JP2010217786A - Fixing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing device and an image forming apparatus capable of shortening startup time while suppressing generation of flicker and a harmonic current. <P>SOLUTION: The fixing device includes: a fixing heater 10; a temperature detection sensor 11 detecting the temperature of the fixing heater 10; a fixing heater drive circuit 12 including a triac drive circuit 16 driving the fixing heater 10 by a triac system and an inverter drive circuit 17 driving the fixing heater 10 by an inverter system and driving the fixing heater 10; and a fixing heater temperature control part 13 controlling the fixing heater drive circuit 12. The fixing heater temperature control part 13 drives the fixing heater 10 by controlling either the triac drive circuit 16 or the inverter drive circuit 17 on the basis of the temperature of the fixing heater 10 detected by the temperature detection sensor 11. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

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

  In an image forming apparatus such as a printer, a copying machine, or a facsimile machine using an electrophotographic process, there is a fixing device that melts and pressurizes a toner image formed on a recording medium (including plain paper, OHP, etc.) with heat. in use. The performance required for the fixing device includes a shortening of the rise time until the target temperature is reached, and a small temperature fluctuation with respect to the target temperature during image formation (reduction in temperature ripple).

  In general, a halogen heater is often used as a heating unit of a fixing device. The halogen heater has a characteristic that the resistance value is low at a low temperature and the resistance value increases as the temperature increases. For this reason, when the halogen heater is turned on, a large current (inrush current) flows due to a small resistance value of the halogen heater, and a sudden current change occurs. When the external power supply line has an impedance, there is a problem that a power supply fluctuation occurs due to the impedance and a sudden current change, and flickering occurs in an external lighting device sharing the same power supply due to the power supply fluctuation.

  In response to this problem, the triac method, in which power is supplied in synchronization with the zero cross of the input AC power supply, is used for the current control (power control) method of the fixing heater (halogen heater) by phase control using a triac as a switching element. It has been. However, there is a problem in that harmonic current is generated by performing phase control, causing voltage waveform distortion in the AC power supply.

  In order to solve these problems, there is already known a method of suppressing the generation of flicker / harmonic current by using an inverter system as a power supply control system of the fixing heater. For example, Patent Document 1 discloses a method using a heater that performs inverter-based power control for the purpose of effectively controlling the temperature of the fixing device.

  However, the inverter type fixing heater driving circuit increases the power loss because the number of switching elements and filter elements is increased as compared with the fixing heater driving circuit using the conventional triac. If the power loss is large, the maximum power is supplied to the fixing heater. When the fixing heater is started up, the power supplied to the fixing heater is reduced by the amount of power loss. There is a problem that the rise time of the fixing heater becomes longer than that of the fixing heater driving circuit using.

  The present invention has been made in view of the above, and an object of the present invention is to provide a fixing device and an image forming apparatus that can shorten the rise time while suppressing generation of flicker and harmonic current.

  In order to solve the above-described problems and achieve the object, the present invention includes a fixing heater, a temperature detection sensor for detecting the temperature of the fixing heater, a triac drive circuit and an inverter for driving the fixing heater by a triac system. A fixing heater driving circuit that drives the fixing heater, and a fixing heater temperature control unit that controls the fixing heater driving circuit, and the fixing heater temperature control unit includes: The fixing heater is driven by controlling either the triac driving circuit or the inverter driving circuit based on the temperature of the fixing heater detected by a temperature detection sensor.

  According to the present invention, the fixing heater temperature control unit can drive the fixing heater by controlling either the triac drive circuit or the inverter drive circuit based on the temperature of the fixing heater detected by the temperature detection sensor. The rise time is shortened while suppressing the generation of flicker and harmonic current.

FIG. 1 is a diagram illustrating a configuration of an image forming apparatus according to the present embodiment. FIG. 2 is a diagram illustrating a configuration of a fixing device in the image forming apparatus. FIG. 3 is a diagram illustrating a circuit configuration of the fixing heater driving circuit and the fixing heater temperature control unit. FIG. 4 is a diagram illustrating a control mechanism by the fixing heater temperature control unit in a state where the triac drive circuit is connected to the fixing heater. FIG. 5 is a diagram for explaining phase control by the triac drive circuit. FIG. 6 is a diagram showing a control mechanism by the fixing heater temperature control unit in a state where the inverter drive circuit is connected to the fixing heater. FIG. 7 is a diagram for explaining the crest value control by the inverter drive circuit. FIG. 8 is a summary of the characteristics of the triac drive method and the inverter drive method. FIG. 9 is a diagram for explaining a fixing heater energization control method performed for each operation mode in the image forming apparatus according to the present embodiment. FIG. 10 is a flowchart illustrating a fixing heater startup method by the fixing heater temperature control unit. FIG. 11 is a diagram for explaining the relationship between heater drive control and heater supply power when the fixing heater is started up.

  Exemplary embodiments of a fixing device and an image forming apparatus according to the present invention are explained in detail below with reference to the accompanying drawings. FIG. 1 is a diagram showing a configuration of an image forming apparatus according to the present embodiment, and FIG. 2 is a diagram showing a configuration of a fixing device in the image forming apparatus. The image forming apparatus according to the present embodiment performs a predetermined process on a scanner unit 1 for reading an image and an image read by the scanner unit 1, and records a toner image 9 corresponding to the image after the process is performed. The engine unit 2 for transferring to the paper 8, the paper feed tray 3 for storing the recording paper 8, and the fixing device 4 for fixing the toner image 9 transferred to the recording paper 8 by the engine unit 2. ing.

  The scanner unit 1 scans and exposes a document to convert document information on the document into an image signal, and outputs the image signal to the engine unit 2. When an image signal is output from the scanner unit 1, the engine unit 2 performs image processing such as color conversion and gradation correction on the image signal output from the scanner unit 1. The engine unit 2 forms an electrostatic latent image on an image carrier (not shown) according to the image subjected to image processing, and attaches toner to the formed electrostatic latent image to form a toner image 9. The formed toner image 9 is transferred from the paper feed tray 3 to the recording paper 8 conveyed via the conveying path 5, and the recording paper 8 is sent out toward the fixing device 4.

  The fixing device 4 includes a cylindrical fixing roller 6 having a fixing heater 10 made of, for example, a halogen heater, a pressure roller 7 pressed against the fixing roller 6, a temperature detection sensor 11 made of, for example, a thermistor, and the fixing heater 10. And a fixing heater temperature control unit 13 electrically connected to the temperature detection sensor 11 and the fixing heater driving circuit 12. When the recording paper 8 to which the toner image 9 has been transferred is sent from the engine unit 2 to the fixing device 4 via the conveyance path 5, the recording paper 8 is heated by the heat from the fixing roller 6 and the pressure from the pressure roller 7. The toner image 9 transferred to 8 is fixed and discharged toward a paper discharge tray (not shown).

  FIG. 3 is a diagram illustrating a circuit configuration of the fixing heater driving circuit 12 and the fixing heater temperature control unit 13. The fixing heater driving circuit 12 is a circuit that drives the fixing heater 10. The fixing heater drive circuit 12 includes a power relay 14, a zero cross detection circuit 15, a triac drive circuit 16, an inverter drive circuit 17, and a changeover switch 18.

  The power relay 14 transmits the power of the AC power source 19 to the fixing heater driving circuit 12. The zero-cross detection circuit 15 detects the timing at which the AC voltage signal supplied from the AC power supply 19 crosses 0 V, and transmits it to the fixing heater temperature controller 13 as a zero-cross signal. The triac drive circuit 16 is a circuit that performs energization control to the fixing heater 10 by a triac system in which energization is performed in synchronization with a zero cross signal by phase control using a triac as a switching element. The inverter drive circuit 17 is a circuit that performs energization control to the fixing heater 10 by an inverter method in which energization is performed according to increase / decrease of the duty of the PWM signal by duty control of the PWM signal. The changeover switch 18 is a switch for switching between supplying electric power to the fixing heater 10 by the triac drive circuit 16 or by the inverter drive circuit 17.

  The alternating current input from the alternating current power source 19 to the fixing heater drive circuit 12 is branched through the power relay 14 and the zero cross detection circuit 15 and supplied to the triac drive circuit 16 or the inverter drive circuit 17 depending on the state of the changeover switch 18. Is done. The fixing heater 10 is connected to the output portion of the fixing heater driving circuit 12.

  The fixing heater temperature control unit 13 controls the temperature of the fixing heater 10 by controlling the fixing heater driving circuit 12. Specifically, the fixing heater temperature control unit 13 sends a heater temperature control signal for controlling the temperature of the fixing heater 10 to the triac drive circuit 16 or the inverter drive circuit 17, thereby controlling the heater temperature by the triac drive circuit 16. Alternatively, the heater temperature control is performed by the inverter drive circuit 17.

  A temperature detection signal indicating the temperature of the fixing roller 6 (fixing heater 10) is sent to the fixing heater temperature control unit 13 by the temperature detection sensor 11 provided in the vicinity of the fixing roller 11 (fixing heater 10), and the fixing heater temperature control is performed. The unit 13 determines from this temperature detection signal whether the heater temperature control signal is sent to the triac drive circuit 16 or the inverter drive circuit 17. Then, the changeover switch 18 is switched so that the drive circuit determined to be used supplies power to the fixing heater 10, a heater temperature control signal is sent to the drive circuit determined to be used, and the fixing heater 10 is started up.

  Therefore, the image forming apparatus according to the present embodiment is configured such that when the fixing heater 10 is started up, the driving of the fixing heater 10 by the fixing heater driving circuit 12 can be switched to the triac type or the inverter type. For this reason, the fixing heater 10 is driven by an inverter method until the temperature of the fixing heater 10 reaches a temperature at which no inrush current occurs, and after the heater temperature reaches a temperature at which no inrush current occurs, the driving method of the fixing heater 10 Can be switched to the triac system.

  FIG. 4 is a diagram showing a control mechanism by the fixing heater temperature control unit 13 in a state where the triac drive circuit 16 is connected to the fixing heater 10. In the figure, the changeover switch 18 is connected to the triac drive circuit 16, and the alternating current from the alternating current power supply 19 is supplied to the fixing heater 10 after being supplied to the triac drive circuit 16. It can also be seen that the fixing heater temperature control unit 13 controls the triac drive circuit 16. Further, a switch state signal indicating a switch switching state and a switch switching signal for instructing switch switching are exchanged between the fixing heater temperature control unit 13 and the changeover switch 18.

  In general, a halogen heater is often used as the heater used for the fixing heater 10. The halogen heater has a characteristic that the resistance value is low at a low temperature and the resistance value increases as the temperature increases. For this reason, when the halogen heater is turned on, a large current (inrush current) flows due to a small resistance value of the halogen heater, and a sudden current change occurs. When the external power supply line has an impedance, a power supply fluctuation occurs due to the impedance and a sudden current change, and flickering occurs in an external lighting device or the like sharing the same power supply due to the power supply fluctuation.

  On the other hand, the triac drive circuit 16 uses the triac method for driving the fixing heater 10 (halogen heater), thereby energizing in synchronism with the zero cross signal of the AC power supply input by phase control. Accordingly, the TRIAC drive circuit 16 can perform control to gradually increase the energization rate of the fixing heater 10, so that rapid current change can be suppressed and flicker can be suppressed. FIG. 5 is a diagram for explaining phase control by the triac drive circuit 16.

  FIG. 6 is a diagram showing a control mechanism by the fixing heater temperature control unit 13 in a state where the inverter drive circuit 17 is connected to the fixing heater 10. In the figure, the changeover switch 18 is connected to the inverter drive circuit 17, and the AC current from the AC power supply 19 is supplied to the inverter drive circuit 17 and then to the fixing heater 10. It can also be seen that the fixing heater temperature control unit 13 controls the inverter drive circuit 17. Further, a switch state signal indicating a switch switching state and a switch switching signal for instructing switch switching are exchanged between the fixing heater temperature control unit 13 and the changeover switch 18.

  As described above, the triac drive circuit 16 can suppress a sudden change in current and suppress the occurrence of flicker by performing phase control. However, the harmonic current is generated by performing the phase control, causing the AC power supply 19 to generate voltage waveform distortion.

  On the other hand, the energization control of the fixing heater 10 by the inverter drive circuit 17 is performed by the duty control of the PWM signal. Depending on the increase or decrease of the duty of the input PWM signal, the amplitude of the current obtained by full-wave rectification of the input AC current is increased or decreased, and this is supplied to the fixing heater 10, whereby energization control is performed. Therefore, since the inverter drive circuit 17 performs switching at a high frequency compared with the commercial power supply frequency, the harmonic current can be suppressed. Furthermore, since the inverter drive circuit 17 can perform multi-stage energization control to the fixing heater 10 while suppressing the harmonic current, it is also effective in suppressing flicker generation. FIG. 7 is a diagram for explaining the crest value control by the inverter drive circuit 16.

  FIG. 8 is a summary of the characteristics of the triac drive method and the inverter drive method. In the triac drive system, it is difficult to achieve both suppression of harmonic current and suppression of flicker. On the other hand, in the inverter drive system, it is possible to suppress flicker while suppressing harmonic current. Moreover, the inverter drive system has a feature that energization control with a high degree of freedom can be performed while suppressing generation of harmonic current.

  On the other hand, since the inverter drive circuit 17 is configured to increase or switch circuit elements as compared to the triac drive circuit 16, the circuit loss is large.

  FIG. 9 is a diagram for explaining an energization control method of the fixing heater 10 performed for each operation mode in the image forming apparatus according to the present embodiment. When the fixing heater 10 is started to reach a temperature at which the toner image can be fixed on the recording paper from a state in which the fixing heater 10 is cooled, the fixing heater 10 is instructed to increase the temperature to a temperature at which fixing can be performed in a short time. Supplies the maximum output power in the fixing heater drive circuit. Therefore, it is desired that the output power loss with respect to the input power is small.

  Therefore, in the image forming apparatus according to the present embodiment, when the fixing heater 10 is started up, the heater driving is performed while appropriately switching between the triac drive circuit 16 and the inverter drive circuit 17. By doing this, it is possible to raise the fixing heater 10 to a desired temperature with efficient power consumption while suppressing generation of harmonic current / flicker when the fixing heater 10 is started up.

  On the other hand, during image formation in which the image forming apparatus performs normal image formation, it is desirable that the temperature of the fixing heater 10 is less fluctuated with respect to the target temperature. This is because when the temperature of the fixing heater 10 fluctuates with respect to the target temperature during image formation, unevenness appears in color development of the image after fixing. Further, during standby / image formation, it is not necessary to supply the maximum output power to the fixing heater 10 unlike when the fixing heater 10 is started up. Therefore, there is no problem as long as it is about the difference between the loss amount of the triac drive circuit 16 and the loss amount of the inverter drive circuit 17. Therefore, only the inverter drive circuit 17 having a high degree of freedom in energization control is used during standby / image formation. By doing so, it is possible to perform temperature control that suppresses fluctuations with respect to the target temperature while suppressing generation of harmonic current / flicker.

  Next, a method for starting up the fixing heater 10 by the fixing heater temperature control unit 13 will be described. FIG. 10 is a flowchart showing a method for starting up the fixing heater 10 by the fixing heater temperature control unit 13.

  First, when the fixing heater temperature control unit 13 receives a startup request for the fixing heater 10 from a control unit (not shown), the fixing heater temperature control unit 13 receives a temperature detection signal from the temperature detection sensor 11 (step S1).

  Next, the fixing heater temperature control unit 13 determines whether or not the temperature T of the fixing heater 10 is smaller than a temperature T1 that is a temperature at which no inrush current occurs in the fixing heater 10 (step S2). The temperature T1 is a preset value.

  When the fixing heater temperature control unit 13 determines that the temperature T of the fixing heater 10 is lower than the temperature T1 (step S2: Yes), the fixing heater temperature control unit 13 sends a switch switching signal to the changeover switch 18, and converts the electric power to the fixing heater 10 into an inverter drive circuit. The changeover switch 18 is switched so as to be supplied by the switch 17 (step S3).

  Next, when the fixing heater temperature control unit 13 receives a switch status signal indicating that the switch has been switched from the changeover switch 18, the fixing heater temperature control unit 13 sends a heater temperature control signal to the inverter drive circuit 17 and uses the inverter drive circuit 17. Heater temperature control is started (step S4), and the process returns to step S1 again.

  On the other hand, if the fixing heater temperature control unit 13 determines in step S2 that the temperature T of the fixing heater 10 is not lower than the temperature T1 (step S2: No), the fixing heater 10 sends a switch switching signal to the changeover switch 18. The changeover switch 18 is switched so as to supply power to the TRIAC drive circuit 16 (step S5).

  Next, when the fixing heater temperature control unit 13 receives the switch state signal from the changeover switch 18, the fixing heater temperature control unit 13 sends a heater temperature control signal to the triac drive circuit 16 and starts heater temperature control using the triac drive circuit 16 (step S6). ).

  Next, the fixing heater temperature control unit 13 receives the temperature detection signal again from the temperature detection sensor 11 (step S7), and the temperature T of the fixing heater 10 is higher than the temperature T2 at which the start-up of the fixing heater 10 is determined. It is determined whether it is larger (step S8). The temperature T2 is a preset value.

  When the fixing heater temperature control unit 13 determines that the temperature T of the fixing heater 10 is higher than the temperature T2 (step S8: Yes), the start-up process is finished and the process proceeds to a temperature control mode during image formation (step S9). .

  On the other hand, when the fixing heater temperature control unit 13 determines that the temperature T of the fixing heater 10 is not greater than the temperature T2 (step S8: No), the process returns to step S7 and repeats the following steps. In this way, the starting process of the fixing heater 10 is executed.

  FIG. 11 is a diagram for explaining the relationship between heater drive control and heater supply power when the fixing heater 10 is started up. As shown in the figure, the heater temperature control by inverter drive is performed at the start of startup, and the switching process is started when the temperature T of the fixing heater 10 becomes higher than the temperature T1, and when the switching process is completed, the heater by the triac drive is started. It can be seen that temperature control is performed.

  As described above, according to the image forming apparatus of the present embodiment, in the fixing device, the fixing heater temperature control unit determines whether the triac drive circuit and the inverter drive circuit are based on the temperature of the fixing heater detected by the temperature detection sensor. Since either of them can be controlled to drive the fixing heater, the rise time can be shortened while suppressing the generation of flicker and harmonic current.

  In the above embodiment, the image forming apparatus according to the present invention is described by taking an example in which the image forming apparatus is applied to a multifunction machine having at least two functions among a copy function, a printer function, a scanner function, and a facsimile function. The present invention can be applied to any image forming apparatus such as a printer, a scanner apparatus, and a facsimile apparatus.

DESCRIPTION OF SYMBOLS 1 Scanner part 2 Engine part 3 Paper feed tray 4 Fixing device 5 Conveyance path 6 Fixing roller 7 Pressure roller 8 Recording paper 9 Toner image 10 Fixing heater 11 Temperature detection sensor 12 Fixing heater drive circuit 13 Fixing heater temperature control part 14 Power relay 15 Zero Cross Detection Circuit 16 Triac Drive Circuit 17 Inverter Drive Circuit 18 Changeover Switch 19 AC Power Supply

JP 2008-076549 A1

Claims (5)

A fixing heater;
A temperature detection sensor for detecting the temperature of the fixing heater;
A fixing heater driving circuit for driving the fixing heater, comprising a triac driving circuit for driving the fixing heater by a triac method and an inverter driving circuit for performing an inverter method;
A fixing heater temperature control unit for controlling the fixing heater driving circuit,
The fixing heater temperature control unit includes:
Controlling either the triac drive circuit or the inverter drive circuit based on the temperature of the fixing heater detected by the temperature detection sensor to drive the fixing heater;
A fixing device characterized by the above. The fixing heater temperature control unit controls the inverter driving circuit to drive the fixing heater when the temperature of the fixing heater is lower than a predetermined temperature at which no inrush current is generated in the fixing heater;
The fixing device according to claim 1. The fixing heater temperature control unit controls the triac drive circuit to drive the fixing heater when the temperature of the fixing heater is equal to or higher than a predetermined temperature at which no inrush current is generated in the fixing heater;
The fixing device according to claim 1, wherein: The fixing heater driving circuit further includes a changeover switch that switches connection of the triac driving circuit and the inverter driving circuit to the fixing heater according to an instruction from the fixing heater temperature control unit,
The fixing device according to any one of claims 1 to 3, wherein   An image forming apparatus comprising the fixing device according to claim 1.

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