JP6693074B2 - Fixing device and image forming apparatus - Google Patents

Description

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

  In Japanese Patent Application Laid-Open No. 2004-242242, a storage medium that stacks and stores sheet-shaped transported media and a roller member that is in contact with the transported media stored in the storage means are rotated by an electric motor to transport the transported media in a predetermined manner. A feeding means for feeding to a road, a detecting means for detecting the rotation amount of the roller member or the electric motor, and the feeding means performs a predetermined feeding operation based on the rotation amount detected by the detecting means. The control means for adjusting the control amount supplied to the electric motor, the monitoring means for monitoring the adjusted control amount adjusted by the control means, and the control means for adjusting the adjusted control amount monitored by the monitoring means. There is disclosed a sheet conveying device including a first determining unit that determines the type of a medium to be transported that is fed by the feeding unit.

  In Japanese Patent Laid-Open No. 2004-242242, a heating member that has a heater inside and rotates, a pressing member that nips a recording sheet on which an unfixed toner image is transferred to the heating member, and a sheet passing area of the recording sheet are provided. Also facing the heating member on the outer side in the direction of the rotation axis, a temperature sensor for detecting the surface temperature of the heating member, and a sheet passing time and a sheet non-passing time between the heating member and the pressing member. And a means for predicting a difference between the temperature detected by the temperature sensor and the actual surface temperature in the paper passing area of the heating member based on the paper passing time and the non-paper passing time, and the predicted temperature difference. And a temperature control unit that controls the energization of the heater in consideration of the above.

  Patent Document 3 includes a fixing member that is heated by a heating source and a pressure member that forms a fixing nip portion between the fixing member and the fixing member. In a fixing device for fixing the carried toner, a roller member arranged upstream of the fixing nip portion and rotating while contacting with the recording sheet is provided, and a frictional force or a peeling force between the roller member and the recording sheet. And a fixing control unit that controls a fixing condition including at least one of temperature control, conveyance speed control, and surface pressure control based on a measurement result of the force measurement unit. A characteristic fixing device is disclosed.

JP, 2007-182265, A JP, 2002-278358, A JP, 2005-1544, A

  If the user erroneously sets the thickness of the recording medium on which the image is formed, the fixing temperature for fixing the image on the recording medium is fixed at the fixing temperature corresponding to the recording medium erroneously set by the user. However, fixing failure may occur.

  The present invention provides a fixing device capable of suppressing fixing at a fixing temperature corresponding to the incorrectly set recording medium thickness, as compared with the case where a setting error of the recording medium thickness is not detected. An object is to provide an image forming apparatus.

In order to achieve the above object, the fixing device according to claim 1 is a fixing device for fixing an image formed on a recording medium, a driving device for driving the fixing device, and a detection for detecting a load of the driving device. means and the said recording medium is detected before the peak value of the load of said driving means when said recording medium from the peak value of the load of said driving means when rush to the fixing means is discharged from the fixing unit A detection unit that detects the thickness of the recording medium from the average value of the load of the drive unit.

  According to a second aspect of the present invention, the detection unit detects the thickness of the recording medium from the comparison result of the peak value of the load of the driving unit and the threshold value when the recording medium enters the fixing unit.

  According to a third aspect of the present invention, the detection unit sets the threshold value according to the width of the recording medium.

According to a fourth aspect of the invention, when the preset thickness of the recording medium and the thickness of the recording medium detected by the detecting unit are different, the thickness of the recording medium detected by the detecting unit is different. And a control unit that controls the fixing temperature of the fixing unit according to the above, and the detection unit sets the thickness of the recording medium to a first thickness when the peak value is less than a first threshold value. When the peak value is greater than or equal to a first threshold value, the thickness of the recording medium is detected as a second thickness that is thicker than the first thickness, and the control unit detects the detection unit. When the thickness of the recording medium detected by the above is the first thickness, the fixing unit is controlled so that the fixing temperature is lowered after the recording medium enters the fixing unit, and the detection is performed. The thickness of said recording medium detected by means The second case of the thickness of the recording medium to control said fixing means so as to maintain the fixing temperature when the rush to the fixing means.

  According to a fifth aspect of the present invention, the detection means sets the thickness of the recording medium to the second value when the peak value is equal to or more than a first threshold value and less than a second threshold value that is greater than the first threshold value. The thickness of the recording medium is detected as a third thickness larger than the second thickness when the peak value is equal to or greater than a second threshold, and the control unit When the thickness of the recording medium detected by the detection unit is the third thickness, the fixing unit is controlled so that the fixing temperature rises after the recording medium enters the fixing unit.

The invention according to claim 6 further comprises a warning unit that warns when the preset thickness of the recording medium is different from the thickness of the recording medium detected by the detecting unit.

An image forming apparatus according to a seventh aspect of the present invention is an image forming unit that forms an image on a recording medium, and the fixing device according to any one of the first to sixth aspects that fixes the image formed on the recording medium. , Is provided.

According to the first and seventh aspects of the invention, as compared with the case where the setting error of the thickness of the recording medium is not detected, the fixing is performed at the fixing temperature corresponding to the incorrectly set thickness of the recording medium. It can be suppressed.

  According to the second aspect of the invention, the device can be simplified as compared with the case where the sensor for detecting the thickness of the recording medium detects the thickness of the recording medium.

  According to the third aspect of the present invention, the thickness of the recording medium can be detected more accurately than in the case where the threshold value is set regardless of the width of the recording medium.

  According to the invention described in claim 4, when the thickness of the recording medium is two types, the fixing is excellently performed as compared with the case where the control of the fixing temperature is fixed regardless of the thickness of the recording medium. You can

  According to the invention described in claim 5, when the thickness of the recording medium is three types, the fixing is performed satisfactorily as compared with the case where the control of the fixing temperature is fixed regardless of the thickness of the recording medium. You can

According to the invention described in claim 6 , when the preset thickness of the recording medium and the thickness of the recording medium detected by the detecting means are different from each other, the user can be promptly promptly compared with the case where no warning is given. Can inform you of abnormalities.

It is a schematic configuration diagram showing a configuration of an image forming apparatus. FIG. 3 is a schematic cross-sectional view showing the configuration of the fixing device in a state where the pressure roll is located at the separated position. FIG. 3 is a schematic cross-sectional view showing the configuration of the fixing device in a state where the pressure roll is located at the pressure position. FIG. 3 is a block diagram showing a main configuration of an electric system of the image forming apparatus. It is a graph which shows an example of time series data of a detection result by a torque primary detecting element at the time of normal. FIG. 6 is a schematic configuration diagram for explaining a timing when a sheet rushes into a fixing device. FIG. 3 is a schematic configuration diagram for explaining the timing of discharging a sheet from a fixing device. 6 is a flowchart showing a processing flow of a fixing temperature control program. FIG. 6 is a diagram for explaining a pattern of changes in fixing temperature. FIG. 6 is a diagram for explaining a pattern of changes in fixing temperature.

  Embodiments for carrying out the present invention will be described below in detail with reference to the drawings.

  The configuration of the image forming apparatus 10 according to the present exemplary embodiment will be described with reference to FIGS. 1 to 3. In the following, yellow is represented by Y, magenta is represented by M, cyan is represented by C, and black is represented by K, and when it is necessary to distinguish each component and toner image (image) for each color, A description will be given by adding color codes (Y, M, C, K) corresponding to each color to the end. Further, in the following, in the case where the respective components and the toner image are collectively referred to without being distinguished for each color, the description of the color at the end of the code is omitted.

  (overall structure)

  As shown in FIG. 1, inside the apparatus body 10A of the image forming apparatus 10, an image processing unit that performs image processing for converting input image data into gradation data of four colors of Y, M, C, and K. 12 are provided.

  Further, on the center side of the apparatus main body 10A, image forming units 16 that form toner images of respective colors are arranged at intervals in a direction inclined with respect to the horizontal direction. Further, a primary transfer unit 18 is provided above the image forming units 16 of the respective colors in the vertical direction, and the toner images formed by the image forming units 16 of the respective colors are transferred in multiple layers.

  Further, on the side of the primary transfer unit 18 (on the left side in FIG. 1), a sheet P as an example of a recording medium conveyed along a conveyance path 60 by a supply conveyance unit 30 described later is superposed on the primary transfer unit 18. A secondary transfer roll 22 is provided for transferring the toner image transferred to the.

  A fixing device 24, which is an example of a fixing unit, is provided on the downstream side of the secondary transfer roll 22 in the transport direction of the paper P (hereinafter, referred to as “paper transport direction”). Further, the fixing device 24 fixes the toner image transferred to the paper P on the paper P by heat and pressure.

  Further, on the downstream side of the fixing device 24 in the paper conveyance direction, a discharge roll 28 that discharges the paper P on which the toner image is fixed to a discharge portion 26 provided at the top of the apparatus main body 10A of the image forming apparatus 10. It is provided.

  On the other hand, a supply / conveyance unit 30 for supplying and conveying the paper P is provided below and laterally of the image forming unit 16 in the vertical direction. In addition, above the primary transfer unit 18 in the vertical direction, the toner cartridges 14 that can be attached to and detached from the apparatus body 10A from the front of the apparatus body 10A and that are filled with the toner to be supplied to the developing device 38 are divided into four color cartridges. Individual pieces (14K to 14Y) are arranged side by side in the device width direction. The toner cartridge 14 for each color has a cylindrical shape extending in the depth direction of the apparatus, and is connected to the developing device 38 for each color via a replenishing pipe (not shown).

  (Image forming unit)

  As shown in FIG. 1, the image forming units 16 for the respective colors have the same configuration. The image forming unit 16 includes a rotating cylindrical image carrier 34 and a charger 36 that charges the surface of the image carrier 34.

  The image forming unit 16 also includes an LED (Light Emitting Diode) head 32 that irradiates the surface of the charged image carrier 34 with exposure light. Further, the image forming unit 16 develops the electrostatic latent image formed by irradiation of the exposure light from the LED head 32 with a developer (toner charged to a negative electrode in the present embodiment) to visualize it as a toner image. The container 38 is provided. The image forming unit 16 also includes a cleaning blade (not shown) that cleans the surface of the image carrier 34.

  A developing roller 39 is arranged in the developing device 38 so as to face the image carrier 34, and the developing device 38 uses the developing roller 39 to develop the electrostatic latent image formed on the image carrier 34 with a developer. It is developed and visualized as a toner image.

  The charger 36, the LED head 32, the developing roll 39, and the cleaning blade are arranged in this order from the upstream side to the downstream side in the rotation direction of the image holding body 34 so as to face the surface of the image holding body 34. Has been done.

  (Transfer part (primary transfer unit / secondary transfer roll))

  The primary transfer unit 18 includes an endless intermediate transfer belt 42, and a drive roll 46 around which the intermediate transfer belt 42 is wound and rotationally driven by a motor (not shown) to orbit the intermediate transfer belt 42 in the direction of arrow A. ing. Further, the primary transfer unit 18 is wound around the intermediate transfer belt 42, and is provided with a tension applying roll 48 that applies tension to the intermediate transfer belt 42, and is arranged above the tension applying roll 48 in the vertical direction and driven by the intermediate transfer belt 42. And a rotating auxiliary roll 50. The primary transfer unit 18 also includes primary transfer rolls 52 that are arranged on the opposite sides of the image carriers 34 of the respective colors with the intermediate transfer belt 42 interposed therebetween.

  With the above configuration, the toner images of Y, M, C, and K that are sequentially formed on the image carrier 34 of the image forming unit 16 of each color are transferred onto the intermediate transfer belt 42 by the primary transfer rolls 52 of each color. It is transcribed multiple times.

  Further, a cleaning blade 56 that contacts the surface of the intermediate transfer belt 42 and cleans the surface of the intermediate transfer belt 42 is disposed on the opposite side of the drive roll 46 with the intermediate transfer belt 42 interposed therebetween.

  Further, on the opposite side of the auxiliary roll 50 with the intermediate transfer belt 42 interposed therebetween, a secondary transfer roll 22 that transfers the toner image transferred onto the intermediate transfer belt 42 onto the conveyed paper P is provided. The secondary transfer roll 22 is grounded, the auxiliary roll 50 forms a counter electrode of the secondary transfer roll 22, and the secondary transfer voltage is applied to the auxiliary roll 50, so that the paper P The toner image is transferred to.

  (Supply and transport unit)

  The supply / conveyance unit 30 is provided below the image forming unit 16 in the apparatus main body 10A in the vertical direction, and includes a paper feed member 62 on which a plurality of paper sheets P are stacked.

  Further, the supply / conveyance unit 30 includes a paper feed roll 64 that sends out the paper P stacked on the paper feed member 62 to the conveyance path 60, and a separation roll 66 that separates the paper P sent out by the paper feed roll 64 one by one. And a positioning roll 68 for adjusting the conveyance timing of the paper P. The rolls are arranged in this order from the upstream side to the downstream side in the paper transport direction.

  With the above-described configuration, the sheet P supplied from the sheet feeding member 62 is set to the contact portion (secondary transfer position) between the intermediate transfer belt 42 and the secondary transfer roll 22 by the rotating positioning roll 68 at a predetermined timing. Sent out.

  (Fixing device)

  As shown in FIGS. 2 and 3, the fixing device 24 according to the present embodiment includes a coil unit 100, an external magnetic member 102 including soft ferrite, a heating belt 104, and a pressure roll 106. Note that FIG. 2 shows an example of a state in which the pressure roll 106 is moved to the separated position separated from the heating belt 104. In addition, FIG. 3 illustrates an example of a state in which the pressure roll 106 is in contact with the heating belt 104 and is moved to a pressure position where the heating belt 104 is pressed.

  Inside the coil unit 100, a plurality of exciting coils 108 that generate a magnetic field by supplying power from a fixing power supply (not shown) are provided. The heating belt 104 is an endless belt including a heat generating layer that generates heat by electromagnetic induction. Further, in a region inside the inner peripheral surface of the heating belt 104, a sliding sheet 109, a pressing pad 110 formed by including a liquid crystal polymer, and an internal magnetic member 112 formed by including a temperature-sensitive magnetic alloy are provided. It is provided.

  On the other hand, the pressure roll 106 includes a mandrel 114 formed of a metal such as aluminum and a sponge elastic layer 116 such as foamed silicon rubber. Further, the pressure roll 106 is movable by a latch mechanism 131 (see FIG. 4) between a separated position (position in FIG. 2) and a pressure position (position in FIG. 3).

  Further, when the pressure roll 106 is at the separated position, the drive target of the motor 132 (see FIG. 4) as an example of a drive unit is switched to the heating belt 104 by the switching unit 133 (see FIG. 4), and heating is performed. The belt 104 is driven (rotated). On the other hand, when the pressure roll 106 is moved to the pressure position by the latch mechanism 131, the drive target of the motor 132 is switched to the pressure roll 106 by the switching unit 133, and the pressure roll 106 is driven (rotated). As a result, the heating belt 104 is driven to rotate as the pressure roll 106 rotates.

  With the above configuration, the sheet P conveyed to the fixing device 24 is heated and pressed by the fixing device 24, and the toner image is fixed on one surface (image forming surface) of the sheet P.

  Further, the supply / conveyance unit 30 forms the toner image on the other surface of the sheet P having the toner image fixed on one surface thereof by the fixing device 24, without discharging the sheet P to the discharge section 26 as it is by the discharge roller 28. The double-sided conveyance device 70 used for the.

  The double-sided conveyance device 70 conveys the paper P along the double-sided conveyance path 72 and the double-sided conveyance path 72 in which the front and back of the paper P is reversed and the paper P is conveyed from the discharge roll 28 toward the alignment roll 68. A roll 74 and a transport roll 76 are provided.

  (Other)

  The image forming apparatus 10 includes a sheet detection sensor 80 provided on the upstream side in the sheet conveyance direction of the fixing device 24 along the conveyance path 60, and a sheet detection sensor 82 provided on the downstream side. The paper detection sensors 80 and 82 according to the present embodiment are, for example, reflective sensors that include a pair of a light emitting element and a light receiving element. The sheet detection sensors 80 and 82 emit light from the light emitting element to the detection position on the transport path 60 corresponding to the installation position. Further, the paper detection sensors 80 and 82 output a signal (hereinafter, referred to as “detection signal”) having a signal level corresponding to the amount of light received by the light receiving element. The light emitted from the light emitting element is reflected by the paper P while the paper P is being transported to the detection position. Therefore, the sheet detection sensors 80 and 82 output detection signals having different signal levels during the period when the sheet P is conveyed to the detection position and the period where the sheet P is not conveyed.

  As described above, in the present embodiment, the reflection type sensor is applied as the paper detection sensors 80 and 82, but the present invention is not limited to this, and another sensor such as a transmission type sensor is applied. Good.

  (Image forming process)

  First, the image processing unit 12 sequentially outputs the gradation data of each color to the LED head 32 of each color. Then, the exposure light emitted from the LED head 32 in accordance with the gradation data is applied to the surface of the image carrier 34 charged by the charger 36. As a result, an electrostatic latent image is formed on the surface of the image carrier 34. The electrostatic latent image formed on the image carrier 34 is developed by the developing device 38 of each color and visualized as a toner image of each color of Y, M, C and K.

  Further, the primary transfer rolls 52 of the primary transfer unit 18 multiple-transfer the toner images of the respective colors formed on the image carrier 34 onto the rotating intermediate transfer belt 42.

  The toner images of the respective colors, which are transferred in a multiple manner onto the intermediate transfer belt 42, are transferred to the paper P that has been conveyed along the conveyance path 60 from the paper feed member 62 by the paper feed roll 64, the separation roll 66, and the alignment roll 68. Secondary transfer is performed at the secondary transfer position by the secondary transfer roll 22.

  Further, the paper P on which the toner image is transferred is conveyed to the fixing device 24. Then, the toner image is fixed on the sheet P by the fixing device 24. The paper P on which the toner image is fixed is discharged to the discharge unit 26 by the discharge roll 28.

  On the other hand, when images are formed on both sides of the paper P, the paper P having the toner image fixed on one surface (front surface) by the fixing device 24 is not directly discharged to the discharge unit 26 by the discharge roll 28. By rotating the discharge roll 28 in the reverse direction, the paper conveyance direction of the paper P is switched. Then, the paper P is transported by the transport rollers 74 and 76 along the double-sided transport path 72.

  The sheet P conveyed along the double-sided conveyance path 72 is reversed on the front and back sides and conveyed again to the alignment roll 68. Then, after the toner image is transferred and fixed on the other surface (back surface) of the paper P, the paper P is discharged to the discharge unit 26 by the discharge roll 28.

  Next, with reference to FIG. 4, a description will be given of a main configuration of an electric system of the image forming apparatus 10 according to the present exemplary embodiment.

  As shown in FIG. 4, the image forming apparatus 10 according to the present exemplary embodiment includes a CPU (Central Processing Unit) 120 as an example of a detection unit and a control unit that controls the overall operation of the image forming apparatus 10, and various types. A ROM (Read Only Memory) 122 in which programs and various parameters are stored in advance is provided. Further, the image forming apparatus 10 includes a RAM (Random Access Memory) 124 used as a work area or the like when the CPU 120 executes various programs, and a nonvolatile storage unit 126 such as a flash memory.

  The image forming apparatus 10 also includes a communication line I / F (Interface) unit 128 that transmits and receives communication data to and from an external device. In addition, the image forming apparatus 10 receives an instruction from the user to the image forming apparatus 10, and also includes an operation display unit 130 as an example of a warning unit that displays various kinds of information regarding the operation status of the image forming apparatus 10 to the user. I have it. The operation display unit 130 is, for example, a display button that realizes acceptance of an operation instruction by executing a program, a display having a touch panel on a display surface on which various information is displayed, and a hardware key such as a numeric keypad and a start button. including.

  The image forming apparatus 10 also includes a torque detection unit 134 as an example of a detection unit that detects a load (torque) of the motor 132 that rotationally drives the heating belt 104 or the pressure roll 106. The torque detection unit 134 according to the present embodiment is connected to the motor 132 and detects the torque of the motor 132 as the value of the current flowing through the motor 132.

  The configuration of the torque detection unit 134 according to the present embodiment is not particularly limited as long as the torque of the motor 132 can be detected. For example, as the torque detection unit 134, a configuration in which the voltage between the shunt resistors is measured to detect the current may be applied. Further, for example, as the torque detection unit 134, a configuration in which a resistor is provided on a path through which a current flows in the motor 132 and the voltage between the resistors is measured to detect the current may be applied. Further, for example, as the torque detection unit 134, it is possible to apply a configuration in which a current sensor including a Hall element is provided on the path of the current flowing through the motor 132 to detect the current. Further, the torque detection unit 134 may be configured to convert the detected current into a voltage and output the voltage. Furthermore, for example, as the torque detection unit 134, a torque detector that detects the torque of the motor 132 may be applied.

  The image forming apparatus 10 also includes an image forming unit 136 including components such as the image forming unit 16 and the primary transfer unit 18 that perform various processes related to image formation on the paper P. Then, the CPU 120, the ROM 122, the RAM 124, the storage unit 126, the communication line I / F unit 128, the operation display unit 130, the latch mechanism 131, the motor 132, the switching unit 133, the torque detection unit 134, the image forming unit 136, and the paper detection sensor. The respective units 80 and 82 are connected to each other via a bus 138 such as an address bus, a data bus, and a control bus.

  With the above configuration, the image forming apparatus 10 according to the present exemplary embodiment allows the CPU 120 to access the ROM 122, the RAM 124, and the storage unit 126, and to communicate with an external device via the communication line I / F unit 128. Send and receive data respectively. Further, the image forming apparatus 10 causes the CPU 120 to acquire various instruction information via the operation display unit 130 and display various information on the operation display unit 130, respectively. Further, the image forming apparatus 10 causes the CPU 120 to control the motor 132, acquire the current value output from the torque detection unit 134, and control the image forming unit 136, respectively.

  Further, in the image forming apparatus 10, the CPU 120 acquires the detection signals output from the paper detection sensors 80 and 82, respectively. Therefore, in the image forming apparatus 10, the CPU 120 detects whether or not the sheet P has passed the detection positions of the sheet detection sensors 80 and 82 based on the signal level of the obtained detection signal.

  By the way, although the paper P has various thicknesses, for example, when the papers P have different thicknesses, the fixing temperature (heating temperature of the heating belt 104) in the fixing device 24 is set when the paper conveying speed is the same. It needs to be controlled differently. For example, if the paper P is thick paper and fixing is performed at a fixing temperature corresponding to thin paper, the fixing temperature may be too low and the toner may not be sufficiently fixed. On the other hand, if the paper P is a thin paper and is fixed at the fixing temperature corresponding to the thick paper, the fixing temperature may be too high and the paper P may be curled or hot offset may occur.

  Further, the fixing temperature is set in accordance with the thickness of the paper P preset by the operation of the user, for example. However, when the user mistakenly sets the thickness of the paper P, the fixing temperature is set to the original fixing temperature. The fixing is performed at a different fixing temperature, and the above problem occurs.

  Therefore, in the image forming apparatus 10 according to the present exemplary embodiment, the thickness of the sheet P is detected from the torque of the motor 132 when the sheet P enters the fixing device 24, and the detected thickness is previously set by the user's operation. When the thickness of the paper P is different from the set thickness, the fixing temperature of the fixing device 24 is controlled according to the detected thickness.

  Hereinafter, the fixing temperature control according to the present embodiment will be described in detail with reference to FIGS. Note that FIG. 5 shows the time series data of the current value output from the torque detection unit 134 in a state where the four sheets P are conveyed one by one in order in the normal state by the fixing device 24 and the image is fixed. Shows an example. 6 and 7 are views for explaining the time series data of the current values shown in FIG. 5, and show the conveyance position of the paper P. Further, in order to avoid complication, the intermediate transfer belt 42 is shown by a broken line in FIGS. 6 and 7.

  As shown in FIG. 5, the current value output from the torque detection unit 134 has a peak value that is convex upward when the leading edge of the sheet P enters the fixing device 24, and the trailing edge of the sheet P is from the fixing device 24. The peak value is convex downward when discharged. Here, the larger the thickness of the paper P, the larger the peak value of the upward convex. Therefore, the thickness of the sheet P is detected from the peak value that is convex upward. In the present embodiment, a case will be described in which the thickness of the paper P is detected from the peak value that is convex upward. It should be noted that the larger the thickness of the sheet P, the larger the absolute value of the downwardly convex peak value. Therefore, the thickness of the paper P may be detected from the peak value that is convex downward. Further, the thickness of the sheet P may be detected from the average value of the peak values of the upward convex and the peak values of the downward convex. In addition, the thickness of the sheet P is calculated from the average value of the current values during the passage of the paper, that is, the average value of the current values detected from the detection of the upward convex peak value to the downward convex peak value. It may be detected.

  Next, the principle of the time series change of the current value shown in FIG. 5 will be described with reference to FIGS. 6 and 7. As shown in FIG. 6, when the pressure roller 106 is moved to the pressure position and is in the latch ON state, when the leading edge of the sheet P enters the nip portion between the heating belt 104 and the pressure roller 106 in the fixing device 24. A force in the direction opposite to the rotation direction of the pressure roll 106 (force indicated by arrow D in FIG. 6) acts on the pressure roll 106, and the torque of the motor 132 increases. Therefore, the current value output from the torque detection unit 134 also increases, and becomes a peak value convex upward. After that, the sheet P is sandwiched by the fixing device 24 and conveyed, and the force in the reverse direction when the sheet P enters the fixing device 24 does not work, so that the current value decreases.

  On the other hand, as shown in FIG. 7, when the trailing edge of the paper P is discharged from the nip portion, the pressure roll 106 exerts a force in the same direction as the rotation direction of the pressure roll 106 (arrow E in FIG. 7). Force) and the torque of the motor 132 decreases. Therefore, the current value output from the torque detection unit 134 also decreases, and has a downwardly convex peak value.

  In the following, the upward convex peak value may be referred to as the upper peak value, and the downward convex peak value may be referred to as the lower peak value.

  Next, with reference to FIG. 8, the operation of the image forming apparatus 10 according to the present exemplary embodiment when the fixing process is executed will be described. 8. FIG. 8 is a flowchart showing the flow of processing of the fixing temperature control program executed by the CPU 120 each time an image forming instruction for the paper P is input. The fixing temperature control program is installed in the ROM 122 in advance. Further, here, for the sake of simplicity, the description of the process of forming an image on the sheet P in the above-described image forming step will be omitted.

  The thickness of the sheet P is set in advance by the user operating the setting screen (not shown) of the thickness of the sheet P displayed on the operation display unit 130, and the set thickness of the sheet P is set. Are stored in the storage unit 126. Note that the user may set the thickness of the paper P by setting a desired size from a plurality of predetermined standard sizes on the setting screen, or by inputting a size other than the standard size. The thickness of the paper P may be set.

  In step S100, the CPU 120 acquires the detection signal output from the paper detection sensor 80.

  In step S102, the CPU 120 determines, based on the detection signal acquired in step S100, whether the leading edge of the paper P has passed the detection position of the paper detection sensor 80 on the transport path 60. If the determination is negative, the CPU 120 returns to step S100, while if the determination in step S102 is positive, the process proceeds to step S104.

  In the case where the paper detection sensor 80 is not provided, for example, the CPU 120 detects the paper P when the period after the conveyance of the paper P from the paper feed member 62 is started becomes equal to or more than the threshold value. It may be determined that the leading edge has passed the detection position of the sheet detection sensor 80 on the transport path 60. Further, the threshold value in this case may be appropriately determined based on the distance of the transport path 60 from the sheet feeding member 62 to the fixing device 24 and the transport speed of the sheet P.

  In step S104, CPU 120 acquires the current value output from torque detection unit 134.

  In step S106, the CPU 120 acquires the detection signal output from the paper detection sensor 82.

  In step S108, the CPU 120 determines, based on the detection signal acquired in step S104, whether the leading edge of the paper P has passed the detection position of the paper detection sensor 82 on the transport path 60. If this determination is negative, the CPU 120 returns to step S104, while if the determination of step S108 is positive, the process proceeds to step S110.

  In a case where the paper detection sensor 82 is not provided, for example, the CPU 120 detects the paper P when the period after the conveyance of the paper P from the paper feeding member 62 is started is equal to or more than the threshold value. It may be determined that the leading edge has passed the detection position of the paper detection sensor 82 on the transport path 60. Further, the threshold value in this case may be appropriately determined based on the distance of the transport path 60 from the sheet feeding member 62 to the fixing device 24 and the transport speed of the sheet P. Further, when the upper peak value is detected from the current value of the detection signal acquired in step S104, it may be determined that the leading edge of the paper P has passed the detection position of the paper detection sensor 82 on the transport path 60.

  The current value acquired in step S104 is the current value acquired during the period from when the leading edge of the paper P passes through the paper detection sensor 80 and enters the fixing device 24 until it passes through the paper detection sensor 82. The value will include the upper peak value.

  Therefore, in step S110, the peak value of the current value obtained in step S104 is obtained, and the thickness of the paper P is detected from the obtained peak value. Specifically, the thickness of the paper P is obtained by comparing the peak value with a predetermined threshold value for obtaining the thickness of the paper P. In the present embodiment, a case will be described where three types of sheets having different thicknesses are detected.

  For example, as shown in FIG. 9, a first threshold TH1 and a second threshold TH2 larger than the first threshold TH are set in advance. When the peak value Pk is less than the first threshold value TH1, the thickness of the paper P is detected as the first thickness D1. When the peak value Pk is equal to or greater than the first threshold TH1 and less than the second threshold TH2, the thickness of the sheet P is detected as the second thickness D2 that is thicker than the first thickness D1. Further, when the peak value Pk is equal to or larger than the second threshold value TH2, it is detected as the third thickness D3 which is thicker than the second thickness D2. The thickness of the paper P may be two or four or more, and the threshold for detecting the thickness of the paper P may be appropriately set according to the number of types of the paper P. Good.

  The peak value Pk may differ depending on the width of the paper P, that is, the length of the paper P in the direction orthogonal to the transport direction. For example, as the width of the paper P increases, the peak value Pk may increase accordingly. Therefore, the threshold value for detecting the thickness of the paper P may be increased as the width of the paper P increases. The width of the paper P is acquired from the preset type of the paper P.

  In step S112, the CPU 120 reads the preset thickness of the paper P from the storage unit 26, and determines whether the thickness of the paper P detected in step S110 is different from the preset thickness of the paper P. To do. If the determination in step S112 is affirmative, the process proceeds to step S114, while if the determination is negative, the process proceeds to step S118.

  In step S114, CPU 120 warns the user by displaying a message on operation display unit 130 indicating that a paper P having a thickness different from the preset thickness of paper P is being processed.

  In step S116, the CPU 120 controls the fixing temperature according to the thickness of the paper P detected in step S110. In the present embodiment, when the paper P has the first thickness D1, the fixing temperature is controlled so that the change in the fixing temperature becomes the pattern PT1 shown in FIG. 9, for example. The pattern PT1 is a pattern in which the fixing temperature gradually decreases. Further, when the paper P has the second thickness D2, the fixing temperature is controlled so that the change of the fixing temperature becomes the pattern PT2 shown in FIG. 9, for example. The pattern PT2 is a pattern in which the fixing temperature is maintained constant.

  Here, for example, when the preset paper P has the first thickness D1, but the paper P detected in step S110 has the second thickness D2, a pattern corresponding to the first thickness D1 is obtained. If the fixing temperature is controlled so as to be PT1, the fixing temperature may be too low and fixing failure may occur. Therefore, the fixing temperature is controlled so that the pattern PT2 corresponds to the second thickness D2 of the paper P detected in step S110. As a result, defective fixing is suppressed.

  On the contrary, when the preset paper P has the second thickness D2 but the paper P detected in step S110 is the first thickness D1, the pattern PT2 corresponding to the second thickness D2 is obtained. If the fixing temperature is controlled so as to become, the fixing temperature may be too high and the paper P may be curled or hot off. Therefore, the fixing temperature is controlled so that the pattern PT1 corresponds to the first thickness D1 of the paper P detected in step S110. As a result, curling or hot-off of the paper P is suppressed.

  Further, in the present embodiment, when the paper P has the third thickness D3, the fixing temperature is controlled so that the change in the fixing temperature becomes the pattern PT3 shown in FIG. 10, for example. The pattern PT3 is a pattern that raises the fixing temperature. Further, when the paper P has the third thickness D3, fixing may be skipped as shown in FIG. Specifically, for example, as shown in FIG. 10, after the fixing of the first sheet P is completed, the conveyance of the second sheet P is stopped, and after the elapse of a predetermined period t, the second sheet P is transferred. The conveyance of P is restarted. By skipping fixing in this way, the fixing temperature rises quickly. It should be noted that the period t during which the conveyance of the paper P is stopped may be set to a time at which the target fixing temperature is obtained.

  Here, for example, when the preset paper P has the first thickness D1, but the paper P detected in step S110 has the third thickness D3, a pattern corresponding to the first thickness D1 is obtained. If the fixing temperature is controlled so as to be PT1, the fixing temperature may be too low and fixing failure may occur. Therefore, the fixing temperature is controlled so that the pattern PT3 corresponds to the third thickness D3 of the paper P detected in step S110, the conveyance of the paper P is stopped, and the paper is fed after a predetermined period t has elapsed. The conveyance of P is restarted. As a result, defective fixing is suppressed. Note that the conveyance speed may be reduced instead of stopping the conveyance of the paper P. Further, when the fixing is skipped and the conveyance of the paper P is restarted, the thickness of the paper P is detected again, and it is determined whether or not the detected thickness of the paper P is different from the preset thickness of the paper P. It may be determined.

  On the other hand, in step S118, since the thickness of the sheet detected in step S110 is the same as the preset thickness of the sheet P, the change in the fixing temperature becomes a pattern corresponding to the preset thickness of the sheet P. Control the fixing temperature.

  As described above, in the present embodiment, when the thickness of the sheet P detected from the torque of the motor 132 when the sheet P enters the fixing device 24 is different from the preset thickness of the sheet P, the detected sheet P is detected. The fixing temperature of the fixing device 24 is controlled according to the thickness of P. As a result, the occurrence of defective fixing is suppressed.

  In the present embodiment, the case where the fixing temperature is controlled according to the detected thickness of the paper P has been described, but the fixing temperature may be controlled and the conveyance speed of the paper P may be controlled. For example, as the conveyance speed of the sheet P is increased, the amount of heat per unit time that the sheet P receives from the fixing device 24 becomes smaller, and the same effect as that of lowering the fixing temperature is obtained, and the conveyance speed of the sheet P is decreased. The amount of heat that the paper P receives from the fixing device 24 per unit time increases, and the same effect as raising the fixing temperature can be obtained. Therefore, the degree of fixing can be easily adjusted by controlling the fixing temperature and the conveying speed.

  Further, in the present embodiment, the case where a so-called IH (Induction Heating) type fixing device that performs heating by electromagnetic induction is used has been described, but the present invention is not limited to this. For example, another type of fixing device using a halogen lamp or the like may be used.

  Further, although the case where the fixing temperature control program is preinstalled in the ROM 122 has been described in the present embodiment, the present invention is not limited to this. For example, the fixing temperature control program may be stored in a storage medium such as a CD-ROM (Compact Disk Read Only Memory) or provided, or may be provided via a network.

  Further, in the present embodiment, the case where the fixing temperature control is realized by a software configuration by using a computer by executing a program has been described, but the present invention is not limited to this. For example, the fixing temperature control may be realized by a hardware configuration or a combination of the hardware configuration and the software configuration.

  In addition, the configuration of the image forming apparatus 10 described in the present embodiment (see FIGS. 1 to 4) is an example, and unnecessary portions may be deleted or new portions may be added without departing from the scope of the present invention. Needless to say, you can add or.

  Further, the processing flow of the fixing temperature control program described in the present embodiment (see FIG. 8) is also an example, and unnecessary steps may be deleted or new steps may be added without departing from the scope of the present invention. It goes without saying that the processing order may be added or changed.

10 image forming device 24 fixing device 104 heating belt 106 pressure roll 120 CPU
132 motor 134 torque detection unit 136 image forming unit P paper

Claims (7)

A fixing means for fixing the image formed on the recording medium,
Drive means for driving the fixing means,
Detection means for detecting the load of the drive means,
Of the driving means detected by the peak value of the load of said driving means when said recording medium from the peak value of the load is discharged from said fixing means of said driving means when said recording medium enters into said fixing means Detection means for detecting the thickness of the recording medium from the average value of the load,
Fixing device equipped with. The fixing device according to claim 1, wherein the detection unit detects the thickness of the recording medium from a comparison result of a peak value of a load of the driving unit and a threshold when the recording medium enters the fixing unit. The fixing device according to claim 2, wherein the detection unit sets the threshold value according to a width of the recording medium. When the preset thickness of the recording medium and the thickness of the recording medium detected by the detecting unit are different, the fixing unit is adjusted to the thickness of the recording medium detected by the detecting unit. And a controller for controlling a fixing temperature, wherein the detector detects the thickness of the recording medium as a first thickness when the peak value is less than a first threshold value, and the peak value is When the thickness is equal to or larger than a first threshold, the thickness of the recording medium is detected as a second thickness that is thicker than the first thickness,
When the thickness of the recording medium detected by the detecting unit is the first thickness, the control unit controls the fixing temperature to decrease after the recording medium enters the fixing unit. When the thickness of the recording medium detected by the detecting unit is the second thickness, the fixing unit is controlled so as to maintain the fixing temperature when the recording medium enters the fixing unit. The fixing device according to claim 2 or 3, which controls the fixing unit. The detection means detects the thickness of the recording medium as the second thickness when the peak value is greater than or equal to a first threshold and less than a second threshold that is greater than the first threshold, and When the peak value is equal to or greater than the second threshold value, the thickness of the recording medium is detected as a third thickness that is thicker than the second thickness,
When the thickness of the recording medium detected by the detecting unit is the third thickness, the control unit controls the fixing unit so that the fixing temperature rises after the recording medium enters the fixing unit. The fixing device according to claim 4. 6. The warning device according to claim 1, further comprising a warning unit that warns when a preset thickness of the recording medium and a thickness of the recording medium detected by the detection unit are different. Fixing device. An image forming means for forming an image on a recording medium,
The fixing device according to claim 1, which fixes an image formed on the recording medium,
An image forming apparatus equipped with.