Heater circuit and image forming apparatus

Abstract

To provide a heater circuit that, in order to prevent damage in advance, initially checks the presence or absence of an abnormality in a planar heater with DC power, and when there is no abnormality, energizes the planar heater with AC power, and an image forming apparatus.SOLUTION: A heater circuit comprises: a heater 35; an AC power supply that is connected with an AC current line L1 supplying AC current to the heater 35; a DC power supply that is connected with a DC current line L2 supplying DC current to the heater 35; a heater temperature detection unit 36 that, when the DC current is supplied to the heater 35, detects the temperature of the heater; and a control board 80 that determines whether the heater is in a circuit abnormality state on the basis of comparison between the temperature detected by the heater temperature detection unit 36 and a threshold. When determining that the heater is in the circuit abnormality state, the control board 80 does not perform a fixing operation with the AC power supply. The control board 80 determines whether the heater is in the circuit abnormality state before determining whether to perform the fixing operation.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a heater circuit and an image forming apparatus including a fixing device having the heater circuit. [Background technology]

[0002] Electrophotographic image forming devices print by forming a toner image on paper and fixing the toner image to the paper using a fixing device. The fixing device is equipped with a heating member and a pressure member, and performs the fixing process by sandwiching the paper between the two members and applying heat and pressure. The heating member is heated by a heat generating element (heater), and the temperature of the heating member is controlled by the current flowing through the planar heater.

[0003] The current used is alternating current (AC) power. Compared to direct current (DC) power, AC power has a larger amount of power and puts an overload on the circuit. If a problem occurs in the planar heater circuit and an overcurrent is generated in the planar heater, it can cause the fixing device to break down.

[0004] Patent document 1 describes a method for detecting abnormalities in an auxiliary lamp by turning on only an auxiliary lamp out of multiple lamps for a predetermined period of time at any time when printing processing is not being performed and detecting the change in temperature of the heating roller during that time.

[0005] Patent Document 2 describes a method for cutting off power to a heat source when the current flowing to the heat source exceeds a predetermined value.

[0006] Patent Document 3 describes a method in which a current sensor and a circuit breaker are provided for each of a plurality of heat generating parts, and abnormalities in the heat generating parts are detected individually using the detected current amounts. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2010-244051 A [Patent Document 2] JP 2017-090570 A [Patent Document 3] JP 2018-073769 A Summary of the Invention [Problem to be solved by the invention]

[0008] Planar heaters have an excellent temperature-raising effect, and so in recent years they are often used as heating elements for heating elements. Planar heaters are often placed in close proximity to the heating element. When an abnormal current flows through a planar heater, the temperature of the planar heater rises suddenly, and not only the heater itself but also the heating element itself and surrounding parts may be damaged. This places a burden on users, such as repairing the device and replacing parts. Also, even if an abnormality in the planar heater is detected and the circuit operation is stopped, it is often too late.

[0009] The present invention aims to prevent damage to the heater by first checking for the presence or absence of an abnormality in the heater using DC power, and if no abnormality is found, supplying AC power to the heater. [Means for solving the problem]

[0010] A heater circuit according to one aspect of the present invention includes a heater, an AC power supply connected to an AC current line that supplies AC current to the heater, a DC power supply connected to a DC current line that supplies DC current to the heater, a heater temperature detection unit that detects the temperature of the heater when the DC power supply is supplied to the heater, and a control unit that determines whether or not a circuit abnormality is occurring based on a comparison between the temperature detected by the heater temperature detection unit and a predetermined threshold value, and the control unit does not perform fixing operation using the AC power supply if it determines that a circuit abnormality is occurring. An image forming apparatus according to one aspect of the present invention includes an image forming section that forms an image on a sheet of paper, and a heater circuit according to one aspect of the present invention. Effect of the Invention

[0011] According to the present invention, the heater is first checked for abnormalities using DC power, which has a relatively smaller current than AC power, and if no abnormalities are found, AC power is applied to the heater. Therefore, when an abnormality is detected, a relatively small current flows through the heater, and even if current is passed through the heater when an abnormality occurs, the heater is less likely to be damaged, making it possible to prevent damage to the heater before it occurs. [Brief description of the drawings]

[0012] [Figure 1] FIG. 2 is a front cross-sectional view showing the structure of the image forming apparatus. [Diagram 2] FIG. 2 is a schematic cross-sectional view of a fixing device. [Diagram 3] FIG. 2 is a diagram showing an example of an electrical configuration of a heater circuit. [Figure 4] 4 is a flowchart showing an operation of the image forming apparatus. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Each embodiment will be described in detail below with reference to the accompanying drawings.

[0014] An image forming apparatus according to an 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. Figure 1 is a front cross-sectional view showing the structure of an image forming apparatus 1 in this embodiment.

[0015] The image forming apparatus 1 is configured by including an apparatus main body 99, an operation unit 4, an image forming unit 61, a paper feed unit 14, and the like.

[0016] When the image forming apparatus 1 performs a printing operation, the image forming unit 61 forms a toner image on the paper P fed from the paper feed unit 14 based on image data and the like obtained from the outside.

[0017] When color printing is performed, the magenta image forming unit 61M, the cyan image forming unit 61C, the yellow image forming unit 61Y, and the black image forming unit 61BK of the image forming section 61 form a toner image on the photosensitive drum through processes of charging, exposing, and developing based on an image consisting of each color component constituting the image data, and the toner image is transferred onto the intermediate transfer belt 991 by the primary transfer roller 6. The cartridge 61M contains magenta toner, the cartridge 61C contains cyan toner, the cartridge 61Y contains yellow toner, and the cartridge 61BK contains black toner. These cartridges are detachable from the device main body 99, and when the toner runs out, the user or maintenance staff replaces them with new cartridges.

[0018] 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 feed unit 14.

[0019] The fixing device 20 holds the paper P having the toner image thereon at a nip portion N and applies heat and pressure to 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 having the color image formed thereon and having undergone the fixing process is discharged to a discharge tray 151. The paper feed section 14 stores the paper P.

[0020] The operation unit 4 includes, for example, a menu key for calling up a menu, a decision key for confirming various operations and settings, a start key, etc. The display unit 41 is a liquid crystal display (LCD: Liquid Crystal Display) or an organic light-emitting diode (OLED: Organic Light-Emitting Diode) display, etc., and displays messages, operation screens, etc. to the user.

[0021] 2 is a schematic cross-sectional view of the fixing device 20. The fixing belt 21 rotates in the direction indicated by the arrow 21y around a rotary shaft 21a, and has a heater 35 at a position facing the inner surface of the fixing belt 21. 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. In this embodiment, the heater 35 will be described as being a planar ceramic heater.

[0022] Pressure member 22 rotates in the direction indicated by arrow 22y about rotation shaft 22a, applies pressure to the outer surface of fixing belt 21, and also clamps transported paper P at nip portion N to apply pressure to paper P. As paper P is transported in the direction indicated by arrow Y, the toner image is heated by fixing belt 21 and is pressurized by pressure member 22, so that the toner image is fixed to paper P.

[0023] FIG. 3 is a schematic diagram of a heater power supply control device 70 of the fixing device 20 having the heater 35 and the like.

[0024] 3, the heater power supply control device 70 is made up of a heater power switching drive unit 60 and a control board 80. However, in FIG. 3, the configuration of the fixing device 20 is also shown and described.

[0025] The fixing device 20 includes a heater temperature control unit 34 (THERMO CUT OFF), a heater 35, and a thermistor (an example of a heater temperature detection unit in the claims) 36. The heater temperature control unit 34 (THERMO CUT OFF) and the heater 35 are connected in series. The control board 80 includes a CPU (Central Processing Unit) 82.

[0026] The heater power switching drive unit 60 includes a fuse 61, a relay 62, a cutoff circuit 63, a first TRIAC (first switching element) 65, a second TRIAC (second switching element) 64, and a third TRIAC (third switching element) 66. The fuse 61 and relay 62 are connected in series and are collectively referred to as an AC stop control unit.

[0027] A TRIAC (Triode for Alternating Current) is a switching element that can control bidirectional current with one gate electrode.

[0028] The fuse 61 of the AC stop control unit has one end connected to one end (LIVE side) of the AC power source 67, and the other end connected to one end of the relay 62.

[0029] The other end of the relay 62 is connected to a first heater power transmission line L1 (an AC line in the claims: a cable or a conductive pattern). The first heater power transmission line L1 is connected to an input end of the heater temperature control unit 34 (THERMO CUT OFF).

[0030] The heater temperature control unit 34 (THERMO CUT OFF) is a thermal fuse, which turns off when a predetermined threshold value is reached, thereby cutting off the circuit.

[0031] On the other hand, one end of the first TRIAC (first switching element) 65 is connected to the other end (NEUTRAL side) of the AC power supply 67, and the other end is connected to the first heater power transmission line L1. This first heater power transmission line L1 (cable or conductive pattern) is connected to the output end of the heater 35.

[0032] Furthermore, in this embodiment, the input terminal of the interrupter circuit 63 is connected to a DC power supply 68, and the output terminal of the interrupter circuit 63 is connected to an input terminal of a second TRIAC (second switching element) 64. Also, the output terminal of the second TRIAC (second switching element) 64 is connected to the first heater power transmission line L1.

[0033] Next, the control board 80 will be described. The control board 80 is composed of a CPU section 82 (Central Processing Unit), a RAM (Random Access Memory), a ROM (Read Only Memory), and a dedicated hardware circuit. The CPU section 82 functions as a control section by operation according to a control program stored in the ROM. The CPU section 82 is an example of a control section in the claims. The CPU section 82 has the following connection configuration. The operation will be described later.

[0034] The CPU section 82 outputs a HEAT_ON signal, a DC_ON signal, and a RELAY_ON signal, and receives an output TH (temperature: thermistor current or thermistor voltage) from the thermistor (heater temperature detection section) 36 .

[0035] The HEAT_ON signal is output to the gate of the first TRIAC (first switching element) 65. The DC_ON signal from the CPU unit 82 is output to the gates of the interrupter circuit 63, the second TRIAC (second switching element) 64, and the third TRIAC (third switching element) 65.

[0036] The CPU section 82 is connected to the relay 62 , and the RELAY_ON signal from the CPU section 82 is input to the drive coil of the relay 62 .

[0037] Furthermore, the CPU section 82 receives an output TH (temperature: thermistor current or thermistor voltage) from a thermistor (heater temperature detection section) 36.

[0038] The relationships among the AC voltage Vi, the AC current Ii, the DC voltage Vd, and the DC current Id are AC voltage Vi>DC voltage Vd, and AC current Ii>DC current Id.

[0039] The control board 80 loads the following programs from the ROM to the RAM. In accordance with these programs, the CPU unit 82 executes AC power stop processing at the start of printing, DC power supply processing before printing, surface heater abnormality determination processing, error processing, and AC power supply processing during normal printing, etc. An outline of these processes will be described below.

[0040] In the AC stopping process at the start of printing, the CPU unit 82 stops the output of the RELAY_ON signal and HEAT_ON signal in response to a print start instruction (before heater is turned on: before fixing), turns off the relay 62 and the first TRIAC (first switching element) 65 of the AC stop control unit, and stops the supply of AC power Pi (AC voltage Vi × AC current Ii) to the heater 35.

[0041] In the pre-printing DC power supply process, the CPU unit 82, in response to a print start instruction (before heater is turned on: before fixing), outputs a DC_ON signal that turns on the cutoff circuit 63, the second TRAIAC 64, and the third TRAIAC 66, supplies DC power (DC voltage Vd x DC current Id) from the DC power source to the fixing device 20, and causes it to flow to earth 69 via the third TRAIAC 66 to drive the heater 35 at low power.

[0042] In the planar heater abnormality determination process, the CPU section 82 reads the output (TH) from the thermistor (36: temperature detection sensor) of the fixing device 20 in response to the supply of DC power Pd, and determines whether the temperature is equal to or lower than the threshold value (reference value) stored in the memory 84. Note that, taking into consideration cases of disconnection, it may be determined that an abnormality exists even when no increase in temperature is observed, and the same control as when the temperature is equal to or higher than the threshold value (reference value) may be performed.

[0043] In error processing, when the CPU section 82 detects a temperature above the threshold (high temperature: abnormality), it displays an error on the display section 41. Also, the fixing operation by the AC power supply 67 is not performed.

[0044] In the normal printing AC power supply process, when the CPU section 82 is below the threshold (constant current: low temperature), it determines that the heater 35 is normal, accepts a print start instruction, outputs a RELAY_ON signal to the relay 62 of the AC stop control section, turns the DC_ON signal off (low level), outputs a HEAT_ON signal, and turns on the relay 62 and the first TRIAC 65 ​​of the AC stop control section to supply AC power 67 (AC voltage Vi × AC current Ii) to the heater 35.

[0045] That is, the heater power supply control device 70 has a configuration in which a TRIAC is inserted into the heater power supply lines (L1, L2) to input AC power and DC power mutually exclusively.

[0046] This allows an abnormality in the DC power to be detected before the heater 35 is turned on (before it is driven), thereby reducing the possibility of the heater 35 being damaged and preventing the damage caused by the abnormality from spreading.

[0047] The operation of the heater power supply control device 70 configured as above will be described with reference to the flow chart of FIG.

[0048] Please refer to Fig. 4. First, when a print start command is input, the CPU section 82 stops output of the RELAY_ON signal and HEAT_ON signal before fixing by performing AC stop processing at the start of print.

[0049] That is, the CPU part 82 turns off the relay 62 and the first TRIAC (first switching element) 65 of the AC stop control part. As a result, the supply of AC power (AC voltage Vi × AC current Ii) to the heater 35 is stopped.

[0050] Furthermore, the CPU section 82 performs pre-printing DC power supply processing, and outputs a DC_ON signal in response to a print start instruction (before heaters are turned on: before fixing) (S10).

[0051] That is, the CPU unit 82 turns on the interrupter circuit 63, the second TRAIAC 64, and the third TRAIAC 66 (in a drive state). As a result, DC power (DC voltage Vd×DC current Id) from the DC power supply 68 is supplied to the fixing device 20 (planar heater temperature control unit 34, heater 35) via the second heater power transmission line (DC current line) L2, and flows to the earth 69 via the third TRAIAC 66. That is, low DC power (DC voltage Vd, DC current Id) equal to or lower than the AC power flows through the planar heater 35.

[0052] Next, the CPU section 82 reads the output (TH) from the thermistor 36 of the fixing device 20 as the heater abnormality determination process starts with the output (high level) of the DC_ON signal (with the supply of DC power) (S12).

[0053] Then, the CPU section 82 performs a heater abnormality determination process to determine whether or not the output indicates a circuit abnormality including a temperature abnormality (S14). That is, a direct current is applied to check for the presence or absence of an overcurrent.

[0054] Specifically, the CPU section 82 judges whether the output (TH) from the thermistor 36 is equal to or lower than a threshold value (voltage or current).

[0055] In step S14, if the CPU section 82 determines that the temperature is abnormal (a circuit abnormality as defined in claims), it causes the display section 41 to display a message indicating an error (S16).

[0056] As a result, even if a sudden temperature rise occurs because the heater 35 is in contact with the belt, an abnormality in the temperature of the heater 35 can be detected with a relatively small current of DC power before a relatively large current of AC power is supplied to the fixing device 20, thereby preventing damage to the heater 35 and peripheral devices. This makes it possible to avoid problems such as a sudden rise in temperature of the heater 35, which is a planar heater, causing damage to not only the heater 35 itself, but also the heating member body and surrounding parts.

[0057] Furthermore, in step S14, if the CPU section 82 determines that there is no abnormality in the temperature (below the threshold: temperature is low), it performs normal printing AC power supply instruction processing, determines that the surface heater 35 is normal, accepts a print start instruction, outputs a HEAT_ON signal to the relay 62 of the AC stop control section, turns the DC_ON signal off (low level), and outputs the HEAT_ON signal to turn the relay 62 of the AC stop control section and the first TRIAC 65 ​​on (driven state) (S18).

[0058] As a result, the cutoff circuit 63, the second TRAIAC 64, and the third TRAIAC 66 are turned off (non-driven), and the supply of DC power Pd to the second heater power transmission line L2 is stopped, but AC power flows through the fuse 61, the relay 62, and the first heater power transmission line L1 to the fixing device 20 (heater temperature control unit 34, heater 35), and then flows to the other end (NEUTRAL) of the AC power source via the first heater power transmission line L1 and the first TRIAC 65.

[0059] In this way, the heater power supply control device 70 detects an abnormality in the heater 35 by inserting a TRIAC (Triode for Alternating Current) in the heater power supply lines (L1, L2) to allow exclusive input of AC (Alternating Current) and DC (Direct Current), and stops the supply of AC power until the abnormality is resolved, thereby reducing the possibility of damage and preventing the spread of damage caused by the abnormality.

[0060] In other words, even if the heater 35 is close to or in contact with the heating member and the temperature of the heater 35 has risen before AC power is supplied, a small DC power is supplied before AC power is supplied and an abnormality determination is performed, so that an abnormality determination can be performed without damaging the heater 35.

[0061] This reduces the possibility of damage to the heater 35 and surrounding components, and minimizes damage from failure.

[0062] The present invention is not limited to the configuration of the above embodiment, and various modifications are possible. In the above embodiment, the configuration and processing shown in the above embodiment using Figures 1 to 3 are merely one embodiment of the present invention, and the present invention is not limited to the configuration and processing. For example, in the above embodiment, an example of a switching element is described as a TRIAC (Triode for Alternating Current), but any switching element that can pass power (current) to both sides by gate control may be used. [Explanation of symbols]

[0063] 1. Image forming device 4 Control section 6 Image forming section 21 Fixing belt 20 Fixing device 34 Heater temperature control unit 35 Heater 36 Thermistor (heater temperature detector) 80 Control section 60 Heater power switching drive unit 61 Fuse 62 Relay 63 Breaking Circuit 65 The first TRIAC 64 The second TRIAC 66 The third TRIAC

Claims

1. A heater and an AC power source connected to an AC line that supplies AC current to the heater; a DC power supply connected to a DC line for supplying a DC current to the heater; a heater temperature detection unit that detects a temperature of the heater when the direct current power is supplied to the heater; a control unit that determines whether or not a circuit is abnormal based on a comparison between the temperature detected by the heater temperature detection unit and a predetermined threshold value, The control unit is a heater circuit that does not perform a fixing operation using the AC power source when it determines that the control unit is in an abnormal state.

2. The heater circuit according to claim 1 , wherein the control unit determines whether or not to perform the fixing operation after determining whether or not the circuit is in an abnormal state.

3. a first switching element connected to the AC current line, a second switching element connected to the DC current line, and a third switching element connected to the DC current line; 3. The heater circuit according to claim 2, wherein when the control unit determines that the circuit is in an abnormal state, it outputs an off signal to the first switching element, and when the control unit does not determine that the circuit is in an abnormal state, it outputs an on signal to the first switching element and outputs off signals to the second switching element and the third switching element.

4. The heater circuit according to claim 1 , wherein the heater is a planar ceramic heater.

5. an image forming unit that forms an image on a sheet; An image forming apparatus comprising: the heater circuit according to claim 1 .

Images