JP4672291B2 - Image forming apparatus - Google Patents

Description

The present invention is a copying machine, a facsimile, relates to an image forming apparatus and an image forming method used for this, such as a printer, particularly, those related to the image forming equipment for forming images on both sides of a recording medium such as transfer paper is there.

  Conventionally, a switchback method, a one-pass method, or the like is known as a method for forming images on both surfaces of a recording medium such as transfer paper with toner. In the switchback method, the recording medium is passed through a transfer unit and a fixing unit, an image is recorded on one surface of the recording unit, and then the recording unit is reversed by a reverse conveyance path. Then, the image is recorded on the other side by switching back to the transfer unit and the fixing unit. On the other hand, the one-pass method is a method in which a recording medium having a toner image transferred on both sides by a double-side transfer unit is passed through a fixing unit, and an image can be recorded on both sides without switching the recording unit back. The one-pass method is superior to the switchback method in the following points. In other words, cost increases by providing a complicated mechanism for switchback, longer image formation time by switchback, and jamming by switching back the curled recording medium by heating by the fixing means are all avoided. It is a point to get. As an image forming apparatus that forms an image by the one-pass method, for example, those described in Patent Document 1 and Patent Document 2 are known.

JP 2003-295661 A JP 2004-86090 A

  In an image forming apparatus that forms an image on both sides of a recording medium by a one-pass method, it is known that a difference in image quality between the front and back of the recording medium is easily noticeable. The present inventor conducted intensive research on the cause of such a difference in image quality, and found the following. That is, the appropriate value of the heating amount per unit time of the unfixed toner image varies depending on the toner adhesion amount per unit area. If the heating amount is much lower than the appropriate value, fixing failure will occur. On the contrary, if the heating amount greatly exceeds an appropriate value, hot offset is caused. This hot offset is a phenomenon in which a toner image is transferred to a heating member that is pressed while heating the recording medium in the heat-fixing device, thereby causing white spots in the image on the recording medium. The heating amount per unit time does not cause hot offset or fixing failure as much as possible even if the unfixed toner image is a character image with a relatively small amount of toner adhesion or a solid image with a relatively large amount of toner adhesion. It is set to such a value. For this reason, unless there is an extraordinary situation, there will be no situation where a hot offset or a fixing failure occurs to cause a difference in image quality between the front and back of the recording medium. However, the image quality greatly depends not only on the presence or absence of hot offset or fixing failure, but also on the glossiness of the image. The glossiness of the image varies greatly even if the difference in the toner adhesion amount is slight. For this reason, in the one-pass image forming apparatus, it was found that the difference in image quality between the front and back of the recording body is likely to occur due to the difference in glossiness of the image due to the difference in the toner adhesion amount between the front and back of the recording body. .

  Note that the image forming apparatus described in Patent Document 1 includes a fixing roller pair that heats a recording medium while being sandwiched between rollers as a heat fixing unit. In the fixing roller pair, the separation property of the recording medium from the fixing roller which is more easily attached to the recording medium after the fixing process is improved. If the recording body does not stick to the fixing roller and is not separated, the contact surface with the fixing roller is excessively heated. And a difference in glossiness appears between the other surface. Therefore, the separability from the fixing roller, which tends to stick, is improved. Thereby, if there is no difference in the toner adhesion amount of the unfixed toner image between the front and back, the difference in glossiness can be suppressed. However, when there is a difference in the toner adhesion amount, the difference in glossiness cannot be suppressed.

  On the other hand, in the conventional one-pass method, a toner image is formed on a first surface and a second surface of a recording medium using a common toner image forming unit, and a separate toner image forming unit is used. There is a method for forming a toner image. The image forming apparatus of Patent Document 2 using the former method cannot form an image on a recording medium when the toner image forming unit fails. In the period until the toner image forming means is repaired, the image cannot be output at all, and the downtime of the apparatus becomes serious. On the other hand, the image forming apparatus of Patent Document 1 using the latter method is in a single-sided print mode in which an image is formed only on one side of a recording medium even if one of two toner image forming units fails. Thus, an image can be formed using the other. For this reason, the downtime of the apparatus can be reduced as compared with the image forming apparatus disclosed in Patent Document 2.

  However, even in the image forming apparatus disclosed in Patent Document 1, if any one of the toner image forming units fails, the double-sided print mode in which images are formed on both sides of the recording medium cannot be executed. For this reason, the down time could not be reduced sufficiently.

The present invention is more has been made in view of the background, it is an purpose of that, the image forming apparatus capable of suppressing the difference in glossiness of the image due to toner adhesion amount is different on the front and back sides of the recording medium Is to provide.

In the later-described reference technique, it is possible in addition to achieving the above Symbol purpose, to further reduce the downtime due to the failure of a toner image forming means for forming images on both sides of the recording medium.

In order to achieve the above object, an invention according to claim 1 is an image information acquisition means for acquiring image information, and a first toner image transferred to the first surface of the recording medium is heated and fixed on the first surface. a heating fixing unit that allowed to heat fixing the second toner image transferred on the second surface of said recording medium to said second surface, said first toner image formed on the surface of the image bearing member based on the image information and the double-sided transfer means, while transferring the first surface of the front of the recording material is sent to the heating fixing unit, the second toner image formed on the surface of the image bearing member based on the image information by double-sided transfer means, and transferring the second surface of the front of the recording material is sent to the heating fixing unit, and a toner image forming means for forming a toner image on both surfaces of the recording medium, and a recording material The first surface heating means for heating the recording medium from the first surface side, and the recording body from the second surface side. In the image forming apparatus having the second surface heating unit in the heat fixing unit, the first surface toner adhesion amount, which is the toner adhesion amount to the first surface of the recording medium via the toner image forming unit, and the second surface A toner adhesion amount detecting means for detecting a toner adhesion amount on the second surface as a toner adhesion amount, a first surface heating temperature as a heating temperature by the first surface heating means, and a heating temperature by the second surface heating means. Heating temperature control means for respectively controlling a certain second surface heating temperature is provided, and when the fixing process by the heat fixing means is performed on the recording medium on which the toner images are formed on both surfaces, Based on the detection result of the first surface toner adhesion amount, the first surface heating temperature is controlled so as to increase the first surface heating temperature as the first surface toner adhesion amount increases. Then, based on the detection result of the second surface toner adhesion amount, a process of controlling the second surface heating temperature so as to increase the second surface heating temperature as the second surface toner adhesion amount increases is performed. As described above, the heating temperature control means constitutes a pair of fixing belt units that move the fixing belt endlessly while being stretched by a plurality of stretching members, and the fixing belt units are provided as the heating and fixing means. A belt heating means for forming a fixing nip by bringing the respective fixing belts into contact with each other at a place where the fixing belt is hung on the nip forming roller, and heating a portion of the fixing belt different from the hung place. The first surface heating means is the one in which the fixing belt is brought into contact with the first surface of the recording medium sandwiched between the fixing nips of the pair of fixing belt units. And the one that makes the fixing belt contact the second surface of the recording medium sandwiched between the fixing nips functions as the second surface heating means.
According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, each of the pair of fixing belt units is provided with a belt cooling means for cooling the fixing belt portion that has passed through the fixing nip. To do.
According to a third aspect of the present invention, in the image forming apparatus according to the first or second aspect, the entire region in the conveyance direction of the recording medium is divided into a plurality of divided regions, and the first surface toner adhesion amount and the first amount in each divided region are divided. The toner adhesion amount detection means is configured to calculate the two-surface toner adhesion amount, and the heating is performed so that the first surface heating temperature and the second surface heating temperature are controlled for each divided region based on the calculation result. The temperature control means is configured.
According to a fourth aspect of the present invention, there is provided the image forming apparatus according to any one of the first to third aspects, wherein the first image carrier that exclusively carries the toner image formed on the first surface and the second surface. A second image carrier that exclusively carries the toner image to be formed, and intermediate transfer of the first toner image on the first image carrier to the surface of the first intermediate transfer member and then the first image on the first surface. The toner image forming means is configured to transfer the second toner image on the second image bearing member onto the surface of the second intermediate transfer member and then transfer the second toner image onto the second surface. The first intermediate transfer member and the second intermediate transfer member are arranged in non-contact with each other.
According to a fifth aspect of the present invention, in the image forming apparatus of the fourth aspect, as the first image carrier, a plurality of toner images carrying the toner images having different colors are used, and the second image carrier is used. A plurality of toner images carrying the toner images of different colors are used, and a plurality of toner images on the first image carrier are transferred onto the first intermediate transfer belt, respectively, The toner image forming means is configured so that the toner images on the second image carrier are transferred onto the second intermediate transfer belt in an overlapping manner.
According to a sixth aspect of the present invention, in the image forming apparatus according to the fourth or fifth aspect, the recording body feeding portion of the recording body housing means for feeding the recording body accommodated therein toward the double-side transfer means, and the toner It is characterized in that the recording member receiving portion of the image forming means has the same height in the vertical direction.
According to a seventh aspect of the present invention, in the image forming apparatus of the sixth aspect, the recording medium discharging portion of the toner image forming means and the recording medium that has passed through the heating and fixing means are discharged to the outside of the image forming apparatus casing. It is characterized in that the recording member receiving portion of the discharging means has the same height.

In these inventions, by controlling the first surface heating temperature in accordance with the first surface toner adhesion amount, the fixing process is performed on the unfixed toner image on the first surface with a heating amount suitable for the toner adhesion amount. Do. On the other hand, by controlling the second surface heating temperature in accordance with the second surface toner adhesion amount, the fixing process is performed on the unfixed toner image on the second surface with a heating amount suitable for the toner adhesion amount. With these fixing processes, on any surface, the heating amount is increased so that the glossiness of the image is excessively conspicuous, or the heating amount is reduced so that the glossiness of the image hardly appears. Fixing is performed with a heating amount that causes gloss to appear. Then, the glossiness of the front and back images can be made uniform regardless of the difference in the toner adhesion amount between the front and back of the recording medium. Accordingly, it is possible to suppress the difference in glossiness of the image due to the difference in the toner adhesion amount between the front and back of the recording medium.

A reference technique different from the present invention will be described.
In the reference technique, image information acquisition means for acquiring image information and a first toner image are formed on the first surface of the recording medium based on the image information, while the second toner is formed on the second surface of the recording medium. A toner image forming unit that forms an image; and a heat fixing unit that heat-fixes the toner image on both sides of the recording medium via the toner image forming unit, and that heats the recording medium from the first surface side. The heating and fixing unit includes a surface heating unit and a second surface heating unit that heats the recording medium from the second surface side, and the amount of toner attached to the first surface of the recording medium via the toner image forming unit. A toner adhesion amount detecting means for detecting a first surface toner adhesion amount and a second surface toner adhesion amount that is a toner adhesion amount on the second surface, and a first surface heating temperature that is a heating temperature by the first surface heating means. And at the heating temperature by the second surface heating means Heating temperature control means for respectively controlling the second surface heating temperature, and when the fixing process by the heating fixing means is performed on the recording medium on which the toner images are formed on both sides, The first surface heating temperature is controlled based on the detection result of the first surface toner adhesion amount, while the second surface heating temperature is controlled based on the detection result of the second surface toner adhesion amount. In the image forming apparatus comprising the heating temperature control means, as the toner image forming means, a first toner image forming means for forming a first toner image on the first surface and a second toner image on the second surface are formed. A first toner image forming unit and an abnormality detecting unit for detecting an abnormality of the second toner image forming unit, and the image information is recorded on the recording medium. Information for outputting an image to a surface, and the abnormality detection unit detects an abnormality in either the first toner image forming unit or the second toner image forming unit In the first toner image forming unit and the second toner image forming unit, the first toner image forming unit and the second toner image forming unit are configured so that an image is formed only on one side of the recording body by the one in which no abnormality is detected. Control means for controlling the second toner image forming means is provided.
Further, specific example 1 of the reference technique includes an information transmission unit that transmits information to the operator in the reference technique, and the abnormality detection unit detects one of the first toner image forming unit and the second toner image forming unit. When an abnormality is detected, only one of the first toner image and the second toner image that corresponds to the first toner image forming unit or the second toner image forming unit in which no abnormality is detected. Then, after forming on one surface of the recording medium, the information transmitting means transmits information to the operator that the operation to set the image forming apparatus main body by turning the recording body upside down is performed. Based on the operation by the operator, the first toner image forming means or the second toner image forming unit in which no abnormality is detected is detected as one of the first toner image and the second toner image that has not been formed on the recording medium. The recording by the toner image forming means So as to perform the control of the formation on the other side, it is characterized in that constitute the control means.
Further, specific example 2 of the reference technique is that, in the reference technique, when an abnormality of either the first toner image forming unit or the second toner image forming unit is detected by the abnormality detecting unit, an abnormality is detected. Control that alternately forms the first toner image and the second toner image only on one side of a plurality of recording media using only the first toner image forming unit or the second toner image forming unit that has not been performed. The control means is configured so as to be performed.
Further, specific example 3 of the reference technique includes a first surface heating unit that heats the recording medium from the first surface side as the heat fixing unit in the reference technique, specific example 1 or specific example 2, and the recording medium. In the case where an abnormality of either the first toner image forming means or the second toner image forming means is detected by the abnormality detecting means using a device having a second surface heating means for heating from the second surface side Control is performed to generate heat only from the first surface heating unit and the second surface heating unit corresponding to the first toner image forming unit or the second toner image forming unit in which no abnormality is detected. Thus, the control means is configured as described above.
In these cases , when an abnormality occurs in either the first toner image forming unit or the second toner image forming unit and there is an instruction to execute double-sided printing to form images on both sides of the recording medium, the abnormality is detected. A toner image is formed on only one side of the recording medium by the toner image forming means that is not generated. For this reason, the downtime of the apparatus can be further reduced as compared with a case where image formation is not performed at all without receiving an instruction to execute double-sided printing.

Hereinafter, an image forming apparatus according to the present invention, an electrophotographic printer (hereinafter, simply referred to as a printer) Before describing implementation form of, it is described printer according to the first reference embodiment.
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 the figure, this printer 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). . 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 means. A developing device 5Y and the like are provided. In the photoreceptor 1Y, an aluminum cylinder having a diameter of 30 to 120 [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 1 </ b> Y is exposed and scanned by the laser beam L to carry 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. Then, primary transfer is performed on 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 intermediate 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 may use a two-component developer containing toner and a magnetic carrier, or may use only toner powder. The toner may be a pulverized toner manufactured by a pulverization method or a toner formed in a spherical shape.

  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 in the drawing. The image data processing apparatus E1 as image information acquisition means acquires image information sent from a personal computer (hereinafter referred to as a personal computer) or the like. Based on the image information, an exposure scanning control signal is generated and sent to the exposure apparatus 7. The exposure device 7 serving as a latent image forming unit irradiates each photoconductor 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.

  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 so as to overlap in the 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 27 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 feed cassettes (25, 26) serving as recording medium accommodation means and the manual feed tray 27, a paper feed path 32 having a pair of registration rollers 31 and a paper feed guide path 33 merging therewith are arranged. It is installed. 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 31 a and the second registration roller 31 b 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 to a secondary transfer nip described later. On the other hand, the manual paper feed roller 30 is in contact with the uppermost transfer paper P of the transfer paper bundle placed on the manual feed tray 27. Then, by being driven to rotate by a driving means (not shown), the uppermost transfer paper P is sent out toward the paper feed guide path 33. 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-sided transfer device that is a double-sided transfer unit. This double-sided transfer device 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 rollers, sandwich the first intermediate transfer belt 8 that is moved endlessly in this way between the photoreceptors 1Y, 1M, 1C, and 1K, respectively. The next transfer nip is formed. Then, in response to a power supply (not shown), 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. In addition to these four primary transfer rollers 9Y, 9M, 9C, and 9K, all the above-mentioned 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. In each primary transfer nip, Y, M, C, and K toner images on the photoreceptors 1Y, 1M, 1C, and 1K are superimposed on the first intermediate transfer belt 8 by the action of the nip pressure and the primary transfer bias. Next transferred. 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 four-color toner image that is a visible image formed on the first intermediate transfer belt 8 is secondarily transferred to a second intermediate transfer belt 16 or a transfer sheet P described later at the secondary transfer nip.

  Transfer residual toner that has not been secondarily transferred to the second intermediate transfer belt 16 or the transfer paper P described later 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 abut on the outer surface (front surface) side of the loop, and a first cleaning device 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. 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 second transfer unit 24 of the double-sided transfer device is disposed on the right side of the first transfer unit 15 in the drawing, and includes a second intermediate transfer belt 16 that is a second intermediate transfer member, a second cleaning device 18, and a transfer. A charger 23 is provided. 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 is a metal roller or a roller whose core metal is covered with a conductive rubber layer, and a secondary transfer bias having a polarity (for example, plus polarity) opposite to that of toner is supplied from a power source (not shown). . 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, if this four-color toner image is the first toner image to be transferred to the first surface (the surface facing upward on the stack unit 40 described later) which is one surface of the transfer paper P, the transfer is performed. 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 by the action of the nip pressure and the secondary transfer bias at the secondary transfer nip as a nip. The 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 to the second surface, which is the other surface of the transfer paper P, 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 described above, 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. In this configuration, the first intermediate transfer belt 8 is separated from the transfer paper P at the outlet of the secondary transfer nip, and the transfer paper 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, a transfer charger 23 is disposed with a predetermined gap on the stretched portion of the second intermediate transfer belt 16 by the backup roller 21. 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. By this charge application, 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. .

  As described above, the double-sided transfer device including the two transfer units (15, 24) first transfers the second toner image onto the second surface of the transfer paper P at the secondary transfer nip, 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 on which double-sided transfer has been completed by the third transfer is separated from the second intermediate transfer belt 16 and sent to a heating and fixing device 35 described later. 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 cleaned. The 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 heat fixing device 35 as heat fixing means is disposed. The heat fixing device 35 includes a first fixing roller 35a and a second fixing roller 35b that contact each other while rotating in the forward direction to form a fixing nip. Each of the first fixing roller 35a and the second fixing roller 35b has heating means such as a halogen lamp (not shown), and heats the transfer paper P sandwiched between the fixing nips from both sides. By this heating, the full color images respectively formed on both surfaces of the transfer paper P are fixed on the transfer paper P by the softening of the toner constituting the image. After the fixing, the transfer paper P is reversed along the reversing guide member 36 and then discharged to the outside through a pair of paper discharge rollers 37 serving as discharge means. And it is stacked on the stack part 40 formed on the upper surface of the housing of the printer body.

  The surface temperature of the first fixing roller 35a serving as the first surface heating unit and the second fixing roller 35b serving as the second surface heating unit are detected by a first temperature detecting unit and a second temperature detecting unit (not shown), respectively. The first temperature detection means and the second temperature detection means respectively transmit to the control unit E2 disposed at the top of the printer body. The controller E2 performs ON / OFF control of power supply to the heat generating means of the first fixing roller 35a and the second fixing roller 35b based on the detection result of the surface temperature sent from these temperature detecting means. By this control, the surface temperatures of the first fixing roller 35a and the second fixing roller 35b change.

  As described above, the printer performs the toner image transfer process by the double-side transfer device on both sides of the transfer paper P before being transferred to the heat fixing device 35. 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 this printer, 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. Is called a tandem system. 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, in order to align the page numbers of the transfer sheets P stacked in this manner in order from the smallest, for the images of two page numbers that are consecutive odd and even, the first with the larger page number is the first. Formed as a toner image. 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 to 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.

  In the printer having the above-described configuration, the combination of the four process cartridges 6Y, 6M, 6C, 6K, the exposure device 7, and the double-side transfer device allows the first surface on the first surface of the recording medium based on the image information. While forming a toner image, a toner image forming means for forming a second toner image on the second surface of the recording medium is configured.

  FIG. 3 is a block diagram showing a part of the electric circuit of the printer. In the figure, the heat fixing device 35 includes a first temperature detecting means 35c, a first heat generating means 35e, a second temperature detecting means 35f, and a second heat generating means in addition to the first fixing roller 35a and the second fixing roller 35b described above. 35d and the like. The first temperature detection unit 35c and the second temperature detection unit 35f detect the surface temperatures of the first fixing roller 35a and the second fixing roller 35b, respectively, and output a digital temperature signal to the control unit E2. The control unit E2 includes a first temperature target value and a second temperature target value, which are target values for the values of the digital temperature signals sent from the first temperature detection means 35c and the second temperature detection means, respectively, such as a RAM (not shown). Is stored in the storage means. When the value of the digital temperature signal sent from the first temperature detection means 35c is lower than the first temperature target value by a predetermined value or more, the power supply to the first heat generation means 35e is turned on, and the first The surface temperature of the fixing roller 35a is raised to the first target value. On the other hand, when the value of the digital temperature signal sent from the second temperature detection means 35f is lower than the second temperature target value by a predetermined value or more, the power supply to the second heat generation means 35d is turned on, and the second The surface temperature of the fixing roller 35b is raised to the first target value. By such control, the surface temperatures of the first fixing roller 35a and the second fixing roller 35b are maintained near the first temperature target value and the second temperature target value, respectively.

  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 control unit 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 multi-color toner image. In many cases, the multicolor toner image includes a portion in which the toner adhesion amount is considerably increased, such as a color photographic image portion. On the other hand, a single color 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.

  The controller E2 also functions as heating temperature control means. Specifically, when the first surface toner adhesion amount is detected as “relatively large”, the above-described first temperature target value is set 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, in order to control the surface temperature of the first fixing roller 35a so as to approach the set first temperature target value, the power supply to the first heat generating unit 35e is turned ON / OFF. On the other hand, the surface temperature of the second fixing roller 35b is similarly controlled based on the second surface toner adhesion amount.

  In this printer that performs such control, the fixing process is performed on any surface of the transfer paper P with a heating amount that causes an appropriate gloss to appear. As a result, the glossiness of the front and back images can be made 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.

FIG. 4 is a schematic configuration diagram showing a first modified apparatus of the printer according to the first reference embodiment. In the first modified apparatus 100, the positional relationship of each process cartridge 106Y, M, C, K and exposure apparatus 107 with respect to the first transfer unit 115 is opposite to that of the printer shown in FIG. Specifically, each process cartridge 106Y, M, C, K is disposed above the first transfer unit 115, and an exposure device 107 is disposed further above. In the first transfer unit 115, a second tension roller 160 and a tertiary transfer backup roller 161 are added as a plurality of rollers for stretching the first intermediate transfer belt 108.

  In the first modified apparatus 100, the nip expansion roller (19 in FIG. 1) and the backup roller (21 in FIG. 1) are eliminated from among the plurality of rollers that stretch the second intermediate transfer belt 116. Further, the transfer charger (23 in FIG. 1) disposed to face the backup roller via the second intermediate transfer belt 16 is also eliminated. Instead, a tertiary transfer roller 162, a separation roller 163, and a second tension roller 164 are added. The tertiary transfer roller 162 sandwiches two intermediate transfer belts with the tertiary transfer backup roller 161 in the first transfer unit 115 to form a tertiary transfer nip. This tertiary transfer nip is continuous with the secondary transfer nip formed by sandwiching two intermediate transfer belts between the secondary transfer backup roller 112 and the secondary transfer roller 117 on the upstream side. is doing.

  The separation roller 163 replaces the backup roller of the printer shown in FIG. 1. The separation roller 163 separates the transfer paper P from the second intermediate transfer belt 116 whose direction of movement is changed by about 90 ° in accordance with the curvature thereof, and is heated. It is sent to the fixing device 35. The second cleaning device 118 cleans the transfer residual toner on the second intermediate transfer belt 116 while being backed up by the tension roller 120.

  FIG. 5 is an enlarged configuration diagram showing the secondary transfer nip and its surroundings in the first modified apparatus 100. The secondary transfer backup roller 112 pressing the two intermediate transfer belts from the back surface of the first intermediate transfer belt 108 toward the secondary transfer roller 117 is grounded. On the other hand, the secondary transfer roller 117 is applied with a secondary transfer bias having a polarity opposite to that of the toner (plus polarity in the illustrated example) by a power source. The first toner image on the first intermediate transfer belt 108 is electrostatically attracted to the secondary transfer roller 117 side by the influence of the secondary transfer bias, and is electrostatically transferred onto the second intermediate transfer belt 116. Is done. In the secondary transfer, a transfer system that electrostatically attracts toner toward the secondary transfer roller 17 is employed.

  FIG. 6 is an enlarged configuration diagram showing the tertiary transfer nip and its surroundings in the first modified apparatus 100. The tertiary transfer backup roller 161 pressing the two intermediate transfer belts from the back surface of the first intermediate transfer belt 108 toward the tertiary transfer roller 162 is connected to the ground in the same manner as the secondary transfer backup roller. In contrast, a tertiary transfer bias having the same polarity as the toner (minus polarity in the illustrated example) is applied to the tertiary transfer roller 162 by a power source. The first toner image secondarily transferred onto the second intermediate transfer belt 116 at the second transfer nip is electrostatically pushed toward the third transfer backup roller 161 side due to the influence of the third transfer bias. It is. Then, tertiary transfer is performed on the first surface of the transfer sheet P sandwiched between the two intermediate transfer belts. An electrostatic extrusion transfer system that electrostatically extrudes toner from the tertiary transfer roller 162 side toward the transfer paper P is employed. Conventionally, in such a transfer method, during the third transfer, the second toner image that has been secondarily transferred to the second surface of the transfer paper P at the second transfer nip is electrostatically similar to the first toner image. The present inventors thought that the ink was extruded and returned to the first intermediate transfer belt 108. However, when actually tested, it was surprising that the second toner image could be held on the second surface of the transfer paper P without electrostatic extrusion. In the tertiary transfer method, unlike the transfer charger of the printer shown in FIG. 1, the first toner image can be tertiary transferred while the first toner image and the second toner image are in close contact with the transfer paper P. . Therefore, it is possible to avoid toner dust caused by charging the exposed second surface of the transfer paper P and to form a higher quality image. Moreover, generation | occurrence | production of ozone accompanying a corona charge can also be avoided.

  In the method shown in the figure, when a tertiary transfer bias having a polarity opposite to that of the toner is applied to the tertiary transfer backup roller 161 and the tertiary transfer roller 162 is grounded and pulled to the tertiary transfer backup roller 161, reverse transfer is performed. It has happened. The first toner image on the second intermediate transfer belt 116 is electrostatically attracted to the first surface of the transfer paper P, and at the same time, the second toner image is transferred from the second surface of the transfer paper P onto the first intermediate transfer belt 108. It was pulled back and brought back. Therefore, the tertiary transfer at the tertiary transfer nip needs to be performed by the electrostatic transfer of the extrusion method. That is, of the two transfer bias members in the secondary transfer nip and the tertiary transfer nip, the toner image is placed on the transfer bias member side for the one disposed on the downstream side of the surface movement direction of the intermediate transfer belts. A transfer bias having a polarity for electrostatic movement is applied so as to move away from the transfer paper P toward the transfer paper P.

  In the first modification apparatus 100, the image area ratio on the first surface of the transfer paper P is determined by a known method based on the image information for the first surface acquired by the control unit E2 by the image data processing device E1. calculate. This image area ratio is the ratio of the image portion to the total area of the first surface. Further, the control unit E2 calculates an image area ratio on the second surface of the transfer paper P by a known method based on the image information for the second surface acquired by the image data processing device E1. The toner adhesion amount on the transfer paper P has a correlation with the image area ratio on the surface. Therefore, the control unit E2 is configured to detect the first surface toner adhesion amount and the second surface toner adhesion amount based on the image area ratio of the first surface and the image area ratio of the second surface. As a detection method, the image area ratio of the first surface or the second surface may be detected as it is as the first surface toner adhesion amount or the second surface toner adhesion amount. Further, the relationship between the image area ratio and the toner adhesion amount is investigated in advance and a data table is created, and the first surface toner adhesion amount and the second surface toner adhesion amount corresponding to the calculated image area ratio are specified from this data table. You may make it make it.

In the first variation apparatus 100 having the above-described configuration, the first surface toner adhesion amount is higher than that of the printer according to the first embodiment that simply detects the toner adhesion amount based on whether the toner image is a multicolor toner image. And the second surface toner adhesion amount can be accurately detected. Thus, the difference in glossiness between the front and back sides can be reliably suppressed as compared with the printer according to the first reference embodiment .

FIG. 7 is a schematic configuration diagram showing a second modification apparatus 200 of the printer according to the first reference embodiment . In the second modified apparatus 200, the first transfer unit 215 and the second transfer unit 224 stretch the first intermediate transfer belt 208 and the second intermediate transfer belt 216 in a horizontally long shape, respectively. Then, the first intermediate transfer belt 208 and the second intermediate transfer belt 216 disposed below in the drawing are brought into contact with each other at a horizontally long stretched portion to form a secondary transfer nip.

The second modification apparatus 200 includes two process cartridges for each color. One for the first system and one for the second system. Among these, the process cartridges 206Y, M, C, and K for the first system have the photosensitive members 201Y, M, C, and K attached to the first intermediate transfer belt 208, respectively, in the upper portion of the first transfer unit 215 in the drawing. It arrange | positions so that it may contact | abut. Then, Y, M, C, and K toner images are formed on the first intermediate transfer belt 208 for primary transfer. The four-color toner image obtained by the superimposing primary transfer corresponds to the first toner image in the printer according to the first reference embodiment. Then, the first intermediate transfer belt 208 is sent to the secondary transfer nip where the first intermediate transfer belt 208 and the second intermediate transfer belt 216 come into contact with each other in the clockwise endless movement in the drawing.

On the other hand, the process cartridges 276Y, M, C, and K for the second system contact the photoreceptors 271Y, 271Y, M, C, and K on the second intermediate transfer belt 216, respectively, below the second transfer unit 224 in the drawing. It is arranged to make it. Then, Y, M, C, and K toner images for primary transfer are superimposed on the second intermediate transfer belt 216 and formed. The four-color toner image obtained by the superimposing primary transfer corresponds to the second toner image in the printer according to the first reference embodiment. The second intermediate transfer belt 216 is fed to the above-described secondary transfer nip as the counterclockwise endless movement of the second intermediate transfer belt 216 in the drawing. The optical writing of the process cartridges 276Y, M, C, and K for the second system to the photoreceptors 271Y, M, C, and K is performed by the exposure apparatus 277 for the second system. The exposure device 277 is disposed below the process cartridges 276Y, M, C, and K for the second system. On the other hand, the exposure apparatus 207 for the first system is arranged above the process cartridges 206Y, M, C, K for the first system in the drawing.

  The second modification apparatus 200 includes a printer unit 290 for printing an image on the transfer paper P, and a paper feeding unit 291 as a recording material storage unit that stores the transfer paper P to be supplied to the printer unit. It is composed of separate bodies. The paper feeding unit 291 rotates the paper feeding roller 292 pressed against the uppermost transfer paper P in the bundle of transfer paper accommodated therein at a predetermined timing, thereby transferring the transfer paper P to the printer unit. The paper is sent out toward the paper feed path 288 of 290.

  The transfer paper P sent into the paper feed path 288 is sandwiched between the rollers of the registration roller pair 231 disposed near the end of the paper feed path 288. Then, the secondary transfer nip is synchronized with the first toner image on the first intermediate transfer belt 208 of the first transfer unit 215 and the second toner image on the second intermediate transfer belt 216 of the second transfer unit 224. It is sent out toward.

  FIG. 8 is a schematic diagram showing the secondary transfer nip and the surrounding configuration in the second modification apparatus 200. The first transfer unit 215 includes an upstream secondary transfer counter roller 282 and a downstream secondary transfer counter roller 284 as two of a plurality of stretching rollers that stretch the first intermediate transfer belt 208. is doing. The second transfer unit 224 includes an upstream secondary transfer roller 281 and a downstream secondary transfer roller 284 as two of the plurality of stretching rollers that stretch the second intermediate transfer belt 216. is doing. In the secondary transfer nip, a stretched portion between both secondary transfer opposing rollers (282, 284) in the first intermediate transfer belt 208 is stretched between both secondary transfer rollers (281, 283) in the second intermediate transfer belt 216. It is formed in the part. Both of the secondary transfer counter rollers (282, 284) are grounded.

  In the second modified apparatus 200, two-stage secondary transfer, upstream secondary transfer and downstream secondary transfer, is performed in the secondary transfer nip. Specifically, the transfer paper P fed into the secondary transfer nip first passes through the upstream secondary transfer portion in the nip. In the upstream secondary transfer portion, both intermediate transfer belts (208, 216) are sandwiched between the upstream secondary transfer opposing roller 282 and the upstream secondary transfer roller 284. Then, the toner image on any one of the intermediate transfer belts is secondarily transferred to any one surface of the transfer paper P under the influence of the upstream secondary transfer electric field formed between both rollers. In the illustrated example, in the upstream secondary transfer portion, the upstream secondary transfer roller 281 that is in contact with the back surface of the second intermediate transfer belt 216 has a positive upstream secondary having a polarity opposite to the charging polarity of the toner. A transfer bias is applied. Therefore, the first toner image on the first intermediate transfer belt 208 is electrostatically attracted toward the upstream secondary transfer roller 281 and is transferred to the first surface (the surface facing upward in the drawing) of the transfer paper P. Secondary transferred. In the illustrated example, the electrostatic attraction transfer method is adopted as the upstream secondary transfer method.

  The transfer sheet P that has been subjected to the upstream secondary transfer in this manner then enters the downstream secondary transfer portion. In the downstream secondary transfer portion, both intermediate transfer belts (208, 216) are sandwiched between the downstream secondary transfer opposing roller 284 and the downstream secondary transfer roller 283. Then, the toner image on any one of the intermediate transfer belts is secondarily transferred to any one surface of the transfer paper P under the influence of the downstream secondary transfer electric field formed between both rollers. In the illustrated example, in the downstream secondary transfer portion, the downstream secondary transfer roller 283 that is in contact with the back surface of the second intermediate transfer belt 216 has a negative downstream secondary transfer bias that is the same as the charging polarity of the toner. Applied. Therefore, the second toner image on the second intermediate transfer belt 216 is electrostatically pushed from the downstream secondary transfer roller 283 side toward the downstream secondary transfer counter roller 284 side, and the second toner image on the transfer paper P is transferred. Secondary transfer is performed on two surfaces (surfaces facing downward in the figure). In the illustrated example, an electrostatic extrusion transfer system is adopted as a downstream secondary transfer system. The present inventors have confirmed by experiments that the following reverse transfer is not caused when the two-step next transfer as shown in the figure is adopted. That is, the first toner image previously transferred onto the first surface of the transfer paper P is reversely transferred from the first surface toward the first intermediate transfer belt 208 during the downstream secondary transfer. It is a phenomenon.

  The transfer paper P on which the toner images are secondarily transferred on both sides at the secondary transfer nip moves from the right side to the left side in the drawing along with the endless movement of both intermediate transfer belts (208, 216), and the heat fixing device 235. To be passed on. Then, the transfer paper P subjected to the fixing process by the heat fixing device 235 passes through the paper discharge roller pair 237 and is then discharged onto the stack unit 240 fixed to the left side surface of the printer in the drawing.

  The first intermediate transfer belt 208 and the second intermediate transfer belt 216 face each other in a non-contact manner on the upstream side of the secondary transfer nip in the belt moving direction, and the belts gradually move toward the secondary transfer nip. Move to get closer. Thus, the sheet feeding path 288 is disposed in a region where the intermediate transfer belts face each other in a non-contact manner. The transfer paper P discharged from the registration roller pair 231 disposed near the end of the paper feed path 288 passes through a region where both intermediate transfer belts move toward each other toward the secondary transfer nip, It is surely and smoothly guided toward the secondary transfer nip. Therefore, even if the transfer paper P is thin and extremely weak, it is difficult for jamming or the like to occur.

  On the other hand, both intermediate transfer belts are opposed to each other in a non-contact manner downstream of the secondary transfer nip in the belt moving direction, and move so as to gradually move away from each other. The heat fixing device 235 is arranged so that the end portion on the transfer paper receiving side enters the region where the both intermediate transfer belts face each other in a non-contact manner. The transfer paper P delivered from the secondary transfer nip is reliably and smoothly guided to the heat fixing device 235 entering the area. Therefore, this also makes it difficult for jams to occur.

  When two-stage secondary transfer of upstream secondary transfer and downstream secondary transfer is performed in the nip as in the second modification apparatus 200, the secondary transfer nip and its surrounding configuration are shown in FIG. The configuration shown in FIG. Compared with the configuration shown in FIG. 8, the two secondary transfer counter rollers (282, 284) in the first transfer unit 215 and the two secondary transfer rollers (281, 283) in the second transfer unit 224 However, it can be seen that the units are replaced. In the upstream secondary transfer portion, an upstream secondary transfer bias having a polarity opposite to the charging polarity of the toner is applied to the upstream secondary transfer roller 281 that is in contact with the back surface of the first intermediate transfer belt 208. . Then, the second toner image on the second intermediate transfer belt 216 is electrostatically attracted toward the upstream side secondary transfer roller 81 and secondarily transferred onto the second surface of the transfer paper P (electrostatic attraction). Transfer method). On the other hand, in the downstream secondary transfer portion, the downstream secondary transfer bias having the same negative polarity as the toner charging polarity is applied to the downstream secondary transfer roller 283 that is in contact with the back surface of the first intermediate transfer belt 208. Has been. Then, the first toner image on the first intermediate transfer belt 208 is electrostatically pushed from the downstream secondary transfer roller 283 side toward the downstream secondary transfer opposing roller 284 side, and the first toner image on the transfer paper P is transferred. Secondary transfer is performed on one surface (electrostatic extrusion transfer method). The present inventors have confirmed by experiments that the following reverse transcription is not caused when the two-step secondary transfer as shown in the figure is adopted. That is, the second toner image previously transferred onto the second surface of the transfer paper P is reversely transferred from the second surface toward the second intermediate transfer belt 216 during the downstream secondary transfer. It is a phenomenon.

  Further, the configuration shown in FIG. 10 may be adopted as the secondary transfer nip and its surrounding configuration. In the figure, the upstream secondary transfer roller 281 stretches the second intermediate transfer belt 216, while the downstream secondary transfer roller 283 stretches the first intermediate transfer belt 208. In the upstream secondary transfer portion, a negative upstream secondary transfer bias that is the same as the toner charging polarity is applied to the upstream secondary transfer roller 281 that is in contact with the back surface of the second intermediate transfer belt 216. Then, the second toner image on the second intermediate transfer belt 216 is electrostatically pushed from the upstream side secondary roller 281 side toward the upstream side secondary transfer counter roller 282 side, and the second toner image on the transfer paper P is secondly transferred. Secondary transfer onto the surface (electrostatic extrusion transfer method). On the other hand, in the downstream secondary transfer portion, the downstream secondary transfer bias having the same negative polarity as the toner charging polarity is applied to the downstream secondary transfer roller 283 that is in contact with the back surface of the first intermediate transfer belt 208. Has been. Then, the first toner image on the first intermediate transfer belt 208 is electrostatically pushed from the downstream secondary transfer roller 283 side toward the downstream secondary transfer opposing roller 284 side, and the first toner image on the transfer paper P is transferred. Secondary transfer is performed on one surface (electrostatic extrusion transfer method). The present inventors have confirmed by experiments that the following reverse transcription is not caused when the two-step secondary transfer as shown in the figure is adopted. That is, the second toner image previously transferred onto the second surface of the transfer paper P is reversely transferred from the second surface toward the second intermediate transfer belt 216 during the downstream secondary transfer. It is a phenomenon.

  Further, the configuration shown in FIG. 11 may be adopted as the secondary transfer nip and its surrounding configuration. In the figure, the upstream secondary transfer roller 281 stretches the first intermediate transfer belt 208, while the downstream secondary transfer roller 283 stretches the second intermediate transfer belt 216. In the upstream secondary transfer portion, a negative secondary transfer bias that is the same as the charging polarity of the toner is applied to the upstream secondary transfer roller 281 that is in contact with the back surface of the first intermediate transfer belt 208. . Then, the first toner image on the first intermediate transfer belt 208 is electrostatically pushed from the upstream side secondary transfer roller 281 side toward the upstream side secondary transfer counter roller 282 side, and the first toner image on the transfer paper P is transferred. Secondary transfer is performed on one surface (electrostatic extrusion method). On the other hand, in the downstream secondary transfer portion, the downstream secondary transfer bias having the same negative polarity as the toner charging polarity is applied to the downstream secondary transfer roller 283 in contact with the back surface of the second intermediate transfer belt 216. Applied. Then, the second toner image on the second intermediate transfer belt 216 is electrostatically pushed from the downstream secondary transfer roller 283 side toward the downstream secondary transfer counter roller 284 side, and the second toner image on the transfer paper P is transferred. Secondary transfer is performed on two surfaces (electrostatic extrusion transfer method). The present inventors have confirmed by experiments that the following reverse transcription is not caused when the two-step secondary transfer as shown in the figure is adopted. That is, the first toner image previously transferred onto the first surface of the transfer paper P is reversely transferred from the first surface toward the first intermediate transfer belt 208 during the downstream secondary transfer. It is a phenomenon.

  Although the example in which the rollers (281, 283) are used as the transfer bias member has been described with reference to FIGS. 8 to 11, a non-roller-shaped member may be used. Moreover, although the example which employ | adopted the roller (282,284) as a counter electrode member facing a transfer bias member was demonstrated, you may employ | adopt a non-roller-shaped counter electrode member.

In the two-stage secondary transfer, after the transfer from the first intermediate transfer belt 208 to the second surface of the transfer paper P is performed on the upstream side, the second transfer of the transfer paper P from the second intermediate transfer belt 216 is performed on the downstream side. There are two cases: a case where the transfer is performed on two surfaces and a case where the transfer is performed in the reverse order. In addition, two types of transfer methods, namely an electrostatic attraction method and an electrostatic extrusion method, are established on the upstream side and the downstream side, respectively. Therefore, by combining these, eight kinds of two-stage secondary transfer methods can be established. The present inventors tested all of these eight two-stage secondary transfer methods and examined the presence or absence of reverse transfer during downstream secondary transfer. Table 1 below shows the relationship between these eight two-stage secondary transfer methods and the presence or absence of reverse transfer during downstream secondary transfer.

  As shown in Table 1, in the eight two-stage secondary transfer methods, the secondary transfer during the secondary transfer on the downstream side did not occur only in the four ways of experiment numbers 3, 4, 7, and 8. Met. Focusing on these, it can be seen that all downstream secondary transfer is performed by the electrostatic extrusion method. On the other hand, paying attention to Experiment Nos. 1, 2, 5, and 6 in which reverse transfer occurred, it can be seen that downstream secondary transfer is performed by the electrostatic attraction method. Therefore, it has been found that when the two-stage secondary transfer method is performed, reverse transfer is caused unless the electrostatic extrusion transfer method is adopted for the downstream secondary transfer. In the first variation apparatus 100 described above, the same eight methods are established for continuous transfer (“secondary, third order” or “third order, second order”) in the nip. As a result of testing all of these eight patterns, the present inventors have obtained the same result that reverse transfer is caused unless the extrusion electrostatic transfer method is adopted at the subsequent transfer in the continuous transfer.

In the first modified apparatus described above, the control unit E2 is configured to detect the first surface toner adhesion amount and the second surface toner adhesion amount based on the image area ratio of the first surface and the second surface. It was. With this configuration , the first- surface toner adhesion amount and the second-surface toner adhesion amount are more accurately detected than the printer according to the first reference embodiment. However, in the case of forming a multicolor toner image by superimposing a plurality of single color toner images as in the printer described so far, even if the image area ratio is the same, there is a difference in the toner adhesion amount. come. Even if the image area ratio is the same, the toner adhesion amount is larger in the multicolor solid image than in the single color solid image. Therefore, in the second modification apparatus 200, the number of recording pixels for each color is calculated based on the image information acquired by the image data processing apparatus E1, and the first surface toner adhesion amount and the second amount are calculated based on the calculation result. The controller E2 is configured to detect the surface toner adhesion amount. Specifically, image information sent from a personal computer or the like is divided into image information for each color of Y, M, C, and K. The Y, M, C, and K recording pixel numbers are calculated based on the image information for each color, and the first surface toner adhesion amount and the second surface toner adhesion amount are detected based on the total of the calculation results. . As a detection method, the total number of recording pixels for each color may be detected as it is as the first surface toner adhesion amount or the second surface toner adhesion amount. In addition, the relationship between the number of recording pixels and the toner adhesion amount is previously investigated and a data table is created, and the toner adhesion amount corresponding to the number of recording pixels of each color is specified from this data table, and the total of these is first calculated. The surface toner adhesion amount and the second surface toner adhesion amount may be detected as this data table. Further, the toner adhesion amount corresponding to the total number of recording pixels of each color may be specified from the data table. Further, the toner adhesion amount corresponding to the number of recording pixels may be calculated based on a predetermined algorithm instead of the data table.

  In the second modification device 200 having such a configuration, the first surface toner adhesion amount and the second surface toner adhesion amount are more accurately determined than the first modification device that detects the toner adhesion amount based on the image area ratio. Can be detected.

Next, the copying machine according to the embodiment will be described. The copying machine according to the embodiment differs from the printer according to the first reference embodiment in the points described below.
Figure 12 is a schematic diagram showing a copying machine according to the implementation embodiments. In the figure, the printer includes a printer unit 300A, an operation / display unit 390, a paper feeding device 340, an automatic image reading device 300B, a paper replenishing device 300C, and the like.

  The printer unit 300A includes a first image forming unit disposed above and a second image forming unit disposed below the paper conveyance path 343A. The first image forming unit includes four first toner image forming units 380Y, M, C, and K, and a first transfer unit 320. Further, the second image forming unit includes four second toner image forming units 381Y, M, C, and K, and a second transfer unit 330.

  The first transfer unit 320 has a first intermediate transfer belt 321 that moves endlessly in the direction of the arrow in the figure, and four first toner image forming units 380Y, 380, M, C and K are arranged. In addition, the second transfer unit 330 has a second intermediate transfer belt 331 that moves endlessly in the direction of the arrow in the drawing. Four second toner image forming portions 381Y, M, C, and K are arranged on the side of the side stretched surface of the second intermediate transfer belt 331.

  Each toner image forming portion (380Y, M, C, K, 381Y, M, C, K) has a photoreceptor (301Y, M, C, K) as an image carrier. The photoreceptors 301Y, M, C, and K of the first toner image forming portions 380Y, M, C, and K are disposed at equal intervals, and at least at the time of image formation, are in contact with the upper stretched surface of the first intermediate transfer belt 321. . Hereinafter, the belt surface that contacts in this way is referred to as a first image receiving surface.

  On the other hand, the photoreceptors 301Y, M, C, and K of the second toner image forming portions 381Y, M, C, and K are also arranged at equal intervals, and at least at the time of image formation, respectively on the upper stretch surface of the second intermediate transfer belt 321. Contact. Hereinafter, the belt surface that contacts in this way is referred to as a second image receiving surface.

  The first intermediate transfer belt 321 is stretched by a plurality of rollers in a horizontally long posture that takes a space in the horizontal direction rather than in the vertical direction, and in a posture in which the first image receiving surface extends substantially horizontally. The first toner image forming portions 380Y, M, C, and K are arranged in parallel so as to be in contact with the substantially horizontal first image receiving surface.

  On the other hand, the second intermediate transfer belt 331 is stretched so as to be inclined from the upper left to the lower right in the drawing. The second toner image forming units 381Y, M, C, and K are illustrated in the second intermediate transfer belt 331 so as to be in contact with the second image receiving surface of the second intermediate transfer belt 331 that is stretched in such an oblique posture. In the middle right side, they are arranged in parallel so as to form an oblique arrangement from the upper left to the lower right in the figure.

  FIG. 13 is an enlarged configuration diagram illustrating one of the four first toner image forming units 380Y, M, C, and K. The four first toner image forming units 380Y, 380, Y, M, C, and K have substantially the same configuration except that the toner colors to be handled are different from each other. Therefore, in FIG. The subscripts C and K are omitted. In the drawing, the photosensitive member 301 is driven to rotate counterclockwise in the drawing by a driving means (not shown) during operation of the printer unit (300A). Around the photosensitive member 301, there are image forming members such as a scorotron charger 303, an exposure device 304, a developing device 305, a belt cleaning device 320 A, and a photostatic device Q as charging means, a potential sensor S 1, an image sensor S 2, etc. Is arranged.

  The drum-shaped photosensitive member 301 is formed by coating an organic photosensitive layer (OPC), which is a photoconductive substance, on an aluminum cylindrical surface having a diameter of about 30 to 120 [mm], for example. An amorphous silicon (a-Si) layer may be coated. Further, it may be a belt shape instead of a drum shape.

  The photoconductor cleaning device 302 includes a cleaning brush, a cleaning blade, a recovery member, and the like, and removes and recovers transfer residual toner remaining on the surface of the photoconductor after passing through a primary transfer nip described later.

  The scorotron charger 303 uniformly charges the surface of the photoconductor 301 that is rotationally driven to, for example, a negative polarity. As a charging means for performing such uniform charging, a corotron charger may be used instead of the scorotron charger. Alternatively, a charging bias member to which a charging bias is applied may be in contact with the surface of the photoreceptor 1.

  The exposure device 304 optically scans the surface of the photoreceptor 1 after uniform charging with light generated based on image data corresponding to one of the colors, and an electrostatic latent image is formed on the surface of the photoreceptor 1. Form. In the example shown in the drawing, an exposure device 304 that includes an LED (light emitting diode) array and an imaging element is used. A laser scanning method using a light beam modulated in accordance with image data to be formed using a laser light source, a polygon mirror, or the like may be used.

  The developing device 305 is of a two-component developing system that develops an electrostatic latent image on the photoreceptor 301 using a two-component developer containing toner and a magnetic carrier. The two-component developer is conveyed in the depth direction in the figure while being stirred by two conveying screws 305c. The developer conveying directions of these two conveying screws 305c are opposite to each other. For example, if the developer conveying direction of the left conveying screw 305c in the drawing is the front side from the back side in the drawing, the developer conveying direction of the right conveying screw 305c is the front side to the back side in the drawing. The two-component developer transported to the end in the depth direction of the developing device 5 by the former transport screw 305c is transferred to the latter transport screw 305c. Then, in the process of being stirred and conveyed from the end portion toward the opposite end portion, a part thereof is carried on a developing roll 305b described later. The two-component developer that is not carried or returned from the developing roll 305b to the right conveying screw 305c is transferred to the left conveying screw 305c at the opposite end. In this way, the two-component developer is circulated and conveyed in the developing device 305. As the developing device 305, a one-component developing method using a one-component developer containing toner as a main component without including a magnetic carrier may be used.

  The developing roll 305a is a non-magnetic cylinder made of stainless steel, aluminum, or the like, and has a sleeve that is driven to rotate clockwise in the drawing by a driving means (not shown), and a magnet roller that is internally fixed so as not to rotate. is doing. The magnet roller has a plurality of magnetic poles divided in the circumferential direction inside the sleeve. The two-component developer conveyed by the conveyance screw 305c on the right side in the drawing is attracted by the magnetic force generated by the magnet roller and is pumped up on the surface of the sleeve that is driven to rotate. Then, prior to being transported to the developing area facing the photoreceptor 301 along with the sleeve surface, the sheet passes through a regulation position which is a position facing the blade 305b.

  The blade 305b is disposed so that its tip is close to the sleeve surface through a predetermined gap. Then, when the two-component developer on the sleeve surface passes through the regulation position immediately below, the thickness of the two-component developer is regulated to a predetermined size.

  The two-component developer whose layer thickness is regulated in this way is transported to the developing area which is the position facing the photoreceptor 301 as the sleeve rotates. The electrostatic latent image formed by attenuating charges by optical scanning with respect to the surface of the photoreceptor 301 uniformly charged to the negative polarity is rubbed against the two-component developer on the sleeve surface in the development region. . Then, it is developed into one of Y, M, C, and K colors by the adhesion of negatively chargeable toner having the same polarity as the latent image. In the first toner image forming unit 380, so-called reversal development is performed. As a result, a toner image of any one of Y, M, C, and K is formed on the photoreceptor 301.

  As the toner, a spherical or irregular toner obtained by a conventionally known method is used. The volume average particle diameter is 20 [μm] or less, preferably 10 [μm] or less, and 4 [μm] or more. As the magnetic carrier, those obtained by a conventionally known method are used. The volume average particle size is preferably about 25 [μm] to 60 [μm].

  The two-component developer that has consumed toner in the developing area returns to the developing device 305 as the sleeve rotates. Then, under the influence of a repulsive magnetic field formed by magnetic poles having the same polarity and adjacent to each other of the magnet roller, the magnet roller is detached from the sleeve surface and returned onto the conveying screw 305c on the right side in the drawing, and then on the left side in the drawing. It is delivered to the conveying screw 305c.

  A toner concentration sensor 305e is disposed below the left conveying screw 305c in the drawing, and detects the magnetic permeability of the two-component developer conveyed by the left conveying screw 305c.

  When the control unit 395 determines that the toner concentration of the two-component developer is less than a predetermined threshold based on the output signal from the toner concentration sensor 305e, the two-component developer out of eight toner supply units (not shown) Is driven for a predetermined time. Each of these eight toner supply units includes four developing devices of the first toner image forming unit (380Y, M, C, K) or 4 of the second toner image forming unit (381Y, M, C, K). This corresponds to any one of the two developing devices. It is connected to any of the four Y, M, C, and K toner bottles (386Y, M, C, and K in FIG. 14) that are detachably set in the bottle storage unit 385 at the top of the printer unit (300A). . Then, the toner of a predetermined color is supplied from the connected toner bottle onto the conveying screw 305c on the left side in the drawing in the corresponding developing device. As a result, the toner concentration of the two-component developer that has consumed the toner by the development is recovered. As the toner supply means having such a configuration, a system that sucks the toner in the toner bottle and conveys it to the developing device with a suction force of a conventionally known Mono pump is preferable. According to this method, there are few restrictions on the installation location of the toner bottle, which is advantageous for space allocation in the printer unit (300A). Further, since the toner can be replenished in a timely manner, it is not necessary to provide a large toner storage space in the developing device 305, and the developing device 305 can be downsized.

  FIG. 14 is an enlarged configuration diagram showing one of the four second toner image forming units (381Y, M, C, K). The four second toner image forming portions (381Y, M, C, K) have substantially the same configuration except that each of the handled toner colors is different. The subscript K is omitted. The second toner image forming unit 381 has the same constituent members as the first toner image forming unit (380), but the rotation direction of the photosensitive member 301 is different. Each of them forms an object with respect to the y axis passing through the rotation axis 301a of the photosensitive member 301. Although this shape is related to the arrangement of members provided around the photoreceptor 301, it is an important matter. Specifically, consideration is given to a method of connecting a connecting portion with the printer unit main body, for example, a connecting portion with a driving means, an electrical connecting portion, a toner supplying portion, and a toner discharging portion. Accordingly, the first toner image forming unit (380Y, M, C, K) and the second toner image forming unit (381Y, M, C, K) can be compatible. Therefore, it is not necessary to manufacture the developing device, the belt cleaning device, and the parts separately for the first toner image forming unit and the second toner image forming unit, and the efficiency in manufacturing parts and managing parts is high, and the overall cost is reduced. Can be achieved.

  In FIG. 12 described above, the printer unit 300A includes a double-side transfer device having a first transfer unit 320 as a transfer device and a second transfer unit 330 as a transfer device. The first transfer unit 320 stretches the first intermediate transfer belt 321 with a plurality of rollers 323, 324, 325, 326 (two), 327, 328, and 329 to form first toner image forming units 380 Y, 380, The C and K photoconductors 301Y, 301M, 301C, and 301K are brought into contact with each other. By this contact, the first image forming unit transfers the Y, M, C, and K toner images on the photosensitive members 301Y, 301M, 301C, and 301K onto the first intermediate transfer belt 321 in a superimposed manner. A primary transfer nip for C and K is formed. The first intermediate transfer belt 321 is endlessly moved clockwise in the figure while forming these four primary transfer nips. In each primary transfer nip, any one of four primary transfer rollers 322 to which a primary transfer bias is applied by a power source (not shown) is placed between the photoreceptors 301Y, M, C, and K and the first intermediate transfer belt 321. Is sandwiched. Under the influence of the primary transfer bias and the nip pressure, the toner images of the respective colors are primarily transferred onto the first intermediate transfer belt 321 at each primary transfer nip.

  A belt cleaning device 320 </ b> A is provided on the outer periphery of the first intermediate transfer belt 321 at a position facing the roller 323. This roller 323 functions as a first cleaning backup roller. The belt cleaning device 320 </ b> A wipes off transfer residual toner remaining on the surface of the first intermediate transfer belt 321 after passing through each primary transfer nip and foreign matters such as paper dust. The members related to the first intermediate transfer belt 321 are integrally configured as the first transfer unit 320 and can be attached to and detached from the printer unit 300A.

  On the other hand, in the second transfer unit 330, the second intermediate transfer belt 331 is stretched around a plurality of rollers 333, 334, 335, and 336 (two) and is brought into contact with the photoreceptors 301Y, M, C, and K. By this contact, the second image forming unit transfers the Y, M, C, and K toner images on the photoreceptors 301Y, 301M, 301K, and Y onto the second intermediate transfer belt 331 in a superimposed manner. A primary transfer nip for C and K is formed. The second intermediate transfer belt 331 moves endlessly counterclockwise in the figure while forming these four primary transfer nips. In each primary transfer nip, any one of the four primary transfer rollers 332 to which a primary transfer bias is applied by a power source (not shown) is placed between the photosensitive bodies 301Y, M, C, and K and the second intermediate transfer belt 331. Is sandwiched. Under the influence of the primary transfer bias and the nip pressure, the toner images of the respective colors are primarily transferred to the second intermediate transfer belt 331 at each primary transfer nip.

  A belt cleaning device 330 </ b> A is provided on the outer periphery of the second intermediate transfer belt 331 at a position facing the roller 333. This roller 333 functions as a second cleaning backup roller. The belt cleaning device 330A wipes off unnecessary toner remaining on the surface of the second intermediate transfer belt 331 after passing through each primary transfer nip and foreign matters such as paper dust. Members related to the second intermediate transfer belt 31 are also integrally formed as the second transfer unit 330 and can be attached to and detached from the printer unit 300A.

The intermediate transfer belts (321 and 331) have, for example, a resin or rubber belt base having a thickness of 50 to 600 [μm], and an electric resistance that can electrostatically transfer a toner image by applying a transfer bias. Values can be used. More specifically, examples in which the volume resistance value is adjusted to 10 ⁶ to 10 ¹² [Ωcm] by dispersing carbon in a material such as polyamide can be exemplified. At both ends of the intermediate transfer belt (312, 331) in the belt width direction or in the vicinity thereof, protrusions for stopping the belt are provided so as to extend over the entire circumference of the belt. The protrusions abut against the side surfaces of the stretching roller, thereby preventing the belt from being offset.

As the four primary transfer rollers 322 as the transfer means of the first belt unit and the four primary transfer rollers 332 as the transfer means of the second belt unit, for example, those having the following configurations can be used. That is, the surface of a metal roller as a core metal is coated with a conductive rubber material, and a bias is applied to the core metal part from a power source (not shown). In the first embodiment, a conductive rubber material obtained by dispersing carbon in urethane rubber is used, and the volume resistance is adjusted to about 10 ⁵ Ωcm.

  The printer unit 300A can output a monochrome image using only K toner. When outputting a monochrome image, the toner image forming units 380Y, M, and C for Y, M, and C in the first belt unit are not used. In addition to not operating the toner image forming units 380Y, 380Y, 380C, a mechanism is provided for keeping them in contact with the intermediate transfer belt. An internal frame (not shown) that supports the roller 326 and the primary transfer roller 322 is provided, and is supported so as to be rotatable around a certain point. Then, by rotating in a direction away from the photoconductor, only the photoconductor 301K is brought into contact with the first intermediate transfer belt 321 and an image forming process is executed to create a monochrome image using black toner. Such a configuration is advantageous in terms of improving the life of the photoreceptor. Similarly, the second belt unit is configured to retract the toner image forming portions 381Y, M, and C from the second intermediate transfer belt 331 when a monochrome image is output.

On the outer periphery of the first intermediate transfer belt 321, a secondary transfer roller 346 serving as a transfer unit is disposed in the vicinity of the support roller 328, and the first intermediate transfer belt 321 is sandwiched between the support roller 328 and the second transfer roller 346. The next transfer nip is formed. The secondary transfer roller 346 is obtained by coating the surface of a metal roller serving as a core metal with conductive rubber, and a secondary transfer bias is applied to the core metal portion from a power source (not shown). The conductive rubber has a volume resistance adjusted to about 10 ⁷ Ωcm by carbon dispersion.

  A registration roller pair 345 is disposed on the right side of the secondary transfer nip in the drawing. The registration roller pair 345 temporarily interrupts the rotation of both rollers after a transfer sheet sent from a sheet feeding device 340 described later is sandwiched between the rollers. Then, the transfer paper is sent out toward the secondary transfer nip at a timing that can be synchronized with the four-color toner image that is the superimposed toner image on the first intermediate transfer belt 321. The transferred transfer paper has a four-color toner image brought into close contact with a first surface (a surface facing the upper side in the drawing) which is one surface of the transfer paper at the secondary transfer nip. The four-color toner image on the first intermediate transfer belt 321 passes through the secondary transfer nip while being secondarily transferred to the first surface under the influence of the secondary transfer bias and the nip pressure.

  The transfer paper that has passed through the secondary transfer nip leaves the first intermediate transfer belt 321 and is transferred onto the upper stretched surface of the second intermediate transfer belt 331. Above this upper stretch surface, a transfer charger 347 is disposed so as to face the upper stretch surface with a predetermined gap. Between the transfer charger 347 and the second intermediate transfer belt 331, the four-color toner image on the second intermediate transfer belt 331 is placed on the second surface (the surface facing the lower side in the figure) which is the other surface of the transfer paper. This is the charger transfer position for transfer. The transfer charger 347 is a known type, and a thin wire of tungsten or gold is used as a discharge electrode, held by a casing, and a transfer current is applied to the discharge electrode from a power source (not shown). While the transfer paper P is passed between the second intermediate transfer belt 331 and the transfer charger 347, the four-color toner on the second intermediate transfer belt 331 is given to the first surface with the charge generated from the transfer charger 347. The image is secondarily transferred collectively onto the second surface of the transfer paper. The secondary transfer bias described above and the charge applied by the transfer charger 347 are both positive in polarity opposite to the polarity of the toner.

  On the right side of the printer unit 300A in the drawing, a paper feeding device 340 that accommodates transfer paper is provided. A plurality of paper feed cassettes 340a containing a large amount of transfer paper in the upper stage, for example, and three lower paper feed cassettes 340b, c, and d are arranged below the paper surface so that they can be pulled out to the right side (operation surface side). It is installed. Different types of transfer paper are stored in these paper feed trays 340a and paper feed cassettes 340b, c, d. Among these, the uppermost transfer sheet is selectively fed and separated by the corresponding sheet feeding / separating means 341A to 341D, and only one sheet is reliably transferred to the sheet conveying paths 343B and 343A by the plurality of conveying roller pairs 342B. Sent.

  A pair of registration rollers 345 are provided in the paper conveyance path 343A in order to take a feeding timing for feeding the transfer paper to the secondary transfer nip. Further, a lateral registration correction mechanism 344 for setting the position perpendicular to the transfer sheet conveyance direction to a normal position is provided in the sheet conveyance path 343A. Examples of the lateral registration correction mechanism 344 include those described below. That is, the transfer sheet is slid and conveyed so that the transfer sheet includes a reference guide in the horizontal direction and a pair of skew rollers, not shown, and presses the horizontal end of the transfer paper against the reference guide. Then, the transfer paper is aligned with a predetermined position. The reference guide is moved and arranged at a predetermined position according to the size of the transfer paper. The lateral registration correction mechanism 344 is configured by a regulating member that presses both sides of the transfer paper for a short time and a plurality of times from both lateral directions of the transfer paper with respect to the transfer paper transport direction to align the transfer paper at a predetermined position. The jogger method may be used.

  The transfer paper is conveyed from the registration roller pair 345 toward the secondary transfer nip as the third transfer position where the first intermediate transfer belt 321 and the secondary transfer roller 346 come into contact with each other. Thereafter, the second intermediate transfer belt 331 and the transfer charger 347 are conveyed toward the corresponding fourth transfer position.

  Transfer paper can be supplied to the paper conveyance path 343C having the conveyance roller pair 342C from another paper supply device 300C that can be installed upstream in the conveyance direction. The upper paper feed surface of the paper feed tray 340a is arranged so that the uppermost transfer paper on the paper feed tray 340a is fed and then conveyed almost horizontally without being bent. Therefore, even thick transfer paper and highly rigid paperboard can be reliably fed. In addition, it is advantageous to employ an air paper feed made up of a vacuum mechanism so that the paper feed tray 340a can reliably feed a transfer paper having various characteristics. Although not shown, a sensor for detecting transfer paper is provided at a key point of the paper conveyance path, and serves as a trigger for various signals based on the presence of the transfer paper.

  A paper conveying device 350 is disposed on the left side of the second belt unit of the second transfer unit 330 in the drawing. On the further left side, a heat fixing device 400 having two fixing rollers is provided. A type having a heater inside the roller, a belt fixing device that runs a heated belt, a fixing device that employs induction heating as a heating method, and the like can be employed. In order to make the color and glossiness of the images on both sides of the transfer paper the same, the material, hardness, surface properties, etc. of the fixing roller are made to be the same up and down. Further, the control unit 395 controls the fixing conditions based on whether the image is full-color and monochrome images, single-sided or double-sided, or the optimum fixing conditions according to the type of transfer paper. A cooling roller pair 370 having a cooling function is provided in the conveyance path after fixing in order to cool the transfer paper after fixing and stabilize the unstable toner state at an early stage. As the cooling roller pair 370, a heat pipe structure roller having a heat radiating portion can be adopted. The cooled transfer paper is discharged and stacked by a discharge roller pair 371 on a discharge stack unit 375 provided on the left side of the printer unit 300A. The paper discharge stack unit employs a mechanism in which a receiving member is moved up and down by an elevator mechanism (not shown) according to the stack level in order to stack a large amount of transfer paper. Note that the transfer paper can also be transported to another post-processing apparatus through the paper discharge stack section 75. As another post-processing apparatus, an apparatus for bookbinding such as punching, cutting, folding, and binding can be connected.

The toner bottles 386Y, M, C, and K for each color in which unused toner is stored are detachably stored in the bottle storage unit 385. The bottle accommodating portion 385 is on the back side when viewed from the operation direction on the upper surface of the printer unit 300A, and a plane portion is secured on the front side of the upper surface of the printer unit 300A, so that it can be used as a work table. The toner supply means described above supplies toner to each developing device as necessary . The implementation mode, in a first image forming unit is disposed vertically and the second image forming unit, for a developing device for handling of the same color toner to each other, so as to supply the toner from a common toner bottle Yes, but can be separate. The toner bottle 386K for black toner, which is highly consumed, can have a particularly large capacity.

  The operation / display unit 390 provided on the upper surface of the printer unit 300A is provided with a keyboard and the like, and conditions for image formation can be input. In addition, various information can be displayed on a display unit such as a display, which facilitates information exchange between the operator and the printer unit 300A.

  A waste toner storage unit 387 provided in the printer unit 300A is connected to a photoconductor cleaning device 302, belt cleaning devices 320A and 330A for an intermediate transfer belt, a belt cleaning device 350A for a paper transport device 350, and the like. Then, foreign substances such as waste toner and paper dust sent from these are collected and stored in a lump. Since these cleaning devices (302, 320A, 330A, 350A) do not include a large-capacity waste toner storage unit, the belt cleaning device can be reduced in size and the waste toner disposal operability is also good. A full sensor (not shown) is used to issue a warning about toner disposal in the waste toner storage unit 387 or container replacement.

  Various power supplies, control boards, and the like are protected and housed in a sheet metal frame in a control unit 395 provided in the printer unit 300A. The inside of the image forming apparatus becomes hot due to heat from the heat fixing device 400 or heat generated from the electrical equipment. However, as a countermeasure, a fan 396 is provided to prevent deterioration of the function due to heat of the internal members. The fan 396 is coupled to the heat radiating portion of the cooling roller pair 370 to ensure the cooling effect of the cooling roller pair 370.

  An automatic image reading device (ADF) 300 </ b> B that reads an image of the original while automatically conveying the original by a known technique is provided on the upper portion of the paper feeding device 340, and reading information obtained by this is sent to the control unit 395. . Based on the read information sent, the printer unit 300A is driven and controlled to output the same image as the original. Further, image information from a personal computer (not shown) or the like can be sent to the printer unit 300A and an image corresponding to the image information can be output. Furthermore, it is also possible to send image information sent from a telephone line (not shown) and output an image corresponding to the image information. A paper supply device 300 </ b> C for supplying transfer paper to the paper supply device 340 is disposed on the right side of the paper supply device 340 in the drawing.

Next, the operation at the time of single-sided recording in which the printer unit 300A forms a full-color image on one side of the transfer paper will be described.
There are basically two types of single-sided recording methods that can be selected. One of the two types is a method in which the four-color toner image transferred to the first intermediate transfer belt 321 is secondarily transferred collectively to the first surface of the transfer paper. The other method is a method in which the four-color toner images transferred to the second intermediate transfer belt 331 are collectively transferred to the second surface of the transfer paper. In the case where the image data consists of a plurality of pages, it is convenient to control the image forming order so that the pages are aligned on the paper discharge stack unit 375. Therefore, the former method, in which the image data of the last page is recorded in order and the page order is aligned, will be described.

  When the printer unit 300A is operated, the first intermediate transfer belt 321 and the photoreceptors 301Y, M, C, and K in the first toner image forming units 380Y, M, C, and K rotate. At the same time, the second intermediate transfer belt 331 moves endlessly, but the photoreceptors 301Y, M, C, and K in the second toner image forming portions 381Y, M, C, and K are separated from the second intermediate transfer belt 331 and do not rotate. Put into a state. Then, image formation by the first toner image forming unit 380Y is started. By the operation of the exposure device 304 composed of an LED (light emitting diode) array and an imaging element, light corresponding to image data for yellow emitted from the LED is irradiated onto the surface of the photoreceptor 301Y uniformly charged by the charging device 303. Thus, an electrostatic latent image is formed.

  The electrostatic latent image is developed into a Y toner image by the developing device of the first toner image forming unit 381Y for Y, and is electrostatically primary on the first intermediate transfer belt 321 at the primary transfer nip for Y. Transcribed. Such latent image formation, development, and primary transfer operation are similarly performed sequentially at the photoconductors 301M, C, and K sides at the same timing. Then, the M, C, and K toner images are sequentially superimposed on the Y toner image on the first intermediate transfer belt 321 at the primary transfer nip for M, C, and K, and are primarily transferred. A four-color toner image is formed on the first intermediate transfer belt 321 by the superimposed primary transfer.

  On the other hand, the paper feed device 340 feeds transfer paper corresponding to image data from any of the internal paper feed tray 340a or paper feed cassettes 340b, c, d to any one of the paper feed / separation means 341A, B, C, D. Send out by. Then, the paper is conveyed toward the paper feed path 343A of the printer unit 300A by the conveyance roller pairs 342B and 342C.

  The transfer sheet sent to the paper feed path 343A of the printer unit 300A enters the lateral registration correction mechanism 344. The lateral registration correction mechanism 344 detects the inclination of the posture from the conveyance direction of the transfer paper that is being conveyed from the paper feeding device 340 serving as the recording medium supply unit toward the double-sided transfer device (first and second transfer units). It is an inclination correction means for correcting. A pair of guide plates arranged in the paper surface direction orthogonal to the transport direction on the upstream side of the registration roller pair 345 is abutted against both ends orthogonal to the transport direction of the transfer paper, so that the posture of the transfer paper is inclined. to correct. The two guide plates of the guide plate pair can be moved in the direction of the sheet orthogonal to the transport direction, and the distance between the plates can be made the width of the transfer paper by moving according to the width of the fed transfer paper. Can be matched.

  The transfer sheet whose inclination of the posture is corrected by the lateral registration correction mechanism 344 reaches between the rollers of the registration roller pair 345, where the timing is measured and the sheet is sent to the secondary transfer nip. Then, at the secondary transfer nip, the four-color toner images on the first intermediate transfer belt 321 are secondarily transferred collectively to the first surface. The transfer residual toner is cleaned on the front surface of the first intermediate transfer belt 321 that has passed through the secondary transfer nip by the belt cleaning device 320A.

  In each of the first toner image forming units 380Y, 380M, 380K, the transfer residual toner remaining on the photoreceptors 301Y, 301M, C, and K after passing through the primary transfer nip is transferred to the belt cleaning device (320A). ) To be cleaned. As described above, the belt cleaning device (320A) removes the transfer residual toner from the first intermediate transfer belt 321 with a cleaning brush or a cleaning blade. The removed foreign matter such as toner is sent to the collecting unit 387 by the collecting means. Sensors S1 and S2 detect whether the surface potential after exposure on the surface of the photoconductor and the concentration of toner attached to the surface of the photoconductor after the development process are appropriate, and appropriately set image forming conditions. Information is sent to a control means (not shown) for control. Further, the surface of the photoreceptor 301 after cleaning is initialized by removing the residual charges by the static eliminating device Q.

  The transfer paper on which the first toner image, which is a four-color toner image, is secondarily transferred to the first surface at the secondary transfer nip is transferred to the second intermediate transfer belt 331 of the second transfer unit, and then the paper transport device. It is sent to the heat fixing device 400 via 350. At this time, prior to delivery to the heat fixing apparatus 400, the charge is applied to the transfer paper by the charge eliminating / separating charger 358. By this application, the transfer paper that has been electrostatically attracted to the belt member 351 can be easily separated from the belt member 351.

  In the heat fixing device 400, each color toner in the full color image formed on the first surface of the transfer paper is melted and mixed by heating. The toner thus fixed is rubbed against a guide member or the like in the conveyance path until the toner is completely fixed on the transfer paper, and an image is lost or distorted. In order to prevent this problem, the transfer paper that has passed through the heat fixing device 400 is delivered to a cooling roller pair 370 that is a cooling means. Then, after the toner is completely fixed, the paper is discharged onto the paper discharge stack unit 375 by the paper discharge roller 371.

  Since the image forming order is programmed so that the transfer sheets of young pages are sequentially stacked on the paper discharge stack unit 375, the page order is aligned in the stack unit 375. Since the paper discharge stack unit 375 is lowered as the number of transfer sheets to be discharged increases, the transfer sheets can be stacked in an orderly and reliable manner, and the page order is not disturbed. Instead of directly stacking the recorded transfer paper on the paper discharge stack unit 375, it is possible to carry out a punching process or transport it to a post-processing device such as a sorter, a collator, a binding device or a folding device.

  In another method of forming an image on one side of the transfer paper, an image of a young page is formed so as not to form an image in the first toner image forming units 380Y, 380Y, M, C, and K and to align pages. The difference is that images are formed in order from the data. However, the description is omitted because it is basically the same as the one-side recording process described above.

Next, the operation during double-sided recording in which images are formed on both sides of the transfer paper will be described.
When an image signal is input to the printer unit 300A, the Y, M, C, and K photoconductors 301Y, M, C, and K of the first toner image forming units 380Y, M, C, and K described in the single-side recording operation are input. A K toner image is formed. These are primary-transferred by being sequentially superimposed on the first intermediate transfer belt 321 at the primary transfer nips for Y, M, C, and K. As a result, a first toner image that is a four-color toner image is formed on the first intermediate transfer belt 321. In parallel with this step, Y, M, C, and K toner images are formed on the photoreceptors 301Y, M, C, and K of the second toner image forming portions 381Y, M, C, and K, respectively. These are primary-transferred by sequentially superposing them on the second intermediate transfer belt 331 at the primary transfer nips for Y, M, C, and K. As a result, a second toner image that is a four-color toner image is formed on the second intermediate transfer belt 331. In this way, the first toner image and the second toner image are formed on the first intermediate transfer belt 321 and the second intermediate transfer belt 331.

  The unit intervals of the second toner image forming units 381Y, M, C, and K are smaller than the unit intervals of the first toner image forming units 380Y, M, C, and K. In the second transfer unit, the primary transfer is completed faster than the first transfer unit.

  The transfer paper, which is timed and sent from the registration roller pair 345 to the secondary transfer nip, is subjected to the second intermediate after the four-color toner image on the first intermediate transfer belt 321 is secondarily transferred to the first surface. It is transferred onto the transfer belt 331. The four-color toner image on the second intermediate transfer belt 331 is secondarily transferred to the second surface at the fourth transfer position where the second intermediate transfer belt 331 and the transfer charger 347 face each other with a predetermined gap. The

  The transfer paper on which the full color images are formed on both sides in this way is sent to the paper transport device 350. The paper conveying device 350 includes a belt device having a belt member 351 and a plurality of stretching rollers that stretch the belt member 351. Specifically, the plurality of stretching rollers are an entrance roller 352, a support roller separation roller 354, a cleaning backup roller 355, and a tension roller 356. In addition to the belt device configured as described above, the paper conveying device 350 includes a belt cleaning device 350A, a separation charger 358, a driving unit, and the like. Then, the cleaning backup roller 355 is rotationally driven by the driving means, thereby causing the belt member 351 to endlessly move counterclockwise in the drawing. The transfer paper delivered from the second transfer unit 330 to the paper conveyance device 350 is conveyed toward the heat fixing device 400 while being held on the surface of the belt member 351. Then, separation from the belt surface is promoted by the application of electric charge from the separation charger 358, while the belt is separated from the belt surface at the belt support position by the separation roller 354 and transferred to the heat fixing device 400. Thereafter, a fixing process by heating or pressurization is performed in the heat fixing apparatus 400, and the toner images on both sides are respectively melted and mixed. Further, after passing through the cooling roller pair 370 and the paper discharge roller 371, the paper is discharged onto the paper discharge stack unit 375.

  When double-sided recording is performed on a plurality of pages of transfer paper, the image forming order is controlled so that an image of a young page becomes the bottom surface and is stacked on the paper discharge stack unit 375. As a result, when the paper is taken out from the paper discharge stack 375 and the top and bottom surfaces are reversed, the recorded matter is one page in order from the top, the second page is the second, the third page is the second, the fourth is the back, and the page order is aligned. Such control of image forming sequence and control such as increasing the power input to the heating and fixing device 400 compared to single-sided recording are executed by the control unit 395.

  Although an example in which full-color recording is performed regarding the single-sided recording operation and the double-sided recording operation has been described, monochrome recording using only black toner is also possible. When the need for maintenance or parts replacement arises, maintenance is performed by opening an unillustrated exterior cover or the like.

As described above, the copying machine according to the embodiment uses two types of photoconductors as image carriers. It functions as a first image carrier that exclusively carries the toner image transferred to the first surface (the surface facing upward in the figure) of the transfer paper, and exclusively carries the toner image transferred to the second surface. It functions as a second image carrier. The four photoconductors functioning as the first image carrier are disposed in the first toner image forming units 380Y, M, C, and K. The four photoconductors functioning as the second image carrier are disposed in the second toner image forming portions 381Y, M, C, and K. The first surface in this manner, by using separate dedicated photoreceptor corresponding to, respectively, respectively of the second surface, first as in the example printer and its first modification according to the first referential embodiment apparatus (100) Unlike the case of using only the photoconductor having the functions of the one image carrier and the second image carrier, the following becomes possible. That is, a second toner image to be transferred to the second surface is formed on the photoconductor and is primarily transferred to the first intermediate transfer belt 321 and then the first toner image to be transferred to the first surface is photosensitive. There is no need to do things on the body. Then, the first toner image and the second toner image can be formed in parallel on the photoconductor that functions as the first image carrier and the photoconductor that functions as the second image carrier. As a result, the image forming speed can be increased as compared with the case where only the photoconductor having the functions of the first image carrier and the second image carrier is used.

In the copying machine according to the embodiment , as already described, the first intermediate transfer belt 321 and the second intermediate transfer belt 331 are arranged in a non-contact manner. By arranging in this way, avoiding rubbing of the unfixed toner image due to a subtle difference in linear velocity between the intermediate transfer belts when the transfer paper is sandwiched between the belts and conveyed while contacting both belts, Furthermore, a toner image without disturbance can be formed. Further, even if a failure that requires stopping one of the intermediate transfer belts occurs, the single-sided printing can be performed by operating the other intermediate transfer belt in the single-sided printing mode.

FIG. 15 is an enlarged configuration diagram illustrating the heat fixing device 400 and a part of the paper transport device 350 of the copying machine according to the embodiment . As shown in the figure, in the third modification apparatus, the heat fixing apparatus 400 is not the fixing roller pair type as described above but the belt type. The heat fixing apparatus 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 drawing by the first nip forming roller 403a that is rotated clockwise in the drawing while being stretched between the first nip forming roller 403a and the first heating roller 404a that are the extending 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 cause the first fixing belt 402a and the second fixing belt 402b to contact each other at a place 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. To form a fixing nip. 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. The heating downstream first temperature sensor 406a and the heating downstream second temperature sensor 406b are the surface temperatures of the first fixing belt 402a and the second fixing belt 402b immediately after being heated by the first heating roller 404a and the second heating roller 404b, respectively. Is detected 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.

  The transfer paper P separated from the belt member 351 of the paper conveyance device 350 by the separation charger 358 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.

  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 being heated by the first heating roller 404a and the second heating roller 404b as much as possible. Has been.

  Conventionally, in a belt fixing type heat fixing apparatus, a heat generation source is provided inside a nip forming roller that forms a fixing nip, and the nip forming roller often functions as a heating unit. However, as described above, as the nip forming roller, a roller provided with an elastic layer is used for the purpose of improving the adhesion between the transfer paper and the fixing belt or forming the fixing nip widely in the paper conveyance direction. Is desirable. When such a nip forming roller is caused to function as a heating means, heat is stored in the thick elastic layer, so that the responsiveness to temperature change is deteriorated. Specifically, even if the power supply to the heat source is turned on in order to raise the fixing temperature, it takes a considerable time to raise the temperature of the fixing belt through the thick elastic layer. On the contrary, even if the power supply to the heat source is turned off to lower the fixing temperature, it is equivalent to lowering the temperature of the fixing belt due to heat conduction from the accumulated elastic layer to the fixing belt. It takes time.

Therefore, in the copying machine according to the embodiment , the first fixing belt 402a and the second fixing belt are different from the portions where the elastic layer is provided and the portions around the first nip forming roller 403a and the second nip forming roller 403b. 402b is heated. Specifically, the first fixing belt 402a and the second fixing belt 402b are heated by the first heating roller 404a and the second heating roller 404b that do not form a nip.

  In such a configuration, the heat generated from the heat source is transmitted to the first fixing belt 402a and the second fixing belt 402b without accumulating heat in the thick elastic layer. Then, compared with the case where the first nip forming roller 403a and the second nip forming roller 403b function as a heating unit, the responsiveness of the temperature change of the first fixing belt 402a and the second fixing belt 402b is improved. Accordingly, it is possible to suppress a situation in which heating with an appropriate heating amount is not performed due to poor responsiveness of temperature change of the fixing belt.

  Note that the heat fixing device 400 may be provided with first cooling means 407a and second cooling means 407b as shown in FIG. 16 in order to further improve the temperature drop response of the first fixing belt 402a and the second fixing belt 402b. The illustrated first cooling means 407a and second cooling means 407b heat the first fixing belt 402a and the second fixing belt 402b immediately after being separated from the first nip forming roller 402a and the second nip forming roller 402b. ing. Instead of the roller-type cooling unit shown in the figure, other types such as a cooling unit that supplies air to the fixing belt may be adopted.

In the printer and the modification apparatus according to the first reference embodiment described above , the first-surface toner adhesion amount and the second-surface toner adhesion amount are detected per transfer sheet P. In such detection, for example, when there is a color solid image portion on only a part of the paper surface and a large portion of the paper surface is a character image portion, it is possible to accurately grasp the toner adhesion amount of each image portion. could not. As a result, each image portion could not be heated with an appropriate heating amount.

Therefore, in the copying machine according to the embodiment, the entire area in the conveyance direction of the transfer paper P is divided into a plurality of divided areas, and the first surface toner adhesion amount and the second surface toner adhesion amount in each divided area are calculated. And based on this calculation result, the control part E2 is comprised so that 1st surface heating temperature and 2nd surface heating temperature may be controlled for every division area. Specifically, first, the ADF 300B, which is an image information acquisition unit, converts R (red), G (green), and B (blue) image information read from a document into Y, M, C, and K image information. Then, it is sent to the control unit E2. The control unit E2 calculates the number of Y, M, C, and K recording pixels for the first and second surfaces of the transfer paper P based on the sent Y, M, C, and K image information. Next, the number of recording pixels of each color is divided for each divided region. For example, when the paper surface is divided into four areas such as the first, second, third, and fourth areas from the front end side, the number of recording pixels of each color is set to the first, second, third, and fourth areas. Each pixel is divided into the number of pixels corresponding to.

  Once the number of recording pixels for each color is calculated for each divided region, the first surface toner adhesion amount and the second surface toner adhesion amount are detected for each divided region based on the total number of each color recording pixel for each divided region. To do. And based on a detection result, 1st surface heating temperature and 2nd surface heating temperature are controlled for every division area. For example, while the first divided area of the first surface of the transfer paper P enters the fixing nip, the first surface heating temperature is controlled based on the first surface toner adhesion amount of the first divided area, and the first While the second divided area of one surface enters the fixing nip, the first surface heating temperature is controlled based on the first surface toner adhesion amount of the second divided area. Since the responsiveness of the temperature change of the fixing belt is accelerated as described above, such control is possible.

When the first surface heating temperature and the second surface heating temperature are controlled for each divided region in this way, it is necessary to manage the surface temperature of the fixing belt more strictly than in the past. Specifically, conventionally, heating to the fixing belt has been controlled on / off based on the surface temperature of the fixing belt immediately before entering the fixing nip. However, in this example, in order to realize delicate management of the surface temperature of the fixing belt, it is necessary to grasp the temperature distribution in the belt circumferential direction of the fixing belt after passing through the fixing nip. This is because the temperature of the fixing belt after passing through the fixing nip varies, and the belt cannot be accurately heated to a desired temperature without grasping this. Therefore, it is necessary to slightly change the heating amount for the fixing belt based on the grasped temperature distribution. Therefore, in the copying machine according to the embodiment , the first fixing belt unit 401a and the second fixing belt 402a are provided with a heating downstream temperature sensor (406a, b) and a heating upstream temperature sensor (405a, b). Then, based on the detection result by the heating downstream temperature sensor that detects the surface temperature of the fixing belt before heating, the temperature variation in the circumferential direction of the fixing belt after passing through the fixing nip is detected. Further, based on the detection result, the heating temperature for the fixing belt is set so that the heating temperature is appropriate for each of the divided regions.

Next, a copying machine according to the second reference embodiment will be described.
The basic configuration of the copying machine according to the second embodiment is the same as that of the copying machine according to the embodiment shown in FIG. 12 unless otherwise specified. In FIG. 12 described above, the first image forming unit including the four first toner image forming units 380Y, M, C, and K and the first transfer unit 320 has the first toner on the first surface of the transfer paper P. It functions as first toner image forming means for forming an image. The second image forming unit including the four second toner image forming units 381Y, M, C, and K and the second transfer unit 330 forms the second toner image on the second surface of the transfer paper P. It functions as toner image forming means.

FIG. 17 is a block diagram showing a part of the electric circuit of the copying machine according to the second embodiment. The control unit E2, which is a control unit, includes a first image forming unit, a second image forming unit, an operation / display device 390, a heat fixing device 400, an image data processing device E1, which is an image information acquisition unit, an abnormality detection unit 500, a cassette sensor 501 etc. are connected.

  The cassette sensor 501 individually detects the loading / unloading of the four sheet feeding cassettes 340a, b, c, d with respect to the sheet feeding device 340, and outputs a detection signal to the control unit E2.

  The heat fixing device 400 includes a first heater 408a and a second heater 408b. These are heat sources included in the first heating roller 404a and the second heating roller 404b shown in FIG. When the power is supplied to the first heater 408a, the first heating roller 404a generates heat. In addition, the second heating roller 404b generates heat by supplying power to the second heater 408b.

  The operation / display unit 390 can execute the following program. In other words, the operator is allowed to select four abnormality countermeasure operation modes of “abnormality single-sided omission mode”, “abnormality double-sided output mode”, “abnormality single-sided alternate output mode”, and “abnormality double-sided stop mode”. It is a program for. Then, the operator is made to select any one mode, and the result is sent as a mode selection signal to the control unit E2. The control unit E2 sets the abnormality countermeasure operation mode in accordance with the mode selection signal sent from the operation / display unit 390. The four abnormality countermeasure operation modes will be described in detail later.

The abnormality detection unit 500 includes a plurality of sensors (not shown) for detecting the abnormality of the first image forming unit and the abnormality of the second image forming unit, respectively. Examples of these sensors include those listed below.
・ A thermal sensor that detects the current load of a power source such as a drive motor.
A belt speed sensor that detects marks provided at a predetermined pitch over the entire circumference of the belt to detect the moving speed of the belt.
A potential sensor that detects the surface potential of the photoreceptor.
-Toner density sensor.

  The abnormality detection unit 500 detects an abnormality of the first image forming unit and an abnormality of the second image forming unit based on the detection results by these sensors, and outputs an abnormality detection signal to the control unit E2. When an abnormality detection signal is sent from the abnormality detection unit 500, the control unit E2 controls the printing process based on the abnormality and the above-described abnormality countermeasure operation mode.

  The control unit E2 detects whether an abnormality in one of the first image forming unit or the second image forming unit is detected, a duplex printing command is issued, and the “single-side omission mode when abnormal” is set. The following control is performed. That is, first, the image forming unit in which no abnormality has occurred among the data for the first toner image and the data for the second toner image included in the image information sent from the image data processing apparatus. Pick up only those that correspond to. Then, only one of the first toner image and the second toner image based on the picked-up data is formed on the first surface or the second surface of the transfer paper P by the image forming unit on which no abnormality has occurred. For example, when an abnormality of the first image forming unit is detected, only the data for the second toner image included in the image information is picked up. Then, only the second toner image is formed on the second surface by the second image forming unit. Even in the case of image information for continuously forming images over a plurality of pages on a plurality of transfer papers P, only the second toner images are sequentially formed on the second surface on the plurality of transfer papers P. . If an abnormality of the second image forming unit is detected, the reverse control is performed. Specifically, only the data for the first toner image included in the image information is picked up. Then, only the first toner image is formed on the first surface by the first image forming unit.

  In addition, the control unit E2 detects an abnormality in either the first image forming unit or the second image forming unit, issues a double-sided print command, and sets the “abnormal one-sided alternate output mode”. The following control is performed. That is, first, only the data corresponding to the image forming unit in which no abnormality has occurred among the data for the first toner image and the data for the second toner image included in the image information is picked up. Then, only one of the first toner image and the second toner image based on the picked-up data is formed on one surface of the transfer paper P by the image forming unit where no abnormality has occurred. Next, character information indicating that an operation of setting the printout paper discharged outside the machine upside down is necessary is displayed on the operation / display unit 390 as information transmission means. Then, when the cassette sensor 501 detects the loading / unloading of the paper feed cassette, this time, the first toner image and the second toner image that are not formed first are the ones in which no abnormality has occurred. It is formed on the other surface of the transfer paper P by the image forming unit. For example, when an abnormality of the first image forming unit is detected, first, only the second toner image is formed on one surface of the transfer paper P by the second image forming unit. Then, after the above-described character information is displayed, when the insertion / removal of the paper feed cassette is detected, only the first toner image is formed on the other surface of the transfer paper P by the second image forming unit. The same applies to the case where images over a plurality of pages are continuously output to a plurality of transfer sheets P. Specifically, first, only the second toner image is continuously formed on one surface of the plurality of transfer sheets P by the second image forming unit. Then, after the paper feeding cassette is put in and out, only the first toner image is continuously formed on the other surface by the second image forming unit on the plurality of transfer papers P.

  In such control, even if an abnormality occurs in either the first image forming unit or the second image forming unit, only the image forming unit in which no abnormality has occurred is used to transfer the transfer paper P. Images can be formed on both sides. In addition, although the example using the operation / display unit 390 that transmits character information to the operator has been described as the information transmission means, information of a different type from character information such as voice information and moving image information may be transmitted. Good.

  In addition, the control unit E2 detects an abnormality in either the first image forming unit or the second image forming unit, issues a double-sided print command, and sets the “abnormal one-sided alternate output mode”. The following control is performed. That is, first, a first toner image is formed on one surface of the transfer paper P by an image forming unit in which no abnormality has occurred. Next, a new transfer paper P is fed, and a second toner image is formed on one surface of the transfer paper P by an image forming unit in which no abnormality has occurred. That is, instead of forming the first toner image and the second toner image on the first surface and the second surface of one transfer sheet P, respectively, two sheets are formed by the image forming unit on which no abnormality has occurred. The first toner image and the second toner image are alternately formed on one side of each transfer paper P. For example, when an abnormality in the first image forming unit is detected, the second image forming unit forms the first toner image on the second surface of the first transfer sheet P, and then the second sheet. A second toner image is formed on the second surface of the transfer paper P. The same applies to the case where images over a plurality of pages are continuously output to a plurality of transfer sheets P. Specifically, the first toner image and the second toner are respectively formed on the second surface of the first sheet, the second sheet, the third sheet, the fourth sheet, the fifth sheet, the sixth sheet,... Image, first toner image, second toner image, first toner image, second toner image,...

  In such control, all the images to be formed on the first and second surfaces of the transfer paper P can be output without forcing the operator to reverse the printout paper upside down. .

  Further, the control unit E2 detects an abnormality in either the first image forming unit or the second image forming unit, issues a double-sided print command, and sets “abnormality duplex stop mode”. Performs the following control. That is, an alarm is displayed on the operation / display unit 390 without accepting the duplex printing command.

  In addition, when executing any one of “abnormal one-sided omission mode”, “abnormal one-sided output mode” or “abnormal one-sided alternate output mode”, the control unit E2 sets the heating and fixing device 400 as follows. Configured to control. That is, power is supplied only to the first heater 408a and the second heater 408b corresponding to the image forming unit that is not detected to be abnormal, and only the heating roller that contains it is heated. . For example, when an abnormality in the first image forming unit is detected, power is supplied only to the second heater 408b, and only the second heating roller 404b of both the heating rollers is heated. In addition, when an abnormality in the second image forming unit is detected, power is supplied only to the first heater 408a, and only the first heating roller 404a of both the heating rollers is caused to generate heat.

  In such a control, when an abnormality in one of the image forming units is detected, the transfer sheet P is used when the failure countermeasure operation mode in which an image is formed using only the other image forming unit is executed. It is possible to avoid wasteful energy consumption due to unnecessary heating of the first surface and the second surface on which the toner image is not formed.

  Note that the present invention can also be applied to an image forming apparatus that uses a liquid developer containing toner and a liquid carrier instead of a powder toner. The present invention can also be applied to an image forming apparatus that forms an image by a direct recording method instead of an electrophotographic method. In this direct recording method, regardless of the latent image carrier, a toner group that has been ejected in the form of dots from a toner flying device is directly attached to an intermediate transfer body or recording body to form a pixel image, thereby directly It is a method to form.

As described above, in the printer and each modification example device according to the first reference embodiment, based on the image information acquired by the image data processing device E1 as the image information acquisition unit or the ADF 300B as the control unit E2 as the toner adhesion amount detection unit, What detects the first surface toner adhesion amount and the second surface toner adhesion amount is used. In such a configuration, the first surface toner adhesion amount and the second surface toner adhesion amount can be detected without providing an optical sensor for optically detecting the toner adhesion amount.

  Further, in the first modified apparatus, the image area ratio on the first surface and the image area ratio on the second surface are calculated based on the image information acquired by the image data processing device E1, and the calculation results are used as they are. Alternatively, the control unit E2 detects values obtained by performing predetermined arithmetic processing on the calculation results as the first surface toner adhesion amount and the second surface toner adhesion amount, respectively. In such detection, the first surface toner adhesion amount and the second surface toner are more than in the case where the toner adhesion amount is detected based on whether the image is a multicolor toner image as in the printer according to the first embodiment. The amount of adhesion can be determined accurately. Thus, the difference in glossiness between the images on the front and back of the transfer paper P can be more reliably suppressed.

  Further, in the second modification device, the first surface recording pixel number and the second surface recording pixel number are calculated based on the image information acquired by the image data processing device E1, and the calculation result is used as it is or The control unit E2 detects values obtained by performing predetermined calculation processing on the calculation results as the first surface toner adhesion amount and the second surface toner adhesion amount, respectively. Also in such detection, the first surface toner adhesion amount and the second surface toner are more than in the case where the toner adhesion amount is detected based on whether or not the image is a multicolor toner image as in the printer according to the first embodiment. The amount of adhesion can be determined accurately. Thus, the difference in glossiness between the images on the front and back of the transfer paper P can be more reliably suppressed.

In the copying machine according to the embodiment, the toner image forming unit is configured to form a multicolor image by superimposing single-color images having different colors as the first toner image and the second toner image, and Based on the image information acquired by the image data processing device E1, the number of first side recording pixels and the number of second side recording pixels for each color are calculated, and the total number of first side recording pixels for each color is calculated. The control unit E2 detects the total of the numbers as they are or the values obtained by performing arithmetic processing on the total as the first surface toner adhesion amount and the second surface toner adhesion amount, respectively. In such detection, for the reasons described above, the first surface toner adhesion amount and the second surface toner adhesion amount of the transfer paper P on which the multicolor toner image is formed are obtained more accurately than in the second modification device. Can do. Thus, the difference in glossiness between the images on the front and back of the transfer paper P can be more reliably suppressed.

In the printer according to the first reference embodiment, the toner image forming unit is configured to form a multicolor image by superimposing single-color images having different colors as the first toner image and the second toner image, and Then, based on the image information acquired by the image data processing device E1, it is determined whether the toner images on the first surface and the second surface are multicolor toner images by superimposing a plurality of colors, and the determination result is A controller that detects the first-surface toner adhesion amount and the second-surface toner adhesion amount based on the first surface toner adhesion amount is used as the control unit E2. In such detection, the first-surface toner adhesion amount and the second-surface toner adhesion amount can be obtained by a simpler calculation process than each modified apparatus.

In addition, the copying machine according to the embodiment includes a pair of fixing belt units that move the fixing belt endlessly while being stretched by a plurality of stretching members, and the fixing belts contact each other at a place where the fixing belt is wound around the nip forming roller. Each fixing belt unit has a belt heating unit that forms a fixing nip by contacting the belt and heats a belt portion different from the winding portion, and the transfer paper P sandwiched between the fixing nips of the pair of fixing belt units. The first surface of the transfer sheet P functions as a first surface heating unit, and the second surface of the transfer paper P sandwiched in the fixing nip functions as a second surface heating unit. This is used as a heat fixing device. In such a configuration, the response speed of the heating temperature change can be increased as compared with the case where the fixing roller pair is used as the heating unit. Therefore, even in the continuous print mode, the first surface and the second surface of each transfer sheet P are used. On the other hand, the fixing process can be performed with an appropriate heating amount. As a result, the difference in image glossiness between the front and back surfaces of a plurality of transfer sheets P that are continuously output in the continuous print mode can be suppressed.

In the copying machine according to the embodiment, each of the pair of fixing belt units is provided with belt cooling means for cooling the fixing belt portion that has passed through the fixing nip. Thereby, since the response speed of the heating temperature change can be further increased, it is possible to more reliably suppress the difference in image glossiness between the front and back sides of the plurality of transfer sheets P continuously output in the continuous print mode. .

In the copier according to the embodiment, the entire area in the transport direction of the transfer paper P is divided into a plurality of divided areas, and the first surface toner adhesion amount and the second surface toner adhesion amount in each divided area are calculated. The control unit E2 is configured to control the first surface heating temperature and the second surface heating temperature based on the calculation result for each divided region. In such a configuration, for the reason described above, not only the difference in glossiness of the image on the front and back of the transfer paper P but also the difference in glossiness of the image due to the deviation of the toner adhesion amount distribution on the same surface of the transfer paper P is suppressed. You can also

Further, in the second modification apparatus 200 and the copying machine according to the embodiment , as the first image carrier, four photosensitive members that carry toner images of different colors are used, and as the second image carrier, Four photoconductors that carry toner images of different colors are used. The four toner images on the first image carrier are transferred onto the first intermediate transfer belt 321 while being superposed on the first intermediate transfer belt 321, while the toner images on the four second image carriers are respectively transferred to the second intermediate transfer belt 331. The toner image forming unit is configured to transfer the images in a superimposed manner. In this configuration, for the reasons described above, the first toner image and the second toner image can be formed in parallel on the photoconductor that functions as the first image carrier and the photoconductor that functions as the second image carrier. It becomes possible. As a result, the image forming speed can be increased as compared with the case where only the photoconductor having the functions of the first image carrier and the second image carrier is used.

Further, in the second modification apparatus 200 and the copying machine according to the embodiment , as the first image carrier, four photosensitive members that carry toner images of different colors are used, and as the second image carrier, While using four photoconductors carrying toner images of different colors and transferring the toner images of the four photoconductors functioning as the first image carrier on the first intermediate transfer belt, The double-sided transfer device is configured so that the toner images on the other four photoconductors functioning as the two-image carrier are transferred onto the second intermediate transfer belt, respectively. In such a configuration, even when a multicolor toner image is formed in which the amount of toner on the transfer paper surface is larger than that of a single color toner image, the surface roughness Ra differs between the front and back surfaces of the transfer paper, thereby improving image fixability. It is possible to suppress the occurrence of a difference or a hot offset of the image on either the front or back side.

Further, in the second modification apparatus 100 and the copying machine according to the embodiment, the secondary transfer is a paper discharge unit of the paper feeding device (291, 340) as the recording body accommodating unit and the paper receiving unit of the toner image forming unit. The nip entrance is the same height in the vertical direction. In such a configuration, as shown in FIGS. 9 and 14, the paper feed path (288, 343A) from the paper feed device to the secondary transfer nip entrance is formed into a linear shape without bending in the vertical direction. Reduces jamming of transfer paper in the paper feed path. As a result, high-speed paper feeding is possible, and the image forming speed can be increased.

Further, in the second modification apparatus 200 and the copying machine according to the embodiment , as shown in FIGS. 9 and 14, the secondary transfer nip outlet and the charger transfer position which are the recording medium discharge portion of the toner image forming means. The exit and the nip portion that is the recording member receiving portion of the pair of paper discharge rollers as the discharge means are set to the same height. In such a configuration of the paper transport path, in the path from the recording medium discharge unit of the double-side transfer device to the pair of paper discharge rollers, a linear shape without bending in the vertical direction is formed, and transfer in this path is performed. Reduce paper jams. As a result, the paper can be fed at a higher speed, and the image forming speed can be increased.

Further, in the copying machine according to the second reference form, an operation / display unit 390 is provided as information transmission means for transmitting information to the operator, and the abnormality detection means 500 selects either the first image forming unit or the second image forming unit. If one of the abnormalities is detected, after forming only one of the first toner image and the second toner image corresponding to the image forming portion where no abnormality is detected on one surface of the transfer paper P The character information indicating that the operation of turning the transfer paper P upside down and setting it in the paper feed cassette is necessary is transmitted to the operator by the operation / display unit 390, and based on the subsequent operation by the operator, Of the one toner image and the second toner image, the other side of the transfer paper P that has not been previously formed on the transfer paper P is detected by the first image forming unit or the second image forming unit in which no abnormality is detected. Let the control to form As described above, constitute a control means serving controller E2. In such a configuration, even if an abnormality occurs in any one of the image forming units for the reason described above, only the image forming unit in which no abnormality has occurred is used, and the first surface and the second surface of the transfer paper P are used. A first toner image and a second toner image can be formed on the surface, respectively.

Further, in the copying machine according to the second reference embodiment, when the abnormality detecting unit 500 detects an abnormality in either the first image forming unit or the second image forming unit, the abnormality is not detected. The control unit E2 performs control so that the first toner image and the second toner image are alternately formed on only one side of the plurality of transfer sheets P using only one image forming unit or the second image forming unit. Is configured. In such a configuration, for the reason described above, even if an abnormality occurs in any one of the image forming units, the first transfer paper P is not forced to force the operator to perform the upside down resetting operation of the printout paper. All images to be formed on the surface and the second surface can be output.

In the copying machine according to the second reference embodiment, as the heat fixing device 400 serving as the heat fixing unit, the first heating roller 404a serving as the first surface heating unit for heating the transfer paper P from the first surface side, and the second surface. What has the 2nd heating roller 404b which is the 2nd surface heating means heated from the side is used. When the abnormality detection unit 500 detects an abnormality in either the first image forming unit or the second image forming unit, an abnormality is detected between the first heating roller 404a and the second heating roller 404b. The control unit E2 is configured to perform control to generate heat only in the one corresponding to the image forming unit that has not been performed. In this configuration, as described above, when an abnormality in one of the image forming units is detected, the failure countermeasure operation mode for forming an image using only the other image forming unit is executed. It is possible to avoid wasteful energy consumption due to unnecessary heating of the first surface and the second surface of the paper P on which the toner image is not formed.

1 is a schematic configuration diagram of a printer according to a first reference embodiment. FIG. 3 is an enlarged configuration diagram illustrating a process unit for Y of the printer. FIG. 2 is a block diagram showing a part of an electric circuit of the printer. The schematic block diagram which shows a 1st modification apparatus. The expanded block diagram which shows the secondary transfer nip and its circumference | surroundings in the said 1st modification apparatus. FIG. 6 is an enlarged configuration diagram showing a tertiary transfer nip and its surroundings in the first modification apparatus. The schematic block diagram which shows the 2nd modification apparatus. The schematic diagram which shows the 1st example of the secondary transfer nip and its surrounding structure in the 2nd modification apparatus. The schematic diagram which shows the 2nd example of the secondary transfer nip and surrounding structure. The schematic diagram which shows the 3rd example of the secondary transfer nip and surrounding structure. The schematic diagram which shows the 4th example of the secondary transfer nip and surrounding structure. 1 is a schematic configuration diagram showing a copier according to an embodiment. FIG. 3 is an enlarged configuration diagram illustrating one of four first toner image forming units in the copier . FIG. 3 is an enlarged configuration diagram illustrating one of four second toner image forming units in the copier . FIG. 2 is an enlarged configuration diagram illustrating a heat fixing device and a part of a paper conveying device of the copier . FIG. 6 is an enlarged configuration diagram showing a modification of the heat fixing device of the copier . The block diagram which shows a part of electric circuit of the copying machine which concerns on a 2nd reference form.

Explanation of symbols

1Y, M, C, K photoconductor (image carrier)
35, 135, 235, 400 Heat fixing device 35a First fixing roller (first surface heating means)
35b Second fixing roller (second surface heating means)
401a First fixing belt unit (first surface heating means)
401b Second fixing belt unit (second surface heating means)
101Y, M, C, K photoconductor (image carrier)
201Y, M, C, K photoconductor (first image carrier)
271Y, M, C, K photoconductor (second image carrier)
301Y, M, C, K photoconductor (image carrier)
300B ADF (image information acquisition means)
400 Heat Fixing Device E1 Image Data Processing Device (Image Information Acquisition Unit)
E2 control unit (heating temperature control means, toner adhesion amount detection means)
P Transfer paper (recording medium)

Claims (7)

Image information acquisition means for acquiring image information, and a first toner image transferred to the first surface of the recording medium is heat-fixed on the first surface and the second toner transferred to the second surface of the recording medium a heat fixing means allowed to heat fix the image to said second surface, said first toner image formed on the surface of the image carrier on the basis of the image information, by means of a double-sided transfer means before being sent to the heating fixing unit while transcription of the first surface of the recording medium, before the second toner image formed on the surface of the image carrier on the basis of the image information, by double-sided transfer means, to be sent to the heating fixing unit is transferred to the second surface of the recording material, and a toner image forming means for forming a toner image on both surfaces of the recording medium, and a first surface heating means for heating the recording medium from the first surface side, An image having a second surface heating means for heating the recording medium from the second surface side in the heat fixing means. In forming apparatus,
A toner adhesion amount for detecting a first surface toner adhesion amount that is a toner adhesion amount to the first surface of the recording medium via the toner image forming means and a second surface toner adhesion amount that is a toner adhesion amount to the second surface, respectively. A detection means, and a heating temperature control means for controlling a first surface heating temperature that is a heating temperature by the first surface heating means and a second surface heating temperature that is a heating temperature by the second surface heating means, respectively, In performing the fixing process by the heat fixing unit on the recording medium on which the toner images are formed on both sides, the first surface toner is based on the detection result of the first surface toner adhesion amount by the toner adhesion amount detection unit. The first surface heating temperature is controlled to increase the first surface heating temperature as the adhesion amount increases, while the second surface toner is detected based on the detection result of the second surface toner adhesion amount. As the amount of deposition is increased to perform a process of controlling the second surface heating temperature so as to increase the second side heating temperature, as well as constituting the heating temperature control means,
As the heating and fixing means, a pair of fixing belt units that endlessly move the fixing belt while being stretched by a plurality of stretching members, and the fixing belt units are provided in the fixing belt units, and the fixing belts are wound around the nip forming rollers. And a belt heating means for heating a portion of the fixing belt that is different from the portion around which the belt is wound. The one in which the fixing belt is brought into contact with the first surface of the recording medium sandwiched functions as the first surface heating means, and the second belt in which the fixing belt is brought into contact with the second surface of the recording medium sandwiched in the fixing nip. An image forming apparatus using what is used as a surface heating means. The image forming apparatus according to claim 1.
An image forming apparatus, wherein each of the pair of fixing belt units is provided with belt cooling means for cooling a fixing belt portion that has passed through the fixing nip. The image forming apparatus according to claim 1 or 2,
The toner adhesion amount detection means is configured to divide the entire area in the conveyance direction of the recording medium into a plurality of divided areas and calculate the first surface toner adhesion amount and the second surface toner adhesion amount in each divided area, An image forming apparatus comprising: the heating temperature control unit configured to control the first surface heating temperature and the second surface heating temperature for each divided region based on a calculation result. The image forming apparatus according to any one of claims 1 to 3,
The first image carrier that exclusively carries the toner image formed on the first surface and the second image carrier that exclusively carries the toner image formed on the second surface are used. The first toner image on the image carrier is intermediately transferred to the surface of the first intermediate transfer member and then transferred to the first surface, while the second toner image on the second image carrier is transferred to the second intermediate transfer member. The toner image forming means is configured to transfer the toner image to the second surface after the intermediate transfer to the surface of the toner image, and the first intermediate transfer member and the second intermediate transfer member are arranged in non-contact with each other. An image forming apparatus. The image forming apparatus according to claim 4.
As the first image carrier, a plurality of toner images carrying the toner images having different colors are used, and as the second image carrier, a plurality of toner images carrying the toner images having different colors are used, and A plurality of toner images on the first image carrier are transferred onto the first intermediate transfer belt, respectively, while a plurality of toner images on the second image carrier are transferred to the second intermediate transfer belt, respectively. An image forming apparatus characterized in that the toner image forming means is configured to transfer the toner image in a superimposed manner. The image forming apparatus according to claim 4 or 5,
The recording body feeding section of the recording body housing section that feeds the recording body housed inside toward the double-sided transfer section and the recording body receiving section of the toner image forming section have the same height in the vertical direction. An image forming apparatus. The image forming apparatus according to claim 6.
The recording material discharge portion of the toner image forming means and the recording material receiving portion of the discharge means for discharging the recording material that has passed through the heating and fixing means to the outside of the image forming apparatus housing are characterized by the same height. Image forming apparatus.

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