JP2006184641A - Belt heating method, fixing device, and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a belt heating method in which a belt member can be heated within a prescribed temperature range simply by passing of the belt member through a heating region, a fixing device, and an image forming apparatus. <P>SOLUTION: A first temperature sensor 67 is arranged on the front side in the belt moving direction of a back surface heating roller 63 to detect the back surface temperature of the fixing belt 62 just before reaching the back surface heating roller 63. A controller within the image forming apparatus regulates the calorific value of a halogen lamp 63b by on/off control of a back surface heating power source from the difference between the value of a digital temperature signal sent from the first temperature sensor 67 and a first temperature target value. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a belt heating method for heating an endlessly moving belt member to a temperature within a predetermined range, a fixing device including the endlessly moving belt member, and an image forming apparatus.

  Conventionally, as a method of forming an image on both sides of a recording medium, a so-called switchback method, a one-pass method, and the like are known. In the switchback method, after a recording medium having an image formed on one surface after passing through the transfer device and the fixing device is reversed, the recording material is switched back to the transfer device and the fixing device, and also on the other surface. This is a method for forming an image. On the other hand, in the one-pass method, an image is formed on both sides of the recording body without switching back by passing the recording body on which the image is transferred on both sides by the double-side transfer means through the fixing means. The one-pass method is superior to the switchback method in the following points. That is, it is possible to avoid cost increase by providing a complicated mechanism for switchback, prolonged image formation time by switchback, and jamming by switching back a recording medium curled by heating by a fixing means. It is.

  However, such a one-pass method has a problem that the image is easily disturbed when the recording medium after the double-side transfer is sent from the double-side transfer means to the fixing means. Such image disturbance occurs as follows. That is, when the recording medium separated from the double-sided transfer unit is delivered to the fixing unit, any one of the unfixed images existing on both sides of the recording medium is arranged between the double-sided transfer unit and the inside of the fixing unit. The guide member or the like provided is rubbed and disturbed.

  Therefore, in Patent Document 1, a driven rotatable spur having a plurality of protrusions on the peripheral surface is provided between the double-sided transfer unit and the fixing unit, thereby guiding the recording body from the double-sided transfer unit to the fixing unit. An image forming apparatus has been proposed. In Patent Document 1, it is assumed that the following can be realized by this image forming apparatus. That is, the recording medium is guided from the double-sided transfer unit to the fixing unit without disturbing the image on the back side by rotating the spur in a state where the protrusion is stuck on the back side of the recording body with the movement of the recording body. I can do it.

  However, even if the spur protrusion is sharp, if it is pierced, the unfixed image will be disturbed. Furthermore, since it is extremely difficult to clean a spur having a complicated shape provided with a plurality of protrusions every time the recording medium passes, the toner adhering to the protrusions is transferred to the succeeding recording medium to disturb the image. There is a high possibility that it will end.

  Therefore, the present applicant has proposed an image forming apparatus having a configuration in which a one-pass method and a so-called belt fixing method are used in combination in Patent Document 2. FIG. 11 is a schematic configuration diagram showing a belt fixing type fixing device used in the image forming apparatus. In the drawing, a fixing device 60 as fixing means includes a front surface heating roller 61, a fixing belt 62 as an endless belt member, a back surface heating roller 63, a nip back roller 64, a cleaning roller 65, and the like. The fixing belt 62 is stretched with a predetermined tension while being supported from the back surface by the back surface heating roller 63 and the nip back side roller 64. Then, it is endlessly moved clockwise in the figure by driving the nip back side roller 64 that is rotated clockwise in the figure by a driving means (not shown).

  The front surface heating roller 61 and the back surface heating roller 63 are respectively made of metal pipe members 61a and 63a that are rotatably supported by support means (not shown), and halogen lamps that are non-rotatably disposed therein. 61b, 63b. The pipe members 61a and 63a are heated from the inner surface by radiation from the halogen lamps 61b and 63b, which are heat sources. The front surface heating roller 61 is in contact with the front surface of the fixing belt 62 so as to sandwich the fixing belt 62 with a later-described nip back roller 64 to form a fixing nip. In the fixing nip, the fixing belt 62 is heated from the front surface by heat conduction from the pipe member 61b. Further, the back surface heating roller 63 heats the back surface of the fixing belt 62 approaching the stretched position by heat conduction from the pipe member 63b. A back surface temperature detection sensor 66 is disposed in a region immediately before the fixing belt 62 reaches the fixing nip. The back surface temperature detection sensor 66 detects the temperature of the back surface of the fixing belt. Based on the temperature signal from the back surface temperature detection sensor 66, the power supply to the halogen lamp 63b is ON / OFF controlled. By this ON / OFF control, the back surface temperature of the fixing belt 62 immediately before reaching the fixing nip is controlled within a predetermined range (for example, 160 to 180 ° C.).

  The nip back roller 64 has a metal cored bar 64b and a thick elastic layer 64a made of rubber or the like coated thereon. The thick elastic layer 64a is flexibly elastically deformed by pressing from the front surface heating roller 63 via the fixing belt 62, thereby forming a larger fixing nip in the belt circumferential direction. ing.

  The transfer paper P, which is a recording medium on which the toner images are transferred on both sides by a double-side transfer means (not shown), is conveyed toward the fixing means 60 from below in the figure by the double-side transfer means. Then, after the front end of the entire region in the circumferential direction of the fixing belt 62 hits the region between the stretched portion by the back surface heating roller 63 and the fixing nip, it is gradually brought into close contact with the fixing belt 62. However, it is conveyed toward the fixing nip. When the fixing nip is reached, one side of the fixing belt 62 heated by the back surface heating roller 63 is closely attached and heated, and at the same time, the other side is strongly attached to the front surface heating roller 61. Heated. It is heated from both sides at the fixing nip. By such heating from both sides, the toner images present on both sides of the transfer paper P are respectively heated and pressed to be fixed on the respective sides.

  The transfer paper P that has passed through the fixing nip is sent to a paper discharge path (not shown) as the surface of the fixing belt 62 and the front surface heating roller 61 moves, and then discharged outside the apparatus. Further, a small amount of fixing residual toner (offset toner) adhering to the surface of the fixing belt 62 after passing through the fixing nip is electrostatically applied to the belt front surface by the cleaning roller 65 to which a cleaning bias is applied. Removed from.

  In such a configuration in which the fixing device 60 and the one-pass method are used in combination, the transfer belt P is guided toward the fixing nip without rubbing the toner image by contacting the transfer paper P while the fixing belt 62 moves on the surface. be able to. Therefore, image disturbance due to rubbing the unfixed toner image can be suppressed. Further, unlike the spur described in Patent Document 1, the fixing belt 62 is easily cleaned by a known means such as the cleaning roller 65 shown in FIG. 11 even if toner contamination occurs due to an offset or the like. be able to. Therefore, it is possible to easily suppress a situation in which the subsequent transfer paper P is soiled by toner adhering to a guide member such as a spur or the fixing belt 62.

  When the transfer paper P passes through the fixing nip, the heat amount of the fixing belt 62 is taken away by the transfer paper P, and the temperature of the fixing belt 62 immediately after passing through the fixing nip is remarkably lowered. In the fixing device 60, the temperature of the fixing belt 62 immediately before reaching the fixing nip is detected. For this reason, once the fixing belt has been heated by passing through the belt heating region formed by the back surface heating roller 63, the back surface temperature detection sensor 66 detects the temperature that has decreased due to the amount of heat taken away by the transfer paper P. . Based on this detection result, the contents of ON / OFF control of power supply to the halogen lamp 63b are changed. Then, when the fixing belt passes through the belt heating region again, the amount of heat taken from the transfer paper by the fixing belt 62 is compensated. As a result, in the fixing device 60, the fixing belt 62 can pass through the belt heating region at least twice, so that the fixing belt can be within a predetermined temperature range (for example, 160 to 180 ° C.).

  Patent Document 3 proposes a fixing device that detects the temperature of the fixing belt immediately after passing through the fixing nip. In this way, by detecting the temperature of the fixing belt immediately after passing through the fixing nip, the amount of heat of the fixing belt 62 taken away by the transfer paper P can be detected immediately after the transfer paper P passes through the fixing nip. If the content of the ON / OFF control of the power supply to the halogen lamp 63b is changed based on the detection result so as to compensate for the amount of heat taken from the transfer paper to the fixing belt in the belt heating region, the fixing belt once becomes the belt. The fixing belt 62 can be set within a predetermined temperature range (for example, 160 to 180 ° C.) simply by passing through the heating region.

JP-A-10-142869 JP 2004-109733 A Japanese Patent Laid-Open No. 11-194661

  However, while the fixing belt passes through the fixing nip and reaches the back surface heating roller 63, the amount of heat of the fixing belt 62 may be lost due to disturbance factors such as environmental fluctuations, and the temperature of the fixing belt may decrease. As in Patent Document 3, in a fixing device that detects the temperature of the fixing belt immediately after passing through the fixing nip, the temperature decrease of the fixing belt between the time when the fixing belt passes through the fixing nip and reaches the back surface heating roller 63 is as follows. It cannot be detected. For this reason, there is a problem that the fixing belt may not be within a predetermined temperature range (for example, 160 to 180 ° C.) by one heating.

  SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object of the present invention is to provide a belt heating method and fixing capable of bringing a belt member into a predetermined temperature range only once the belt member passes through the heating region. An apparatus and an image forming apparatus are provided.

In order to achieve the above object, the invention of claim 1 is a belt heating method in which a belt member that is endlessly moved while being supported from a back surface by a plurality of stretching members is heated to a temperature within a predetermined range by a heating means, The heating amount of the belt is adjusted based on the belt member partial temperature between the heating unit and the tension member disposed upstream of the heating unit in the belt conveyance direction.
Further, the invention of claim 2 forms a fixing nip by abutting the belt member that moves endlessly, a plurality of tension members that are stretched while supporting the belt member from the back surface, and the front surface of the belt member. In a fixing device that includes a pressure member and a heating unit that heats the belt member, and that fixes the toner image by sandwiching the recording member in the fixing nip, the heating unit and the heating unit are arranged upstream of the belt conveyance direction. A temperature detecting means for detecting a belt member partial temperature with a tension member arranged on the side; and a control means for controlling the amount of heat generated by the heating means based on the temperature detection result. Is.
According to a third aspect of the present invention, there is provided the fixing device according to the second aspect, further comprising second temperature detecting means for detecting a belt member partial temperature until the belt member reaches the fixing nip from the heating means. It is characterized by this.
According to a fourth aspect of the present invention, in the fixing device according to the second or third aspect, the heating means is a heating body that heats one of the plurality of stretching members, and the heating body includes the stretching member. It heats in contact with a member.
According to a fifth aspect of the present invention, in the fixing device according to the second or third aspect, the heating means is a heating body that heats one of the plurality of stretching members, and the heating body includes the stretching member. Heating is performed without contact with the member.
According to a sixth aspect of the present invention, in the fixing device according to the second or third aspect, the heating means includes a magnetic field generating means and a heating element, and the heating element is heated by electromagnetic induction by a magnetic field generated by the magnetic field generating means. Thus, the belt member is heated.
According to a seventh aspect of the present invention, in the fixing device according to any one of the second to sixth aspects, a pressure member heating means for heating the pressure member is provided, the recording medium is sandwiched between the fixing nips, and toner is provided on both sides thereof An image fixing process is performed.
According to an eighth aspect of the present invention, in the fixing device according to any one of the second to seventh aspects, the belt member is configured to convey the recording body that has entered the fixing device to the fixing nip. The conveying direction in which the member conveys the recording body to the fixing nip is inclined at a predetermined inclination angle with respect to the fixing device entering direction of the recording body.
According to a ninth aspect of the present invention, there is provided an image carrier that carries a toner image, a visible image forming unit that forms a toner image on the surface of the image carrier, and a toner image on the image carrier. An image forming apparatus comprising: a double-side transfer means for transferring to both sides; and a fixing means for fixing a toner image on both sides of the recording medium, wherein the fixing means is the fixing device according to claim 2. It is characterized by.

  According to the first to ninth aspects of the present invention, the amount of heat is deprived by the contact of the member such as the recording body or the environment, so that the heating means and the stretching member disposed on the upstream side in the belt conveying direction from the heating means. The temperature of the belt member portion between them is the lowest on the circumference of the belt member. Based on the temperature of the belt member portion that is the lowest on the circumference of the belt member, the heating amount to the belt member is adjusted so that the temperature of the belt member is within a predetermined range. As a result, once the belt member passes through the heating means, it is possible to make up for the amount of heat deprived by the contact of the member such as the recording medium or the environment, and to bring the belt member to a temperature within a predetermined range.

Hereinafter, as an image forming apparatus to which the present invention is applied, an embodiment of an electrophotographic printer (hereinafter simply referred to as a printer) will be described.
First, the basic configuration of the printer will be described. FIG. 1 is a schematic configuration diagram of the printer, showing the printer from the front direction. In FIG. 1, the printer 100 includes four process cartridges 6Y, 6M, 6C, and 6K for generating toner images of yellow, magenta, cyan, and black (hereinafter referred to as Y, M, C, and K). Yes. These use Y, M, C, and K toners of different colors as the image forming material, but the other configurations are the same and are replaced when the lifetime is reached. Taking a process cartridge 6Y for generating a Y toner image as an example, as shown in FIG. 2, a drum-shaped photosensitive member 1Y as an image carrier, a drum cleaning device 2Y, a charge eliminating device 3Y, a charging device 4Y, and a developing device 5Y. Etc. In the photoreceptor 1Y, an aluminum cylinder having a diameter of 30 to 100 [mm] is covered with a surface layer of an organic semiconductor that is a photoconductive substance. An amorphous silicon surface layer may be coated. Further, it may be a belt shape instead of a drum shape. The charging device 4Y uniformly charges the surface of the photoreceptor 1Y that is rotated clockwise in the drawing by a driving unit (not shown). The uniformly charged surface of the photoreceptor 1Y is exposed and scanned by a laser beam L emitted from an exposure apparatus (7) described later, and carries a Y electrostatic latent image. The Y electrostatic latent image is developed into a Y toner image by the developing device 5Y using Y toner. The process cartridge 6Y having such a configuration performs an image forming process for forming a toner image on the surface of the photoreceptor 1Y as an image carrier together with the exposure device (7). Therefore, in the printer 100, each process cartridge 6Y, M, C, K functions as a visible image forming unit that forms a toner image on the surface of the image carrier in combination with the exposure device (7). ing.

  The Y toner image developed on the photoreceptor 1Y is primarily transferred onto a first intermediate transfer belt 8 described later. The drum cleaning device 2Y removes the toner remaining on the surface of the photoreceptor 1Y after the primary transfer process. Further, the charge removal device 3Y removes the residual charge of the photoreceptor 1Y after cleaning. By this charge removal, the surface of the photoreceptor 1Y is initialized and prepared for the next image formation. In the other process cartridges 6M, C, and K, M, C, and K toner images are similarly formed on the photoreceptors 1M, C, and K, and are primarily transferred onto the first intermediate transfer belt 8. The developing device (such as 5Y) may use a two-component developer containing toner and a magnetic carrier, or may use only toner powder.

  In FIG. 1 described above, an exposure device 7 is disposed below the process cartridges 6Y, 6M, 6C, and 6K, and an image data processing device E1 is disposed on the left side of the drawing. The image data processing device E1 generates an exposure scanning control signal based on an image information signal sent from a personal computer or the like and sends it to the exposure device 7. The exposure device 7 serving as a latent image forming unit irradiates each of the photoreceptors 1Y, 1M, 1C, and 1K in the process cartridges 6Y, 6M, 6C, and 6K with a laser beam L emitted based on the exposure scanning control signal. Electrostatic latent images for Y, M, C, and K are formed on the photoreceptors 1Y, 1M, 1C, and 1K exposed by this irradiation. The exposure device 7 irradiates the photoconductor with a laser beam (L) emitted from a light source through a plurality of optical lenses and mirrors while scanning with a polygon mirror rotated by a motor. Instead of the exposure apparatus 7 having such a configuration, an exposure unit that irradiates LED light from the LED array may be employed. In addition, a sealing member (not shown) is provided on the casing of the exposure device 7 in order to prevent contamination of internal components due to the toner falling from the photoreceptors 1Y, 1M, 1C, and 1K disposed above the exposure device 7. Is provided.

  On the lower side of the exposure apparatus 7 in the figure, a first paper cassette 25 having a first paper feed roller 28 and a second paper cassette 26 having a second paper feed roller 29 are arranged in a vertical direction. It is installed. Each of these cassettes accommodates a transfer paper bundle in which a plurality of transfer papers P as recording bodies are stacked. On the right side of the second paper cassette 26 in the drawing, a manual tray 25 having a manual paper feed roller 30 is provided so as to extend from the side surface of the housing, not within the housing of the printer body. Also, a transfer bundle is placed.

  Between the two paper feeding cassettes (25, 26) and the manual feed tray 25, a paper feeding path 32 having a pair of registration rollers 31 and a paper feeding guide path 33 that joins the paper feeding path are arranged. The paper feed guide path 33 has a pair of transport rollers 34. The first paper feed roller 28 and the second paper feed roller 29 are in contact with the first transfer paper P of the transfer paper bundle accommodated in the first paper cassette 25 and the second paper cassette 26, respectively. Then, the uppermost transfer paper P is sent out toward the paper feed path 32 by being driven to rotate by a driving means (not shown). The transferred transfer paper P is sandwiched between the first registration roller 31a and the second registration roller 31b of the registration roller pair 31 disposed near the end of the paper feed path 32. The registration roller pair 31 rotationally drives both rollers in the forward direction so as to sandwich the transfer paper P, but once the recording medium is sandwiched between the rollers, the rotation of both rollers is temporarily stopped. Then, rotation is resumed at an appropriate timing, and the transfer paper P is sent out toward a secondary transfer nip described later. It functions as a pair of timing rollers.

  The manual feed roller 30 is in contact with the uppermost transfer sheet P of the transfer sheet bundle placed on the manual feed tray 27. Then, the uppermost transfer paper P is sent out toward the paper feed guide path 33 by being driven to rotate by a driving means (not shown). The fed transfer paper P reaches the vicinity of the end of the paper feed path 32 via a pair of transport rollers 34 that are rotated in the forward direction while being in contact with each other by a driving unit (not shown). Then, it is sandwiched between the first registration roller 31a and the second registration roller 31b.

  The electrostatic latent images for Y, M, C, and K formed on the respective photoreceptors 1Y, 1M, 1C, and 1K undergo a transfer process by a double-side transfer unit. This double-sided transfer means has a first transfer unit 15 and a second transfer unit 24. The first transfer unit 15 is disposed above the process cartridges 6Y, 6M, 6C, and 6K, and includes a first intermediate transfer belt 8, four primary transfer rollers 9Y, M, C, K, A first cleaning device 10 is provided. A secondary transfer backup roller 12, a first cleaning backup roller 13, a tension roller 14 and the like are also provided. The first intermediate transfer belt 8 as the first intermediate transfer member is endlessly moved counterclockwise in the figure by the rotational driving of at least one of the three rollers while being stretched around these three rollers. The four primary transfer rollers 9Y, 9M, 9C, and 9K, which are transfer bias members, sandwich the first intermediate transfer belt 8 that is moved endlessly in this manner between the photoreceptors 1Y, 1M, 1C, and 1K, respectively. The next transfer nip is formed. Then, a primary transfer bias having a polarity (for example, plus) opposite to that of the toner is applied to the back surface (loop inner peripheral surface) of the first intermediate transfer belt 8 by a power source (not shown). In addition to the four primary transfer rollers 9Y, 9M, 9C, and 9K, all the above-described three rollers are electrically grounded.

  The first intermediate transfer belt 8 sequentially passes through the primary transfer nips for Y, M, C, and K along with the endless movement thereof. At each primary transfer nip, the Y, M, C, and K toner images on the photoreceptors 1Y, 1M, 1C, and 1K are primarily transferred in a superimposed manner under the influence of the nip pressure and the primary transfer bias. As a result, a four-color superimposed toner image (hereinafter referred to as a four-color toner image) is formed on the first intermediate transfer belt 8. The secondary transfer backup roller 12 over which the first intermediate transfer belt 8 is stretched is disposed so as to bite into a second intermediate transfer belt 16 described later. By such a biting arrangement, a secondary transfer nip is formed in which the first intermediate transfer belt 8 and the second intermediate transfer belt 16 are in wide contact with each other in the circumferential direction. In the secondary transfer nip, the first transfer belt 8 and the second intermediate transfer belt 16 are brought into contact with each other while moving their surfaces in the same direction. The visible four-color toner image formed on the first intermediate transfer belt 8 is secondarily transferred to the second intermediate transfer belt 16 or the transfer paper P at the secondary transfer nip. In place of the four primary transfer rollers 9Y, 9M, 9C, and 9K of the bias application method, a charger method that discharges from the electrode may be used. The first intermediate transfer belt 8 is an endless belt having a rubber base, and has an electric resistance value suitable for electrostatic transfer of toner images from the photoreceptors 1Y, 1M, 1C, and 1K. It has been adjusted. You may use the thing of the 2 layer structure which consists of a resin film layer (for example, polyimide layer) and a rubber layer (for example, urethane rubber layer), or the multilayer structure beyond it. The surface hardness of the first intermediate transfer belt 8 is desirably 65 degrees or less, and the printer 100 uses the first intermediate transfer belt 8 having a JIS-A hardness of 50 degrees.

  The transfer residual toner that has not been secondarily transferred to the second intermediate transfer belt 16 or the transfer paper P is attached to the first intermediate transfer belt 8 after passing through the secondary transfer nip. This is cleaned by the first cleaning device 10. Specifically, the first intermediate transfer belt 8 includes a first cleaning device 10 disposed so as to contact the outer surface (front surface) side of the loop, and a first cleaning device 10 disposed on the inner surface side of the loop. It is sandwiched between the cleaning backup roller 13. Then, the transfer residual toner on the front surface is mechanically or electrostatically collected by the first cleaning device 10 and cleaned.

  The second transfer unit 24 of the double-side transfer means is disposed on the right side of the first transfer unit 15 in the figure, and includes a second intermediate transfer belt 16, a second cleaning device 18, a transfer charger 23, and the like. Yes. A secondary transfer roller 17, a nip expansion roller 19, a tension roller 20, a backup roller 21 and the like are also provided. While being stretched around these four rollers, the second intermediate transfer belt 16 is endlessly moved clockwise in the drawing by the rotational drive of at least one of the rollers. The secondary transfer backup roller 12 of the first transfer unit 15 described above bites into the bridging portion of the second intermediate transfer belt 16 between the secondary transfer roller 17 and the nip expansion roller 19 to form a secondary transfer nip. . The secondary transfer roller 17 serving as a transfer bias member is a metal roller or a roller in which a conductive rubber layer is coated on a metal core, and a secondary transfer bias having a polarity (for example, plus polarity) opposite to that of toner by a power source (not shown). Is supplied. All the other rollers in the second transfer unit 24 are grounded.

  The registration roller pair 31 is directed toward the secondary transfer nip at a timing at which the transfer paper P sandwiched between the rollers can be brought into close contact with the four-color toner image primarily transferred onto the first intermediate transfer belt 8. Send it out. However, when the four-color toner image is the first toner image to be transferred to the first surface of the transfer paper P (the surface facing upward on the stack unit 40 described later), the transfer paper P is not sent out. . Therefore, at this time, the first toner image on the first intermediate transfer belt 8 is secondarily transferred onto the second intermediate transfer belt 16 under the action of the nip pressure and the secondary transfer bias at the secondary transfer nip. On the other hand, when the four-color toner image on the first intermediate transfer belt 8 is the second toner image to be transferred to the second surface of the transfer paper P (the surface facing downward on the stack portion 40), The registration roller pair 31 feeds the transfer paper P in synchronization with the second toner image. Therefore, the second toner image is secondarily transferred onto the second surface of the transfer paper P (the surface facing downward on the stack unit 40 described later) at the secondary transfer nip, and becomes a full color image combined with the white color of the transfer paper P. . At this time, the first toner image previously transferred to the second intermediate transfer belt 16 is brought into close contact with the first surface of the transfer paper P sent to the secondary transfer nip. However, since the first toner image is attracted to the belt side by the action of the secondary transfer bias, it is in close contact with the first surface of the transfer paper P, but is not secondarily transferred there.

  In the first transfer unit 15, the secondary transfer backup roller 12 stretches the first intermediate transfer belt 8 in a shape that substantially reverses its moving direction. The second intermediate transfer belt 16 is brought into contact with the first intermediate transfer belt portion whose direction of movement is being reversed to form a secondary transfer nip. Therefore, at the outlet of the secondary transfer nip, the first intermediate transfer belt 8 is separated from the transfer sheet P, and the transfer sheet P is held and conveyed only on the surface of the second intermediate transfer belt 16. Then, in the second transfer unit 24, the second intermediate transfer belt 16 is sent to the tertiary transfer unit with the endless movement of the second intermediate transfer belt 16. In the tertiary transfer portion of the second transfer unit 24, the transfer charger 23 is disposed to face the stretched portion of the second intermediate transfer belt 16 by the backup roller 21 with a predetermined gap therebetween. The transfer sheet P on the second intermediate transfer belt 16 is given a charge of the opposite polarity (for example, plus polarity) to the toner by the transfer charger 23 on the second surface side. As a result, the first toner image sandwiched between the first surface of the transfer paper P and the second intermediate transfer belt 16 is thirdarily transferred to the first surface of the transfer paper P to form a full color image. The second intermediate transfer belt 16 is an endless belt having a resin (for example, polyimide) substrate having a thickness of about 50 to 600 [μm]. Secondary transfer of the toner image from the first intermediate transfer belt 8 is performed. It is adjusted to an electrical resistance value suitable for performing.

  As described above, the double-sided transfer unit having the two transfer units (15, 24) transfers the second toner image to the second surface on the second surface at the secondary transfer nip with respect to the transfer paper P, and then transfers the tertiary image. The transfer unit transfers the first toner image onto the first surface of the first stage. As a member to which the primary transfer bias and the secondary transfer bias are applied, members having other shapes such as a brush may be used instead of the rollers (9, 17). Further, instead of the electrostatic transfer method in which a transfer bias is applied to the member, a non-contact discharge method may be employed.

  In the second transfer unit 24, the transfer paper P that has undergone the double-side transfer process by the third transfer is separated from the second intermediate transfer belt 16 and sent to a fixing device 60 described later. On the other hand, the second intermediate transfer belt 16 after passing through the tertiary transfer portion is sandwiched between the backup roller 21 and the second cleaning device 18 so that the transfer residual toner on the surface is mechanically or electrostatically. To be cleaned. If the second cleaning device 18 is always in contact with the second intermediate transfer belt 16, the first toner image secondarily transferred onto the second intermediate transfer belt 16 is also cleaned. Therefore, the second cleaning device 18 is brought into contact with and separated from the second intermediate transfer belt 16 by being swung in the direction of the arrow in the figure by a swing mechanism (not shown). At least while the first toner image passes through the cleaning position, the first toner image is separated from the second intermediate transfer belt 16 to avoid cleaning the first toner image.

  Above the second transfer unit 24 in the figure, a fixing device 60 serving as fixing means is disposed. The transfer paper P on which the full-color image as a toner image is transferred on both sides by the double-side transfer means is sent to the fixing device 60 and subjected to fixing processing of the full-color image. The fixing device 60 performs a fixing step of fixing the toner images transferred on both sides of the transfer paper P as a recording medium on both sides.

  The transfer sheet P on which the fixing process has been performed on the full-color images on both sides is reversed along the reversing guide member 36, and is then discharged to the outside through the pair of discharge rollers 37. And it is stacked on the stack part 40 formed on the upper surface of the housing of the printer body.

  As described above, in the process of transporting the transfer paper P from the secondary transfer nip to the downstream side in the belt moving direction, the printer 100 applies toner to the transfer paper P from both sides thereof by the double-side transfer unit. Image transfer processing is performed. Therefore, image formation by the one-pass method can be performed on both surfaces of the transfer paper P. Further, since the transfer paper P is not directly brought into contact with the photoconductor (1Y, M, C, K) as the image carrier, it is possible to suppress the adhesion of paper powder to the photoconductor. As in the printer 100, a plurality of image carriers such as photoconductors are arranged side by side, and a visible image formed by each is continuously superimposed and transferred to form a superimposed image such as a multicolor image. The method is called tandem method. In contrast, after forming a visible image on one image carrier and transferring it to the intermediate transfer member, the visible image is formed again on the image carrier and transferred onto the visible image on the intermediate transfer member. There is also a method of forming a superimposed image by repeating the process. In this method, the steps of visible image formation and transfer must be repeated. On the other hand, in the tandem method, a plurality of visible images to be superimposed and transferred can be formed almost simultaneously on the corresponding image carriers, so that the image forming time can be greatly shortened.

  As described above, the first toner image is formed prior to the second toner image. Then, after secondary transfer from the first intermediate transfer belt 8 to the second intermediate transfer belt 16 at the secondary transfer nip, it is tertiary transferred onto the first surface of the transfer paper at the tertiary transfer portion. The first surface is a surface facing upward in the stack portion 40. Therefore, the transfer sheets P stacked on the stack unit 40 are sequentially stacked with the first toner image formed in the front direction facing up and the second toner image formed thereafter facing up. Go. In this printer 100, in order to align the page numbers of the transfer sheets P stacked in this way in order from the smallest, the images having two page numbers that are odd and even are consecutive. One toner image is formed. For example, the second page image is formed as the first toner image prior to the first page image. As a result, even if documents of several pages are output continuously, the page numbers can be aligned in order from the bottom in the stack unit 40. However, when executing the single-sided print mode in which an image is formed only on the second surface of the transfer paper P, the images are formed in order from the image with the smallest page number, and each image is secondarily transferred onto the second surface of the transfer paper P. . Thus, even in the single-sided printing mode, the page numbers can be aligned in order from the bottom in the stack unit 40.

  In the four photoreceptors 1Y, 1M, 1C, and 1K, each color toner image formed for the second toner image is formed as a non-mirror image (hereinafter referred to as a normal image). This is because each formed color toner image changes into a mirror image and a normal image in the process of reaching the transfer paper P through two transfer processes of primary transfer and secondary transfer. By forming a normal image on each photoconductor, a normal image is formed on the second surface of the transfer paper P. On the other hand, since each color toner image formed for the first toner image is subjected to the third transfer, the transfer process is increased once more than the second toner image. Therefore, it is formed as a mirror image on each photoconductor. As a result, a normal image, a mirror image, and a normal image change every transfer, and a normal image can be formed on the first surface of the transfer paper P.

  A bottle container 54 is disposed above the first transfer unit 15 in the drawing. In the bottle container 54, toner bottles BY, BM, BC, BK containing toner to be supplied to the developing devices in the process cartridges (6Y, M, C, K) are stored.

  As shown in FIG. 3, the printer 100 forms an image based on an image information signal sent from a personal computer (hereinafter referred to as a personal computer) 200 or the like. Although FIG. 3 shows an example of the image forming system in which the personal computer 200 and the printer 100 are connected by a communication cable, a wireless connection may be adopted. An operation indicator 51 such as a touch panel is fixed to the left front corner of the printer main body. The user can input various parameters such as image forming process conditions and paper conditions according to the guide display appearing on the display of the operation display 51. Switching between the single-sided printing mode and the double-sided printing mode described above is performed by operating a mode switching button prepared on the operation display 51. Further, the selection of the paper type (selection of the paper storage cassette) is also performed by operating the operation indicator 51. However, the switching of these modes and the selection of the paper type can also be performed by transmitting a setting signal from the personal computer 200.

  A front door 52 is provided on the front surface of the printer main body so as to be freely opened and closed. When the front door 52 is opened, the support 53 that supports the first transfer unit (15) (not shown) is largely exposed. The support 53 is configured to be slidable on a guide rail (not shown) in the front-rear direction of the printer main body, and is pulled out from the printer main body toward the front side to expose the first transfer unit (15). . The exposure facilitates maintenance and inspection work of the first transfer unit. When the front door 52 is opened, the end faces of the toner bottles BY, BM, BC, BK in the bottle container 54 disposed above the support 53 are exposed. The toner bottles BY, BM, BC, and BK, each having an exposed end surface, can be attached to and detached from the bottle container 54 in the front-rear direction of the printer. When the front door 52 is opened, the toner bottles BY, BM, BC, and BK can be attached to and detached from the printer main body in the front-rear direction. It is not a configuration in which the upper surface of the printer main body on which the stack unit 40 is formed is an upper door that can be freely opened and closed, and the toner bottles BY, BM, BC, and BK are attached and detached vertically. Therefore, even when an optional scanner device (not shown) is arranged above the printer 100 to constitute a copier, the toner bottles BY, BM, BC, and BK can be attached and detached. The first paper cassette 25 and the second paper cassette 26 described above are arranged below the front door 52, and are configured to be attached to and detached from the printer main body by sliding movement in the front-rear direction. Even if the front door 52 is opened, the detachability of the first paper cassette 25 and the second paper cassette 26 and the operability of input to the operation display 51 are not impaired.

Next, a characteristic configuration of the printer 100 according to the present embodiment will be described.
FIG. 4 is an enlarged configuration diagram showing the fixing device 60 together with a part of the second transfer unit 24. In the figure, a fixing device 60 includes a front surface heating roller 61, a fixing belt 62 as an endless belt member, a back surface heating roller 63, a nip back roller 64, a cleaning roller 65, a second temperature sensor 66, a first temperature. A sensor 67 and the like are included.

  The fixing belt 62 is stretched with a predetermined tension while being supported from the back surface by the back surface heating roller 63 and the nip back side roller 64. Then, it is endlessly moved clockwise in the figure by driving the nip back side roller 64 that is rotated clockwise in the figure by a driving means (not shown). As a material for the fixing belt 62, it is desirable to use a material having excellent heat resistance and durability. This is because, for reasons that will be described later, the temperature is raised from about 140 to 180 [° C.] by heating from the front surface and the back surface. Examples of the material excellent in heat resistance and durability include polyimide, polyetherimide, PES (polyether sulfide), PFA (tetrafluoroethylene perfluoroalkyl vinyl ether copolymer resin) and the like. Further, the structure of the fixing belt 62 may be either a single layer or a multilayer, but it is desirable to use a material having excellent toner releasability on at least the front surface. This is for the purpose of suppressing a partial offset of the first toner image from the first surface of the transfer paper P. A material suitable for the front surface is a coat layer having a thickness of about 10 [μm] obtained by adding a conductive material to a fluororesin such as PTFE (tetrafluoroethylene resin) or PFA. Further, fluorine rubber or silicon rubber may be used. Further, the thickness of the fixing belt 62 is 100 [μm] or less, preferably 40 [μm] or less. The conveyance direction in which the fixing belt 62 conveys the transfer paper P to the fixing nip is inclined at a predetermined inclination angle (30 ° to 60 °) with respect to the transfer paper conveyance direction of the second intermediate transfer belt 16.

  The front surface heating roller 61 has a metal pipe member 61a that is rotatably supported by a support means (not shown), and a halogen lamp 61b that is non-rotatably disposed therein. The pipe member 61a is heated from the inner surface by radiation from the halogen lamp 61b as a heat source. In addition, a fixing nip is formed by contacting the front surface of the fixing belt 62 so as to sandwich the fixing belt 62 with a nip back side roller 64 described later. In this fixing nip, the fixing belt 62 is heated from the front surface by heat conduction. The fixing device 60 also includes a front surface heating power source, a front surface temperature detection sensor, a front surface heating control circuit, and the like (not shown). The front surface heating power source supplies voltage to the halogen lamp 61B. The front surface temperature detection sensor detects the temperature of the front surface of the fixing belt 62 immediately after passing through the fixing nip, and outputs a temperature signal corresponding to the detection result.

  The nip back roller 64 has a metal cored bar 64b and a thick elastic layer 64a made of rubber or the like coated thereon. Then, the thick elastic layer 64a is flexibly elastically deformed by pressing from the front surface heating roller 61 via the fixing belt 62, thereby forming the fixing nip larger in the belt circumferential direction. Yes.

  The cleaning roller 65 has a metal core 65b and an elastic layer 65a coated thereon, and is in contact with the front surface of the fixing belt 62 immediately after passing through the fixing nip. It is arranged to rotate counterclockwise. The elastic layer 65 a has a surface roughness (Rz) that is rougher than the front surface of the fixing belt 62. A small amount of unfixed toner (offset toner, etc.) adhering to the front surface of the fixing belt 62 after passing through the fixing nip is softened by heating, so that the surface is rougher from the front surface. Transfer to the cleaning roller 65. By this transfer, the toner adhering to the front surface of the fixing belt 62 is cleaned. When the toner is transferred to the surface of the cleaning roller 65 serving as a cleaning unit, the fixing residual toner is removed by a cleaning blade (not shown) in contact with the cleaning roller 65. In the printer (100), the linear velocity of the second intermediate transfer belt 16 of the second transfer unit 24 and the linear velocity of the fixing belt 62 of the fixing device 60 are set to be equal.

  The back surface heating roller 63 has a metal pipe member 63a that is rotatably supported by a supporting means (not shown), and a halogen lamp 63b that is non-rotatably disposed therein. The pipe member 63a is heated from the inner surface by radiation from the halogen lamp 63b as a heat source. The back surface heating roller 63 heats the back surface of the fixing belt 62 approaching the stretch position by heat conduction from the pipe member 63b. Further, the back surface heating roller 63 has a back surface heating power source (not shown) for supplying a voltage to the halogen lamp 63b, a back surface heating control circuit for controlling the back surface heating power source, and the like.

  The second temperature sensor 66 is disposed in front of the nip back roller 64 in the belt moving direction, and detects the back surface temperature of the fixing belt 62 immediately before reaching the fixing nip. On the other hand, the first temperature sensor 67 is disposed on the front side of the back surface heating roller 63 in the belt moving direction, and detects the back surface temperature of the fixing belt 62 immediately before reaching the back surface heating roller 63.

  FIG. 5 is a block diagram showing a part of the heating control circuit. In the drawing, a second temperature sensor 66 and a first temperature sensor 67 each detect the back surface temperature of the fixing belt 62 and output a digital temperature signal to the control unit E2. The controller E2 stores the first temperature target value (for example, 160 to 180 ° C.) at the fixing nip of the fixing belt 62 in a storage unit such as a RAM (not shown). The transfer paper P is not allowed to enter the fixing nip portion until the value of the digital temperature signal sent from the second temperature sensor 66 reaches the first temperature target value. Further, the control unit E2 adjusts the heat generation amount of the halogen lamp by ON / OFF control of the back surface heating power source from the difference between the value of the digital temperature signal sent from the first temperature sensor 67 and the first temperature target value. . When the value of the digital temperature signal sent from the second temperature sensor 66 becomes the first temperature target value (for example, 160 to 180 ° C. or the like) by such control, the transfer paper P enters the fixing nip and is transferred. Fix the toner image on the paper.

  In this embodiment, the first temperature sensor 67 detects the temperature of the fixing belt 62 immediately before reaching the back surface heating roller 63. The temperature of the fixing belt 62 immediately before heating is the lowest on the circumference of the fixing belt 62 due to a temperature decrease of the fixing belt caused by the transfer paper P passing through the fixing nip and a temperature decrease caused by the environment. As a result, the fixing belt 62 can be quickly raised to the temperature target value as compared with the conventional one in which the heat generation amount of the halogen lamp 63b is adjusted based on the temperature immediately after passing through the fixing nip. Further, the temperature of the fixing belt 62 immediately before reaching the fixing nip is detected by the second temperature sensor 66, and when this temperature is less than the target value, the transfer paper is prevented from entering the fixing nip. This prevents the transfer paper from passing through the fixing nip when the fixing belt is not sufficiently heated. Therefore, it is possible to suppress the occurrence of fixing failure.

  The front surface temperature detection sensor outputs a digital temperature signal to the control unit E2. The controller E2 stores the second temperature target value (for example, 160 to 180 ° C.) of the front surface heating roller 61 in a storage unit such as a RAM (not shown). Then, the power supply from the surface heating power source to the halogen lamp 61b is ON / OFF controlled so that the value of the digital temperature signal sent from the surface temperature detection sensor becomes the second temperature target value.

  The transfer paper P on which the full-color images are transferred on both sides by the double-side transfer means is conveyed toward the fixing means 60 from below in the figure by the second intermediate transfer belt 16 of the second transfer unit 24. Then, after the leading end of the entire area in the circumferential direction of the fixing belt 62 hits the area between the stretched portion by the back surface heating roller 63 and the fixing nip, it is gradually brought into close contact with the fixing belt 62. Then, the toner is conveyed toward the fixing nip. When the fixing nip is reached, the first surface is strongly adhered to the fixing belt 62 heated by the back surface heating body 67 and heated, and at the same time, the second surface is firmly adhered to the front surface heating roller 61. It is squeezed and heated. It is heated from both sides at the fixing nip. By such heating from both sides, full-color images (not shown) existing on both sides of the transfer paper P are respectively heated and pressed to be fixed on each side.

  In this embodiment, the fixing belt 62 contacts the transfer paper P while moving on the surface of the transfer paper P conveyed toward the fixing device 60 by the second intermediate transfer belt 16 of the second transfer unit 24. Then, the transfer paper P is guided toward the fixing nip without rubbing the first toner image on the first surface of the transfer paper P. Therefore, image disturbance due to rubbing the unfixed toner image can be suppressed.

  Further, the conveyance direction in which the fixing belt 62 conveys the transfer paper P to the fixing nip is inclined at a predetermined inclination angle (30 ° to 60 °) with respect to the transfer paper conveyance direction of the second intermediate transfer belt 16. In this way, the fixing belt 62 conveys the transfer sheet P to the fixing nip by inclining the conveyance direction with respect to the transfer sheet conveying direction of the second intermediate transfer belt 16 at a predetermined inclination angle, so that the back surface heating roller of the fixing belt The transfer paper P is conveyed toward the fixing nip while being gradually brought into close contact with the region between the tensioning portion 63 and the fixing nip. As a result, the transfer paper P is conveyed to the fixing nip while maintaining appropriate adhesion to the fixing belt. Therefore, the transfer paper P can be smoothly guided toward the fixing nip without rubbing the first toner image on the first surface of the transfer P.

  Further, the control unit E2 may control the back surface temperature of the fixing belt 63 to be lower in the single-sided process than in the double-sided process. In the double-sided processing, the surface heating roller 61 has a surface temperature controlled to a value that can sufficiently soften the toner of the second toner image carried on the second surface of the transfer paper P in contact therewith. Is done. Further, the back surface temperature of the fixing belt 62 is controlled to a value that can sufficiently soften the toner of the first toner image carried on the first surface of the transfer paper P in contact therewith. However, in the single-side processing, since the first toner image is not formed on the first surface of the transfer paper P, it is not necessary to soften the toner of the first toner image by the fixing belt 62. Nevertheless, if the back surface temperature of the fixing belt 62 is controlled to a value sufficient to soften the toner of the first toner image, energy is wasted. Thus, as described above, in one-sided processing, wasteful energy consumption can be effectively suppressed by controlling the back surface temperature of the fixing belt 63 to be lower than that in the case of double-sided processing.

  Further, the control unit E2 may control the heating temperatures for the first surface and the second surface of the transfer paper P to values corresponding to the surface roughness Ra. Specifically, an optical sensor unit 60 serving as a surface characteristic detecting means is provided between the registration roller pair 31 and the above-described secondary transfer nip, and the surface roughness is detected as the surface characteristic of the transfer paper P, and the detection is performed. A temperature target value is determined based on the result. A fixing temperature data table in which the surface roughness Ra is associated with an appropriate fixing temperature value is stored in storage means such as a RAM (not shown) of the control unit E2. This appropriate fixing temperature is the value of the heat fixing temperature at which the toner image can be fixed most satisfactorily on the surface of the transfer paper P having the surface roughness Ra, and was investigated by a preliminary test. The higher the surface roughness Ra, the higher the temperature value. This is because the temperature of the toner image on the transfer paper P becomes harder as the surface roughness Ra increases.

  The control unit E2 specifies appropriate fixing temperature values corresponding to the surface roughness Ra of the first surface and the surface roughness Ra of the second surface calculated based on the transfer paper P passing through the optical sensor unit 60. Specifically, the first surface fixing temperature appropriate value corresponding to the calculated first surface roughness Ra and the second surface fixing temperature appropriate value corresponding to the second surface roughness Ra are set as the above-described fixing temperature data. Identify from the table. Then, the above-described first temperature target value and second temperature target value used in the surface temperature control of the front surface heating roller 61 and the back surface heating roller 63 are respectively set to the first surface fixing temperature appropriate value and the second temperature fixing value. Change to the same value as the appropriate value for the surface fixing temperature. Then, the first surface and the second surface of the transfer paper P that have passed through the secondary transfer nip and sent to the fixing device 60 are heated in accordance with the changed first temperature target value and second temperature target value, respectively. The That is, the heating temperature for the first surface and the second surface of the transfer paper P by the fixing device 60 is controlled to a value corresponding to the surface roughness Ra by the control unit E2, which is a heating and fixing temperature control means. By such control, it is possible to suppress a situation in which the surface roughness Ra is different between the front and back surfaces of the transfer paper P, resulting in a difference in image fixability, or a hot offset of the image occurring on either of the front and back sides. Can do.

Further, the control unit E2 controls the transfer paper P based on the first surface toner adhesion amount that is the toner adhesion amount to the first surface of the transfer paper P and the second surface toner adhesion amount that is the toner adhesion amount to the second surface. You may make it control the heating temperature with respect to a 1st surface and a 2nd surface.
An image data processing device E1 for acquiring image information sent from a personal computer or the like is connected to the control unit E2. Based on the image information acquired by the image data processing device E1, the controller E2 is the first surface toner adhesion amount that is the toner adhesion amount to the first surface of the transfer paper P and the toner adhesion amount to the second surface. The toner adhesion amount on the second surface is detected. It functions as a toner adhesion amount detection means. In the example of the illustrated apparatus, the control unit E2 superimposes a plurality of colors on the first toner image transferred to the first surface based on the image information for the first surface sent from the image data processing device E1. It is determined whether or not the toner image is a multicolor toner image obtained by combining. In many cases, the multicolor toner image includes a portion where the toner adhesion amount is considerably increased, such as a color photographic image portion. In contrast, a monochromatic toner image often has a small toner adhesion amount such as a character image. Therefore, the control unit E1 determines whether the toner adhesion amount on the first surface is “relatively large” or “relatively small” depending on whether the first toner image is a multicolor toner image or a single color toner image. Detect in stages. Similarly, the toner adhesion amount on the second surface is detected in two stages of “relatively large” and “relatively small” based on the image information for the second surface sent from the image data processing device E1. To do.

  When the control unit E2 detects that the first surface toner adhesion amount is “relatively large”, the control unit E2 sets the above-described first temperature target value to a relatively high value. On the other hand, when it is detected that “relatively small”, the above-described first temperature target value is set to a relatively low value. The first temperature target value is switched based on the first surface toner adhesion amount. Then, the power supply to the halogen lamp 63b is turned ON / OFF to control the temperature of the fixing belt 63 before passing through the fixing nip so as to approach the set first temperature target value. On the other hand, the surface temperature of the front surface heating roller 61 is similarly controlled based on the second surface toner adhesion amount.

  By performing such control, it is possible to make the glossiness of the front and back images uniform regardless of the difference in the toner adhesion amount between the front and back surfaces of the transfer paper P. Therefore, the difference in glossiness of the image due to the difference in the toner adhesion amount between the front and back surfaces of the transfer paper P can be suppressed.

  In the present embodiment, as described above, the heat generating source of the back surface heating roller 63 or the front surface heating roller is the halogen lamps 63b and 61b, and the roller is heated by the radiant heat (non-contact) of the heat generating source. It is not limited to this. For example, a resistance heating element may be attached to the roller, and the roller may be directly heated, or the roller may be heated by electromagnetic induction using a magnetic field generating means.

  FIG. 6 is a diagram illustrating an example in which the back surface heating roller 63 is heated using electromagnetic induction. 6A is a cross-sectional view in the horizontal direction, and FIG. 6B is a cross-sectional view in the longitudinal direction. As shown in FIG. 6, a bobbin 163 a that changes a magnetic field and an induction coil 163 b that is wound on the bobbin 163 a and flows a high-frequency alternating current are installed as magnetic field generating means inside the back surface heating roller 63. An insulating film 164 is provided between the induction coil 163b and a metal pipe member which is a heating element of the back surface heating roller 63. When a current flows through the induction coil 163b, a magnetic force is generated, and the metal pipe member is induction-heated by this magnetic force. The back surface heating roller 63 is heated by heating the metal pipe member. By using electromagnetic induction as a heating method, it is possible to prevent heating of members other than the conductor, so that it is possible to eliminate problems caused by heating unnecessary portions and waste of energy.

  FIG. 7 is a cross-sectional view of the back surface heating roller 263 showing an example in which the back surface heating roller 263 is heated using a resistance heating element. As shown in FIG. 7, this back surface heating roller 263 has a heating resistance layer 263b obtained by combining graphite, carbon black, lead dioxide, etc. with a resin on the outer peripheral surface of a metal pipe member 263a. . An electrode connected to a back surface heating power source (not shown) is in contact with the heating resistance layer 263b. By supplying power from the back surface heating power source to the heat generating resistance layer through the electrodes, the heat generating resistance layer generates heat, and the back surface heating roller is heated. In addition to the configuration shown in FIG. 7, the heat generating resistance layer 263 b may be provided on the inner peripheral surface of the metal pipe member 263 a, and the back surface heating roller itself does not generate heat without using the metal pipe member. It is good as a body. In this way, by using a heating method using a resistance heating element, the heat generated by the resistance heating element is directly propagated to the surface of the back surface heating roller, so that the amount of heat lost on the surface of the back surface heating roller can be readily compensated. . Therefore, it is not necessary to increase the heat capacity of the back heating roller. Therefore, according to the fixing device, the heat capacity of the heating roller can be reduced, so that the standby time can be shortened and the power consumption can be reduced.

  In the present embodiment, one of the rollers that stretch and support the fixing belt 62 is the back surface heating roller 63 that heats the fixing belt 62, but is not limited thereto. For example, as shown in FIG. 8, after passing through the tension position by the lower tension roller 66 disposed closest to the second transfer unit 24 which is a part of the double-side transfer means, A back surface heating body 67 that heats the fixing belt 62 may be provided in a region before reaching. In this case, the first temperature sensor 67 is disposed immediately before the fixing belt reaches the back surface heating body 67. By configuring the back surface side heating means so as to heat the back surface area of the fixing belt 62 after passing the position where the lower stretching roller 66 is stretched, the following becomes possible. That is, as shown in FIG. 4, the heat source of the fixing device 60 is supplied from the second transfer unit 24, which is a double-sided transfer means, as compared with the case where one of the above-mentioned stretching rollers is used as a back surface heating roller to heat the back surface of the fixing belt 62. You can keep away. As a result, the adverse effect on the image due to the second transfer unit 24 being heated by the fixing device 60 can be suppressed.

  FIG. 9 is a schematic configuration diagram of a printer 300A according to the second embodiment. A printer 300A shown in FIG. 9 includes a first image forming unit 380Y, 380M, 380C, and 380K that forms a toner image to be transferred onto the first surface of the transfer paper P, and a toner image that is transferred onto the second surface of the transfer paper P. Second image forming units 381Y, 381M, 381C, and 381K. The toner image transferred to the first surface formed by the first image forming unit 380 is transferred to the first intermediate transfer belt 321 and then transferred to the first surface of the transfer paper P. On the other hand, the toner image transferred to the second surface formed by the second image forming unit 381 is transferred to the second intermediate transfer belt 331 and then transferred to the second surface of the transfer paper P. The transfer paper P having the toner images transferred on both sides in this way is conveyed to the fixing device 400 by the conveying device 350.

  FIG. 10 is an enlarged configuration diagram illustrating the heat fixing device 400 and a part of the paper transport device 350 of the printer 300A. As shown in the figure, the heat fixing device 400 includes a pair of fixing belt units, a first fixing belt unit 401a and a second fixing belt unit 401b.

  A first fixing belt unit 401a serving as a first surface heating unit includes a first fixing belt 402a, a first nip forming roller 403a, a first heating roller 404a, a heating upstream first temperature sensor 405a, a heating downstream first temperature sensor 406a, and the like. Have. The first fixing belt 402a is rotated clockwise in the figure by the first nip forming roller 403a that is rotated clockwise in the figure while being stretched between the first nip forming roller 403a and the first heating roller 404a that are tension members. It can be moved endlessly. Further, the second fixing belt unit 401b serving as the second surface heating means has substantially the same configuration as the first fixing belt unit 401a. The image forming apparatus includes a second fixing belt 402b, a second nip forming roller 403b, a second heating roller 404b, a heating upstream second temperature sensor 405b, a heating downstream second temperature sensor 406b, and the like.

  The first fixing belt unit 401a and the second fixing belt unit 401b contact the first fixing belt 402a and the second fixing belt 402b with each other at the places where the first fixing belt 402a and the second fixing belt 402b are wound around the first nip forming roller 403a and the second nip forming roller 403b. The fixing nip is formed. Each of the first heating roller 404a and the second heating roller 404b serving as heating means has a metal roller and heat generation means such as a halogen lamp. Then, the first fixing belt 402a and the second fixing belt 402b are heated while being stretched at a place different from the belt running place by the first nip forming roller 403a and the second nip forming roller 403b. The first fixing belt 402a and the second fixing belt 402b heated by the first heating roller 404a and the second heating roller 404b enter the fixing nip.

  The heating upstream first temperature sensor 405a and the heating upstream second temperature sensor 405b know the surface temperatures of the first fixing belt 402a and the second fixing belt 402b immediately before being heated by the first heating roller 404a and the second heating roller 404b. Detect by technology. And a detection result is sent to the control part (E2) which is not illustrated as a heating upstream 1st temperature signal and a heating upstream 2nd temperature signal. Further, the heating downstream first temperature sensor 406a and the heating downstream second temperature sensor 406b detect the back surface temperatures of the first fixing belt 402a and the second fixing belt 402b immediately before reaching the fixing nip by a known technique. And a detection result is sent to the control part (E2) which is not illustrated as a heating downstream 1st temperature signal and a heating downstream 2nd temperature signal.

  When the heating downstream first temperature sensor 406a and the heating downstream second temperature sensor 406b detect that the first fixing belt 402a and the second fixing belt 402b are within a predetermined range, the transfer paper P is separated by the separation charger 358. The toner is separated from the belt member 351 of the conveying device 350 and enters the fixing nip of the heat fixing device 400. The first surface and the second surface are heated by the first fixing belt 402a and the second fixing belt 402b to fix the first toner image and the second toner image, and then are received by the cooling roller pair 370 described above. Passed.

  On the other hand, the amount of heat accumulated in the first fixing belt 402a and the second fixing belt 402b while the belt goes around is deprived by the transfer paper P, the environment, and the like, and how much the temperature is lowered. It is detected by the heating roller 404b. And based on the detection result detected with the 1st heating roller 404a and the 2nd heating roller 404b, a control part (E2) adjusts the heating amount of the 1st heating roller 404a and the 2nd heating roller 404b.

  The first nip forming roller 403a and the second nip forming roller 403b are obtained by coating a metal cored bar with an elastic layer made of an elastic material such as rubber. By deforming the elastic layer at the fixing nip, the adhesion between the first fixing belt 402a and the first surface of the transfer paper P is improved, or the adhesion between the second fixing belt 402b and the second surface of the transfer paper P is improved. And the size of the fixing nip in the paper conveyance direction can be increased.

  The first fixing belt 402a and the second fixing belt 402b are made of a heat-resistant resin such as polyimide or polyamide so as to suppress thermal damage caused by heating to the first heating roller 404a and the second heating roller 404b as much as possible. Has been.

  In the above description, the image forming apparatus provided with the one-pass double-sided transfer method has been described. However, the present invention is not limited to this, and can be applied to an image forming device employing a belt fixing method. Further, the present invention is not limited to the image forming apparatus, and can be applied to various apparatuses that heat and use an endless belt such as a belt heater.

(1)
As described above, according to the belt heating method of the present embodiment, heating to the belt is performed based on the temperature of the belt member portion between the heating unit and the stretching member disposed on the upstream side in the belt conveyance direction from the heating unit. By adjusting the amount, once the belt member passes through the heating means, the belt member can be brought to a temperature within a predetermined range.
(2)
Further, according to the fixing device of the present embodiment, the fixing belt 62 as a belt member includes a back surface heating roller 63 as a heating unit and a tension member disposed upstream of the back surface heating roller 63 in the belt conveyance direction. A first temperature sensor is provided as temperature detecting means for detecting a partial temperature of the fixing belt. Accordingly, it is possible to detect the temperature of the fixing belt which has been lowered due to the amount of heat taken away by contact of a member such as transfer paper or the environment. Further, the control unit E2 controls the amount of heat generated by the back surface heating roller 63 (heat generation source) based on the temperature detection result. As a result, the temperature of the fixing belt, which has been lowered due to heat loss due to contact with the member such as transfer paper or the environment, can be returned to a predetermined range of temperature once passing through the back surface heating roller 63. Accordingly, the temperature of the fixing belt in the fixing nip can be kept within a predetermined range even in continuous printing of thick paper that takes a large amount of heat from the fixing belt or in an environment where the fluctuation is severe. As a result, fixing failure and the like can be suppressed.
(3)
In addition, according to the fixing device of the present embodiment, the second temperature sensor 66 is provided as the second temperature detecting unit that detects the partial temperature of the fixing belt until the fixing belt reaches the fixing nip from the heating unit. ing. As a result, it is possible to accurately detect whether or not the fixing belt is within a predetermined temperature range in the fixing nip, and fixing defects can be suppressed.
When only the first temperature sensor 67 is used to control the amount of heat generated by the back surface heating roller 63 (heat generation source) and to detect that the fixing belt is within a predetermined temperature range, it is necessary to rotate the fixing belt at least once. There is. That is, after the fixing belt is heated to a predetermined temperature range, the temperature of the fixing belt is detected again by the first temperature sensor 67 to determine that the fixing belt is at the predetermined temperature. On the other hand, in the fixing device of the present embodiment, the second temperature sensor disposed upstream of the first temperature sensor 67 in the belt moving direction detects whether or not the fixing belt is within a predetermined temperature range. Yes. Therefore, it can be detected before the belt makes a full circuit whether or not the heat amount taken by the fixing belt by the environment, transfer paper, or the like is compensated by the back surface heating roller to be within a predetermined temperature range. As a result, it is possible to detect whether or not the belt is at a predetermined temperature earlier than the detection of whether or not the first temperature sensor 67 is within a predetermined temperature range. Thereby, the speed of continuous printing can be increased.
(4)
Further, according to the fixing device of the present embodiment, one of the plurality of stretching members is the back surface heating roller 63 provided with a heat source as a heating body, and the pipe member with the heat source as a resistance heating body. Heating in contact with. In such a configuration, since the heat generated by the resistance heating element directly propagates to the surface of the back surface heating roller, the amount of heat lost on the surface of the back surface heating roller can be compensated immediately compared to the method of heating the pipe member in a non-contact manner using radiant heat. be able to. Therefore, it is not necessary to increase the heat capacity of the back heating roller. As a result, it is possible to reduce the heat capacity of the heating roller as compared with a method in which the pipe member is heated in a non-contact manner, shorten the standby time, and reduce power consumption.
(5)
Further, the heat source may be a heater such as a halogen lamp, and the pipe member may be heated in a non-contact manner by radiant heat. In such a configuration, the heat generating source can be fixed and the pipe member can be heated, so that it can be connected to the power source with a simple configuration as compared with the heating method in which the rotating pipe member is contacted and heated.
(6)
Further, the pipe member may be heated by a heating method using electromagnetic induction. In such a configuration, the rotating pipe member can be heated in a non-contact manner, so that it can be connected to the power source with a simple configuration. In addition, the temperature of the fixing belt 62 can be raised with less energy and the temperature rise time on the back surface of the belt can be shortened compared to the case of heating by the radiation method.
(7)
Further, according to the fixing device of the present embodiment, the front surface heating roller is provided as a pressure body heating means for heating the pressure body, the recording body is sandwiched between the fixing nips, and toner images are formed on both surfaces thereof. Fixing process is performed. Thus, the image can be fixed on both sides of the transfer paper by passing the transfer paper once through the fixing nip.
(8)
Further, according to the fixing device of the present embodiment, the fixing belt 62 conveys the transfer paper P that has entered the fixing device 60 to the fixing nip. The conveyance direction in which the fixing belt 62 conveys the transfer paper P to the fixing nip is inclined at a predetermined inclination angle (30 ° to 60 °) with respect to the fixing device entering direction of the transfer paper P. As a result, the transfer paper P is conveyed toward the fixing nip while gradually coming into close contact with the fixing belt. Accordingly, the transfer paper P can be smoothly guided toward the fixing nip without rubbing the first toner image on the first surface of the transfer paper P.
(9)
In addition, according to the image forming apparatus of the present embodiment, fixing failure can be suppressed by using the fixing device having the features (2) to (8). In addition, since the fixing belt can be quickly heated to a temperature within a predetermined range, the printing time can be shortened continuously.

1 is a schematic configuration diagram of a printer according to an embodiment. FIG. 3 is an enlarged configuration diagram illustrating a process unit for Y of the printer. FIG. 2 is a perspective view illustrating an image forming system including the printer and a personal computer. FIG. 3 is an enlarged configuration diagram illustrating a fixing device of the printer together with a part of a second transfer unit. FIG. 2 is a block diagram showing a part of an electric circuit of the printer. The figure which shows the example which made the heating system using the electromagnetic induction the heat source of the back surface heating roller of the printer. The figure which shows the example which made the heating system using the resistance heating element the heat source of the back surface heating roller of the printer. The figure which shows the example which used the heating means which heats the belt of the printer as a back surface heating body. FIG. 6 is a schematic configuration diagram of a printer according to a second embodiment. FIG. 9 is an enlarged configuration diagram illustrating a heat fixing device and a part of a paper transport device of a printer according to a second embodiment. 1 is a diagram illustrating a conventional fixing device.

Explanation of symbols

1Y, M, C, K photoconductor (image carrier)
6Y, M, C, K Process cartridge (part of visible image forming means)
7 Exposure equipment (part of visible image forming means)
15 First transfer unit (part of double-sided transfer means)
24 Second transfer unit (part of double-sided transfer means)
60 Fixing device (fixing means)
61 Front surface heating roller 61 (front surface heating body)
62 Fixing belt (belt member)
63 Back surface heating roller (stretching member)
64 Nip back roller (stretching member)
65 Cleaning roller (cleaning means)
66 Second temperature sensor 67 First temperature sensor

Claims (9)

A belt heating method of heating a belt member that moves endlessly while being supported from a back surface by a plurality of stretching members to a temperature in a predetermined range by a heating means,
A belt heating method, comprising: adjusting a heating amount of a belt based on a belt member partial temperature between the heating unit and a tension member disposed upstream of the heating unit in the belt conveyance direction. A belt member that moves endlessly, a plurality of tension members that are stretched while supporting the belt member from the back surface, a pressure member that abuts against the front surface of the belt member to form a fixing nip, and the belt member. A fixing device that includes a heating unit that heats the recording medium, and fixes the toner image by sandwiching the recording medium in the fixing nip.
A temperature detecting means for detecting a belt member partial temperature between the heating means and a tension member disposed upstream of the heating means in the belt conveying direction; and a heating value of the heating means based on a temperature detection result. And a control unit for controlling the fixing device. The fixing device according to claim 2.
A fixing device comprising: a second temperature detecting means for detecting a belt member partial temperature until the belt member reaches the fixing nip from the heating means.   4. The fixing device according to claim 2, wherein the heating unit is a heating body that heats one of the plurality of stretching members, and the heating body is heated in contact with the stretching member. A fixing device characterized. The fixing device according to claim 2 or 3,
The fixing device according to claim 1, wherein the heating unit is a heating body that heats one of the plurality of stretching members, and the heating body heats the stretching members in a non-contact manner. The fixing device according to claim 2 or 3,
The heating unit includes a magnetic field generation unit and a heating element, and the heating member is heated by electromagnetic induction by a magnetic field generated by the magnetic field generation unit to heat the belt member. . The fixing device according to any one of claims 2 to 6,
A fixing device comprising a pressure member heating means for heating the pressure member, wherein the recording medium is sandwiched between the fixing nips and a toner image is fixed on both surfaces thereof. The fixing device according to any one of claims 2 to 7,
The belt member is configured to convey the recording member that has entered the fixing device to the fixing nip, and a conveying direction in which the belt member conveys the recording member to the fixing nip is determined by fixing the recording member. A fixing device, which is inclined at a predetermined inclination angle with respect to the apparatus entering direction. An image carrier that carries a toner image, a visible image forming unit that forms a toner image on the surface of the image carrier, a double-side transfer unit that transfers the toner image on the image carrier to both sides of the recording medium, An image forming apparatus comprising fixing means for fixing a toner image on both sides of the recording medium,
9. The image forming apparatus according to claim 2, wherein the fixing unit is the fixing device according to claim 2.

Images