JP2007025540A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus provided with a fixing device which uses an external heat roller to make a surface temperature of a pressure roller uniform and allows the most suitable fixing temperature for paper quality to be set by automatically detecting the paper quality of a recording paper to be fixed. <P>SOLUTION: The fixing device includes a heat roller having a heating means, the pressure roller for pressing the heat roller, the external heat roller brought into contact with the pressure roller, a detection means for detecting the paper quality of the recording paper to be fixed, and a control means which performs control so as to automatically set the surface temperature of the external heat roller to a first or second temperature in accordance with a detection result of the detection means. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a fixing device used for an image forming apparatus such as a copying machine, a printer, a facsimile machine, and a multifunction machine having these functions.

  In an electrophotographic image forming apparatus such as a copying machine, a printer, a facsimile machine, or a multifunction machine having these functions, a latent image corresponding to an original is formed on a photosensitive member, and toner is applied to the latent image. Thus, the visualized toner image is transferred onto a recording paper (transfer material), and then the toner image transferred onto the recording paper is fixed.

  As a fixing device for fixing such a toner image, a recording sheet onto which the toner image is transferred is sandwiched between a heating roller incorporating a halogen heater or the like (hereinafter referred to as a heater) and a pressure roller that presses the heating roller. There is a heat roller fixing type fixing device that heats and pressurizes while transporting, and such a fixing device is widely used because of its simple structure and good fixability on recording paper.

  Here, the heating roller incorporates a heater inside the cored bar, and the surface of the cored bar is covered with silicone rubber. Since silicone rubber has poor heat conductivity, it takes a long time for the heat of the internal heater to be conducted to the surface of the heating roller. For this reason, when fixing on recording paper continuously, the surface temperature of the heating roller decreases, the heat of the internal heater is not sufficiently supplied and the fixing is performed at a low temperature, and so-called cold offset occurs. There is a risk of doing.

  In order to solve this problem, an external heating roller having its own heater is brought into contact with the heating roller. When the surface temperature of the heating roller decreases, the heating roller is heated by the external heating roller, and the surface of the heating roller is There is a fixing device that prevents a decrease in temperature (see, for example, Patent Document 1).

Further, when the recording paper to be fixed is a thick paper such as a postcard, it is desirable to fix at a higher temperature. Therefore, when the surface temperature of the heating roller can be set to two temperatures and the cardboard is fixed, the high temperature switching button is operated to energize the heater of the heating roller to increase the surface temperature of the heating roller. There is a fixing device in which the pressure roller is driven to rotate by the rotation of the heating roller to raise the temperature of the heating roller (see, for example, Patent Document 2).
Japanese Patent Laid-Open No. 11-24489 Japanese Examined Patent Publication No. 7-58414

  In the heat roller type fixing device described above, rotation of each roller of the fixing device is stopped when no paper is passed. The core of the pressure roller is covered with a silicone rubber foam. Therefore, in this state, no heat is supplied to the pressure roller, and the heating roller is cooled. For this reason, immediately after the start of printing, there is a problem that heat to be conducted to the recording paper is conducted to the pressure roller at a low temperature, resulting in poor fixing. Therefore, a fixing device in which a heater is also incorporated in the pressure roller is known.

  However, in order to raise the surface temperature of the pressure roller to an appropriate temperature, the temperature of the heater located inside the silicone rubber must be made higher, and there is a problem with the durability of the pressure roller. Therefore, by bringing the external heating roller into contact with the pressure roller, the heat of the external heating roller is conducted to the surface of the heating roller, and the surface temperature of the heating roller becomes uniform in a short time.

  Further, it is desirable to change the fixing temperature depending on the quality of the recording paper to be fixed. For example, when the recording paper is a coated paper, an image defect is likely to occur when the fixing temperature is high, and when the recording paper is a thick paper such as a postcard, the fixing strength is lowered when the fixing temperature is low. .

  However, when operating an image forming apparatus such as a copying machine, there are many people who care about the size and the like of a document to be copied, but few people consider the quality of the recording paper placed on a tray or the like. Therefore, even if it is expected that the user operates the high temperature switching button as in Patent Document 2, it is difficult to implement in practice.

  The present invention has been made in view of such a problem. By using an external heating roller, the surface temperature of the pressure roller is made uniform, and the quality of the recording paper to be fixed is automatically detected. An object of the present invention is to propose an image forming apparatus including a fixing device capable of setting an optimum fixing temperature according to paper quality.

The above object can be achieved by any of the following configurations.
[1] A heating roller having a heating unit, a pressure roller that presses the heating roller, an external heating roller that contacts the pressure roller, a detection unit that detects the quality of the recording paper to be fixed, and the detection unit An image forming apparatus comprising: control means for controlling to automatically set the surface temperature of the outer heating roller to the first temperature or the second temperature in accordance with the detection result.
[2] A heating roller having a heating unit, a pressure roller that presses the heating roller, an external heating roller that contacts the pressure roller, a detection unit that detects the quality of the recording paper to be fixed, and the detection unit An image forming apparatus comprising: an operation unit capable of manually setting the surface temperature of the outer heating roller to the first temperature or the second temperature according to the detection result.

  According to the image forming apparatus of the present invention, the surface temperature of the pressure roller is made uniform by using the external heating roller, and the paper quality of the recording paper to be fixed is automatically detected, so that the paper quality is matched. The optimum fixing temperature can be set automatically or manually.

  Embodiments relating to the fixing device of the present invention will be described.

  First, an image forming apparatus using a fixing device according to the present invention will be described with reference to the basic configuration diagram of FIG.

  In FIG. 1, reference numeral 1 denotes a photosensitive drum which is an electrophotographic photosensitive member. The photosensitive drum 1 is rotationally driven in a direction indicated by an arrow at a predetermined peripheral speed, and a surface of the photosensitive drum 1 is negatively charged by a charger 2. Uniformly charged to VH.

  An exposure device 3 outputs a laser beam modulated in accordance with a time-series digital pixel signal of image information input from an image reading device (not shown), a computer, or the like. The uniformly charged surface of the photosensitive drum 1 is scanned and exposed by this laser beam. As a result, the absolute value of the potential of the exposed portion of the photosensitive drum 1 decreases to become the potential VL, and an electrostatic latent image is formed on the surface of the photosensitive drum 1.

  The developing device 4 includes a developing roller 4a that is rotationally driven. The developing roller 4a is disposed opposite to the photosensitive drum 1, and a thin layer of negatively charged toner is formed on the outer peripheral surface thereof. A developing bias voltage whose absolute value is smaller than the potential VH of the photosensitive drum 1 and larger than the potential VL is applied to the developing roller 4a, whereby the toner on the developing roller 4a becomes the potential of the photosensitive drum 1. Reversal development is performed only on the VL portion, and a toner image is formed.

  On the other hand, the recording paper P, which is a transfer material fed from a paper supply unit (not shown), passes through the registration rollers 9 and is synchronized with the photosensitive drum 1 and the charged transfer pole 5 at an appropriate timing synchronized with the rotation of the photosensitive drum 1. To the transfer area formed in The toner image on the photosensitive drum 1 is transferred to the recording paper P by the charged transfer pole 5 to which a transfer bias is applied.

  Reference numeral 6 denotes a fixing guide, and the recording paper P onto which the toner image has been transferred is conveyed to the fixing device 7 where the toner image transferred onto the recording paper P is fixed. The recording paper P that has passed through the fixing device 7 and has been fixed with the toner image is discharged onto a paper discharge tray (not shown).

  On the other hand, the photosensitive drum 1 from which the recording paper P has been separated is removed by the cleaning device 8 to remove the transfer residual toner and the like adhering to the surface thereof, and the cleaned photosensitive drum 1 is repeatedly subjected to the next image formation. To be served.

  Although the above-described image forming apparatus is an apparatus that forms a monochrome image, the fixing apparatus of the present invention is also applied to an apparatus that forms a color image.

  Next, an embodiment of a fixing device according to the present invention will be described with reference to FIG. FIG. 2 is a cross-sectional view of the fixing device.

  In FIG. 2, a fixing device 7 includes a heating roller 71 incorporating a halogen heater H1 as a heating means for thermally fixing a toner image, a pressure roller 72 pressing the heating roller 71 from below, and a halogen heater H2. An outer heating roller 73 that contacts the pressure roller 72 to prevent a temperature drop of the pressure roller 72, a temperature sensor 75 that detects the surface temperature of the heating roller 71, and a temperature sensor 76 that detects the surface temperature of the outer heating roller 73. Etc.

  The heating roller 71 includes a halogen heater H1 provided at the center, a cored bar 71a formed in a cylindrical shape from aluminum, iron, copper, or an alloy thereof, and silicone rubber or fluorine positioned on the outer surface of the cored bar 71a. A heat-resistant elastic body 71b formed of rubber or the like, and a release layer 71c that covers the heat-resistant elastic body 71b and is formed of a fluororesin such as PFA (perfluoroalkoxy) or PTFE (polytetrafluoroethylene). Composed.

  The pressure roller 72 is formed of a PFA tube, for example, a cored bar 72a made of stainless steel, a rubber roller 72b made of silicon rubber foam positioned on the outer peripheral surface of the cored bar 72a, and an outer peripheral surface of the rubber roller 72b. And a release layer 72c. The pressure roller 72 is biased by a biasing member (not shown) and presses the heating roller 71 from below.

  The outer heating roller 73 includes a halogen heater H2 provided in the center as auxiliary heating means, and a cylindrical member 73a formed in a cylindrical shape from aluminum, iron, copper, or an alloy thereof. And is compact.

  The temperature sensors 75 and 76 are composed of a thermistor, a thermocouple, or the like.

  Here, when the pressure roller 72 is driven counterclockwise by being driven by a motor (not shown), the heating roller 71 is rotated clockwise and the outer heating roller 73 is also rotated clockwise. Accordingly, for example, the recording paper P on which the toner image is formed by the image forming apparatus shown in FIG. 1 is sandwiched and heated and pressed by the nip portion N formed by the heating roller 71 and the pressure roller 72. As a result, the toner image on the recording paper P is fixed.

  In some cases, at least one of the heating means of the heating roller 71 and the heating means of the external heating roller 73 may be an induction heating method.

  Here, it is desirable to change the temperature of the nip portion N in accordance with the quality of the recording paper P in order to prevent image defects and insufficient fixing strength from occurring during fixing. For this purpose, a configuration for switching the temperature of the nip portion N by automatically switching the temperature of the outer heating roller 73 in accordance with the thickness of the recording paper P will be described with reference to FIGS. FIG. 3 is a block diagram for controlling the temperature of the external heating roller 73 to be automatically switched, and FIG. 3 is a flowchart for automatically switching the temperature of the external heating roller 73.

  First, in the block diagram of FIG. 3, the control means 101 comprises a CPU or the like, and controls to switch the temperature of the external heating roller 73 according to input information of each means.

  The paper thickness detection means 102 automatically detects the paper thickness of the recording paper P. The thickness of the recording paper P is detected and the thickness information is sent to the control means 101. The control means 101 uses the paper thickness to control the thickness of the recording paper P. It is determined whether or not.

  In order to automatically detect the thickness of the recording paper P, for example, the registration roller 9 or the transport roller positioned before and after the registration roller 9 is used, one of the two rollers is a fixed roller, and the other is a movable roller. What is necessary is just to measure the displacement amount of the movable roller according to the paper thickness. For example, the first lever is engaged with the movable roller, the second lever is engaged with the first lever, and the displacement amount of the movable roller is amplified by amplifying the displacement amount of the second lever. May be detected by a photo sensor or the like.

  Whether the card is thick or not is determined, for example, since the thickness of the postcard is 0.20 mm to 0.25 mm.

  The outer heating roller temperature sensor 103 corresponds to the temperature sensor 76 described above.

  The outer heating roller heating unit 104 corresponds to the above-described halogen heater H2.

  Next, in the flowchart of FIG. 4, the feeding of the recording paper P is started (F1), and when the paper thickness detecting unit 102 detects the paper thickness of the recording paper, the control unit 101 determines based on the paper thickness. It is determined whether the paper is thick (F2). When the sheet is not thick paper (N in F2), the control unit 101 controls the external heating roller heating unit 104 while taking into consideration the surface temperature detected by the external heating roller temperature sensor 103, thereby setting the surface temperature of the external heating roller 73 to the first level. The temperature is set to 1 (for example, 120 ° C.) (F3), and fixing is performed (F5). On the other hand, when the paper is thick (Y in F2), the control unit 101 similarly controls the external heating roller heating unit 104 to set the surface temperature of the external heating roller 73 to a second temperature (for example, 200 ° C.) ( F4) and fixing are performed (F5).

  The temperature of the nip portion N is estimated to be about 190 ° C. when the surface temperature of the outer heating roller 73 is set to 120 ° C., and about 290 ° C. when the surface temperature of the outer heating roller 73 is set to 200 ° C. Estimated to be 200 ° C.

  As a result, when the recording paper P is a coated paper whose thickness is not thick, an image defect does not occur due to a high fixing temperature, and when the recording paper P is a thick paper such as a postcard. In addition, the fixing strength does not decrease due to a low fixing temperature.

  Further, instead of the paper thickness detecting means 102, surface roughness detecting means for detecting whether the recording paper P is rough paper by detecting the surface roughness is provided, and the control means 101 determines the surface roughness. Thus, the outer heating roller heating means 104 may be controlled.

  In this case, when the surface roughness of the recording paper is, for example, 3.0 μm or more, the surface temperature of the external heating roller 73 is set to the second temperature (for example, 200 ° C.), and the surface roughness of the recording paper is, for example, 3 If it is less than 0 μm, the surface temperature of the outer heating roller 73 is set to the first temperature (for example, 120 ° C.).

  The surface roughness detection means is a stylus type surface roughness measuring instrument that slides a stylus with a sharp tip in contact with the surface of the recording paper and slid lightly to indicate the movement of the stylus. Alternatively, it may be a light wave interference type surface roughness measuring instrument that forms an interference fringe from the phase difference between the reflected light from the measurement surface and the reflected light from the standard reflection surface.

  In the above configuration, the surface temperature of the outer heating roller 73 is controlled to be automatically switched to the first temperature or the second temperature according to the detected thickness of the recording paper P. The surface temperature may be switched manually. The configuration in this case will be described with reference to the block diagram of FIG. A description of the same means as described above is omitted.

  The paper thickness detection unit 202 automatically detects the thickness of the fed recording paper, and the control unit 201 determines whether the paper is thick based on the paper thickness, as described above. However, in this case, the result determined by the control unit 201 is displayed on the display unit 205 such as a liquid crystal display. Therefore, the user visually recognizes the display means 205 and operates the operation means 206 such as a keyboard and inputs it to the control means 201, so that the operation means 201 performs external heating while taking into account the surface temperature detected by the external heating roller temperature sensor 203. The roller heating means 204 is controlled to switch the surface temperature of the outer heating roller 73 to the first temperature or the second temperature.

  In this case, since the user operates the operation unit 206 to control the surface temperature of the outer heating roller 73, the operation may be performed as displayed on the display unit 205 by the detection of the paper thickness detection unit 202. In some cases, the user can arbitrarily set a high fixing temperature when the paper is thin or rough, or set a low fixing temperature when the paper is thick or coated.

  In this case as well, instead of the paper thickness detecting means 202, a surface roughness detecting means may be used.

  Furthermore, it is desirable to display the set surface temperature on a display means such as a liquid crystal display, regardless of whether the surface temperature of the external heating roller 73 is set automatically or manually.

1 is a basic configuration diagram of an image forming apparatus. FIG. 3 is a cross-sectional view of a fixing device. It is a block diagram which controls to switch the temperature of an outside heating roller automatically. It is a flowchart which switches the temperature of an external heating roller automatically. It is a block diagram which switches the temperature of an external heating roller manually.

Explanation of symbols

DESCRIPTION OF SYMBOLS 7 Fixing device 71 Heating roller 72 Pressure roller 73 Outer heating roller 75,76 Temperature sensor 101,201 Control means 102,202 Paper thickness detection means 205 Display means 206 Operation means P Recording paper N Nip part H1, H2 Halogen heater

Claims (5)

A heating roller having heating means;
A pressure roller for pressing the heating roller;
An external heating roller in contact with the pressure roller;
Detection means for detecting the quality of the recording paper to be fixed;
Control means for controlling to automatically set the surface temperature of the outer heating roller to the first temperature or the second temperature according to the detection result of the detection means;
An image forming apparatus comprising: A heating roller having heating means;
A pressure roller for pressing the heating roller;
An external heating roller in contact with the pressure roller;
Detection means for detecting the quality of the recording paper to be fixed;
Operation means capable of manually setting the surface temperature of the outer heating roller to the first temperature or the second temperature according to the detection result of the detection means;
An image forming apparatus comprising: When the second temperature is higher than the first temperature and the recording paper is thick paper, the second temperature is set. When the recording paper is not thick paper, the second temperature is set to the first temperature. The image forming apparatus according to claim 1, wherein the image forming apparatus is set. When the second temperature is higher than the first temperature and the surface roughness of the recording paper is equal to or higher than a predetermined roughness, the second temperature is set, and the surface roughness of the recording paper is The image forming apparatus according to claim 1, wherein the first temperature is set when the roughness is less than a predetermined roughness. The image forming apparatus according to claim 1, wherein a surface temperature of the outer heating roller to be set is displayed on a display unit.

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