JP2013024902A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus that prevents an increase in power consumption, a reduction in stability of an image due to adhesion of toner, and a reduction in feeding ability of a transfer material, while reducing an influence due to brightness difference to the quality of an image.SOLUTION: On the upstream side of a fixing device in a transfer material conveying direction, heating means is provided, which is controlled to heat at least one of a partial area including a tip portion in the transfer material conveying direction of a transfer material directed toward the fixing device, and a partial area including a rear end portion in the transfer material conveying direction.

Description

  The present invention relates to an image forming apparatus including a fixing device that fixes a toner image onto a transfer material.

  An image forming apparatus employing an electrophotographic system includes a fixing device that fixes a toner image onto a transfer material. In this fixing apparatus, the toner image is fixed to the transfer material by heating and pressurizing the transfer material onto which the toner image has been transferred.

  The fixing device is configured such that when fixing a toner image on a transfer material, the fixing material heated to a predetermined temperature is pressed against the transfer material while rotating, thereby fixing the toner image while fixing the toner image. A structure for carrying is generally adopted.

  In such a configuration, when the transfer material onto which the toner image has been transferred enters the fixing device, the transfer material close to room temperature comes into contact with the fixing member heated to a predetermined temperature, so that the heat of the fixing member is transferred. Deprived of the material, its temperature drops. While the transfer material is being fixed, since the transfer material continues to contact the rotating fixing member, the temperature of the fixing member changes at a temperature lower than the predetermined temperature. When the fixing to the transfer material is completed, the transfer material is separated from the fixing member, so that the temperature of the fixing member rises and recovers to a predetermined temperature.

  During the period from the completion of fixing the preceding transfer material to the start of fixing the subsequent transfer material, the fixing member does not come into contact with the transfer material, so that the heat of the fixing member is not lost to the transfer material. When the fixing to the subsequent transfer material is started, the heat of the fixing member is again taken away by the transfer material, and the temperature is lowered.

  As described above, when the toner image is fixed on the transfer material by rotating the fixing member, there is a difference in temperature between the area that contacts the transfer material and the area that does not contact the transfer material on the peripheral surface of the fixing member. End up. Since a material having low thermal conductivity is often used for the fixing member, the above temperature difference remains even after the fixing member makes one rotation. Then, the region where the temperature difference on the peripheral surface of the fixing member is brought into contact with the transfer material again for fixing the toner image affects the fixing of the toner image.

  That is, the gloss level of the image fixed by the high temperature region on the fixing member is increased, but the gloss level of the image fixed by the low temperature region of the fixing member is low. In particular, the more rapid the temperature change in the fixing member described above, the more noticeable gloss steps appear in the image, and the quality of the image is impaired.

  As described above, a gloss level difference appears due to the temperature difference on the peripheral surface of the fixing member caused by the heat of the fixing member being taken away by the transfer material. Therefore, by reducing the temperature difference between the fixing member and the transfer material, the heat taken away by the fixing member coming into contact with the transfer material is reduced, so that the temperature difference on the peripheral surface of the fixing member is reduced and the image is displayed. It is possible to reduce the gloss level difference that appears.

  In Patent Document 1, a cooling unit that cools a pressure member that presses against a fixing member and a preheating unit that heats a transfer material are controlled so as to reduce a temperature difference between the pressure member and the transfer material. In addition, an image forming apparatus that does not cause poor fixing image quality due to a gloss difference is described.

  In Patent Document 2, the first pressing member and the second pressing member in contact with the fixing member pre-heat the transfer material before transferring the toner image, and the second pressing member after transferring the toner image. An image forming apparatus is described in which a toner image is fixed by a fixing member and a gloss level difference is not generated.

  In Patent Document 3, air outside the apparatus is guided to the fixing device and cooled, and then the air heated by the fixing device cooling is sent to the image supporting member conveyance path on either or both of the upstream and downstream sides of the transfer unit. There is described an image forming apparatus capable of preventing a gloss level difference by preheating a member.

JP 2006-330556 A JP 2006-337898 A JP 2007-57775 A

  In each of the image forming apparatuses described in Patent Documents 1 to 3, the entire transfer material is preheated to reduce the temperature difference between the fixing member and the transfer material, thereby preventing the occurrence of a gloss level difference. However, in such a case, since a lot of energy is required, there is a problem that power consumption increases.

  Further, when the entire transfer material is preheated as described above, the temperature in the image forming apparatus is excessively increased, and the toner is fixed due to heat. Then, there is a problem that the stability of the image is lowered by transferring and fixing the toner which is fixed to the transfer material.

  Further, when the entire transfer material is preheated as described above, there is a problem in that the preheated transfer material is likely to curl and the transfer material feeding property is lowered, such as a jam.

  The present invention has been made in view of the above problems, and while reducing the influence on the image quality due to the gloss level difference, the power consumption is increased, the stability of the image is decreased due to toner fixation, and the transfer material is fed. An object of the present invention is to provide an image forming apparatus capable of preventing the deterioration of the property.

  The invention described in claim 1 has a rotatable fixing member and a first heating means for heating the fixing member, and the fixing member is heated by the first heating means and heated. In an image forming apparatus including a fixing device that fixes a toner image on a transfer material to the transfer material by applying heat and pressure to the transfer material while rotating the fixing member, on the upstream side in the transfer material conveyance direction from the fixing device. A second heating unit configured to heat the transfer material toward the fixing device, a part of the transfer material including the front end in the transfer material conveyance direction, and a part of the transfer material including the rear end in the transfer material conveyance direction. An image forming apparatus comprising: a control unit that controls the second heating unit to heat at least one of the regions.

  According to the second aspect of the present invention, the second heating unit is provided on the upstream side in the transfer material conveyance direction from the transfer unit that transfers the toner image to the transfer material, and is heated by the second heating unit. The image forming apparatus according to claim 1, wherein a toner image is transferred in the transfer unit.

  According to a third aspect of the present invention, the second heating unit is provided on the downstream side in the transfer material conveyance direction from the transfer unit that transfers the toner image to the transfer material and on the upstream side in the transfer material conveyance direction from the fixing device. The image forming apparatus according to claim 1, wherein the second heating unit heats the transfer material onto which the toner image is transferred in the transfer unit.

  According to a fourth aspect of the present invention, in the transfer material, the control means includes a part of the transfer material including a transfer material conveyance direction front end portion and a transfer material transfer direction rear end portion of the transfer material. The image forming apparatus according to claim 3, wherein the image forming apparatus is controlled to heat an area other than the area where the toner image is transferred.

  The invention according to claim 5 is characterized in that the control means controls to change a heated region in the transfer material based on the content of the toner image transferred to the transfer material. The image forming apparatus according to claim 1.

  The invention described in claim 6 has image quality setting means for setting the image quality of the toner image formed on the transfer material, and the control means is set to form a high quality image by the image quality setting means. 6. If the transfer material is not set to form a high-quality image by the image quality setting means, control is performed to heat a wider area than the area to be heated. The image forming apparatus described in the above.

  According to a seventh aspect of the present invention, the second heating unit is divided and provided in a direction orthogonal to the transfer material conveyance direction, and the control unit is divided and provided with the second heating unit. 6. The image forming apparatus according to claim 5, wherein the units are individually controlled.

  The invention according to claim 8 is characterized in that the control means controls to operate only the second heating means corresponding to the area where the toner image is formed in the transfer material. The image forming apparatus described.

  The invention according to claim 9 has a conveyance control means for controlling the conveyance of the transfer material, and the control means controls to heat only a part of the transfer material including the front end in the transfer material conveyance direction. The transport control unit controls the transfer material so as not to contact the area of the fixing member in contact with the rear end portion of the preceding transfer material in the transfer material transport direction when the toner image is fixed to the transfer material. The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus.

  The invention according to claim 10 has a conveyance control means for controlling the conveyance of the transfer material, and the control means controls to heat only a part of the transfer material including the rear end portion in the transfer material conveyance direction. The transport control unit controls the transfer material so as not to contact the region of the fixing member that contacts the leading end of the transfer material in the transfer material conveyance direction when the toner image is fixed to the transfer material. The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus.

  According to the image forming apparatus of the present invention, the control unit includes a partial region including the front end portion in the transfer material conveyance direction (hereinafter referred to as “front end portion”) of the transfer material toward the fixing device and the rear portion in the transfer material conveyance direction. The second heating means is controlled to heat a part of the region including the end portion (hereinafter referred to as “rear end portion”).

  As described above, when a part of the region including the front end portion of the transfer material and a part of the region including the rear end portion are warmed, the temperature change of the fixing member due to the contact between the transfer material and the fixing member is moderated. Therefore, it is possible to make the gloss level difference appearing in the image inconspicuous and maintain the quality of the image.

  At the same time, since a part of the transfer material is heated, the power consumption is increased, the stability of the image is lowered due to the fixing of the toner due to the increase in the internal temperature, and the transfer material is supplied due to the occurrence of curling. It is possible to prevent a decrease in feedability.

1 is a schematic diagram illustrating an overall image of an image forming apparatus according to a first embodiment of the present invention. 1 is a schematic diagram illustrating an overall image of a fixing device according to a first embodiment of the present invention. It is the figure which expanded the 2nd heating means vicinity in the 1st Embodiment of this invention. FIG. 3 is a block diagram illustrating an electrical relationship of each component in the image forming apparatus according to the first embodiment of the present invention. FIG. 6 is a diagram illustrating a change in the surface temperature of the fixing belt when fixing a toner image when the paper is not preheated. It is the figure which showed a mode that preliminary heating was performed with respect to a paper. FIG. 6 is a diagram illustrating changes in the surface temperature of the fixing belt during toner image fixing in a case where a partial area including a leading end portion and a partial area including a trailing end portion of a sheet are preheated. FIG. 10 is a diagram showing a change in the surface temperature of the fixing belt during toner image fixing when only a part of the area including the leading end of the sheet is preheated. FIG. 5 is a diagram showing a change in the surface temperature of the fixing belt during toner image fixing when only a part of the area including the rear end of the sheet is preheated. It is the figure which looked at a mode that a paper approachs into the 2nd heating means from the upper part. It is a flowchart which shows the example of control of CPU300 in the 5th Embodiment of this invention.

  Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a schematic diagram showing the overall configuration of the image forming apparatus according to the first embodiment of the present invention.

  The image forming apparatus 1000 includes an image reading unit 100, an image forming unit 200, a paper feeding unit 20, and the like.

  The image reading unit 100 includes an automatic document feeder DF, an optical system 101, a CCD image sensor 102, and the like.

  The image forming unit 200 includes image forming units 10Y, 10M, 10C, and 10K that form toner images corresponding to the colors yellow, magenta, cyan, and black, and intermediate portions on which toner images formed by the image forming units are transferred. The image forming apparatus includes a transfer belt 6, a secondary transfer portion 7A that transfers a toner image on the intermediate transfer belt 6 to a sheet as a transfer material, a fixing device 9 that fixes the toner image transferred to the sheet, and the like. The secondary transfer portion 7A serves as a transfer portion in the present invention.

  The paper feed unit 20 includes paper feed trays 20A to 20C, pickup rollers 21A to 21C, and the like, and appropriate paper is fed from the paper feed unit 20 at an appropriate timing.

  In the operation unit 30 serving as the image quality setting means of the present invention, settings relating to image formation contents, an instruction to start image formation, and the like are performed. As will be described later, settings relating to the image quality of the formed image can be made.

  When the operation unit 30 is instructed to start image formation, the document D placed on the document table 103 of the automatic document feeder DF is conveyed to the document reading unit. Then, reflected light of the light irradiated on the document from a light source (not shown) is read by the CCD image sensor 102 via the optical system 101.

  Various kinds of image processing are performed on the signal read by the CCD image sensor 102. Based on the image signal subjected to the image processing, the image forming units 10Y to 10K form toner images of the respective colors.

  The image forming unit 10Y that forms a yellow toner image includes a photoreceptor 1Y, a charging unit 2Y, an exposure unit 3Y, a developing unit 4Y, and a cleaning unit 8Y. The photoconductor 1Y is rotated counterclockwise in FIG. 1, and is uniformly charged by the charging unit 2Y. The exposure unit 3Y irradiates the charged photoconductor 1Y with laser light based on the image signal to form an electrostatic latent image corresponding to a yellow image.

  When the electrostatic latent image is formed, yellow toner is then sent to the electrostatic latent image by the developing unit 4Y, and a yellow toner image is formed on the photoreceptor 1Y. The formed toner image is transferred to the intermediate transfer belt 6 in the primary transfer portion 7Y.

  The toner remaining on the surface of the photoreceptor 1Y without being completely transferred to the intermediate transfer belt 6 is removed by the cleaning unit 8Y to prepare for the next toner image formation.

  The image forming unit 10M that forms a magenta toner image, the image forming unit 10C that forms a cyan image, and the image forming unit 10K that forms a black image are all image forming units that form a yellow image. Since it has the same configuration as 10Y, its detailed description is omitted.

  The intermediate transfer belt 6 is an endless belt wound around a plurality of rollers, and is rotated clockwise in FIG. In order from the yellow toner image, the primary transfer units 7M, 7C, and 7K sequentially transfer the toner image to the intermediate transfer belt 6 at an appropriate timing, whereby an appropriate color toner image corresponding to the original image is transferred to the intermediate transfer belt. 6 is formed.

  On the other hand, the paper fed from any of the paper feed trays 20A to 20C is transported by the transport roller pairs 22A to 22D, and reaches the registration roller pair 23 as the second heating means of the present invention. Although the detailed description of the registration roller pair 23 will be described later, the registration roller pair 23 corrects skew in the sheet conveyance direction, and includes a partial region including the leading end portion of the sheet and a rear end portion. The sheet area is heated, and the sheet is conveyed to the secondary transfer section 7A so as to coincide with the color toner image on the intermediate transfer belt 6.

  In the secondary transfer portion 7A, the color toner image on the intermediate transfer belt 6 is transferred to the conveyed paper. The sheet on which the color toner image has been transferred is conveyed toward the fixing device 9. The toner remaining on the intermediate transfer belt 6 without being transferred onto the sheet is removed by the intermediate transfer belt cleaning unit 8A to prepare for the next toner image formation.

  The color toner image is fixed to the paper on which the color toner image has been transferred by applying heat and pressure by the fixing device 9. The sheet on which the color toner image is fixed is conveyed toward the discharge roller pair 24 and is discharged to the discharge tray 25.

  When images are formed on both sides of a sheet, when the color toner image is fixed on the surface of the sheet in the fixing device 9, the sheet is conveyed toward the reversing path 27A by the branching unit 26, and is conveyed by the reversing unit 27B. The leading and trailing edges of the direction are reversed. The sheet with the front and rear ends reversed is conveyed to the registration roller pair 23 through the reverse path 27C, and a part of the region including the leading end and a part of the region including the trailing end are heated again.

  Thereafter, the color toner image corresponding to the image formed on the back surface of the paper is transferred as described above in the secondary transfer portion 7A, and the color toner image on the back surface is fixed by the fixing device 9, and the discharge roller pair 24 discharges the discharge tray. 25 is discharged.

  FIG. 2 is a cross-sectional view illustrating the configuration of the fixing device 9. In the fixing device 9, a fixing belt 91 that is an endless belt is wound around a heating roller 92 and a fixing roller 93.

  The heating roller 92 incorporates a halogen lamp 92A which is the first heating means in the present invention. By operating the halogen lamp 92A, heat is transmitted from the heating roller 92 to the fixing belt 91, and the fixing belt 91 is heated to a predetermined temperature suitable for fixing.

  The fixing roller 93 is rotated clockwise in FIG. 2 by a driving unit (not shown). As the fixing roller 93 rotates in the clockwise direction, the fixing belt 91 rotates in the clockwise direction, and the heating roller 92 also rotates in the clockwise direction. In this way, the fixing belt 91 is uniformly heated by the heating roller 92.

  The pressure roller 94 is pressed against the fixing roller 93 when the toner image is fixed, and is rotated counterclockwise following the fixing roller by the pressure contact. On the other hand, when the toner image is not fixed, the pressure contact with the fixing roller 93 is released. The pressure contact with the fixing roller 93 and the pressure contact release are performed by a pressure contact release mechanism (not shown).

  When the toner image is fixed, the sheet onto which the toner image has been transferred enters the nip portion N between the fixing roller 93 and the pressure roller 94, is heated by the fixing belt 91 in the nip portion N, and is added. The toner image is fixed by being pressed with a predetermined pressure by the pressure roller 94.

  The pressure roller 94 incorporates a halogen lamp 94A, and the pressure roller 94 is heated to a predetermined temperature by operating the halogen lamp 94A. The temperature of the pressure roller 94 when heated by the halogen lamp 94A is set in advance so as to be lower than the temperature of the fixing belt 91.

  FIG. 3 is an enlarged view of the vicinity of the registration roller pair 23 in the image forming apparatus 1000. The registration roller pair 23 includes a driving roller 23A and a driven roller 23B. The driving roller 23A is rotated in the clockwise direction in FIG. 3 by a driving unit (not shown), and the driven roller 23B is rotated in the counterclockwise direction by the pressure contact with the driving roller 23A when the driving roller 23A is rotated. .

  The drive roller 23A includes a halogen lamp 23C. By operating the halogen lamp 23C, heat is transmitted to the sheet toward the secondary transfer portion 7A, and the sheet is preheated.

  FIG. 4 is a block diagram showing an electrical configuration in the image forming apparatus 1000. The same reference numerals as those in FIG. 1 are attached to the same components as those shown in FIG.

  The CPU 300 serving as a control unit and a conveyance control unit in the present invention is read by the image reading unit 100 by controlling the image reading unit 100 and the image forming unit 200 based on setting information in the operation unit 30. An appropriate image is formed on the sheet based on the obtained image data.

  In addition, the CPU 300 controls the paper feed unit 20 and the conveyance roller pairs 22A to 22D to feed and carry paper at an appropriate timing.

  Further, the CPU 300 controls the operation of the registration roller pair 23. Specifically, the rotation of the driving roller 23A is controlled to control the timing of sheet conveyance, and the operation of the halogen lamp 23C is controlled to appropriately preheat the sheet.

  FIG. 5 is a diagram showing a change in the surface temperature of the fixing belt 91 when the paper is not preheated before the toner image is fixed on the paper. In FIG. 5, the vertical axis indicates the surface temperature of the fixing belt 91, and the horizontal axis indicates the position in the circumferential direction of the fixing belt 91.

  When the toner image is fixed on the paper, the fixing belt 91 is heated to a predetermined temperature T suitable for fixing, and is pressed against the paper while being rotated by the rotation of the fixing roller 93 while being in pressure contact with the pressure roller 94. To fix. The temperature T is, for example, 195 ° C.

  When the sheet is conveyed to the fixing device 9 and reaches the nip portion N between the fixing belt 91 and the pressure roller 94, the sheet and the fixing belt 91 come into contact with each other, so that the heat of the heated fixing belt 91 is close to room temperature. A phenomenon occurs in which the surface temperature of the fixing belt 91 is lowered due to the paper.

  As shown in FIG. 5, when the paper reaches the nip portion N, the temperature of the fixing belt 91 is lowered at a position a <b> 1 in contact with the paper. The surface temperature of the fixing belt 91 in contact with the paper is stabilized when the temperature reaches a temperature equilibrium T1. The temperature T1 at which the temperature is balanced varies depending on the paper temperature, but decreases to about 185 ° C.

  While fixing is performed on the sheet, that is, while the sheet is in contact with the fixing belt 91, the surface temperature of the fixing belt 91 remains T1. When the fixing to the sheet is completed and the sheet is separated from the fixing belt 91, the heat of the fixing belt 91 is not removed, and the surface temperature rises to a predetermined temperature T at the position a2 (a2-a1 = f and f are the lengths in the paper transport direction).

  Until the succeeding sheet reaches the nip portion N, the surface temperature of the fixing belt 91 remains at the predetermined temperature T. When the succeeding sheet reaches the nip portion N, the sheet is deprived of heat, so that the surface temperature of the fixing belt 91 decreases again at the position a3 and is stabilized at the temperature T1 (a3-a2 = d, d Is the length of the gap between the previous and subsequent sheets).

  As described above, when the paper is fixed, the heat of the fixing belt 91 is taken away by the paper, so that a temperature step occurs in the circumferential surface direction of the fixing belt 91. This temperature step remains even after the fixing belt 91 makes one rotation, and when the fixing is performed on the sheet again by the temperature step portion, the fixed image is affected.

  Specifically, the glossiness of the image fixed by the portion where the surface temperature of the fixing belt 91 is T1 is lower than the glossiness of the image fixed by the portion where the surface temperature of the fixing belt 91 is T. . As described above, the temperature difference in the fixing belt 91 appears as a gloss difference in the image.

  In particular, as shown in FIG. 5, when the surface temperature of the fixing belt 91 suddenly decreases or increases at the positions a 1, a 2, and a 3, these positions of the fixing belt 91 are rotated after the fixing belt 91 makes one rotation. If the fixing is performed again, the boundary between the high and low gloss portions of the image clearly appears, and the quality of the image is significantly reduced.

  FIG. 6 is a diagram showing a state in which the paper P is preheated by the registration roller pair 23.

  The leading edge of the sheet P fed and conveyed from the sheet feeding unit 20 is abutted against the nip portion between the driving roller 23A and the driven roller 23B of the registration roller pair 23, thereby correcting the skew in the conveying direction. The

  When the skew in the transport direction is corrected, the registration roller pair 23 next preheats a part of the area including the leading end of the paper P. Specifically, as shown in FIG. 6A, the CPU 300 controls the driving roller 23A and the driven roller 23B to support the leading end portion of the paper P, make the paper stationary, and start the halogen lamp 23C.

  When a part of the area including the leading edge of the sheet P is heated for a predetermined time, the CPU 300 stops the activation of the halogen lamp 23C, and further rotates the driving roller 23A in the clockwise direction to thereby transfer the sheet P to the secondary transfer unit. It is conveyed in the 7A direction. Next, in order to preheat the area including the rear end portion of the paper P, the drive roller 23A is stopped from rotating so that the drive roller 23A and the driven roller 23B use the paper P as shown in FIG. The rear end of the sheet is held, the sheet is stopped, and the halogen lamp 23C is activated.

  When a part including the rear end portion of the paper P is heated for a predetermined time, the activation of the halogen lamp 23C is stopped, and the driving roller 23A is rotated in the clockwise direction to convey the paper P in the direction of the secondary transfer portion 7A. .

  In this way, a part of the area including the leading end and a part of the area including the trailing end of the sheet are preheated.

  FIG. 7 shows changes in the surface temperature of the fixing belt 91 when the fixing device 9 performs fixing on a sheet preliminarily heated in a part of the region including the leading end and a part of the region including the trailing end. It is a figure. The implementation conditions in FIG. 7 are the same as the conditions shown in FIG. 5 except that the paper is preheated.

  When a part of the area including the leading end of the sheet and a part of the area including the trailing end are preheated, the temperature difference between the preheated area and the fixing belt 91 is small. The degree of the surface temperature drop of 91 is reduced.

  As shown in FIG. 7, when the preheated paper on which the toner image is transferred reaches the nip portion N, the surface temperature of the fixing belt 91 starts to decrease from a position a1 on the peripheral surface.

  Since a part of the area including the leading edge of the sheet is preheated, the surface temperature of the fixing belt 91 is gradually decreased. The surface temperature of the fixing belt 91 that is in contact with the sheet becomes stable when the temperature reaches a temperature equilibrium T1.

  When the trailing edge of the sheet approaches the nip portion N, the preheated area of the sheet comes into contact with the fixing belt 91, so that the surface temperature of the fixing belt 91 starts to rise gradually, and at the position a2. The temperature rises to T.

  Until the succeeding sheet reaches the nip portion N, the surface temperature of the fixing belt 91 remains at the predetermined temperature T. When the succeeding sheet reaches the nip portion N, the sheet is deprived of heat, and the surface temperature of the fixing belt 91 starts to decrease again at the position a3.

  Also for the subsequent paper, since a part of the area including the leading edge is preheated, the surface temperature of the fixing belt 91 gradually decreases from the position a3.

  As shown in FIG. 7, when a part of the area including the leading end of the sheet and a part of the area including the trailing end are preheated, the surface temperature change due to the preheated sheet coming into contact with the fixing belt 91 is changed. As compared with the case shown in FIG.

  When the change in the surface temperature of the fixing belt 91 becomes gentle, the gloss level difference that appears in the image when the fixing is performed again becomes similarly gentle, so that the appearance of the image becomes inconspicuous. Therefore, it is possible to prevent a reduction in image quality.

  As described above, according to the first embodiment of the present invention, before the toner image is fixed by the fixing device 9, the partial region including the leading edge of the sheet by the second heating unit and The CPU 300 controls to heat a part of the area including the rear end.

  By controlling in this way, the temperature difference of the fixing belt caused by the contact between the fixing belt 91 and the paper can be made gentle. As a result, when the toner image is fixed by the temperature step portion after one rotation of the fixing belt 91, the gloss step generated in the image can be made inconspicuous, and the deterioration of the image quality can be prevented. .

  In addition, since it is configured to preheat only a part of the area including the leading end of the sheet and a part of the area including the trailing end, it is possible to reduce power consumption compared with the case where the entire sheet is preheated. Become.

  Further, since it is possible to suppress a temperature rise in the image forming apparatus 1000, it is possible to prevent a deterioration in image quality due to toner fixation.

  Furthermore, curling generated by the preliminary heating can be reduced, so that it is possible to suppress a decrease in paper feeding performance such as jam.

  The example in which the CPU 300 controls to preheat a part of the area including the leading edge and a part of the area including the trailing edge of the paper has been described above.

  However, it is not always necessary to pre-heat both the partial area including the leading end of the sheet and the partial area including the trailing end. Depending on various conditions such as the width of the interval between the preceding sheet and the succeeding sheet, the length of the fixing belt 91, and the length in the sheet conveyance direction, only one of the regions may be preheated.

  Specifically, when the following paper and the area where the trailing edge of the preceding paper in contact with the fixing belt 91 do not contact each other due to the above conditions, the leading edge of the preceding paper is included. By preheating only the area of the portion, it is possible to prevent the image quality of the subsequent paper from being deteriorated.

  Similarly, if the following paper and the region where the leading edge of the preceding paper in contact with the fixing belt 91 do not contact each other due to the above-described conditions, a part of the paper including the trailing edge of the preceding paper may not be in contact with each other. By preheating only the area, it is possible to prevent the image quality of the subsequent paper from deteriorating.

  Next, a second embodiment of the present invention will be described with reference to the drawings. In the second embodiment, the configuration of the image forming apparatus 1000 can be the same as the configuration described in the first embodiment, and thus detailed description thereof is omitted.

  In the second embodiment, only a part of the area including the leading end of the sheet is preheated, and further, the timing of the subsequent sheet conveyance is controlled.

  As shown in FIG. 6A, the sheet P fed from the sheet feeding unit 20 and reaching the registration roller pair 23 is supported at its leading end by a driving roller 23A and a driven roller 23B, and preheated. .

  When the preliminary heating of a part of the area including the leading edge of the sheet is completed, the CPU 300 stops the halogen lamp 23C and rotationally drives the driving roller 23A so that the part of the area including the trailing edge of the sheet is not heated. It is conveyed in the direction of the secondary transfer unit 7A.

  The toner image is transferred in the secondary transfer portion 7A to the paper in which a part of the area including the leading end of the paper is heated, and the toner image is fixed in the fixing device 9.

  FIG. 8 is a diagram showing a change in the surface temperature of the fixing belt 91 when the fixing device 9 performs fixing on a sheet in which only a part of the region including the leading end is preheated. Each condition in FIG. 8 is the same as the condition shown in FIG. 5 except that the sheet is preheated.

  When only a part of the area including the leading end of the sheet is preheated, the degree of the surface temperature of the fixing belt 91 when the part of the area including the leading end of the heated sheet passes through the nip portion N. Becomes smaller.

  As shown in FIG. 8, when the preheated paper on which the toner image is transferred reaches the nip portion N, the surface temperature of the fixing belt 91 starts to decrease from the position a1 on the circumferential surface of the fixing belt 91.

  Since a part of the area including the leading edge of the sheet is preheated, the surface temperature of the fixing belt 91 is gradually decreased. The surface temperature of the fixing belt 91 that is in contact with the sheet becomes stable when the temperature reaches a temperature equilibrium T1.

  Since the trailing edge of the sheet is not preheated, when the trailing edge of the sheet reaches the nip portion N, the surface temperature of the fixing belt 91 rapidly increases from the temperature T1 to the temperature T at the position a2.

  Until the next sheet reaches the nip portion N, the surface temperature of the fixing belt 91 remains at the predetermined temperature T. When the next sheet reaches the nip portion N, the sheet is deprived of heat, so that the surface temperature of the fixing belt 91 starts to decrease again at the position a3.

  Also for the next sheet, since a part of the area including the leading end is preheated, the surface temperature of the fixing belt 91 gradually decreases from the position a3.

  As shown in FIG. 8, when only a part of the area including the leading end of the sheet is preheated, the surface temperature change due to the contact of the partial area including the leading end of the sheet with the fixing belt 91 becomes gentle. However, the surface temperature change due to the rear end portion not preheated being separated from the fixing belt 91 becomes abrupt.

  Further, when fixing the succeeding sheet, the temperature change of the fixing belt 91 due to the contact between the leading edge of the preceding sheet and the fixing belt 91 is gradual. Will not appear and will not lead to a reduction in image quality.

  On the other hand, a region of the fixing belt 91 in which a rapid temperature change caused by the contact and separation between the rear end portion of the preceding paper and the fixing belt 91 comes into contact with the succeeding paper during the fixing of the succeeding paper. As a result, a gloss level difference clearly appears in the image formed on the subsequent sheet.

  Therefore, in order to prevent the gloss level difference from appearing on the following paper in such a case, the gloss level difference is prevented from appearing clearly in the image by controlling the conveyance timing of the subsequent paper.

  Specifically, when the succeeding sheet is transported toward the fixing device 9, the succeeding sheet and the region where the rapid temperature change occurs in the fixing belt 91 (position a2 in FIG. 8) should not be brought into contact. In addition, the CPU 300 controls the conveyance roller pairs 22A to 22D or the registration roller pair 23.

  In this way, by preheating only the leading edge of the sheet and further controlling the timing of conveyance of the subsequent sheet, the subsequent sheet and the area where the trailing end of the preceding sheet in the fixing belt 91 is in contact with each other. Even when they are in contact with each other, it is possible to prevent a reduction in image quality due to a clear appearance of a gloss level difference, and to further reduce power consumption.

  Next, a third embodiment of the present invention will be described with reference to the drawings. In the third embodiment, the configuration of the image forming apparatus 1000 can be the same as the configuration described in the first embodiment, and thus detailed description thereof is omitted.

  In the third embodiment, only a part of the area including the trailing edge of the sheet is preheated, and further, the timing of the subsequent sheet conveyance is controlled.

  The sheet P fed from the sheet feeding unit 20 and reaches the registration roller pair 23 is corrected in skew in the transport direction, and then, as shown in FIG. 6 (b), the trailing end is driven roller 23A and driven roller. 23B and preheating is performed.

  When the preheating of a part of the area including the rear end of the sheet is completed, the CPU 300 stops the halogen lamp 23C, rotates the driving roller 23A, and conveys the sheet in the direction of the secondary transfer unit 7A.

  A toner image is transferred in the secondary transfer portion 7A to the paper in which a part of the area including the rear end portion of the paper is heated, and the toner image is fixed in the fixing device 9.

  FIG. 9 is a diagram illustrating a change in the surface temperature of the fixing belt 91 when the fixing device 9 performs fixing on a sheet in which only a part of the region including the rear end portion is preheated. Each condition in FIG. 9 is the same as the condition shown in FIG. 5 except that the sheet is preheated.

  Since the leading edge of the sheet is not preheated, when the leading edge of the sheet reaches the nip portion N, the surface temperature of the fixing belt 91 suddenly increases from the temperature T to the temperature T1 at the position a1 on the circumferential surface of the fixing belt 91. It goes down and stabilizes when it reaches temperature T1 where temperature equilibrium is reached.

  When only a part of the area including the rear end of the sheet is preheated, the surface temperature of the fixing belt 91 increases when a part of the area including the rear end of the heated sheet passes through the nip portion N. The degree of is reduced.

  As shown in FIG. 9, when the preheated area of the paper comes into contact with the fixing belt 91, the surface temperature of the fixing belt 91 starts to gradually increase, and when the trailing edge of the paper reaches the nip portion N, the fixing belt. The surface temperature of 91 rises to the temperature T at the position a2.

  Until the next sheet reaches the nip portion N, the surface temperature of the fixing belt 91 remains at the predetermined temperature T. When the next sheet reaches the nip portion N, the sheet is deprived of heat, so that the surface temperature of the fixing belt 91 rapidly decreases again to the temperature T1 at the position a3.

  As shown in FIG. 9, when only a part of the area including the trailing edge of the sheet is preheated, the temperature change due to the preheated area of the sheet coming into contact with the fixing belt 91 becomes gentle. The temperature change due to the separation of the tip portion not preheated from the fixing belt 91 becomes abrupt.

  Further, when fixing the succeeding sheet, the temperature change of the fixing belt 91 due to the contact between the trailing edge of the preceding sheet and the fixing belt 91 is gradual. A step does not appear, and the quality of the image does not deteriorate.

  On the other hand, an area in the fixing belt 91 where a rapid temperature change caused by the contact between the leading edge of the preceding sheet and the fixing belt 91 is brought into contact with the succeeding sheet when the succeeding sheet is fixed. As a result, a gloss level difference appears clearly in the image.

  Therefore, in order to prevent a gloss level difference from appearing on the subsequent sheet in such a case, the conveyance timing of the subsequent sheet is controlled based on the same concept as that in the second embodiment of the present invention. Thus, it is possible to prevent the gloss difference from appearing clearly in the image.

  Specifically, when the succeeding sheet is conveyed toward the fixing device 9, the succeeding sheet is brought into contact with the region (positions a <b> 1 and a <b> 3 in FIG. 9) where a rapid temperature change occurs in the fixing belt 91. The CPU 300 controls the conveyance roller pairs 22A to 22D or the registration roller pair 23 so as not to cause them.

  In this way, by preheating only the trailing edge of the sheet and further controlling the timing of the conveyance of the subsequent sheet, the subsequent sheet and the area where the leading end of the preceding sheet contacts the fixing belt 91 are made. Even when they are in contact with each other, it is possible to prevent a reduction in image quality due to a clear appearance of a gloss level difference, and to further reduce power consumption.

  Next, a fourth embodiment of the present invention will be described with reference to the drawings. In the fourth embodiment, the configuration of the image forming apparatus 1000 can be substantially the same as the configuration described in the first embodiment, and thus detailed description of overlapping portions is omitted. To do.

  FIG. 10 is a view of the state in which the paper P is conveyed toward the registration roller pair 23 as viewed from above. In the present embodiment, five halogen lamps 23D to 23H are built in the drive roller 23A in a state of being arranged in a direction orthogonal to the transport direction.

  The CPU 300 can individually control the operations of the five halogen lamps 23D to 23H. The CPU 300 controls the operation of the five halogen lamps based on the contents of the image formed on the paper.

  Specifically, as shown in FIG. 10, when an image is to be formed on the paper P only in a part of the region in the direction orthogonal to the transport direction, the region where the image is to be formed. The CPU 300 is controlled so that only the halogen lamp built in the position corresponding to is operated (halogen lamp 23F) and only the area including the front end and the area including the rear end corresponding to the area where the image is formed is heated. To do.

  By controlling in this way, it is possible to pre-heat only a part of the area including the front end and the part including the rear end corresponding to the area where the gloss level difference may be noticeable. Therefore, it is possible to prevent the image quality from being deteriorated due to the difference in gloss and to suppress excessive power consumption.

  Next, a fifth embodiment of the present invention will be described with reference to the drawings. In the fifth embodiment, the configuration of the image forming apparatus 1000 can be the same as the configuration described in the first embodiment, and a detailed description thereof will be omitted.

  In the fifth embodiment, the preheating area is changed according to the image quality required for the image formed on the paper.

  For example, if the operation unit 30 is set to form a high-quality image before the start of image formation, the CPU 300 expands the preheating area on the paper as compared to the case where such setting is not made. Control.

  FIG. 11 is a flowchart illustrating a control example of the CPU 300 in the fifth embodiment.

  First, the CPU 300 determines whether or not the setting of the image quality of the output image has been made in the operation unit 30 (step S1).

  If it is determined that image quality has not been set (step S1: No), CPU 300 waits until image quality has been set.

  If it is determined that the image quality has been set (step S1: Yes), the CPU 300 determines whether or not the setting is to output a high-quality image (step S2).

  If it is determined that the setting for outputting a high-quality image has not been made (step S2: No), the CPU 300 determines the time during which the registration roller pair 23 holds the leading edge or trailing edge of the sheet for preheating as t1. Is set (step S3), and the process is terminated.

  On the other hand, if it is determined that the setting to output a high-quality image has been made (step S2: Yes), the CPU 300 is the time during which the registration roller pair 23 carries the leading edge or trailing edge of the sheet for preheating. Is set to t2 (step S4), and the process ends. Here, time t2 is longer than time t1.

  By controlling the CPU 300 as described above, when the setting for outputting a high-quality image is made, it is possible to lengthen the time for carrying the paper for preheating. If the time for carrying the paper is lengthened, the time for heat to be transmitted from the driving roller 23A to the paper becomes long, so that a wider area of the paper can be preheated.

  As described above, when a high-quality image is output, by preheating a wider area, the change in the surface temperature of the fixing belt 91 shown in FIG. It is going to disappear.

  In addition to the control based on the setting of high-quality image formation in the operation unit 30, when forming an image that generally requires high image quality, such as a photographic image, for example, The CPU 300 may control to preheat a wider area.

  In each of the embodiments described above, a part of the area including the leading edge of the sheet or a part of the area including the trailing edge is preliminarily heated upstream from the secondary transfer portion 7A. The toner image was transferred to the heated paper in the secondary transfer portion 7A, and the paper on which the toner image was transferred was conveyed to the fixing device 9.

  However, the present invention can be realized even if the second heating unit is provided on the downstream side of the secondary transfer portion 7A as long as it is on the upstream side of the fixing device 9.

  In this case, the second heating means is provided downstream from the secondary transfer portion 7A and upstream from the fixing device 9, and the second heating means preheats the sheet on which the toner image has been transferred. Become.

  With such a configuration, the interval between the preheating of the paper and the fixing of the toner image is reduced, so that heat is dissipated from the preheated area until the paper reaches the nip portion N of the fixing device 9. Less. That is, there is little decrease in the temperature of the preheated area after the paper is preheated until it reaches the nip portion N.

  Then, the change in the surface temperature due to the contact of the paper with the fixing belt 91 becomes more gradual than the change in each of the embodiments described above. Therefore, the gloss level difference appearing in the image becomes less conspicuous and a good image can be formed.

  In this case, the CPU 300 controls the second heating unit so as to preheat the area other than the area where the image is formed, thereby directly heating the toner image already transferred onto the sheet and Since preheating can be performed without disturbing the image, it is possible to provide a better image.

  The second heating means in the present invention is not limited to the configuration of the roller pair described in FIG. For example, the present invention can be realized even if a configuration in which a sheet-like heating member is provided and the heating member is pressed against the paper when preheating the paper, or a configuration in which warm air is blown onto the paper is adopted. is there.

  In addition, the present invention is not limited to the above-described embodiments, and different embodiments can be adopted without departing from the present invention.

1000 Image forming apparatus 100 Image reading unit 200 Image forming unit 300 CPU
6 Intermediate transfer belt 7A Secondary transfer portion 9 Fixing device 91 Fixing belt 92 Heating roller 92A Halogen lamp 93 Fixing roller 94 Pressure roller 10Y Image forming means (yellow)
10M image forming means (magenta)
10C image forming means (cyan)
10K image forming means (black)
20 Paper Feed Unit 23 Registration Roller Pair 23A Drive Roller 23C Halogen Lamp

Claims (10)

A rotatable fixing member;
First heating means for heating the fixing member,
A fixing device for fixing the toner image on the transfer material to the transfer material by heating the fixing member by the first heating unit and applying heat and pressure to the transfer material while rotating the heated fixing member; In the image forming apparatus provided,
A second heating means provided on the upstream side of the fixing device in the transfer material conveyance direction for heating the transfer material toward the fixing device;
Controlling the second heating means to heat at least one of a part of the transfer material including a front end portion in a transfer material conveyance direction and a part of a region including a rear end part in the transfer material conveyance direction. And an image forming apparatus comprising: a control unit. The second heating unit is provided on the upstream side in the transfer material conveyance direction from the transfer unit that transfers the toner image to the transfer material,
The image forming apparatus according to claim 1, wherein a toner image is transferred at the transfer unit to the transfer material heated by the second heating unit. The second heating unit is provided on the downstream side in the transfer material conveyance direction from the transfer unit that transfers the toner image to the transfer material and on the upstream side in the transfer material conveyance direction from the fixing device,
The image forming apparatus according to claim 1, wherein the second heating unit heats a transfer material onto which a toner image is transferred in the transfer unit.   The control means includes a region other than the region where the toner image on the transfer material is transferred, as a partial region including the front end portion in the transfer material conveyance direction and a partial region including the rear end portion in the transfer material conveyance direction. The image forming apparatus according to claim 3, wherein the region is controlled to be heated.   5. The control unit according to claim 1, wherein the control unit performs control so as to change a region to be heated in the transfer material based on a content of a toner image transferred to the transfer material. Image forming apparatus. Image quality setting means for setting the image quality of the toner image formed on the transfer material;
When the setting for forming a high-quality image is made by the image-quality setting means, and when the setting for forming a high-quality image is not made by the image-quality setting means in the transfer material, The image forming apparatus according to claim 5, wherein the image forming apparatus is controlled to heat an area wider than the area to be heated. The second heating means is divided and provided in a direction perpendicular to the transfer material conveyance direction,
6. The image forming apparatus according to claim 5, wherein the control unit individually controls the second heating unit provided separately.   The image forming apparatus according to claim 7, wherein the control unit controls to operate only the second heating unit corresponding to a region where a toner image is formed on the transfer material. It has a conveyance control means for controlling the conveyance of the transfer material,
The control means controls to heat only a part of the transfer material including the front end in the transfer material conveyance direction,
The conveyance control unit controls the transfer material so as not to contact a region in contact with the rear end portion in the transfer material conveyance direction of the preceding transfer material on the fixing member when the toner image is fixed to the transfer material. The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus. It has a conveyance control means for controlling the conveyance of the transfer material,
The control means controls to heat only a part of the transfer material including the rear end portion in the transfer material conveyance direction,
The transport control unit controls the transfer material so as not to contact a region of the fixing member that is in contact with the leading end portion of the preceding transfer material in the transfer material transport direction when the toner image is fixed to the transfer material. The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus.

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