JP2007212536A - Image heating device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image heating device which rises rapidly by improving the control accuracy of a current value in course of energizing control for an energized heating element and applying more currents when starting up the energized heating element. <P>SOLUTION: The image heating device has: the energized heating elements 302a and 302b for heating a developed image formed on a recording medium P; a current detection means 507 for detecting the current applied to the energized heating elements; and a control means 501 for controlling the energizing of the energized heating element. On the basis of a current value Is detected based on an output signal from the current detection means in a current value detection period before starting energizing control for the energized heating element, the control means obtains an energizing condition for controlling the energized heating element at a target current value It larger than the current value Is in a current control period when the energizing control for the energized heating element is performed, and changes a control state from the current value detection period to the current control period. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image heating apparatus suitable for use as a fixing device mounted on an electrophotographic image forming apparatus.

  In an image forming apparatus such as an electrophotographic copying machine or printer, a fixing device (fixing) is used to heat and fix an unfixed toner image (developed image) formed on a recording medium such as recording paper after the power is turned on. Must be raised to a predetermined temperature (target temperature). In order to rapidly increase the temperature of the fixing device, it is necessary to increase the amount of current supplied to a heater (electric heating element) for heating the unfixed toner image formed on the recording medium.

  However, in an image forming apparatus using a commercial AC power supply, there is a restriction due to the current rating of the outlet, and only a current less than the rated current can be used.

In view of this, as disclosed in Japanese Patent Application Laid-Open No. 2004-133620, a means for detecting a current flowing through the fixing device is provided, and control is performed to supply a larger amount of current to the fixing device below the rated current.
JP-A-10-274901

  However, in the image forming apparatus having the above-described current detection means, the current value cannot be accurately derived under any use conditions due to variations in heater resistance and input voltage in the fixing device. Therefore, even when setting the upper limit current value that can be used in a commercial AC power supply, it is necessary to provide a margin that includes component variations with respect to the standard setting value. Was limited.

  The present invention has been made in consideration of the above-described variations, and can improve the control accuracy of the current value during the energization control of the energization heating element, and can supply more current when the energization heating element is started up. An object of the present invention is to provide an image heating apparatus that rises quickly.

A typical configuration of an image heating apparatus according to the present invention is an image heating apparatus used in an image forming apparatus that forms an image on a recording medium, and is energized heat generation for heating a developed image formed on the recording medium. A current detection means for detecting a current supplied to the energization heating element, and a control means for controlling energization of the energization heating element,
The control means controls the energization of the energization heating element based on the current value Is detected based on the output signal of the current detection means in the current value detection period before the energization control of the energization heating element is started. In the current control period in which the current value is applied, an energization condition for controlling the energization heating element with a target current value It larger than the current value Is is obtained, and the control state is changed from the current value detection period to the current control period. This is an image heating apparatus.

  According to the present invention, it is possible to improve the control accuracy of the current value during energization control of the energization heating element, and to supply a larger amount of current when the energization heating element is started up, and to provide an image heating apparatus that rises quickly. .

  Hereinafter, the present invention will be described in detail with reference to the drawings.

(1) Image Forming Apparatus FIG. 1 is a structural model diagram of an example of an image forming apparatus in which the image heating apparatus according to the present invention can be mounted as an image heating fixing apparatus. This image forming apparatus is a laser beam printer using an electrophotographic system. In this printer, the conveyance reference of the recording paper (recording medium) is the center of the longitudinal width orthogonal to the recording paper conveyance direction on the surface of the recording paper and the longitudinal length of the heater (heating source) provided in the fixing device. This is a central reference transport for transporting the recording paper in a state in which the center coincides.

  The printer of this embodiment includes a deck 101 that stores a recording sheet P as a recording medium at a lower portion of a printer main body (image forming apparatus main body) 100 constituting a housing of the printer. Around the deck 101, a deck paper presence sensor 102 that detects the presence or absence of the recording paper P in the deck 101, a paper size detection sensor 103 that detects the size of the recording paper P in the deck 101, and the recording paper from the deck 101. A pickup roller 104 for feeding out P is provided. A deck paper feed roller 105 that transports the recording paper P fed by the pickup roller 104 along the transport direction of the recording paper P is paired with the paper feed roller 105 to prevent double feeding of the recording paper P. A retard roller 106 is provided. A sheet feeding sensor 107 that detects a sheet feeding conveyance state from a double-side reversing unit, which will be described later, and a sheet feeding sensor for conveying the recording sheet P further downstream are provided downstream of the sheet feeding roller 105 in the recording sheet P conveying direction. A paper conveyance roller 108 is provided. Further, a registration roller pair 109 that conveys the recording paper P in synchronization with the printing timing, and a pre-registration sensor 110 that detects the conveyance state of the recording paper P to the registration roller pair 109 are provided.

  Further, on the downstream side of the registration roller pair 109 in the conveyance direction of the recording paper P, a drum-type electrophotographic photosensitive member (hereinafter referred to as a photosensitive drum) as an image carrier, process means acting on the photosensitive drum 1, and The process cartridge 112 is integrated into a cartridge. The cartridge 112 is detachably attached to the printer main body 100. The cartridge 112 serves as process means, a charging roller (charging means) 2 that uniformly charges the outer peripheral surface (surface) of the photosensitive drum 1, and a developing device that develops an electrostatic latent image formed on the surface of the photosensitive drum 1. (Developing means) 136 and the like. The developing device 136 includes a toner container 135 that stores toner (developer), a developing roller 134 that transfers the toner in the toner container 135 to the surface of the photosensitive drum 1, and the like. An electrostatic latent image is formed on the surface of the photosensitive drum 1 by irradiating a laser beam corresponding to an image signal from a laser scanner unit 111 described later. The latent image is visualized (developed) by transferring toner to the electrostatic latent image by the developing roller 134 of the developing device 136. Then, in synchronization with the formation of the electrostatic latent image, the recording paper P is sent to the transfer portion between the surface of the photosensitive drum 1 and the surface of the transfer roller 113 (transfer means) by the registration roller pair 109. The transfer roller 113 transfers the toner image on the surface of the photosensitive drum 1 onto the recording paper P while the recording paper P passes through the transfer portion. Reference numeral 114 denotes a discharge member (hereinafter referred to as a charge eliminating needle) for removing charges on the recording paper P and promoting separation of the recording paper P from the surface of the photosensitive drum 1.

  Further, a conveyance guide 115 and a fixing device 200 that thermally fixes the toner image transferred onto the recording paper P are disposed downstream of the static elimination needle 114 in the recording paper P conveyance direction. A fixing paper discharge sensor 119 for detecting a conveyance state from the fixing device 200 and a double-sided flapper 120 for switching the destination of the recording paper P conveyed from the fixing device 200 to a paper discharge unit or a double-side reversing unit are provided. Has been. A paper discharge sensor 121 that detects the conveyance state of the recording paper P in the paper discharge unit and a paper discharge roller pair 122 that discharges the recording paper P are disposed downstream of the paper discharge unit in the conveyance direction of the recording paper P. ing.

  On the other hand, the recording paper P after one-sided printing is reversed in order to print on both sides of the recording paper P, and the recording paper P is fed to the double-side reversing part side for feeding again to the image forming part by forward / reverse rotation. A reversing roller pair 123 to be switched back is provided. Further, the recording paper P is transported from a reversing sensor 124 that detects the transport state of the recording paper P to the pair of reversing rollers 123 and a lateral registration portion (not shown) for aligning the longitudinal width of the recording paper P. For this purpose, a D-cut roller 125 is provided. Further, a double-sided sensor 126 for detecting the conveyance state of the recording paper P in the double-side reversing unit and a double-sided conveyance roller pair 127 for conveying the recording paper P from the double-side reversing unit to the paper feeding unit are provided.

  The laser scanner unit 111 includes a laser unit 129 that emits laser light modulated based on an image signal sent from an external device 128 such as a host computer. A polygon mirror 130 for scanning the surface of the photosensitive drum 1 with the laser beam from the unit 129, a scanner motor 131 that rotates the mirror 130, an imaging lens group 132, and a folding mirror 133 are provided.

  Reference numeral 3 denotes a high voltage power supply, which has a high voltage circuit for applying a predetermined bias to the charging roller 2, the developing roller 134, the transfer roller 113, and the charge eliminating needle 114, in addition to a power supply control circuit 500 described later. . A main motor M1 rotates the photosensitive drum 1, the charging roller 2, the developing roller 134, the transfer roller 113, a roller for transporting the recording paper P, and the like via a gear train.

  A printer control unit 4 controls the entire printer, and includes a memory such as a RAM and a ROM, a timer, an MPU having an I / O port, and various input / output control circuits (not shown). The printer control unit 4 is connected to the external device 128 via the interface 136.

(2) Fixing device 200
FIG. 2 is a cross-sectional side view of an example of a film heating type fixing device 200.

  The fixing device 200 of this embodiment is a pressure roller drive type.

  In this fixing device 200, a guide member (heating source support member) 204 holding a ceramic heater (heating source) 205 is passed through a sleeve-like fixing film (moving member) 201 having flexibility and a pressure roller (moving member). The pressurizing member 202 is brought into pressure contact with a predetermined pressing force. Thus, a nip portion (pressure nip portion, fixing nip portion) N is formed between the fixing film 201 and the pressure roller 202. The film 201, the guide member 204, the heater 205, and the pressure roller 202 are elongated members each having a longitudinal direction in a direction orthogonal to the conveyance direction of the recording paper P.

  The film 201 is composed of an endless single layer mainly composed of heat-resistant PTFE, PFA, FEP or the like for reducing heat capacity as part of speeding up the fixing process, and the total layer thickness is preferably 100 μm or less. Is taken to be 40 μm or more and 80 μm or less. Alternatively, it is composed of a composite layer in which PTFE, PFA or FEP is coated on the outer peripheral surface of an endless substrate mainly composed of polyimide, polyamideimide, PEEK, PES or PPS, and the total layer thickness is preferably 100 μm or less, preferably The thickness is 40 μm or more and 80 μm or less.

  The guide member 204 is formed into a substantially semicircular saddle shape with a cross section made of a high heat resistant resin material such as PPS or liquid crystal polymer. The guide member 204 has a function of supporting the heater 301 and guiding the inner surface of the film 201 over the entire longitudinal direction.

  The pressure roller 202 has a cylindrical elasticity mainly composed of heat-resistant and releasable silicone rubber on the outer peripheral surface of a columnar or substantially columnar core 203 mainly composed of iron, aluminum or the like. It is constituted by coating the layer 204. The pressure roller 202 is rotated in the direction of the arrow when a driving gear (not shown) provided at one end of the core metal 203 receives a rotational force from the fixing motor M2.

(3) Ceramic heater 205
FIG. 3 is a schematic configuration model diagram of the heater 205.

  The heater 205 includes a thin plate substrate 301 whose main component is ceramics typified by alumina. The substrate 301 is an elongated member having a longitudinal direction in a direction orthogonal to the conveyance direction of the recording paper P. On one surface of the substrate 301, heating element patterns (conducting heating elements) 302a and 302b mainly composed of Ag / Pd (silver palladium) are applied along the longitudinal direction of the substrate 301 by screen printing or the like. . The heating patterns 302a and 302b are coated with power supply electrodes 303a and 303b mainly composed of Ag on one end and the common electrode 303c on the other end by screen printing or the like. The heat generation patterns 302a and 302b are covered with an insulating protective layer 304 mainly composed of glass or fluorine.

  Hereinafter, the heater unit formed by the heating element pattern 302a is referred to as a main heater, and the heater unit formed by the heating element pattern 302b is referred to as a sub-heater. The two main heaters 302a and sub heaters 302b have greatly different heat distributions. The heat distribution of the main heater 302a is bilaterally symmetric at the center of the substrate 301 with respect to the heater center position C in the longitudinal direction of the heater 205. On the other hand, the heat distribution of the sub-heater 302b is symmetrical with respect to the heater center position C at the end of the substrate 301 that partially overlaps the central portion of the substrate 301.

(4) Thermistor TH1, TH2, TH3
On the substrate 301 of the heater 205, three thermistors (temperature detection means) TH1, TH2, TH3 are disposed in contact with the surface opposite to the surface on the main heater 302a and sub heater 302b side. The arrangement of the thermistors TH1, TH2, TH3 is indicated by arrows E, F, G. Each thermistor TH1, TH2, TH3 is arranged so as to straddle the main heater 302a and the sub heater 302b in the short direction of the substrate 301 (the conveyance direction of the recording paper P). The thermistor TH1 is disposed at a position corresponding to the heat distribution of the main heater 302a. The thermistors TH2 and TH3 are arranged at positions corresponding to the heat distribution of the sub heater 302b. Each thermistor TH1, TH2, TH3 detects the temperature of the heater 205, and outputs detection signals (temperature information) St1, St2, St3 to a CPU (control means) 501.

(5) Power supply control circuit 500
FIG. 4 is a diagram illustrating an example of a power supply control circuit 500 that supplies power to the heater 205.

  The power control to the heater 205 is controlled independently by the main heater 302a and the sub heater 302b.

  The power supply control circuit 500 includes a CPU (Central Processing Unit) 510, a first triac 502, a second triac 503, an AC power source 504, and a current detection circuit 507.

  In the power supply control circuit 500, the first triac 502 and the main heater 302a are connected in series, the second triac 503 and the sub heater 302b are connected in series, and they are connected to the AC power source 504 in parallel. is there. The first and second triacs 502 and 503 are turned ON / OFF by turning ON / OFF the first and second heater drive signals S1 and S2 output when the CPU 501 takes in a print instruction signal output from the external device 128. Be controlled.

  The current detection circuit 507 is inserted between the first and second triacs 502 and 503 and the AC power source 504. The current detection circuit 507 will be described later. The adjustment of the amount of current applied to the heaters 302a and 302b is realized by phase control that controls the current applied to the heaters 302a and 302b by turning on and off the energization at a phase angle within one half wave of the AC power supply. To do.

  The CPU 501 controls energization to the heaters 302 a and 302 b using a zero cross signal output from a zero cross detection circuit (not shown) that detects the zero cross timing of the AC power source 504. FIG. 5A is a diagram illustrating the driving timing of the zero cross signal and the heater driving signals S1 and S2. The heater drive signal S1 is turned on after a predetermined time t1, t2 from the falling timing of the zero cross signal to control energization to the heaters 302a, 302b. Thereby, a heater current having a waveform as shown in the figure is obtained. FIG. 5B shows a table representing the relationship between the timings t1 and t2 when the heater driving signal S1 is turned ON and the current Irms applied to the heaters 302a and 302b at the timings t1 and t2. This table is for the case where the frequency of the AC power source 504 is 50 Hz, and represents the applied current when energized in all phases as 100%.

(6) Current detection circuit 507
The configuration and operation of the current detection circuit 507 will be described. FIG. 6 is a diagram illustrating an example of the current detection circuit 507. FIG. 7 is a waveform diagram of each part in the circuit.

  The current detection circuit 507 detects the total current value of the current flowing through the main heater 302a and the sub heater 302b, and outputs a predetermined current value, that is, a current level detection signal S6 described later.

  In FIG. 7, (a) shows a waveform when a full-wave current flows through each heater 302a, 302b, and (b) shows each heater 302a, 302a, by turning ON / OFF energization at a phase angle within one half wave. The waveform in the case of performing phase control for controlling the current applied to 302b is shown.

  In FIG. 6, terminals 646 and 647 are connected between an AC power source 504. Reference numeral 645 denotes a current transformer. A current (heater current) I601 that is applied to the main heater 302a and the sub heater 302b is applied to the first terminal and the second terminal which are input terminals. A rectifier circuit composed of resistors 640 and 643 and diodes 642 and 644 is connected to terminals 3 and 4 which are output terminals of the current transformer 645. A half-wave AC voltage Vt corresponding to the level of the current I601 is generated at the output of the rectifier circuit. Reference numerals 641 and 639 denote resistors connected to the output portion of the rectifier circuit.

  The output part of the rectifier circuit is connected to an integrating circuit composed of an operational amplifier 633, an FET 636, a capacitor 634, and resistors 635 and 638. In the integrating circuit, an AC voltage is integrated in one cycle, and a voltage corresponding to the integrated value is generated between the terminals of the capacitor 634. The voltage across the capacitor 634 is cleared to 0V every cycle by the operation of the FET 636 driven by the RST signal. Reference numeral 637 denotes a resistor connected to the RST signal input portion of the FET 636. The RST signal is a signal output from the CPU 501 at a predetermined timing with respect to the zero cross point of the AC power source 504. The voltage Vint at the output terminal of the operational amplifier 633 can be expressed by the following equation.

  Here, ΣVt is an integral value of the output voltage Vt of the rectifier circuit. An output of the operational amplifier 633 is input to a differential circuit including an operational amplifier 628, resistors 631, 632, 630, and 629, and a diode 627. As for the resistors in the differential circuit, the resistors 630 and 631, and the resistors 629 and 632 are set to the same resistance value. The differential circuit receives the output voltage Vint of the integrating circuit and the output voltage Vt of the rectifying circuit. The output voltage Vcs of the differential circuit is expressed as follows.

  Here, R 631 is the resistance value of the resistor 631, and R 632 is the resistance value of the resistor 632. Although the output voltage Vcs of the differential circuit is peak-held by the capacitor 626, it is cleared to 0V every cycle by the operation of the FET 625 driven by the RST signal. Reference numeral 624 denotes a resistor connected to the RST signal input portion of the FET 625. The output voltage Vcs of the differential circuit is at a level corresponding to the average value of the half cycle section of the current flowing through the main heater 302a and the sub heater 302b.

  The output voltage Vcs of the differential circuit is output as the current level detection signal S6 via the operational amplifier 622 and input to the analog input port of the CPU 501. Reference numerals 623 and 620 denote resistors. Reference numeral 651 denotes an output terminal of the current detection circuit 507.

(7) Heater current calculation process of CPU501 CPU501 performs the calculation process which calculates the absolute value of an electric current based on the current level detection signal S6 output from the current detection circuit 507.

  FIG. 8 is a flowchart of the current value calculation process in the current value detection period. The current value calculation process (operation related to the current value detection period) in the current value detection period is executed in a period other than the operation related to the printing (image formation) operation of the printer.

  First, the current level detection signal S6 is sampled in S902. FIG. 9 is a diagram illustrating the relationship between the applied current Irms [%] and the phase angle θ.

  As shown in FIG. 9, by starting energization at a predetermined phase angle of 102.8 °, a current corresponding to 60% at 100% energization is applied. In the present embodiment, sampling of 5 waves (100 msec) is performed for a 50 Hz AC input. Sampling is performed within a predetermined section S within one cycle of the waveforms shown in FIGS. 7A and 7B, whereby the level signal Vs corresponding to the heater current can be sampled.

  Next, in S903, the level signal Vs is averaged five times, and the process proceeds to the current calculation process in S904. FIG. 10 shows the relationship between the level signal Vs corresponding to the heater current and the average current value Is supplied to the heaters 302a and 302b. These are in a proportional relationship, and in this embodiment, the level signal Vs = 0.1 A is set to correspond to the average current value Is = 1.0 A. Therefore, the average current value Is can be calculated from the measurement result of the level signal Vs.

  In step S905, current correction processing is performed. The current value calculated in S904 is the average current value of the AC waveform applied to the heaters 302a and 302b. On the other hand, since the amount of electric power generated in the heaters 302a and 302b is determined by the effective current value, the average current value Is calculated in S904 is converted into the effective current value Is'. The conversion uses a coefficient RMSCONV determined by the table shown in FIG. The coefficient RMSCONV indicates the ratio between the effective current value Is ′ and the average current value Is. When phase control is performed, the value changes depending on the phase angle at which energization is started. The table shown in FIG. 11 shows the relationship of the coefficient RMSCONV to the applied current Irms [%] during phase control. Correction is performed using the following equation.

  If the current level signal that has been averaged five times in S903 is Vs = 0.6A, the average current value is Is = 6.0A. On the other hand, when the applied current in the current value detection period is Irms = 60%, RMSCONV = 1.39 according to the table shown in FIG. 11. Therefore, when the average current value Is = 6.0 A is converted into the effective current, Is ′ = It becomes 8.34A.

  Next, the process proceeds to the current value switching process of S906. In this embodiment, the target current value (target current value) It that can be input to the heaters 302a and 302b is 12.5A. From the relationship with the effective current value Is ′, the applied current Irms [%] when the target current value It is applied is obtained by the following equation.

Irms = 60% × 12.5A / 8.34A = 89.9%
From the relationship between the applied current Irms [%] and the phase angle θ shown in FIG. 9, a current of 12.5 A can be supplied by performing energization control at a phase angle of 60 °. Therefore, after the end of the current value detection period shown in FIG. 8, the heaters 302a and 302b are energized and controlled at a phase angle of 60 ° until the heater temperature reaches a predetermined temperature (target temperature) as will be described later.

(8) Heat Fixing Operation of Fixing Device 200 In the fixing device 200 of this embodiment, when the CPU 501 takes in a print instruction signal, the fixing motor M2 rotates the pressure roller 202 in the direction of the arrow as shown in FIG. Then, due to the sliding frictional force with the surface of the film 201 due to the rotation of the pressure roller 202, the rotational force acts on the film 201 and the film 201 rotates around the guide member 204 in the direction of the arrow. Then, based on the detection signals St1, St2, St3 of the thermistors TH1, TH2, TH3, the CPU 501 performs ON / OFF control of the triacs 502, 503 so that the temperature of the heater 205 becomes a predetermined temperature. Thus, the heaters 302a and 302b are temperature-controlled to a predetermined temperature. In this state, the recording paper P is introduced into the nip N, and the heat of the heater 205 is applied to the recording paper P through the film 201 while the recording paper P is nipped and conveyed at the nip P, whereby the recording paper P The unfixed toner image t is heat-fixed on the recording paper P. The recording paper P is separated from the surface of the film 30 by the curvature and discharged.

  In the power supply control circuit 500 of this embodiment, the CPU 501 energizes a current having a predetermined phase angle and starts sampling the level signal Vs for 5 waves (100 msec) before starting energization control of the heaters 302a and 302b. A detection period is provided. The average current value Is is obtained based on the sampled level signal Vs, and the relationship between the phase angle for controlling the energization of the heaters 302a and 302b based on the average current value Is and the target current It that can be supplied to the heaters 302a and 302b. Check. That is, the energization condition for controlling the heaters 302a and 302b with the target current It larger than the average current value Is is obtained. Thereby, the phase angle with respect to the target current It can be accurately calculated. Then, the phase angle at which the maximum usable current according to the target current It can be applied is obtained, and the energization control of the heaters 302a and 302b is performed with the current value of the phase angle. That is, the control state is changed from the current value detection period to a current control period for performing energization control of the heaters 302a and 302b. As a result, in an arbitrary use environment, a maximum usable current can be applied to the heater in consideration of variations in various components after 100 msec of starting energization of the heater. This makes it possible to minimize the heater startup.

  That is, the power supply control circuit of the present embodiment provides a current value detection period at the beginning of energization of the heater, and measures the applied current when energized at a predetermined phase angle. From the measured current value and the target value of the maximum current that can be supplied, a phase angle at which the maximum current that can be supplied can be input is calculated. Then, the heater startup time can be reduced as much as possible by applying the maximum current that can be supplied when the heater is started up to the heater based on the phase angle. By shortening this processing, it is possible to shorten the time from receiving the print signal to the completion of the first sheet discharge (First Print Out Time: FPOT), so the waiting time when the user performs printing is shortened. The

  In this embodiment, the number of level signal samplings is 5 in the current value detection period, but the number of level signal samplings is not limited to 5 depending on the detection accuracy.

  In the first embodiment, the method for calculating the phase angle for supplying the maximum current that can be supplied when the current value detection period is provided in the initial energization of the heater and the current control period is shifted has been described.

  In this embodiment, the timing of the current value detection period will be described as an application example. Members / portions common to those of the first embodiment are denoted by the same reference numerals, and description thereof is omitted. The same applies to Example 3 described later.

  The fixing device shown in the present embodiment aims to reduce the heater start-up time as much as possible by applying the maximum current that can be supplied when the heater is started up to the heater. This is because FPOT can be shortened by shortening the heater start-up time, so that the waiting time when the user performs printing can be shortened.

  The operation of the fixing device 200 can be roughly divided into the following four processes.

  1) Warm-up processing when power is turned on or when returning to sleep mode (standby mode).

  2) Heater start-up process (pre-rotation) at the start of printing.

  3) Print processing during printing.

  4) Heater lowering process (post-rotation) when recording paper is discharged.

  For the current value detection period described in the first embodiment, the current value Is is measured while the current is reduced, and the maximum supply current is calculated. Performing this process at the beginning of the heater start-up process in 2) is limited in terms of input power.

  Therefore, in the present embodiment, the current value detection period is preferably performed at the beginning of the warm-up process in the above 1), and the phase angle at which the maximum current can be supplied is stored in a storage unit (not shown). Keep it. The storage location of the phase angle may be a memory in the CPU 501 or another storage means may be used. In the heater start-up process of 2), the maximum current is supplied from the initial stage of heater energization at the stored phase angle. That is, the CPU 501 uses the phase angle θ stored in the storage unit to start energization control of the heaters 302a and 302b with the applied current Irms when the printing operation of the image forming apparatus starts.

  Accordingly, it is possible to provide a fixing device (fixing device) that can always realize the shortest FPOT during a printing operation.

  FIG. 12 shows a cross-sectional side view of another example of the fixing device. This fixing device is a so-called heat roller type fixing device, and can be mounted on the image forming apparatus instead of the fixing device 200 of the first embodiment.

  The fixing device 200 </ b> A of this embodiment includes an elongated cylindrical fixing roller 700 having a halogen heater 730 therein, and a pressure roller (pressure) that contacts the outer peripheral surface (surface) of the fixing roller 700 to form a nip portion N. Member) 720.

  The fixing roller 700 has a core metal 701 made of aluminum and a PFA release layer 702 coated on the surface layer.

  The heater 730 has a filament 730b as an energization heating element in a glass bulb 730a. The heater 730 is ON / OFF-controlled by the ON / OFF of the first heater drive signal S1 output from the CPU 501 by the first triac 502 in the power supply control circuit 500 of the first embodiment. The operation related to the current value detection period for the filament 730b of the heater 730 and the operation related to the energization control by the power supply control circuit 500 are the same as those in the first embodiment. The heater light distribution of the heater 730 has a symmetrical distribution with respect to the sheet passing reference.

  The pressure roller (pressure member) 720 has an elastic layer 722 of silicone rubber on an aluminum cored bar 721 and a release layer 723 of PFA on the surface layer. A nip portion N is formed between the two.

  In the fixing device 200 </ b> A of this embodiment, the recording paper P is guided to the nip portion N by the entrance guide 705. The recording paper P is heated and pressed by the fixing roller 700 and the pressure roller 720 heated by the heater 730. As a result, the toner image t on the recording paper P is fixed to the recording paper P. The recording paper P is peeled off from the separation claw 706 that contacts the outer peripheral surface (front surface) of the fixing roller 700 or from the separation claw 707 that contacts the outer peripheral surface (front surface) of the pressure roller 720, and then the paper discharge guide 708 is removed. Through the paper discharge roller 709 and discharged outside the apparatus.

  The main thermistor 740 is in contact with the surface of the fixing roller 700. The thermistor 740 outputs a detection signal on the surface of the fixing roller 700 to the CPU 501. Based on the signal, the CPU 501 performs ON / OFF control of the triac 502 so that the temperature of the heater 730 becomes a predetermined temperature. For example, when a thin (low heat capacity) fixing roller having a core metal 701 of 1 mm or less is used as the fixing roller 700, the rising speed of the fixing roller temperature is the same as that of the film-type on-demand fixing device 200 shown in the first embodiment. Similar behavior. Therefore, the same energization control as in the first embodiment is performed on the heater 730, so that the rising speed of the fixing roller 700 can be increased, and at the same time, the effect of increasing the FPOT is great.

  On the other hand, as described in the first embodiment, when the maximum usable current can be input to the heater 730, the start-up time is shortened also in the fixing device 200A using the fixing roller 730 having a large heat capacity. In this respect, a great effect can be obtained.

Configuration model diagram of an example of an image forming apparatus Cross-sectional side view of an example of a fixing device according to Embodiment 1 Schematic model diagram of heater The figure showing an example of a power supply control circuit (A) is a diagram showing the drive timing of the zero cross signal and the heater drive signal, (b) is a diagram showing the relationship between the timing when the heater drive signal is turned on and the current Irms applied to the heater at the timings t1 and t2. Diagram showing an example of current detection circuit Waveform diagram of each part in the current detection circuit Flow chart of current value calculation processing in current value detection period The figure showing the relationship between the applied current Irms [%] and the phase angle θ The figure showing the relationship between the level signal Vs according to the heater current and the average current value Is energized to the heater The figure showing the relation of coefficient RMSCONV with respect to applied current Irms [%] at the time of phase control Cross-sectional side view of an example of a fixing device according to Embodiment 3

Explanation of symbols

200: fixing device, 201: fixing film, 202: pressure roller,
205: Ceramic heater, 302a: Main heater, 302b: Sub heater
501: CPU, 507: current detection circuit, 200A: fixing device, 700: fixing roller,
720: Pressure roller, 730: Halogen lamp, 730b: Filament, P: Recording paper

Claims (7)

An image heating apparatus used in an image forming apparatus for forming an image on a recording medium,
An energization heating element for heating the developed image formed on the recording medium;
Current detection means for detecting a current supplied to the energization heating element;
Control means for controlling energization of the energization heating element;
Have
The control means controls the energization of the energization heating element based on the current value Is detected based on the output signal of the current detection means in the current value detection period before the energization control of the energization heating element is started. In the current control period in which the current value is applied, an energization condition for controlling the energization heating element with a target current value It larger than the current value Is is obtained, and the control state is changed from the current value detection period to the current control period. An image heating apparatus.   The image heating apparatus according to claim 1, wherein the control unit detects a current value Is when energizing at a predetermined phase angle θref in the current value detection period.   The image heating apparatus according to claim 1, wherein the current value Is detected by the control unit during the current value detection period is an average current value. When the controller applies a current of Irmsref [%] at a phase angle θref to the energization heating element during the current value detection period, after converting the detected average current value Is into an effective current value Is ′, 4. The image heating apparatus according to claim 3, wherein an applied current Irms [%] corresponding to the phase angle θ during the current control period is obtained from the relationship of the following equation based on the relationship with the target current value It.
Irms = Irmsref × It / Is´   The image heating apparatus according to claim 4, further comprising storage means for storing the phase angle θ during the current control period.   The control means uses the phase angle θ stored in the storage means to start energization control to the energization heating element by the applied current Irms at the start of an image forming operation of the image forming apparatus. The image heating apparatus according to claim 5.   The image heating apparatus according to claim 1, wherein the control unit executes an operation related to the current value detection period in a period other than an operation related to an image forming operation of the image forming apparatus.