JPH056045A - Image forming device - Google Patents

Abstract

PURPOSE:To provide an image forming device where the abnormal temperature rise of a heating surface such as the surface of a fixing roller for giving heat to an unfixed developer image on a transfer material is prevented from occurring. CONSTITUTION:The abnormal temperature rise is decided in the middle of controlling paper feeding interval. In order to decide the abnormal temperature rise, a temperature T1 which is detected by a thermistor when t1 seconds elapses after a transfer paper passes through a nipping part between the fixing roller and a pressure roller is compared with a temperature T2 which is detected by the thermistor when t2 seconds elapses after the transfer paper passes through the nipping part, and the compared result is expressed in temperature gradient obtained from a next equation (1) (step 501). Temperature gradient Mt=(T2-T1)/(t2-t1)...(1). The value of the temperature gradient Mt is compared with each threshold, and interval time showing the paper feeding interval is set based on the compared result.

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 such as an electrophotographic copying apparatus and an electrostatic information recording apparatus, and more particularly to an image forming apparatus having a heat fixing device.

[0002]

2. Description of the Related Art Generally, an image forming apparatus such as an electrophotographic copying machine has a housing 1 as shown in FIG. A process cartridge 2 is detachably provided in the housing 1. The process cartridge 2 has a container 5 in which a photosensitive drum 3 and a developing device 4 for developing a latent image on the photosensitive drum 3 are incorporated. The developing device 4 is integrally formed with the container 5, and includes a toner container portion 6 that contains toner, and a developing sleeve 7 that carries the toner of the toner container portion 6 to the photosensitive drum 3.

A primary charger 8 is arranged near the photosensitive drum 3, and the primary charger 8 charges the surface of the photosensitive drum 3 to a predetermined polarity.

A laser beam generator 9 is arranged above the photosensitive drum 3. The laser beam generator 9 irradiates the photosensitive drum 3 with a laser beam, and a latent image corresponding to a predetermined image is formed on the photosensitive drum 3.

A cassette 10 is provided on the upstream side of the photosensitive drum 3.
A sheet feeding roller 12 is arranged to feed the transfer sheet 11 stored in the photosensitive drum 3 to the photosensitive drum 3.

A conveying roller 13 is arranged below the photosensitive drum 3. The transport roller 13 transports the transfer paper 11 from the photosensitive drum 3 toward the downstream side thereof.

A fixing device 14 is arranged on the downstream side of the photosensitive drum 3. As shown in FIG. 12, the fixing device 14 includes a fixing roller 15 having a heating element (not shown) inside.
Have. The surface of the fixing roller 15 has a thermistor 17
Is attached. The fixing roller 15 is heated by the heating element inside thereof, and the surface temperature of the fixing roller 15 is detected by the thermistor 17. The heating element is the thermistor 1
Based on the temperature detected at 7, the ON / OFF operation is performed so that the surface temperature of the fixing roller 15 is maintained at the fixing temperature.

A pressure roller 16 is rotatably pressed against the fixing roller 15, and the pressure roller 16 and the fixing roller 15 cooperate with each other to form a nip portion for nip-conveying the transfer paper. The pressing force of the pressure roller 16 against the fixing roller 15 is kept constant.

A transferable area of the transfer paper is defined in the nip portion, and the transferable area of the transfer paper is represented by a length along the longitudinal direction of the fixing roller 15 in the nip portion.
For example, as shown in FIG. 12, the passable area of the transfer paper corresponds to the area from the point a to the point b of the fixing roller 15 so that the point a of the fixing roller 15 is the left end position of the transfer paper. It has been decided.

[0010]

When an operation of forming an image on a transfer sheet having a width dimension smaller than the length dimension of the transferable area of the transfer sheet is performed, heat of a portion of the fixing roller 15 which overlaps with the transfer sheet is generated. Since it is taken by the transfer paper, the temperature of the portion of the fixing roller 15 that overlaps the transfer paper becomes lower than the fixing temperature, and the temperature of the other portion of the fixing roller 15 becomes a temperature near the fixing temperature.

However, the thermistor 17 causes the fixing roller 15 to
The surface temperature of the fixing roller 15 is determined to be lower than the fixing temperature by detecting the temperature of the portion overlapping with the transfer sheet, so that the fixing roller 15 overlaps with the transfer sheet by its internal heating element. It is heated until the surface temperature of the portion becomes substantially equal to the fixing temperature, and the fixing roller 15
The other part is heated until its surface temperature is higher than the fixing temperature. As a result, the local temperature of the fixing roller 15 may rise to an abnormal temperature higher than the fixing temperature, and the abnormal temperature may deform the fixing roller 15 and members such as gears provided around the fixing roller 15. .

An object of the present invention is to provide an image forming apparatus capable of preventing an abnormal temperature rise of a heating surface such as a fixing roller surface for applying heat to an unfixed developer image on a transfer material. It is in.

[0013]

According to the present invention, the above object is achieved by bringing the unfixed developer image onto the transfer material by contacting the heated surface with the unfixed developer image on the transfer material. In an image forming apparatus including a fixing device for fixing the temperature on the heating surface and performing control for maintaining the temperature of the heating surface at the fixing temperature, an allowable upper limit of the temperature of at least a part of the heating surface is preset. An abnormal temperature rise determining means for determining whether or not an abnormal temperature rise exceeding the temperature has occurred, and a feeding unit for controlling an interval for feeding the transfer material toward the fixing device based on a result of the determination by the abnormal temperature rise determining means. This is achieved by having a paper space control means.

[0014]

In the image forming apparatus of the present invention, the abnormal temperature rise determination means and the paper feed interval control means are used.

During fixing, the transfer material and the heating surface contact each other, and the unfixed developer image on the transfer material is fixed on the transfer material by the heat from the heating surface. After the contact between the heating surface and the transfer material, the temperature of the overlapping portion of the heating surface with the transfer material becomes lower than the temperature of other portions, and the heating surface is heated until the temperature reaches the fixing temperature. When the abnormal temperature rise determination means determines that the abnormal temperature rise of the heating surface has occurred, the paper feed interval control means controls the paper feed interval from the next transfer material, and the controlled paper feed is performed. Temperature control is performed on the heating surface within a time period indicating the interval.

[0016]

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

FIG. 1 is a block diagram showing an embodiment of the image forming apparatus of the present invention, FIG. 2 is a perspective view showing the main part of the fixing device of the image forming apparatus of FIG. 1, and FIG. 3 is the image forming apparatus of FIG. 4 is a flow chart showing an image forming operation of FIG. 4, FIG. 4 is a flow chart showing a paper feed interval control in the image forming operation of FIG. 3, 5 is a flow chart showing an abnormal temperature rise determination in the paper feed interval control of FIG. 4, and FIG. it is a diagram showing a relationship between temperatures T ₁ and temperature T ₂ after the nip passage.

The image forming apparatus includes a housing 1 as shown in FIG. A process cartridge 2 is detachably provided in the housing 1. Process cartridge 2
Has a container 5 in which a photosensitive drum 3 and a developing device 4 for developing a latent image on the photosensitive drum 3 are incorporated.
The developing device 4 is integrally formed with the container 5, and includes a toner container portion 6 that contains toner, and a developing sleeve 7 that carries the toner of the toner container portion 6 to the photosensitive drum 3.

A primary charger 8 is arranged near the photosensitive drum 3, and the primary charger 8 charges the surface of the photosensitive drum 3 to a predetermined polarity.

A laser beam generator 9 is arranged above the photosensitive drum 3. The laser beam generator 9 irradiates the photosensitive drum 3 with a laser beam, and a latent image corresponding to a predetermined image is formed on the photosensitive drum 3.

A cassette 10 is provided on the upstream side of the photosensitive drum 3.
A sheet feeding roller 12 is arranged to feed the transfer sheet 11 stored in the photosensitive drum 3 to the photosensitive drum 3.

A conveying roller 13 is arranged below the photosensitive drum 3. The transport roller 13 transports the transfer paper 11 from the photosensitive drum 3 toward the downstream side thereof.

A fixing device 14 is arranged on the downstream side of the photosensitive drum 3. As shown in FIGS. 1 and 2, the fixing device 14 has a fixing roller 15 having a heating element (not shown) inside. A thermistor 17 is attached to the surface of the fixing roller 15. The fixing roller 15 is heated by the heating element inside thereof, and the surface temperature of the fixing roller 15 is detected by the thermistor 17. The heating element is turned on / off based on the temperature detected by the thermistor 17 so that the surface temperature of the fixing roller 15 is maintained at the fixing temperature.

A pressure roller 16 is rotatably pressed against the fixing roller 15, and the pressure roller 16 and the fixing roller 15 cooperate with each other to form a nip portion for conveying the transfer paper under pressure. The pressing force of the pressure roller 16 against the fixing roller 15 is kept constant.

A transfer paper passage area is defined in the nip portion, and the transfer paper passage area is represented by a length along the longitudinal direction of the fixing roller 15 in the nip portion.
For example, as shown in FIG. 2, the passable area of the transfer sheet corresponds to the area from the point a to the point b of the fixing roller 15 so that the point a of the fixing roller 15 is the left end position of the transfer sheet. It has been decided.

When an image is formed on the transfer paper 11, as shown in FIG. 3, first, the temperature of the fixing device 14 is controlled (step 301). The fixing roller 15 of the fixing device 14 is heated by the heating element inside thereof. The heating element is turned on / off based on the temperature detected by the thermistor 20, and the surface temperature of the fixing roller 15 is maintained near the fixing temperature.

Next, when a request for an image forming operation is input (step 302), paper feed interval control is performed (step 303). In the paper feed interval control, an abnormal temperature rise determination is performed, and the paper feed interval is determined based on the result of the determination. The details of the paper feed interval control will be described later.

When the paper feed interval is determined, the paper feed operation is performed based on the paper feed interval (step 304). First,
The paper feed roller 12 is driven to transfer the transfer paper 1 in the cassette 10.
1 is the photosensitive drum 3 so as to be synchronized with the rotation of the photosensitive drum 3.
Be transported to.

Then, a latent image forming operation is performed (step 305). The surface of the rotating photosensitive drum 3 is uniformly charged by the primary charger 8 and then the laser beam is received from the laser beam generator 9 to form a latent image on the photosensitive drum 3.

The latent image on the photosensitive drum 3 is visualized as a toner image by the developing device 4. The toner image on the photosensitive drum 3 is transferred onto the transfer paper 11, and an unfixed toner image is formed on the transfer paper 11.

Then, a fixing operation for fixing the unfixed toner image as a permanent image on the transfer paper 11 is performed (step 306). Transfer paper 1 transported by the transport roller 13
1 is inserted into the nip portion. The transfer paper 11 receives heat and pressure while passing through the nip portion. The unfixed toner image is transferred to the transfer paper 11 as a permanent image by heat and pressure, and the transfer paper 11 is carried out of the housing. As a result, image formation by a series of operations is completed.

Next, the paper feed interval control will be described in detail. When the paper feed interval is controlled, as shown in FIG.
Whether or not 1 corresponds to the control target is determined based on the width dimension of the transfer paper 11. (Step 401).

When it is determined that the transfer paper 11 is the control target, an abnormal temperature rise determination for the fixing roller 15 is performed (step 402), and when the result of the determination indicates an abnormal temperature rise, the paper feed interval is changed. (Step 40)
4).

In the abnormal temperature rise determination, as shown in FIG. 5, the thermistor 17 is passed t ₁ seconds after the transfer paper 11 passes through the nip portion between the fixing roller 15 and the pressure roller 16.
The temperature T ₁ detected by the above is compared with the temperature T ₂ detected by the thermistor 17 t ₂ seconds after the transfer paper 11 passes through the nip portion, and the result of the comparison is calculated by the following equation (1). It is represented by a gradient (step 501).

Temperature gradient M _t = (T ₂ −T ₁ ) / (t ₂ −t ₁ ) ... (1) The temperature gradient M _t is compared with _a threshold Ma (step 50).
2). When the temperature gradient M _t and the threshold M _a match, the time S ₁ is set as the sensation time for determining the paper feed interval (step 503).

[0036] When the temperature gradient M _t and the threshold M _a mismatch, the temperature gradient M _t is compared with a threshold M _b (step 504). When the temperature gradient M _t and the threshold M _b match, S ₂ is set as the interval time for determining the paper feed interval (step 505).

When the temperature gradient M _t and the threshold value M _b do not match, S ₃ is set as the interval time for determining the paper feed interval (step 506).

When the image forming operation is continuously performed on the transfer paper having a sufficiently small width, it is determined that the transfer paper 11 is the target of the paper feed interval control (step 40 in FIG. 4).
1) Next, an abnormal temperature rise determination for the fixing roller 15 is performed (step 402 in FIG. 4). First, the temperature gradient M _t accompanying the passage of the first sheet of transfer paper 11 through the nip portion is calculated (step 501 in FIG. 5). Since the width of the transfer paper 11 is sufficiently small, the temperature of the portion of the fixing roller 15 that overlaps with the transfer paper 11 becomes lower than the temperature of the other portion, so that the heat amount of the other portion of the fixing roller 15 is the transfer paper 11. The temperature of the portion of the fixing roller 15 overlapping the transfer paper 11 rises again. Next, the presence or absence of an abnormal temperature rise is predicted from the value of the gradient M _ta obtained from the temperature T _{1 of} the fixing roller 15 after t ₁ seconds and the temperature T ₂ after t ₂ seconds, and the temperature gradient M _ta A time interval indicating a paper feed interval is set according to the value. Therefore, the temperature control can be performed so that the abnormal temperature rise of the fixing roller 15 does not occur during the set time interval. When the width dimension of the transfer paper 11 is equal to the length dimension of the passable area of the transfer paper, the temperature gradient becomes M _tc as shown in FIG. It is determined that it is not.

Next, another image forming apparatus will be described. 7 is a view showing a state in which a cassette is mounted in another embodiment of the image forming apparatus of the present invention, FIG. 8 is a plan view showing the cassette of FIG. 7, and FIG. 9 is a side view showing the cassette of FIG. is there.

Another image forming apparatus is provided with a transfer paper size detecting means for detecting the width dimension of the transfer paper 11 and a counting means for counting the number of paper feeds. The width dimension of the transfer paper detected by the transfer paper size detection means and the number of paper feeds counted by the counting means are given to the paper feed interval control means. The paper feed interval is controlled based on the. Therefore, since the paper feed interval is controlled under the preset condition, the control can be facilitated.

As shown in FIGS. 7 to 9, the transfer sheet size detecting means is provided with a plurality of protrusions 20 provided on the side surface of the cassette 10 and a plurality of mounting portions of the cassette 10 of the housing 1. And a switch 21. When the cassette 10 is mounted on the mounting portion of the cassette 10 of the housing 1, the protrusion 20 pushes the corresponding switch 21,
The width dimension of the transfer paper 11 in the cassette 10 is detected by the operation of.

Still another image forming apparatus will be described. FIG. 10 is a perspective view showing the main part of a fixing device used in still another embodiment of the image forming apparatus of the present invention.

A fixing device 14 of still another image forming apparatus.
As shown in FIG. 10, has a fixing roller 15 and a pressure roller 16 in which a heating element is provided. A thermistor 17 is attached to one end of the fixing roller 15, and a thermistor 22 is attached to the other end. Whether or not an abnormal temperature rise occurs due to fixing of transfer paper having a small width dimension is determined based on the temperature detected by the thermistor 22, and the result of the determination is used to determine the sheet feeding interval. Therefore, temperature control can be performed so as to reduce the difference between the temperature of the portion of the fixing roller 15 that overlaps with the transfer paper and the temperature of the other portion, and an abnormal temperature rise in the other portion of the fixing roller 15 can occur. Can be prevented.

[0044]

As described above, according to the image forming apparatus of the present invention, when the abnormal temperature rise determination means determines that the abnormal temperature rise occurs, the paper feed interval control means operates. Since the feeding interval of the transfer material is controlled, the controlled feeding interval can be set to a value at which the temperature control of the heating surface can be executed, and the abnormal temperature rise of the heating surface can be prevented. Can be prevented.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of an image forming apparatus of the present invention.

FIG. 2 is a perspective view showing a main part of a fixing device of the image forming apparatus of FIG.

3 is a flowchart showing an image forming operation of the image forming apparatus of FIG.

FIG. 4 is a flowchart showing a paper feed interval control in the image forming operation of FIG.

5 is a flowchart showing an abnormal temperature rise determination in the paper feed interval control of FIG.

FIG. 6 is a diagram showing a relationship between a temperature T ₁ and a temperature T ₂ after a transfer sheet has passed through a nip portion.

FIG. 7 is a diagram showing a state in which a cassette is attached to another embodiment of the image forming apparatus of the present invention.

8 is a plan view showing the cassette of FIG. 7. FIG.

9 is a side view showing the cassette of FIG. 7. FIG.

FIG. 10 is a perspective view showing a main part of a fixing device used in still another embodiment of the image forming apparatus of the present invention.

FIG. 11 is a configuration diagram showing a conventional image forming apparatus.

12 is a perspective view showing a main part of a fixing device of the image forming apparatus of FIG.

13 is a diagram showing the relationship between the temperature distribution of the fixing roller of the fixing device of FIG. 12 and the width dimension of the transfer paper.

[Explanation of symbols]

10 cassettes 11 Transfer paper 14 Fixing device 15 Fixing roller 16 Pressure roller 17,22 Thermistor 20 protrusions 21 switch

Claims (4)

[Claims] 1. A fixing device for fixing the unfixed developer image on the transfer material by bringing the heated surface, which is heated, into contact with the unfixed developer image on the transfer material, and the temperature of the heated surface. In an image forming apparatus in which control is performed to maintain the fixing temperature at a fixing temperature, an abnormality that determines whether or not an abnormal temperature rise has occurred in which at least part of the temperature of the heating surface exceeds a preset upper limit temperature An image forming method, comprising: a temperature rise determination means; and a paper feed interval control means for controlling an interval at which the transfer material is fed toward the fixing device based on a result of the determination by the abnormal temperature rise determination means. apparatus. 2. A first temperature detecting means for detecting the temperature of the heating surface, the detected temperature being used for controlling the temperature of the heating surface, wherein the abnormal temperature rise determining means is adapted to supply the transfer material. The presence or absence of an abnormal temperature rise within a predetermined period is predicted based on the change in the temperature detected by the first temperature detecting means during the time from the paper feeding to the next transfer material, and the result of the prediction is calculated. The image forming apparatus according to claim 1, wherein the determination result is used. 3. A counting means for counting the number of fed transfer materials, and a transfer material size detecting means for detecting the width dimension of the transfer material, wherein the abnormal temperature rise determining means is the counting means. It is assumed that the presence or absence of an abnormal temperature rise is predicted based on the counted number of transfer materials and the width dimension of the transfer material detected by the transfer material size detecting means, and the result of the prediction is used as the determination result. The image forming apparatus according to Item 1. 4. A first temperature detecting means for detecting a temperature of a heating surface, the detected temperature being used for controlling the temperature of the heating surface, and a temperature detection of the heating surface by the first temperature detecting means. A second temperature detection means for detecting the temperature of another portion different from the portion, and the abnormal temperature rise determination means determines whether or not an abnormal temperature rise has occurred based on the temperature detected by the second temperature detection means. The image forming apparatus according to claim 1.