JP2016109946A - Fixing device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To quickly warm up a resistor heater itself by directly detecting the temperature of the resistor heater and to efficiently shorten a warm-up period.SOLUTION: A fixing device includes a fixing rotary body including heating means, a pressure rotary body coming into contact with the fixing rotary body, to form a nip part, rotary drive means for rotating at least one of the fixing rotary body and the pressure rotary body, and control means for controlling the energization control of the heating means and the drive of the rotary drive means. Further, the fixing device includes temperature detection means for detecting the temperature of the resistor heater. In a warm-up period, the control means starts the energization of the resistor heater in such a state that the rotary drive means is stopped. When the temperature detection means detects that the temperature of the resistor heater becomes a predetermined temperature or more, the control means starts the rotation of the rotary drive means.SELECTED DRAWING: Figure 4

Description

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

  In an image forming apparatus using an electrophotographic system such as a printer, a facsimile machine, a copying machine, or the like, a member to be transferred such as paper is passed through a nip portion formed by pressing a fixing roller having a heating unit and a pressure roller. Thus, the unfixed toner image is melted and fixed on the transfer member by heating and pressing.

  Conventionally, halogen heaters have been widely used as heating means. However, when halogen heaters are turned on, a large current (inrush current) flows in a temporary overload condition, causing a voltage drop and flicker failure such as flickering of fluorescent lamps. May occur. In order to suppress this inrush current, countermeasures such as phase control have been taken, but a new problem of generating noise (noise terminal voltage) occurs and a noise filter is required.

  Therefore, it is conceivable to use a resistor heater such as a carbon heater as a heating means. According to this resistor heater, no inrush current is generated and no additional filter circuit for suppressing noise is required.

  However, the resistor heater has a large heat capacity and requires electric power to warm the resistor heater itself, and the warm-up period becomes longer than when a halogen heater is used. For this reason, it is conceivable to take measures to warm the resistor heater itself by energizing the resistor heater with the fixing roller and the pressure roller stopped rotating.

  In the warm-up period of the fixing device, a technique for shortening the warm-up period by stopping the rotation of the fixing roller or the like until the predetermined temperature is reached or slowing the rotation speed has been proposed (for example, Patent Documents 1 to 3). ).

JP 2005-172966 A JP 2001-154530 A JP-A-10-213987

  However, all of the proposed techniques measure the surface temperature of the roller, and control the rotation of the roller based on the measured roller surface temperature. It takes time for the heat from the heater to reach the roller surface. Warm-up period can be shortened efficiently if the roller heater can start rotating at the timing when the resistor heater itself is warmed up and sufficient heat generation performance can be demonstrated. In the method, temperature detection is inevitably delayed.

  Therefore, an object of the present invention is to directly detect the temperature of the resistor heater, to quickly warm the resistor heater itself, and to efficiently shorten the warm-up period.

  The fixing device according to the present invention that achieves the above object includes a fixing rotator having a heating unit, a pressure rotator that presses against the fixing rotator to form a nip portion, and at least a fixing rotator and a pressure rotator A rotation driving means for rotating one; and a control means for controlling the energization control of the heating means and the driving of the rotation driving means. A fixing device that heats and pressurizes the toner image by passing the toner image to melt and fix the toner image on the transfer member, wherein the heating unit is a resistor heater, and further includes a temperature detection unit that detects the temperature of the resistor heater. In the warm-up period, the control means starts energizing the resistor heater in a state where the rotation driving means is stopped, and the temperature of the resistor heater is set to a predetermined set temperature. When detecting said temperature detecting means that it is now above, wherein the causing the rotation drive means rotating started.

  In the present invention, “warm-up” refers to heating the fixing rotator to a predetermined fixable temperature after the main power is turned on, and inputting an image forming signal for a predetermined time while the main power is turned on. In other words, it means that the fixing rotator is heated from a state (standby state) where the fixing rotator is maintained at a temperature lower than the fixable temperature to a fixable temperature. The “warm-up period” is a period during which the above warm-up operation is performed.

  The temperature detecting means may detect that the temperature of the resistor heater has become equal to or higher than a preset temperature based on a current value flowing through the resistor heater.

  Alternatively, the temperature detecting means may detect that the temperature of the resistor heater has become equal to or higher than a set temperature by power consumption of the resistor heater.

  In addition, the temperature detecting means may detect that the temperature of the resistor heater has become equal to or higher than a preset temperature based on the accumulated power consumption of the resistor heater.

  The control means may change the rotational speed of at least one of the fixing rotator and the pressure rotator by the rotation driving means in a warm-up period in a stepwise manner.

  Alternatively, the control means may make the rotation speed of at least one of the fixing rotator and the pressure rotator by the rotation driving means during the warm-up period slower than the rotation speed during the fixing operation.

  Further, when the temperature detected by the temperature detecting means does not reach the set temperature at which the rotation driving means starts to rotate even after a predetermined time has elapsed since the energization of the resistor heater is started, The rotation driving means may be forcibly started to rotate.

  Alternatively, when the temperature detected by the temperature detecting means does not reach the set temperature at which the rotation driving means starts rotating even after a predetermined time has elapsed since the energization of the resistor heater was started, The energization of the resistor heater may be stopped.

  A halogen heater is further provided as the heating means, the halogen heater is provided in the vicinity of the resistor heater, and the control means starts energizing the halogen heater after energizing the resistor heater. Also good.

  A storage means is further provided, and the set temperature is stored in the storage means in an updatable manner, and the control means sets the set temperature as a predetermined value when the update request for the set temperature is made. The time-dependent change characteristic of any one of current value, power consumption, and integrated power consumption may be measured, and a new set temperature may be determined and updated from the measured change-time characteristic.

  According to the present invention, there is provided an image forming apparatus comprising the fixing device as described above.

  In the fixing device of the present invention, since the rotation driving means is stopped until the temperature of the resistor heater reaches a predetermined set temperature, the resistor heater itself can be quickly warmed. Further, since the temperature of the resistor heater is directly detected, the rotation driving means can be started at a timing at which the resistor heater itself can be warmed up and exhibit sufficient heat generation performance, and the warm-up period can be shortened efficiently.

1 is a schematic diagram illustrating an embodiment of an image forming apparatus according to the present invention. 1 is a schematic view showing an embodiment of a fixing device according to the present invention. 1 is a control circuit and a configuration diagram illustrating an embodiment of a fixing device according to the present invention. 7 is a timing chart showing fixing roller rotation driving and ON / OFF of a carbon heater in a warm-up operation. It is a figure which shows the time-dependent change of the surface temperature of a fixing belt, and the power consumption of a carbon heater. 6 is a flowchart illustrating an example of control of the fixing device of the present invention. 10 is a flowchart when the rotation speed of the fixing roller during the warm-up period is changed stepwise. 10 is a flowchart in a case where the rotation speed of the fixing roller during the warm-up period is slower than the rotation speed in the normal fixing operation. 6 is a flowchart illustrating a control example for preventing local overheating of the fixing belt. FIG. 10 is a diagram showing a change with time of the surface temperature of the fixing belt when the control shown in FIG. 9 is performed. 10 is a flowchart illustrating another control example for preventing local overheating of the fixing belt. It is a schematic block diagram which shows other embodiment of the fixing device which concerns on this invention. 13 is a timing chart showing fixing roller rotation driving and ON / OFF of a halogen heater and a carbon heater in a warm-up operation of the fixing device shown in FIG. 12. 6 is a flowchart illustrating an example of control of the fixing device of the present invention.

  Hereinafter, a fixing device and an image forming apparatus according to the present invention will be described with reference to the drawings. However, the present invention is not limited to these embodiments.

  FIG. 1 is a schematic diagram showing an embodiment of an image forming apparatus and a fixing device of the present invention. The image forming apparatus D in FIG. 1 is a so-called tandem color printer. Of course, in addition to a printer, the present invention can also be applied to a copying machine having a scanner, a facsimile, or a multi-function machine having these functions combined. Further, the image forming method is not limited to the tandem method, and other methods, for example, four developing devices are arranged around the rotation shaft, and these are sequentially opposed to the electrostatic latent image carrier to be full color. A so-called four-cycle method of creating an image or a monochrome method of creating a monochrome image with one developing device may be used.

  The image forming apparatus D includes an endless intermediate transfer belt 33 having conductivity. The intermediate transfer belt 33 is hung on a pair of rollers 31 and 32 disposed on both the left and right sides in the drawing. The roller 32 is connected to a motor (not shown), and the roller 32 rotates counterclockwise by driving the motor, whereby the intermediate transfer belt 33 and the roller 31 in contact therewith are driven to rotate. A secondary transfer roller 34 is in pressure contact with the outside of the belt portion supported by the roller 32. The toner image formed on the intermediate transfer belt 33 at the nip portion (secondary transfer region) between the secondary transfer roller 34 and the intermediate transfer belt 33 is transferred onto the conveyed paper P.

  A cleaning member 35 for cleaning the surface of the intermediate transfer belt 33 is provided outside the belt portion supported by the roller 31. The cleaning member 35 is in pressure contact with the roller 31 via the intermediate transfer belt 33, and untransferred toner is collected at the contact portion.

  Below the intermediate transfer belt 33 suspended between the rollers 31 and 32, yellow (Y), magenta (M), cyan (C), black ( K) four image forming units 2Y, 2M, 2C, and 2K (hereinafter may be collectively referred to as “image forming unit 2”). In these image forming units 2, corresponding color toner images are created using the respective color developers.

  The image forming unit 2 includes a cylindrical photoconductor 20 as an electrostatic latent image carrier. Around the photoconductor 20, a charger 21, a developing device 23, a primary transfer roller 24, and a photoconductor cleaning member 25 are arranged in this order along the rotation direction (clockwise direction). The primary transfer roller 24 is in pressure contact with the photoconductor 20 with the intermediate transfer belt 33 interposed therebetween to form a nip portion (primary transfer region). An exposure device 22 is disposed below the image forming unit 2.

  In the embodiment shown in this figure, a roller charging type is used as the charger 21, but the type of the charger 21 is not particularly limited, and a corona discharge type charging charger, a blade-shaped charging member, Of course, a brush-like charging member or the like may be used. In this embodiment, a plate-like blade is used as the photosensitive member cleaning member 25, and one end thereof is brought into contact with the outer peripheral surface of the photosensitive member 20 to collect and remove toner remaining on the surface of the photosensitive member 20. The photosensitive member cleaning member 25 is not limited to a plate blade, and for example, a fixed brush, a rotating brush, a roller, and a combination of these members can also be used. Note that the photoconductor cleaning member 25 is not necessarily provided, and a cleanerless system in which the developing device 23 collects untransferred toner on the photoconductor 20 may be employed.

  Above the intermediate transfer belt 33, hoppers 4Y, 4M, 4C, and 4K (hereinafter sometimes collectively referred to as “hopper 4”) containing toner to be supplied to the developing devices 23 of the respective colors are arranged. A paper feed cassette 50 is detachably disposed as a paper feed device below the exposure device 22. The sheets (transferred members) P stacked and accommodated in the sheet feeding cassette 50 are sent out one by one to the conveyance path in order from the uppermost sheet by the rotation of the sheet feeding roller 51 disposed in the vicinity of the sheet feeding cassette 50. The paper P sent out from the paper feed cassette 50 is conveyed to the registration roller pair 52 and is sent out to the secondary transfer area at a predetermined timing.

  The image forming apparatus D can be switched between a monochrome mode in which a monochrome image is formed using one color toner (for example, black) and a color mode in which a color image is formed using four color toners.

  An image forming operation example in the color mode will be briefly described. First, in each image forming unit 2, the outer peripheral surface of the photoreceptor 20 that is rotationally driven at a predetermined peripheral speed is charged by the charger 21. Next, light corresponding to image information is projected from the exposure device 22 on the surface of the charged photoconductor 20 to form an electrostatic latent image. Subsequently, the electrostatic latent image is made visible by toner as a developer supplied from the developing device 23. When the toner image of each color formed on the surface of the photoreceptor 20 in this way reaches the primary transfer region by the rotation of the photoreceptor 20, the toner image is transferred from the photoreceptor 20 to the intermediate transfer belt in the order of yellow, magenta, cyan, and black. 33 is transferred (primary transfer) and superimposed.

  Untransferred toner remaining on the photoconductor 20 without being transferred to the intermediate transfer belt 33 is scraped off by the photoconductor cleaning member 25 and removed from the outer peripheral surface of the photoconductor 20.

  The superimposed four color toner images are conveyed to the secondary transfer region by the intermediate transfer belt 33. On the other hand, the paper P is conveyed from the registration roller pair 52 to the secondary transfer area in accordance with the timing. Then, the four color toner images are transferred (secondary transfer) from the intermediate transfer belt 33 to the paper P in the secondary transfer region. The paper P on which the four color toner images are transferred is conveyed to the fixing device 1. In the fixing device 1, the paper P passes through a nip portion between the fixing roller 11 and the pressure roller 12 that are in pressure contact with each other via the fixing belt 14. During this time, the paper P is heated and pressurized, and the toner image on the paper P is melted and fixed on the paper P. A specific configuration of the fixing device 1 will be described later. The paper P on which the toner image is fixed is discharged to a paper discharge tray 54 by a discharge roller pair 53.

  On the other hand, the intermediate transfer belt 33 that has passed through the secondary transfer region is cleaned by the cleaning blade 35. Thereafter, the rotational drive of each photoconductor 20 and the intermediate transfer belt 33 is stopped.

  FIG. 2 is a schematic configuration diagram of the fixing device 1 mounted on the image forming apparatus D of FIG. In this fixing device 1, a fixing belt 14 is suspended between a heating roller (heating means) 13 and a fixing roller 11 to form a fixing rotating body, and a pressure roller (pressure rotating body) 12 is fixed. The belt 14 and the fixing roller 11 are pressed against each other. The fixing roller 11 is rotated counterclockwise by a motor M serving as a rotation driving unit, whereby the fixing belt 14, the pressure roller 12, and the heating roller 13 are driven to rotate. The motor M may be provided not on the fixing roller 11 but on the heating roller 13 or the pressure roller 12 to be driven and rotated, and the other rollers may be driven to rotate. The heating roller 13 incorporates a rod-like carbon heater (resistor heater, heating means) 15 in the longitudinal direction of the heating roller 13. A temperature sensor 17 that detects the surface temperature of the fixing belt 14 is installed on the outer peripheral portion of the heating roller 13.

  In the fixing device 1 having such a configuration, the conveyed paper P is formed by the fixing belt 14 and the pressure roller 12 so that the surface on which the unfixed toner image t is placed is on the fixing belt 14 side. Pass through the nip. While passing through the nip portion, the toner image t is heated and pressurized, and the toner image t is melted and fixed on the paper P. Thereafter, the paper P is discharged to a paper discharge tray 54 (shown in FIG. 1).

  The fixing device 1 includes a control unit that comprehensively controls the fixing processing operation, a ROM that stores a control program for the control unit to perform control, and a RAM that provides the control unit with a work area for performing the control. With. The controller performs heating control so that the fixing temperature at the fixing nip is maintained at a temperature suitable for fixing an unfixed toner image. More specifically, the control unit acquires information about the temperature detected by the temperature sensor 17 and executes heating control so that the temperature detected by the temperature sensor 17 approaches a target temperature set based on the type of paper. At this time, the control unit sets a set power value according to the temperature detected by the temperature sensor 17, and the heater control circuit performs on / off control of power from the power source to be input to the carbon heater 15 in accordance with a command from the control unit. To do. The drive control circuit supplies power to the motor M in accordance with a command from the control unit, and rotates and stops the fixing roller.

  FIG. 3 shows a control circuit and a configuration diagram of the fixing device 1. The electric power supplied from the power source is sent to the carbon heater 15 via a noise filter in the fixing drive circuit. The electric power supplied to the carbon heater 15 is controlled by an ON / OFF control signal from the heater control circuit. Specifically, the triac is turned ON / OFF when a control signal is input from the control unit to the phototriac coupler in the heater control circuit. In actual ON / OFF of the carbon heater 15, electric power is supplied to the carbon heater 15 when the triac is turned ON, and the electric power is cut off when the triac is turned OFF.

  On the other hand, in the drive control of the fixing roller 11, the drive control circuit drives the motor M in accordance with the rotation control signal output from the control unit to control the rotation of the fixing roller 11.

  The heater temperature detection means detects the current value, voltage value, power consumption, and integrated power consumption to the carbon heater 15 by the current detection means and voltage detection means in the fixing drive circuit, and detects the temperature of the carbon heater 15. That is, in the resistor heater such as the carbon heater 15, the amount of electric power is equal to the amount of heat, so that the temperature of the carbon heater 15 can be detected based on the detected power consumption (current × voltage) and accumulated power consumption. Normally, the voltage value does not change greatly, so that the temperature of the carbon heater 15 can also be detected by detecting the current value. The resistor heater that can be used in the present invention is not limited to a carbon heater, and a conventionally known one can be used.

  In order to fix the toner image t on the paper P, it is necessary to raise the temperature of the fixing belt 14 to a predetermined temperature. A warm-up operation for raising the temperature of the fixing belt 14 to a temperature at which the fixing process can be performed will be described.

  FIG. 4 is a timing chart showing rotation driving of the fixing roller and ON / OFF of the carbon heater in the warm-up operation of the fixing device according to the present invention. First, at time t1, an ON instruction signal is sent from the control unit to the triac in the heater control circuit, and power is supplied to the carbon heater. At this time, the fixing roller is not yet driven to rotate. Next, at time t2, when the control unit determines that the carbon heater has reached a predetermined set temperature or more based on a signal from the heater temperature detection means, the control unit drives the fixing roller to the drive control circuit at a predetermined rotational speed. An instruction signal is sent, and the motor M is driven by the drive control circuit, and the fixing roller starts to rotate. At time t3, when an OFF instruction signal is output from the control unit to the heater control circuit and the drive control circuit, the power supply to the carbon heater is turned off, and the rotation driving of the fixing roller is also turned off.

  FIG. 5 shows changes over time in the power consumption of the carbon heater and the surface temperature of the fixing belt. In the case of a conventional fixing device in which the rotation of the fixing roller is turned ON simultaneously with the carbon heater ON, the surface temperature of the fixing belt is increased at a constant speed up to a fixing temperature of 170 ° C. as shown by the broken line in FIG. To do.

  On the other hand, in the case of the fixing device of the present invention in which the carbon heater is turned on in a state where the rotation driving of the fixing roller is turned off and the power consumption of the carbon heater reaches 1160 W and the rotation driving of the fixing roller is turned on. As indicated by the solid line 5, the surface temperature of the fixing belt rapidly rises to over 160 ° C. Even if the power consumption exceeds 1160 W, the surface temperature of the fixing belt increases due to the heat capacity of the carbon heater and the residual heat. When the rotation of the fixing roller is started, the surface temperature of the fixing belt rapidly decreases. Thereafter, the temperature is raised to a fixing temperature of 170 ° C. at a constant rate. As is apparent from FIG. 5, the time required for the surface temperature of the fixing belt to reach the fixing temperature of 170 ° C. is faster in the fixing device of the present invention than in the conventional fixing device.

  However, if the carbon heater is turned on while the rotation driving of the fixing roller is turned off, the surface temperature of the fixing belt may be excessively increased and the fixing belt may be damaged. For reference, the time-dependent change in the surface temperature of the fixing belt when the carbon heater is continuously turned on while the rotation of the fixing roller is OFF is indicated by a one-dot chain line in FIG. In this case, the surface temperature of the fixing belt exceeds 170 ° C., and the temperature continues to rise, and there is a risk that the fixing belt may be broken or emit smoke. Therefore, it is important to turn on the fixing roller when the fixing belt is not damaged and the carbon heater is warmed. Therefore, in the fixing device of the present invention, the temperature detection means directly detects the temperature of the carbon heater, and when the temperature of the carbon heater reaches the set temperature, the fixing roller starts to rotate.

  FIG. 6 shows an example of a control flowchart of the warm-up period in the fixing device of the present invention. When the main power supply of the image forming apparatus is turned on (step S101), the carbon heater of the heating roller is turned on and heating of the heating roller is started (step S102). At this time, the rotation driving of the fixing roller is in an OFF state. Then, it is determined whether or not the temperature detected by the carbon heater by the temperature detecting means has reached a predetermined set temperature (step S103). When the detected temperature of the carbon heater reaches a predetermined set temperature, the fixing roller is driven to rotate (step S104). Then, the normal fixing operation is performed.

  As the temperature detection means for detecting the temperature of the carbon heater, a means for detecting the current value flowing through the carbon heater, a means for detecting the power consumption or the integrated power consumption of the carbon heater, and the like can be suitably used.

  In order to efficiently raise the surface temperature of the fixing belt to the fixing temperature, the rotational driving speed of the fixing roller during the warm-up period may be different from the rotational speed in the normal fixing operation.

  FIG. 7 shows a flowchart when the rotation speed of the fixing roller during the warm-up period is changed stepwise. When the main power supply of the image forming apparatus is turned on (step S201), the carbon heater of the heating roller is turned on and heating of the heating roller is started (step S202). At this time, the rotation driving of the fixing roller is in an OFF state. Then, it is determined whether or not the temperature detected by the carbon heater by the temperature detecting means has reached a predetermined set temperature (step S203). When the temperature of the carbon heater reaches a predetermined set temperature, the fixing roller is rotationally driven at the rotational speed V1 (step S204). When the driving time reaches the predetermined time T1 (step S205), the fixing roller is changed from the rotation speed V1 to the rotation speed V2 (step S206). When the driving time reaches the predetermined time T2 (step S207), the fixing roller is changed from the rotational driving V2 to the rotational speed V3 (step S208). Thereafter, when the driving time reaches the predetermined time T3 (step S209), the fixing roller is set to the rotation speed in the normal fixing operation (step S210).

  It is preferable that the rotation speeds V1 to V3 of the fixing roller be lower than the rotation speed in the normal fixing operation and increase in this order. Table 1 shows a preferred example of the rotation speed and driving time. Note that the number of changes in the rotation speed of the fixing roller is not limited, and may be changed in two steps or may be changed in four or more steps. Further, there is no limitation on the driving time.

  FIG. 8 shows a flowchart when the rotation speed of the fixing roller during the warm-up period is slower than the rotation speed in the normal fixing operation. When the main power supply of the image forming apparatus is turned on (step S301), the carbon heater of the heating roller is turned on and heating of the heating roller is started (step S302). At this time, the rotation driving of the fixing roller is in an OFF state. Then, it is determined whether or not the temperature detected by the carbon heater by the temperature detecting means has reached a predetermined set temperature (step S303). When the detected temperature of the carbon heater reaches a predetermined set temperature, the fixing roller is rotationally driven at a rotational speed V4 that is slower than the rotational speed in the normal fixing operation (step S304). When the driving time reaches the predetermined time T4 (step S305), the fixing roller is changed from the rotation speed V4 to the rotation speed in the normal fixing operation (step S306). When the rotation speed in the normal fixing operation of the fixing roller is 135 mm / sec, the rotation speed V4 is 90 mm / sec, and the drive time T4 is 3 to 4 sec.

  Also, in order to prevent damage due to local overheating of the fixing belt when the temperature detection means is not detected correctly or cannot be detected normally, the control unit has passed a predetermined time or more after starting energization of the carbon heater. However, if the temperature detected by the carbon heater by the temperature detecting means does not reach a predetermined set temperature, it is desirable to forcibly drive the fixing roller to rotate and / or to stop energizing the carbon heater.

  FIG. 9 is a flowchart showing an example of control in such a case. When the main power supply of the image forming apparatus is turned on (step S401), the carbon heater of the heating roller is turned on and heating of the heating roller is started (step S402). At this time, the rotation driving of the fixing roller is in an OFF state. Then, it is determined whether the temperature detected by the carbon heater by the temperature detecting means has reached a predetermined set temperature (step S403). When the detected temperature of the carbon heater reaches a predetermined set temperature, the fixing roller is driven to rotate (step S405). Then, the normal fixing operation is performed. On the other hand, even if a predetermined time elapses after the carbon heater is turned on, the detected temperature of the carbon heater does not reach a predetermined set temperature (“N” in step S403, “Y” in step S404). It is rotationally driven (step S405). This prevents local overheating of the fixing belt. The predetermined time is set in consideration of the normal warming time of the carbon heater and its variation.

  FIG. 10 shows changes with time in the surface temperature of the fixing belt when the control shown in FIG. 9 is performed. When a predetermined time elapses after the carbon heater is turned on with the rotation driving of the fixing roller being OFF, the surface temperature of the fixing belt reaches about 190 ° C. Even if the surface temperature of the fixing belt reaches about 190 ° C., if the fixing roller is not driven to rotate, the surface temperature of the fixing belt continues to rise and exceeds the temperature of 220 ° C. and enters the abnormal temperature range. On the other hand, when the surface temperature of the fixing belt reaches about 190 ° C., when the fixing roller is forcibly driven to rotate, the surface temperature of the fixing belt decreases and maintains about 180 ° C. Is prevented from overheating.

  FIG. 11 is a flowchart showing another control example for preventing local overheating of the fixing belt. When the main power supply of the image forming apparatus is turned on (step S501), the carbon heater of the heating roller is turned on and heating of the heating roller is started (step S502). At this time, the rotation driving of the fixing roller is in an OFF state. Then, it is determined whether the temperature detected by the carbon heater by the temperature detecting means has reached a predetermined set temperature (step S503). When the detected temperature of the carbon heater reaches a predetermined set temperature, the fixing roller is driven to rotate (step S505). Then, the normal fixing operation is performed. On the other hand, if the detected temperature of the carbon heater does not reach the predetermined set temperature even after a predetermined time has elapsed since the carbon heater was turned on (“N” in step S503, “Y” in step S504), the carbon heater It is turned off (step S506). Such control also prevents local overheating of the fixing belt. It goes without saying that the fixing roller is driven to rotate simultaneously with turning off the carbon heater.

  FIG. 12 is a schematic configuration diagram showing another embodiment of the fixing device according to the present invention. The embodiment shown in FIG. 12 is basically the same as the above-described embodiment except for the portion related to the halogen heater. Therefore, in the following description, emphasis will be placed on the description of parts different from the above-described embodiment, and common parts will be described. Description is omitted.

  In the fixing device shown in FIG. 12, a halogen heater 16 is further provided in the vicinity of the upper side of the carbon heater 15 built in the heating roller 13. The ON / OFF control of the halogen heater 16 is performed independently of the ON / OFF control of the carbon heater 15, and specifically, is controlled by the control unit via the halogen heater control circuit. In the normal fixing operation, the control unit performs ON / OFF control of the carbon heater 15 and the halogen heater 16 according to the temperature detected by the temperature sensor 17.

  FIG. 13 is a timing chart showing fixing roller rotation driving and ON / OFF of the halogen heater and the carbon heater in the warm-up operation of the fixing device shown in FIG. First, at time t1, an ON instruction signal is sent from the control unit to the carbon heater control circuit, and power is supplied to the carbon heater. At this time, the fixing roller is not yet driven to rotate. Next, at time t2, when the control unit determines that the carbon heater has reached a predetermined set temperature or more based on a signal from the heater temperature detection means, the control unit drives the fixing roller to the drive control circuit at a predetermined rotational speed. The instruction signal is sent, the motor is driven by the drive control circuit, and the fixing roller starts to rotate. Then, at time t4, which is a predetermined delay time Δt after the carbon heater is turned on, an ON instruction signal is sent from the control unit to the halogen heater control circuit, and electric power is supplied to the halogen heater. The delay time Δt is a time during which the filament of the halogen heater is sufficiently heated by the carbon heater and the inrush current of the halogen heater becomes a predetermined value or less. Thereafter, at time t3, when an OFF instruction signal is output from the control unit to the halogen heater control circuit, the carbon heater control circuit, and the drive control circuit, the power supply to the carbon heater and the halogen heater is turned off, and at the same time, the fixing roller Is also turned off.

  The mounting position of the halogen heater is preferably close to and above the carbon heater from the viewpoint of efficiently obtaining heat from the carbon heater. In this embodiment, one halogen heater and one carbon heater are provided. However, even in a case where there are a plurality of halogen heaters and carbon heaters, the halogen heater is disposed above the carbon heater. The heat from the carbon heater can be obtained efficiently. In this embodiment, the ON timing of the halogen heater is set after the predetermined delay time Δt. However, other conditions that can determine that the current flowing through the halogen heater is equal to or less than the predetermined value may be used as the ON condition of the halogen heater. . Examples of such conditions include the temperature of the halogen heater itself and the surface temperature of the fixing belt.

  When the carbon heater is deteriorated with time and replaced with a new one, when the apparatus is initialized, when maintenance / inspection is performed, it is preferable to update the set temperature at which the fixing roller is started to rotate during the warm-up period. FIG. 14 is a flowchart showing an example of control in such a case. The control example shown in this flowchart is a case where whether or not the carbon heater has reached the set temperature is detected by the value of the current flowing through the carbon heater.

  When the main power supply of the image forming apparatus is turned on (step S601), it is first determined whether or not there is a request for changing the set value of the current value for starting the rotation driving of the fixing roller (step S602). When there is a request for changing the set value of the current value, the set current value is set to a predetermined value (step S603). This predetermined value is usually the center value in the specification of the carbon heater. Next, the carbon heater of the heating roller is turned on and heating of the heating roller is started (step S604). At this time, the rotation driving of the fixing roller is in an OFF state. Then, the current consumption characteristic is measured by the current detection means provided in the heater temperature detection means (step S605). On the other hand, when there is no request for changing the set value of the current value, the set current value is read from the storage unit (RAM) (step S610), and then the carbon heater is turned on and heating of the heating roller is started (step S610). S611). At this time, the rotation driving of the fixing roller is in an OFF state.

  Next, it is determined whether or not the current value has reached the set current value (step S606). When the current value reaches the set current value, the fixing roller is driven to rotate (step S607). Then, it is determined whether or not the measurement within the current consumption measurement range is completed (step S608). Here, the current consumption measurement range is a range defined by a current consumption value or time determined in advance from the carbon heater characteristics. Next, when the measurement of the current consumption characteristic is completed, a set value of a current value for starting rotation driving of the fixing roller is calculated from the current consumption characteristic, and is written and updated in the storage unit (RAM) as the set current value (step). S609). Thereafter, the normal fixing operation is performed. In addition, when detecting whether the carbon heater has reached the set temperature based on the power consumption or the integrated power consumption, it can be updated in the same manner.

  The embodiments described above are all fixing devices using a fixing belt. However, the present invention is also applicable to a fixing device using a fixing roller as a fixing rotating body by directly pressing a fixing roller and a pressure roller. Applied. The warm-up method of the present invention can also be applied when shifting from a so-called standby state to a fixable state.

  The fixing device of the present invention is useful in that the warming-up period can be efficiently shortened because the rotation driving means starts rotating at a timing at which the resistor heater itself warms up and exhibits sufficient heat generation performance.

1 Fixing Device 11 Fixing Roller (Fixing Rotator)
12 Pressure roller (Pressure rotating body)
13 Heating roller (fixing rotator)
14 Fixing belt (fixing rotating body)
15 Carbon heater (resistor heater, heating means)
16 Halogen heater P Paper (transferred member)
t Toner image

Claims (11)

A fixing rotator having heating means; a pressure rotator that presses against the fixing rotator to form a nip portion; a rotation driving means that rotates at least one of the fixing rotator and the pressure rotator; and And a control means for controlling the drive of the rotation drive means, and heating and pressurizing the toner image by passing a transfer member having an unfixed toner image formed on one side through the nip portion. In a fixing device that melts and fixes to a member to be transferred,
The heating means is a resistor heater;
A temperature detecting means for detecting the temperature of the resistor heater;
In the warm-up period, the control means starts energization of the resistor heater in a state where the rotation driving means is stopped, and the temperature of the resistor heater becomes equal to or higher than a predetermined set temperature. When the detecting means detects, the fixing device starts rotating the rotation driving means.   The fixing device according to claim 1, wherein the temperature detection unit detects that the temperature of the resistor heater has become equal to or higher than a preset temperature based on a current value flowing through the resistor heater.   The fixing device according to claim 1, wherein the temperature detecting unit detects that the temperature of the resistor heater is equal to or higher than a set temperature based on power consumption of the resistor heater.   The fixing device according to claim 1, wherein the temperature detection unit detects that the temperature of the resistor heater has become equal to or higher than a set temperature based on the accumulated power consumption of the resistor heater.   The fixing device according to claim 1, wherein the control unit changes a rotation speed of at least one of the fixing rotator and the pressure rotator by the rotation driving unit in a warm-up period in a stepwise manner.   5. The control unit according to claim 1, wherein at least one of a rotation speed of the fixing rotator and the pressure rotator by the rotation driving unit during the warm-up period is slower than a rotation speed during a fixing operation. The fixing device according to 1.   If the temperature detected by the temperature detecting means does not reach the set temperature for starting the rotation driving means even after a predetermined time has elapsed since the energization of the resistor heater is started, The fixing device according to claim 1, wherein the rotation driving unit is forcibly started to rotate.   If the temperature detected by the temperature detecting means does not reach the set temperature for starting the rotation driving means even after a predetermined time has elapsed since the energization of the resistor heater is started, The fixing device according to claim 1, wherein the energization to the resistor heater is stopped. Further comprising a halogen heater as the heating means, the halogen heater is provided in the vicinity of the resistor heater,
The fixing device according to claim 1, wherein the control unit starts energizing the halogen heater after energizing the resistor heater. A storage means,
The set temperature is stored in the storage means in an updatable manner,
When the update request for the set temperature is made, the control means energizes the resistor heater with the set temperature as a predetermined value, and changes with time of any of current value, power consumption, and integrated power consumption Measure the characteristics
The fixing device according to claim 1, wherein a new set temperature is determined and updated from the measured aging characteristics.   An image forming apparatus comprising the fixing device according to claim 1.