JP2004212769A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent damage caused by the temperature rise of the ends of a fixing device and improve the throughput of small-sized sheets of paper without a cost increase even in an image forming apparatus such as a low end printer. <P>SOLUTION: When it is judged that the sizes of the recording media consecutively passed and used are small and temperature rise has occurred in the ends of the fixing means due to a large number of prints produced consecutively, the driving speed of the fixing means is decreased with the timing of the finish of transfer onto the paper, and also fixing temperature is lowered. Thus the speed at which the recording media are passed through the fixing means is restricted and images are fixed at a lower temperature. As a result, temperature increases of the ends of the fixing means are reduced, and the throughput during the passage of the small-size recording media can be improved. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an image forming apparatus such as an electrophotographic laser beam printer.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, as an image heat fixing device provided in an image forming apparatus employing an electrophotographic method, an electrostatic recording method, or the like, a recording material (sheet material) in which an unfixed toner image is formed and supported by a toner image forming unit is used. The toner image is heated and pressed as a permanent image on paper by introducing the toner image into a fixing nip portion, which is a pressure contact portion between a fixing roller and a pressure roller, which are rotated while being pressed against each other. A so-called heat roller type heat fixing unit for fixing is widely used.
[0003]
In particular, a heating / fixing unit that does not supply power during standby and keeps power consumption as low as possible, more specifically, a thin film between a heating body (hereinafter referred to as a heater) attached to a support and a pressure roller. (Hereinafter referred to as a fixing film), there is a heating and fixing means by a film heating method of heating and fixing an unfixed toner image on the sheet by the heat of a heater through the fixing film. References 1 to 4).
[0004]
The above two types of heat fixing means constituting the image heat fixing device have one or more fixing temperature detecting means for controlling the temperature at which the toner image is heated and fixed. The fixing temperature detecting means generally uses a thermistor, and is provided in contact with the heater or the pressure roller to detect the temperature of the heater or the pressure roller. Recently, a method of detecting a temperature at which heat is fixed by measuring radiant heat of a heater or a pressure roller has been studied.
[0005]
In the image heat fixing device as described above, when the small-sized paper having a width smaller than the large-sized paper having the maximum width that can be passed through the device is continuously passed, and the toner image is heated and fixed, The temperature of the non-sheet passing portion of the fixing device becomes higher than a certain temperature regulation temperature of the sheet passing portion due to heat generation. This phenomenon is called a temperature rise at the end of the fixing device or a temperature rise at the non-sheet passing portion.
If the temperature rise at the end of the fixing device is high, the temperature of the components of the fixing member and the pressure roller exceeds the temperature rise limit, which leads to damage to these components.
[0006]
Further, when printing on wide plain paper in a state in which the temperature rise at the end is high, hot offset or the like occurs due to the temperature being too high.
[0007]
In order to prevent the edge temperature from rising, a sub-thermistor for detecting the temperature rise of the edge is arranged in addition to the main thermistor for controlling the temperature of the fixing device, and the paper feed interval is extended when the temperature of the sub-thermistor becomes high. In this case, control is performed such that the throughput (representing the number of prints per unit time) is reduced to suppress the temperature rise of the non-sheet passing portion (for example, see Patent Document 5).
[0008]
However, in recent years, the throughput has been particularly increased, and as a result, the difference between the normal temperature and the temperature at which the temperature adjustment temperature itself increases to damage the fixing device has been reduced.
[0009]
Therefore, if the paper feeding interval is merely increased, for example, in a printer of 24 ppm (print per minute: the number of prints per minute), the paper feeding interval may have to be increased to about 2 ppm to greatly reduce the throughput. Is coming.
[0010]
Therefore, the image forming speed (process speed) of the printer itself is reduced to half (half speed), thereby lowering the fixing temperature and increasing the margin for the end temperature rise limit, and reducing the throughput of small size paper by half the speed. It has been done to suppress.
[Patent Document 1]
JP-A-63-313182
[Patent Document 2]
JP-A-2-15778
[Patent Document 3]
JP-A-4-44075
[Patent Document 4]
JP-A-4-204980
[Patent Document 5]
JP-A-2002-91226
[0011]
[Problems to be solved by the invention]
However, changing the process speed also changes the speed of the photosensitive drum and transfer roller, so it is necessary to change many electrophotographic process conditions (primary charging, development, transfer, laser light amount, etc.). Printers for personal and SOHO sold in Japan) require a new circuit to switch between them, which has been a factor of cost increase.
[0012]
Further, the main control circuit (CPU) for controlling the timing of these electrophotographic process conditions requires a large ROM capacity for switching, which has caused a cost increase.
[0013]
Accordingly, it is an object of the present invention to prevent damage due to a rise in the temperature of the end of a fixing device and increase throughput of small-size paper without increasing costs even in an image forming apparatus such as a low-end printer. It is in.
[0014]
[Means for Solving the Problems]
In order to solve the above problem, the present invention is an image forming apparatus having the following configuration.
[0015]
That is, a toner image forming unit that generates an unfixed toner image on the conveyed recording material, and a non-fixed toner on the recording material by nipping and conveying the recording material from the toner image forming unit side to a driven fixing member. A fixing unit that heats and fixes the image with a fixing member whose temperature has been adjusted to a predetermined fixing temperature.
The recording material is conveyed at a first recording material conveyance speed and a first recording material feeding interval, and an unfixed toner image is generated on the recording material by a toner image forming unit, and the recording material from the toner image forming unit side Is driven at a first driving speed substantially corresponding to the first recording material conveying speed, and is nipped and conveyed between fixing members of a fixing unit adjusted to a first fixing temperature to fix unfixed recording material on the recording material. A first control mode for fixing the toner image,
The temperature detecting means for detecting the temperature rise at the end of the fixing means when a small-size recording material having a width smaller than the large-size recording material having a maximum width that can be passed through the apparatus has a temperature higher than a preset temperature. Upon detection, the recording material is changed to a second recording material feeding interval longer than the first recording material feeding interval and conveyed, and an unfixed toner image is generated on the recording material by the toner image forming unit. After the trailing end of the recording material has passed the toner image forming unit, the driving speed of the fixing unit is changed to a second driving speed lower than the first driving speed, and the fixing temperature is changed to the first fixing speed. The unfixed toner image on the recording material is fixed by changing the temperature to a second fixing temperature lower than the temperature, and when the recording material passes between the fixing members, the driving speed of the fixing unit is changed to the first fixing temperature. A second control mode for changing to drive speed,
An image forming apparatus comprising:
[0016]
In the above-described image forming apparatus, the second control mode is performed when it is determined that the recording material being used is a small-sized material, the number of continuous prints is large, and the temperature of the fixing unit has risen at the end. This is a control mode in which the driving speed of the fixing unit is reduced and the fixing temperature is set to a low temperature at the timing of the end of the transfer, thereby suppressing the speed at the time of recording material passing in the fixing unit. Since the fixing can be performed at a low temperature, an increase in the temperature of the end portion of the fixing unit can be reduced, and the throughput when a small-sized recording material is passed can be increased.
[0017]
BEST MODE FOR CARRYING OUT THE INVENTION
(First Embodiment)
(1) Example of image forming apparatus
FIG. 1 is a schematic configuration diagram of an image forming apparatus according to the present embodiment. The image forming apparatus of the present embodiment is a laser beam printer using a transfer type electrophotographic process.
[0018]
Reference numeral 1 denotes a rotating drum type electrophotographic photosensitive member (hereinafter, referred to as a photosensitive drum) as an image carrier, which is driven to rotate at a predetermined peripheral speed in a clockwise direction indicated by an arrow. On the peripheral surface of the photosensitive drum 1 driven to rotate, uniform charging of a predetermined polarity and potential is performed by a charging roller 2 as a charging unit, and scanning exposure L of image information is performed by a laser scanner 3 as an exposure unit. Thus, an electrostatic latent image of image information is formed on the surface of the photosensitive drum. The electrostatic latent image is visualized as a toner image by a toner developing device 4 as a developing unit.
[0019]
On the other hand, a recording sheet (hereinafter, referred to as a sheet) P as a recording material (sheet material) loaded in the sheet feeding cassette 5 is separated by a sheet feeding roller 6 driven one rotation based on a sheet feeding start signal. Then, the paper is conveyed to the conveyance roller 7, and is drawn and conveyed to a paper sheet conveyance path 10 which reaches a transfer nip portion T which is a pressure contact portion between the photosensitive drum 1 and the transfer roller 11. In the printer of the present embodiment, the paper is conveyed on the basis of the center, and the paper P fed from the paper feed cassette 5 is also narrowed toward the center by the center-based width regulating plate.
[0020]
During the conveyance, the leading end of the sheet is conveyed to a matching transfer section T by a TOP sensor (paper feed sensor) 9 by a registration roller 8.
[0021]
The TOP sensor 9 is disposed between the registration roller 8 and the transfer section T in the paper feed path 10 to detect the positions of the leading edge and the trailing edge of the sheet transported by the register roller 8 and to detect the leading edge of the sheet. An image writing timing for the photosensitive drum 1 is controlled by a signal.
[0022]
The sheet P conveyed to the transfer nip portion T is nipped and conveyed through the transfer nip portion, and the unfixed toner image on the photosensitive drum 1 side is sequentially electrostatically transferred to the surface of the sheet P by the transfer bias applied to the transfer roller 11. Will be done.
[0023]
The sheet P that has exited the transfer nip portion T is separated from the surface of the photosensitive drum 1 and introduced into an image heat fixing device (hereinafter, referred to as a fixing device) 12 as a fixing unit. The applied toner image is heated and pressed and fixed as a permanent fixed image. The paper P is discharged as an image forming product (print / copy) onto a paper discharge tray 15 by a paper discharge roller 14 through a paper discharge conveyance path 13.
[0024]
M is a main motor of the printer, and 100 is a main control circuit (CPU) of the printer. The main motor M includes a photosensitive roller 1, a transfer roller 11, a developing unit 4, a pressure roller 22, which will be described later, of the fixing unit 12, a sheet feeding / conveying mechanism 6 to 8, a sheet discharging / conveying mechanism 14, and other parts of the printer. A driving force is applied to the drive mechanism via a power transmission mechanism including a speed reduction mechanism, a clutch, and the like. The printer of this example is a low-end printer that drives the photosensitive drum 1 and the fixing device 12 by one main motor.
[0025]
The main control circuit 100 controls the sequence of the main motor M and the image forming process operation mechanism of the entire printer.
[0026]
(2) Fixing device 12
2 and 3 are a perspective model diagram and an enlarged horizontal model diagram of a main part of the fixing device 12. The fixing device 12 of this embodiment is a heating device of a film heating system of a pressure rotating body driving system (tensionless type) disclosed in JP-A-4-44075-44083 and the like.
[0027]
Reference numerals 21 and 22 denote first and second fixing members which are pressed against each other to form a fixing nip portion N. In this example, the first fixing member 21 is a fixing film assembly as a heating unit, and the second fixing member 22 is an elastic pressing roller as a pressing unit.
[0028]
In the fixing film assembly 21 as a heating unit, reference numeral 23 denotes a ceramic heater (hereinafter, referred to as a heater) as a heating element. The heater 23 is basically composed of an elongated thin plate-shaped ceramic substrate having a longitudinal direction perpendicular to the paper passing direction and a heating resistor layer provided on the substrate surface. This is a heater with a low heat capacity that rises in temperature with a steep rising characteristic.
[0029]
Reference numeral 24 denotes a heat-insulating heater support made of a heat-resistant resin or the like, on which the heater 23 is fixedly supported. The heater 23 is fitted in a groove formed on the lower surface of the heater support 24 along the length of the heater with the heater surface side exposed downward and fixed with a heat-resistant adhesive or the like.
[0030]
Reference numeral 25 denotes a cylindrical (endless) heat-resistant fixing film as a heat transfer member, which is loosely fitted to a heater support 24 including the heater 23 described above. The fixing film 25 has a film thickness of 100 μm or less, preferably 50 μm or less and 20 μm or more, and has a heat-resistant single layer of PTFE, PFA, or FEP, or polyimide or polyamide imide in order to reduce the heat capacity and improve the quick start property. , PEEK, PES, PPS and the like can be used as a composite layer film having an outer peripheral surface coated with PTFE, PFA, FEP or the like. It can be made of metal.
[0031]
The elastic pressure roller 22 as a pressing means includes a core metal 22a and an elastic layer 22b made of a heat-resistant rubber such as silicone rubber or fluorine rubber, or a foam of silicone rubber. Both ends of the core metal 22a are freely rotatable. It is arranged to support the bearing.
[0032]
An assembly of the above-described heater 23, heater support 24, fixing film 25, and the like is disposed above the pressure roller 22 in parallel with the pressure roller 22 with the heater 23 facing downward, and the heater support 24 is not shown. Is pressed downward by the urging member to press the lower surface of the heater 23 against the upper surface of the pressure roller 22 via the fixing film 25 against the elasticity of the roller elastic layer, thereby fixing the heater 23 with a predetermined width as a heating unit. A nip N is formed.
[0033]
The pressure roller 22 receives the driving force of the main motor M (FIG. 1) via a power transmission mechanism (not shown) using the main motor M (FIG. 1) as a fixing device driving unit, and rotates the predetermined rotational peripheral speed in the counterclockwise direction of the arrow in FIG. Is driven to rotate.
[0034]
A rotational force acts on the cylindrical fixing film 25 by the frictional contact between the pressing roller 22 and the fixing film 25 at the fixing nip portion N by the rotational driving of the pressing roller 22, and the fixing film 25 While being in close contact with the downward surface and sliding, the outer periphery of the heater support 24 is driven to rotate clockwise as indicated by the arrow. The heater support 24 is also a rotation guide member for the cylindrical fixing film 25.
[0035]
In order to smooth the sliding between the inner surface of the fixing film 25 and the surface of the heater 23 and rotate the fixing film 25 smoothly, heat resistance between the inner surface of the fixing film 25 and the outer surfaces of the heater 23 and the heater support 24. Grease etc. are interposed.
[0036]
The pressure roller 22 is driven to rotate, whereby the cylindrical fixing film 25 is driven to rotate, and the heater 23 is energized, and the heater quickly rises to a predetermined temperature and the temperature is controlled. In the state, the sheet P carrying the unfixed toner image t is introduced between the fixing film 25 and the pressure roller 22 of the fixing nip portion N from the transfer nip portion T side, and the toner image of the sheet P is introduced in the fixing nip portion N. The supporting side surface is in close contact with the outer surface of the fixing film 25, and the fixing nip N is conveyed together with the fixing film 25. In the nipping and conveying process, the sheet P is heated by the heat of the fixing film 25 heated by the heater 23, and the unfixed toner image t on the sheet P is heated and pressed onto the sheet P to be fused and fixed. The paper P that has passed through the fixing nip N is separated from the surface of the fixing film 25 by a curvature and discharged and conveyed.
[0037]
(3) heater 23
FIG. 4 is a structural diagram of an example of the ceramic heater 23 as a heating element. (A) is a partially cutaway plan model diagram on the heater front side, (b) is a plan model diagram on the heater back side, and (c) is an enlarged cross-sectional model diagram.
[0038]
This heater 23
▲ 1 ▼. A ceramic substrate (highly insulating and high thermal conductive substrate) a made of ceramics such as alumina, aluminum nitride, and silicon carbide having a long side in a direction perpendicular to the transport direction of the paper P;
▲ 2 ▼. A screen or the like along the length of the substrate at a central portion in the width direction of the substrate on the front side of the ceramic substrate a, about 10 μm in thickness, about 1 to 3 mm in width in a linear or narrow band shape, and formed by firing. For example, Ag / Pd (silver palladium), RuO ₂ , Ta ₂ Heating resistor layer of N or the like (electric heating element, electric resistance material) b,
(3). Power supply electrode portions cc formed of Ag / Pt (silver / platinum), which are electrically connected to both ends in the longitudinal direction of the heating resistor layer b;
▲ 4 ▼. An insulating protective layer d provided on the surface of the heating resistor layer b, such as a thin glass coat or a fluororesin coat, which is electrically insulated and can withstand rubbing with the fixing film 25;
▲ 5 ▼. First and second thermistors TH1 and TH2 as temperature detecting means provided on the back side of the ceramic substrate a;
Etc.
[0039]
The heater 23 is fitted into a heater fitting groove formed on the lower surface of the heater support 24 along the longitudinal direction with the heater surface side outside, and is adhered and held with a heat resistant adhesive.
[0040]
A is the effective heating length of the heating resistor layer b, which substantially corresponds to the width of a large-size sheet having the maximum width that can be passed through the apparatus. B is the width of a small-size sheet having the minimum width that can be passed through the apparatus, and CC is a non-sheet passing portion (difference area between A and B) generated when the small-size sheet is passed.
[0041]
The first thermistor TH1 (hereinafter, referred to as a main thermistor) is disposed at a heater back surface position corresponding to a substantially central portion in a longitudinal direction of the heater as a sheet passing portion for sheets of both large and small sizes for controlling a heater temperature. . The second thermistor TH2 (hereinafter, referred to as a sub thermistor) is disposed at a heater rear surface position corresponding to the non-sheet passing portion C when small-size paper is passed, for detecting an end temperature rise. Typical methods for installing the thermistors TH1 and TH2 include a method of bonding the heater 23 to the heater 23 with a heat-resistant adhesive and a method of pressing the heater 23 by using the pressure of a spring member.
[0042]
(4) Heater drive circuit 200
FIG. 5 is a block diagram of the heater drive circuit 200 of the fixing device 12. The power supply electrodes c and c of the heater 23 are connected to the heater drive circuit 200 via a power supply connector (not shown).
[0043]
In the heater drive circuit 200, 31 is an AC power supply, 32 is a triac, and 33 is a zero-cross generation circuit. The triac 32 is controlled by a printer main control circuit (CPU) 100. The triac 32 turns on and off the heating resistor layer b of the heater 23.
[0044]
The AC power supply 31 sends a zero cross signal to the main control circuit unit 100 via the zero cross detection circuit 33. The main control circuit 100 controls the triac 32 based on the zero cross signal. When power is supplied from the triac 32 to the heating resistor layer b of the heater 23, the entire heater 23 rapidly rises in temperature.
[0045]
The main and sub thermistors TH1 and TH2 detect the temperature of the heater 23, respectively, and their outputs are taken into the main control circuit unit 100 via A / D converters 34 and 35.
[0046]
The main control circuit unit 100 controls the heater energizing power by controlling the phase and wave number of the AC voltage applied to the heater 23 by the triac 32 based on the heater temperature information from the main thermistor TH1, and the temperature of the heater 23 becomes a predetermined value. Control is performed so as to be maintained at the control target temperature (set fixing temperature).
[0047]
That is, the temperatures of the main and sub thermistors TH1 and TH2 are monitored as voltage values by the control circuit section 100, and the heaters 23 are controlled so that the heater temperature (paper passing section temperature) is maintained at a predetermined set fixing temperature. Is controlled.
[0048]
As a typical temperature control method, PI control is used. As a power control method, there are a wave number control, a phase control, and the like. Here, the phase control will be described.
[0049]
That is, the main control circuit unit 100 detects the temperature of the main thermistor TH1 every 2 μsec, and determines the amount of power supply to the heater 23 by PI control so that the main control circuit unit 100 controls the temperature to a desired temperature. . For example, in order to specify the power in 5% steps, generally, an energization angle of 5% is used for one half-wave of an AC waveform supplied from a power supply. The energization angle is determined as the timing at which the triac 32 is turned on starting from the point when the zero-cross signal is detected by the zero-cross generation circuit 33.
[0050]
(5) Edge temperature rise countermeasures
The main control circuit unit 100 controls the heater driving circuit so that the electric power applied to the ceramic heater 23 is excessively increased by the amount of heat applied to the paper P during the period when the paper P passes through the fixing nip portion N of the fixing device 12. The control of 200 is performed so as to keep the temperature of the ceramic heater 23 constant. At this time, when a narrow sheet passes through the fixing nip portion N, the temperature of the ceramic heater end corresponding to the non-sheet passing portion C where the sheet does not pass increases.
[0051]
If the temperature of the end portion of the ceramic heater corresponding to the non-sheet passing portion C is too high, the temperature of the ceramic heater 23, the fixing film 25, the pressing roller 22, and the heater support 24 that are in contact with the ceramic heater 23 It rises too much, melts, deforms and degrades, and can no longer function normally.
[0052]
This temperature rise at the end will be described a little more with reference to FIGS. FIG. 6 is a diagram showing a positional relationship between the ceramic heater 23, the main and sub thermistors TH1 and TH2, and the paper P being conveyed. The arrow in the figure indicates the paper transport direction, and the width of the paper P in the direction perpendicular to the paper transport direction is defined as the width. (A) shows a state in which the paper P passed through the fixing device has a maximum width. (B) shows a state in which the paper P passed through the fixing device has the maximum width. The main thermistor TH1 always arranges the position of the paper P to be passed, regardless of the size of the paper P, at a position where the paper P passes, that is, an arbitrary position in the paper passing width area B of the minimum size paper P. The sub-thermistor TH2 allows paper to pass while the largest width of the conveyed paper P passes, but does not pass while the minimum width paper P passes. That is, it is arranged at an arbitrary position in the non-sheet passing portion C outside the sheet passing width region B of the minimum size sheet P.
[0053]
(C) shows an example of the temperature distribution along the length of the ceramic heater 23 when the paper P having the minimum width is passed. When a narrow sheet is passed, a space is created between the ceramic heater 23 and the pressure roller 22 just outside the sheet end (non-sheet passing section) C due to the thickness of the sheet, and the ceramic heater 23 generates heat. There is an area where heat is not transmitted to the sheet or the pressure roller 22. Therefore, when the temperature of this region indicated by DD in the non-sheet passing portion C is controlled to the target temperature using the main thermistor TH1, the temperature rises as shown in the figure. In particular, when multiple narrow and thick envelopes are multi-fed, the temperature rises sharply as shown in FIG. 7. For example, when the target temperature is 200 ° C., the temperature in the region DD is 300 ° C. May be reached. Such high temperatures result.
[0054]
Such high temperatures at the ends exceed the temperature rise limits of the pressure roller 22 and the heater support 24, and may lead to damage to these components.
[0055]
In addition, when printing on a wide plain paper in a state where the end portion is at such a high temperature, a hot offset or the like occurs due to an excessively high temperature.
[0056]
As described above, in the related art, in order to prevent the end temperature from rising, the conventional method is to control the temperature increase in the non-sheet passing portion by increasing the paper feeding interval and reducing the throughput when the temperature of the sub thermistor becomes high. Had been done.
[0057]
However, in this case, as described above, it is necessary to change many electrophotographic process conditions (primary charging, development, transfer, laser light amount, and the like), and a low-end printer requires a new circuit for switching between them. It became a cost increase factor.
[0058]
Further, the main control unit (CPU) for controlling the timing of these electrophotographic process conditions requires a large ROM capacity for switching, which has been a factor of cost increase.
[0059]
Thus, in the present embodiment, even in an image forming apparatus such as a low-end printer, it is possible to prevent damage due to a rise in the temperature of the end of the fixing device and increase the throughput of small-sized paper without increasing the cost. For this reason, when the detected temperature of the sub-thermistor TH2 for detecting the temperature rise at the end of the fixing device is lower than a preset temperature (normal time), the main control circuit 100 controls the printer in the first control mode 1) described below. When the detected temperature of the sub thermistor TH2 is equal to or higher than a preset temperature (when the temperature of the end is raised), the printing operation is performed in the second control mode 2) described below.
[0060]
1) First control mode (normal time)
This first control mode is performed when the detected temperature of the sub-thermistor TH2 for detecting the temperature rise at the end of the fixing unit 12 is lower than a preset temperature, that is, when the paper used for the printer is a large-size material. A control mode that is performed when the temperature of the end is not raised in the fixing unit 12 or when the number of continuous prints is small and the degree of the temperature rise in the end is within the allowable range even if the paper passing through is a small size material. The main control circuit 100 conveys the sheet P at a predetermined first sheet conveyance speed and a predetermined first sheet feeding interval, and transfers an unfixed toner image to the sheet at the transfer nip portion T, The fixing nip of the fixing device 12 in which the sheet from the transfer nip portion T side is driven at a predetermined first driving speed substantially corresponding to the first sheet conveying speed and the temperature is adjusted to a predetermined first fixing temperature. Not fixed on paper by nipping and transporting between sections N It is to print out by fixing the toner image.
[0061]
2) Second control mode (at the time of temperature rise at the end)
This second control mode is used when the detected temperature of the sub-thermistor TH2 for detecting the temperature rise at the end of the fixing device 12 is equal to or higher than a preset temperature, that is, when the paper used in the printer is a small size material. This is a control mode that is performed when it is determined that the end of the fixing unit 12 is heated due to a large number of continuous prints. The transfer speed is changed to an interval, an unfixed toner image is generated on the paper at the transfer nip T, and after the rear end of the paper passes the transfer nip T, the driving speed of the fixing device 12 is changed to the first speed. Change the second driving speed lower than the driving speed, and change the fixing temperature to the second fixing temperature lower than the first fixing temperature, and adjust the temperature to fix the unfixed toner image on the paper. When the paper has passed through the fixing nip, The driving speed of the vessel 12 is to print out by changing the first drive speed.
[0062]
FIG. 8 is a specific control flowchart for executing the second control mode for the end-portion temperature rise countermeasure.
[0063]
The sub-thermistor TH2 for detecting an end temperature rise is disposed at the end of the ceramic heater 23, and the detected temperature information is transmitted to the main control circuit unit 100. When the sub-thermistor temperature becomes 260 ° C. or higher (601), the main control circuit unit 100 enters a second paper feed interval changing mode for increasing the feed interval (602). In this mode, the TOP sensor 9 detects the trailing edge of the sheet (603), and when the trailing edge of the sheet has passed through the transfer nip T (604), the fixing target temperature is set to the normal target temperature (first fixing temperature). The main control circuit unit 100 sets the driving speed of the main motor M, that is, the driving speed of the fixing unit 12 via the motor driver 36 (FIG. 5) to the first fixing temperature by setting the second fixing temperature 40 ° C. lower (605). The driving speed is changed from the driving speed to the second driving speed to be slowed down (606). When the sheet passes through the fixing nip N (607), the driving speed of the main motor, that is, the driving speed of the fixing device 12 is returned to the first driving speed which is a normal speed (608).
[0064]
In the above description, “the timing at which the paper trailing end passes through the transfer nip portion” and “the timing at which the paper trailing edge passes through the transfer nip portion” are defined by the main control circuit 100 when the TOP sensor 9 detects the trailing edge of the paper, the paper transport speed, 9 to the transfer nip T and further to the fixing nip N.
[0065]
As a result, as shown in FIG. 9, the rise in the temperature at the end of the fixing device is reduced. That is, in a low-end printer in which the photosensitive drum 1 and the fixing device 21 are driven by one main motor M, fixing can be performed at a low temperature by suppressing the speed at the time of paper feeding of the fixing device. Throughput can be increased.
[0066]
(Second embodiment)
FIG. 10 is a control flowchart at the time of the second control mode for the end portion temperature rising countermeasure in the present embodiment.
[0067]
When the sub thermistor temperature becomes 260 ° C. or higher (901), the main control circuit 100 enters a second paper feed interval changing mode for increasing the feed interval (902). In this mode, the TOP sensor 9 detects the trailing edge of the paper (903), and from the timing (904) at which the trailing edge of the paper has passed through the transfer nip T, the fixing target temperature is gradually reduced by 40 ° C. from the normal target temperature. (905), and the main control circuit unit 100 gradually reduces the driving speed of the main motor M, that is, the driving speed of the fixing device 12 via the motor driver 36 (906). When the sheet passes through the fixing nip N (907), the main motor driving speed, that is, the driving speed of the fixing device 12 is returned to the first driving speed which is a normal speed (908).
[0068]
The speed step change control in step (907) of this embodiment is executed regardless of whether the length of the sheet is short or long. The length of the sheet to be conveyed is detected by the main control circuit 100 by calculating from the sheet conveyance speed and the time when the TOP sensor 9 detects the leading and trailing ends of the sheet.
[0069]
As a result, as shown in FIG. 11, in the case of paper having a narrow width and a long length, when paper is present in the fixing nip, the motor speed is changed gradually without abrupt change. Can be prevented from scattering and the rise in the temperature at the end of the fixing device can be reduced.
[0070]
That is, in a low-end printer in which the photosensitive drum 1 and the fixing device 21 are driven by one main motor M, fixing can be performed at a low temperature by suppressing the speed at the time of paper feeding of the fixing device. Throughput can be increased.
[0071]
(Other)
1) In the present invention, the image forming principle and process of the image forming apparatus are not limited to the transfer type electrophotographic method of the embodiment, but may be any other transfer type or direct type electrostatic recording method, magnetic recording method and the like. .
[0072]
2) The fixing means is not limited to the heating device of the film heating system of the pressure rotating body driving system (tensionless type) of the embodiment, and various heat fixing systems such as an electromagnetic induction heating system can be used. I can do it.
[0073]
Although various examples and embodiments of the present invention have been shown and described, those skilled in the art will appreciate that the spirit and scope of the present invention is not limited to the specific description and figures herein. It will be appreciated that various modifications and changes are set forth which are all set forth in the following claims.
[0074]
Examples of embodiments of the present invention are listed below.
[0075]
[Embodiment 1] A toner image forming unit that generates an unfixed toner image on a conveyed recording material, and the recording material from the toner image forming unit side is nipped and conveyed between driven fixing members to convey the recording material on the recording material. A fixing unit that heats and fixes the unfixed toner image with a fixing member whose temperature has been adjusted to a predetermined fixing temperature.
The recording material is conveyed at a first recording material conveyance speed and a first recording material feeding interval, and an unfixed toner image is generated on the recording material by a toner image forming unit, and the recording material from the toner image forming unit side Is driven at a first driving speed substantially corresponding to the first recording material conveying speed, and is nipped and conveyed between fixing members of a fixing unit adjusted to a first fixing temperature to fix unfixed recording material on the recording material. A first control mode for fixing the toner image,
If the temperature detecting means detects the temperature rise at the end of the fixing means when a recording material having a size smaller than the maximum size of the recording material that can be passed through the apparatus is detected, the recording is performed when a temperature equal to or higher than a preset temperature is detected. The recording material is changed to a second recording material feeding interval longer than the first recording material feeding interval, is conveyed, and an unfixed toner image is generated on the recording material by toner image forming means. After the rear end has passed through the toner image forming unit, the driving speed of the fixing unit is changed to a second driving speed lower than the first driving speed, and the fixing temperature is lower than the first fixing temperature. The unfixed toner image on the recording material is fixed by changing the temperature to the second fixing temperature, and when the recording material passes between the fixing members, the driving speed of the fixing unit is changed to the first driving speed. A second control mode,
An image forming apparatus comprising:
[0076]
[Embodiment 2] A toner image forming unit that generates a toner image on a recording material at a predetermined conveyance speed,
A fixing device having a heating unit and a pressurizing unit for applying pressure to the heating unit, for fixing the unfixed toner image to the recording material by nipping and conveying the recording material between the heating unit and the pressurizing unit When,
A fixing unit driving unit capable of changing the speed of rotating the heating unit or the pressing unit of the fixing unit;
A first temperature detecting unit disposed at a position where all the size recording materials that can be passed through the heating unit and the pressurizing unit of the fixing device during the passing of the paper;
While the recording material having the largest size that can be passed is passed between the heating unit and the pressing unit of the fixing device, the recording material is held between the heating unit and the pressing unit. Second temperature detecting means disposed at a position where the recording material is not sandwiched in the paper,
Control means for controlling the heating means to be a preset first fixing temperature based on the temperature detected by the first temperature detection means,
A recording material transport position detecting means comprising at least one or more sensors for detecting the transport position of the recording material;
Throughput control means for controlling the throughput of the image forming apparatus;
With
When the control unit detects that the temperature detected by the second temperature detection unit is equal to or higher than a preset temperature, the control unit changes the throughput control, and the recording material conveyance position detection unit detects a change in the recording material after position. An image forming apparatus, wherein the driving speed of the fixing device driving unit and the fixing temperature are changed after the end passes through the toner image forming unit.
[0077]
Embodiment 3 In the image forming apparatus according to Embodiment 2, the fixing device driving unit drives the toner image forming unit at the same time.
[0078]
【The invention's effect】
As described above, according to the present invention, even in an image forming apparatus such as a low-end printer, it is possible to prevent damage due to a rise in the temperature of the end of the fixing device and increase the throughput of small-sized paper without increasing the cost. Can be made possible.
[Brief description of the drawings]
FIG. 1 is a schematic configuration model diagram of an example of an image forming apparatus according to a first embodiment.
FIG. 2 is a schematic perspective view of a main part of the fixing device.
FIG. 3 is an enlarged cross-sectional model view of a main part of the fixing device.
FIG. 4 is a configuration explanatory view of an example of a ceramic heater as a heating element.
FIG. 5 is a block diagram of a heater drive circuit.
FIG. 6 is an explanatory diagram of a decrease in temperature rise at the end of the fixing device (part 1).
FIG. 7 is an explanatory diagram of a decrease in temperature rise at the end of the fixing device (part 2).
FIG. 8 is a control flowchart in a second control mode for fixing the temperature rise of the end portion of the fixing device in the first embodiment.
FIG. 9 is a graph of the operation.
FIG. 10 is a control flowchart in a second control mode for fixing the temperature rise of the end portion of the fixing device in the second embodiment.
FIG. 11 is a graph of the operation.
[Explanation of symbols]
1. photosensitive drum, 3. scanner unit, 5 paper cassette, P paper, 6 paper feed roller, 7 transport roller, 8 registration roller, 9 paper feed sensor, 10. paper feed path, 11 transfer roller, 12 fixing device, 14 discharge roller, 21 fixing film assembly, 22 pressure roller, 23 ceramic heater, 25 Fixing film, TH1 main thermistor, TH2 sub thermistor, 100 main control circuit (CPU), 200 heater driving circuit, M main motor

Claims (1)

A toner image forming unit for generating an unfixed toner image on the conveyed recording material, and a recording material from the toner image forming unit side nipped and conveyed between the driven fixing members to convey the unfixed toner image on the recording material. Fixing means for fixing by heating with a fixing member whose temperature has been adjusted to a predetermined fixing temperature,
The recording material is conveyed at a first recording material conveyance speed and a first recording material feeding interval, and an unfixed toner image is generated on the recording material by a toner image forming unit, and the recording material from the toner image forming unit side Is driven at a first driving speed substantially corresponding to the first recording material conveying speed, and is nipped and conveyed between fixing members of a fixing unit adjusted to a first fixing temperature to fix unfixed recording material on the recording material. A first control mode for fixing the toner image,
The temperature detecting means for detecting the temperature rise at the end of the fixing means when a small-size recording material having a width smaller than the large-size recording material having a maximum width that can be passed through the apparatus has a temperature higher than a preset temperature. Upon detection, the recording material is changed to a second recording material feeding interval longer than the first recording material feeding interval and conveyed, and an unfixed toner image is generated on the recording material by the toner image forming unit. After the trailing end of the recording material has passed the toner image forming unit, the driving speed of the fixing unit is changed to a second driving speed lower than the first driving speed, and the fixing temperature is changed to the first fixing speed. The unfixed toner image on the recording material is fixed by changing the temperature to a second fixing temperature lower than the temperature, and when the recording material passes between the fixing members, the driving speed of the fixing unit is changed to the first fixing temperature. A second control mode for changing to drive speed,
An image forming apparatus comprising:

Images