JP2003330315A - Image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To ensure margin for a thermal-protector actuation temperature and prevent blowout of a fuse regardless of a paper passage method which does not meet a paper passage standard. <P>SOLUTION: In a positional relationship between paper sensors which paper passes in a series of printing operations, a main thermister and a sub-thermister, and a thermal protector, the thermal protector is disposed between one of the paper sensors and the main thermister or the sub-thermister. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixing device used in an electrophotographic copying machine, a laser beam printer, etc., and an image forming apparatus used in the fixing device.

[0002]

2. Description of the Related Art Conventionally, as a fixing device in an image forming apparatus such as a copying machine or a printer, a heat roller system or an on-demand system is known.

The heat roller system is a pressure contact nip portion (fixing nip portion) between a heating roller (fixing roller) maintained at a predetermined heating temperature by a built-in heat source such as a halogen heater and an elastic pressure roller pressed against the heating roller. The recording material is introduced into the recording medium and is nipped and conveyed to heat and fix the unfixed image on the recording material surface by the heat of the aging roller.

Among the above-mentioned fixing roller and pressure roller, the fixing roller which comes into contact with the surface of the recording material is a cylindrical roller whose surface is made of a material having a good releasability and which is disposed inside the halogen roller. The heater heats the toner through the cylindrical roller. On the other hand, the pressure roller that comes into contact with the back surface of the recording material is configured by providing an elastic layer on the core metal, and applies appropriate pressure to the toner layer.

The on-demand type heating device eliminates the disadvantages of the heat roller type with large energy loss, and enables quick start and power saving. This is because the heat capacity of the fixing device is reduced by using a heater such as ceramics and a thin film such as polyimide as an alternative to the halogen heater and the fixing roller in the heating roller system. Is the solution.

Further, the above heat roller type or on-demand type fixing device is usually provided with an excessive temperature rise preventing element (thermal protector) as a safety device for preventing ignition or the like when the fixing device is out of control. The thermal protector operates in an abnormally high temperature state, so that the heat generation path is cut off in a hardware manner. Examples of the thermal protector include a thermal fuse and a thermoswitch.

The thermal protector is in direct contact with or fixed to a heating member portion or a fixing roller portion which is within the width of the recording material passing through. When the temperature at the arrangement portion maintains a predetermined abnormally high temperature state, the thermal protector operates and shuts off the heat generation path.

The position of the thermal protector with respect to the longitudinal direction (the direction orthogonal to the carrying direction) is usually in conformity with the sheet passing reference position of the image forming apparatus. When passing small size paper such as envelopes and business cards, to prevent the thermal protector from erroneously operating due to the temperature rise in the non-paper passing area of the fixing device, the minimum paper passing width of the recording material is within the reference position. The above-mentioned thermal protector was arranged in the range. That is, in the case of an image forming apparatus which is the center reference with respect to the longitudinal direction, in the vicinity of the center sheet passing reference line, and in the case of an image forming apparatus which is the end reference, in the vicinity of the edge sheet passing reference line, the thermal protector Had been placed.

Further, in an image forming apparatus having these fixing devices, a plurality of temperature detecting elements (thermistors) are provided in a heating body provided in the fixing device, and these are used to control the temperature of the heating body. There is known one that performs adjustment (power) control.

In this type of image forming apparatus, a first thermistor (main thermistor) is provided in the central portion of the heating body (the range in which the minimum sheet passing width of the recording material is within the sheet passing reference position), and further heating is performed. A second thermistor (sub-thermistor) is provided at the end of the body. When the main thermistor controls the electric power to keep the heating element at the target temperature according to the temperature detected by the main thermistor and the main thermistor or the sub-thermistor detects an upper limit temperature indicating an abnormally high temperature of the heating element, the main body of the image forming apparatus is detected. The reset control is performed to shut off the main power source of and to stop the power supply to the heating element. Further, when recording paper (hereinafter, referred to as small size paper) having a relatively narrow width with respect to the longitudinal heating area of the fixing device such as an envelope is continuously fed, the sub-portion at the end portion due to the temperature rise in the non-sheet feeding portion It is possible to control the temperature of the main thermistor or change the throughput depending on the temperature condition detected by the thermistor.

[0011]

However, in the case of the conventional thermal protector arrangement configuration, the thermal protector is set to the non-sheet passing area depending on the positional relationship of the recording material presence sensor, the recording material passage sensor, or the sub thermistor. There was a possibility that it was printed in the state and the state could not be detected from the output of the sub thermistor.

FIG. 4 is a schematic transparent plan view of a conventional image forming apparatus, in which the sheet passing standard is the center standard with respect to the longitudinal direction.
In the image forming apparatus shown in the conventional example, the maximum paper passing width in manual paper feeding is LTR size (216 mm), and the guaranteed minimum paper passing width is 3 (inch) × 5 (inch) business card size (7
6.2 mm). As a recording material sensor that always detects the recording material for a series of printing operations, a recording material presence sensor Sf1 that controls the presence or absence of the recording material in the manual feed tray 213 is fed to the manual feed section 21 and is being conveyed. The top sensor St, which controls the timing of arrival of the leading edge of the sheet in the sheet conveyance direction and the detection of the recording material sheet conveyance length,
2 and a paper discharge sensor Sd for detecting the recording material discharge timing from the fixing unit 24 are arranged in the paper discharge unit 25, respectively.

When the recording material sensor does not detect the passage of the recording material at a predetermined timing during printing, control is performed to stop the printing operation. Therefore, in order to complete a series of printing, the recording material sensor is used. Must pass all sensors.

The position of the recording material sensor with respect to the longitudinal direction is the recording material presence sensor Sf1 when viewed from the sheet passing reference line A.
In FIG. 4, the right side 33 mm point, the tob sensor St is arranged on the right side 33 mm point, and the paper discharge sensor Sd is arranged on the paper passing reference line A.

The main thermistor 11 that controls the temperature detection for controlling the fixing temperature during paper passing is a sub-thermistor 12 that controls the detection of abnormally high temperature of the heating element at the time of 20 mm on the right side as viewed from the paper passing reference line A. 95mm on the right side
It is located at the point. With the above thermistor arrangement, the temperature rise at the end of the heating element can be detected by the output of the sub-thermistor 12 for a recording material having a width of B5 size (182 mm) or less, and the throughput is reached when a predetermined high temperature state is reached. Since it is possible to control such as dropping the printer or suspending printing for a fixed time, it is possible to reduce damage to the fixing device.

The thermal fuse 100 as a thermal protector is in contact with the heating body, but the length of the contacting portion is 10 mm, and the center of gravity of the thermal fuse 100 passes through the paper reference line A.
It is located at a point 20 mm on the left side as viewed from the side.

The minimum sheet passing width of this image forming apparatus is 76.2.
In the case of the center reference, the minimum sheet width range is 38.1 mm to the left and right when viewed from the reference line A, so the recording material sensor, main thermistor 11, and thermal protector are within that range.

However, even in the above configuration, there is a possibility that a series of printing operations are completed by the bear in which the thermal protector is in the non-sheet passing area, and the state cannot be detected from the output of the sub thermistor.

As shown in FIG. 4, the manual feed tray 21
If the recording material width regulation plate 212 provided in No. 0 is widened to the maximum, and an envelope or the like having a width of 110 mm is passed to the right end, the thermal protector 100 is set in the non-sheet passing area. Recording material sensor, main thermistor 11,
All the sub thermistors 12 are passed. That is, there is a possibility that a series of printing operations will be completed.

As described above, when it is possible to pass a sheet by a sheet feeding method different from the specifications, it is possible to print with the thermal protector in the non-sheet passing area depending on the positional relationship between the recording material sensor and each thermistor. In addition, since it cannot be detected that the paper is small size, the temperature of the thermal protector is likely to rise due to the temperature rise in the non-sheet passing portion, and the margin for the operating rated temperature of the thermal protector may be reduced.

Therefore, the present invention has been made in order to solve the above-mentioned conventional problems. Even when the sheet can be fed by a sheet feeding method different from the specification, the operating rated temperature of the thermal protector is not satisfied. An object of the present invention is to provide an image forming apparatus that can secure a margin.

[0022]

SUMMARY OF THE INVENTION The present invention for solving the above-mentioned problems has a pressure contact portion formed by bringing a pair of fixing rotators into pressure contact with each other, and a temperature detecting element for detecting the temperature of a heating portion. A fixing device that heats and fixes the toner image on the recording paper at the pressure contact portion while controlling the fixing temperature control during paper feeding by the output of the temperature detection element, and includes an excessive temperature rise prevention element of the heating portion. In a fixing device, a recording material sensor such as a recording material presence sensor or a recording material passage sensor provided on a recording material conveying path in an image forming apparatus that supports the recording material, through which the recording material always passes during a series of printing operations. For each of them, any one of the surfaces that pass through the recording material sensor, are orthogonal to the transport surface, and are parallel to the transport direction, and pass through the temperature detection element, are orthogonal to the transport surface, and are the transport direction. The area between the plane parallel to And it is characterized in that it contains some or all of the heating prevention device.

Alternatively, it has a pressure contact portion formed by bringing a pair of fixing rotary members into pressure contact with each other, and has a plurality of temperature detection elements for detecting the temperature of the heating portion, of which the main temperature detection element outputs a signal. A fixing device that heats and fixes the toner image on the recording paper at the pressure contact part while controlling the fixing temperature control in the paper, and changes the fixing control and the conveyance control by the output of the sub temperature detection element. In a fixing device including a temperature prevention element, a recording material presence sensor or a recording material passage sensor, which is provided on a recording material conveying path in an image forming apparatus including the fixing device, causes the recording material to be surely removed during a series of printing operations. For each of the recording material sensors and the main temperature detecting elements that pass therethrough, any one of the surfaces that pass through the recording material sensor or the main temperature detecting element, are orthogonal to the conveying surface, and are parallel to the conveying direction, Sub temperature detection It passed the child, and perpendicular to the transport plane,
A part or all of the excessive temperature rise prevention element is included in a portion sandwiched between a plane parallel to the transport direction.

Here, the abnormal high temperature detection threshold value of the heating portion based on the output of the sub-temperature detection element is characterized in that the operating rated temperature of the excessive temperature rise prevention element is used as a reference.

Further, the fixing device provided in the above-mentioned image forming apparatus includes a heating body for heating the recording material through the thin film and a pressurizing device for heating the heating body through the thin film. It has a pressure body.

As an operation of the present invention, by adopting the above-mentioned constitution, it is possible to feed the paper by a method different from the specification, and the excessive temperature rise prevention element (thermal protector) is arranged in a series even in the non-paper feed area. Even if you print
In such a case, the main temperature detecting element (main thermistor) or the sub temperature detecting element (sub thermistor) is always in the non-sheet passing area. When the main thermistor is in the non-sheet passing area, the fixing temperature control of the heating unit follows the output of the main thermistor, so that the thermal protector does not reach the operating temperature. When only the sub-thermistor is in the non-sheet passing area, the margin for the operating temperature of the thermal protector is secured by using the rated operating temperature of the thermal protector as a reference as the abnormal high temperature detection threshold due to the output. It is possible to change the control to prevent the thermal protector from reducing the margin for the operating rated temperature of the thermal protector due to the temperature rise in the non-paper passing portion caused by printing in the non-paper passing area. It will be possible.

[0027]

BEST MODE FOR CARRYING OUT THE INVENTION First Embodiment The details of the present invention will be described with reference to the drawings by way of specific examples.

FIG. 1 is a schematic sectional view of an image forming apparatus according to this embodiment. In FIG. 1, reference numeral 1 is a photosensitive drum which rotates in the direction of an arrow, and the drum is a well-known one having a photoconductive layer 1a. The latent image forming means, the developing means, and the cleaning means for removing the residual toner after transfer are not shown.
However, in the illustrated apparatus, the toner image formed on the photosensitive drum reaches the transfer portion 23 in a negatively charged state. The recording paper P conveyed in synchronism with the image on the photosensitive drum 1 is loaded on an automatic paper feed mechanism such as a manual paper feed tray 210 or a cassette paper feed tray 200, and recording material presence / absence sensors Sf1 and Sf2 are provided for each of them.
Are arranged. When there is no recording material P in the paper feed tray, the user is notified of “no recording material” at the time when the print signal is received, and the print operation and control are stopped.

In manual paper feeding, the inner bottom plate 213 is pushed upward by a spring 214, and the manual paper feeding roller 211, which is cut out at a part of the circumference, makes one rotation, so that one paper is fed from the manual paper feeding tray 210. Are sent out one by one. The same mechanism is used to feed recording material P in cassette paper feeding.
Is sent out.

The recording material P sent out reaches the resist portion 22 by the guide plate. Then, the registration roller 221 is driven in synchronization with the arrival of the transfer position of the toner image, and the recording material P passing through the registration section 22 passes through the top sensor St,
It reaches the transfer unit 23. The top sensor St controls the timing of arrival of the leading edge of the recording material P and the conveyance length.

In the transfer section 23, a transfer current having an opposite polarity to the toner image (applied voltage: +2 to 3 kV) is applied to the non-printing surface of the recording material by the transfer roller 231 to transfer the toner image on the drum 1 to the recording material. Transfer to P. After the transfer, the recording material P is separated from the drum 1 and conveyed to the fixing device 24. After the transferred image is fixed, the recording material P passes through the paper discharge sensor Sd and is carried out of the machine. Estimated from the leading edge arrival timing of the recording material P detected by the top sensor St and the transport length,
Timing at which the leading edge reaches the discharge sensor Sd and the discharge sensor S
When the d transit time is out of the predetermined time range, the user is notified of "recording material jam" and the printing operation and control are stopped.

Here, in the present embodiment, each of the recording material sensors described above uses a detection device including a sensor lever and a photo sensor (not shown).

The fixing device 24 is a pressure roller moving type on-demand fixing device, and presses the film supporting means 16 holding the ceramic heating body 10 through the cylindrical heat resistant film 15. The roller 17 is brought into pressure contact with a predetermined pressing force to form a fixing nip portion with the heating body 10.

Electric heating of the heating element 10 can be appropriately controlled by a temperature control means (not shown). The temperature control means uses the side of the heating element 10 on which the heating element is formed as the heating element surface and the main temperature detecting element 11 (hereinafter referred to as "main thermistor") attached to the back surface of the heating element 10 and the main thermistor. It has a CPU (not shown) that controls a triac (not shown) based on the temperature detected by 11 and controls the energization of the heating element 10.

A thermal fuse 100 as a thermal protector is in contact with a predetermined position on the rear surface (on the side opposite to the heat generating body) of the heating element 10 with an appropriate pressing force, and that portion has a predetermined operating temperature, in the present embodiment. 228 (+ 0--
6) When the temperature reaches 100 ° C., the thermal fuse 100 is activated to cut off the power supply to the heating element 10.

FIG. 2 is a schematic transparent plan view of the image forming apparatus according to this embodiment, in which the sheet passing reference is the center reference with respect to the length. In the image forming apparatus according to the present exemplary embodiment, the maximum paper passing width in manual paper feeding is LTR size (216 m
m)), the minimum guaranteed paper width is 3 (inch) x 5 (inc)
It is a business card size (76.2 mm) of h).

The position of the recording material sensor with respect to the longitudinal direction is
When viewed from the sheet passing reference line A, the recording material presence sensor Sf1 is shown in FIG.
The right side 33 mm point, the top sensor St is arranged on the right side 33 mm point, and the sheet discharge sensor Sd is arranged on the sheet passing reference kneading A.

The longitudinal length of the contact portion between the thermal fuse 100 and the heating element 10 is 10 mm, and the center of gravity thereof is arranged at a point 20 mm on the left side as viewed from the paper reference line A.

The main thermistor 11 is arranged at a point 30 mm on the left side of the sheet passing reference line A. The minimum sheet-passing width of this image forming apparatus is 76.2 mm, and the minimum sheet-passing width range is 38.1 mm to the left and right when viewed from the sheet-passing reference line A. Therefore, the recording material sensor, the main thermistor 11, and the thermal fuse 100 have the same range. It fits inside.

In this embodiment, all of the temperature fuse 100 is provided between a straight line M passing through the main thermistor 11 and parallel to the sheet passing reference line A, and a straight line D passing through the sheet discharge sensor Sd and parallel to the sheet passing reference line A. The layout is such that (In the case of the present embodiment, the thermal fuse 100 simultaneously operates the parallel lines M
And recording material presence sensor Sf1 or top sensor St
It is configured to be included also between a straight line T passing through and a line T parallel to the sheet passing reference line A. By adopting such a configuration, even in the case where the thermal fuse 100 is made to pass through a sheet in a series of printing operations in which the recording material P passes through all the recording material sensors, Since the main thermistor 11 always reaches the non-sheet passing area, the temperature fuse 100 does not reach the operating temperature due to the non-sheet passing temperature rise, and it is possible to prevent the margin of the temperature fuse from the rated operating temperature from decreasing.

As described above, like the first embodiment, the recording material presence sensor or the recording material passage sensor in the image forming apparatus,
For each recording material sensor through which the recording material always passes during a series of printing operations, one of the surfaces that pass through the recording material sensor, are orthogonal to the transport surface, and are parallel to the transport direction, and the temperature detection Since the thermal protector is included in the part that passes through the element, is orthogonal to the transport surface, and is sandwiched by the planes parallel to the transport direction, the operating temperature reaches the operating temperature even if the thermal protector is printed as a non-sheet passing area. It does not become as hot as usual. Therefore, the reliability of the thermal protector can be improved. It is desirable that the thermal protector is included between the two surfaces, but even if it is a part, the same effect as that of the present embodiment can be obtained.

<Embodiment 2> An image forming apparatus according to Embodiment 2 is different from Embodiment 1 in that the main thermistor 11 is located between a straight line D-T passing through each recording material sensor and parallel to a sheet passing reference line. And the heating element 10
If a sub-temperature detecting element 12 (hereinafter referred to as "sub-thermistor") is brought into contact with a predetermined position on the back surface with an appropriate pressing force and its output exceeds 215 ° C for 1 second or longer, fixing (not shown) is performed. The control circuit reduces the print throughput so that the temperature of the sub-thermistor 12 does not reach the rated operating temperature of the thermal fuse 100. The control change is not limited to throughput reduction, but may be control for lowering the temperature of the subthermistor 12 during printing, such as waiting for printing for a certain period of time or until the temperature drops to a predetermined temperature.

In the case of the first embodiment, the thermal fuse 100 is arranged between the recording material sensor and the main thermistor 11, and when the thermal fuse 100 is printed in the non-sheet passing area, the main thermistor 11 is also non-conductive. Since the structure is located in the paper passing area, a margin for the operating temperature of the thermal fuse 100 is secured, but the temperature in the paper passing area is clearly lower than in the non-paper passing area, so the recording material P discharged at that time is fixed. Is worse, which is not desirable for usability.

FIG. 3 is a schematic transparent plan view of the image forming apparatus according to the second embodiment. The main thermistor 11 is arranged at a point 20 mm on the right side with respect to the sheet passing reference line A, and the sub thermistor 12 is arranged at a point 95 mm on the left side. The main thermistor 11 is within the minimum paper passing width range, and the output of the sub thermistor 12 allows the B5 size width (182
mm) and the following recording material P is passed through the center,
The temperature rise at the end of the heating element 10 can be detected.

According to FIG. 3, the main thermistor 11 is
Since it is arranged between a straight line T passing through the recording material presence sensor Sf1 or the top sensor St and parallel to the sheet passing reference line A, and a straight line D passing through the sheet discharge sensor Sd and parallel to the sheet passing reference line A, a series of The main thermistor 11 always exists in the paper passing area when the printing of is completed. Therefore, the discharged recording material P can secure sufficient fixing property. On the other hand, the thermal fuse 100 is arranged at a portion sandwiched by a straight line S and a straight line D (or straight lines T and M) that pass through the sub thermistor 12 and are parallel to the sheet passing reference line A. Therefore, when the series of printing is completed with the thermal fuse 100 in the non-sheet passing area, the sub thermistor 12 also exists in the non-sheet passing area. Since the abnormal high temperature detection threshold value at the output of the sub thermistor 12 is lower than the operating temperature of the thermal fuse 100, the temperature fuse 100 is lowered by lowering the temperature in the non-sheet passing area by changing the control when the threshold value is exceeded. It was possible to prevent the margin from being reduced with respect to the operating rated temperature of.

By adopting the configuration of the second embodiment,
It is possible to provide an image forming apparatus capable of sufficiently securing the fixing property of a recording material discharged regardless of the recording material passing position and improving the reliability of a thermal protector.

[0047]

As described above, according to the present invention, a recording material sensor such as a recording material presence sensor or a recording material passage sensor in an image forming apparatus passes a recording material sensor which is always passed during a series of printing operations, Any one of the surfaces that are orthogonal to the transport surface and that are parallel to the transport direction, and any one of the surfaces that pass through the main thermistor or the sub-thermistor and that are orthogonal to the transport surface and that are parallel to the transport direction. By including the thermal protector in the area sandwiched between the surface and the surface, even if the thermal protector is printed as a non-sheet passing area, the thermal protector will not reach the operating temperature, so the reliability of the thermal protector is improved. Can be improved.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of an image forming apparatus based on a first embodiment.

FIG. 2 is a schematic transparent plan view of the image forming apparatus according to the first embodiment.

FIG. 3 is a schematic transparent plan view of the image forming apparatus according to the second embodiment.

FIG. 4 is a schematic transparent plan view of a conventional image forming apparatus.

[Explanation of symbols]

Sf1 Manual Feed Tray-Recording Material Presence / Absence Sensor St top sensor Sd paper ejection sensor A paper passing reference line A straight line passing through T Sf1 or St and parallel to the paper passing reference line Straight line passing through D Sd and parallel to the paper passing reference line

Claims (4)

[Claims] 1. A pressure contact portion formed by bringing a pair of fixing rotators into pressure contact with each other, a temperature detection element for detecting a temperature of a heating portion, and a sheet being fed by an output of the temperature detection element. A fixing device for heating and fixing a toner image on a recording paper at the pressure contact portion while controlling the fixing temperature control. In a fixing device having an excessive temperature rise prevention element of the heating portion, the image forming apparatus includes the fixing device. For each recording material sensor such as a recording material presence sensor or a recording material passage sensor provided on the recording material conveyance path, through which the recording material always passes during a series of printing operations, the recording material sensor passes through the recording material sensor At a position sandwiched between any one of the surfaces that are orthogonal to the conveyance direction and that is parallel to the conveyance direction and the surface that passes through the temperature detection element and that is orthogonal to the conveyance surface and parallel to the conveyance direction. Part or all of the overheating prevention element is included An image forming apparatus comprising Rukoto. 2. A pressure contact portion formed by bringing a pair of fixing rotators into pressure contact with each other, and a plurality of temperature detection elements for detecting the temperature of the heating portion. A fixing device that heats and fixes the toner image on the recording paper at the pressure contact part while controlling the fixing temperature control in the paper, and changes the fixing control and the conveyance control by the output of the sub temperature detection element. In a fixing device having a temperature preventing element, a recording material presence sensor or a recording material passage sensor provided on a recording material conveyance path in an image forming apparatus having the fixing device is used to ensure that the recording material is not present during a series of printing operations. Regarding each of the recording material sensors and the main temperature detecting element passing therethrough, any one of the respective surfaces which pass through the recording material sensor or the main temperature detecting element, are orthogonal to the conveying surface, and are parallel to the conveying direction.
Part or all of the excessive temperature rise prevention element is included in a portion sandwiched between two surfaces and a surface that passes through the sub-temperature detection element, is orthogonal to the conveyance surface, and is parallel to the conveyance direction. An image forming apparatus characterized by. 3. The image forming apparatus according to claim 2, wherein the abnormal high temperature detection threshold value of the heating portion due to the output of the sub-temperature detection element is based on the operating rated temperature of the excessive temperature rise prevention element. An image forming apparatus characterized by the above. 4. The image forming apparatus according to claim 1, wherein the fixing device heats the recording material through a thin film, and a pressing member pressurizes the heating material through the thin film. An image forming apparatus having a pressure body.