JP3313970B2 - Image forming device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an image forming apparatus such as an electrophotographic copying machine and a printer.

[0002]

2. Description of the Related Art Conventionally, an image fixing apparatus used in an image forming apparatus which transfers a toner image as an unfixed image onto a recording material and heat-fixes the toner image to form a permanent image has a structure as shown in FIG. It has become. In FIG. 2, reference numeral 1 denotes a fixing roller as a recording material conveying means. For example, a release resin layer 12 such as PFA or PTFE is provided on a core metal 11 such as aluminum or iron. Are provided to heat the fixing roller from the inside.

On the other hand, the pressing roller 2 is pressed against the fixing roller by a pressing means (not shown) to form a fixing nip N. The pressure roller includes, for example, a core layer 21 made of aluminum or iron, an elastic layer 22 made of heat-resistant silicone sponge rubber, and a release layer made of a resin having good mold release properties such as PFA and PTFE. 23 are formed.

The unfixed toner 7 is fixed on a recording material by being heated and pressed in a fixing nip.

Reference numeral 4 denotes an entrance guide, which conveys a recording material 6 on which unfixed toner is formed to a fixing nip and fixes the recording material 6 as a permanent image on the recording material.

Reference numeral 5 denotes a thermistor which is a temperature detecting sensor for detecting the surface temperature of the fixing roller, which is in contact with the surface of the fixing roller, and turns on / off the power supply to the heater so that the temperature of the surface of the fixing roller becomes constant. (The electric circuit that turns on and off the current is not shown). In a fixing device having a cleaning mechanism, the thermistor can be provided in the recording material passing area. However, in a fixing device having no cleaning mechanism as shown in FIG. ing.

The longitudinal dimension of the heater as the heat source is determined according to the maximum width of the recording material that can be fixed by the image fixing device, and the longitudinal dimension of the fixing roller is determined accordingly.
The maximum width of a recording material in a personal printer or the like is mainly divided into two types, one of which is A4 length (width 210 mm),
Alternatively, a heater using LETTRE length (width 216 mm) as the maximum width of the recording material, and the other A3 length (width 297 mm)
Is the largest width.

The rated capacity of the heater is determined by the maximum width of the recording material that can be fixed, the number of sheets that can be fixed per unit time (hereinafter referred to as “throughput”), the rated voltage, and the like. Also, when turning on / off the energization of the heater, the screen of the computer display on the same power supply line is instantaneously distorted, and in order to solve the problem that the lighting equipment is momentarily darkened,
It is necessary to reduce the rated power of the heater. As one of the means for this, while securing the amount of heat required for fixing,
In order to reduce the rated capacity of the heater, a measure such as dividing the heater into a plurality of heaters (generally, two heaters) is employed.

The heat distribution of the heater is determined so that the temperature distribution on the surface of the fixing roller becomes uniform during fixing of the recording material. With a single heater, the light distribution is such that the fixing roller is evenly heated over its length. In the two-heater system, one is a main heater that heats the center of the fixing roller in the longitudinal direction, and the other is a sub-heater that heats both ends of the fixing roller in the longitudinal direction. FIG. 3 shows a simple light distribution diagram of each heater.

The size of the recording material is not limited to one type. The recording material has the maximum width that can be fixed by the fixing device, the recording material having a width smaller than the maximum width, the length in the recording material conveyance direction, the thickness of the recording material, There are many different types of recording materials, and in order to secure fixing performance that satisfies all of them, in a fixing device that employs a two-heater system, energization of each heater is controlled by energization control according to the size of the recording material. Is going.

In such an image fixing apparatus, when the power of the image forming apparatus main body is turned on, the power supply to the heater is started, and the fixing roller is heated by turning on the heater. In this state, only the temperature of the fixing roller rises, the temperature difference from the temperature of the pressure roller increases, and when the roller pair rotates during image fixing, the pressure roller largely removes heat from the fixing roller. Instantaneously drops significantly, causing poor fixing.

Therefore, when the temperature of the fixing roller reaches a predetermined temperature, the fixing roller is rotated, and the pressure roller is also rotated by the rotation of the fixing roller. The fixing roller temperature is raised to the standby temperature while rotating the roller pair so that the difference between the fixing rollers becomes small. The period during which the fixing roller temperature is raised from a predetermined temperature to the standby temperature is referred to as pre-multiple rotation. Also, a certain predetermined temperature is referred to as a pre-multi-rotation start temperature.

By turning on the heaters in this way,
Preparing for image fixing while shortening the time required to enter the standby state.

The period from when the image forming apparatus is in a standby state until an image forming command is input and an electrostatic latent image is formed on the photosensitive member is referred to as pre-rotation. Since the pre-rotation is immediately before the image fixing, the heater is turned on and the fixing roller is rotated while the temperature of the fixing roller is raised to the fixing temperature required for the image fixing.

When image information for image formation is sent from a host computer or the like to the image forming apparatus in a state in which the fixing device can fix, the image information is converted into an image signal capable of laser oscillation, and laser oscillation is performed. An electrostatic latent image is formed on the photoreceptor. At this time, the time required for converting the image information into the image signal differs depending on the image information. That is, while complex image information, for example, an image such as a photograph, requires a long time, simple image information, for example, an image such as a document, is converted into an image signal in a short time.

Therefore, when a plurality of pages are continuously printed,
The distance between the recording materials differs depending on the image information.

If the succeeding image is simple, the interval between the recording materials is small, and the image forming apparatus can output the image at a predetermined throughput. The conveyance interval becomes large, and the output becomes impossible at a predetermined throughput of the image forming apparatus. For example, a printer capable of outputting 20 images per minute can output a simple image on a plurality of pages at a throughput of 20 images per minute. Can only be output with.

[0018]

In the above conventional example, the time during which the fixing device is in a standby state (standby state) (hereinafter referred to as a "start-up time") depends on the heat capacity of the core of the fixing roller and the rated output of the heater. It depends greatly. The startup time tends to be shortened as a user's need. However, the rated output of the heater must be obtained by subtracting the power required for the entire image forming apparatus from the rated power of the household indoor outlet, and the rated output of the heater cannot be increased excessively for the purpose of greatly shortening the startup time. Therefore, in order to reduce the heat capacity of the metal core and shorten the startup time, a method of reducing the thickness of the metal core is used.

However, although thinning the core metal is effective for shortening the start-up time, the heat capacity of the core metal is small. (Hereinafter, referred to as “overshoot”).

The overshoot causes the temperature of the fixing roller to be higher than the fixing temperature, and unfixed toner on the recording material is separated from the surface of the fixing roller and the recording material. After one rotation of the fixing roller, the image is fixed on the recording material and appears on the recording material as an offset. Since this offset is an offset that occurs when the surface of the fixing roller becomes too hot, it will be particularly referred to as a high-temperature offset.

FIG. 4 schematically shows how a high-temperature offset occurs. When the unfixed image is conveyed to the fixing device while the fixing roller is significantly higher than the fixing temperature (4-a), the toner is separated on the fixing roller and the recording material (4-b). ), The offset toner transferred onto the fixing roller is rotated one revolution of the fixing roller (fixing roller circumference:
L), the image is fixed on the recording material again (4-c).

However, if the recording material is started in anticipation of the overshoot, when the recording material enters the fixing nip, the fixing roller temperature does not reach the fixing-possible temperature, causing a fixing defect.

This problem can be solved by increasing the heat capacity of the cored bar by increasing the thickness of the cored bar of the fixing roller, and this is solved by the heat storage effect. Contrary to shortening time.

In a case where continuous printing of a plurality of pages from 1 to n pages is performed, the conveyance interval between recording materials differs depending on the amount of image information, and becomes large when the subsequent image information is complicated. However, even if the transport interval becomes longer, if a print command for a plurality of pages is input from a host computer or the like, the heater is controlled in the same manner as during the fixing operation, so that the transport interval of the recording material becomes longer. If the same energization control as during the fixing operation is performed in a state where the recording material does not exist in the fixing nip, the surface temperature of the fixing roller increases. When the subsequent recording material is conveyed to the fixing device in such a state, the high-temperature offset described above occurs in the subsequent recording material.

This becomes more apparent when the thickness of the cored bar is reduced and the heat capacity of the fixing roller is reduced for the purpose of shortening the startup time as described above.

An object of the present invention is to solve the above-mentioned problems in the conventional example, and to perform high-speed offset while preventing a high-temperature offset irrespective of the interval between recording materials when performing continuous printing of a plurality of pages. It is an object of the present invention to provide an image forming apparatus capable of ensuring excellent fixability.

It is a further object of the present invention to provide an image forming apparatus capable of suppressing a high-temperature offset without significantly increasing the rise time of the fixing means.

[0028]

In order to achieve the above object, an image forming apparatus according to the present invention comprises an image forming apparatus having a fixing unit for fixing an unfixed toner on a recording material by heating and pressing. A first heat source that generates a large amount of heat at a longitudinal central portion of the fixing unit, a second heat source that generates a large amount of heat at both longitudinal ends of the fixing unit, and a temperature detecting unit that detects a temperature of the fixing unit. Power supply control means for controlling power supply to the first and second heat sources such that the temperature detected by the temperature detection means becomes a target temperature,
The energization control unit includes a determination unit that determines whether a recording material conveyance interval is greater than a predetermined interval during execution of continuous printing of a plurality of pages. When it is determined that the temperature has also become large, in controlling the energization to the first and second heat sources so that the temperature detected by the temperature detecting means becomes the target temperature, the temperature rise in the central part of the fixing means is controlled. In order to suppress, the ratio of the amount of power supplied to the first heat source to the amount of power supplied to the second heat source is reduced as compared with the case where it is determined that the recording material conveyance interval is smaller than a predetermined interval. I do.

Preferably, the power supply control means turns off the power supply to the first heat source when it is determined that the recording material conveyance interval is larger than the predetermined interval.

Preferably, further, after the power is turned on,
When the temperature detected by the temperature detecting means is between a predetermined temperature and a standby temperature, the ratio of the amount of power supplied to the first heat source to the amount of power supplied to the second heat source is set to 1 /
When the print signal is input in the standby state, the ratio of the amount of power to the first heat source to the amount of power to the second heat source is set to 0 to 1/7.

[0031]

According to the present invention, it is determined whether or not the recording material conveyance interval is larger than a predetermined interval during execution of continuous printing of a plurality of pages, and the recording material conveyance interval is larger than the predetermined interval. If it is determined that the temperature of the fixing unit has reached the target temperature, the temperature of the fixing unit is controlled so that the temperature detected by the temperature detecting unit becomes the target temperature. In comparison with the case where it is determined that the recording material conveyance interval is smaller than the predetermined interval, the heat generation amount at both ends in the longitudinal direction of the fixing unit is large. The ratio of the amount of electricity supplied to the first heat source which generates a large amount of heat is reduced.

Therefore, the amount of heat generated in the central portion in the longitudinal direction of the fixing means is suppressed, so that the temperature rise in the central portion of the fixing means can be suppressed, the temperature distribution can be made uniform, and continuous printing of a plurality of pages can be performed. In addition, it is possible to secure necessary and sufficient fixability while preventing high-temperature offset regardless of the interval between the recording materials.

According to the invention, when the detected temperature is between the predetermined temperature and the standby temperature after the power is turned on,
The ratio of the amount of power to the first heat source to the amount of power to the second heat source is set to 1/7 to 1/3, and when a print signal is input in a standby state, the ratio is changed to the second heat source. The ratio of the amount of current supplied to the first heat source to the amount of current supplied is set to 0 to 1/7.

Therefore, the standby state can be set without extending the start-up time, and the temperature distribution of the fixing roller can be made uniform and overshoot can be suppressed.
It is possible to prevent the occurrence of high-temperature offset.

[0035]

Embodiments of the present invention will be described below with reference to the drawings.

A first embodiment of the present invention will be described with reference to FIG.

Since the configuration of the fixing device according to the first embodiment is the same as that of the conventional example shown in FIG. 2, the duplicate description will be omitted.

The fixing device described in the present invention is capable of passing a recording material up to a maximum length LETRE (width 216 mm). The conveyance is center reference conveyance in which the center of the recording material coincides with the center of the fixing roller. The light distribution is also symmetrical with respect to the central reference. A halogen heater is used as the heater, and the rated power is 750 W.

The fixing roller has a diameter of 25 mm and a thickness of 0.7.
mm of aluminum as a core metal and a thickness of 30
It covers a μm PFA tube.

The pressing roller covers an iron core bar having a diameter of 8 mm, an elastic layer made of silicon sponge rubber having a thickness of 6 mm, and further covers a PFA tube having a thickness of 40 μm as a release layer on the elastic layer. The pressure roller has a hardness of 38 degrees (500 g load by Asker C hardness tester) and is pressed against the fixing roller with a pressing force of 100 N (Newton) to obtain a fixing nip having a width of about 3.5 mm.

Using the image fixing device having such a configuration,
When performing continuous printing of a plurality of pages 1 to n, FIG.
When a print command is input from a host computer or the like, the image forming apparatus starts up the scanner device, determines the voltage to be applied to the transfer roller, and raises the fixing roller temperature to a feasible temperature for image formation. At the same time, power is supplied to the heater, and at the same time, in preparation for writing an electrostatic latent image on the photoconductor, image information from a host computer or the like is converted into an image signal capable of laser transmission. The time required for conversion to an image signal is determined by the amount of image information. When the amount of information such as a photographic image is large, the time required for conversion to an image signal is long, while the amount of information such as a document is small. In such a case, no time is required for conversion to the image signal.

Therefore, depending on the amount of subsequent image information, 1
, 2, 2-3, 3-4, ..., n-2 to n-1, n-1
The conveyance interval between the recording materials, that is, the n-th page, is determined. If the amount of image information on the m + 1 (m is arbitrary) +1 page is large and it takes time to convert the image signal into an image signal, then from page m to m
The transport interval up to page +1 increases. If the amount of image information on the (m + 1) th page is small and conversion to an image signal does not take a long time, the transport interval between the (m) th page and the (m + 1) th page is minimized. The conveyance interval between the predetermined recording materials of the image forming apparatus used in this embodiment is 50 mm.

In this embodiment, as described above, the conveyance interval between the recording materials is increased by the amount of image information, and in a state where the recording material does not exist in the fixing nip, the energization ratio to the heater is reduced to reduce the surface temperature of the fixing roller. By suppressing the rise, high-temperature offset generated in the subsequent recording material is prevented.

The on / off control of the heater is performed at the time of normal image fixing, that is, when the conveyance interval between recording materials is 50 mm, the thermistor detection temperature is set to + α ° C. with respect to the temperature control temperature: Ta ° C. Turn off the power to the heater when
On the other hand, in the present embodiment, when the interval between the recording materials is 51 to 79 mm, the same control as in the case of 50 mm is performed. However, when the temperature becomes 80 to 119 mm, the power supply to the heater is turned off when the thermistor detection temperature becomes −β ° C., and the power supply to the heater is turned on when the thermistor temperature reaches −2 ° C., and the thermistor detection temperature rises. If the recording material conveyance interval is 120 to 149 mm, control is performed so that the power supply to the heater is turned off when the recording material conveyance interval is 120 to 149 mm. When the recording material interval is 150 to 199 mm, the power supply to the heater is turned on when the temperature of the recording material reaches 150 ° C. -3 ℃ The power supply to the heater was turned off, and the power supply to the heater was controlled to be turned on when the temperature detected by the thermistor dropped to -5β ° C. Also, 200
When it was not less than mm, the power supply to the heater was turned off regardless of the thermistor detection temperature. Then, when the conversion of the image information into the image signal is completed and the writing of the electrostatic latent image on the photosensitive member is started, the energization of the heater is controlled at the time of normal fixing.

This is shown as a flow chart in FIG.

The recording material conveyance interval is determined by the time difference between the writing start timing of the electrostatic latent image corresponding to the preceding recording material and the writing start timing of the electrostatic latent image corresponding to the subsequent recording material, and the length of the recording material. I asked.

Table 1 shows the occurrence of high-temperature offsets when the energization control in this embodiment is used and when the energization control in the conventional example is used.

[0048]

[Table 1]

As can be seen from Table 1, in the conventional example, the high-temperature offset which occurs when the conversion process into the image signal takes a long time and the recording material conveyance interval becomes large is determined by controlling the energization control in this embodiment. If it is used, it becomes possible to prevent the occurrence of high-temperature offset even when the recording material conveyance interval becomes large. Further, when the core of the fixing roller is thin as in this example, the heat capacity of the fixing roller is small even if the temperature of the thermistor becomes −5β ° C., so that the recording material is fixed before entering the fixing nip. The roller surface temperature could be raised uniformly to Ta ° C., and no image fixing failure was caused.

Also, in this embodiment, when an image forming apparatus having an automatic double-sided printing mechanism performs double-sided printing, after the image on the front side is fixed, the recording material is inverted by the automatic double-sided printing mechanism, and In order to print, paper is fed again from the paper feeder,
After the image information is converted into an image signal, an image is formed on the recording material, and the image on the back surface is again fixed by the fixing device. It is of course effective to suppress the rise in the temperature of the front surface of the fixing roller and to prevent the high-temperature offset generated on the back surface by reducing the temperature.

A second embodiment of the present invention will be described with reference to FIG.

Note that, in the configuration of the fixing device according to the second embodiment, the description of the same parts as those of the conventional example shown in FIG. 2 will be omitted.

The fixing device described in the present embodiment has two types of heat sources, namely, a main heater as a central heating element and a sub-heater as an end heating element. The power supply control to the power supply is independently controlled according to the size of the recording material.

As a recording material, maximum A3 length (297 mm width)
The paper can be fed to the center, and the conveyance is center reference conveyance in which the center of the recording material coincides with the center of the fixing roller, and the light distribution of the heater also has a symmetric distribution with respect to the center reference. A halogen heater is used as the heater, and the rated power is 500 W for both the main and sub heaters.

The fixing roller has a diameter of 40 mm and a thickness of 1 mm.
Aluminum as core metal, 50μm thick as release layer
Of PFA tubes.

The pressure roller is composed of an elastic layer made of silicon sponge rubber having a thickness of 8 mm on an iron core having a diameter of 14 mm,
Further, a 50 μm-thick PFA tube is coated as a release layer on the elastic layer, the hardness as a pressure roller is set to 52 degrees (500 g load by Asker C hardness tester), and fixed by a pressing force of 20 N (Newton). By pressing against the roller, a fixing nip having a width of about 5 mm is obtained.

Using the image fixing device having such a configuration,
In the case of performing continuous printing of a plurality of pages 1 to n, as shown in FIG. 5 described above, when a print command is input from a host computer or the like, the image forming apparatus performs a scanner device for image formation. At the same time as starting up, determining the voltage to be applied to the transfer roller, energizing the heater to raise the fixing roller temperature to the feasible temperature, and preparing to write the electrostatic latent image on the photoconductor, Image information from a host computer or the like is converted into an image signal capable of laser emission. The time required for conversion to an image signal is determined by the amount of image information. For an image having a large amount of information such as a photographic image, it takes time to convert the image signal, whereas the amount of information such as a document is small. If it is an image, no time is required for conversion to an image signal.

Therefore, depending on the amount of subsequent image information, 1
, 2, 2-3, 3-4, ..., n-2 to n-1, n-1
The conveyance interval between the recording materials, that is, the n-th page, is determined. If the amount of image information on the m + 1 (m is arbitrary) +1 page is large and it takes time to convert the image signal into an image signal, then from page m to m
The conveying interval from the + 1st page to the + 1st page is widened, and when the amount of image information on the (m + 1) th page is small and no time is required for conversion into an image signal, the recording material conveying interval from the (m) th page to the (m + 1) th page is minimum. The predetermined interval between the recording materials in the image forming apparatus used in this example is 50 mm (minimum value).

As described above, in a state where the recording material is not present in the fixing nip, the power supply to the main heater is turned off and the surface temperature of the central portion of the fixing roller is determined in accordance with the recording material conveyance interval which varies depending on the image information amount. Is prevented from rising, thereby preventing a high-temperature offset generated in a subsequent recording material.

The power supply to the main and sub heaters is controlled by alternately turning on and off the main and sub heaters corresponding to the image size so as to obtain an optimum fixing property in accordance with the image size to be passed. The temperature is controlled so as to obtain a uniform temperature distribution. In the control in this embodiment, A
In the three vertical sizes, the main heater was alternately turned on for 500 msec and the sub heater was alternately turned on for 400 msec so that a uniform temperature distribution was provided over the length of the fixing roller. For other recording material sizes, the energization control is performed by determining the alternate lighting time of the main / sub heater that is optimal for each recording material size.

In the case where the A3 vertical size sheet is passed under such power supply control of the main and sub heaters, at the time of normal image fixing, that is, when the distance between the recording materials is 50 mm, the thermistor detection temperature is set. However, when the temperature becomes + δ ° C with respect to the temperature of the controlled temperature: Ta ° C, the power supply to the main / sub heater is turned off.
If power is supplied and the thermistor detection temperature does not reach + δ ° C., power is supplied to the sub-heater for 400 msec. Thus, 500 msec to the main heater and 4 to the sub heater
The thermistor detection temperature reaches + δ ° C. by alternately energizing for 00 msec, and the thermistor detection temperature becomes Ta ± δ.
The energization control is performed so as to be in the range of ° C.

When the interval between the recording materials is 50 mm, the above-described energization control is performed, which is a feature of this embodiment.
When the conveyance interval between the recording materials widened, the following energization control was performed. In the case of 51 to 89 mm, the same control as in the case of 50 mm was performed. However, in the case of 90 mm or more, when the thermistor detection temperature became −δ ° C., the main heater was not energized, and only 500 ms was supplied to the sub heater.
By alternately repeating non-energization of ec and energization of 400 msec, energization control to the sub-heater is performed so that the thermistor detection temperature is in the range of Ta ± δ ° C. 89m recording material
m, the thermistor detection temperature is in the range of Ta ± δ ° C. when only the sub-heater is turned on, and it is not possible to maintain the temperature necessary and sufficient for fixing over the length of the fixing roller. When the recording material is conveyed at intervals of 90 mm or more, the temperature control is performed so that the amount of heat taken by the recording material from the fixing roller and the pressure roller is reduced so that the thermistor detection temperature is in the range of Ta ± δ ° C. If performed, the surface temperature of the central portion of the fixing roller can reach a temperature necessary and sufficient for fixing before the recording material enters the fixing nip, and no fixing failure or the like is caused. Note that the recording material conveyance interval is 200 m as in the first invention.
m, the power supply to both the main and sub heaters was turned off regardless of the thermistor detection temperature.

This is shown in FIG. 9 as a flowchart.

In the energization control of this embodiment, the control of energization to the heater is performed at the same time as the start of writing the electrostatic latent image to the photosensitive member after the conversion of the image information into the image signal is completed.

The recording material interval was determined from the time difference between the timing of starting to write the image signal of the preceding recording material on the photoconductor and the timing of starting to write the image signal of the succeeding recording material on the photoconductor, and the length of the recording material.

Table 2 shows the occurrence of a high-temperature offset when the energization control is performed in the conventional example and when the energization control is performed in the present embodiment.

[0067]

[Table 2] As can be seen from Table 2, in the energization control of the conventional example, the conveyance interval between the recording materials is increased, and after the recording material is not present in the fixing nip, the high-temperature offset generated in the conveyed recording material. Can be prevented by using the power supply control of the heater used in the present embodiment. In the case where the thickness of the core metal of the fixing roller is thin as employed in the present embodiment, the heat capacity of the fixing roller is small, so that the recording material extends along the longitudinal direction of the fixing roller before entering the fixing nip. A uniform temperature distribution can be obtained, and no image fixing failure was caused.

Also, in this embodiment, the image forming apparatus having the automatic double-sided printing mechanism was effective in preventing the high-temperature offset generated on the back surface of the recording material when performing double-sided printing. is there.

A third embodiment of the present invention will be described with reference to FIG.

The fixing device according to the third embodiment has the same configuration as that of the fixing device according to the second embodiment, and a description thereof will not be repeated.

The fixing device described in this embodiment is capable of passing a recording material up to a maximum width of A3 (297 mm), is conveyed by the center reference where the center of the recording material coincides with the center of the fixing roller, and has a heater arrangement. The light distribution is also symmetrical with respect to the central reference. FIG. 3 shows the light distribution of the main heater and the sub heater. The heater uses a halogen heater, and the rated power is 500 W for both the main and sub heaters.

The fixing roller has a diameter of 40 mm and a thickness of 1 mm.
Aluminum as core metal, 50μm thick as release layer
Of PFA tubes.

The pressure roller has an elastic layer made of silicon sponge rubber having a thickness of 8 mm on an iron core having a diameter of 14 mm.
Further, a 50 μm-thick PFA tube is coated as a release layer on the elastic layer, the hardness as a pressure roller is set to 52 degrees (500 g load by Asker C hardness tester), and fixed by a pressing force of 200 N (Newton). By pressing against the roller, a fixing nip having a width of about 5 mm is obtained.

Using the image fixing device having such a configuration,
As shown in FIG. 7, the heater control when printing is performed by detecting the temperature of the temperature sensor when the main body power switch is turned on, and when the temperature is lower than the preceding multi-rotation start temperature T1, both the main and sub heaters are turned on. The fixing roller is heated as lighting.

When the detected temperature has reached the pre-multi-rotation start temperature, the main heater is turned on and off alternately for 100 msec, and the sub-heater is turned on. As described above, the heater control during the pre-rotation is performed until the detected temperature reaches the pre-rotation start temperature T2.

If a print signal is present,
As the heater control during the pre-rotation, the main heater is not turned on, and only the sub heater is turned on. Such heater control during the pre-rotation is performed until laser oscillation is performed in order to form a latent electrostatic latent image on the photoconductor.

This is shown in FIG. 10 as a flowchart.

If no print signal is input, heater control is performed to maintain the standby state. If a print signal is input, heater control during pre-rotation is performed to prepare for image fixing.

The start-up time and the occurrence of high-temperature offset when the fixing device is started up by performing such heater control are described in the present embodiment and the conventional heater control in which the thickness of the fixing roller is 1 mm and the conventional heater control is performed. Example and fixing roller thickness is 3mm
Table 3 shows the results of a comparison with a comparative example in which the heater control was performed for a long time.

The start-up time is the time from the room temperature of 15 ° C. (detection temperature of 15 ° C.) to the standby state, and the high-temperature offset is weighed at 60 g / m 2 or 75 g / m 2.
No. 2 recording material was used.

[0081]

[Table 3]

As described above, the present example can be started up without a large difference in the start-up time even when compared with the conventional example, and there is no occurrence of the high-temperature offset that occurs in the conventional example. Further, in the comparative example, although the high-temperature offset does not occur, the start-up time is about twice or more, which is contrary to the shortening of the start-up time which is a user's need.

As described above, according to the present embodiment, it is possible to achieve both a reduction in the start-up time and a prevention of high-temperature offset.

[0084]

As described above, according to the present invention,
In a case where continuous printing of a plurality of pages is performed, a necessary and sufficient fixing property can be secured while preventing high-temperature offset regardless of the interval between recording materials.

Further, it is possible to suppress the high-temperature offset without significantly increasing the rise time of the fixing means.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a fixing device according to a first embodiment of the present invention.

FIG. 2 is an explanatory diagram of a conventional fixing device.

FIG. 3 is a light distribution diagram of a main heater and a sub heater.

FIG. 4 is a diagram simply showing the occurrence of a high-temperature offset.

FIG. 5 is a diagram showing a flow of image information between the host computer and the image forming apparatus.

FIG. 6 is a schematic diagram of a fixing device according to a second embodiment.

FIG. 7 is a diagram showing a thermistor detection temperature and a state of a heater according to a third embodiment.

FIG. 8 is a flowchart according to the first embodiment;

FIG. 9 is a flowchart of a second embodiment.

FIG. 10 is a flowchart according to a third embodiment;

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 fixing roller 2 pressure roller 3 heater 4 entrance guide 5 temperature detection sensor (thermistor) 6 recording material 7 toner 11 core metal 12 release resin layer 21 core metal 22 elastic layer 23 release layer N fixing nip

────────────────────────────────────────────────── ─── Continuation of front page (56) References JP-A-54-43039 (JP, A) JP-A-7-219382 (JP, A) JP-A-3-185482 (JP, A) JP-A-6-218 11998 (JP, A) JP-A-5-134575 (JP, A) JP-A-6-11999 (JP, A) JP-A 8-69208 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G03G 13/20 G03G 15/20

Claims (3)

(57) [Claims] 1. An image forming apparatus having a fixing unit for fixing an unfixed toner on a recording material by applying heat and pressure to the first fixing unit .
A heat source and a second heat generating unit that generates a large amount of heat at both ends in the longitudinal direction of the fixing unit.
A heat source, a temperature detecting unit for detecting a temperature of the fixing unit, and a temperature detected by the temperature detecting unit as a target temperature.
Control the energization of the first and second heat sources so that
Power supply control means, the power supply control means, during the execution of continuous printing of a plurality of pages,
Whether the recording material conveyance interval is longer than the specified interval
The recording material conveyance interval is predetermined.
If it is determined that the interval exceeds
So that the temperature detected by the output means becomes the target temperature.
In controlling the energization of the first and second heat sources,
In order to suppress the temperature rise in the central part of the fixing means,
If it is determined that the recording material conveyance interval is smaller than the specified interval
As compared to the case, the second heat source
An image forming apparatus characterized in that the ratio of the amount of electricity to one heat source is reduced. 2. An image forming apparatus according to claim 1, wherein :
The energization control means may determine that the recording material conveyance interval is the predetermined interval.
An image forming apparatus characterized in that when it is determined that the first heat source has become larger , the power supply to the first heat source is turned off. 3. An image forming apparatus according to claim 1, wherein
In the apparatus, after the power is turned on, the temperature detected by the temperature detecting means is
When the temperature is between the predetermined temperature and the standby temperature,
Energizing the first heat source with respect to the amount of energizing the second heat source
The amount ratio is set to 1/7 to 1/3, and when a print signal is input in a standby state,
Energizing the first heat source with respect to the amount of energizing the second heat source
An image forming apparatus wherein the ratio of the amounts is 0 to 1/7 .