JP4971765B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus such as an electrophotographic system or an electrostatic recording system, and more particularly to an image forming apparatus capable of forming a multicolor full color image.

  In recent years, in addition to toner images of four colors of cyan (C), magenta (M), yellow (Y), and black (K), a transparent toner image, a gray toner image, and the like are transferred, thereby adding an added value image. Has been proposed.

  By the way, the fixing device for fixing the unfixed toner image transferred on the sheet has a toner loading amount limitation. Therefore, in addition to the toner loading amount optimally imaged on the sheet, a transparent toner or the like is loaded. If this happens, a cold offset occurs. In this case, it is conceivable to control the toner amount to be within the limit amount including the transparent toner. However, since the amount of the colored toner has to be reduced by the amount of the transparent toner, the image quality is deteriorated.

Further, many techniques have been proposed for developing a colorless (transparent) toner image in addition to a colored toner image and transferring / fixing a toner image in which colored and colorless are mixed on a sheet. Further, there has been proposed a technique for changing the fixing condition of the fixing device between the case of fixing only with a colored toner image and the case of fixing an image obtained by superimposing a colored toner image and a colorless toner image (Patent Document 1). reference).
JP 2002-318482 A

  There are cases where overlaying colorless (transparent) toner images produces the same effect as using glossy paper, protecting the surface to provide a waterproof effect, and protecting colored toner images. It is done.

  In this case, in order to form a colorless toner image, a complicated process such as creation of image video data is removed, a uniform potential is formed on the photosensitive drum, and the colorless toner image is transferred onto the sheet. A simple device is required. Further, the colorless toner image needs to be uniformly transferred and fixed on the entire surface of the sheet regardless of the amount of the colored toner applied.

  In such a case, it is impossible to control the amount of colorless toner applied to the amount of colored toner applied. However, considering the protection of the fixing device and the image quality, it is not easy to change the fixing conditions in consideration of the applied amount.

  SUMMARY OF THE INVENTION Accordingly, the present invention provides an image forming apparatus that can easily form an optional color toner image such as a uniform transparent toner image on a colored toner image without changing the fixing conditions of the fixing means. With the goal.

In order to achieve the above object, an image forming apparatus according to claim 1 includes an intermediate transfer member that carries and conveys a toner image, a first forming unit that forms a colored toner image to be transferred to the intermediate transfer member, and Second forming means for forming a transparent toner image to be transferred to the intermediate transfer member, transfer means for transferring the toner image superimposed on the intermediate transfer member to the sheet, and fixing for fixing the toner image formed on the sheet An image forming apparatus comprising: a detecting unit configured to detect a combined amount of the color toner and the transparent toner per unit area of the image to be formed on the sheet based on the input image information; and the transparent toner and the color When an image is formed on a sheet using toner, a transparent toner image is formed on the lowermost layer on the intermediate transfer member and the colored toner is formed on the transparent toner when the detection result of the detection unit is a predetermined amount or less. The And the first mode in which the transparent toner and the colored toner superimposed on the intermediate transfer member are collectively transferred to the sheet by the transfer unit, and the sheet is fixed only once by the fixing unit, When the detection result exceeds a predetermined amount, the colored toner image formed on the intermediate transfer member is transferred onto the sheet by the transfer unit and then fixed by the fixing unit, and is also formed on the intermediate transfer member. Control means for covering the colored toner image fixed on the sheet with the transparent toner and controlling to execute the second mode of fixing the transparent toner to the sheet again by the same fixing means. To do.

  According to the present invention, since the fixing of the color toner image and the fixing of the optional color toner image such as the transparent toner image are separately performed, the color toner image can be uniformly formed on the color toner image without changing the fixing condition of the fixing unit. A transparent toner image or the like can be easily formed. Therefore, it is possible to provide an image forming apparatus with high added value without increasing the apparatus cost and without performing complicated loading amount control.

  Hereinafter, an example of an embodiment of the present invention will be described with reference to the drawings. 1 is a schematic sectional view of an image forming apparatus as an example of an embodiment of the present invention, FIG. 2 is a control block diagram of the image forming apparatus as an example of an embodiment of the present invention, and FIG. 3 is an example of an operation unit. FIG. 4A is an explanatory diagram for explaining the one-sheet pasting control, FIG. 4B is an explanatory diagram for explaining the two-sheet pasting control, and FIG. 5 is a diagram of the toner image from the photosensitive drum to the intermediate transfer member. It is explanatory drawing for demonstrating transfer timing. FIG. 6 is a time chart for explaining the transfer timing of the toner image from the photosensitive drum to the intermediate transfer member, and FIG. 7 is a flowchart for explaining the operation example of the image forming apparatus as an example of the embodiment of the present invention. FIG. FIG. 8 is a diagram for explaining an example of normal sheet conveyance, FIG. 9 is a diagram for explaining an example of sheet conveyance in double-sided image formation, and FIG. 10 is a diagram for explaining an example of sheet conveyance in multiple image formation. It is.

[Configuration of Image Forming Apparatus]
As shown in FIG. 1, a color image forming apparatus according to an embodiment of the present invention includes a digital color image reader unit (hereinafter abbreviated as “reader unit”) 201 in the upper part and a digital color image printer unit (lower part). Hereinafter, the image processing unit 203 is provided between the reader unit 201 and the printer unit 202.

  In the reader unit 201, the original 30 is placed on the original table glass 31 and exposed and scanned by the exposure lamp 32, whereby the reflected light image from the original 30 is condensed by the lens 33 onto the CCD sensor 34 integrated with the RGB three-color separation filter. Then, the color separation image analog signal is obtained. The color-separated image analog signal is digitized through an amplifier circuit (not shown), processed by the image processing unit 203, and sent to the printer unit 202.

  In the printer unit 202, the photosensitive drum 1 that is an image carrier is supported rotatably in the direction of the arrow. Around the photosensitive drum 1, there are a pre-exposure LED 11, a primary charger 2, a laser exposure unit 3, a potential sensor 12, a rotating developer 4 (developers 4k, 4y, 4c, 4m, 4s1, 4s2), and an intermediate transfer member. 5a, a test patch density sensor 13, and an intermediate transfer body cleaner 6 are arranged.

  In the laser exposure unit 3, the image signal from the reader unit 201 is converted into an optical signal by a laser output unit (not shown), and the converted laser beam is reflected by the polygon mirror 3a and passes through the lens 3b and the mirror 3c. Projected onto the surface of the photosensitive drum 1.

  At the time of image formation by the printer unit 202, the photosensitive drum 1 is rotated in the direction of the arrow, and the photosensitive drum 1 after the charge removal by the pre-exposure LED 11 is uniformly charged by the primary charger 2, and then the light for each separated color. Irradiate the image to form a latent image.

  Next, a predetermined developing device is operated to develop the latent image on the photosensitive drum 1, and a toner image using a resin as a base is formed on the photosensitive drum 1. The developing devices 4k, 4y, 4c, 4m, 4s1, and 4s2 are alternatively arranged close to the photosensitive drum 1 in accordance with each separation color by the rotation of a developing rotary motor (not shown).

  The developed toner image on the photosensitive drum 1 is transferred to the belt-shaped intermediate transfer member 5a by the high voltage applied by the primary transfer charger 5b. In the present embodiment, in the case of a sheet (for example, 250 mm) of ½ or less of the entire circumference of the intermediate transfer member 5a, an image can be simultaneously formed on the region on the intermediate transfer member 5a corresponding to two sheets. It is. The case where images corresponding to these two sheets are simultaneously formed on the intermediate transfer member 5a is referred to as “two-sheet pasting control”, and an image corresponding to one sheet is formed on the intermediate transfer member 5a. The case where image formation is performed is referred to as “single sheet paste control”.

  In the case of single-sheet pasting control, as shown in FIG. 4A, the toner image is formed starting from a fixed point PTA on the intermediate transfer member 5a, and the size of the intermediate transfer member 5a of the sheet A changes in size in the rotation direction. Even so, the fixed point PTA is controlled to be imaged at the tip. On the other hand, in the case of the two-sheet pasting control, the toner image corresponding to the first sheet A is formed so that the fixed point PTA is at the front end as in the case of the one-sheet pasting control. The second sheet B is imaged so that the fixed point PTB, which is a point separated by 180 in the rotational direction of the intermediate transfer member 5a at the fixed point PTA, is the leading end. In the case of the two-sheet pasting control, similarly to the one-sheet pasting control, even if the sheet size changes, an image is formed so that the fixed points PTA and PTB are at the leading ends.

  Here, the control for forming the front of the toner image so that the fixed point PTA is at the head is A-side image formation (or A-side pasting control), and the control for forming the fixed point PTB is at the front is B-side image forming. (Or B surface pasting control).

  As the intermediate transfer member 5a is rotated, the toner image on the photosensitive drum 1 is transferred to the intermediate transfer member 5b by the primary transfer charger 5b. In this way, a desired number of each color image is transferred onto the intermediate transfer member 5a to form a full color image. In the case of full-color image formation, for example, after the transfer of toner images of four colors (c, m, y, k) to the intermediate transfer body 5a is completed, secondary transfer chargers (transfer means) are supplied from the paper feed cassettes 7a to 7d. The sheet is conveyed to the position 5c, and the secondary transfer to the sheet is performed. As shown in FIG. 8, the sheet on which the secondary transfer of the four color toner images has been completed passes through the secondary transfer charger 5c, and then the fixing unit (fixing means) 9 fixes the unfixed toner image. Will be discharged.

  The photosensitive drum 1 after completion of the primary transfer is subjected to the image forming process again after the residual toner on the surface is cleaned by the photosensitive drum cleaner 7. The intermediate transfer member 5a after the completion of the secondary transfer is subjected to the image forming process again after the residual toner on the surface is cleaned by the intermediate transfer member cleaner 6.

  When images are formed on both sides of a sheet, referring to FIG. 9, after the sheet having an image formed on one side is discharged from the fixing device 9, the conveyance path switching flapper 19 is immediately driven to Is guided to the conveying vertical path 20 and once sent to the reversing path 21a. The sheet sent to the reversing path 21 a is conveyed in the opposite direction to the fed direction with the rear end when it is fed at the top by the reverse rotation of the reversing roller 21 b and stored in the double-sided path 22. Thereafter, an image is formed again on the other surface of the sheet by the image forming process described above. When images are formed on both the front and back sides of a sheet in this way, the first side on which the image is first formed on the sheet is referred to as “both side first side”, and the second side on which the image is formed next is referred to as “both sides” The second side.

  In this embodiment, the intermediate transfer is performed by operating the eccentric cam 25 adjacent to the secondary transfer charger 5c at a desired timing and operating a cam follower (not shown) integrated with the secondary transfer charger 5c. The gap between the body 5a and the secondary transfer charger 5c can be adjusted. For example, during standby or when the power is turned off, the secondary transfer charger 5c is adjusted to be separated from the intermediate transfer member 5a.

  Next, the intermediate transfer member reference signal used for controlling the image forming operation will be described.

  As described with reference to FIG. 4, in the image formation on the intermediate transfer member 5a performed so that the fixed point PTA is at the tip, a sensor and a sensor (not shown) are provided on the intermediate transfer member 5a in order to match the formed images of the respective color toner images. And a detection flag. FIG. 5 shows the state of the photosensitive drum 1 and the intermediate transfer member 8a immediately after the start of latent image formation. The leading edge of the latent image overlaps the position corresponding to the leading edge of the sheet during A-side transfer. FIG. 5 shows the relationship between the latent image (laser) and the intermediate transfer member reference signal A. The intermediate transfer member reference signal A falls before Tprei time with respect to the latent image formation start timing. It has become. A similar signal is also prepared for the B-side transfer, and this is referred to as an intermediate transfer body reference signal B. These intermediate transfer member reference signals are generated when the intermediate transfer member 5a is rotating. Also, the photosensitive drum motor can be driven at a plurality of speeds so as to correspond to the fixing speed.

  Next, toner density control in the rotary developing device (toner image forming means) 4 will be described.

  As shown in FIG. 1, each toner in the magenta developing unit 4m, the cyan developing unit 4c, and the yellow developing unit 4y reflects near-infrared light having a wavelength of about 960 nm. Near-infrared light is irradiated to the toner image developed on the transfer body 5a. Then, the comparison between the reflection component on the intermediate transfer body 5a and the direct light from the irradiation light source is detected by the test patch density sensor 13, and converted by the A / D converter 752 (see FIG. 2) to detect the toner density. . From this detection result, the toner density in the developing device is calculated. For black, yellow, magenta, and cyan toners, toner corresponding to the toner density signal is supplied from a toner cartridge (not shown) to the developing devices 4k, 4y, 4m, and 4c.

  Next, the fixing device 9 will be described.

  As shown in FIG. 1, the fixing device 9 includes an upper fixing roller 9a, a lower fixing roller 9b, and a fixing web 9c. The toner on the sheet is melted by the heat energy of the fixing rollers 9a and 9b. The melted toner is fixed on the sheet by the pressure between 9a and 9b.

  An upper fixing heater 9e and a lower fixing heater 9f are incorporated in substantially the center of the upper fixing roller 9a and the lower fixing roller 9b, respectively. The surfaces of the upper fixing roller 9a and the lower fixing roller 9b are formed by an upper fixing heater 9e and a lower fixing heater 9f, and an upper fixing thermistor 781 and a lower fixing thermistor 782 (see FIG. 2). , Controlled to an optimal surface temperature.

  The fixing web 9c contacts the upper fixing roller 9a when necessary to remove dirt on the upper fixing roller 9a or offset toner. At that time, a winding device built in the fixing web 9c can improve the cleaning performance by bringing the new surface of the fixing web 9c into contact with the fixing upper roller 9a.

  The fixing device 9 includes a fixing drive motor (not shown) that drives the fixing rollers 9a and 9b and the sheet conveying unit 9g. The fixing drive motor is driven by a fixing drive motor driver 761 (see FIG. 2) (not shown).

  In the present embodiment, in order to eliminate the difference in fixability depending on the type of sheet, the fixing speed corresponding to four types of sheets can be realized. For example, if the peripheral speed at the time of image formation on the photosensitive drum 1 (hereinafter referred to as “process speed”) is VP, the plain paper fixing speed VFN = VP. The fixing speed VFD for the second side of both sides is smaller than VFN, the fixing speed for thick paper VFT is smaller than VFD, and the fixing speed for OHP VFO is smaller than VFT. Therefore, the relationship of VP = VFN> VFD> VFT> VFO is established, and the fixing drive motor driver 761 is configured to realize these four types of fixing speeds.

  The conveyance speed of the sheet conveyance unit 9g is set to be the same as the peripheral speed of the fixing rollers 9a and 9b. Also, the fixing speed VFD for double-sided and double-sided is used for double-sided and double-sided that fixes two or more colors of toner, and is not used in the single-color mode in which only one-color toner is fixed on both sides of the double-sided. The fixing operation is performed at the fixing speed VFN.

[Operation of Image Forming Apparatus]
Next, referring to FIG. 2, a control system of the image forming apparatus as an example of the embodiment of the present invention will be described.

  The control system of the image forming apparatus as an example of the embodiment of the present invention mainly includes a reader controller 700 that controls the reader unit 201 and the image processing unit 203, and a printer controller 701 that controls the printer unit 202.

  The reader controller 700 is connected with an optical motor driver 702, an RDF control unit 703, a CCD driver 704, a ROM 705, a ROM 706, and an I / O 707.

  The optical motor driver 702 drives an optical motor (not shown) that moves the scanning mirrors 32a, 32b, and 32c and the exposure lamp 32. The RDF control unit 703 controls the automatic document feeder 400 that automatically replaces documents. The CCD driver 704 controls the CCD sensor 34 for image reading. The ROM 705 stores a control program of the reader controller 700 and the RAM 706 stores data such as control values. The RAM 706 is battery-backed up with a battery so that data can be retained even when the power is turned off. The I / O 707 drives a load such as the exposure lamp 32.

  Connected to the printer controller 701 are a ROM 750, a RAM 751, an A / D 752, a D / A 753, an I / O 754, a sorter controller 708, and a laser driver 709.

  The ROM 750 stores a control program of the printer controller 701 and the like, and the RAM 751 stores data such as control values. The A / D 752 converts analog signals from the potential sensor 12, the test patch density sensor 13, the upper thermistor 781, the lower thermistor 782, the temperature sensor 783, the humidity sensor 784, and the like into digital data. The D / A 753 outputs the analog set value to the high voltage control unit 770 and the like. The I / O 754 drives loads such as a motor and a clutch. Connected to the I / O 754 are a rotary developing device rotation motor driver 760, a drum motor driver 762, a paper feed motor driver 763, a secondary transfer rotary attachment / detachment motor driver 764, an intermediate transfer member cleaner attachment / detachment driver 765, a fixing drive motor driver 761, and the like. Is done.

  The sorter controller 708 communicates with the printer controller 701 and responds to stacking control and stapling instructions in accordance with the stacking mode instructions in the non-sort mode, sort mode, and group mode set in the operation unit 710 (see FIG. 3). Perform stapling control.

  An image memory unit 204 and an external IF processing unit 720 are connected to the image processing unit 203 arranged between the printer controller 701 and the reader controller 700. The image memory unit 204 includes a page memory unit 730, a memory controller unit 732, a compression unit 733, and an HDD 734.

[Operation section]
Next, the operation unit 710 of the image forming apparatus which is an example of the embodiment of the present invention will be described with reference to FIG.

  The operation unit 710 is provided with a numeric keypad 351 used for setting the number of image formations and inputting a numerical value for mode setting, and a clear / stop key 352 used for stopping the set number of image formations and the image formation operation. . Further, the operation unit 710 is provided with a reset key 353, a start key 354, and a display panel 369 for returning a set mode such as the number of formed images, an operation mode, and a selected paper feed stage to a specified value.

  The image forming operation is started by pressing the start key 354. The display panel 369 is configured by a liquid crystal panel or the like, and the display content changes according to the setting mode in order to facilitate detailed mode setting. In the present embodiment, the cursor on the display panel 369 is moved with the cursor keys 366 to 368, and the setting is determined with the OK key 364. Such a setting method can also be configured by a touch panel.

  In addition, a paper type setting key 371, a duplex mode setting key 375, LEDs 370, and 372 to 374 are arranged on the operation unit 710.

  A paper type setting key 371 is pressed when an image is formed on a recording material thicker than the standard. When the thick paper mode is set by the paper type setting key 371, the LED 370 is controlled to be lit. In the present embodiment, only the thick paper mode can be set, but the function can be expanded so that the mode for OHP or other special paper can be set as necessary.

  The duplex mode setting key 375 can set four types of duplex modes. For example, “single-single mode” for single-sided output from a single-sided original, “single-both mode” for double-sided output from a single-sided original, “both-both mode” for double-sided output from a double-sided original, “Both-one mode” can be set.

  The LEDs 372 to 374 are lit according to the set duplex mode. For example, in the “single-single mode”, the LEDs 372 to 374 are all turned off, in the “single-both mode”, only the LED 372 is lit, in the “both-both mode”, only the LED 373 is lit, and in the “both-single mode”. Control is performed so that only the LED 374 is lit.

  Next, the four-color image forming operation on plain paper in which the thick paper mode is not set in the “one-one mode” in which the automatic document feeder 400 is not used will be described.

  In this case, since the sheet on which the image is formed is plain paper, the speed setting for the fixing drive motor driver 761 is set to be the same VFN as the image forming speed (process speed) VP of the photosensitive drum 1.

  First, the operator sets the number of images to be formed with the ten key 351, selects the paper feed stage with the paper selection key 303, and instructs the start of operation with the start key 354. Then, the printer controller 701 instructs a drive motor necessary for image formation, for example, each driver of a photosensitive drum drive motor, a fixing drive motor, a paper feed drive motor, and a main drive motor. Next, after the driving state of each drive motor is stabilized, the sheet feeding operation is started from the designated sheet feeding stage (cassettes 7a, 7b, etc.).

  Image formation on the intermediate transfer member 5a is performed by sending image data separated into each color from the image processing unit 203 to the printer unit 204 so as to match the reference signal of the intermediate transfer member 5a. The sheet fed from the designated paper feed stage is conveyed by the registration roller 50 at a timing that can correspond to the reference position on the intermediate transfer member 5a, and the image is transferred to a predetermined position on the secondary transfer charger 5c. .

  Next, the transfer timing of the toner image from the photosensitive drum 1 to the intermediate transfer member 5a will be described with reference to FIGS.

  FIG. 5 shows the positional relationship between the photosensitive drum 1 and the intermediate transfer member 5a at the start timing of latent image writing. An image corresponding to the sheet A is primarily transferred from a fixed point PTA on the intermediate transfer member 5a. It is a state of A side image formation of the 1 sheet sticking control. In this embodiment, since a full-color image is formed in the order of magenta, cyan, yellow, and black, for example, when the primary transfer of magenta is completed and writing of the latent image of cyan to the photosensitive drum 1 is started next. It is a state of. After the time LLT from the laser writing position to the transfer position has elapsed at the process speed VP, the cyan primary transfer operation is started.

[Intermediate transfer member reference signal and each image forming operation]
FIG. 6 is a timing chart of the state of FIG. 5 and shows the relationship between the intermediate transfer member reference signal, which is the basis of the timing control of the present embodiment, and each image forming operation.

  Settings are made for the image processing unit 203 so that a latent image can be formed after Tprei time from the fall of the intermediate transfer body reference signal A. The timing for the primary transfer operation executed after the distance LLT from the latent image start timing is also determined based on this signal.

  The document information sent from the reader unit 201 is processed by the image processing unit 203, and the photosensitive drum 1 uniformly charged by the primary charger 2 is irradiated with laser light to form a latent image. First, development is performed by the magenta developer 4m. The developed image information is transferred by the primary transfer charger 5b onto the intermediate transfer member 5a corresponding to the sheet. This M (magenta) latent image formation, development, and transfer image forming operations are executed while the photosensitive drum 1 and the intermediate transfer member 5a rotate once, and similarly, the remaining three colors C (cyan), Y (Yellow) and K (Black) are also executed. In addition, the setting for the image processing unit 203 at this time is performed for each image formation.

  As described above, the toner image on the intermediate transfer member 5a on which the four color images are primarily transferred is transferred to the sheet that has been conveyed by the registration roller 50 at a timing suitable for the secondary transfer in the secondary transfer charger 5c. Next transferred. At that time, a secondary transfer high voltage is applied between the intermediate transfer member 5a and the sheet by the secondary transfer charger 5c to form a secondary transfer current, whereby the toner image is secondarily transferred to the sheet.

  The recording material P passing through the secondary transfer charger 5c and carrying the toner image is conveyed to the fixing device 9 by the sheet conveying portion 9g driven at the same speed (VP) as the intermediate transfer member 5a, and the fixing speed VFN. = Fixed at VP and then discharged.

  Next, the fixing speed in the thick paper mode will be described.

  In order to fix the toner on the cardboard, more energy is required compared to the plain paper. Therefore, the fixing speed is slower than that of the plain paper and the energy per unit area / time is increased. Is secured. In this case, conventionally, the distance from the secondary transfer charger 5c to the contact position of the upper and lower fixing rollers 9a and 9b is made larger than the maximum image-capable size for thick paper. Then, while the peripheral speed of the intermediate transfer member 5a, which is the image forming speed (process speed) VP, is kept constant, the sheet is reduced to a fixing speed VF different from the speed of the intermediate transfer member 5a by the sheet conveying unit 9g. The sheet conveying unit 9g was used as a speed conversion area. Therefore, it is necessary to secure a sheet conveying portion 9g having a size corresponding to the maximum image-capable size of thick paper, and there is a disadvantage that the apparatus is enlarged.

  Therefore, in the present embodiment, the speed of the intermediate transfer member 5a can be varied in the same manner as the fixing speed, and when the fixing speed VF must be slower than the image forming speed VP, the intermediate transfer body 5a is intermediate after the final color transfer. The speed of the transfer body 5a is reduced to the fixing speed. Thereby, it is not necessary to secure a size as a speed conversion area in the sheet conveying unit 9g, and an increase in the size of the apparatus is avoided.

  Next, the special color (optional color) developing devices 4s1 and 4s2 will be described.

  In the present embodiment, the station provided in the rotary developing device 4 includes two-color spot color developing devices 4s1 in addition to the usual four-color (Y, M, C, K) developing devices 4y, 4m, 4c, and 4k. , 4s2. By using the developing units 4s1 and 4s2, it is possible to perform printing using spot colors in addition to normal full color development. In this development sequence, in addition to the above-described four-color image formation sequence, a toner image obtained by developing the latent image formed on the photosensitive drum 1 with the spot color developing devices 4s1 and 4s2 is superimposed on the rotating intermediate transfer member 5a. Later, secondary transfer is performed on the sheet.

  In this embodiment, a transparent toner developing station is provided in only one of the two spot color developing devices 4s1 and 4s2. The image formation with the transparent toner enables special processing such as glossing or coating on the image formed with four colors. The use of the special color development station in the present embodiment is not intended only for transparent toner. In addition, various toners other than YMCK, such as light color toner, orange, and gray toner, can be used.

  Next, with reference to FIG. 7, an operation example of the image forming apparatus which is an example of the embodiment of the present invention will be described.

  First, in step S1, the memory controller 732 (see FIG. 2) of the image memory unit 204 adds the density of the colored toner and the colorless toner to be imaged, and calculates the applied toner amount.

  Next, in step S2, it is determined whether or not the toner application amount calculated in step S1 exceeds a limit application amount that is a toner density that can be fixed together by the fixing device 9. If it is determined that the limit amount has been exceeded, the process proceeds to step S4, and if not, the process proceeds to step S3.

  Note that the limited application amount, which is the toner density that can be fixed together, is a value that is determined in advance for each fixing device.

  In step S3, assuming that the batch fixing by the fixing device 9 is impossible, a multiple transfer sequence is selected, and after the colored toner is fixed, control for transferring and fixing the transparent toner again is executed.

  On the other hand, in step S4, assuming that batch fixing by the fixing device 9 is possible, a batch fixing sequence is selected, color toner and transparent toner are transferred onto the sheet by secondary transfer, and then the fixing device 9 Execute the control to fix all at once.

  Next, with reference to FIG. 8 and FIG. 9, the image formation of the transparent toner image in the batch fixing sequence in step S4 will be described.

  First, the toner images of a plurality of colors developed on the photosensitive drum 1 are sequentially primary transferred onto the intermediate transfer member 5a. At this time, the transparent toner image is also transferred onto the intermediate transfer member 5a in the same manner as the plurality of colored toner images.

  After all the toner images have been primarily transferred onto the intermediate transfer member 5a, secondary transfer is performed by the secondary transfer charger 5c, for example, on the sheet conveyed from the paper feed cassette 7a. The sheet on which the toner images of a plurality of colors are secondarily transferred is conveyed by the sheet conveying unit 9g and reaches the fixing device 9, and the unfixed toner image is fixed on the sheet by the fixing device 9.

  In the case of image formation on only one side of the sheet that has passed through the fixing device 9, as shown in FIG. 8, the flapper 19 moves to the side for discharging the sheet to the outside of the apparatus, and the sheet on which the toner image is fixed is It is conveyed outside.

  In the case of a double-sided image forming sequence in which image formation is performed on both sides, as shown in FIG. 9, the flapper 19 moves to the side where the sheet is conveyed to the reversing path 21a via the conveying vertical path 20, and the toner image is fixed. After the sheet is conveyed to the reversing path 21a, the sheet is reversed and sent to the duplex path 22. The sheet conveyed through the double-sided path 22 is retransmitted to the secondary transfer charger 5c in order to transfer the toner image that has been primarily transferred to the intermediate transfer member 5a again, and the same processing as described above is repeated.

  Next, with reference to FIG. 10, the image formation of the transparent toner image in the multiple transfer sequence in step S3 will be described.

  First, only four colors of colored toner are developed on the photosensitive drum 1 and are primarily transferred onto the intermediate transfer member 5a. After all the colored toner images are primarily transferred onto the intermediate transfer member 5a, secondary transfer is performed by the secondary transfer charger 5c, for example, on the sheet conveyed from the paper feed cassette 7a. The sheet on which the color toner image is secondarily transferred is conveyed by the sheet conveying unit 9g and reaches the fixing device 9, and the fixing device 9 fixes the unfixed toner image on the sheet.

  The sheet that has passed through the fixing device 9 then passes through a multiple image forming path in order to transfer a transparent toner image onto the same surface. At that time, the flapper 19 moves to the side where the sheet is conveyed to the conveyance vertical path 20, and the flapper 26 moves to the side where the sheet is conveyed to the duplex path 22 without inverting the sheet. As a result, the sheet is conveyed again to the secondary transfer charger 5c. Meanwhile, the transparent toner image is developed on the photosensitive drum 1 and the other colored toners are not developed, and only the transparent toner image is primarily transferred onto the intermediate transfer member 5a.

  Then, the transparent toner image on the intermediate transfer member 5a is secondarily transferred onto the sheet re-fed to the position of the secondary transfer charger 5c without being inverted. Thereafter, if the single-sided image formation is performed, the flapper 19 moves to the side for discharging the sheet to the outside of the apparatus, and the sheet on which the transparent toner image is fixed by the fixing device 9 is discharged to the outside of the apparatus.

  In the case of double-sided image formation, the flapper 19 moves to the side where the sheet is conveyed to the reversing path 21a via the conveying vertical path 20, conveys the sheet on which the toner image has been fixed to the reversing path 21a, and then Inverted and sent to the duplex path 22. The sheet conveyed through the double-sided path 22 is retransmitted to the secondary transfer charger 5c in order to transfer the toner image primary-transferred to the intermediate transfer member 5a to the back side again, and the same processing as described above is repeated. .

  As described above, in this embodiment, when the toner application amount exceeds the limit application amount that is the toner concentration that can be fixed together by the fixing device 9, the fixing of the colored toner image and the fixing of the transparent toner image are performed. Are done separately.

  Thereby, a uniform transparent toner image can be easily formed on the colored toner image without changing the fixing conditions of the fixing device 9. Therefore, it is possible to provide an image forming apparatus with high added value without increasing the apparatus cost and without performing complicated loading amount control.

  Note that the configurations of the toner image forming unit, transfer unit, fixing unit, multiple transport unit, determination unit, and the like of the present invention are not limited to those exemplified in the above embodiment, and do not depart from the spirit of the present invention. In FIG.

1 is a schematic sectional view of an image forming apparatus as an example of an embodiment of the present invention. 1 is a control block diagram of an image forming apparatus as an example of an embodiment of the present invention. It is a figure which shows an example of an operation part. (A) is explanatory drawing for demonstrating 1 sheet sticking control, (b) is explanatory drawing for demonstrating 2 sheet sticking control. FIG. 6 is an explanatory diagram for describing transfer timing of a toner image from a photosensitive drum to an intermediate transfer member. FIG. 4 is a time chart for explaining the transfer timing of a toner image from a photosensitive drum to an intermediate transfer member. FIG. 6 is a flowchart for explaining an operation example of an image forming apparatus which is an example of an embodiment of the present invention. FIG. 6 is a diagram for explaining an example of normal sheet conveyance. FIG. 10 is a diagram for explaining an example of sheet conveyance in double-sided image formation. FIG. 10 is a diagram for explaining an example of sheet conveyance in multiple image formation.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Photosensitive drum 1hp Moving drum home position sensor 2 Primary charger 3 Laser exposure part 3a Polygon mirror 3b Lens 3c Mirror 4 Rotating developing device (toner image forming means)
4k Black developing unit 4m Magenta developing unit 4c Cyan developing unit 4y Yellow developing unit 4s1 Special color developing unit 4s2 Special color developing unit 5a Intermediate transfer member 5b Primary transfer charging unit 5c Secondary transfer charging unit (transfer means)
5hp intermediate transfer member home position sensor 6 intermediate transfer member cleaner 7 photosensitive drum cleaner 7a right cassette 7b first stage cassette 7c second stage cassette 7d left cassette 9 fixing device (fixing means)
9a Upper fixing roller 9b Lower fixing roller 9c Web 9e Upper fixing heater 9f Lower fixing heater 10 Non-contact ATR sensor 11 Pre-exposure LED
12 Potential sensor 13 Test patch density sensor 19 Flapper 20 Double-sided vertical path (multiple conveying means)
21a Inversion path 21b Inversion roller 22 Double-sided path (Multiple conveying means)
25 Secondary transfer roller cleaner 30 Document 31 Document table 32 Exposure lamp 33 Lens 34 CCD sensor 201 Reader unit 202 Printer unit 400 Automatic document feeder 700 Reader controller 701 Printer controller

Claims (2)

An intermediate transfer member for carrying and conveying a toner image;
First forming means for forming a colored toner image to be transferred to the intermediate transfer member;
Second forming means for forming a transparent toner image to be transferred to the intermediate transfer member;
Transfer means for transferring the toner image superimposed on the intermediate transfer member to a sheet;
Fixing means for fixing a toner image formed on a sheet, and an image forming apparatus comprising:
Detection means for detecting the combined amount of colored toner and transparent toner per unit area of the image to be formed on the sheet based on the input image information;
When an image is formed on a sheet using a transparent toner and a colored toner, a transparent toner image is formed on the lowermost layer on the intermediate transfer body when the detection result of the detection means is a predetermined amount or less, and the transparent toner A first mode in which colored toner is overlaid, and the transparent toner and colored toner superimposed on the intermediate transfer member are collectively transferred to a sheet by the transfer unit, and the sheet is fixed only once by the fixing unit. Run
When the detection result exceeds a predetermined amount, the colored toner image formed on the intermediate transfer member is transferred onto the sheet by the transfer unit, and then fixed by the fixing unit and formed on the intermediate transfer member. Control means for covering the colored toner image fixed on the sheet with the formed transparent toner and controlling to execute the second mode in which the transparent toner is fixed to the sheet again by the same fixing means. An image forming apparatus. When forming an image on a sheet using only colored toner, the control unit controls the colored toner transferred on the sheet to be heated only once by the fixing unit. Item 2. The image forming apparatus according to Item 1.

Images