JP2005345672A - Fixing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a uniform nip shape by restraining the deflection of a belt tensioning and laying member to the utmost, by making the tension of a belt uniform in the axial direction. <P>SOLUTION: The fixing device is equipped with a heating roller, a pressure roller 2 pressed on the heating roller, the belt tensioning and laying member 4 arranged on an upstream side in a paper transporting direction with respect to the pressure roller and disposed on the pressure roller via a tension spring, and a belt wound around the outer circumferences of the pressure roller and the belt tensioning and laying member and moving, in a state where a fixing nip is formed between the heating roller and the belt. The shape of the pressure roller is a crown shape, and the shape of the belt tensioning and laying member is made the shape that the wound circumference of the belt in the axial direction is the same. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a heating roller, a pressure roller that presses against the heating roller, a belt that is attached to the outer periphery of the pressure roller and moves while being sandwiched between the heating roller, and the belt is stretched. The present invention relates to a fixing device that includes a belt stretching member and fixes an unfixed toner image formed on a sheet material.

  In image forming apparatuses such as copying machines, printers, and facsimiles, as a heating roll type fixing apparatus that heats and fixes an unfixed toner image on a transfer material, the surface is covered with an elastic body and can be rotated with a built-in heating source. A heating roller, a belt stretched by a plurality of support rollers, and a belt is wound around the heating roll by a predetermined angle to form a nip region, and at the outlet of the nip region, a pressure larger than other portions is locally applied. In addition, there has been proposed a fixing device (see Patent Document 1) that is provided with a pressure unit that causes distortion on the elastic body on the surface of the heat fixing roll, and facilitates the discharge of the sheet material from the nip portion.

  In this conventional fixing device, since the surface of the heat fixing roller has a distortion due to the presence of the pressure means, the toner is in contact with the surface of the heat fixing roller at the exit of the nip region. The surface distortion is instantaneously released. For this reason, when the sheet material is discharged from the nip portion, the adhesion force between the toner and the heat fixing roller is reduced to suppress the sheet material from being wound around the heat fixing roller. Can be easily peeled off. In this way, the above-mentioned apparatus eliminates the peeling claw that has been conventionally required.

  However, in the fixing device structure disclosed in Patent Document 1, a movable belt stretched around a plurality of support rollers is wound around a heating roll by an angle capable of forming a nip by a pressure unit, and locally at the outlet of the nip region. Since it is driven by applying a large pressure, a plurality of support rolls and their rotary bearings are required. In addition, the circumference of the belt is lengthened, and the fixing device is complicated and upsized. The complicated, large and expensive construction of the fixing device inevitably makes the image forming apparatus equipped with the fixing device complicated, large and expensive.

  In addition, the belt is heated at a nip portion with a rotatable heat fixing roller with a built-in heating source. However, in a configuration in which the belt is stretched by a plurality of support rollers to increase the peripheral length, the belt moves along a predetermined path. Sometimes, heat energy is taken away by a plurality of support rollers, and natural heat dissipation increases with the length of the circumference. For this reason, it takes a long time to reach a predetermined temperature, and a so-called warm-up time from when the power is turned on to when fixing is required is not preferable.

  Further, in the configuration in which the belt is wound around the heating roller at an angle capable of forming a nip, and a pressure larger than that of other portions is locally applied at the exit of the nip portion to form a strain in the elastic layer of the heat fixing roll, the sheet material is heated. Although it is suitable for suppressing winding around the roller, the sheet material discharged along the strain of the elastic layer may curl following this strain or generate wrinkles due to local high pressure. Bring deformation.

  In view of this, the present applicant disclosed in Patent Document 2 that the structure of the heat roller type fixing device can be simplified, downsized, and cost can be reduced, the warm-up time can be shortened, the stress on the sheet material can be reduced, and the occurrence of curling can be achieved. We have proposed a fixing device that can suppress the deformation of discharged sheet material such as the occurrence of wrinkles.

This will be described with reference to FIG. A heating roller 1, a pressure roller 2 pressed against the heating roller, a belt stretching member 4 disposed on the upstream side in the paper conveying direction with respect to the pressure roller 2, the pressure roller 2 and the belt tensioning A belt 3 is provided which is attached to the outer periphery of the frame member 4 and moves with a fixing nip (contact surface) 4a formed between the roller 1 and the heating roll 1. The heating roller 1 is covered with an elastic layer 1c on the outer periphery of a cored bar 1b and has a heating source 1a made of a halogen lamp inside, and rotates in the direction A in the figure. The elastic layer 1 c of the heating roller 1 is in contact with the pressure roller 2 and the belt 3 supported by the belt stretching member 4. The pressure roll 2 is coated with an elastic layer 2c on the outer periphery of the cored bar 2b and rotates in the direction B in the figure. The transfer material 5 such as paper enters from the C direction and is discharged in the L direction.
Patent No. 3084692 JP2004-4234

  By the way, in order to shorten the warm-up time, when a thin heating roller or pressure roller is used, the strength is lowered, so that the roller is likely to be bent. Therefore, in order to absorb the deflection and make the nip shape uniform, a so-called crown-shaped roller in which the outer diameter of the central portion in the axial direction of the roller is larger than both end portions is generally used.

  FIG. 2 is a plan view showing a state in which the belt 3 is attached to the pressure roller 2 and the belt stretching member 4 when the pressure roller of FIG. Tension springs 6 are arranged at both ends of the pressure roller 2 and both ends of the belt stretching member 4, thereby urging the belt stretching member 4 in the direction of arrow T, and applying belt tension G to the belt 3. Since the pressure roller 2 rotates in the direction B, a contact force to the heating roller 1 is generated in the belt stretching member 4.

When the pressure roller has a crown shape, the tension G applied to the belt stretching member 4 is larger at the axial central portion 4b than at both axial end portions 4c, and at the axial central portion 4b of the belt stretching member 4. The bending occurs in the tension applying direction from the position of the dotted line in the figure. When the belt stretching member 4 is bent, the contact position between the belt stretching member 4 and the heating roller 1 fluctuates. As a result, the nip width becomes non-uniform in the axial direction, the amount of heat transfer to the toner becomes unstable, and the gloss And the image quality characteristics such as the fixing strength become non-uniform in the axial direction.
Also, if the belt tension is uneven, there will always be a part where a large force is locally applied to the belt and the tension member, and therefore there will be a part where the frictional force between the belt and the tension member is large. The belt or the tension member is scraped off. Doing so shortens the belt life, changes the shape of the tension member over time, fluctuates the fixing characteristics, and scrapes between the pressure roller and the belt due to scraping of the belt or tension member. Problems such as fluctuations in the fixing speed occur.

  The present invention solves the above-mentioned problem, and by making the belt tension uniform in the axial direction, it is possible to suppress the bending of the belt stretching member as much as possible and to form a uniform nip shape. Another object of the present invention is to provide a fixing device capable of improving the durability of the belt stretching member.

  For this purpose, the fixing device according to the present invention is disposed on the upstream side of the pressure roller with respect to the heating roller, the pressure roller pressed against the heating roller, and the pressure roller via a tension spring. A belt stretching member disposed, and a belt that is attached to the outer periphery of the pressure roller and the belt stretching member and moves with a fixing nip formed between the heating roller and the pressure roller. The shape is a crown shape, and the shape of the belt stretching member is a shape in which the belt belt circumferential length in the axial direction is the same.

  According to the present invention, by making the belt tension uniform in the axial direction, it is possible to suppress the bending of the belt stretching member as much as possible and to form a uniform nip shape. Further, since the belt tension is uniform, the belt or the tension member is not scraped, the life of the belt is improved, the shape of the tension member is not changed, and the belt or the tension member is scraped. Therefore, slip does not occur between the pressure roller and the belt, and the fixing speed does not fluctuate.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram illustrating an embodiment of a fixing device according to the present invention. In the figure, 1 is a heating roller, 1a is a halogen lamp, 1b is a roller core, 1c is an elastic layer, 2 is a pressure roller, 2b is a roller core, 2c is an elastic layer, 3 is a belt, 4 is a belt stretcher A member, 4a is a heating roller contact surface, 5 is a sheet material, 5a is an unfixed toner image, and L is a pressing portion tangent.

  In FIG. 1, a heating roller 1 is, for example, a heating member having a built-in rotation of 1050 W as a heating source and two columnar halogen lamps 1a, and a pipe member having an outer diameter of about 25 mm and a wall thickness of about 0.7 mm. This is a heating-side rotary moving body formed by disposing a heating source inside the roller cored bar 1b and covering the outer periphery with an elastic layer 1c having a thickness of about 0.4 mm.

  The pressure roller 2 is a pressure member that is disposed opposite to the heating roller 1 and presses and urges to form a fixing nip. For example, the pressure roller 2 has an outer diameter of about 25 mm or 24.8 mm and is outside the roller core 1b of the heating roller 1. A pipe material having a small diameter and a thickness of about 0.7 mm is used as a roller core 2b, and the outer periphery thereof is covered with an elastic layer 2c having a thickness of about 0.2 to 0.3 mm that is thinner than the elastic layer of the heating roller 1. By forming the elastic layer, the rotating moving body on the other side has a harder surface than the elastic layer of the heating roller 1. As the pressure roller 2 having a hard surface, the surface whose surface is harder than the elastic layer of the heating roller 1 is a roller core metal or a roller core metal, and has an elastic layer on the surface. May be.

  The pressure roller 2 uses a thin roller in order to shorten the warm-up time. However, since the strength is lowered, the roller is likely to be bent. Therefore, in order to absorb the deflection and make the nip shape uniform, a so-called crown-shaped roller is used in which the outer diameter of the central portion in the axial direction of the roller is larger than both end portions.

  The belt 3 is an endless belt which is sandwiched between the heating roller 1 and the pressure roller 2 and stretched around the outer periphery of the pressure roller 2 and the belt stretching member 4 so as to be movable. Having a thickness of The material may be a heat resistant resin such as a polyimide tube or silicon, rubber, or the like, but a metal belt made of a stainless steel base material or a nickel electroformed tube excellent in thermal conductivity is preferable.

  In the fixing device of the present embodiment, the belt 3 is stretched by applying tension to the heat-resistant belt 3 by the cooperation of the pressure roller 2 and the belt stretching member 4, and the belt 3 is wound around the heating roller 1 to fix the fixing nip. And the sheet material 5 on which the unfixed toner image 5a is formed is passed through the fixing nip to be fixed. The pressure contact force between the heating roller 1 and the pressure roller 2 is 10 kg or less, the nip width is about 10 mm as a whole, and is rotatable in the direction of the arrow shown.

  In the present embodiment, two heating sources 1a are built in the heating roller 1, and when the heating elements of the halogen lamp are configured in different arrangements and selectively lit, the belt 3 described later is heated. The fixing nip portion wound around the roller 1 and the portion where the belt stretching member 4 slides on the heating roller 1 or under different conditions such as a wide sheet material and a narrow sheet material. Temperature control can be easily performed.

  Originally, when the sheet material 5 on which the unfixed toner image 5a is formed is passed through the fixing nip and fixed, the sheet material 5 is imparted with a curling behavior that deforms along the outer periphery of the heating roller 1 and is wound around the heating roller 1 side. It will be easier. According to the present embodiment, since the outer diameters of the heating roller 1 and the pressure roller 2 are configured to be as small as about 25 mm, the sheet material 5 after fixing does not wrap around the heating roller 1 or the belt 3. Means such as a peeling claw or a peeling plate for forcibly peeling the sheet material 5 are unnecessary.

  Furthermore, when the pressure roller 2 having a harder surface than the elastic layer coated on the surface of the heating roller 1 is disposed opposite to the heating roller 1 and pressed and urged, the elastic layer of the heating roller 1 is elastically deformed and dented. A concave fixing nip is formed. When the heating roller 1 forms a concave fixing nip, the unfixed toner image formed on the sheet material is fixed and applied to the sheet material 5 that has passed through the fixing nip. And the elastic layer of the heating roller 1 is elastically deformed in the direction away from the heating roller 1 by the pressing of the pressure roller 2 that is harder than the elastic layer coated on the surface of the heating roller 1, and fixing. Curling behavior can be imparted to the opposite side of the heating roller 1 at the exit of the nip.

  In addition, the degree of curl behavior imparted to the sheet material 5 with respect to the moving direction of the belt 3 by the hardness balance and pressing force of the pressure roller 2 and the heating roller 1 is not wound around the heating roller 1. Can be easily adjusted in the direction away from the. As a result, the sheet material 5 after fixing can be removed without forcing off the heating roller 1 and the belt 3 without being wrapped around the heating roller 1 and the belt 3, and extremely stable image fixing is possible. Furthermore, if a PFA (peroxy-alkoxy-fluoro resin) layer of about 30 μm is provided on the surface layer of the elastic layer 1 c of the heating roller 1, the rigidity is improved by that much and the sheet material 5 and the toner are easily peeled. be able to.

  In consideration of the influence on the surface layer of the heating roller 1 facing the belt 3 and the influence of contact with the toner image surface during double-side fixing to the sheet material 5, for example, a rubber material such as PFA or silicon may be used as the surface layer. . When the heating roller 1 is heated to a predetermined temperature by warming up, the belt 3, the pressure roller 2, and the belt stretching member 4 are also increased to a predetermined temperature and stored. When a member having high thermal conductivity is used for the belt 3, the pressure roller 2, and the belt stretching member 4, the heat absorbed by the sheet material 5 at the fixing nip due to fixing of the toner image on the sheet material 5 is generated. Since the pressure roller 2 and the belt stretching member 4 can be efficiently returned to the belt 3, it is possible to suppress a decrease in the temperature of the heat-resistant belt 3 particularly when fixing is performed by passing a plurality of sheet materials 5 continuously. it can.

  The belt stretching member 4 is disposed upstream of the nip portion between the heating roller 1 and the pressure roller 2 in the conveying direction of the sheet material 5, and for example, the heating roller 1 is centered on the rotation axis of the pressure roller 2. It is arranged so as to be swingable in the direction of the center of rotation. The belt stretching member 4 is configured to stretch the belt 3 in the tangential direction of the heating roller 1 at an initial position where the sheet material 5 enters the fixing nip when the sheet material 5 does not pass through the fixing nip.

  If the fixing pressure is large at the initial position where the sheet material 5 enters the fixing nip, the sheet material 5 may not enter smoothly and may be fixed with the leading edge of the sheet material broken. When the belt stretching member 4 is configured to stretch in the tangential direction of the heating roller 1 on the upstream side in the conveying direction of the sheet material 5, an introduction port portion that allows the sheet material 5 to enter smoothly can be formed, and a stable sheet can be formed. The material 5 can enter. In addition, if the fixing pressure is large at the end position where the sheet material 5 is discharged from the fixing nip, the sheet material 5 enters and is heated at the fixing nip, and finally the large fixing pressure is applied at the end position. Since the heating roller 1 side is concave and the curvature is large, the sheet material 5 is difficult to wind around the heating roller 1 and easily peels from the heating roller 1.

  If the belt stretching member 4 is structured such that it does not press the heating roller 1 when paper is not passed, but presses the heating roller 1 only when paper is passed, there is a gap between the belt 3 and the belt stretching member 4 when paper is not passed. The gap becomes a heat insulating layer and the amount of heat taken from the heating roller 1 via the belt 3 can be reduced, so that the warm-up time can be shortened. When the sheet material 5 passes through the fixing nip, the gap between the belt 3 and the belt stretching member 4 disappears, and the sheet material 5 is pressed against the belt 3 at the fixing nip portion and pressed against the heating roller 1. Therefore, stable fixing becomes possible. At this time, if the pressing force is adjusted to a desired pressure, proper fixing can be achieved.

  Further, the belt stretching member 4 is inserted into the inner periphery of the belt 3 to apply tension to the belt 3 in cooperation with the pressure roller 2 and wind the belt 3 around the heating roller 1 to form a nip. The belt sliding member (the belt 3 slides on the belt stretching member 4) is arranged in a substantially half-moon shape. The belt sliding member 4 may be made of a metal such as an aluminum alloy having excellent thermal conductivity, but is preferably made of a plastic having excellent thermal conductivity from the viewpoint of shortening the warm-up time. As a more preferable condition, the surface of the plastic belt sliding member is subjected to a metal coating treatment such as copper plating, nickel plating or vapor deposition for the purpose of improving thermal conductivity, and the axial length is also set. If the length of the elastic layer covering portion of the heating roller 1 is shorter than the axial length, it is possible to further exhibit characteristics excellent in thermal response under a small heat capacity.

  FIG. 3 shows one embodiment of the present invention, where FIG. (A) is a plan view of the belt stretching member (viewed from the direction of the arrow in FIG. (C)), and FIG. Sectional drawing which follows an A line and a BB line, FIG. (C) is a figure which shows a belt shape.

  In the present embodiment, on the semicircular surface 4d of the belt stretching member 4, the axially opposite end portions 4c are formed so as to be gradually higher than the axial central portion 4b, and the crown-shaped pressure roller 2 and the belt stretching are formed. When the belt 3 is stretched over the member 4, both end portions in the axial direction are attached to both end portions in the axial direction with a small diameter on the pressure roller 2 side, and both end portions in the axial direction where the distance becomes longer on the belt stretch member 4 side. The axial center portions are attached to the portions 4c, and the axial center portions are attached to the large diameter axial central portion on the pressure roller 2 side, and the distance is shortened on the belt stretching member 4 side. 4b, and the belt belt circumferential lengths 3 'and 3 "are the same in the axial direction of the belt stretching member 4. As a result, by making the belt tension uniform in the axial direction, Suppresses the bending of the belt tension member as much as possible, and forms a uniform nip shape Door can be.

  FIG. 4 shows another embodiment of the present invention, where FIG. (A) is a plan view of the belt tension member (viewed from the direction of the arrow in FIG. (C)), and FIG. (B) is A in FIG. A sectional view taken along line -A and line BB, and FIG. (C) is a diagram showing a belt shape.

  In the present embodiment, on the surface opposite to the heating roller 1 of the semicircular surface 4d of the belt stretching member 4, a surface in which both axial end portions 4c are gradually higher than the axial central portion 4b is formed, and a crown shape is formed. When the belt 3 is stretched between the pressure roller 2 and the belt stretching member 4, both end portions in the axial direction are attached to both end portions in the axial direction of a small diameter on the pressure roller 2 side, and the belt stretching member 4 On the side, it is attached to the axially opposite end portions 4c where the distance is long, and each axially central portion is attached to the large-diameter axially central portion on the pressure roller 2 side, and the belt stretching member 4 side In this case, the belt is attached to the central portion 4b in the axial direction where the distance becomes short, and the belt attachment circumferential lengths 3 'and 3 "are the same in the axial direction of the belt stretching member 4. As a result, the belt tension is reduced. By making it uniform in the axial direction, the bending of the belt stretching member is suppressed as much as possible, It is possible to form an nip shape.

  FIG. 5 is a schematic diagram of an overall configuration showing an example of an image forming apparatus to which the present invention is applied. In the figure, 10 is an image forming apparatus, 10a is a housing, 10b is a door, 11 is a paper transport unit, 15 is a cleaning means, 17 is an image carrier, 18 is an image transfer transport means, 20 is a developing means, and 21 is a scanner. Means, 30 is a paper feed unit, 40 is fixing means, W is an exposure unit, and D is an image forming unit.

  In FIG. 5, the image forming apparatus 10 includes a housing 10a, a paper discharge tray 10c formed on the top of the housing 10a, and a door 10b that is openably and detachably mounted on the front surface of the housing 10a. 1 includes an exposure unit (exposure means) W, an image forming unit D, a transfer belt unit 29 having an image transfer and conveyance means 18, and a paper feed unit 30, and a paper conveyance unit 11 is arranged in the door body 10b. ing. Each unit has a configuration that can be attached to and detached from the main body, and can be removed and repaired or replaced integrally during maintenance or the like.

  The image forming unit D includes image forming stations Y (for yellow), M (for magenta), C (for cyan), and K (for black) that form a plurality (four in this embodiment) of different color images. I have. In each of the image forming stations Y, M, C, and K, an image carrier 17 that is a photosensitive drum, a charging unit 19 that is a corona charging unit and a developing unit that are disposed around the image carrier 17 are provided. Means 20 are included. These image forming stations Y, M, C, and K are arranged in parallel on the lower side of the transfer belt unit 29 so that the image carrier 17 faces upward along an oblique arched line. The order of arrangement of the image forming stations Y, M, C, and K is arbitrary.

  The transfer belt unit 29 is disposed below the housing 10a and is driven to rotate by a drive source (not shown), a driven roller 13 disposed obliquely above the drive roller 12, a tension roller 14, An image transfer conveying means 18 comprising an intermediate transfer belt that is stretched between these three and at least two rollers and is driven to circulate in the direction of the arrow in the figure, and a cleaning means 15 that contacts the surface of the image transfer conveying means 18. I have. The driven roller 13, the tension roller 14, and the image transfer / conveying means 18 are disposed in a direction inclined to the left in the drawing with respect to the driving roller 12, so that the belt conveying direction when driving the image transfer / conveying means 18 is downward. The belt surface 18a is positioned below, and the belt surface 18b whose transport direction is upward is positioned above.

  Accordingly, the image forming stations Y, M, C, and K are also arranged in a direction inclined to the left in the drawing with respect to the driving roller 12. Then, the image carrier 17 is brought into contact with the belt surface 18a facing downward in the transport direction of the image transfer transport unit 18 along the arched line, and is rotationally driven in the transport direction of the image transfer transport unit 18 as indicated by the arrows in the drawing. The The flexible endless sleeve-shaped image transfer / conveyance means 18 is brought into contact with the image carrier 17 from substantially the same wrapping angle so as to be covered from above, so that the image carrier 17 and the image transfer / conveyance means 18 are in contact with each other. The contact pressure and the nip width can be adjusted by controlling the tension applied to the image transfer / conveying means 18 by the tension roller 14, the arrangement interval of the image carrier 17, the winding angle (arch curvature), and the like. .

The drive roller 12 also serves as a backup roller for the secondary transfer roller 39. For example, a rubber layer having a thickness of about 3 mm and a volume resistivity of 10 ⁵ Ω · cm or less is formed on the peripheral surface of the drive roller 12, and the secondary transfer roller is grounded through a metal shaft. This is a conductive path for the secondary transfer bias supplied through the terminal 39. As described above, by providing the driving roller 12 with a rubber layer having high friction and shock absorption, it is difficult for the impact when the sheet material enters the secondary transfer portion to be transmitted to the image transfer conveying means 18, and the image quality is deteriorated. Can be prevented. Further, by making the diameter of the driving roller 12 smaller than the diameters of the driven roller 13 and the backup roller 14, the sheet material after the secondary transfer can be easily peeled off by the elastic force of the sheet material itself. Further, the driven roller 13 is also used as a backup roller for the cleaning means 15 described later.

  Note that the image transfer conveying means 18 is disposed in a direction inclined to the right in the drawing with respect to the driving roller 12, and correspondingly, each of the image forming stations Y, M, C, K is also illustrated with respect to the driving roller 12. And may be arranged along an oblique arch shape in a direction inclined to the right side.

  The cleaning unit 15 is provided on the side of the belt surface 18a facing downward in the transport direction, and a cleaning blade 15a that removes toner remaining on the surface of the image transfer transport unit 18 after the secondary transfer, and a toner transport that transports the collected toner A member 15b is provided. The cleaning blade 15 a is in contact with the image transfer / conveyance means 18 at a portion where the image transfer / conveyance means 18 is wound around the driven roller 13. Further, a primary transfer member 16 is brought into contact with the back surface of the image transfer conveying unit 18 so as to face an image carrier 17 of each of the image forming stations Y, M, C, and K described later. A transfer bias is applied.

  The exposure means W is disposed in a space formed obliquely below the image forming unit D disposed in the oblique direction. A paper feeding unit 30 is disposed below the exposure unit W and at the bottom of the housing 10a. The exposure means W is entirely housed in a case, and the case is disposed in a space formed obliquely below the belt surface facing downward in the transport direction. A single scanner means 21 comprising a polygon mirror motor 21a and a polygon mirror (rotating polygon mirror) 21b is horizontally disposed at the bottom of the case, and a plurality of laser light sources 23 modulated by image signals of respective colors. In the optical system B that reflects and scans the laser beam by the polygon mirror 21b and deflects and scans the image carrier, the single f-θ lens 22 and the scanning light path of each color are not parallel to the image carrier 17 respectively. A plurality of reflecting mirrors 24 are arranged so as to be folded.

  In the exposure means W configured as described above, an image signal corresponding to each color is emitted from the polygon mirror 21b with a laser beam modulated and formed based on a common data clock frequency, and the f-θ lens 22 and the reflection mirror 24 are passed through. After that, the image carrier 17 of each image forming station Y, M, C, K is irradiated to form a latent image. By providing the reflection mirror 24, the scanning optical path can be bent, the height of the case can be lowered, and the optical system can be made compact. In addition, the reflection mirror 24 is arranged so that the scanning optical path lengths to the image carrier 17 of the image forming stations Y, M, C, and K are the same. In this way, the length of the optical path from the polygon mirror 21b of the exposure means W to the image carrier 17 to the image carrier 17 (optical path length) for each image forming unit D is configured to be substantially the same, thereby scanning in each optical path. The scanning widths of the emitted light beams are also substantially the same, and no special configuration is required for image signal formation. Therefore, the laser light source can be modulated and formed based on a common data clock frequency even though it is modulated corresponding to images of different colors by different image signals, and uses a common reflecting surface. Color misregistration caused by a relative difference in the sub-scanning direction can be prevented, and a simple and inexpensive color image forming apparatus can be configured.

  Further, in this embodiment, by arranging the scanning optical system below the apparatus, the vibration of the scanning optical system due to the vibration that the drive system of the image forming means gives to the frame that supports the apparatus can be minimized. Degradation of image quality can be prevented. In particular, by arranging the scanner means 21 at the bottom of the case, the vibration that the polygon motor 21a itself gives to the entire case can be minimized, and deterioration of the image quality can be prevented. Further, by making the number of polygon motors 21a, which are vibration sources, one, vibration applied to the entire case can be minimized.

  The sheet feeding unit 30 includes a sheet feeding cassette 35 in which sheet materials are stacked and held, and a pickup roller 36 that feeds sheet materials one by one from the sheet feeding cassette 35. The paper transport unit 11 includes a gate roller pair 37 (one roller is provided on the housing 10a side) that regulates the timing of feeding the sheet material to the secondary transfer unit, the drive roller 12, and the image transfer transport means 18. A secondary transfer roller 39 as a secondary transfer unit that is pressed against the main body, a main recording medium conveyance path 38, a fixing unit 40, a discharge roller pair 41, and a duplex printing conveyance path 42 are provided.

  The secondary image (unfixed toner image) secondarily transferred to the sheet material is fixed at a predetermined temperature at the nip portion formed by the fixing unit 40. In this example, the fixing means 40 is disposed in a space formed obliquely above the belt surface 18b facing upward in the transfer belt conveyance direction, in other words, in a space opposite to the image forming station with respect to the transfer belt. Therefore, heat transfer to the exposure unit W, the image transfer conveyance unit 18, and the image forming unit can be reduced, and the frequency of performing the color misregistration correction operation for each color can be reduced. In particular, the exposure unit W is located farthest from the fixing unit 40, and the displacement of the scanning optical system component due to heat can be minimized, thereby preventing color misregistration. In the present embodiment, since the image transfer conveying means 18 is arranged in a direction inclined with respect to the driving roller 12, a large space is generated in the right space in the figure, and the fixing means 40 can be arranged in that space. In addition, downsizing can be realized, and heat generated by the fixing unit 40 is transmitted to the exposure unit W, the image transfer conveyance unit 18 and the image forming stations Y, M, C, and K located on the left side. Can be prevented. Further, since the exposure unit W can be arranged in the space on the lower left side of the image forming unit D, the vibration of the scanning optical system of the exposure unit W due to the vibration applied to the housing 10a by the drive system of the image forming means is minimized. The image quality can be suppressed and deterioration of the image quality can be prevented.

  Further, the corona charging means 19 is adopted as the charging means in accordance with the absence of the cleaning means. When the charging unit is a roller, a small amount of primary transfer residual toner existing on the image carrier 17 accumulates on the roller to cause a charging failure, but the corona charging unit 19 which is a non-contact charging unit. Can prevent toner from adhering and can prevent charging failure.

  In addition, the intermediate transfer belt is configured to come into contact with the image carrier 17 as the image transfer / conveying means 18, but the sheet material is adsorbed and transported to the surface, and the toner images are sequentially superimposed and transferred onto the surface of the sheet material. The sheet material conveying belt for forming and conveying the image may be configured to contact the image carrier 17 as the image transfer conveying means 18. In this case, the belt conveyance direction of the sheet material conveyance belt as the image transfer conveyance means 18 is upward in the opposite direction on the lower surface in contact with the image carrier 17.

1 is a diagram illustrating an embodiment of a fixing device according to the present invention. It is a figure for demonstrating the subject of this invention. It is a figure for demonstrating one Embodiment of this invention. It is a figure for demonstrating other embodiment of this invention. 1 is a schematic diagram illustrating an example of an image forming apparatus to which the present invention is applied.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Heating roller, 2 ... Pressure roller, 3 ... Belt, 4 ... Belt tension member, 4a ... Contact surface 4b ... Axis direction center part, 4c ... Axial direction both ends

Claims (2)

A heating roller, a pressure roller pressed against the heating roller, a belt stretching member disposed on the upstream side of the pressure roller in the paper conveyance direction, and disposed on the pressure roller via a tension spring; A belt that is attached to the outer periphery of the pressure roller and a belt stretching member and that moves with a fixing nip formed between the pressure roller and the heating roll, and the pressure roller has a crown shape, and the belt A fixing device characterized in that the shape of the tension member is the same in the belt belt circumferential length in the axial direction. The belt stretching member has a semicircular cross section, and a semicircular surface of the belt stretching member is formed with a surface in which both end portions in the axial direction are gradually higher than the central portion in the axial direction. The fixing device described.

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