JP5516310B2 - Heating control method for fixing process, fixing device for implementing the heating control method, and image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile machine, or a multifunction machine having both functions, and more particularly, a fixing device for fixing a toner image formed on an image carrier onto a recording medium and the same. The present invention relates to an image forming apparatus.

  In a conventional electrophotographic image forming apparatus, a copy or a recorded material is obtained by heat-fixing an unfixed image transferred from an image carrier to a recording medium. During the fixing process, the recording medium carrying the unfixed image is heated while nipping and pressing, so that the developer contained in the unfixed image, in particular, the toner is melted and softened and penetrated into the recording medium. Toner is fixed on the recording medium.

  The pressure heating of the recording medium in the fixing process is performed by pressing the pressure roller or the pressure belt against a fixing member such as a fixing roller or a fixing belt heated by a built-in fixing heater or a fixing heater arranged outside. This is realized by forming a nip portion and passing a recording medium through the nip portion. At that time, the fixing device has a problem of stably controlling the temperature of the fixing member. In the conventional fixing device, the surface temperature of the fixing member is detected by a temperature detection means such as a thermistor. When the detected temperature is lower than the predetermined temperature, the fixing heater is turned on. When the detected temperature is higher than the predetermined temperature, the fixing heater is turned on. The fixing member is controlled to the set temperature by On / Off control. However, in the case of a fixing member with a built-in fixing heater, there is a tendency for time deviation to occur between the timing of turning on / off the heating source and the change in the surface temperature of the fixing member, and in the external heating method, the surface temperature of the fixing member is uneven. There is a problem that fixing is likely to occur, resulting in fixing failure, gloss unevenness, and hot offset.

  Therefore, the power supply voltage obtained by rectifying the AC power supply with a rectifier is supplied to an inverter in which a switching element is connected in series to the heater load, the pulse width is modulated, and the heated member is heated to a desired temperature according to the heater on / off time ratio. The “PWM control” for controlling the above has been adopted (for example, Patent Document 1 and Patent Document 2).

  In recent years, fixing devices having a small heat capacity have been developed one after another from the viewpoint of energy saving. In such a low heat capacity fixing device, the heat storage member capable of making the temperature uniform with respect to the input electric power is small or does not have the heat storage member. Therefore, the method of inputting the electric power is directly reflected in the temperature of the fixing device. Tend. In particular, in a fixing device that has a fast thermal response as in the induction heating method and heats a local portion of the fixing member, uneven temperature in the circumferential direction of the fixing member appears remarkably. This phenomenon causes adverse effects on the image surface such as fixability and glossiness in the paper surface. In addition, it is necessary to increase the set temperature because of the temperature unevenness in the circumferential direction, and it has been necessary to use it in such a way as to consume more energy than necessary.

  In such a fixing device that performs local heating, particularly a low heat capacity fixing device that quickly rises and consumes less power, uneven temperature in the circumferential direction of the fixing member becomes a problem when the heat source is not lit. In view of the above, an object of the present invention is to propose a heating control method for a fixing device that reduces temperature unevenness in the circumferential direction of the fixing member, and precise control is performed by the fixing device employing such a heating control method. It is to obtain a good image and realize energy saving.

  The above-described problem is a heating control method for a fixing device in which a fixing member that forms a fixing nip together with a pressure unit is locally heated by a PWM drive system, and a recording medium sandwiched and conveyed by the fixing nip is heated and pressed. This is solved by detecting heating on / off in the rotation direction of the fixing member, and controlling to determine the heating position in the next temperature control cycle based on the detected information on the rotation direction on / off.

  A fixing device that locally heats a fixing member that forms a fixing nip together with a pressure unit, obtains temperature information of the fixing member, and determines a required power for a subsequent temperature control cycle based on the obtained temperature information of the fixing member. In the heating control method for the above, local heating is performed by a PWM drive method, and heating on / off in the rotation direction of the fixing member is detected, and information on the detected rotation direction on / off is taken into account, and the next temperature control is performed. If the heating on / off in the cycle is corrected, the above problem can be solved reliably. At this time, it is assumed that the heating on / off pattern in the rotation direction of the fixing member is stored for one or more rotations of the fixing member, and that local heating is performed by an induction heating method.

  A fixing member; means for locally heating the fixing member; pressure means for forming a fixing nip with the fixing member; means for obtaining temperature information of the fixing member; and temperature information of the obtained fixing member. And a controller that determines the required power of the temperature control cycle for heating the fixing member, the local heating means operates in a PWM drive system, and detects heating on / off in the rotation direction of the fixing member. If the local heating means is controlled so as to determine the on / off timing in the next temperature control cycle based on the detected rotation direction on / off information, the above problem can be solved in terms of apparatus.

  A fixing member; means for locally heating the fixing member; pressure means for forming a fixing nip with the fixing member; means for obtaining temperature information of the fixing member; and temperature information of the obtained fixing member. And a controller that determines the required power of the temperature control cycle for heating the fixing member, the local heating means operates in a PWM drive system, and detects heating on / off in the rotation direction of the fixing member. If the local heating means is controlled so as to correct the on / off timing in the next temperature control cycle in consideration of the detected rotational direction on / off information, the above-mentioned problem can be reliably solved in terms of apparatus.

  In a heating control method for a fixing device, a fixing member that forms a fixing nip together with a pressing unit is locally heated by a PWM drive system, and a recording medium sandwiched and conveyed by the fixing nip is heated and pressed to fix the fixing member. Heating on / off in the rotation direction is detected, and based on the detected rotation direction on / off information or in consideration of the information, the fixing member portion that is on or off rotates and returns to the heating unit. If the heating pattern in the next temperature control cycle is determined so that the place where the previous lighting was off can be preferentially heated, the temperature unevenness in the circumferential direction of the fixing member Can be reduced. The power calculation required in the temperature control cycle basically uses feedback control that calculates how much power is required in the next cycle by looking at the temperature as usual.

  If the heating on / off pattern in the rotation direction of the fixing member is stored beyond one rotation of the fixing member, it is possible to avoid a situation in which a portion where the fixing member is continuously turned off and not heated is generated.

1 is a diagram showing an overview of an entire color copying machine. FIG. 3 is a diagram illustrating a main configuration of a fixing device. It is a graph explaining the lighting pattern by control which concerns on this invention.

  The best mode for carrying out the present invention will be described below with reference to the drawings. First, FIG. 1 shows a schematic configuration of a color copying machine which is an example of an electrophotographic image forming apparatus provided with a fixing device according to the invention. The mechanism of the entire image forming apparatus of this color copying machine is basically the same as the conventional one, and a predetermined apparatus necessary for forming an image around the photosensitive member, such as a charging device, an exposure device, a developing device, And an image information reading device for a document and a paper feeding unit. Since it is a well-known configuration and operation, only a brief description will be given below, but the contents are also included as long as it is recognized that the configuration and operation are well-known in terms of not being described.

  A color copying machine (hereinafter simply referred to as a copying machine) 1 forms a tandem image forming unit by arranging four image forming units of yellow, cyan, magenta, and black side by side at the center of the apparatus main body. In the tandem image forming unit, image forming means as individual toner image forming means are arranged. In each of the image forming means, drum-shaped photoconductors 11Y, 11M, 11C, and 11K as latent image carriers (hereinafter, Y, M, C, and Y indicating yellow, cyan, magenta, and black are shown for simplification of display). A charging device 12, a developing device 13, a photoconductor cleaning device 15 and the like are provided around K).

  An optical writing unit 2 as a latent image forming unit is provided below the tandem image forming unit. The optical writing unit 2 forms an electrostatic latent image for each color by irradiating the surface of each photoconductor 11 with laser light based on image data from the document reading unit 4 on the upper side of the copying machine. The document reading unit 4 includes a light source, a polygon mirror, an f-θ lens, a reflection mirror, and the like. The document reading unit 4 irradiates the document D disposed on the contact glass 5, converts the image data into an electrical signal, and performs optical writing. Transmit to unit 2.

  An intermediate transfer belt 17 in the form of an endless belt is provided as an intermediate transfer member immediately above the tandem image forming unit. The intermediate transfer belt 17 is wound around a plurality of support rollers, and a drive motor (not shown) serving as a drive source is disposed on a rotation shaft of a drive roller (for example, a transfer roller disposed in the secondary transfer unit) among the support rollers. Are connected. A belt cleaning device 16 is provided upstream of the tandem image forming portion of the intermediate transfer belt 17. When the drive motor is driven, the intermediate transfer belt 17 rotates in the counterclockwise direction in the figure and the followable support roller rotates. A primary transfer device (not shown) for transferring the toner image formed on the photoreceptor 11 onto the intermediate transfer belt 17 is provided inside the intermediate transfer belt 17.

  A secondary transfer roller 6 as a secondary transfer device is provided downstream of the primary transfer device in the driving direction of the intermediate transfer belt 17. A transfer support roller 18 is disposed on the opposite side of the secondary transfer roller 6 and the intermediate transfer belt 17 and functions as a pressing member.

  In addition, the copying machine 1 includes a paper feeding cassette 7, a paper feeding roller 8, a registration roller, and the like at the lower part thereof. Further, a fixing device 19 for fixing an image on the recording medium P and a paper discharge roller 9 are provided downstream of the secondary transfer roller 6 with respect to the traveling direction of the recording medium P to which the toner image has been transferred by the secondary transfer roller 6. ing.

  Next, the operation of the copying machine will be described. The photosensitive member 11 is rotated by individual image forming means, and the surface of the photosensitive member 11 is uniformly charged by the charging device 12 as the photosensitive member rotates. Next, an electrostatic latent image is formed on the photoreceptor 11 by irradiating the writing light from the optical writing unit 2. Thereafter, toner is attached by the developing device 13 to make the electrostatic latent image visible, and a single color image of yellow, magenta, cyan, and black is formed on each photosensitive drum 11. Further, the drive roller is rotated by a drive motor (not shown), the other support rollers are driven to rotate, the intermediate transfer belt 17 is rotated and conveyed, and the visible image is transferred onto the intermediate transfer belt 17 by the primary transfer device. Transfer sequentially. As a result, a composite color image is formed on the intermediate transfer belt 17. The surface of the photoconductor 11 after the image transfer is cleaned by removing residual toner with the photoconductor cleaning device 15 to prepare for image formation again.

  In accordance with the timing of image formation, the leading edge of the recording medium P is fed from the paper feed cassette 7 by the paper feed roller 8, conveyed to the registration rollers, and temporarily stops. Then, the sheet is conveyed between the transfer support roller (secondary transfer counter roller) 18 and the intermediate transfer belt 17 while taking timing with the image forming operation. Here, the intermediate transfer belt 17 and the transfer support roller 18 form a so-called secondary transfer nip across the recording medium P, and the secondary transfer roller 6 transfers the toner image on the intermediate transfer belt 17 onto the recording medium P. Secondary transfer. After the secondary transfer, the recording medium P is separated from the intermediate transfer belt 17 and the transfer support roller 18 by a separating member (not shown), and then discharged to the outside through the paper discharge roller 9. On the other hand, the intermediate transfer belt 17 after image transfer is removed by the belt cleaning device 16 to remove residual toner remaining on the intermediate transfer belt 17 after image transfer, and is prepared for re-image formation by the tandem image forming unit.

  The fixing device 19 to which the recording medium P after image transfer is fed includes a fixing roller 20 and a pressure roller 30 as shown in detail in FIG. The fixing roller 20 includes a fixing sleeve 21 heated by an induction overheating method (IH method), a sponge member 22 on the inner peripheral side thereof, and an innermost core metal 23, and the pressure roller 30 is a core metal 32. And a rubber member 31 and a built-in halogen heater 33, and the fixing roller 20 and the pressure roller 30 face each other to form a nip portion. The reason why the fixing roller 20 has a foam member 22 that is a foam and the pressure roller 30 has a rubber member 31 that is an elastic body is to have an appropriate surface pressure and nip width when the rollers are pressed against each other. In this example, the sponge member 22 of the fixing roller 20 has a hardness of about 35 Hs, the rubber member 31 of the pressure roller 30 has a thickness of about 3 mm on the surface and a hardness of about 60 Hs, and the diameter of each roller is about 40 mm. .

  An IH heater 25 is disposed at a position facing the fixing roller 20 on the side opposite to the nip portion. The IH heater 25 includes an IH coil 26 between the cover inner side 28 and the cover outer side 27 on the side close to the fixing roller 20, and the fixing sleeve 21 rotates while being locally heated by the IH heater 25. The fixing sleeve 21 is composed of, for example, a metal body for heat generation (15 μm), silicone rubber (200 μm), and a PFA surface layer (30 μm). The recording medium P guided by the pressure guide plate 41 from the secondary transfer portion and carrying the unfixed toner T is nipped and conveyed between the fixing roller 20 and the pressure roller 30 to heat and press the toner image on the recording medium. After that, the recording medium P is discharged from the discharge path between the separation plate 43 and the fixing device cover 50. The fixing device cover 50 can be rotated about a fulcrum 50a to open the fixing device.

  The temperature of the surface of the fixing sleeve 21 is detected by temperature detection means 62 supported by the spur 42 so as to be maintained in a predetermined temperature range. In this example, a thermopile is used as the temperature detection means 62. On the other hand, the surface temperature of the pressure roller 30 is detected by a pressure thermistor 61 and the halogen heater 33 is controlled. Thermopile is a sensor with good time response that generates an electromotive force according to the temperature difference from the cold junction by condensing the infrared rays radiated from the object at the hot junction where many thermocouples are connected in series. It is. An atmosphere sensor (not shown) is provided to compensate for changes in the temperature of the thermopile itself (particularly the temperature of the cold junction).

  In this example, there is one thermopile, but it may be increased by providing a temperature sensor for each paper width. In order to prevent a temperature rise in the non-sheet passing portion, a coil for canceling out the magnetic flux density entering the fixing sleeve 21 is provided (not shown). The cancel coil can change the portion that suppresses heat generation according to the paper width.

  Further, the fixing sleeve 21 is provided with a side guide (not shown) for preventing slippage at the end portion, and the side guide comes into contact with the fixing sleeve 21 when the fixing sleeve 21 approaches one of the longitudinal directions of the fixing roller 20. , It has a structure that regulates further deviation. It may be adhered to the sponge member 22 so that the slip itself does not occur.

  In the fixing device 19 having the above-described configuration, the lighting rate of the IH heater 25 is controlled by a control unit (not shown) according to the output of the thermopile 62 that detects the surface temperature of the fixing sleeve 21 (On / Off). Control), temperature control necessary for the fixing process is performed.

  However, in such a fixing device that is a local heating and particularly has a small heat capacity and a low thermal conductivity, the thermal conductivity in the circumferential direction is also low, so that the input power to the IH heater appears as it is as the surface temperature of the fixing sleeve 21 and lights up. In the rate control, the temperature of the off portion is lowered, and there is a problem that temperature unevenness is likely to occur in the circumferential direction of the fixing sleeve.

  When calculating the power of the next temperature control period while detecting the current temperature in a temperature control process such as PID control, it is excellent for maintaining the fixing member in a certain temperature range from a long-term viewpoint. However, since the thermal response is not fast enough to control the temperature unevenness in the circumferential direction of the fixing roller, there is a limit in eliminating the temperature unevenness in the circumferential direction. Therefore, it is necessary to perform control earlier in time than control for detecting and feeding back the temperature.

  Therefore, in addition to the conventional control method that performs temperature feedback control, a temperature control in the circumferential direction can be reduced by adding a control method that operates earlier in time. Whether the lighting state of the heating source when a certain surface area of the member to be heated passes through the heating part is an On state or an Off state in the temperature control cycle, the member to be heated rotates and the certain surface region Until it returns to the heating section, determine the lighting pattern within the temperature control cycle so that the place where the lighting before the heated member was turned off is preferentially heated, and the circumferential direction To reduce temperature unevenness. This is a control method that combines temperature feedback control and control that preferentially heats the OFF portion by remembering the lighting pattern one round before and that works earlier in time. On the other hand, if only the temperature control process that measures the actual temperature and reflects the measured temperature result in the next control cycle, it takes time to be reflected as the temperature. Proper temperature control becomes difficult without being in time.

  For example, consider a case where On / Off can be switched in a minimum of 40 ms from the accuracy of the soft timer. If the temperature control cycle is 200 ms and the lighting is 60%, the unit is turned on for 120 ms (minimum lighting time 3 times) in the temperature control cycle 200 ms, and the remaining 80 ms (minimum lighting time 2 times) is turned off. The lighting rate of 60% will be realized. The minimum lighting time of 40 ms is the minimum unit of lighting, and there are five during the temperature control period of 200 ms, and ON / OFF can be freely performed in this minimum unit of 40 ms. The fixing member is determined by determining the lighting pattern in five minimum units within the temperature control period so that the heated portion that is turned off one rotation before the fixing member turns on preferentially when it comes to the heating section. Reduces temperature unevenness in the circumferential direction.

  In other words, the on / off control according to the present invention uses a lighting pattern that indicates which of the five times during which the on / off of the temperature control cycle 200 ms can be freely turned on, and the lighting pattern one rotation before the fixing roller. This control is determined based on whether the lighting is correct. For example, in this temperature control, it is assumed that 60% lighting is necessary by temperature feedback control. It is only necessary to light three of the five smallest units in the temperature control cycle. Assuming that the period of one rotation of the fixing roller is 320 ms at this time, as shown in FIG. 3, it is referred to what lighting is the five minimum lighting units from 320 ms before to 120 ms before 400 ms. If the lighting of the five minimum units is On, Off, Off, On, On, the second and third minimum units are preferentially set to On in the control cycle after the base point 400 ms. The second and third positions of the minimum unit are Off before one rotation of the fixing roller, and the temperature is predicted to be lower than the On portion. Where the remaining one is lit, it may be anywhere in the first, fourth, and fifth smallest units, but ideally the second and third most distant fifth lights should be lit. In this way, temperature unevenness in the circumferential direction of the fixing roller is suppressed. By performing such control, the fixing process can be completed with good fixing property and minimum energy.

  In the case of low power, which requires only 40% lighting by temperature feedback control to maintain the fixing device in a certain temperature range, it is possible to turn on 40% by lighting two of the five minimum lighting units. In some cases, the Off part one cycle before cannot be turned on (because the previous part is also lighted 40%, there are 3 of the Off parts). In this case, the lighting pattern of the control cycle may be determined only by the lighting pattern one rotation before the fixing roller, but it is more preferable to turn on the Off portion with reference to the lighting pattern one cycle before the rotation. is there. This is because even if one cycle before the rotation is Off, both the On state and the Off state exist two cycles before, and the place that is off for two consecutive cycles should be turned on preferentially. Therefore, when the required power is small or the minimum lighting unit is even smaller, a lighting pattern having a rotation period of two or more revolutions may be referred to.

DESCRIPTION OF SYMBOLS 1 Copier 2 Optical writing unit 4 Original reading part 5 Contact glass 6 Secondary transfer roller 7 Paper feed cassette 8 Paper feed roller 9 Paper discharge roller 11 Photoconductor 12 Charging device 13 Developing device 15 Photoconductor cleaning device 16 Belt cleaning device Reference Signs List 17 Intermediate transfer belt 18 Transfer support roller 19 Fixing device 20 Fixing roller 21 Fixing sleeve 22 Sponge member 23 Core metal 25 IH heater 26 IH coil 27 Cover outside 28 Cover inside 30 Pressure roller 31 Rubber member 32 Core metal 33 Halogen heater 41 Addition Pressure guide plate 42 Spur 43 Separation plate 50 Fixing device cover 61 Pressure thermistor 62 Thermopile (temperature detection means for fixing sleeve)

JP 2004-198537 A JP 2007-133292 A

Claims (7)

In a heating control method for a fixing device in which a fixing member that forms a fixing nip together with a pressure unit is locally heated by a PWM drive system, and a recording medium that is nipped and conveyed by the fixing nip is heated and pressed to fix it.
A heating control method comprising: detecting heating on / off in a rotation direction of a fixing member; and controlling to determine a heating position in a next temperature control cycle based on the detected rotation direction on / off information. A fixing device that locally heats a fixing member that forms a fixing nip together with a pressure unit, obtains temperature information of the fixing member, and determines a required power for a subsequent temperature control cycle based on the obtained temperature information of the fixing member. In the heating control method for
The local heating is performed by the PWM drive method. The heating on / off in the rotation direction of the fixing member is detected, and the heating on / off in the next temperature control cycle is corrected in consideration of the information on the detected rotation direction on / off. The heating control method characterized by the above-mentioned.   The heating control method according to claim 1, wherein a heating on / off pattern in the rotation direction of the fixing member is stored over one rotation of the fixing member.   The heating control method according to any one of claims 1 to 3, wherein the local heating is performed by an induction heating method. A fixing member; means for locally heating the fixing member; pressure means for forming a fixing nip with the fixing member; means for obtaining temperature information of the fixing member; and temperature information of the obtained fixing member. A fixing unit including a control unit that determines a required power of a temperature control cycle for heating the fixing member based on
The local heating means operates in a PWM drive system, detects heating on / off in the rotation direction of the fixing member, and determines the on / off timing in the next temperature control cycle based on the detected rotation direction on / off information. The fixing device is characterized by controlling the local heating means. A fixing member; means for locally heating the fixing member; pressure means for forming a fixing nip with the fixing member; means for obtaining temperature information of the fixing member; and temperature information of the obtained fixing member. A fixing unit including a control unit that determines a required power of a temperature control cycle for heating the fixing member based on
The local heating means operates in the PWM drive system, detects heating on / off in the rotation direction of the fixing member, and corrects the on / off timing in the next temperature control cycle by taking into account the information on the detected rotation direction on / off. A fixing device characterized by controlling local heating means.   An image forming apparatus equipped with the fixing device according to claim 5.

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