JP2008040420A - Image heating device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To achieve both registance to noise due to a stick slip of a belt and durability in a belt heating type image heating device. <P>SOLUTION: The image heating device which has an endless belt 12 for heating an image (t) on a recording material P, a nip forming member 18 forming a heating nip N with the belt, a slide member 13 provided slidably on the belt as the belt rotates, a detecting means 26 of detecting the peripheral speed of the belt, and a control means 100 of controlling the peripheral speed of the belt at least during image heating processing to a set speed according to the output of the detecting means, and can execute a mode wherein the belt can be rotated at a set speed slower than that in the image heating processing for a set time in non-image-heating-processing without performing the speed control by the control means is characterized in that the set speed of the belt in this mode is increased when the peripheral speed of the belt detected in the mode decreases below the set speed. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention is used in an image forming apparatus such as a copying machine, an LBP, a facsimile, a microfilm reader printer, a display device, and a recording machine that employs an image forming process means such as electrophotography, electrostatic recording, and magnetic recording. The present invention relates to an image heating apparatus for heating an image on a material.

  Examples of the image heating device include a fixing device that fixes an unfixed image on the recording material, and a gloss increasing device that increases the gloss of the image by heating the image fixed on the recording material. it can.

  In the image forming apparatus as described above, there is a belt (film) heating type image heating apparatus as one of practical apparatuses of a fixing apparatus for fixing an unfixed image formed on a recording material. This image heating device is provided with an endless belt for heating an image on a recording material, a nip forming member for forming a heating nip with the belt, and a belt slidable as the belt rotates. And a sliding member.

  More specifically, it has a fixedly supported heating body, an endless belt that is conveyed while being in close contact with the heating body, and a pressure body that causes the recording material to be in close contact with the heating body via the belt. . The apparatus heats the image on the recording material by applying heat from the heating body to the recording material via a belt.

  Such a belt heating type apparatus can use a low heat capacity heating element or a thin film belt that is rapidly heated. Therefore, it has advantages such as power saving and shortening of the wait time (quick start property), and lowering the temperature rise in the apparatus such as an image forming apparatus, which is effective. .

  However, in a low temperature environment, fixing performance may be insufficient when performing a quick start. Therefore, in order to ensure fixability in a low-temperature environment, the belt is heated while it is heated for a certain period of time before the recording material is transported, and the recording material transport is started while the pressure roller, belt, etc. are sufficiently warmed. A mode (pre-rotation mode) is provided.

  Further, such a belt heating type fixing device has a very small heat capacity compared to other fixing devices such as a heat roller type. For this reason, when a small-size recording material (a recording material having a narrow width in the direction perpendicular to the conveyance direction) is continuously fed, the temperature of the non-sheet passing portion is likely to increase, and paper wrinkles, curls, Such problems may occur. Therefore, when the non-sheet passing portion temperature rises during continuous feeding of small size recording materials, the sheet passing is temporarily stopped and the belt is rotated for a certain time to correct the non-sheet passing portion temperature rise. May have a mode (post-rotation mode). Further, there is a case where a mode (post-rotation mode) for correcting the temperature rise of the non-sheet passing portion by rotating the belt for a certain time after the job is completed may be provided.

  In these pre-rotation mode and post-rotation mode, since the rotation time is more important than the rotation speed of the belt, in many cases, it is rotated at the lowest possible speed from the viewpoint of belt durability (rather than the process speed). Slow enough).

Patent Document 1 discloses that the belt is rotated in a temperature-controlled state for a certain period of time before the recording material is conveyed in order to ensure fixability at a low temperature. This makes it possible to ensure the fixability even in a low temperature environment, and the belt travel distance can be shortened.
JP 2000-075584 A

  However, as the durability progresses, the rotational resistance of the belt increases due to the deterioration of grease on the inner surface of the belt and the progress of shaving of the inner surface of the belt. If it does so, stick slip may generate | occur | produce between a belt and the heating body (heater surface etc.) to which the belt is pressurized (contact | adhered). In particular, the slower the rotation speed of the belt, the more likely it becomes stick-slip, which may become a problem due to abnormal noise.

  In order to avoid this, it is conceivable to set the belt rotation speed in the pre-rotation mode and the post-rotation mode in advance so that stick slip does not occur. However, in this case, even in a situation where durability has not progressed so much, that is, when there is no concern about stick slip, the uniform rotation speed is increased, so the mileage of the belt extends more than necessary, This will affect the durability of the belt.

  The present invention has been made in view of such technical problems. The purpose of the image heating apparatus of the belt heating method is to make it possible to achieve both noise countermeasures and durability performance due to stick-slip of the belt.

  In order to achieve the above object, a typical configuration of an image heating apparatus according to the present invention includes an endless belt for heating an image on a recording material, and a nip forming member for forming a heating nip between the belt. A sliding member provided slidably with the belt as the belt rotates, a detecting means for detecting the peripheral speed of the belt, and at least the peripheral speed of the belt during image heating processing according to the output of the detecting means And a control means for controlling the belt so as to become a set speed, and the belt is rotated at a set speed slower than that during the image heating process during the non-image heating process without performing the speed control by the control means. In the image heating apparatus capable of executing the mode, the belt setting speed in this mode is changed to a higher speed when the belt peripheral speed detected in this mode falls below the setting speed. To.

  Another typical configuration of the image heating apparatus according to the present invention for achieving the above object is to form a heating nip between an endless belt for heating an image on a recording material and the belt. And a slidable member that is slidable with the belt as the belt rotates, and the belt is set at a slower setting speed during the non-image heating process than during the image heating process. In the image heating apparatus capable of executing the rotation mode, the set speed in the latter half of use of the belt in this mode is set to be higher than the set speed in the initial use of the belt.

  According to the present invention, it is possible to achieve both noise countermeasures due to stick-slip of the belt and durability.

(1) Schematic Configuration of Example Image Forming Apparatus FIG. 1 is a schematic configuration diagram of an example image forming apparatus in which an image heating apparatus according to the present invention is mounted as a fixing device. The image forming apparatus of this example is a multifunctional image forming apparatus using a transfer type electrophotographic process, which includes an image reading scanner unit.

  The image forming apparatus main body A has an image reading scanner unit B as an image reading unit for reading image information of a document at the upper part, an image forming unit C as an image forming unit at the lower part, and further at the lower part. The seat deck D is assembled.

a) Image reading scanner section B
Reference numeral 202 denotes a platen glass fixed in a horizontal position, on which a book document, a cardboard sheet, a book document or a sheet-like document is placed according to a predetermined placement standard with an image surface to be read downward. Then, the back side is pressed by the original platen 203 and set in a stationary state.

  When the reading start key is pressed, the scanning unit including the scanning light source 201 and the scanning mirror 204 disposed on the lower surface side of the glass 202 moves from the home position indicated by the solid line on the left side of the glass to the right side along the lower surface of the glass. It is driven forward at a predetermined speed in the direction of arrow a.

  As a result, the downward image surface of the document placed and set on the glass 202 is sequentially illuminated and scanned from the left side to the right side. Then, the original surface reflected light of the illumination scanning light enters the light receiving element (photoelectric conversion element) 206 through the lens 205 and is photoelectrically read, processed by the image processing unit, converted into an image information electrical signal, and the image forming unit. It is transmitted to the C laser scanner 111.

  When the moved scanning units 201 and 204 move to a predetermined forward movement end point, the scanning units 201 and 204 return to the initial home position.

b) Image forming unit C
FIG. 2 is an enlarged view of a main part of the image forming unit C. 1 and 2, reference numeral 112 denotes a rotating drum type electrophotographic photosensitive member (hereinafter referred to as a drum) as an image carrier. The drum 112 is rotationally driven at a predetermined peripheral speed (process speed) in the clockwise direction of the arrow. In the rotation process, the drum 112 is subjected to a uniform charging process with a predetermined polarity and potential by the charger 122, and laser beam scanning exposure corresponding to image information from the laser scanner 111 and the image writing optical system 113 is performed on the uniformly charged surface. Receive b. Thereby, an electrostatic latent image corresponding to the scanning exposure pattern is formed on the drum surface.

  The electrostatic latent image formed on the drum surface is developed as a toner image by the developing device 114. In the transfer nip portion T where the toner image is a contact portion between the drum 112 and the transfer charging roller 115, the recording material P fed to the transfer nip portion T at a predetermined control timing from a paper feed portion side described later. (Hereinafter referred to as “paper”).

  The paper P that has received the transfer of the toner image through the transfer nip T is sequentially separated from the drum surface, and is conveyed to the fixing device 118 through the conveyance guide unit 117. The paper P is heated and pressurized in the process of being nipped and conveyed by the fixing nip portion N of the fixing device 118 and undergoes a fixing process for an unfixed toner image.

  On the other hand, the drum surface after paper separation is subjected to a removal process of residual adhered contaminants such as transfer residual toner by a cleaning device 123 and subjected to a charge removal process by an eraser lamp 124 and the like, and is repeatedly used for image formation.

  In the single-sided printing mode, the paper P that has passed through the fixing device 118 is discharged and stacked on a paper discharge tray (or sorter) 120 disposed outside the apparatus by a discharge roller 119.

  In the duplex printing mode, the sheet on which the image is formed on the first surface discharged from the fixing device 118 is sandwiched between the discharge rollers 119, and the discharge roller 119 is turned on when the trailing edge of the sheet passes the branch point 207. It reverses and is temporarily placed on the double-sided tray 121. Thereafter, the toner is transported by the transport rollers 104 and 105, reaches the registration roller 106, and is fed again to the transfer nip T at a predetermined control timing. As a result, an image is formed on the second surface of the reversed sheet in the same manner as described above, and then discharged and stacked on the discharge tray 120.

  The registration roller 106 is composed of a roller pair of a driving roller and a pinch roller that are in contact with each other. When the driving is stopped, the leading edge of the sheet fed from the sheet feeding unit at the pressure nip R of both the roller pairs is temporarily stored. In the received state, the sheet is held in a temporary standby state. It also has the function of correcting the skew of the paper. The sheet is fed to the transfer nip T by rotating the driving roller at a predetermined peripheral speed at a predetermined control timing. When the trailing edge of the sheet passes through the pressure nip portion R of the registration roller 106, the driving roller is stopped to receive the leading edge of the next sheet.

  22 and 23 are photo-interrupters as paper detection sensors, which are provided with flag portions (actuators) 24 and 25, respectively. The paper detection sensor 22 detects the arrival and passage of paper at the paper exit side position of the registration roller 106. The paper detection sensor 23 detects the arrival and passage of paper at the paper exit side position of the fixing device 118. The paper detection signals of the paper detection sensors 22 and 23 are input to the control circuit unit (CPU) 100 via the A / D converter 103 (FIG. 7), respectively. The control circuit unit 100 controls the image forming sequence based on the input signals from the paper detection sensors 22 and 23 and detects the occurrence of paper jam between the registration roller 106 and the fixing device 118.

  Here, the image forming apparatus main body A functions as a copying machine if the processing signal of the image processing section of the image reading scanner section B is input to the laser scanner 111 as described above. If an output signal from an external computer is input, it functions as a printer. Further, if a signal from another facsimile apparatus is received or a signal from the image processing section of the image reading scanner section B is transmitted to another facsimile apparatus, the apparatus functions as a facsimile apparatus. In FIG. 7, reference numeral 200 denotes an external device such as an external computer or another facsimile machine, which is connected to the control circuit unit 100 of the image forming apparatus main body A via an interface IF.

c) Seat deck D
A sheet cassette 1 is attached to the lower part of the image forming unit C. The sheet cassette 1 is configured as one feeding unit with two cassettes, a lower cassette 1a and an upper cassette 1b. In this example, two feeding units U1 and U2 are mounted, and four cassettes are mounted. One feeding unit U1 located at the upper side is detachably attached to the apparatus main body A, and the lower feeding unit U2 is detachably attached to the seat deck D. Then, one sheet of paper is automatically fed to the selected cassette.

  That is, the sheets stored in the cassettes 1a and 1b are fed out by the pickup roller 3 serving as a feeding rotating body, and separated and fed one by one by the cooperative action of the feed roller 4 and the retard roller 5. . Then, the sheet is conveyed by the conveying rollers 104 and 105, guided to the registration roller 106, and fed to the transfer nip T of the image forming unit C by the roller 106 in synchronization with the image forming operation.

  In addition to the paper cassette 1, a manual feed tray 6 is disposed on the side surface of the apparatus main body A, and the paper on the tray 6 is fed to the registration roller 106 by the manual paper feed roller 7.

(2) Fixing device 118
The fixing device 118 in this embodiment is basically a heating device of a belt heating method / pressure member driving method (tensionless type) disclosed in JP-A-4-44075 to 44083, 4-204980 to 204984, and the like. is there.

  In the following description, the longitudinal direction of the fixing device or the members constituting the fixing device is a direction parallel to the direction orthogonal to the recording material conveyance direction in the recording material (paper) conveyance path surface. Regarding the fixing device, the front is the surface on the recording material introduction side, and the left and right are the left or right when the device is viewed from the front. The width of the recording material is a recording material dimension in a direction orthogonal to the recording material conveyance direction on the recording material surface.

  3 is an enlarged cross-sectional model view of the main part of the fixing device 118, FIG. 4A is a front model view of the main part, and FIG.

  Reference numeral 10 denotes a fixing belt assembly (hereinafter referred to as an assembly), and 18 denotes an elastic pressure roller as a pressure rotator (nip forming member). A fixing nip portion (heating nip) N is formed by pressure contact between the assembly 10 and the pressure roller 18.

  In the assembly 31, reference numeral 12 denotes a heat-resistant belt having a cylindrical shape (sleeve shape) and having flexibility as an endless belt (heating rotating body) for heating an image on a recording material. Reference numeral 11 denotes a fixing stay (heater holding member / film guide member: hereinafter referred to as stay) made of heat-resistant resin having a substantially semicircular arc shape in cross section. Reference numeral 13 denotes a ceramic heater (sliding member: hereinafter referred to as a heater) as a heat source (heating body). The ceramic heater 13 is fitted on the outer surface of the stay 11 by being fitted into a recessed groove provided along the length of the stay. It is set up. The belt 12 is loosely fitted to the stay 11 to which the heater 13 is attached. Reference numeral 14 denotes a pressurizing member having a U-shaped rigidity, and is disposed inside the stay 11. Reference numeral 15 denotes an end holder that is fitted to the outward projecting arms 14 a at the left and right ends of the pressing member 14, and 15 a is a flange portion that is integral with the end holder 15.

  The belt 12 has a total thickness of about 40 to 100 μm in order to reduce the heat capacity and improve the quick start performance. A coating layer in which a conductive agent is added to a fluororesin such as PTFE / PFA on the outer periphery of a base layer composed of at least a heat-resistant material such as a polyimide film having heat resistance, releasability, strength, and durability. Is provided.

  The belt 12 in this example includes at least a base layer composed of polyimide or the like, a coating layer coated with a thin fluorine resin or the like on the outer periphery thereof, a primer layer provided between the base layer and the coating layer, 3 layers or more. The primer layer and the coating layer have conductive or semiconductive electrical characteristics, and the base layer has insulating electrical characteristics.

  The heater 13 in this embodiment is a horizontally long and thin plate-shaped heating body having a low heat capacity and having a direction perpendicular to the moving direction of the belt 12 as a longitudinal direction. The thin plate-shaped ceramic substrate and the surface of the substrate along the length. This is a member having a low heat capacity as a whole, with the formed resistance heating element as a basic component. The electric power is supplied to the resistance heating element to quickly generate heat and temperature, and the temperature is controlled to a predetermined fixing temperature by a temperature control system.

FIG. 5 is a schematic configuration diagram of an example of such a heater 13. 13a is a thin ceramic substrate as a heater substrate with high insulation and high thermal conductivity, and is made of ceramics such as alumina, aluminum nitride, silicon carbide. 13b is a layer of a resistance heating element such as Ag / Pd, RuO ₂ , Ta ₂ N, etc., which is applied to the surface side of the ceramic plate 13a along the length by screen printing or the like, and then fired. It is formed. Reference numeral 13c denotes a power supply electrode portion such as Ag / Pt for the resistance heating element layer 13b, which is electrically connected to both ends of the resistance heating element layer 13b and formed on the ceramic plate surface. Reference numeral 13d denotes an insulating protective layer formed on the surface side of the ceramic plate 13a, which covers the resistance heating element layer 13b and a part of the feeding electrode portion 13c. This insulating protective layer 13d electrically insulates and protects the resistance heating element layer 13b and a part of the feeding electrode portion 13c, and can withstand sliding against the inner surface of the belt. It is a fluorine coat layer. TH1 and TH2 are a main thermistor and a sub thermistor as first and second temperature detecting means provided on the back side of the ceramic plate 13a. L13b is a full length area of the resistance heating element layer 13b, and the full length area L13b of the resistance heating element layer 13b generates heat by being fed between the feeding electrode portions 13c and 13c. That is, the full length region L13b of the resistance heating element layer 13b is an effective heat generation length region of the heater 13.

  The heater 13 is fitted into the heater fitting groove formed along the length of the lower surface of the stay 11 with the heater surface side (the surface side on which the insulating protective layer 13d is formed) facing outside and bonded with a heat resistant adhesive. It is held.

  The pressure roller 18 includes a core shaft 18a made of aluminum, iron, stainless steel, a roller portion 18b made of a heat-resistant rubber elastic body having good releasability such as silicon rubber, and a surface on which a fluororesin is dispersed. It consists of a coat layer 18c. The surface coat layer 18c is provided for reasons such as transportability of the paper P and belt 12 and prevention of toner contamination.

  The pressure roller 18 is disposed such that the left and right end portions of the cored bar 18 a are rotatably supported by bearings between the left and right side plates 16 </ b> L and 16 </ b> R of the apparatus frame 16 via a bearing member 17.

  The assembly 10 is arranged in parallel with the pressure roller 18 with the heater 13 side facing. The left and right end holders 15 are each urged in the axial direction of the pressure roller 18 with a predetermined force by the pressure spring 19. Thereby, the surface of the heater 13 is brought into pressure contact with the pressure roller 18 through the belt 12 against the elasticity of the elastic layer 18b, and is necessary for heat fixing between the belt 12 and the pressure roller 18. A fixing nip () N having a predetermined width is formed in the paper conveyance direction c. Reference numerals 20 and 21 denote entrance guides and exit guides assembled to the apparatus frame 16.

  G is a drive gear fixed to one end of the cored bar 18 a of the pressure roller 18. When the rotational force of the fixing motor M is transmitted to the gear G via a power transmission mechanism (not shown), the pressure roller 18 is rotationally driven in the clockwise direction of the arrow in FIG. Due to the rotational drive of the pressure roller 18, a rotational force acts on the belt 12 by the frictional force at the fixing nip N between the pressure roller 18 and the outer surface of the belt 12. As a result, the belt 12 rotates around the stay 11 in the counterclockwise direction indicated by the arrow while the inner surface of the belt 12 is in close contact with the heater 13 in the fixing nip N and slides. The belt 12 rotates at a speed substantially corresponding to the rotation speed of the pressure roller 18. The left and right flange portions 15a serve to receive the belt end on the near side and restrict the movement when the rotating belt 12 moves to the left or right side along the length of the stay 11. Grease (lubricant) is applied to the inner surface of the belt 12 to ensure the slidability of the belt 12 with respect to the heater 13 and the stay 11.

  The recording material P introduced into the fixing nip N is nipped and conveyed by the rotation of the pressure roller 18 and the belt 12. In this embodiment, the recording material P is conveyed by the so-called central reference conveyance centered on the recording material. That is, the recording material width direction central portion passes through the longitudinal center portion of the belt 12 for recording materials of any width that can be used in the apparatus. S is the reference line (virtual line) of the center of the recording material.

  WP1 is a sheet passing area width of the maximum width sheet (maximum size sheet) that can be used in the apparatus. WP2 is a sheet passing area width of a sheet (small size sheet) having a width smaller than the maximum size sheet. WP3 is a non-sheet passing portion width (a difference between the maximum size sheet passing area width WP1 and the small size sheet passing area width WP2) generated when a small size sheet is passed. The resistance heating element layer full length region L13b, which is the effective heat generation length region of the heater 13, is the same as or slightly larger than the width of the maximum size sheet.

  The main thermistor TH1 is arranged in contact with the back surface of the heater at a substantially central position of the effective heat generation length region L13b of the heater 13 so as to detect the temperature of the heater portion where the paper of any size is passed. It is set up. The sub-thermistor TH2 detects the temperature of the heater portion corresponding to the non-sheet passing portion when the small-size sheet is passed, and is at the end position of the effective heat generation length region L13b of the heater 13 with respect to the heater back surface. They are arranged in contact with each other. The sub-thermistor TH2 can also be configured to be disposed in elastic contact with the inner surface of the belt 12 so as to detect the temperature of the film portion corresponding to the non-sheet passing portion.

  When the heater 13 is energized to the resistance heating element layer 13b from the fixing heater driving circuit 102 (FIG. 7) as the power supply unit, the energized heat generation layer 13b generates heat, and the heater 13 has an effective heat generation length. The temperature rises rapidly in the entire region L13b. The heater temperature is detected by the main thermistor TH 1 and the sub-thermistor TH 2, and electrical information related to the heater temperature is input to the control circuit unit 100 via the A / D converter 103. The control circuit unit 100 determines the temperature control content of the heater 13 based on the outputs of the main thermistor TH1 and the sub-thermistor TH2, and controls the energization from the heater drive circuit 101 to the heater 13.

  Thus, the control circuit unit 100 controls the fixing motor driving circuit 101 based on a predetermined control signal to start the rotational driving of the pressure roller 18. Further, the fixing heater driving circuit 102 is controlled to start heating up the heater 13. The stay 11 heats and holds the heater 13 and serves as a belt inner surface guide member. In a state where the rotation speed of the belt 12 becomes steady and the temperature of the heater 13 rises to a predetermined level, the sheet P carrying the unfixed toner image t on the fixing nip portion N is guided along the entrance guide 20 from the image forming portion side. Introduced. The toner image carrying surface side of the paper P faces the belt 12. The sheet P is brought into close contact with the heater 13 via the belt 12 in the fixing nip portion N and moves and passes through the fixing nip portion N together with the belt 12. In the moving and passing process, heat is applied to the paper P by the belt 12 heated by the heater 13, and the toner image t is heated and fixed on the paper surface. The paper P that has passed through the fixing nip N is separated from the surface of the belt 12 by the curvature, and is discharged and conveyed.

Further, a detecting means (belt rotational speed detecting means) for detecting the peripheral speed of the rotating belt 12 is provided. In this embodiment, as the detecting means, as shown in FIGS. 4A and 6, light from a peripheral belt portion is emitted to a part of the outer surface of the belt portion outside the maximum size paper passing area width WP1 of the belt 12. A reflective material (marking part) 12a having a high reflectance was coated. In addition, on the side of the belt end where the reflecting material 12a is formed, the reflective sensor 26 is disposed in a fixed position above the rotational locus position of the reflecting material 12a as the belt 12 rotates. The reflective material 12 a rotates with the rotation of the belt 12 and passes under the reflective sensor 26 once per rotation of the belt 12. The reflective sensor 26 detects reflected light from the reflective material 12 a every time the reflective material 12 a passes, and sends the detection signal to the control circuit unit 100 via the A / D converter 103. The control circuit unit 100 calculates the time required for the belt 12 to make one revolution from the input interval of the detection signal and the belt circumferential length, and detects the actual circumferential speed of the belt 12. The control circuit unit 100 controls the fixing motor drive circuit 101 so that at least the peripheral speed of the belt 12 at the time of image fixing processing (at the time of image heating processing) becomes a set speed in accordance with the output of the detecting means, that is, the detected peripheral speed. I have control.
18d is a member for cleaning the reflecting material 12a, and is provided in the pressure roller end region corresponding to the rotation locus position of the reflecting material 12a accompanying the rotation of the belt 12 in the roller circumferential direction.

(3) Pre-rotation mode of the fixing device 118 When the printing operation is performed in a low-temperature environment, the control circuit unit 100 before the sheet P carrying the unfixed toner t arrives at the fixing device 118 in order to ensure fixing performance. During the non-image heating process, a “pre-rotation mode” in which the belt 12 and the pressure roller 18 are preheated is executed. In this pre-rotation mode, the speed of the belt 12 is not controlled, and the belt 12 is rotated at a set speed that is slower than the time of image heating processing (at the time of paper nipping conveyance and printing) for a predetermined time.

  For example, when the temperature detected by the temperature detection unit of the fixing device is equal to or lower than a predetermined temperature (for example, 15 ° C. or lower), the control circuit unit 100 determines that the temperature is in a low temperature environment, Execute.

  In the pre-rotation mode, the power supply to the heater 13 is turned on, the fixing motor M is turned on, and the belt 12 is temperature-controlled at a predetermined rotation speed setting value for a predetermined time (for example, about 10 seconds), This is a control mode in which the belt 12 and the pressure roller 18 are preheated.

  In this pre-rotation mode, the sheet is not nipped and conveyed at the fixing nip portion N, so the belt rotation speed is set as low as possible in consideration of the durability of the belt 12. For example, the rotation speed value is set to 1/4 of the rotation speed setting value of the belt 12 during the image heating process.

  Then, after the pre-rotation mode is executed for a predetermined time (for example, about 10 seconds) and the belt 12 and the pressure roller 18 are sufficiently warmed, the conveyance of the sheet to the fixing device 118 is started.

  The control circuit unit 100 does not execute the pre-rotation mode unless it is in a low temperature environment.

(4) Post-rotation mode of the fixing device 118 During a printing operation in which small-size paper is continuously passed, the temperature rises in the non-sheet passing area WP3 of the fixing device 118 (edge temperature rise), causing various problems. cause. Based on the temperature detected by the sub-thermistor TH2 that detects the temperature rise at the end, the control circuit unit 100 sets a “reverse rotation mode” that corrects the temperature rise at the end when an end temperature rise above a certain level occurs. Execute. Also in the post-rotation mode, the belt 12 is rotated at a set speed slower than the time of image heating processing (at the time of paper nipping conveyance and printing) without controlling the speed of the belt 12 for a predetermined time.

  In the post-rotation mode, when the temperature of the non-sheet passing portion advances during continuous feeding of the small size recording material, the feeding is temporarily stopped and the belt 12 is kept for a predetermined time (for example, about 10 seconds) for a predetermined time. Rotate at the rotation speed setting value to correct the end temperature rise sufficiently. After the correction, the next paper is accepted. In addition, after the job is completed, the belt 12 is rotated at a predetermined rotational speed setting value for a predetermined fixed time (for example, about 10 seconds) to sufficiently correct the temperature rise at the end portion, and then the next job is accepted. is there.

  In the post-rotation mode, as in the case of the pre-rotation mode, the sheet is not nipped and conveyed by the fixing nip portion N. Therefore, considering the durability of the belt 12, the belt rotation speed is set as low as possible. The For example, the rotation speed value is set to 1/4 of the rotation speed setting value of the belt 12 during the image heating process.

  The post-rotation mode is executed following the image heating process, and the rotation of the belt 12 is stopped when the post-rotation mode ends.

(5) Belt rotation speed setting value change control in the front rotation mode and the rear rotation mode As described above, in the front rotation mode and the rear rotation mode, the rotation time of the belt 12 is more important than the rotation speed. Therefore, the belt is rotated at the slowest possible speed from the viewpoint of belt durability. That is, it is rotated at a speed sufficiently slower than the process speed. However, as the durability progresses, the rotational resistance of the belt increases due to the deterioration of grease on the inner surface of the belt and the progress of shaving of the inner surface of the belt. As a result, stick slip may occur between the belt 12 and the heater 13 and the stay 11 which are inner members that slide while the inner surface of the belt is in close contact. The stick slip is more likely to occur as the rotation speed of the belt is slower, and is particularly likely to occur when the rotation speed of the belt 12 is decelerated for post-rotation. In some cases, the stick-slip becomes a noise and causes a problem.

  Therefore, in order to prevent the occurrence of abnormal noise due to stick-slip even if the durability is advanced, in this embodiment, the occurrence of stick-slip in the front rotation mode and the rear rotation mode (or abnormal noise due to stick-slip occurs). Detectable status: the same applies hereinafter). When the occurrence of stick-slip is detected, set value change control for increasing the belt rotation speed set value in the pre-rotation mode and the post-rotation mode to a predetermined value is performed. The rotation mode is executed. As a result, even if the durability progresses, the occurrence of stick-slip of the belt is prevented in the front rotation mode and the rear rotation mode, and the generation of abnormal noise is prevented.

  In this embodiment, the belt peripheral speed detecting means 12a and 26 are used as means for detecting the occurrence of stick-slip of the belt. That is, the control circuit unit 100 detects the actual belt peripheral speed by the detecting means 12a and 26 when the fixing device 118 executes the pre-rotation mode and the post-rotation mode. Then, the detected peripheral speed value is compared with a predetermined determination value. If the detected peripheral speed value is less than or equal to the judgment value, it is judged that stick slip has occurred or is in a state where it is likely to occur, and the belt rotational speed setting value is changed during execution of the front rotation mode and the rear rotation mode. Then, reset the speed setting value faster than the original setting value. Then, the rotation speed of the fixing motor M is uniformly changed so as to meet the belt rotation speed reset value.

  The above-described determination value for determining that a stick-slip of the belt has occurred or is likely to occur in the pre-rotation mode or the post-rotation mode will be described.

  As described above, the belt heating type fixing device 118 has a configuration in which the belt 12 is driven to rotate by driving the pressure roller, so that the pressure roller 18 is heated in a low state and a high state. The thermal expansion state of the pressure roller changes. As a result, the rotation speed of the belt 12 changes. The amount of change in the rotational speed depends on the thickness of the rubber portion 18b of the pressure roller 18, but is approximately ± 1 to 2% at maximum. Further, in the case of a Φ24 belt, the speed change for the entire circumference of the belt is smaller and is about ± 0.5% at the maximum. On the other hand, stick slip is a phenomenon in which instantaneous belt rotation stops continuously, and the rotation speed becomes slow by at least 3.0% or more in one belt period.

  From the above, although depending on the rubber thickness of the pressure roller 18 and the thermal expansion coefficient of the rubber, the actual belt rotational speed detected by the belt peripheral speed detecting means 12a and 26 is approximately 3 with respect to a predetermined set value. When the speed is reduced by more than%, the above set value change control is executed. That is, [predetermined set value × 0.97] is set as a determination value, and it is determined that stick slip has occurred or is in a state where it is likely to occur when the actual measured value of the belt rotational speed is less than that. The new speed setting value is, for example, 10% UP of the old setting value. In this case, the rotation speed of the fixing motor M is increased by 10%.

  And by repeating the above set value change, when the belt rotation speed setting value at the time of execution of the pre-rotation mode and the post-rotation mode finally exceeds the belt rotation speed setting value at the time of image heating processing, It is determined that the belt 12 has reached the end of its life. In this case, the control circuit unit 100 displays an alarm display 130a on the operation unit 130 (FIG. 7) to prompt a serviceman call.

In the normal fixing process (at the time of image heating process), the control circuit unit 100 has a predetermined set value at which the rotational speed of the belt 12 detected by the belt peripheral speed detecting means 12a and 26 is a target speed. Feedback control is performed. Specifically, the rotational speed of the pressure roller 18 is increased or decreased, that is, the rotational speed of the fixing motor M is increased or decreased, so that the rotational speed of the belt is maintained at a predetermined set value.
On the other hand, as described above, the control circuit unit 100 does not perform feedback control of the rotational speed of the belt 12 during the pre-rotation mode or the post-rotation mode (non-image heating process). That is, the control circuit unit 100 does not perform feedback control such as increasing or decreasing the rotation speed of the pressure roller 12 according to the rotation speed of the belt 12 detected by the belt peripheral speed detection means 12a and 26.

  FIG. 8 is a flowchart of a specific control example for the pre-rotation mode.

  Steps S1 and S2: When the power of the image forming apparatus main body is turned on, the temperature is detected by a thermistor (for example, main thermistor TH1) in the fixing device, and the control circuit unit 100 picks up the data.

  Steps S3, S4, and S12: If the thermistor detection temperature T is 15 ° C. or lower, it is determined that the temperature is low and the pre-rotation mode for preheating the fixing device 118 is entered. When the detected temperature T is higher than 15 ° C., the process shifts to the normal print operation mode without the pre-rotation mode.

  Step S5: When the pre-rotation mode is entered, first, the heater 13 is turned on, and the heater temperature is raised to a predetermined level to adjust the temperature. At substantially the same time as the heater 13 is turned on, the fixing motor M is turned on, and the rotation of the film by the driving of the pressure roller 18 is started.

  The belt rotation speed setting value Va in the pre-rotation mode is set to an initial value of the 1/4 rotation speed (Va) when the belt rotation speed setting value at the time of image heating processing (at the time of paper nipping conveyance and lint execution) is V. = 1 / 4V).

  Steps S6 and S7: One second after the start of driving when the rotation of the fixing motor M is stabilized, the belt rotational speed is measured by the belt peripheral speed detecting means 12a and 26 to determine the actual belt rotational speed.

  Step S8: The belt rotation speed measurement value Vx is compared with a predetermined stick-slip determination value Vy. The determination value Vy is set to [Va × 0.97] (speed value obtained by reducing the belt rotation speed setting value Va by 3%).

  Steps S9, S10, and S11: If the measured value Vx is larger than the determination value Vy in step S8, it is determined that stick slip has not occurred, and the determination value Vy is deferred. Then, as long as the time A after entering the pre-rotation mode in step S4 does not pass 10 seconds, the steps of measuring the belt rotation speed, judging the belt rotation speed, and comparing with the determination value Vy are repeated.

  Step S13: If the measured value Vx is less than or equal to the determination value Vy in step S8, it is determined that stick slip has occurred or is in a state where it is likely to occur, and the belt rotation speed setting value Va is immediately determined. Is changed to a new set value Vb. The new set value Vb is a speed value that is 10% UP of the old set value Va before the change.

  Steps S14 and S15: The new set value Vb is compared with the belt rotation speed set value V during the image heating process, and if the new set value Vb is larger than the set value V, it is determined that the belt 12 has reached the end of its life. And display the life alarm.

  Step S16: If the new set value Vb is less than or equal to the set value V in step S14, the fixing motor M is driven with the new set value Vb. One second after the start of driving when the rotation of the fixing motor M at the new set value Vb is stabilized, the belt rotational speed is measured by the rotational speed detecting means 12a and 26, and the process proceeds to step S7 again to determine the actual belt rotational speed. to decide.

  In the next step S8, the stick-slip determination value Vy is changed to a speed value that is 3% lower than the new set value Vb, and the actual belt under the changed set value Vy and the new set value Vb. The stick-slip is determined again by comparing the rotation speed measurement value Vx. The stick-slip determination is started one second after the fixing motor M starts to be driven at the rotation speed of the new setting value Vb.

  In the subsequent pre-rotation mode, similar control is performed based on the new set value Vb updated in the previous pre-rotation mode.

  The above is the case of the pre-rotation mode. Similarly, in the case of the post-rotation mode, the stick-slip determination based on the comparison between the actual belt rotation speed measured value Vx and the stick-slip determination value Vy and the new set value Vb of the belt rotation speed set value Va in the post-rotation mode are performed. Update change control is performed.

  In the first embodiment, the number of the reflecting members 12a for detecting the belt rotation speed is one. The stick-slip of the belt 12 may be provided with a plurality of reflecting members 12 a in the circumferential direction of the belt 12 in consideration of instantaneous braking continuously. As a result, the belt speed sampling time can be shortened, and the accuracy of capturing stick-slip can be increased.

  In Examples 1 and 2, a combination of the reflective member 12a and the reflective sensor 26 as a reflected light detection unit is used as the belt peripheral speed detecting means. The belt peripheral speed detecting means is not limited to this, and for example, a means configuration for detecting the belt rotation speed by cutting a plurality of slits at the end of the belt 12 and measuring the passage time between the slits with a photo interrupter. It is also possible to do.

  In the first to third embodiments, by detecting the belt rotation speed, stick slip of the belt 12 is detected, and the set value of the belt rotation speed in the front rotation mode and the rear rotation mode is changed and controlled.

  In addition to this, without actually detecting stick-slip of the belt 12, the belt rotation speed setting value and the total belt rotation time (integrated rotation time) at which stick-slip occurs at the set value are experimentally determined in advance. Ask for a relationship. Then, the total rotation time of the belt 12 is integrated and counted by the counter function unit 100a by the control circuit unit 100. A setting that increases the belt rotation speed setting value in the pre-rotation mode and the post-rotation mode stepwise in accordance with a predetermined cumulative number of recording material transported and counted by the counter function unit 100a, that is, every time a predetermined time is reached. A value change control configuration is also possible.

  FIG. 9 is a flowchart of the control example. In the pre-rotation mode and the post-rotation mode, when the total rotation time Ta of the belt rotation by the initial setting value Va (= 1 / 4V) reaches a predetermined time T1, the belt rotation speed setting value is changed to the second setting value Vb. Change control. The second set value Vb is a speed value that is 10% higher than the initial set value Va.

  When the total rotation time Tb of the belt rotation by the second set value Vb reaches a predetermined time T2, the belt rotation speed set value is changed to the third set value Vc. The third set value Vc is a speed value that is 10% higher than the second set value Vb.

  In this way, the control circuit unit 100 counts the total rotation time of the belt 12 according to the belt rotation speed setting value at that time, and sets the belt rotation speed in the pre-rotation mode and the post-rotation mode every time a predetermined time is reached. Increase the value step by step. When the set value that is gradually raised finally becomes larger than the belt rotation speed setting value V at the time of paper nipping and conveying, it is determined that the belt 12 has reached the end of its life, and a life alarm is displayed. .

  Here, the total belt rotation time (integrated rotation time) is equivalent to the cumulative number of recording material conveyed. That is, it is predicted in advance how many cumulative recording material transported sheets will cause stick slip, and the control circuit unit 100 causes the counter function unit 100a to cumulatively count the cumulative recording material transported sheet number. Then, according to a predetermined cumulative recording material conveyance number, that is, every time the predetermined cumulative recording material conveyance number is reached, a setting value change control for gradually increasing the belt rotation speed setting value in the front rotation mode and the rear rotation mode. A configuration is also possible.

  It is also possible to detect the occurrence of stick-slip by capturing the increase in the load torque of the fixing motor M. When the motor current is sampled and exceeds a predetermined current value, it is determined that stick-slip has occurred.

  That is, in the fourth embodiment, the setting speed of the belt 12 in the latter period of use in the pre-rotation mode and the rear rotation mode is made faster than the setting speed in the initial period of use of the belt. It is characterized by being below the set speed. The post-rotation mode is executed following the image heating process, and the rotation of the belt 12 is stopped when the post-rotation mode ends.

  In the first to fourth embodiments, the stick-slip determination in the two modes of the pre-rotation mode and the post-rotation mode and the change control of the belt rotation speed setting value are performed. Further, it is possible to adopt a configuration in which setting value change control is performed.

  The fixing device shown in FIG. 10 is an image heating device using an electromagnetic induction heating method. Reference numeral 31 denotes an endless fixing belt as a heating rotator. The belt 31 is flexible by electromagnetic induction heat generation, and is suspended and stretched between the drive roller 32, the tension roller 33, and the pressure pad 34. A fixing nip N having a predetermined width is formed on the pressure pad 34 by pressing the elastic pressure roller 35 with the belt 31 interposed therebetween. Reference numeral 36 denotes an exciting coil unit which is disposed in close proximity to the outer surface of the belt portion between the driving roller 32 and the tension roller 33. The driving roller 32 is rotationally driven in the clockwise direction of the arrow by the fixing motor M, so that the belt 31 rotates in the clockwise direction of the arrow while the inner surface side slides on the surface of the pressure pad 34 in the fixing nip portion N. Driven. The pressure roller 35 rotates following the rotation of the belt 31.

  In a state where the fixing motor M is turned on and the belt 31 is rotating, a high frequency current is supplied from the excitation circuit 37 to the excitation coil of the excitation coil unit. Then, the belt 31 is heated by electromagnetic induction heat due to the action of the alternating magnetic flux generated in the exciting coil unit 36. The temperature of the belt 31 is detected by the temperature detection means TH 1 and TH 2 and fed back to the control circuit unit 100. Based on the temperature detection signals from the temperature detection means TH1 and TH2, the control circuit unit 100 supplies power from the excitation circuit 37 to the excitation coil of the excitation coil unit 36 so that the temperature of the belt 31 is maintained at a predetermined fixing temperature. To control. In this state, the sheet P carrying the unfixed toner image t is introduced from the image forming unit into the fixing nip N, and the toner image t is heated and pressurized and fixed on the sheet surface.

  As described above, even in the fixing device in which the belt 31 slides in close contact with the pressure pad 34, stick slip occurs due to the sliding between the pressure pad 34 and the belt 31. About the countermeasure, it can respond by the method similar to Examples 1-4.

Schematic configuration diagram of an example of an image forming apparatus Enlarged view of the main part of the image forming unit Magnified cross-sectional schematic diagram of the main part of the fixing device (A) is a front model diagram of the main part, and (b) is a longitudinal front model diagram. Configuration diagram of an example of a ceramic heater Perspective model view of belt rotation measure detection means Block diagram of the fixing device control system Flow chart showing specific control Flowchart showing control in embodiment 4 Schematic configuration diagram of a fixing device in Embodiment 5.

Explanation of symbols

  A..Image forming apparatus main body, B..Image reading scanner section, C..Image forming section, D..Sheet deck, 112..Photosensitive drum, 115..Transfer roller, N..Transfer nip section, 118. ..Fusing device, 11 ..Stay, 12 ..Fusing belt, 13 ..Heater (heating body), 18 ..Pressure roller, M ..Fixing motor, 12 a ..Light reflecting material (marking part), 26 ..Reflection type sensors 22, 23 .. First and second paper detection sensors (photo interrupters) 24, 25 ..Flag unit (actuator), 100 ..Control circuit unit (CPU)

Claims (8)

An endless belt for heating an image on a recording material, a nip forming member for forming a heating nip with the belt, a sliding member provided slidably with the belt as the belt rotates, and a belt Detecting means for detecting the peripheral speed of the belt, and control means for controlling at least the peripheral speed of the belt during the image heating process to be a set speed in accordance with the output of the detecting means. In an image heating apparatus capable of executing a mode in which a belt is rotated at a set speed slower than that at the time of image heating processing over a set time during non-image heating processing without performing control,
An image heating apparatus characterized in that when the peripheral speed of the belt detected in this mode falls below a set speed, the set speed of the belt in this mode is changed to a high speed.   2. The image heating apparatus according to claim 1, wherein a warning is urged when a speed at which the belt can be set in the mode reaches an upper limit set speed.   The image heating apparatus according to claim 1, wherein the mode is executed subsequent to the image heating process, and the belt is stopped when the mode ends.   4. The image heating apparatus according to claim 1, wherein the sliding member has a heater for heating the belt or a pad for pressing the belt from the inside in the heating nip. An endless belt for heating the image on the recording material, a nip forming member that forms a heating nip with the belt, and a sliding member that is slidable with the belt as the belt rotates. In an image heating apparatus capable of executing a mode in which a belt is rotated at a set speed slower than that during image heating processing over a set time during non-image heating processing,
An image heating apparatus characterized in that a set speed in the latter half of use of the belt in this mode is made faster than a set speed in the early stage of using the belt.   6. The image heating apparatus according to claim 5, wherein a set speed at a later stage of use of the belt in the mode is equal to or lower than a set speed at the time of image heating processing.   7. The image heating apparatus according to claim 5, wherein the mode is executed subsequent to the image heating process, and the belt is stopped when the mode ends.   8. The image heating apparatus according to claim 5, wherein the sliding member has a heater for heating the belt or a pad for pressing the belt from the inside in the heating nip.

Images