JPH05323826A - Image forming device - Google Patents

Abstract

PURPOSE:To prevent temperature of a fixing roll from being lowered due to deficiency of supplied heat quantity by a heater of the fixing roll when recording paper of a large size is continuously passed in the image forming device provided with a heat roll fixing device. CONSTITUTION:A pair of rolls is constituted of the fixing roll 1 and a press roll 3 and the press roll 3 is pressurized to the fixing roll 1 with a pressure spring 4 provided compressed between a mobile supporting member 7 and a bearing 3c. A cam follower part 7a at a bottom edge of the mobile supporting member 7 is brought into contact with a cam 8. The cam 8 is connected by a servo motor, etc., and the rotational angle of the servo motor is controlled by a control circuit part 6 according to the temperature detected by a thermister 5. Thus, since the pressurizing force between the pair of rolls 1 and 3 is controlled in inversely proportional relation to fixing temperature, good fixing is carried out up to a low fixing temperature.

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art First, the construction of an electrophotographic copying machine and the outline of an image forming operation will be described with reference to FIG.

The image reading system is of a fixed platen type and an optical system moving type.

The first mirror base 21 has a first mirror 21a.
And an illumination lamp 21b are provided. First mirror stand 2
1 moves along the platen glass 25.

The second mirror base 22 has a second mirror 22a.
And a third mirror 22b. Second mirror stand 2
2 moves in the same direction at half the speed of the first mirror base 21.

The document D placed on the document table glass 25 is illuminated by the illumination lamp 21b, and the reflected light from the document D is reflected by the first mirror 21a, the second mirror 22a, and the third mirror 22b to proceed. The first mirror base 21 and the second mirror base 22 start moving from the image forming start position called the home position, which is the position of HP in FIG. 8, and read the document D while moving to the right in the drawing, Mirror 22
The original image reflected by b advances to the lens 23, and is formed on the exposure section 31a on the photosensitive drum 31 via the lens 23 and the fixed fourth mirror 24.

Recording paper P is stored in the cassette 27. The size of the recording paper P is detected by the cassette detecting means 28.

Around the photosensitive drum 31, a charger 32,
An image forming unit such as an exposure unit 31a, a developing device 33, a transfer charging device 34, a cleaning device 35, and the like is arranged, and an image forming process such as charging, exposure, development, transfer, and cleaning is performed.

The recording sheet P after transfer is conveyed to the fixing device 11 by the conveying section 37.

When a copy start button (not shown) on the operation unit of the copying machine is pressed, the copy operation is started.

When the control conditions are met and the image formation can be started, a signal for starting the image formation is issued from the control circuit section 6, and the first mirror base 21 and the second mirror base 22 are moved to form the image formation. Then, a toner image is formed on the photosensitive drum 31.

On the other hand, the recording paper P fed from the cassette 27 once stands by at the registration roller section 36, and when image formation can be started, the photosensitive drum 31 is synchronized with the movement of the first mirror base 21. The toner image on the photosensitive drum 31 is transferred to the transfer unit 31 b and then transferred to the fixing device 11 by the transfer unit 37. The fixing device 11 fixes the toner image on the recording paper P and discharges it to the outside of the machine.

In the case of repeatedly forming an image, the first mirror base 21 moves a predetermined length, then returns to the home position HP, and when the image formation becomes possible, the first mirror base 21 moves again to repeat the above-mentioned image formation. The recording paper P is intermittently fed and passes through the fixing device 11.

The above operation and all other operations of the copying machine are as follows.
It is controlled by the control circuit unit 6.

Next, the fixing device 11 will be described.

Conventionally, a heat roller fixing device is widely used as the fixing device 11 in an image forming apparatus such as an electrophotographic copying machine or a laser printer.

The heat roller fixing device 11 fixes the toner image formed on the recording material, for example, the recording paper P in the previous step to the recording paper P, so that the recording paper P carrying the toner image is held under pressure. By passing between the roller pair 1 and 3, pressure and heat are applied to the recording paper P and the toner so that the toner permeates between the fibers of the paper and is fixed.

In order to obtain good fixing, the roller temperature and the pressing force between the roller pairs 1 and 3 in an appropriate range are required. It is known that the roller temperature and the pressing force can complement each other. For example, even if the roller temperature is set low, the fixing property can be kept good if the pressing force is increased.

FIG. 7 is a schematic vertical cross-sectional view showing the structure of an example of the heat roller fixing device 11.

The fixing roller 1 has a hollow cylindrical core metal and a fluororesin film formed on the core metal.

Inside the fixing roller 1 is a heater 2 which is a heat source.

The pressure roller 3 has a silicon rubber layer 3b formed on a core metal 3a and is pressed against the fixing roller 1 by a pressure spring 4 to rotate together with the fixing roller 1. A thermistor 5 as a temperature detecting means is in contact with the outer surface of the fixing roller 1.

A control circuit section 6 provided as a control device of the image forming apparatus drives the heater 2 by turning on / off the heater 2 according to the roller temperature detected by the thermistor 5 to drive the temperature of the fixing roller 1 within a set constant range. maintain.

In order to maintain the temperature of the fixing roller 1,
The average amount of heat released from the heater 2 per unit time is at least relative to the total amount of heat released from the fixing device 11 including the fixing roller 1 and the total amount of heat released per unit time such as the amount of heat absorbed by the recording paper P and toner during fixing. Must be equal or greater. If they are equal, the temperature can be maintained by continuously turning on the heater 2, and if it is more than that, the temperature can be maintained by supplying heat so as to be equal by the on / off control drive.

[0025]

However, the power consumption of the heater has an upper limit depending on the power supply specifications of the image forming apparatus, and the amount of heat that can be supplied from the heater is also limited.

Therefore, when a recording paper having a large basis weight or a recording paper which has absorbed moisture is passed or the temperature of the recording paper is low, or when the recording paper is continuously passed at a high speed or a recording paper having a large size is continuously passed. Under adverse conditions, the amount of heat taken from the fixing roller to the recording paper per unit of average time becomes larger than the amount of heat per unit of time supplied from the heater, and the roller temperature drops. For this reason, there is a problem that a fixing failure occurs or the image forming operation must be interrupted before the fixing failure occurs, and a desired number of images cannot be obtained.

Here, it is known that the roller temperature and the pressing force can complement each other. For example, even if the roller temperature is set low, the fixing property can be kept good if the pressing force is increased.

Therefore, it is possible to set the pressing force between the pair of rollers in advance so that the fixing property is good even when the roller temperature becomes low as described above.

However, the continuous application of a large pressure exerts a bad influence on the life of the roller, and the roller must be replaced frequently.

The present invention has been made in view of the above points, and is provided with a fixing device which can alleviate the deterioration of the fixing property even when the temperature of the roller is lowered and which does not adversely affect the life of the roller. Another object of the present invention is to provide an image forming apparatus.

[0031]

The above object is achieved by the present invention described in (1) to (10) below.

According to a first aspect of the present invention, in an image forming apparatus having a heat roller fixing device and having temperature detecting means for detecting the roller temperature of the heat roller fixing device, the pressure applied between the pair of rollers is variable. An image forming apparatus comprising: a pressure device, and a control device that changes the pressure applied between the roller pair by the pressure device based on the roller temperature detected by the temperature detection device.

According to a second aspect of the present invention, when the roller temperature detected by the temperature detecting means is within a preset roller temperature allowable range and the roller temperature is high, the pressing force is small,
The image forming apparatus according to the first aspect of the invention is provided with a control device that sets a large pressing force when the roller temperature is low.

According to a third aspect of the present invention, the roller temperature is detected by the temperature detecting means while the recording material to be fixed is passing through the heat roller fixing device, and the pressure applying means rolls the roller based on the detected roller temperature. The image forming apparatus according to the first or second invention is characterized in that a setting value of a pressing force applied between the pair is changed.

A fourth aspect of the present invention is provided with a control device for changing the pressure applied between the pair of rollers by the pressing means before the recording material passes through the heat roller fixing device and the next recording material passes. The image forming apparatus according to any one of the first to third aspects of the invention.

According to a fifth aspect of the present invention, in an image forming apparatus having a heat roller fixing device and having a temperature detecting means for detecting the roller temperature of the heat roller fixing device, an image forming operation is performed by applying a pressure applied between a pair of rollers. Not including the pressurizing force at the time of standby, equipped with a pressurizing unit that is variable during image forming operation,
In the standby state where the image forming operation is not performed, the pressing force applied between the pair of rollers by the pressurizing unit is set to the standby pressing force, and after the image forming operation is started, it is changed to the initial setting pressing force during the image forming operation. An image forming apparatus comprising a device.

According to a sixth aspect of the present invention, the image forming apparatus according to the fifth aspect is provided with a control device for making the magnitude of the pressure applied during standby smaller than the magnitude of the pressure applied during image formation. Is.

A seventh aspect of the present invention is provided with a control device for changing the pressing force applied between the roller pair by the pressing means after the last recording material has passed to the pressing force at the standby time, and thereafter making the standby state. The image forming apparatus according to the fifth or sixth invention is characterized in that.

According to an eighth aspect of the present invention, in an image forming apparatus having a heat roller fixing device and having temperature detecting means for detecting the roller temperature of the heat roller fixing device, the pressure applied between the pair of rollers is variable. And a controller for changing the set value of the pressing force applied between the roller pair by the pressurizing means based on the roller temperature detected by the temperature detecting means and the rate of change of the roller temperature. The image forming apparatus.

In a ninth aspect of the present invention, the roller temperature is detected by the temperature detecting means while the recording material to be fixed is passing through the heat roller fixing device, and the detected roller temperature and the change rate of the roller temperature are calculated. The image forming apparatus according to the eighth aspect of the invention is characterized in that the image forming apparatus includes a control device that changes the set value of the pressing force applied between the pair of rollers by the pressurizing means.

A tenth aspect of the present invention is provided with a control device for changing the pressure applied between the pair of rollers by the pressing means until the recording material passes through the heat roller fixing device and the next recording material passes. The image forming apparatus according to the eighth or ninth invention is characterized in that.

[0042]

In the present invention having such a structure, the set value of the pressing force of the roller pair can be changed in a plurality of steps depending on the detected roller temperature or the roller temperature and the change rate of the roller temperature. It is possible to reduce the deterioration of the fixing property by increasing the pressing force.

Further, after the roller temperature or the rate of change between the roller temperature and the roller temperature is detected, the pressure applied to the roller pair is changed before the next recording material passes between the pair of fixing rollers. Therefore, the pressure applied to the roller temperature is set. Can be changed quickly.

Further, since the pressing force is set low in the standby state where the image forming operation is not performed, it is possible to reduce the reduction of the roller life due to the pressurization.

[0045]

Embodiments of the present invention will be described below with reference to the drawings. In the present invention, the image forming apparatus as a whole is not necessary for the explanation, so that it is omitted and only the necessary portions are shown.

[First Embodiment] FIG. 1 is a schematic cross-sectional view of a heat roller fixing device and a control circuit portion showing a first embodiment of the present invention.

The fixing roller 1 has a fluororesin film formed on a cylindrical cored bar.

Inside the fixing roller 1 is a heater 2 which is a heat source.

The pressure roller 3 has a silicon rubber layer 3b formed on a core metal 3a. A core metal 3a of the pressure roller 3 is supported by a bearing 3c, and the bearing 3c is movably guided by a guide member (not shown) parallel to a line connecting the centers of the fixing roller 1 and the pressure roller 3. The pressure roller 3 is brought into pressure contact with the fixing roller 1 by the pressure spring 4 pressing the bearing 3c in the axial direction of the fixing roller 1, and rotates together with the fixing roller 1.

A thermistor 5 as a temperature detecting means is in contact with the outer surface of the fixing roller 1.

The control circuit section 6 provided as a control device drives the heater 2 by turning on / off the heater 2 according to the temperature of the fixing roller 1 detected by the thermistor 5 to drive the temperature of the fixing roller 1 within a set constant range. maintain.

The pressure spring 4 is a compression spring, one end 4a of which is contracted to the bearing 3c of the pressure roller 3 and the other end 4b of which is in contact with the movable support member 7 to press the pressure roller 3 to the fixing roller 1. To do.

The movable support member 7 is guided by the guide member 7b and movably slides in the compression / restoration direction of the pressure spring 4, and the cam 8 in contact with the cam follower portion 7a of the movable support member 7 is rotated to move the movable support member. The position of 7 is changed to change the pressure of the pressure roller 3.

The cam 8 is formed such that the outer peripheral cam surface from the position L0 of the lift 0 to the position LMAX of the maximum lift continuously (illustrated) or in a stepwise manner changes the radial length from the cam shaft 8c. It is driven by a drive source (not shown), for example, a servo motor, and the rotational position is controlled by the control circuit unit 6.

The appropriate set value of the pressing force corresponding to the roller temperature is previously obtained by an experiment, and the pressing spring 4, the cam 8 and the cam spring 8, so that the pressing force corresponding to the detected roller temperature is applied to the pressing roller 3. The drive source and the control circuit unit 6 are designed.

A detection element 9 for detecting the presence / absence of the recording paper P, such as a reflection type photosensor, is arranged near the exit of the recording paper P between the roller pair 1 and 3.

The following operation is performed in the above configuration.

The pressing force and the roller temperature of the fixing device are initially set to standard values, that is, the pressing force and the roller temperature at the position L0 of the lift 0 are 180 ° C to 185 ° C. The cam 8 is in the rotational position of FIG.

The control circuit section 6 receives the roller temperature signal from the thermistor 5 at each occasion, and turns on / off the heater 2 in order to maintain the roller temperature within the standard setting range. When image formation is started and the recording paper P passes through the fixing device 11,
The detection element 9 notifies the control circuit unit 6 that the recording paper P is passing. When the roller temperature when the recording paper P is passing is within the standard set temperature range, the pressing force remains the standard value.

Even if the heater 2 is continuously driven, the roller temperature continues to drop due to the passage of paper, and when the roller temperature falls below the standard set temperature range, the control circuit unit 6 causes the recording paper P to pass through the fixing device 11. Until the next recording sheet P arrives, the cam 8 is rotated by an appropriate angle by a drive source (not shown) so that the pressing force corresponds to the temperature of the passing roller, and the rotation shown in FIG. To the position. Then, the movable support member 7 is pushed up by the cam 8, the pressure spring 4 is compressed, and the pressure force of the pressure roller 3 to the fixing roller 1 is increased.

When the roller temperature continues to decrease, the cam 8 increases the lift so as to match the roller temperature and increases the pressure. After the cam 8 has rotated to the lift LMAX position, when the roller temperature becomes lower than the temperature corresponding to the pressurizing force variable range, the image forming operation is interrupted.

The result of the above operation will be described based on whether the fixability is good or bad.

Here, the fixing property evaluation is simplified,
It is expressed in three levels of "good", "normal", and "bad".

For example, when the pressing force is set to 10 kg and the roller temperature control range is set to 180 to 185 ° C., the fixing property is “good.” However, recording paper having a large basis weight is continuously passed,
When the roller temperature decreases to 175 ° C., the fixability becomes “normal”, and at 170 ° C. or less, the fixing property becomes “poor”.

In this example, since the pressure applied to the roller temperature was set as shown in Table 1, the fixability could be maintained at "normal" or higher even if the roller temperature was lowered to 155 ° C. That is, the fixing temperature is less than 170 ° C., which is considered to be poor only by heating the roller temperature allowable range with the standard pressure.
It was possible to spread to a temperature as low as 5 ° C.

When the applied pressure is 15 kg or more, the roller is deflected by the applied pressure, and the applied pressure distribution in the roller axial direction is deteriorated. Therefore, the upper limit of the set value of the applied pressure is set to 14 kg.

In the image forming apparatus having the fixing device configured and operating as described above, even when the amount of heat taken away by continuous sheet feeding or the like becomes larger than the amount of heat supplied by the heater 2 and the roller temperature drops. Since the setting can be changed to the pressing force corresponding to the roller temperature, it is possible to reduce the deterioration of the fixability and delay the time when the image forming operation is interrupted. "Other Embodiments""SecondEmbodiment" FIG. 4 is a schematic cross-sectional view of a heat roller fixing device showing a second embodiment of the present invention and a diagram of a control circuit section.

What is different from the first embodiment is the shape of the cam 18. Groove 18a for pressurizing the cam surface during standby
And a curved surface portion 18b for passing paper. That is, the cam 18 has a shape that gradually increases from the L0 position of the lift 0 as the cam 18 rotates counterclockwise in FIG. 4, and reaches the maximum lift LMAX position at a rotation angle of about 270 degrees. A groove 18a is provided between the maximum lift position LMAX and the L0 position of the lift 0 in the clockwise direction.
When the cam follower portion 7a of the movable support member 7 is inserted into the movable support member 7, the movable support member 7 is at the lowest position. In this case, the cam follower portion 7a has a semicylindrical shape or a hemispherical shape.

In the first embodiment, the standard pressurizing force, that is, the pressurizing force at the time of image formation remains in the standby state, but in the second embodiment, the standby pressurizing force smaller than the pressurizing force at the time of image forming is applied. Set.

Since no image forming operation is performed during standby, the pressure applied to the roller pair may be small. Rather, the smaller the life of the pressure roller 3, the better.

In the standby state, the cam 18 is at the position shown in FIG. 5, and the cam follower portion 7a of the movable support member 7 has the cam 18
Since the pressure roller 3 is fitted in the groove 18a of the pressure roller 3, the pressure of the pressure roller 3 against the fixing roller 1 is small.

Upon receipt of the image formation start signal, the control circuit section 6 rotates the cam 18 counterclockwise before the recording paper P reaches the fixing device 11, and reaches the initial setting pressure as shown in FIG. Set to L0.

During image formation, the set value of the pressing force is changed corresponding to the roller temperature as in the first embodiment.

The control circuit section 6 controls the last recording sheet P of continuous paper passage.
After passing, the cam 18 is rotated to the position shown in FIG. 5 to change the pressing force applied between the roller pair to the standby pressing force, and then the image forming apparatus is set to the standby state.

By making the roller pressure as small as possible except when forming an image, the life of the pressure roller can be greatly extended.

According to the study by the present inventor, compared with the case where a pressure of 10 kg is constantly applied, the pressure roller life can be approximately doubled when the standby time is 3 kg and the image formation is 10 kg. It was

The comparison of the service lives was carried out by continuously operating the fixing device in a heated / pressurized state until the rubber hardness of the pressure roller reached 90% of the initial value. The cycle between the standby time and the image formation time was set to every hour.

[Third Embodiment] The third embodiment is provided with a fixing device having the same structure as that of the first or second embodiment, and is further provided with information for setting the pressing force.

In the first or second embodiment, the set value of the pressing force is changed according to the roller temperature when the recording paper passes through the fixing device.

On the other hand, in the third embodiment, the set value of the pressing force is changed not only by the roller temperature when the recording paper passes through the fixing device but also by the roller temperature and the change rate of the roller temperature.

Since the detection element 9 detects that the recording paper P is passing through the fixing device 11, it notifies the control circuit section 6 of the start and end of passage. The control circuit unit 6 detects the roller temperature immediately after the start of the passage and the roller temperature immediately after the end of the passage based on the information on the passage start and the passage end, and calculates the rate of change of the roller temperature.

The control circuit section 6 determines the set value of the pressing force from the roller temperature and the rate of change of the roller temperature, and rotates the cam 8 to change the pressing force.

In the third embodiment, since the pressing force is set in consideration of not only the roller temperature but also the rate of change of the roller temperature, the pressing force can be set more accurately with respect to the decrease of the roller temperature.

For example, in the case where the roller temperature is greatly decreased by passing the paper, the roller temperature is further lowered while the next recording paper P passes through the fixing device 11, and the roller before the previous recording paper P is passing. The pressing force set from the temperature may be insufficient.

When the size of the recording paper P or the type of the recording paper P is different, the appropriate pressing force with respect to the roller temperature is different.

It has also been confirmed that the roller temperature may temporarily drop and then rise during continuous sheet feeding.

Even in the above case, an appropriate pressure can be set by adding the rate of change of the roller temperature.

[0088]

As described above, the set value of the roller pressing force can be changed in a plurality of steps depending on the detected roller temperature or the detected roller temperature and the change rate of the roller temperature. Therefore, when the roller temperature is lowered, It is possible to reduce the deterioration of the fixing property by increasing the pressing force.

Further, by detecting the roller temperature when the recording material passes between the pair of rollers or the rate of change between the roller temperature and the roller temperature, it is possible to detect the roller temperature change due to the recording material more accurately. It can be changed to a different pressure.

Further, since the pressing force is changed until the next recording material passes between the pair of fixing rollers after the roller temperature or the rate of change between the roller temperature and the roller temperature is detected, the pressing force can be set quickly with respect to the roller temperature. Can be changed.

Further, by setting the applied pressure low in the standby state where the image forming operation is not performed, it is possible to reduce the reduction of the roller life due to the pressurization.

[Brief description of drawings]

FIG. 1 is a schematic vertical cross-sectional view of a heat roller fixing device showing a first embodiment of the present invention.

FIG. 2 is a schematic vertical sectional view for explaining the movement of the cam according to the first embodiment.

FIG. 3 is a schematic vertical sectional view for explaining the movement of the cam according to the first embodiment.

FIG. 4 is a schematic longitudinal sectional view of a heat roller fixing device showing a second embodiment of the present invention.

FIG. 5 is a schematic vertical sectional view for explaining the movement of the cam according to the second embodiment.

FIG. 6 is a schematic vertical sectional view for explaining the movement of the cam according to the second embodiment.

FIG. 7 is a schematic vertical sectional view of a conventional heat roller fixing device.

FIG. 8 is a vertical sectional view of an electrophotographic copying machine.

[Explanation of symbols]

 1 Fixing Roller 2 Heater 3 Pressure Roller 4 Pressure Spring 5 Thermistor 6 Control Circuit Section 7 Movable Support Member 8, 18 Cam 9 Detection Element

Claims (10)

[Claims] 1. An image forming apparatus having a heat roller fixing device and having temperature detecting means for detecting the roller temperature of the heat roller fixing device, comprising: An image forming apparatus comprising: a control device that changes a pressure applied between a pair of rollers by a pressure means based on a roller temperature detected by a detection means. 2. When the roller temperature detected by the temperature detecting means is within a preset roller temperature allowable range, the pressure is set low when the roller temperature is high, and is set high when the roller temperature is low. The image forming apparatus according to claim 1, further comprising: 3. The temperature detection means detects the roller temperature while the recording material to be fixed is passing through the heat roller fixing device,
3. The image forming apparatus according to claim 1, wherein the pressing unit changes the set value of the pressing force applied between the pair of rollers based on the detected roller temperature. 4. A control device is provided which changes the pressure applied between the pair of rollers by the pressing means before the recording material passes through the heat roller fixing device and the next recording material passes. The image forming apparatus according to claim 1. 5. An image forming apparatus comprising a heat roller fixing device and having a temperature detecting means for detecting the roller temperature of the heat roller fixing device, wherein the pressure applied between the pair of rollers is the pressure applied during standby when the image forming operation is not performed. In addition, the pressurizing unit that is variable during the image forming operation is provided, and when the image forming operation is not performed in the standby state, the pressurizing force applied between the roller pair by the pressurizing unit is set to the standby pressurizing force to start the image forming operation An image forming apparatus comprising a control device for changing the pressure to an initial setting pressure during an image forming operation. 6. The image forming apparatus according to claim 5, further comprising a control device for making the magnitude of the pressing force at the time of standby smaller than the magnitude of the pressing force at the time of image formation. 7. A control device is provided, which changes the pressing force applied between the pair of rollers by the pressurizing means after the last recording material has passed to the pressing force at the time of standby and then puts it in the standby state. The image forming apparatus according to claim 5. 8. An image forming apparatus comprising a heat roller fixing device and having a temperature detecting means for detecting a roller temperature of the heat roller fixing device, comprising a pressure means for varying a pressure applied between the pair of rollers, An image forming apparatus comprising: a control device that changes a set value of a pressing force applied between a pair of rollers by a pressurizing unit based on a roller temperature detected by a detecting unit and a change rate of the roller temperature. 9. The temperature detection means detects the roller temperature while the recording material to be fixed is passing through the heat roller fixing device,
9. The image forming apparatus according to claim 8, further comprising a control device for changing the set value of the pressing force applied between the pair of rollers by the pressing means based on the detected roller temperature and the change rate of the roller temperature. 10. A control device is provided for changing the pressure applied between the pair of rollers by the pressing means before the recording material passes through the heat roller fixing device and the next recording material passes. The image forming apparatus according to claim 8.