JP2004234996A - Heating device, fixing device, and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enhance heating efficiency and shorten rise time of a fixing roller. <P>SOLUTION: A capacitor 35 of an auxiliary power source circuit 2 is charged with a main power source circuit 21 which rectifies voltage supplied from a commercial AC power source 23 and outputs, the supply of the power from the main power source circuit 21 to a fixing heater 12 and the supply of the power from the auxiliary power source circuit 22 are changed over, and when a fixing unit 7 is raised, power is supplied from he capacitor 35 of the auxiliary power source circuit 22 to the fixing heater 12, and the fixing heater 12 is heated to the specified temperature in a short time. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to, for example, a heating device for heating various materials and devices, and a fixing device using the same, and an image forming apparatus such as an electrophotographic copying machine, a printer device, and a facsimile device, and particularly to a reduction in startup time. is there.
[0002]
[Prior art]
[Patent Document 1] Japanese Unexamined Utility Model Application Publication No. Sho 63-150967 [Patent Document 2] Japanese Patent Application Laid-Open No. Hei 10-282821 [Patent Document 3] Japanese Patent Application Laid-Open No. 2000-315567 An image forming apparatus such as a copying machine or a printer is a plain paper. An image is formed on a recording medium such as an OHP or the like. This image forming apparatus employs an electrophotographic method from the viewpoint of high-speed image formation, image quality, cost, and the like. The electrophotographic method is a method in which a toner image is formed on a recording medium and the formed toner image is fixed on the recording medium by heat and pressure. As a fixing method, a heat roller method is currently most frequently used in terms of safety and the like. Have been. In the heat roller method, a fixing roller heated by a heat-generating member such as a halogen heater and a pressure roller arranged opposite to the fixing roller are pressed against each other to form a mutual press contact portion called a nip portion, and a toner image is formed on the nip portion. Is a method of heating through a recording medium on which is transferred.
[0003]
2. Description of the Related Art In recent years, environmental issues have become important, and energy saving has been progressing in image forming apparatuses such as copiers and printers. In considering the energy saving of the image forming apparatus, what cannot be ignored is the power saving of the fixing device that fixes the toner on the recording medium. In order to reduce the power consumption of the fixing device during standby of the image forming apparatus, the temperature of the fixing roller is maintained at a constant temperature slightly lower than the fixing temperature during standby, so that the temperature immediately rises to the usable temperature at the time of use, and the user can use the device. Or waiting for the temperature of the fixing roller to rise. In this case, even when the fixing device is not used, a certain amount of power is supplied to consume extra energy. It is said that the energy consumption during standby increases from about 70% to 80% of the energy consumption of the device.
[0004]
In order to shorten the heating time of the fixing roller, it is preferable to increase the input energy per unit time, that is, the rated power. In fact, many high-speed machines with a high printing speed are compatible with a power supply voltage of 200 V. However, in a general office in Japan, the commercial power supply is 100 V and 15 A, and it is necessary to perform a special work on a power supply in an installation place to correspond to 200 V, which is not a general solution. Also, products that increase the total input power by using two 100V15A systems have been put to practical use, but they cannot be installed unless there are two outlets nearby. For this reason, even if it is attempted to raise the temperature of the fixing roller in a short time, the upper limit of the input energy cannot be increased.
[0005]
In order to improve this, a fixing roller having a built-in heat-generating member is reduced in thickness. However, it is insufficient to raise the temperature of the fixing roller in a short time. Since the fixing heater energizes and heats the input voltage from the AC power supply, the current Ih that can be supplied to the fixing device is the amount of the current It that is supplied from the AC power supply, excluding the current Ie used by devices other than the fixing device. The current flowing through the fixing heater is controlled with the current Ih as an upper limit, so that the fixing heater is maintained at a predetermined temperature. The ratio between the current It and the current Ie is set based on when the current Ie used in a device other than the fixing device is the largest.
[0006]
The amount of heat generated by the fixing heater is proportional to the current supplied to the heater, and the larger the current, the faster the temperature of the fixing roller can be raised. Thus, for example, as shown in Patent Literature 1 and Patent Literature 2, a secondary battery as an auxiliary power supply is charged during standby of the fixing device, and when the fixing device is started, the main power supply and the secondary battery or the primary battery are used. The power supply is used to shorten the rise time, or as shown in Patent Document 3, an auxiliary power supply using a large-capacity capacitor is used in addition to the main power supply. Disconnect the connection, connect the main power supply and the auxiliary power supply, charge the auxiliary power supply, and supply power from the main power supply and the auxiliary power supply to the heating unit when starting the heating unit from the standby state to shorten the temperature of the heating unit. The temperature is raised to a predetermined temperature over time.
[0007]
[Problems to be solved by the invention]
However, since the power supplied to the fixing heater and the power for charging the auxiliary power are turned on and off by using a contact driving element such as a relay, it is difficult to control a current input from a commercial AC power supply. It is.
[0008]
In addition, since the battery or capacitor cannot be charged during the copying operation, if the copying operation is continued after the main switch of the copying machine or the like is turned on, the battery or the capacitor serving as the auxiliary power supply is insufficiently charged. In many cases, sufficient power cannot be supplied from the auxiliary power supply, and the startup time at startup cannot be reduced.
[0009]
Further, a dedicated fixing heater must be provided for supplying power from the auxiliary power supply, which has a disadvantage that the configuration becomes complicated and the apparatus becomes expensive.
[0010]
SUMMARY OF THE INVENTION An object of the present invention is to provide a heating device, a fixing device, and an image forming apparatus which can improve such disadvantages, improve the heating efficiency and shorten the rise time.
[0011]
[Means for Solving the Problems]
A heating device according to the present invention includes a main power supply circuit, an auxiliary power supply circuit, and a heating unit. The main power supply circuit rectifies and outputs a voltage supplied from a commercial AC power supply, and the auxiliary power supply circuit controls the conduction ratio. It has a power storage element connected in series with the element, the heating unit is connected in series with the control element that controls the conduction ratio, is directly connected to the output end of the main power supply circuit, and has a rectifier and a drive element that performs opening and closing operations. Connected to the auxiliary power supply circuit via a parallel circuit of elements, charges the storage element of the auxiliary power supply circuit with the voltage from the main power supply circuit, and supplies power to the heating unit from the main power supply circuit or power from the auxiliary power supply circuit. Is switched.
[0012]
When heating the heating unit is started, electric power is supplied from the auxiliary power supply circuit to the heating unit, and the amount of heat supplied to the heating unit is increased.
[0013]
Further, when the charging voltage of the power storage element of the auxiliary power supply circuit is higher than the voltage of the commercial AC power supply, power is supplied to the heating unit from the auxiliary power supply circuit to stabilize the temperature of the heating unit.
[0014]
Furthermore, the main power supply circuit has a current detection means for detecting the output current, and when the output current detected by the current detection means is equal to or less than a predetermined reference value, the storage element of the auxiliary power supply circuit is charged, The storage element is charged as appropriate.
[0015]
Further, the auxiliary power supply circuit is provided with a means for indicating that the charging voltage of the power storage means is equal to or higher than a predetermined value, thereby preventing a risk of electric shock during maintenance.
[0016]
The fixing device of the present invention is characterized in that it has the heating device, raises the temperature to a predetermined temperature in a short time, and stably maintains the raised temperature.
[0017]
This fixing device is used in an electrophotographic image forming apparatus, and the startup time of the image forming apparatus is reduced.
[0018]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 1 is a block diagram of a copying machine according to the present invention. As shown in the figure, for example, a color tandem copying machine 1 includes a scanner unit 3 that exposes a document sent from an automatic document feeder 2, photoelectrically converts reflected light from the document, and performs signal processing. Writing unit 4 that emits a laser beam in response to a signal from the printer, image forming units 6C, 6Y, 6M, 6Bk of cyan C, yellow Y, magenta M, and black Bk arranged along the transfer belt 5, and an image forming unit 6 includes a fixing unit 7 and a paper feeding unit 8 provided on the downstream side. The image forming units 6C, 6Y, 6M, and 6Bk each include a photoconductor 9 that forms a latent image by the laser beam from the writing unit 4, a charging unit 10 that uniformly charges the surface of the photoconductor 9, and a photoconductor 9 And a developing unit 11 for adhering toner to the latent image formed thereon to visualize the toner image, and transfers toner images of cyan C, yellow Y, magenta M, and black Bk to transfer paper. The fixing unit 7 includes a fixing roller 13 having a fixing heater 12 and a pressure roller 14, as shown in the cross-sectional view of FIG. 2, and heats and presses the toner image transferred onto the transfer paper 15 to fix the toner image.
[0019]
The heating device 20 for heating the fixing heater 12 of the fixing roller 13 has a main power supply circuit 21 and an auxiliary power supply circuit 22 as shown in the circuit diagram of FIG. The main power supply circuit 21 inputs an AC voltage from a commercial AC power supply 23 to a rectifier circuit 25 via a power relay 24 which is a contact driving element. The output of the rectifier circuit 25 is connected to an input current sensor 26, a fixing heater 12 via a low-pass filter unit including a reactance 27 and a capacitor 28, and a switching element 29 for controlling the duty of the fixing heater 12. The fixing roller 13 is provided with a surface temperature sensor 30 for detecting a surface temperature, for example, a thermistor. The auxiliary power supply circuit 22 is connected in parallel to the fixing heater 12 and the switching element 29, is connected in series to a parallel circuit of a power relay 31 and a diode 32, which are contact driving elements, and is duty-controlled by the switching element 33. For example, it has a capacitor 35 composed of an electric double layer capacitor and a voltage detection circuit 36 for detecting an output voltage between both ends of the capacitor 35. The drive circuits 37 and 38 for the switching elements 29 and 33, the input current sensor 26, the surface temperature sensor 30, and the voltage detection circuit 36 are connected to an inverter control circuit 39. The output of the rectifier circuit 25 is divided and supplied to the inverter control circuit 39 by the resistors 41 and 42. The inverter control circuit 39 controls the lighting of the fixing heater 12, the temperature of the fixing roller 13, and the charging of the capacitor 35. The inverter control circuit 39 uses a control signal sent from the engine control unit 43 according to the operation state of the copying machine 1. And the power supply to the fixing heater 12 is switched between the power supplied from the AC power supply 23 and the output voltage of the capacitor 35 of the auxiliary power supply circuit 22. Further, the energization of the fixing heater 12 and the capacitor 35 is performed by controlling the operation of the switching elements 29 and 33 by the respective driving circuits 37 and 38, and the conduction ratio of the switching elements 29 and 33 is applied to the fixing heater 12 and the capacitor 35. The control is performed according to the value of the supplied current.
[0020]
When charging the capacitor 35, the power relay 31 is opened and the power is supplied via the diode 32. When the capacitor 35 is supplied with electricity to the fixing heater 12, the power relay 32 is closed and the diode 32 is bypassed and supplied with power.
[0021]
In the lighting control of the fixing heater 12, when the copying machine 1 is started, that is, when the power is turned on or when the fixing roller 13 returns from the standby mode in which the temperature of the fixing roller 13 is set to a low temperature, the temperature of the fixing roller 13 is set to the target temperature, for example. When the temperature is 180 ° C. or less and the voltage of the capacitor 35 is a reference voltage close to the peak voltage of the AC power supply 23, for example, 110 V or more, the power relay 24 of the AC power supply system is turned off and the power relay 31 of the auxiliary power supply system is turned on. Power is supplied from the capacitor 35 to the fixing heater 12. Since the capacitor 35 can be charged with a DC voltage up to the peak voltage of the AC power supply 23, a current larger than that supplied from the AC power supply 23 can flow to the fixing heater 12. Therefore, when the power relay 24 of the AC power supply system is turned off and the power relay 31 of the auxiliary power supply system is turned on, the inverter control circuit 39 increases the conduction ratio of the switching element 29 and sets the conduction ratio of the switching element 33 to 100%. A large current flows through the fixing heater 12. That is, the conduction ratio of the switching element 29 and the input current of the fixing heater 12 are substantially proportional as shown in FIG. 4, and the input current of the fixing heater 12 can be increased by increasing the conduction ratio of the switching element 29. . As a result, a larger current can be supplied to the fixing heater 12 than when power is supplied from the AC power supply 23 to the fixing heater 12, and the amount of heat supplied to the fixing roller 13 is greatly increased. Is restored, the rise time of the fixing roller 13 can be shortened.
[0022]
When a current is supplied from the capacitor 35 to the fixing heater 12, even if the switching element 33 is not turned on, the discharge can be performed by the parasitic diode existing in parallel. The voltage is sufficiently low with respect to the forward voltage of the parasitic diode. For example, for a voltage drop of 0.2 V due to the ON resistance of the switching element 33, a voltage drop of the parasitic diode is 0.7 V. The switching element 33 is turned on to efficiently supply current from the capacitor 35 to the fixing heater 12.
[0023]
When a current flows through the fixing heater 12, the capacitor 35 discharges to lower the charging voltage. Therefore, the voltage of the capacitor 35 is detected by the voltage detection circuit 36, and when the voltage of the capacitor 35 falls to, for example, 100 V or less which is the voltage of the AC power supply 23, the power relay 31 is turned off and the power relay 24 is turned on to The power is supplied to the fixing heater 12 from the power supply system, and the capacitor 35 is charged when the input current detected by the input current sensor 26 has a margin. In order to charge the capacitor 35, an upper limit value of the charging current and a charging coefficient for the upper limit value are set in advance according to the operation state of the copying machine 1. For example, when the upper limit of the current flowing to the main power supply circuit 21 is 13 A when the copying machine 1 is not operating and the upper limit of the current flowing to the main power supply circuit 21 is 9 A while the copying machine 1 is operating, the upper limit current and the fixing The capacitor 35 is charged by varying the conduction ratio of the switching element 33 according to the conduction ratio of the switching element 29 that controls the current flowing through the heater 12.
[0024]
Since the electric double layer capacitor constituting the capacitor 35 does not involve a chemical reaction, it can be rapidly charged for about several minutes. When charging the capacitor 35, the inverter control circuit 39 turns off the switching element 33 when the charging voltage of the capacitor 35 detected by the output voltage detecting circuit 36 reaches a predetermined charging voltage, for example, 130V. To end. By charging the capacitor 35 when the input current has a margin or during standby, when the fixing heater 12 is started up or when the copier 1 is operating and necessary, the capacitor 35 is charged. Current can be supplied stably.
[0025]
By charging the capacitor 35, the voltage remains in the capacitor 35 even when the power of the copier 1 is not turned on. If maintenance of the copying machine 1 is performed in this state, there is a risk of electric shock. Therefore, as shown in the circuit diagram of FIG. 5, the charging voltage is divided by the resistors 44 and 45 to the voltage detection circuit 36 for detecting the charging voltage of the capacitor 35, and the divided voltage is input to the inverter control circuit 39 as a detection signal. , 45 are provided in series with a display means 46 such as a light emitting diode, for example, to display the state of charge of the capacitor 35. By displaying the state of charge of the capacitor 35 in this way, it is possible to prevent electric shock due to the voltage of the capacitor 35 during maintenance. Here, the display means 46 may be connected to both ends of a series circuit of the capacitor 35 and the switching element 33. Further, in order to reduce the influence of ON / OFF of the switching element 33, the collector voltage of the switching element 33 may be detected together.
[0026]
There is a limit to the current that can be supplied from the power supply to which the copying machine 1 is connected. When the copying machine 1 is continuously operated, the upper limit current assigned to the fixing heater 12 is supplied from the main power supply circuit 21 of the heating device 20. In some cases, the temperature of the fixing roller 13 cannot be maintained. This is particularly remarkable when the heat radiation from the fixing roller 13 is large, such as at low temperatures or when passing thick paper. Therefore, when the current supplied from the auxiliary power supply circuit 22 can flow more than the current supplied from the main power supply circuit 21 to the fixing heater 12, that is, when the capacitor 35 is sufficiently charged, the current is supplied from the capacitor 35 to the fixing heater 12. Thus, it is possible to prevent the temperature of the fixing roller 13 from being lowered while the copying machine 1 is operating. Therefore, while the copying machine 1 is operating, the inverter control circuit 39 detects the input current of the main power supply circuit 21 detected by the input current sensor 26 provided in the main power supply circuit 21 and the input current of the capacitor 35 detected by the voltage detection circuit 36. By comparing the current that can be supplied to the fixing heater 12 according to the charge amount, the power consumption of each part of the copying machine 1 increases, the input current of the main power supply circuit 21 is limited and reduced, and the charge amount of the capacitor 35 is reduced. Accordingly, when the current that can be supplied to fixing heater 12 is larger than the input current of main power supply circuit 21, a current is supplied from capacitor 35 to fixing heater 12, and the temperature of fixing roller 13 is set to a predetermined temperature while copying machine 1 is operating. maintain.
[0027]
For example, when the total input current of the copying machine 1 is 15 A, the current consumption of the fixing heater 12 is 13 A or less when the copying machine 1 is not operating, and the upper limit is about 9 A when the copying machine 1 is operating. . The inverter control circuit 39 controls the temperature of the fixing roller 13 detected by the surface temperature sensor 30 to a predetermined value, for example, 180 ° C., with the conduction ratio corresponding to this current as an upper limit. Although the fixing heater 12 is driven under such conditions, if the charging voltage of the capacitor 35 detected by the output voltage detecting circuit 36 is higher than the reference voltage, for example, 110 V, while the copying machine 1 is operating, Power supply from the power supply circuit 21 to the fixing heater 12 is cut off, and current flows from the capacitor 35 to the fixing heater 12. The current flowing from the capacitor 35 to the fixing heater 12 is proportional to the charging voltage of the capacitor 35 as shown in FIG. 6, for example, when the capacitor 35 is charged to the peak voltage of the AC power supply 23, the charging voltage becomes 140 V, A current of 18 A can flow through 12. The current can be greatly increased from the current flowing from the main power supply circuit 21.
[0028]
【The invention's effect】
As described above, the present invention charges a storage element of an auxiliary power supply circuit with a main power supply circuit that rectifies and outputs a voltage supplied from a commercial AC power supply and supplies power to the heating unit from the main power supply circuit. Since the power supply from the auxiliary power supply circuit is switched, when the power supplied from the commercial AC power supply to the main power supply circuit decreases, the power supply from the auxiliary power supply circuit to the heating unit can be performed. The part can be stably heated.
[0029]
In addition, when heating the heating unit, electric power is supplied from the auxiliary power supply circuit to the heating unit, the amount of heat supplied to the heating unit is increased, and the heating unit can be heated to a predetermined temperature in a short time.
[0030]
Further, when the charging voltage of the power storage element of the auxiliary power supply circuit is higher than the voltage of the commercial AC power supply, electric power is supplied to the heating unit from the auxiliary power supply circuit, and the temperature of the heating unit can be constantly maintained stably.
[0031]
Further, a current detecting means for detecting an output current is provided in the main power supply circuit, and when the output current detected by the current detecting means is equal to or less than a predetermined reference value, the storage element of the auxiliary power supply circuit is charged. Thus, the power storage element can be appropriately charged, and a large amount of power can be stably supplied from the power storage element to the heating unit.
[0032]
Further, by providing the auxiliary power supply circuit with a means for indicating that the charging voltage of the power storage means is equal to or higher than the predetermined value, the risk of electric shock during maintenance can be prevented, and safety can be improved.
[0033]
Further, by using this heating device for the fixing device of the image forming apparatus, the temperature of the fixing device can be raised to a predetermined temperature in a short time and the raised temperature can be stably maintained.
[0034]
By using this fixing device in an electrophotographic image forming apparatus, the start-up time of the image forming apparatus can be shortened and a high quality image can be stably formed.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of a copying machine according to the present invention.
FIG. 2 is a cross-sectional view illustrating a configuration of a fixing unit.
FIG. 3 is a circuit diagram illustrating a configuration of a heating device that heats a fixing heater.
FIG. 4 is an output characteristic diagram with respect to a conduction ratio and an input current.
FIG. 5 is a circuit diagram showing a configuration of a voltage detection circuit.
FIG. 6 is a graph showing a change characteristic of a fixing heater current with respect to a capacitor charging voltage.
[Explanation of symbols]
1; copying machine; 2; automatic document feeder; 3; scanner unit;
5; transfer belt; 6; image forming unit; 7; fixing unit;
9; photoconductor, 12; fixing heater, 13; fixing roller, 14;
20; heating device, 21; main power supply circuit, 22; auxiliary power supply circuit,
23; commercial AC power supply, 24; power relay, 25; rectifier circuit,
26; input current sensor, 29, 33; switching element,
30; surface temperature sensor, 31; power relay, 32; diode,
35; a capacitor; 36; a voltage detection circuit, 37, 38;
39; an inverter control circuit.

Claims (7)

It has a main power supply circuit, an auxiliary power supply circuit, and a heating unit,
The main power supply circuit rectifies and outputs the voltage supplied from the commercial AC power supply,
The auxiliary power supply circuit has a storage element connected in series with a control element that controls the conduction ratio,
The heating unit is connected in series with the control element that controls the conduction ratio, is directly connected to the output terminal of the main power supply circuit, and is connected to the auxiliary power supply circuit through a parallel circuit of a drive element that performs opening and closing operations and a rectifying element. And
A heating device that charges a storage element of an auxiliary power supply circuit with a voltage from a main power supply circuit and switches between supplying power to the heating unit from the main power supply circuit and supplying power from the auxiliary power supply circuit. The heating device according to claim 1, wherein when starting heating the heating unit, electric power is supplied from the auxiliary power supply circuit to the heating unit. The heating device according to claim 1, wherein power is supplied from the auxiliary power supply circuit to the heating unit when the charging voltage of the storage element of the auxiliary power supply circuit is higher than the voltage of the commercial AC power supply. 2. The power supply element of the auxiliary power supply circuit, wherein the main power supply circuit has current detection means for detecting an output current, and when the output current detected by the current detection means is equal to or less than a predetermined reference value. 4. The heating device according to any one of claims 1 to 3. 5. The heating device according to claim 4, wherein said auxiliary power supply circuit is provided with means for indicating that the charging voltage of the power storage means is equal to or higher than a predetermined value. A fixing device comprising the heating device according to claim 1. An image forming apparatus comprising the fixing device according to claim 6.

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