JP2014081473A - Image forming apparatus - Google Patents

Abstract

An image forming apparatus capable of maintaining good separation of a recording medium from a fixing member without reducing the productivity of the recording medium on which an image has been formed, even if the recording medium has a small heat capacity. .
Based on thickness-related information related to the thickness of the recording paper P, the image forming conditions that affect the separation property when the portion of the recording paper P in the conveyance direction is separated from the surface of the heating roller 20 are changed. The control part which controls to do is provided. For example, based on the value of mass (basis weight) per unit area of the recording paper P, at least one of the toner adhesion amount and the fixing temperature in the fixing device 19 is controlled with respect to the image portion on the leading end side in the conveyance direction of the recording paper P.
[Selection] Figure 2

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile machine, and a multifunction machine having these functions.

  Conventionally, as a fixing device used in this type of image forming apparatus, in order to separate a heat-fixed recording medium from a fixing member such as a heating belt or a fixing roller, a fixing member and a pressure member that pressurizes the fixing member are used. There is known a fixing device provided with a separation claw near the exit of the fixing nip portion. However, when the separation claw is used, the claw portion at the tip of the separation claw may damage the image surface of the recording medium. Further, in the configuration in which the separation claw is disposed in contact with the surface of the fixing member, the surface of the fixing member is easily damaged, so that the scar on the fixing member due to the separation claw is transferred to the image at the time of fixing, and the image quality may be degraded.

  In order to reduce the scratch on the image surface and the surface of the fixing member, Patent Document 1 includes a fixing device having a mechanism capable of contacting and separating the separation claw with respect to the surfaces of the fixing roller and the pressure roller. An image forming apparatus is disclosed. In the image forming apparatus disclosed in Patent Document 1, a mechanism for contacting and separating the separation claw is controlled according to the paper type of a recording material (recording medium) onto which an image is transferred and the margin width at the leading end in the recording material conveyance direction. Further, the recording material is prevented from being wound around the fixing roller and the pressure roller. Further, as compared with the configuration in which the separation claw is always in contact with the fixing roller and the pressure roller, it is possible to reduce the scratch on the roller surface and prevent the image quality from being deteriorated. However, in this fixing device, the structure of the mechanism for contacting and separating the separation claw is complicated, and there is a risk that the cost increases.

  Therefore, as a fixing device that does not use a separation claw, there is known a fixing device that uses a curvature of a fixing roller or a heating belt to separate the recording medium after fixing from the fixing roller or the heating belt. However, such a fixing device that does not use a separation claw has the following problems.

  The recording medium is supported at one point of the fixing nip portion after the leading end of the recording medium passes through the fixing nip portion and reaches the paper discharge roller. The transport behavior becomes unstable. In particular, when the recording medium is thin paper, the paper is easily wound around the fixing member due to the influence of the adhesive force between the toner, which is an image forming material, and the fixing member, and jamming occurs due to winding.

  In order to reduce the adhesive force between the toner and the fixing member, it is considered to increase the amount of heat supplied from the fixing member to the recording medium, thereby completely melting the toner and preventing the recording medium from being wound around the fixing member. It is done. However, for a recording medium such as thin paper with a small heat capacity, if the amount of heat supplied from the fixing member is increased, the temperature of the recording medium to be discharged increases, and the recording medium becomes an adhesive and the recording medium becomes a fixing roller or an additive. It winds around a fixing member such as a pressure roller.

  Patent Document 2 discloses an image forming apparatus aimed at realizing stable paper conveyance by preventing jamming even when the recording medium is a paper type such as thin paper. The image forming apparatus disclosed in Patent Document 2 can detect the temperature of the preceding recording material (recording medium) and change the subsequent recording material supply interval according to the temperature. Then, when the detected temperature of the preceding recording material is higher than a predetermined threshold temperature, control is performed to increase the subsequent recording material supply interval. For example, the type of the recording material is determined based on the detection result of the temperature of the recording material, and when it is determined that thin paper having a small heat capacity has been passed, the recording material supply interval is increased. This prevents the occurrence of jamming of the recording material.

  However, in the image forming apparatus disclosed in Patent Document 2, the recording material supply interval is widened depending on the type of paper such as thin paper. Therefore, the number of images formed per unit time is reduced, and the productivity of an image-formed recording medium is reduced. There is a problem that it ends up.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a recording medium from a fixing member without reducing the productivity of an image-formed recording medium even if the recording medium has a small heat capacity. It is an object of the present invention to provide an image forming apparatus that can maintain good separability.

  In order to achieve the above object, a first aspect of the present invention relates to a toner image forming means for forming a toner image on a recording medium, and a fixing member in which a recording medium on which the toner image is formed is conveyed. A fixing unit that fixes the toner image on the recording medium by bringing the recording medium into contact with the recording medium, and transporting the recording medium based on thickness-related information related to the thickness of the recording medium The image forming apparatus includes a control unit that controls to change an image forming condition that affects a separation property when a portion on the front side in the direction is separated from the surface of the fixing member.

  According to the present invention, based on the thickness-related information related to the thickness of the recording medium, the image forming condition that affects the separation property when the portion of the recording medium in the conveyance direction leading end side is separated from the surface of the fixing member is changed. To do. As a result, according to the thickness of the recording medium, the adhesive force of the toner at the front end portion in the conveyance direction of the recording medium can be adjusted to a level that does not cause the recording medium to be wound around the fixing member. Therefore, even when the image forming target recording medium is a thin recording medium having a small heat capacity, it is possible to maintain good separation of the recording medium from the fixing member. In addition, in order to maintain the separation property of the recording medium from the fixing member, it is not necessary to increase the conveyance interval of a plurality of recording media on which images are continuously formed, so that the productivity of the image-formed recording medium is reduced. There is nothing. Therefore, even if the recording medium has a small heat capacity, it is possible to maintain good separation of the recording medium from the fixing member without reducing the productivity of the recording medium on which the image has been formed.

1 is a schematic configuration diagram illustrating an example of an overall configuration of a copier according to an embodiment of the present invention. 1 is a schematic configuration diagram illustrating an example of a fixing device provided in a copier according to an embodiment. FIG. 3 is a plan view for explaining a margin area of recording paper. The graph for demonstrating the change of target temperature when letting plain paper and thin paper pass as recording paper. 6 is a graph showing temporal changes in each temperature when changing the fixing target temperature of the fixing roller according to the temperature of the pressure roller.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a schematic configuration diagram showing an example of the overall configuration of an image forming apparatus according to an embodiment of the present invention.
In FIG. 1, a tandem type color copying machine (hereinafter referred to as “copying machine”) 1 as an image forming apparatus of the present embodiment includes an apparatus main body 10, an optical writing unit 2 as exposure means, and image information of a document D. And an original reading unit 4 as image reading means for reading. Further, the copying machine 1 is provided with a sheet feeding unit 7 as a recording medium accommodating unit that accommodates a recording sheet P as a recording material (transfer material) as a recording medium on which an image is formed, below the apparatus main body 10. It has been.

  Further, in the apparatus main body 10 of the copying machine 1, a plurality of photosensitive drums 11Y, 11M, 11C, and 11BK (image carriers) on which toner images of a plurality of colors (yellow, magenta, cyan, and black) are formed are formed. Hereinafter, the suffixes Y, M, C, and BK are omitted as appropriate). Around these photosensitive drums 11, there are a charging unit 12 as charging means for charging the photosensitive drum 11, and developing means for developing the electrostatic latent image formed on the photosensitive drum 11 with toner of each color. And a cleaning unit 15 for collecting untransferred toner on the photosensitive drum 11 are provided.

  Each photosensitive drum 11 is driven to rotate in the direction of the arrow in the figure, charged to a predetermined potential by the charging unit 12, and then a predetermined intensity such as laser light or LED light emitted from the optical writing unit 2 based on input image information. The exposure light is scanned and irradiated in the main scanning direction substantially parallel to the photosensitive drum rotation axis. Further, the photosensitive drum 11 is driven to rotate about a rotation axis (axis perpendicular to the paper surface of FIG. 1), so that the exposure light from the optical writing unit 2 is moved in the moving direction of the surface of the photosensitive drum 11. Scanning is performed in a certain sub-scanning direction.

  The apparatus main body 10 of the copying machine 1 is provided with an intermediate transfer belt 17 as an intermediate transfer member that can be driven in the direction of the arrow in the drawing. A primary transfer unit such as a primary transfer bias roller (not shown) to which a predetermined bias is applied is provided so as to face the photosensitive drums 11Y, 11M, 11C, and 11BK through the intermediate transfer belt 17. By these primary transfer units, the toner images of a plurality of colors formed on the respective photosensitive drums 11 are transferred onto the intermediate transfer belt 17 in a superimposed manner. Around the intermediate transfer belt 17, an intermediate transfer belt cleaning unit 16 as an intermediate transfer member cleaning unit and a secondary transfer roller 18 as a secondary transfer unit to which a predetermined bias is applied are disposed. ing. The intermediate transfer belt cleaning unit 16 cleans the surface of the intermediate transfer belt 17, and the secondary transfer roller 18 transfers a color image composed of a plurality of superimposed toner images formed on the intermediate transfer belt 17 onto the recording paper P. To do.

  Further, in the apparatus main body 10 of the copying machine 1, a toner image (unfixed) on the recording paper P is positioned above the secondary transfer roller 18 in the drawing and on the conveyance path of the recording paper P that has passed through the secondary transfer roller 18. An electromagnetic induction heating type fixing device 19 is provided as fixing means for fixing the image).

  In the copying machine 1 of the present embodiment, the toner image forming means for forming a toner image on the recording paper P includes a photosensitive drum 11, a charging unit 12, an optical writing unit 2, a developing unit 13, a primary transfer unit, The secondary transfer roller 18 is configured.

In addition, the copying machine 1 according to the present embodiment includes an operation display panel as an operation unit (not shown) including, for example, a display device having a touch panel function. This operation display panel is operated by the user when inputting the number of image formations or performing an image formation start operation. In addition, the operation display panel inputs information on the mass [g / m ² ] per unit area of the recording paper P as thickness-related information related to the thickness of the recording paper P that is an image formation target by an input operation of the user. It also functions as information input means.

Further, the copying machine 1 of the present embodiment includes a control unit as a control means (not shown) that controls the entire copying machine 1. The control unit includes a CPU, a RAM, a ROM, an I / O interface, and the like, and can perform various controls by reading and executing a predetermined control program. In addition, the control unit determines when the portion on the leading end side in the conveyance direction of the recording paper P is separated from the surface of the fixing member of the fixing device 19 based on the thickness related information related to the thickness of the recording paper P to be image formed. It also functions as a means for controlling the image forming conditions that affect the separation property to be changed. For example, the control unit attaches the toner by the toner image forming unit to the image portion on the front side in the conveyance direction of the recording paper P based on the value of the mass [g / m ² ] per unit area of the recording paper P to be image formed. At least one of the amount and the temperature in the fixing device 19 can be controlled.

  Further, the copying machine 1 of the present embodiment includes a storage unit (not shown) as a storage unit that stores a set value of a target temperature of a fixing roller 20 (described later) as a heating fixing member. The storage unit can be configured by, for example, a RAM, a ROM, a semiconductor memory such as a flash memory, a magnetic storage medium such as a magnetic disk, an optical storage medium such as an optical disk, and the like.

Hereinafter, an operation during normal color image formation in the copying machine 1 of the present embodiment will be described.
First, image information of the document D placed on the contact glass 5 is optically read by the document reading unit 4. Specifically, the document reading unit 4 scans the image of the document D on the contact glass 5 while irradiating light emitted from an illumination lamp. Then, the light reflected by the document D is imaged on the color sensor via the mirror group and the lens. The color image information of the document D is read for each RGB (red, green, blue) color separation light by the color sensor, and then converted into an electrical image signal. Further, color conversion processing, color correction processing, spatial frequency correction processing, and the like are performed by the image processing unit based on the RGB color separation image signals to obtain yellow, magenta, cyan, and black color image information. Then, the image information of each color of yellow, magenta, cyan, and black is transmitted to the optical writing unit 2. Then, from the optical writing unit 2, exposure light composed of laser light or LED light based on the image information of each color is emitted toward the corresponding photosensitive drums 11Y, 11M, 11C, and 11BK and scanned. .

  On the other hand, each of the four photosensitive drums 11Y, 11M, 11C, and 11BK rotates in the arrow direction (clockwise) in FIG. First, the surfaces of the photosensitive drums 11Y, 11M, 11C, and 11BK are uniformly charged at a portion facing the charging unit 12, and a predetermined charging potential is formed on the photosensitive drums 11Y, 11M, 11C, and 11BK. (Charging process). Thereafter, the surfaces of the charged photoconductive drums 11Y, 11M, 11C, and 11BK reach the irradiation positions of the corresponding exposure light such as laser light.

  In the optical writing unit 2, exposure light such as laser light corresponding to an image signal is emitted from each of the four light sources corresponding to each color (exposure process). The exposure light such as each laser beam passes through a different optical path for each color component of yellow, magenta, cyan, and black.

  For example, laser light as exposure light corresponding to the yellow component is irradiated on the surface of the first photosensitive drum 11Y from the left in FIG. At this time, the yellow component laser light is scanned in the main scanning direction along the rotation axis direction of the photosensitive drum 11Y by the polygon mirror that rotates at high speed, and also in the sub-scanning direction that is the surface moving direction by the photosensitive drum 11Y. Scanned. As a result, an electrostatic latent image corresponding to the yellow component is formed on the photosensitive drum 11Y charged by the charging unit 12.

  Similarly, laser light as exposure light corresponding to the magenta component is irradiated on the surface of the second photosensitive drum 11M from the left in FIG. 1, and an electrostatic latent image corresponding to the magenta component is formed. Laser light as cyan component exposure light is applied to the surface of the third photosensitive drum 11C from the left in FIG. 1 to form an electrostatic latent image of cyan component. The black component laser light is applied to the surface of the fourth photosensitive drum 11BK from the left in FIG. 1 to form an electrostatic latent image of the black component.

  Thereafter, the surfaces of the photoconductive drums 11Y, 11M, 11C, and 11BK on which the electrostatic latent images of the respective colors are formed reach positions facing the developing unit 13, respectively. Then, the respective color toners are supplied from the developing units 13 onto the photosensitive drums 11Y, 11M, 11C, and 11BK, and the latent images on the photosensitive drums 11Y, 11M, 11C, and 11BK are developed (developing step).

  Thereafter, the surfaces of the photoconductive drums 11Y, 11M, 11C, and 11BK after the development process reach the portions facing the intermediate transfer belt 17, respectively. A primary transfer bias roller (not shown) is provided so as to contact the inner peripheral surface of the intermediate transfer belt 17 at each facing portion. The toner images of the respective colors formed on the photosensitive drums 11Y, 11M, 11C, and 11BK are sequentially superimposed and transferred onto the intermediate transfer belt 17 at a position where the primary transfer bias roller faces (primary transfer). Process).

  Then, the surfaces of the photosensitive drums 11Y, 11M, 11C, and 11BK after the primary transfer process reach positions facing the cleaning unit 15, respectively. Then, the untransferred toner remaining on the photosensitive drums 11Y, 11M, 11C, and 11BK is collected by the cleaning unit 15 (cleaning process). Thereafter, the surfaces of the photoconductive drums 11Y, 11M, 11C, and 11BK pass through a static eliminating unit (not shown), and a series of image forming processes on the photoconductive drums 11Y, 11M, 11C, and 11BK is completed.

  Thereafter, the intermediate transfer belt 17 on which the toner images of the respective colors are transferred in a superimposed manner reaches a position facing the secondary transfer roller 18. At this position, the secondary transfer backup roller 18 ′ sandwiches the intermediate transfer belt 17 between the secondary transfer roller 18 and forms a secondary transfer nip. The four-color toner images formed on the intermediate transfer belt 17 are transferred onto the recording paper P conveyed to the position of the secondary transfer nip (secondary transfer step). At this time, untransferred toner that has not been transferred to the recording paper P remains on the intermediate transfer belt 17.

  Thereafter, the intermediate transfer belt 17 reaches the position of the intermediate transfer belt cleaning unit 16. At this position, the intermediate transfer belt cleaning unit 16 cleans and collects the untransferred toner on the intermediate transfer belt 17. Thus, a series of transfer processes performed on the intermediate transfer belt 17 is completed.

  Here, the recording paper P conveyed to the position of the secondary transfer nip passes from the paper supply unit 7 disposed below the apparatus main body 10 via a conveyance path K1 in which a paper supply roller 8 and a registration roller are installed. It is what was conveyed. Specifically, a plurality of recording papers P are stored in the paper supply unit 7 in an overlapping manner. When the paper feed roller 8 is driven to rotate counterclockwise in FIG. 1, the uppermost recording paper P is fed toward the transport path K1.

  The recording paper P transported to the transport path K1 temporarily stops at the position of the roller nip of a registration roller (not shown) that has stopped rotating. Then, the registration roller is rotationally driven in time with the color image on the intermediate transfer belt 17, and the recording paper P is conveyed toward the secondary transfer nip. In this way, a desired color image in which a plurality of color toner images are superimposed is transferred onto the recording paper P.

  Thereafter, the recording paper P on which the color image has been transferred at the position of the secondary transfer nip is conveyed to the position of the fixing device 19. At this position, the recording sheet P is held between a fixing roller 20 as a heating fixing member and a pressure roller 30 as a pressing fixing member, which will be described later, and a color image transferred to the surface by heat and pressure is transferred. It is fixed on the recording paper P. Then, as shown in the direction of the broken line arrow in the figure, the recording paper P after the fixing process is discharged as an output image onto the output tray of the apparatus body 10 by the paper discharge roller 9, and a series of image forming processes is completed. To do.

Next, the configuration and operation of the fixing device 19 installed in the apparatus main body 10 of the copier 1 of the present embodiment will be described in detail.
FIG. 2 is a schematic configuration diagram showing an example of a fixing device provided in the copying machine according to the present embodiment.
As shown in FIG. 2, the fixing device 19 includes a fixing roller 20 as a heating fixing member, and a pressure as a pressure fixing member (pressure member) that presses against the fixing roller 20 to form a fixing nip portion Nf. And a roller 30. The fixing device 19 includes an induction heating unit 25 that is a magnetic flux generating unit that faces the outer peripheral surface of the fixing roller 20 and functions as a part of the heating unit. Further, the fixing device 19 includes an inlet guide plate 41, a spur guide plate 42, a separation guide plate 43, an outlet guide plate 50, a thermistor 61 as a fixing member temperature detecting means for pressurization, and a thermistor 62 as a fixing member temperature detecting means for heating. , Etc.

  Here, the fixing roller 20 is formed by sequentially laminating a heat insulating elastic layer 22 made of foamed silicone rubber or the like and a sleeve layer 21 on a core metal 23 made of, for example, iron or stainless steel, and has an outer diameter. It is molded to about 40 [mm].

  The sleeve layer 21 of the fixing roller 20 is, for example, a multilayer structure in which a base material layer, a first antioxidant layer, a heat generating layer, a second antioxidant layer, an elastic layer, and a release layer are sequentially laminated from the inner peripheral surface side. is there. Specifically, the base material layer is formed of stainless steel having a thickness of about 40 [μm], and the first antioxidant layer and the second antioxidant layer are strike-plated with nickel having a thickness of 1 [μm] or less. It is formed by processing. The heat generating layer is made of copper having a thickness of about 10 [μm], and the elastic layer is made of silicone rubber having a thickness of about 150 [μm]. Further, the release layer is formed of PFA (tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer) having a layer thickness of about 30 [μm].

  In the fixing roller 20 configured as described above, the heat generating layer of the sleeve layer 21 is electromagnetically heated by the magnetic flux generated from the induction heating unit 25. The configuration of the fixing roller 20 is not limited to that of the present embodiment. For example, the sleeve layer 21 can be separated without being bonded to the heat insulating elastic layer 22 (fixing auxiliary roller). However, when the sleeve layer 21 (fixing sleeve) is separated, it is preferable to install a member for preventing the sleeve layer 21 from moving in the width direction (thrust direction) during operation.

  At a position facing the fixing roller 20 and upstream of the fixing nip portion Nf in the recording paper conveyance direction, there are a plurality in the width direction (direction perpendicular to the paper surface of FIG. 2) parallel to the rotation axis of the fixing roller 20. A spur guide plate 42 in which the spurs are arranged in parallel is provided. The spur guide plate 42 is disposed at a position facing a fixing surface (surface on which an image is fixed) of the recording paper P fed into the fixing nip portion Nf, and guides the recording paper P to the fixing nip portion Nf. It is. The spur guide plate 42 is formed in a sawtooth shape so that the spur does not rub even if the spur contacts an unfixed image on the recording paper P.

  Further, separation is performed at a position facing the fixing roller 20 and a position facing the fixing surface of the recording paper P sent from the fixing nip portion Nf (a position downstream of the fixing nip portion Nf in the recording paper conveyance direction). A guide plate 43 is installed. The separation guide plate 43 is for preventing a problem that the recording paper P after the fixing process sent out from the fixing nip portion Nf is attracted to and wound around the fixing roller 20. That is, when the recording paper P after the fixing process is attracted to the fixing roller 20, the separation guide plate 43 comes into contact with the leading end of the recording paper P to forcibly separate the recording paper P from the fixing roller 20. . Here, in the illustrated example, the separation guide plate 43 has a predetermined gap between its tip and the surface of the fixing roller 20 so that the tip of the separation guide plate 43 does not touch and damage the surface of the fixing roller 20. In addition, the fixing roller 20 is disposed in a non-contact manner. Note that the separation guide plate 43 may be disposed in contact with the surface of the fixing roller 20 so that the tip thereof does not damage the surface of the fixing roller 20.

  A thermistor 62 serving as a fixing member temperature detecting means for heating is disposed at a position upstream of the fixing nip portion Nf in the recording sheet conveyance direction and close to the fixing nip portion Nf. The thermistor 62 is a contact-type temperature detection sensor that comes into contact with the fixing roller 20, and opposes the width direction end on the rotation drive unit side of both ends in the width direction (rotation axis direction) of the outer peripheral surface of the fixing roller 20. The surface temperature of the end portion in the width direction of the fixing roller 20 is detected.

  Further, a thermopile (not shown) as a fixing member temperature detecting means for heating is disposed at a position facing the central portion in the width direction of the fixing roller 20. The thermopile is a non-contact temperature detection sensor and is an element that measures the temperature of an object from infrared rays emitted from the object. The infrared rays emitted from the object are absorbed by the heat conversion film inside the thermopile and converted to heat. Thereafter, the temperature is detected by a large number of micro thermocouples formed on the heat conversion film. Then, the temperature on the fixing roller 20 (fixing temperature) is detected by the thermistor 62 and the thermopile, and the heating amount by the induction heating unit 25 is adjusted based on the detection result by the thermistor 62 and the thermopile. In the present embodiment, the induction heating unit 25 is controlled so that the fixing temperature during the fixing process (at the time of paper passing) becomes a predetermined target temperature setting value (for example, 160 to 165 [° C.]). ing.

  In FIG. 2, a pressure roller 30 as a pressure fixing member (pressure member) includes, for example, a cylindrical member 32 made of steel, aluminum, etc., an elastic layer 31 made of silicone rubber, and PFA. A release layer (not shown) is formed. The elastic layer 31 of the pressure roller 30 is formed to have a thickness of 1 to 5 [mm], for example. The release layer of the pressure roller 30 is formed so that the layer thickness is, for example, 20 to 200 [μm]. The pressure roller 30 is in pressure contact with the fixing roller 20. Then, the recording paper P is conveyed to a fixing nip portion Nf) where the fixing roller 20 and the pressure roller 30 are in pressure contact with each other.

  In this embodiment, in order to increase the heating efficiency of the fixing roller 20, the pressure roller 30 is provided with a heater 33 such as a halogen heater as a heating unit. By supplying electric power to the heater 33, the pressure roller 30 is heated by the radiant heat of the heater 33, and the surface of the fixing roller 20 is heated via the pressure roller 30.

  A thermistor 61 as a pressure fixing member temperature detecting means for contacting the pressure roller 30 is disposed at a position upstream of the fixing nip portion Nf in the recording sheet conveyance direction and close to the fixing nip portion Nf. It is installed. The thermistor 61 is a contact-type temperature detection sensor, and is disposed at the end in the width direction of the pressure roller 30 on the rotation drive unit side, and detects the surface temperature of the end in the width direction of the pressure roller 30.

  In addition, a thermopile (non-contact type temperature detection sensor) (not shown) as a pressure fixing member temperature detection means is disposed at a position facing the central portion in the width direction of the pressure roller 30. Then, the temperature on the pressure roller 30 is detected by the thermistor 61 or the thermopile, and the heating amount by the heater 33 is adjusted based on the detection result by the thermistor 61 or the thermopile.

  Here, a position facing the pressure roller 30 and a position facing the non-fixing surface of the recording paper P fed into the fixing nip portion Nf (position upstream of the fixing nip portion Nf in the recording paper conveyance direction). Is provided with an inlet guide plate 41. The inlet guide plate 41 guides the recording paper P fed into the fixing nip portion Nf to the fixing nip portion Nf.

  Further, at a position facing the pressure roller 30 and facing the non-fixing surface of the recording paper P sent from the fixing nip portion Nf (a position downstream of the fixing nip portion Nf in the recording paper conveyance direction). The exit guide plate 50 is installed. The exit guide plate 50 is for guiding the recording paper P after the fixing process sent from the fixing nip portion Nf toward the conveyance path after the fixing process.

  The induction heating unit 25 includes a coil unit 26 such as an excitation coil, a core unit 27 such as an excitation coil core, a coil guide 28, and the like. The coil portion 26 is wound in the width direction (direction perpendicular to the paper surface of FIG. 2) by winding a litz wire bundled with thin wires on a coil guide 28 disposed so as to cover a part of the outer peripheral surface of the fixing roller 20. It is an extension.

  The coil guide 28 is made of, for example, a highly heat-resistant resin material such as PET (polyethylene terephthalate) containing about 45% of a glass material, and holds the coil portion 26 facing the outer peripheral surface of the fixing roller 20. . In the present embodiment, the gap between the opposing surface of the coil guide 28 of the induction heating unit 25 and the outer peripheral surface of the fixing roller 20 is set to 2 ± 0.1 [mm].

  The core portion 27 is made of a ferromagnetic material such as ferrite (relative magnetic permeability: about 2500), for example, and forms an efficient magnetic flux toward the heat generating layer of the fixing roller 20, and includes an arch core, a center core, It consists of a side core.

  The induction heating unit 25, the coil unit 26, the core unit 27, the coil guide 28, and the sleeve layer 21 of the fixing roller 20 described above function as a fixing member heating unit for heating.

  In the present embodiment, the induction heating unit 25 is disposed on the side opposite to the pressure roller side of the fixing roller 20 (the side on the left side in FIG. 2).

  The fixing device 19 having the above configuration operates as follows, for example. The fixing roller 20 is driven to rotate counterclockwise in FIG. 2 by a driving motor (not shown) as a driving source, and the pressure roller 30 rotates clockwise accordingly. The sleeve layer 21 (heat generation layer) of the fixing roller 20 is heated by the magnetic flux generated from the induction heating unit 25 at a position facing the induction heating unit 25.

  More specifically, for example, a high-frequency alternating current of 10 [kHz] to 1 [MHz] (preferably 20 [kHz] to 800 [kHz]) is supplied from a power supply unit (not shown) including a frequency variable oscillation circuit to the coil unit 26. Energized. As a result, the magnetic lines of force are alternately switched in both directions from the coil portion 26 toward the sleeve layer 21 of the fixing roller 20. By forming the alternating magnetic field in this way, an eddy current is generated in the heat generating layer of the sleeve layer 21, and the heat generating layer generates Joule heat due to its electric resistance and is inductively heated. Thus, the sleeve layer 21 (fixing roller 20) is heated by induction heating of its own heat generation layer.

  Thereafter, the surface of the fixing roller 20 heated by the induction heating unit 25 reaches the fixing nip portion Nf where the pressure roller 30 is in contact. Then, the toner image T (toner) on the conveyed recording paper P is heated and melted.

  More specifically, the recording paper P carrying the toner image T through the image forming process (image forming process) described above, as shown in the conveyance direction indicated by the arrow Y1 in FIG. The sheet is fed into the fixing nip portion Nf between the fixing roller 20 and the pressure roller 30 while being guided by the plate 42). Then, the toner image T is fixed on the recording paper P by the heat received from the fixing roller 20 and the pressure received from the pressure roller 30, and the recording paper P is fixed to the fixing roller 20 as shown in the conveying direction of the arrow Y2 in FIG. And the pressure roller 30.

  The surface of the fixing roller 20 that has passed through the fixing nip portion Nf then reaches the position facing the induction heating unit 25 again.

  The series of operations as described above are continuously repeated to complete the fixing step in the image forming process (image forming process).

  In the fixing device 19 of the present embodiment, the configuration using the electromagnetic induction heating method as the heating method of the fixing roller 20 has been described. However, the present invention is not limited to this, and a heater heating method using a halogen heater or the like is used. May be. Further, at least one of the fixing roller 20 and the pressure roller 30 is not limited to a roller-like rotating body, and may be an endless belt-like rotating body, or a belt fixing device using an endless belt that has been proposed conventionally. Good. The fixing device 19 of this embodiment is an example, and does not limit the form of the fixing device to which the present invention can be applied.

  In the copying machine 1 of the present embodiment, if the fixing temperature is too high when the image leading edge of the recording paper P passes through the fixing nip Nf of the fixing device 19, the toner is likely to melt. The melted toner sticks between the recording paper P and the fixing roller 20 like an adhesive, and the recording paper P may be wound around the fixing roller 20. In addition, even when the amount of toner attached to the leading edge of the image is large, there is a possibility that similar wrapping may occur with the melted toner. In particular, when the recording paper P is a thin paper having a small weight per unit area, the winding is likely to occur.

Therefore, in the copying machine 1 of the present embodiment, when the front end portion of the recording paper P in the transport direction is separated from the surface of the fixing roller 20 with respect to the front end portion of the recording paper P in the transport direction or the vicinity thereof. Control is performed by the above-described control means so as to change the image forming condition that affects the separation of the image. Specifically, when the basis weight [g / m ² ], which is the mass per 1 [m ² ], of the recording paper P that is an image formation target (fixing process target) is equal to or less than a preset first threshold value, the recording is performed. It is determined that the paper P is thin paper. Then, the target value of the fixing temperature of the fixing roller 20 with respect to the image leading edge margin of the recording paper P (hereinafter referred to as “fixing target temperature”) is lowered, or the toner adhesion amount at the leading edge of the image is reduced. As described above, the image forming conditions are changed. As a result, the recording device P is prevented from being wound around the fixing roller 20 by the fixing device 19, and jamming of the recording paper P is prevented.

First, temperature control for lowering the fixing temperature for the image leading edge margin of the recording paper P will be described.
FIG. 3 is a plan view for explaining a blank area of the recording paper P. FIG. For the image forming area G surrounded by the one-dot chain line in FIG. 3, the margin on the leading side in the transport direction of the recording paper P is the leading edge margin a, and the margin on the trailing end in the transport direction is the trailing image margin b. Call. Of the margins at both ends in the width direction orthogonal to the conveyance direction of the recording paper P, the margin on the right side in the width direction is referred to as an image right end margin portion c, and the margin on the left side in the width direction is referred to as an image left end margin portion d.

Table 1 shows an example of the fixing target temperature for each paper type (paper thickness) of the recording paper P and the correction temperature of the leading edge margin of the image. In Table 1, the paper thickness is classified by basis weight [g / m ² ], which is the mass per square meter. In order to obtain the basis weight of the recording paper P actually used on the copying machine side, for example, the user can select from a plurality of basis weights displayed on the operation display panel, or the user can directly input a numerical value. Or enter. Further, the thickness of the recording paper P is measured by a laser displacement meter inside the copying machine, or the mass of the recording paper P per 500 sheets is measured by a mass measuring device (for example, a digital scale) in the paper feeding unit 7. May be.

In this embodiment, as shown in Table 1, the paper thickness is defined by the basis weight, which is the mass per unit area, and specifically, the recording paper P having a basis weight of 52 to 59 [g / m ² ]. Is "thin paper". That is, the recording paper P whose basis weight is not more than the first threshold value (59 [g / m ² ]) is defined as “thin paper”. Similarly, the recording paper P with a basis weight of 60 to 81 [g / m ² ] is “plain paper”, the recording paper P with a basis weight of 82 to 169 [g / m ² ] is “thick paper 1”, and the basis weight is 170-220 the recording paper P [g / ^{m 2]} "thick 2" basis weight to the recording paper P of 221~256 [g / ^{m 2]} and "thick paper 3".

  The set temperature in Table 1 is a set value of a fixing target temperature set as a target in advance for each paper type, and the detection results of the thermistor 62 and the thermopile so that the surface of the fixing roller 20 becomes this set temperature. The induction heating unit 25 is controlled based on the above. Specific set temperatures are 160 [° C.] for thin paper, 165 [° C.] for plain paper, 175 [° C.] for thick paper 1, 185 [° C.] for thick paper 2, and for thick paper 3 195 [° C.].

  Further, the image leading edge margin correction temperature in Table 1 means that the image leading margin portion a of the recording paper P passes through the fixing nip portion Nf of the fixing device 19 in order to prevent the recording paper P from being wound around the fixing roller 20. The fixing temperature [° C.] corrected with respect to the target temperature of the surface of the fixing roller 20 when passing. In the present embodiment, only when the recording paper P is thin, the fixing temperature corrected for the image leading edge margin a is set. For example, if the correction value is 5 [° C.], 155 [° C.] lower by the correction value 5 [° C.] than the set temperature of 160 [° C.] is set as the fixing temperature for the leading edge margin a. On the other hand, in the case of other plain papers and thick papers 1 to 3, the fixing temperature is not corrected for the image leading edge margin a.

  FIG. 4 is a graph for explaining the change over time in the target temperature when plain paper and thin paper are passed as the recording paper P. FIG. 4 shows an example in which two sheets of thin paper are continuously passed after the plain paper is passed, and then one plain paper is passed.

  As shown in FIG. 4, the target temperature is maintained at 165 [° C.] during the passing of plain paper. Then, after the plain paper is passed, information on the next image forming job is acquired. When the next image forming job is two continuous thin sheets and the width of the leading edge margin a of the recording paper is, for example, 5 [mm], the correction value from the normal target temperature is, for example, 5 [° C.]. . Therefore, the target temperature is changed to 155 [° C.] obtained by subtracting the correction value 5 [° C.] from the normal target temperature 160 [° C.] for thin paper. Thereby, the temperature control of the induction heating unit 25 is performed so that the temperature detected by the thermistor 62 and the thermopile that detect the temperature of the surface of the fixing roller 20 is 155 [° C.]. Although the correction value is 5 [° C.], the correction value is an appropriate value within 10 [° C.] in consideration of the temperature following after the margin at the image leading edge due to the difference in heat capacity of the fixing device 19. It is preferable to set.

  After the surface of the fixing roller 20 reaches 155 [° C.] which is the corrected fixing target temperature, the thin paper onto which the toner has been transferred enters the fixing nip portion Nf of the fixing device 19. The fixing target temperature is switched to 160 [° C.] at the timing when the thin paper image leading edge portion a passes through the fixing nip portion Nf. Thereby, the temperature control of the induction heating unit 25 is performed so that the temperature detected by the thermistor 62 and the thermopile that detect the temperature of the surface of the fixing roller 20 is 160 [° C.]. By this temperature control, the temperature of the surface of the fixing roller 20 becomes 160 [° C.]. Thereby, in the image forming area G of the recording paper P, the fixing process is performed at the normal fixing target temperature of the thin paper.

  Since the thin paper is continuously fixed, the fixing target temperature is lowered to 155 [° C.] after passing the thin paper of the preceding image forming job, and the image leading edge portion a of the recording paper P is set to the fixing nip portion Nf of the fixing device 19. Let it pass. The fixing target temperature is switched to 160 [° C.] at the timing when the image leading edge margin “a” of the thin paper passes through the fixing nip portion Nf, and in the image forming region G, the fixing process is performed at the fixing target temperature of the normal thin paper.

  Then, after the fixing of the two thin sheets is completed, information on the next image forming job is acquired. Since the next image forming job is plain paper, fixing is performed by switching the fixing target temperature to 165 [° C.]. Note that the information of the next image forming job is acquired after the preceding recording paper P is passed, but may be acquired before or during the passing of the preceding recording paper P.

  As described above, when the recording paper P is thin, the fixing target temperature of the image leading edge margin a is corrected, and fixing is performed at a temperature lower than the normal fixing target temperature. As a result, the curl along the curvature of the fixing roller 20 does not easily occur at the image leading edge margin “a” of the thin paper, and the leading end of the thin paper that has passed through the nip portion of the fixing device 19 is peeled off from the surface of the fixing roller 20 favorably. Can be prevented.

  In addition, since the image leading edge margin a of the recording paper P passes through the nip portion of the fixing device 19 and is switched to the normal fixing target temperature, there is a time lag for the surface of the fixing roller 20 to rise to the fixing target temperature. An excessive amount of heat is not supplied to the toner in the vicinity of the image leading edge margin a. For this reason, it is possible to suppress the adhesion between the recording paper P and the fixing roller 20 due to the melting of the toner, and to prevent the winding.

  Furthermore, after the image leading edge margin a of the thin paper passes through the nip portion of the fixing device 19, the temperature is raised and returned to the normal fixing target temperature, so that fixing failure due to insufficient fixing heat can be prevented.

  Next, in order to prevent the recording paper P from being wrapped around the fixing roller 20, when the recording paper P is a thin paper, control for reducing the amount of toner attached to the leading edge of the image will be described.

Table 2 shows an example of the toner 2C adhesion amount and the image leading edge 2C adhesion amount for each paper type (paper thickness) of the recording paper P. In Table 2, the adhesion amount of the image leading edge 2C is the toner adhesion amount [mg / cm ² ] per square centimeter at the image leading edge portion a ′ downstream from the image leading edge margin portion a shown in FIG. That means. The width of the image front end a ′ is, for example, about 1 to 10 [mm], and more preferably 3 to 6 [mm].

As shown in Table 2, the 2C adhesion amount is 0.85 ± 0.05 [mg / cm ² ] for all paper types. However, the image tip 2C adhesion amount differs from other paper types as an amount obtained by subtracting the correction amount for only thin paper. For example, the correction amount is 0.1 [mg / cm ² ], and the image tip 2C adhesion amount of thin paper is 0.75 ± 0.05 [mg / cm ² ].

  By reducing the toner adhesion amount at the image leading edge a ′ of the recording paper P, the adhesive force of the toner is weakened, and the melted toner generated when the toner adhesion amount is large, like the adhesive, the recording paper P and the fixing roller 20. It is possible to prevent winding defects that are stuck between the two.

Note that the correction amount of the toner adhesion amount is preferably 0.1 [mg / cm ² ] or less so that the difference in glossiness does not occur between the portion where the toner adhesion amount is reduced and the portion where the toner adhesion amount is not.

  Here, in this embodiment, when the temperature of the pressure roller 30 during paper passing is high, the amount of heat applied from the pressure roller 30 to the fixing roller 20 is large, and the fixing target temperature during paper passing of the fixing roller 20 is lowered. However, the toner image is fixed on the recording paper P by the contribution of the heat amount from the pressure roller 30. At this time, even if the temperature control for lowering the fixing target temperature on the surface of the fixing roller 20 at the image leading edge margin a of the recording paper P is performed, the temperature of the fixing roller 20 surface does not decrease as intended, and the winding of the recording paper P is effectively performed. There is a risk that it cannot be prevented.

  As a result of extensive studies by the present inventors, it has been found that the winding of the recording paper P can be prevented by lowering the fixing target temperature of the fixing roller 20 in accordance with the temperature of the pressure roller 30.

  FIG. 5 is a graph showing temporal changes in each temperature when the fixing target temperature of the fixing roller 20 is changed according to the temperature of the pressure roller 30. In FIG. 5, when the detected temperature of the pressure roller 30 exceeds the pressure temperature threshold Tth, which is a predetermined second threshold, an increase from the pressure temperature threshold Tth is ΔT. The range in which the fixing target temperature of the fixing roller 20 can be lowered is a value obtained by multiplying the temperature ΔT of the increase from the temperature at which the temperature of the pressure roller 30 becomes the pressure temperature threshold Tth by the correction coefficient C. The pressurization temperature threshold Tth and the correction coefficient C can be changed as appropriate by the designer. When the winding due to the high temperature of the fixing roller 20 occurs, the pressurization temperature threshold Tth or the correction coefficient C is changed to fix the fixing temperature. It is preferable to lower the temperature of the fixing roller 20 within a range that can ensure the above.

  In this embodiment, when the recording paper P having a small basis weight such as thin paper is passed, if the temperature of the pressure roller 30 is low, the amount of heat given from the pressure roller 30 to the fixing roller 20 is expected. Because it is not possible, the target temperature during paper feeding cannot be lowered. For this reason, it is conceivable that the recording paper P is likely to be wound around the fixing roller 20. In view of this, the present inventors have intensively studied. When the temperature of the pressure roller 30 is low when passing thin paper, a margin that exceeds a predetermined amount during image forming operation is provided. It has been found that the winding of the recording paper P can be prevented without lowering the temperature and productivity.

  Table 3 shows an example of the margin width defined for each paper type (paper thickness) of the recording paper P. Table 4 shows an example of the margin width defined in more detail for thin paper.

In Table 3, for the plain paper and the thick papers 1 to 3 whose basis weight, which is the mass per unit area of the recording paper P, exceeds 59 [g / m ² ] which is the first threshold, the recording paper P is conveyed. The widths of the image leading edge margin a and the image trailing edge margin b (see FIG. 3) in the direction (sub-scanning direction when forming a latent image) are each defined as 0 to 3 [mm]. On the other hand, for thin paper having a basis weight of 59 [g / m ² ] that is easy to wind around the fixing roller 20 and having the first threshold value of 59 [g / m ² ], the image leading edge margin a and the trailing edge margin of the recording paper P are used. The margin width of the part b is 3 to 5 [mm], respectively, which is larger than other paper types. That is, for the thin paper, the width of the image leading edge margin portion a and the image trailing edge margin portion b of the recording paper P is secured to be as large as 3 to 5 [mm]. Since no toner image is formed in the margin, it is possible to prevent the recording paper P from being caught due to adhesion between the recording paper P and the fixing roller 20 due to melting of the toner.

  Note that the widths of the image right end margin portion c and the image left end margin portion d (see FIG. 3) on both ends in the width direction orthogonal to the conveyance direction of the recording paper P (main scanning direction during latent image formation) are also described above. By defining the same value as the image leading edge margin a and the image trailing edge margin b, it is possible to reliably prevent winding of the recording paper P in the width direction.

  Note that the upper limit of the width of the leading edge margin a and the trailing edge margin b of the thin paper is defined as 5 [mm] for the following reason. That is, when the width of the image leading edge portion a and the image trailing edge margin portion b is larger than 5 [mm], even if the winding margin of the image leading edge portion a is increased, the image surface is on the trailing edge margin side. This is because the margin for winding the trailing edge margin becomes smaller. By setting the upper limit of the width of the image leading edge margin “a” to 5 [mm], the image trailing edge margin “b” becomes 3 [mm] or more at the image trailing edge margin “b” as shown in Table 4. The winding of the leading edge margin a and the trailing edge margin b of the image is eliminated. In the example shown in Table 4, the sum of the width of the image leading edge margin portion a and the width of the image trailing edge margin portion b secures a value of 6 to 8 [mm] or more. Further, the thin paper is further finely divided according to the basis weight (mass per unit area) to define the prescribed amount of the margin in the sub-scanning direction, the width of the leading margin, and the width of the trailing margin. By ensuring the width of the trailing edge margin of 3 [mm] or more, it is effective to prevent the recording paper P from being wound around the pressure roller 30 when performing reverse printing in double-sided printing on the same recording paper P. is there.

What has been described above is merely an example, and the present invention has a specific effect for each of the following modes.
(Aspect A)
A toner image forming unit such as a photosensitive drum 11 and a developing unit 13 that forms a toner image on a recording medium such as recording paper P, and a recording medium on which the toner image is formed are conveyed to a heated fixing roller 20. An image forming apparatus such as the copying machine 1 including a fixing unit such as a fixing device 19 that fixes a toner image on a recording medium by contacting the fixing member such as a thickness of the recording medium. Based on the related information, a control unit such as a control unit that controls to change the image forming condition that affects the separation property when the portion on the leading end side in the conveyance direction of the recording medium separates from the surface of the fixing member is provided.
According to this, as described in the above embodiment, based on the thickness-related information related to the thickness of the recording medium, the separation property when the portion on the leading end side in the conveyance direction of the recording medium is separated from the surface of the fixing member. Change image forming conditions that affect As a result, according to the thickness of the recording medium, the adhesive force of the toner at the front end portion in the conveyance direction of the recording medium can be adjusted to a level that does not cause the recording medium to be wound around the fixing member. Therefore, even when the image forming target recording medium is a thin recording medium having a small heat capacity, it is possible to maintain good separation of the recording medium from the fixing member. In addition, in order to maintain the separation property of the recording medium from the fixing member, it is not necessary to increase the conveyance interval of a plurality of recording media on which images are continuously formed, so that the productivity of the image-formed recording medium is reduced. There is nothing. Therefore, even if the recording medium has a small heat capacity, it is possible to maintain good separation of the recording medium from the fixing member without reducing the productivity of the recording medium on which the image has been formed.
(Aspect B)
In the aspect A, the thickness-related information of the recording medium such as the recording paper P is information on the mass (basis weight) per unit area of the recording medium, and the control unit is configured to determine the mass per unit area of the recording medium. Based on the value, the condition that affects the separation property when the portion on the leading end side in the conveyance direction of the recording medium separates from the surface of the fixing member is changed.
According to this, as described in the above embodiment, the condition affecting the separation property is changed based on the mass value per unit area of the recording medium that is easily quantified as the thickness-related information of the recording medium. Accordingly, it is possible to maintain the separation property of the recording medium having a small heat capacity from the fixing member with higher accuracy.
(Aspect C)
In the above aspect A or B, the image forming condition changed by the control means is at least one of the toner adhesion amount by the toner image forming means and the temperature at the fixing means with respect to the image portion on the leading end side in the conveyance direction of the recording medium such as recording paper P It is.
According to this, as described in the above embodiment, in the case of a recording medium having a small heat capacity, at least one of the toner adhesion amount by the toner image forming unit and the temperature at the fixing unit with respect to the image portion at the leading end side in the conveyance direction of the recording medium. By changing the above, it is possible to more reliably maintain the separation of the recording medium from the fixing member.
(Aspect D)
In the above aspect C, the fixing unit includes a heating fixing member such as the fixing roller 20, a pressure fixing member such as the pressure roller 30 that presses the heating fixing member to form the nip portion Nf, and a heating member. A heating unit such as an induction heating unit 25 and a coil unit 26 for heating the fixing member, and a temperature detection unit such as a thermistor 62 for detecting the temperature of the heating fixing member, and setting of a target temperature of the heating fixing member A storage means such as a semiconductor memory for storing the value is further provided, and the control means detects the mass per unit area (basis weight) of the recording medium such as the recording paper P by the temperature detection means when it is equal to or less than the first threshold value. The heating temperature of the heating means when the portion on the front side in the conveyance direction of the recording medium passes through the nip portion Nf is controlled so that the temperature of the heated fixing member is lower than the set value of the target temperature.
According to this, as described in the above embodiment, in the case of a recording medium having a small heat capacity, the temperature of the heating fixing member is controlled to be lower than usual, so that there is no gap between the recording medium and the heating fixing member. The adhesive strength of the toner is weakened, and the recording paper P can be prevented from being wrapped around the heating fixing member.
(Aspect E)
In the above aspect D, the fixing unit further includes a temperature detection unit such as a thermistor 61 that detects the temperature of a pressure fixing member such as the pressure roller 30, and the control unit includes a recording medium such as a recording sheet P. When the mass per unit area (basis weight) is equal to or less than the first threshold value, the temperature of the fixing member for heating such as the fixing roller 20 is controlled to be lowered according to the detection result of the temperature of the fixing member for pressure.
According to this, as described in the above embodiment, by controlling the temperature of the heating fixing member in consideration of the temperature of the pressure fixing member, the heating fixing member and the pressure fixing member can be controlled. An excessive amount of heat is not supplied to the nip portion Nf, so that an increase in toner adhesive force can be prevented, and winding of the recording medium around the heating fixing member can be more reliably prevented.
(Aspect F)
In the above aspect E, when the temperature detection result of the pressure fixing member such as the pressure roller 30 exceeds the second threshold value, the control means records the recording paper P with respect to the temperature exceeding the second threshold value. The correction temperature is calculated by performing correction according to the mass (basis weight) per unit area of the recording medium, and the temperature of the heating fixing member such as the fixing roller 20 becomes lower than the set value of the target temperature by the correction temperature. As described above, the heating temperature of the heating fixing member is controlled.
According to this, as described in the above embodiment, the amount of heat supplied to the nip portion Nf between the heating fixing member and the pressure fixing member can be accurately controlled, and the recording medium is wound around the heating fixing member. It is possible to prevent more reliably and to prevent fixing defects such as toner peeling due to insufficient heat.
(Aspect G)
In aspect E, the control means has a mass (basis weight) per unit area of a recording medium such as recording paper P that is equal to or lower than a first threshold value, and a temperature of a pressure fixing member such as a pressure roller 30. If the detection result is smaller than the second threshold value, the toner image forming means is controlled so as to widen the width of the leading edge margin a where no image is formed on the leading edge side in the conveyance direction of the recording medium.
According to this, as described in the above embodiment, there is no toner in the leading edge margin a of the recording medium, and no toner adhesive force is generated in the leading edge margin, so that the width of the leading margin is widened. Thus, it is possible to more reliably prevent the recording medium from being wound around the heating fixing member. In particular, when the temperature of the pressure fixing member is low when passing a thin paper as the recording medium through the nip portion Nf, the width of the leading edge margin portion exceeding a predetermined specified amount during the image forming operation is set. Winding can be effectively prevented.
(Aspect H)
In the above aspect G, the control means includes the width of the leading edge margin a where no image is formed on the leading side in the transport direction of the recording medium such as recording paper P, and the trailing edge margin where no image is formed on the trailing end in the transport direction of the recording medium. Control is performed so as to increase the width of the leading edge margin within a range in which the sum of the width of the portion b is equal to or greater than a predetermined lower limit value.
According to this, as described in the above embodiment, widening the margin at the leading edge margin is effective for preventing wrapping, but if it is too wide, the image formed on the recording medium is shifted to the rear side and the trailing margin is formed. The width of the portion b is shortened, and there is a risk that winding will occur when an image is formed on the second surface (back surface) during double-sided image formation. By making the sum of the width of the leading edge margin “a” and the width of the trailing edge margin “b” of the recording medium equal to or greater than a predetermined lower limit value, the width of the leading edge margin that prevents the recording medium from being wrapped at the leading end side in the transport direction is sufficiently large In addition, it is possible to secure the width of the trailing edge margin portion that prevents the recording medium from being wound on the trailing edge side in the conveyance direction.
(Aspect I)
In any one of the above aspects C to H, the control unit is configured such that when the mass (basis weight) per unit area of the recording medium such as the recording paper P is equal to or less than the first threshold value, the image portion on the leading end side in the conveyance direction of the recording medium The toner image forming unit is controlled such that the toner adhesion amount with respect to the toner is less than the toner adhesion amount with respect to a portion other than the image portion on the leading end side in the transport direction.
According to this, as described in the above embodiment, in the case of a recording medium having a small heat capacity, the toner adhesion amount between the recording medium and the heat fixing member is weakened by reducing the toner adhesion amount at the leading end portion of the image. Thus, it is possible to reliably prevent the recording medium from being wound around the heat fixing member.

  In the above-described embodiment, an example in which the present invention is applied to a tandem type color copying machine including a fixing device has been described. However, the embodiment of the present invention is not limited to this example. For example, the present invention can be applied to other types of image forming apparatuses such as color copiers and black and white copiers as long as they include a fixing device. The present invention can also be applied to an image forming apparatus such as a printer, a facsimile, and a multifunction machine having these functions in addition to a copying machine.

DESCRIPTION OF SYMBOLS 1 Color copier 2 Optical writing part 4 Original reading part 7 Paper feeding part 10 Main body 11 (11Y, 11M, 11C, 11BK) Photosensitive drum 13 Developing part 16 Intermediate transfer belt cleaning part 17 Intermediate transfer belt 19 Fixing apparatus 20 Fixing Roller 21 Sleeve layer 25 Induction heating part 26 Coil part 27 Core part 30 Pressure roller 33 Heater 61 Thermistor (for temperature detection of pressure roller)
62 Thermistor (for detecting the temperature of the fixing roller)
a image leading edge margin b image trailing margin margin C correction coefficient G image forming area P recording sheet Tth temperature threshold

JP 2005-173486 A JP 2006-38920 A

Claims (9)

Toner image forming means for forming a toner image on a recording medium;
A fixing unit configured to fix the toner image on the recording medium by bringing the recording medium on which the toner image is formed and being conveyed into contact with a heated fixing member;
Based on thickness-related information related to the thickness of the recording medium, control is performed so as to change the image forming condition that affects the separation property when the portion on the leading end side in the conveyance direction of the recording medium is separated from the surface of the fixing member. An image forming apparatus comprising control means for performing The image forming apparatus according to claim 1.
The thickness-related information of the recording medium is information on the mass per unit area of the recording medium,
The control unit changes a condition that affects a separation property when a portion of the recording medium in the conveyance direction front end side separates from the surface of the fixing member based on a mass value per unit area of the recording medium. An image forming apparatus. The image forming apparatus according to claim 1 or 2,
The image forming condition to be changed by the control unit is at least one of a toner adhesion amount by the toner image forming unit and a temperature in the fixing unit with respect to an image portion on the leading end side in the conveyance direction of the recording medium. apparatus. The image forming apparatus according to claim 3.
The fixing unit includes a heating fixing member, a pressure fixing member that presses against the heating fixing member to form a nip portion, a heating unit that heats the heating fixing member, and a temperature of the heating fixing member Temperature detecting means for detecting
A storage means for storing a set value of a target temperature of the heating fixing member;
When the mass per unit area of the recording medium is equal to or less than a first threshold, the control unit is configured so that the temperature of the heating fixing member detected by the temperature detection unit is lower than the set value of the target temperature. An image forming apparatus characterized by controlling a heating temperature of the heating means when a portion of the recording medium in the transport direction passes through the nip portion. The image forming apparatus according to claim 4.
The fixing means further includes a temperature detecting means for detecting the temperature of the pressing fixing member,
When the mass per unit area of the recording medium is equal to or less than a first threshold, the control unit controls the temperature of the heating fixing member to be lowered according to the temperature detection result of the pressure fixing member. An image forming apparatus. The image forming apparatus according to claim 5.
When the detection result of the temperature of the pressure fixing member exceeds a second threshold, the control means corrects the temperature exceeding the second threshold according to the mass per unit area of the recording medium. And calculating a correction temperature, and controlling the heating temperature of the heating fixing member so that the temperature of the heating fixing member is lower than the set value of the target temperature by the correction temperature. Forming equipment. The image forming apparatus according to claim 5.
When the mass per unit area of the recording medium is equal to or less than a first threshold value and the detection result of the temperature of the pressure fixing member is smaller than a second threshold value, the control means transports the recording medium. An image forming apparatus, wherein the toner image forming unit is controlled so as to widen a width of a front end margin portion where no image is formed on the front end side. The image forming apparatus according to claim 7.
The control means is configured such that the sum of the width of the leading edge blank portion where no image is formed on the leading edge side in the conveyance direction of the recording medium and the width of the trailing edge margin portion where no image is formed on the trailing edge side in the conveyance direction of the recording medium An image forming apparatus, wherein the width of the leading edge margin portion is controlled to be widened within a range equal to or greater than a lower limit value. The image forming apparatus according to any one of claims 3 to 8,
When the mass per unit area of the recording medium is equal to or less than the first threshold, the control means is configured such that the amount of toner attached to the image portion on the leading side in the transport direction of the recording medium is other than the image portion on the leading side in the transport direction. An image forming apparatus, wherein the toner image forming unit is controlled so as to be less than a toner adhesion amount to a portion.

Images