JPH10186936A - Image forming device and its method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attain stable fixation, without causing the dropping of a fixing temp. due to the passage of a paper sheet and the overrising of temp. due to the control of the fixing temp. by changing the set temp. of a fixing means to a high set temp. higher than a standard temp. as a normal set temp., at the time of forming an image. SOLUTION: When an instruction to start copying is issued from a final control element 202, a CPU 201 generates an image formation starting signal, for instructing each part to start the formation of the image. In other words, each of control parts and driving parts after receiving the image formation starting signal starts the operation of preparing to start the formation of the image. A fixing temperature control part 90C after receiving the image formation starting signal changes the set temp. in a fixing unit 90 to the high set temp. from the standard set temp. In other words, the set temp. is switched to a high set temperature of 200 deg.C from a standard set temperature of 190 deg.C, for instance, with the image formation starting signal, so that the temp. of a heater 96 in a heating roller 91 is controlled to keep the high set temp. Further, the CPU 201 sets time to keep the high set temp.

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 provided with an exposing means and a fixing means of a heat roller type and an image forming method by the image forming apparatus, and more particularly to an improvement in fixing temperature control.

[0002]

2. Description of the Related Art In an electrophotographic electrostatic image forming apparatus, an electrostatic latent image formed on a photoreceptor is developed with a powder developer to transfer the image to recording paper, and then fixed by a fixing device. Thus, an image is formed.

In a fixing device of a heat roller fixing type used in such an image forming apparatus, generally, a pressure roller including a heat roller rotates in synchronization with a drive speed of a photosensitive member so as to synchronize with a conveyance speed of a recording paper. The structure is driven.

Further, in this type of fixing device, a predetermined set temperature (standard set temperature) is set in order to keep the fixing temperature constant, and a temperature at which a heater in a heat roller is driven so as to maintain this fixing temperature. Control is being performed.

[0005]

FIG. 10 shows this state. Here, an image formation start signal (FIG. 10A), a recording sheet developed and transferred by the start of image formation passing through a fixing device (FIG. 10B), and a temperature of a fixing roller at that time. (FIG. 10 (c)) is shown.

In this case, the heater is turned off because the fixing temperature is slightly higher than the set temperature (FIG. 10C).
When the sheet is passed through the fixing device (FIG. 10B), the heat is suddenly taken off by the recording sheet (FIG. 10C).

The fixing temperature is greatly reduced due to the time until the sensor detects the temperature drop or the delay from the time when the heater is turned on to the time when the temperature of the heat roller rises (FIG. 10).
(C)), a fixing failure may occur.

To prevent such a situation, FIG.
A method like the following is also considered. That is, there is known control for forcibly turning on the heater in the heat roller (FIG. 11B) at the same time as the start of image formation (FIG. 11A).

In this case, since the heater is forcibly turned on without temperature control, the temperature tends to rise too much as shown in FIG. Further, even when the fixing temperature is higher than the set temperature immediately after image formation or the like, heating is further performed, and an excessive temperature rise occurs.

As a result, the toner is excessively melted and the adhesion to the surface of the heat roller is increased, and the toner adheres and transfers to the surface of the heat roller, and the toner re-transfers to the recording paper at the next fixing, thereby recording. A so-called offset phenomenon that causes contamination on paper may occur.

When the heater is not turned on at the start of image formation and the sensor detects a decrease in temperature in the course of paper feeding and the heater is turned on, the response is delayed and the paper feeding ends. Is still heated, and an excessive temperature rise may occur at the end of image formation. When the next image formation is started in this state, an offset phenomenon similar to the above case may occur.

As described above, some problems remain in the conventional fixing device temperature control. SUMMARY OF THE INVENTION It is an object of the present invention to realize an image forming apparatus capable of performing stable fixing without lowering a fixing temperature due to paper passing and an excessive temperature rise caused by controlling the fixing temperature, and a control method thereof.

[0013]

That is, the present invention, which constitutes means for solving the problems, is described in the following (1) to (8).

(1) The invention according to claim 1 is a photoconductor,
An exposure unit for forming an electrostatic latent image on the photoconductor, a developing unit for developing the electrostatic latent image formed on the photoconductor to form a toner image, and a developing unit formed by the developing unit. Transfer means for transferring the toner image on the photoreceptor to recording paper, fixing means for fixing the toner image on the recording paper by heating with a heat roller at a predetermined temperature, and fixing means for forming the image. Control means for changing the set temperature to a higher set temperature than a standard set temperature, which is a normal set temperature.

According to the invention of the image forming apparatus, the control unit changes the set temperature of the fixing unit to a higher set temperature than the standard set temperature which is a normal set temperature during image formation. Since the temperature is controlled so as to reach the high temperature set temperature, there is no possibility that the temperature will drop significantly below the set temperature due to the passage of the recording paper. Further, since the temperature is different from the forced lighting of the heater, an excessive temperature rise that greatly exceeds the set temperature does not occur.

Therefore, stable fixing can be performed without lowering the fixing temperature due to paper passing or excessive temperature rise caused by controlling the fixing temperature. (2) An image forming apparatus according to claim 2, wherein the control means of the image forming apparatus according to claim 1 maintains the high temperature set temperature for a predetermined time from the start of image formation.

According to the invention of the image forming apparatus, the control unit changes the set temperature of the fixing unit to a high set temperature higher than the standard set temperature which is a normal set temperature at the time of image formation.
Since the high temperature setting temperature is maintained for a predetermined time, the temperature is controlled so that the high temperature setting temperature is maintained for a certain period of time from the start of image formation. Will not occur. Further, since the temperature is different from the forced lighting of the heater, an excessive temperature rise that greatly exceeds the set temperature does not occur.

Therefore, stable fixing can be performed without lowering the fixing temperature due to paper passing or excessive temperature rise caused by controlling the fixing temperature. (3) The invention according to claim 3 is characterized in that the control means of the image forming apparatus according to claim 1 or 2 continuously lowers the temperature to the standard set temperature after changing to the high temperature set temperature. Image forming apparatus.

In the invention of this image forming apparatus, the control unit changes the set temperature of the fixing unit to a higher set temperature than the standard set temperature which is a normal set temperature during image formation. Since the temperature is controlled so as to reach the high temperature set temperature, there is no possibility that the temperature will drop significantly below the set temperature due to the passage of the recording paper. Further, since the temperature is different from the forced lighting of the heater, an excessive temperature rise that greatly exceeds the set temperature does not occur.

Further, since the temperature is continuously lowered from the high temperature set temperature at the start of image formation to the standard set temperature, no large temperature fluctuation occurs after the recording paper passes. Therefore, stable fixing can be performed without lowering the fixing temperature due to the passing of paper or excessive temperature rise caused by controlling the fixing temperature.

(4) According to a fourth aspect of the present invention, the control means of the image forming apparatus according to the first or second aspect reduces the temperature to the standard set temperature stepwise after changing to the high temperature set temperature. An image forming apparatus characterized in that:

In the invention of the image forming apparatus, the control unit changes the set temperature of the fixing unit to a high set temperature higher than the standard set temperature which is a normal set temperature during image formation. Since the temperature is controlled so as to reach the high temperature set temperature, there is no possibility that the temperature will drop significantly below the set temperature due to the passage of recording paper. Further, since the temperature is different from the forced lighting of the heater, an excessive temperature rise that greatly exceeds the set temperature does not occur.

Further, since the temperature is gradually decreased from the high temperature set temperature at the start of image formation to the standard set temperature, no large temperature fluctuation occurs after the recording paper passes. Therefore, stable fixing can be performed without lowering the fixing temperature due to the passing of paper or excessive temperature rise caused by controlling the fixing temperature.

(5) According to a fifth aspect of the present invention, an electrostatic latent image is formed on a photosensitive member, the electrostatic latent image is developed to form a toner image, and the toner image is transferred to a recording paper. An image forming method for fixing the toner image by heating the toner image with a heat roller having a predetermined set temperature, wherein a fixing set temperature is higher than a standard set temperature which is a normal set temperature during image formation. The image forming method is characterized in that the image forming method is changed to:

In the invention of the image forming method, the fixing temperature is changed to the high temperature which is higher than the standard temperature which is a normal temperature at the time of image formation. , The temperature does not drop significantly below the set temperature due to the passage of the recording paper. Further, since the temperature is different from the forced lighting of the heater, an excessive temperature rise that greatly exceeds the set temperature does not occur.

Therefore, stable fixing can be performed without lowering the fixing temperature due to the passing of the paper and without excessively increasing the temperature caused by controlling the fixing temperature. (6) The invention according to claim 6 is the image forming method according to claim 5, wherein the high temperature setting temperature is maintained for a predetermined time from the start of image formation.

According to the invention of this image forming method, at the time of image formation, the set temperature for fixing is changed to a high set temperature higher than the standard set temperature which is a normal set temperature, and the set high temperature is maintained for a predetermined time. Therefore, since the temperature is controlled so as to reach the high temperature set temperature for a certain period of time from the start of image formation, there is no possibility that the temperature will drop significantly below the set temperature due to the passage of the recording paper. Further, since the temperature is different from the forced lighting of the heater, an excessive temperature rise that greatly exceeds the set temperature does not occur.

Therefore, stable fixing can be performed without lowering the fixing temperature due to paper passing or excessive temperature rise caused by controlling the fixing temperature. (7) According to a seventh aspect of the present invention, in the image forming method according to the fifth or sixth aspect, the temperature is continuously lowered to the standard set temperature after changing to the high temperature set temperature. Image forming method.

In the invention of this image forming method, the fixing set temperature is changed to a higher set temperature than the standard set temperature which is a normal set temperature at the time of image formation. , The temperature does not drop significantly below the set temperature due to the passage of the recording paper. Further, since the temperature is different from the forced lighting of the heater, an excessive temperature rise that greatly exceeds the set temperature does not occur.

Further, since the temperature is continuously lowered from the high temperature set temperature at the start of image formation to the standard set temperature, no large temperature fluctuation occurs after the recording paper passes. Therefore, stable fixing can be performed without lowering the fixing temperature due to the passing of paper or excessive temperature rise caused by controlling the fixing temperature.

(8) In the invention according to claim 8, in the image forming method according to claim 5 or 6, after the temperature is changed to the high temperature set temperature, the temperature is gradually lowered to the standard set temperature. An image forming method characterized by the following.

In the invention of this image forming method, the fixing set temperature is changed to the high set temperature higher than the standard set temperature which is a normal set temperature at the time of image formation. , The temperature does not drop significantly below the set temperature due to the passage of the recording paper. Further, since the temperature is different from the forced lighting of the heater, an excessive temperature rise that greatly exceeds the set temperature does not occur.

Further, since the temperature is gradually decreased from the high temperature set at the start of image formation to the standard temperature, no large temperature fluctuation occurs after the recording paper passes. Therefore, stable fixing can be performed without lowering the fixing temperature due to the passing of paper or excessive temperature rise caused by controlling the fixing temperature.

[0034]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An image forming apparatus and a control method thereof according to the present invention will be described with reference to the drawings. <Mechanical Configuration> First, the overall mechanical configuration of the image forming apparatus used in the embodiment of the present invention will be described with reference to FIG. Here, a description will be given of a case where the image forming apparatus 1 is a copying machine as an example.

An automatic document feeder 10 is provided above the image forming apparatus 1, and a document G set on a document placing tray 11 is fed onto a document placing plate 14 by a transport mechanism 12. The original G placed on the original placing plate 14 is
The document is discharged to the document receiving section 13 by the transport mechanism 12 at the timing of the end of the exposure.

In the image forming apparatus 1, a charging device 22, a developing device 23, a transfer device 24, a separating device 25, and a cleaning device 2 are provided on the outer periphery of a drum-shaped photosensitive member 21 serving as an image forming means.
6 are arranged in the order of operation, and these are integrally formed as the image forming unit 20.

After a charge is applied to the photosensitive layer surface of the photosensitive member 21 by the charger 22, the original G placed on the original placing plate 14 provided at the uppermost portion of the image forming apparatus 1 is moved to the inside of the image forming apparatus 1. Exposure is started by an exposure lamp 32 provided in an optical frame 31 of an exposure optical unit 30 arranged at an upper position.

A mirror 33 moving integrally with the exposure lamp 32, V-shaped mirrors 34 and 35 moving half the moving distance of the mirror 33,
Exposure is performed in the direction of the arrow by mirrors 37 and 38 arranged in a V-shape via an imaging lens 36 and a mirror 39 for irradiating an image on the photoconductor 21 to form an electrostatic latent image on the photosensitive layer surface of the photoconductor 21. .

Next, the developing device 2 in the image forming unit 20
At step 3, the electrostatic latent image is developed to form a visible image based on a toner image on the photosensitive layer surface of the photosensitive member 21. Further, a double-sided copy paper supply unit 40 and paper supply units 50, 60, 70 are arranged at lower and upper positions in the image forming apparatus 1, respectively, and the paper supply units 50, 60, 70 have recording papers of different sizes. P is stored.

For example, when the recording paper P stored in the paper supply unit 50 is selected, only one recording paper P is supplied by the paper supply roller 51, and the recording paper P is transported by the guide roller 52. I do.

Similarly, when the recording paper P stored in the paper feeding units 60 and 70 is selected, only one recording paper P is fed by the paper feeding rollers 61 and 71 and the recording paper P is fed. Is conveyed by guide rollers 62 and 72.

Then, the recording paper P is transported by the transport mechanism 81 in the direction of the photosensitive member 21 on which the toner image has been formed. Then, the recording paper P is temporarily stopped by a registration roller 82 provided in the image forming apparatus 1, and the recording paper P is fed so that the toner image formed on the photoconductor 21 and the recording paper P coincide with each other.

Next, the toner image on the photosensitive member 21 is transferred to the transfer unit 2.
4, the recording paper P is transferred to the recording paper P,
5 separates from the photoconductor 21 surface. Then, the recording paper P is transported to the fixing device 90 by the transport device 83.

The fixing device 90 includes a heating roller 91 and a pressure roller 92. The toner image on the recording sheet P is stably fixed on the recording sheet P by the heating roller 91 and the pressure roller 92. .

The recording paper P on which the fixing has been completed is discharged by a discharge guide roller 84. In the case of one-sided copying, the discharge switching member 85 is lowered, and the recording paper P is discharged onto the discharge tray 86 as it is.

In the case of double-sided copying, the discharge switching member 85 is raised, the recording paper guide 87 is opened, and the recording paper P is transported in the direction of the dashed arrow. Further, the recording paper P is transported downward by the transport mechanism 88, is switched back by the recording paper reversing unit 89, and the rear end of the recording paper P is transported into the double-sided copy feeding unit 50 as the leading end. You.

The recording paper P is moved in the paper feeding direction by a transport belt 41 provided in a two-sided copy paper feeding unit 50, the recording paper P is fed again by a paper feed roller 42, and the recording paper P is fed by a transport roller 43. Is guided to the transport path 80.

Again, as described above, the recording paper P is conveyed in the direction of the photoreceptor 21, the toner image is transferred to the back surface of the recording paper P, fixed by the fixing device 90, and then discharged to the discharge tray 86. In addition to the above-described sheet feeding, the image forming apparatus 1 also includes a manual sheet feeding device 2 that performs sheet feeding by manual feeding.

Next, the structure of the fixing device 90 will be described with reference to FIG. FIG. 3 shown here is a schematic diagram of a side surface of the fixing device 90. In a housing 93 of the fixing device 90, a heating roller 91, a pressure roller 92, and a temperature fuse 94 are arranged.

A temperature sensor 95 is disposed in the housing 93, and this temperature information is transmitted to a control unit described later. Then, based on this temperature information, the temperature of two heating lamps (heaters) 96 built in the heating roller 91 is controlled by the control unit.

The toner of the toner image that has not been sufficiently fixed on the recording paper P may adhere to the heating roller 91 as dirt. The adhered toner is removed from the cleaning web 11.
0 wipes off the pressure contact with the heating roller 91.
The cleaning web 110 is wound around the original winding shaft 111, is wound by the rotation of the winding shaft 112, and is slid in pressure contact with the heating roller 91 by, for example, an elastic roller 113, so that a fresh surface is always in contact with the heating roller 91. It is configured as follows.

<Electrical Configuration> The image forming apparatus 1 configured as described above is electrically configured as shown in FIG.

A CPU 201 for controlling the entire image forming apparatus 1 in response to an instruction from an operation section described later, an operation section 202 for performing various operations, instructions and selections, and a display for displaying information on the operation of the image forming apparatus 1 A section 203 is provided.

Further, the photoreceptor driving section 21M for driving the above-described photoreceptor 21, the transport driving section 80M for driving the above-described transport belt, the high-voltage control section 22C for driving the above-described charger 22, and the above-described developing device A developing unit driving unit 23M for driving the driving unit 23 is provided, and these various driving units and a control unit are configured to be controlled by the CPU 201.

The fixing device 90 is provided with a fixing temperature controller 90C for controlling the fixing temperature. The fixing temperature control unit 90C includes a temperature sensor 95 for detecting the temperature of the heating roller 91 and a heater 96 for heating the heating roller 91. Further, a fixing device driving unit 90M for rotating and driving the heating roller 91 and the pressure roller 92
Executes driving in accordance with instructions from the CPU 201 and the fixing temperature control unit 90C.

<Processing Procedure in Image Forming (1)> Here, referring to the flow chart of FIG. 1 and the time chart of FIG. 5, the processing procedure in fixing with switching of the set temperature will be described in detail as a first embodiment. Will be described.

Here, the standard set temperature T1 is set to 190
The description will be made on the assumption that the high temperature set temperature T2 is 200 ° C. as a set temperature higher than the standard set temperature. Note that the temperature is not limited to this specific example, and the high temperature set temperature may be any value that is set by increasing the temperature in advance so as to correspond to the temperature decrease that occurs during paper passing, as described later.

When a copy start instruction is given from the operation unit 202, the CPU 201 generates an image formation start signal (FIG. 5A), and instructs the above-described units to start image formation (S1 in FIG. 1). That is, each control unit and each drive unit that has received the image formation start signal starts an operation for preparing for the start of image formation.

The fixing temperature control section 90 C, which has received the image formation start signal, sets the set temperature T in the fixing device 90.
Is changed from the standard set temperature T1 to the high set temperature T2 (T1 → T2 in FIG. 1S2, FIGS. 5A and 5B).

That is, in this embodiment, the image formation start signal changes the standard set temperature of 190 ° C. to 200 ° C.
, And the temperature of the heater 96 in the heating roller 91 is controlled so as to maintain this high temperature set temperature.

The CPU 201 sets a time for keeping the high temperature set temperature (the maximum value tmax of the timer value t) (FIG. 1).
S3). The time tmax is preferably close to the time from when the image formation start signal is generated to when the recording paper has completely passed through the fixing device 90, in order to prevent the temperature from dropping due to paper passing.

Here, the timer value t is counted with reference to the clock of the CPU 201 (S4 in FIG. 1), and the temperature control is performed so that the above-mentioned high temperature set temperature T2 is maintained until tmax elapses.

Here, the fixing roller temperature by such temperature control will be described in detail. In this case, when the temperature is changed from the standard set temperature to the high set temperature (S2 in FIG. 1), the fixing roller temperature starts increasing from around 190 ° C. (FIG. 5D) to around 200 ° C. (FIG. 5D). . And 200
When the temperature reaches around ° C., temperature control is performed around the 200 ° C. (FIG. 5D).

When the recording paper is fed into the fixing device 90 and fixing is performed, heat is deprived of the recording paper, and the temperature of the heating roller 91 decreases slightly (FIG. 5D). But,
Since the preset high temperature is higher than the normal standard temperature, the temperature of the heating roller 91 does not fall below the standard temperature. Further, since the temperature control is performed centering on the high temperature set temperature, the detection of the temperature drop by the sensor 95 is also performed promptly, so that the temperature drop does not become large.

Further, since it is different from the conventional forced heater ON, it is possible to prevent a situation in which the temperature of the heating roller 91 excessively rises during and after sheet passing (FIG. 5D).

When tmax has elapsed (FIG. 1S
5) The set temperature is set from the high set temperature T2 to the standard set temperature T1 (S6 in FIG. 1). As a result, the fixing roller temperature starts dropping to around 190 ° C. (FIG. 5).
(D) →). Then, when the temperature reaches around 190 ° C., temperature control is performed around the 190 ° C. (FIG. 5).
(D)).

Therefore, according to this embodiment, even if the heat is taken away by the recording paper and the temperature of the heating roller 91 is slightly lowered, the temperature is set in advance to the high temperature set temperature T2 higher than the normal standard set temperature T1. Therefore, the temperature of the heating roller 91 does not fall below the standard set temperature T1. During a predetermined time including the paper passing period, the temperature is controlled so as to maintain the high temperature set temperature T2, so that the sensor 95 detects the temperature drop promptly, so that the temperature drop does not increase. Since it is different from the conventional forced heater ON, it is possible to prevent a situation in which the temperature of the heating roller 91 excessively rises during and after sheet passing. Such an effect can be obtained.

<Processing Procedure in Image Forming (2)> Here, referring to the flow chart of FIG. 6 and the time chart of FIG. 7, the processing procedure in the fixing with the switching of the set temperature will be described in detail as a second embodiment. Will be described.

Here, the standard set temperature T1 is set to 190
The description will be made on the assumption that the high temperature set temperature T2 is 200 ° C. as a set temperature higher than the standard set temperature. Note that the temperature is not limited to this specific example, and the high temperature set temperature may be any value that is set by increasing the temperature in advance so as to correspond to the temperature decrease that occurs during paper passing, as described later.

When a copy start instruction is issued from the operation unit 202, the CPU 201 generates an image formation start signal (FIG. 7A), and instructs the above-described units to start image formation (S1 in FIG. 6). That is, each control unit and each drive unit that has received the image formation start signal starts an operation for preparing for the start of image formation.

The fixing temperature control section 90 C receiving the image formation start signal sets the set temperature T in the fixing device 90.
Is changed from the standard set temperature T1 to the high set temperature T2 (T1 → T2 in FIG. 6S2 and FIGS. 7A and 7B).

That is, in this embodiment, the image formation start signal changes the standard setting temperature from 190 ° C. to 200 ° C.
, And the temperature of the heater 96 in the heating roller 91 is controlled so as to maintain this high temperature set temperature.

The CPU 201 sets a time for keeping the high temperature set temperature (the maximum value tmax of the timer value t) (FIG. 6).
S3). The time tmax is preferably close to the time from when the image formation start signal is generated to when the recording paper has completely passed through the fixing device 90, in order to prevent the temperature from dropping due to paper passing.

Here, the timer value t is counted with reference to the clock of the CPU 201 (S4 in FIG. 6), and until the time tmax elapses (S4 to S6 in FIG. 6), the above-mentioned high temperature set temperature T2 is used as a start temperature. Temperature control is performed so as to maintain the high temperature set temperature T2 '= (T2 -t / α) corresponding to the value t.

Here, α = tmax / (T2−T1)
And keep it. As a result, as shown in FIG. 7B, a characteristic is obtained in which the set temperature T2 'smoothly changes from T2 to T1 over time tmax.

Here, the fixing roller temperature by the temperature control that changes with time will be described in detail. In this case, when the temperature is changed from the standard set temperature T1 to the high set temperature T2 '(S2 in FIG. 6), the fixing roller temperature starts increasing from around 190.degree. C. (FIG. 7D) to around 200.degree. (D)).

Then, when the temperature reaches around the high temperature set temperature T2 'at that time, temperature control is performed centering on the temperature (FIG. 7 (d)). Then, when the recording paper is fed into the fixing device 90 and the fixing is performed, heat is deprived by the recording paper, and the temperature of the heating roller 91 is slightly lowered (FIG. 7D). However, the high set temperature T higher than the normal standard set temperature T1
Since the temperature is set to 2 'in advance, the temperature of the heating roller 91 does not drop significantly from the standard set temperature T1.

Further, since temperature control is performed centering on the high temperature set temperature T2 ', the detection of the temperature drop by the sensor 95 is also performed promptly, so that the above-mentioned temperature drop does not increase.

Further, since it is different from the conventional forced on of the heater, it is possible to prevent a situation in which the temperature of the heating roller 91 excessively increases during and after the sheet passing (FIG. 7D).

When tmax elapses (see FIG. 6S
6) The set temperature is set from the high set temperature T2 to the standard set temperature T1 (S7 in FIG. 6). Since the high temperature set temperature T2 'is approaching the standard set temperature T1 at the elapse of tmax, the temperature of the heating roller 91 is also approaching the standard set temperature T1 (FIG. 7), and smooth temperature control can be performed.

When the temperature reaches about 190 ° C., which is the standard set temperature T 1, temperature control is performed around that 190 ° C. (FIG. 7D). Therefore, according to this embodiment, even if the heat is deprived by the recording paper and the temperature of the heating roller 91 is slightly lowered, the high temperature setting temperature T2 'which is higher than the normal standard setting temperature T1 is preset. Therefore, the temperature of the heating roller 91 does not drop below the standard set temperature T1. During a predetermined time including the paper passing period, the temperature control is performed so as to maintain the high temperature set temperature T2 '. Therefore, the temperature drop is detected quickly by the sensor 95, so that the temperature drop does not increase. . Since it is different from the conventional forced heater ON, it is possible to prevent a situation in which the temperature of the heating roller 91 excessively rises during and after sheet passing. At the time when tmax elapses, the high temperature set temperature T2 'is approaching the standard set temperature T1, so that the temperature of the heating roller 91 is also approaching the standard set temperature T1, and smooth temperature control can be performed. Such an effect can be obtained.

<Processing Procedure in Image Forming (3)> Here, referring to the flowchart in FIG. 8 and the time chart in FIG. 9, the processing procedure in the fixing with the switching of the set temperature will be described in detail as a third embodiment. Will be described.

Here, the standard set temperature T1 is set to 190
The description will be made on the assumption that the high temperature set temperature T2 is 200 ° C. as a set temperature higher than the standard set temperature. Note that the temperature is not limited to this specific example, and the high temperature set temperature may be any value that is set by increasing the temperature in advance so as to correspond to the temperature decrease that occurs during paper passing, as described later.

When a copy start instruction is issued from the operation unit 202, the CPU 201 generates an image formation start signal (FIG. 9A), and instructs the above-described units to start image formation (S1 in FIG. 8). That is, each control unit and each drive unit that has received the image formation start signal starts an operation for preparing for the start of image formation.

The fixing temperature control section 90 C receiving the image formation start signal sets the set temperature T in the fixing device 90.
Is changed from the standard set temperature T1 to the high set temperature T2 (T1 → T2 in FIG. 8S2, FIGS. 9A and 9B).

That is, in this embodiment, the image formation start signal changes the standard set temperature of 190 ° C. to 200 ° C.
, And the temperature of the heater 96 in the heating roller 91 is controlled so as to maintain this high temperature set temperature.

The CPU 201 sets a time (maximum value tmax of the timer value t) for keeping the high temperature set temperature (FIG. 8).
S3). The time tmax is preferably close to the time from when the image formation start signal is generated to when the recording paper has completely passed through the fixing device 90, in order to prevent the temperature from dropping due to paper passing.

Here, the timer value t is counted with reference to the clock of the CPU 201 (S4 in FIG. 8), and until the time tmax elapses (S4 to S6 in FIG. 8), the above-mentioned high temperature set temperature T2 is used as a start temperature. Temperature control is performed so as to maintain the high temperature set temperature T2 '= (T2 -t / α) corresponding to the value t.

Here, α = tmax / (T2−T1)
And a process control loop for temperature control (S4 to S8 in FIG. 8).
By inserting a waiting time of tmax / n (S6 in FIG. 8) into 7), as shown in FIG. 9B, the set temperature T2 'is changed from T2 to T1 in n steps over the time of tmax. Variable characteristics are obtained.

The waiting time in this case is reset every time. Further, n which determines the waiting time may be appropriately determined according to the difference between T2 and T1, tmax and the like. It should be noted that by increasing the value of n, the above-described continuously changing characteristic is approached. In FIG. 9, n
= 6 is illustrated.

Here, the fixing roller temperature by the temperature control that changes with time will be described in detail. In this case, when the temperature is changed from the standard set temperature T1 to the high set temperature T2 '(S2 in FIG. 8), the fixing roller temperature starts increasing from around 190.degree. C. (FIG. 9D) to around 200.degree. (D)).

Then, when the temperature reaches around the high temperature set temperature T2 'at that time, temperature control is performed centering on the temperature (FIG. 9D). Then, when the recording paper is fed into the fixing device 90 and fixing is performed, heat is deprived by the recording paper, and the temperature of the heating roller 91 decreases slightly (FIG. 9D). However, the high set temperature T higher than the normal standard set temperature T1
Since the temperature is set to 2 'in advance, the temperature of the heating roller 91 does not drop significantly from the standard set temperature T1.

Further, since the temperature control is performed centering on the high temperature set temperature T2 ', the detection of the temperature drop by the sensor 95 is also performed promptly, so that the above-mentioned temperature drop does not increase.

Further, since it is different from the conventional forced heater ON, it is possible to prevent a situation in which the temperature of the heating roller 91 excessively rises during and after sheet passing (FIG. 9D).

Then, when tmax has elapsed (FIG. 8S
7) The set temperature is set from the above-mentioned high temperature set temperature T2 to the standard set temperature T1 (S8 in FIG. 8). Since the high temperature setting temperature T2 'approaches the standard setting temperature T1 at the elapse of tmax, the temperature of the heating roller 91 also approaches the standard setting temperature T1 (FIG. 9), and smooth temperature control can be performed.

When the temperature reaches about 190 ° C., which is the standard set temperature T 1, temperature control is performed around that 190 ° C. (FIG. 9D). Therefore, according to this embodiment, even if the heat is deprived by the recording paper and the temperature of the heating roller 91 is slightly lowered, the high temperature setting temperature T2 'which is higher than the normal standard setting temperature T1 is preset. Therefore, the temperature of the heating roller 91 does not drop below the standard set temperature T1. During a predetermined time including the paper passing period, the temperature control is performed so as to maintain the high temperature set temperature T2 '. Therefore, the temperature drop is detected quickly by the sensor 95, so that the temperature drop does not increase. . Since it is different from the conventional forced heater ON, it is possible to prevent a situation in which the temperature of the heating roller 91 excessively rises during and after sheet passing. At the time when tmax elapses, the high temperature set temperature T2 'is approaching the standard set temperature T1, so that the temperature of the heating roller 91 is also approaching the standard set temperature T1, and smooth temperature control can be performed. Such an effect can be obtained.

<Other Embodiments> In the above-described embodiments, the high-temperature set temperature T2 is maintained for a predetermined time, or the high-temperature set temperature T2 'is decreased continuously or stepwise. However, it is also possible to combine these.

That is, the first half of tmax is maintained at T2, and the set temperature is controlled so as to decrease continuously or stepwise in the second half. By doing so, the same effects as those of the above-described embodiments can be obtained, and satisfactory fixing can be performed.

[0099]

As described above, according to the present invention, the following effects can be obtained. (1) According to the first aspect of the present invention, the control unit changes the set temperature of the fixing unit to a high set temperature higher than the standard set temperature which is a normal set temperature during image formation.
Because it is controlled to reach the high temperature setting when passing paper,
The temperature does not drop significantly below the set temperature due to the passage of the recording paper, and is different from the forced lighting of the heater, so that an excessive rise in temperature that greatly exceeds the set temperature does not occur. Therefore, stable fixing can be performed without lowering the fixing temperature due to paper passing or excessive temperature rise caused by controlling the fixing temperature.

(2) According to the second aspect of the invention, the control unit changes the set temperature of the fixing unit to a high set temperature higher than the standard set temperature, which is a normal set temperature, at the time of image formation. Is maintained for a predetermined time, so that the temperature is controlled so as to be at the high temperature set temperature for a certain time from the start of image formation. ,
Since this is also different from the forced lighting of the heater, there is no occurrence of an excessive temperature rise that greatly exceeds the set temperature.
Therefore, stable fixing can be performed without lowering the fixing temperature due to paper passing or excessive temperature rise caused by controlling the fixing temperature.

(3) According to the third aspect of the invention, the control unit changes the set temperature of the fixing unit to a higher set temperature than the standard set temperature which is a normal set temperature during image formation. Since the temperature is controlled so as to reach the high temperature when the paper is printed, the temperature does not drop significantly below the set temperature due to the passage of the recording paper. Further, since the temperature is different from the forced lighting of the heater, an excessive temperature rise that greatly exceeds the set temperature does not occur.

Since the temperature is continuously lowered from the high temperature set temperature at the start of image formation to the standard set temperature, no large temperature fluctuation occurs after the recording paper passes. Therefore, stable fixing can be performed without lowering the fixing temperature due to paper passing or excessive temperature rise caused by controlling the fixing temperature.

(4) In the invention according to claim 4, the control means of the image forming apparatus according to claim 1 or 2 causes the control means to set the temperature of the fixing means at a normal set temperature at the time of image formation. Since the set temperature is changed to a higher set temperature than a certain standard set temperature, it is controlled to be the high set temperature at the time of paper passing, so the temperature may drop significantly below the set temperature when the recording paper passes. There is no. Further, since the temperature is different from the forced lighting of the heater, an excessive temperature rise that greatly exceeds the set temperature does not occur.

Since the temperature is gradually decreased from the high temperature set at the start of image formation to the standard temperature, no large temperature fluctuation occurs after the recording paper passes. Therefore, stable fixing can be performed without lowering the fixing temperature due to paper passing or excessive temperature rise caused by controlling the fixing temperature.

(5) According to the fifth aspect of the present invention, the fixing temperature is changed to a higher temperature than the standard setting temperature, which is a normal setting temperature, at the time of image formation. Since the temperature is controlled so as to reach the high temperature setting temperature, the temperature does not drop significantly below the set temperature due to the passage of the recording paper. No significant temperature rise occurs. Therefore, stable fixing can be performed without lowering the fixing temperature due to paper passing or excessive temperature rise caused by controlling the fixing temperature.

(6) In the sixth aspect of the present invention, the fixing temperature is changed to a higher temperature than the standard temperature, which is a normal temperature, at the time of image formation, and the high temperature is set for a predetermined time. Since the temperature is maintained, the temperature is controlled so as to reach the high temperature setting for a certain period of time from the start of image formation. Since the lighting is different from the lighting, an excessive temperature rise that greatly exceeds the set temperature does not occur. Therefore, stable fixing can be performed without lowering the fixing temperature due to paper passing or excessive temperature rise caused by controlling the fixing temperature.

(7) According to the seventh aspect of the present invention, the fixing temperature is changed to a higher temperature than the standard setting temperature, which is a normal setting temperature, during image formation. Since the temperature is controlled so as to reach the high temperature setting temperature, the temperature does not drop significantly below the set temperature due to the passage of the recording paper. No significant temperature rise occurs.

Further, since the temperature is continuously lowered from the high temperature set at the start of image formation to the standard temperature, a large temperature fluctuation does not occur after the recording paper passes. Therefore, stable fixing can be performed without lowering the fixing temperature due to paper passing or excessive temperature rise caused by controlling the fixing temperature.

(8) In the invention according to the eighth aspect, the fixing temperature is changed to the high temperature which is higher than the standard temperature which is a normal temperature at the time of image formation. Since the temperature is controlled so as to reach the high temperature setting temperature, the temperature does not drop significantly below the set temperature due to the passage of the recording paper. No significant temperature rise occurs.

Since the temperature is gradually decreased from the high temperature set at the start of image formation to the standard temperature, no large temperature fluctuation occurs after the recording paper passes. Therefore, stable fixing can be performed without lowering the fixing temperature due to paper passing or excessive temperature rise caused by controlling the fixing temperature.

[Brief description of the drawings]

FIG. 1 is a flowchart showing a processing procedure of fixing temperature control accompanied by switching of a set temperature in a first embodiment of the present invention.

FIG. 2 is a cross-sectional view illustrating a mechanical cross-sectional configuration of the image forming apparatus used in the embodiment of the present invention.

FIG. 3 is a cross-sectional view illustrating a cross-sectional configuration of a fixing device used in the embodiment of the present invention.

FIG. 4 is a configuration block diagram illustrating an electrical configuration of the image forming apparatus used in the embodiment of the present invention.

FIG. 5 is a time chart showing a state of fixing accompanied by switching of a set temperature in the first embodiment of the present invention.

FIG. 6 is a flowchart illustrating a processing procedure of fixing temperature control accompanied by switching of a set temperature in a second embodiment of the present invention.

FIG. 7 is a time chart showing a state of fixing accompanied by switching of a set temperature in a second embodiment of the present invention.

FIG. 8 is a flowchart showing a processing procedure of fixing temperature control accompanied by switching of a set temperature in a third embodiment of the present invention.

FIG. 9 is a time chart showing a state of fixing accompanied by switching of a set temperature in a third embodiment of the present invention.

FIG. 10 is a time chart showing a state of fixing without switching a set temperature or forcibly turning on a heater in a conventional fixing device.

FIG. 11 is a time chart showing a state of fixing with forced heater-on in a conventional fixing device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Image forming apparatus 2 Paper feeder 10 Automatic original feeder 20 Image forming unit 21 Photoconductor 21M Photoconductor drive part 22 Charger 22C High voltage control part 23 Developing device (developing means) 23M Developing device drive section 24 Transfer device (Transfer device) 25) Separator 26 Cleaning device 30 Exposure optical unit (exposure means) 32 Exposure lamp 33-35 Mirror 36 Imaging lens 37-39 Mirror 41 Transport belt 80 Transport path 80M Transport drive section 90 Fixing device (fixing means) 90C Fixing temperature Control unit (control means) 90M Fixing unit driving unit 91 Heating roller 92 Pressure roller 93 Housing 94 Temperature fuse 95 Temperature sensor 96 Heater 110 Cleaning web 111 Main winding shaft 112 Axis 113 Elastic roller 201 CPU 202 Operating unit 203 Display unit

Claims (8)

[Claims] 1. A photoconductor, an exposure unit for forming an electrostatic latent image on the photoconductor, and a developing unit for developing the electrostatic latent image formed on the photoconductor to form a toner image Transfer means for transferring the toner image on the photoreceptor formed by the developing means to recording paper, fixing means for fixing the toner image on the recording paper by heating with a heat roller at a predetermined set temperature, An image forming apparatus comprising: a control unit configured to change a set temperature of the fixing unit to a high set temperature higher than a standard set temperature which is a normal set temperature during image formation. 2. The image forming apparatus according to claim 1, wherein the control unit maintains the high temperature set temperature for a predetermined time from the start of image formation. 3. The image forming apparatus according to claim 1, wherein the control unit continuously lowers the temperature to the standard set temperature after changing to the high temperature set temperature. 4. The image forming apparatus according to claim 1, wherein the control unit gradually reduces the temperature to the standard set temperature after changing to the high temperature set temperature. 5. An electrostatic latent image is formed on a photoreceptor, the electrostatic latent image is developed to form a toner image, the toner image is transferred to a recording paper, and the toner image is transferred to a predetermined temperature. An image forming method in which fixing is performed by heating with a heat roller, wherein the setting temperature of fixing is changed to a high setting temperature higher than a standard setting temperature which is a normal setting temperature during image formation. Forming method. 6. The image forming method according to claim 5, wherein the set high temperature is maintained for a predetermined time from the start of image formation. 7. The image forming method according to claim 5, wherein the temperature is continuously lowered to the standard set temperature after the temperature is changed to the high temperature set temperature. 8. The image forming method according to claim 5, wherein the temperature is gradually lowered to the standard set temperature after the temperature is changed to the high temperature set temperature.