JP2023034157A - Heater circuit and image forming apparatus - Google Patents

Abstract

[Problem] An abnormality is detected by passing current through the heater in a way that prevents damage to the heater. [Solution] When the fixing device 20 is not performing the fixing operation (before the fixing operation), the control unit 3 turns on the DC current line L2 (turns off the AC current line L1) to supply a DC current to the heater 35. If the overcurrent detection unit 54 does not detect an overcurrent, the control unit 3 turns on the AC current line L1 (turns off the DC current line L2) to supply an AC current to the heater 35 and perform the fixing operation. If the overcurrent detection unit 54 detects an overcurrent, the control unit 3 turns off the relay circuit 33, does not turn on the AC current line L1, and causes the display unit 41 to display an error message indicating that an abnormality has occurred in the heater 35. [Selected Figure] Figure 3

Description

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

An electrophotographic image forming apparatus performs printing by forming a toner image on a sheet and fixing the toner image on the sheet with a fixing device. The fixing device includes a heating member and a pressure member, and performs fixing processing by sandwiching the paper between the two members and applying heat and pressure to the paper. The heating element is heated by a heating element (heater), and the temperature of the heating element is controlled by the current flowing through the heater.

If some problem occurs in the heater circuit and an overcurrent is generated in the heater, it may cause a malfunction of the fixing device. Therefore, it is necessary to immediately detect any abnormality in the heater.

Japanese Patent Laid-Open No. 2004-100000 discloses a technique in which only an auxiliary lamp among a plurality of lamps is turned on for a predetermined period of time at an arbitrary timing when printing is not being performed, and an abnormality of the auxiliary lamp is detected by detecting a change in temperature of a heating roller during that period. It describes how to do it.

Patent Literature 2 describes a method of interrupting the power supply to the heat source when the current flowing to the heat source exceeds a predetermined value.

Patent Literature 3 describes a method in which a current sensor and a circuit breaker are provided for each of a plurality of heat-generating portions, and abnormalities in the heat-generating portions are individually detected using the amount of current detected.

JP 2010-244051 A JP 2017-090570 A JP 2018-073769 A

In recent years, planar heaters are often used as heating elements for heating members because of their excellent temperature raising effect. A planar heater is often placed in close proximity to a heating member. When an abnormal current flows through the planar heater, the temperature of the planar heater suddenly rises, and the heater itself, as well as the heating member body and surrounding parts, may be damaged. As a result, the user has to bear the burden of repairing the device or replacing parts.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a heater circuit and an image forming apparatus that detect an abnormality by energizing a heater in a manner that suppresses damage to the heater.

The heater circuit in the present invention includes a heater, an AC power supply connected to an AC current line that supplies an AC current to the heater, a DC power supply connected to a DC current line that supplies a DC current to the heater, and the AC power supply. a switch unit connected to a current line for switching between conduction and non-conduction of the alternating current line; a first switching unit connected to the alternating current line for switching between on and off of the alternating current flowing through the alternating current line; line, and turns off the direct current flowing in the direct current line when the first switching unit is on, and turns on the direct current flowing in the direct current line when the first switching unit is off. a switching unit, an overcurrent detection unit connected to the DC current line for detecting an overcurrent flowing through the DC current line, and an instruction signal for controlling operations of the first switching unit, the second switching unit, and the switching unit. When the overcurrent detection unit detects the overcurrent, the control unit outputs an instruction signal to turn off the alternating current flowing in the alternating current line, and the overcurrent detection unit does not detect the overcurrent, the controller outputs an instruction signal to turn on the alternating current flowing in the alternating current line.

Further, an image forming apparatus according to the present invention includes an image forming section that forms an image on a sheet of paper, and the heater circuit described above.

According to the present invention, by passing a direct current through the heater and detecting whether or not an overcurrent has occurred, even if an overcurrent occurs, the direct current has a smaller current value than the alternating current, so the temperature of the heater rises sharply. This reduces the possibility of damage to the heater itself and its peripheral members, thereby minimizing the damage caused by failure.

When a planar heater is used as a heating element of a heating member of a fixing device of an image forming apparatus, the planar heater is arranged close to the heating member. Therefore, when the temperature rises rapidly due to an AC overcurrent flowing through the planar heater, there is a high possibility that not only the heater itself but also the surrounding members will be thermally damaged at that point.

However, by applying a direct current to the planar heater when the fixing operation is not performed and checking for overcurrent, even if an overcurrent occurs, the temperature rises enough to damage the planar heater and surrounding materials. do not. In other words, it is possible to reduce the possibility of component breakage and avoid failure of the device.

1 is a front sectional view showing the structure of an image forming apparatus; FIG. It is the figure which showed the schematic sectional drawing of a fixing device. It is the figure which showed an example of the electrical structure of a heater circuit.

An image forming apparatus according to one embodiment of the present invention will be described below with reference to the drawings. In this embodiment, a color electrophotographic image forming apparatus will be described as an example, but the present invention can also be applied to a monochrome printing image forming apparatus. FIG. 1 is a front sectional view showing the structure of an image forming apparatus 1 according to this embodiment.

The image forming apparatus 1 includes an apparatus main body 99, an operation section 4, an image forming section 6, a paper feeding section 14, and the like.

When the image forming apparatus 1 performs a printing operation, the image forming section 6 forms a toner image on the paper P fed from the paper feeding section 14 based on image data obtained from the outside.

When performing color printing, the image forming unit 6M for magenta, the image forming unit 6C for cyan, the image forming unit 6Y for yellow, and the image forming unit 6Bk for black of the image forming section 6 each form image data. A toner image is formed on the photoreceptor drum by charging, exposing and developing processes based on the image composed of the color components, and the toner image is transferred onto the intermediate transfer belt 991 by the primary transfer roller.

Cartridge 61M contains magenta toner, cartridge 61C contains cyan toner, cartridge 61Y contains yellow toner, and cartridge 61Bk contains black toner. These cartridges are detachable from the apparatus main body 99, and when the remaining amount of toner runs out, the user or maintenance staff replaces them with new cartridges.

The toner images of each color transferred onto the intermediate transfer belt 991 are superimposed on the intermediate transfer belt 991 by adjusting the transfer timing to form a color toner image. The secondary transfer roller 992 transfers the color toner image formed on the surface of the intermediate transfer belt 991 onto the paper P conveyed from the paper feeding unit 14 .

The fixing device 20 nips the paper P having the toner image in the nip portion N and heats and presses the paper P to fix the toner image. The fixing device 20 has a fixing belt 21 and a pressure member 22 . The paper P on which the fixing process has been completed and the color image has been formed is discharged to the discharge tray 151 . The paper feeding unit 14 accommodates the paper P. As shown in FIG.

The operation unit 4 includes, for example, a menu key for calling up a menu, an enter key for confirming various operations and settings, a start key, and the like. The display unit 41 is a liquid crystal display (LCD), an organic light-emitting diode (OLED) display, or the like, and displays messages, operation screens, and the like to the user. Also, the display unit 41 corresponds to the notification unit of the present invention.

FIG. 2 is a diagram showing a schematic cross-sectional view of the fixing device 20. As shown in FIG. The fixing belt 21 rotates about the rotary shaft 21a in the direction indicated by the arrow 21y, and has a heater 35 facing the inner surface of the fixing belt 21. As shown in FIG. The heater 35 heats the fixing belt 21 and is a planar ceramic heater or the like. The heater 35 may be a heating member such as a halogen lamp.

The pressure member 22 rotates about a rotary shaft 22a in the direction indicated by an arrow 22y, presses the outer surface of the fixing belt 21, and nips the conveyed paper P at the nip portion N to press the paper P. pressure. The toner image is fixed on the paper P by being heated by the fixing belt 21 while the paper P is conveyed in the direction of the arrow Y and being pressed by the pressure member 22 .

FIG. 3 is a diagram showing an example of an electrical configuration of a heater circuit having the heater 35. As shown in FIG. The heater 35 is connected to an alternating current line L<b>1 to which alternating current is supplied from the commercial power source 31 and to a direct current line L<b>2 to which direct current is supplied from the direct current power source 51 . Note that the DC power supply 51 supplies the same DC current value as the DC current value when the DC current supplied to the heater 35 is generated based on the AC current supplied from the commercial power supply 31 .

A fuse 32, a relay circuit 33, a thermostat 34, a heater 35 and a triac 36 are connected in series to the alternating current line L1. The fuse 32 cuts off the AC current line L1 when a current equal to or greater than a predetermined value larger than the current value when driving the heater flows. The relay circuit 33 turns ON/OFF the conduction of the alternating current line L1 according to the signal transmitted from the control unit 3 . The triac 36 switches on/off the alternating current flowing through the alternating current line L1 according to a signal transmitted from the control unit 3 . The triac 36 corresponds to the first switching section in the claims.

The thermostat 34 detects the temperature of the heater 35 and turns off the conduction of the alternating current line L1 when the detected temperature reaches a predetermined value higher than the temperature when the heater is driven.

The direct current line L2 has the triacs 52 and 53, the heater 35 and the overcurrent detector 54 connected in series. The triacs 52 and 53 turn on and off the direct current flowing through the direct current line L2 in accordance with the signal sent from the control section 3 . The triacs 52 and 53 correspond to switching elements in the claims.

The overcurrent detection unit 54 detects the current flowing through the DC current line L2, and outputs a detection signal to the control unit 3 when a current having a value predetermined as a current value indicating an eddy current state flows (when an overcurrent occurs). output to

The inverter circuit 55 receives the instruction signal S1 output from the control unit 3 to the triac 36 and outputs a signal S2 obtained by logically inverting the signal S1 to the triacs 52 and 53 . The triac 52, triac 53 and inverter circuit 55 correspond to the second switching section in the claims.

The control unit 3 includes a CPU (Central Processing Unit), RAM (Random Access Memory), ROM (Read Only Memory), a dedicated hardware circuit, etc., and controls the operation of the heater circuit. Specifically, the control unit 3 performs control to output an emergency stop signal to the relay circuit 33 when an abnormality occurs during operation of the heater circuit. The control unit 3 controls the relay circuit 33 to turn off the AC current line L1 by turning off the internal switch according to this emergency stop signal.

Furthermore, the control unit 3 outputs a signal S1 to the triac 36 and the inverter circuit 55 to control on/off of the alternating current flowing through the alternating current line L1 and the direct current flowing through the direct current line L2. As described above, the triac 36 and the triacs 52 and 53 are supplied with mutually inverted signals.

Therefore, when the triac 36 is on, the triacs 52 and 53 are off, and alternating current flows through the alternating current line L1. That is, alternating current is supplied to the heater 35 . When the triac 36 is turned off, the triacs 52 and 53 are turned on and a direct current flows through the direct current line L2. That is, a DC current is supplied to the heater 35 .

Next, the operation of the heater circuit will be described. When the fixing device 20 is not performing a fixing operation (for example, before the fixing operation), the controller 3 outputs a signal S1 for turning on the direct current flowing through the direct current line L2 (that is, turning off the alternating current). Thereby, a DC current is supplied to the heater 35 . Then, the overcurrent detector 54 detects whether or not an overcurrent is generated in the DC current line L2.

At this time, if the overcurrent detection unit 54 does not detect an overcurrent, the control unit 3 outputs a signal S1 that turns on the alternating current flowing through the alternating current line L1 (that is, turns off the direct current). As a result, an alternating current is supplied to the heater 35 to perform the fixing operation.

On the other hand, when the overcurrent detection unit 54 detects an overcurrent, the control unit 3 turns off the relay circuit 33 to make the alternating current line L1 non-conductive, and the display unit 41 indicates that the heater 35 is abnormal. display an error message indicating that Thereby, the user can know that the fixing device 20 has an abnormality.

As described above, in the present embodiment, the DC current supplied from the DC power supply 51 is passed through the heater 35 and the presence or absence of overcurrent is checked. Since the value of the current to be handled is smaller than when the AC current supplied to the heater 35 is generated using the AC current from the commercial power supply 31, even if the DC current is supplied to the heater 35 in a state where the heater 35 is abnormal. The temperature of the heater 35 does not rise sharply, the possibility of damage to the heater 35 itself and its surrounding members can be reduced, and the damage caused by equipment failure can be minimized.

In particular, when the heater 35 is a planar heater, the planar heater is placed in contact with the inner surface of the fixing belt 21 . Therefore, when the temperature of the heater 35 suddenly rises due to overcurrent or the like, there is a high possibility that the fixing belt 21 is also damaged by the heat.

However, by turning on the DC current line L2 and applying a DC current to the heater 35 before the fixing operation, even if an overcurrent occurs, the temperature does not rise to the extent that the heater 35 or the fixing belt 21 is damaged. It can reduce the chance of breakage.

1 Image forming apparatus 3 Control unit 4 Operation unit 6 Image forming unit 20 Fixing device 21 Fixing belt 21a Shaft 22 Pressure member 22a Shaft 31 AC power supply 32 Fuse 33 Relay circuit 34 Thermostat 35 Heaters 36, 52, 53 Triac 41 Display unit 51 DC power supply 54 Overcurrent detector L1 AC current line L2 DC current line

Claims (4)

a heater;
an alternating current power supply connected to an alternating current line that supplies alternating current to the heater;
a DC power supply connected to a DC current line that supplies DC current to the heater;
a switch unit connected to the alternating current line and switching between conduction and non-conduction of the alternating current line;
a first switching unit connected to the alternating current line for switching between on and off of the alternating current flowing through the alternating current line;
is connected to the DC current line, turns off the DC current flowing through the DC current line when the first switching unit is ON, and turns ON the DC current flowing through the DC current line when the first switching unit is OFF; a second switching unit for switching;
an overcurrent detection unit connected to the direct current line and detecting an overcurrent flowing through the direct current line;
A control unit that outputs an instruction signal for controlling operations of the first switching unit, the second switching unit, and the switch unit,
When the overcurrent detection unit detects the overcurrent, the control unit outputs an instruction signal to turn off the alternating current flowing in the alternating current line, and the overcurrent detection unit does not detect the overcurrent. In this case, the controller outputs an instruction signal to turn on the alternating current flowing in the alternating current line. The second switching unit has an inverting circuit and a switching element for inverting the instruction signal output from the control unit to the first switching unit,
When the control unit outputs an instruction signal to turn on the alternating current flowing in the alternating current line to the first switching unit, the inverting circuit outputs a signal obtained by inverting the instruction signal to the switching element. Turn off the direct current flowing in the direct current line,
When the control unit outputs an instruction signal to turn off the alternating current flowing in the alternating current line to the first switching unit, the inverting circuit outputs a signal obtained by inverting the instruction signal to the switching element. 2. The heater circuit of claim 1, wherein the direct current flowing in the direct current line is turned on. an image forming unit that forms an image on paper;
3. An image forming apparatus comprising the heater circuit according to claim 1 or 2. 4. The image forming apparatus according to claim 3, further comprising a notification section that notifies that an abnormality has occurred when the overcurrent detection section detects the overcurrent.

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