JPH05127552A - Image fixing device - Google Patents

Abstract

PURPOSE:To automatically perform warm-up to always keep the temperature of the roller of an image fixing device by which a powder image formed on a recording medium is fixed at a specified temperature. CONSTITUTION:This device is provided with a heater driver part 8 for heating the roller, a roller driving part 10 for rotating the roller, and a storage means 12 where a driving table for them is stored. A CPU 1 controls to drive the roller in high speed roller driving time by 1st speed which is used at the time of fixing and in a roller driving period by 3rd speed which is lower than the 1st speed and higher than 2nd speed at the time of standing by. Then, the roller driving period by the 3rd speed is decided by measuring the time obtained until a temperature detection part 4 detects that the temperature of the roller attains specified temperature by means of a timer 11 and referring to the driving table.

Description

Detailed Description of the Invention

[0001]

The present invention relates to a laser beam printer,
The present invention relates to an image fixing device which is used in a copying machine or the like and controls a fixing temperature and a rotation speed of a fixing roller.

[0002]

2. Description of the Related Art In recent years, as the functions of computer systems such as personal computers have been improved, high-speed and high-quality printers have been demanded. An electrophotographic method has been put into practical use as a high-speed printer. In a general electrophotographic apparatus of this type, a uniformly charged photoconductor is exposed with a laser beam or the like to form a latent image, which is developed with fine powder (hereinafter referred to as toner) to form a powder image. (Hereinafter referred to as a toner image) is formed. This toner image is transferred to a recording medium (hereinafter referred to as recording paper), and the toner image transferred to the recording paper is fixed on the recording paper by heat, pressure, or both,
Get the output image.

The image fixing device used for such fixing is
It is composed of a heating roller having at least a heating means and a pressure roller in pressure contact with a fixing roller, and conveys recording paper having a toner image formed on the surface between the pair of heated and pressurized rollers while sandwiching the recording paper. , Heat and pressure are applied to the toner image for a short time to fix it on the recording paper.

A conventional image fixing device will be described below with reference to FIG.
~ It demonstrates using FIG. 8 is a cross-sectional view showing the configuration of the image fixing device, FIG. 9 is an enlarged view of a fixing portion, FIG. 10 is a block configuration diagram of a temperature controller of the image fixing device, and FIG. 11 is a conventional image. FIG. 12 is a control flow of the fixing device, and FIG. 12 shows a control result of the conventional image fixing device.

In FIG. 8, reference numeral 101 denotes a heating roller, which is connected to a driving source (not shown) and has a side wall (not shown).
It is rotatably supported by. 103 is a heater,
It is housed in the heating roller 101. Reference numeral 4 is a temperature detection using a thermistor or the like, and detects the heating roller surface temperature. A pressure roller 102 includes a pressure roller support member 1
04, it is supported by the heating roller 101 so as to be able to come into contact with and separate from it. The pressure roller support member 104 is supported by a pin 110 on a side wall (not shown), and is urged by an urging member (not shown) at the end thereof by an urging force f in the direction of arrow A, so that the pressure roller 102 is pressed. Is pressed against the heating roller 101. At that time, the pressure contact force F between the pressure roller 102 and the heating roller 101
Becomes like the formula (1) by the lever principle.

F = f × (L ₂ / L ₁ ) ... (1) The heating roller 101 is a metal roller whose surface is thinly coated with silicon rubber or the like, and the pressure roller 102 is a thin fluororesin on the surface. A rubber roller with a film.

By pressing both rollers into contact with each other, the pressure roller 102 is deformed as shown in FIG. 9 to increase the contact area, and the heating time of the recording paper (the time required to move from point a to point b) is lengthened. There is.

Next, during the fixing operation, the heating roller 101 in FIG. 8 rotates in the C direction and the pressure roller 102 in the D direction at the same peripheral speed, and the recording paper 113 on which the toner image 112 is formed is , B direction. Recording paper 113 guided to the image fixing device by the recording paper guide 111
Is the heating roller 101 heated by the heater 103.
And the pressure roller 102. At that time, the unfixed toner image is brought into pressure contact with the surface of the heating roller 101, heat is momentarily applied to melt the toner, and the toner is fused to the recording paper 113, and the toner image is fixed on the recording paper 113. The recording paper 113 exiting the image fixing device is discharged onto the discharge rollers 107 and 108.
Is discharged onto the paper discharge tray 109.

Next, the temperature control of the image fixing device will be described in detail with reference to FIG. A central processing unit (hereinafter referred to as CPU) as a control means outputs digital data corresponding to the actual temperature to the data latch unit 2. The latched data is output to the data comparison unit 3. On the other hand, the temperature of the fixing device is detected by a temperature detecting section 4 as a temperature detecting means installed in contact with the surface of the heating roller 101. The temperature detector 4 uses a thermistor, and the fact that the resistance value of the thermistor changes depending on the temperature is used to convert the potential across the thermistor into digital data by the A / D converter 5 and output it to the data comparator 3. To do. The data comparison unit 3 compares the data of the data latch unit 2 with the data of the A / D conversion unit 5, and if the value of the data latch unit 2 indicates a higher temperature, a high level (hereinafter referred to as HI level) is set, otherwise In this case, a low level (hereinafter referred to as LO level) is output to the gate unit 7. The error detection unit 6 to be described later normally outputs the HI level (when no error is detected) to the gate unit 7. The gate unit 7 is composed of an AND circuit, and when no error is detected, the output level of the data comparison unit 3 is directly input to the heater driver unit 8. If the input is HI level, the heater driver unit 8 turns on the fixing device heater 9, and the input is L
If it is at O level, the fixing device heater 9 is turned off.

On the other hand, the output of the temperature detector 4 is the error detector 6
Has also been entered. The error detector 6 normally outputs the HI level as described above, but if the output potential of the temperature detector 4 is a potential corresponding to, for example, −10 ° C. or lower, the thermistor opens, and the temperature is 230 ° C. or higher. If it is a potential to be controlled, it is determined that the control has failed, and the LO level is output to the gate unit 7. At this time, the gate section 7 which is an AND circuit always outputs the LO level, so that the input of the heater driver 8 becomes LO and the fixing device heater 9 is turned off. In addition, since the image fixing device generally handles high temperatures, the heating roller 1 is used for safety.
01, a thermostat or the like is arranged (not shown), the surface temperature of the heating roller 101 is independently monitored, and when a high temperature equal to or higher than a set value is detected, the fixing device heater 9 is forcibly turned off. It is taken. The output of the A / D converter 5 and the signal of the error detector 6 are connected to the CPU 1, so that the CPU 1 can monitor the current fixing device temperature and know the occurrence of an error.

Next, the control flow of the conventional image fixing device will be described in detail with reference to FIG. (Step 11a) First, the power of the entire apparatus is turned on.

(Step 11b) The heating roller surface temperature is set to the standby temperature Tst (for example, 150 ° C.).

(Step 11c) When the temperature is set, the heater is turned on and the surface temperature of the heating roller rises.
Starts monitoring the heating roller surface temperature and waits until the surface temperature reaches the process initialization start temperature Tin (for example, 100 ° C.). The process initialization start temperature Tin is the heating roller 1
01 is a temperature at which the toner adhered on 01 is sufficiently softened, and T
Pressure roller 102, heating roller 101 at a temperature less than in
When the roller is rotated, the roller surface may be damaged.

(Step 11d) When the surface temperature of the heating roller reaches Tin, the heating roller 101 and the pressure roller 1
Rotate 02 together. The rotation speed is the fixing speed (hereinafter Va
Is described).

(Step 11e) The initialization of the electrophotographic process is started. Do not proceed to the next step until the process initialization is completed.

(Step 11f) Wait until the heating roller surface temperature reaches the standby temperature Tst. During this time, the pressure roller surface temperature also approaches the standby temperature Tst.

(Step 11g) The rotation of the heating roller and the pressure roller is stopped. This completes the warm-up.

(Step 11h) The presence or absence of a print start command is determined.

(Step 11i) When there is no print start command, the temperature of the heating roller surface is always set to Tst during standby.

(Step 11j) The CPU 1 checks for an error. If an error such as abnormal high temperature or thermistor open occurs, error processing is performed. The error processing includes forcibly turning off the heater. If no errors are detected,
Return to step 11b.

(Step 11k) When there is a print start command, the heating roller surface temperature is set to the operating temperature Tpr. Tpr is set to a temperature higher than the standby temperature Tst (for example, 160 ° C.). The reason why the surface temperature of the heating roller in the standby state is set low is that the power consumption is reduced, and a unit (for example, a developing unit. Best results may be obtained by placing the image unit on top of the image fixing device).

(Step 11l) The heating roller 101 and the pressure roller 102 start rotating. The rotation speed is Va.

(Step 11m) Each printing process is sequentially activated to form an image.

(Step 11n) The CPU 1 checks for an error. If an error such as abnormal high temperature or thermistor open occurs, error processing is performed. Error handling stops the entire electrophotographic process.

(Step 11o) It is checked whether the entire printing process is completed. If it is in the middle of the process, the process returns to step 11n.

(Step 11p) If the entire printing process is completed, the rotation of the heating roller 101 and the pressure roller 102 is stopped, and the process returns to step 3-8.

Next, the actual control result based on the above operation flow will be described in detail with reference to FIG. The thin line graph in FIG. 12 shows the actual temperature detected by the thermistor on the heating roller surface, and the thick line graph is the set value of the heating roller surface temperature set by the CPU 1. At time X0 on the time axis, the power of the entire device is turned on. Immediately after the power is turned on, the heating roller surface temperature is set to the standby temperature Tst. With the temperature setting, the heater 103 in the heating roller 101 is turned on, and the surface temperature of the heating roller starts to rise. Eventually, the surface temperature of the heating roller reaches the temperature Tin at which the toner is sufficiently softened. When the time point at which Tin is reached is X1, the heating roller 10 is between X0 and X1.
1, both pressure rollers 102 are stopped. If the rollers are rotated before the toner softens, each roller may be damaged.

When the heating roller surface temperature reaches Tin,
Both the heating roller 101 and the pressure roller 102 start rotating. The rotation speed is the fixing speed Va. At the same time, the electrophotographic process is initialized. In initialization, the presence / absence of units necessary to execute the electrophotographic process, the position of each unit, and various motor operation checks are performed. If an error is detected in these checks, error processing is performed and all operations are stopped.

The rotation of the heating roller 101 and the pressure roller 102 is continued until the surface temperature of the heating roller reaches the standby temperature Tst. If the time point at which Tst is reached is X2, the fact that both rollers are rotating at the rotation speed Va is X1.
To X2. The reason why the temperature rising rate gradient of the heating roller surface temperature from X1 to X2 is different is that the heat of the heating roller 101 is absorbed by the pressure roller 102 because the roller is rotated after X1.

At the time of X2, the rotation of the heating roller 101 and the pressure roller 102 is stopped, and the warm-up period is completed. After that, the process is in a standby state, and if a print start command is given, each electrophotographic process is activated to form an image. The surface temperature of the heating roller 101 overshoots after X2 and rises to a temperature exceeding the fixable temperature Taw.
± 3 ° C centering on Tst as the waiting time elapses
It stabilizes to some extent. When the image fixing device is left for a long time in this standby state, the heating roller 101 and the pressure roller 1
02 is always in contact with the same part, so the surface temperature on the pressure roller side is
Gradually decreases.

In this state, it is assumed that a print start command is given at time X3. Immediately after the print start command, the heating roller 10
1 and the pressure roller 102 start rotating at the rotation speed Va. Almost at the same time, the heating roller surface temperature is set to Tpr which is higher than the set temperature Tst during standby. However, the actual surface temperature of the heating roller drops sharply when both rollers start to rotate. Therefore, the fixing temperature Taw does not reach at the time X4 when the recording paper reaches the entrance of the image fixing device.

In order to solve this problem, there is a method in which the heating roller 101 and the pressure roller 102 are rotated at a certain low speed during standby to supply the heat of the heating roller 101 to the entire circumference of the pressure roller 102. .. Since heat flows from the high temperature portion to the low temperature portion, the heat of the heating roller 101 can be supplied to the pressure roller 102 by moving the contact portion between the heating roller 101 and the pressure roller 102. The rotation speed at this time is
In consideration of noise and the life of each roller, it is common to rotate them at the lowest speed possible.

[0033]

In an image fixing device in which the surface temperature of the heating roller is set to be different during waiting and during operation (higher during operation), the temperature of the heating roller is increased immediately after warm-up. In the case of the method of stopping the pressure roller and making it stand by, the temperature of the pressure roller side that does not have a heat source during the stand-by decreases significantly, so printing start is instructed,
When the recording paper on which the toner image is formed reaches the entrance of the fixing device, the surface temperature of the pressure roller does not reach the fixable temperature,
Even if fixing failure (cold offset with no gloss) occurs or even if the fixing temperature is reached, only the area where the pressure roller and the heating roller are in contact during standby is high temperature, so the fixed image has uneven gloss. Occurs.

When the method of rotating the heating roller and the pressure roller at a low speed during standby is adopted, if printing is started a long time after warming up, the temperature of the heating roller during fixing is the fixable temperature Taw. Reach However, if printing is started after a relatively short time of about several minutes in the standby state, the temperature of the heating roller sharply drops immediately after starting to rotate the heating roller and the pressure roller, and as a result, fixing is performed. The possible temperature Taw may not be reached. This is because the center of the pressure roller is still in a low temperature state at the end of warm-up, and the heat supplied from the heating roller is absorbed in the center of the pressure roller at the rotation speed set in consideration of noise, roller life, etc. It is considered that the surface temperature of the pressure roller is substantially low except for the portion in contact with the heating roller.
Another factor is that the image fixing device unit itself has not reached a sufficiently high temperature at the end of normal warm-up. In these cases as well, the surface temperature of the heating roller does not reach the fixable temperature at the actual start of fixing, and fixing failure occurs.

The present invention has been made in consideration of the above problems, and an object of the present invention is to provide an image fixing device in which warm-up is automatically performed so that the roller temperature can be kept at a predetermined temperature in any case.

[0036]

In order to achieve the above object, the image fixing device of the present invention is arranged such that a recording medium on which a powder image is formed is sandwiched by two rollers and is heated and conveyed so that the powder image is formed. In the image fixing device for fixing the roller, the roller is driven at the first speed during the fixing operation while the roller temperature is between the first temperature and the second temperature higher than the first temperature until the second temperature is reached. The roller is driven at a third speed, which is lower than the first speed and higher than the waiting second speed for a period determined according to time, and thereafter is controlled to be driven at the second speed. It has a control means.

[0037]

In the image fixing apparatus of the present invention having the above-described structure, when the roller is still low in temperature, the roller is driven at the first speed which is the highest speed during fixing, and the temperature of the heating roller is changed to the pressure roller at high speed. Then, the roller is driven at a third speed which is higher than the slowest second speed in standby and intermediate speed lower than the first speed, and the temperature rises sufficiently to the center of the roller. To do it. In this case, the time until the surface temperature of the roller rises to the target second temperature at the first speed is measured with a timer, and if the time is long, it takes a long time for the temperature to rise to the center of the roller. Judgment is made and the driving of the roller is decided at the third speed according to the measured time. After the temperature is sufficiently transmitted to the center of the roller in this way, the roller is driven at the second temperature until a print command is issued.

[0038]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An image fixing device according to an embodiment of the present invention will be described below with reference to FIGS. FIG. 1 is a block diagram showing the configuration of the image fixing device of the present embodiment, FIG. 2 shows the temperature change of the heating roller as the control result of the image fixing device of the present embodiment, and FIG. 3 shows the first embodiment. FIG. 4 shows a control flow in the example, and FIG. 4 shows a control flow in the image fixing device of the second embodiment of the present invention.

In FIG. 1, components having the same functions as those of the conventional example are designated by the same reference numerals and the description thereof will be omitted. Although not shown in the conventional example, 10 is controlled by the CPU 1, and a roller drive unit as a drive unit for rotating the heating roller 101 and the pressure roller 102, and 11 is a roller drive unit 10 based on temperature information from the temperature detection unit 4. A timer for counting the time for determining the drive period of the roller drive unit 12 is a storage unit for storing a table for determining the drive period of the roller drive unit 10 according to the time counted by the timer 11.

First, the operation flow of the image fixing device according to the first embodiment of the present invention will be described in detail with reference to FIG.

(Step 3a) First, the entire image fixing device shown in FIG. 1 is turned on. The heating roller temperature at this time is Ton.

(Step 3b) Temperature Ton at power-on
The timer 11 is started in order to measure the time from when the heating roller surface temperature reaches the standby temperature Tst.

(Step 3c) The surface temperature of the heating roller is set to the standby temperature Tst (for example, 150 ° C.). With this setting, the fixing device heater 9 is turned on, and the surface temperature of the heating roller 101 starts to rise. (Step 3d) The CPU 1 starts monitoring the heating roller surface temperature, and waits until the surface temperature reaches the process initialization start temperature Tin (for example, 100 ° C.) as the first temperature.
If the surface temperature> Tin, immediately proceed to the next step.
The process initialization start temperature Tin is a temperature at which the toner adhered on the heating roller 101 is sufficiently softened, and if the pressure roller 102 and the heating roller 101 are rotated below Tin, the roller surface may be damaged.

(Step 3e) The heating roller surface temperature is T
When it reaches in, the CPU 1 activates the roller driving unit 10 to rotate both the heating roller 101 and the pressure roller 102. The rotation speed is the fixing speed Va as the first speed.

(Step 3f) The initialization of the electrophotographic process is started.

(Step 3g) Wait until the process initialization is completed. The surface temperature of the heating roller continues to rise even during the process initialization. When the initialization is completed, the process proceeds to step 3i.

(Step 3h) Although the initialization has not been completed, the heating roller surface temperature may reach Tst, so this is checked. If it has not reached Tst, the process returns to step 3g.

(Step 3i) If Tst is reached, the timer operation of the timer 11 is stopped and the timer 1
The value of 1 is retained. Although not specified in this flow, once step 3i has been passed, a flag is set and this flag is referred to, and thereafter, step 3h is always No.
Then, the process proceeds to step 3j, and step 3j is controlled so as to immediately proceed to Yes.

(Step 3j) Wait until the surface temperature of the heating roller reaches the standby temperature Tst. During this time, the surface temperature of the pressure roller approaches the standby temperature Tst as the second temperature.

(Step 3k) According to the value of the timer 11, the period C1 in which the heating roller is rotated at the speed Vs2 as the third speed is obtained. The period C1 is obtained by accessing the table shown in FIG. Specifically, the time elapsed after the power is turned on (the value of the timer 11) is used as an address, and the data of the period C1 in which the roller is rotated is stored for each address. For example, if the elapsed time from turning on the power to reaching the temperature Tst as the second temperature is 170 seconds or more, the period C1 for rotating the heating roller at the rotation speed Vs2 is 5 minutes from FIG. 5, and the speed Vs2 is 5 minutes. Will continue for a minute.

At step 3k, the warm-up period ends. (Step 3l) The presence or absence of a print start command is determined. If there is no print start command, the process proceeds to step 3m, and if there is a print start command, the process proceeds to step 3t.

(Step 3m) When there is no print start command, the temperature of the heating roller surface is always set to the standby temperature Tst.
To maintain.

(Step 3n) The value of C1 is stored in the storage device 12
Look up from the table. If C1> 0, step 3o
If C1 = 0, go to step 3q.

(Step 3o) When C1> 0, the rotation speeds of the heating roller 101 and the pressure roller 102 are set to Vs.
Set to 2.

(Step 3p) Specified time (eg 10 m)
s) After waiting, decrement the period C1 by one.
Go to step 3r.

(Step 3q) When C1 = 0, the rotation speeds of the heating roller 101 and the pressure roller 102 are set to the speed Vs1 as the second speed.

(Step 3r) The CPU 1 checks for an error. If an error such as abnormal high temperature or thermistor open occurs, error processing is performed. If there is an error, go to step 3s. If no error is detected, the process returns to step 3l.

(Step 3s) Error processing is performed. Stop the entire xerographic process and display the error item.

(Step 3t) When there is a print start command, the heating roller surface temperature is set to the operating temperature Tpr. The temperature Tpr is set to be higher than the standby temperature Tst (for example, 160 ° C.). The reason why the surface temperature of the heating roller in the standby state is set low is that the power consumption is reduced, and a unit (for example, a developing unit. The best result may be obtained by disposing the developing unit on the image fixing device).

(Step 3u) At the temperature Tpr, the rotation of the heating roller 101 and the pressure roller 102 is started by the roller driving unit 10 under the control of the CPU 1 at the fixing speed Va.

(Step 3v) Each printing process is sequentially activated to form an image.

(Step 3w) The CPU 1 checks for an error. If an error such as an abnormally high temperature or thermistor open occurs, proceed to step 3s.

(Step 3x) Fixed time (eg 10 m)
s) Wait, and if C1> 0, decrement C1 by 1.

(Step 3y) It is checked whether the entire printing process is completed. Step 3 if in the process
Return to w and step 3 if the entire printing process is completed.
Return to l.

Next, the operation flow of the image fixing apparatus of the second embodiment according to the present invention will be described in detail with reference to FIG.

(Step 4a) First, the power of the entire apparatus is turned on. The heating roller temperature at this time is Ton.

(Step 4b) The period C1 in which the roller is rotated at the speed Vs2 is calculated according to the temperature Ton. Period C
1 is obtained by accessing the table shown in FIG.
Specifically, the value of the heating roller temperature Ton is used as an address,
The data of the period C1 in which the roller rotates for each address is stored. For example, if Ton is 10 ° C. or lower, the drive at the speed Vs2 is continued for 5 minutes from FIG.

(Step 4c) The surface temperature of the heating roller is set to the standby temperature Tst (for example, 150 ° C.). With this setting, the fixing device heater 9 is turned on, and the surface temperature of the heating roller 101 starts to rise.

(Step 4d) The CPU 1 starts monitoring the heating roller surface temperature, and waits until the surface temperature reaches the process initialization start temperature Tin (for example, 100 ° C.). If the surface temperature> Tin, immediately proceed to the next step. The process initialization start temperature Tin is a temperature at which the toner adhered on the heating roller 101 is sufficiently softened, and if the pressure roller 102 and the heating roller 101 are rotated below Tin, the roller surface may be damaged.

(Step 4e) The heating roller surface temperature is T
If it reaches in, heating roller 101, pressure roller 10
Rotate 2 together. The rotation speed is the fixing speed Va.

(Step 4f) The initialization of the electrophotographic process is started.

(Step 4g) Wait until the process initialization is completed.

(Step 4h) Wait until the heating roller surface temperature reaches the standby temperature Tst. During this time, the pressure roller surface temperature also approaches the standby temperature Tst. The warm-up period ends when the heating roller surface temperature reaches Tst.

(Step 4i) The presence or absence of a print start command is determined. If there is no print start command, the process proceeds to step 4j. If there is a print start command, the process proceeds to step 4q.

(Step 4j) When there is no print start command, the temperature of the heating roller surface is always set to the standby temperature Tst.
To maintain.

(Step 4k) The value of C1 is checked. C1
If> 0, go to step 4l; if C1 = 0, go to step 4n.

(Step 4l) If C1> 0, the heating roller and pressure roller rotation speeds are set to Vs2.

(Step 4m) Specified time (eg 10m)
s) After waiting, decrement C1 by 1. Go to step 4o.

(Step 4n) When C1 = 0, the rotation speed of the heating roller and the pressure roller is set to Vs1.

(Step 4o) The CPU 1 checks for an error. If an error such as abnormal high temperature or thermistor open occurs, error processing is performed. If there is an error, go to step 4p. If no error is detected, the process returns to step 4i.

(Step 4p) Error processing is performed. Stop the entire xerographic process and display the error item.

(Step 4q) When there is a print start command, the heating roller surface temperature is set to the operating temperature Tpr. Tpr is set to a temperature higher than the standby temperature Tst (for example, 160 ° C.). The reason why the surface temperature of the heating roller in the standby state is set low is that the power consumption is reduced, and a unit (for example, a developing unit. The best result may be obtained by disposing the developing unit on the image fixing device).

(Step 4r) The rotation speed of the heating roller 101 and the pressure roller 102 is started at Va.

(Step 4s) Each printing process is sequentially activated to form an image.

(Step 4t) The CPU 1 checks for an error. If an error such as abnormal high temperature or thermistor open occurs, proceed to step 4p.

(Step 4u) Specified time (eg 10 m)
s) Wait, and if C1> 0, decrement C1 by 1.

(Step 4v) It is checked whether the entire printing process is completed. Step 4 if in the process
Returning to step t, if the entire printing process is completed, step 4
Return to i.

Next, with reference to FIG. 2, how the temperature and the rotation speed of the heating roller 101 are controlled by the above-described operation flow will be described. The horizontal axis of FIG. 2 shows the elapsed time, the vertical axis shows the heating roller surface temperature, the thin line graph shows the actual temperature change detected by the thermistor on the heating roller surface, and the thick line graph. Is CP
It is a set value of the heating roller surface temperature set by U1. The control results are almost the same in both the first and second embodiments. At the time of the time axis X0, the power of the entire device is turned on.
In the case of the first embodiment, the timer 11 is started immediately after this, and in the case of the second embodiment, the rotation speeds of the heating roller and the pressure roller are changed immediately after the start of the standby state according to the surface temperature of the heating roller. The period C1 in which the speed is Vs2 as the third speed is determined. Immediately after the power is turned on, the heating roller surface temperature is set to the standby temperature Tst. With the temperature setting, the heater in the heating roller is turned on and the surface temperature of the heating roller starts to rise. Eventually, the surface temperature of the heating roller reaches the temperature Tin at which the toner is sufficiently softened. Assuming that the time point when the temperature reaches the temperature Tin is X1, the heating roller 1 is between X0 and X1.
01, the pressure roller 102 is stopped. If the rollers are rotated before the toner softens, each roller may be damaged.

When the surface temperature of the heating roller reaches the temperature Tin, both the heating roller 101 and the pressure roller 102 start rotating. The rotation speed is the speed Va as a first speed equal to the fixing speed. At the same time, the electrophotographic process is initialized. In initialization, the presence / absence of units necessary to execute the electrophotographic process, the position of each unit, and various motor operation checks are performed. If an error is detected in these checks, error processing is performed and all operations are stopped.

The rotation of the heating roller 101 and the pressure roller 102 is continued until the surface temperature of the heating roller reaches the standby temperature Tst. If the time point at which Tst is reached is X2, the fact that both rollers are rotating at the rotation speed Va is X1.
To X2. The difference in the rising speed gradient of the heating roller surface temperature from X1 to X2 is because the roller that was stopped before X1 is rotated and the heat of the heating roller is absorbed by the pressure roller. At the time of X2, the warm-up period ends, and after that, the process is in a standby state, and when a print start command is given, each electrophotographic process is activated to form an image. In the case of the second embodiment, the period C1 in which the rotational speeds of the heating roller 101 and the pressure roller 102 are Vs2 after the transition to the standby state is determined according to the value of the timer at the time of X2. The surface temperature of the heating roller 101 is X2
Thereafter, overshoot occurs and the temperature rises to a temperature exceeding the fixable temperature Taw, but as the standby time elapses, Ts
Stabilizes around ± 3 ° C with t as the center.

In the standby state, the heating roller 101 and the pressure roller 102 are rotated for a period C1 at a speed Vs2 set to a speed lower than the fixing speed Va and higher than the normal standby rotation speed Vs1. The heating roller 101 can give a larger amount of heat to the pressure roller than in the case of rotating at the normal rotation speed Vs1 during standby.

In the present invention, the heating roller 101 and the pressure roller 1
02 is rotated at the rotation speed Vs2 also during the speed Va
It is obvious that if both rollers are driven by, the better result will be obtained, but noise should be reduced as much as possible during standby, and each roller has a life, so that the fixing speed (V
There is a problem in rotating in a). In this embodiment, Va is 50 rpm, Vs1 is 1 rpm, and Vs2 is 10 r.
It is set to about pm.

The period in which the heating roller 101 and the pressure roller 102 are rotated at the rotation speed Vs2 is from the time point X2 in the standby state to the time point X2 'after the lapse of the time period C1. X
After 2 ', heating roller 101 and pressure roller 10
The rotation speed of No. 2 is set to Vs1, which is a normal waiting speed as the second speed, and in the standby state thereafter, the heating roller 101 and the pressure roller 102 are driven at the rotation speed Vs1.

After the above, it is assumed that the print start command is given at the time of X3. Here, it is assumed that X3 is a time point several minutes after the warm-up ends, which is a problem in the conventional example. Immediately after the print start command, the heating roller 101 and the pressure roller 102 start rotating at the fixing speed Va. Almost at the same time, the heating roller surface temperature is set to Tpr which is higher than the set temperature Tst during standby. Immediately after the heating roller and the pressure roller start rotating, the heating roller 101
No sharp decrease in temperature is observed, and the surface temperature of the heating roller can sufficiently satisfy the fixable temperature Taw at time X4 when the recording paper reaches the entrance of the image fixing device after a slight undershoot.

Next, the actual control contents based on the above operation flow when the heating roller temperature Ton when the power is turned on is equal to or higher than Tst will be described in detail with reference to FIG. The graph drawn with a thin line in FIG. 7 shows the actual temperature detected by the thermistor on the heating roller surface, and the graph drawn with a thick line is the set value of the heating roller surface temperature set by the CPU 1. Immediately after the power is turned on, the heating roller surface temperature is set to the standby temperature Tst. Since the heating roller surface temperature has already reached Tst, both the heating roller 101 and the pressure roller 102 start rotating at the fixing speed Va, and at the same time, the electrophotographic process is initialized, and at the same time as the completion of the initialization, the standby Enter the state.

Based on the control flow of the first embodiment shown in FIG. 3, if the heating roller temperature at power-on is already Tst, steps 3a to 3i are processed in a very short time. Therefore, the value of the timer 11 is almost 0, and the value of the period C1 is also 0. Further, based on the control flow of the second embodiment shown in FIG. 4, since the heating roller temperature at power-on is Tst or higher, step 4
The period C1 is set to 0 in b.

If X2 is the time point at which the standby state is entered,
Both rollers are rotating at the rotation speed Va from X0 to X2. At the time of X2, the warm-up period ends, and after that, the process is in a standby state, and when a print start command is given, each electrophotographic process is activated to form an image.
Since the value of the period C1 is 0, the heating roller 10 on standby
1, The rotation speed of the pressure roller 102 is always set to the speed Vs1. At this point, the pressure roller 102 has already reached a sufficiently high temperature, and the heat of the heating roller 101 is not extremely taken away.

After the above, it is assumed that the print start command is given at the time of X3. Here, it is assumed that X3 is a time point several minutes after the warm-up ends, which is a problem in the conventional example. Immediately after the print start command, the heating roller 101 and the pressure roller 102 start rotating at the fixing speed Va. Almost at the same time, the heating roller surface temperature is set to Tpr which is higher than the set temperature Tst during standby. Immediately after the heating roller and the pressure roller start rotating, the heating roller 101
No sharp decrease in temperature is observed, and the surface temperature of the heating roller can sufficiently satisfy the fixable temperature Taw at time X4 when the recording paper reaches the entrance of the image fixing device after a slight undershoot.

The details of one embodiment of the present invention have been described above, but the roller driving portions of the heating roller and the pressure roller in this embodiment have a structure in which the driving speed can be set arbitrarily. When the driving means of these rollers can set only a single speed, if the distribution of the driving on period and the driving off period is appropriately determined, that is, if the driving means is controlled to be turned on intermittently, Similar effects can be obtained.

[0100]

As is apparent from the above description, the image fixing device of the present invention has a high-speed roller driving period of a first speed used for fixing during warm-up, and a second speed during standby at a speed lower than the first speed. And a roller driving period at a third speed that is higher than the above speed, and the roller driving period at the third speed is determined by the time until the predetermined second temperature is reached during the roller driving period at the first speed. By controlling with the control means, it is possible to prevent a sharp decrease in the surface temperature of the heating roller immediately after the rotation of the heating roller and the pressure roller is started with a very simple structure, and to prevent fixing failure (cold offset) and fixing unevenness. It is possible to obtain a high-quality image with no image.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an image fixing device according to a first embodiment of the present invention.

FIG. 2 is a graph showing a time course of a heating roller temperature and a driving speed of the image fixing apparatus of the embodiment.

FIG. 3 is a flowchart showing the operation of the image fixing device of the embodiment.

FIG. 4 is a flowchart showing the operation of the image fixing device according to the second embodiment of the present invention.

FIG. 5 is a graph showing the table contents stored in the storage means of the first embodiment of the present invention.

FIG. 6 is a graph showing the operation of the second embodiment of the present invention.

FIG. 7 is a graph showing a time course of a heating roller temperature and a driving speed of the image fixing apparatus of the embodiment.

FIG. 8 is a cross-sectional view showing a configuration near a roller of a conventional image fixing device.

FIG. 9 is an enlarged cross-sectional view around a roller of the conventional image fixing device.

FIG. 10 is a block diagram showing a configuration of the conventional image fixing device.

FIG. 11 is a flowchart showing an operation of the conventional image fixing device.

FIG. 12 is a graph showing a time course of a heating roller temperature and a driving speed of the conventional image fixing device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 CPU (control means) 4 Temperature detection part (temperature detection means) 8 Heater driver part 9 Fixing device heater 10 Roller drive part (drive means) 11 Timer 12 Storage means 101 Heating roller 102 Pressure roller

Claims (2)

[Claims] 1. Two rollers pressed against each other, a heating means for heating one of the rollers, a driving means for rotating the roller, and a temperature detecting means for detecting the surface temperature of at least one of the rollers. And a control means for controlling the heating means and the driving means in accordance with the output from the temperature detecting means, and sandwiching the recording medium on which the powder image is formed by the driving means between the rollers. An image fixing device that conveys the powder image to fix the powder image on the recording medium, wherein a rotation speed of the roller by the control unit is a first speed during a fixing operation and a second speed during a standby operation. It has a third speed that is lower than the first speed and higher than the second speed, and the temperature of the roller after the power is turned on by the control means is a predetermined first temperature and the first temperature. Higher The roller is rotated at the first speed during the second temperature set to the temperature, and after the second temperature is reached, while there is no print start command, from the predetermined time point after the power is turned on, Rotating the roller at the third speed during a period corresponding to the time to reach the second temperature,
After that, the image fixing device is configured to rotate the roller at the second speed. 2. Two rollers pressed against each other, a heating means for heating one of the rollers, a driving means for rotating the roller, and a temperature detecting means for detecting the surface temperature of at least one of the rollers. And a control means for controlling the heating means and the driving means in accordance with the output from the temperature detecting means, and sandwiching the recording medium on which the powder image is formed by the driving means between the rollers. An image fixing device that conveys the powder image to fix the powder image on the recording medium, wherein a rotation speed of the roller by the control unit is a first speed during a fixing operation and a second speed during a standby operation. It has a third speed that is lower than the first speed and higher than the second speed, and the temperature of the roller after the power is turned on by the control means is a predetermined first temperature and the first temperature. Higher The roller is rotated at the first speed during the second temperature set to the temperature, and after the second temperature is reached, while there is no print start command, the power is turned on at a predetermined time. An image fixing device in which the roller is rotated at the third speed during a period corresponding to the temperature indicated by the temperature detecting means, and thereafter, the roller is rotated at the second speed.