JP6500702B2 - Heating device and image forming apparatus - Google Patents

Description

  The present disclosure relates to a heating device, and more particularly to a heating device used in an image forming apparatus.

  In an electrophotographic image forming apparatus, there is a fixing and heating process of fixing a toner image on a recording sheet semipermanently by applying heat and pressure. In such an image forming apparatus, in order to keep the temperature of the fixing heating device constant, control is frequently performed to repeatedly switch on and off the heater.

  When power supply to the heater is started, an inrush current larger than the rated current may occur. When the rush current is generated, there is a problem that a sudden voltage fluctuation causes a flicker phenomenon such as flickering of peripheral devices connected to the same AC power source as the fixing heating device, for example, a lighting device.

  JP 2005-003710 A (Patent Document 1) relates to a technology for suppressing the voltage drop due to the rush current, and a bypass means is provided in parallel to the power factor improvement means and power supply to the load is started. Discloses a configuration for conducting the Specifically, Patent Document 1 discloses a technique for preventing a voltage drop due to the current flowing to the power factor improvement means and the impedance of the power factor improvement means.

  Moreover, regarding the technique which suppresses rush current, Unexamined-Japanese-Patent No. 2005-251561 (patent document 2) is the constant voltage output circuit which has a slow-up function which makes the power supply to a heater increase gradually, and the said constant voltage output circuit. Discloses a power supply circuit for supplying power to the heater through another path, and a switching means for switching between the constant voltage output circuit and the power supply circuit. Specifically, the control / control of the triac is controlled, the constant voltage output circuit and the heater are connected when slowing up is performed, the low voltage output circuit is shorted during steady lighting, and the power supply circuit is directly connected to the heater.

JP 2005-003710 A JP, 2005-251561, A

  However, the techniques disclosed in Patent Document 1 and Patent Document 2 can not reduce common mode noise. Therefore, it is also conceivable to add a common mode choke coil (hereinafter also referred to as "CCL") that reduces common mode noise. However, there is a problem that the addition of CCL causes power loss consumed by CCL.

  The present disclosure has been made to solve the problems as described above, and an object in one aspect is to reduce power loss generated in a coil and to reduce noise in accordance with a mode of power supply. It is possible to provide a heating device that can

  The heating device includes a heating unit configured to be connected to an AC power supply via a first conductor and a second conductor, a switching element provided in at least one of the first conductor and the second conductor, and a first conductor. And a second conductor, a common mode choke coil consisting of a pair of coils, a shorting means for shorting one of the common mode choke coils, and a control unit electrically connected to the switching element and the shorting means. Equipped with The control unit cancels the short circuit in the short circuit means in the first mode in which the switching element is controlled to limit the AC power supplied to the heating unit, and the heating unit further heats the AC power more than the first mode. In the second mode of feeding to the short circuit by the short circuit means is enabled.

  Preferably, the short circuit shorts the switching element together with one of the common mode choke coils.

  Preferably, the device further comprises a normal mode choke coil provided in a conductor in which the switching element is disposed, and the short circuit means shorts the normal mode choke coil together with one of the common mode choke coils.

  Preferably, the apparatus further includes a temperature measurement unit that measures the temperature of the heating unit and outputs the measurement result to the control unit, and the control unit performs on / off control of the switching element according to the temperature of the heating unit.

  More preferably, the temperature measuring unit further measures the temperature of the object to be heated by the heating unit, and the control unit is configured to set the temperature of the object to be heated when power supply is started in the second mode. The short circuit is enabled in the second mode only if it is below the temperature.

  Preferably, the short circuit means includes at least one of an electromagnetic relay and a solid state relay.

  According to another aspect, an image forming apparatus includes an image forming unit that forms a toner image on a recording material, and a fixing heating unit that fixes the toner image on the recording material. The fixing heating unit includes a heating unit configured to be connected to an AC power supply via the first conductor and the second conductor, a switching element provided in at least one of the first conductor and the second conductor, and the first heating unit. A control unit electrically connected to a common mode choke coil composed of a pair of coils respectively disposed in the conductor and the second conductor, a short circuit means for shorting one coil of the common mode choke coil, a switching element and the short circuit means And including. The control unit cancels the short circuit in the short circuit means in the first mode in which the switching element is controlled to limit the AC power supplied to the heating unit, and the heating unit further heats the AC power more than the first mode. In the second mode of feeding to the short circuit by the short circuit means is enabled.

  Preferably, the control unit enables a short circuit by the short circuit in the second mode only during a warm-up operation to enable processing required for image formation to be started.

  According to the heating device according to one embodiment, it is possible to reduce the power loss generated in the coil and to reduce the noise according to the mode of power supply.

FIG. 2 is a diagram for explaining an exemplary configuration of an image forming apparatus according to an embodiment. It is a figure explaining the example of composition of the heating device according to an embodiment. It is a figure explaining phase control and zero crossing control. It is a figure which shows an equivalent circuit when the relay of a heating device is turned on and off. It is a figure explaining the effect of the heating device according to this embodiment. It is a figure explaining operation | movement of a relay at the time of switching from phase control to zero crossing control according to embodiment. It is a figure explaining control to a heating section according to an operation mode of an image forming device according to an embodiment. It is a figure explaining the example of composition of the heating device according to other embodiments. It is a figure explaining control to a heating part according to the operation mode of the image forming device in other embodiments. It is a figure explaining the example of composition of the heating device according to other embodiment. It is a figure explaining the example of composition of the heating device according to other embodiment. It is a figure explaining control to a heating section according to an operation mode of an image forming device according to a modification.

  The heating device and the image forming apparatus in each embodiment based on the present invention will be described below with reference to the drawings. In the embodiments described below, when the number, the amount, and the like are mentioned, the scope of the present invention is not necessarily limited to the number, the amount, and the like unless otherwise specified. In addition, the same parts and corresponding parts may be denoted by the same reference numerals, and repeated descriptions may not be repeated. Moreover, it is planned from the beginning to use combining the structure in each embodiment suitably.

[A. Embodiment 1-Short circuit one coil of common mode choke coil]
(A1. Image forming apparatus 100)
FIG. 1 is a diagram for explaining an exemplary configuration of an image forming apparatus 100 according to the embodiment. The image forming apparatus 100 is an electrophotographic image forming apparatus such as a laser printer or an LED printer. As shown in FIG. 1, the image forming apparatus 100 includes an intermediate transfer belt 1 as a belt member at a substantially central portion inside. Below the lower horizontal portion of the intermediate transfer belt 1, four image forming units 2Y, 2M, 2C, 2K corresponding to the respective colors of yellow (Y), magenta (M), cyan (C) and black (K) Are arranged side by side along the intermediate transfer belt 1 and have photosensitive drums 3Y, 3M, 3C, and 3K, respectively.

  Around the photosensitive drums 3Y, 3M, 3C and 3K, along the rotational direction thereof, the chargers 4Y, 4M, 4C and 4K, the print head parts 5Y, 5M, 5C and 5K and the developing device 6Y , 6M, 6C, and 6K, and primary transfer rollers 7Y, 7M, 7C, and 7K facing the respective photosensitive drums 3Y, 3M, 3C, and 3K with the intermediate transfer belt 1 interposed therebetween.

  The secondary transfer roller 9 is in pressure contact with the portion of the intermediate transfer belt 1 supported by the intermediate transfer belt drive roller 8, and secondary transfer is performed in the area. A fixing heating unit 20 having a fixing roller 10, a pressure roller 11, and a heating unit 26 is disposed at a downstream position of the transport path R1 behind the secondary transfer area. Fixing heating is performed by a pressure contact portion between the fixing roller 10 and the pressure roller 11.

  At the lower part of the image forming apparatus 100, a sheet feeding cassette 30 is detachably disposed. The sheets P stacked and stored in the sheet feeding cassette 30 are fed one by one from the uppermost sheet to the conveyance path R1 by the rotation of the sheet feeding roller 31.

  In the present embodiment, the image forming apparatus 100 employs, as an example, an intermediate transfer method having a plurality of imaging units (2Y, 2M, 2C, 2K), but is not limited to this. The image forming apparatus may be an electrophotographic system and may include a fixing heating unit. Specifically, the image forming apparatus may have a single imaging unit or may be of a rotary type.

(A2. General Operation of Image Forming Apparatus 100)
Next, an outline operation of the image forming apparatus 100 configured as described above will be described. When an image signal is input from an external device (for example, a personal computer or the like) to the main body control unit 70 of the image forming apparatus 100, the main body control unit 70 converts the image signal into yellow, cyan, magenta, and black. And print heads 5Y, 5M, 5C, and 5K of the image forming units 2Y, 2M, 2C, and 2K based on the input digital signals to perform exposure.

  Thereby, the electrostatic latent images formed on the photosensitive drums 3Y, 3M, 3C, 3K are developed by the developing devices 6Y, 6M, 6C, 6K, respectively, to form toner images of the respective colors. The toner images of the respective colors are sequentially superimposed and primarily transferred onto the intermediate transfer belt 1 moving in the direction of arrow A in FIG. 1 by the actions of the respective primary transfer rollers 7Y, 7M, 7C, 7K.

  The toner images thus formed on the intermediate transfer belt 1 are collectively secondarily transferred onto the sheet P by the action of the secondary transfer roller 9.

  The toner image secondarily transferred to the sheet P reaches the fixing and heating unit 20. The toner image is fixed on the sheet P by the action of the fixing roller 10 heated by the heating unit 26 provided in the fixing heating unit 20 and the pressure roller 11. The sheet P on which the toner image is fixed is discharged onto the sheet discharge tray 60 via the sheet discharge roller 50.

  Examples of the heating device for heating the heating unit 26 include an infrared heating device such as a halogen heater, and a resistor heating device such as a thermal heater or a ceramic heater. Alternatively, the fixing roller 10 may be inductively heated using a magnetic flux generator (not shown). Hereinafter, the configuration and control of the heating device will be described.

(A3. Configuration of heating device 12A)
FIG. 2 is a diagram for explaining a configuration example of a heating device according to the embodiment. As shown in FIG. 2, the heating device 12A includes an AC power supply 21, a CCL 22, a relay 23A, a triac 24, a control unit 25A, a heating unit 26, and a temperature measurement unit 27.

  The heating unit 26 is connected to the AC power supply 21 via two conductors. A triac 24 which is a switching element is provided on at least one of these two conductors.

  The temperature measurement unit 27 measures the temperatures of the heating unit 26 and the fixing roller 10, and outputs the measurement result to the control unit 25A. For example, a thermistor may be used as the temperature measurement means.

  The control unit 25A is electrically connected to the relay 23A and the triac 24, and performs on / off control of each. The control unit 25A can switch the mode of supplying power to the heating unit 26 by controlling the on / off of the triac 24.

  In addition, an electromagnetic relay may be used as relay 23A which is a short circuit means, and a solid state relay (semiconductor relay) may be used.

(A4. Control of power supply to heating unit 26)
The heating device 12A has, as a mode for supplying power to the heating unit 26, a power limiting mode for limiting AC power to be supplied, and a rated power mode for supplying AC power to the heating unit more than the power limiting mode. In the present embodiment, as an example, the control unit 25A performs phase control in the power limiting mode and performs zero crossing control in the power limiting mode. Specifically, the control unit 25A performs on / off control of the triac 24 to perform phase control and zero cross control.

  Although phase control is used as the power limit mode in the present embodiment, the present invention is not limited to this. In another aspect, for example, PAM (Pulse Amplitude Modulation) control or PWM (Pulse Width Modulation) control may be used. When PAM control is used, the heating device 12A includes a rectifier circuit and an active filter for boosting and smoothing a DC voltage output from the rectifier circuit, instead of the TRIAC 24. Specifically, the control unit 25A can realize the power limiting mode by controlling the duty ratio of the switching element of the active filter. A power transistor may be used as an example of the switching element.

  FIG. 3 is a diagram for explaining phase control and zero cross control. First, phase control will be described. The heating device 12A performs phase control to suppress a rapid change in current value when power supply to the heating unit 26 is started and stopped.

  Specifically, referring to FIG. 3A, control unit 25A adds gate trigger current Igt (A) sufficient to turn on triac 24 in the middle of an alternating current half wave, and strikes triac 24. Control the angle (θ). The heating device 12A gradually reduces the firing angle of the triac 24 as the power supply to the heating unit 26 is started. As a result, the power supplied to the heating unit 26 gradually increases. On the other hand, when stopping the power supply to the heating unit 26, the heating device 12A gradually increases the firing angle of the triac 24. As a result, the power supplied to the heating unit 26 gradually decreases.

  Next, zero cross control will be described. Referring to FIG. 3B, control unit 25A applies gate trigger current Igt (A) to the gate of triac 24 at a zero crossing point at which the output voltage of AC power supply 21 becomes 0 (V). The control unit 25A can supply rated power to the heating unit 26 by applying a gate trigger current to the triac 24 at each zero crossing point in the zero crossing control.

  In phase control, the current applied to the heating unit 26 is discontinuous rather than sinusoidal, and thus contains many harmonic components. Therefore, at the time of phase control, the heating device 12A strongly generates common mode noise as compared to normal mode noise.

  On the other hand, in the zero cross control, the heating device 12A strongly generates normal mode noise as compared to common mode noise. Therefore, in order to cope with both noises, it is conceivable that the heating device has a CCL and a normal mode choke coil (hereinafter also referred to as "NCL").

  In such a case, the heating device causes power loss in a total of three coils of CCL (two coils) and NCL (one coil) at the time of phase control and zero cross control.

  However, depending on the switching frequency of the TRIAC 24, the normal mode at the time of phase control may be substantially negligible. In this case, unnecessary power loss occurs in the NCL (one coil). On the other hand, at the time of zero cross control, since common mode noise can be substantially ignored, unnecessary power loss occurs in the CCL (two coils).

  Therefore, heating device 12A according to the present embodiment reduces unnecessary power loss by reducing noise of both common mode noise and normal mode according to the heating mode to heating unit 26 using one CCL. . The specific control will be described below.

  FIG. 4 is a diagram showing an equivalent circuit when the relay 23A of the heating device 12A is turned on and off. The CCL includes a pair of coils in which two conductors are wound in opposite directions in one core. Therefore, as shown in FIG. 4A, when the relay 23A is in the off state, both of the two coils constituting the CCL 22 are in the conductive state. Therefore, when the relay 23A is in the off state, the CCL 22 functions as a common mode choke coil and can reduce common mode noise.

  On the other hand, as shown in FIG. 4B, when the relay 23A is in the ON state, only one of the two coils constituting the CCL 22 (hereinafter also referred to as "one coil of the CCL 22") is conductive. It is in the state. Therefore, when the relay 23A is in the on state, the CCL 22 functions as a normal mode choke coil.

  Therefore, at the time of phase control, control unit 25A turns off relay 23A in order to reduce common mode noise. Further, at the time of zero cross control, control unit 25A turns on relay 23A in order to reduce normal mode noise.

(A5. Summary)
FIG. 5 is a view for explaining the effect of the heating device according to the present embodiment. Referring to FIG. 5, heating device 12A includes a large amount of harmonic components in the current applied to heating unit 26 at the time of phase control. Therefore, the main noise of the heating device 12A is common mode noise. The heating device 12A turns off the relay 23A during phase control. As a result, the CCL 22 functions as a common mode choke coil, and can reduce common mode noise which is the main noise. At this time, the power loss due to the coil of the heating device 12A is only for two coils constituting the CCL 22. Therefore, at the time of phase control, the heating device can reduce unnecessary power loss for one coil as compared to a heating device provided with CCL (two coils) and NCL (one coil).

  On the other hand, the main noise of the heating device 12A at the time of zero cross control is normal mode noise. The heating device 12A turns on the relay 23A at the time of zero cross control. As a result, the CCL 22 functions as a normal mode choke coil, and can reduce normal mode noise which is the main noise. At this time, the power loss due to the coil of the heating device 12A is only for one coil of the CCL 22. Therefore, at the time of zero crossing control, the heating device can reduce unnecessary power loss for two coils as compared with the heating device provided with CCL and NCL.

  According to the above, the heating apparatus according to the present embodiment can reduce common mode noise in the power control mode (phase control) and normal mode noise in the rated power mode (zero cross control) using one CCL. . That is, the heating device does not have to place both CCL and NCL choke coils in the heating device to reduce both noises. Thus, the heating device can reduce unnecessary power loss. Specifically, the heating device can reduce unnecessary power loss for one coil in the power control mode, and reduce unnecessary power loss for two coils in the rated power mode. it can.

(A6. Control of relay 23A)
Next, the timing of controlling the relay 23A will be described. FIG. 6 is a diagram for explaining the operation of the relay when switching from phase control to zero cross control according to the embodiment.

  The control unit 25A uses the temperature of the heating unit 26 to switch between phase control and zero cross control. Specifically, the control unit 25A performs phase control when the temperature of the heating unit 26 is lower than or equal to a predetermined temperature Tth (° C.). On the other hand, control part 25A performs zero crossing control, when temperature of heating part 26 exceeds predetermined temperature Tth (degreeC). In the present embodiment, the predetermined temperature Tth (° C.) is 180 ° C. The predetermined temperature may be changed according to the ambient temperature, the ambient humidity, and the like.

  Referring to FIG. 6, power supplied from the top to heating unit 26, output voltage of AC power supply 21, control mode of control unit 25A, gate current of triac 24, and state of relay 23A are shown.

  The control unit 25A performs phase control to suppress the inrush current with the start of power supply to the heating unit 26. As the amount of power supplied to the heating unit 26 increases, the temperature of the heating unit 26 rises. At time Ts in FIG. 6, since the temperature of the heating unit 26 reaches Tth (° C.), the control unit 25A changes the power supply mode to the heating unit 26 from phase control to zero cross control.

  The control unit 25A turns on the relay 23A at time Tr in accordance with the change from phase control to zero cross control. This time Tr may be simultaneously with or immediately after the switching time Ts to the zero cross control. The reason is that if the relay 23A is turned on while performing phase control, the CCL 22 can not reduce common mode noise and common mode noise is emitted to the heating device and peripheral devices.

  Therefore, the control unit 25A can reliably reduce common mode noise by turning on the relay 23A simultaneously with or immediately after the transition to the zero cross control.

(A7. Control according to the operation mode of the image forming apparatus)
FIG. 7 is a diagram for describing control of the heating unit 26 according to the operation mode of the image forming apparatus 100 according to the embodiment. Referring to FIG. 7, the power supplied to heating unit 26 from above, the temperature of heating unit 26, the operation mode of image forming apparatus 100, the control mode of control unit 25A, and the state of relay 23A are shown.

  In FIG. 7, “warm up” refers to an operation of raising the temperature of the fixing roller 10 of the fixing heating unit 20 to a predetermined temperature Tp (° C.) in order for the image forming apparatus 100 to form an image. In the present embodiment, for example, Tp (° C.) is set to 180 ° C. "Standby" refers to an operation of maintaining the temperature of the fixing roller 10 at Tp (.degree. C.) so that image formation can be performed immediately. “Printing” refers to an operation of the image forming apparatus 100 for forming an image on a recording material.

  Referring to FIG. 7, at time T0, image forming apparatus 100 is activated. “Startup” also includes the case where the image forming apparatus 100 recovers from a sleep mode or the like that reduces power consumption.

  After startup, the image forming apparatus 100 performs a warm-up operation. At time T0, control unit 25A starts power supply to heating unit 26 by phase control. The temperature of the heating unit 26 rises as the amount of power supplied increases.

  At time T1, since the temperature of the heating unit 26 exceeds Tth (° C.), the control unit 25A switches control of power supply to the heating unit 26 from phase control to zero-cross control. Furthermore, at time T1, the control unit 25A turns on the relay 23A.

  At time T2, the temperature of the fixing roller 10 reaches Tp (° C.). At time T2, in order to suppress the overshoot of the fixing roller 10, the control unit 25A changes the power supply to the heating unit 26 from the zero cross control to the phase control to reduce the amount of supplied power. Furthermore, at time T2, the control unit 25A turns off the relay 23A. The temperature of the heating unit 26 decreases as the amount of power supplied decreases.

  At time T3, the control unit 25A stops the power supply to the heating unit 26. After time T3, the image forming apparatus 100 switches from the warm-up mode to the standby mode. In the standby mode, the image forming apparatus 100 repeats energization and interruption to the heating unit 26 in order to maintain the temperature of the fixing roller 10 at Tp (° C.).

  At time T4, since the temperature of the fixing roller 10 falls below Tp (° C.), the control unit 25A starts power supply to the heating unit 26 by phase control.

  At time T5, the control unit 25A switches the control of the power supply to the heating unit 26 from phase control to zero cross control because the temperature of the heating unit 26 exceeds Tth (° C.). Furthermore, at time T5, the control unit 25A turns on the relay 23A.

  At time T6, the temperature of the fixing roller 10 reaches Tp (° C.). At time T6, in order to suppress the overshoot of the fixing roller 10, the control unit 25A changes the power supply to the heating unit 26 from the zero cross control to the phase control to reduce the amount of supplied power. Furthermore, at time T6, the control unit 25A turns off the relay 23A.

  At time T7, the control unit 25A stops the power supply to the heating unit 26. In the standby state, the control unit 25A repeats a series of control from time T3 to T7.

  At time T8, the image forming apparatus 100 receives the user's input and switches from the standby mode to the print mode. At time T8, the control unit 25A starts power supply to the heating unit 26 by phase control.

  At time T9, since the temperature of the heating unit 26 exceeds Tth (° C.), the control unit 25A switches control of power supply to the heating unit 26 from phase control to zero cross control. Furthermore, at time T9, the control unit 25A turns on the relay 23A. The image forming apparatus 100 forms an image in a state where the temperature of the fixing roller 10 is stable in the vicinity of Tp (° C.).

  At time T10, the image forming apparatus 100 ends the image forming operation. During image formation, the heat supplied from the heating unit 26 and the heat consumed by the sheet are balanced. However, after the image formation, the heat consumed by the sheet is not necessary, and the temperature of the fixing roller 10 overshoots.

  Therefore, at time T10, the control unit 25A changes the power supply to the heating unit 26 from the zero cross control to the phase control to reduce the amount of supplied power. Furthermore, at time T10, the control unit 25A turns off the relay 23A.

  At time T11, the control unit 25A stops the power supply to the heating unit 26. After time T11, the image forming apparatus 100 switches from the print mode to the standby mode.

  According to the above, heating device 12A according to the present embodiment can control power supply to heating unit 26 in accordance with the operation mode of image forming apparatus 100. Furthermore, the heating device can reduce unnecessary power loss due to the coil in each operation mode.

[B. Embodiment 2-Short Circuit in Embodiment 1]
In the first embodiment, the relay 23A, which is a shorting means, shorts one coil of the CCL 22. The shorting means in this embodiment shorts the triac together with one coil of the CCL 22. The configuration, control, and effects of the heating device according to the present embodiment will be described below. In the present embodiment, the configuration and operation of the image forming apparatus excluding the heating device are the same as in the first embodiment, and therefore the details thereof will not be repeated.

(B1. Configuration of heating device 12B)
FIG. 8 is a view for explaining an example of the arrangement of a heating apparatus according to another embodiment. The same reference numerals as in FIG. 2 are not repeated.

  As shown in FIG. 8, the heating device 12B includes an AC power supply 21, a CCL 22, a relay 23B, a triac 24, a control unit 25B, a heating unit 26, and a temperature measurement unit 27.

  The relay 23B of the heating device 12B is different from the relay 23A of the heating device 12A in the short-circuited device. Specifically, the relay 23A of the heating device 12A shorts one coil of the CCL 22. On the other hand, the relay 23B of the heating device 12B shorts the triac 24 together with one coil of the CCL 22.

(B2. Control of relay 23B)
In the first embodiment, when the temperature of the heating unit 26 reaches Tth (° C.), the control unit 25A switches from phase control to zero cross control. On the other hand, the control unit 25B in the present embodiment performs phase control when the temperature of the heating unit 26 is less than Tth (° C.), and turns on the relay 23B when the temperature is equal to or more than Tth (° C.).

  When the relay 23B is turned on, the power of the AC power supply 21 is always supplied to the heating unit 26. Therefore, when the relay 23B is turned on, the heating device 12B is in the rated power mode.

  In addition, when the relay 23B is turned on, as in the first embodiment, only one coil of the CCL 22 is brought into conduction. Therefore, when the relay 23A is in the on state, the CCL 22 functions as a normal mode choke coil. On the other hand, when the relay 23B is in the off state, the CCL 22 functions as a common mode choke coil.

  Furthermore, when the relay 23B is in the on state, in addition to one coil of the CCL 22, the triac 24 is also shorted. Therefore, when the relay 23B is in the ON state, the power loss in the triac 24 and the power for controlling the triac 24 by the control unit 25B can be reduced in addition to the power loss in one coil of the CCL 22.

  According to the above, the heating apparatus according to the present embodiment can suppress common mode noise at the time of phase control and normal mode noise at the time of rated power application using one CCL. Furthermore, the heating device can reduce power consumption more than the heating device according to the first embodiment in the rated power mode.

(B3. Control according to the operation mode of the image forming apparatus)
FIG. 9 is a diagram for describing control of the heating unit 26 according to the operation mode of the image forming apparatus 100 according to another embodiment. Referring to FIG. 9, the power supplied to heating unit 26 from above, the temperature of heating unit 26, the operation mode of image forming apparatus 100, the control mode of control unit 25B, and the state of relay 23B are shown. The same reference numerals as those in FIG. 7 are not repeated.

  At time T1, since the temperature of the heating unit 26 exceeds Tth (° C.), the control unit 25B switches the mode of power supply to the heating unit 26 from the phase control mode to the rated power mode. Specifically, control unit 25B turns on relay 23B at time T1.

  At time T2, the temperature of the fixing roller 10 reaches Tp (° C.). At time T2, in order to suppress the overshoot of the fixing roller 10, the control unit 25B changes the mode of power supply to the heating unit 26 from the rated power mode to the phase control mode to reduce the amount of supplied power. Specifically, at time T2, the control unit 25B turns off the relay 23B and controls the triac 24 by phase control.

  According to the above, the heating device 12B according to the present embodiment can control the power supply to the heating unit 26 in accordance with the operation mode of the image forming apparatus 100. Furthermore, the heating device can reduce power consumption more than the heating device according to the first embodiment in the rated power mode in each operation mode.

[C. Embodiment 3 Addition and Short Circuit of Normal Mode Choke Coil]
In the present embodiment, unnecessary power loss is reduced as well as normal mode noise generated in the power limiting mode (phase control). In the present embodiment, the configuration and operation of the image forming apparatus excluding the heating device are the same as in the first embodiment, and therefore the details thereof will not be repeated.

  At the time of phase control, depending on the switching frequency of the TRIAC 24, both common mode noise and normal mode noise may occur to an extent that the heating device and / or peripheral devices are affected. In such a case, the heating device needs to reduce normal mode noise as well as common mode noise. That is, the heating device needs to have NCL in addition to CCL.

(Configuration of c1. Heating device 12C)
FIG. 10 is a view for explaining an example of the configuration of a heating apparatus according to still another embodiment. The same reference numerals as in FIG. 2 are not repeated.

  As shown in FIG. 10, the heating device 12C includes an AC power supply 21, a CCL 22, a relay 23C, a triac 24, a control unit 25C, a heating unit 26, a temperature measurement unit 27 and an NCL 28.

(C2. Control of relay 23C)
The control unit 25C performs phase control when the temperature of the heating unit 26 is less than Tth (° C.), and turns on the relay 23C when the temperature is equal to or more than Tth (° C.).

  When the relay 23C is turned on, the power of the AC power supply 21 is always supplied to the heating unit 26. Thus, when the relay 23C is turned on, the heating device 12C enters the rated power mode.

  According to the above, heating device 12C can reduce common mode noise and normal mode noise in the power limiting mode, and normal mode noise in the rated power mode. Furthermore, when the relay 23C is in the on state, unnecessary power consumed in one coil of the CCL 22 and the NCL 28 can be reduced.

(C3. Control according to the operation mode of the image forming apparatus)
Also in the present embodiment, the control unit 25C can control the triac 24 and the relay 23C according to the operation mode of the image forming apparatus 100. Since the control content is the same as the control content shown in FIG. 7, the details thereof will not be repeated.

[D. Embodiment 4 In Embodiment 3, the TRIAC is also Shorted]
In the third embodiment, the relay 23C, which is a short circuit means, shorts one coil of the CCL 22 and the NCL 28. The short circuit means in this embodiment shorts the triac 24 together with one coil of the CCL 22 and the NCL 28. In the present embodiment, the configuration and operation of the image forming apparatus excluding the heating device are the same as in the first embodiment, and therefore the details thereof will not be repeated.

(Structure of d1. Heating device 12D)
FIG. 11 is a view for explaining an example of the arrangement of a heating apparatus according to still another embodiment. As illustrated in FIG. 11, the heating device 12D includes an AC power supply 21, a CCL 22, a relay 23D, a triac 24, a control unit 25D, a heating unit 26, a temperature measurement unit 27, and an NCL 28.

  The relay 23D of the heating device 12D is different from the relay 23C of the heating device 12C in the short-circuited device. Specifically, the relay 23C of the heating device 12C shorts one coil of the CCL 22 and the NCL 28. On the other hand, the relay 23D of the heating device 12D shorts the triac 24 together with one coil of the CCL 22 and the NCL 28.

(D2. Control of relay 24D)
The control unit 25D performs phase control when the temperature of the heating unit 26 is less than Tth (° C.), and turns on the relay 23D when the temperature is equal to or more than Tth (° C.).

  When the relay 23D is turned on, the power of the AC power supply 21 is always supplied to the heating unit 26. Thus, when the relay 23D is turned on, the heating device 12D goes into the rated power mode.

  According to the above, the heating apparatus according to the present embodiment can reduce common mode noise and normal mode noise in the power limiting mode and can reduce normal mode noise in the rated power mode. Furthermore, in the rated power mode, the heating device can further reduce the power loss in the triac and the power loss at which the control unit controls the triac as compared to the heating device according to the third embodiment.

(D3. Control according to the operation mode of the image forming apparatus)
Also in the present embodiment, the control unit 25D can control the triac 24 and the relay 23D in accordance with the operation mode of the image forming apparatus 100. Since the control content is the same as the control content shown in FIG. 9, the details will not be repeated.

[E. Modification-Relay control only at initial heating]
In the first to fourth embodiments, in each operation mode of the image forming apparatus 100, the control unit performs on / off control of the relay. On the other hand, in the present modification, on / off control of the relay is performed only in the warm-up mode.

  The reason is that when using a contact-type electromagnetic relay as the relay, there is a problem that the relay life is shortened if the relay on / off control is performed each time the power supply to the heating unit 26 is started and stopped.

  In addition, the warm-up mode has a longer time of zero cross control (relay on state) compared to other modes. Therefore, the heating device can reduce the power loss in one coil of the CCL 22 for a longer time than the other modes by performing on / off control of the relay only in the warm-up mode.

  So, in this modification, it is possible that a control part performs ON / OFF control of a relay only in warm-up mode. The following description will be given using the heating device 12A according to the first embodiment as an example. The present modification is also applicable to the heating devices 12B, 12C and 12D.

  FIG. 12 is a diagram for describing control of the heating unit 26 according to the operation mode of the image forming apparatus 100 according to the modification. The same reference numerals as those in FIG. 7 are not repeated.

  Control unit 25A receives input of operation mode information of image forming apparatus 100 from main body control unit 70. At time T1 in FIG. 12, since the temperature of the heating unit 26 has reached Tth (° C.), the control unit 25A switches control of power supply to the heating unit 26 from phase control to zero cross control. Further, at time T1, control unit 25A determines that the operation mode of image forming apparatus 100 is the warm-up mode, and turns on relay 23A.

  At time T2, the control unit 25A switches from zero-cross control to phase control, and turns off the relay 23A.

  At time T5, the control unit 25A switches the control of the power supply to the heating unit 26 from phase control to zero cross control because the temperature of the heating unit 26 exceeds Tth (° C.). At time T5, control unit 25A determines that the operation mode of image forming apparatus 100 is not the warm-up mode, and does not turn on relay 23A.

  According to the above, the life of the relay can be extended, and the reliability of the heating device can be improved. Further, the heating device can reduce the power loss in one coil of the CCL for a longer time than the other modes by performing on / off control of the relay only in the warm-up mode. Therefore, the heating device in the present embodiment can achieve both improvement in reliability and reduction in power consumption.

  In another aspect, the control unit 25A may control the relay 23A based on the temperature of the fixing roller 10, which is an object to be heated, instead of the operation mode of the image forming apparatus 100. Specifically, the relay 23A may be turned on during the rated power mode only when the temperature of the fixing roller 10 at the start of the rated power mode is equal to or lower than a predetermined temperature. In the present embodiment, as an example, the predetermined temperature is 50.degree. The control using FIG. 12 will be described below.

  At time T1, the control unit 25A switches from the phase control mode to the rated power mode. Further, at time T1, the control unit 25A determines that the temperature of the fixing roller 10 is 50 ° C. or less, and turns on the relay 23A. Even if the temperature of the fixing roller 10 exceeds 50 ° C., the control unit 25A keeps the relay 23A in the on state until time T2 when the rated power mode ends. Then, at time T2, the control unit 25A switches from the rated power mode to the phase control mode and puts the relay 23A in the off state.

  On the other hand, at time T5, the control section 25A switches the phase control mode to the rated power mode, determines that the temperature of the fixing roller 10 exceeds 50 ° C., and does not turn on the relay.

  According to the above, the control unit 25A can perform on / off control of the relay only in the warm-up mode without receiving the input of the operation mode information of the image forming apparatus 100 from the main body control unit 70.

  It should be understood that the embodiments disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is indicated not by the above description but by the claims, and is intended to include all the modifications within the meaning and scope equivalent to the claims.

  1 Intermediate Transfer Belt, 2Y, 2M, 2C, 2K Imaging Unit, 3Y, 3M, 3C, 3K Photosensitive Drum, 4Y, 4M, 4C, 4K Charger, 5Y, 5M, 5C, 5K Print Head, 6Y, 6M, 6C, 6K Developer, 7Y, 7M, 7C, 7K Primary Transfer Roller, 8 Intermediate Transfer Belt Drive Roller, 9 Secondary Transfer Roller, 10 Fusing Roller, 11 Pressure Roller, 12A, 12B, 12C, 12D Heating Apparatus, 20 fixing heating unit, 21 AC power supply, 23A, 23B, 23C, 23D relay, 24 triac, 25A, 25B, 25C, 25D control unit, 26 heating unit, 27 temperature measuring unit, 30 sheet feeding cassette, 31 sheet feeding Rollers, 40 sensors, 50 paper discharge rollers, 60 paper discharge trays, 70 main body control unit, 100 image forming apparatus.

Claims (8)

A heating unit configured to be connected to an AC power supply via the first conductor and the second conductor;
A switching element provided on at least one of the first conductor and the second conductor;
A common mode choke coil comprising a pair of coils respectively disposed on the first conductor and the second conductor;
Shorting means for shorting one of the coils of the common mode choke coil;
A control unit electrically connected to the switching element and the short circuit means;
The controller cancels a short circuit in the short circuit in the first mode in which the switching element is controlled to limit the AC power supplied to the heater, and the controller is more than the first mode. A heating device, which enables a short circuit by the short circuit in a second mode of supplying AC power to the heating unit.   The heating device according to claim 1, wherein the short circuit shorts the switching element together with one of the common mode choke coils. It further comprises a normal mode choke coil provided on a conductor in which the switching element is disposed,
The heating device according to claim 1, wherein the short circuit shorts the normal mode choke coil together with one of the common mode choke coils. It further comprises a temperature measurement unit that measures the temperature of the heating unit and outputs the measurement result to the control unit.
The heating device according to any one of claims 1 to 3, wherein the control unit performs on / off control of the switching element according to a temperature of the heating unit. The temperature measurement unit further measures the temperature of the object heated by the heating unit,
The control unit enables the short circuit by the short circuit in the second mode only when the temperature of the object to be heated at the time of starting the power supply in the second mode is equal to or lower than a predetermined temperature. The heating device according to claim 4.   The heating device according to any one of claims 1 to 5, wherein the short circuit means includes at least one of an electromagnetic relay and a solid state relay. An image forming unit that forms a toner image on a recording material;
A fixing heating unit for fixing the toner image to the recording material;
The fixing heating unit is
A heating unit configured to be connected to an AC power supply via the first conductor and the second conductor;
A switching element provided on at least one of the first conductor and the second conductor;
A common mode choke coil comprising a pair of coils respectively disposed on the first conductor and the second conductor;
Shorting means for shorting one of the coils of the common mode choke coil;
A control unit electrically connected to the switching element and the short circuit means;
The controller cancels a short circuit in the short circuit in the first mode in which the switching element is controlled to limit the AC power supplied to the heater, and the controller is more than the first mode. An image forming apparatus, wherein a short circuit by the short circuit is enabled in a second mode of supplying AC power to the heating unit.   8. The image formation according to claim 7, wherein the control unit enables a short circuit by the short circuit in the second mode only during a warm-up operation to start processing required for image formation. apparatus.

Images