JP2002258663A - Heat fixing device and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem of a rapid temperature drop or temperature rise generated in continuous image formation resulting in fixing instability. SOLUTION: In the device, the target temperature for a fixing roll and a fixing belt is varied as needed according to the variation of detected temperature of a temperature detecting means 37 when forming an image.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat fixing device having a fixing belt and an image forming apparatus such as a printer, a copying machine, a facsimile and the like.

[0002]

2. Description of the Related Art A fixing device for fixing a toner image on a sheet to a sheet is used in an image forming apparatus such as a printer, a copying machine, and a facsimile. The fixing device includes a heat fixing device having a fixing belt. Japanese Patent Application Laid-Open No. H11-29882 discloses that, upon receiving a start signal of an image forming operation, a fixing belt surface temperature set value is changed from a fixing high temperature setting temperature to a fixing low temperature setting temperature at the time of fixing after rotation of the fixing belt is started. A thermal fixing device that switches and performs fixing temperature control is described.

[0003]

A thermal fixing device having a fixing belt has a general configuration as shown in FIG.
A high power heater (for example, a 750 W heater) 2 is provided as a heat source inside the heating roller 1, and a power saving heater (for example, a 350 W heater) 4 is provided as a heat source inside the pressure roller 3.

[0004] The power within the range permitted as a fixing device is the total number of W of the heaters, for example, 1100 W. However, since the image forming apparatus generally operates not only the fixing device but also load devices such as a motor, a solenoid and a high-voltage power supply, and peripheral devices such as a sorter and a paper feeding bank, the fixing device is in standby mode when these devices do not consume power. Full-power heating (1100W consumption of the heater) is possible, but with this W number, the W number of the entire apparatus exceeds the allowable W number at the time of image formation. Sometimes it is not allowed.

Therefore, in the above heat fixing apparatus, it has been studied to turn on only the heater 2 and not turn on the heater 4 during image formation. However, when only the heater 2 is turned on at the time of image formation, the temperature of the heat fixing device drops sharply and rises during continuous image formation, and the fixability becomes unstable.

An object of the present invention is to provide a heat fixing device and an image forming apparatus capable of preventing a sharp drop in temperature and a rise in temperature during continuous image formation and stabilizing the fixing property. Aim.

[0007]

Means for Solving the Problems In order to achieve the above object, the invention according to claim 1 comprises a fixing roller and a heating roller, an endless fixing belt stretched over the fixing roller and the heating roller, and A pressure roller pressed against the fixing roller via a fixing belt, and a heat source for heating at least the heating roller of the heating roller and the pressure roller, wherein the fixing roller and the pressure roller In a heat fixing device for fusing a toner image on the sheet to the sheet while nipping and conveying the sheet between the fixing belt and the pressure roller at the formed nip, the temperature of the fixing roller and the fixing belt is adjusted. A first temperature detecting means for detecting, a second temperature detecting means for detecting the temperature of the pressure roller, and a constant periodic interval between the first temperature detecting means and the second temperature detecting means. Control means for controlling the heat source so that the detected temperatures become a constant temperature near the first target temperature and a constant temperature near the second target temperature, respectively. The first target temperature is changed as needed in accordance with a change in the detected temperature.

According to a second aspect of the present invention, in the thermal fixing device according to the first aspect, the first target temperature is reduced during image formation in a full-color image forming mode.

The invention according to claim 3 is the invention according to claim 1 or 2
In the thermal fixing device described above, the first target temperature is increased during image formation in a monocolor image forming mode.

According to a fourth aspect of the present invention, there is provided a heat fixing device according to the first, second or third aspect.

[0011]

FIG. 2 schematically shows an embodiment of the present invention. This embodiment is an example of a color laser printer as an image forming apparatus. The photoreceptor as an image bearing member is wound around a plurality of rollers 6 using, for example, an endless photoreceptor belt 5, and one of the plurality of rollers 6 is used as the image bearing member.
When the two rollers are rotationally driven by a drive source (not shown), the photosensitive belt 5 is rotationally driven in the direction of the arrow.

When a full-color image forming mode is selected by the operation unit and the start key is pressed, the photosensitive belt 5
Is uniformly charged by a charging brush 7 as a charging unit, and then is first exposed to a light beam modulated by a black (hereinafter referred to as K) image signal by a writing device 8 as an exposure unit, and is statically corresponding to the K image signal. Electro latent image (K
A latent image is formed.

K developing device 9 as a developing means, yellow (hereinafter referred to as Y) developing device 10, cyan (hereinafter referred to as C)
Developing device 11 and magenta (hereinafter referred to as M) developing device 12
Are moved to the developing position by the contact / separation mechanisms 13 to 16 during development, respectively, and returned to the home position by the contact / separation mechanisms 13 to 16 during non-development. The K latent image on the photoreceptor belt 5 is developed with a K toner by a K developing unit 9 to become a K toner image.

On the other hand, an endless intermediate transfer belt 17 as an intermediate transfer member is stretched over a plurality of rollers 18 to 20 and abuts on the photoreceptor belt 5 on a roller 6. One of the rollers is rotationally driven by a drive source (not shown), so that the intermediate transfer belt 17 rotates in the direction of the arrow at the same peripheral speed as the photosensitive belt 5. A primary transfer brush 21 serving as a primary transfer means contacts the intermediate transfer belt 17 at a primary transfer portion where the intermediate transfer belt 17 contacts the photoreceptor belt 5 on the roller 6 and a transfer bias from a power source (not shown). Then, the K toner image on the photosensitive belt 5 is transferred to the intermediate transfer belt 17. The photoreceptor belt 5 is cleaned by the photoreceptor cleaning device 22 after the K toner image is transferred, and is uniformly discharged by the discharging brush 23.

Next, after the photosensitive belt 5 is uniformly charged by the charging brush 7, the photosensitive belt 5 is exposed to a light beam modulated by the Y image signal by the writing device 8, and an electrostatic latent image corresponding to the Y image signal is obtained. (Hereinafter referred to as a Y latent image). The Y latent image on the photoreceptor belt 5 is developed with a Y toner by a Y developing device 10 to become a Y toner image, and the Y toner image on the photoreceptor belt 5 is intermediately transferred by a primary transfer brush 21 in a primary transfer section. The toner image is transferred onto the transfer belt 17 so as to overlap the K toner image. The photoreceptor belt 5 is cleaned by the photoreceptor cleaning device 22 after the transfer of the Y toner image, and is uniformly discharged by the discharging brush 23.

Next, after the photosensitive belt 5 is uniformly charged by the charging brush 7, the photosensitive belt 5 is exposed to a light beam modulated by the C image signal by the writing device 8, and an electrostatic latent image corresponding to the C image signal is obtained. (Hereinafter referred to as C latent image) is formed. The C latent image on the photoreceptor belt 5 is developed with a C toner by a C developing device 11 to become a C toner image, and the C toner image on the photoreceptor belt 5 is intermediately transferred by a primary transfer brush 21 in a primary transfer section. The K toner image and the Y toner image are transferred onto the transfer belt 17 in a superimposed manner. The photoreceptor belt 5 is cleaned by the photoreceptor cleaning device 22 after the transfer of the C toner image, and is uniformly discharged by the discharging brush 23.

Next, after the photosensitive belt 5 is uniformly charged by the charging brush 7, the photosensitive belt 5 is exposed to a light beam modulated by the M image signal by the writing device 8, and an electrostatic latent image corresponding to the M image signal is obtained. (Hereinafter referred to as an M latent image). The M latent image on the photoreceptor belt 5 is developed with the M toner by the M developing device 12 to form an M toner image, and the M toner image on the photoreceptor belt 5 is intermediately transferred by the primary transfer brush 21 in the primary transfer section. By transferring the K toner image, the Y toner image, and the C toner image onto the transfer belt 17 in a superimposed manner, a four-color superimposed full-color image is formed on the intermediate transfer belt 17.
The photoreceptor belt 5 is cleaned by the photoreceptor cleaning device 22 after the transfer of the M toner image.
The charge is removed evenly.

The paper feeder 24 feeds the paper to a registration roller 25, and the registration roller 25 sends the paper to a secondary transfer unit in accordance with the full-color image on the intermediate transfer belt 17. This paper is transferred to a secondary transfer unit 26 at a secondary transfer unit.
The full-color image on the intermediate transfer belt 17 is transferred, and the full-color image is fixed by the heat fixing device 27. When a single-sided image is formed, the full-color image is discharged to a discharge tray at the top of the device by a discharge roller.

At the time of forming a double-sided image, the sheet that has passed through the heat fixing device 27 is sent to the registration roller 25 after being turned upside down by the double-sided device 29, and the full-color image on the intermediate transfer belt 17 is transferred by the registration roller 25 as described above. The full-color image on the intermediate transfer belt 17 is transferred to the back surface by the secondary transfer device 26 at the secondary transfer portion, and the full-color image on the back surface is fixed and discharged by the heat fixing device 27. The paper is discharged by a paper roller 28 to a paper discharge tray at the top of the apparatus. Also, the intermediate transfer belt 1
7 is cleaned by the cleaning device 30 after the full-color image transfer.

When a mono-color image forming mode is selected on the operation unit and the start key is pressed, a mono-color image forming process is performed. In this case, the writing device 8 performs writing on the photoreceptor belt 5 with monochromatic image data to form an electrostatic latent image, and this electrostatic latent image is developed by one of the developing units 9 to 12. Is transferred to the intermediate transfer belt 17. The single-color toner image on the intermediate transfer belt 17 is transferred to a transfer sheet, and the transfer sheet is fixed on the toner image by the heat fixing device 27 and is discharged to a discharge tray.

FIG. 3 shows the structure of the heat fixing device 27.
The endless fixing belt 31 is stretched over the fixing roller 32, the heating roller 1, and the auxiliary roller 33, and at least one of these rollers is rotationally driven by a driving source (not shown), so that the fixing belt 31 is conveyed and rotated. The auxiliary roller 33 is disposed below the fixing roller 32. The pressure roller 3 is disposed at a position where the fixing belt 31 is pressed against the fixing roller 32, and is fixed by a pressure mechanism (not shown).
Is pressed against the fixing roller 32. The nip formed by the pressing roller 3 and the fixing roller 32 causes the unfixed toner on the sheet 34 while holding the sheet 34 conveyed between the fixing belt 31 and the pressing roller 3 from below by the pressure. 35 is fused to the paper 34.

The heating roller 1 has a built-in heating heater 2 as a heat source, and is heated by the heating heater 2 to heat the fixing belt 31 while rotating it. The pressure heater 3 is provided with a pressure heater 4 as a heat source inside, and is heated by the pressure heater 4. The thermistor 36 as a temperature detecting means is arranged in contact with the outer peripheral surface of the heating roller 1, and detects the surface temperature of the fixing belt 31 by detecting the surface temperature of the heating roller 1.
The thermistor 37 as a temperature detecting means is
And is disposed in contact with the outer peripheral surface of the pressure roller 3 to detect the surface temperature of the pressure roller 3. The fixing control unit using a CPU (not shown) feeds back the temperature detection signals from the thermistors 36 and 37 so that the surface temperature of the heating roller 1 and the surface temperature of the pressure roller 3 become constant temperatures near the target temperatures. The heater 2 and the pressure heater 4 are controlled, and the surface temperature of the heating roller 1 is adjusted within a control target value ± 5 ° C.

FIG. 1 shows a fixing control section of the heat fixing device 27. One end of the heater 2 and the pressure heater 4 is connected to a relay 4.
5 is connected to one side of a commercial AC power supply 39 via a normally open contact 38, and a triac as a switch element is provided between the other end of the heater 2 and the pressure heater 4 and the other side of the AC power supply 39. 40 and 41 are respectively connected. The triacs 40 and 41 are respectively connected to the control driver 4
2 and 43, the control drivers 42 and 43
Denotes a CPU (microcomputer) 4 as control means
4 is turned on / off.

The coil of the relay 45 is connected to the D through a switching transistor 43 as a switching element.
The control driver 47 is connected between the power supply of C24V and the ground, and the
Is turned on / off, thereby turning on / off the relay 45. Therefore, when the relay 45 is on and the triacs 40 and 42 are turned on, power is supplied from the AC power supply 39 to the heaters 2 and 4 via the triacs 40 and 42, and the heaters 2 and 4 are turned on. 1 and the pressure roller 3 are heated by heaters 2 and 4.

The thermistors 36 and 37 detect the surface temperature of the heating roller 1 and the surface temperature of the pressure roller 3, respectively, and the temperature detection signals from the thermistors 36 and 37 are input to the CPU 44. The CPU 44 has a built-in A
The temperature detection signals from the thermistors 36 and 37 are converted into digital signals by a / D converter, and the surface temperature data of the heating roller 1 and the surface temperature data of the pressure roller 3 are obtained by a program.

The CPU 44 controls the triac 40 via the control driver 42 based on the surface temperature of the heating roller 1 detected by the thermistor 36 to control the heating of the heater 2.
Of the pressure roller 3 detected by the thermistor 37 based on the surface temperature of the pressure roller 3.
The control of the triac 41 via 3 controls the lighting / extinguishing of the pressure heater 4.

The CPU 44 receives a detection signal from a cover switch (SW) 48 for detecting whether or not the main body cover (door) of the color laser printer is opened, and when the main body key is opened, the control driver 47. To turn off the transistor 46,
The relay 45 is turned off. When the main body cover is closed, the CPU 44 turns on the control driver 47 to turn on the transistor 46, thereby turning on the relay 45. Therefore, when the main body cover is open, the heater 2 and the pressure heater 4 do not light up.

FIG. 4 shows a flow chart of the heater control by the fixing control unit. When two heaters and two thermistors are used as in the case of the thermal fixing device 27, the fixing control unit independently performs two heater energization control flows shown in FIG. 4 on the heating roller 1 side and the pressure roller 3 side. Then, control for managing each control target temperature is performed. That is, the CPU 44 controls the energization of the heater 2 and the pressurizing heater 4 independently according to the heater energization control flow shown in FIG.

The CPU 44 always forms a loop at regular intervals and monitors whether there is any factor that turns off the heat fixing device 27 (heaters 2 and 4) (step S).
1). The CPU 44 turns off the relay 45 when there is a factor for turning off the heat fixing device 27 (heaters 2 and 4) such as opening of the main body cover by a command from the control unit of the color laser printer (step S1). S2) The heaters 2 and 4 are turned off (step S3).
The power supply to 4 is stopped. The CPU 44 controls the heat fixing device 2
If there is no cause for turning off the heater 7 (heaters 2 and 4),
The period timer to be counted by the CPU 44 is set to, for example, one second, and the period timer is started (step S4).

Next, the CPU 44 comprises the thermistors 36, 3
7 to obtain the current temperature value (step S
5) The amount of power (ON time) to the heaters 2 and 4 is calculated from the difference between the obtained current temperature value and the control temperature target value (step S6). In general, a method such as a PID calculation method is used as a well-known technique for calculating the amount of electricity supplied to the heater, and a multiplier (gain) of a calculation method including three terms of a proportional term, a differential term, and an integral term is used as a fixing roller. By setting the set value in consideration of the model-specific conditions such as the heat capacity of the heater and the number of W of the heating element, it is possible to achieve optimum temperature control without overshoot and control ripple.

The CPU 44 sets a timer value according to the calculation result of the energization amount (ON time) to the heaters 2 and 4 to the energization time timer and starts the energization time timer (step S7). Then, the outputs to the heaters 2 and 4 are turned on to turn on the heaters 2 and 4 (step S8). In the subsequent processing, the CPU 44 performs a waiting process in a loop of step S9 until the energized time timer that has been started times out, and outputs an output to the heaters 2 and 4 when the energized time timer has expired. The heater is turned off to turn off the heater (step S10).

Next, the CPU 44 proceeds to step S11 until the started period timer expires.
When the cycle timer times out, the energization processing loop for one cycle is completed, so the process returns to step S1 and the energization processing is performed again in the next cycle.

FIG. 5 shows the control driver 42 from the CPU 44,
Reference numeral 43 denotes an output signal for turning on / off the heaters 2 and 4 in the final stage as described above. CPU4
4 performs calculation to determine the on-Duty of the heater 2 and 4 for every predetermined periodic interval, to determine the on-time _{T 0} of the heater 2 and 4. As described above, the time T ₀ is not always constant because a value which determines the difference between the current temperature value and the control target temperature (control target temperature). The CPU 44
At the same time, to turn on the output of the control driver 43, the time T ₀ is turned off the output to the control driver 43 at the same time the time is up. After that, CPU4
4 are control drivers 42 and 43 until the next operation cycle comes.
Keep the output to off. The CPU 44 eliminates the difference between the current temperature value and the control temperature target value by repeatedly performing this cycle.

FIG. 6 shows a control target temperature change processing flow on the heating side (heating roller 1 side) of the fixing control section. CPU4
No. 4 performs this process once for each sheet by triggering the start of the image forming operation (print start) (step S1). The CPU 44 first operates on the pressure side (the pressure roller 3
The current temperature value of the pressure roller 3 is acquired from the thermistor 37 (step S2), and it is determined whether or not the acquired current temperature value is outside a certain temperature range (X ° C. to Y ° C.) (step S2). S3, S5).

When the obtained current temperature value is equal to or lower than the fixed temperature threshold value (X ° C.), the CPU 44 sets the heating-side control target temperature (the control target temperature on the heating roller 1 side) to a fixed temperature, for example, 3 ° C is added (step S4), and if the acquired current temperature value is equal to or higher than the fixed temperature threshold value (Y ° C), the heating side control target temperature (the control target temperature of the heating roller 1) is changed to a fixed temperature. For example, 3 ° C. is subtracted (step S6).

In this case, constant temperature threshold values X ° C., Y ° C.
Is the current temperature value on the pressure side (current temperature value of the pressure roller 3)
Takes a value in a range that does not adversely affect the fixability of the image. That is, when the current temperature value on the pressure side falls below X ° C., the temperature on the heating side is raised, and the heat is transferred to the pressure side through the fixing belt 31 to prevent defective fixing. Further, when the current temperature value on the pressure side rises to Y ° C. or more, the temperature on the heating side is lowered to fix the fixing belt 3.
Excessive fixing is prevented by reducing the wraparound of the temperature from 1 to the pressure side.

FIG. 7 is a flowchart showing a process for changing the heating-side control target temperature of the fixing controller. The CPU 44 performs this process once for each sheet in response to a trigger for starting the image forming operation (print start) (step S1). CPU
Reference numeral 44 determines the image forming mode (print mode) (step S2), and if the print mode is the full-color image forming mode, sets the control target temperature on the heating side to X ° C .; In the case of the mode, the control target temperature on the heating side is set to Y ° C.

By the way, the pressure roller has poor temperature responsiveness, and when the image formation is repeatedly and continuously performed, the heat is easily taken away by the paper, and the temperature drops rapidly. Further, in the image forming mode in which the paper transport interval is long, an overshoot of the temperature of the pressure roller occurs at the paper transport interval.

However, according to the heat fixing device of the present embodiment, the thermistor 36 as a first temperature detecting means for detecting the temperatures of the fixing roller 32 and the fixing belt 31 and the second temperature detecting means for detecting the temperature of the pressure roller 3 A thermistor 37 as a second temperature detecting means, and a heat source such that the temperatures detected at regular intervals by the thermistors 36 and 37 become a constant temperature near the first target temperature and a constant temperature near the second target temperature, respectively. And a CPU 44 as a control means for controlling the heating heater 2 and the pressure heater 4 as the control unit. The first target temperature is changed at any time according to a change in the temperature detected by the thermistor 37 during image formation. The fixing target temperature of the fixing belt (control target temperature of the heating roller) is changed in accordance with the detected temperature of Rukoto can.

In the case of the color image forming mode, the conveyance interval of the paper is long, and the temperature of the pressure roller overshoots between the papers. However, according to the heat fixing device of the present embodiment, during image formation in the full-color image forming mode, the temperature rise of the pressure roller is predicted and the target temperature of the fixing belt is lowered, so that the fixing temperature is set to the target temperature. Can be maintained, and the fixing property can be stabilized.

In the case of the mono-color image forming mode,
When the image formation is repeated and performed continuously, the heat of the pressure roller is easily taken by the paper, and the temperature rapidly drops. However, according to the heat fixing device of the present embodiment, the target temperature of the fixing belt is raised during the image formation by predicting the temperature decrease of the pressure roller in the mono-color image forming mode, so that the fixing temperature is maintained at the target temperature. And fixability can be stabilized.

Further, according to the present embodiment, since the above-mentioned heat fixing device is provided, it is possible to obtain an image-formed product having a stable toner image fixing property.

[0043]

As described above, according to the first aspect of the present invention, it is possible to change the control target temperature of the fixing belt in accordance with the temperature detected by the pressure roller, thereby maintaining the fixing temperature at a target temperature. Fixability can be stabilized. According to the second aspect of the invention, the fixing temperature can be maintained at a target temperature during image formation in the full-color image forming mode, and the fixing property can be stabilized.

According to the third aspect of the invention, the fixing temperature can be maintained at a target temperature in the mono-color image forming mode, and the fixing property can be stabilized. According to the fourth aspect of the invention, it is possible to obtain an image-formed product having a stable toner image fixing property.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a fixing control unit of a heat fixing device according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view schematically showing the embodiment.

FIG. 3 is a front view showing the heat fixing device of the embodiment.

FIG. 4 is a flowchart illustrating a heater energization control flow of a fixing control unit according to the first embodiment.

FIG. 5 is a waveform chart showing an output signal from a CPU to a control driver in the embodiment.

FIG. 6 is a flowchart illustrating a heating-side control target temperature change processing flow of a fixing control unit according to the first embodiment.

FIG. 7 is a flowchart showing a heating-side control target temperature change processing flow of a fixing control unit in the embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Heating roller 2 Heater 3 Pressure roller 4 Pressure heater 31 Fixing belt 32 Fixing roller 36, 37 Thermistor 40, 41 Triac 44 CPU

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H027 DA12 DA38 EA12 EC06 EC07 EC20 FA28 FA35 2H030 AD04 AD07 AD18 BB02 BB23 BB33 BB42 BB63 2H033 AA03 BA11 BA25 BA32 BB18 BB34 CA04 CA07 CA30 CA45 CA48 5H420 CC05 DD03 DD05 EB05 EA05 FF26

Claims (4)

[Claims] An endless fixing belt extending between the fixing roller and the heating roller; a pressure roller pressed against the fixing roller via the fixing belt; A heat source for heating at least the heating roller of the roller and the pressure roller, and nipping a sheet between the fixing belt and the pressure roller at a nip formed by the fixing roller and the pressure roller. In a heat fixing device for fusing a toner image on the sheet to the sheet while being conveyed, first temperature detecting means for detecting the temperatures of the fixing roller and the fixing belt, and detecting the temperature of the pressure roller A second temperature detecting means;
The heat source is controlled such that the temperatures detected by the temperature detecting means and the second temperature detecting means at regular intervals become a constant temperature near the first target temperature and a constant temperature near the second target temperature, respectively. Control means for performing the first temperature control in response to a change in the temperature detected by the second temperature detection means during image formation.
Wherein the target temperature is changed at any time. 2. The heat fixing device according to claim 1, wherein the first target temperature is reduced during image formation in a full-color image forming mode. 3. The heat fixing device according to claim 1, wherein the first target temperature is increased during image formation in a mono-color image forming mode. 4. An image forming apparatus comprising the heat fixing device according to claim 1, 2 or 3.