JP6742578B2 - Image forming device - Google Patents

Description

The present invention relates to an image forming apparatus, and more particularly, to an image forming apparatus such as an electrophotographic copying machine, a printer, or a facsimile, which transfers a toner image onto a sheet and then heats and fixes the image.

An image forming apparatus that forms a toner image on a sheet by an electrophotographic method includes a fixing device for heating and fixing the toner image transferred onto the sheet. It is known that heat generated when the fixing device is driven causes volatile substances to be generated from a roller member or the like forming the fixing nip. Furthermore, recently, it has been recognized that ultrafine particles (hereinafter, referred to as UFP (Ultrafine Particle), mainly including siloxane) are generated from this volatile substance and discharged to the outside of the machine.

UFP itself does not particularly affect the human body or the environment even if it is emitted in a very small amount. However, as environmental awareness has increased in recent years, attention has been paid to emission standards for substances emitted outside the aircraft. Therefore, it is expected that the strictness (for example, BA standard) will continue in the future.

The amount of UFP generated increases as the fixing temperature rises. Regarding the control of the fixing temperature, Patent Document 1 describes that the fixing temperature is lowered at the end of printing in accordance with the number of printed sheets in order to prevent the occurrence of overshoot of the fixing roller or the pressure roller after the end of printing. There is. However, if the fixing temperature is simply lowered, the image quality may be deteriorated due to the lowering of the fixing temperature.

That is, as shown in FIG. 21, the amount of heat given to the paper at the time of fixing the toner image needs to be within the fixed image guarantee region for maintaining a constant image quality, and the amount of heat given to the paper can be secured when the fixing temperature is lowered. Without that, poor image quality will occur.

JP-A-8-166742

An object of the present invention is to provide an image forming apparatus capable of suppressing the occurrence of UFP by lowering the fixing temperature at the end of printing and suppressing the occurrence of defective image quality.

An image forming apparatus according to one aspect of the present invention is
A fixing unit for heating and fixing the toner image transferred from the image carrier onto the sheet by passing through the fixing nip;
Control means for controlling the printing operation including the fixing means,
In an image forming apparatus equipped with
The control means lowers the fixing temperature immediately before the end of printing and performs control for compensating the time for the paper to pass through the fixing nip.
Is characterized by.

In the image forming apparatus, before the paper is separated from the fixing nip at the end of printing, the fixing temperature is lowered and the time for the paper to pass through the fixing nip is secured to secure the heat amount. The compensation control here is control to substantially increase the time for which the paper passes through the fixing nip in order to compensate for the amount of heat corresponding to the decrease in the fixing temperature. For example, it means decreasing the system speed including the paper transport speed or increasing the fixing nip pressure. Decreasing the system speed increases the amount of time the paper passes through the fusing nip to compensate for the amount of heat. When the fixing nip pressure is increased, the nip portion is crushed and the nip width is increased to compensate for the amount of heat.

An image forming apparatus according to one aspect of the present invention is
A fixing unit for heating and fixing the toner image transferred from the image carrier onto the sheet by passing through the fixing nip;
Control means for controlling the printing operation including the fixing means,
In an image forming apparatus equipped with
The control means lowers the fixing control temperature during printing and immediately before the end of printing, and performs control for compensating the time for the paper to pass through the fixing nip,
The control means does not perform control for compensating the time for the paper to pass through the fixing nip after the fixing control temperature is lowered until the actual temperature at the fixing nip is reduced to the target value, and the fixing control temperature is not adjusted. after the actual temperature in the fixing nip reduces decreases to the target value, and have rows control to compensate for the time the paper passes through the fixing nip,
Controlling the time for paper to pass through the fusing nip includes reducing system speeds, including paper transport speed, from a first speed to a second speed,
The control means increases the paper transport speed from the second speed to the first speed for a predetermined time in the time zone after the printing is completed and before the printing of the next paper is started, and then the second speed is applied. To a third speed, which is slower than
Is characterized by.

FIG. 1 is a schematic configuration diagram of an image forming apparatus that is an embodiment. FIG. 3 is a block diagram showing a fixing heater portion and its control mechanism. It is a block diagram showing a control mechanism. It is a graph which shows the amount of UFP discharge at the time of overshoot occurrence. It is a graph which shows the amount of UFP discharge when overshoot does not occur. 6 is a graph showing the relationship between fixing temperature and UFP generation amount. 7 is a graph showing the relationship between the roller temperature and the amount of UFP generated when the fixing roller overshoots at a high temperature. 6 is a graph showing the relationship between the roller temperature and the UFP generation amount when the fixing roller overshoots at a low temperature. 6 is a graph showing a relationship between a fixing temperature and a sheet conveyance speed. 6 is a graph showing the relationship between fixing temperature and fixing nip pressure. 6 is a graph showing a UFP generation amount and the like when printing is completed under normal control. 7 is a graph showing UFP generation amount and the like when the fixing temperature is lowered and the transport speed is lowered at the end of printing. 6 is a graph showing a change in actual fixing temperature with respect to a target value. 6 is a graph showing changes in the actual fixing temperature with respect to the target value when the transport speed is reduced. 6 is a graph showing the UFP generation amount and the like when the conveyance speed is reduced while the fixing temperature is reduced immediately before the end of printing. 6 is a graph showing changes in the actual fixing temperature with respect to the target value when the fixing temperature and the transport speed are gradually reduced. 6 is a graph showing UFP generation amount and the like when the fixing temperature is lowered and the fixing nip pressure is increased at the end of printing. 6 is a graph showing changes in the actual fixing temperature with respect to the target value when the fixing nip pressure is increased. 6 is a graph showing UFP generation amount and the like when the fixing nip pressure is increased while lowering the fixing temperature immediately before the end of printing. 6 is a graph showing changes in the actual fixing temperature with respect to the target value when the fixing temperature is gradually decreased and the fixing nip pressure is gradually increased. 6 is a graph showing the relationship between the fixing temperature and the amount of heat applied to the paper.

Embodiments of an image forming apparatus according to the present invention will be described below with reference to the accompanying drawings. In each figure, the same members and parts are designated by the same reference numerals, and overlapping description will be omitted.

As shown in FIG. 1, the image forming apparatus 1 which is an embodiment is configured to form a color image by a tandem system. That is, four process units 10 (a unit for yellow image 10 y, a unit for magenta image 10 m, a unit for cyan image 10 c, and a unit for black image 10 k) are juxtaposed and formed on each photoconductor 11. The toner images of the respective colors are transferred/combined (primary transfer) onto the intermediate transfer belt 31 which is rotationally driven in the direction of arrow A, by an electric field applied from each transfer roller 32. After that, the synthetic toner image is secondarily transferred onto the recording medium (paper) by the electric field applied from the transfer roller 35.

A charging roller 12, a developing device 13, a cleaning blade 14 for residual toner, and the like are arranged around each photoconductor 11, and a laser scanning optical unit 20 for forming an electrostatic latent image on the photoconductor 11 is further provided. It is arranged. A process in which a toner image is formed on the photoconductor 11 by an electrophotographic method by the process unit 10 of this type, the toner image is primarily transferred onto the intermediate transfer belt 31, and secondarily transferred onto a sheet is well known. ..

The sheets are stacked and stored in the sheet feeding cassette 50, and are fed one by one by the sheet feeding roller 51. The fed paper is conveyed to the secondary transfer portion via the pair of registration rollers 52, and the toner image is secondarily transferred from the intermediate transfer belt 31. Thereafter, the sheet is heated and fixed with the toner in the fixing unit 60, and is ejected from the ejection roller pair 56 to the ejection portion 57.

The fixing unit 60 includes a heating roller 61 and a pressure roller 62. The pressure contact portions of the rollers 61 and 62 form a fixing nip, and the pressure roller 62 is made to have a predetermined pressure or a variable pressure force with respect to the heating roller 61. A mechanism for applying a pressure force to the heating roller 61 by the pressure roller 62 and a mechanism for varying the pressure force are well known. As shown in FIG. 2, the heating roller 61 has a large size heater 65 and a small size heater 66 built therein in the axial direction thereof. The heaters 65 and 66 are driven by drivers 67 and 68 controlled by the CPU 101. A sensor SE1 that detects the temperature of the outer peripheral portion is arranged on the heating roller 61, and the detected value is input to the CPU 101 via the input circuit 69.

As shown in FIG. 3, the control mechanism of the image forming apparatus 1 mainly includes the CPU 101. The CPU 101 includes a main body-attached non-volatile memory 102 and a unit-attached non-volatile memory 103. Further, the CPU 101 controls the process unit 10, and also controls a load 121 including a paper transport system, a toner replenishment motor, or a cooling fan motor. Further, this control mechanism is connected to the controller unit 130, and exchanges necessary information such as image data.

FIG. 4 shows the UFP generation amount (see point B) in a state where overshoot occurs after printing is completed. The target value is PER10=5.00E+10 (pieces/10 min), whereas the calculated value at point B is PER10=7.25E+10 (pieces/10 min), which does not satisfy the BA standard.

FIG. 5 shows the UFP generation amount (see point B) when overshoot does not occur after printing is completed. The calculated value at the point B here with respect to the target value is PER10=3.92E+10 (pieces/10 min), which satisfies the BA standard.

In this way, if the overshoot occurs after the printing is completed, the calculated value of the UFP discharge amount may be doubled. Here, the end of printing means that the trailing edge of the paper (the final paper in the case of continuous printing) has passed through the fixing nip. If the UFP discharge amount overshoot does not occur after such printing is completed, the standard value can be cleared. However, there is a possibility that the standard value cannot be cleared due to overshoot.

The cause of the overshoot of the UFP discharge amount is that the paper passes through the fixing nip when the fixing roller 61 and the exhaust fan continue to rotate after printing (the same state as during printing). It can be presumed that the amount of heat received and carried cannot be released from the fixing roller 61, the temperature of the fixing roller 61 rises, and the UFP generation amount increases from this temperature rising portion.

Here, FIG. 6 shows the relationship between the fixing (printing) temperature and the UFP generation (emission) amount. FIG. 6 shows the measured values for three models, where the black circles are the first model, the black squares are the second model, and the black triangles are the third model. Here, the fixing temperature means the temperature of the central portion in the width direction orthogonal to the sheet passing direction. The amount of UFP generated greatly differs depending on the fixing temperature, and the amount generated with a temperature rise from around 150° C. tends to increase exponentially. The vertical axis of FIG. 6 is an index display, and according to this, when the temperature rises by 10° C., the generation amount may be about 5 to 10 times.

The UFP generation state when the fixing roller 61 overshoots at a high temperature is as shown in FIG. 7, and the UFP generation amount increases as the roller (actual) temperature slightly rises immediately after the end of printing. On the other hand, FIG. 8 shows a UFP occurrence state when the fixing roller 61 overshoots at a low temperature. When the paper comes out of the fixing nip at the end of printing, the temperature of the fixing roller 61 rises, and if the temperature of the fixing roller 61 (150° C. or higher) is different by several degrees, the UFP generation amount becomes about 2 to 3 times. This means that even if the temperature of the fixing roller 61 rises by several degrees Celsius, if the original temperature of the fixing roller 61 is low, the UFP generation amount can be reduced to 1/2 to 1/3.

Specifically, when the temperature of the fixing roller 61 is 190° C. and rises 2° C. at the end of printing to 192° C., the amount of UFP generated is 185° C. and rises 2° C. at the end of printing to 187° C. The UFP generation amount may be 2 to 5 times as large as the case. This means that if the fixing temperature after the paper is discharged from the fixing nip at the end of printing can be set to 185° C., the UFP generation amount is reduced to 1/2 to 1/5 of that at 190° C. There is a possibility to make it.

Therefore, by decreasing the temperature of the fixing roller 61 immediately before the sheet is discharged from the fixing nip at the end of printing, it is possible to suppress the UFP generation amount at the end of printing. On the other hand, as shown in FIG. 21, if the fixing temperature is lowered in order to prevent overshoot, the paper (toner) cannot secure a sufficient amount of heat, which may cause image quality failure.

Therefore, the fixing temperature is lowered immediately before the end of printing and the control for compensating the time for the sheet to pass through the fixing nip is suppressed, thereby suppressing the occurrence of image quality defects and suppressing the discharge amount of UFP. Specifically, control is performed to lower the temperature of the fixing roller 61 while keeping the heat quantity in the fixed image guarantee area shown in FIG.

FIG. 9 shows the relationship between the fixing temperature and the sheet conveyance speed in the fixing nip (rotational speed of the fixing roller 61). By lowering the system speed including the conveyance speed in the fixing nip (from feeding to discharging, and the rotation speed of the photoconductor 11 and the intermediate transfer belt 31), the time for the paper to pass through the fixing nip is increased. , The amount of heat given to the paper can secure a fixed image guarantee area.

The control for compensating the time for the sheet to pass through the fixing nip may be to increase the fixing nip pressure. FIG. 10 shows the relationship between the fixing temperature and the fixing nip pressure. When the fixing nip pressure is increased, the nip width is increased, and as a result, the amount of heat applied to the paper is increased and the fixed image guarantee area can be secured.

FIG. 11 shows the amount of UFP generated when printing is completed by normal control, and FIG. 12 shows the amount of UFP generated when the fixing temperature is lowered and the transport speed is lowered immediately before the end of printing. As shown in FIG. 11, if the printing operation is ended without taking measures against the temperature decrease of the fixing roller 61, the UFP generation amount after the printing is significantly increased. On the other hand, as shown in FIG. 12, when the measure for lowering the temperature of the fixing roller 61 is executed and the printing is ended immediately before the end of the printing, it is possible to suppress the UFP generation amount after the end of the printing.

Further, in consideration of the temperature decrease of the fixing roller 61 from the viewpoint of securing the amount of heat to the paper, FIG. 13 shows a change of the actual fixing temperature with respect to the target value of the fixing temperature. In FIG. 13, when one sheet of paper is fixed, the temperature of the fixing roller 61 decreases by about 4 to 5° C., and the temperature of the fixing roller 61 has a fixed image guarantee region of about ±5° C. with respect to the target value. Showing. Therefore, if the fixing temperature is simply lowered by 5° C., the temperature may be outside the image-guaranteed region, which may cause image quality failure.

FIG. 14 shows the target value when the transport speed is lowered and the actual change of the fixing temperature with respect to the target value as a measure for preventing the image quality from being deteriorated. By lowering the fixing temperature and the transport speed to secure the amount of heat applied to the paper, it becomes possible to prevent the occurrence of image quality defects.

The system speed including the rotation speed of the fixing roller 61 may be decreased after the fixing control temperature is decreased immediately before the end of printing and the actual temperature in the fixing nip is decreased. This control is shown in FIG. In the case of a fixing unit having a large heat capacity, there is a possibility that the actual fixing temperature does not drop to the target value even if the sheet is passed with the fixing temperature lowered. In this case, the sheet is allowed to pass without changing the transport speed (system speed), and the transport speed is reduced after the fixing temperature drops to the target value to secure the necessary amount of heat. Further, in this case, if the fixing temperature is lowered and the conveying speed is lowered at the same time, there is a possibility that the amount of heat applied to the paper is too large to be outside the image guarantee area.

FIG. 16 shows the control when the fixing temperature and the conveyance speed are gradually reduced. When the difference G between the normal fixing temperature and the fixing temperature for suppressing UFP generation is large and the image guarantee areas do not overlap, the fixing temperature and the transport speed are gradually reduced for each temperature at which the image guarantee areas overlap. The target temperature is reached when the paper at the end of printing has run out (when the trailing edge of the paper has passed the fixing nip).

In this case, if the target fixing temperature is lowered once and the target speed is lowered at the same time, the temperature of the fixing roller 61 does not fall immediately, so there is a possibility that the amount of heat applied to the paper is too large to be outside the image guarantee area. There is. Further, if the fixing temperature is lowered without changing the conveying speed, there is a possibility that the amount of heat applied to the paper is too small to be outside the image guarantee area. Therefore, it is necessary to adjust the fixing temperature and the conveyance speed so that the amount of heat applied to the paper is always within the image guarantee area. In the case of a fixing unit having a large heat capacity, as shown in FIG. 16, the fixing temperature and the conveyance speed are gradually reduced at the timing shown in FIG.

In order to execute the above control accurately and according to the situation, it is preferable to constantly detect the surface temperature of the fixing roller 61. In this case, the upper and lower limits of the image security area are set, the temperature of the fixing roller 61 (fixing nip) is monitored, and when the temperature reaches the critical temperature of the image security area, the conveyance speed is switched. This makes it possible to keep the fixing temperature low immediately before the end of printing, while always applying an appropriate amount of heat to the paper.

Further, as indicated by the dotted line in FIGS. 12 and 15, the conveying speed at the fixing nip may be returned to the normal speed after the printing is completed. According to such control, the fixing roller 61 can be efficiently cooled after the printing is completed.

FIG. 17 shows the amount of UFP generated when the fixing temperature is lowered and the nip pressure of the fixing nip is increased immediately before the end of printing. As shown in FIG. 11, if the printing operation is ended without taking measures against the temperature decrease of the fixing roller 61, the UFP generation amount after the end of printing becomes extremely large. On the other hand, as shown in FIG. 17, when the measure for lowering the temperature of the fixing roller 61 is executed immediately before the end of printing and the printing is ended, it is possible to suppress the UFP generation amount after the end of printing.

Further, in consideration of the temperature decrease of the fixing roller 61 from the viewpoint of securing the amount of heat to the paper, it is preferable to consider the change of the actual fixing temperature with respect to the target value of the fixing temperature shown in FIG. In FIG. 13, when one sheet of paper is fixed, the temperature of the fixing roller 61 decreases by about 4 to 5° C., and the temperature of the fixing roller 61 has a fixed image guarantee region of about ±5° C. with respect to the target value. Showing. Therefore, if the fixing temperature is simply lowered by 5° C., the temperature may be outside the image-guaranteed region, which may cause image quality failure.

FIG. 18 shows a target value when the fixing nip pressure is increased and a change in the actual fixing temperature with respect to the target value as a measure for preventing the image quality from being deteriorated. By lowering the fixing temperature and increasing the nip pressure to secure the amount of heat applied to the paper, it is possible to prevent the occurrence of image quality defects.

The fixing nip pressure may be increased after the fixing control temperature is decreased immediately before the end of printing and the actual temperature in the fixing nip is decreased. This control is shown in FIG. In the case of a fixing unit having a large heat capacity, there is a possibility that the actual fixing temperature does not drop to the target value even if the sheet is passed with the fixing temperature lowered. In this case, the sheet is allowed to pass without changing the nip pressure, and the nip pressure is increased after the fixing temperature has dropped to the target value to secure the necessary amount of heat. Further, in this case, if the fixing temperature is lowered and the nip pressure is increased at the same time, there is a possibility that the amount of heat applied to the paper is too large to be outside the image guarantee region.

FIG. 20 shows the control when the fixing temperature is lowered stepwise and the nip pressure is raised stepwise. When the difference G between the fixing temperature at the normal time and the fixing temperature for suppressing UFP generation is large and the image guarantee areas do not overlap, the fixing temperature is gradually decreased for each temperature at which the image guarantee areas overlap, and The pressure is gradually increased until the target temperature is reached when the paper at the end of printing runs out (when the trailing edge of the paper passes through the fixing nip).

In this case, if the target fixing temperature is lowered once and the target nip pressure is raised at the same time, the temperature of the fixing roller 61 does not fall immediately, so that the amount of heat applied to the paper is too large to be outside the image guarantee area. There is a nature. Further, if the fixing temperature is lowered without changing the nip pressure, there is a possibility that the amount of heat applied to the paper is too small to be outside the image guarantee area. Therefore, it is necessary to adjust the fixing temperature and the nip pressure so that the amount of heat applied to the paper is always within the image guarantee area. In the case of a fixing unit having a large heat capacity, the fixing temperature is gradually decreased and the nip pressure is increased at the timing shown in FIG. 19 as shown in FIG.

In order to execute the above control accurately and according to the situation, it is preferable to constantly detect the surface temperature of the fixing roller 61. In this case, the upper and lower limit temperatures of the image guarantee region are set, the temperature of the fixing roller 61 (fixing nip) is monitored, and when the temperature reaches the limit temperature of the image guarantee region, the nip pressure is switched. This makes it possible to keep the fixing temperature low immediately before the end of printing, while always applying an appropriate amount of heat to the paper.

Further, in addition to the above-described two types (conveyance speed control and nip pressure control), in order to perform more accurate and detailed control, the nip is used as a control for compensating the time when the paper passes through the fixing nip. The above-described two types of forms, that is, increasing the pressure and decreasing the sheet conveying speed, may be combined.

The control according to the present invention is an image stabilization control during the printing operation (which is conventionally known control, in which a predetermined toner image is formed on a photoconductor or a transfer belt, and the developing bias or the like is adjusted by detecting the density thereof. The control may be performed when performing the control). When the image stabilization control is performed for about several minutes during printing, the above-described UFP generation overshoot phenomenon occurs. Therefore, it is effective to execute the control according to the present invention during the image stabilization control. Is.

When the printing target paper is switched from a large size (for example, A3 size) to a small size (for example, B5 size), the fixing temperature is lowered and the control for compensating the time for the paper to pass through the fixing nip is executed. Preferably. When the large size paper is switched to the small size paper, both ends of the fixing roller 61 are in a state where the above-mentioned overshoot phenomenon occurs. Therefore, the present invention is also applicable when the paper size is switched from the large size to the small size. It is effective to execute such control.

As shown in FIG. 2, when the large-size heater 65 and the small-size heater 66 are independently arranged in the fixing roller 61, the large-sized heater 65 and the small-sized heater 66 are arranged before the large-sized paper is switched to the small-sized paper. Even if the temperature of the size heater 65 is lowered and the temperature rise of both ends of the fixing roller 61 is suppressed, if paper cannot pass through the both ends, the both ends lose heat escape. End up. This causes UFP to overshoot at both ends of the fixing roller 61, but it is possible to suppress the overshoot by executing the control according to the present invention when switching to the small size paper.

Further, when printing a plurality of images continuously, it is preferable to use a monochrome image as the final image. Since the monochrome image has a low fixing temperature, it is possible to set the fixing temperature to a low value immediately before the end of printing. By bringing a monochrome image to the end of printing, it becomes easy to suppress the occurrence of UFP. For example, in the case of a color image, it can be lowered by 5° C. immediately before the printing is finished, while in the case of a monochrome image, it can be lowered by 10° C. That is, the fact that the target temperature at the end of printing can be (largely) changed between the color image and the monochrome image is used.

Furthermore, when a plurality of images are continuously printed, an image that is less affected by image quality deterioration may be the final printed image. Basically, the fixing temperature changes within the upper and lower limit temperature of the image guarantee area, but if the image quality is affected to some extent, the image with less effect of image quality deterioration is set as the final print image. It is possible to minimize the effect. Further, when it is desired to suppress the amount of UFP generated even if the image quality is sacrificed to some extent, the fixing temperature can be set to be equal to or lower than the temperature of the image guarantee region.

As shown in FIG. 1, the image forming apparatus 1 includes an exhaust unit that sucks the air in the sheet conveyance path 70 that has passed through the fixing nip by the rotation of a fan 71 and exhausts the air to the outside of the apparatus through a filter. The fan 71 may be stopped or the rotation speed thereof may be reduced immediately before printing is completed. Normally, as a measure against UFP overshoot, it is necessary to rotate the fan 71 at a high speed even after printing is completed. However, when the device enters the standby state, if the fan 71 is rotated at full speed, noise becomes annoying. Noise can be suppressed by stopping the fan 71 or reducing the rotation speed.

The image forming apparatus according to the present invention is not limited to the above-mentioned embodiment, but can be variously modified within the scope of the gist.

In particular, the image forming apparatus may have any basic structure or detailed structure, and may be a multifunction peripheral having a communication function, a facsimile function, or the like, in addition to the printing function.

INDUSTRIAL APPLICABILITY As described above, the present invention is useful for an image forming apparatus, and is particularly excellent in that UFP can be suppressed and defective image quality can be suppressed.

DESCRIPTION OF SYMBOLS 1... Image forming apparatus 10... Process unit 11... Photosensitive member 31... Intermediate transfer belt 60... Fixing unit 61... Fixing roller 62... Pressure roller 65, 66... Heater 101... CPU

Claims (7)

A fixing unit for heating and fixing the toner image transferred from the image carrier onto the sheet by passing through the fixing nip;
Control means for controlling the printing operation including the fixing means,
In an image forming apparatus equipped with
The control means lowers the fixing control temperature during printing and immediately before the end of printing, and performs control for compensating the time for the paper to pass through the fixing nip,
The control means does not perform control for compensating the time for the paper to pass through the fixing nip after the fixing control temperature is decreased until the actual temperature at the fixing nip decreases to the target value, and the fixing control temperature is not adjusted. after the actual temperature in the fixing nip reduces decreases to the target value, and have rows control to compensate for the time the paper passes through the fixing nip,
Controlling the time for paper to pass through the fusing nip includes reducing system speeds, including paper transport speed, from a first speed to a second speed,
The control means increases the paper transport speed from the second speed to the first speed for a predetermined time in the time zone after the printing is completed and before the printing of the next paper is started, and then the second speed is applied. Lowering to a third speed, which is slower than
An image forming apparatus characterized by. The control unit gradually lowers the fixing control temperature and the system speed as a control for compensating the time for the sheet to pass through the fixing nip, and heats the sheet in the image guarantee area with respect to the sheet passing through the fixing nip. to always grant, an image forming apparatus according to claim 1, wherein the. Said control means, said image guaranteed by performing the minimum temperature settings over the area to monitor the temperature of the fixing nip, claim wherein reaches the limit temperature of the image security area to switch the system speed, and wherein the 2 The image forming apparatus according to item 1. The image forming apparatus according to claim 1, wherein the control for compensating the time for the sheet to pass through the fixing nip is to increase the nip pressure of the fixing nip and to reduce the system speed including the sheet conveying speed. .. The image forming apparatus according to claim 1, wherein the control unit sets a monochrome image as a final print image when continuously printing a plurality of images. The image forming apparatus according to claim 1, wherein the control unit sets an image, which is less affected by image quality deterioration, as a final print image when continuously printing a plurality of images. Equipped with an exhaust unit that sucks air on the sheet conveyance path after passing through the fixing nip by rotation of a fan and exhausts the air to the outside of the apparatus through a filter,
The control means stops the fan or reduces the rotation speed immediately after printing is finished,
The image forming apparatus according to claim 1, wherein:

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