JP2001282039A - Image forming device - Google Patents

Abstract

(57) Abstract: An image forming apparatus including a fixing device that introduces a sheet into a fixing nip portion, pinches and conveys the sheet, and heats and fixes an unfixed image on the sheet. Provided is an image forming apparatus that does not require a user to perform an extra operation such as a sheet removing operation and that hardly causes a fixing failure even when an emergency stop control of the apparatus is performed due to an abnormally high temperature. A sub-thermistor (second temperature detecting means) monitors a temperature of a non-paper passing portion of a fixing device, and a sheet is formed even when the sub-thermistor detects an abnormally high temperature (temperature T2 or more) of the non-paper passing portion. Without stopping the conveyance of the paper, and then stop the conveyance. At that time, the target temperature of the heater is lowered. Decrease the paper transport speed or adjust the temperature based on the temperature of the sub thermistor.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a recording paper (sheet material; transfer paper, printing paper, Unfixed image (developer image, visible material image) on photosensitive paper, electrostatic recording paper, format sheet, etc.
The present invention relates to an image forming apparatus such as a printer, a copying machine, a facsimile, etc., which outputs an image formed product (print, copy) by heating and fixing an unfixed image as a fixed image on a sheet by a fixing device.

[0002]

2. Description of the Related Art In such an image forming apparatus, an unfixed image (hereinafter, referred to as a toner image) formed and carried on a recording sheet (hereinafter, referred to as a sheet) is fixed as a fixed image by heating and fixing the sheet. As a device (image heating device), a heat roller type or a film heating type fixing device is often used.

A fixing device of a heat roller type includes a fixing roller (heating roller) which is maintained at a predetermined temperature (fixing temperature) as a heating means, and a pressing means which presses against the fixing roller to form a fixing nip portion. The fixing roller is rotated, and the pair of rollers is rotated, and the sheet on which the unfixed toner image is formed and carried is introduced into the fixing nip portion and nipped and conveyed. Is to be fixed.

A fixing device of a film heating type is disclosed in Japanese Unexamined Patent Publication No.
As proposed in Japanese Patent No. 44075, etc., a heating element, a film that slides on the heating element (hereinafter, referred to as a fixing film), and a fixing nip portion that is in pressure contact with the heating element via the fixing film. It has a pressure roller as a pressing means for forming, introduces a sheet on which an unfixed toner image is formed and carried into a fixing nip portion, nips and conveys the sheet, and heats the toner image by heat from a heating element via a fixing film Is fixed on paper as a permanent image. As a heating element, a ceramic heater or the like having a low heat capacity and a rapid temperature rise can be used.
Further, a thin film having a small heat capacity can be used as the fixing film, and by heating only the fixing nip portion, a quick start property is excellent and energy-saving heat fixing can be realized. In particular, power is not supplied during standby, and power consumption can be kept as low as possible.

[0005] The above-mentioned fixing device is provided with a temperature detecting means (temperature detecting means) for controlling the temperature at which heat is fixed. The temperature detecting means generally uses a thermistor, and is provided in contact with a heating element or a pressure roller to detect the temperature of the heating element or the pressure roller. Recently, a method of detecting a temperature at which heat is fixed by measuring radiant heat of a heating element, a pressure roller, or the like has been studied.

By controlling the power supply to the heating element (heater) provided in the heating means by the temperature control circuit including the temperature detecting means as described above, the temperature of the fixing nip portion for nipping and transporting the sheet to heat it is controlled. The temperature is adjusted to a predetermined fixing temperature.

[0007]

Incidentally, in the above-mentioned fixing device, in which a sheet is introduced into a fixing nip portion and nipped and conveyed to heat and fix an unfixed image on the sheet, a so-called "non-sheet-passing portion lift" is used. There is a problem of "warm".

[0008] This is because paper of a smaller size than paper of the maximum size (size: paper length in the direction orthogonal to the paper transport direction to the fixing nip portion, hereinafter referred to as width) that can be used in the apparatus is used. When the sheet is passed, heat is not consumed in the heating of the sheet in the non-sheet passing area of the fixing nip portion corresponding to the size difference portion from the maximum size sheet and heat is stored, so that the small-sized sheet is continuously passed. As a result, the heat storage amount in the non-sheet passing area of the fixing nip increases. Therefore, the temperature of the paper passing area of the fixing nip is maintained at a predetermined fixing temperature, while the temperature of the non-paper passing area is higher than the predetermined fixing temperature.

If the temperature of the non-sheet passing portion rises to an unacceptably high level, the components of the fixing device may suffer from heat loss and deterioration, thereby lowering the durability of the fixing device. If the large size paper is passed while the fixing device is excessively heated in the non-paper passing area during continuous paper feeding, the temperature in the non-paper passing area of the fixing nip is too high. An end hot offset or the like occurs.

Therefore, when the temperature detecting means for controlling the temperature for heating and fixing is a main thermistor,
Separately from this, a temperature detecting means for measuring the temperature of the non-sheet passing portion is provided as a sub thermistor, and a control measure for avoiding the adverse effect due to the temperature rise of the non-sheet passing portion is executed depending on the detected temperature of the sub thermistor. ing.

More specifically, in a printer using a film heating type fixing device, as shown in a flowchart of FIG. 17, the detected temperature of the sub thermistor, that is, the temperature of the non-sheet passing portion during printing is a predetermined temperature T1. If the temperature is lower than T1 ° C, the printing operation is continued as usual (step S1 → S2).

When the temperature of the sub-thermistor is equal to or higher than T1 ° C., when the paper is not sandwiched in the fixing nip portion, the power supply to the heater (ceramic heater) of the fixing device is turned off. The temperature of the non-sheet passing area starts to decrease toward the target temperature, so delay the feeding of the next sheet so that the sheet does not enter the fixing nip until the non-sheet passing area cools sufficiently. Control. Therefore, the temperature of the sub thermistor, that is, the temperature of the non-sheet passing portion is controlled so as not to exceed a certain temperature.

However, since the feeding of the next sheet is delayed, there is a disadvantage that the number of sheets that can be printed per unit time (hereinafter, referred to as throughput) decreases. The time for delaying the paper feeding to minimize the disadvantage is set to a value as far as possible without damaging the main body. At this time, for example, when two sheets are overlapped and passed through due to some trouble (hereinafter, referred to as double feed), the gap between the heater and the pressure roller becomes large, and the temperature of the sub thermistor, that is, In some cases, the temperature of the non-sheet passing portion increased. In preparation for such a case, if the temperature of the sub-thermistor exceeds T2 ° C. by separately giving the boundary value T2, the entire apparatus is emergency stopped, that is, the driving of the heater is stopped to stop the conveyance of the sheet. A sequence is set up. FIG. 18 shows a model diagram of the transfer and the transition of the temperature state of the main thermistor and the sub thermistor at this time.

Although the stage of decreasing the throughput is set to one in the prior art for easy understanding, an apparatus which has a plurality of boundary values and reduces the throughput in a plurality of stages has also been devised.

When the temperature of the sub thermistor is T2 ° C.
, The conveyance is stopped and the heating of the heater is stopped. Thereafter, the temperature gradually decreases until it reaches room temperature. Here, V1 is a predetermined speed at which the paper advances in the apparatus, which is generally called a process speed, and is a speed inherent to the apparatus.

However, if the sub-thermistor detects an abnormally high temperature in the non-sheet passing portion, the user stops the sheet while being pinched by the fixing nip, and the user removes the pinched sheet. I had to work.

Accordingly, the present invention relates to an image forming apparatus including a fixing device for introducing a sheet into a fixing nip portion, nipping and conveying the sheet, and heating and fixing an unfixed image on the sheet. It is an object of the present invention to provide an image forming apparatus which does not require a user to perform an extra operation such as a sheet removing operation even when the temperature is abnormally high and an emergency stop control of the apparatus is performed, and in which a fixing failure hardly occurs. .

[0018]

SUMMARY OF THE INVENTION The present invention is an image forming apparatus having the following configuration.

(1) A first temperature detecting means disposed at a position where sheets of all sizes that can be passed through are sandwiched during the sheet passing, A second temperature detecting means disposed at a position where the sheet of the smallest size that can be passed through is not pinched while the sheet is passed, and at least two or more The heating unit is preset based on a heating unit through which sheets of different sizes are passed and for fixing an unfixed developer to the sheet, and a temperature detected by the first temperature detection unit. Control means for controlling the temperature to be the first temperature;
When the control means detects that the temperature detected by the second temperature detection means is equal to or higher than a preset second temperature, the detection temperature of the second temperature detection means An image forming apparatus for controlling the temperature to be equal to or lower than a third temperature.

(2) In the image forming apparatus according to (1), the preset first temperature takes a plurality of values according to the state of the apparatus, and the preset second temperature is the second temperature. An image forming apparatus, which is set according to one temperature.

(3) In the image forming apparatus described in (1) or (2), when the control unit detects that the second temperature detection unit is higher than the second temperature, An image forming apparatus comprising: a notifying unit that notifies an abnormality of the heating unit.

(4) A first temperature detecting means disposed at a position where sheets of all sizes that can be passed are sandwiched during the sheet passing, and a sheet of the largest size that can be passed during the sheet passing A second temperature detecting means disposed at a position where the sheet of the smallest size that can be passed through is not pinched while the sheet is passed, and at least two or more Heating means for adhering unfixed developer to the paper, through which paper of different sizes is passed, transporting means for transporting the paper, and a temperature detected by the first temperature detecting means. Control means for controlling the heating means to have a first temperature set in advance, wherein the control means sets the temperature detected by the second temperature detection means in advance. If the temperature is lower than the second temperature, the paper is fed at the first transport speed. When the sheet is conveyed and the temperature detected by the second temperature detecting means is equal to or higher than a preset second temperature, the conveyance is continued until the discharge of the sheet is completed. Image forming device.

(5) In the image forming apparatus described in (4), the temperature detected by the second temperature detecting means is:
An image forming method wherein, when the temperature is equal to or higher than a second temperature set in advance, the sheet is conveyed at a second conveyance speed lower than the first conveyance speed until the ejection of the sheet is completed. apparatus.

(6) In the image forming apparatus according to (4) or (5), it is detected that the temperature detected by the second temperature detecting means is equal to or higher than a preset second temperature. An image forming apparatus, wherein the driving of the heating means is stopped at an arbitrary timing within a period from when the sheet is discharged to when the discharge of the sheet is completed.

(7) In the image forming apparatus according to any one of (4) to (6), the preset first temperature takes a plurality of values according to the state of the apparatus and is preset. An image forming apparatus, wherein the second temperature is set according to the first temperature.

(8) First temperature detecting means disposed at a position where sheets of all sizes that can be passed through are sandwiched during the sheet passing, A second temperature detecting means disposed at a position where the sheet of the smallest size that can be passed through is not pinched while the sheet is passed, and at least two or more The heating unit is preset based on a heating unit through which sheets of different sizes are passed and for fixing an unfixed developer to the sheet, and a temperature detected by the first temperature detection unit. Control means for controlling the temperature to be the first temperature;
When the control means detects that the temperature detected by the second temperature detection means is equal to or higher than a preset second temperature, the first temperature detection means sets the first temperature An image forming apparatus, wherein control is performed such that the temperature is lower than a fourth temperature.

(9) In the image forming apparatus described in (8), the preset first temperature takes a plurality of values according to the state of the apparatus, and the preset second temperature is the second temperature. An image forming apparatus, which is set according to one temperature.

<Operation> In other words, even if the second temperature detecting means monitors the non-sheet-passing part temperature rise temperature of the fixing device, and the second temperature detecting means detects an abnormally high temperature in the non-sheet-passing part, the sheet temperature may be reduced. Even if the temperature of the non-sheet passing portion of the fixing device rises to an abnormally high temperature and the device is subjected to emergency stop control, the sequence in which the discharge of the sheet is completed without stopping the conveyance of the sheet and then the conveyance is stopped. Does not require extra operations such as paper removal.

Further, even if the second temperature detecting means detects an abnormally high temperature in the non-sheet passing portion, the conveyance of the paper is not stopped. At this time, the target temperature of the heater is lowered, the paper conveyance speed is reduced, or By performing an operation sequence such as adjusting the temperature based on the temperature of the temperature detecting means, it is possible to minimize fixing defects caused by a decrease in the temperature of the first temperature detecting means (fixing device).

[0030]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 (FIGS. 1 to 8) FIG. 1 is a schematic structural diagram of an image forming apparatus according to the present embodiment. The image forming apparatus of this embodiment is a laser beam printer of a process cartridge type using a transfer type electrophotographic process, develops print data sent from a host computer or the like into dot image information, and outputs the image data by an electrophotographic engine unit. Information is printed on paper.

(1) Overall Schematic Configuration of Printer 100 is a printer main body, 200 is a host computer, and control means (control circuit, CPU) 1 of the printer main body
9 is electrically connected to a cable.

In the printer body 100, reference numeral 1 denotes a drum type electrophotographic photosensitive member (hereinafter, referred to as a photosensitive drum) as an image carrier. The photosensitive drum 1 is rotationally driven at a predetermined peripheral speed in a counterclockwise direction indicated by an arrow.

Reference numeral 2 denotes a primary charging means, by which the peripheral surface of the rotating photosensitive drum 1 is uniformly charged to a predetermined polarity and potential.

Reference numeral 3 denotes a laser beam scanner as image exposure means. An image controller (not shown), which is an image developing unit for developing print data sent from the host computer 200 into dot image information, outputs image data. The laser light of the laser section is blinked and modulated based on the image data, and the scanning exposure L by the modulated laser light is performed.
Is performed on the uniformly charged surface of the rotating photosensitive drum 1. As a result, an electrostatic latent image corresponding to the image information subjected to the scanning exposure L is formed on the surface of the rotating photosensitive drum 1.

Reference numeral 4 denotes a developing means for developing the electrostatic latent image on the surface of the photosensitive drum 1 with toner as a developing material.

Reference numeral 5 denotes a transfer roller as transfer means.
The photosensitive drum 1 is disposed in contact with the lower surface of the photosensitive drum 1 with a predetermined pressing force. The transfer roller 5 and the photosensitive drum 1
Is a transfer nip portion T.

When the control means 19 receives a print start signal from the host computer 200, the paper supply means on the side of the paper supply cassette 6 as the first paper supply port or the manual feed tray (MP The sheet feeding means on the tray (10) side is operated to feed the sheet, and the fed sheet P is introduced into the transfer nip T at a predetermined control timing and is nipped and conveyed. While the paper P is being nipped and conveyed through the transfer nip T, a transfer voltage of a predetermined control is applied to the transfer roller 5 from a transfer bias application power supply (not shown). The polarity of the transfer voltage is opposite to the charge polarity of the toner. As a result, the toner image on the photosensitive drum 1 is sequentially electrostatically transferred to the surface of the paper P at the transfer nip T.

Regarding the paper feeding, when a paper feeding mode (cassette feeding mode) from the paper feeding cassette 6 is selected, an engine control unit (not shown) rotates the paper feeding roller 7 into the paper feeding cassette 6. The sheets P in the stacked storage are separated and fed. From the paper feed cassette 6, mainly wide plain paper (large size paper) is fed. The fed paper P is transferred to the transfer nip T by a path from the paper transport path 8 to the TOP sensor 9.
Will be introduced.

When the paper feed mode (manual paper feed mode) from the manual feed tray 10 is selected, the engine control unit (not shown) rotates the paper feed roller 11 to be stacked and set on the manual feed tray 10. Manual paper P
Are separated and fed one by one. The paper P is fed to the paper transport path 8
→ Introduced into the transfer nip T through the path of the TOP sensor 9. From the manual feed tray 10, mainly special paper (small size paper) for narrow postcards and envelopes is fed.

In the printer according to the present embodiment, both the sheet feeding from the sheet feeding cassette 6 and the sheet feeding from the manual feed tray 10 are fed by the center reference conveyance by the center reference width regulating plate.

The paper P that has passed through the transfer nip T is sequentially separated from the surface of the rotating photosensitive drum 1, introduced into the fixing nip N of the fixing device 13 from the paper transport path 12, and subjected to the heat fixing process of the toner image. Fixing device 1 in printer of this example
Reference numeral 3 denotes a film heating type fixing device. This fixing device 13
Will be described in detail in the next section (2).

The transfer residual toner remaining on the surface of the photosensitive drum 1 after the transfer of the toner image onto the sheet P is collected and reused by the developing means 4 in the case of the printer according to the so-called simultaneous cleaning with development.

The sheet P that has exited the fixing device 13 passes through the sheet transport path 14 → discharge sensor 15 → sheet transport path 16 → discharge roller 17, and forms an image-formed product (printed sheet) on a discharge section (discharge tray) 28. , Copy).

The TOP sensor 9 and the paper discharge sensor 15 monitor whether the paper is being conveyed normally.

The PC is a process cartridge that can be attached to and detached from the printer body. The process cartridge PC of this embodiment is a cartridge in which three process devices of a photosensitive drum 1, a charging unit 2, and a developing unit 4 are collectively attached to and detachable from a printer main body, and an opening / closing door 20 of the printer main body is opened. The door 20 is set in the printer body, and the door 20 is closed and mounted. Removal is performed in the reverse order.

(2) Fixing Device 13 a) Overall Schematic Configuration of Fixing Device 13 FIG. 2 is an external perspective model view of a main part of the fixing device 13, and FIG. The fixing device 13 of this embodiment is disclosed in JP-A-4-44075-44083 and JP-A-4-204.
This is a tensionless type heating film type image heating apparatus disclosed in 980 to 204984 and the like.

Reference numeral 21 denotes a heating unit as heating means, 2
Reference numeral 5 denotes an elastic pressure roller serving as a pressure unit that is brought into pressure contact with the heating unit 21.

The heating unit 21 is mainly a ceramic heater (hereinafter referred to as a heater) as a heating element (heating element).
22, a film guide member (hereinafter, referred to as a stay) 23 having a substantially semi-arc-shaped cross section and a heat-resistant film (hereinafter, referred to as a fixing film) 24 having a cylindrical shape.

The heater 22 in FIG. 3 is horizontally long with the longitudinal direction perpendicular to the paper surface, has a low heat capacity as a whole, and is
Temperature rise / fall quickly with good responsiveness in response to N-OFF. The specific structure of this heater will be described in detail in the next section b).

The stay 23 is made of a heat-resistant and electrically insulating rigid material capable of withstanding a high load, for example, PPS (polyphenylene sulfide), PAI (polyamide imide),
The heater 22 is made of PI (polyimide), PEEK (polyether ether ketone), or the like, and the heater 22 is fitted into a groove provided along the longitudinal direction of the guide member at a substantially central portion of the lower surface of the stay 23 with the front side facing outward. It is fixed and supported.

The cylindrical fixing film 24 is, for example, a heat-resistant film having a thickness of about 40 μm to 100 μm. For example, it is a film in which a releasable heat-resistant resin such as PFA or PTFE is coated on a base film such as polyimide, and the stay 2 in which the heater 22 is fixed and supported as described above.
3 is loosely fitted.

The elastic pressure roller (hereinafter, referred to as a pressure roller) 25 includes a core metal 25a and a roller layer 25b of an elastic and heat-resistant material such as silicone rubber provided concentrically and integrally with the core metal.
And a surface layer 25c, and both ends of the core metal 25a are rotatably supported via a bearing between front and rear chassis side plates (not shown) of the apparatus.

The heater 22 is supported on the lower surface side, and the stay 23 having the cylindrical fixing film 24 fitted thereon is positioned above the pressure roller 25 with the heater 22 facing the upper surface of the pressure roller 24. Then, the stay 23 is held in a state where the stay 23 is pressed against the upper surface of the pressing roller 25 with a predetermined pressing force by the pressing means. Thereby, the heater 22
Between the lower surface of the fixing roller 2 and the upper surface of the pressure roller 25.
The fixing nip portion N having a predetermined width is formed with the fixing nip 4 interposed therebetween.

The pressure roller 25 is rotationally driven at a predetermined peripheral speed in a clockwise direction indicated by an arrow by a fixing device driving motor M as a fixing device driving unit. A rotational force acts on the cylindrical fixing film 24 by the pressure contact frictional force at the fixing nip N between the pressing roller 25 and the outer surface of the fixing film 24 due to the rotational driving of the pressing roller 25, and the fixing film 24 While the inner surface of the pressure roller 2 slides in the fixing nip portion N in close contact with the lower surface of the heater 22,
The stay 23 has a peripheral speed substantially corresponding to the rotational peripheral speed of No. 5.
Is turned around (the pressure roller driving method).

The stay 23 serves as a film guide for holding the heater 22 and for stabilizing the conveyance of the fixing film 24 during rotation. A lubricant such as heat-resistant grease is interposed between the fixing film 24 and the outer peripheral surfaces of the heater 22 and the stay 23 in order to enhance the rotational slidability with the fixing film 24.

The pressure roller 25 is driven to rotate, and accordingly, the cylindrical fixing film 24 rotates around the stay 23, and electricity is supplied to the heater 22, and the heat generated by the heater 22 causes the fixing nip N to reach a predetermined position. When the temperature has risen to the temperature and the temperature has been adjusted, the unfixed toner image t
Is introduced into the fixing nip N, and the fixing nip N is conveyed together with the fixing film 24 rotating in close contact with the outer surface of the fixing film 24 with the toner image bearing surface of the sheet P in the fixing nip N. Go. In the nipping and conveying process, the heat of the heater 22 is applied to the sheet P via the fixing film 24, and the unfixed toner image t on the sheet P is heated and pressed. When the sheet P passes through the fixing nip portion N, the sheet P is conveyed with a curvature separated from the outer surface of the rotating fixing film 24.

B) Heater 22 FIG. 4A is a plan view of the heater 22 with a partial cutout on the front side, and FIG. 4B is a plan view of the back side. The heater 22 is a substantially flat plate having a low heat capacity as a whole, including the following members and portions.

[0058] A long, thin, heat-resistant, low-heat-capacity, good-heat-conductivity, and electrically-insulated elongated flat-plate-shaped heater substrate a having a longitudinal direction in a direction perpendicular to the sheet conveying direction in the fixing nip portion N; A current-generating resistor c that is formed along the longitudinal direction of the heater substrate a along the substrate side (the surface facing the fixing film 24 and the surface facing the fixing nip portion); The power supply electrode portions b and e for the current-carrying heating resistor c and the communication lines d,. A heat-resistant and insulating heater surface protective layer f overcoated with a current-carrying heating resistor c and a communication line d; A main thermistor (main thermistor) j as first temperature detecting means, a sub thermistor (auxiliary thermistor) s as second temperature detecting means, and a front side of the heater substrate a provided on the back side of the heater substrate a. Provided on the back side,
Electrodes g, h, m, n, p, q for the temperature detection and the connection line i, k
-R.

The heater substrate a is a ceramic substrate made of, for example, alumina (aluminum oxide, Al ₂ O ₃ ).

The heating resistor c is formed by applying an electric resistance material paste (resistance paste) such as silver palladium (Ag / Pb) or Ta ₂ N on the surface of the heater substrate by screen printing or the like along the length of the substrate. Then, it is formed by firing.

The power supply electrode portions b and e are provided side by side at one longitudinal end on the surface side of the heater substrate, and one of the power supply electrode portions b is electrically connected to one end of the energized heating resistor c via a conductive extension. It is made to conduct. The other power supply electrode portion e is electrically connected to the other end of the current-carrying resistor c via a communication line d provided on the heater substrate surface in parallel with the current-carrying resistor c.

As described above, a series electric circuit (AC) of the power supply electrode portion b → the current-carrying heating resistor c → the communication line d → the power supply electrode portion e
Line).

Further, a temperature measuring electrode part g, hm, n, p, q
Among them, three of the electrode portions g, n, and p are provided alongside the other longitudinal end on the surface side of the heater substrate, and three of the remaining electrode portions hm,
One is provided on the back side of the heater substrate at a position corresponding to the front and back surfaces of the electrode portions g, n and p. The electrode portions g and h corresponding to the front and back surfaces, the electrode portions n and m, and the electrode portions p and q are respectively formed through holes. Is conducted.

As described above, the paper supply of the printer of this embodiment is the center reference conveyance, and I is the paper passing area of the maximum width size paper,
II is a sheet passing area of the minimum width sheet, and III is a non-sheet passing area (a difference area from the sheet passing area I of the maximum width sheet) generated when the minimum width sheet is passed.

The main thermistor j is always disposed at a paper passing area position through which the paper is passed regardless of the width of the paper that can be used for the printer. In this example, the sheet is arranged at an arbitrary position in the rear surface area of the heater substrate corresponding to the sheet passing area II of the minimum width size sheet.

The sub-thermistor s allows the paper to pass while the largest width paper among the papers that can be used for the printer is passed through, while the sub-thermistor s passes while the smallest width paper is passed. It is arranged at a non-sheet passing area position through which sheets do not pass. In this example, the sheet is disposed at an arbitrary position in the heater substrate back surface area corresponding to the non-sheet passing area III generated when the minimum width size sheet is passed.

Main thermistor j and sub thermistor s
There are a method of attaching to the back surface of the heater substrate with a heat-resistant adhesive and a method of installing by pressing using the pressure of a spring member.

The main thermistor j is electrically connected to the electrodes h and m via the communication lines i and k. In addition, the sub-thermistor s is connected to the electrode section m via the communication lines k and r.
And q are electrically connected.

As described above, the series electric circuit (first DC line) of the electrode section g → the electrode section h → the connection circuit i → the main thermistor j → the connection circuit k → the electrode section m → the electrode section n and the electrode section n
A series circuit (second DC line) of → electrode m → communication circuit k → sub thermistor s → communication circuit r → electrode q → electrode p is configured.

In the above description, the electrode parts beghmm
The conductive portions of the n · p · q, the communication lines d · i · k · r, and the through-holes are formed by, for example, pattern-coating an electric conductor material such as a silver paste by screen printing or the like, and firing. .

In this embodiment, the heater surface protective layer f is a heat-resistant glass coat layer. On the front side of the heater substrate a, the heater heating element c except for the electrodes b, e, g, n and p is provided.
And the communication line d is covered.

The heater 22 is fitted in a heater fitting groove formed longitudinally on the lower surface of the stay 23 with its front side (the front side of the heater substrate provided with the energizing heating resistor c) facing outward. It is crowded.

Then, the power supply connector 26 is attached to the extension 23a (FIG. 2) on one end of the stay 23. Further, the temperature detecting connector 27 is attached to the extension projecting portion 23 b on the other end side of the stay 23. Reference numeral 26a denotes a power supply cable line connecting the power supply circuit to the power supply connector 26, and reference numeral 27a denotes a signal cable line connecting the control means to the temperature detection connector 27.

The power supply circuit composed of a commercial power supply and an AC driver and the like via the power supply connector 26 supplies the power supply cable line 26a and the power supply electrode portion b of the AC line of the heater 22 via the power supply connector 26. e, the heating resistor c of the AC line generates heat and the heater 22
The predetermined effective heating length region quickly rises in temperature.

Further, the heater temperature information detected by the main thermistor i and the sub thermistor s are respectively used as the temperature detecting electrode portions g · n of the first DC line and the temperature detecting electrode portions n · p of the second DC line. Is input to the control means via the temperature detection connector 27 and the signal cable 27a.

The control means controls the power supply circuit based on the heater temperature information from the main thermistor i and the sub thermistor s (phase and wave number control of the AC voltage, etc.) to regulate the temperature of the heater 22 to a predetermined temperature, Printer control and fixing device drive control.

FIG. 5 shows an example of an electric circuit required for driving the heater 22 by heating. One end of each of the main thermistor j and the sub thermistor s is GND
, And the other end is input to the analog voltage detection terminal of the control means 19 via the pull-up resistors 31 and 32. The control means 19 can detect the temperature of each thermistor j · s by measuring the voltage input to each terminal. On the other hand, a drive signal is output from the control means 19, and when the drive signal is OFF, the transistor 33 is also turned off, and power is not supplied to the heating resistor c of the heater 22 and the heater 22 is not heated. When the drive signal is on, the phototriac coupler 3
4 emits light. Accordingly, when a current starts to flow to the light receiving side, the triac 35 is turned on, and the power supply 3
Electric power is supplied from 6 to the energizing heating resistor c of the heater 22 to be heated. The control unit 19 controls the on / off of the drive signal so that the voltage supplied from the main thermistor j or the sub thermistor s matches a voltage corresponding to a predetermined temperature.

C) Countermeasures for Non-Passing Part Temperature Rise FIG. 6 is an explanatory diagram of the non-paper passing part temperature rise that occurs when a narrow sheet is passed. FIG. positional relationship between the paper P _max and the main thermistor j and sub thermistor s heater 22 of the maximum width size, (b) the main thermistor j and the sheet P _min and the heater 22 of minimum width the size of the paper which can be used sheet passing (C) shows an example of the temperature distribution along the length of the heater 22 (= temperature distribution along the length of the fixing nip portion N) when the paper P _min having the minimum width is passed.

When a sheet of narrow width is passed, a space is created between the heater 22 and the pressure roller 25 just outside the end in the sheet width direction at the fixing nip portion N due to the thickness of the sheet. There is an area where the heat generated by the heat transfer 22 is not transmitted to the sheet and the pressure roller 25. For this purpose, this area indicated by (a) and (b) in (c) uses the main thermistor j to set the target temperature (first temperature, predetermined fixing temperature).
When the temperature is adjusted to the above, the temperature rises as shown in the figure. When continuous paper passing is performed, for example, when the target temperature is 200 ° C., the temperatures in the areas A and B may reach as high as 300 ° C.

If the driving of the fixing device 13 is stopped while the non-sheet passing area III (heater end) of the heater 22 is at such a high temperature, the temperature rises for a while thereafter.
This leads to thermal deterioration of the pressure roller 25 and the stay 23. Further, if a wide sheet is used while the heater end portion is at such a high temperature, hot offset or the like occurs due to an excessively high temperature.

That is, the control means controls the heater 22 so that the applied electric power is increased by the amount of heat applied to the sheet during the period when the sheet passes through the fixing nip N.
Is controlled so as to keep the temperature at a predetermined target temperature. At this time, when a narrow sheet passes through the fixing nip portion N, the temperature of the heater end corresponding to the non-sheet passing area III where the sheet does not pass increases. If the temperature at the end of the heater is too high, the heater 22, the fixing film 24 in contact with the heater 22, the pressure roller 25, the stay 2
The temperature of the member such as 3 is too high, melts, deforms and degrades, and thereafter cannot function normally.

FIG. 7 is a flowchart showing the operation of the printer of this embodiment.

The operation when the temperature of the sub-thermistor s is equal to or lower than T2 is the same as that of the conventional example (FIG. 17), and the description is omitted.

When it is detected that the temperature of the sub thermistor s is equal to or higher than a predetermined temperature T2,
The control means 19 immediately stops driving the ceramic heater 22 (step S5). Thereafter, the state of the paper discharge sensor 15 is monitored, and after a sufficient time has passed for the paper to be discharged after the paper discharge sensor 15 detects the trailing edge of the paper, the drive of the transporting means is stopped (step S7).

FIG. 8 is a model showing the control of sheet conveyance in the printer of this embodiment and the transition of the temperature of each thermistor j · s. In the section B in FIG. 8, the transport system is driven.

As described above, the sub-thermistor s monitors the temperature rise in the non-sheet passing portion of the fixing device. Even when the sub thermistor s detects an abnormally high temperature in the non-sheet passing portion, the conveyance of the sheet is not stopped without stopping the sheet conveyance. Even if the temperature of the non-sheet-passing part of the fixing device rises to an abnormally high level and the device is controlled to be in an emergency stop due to the sequence that completes the discharge and then stops the conveyance, the user will need to perform extra operations such as removing the paper. Do not compel.

[Embodiment 2] (FIGS. 9 and 10) FIG. 9 is a flowchart showing a printer operation of the embodiment 2.

The operation when the temperature of the sub-thermistor s is equal to or lower than T2 is the same as that of the conventional example (FIG. AA), and the description is omitted.

Now, when it is detected that the temperature of the sub thermistor s is equal to or higher than a predetermined temperature T2,
The control means 19 stops driving the ceramic heater 22 (step S5), and reduces the transport speed (step S5).
6). Thereafter, the state of the paper discharge sensor 15 is monitored, and after a sufficient time has passed for the paper to be discharged after the paper discharge sensor 15 detects the trailing edge of the paper, the drive of the transporting means is stopped (step S7 → S8). Thereafter, the host computer 200 is notified that the sub-thermistor s has stopped due to detection of an abnormally high temperature (step S9).

FIG. 10 is a model diagram showing the control of sheet conveyance and the transition of the temperature of each thermistor j · s in the second embodiment. In the section B in FIG. 10, the transport system is driven at a speed V2 lower than the normal speed V1.

[Third Embodiment] (FIGS. 11 and 12) FIG. 11 is a flowchart showing the operation of the third embodiment.

When the temperature of the sub thermistor s is equal to or lower than T2, the ceramic heater 22 is controlled so that the temperature of the main thermistor j becomes a predetermined temperature T1 ° C. (step S1).

Now, when it is detected that the temperature of the sub thermistor s is higher than a predetermined temperature T2,
The control means 19 determines that the temperature of the sub thermistor s is T1 or more and T
The ceramic heater 22 is controlled so as to reach a predetermined temperature T3 ° C. of 2 or less (step S6).

FIG. 12 is a diagram showing the progress of the temperature of both thermistors j and s and the state of conveyance at this time. In the section A of FIG. 12, the temperature of the ceramic heater 22 is controlled based on the temperature information of the main thermistor j. Therefore, the temperature of the main thermistor j is constant at T1 ° C. At this time, when a sheet having a small width is passed, the temperature of the sub thermistor s gradually increases from T1 ° C. for the above-mentioned reason. Thereafter, since the temperature of the sub thermistor s reaches T2 ° C., the control means 19 sets the temperature of the sub thermistor s to T3.
The control is started so that the temperature becomes ° C (section B in FIG. 12).
In this section, since the temperature of the sub thermistor s is used as a reference, the temperature of the sub thermistor s becomes constant after a while, but the temperature of the main thermistor j gradually decreases.
When the discharge of the paper is completed, the driving of the ceramic heater 22 is stopped, so that the temperature decreases to the normal temperature, which is the origin. The third embodiment is characterized in that the driving of the ceramic heater 22 is not completely stopped in the section B in FIG.

[Embodiment 4] (FIGS. 13 and 14) FIG. 13 is a flowchart showing the operation of a printer according to the fourth embodiment.

When the temperature of the sub thermistor s is lower than T2, the ceramic heater 22 is controlled so that the temperature of the main thermistor j becomes a predetermined temperature T1 ° C. (step S1).

When it is detected that the temperature of the sub thermistor s is equal to or higher than a predetermined temperature T2,
The control means 19 determines that the temperature of the sub thermistor s is T1 or more and T
The ceramic heater 22 is controlled so as to have a predetermined temperature T3 ° C. of 2 or less (step S6). Further, the paper transport speed is changed to a speed V2 lower than the normal speed V1 and transported (step S7).

FIG. 14 is a diagram showing the progress of the temperature of both thermistors j and s and the state of conveyance at this time. In the section A of FIG. 14, the temperature of the ceramic heater 22 is controlled based on the temperature information of the main thermistor j. Therefore, the temperature of the main thermistor j is constant at T1 ° C. At this time, when a sheet having a small width is passed, the temperature of the sub thermistor s gradually increases from T1 ° C. for the above-mentioned reason. Thereafter, since the temperature of the sub thermistor s reaches T2 ° C., the control means 19 sets the temperature of the sub thermistor s to T3.
In this case, the control is started so that the temperature becomes ° C, and the transport speed is reduced to V2 (section B in FIG. 14). In this section, since the temperature of the sub thermistor s is used as a reference, the temperature of the sub thermistor s becomes constant after a while, but the temperature of the main thermistor j gradually decreases. When the discharge of the paper is completed, the driving of the ceramic heater 22 is stopped.
The temperature drops to room temperature, the origin.

[Embodiment 5] (FIGS. 15 and 16) FIG. 15 is a flowchart showing the operation of a printer according to the fifth embodiment.

At the start of temperature control of the ceramic heater 22, the target temperature is set to a predetermined temperature T1 ° C. (step S1).

Now, when it is detected that the temperature of the sub thermistor s is equal to or higher than the predetermined temperature T2,
The control means 19 sets the target temperature of the ceramic heater 22 to T
The temperature is set to T4 ° C. lower than 1 ° C. (step S6). Further, the transfer speed is changed to V2, which is lower than the normal speed V1, and the transfer is performed (step S7).

FIG. 16 is a diagram showing the progress of the temperature of both thermistors j and s and the state of conveyance at this time. After the temperature of the sub thermistor s exceeds T2 ° C. (section B in FIG. 16), since the target temperature is T4 ° C., the temperature of the main thermistor j becomes constant after decreasing to T4 ° C. The temperature of the sub thermistor s is such that the temperature of the main thermistor j is T
It gradually decreases until it decreases to 4 degrees, and then gradually increases. The temperature T4 is set in advance to a value such that the temperature of the sub thermistor s does not exceed T2 ° C. even when a sheet having the maximum length in the transport direction is passed.

Thus, in the image forming apparatuses of the first to fifth embodiments, even when the temperature of the sub-thermistor s becomes abnormally high, it is possible to provide an image forming apparatus that does not force a user to perform an extra operation.

In the second to fifth embodiments, an image of a fixing failure due to a decrease in the temperature of the main thermistor j (a state in which toner is not sufficiently fixed because heat required for fixing is not secured) is discharged. This can be suppressed as much as possible, and is particularly effective when printing is performed on paper having a long transport direction.

Further, according to the present invention, when an abnormally high temperature of the sub thermistor s is detected, control is performed such as lowering the sheet conveying speed, controlling the temperature with the temperature of the sub thermistor s, and lowering the target temperature of the main thermistor j. However, even with another combination not specified in the embodiment,
It goes without saying that a similar function can be realized.

The control means 19 notifies the host computer 200 when the printer is temporarily stopped and controlled to the standby state based on the fact that the temperature detected by the sub thermistor s is equal to or higher than the predetermined upper limit temperature as described above. At the same time, in order to prevent the user from being confused, a display unit such as a printer console unit or a notification unit such as a lamp is operated to temporarily stop the printer, thereby eliminating the non-permissible non-paper-passage temperature rise of the fixing device 13. Notify that you are waiting.

[Embodiment 6] (FIG. 19) After the temperature of the fixing device 13 has been sufficiently lowered, it is notified that the printer has returned to a state in which the sheet feeding operation and the printing operation can be resumed. The user restarts the interrupted print operation of the printer based on the notification.

The printer has cooling means such as a heat exhaust fan for cooling the inside of the printer. If the heater temperature detected by the sub-thermistor s is higher than a predetermined upper limit temperature, the printer temporary In the stop control process, the drive of the cooling unit may be continued even after the discharge of the sheet on which the immediately preceding print has been performed is completed,
This is effective in shortening the temperature lowering time of the fixing device 13.

When the temperature of the heater 22 is controlled to a target temperature (first temperature, predetermined fixing temperature) set in advance using the main thermistor j, the heater temperature set in the control means 19 is set. A predetermined constant upper limit that is set in advance to allow the target temperature to take a plurality of values in accordance with the state of the apparatus, and to detect a non-sheet-passing portion temperature rise state of the heater using the sub thermistor s It is also effective to adopt a control circuit configuration in which the temperature (second temperature) is set according to the selected temperature of the heater temperature adjustment target temperature.

This embodiment is a specific example. Typically,
The pressure roller 25 has a large heat capacity. Therefore, when printing is performed continuously, the first target temperature T1 is gradually lowered according to the number of prints or the time. As shown in FIG. 19, Ta ° C., C
From the (a + 1) th sheet to the Cb sheet, T1
To change. Specific numerical values include, for example, T
a, Tb, Tc, Td are 190 ° C., 185 ° C., respectively.
180 ° C, 175 ° C, Ca, Cb, Cc are 5
Values unique to each device, such as sheets, 15, and 30 sheets, are used. In the present embodiment, the temperature adjustment target temperature T1 is changed according to the number of sheets to be continuously printed. However, for example, the energization time to the heater 22 may be accumulated, T according to the accumulated energizing time
It is also possible to change 1. In this embodiment, when the target temperature T1 changes in this manner, the predetermined temperature T2 described in the previous embodiment is changed from Te → Tf → T
g → Th. As specific numerical values, for example, Te, Tf, Tg, Th
Values unique to each device such as 215 ° C., 210 ° C., 205 ° C., and 200 ° C. are used. The operation when the sub-thermistor s detects that the temperature is equal to or higher than the temperature T2 can be any of the operations of the above-described embodiments, and thus the description is omitted here. In this embodiment, T2
Is uniformly set to T1 + 25 ° C., for example, T
e, Tf, Tg, and Th are respectively 215 ° C., 210
It is also possible to set arbitrarily such as 200 ° C., 200 ° C. and 190 ° C. Further, in this embodiment, T1 is changed in four stages for the sake of simplicity, but it is needless to say that T1 can be changed in two or more arbitrary stages.

Although the printer of each embodiment is a paper feed system based on the center, the main thermistor j is disposed in the paper passing area in the same manner in the case of the paper feed system based on the left end or the right end. The same effect can be obtained by arranging the sub thermistor s in the region.

The fixing device may be of a heat roller type, an electromagnetic heating type, or the like.

[0113]

As described above, the present invention relates to an image forming apparatus including a fixing device for introducing a sheet into a fixing nip portion, nipping and conveying the sheet, and heating and fixing an unfixed image on the sheet. The temperature detecting means monitors the temperature rise in the non-sheet passing portion of the fixing device, and discharges the sheet without stopping the sheet conveyance even when the second temperature detecting means detects an abnormally high temperature in the non-sheet passing portion. Even if the non-sheet-passing part temperature of the fixing device rises to an abnormally high temperature and the device is subjected to emergency stop control by the device operation sequence of completing the Do not compel.

[Brief description of the drawings]

FIG. 1 is a schematic configuration model diagram of an image forming apparatus according to an embodiment.

FIG. 2 is an external perspective view of a main part of the fixing device.

FIG. 3 is a schematic cross-sectional view of a main part of the fixing device.

FIG. 4 is a schematic diagram of a heater configuration model.

FIG. 5 is a circuit example diagram of a heater control system.

FIG. 6 is an explanatory diagram of a temperature rise in a non-sheet passing portion.

FIG. 7 is a flowchart illustrating a printer operation according to the first embodiment.

FIG. 8 is a diagram illustrating a temperature control and driving method according to the first embodiment.

FIG. 9 is a flowchart illustrating a printer operation according to the second embodiment.

FIG. 10 is a diagram illustrating a temperature control and driving method according to a second embodiment.

FIG. 11 is a flowchart illustrating a printer operation according to a third embodiment.

FIG. 12 is a diagram illustrating a temperature control and driving method according to a third embodiment.

FIG. 13 is a flowchart illustrating a printer operation according to a fourth embodiment.

FIG. 14 is a diagram illustrating a temperature control and driving method according to a fourth embodiment.

FIG. 15 is a flowchart illustrating a printer operation according to the fifth embodiment.

FIG. 16 is a diagram illustrating a temperature control and driving method according to a fifth embodiment.

FIG. 17 is a flowchart showing a conventional printer operation.

FIG. 18 is a view for explaining a conventional temperature control and driving method.

FIG. 19 is an explanatory view of a sixth embodiment.

[Explanation of symbols]

1. image carrier (photosensitive drum), 2. charging means, 3.
Image exposure means, 4 development means, 5 transfer means (transfer roller), 6 first paper feed port (paper feed cassette), 10
..Second paper feed port (manual paper feed tray), 13 fixing device, 18 discharge section, 21 heating means (heating unit), 22 ceramic heater, 23 stay, 2
4 ··· Fixing film, 25 ·· Pressure roller, N ··· Fixing nip, M ··· Motor for driving the fixing device, P ··· Paper,
t ··· unfixed toner image, j · · · first temperature detecting means (main thermistor), s · · · second temperature detecting means (sub thermistor), 19 · · · control means, PC · · · process cartridge

Continued on front page F-term (reference) 2H027 DA12 DC05 DC10 DE01 DE07 DE09 EA12 EC06 EC07 EC09 ED19 ED25 EE04 EE05 EE07 EK10 GB07 2H033 AA29 AA42 BA08 BA11 BA25 BA31 BA32 BA36 BA59 BB18 BB28 BB33 CA37 CA37 CA37 CA38 9A001 HH34 JJ35

Claims (9)

[Claims] 1. A first temperature detecting means disposed at a position where sheets of all sizes that can be passed are sandwiched during sheet passing,
The second sheet is disposed at a position where the sheet of the maximum size that can be passed is sandwiched while the sheet is passed, but the sheet of the smallest size that can be passed is not sandwiched during the sheet passing. A heating means for fixing unfixed developer to the paper, wherein at least two sheets of different sizes are passed, comprising: a temperature detecting means; Control means for controlling the heating means to be at a preset first temperature based on the temperature, wherein the control means detects that the temperature detected by the second temperature detection means is When it is detected that the temperature is equal to or higher than the set second temperature, control is performed such that the temperature detected by the second temperature detecting means is equal to or lower than the second temperature. Characteristic image forming apparatus. 2. The image forming apparatus according to claim 1, wherein
The first temperature set in advance takes a plurality of values according to the state of the device, and the second temperature set in advance is
An image forming apparatus, which is set according to a first temperature. 3. An image forming apparatus according to claim 1, wherein said control means detects that said second temperature is equal to or higher than said second temperature. An image forming apparatus comprising a notifying unit for notifying an abnormality. 4. A first temperature detecting means disposed at a position where sheets of all sizes that can be passed are sandwiched during sheet passing;
The second sheet is disposed at a position where the sheet of the maximum size that can be passed is sandwiched while the sheet is passed, but the sheet of the smallest size that can be passed is not sandwiched during the sheet passing. Heating means for fixing unfixed developing material to the sheet, through which sheets of at least two different sizes are passed, comprising: temperature detecting means; conveying means for conveying the sheet; Based on the temperature detected by the first temperature detection means, control means for controlling the heating means to a preset first temperature, comprising: If the temperature detected by the detecting means is lower than a second temperature set in advance, the sheet is conveyed at a first conveying speed, and the temperature detected by the second temperature detecting means is Even if it is higher than the preset second temperature Until discharge of the sheet is completed, the image forming apparatus characterized by continuing the conveyance. 5. The image forming apparatus according to claim 4, wherein
When the temperature detected by the second temperature detecting means is equal to or higher than a preset second temperature, the second transport speed lower than the first transport speed is required until the discharge of the sheet is completed. An image forming apparatus for conveying a sheet at a speed. 6. The image forming apparatus according to claim 4, wherein the temperature detected by said second temperature detecting means is:
An image forming apparatus, wherein the driving of the heating unit is stopped at an arbitrary timing within a period from when it is detected that the temperature is equal to or higher than a preset second temperature to when the discharge of the sheet is completed. 7. An image forming apparatus according to claim 4, wherein the preset first temperature takes a plurality of values according to the state of the apparatus, and the preset second temperature is Is set according to the first temperature. 8. A first temperature detecting means disposed at a position where sheets of all sizes that can be passed are sandwiched during sheet passing;
The second sheet is disposed at a position where the sheet of the maximum size that can be passed is sandwiched while the sheet is passed, but the sheet of the smallest size that can be passed is not sandwiched during the sheet passing. A heating means for fixing unfixed developer to the paper, wherein at least two sheets of different sizes are passed, comprising: a temperature detecting means; Control means for controlling the heating means to be at a preset first temperature based on the temperature, wherein the control means detects that the temperature detected by the second temperature detection means is An image forming apparatus which, when detecting that the temperature is equal to or higher than a set second temperature, controls the first temperature detecting means to be at a fourth temperature lower than the first temperature. . 9. The image forming apparatus according to claim 8, wherein
The first temperature set in advance takes a plurality of values according to the state of the device, and the second temperature set in advance is
An image forming apparatus, which is set according to a first temperature.