JP2003233274A - Fixing device and image forming apparatus equipped therewith - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing device capable of realizing the shortening of time taken to restore the surface temperature of a fixing body to a temperature at which a color image can be fixed in the case of fixing the color image after a state where the surface temperature of the fixing body has become lower than temperature required to fix the color image because the fixing processing of a black-and-white image has been performed, and to provide an image forming apparatus equipped with the fixing device. <P>SOLUTION: In the case of shifting a mode from a 1st mode for performing the fixing processing in a specified temperature range in which the black-and-white image can be fixed to a 2nd mode for performing the fixing processing of an unfixed image which can be fixed as the color image having a lower limit temperature above the lower limit in the specified temperature range, a controller 25 makes power per unit time applied to an external heating roller 29 greater than that at the fixing processing time in the 1st mode in a shifting period from the completion of the fixing processing in the 1st mode to the starting time of the fixing processing in the 2nd mode or in an optional period from the completion of the fixing processing in the 1st mode to the completion of the fixing processing in the 2nd mode. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixing device used in an image forming apparatus such as a copying machine, a laser beam printer, a facsimile machine, and an image forming apparatus equipped with this fixing device.

[0002]

2. Description of the Related Art Conventionally, copying machines, laser beam printers,
Alternatively, as a fixing device included in an image forming apparatus such as a facsimile machine, a fixing member and a pressure member that are in pressure contact with each other to form a nip area and rotate are provided, and a recording material carrying an unfixed image is recorded in the nip area. A fixing device is known in which the unfixed image is fixed on the recording material by heating and pressurizing it while sandwiching and conveying it between the fixing member and the pressure member.

For example, in such a fixing device, a heating source such as a halogen lamp is built in a fixing roller as a fixing body and a pressure roller as a pressure body. The heating source such as the halogen lamp is on / off controlled based on a signal from a temperature sensor that detects the surface temperature of each of the fixing roller and the pressure roller, and the fixing roller and the pressure roller are controlled to a predetermined set temperature. It will be.

Further, in such a fixing device, a nip portion, which is a nip region, is formed by elastic deformation of the elastic layer of the fixing roller when the pressure roller is pressed against the fixing roller.

A recording sheet, which is a recording material carrying a toner image which is an unfixed image, is heated and pressed while being nipped and conveyed by the fixing roller and the pressure roller in the nip portion, so that the toner image is formed. Is melted, penetrates between the fibers of the recording sheet, and is fixed on the recording sheet.

However, as described above, when the fixing roller and the pressure roller have elastic layers, these elastic layers are made of an elastic material such as silicone rubber having a certain thickness and are relatively heat conductive. Since the rate is low, the temperatures of the fixing roller and the pressure roller are lowered, and there is a possibility that defective fixing may occur. That is, when the surface temperature of the fixing roller or the pressure roller falls below a predetermined set temperature while the recording sheet is being conveyed in the nip portion, each temperature sensor detects this temperature drop and energizes each halogen lamp. However, it takes time for the heat of the halogen lamp to be transferred to the surface through the elastic layer, and during that time, the temperature of the fixing roller or the pressure roller may be lowered, and fixing failure may occur. In particular, when the process speed is increased, defective fixing tends to occur, and in order to prevent the defective fixing, continuous printing is limited.

Therefore, in order to solve such a problem, in the prior art, Japanese Patent Laid-Open Nos. 10-149044 and 11 are disclosed.
As disclosed in Japanese Laid-Open Patent Publication No. 24489, a technique has already been proposed in which an external heating roller, which is an external heating member maintained at a high temperature, is brought into contact with the surface of the fixing roller to reduce the temperature decrease on the surface of the fixing roller. There is.

[0008]

However, the above-mentioned JP-A-10-149044 and JP-A-11-244 have been proposed.
The technique disclosed in Japanese Patent No. 89 has the following problems. That is, in the case where a monochrome image can be output at a throughput equivalent to that of a conventional high-speed machine and a color image can also be output, when the monochrome image is continuously output, the surface temperature of the fixing roller is increased with the progress. However, even within a temperature range sufficient for fixing a black-and-white image, the temperature sometimes drops to an inappropriate temperature for fixing a color image. In other words, a black and white image fixes only one color of black toner on the recording sheet, whereas a color image requires fixing of four colors of cyan, magenta, and yellow color toners at the same time. The temperature required for this is higher than that of a black-and-white image, so that there is a temperature range in which the black-and-white image can be fixed but the color image cannot be fixed.

When a color image is subsequently fixed by the fixing roller in such a temperature range, the printing operation is performed until the surface temperature of the fixing roller reaches the temperature necessary for fixing the color image. I have to stop. In particular, this problem becomes more remarkable as the speed of the device increases.

Therefore, according to the present invention, when a color image is continuously fixed from a state where the surface temperature of the fixing body is lower than the temperature required for fixing the color image by the fixing process of the black and white image, the fixing body is fixed. An object of the present invention is to provide a fixing device capable of shortening the time for returning the surface temperature to a temperature at which a color image can be fixed, and an image forming apparatus including the fixing device.

[0011]

According to the present application, the above object is to provide a fixing member and a pressure member that are in pressure contact with each other to form a nip region and rotate, and to be arranged in contact with an outer peripheral surface of the fixing member. An external heating member that heats the fixing body from the outside by receiving power from a power source and heats the fixing body from the outside, and conveys a recording material carrying an unfixed image in the nip region by the fixing body and the pressing body. In the fixing device for fixing the unfixed image on the recording material by heating and pressurizing the recording material, an unfixed image that can be fixed at the first temperature is provided with an adjusting unit capable of adjusting the electric power from the power source to the external heating member. A first mode in which a fixing process is performed in a predetermined temperature range of the first temperature, and a second mode in which an unfixed image that can be fixed at a second temperature having a lower limit temperature higher than the lower limit of the predetermined temperature range is fixed. Is set to be switchable, and The means is, during the transition from the first mode to the second mode, a transition period from the end of the fixing process in the first mode to the start of the fixing process in the second mode, or the fixing in the first mode. It is possible to increase the electric power per unit time from the power source to the external heating member during the arbitrary period from the end of the processing to the end of the fixing processing in the second mode as compared with that in the fixing processing in the first mode. Is achieved by the first invention.

Further, according to the present application, in the first aspect of the present invention, when the temperature of the fixing member at the end of the fixing process in the first mode is equal to or lower than a predetermined temperature, the adjusting means has the above-mentioned object. The power value from the power supply to the external heating member is larger than that during the fixing process in the first mode in any period from the end of the fixing process in one mode to the start of the fixing process in the second mode or the end of the fixing process. It is also achieved by the second invention of being adapted to.

Further, according to the present application, in the first or second aspect of the invention, the adjusting means is configured such that the number of continuous feeding of the recording material to the nip region in the first mode is a predetermined number or more. In this case, the electric power value from the power source to the external heating member is set to the first heating mode in the first mode in any period from the end of the fixing process in the first mode to the start of the fixing process in the second mode or the end of the fixing process. It is also achieved by the third invention that the size is set to be larger than that during the fixing process.

Further, according to the present application, the above-mentioned object is the adjusting means in any one of the first to third inventions,
From the end of the fixing process in the first mode to the start of the fixing process in the second mode or the end of the fixing process when the total time for the recording material to pass through the nip area in the first mode is a predetermined time or more It is also achieved by the fourth invention that the electric power value from the power source to the external heating member is set to be larger than that during the fixing process in the first mode in any arbitrary period.

Further, according to the present application, in any of the first to fourth inventions, the above-mentioned object is that the unfixed image on the recording material subjected to the fixing process in the first mode is a monochrome image, It is also achieved by the fifth aspect that the unfixed image on the recording material that is subjected to the fixing process in the second mode is a color image.

According to the present application, the above object is an image forming apparatus for recording an image on a recording material by a series of image forming processes, and the fixing apparatus according to any one of the first to fifth inventions. It is also achieved by the sixth invention comprising.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is a sectional view showing the schematic arrangement of a color electrophotographic copying machine (hereinafter referred to as a color copying machine) which is an example of an image forming apparatus according to an embodiment of the present invention. still,
Needless to say, the present invention can be similarly applied to an image forming apparatus such as a printer or a facsimile.

In the color copying machine shown in FIG. 1, an automatic original feeding device 41 for automatically feeding the originals 44 one by one onto the upper part of the color copying machine main body 40, and an automatic original feeding device 41 for feeding the originals. A document reading device 42 for reading an image of the document 44 is provided.

The original reading device 42 illuminates an original 44 placed on a platen glass 43 with a light source 45, and a reflected light image from the original 44 is reflected by optical mirrors 46, 4.
An image reading element 50, such as a CCD, is scanned and exposed through a reduction optical system including the image forming lenses 49 and 49, and the image reading element 50 causes the color material reflected light image of the original document 44 to form a predetermined dot. It is designed to read by density.

The color material reflected light images of the document 44 read by the document reading device 42 are R (red), G (green) and B.
The data of three colors (blue) is sent to the image processing device 51, and in this image processing device 51, R, G, B of the original 44 is sent.
Image processing such as shading correction, gamma correction, and color space processing is performed on the data.

The image data subjected to the predetermined image processing by the image processing device 51 is sent to the exposure device 5 as Y (yellow), M (magenta), C (cyan), and K (black) image data. In the exposure device 5, image exposure with laser light is performed according to the image data.

The exposure of the image by the exposure device 5 is applied to the photosensitive drum (hereinafter, simply referred to as "photosensitive member") 1. The photoconductor 1 is provided so as to be rotatable in the direction of arrow A by a motor (not shown). Around the photoreceptor 1, a primary charger 4, an exposure device 5, a color developing unit 7, a black and white developing unit 8, a transfer charger 9, a cleaner device 6 and the like are arranged.

In forming an image, first, a voltage is applied to the primary charger 4 so that the surface of the photoconductor 1 is uniformly negatively charged at a predetermined charging portion potential. Then, the exposure device 5 including a laser scanner performs exposure based on the image data so that the charged image portion on the photoconductor 1 has a predetermined exposure portion potential to form a latent image. The exposure device 5 is turned on and off based on the image data to form a latent image corresponding to the image.

The three developing devices 7Y, 7M, and 7C for full-color development of the color developing unit 7 and the black and white developing unit 8 form latent images on the photoconductor 1 in Y, M, and C, respectively.
Develop with K toner. When developing the toner of each color, the color developing unit 7 is driven by a motor (not shown).
Is rotated in the direction of arrow R, and the developing device for the color corresponding to the latent image is aligned so as to contact the photoconductor 1.

The toner images of the respective colors developed on the photosensitive member 1 are sequentially transferred by the transfer charger 9 to the intermediate transfer belt 2 (hereinafter referred to as belt 2) as an intermediate transfer member.
The four color toner images are overlaid. A belt cleaner 14 is provided at a position facing the roller 10, which is a transfer belt driving roller, with the belt 2 interposed therebetween, and residual toner on the belt 2 is scraped off by a blade.

The toner image transferred onto the belt 2 is further transferred onto a recording paper, which is a recording material, by the secondary transfer roller 15. During full-color printing, four color toners are superposed on the belt 2 and then transferred onto the recording paper. The recording paper is pulled out from the recording paper cassette 16 by the pickup roller 17 to the conveyance path, and is fed to the nip portion, which is the contact portion between the secondary transfer roller 15 and the belt 2, by the conveyance roller pair 18 and 19.

Further, the toner remaining on the photosensitive member 1 is removed and collected by the cleaner device 6 by a pre-cleaning device (not shown) to make the toner charge easy to clean.
Finally, the photoconductor 1 is uniformly discharged to 0 by a static eliminator (not shown).
The charge is removed to near the bolt to prepare for the next image forming cycle.

The recording paper on which the toner image has been transferred is then
It is fed to the fixing device 3. The toner image on the recording paper is thermally fixed by the fixing device 3 and discharged to the outside of the device.

Here, the image forming timing of the color copying machine is controlled with reference to a predetermined position on the belt 2. The belt 2 is stretched around rollers 10, 11, 12, 13. Of these rollers, the roller 10 is connected to a drive source (not shown) to function as a driving roller for driving the belt 2, the rollers 11 and 12 function as tension rollers for adjusting the tension of the belt 2, and the roller 13 is It functions as a backup roller for the secondary transfer roller 15.

A reflection type sensor 20 for detecting the reference position of the belt 2 is arranged near the roller 12 which is a tension roller. The reflection type sensor 20 detects a marking such as a reflection tape provided on the end portion of the outer peripheral surface of the belt 2 and outputs an I-top signal.

The outer peripheral length of the photosensitive member 1 and the peripheral length of the belt 2 have an integer ratio represented by 1: n (n is an integer). With this setting, the photosensitive member 1 rotates an integral number of times while the belt 2 makes one revolution, and returns to the same state as that of the one revolution of the belt 2 completely. (The belt makes four revolutions), it is possible to avoid color misalignment due to uneven rotation of the photoconductor 1.

In the image forming apparatus of the intermediate transfer type as described above, after the I-top signal is detected, the exposure is started by the exposure device 5 including a laser scanner after a predetermined time has elapsed. Further, as described above, while the belt 2 makes one revolution, the photosensitive member 1 makes an integer rotation and returns to the completely same state as the one revolution of the belt 2, so that the toner image is always formed at the same position on the belt 2. The Rukoto. Further, although the toner image size also changes depending on the paper size, there is a range on the belt 2 where the toner image never falls.

FIG. 2 is a sectional view showing a schematic structure of the fixing device 3.

As shown in FIG. 2, the fixing device 3 has a fixing roller 21 as a fixing body having a halogen heater 22 as a heat source therein and a pressure roller 23 as a pressure body having a halogen heater 24 as a heat source therein. Are rotatably arranged while being in pressure contact with each other by a pressure mechanism (not shown).

The fixing roller 21 and the pressure roller 23 are in contact with thermistors 34 and 36 which are temperature detecting means, respectively. The surface temperatures of the fixing roller 21 and the pressure roller 23 are detected by the thermistors 34 and 36, and the halogen heaters 22 and 24 are controlled by the control device 25 as an adjusting means based on the detected information. In the present embodiment, the temperatures of the fixing roller 21 and the pressure roller 23 are both controlled to be kept constant at a set temperature (here, 180 [° C.]). The unfixed image transferred onto the recording paper and formed with a developer such as toner is a fixing roller 21 and a pressure roller 2.
3 is heated and pressed at a nip portion, which is a nip area formed by pressure contact with 3, and is fixed on the recording paper.

The fixing roller 21 has an HTV (high temperature vulcanization type) silicone rubber layer 21b provided on the outer periphery of an aluminum cored bar 21a, and further has an HTV silicone rubber layer 21b.
A RTV (room temperature vulcanizing type) silicone rubber layer (not shown) is provided as a heat resistant elastic layer on the outer periphery of, and has a thickness of 3 [mm],
The diameter is 40 [mm].

On the other hand, in the pressure roller 23, an HTV silicone rubber layer 23b having a thickness of 1 [mm] is provided on the outer circumference of an aluminum cored bar 23a, and a fluororesin layer (not shown) is provided on the outer circumference of the HTV silicone rubber layer 23b. Is provided,
The diameter is 40 [mm].

By combining the fixing roller 21 and the pressure roller 23 having the above structures, the releasability of the toner is further enhanced.

The external heating roller 29, which is an external heating member, comes into contact with or retracts from the outer peripheral surface of the fixing roller 21 and can be switched to a contact state or a non-contact state with the fixing roller 21.

The external heating roller 29 is moved by a contact retracting mechanism (not shown) so as to contact or retract with respect to the outer peripheral surface of the fixing roller 21. When it comes into contact with the sheet, it is pressed by a spring (not shown) and is rotated by the fixing roller 21.

For example, the external heating roller 29 is supported by a support rod (not shown) such as a heat insulating bush. Then, by moving the support rod, the fixing roller 21 is pressed or retracted. This evacuation is achieved by utilizing a known technique such as a spring clutch and a solenoid.

The external heating roller 29 has halogen heaters 30 and 31 built therein, and the outer periphery thereof has, for example, a metal having a high thermal conductivity such as aluminum, iron or stainless steel, or has a high releasability. The metal surface is coated with rubber, resin, or the like. The external heating roller 29 is held at both ends by a heat insulating bush (not shown) having high heat resistance.

The thermistors 34, 36 and 32 are arranged in contact with the fixing roller 21, the pressure roller 23 and the external heating roller 29, respectively.
The surface temperature of each roller 21, 23, 29 is detected by the controller 25, and the controller 25 controls the halogen heaters 22, 24, 30 based on this temperature information to control each roller 21, 23, 2
The temperature of 9 is controlled to a predetermined set temperature.

As an example of the set temperature, the external heating roller 29 which is an external heating member is set to have a temperature higher than that of the fixing roller 21 which is a fixing body and the pressure roller 23 which is a pressing body. The external heating roller 29 is 220
[° C.], the fixing roller 21 and the pressure roller 23 are 180
Set to [℃].

Next, the driving of the halogen heaters 30 and 31 of the external heating roller 29 will be described in detail.

In this embodiment, as shown in FIG. 2, the halogen heater 3 is used as a heat source inside the external heating roller 29.
In addition to 0, a halogen heater 31 is provided. In the present embodiment, the heater wattages of the halogen heaters 30 and 31 are each set to 300 W, and the halogen heater 31 is driven in addition to the driving of the halogen heater 30 described above, thereby increasing the power and reducing the wattage to 300 W.
Therefore, it is possible to increase the total to 600 W.

Further, when the halogen heater 31 is driven, when the monochrome image which is the first mode is continuously outputted, the surface temperature of the fixing roller 21 is a temperature sufficient for fixing the monochrome image with the progress of the continuous output. Even within the range, if the temperature is lower than the temperature required to fix the color image, the period from the end of fixing the monochrome image to the start of the fixing operation of the color image, which is the second mode It shall be carried out only for. As a result, the electric power per unit time to the external heating roller 29 during that period is increased more than that during black-and-white image fixing.

In this embodiment, the minimum surface temperature of the fixing roller 21 (hereinafter referred to as the lower limit fixing temperature) required to fix the unfixed image on the recording material is when the unfixed image is a black and white image. Is 140 ° C., and 160 ° C. when the unfixed image is a color image.

The timing for starting the fixing operation of the color image is the time when the surface temperature of the fixing roller 21 reaches 160 ° C. which is the lower limit temperature for fixing the color image.

FIG. 3 shows the temperature transition of the fixing roller 21 in the fixing device 3 of this embodiment.

As shown in FIG. 3, the surface temperature of the fixing roller 21 is adjusted at a set temperature of 180 ° C. during standby. Then, when a time period of 2 [s] has elapsed after the recording material carrying the black and white image is inserted into the nip portion by pressure contact with the fixing roller 21 and the pressure roller 23, the surface temperature of the fixing roller 21 is fixed to the color image fixing. Lower limit temperature 1
Below 60 ° C. Time t3 after this time t2 [s]
In [s], when the monochrome image fixing operation is completed and the color image is subsequently fixed, the waiting time until the surface temperature of the fixing roller 21 returns to 160 ° C. or higher, which is the fixing lower limit temperature of the color image, Will be required.

In FIG. 3, the curve indicated by a indicates that the external heating roller 29 is heated when the halogen heater 31 is driven in addition to the halogen heater 30 and the heater wattage is increased as compared with that during black and white image fixing. On the other hand, the curve shown by b shows the case where heat is supplied to the external heating roller 29 by using only the halogen heater 30 as in the conventional case.

Comparing the standby times of a and b shown in FIG. 3, the standby time A (t3 to t4) in the case where the power supplied to the halogen heater of the external heating roller 29 is increased more than that at the time of fixing the black and white image. ) Can be considerably shorter than the standby time B (t3 to t5) when the power supplied to the halogen heater is the same as that used when fixing the black and white image as in the conventional case.

As described above, in the control for increasing the electric power of the heat source of the external heating roller 29, the surface temperature of the fixing roller becomes lower than the temperature required for fixing the color image due to the fixing process of the black and white image. In this state, it is executed only when the color image is fixed subsequently, and when the temperature necessary for fixing the color image is satisfied even after the fixing process of the black and white image, or when the black and white image is continuously fixed. This does not apply when fixing is performed or when a color image is fixed first.

Next, the fixing operation of the fixing device 3 will be described with reference to FIG.
It will be described in detail based on.

When the fixing sequence is started, the above-mentioned control device 25, based on the information received through the above-mentioned image processing device 51, unfixes the recording paper to be fixed to the fixing device 3. It is determined whether the image is a color image (step 501) and the color image is fixed (step 50).
8), or a monochrome image fixing operation is executed.

After the fixing of the color image is completed, the control device 25 similarly determines whether or not the fixed recording paper is the final paper based on the information received through the image processing device 51 (step 510), if it is the final paper, the fixing sequence ends, and if it is not the final paper, the process returns to step 501 again.

Similarly, after the completion of fixing the black and white image, the controller 25 also judges whether or not the fixed recording paper is the final paper.
(Step 503), the fixing sequence ends if it is the final paper, and the process proceeds to step 504 if it is not the final paper.

In step S 504, the control device 25 determines through the image processing device 51 whether the unfixed image on the recording paper to be provided to the fixing device 3 is a monochrome image or a color image. Based on the received information, if it is a monochrome image, the process returns to step 502, and if it is a color image, the process proceeds to step 505.

In step 505, it is determined whether the surface temperature Tf of the fixing roller 21 is maintained at a temperature sufficient to fix a color image. The determination is made by setting the surface temperature Tf of the fixing roller 21 to a preset temperature K1.
(Here, 160 ° C.) is compared, and when the temperature is higher than the set temperature K1, it is determined that the color image can be fixed, and the color image fixing operation is immediately executed (step 509). .

On the other hand, when the surface temperature Tf of the fixing roller 21 is lower than the set temperature K1 and it is determined that the color image cannot be fixed as it is, the surface temperature of the fixing roller 21 is set to the preset temperature. Return to K2 (here, 160 ° C as K1).

The restoration time (transition period) until the surface temperature of the fixing roller 21 returns to the set temperature K2 is directly linked to the down time of the apparatus. Therefore, for the purpose of shortening the restoration time as much as possible, the halogen heater is used. In addition to 30, the halogen heater 31 is driven to drive the external heating roller 2
The heater wattage of No. 9 is controlled to be larger than that when outputting a monochrome image (step 506).

At the subsequent step 507, the control device 25 monitors whether or not the surface temperature of the fixing roller 21 has reached the set temperature K2. If the set temperature K2 has not been reached, the halogen heaters 30 and 31 continue. Is performed (step 506), and when it is reached, the halogen heater 31 is turned off, and the process returns to the control method of controlling the temperature of the external heating roller 29 only by the halogen heater 30 (step 5).
08), and then the fixing operation of the color image is executed (step 509).

Further, in step 510, similarly, the control device 25 similarly determines whether or not the fixed recording paper is the final paper. If the final paper is the final paper, the fixing sequence is ended, and if it is not the final paper, the fixing sequence is repeated. Returning to step 501.

As shown in FIG. 5, the external heating roller 29 is used.
Even if only the halogen heater 30 is used as the heat source of the above and the duty of the driving time of the halogen heater 30 is controlled, the electric power to the heat source of the external heating roller is controlled to be larger than that at the time of fixing the black and white image. good.

Further, the period for increasing the electric power to the external heating roller 29 is not limited to the time when the fixing operation of the color image is started, but is changed until the fixing operation of the color image is ended because the throughput, the temperature control temperature and the like are changed. It may be configured to be appropriately changed within the range up to the arbitrary time.

Further, in the present embodiment, the surface temperature of the fixing roller is actually measured after the completion of the black and white image fixing operation, and it is determined whether or not it is below the fixing lower limit temperature of the color image. It may be assumed that the surface temperature of the fixing roller is lower than the fixing lower limit temperature of the color image when the predetermined number of sheets are inserted.

Similarly, the surface temperature of the fixing roller is changed to a color image when the time when the recording paper carrying the black and white image is passed through the nip portion of the fixing device 3 becomes a predetermined time or more. It may be assumed that the temperature is lower than the lower limit fixing temperature.

Further, although the pressure roller 23 has been described with the halogen heater 24 which is a heat source provided therein, the pressure roller 23 may be configured without the halogen heater 24.

Further, the fixing roller and the pressure roller have a two-roller system including the fixing roller 21 and the pressure roller 23, but a belt system may be used instead of the rollers.

The external heating roller 2 is used as an external heating member.
Although the case of using 9 has been described, it is also possible to use a belt made of resin, rubber, metal or the like or a non-contact type heat source other than the roller.

Further, the case where the external heating roller 29 as the external heating member can be contacted and retracted with respect to the fixing roller 21 as the fixing member has been described. It is also possible to make it always contact.

Further, although the contact type is used as a method for detecting the surface temperature of the fixing roller 21, the pressure roller 23, and the external heating roller 29, it is also possible to make them non-contact.

[0075]

As described above, according to the first invention of the present application, the adjusting means fixes the unfixed image fixable at the first temperature within the predetermined temperature range of the first temperature. When the transition from the first mode to the second mode in which the unfixed image that can be fixed at the second temperature having the lower limit temperature higher than the lower limit of the predetermined temperature range is fixed, the fixing in the first mode is performed. During the transition period from the end of the process to the start of the fixing process in the second mode, or during any period from the end of the fixing process in the first mode to the end of the fixing process in the second mode, the power source to the external heating member Since the power per unit time is set to be higher than that in the fixing process in the first mode, the surface temperature of the fixing body is the temperature required for fixing the color image by the fixing process of the black and white image. Pull from a lower state than When fixing a color image had a surface temperature of the fixing member can be a color image is to shorten the time for returning to a fixable temperature.

According to the second invention of the present application,
The adjusting means operates from a first mode in which an unfixed image that can be fixed at the first temperature is fixed in a predetermined temperature range of the first temperature to a second temperature having a lower limit temperature higher than a lower limit of the predetermined temperature range. When the temperature of the fixing body at the end of the fixing process in the first mode is equal to or lower than a predetermined temperature during the transition to the second mode for fixing the unfixed image that can be fixed, the fixing in the first mode is performed. During the transition period from the end of the process to the start of the fixing process in the second mode, or during any period from the end of the fixing process in the first mode to the end of the fixing process in the second mode, the power source to the external heating member Since the power per unit time is set to be higher than that in the fixing process in the first mode, the surface temperature of the fixing body is the temperature required for fixing the color image by the fixing process of the black and white image. Lower than When fixing the color image is subsequently et al., The surface temperature of the fixing member can be a color image is to shorten the time for returning to a fixable temperature.

Further, according to the third invention of the present application, the adjusting means changes from the first mode in which the unfixed image which can be fixed at the first temperature is fixed within the predetermined temperature range of the first temperature. Continuation of the recording material to the nip area in the first mode at the time of transition to the second mode, which fixes the unfixed image that can be fixed at the second temperature, which has a lower limit temperature higher than the lower limit of the predetermined temperature range. When the number of times of paper passing is a predetermined number or more, a transition period from the end of the fixing process in the first mode to the start of the fixing process in the second mode, or the end of the fixing process in the first mode Since the power per unit time from the power source to the external heating member is set to be larger than that during the fixing process in the first mode in any period until the fixing process in the two modes ends, The surface temperature of the fixing body is controlled by the fixing process. -To reduce the time required to restore the surface temperature of the fixing body to the temperature at which the color image can be fixed when the color image is continuously fixed from a temperature lower than the temperature required for fixing the image. You can

According to the fourth invention of the present application,
The adjusting means operates from a first mode in which an unfixed image that can be fixed at the first temperature is fixed in a predetermined temperature range of the first temperature to a second temperature having a lower limit temperature higher than a lower limit of the predetermined temperature range. At the time of shifting to the second mode for fixing the unfixed image which can be fixed, when the total time of passing the recording material to the nip area in the first mode is a predetermined time or more, the first mode From the power supply during the transition period from the end of the fixing process in step 2 to the start of the fixing process in the second mode, or during any period from the end of the fixing process in the first mode to the end of the fixing process in the second mode. Since the electric power per unit time to the external heating member is set to be larger than that during the fixing process in the first mode, the surface temperature of the fixing member is fixed in order to fix the color image by the fixing process of the monochrome image. The temperature has dropped below the required temperature. Following from the case of fixing a color image, the surface temperature of the fixing member can be a color image is to shorten the time for returning to a fixable temperature.

Further, according to the fifth invention of the present application, the adjusting means changes from the first mode for fixing the unfixed image of the monochrome image to the second mode for fixing the unfixed image of the color image. At the time of transition, the transition period from the end of the fixing process in the first mode to the start of the fixing process in the second mode, or the end of the fixing process in the first mode to the end of the fixing process in the second mode Since the power per unit time from the power source to the external heating member is set to be larger than that during the fixing process in the first mode, the surface of the fixing member is fixed by the black and white image fixing process. Shortening the time to restore the surface temperature of the fixing body to the temperature at which the color image can be fixed when fixing the color image continuously from the state where the temperature is lower than the temperature required to fix the color image. It can be.

According to the sixth invention of the present application,
The adjusting means operates from a first mode in which an unfixed image that can be fixed at the first temperature is fixed in a predetermined temperature range of the first temperature to a second temperature having a lower limit temperature higher than a lower limit of the predetermined temperature range. During the transition to the second mode for fixing the unfixed image that can be fixed, the transition period from the end of the fixing process in the first mode to the start of the fixing process in the second mode, or the first period The power per unit time from the power supply to the external heating member is set to be larger than that during the fixing process in the first mode in an arbitrary period from the end of the fixing process in the mode to the end of the fixing process in the second mode. Therefore, if the surface temperature of the fuser is lower than the temperature required to fix the color image due to the black and white image fixing process and the color image is subsequently fixed, the surface temperature of the fuser is Image fixed It is possible to shorten the time for returning to the ability temperatures.

[Brief description of drawings]

FIG. 1 is a sectional view showing a schematic configuration of an image forming apparatus according to an embodiment of the present invention.

2 is a sectional view showing a schematic configuration of a fixing device provided in the image forming apparatus of FIG.

FIG. 3 is a diagram showing changes in the surface temperature of the fixing member according to the embodiment of the present invention.

FIG. 4 is a flowchart showing a fixing operation of the fixing device according to the embodiment of the present invention.

FIG. 5 is a sectional view showing a schematic configuration of another example of the fixing device according to the embodiment of the present invention.

[Explanation of symbols]

3 fixing device 21 Fixing roller (fixing body) 23 Pressure Roller (Pressure Body) 25 Control device (adjusting means) 29 External heating roller (external heating member)

Continued front page    F-term (reference) 2H027 DA12 DA39 DA45 DA46 EA12                       EC06 ED25 FA28 FA35                 2H030 AD04 AD08 BB02 BB24 BB42                       BB63                 2H033 AA20 AA30 BA25 BA26 BA27                       BA32 BB03 BB06 BB15 BB18                       BB23 BB29 BB30 CA03 CA04                       CA05 CA07 CA20 CA28 CA30                       CA32 CA45                 3K058 AA02 AA62 AA64 BA18 CA28                       CA61 CB15 DA02 GA06

Claims (6)

[Claims] 1. A fixing body and a pressure body which are in pressure contact with each other to form a nip area and rotate, and a fixing body and a pressure body which are arranged in contact with an outer peripheral surface of the fixing body and receive power from a power source to generate heat to generate the fixing body. An external heating member that heats from the outside is provided, and the unfixed image is recorded by heating and pressing while a recording material carrying an unfixed image is nipped and conveyed by the fixing body and the pressure body in the nip region. A fixing device for fixing to a material, comprising adjustment means capable of adjusting electric power from a power source to an external heating member, for fixing an unfixed image fixable at a first temperature within a predetermined temperature range of the first temperature. One mode and a second mode for fixing the unfixed image that can be fixed at a second temperature having a lower limit temperature higher than the lower limit of the predetermined temperature range are set to be switchable. Transition from mode to second mode At this time, from the end of the fixing process in the first mode to the start of the fixing process in the second mode, or from the end of the fixing process in the first mode to the end of the fixing process in the second mode. A fixing device characterized in that the electric power per unit time from the power source to the external heating member can be made larger than that during the fixing process in the first mode in an arbitrary period. 2. The adjusting means starts the fixing process in the second mode from the fixing process in the first mode when the temperature of the fixing body at the end of the fixing process in the first mode is equal to or lower than a predetermined temperature. 2. The fixing according to claim 1, wherein the electric power value from the power source to the external heating member is set to be larger than that during the fixing process in the first mode during a certain period of time or until an end of the fixing process. apparatus. 3. The adjusting means, when the number of times the recording material is continuously passed through the nip area in the first mode is a predetermined number or more, from the end of the fixing process in the first mode to the fixing in the second mode. The power value from the power source to the external heating member is set to be larger than that during the fixing process in the first mode during an arbitrary period from the start of the process to the end of the fixing process. Item 3. The fixing device according to item 2. 4. The adjusting means changes from the end of the fixing process in the first mode to the second mode when the total time for the recording material to pass through the nip region in the first mode is a predetermined time or more. The electric power value from the power source to the external heating member is set to be larger than that during the fixing process in the first mode during an arbitrary period from the start of the fixing process to the end of the fixing process. The fixing device according to claim 3. 5. The unfixed image on the recording material fixed in the first mode is a monochrome image, and the unfixed image on the recording material fixed in the second mode is a color image. The fixing device according to any one of claims 1 to 4. 6. An image forming apparatus for recording an image on a recording material by a series of image forming processes, comprising the fixing device according to any one of claims 1 to 5. Forming equipment.