JP2019095535A - Image forming device - Google Patents

Abstract

To provide an image forming device with which it is possible to satisfy fixation performance by setting within a fixation margin of a thermal dose and secure productivity as much as possible even when there is a large difference in toner quantity in the same page.SOLUTION: The image forming device comprises: an image formation unit for forming a toner-based image on a recording medium by an image signal of each pixel in the same page generated on the basis of image data; a fixation unit for fixing heating the recording medium carrying the toner-based image and fixing the toner-based image; and a control unit capable of executing a first mode in which a conveyance speed at which to convey the recording medium is set to a reference conveyance speed on the basis of a difference between a maximum toner amount and a minimum toner amount in each pixel within the same page and a thermal dose in the fixation unit is set to a first thermal dose higher than a reference thermal dose and a second mode in which the conveyance speed is set to slower than the reference conveyance speed and the thermal dose in the fixation unit is set to a second thermal dose lower than the first thermal dose.SELECTED DRAWING: Figure 9

Description

  The present invention relates to an image forming apparatus, and is suitable for an electrophotographic copying machine, an electrophotographic printer, and the like.

  Conventionally, in an image forming apparatus using an electrophotographic process, a toner image formed on a photosensitive member in an image forming unit is transferred onto a recording material and then passes through a fixing device (fixing unit) as an image heating device. As a result, the toner image is fixed (fixed) on the recording material.

  As a fixing device, a contact type heat fixing device is widely used in which an unfixed toner image formed on a recording material is heated by a heating member to a predetermined fixing temperature, and contact heating is performed to fix as a fixed image. It is used.

  In such a fixing device, a proposal has been made to control the fixing temperature (fixing temperature adjustment temperature, temperature adjustment temperature) of the fixing member based on the image information (toner amount etc.) of the image data as means for optimizing the fixing property (Patent Documents 1 and 2).

  Specifically, when the image data is expressed by arranging dots for each color in Patent Document 1, the number of locations where dots of a plurality of colors overlap is counted, and fixing is performed according to increase or decrease of the coefficient number. It is disclosed to increase or decrease the temperature. Further, in Patent Document 2, it is disclosed that weighting is performed on overlapping of pixels in image data of a plurality of color components, an amount of image data is integrated, and a fixing temperature is set according to the integrated image data amount. There is.

JP, 2006-154413, A JP, 2009-92688, A

  In Patent Document 1 and Patent Document 2, it is necessary to set the fixing temperature adjustment temperature (temperature adjustment temperature) to a fixing temperature range (fixing margin) in which both cold offset and hot offset are not generated. Here, cold offset is an image defect that occurs due to a lack of heat for fixing the toner on the recording material, and a hot offset is reversely due to excessive heat being supplied and the toner being melted too much in the recording material This is an image defect in which toner adheres to the fixing member.

  Here, in Patent Document 1 and Patent Document 2, there is a problem that the fixing margin shown below which is not solved can be narrowed. That is, in recent years, the above-mentioned fixable temperature range (fixing margin) is narrowed due to the increase of the process speed of the image forming apparatus. This is because when the process speed is high, the time for which the recording material passes through the fixing nip is short, heating at a high temperature is necessary to firmly dissolve the toner lower layer, the temperature gradient in the toner layer becomes large, and the toner in the upper layer Is melted too much and hot offset is likely to occur.

  Furthermore, in order to realize a wide color gamut, a method of increasing the amount of toner on the recording material has been taken, and it has become difficult to set the fixing temperature adjustment temperature within the fixing margin. For example, assuming that the maximum toner amount of the toner single color is 100%, when the area of 300% of toner amount and the area of 30% of toner amount are mixed in the image, the fixing temperature control is adjusted to the area of 300% toner amount. When the temperature is set, hot offset may occur in the area of 30% toner amount. Conversely, when the fixing temperature is set in accordance with the area of the 30% toner amount, cold offset may occur in the 300% toner amount portion.

  An object of the present invention is to provide an image forming apparatus capable of satisfying the fixing performance and setting the productivity as much as possible by setting within the fixing margin of the heating amount even when the difference of the toner amount in the same page is large. .

  In order to achieve the above object, an image forming apparatus according to the present invention comprises: an image forming unit for forming an image with toner on a recording material by an image signal of each pixel in the same page generated based on image data; A fixing unit that heats the recording material carrying an image by the toner to fix the image by the toner, and a difference between a maximum toner amount and a minimum toner amount in each pixel in the same page A first mode in which the conveyance speed for conveying the recording material is a reference conveyance speed, and the heating amount in the fixing unit is a first heating amount higher than the reference heating amount; and the conveyance speed is higher than the reference conveyance speed. And a control unit capable of executing a second mode in which the heating amount in the fixing unit is set to a second heating amount lower than the first heating amount.

  According to the present invention, even in the case where the difference in the toner amount in the same page is large, the fixing performance can be satisfied and the productivity can be secured as much as possible by the setting within the fixing margin of the heating amount.

1 is a cross-sectional view showing a schematic configuration of an image forming apparatus provided with a fixing device according to an embodiment of the present invention Sectional view showing the configuration of a fixing device according to an embodiment of the present invention Longitudinal perspective view of a fixing device according to an embodiment of the present invention An explanatory diagram of a video controller according to an embodiment of the present invention Explanatory drawing of the image data processing flow which concerns on 1st Embodiment A graph showing a relationship between an image toner amount and a fixing temperature adjustment temperature at which a fixing margin can be obtained according to the first embodiment A graph showing the relationship between the image toner amount and the fixing temperature adjustment temperature at which the fixing margin can be obtained when the process speed of the image forming apparatus according to the first embodiment is reduced. Graph showing change of fixing margin with process speed of the image forming apparatus according to the first embodiment Explanatory view of print mode and temperature adjustment temperature determination flow according to the first embodiment Image pattern used in the effect confirmation experiment according to the first embodiment Explanatory view of print mode and temperature adjustment temperature determination flow of a comparative example according to the first embodiment Explanatory drawing of the process speed and temperature control temperature determination flow which concern on 2nd Embodiment Explanatory view of print mode and temperature adjustment temperature determination flow according to the third embodiment Image pattern used in the effect confirmation experiment according to the third embodiment

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the attached drawings.

First Embodiment
(Image forming device)
FIG. 1 shows an image forming apparatus P according to an embodiment of the present invention, which includes four image forming stations 3Y, 3M, 3C, 3K arranged substantially in a straight line. Of the four image forming stations 3Y, 3M, 3C, and 3K, 3Y is an image forming station for forming a yellow (hereinafter abbreviated as Y) image as an image forming unit formed of toners of a plurality of colors. An image forming station 3M forms an image of magenta (hereinafter abbreviated as M) color. 3C is an image forming station for forming an image of cyan (hereinafter abbreviated as C) color. 3K is an image forming station for forming an image of black (hereinafter abbreviated as K) color.

  The image forming stations 3Y, 3M, 3C and 3K are drum-shaped electrophotographic photosensitive members (photosensitive drums) 4Y, 4M, 4C and 4K as image bearing members, and charging rollers 5Y, 5M and 5C as charging units. , 5K. Each of the image forming stations 3Y, 3M, 3C, 3K includes an exposure unit 6 as an exposure unit, a developing unit 7Y, 7M, 7C, 7K as a developing unit, and a cleaning unit 8Y, 8M, 8C as a cleaning unit. , 8K.

  When the video controller (printer controller) 30 receives the image information from the external device (the external device 1052 shown in FIG. 1B) such as a host computer, it sends a print signal to the control means 31 and starts the image forming operation. . At the time of image formation, in the image forming station 3Y, the photosensitive drum 4Y is rotated in the direction of the arrow in accordance with a print command by a rotation control unit (drive control means) (not shown).

  First, the outer peripheral surface (surface) of the photosensitive drum 4Y is uniformly charged by the charging roller 5Y, and the charged surface of the photosensitive drum 4Y is exposed by irradiating the laser beam according to the image data by the exposure device 6 And an electrostatic latent image is formed. The latent image is developed into a Y toner image by the developing device 7 Y using Y toner. Thus, a Y toner image is formed on the surface of the photosensitive drum 4Y. The same image forming process is performed in the image forming stations 3M, 3C and 3K.

  Thereby, an M toner image is formed on the surface of the photosensitive drum 4M in the image forming portion, a C toner image is formed on the surface of the photosensitive drum 4C, and a K toner image is formed on the surface of the photosensitive drum 4K.

  Here, the following is generically called process speed regarding the said image formation process. That is, the rotational speed of the photosensitive drum, the moving speed of the intermediate transfer belt described later, the rotational speeds of the first and second fixing members forming the nip portion in the fixing unit, Transport speed of the recording material, etc.

  An endless intermediate transfer belt 9 provided along the arrangement direction of the image forming stations 3Y, 3M, 3C, 3K is stretched around a drive roller 9a, a driven roller 9b and a driven roller 9c. The drive roller 9a is rotated in the direction of the arrow in FIG. 1 in accordance with a print command by a rotation control unit (drive control means) (not shown). Thus, the intermediate transfer belt 9 is rotationally moved at a speed of 100 mm / sec along the image forming stations 3Y, 3M, 3C, 3K.

  Each color is formed on the outer peripheral surface (surface) of the intermediate transfer belt 9 by primary transfer means 10Y, 10M, 10C, 10K opposed to the photosensitive drums 4Y, 4M, 4C, 4K with the intermediate transfer belt 9 interposed therebetween. The toner images of are sequentially transferred in an overlapping manner. As a result, a full color toner image of four colors is formed on the surface of the intermediate transfer belt 9.

  The transfer residual toner remaining on the surfaces of the photosensitive drums 4Y, 4M, 4C, 4K after the primary transfer is removed by a cleaning blade (not shown) provided in the cleaning devices 8Y, 8M, 8C, 8K. Thus, the photosensitive drums 4Y, 4M, 4C, and 4K prepare for the next image formation.

  On the other hand, the recording material S stacked and stored in the feeding cassette 11 provided at the lower part of the image forming apparatus P is separated and fed one by one from the feeding cassette 11 by the feeding roller 12 and supplied to the registration roller pair 13. Will be sent. The registration roller pair 13 feeds the fed recording material S to a transfer nip portion between the intermediate transfer belt 9 and the secondary transfer roller 14. The secondary transfer roller 14 is disposed to face the driven roller 9 b with the intermediate transfer belt 9 interposed therebetween. A bias is applied to the secondary transfer roller 14 from a high voltage power supply (not shown) when the recording material S passes through the transfer nip portion.

  Thus, a full-color toner image is secondarily transferred from the surface of the intermediate transfer belt 9 to the recording material S passing through the transfer nip portion. The recording material S carrying the toner is conveyed to the fixing device F. The recording material S is heated and pressurized by passing through the fixing device F, and the toner image is heat-fixed (fixed) on the recording material S. Then, the recording material S is discharged to the discharge tray 15 outside the image forming apparatus (printer) P via the fixing device (fixing unit) F. The transfer residual toner remaining on the surface of the intermediate transfer belt 9 after the secondary transfer is removed by the intermediate transfer belt cleaning device 16. Thus, the intermediate transfer belt 9 prepares for the next image formation.

  Further, the image forming apparatus is configured as shown in FIG. That is, in FIG. 1B, color signals of R (red), G (green), and B (blue) are input to the color image forming apparatus 1060 from an external device 1052 such as a personal computer. These color signals which are code data are converted into image signals (dot data, image data) of C (cyan), M (magenta), Y (yellow) and B (black) by a printer controller 1053 in the apparatus. Be done. These image data are input to the optical scanning devices 1061, 1062, 1063 and 1064, respectively.

  Then, light beams 1041, 1042, 1043, and 1044 modulated according to the respective image data are emitted from these light scanning devices (details will be described later). Then, the photosensitive surfaces of the photosensitive drums 1071, 1072, 1073, and 1074 are scanned in the main scanning direction by these light beams. The color image forming apparatus according to the present embodiment includes four light scanning devices (1061, 1062, 1063, and 1064) arranged in parallel, each of C (cyan), M (magenta), Y (yellow), and B (black). It corresponds to each color of).

  As the external device 1052, for example, a color image reader provided with a CCD sensor may be used. In this case, the color image reading apparatus and the color image forming apparatus 1060 constitute a color digital copying machine.

(Fixing device (fixing unit))
Next, the fixing device (fixing unit) F as a fixing unit of the toner image will be described. In the following description, regarding the fixing device and members constituting the fixing device, the longitudinal direction is a direction orthogonal to the recording material conveyance direction on the surface of the recording material. The short direction is a direction parallel to the recording material conveyance direction on the surface of the recording material. Also, the width is a dimension in the short side direction. With respect to the recording material, the longitudinal width is a dimension in a direction perpendicular to the recording material conveyance direction on the surface of the recording material.

  FIG. 2 is a cross-sectional view of a fixing device F in which a nip portion is formed by the fixing film 22 as a first fixing member and the pressure roller (pressurizing member) 21 as a second fixing member, which face each other and are pressure-welded. It is. The fixing device F rotationally drives the pressure roller 21 according to a print command by a rotation control unit (drive control means) (not shown), and rotates the fixing film 22 by the conveying force of the pressure roller 21. It is a so-called tensionless type device of so-called film heating type and pressure roller driving type.

  The fixing device F shown in the present embodiment includes a pressure roller (pressure rotary member) 21, a fixing film (fixing rotary member) 22, a heater (heating member) 23, and a heater holder (heating member holding member) 24. It has a rigid stay (rigid member) 25 and the like. The pressure roller 21, the fixing film 22, the heater 23, the heater holder 24 and the rigid stay 25 are all elongated members in the longitudinal direction.

  The heater 23 has a substrate 231 made of a ceramic which is elongated in the longitudinal direction and has heat resistance, insulation, and good thermal conductivity. Then, a resistance heating element (not shown) is formed along the longitudinal direction of the substrate at the center in the short direction of the front side (pressure roller 21 side) of the substrate 231. Inside the both ends in the longitudinal direction of the substrate 231, a feed electrode (not shown) for feeding the resistance heating element is provided. Then, a heat resistant overcoat layer 232 is provided on the surface side of the substrate 231 so as to cover the surface of the resistance heating element (not shown).

  FIG. 3 is a longitudinal perspective view of the fixing device F. As shown in FIG. The heater holder 24 is formed of a liquid crystal polymer having heat resistance and rigidity in a substantially semicircular wedge shape in cross section. The heater holder 24 has a groove formed along the longitudinal direction at the center in the width direction of the lower surface, and the substrate 231 of the heater 23 is fixedly held by the groove to expose the overcoat layer 232 from the groove.

   The fixing film 22 is formed in a cylindrical shape from a flexible heat-resistant resin material. The outer peripheral length of the fixing film 22 is 57 mm. The fixing film 22 has a polyimide layer having a thickness of 50 microns as a cylindrical base layer 221, and has an elastic layer 222 formed of silicone rubber having a thickness of 200 microns on the outer periphery of the base layer 221. Then, on the outer periphery of the elastic layer 222, there is provided a release layer 223 of fluorine resin having a thickness of 15 microns.

  The inner peripheral length of the fixing film 22 is 3 mm larger than the outer peripheral length of the heater holder 24 holding the heater 23. The fixing film 22 is loosely fitted around the heater holder 24 holding the heater 23 with a sufficient circumferential length. That is, the fixing film 22 contains the heater 23.

  The rigid stay 25 is formed of a U-shaped rigid member whose cross section is downward. The rigid stay 25 is disposed at the center of the upper surface of the heater holder 24 in the short direction.

  The pressure roller 21 has a round shaft core metal 211, an elastic layer 212 made of silicone rubber concentrically integrally formed with the core metal 211 on the outer periphery of the core metal 211, and conductive around the elastic layer 212. And a release layer 213 formed of a fluorocarbon resin. The outer peripheral length of the pressure roller 21 is 63 mm. The elastic layer 212 may be formed by foaming heat-resistant rubber such as fluororubber or silicone rubber. The release layer 213 may be an insulating fluorine resin.

  The pressure roller 21 is disposed in parallel with the fixing film 22 below the fixing film 22 and rotatably holds both longitudinal end portions of the cored bar 211 via a bearing member. The core metal 211 of the pressure roller 21 and the rigid stay 25 contact the outer peripheral surface (surface) of the pressure roller 21 and the outer peripheral surface (surface) of the fixing film 22 by pressure springs (not shown) at both ends in the longitudinal direction. It is pressurized to do. The surface of the pressure roller 21 and the surface of the fixing film 22 are brought into contact with each other by the pressure (total pressure 20 kgf), and a nip portion NF of a predetermined width is formed between the surface of the pressure roller 21 and the surface of the fixing film 22.

  The CPU 306 (FIG. 4), which also functions as a rotation control unit (drive control means), can control the drive speed, and the pressure roller 21 has a predetermined peripheral speed (see FIG. 2) according to the print command. Rotate in the direction of the arrow at process speed). At this time, a rotational force acts on the fixing film 22 by the frictional force between the surface of the pressure roller 21 and the surface of the fixing film 22 in the nip portion NF.

  Therefore, the fixing film 22 is driven to rotate the outer periphery of the heater holder 24 in the direction of the arrow while the inner peripheral surface of the fixing film 22 slides in close contact with the heater 23 by the rotational force. At that time, the rotation of the fixing film 22 is guided by the outer peripheral surface of the heater holder 24 formed along the inner peripheral shape of the fixing film 22. Thereby, the rotation of the fixing film 22 is stabilized, and the fixing film 22 rotates while drawing the same rotation locus.

  Further, a CPU 306 (FIG. 4), which also functions as an energization control unit, energizes a resistance heating element (not shown) of the heater 23 according to a print command. The heater 23 heats up the fixing film 22 by the energization.

  The temperature of the heater 23 is detected by a temperature detection element 26 such as a thermistor provided on the back side of the substrate 231 of the heater 23. The energization control unit described above controls energization of a resistance heating element (not shown) so that the heater 23 maintains a predetermined regulated temperature based on the output signal of the temperature detection element 26. As a result, the nip portion NF is maintained at a predetermined temperature control temperature.

(Video controller 30)
The video controller 30 shown in FIG. 4 corresponds to the printer controller 1053 of FIG. 1B. The video controller 30 is an image processing unit (image processing unit) that functions as an image signal generation unit that generates an image signal of each pixel in the same page based on the received image data.

  The video controller 30 includes a host computer interface unit (I / F unit) 302 and an image forming apparatus interface unit (I / F unit) 303 which are mutually connected via a CPU bus 301. The video controller 30 also includes devices such as the ROM 304, the RAM 305, and the CPU 306. The CPU bus 301 includes an address, data and control bus.

  The host interface unit 302 has a function of bidirectionally connecting to a data transmission apparatus such as a host computer via a network. The image forming apparatus interface unit 303 has a function of performing bidirectional communication connection with the image forming apparatus P. The ROM 304 holds control program code for executing image data processing described later by the CPU 306 and other processing.

  A random access memory (RAM) 305 is a memory for holding bitmap data and image information as a result of rendering of the image data received by the image forming apparatus interface unit 303, and holding a temporary buffer area and various processing statuses. The CPU 306 controls each device connected to the CPU bus 301 based on the control program code stored in the ROM 304.

(Image data processing and detection of image density information)
Here, image data processing in the video controller 30 will be described. FIG. 5 shows an image data processing flow. From the host computer, commands such as paper size and operation mode are sent together with the image data as image information (processing S10). When the image data relates to a color image, it is in the form of color information by RGB (red, green, blue) data, and each color information is allocated to device RGB data that can be reproduced by this apparatus and converted. Is performed (processing S11).

  Subsequently, color information of the image data is converted from device RGB data to device YMCK (yellow, magenta, cyan, black) data (hereinafter, YMCK data) (processing S12).

  This YMCK data as an image signal of a pixel formed of toner represents the ratio of the toner amount to the toner amount obtained on the transfer material (recording material) when the laser of each color image forming station is fully lit. It is defined and has a range of 0% to 100%. A data value of 0% means that the laser is completely turned off and the toner amount is zero.

  Then, with respect to YMCK data, the exposure amount of each YMCK color is calculated using a gradation table indicating the relationship between the exposure amount of each color and the amount of toner actually used.

  Here, the amount of image toner in each pixel is calculated (calculated) as a total value, with the data of yellow, magenta, cyan and black in each pixel being up to 100% respectively. For example, when YMCK data as an image signal at a certain pixel is Y = 50%, M = 70%, C = 20%, K = 0%, the image toner amount is 140% (= 50 + 70 + 20 + 0) .

  Thereafter, for each pixel, the exposure amount of each color is converted into an exposure pattern to be actually used (processing S14), and an exposure output is obtained (processing S15).

  Here, in the image forming apparatus P of the present embodiment, in the normal mode, the full color upper limit toner amount that can be set to a different value is set to 200%. As the amount of toner on the recording material S increases, a large amount of heat (heating amount) for fixing is required. Therefore, in the normal mode, energy saving is achieved by generally setting the full color upper limit toner amount as the toner amount capable of expressing a sufficient color gamut. Then, in the image forming apparatus P of the present embodiment, the full color upper limit toner amount can be set to 300% by selecting the high definition mode in which the color gamut is further expanded.

  Further, in the present embodiment, the image toner amount information calculated from the above-described YMCK data is stored in the RAM 305. That is, among the pixels in the same page of the recording material S, the maximum toner amount Dmax, the minimum toner amount Dmin excluding the pixel of the non-exposed data value 0%, and the maximum toner amount and the minimum toner amount. The difference ΔD = Dmax−Dmin is stored in the RAM 305.

  Then, based on the image toner amount information stored in the RAM 305, the CPU 306 (FIG. 4) controls the conveyance speed (process speed) of the recording material to be described later and the heating amount of the fixing unit. That is, the CPU 306 functions as a control unit that controls the conveyance speed (process speed) of the recording material, and a heating amount control unit that controls the heating amount of the toner image by the fixing unit.

  Here, in the present embodiment, the value of ΔD is minimized by excluding the pixels of the non-exposed data value 0% from the determination targets of the minimum toner amount Dmin, and the target image to be switched to the process speed reduction mode is reduced. , Has achieved the maximization of productivity.

(Image toner amount information and toner amount on the recording material S)
Here, the relationship between the image toner amount information and the toner amount on the recording material S will be described. The image toner amount information is difference information between the toner amount information of the pixel which is the maximum exposure amount in the image information acquisition area and the toner amount information of the pixel which is the minimum exposure amount excluding the pixel of 0% exposure amount.
The image toner amount information has a correlation with the actual toner amount per unit area on the recording material S, and the toner amount per unit area on the recording material S is 0.45 to 5 when the image toner amount is 100%. It is 0.50 mg / cm ² . The toner amount per unit area on the recording material S when the image toner amount is 200% is 0.90 to 1.00 mg / cm ² .

  There are mainly two reasons why the toner amount on the recording material S has a certain width. The first reason is that not all toner on the photosensitive drum can be transferred from the photosensitive drum to the intermediate transfer belt 9 at the time of primary transfer. The second reason is that not all toner on the intermediate transfer belt 9 can be transferred onto the recording material S from the intermediate transfer belt 9 during secondary transfer.

(The amount of toner on the recording material S and the optimum temperature control temperature range)
Next, the relationship between the amount of toner on the recording material S and the controlled temperature (fixing temperature) of the heater 23 of the fixing device F will be described with reference to FIGS. Hot offset occurs when an excessive amount of heat (heating amount) is given to a predetermined amount of toner on the recording material S, and fixing failure (cold offset) occurs when only an extremely small amount of heat is given. Do. Therefore, it is necessary to set the temperature control temperature in a temperature range (fixing margin) in which fixing failure (cold offset) does not occur and hot offset does not occur depending on the amount of toner on the recording material S.

  The fixing margin can be determined by changing the image toner amount of the unfixed image t on the recording material S and the temperature adjustment temperature as shown in FIGS. 6 and 7 and confirming the fixing condition of the toner. The fixing margin is different depending on the configuration and the process speed (FIG. 8), and the experiments 1 and 2 shown below were conducted to confirm the fixing margin.

(Experiment 1)
By using the image forming apparatus P and the fixing device F in the present embodiment, the amount of image toner on the recording material S was changed to confirm the fixing margin. The process speed in the normal print mode of the image forming apparatus P is 100 mm / s, and it has a deceleration mode of 50 mm / s as another mode. Further, as a recording material S, a general LBP printing paper, a basis weight of 80 g / m ² , and an LTR (width 216 mm vertical 279 mm) size paper were used.

  FIG. 6 shows the relationship between the amount of image toner on the recording material S and the regulated temperature of the heater 23 in the present embodiment. In FIG. 6, a circle plot and a solid line indicate the lowest temperature control temperature at which fixing failure does not occur, and an angle plot and the broken line indicate the highest temperature temperature at which hot offset does not occur. That is, the area between the solid line and the broken line is the fixing margin in which the fixing failure does not occur.

  From FIG. 6, the fixing margin corresponding to the amount of toner per unit area on the recording material S can be seen. For example, when the toner amount per unit area on the recording material S is 0.25 mg / cm 2 (toner amount information D = 50%), the fixing margin is a range from 193 ° C. to 216 ° C. at 23 ° C. On the other hand, when the toner amount is 1.0 mg / cm 2 (toner amount information D = 200%), the fixing margin is a range from 206 ° C. to 230 ° C. at 24 ° C.

  Here, when the settable full-color upper limit toner amount of the image forming apparatus P is 1.0 mg / cm 2 (in the area on the left side of the position of 1.0 on the horizontal axis), the temperature control temperature of the heater 23 is 206 ° C. By setting the temperature to 216 ° C., the toner can be contained within the fixing margin regardless of the toner amount.

  However, when the full-color upper limit toner amount of the image forming apparatus exceeds 1.0 mg / cm 2, for example, 1.5 mg / cm 2 (toner amount information D = 300%) (horizontal axis is to the left of position 1.5) In the range of 219 ° C. to 243 ° C. is the fixing margin. Therefore, the regulated temperature of the heater 23 must be set at least 219 ° C. In this case, when the toner amount of 1.5 mg / cm 2 and the toner amount of 0.25 mg / cm 2 exist on the same recording material S, hot offset occurs at the position of the toner amount of 0.25 mg / cm 2 .

(Experiment 2)
On the other hand, in the deceleration mode set to 50 mm / s which is half of the process speed of the image forming apparatus P set in Experiment 1, the amount of image toner on the recording material S was changed to confirm the optimum temperature control temperature. In FIG. 7, the fixing margin corresponding to the amount of toner per unit area on the recording material S can be seen. For example, when the toner amount is 0.25 mg / cm 2, the fixing margin is the range of 163 ° C. to 191 ° C. at 28 ° C. On the other hand, when the toner amount is 1.5 mg / cm 2, the fixing margin is a range of 184 ° C. to 214 ° C. for 30 ° C., and the temperature adjustment temperature of the heater 23 may be set between 184 ° C. to 191 ° C.

  Therefore, even if the toner amount of 1.5 mg / cm 2 and the toner amount of 0.25 mg / cm 2 exist on the same recording material S, fixing failure and hot offset do not occur. In this experiment, since the process speed is reduced, the time for the recording material S to pass through the fixing nip portion NF becomes long, and the fixing margin becomes wider than in the case of Experiment 1.

  The reason is considered as follows. That is, when the process speed is low, it takes a long time for the recording material S to pass through the fixing nip NF. Therefore, heating at a low temperature is sufficient to melt the lower layer of the toner firmly, the temperature gradient in the toner layer becomes small, and the occurrence of hot offset due to excessive melting of the toner in the upper layer is suppressed. This widens the fixing margin.

  FIG. 8 is a graph comparing the relationship between the difference ΔD between the maximum toner amount and the minimum toner amount and the fixing margin at process speeds of 100 mm / sec and 50 mm / sec. It can be seen that as the process speed decreases, the fixing margin is broadened. In this regard, when the process speed is high, the time for the recording material S to pass through the fixing nip NF is short. Therefore, it is necessary to heat at a high temperature in order to melt firmly to the toner lower layer, the temperature gradient in the toner layer becomes large, and the toner in the upper layer melts too much and hot offset tends to occur. This tends to narrow the fixing margin.

(Flow of Fixing Mode Setting of This Embodiment)
In the image forming apparatus and the fixing device F of this embodiment, the toner amount information in the same page is acquired (detected and calculated) by the image processing unit. Then, among the obtained toner amount information, the process speed of the image forming apparatus P using difference information between the maximum toner amount and the minimum toner amount and the maximum toner amount excluding the pixel of the data value 0% which is not exposed And the regulated temperature of the heater 23 of the fixing device F.

  The temperature adjustment temperature determination flow in each print mode (general mode, high definition mode) of the present embodiment will be described with reference to the flowchart of FIG. When the image forming apparatus receives a print signal from the host computer (S20), the CPU acquires the pre-printing temperature information of the fixing device from the temperature detection element 26 of the fixing device F. Next, commands such as paper size and operation mode are received from the host computer, and a reference temperature control temperature is determined from the paper size, operation mode, pre-print temperature information, previous print history, etc. (S21).

  This is a temperature control temperature optimum for fixing an image of a standard toner amount, and the temperature control temperature is changed based on the image toner amount information based on the reference temperature control temperature. The reference regulated temperature in the present embodiment is 206.degree.

  Next, it is determined whether the high definition mode is selected by the user (S22), and if it is not selected (if the general mode is selected), the reference temperature adjustment temperature is set to the temperature adjustment temperature of the heater 23 To do (S23).

  If the video controller 30 receives image information from the host computer and the high definition mode is selected, then the following is performed. That is, the information of the maximum toner amount Dmax in each pixel of the image information acquisition area, the minimum toner amount Dmin excluding the pixel of the data value 0% which is not exposed, and the difference ΔD is acquired (S24).

  Next, it is determined whether the maximum toner amount Dmax is larger than 200%, which is the threshold value for the maximum toner amount (S25). If it is determined that the temperature is 200% or less (below the threshold), the temperature adjustment temperature of the heater 23 is set to the reference temperature adjustment temperature determined in S21 (S23). If it is determined that the maximum toner amount Dmax is larger than 200%, then it is determined whether the difference ΔD is larger than 200%, which is the threshold value of the difference (S26).

  If the difference ΔD is determined to be 200% or less, the CPU 306 (FIG. 4) raises the temperature control temperature of the heater 23 by 15 ° C. to the reference temperature control temperature without switching to the deceleration mode as the first mode. The temperature is set (S27). The reason for setting a temperature higher than the reference temperature adjustment temperature as the temperature adjustment temperature of the heater 23 is based on the premise that the maximum toner amount Dmax is larger than 200% which is the threshold value for the maximum toner amount, and a heating amount higher than the reference heating amount is required. It is because.

  The reason for maintaining the conveyance speed of the recording material at the reference conveyance speed (do not switch to the deceleration mode) is to satisfy the fixing performance (do not generate both cold offset and hot offset) without expanding the fixing margin. It is because it is possible. Thereby, image formation can be performed without reducing the productivity.

  On the other hand, when it is determined that the difference ΔD is larger than 200%, the CPU 306 (FIG. 4) performs the following control as the second mode. That is, the process mode of the image forming apparatus P is switched to the decelerating mode in which the process speed of the image forming apparatus P is 1⁄2 of the normal mode, and the temperature adjusted temperature of the heater 23 is set to a temperature lowered 20 ° C.

  The reason for setting the conveyance speed of the recording material slower than the reference conveyance speed (switching to the decelerating mode) is that the fixing performance needs to be satisfied by widening the fixing margin. The reason for setting a temperature lower than the reference temperature as the temperature adjustment temperature of the heater 23 is that the heating amount per unit time is increased by making the conveyance speed of the recording material slower than the reference conveyance speed. It is because it can be lowered.

(Effect confirmation)
In Experiment 3 shown below, the presence / absence of an image defect occurrence and the output time at the time of printing were confirmed in the present embodiment and the comparative example.

(Experiment 3)
The process speed in the normal print mode of the image forming apparatus P is 100 mm / s, and the mode also has a mode of 50 mm / s reduced as another mode. As a recording material S, a general LBP printing paper, a basis weight of 80 g / m ² , and an LTR (width 216 mm vertical 279 mm) size paper were used.

  Images to be printed are the two types of images (a) and (b) shown in FIGS. 10 (a) and 10 (b). The toner amount information is Dmax = 300%, Dmin = 300%, ΔD = 0% in the image (a), Dmax = 300%, Dmin = 50%, ΔD = 250% in the image (b). These images were continuously printed 10 sheets in a high definition mode using an image forming apparatus P.

  In Comparative Example 1, the fixing mode is set according to only the maximum toner amount Dmax without using the toner amount difference ΔD information, the process speed of the image forming apparatus P is not changed, and only the temperature adjustment temperature change of the heater 23 is performed. Do. Also in the comparative example 2, similarly, the fixing mode is set according to only the maximum toner amount Dmax without using the toner amount difference ΔD information, the process speed of the image forming apparatus P is changed, and the temperature control temperature of the heater 23 is changed. Do.

  The fixing mode determination flow of Comparative Example 1 will be described with reference to the flowchart of FIG. The basic flow (S30 to S34) for selecting the high definition mode and acquiring the toner amount information of the image is the same as that of the present embodiment. It is determined whether the obtained maximum toner amount Dmax is larger than 200% (S35), and if it is determined that the maximum toner amount Dmax is 200% or less, the reference temperature adjustment temperature determined in S31 is set as the temperature adjustment temperature of the heater 23 (S33) ). If it is determined that the maximum toner amount Dmax is larger than 200%, a temperature which is 15 ° C. higher than the reference temperature adjustment temperature is set as the temperature adjustment temperature of the heater 23 (S36).

  Next, the fixing mode determination flow of Comparative Example 2 will be described with reference to the flowchart of FIG. The basic flow (S40 to S44) for selecting the high definition mode and acquiring toner amount information of the image is the same as that of the present embodiment. It is determined whether the obtained maximum toner amount Dmax is larger than 200% (S45). If it is determined that the maximum toner amount Dmax is 200% or less, the reference temperature adjustment temperature determined in S41 is set as the temperature adjustment temperature of the heater 23 (S43) ).

  If it is determined that the maximum toner amount Dmax is larger than 200%, the process speed of the image forming apparatus P is set to a deceleration mode of half speed, and the temperature control temperature of the heater 23 is lower than the reference temperature control temperature. A temperature lowered by 20 ° C. is set (S46).

  The experimental results of the present embodiment, Comparative Example 1 and Comparative Example 2 are shown in Table 1.

  In the print of the image (a) shown in FIG. 10 (a), no image failure occurred even in Comparative Example 1 and Comparative Example 2. However, in Comparative Example 2, based on the detection result of Dmax> 200%, even if ΔD <200%, the process speed of the image forming apparatus P becomes a half speed, and the output time becomes long. In contrast to the comparative example 2 described above, in the present embodiment, it is detected that Dmax> 200% and ΔD> 200%, so the process speed of the image forming apparatus P is reduced only by the temperature control temperature change. It is possible to output without doing.

  On the other hand, in the print of the image (b) shown in FIG. 10B, a hot offset has occurred in the 50% toner amount region in Comparative Example 1. In the first comparative example, a temperature that is 15 ° C. higher than the reference regulated temperature according to the detection result of Dmax> 200% is set as the regulated temperature of the heater 23. However, when heated at the set temperature, the toner becomes over-fixed in the 50% toner amount region.

  When the temperature adjustment temperature of the heater 23 is set with the maximum toner amount as described above, hot offset occurs when the low toner amount area is mixed in the same page. In contrast to the comparative example 1 described above, in the present embodiment, since the fixing margin is expanded by reducing the process speed of the image forming apparatus P, no image failure occurs.

  As described above, in the present embodiment, even in the case of an image in which a high toner amount area and a low toner amount area are mixed in the same page, the difference between the toner amounts is detected, and the process speed and fixing temperature control of the image forming apparatus P are adjusted. By changing the temperature, the occurrence of image defects can be prevented (suppressed). Then, in the case of only the high toner amount region, it becomes possible to increase the productivity by changing only the fixing temperature adjustment temperature.

Second Embodiment
In the first embodiment, the fixing margin is expanded by decelerating to a half speed of the normal mode as the decelerating mode according to the toner amount information to secure the fixability, but in the present embodiment, the process is performed according to the toner amount information. Adjust the speed steplessly. Thereby, the maximum productivity can be achieved by adjusting to the optimum process speed which can secure the fixing margin according to the toner amount information. The basic configuration of the image forming apparatus in the present embodiment is the same as that of the first embodiment, and therefore, the elements having the same functions or configurations as those of the first embodiment are denoted by the same reference numerals. The description is omitted.

As described in the first embodiment, the fixing speed determined by the cold offset and the hot offset can be expanded by reducing the process speed. The relationship between the difference ΔD (%) between the maximum toner amount and the minimum toner amount and the process speed V (mm / sec) at which the fixing margin can be secured is expressed by the following equation.
V = −0.4 × (ΔD−200) +100 (Equation 1)
When ΔD> 200, the process speed V (mm / sec) is slower than the process speed 100 (mm / sec) in the normal print mode.

Further, the optimum temperature control temperature T at each process speed V is expressed by the following equation.
T = −0.4 × (100−V) +205 (Equation 2)
When 100> V, the controlled temperature T is lower than the controlled temperature 205 ° C. in the normal print mode.

(Process speed and temperature adjustment temperature setting flow of this embodiment)
The process speed determination flow of the present embodiment will be described with reference to the flowchart of FIG. The basic flow (S50 to S56) to determine whether the difference ΔD is larger than 200% is the same as that in the first embodiment. If it is determined that the difference ΔD is 200% or less, a temperature that is 15 ° C. higher than the reference control temperature is set as the control temperature of the heater 23 (S57). When it is determined that the difference ΔD is larger than 200%, the process speed of the image forming apparatus P is set to the speed calculated from Equation 1, and the temperature adjusted temperature of the heater 23 is calculated from Equation 2. It sets to (S58).

(Effect confirmation)
The presence or absence of an image defect occurrence and the output time when printed in the present embodiment and the first embodiment were confirmed in Experiment 4 shown below.

(Experiment 4)
The process speed in the normal print mode of the image forming apparatus P is 100 mm / s, and the first embodiment has a mode of 50 mm / s decelerated as another mode, and in the present embodiment, it corresponds to toner amount information. Determine the process speed. As a recording material S, a general LBP printing paper, a basis weight of 80 g / m ² , and an LTR (width 216 mm vertical 279 mm) size paper were used. The image to be printed is the image shown in FIG. 10B, and the toner amount information is Dmax = 300%, Dmin = 50%, and ΔD = 250%. Table 2 shows the experimental results when ten images were continuously printed on this image in the high definition mode using the image forming apparatus P.

  In the present embodiment and the first embodiment, no image failure occurred. However, according to the toner amount information in the first embodiment, the mode is switched to the deceleration mode at half the process speed. For this reason, although the output of 10 pages took 65 seconds, in the present embodiment, since the process speed is printed at 80 mm / second, the output can be made in 50 seconds shorter than the first embodiment.

  As described above, in the present embodiment, even in the case of an image in which a high toner amount area and a low toner amount area are mixed in the same page, the difference between the toner amounts is detected, and the process speed and fixing temperature control of the image forming apparatus P are adjusted. By changing the temperature, the occurrence of image defects can be prevented (suppressed). In particular, in the present embodiment, by adjusting the process speed steplessly according to the toner amount information, the maximum productivity can be achieved by adjusting to the optimum process speed capable of securing the fixing margin according to the toner amount information. Can be achieved.

  Further, in the present embodiment, in the case of only the high toner amount region, the productivity can be maximized by changing only the fixing temperature adjustment temperature.

Third Embodiment
In the first embodiment, the difference between the maximum toner amount Dmax of each pixel in the same page and the minimum toner amount Dmin excluding pixels having a data value of 0% which is not exposed is larger than 200%. The process speed has been reduced if is greater than 200%. In the present embodiment, the determination condition of the minimum toner amount Dmin is changed according to the ratio of each color of Y, M, C, and K of the toner image on the recording material S. The basic configuration of the image forming apparatus in the present embodiment is the same as that of the first embodiment, and therefore, the elements having the same functions or configurations as those of the first embodiment are denoted by the same reference numerals. The description is omitted.

  When cold offset occurs, in addition to appearance problems as an image defect, problems such as staining the user's hand touching the toner image and offset when recording materials are stacked occur. However, although the hot offset has a problem in appearance as an image defect, the toner itself is firmly melted and fixed on the recording material S, so there is no problem of toner transfer, and a small amount of offset toner or If the color is low, there is no problem in practical use.

  Therefore, in the present embodiment, the value of ΔD is minimized by excluding the region where the toner amount is extremely low or the color region where visibility is low from the target of determination of the minimum toner amount Dmin, and the ΔD is minimized. Reduce the target image to switch to reduced mode and achieve maximum productivity.

  As a result of confirming the visibility when changing the amounts of Y, M, C, and K colors and performing hot offset, when the toner amount is 15% or less, or 30% or less and Y toner is 15% or more, the offset is performed. However, it has been confirmed that there is no problem in practical use. Therefore, among the obtained toner amount information, the above-mentioned conditions are excluded from the determination conditions of the minimum toner amount Dmin to determine the fixing mode.

(Fixing mode determination flow of the present embodiment)
The fixing mode determination flow of this embodiment will be described with reference to the flowchart of FIG. The basic flow (S60 to S65) to determine whether the maximum toner amount Dmax is larger than 200% is the same as that in the first embodiment.

  Out of the obtained toner amount information, an area in which the toner amount is 15% or less and an area in which the toner amount is 30% or less and the Y toner amount is 15% or more are excluded from Dmin determination targets and Dmin is set (S66) ).

  Next, it is determined whether the difference ΔD is larger than 200% (S67). If it is determined that the difference ΔD is 200% or less, a temperature that is 15 ° C. higher than the reference control temperature is set as the control temperature of the heater 23 (S68). Then, when it is determined that the difference ΔD is larger than 200%, the mode is switched to the deceleration mode in which the process speed of the image forming apparatus P is half of the normal mode, and the reference temperature adjustment is made as the temperature adjustment temperature of the heater 23 A temperature lowered by 20 ° C. with respect to the temperature is set (S69).

(Effect confirmation)
The presence or absence of an image defect occurrence and the output time when printed in the present embodiment and the first embodiment were confirmed in Experiment 5 shown below.

(Experiment 5)
The process speed in the normal print mode of the image forming apparatus P is 100 mm / s, and has a mode of 50 mm / s reduced as another mode. As a recording material S, a general LBP printing paper, a basis weight of 80 g / m ² , and an LTR (width 216 mm vertical 279 mm) size paper were used.
The image to be printed is the image shown in FIG. 14, and on the same page there is a patch with a total toner amount of 270% Y90%, M90%, C90% on the left, Y20% on the right, M10% 30% in total There is a patch of toner amount.

  The obtained toner amount information is ΔD = 0% when Dmax = 270% and Dmin = 270%. The reason is that the area D = 30% in the same page is excluded from the determination condition of Dmin because the condition of toner amount 30% or less and yellow toner amount (Y toner amount) 15% or more is satisfied. . That is, Dmin of the image shown in FIG. 14 is set to 270%, which is the same as Dmax. Table 3 shows the results of an experiment in which this image was continuously printed 10 sheets in the high definition mode using the image forming apparatus P.

  No image defects were found in both the present embodiment and the first embodiment. When the area on the downstream side in the recording material conveyance direction of the 30% area of the toner amount in this embodiment is confirmed with an optical microscope, it is confirmed that the toner is offset in mottles, but can not be confirmed in visual observation .

  Also, in the first embodiment, it takes 65 seconds for the output of 10 pages to switch to the deceleration mode at half the process speed according to the toner amount information, whereas in this embodiment the process speed is 100 mm / It is printed as it is seconds, so it can be output in 40 seconds.

  As described above, in the present embodiment, even in the case of an image in which a high toner amount area and a low toner amount area are mixed in the same page, the toner amount and the difference between the maximum value and the minimum value are detected. Image defects can be prevented from occurring by changing the process speed and the fixing temperature adjustment temperature. In particular, in the present embodiment, the value of ΔD is minimized by excluding the region where the toner amount is extremely low or the color region where visibility is low from the target of determination of the minimum toner amount Dmin, and switching the target image to the process speed reduction mode It can reduce and achieve the maximization of productivity.

  Further, in the present embodiment, in the case of only the high toner amount region, the productivity can be maximized by changing only the fixing temperature adjustment temperature.

(Modification)
As mentioned above, although the preferable embodiment of this invention was described, this invention is not limited to these embodiment, A various deformation | transformation and change are possible within the range of the summary.

(Modification 1)
In the embodiment described above, although it is assumed that the maximum toner amount exceeds the threshold value as a premise that the first mode and the second mode can be executed, the accumulation of the toner amount in the toner amount distribution in the same page The condition may be that a value (total value) or the like exceeds a threshold.

(Modification 2)
In the above-described embodiment, in the second mode, the heating amount is set to be lower than the reference heating amount on the premise that the conveyance speed of the recording material is made slower than the reference conveyance speed. This is because the heating amount per unit time is increased by making the conveyance speed of the recording material slower than the reference conveyance speed, so the heating amount by the heater can be reduced. However, when the maximum toner amount is further increased, the heating amount is set to the reference heating amount, or the heating amount is set to be higher than the reference heating amount on the premise that the recording material conveyance speed is made slower than the reference conveyance speed. You may make it lower than the amount of heating of mode.

(Modification 3)
In the above-described first and second embodiments, the pixel having a data value of 0% is excluded as the determination target of the minimum toner amount Dmin, and in the third embodiment, the region with extremely low toner amount and low visibility The color area was excluded from the determination target of the minimum toner amount Dmin. Although this improves the productivity, it is also possible to include in the determination target of the minimum toner amount Dmin without excluding these.

(Modification 4)
In the embodiment described above, the heating in the fixing unit is performed by the heater, but the present invention is not limited to this, and an electromagnetic induction method using an exciting coil may be used.

  Further, in the above-described embodiment, 200% is used as the threshold, but thresholds having different values may be used.

(Modification 5)
In the third embodiment described above, the configuration of the first embodiment is adopted as the change of the process speed, but the configuration of the second embodiment may be adopted as the change of the process speed. That is, the process speed may be adjusted steplessly according to the toner amount information.

(Modification 6)
In the embodiment described above, the fixing device for fixing the unfixed toner image to the sheet has been described as an example, but the present invention is not limited to this, and the toner image provisionally attached to the sheet to improve the gloss of the image The present invention is similarly applicable to a heating and pressing device (also referred to as a fixing device in this case).

4 · · Photosensitive drum, 30 · · Video controller (printer controller), 306 · CPU · F · · · fixing unit

Claims (13)

An image forming unit for forming an image with toner on a recording material by an image signal of each pixel in the same page generated based on image data;
A fixing unit configured to heat the recording material carrying an image by the toner to fix the image by the toner;
Based on the difference between the maximum toner amount and the minimum toner amount of each pixel in the same page,
A first mode in which a conveyance speed at which the recording material is conveyed is a reference conveyance speed, and a heating amount in the fixing unit is a first heating amount higher than the reference heating amount;
A second mode in which the conveyance speed is set to be lower than the reference conveyance speed and the heating amount in the fixing unit is set to a second heating amount lower than the first heating amount;
And an executable control unit,
An image forming apparatus comprising:   The image forming apparatus according to claim 1, wherein the control unit is capable of executing the first mode and the second mode when the maximum toner amount exceeds a threshold. The first mode is executable when the difference is less than or equal to a threshold,
The image forming apparatus according to claim 2, wherein the second mode is executable when the difference exceeds a threshold.   The control unit is characterized in that, when the maximum toner amount is equal to or less than a threshold value, the conveyance speed at which the recording material is conveyed is the reference conveyance speed, and the heating amount is the reference heating amount. Item 4. An image forming apparatus according to item 2 or 3.   The image forming apparatus according to any one of claims 1 to 4, wherein the second heating amount is lower than the reference heating amount.   The image forming apparatus according to any one of claims 1 to 5, wherein the minimum toner amount is a minimum toner amount excluding pixels having a data value of 0%. Up to 100% of the yellow, magenta, cyan and black data at each pixel,
The minimum toner amount is a minimum toner amount excluding pixels having a total value of 15% or less or a total value of 30% or less and a yellow data value of 15% or more. 5. The image forming apparatus according to any one of 5. The control unit is capable of executing the first mode and the second mode when the maximum toner amount exceeds a threshold.
Data of yellow, magenta, cyan and black in each pixel can be set up to 100% each, and the total value can be set as the full color upper limit toner amount,
8. The image forming apparatus according to claim 7, wherein the threshold value of the maximum toner amount is set to 200% as the full color upper limit toner amount. The heating amount corresponds to the temperature adjustment temperature,
The image forming apparatus according to any one of claims 1 to 8, wherein the reference heating amount corresponds to a reference temperature adjustment temperature.   9. The image forming apparatus according to claim 7, wherein the full color upper limit toner amount as the maximum toner amount can be set to a different value.   The image forming apparatus according to any one of claims 1 to 10, wherein a plurality of print modes having different conveyance speeds of the recording material are provided. An image processing means for generating an image signal of a pixel formed of toners of a plurality of colors from the received image data;
An image forming unit that forms a toner image on a recording material by the image signal;
Transport means for transporting the recording material;
Control means for controlling the transport speed of the transport means;
The recording material conveyed and introduced into the nip portion formed between the fixing rotating body pressed against each other and the pressing body is fixed on the recording material by heating the toner image by the fixing rotating body. Fixing means,
And a heating amount control unit for controlling the heating amount of the toner image by the fixing unit.
Detecting toner amount information of the pixels in the page by the image processing means;
Of the obtained toner amount information, using the difference information between the maximum amount of toner in each pixel in the page and the minimum amount of toner excluding pixels having a data value of 0%, the conveyance speed of the conveyance means And an amount of heating of the toner image by the fixing unit. An image processing means for generating an image signal of a pixel formed of yellow, magenta, cyan and black toners from the received image data;
An image forming unit that forms a toner image on a recording material by the image signal;
Transport means for transporting the recording material;
Control means for controlling the transport speed of the transport means;
The recording material conveyed and introduced into the nip portion formed between the fixing rotating body pressed against each other and the pressing body is fixed on the recording material by heating the toner image by the fixing rotating body. Fixing means,
And a heating amount control unit for controlling the heating amount of the toner image by the fixing unit.
Detecting toner amount information of the pixels in the page by the image processing means;
Among the obtained toner amount information, the maximum toner amount in each pixel in the page and the yellow, magenta, cyan and black data in each pixel are each 100% at the maximum, and the total value is 15% or less. Alternatively, using the difference information from the minimum toner amount excluding pixels having a total value of 30% or less and a yellow data value of 15% or more, the transport speed of the transport unit and the heating amount of the toner image by the fixing unit An image forming apparatus characterized in that