JP2974507B2 - Image forming device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine and a printer.

2. Description of the Related Art Some image forming apparatuses such as copying machines and printers include a fixing device for fixing an unfixed image. As a fixing device for fixing an unfixed image, a heat roller method is widely used in terms of efficiency and the like.

In this heat roller system, it has been considered to reduce the thickness of the heat roller by reducing the thickness of the core of the heat roller in order to reduce the weight of the apparatus and the wait time.

Although the weight of the heat roller can be reduced and the wait time can be reduced by reducing the thickness of the core of the heat roller as described above, the heat conduction by the core decreases and the temperature rise of the non-paper passing portion where the heat is not taken by the recording material. large.

Therefore, it is conceivable to take measures to increase the temperature of the non-sheet passing portion, for example, by switching the heater to be energized according to the size of the recording material and the number of continuous fixing operations.

Further, at the initial stage after the release of the weight, the apparatus is not sufficiently warmed and the fixing property is poor. Therefore, it is conceivable to increase the fixing temperature of the heat roller only at the initial stage.

[0007]

However, there is a difference in the temperature distribution of the heat roller before the start of fixing, that is, when the temperature at the end portion is high, substantially uniform, and when the central portion is high, the non-sheet passing portion rises. In spite of taking measures against the temperature, the temperature of the non-sheet passing portion may increase, or conversely, a fixing failure may occur due to insufficient temperature.

When the fixing temperature at the time of fixing the first sheet is increased, the fixing temperature remains high when the fixing is repeated one sheet at a time. Elimination of the temperature rise is delayed or worsened.

Therefore, if the fixing temperature is increased only at the initial stage after the release of the weight, defective fixing is likely to occur after long-term storage.

[0010]

According to the present invention, there is provided an image forming means for forming an image on a recording material, a heating member heated by a heater, and a pressing member for forming a nip with the heating member. A fixing unit for forming an image on a set number of recording materials, and terminating the image forming operation after outputting through the nip; and a storage unit for storing the size of the recording material and the number of output sheets. Fixing condition setting means for setting a condition, wherein the fixing condition setting means stores a new image forming operation within a predetermined time after the end of the previous image forming operation on the recording material of one size. The fixing condition is determined according to both the size and the number of output sheets of the recording material at the time of the previous image forming operation stored in the means and the size of the recording material at the time of the image forming operation on the recording material of one size this time. Set and last time When a new image forming operation is performed after a predetermined time or more after the image forming operation is completed, the size of the recording material during the current image forming operation is determined regardless of the size of the recording material during the previous image forming operation and the number of output sheets. The fixing condition is set by using

[0011]

【Example】

(First Embodiment) An embodiment of the present invention will be described below with reference to the drawings.

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

After the photosensitive drum 1 is uniformly charged by the charger 2, it is subjected to image exposure 3 to form an electrostatic latent image.

The electrostatic latent image is developed by the developing device 4 with powder toner.

The toner image on the photosensitive member is transferred to a recording material by a transfer charger 5.

The recording material onto which the toner image has been transferred is separated from the photoreceptor by a separation and neutralization unit 6, and then fixed by a fixing device 9.

Reference numeral 10 denotes a cassette for accommodating the recording material P. The cassette 10 is provided with an identification button 11 for identifying the size of the recording material.

The identification button 11 is detected by a recording material size detecting sensor 12, and the detected recording material size is sent to a control circuit 13.

The control circuit 13 also counts the number of continuous fixing.

FIG. 2 is an enlarged sectional view of the fixing device of this embodiment.

The recording material P carrying the unfixed toner image is guided by the entrance guide 14 and is fixed to the fixing roller 15 and the pressure roller 1.
It is led to a nip between 6 where it is fixed by heat and pressure.

The fixing roller 15 comprises a carbon steel core 17 having a thickness of 0.7 mm and a release layer 18 made of a fluororesin coated on the core 17.

Inside the fixing roller 15, two halogen heaters 19 and 20 having different light distributions are inserted.

The pressure roller 16 is provided with a silicone sponge rubber layer 22 on a metal core 21, and a release layer 23 made of fluororesin such as PFA on the silicon sponge rubber layer 22.
Is coated.

Reference numeral 24 denotes a temperature detection sensor for detecting the surface temperature of the fixing roller 15. This detection signal is input to the control circuit 13 and controls the timing of turning on and off the heaters 19 and 20.

Although carbon steel has sufficient strength, it has a smaller heat capacity than aluminum of the same amount, and in particular, has a significantly lower thermal conductivity than aluminum. Therefore, the fixing ability is inferior to that of the aluminum fixing roller, and the temperature rise in the non-sheet passing portion tends to be worse than that of the aluminum roller. However, in order to shorten the weight time by making the fixing roller thinner, carbon steel is very advantageous because aluminum roller has insufficient strength to prevent deformation due to pressure by the pressure roller.

Next, the light distribution of the halogen heaters 19 and 20 will be described.

FIG. 3 shows the light distribution of the main heater 19, and FIG.
Indicates a light distribution of the sub-heater 20.

The main heater has a light distribution that is enhanced at the center so that the temperature rise in the non-sheet passing area is suppressed even when a large amount of small size paper is passed at 700 W, and the sub heater has a maximum sheet passing width in the main heater. Since the edge of the paper does not fix, a 600 W heater with an enhanced light distribution at the edge was used.

When fixing small-size paper, the sub heater is turned off and only the main heater is turned on.

When fixing large-size paper, a method is employed in which two heaters emit light alternately and the light emission interval ratio is controlled. This control will be described with reference to FIGS. The control device turns ON / OF each of the main heater and sub heater.
The main heater is set to T1 seconds, where the temperature is controlled by blinking a single heater (FIG. 5).
By setting the sub-heaters alternately to light for T2 seconds, it is set so that a sheet having the maximum sheet passing width can be fixed well (FIG. 6). Further, by changing the light emission ratio, for example, by changing the main heater to T1-t seconds and the sub-heater to alternately turn on T2 + t seconds from the above example, it is possible to satisfactorily fix different sizes, for example, B4. It becomes possible.

This fixing device was incorporated into a copying machine of 30 cpm in FIG. 1 and a paper passing experiment was conducted. The temperature control temperature is usually 190 ° C., and when paper (small size paper) having a width equal to or less than the width of A4 is passed, control is performed to lower the temperature control temperature by 10 ° C. when 60 or more sheets are passed. The maximum paper passing width is the width of A3, and when paper with a width larger than the width of A4 is passed, the light emission interval T1: T2 between the main heater and the sub-heater is set to 4: 1, and the amount of heat at the end of the main heater The shortage is guaranteed by the sub-heater.

ON according to each paper size and number of paper passing
The / OFF timing configuration was set as shown in Table 1 below.

[0034]

[Table 1]

Here, when an image is formed on a set number of recording materials and output through the nip, the copying operation (image forming operation) is terminated, and for one minute after the completion of the copying operation, the fixing condition of the previous copying is determined by the control circuit 13. Stored in the internal memory.

In this embodiment, if the copying operation to the next one size recording material is started within one minute after the completion of the copying operation to the one size recording material, two copies other than the temperature control are performed. The light emission interval ratio of the heater is also changed continuously from the previous fixing operation. This is because, for example, if a large amount of A4R paper is passed, and if the temperature rise in the non-paper passing area becomes severe, B4R paper is passed and the sub-heater also emits light, it becomes difficult for the end temperature rise to return to a normal state. is there. Therefore, if B4R is passed in the next copying operation within one minute after passing the appropriate number of A4R sheets in the previous copying operation, the paper width in the previous copying operation in the memory and the paper width in the previous copying operation The setting is made such that the fixing is first performed only by the main heater according to the number of times of fixing (the number of sheets passed). B4
Since the temperature of the end portion is raised at the time when the paper is started to pass through the nip, the initial fixing is sufficient even with the main heater alone.

One minute after the end of the copying operation, the paper width and the number of times of the previous copying operation in the memory are reset, and at the time of a new copying, regardless of the paper width and the number of sheets passed during the previous copying operation, the current time. The fixing condition is set according to the paper size and the number of sheets passed during the copying operation.

Table 2 below shows the setting of fixing conditions when the next copy is started within one minute after the end of the copy in this embodiment.

[0039]

[Table 2] The vertical columns in Table 2 show the paper size and the number of sheets passed in the previous copying operation. The horizontal row in Table 2 shows the paper size when the copying operation is started within one minute after the end of the copying operation. The addition of the number of sheets in the table indicates that the number of passed sheets is counted by adding to the previous number of passed sheets.

For example, 20 sheets of B4R are passed within 1 minute after passing 80 sheets of A4R. The temperature is adjusted to 180 ° C. by the first paper passing. In the second paper passing, the rows A4R and 60 to 140 in the figure are checked, and control is performed at the intersection with the B4R column. Therefore, the temperature control temperature is 180 ° C. Until the paper is passed, the temperature is controlled only by the main heater. After 11 sheets, the main: sub ratio is controlled at 8: 1.

The above two tables are stored and the LUT (Lo
ok up Table), and when a new copy is to be made within one minute after the end of the copy, the temperature control temperature is determined with reference to this table.

FIG. 8 shows the operation of this embodiment.

According to the present embodiment, it is possible to prevent the non-sheet-passing portion from being heated up and to have a poor fixing under all conditions.

(Second Embodiment) This embodiment is provided with a mechanism for controlling the paper feeding speed or the time of the pre-rotation before the copying operation in addition to the fixing conditions. Of course, both may be provided.

When a large amount of small-size paper is passed through and a small-size paper is passed within a certain period of time in a state where the temperature rise at the end is severe, the pre-rotation time is extended longer than usual, and the temperature at the end is reduced. After the paper is sufficiently low, the next paper feed is performed. Alternatively, only at the beginning of the next copying operation, the sheet-passing speed can be reduced or the sheet-passing interval can be increased to suppress the temperature rise at the end.

Table 3 below shows the settings of this embodiment.

[0047]

[Table 3]

In the table, A4R is the previous paper passing size, the numbers are the previous number of sheets passed, and the second paper passing is also A4R. Of course, this control is not performed a fixed time after the end of the copying operation.

[0049]

[0050]

[0051]

[0052]

[0053]

[0054]

[0055]

[0056]

[0057]

[0058]

[0059]

[0060]

[0061]

[0062]

[0063]

[0064]

[0065]

[0066]

[0067]

[0068]

[0069]

As described above, according to the present invention, regardless of the temperature state of the heating element before fixing, the fixing operation can be performed without raising the temperature of the non-sheet passing portion or fixing failure.

[Brief description of the drawings]

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

FIG. 2 is a sectional view of a fixing device used in the embodiment of FIG.

FIG. 3 is a diagram showing a light distribution of a main heater.

FIG. 4 is a diagram showing an aperture distribution of a sub-heater.

FIG. 5 is a diagram showing on / off timings when one heater is used.

FIG. 6 is a time chart showing the ON / OFF timing of the heater according to the embodiment of the present invention.

7 is a time chart showing the heater on / off timing when the on / off timing shown in FIG. 6 is shifted by time t.

FIG. 8 is a flowchart illustrating control according to the first embodiment of the present invention.

[Explanation of symbols]

 15 Fixing roller 16 Pressure roller 19 Main heater 20 Sub heater 24 Thermistor

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Hisaaki Senba 3-30-2 Shimomaruko, Ota-ku, Tokyo Inside Canon Inc. (56) References JP-A-2-271378 (JP, A) JP-A-2 JP-146074 (JP, A) JP-A-2-239273 (JP, A) JP-A-2-254481 (JP, A)

Claims (3)

(57) [Claims] An image forming unit for forming an image on a recording material, a heating unit heated by a heater, and a fixing unit including a pressing member for forming a nip with the heating unit. An image forming apparatus for forming an image on a recording material and terminating the image forming operation after outputting through a nip, comprising: a storage unit for storing a recording material size and the number of output sheets; and a fixing condition setting unit for setting a fixing condition. When a new image forming operation is performed within a predetermined time after the end of the previous image forming operation on the recording material of one size, the fixing condition setting unit is configured to perform the recording operation of the previous image forming operation stored in the storage unit. The fixing conditions are set in accordance with both the size and output number of the recording material and the size of the recording material at the time of the image forming operation on the recording material of one size this time, and a predetermined time or more after the end of the previous image forming operation New When performing a suitable image forming operation, the fixing condition is set according to the size of the recording material during the current image forming operation regardless of the size of the recording material during the previous image forming operation and the number of output sheets. Forming equipment. 2. The image forming apparatus according to claim 1, wherein said apparatus further comprises a temperature adjusting means for maintaining said heating element at a predetermined fixing temperature, and said fixing condition setting means sets a fixing temperature. apparatus. 3. The heating element has first and second heaters having different light distributions, and the fixing condition setting means sets a power supply condition to the first and second heaters. The image forming apparatus according to claim 1.