JPH09244461A - Temperature controller for fixing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the light quantity of an exposure lamp from being fluctuated and to precisely maintain the temperature of a fixing device to be the optimum temperature for fixing a developer image on a paper when the paper is passed. SOLUTION: While a copying lamp 2 is turned on, the temperature control of a heat roller 18 is interrupted. On the other hand, a heater lamp 19 is started to be driven in a prescribed time before the turning-on timing of the lamp 2. Therefore, the temperature of the roller 18 can be previously made to rise so as to maintain a temperature range that developer can be fixed by the roller 18 while the paper is passed through the heat rollers 17 and 18 by properly setting the prescribed time counted by a timer. The prescribed time is the time uniquely decided every type of copying machines based on the power consumption of the lamp 2, the carrying speed of the paper and the heat capacity of the roller 18.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a temperature control device for a fixing device applied to an image forming apparatus using an electrophotographic method such as a copying machine, a printer or a facsimile.

[0002]

2. Description of the Related Art An image forming apparatus such as a copying machine is provided with an exposure lamp and a fixing lamp which consume a relatively large amount of electric power to the apparatus, and the exposure lamp illuminates an original. If the fixing lamp is turned on in the meantime, the electric power to the fixing lamp is temporarily lowered due to the current to the fixing lamp, and in response to this, the light amount of the exposure lamp is reduced, causing uneven density in the image. . Therefore, JP-A-61
In the configuration disclosed in Japanese Patent Laid-Open No. 102675, the exposure lamp lighting period is considered in consideration of the fact that the voltage drop when the fixing lamp is switched from the extinguished state to the lit state has an influence over the uneven density of the exposure lamp exceeding the allowable range. In the middle, control is performed to prohibit the fixing lamp from switching from off to on.

In the configuration disclosed in Japanese Patent Laid-Open No. 63-83739, the fixing lamp is fixed when the extinguishing state of the fixing lamp is detected immediately before the exposure lamp is turned on in the lighting cycle of the exposure lamp during copying. When the lighting state of the fixing lamp is detected immediately before the exposure lamp is turned on by increasing the amount of heat supplied to the fixing means in excess of the normal temperature by continuing to turn on until the set upper temperature such as the upper limit temperature is reached,
The normal temperature control is performed as it is, and the heat supply to the fixing unit is not increased, so that the heat amount supplied to the fixing unit is increased within a range that does not affect the lighting state of the exposure lamp to improve the fixability. ing.

Further, in the structure disclosed in Japanese Patent Application Laid-Open No. 61-267063, in order to prevent a temperature drop during multi-copying, the power of the exposure lamp is turned on when the exposure lamp is turned off and turned off repeatedly. I try to turn it.

[0005]

However, in the structure disclosed in Japanese Patent Laid-Open No. 61-102675, there is no influence on the exposure operation which is being executed, despite the timing at which the fixing lamp should be turned on. Therefore, since the lighting start timing of the fixing lamp is delayed, the heat supply amount of the heating source of the fixing unit per unit time, the heat amount (heat capacity) retained by the fixing roller, and the dissipation of heat (paper is taken from the fixing unit). It does not matter if it is well balanced with the amount of heat), but when copying in a low temperature environment where heat dissipation is large, such as when low temperature paper is passed, the fixing roller with a small diameter and thin wall When copying using a fixing unit having a small heat capacity, or when the amount of heat transmitted to the individual sheets from the fixing unit is small even if the sheet conveying speed is high (high speed machine etc.), the amount of heat of the fixing unit is small. Or when taken away to the amount can not be accommodated in a poor fixing conditions, or waits for the recovery of the temperature of the suspended to the fixing means copying operations, it had to to lower the conveying speed of the sheet.

Further, in the structure disclosed in Japanese Patent Laid-Open No. 63-83739, although there is some effect in improving the fixing property under the above-mentioned poor conditions, the temperature control cycle of the fixing means (fixing lamp Although the exposure start time in (ON / OFF) is different due to various factors, the timing at which the sheet passes through the fixing unit is not considered, and the temperature control is performed by detecting the OFF state and the ON state of the fixing lamp. However, the following problems occur.

In the first place, the actual fixing temperature of the fixing means (the surface temperature of the nip portion of the fixing roller etc.) is determined by the amount of heat supplied from the heating source, the heat capacity of the fixing means and the heat taken away by the paper, etc. When the heat capacity of the unit is relatively small and the amount of heat supplied is relatively large, the changing speed of the actual fixing temperature of the fixing unit when the heat source is turned on becomes large. Therefore, immediately after the heat source is extinguished while the temperature of the fixing unit is relatively high, the temperature of the fixing unit is the upper limit of the allowable fixing temperature (a temperature at which the temperature on the sheet is high offset and the image on the paper is damaged if the temperature is higher than this temperature). .) Has been reached, and the heat source must be turned off early in consideration of the case where the time from turning off the heat source to the timing when the paper passes through the fixing means is not sufficient. On the other hand, even if the temperature of the fixing unit is relatively high, the heat source cannot be turned on after the start of exposure due to the influence on the exposure, so that a defective fixing area with low fixing strength occurs at the trailing edge of the sheet.

Further, the above-mentioned technique has a problem that the fixability of individual sheets which are continuously fixed cannot be averaged, and the amount of heat supplied is efficiently adjusted by the fixing means. Not used,
Inducing a temperature rise in the copier.

It is an object of the present invention that the light quantity of an exposure lamp does not fluctuate and the temperature of a fixing device when a sheet passes is accurately set to an optimum temperature for fixing a developer image on the sheet. An object of the present invention is to provide a temperature control device for a fixing device that can maintain the temperature.

[0010]

According to a first aspect of the present invention, driving of the heat generating means is started for a predetermined time before the lighting start timing of the exposure light source, and a developer image is generated when the sheet passes through the fixing device. To stop the driving of the heat generating means at the timing after lighting of the exposure light source, which is determined based on the heat generation amount of the heat generating means, the heat capacity of the fixing device, and the passing speed of the paper so as to realize the optimum temperature for fixing. Means are provided. Therefore, in the present invention,
The fixing device achieves the optimum temperature for fixing the developer image when the sheet passes through the fixing device after the driving of the heat generating device is stopped by the drive stopping device.

According to a second aspect of the present invention, the drive stopping means includes temperature measuring means for measuring the temperature of the fixing device, and means for changing the drive stopping timing of the heat generating means based on the temperature measured by the temperature measuring means. And are included.
Therefore, in the present invention, by changing the drive stop timing of the heat generating means after the exposure light source is turned on according to the temperature of the fixing device measured by the temperature measuring means,
The temperature of the fixing device when the sheet passes can be more accurately set to the optimum temperature for fixing the developer image.

According to a third aspect of the present invention, the drive stop timing setting means includes means for changing the drive stop timing of the heat generating means according to the size of the sheet passing through the fixing device. Therefore, in the present invention, the fixing device when the sheet passes by changing the driving stop timing of the heat generating means after the exposure light source is turned on in consideration of the size of the sheet that affects the heat radiation amount of the fixing device. Can be set to a temperature most suitable for fixing the developer image more accurately.

[0013]

FIG. 1 is a front sectional view of a copying machine which is an electrophotographic image forming apparatus to which the present invention is applied. A document cover 31 is provided on the top of the copying machine body 30.
An original table 26 of a transparent glass body covered with is provided. Below the document table 26, a copy lamp 2 and a first mirror are mounted, and the lamp unit 32 is horizontally reciprocally movable. The mirror unit moves at a speed half the speed of the lamp unit. 5, a mirror unit 23 fixed at a fixed position, and a lens 24 movable to a position according to the copy magnification are provided.
A photoconductor 6 is rotatably supported at a substantially central portion of the copying machine main body 30. Around the photosensitive member 6, the main charger 3, the developing cartridge 7, the transfer charger 15,
The cleaner 29 and the static elimination lamp 1 are sequentially arranged in the rotation direction of the photoconductor 6 to form a copying process section. The heat rollers 17 and 18, the heater lamp 19, the thermistor 21a, and the thermal fuse 2 are provided close to the copying process unit.
A fixing device 33 including 1b is provided. At the bottom of the copier body 30, a paper cassette 25 containing paper is stored.
Is installed. A paper conveyance path including the paper feed rollers 11 and 12, the PS roller 13 and the peeling roller 16 is formed between the paper feed cassette 25 and the paper ejection tray 34 via the copying process unit and the fixing device. .

In the main body 30 of the copying machine constructed as described above, when the operator operates a copy switch on the operation panel (not shown), the following copying operation is started. First, the lamp unit 32 moves in the arrow A direction to the home position detected by the sensor 27, and the mirror unit 5 also moves in the arrow A direction accordingly.
Next, the copy lamp 2 is turned on, and the lamp unit 32
And the mirror unit 5 starts moving in the direction of arrow B.
By the movement of the lamp unit 32 and the mirror unit 5, the image of the document placed on the document table 26 is exposed by the copy lamp 2, and the reflected light of the light of the copy lamp 2 on the document is reflected by the mirror unit 5 and the mirror. The light is distributed to the photoconductor 6 through the unit 23 and the lens 24. The surface of the photoconductor 6 is charged with a single polarity by the main charger 3 prior to the exposure of the reflected light from the document, and the surface of the photoconductor 6 is electrostatically latentized by the exposure of the reflected light from the document. An image is formed. A developer is supplied to the electrostatic latent image from the developing cartridge 7 to visualize the developer image.

On the other hand, prior to the movement of the lamp unit 32 or the like, the feeding of paper from the paper feeding cassette 25 is started by the rotation of the paper feeding rollers 11 and 12, and the fed paper is fed to the PS roller 13 at its leading end. It is stopped in the contact state. The PS roller 13 starts rotating at the timing when the front end of the paper and the front end of the developer image formed on the surface of the photoconductor 6 face each other between the photoconductor 6 and the transfer charger 15, and the PS roller 13 moves. The corona discharge transfers the developer image to the surface of the paper. The sheet on which the developer image is transferred is conveyed to the fixing device 33. The fixing device 33 is
The paper is heated and pressed by the upper and lower heat rollers 17 and 18, and the developer image is melted and fixed on the paper. The paper on which the developer image is fixed is discharged to the paper discharge tray 34.

FIG. 2 is a block diagram showing the structure of the control section of the copying machine. The control unit of the copying machine main body 30 is a ROM
The CPU 51 includes a CPU 52 and a RAM 53. A program that defines the operation of the CPU 51 is written in advance in the ROM 52, and the CPU 51 centrally controls each input / output device according to this program. Data input / output during this time is stored in a predetermined memory area of the RAM 53. The CPU 51 is provided with sensors such as a sheet detection sensor S1 for detecting the presence or absence of a sheet in the conveyance path and input devices such as various key switches SW1 provided on the operation panel via the interfaces 54 and 55. It is connected. Further, to the CPU 51, a motor drive circuit 59 such as a main motor M1 for supplying rotation to the photoconductor 6 via the interfaces 56 to 58, and a sheet feeding solenoid SOL for transmitting the rotation of the motor to the sheet feeding roller.
1 etc. Solenoid drive circuit 60 and heater lamp 1
An output device such as a drive circuit 61 for controlling the lighting of 9 is connected. A control circuit 63 that controls the lighting of the copy lamp 2 is connected to the CPU 51 via an interface 62. In addition to this, the CPU 51 is connected with a display circuit for driving the display on the operation panel. CPU51 is a detection signal of the sensor,
The operation signals of the key switches are read, and the motors, solenoids, lamps, etc. are driven and controlled according to the programs in the ROM 52 according to the contents of these signals.

FIG. 3 is a diagram showing in detail the structure of the fixing device of the copying machine. The fixing device 33 includes a pair of upper and lower heat rollers 17 and 18 rotatably. The upper heat roller 18 is formed in a hollow cylindrical shape, and a heater lamp 19 is provided inside the heat roller 18. The lower heat roller 17 is in pressure contact with the upper heat roller 18 by a predetermined pressure via a biasing means (not shown). A paper guide 41 is provided on the upstream side of the heat rollers 17 and 18 in the paper transport direction. The paper guide 41 guides the paper on which the developer image is transferred between the upper and lower heat rollers 17 and 18. The peeling claw 42 is in contact with the peripheral surface on the downstream side of the upper heat roller 18.
The peeling claw 42 peels the sheet passing between the upper and lower heat rollers 17 and 18 from the peripheral surface of the upper heat roller 18.

Further, a thermistor 21a and a thermal fuse 21b are provided close to the peripheral surface of the upper heat roller 18. The thermistor 21a detects the temperature of the upper heat roller 18 and inputs it to the CPU 51 of the control unit. That is, the thermistor 21a converts the detected temperature into a resistance value and outputs the resistance value, and the output signal is converted into digital data by the A / D conversion circuit and input to the CPU 51. CPU5
1 indicates that the copy lamp 2 is not lit,
So that the detection output of the thermistor 21a becomes a predetermined value,
The process control for turning on / off the heater lamp 19 is executed. The temperature fuse 21b is connected to a part of the power supply circuit from the AC power supply to the heater lamp 19 via the heater lamp drive circuit 61, and the temperature of the heat roller 18 abnormally rises when the thermistor 21a fails. At this time, the power to the heater lamp 19 is cut off.

FIG. 4 is a flowchart showing the processing procedure of the control unit of the copying machine according to the embodiment of the invention described in claim 1. When the power of the copying machine body 30 is turned on, the CP
U51 executes the initial operation, sets each input / output device in a state in which the copy operation is possible (s1), and waits for the operator to operate the copy switch (s2). When the copy switch is operated, the CPU 51 turns on the main motor, the high voltage output unit and the static elimination lamp (s3). Next, the CPU 51 starts the paper feeding operation (s4), turns on the heater lamp 19, and activates the timer (s).
5). This timer is used in the memory area MA1 of the RAM 53.
And constitutes a part of the drive stopping means of the present invention for measuring a predetermined time set in advance. CPU
A lamp 51 turns on the copy lamp 2 when a certain time elapses after turning on the heater lamp 19 and turns on the lamp unit 3
2 and the operation of the mirror unit 5 are started at the same time,
Normal temperature control for turning on / off the heater lamp 19 is interrupted (s6). For a certain period of time, the portion of the photoconductor 6 that started to rotate in synchronism with the lighting of the heater lamp 19 and that faced the main charger 3 before the start of rotation reaches the position where the reflected light from the document is exposed. It's time to go. When the timer expires after a predetermined time has passed (s7), the CPU 51 turns off the heater lamp 19 (s8). When the sensor provided on the downstream side of the paper feed roller 12 no longer detects the paper (s9), the CPU 51 turns off the copy lamp 2 and returns the lamp unit 32 and the mirror unit 5, and at the same time, the temperature interrupted at s6. Control is resumed (s10). After this, the CPU 51
Determines whether or not the multi-copy mode is set (s1
1) In the multi-copy mode, the processes of s4 to s11 are repeated. CPU if not in multi-copy mode
51 turns off the high voltage output, the static elimination lamp 1 and the main motor (s12), and returns to s2 where the operation of the copy switch is awaited.

FIG. 5 is a timing chart showing the drive state of the copy lamp, the drive state of the heat roller and the temperature change in the above processing. The CPU 51 suspends the temperature control of the heat roller 18 while the copy lamp 2 is turned on by the processing of s6 in FIG.
The heater lamp 19 starts to be driven for a predetermined time prior to the lighting timing of the copy lamp 2 by the processing of to s7. Therefore, by appropriately setting the predetermined time measured by the timer, the leading edge of the paper is set to the heat roller 1
Before the temperature reaches 7 and 18, the temperature range in which the heat roller 18 can fix the developer while the paper is passing through the heat rollers 17 and 18 (range of 175 to 190 ° C., hereinafter referred to as optimum temperature). The temperature of the heat roller 18 can be raised in advance so as to maintain the temperature. This predetermined time, that is, the time counted by the timer in s5 to s7 is uniquely determined for each model of the copying machine by the power consumption of the heater lamp 2, the sheet conveyance speed, the heat capacity of the heat roller 18, and the like. It's time. Since the normal temperature control is restarted after the copy lamp 2 is turned off, if the temperature of the heat rollers 17, 18 decreases as the paper passes, the heater lamp 19 is restarted by the restarted temperature control.
Is driven, and the temperatures of the heat rollers 17 and 18 return to the optimum temperatures.

When copying work is performed continuously on a plurality of sheets at the time of multi-copy, the temperature of the lower heat roller 17 gradually rises, and accordingly, the temperature of the upper heat roller 18 is lowered. The amount of heat transferred to the heat roller 17 on the side is reduced. Therefore, the preheating time of the heat roller 18 can be shortened as the continuous time of the copying operation during the multi-copy increases. Therefore,
At the time of multi-copy, the number of sheets of paper passing through the fixing device 33 is counted, and the timer time is changed based on the relationship between a predetermined count value and the lighting time of the heater lamp 19 as shown in FIG. 6, for example. You may do it.

FIG. 7 is a diagram showing an example of a power supply input detection circuit of a copying machine according to another embodiment of the invention described in claim 1. In FIG. The amount of heat generated by the heater lamp 19 greatly depends on the input voltage. Therefore, the amount of heat generated by the heater lamp 19 can be more accurately maintained by reading the input voltage and correcting the lighting time according to this value. You can Therefore, after the commercial power supply is input to the transformer 8a and converted into the secondary power supply, full-wave rectification by the diode bridge 8b and smoothing by the capacitor 8c are performed, and the smoothed voltage is divided by the resistors 8d and 8e, and the operational amplifier 8f To the A / D port of the CPU 51 via. Since this circuit does not have a voltage stabilizing circuit, the fluctuation of the commercial power source is level-converted as it is, and the CPU 51 outputs it as an analog voltage.
And is converted into digital data of the power supply voltage inside the CPU 51.

FIG. 8 is a flow chart showing a processing procedure of the control unit of the copying machine including a processing of changing the predetermined time for driving the heater lamp according to the level of the input voltage. CP
U51 is detected by the power supply input voltage detection circuit 8 shown in FIG. 6 between the processing of s4 and the processing of s5 shown in FIG. 4, that is, until the heater lamp 19 is turned on after the start of the paper feeding operation. The output is read (s21), and the driving time of the heater lamp 19 to be set in the timer is determined (s2).
2). The relationship between the power input voltage and the lighting time of the heater lamp 19 shown in FIG. 9, for example, is stored in advance in the ROM 52, and the CPU 51 reads the drive time corresponding to the read power input voltage data and sets it in the timer.

By this processing, the lighting time of the heater lamp 19 is corrected according to the level of the input voltage that affects the heat generation amount of the heater lamp 19, and the paper is heated by the heat roller 17 while the temperature control of the heat roller 18 is interrupted. , 1
Even when the heat roller 18 has passed between 8 and 10, the temperature of the heat roller 18 can be accurately maintained at the optimum temperature.

FIG. 10 shows the first aspect of the invention described in claim 2.
4 is a flowchart showing a processing procedure of a control unit of the copying machine according to the embodiment. CP that constitutes the control unit of this copying machine
U51 is after the processing of s1 to s4 shown in FIG.
After the paper feeding operation is started, the copy lamp 2 is turned on, the scanning of the original image is started, and at the same time, the heater lamp 19 is turned on (s31). At this time, the CPU 51 causes the heat roller 1 to
8 Normal temperature control is interrupted. The CPU 51 turns on the copy lamp 2 after a lapse of a predetermined time to start scanning the original image (s32). Thereafter, the CPU 51 reads the temperature detected by the thermistor 21a, turns on the heater lamp 19 until the temperature of the heat roller 18 becomes equal to or higher than the reference temperature (s33, s34), finishes scanning the original image, and turns off the copy lamp 2. Then, the normal temperature control of the heat roller 18 is restarted (s35, s36). Here, the reference temperature is, for example, a temperature higher by about 5 ° C. than the optimum temperature.

By this processing, the heater lamp 19 is continuously driven until the heat roller 18 reaches a predetermined temperature,
Even when the paper passes between the heat rollers 17 and 18 while the temperature control of the heat roller 18 is interrupted,
The temperature of the heat roller 18 can be maintained at the optimum temperature.

FIG. 11 is a diagram showing the configuration of a zero-cross detection circuit provided in the above copying machine. FIG.
FIG. 4 is a diagram showing signal waveforms at various parts of this zero-cross detection circuit. The AC power supply having the waveform shown in FIG. 12A is input to the transformer 71, and the diodes D1 to D4 are input.
In the diode bridge 72 constituted by FIG.
The waveform is shaped into the waveform shown in FIG. 2B, and the comparator 73 produces the waveform shown in FIG. Furthermore, the inverter 7
4 inverts the waveform as shown in FIG.
Input to the interrupt terminal of U51. As a result, the CPU 51
Recognizes the zero crossing point of the AC power supply.

Therefore, in the CPU 51, the odd-numbered input signal from the zero-cross detection circuit 70 to the interrupt terminal is set as the 0th cycle, and the even-numbered input signal is set as the first cycle, and two consecutive 0th and 1st cycles are set. By turning on / off the voltage application to the heater lamp 19 based on the input signal, the heater lamp 19 is controlled to be lit by so-called proportional control, and the heat roller 1
It is possible to prevent the temperature of 8 from changing rapidly.

FIG. 13 shows a second aspect of the invention described in claim 2.
4 is a flowchart showing a processing procedure of a control unit of the copying machine according to the embodiment. CP that constitutes the control unit of this copying machine
U51 reads the temperature detected by the thermistor 21a (s41) between the processing of s4 and the processing of s5 shown in FIG. The driving time of the heater lamp 19 to be set in the timer is determined based on the relationship between the temperature of the heat roller 18 and the lighting time stored in advance (s42). The relationship between the current temperature of the heat roller 18 and the lighting time of the heater lamp 19 shown in FIG. 14, for example, is stored in advance in the ROM 52, and the CPU 51 reads the drive time corresponding to the current temperature of the heat roller 18 and uses it in a timer. Set. By this processing, the lighting time of the heater lamp 19 is corrected according to the current temperature of the heat roller 18, and even when the paper passes between the heat rollers 17 and 18 in the state where the temperature control of the heat roller 18 is interrupted, the heat is applied. The temperature of the roller 18 can be accurately maintained at the optimum temperature.

In the relationship shown in FIG. 14, the control temperature of the heat roller 18 is 185 ± 3 ° C., the diameter of the heat roller 18 is 25 mm, and the power consumption of the heater lamp 19 is 800.
W is the optimum time when the paper conveyance speed in the copying process is 90 mm / sec.

FIG. 15 shows a third aspect of the invention described in claim 2.
4 is a flowchart showing a processing procedure of a control unit of the copying machine according to the embodiment. CP that constitutes the control unit of this copying machine
U51 is before and after driving the heater lamp 19 for a preset time Ts during the waiting period until the copy switch is operated after the power is turned on, that is, during the processing of s1 and s2 shown in FIG. The temperature rise of the heat roller 18 per unit time is calculated from the detection output of the thermistor 21a, and the calculation result is stored in the RAM 53 (s51 to s57). The CPU 51 reads the calculation result stored in the RAM 53 when the timer is started in s5, and relates to the relationship between the temperature rise of the heat roller 18 per unit time and the lighting time of the heater lamp 19 stored in advance in the ROM 52. Based on this, the driving time of the heater lamp 19 to be set in the timer is determined. The ROM 52
In FIG. 16, the relationship between the temperature rise of the heat roller 18 and the lighting time of the heater lamp 19 per unit time is stored in the state shown in FIG. 16, for example.

By the above processing, it is possible to correct the error of the optimum lighting time of the heater lamp 19 due to the individual difference of the heat capacity of the heat roller 18 and the heat generation amount of the heater lamp 19, and the temperature control of the heat roller 18 is interrupted. In this state, the temperature of the heat roller 18 can be accurately maintained at the optimum temperature while the sheet passes between the heat rollers 17 and 18.

FIG. 17 shows a fourth aspect of the invention described in claim 2.
4 is a flowchart showing a processing procedure of a control unit of the copying machine according to the embodiment. CP that constitutes the control unit of this copying machine
U51 turns on the heater lamp 19 in synchronization with the feeding of the paper (s4, 5), and starts turning on the copy lamp 2 (s6). When the heater lamp 19 is turned on, the temperature detected by the thermistor 21a is changed. The time is read and stored in the RAM 53 (s61), the time to be set in the timer is determined based on the previous temperature correction data stored in the RAM 53, the determined time is set and the timer is activated (s62, s63). ). The CPU 51 turns off the heater lamp 19 when the timer times out (s64, s65), reads the detected temperature of the thermistor 21a (s66), and calculates the difference from the detected temperature of the thermistor 21a read when the heater lamp 19 is turned on. The current temperature correction data is stored in the RAM 53 (s67).

By the above processing, the heat roller 1 of the last time
It is possible to determine the lighting time of the heater lamp 19 in the current temperature increasing process based on the temperature correction data in the temperature increasing process of No. 8, and not only the individual difference of each member constituting the fixing device 33 but also the outside temperature such as the temperature. In consideration of the influence of the environment, the control for maintaining the temperature of the heat roller 18 at the optimum temperature while the paper is passing between the heat rollers 17 and 18 while the temperature control of the heat roller 18 is being interrupted is more accurate. It can be done very carefully. FIG.
6 is a flowchart showing a processing procedure of a control unit of the copying machine according to the embodiment of the invention described in claim 3. CPU5
1 detects the paper size to be fed before starting the paper feeding operation in s4 shown in FIG. 4 (s71), and determines the time measured by the timer according to the detected paper size (s7).
2). The relationship between each paper size and the lighting time of the heater lamp 19 is stored in advance in the ROM 52, and the time to be set in the timer is determined with reference to this relationship.

The amount of heat transferred from the heat roller 18 to the paper passing between the heat rollers 17 and 18 changes depending on the size of the paper, but even if the size of the paper changes due to this processing, the heat roller 18 will not be affected. The control for maintaining the temperature of the heat roller 18 at the optimum temperature can be accurately performed while the sheet passes between the heat rollers 17 and 18 with the temperature control being interrupted.

Further, as shown in FIG. 19, the CP of the control unit
The U51 waits until the temperature of the heat roller 18 drops after stopping the driving of the heater lamp 19, measures the temperature drop of the heat roller 18 at a predetermined time based on the temperature detected by the thermistor 21a, and stores it in the RAM 52. (S
82-s88), the next lighting time of the heater lamp 19 may be determined based on this lowered temperature (s).
81). In this case, the heat roller 1 is previously stored in the ROM 52.
The relationship between the lowering temperature of No. 8 and the lighting time of the heater lamp 19 is stored, and the time to be set in the timer can be determined by referring to this relationship.

By this processing, the paper is heated while the temperature control of the heat roller 18 is interrupted in order to cope with the case where the size of the paper passing between the heat rollers 17 and 18 is changed without detecting the paper size. Rollers 17, 18
The control for maintaining the temperature of the heat roller 18 at the optimum temperature can be accurately performed during the passage through the space.

[0038]

According to the first aspect of the present invention, the heat generating means of the fixing device is driven during a certain period of time before the exposure light source is turned on, so that the drive stop means turns on the exposure light source. While the sheet is passing through the fixing device after the driving of the heating device is stopped, the temperature of the fixing device can be set to the optimum temperature for fixing the developer image without driving the heating device. The power supplied to the exposure light source is not reduced and the image does not have uneven density.

According to the second aspect of the invention, when the sheet passes through by changing the driving stop timing of the heat generating means after the exposure light source is turned on according to the temperature of the fixing device measured by the temperature measuring means. The temperature of the fixing device can be more accurately set to the optimum temperature for fixing the developer image.

According to the third aspect of the present invention, the driving stop timing of the heat generating means after the exposure light source is turned on is changed in consideration of the size of the paper which influences the heat radiation amount of the fixing device. The temperature of the fixing device when the toner passes through can be more accurately set to the optimum temperature for fixing the developer image.

[Brief description of drawings]

FIG. 1 is a schematic front cross-sectional view of a copying machine according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration of a control unit of the copying machine.

FIG. 3 is a diagram showing a configuration of a fixing device of the copying machine.

FIG. 4 is a flowchart showing a processing procedure of a control unit of the copying machine according to the embodiment of the invention described in claim 1;

FIG. 5 is a timing chart showing the relationship between the drive state of the copy lamp, the drive state of the heat roller, and the temperature change in the above process.

FIG. 6 is a diagram showing the relationship between the number of sheets of paper passing through the fixing device 33 and the lighting time of the heater lamp 19 during multi-copy.

FIG. 7 is a diagram showing an example of a power supply input detection circuit of a copying machine according to another embodiment of the invention described in claim 1;

FIG. 8 is a flowchart showing a processing procedure of the control unit of the copying machine including a processing of changing a predetermined time for driving the heater lamp according to the level of the input voltage.

FIG. 9 is a diagram showing a relationship between a power supply input voltage and a lighting time of a heater lamp 19.

FIG. 10 is a flowchart showing a processing procedure of a control unit of the copying machine according to the first embodiment of the invention described in claim 2;

FIG. 11 is a diagram showing a configuration of a zero-cross detection circuit provided in the copying machine.

FIG. 12 is a diagram showing a signal waveform in each part of the zero-cross detection circuit.

FIG. 13 is a flowchart showing a processing procedure of a control unit of a copying machine according to a second embodiment of the invention described in claim 2;

14 is a diagram showing the relationship between the current temperature of the heat roller 18 and the lighting time of the heater lamp 19. FIG.

FIG. 15 is a flowchart showing a processing procedure of a control unit of a copying machine according to a third embodiment of the invention described in claim 2;

16 is a diagram showing the relationship between the temperature rise of the heat roller 18 per unit time and the lighting time of the heater lamp 19. FIG.

FIG. 17 is a flowchart showing a processing procedure of a control unit of a copying machine according to a fourth embodiment of the invention described in claim 2;

FIG. 18 is a flowchart showing a processing procedure of a control unit of the copying machine according to the embodiment of the invention described in claim 3;

FIG. 19 is a flowchart showing a processing procedure of a control unit of a copying machine according to another embodiment of the invention described in claim 3;

[Explanation of symbols]

 2-Copy lamp (exposure light source) 6-Photoreceptor 17, 18-Heat roller 21a-Thermistor (temperature measuring means) 33-Fixing device

Claims (3)

[Claims] 1. A temperature of a fixing device used in a copying machine using an electrophotographic method, which heats and presses a developer image formed on the basis of reflected light of an original from light of an exposure light source to fix it on a sheet. Regarding a control device for executing process control with a preset constant temperature as a target value, the process control is interrupted and driving of the heat generating means is started in advance of a predetermined time before the lighting start timing of the exposure light source,
After turning on the exposure light source determined based on the heat generation amount of the heat generating means, the heat capacity of the fixing device and the passing speed of the paper so that the optimum temperature for fixing the developer image is realized when the paper passes through the fixing device. A temperature control device for a fixing device, characterized in that drive stop means for stopping the drive of the heat generating means is provided at the timing. 2. The drive stopping means comprises temperature measuring means for measuring the temperature of the fixing device, and means for changing the drive stopping timing of the heat generating means based on the temperature measured by the temperature measuring means.
The temperature control device for a fixing device according to claim 1, further comprising: 3. The temperature control device for a fixing device according to claim 1, wherein the drive stop timing setting device includes a device for changing the drive stop timing of the heat generating device in accordance with the size of a sheet passing through the fixing device.