JP2002124370A - Induction heating device, and image processing device provided with the induction heating device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an induction heating device, that is capable of making efficient control operation by avoiding increase of loss, at a low power occurring in the inverter. SOLUTION: The induction heating inverter is constructed of an induction coil 2 connected in parallel, and a switching element 5 that connects and disconnects the supply of direct current power source to the capacitor 4. Switching operation is controlled by a circuit 71, that controls a drive circuit 6 of the element. In order to fix the operation of inverter in the input power, in which the inverter operates at the maximum efficiency, the frequency of the control circuit 71 is made a constant value. The heating control is made, by controlling 'on'/'off' of the operation of the control circuit 71 of the fixed frequency. This control input is conducted through feedback of the detected voltage of the temperature transducer 12.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an induction heating apparatus in which a high frequency current is supplied to an induction coil by an inverter, and controls an inverter operable under conditions of input power at which a maximum efficiency or a minimum loss is achieved by an on / off operation. The present invention relates to a power-saving induction heating device capable of controlling heat generation by performing heat generation, and which can be used also in a heating and fixing section of toner in an electrophotographic process.

[0002]

2. Description of the Related Art Conventionally, in an image processing apparatus such as a copying machine, a printer, and a facsimile, an image is formed by an electrophotographic system. In this method, in order to fix the developed toner image on an image forming material such as a recording sheet or paper,
A fixing device is provided. The main part of this fixing device is composed of a fixing roller that heats the sheet to which the unfixed toner is attached, and a pressure roller that presses the sheet between the fixing roller and pinches and conveys the sheet. Such a fixing device conventionally includes a halogen lamp or the like as a heater inside the fixing roller, heats the fixing roller with the lamp, and raises the fixing roller to a predetermined target temperature suitable for fixing required by the toner. Was something. However, such a heating method using a halogen lamp takes a long time to heat the fixing roller to a required temperature, and also causes a large loss of the heater itself, so that environmental problems such as global warming are present. There is a concern that the system will be closed up and adverse effects on the environment. To solve this problem, a fixing device with high efficiency and a short rise time is required.

Under such circumstances, it has been studied to use an induction heating device for heating during fixing. An induction heating device generates high frequency current through an induction coil disposed near a heating member, generates electromagnetic waves, and causes induction (eddy) current due to the electromagnetic waves to flow through a conductive layer of the heating member, thereby heating with Joule heat accompanying the induction current. The heating to a predetermined temperature is performed by controlling the high-frequency current. 2. Description of the Related Art A fixing device using an induction heating method has attracted attention because it has a characteristic that a fixing roller can be instantaneously heated by an eddy current caused by an electromagnetic wave, and the time required for heating can be dramatically shortened. In other words, the preheating operation required by the conventional halogen lamp method, that is, the operation of continuously supplying power to raise the temperature of the fixing unit to a predetermined temperature quickly at the time of re-use even when the apparatus is in standby without using the apparatus, results in a result. It is considered as one of the methods that can contribute to environmental problems because it can reduce wasteful electric power and has good heating efficiency. Copiers using fixing by induction heating usually detect the temperature of the fixing roller with a thermistor, control an inverter for induction heating according to the detected voltage, and supply a high-frequency current generated by the inverter to the induction coil. Then, the fixing roller is operated to reach the target temperature. Therefore, when the target temperature changes or the fixing temperature changes, the operation of the inverter is controlled so as to change the power supplied to the induction coil.

[0004]

By the way, the inverter for induction heating which performs such a control operation is required to operate with high efficiency, and is usually designed to have the maximum efficiency at the rated power used. . FIG. 5 is a diagram showing power efficiency and loss as characteristics of the inverter with respect to input power. As shown in FIG. 5, the loss of the inverter does not always reach the maximum at the maximum power, but tends to increase at low power. In particular, depending on the circuit configuration of the inverter and the selection of circuit constants, it is possible to avoid a hard switching operation (operation in which the switching loss of the voltage and current of the switching element becomes large) at the time of low power as shown in FIG. It often happens that power is not saved, which hinders power saving. The present invention has been made in view of such problems in the conventional induction heating device, and has as its object to provide a conventional inverter with an increase in loss at low power or conditions under which hard switching occurs (for example, when the load is In the case of lightness, it is generated depending on the circuit system and operating conditions. (Refer to FIGS. 6 and 7 described below.) In addition, the induction heating device capable of reducing the loss and performing the energy-saving operation and the induction heating device are provided. An object of the present invention is to provide an image processing apparatus (for example, a copying machine, a facsimile, a printer, or a multifunction peripheral thereof).

[0005]

According to a first aspect of the present invention, there is provided an induction heating apparatus comprising an induction coil for inductively heating a heating member, switching means for interrupting an input to the induction coil, and control means for controlling on / off of the switching means. In the induction heating device having an inverter, the control unit performs a constant control operation to supply power such that the induction heating inverter operates at at least one of the maximum conversion efficiency and the minimum loss. An induction heating apparatus comprising means for controlling an output from the means by an on / off operation.

According to a second aspect of the present invention, there is provided the induction heating device according to the first aspect, further comprising a temperature detecting means for detecting a temperature of the heating member heated by the induction coil, and turning on / off an output from the control means for detecting the detected temperature. It is characterized in that feedback is provided through means for controlling by an OFF operation.

According to a third aspect of the present invention, there is provided an image processing apparatus in which the induction heating device according to the first or second aspect is used as an electrophotographic image heating and fixing means.

According to a fourth aspect of the present invention, there is provided the image processing apparatus according to the third aspect, further comprising means for operating the induction heating device when the image processing apparatus is in a standby state with low power consumption. It is characterized by.

According to a fifth aspect of the present invention, in the image processing apparatus according to the third or fourth aspect, the induction heating device is operated when a heating member in the heat fixing processing means is at a temperature lower than a predetermined temperature. It is characterized by comprising means.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described based on the following embodiments shown in the accompanying drawings. Prior to the description of the present embodiment, an induction heating device (preceding example) on which the present embodiment is based will be described below. This example shows an apparatus applied to an image heating and fixing means in an electrophotographic image processing apparatus (for example, a copying machine, a facsimile, a printer, or a multifunction peripheral thereof). FIG. 6 shows a schematic configuration of the induction heating device of the prior art. FIG. 7 shows an example of an operation waveform of a switching element that supplies power to a coil (induction coil). Reference numeral 1 in FIG. 6 denotes a fixing roller to be heated. Reference numeral 2 denotes a coil (induction coil) for generating an electromagnetic wave, and reference numeral 4 denotes a capacitor. The supply of DC power (not shown) to the coil 2 and the capacitor 4 connected in parallel is interrupted by the switching element 5.
These are the basic elements that make up the induction heating inverter. The switching element 5 includes a driving circuit 6, a driving circuit 6,
The switching operation is performed by the control circuit 7 of FIG. The detection voltage of the temperature sensing element (thermistor or the like) 12 and the detection voltage of the input of the switching element 5 for controlling the resonance operation under the ZVS (zero volt switching) condition are supplied to the control circuit 7 via the amplifier 9 and the Trig signal output amplifier 11, respectively. Is input to Referring to FIGS. 6 and 7, the operation of the prior art will be described. By switching the switching element 5 of the inverter, a high-frequency current flows through the coil 1 to generate an eddy current in the fixing roller and heat it. This temperature is detected by the thermistor 12, compared with a reference voltage, and PWM or frequency control is performed to change the pulse width or frequency so that the temperature of the fixing roller 1 becomes constant. In this case, the input voltage of the switching element 5 is monitored so that the switching element 5 operates with the minimum switching loss, and the control circuit 7 is triggered by the output of the Trig signal output amplifier 11 that detects zero of the input voltage of the switching element 5. Then, the switching element 5 is turned on, and the switching element 5 is operated under the ZVS (zero volt switching) condition in which the time zone where the current and the voltage intersect is minimized.

FIG. 7 is a diagram showing operation waveforms of such an inverter. Note that, in the same figure, the current and voltage waveforms of the switching element are plotted on the same time axis (in this example,
FET drain current Id, drain-source voltage V
ds) together. FIG. 7A shows the operation under the ZVS condition. However, in practice, the time zone at which the current and the voltage intersect may not be able to be set to zero due to a change in the load of the inverter, and such an operation under the ZVS condition cannot always be obtained. FIG. 7A shows a case where the load is heavy, and FIG. 7B shows a case where the load is light. As shown in the waveform when the load is light, depending on the operating conditions,
The current Id and the voltage Vds overlap (the shaded portion in the figure), resulting in a hard switching operation, and the loss increases. FIG.
Shows the characteristics of the efficiency and the loss with respect to the input power Pin of such an inverter, and the inverter usually has a maximum load (in the figure, an input power Pin with respect to the maximum load).
(Indicated as 1), it is designed to have the maximum efficiency near, but at light load, depending on the circuit system and operating conditions,
As shown in the low-power operation in the loss curve of FIG. 5, hard switching is likely to occur, the loss does not decrease when the load is light, and the loss often becomes larger than at the maximum load.

According to the present invention, there is provided a system in which a hard switching state does not occur due to the operation of the above-mentioned prior art system.
The present invention relates to an induction heating device which can always operate at a maximum efficiency with a small loss of an inverter, and its embodiment will be described below. This example shows an apparatus applied to an image heating and fixing means in an electrophotographic image processing apparatus (for example, a copying machine, a facsimile, a printer, or a multifunction peripheral thereof). FIG. 1 is a diagram illustrating a configuration of an induction heating device according to the present embodiment. Reference numeral 1 in FIG. 1 denotes a fixing roller to be heated. Reference numeral 2 denotes a coil (induction coil) for generating an electromagnetic wave, and reference numeral 4 denotes a capacitor. Coil 2 connected in parallel
The supply of DC power (not shown) to the capacitor 4 is interrupted by the switching element 5. These are the basic elements that make up the induction heating inverter. The switching element 5, the switching operation is controlled by the control circuit ₇₁ for controlling the driving circuit 6. A control amplifier 8 that feeds back a detection voltage of a temperature sensing element (such as a thermistor) 12 to an operation of the switching element 5 is provided. In the device of this embodiment, the inverter fixes the input power Pin of the inverter to Pin1 (see FIG. 5) so that the inverter operates at the maximum efficiency. Therefore, to operate fixed to a constant value a frequency of the control circuit ₇₁ for controlling the drive circuit 6 (In the prior example, was subjected to control to the target temperature set value by changing the frequency). Temperature control of the fixing roller 1 is either on / off operation of the control circuit 7 ₁ fixed frequency, thinning control output is carried out by controlling the one of the intermittent. By performing such control, power is intermittently supplied to the inverter that generates the drive current for the coil 2. As means for performing the on / off control, and the temperature of the thermistor 12 is compared with the reference voltage which is a target temperature set point, the control circuit _71, a signal for turning on / off the operation An output control amplifier 8 is provided.

FIG. 2 shows waveforms for explaining the operation of this embodiment. The ON / OFF control signal output from the control amplifier 8 and the current and voltage waveforms of the switching element 5 controlled by the ON / OFF control signal are shown in FIG. (In this example, the drain current Id and the drain-source voltage Vds of the FET) are shown. As shown by the operation waveforms in the figure, the switching element 5 operates during the on period of the on / off control signal to supply power to the inverter, and the switching element 5 suspends operation during the off period to supply power to the inverter. To stop. In this case, the switching element 5 is operated at a voltage and a current in a state where power is supplied at the maximum efficiency during the operation period. The operation of the inverter may not always have the minimum loss at the maximum efficiency, and in such a case, a condition for controlling the input power with a small loss may be selected. FIG. 3 shows an example of operation when hard switching occurs (at the time of operation when the load of FIG. 7B by the circuit shown in FIG. 6 is light) and an operation state of this embodiment, respectively.
(A) and (B). In the figure, T is the controlled temperature, Pin is the input power of the inverter, Pl
oss indicates power loss. As shown in FIG. 3A, in the control in a state where the hard switching occurs in the low power operation mode, switching loss occurs continuously, and the total power loss becomes large. On the other hand, in the present embodiment shown in FIG. 3 (B), since the on / off operation is performed with a large power that does not cause hard switching and minimizes the loss, the total loss power is reduced. Can be operated. In the case where the temperature T is large, as in the case of the present embodiment shown in FIG. 3B, when the OFF interval is long, the ripple of the temperature of the fixing roller becomes large. An operation in which efficiency is prioritized is performed as long as no problem occurs in the result. Although not shown in FIG. 1, the circuit constituting the inverter of this embodiment includes a Trig signal output amplifier 11 for controlling the resonance operation as in the conventional example. Also, here has been described only in the control of turning on / off operation of the control circuit 7 _first fixed frequency, the ON / OFF signal, decimating control decimating the drive signal, or a drive signal for controlling the intermittent output A similar function can be realized by using a signal.

Next, a preferred application example of the induction heating device which operates with low power consumption shown in the above embodiment will be described. Although it has been described with reference to FIG. 3B that power-saving induction heating can be performed by the above-described embodiment, as shown in FIG. 3B, in the control of the inverter according to this embodiment, a fixed-frequency control circuit is used. 7 ₁ of the operation on / off and to turn on / off control signal as to be longer off time,
Power loss is reduced. In this case, as shown by T in FIG. 3B, the temperature change becomes larger than in the prior example of FIG. 3A, but in the case of induction heating, the fixing roller 1 is heated in a short time due to heating by electromagnetic induction. There is an advantage that the temperature of can be increased. For this reason, the induction heating device can be suitably implemented in the standby mode where there is no problem even if the temperature change is large. The standby mode is an operation conventionally used in a copying machine or the like, in which the temperature of the fixing roller 1 is set lower than the use temperature, and the standby mode is a standby mode in a low power consumption state. Since it is desirable that the return from the standby state be performed promptly, the induction heating device of the present invention, which can shorten the startup time to the use state and realize the energy saving effect of the standby state, is effective for this purpose. Will provide the means. On the other hand, since the temperature of the fixing roller 1 can be increased in a short time by the induction heating device, conventionally, when returning the heat fixing processing unit from the low power consumption state, it is determined as a startup time to the use state. Fixing roller 1 during standby required to clear the set target time
Target temperature can be kept low. Therefore, the induction heating device of the present invention is an effective means even in such a case. For example, even when the target temperature setting of the fixing roller at the time of standby is controlled to be 125 ± 25 ° C. lower than the conventional target temperature of 185 ° C., it is possible to secure the conventional start-up time. Such an operation can be realized by changing the setting of the temperature reference voltage in the circuit configuration of FIG.

Next, the power-saving operation mode, which operates by turning on / off the operation of the fixed-frequency control circuit shown in the above-described embodiment, and the operation mode by variable frequency or PWM control are selected by switching. An embodiment of an induction heating device capable of performing an operation in a mode will be described. The following example shows an apparatus applied to an image heating and fixing unit in an electrophotographic image processing apparatus (for example, a copying machine, a facsimile, a printer, or a multifunction peripheral thereof). FIG. 4 is a diagram illustrating a configuration of the induction heating device according to the present embodiment. Reference numeral 1 in FIG. 4 denotes a fixing roller to be heated. Reference numeral 2 denotes a coil (induction coil) for generating an electromagnetic wave, and reference numeral 4 denotes a capacitor. The supply of DC power (not shown) to the coil 2 and the capacitor 4 connected in parallel is interrupted by the switching element 5. These are the basic elements that make up the induction heating inverter. The switching element 5, the switching operation is controlled by the control circuit 7 ₂ for controlling the driving circuit 6. It has two control systems for feeding back the detection voltage of the temperature sensing element (thermistor or the like) 12 to the operation of the switching element 5.

[0016] 1 strains, fixed frequency mode for controlling the operation of the inverter by the control circuit 7 ₂ operation on / off operating at (inverter frequency corresponding to the input power to operate at maximum efficiency) (Figure 1 This is a system that executes the same configuration. In the feedback loop of this system, the temperature of the thermistor 12 is compared with a reference voltage serving as a target temperature set value, and the control circuit 7 is controlled according to the comparison result.
₂ is provided with a control amplifier 8 for outputting a signal for turning on / off the operation. Another system is PWM
Or is a system for executing a mode for controlling the operation of the inverter (based on the same configuration as FIG. 6) by operating the control circuit 7 ₂ in the frequency control. The feedback loop of the system, the temperature of the thermistor 12 is compared with the reference voltage which is a target temperature set point, the control circuit 7 ₂ in accordance with the comparison result, PWM or for frequency control to change the pulse width or frequency Is provided. In this embodiment, two control systems are switched and used. Therefore, controlling a switching circuit 10 performs switching of the control circuit 7 ₂ by the control switching signal to the feedback loop for performing a mode that operates in mode or PWM & Frequency control operates at a fixed frequency, different operating inverter Is performed.

[0017] For example, as the control switching signal, using a standby signal generated when moving to the energy-saving standby mode, by switching the control switching circuit 10 by the standby signal, so that exert control circuit 7 ₂ operating at a fixed frequency . That is,
It switched by, inputs a detection value of the thermistor 12 to the control amplifier 8, on / off control operation of the control circuit 7 ₂ by a signal from the control amplifier 8. The control switching signal when the operation is inputted to the control circuit 7 _2, the switching to the mode that operates at a fixed frequency. Here, although described only in control of turning on / off operation of the control circuit 7 ₂ fixed frequency, the ON / OFF signal, decimating control decimating the drive signal, or, for control of intermittently outputs a drive signal A similar function can be realized by using the signal of Also, the return signal from the standby state, switches the control switching circuit 10, so that exert control circuit 7 ₂ in PWM or frequency control is another mode.
That is, the detection value of the thermistor 12 is changed to PW by switching.
M or type to the amplifier 9 which outputs a signal for frequency control, to operate the control circuit 7 ₂ by a signal from the amplifier 9. With the above operation, on / off control is performed during the standby time when the input power is the smallest, and by performing PWM or frequency control during use, the operation can be optimized in terms of both energy saving and control performance.

Next, a description will be given of an embodiment in which the switching operation in the induction heating apparatus capable of switching the control mode shown in FIG. 4 is performed by another method. In the above embodiment, the control is switched at the time of transition to the energy saving standby mode and at the time of returning from the energy saving standby mode. In the present embodiment, the control is switched based on the temperature of the fixing roller. . As described above, when driving the inverter with low power, it is possible to increase the efficiency by operating in the fixed frequency operation mode. When the temperature falls below the temperature and becomes lower, the control mode is switched by the detection signal. The control mode can be switched basically in the same manner as in the above-described induction heating device of FIG. However, the control switching circuit 10 and the control circuit 7
_As the control switching signal of No. ₂ , it is detected that the temperature state of the fixing roller has become lower than a predetermined temperature and that the fixing roller has returned to a high temperature, and the detection signal is used. Since the temperature of the fixing roller is detected by the thermistor 12, it is checked whether the detected voltage value has dropped below a predetermined value or has risen above a predetermined value, and a control switching signal generated according to the check result is transmitted to the control switching circuit 10 and the control circuit. 7 ₂ respectively input, and activates the switch. When operating in the energy saving standby mode, these predetermined values are set to values corresponding to the temperatures held by the fixing roller during standby and during use. In addition,
Again, it is described only in control of turning on / off operation of the control circuit 7 ₂ fixed frequency, on / off signal, thinning control decimating the drive signal, or a signal for controlling the intermittent output a drive signal By doing so, a similar function can be realized.

[0019]

(1) Effects corresponding to the first aspect of the invention The on / off, thinning, and intermittent control operations of the induction heating inverter are performed with the maximum efficiency or the minimum loss, so that the conversion efficiency is good and the energy is saved. It is possible to provide an induction heating device capable of controlling heating. (2) Effects corresponding to the second aspect of the invention In addition to the effects of the above (1), by performing feedback control based on the temperature detected by the temperature detecting means of the heating member, the temperature of the heating member can be controlled. An induction heating device having high temperature control performance can be provided. (3) Effects corresponding to the third aspect of the invention An image processing apparatus (for example, a copying machine, Facsimile, printer, or a multifunction peripheral thereof)
By realizing the effect (2), the performance of the image processing apparatus can be improved. (4) Effects corresponding to the invention of claim 4 In addition to the effect of the above (3), when the image processing apparatus is in a standby state with low power consumption, it is turned on with the maximum efficiency or the minimum loss of the induction heating inverter. / Off, thinning, intermittent control operation, and temperature control,
Since the input power is small, it is possible to enhance the energy saving efficiency during standby, which was low energy saving efficiency in the past. Enables optimization of operation on both sides. (5) Effects corresponding to the fifth aspect of the invention In addition to the effects of the above (3) and (4), the temperature of the heating member (for example, the fixing roller) in the heating and fixing processing means is fed back, so that the fixing Since the inverter can be controlled at the lowest temperature that satisfies the performance, it is possible to provide an energy-saving type image processing apparatus with little loss.

[Brief description of the drawings]

FIG. 1 shows a schematic configuration of an embodiment of an induction heating device using an inverter according to the present invention.

FIG. 2 shows an operation waveform in the embodiment of FIG. 1, showing an on / off control signal fed back, a current of a switching element, and a voltage waveform.

3A and 3B show an operation state of the induction heating device, wherein FIG. 3A shows a case where hard switching has occurred, and FIG. 3B shows a case according to the present invention.

FIG. 4 shows a schematic configuration of another embodiment of the induction heating device using the inverter according to the present invention.

FIG. 5 shows characteristics of an inverter with respect to input power,
FIG. 3 is a diagram illustrating power efficiency and loss.

FIG. 6 shows a schematic configuration of one induction example of an induction heating device using an inverter.

7A and 7B show current and voltage waveforms of a switching element during operation of an inverter. FIG. 7A shows a case where a load is heavy, and FIG.
Indicates the case where the load is light.

[Explanation of symbols]

1. Heating member 2. Induction coil
4 ... capacitor, 5 ... switching device, 6 ... drive circuit, _7,7 1,
7 ₂ : drive control circuit, 10: control switching circuit,
11 ... temperature-sensitive element (thermistor, etc.)

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Akiko Miyahara 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Co., Ltd. (72) Inventor Jiro Ouchi Shimido, Nakanamiji, Shibata-cho, Shibata-gun, Miyagi Prefecture 3-1 In Tohoku Ricoh Co., Ltd. (72) Masae Sugawara Inventor Masamichi Sugawara, Shibata-cho, Shibata-gun, Miyagi Prefecture Nakamei Ichimoji 3-1 F-term in Tohoku Ricoh Co., Ltd. 2H033 BE06 CA07 CA27 CA45 CA48 3K059 AB19 AB20 AB23 AB28 AC33 AD03 AD07 AD25 BD02 BD07 CD09 CD10 CD13 CD18 CD66 CD75 CD77

Claims (5)

[Claims] 1. An induction heating apparatus comprising: an induction coil for induction heating of a heating member; switching means for interrupting an input to the induction coil; and control means for controlling on / off of the switching means. The control means performs a constant control operation so as to supply electric power for operating the inverter with at least one of the maximum conversion efficiency and the minimum loss, and the output from the control means is controlled by an on / off operation. An induction heating device, comprising: 2. The induction heating apparatus according to claim 1, further comprising temperature detection means for detecting the temperature of the heating member heated by the induction coil, and controlling the detected temperature by turning on / off an output from the control means. Induction heating device characterized by feeding back via means. 3. An image processing apparatus, wherein the induction heating apparatus according to claim 1 is used as an electrophotographic image heating / fixing unit. 4. The image processing apparatus according to claim 3, further comprising means for operating the induction heating device when the image processing apparatus is in a standby state with low power consumption. apparatus. 5. The image processing apparatus according to claim 3, further comprising means for operating the induction heating device when a heating member in the heating and fixing processing means is at a temperature lower than a predetermined temperature. Characteristic image processing device.