Image forming apparatus and electrical equipment

Abstract

To provide an image forming device that operates with AC power, and even when the AC power supplied is switched to DC power, can prevent components from being damaged.SOLUTION: An image forming device 100 comprises a circuit 38 for AC having a heater 36, and a triac 33 for load control that is connected in series with the heater 36 to control the heater 36. The image forming device 100 further comprises: an overcurrent operation circuit 37 that is connected in parallel with the circuit 38 for AC, and in which current flows when the circuit 38 for AC is made to be supplied with DC power; and a poly switch 23 that is connected in series with the circuit 38 for AC and the overcurrent operation circuit 37. When an overcurrent flows in the overcurrent operation circuit 37, the poly switch 23 cuts off the current.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to an image forming apparatus and an electrical device that are powered by an AC power source. [Background technology]

[0002] Many electrical devices are used while connected to a commercial power source. Therefore, these electrical devices are configured to be driven by an AC power source. If a DC power source is supplied to such electrical devices, problems may occur, such as malfunctions or damage to the components driven by the AC power source.

[0003] For example, in recent years, as the use of solar power generation has become widespread, there are cases where AC power is supplied to electrical equipment from a solar power generation power conditioner that converts the DC power obtained by power generation into AC power. In this case, a malfunction of the solar power generation power conditioner may cause a malfunction in which DC power is supplied to the electrical equipment, instead of the AC power that should be supplied. If such a malfunction occurs, the electrical equipment receiving power from the solar power generation power conditioner may experience malfunctions or damage to components driven by the AC power.

[0004] Here, electrical equipment refers to equipment that operates by electricity, such as household electrical appliances (home appliances) and office equipment. For example, image forming devices such as copiers, facsimile machines, printers, and multifunction machines are also electrical equipment. Image forming devices form a toner image on paper using a photosensitive drum, and fix the toner image on the paper to form an image on the paper. This fixing is thermal fixing, which is performed by heating the toner image using a heater. In such image forming devices, the heater is connected in series with a triac for controlling the operation of the heater, a thermostat for protecting the heater by cutting off the current flowing through the heater when the heater becomes too hot, and a power relay for protecting the heater by cutting off the current flowing through the heater when an abnormality in the power supply is detected.

[0005] Here, a triac is a three-terminal semiconductor switching element, and is widely used as an AC switch. Specifically, when a trigger pulse current is applied to the gate terminal of a triac, it becomes conductive (on state), and when the half cycle of the AC current that is conducted ends, it is cut off (off state). In other words, when a trigger pulse current is applied to the gate terminal of a triac, it becomes on state, and when the AC voltage applied to the triac becomes 0V, it automatically becomes off state. This makes it easy to control the operation of a load connected to the triac by controlling the timing of applying the trigger pulse current. However, when a DC voltage is applied to the triac, it never becomes 0V, so it does not automatically become off state, and the DC voltage continues to be applied to the triac.

[0006] For example, Patent Document 1 discloses a temperature control circuit that adjusts the temperature of a heater by controlling the AC voltage of a commercial power source or the like that is applied to a heater, which is a load, using a triac, which is a switching element. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 6-236127 Summary of the Invention [Problem to be solved by the invention]

[0008] In the temperature control circuit disclosed in Patent Document 1, if voltage continues to be applied to the heater, the heater temperature rise will not stop, resulting in an abnormal temperature rise. However, as described above, since a thermostat, power relay, etc. are connected to the heater, if these operate normally, the voltage supply to the heater will be stopped and the temperature rise of the heater will be stopped.

[0009] However, as described above, when a DC voltage is applied due to a failure of the photovoltaic power conditioner, etc., even if an attempt is made to separate the contacts of the thermostat and the power relay, unlike when an AC voltage is applied, an arc discharge occurs between the contacts, causing the contacts to fuse together and not be able to be disconnected, and the thermostat and the power relay may remain in a short-circuited state. If the thermostat and the power relay remain in a short-circuited state, voltage will continue to be applied to the heater, causing the heater temperature to rise unstoppably, and causing each component to break and fail. In addition, the heater may catch fire, which may cause a serious accident.

[0010] The present invention has been made in consideration of the above-mentioned circumstances, and its purpose is to provide an image forming apparatus and electrical equipment that operate on AC power and that can prevent damage to each component even when the AC power supplied is switched to a DC power source. [Means for solving the problem]

[0011] An electrical device according to one embodiment of the present invention is an electrical device comprising an AC circuit having a load and a load control member connected in series with the load to control the load, and comprising: an overcurrent operation circuit connected in parallel to the AC circuit and through which a current flows when a DC power source is supplied to the AC circuit; and an overcurrent interruption unit connected in series to the AC circuit and the overcurrent operation circuit, wherein the overcurrent interruption unit interrupts a current when an overcurrent flows in the overcurrent operation circuit.

[0012] As a result, when a DC power source is supplied to a load that is normally operated by an AC power source, an overcurrent flows through the overcurrent operation circuit connected in parallel to the AC circuit including the load, which causes the overcurrent interrupter to operate and cut off the input to the load. Therefore, if the input to the load is not cut off, the load control member will not be able to control the load due to the input of DC, and the load may malfunction, but since the overcurrent interrupter cuts off the input to the load, the malfunction of the load can be suppressed. Therefore, problems such as breakdowns caused by the malfunction of the load can be prevented.

[0014] As a result, when the DC power supply operation unit becomes conductive due to the supply of DC power, a circuit is formed in which the overcurrent operation circuit and the AC circuit are connected in parallel, but since the current limiting resistor unit of the overcurrent operation circuit has a lower resistance value than the load of the AC circuit, current flows mainly through the overcurrent operation circuit, causing an overcurrent, which then activates the overcurrent interrupter. In this way, when DC power is supplied, the overcurrent interrupter quickly activates to cut off the input to the load, preventing problems caused by the load malfunctioning.

[0016] This makes it possible to easily configure a DC power supply unit that is conductive (turned on) when DC power is supplied to the AC circuit.

[0017] In the above-described electrical device, the load may be a heater for forming an image on a recording medium by thermally fixing a toner image formed on the recording medium.

[0018] In this way, when the load is a heater, if the input to the heater is not stopped, the heater will continue to generate heat and may eventually catch fire, but when DC power is supplied, the overcurrent cut-off unit operates and cuts off the input to the heater, stopping the heater so that it does not continue to generate heat and preventing malfunctions.

[0019] Moreover, an image forming apparatus according to one aspect of the present invention is an image forming apparatus that forms a toner image on a recording medium and forms an image on the recording medium by fixing the toner image formed on the recording medium, and is characterized in that it comprises an AC circuit having a heater that is a load for thermally fixing the toner image formed on the recording medium and a load control member connected in series with the heater to control the heater, an overcurrent operation circuit that is connected in parallel to the AC circuit and through which a current flows when a DC power source is supplied to the AC circuit, and an overcurrent interruption unit that is connected in series to the AC circuit and the overcurrent operation circuit, and the overcurrent interruption unit interrupts the current when an overcurrent flows in the overcurrent operation circuit.

[0020] As a result, when DC power is supplied to a heater for thermally fixing a toner image in an image forming device that is normally powered by AC power, an overcurrent flows through an overcurrent operation circuit connected in parallel to an AC circuit including the heater, which causes the overcurrent cut-off unit to operate and cut off the input to the heater. Therefore, if the input to the heater is not cut off, the load control member will not be able to control the heater due to the input of DC, and the heater will continue to generate heat, but since the overcurrent cut-off unit cuts off the input to the load, the heater can stop generating heat. This makes it possible to prevent problems such as the heater continuing to generate heat and catching fire. Effect of the Invention

[0021] According to the present invention, in an image forming apparatus and electrical equipment that operate on AC power, even if the AC power being supplied is switched to a DC power, damage to each component can be suppressed. [Brief description of the drawings]

[0022] [Figure 1] 1 is a perspective front view showing a schematic configuration of an image forming apparatus according to an embodiment of the present invention; [Diagram 2]2 is a block diagram illustrating a control configuration for a fixing device in the image forming apparatus according to the embodiment of the present invention. FIG. [Diagram 3] 2 is a block diagram illustrating a control configuration for a heater of a fixing device in an image forming apparatus according to an embodiment of the present invention. FIG. [Figure 4] 5 is a timing chart showing an example of an operation of a heater or the like of the image forming apparatus according to the embodiment of the present invention. [Diagram 5] 6 is a timing chart showing an example of the operation of a heater or the like in an image forming apparatus as a comparative example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to the drawings.

[0024] (Embodiment) An image forming apparatus according to an embodiment of the present invention will be described with reference to the drawings. Fig. 1 is a perspective front view showing a schematic configuration of an image forming apparatus according to an embodiment of the present invention.

[0025] The image forming apparatus 100, which is an electrical device, is a multifunction machine having a copy function, a scanner function, a facsimile function, and a printer function, and transmits to the outside an image of an original G read by an image reading device 102. The image forming apparatus 100 also forms an image of the original G read by the image reading device 102 or an image received from the outside on a sheet P such as paper, in color or monochrome.

[0026] An original feeder 160 (automatic document feeder (ADF)) is provided above the image reading unit 130 and is supported so as to be freely opened and closed relative to the image reading unit 130. The image reading device 102 includes the original feeder 160. The original feeder 160 sequentially transports one or more originals G one by one. The image reading device 102 reads the originals G transported one by one of the one or more originals G by the original feeder 160. The image reading device 102 includes an original placement table 130a on which the originals G are placed, and a placed original reading function that reads the original placed on the original placement table 130a. When the original feeder 160 is opened, the image forming device 100 opens the original placement table 130a above the image reading unit 130, allowing the originals G to be placed manually. Further, the document feeder 160 includes a document placement tray 161 on which the document G is placed, and a document discharge tray 162 on which the document G discharged to the outside is stacked. The image reading device 102 includes a transported document reading function for reading the document G transported by the document feeder 160. The document feeder 160 transports the document G placed on the document placement tray 161 onto the document reading section 130b in the image reading section 130. The image reading section 130 scans the scanning optical system 130c to read the document placed on the document placement table 130a or reads the document G transported by the document feeder 160 to generate image data.

[0027] The image forming apparatus main body 101 includes an image transfer section 50, an optical scanning device 1, an intermediate transfer belt device 70, a secondary transfer device 11, a fixing device 12, a sheet transport path S, a paper feed cassette 18, and a sheet discharge tray 141.

[0028] The image forming apparatus 100 handles image data corresponding to a color image using the colors black (K), cyan (C), magenta (M), and yellow (Y), or a monochrome image using a single color (e.g., black).

[0029] The image transfer unit 50 of the image forming apparatus 100 has four image stations Pa, Pb, Pc, Pd corresponding to the colors black, cyan, magenta, and yellow. Each of the image stations Pa, Pb, Pc, Pd includes a developing device 2, a photoconductor drum 3, a drum cleaning device 4, and a charger 5, and four types of toner images are formed by the image stations Pa, Pb, Pc, Pd. In other words, four each of the developing devices 2, photoconductor drums 3, drum cleaning devices 4, and chargers 5 are provided, each corresponding to black, cyan, magenta, and yellow.

[0030] The optical scanning device 1 exposes the surface of the photoreceptor drum 3 to light to form an electrostatic latent image. The developing device 2 develops the electrostatic latent image on the surface of the photoreceptor drum 3 to form a toner image on the surface of the photoreceptor drum 3. The drum cleaning device 4 removes and collects residual toner on the surface of the photoreceptor drum 3. The charger 5 uniformly charges the surface of the photoreceptor drum 3 to a predetermined potential. Through the series of operations described above, a toner image of each color is formed on the surface of each photoreceptor drum 3.

[0031] The intermediate transfer belt device 70 includes an intermediate transfer roller 6, an endless intermediate transfer belt 71, an intermediate transfer driving roller 72, an intermediate transfer driven roller 73, and a cleaning device 9. The intermediate transfer belt 71 is an endless belt that can rotate, and is wound around the intermediate transfer driving roller 72 and the intermediate transfer driven roller 73. In other words, the intermediate transfer belt 71 is stretched around the intermediate transfer driving roller 72 and the intermediate transfer driven roller 73. Four intermediate transfer rollers 6 are provided inside the intermediate transfer belt 71 so as to form four types of toner images corresponding to the respective colors. The intermediate transfer rollers 6 transfer the toner images of the respective colors formed on the surfaces of the photosensitive drums 3 to the intermediate transfer belt 71.

[0032] The image forming apparatus 100 sequentially transfers and superimposes the toner images of each color formed on the surface of each photosensitive drum 3, forming a color toner image on the surface of an intermediate transfer belt 71 that is stretched between an intermediate transfer driving roller 72 and an intermediate transfer driven roller 73. A cleaning device 9 removes and collects waste toner that has not been transferred to the sheet P and remains on the surface of the intermediate transfer belt 71.

[0033] The secondary transfer device 11 forms a transfer nip area TN between the secondary transfer roller 11a and the intermediate transfer belt 71, and conveys a sheet P conveyed through a sheet conveying path S by pinching it in the transfer nip area TN. When the sheet P passes through the transfer nip area TN, the toner image on the surface of the intermediate transfer belt 71 is transferred to the sheet P, and the sheet P is conveyed to the fixing device 12.

[0034] The fixing device 12 includes a fixing roller 31 and a pressure roller 32 that rotate while sandwiching the sheet P. The fixing device 12 sandwiches the sheet P, on which the toner image has been transferred, between the fixing roller 31 and the pressure roller 32, and applies heat and pressure to fix the toner image to the sheet P. Specifically, a heater 36 (see FIG. 3 ), which is a heat source, is disposed inside the fixing roller 31, and the surface of the fixing roller 31 that comes into contact with the sheet P on which the toner image has been transferred is heated by the heat generated by the heater 36.

[0035] The paper feed cassette 18 is a cassette for storing sheets P used for image formation, and is provided below the optical scanning device 1. The sheet P is pulled out from the paper feed cassette 18 by a pickup roller 16 and conveyed to a sheet conveying path S. The sheet P conveyed to the sheet conveying path S is conveyed to a discharge roller 17 via a secondary transfer device 11 and a fixing device 12, and is discharged to a sheet discharge tray 141 in a discharge section 140. A conveying roller 13, a registration roller 14, and a discharge roller 17 are arranged on the sheet conveying path S. The conveying roller 13 promotes the conveyance of the sheet P. The registration roller 14 temporarily stops the sheet P and aligns the leading edge of the sheet P. The registration roller 14 conveys the stopped sheet P in accordance with the timing of the color toner image on the intermediate transfer belt 71. The color toner image on the intermediate transfer belt 71 is transferred to the sheet P in a transfer nip area TN between the intermediate transfer belt 71 and the secondary transfer roller 11a.

[0036] In FIG. 1, the number of sheet feed cassettes 18 is one, but the present invention is not limited to this. A configuration may be provided in which a plurality of sheet feed cassettes 18 are provided to stack different types of sheets P, respectively.

[0037] Furthermore, when forming an image on the back side of the sheet P in addition to the front side, the image forming apparatus 100 conveys the sheet P in the reverse direction from the discharge rollers 17 to a sheet inversion path Sr. The image forming apparatus 100 inverts the sheet P conveyed in the reverse direction and guides it again to the registration rollers 14. The image forming apparatus 100 also forms an image on the back side of the sheet P guided to the registration rollers 14 in the same manner as on the front side, and conveys the sheet P to the sheet discharge tray 141.

[0038] Here, the image forming apparatus 100 is generally used while being connected to a commercial power source. In other words, the image forming apparatus 100 is driven by an AC power source. If a DC power source is supplied to the image forming apparatus 100, it may not operate normally, which may cause a breakdown or the like.

[0039] Next, a control operation of the fixing device 12 in the image forming apparatus 100 will be described with reference to the drawings. In particular, a control operation of the heater 36 of the fixing device 12 will be described.

[0040] Fig. 2 is a block diagram showing a control configuration for a fixing device in an image forming apparatus according to an embodiment of the present invention, and Fig. 3 is a block diagram showing a control configuration for a heater of the fixing device in an image forming apparatus according to an embodiment of the present invention.

[0041] As shown in Fig. 2, the image forming apparatus 100 is connected to a power source 20. The power source 20 is, for example, a power conditioner for solar power generation that supplies power obtained by solar power generation. As described above, the image forming apparatus 100 is driven by an AC power source. The power source 20 converts DC power obtained by solar power generation into AC power and supplies it to the image forming apparatus 100.

[0042] The image forming apparatus 100 includes a control unit 180 that controls the operation of each component of the image forming apparatus 100. The control unit 180 is configured using, for example, a CPU, a non-volatile memory, and the like, and controls the operation of each component of the image forming apparatus 100. Each component operates upon receiving an instruction from the control unit 180, and the control unit 180 grasps the operating state of each component by signals from each component and manages the operation of each component. Although details will be described later, the control unit 180 outputs a signal g1 to the load control triac 33 in order to control the temperature of the heater 36 (see FIG. 3). When DC power is input from the power source 20, the control unit 180 outputs a signal g2 to the DC power control triac 21 (see FIG. 3).

[0043] Each member of the image forming apparatus 100 operates using AC power supplied from the power source 20 as a driving source. Although omitted in FIG. 2, as described above, the image forming apparatus 100 includes various members such as the image transfer section 50, the optical scanning device 1, the intermediate transfer belt device 70, the secondary transfer device 11, and motors for driving the rollers 13 to 17, in addition to the fixing device 12. Each of these members also operates based on the AC power supplied from the power source 20.

[0044] As described above, the fixing device 12 includes the fixing roller 31 and the pressure roller 32, and the heater 36 for heating the fixing roller 31 is disposed inside the fixing roller 31. As shown in Fig. 3, a circuit is formed for temperature control and overcurrent protection of the heater 36. The heater 36 is capable of generating sufficient heat to heat the fixing roller 31 and fix the toner image on the sheet P, and its resistance value and the like differ depending on the model of the image forming apparatus 100. For example, the resistance value is selected so that a current of about 3 to 4 times the rated current of the heater 36 flows.

[0045] 3, the fixing device 12 includes a heater 36, and an AC circuit 38 having a load control triac 33, a thermostat 34, and a power relay 35 connected in series to the heater 36. An overcurrent operation circuit 37 is connected in parallel to the AC circuit 38. The overcurrent operation circuit 37 has a DC power supply control triac 21 and a current limiting resistor 22, which are connected in series. A polyswitch 23 is connected in series to the AC circuit 38 and the overcurrent operation circuit 37, and AC power is supplied from a power source 20 to a circuit formed by the AC circuit 38, the overcurrent operation circuit 37, and the polyswitch 23.

[0046] First, the configuration of the AC circuit 38 will be described. The heater 36 is a heat source, and generates heat when power is supplied. The heater 36 generates heat, which heats the fixing roller 31, and when the sheet P passes between the fixing roller 31 and the pressure roller 32, the toner (toner image) formed on the sheet P melts, and the toner image is fixed on the sheet P to form an image.

[0047] The load control triac 33 controls the temperature of the heater 36. A triac is a switching element used to control AC current, capable of passing current in both directions, and turns on to conduct current when a trigger signal is applied to the gate terminal. When the AC current being conducted becomes zero, the triac turns off and the AC current is cut off.

[0048] For example, when AC power is supplied to a circuit consisting of a load and a triac connected in series, the time that current is passed through the load can be controlled by controlling the timing of the trigger signal given to the triac. Also, since the triac automatically turns off and cuts off the current when the current passing through it becomes zero, there is no need to give it a signal both on and off. However, when DC current is passed through a triac, unlike AC, the current is constant and never becomes zero, so once a trigger signal is given to the triac to turn it on, it will never turn off and the current will continue to flow.

[0049] A signal g1 for controlling the heater 36 is input from the control unit 180 to the load control triac 33, and when the signal g1 is input to the load control triac 33, the load control triac 33 turns on and an AC current flows through the heater 36. When the AC current becomes 0, the load control triac 33 turns off, and no AC current flows through the heater 36 even if the AC current increases thereafter.

[0050] Thermostat 34 has a function of detecting temperature, and when the detected temperature reaches or exceeds a predetermined temperature, it opens the contacts to cut off the current. Specifically, if the temperature near heater 36 rises too high and reaches an abnormal value, there is a risk of heater 36 breaking down, so thermostat 34 operates to separate the contacts. This cuts off the current to heater 36, and heater 36 stops generating heat.

[0051] The power relay 35 has a function of detecting an abnormality in the power supply circuit used for the control signal, and if an abnormal value is detected, it opens the contacts to cut off the current. Specifically, if the voltage value of the power supplied from the power source 20 becomes abnormal, the control signal becomes abnormal and a control abnormality occurs, so the power relay 35 operates to open the contacts. This cuts off the current to the heater 36, and the heater 36 stops generating heat.

[0052] The AC circuit 38, which has the heater 36, the load control triac 33, the thermostat 34, and the power relay 35, operates normally when powered by an AC power source. If a DC power source were input to the AC circuit 38, a constant current would always flow and would never become zero, as with AC. This would make it impossible for the load control triac 33 to control the heater 36, causing the heater 36 to operate abnormally.

[0053] Furthermore, if a direct current flows through the thermostat 34 and the power relay 35, there is a possibility that the contacts of the thermostat 34 and the power relay 35 may melt due to arc discharge. If these contacts melt, the contacts will not be separated and the short circuit state will be maintained, so the current to the heater 36 will not be cut off.

[0054] In other words, the AC circuit 38 operates normally when an AC power source is input, and even if an abnormality occurs, the thermostat 34 or power relay 35 cuts off the current to properly protect the heater 36 from abnormal operation, but when a DC power source is input, it does not operate normally and there is a possibility that it will not be properly protected.

[0055] Next, the configuration of the overcurrent operation circuit 37 will be described. The DC power supply control triac 21 is a triac, so as described above, once it is turned on, it will not turn off when a DC current is flowing. The DC power supply control triac 21 is turned on and becomes conductive when a signal g2 is input from the control unit 180. When DC power is input from the power supply 20, the control unit 180 detects that DC power is being supplied from the power supply 20 and outputs a signal g2 to the DC power supply control triac 21.

[0056] Here, the control unit 180 has a current sensor 181 using a Hall element. Although not shown, the current sensor 181 scales the output waveform from the power supply 20 and inputs it to a CPU (not shown) of the control unit 180. The CPU may detect whether the output waveform from the power supply 20 is AC or DC. When it is detected that the output waveform from the power supply 20 is DC, the control unit 180 outputs a signal g2.

[0057] It should be noted that other methods may be used to detect that DC power is being output from the power supply 20, rather than using the current sensor 181 using a Hall element. For example, a detection circuit may be provided that uses an electronic element to detect a zero-cross signal in the output from the power supply 20, and detects that DC power is being output when no zero-cross signal is detected. Such a detection circuit may use, for example, a photocoupler.

[0058] The current-limiting resistor 22 is a resistor having a resistance value sufficiently lower than that of the heater 36. The current-limiting resistor 22 preferably has pressure resistance, and may be, for example, a cement resistor. The resistance value of the cement resistor is, for example, 0.5 Ω, which is sufficiently lower than the resistance value of the heater 36.

[0059] Next, the polyswitch 23 will be described. The polyswitch 23 is an overcurrent protection element that cuts off current when a current equal to or greater than a predetermined current value flows. In addition, the polyswitch 23 can be used repeatedly because it can release the cutoff and allow current to flow again if the temperature drops after cutting off the current. Note that an overcurrent is, for example, 20 A to 30 A. In other words, if a current of 20 A or more tries to flow through the polyswitch 23, the polyswitch 23 cuts off the current.

[0060] The operation of the circuit configured by the AC circuit 38, the overcurrent operation circuit 37, and the polyswitch 23 in the fixing device 12 will be described.

[0061] First, in a normal state, AC power is supplied to the image forming apparatus 100 from the power source 20. In this state, the signal g2 is not input to the DC power supply control triac 21, and the DC power supply control triac 21 is in an off state. Therefore, the AC current flows through the path C1 of the polyswitch 23, the power relay 35, the thermostat 34, the heater 36, and the load control triac 33, and no current flows through the DC power supply control triac 21 or the current limiting resistor 22. In this state, the control unit 180 outputs the signal g1 to the load control triac 33 to control the temperature of the heater 36.

[0062] However, if a problem occurs in the power supply 20 and DC power is supplied from the power supply 20, the image forming apparatus 100 is supplied with DC power from the power supply 20. In this case, the current sensor 181 detects that DC power is being supplied from the power supply 20, and the control unit 180 outputs a signal g2 to the DC power supply control triac 21. When the signal g2 is input to the DC power supply control triac 21, the DC power supply control triac 21 turns on, and a current also flows through the DC power supply control triac 21 and the current limiting resistor unit 22. That is, a current flows through the path C2. In addition, since the current input to the load control triac 33 does not become 0, a current also continues to flow through the path C1. That is, a current flows through the paths C1 and C2.

[0063] Therefore, the overcurrent operation circuit 37 and the AC circuit 38 are connected in parallel, and a current flows through the circuit configured by connecting them in series to the polyswitch 23. Here, the resistance value of the current limiting resistor 22 is sufficiently smaller than that of the heater 36, so that the current flowing through the path C2 is larger than that through the path C1. Furthermore, when AC power is supplied from the power source 20, the current flows to the heater 36 side due to the cutoff by the DC power control triac 21. However, when the DC power control triac 21 is turned on and a current flows through the circuit in which the overcurrent operation circuit 37 and the AC circuit 38 are connected in parallel, a current larger than that in the state where a current flows only through the AC circuit 38 flows through the polyswitch 23. As a result, a current (overcurrent) of a predetermined value or more flows through the polyswitch 23, and the polyswitch 23 is cut off.

[0064] The above-mentioned operation will be described with reference to the drawings. Fig. 4 is a timing chart showing an example of the operation of the heater and the like of the image forming apparatus according to the embodiment of the present invention.

[0065] 4, from time t1 to time t7, normal operation occurs, and AC power is supplied from power supply 20. Then, at time t7, some factor causes power supply 20 to supply DC power, and thereafter, power supply 20 continues to supply DC power.

[0066] The control unit 180 controls the temperature of the heater 36, and at time t1 outputs a pulse signal g1 to the load control triac 33. When the signal g1 is input to the load control triac 33, the load control triac 33 turns on and maintains the on state until time t2 when the AC current flowing through the load control triac 33 becomes zero. An AC current having the same waveform as the AC power supplied from the power source 20 flows through the load control triac 33 and the heater 36.

[0067] In this way, an AC current flows through the heater 36 from time t1 to time t2. Here, if the signal g1 is not input to the load control triac 33 at time t2, the load control triac 33 turns off at time t2. However, since the control unit 180 further outputs the signal g1 at time t2, the load control triac 33 remains on, and AC power flows continuously through the heater 36. Then, the on state is maintained until time t3 when the AC current flowing through the load control triac 33 becomes 0 again. As a result, an AC current also flows continuously through the heater 36 until time t3. Therefore, the heater 36 continues to generate heat from time t1 to time t3. Then, since the control unit 180 does not output the signal g1 at time t3, the load control triac 33 turns off, and the current flowing through the heater 36 becomes 0.

[0068] At time t4, the control unit 180 outputs signal g1, but until then (from time t3 to time t4), no current flows through the heater 36, and the heater 36 stops generating heat. By controlling the output of signal g1 in this manner, the control unit 180 controls the heater 36 to start and stop generating heat, thereby controlling the temperature of the heater 36.

[0069] The control unit 180 outputs a signal g1 at time t4, and further outputs the signal g1 at times t5 and t6 when the AC current flowing through the load control triac 33 becomes zero, so that an AC current continues to flow through the heater .

[0070] Incidentally, from time t1 to time t7, the DC power supply control triac 21 is not turned on, so that the AC current flows only through the path C1, and does not flow through the path C2.

[0071] Then, when DC power is supplied from the power supply 20 at time t7, the current flowing through the load control triac 33 becomes a constant value, similar to the DC power supplied from the power supply 20. However, the control unit 180, which detects by the current sensor 181 that DC power is being supplied from the power supply 20, outputs a signal g2 to the DC power supply control triac 21. The input of the signal g2 to the DC power supply control triac 21 turns on the DC power supply control triac 21. This causes the DC current to flow not only through the path C1 but also through the path C2.

[0072] When a current flows through the paths C1 and C2, the value of the current flowing through each of the paths C1 and C2 is determined according to the resistance values ​​of the AC circuit 38 and the overcurrent operation circuit 37. As described above, the resistance value of the current limiting resistor 22 is sufficiently larger than the resistance value of the heater 36, so the value of the current flowing through the overcurrent operation circuit 37 (the value of the current flowing through the path C2) is much larger than the value of the current flowing through the AC circuit 38 (the value of the current flowing through the path C1). In addition, the value of the current flowing through the path C2 is much larger than the state in which no current flows only through the path C1, and an overcurrent flows. When an overcurrent flows, the polyswitch 23 operates to cut off the current flowing through the paths C1 and C2. As a result, the current flowing through the heater 36 becomes zero, and the heater 36 stops generating heat.

[0073] In this way, when DC power is supplied from the power source 20, the heater 36 stops generating heat, and it is possible to prevent problems such as the heater 36 continuing to generate heat and catching fire.

[0074] (Comparative Example) For comparison, the operation of the heater and the like of an image forming apparatus of a comparative example, which is different from the present invention and does not have an overcurrent operation circuit 37, will be described with reference to the drawings. Fig. 5 is a timing chart showing an example of the operation of the heater and the like of the image forming apparatus of the comparative example.

[0075] The image forming apparatus according to the comparative example does not include the overcurrent operation circuit 37, and has a circuit in which the poly switch 23 and the AC circuit 38 are connected in series, that is, a circuit that does not have the path C2 in this embodiment and is composed only of the path C1. The other configuration is the same as that of the image forming apparatus 100 according to the first embodiment. Therefore, in the following description, the same members as those in this embodiment are denoted by the same reference numerals.

[0076] 4, AC power is supplied from the power supply 20 from time t1 to t7, and at time t7, DC power is supplied from the power supply 20. As shown in FIG 5, in the comparative example, the heater 36 also operates normally from time t1 to t7 during which AC power is being supplied from the power supply 20.

[0077] As shown in Fig. 5, times t1 to t7 are the same as in this embodiment, but when DC power is supplied from the power source 20 at time t7, the current flowing through the load control triac 33 does not become 0, so the load control triac 33 does not turn off. Therefore, after time t7, a current continues to flow through the heater 36. In this case, the value of the current flowing through the heater 36 does not change significantly, and an overcurrent does not flow, so the polyswitch 23 does not operate and does not cut off the current. Therefore, a current continues to flow through the heater 36, and the heater 36 continues to generate heat.

[0078] Furthermore, if the AC power supply from power supply 20 changes to a DC power supply, power relay 35 detects this abnormality and attempts to cut off the contacts and cut off the current to heater 36. However, because DC current flows through power relay 35, there is a possibility that the contacts of power relay 35 will melt due to an arc discharge, causing the contacts to not be cut off and resulting in a short circuit, and current will continue to flow to heater 36.

[0079] Thereafter, if the heater 36 continues to generate heat, the thermostat 34 will detect the abnormal temperature and attempt to cut off the current to the heater 36 by disconnecting the contacts. However, because direct current is still flowing, there is a possibility that the contacts of the thermostat 34 will melt due to an arc discharge, causing the contacts to not disconnect and resulting in a short circuit, and current will continue to flow to the heater 36.

[0080] In this way, when DC power is supplied from power supply 20, the polyswitch 23, thermostat 34, and power relay 35, which are components for protecting heater 36, do not function properly, and heater 36 continues to generate heat, eventually resulting in a problem of fire.

[0081] As described above, according to the image forming apparatus 100 of this embodiment, even if the power source 20, which normally supplies AC power, starts supplying DC power due to some factor, the current flowing through the heater 36 can be cut off, thereby preventing the heater 36 from continuing to generate heat, which would otherwise occur.

[0082] Note that, instead of the electronic components and other components in the above-described embodiment, components having similar functions may be used. For example, the configuration using the polyswitch 23 as a component for cutting off current when an overcurrent occurs has been described, but the present invention is not limited to this, and the polyswitch 23 can be replaced with other overcurrent protection components such as a fuse. In addition, the load control triac 33 and the DC power supply control triac 21 control the current flowing through the heater 36 and the current limiting resistor 22, respectively, but depending on the degree of control, they can be replaced with other components such as a thermostat or a power relay.

[0083] In this embodiment, the resistance value of the current limiting resistor 22 is set to 0.5 Ω, and the polyswitch 23 is set to not pass a current of more than 20 A. As described above, since the heater 36 differs depending on the model of the image forming apparatus 100, the current limiting resistor 22 and the polyswitch 23 may be selected to have preferred values ​​depending on the capacity of the heater 36 used in the image forming apparatus 100, etc.

[0084] The overcurrent at which the polyswitch 23 cuts off the current may be set appropriately based on the capacity of the heater 36, etc. The resistance value of the current limiting resistor 22 may be determined based on the resistance value of the heater 36, etc. In other words, the resistance value of the current limiting resistor 22 may be determined so that an overcurrent flows through the overcurrent operation circuit 37 when the DC power supply control triac 21 is turned on and the parallel circuit of the overcurrent operation circuit 37 and the AC circuit 38 is formed. Then, a polyswitch 23 capable of cutting off this overcurrent may be selected. (Another embodiment) Although the embodiment of the present invention has been described above, the present invention is not limited to the above embodiment. For example, in the above embodiment, the image forming apparatus 100 is configured to stop the heater 36 from generating heat when the AC power supplied from the power source 20 changes to a DC power source, but other parts in the image forming apparatus 100 that operate using the AC power source may be configured to stop generating heat when a DC power source is supplied.

[0085] Further, a heater operated by an AC power source in an electric device other than image forming apparatus 100 may be configured to stop when a DC power source is supplied, or a component other than the heater may be configured to stop.

[0086] The present invention is not limited to the above-described embodiment, but can be embodied in various other forms. Therefore, the embodiment is merely illustrative in all respects and should not be interpreted as being limited. The scope of the present invention is indicated by the claims, and is not restricted in any way by the text of the specification. Furthermore, all modifications and changes within the equivalent scope of the claims are within the scope of the present invention. [Explanation of symbols]

[0087] 1 Optical scanning device 2. Developing device 3 Photoconductor drum 4 Drum cleaning device 5. Charger 6 Intermediate transfer roller 9 Cleaning Equipment 11 Secondary transfer device 11a Secondary transfer roller 12 Fixing device 13 Conveyor roller 14 Registration roller 16 Pickup roller 17 Discharge roller 18 Paper feed cassette 20 Power supply 21 Triac for DC power supply control (DC power supply operating part) 22 Current limiting resistor 23 Polyswitch (overcurrent cutoff section) 31 Fuser roller 32 Pressure roller 33 Load control triac (load control component) 34 Thermostat 35 Power Relay 36 Heater 37 Overcurrent operation circuit 38 AC circuit 50 Image transfer section 70 Intermediate transfer belt device 71 Intermediate transfer belt 72 Intermediate transfer drive roller 73 Intermediate transfer driven roller 100 Image forming equipment (electrical equipment) 101 Image forming apparatus main body 102 Image reading device 130 Image reading unit 130a Document stand 130b Document reading section 130c Scanning optics 141 Sheet output tray 160 Document feeder 161 Document tray 162 Document output tray 180 Control Unit 181 Current Sensor C1 pathway C2 Pathway G Manuscript g1, g2 signal P-sheet Pa, Pb, Pc, Pd Imaging Station S Sheet transport path Sr sheet inversion pathway TN Transfer nip area t1~t7 time

Claims

1. An electric device including an AC circuit having a load and a load control member which is a triac connected in series with the load to control the load, an overcurrent operation circuit, which is connected in parallel to the AC circuit and is configured by arranging in series a DC power supply operation unit which is a triac that is turned on by a signal transmitted when a state in which a DC power supply is supplied to the AC circuit, and a current limiting resistor unit having a resistance value lower than that of the load, and through which a current flows when a state in which a DC power supply is supplied to the AC circuit is reached; an overcurrent interruption unit which is a polyswitch connected in series to the AC circuit and the overcurrent operation circuit, The electric device, wherein the overcurrent interruption unit interrupts a current when an overcurrent flows through the overcurrent operation circuit.

2. 2. The electrical device according to claim 1 , The electrical device, wherein the load is a heater for forming an image on a recording medium by thermally fixing a toner image formed on the recording medium.

3. An image forming apparatus that forms a toner image on a recording medium and fixes the toner image formed on the recording medium to form an image on the recording medium, a heater which is a load for thermally fixing the toner image formed on the recording medium; a load control element, which is a triac connected in series with the heater to control the heater; an overcurrent operation circuit, which is connected in parallel to the AC circuit and is configured by arranging in series a DC power supply operation unit which is a triac that is turned on by a signal transmitted when a state in which a DC power supply is supplied to the AC circuit, and a current limiting resistor unit having a resistance value lower than that of the load, and through which a current flows when a state in which a DC power supply is supplied to the AC circuit is reached; an overcurrent interruption unit which is a polyswitch connected in series to the AC circuit and the overcurrent operation circuit, an overcurrent interruption unit that interrupts a current when an overcurrent flows through the overcurrent operation circuit;

Images