JP5350087B2 - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a control technique for reducing a time difference between timing of switching electric power on fixing temperature control and timing of updating an electric power value, in a fixing device using control comprised of a combination of phase control and wave number control. <P>SOLUTION: An image forming apparatus includes a fixing device 23 which has the first control pattern comprised of the combination of the phase control and the wave number control with four full wave of an AC source as a control cycle and the second control pattern comprised of only the phase control with one full wave as the control cycle, and executes control by combining the first control pattern and the second control pattern so as to reduce the time difference between switching timing and timing of updating the electric power value of the first control pattern or the second control pattern when switching the power supply. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to an image forming apparatus using an electrophotographic process and the like, a heater power control method for a fixing device for fixing the toner image on a recording paper, and an image forming apparatus using the heater power control method.

  Conventionally, for example, in an image forming apparatus such as a copying machine or a printer using an image forming process such as electrophotography, electrostatic recording, and magnetic recording, an unfixed toner image on a recording medium such as a recording material or an OHP sheet is a permanent image. Therefore, a heat fixing device for fixing by melting with heat is provided.

  In the image forming apparatus, a heat roller type heat fixing device using a halogen heater as a heat source or a film fixing type heat fixing device using a ceramic heater as a heat source is used as the fixing heating device (Patent Documents 1 to 4). reference).

  In addition, various systems and configurations such as an IH fixing system, a flash heating system, and an oven heating system are known and put into practical use.

  In particular, the film fixing type heat fixing apparatus that heats a film having a very small heat capacity from the inside has high energy efficiency and a high temperature increase rate. For this reason, it is sufficient to heat only at the time of printing, and there is an advantage that the time from when the power is turned on until it becomes ready for printing is short, and the power consumption at the time of printing standby is greatly reduced.

  In general, the heater is connected to an AC power source via a switching element such as a triac, and power is supplied by the AC power source. The fixing heating device is provided with a temperature detecting element, for example, a thermistor temperature sensitive element. The temperature of the fixing heating device is detected by the temperature detection element, and the power supply to the heater is turned on / off by the engine controller turning on / off the switching element based on the detected temperature information. Is controlled to a target constant temperature.

  On / off control to the ceramic heater is performed by phase control of commercial power supply (see Patent Document 5 and Patent Document 6), wave number control (see Patent Document 7), or a combination of phase control and wave number control (see Patent Document 8). Done.

  The heater is connected to an AC power supply via a switching control element such as a triac, and a temperature detection element such as a thermistor temperature sensing element is provided in a heat fixing device to which electric power is supplied by the AC power supply. The temperature detection element detects the temperature of the fixing device, and based on the detected temperature information, the engine cotton roller of the device turns on / off the switching element, thereby turning on / off the power supply to the heater, The temperature of the heat fixing device is adjusted and controlled to a target temperature.

  The phase control is a method of supplying power to the heater by turning on the heater at an arbitrary phase angle within one half wave of the AC power supply. FIG. 13A shows an example of a phase control table. The wave number control is a power control method in which the heater is turned on / off in units of half wave of the AC power supply. Control in which phase control and wave number control are combined is a power control method in which a half of a plurality of half waves is phase-controlled and the remaining wave number is controlled.

  Reasons for selecting the phase control include flickering of lighting equipment, so-called flicker and suppression of temperature ripple of the fixing heating device. Flicker is caused by the fluctuation of the load current of the device and the internal impedance of the connected AC commercial power supply or the impedance of the indoor power distribution network, causing a sudden fluctuation in the AC power supply voltage of the AC commercial power supply. This refers to malfunctions such as flickering of connected lighting equipment.

  In the phase control, since a current flows every half wave, a change amount and a change period of the current are small, and the occurrence of flicker can be suppressed. Further, since the power can be controlled for each half wave, there is an advantage that the temperature adjustment control of the fixing heating device is quick and the temperature ripple of the fixing heating device can be reduced. On the other hand, since the heater is turned on at an arbitrary phase angle within one half wave of the AC power supply, there is a demerit that harmonic current distortion and switching noise occur due to a rapid current fluctuation that occurs when the heater is turned on.

  Reasons for selecting wave number control include suppression of harmonic current distortion and switching noise. This is because the wave number control in which the heater on / off control is always performed at the zero cross point is less likely to occur than the phase control that is switched in the middle of the half wave of the AC power supply. On the other hand, the load current fluctuation of the apparatus is larger than that of the phase control, and the voltage fluctuation of the AC power supply is larger.

  The reason for selecting control that combines phase control and wave number control is advantageous for suppressing harmonic current distortion and switching noise compared to phase control alone, and advantageous for suppressing flicker compared to only wave number control. It can be mentioned. Higher harmonic current distortion and switching noise tend to occur more when the voltage of the AC AC power supply used is higher. Therefore, it is necessary to adopt a control method according to the AC commercial power supply voltage in the region where the image forming apparatus is used. For example, a phase control system advantageous for flicker is used for an AC commercial power supply voltage region of 100 to 120V, and a wave number control system advantageous for harmonic current distortion and switching noise is used for an AC commercial power supply voltage region of 220V to 240V. Is used to control the heater. However, with the increase in heater power of the fixing heating device due to the recent increase in the speed of the image forming apparatus, it is difficult to satisfy the harmonic current distortion regulation with only phase control after satisfying the fixing performance, and the wave number There were cases where flicker regulations could not be satisfied by control alone. In that case, control combining phase control and wave number control is effective as a method that satisfies both harmonic current distortion regulation and flicker regulation.

  FIG. 13B shows a table example of heater power control combining phase control and wave number control as Table 2. The supply power ratio to the heater is described so as to be the same power as that of the adjacent table 1.

  In the example of FIG. 13B, eight half waves (four full waves) are set as one control period, and six half waves are controlled by wave number control and two half waves are controlled by phase control. In Table 2, the case where the heater power supply ratio is duty 4/12 (= 33.3%) will be described. The control unit transmits an ON signal to the transistor at the timing of Tc and performs phase control so that the power duty of the first wave and the half wave of the second wave is 33.3%. Then, by turning on two half-waves of the remaining six half-waves by wave number control and turning off all other four half-waves, approximately 33.3% of power is supplied in one control cycle.

  In this way, 13 stages of the heater control table that divides the heater supply power from 0% to 100% into 12 steps are determined in advance, and the control unit can perform heater energization control based on the heater power control table. . Flicker is suppressed because phase control is included compared to wave number control, and harmonic current distortion is suppressed because it includes wave number control compared to phase control.

JP-A-63-313182 Japanese Patent Laid-Open No. 2-157878 JP-A-4-44075 JP-A-4-44076 Japanese Patent Laid-Open No. 09-101718 JP 09-106215 A JP 2000-268939 A JP 2003-123941 A

  For example, in recent image forming apparatuses, full-color images are formed, and higher printing speed and higher image quality are important. Further, there is a need for more added value from the market than before, such as energy saving and the time for outputting the first transfer paper after the start of printing, that is, shortening the first printout time.

  Against this background, as the printing speed is increased and the first printout time is shortened, the power required for the heater also tends to increase in the conventional film fixing type fixing device using the ceramic heater. . An increase in heater power means, in other words, a decrease in the resistance value of the heater. The decrease in the resistance value of the heater means an increase in the current of the AC power supply when the heater power is supplied, and this increase in current causes further harmonic distortion and flicker.

  Further, in order to achieve further higher image quality, there is a demand for reduction of temperature ripple and temperature unevenness of the fixing heating device. For example, as the printing speed increases, the amount of heat per unit time taken from the fixing device to the transfer paper increases, resulting in temperature unevenness of the fixing heating device, and particularly uneven glossiness of images that require high gloss. Becomes more prominent. This is because, when the transfer paper is conveyed to the nip portion of the fixing device, the heat of the film (or roller) of the fixing device is taken away by the paper, so that the film surface temperature after one rotation of the film is particularly lowered. For this reason, the image on the transfer paper fixed at the temperature lowering portion appears as uneven glossiness of the image because the fixing temperature is insufficient.

  As a measure to reduce the uneven gloss of the image due to the temperature unevenness of the fixing device, the power corresponding to the amount of heat taken away by the paper in advance before the paper reaches the nip of the fixing device is used as a target for normal image formation. Correction power superimposition control is performed in which power is superimposed and applied.

  As another countermeasure, there is a method of changing a roller or the like constituting the fixing device to a configuration that easily stores heat. However, since it takes a long time to reach a predetermined fixing temperature at which an image can be formed from the start of printing, there is a problem that the first printout time is delayed as a result. In other words, since there is a trade-off relationship between the improvement of temperature unevenness and the reduction of the first printout time, it is necessary to design the fixing device in balance between the two.

  On the other hand, restrictions on harmonic current distortion have been strengthened for more efficient use of energy, and not only integer multiple harmonic current distortion of the fundamental frequency of AC power supply but also non-integer multiple harmonic current distortion (order) (Interharmonic) is required. For this reason, particularly in a high-speed full-color image forming apparatus, it is difficult to satisfy the harmonic current distortion standard by the conventional heater control only by the phase control due to the decrease in the heater resistance value as described above.

  In addition, in order to satisfy the harmonic current distortion standard, when using heater control with only wave number control that is most advantageous for harmonic current distortion suppression, when performing heater power on / off in half wave units of AC power supply It causes temperature ripple and makes it difficult to satisfy flicker regulations.

  For this reason, particularly in a high-speed full-color image forming apparatus, both harmonic current distortion regulation and flicker regulation are satisfied by using a control in which the aforementioned phase control and wave number control are combined.

  However, in the case of control combining this phase control and wave number control, the update timing of the input power to the fixing heater is every control cycle as described above. For this reason, there is a demerit that a time lag corresponding to one control cycle occurs at the maximum when the power switching control on which the correction power is superimposed is performed at a predetermined timing.

  FIG. 14 is an explanatory diagram schematically showing this time lag.

  The figure shows an example of power control in which the power is increased at the timing T1 to the power W2 higher than the target power W1 at the time of normal image formation, and is returned to the original power W1 at the timing T2 after 100 msec.

  Here, for example, when the frequency of the commercial AC power supply is 50 Hz, one full wave is 20 msec. Therefore, in one control cycle (4 full waves) of control combining phase control and wave number control, it is 80 msec.

  The timing T1 for changing to W2 and the timing T0 at the end of the power pattern for one control cycle updated immediately before T1 are not matched. Therefore, even if the power is switched at the timing T1 while the power pattern for one control period is turned on as shown in the figure, the switching is performed at the next power update timing T11. For this reason, the input power to the heater is switched at a timing T11 delayed by t11 from the predetermined timing T1.

  On the other hand, even when the control is performed to return the power from W2 to W1 at the timing T2, even if the power is switched at the timing T2 while the power pattern for one control period is turned on as shown in FIG. It will be switched at. For this reason, the input power to the heater is switched at the timing T22 that is delayed by t22 from the predetermined timing T2. As a result, the period during which the power to W2 is increased is actually as short as 80 msec with respect to 100 msec on control.

  As described above, the time until the power is actually switched is delayed by about 80 msec for a maximum of one control cycle, and the power increase period is shortened, so that the temperature of the fixing device is insufficient. As a result, uneven gloss may occur in an image fixed at a temperature lower than a predetermined temperature.

  The present invention has been made in view of the above-mentioned problems, and uses temperature control combined with phase control to reduce the time difference between the control power switching timing and the actual power switching timing, thereby suppressing temperature unevenness. It is an object of the present invention to provide a control technology for a fixing heating device. Another object of the present invention is to provide a control technique for an image forming apparatus that includes the fixing device to reduce uneven glossiness and satisfy both the flicker and power harmonic distortion regulations.

  In order to achieve the above object, the present invention has the following configuration.

Image forming means for forming a toner image on transfer paper using an electrophotographic process;
A fixing device that heats the toner image by heat of a heating unit and pressurizes the transfer paper;
Switch means for supplying or cutting off power from an AC power source to the heating means;
Zero-cross detection means for detecting zero-cross of the AC power supply;
Phase control for energizing and controlling the switch means at a predetermined phase angle of one half wave of the AC power source based on the zero cross, and full energization of the switch means for each half wave of the AC power source based on the zero cross Or perform wave number control to de-energize control,
In addition, a plurality of N half-waves of the AC power supply are set as one control cycle, and the phase control is performed on a part of the half-waves, and the wave number control is performed on the remaining half-waves according to the supplied power. An image forming apparatus having a first input power pattern and having a control means for changing the power supplied to the heating means at a predetermined timing.
The control means further includes a second input power pattern in which a continuous M number of half waves smaller than N is used as one control period,
The first input power pattern and the first input power pattern so that a time difference between the predetermined timing of changing the supplied power and the timing of changing the power of the first input power pattern or the second input power pattern is reduced. An image forming apparatus comprising: selecting a combination pattern in combination with the second input power pattern.

  According to the present invention, in a fixing device using control that combines phase control and wave number control, fixing that suppresses temperature unevenness by reducing the time difference between the power switching timing in fixing temperature control and the actual power switching timing as much as possible. A heating device can be provided. In addition, by providing the fixing device, it is possible to provide an image forming apparatus that can reduce gloss unevenness and satisfy both regulations of flicker and power harmonic distortion.

1 is a schematic diagram of an image forming apparatus according to an embodiment of the present invention. Explanatory drawing of the scanner unit concerning the Example of this invention 1 is a schematic diagram of a fixing device according to an embodiment of the present invention. Schematic diagram of a ceramic heater according to an embodiment of the present invention. Explanatory drawing which shows the fixing drive circuit concerning the Example of this invention. Explanatory drawing which shows the phase control concerning the Example of this invention Explanatory drawing which shows the wave number control in connection with the Example of this invention Explanatory drawing which shows the control which combined the phase control and wave number control in connection with the Example of this invention Fixing control timing chart according to the first embodiment of the present invention Flowchart of fixing control according to the first embodiment of the present invention. Fixing control timing chart according to the second embodiment of the present invention Fixing control timing chart according to the third embodiment of the present invention Explanatory drawing of the control table concerning the Example of this invention Conventional fixing control timing chart

  DESCRIPTION OF EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings.

  Hereinafter, a color laser beam printer will be described as an example of an embodiment of the present invention. However, the present invention is not limited to a color laser beam printer, and can be applied to all image forming apparatuses using an electrophotographic process.

  Also, the description of the same parts as those described in the conventional technical example is omitted or simplified.

  First, the configuration of a tandem type color laser beam printer 200, which is an example of an image forming apparatus targeted by the present invention, will be described.

  FIG. 1 is a diagram showing a schematic configuration of a tandem type color laser beam printer 200.

  The color laser beam printer 200 is a so-called tandem type printer in which an image forming unit is provided for each color of black (Bk), yellow (Y), magenta (M), and cyan (C). Each image forming unit includes a photosensitive drum 18, a primary charger 16 that uniformly charges the photosensitive drum 18, a scanner unit 11 that irradiates a laser beam 13 on the photosensitive drum 18 to form a latent image, and develops the latent image. Then, a developing device 14 (developing roller 17) for making a visible image is provided. Furthermore, a primary transfer roller 19 that transfers the visible image to the intermediate transfer belt 50, a secondary transfer roller 42 that transfers the transferred visible image from the intermediate transfer belt 50 to the transfer paper, and a cleaning device 15 that removes residual toner on the photoreceptor. Etc. are also provided. In FIG. 1, a, b, c, and d are added as subscripts of the above-described symbols in order to distinguish the components having the same function constituting the image forming section for each color.

  Here, a detailed configuration of the scanner unit 11 will be described. FIG. 2 is a diagram illustrating a configuration of the scanner unit 11.

  When there is an image formation instruction from an external device such as a personal computer, the image information is converted into an image signal (VDO signal) 101 for turning on / off the laser beam as the exposure means in the control circuit in the color laser beam printer 200. Converted. This image signal (VDO signal) 101 is input to the laser unit 102 in the scanner unit 11. Reference numeral 103 denotes a laser beam that is on / off modulated by the laser unit 102. Reference numeral 104 denotes a scanner motor that regularly rotates a rotary polygon mirror (polygon mirror) 105. An imaging lens 106 focuses the laser beam 107 changed by the polygon mirror 105 on the photosensitive drum 18 that is a surface to be scanned.

  With this configuration, the laser beam 107 modulated by the image signal 101 performs horizontal scanning (scanning in the main scanning direction) on the photosensitive drum 108, and a latent image is formed on the photosensitive drum 108.

  Reference numeral 109 denotes a beam detection port, which takes in a beam from a slit-shaped entrance port. The laser beam entering from the entrance is guided to the photoelectric conversion element 111 through the optical fiber 110. The laser beam converted into an electric signal by the photoelectric conversion element 111 is amplified by an amplifier circuit (not shown) and then becomes a horizontal synchronization signal.

  Returning to FIG. The transfer sheet as a recording medium fed from the cassette 22 stands by at the registration roller 21 in order to take timing with the image forming unit. In the vicinity of the registration roller 21, a registration sensor 24 for detecting the leading edge of the fed transfer paper is provided. An image forming apparatus control unit (not shown: hereinafter referred to as “control unit”) that controls the image forming unit detects the timing at which the leading edge of the paper reaches the registration roller 21 based on the detection result of the registration sensor 24. Then, an image of the first color (yellow color in the example in the figure) is formed on the photosensitive drum 18a which is an image carrier, and the temperature of the heater (heating heater) of the fixing device 23 is controlled to be a predetermined temperature. .

  Reference numeral 50 denotes an intermediate transfer belt 50 arranged so as to penetrate each color image forming unit. The intermediate transfer belt 50 is driven to rotate along with the rotation of the photosensitive drum 18. When a high voltage is applied to the primary transfer roller 19 as a primary transfer bias, the intermediate transfer belt 1 is formed based on the reference position of the intermediate transfer belt 50. The color toner images are sequentially transferred onto the intermediate transfer belt 50.

  Similarly, the image of the second color (magenta in the example in the figure) is placed on the first color image formed on the intermediate transfer belt 50 at the timing of the first color image leading edge and the second color image forming process. Is superimposed and transferred. Similarly, the image of the third color (cyan in the example in the figure) and the image of the fourth color (black in the example in the figure) are sequentially superimposed and transferred onto the intermediate transfer belt 50 at the timing of each image forming process. The

  Reference numeral 42 denotes a secondary transfer roller for secondary transfer of the toner image formed on the intermediate transfer belt 50 onto the transfer paper, and is retracted to a position separated from the intermediate transfer belt 50 during image formation.

  Transfer paper, which is a transfer material, is fed from the cassette 22 and waits at the registration roller 21 in order to take timing with the image forming unit. Further, a registration sensor 24 for detecting the leading edge of the fed transfer paper is provided in the vicinity of the registration roller 21. The control circuit takes the timing of the leading edge position of the paper detected by the registration sensor 24 and the leading edge position of the image formation in the paper conveying direction (sub-scanning direction) and re-transfers the transfer paper waiting by the registration roller 21. At this time, the secondary transfer roller 42 contacts the intermediate transfer belt 50, and when a high voltage is applied as a secondary transfer bias to the secondary transfer roller 42, the four color toner images on the intermediate transfer belt 50 are transferred onto the transfer paper. Are collectively transferred.

  The transfer paper onto which the four color toner images have been transferred passes through the nip portion of the fixing device 23 having a built-in heater, whereby the toner is pressurized and heated to be melted and fixed on the transfer paper. The state of conveyance of the transfer paper before and after the fixing device 23 is monitored by a pre-fixing sensor 37 and a fixing paper discharge sensor 38, and the transfer paper that has passed through the fixing device 23 is discharged to the outside of the apparatus and full-color image formation is completed.

  Next, as the fixing device 23, a film fixing device using a ceramic heater using ceramic as a heat source will be described. FIG. 3 is a schematic configuration diagram showing a fixing device in which the heater is applied as the ceramic heater 640.

  Reference numeral 610 denotes a stay, and the stay 610 includes a main body 611 having a U-shaped cross section that supports the ceramic heater 640 in an exposed manner, and a pressure unit 613 that presses the main body toward the pressure roller 620 facing the main body 611. Has been. Here, in the ceramic heater, the heating element may be on the side opposite to the nip portion described later or on the nip portion side. Reference numeral 614 denotes a heat-resistant film (hereinafter abbreviated as “film”) having a circular cross section that is externally fitted to the stay 610.

  The pressure roller 620 forms a pressure nip portion (fixing nip portion) N with the film 614 sandwiched between the pressure roller 620 and acts as a film outer surface contact driving means for driving the film 614 to rotate. The film driving roller / pressure roller 620 includes a cored bar 620a, an elastic body layer 620b made of silicon rubber or the like, and an outermost release layer 620c. The film 614 is sandwiched between the surface of the ceramic heater 640 with a predetermined pressing force by a bearing means and a biasing means (not shown). When the pressure roller 620 is rotationally driven by the motor M, a conveying force is applied to the film by a frictional force between the pressure roller 620 and the outer surface of the film 614.

  Next, FIG. 4 shows an outline of the positional relationship among the ceramic heater, the temperature detection element 605, and the excessive temperature rise prevention means 602. 4A is a cross-sectional view of the ceramic heater, and FIG. 4B shows a surface on which the heating element 601 is formed.

The ceramic heater is composed of a ceramic insulating substrate 607 such as SiC, AlN, Al ₂ O ₃ , a heating element 601 (an energizing heating resistance layer) formed by paste printing or the like on the surface of the insulating substrate, and protects the heating element. It is comprised from the protective layers 606, such as glass. On the protective layer, a temperature detection element 605 such as a thermistor for detecting the temperature of the ceramic heater and an excessive temperature rise prevention means 602 as means for preventing the excessive temperature rise are disposed. The excessive temperature rise prevention means 602 is, for example, a thermal fuse or a thermo switch.

  The heating element 601 includes a portion that generates heat when electric power is supplied, a conductive portion 603 connected to the heating portion, and an electrode 604 to which electric power is supplied via a connector. The heating element 601 can pass paper. The maximum recording paper width LF is almost the same length. A HOT-side terminal of the AC power supply is connected to one of the two electrodes 604 via an excessive temperature rise prevention means 602. The electrode part is connected to a triac that controls the heating element, and is connected to the NEUTAL terminal of the AC power supply.

  FIG. 5 shows a drive and control circuit for the ceramic heater according to the present invention. Reference numeral 621 denotes an AC power source for connecting the image forming apparatus. The image forming apparatus supplies a commercial power source to the heating element 601 of the ceramic heater 640 via an AC filter (not shown) to thereby generate the heating element 601 of the ceramic heater. Cause heat.

  The power supply to the heating element 601 is controlled by the triac 639 to be energized or interrupted. The resistors 631 and 632 are bias resistors for the triac 639, and the phototriac coupler 633 is a device for isolating the primary and secondary. The triac 639 is turned on by energizing the light emitting diode of the phototriac coupler 633. The resistor 634 is a resistor for limiting the phototriac current, and is turned on / off by the transistor 635. Transistor 635 operates in accordance with an ON signal from engine control circuit 316 via resistor 636.

  The AC power is input to the zero cross detection circuit 618 through an AC filter. The zero-cross detection circuit 618 notifies the engine control circuit 316 as a pulse signal that the commercial AC power supply is at a voltage lower than a certain threshold value. Hereinafter, this signal transmitted to the engine control circuit 316 is referred to as a “zero cross signal”. The engine control circuit 316 detects the pulse edge of the zero cross signal and uses it as a timing signal for turning on / off the triac 639.

  Reference numeral 605 denotes a temperature detection element for detecting the temperature of the ceramic heater on which the heating element 601 is formed, for example, a thermistor temperature sensing element. In order to secure an insulation distance from the heating element 601 on the ceramic heater 640, a dielectric breakdown voltage is provided. It is arrange | positioned through the insulator which has. The temperature detected by the temperature detection element 605 is detected as a divided voltage between the resistor 637 and the temperature detection element 605 and input to the engine control circuit 316 as a TH signal to the A / D port of the CPU in the control circuit. The temperature of the ceramic heater 640 is monitored by the engine control circuit 316 as a TH signal, and the engine control circuit 316 compares the set temperature of the predetermined ceramic heater with the electric power to be supplied to the heating element 601 constituting the ceramic heater. calculate. When heater power control is performed by phase control, which will be described later, the heater-on signal is converted from the edge of the zero-cross signal to the time to be transmitted corresponding to the supplied power. That is, the phase angle at which the heater is to be turned on is determined from the phase angle of the AC voltage. Based on the set time, the engine control circuit 316 transmits a heater drive signal to the transistor 635 in synchronization with the zero cross signal, and energizes the heater 640 at a predetermined timing. As described above, based on the temperature information from the temperature detection element 605, the engine control circuit 316 turns on / off the power supply to the heater 640, and the temperature of the heat fixing device becomes the target temperature (within the set temperature range). It is controlled as follows.

  If the heating element reaches a thermal runaway due to a failure of the engine control circuit 316 and the like, and the excessive temperature rise prevention means 602 exceeds a predetermined temperature, the excessive temperature rise prevention means 602 is opened. With the opening of the excessive temperature rise prevention means 602, the energization path to the ceramic heater 640 is interrupted, and the energization to the heating element 601 is interrupted to protect against failure.

  Reference numeral 625 denotes current detection means using a current transformer for detecting a current flowing to the ceramic heater 640 of the fixing device 23. The current flowing to the ceramic heater 640 is converted into a voltage by the current transformer 625. After the voltage is rectified to a positive voltage by the rectifier circuit 626, an A of a CPU (not shown) in the engine control circuit 316 as an analog signal corresponding to the average value of the current flowing to the ceramic heater 640 by the average current calculation circuit 627 / D port. The control circuit 316 constantly monitors the current, determines a phase angle so as not to exceed a predetermined maximum effective current from the detected average current, and controls the maximum power to the ceramic heater 640.

  Next, a method for controlling the power supplied to the heater of the fixing device will be described.

  FIG. 6 shows an example of heater power control by phase control. The logic of the zero cross signal (10-b) is switched at a point at which the AC power supply voltage waveform (10-a) is switched from positive to negative and from negative to positive. The zero cross signal transmits a repetitive pulse to the engine control circuit 316 at a cycle T (= 1/50 sec) of the commercial power supply frequency (50 Hz), and the voltage waveform of the commercial power supply has a phase angle of 0 °, 180 at the edge of the pulse. The timing when 0V (zero cross) is shown at °. When the engine control circuit 316 turns on the heater drive signal (10-c) after Ta time from the rising and falling edges, the triac 639 is turned on and the heater 640 is shown in the hatched portion of the heater current (10-d). Is energized and supplied with power. Since the triac 639 is turned off at the next zero cross point after the heater is turned on, the energization to the heater is turned off. Therefore, by turning on the heater drive signal after a time Ta from the edge of the zero cross signal, The same power is supplied to the heater even in the half wave.

  Further, when the heater driving signal is turned on after a time Tb different from the time Ta, the energization time to the heater changes, so that the power supplied to the heater can be changed. In this way, the power supplied to the heater can be controlled by changing the time for which the heater drive signal is turned on from the edge of the zero cross signal for each half wave. When increasing the power supply to the heater, the timing for transmitting the heater drive signal from the edge of the zero cross signal is advanced, and conversely, when reducing the power supply, the heater drive signal is transmitted from the edge of the zero cross signal. Slow timing. The temperature of the ceramic heater 640 is controlled by performing this control in one cycle or every plural cycles as necessary.

  In the phase control, as shown in FIG. 6, since the energization of the heater is turned on in the middle of the half wave of the AC power supply waveform, the current flowing through the heater suddenly rises and the harmonic current flows. In the example shown in the figure, the current waveform flowing through the heater 640 is a positive / negative symmetrical current waveform. Since the harmonic current component of the heater current generally increases as the amount of current rise increases, the order of the harmonic current that becomes maximum when the phase angle is 90 °, that is, when the supplied power is 50%, is large. In addition, since a rising edge of this current occurs every half-wave, many harmonic currents flow, and it is essential to comply with harmonic regulations. Therefore, circuit components such as a filter are often required. On the other hand, since a current smaller than one half wave flows every half wave, there is a merit that the amount of change in the current is small and the change cycle is fast, so that the influence on flicker is small.

  FIG. 7 shows a pattern example of the heater power control table by wave number control. In the wave number control, on / off control (full energization / non-energization control) is performed in units of half wave of the AC power supply. When turning on, the heater drive signal is turned on together with the edge of the zero cross signal. Then, for example, eight half waves are set as one control cycle, and the power supplied to the heater is controlled by changing the number of half waves that are turned on in one control cycle. In FIG. 7, since four half waves of the eight half waves are turned on, the power supplied to the heater is 50%. In this way, a heater control pattern obtained by dividing the heater supply power from 0% to 100% into 12 parts is determined in advance, and the control circuit 316 can perform heater power control based on the heater control pattern. Here, when turning on, two consecutive half waves are turned on. In wave number control, the heater is always turned on / off at zero crossing, so there is no sharp rising edge of current as in phase control, and the harmonic current is very small. On the other hand, since the current flows in half-wave units, the amount of change in the current is large and the change cycle is long, so the effect on flicker is large. Therefore, by devising the position (control pattern) of the half wave that is turned on within one control cycle, the influence of the current fluctuation cycle on the flicker is minimized.

  FIG. 8 shows a pattern example of heater power control in which phase control and wave number control are combined. In the example of FIG. 12, eight half waves (multiple N, N is an even number) are set as one control cycle, of which six half waves are controlled by wave number control, and two half waves are controlled by phase control, and the heater supply power ratio duty4 / The case of 12 (= 33.3%) is shown. The control circuit 316 transmits an ON signal to the transistor 635 at the timing of Tc and performs phase control so that the power duty of the first and second half waves is 33.3%, and the remaining six half waves. 2 half-waves are turned on by wave number control, and the other 4 half-waves are all turned off. As a result, about 33.3% of power is supplied in one control cycle. In this way, a heater control table in which the heater supply power is divided into 0% to 100% is divided into 12 as shown in FIG. 13, and the engine control circuit 316 performs heater energization control based on the heater power control pattern. It can be carried out. Flicker is suppressed because phase control is included compared to wave number control, and harmonic current distortion is suppressed because it includes wave number control compared to phase control.

  An embodiment in which the time difference between the power switching timing in the fixing temperature control and the actual power switching timing is reduced as much as possible by using heater power control combining the phase control and wave number control will be described with reference to FIGS.

  FIG. 9 is a timing chart of the first embodiment, and FIG. 10 is a flowchart of the first embodiment.

  In this embodiment, two types of heater power control tables (table 1: phase control, table 2: control combining phase control and wave number control) are recorded in the recording unit in the engine control circuit 316, and engine control is performed. A circuit 316 switches between the heater power control tables. Table 1 shows a second input power pattern, and Table 2 shows a first input power pattern. Table 1 is an advantageous phase control pattern for flicker, although it is generally disadvantageous for power supply harmonic distortion. The engine control circuit 316 controls the power supplied to the heater by adjusting the phase angle at which the heater starts energizing every commercial AC power cycle (one full wave). Table 2 is a heater power control pattern that combines phase control and wave number control that are effective for both power harmonic distortion suppression and flicker suppression. The pattern is a combination of phase control and wave number control for one control cycle of four full waves, and the temperature of the fixing heating device is controlled by the temperature of the heater 640 by the temperature detection element 605, and the engine control unit performs one cycle (four full waves). An optimum heater power control pattern is selected from Table 2 for each time.

  The control circuit calculates in advance the cycle TA of the commercial AC power supply from the repetition cycle of the zero cross signal (S700). For example, when the frequency of the commercial AC power supply is 50 Hz, the one cycle TA is 20 msec. At this time, one control cycle (2 half waves, M number) of Table 1 is determined to be 20 msec, and one control cycle (4 full waves) of Table 2 is determined to be 80 msec (S701).

  In order for the color laser beam printer 200 to perform image formation, the engine control circuit 316 selects from the table 2 a heater power control pattern for raising the temperature of the fixing heating device and performing pre-rotation (S702).

  When the image forming operation is started, the transfer paper on which the four color toner images on the intermediate transfer belt 50 are copied by the secondary transfer is conveyed, and when the leading edge of the transfer paper reaches the upstream pre-fixing sensor, Based on the signal, the engine control circuit detects the paper leading edge position (S703). Further, a time T2 for the transfer paper to reach the fixing nip N is calculated based on the detection timing of the leading end conveyance position of the pre-fixing sensor (conveyance sensor) (S704).

  A timing T1 that is a predetermined time before (here, 100 msec) from the timing T2 when the paper reaches the fixing nip N of the paper is calculated (S705). Between the timings T1 and T2, the control circuit supplies the fixing power during normal image formation. A power W2 higher than the power W1 required for fixing is set. Here, for convenience of explanation, an example in which the power supplied to the heater is directly changed from the set value W1 to W2 will be described. However, actually, the set temperature of the ceramic heater is not equivalent to the power itself but corresponds to an increase in power. It is more realistic to raise the value. Even when the set temperature value is increased, the power supplied to the heater can be increased as a result.

  The reason for setting the power W2 is to reduce temperature unevenness of the fixing heating device in order to achieve further higher image quality. For example, as the printing speed increases, the amount of heat per unit time taken from the fixing device to the transfer paper increases, resulting in temperature unevenness of the fixing heating device, and particularly uneven glossiness for images that require high gloss. Is becoming more noticeable. This is because when the transfer paper is conveyed to the nip portion of the fixing device, the heat of the film (or roller) of the fixing device is taken away by the paper, so that the film surface temperature after one rotation of the film is particularly lowered. For this reason, the image on the transfer paper fixed at the temperature lowering portion appears as uneven glossiness of the image because the fixing temperature is insufficient. As a measure to reduce the uneven glossiness of the image due to the temperature unevenness of the fixing device, the power for assuming the amount of heat taken by the paper in advance before the paper reaches the nip of the fixing device is used as a target for normal image formation. Corrected power superposition control is performed in which power is superimposed on power and applied.

  The engine control circuit 316 calculates a timing T1 at which the power is increased to W2, and predicts a timing T0 at the end of the power pattern for one control cycle updated immediately before the timing T1 from the fixing power update cycle (S706). ).

  In the present embodiment, it is explained that the table 1 and the table 2 at the time of power switching are used in combination according to the difference between the power increase timing T1 and the timing T0 at the end of the power pattern for the immediately preceding control period. To do.

  In the power pattern shown in FIG. 9, a square indicates a control cycle of phase control (Table 1), and a rectangle indicates a combination of phase control and wave number control ( Table 2) is one control cycle. That is, these schematically represent the control table shown in FIG. Further, the symbols W1 and W2 shown in the respective squares and rectangles indicate the supplied power, and the same symbols indicate the same input power. That is, if W1 in the square and W1 in the rectangle are the same, the table is different between Table 1 and Table 2, but the power supply (power supply ratio to the heater) is the same.

The engine control circuit 316 calculates T1-T0, and selects the power pattern shown in FIG. 9 as follows according to the relationship between the result and the cycle TA of the commercial AC power supply (S707).
0 ≦ T1-T0 <0.5 × TA: power pattern 11
0.5 × TA ≦ T1-T0 <1.5 × TA: power pattern 12
1.5 × TA ≦ T1-T0 <2.5 × TA: power pattern 13
2.5 × TA ≦ T1-T0 <3.5 × TA: power pattern 14
3.5 × TA ≦ T1-T0 <4.0 × TA: power pattern 15
For example, when the power pattern 12 is selected as a result of the calculation, the end timing of the power pattern for one control period of Table 2 updated immediately before the switching timing T1 is T02, and the control period (80 msec) After completion, the power table is switched from 2 to 1. By performing phase control for one period (one full wave) as the power setting of W1 in the power table 1, the shift t11 ′ when switching to the power of W2 at timing T1 can be minimized (within 20 msec). it can. At this time, the timing at which the power is actually switched to W2 is the timing of T11 ′ taking t11 ′ into account.

  Since the period set to the power W2 is 100 msec in this example, the control is performed by combining one control cycle (20 msec) of Table 1 and one control cycle (80 msec) of Table 2. If the power setting control of W2 is to be performed using only the table 2, the control cycle is 80 msec. Therefore, it can be set only at an integer multiple of 80 msec, 160 msec, 240 msec, and the like. By combining Table 1, control is possible even if the power setting period is not necessarily an integral multiple of the control period of Table 2. That is, after setting the power of W2 in the table 2 at the timing of T11 ', the table is switched from 2 to 1, and the power of W2 is set in the table 1. Here, when setting the power W2, the order of using the two tables may be reversed, and the table 1 may be used first and then switched to the table 2. In addition, when the power setting period of W2 is required, for example, 120 msec, it can be realized by additionally performing phase control for one cycle.

  On the other hand, in the case of controlling to return the power from W2 to W1 at the timing T2, the deviation of t11 ′ remains as the deviation of t22 ′ almost as it is, so that the heater is turned on at a timing T22 ′ delayed by t22 ′ from T2. The input power is switched. As described above, the shift of the power switching timing can be corrected as compared with the conventional case, and the necessary power can be supplied to the fixing device at the necessary timing.

  The duration of use of phase control by the table 1 added in the present embodiment is about 100 msec, which is a short time here, which is sufficient as compared with the filter time constant of the measuring instrument recognized in the harmonic distortion standard. small. Therefore, even if the control as in the present embodiment is performed, there is no problem because the measurement result of the harmonic distortion is not significantly deteriorated. Further, flicker is also a problem because it is a control in which phase control advantageous to flicker is added at the time of power switching.

  An example of power control is described in which the power to the heater is increased for a predetermined time before the transfer paper reaches the fixing heating device. However, the power control is not limited to such power control. It is also effective when performing control to increase or decrease power at a predetermined timing. Further, it goes without saying that it is effective not only when the power is increased for a predetermined time but also when the value of the target temperature for performing the temperature adjustment control of the fixing heating device is increased.

  In addition, although the present embodiment is described here in the case where there are two types of heater power control tables stored in the recording unit of the engine control circuit 316, this is only an example, and three or more types of multiple tables are included. Application is possible if it is stored in the recording unit. For example, when the commercial AC power supply voltage is high (for example, 220 V to 240 V), there is often a relatively margin with respect to the flicker standard. Therefore, a control table combining phase control and wave number control that is optimal according to the input voltage. May be provided. In the phase control, the energization timing to the heater may be calculated from a relational expression between the power supplied to the heater and the phase angle of the commercial AC power source energizing the heater, instead of the table.

  Furthermore, the arrival time T2 to the fixing nip N calculated by the engine control circuit 316 from the detection result of paper is obtained by dividing the conveyance distance between the pre-fixing sensor and the fixing nip by the conveyance speed, and removing the chatter of the control unit. It can be obtained by subtracting the output delay time of the pre-fixing sensor included. The arrival times corresponding to several transport speeds that can be set in the image forming apparatus may be recorded in advance in the recording unit of the control unit. In addition, the registration sensor 24, the pre-fixing sensor 37, the fixing discharge sensor 38, and the like on the transfer paper conveyance path may be used to calculate or interpolate speeds including minute speed fluctuations due to environmental changes of the image forming apparatus. good.

  These supplementary explanations can be similarly applied to the second and third embodiments described later.

  As described above, according to the present invention, in the fixing device using the control combining the phase control and the wave number control as the power supply control to the heater, the power switching timing on the fixing temperature control and the actual power switching timing Can be reduced as much as possible. Control is possible even if the power switching period is not necessarily an integral multiple of the control period. For this reason, fixing power switching control can be performed at an optimal timing than before, and a fixing heating device in which temperature unevenness is suppressed can be provided. In addition, by providing the fixing device, it is possible to provide an image forming apparatus that can reduce gloss unevenness and satisfy both regulations of flicker and power harmonic distortion.

  The fixing power switching control in this embodiment is characterized in that only the table 1 is used during the power increase period. FIG. 11 is a timing chart of the second embodiment.

  Here, the fixing power switching control of the second embodiment will be described with reference to FIG. Parts that are the same as those described in the first embodiment are omitted or simplified, and are denoted by the same reference numerals used in the description of the first embodiment.

Similarly to the first embodiment, the engine control circuit 316 calculates T1-T0, and selects the power pattern shown in FIG. 11 as follows according to the result.
0 ≦ T1-T0 <0.5 × TA: power pattern 21
0.5 × TA ≦ T1-T0 <1.5 × TA: power pattern 22
1.5 × TA ≦ T1-T0 <2.5 × TA: power pattern 23
2.5 × TA ≦ T1-T0 <3.5 × TA: power pattern 24
3.5 × TA ≦ T1-T0 <4.0 × TA: power pattern 25
For example, when the power pattern 22 is selected as a result of the calculation, the end timing of the power pattern for one control cycle of Table 2 updated immediately before the switching timing T1 is T02, and the end of the control cycle (80 msec) Later, the power table is switched from 2 to 1. By performing phase control for one period (one full wave) as the power setting of W1 in the power table 1, the shift t11 ′ when switching to the power of W2 at timing T1 can be minimized (within 20 msec). it can. At this time, the timing at which the power is actually switched to W2 is the timing of T11 ′ taking t11 ′ into account.

Since the period set to the power W2 is 100 msec in this example, the control is performed only in the five control periods (100 msec) of Table 1. Since one control cycle of Table 1 is 20 msec, it can be set to 20 msec, 40 msec, 60 msec, etc., which are integral multiples of this. By using Table 1, control is possible even if the power setting period is not necessarily an integral multiple of the control period of Table 2. In addition, when the power setting period of W2 is required, for example, 120 msec, it can be realized by additionally performing phase control for one cycle.
On the other hand, in the case of controlling to return the power from W2 to W1 at the timing T2, the deviation of t11 ′ remains as the deviation of t22 ′ almost as it is, so that the heater is turned on at a timing T22 ′ delayed by t22 ′ from T2. The input power is switched. As described above, the shift of the power switching timing can be corrected as compared with the conventional case, and the necessary power can be supplied to the fixing device at the necessary timing.

  Note that the duration of use of phase control by the table 1 added in this embodiment is as short as about 200 msec, even in the case of the power pattern 25, and is a measuring instrument approved by the harmonic distortion standard. The filter time constant is sufficiently small. Therefore, even if the control as in the present embodiment is performed, there is no problem with the measurement result of the harmonic distortion. Further, there is no problem with flicker because phase control advantageous to flicker is added at the time of power switching.

  By adopting the control as described above, as in the first embodiment, it is possible to perform the fixing power switching control at an optimal timing than before, and to provide a fixing heating device that suppresses temperature unevenness. it can. In addition, by providing the fixing device, it is possible to provide an image forming apparatus that can reduce the deterioration of image quality and satisfy both the flicker and power harmonic distortion regulations.

  The fixing power switching control according to the present embodiment is characterized in that the timing of using a combination of Table 1 and Table 2 at the time of power switching is different. FIG. 12 is a timing chart of the third embodiment.

  Here, the fixing power switching control of the third embodiment will be described with reference to FIG. Parts that are the same as those described in the first embodiment are omitted or simplified, and are denoted by the same reference numerals used in the description of the first embodiment.

  The engine control circuit 316 calculates the timing T1 at which the power is increased to W2, and predicts the timing T0 ′ at the end of the power pattern two control cycles updated immediately before the timing T1 from the fixing power update cycle. .

In the present embodiment, it will be described that Table 1 and Table 2 are used in combination in accordance with the difference between the power increase timing T1 and the end timing T0 ′ of the power pattern two control cycles before. .
The control circuit 316 calculates T1-T0 and selects the power pattern shown in FIG. 4 as follows according to the result.
4.0 ≦ T1-T0 <4.5 × TA: power pattern 31
4.5 × TA ≦ T1-T0 <5.5 × TA: power pattern 32
5.5 × TA ≦ T1−T0 <6.5 × TA: power pattern 33
6.5 × TA ≦ T1-T0 <7.5 × TA: power pattern 34
7.5 × TA ≦ T1-T0 <8.0 × TA: power pattern 35
For example, when the power pattern 32 is selected as a result of the calculation, the timing at the end of one control cycle of Table 2 that is updated two control cycles before the switching timing T1 is T02 ′, so that the control cycle (80 msec) After the end of, the power table is switched from 2 to 1. By performing phase control for one cycle (one full wave) as the power setting of W1 in the power table 1, the shift t11 ′ when switching to the power of W2 at timing T1 is absorbed to the minimum (within 20 msec). Thereafter, the table is returned to 2 again, and the combined control of phase control and wave number control for one cycle (4 full waves) is performed as the power setting of W1 in Table 2. At this time, the timing at which the power is actually switched to W2 is the timing of T11 ′ taking t11 ′ into account.

  Hereinafter, similarly to the second embodiment, since the period set to the power W2 is 100 msec in this example, the control is performed only in five control cycles (100 msec) of Table 1. In the second embodiment, if the margin for the harmonic distortion standard is reduced, this embodiment may be effective.

  By adopting the control as described above, as in the first embodiment, it is possible to perform the fixing power switching control at an optimal timing than before, and to provide a fixing heating device that suppresses temperature unevenness. it can. In addition, by providing the fixing device, it is possible to provide an image forming apparatus that can reduce the deterioration of image quality and satisfy both the flicker and power harmonic distortion regulations.

13 Laser light 18 Photosensitive drum 11 Scanner unit (corresponding to image forming means)
14 Developing unit 19 Primary transfer roller 22 Paper feed cassette 23 Fixing unit (corresponding to fixing device)
24 registration sensor 37 pre-fixing sensor 38 fixing discharge sensor 42 secondary transfer roller 50 intermediate transfer belt 102 laser unit 316 engine control circuit (corresponding to control means)
601 Heating element 602 Thermal fuse 605 Thermistor 610 Stay 614 Heat resistant film 618 Zero cross detection circuit (corresponding to zero cross detection means)
620 Pressure roller 625 Current transformer 639 Triac (corresponding to switch means)
640 Ceramic heater (corresponding to heating means)

Claims (8)

Image forming means for forming a toner image on transfer paper using an electrophotographic process;
A fixing device that heats the toner image by heat of a heating unit and pressurizes the transfer paper;
Switch means for supplying or cutting off power from an AC power source to the heating means;
Zero-cross detection means for detecting zero-cross of the AC power supply;
Phase control for energizing and controlling the switch means at a predetermined phase angle of one half wave of the AC power source based on the zero cross, and full energization of the switch means for each half wave of the AC power source based on the zero cross Or perform wave number control to de-energize control,
In addition, a plurality of N half-waves of the AC power supply are set as one control cycle, and the phase control is performed on a part of the half-waves, and the wave number control is performed on the remaining half-waves according to the supplied power. An image forming apparatus having a first input power pattern and having a control means for changing the power supplied to the heating means at a predetermined timing.
The control means further includes a second input power pattern in which a continuous M number of half waves smaller than N is used as one control period,
The first input power pattern and the first input power pattern so that a time difference between the predetermined timing of changing the supplied power and the timing of changing the power of the first input power pattern or the second input power pattern is reduced. An image forming apparatus comprising: selecting a combination pattern in combination with the second input power pattern.   The image forming apparatus according to claim 1, wherein the second input power pattern is an input power pattern that performs phase control or wave number control in all of the half waves.   2. The image forming apparatus according to claim 1, wherein the second input power pattern is an input power pattern in which phase control is performed on a part of the half waves and wave number control is performed on the remaining half waves. . A conveyance sensor that is arranged upstream of the fixing device in the conveyance direction of the transfer paper and detects the leading edge conveyance position of the transfer paper;
The control means calculates the predetermined timing from the detection result of the transport sensor,
2. The image according to claim 1, wherein the power supplied to the fixing device is increased from the predetermined timing for a predetermined time from the predetermined timing before the leading edge of the transfer paper reaches the fixing device as compared with the fixing time of the transfer paper. Forming equipment.   The image forming apparatus according to claim 4, wherein the control unit performs power control using only the second input power pattern for the predetermined time.   The control means controls the temperature of the heating means within a set temperature range and changes the set temperature based on the detection result of the temperature detection means provided for detecting the temperature of the heating means. The image forming apparatus according to claim 1, wherein the power supplied to the heating unit is changed.   2. The image forming apparatus according to claim 1, wherein N and M are positive even numbers.   The image forming apparatus according to claim 1, wherein the heating unit is a heater having an energization heating resistance layer that generates heat when energized.

Images