JPH0954516A - Fixing device - Google Patents

Abstract

(57) Abstract: The present invention has a large fixing temperature ripple, defective fixing due to a decrease in fixing temperature, hot offset due to an increase in fixing temperature, damage to parts of a fixing device, and shortened life of a fixing heater. The problem is to solve the problem. According to the present invention, a fixing temperature control means 27 forcibly starts energization of a fixing heater immediately before the start of scanning an original by an optical scanner even if the fixing temperature of the fixing roller is higher than a set temperature.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a copying machine, a printer,
The present invention relates to a fixing device used in an optical image forming apparatus having an optical scanner such as a facsimile.

[0002]

2. Description of the Related Art An image forming apparatus such as a copying machine, a printer or a facsimile does not have an image pickup device such as a CCD but illuminates an original with an illumination lamp and irradiates the reflected light on an image carrier composed of a photoconductor. 2. Description of the Related Art There is an optical image forming apparatus including an optical scanner that exposes an original image on an image carrier by scanning an original, and a fixing device. Here, the fixing device fixes the toner on the sheet passing between them by pressing and heating by the pressure roller and the fixing roller, heats the fixing roller by the fixing heater, and detects the temperature by, for example, a thermistor, There is a thermal fixing device that controls the fixing temperature of the fixing roller to a predetermined temperature by performing a normal energization control on the fixing heater based on the temperature detected by the thermistor by the fixing temperature control means.

In this optical image forming apparatus, for example, a copying machine, when energization of the fixing heater is started during scanning of an original by the optical scanner, a voltage drop of the power supply voltage occurs at the moment when the energization starts, but at that moment. In addition, the illumination lamp of the optical scanner becomes dark, and a problem occurs that a band-shaped black portion appears on the copy. Therefore, the fixing temperature control means normally does not start energizing the fixing heater anew even when the fixing temperature of the fixing device becomes low during the scanning of the document by the optical scanner. Further, recently, a thermal fixing device has adopted a thin roller as a fixing roller in order to shorten the rising time.

In Japanese Patent Laid-Open No. 5-150684, in a temperature control device for a fixing device for controlling energization / de-energization of a heater according to the output of the temperature detection device, the temperature of the fixing device detected by the temperature detection device is detected. Of the control target temperature is higher or lower than the control target temperature for each predetermined period, a counting means for counting the number of times the determination means determines that the temperature is high and a number of times the temperature is determined to be low, and the counting means. When the number of times determined to be high reaches a predetermined value, energization to the heating heater is stopped, and when the number of times determined to be low reaches a predetermined value, the heating heater is energized, and a temperature ripple is reduced. A temperature control device for a fixing device is described.

[0005]

Recently, the thermal fixing device has been
Since a thin roller is adopted as the fixing roller in order to shorten the rising time, the heat capacity of the fixing roller becomes small, the rising speed becomes fast, and the temperature ripple of the fixing roller tends to become large. As described above, the optical image forming apparatus does not start energizing the fixing heater anew even when the fixing temperature of the fixing device becomes low during scanning of the original by the optical scanner. A with a paper passing width of a minute
The fixing temperature of the fixing roller is considerably lowered during fixing of the toner on the three size sheets, which causes defective fixing.

Further, the temperature control device for the fixing device may be effective in reducing the temperature ripple in a copying machine using a printer or CCD in which the fixing heater (heating heater) can be freely turned on and off. However, it is effective in the optical image forming apparatus due to the restriction that the energization of the fixing heater is not newly started even when the fixing temperature of the fixing device becomes low during the scanning of the document by the optical scanner as described above. is not.

Further, in the thermal fixing device, there is always a temperature ripple of the fixing roller, and if the fixing heater is energized, the fixing temperature is being raised and the fixing temperature is high (fixing heater). If the fixing heater is forcibly energized (just before turning off), the fixing temperature will rise to a high temperature, which will cause hot offset.In severe cases, the fixing bearing supporting the fixing roller and the sheet from the fixing roller will be separated. As a result, the fixing and separating claw is damaged.

Further, the fixing temperature control means normally sees the temperature data from the thermistor in the unit of 0.01 to 0.5 seconds, but the temperature data from the thermistor also has a ripple. However, even if the fixing roller linearly moves up, the temperature data of the thermistor at 0.01 second intervals may happen to rise or fall as shown in FIG. 7 due to noise pickup.

Therefore, even if the temperature data and the temperature gradient from 0.01 second before the thermistor are seen, it cannot be known whether the true fixing temperature is rising or falling, and the true fixing temperature is erroneously determined. I have something to do. For example, in FIG.
In the above, temperature data obtained by converting the resistance value of the thermistor at time A ₁ is T ₁ ℃, temperature data obtained by converting the resistance value of the thermistor at time (A ₁ +0.01) seconds is T ₂ ℃
Then, if T ₁ > T ₂ and the gradient of the fixing temperature is lowered, the fixing temperature may be erroneously determined by the temperature data from the thermistor.

Further, when the fixing heater is finely divided, for example, 0.
If it is turned on and off every 1 second, the life of the fixing heater is extremely shortened. The present invention can reduce the ripple of the fixing temperature to reduce the fixing temperature, resulting in poor fixing, hot offset due to the increase in the fixing temperature, and damage to the fixing device parts.
An object of the present invention is to provide a fixing device capable of preventing the fixing heater from having a short life.

[0011]

In order to achieve the above object, the invention according to claim 1 is used in an optical image forming apparatus having an optical scanner for scanning an original and passes between a pressure roller. A fixing roller that fixes the toner on the sheet, a fixing heater that heats the fixing roller, and a normal energization control for the fixing heater to control the fixing temperature of the fixing roller to scan the original of the optical scanner. In a fixing device having a fixing temperature control unit that does not start a new energization of the fixing heater, the fixing temperature control unit determines that the fixing temperature of the fixing roller is higher than a set temperature immediately before the start of document scanning of the optical scanner. Also forcibly starts energization of the fixing heater.

According to a second aspect of the present invention, in the fixing device according to the first aspect, the fixing temperature control means energizes the fixing heater after a fixed time has elapsed since the energization of the fixing heater was forcibly started. The control is switched to normal energization control.

According to a third aspect of the present invention, in the fixing device according to the first aspect, the fixing temperature control means performs the fixing only when the fixing temperature gradient of the fixing roller is lowered immediately before the start of scanning the original by the optical scanner. The energization of the heater is started.

According to a fourth aspect of the present invention, in the fixing device according to the third aspect, the fixing temperature control means sets the fixing temperature of the fixing roller 0 to 1 second before the start of scanning the original by the optical scanner, and Further, the fixing temperature gradient of the fixing roller is examined at the fixing temperature of the fixing roller 0.2 to 1.5 seconds before.

According to a fifth aspect of the present invention, in the fixing device according to the first aspect, the fixing temperature control means forcibly starts energization of the fixing heater immediately before the start of scanning the original by the optical scanner, and the fixing heater. Is continuously lit for at least 0.5 seconds.

According to a sixth aspect of the present invention, in the fixing device according to the first aspect, the fixing temperature control means has the fixing temperature gradient of the fixing roller is lowered immediately before the start of scanning the original by the optical scanner, and the fixing roller is provided. The energization of the fixing heater is started only when the fixing temperature is not higher than the predetermined temperature.

According to a seventh aspect of the present invention, in the fixing device according to the first aspect, the fixing temperature control means has the fixing temperature gradient of the fixing roller is lowered immediately before the start of scanning the original of the optical scanner, and the fixing roller is provided. The fixing heater is started to be energized only when the fixing temperature is not higher than the sum of the set temperature and the predetermined temperature which is higher than the predetermined temperature. The smaller of 10 ° C. and the product of the temperature drop of the fixing roller per second during the rotation and the time from the arrival of the sheet in the fixing device to the turning on of the fixing heater. And the lowering temperature of the fixing roller per second and the time from when the sheet comes to the fixing device to when the fixing heater can be turned on. When not it is an 5 the predetermined value.

[0018]

2 and 3 show an embodiment of the present invention. This embodiment is an embodiment of the invention according to claims 1 to 5, and is an optical image forming apparatus including an electrophotographic apparatus such as a facsimile having an optical scanner, a printer, a digital copying machine, an optical copying machine, or the like. Is used to apply at least heat and pressure to the toner on the transfer paper sheet to fix the toner on the transfer paper.

The fixing device 10 of this embodiment includes a fixing roller 11 which is heated and rotationally driven, and the fixing roller 1.
1. A fixing drive unit that rotationally drives 1 and a pressure roller 12 that is an elastic roller that is pressed against and driven by the fixing roller 11.
A fixing heater 13 for heating the fixing roller 11, a fixing roller pressure contact unit 14 including a pressure spring for pressing the pressure roller 12 against the fixing roller 11, and a bracket 24.
Is supported by the fixing roller 11 and abuts on the fixing roller 11.
It has a temperature detecting element 15 including a thermistor for detecting the surface temperature (fixing temperature) of the sheet 1.

The length of the fixing roller 11 is 240 to 310 mm in an apparatus for passing A4 transfer paper, and 320 to 390 mm in an apparatus for passing A3 transfer paper. Also,
The fixing roller 11 has a diameter of φ10 to φ40 mm,
Material is aluminum tube (A5052, A5056, A6
063, A3003 or an alloy based on it, having a wall thickness of 0.4 to 1.0 mm, a stainless steel pipe (SUS304, SUS430, SUS416 or an alloy based on this) or a carbon steel pipe (STKM1)
1, STKM12) having a wall thickness of 0.25 to 0.5 mm is used.

The fixing roller 11 is coated with a fluororesin having a length of 218 to 258 mm in an apparatus for passing A4 transfer paper, and is 299 to 339 mm in a length for an apparatus passing A3 transfer paper. It has a coating. The type of the fluororesin includes any one of a tetrafluoroethylene resin, a perfluoroalkoxy resin, a perfluoroethylenepropylene resin, or a mixed resin thereof.

The pressure roller 12 has a diameter of φ10 to φ40.
The thickness of the rubber is 3 to 10 mm. The pressure roller 12 is an elastic roller made of silicone rubber, and the rubber hardness of the silicone rubber is the same between JIS A8 and JIS 40. In a device for passing A4 transfer paper, the length of the rubber portion is small. The length of the rubber portion is 305 to 340 mm in a device that passes 220 to 240 mm and A3 transfer paper. The presence or absence of fluororesin on the rubber of the pressure roller 12 does not matter.

A halogen heater is used as the fixing heater 13, and 350 W to 90 W is used in an apparatus for passing A4 transfer paper.
0W, 500W for a device that passes A3 transfer paper
~ 1200W is used. Example 1 of this embodiment
0, specifically, the fixing roller 11 has, for example, a diameter of 30 mm, a carbon steel pipe STKM 11 of a material, a wall thickness of 0.4 mm, a surface mainly made of perfluoroalkoxy resin, and a length of 365 mm. ~ 375 mm. The pressure roller 12 has, for example, a diameter of 25 mm, a rubber wall thickness of 0.45 to 5 mm, and a rubber portion length of 310 to 320.
mm. As the fixing heater 13, a 900 W heater is used, for example.

In the image forming apparatus including, for example, an optical copying machine in which the tenth embodiment is used, the copying operation is started by turning on the copy button, and first, the drum-shaped photosensitive member 16 as the image carrier is set. After being rotated by the driving means and the photoconductor 16 is uniformly charged by the charging means, the document on the document table is illuminated by the light source including the illumination lamp of the optical scanner, and the reflected light is transmitted through the optical system to the photoconductor. 16 is irradiated, and the document on the platen is scanned by the movement of the optical scanner.
The original image is exposed to form an electrostatic latent image.

In the digital copying machine, the optical scanner illuminates a document on the document table with a light source including an illumination lamp, irradiates the reflected light to an image pickup device such as a CCD through an optical system, and the optical scanner. The document image is read by scanning the document on the document table by moving the document. In this case, the image signal from the image pickup device is converted into an optical signal by an exposure unit such as a laser writing device after being subjected to a predetermined image processing in an image processing unit, and is irradiated onto the photoconductor 16 to expose the original image. Then, an electrostatic latent image is formed on the photoconductor 16.

The electrostatic latent image on the photoconductor 16 is developed by the developing means to become a toner image, which is transferred by the transfer means 18 onto the transfer paper 17 fed from the paper feeding device. The transfer paper 17 is guided and conveyed by the guide plate 19, and is guided between the fixing roller 11 and the pressure roller 12 by the fixing entrance guide plate 20 in the fixing device 10. The fixing roller 11 and the pressure roller 12 are the transfer paper 17
The toner on the transfer paper 17 is fixed to the transfer paper 17 by applying pressure and heat to the upper toner. The transfer paper 17 that has passed between the fixing roller 11 and the pressure roller 12 has an exit guide plate 21.
And is discharged to the outside.

The fixing separation plate 22 separates the transfer paper 17 from the fixing roller 11. The fixing roller 11 is rotatably supported by a fixing bearing 23, and is rotationally driven by a fixing driving unit via a fixing gear 24. As shown in FIG. 1, the fixing heater 13 is heated by the fixing heater drive circuit 25 when AC power is supplied thereto, and the fixing heater drive circuit 25 and the fixing drive means 26 are controlled by a control section 27 which also serves as a fixing temperature control means. . The controller 27 converts the temperature detection signal input from the thermistor 15 into a digital signal by the A / D converter, and based on the digital signal, the fixing heater drive circuit 2
5 is controlled to control the energization of the fixing heater 13. Also,
The control unit 27 controls each unit of the copying machine based on an input signal from each sensor or the operating unit in the copying machine to start the above-described copying operation by turning on the print button and continuously for the number of sheets set by the operating unit. To repeat.

FIG. 4 shows a fixing temperature control flow of the control unit 27, and FIG. 10 shows an example of the fixing temperature change. Control unit 27
Checks the input signal from the copy button, and when the copy button is turned on, in step S1, the thermistor 15
The temperature data from is checked to determine whether or not the fixing temperature gradient of the fixing roller 11 has decreased. If the fixing temperature gradient has decreased, the fixing heater drive circuit 25 is forced to the fixing heater 13 in step S2. Is started, the optical scanner is moved forward in step S3 to start scanning the original, and then the process proceeds to step S4. Here, the control unit 27
Returns the optical scanner to the home position after the document scanning by the forward movement of the optical scanner is completed.

If the fixing temperature gradient is not lowered, the control unit 27 advances the optical scanner in step S7 to start the document scanning, and then proceeds to step S4.
In step S4, the control unit 27 checks the temperature data from the thermistor 15 to scan the temperature data from the thermistor 15 to set the fixing temperature of the fixing roller 11 while the document is being scanned by the forward movement of the optical scanner (except when the optical scanner returns to the original position). Even when the temperature is close to the temperature T ° C., the fixing heater 13 is prohibited from being energized and the fixing heater driving circuit 25 is stopped from being energized (the fixing heater 13 is allowed to continue energizing), and the fixing temperature of the fixing roller 11 becomes ( When the temperature reaches T + α) ° C, the fixing heater drive circuit 25
Then, the heater normal control (scan mode) of stopping the energization of the fixing heater 13 is performed. Where α is 0 to 5 ° C
It is.

When the scanning of the document by the forward movement of the optical scanner is completed in step S5, the control section 27 checks the temperature data from the thermistor 15 in step S6 to set the fixing temperature of the fixing roller 11 to the set fixing temperature T ° C. The heater normal control in which the fixing heater driving circuit 25 energizes the fixing heater 13 and the fixing heater driving circuit 25 stops the energization of the fixing heater 13 when the fixing temperature of the fixing roller 11 reaches (T + α) ° C. Do (general). The control unit 27 performs the process of step S5 until the next print button is turned on.

Here, the energization of the fixing heater 13 is stopped when the fixing temperature reaches (T + α) ° C., but the temperature at which the energization of the fixing heater 13 is turned on (started) and the energization of the fixing heater 13 are turned off. Even if the temperature is the same (stopped), the response of the thermistor 15 is delayed, and it takes some time from when the fixing heater 13 is turned on until the fixing temperature rises, so that the fixing temperature is normally controlled. ,
As shown in FIG. 5, when the fixing heater 13 is turned on when the fixing temperature gradient is lowered, the fixing temperature is then 2 to 3 ° C.
Go down.

As described above, the control unit 27 solves the above-mentioned reason, that is, the problem that the illumination lamp of the optical scanner is temporarily darkened at the start of energization of the fixing heater and a band-like black portion is generated in the copy. To prevent this, a new fixing heater 13 is
It is possible to continue energizing the fixing heater 13 while the fixing heater 13 is being energized, and stop energizing the fixing heater 13 to the fixing heater drive circuit 25 when a predetermined temperature (T + α) is reached. (Normal heater control (scan mode) in step S4).

However, in such a heater normal control (scan mode), when the size of the transfer paper is A3 and the document scanning time by the optical scanner becomes long as shown in FIG. 5, the fixing temperature of the fixing roller 11 becomes high. The temperature drops extremely and the temperature becomes lower than the temperature at which fixing failure occurs. This is particularly remarkable in a low temperature environment such as 10 ° C. Therefore, in order to eliminate fixing failure, the control unit 27 forcibly energizes the fixing heater 13 to the fixing heater driving circuit 25 immediately before the original scanning period by the optical scanner in which the new fixing heater 13 is not energized. By making it start, it is expected that the fixing temperature will drop and it will be raised.

In this case, if the energization of the fixing heater 13 is started when the normal fixing temperature ripple is high as shown by the broken line in FIG. 6, the fixing temperature becomes considerably high, which causes a hot offset. This is not desirable because it will cause damage to 23 and the fixing separation claw 24. Therefore, the control unit 27 determines in step S1 whether or not the fixing temperature gradient of the fixing roller 11 is lowered. Only when the fixing temperature gradient is lowered, the control unit 27 is forcibly fixed to the fixing heater drive circuit 25 in step S2. Heater 1
3 is started, and if the fixing temperature gradient is not lowered, the fixing heater 13 is not forcibly started to be energized. Therefore, if the fixing temperature gradient is not lowered, the fixing temperature will not be greatly increased as shown by the solid line in FIG.

In step S1, the control section 27 checks (sees) the fixing temperature gradient with the two temperature data from the thermistor 15 immediately before the scanning of the original by the optical scanner, but in order to see the true fixing temperature gradient, the control section 27 sees step S1. "Fixing temperature 0 to 1 second before the start of document scanning by the optical scanner"
÷ See the fixing temperature gradient at "fixing temperature 0.2 to 1.5 seconds (preferably 0.2 to 1 second) before the fixing temperature". If the value of the fixing temperature gradient is smaller than 1, the control unit 27 determines that the fixing temperature gradient is lower, and if the value of the fixing temperature gradient is greater than 1, the fixing temperature gradient is higher. to decide.

When the control unit 27 determines in step S1 that the fixing temperature gradient is lowered and forces the fixing heater drive circuit 25 to energize the fixing heater 13 in step S2, the controller 27 of the fixing heater 13 operates. The time during which the power is forcibly and continuously performed is set to at least 0.5 seconds or more. This is to prevent the fixing heater 13 from having a short life. When the fixing heater is energized for 0.5 seconds and then stopped for 0.5 seconds, the life until the fixing heater is cut off and the energization of the fixing heater is 0.1
The latter is 1/3 of the former with respect to the life until the fixing heater is cut off when the operation of performing the operation for 2 seconds and then stopping for 0.1 second is repeated.

As described above, this embodiment is an embodiment of the invention described in claim 1 and is used in an optical image forming apparatus having an optical scanner for scanning an original, and is used together with the pressure roller 12. The fixing roller 11 for fixing the toner on the sheet 17 made of a transfer paper passing through the space, the fixing heater 13 for heating the fixing roller 11, and the fixing heater 1.
3 is subjected to normal energization control to control the fixing temperature of the fixing roller 11 and does not start new energization of the fixing heater 13 at the time of scanning an original by the optical scanner. In the apparatus, the fixing temperature control means 27 forcibly starts the energization of the fixing heater 13 even if the fixing temperature of the fixing roller 11 is higher than the set temperature immediately before the start of scanning the original by the optical scanner, so that the fixing roller is thin. Even in this case, the fixing temperature does not largely drop during the fixing operation, and the fixing failure due to the drop of the fixing temperature can be prevented.

Further, the present embodiment is an embodiment of the invention described in claim 2, and in the fixing device according to claim 1, the fixing temperature control means 27 is forced to the fixing heater 13.
Since the energization control of the fixing heater 13 is switched to the normal energization control after a lapse of a certain time after the energization of the fixing roller 13 is started, even if the fixing roller is thin, the fixing temperature may largely drop during the fixing operation. In addition, it is possible to prevent defective fixing due to a decrease in fixing temperature.

Further, the present embodiment is an embodiment of the invention described in claim 3, and in the fixing device according to claim 1, the fixing temperature control means 27 is a fixing roller immediately before the start of scanning the original of the optical scanner. Since the energization of the fixing heater 13 is started only when the fixing temperature gradient of 11 is lowered, it is possible to prevent the fixing temperature from becoming such a high temperature that hot offset occurs and the fixing device parts are damaged. It is possible to prevent hot offset and damage to fixing device parts.

Further, the present embodiment is an embodiment of the invention described in claim 4, and in the fixing device according to claim 3, the fixing temperature control means 27 is 0 to 1 for starting the scanning of the original of the optical scanner. Since the fixing temperature gradient of the fixing roller 11 is examined at the fixing temperature of the fixing roller 11 before 2 seconds and the fixing temperature of the fixing roller 11 at 0.2 to 1.5 seconds before that, an appropriate time interval is set. Thus, the fixing temperature gradient can be seen, and erroneous determination of the fixing temperature gradient can be prevented.

Further, the present embodiment is an embodiment of the invention described in claim 5, and in the fixing device according to claim 1, the fixing temperature control means 27 is forcibly forced immediately before the start of the original scanning of the optical scanner. Since the fixing heater 13 is started to be energized and the fixing heater 13 is continuously turned on for at least 0.5 seconds or more, the fixing heater can be energized for a minimum required time and the life of the fixing heater is shortened. Can be prevented.

FIG. 8 shows a fixing temperature control flow of the controller in another embodiment of the present invention. This embodiment is an embodiment of the invention according to claim 6. In this embodiment, in the above embodiment, the control unit 27 checks the input signal from the copy button as shown in FIG. 8 and when the copy button is turned on, checks the temperature data from the thermistor 15 in step S8. It is determined whether the fixing temperature of the fixing roller 11 is higher than a predetermined temperature (set temperature + A (5 to 10) ° C.) immediately before the scanning of the original by the optical scanner, and the fixing temperature is higher than the predetermined temperature. If not, the process proceeds to step S1, and if the fixing temperature is higher than the determined temperature, the process proceeds to step S7.

In this way, when the energization of the fixing heater 13 is forcibly started immediately before the start of the original scanning by the optical scanner, the fixing temperature of the fixing roller 11 immediately before the start of the original scanning is set to a predetermined temperature (set temperature + A ( 5-10)
If the condition that the temperature is not higher than (° C) is added, the fixing temperature will be higher (the temperature ripple will be larger).
Can be prevented.

Therefore, this embodiment is characterized by claim 6.
In the fixing device according to claim 1, which is an embodiment of the described invention, the fixing temperature control unit 27 has a fixing temperature gradient of the fixing roller 11 immediately before the start of document scanning of the optical scanner, and The fixing heater 1 only when the fixing temperature is not higher than the predetermined temperature.
Since the energization of No. 3 is started, it is possible to prevent the fixing temperature from touching a high temperature by looking at the fixing temperature at that time in addition to the fixing temperature gradient, and it is possible to reduce the temperature ripple.

In the above embodiment, the fixing roller 11
Becomes thinner, the temperature ripple tends to increase depending on whether or not the pressure roller 12 is warm. Therefore, in the embodiment of the invention described in claim 7, in the embodiment of the invention described in claim 6, the controller 27 rotates the fixing roller 11 to the fixing drive means 26 while the fixing heater 13 is off. The temperature data from the thermistor 15 is driven to check the fixing temperature drop of the fixing roller 11 and the above "determined temperature (set temperature + A ° C)"
By setting A ° C. in the following manner, finer fixing temperature control is performed and the ripple of the fixing temperature is reduced.

That is, the controller 27 controls the fixing heater 13
When the fixing roller 11 is turned off and the fixing roller 11 is rotationally driven, “Fixing roller fall temperature per second × fixing device 10”
The temperature is calculated by calculating "the time from when the transfer paper comes between the fixing roller 11 and the pressure roller 12 to when the fixing heater 13 can be turned on (when the optical scanner finishes scanning the original)". "The smaller value of this temperature and 10 ° C, and the larger value of this value compared to 5 ° C"
Is referred to as A above. However, the control unit 27 controls the above “fixing roller fall temperature per second × fixing roller 11 of the fixing device 10”.
Further, when there is no temperature data obtained by calculating "time from when the transfer paper comes between the pressure roller 12 and when the fixing heater 13 can be turned on", A = 5.

The control unit 27 resets the value of A after completion of the copying operation and sets the initial value to A = 5. The control unit 27
Specifically, A is calculated by the following formula (see FIG. 9). A = (fixing temperature immediately after the start of rotation of the fixing roller 11−0.
(Fixing temperature after 5 seconds) × 2 × {(length of transfer paper (420 mm for A3 transfer paper))-(distance between transfer position of transfer means 18 and fixing position of fixing device 10)-(photosensitive Distance between light irradiation position on body 16 and transfer position)} /
(Linear Velocity of Fixing Roller 11) The “fixing temperature after 0.5 seconds” in this equation may be the fixing temperature after 1 second, in which case the above “× 2” is not necessary. In the heater normal control (scan mode),
The fixing heater 13 cannot be newly turned on until the rear end of the transfer sheet comes to a position (on the side of the paper feeding device) closer to the transfer position than the transfer position by the distance between the light irradiation position on the photoconductor 16 and the transfer position. .

As described above, this embodiment is characterized by claim 7.
In the fixing device according to claim 1, which is an embodiment of the described invention, the fixing temperature control unit 27 has a fixing temperature gradient of the fixing roller 11 immediately before the start of document scanning of the optical scanner, and The energization of the fixing heater 13 is started only when the fixing temperature is not higher than the sum of the set temperature and the predetermined temperature higher than the predetermined temperature.
When the fixing heater 13 is off and the fixing roller 11 is rotating, the predetermined temperature is the temperature drop of the fixing roller 11 per second and the fixing heater 13 can be turned on after a sheet arrives in the fixing device. Product of time to become and 10
The lower value of 5 ° C. and the higher value of 5 ° C. are set, and the temperature drop of the fixing roller 11 per second and the time from when the sheet arrives at the fixing device to when the fixing heater 13 can be turned on. When there is no such value, the predetermined value is set to 5. Therefore, by checking the drop in the fixing temperature and controlling the energization of the fixing heater in consideration of this, a more detailed fixing temperature control can be performed, and in any state It is possible to prevent the fixing temperature from touching the high temperature side according to the state, and to reduce the ripple of the fixing temperature.

[0049]

As described above, according to the first aspect of the present invention, the toner on the sheet passing between the pressure roller and the optical image forming apparatus having the optical scanner for scanning the original is removed. A fixing roller for fixing, a fixing heater for heating the fixing roller, a normal energization control for the fixing heater to control the fixing temperature of the fixing roller, and a new heater for the fixing heater at the time of scanning an original by the optical scanner. In the fixing device having a fixing temperature control unit that does not start the energization, the fixing temperature control unit forcibly forces the fixing roller to set the fixing temperature even if the fixing temperature of the fixing roller is higher than the set temperature immediately before the start of scanning the original by the optical scanner. Since the energization of the fixing heater is started, even if the fixing roller is thin, the fixing temperature does not drop significantly during the fixing operation, and Fixing failure can be prevented.

According to a second aspect of the present invention, in the fixing device according to the first aspect, the fixing temperature control means forcibly starts energization of the fixing heater, and after a lapse of a predetermined time, the fixing heater. Since the energization control is switched to the normal energization control, even if the fixing roller is thin, the fixing temperature does not largely drop during the fixing operation, and the fixing failure due to the drop in the fixing temperature can be prevented.

According to a third aspect of the invention, in the fixing device according to the first aspect, the fixing temperature control means is provided only when the fixing temperature gradient of the fixing roller is lowered immediately before the start of scanning the original by the optical scanner. Since the energization of the fixing heater is started, it is possible to prevent the fixing temperature from becoming such a high temperature that hot offset occurs and fixing device parts are damaged, and hot offset and fixing device parts are prevented from being damaged. can do.

According to a fourth aspect of the present invention, in the fixing device according to the third aspect, the fixing temperature control means has a fixing temperature of the fixing roller 0 to 1 second before the start of scanning the original by the optical scanner, Since the fixing temperature gradient of the fixing roller is checked at the fixing temperature of the fixing roller 0.2 to 1.5 seconds before this, the fixing temperature gradient can be observed by setting an appropriate time interval. It is possible to prevent erroneous determination of the temperature gradient.

According to a fifth aspect of the present invention, in the fixing device according to the first aspect, the fixing temperature control unit forcibly starts the energization of the fixing heater immediately before the start of scanning the original by the optical scanner, and the fixing heater is started. Fixer heater at least 0.
Since the fixing heater is continuously turned on for 5 seconds or more, the fixing heater can be energized for a minimum required time and the life of the fixing heater can be prevented from being shortened.

According to a sixth aspect of the present invention, in the fixing device according to the first aspect, the fixing temperature control means has the fixing temperature gradient of the fixing roller lowered immediately before the start of scanning the original by the optical scanner, and Since the energization of the fixing heater is started only when the fixing temperature of the fixing roller is not higher than the predetermined temperature, it is possible to prevent the fixing temperature from touching the high temperature by not only the fixing temperature gradient but also the fixing temperature at that time. Therefore, the temperature ripple can be reduced.

According to a seventh aspect of the invention, in the fixing device according to the first aspect, the fixing temperature control means has a lowering of the fixing temperature gradient of the fixing roller immediately before the start of scanning the original by the optical scanner, and The energization of the fixing heater is started only when the fixing temperature of the fixing roller is not higher than the sum of the set temperature and the predetermined temperature, which is the predetermined temperature when the fixing heater is off. When the roller is rotating, the product of the temperature drop of the fixing roller per second and the time from the arrival of the sheet in the fixing device to the turning on of the fixing heater and 10 ° C. The smaller value and the larger value of 5 ° C. are set to the temperature drop of the fixing roller per second and until the fixing heater can be turned on after the sheet arrives at the fixing device. 5 the predetermined value when there is no time
Therefore, the fixing temperature can be controlled more finely by controlling the energization of the fixing heater by investigating the decrease in the fixing temperature and adding this to the fixing heater. It is possible to prevent the side from touching and reduce the ripple of the fixing temperature.

[Brief description of drawings]

FIG. 1 is a block diagram showing part of an exemplary embodiment of the present invention.

FIG. 2 is a schematic view showing the embodiment example.

FIG. 3 is a side view showing the embodiment.

FIG. 4 is a flowchart showing a fixing temperature control flow of a control unit in the embodiment.

FIG. 5 is a diagram showing an example of a change in fixing temperature of a conventional fixing device.

FIG. 6 is a diagram showing an example of a change in fixing temperature according to the exemplary embodiment.

FIG. 7 is a diagram showing an example of a temperature detected by a thermistor in the fixing device.

FIG. 8 is a flowchart showing a fixing temperature control flow of a control unit in another embodiment of the present invention.

FIG. 9 is a diagram for explaining the example of the embodiment.

FIG. 10 is a diagram showing an example of a change in fixing temperature according to the embodiment.

[Explanation of symbols]

 11 Fixing Roller 12 Pressure Roller 13 Fixing Heater 15 Thermistor 25 Fixing Heater Drive Circuit 26 Fixing Drive Means 27 Control Unit

Claims (7)

[Claims] 1. A fixing roller used in an optical image forming apparatus having an optical scanner for scanning an original, fixing a toner on a sheet passing between a pressure roller and a fixing heater heating the fixing roller. And a fixing temperature control unit that controls the fixing temperature of the fixing roller by performing a normal energization control on the fixing heater and does not start a new energization of the fixing heater when scanning an original by the optical scanner. In the apparatus, the fixing temperature control means forcibly starts energization of the fixing heater immediately before the start of scanning the original by the optical scanner even if the fixing temperature of the fixing roller is higher than a set temperature. . 2. The fixing device according to claim 1, wherein the fixing temperature control means controls the energization of the fixing heater to a normal energization control after a fixed time has elapsed after the energization of the fixing heater is forcibly started. Fixing device characterized by switching to. 3. The fixing device according to claim 1, wherein the fixing temperature control means starts energization of the fixing heater only when the fixing temperature gradient of the fixing roller is lowered immediately before the start of scanning the original by the optical scanner. A fixing device characterized by the above. 4. The fixing device according to claim 3, wherein the fixing temperature control means sets 0 when the scanning of the original by the optical scanner is started.
~ 1 second before the fixing temperature of the fixing roller and 0.2 ~ 1.5 seconds before the fixing temperature of the fixing roller, the fixing temperature gradient of the fixing roller is examined. . 5. The fixing device according to claim 1, wherein the fixing temperature control means forcibly starts energization of the fixing heater immediately before the start of scanning the original by the optical scanner, and the fixing heater is operated for at least 0.5 seconds. A fixing device characterized by being continuously turned on. 6. The fixing device according to claim 1, wherein the fixing temperature control means determines that the fixing temperature gradient of the fixing roller has decreased immediately before the start of scanning the original by the optical scanner, and the fixing temperature of the fixing roller is determined. A fixing device, wherein the energization of the fixing heater is started only when the temperature is not higher than the predetermined temperature. 7. The fixing device according to claim 1, wherein the fixing temperature control means determines that the fixing temperature gradient of the fixing roller is lowered immediately before the start of scanning the original by the optical scanner, and the fixing temperature of the fixing roller is determined. Temperature is not higher than the sum of the set temperature and the predetermined temperature, the energization of the fixing heater is started, and the predetermined temperature is set when the fixing heater is off and the fixing roller is rotating. The product of the temperature drop of the fixing roller per second and the time from when the sheet comes to the fixing device to when the fixing heater can be turned on, which is the smaller of 10 ° C. and 5 ° C. Is set to a larger value, the predetermined temperature is set to the predetermined value when the temperature drop of the fixing roller per second and the time until the fixing heater can be turned on after the sheet arrives at the fixing device. A fixing device which is characterized in that a 5.