JP2012032654A - Image forming device and temperature control method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a paper jam by suppressing occurrence of a curl in longitudinal feeding and a curl in transverse feeding without causing deterioration in fixability.SOLUTION: Occurrence of a curl in a first face is suppressed by lowering a temperature of an end in a longitudinal direction at a fixing unit during the image fixation of a first face. Deterioration of the fixability at the end in the longitudinal direction of the first face is prevented by raising a temperature of the end in the longitudinal direction at the fixing unit during the image fixation of a second face. An image forming device includes a toner image forming unit for forming a toner image on a recording medium conveyed by a conveyance means, a fixing unit for fixing the toner image on the recording medium with a heating unit, a temperature control unit for controlling the temperature of the heating unit, and a re-feeding unit for re-feeding the recording medium after the fixation to the toner image forming unit.

Description

  The present invention relates to an image forming apparatus capable of performing image formation a plurality of times on the same recording medium, and a temperature control method in fixing.

  2. Description of the Related Art Conventionally, in various image forming apparatuses such as copying machines and laser beam printers, a double-sided image forming apparatus that automatically forms an image on both the front and back surfaces of a sheet-like recording medium such as paper is known. In this double-sided image forming apparatus, a toner image is formed on a first surface (for example, the front surface) of a recording medium in an image forming unit including an image carrier such as a photosensitive drum, and the first toner image is fixed to the toner image by a fixing unit. A second heat treatment is performed to fix on the recording medium.

  Next, the recording medium on which the toner image is fixed on the first surface (for example, the front surface) is turned upside down by the front and back reversing means such as the switchback means, and the reversed recording medium is sent to the image forming unit again. A toner image is formed on the second surface (for example, the back surface) of the medium, and the toner image is fixed on the recording medium by a second heat treatment by a fixing unit. In this way, image formation is automatically performed on both the front and back sides of the recording medium.

  However, when image formation is performed on both the front and back surfaces of the recording medium, curling (curl) occurs in the recording medium due to the first heat treatment, and therefore the photosensitive drum is formed during image formation on the second surface (for example, the back surface) of the recording medium. In some cases, a recording medium is wound around an image carrier such as the image carrier and is difficult to separate.

  The heat source of the fixing heating unit is disposed on the heated surface side of the recording medium. Therefore, in the heat treatment at the time of fixing the toner image on the first surface (for example, the front surface) of the recording medium, the first surface (for example, the front surface) of the recording medium that is the heated side of the recording medium is the second surface (for example, the back surface). Greatly expands. For this reason, the recording medium after fixing is curled around the second surface (for example, the back surface).

  When the recording medium curled on the second side (for example, the back side) is turned upside down by switchback conveyance and supplied again to the image forming unit to form an image, the curled portion generated on the recording medium is image bearing such as a photosensitive drum. It will be in a state of being wrapped around the outer peripheral surface of the body. In the normal state, the image is formed and the recording medium is separated from the image carrier and carried out. However, if the recording medium is wound around the outer peripheral surface of the image carrier, the recording medium cannot be transported and is jammed. Will occur.

  Conventionally, the heat treatment temperature (fixing temperature control) at the time of fixing on the first surface (front side surface) of the recording medium is uniform with respect to the problem of conveyance failure due to the occurrence of curling at the time of double-sided image formation on the recording medium. However, in this case, the fixability of the entire image forming area on the first surface (for example, the front surface) may be significantly reduced.

  On the other hand, the heat treatment temperature (fixing temperature control) on the rear end side in the transport direction of the first surface (for example, the front surface) of the recording medium is lowered, and thereby the front end side in the transport direction on the second surface (for example, the back surface). A method has been proposed that suppresses the amount of curling in the portion that becomes the same and prevents the deterioration of the fixing property of the entire image forming area (see, for example, Patent Document 1). However, in this case, it is not possible to prevent a decrease in fixability of the image forming region on the rear end side in the conveyance direction of the first surface (for example, the front surface) where the heat treatment temperature during fixing is decreased. There's a problem.

  Further, in order to improve the above problem, the temperature adjustment at the rear end of the recording medium is lowered from the normal temperature adjustment at the time of image fixing on the first surface, thereby suppressing the occurrence of curling at the rear end of the first surface, Patent Document 2 discloses a method for preventing deterioration of the fixing property at the rear end of the recording medium on the first surface by increasing the temperature control at the front end of the recording medium from the room temperature control at the time of fixing the image on the second surface. .

Japanese Patent Laid-Open No. 10-10915 JP 2008-158242 A

  However, the method of Patent Document 2 has little effect in curling during toe feed (toy curl), and the amount of curl at the end also increases in curl during transverse eye feed. Therefore, it is required to improve both curl suppression and fixability.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus that solves the above-described problems and obtains good fixability and suppresses curling occurring on a recording medium to prevent paper jamming.

  The present invention suppresses the occurrence of curling of the first surface of the recording medium by lowering the temperature of the longitudinal end of the heating means of the fixing unit during image fixing of the first surface, and the image of the second surface. During fixing, the temperature at the longitudinal end of the heating unit of the fixing unit is raised to prevent deterioration of the fixing property at the longitudinal end of the heating unit on the first surface.

  The present invention includes an aspect of the image forming apparatus and an aspect of a temperature control method in fixing of the image forming apparatus.

[Mode of image forming apparatus]
In an aspect of the image forming apparatus according to the present invention, a first form of the image forming apparatus includes a toner image forming unit that forms a toner image on a recording medium conveyed by a conveying unit, and the recording medium that forms a toner image by a heating unit. A double-sided printing is possible by including a fixing unit for fixing on top, a temperature control unit for controlling the temperature of the heating unit, and a re-supplying unit for re-supplying the recording medium after fixing to the toner image forming unit.

  In the temperature control at the time of fixing to the same recording medium, the present invention varies the heating distribution in the longitudinal direction, which is a direction orthogonal to the conveyance direction of the recording medium, in the heating unit, and the end of the recording medium in the direction orthogonal to the conveyance direction. The part and the central part are heated at different heating temperatures.

  The temperature control unit controls the temperature of the end portion in the longitudinal direction of the heating unit to be lower than the temperature of the other part of the heating unit during the first fixing in which the toner image formed on one surface of the recording medium is heat-treated. Next, at the second fixing time when the toner image formed on the other surface of the recording medium is heat-treated, the temperature at the end in the longitudinal direction of the heating portion is controlled to be higher than the temperature at the first fixing time. To do.

  The heating unit of the present invention controls the temperature of the end in the direction orthogonal to the conveyance direction of the recording medium at the time of the first fixing in which the toner image formed on one surface of the recording medium is heated by this temperature control. At the time of the second fixing in which the toner image formed on the other surface of the recording medium is heated at a temperature lower than the temperature at the central portion and the toner image formed on the other surface is heated, the temperature at the end in the conveyance direction of the recording medium is set higher than the temperature at the central portion. Also, the end portion at the time of the first fixing is heated at a temperature higher than the temperature.

  FIG. 1 is a diagram for explaining temperature control during fixing by the heating unit of the present invention. In FIG. 1, the configuration of the toner image forming unit, the fixing unit, and the resupply unit included in the image forming apparatus that performs double-sided printing is omitted, and the temperature of the heating unit 100 is controlled by the temperature control unit 400. . The temperature control unit 400 may be configured to include a control circuit dedicated to temperature control, or may be configured to be incorporated in a control device (not shown) that controls the image forming apparatus.

  In FIG. 1, the fixing unit includes a heating unit 100, and the temperature of the heating unit 100 is controlled by the temperature control unit 400 during the first fixing and the second fixing. During the first fixing, the heating unit 100 heats the first surface 301 of the recording medium 300. At this time, the leading end A of the recording medium 300 is first conveyed with respect to the heating unit 100.

  During the first fixing, the central portion 100A of the heating unit 100 is controlled to a predetermined temperature, and the temperature of the longitudinal end portion 100B is controlled to be lower than the central portion 100A. By this temperature control, the central temperature processing unit 200 and the low temperature processing unit 201 are formed on the first surface 301 of the recording medium 300 that has been heated by passing through the heating unit 100. The central temperature processing unit 200 performs a sufficient fixing process by controlling the central part 100A to a predetermined temperature.

  On the other hand, the low temperature processing unit 201 suppresses the occurrence of curling at both sides along the conveyance direction of the recording medium 300 by controlling the longitudinal end portion 100B at a lower temperature than the central portion 100A, but is heated. Since the temperature is low, the fixing state is insufficient.

  After the first fixing process is completed, the front and back of the recording medium 300 are reversed, and the reversed recording medium 300 is again passed through the heating unit 100 to perform the second fixing process.

  Here, the recording medium 300 is reversed so that the second surface 302 on the opposite side faces the heating unit 100, and the rear end B side of the recording medium 300 that has passed through the heating unit 100 in the first fixing is the leading end. Then, the second fixing process is performed by heating the heating unit 100 again and heating the heating unit 100 again.

  During the second fixing, the central portion 100A of the heating unit 100 is controlled to a predetermined temperature, and the temperature of the longitudinal end portion 100B is controlled to be higher than the temperatures at the central portion and the first fixing.

  By this temperature control, the central temperature processing unit 200 and the high temperature processing unit 202 are formed on the second surface 302 of the recording medium 300 heated by passing through the heating unit 100. The central temperature processing unit 200 performs a sufficient fixing process by controlling the central part 100A to a predetermined temperature. On the other hand, the high temperature processing unit 202 controls the longitudinal end portion 100B to a temperature higher than the temperature at the time of the first fixing, so that both sides of the recording medium 300 that are in an insufficiently fixed state in the first fixing process. The fixing state of the part is made good.

  Accordingly, the central portion of the recording medium 300 is heated at a predetermined temperature at which sufficient fixing is performed on both the first surface 301 and the second surface 302, and the first surface 301 is formed on both side portions along the conveyance direction of the recording medium 300. Is subjected to a low temperature process by the first fixing process, and the second surface 302 is subjected to a high temperature process by the second fixing process.

  Since the first fixing process is a low-temperature process, the occurrence of curling is suppressed, and the second fixing process is a high-temperature process. It becomes.

  According to this control, the temperature of the longitudinal end portion of the heating unit is controlled to be lower than the temperature of the other part of the heating unit at the time of the first fixing, thereby moving along the conveyance direction of the first surface of the recording medium. Further, since the temperature rise on both sides can be suppressed low, the occurrence of curling of the recording medium can be suppressed.

  Next, the temperature at the end of the heating portion in the longitudinal direction at the time of the second fixing is controlled to be higher than the temperature at the center and the temperature at the time of the first fixing, so that the temperature is insufficient at the time of the first fixing. Insufficiency in fixing can be compensated and deterioration of fixing can be prevented.

  According to a second aspect of the image forming apparatus of the present invention, between the first fixing time for printing one surface of the recording medium and the second fixing time for printing the other surface in double-sided printing, A switchback unit is provided that conveys the recording medium in the conveyance direction by reversing and conveying the front end and the rear end. The recording medium is introduced into the fixing unit and heated at the time of the second fixing by reversal conveyance, with the surface opposite to the surface at the first fixing. The heating unit heats the temperature at the end in the direction orthogonal to the conveyance direction of the recording medium at a temperature lower than the temperature at the center during the first fixing, and records the temperature at the rear end of the recording medium. Heating is performed at a temperature lower than the temperature at the tip and center of the medium.

  On the other hand, at the time of the second fixing, the temperature of the end portion in the direction orthogonal to the conveyance direction of the recording medium is heated higher than the temperature at the time of the first fixing, and the temperature of the leading end portion of the recording medium is set. Heating is performed at a higher temperature than the central portion and the rear end portion of the recording medium. As a result, the end of the recording medium heat-treated at the low temperature at the first fixing is heat-treated at the high temperature at the second fixing. Since the recording medium is reversed and conveyed, the portion that is heat-treated at a low temperature during the first fixing and the portion that is heat-treated at the high temperature during the second fixing are the front and back surfaces of the same portion of the recording medium. It corresponds to.

  According to this control, curling at the left and right side portions in the conveyance direction of the recording medium can be suppressed, and curling at the front and rear end portions in the conveyance direction of the recording medium can be suppressed.

  In the third embodiment of the image forming apparatus of the present invention, the heating unit differs in the heating distribution at the central portion in the longitudinal direction and the heating distribution at the end portion in the longitudinal direction, and the temperature control unit is arranged at the end in the longitudinal direction of the heating unit. The temperature of the heat distribution of the part is variable.

  According to this, by changing the temperature of the heating distribution at the end in the longitudinal direction of the heating unit, the heating temperature of the recording medium at the time of the first fixing and the heating of the recording medium at the time of the second fixing. The temperature can be switched.

  Next, a heating unit provided in the image forming apparatus of the present invention will be described. One form of the heating unit of the image forming apparatus of the present invention includes a first heating element in which the heating distribution in the central portion in the longitudinal direction is higher than the heating distribution in the end portion in the longitudinal direction, and the central heating unit in the longitudinal direction. The second heating element has a heating distribution that is lower in temperature than the heating distribution at the end in the longitudinal direction. The first heating element and the second heating element are arranged along the conveyance direction of the recording medium. The temperature control unit changes the temperature of the heating distribution at the end in the longitudinal direction of the heating unit by changing the lighting ratio between the first heating element and the second heating element.

  According to this, the lighting ratio can be changed by changing the electric power supplied to the first heating element and the second heating element, and the temperature of the heating distribution at the end in the longitudinal direction of the heating part can be changed.

  The first heating element and the second heating element have a width in the conveyance direction of the recording medium, a thickness in a direction orthogonal to the conveyance direction of the recording medium, or a width at the center and the end in the longitudinal direction. By varying both thicknesses, the heating distribution can be varied.

  Narrow and thin parts have a small heat capacity, so the temperature rise is high for the same amount of heating, and wide parts and thick parts have a large heat capacity. On the other hand, the temperature rise is low. As a result, the heating distribution can be varied.

  In the image forming apparatus of the present invention, another form of the heating unit includes a third heating element that forms a heating distribution in the central part in the longitudinal direction and a fourth heating element that forms a heating distribution in the end part in the longitudinal direction. It is set as the structure provided with. The third heating element and the fourth heating element are arranged in a direction orthogonal to the conveyance direction of the recording medium.

  Next, a temperature control unit provided in the image forming apparatus of the present invention will be described. The 1st form of the temperature control part of this invention makes variable the temperature of the heating distribution of the edge part of the longitudinal direction of a heating part by changing the electric power supplied to a 4th heating element. In the third heating element, the heating distribution in the central portion in the longitudinal direction of the heating portion is set to a predetermined temperature, and the central portion along the conveyance direction of the recording medium is the same during the first fixing and the second fixing. Temperature can be controlled.

  The second form of the temperature control unit of the present invention controls the cooling amount of the cooling mechanism provided in the fixing unit and makes the temperature of the heating distribution at the end in the longitudinal direction variable.

  According to this, by controlling the cooling amount of the cooling mechanism, the heated temperature at the end in the longitudinal direction can be adjusted to the temperature of the predetermined heating distribution.

[Mode of Temperature Control Method in Fixing of Image Forming Apparatus]
The temperature control method in the fixing of the image forming apparatus of the present invention includes a toner image forming unit that forms a toner image on a recording medium conveyed by a conveying unit, and a fixing that fixes the toner image on the recording medium by a heating unit. Fixing portion of an image forming apparatus capable of double-sided printing, a temperature control portion that controls the temperature of the heating portion, and a resupply portion that re-feeds the recording medium after fixing to the toner image forming portion In the first embodiment, in the first embodiment, in the temperature control process at the time of fixing to the same recording medium by the temperature control unit, the toner image formed on one surface of the recording medium is heated for the first time. At the time of fixing, a first control step for controlling the temperature of the end portion in the longitudinal direction, which is a direction orthogonal to the conveyance direction of the recording medium in the heating unit, to be lower than the temperature of the other part of the heating unit; On the face A second control step of controlling the temperature of the end portion in the longitudinal direction of the heating unit to be higher than the temperature of the central portion and the temperature at the time of the first fixing at the time of the second fixing in which the formed toner image is heat-treated; Is provided.

  According to this control, the temperature of the longitudinal end portion of the heating unit is controlled to be lower than the temperature of the other part of the heating unit at the time of the first fixing, thereby moving along the conveyance direction of the first surface of the recording medium. Further, since the temperature rise on both sides can be suppressed low, the occurrence of curling of the recording medium can be suppressed.

  Next, by controlling the temperature of the end portion in the longitudinal direction of the heating portion at the time of the second fixing, higher than the temperature at the time of the first fixing, the fixing property caused by the insufficient temperature at the time of the first fixing. Can be compensated for, and deterioration of fixability can be prevented.

  In the second form of the temperature control process of the present invention, the first control process is such that the temperature at the end portion in the longitudinal direction of the heating part is lower than the temperature of the other part of the heating part during the first fixing. In addition, the temperature of the rear end portion of the recording medium is controlled to be lower than the temperature of the other portion of the recording medium, and the second control step is the temperature of the longitudinal end portion of the heating unit at the time of the second fixing. Is controlled to be higher than the temperature at the time of the first fixing, and the temperature of the leading end of the recording medium is controlled to be higher than the temperature of the other part of the recording medium, and the first control step and the second control step. Between the recording medium and the recording medium in the conveying direction, the leading edge and the trailing edge of the recording medium are conveyed by being reversed and conveyed, and the end of the recording medium heated at a low temperature at the first fixing is heated at the second fixing. Heat treatment with.

  According to this control, curling at the left and right side portions in the conveyance direction of the recording medium can be suppressed, and curling at the front and rear end portions in the conveyance direction of the recording medium can be suppressed.

  In the third embodiment of the temperature control process of the present invention, the heating section is configured such that the heating distribution at the central portion in the longitudinal direction and the heating distribution at the end portions in the longitudinal direction are different, and the heating distribution at the end portions in the longitudinal direction is different. The temperature is variable.

  According to this, by changing the temperature of the heating distribution at the end in the longitudinal direction of the heating unit, the heating temperature of the recording medium at the time of the first fixing and the heating of the recording medium at the time of the second fixing. The temperature can be switched.

  The heating section includes a first heating element in which the heating distribution in the central portion in the longitudinal direction is higher than the heating distribution in the longitudinal end portion, and the heating distribution in the longitudinal central portion is the heating distribution in the longitudinal end portion. In the configuration in which the second heating elements having a lower temperature are arranged along the conveyance direction of the recording medium, the temperature control step of the present invention includes the lighting ratio between the first heating element and the second heating element. By changing the above, the temperature of the heating distribution at the end in the longitudinal direction of the heating unit is made variable.

  According to this, the lighting ratio can be changed by changing the electric power supplied to the first heating element and the second heating element, and the temperature of the heating distribution at the end in the longitudinal direction of the heating part can be changed.

  The heating unit includes a third heating element that forms a heating distribution at the center in the longitudinal direction and a fourth heating element that forms a heating distribution at the end in the longitudinal direction in a direction orthogonal to the conveyance direction of the recording medium. In the arrangement, the temperature control process of the present invention changes the temperature of the heating distribution at the end in the longitudinal direction of the heating unit by changing the power supplied to the fourth heating element.

  In the fourth form of the temperature control process of the present invention, the cooling amount of the cooling mechanism provided in the fixing unit is controlled, and the temperature of the heating distribution at the end in the longitudinal direction is made variable. According to this, by controlling the cooling amount of the cooling mechanism, the heated temperature at the end in the longitudinal direction can be adjusted to the temperature of the predetermined heating distribution.

  As described above, according to the image forming apparatus and the temperature control method of the present invention, good fixability can be obtained, and curling occurring on the recording medium can be suppressed to prevent paper jam.

It is a figure explaining the temperature control at the time of fixing by the heating part of this invention. It is a figure for demonstrating the whole structure of the image forming apparatus provided with the automatic double-sided image formation mechanism. FIG. 2 is a schematic cross-sectional view for explaining a configuration of a fixing device. It is a top view for demonstrating schematic structure of the 1st structural example of the heating part of this invention. It is a perspective view for demonstrating schematic structure of the 1st structural example of the heating part of this invention. It is a figure for demonstrating the temperature control (temperature control) by the fixing temperature control part of this invention. It is a figure for demonstrating the example of control which controls the temperature of the center part and edge part of the length direction of the heating part of this invention. It is a figure for demonstrating the example of control which controls the temperature of the center part and edge part of the length direction of the heating part of this invention. FIG. 6 is a diagram for explaining a relationship between a curl amount at a rear end portion of a sheet and a heater temperature. It is a figure for demonstrating the curl by a horizontal eye feed and a vertical eye feed. It is a perspective view for demonstrating the 2nd, 3rd structural example of the heating part of this invention. It is a perspective view for demonstrating the 4th, 5th, 6th structural example of the heating part of this invention. It is a perspective view for demonstrating the 7th, 8th structural example of the heating part of this invention. It is a figure for demonstrating the temperature control (temperature control) of the 8th structural example of the heating part of this invention. It is a figure for demonstrating the example of the length of the edge part which performs temperature control of a recording medium.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. First, the overall structure of the image forming apparatus having the automatic double-sided image forming mechanism shown in FIG. The image forming apparatus of FIG. 2 shows a configuration example in which a recording medium is reversed by a switchback type reversing mechanism to automatically form a double-sided image.

  In a paper cassette 17 arranged at the lowermost part of the apparatus main body, papers 18 are accommodated as a sheet-like recording medium in a stacked form. Each of the sheets 18 is taken out from the sheet cassette 17 by the rotation of the sheet feeding roller 16 and is sequentially sent out toward the sheet feeding side conveying path by the conveying roller pair 8.

  The sheet 18 is conveyed so as to abut against the registration roller pair 10 disposed in the sheet feeding side conveyance path and the skew state is corrected, and then the cylindrical photosensitive drum 1 constituting the image forming unit at an appropriate timing. The transfer roller 5 is transported into a transfer area which is a nip portion arranged to face the transfer roller 5, and the first image formation (printing) is performed on the first surface (for example, the front surface) of the paper 18 in the nip portion.

  In image formation, the outer peripheral surface of the photosensitive drum 1 is uniformly charged by the charging device 2, and image writing is performed on the outer peripheral surface of the photosensitive drum 1 after the uniform charging by the exposure device 3 to form an electrostatic latent image. Is done. The electrostatic latent image is supplied with toner from the developing device 4 and developed to be visualized to form a toner image. The toner image formed on the photosensitive drum 1 is transferred onto the paper 18 by the transfer bias applied to the transfer roller 5, and the first image formation (for example, the front surface) of the paper 18 ( Printing). Residual toner remaining on the photosensitive drum 1 without being completely transferred onto the paper 18 is removed from the photosensitive drum 1 by the cleaner 7.

  On the other hand, the sheet 18 on which the toner image has been transferred has both the electric field effect of the separation bias applied through the separation charge eliminating needle 6 and the curvature separation effect on the outer peripheral surface of the substantially cylindrical photosensitive drum 1. The conveyance is continued after being separated from the outer peripheral surface. In this way, the paper 18 carrying the unfixed toner image on the first surface (for example, the front surface) is transferred to the fixing nip 23 between the film 25 and the pressure roller 28 provided in the fixing device 19 constituting the fixing means. The unfixed toner image is fixed by the heating process in the fixing device 19.

  The paper 18 on which the toner image is fixed is discharged as it is toward the outside of the apparatus by a pair of paper discharge rollers 21 when a single-sided image is formed. On the other hand, when forming a double-sided image, image formation (printing) is performed on the second side (for example, the back side) of the paper 18.

  On the transport path, a swing flapper 20 that distributes the transport path of the paper 18 when forming a single-sided image and when forming a double-sided image is disposed downstream of the fixing device 19 in the transport direction. 2 is switched to the position indicated by the solid line in FIG. 2, the sheet 18 having the toner image fixed on the first surface (for example, the front surface) is transferred to the reversing roller pair 13 provided in the automatic duplex conveyance unit of the switchback reversing method. It is conveyed toward.

  The paper 18 is once transported downstream on the transport path by the rotation of the reverse roller pair 13. The reversing roller pair 13 stops before the rear end portion of the paper 18 is completely removed from the reversing roller pair 13 and then rotates in reverse. As a result, the paper 18 is in a state where the rear end side is reversed to the front end side while being conveyed to the reversing roller pair 13, and the front and back sides are reversed with respect to the image forming unit. It is conveyed again toward the paper feed side by the roller pair 14 and the double-sided second conveyance roller pair 15.

  Thereafter, similarly to the image formation on the first surface (for example, the front surface), the paper 18 is supplied to the registration roller pair 10 and is conveyed again to the image forming unit. At this time, a toner image corresponding to the second surface (for example, the back surface) is formed on the photosensitive drum 1, and transferred onto the second surface (for example, the back surface) of the paper 18 by the transfer roller 5.

  After the toner image is transferred to the second surface (for example, the back surface), the sheet 18 is conveyed to the fixing device 19 in the same manner as the first surface (for example, the front surface). The paper 18 is heated and fixed on the toner image on the second surface (for example, the back surface) in the fixing device 19, and then the swing flapper 20 is switched to the broken line position in FIG. Is done. The paper discharge roller pair 21 discharges the paper 18 to the outside of the apparatus by a conveying action. On the transport path, a registration sensor 9 is provided at a position in front of the registration roller pair 10 at a joining position of the transport path on the paper cassette 17 side and the transport path for returning the reversed paper.

  When double-sided image formation is performed, image formation (printing) is sequentially performed on the first side and the second side (front and back sides) of the paper 18 (recording medium). In this image formation, in order to fix the toner images formed on the front and back surfaces of the paper 18, two heat treatments are sequentially executed in the fixing device 19. The temperature of the heat treatment performed in the two fixing processes for the first surface and the second surface (both front and back surfaces) of the paper 18 in the fixing device 19 is preferably controlled by a fixing temperature control unit (controller) (not shown). Is done. Although not shown, the fixing temperature control unit may be provided in a control unit that controls the image forming apparatus in addition to a configuration in which a dedicated control unit is provided.

  Prior to describing the control operation by the fixing temperature control unit, the structure of the fixing device 19 will be described. FIG. 3 is a schematic cross-sectional view for explaining the configuration of the fixing device 19. A film 25 constituting a part of the heating mechanism is provided inside the fixing device 19, and an appropriate pressure such as a spring whose illustration is omitted from the pressure roller 28 with respect to the lower surface side of the film 25. It arrange | positions so that it may press-contact by an urging means. The paper 18 (recording medium) is passed as a heated body through the fixing nip 23 formed at the press contact portion between the film 25 and the pressure roller 28. The unfixed toner image on the paper 18 is heat-fixed by a heating action and a pressure action at the fixing nip 23.

  The film 25 is supported so as to be slidable annularly along the outer peripheral surface of a film guide 24 as a heating support member attached to a pressure stay having rigidity and heat resistance. The heating surface of the elongated plate-like heater 22 is attached to a part of the sliding surface formed on the lower surface side of the film guide 24 in the figure so as to be exposed downward. The heater 22 can be formed by a ceramic heater, for example. The heater 22 constitutes a heating body that applies heat necessary for the fixing process to the fixing nip 23 formed at the press contact portion between the pressure roller 28 and the film 25. It arrange | positions so that the inner peripheral surface of the film 25 may be in the state which contact | adhered to the heating surface of the illustration lower surface side of the heater 22 so that sliding was possible.

  The film 25 is formed of a material having a small heat capacity such as polyimide, polyamideide, PEEK, PES, PPS, PFA, PTFE, FEP having heat resistance and thermoplasticity. The surface layer of the film 25 is mixed or singly coated with a heat-resistant resin having good releasability, such as PFA, PTFE, FEP, etc., in order to prevent offset and ensure the division of the recording material.

  The film guide 24 as a heating support member is formed of, for example, a liquid crystal polymer, a phenol resin, PPS, PEEK, or the like. The film guide 24 is configured as a heat insulating member that holds the heater 22 at the lower end and prevents heat radiation in the direction opposite to the fixing nip 23. The film guide 24 has a shape and a size that allow the film 25 to move with a margin in the conveyance direction of the paper 18 (recording medium) (the direction from the right to the left in FIG. 3).

  As the heater 22, for example, what is known as a tensionless type can be adopted, and heat resistance, insulation, and good heat conduction extending in a slender shape along a longitudinal direction orthogonal to the conveyance direction of the paper 18 are adopted. And a resistance heating element is disposed along the longitudinal direction (image forming width direction) of the heater substrate. Feeding electrodes (not shown) are arranged at both longitudinal ends of the resistance heating element, and the heater 22 is heated by supplying heating power from the feeding electrodes. The heat treatment temperature can be detected by a thermistor (temperature sensing element) disposed immediately above the heater substrate.

  For example, the pressure roller 28 forms a primer layer on the outer peripheral side of a metal core made of a metal member such as aluminum via an elastic layer made of a heat-resistant rubber such as silicon rubber or fluorine rubber or a foam of silicon rubber. A release layer composed of a tube of PFA, PTFE, FEP or the like can be formed on the surface layer of the primer layer. The primer layer is formed to have electrical conductivity, and when the high resistance paper such as dry paper is passed through, the surface of the primer layer is negatively charged. Thus, an electrostatic offset that adheres again to the film 25 side is prevented.

  The pressure roller 28 can be rotationally driven by a driving unit including a fixing motor, and the driving unit can be appropriately driven and controlled by a fixing drive control unit (controller) (not shown). Following the rotational driving of the pressure roller 28, the film 25 is moved while being slid in an annular shape, and the paper 18 (recording medium) introduced into the fixing nip 23 is pressed in a state of being in close contact with the film 25. It is configured to be conveyed (moved). By transporting the paper 18 into the fixing nip 23, the unfixed toner image carried on the paper 18 is fixed by heat from the heater 22 and nip pressure by the pressure roller 28.

  Further, since the film 25 rotates while sliding against the heating surface of the heater 22 and the sliding surface of the film guide (heating support) 24 disposed on the inner side, the heating surface of the heater 22 and the film It is necessary to keep the frictional resistance between the sliding surface of the guide 24 and the inner peripheral surface of the film 25 small. For this reason, the heat-resistant grease for maintaining the follow-up drivability and slidability of the film 25 at the portion where the film 25 is in close contact with the heating surface of the heater 22 and the sliding surface of the film guide 24 A small amount of lubricant such as As a result, the film 25 can be smoothly rotated.

  The energization control to the heater 22 of the fixing device 19 having the above-described configuration is suitably controlled by a fixing temperature control unit (controller), and the heat treatment temperature at the time of fixing the unfixed toner image on the paper 18 is appropriately adjusted. .

  Next, the 1st structural example of the heating part which comprises the heater of this invention is demonstrated using FIG. FIG. 4 is a plan view showing a schematic configuration of the heating unit 101 of the first configuration example, and FIG. 5 is a perspective view. 4 (a) and 5 (a) show the state before heating the recording medium 300, and FIGS. 4 (b) and 5 (b) show the heating state during the first fixing. FIGS. 5C and 5C show the heating state at the time of the second fixing.

  The heating unit 101 of the first configuration example includes two heating elements 102 and 103. The lengths of the heating elements 102 and 103 in the longitudinal direction are at least equal to or longer than the width of the recording medium 300, and are arranged so that the longitudinal direction intersects the conveyance direction of the recording medium 300. Further, the two heating elements 102 and 103 are arranged along the conveyance direction of the recording medium 300.

  The heating element 102 has a center portion 102A and an end portion 102B, and the width in the transport direction of the center portion 102A is narrower than the width in the transport direction of the end portion 102B. On the other hand, the heating element 103 has a center portion 103A and an end portion 103B, and the width in the transport direction of the center portion 103A is formed wider than the width in the transport direction of the end portion 103B.

  In the heating element 102 and the heating element 103, the shape connecting the center portion and the end portion can be formed by being curved with a predetermined curvature. This curved shape is determined so as to have a predetermined heating distribution.

  When electric power is supplied to the heating elements 102 and 103 to generate heat, a portion where the volume of the heating element of the heating element is small becomes high temperature, and a portion where the volume is large becomes low temperature. For this reason, the central portion 102A of the heating element 102 becomes a high temperature portion, and the end portion 102B becomes a low temperature portion. On the other hand, the central portion 103A of the heating element 103 is a low temperature portion, and the end portion 103B is a high temperature portion.

  The heating element 102 can have the end portion 102B as a low temperature portion and the central portion 102A as a high temperature portion by widening the end portion 102B and narrowing the width of the central portion 102A. In addition, the heating element 103 can have the end portion 103B as a high temperature portion and the central portion 103A as a low temperature portion by narrowing the width of the end portion 102B and widening the width of the central portion 103A.

  The recording medium 300 that passes through the heating unit 101 is heated by the heating element 102 and the heating element 103. In the heat treatment by the heating unit 101, the heating element 102 and the heating element 103 can be controlled in temperature independently, and each heating element 102, 103 has a central heating distribution and an end heating distribution. Therefore, the heating state can be adjusted depending on the position on the recording medium 300 by adjusting the heating state of the heating element 102 and the heating element 103. The heating state of the heating element 102 and the heating element 103 can be adjusted by adjusting the lighting ratio of both the heating elements and the amount of power to be supplied.

  At the time of the first fixing, as shown in FIGS. 4B and 5B, the central portion of the heating unit 101 is set to a temperature suitable for fixing, and the end portion is controlled to be lower than the temperature of the central portion. Then, the recording medium 300 is allowed to pass with its first surface (for example, the surface, the surface indicated by A and B in the figure) facing the heating surface of the heating unit 101. This temperature control can be performed mainly by heating by the heating element 102 by making the amount of power supplied to the heating element 102 larger than the amount of power supplied to the heating element 103.

  By this temperature control, the central portion along the conveyance direction of the recording medium 300 is heated at a temperature suitable for fixing, so that sufficient fixing is performed. On the other hand, since both sides along the conveyance direction of the recording medium 300 are heated at a low temperature, the curling amount is suppressed but the fixing is insufficient.

  Next, after reversing the front and back of the recording medium on which the first fixing is completed, the second fixing is performed. At the time of the second fixing, as shown in FIGS. 4C and 5C, the central portion of the heating unit 101 is set to a temperature suitable for fixing similarly to the first fixing, and the temperature of the end portion is set. Is controlled to be higher than the temperature of the first time, and the recording medium 300 is passed through the second surface (for example, the rear surface, the surface indicated by a and b in the figure) facing the heating surface of the heating unit 101. . This temperature control can be performed mainly by heating by the heating element 103 by making the amount of power supplied to the heating element 103 larger than the amount of power supplied to the heating element 102.

  By this temperature control, the central portion along the conveyance direction of the recording medium 300 is heated at a temperature suitable for fixing, so that sufficient fixing is performed. On the other hand, since both sides along the conveyance direction of the recording medium 300 are heated at a temperature higher than the temperature at the time of the first fixing, the first insufficient fixing is compensated for. Sufficient fixing is performed for the part.

  Hereinafter, an embodiment of temperature control (temperature control) by the fixing temperature control unit will be described. The temperature control (temperature adjustment) by the fixing temperature control unit is executed as shown in FIG. 6, for example. 6A shows the temperature at the center of the heating unit, FIGS. 6B and 6C show the temperature at the end of the heating unit, and FIG. 6B is an example of temperature control. 6 (c) is another example of temperature control.

  In the temperature control shown in FIG. 6, first, the first surface (for example, the front surface) of the first recording medium (paper) is fixed, and then the second surface (for example, the same first recording medium (paper)). , Back surface).

  In the temperature control example shown in FIG. 6B, in the temperature control of the first surface for performing the first fixing, the temperature of the central portion in the longitudinal direction of the heating unit is set to 190 ° C., for example, and the longitudinal end of the heating unit is set. The temperature of the part is set to 170 ° C., for example. Here, 190 ° C. is a temperature sufficient for fixing, and 170 ° C. is a temperature insufficient for fixing although curling is suppressed. The values of 190 ° C. and 170 ° C. are merely examples, and the temperature is not limited to this temperature. The temperature of the central portion in the longitudinal direction of the heating portion is set to a temperature sufficient for fixing, and the longitudinal direction of the heating portion is set. The temperature of the end is set to a low temperature that suppresses the occurrence of curling.

  Next, in the temperature control of the second surface where the second fixing is performed, the temperature of the central portion in the longitudinal direction of the heating unit is set to 190 ° C., for example, and the temperature of the end portion in the longitudinal direction of the heating unit is set to 210 ° C., for example. . Here, 190 ° C. is a temperature sufficient for fixing, and 210 ° C. is a temperature higher than the temperature in the first fixing in order to improve the fixing property. The values of 190 ° C. and 210 ° C. are merely examples, and the temperature is not limited to this temperature. The temperature of the central portion in the longitudinal direction of the heating portion is set to a temperature sufficient for fixing, and the longitudinal direction of the heating portion is set. The temperature of the end is set to a high temperature suitable for improving the fixing property that was insufficient in the first fixing.

  In another temperature control example shown in FIG. 6C, in the temperature control of the first surface for the first fixing, the temperature of the central portion in the longitudinal direction of the heating unit is set to 190 ° C., for example, and the longitudinal direction of the heating unit The temperature at the end of the recording medium is set to 170 ° C., for example, and the temperature is lowered to 160 ° C. at the rear end in the recording medium conveyance direction. Here, 190 ° C. is a temperature sufficient for fixing, 170 ° C. is a temperature at which curling is suppressed at both sides along the recording medium conveyance direction, and 160 ° C. is a rear end in the recording medium conveyance direction. This is a temperature at which the occurrence of curling at the portion is suppressed.

  The values of 190 ° C., 170 ° C., and 160 ° C. are merely examples, and are not limited to this temperature. The temperature of the central portion along the longitudinal direction of the heating portion is set to a temperature sufficient for fixing, The temperature of the end portion in the longitudinal direction of the heating unit is set to a low temperature that suppresses curling.

  Next, in the temperature control of the second surface where the second fixing is performed, the temperature of the central portion in the longitudinal direction of the heating unit is set to, for example, 190 ° C., and the temperature of the end portion in the longitudinal direction of the heating unit is increased to, for example, 210 ° C. Further, the temperature is increased to 220 ° C. at the front end in the conveyance direction of the recording medium.

  Here, 190 ° C. is a temperature sufficient for fixing, 210 ° C. is a temperature higher than the temperature in the first fixing in order to improve the fixing property, and 220 ° C. is about the front end in the conveyance direction of the recording medium. This is a temperature for raising the temperature of the rear end portion lowered in the first fixing.

  The values of 190 ° C., 210 ° C., and 220 ° C. are merely examples, and the temperature is not limited to this temperature. The temperature of the central portion in the longitudinal direction of the heating unit is set to a temperature sufficient for fixing, and the heating unit The temperature at the end in the longitudinal direction of the recording medium is set to a high temperature suitable for improving the fixability, which was insufficient in the first fixing, and the temperature at the leading end in the conveyance direction of the recording medium is decreased at the first fixing. This is a temperature for raising the temperature of the rear end.

  The temperature control for the first sheet is repeated for the second and third recording media (paper).

  An example of controlling the temperature of the central part and the end part in the length direction of the heating part will be described with reference to FIGS. 7 and 8 show an example in which the temperature control of the central part and the end part in the length direction of the heating part is performed by adjusting the power supplied to the two heating elements constituting the heating part. FIG. 7 shows an example of the temperature control shown in FIG. 6B, and FIG. 8 shows an example of the temperature control shown in FIG.

  FIG. 7A shows the temperature at the center shown in FIG. 6A, and FIG. 7B shows the temperature at the end shown in FIG. 6B. In order to obtain the temperature characteristics of the heating section, the heating element 102 is supplied with electric power as shown in FIG. 7C, and the heating element 103 is supplied with electric power as shown in FIG. 7D.

  In the first surface, the temperature of the end portion in the length direction of the heating unit is lowered by lowering the power supply amount to the heating element 103 than the power supply amount to the heating element 102. On the second surface, the temperature of the end portion in the length direction of the heating unit is raised by increasing the amount of power supplied to the heating element 103 higher than the amount of power supplied to the heating element 102.

  FIG. 8A shows the temperature of the central part shown in FIG. 6A, and FIG. 8B shows the temperature of the end part shown in FIG. 6C. In order to obtain the temperature characteristics of the heating unit, the heating element 102 is supplied with electric power as shown in FIG. 8C, and the heating element 103 is supplied with electric power as shown in FIG. 8D.

  In the first surface, by lowering the power supply amount to the heating element 103 than the power supply amount to the heating element 102, the temperature of the end portion in the length direction of the heating unit is lowered, and the recording medium is conveyed in the conveyance direction. The power supply amount to the heating element 102 is reduced at the rear end.

  In the second surface, by increasing the amount of power supplied to the heating element 103 higher than the amount of power supplied to the heating element 102, the temperature at the end of the heating unit in the length direction is increased, and the recording medium is conveyed in the conveyance direction. The amount of power supplied to the heating element 102 is increased at the tip.

  Here, the temperature control is performed by the amount of electric power supplied to the two heating elements, but the temperature control may be performed by the lighting ratio of the two heating elements. In the temperature control based on the lighting ratio, for example, the lighting ratio can be controlled by controlling the power applied to each heating element by PWM control.

  FIG. 9 shows the relationship between the heater temperature and the curl amount at the leading edge of the recording medium on the first surface during horizontal stitch feeding in an environment of temperature 40 ° C./humidity 90%. In order to prevent paper jamming due to curling of the second surface of the drum due to curling at the time of fixing the first surface, it is necessary to make the curl amount of the trailing edge of the recording medium of the first surface smaller than 20 mm.

  According to the characteristics shown in FIG. 9, the temperature must be adjusted to a temperature of less than 165 ° C. in order to make the curl amount smaller than 20 mm. However, in order to reliably fix the toner on the paper, a temperature of 180 ° C. or higher is required in FIG.

  Therefore, in order to obtain a reliable fixing property with a curl amount of 20 mm or less, the characteristics of the curl amount and the heater temperature must be in the region P in FIG. However, since the illustrated characteristics do not pass through the above-described region, both the curl amount and the fixability cannot be satisfied.

  However, if it is assumed that the toner image does not fall off even if the toner image on the recording medium after fixing is lightly rubbed, a temperature of about 160 ° C. is sufficient. It will deteriorate over the entire recording medium.

  Therefore, if fixing is performed at a heat treatment temperature of 160 ° C. over the entire area of the recording medium, the amount of curling can be suppressed to a good level, but on the other hand, it is assumed that the fixing property deteriorates over the entire area of the recording medium. It becomes wearing state.

  Therefore, in the present embodiment, the normal 190 ° C. is applied to both sides along the recording medium conveyance direction, which is a range related to paper jamming due to drum winding of the second surface (for example, the back surface) of the recording medium. By controlling the heat treatment temperature to 170 ° C., which is about 20 ° C. lower than the heat treatment temperature, the occurrence of side curl is suppressed. On the other hand, with respect to the other portions, sufficient fixing properties are ensured by controlling the heat treatment temperature to be a normal 190 ° C.

  The amount of curl generated on the side portion along the conveyance direction of the first surface (for example, the front surface) of the recording medium is reduced by the control operation of the fixing temperature control unit as described above. Is on the assumption. Therefore, at the time of the second fixing for fixing the toner image on the second surface (for example, the back surface) of the recording medium after the switchback reversal operation, the fixing heat treatment temperature for the side portion along the transport direction is set to the first surface (for example, the On the surface), the heat treatment temperature is controlled to about 210 ° C. by increasing 20 ° C. from the normal heat treatment temperature by the amount lowered by 20 ° C., thereby ensuring sufficient fixability.

  As described above, in the present exemplary embodiment, at the time of the first fixing, fixing is performed at a low heat treatment temperature on the side portion along the conveyance direction on the first surface (for example, the front surface) of the recording medium. The curl generation amount is suppressed, and the fixing property of the image forming area excluding the side portion is prevented from being lowered. Then, by fixing the side portion along the conveyance direction subjected to the low-temperature heat treatment at the time of the first fixing at the second fixing at a heat treatment temperature higher than that at the time of the first fixing, It is possible to prevent the occurrence of fixing failure at the side portions along the conveyance direction of two surfaces (for example, the back surface), and as a result, both the occurrence of curling and the deterioration of the fixing property at the time of double-sided image formation on the recording medium can be simultaneously prevented. can do.

  Next, curl by horizontal stitch feed and vertical stitch feed will be described with reference to FIG. The paper that is the recording medium has a grain according to the direction of the fibers, the paper with the fibers arranged parallel to the long side of the whole paper is called the vertical eye, and the paper with the fibers arranged perpendicular to the long side of the whole paper is called the horizontal eye. I'm calling. Here, the paper feed with the horizontal direction of the recording medium as the transport direction is referred to as a horizontal feed, and the paper feed with the vertical direction of the recording medium as the transport direction is referred to as a vertical feed.

  FIG. 10B shows a state of occurrence of curling in vertical eye feed. In the case of longitudinal feed, the end of the heater 22 in the longitudinal direction has the maximum curl amount.

  FIG. 10A shows a state of occurrence of curling in the horizontal eye feed. Even in the case of the horizontal feed, the end portion in the longitudinal direction of the heater 22 has the maximum curl amount in addition to the front and rear end portions in the conveyance direction of the recording medium.

  Therefore, as shown in the temperature example of the heater end in FIGS. 6C and 8, the first surface has an end temperature lowered by 20 ° C. with respect to the center temperature, and the rear end of the longitudinal end is 30 ° C. Lower. On the second side, the end temperature is raised by 20 ° C. with respect to the center temperature, and the rear end of the longitudinal direction is raised by 30 ° C.

  As described above, the first surface lowers the temperature at the end in the longitudinal direction with respect to the center temperature, and further lowers the temperature at the rear end of the end in the longitudinal direction. Furthermore, on the second surface, the temperature at the end in the longitudinal direction is raised by the amount lowered by the first surface with respect to the center temperature, and at the rear end of the longitudinal end, the control is raised by the amount lowered by the first surface. By doing so, it is possible to prevent the curl from occurring in the first eye, and automatic double-sided image formation can be performed without paper jam when the second surface is printed. In addition, by raising the temperature control of the second surface from that of the first surface, sufficient fixing properties can be obtained over the entire area of the paper.

  Next, another configuration example of the heating unit of the present invention will be described with reference to FIGS. Second and third configuration examples of the heating unit will be described with reference to FIGS. The heating unit 111 of the second configuration example includes two heating elements 112 and 113. The lengths of the heating elements 112 and 113 in the longitudinal direction are at least equal to or longer than the width of the recording medium 300, and are arranged so that the longitudinal direction intersects the conveyance direction of the recording medium 300. Further, the two heating elements 112 and 113 are arranged along the conveyance direction of the recording medium 300.

  The heating unit 121 of the third configuration example includes two heating elements 122 and 123. The length of the heating element 122 in the longitudinal direction is at least the same as or longer than the width of the recording medium 300, and the heating element 122 is divided into two in the longitudinal direction. It is formed at least as long as the width of the recording medium 300. The two heating elements 122 and 123 are arranged so that the longitudinal direction intersects the conveyance direction of the recording medium 300, and the two heating elements 122 and 123 are arranged along the conveyance direction of the recording medium 300.

  In the first configuration example, the heating element 102 and the heating element 103 have a curved shape having a predetermined curvature in the shape connecting the central portion and the end portion, so that the width in the transport direction between the central portion and the end portion is different. ing. On the other hand, the heating unit 111 of the second configuration example and the heating unit 121 of the third configuration example have a shape connecting the center portion and the end portion to a linear shape having a predetermined inclination, thereby the center portion and the end portion. Different widths in the transport direction of the parts. The heating element 122 included in the heating unit 121 of the third configuration example includes two heating elements 122a and 122b that are divided into two in the longitudinal direction, and each heating element 122 and 123 has a shape that connects the center and the end. Are formed in a straight line shape having a predetermined inclination.

  When electric power is supplied to the heating elements 112, 113, 122, and 123 to generate heat, a portion where the heating element has a narrow width in the transport direction becomes high temperature, and a portion where the width in the transport direction is wide becomes low. Therefore, the central portion 112A of the heating element 112 becomes a high temperature portion, the end portion 112B becomes a low temperature portion, the central portion 113A of the heating element 113 becomes a low temperature portion, and the end portion 113B becomes a high temperature portion. Further, the central portion 122A of the heating element 122 becomes a high temperature portion, the end portion 122B becomes a low temperature portion, the central portion 123A of the heating element 123 becomes a low temperature portion, and the end portion 123B becomes a high temperature portion.

  The recording medium 300 passing through the heating units 111 and 121 is heated by the heating element 112 and the heating element 113, or the heating element 122 and the heating element 123. In the heat treatment by the heating units 111 and 121, the heating element 112 and the heating element 113, or the heating element 122 and the heating element 123 can be controlled independently of each other, and the heating element 112 and the heating element 113, Alternatively, since the heating element 122 and the heating element 123 can have different heating distributions at the center and the heating distribution at the end, the heating state of the heating element 112 and the heating element 113 or the heating element 122 and the heating element 123 is adjusted. By doing so, the heating state can be adjusted according to the position on the recording medium 300. The heating state of the heating element 112 and the heating element 113 or the heating element 122 and the heating element 123 can be adjusted by adjusting the lighting ratio of both the heating elements and the amount of power to be supplied.

  Next, the 4th-6th structural example of a heating part is demonstrated using Fig.12 (a)-(c). In the first and second configuration examples, the widths in the transport direction of the central portion and the end portions of the heating elements included in the heating portion are different. On the other hand, the fourth to sixth configuration examples vary the thicknesses of the heating elements provided in the heating unit in the direction orthogonal to the conveyance direction of the central part and the end part.

  The heating unit 131 of the fourth configuration example includes two heating elements 132 and 133. The lengths of the heating elements 132 and 133 in the longitudinal direction are at least the same as or longer than the width of the recording medium 300, and are arranged so that the longitudinal direction intersects the conveyance direction of the recording medium 300. In addition, the two heating elements 132 and 133 are arranged along the conveyance direction of the recording medium 300.

  The heating unit 141 of the fifth configuration example includes two heating elements 142 and 143. The length of the heating element 142 in the longitudinal direction is at least the same as or longer than the width of the recording medium 300. The heating element 142 is divided into two in the longitudinal direction, and the combined length of the two divided parts is: It is formed at least as long as the width of the recording medium 300. Each of the two heating elements 142 and 143 is arranged so that the longitudinal direction intersects the conveyance direction of the recording medium 300, and the two heating elements 142 and 143 are arranged along the conveyance direction of the recording medium 300.

  In the heating unit 131 of the fourth configuration example, the shape connecting the center portion and the end portion is a curved shape having a predetermined curvature or a linear shape having a predetermined inclination, and thereby the center portion and the end portion in the transport direction. It is the structure which makes width differ. FIG. 12A shows a configuration example in which the shape connecting the center portion and the end portion is a curved shape having a predetermined curvature.

  The heating element 142 included in the heating unit 141 of the fifth configuration example includes two heating elements 142a and 143b that are divided into two in the longitudinal direction, and each heating element 142a and 142b has a shape connecting the center and the end. Is a linear shape having a predetermined inclination, whereby the width in the transport direction of the central portion and the end portion is made different. FIG. 12B shows a configuration example in which the shape connecting the central portion and the end portion is a linear shape having a predetermined inclination.

  The heating unit 151 of the sixth configuration example includes two heating elements 152 and 153. The lengths of the heating elements 152 and 153 in the longitudinal direction are at least equal to or longer than the width of the recording medium 300, and are arranged so that the longitudinal direction intersects the transport direction of the recording medium 300. Further, the two heating elements 152 and 153 are arranged along the conveyance direction of the recording medium 300.

  The heating unit 151 of the sixth configuration example has a configuration in which the thickness is different between the central portion and the end portion. The heating element 152 is formed such that the thickness of the central portion 152A is reduced and the thickness is reduced at the end. On the other hand, the heating element 153 is formed such that the thickness of the central portion 152A is reduced and the thickness is reduced at the end.

  When power is supplied to the heating elements 132, 133, 142, 143, 1522, and 153 of the heating units 131, 141, and 151 to generate heat, the thickness of the heating elements in the direction perpendicular to the conveying direction of the heating member is thin. Becomes high temperature, and the thick part becomes low temperature. Therefore, the central portion 132A of the heating element 132 becomes a high temperature portion and the end portion 132B becomes a low temperature portion, and the central portion 133A of the heating element 133 becomes a low temperature portion and the end portion 133B becomes a high temperature portion. The central portion 142A of the heating element 142 becomes a high temperature portion, the end portion 142B becomes a low temperature portion, the central portion 143A of the heating element 143 becomes a low temperature portion, and the end portion 143B becomes a high temperature portion. Further, the central portion 152A of the heating element 152 becomes a high temperature portion, the end portion 152B becomes a low temperature portion, the central portion 153A of the heating element 153 becomes a low temperature portion, and the end portion 153B becomes a high temperature portion.

  The recording medium 300 passing through the heating units 131 to 151 is heated by the heating element 132 and the heating element 133, the heating element 142 and the heating element 143, or the heating element 152 and the heating element 153. In the heat treatment by the heating units 131 to 151, the heating element 132 and the heating element 133, the heating element 142 and the heating element 143, or the heating element 152 and the heating element 153 can be controlled independently. Since the heating distribution at the center and the heating distribution at the end can be made different from each other, the heating element 132 and the heating element 133, the heating element 142 and the heating element 143, or the heating element 152 and the heating element 153 are heated. By adjusting the state, the heating state can be adjusted depending on the position on the recording medium 300.

  The heating element 132 and the heating element 133, the heating element 142 and the heating element 143, or the heating element 152 and the heating element 153 can be adjusted by adjusting the lighting ratio of both the heating elements and the amount of power supplied. .

  Next, seventh and eighth configuration examples of the heating unit will be described with reference to FIGS.

  The seventh configuration example is a configuration in which the heating distribution is made different by changing the heat radiation state of the central portion and the end portion of the heating element included in the heating portion. FIG. 13A is a diagram for explaining a seventh configuration example.

  The heating unit 161 of the seventh configuration example includes two heating elements 162 and 163. The lengths of the heating elements 162 and 163 in the longitudinal direction are at least equal to or longer than the width of the recording medium 300, and are arranged so that the longitudinal direction intersects the conveyance direction of the recording medium 300. Further, the two heating elements 162 and 163 are arranged along the conveyance direction of the recording medium 300.

  The heating unit 161 of the seventh configuration example is a configuration in which a heat radiating member is provided on the heat generating member, and the installation position of the heat radiating member for the two heating elements is different between the central portion and the end portion. In FIG. 13A, the heating element 162 has a configuration in which the heat dissipation member 164 is not disposed in the center portion 162A, and the heat dissipation member 164 is disposed in the end portion 162B, and the heating element 163 has the heat dissipation member 164 disposed in the center portion 163A. The heat dissipating member 164 is not disposed at the end 162B.

  When electric power is supplied to the heating elements 162 and 163 of the heating unit 161 to generate heat, the portion of the heating element where the heat dissipating member is not disposed becomes high temperature, and the portion where the heat dissipating member is disposed becomes low temperature. Therefore, the central portion 162A of the heating element 162 becomes a high temperature portion and the end portion 132B becomes a low temperature portion, and the central portion 163A of the heating element 163 becomes a low temperature portion and the end portion 163B becomes a high temperature portion.

  The recording medium 300 that passes through the heating unit 161 is heated by the heating element 162 and the heating element 163. In the heat treatment by the heating unit 161, the heating element 162 and the heating element 163 can independently control the temperature, and the heating distribution at the center and the heating distribution at the end can be made different. Therefore, the heating state can be adjusted depending on the position on the recording medium 300 by adjusting the heating state of the heating element 162 and the heating element 163.

  The adjustment of the heating element 162 and the heating element 163 can be performed by adjusting the lighting ratio of both the heating elements and the amount of power to be supplied.

  In the eighth configuration example, the heating unit is configured to vary the heating distribution by disposing heating elements separated at the center and the end. FIG. 13B is a diagram for explaining an eighth configuration example.

  The heating unit 171 of the eighth configuration example includes three heating elements 172 to 174. The heating elements 172 to 174 are arranged in the longitudinal direction, and the combined length is at least the same as or longer than the width of the recording medium 300, and is arranged so that the longitudinal direction intersects the conveying direction of the recording medium 300.

  The heating unit 171 of the eighth configuration example has a configuration in which three heating elements are arranged along a direction intersecting the transport direction so that the heating distribution at the center portion and the end portion is different. In FIG. 13B, the heating element 172 is arranged at the center, the heating elements 173 and 174 are arranged at the ends, and the heating elements 172 to 174 are individually driven, so that the temperatures at the center and the ends are independent. And control.

  FIG. 14 shows an example in which the temperature of the central portion and the end portion in the length direction of the heating unit is controlled by adjusting the power supplied to the three heating elements constituting the heating unit of the eighth configuration example. .

  FIG. 14A shows the temperature at the center, and FIG. 14B shows the temperature at the end. In order to obtain the temperature characteristics of the heating section, the heating elements 173 and 174 are supplied with electric power as shown in FIG. 8C, and the heating element 172 is supplied with electric power as shown in FIG. 8D. .

  In the first surface, the temperature of the end portion in the length direction of the heating unit is lowered by lowering the power supply amount to the heating elements 173 and 174 than the power supply amount to the heating element 172. In the second surface, the power supply amount to the heating elements 173 and 174 is higher than the power supply amount to the heating element 172 and higher than the power supply amounts to the heating elements 173 and 174 on the first surface. Thus, the temperature of the end portion in the length direction of the heating unit is increased.

  The ninth configuration example is a configuration in which an end cooling mechanism is provided. An example of the configuration of the end cooling mechanism is shown in FIG.

  An end cooling mechanism is provided on at least one of both ends of the substantially cylindrical film 25 and both ends of the pressure roller 28. FIG. 10A shows a configuration in which end cooling mechanisms 180 are provided at both ends of the film 25 and end cooling mechanisms 181 are provided at both ends of the pressure roller 28.

  The end cooling mechanism can be constituted by, for example, a cooling fan and a shutter that opens and closes the cool air generated by the cooling fan. By opening the shutter, the cool air is applied to the film 25 or the pressure roller 28, To lower the temperature of the portion in contact with the recording medium. By controlling the shutter, the temperature of the longitudinal end portion of the heating unit is controlled to be different between the first surface and the second surface.

  According to this configuration, in the case of a small-sized recording medium having a short paper width direction, the problem that the end temperature of the film 25 or the pressure roller 28 that does not speed the recording medium rises can be solved. Further, by adopting this configuration, even if the heating unit includes a conventional heating element, the temperature of the end portion is adjusted between the first fixing time and the second fixing time, and the second surface is adjusted. A double-sided image can be automatically formed without paper jam when printing. In addition, by increasing the temperature control of the second surface from the first surface, it is possible to obtain sufficient fixability over the entire area of the sheet.

  Next, an example of the length of the end portion for controlling the temperature of the recording medium and an example of the temperature control of the image forming apparatus of the present invention will be described.

  In FIG. 15, the end portions E1 and E2 in the conveyance direction of the recording medium can be determined based on dimensions when the recording medium comes into contact with the rotor when the recording medium is wound around the roller. For example, when the diameter of the roller is about 10 mm and the recording medium is wound around a quarter of the roller, the length of the ends E1 and E2 is about 15 mm because the length of the ends E1 and E2 is about 15 mm. Is set to 15 mm or more. Further, the end E3 in the direction orthogonal to the recording medium conveyance direction can be determined based on the dimension that the conveyance device holds the recording medium in conveying the recording medium. For example, 10 mm or more can be set as an example.

Examples of temperature control of the image forming apparatus of the present invention are shown in Table 1 below.

  In Table 1, Example 1 shows an example in which the conveyance of the recording medium is known to be horizontal feed, and Example 2 shows an example in which the conveyance of the recording medium is known to be vertical feed. Embodiments 3 and 4 show examples in which it is unknown whether the recording medium is transported in the horizontal direction or the vertical direction.

  When the conveyance of the recording medium of Example 1 is horizontal feed, the curl at the leading end and the trailing end is large, so the temperatures at the leading end and trailing end (E2, E1) are set in the printing process for the first side. In the second printing process, the temperature is increased.

  In the case where the conveyance of the recording medium of Example 2 is the vertical stitch feed, the curl at the end in the direction orthogonal to the transport direction is large, so the temperature at the end (E3) at both ends is lowered in the printing process for the first side. In the printing process on the second side, the temperature is raised.

  In the first and second embodiments, whether the recording medium is transported in the horizontal direction or the vertical direction can be determined, for example, by a paper cassette that stores the recording medium. It sends to a control part and controls temperature control based on this classification signal.

  If it is unknown whether the recording medium is transported horizontally or longitudinally, in the third embodiment, the temperatures of the end portions (E2, E1) of the leading and trailing ends are set in the printing process of the first surface. The temperature is raised in the printing process on the second side, the temperature of the end (E3) at both ends is lowered in the printing process on the first side, and the temperature is raised in the printing process on the second side.

  In addition, as in the embodiment, even if the temperature is simply adjusted so that the temperature of the end portions (E1, E2, E3) E1 around the recording medium is lower than the temperature of the central portion (C), a certain degree of effect is achieved. Can be played.

  The embodiments of the invention made by the present inventor have been specifically described above. However, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the scope of the invention. Not too long.

  For example, each of the embodiments described above applies the present invention to a printer, but the present invention can be similarly applied to other image forming apparatuses such as a copying machine and a facsimile.

  As described above, the present invention can be widely applied to image forming apparatuses that perform a wide variety of double-sided image formation such as printers, copiers, and facsimiles.

DESCRIPTION OF SYMBOLS 1 Photosensitive drum 2 Charging apparatus 3 Exposure apparatus 4 Developing apparatus 5 Transfer roller 6 Separating static elimination needle 7 Cleaner 8 Conveying roller pair 9 Registration sensor 10 Registration roller pair 13 Reverse roller pair 14 Conveying roller pair 15 Conveying roller pair 16 Paper feeding roller 17 Paper cassette 18 Paper 19 Fixing device 20 Swing flapper 21 Discharge roller pair 22 Heater 23 Fixing nip 24 Film guide 25 Film 28 Pressure roller 100 Heating unit 100A Central part 100B Longitudinal end part 101 Heating part 102 Heating element 102A Central part 102B End Part 103 Heating element 103A Central part 103B End part 111 Heating part 112 Heating element 112A Central part 112B End part 113 Heating element 113A Central part 113B End part 121 Heating part 122, 122a, 122b Heating element 122A Center 122B end portion 123 heating element 123A central portion 123B end portion 131 heating portion 132 heating element 132A central portion 132B end portion 133 heating element 133A central portion 133B end portion 141 heating portion 142, 142a, 142b heating element 142A central portion 142B end portion 143 Heating element 143A Central part 143B End part 151 Heating part 152 Heating element 152A Central part 152B End part 153 Heating element 153A Central part 153B End part 161 Heating part 162 Heating element 162A Central part 162B End part 163 Heating element 163B 164 Heat dissipation member 171 Heating unit 172, 173, 174 Heating element 180 End cooling mechanism 181 End cooling mechanism 200 Central temperature processing unit 201 Low temperature processing unit 202 High temperature processing unit 300 Recording medium 301 First 302 second surface 400 temperature controller

Claims (11)

A toner image forming unit that forms a toner image on a recording medium conveyed by a conveying unit; a fixing unit that fixes the toner image on the recording medium by a heating unit; and a temperature control unit that controls the temperature of the heating unit. An image forming apparatus capable of double-sided printing, and a resupply unit that re-feeds the recording medium after fixing to the toner image forming unit.
The temperature controller is
In temperature control during fixing to the same recording medium,
Different heating distribution in the longitudinal direction, which is a direction orthogonal to the conveyance direction of the recording medium in the heating unit, and heating the end and the central part in the direction orthogonal to the conveyance direction in the recording medium at different heating temperatures,
The heating unit is
During the first fixing in which the toner image formed on one surface of the recording medium is heat-treated, the temperature of the end in the direction orthogonal to the conveyance direction of the recording medium is heated to be lower than the temperature of the central portion. ,
At the time of the second fixing in which the toner image formed on the other surface of the recording medium is heat-treated, the temperature of the end in the transport direction of the recording medium is higher than the temperature at the center, and the first An image forming apparatus, wherein the end portion at the time of fixing is heated at a temperature higher than the temperature. In double-sided printing, between the first fixing time for printing one side of the recording medium and the second fixing time for printing the other surface, the leading and trailing edges of the recording medium in the transport direction are Provided with switchback means for carrying it in reverse conveyance,
The heating unit heats the temperature of the end in the direction orthogonal to the conveyance direction of the recording medium at a temperature lower than the temperature of the center during the first fixing, and the rear end of the recording medium Is heated at a temperature lower than the temperature at the tip and center of the recording medium,
At the time of the second fixing, the temperature of the end in the direction orthogonal to the conveyance direction of the recording medium is heated higher than the temperature at the time of the first fixing, and the temperature of the leading end of the recording medium The image forming apparatus according to claim 1, wherein the image forming apparatus is heated at a higher temperature than the central portion and the rear end portion of the recording medium. The heating unit includes a first heating element in which a heating distribution in a central portion in the longitudinal direction is higher than a heating distribution in an end portion in the longitudinal direction;
A second heating element, wherein the heating distribution in the central portion in the longitudinal direction is lower than the heating distribution in the end portions in the longitudinal direction,
The first heating element and the second heating element are arranged along the conveyance direction of the recording medium,
The said temperature control part makes variable the temperature of the heating distribution of the edge part of the longitudinal direction of the said heating part by changing the lighting ratio of a 1st heating element and a 2nd heating element. Item 3. The image forming apparatus according to Item 1 or 2. The first heating element and the second heating element are:
The heating distribution is made different by changing at least one of the width in the transport direction of the recording medium and the thickness in the direction orthogonal to the transport direction of the recording medium at the central portion and the end portion in the longitudinal direction. The image forming apparatus according to claim 3. The heating unit includes a third heating element that forms a heating distribution in the central portion in the longitudinal direction, and a fourth heating element that forms a heating distribution in an end portion in the longitudinal direction,
The third heating element and the fourth heating element are arranged in a direction orthogonal to the conveyance direction of the recording medium,
The said temperature control part makes variable the temperature of the heating distribution of the edge part of the longitudinal direction of the said heating part by changing the electric power supplied to a 4th heating element, The Claim 1 or 2 characterized by the above-mentioned. Image forming apparatus.   The image forming apparatus according to claim 1, wherein the temperature control unit controls a cooling amount of a cooling mechanism provided in the fixing unit to vary a temperature of a heating distribution at an end portion in the longitudinal direction. . A toner image forming unit that forms a toner image on a recording medium conveyed by a conveying unit; a fixing unit that fixes the toner image on the recording medium by a heating unit; and a temperature control unit that controls the temperature of the heating unit. And an image forming apparatus capable of double-sided printing, including a re-feed unit that re-feeds the recording medium after fixing to the toner image forming unit,
In the temperature control process at the time of each fixing when performing double-sided printing on the same recording medium by the temperature control unit by two times of straightening,
At the time of the first fixing in which the toner image formed on one surface of the recording medium is heat-treated, the temperature of the end portion in the longitudinal direction, which is a direction orthogonal to the conveyance direction of the recording medium, is heated in the heating unit. A first control step for controlling the temperature lower than the temperature of the other part of the part;
At the time of the second fixing in which the toner image formed on the other surface of the recording medium is heat-treated, the temperature of the end portion in the longitudinal direction of the heating unit is higher than the temperature at the center, and the first time And a second control step of controlling the temperature higher than the temperature at the time of fixing. In the temperature control step,
In the first control step, the temperature of the longitudinal end of the heating unit is lower than the temperature of the other part of the heating unit and the temperature of the rear end of the recording medium is the first fixing. Control the temperature below the other part of the recording medium,
In the second control step, the temperature at the longitudinal end of the heating unit is controlled to be higher than the temperature at the first fixing at the time of the second fixing, and the temperature at the leading end of the recording medium is controlled. Control the temperature higher than the temperature of other parts of the recording medium,
Between the first control step and the second control step, the recording medium is conveyed by reversing and conveying the front end and the rear end in the conveyance direction,
The temperature control method according to claim 7, wherein an end portion of the recording medium that has been heat-treated at the time of the first fixing is heat-treated at a high temperature at the time of the second fixing. The heating unit includes a first heating element in which a heating distribution in a central portion in the longitudinal direction is higher than a heating distribution in an end portion in the longitudinal direction;
A second heating element, wherein the heating distribution in the central portion in the longitudinal direction is lower than the heating distribution in the end portions in the longitudinal direction,
Arranging the first heating element and the second heating element along a conveyance direction of the recording medium;
The temperature control step makes the temperature of the heating distribution at the end portion in the longitudinal direction of the heating unit variable by changing a lighting ratio between the first heating element and the second heating element. Item 9. The temperature control method according to Item 7 or 8. The heating unit includes a third heating element that forms a heating distribution in the central portion in the longitudinal direction, and a fourth heating element that forms a heating distribution in an end portion in the longitudinal direction,
The third heating element and the fourth heating element are arranged in a direction orthogonal to the conveyance direction of the recording medium,
The temperature control step makes the temperature of the heating distribution at the end in the longitudinal direction of the heating unit variable by changing the power supplied to the fourth heating element. Temperature control method.   The temperature control method according to claim 7 or 8, wherein the temperature control step controls a cooling amount of a cooling mechanism provided in the fixing unit to vary a temperature of a heating distribution at an end portion in the longitudinal direction. .