JP2008020533A - Fixing device and image forming apparatus equipped therewith - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent the occurrence of abnormal noise by preventing a sticking phenomenon of a fixing film 18a and a viscosity decrease of a lubricant by a simple configuration. <P>SOLUTION: The driving speed of rotary driving means (fixing motor) is changed in correspondence to a tendency, if any, in image forming conditions of the apparatus, for example, the temperature rise in both end portions in the longitudinal direction of a heating element 18e, and thereby the temperature rise at the ends of the heating element 18e is prevented and the resonance point of the apparatus is changed. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a fixing device that forms an image using an electrophotographic method and an image forming apparatus including the same.

  In general, in various image forming apparatuses such as copiers and printers using an electrophotographic system, a toner image formed on a latent image carrier (photosensitive drum) is transferred to a sheet-like recording medium such as recording paper. The sheet-like recording medium to which the toner image has been transferred is passed through the fixing nip portion of the fixing device, and the toner image is permanently fixed. Those using such a fixing film are being widely adopted. In the fixing device using the fixing film, a heating body (heater) is disposed in contact with the inner peripheral surface side of the fixing film, and a pressure roller applies a relatively large pressure to the outer peripheral surface side of the fixing film. The toner image is fixed by applying a fixing action based on heating and pressure at a fixing nip portion formed at a contact portion between the fixing film and the pressure roller. It has come to be.

  On the other hand, in such a fixing device using a fixing film, the heating temperature is set to be relatively high because the heat capacity of the fixing film is small, and grease or the like is provided between the fixing film and the heating body (heater). Often, a lubricant is interposed. The lubricant is intended to smoothly feed the fixing film while ensuring the driving force of the pressure roller by reducing the frictional resistance between the fixing film and the heating body.

  However, as described above, in the fixing device, the action of high temperature and high pressure is intensively applied to the fixing nip portion, so that the fixing film may stick to the surface of the heating body. When such a fixing film sticking phenomenon occurs, a so-called stick slip is generated, and a resonance phenomenon occurs with a heating body or the like with the movement of the fixing film, causing abnormal noise or distorting the image. Sometimes.

  In addition, the heating element placed in contact with the fixing film is usually based on a detected temperature obtained by a temperature detecting member such as a thermistor provided at a position corresponding to the central portion of the image forming area. The energization control is performed so that the part is maintained at an appropriate fixing temperature. Therefore, for example, when a small-sized recording paper having a narrow width is continuously passed over a plurality of sheets, a so-called edge temperature rising phenomenon occurs at both end portions located on the outer side from both edges in the width direction of the recording paper. May occur, thereby reducing the viscosity of the lubricant such as the grease described above. Further, due to such a decrease in the viscosity of the lubricant, the sticking phenomenon of the fixing film as described above may occur and abnormal noise may be generated.

JP-A-3-210588

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a fixing device and an image forming apparatus using the same, which can prevent the occurrence of abnormal noise due to the sticking phenomenon of the fixing film and the decrease in the viscosity of the lubricant. .

  In order to achieve the above object, in the fixing device and the image forming apparatus using the same according to the present invention, a pressure roller that is driven by an appropriate rotation driving unit with respect to a fixing film that is arranged so as to be movable in contact with the heating member. The toner image is fixed by passing a sheet-like recording medium on which a toner image is formed through a fixing nip portion formed by pressure contact with the toner image. In the fixing device in which the means is driven and controlled by the fixing drive control means, the fixing drive control means is configured such that when the rear end portion of the sheet-like recording medium is in the fixing nip portion or in the sheet-like shape in the fixing nip portion. When there is no recording medium, the steady driving speed of the rotation driving means is increased and changed to a high speed rotation speed that rotates at a higher speed.

  According to the fixing device having such a configuration and the image forming apparatus using the fixing device, for example, an appropriate one corresponding to an image forming condition or the like in a case where a tendency to increase in temperature is generated at both end portions in the axial direction of the heating body. The timing is changed so that the drive speed of the rotation drive means is increased at the timing, so that the temperature distribution of the heating element is averaged in the axial direction, and it is possible to prevent the occurrence of temperature rise at the end of the heating element, etc. Therefore, the sticking phenomenon of the fixing film and the decrease in the viscosity of the lubricant are prevented in advance. Further, since the resonance point of the apparatus is changed in accordance with the change of the driving speed, the generation of abnormal noise is avoided.

  As described above, in the fixing device according to the present invention and the image forming apparatus using the fixing device, the driving speed of the rotation driving unit is set by the fixing driving control unit, for example, when there is a tendency to increase the temperature at both ends in the longitudinal direction of the heating body. In accordance with image forming conditions such as the above, the fixing drive control means for changing the drive speed of the rotary drive means to be increased is provided, so that the temperature rise at the end of the heating body is prevented. By changing the resonance point of the device, it is possible to prevent the occurrence of abnormal noise by preventing the sticking film sticking phenomenon and the viscosity of the lubricant from decreasing, which can greatly improve the reliability of the device at low cost. it can.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. First, the overall structure will be outlined by taking a laser printer as an example of an image forming apparatus to which the present invention is applied as an example.

  A control system 1 as shown in FIG. 2, for example, is mounted in the main body of the laser printer 10 shown in FIG. 1, and image information sent from an external device 2 such as a host computer is received. Are received by the video controller 3 in the laser printer 10. The image information received by the video controller 3 is converted into a video signal in page units and sent to an image forming device controlled by the engine controller 4, while a conveying device and a fixing device also controlled by the engine controller 4. The image forming operation is executed in cooperation with

  The above-described engine controller 4 is provided with a fixing drive control means 4a. Based on a command from the fixing drive control means 4a, a control for a fixing drive motor for driving the fixing device described in detail later. The action is to be executed.

  In the image forming apparatus in the laser printer 10, light modulation information 11a is emitted from the laser emission writing unit 11 based on the video signal described above, and the light modulation information 11a is scanned in the direction perpendicular to the paper surface while the process cartridge 12 is scanned. A spot image is formed on a photosensitive drum 121 provided as an image carrier. The light spot irradiated on the photosensitive drum 121 is reciprocally scanned in the axial direction (main scanning direction), whereby an electrostatic latent image corresponding to the above-described image information is formed on the photosensitive drum 121. Then, an unfixed toner image is formed by supplying developer (toner) to the electrostatic latent image on the photosensitive drum 121 from a developing device 122 that is also integrally provided in the process cartridge 12. It has become so.

  On the other hand, a main paper feeding unit 13 for feeding a sheet-like recording medium cut to a prescribed size (hereinafter simply referred to as recording paper) is disposed on the lower side of the apparatus main body. A box-shaped cassette housing 13a constituting the main paper feeding unit 13 is mounted so as to be detachable from the apparatus main body, and an intermediate support plate provided inside the cassette housing 13a. On the upper surface side of 13b, recording paper of an appropriate size (not shown) is stored in a laminated form. The lowermost surface of the recording paper in the stacking direction is supported by the middle support plate 13b, and the middle support plate 13b is urged upward by the paper feed pressurizing spring 13c, thereby recording. The paper is held in a state where it is lifted upward.

  A paper feed roller 13e formed of a cylindrical member is provided at the front end portion (left end portion in the drawing) of the cassette housing 13a in the paper feed direction. With respect to the rotation shaft of the paper feed roller 13e, the rotational driving force is intermittently connected at an appropriate timing through on / off control of an electromagnetic clutch (not shown). Then, the uppermost surface in the stacking direction of the recording paper supported so as to be lifted upward by the above-described middle support plate 13b is fed in a state of being in contact with the outer peripheral surface of the paper feed roller 13e from the lower side. The paper operation is performed, and the recording paper is sent out to the paper feed path 14 side by the rotation of the paper feed roller 13e, and is abutted against the nip portion of the pair of registration rollers 15 and 15 provided in the paper feed path 14. Thus, the image is sent to the transfer area facing the above-described photosensitive drum 121 while taking an appropriate timing.

  On the other hand, in the transfer area of the photosensitive drum 121 described above, a transfer roller 17 as a contact transfer member is disposed so as to be in contact with the surface of the photosensitive drum 121. A transfer bias is applied to the transfer roller 17, and the unfixed toner image formed on the photosensitive drum 121 is electrostatically transferred onto the recording paper by the transfer bias. Further, the toner remaining on the photosensitive drum 121 after the transfer is scraped off by the sliding contact force of the cleaning blade 123 arranged so as to come into pressure contact with the surface of the photosensitive drum 121.

  Further, the recording paper carrying the unfixed toner by the transfer operation described above is conveyed toward the fixing device 18 arranged adjacent to the upper position of the process cartridge 12. In the fixing device 18, a fixing film (fixing body) 18 a constituting a heating unit is arranged in a ring shape, and a pressure roller (pressure body) 18 b is provided so as to be in pressure contact with the fixing film 18 a. Has been placed. The unfixed toner on the recording paper is melted and the toner image is fixed by a fixing action based on pressure and heating in the fixing nip portion N formed in the pressure contact portion between the fixing film 18a and the pressure roller 18b. To be done. A detailed configuration regarding the fixing device 18 will be described later.

  Further, the recording paper on which the toner image is fixed by such a heat fixing operation is sent out from the exit portion of the fixing device 18 into the paper discharge passage 21 provided in the paper discharge portion 20 disposed on the upper side of the device. Thereafter, the paper is discharged onto a paper discharge tray 23 provided at the uppermost position of the apparatus main body by a discharge conveyance action of a paper discharge roller 22 provided in the paper discharge passage 21. An extension tray 24 is connected to a rear end portion of the paper discharge tray 23 in the paper feeding direction (right direction in the drawing). The extension tray 24 is a space formed immediately below the paper discharge tray 23 described above. It is configured to be housed so as to slide inside.

Next, the structure of the fixing device 18 described above will be described in detail.
First, as shown in FIG. 3, in the electrophotographic process in the present embodiment, an unfixed toner image composed of unfixed toner T charged on the minus side is carried on the recording paper P, and the recording paper P However, it is sent to the fixing device 18 through the conveying means 19.

  A fixing film (fixing body) 18a provided in the fixing device 18 is supported so as to be slidable along the surface of a film guide 18d attached to a pressure stay 18c having rigidity and heat resistance. A heating body (heater) 18e having an elongated plate shape is attached to the film guide 18d. The heating body 18e has an inner periphery of the fixing film 18a so as to apply heat necessary for a fixing process to a fixing nip N formed at a pressure contact portion between the pressure roller (pressure body) 18b and the fixing film 18a. The arrangement relationship is slidably in close contact with the surface.

  On the other hand, the heating body 18e described above has a configuration as shown in FIG. 4 in particular and extends in an elongated shape along a direction substantially perpendicular to the conveyance direction A of the recording paper as the heated body. A heat-resistant / insulating / good heat-conductive substrate 18f is provided, and the surface side of the substrate 18f, that is, the pressure-contact side to the fixing film 18a, is along the longitudinal direction (image width direction). A resistance heating element 18g is arranged, and heating power is supplied from power supply electrodes 18h, 18h arranged at both longitudinal ends of the resistance heating element 18g.

  Further, on the back side of the substrate 18f described above, three thermistors (temperature sensing elements) for detecting the temperature of the heating body 18e, that is, the central portion in the longitudinal direction (image width direction) of the heating body 18e are arranged. One main thermistor 18i that detects the temperature of the central portion, and two sub thermistors 18j that are disposed at both ends in the longitudinal direction (image width direction) of the heating body 18e and detect the temperature of the both ends. 18k.

As the heating element 18e in the present embodiment, a so-called tensionless type disclosed in, for example, JP-A-4-44075 to 44083, JP-A-4-204980 to 204984, and the like is adopted. As the substrate 18f, for example, an alumina or aluminum nitride substrate having a thickness of 1 mm, a width of 10 mm, and a length of 330 mm is employed. Further, as the resistance heating element 18g, for example, Ag / Pd (silver palladium) or RuO is coated with an electric resistance material such as Ta ₂ N by screen printing in a linear or narrow strip shape having a thickness of about 10 μm and a width of 1 to 3 mm. Is used. Further, the power feeding electrode 18h is formed of a screen printing pattern layer such as Ag, for example, and an overcoat layer made of, for example, a heat-resistant body glass layer having a thickness of about 10 μm is deposited thereon.

  Such a driving system of the fixing device 18 is configured such that the above-described pressure roller (pressure body) 18b is driven by a rotational driving means such as a fixing driving motor (see FIG. 2). On the other hand, the driving control of the fixing driving motor is executed by the fixing driving control means 4a in the engine controller 4, while the fixing film (fixing body) 18a follows the pressure roller 18b and slides in an annular manner. It has been made into a configuration. A lubricant such as grease is interposed between the fixing film 18a and the heating body 18e in order to maintain the following driveability and sliding property of the fixing film 18a. The lubricant is arranged over almost the entire length in the longitudinal direction (image width direction) of the heating body 18e.

  On the other hand, the fixing drive control means 4a in the engine controller 4 that drives and controls the fixing drive motor of the fixing device 18 stores a program for performing a control operation as shown in FIG.

  That is, as shown in FIG. 5, first, when image data such as a sentence or a figure is received from an external device (see reference numeral 2 in FIG. 2) by a video controller (see reference numeral 3 in FIG. 2) ( Step 101), the video controller 3 that has received the image data performs appropriate image processing, and an instruction to execute an image forming operation is transmitted to the engine controller 4 (step 102). The start-up preparation (pre-processing) of the image forming device and the fixing device 18 is started in accordance with an instruction from the engine controller 4 that has received the image forming execution instruction (step 103). And the energization of the heating body (heater) 18e is started in the fixing device 18, and pre-processing for raising the temperature is performed.

  When each pre-process in the image forming apparatus and the fixing device 18 is completed and the process proceeds to the preparation completion stage (Yes in Step 104), the conveyance of the recording paper (sheet-like recording medium) by the conveyance device is performed. Then, each image forming process such as an image forming process and a fixing process is executed (step 105). The image forming process is repeated until one job is finished (step 106), and after the job is finished, appropriate post-processing is executed in the image forming device and the fixing device 18 (step 107).

Here, an example of the processing operation of the fixing device 18 when a narrow and small-sized recording sheet is continuously passed will be described.
As described above, when a preprocessing instruction is received from the engine controller 4 (see step 102 in FIG. 5), based on the paper type and size of the recording paper to be passed through the fixing device 18 and the holding temperature state of the fixing device 18. A target temperature for controlling the heating element 18e, for example, a preprocessing target temperature, a sheet-to-paper target temperature, and a sheet passing target temperature as shown in FIG. 6, are respectively determined, and the longitudinal direction (image width) of the heating element 18e is determined. The heating element 18e is energized at an appropriate energization ratio until the main thermistor 18i arranged in the center part of the direction detects the respective target temperatures. FIG. 6 shows the relationship between the control temperature when nine sheets of narrow, small size and thick paper are continuously fed and the detected temperatures of the main thermistor 18i and the sub-thermistors 18j, 18k. An example is shown.

  When each preprocessing in the image forming device and the fixing device 18 is completed, the recording paper is transported (passed) to the fixing device 18 by the transport device. Temperature control at the time of the paper transport is detected by the main thermistor 18i. The heating element 18e is energized so as to replenish the heat taken away by passing the recording paper. As a result, the energization rate to the heating element 18e is increased, but the detected temperatures of the sub-thermistors 18j and 18k disposed at both ends in the rotation axis direction (image width direction) through which the recording paper does not pass are correspondingly detected. It rises and tends to be a so-called end temperature rise. In order to prevent such edge temperature rise, the target temperature at the time of paper interval is set to a value obtained by subtracting so as to be slightly lower than the target temperature at the time of paper passing. As a result, the heating element energization rate is lowered between the sheets, and the detected temperatures of the sub-thermistors 18j and 18k arranged at both ends are also lowered.

  After the control operation at the time of passing the sheet and the interval between the sheets is repeated until the end of the job, the energization to the heating element 18e is stopped according to the job end instruction from the engine controller 4 (see FIG. 2), and the post-processing is performed. Is called. Then, the energization stop state for the heating element 18e is maintained until the next temperature control instruction is issued, and the rotation driving means including the fixing motor constituting the driving system of the fixing device 18 is put on standby.

  On the other hand, the above-described engine controller 4 includes a fixing motor driving control for changing the driving speed of the fixing motor constituting the rotation driving means of the fixing device 18 in accordance with preset image forming conditions as will be described later. Means are provided. The fixing motor drive control means includes a condition setting means for setting image forming conditions related to the temperature at both ends in the longitudinal direction (image width direction) of the heating body (heater) 18e, and the temperature at both ends of the heating body 18e. Condition determining means for determining whether or not an image forming condition involved is satisfied, speed storage means for storing a steady driving speed of a fixing motor as the rotation driving means, and the condition determining means are arranged at both ends of the heating body 18e. When it is determined that the image forming conditions related to the part temperature are satisfied, the steady drive speed is increased and changed to an abnormal noise avoidance drive speed (high speed rotation speed) that rotates at a higher speed. And a speed changing means for returning the abnormal noise avoiding drive speed (high speed rotation speed) to the steady drive speed after an appropriate time has elapsed. And a program for controlling operation of the "abnormal sound avoidance mode" as follows.

First, whether or not to execute the “abnormal noise avoidance mode” is determined by checking whether image forming conditions as shown in Table 1 below are satisfied during continuous feeding of recording paper, for example. It is determined.

  The first item in Table 1 is to prevent the viscosity of a lubricant such as grease interposed between the heating body (heater) 18e and the fixing film (fixing body) 18a from decreasing. This is an image forming condition when the sub-thermistors 18j and 18k arranged on both ends in the longitudinal direction (image width direction) of the heating body 18e detect 220 ° C., for example. The second item is that the temperature of both end portions rises higher than the central portion during continuous paper passing when the recording paper (transfer paper) does not pass through both end portions of the heating element 18e. This is an image forming condition when the recording paper is passed. Furthermore, the third item is an image forming condition in the case of thick paper that takes more heat from the central portion of the heating body 18e during image formation. The image forming conditions shown in Table 1 may be determined independently of each other, or may be determined by combining any of the conditions.

  Then, as shown in FIG. 7, when the image forming conditions as shown in Table 1 described above are satisfied (step 201, Yes), the recording paper passing through the fixing nip N at that time point It is a stage before 30 mm before the trailing edge passes through the fixing nip N (step 202, Yes), and it takes one second or more until the leading edge of the recording paper on which the next image formation is performed enters the fixing nip N. The “abnormal sound avoidance mode” is executed only when there is (step 203, Yes).

  In the “abnormal noise avoidance mode”, the current steady driving speed of the fixing motor is first stored and stored in the speed storage means (step 204), and then, for example, 20% of the current steady driving speed of the fixing motor is 20%. The speed is increased to set an abnormal noise avoidance drive speed (high speed rotation speed) (step 205). Then, after the abnormal noise avoidance drive speed (high speed rotation speed) in which the steady drive speed of the fixing motor is increased is maintained for an appropriate time, the leading edge of the next recording sheet enters the fixing nip portion N. When 1 second before the timing (step 206, Yes), the original driving speed of the fixing motor stored as described above is restored (step 207).

  Such an “abnormal sound avoidance mode” is repeated until a job end instruction is received (No at Step 208), and is completed by performing the post-processing as described above when the job ends (Step 208, Yes). .

  On the other hand, when the image forming conditions as shown in Table 1 are not satisfied (No in step 201), the image forming process is performed without changing the steady driving speed of the fixing motor. Continue (step 209).

  As described above, in the fixing device 18 according to the present exemplary embodiment, when an image formation condition of the device, for example, when a tendency of temperature increase occurs at both end portions in the longitudinal direction of the heating body (heater) 18e, the temperature increase at the end portion is supported. Then, the steady drive speed of the fixing motor as the rotation drive means is increased, for example, to change to an abnormal noise avoidance drive speed (high speed rotation speed), whereby the temperature distribution of the heating element 18e is in the longitudinal direction (image width direction). Thus, the temperature rise at the end of the heating element 18e does not occur, and the sticking phenomenon of the fixing film and the decrease in the viscosity of the lubricant as in the conventional apparatus are prevented in advance. Further, since the resonance point of the apparatus is changed in accordance with the change of the driving speed of the fixing motor, the generation of abnormal noise is avoided.

  As mentioned above, although the embodiment of the invention made by the present inventor has been specifically described, the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the scope of the invention. Not too long.

  In the above-described embodiment, the presence / absence of high-speed rotation is determined based on the image forming conditions. However, high-speed rotation may be performed at all times, such as between sheets during continuous printing, or a predetermined number of prints may be determined. It is also possible to perform control so that high-speed rotation is performed once for each number of sheets.

  Further, although the above-described embodiment is an application of the present invention to a printer, the present invention can be similarly applied to other image forming apparatuses such as a copying machine.

  The image forming apparatus according to the present invention described above can be widely applied to a wide variety of image forming apparatuses such as copying machines as well as image forming apparatuses such as printers.

It is side explanatory drawing showing the internal schematic structure of the printer to which this invention is applied. FIG. 2 is a block diagram schematically illustrating a control system for an image forming operation in the printer illustrated in FIG. 1. FIG. 2 is an explanatory longitudinal cross-sectional view illustrating an enlarged structure of the fixing device illustrated in FIG. 1. FIG. 4 is an explanatory plan view showing a schematic structure of a pressure member used in the fixing device shown in FIG. 3. FIG. 2 is a flowchart schematically showing an outline of an image forming operation in the printer shown in FIG. 1. It is a diagram showing the temperature transition when a small size recording paper with a narrow paper passing width is continuously passed. It is a flowchart showing the control operation of the “abnormal noise avoidance mode” according to the embodiment of the present invention.

Explanation of symbols

10 Laser printer (image forming device)
DESCRIPTION OF SYMBOLS 12 Process cartridge 121 Photosensitive drum 122 Developing device 13 Main paper feed unit 14 Paper feed path 15 Registration roller 18 Fixing device 18a Fixing film (fixing body)
18b Pressure roller (Pressure body)
18c Pressure stay 18d Film guide 18e Heating body (heater)
N Fixing nip T Unfixed toner P Recording paper

Claims (7)

A sheet-like image in which a toner image is formed on a fixing nip formed by pressing a pressure roller driven by an appropriate rotation driving unit against a fixing film arranged so as to be movable in contact with a heating body A fixing device configured to fix the toner image by passing a recording medium, wherein the rotation driving unit is driven and controlled by a fixing driving control unit;
The fixing drive control means increases the steady drive speed of the rotation driving means when there is a rear end portion of the sheet-like recording medium in the fixing nip portion or when there is no sheet-like recording medium in the fixing nip portion. A fixing device configured to change to a high-speed rotation speed that rotates at a higher speed.   The fixing drive control means is configured to change the steady drive speed of the rotation drive means to a high-speed rotation speed in accordance with an image forming condition related to the end temperature of the heating body. The fixing device according to claim 1. The fixing drive control means includes
Condition setting means for setting image forming conditions related to the end temperature of the heating body;
Condition determining means for determining whether or not an image forming condition related to an end temperature of the heating body is satisfied;
Speed storage means for storing a steady drive speed of the rotation drive means;
When the condition determining means determines that the image forming condition relating to the end temperature of the heating body is satisfied, the steady driving speed is changed to a high speed rotation speed and the rotation driving means is instructed. Speed changing means for returning the high speed rotation speed to the steady driving speed after time has elapsed;
The fixing device according to claim 2, further comprising:   The image forming condition related to the end temperature of the heating body is a detected temperature of the end in the rotation axis direction of the fixing film, and a sheet width and a sheet thickness of the sheet-like recording medium. The fixing device according to 3.   The said condition determination means is comprised so that it may be determined whether any one of the image formation conditions in connection with the edge part temperature of the said heating body is satisfy | filled. Fixing device.   The speed changing unit is configured to change so as to increase a steady driving speed of the rotation driving unit between sheets in which the sheet-like recording medium is not passed through the fixing nip portion. The fixing device according to claim 3. An image forming apparatus comprising the fixing device according to claim 1.

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