JP2008139411A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent a conveyance defect jam caused by conveyance abnormality (such as image irregularities by a slip between a film and a sheet material and a slip between a pressure roller and a sheet material) which has been easy to be caused in a film heating/fixing device in a pressure roller driving system. <P>SOLUTION: In the image forming apparatus, when the driving of a fixing motor is started (S102), and the tip of a sheet material reaches a paper feed sensor (S103, Yes), a fixing motor current I1 is detected by a current detection means, and, when the tip of the sheet material reaches a nip N (S105, Yes), a fixing motor current I2 is detected by a current detection means (S106), and when the difference (I2-I1) between the detected fixing motor currents is less than a threshold ΔI (S107, No), the speed of fixing motors is increased by a fixing motor speed changing means (S10). <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image forming apparatus, and more particularly to an image heat fixing apparatus provided in an electrophotographic image forming apparatus such as a laser beam printer.

  2. Description of the Related Art Conventionally, in an image heat fixing device (hereinafter simply referred to as a fixing device) provided in an image forming apparatus that employs an electrophotographic method, an electrostatic recording method, etc., the following method of heat fixing means has been widely used. ing. That is, the sheet material carrying the toner image is passed through a pressure nip region formed by a fixing roller and a pressure roller that are rotated in pressure contact with each other. This is a so-called heat roller type heat fixing means for fixing the toner image as a permanent image on the sheet material.

  In addition, a heating and fixing unit that does not supply power particularly during standby and suppresses power consumption as much as possible is used. Specifically, a sheet material is transported between a heating element (hereinafter referred to as a heater) attached to a support and a pressure roller via a thin film (hereinafter referred to as a fixing film) on the sheet material. This is a film heating method for fixing a toner image by heating.

  The above-mentioned two types of heat fixing means constituting the fixing device have one or more fixing temperature detecting means for controlling the temperature for heat fixing. The fixing temperature detecting means generally uses a thermistor, and detects the temperature of the heater or the pressure roller by being provided in contact with the heater or the pressure roller. Recently, a technique for detecting the temperature for heating and fixing by measuring the radiant heat of the heater and the pressure roller has been studied.

  FIG. 5 is a schematic cross-sectional view showing a typical example of a heat fixing unit using the film heating method. In FIG. 5, the heating unit 510 mainly includes a heater 511, a guide member 512 as a support, and a fixing film 513. The heater 511 is fixed to a guide member 512 that guides the rotational movement of the fixing film 513. The guide member 512 is formed of, for example, a heat-resistant resin member, holds a heater 511 as a heating member, and also serves as a guide for the fixing film 513. Further, heat-resistant grease or the like is interposed between the fixing film 513 and the outer peripheral surfaces of the heater 511 and the guide member 512 in order to enhance the rotational slidability with the fixing film 513. Reference numeral 514 denotes a pressure roller.

  As a driving method of the fixing film 513 in the film heating type fixing device, there is a method in which a driving roller (not shown) is provided on the inner peripheral surface of the fixing film 513 and the fixing film 513 is driven while tension is applied. Further, there is known a system in which the fixing film 513 is loosely fitted to the film guide and the pressure roller 514 is driven to rotate the fixing film 513 with respect to the pressure roller 514. Of these methods, since the number of components is small in recent years, the latter pressure roller driving method is often employed. The fixing device described with reference to FIG. 5 is of a pressure roller driving system in which the guide member 512 corresponds to a film guide.

  In order to detect the temperature of the heater 511, a thermistor 515 is generally provided as a fixing temperature detecting means. As a typical means for installing the thermistor 515, there are a method of adhering to the heater 511 with a heat-resistant adhesive and a method of installing by pressing using the pressure of a spring-like member.

  Actually, as shown in FIG. 6, a heater (here, particularly a ceramic heater) 511 is fixed to a stay 501 for fixing its position. Further, a pressure roller 514 is disposed so as to face each other through the fixing film 513. As the pressure roller 514 is driven, the sheet material 2 held at a position where the pressure roller 514 and the fixing film 513 come into contact (hereinafter referred to as a fixing nip N) is conveyed. Meanwhile, the toner T carried on the sheet material 2 is fixed to the sheet material 2 by the pressure supplied from the pressure roller 514 and the heat supplied from the ceramic heater 511. Among the plurality of thermistors, the main thermistor 515 is always disposed at a position where the sheet material 2 passes through any position of the sheet material 2 that can be conveyed.

  Here, a configuration of an image forming apparatus including a film heating type heat fixing unit will be described. FIG. 7 is a diagram for explaining a conventional technique of a printer as an image forming apparatus.

The sheet material 2 loaded in the sheet feeding cassette 1 is fed by a cassette feeding roller 3 and fed by a conveying roller 4 onto a sheet material conveying path 5 in the printer, and an image timing and a sheet are fed by a sheet feeding sensor 7. The positions of the front and rear ends of the material 2 are detected. Further, the leading edge of the sheet material 2 is aligned by the sheet feed sensor 7 with the registration roller 6, and the sheet material 2 is conveyed to the transfer roller 8 and the photosensitive drum 9. The sheet material 2 to which the toner has been transferred by the transfer roller 8 and the photosensitive drum 9 is a pressure roller 10 (reference numeral 514 in FIG. 6; the same applies hereinafter) for fixing the toner to the sheet material 2, a fixing film 11 (513), It is conveyed to the ceramic heater 11-a (511) and fixed by pressure. Thereafter, the paper is discharged by the paper discharge roller 12. Here, the pressure roller 10 (514) is driven by a fixing motor (not shown), and the fixing film 11 (513) and the sheet material 2 are conveyed following the pressure roller 10 (514). The CPU 13 controls the heater driving circuit 14 to control the temperature of the ceramic heater 11-a (511). Reference numeral 15 denotes a scanner unit, and 11-b (515) denotes a thermistor.
JP 2005-338698 A

  However, among the above-mentioned film heating type fixing devices, the pressure roller driving type fixing device (hereinafter referred to as a pressure roller driving type film heating fixing device) has the following problems. That is, the rotation of the fixing film is a driven rotation that depends on the rotation driving of the pressure roller, and depending on the sheet material passing condition, conveyance abnormality (image disturbance due to slip between film and sheet material, or slip between pressure roller and sheet material, etc.) ) Conveyance failure jam due to

  The present invention has been made paying attention to the above points, and image formation that prevents the occurrence of a conveyance failure jam due to a conveyance abnormality caused by a slip that is likely to occur in a pressure roller driving type film heating and fixing apparatus. An object is to provide an apparatus.

  The image forming apparatus of the present invention can solve the above problems by including the following configuration.

  (1) A heating unit for fixing an unfixed developer on a recording medium to the recording medium, a pressurizing unit for applying pressure to the heating unit, and a fixing unit that rotationally drives the heating unit or the pressurizing unit. A fixing device driving means, a current detecting means for detecting a current supplied to the fixing device driving means, and a fixing device driving speed changing means for changing the speed of the fixing device driving means, wherein the fixing device driving speed changing means comprises: An image forming apparatus characterized in that the speed of the fixing device driving means is changed based on a current detection result by the current detecting means.

  (2) Heating means for fixing the unfixed developer on the recording medium to the recording medium, pressurizing means for applying pressure to the heating means, and fixing for rotationally driving the heating means or the pressurizing means A driving unit, a current detecting unit that detects a current supplied to the fixing unit driving unit, and a pressing force varying unit that varies a pressing force of the pressing unit, and the pressing force varying unit includes the current detecting unit. An image forming apparatus, wherein the pressing force of the pressurizing unit is changed based on a current detection result by the unit.

  (3) In the image forming apparatus according to (1) or (2), a recording medium detection unit that detects that the recording medium has passed through the heating unit, and a detection result by the recording medium detection unit Comparing the time and the jam detection time, the jam detection means for detecting the conveyance failure jam based on the comparison result, and the jam detection time variable means for changing the jam detection time, the jam detection time variable means, An image forming apparatus, wherein the jam detection time is changed based on a current detection result by the current detection means.

  (4) The image forming apparatus according to (1), further including an environmental temperature detecting unit that detects a temperature in the image forming apparatus, and an environmental humidity detecting unit that detects a humidity in the image forming apparatus, The fixing device driving speed changing means is based on the temperature detection result by the environmental temperature detection means, the humidity detection result by the environmental humidity detection means, and the current detection result by the current detection means. An image forming apparatus characterized by changing the speed of the image forming apparatus.

  (5) The image forming apparatus according to (2), further including an environmental temperature detecting unit that detects a temperature in the image forming apparatus, and an environmental humidity detecting unit that detects a humidity in the image forming apparatus, The pressurizing variable means is based on the temperature detection result by the environmental temperature detection means, the humidity detection result by the environmental humidity detection means, and the current detection result by the current detection means. An image forming apparatus characterized in that

  According to the present invention, it is possible to cause a conveyance failure jam due to a conveyance abnormality (an image disorder due to a slip between a film and a sheet material or a slip between a pressure roller and a sheet material) that is likely to occur in a film heating and fixing device of a pressure roller driving system. Occurrence can be prevented.

  Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to examples.

  1, FIG. 2, FIG. 3 and FIG. 7 are diagrams for explaining an embodiment of the present invention.

  In FIG. 7, a sheet material (corresponding to a recording medium) 2 stacked in a sheet feeding cassette 1 is fed by a cassette feeding roller 3 and fed by a conveying roller 4 onto a sheet material conveying path 5 in the printer. The paper feed sensor 7 detects the image timing and the positions of the leading and trailing edges of the sheet material 2. Further, the leading edge of the sheet material 2 is aligned by the sheet feed sensor 7 with the registration roller 6, and the sheet material 2 is conveyed to the transfer roller 8 and the photosensitive drum 9. The sheet material 2 to which the toner (corresponding to the developing material) is transferred by the transfer roller 8 and the photosensitive drum 9 is a pressure roller (corresponding to the pressing means) 10 for fixing the toner to the sheet material 2 and a fixing film (heating (Corresponding to the means) 11, and conveyed to the ceramic heater 11-a and fixed by pressure. Thereafter, the paper is discharged by the paper discharge roller 12. Here, the pressure roller 10 is driven by a fixing motor (not shown) (corresponding to a fixing device driving means), and the fixing film 11 and the sheet material 2 are conveyed following the pressure roller 10. Here, the temperature of the ceramic heater 11-a is detected by the thermistor 11-b and transmitted to the CPU 13. The CPU 13 controls the power applied to the ceramic heater 11-a via the heater drive circuit 14 so that the temperature of the thermistor 11-b becomes a desired constant temperature.

  The CPU 13 performs control so that the applied power is increased by the amount of heat applied to the sheet material 2 during the period when the sheet material 2 passes through the ceramic heater 11-a so as to keep the temperature of the ceramic heater 11-a constant. To control.

  Next, the driving current of the fixing motor will be described with reference to FIG. As shown in FIG. 2, in a normal time when no slip occurs, a starting current I0 flows when the fixing motor is started, and a steady current I1 flows during steady rotation. Further, since the torque applied to the fixing motor is increased by the amount of the sheet material 2 when the sheet is passed, a current I2 during passing I1 <I2 flows. On the other hand, when a fixing slip occurs, as shown in FIG. 3, the torque is larger than that during steady rotation (steady current I1), and the torque applied to the fixing motor than during normal paper feeding (current I2 during paper feeding). Is small. Therefore, a current I1 <I3 <I2 (referred to as a slip occurrence current in FIG. 3) I3 flows. Here, since (I3-I1) <(I2-I1), the CPU (corresponding to current detection means) 13 monitors the current flowing through the fixing motor (hereinafter referred to as the fixing motor current), and the fixing motor current Based on the value of the difference (I2−I1), the following determination is made. That is, if the difference (I2-I1) in the fixing motor current is equal to or greater than the threshold value ΔI, it is determined that the motor is operating normally, and if it is less than the threshold value ΔI, it is determined that slip has occurred. When it is determined that a slip has occurred, the CPU (corresponding to the fixing device driving speed changing means) 13 increases the speed of the fixing motor and increases the torque to eliminate the occurrence of the slip.

  Next, according to the flowchart of FIG. 1, the operation at the time of occurrence of slip in the present embodiment will be described.

  In FIG. 1, upon receiving a print command (step S101, hereinafter simply referred to as S101), the CPU 13 starts driving the fixing motor (S102). When the leading edge of the sheet material is detected by the paper feed sensor 7 (S103), the fixing motor current (I1) is detected (S104). After the timing when the leading edge of the sheet material enters the fixing nip N (S105), the fixing motor current (I2) is detected (S106). It is determined whether or not the difference (I2−I1) between the fixing motor currents is equal to or greater than a threshold value ΔI (S107). S108), S106 to S108 are repeated until the toner passes through the fixing nip N. If the fixing nip N is passed, the process is terminated (S109).

  If the difference (I2-I1) in the fixing motor current is less than the threshold value ΔI in S107, it is assumed that slip has occurred and the speed of the fixing motor is increased (S110).

  By controlling as described above, a conveyance abnormality (such as an image disturbance due to a slip between the film and the sheet material or a slip between the pressure roller and the sheet material) that is likely to occur in the pressure roller driving type film heating and fixing apparatus is caused. Can be detected. Further, it is possible to prevent the occurrence of a conveyance failure jam by increasing the speed of the fixing motor.

  In this embodiment, when the difference (I2−I1) in the fixing motor current is less than the threshold value ΔI, the CPU (corresponding to the pressurizing variable means) 13 increases the pressurizing force of the pressure roller 10 to cause the slip. Eliminate the occurrence of

  FIG. 4 is a flowchart for explaining the operation when a slip occurs in this embodiment. As shown in FIG. 4, when the difference (I2-I1) in the fixing motor current is less than the threshold value ΔI in S907, the pressure is increased (S910).

  By controlling as described above, it is detected that a conveyance abnormality that is likely to occur in the film heating and fixing apparatus of the pressure roller driving system is detected, and the pressure of the pressure roller 10 is increased, thereby causing a conveyance failure jam. Occurrence can be prevented. Here, the conveyance abnormality is image disturbance due to slip between the film and the sheet material, or slip between the pressure roller and the sheet material.

  Note that the processing from S901 to S909 is the same as S101 to S109 (excluding S110) in FIG. 1 of the first embodiment except S910.

[Other examples]
As another embodiment, a paper discharge sensor (not shown) (corresponding to a recording medium detection means) that detects the presence or absence of the sheet material 2 after fixing is provided, and a CPU 13 (corresponding to a jam detection means) based on the detection result of the paper discharge sensor. ) Is an image forming apparatus configured to detect a conveyance failure jam. At this time, the CPU 13 determines that a conveyance failure jam occurs when the trailing edge of the sheet material 2 cannot be detected by the paper discharge sensor even after a predetermined time has elapsed since the leading edge of the sheet material 2 was detected by the paper discharge sensor. The time that is the basis for determining the conveyance failure jam is set as a jam detection time, and for example, a time is set by adding a margin to the time during which the sheet material 2 is passed from the leading edge to the trailing edge in a normal state. Here, the CPU (corresponding to the jam detection time varying means) 13 is configured to vary the jam detection time. That is, when the difference (I2-I1) in the fixing motor current is less than the threshold value ΔI, it is determined that slip has occurred, and the fixing motor speed is increased or the pressure applied to the pressure roller is increased. Make jam detection time longer than normal. By doing so, it is possible to eliminate the occurrence of slip and to prevent the operation from being stopped while the occurrence of slippage is detected and the occurrence of slip is eliminated.

  As still another embodiment, in order to detect the occurrence of slip, a temperature sensor (not shown) for detecting the temperature and humidity inside the image forming apparatus (corresponding to environmental temperature detecting means) and a humidity sensor (not shown) ( A configuration provided with an environmental humidity detecting means) may be used. In this case, it is determined that slip has occurred based not only on the difference in the fixing motor current (I2-I1) but also on the detection results of the temperature sensor and humidity sensor, and the speed of the fixing motor is increased or the pressure applied to the pressure roller is increased. Enlarge.

Flowchart for explaining processing when slip occurs according to Embodiment 1 Graph showing the change over time of the fixing motor current during normal operation Graph showing the change over time of the fixing motor current when slip occurs Flowchart for explaining processing at the time of occurrence of slip according to Embodiment 2 Sectional view explaining film heating type heat fixing means The perspective view explaining the heat fixing means of a film heating system Schematic configuration cross-sectional view of an image forming apparatus having a film heating type heat fixing means

Explanation of symbols

1 Paper cassette 2 Sheet material (equivalent to recording medium)
3 Feed roller 4 Transport roller 5 Sheet material transport path 6 Registration roller 7 Feed sensor 8 Transfer roller 9 Photosensitive drum 10 Pressure roller (corresponding to pressure means)
11 Fixing film (equivalent to heating means)
11-a Ceramic heater 11-b Thermistor 12 Paper discharge roller 13 CPU (corresponding to current detecting means, fixing device driving speed changing means, pressure changing means, jam detecting means, jam detecting time variable means)
14 Heater drive circuit 15 Scanner unit

Claims (5)

Heating means for fixing an unfixed developer on the recording medium to the recording medium;
Pressurizing means for applying pressure to the heating means;
A fixing device driving means for rotationally driving the heating means or the pressure means;
Current detection means for detecting current supplied to the fixing device driving means;
Fixing device driving speed changing means for changing the speed of the fixing device driving means;
With
The image forming apparatus, wherein the fixing device driving speed changing means changes the speed of the fixing device driving means based on a current detection result by the current detecting means. Heating means for fixing an unfixed developer on the recording medium to the recording medium;
Pressurizing means for applying pressure to the heating means;
A fixing device driving means for rotationally driving the heating means or the pressure means;
Current detection means for detecting current supplied to the fixing device driving means;
A pressing force variable means for changing the pressing force of the pressurizing means;
With
The image forming apparatus according to claim 1, wherein the pressing force varying unit changes the pressing force of the pressurizing unit based on a current detection result by the current detecting unit. The image forming apparatus according to claim 1, wherein
Recording medium detection means for detecting that the recording medium has passed through the heating means;
A jam detection unit that compares a time according to a detection result by the recording medium detection unit with a jam detection time, and detects a conveyance failure jam based on the comparison result;
A jam detection time varying means for varying the jam detection time;
With
The image forming apparatus according to claim 1, wherein the jam detection time variable means changes the jam detection time based on a current detection result by the current detection means. The image forming apparatus according to claim 1,
Environmental temperature detecting means for detecting the temperature in the image forming apparatus;
Environmental humidity detecting means for detecting humidity in the image forming apparatus;
With
The fixing device driving speed changing means is based on the temperature detection result by the environmental temperature detection means, the humidity detection result by the environmental humidity detection means, and the current detection result by the current detection means. An image forming apparatus characterized in that the speed of the means is changed. The image forming apparatus according to claim 2.
Environmental temperature detecting means for detecting the temperature in the image forming apparatus;
Environmental humidity detecting means for detecting humidity in the image forming apparatus;
With
The pressurizing variable means is configured to apply the pressurizing means based on the temperature detection result by the environmental temperature detection means, the humidity detection result by the environmental humidity detection means, and the current detection result by the current detection means. An image forming apparatus characterized by changing pressure.

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