JPH05297658A - Image forming device - Google Patents

Abstract

PURPOSE:To prevent defective fixation or an image forming disabling state from occurring which is caused because the capacity of the heater of a fixing device is restricted and fixing temperature is not secured for all conditions in an image forming device provided with the heat roller fixing device. CONSTITUTION:At a step 1, when the temperature of the roller is detected, the signal thereof is sent to a control circuit part. At a step 2, a standby time is found out from a roller temperature/standby time transformation table expressing the relation between the standby time until an image is started to be formed and the temperature of the roller stored in the control circuit part. At a step 3, the standby time is set. At a step 4, it is judged whether the respective image forming actions can be executed or not. When it is judged at a step 5 that the time elapses over the standby time set at the step 3, the respective image forming actions are started at a step 6. Besides, the standby time may be set together with the temperature of the roller and the size of a recording paper or the variation of the temperature of the roller.

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 equipped with a heat roller fixing device such as an electrophotographic copying machine and a laser printer, which is capable of intermittently passing a recording sheet and repeatedly forming an image. Regarding

[0002]

2. Description of the Related Art Conventionally, a heat roller fixing device has been widely used as a fixing device in image forming apparatuses such as electrophotographic copying machines and laser printers.

The heat roller fixing device fixes the toner image formed on the recording paper in the previous step to the recording paper. The pressure and heat are applied to the recording paper and the toner so that the toner permeates between the fibers of the recording paper and is fixed.

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

The image reading system is of a fixed type and movable optical system.

The first mirror base 51 has a first mirror 51a.
And an illumination lamp 51b are provided. First mirror stand 5
1 moves along the platen glass 55.

The second mirror base 52 has a second mirror 52a.
And a third mirror 52b. Second mirror stand 5
2 moves in the same direction at half the speed of the first mirror table 51.

The original D placed on the original table glass 55 is illuminated by the illumination lamp 51b, and the reflected light from the original D is reflected by the first mirror 51a, the second mirror 52a, and the third mirror 52b to proceed. The first mirror base 51 and the second mirror base 52 start moving from the position called the home position where image formation can be started, the position of HP in FIG. 4, and read the document D while moving to the right in the drawing, 3 mirrors 5
The original image reflected by 2b advances to the lens 53, and the lens 53
And the exposure unit 6 on the photosensitive drum 61 via the fourth mirror 54.
An image is formed on 1a.

Recording paper P is stored in the cassette 57. The size of the recording paper P is cassette size detection means 58.
Detected by.

Around the photosensitive drum 61, a charger 62,
Image forming means such as an exposure unit 61a, a developing device 63, a transfer charging device 64, a cleaning device 65, and the like are arranged, and image forming processes such as charging, exposure, development, transfer, and cleaning are performed.

The recording sheet P after transfer is conveyed to the fixing device 68 by the conveying section 67.

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 60, and the first mirror base 51 and the second mirror base 52 are moved to form the image formation. Then, a toner image is formed on the photosensitive drum 61.

On the other hand, the recording paper P fed from the cassette 57 once stands by at the registration roller section 66, and when the image formation can be started, the photosensitive drum 61 of the photosensitive drum 61 is synchronized with the movement of the first mirror base 51. The toner image on the photosensitive drum 61 is transferred to the transfer unit 61 b, and after being transferred, the transfer unit 67 transfers the toner image to the fixing device 68. The fixing device 68 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 51 moves a predetermined length and then returns to the home position HP, and when the image formation can be started, the first mirror base 51 moves again to repeat the above image formation. The recording paper P is intermittently fed and passes through the fixing device 68.

The above operation and all other operations of the copying machine are as follows.
It is controlled by the control circuit unit 60.

Next, the fixing device will be described.

FIG. 5 is a schematic sectional view of the structure of the heat roller fixing device.

The fixing roller 81 has a fluororesin film formed on a cylindrical cored bar. Inside the fixing roller 81 is a heater 82 which is a heat source.

The pressure roller 83 has a silicon rubber layer 83b formed on a core metal 83a, and is pressed against the fixing roller 81 by a pressure spring 84 to form a fixing nip and rotate together with the fixing roller 81. The recording paper P passes through the nip portion and fixes the toner on the recording paper.

On the outer surface of the fixing roller 81, a thermistor 85 serving as a temperature detecting means for the roller temperature is brought into contact.

Near the exit of the fixing nip, the paper detection means 8
9 is provided to detect the passage of the recording paper P.

FIG. 6 shows a flowchart of the roller temperature control.

The control circuit 60 controls ON / OFF of the heater 82 by the roller temperature detected by the thermistor 85 to drive the heater 82, and maintains the temperature of the fixing roller 81 within a set constant range.

In order to maintain the temperature of the fixing roller 81, the total amount of heat released from the fixing roller 81 per unit time must be at least equal to or more than the average amount of heat supplied from the heater 82 per unit time. I have to. If they are equal, the temperature can be maintained by continuously turning on the heater 82. 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.

The total amount of heat released from the fixing roller 81 is determined by the heat radiation of the fixing device itself including the fixing roller 81 and the recording paper P intermittently.
Is the amount of heat absorbed by the recording paper P and the toner when the toner is passed through the fixing device and fixed.

[0027]

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

Therefore, even if the image is formed once, that is, one sheet of recording paper passes through the fixing device, the temperature drop of the fixing roller is small, but paper having a large basis weight or paper that has absorbed moisture or paper is passed. When the temperature is low, or under bad conditions such as when large size paper is repeatedly passed at high speed, the average amount of heat lost per unit time from the fixing roller to the paper is the average amount of heat supplied from the heater per unit time. And the roller temperature decreases. For this reason, fixing failure may occur,
The image forming operation must be interrupted before fixing failure occurs, and a desired number of images cannot be obtained.

It is also possible to solve the above problems by uniformly reducing the image forming speed per unit time and reducing the average number of recording papers passing through the fixing device per unit time. Since the temperature of the fixing roller does not drop under the condition of the recording paper in normal use, it is not necessary to slow down the image forming speed per unit time, and the specification performance of the image forming apparatus is deteriorated, which is not preferable.

The present invention has been made in view of the above points, and in continuous image formation under adverse conditions without slowing down the image forming speed per unit time under the condition of recording paper in normal use, An object of the present invention is to provide an image forming apparatus provided with a fixing device capable of continuing the image forming operation up to a desired number without interrupting the image forming operation without deteriorating the fixing property.

[0031]

Such an object is achieved by the following first, second, third and fourth inventions.

A first aspect of the present invention is an image forming apparatus which comprises a heat roller fixing device having a roller temperature detecting means for detecting a roller temperature, and which can intermittently pass a recording sheet to repeatedly form an image. In the image forming apparatus, the image forming apparatus further includes a control unit that controls the timing of starting image formation of each of the image formations to be repeated according to the detected roller temperature.

A second aspect of the present invention comprises a heat roller fixing device having a roller temperature detecting means for detecting the roller temperature, and a size detecting means for detecting the size of the recording paper,
In an image forming apparatus capable of repeatedly forming images by intermittently passing the recording paper, the start time of each image formation of the repeated image formation is detected by the roller temperature and the size of the recording paper to be fixed. The image forming apparatus is characterized by having control means for performing variable control according to the above.

A third aspect of the present invention is provided with a heat roller fixing device having a roller temperature detecting means for detecting the roller temperature, and has a paper detecting means for detecting that the recording paper has passed through the heat roller fixing device. In the image forming apparatus capable of repeatedly forming an image by intermittently passing the recording paper, the roller temperature and the change in the roller temperature during the passage of the recording paper to be fixed pass through the heat roller fixing device. And an image forming apparatus having a control means for performing control to change the start timing of each image formation of the image formation which is repeatedly detected according to the detected roller temperature and the change of the roller temperature. Is.

According to the fourth aspect of the present invention, the waiting time provided for changing the timing of starting image formation is the difference between the fixing temperature set to be maintained during image formation and the detected roller temperature and the primary temperature. The image forming apparatus according to any one of the first to third inventions, characterized in that the relationship is represented by a formula.

[0036]

According to the present invention having such a configuration, in the case of repeatedly forming an image, even when the roller temperature is lowered by the passage of the sheet, the timing of starting each image formation of the repeated image formation can be started. Since the control is performed to start the image formation after a waiting time according to the detected roller temperature, the roller temperature rises by the waiting time and fixing failure occurs or the image forming operation is not interrupted. The roller temperature does not drop so that it does not occur, stable and good fixability can be obtained, and a desired number of images can be obtained.

Further, the waiting time is changed according to the detected roller temperature and the size of the recording paper to be fixed. Therefore, in the case of a large-sized recording paper with a large decrease in the roller temperature, the waiting time should be increased to obtain a sufficient roller temperature. It is possible to prevent the delay of the image forming speed per unit time by setting the standby time for small size paper having a small decrease in roller temperature to be short.

The waiting time is determined by detecting the roller temperature while the recording paper to be fixed is passing through the heat roller fixing device.
Since the temperature changes according to the detected roller temperature and the change in roller temperature, if the rate of decrease of the roller temperature is large, the standby time is extended to recover the roller temperature sufficiently, and the recording paper with a low rate of decrease of the roller temperature waits. By setting the time short, it is possible to prevent the image forming speed per unit time from becoming slow.

[0039]

Embodiments of the present invention will be described below with reference to the drawings.

[First Embodiment] This embodiment has a control circuit section 60 for controlling as follows in a copying machine configuration similar to the conventional example shown in FIGS. 4 and 5.

FIG. 1 shows a flowchart of this embodiment.

In the same way as the conventional example, the fixing device 6 is operated in step 1.
8 fixing roller 81 temperature (hereinafter referred to as roller temperature)
Is detected by the thermistor 85, and the control circuit unit 60
Is controlled within a fixed fixing temperature range set so as to be maintained during image formation.

The set temperature is 180 ° C., and if the detected roller temperature is 180 ° C. or lower, the heater 82 is turned on,
If the temperature is higher than 180 ° C., it is turned off to limit the range to ± 5 ° C.

Even if the heater 82 is turned on / off after detecting the roller temperature, the actual rise / fall of the roller temperature is delayed, and as a result, the roller temperature is controlled within a certain range.
In this embodiment, the temperature range is ± 5 ° C.

In the case of repeatedly forming an image, FIG.
As shown in step 2 of step 1, the control circuit section 60 performs this control and simultaneously sets the waiting time according to the detected roller temperature (step 3). For example, Table 1 “Temperature-standby time conversion table” is used.

The waiting time has a relationship represented by a linear expression with the difference between the fixing temperature set to be maintained during image formation and the detected roller temperature at a roller temperature of 174 ° C. or lower.

The detected roller temperature is x, the conversion coefficient is a,
When the fixing set temperature is b and the correction constant is c, the standby time y is represented by the following relational expression.

Y = a (b-x + c) In the case of the "temperature-standby time conversion table" in Table 1, the following numerical values are obtained.

A = 0.2 b = 180 c = −3 However, when image formation is continuously performed for x ≦ 174, the first mirror base 51 returns to the home position HP, and the recording paper P is set to the registration roller portion. In the case of repeating the image formation such as the standby state at 66, each image formation can be started at step 4, and then the first mirror stand 51 is copied for the standby time set at step 5. After waiting at the start position, the movement is started in step 6 to start image formation.

When the recording paper P passes through the fixing device 68, the heat of the fixing roller 81 is removed and the roller temperature is lowered.

If the lowered roller temperature is within the non-waiting set temperature range that does not require waiting, the waiting time is set to zero and continuous image formation is performed in the shortest time.

In the case of the "temperature-standby time conversion table" in Table 1, the non-standby set temperature range is 175 ° C or higher.

When the roller temperature becomes lower than the non-standby set temperature range, the start of image formation is delayed by the standby time corresponding to the roller temperature.

The time lag between the time when the roller temperature becomes lower than the non-standby set temperature range and the time when each image formation can be started differs depending on the copy mode and the like.

For example, in the case of a large-sized recording paper P, the start of image formation on the recording paper P next to the recording paper P whose roller temperature is low can be delayed. However, with the recording paper P of a small size, since the image formation of the next recording paper P has already started, the start of image formation on the next next recording paper P is delayed. In some cases, it may be the recording sheet P later.

The timing of delaying the start of image formation is preferably after the time when the roller temperature falls below the non-standby set temperature range and as early as possible.

By the above operation, the number of sheets of recording paper P passing through the fixing device per average time is reduced according to the roller temperature. As a result, the roller temperature does not fall below a certain temperature, and since image formation is performed at a sheet passing interval necessary and sufficient to maintain the roller temperature, good fixing performance is maintained and the image forming operation is interrupted. It is possible to continuously perform image formation until the desired number of sheets is obtained.

[Other Embodiments] [Second Embodiment] FIG. 2 shows a flowchart of this embodiment.

In this embodiment, a size detecting means for detecting the size of the recording paper P is provided and the size of the recording paper is detected in advance. As shown in the "temperature-standby time conversion table" in Table 2, the wait time is determined according to the size of the recording paper P and the detected roller temperature.

The ratio of the passage time and the non-passage time of the recording paper P passing through the fixing device differs depending on the size of the recording paper P.
The average amount of heat per unit time taken from the fixing roller 81 to the recording paper P changes. The larger the recording paper P, the greater the amount of heat transfer from the fixing roller to the recording paper P per average unit time.

Therefore, if the "temperature-standby time conversion table" is used for the maximum size recording paper P that can be passed, in the case of a small size recording paper P, the standby time is longer than the minimum required length. Become.

On the other hand, in this embodiment, by using the "temperature-standby time conversion table" for each size of the recording paper P, the optimum waiting time for the size of the recording paper P is determined and the image is formed. It is possible to continue the image forming operation up to the desired number of sheets without deteriorating the performance, without interrupting the image formation, and without waiting more than necessary.

In FIG. 2, in step 1, the cassette size detecting means 58 shown in FIG. 4 detects the type of the cassette 57, and the size of the recording paper P is detected accordingly. In step 2, the thermistor 85 detects the temperature of the fixing roller 81. In step 3, the recording paper size detected in step 1 and the temperature of the fixing roller 81 detected in step 2 are input, the waiting time is obtained from Table 2 in the storage device, and the waiting time is set in step 4. .. After each image formation can be started in step 5, the first mirror base 51 stands by at the copy start position for the waiting time set in step 6, and starts moving in step 7 to start image formation. Start. In this case as well, if the recording paper size is large, there will be a waiting time, but the fixing roller
If the temperature of 1 is within the non-standby set temperature range that does not require standby, the standby time is set to zero and continuous image formation is performed in the shortest time.

[Embodiment 3] FIG. 3 shows a flowchart of this embodiment.

In this embodiment, there is a detecting means for detecting that the recording paper P is passing through the heat roller fixing device 68.
The temperature T1 of the recording paper P fixed in step 1 at the start of passage of the fixing device is detected, the temperature T2 of the fixing roller 81 at the end of passage of the recording paper P is detected in step 2, and the roller temperature change T1 is detected in step 3. “T2 = ΔT” is obtained, and in step 4, the “temperature-temperature change-standby time conversion table” shown in Table 3 is obtained from the temperature change T1-T2 = ΔT and the temperature of the fixing roller 81.
The standby time is set by (step 5). Since the paper detection means 89 provided on the exit side of the fixing device in FIG. 5 detects that the recording paper P is passing through the fixing device, the passage start and the passage end are controlled. Inform the circuit unit 60. The control circuit 60 detects the roller temperature immediately after the passage start and the roller temperature immediately after the passage end based on the information of the passage start and the passage end, and calculates the change of the roller temperature.

The control circuit unit 60 determines the waiting time from the roller temperature and the change in the roller temperature according to the "temperature-temperature change-waiting time conversion table" shown in Table 3.

The steps 6 to 8 are the same as those in the previous embodiments.

In the present embodiment, the waiting time is determined in consideration of not only the roller temperature but also the rate of change of the roller temperature, so that the waiting time can be made more accurate with respect to the decrease of the roller temperature.

For example, when the power supply voltage drops and the heat supply from the heater 82 of the fixing roller becomes small, the roller temperature rises slowly and the roller temperature drops greatly due to the passage of paper, and the next recording paper P is The roller temperature may further decrease while passing through the fixing device 68, and the roller temperature may not be recovered within the waiting time set from the roller temperature during which the preceding recording paper P is passing.

Even in such a case, an appropriate waiting time can be determined by taking the rate of change of the roller temperature into consideration.

In the above three examples, the present invention is applied to an electrophotographic copying machine, but not limited to the copying machine, a heat roller fixing device is provided, and recording paper is intermittently passed to repeatedly form an image. The present invention can be applied to any image forming apparatus capable of performing the above.

[0072]

As described above, in the case of repeatedly forming an image, even when the roller temperature is lowered by passing a sheet, each image forming start of the repeated image formation can be started. Since the control is performed so that the image formation is started after the standby time corresponding to the detected roller temperature from the time, the roller temperature rises by the standby time and fixing failure occurs or the image forming operation must be interrupted. The temperature of the roller does not decrease so that stable fixing properties can be obtained, and a desired number of images can be obtained.

When the standby time is changed according to the detected roller temperature and the size of the recording paper to be fixed, the standby time for a small size recording paper with a small decrease in roller temperature is set to be short, It is possible to prevent the image forming speed per unit time from becoming slow.

The waiting time is detected by detecting the roller temperature while the recording paper to be fixed is passing through the heat roller fixing device.
When the roller temperature is changed according to the detected roller temperature and the change in the roller temperature, if the roller temperature decrease rate is large, the standby time is lengthened to recover the roller temperature sufficiently and By setting the standby time short, it is possible to prevent the image forming speed per unit time from becoming slow.

[Brief description of drawings]

FIG. 1 is a flow chart of a first embodiment of the present invention.

FIG. 2 is a flow chart of a second embodiment of the present invention.

FIG. 3 is a flow chart of a third embodiment of the present invention.

FIG. 4 is a sectional view of an electrophotographic copying machine.

FIG. 5 is a sectional view of a heat roller fixing device.

FIG. 6 is a flowchart of roller temperature control.

[Explanation of symbols]

 51 first mirror base 58 cassette size detection means 60 control circuit section 66 registration roller 68 fixing device 81 fixing roller 85 thermistor 89 paper detection means P recording paper

Claims (4)

[Claims] 1. An image forming apparatus comprising a heat roller fixing device having a roller temperature detecting means for detecting a roller temperature and capable of repeatedly forming an image by intermittently passing a recording sheet and forming an image repeatedly. 2. An image forming apparatus comprising: a control unit that controls to change the start timing of each image formation according to the detected roller temperature. 2. A heat roller fixing device having a roller temperature detecting means for detecting the roller temperature, and a size detecting means for detecting the size of the recording paper, and the recording paper is intermittently passed to repeatedly form an image. In the image forming apparatus capable of performing the image forming apparatus, the image forming apparatus has a control unit that controls the start time of each image forming of the image forming operation to be variable according to the detected roller temperature and the size of the recording paper to be fixed. An image forming apparatus characterized by the above. 3. A heat roller fixing device having a roller temperature detecting means for detecting a roller temperature is provided, and a paper detecting means for detecting that the recording paper is passing through the heat roller fixing device is provided. In an image forming apparatus capable of repeatedly performing image formation by repeatedly passing a sheet, a roller temperature and a change in roller temperature while a recording sheet to be fixed is passing through a heat roller fixing device are detected and repeatedly performed. An image forming apparatus, comprising: a control unit that controls the start timing of each image formation to be variable in accordance with the detected roller temperature and a change in the roller temperature. 4. A standby time provided for changing the timing of starting image formation is expressed by a linear expression with a difference between a fixing temperature set to be maintained during image formation and a detected roller temperature. The image forming apparatus according to any one of claims 1 to 3, wherein