JP2019035809A - Fixation device and image formation apparatus - Google Patents

Abstract

To suppress the occurrence of the recess on a heat transmission member at the cleaning.SOLUTION: A fixation device includes: first temperature measurement means which measures the temperature of a nip part; and second temperature measurement means which measures the temperature of a portion other than the nip part of a heat transmission member, in a case where the temperature difference between the temperature measured by the first temperature measurement means and the temperature measured by the second temperature measurement means is equal to or greater than a prescribed value when executing cleaning of the fixation device, executes the idle rotation of a pressing member, stops the rotation of the pressing member so that a portion adjacent to the portion of the pressing member located in the nip part before the idle rotation is located in the nip part, and performs heating with the heat of a heating element in the state where the rotation of the pressing member is stopped.SELECTED DRAWING: Figure 6

Description

  The present invention relates to a heat generating member for heating a recording medium and a heating device using the heat generating member, and more particularly to a fixing device mounted on an image forming apparatus such as an electrophotographic copying machine or an electrophotographic printer.

  Conventionally, discharge control is performed to prevent accumulation of toner stains on the pressure roller, and to prevent the recording material from being wound around the pressure roller and the recording material from being stained. Specifically, when the fixing device is stopped after post-rotation, the fixing nip portion is heated to melt the toner in the fixing nip portion of the toner adhering to the pressure roller due to an offset or the like, so that it is higher than before the melting. Make a large toner mass.

  Thereafter, since the surface temperature of the fixing film having a small heat capacity becomes lower than the temperature of the pressure roller having a large heat capacity, the above-mentioned molten toner is transferred to the fixing film having a low temperature. The transferred toner is transferred to the recording material when the next recording material passes through the fixing nip portion, and is discharged together with the recording material.

  The offset toner at this time is a small amount of toner that is invisible because the recording material is passed through several to several tens of sheets, and the toner discharged to the recording material is naturally visible. There are no levels.

  Furthermore, toner clumps that cannot be recovered even by discharge control and toner contamination mixed with paper dust generated from the recording material are discharged by cleaning control using cleaning paper. As shown in FIG. 4, the cleaning paper used at this time is preliminarily fixed with toner (cleaning image) having a circumferential length L2 × longitudinal width L1 of the fixing member or pressure member. This cleaning sheet is set on the sheet feeding means so that the toner surface is conveyed to the member to be cleaned, and the cleaning operation is started.

  FIG. 5 is a view showing a cross section of the fixing unit during the cleaning control.

  In the cleaning control, the rotation driving is stopped after carrying the temperature-controlled idling rotation so that the toner fixing portion of the cleaning sheet comes to the nip position, and the stop heating is performed similarly to the discharge control. Due to the stop heating, the toner stain in the nip is melted and integrated with the toner on the cleaning paper.

  When the fixing member and the pressure member are advanced by the nip width after cooling for a predetermined time after the stop heating, the toner stain is collected on the cleaning paper side.

  When the cleaning of the fixing film nip A shown in FIG. 5 is completed, the nip B is cleaned. This is repeated sequentially and is performed on the entire circumference of the fixing member or the pressure member in the circumferential direction, whereby the adhered toner stains are cleaned.

  Next, heater temperature and pressure roller driving during cleaning control will be described.

  FIG. 15 is a graph showing the behavior of a heater and a motor during conventional cleaning control.

  The heater temperature transition in FIG. 15 indicates the heater temperature transition detected by the temperature detection sensor 25 in FIG. 5, and the arrows indicate ON / OFF of the motor driving of the pressure roller. Further, the detection of the paper sensor of the fixing device is shown, indicating that the cleaning paper has entered the nip. When the cleaning command is received, the cleaning preparation operation indicated by the period P1 is started. The fixing device is heated with the heater ON motor ON, and idling is performed at a target temperature (eg, 180 ° C.). After that, the cleaning sheet on which the cleaning image is fixed enters the fixing nip and waits for the timing when the leading edge of the image reaches the nip portion. Next, a period P2 in FIG. 15 indicates that cleaning is being performed. During the cleaning preparation operation in the period P1 in FIG. 15, the heater ON and the motor OFF are stopped and heated at the timing when the leading edge of the image on the cleaning sheet reaches the nip portion. After a predetermined time (example 2 seconds) has passed at the target temperature (example 180 ° C.), the heater is turned off, and stop cooling is performed for a predetermined time (example 3 seconds). After cooling for a predetermined time, the pressure roller motor is driven by the nip width, and the heating and stop cooling are again performed for a predetermined time, and this is repeated for the circumference of the fixing film or pressure roller, so that the entire cleaning is performed. Do. For example, if the pressure roller is φ30 and the nip width is 10 mm, stop heating and movement are performed 10 times.

  The toner stain transferred to the cleaning paper is finally discharged together with the cleaning paper in the period P3. This is the control for collecting toner stains on the fixing film and the pressure roller on the cleaning paper.

JP 2004-317929 A

  In Patent Document 1, cleaning control as described above (heating when stopped) is performed in order to collect toner adhering to the pressure roller onto a cleaning sheet. However, in a fixing device in which the fixing member and the pressure member have a certain diameter, in order to clean the entire circumference, the cleaning operation must be performed finely and repeatedly. However, if a long time elapses during the cleaning control, a large recess is generated in the fixing film during driving for changing the nip position.

  FIG. 16 is a graph showing the transition of the cleaning control temperature when a film recess occurs in the conventional fixing device.

  Cleaning control is started in period P1, and the temperature of the heater rises to the target temperature by temperature-controlled idling rotation (eg, 180 ° C.), and the film surface temperature in the nip is in contact with the heater. The same temperature transition is shown (hereinafter referred to as film surface temperature T1). Further, the film surface temperature T2 (measured by the non-contact thermometer 50 in FIG. 5) at the upstream position of the nip rises in the same manner as in the nip during the period P1 during the temperature-controlled idling rotation.

  Next, in the period P2, the cleaning paper reaches the nip portion, and stop heating is performed. At this time, since the film surface temperature T2 in the nip is in contact with the heater that generates heat during the stop heating, the temperature does not decrease. In addition, the temperature drop is slight because the pressure roller is in contact with the pressure roller warmed by the temperature-controlled idling rotation during the cooling time after the stop heating. However, since the film surface temperature T2 outside the nip is exposed to the air around the fixing unit as shown in FIG. This temperature drop is uniformly reduced on the film surface other than in the nip.

  For this reason, the surface temperature of the film surface position F or the like located downstream in the rotation direction in FIG. 5 has dropped to near room temperature immediately before the stop heating is performed (the round frame in FIG. 16).

  As described above, if the temperature of the film surface F (outside of the nip) is decreased immediately before the stop heating of the cleaning control, the temperature difference from the film surface E (inside of the nip) where the stop heating of cleaning is performed is large. (Broken arrows in FIG. 16).

  If there is a temperature difference between the heated nip and the unheated nip, a large dent will occur during rotation (the film surface temperature outside the nip points from the outside of the nip to the 90 ° position around the film circumference). ).

  FIG. 17 is a diagram illustrating a mechanism for generating film recesses.

  When stop heating is performed with the film unit cooled, only the nip portion of the fixing film and the pressure roller and the vicinity of the upstream and downstream of the fixing film are thermally expanded as indicated by the solid film portion in FIG. In addition, no thermal expansion occurs except in the vicinity of the nip portion and the upstream and downstream of the nip. Therefore, a thermal stress is applied by generating a portion that thermally expands in the circumferential direction of the fixing film and a portion that does not thermally expand (location where thermal stress is applied in FIG. 17A).

  For this reason, as shown in FIG. 17B, when driving is performed in a state where thermal stress is applied, the thermally expanded film in the vicinity of the nip portion and the upstream and downstream of the nip is moved downstream in the rotation direction by the pressure roller which is a rotation drive source. Pulled to the side. As a result, the stress due to the rotational drive is further concentrated in the portion where the thermal stress is applied (A portion in FIG. 17B), and the film is permanently deformed, so that the fixing film dent is generated.

  When a film dent occurs, the dent does not adhere to the surface of the recording material, and the toner image on the recording material cannot be permanently fixed, resulting in an image defect. Moreover, if it continues using it in the state in which the dent has generate | occur | produced, stress will concentrate on a dent part and will lead to the crack of a fixing film.

  Accordingly, an object of the present invention is to provide a fixing device capable of suppressing the occurrence of a dent in a heat transfer member during cleaning.

In order to achieve this object, the fixing device of the present invention provides:
A fixing device for fixing an unfixed toner image on a recording medium,
A heating element;
A rotatable heat transfer member for transferring heat of the heating element to a recording medium;
A rotatable pressing member that forms a nip portion capable of sandwiching the recording medium with the heat transfer member;
A temperature difference detecting means for detecting a temperature difference between the inside and the outside of the nip portion;
Have
When the heat transfer member and the pressing member are stationary, heating is performed by the heating element, and when the heat transfer member and the pressing member are rotating, the heating element is heated. When the temperature difference between the inside and outside of the nip portion is equal to or greater than a predetermined value, the heating at the time of rotation is performed until the temperature difference becomes less than the predetermined value. Thereafter, the portion of the pressing member that has not been heated at rest is positioned at the nip portion, the rotation of the pressing member is stopped, and the heating at rest is performed.

  According to the present invention, when the temperature difference between the nip portion of the heat transfer member and the portion other than the nip portion is equal to or larger than a predetermined value, the temperature difference is reduced by executing idling of the pressing member. This suppresses the generation of a dent in the heat transfer member.

1 is a diagram illustrating an overall configuration of an image forming apparatus according to an exemplary embodiment of the present invention. 1 is a longitudinal sectional view of a fixing device according to an embodiment of the present invention. It is a figure which shows arrangement | positioning of the thermistor and safety device of embodiment of this invention, and an electricity supply control structure. It is a figure which shows the cleaning paper used by embodiment of this invention. FIG. 2 is a diagram schematically illustrating a cross section of a fixing unit during cleaning control in the embodiment of the present invention. It is a figure which shows the temperature transition at the time of cleaning control in embodiment of this invention. It is a figure which shows the state of the fixing film at the time of changing control in embodiment of this invention. 1 is a block diagram of an image forming apparatus according to an embodiment of the present invention. 3 is a flowchart illustrating an operation of the image forming apparatus according to the embodiment of the present invention. It is a figure which shows the image for cleaning on the cleaning paper used in other embodiment of this invention. It is a graph which shows the temperature transition at the time of the film dent countermeasure control of other embodiment of this invention. It is sectional drawing which shows the structure of the image forming apparatus of other embodiment of this invention. It is a block block diagram of other embodiment of this invention. It is a flowchart which shows operation | movement of other embodiment of this invention. It is a graph which shows the heater and motor behavior at the time of the conventional cleaning control. It is a graph which shows the cleaning control temperature transition at the time of generation | occurrence | production of the film recess of the conventional fixing device. It is a figure which shows the generation | occurrence | production mechanism of a film dent.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

The dimensions, materials, shapes, and relative arrangements of the components described in the following embodiments should be changed as appropriate according to the configuration of the apparatus to which the present invention is applied and various conditions. Therefore, unless specifically stated otherwise, the scope of the present invention is not intended to be limited thereto.
<First Embodiment>
An embodiment to which the present invention is applied will be described by exemplifying a copying machine as an image forming apparatus equipped with a fixing device.

  FIG. 1 is a diagram illustrating the overall configuration of the image forming apparatus.

  As shown in the figure, the image forming apparatus is a laser printer using a transfer type electrophotographic process.

  The photosensitive drum 1 is a rotating drum type as an image carrier, and rotates at a predetermined speed in the circumferential direction. The photosensitive drum 1 is configured by forming a photosensitive material such as an OPC or an amorphous silicon drum on a cylindrical substrate such as aluminum or nickel.

  By rotating the surface of the rotating photosensitive drum 1 in contact with the charging roller 2, the surface of the photosensitive drum 1 is uniformly charged. The photosensitive drum 1 whose surface is uniformly charged is subjected to scanning exposure with a laser beam L modulated in accordance with image information output from a laser beam scanner 3 as image exposure means. As a result, an electrostatic latent image corresponding to the image information is formed on the surface of the photosensitive drum 1. The electrostatic latent image is developed as a toner image by supplying toner (developer) from the developing device 4.

  On the other hand, the recording medium P is separated and fed one by one from the sheet feeding cassette 5 by the feeding roller 6 and sent to the registration roller 7. The recording medium P is synchronized with the toner image formed on the surface of the photosensitive drum 1 by the registration roller 7 and is introduced into the transfer nip T formed by the photosensitive drum 1 and the transfer roller 9. The registration roller 7 controls the leading edge of the toner image on the photosensitive drum 1 and the leading edge of the recording medium P so that they enter the transfer nip at the same timing.

  The recording medium P introduced into the transfer nip T is nipped and conveyed by the transfer nip T, and a transfer bias having a polarity opposite to that of the toner is applied to the transfer roller 9 from the transfer bias application power source (not shown) on the transfer roller 9. Applied. Then, the toner image on the photosensitive drum 1 is transferred onto the recording medium P due to electrostatic characteristics.

  The recording medium P that has received the transfer of the toner image at the transfer nip T is separated from the surface of the photosensitive drum 1 and conveyed to the fixing device 11. The toner image on the recording medium P is permanently fixed on the recording medium P by being heated and pressed by the fixing device 11. The recording medium P exiting the fixing device 11 is discharged from the discharge port 13 onto the discharge tray 14. In double-sided printing, the first surface is discharged from the fixing device 11 according to the above procedure, and is then transported to the reverse transport path 15 and waits at the registration roller 7. The timing at which the electrostatic latent image on the second surface is formed on the photosensitive drum 1 is measured, and the paper is fed from the registration roller 7 and printing on the second surface is performed. After the transfer of the toner image, the toner and paper dust on the surface of the photosensitive drum 1 are removed by the cleaning device 10 to clean the surface of the photosensitive drum 1 and repeatedly used for image formation.

(1) Fixing Device Next, the fixing device of this embodiment will be described in detail.

  FIG. 2 is a longitudinal sectional view of the fixing device 11. In the following description, with respect to the fixing device 11 or the members constituting the fixing device 11, the longitudinal direction is a direction orthogonal to the conveyance direction of the recording medium P, and the short direction is the conveyance direction of the recording medium P. The same direction.

  The fixing device 11 includes a ceramic heater 23 as a heat generating member, a fixing film 22 (heat transfer member) as a flexible member, a stay 21 as a guide member, and a pressure roller 24 as a pressure member. . The stay 21, the fixing film 22, the heater 23, and the pressure roller 24 are all elongated members in the longitudinal direction.

  The stay 21 is formed in a vertical cross-sectional shape using a predetermined material having heat resistance and rigidity, and a heater 23 is held on the stay 21. The fixing film 22 has heat resistance, is formed in an endless shape (cylindrical shape), and transfers heat from the heater 23 to the recording medium P. The fixing film 22 is fitted on the stay 21 and can be rotated. The inner peripheral length of the fixing film 22 and the outer peripheral length of the stay 21 are larger in the fixing film 22 by about 3 mm, for example. Therefore, the fixing film 22 is externally fitted to the stay 21 with a margin in the circumference. In the heater 23, the substrate 27 is fixed in the groove of the stay 21 with the surface thereof facing the nip portion N surface. Thereby, the overcoat layer 28 of the heater 23 is brought into contact with the inner peripheral surface of the fixing film 22. A lubricant (not shown) is interposed between the inner peripheral surface of the fixing film 22 and the outer peripheral surface of the stay 21. Thereby, the sliding resistance when the stay 21 and the inner peripheral surface of the fixing film 22 rotate in contact with each other is reduced. A non-contact infrared thermometer 50 is provided to measure the surface temperature of the film outside the fixing nip. A contact type thermistor may be used instead of the non-contact infrared thermometer 50.

  Next, each member in the fixing device 11 will be described in detail.

(A) Fixing film The fixing film 22 has a base layer (not shown) made of a heat-resistant resin-based material or a metal material, a heat-resistant elastic layer as an intermediate layer, and a fluororesin coated on the outer peripheral surface thereof. Thus, a composite layer film as a release layer can be used. Here, as a heat-resistant resin constituting the base layer in order to reduce the heat capacity and increase the startup time, polyimide, polyimide amide, PEEK (polyether ether ketone), PES (polyether sulfone) having a thickness of 20 to 100 μm are used. ), PPS (polyphenylene sulfide) or the like. Moreover, as a metal material which comprises a base layer, 15-50 micrometers thick SUS (stainless steel), Ni, etc. are used. Moreover, as the heat resistant elastic layer, silicon rubber, fluorine rubber or the like having a thickness of 50 to 500 μm is used. Moreover, as a fluororesin which comprises a mold release layer, 5-40 micrometers PTFE, PFA, FEP, etc. are used. Here, PTFE is polytetrafluoroethylene, PFA is a tetrafluoroethylene perfluoroalkyl vinyl ether copolymer, and FEP is a tetrafluoroethylene hexafluoropropylene copolymer. The film 22 includes a film having a heat resistant elastic layer and a film 22 having no heat resistant elastic layer. The film 22 has a diameter of 24φ and is rotated by driven rotation with the pressure roller 24.

(B) Heater The heater 23 is an overcoat layer in which a 1 mm thick AL2O3 (alumina) substrate 27 is screen-printed with an Ag heating resistor 26 in a predetermined width and thickness, and the surface of the heating element is coated with protective glass. 28 is fixed to the stay 21.

  As the substrate 27, an alumina plate having a thickness of 1.0 mm was used. For the heating resistor 26 provided along the longitudinal direction of the substrate 27 on the substrate 27, a conductive paste applied to the substrate 27 or a nichrome wire fixed to the substrate by a known method such as adhesion is used. May be. In this embodiment, a conductive paste containing a silver / palladium alloy was uniformly applied to the image surface side of the transfer material of the substrate 27 by a screen printing method and then baked.

(C) Stay The stay 21 can be composed of, for example, a high heat-resistant resin such as polyimide, polyamideimide, PEEK, PPS, or liquid crystal polymer, or a composite material of these resin and ceramic, metal, glass, or the like. In the present embodiment, the stay 21 is formed into a vertical cross-sectional shape by a liquid crystal polymer. Both ends of the stay 21 in the longitudinal direction are held by a pair of side plates (not shown) of the fixing device 11. A concave groove is provided along the longitudinal direction on the surface of the stay 21 on the pressure roller 24 side, and a heater 23 is held in the groove.

(D) Pressure roller The pressure roller 24 (pressing member) includes a cored bar 24a, an elastic layer 24b provided around the cored bar 24a, and an outermost layer provided around the elastic layer 24b. And a mold layer 24c. The pressure roller 24 is held in a rotatable state at both ends in the longitudinal direction of the cored bar 24 a by a pair of side plates of the fixing device 11. In this embodiment, the core metal 24a is made of aluminum, the elastic layer 24b is made of silicon rubber containing a microballoon, and the release layer 24c is made of a PFA tube. The outer diameter of the pressure roller 24 was 20 mm, and the thickness of the release layer was 30 μm. The pressure roller 24 disposed below the fixing film 22 and in parallel with the fixing film 22 is pressed toward the stay 21 by pressure means such as a pressure spring at both ends of the cored bar. As a result, the fixing film 22 can be sandwiched between the surface of the pressure roller 24 and the heater 23, and a nip portion N having a predetermined width necessary for heating and fixing an unfixed toner image on the recording medium P is formed. .

(D) Arrangement of Thermistor / Safety Device FIG. 3 is a diagram showing the thermistor 25, the arrangement of the safety device, and the energization control configuration.

  The heater 23 has a thermistor 25 (first temperature measuring means) on the back surface (surface opposite to the nip portion N) of the substrate 27. The thermistor 25 is provided for measuring the temperature of the heater 23. In the present embodiment, a thermistor that is in contact with and contacted with the back side of the heater 23 is used as the thermistor 25. The thermistor 25 is provided with, for example, a heat insulating layer on a support (not shown), an element of a chip thermistor is fixed on the heat insulating layer, and the element is pressed against the back surface of the substrate 27 with a predetermined pressure. In this configuration, the support is brought into contact with the back surface of the substrate 27.

  In the present embodiment, the thermistor 25 is installed at two locations in the longitudinal direction of the heating resistor 26, and one of the thermistors 25 b is in the minimum size sheet passing area through which the recording medium P in the longitudinal direction of the heating resistor 26 always passes. Is provided. The other thermistor 25a is installed in a portion corresponding to a non-sheet passing area when a B5 size recording medium in the longitudinal direction of the heating resistor is passed in the R direction. According to this arrangement form, the temperature of the paper passing area is controlled by the thermistor 25b, and the temperature of the non-paper passing area at the time of small size paper passing is controlled by the thermistor 25a. That is, the temperature control of the sheet passing area is performed by the thermistor 25b, and the thermistor 25a performs the throughput control so that the abnormal temperature rise in the non-sheet passing area at the time of small size continuous sheet passing does not occur.

  The heater in the present embodiment is configured to suppress the temperature rise in the non-sheet passing area. For this reason, although the possibility of entering the throughput control is very low, the edge temperature rise may occur in extremely small-sized continuous paper passing such as a postcard. Therefore, such throughput control is installed.

  The heater 23 has a safety device on the back surface (the surface opposite to the nip portion N) of the substrate 27, and is provided to cut off the energization when an abnormal temperature rise of the heater occurs. In this embodiment, a thermo switch 31 is used as a safety device, and a bimetal is provided inside as a configuration, and an aluminum cap member covers the bimetal. When the cap member contacts the back surface of the substrate 27, the heater temperature is transmitted to the bimetal via the cap member. With this configuration, when the heater is abnormally heated, the heater temperature is transmitted to the bimetal, and when the critical temperature is reached, the bimetal is deformed to cut off the energization of the heater. In this embodiment, a thermo switch is used as a safety device, but a safety device such as a thermal fuse may be used.

(6) Heat Fixing Operation of Fixing Device Next, the heat fixing operation of the fixing device 11 will be described.

  A driving gear (not shown) provided at the end of the cored bar 24a of the pressure roller 24 in FIG. 2 is rotationally driven in the arrow direction by a fixing motor (not shown), so that the pressure roller 24 is moved in the arrow direction. Rotate. Due to the rotation of the pressure roller 24, a rotational force acts on the fixing film 22 by the frictional force between the surface of the pressure roller 24 and the surface of the fixing film 22 at the nip portion N, and the fixing film 22 is rotated in a driven manner. At this time, the heat of the heater 23 is driven by rotating in the arrow direction at the same speed as the rotation speed of the pressure roller 24 while sliding in close contact with the surface of the heater 23 inside the fixing film 22. This is transmitted to the recording medium P in the nip N via the fixing film 22.

  The drive gear provided at the end of the cored bar 24a of the pressure roller 24 in FIG. 2 is provided with a rotation speed measuring member 70 for detecting the rotation speed, and the rotation speed of the pressure roller 24 can be detected. .

  As shown in FIG. 3, when a printing operation signal is received, energization of the heater 23 is started, and the control unit 41 as the control means turns on the triac 42 as the energization control means. Thereby, electricity is supplied from the AC power supply 43 to the electrode power supply unit (not shown) of the heater 23 via the thermo switch 31 that is a temperature detection type safety device. When the heater 23 is energized from the electrode at the heater end, the entire heating resistor (not shown) generates heat and the temperature rises. The thermistor 25 detects the temperature of the substrate 27 that is heated in accordance with the temperature rise and continues energization until the temperature of the substrate 27 reaches the target temperature, during which the control unit 41 outputs the output (detected temperature) of the thermistor 25. A / D convert and capture. When the target temperature is reached, based on the output signal from the thermistor 25, the electric power supplied to the heater 23 by the triac 42 is controlled by phase control or frequency control to control the temperature of the heater 23. That is, the control unit 41 controls the triac 42 so as to raise the heater when the temperature detected by the thermistor 25 is lower than a predetermined set temperature and to lower the heater 23 when the detected temperature is higher than the set temperature. The heater 23 is adjusted to keep the set temperature.

  The recording medium P is introduced into the nip portion N in a state where the temperature of the heater 23 rises to the set temperature and the rotation peripheral speed of the fixing film 22 is stabilized by the rotation of the pressure roller 24. Then, the recording medium P is nipped and conveyed together with the fixing film 22 in the short direction perpendicular to the longitudinal direction of the substrate 27 of the heater 23 at the nip portion N. As a result, the heat of the heater 23 is applied to the recording medium P via the fixing film 22, and the unfixed toner image t on the recording medium P is heated and fixed to the recording medium P. The recording medium P that has exited the nip N is separated from the surface of the fixing film 22 and conveyed. When these printing operations are finished, the triac 42 is turned off and the energization of the heater 23 is finished.

(7) Cleaning Operation of Fixing Device Next, the cleaning operation of the fixing device in the present embodiment will be described.

  Discharge control is performed to prevent accumulation of toner stains on the pressure roller 24 and to prevent the recording medium P from being wound around the pressure roller 24 and from being dirty on the recording medium P. Specifically, when the fixing device 11 is stopped after post-rotation, the fixing nip portion N is heated to melt the toner in the fixing nip portion N out of the toner adhered to the pressure roller 24 by offset or the like, Make the toner mass larger than before melting.

  Thereafter, since the surface temperature of the fixing film having a small heat capacity becomes lower than the temperature of the pressure roller 24 having a large heat capacity, the above-described molten toner is transferred to the fixing film 22 having a low temperature. The transferred toner is transferred to the recording medium P when the next recording medium P passes through the fixing nip portion N, and is discharged together with the recording medium P.

  The offset toner at this time is a small amount of toner that is invisible so that the recording medium P is passed through several to several tens of sheets, and the toner discharged to the recording medium P is naturally also visible. Is invisible level.

  Toner agglomerates that cannot be recovered even by discharge control and toner contamination mixed with paper dust generated from the recording medium P are discharged by cleaning control using a cleaning sheet (cleaning recording medium).

  FIG. 4 is a diagram showing the cleaning paper CP1 (cleaning recording medium) used in the present embodiment.

  As shown in the drawing, the cleaning sheet CP1 is preliminarily fixed with toner (cleaning image) having a circumferential length L2 × longitudinal width L1 of the fixing film 22 or the pressure roller 24. The cleaning sheet CP1 is set in the sheet feeding cassette 5 so that the toner surface is conveyed to the member to be cleaned, and the cleaning operation is started.

  FIG. 5 is a diagram schematically showing a cross section of the fixing unit during the cleaning control.

  In the cleaning control, the rotation driving is stopped while the temperature of the temperature-controlled air rotation is carried out so that the toner fixing portion of the cleaning sheet CP1 is located at the nip position, and the stop heating is performed similarly to the discharge control. Due to the stop heating, the toner stain in the nip is melted and integrated with the toner on the cleaning paper CP1.

  When the fixing film 22 and the pressure roller 24 are advanced by the nip width (rotated by a predetermined amount) after cooling for a predetermined time after the stop heating, the toner stain is collected on the cleaning paper side.

  When the cleaning of the nip A portion of the fixing film 22 shown in FIG. 5 is completed, the nip B portion is cleaned. This is repeated sequentially, and is performed on the entire circumference in the circumferential direction of the fixing film 22 or the pressure roller 24, thereby cleaning the adhered toner stains.

  In the cleaning operation of the fixing device 11, the cause of the film recess is that there is a difference between the film surface temperature T 1 in the fixing nip N and the film surface temperature T 2 other than the nip portion.

  Therefore, in the present embodiment, the film surface temperature T1 and the film surface temperature T2 are accurately detected, and the control is changed when the detected temperature difference becomes a predetermined value or more. Specifically, the film surface temperature T1 is measured with a thermistor 25 installed behind the fixing nip N, and the film surface temperature T2 is measured with an infrared thermometer 50 (second temperature measuring means) installed outside the nip. Calculate the difference.

  Details of the cleaning operation of the present embodiment will be described.

  FIG. 6 is a diagram showing a temperature transition at the time of cleaning control for countermeasures against film dents.

  1) The film surface temperature T1 is measured by the thermistor 25 during the cleaning control. In the example of FIG.

  2) The film surface temperature T2 is measured with an infrared thermometer 50. In the example of FIG.

  3) The temperature difference (X in FIG. 6) between the film surface temperature T1 and the film surface temperature T2 is calculated. In the example of FIG. 6, it is 180-100 = 80 degreeC.

  4) When the temperature difference (X in FIG. 6) is equal to or greater than a predetermined temperature difference (80 ° C. in the present embodiment), the cleaning control is temporarily stopped and the temperature control idle rotation is started. The film surface temperature T1 becomes 180 ° C. and the film surface temperature T2 becomes 170 ° C. due to the temperature controlled idling. Since the temperature difference on the film surface at this time is less than 80 ° C., permission to resume the cleaning control is issued.

  5) The cleaning control is temporarily stopped in 4), and at the same time when the temperature-controlled idling rotation is started, the cleaning sheet is conveyed out of the nip and is automatically or manually set on the sheet feeding means.

  6) The position at which the cleaning is interrupted is calculated from the elapsed time from the point of time when shifting to the temperature controlled idling rotation in 4) and the rotation speed of the fixing motor drive.

  7) The temperature difference between the film surface temperatures T1 and T2 becomes less than a predetermined value due to the temperature-controlled idle rotation of 4), the cleaning restart permission is given, and the cleaning paper CP1 is set in the paper feeding means. Check. When these are confirmed, a portion adjacent to the portion where the pressure roller 24 is located in the fixing nip portion N comes to the fixing nip portion N before the temperature-controlled air rotation. Then, the timing is adjusted so that the cleaning image of the cleaning paper CP1 comes to the fixing nip N, and the paper feeding and cleaning control is resumed. The temperature difference between the film surface temperature T1 in the nip and the film surface temperature T2 outside the nip is reduced by the temperature-controlled idle rotation, and the thermal stress is reduced.

  In this state, even when the cleaning control is stopped for a predetermined time (heater ON, motor OFF), cooled for a predetermined time, and then pulled downstream by the pressure roller as a rotation drive source, Therefore, the cleaning control can be continued. In addition, even after the cleaning is stopped, the cleaning can be completed because the operation is resumed from the position where the rotation is interrupted from the rotation speed and the elapsed time.

  FIG. 7 is a diagram illustrating the state of the fixing film 22 when the control is changed.

  FIG. 7A is a diagram illustrating a state of the nip portion during the cleaning control. Immediately after the start of cleaning control, the temperature of the film surface indicated by the dotted line in FIG. 7 (a) is as follows. It gradually decreases. On the other hand, since the heater is heated in the nip portion between the fixing film and the pressure roller indicated by the solid line portion of the film and in the vicinity of the upstream and downstream of the nip, thermal expansion occurs. Therefore, in the latter half of the cleaning control, thermal stress is applied due to the occurrence of a portion that thermally expands in the circumferential direction of the fixing film and a portion that does not thermally expand (location where thermal stress is applied in FIG. 7A).

  FIG. 7B shows a state in which the temperature difference between the film surface temperature T1 in the nip and the film surface temperature T2 outside the nip is determined to be equal to or greater than a predetermined value during the stop heating of the cleaning control, and the state is shifted to the temperature-controlled air rotation. FIG. In the state of FIG. 7B, the entire circumferential direction of the fixing film is warmed by the temperature-controlled idle rotation. Since the whole is in a heated state, the temperature difference between the film surface temperature T1 in the nip and the film surface temperature T2 outside the nip is reduced, and the thermal stress is reduced. For this reason, stop heating is performed again by cleaning control (heater ON, motor OFF), and even if the film is pulled downstream in the rotational direction by a pressure roller, which is a rotational drive source, printing does not occur with no film depression. Can be implemented.

  FIG. 8 is a block diagram of the image forming apparatus of this embodiment.

  As shown in FIG. 8, the image forming apparatus includes a fixing device 11, a current / voltage supply unit 400, a pressure roller drive control unit 300, an image process unit 200, an operation unit 100, an optical unit 600, and a control unit 700. ing.

The control unit 700 includes a CPU (Central Processing Unit) 701, an I / F (interface) unit 702, a RAM (Random Access Memory) 703, and a ROM (Read Only Memory) 704.
The operation unit 100 outputs an operation instruction from the outside to the CPU 701 of the control unit 700.

  Under the control of the CPU 701, the image process unit 200 forms a toner image based on image data output from the scanner unit or image data from a host computer (not shown), and the formed toner image is supplied from the paper feed cassette 5. Is transferred to a recording medium P.

  The pressure roller drive control unit 300 drives the pressure roller 24 under the control of the CPU 701.

  A pattern in which an AC voltage is supplied to the heating resistor 26 is controlled by the CPU 701 from print information obtained from the operation unit 100 and a host computer (not shown) so that the heater 23 generates heat. In the energization pattern for individually controlling energization, nine half waves are used as one block pattern, and in the case of 50 Hz, since one half wave is 10 msec, the electrodes are switched every 10 msec. In addition, the method of individually controlling is not limited.

  During the cleaning control, the CPU 701 detects the film surface temperature T1 in the nip from the output of the thermistor 25, detects the film surface temperature T2 in the nip with the infrared thermometer 50, and determines the temperature difference between the film surface temperature T1 and the film surface temperature T2. calculate. Further, the CPU 701 determines whether or not the temperature difference is within a predetermined value. If the temperature difference is larger than the predetermined value, the CPU 701 temporarily stops the cleaning control and starts the temperature-controlled idling rotation. And it becomes possible to avoid the convexity which generate | occur | produces on the film surface by performing temperature control air rotation until a temperature difference becomes below a predetermined value.

  When the temperature difference becomes equal to or less than a predetermined value, the CPU 701 gives permission to resume cleaning control.

  The I / F unit 702 is a device for connecting the CPU 701 and a network such as a LAN, and is specifically realized by a LAN card, a LAN board, or the like. The I / F unit 702 receives an image formation execution instruction transmitted from the outside and outputs it to the CPU 701.

  The ROM 704 holds a program executed by the CPU 701 for controlling the image forming apparatus. Specifically, a pressure roller rotation control program 704a, a temperature control program 704b, a supply power control program 704c, a temperature difference calculation program 704d, a cleaning position calculation program 704e, and the like are held.

  Next, the operation of the image forming apparatus of this embodiment will be described.

  FIG. 9 is a flowchart showing the operation of the image forming apparatus of this embodiment. The following operations are executed under the control of the CPU 701.

  In the image forming apparatus in the standby state, when a cleaning command is received (step S101), the temperature-controlled idling rotation is started (step S102), and the cleaning operation is started. After reaching the target temperature (step S103), the cleaning paper is fed (step S104). After the leading edge of the cleaning image reaches the fixing nip (step S105), the heater is turned on, the motor is turned off, and stop heating (step S106) is performed (2 seconds in this embodiment). Next, the heater is turned off (step S107), and cooling is performed (3 seconds in this embodiment). After cooling for a predetermined time, measurement is performed using the film surface temperature T1 at the next nip position (outside the nip) (step S108). It is determined whether the difference between the next nip position and the temperature in the nip is less than a predetermined value (step S109).

  If the temperature difference between the next nip position and the nip is greater than or equal to a predetermined value, the cleaning sheet is conveyed out of the nip (step S110). Then, the cleaning control is temporarily stopped, and the temperature control idling rotation is started (step S111). Next, the time elapsed count from the time when the temperature controlled idling rotation is started is started (step S112). Then, the temperature-controlled idling rotation is continued until the temperature difference between the next nip position and the nip becomes less than a predetermined value (step S113). When the temperature difference between the next nip position and the nip is less than a predetermined value, the position at which the cleaning is interrupted is calculated from the elapsed time from the start of the temperature controlled idling rotation and the rotation speed of the fixing drive (cleaning position calculation program 704e, Step S114). If the cleaning paper is in the paper feed permission position, the cleaning paper is conveyed into the nip (step S115). When the cleaning sheet is conveyed into the nip and the cleaning image reaches the cleaning interruption position on the pressure roller, the conveyance is stopped (step S116), and the process proceeds to step S106.

  On the other hand, if the temperature difference between the next nip position and the nip is less than a predetermined value in step S109, it is determined whether cleaning has been performed on the entire circumference (step S117). If the cleaning has not been performed all around, the sheet is conveyed by the nip width (8 mm in this embodiment) (step S118), and the process proceeds to step S106.

  On the other hand, if the cleaning has been performed all around in step S117, the cleaning paper is discharged (step S119), and the temperature-controlled idling rotation is terminated (step S120). The cleaning control is terminated and the standby state is entered (step S121).

  By executing the above flow, it becomes possible to avoid the convexity generated on the film surface during the cleaning control, and the cleaning can be completed.

In this embodiment, when the cleaning that has been interrupted is restarted, the portion adjacent to the portion where the pressure roller 24 is located in the fixing nip portion N comes to the fixing nip portion N before the temperature controlled idling rotation. However, the present invention is not limited to this.
The area where the pressure roller 24 has not been cleaned may be brought to the fixing nip portion N, and the process may be repeated until the entire area of the pressure roller 24 is cleaned.
Second Embodiment
Next, another embodiment of the present invention will be described. In this embodiment, by detecting the rotation speed of the driving unit of the fixing device, it is possible to accurately determine the cleaning interruption position, and to perform film recess prevention and cleaning with high accuracy. Since the main body outline and the fixing configuration in this embodiment are the same as those in the first embodiment, they are omitted.

  FIG. 10 is a diagram showing a cleaning image on the cleaning paper used in the present embodiment.

  In the present embodiment, as shown in FIG. 10, a cleaning sheet CP2 (cleaning recording medium) on which a cleaning image is printed on the front surface and the back surface is set at a sheet feeding position.

  Next, details of the present embodiment will be described.

  FIG. 11 is a graph showing a temperature transition during film dent countermeasure control according to the present embodiment.

  FIG. 12 is a cross-sectional view showing the configuration of the image forming apparatus of this embodiment.

    1) The film surface temperature T1 is measured by the thermistor 25 during the cleaning control. In the example of FIG.

  2) The film surface temperature T2 is measured with an infrared thermometer 50. In the example of FIG.

  3) The temperature difference (X in FIG. 11) between the film surface temperature T1 and the film surface temperature T2 is calculated. In the example of FIG. 11, 180−100 = 80 ° C.

4) When the temperature difference (X in FIG. 11) is a predetermined temperature difference (80 ° C. in this embodiment) or more,
The cleaning control is temporarily stopped, and the temperature control idle rotation is started. The film surface temperature T1 becomes 180 ° C. and the film surface temperature T2 becomes 170 ° C. due to the temperature controlled idling. Since the temperature difference on the film surface at this time is less than 80 ° C., permission to resume the cleaning control is issued.

  5) The cleaning control is temporarily stopped in 4), and at the same time when the temperature control and the idling rotation are started, the cleaning paper is conveyed out of the nip, conveyed to the reverse conveyance path 15 shown in FIG. 12, and the cleaning paper CP2 is reversed, It waits at the registration roller 7 shown in FIG.

  6) The position at which the cleaning is interrupted is calculated from the rotation speed of the fixing motor drive from the time when the rotation speed measurement member 70 (rotation speed measuring means) shifts to the temperature-controlled air rotation in 4) (Z in FIG. 11). From the time).

  7) Confirm that the temperature difference between the film surface temperatures T1 and T2 is less than the predetermined value due to the temperature controlled idling rotation of 4), that the cleaning restart permission has been issued, and that the cleaning paper is waiting on the paper feeding means. To do. When these are confirmed, the timing is adjusted so that the cleaning image of the cleaning paper comes to the position where the cleaning is interrupted, and the paper feeding and cleaning control is resumed.

  The temperature difference between the film surface temperature T1 in the nip and the film surface temperature T2 outside the nip is reduced by the temperature-controlled idle rotation, and the thermal stress is reduced.

  In this state, the heating of the cleaning control is stopped for a predetermined time (heater ON, motor OFF), the cooling is performed for a predetermined time, and even if the film is depressed by the pressure roller as a rotation driving source downstream in the rotation direction. Therefore, the cleaning control can be continued. Even after cleaning is stopped, the number of rotations is detected, the interrupted position is accurately determined and restarted, so that cleaning can be completed and dirt can be accurately removed.

FIG. 13 is a block diagram of this embodiment.
As shown in FIG. 13, the image forming apparatus includes a fixing device 11, a current / voltage supply unit 400, a pressure roller drive control unit 300, an image process unit 200, an operation unit 100, an optical unit 600, and a control unit 700. ing.

  The control unit 700 includes a CPU (Central Processing Unit) 701, an I / F (interface) unit 702, a RAM (Random Access Memory) 703, and a ROM (Read Only Memory) 704. The operation unit 100 outputs an operation instruction from the outside to the CPU 701 of the control unit 700.

  Under the control of the CPU 701, the image process unit 200 forms a toner image based on image data output from the scanner unit or image data from a host computer (not shown), and the formed toner image is supplied from the paper feed cassette 5. Is transferred to a recording medium P.

  The pressure roller drive control unit 300 drives the pressure roller 24 under the control of the CPU 701.

  A pattern in which an AC voltage is supplied to the heating resistor 26 is controlled by the CPU 701 from print information obtained from the operation unit 100 and a host computer (not shown) so that the heater 23 generates heat. In the energization pattern for individually controlling energization, nine half waves are used as one block pattern, and in the case of 50 Hz, since one half wave is 10 msec, the electrodes are switched every 10 msec. In addition, the method of individually controlling is not limited.

  During the cleaning control, the CPU 701 detects the film surface temperature T1 in the nip from the output of the thermistor 25, detects the film surface temperature T2 in the nip with the non-contact thermometer 50, and the temperature difference between the film surface temperature T1 and the film surface temperature T2 is detected. Is calculated. Further, the CPU 701 determines whether or not the temperature difference is within a predetermined value. If the temperature difference is larger than the predetermined value, the CPU 701 temporarily stops the cleaning control and starts the temperature-controlled idling rotation. And it becomes possible to avoid the convexity which generate | occur | produces on the film surface by performing temperature control air rotation until a temperature difference becomes below a predetermined value.

  When the temperature difference becomes equal to or less than a predetermined value, the CPU 701 gives permission to resume cleaning control.

  The I / F unit 702 is a device for connecting the CPU 701 and a network such as a LAN, and is specifically realized by a LAN card, a LAN board, or the like. The I / F unit 702 receives an image formation execution instruction transmitted from the outside and outputs it to the CPU 701.

  Further, the CPU 701 detects the number of rotations of the pressure roller 24 by the rotation number measurement member 70 provided on the pressure roller 24 and calculates the travel distance from a predetermined timing, whereby the nip position of the pressure roller 24 is calculated. Can be stopped at any position.

  The ROM 704 holds a program executed by the CPU 701 for controlling the image forming apparatus. Specifically, a pressure roller rotation control program 704a, a temperature control program 704b, a supply power control program 704c, a temperature difference calculation program 704d, a cleaning position calculation program 704e, and the like are held.

  Next, the operation of the image forming apparatus of this embodiment will be described.

  FIG. 14 is a flowchart showing the operation of the present embodiment. The following operations are executed under the control of the CPU 701.

  In the image forming apparatus in the standby state, when a cleaning command is received (step S201), temperature-controlled idling rotation is started (step S202), and a cleaning operation is started. After reaching the target temperature (step S203), the cleaning paper is fed (step S204). After the leading edge of the cleaning image reaches the fixing nip (step S205), the heater is turned on, the motor is turned off, and stop heating (step S206) is performed (in this embodiment, 2 seconds). Next, the heater is turned off (step S207), and cooling is performed (3 seconds in this embodiment). After cooling for a predetermined time, measurement is performed using the film surface temperature T1 at the next nip position (outside the nip) (step S208). It is determined whether the difference between the next nip position and the temperature in the nip is less than a predetermined value (step S209).

  If the temperature difference between the next nip position and the nip is greater than or equal to a predetermined value, the cleaning paper is conveyed out of the nip and retracted to the double-sided path by switchback (step S210). Then, the cleaning control is temporarily stopped, and the temperature controlled idling rotation is started (step S211). Next, the rotational speed detection of the drive means from the time when the temperature-controlled air rotation is started is started (step S212). Then, the temperature-controlled idling rotation is continued until the temperature difference between the next nip position and the nip becomes less than a predetermined value (step S213). When the temperature difference between the next nip position and the nip is less than a predetermined value, the position where the cleaning is interrupted is calculated from the rotational speed of the driving means from the start of the temperature controlled idling rotation (cleaning position calculation program 704e, step S214). If the cleaning paper is in the paper feed permission position, the cleaning paper is conveyed into the nip (step S215). When the cleaning sheet is conveyed into the nip and the cleaning image reaches the cleaning interruption position on the pressure roller, the conveyance is stopped (step S216), and the process proceeds to step S206.

  On the other hand, if the temperature difference between the next nip position and the nip is less than a predetermined value in step S209, it is determined whether cleaning has been performed on the entire circumference (step S217). If the cleaning has not been performed all around, the sheet is conveyed by the nip width (8 mm in this embodiment) (step S218), and the process proceeds to step S206.

  On the other hand, if the cleaning has been performed all around in step S217, the cleaning paper is discharged (step S219), and the temperature-controlled idling rotation is terminated (step S220). The cleaning control is terminated and the standby state is entered (step S221).

  By executing the above flow, it becomes possible to avoid the convexity generated on the film surface during the cleaning control, and the cleaning can be completed.

  The rotational speed detection member of the driving means used in the present embodiment includes a reflection type photo sensor, a home position sensor, a motor electromotive force detection sensor, and the like. It doesn't matter.

DESCRIPTION OF SYMBOLS 11 ... Fixing device 22 ... Fixing film 23 ... Heater 24 ... Pressure roller 25 ... Thermistor 26 ... Heating resistor 50 ... Infrared thermometer 60 ... Cleaning paper 70 ... Rotation speed detection member P ... Recording medium

Claims (9)

A fixing device for fixing an unfixed toner image on a recording medium,
A heating element;
A rotatable heat transfer member for transferring heat of the heating element to a recording medium;
A rotatable pressing member that forms a nip portion capable of sandwiching the recording medium with the heat transfer member;
A temperature difference detecting means for detecting a temperature difference between the inside and the outside of the nip portion;
Have
When the heat transfer member and the pressing member are stationary, heating is performed by the heating element, and when the heat transfer member and the pressing member are rotating, the heating element is heated. When the temperature difference between the inside and outside of the nip portion is equal to or greater than a predetermined value, the heating at the time of rotation is performed until the temperature difference becomes less than the predetermined value. Then, the fixing device is characterized in that the portion of the pressing member that has not been heated at rest is positioned at the nip portion, the rotation of the pressing member is stopped, and the heating at rest is performed.   The fixing device according to claim 1, wherein the cleaning is performed by sandwiching a cleaning recording medium on which a cleaning image is formed in the nip portion.   The fixing device according to claim 2, wherein the cleaning recording medium is retracted to a position other than the nip portion when the rotation heating is started.   When the temperature difference becomes less than the predetermined value after performing the heating at the time of rotation, the cleaning recording medium retracted to a position other than the nip portion is conveyed again to the nip portion. The fixing device according to claim 3.   5. The heat generation of the heating element is adjusted based on the detection result of the temperature difference detection means during the execution of the heating at the time of rotation. 6. Fixing device. Further comprising drive means for rotating the pressing member;
Based on the rotational speed of the driving means and the elapsed time since the heating during rotation, a portion adjacent to the portion of the pressing member located in the nip portion before the heating during rotation is the nip portion. 6. The fixing device according to claim 1, wherein the rotation of the pressing member is stopped so as to be positioned in the fixing device. Driving means for rotating the pressing member;
A rotation speed measuring means for measuring the rotation speed of the drive means; and
Based on the rotation speed of the rotation speed measuring means, the rotation of the pressing member is stopped so that a portion adjacent to the pressing member positioned in the nip portion is positioned in the nip portion before the heating during rotation. The fixing device according to claim 1, wherein the fixing device is a fixing device. Image forming means for forming a toner image on the recording medium;
An image forming apparatus comprising: the fixing device according to claim 1, which fixes the toner image formed by the image forming unit. Image forming means for forming a toner image on the recording medium;
The fixing device according to any one of claims 2 to 4, wherein the toner image formed by the image forming unit is fixed.
A reversing conveyance path for reversing and conveying the recording medium in order to form images on both sides of the recording medium;
The cleaning recording medium has a cleaning image formed on both sides,
When shifting to the heating at the time of rotation, the cleaning recording medium is conveyed to the reverse conveying path, the rotation of the pressing member is stopped, and the heating of the heating element is performed while the rotation of the pressing member is stopped. When the temperature difference becomes less than the predetermined value, the reversed recording medium for cleaning is conveyed again to the nip portion.

Images