JP2016090807A - Fixing device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixing device that can effectively prevent fixing failure due to uneven heating of a fixing part.SOLUTION: A fixing device includes: a fixing member that rotates in contact with an unfixed image on a recording medium; a pressure member that forms a nip part with the fixing member; a heat source that heats the fixing member; sensors that are arranged so as to detect the temperature of the entire range in the longitudinal direction of the fixing member in contact with the recording medium and have a plurality of temperature detection elements detecting the surface temperature of the fixing member; and a control part that controls the temperature of the heat source on the basis of outputs from some of the temperature detection elements of the sensors.SELECTED DRAWING: Figure 8

Description

  The present invention relates to a fixing device and an image forming apparatus.

  In recent years, there has been a strong market demand for energy saving and high speed for image forming apparatuses such as printers, copiers, and facsimiles.

  In the image forming apparatus, a developer image is formed on the image carrier by an image forming process such as electrophotographic recording, electrostatic recording, and magnetic recording. This developer image is transferred to a recording medium such as a recording material sheet, printing paper, photosensitive paper, or electrostatic recording medium. The developer image transferred to the recording medium is heated and pressurized by a fixing device and fixed on the recording medium. As the fixing device, a contact heating type fixing device such as a heat roller method, a film heating method, and an electromagnetic induction heating method is widely adopted.

  As an example of such a fixing device, a belt-type fixing device (for example, Patent Document 1) and a surf fixing or film fixing fixing device (for example, Patent Document 2) using a ceramic heater are known.

  In any of these methods, in recent years, a fixing roller or a fixing belt having a very small heat capacity has been used for energy saving.

  In the conventional fixing device, the temperature of the fixing roller has one temperature sensor at the end of the fixing roller and one temperature sensor at the center, and the heater that heats the fixing roller based on the output of the temperature sensor is excessively heated. Was preventing.

  Therefore, the smaller the heat capacity of the fixing roller, the more uneven the heating occurs. The uneven heating causes the fixing defect.

  In this regard, a temperature sensor that detects the occurrence of abnormal heat generation is provided so as to cover the entire heat generating area on the peripheral surface of the fixing belt, and when the control section detects the abnormal heat generation section by this temperature sensor, Has been proposed (for example, Patent Document 3).

  However, this technology only detects abnormal heat generation. Accordingly, it is not possible to prevent the occurrence of fixing failure due to temperature unevenness due to cooling of the fixing roller.

  In view of the above problems, an object of the present invention is to provide a fixing device that can effectively prevent fixing failure due to uneven heating of a fixing unit.

  The present invention for solving the above-described problems includes a fixing member that rotates in contact with an unfixed image on a recording medium, a pressure member that forms a nip portion between the fixing member, and a heat source that heats the fixing member. And a sensor having a plurality of temperature detection elements that detect the surface temperature of the fixing member, and a temperature detection of a part of the sensor. There is provided a fixing device including a control unit that performs temperature control of a heat source based on an output of an element.

  According to the present invention, it is possible to detect local temperature unevenness, and the heat source and the fixing roller are controlled so as to eliminate the temperature unevenness. Therefore, a fixing device that can efficiently reduce fixing unevenness is provided. Can be provided.

1 is a diagram illustrating a configuration example of an image forming apparatus. FIG. 2 is a cross-sectional view illustrating a configuration of a fixing device. It is a figure which shows the arrangement position with respect to the fixing belt of a sensor. It is the figure which showed the temperature detection range at the time of using two sensors. It is the figure which showed the temperature detection range at the time of using one sensor. FIG. 6 is a diagram illustrating a temperature distribution of a fixing roller when a recording medium having a tab is passed. FIG. 6 is a diagram illustrating a temperature distribution of a fixing belt when there is a dark image. 4 is a flowchart illustrating an operation performed by a control unit of the image forming apparatus.

  Hereinafter, a fixing device and an image forming apparatus according to an embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 is a diagram illustrating an example of an image forming apparatus 1 according to the present embodiment. As shown in FIG. 1, a printer as an example of an image forming apparatus 1 according to the present embodiment includes a paper feed unit 4, a pair of registration rollers 6, a photosensitive drum 8 as an image carrier, and a transfer unit 10. And a fixing device 20.

  The paper feeding means 4 feeds the paper P as a recording medium stored in a stacked state and the paper P stored in the paper feeding tray 14 one by one in order from the top. And a roller 16. The paper P sent out by the paper feed roller 16 is temporarily stopped at the registration roller 6, and after the position deviation is corrected, the timing synchronized with the rotation of the photosensitive drum 8, that is, the toner formed on the photosensitive drum 8. The image is sent to the transfer portion N by the registration roller 6 at the timing when the leading edge of the image coincides with the predetermined position at the leading edge of the sheet P in the transport direction.

  Around the photosensitive drum 8, in the rotation direction indicated by the arrows, a charging roller 18 as a charging unit, a mirror 25 constituting a part of an exposure unit (not shown), a developing unit 22 including a developing roller 22a, A transfer unit 10 and a cleaning unit 24 including a cleaning blade 24a are arranged.

  Between the charging roller 18 and the developing means 22, the exposure light beam Lb is irradiated on the exposure unit 26 on the photosensitive drum 8 via the mirror 25 and scanned.

  The image forming operation in the printer according to this embodiment is performed in the same manner as in the past. That is, when the photosensitive drum 8 starts to rotate, the surface of the photosensitive drum 8 is uniformly charged by the charging roller 18, and an image to be created by irradiating and scanning the exposure light beam Lb on the exposure unit 26 based on image information. An electrostatic latent image corresponding to is formed.

  The electrostatic latent image is moved to the developing means 22 by the rotation of the photosensitive drum 8, where toner is supplied to be visualized to form a toner image.

  The toner image formed on the photosensitive drum 8 is transferred onto the paper Pa that has entered the transfer portion N at a predetermined timing by applying a transfer bias voltage by the transfer means 10.

  The paper P carrying the toner image is conveyed toward the fixing device 20, fixed by the fixing device 20, discharged to a paper discharge tray (not shown), and stacked.

  The fixing device 20 includes a fixing roller 301 that is heated by a heat source and heats the paper P, and a pressure roller 310 that is disposed to face the fixing roller 301 and presses the paper P toward the fixing roller 301. The paper P is passed through a nip formed by the fixing roller 301 and the pressure roller 310 and fixed.

  Residual toner remaining on the photosensitive drum 8 without being transferred at the transfer portion N reaches the cleaning means 24 as the photosensitive drum 8 rotates, and is scraped off by the cleaning blade 24 a while passing through the cleaning means 24. To be cleaned.

  Thereafter, the residual potential on the photosensitive drum 8 is removed by a neutralizing unit (not shown), and is prepared for the next image forming process.

  FIG. 2 is a block diagram showing an embodiment of the fixing device 20 of the present invention. As shown in FIG. 2, the fixing device 20 has a hollow shape that is heated by a heat source (heater 302), and contacts the toner image that is an unfixed image on the recording medium to heat and melt the toner image. A member (fixing roller 301) and a pressure member (pressure roller 310) that is arranged on the outer peripheral side of the fixing member so as to be in pressure contact with the fixing member and forms a nip portion with the fixing member. Hereinafter, the longitudinal direction (the depth direction in FIG. 2) of the fixing roller 301 is also referred to as an axial direction, and the rotation direction of the fixing roller 301 is also referred to as a circumferential direction.

  In this embodiment, an example is described in which the roller that is thin and elastically deformed is the fixing roller 301, and the roller that is more rigid than the roller that is elastically deformed is the pressure roller 310, but conversely, the fixing roller 301 is highly rigid. A hollow roller that elastically deforms may be used as the roller and the pressure roller 310.

  Here, the fixing roller 301 is a thin cylindrical body that rotates in the direction of the arrow in FIG. 2, and a heater 302 as a heat source is disposed inside the cylindrical body. The fixing roller 301 is a multi-layered structure in which an elastic layer 304 and a release layer 305 are laminated in this order on a cylindrical cored bar portion 303, and a nip portion is brought into contact with the pressure roller 310. Form.

  The innermost core part 303 of the fixing roller 301 is made of an iron-based material such as SUS304, for example. In addition, Cu, Ni, PI, or the like may be used.

  A heater 302 as a heat source is provided inside the cored bar portion 303 of the fixing roller 301. As the heater 302, for example, a halogen heater, a planar heater, or the like can be used. Alternatively, the fixing roller 301 may be heated from the outer peripheral side of the fixing roller 301 by using electromagnetic induction overheating means.

  The fixing roller 301 is heated by a heater 302 whose output is controlled by a power supply unit included in the image forming apparatus 1, and heat is applied to the toner image T on the paper P from the surface thereof. Note that the output control of the heater 302 is performed based on a detection result by a temperature detection unit (such as a thermopile array) which is a sensor 20S provided so as to be able to detect the surface temperature of the fixing roller 301. By controlling the output of the heater 302, the temperature of the fixing roller 301, that is, the fixing temperature can be controlled to a desired temperature.

  As the elastic layer 304 of the fixing roller 301, for example, an elastic material such as fluorine rubber, silicone rubber, and foamable silicone rubber is used. By providing the elastic layer 304 on the core of the fixing roller 301, the separation of the paper P after passing through the nip portion is improved, and the glossiness of the output image when forming a color image is improved.

  Further, as the release layer 305 of the fixing roller 301, for example, PFA (tetrafluoroethylene / fluorofluorovinylvinyl ether copolymer resin), polyimide, polyetherimide, PES (polyether sulfide), or the like can be used. By providing the release layer 305 on the surface layer of the fixing roller 301, the releasability (peelability) with respect to the toner image T is ensured.

  The pressure roller 310 includes a cored bar portion 311, an elastic layer 312, and a release layer 313. The cored bar 311 is a rigid body, and the elastic layer 312 and the release layer 313 may be configured similarly to the fixing roller 301. The pressure roller 310 is pressed against the fixing roller 301 by a pressing unit (not shown), and a nip portion is formed between the pressure roller 310 and the fixing roller 301.

  A guide plate for guiding the conveyance of the recording medium P is disposed on the entrance side of the nip portion between the fixing roller 301 and the pressure roller 310.

  The fixing device 20 is controlled by the control unit 401. The control unit 401 controls the drive unit 402 that drives the heater 302 and the pressure roller 310 based on the output of the sensor 20S. When the drive unit 402 rotates the pressure roller 310 in the direction indicated by the arrow X1, the fixing roller 301 contacting the pressure roller 310 is driven and rotated in the direction indicated by the arrow X2.

  As the sensor 20S, an array type temperature sensor including a plurality of temperature detection elements for detecting temperature can be used. Specifically, the sensor 20S can use a thermopile array that uses a thermopile that detects the temperature of the detection target without contacting the temperature detection element.

  The sensor 20S may further include a shift register that converts a parallel signal composed of outputs of a plurality of temperature detection elements into a serial signal and outputs the serial signal. The control unit 401 can determine the temperature detected for each temperature detection element based on the signal input from the sensor 20S.

  The sensor 20S desirably uses a linear thermopile array in which temperature detection elements are linearly arranged. By arranging the sensor 20S so that the longitudinal direction of the linear thermopile array is parallel to the longitudinal direction of the fixing unit, the entire region of the fixing unit in the longitudinal direction, that is, from one end to the other end of the region where the fixing unit heats the recording medium P. This is because the temperature can be detected for the entire area.

  Instead of the linear thermopile array, an area thermopile array in which the temperature detection elements are arranged in a rectangular shape can be used.

  In the present embodiment, the sensor 20S uses a thermopile array and is arranged so that the detection range covers the entire longitudinal direction of the fixing roller 301 which is a heating body. Accordingly, it is possible to cope with both temperature control of the fixing roller 301 and deterioration in fixing quality due to local temperature unevenness.

  FIG. 3 is a diagram showing the arrangement position of the sensor 20 </ b> S with respect to the fixing roller 301. As shown in FIG. 3, the fixing device 20 can include a plurality of sensors 20 </ b> S along the longitudinal direction of the fixing roller 301 that is a fixing member.

  The sensor 20S is arranged such that there is no gap in the temperature range detected by each temperature detection element of the thermopile array in the range where the recording medium P contacts in the longitudinal direction of the fixing roller 301 which is a heating body. Some of the temperature detection elements are used to control the temperature of the fixing roller 301 which is a heating body. By detecting the temperature without any gaps in this way, it is possible to detect a temperature that could not be detected by the prior art.

  Each sensor 20 </ b> S is desirably arranged so that the arrangement direction of the temperature detection elements is parallel to the longitudinal direction of the fixing roller 301.

  The fixing device 20 is disposed so as to include at least a range in which the fixing roller 301 heats the recording medium P. The range detected by each temperature detection element of the sensor 20S is arranged so as to cover the entire range of the area where the recording medium P of the fixing roller 301 is heated, that is, the area where the recording medium P contacts in the longitudinal direction of the fixing roller 301. It is desirable.

  However, if it is not possible to cover the entire area, it is between the range where one temperature detection element detects the temperature and the range where other temperature detection elements adjacent to this temperature detection element detect the temperature. There may be a range where the temperature is not detected.

  In this case, the sensor 20S is arranged so that the range in which the fixing roller 301 heats the paper P is included in the range from one end to the other end of the range in which the temperature is detected by the sensor 20S.

  FIG. 4 is a diagram showing a temperature detection range when two sensors 20S are used. As shown in FIG. 4, the fixing roller 301 includes a central heating unit 302 </ b> A that heats the central part of the fixing roller 301 and an end heating unit 302 </ b> B that heats the longitudinal end of the fixing roller 301. . The control unit 401 assigns outputs of some temperature detection elements of the sensor 20S to each heat source and controls the temperature of each heat source.

  In this case, the corresponding central heating unit 302A or end heating unit 302B can be determined for each temperature detection element of the sensor 20S.

  For example, among the temperature detection elements of the sensor 20S, a certain element detects the temperature of a part 401A of the heating part of the end heating unit 302B that heats one end. The temperature of a part 401D of the heating portion of the end portion heating unit 302B in which the other element heats the other end portion is detected. Furthermore, another element detects the temperature of the part 401B and 401C of the part which the center heating part 302A heats.

  If it sets in this way, temperature control of central heating part 302A and end part heating part 302B will become easier.

  FIG. 5 is a diagram showing a temperature detection range when one sensor 20S is used. As shown in FIG. 5, when the temperature of the fixing roller 301 is detected by one sensor 20S, it is necessary to dispose the sensor 20S with a greater distance from the fixing roller 301 than when a plurality of sensors 20S are used.

  As the sensor 20S, a sensor with a larger number of temperature detection elements or a sensor with a wider angle lens can be used than when a plurality of sensors 20S are used.

  Among the temperature detection elements of the sensor 20S, a certain element detects the temperature of a part 601A of the heating portion of the end heating unit 302B that heats one end. The temperature of a part 501C of the heating portion of the end portion heating unit 302B in which the other element heats the other end portion is detected. Further, another element detects the temperature of a part 501B of the heated portion of the central heating unit 302A.

  With this configuration, the fixing device 20 can be manufactured at a lower cost than when a plurality of sensors 20S are used.

  FIG. 6 is a diagram showing the temperature distribution of the fixing roller 301 when the recording medium PT with the tab T is passed. In the graph 601, the vertical axis represents temperature, and the horizontal axis represents the distance from one end of the fixing roller 301. A broken line 602 indicates a fixing temperature which is a reference temperature used for fixing.

  As shown in FIG. 6, when the recording medium PT having the tab T in the direction of the downward arrow is passed through the fixing device 20, the temperature of the fixing roller 301 in the portion of the tab T is the fixing temperature as shown in the graph 601. And temperature unevenness may occur. In such a case, fixing failure may occur.

  Even in such a case, according to the fixing device 20 of the present embodiment, it is possible to specify a place where the temperature is low, and it is possible to finely control the temperature of the fixing roller 301.

  FIG. 7 is a diagram showing the temperature distribution of the fixing roller 301 when there are dark images G1 and G2. In the graph 701, the vertical axis represents temperature, and the horizontal axis represents the distance from one end of the fixing roller 301. A broken line 702 indicates a fixing temperature which is a reference temperature used for fixing.

  As shown in FIG. 7, in the dark images G1 and G2, the temperature unevenness of the fixing roller 301 is lower than the fixing temperature, and the developer may be peeled off.

  In such a case, one element can detect the temperature of the portion 703A and another element can detect the temperature of the portion 703B. Therefore, based on the output of the sensor 20S, the control unit 401 can perform control so as to increase the temperature of the heat source corresponding to the low temperature portion or to perform a soaking operation.

  Here, the soaking operation includes an operation of rotating the fixing roller 301 while heating a heat source corresponding to a portion where the temperature of the fixing roller 301 is low. During this soaking operation, the image forming apparatus 1 may stop image formation.

  In addition, the control unit 401 stops the operation of the fixing device 20 or reduces the speed of the fixing operation when the temperature deviation between the high temperature portion and the low temperature portion becomes a threshold value or more in the sheet passing area of the fixing roller 301. Therefore, it is possible to control so as to reduce the productivity and suppress the temperature deviation.

  The fixing device 20 is designed so that the conveyance speed at the end of the recording medium P is increased so that the recording medium P is not wrinkled. This is often realized by making the outer diameter of the fixing roller or the pressure roller 310 facing the fixing roller larger than the center. In the case of such a fixing device 20, if the temperature difference between the center portion is high and the end portion temperature is low or more than a certain level, wrinkles are prevented by the thermal expansion of the fixing roller and the pressure roller 310. Since the difference in the outer diameter is eliminated, wrinkles occur.

  If the temperature difference is excessive in the longitudinal direction as described above, various adverse effects other than wrinkles occur. Therefore, the control unit 401 controls the temperature difference between the high temperature part and the low temperature part to be within a designed allowable range. You can also

  The control unit 401 starts printing if the temperature within the width of the recording medium P to be passed next is within a predetermined length in the longitudinal direction of the fixing roller 301.

  In the prior art, since there are few points to detect the temperature, printing could not be started until the point at which the temperature is detected reaches the predetermined temperature. Formation is possible. Therefore, even if the temperature of a part of the fixing roller 301 deviates from the fixing temperature, the control unit 401 starts image formation as long as the heating range that is the region through which the recording medium P passes satisfies the temperature. This control can reduce the waiting time for starting image formation.

  In this control, the control unit 401 can selectively change the temperature detection element used for temperature detection. That is, the temperature detecting element for detecting the temperature is selectively changed between fixing a wide recording medium P such as A3 and fixing a narrow recording medium P such as a postcard size. be able to. Specifically, the control unit 401 discards an output bit from a temperature detection element that is not used for temperature detection, or selectively selects an output bit from a temperature detection element to be used, from the serial signal output by the sensor 20S. Can be changed.

  FIG. 8 is a flowchart illustrating an operation performed by the control unit 401 of the image forming apparatus 1. As shown in FIG. 8, in step 801, the control unit 401 reads the output value of the sensor 20S and determines the temperature for each temperature detection element.

  In step 802, the control unit 401 determines whether there is a temperature detection element that detects a temperature that is less than the fixing temperature, which is a temperature range suitable for fixing. If it is determined that there is a temperature detection element that detects a temperature lower than the fixing temperature, the control unit 401 proceeds to step 803, and if it is determined that there is no temperature detection element, the control unit 401 proceeds to step 806.

  In step 803, the control unit 401 determines whether the detection position of the temperature detection element that has detected a temperature lower than the fixing temperature is within the range of the recording medium P on which the next image formation is to be performed. When the control unit 401 determines that the detection position of the temperature detection element that has detected a temperature lower than the fixing temperature is within the range of the recording medium P on which the next image formation is to be performed, the control unit 401 proceeds to step 804 and determines that it is not within the range. If yes, go to Step 809.

  In step 804, the control unit 401 determines whether the temperature deviation, which is the difference between the temperature of the highest temperature portion and the temperature of the lowest temperature portion, exceeds a threshold value. If the control unit 401 determines that the temperature deviation is higher than the threshold value, the control unit 401 proceeds to step 808, and if it is determined that the temperature is equal to or lower than the threshold value, the control unit 401 proceeds to step 805.

  In step 805, the control unit 401 heats the heat source corresponding to the low temperature portion, performs the heating operation of the fixing roller 301, and returns to step 801.

  In step 806, the control unit 401 determines whether or not the temperature at the highest temperature exceeds the threshold value. If the control unit 401 determines that the temperature of the highest temperature portion is higher than the threshold value, the control unit 401 proceeds to step 807. If it is determined that the temperature is equal to or lower than the threshold temperature, the control unit 401 proceeds to step 809.

  In step 807, the control unit 401 performs the cooling operation of the fixing roller 301 and returns to step 801. The cooling operation includes an operation of stopping heating of the heat source and stopping or rotating the fixing roller 301.

  In step 808, the control unit 401 performs a soaking operation of the fixing roller 301 and returns to step 801.

  In step 809, the control unit 401 forms an image.

  As described above, the fixing device 20 of the present embodiment includes the sensor 20S having a plurality of temperature detection elements arranged so that the heating region of the recording medium P in the longitudinal direction of the fixing unit is included in the temperature detection range. And a control unit 401 that controls the heat source and the fixing roller 301 so that the lowest temperature portion detected based on the output of the sensor 20S satisfies the fixing temperature.

  Therefore, local temperature unevenness can be detected, and the heat source and the fixing roller 301 are controlled so as to eliminate the temperature unevenness, so that it is possible to efficiently reduce fixing unevenness.

1: Image forming apparatus 8: Photoconductor drum 10: Transfer means 20: Fixing device 20S: Sensor 301: Fixing roller 302: Heat source 310: Pressure roller 401: Control unit 402: Driving unit

Japanese Patent No. 4818826 Japanese Patent No. 2861280 JP 2012-177790 A

Claims (10)

A fixing member that rotates in contact with an unfixed image on a recording medium;
A pressure member that forms a nip portion with the fixing member;
A heat source for heating the fixing member;
A sensor having a plurality of temperature detection elements which are arranged so as to be able to detect the temperature of the entire range in which the recording medium contacts in the longitudinal direction of the fixing member, and which detects the surface temperature of the fixing member;
A controller that controls the temperature of the heat source based on the output of a part of the temperature detection elements of the sensor;
A fixing device. The controller is
The fixing device according to claim 1, wherein the temperature detection element used for the temperature control is selectively changed. The controller is
If it is determined that the temperature deviation, which is the difference between the temperature of the highest temperature part and the temperature of the lowest temperature part, exceeds the threshold, the image forming operation is stopped or the temperature equalization operation is performed to reduce the temperature deviation. The fixing device according to claim 1 or 2, wherein the fixing device is performed. The controller is
Even if a portion outside the fixing temperature, which is a temperature range suitable for fixing to the fixing member, is detected based on the output of the sensor, if the portion does not enter the heating range of the recording medium to be fixed next, image formation is performed. The fixing device according to claim 1, wherein the fixing device performs the operation. The controller is
4. The cooling operation according to claim 1, wherein a cooling operation is performed when it is determined based on the output of the sensor that the fixing member has a portion higher than a fixing temperature that is a temperature range suitable for fixing. Fixing device. The controller is
The fixing member is heated by controlling the heat source so as to enter the fixing temperature when at least a part of the output of the temperature detecting element of the sensor falls below a fixing temperature which is a temperature range suitable for fixing. The fixing device according to 1. The sensor is
The fixing device according to claim 1, wherein the fixing device is a linear thermopile array in which the plurality of temperature detection elements are linearly arranged. The sensor is
The fixing device according to claim 1, wherein a plurality of fixing devices are arranged along a longitudinal direction of the fixing member. The heat source is
An end heating unit for heating the end of the fixing member;
A central heating part for heating the central part of the fixing member;
With
The controller is
The fixing device according to claim 1, wherein temperature control of the end heating unit and the central heating unit is performed using a part of the output of the sensor.   An image forming apparatus comprising the fixing device according to claim 1.

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