secondary transfer roller 7 as compared with the normal image formation. Accordingly, as shown in FIG. 15, the state where the secondary transfer roller 7 is in contact with the intermediate transfer belt 10 and the secondary transfer bias is positive continues for one rotation of the secondary transfer roller 7. As a result, cleaning by retransfer of the toner adhering to the surface of the secondary transfer roller 7 to the intermediate transfer belt 10 can be performed over the entire circumference of the secondary transfer roller 7. The extent to which the space between the sheets can be widened and the cleaning of the entire circumference of the secondary transfer roller 7 depends on the switching time of the secondary transfer device 22, but it is necessary to widen at least one rotation of the secondary transfer roller 7. is there.

  When the surface of the secondary transfer roller 7 is soiled by toner that protrudes from the sheet during the image formation without the trailing edge, if the secondary transfer roller 7 is separated from the intermediate transfer belt 10 immediately after passing through the sheet, the secondary transfer roller 7 The surface remains dirty. Therefore, when image formation without a trailing edge is performed, the distance between the sheets is made longer than that during normal image formation. Thus, it is possible to provide a time for the toner attached to the surface of the secondary transfer roller 7 to be retransferred to the intermediate transfer belt 10 with the secondary transfer roller 7 in contact with the intermediate transfer belt 10. As a result, it is possible to simultaneously prevent toner contamination due to borderless image formation and toner contamination due to the inter-paper toner pattern.

  In the above configuration, the toner density can be kept stable by creating and detecting a toner adhesion amount detection pattern between sheets. In addition, by separating the secondary transfer device 22 between the sheets in such a configuration, it is possible to prevent the toner pattern formed between the sheets from adhering to the secondary transfer roller 7, and to prevent the back side of the sheet from being stained. Can be prevented.

  Further, in the above configuration, by creating a toner discharge pattern between the sheets, the deteriorated toner can be replaced with a new toner to maintain good image quality. Further, by separating the secondary transfer device 22 between the sheets in such a configuration, it is possible to prevent the toner pattern formed between the sheets from adhering to the secondary transfer roller 7 and to prevent the back of the sheet from being stained. Can be prevented.

  In the above-described configuration, it is possible to prevent the apparatus from being stopped due to blade turning by creating a blade turning prevention pattern between sheets. Further, by separating the secondary transfer device 22 between the sheets in such a configuration, it is possible to prevent the toner pattern formed between the sheets from adhering to the secondary transfer roller 7, and the occurrence of stains on the back of the sheet. Can be prevented. Blade turning is likely to occur when the frictional force between the object to be cleaned and the blade is increased. Therefore, the frictional force is likely to increase under a condition where the amount of toner input is small, and thus is likely to occur. Even in such a case, by periodically inputting the toner pattern between the sheets to the blade, it is possible to prevent the frictional force from increasing and prevent the blade from turning up.

  Further, in the above-described configuration, the color misregistration can be corrected by creating a color misregistration detection pattern between the sheets, detecting the color misregistration, and adjusting the image forming position. In addition, by separating the secondary transfer device 22 between the sheets in such a configuration, it is possible to prevent the toner pattern formed between the sheets from adhering to the secondary transfer roller 7, and to prevent the back side of the sheet from being stained. Can be prevented. Note that color misregistration detection and correction at this time are performed by a general technique.

  In each of the above embodiments, the color copying machine 100 is shown as the image forming apparatus. However, the image forming apparatus to which the present invention is applicable is not limited to this, and a single color copying machine, printer, plotter, facsimile, having only one photoconductor, The present invention is also applicable to an image forming apparatus such as a multifunction machine. In each of the above embodiments, the secondary transfer device 22 that transfers the toner image on the intermediate transfer belt 10 to a sheet as a transfer unit is shown. However, the transfer unit to which the present invention can be applied is not limited thereto, and one or The present invention can also be applied to a transfer device that directly transfers toner images on a plurality of image carriers onto a sheet.

6 Contact / separation means (secondary transfer contact / separation mechanism)
7 Transfer member (secondary transfer roller)
10 Image carrier (intermediate transfer belt)
22 Transfer section (secondary transfer device)
40 Image carrier (photoconductor)
70 No-margin image area 100 Image forming apparatus (color copying machine)
L width of blank image area

JP 2001-31154 A JP-A-8-248787 Japanese Patent No. 4372716 JP 2012-18369 A JP 2006-220991 A JP 2004-45457 A

Claims (13)

An image carrier having a toner image carried on a surface thereof, and a transfer portion having a transfer member for transferring the toner image to a recording sheet conveyed in a predetermined conveyance direction, and a rear end relative to the recording sheet In an image forming apparatus capable of performing rear endless image formation for forming the toner image without providing a margin and double-sided image formation for forming an image on both sides of the recording sheet,
When the width of the toner image formed in the non-blank image area having no trailing edge margin in the direction perpendicular to the conveyance direction of the recording sheet is less than a predetermined value, double-sided image formation is permitted, and the predetermined value or more is permitted. In this case, the image forming apparatus prohibits double-sided image formation. The image forming apparatus according to claim 1.
2. The image forming apparatus according to claim 1, wherein the predetermined value is increased as a pixel area of the toner image formed in the blank image area is reduced. The image forming apparatus according to claim 1.
When the thickness of the recording sheet is equal to or less than a thickness at which double-sided image formation is possible, the predetermined value is increased as the thickness of the recording sheet increases. The image forming apparatus according to claim 1.
When the thickness of the recording sheet is equal to or less than the thickness at which double-sided image formation is possible, the predetermined value is determined according to the pixel area of the toner image formed in the blank image area and the thickness of the recording sheet. An image forming apparatus characterized by determining a value. The image forming apparatus according to any one of claims 1 to 4,
The transfer member is made of a foam member, and has a pattern formation mode for forming a toner pattern between the recording sheets during continuous image formation. When the toner pattern formed in the pattern formation mode enters the transfer portion An image forming apparatus comprising contact means for separating the transfer member from the image carrier. The image forming apparatus according to claim 5.
The image forming apparatus, wherein the transfer member has an Asker C hardness of 60 degrees or less. The image forming apparatus according to claim 5.
The image forming apparatus, wherein the transfer member has an Asker C hardness of 45 degrees or less. The image forming apparatus according to any one of claims 5 to 7,
When performing image formation without a trailing edge, the image forming apparatus is characterized in that the distance between the recording sheets is made longer than that during normal image formation. The image forming apparatus according to claim 8.
When performing image formation without a trailing edge, the image forming apparatus is characterized in that the distance between recording sheets is increased by at least one rotation of the transfer member as compared with normal image formation. The image forming apparatus according to any one of claims 5 to 9,
The image forming apparatus according to claim 1, wherein the toner pattern is used to detect an amount of toner attached to the image carrier. The image forming apparatus according to any one of claims 5 to 9,
The image forming apparatus according to claim 1, wherein the toner pattern is a toner discharge pattern for replacing deteriorated toner. The image forming apparatus according to any one of claims 5 to 9,
The image forming apparatus according to claim 1, wherein the toner pattern is a blade turning prevention pattern for preventing the blade from turning when the toner is input to the cleaning blade. The image forming apparatus according to any one of claims 5 to 9,
The image forming apparatus according to claim 1, wherein the toner pattern is a color misregistration detection pattern that is used for image registration by detecting color misregistration.

Images