JP2004163594A - Heating device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To appropriately control a heating means (infrared heater) before becoming unusable due to the disconnection etc. <P>SOLUTION: A voltage to be outputted from a DC power generation circuit 20 to the heating means 14 is controlled at a prescribed target value (heater rated-voltage) by a control means 17, and the reduction ratio (a ratio to an initial value) of the current flowing in the heating means and detected by a current detecting means 10 at the time of controlling is calculated, and then, by comparing the obtained value with the current reduction ratio of the using limit (prediction based on the known reduction ratio at the disconnection time), whether the heating means reaches the usable limit is decided, then, information on the usable limit is given before the occurrence of the disconnection. The decision of the use propriety is performed every fixed period, and data on the decision is accumulated as history data. Error checking is applied on the current reduction ratio based on the history data, and also, by referring to the history data, it is confirmed whether or not the failure is an early accident such as a sudden disconnection, and then, the heating means is appropriately controlled. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a heating device that drives a resistor with a DC whose voltage can be controlled, and more specifically, to the heating device and the fixing of a toner image, which include means for predicting a use limit such as disconnection due to deterioration of the resistor. The present invention relates to a device for forming an image by an electrophotographic process using the heating device (for example, a copying machine, a printer, a facsimile machine, and a device combining these functions).
[0002]
[Prior art]
2. Description of the Related Art Conventionally, a heating device that drives a resistor with controllable power is mounted on various devices and used to change temperature conditions in the devices.
For example, in a copying machine that forms an image by an electrophotographic method, it is known that a temperature condition necessary for a process of fixing a toner image on recording paper by melting and pressing is set by heating control of a resistor heater. For example, Patent Documents 1 and 2 below can be exemplified.
[0003]
[Patent Document 1]
JP 2000-315567 A
[Patent Document 2]
JP-A-2002-51467
[0004]
Patent Document 1 discloses a configuration in which power supply to a heating unit (halogen heater) is divided into a form in which only a main power supply and an auxiliary power supply are added, and power stored in a capacitor of the auxiliary power supply is added to the main power supply at the time of start-up. It is what it was. In this case, a DC power is supplied to the heating means.
Patent Document 2 discloses a configuration in which AC power is supplied, and the AC power is switched at a high frequency to control the power applied to a heating unit (fixer heater).
However, in Patent Literature 1, when the power is supplied to the heating means by turning on / off the DC power, a large change in current applied to the heating means occurs. In Patent Literature 2, a pulse voltage is applied to the heating means. Therefore, in any of the examples, there is a factor that the deterioration of the heating means progresses rapidly and shortens the life. In the latter case, since the AC power is switched at a high frequency, there is also a problem that the noise terminal voltage increases and the filter becomes large in size and high in cost.
[0005]
By the way, it is known that the characteristics (including changes with time such as life) of various heaters (lamps) using resistors used as heating means are as follows. Here, an infrared heater (lamp) conventionally used as a heating means for fixing in an electrophotographic process will be described as an example.
Infrared heaters are such that most of the input power is infrared rays and heat rays. For example, when the temperature of the filament is 3000 ° K, 84% is infrared rays.
In this type of heater, a value [lm / W] obtained by dividing the luminous flux [lm] by the power consumption [W] is used to represent the efficiency. This value indicates the ratio of luminous flux to power consumption. The higher the filament temperature, the higher this value.
When the voltage is changed by turning on the heater, the temperature of the filament changes, and the resistance changes according to the change, and the current, power, luminous flux, efficiency, and life change. This change in characteristics is not necessarily constant depending on the type of light bulb, shape, filament manufacturing conditions, etc.If these conditions are specified, a certain relational expression holds, so apply this relational expression. It is possible to determine the change.
As a long-term change over time, when the integrated lighting time from the start of use elapses in a unit of 100 hours to 1000 hours, the luminous flux gradually attenuates as the time elapses. This is because the tungsten particles evaporate from the surface of the filament, which is heated to a high temperature, and adhere to (blacken) the glass of the enclosed bulb, and the filament becomes thin. In this state, the luminous flux only attenuates. Instead, the current gradually decreases, the power and efficiency gradually change, and eventually the wire breaks. The way light flux, current, power, and efficiency change over time is called working, and is used by developers as basic data when developing products.
[0006]
In addition, when referring to the life, generally, the life is the time until the lighting becomes impossible (: the entire life) or the lighting until the luminous flux becomes a certain ratio of the standard initial luminous flux before the lighting becomes impossible, for example, 80%. Time (: effective life).
It is known that the reduction rate of the luminous flux upon disconnection is, for example, 16 to 20% for a vacuum coil light bulb, 8 to 10% for a gas-filled single coil light bulb, and 5 to 6% for a gas-filled double coil light bulb. . Further, it is known that the rate of decrease in current at the time of disconnection is about 9% for a vacuum coil bulb and about 3% for a gas-filled bulb.
Further, it is known that the effect of the use condition on the life is shortened by, for example, approximately 2 to 8% (within 10%) when the blinking is repeated like a blinking sign. In particular, the ratio is larger for thicker filaments, but the cause is blinking and overshooting. (At the beginning of lighting the bulb, the electric resistance of the filament is much smaller than that of incandescent lamps. This is considered to be caused by the occurrence of a current flowing phenomenon) and repeated heating of a part of the filament.
In a tungsten lamp, a 1% error in voltage is said to indicate an error of about 14% in the life. By detecting this voltage error, it is converted into a life at the rated voltage, and the voltage at the rated voltage is calculated. Enables collation with work data.
[0007]
[Problems to be solved by the invention]
Since the characteristics such as the life of the heater (lamp) using the resistor are captured as described above, even when the deterioration of the heater progresses quickly (for example, see Patent Documents 1 and 2). It is possible to predict the life of the heater used. On the other hand, conventionally, in the case of an image forming apparatus such as a copying machine, since the operation history of the apparatus is stored as management information, it is possible to know the approximate apparatus state including the operating conditions of the heater, the integrated operation time, and the like. In the market based on the data, maintenance personnel actually check at the time of inspection and replace parts when necessary.
However, variations in device characteristics and cases in which inspections are not performed in a timely manner may overlap, and even if the heaters are approaching the usage limit and the characteristics are degraded, they may be left as they are, or in the worst case, As a result, there is a situation in which quick response and replacement of the heater during maintenance for replacement of the heater are not performed.
SUMMARY OF THE INVENTION The present invention has been made in view of the above-described problems of the related art, and has as its object to heat a heating unit having a resistor as an element, a DC power supply for supplying DC power to the heating unit, and heating from a DC power supply. In a heating device having a power supply control means for controlling a voltage output to the means, it is possible to monitor a change over time of the heating means and perform appropriate management at a usable limit that can be predicted before a disconnection occurs. An object of the present invention is to provide the heating device having the above means and an image forming apparatus using the heating device for fixing a toner image.
[0008]
[Means for Solving the Problems]
The invention according to claim 1 is a heating apparatus including a heating unit having a resistor as an element, a DC power supply for supplying DC power to the heating unit, and a power supply control unit for controlling a voltage output from the DC power supply to the heating unit. A current detecting means for detecting a current supplied to the heating means, and a current detected by the current detecting means when a voltage output from the DC power supply to the heating means is controlled to a predetermined target value by the power control means. By comparing the current decrease rate of the current with respect to the initial current value with the current decrease rate at the predicted use limit, thereby determining whether the heating means has reached the use limit. It is a characteristic heating device.
[0009]
According to a second aspect of the present invention, in the heating device according to the first aspect, the predetermined target value controlled by the power supply control means is a rated voltage value of the heating device.
[0010]
According to a third aspect of the present invention, in the heating device according to the first or second aspect, the availability determination unit performs a determination process at regular intervals and stores data relating to each determination as history data. It is characterized by having.
[0011]
According to a fourth aspect of the present invention, in the heating device according to the third aspect, a means for presenting the accumulated history data when the usability determining means determines that the heating means has reached a use limit is reached. It is characterized by having.
[0012]
According to a fifth aspect of the present invention, in the heating device according to any one of the first to fourth aspects, when the usability determining unit determines that the heating unit has reached the usage limit, the unit notifies the user of the fact. It is characterized by having.
[0013]
According to a sixth aspect of the present invention, there is provided an image forming apparatus having an image forming unit by an electrophotographic process, wherein the heating unit according to any one of the first to fifth aspects is used to heat a fixing portion of a toner image in the image forming unit. An image forming apparatus characterized by using:
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
The present invention will be described based on the following embodiments shown in the accompanying drawings.
As an embodiment related to the heating device, a heating unit used in a fixing unit of an image forming apparatus that forms an image by an electrophotographic process is exemplified here.
Further, when the image forming apparatus exemplified in the embodiment is a copying machine, a series of operations of reading a document, forming an image based on document image data, and finally outputting a copy in response to a user operation of a copy request. It is necessary to provide a component (not shown) for performing the copying process described above, but the configuration can be the same as that of the existing apparatus except for the heater circuit (see FIG. 1) of the fixing unit.
That is, the operation unit is provided with keys, a display, and the like for allowing the user to issue setting conditions and start instructions in a dialog system. For reading the document, a mechanism using an ADF (automatic document feeder) or a scanner scanning method is used.
In addition to a main power switch provided to switch on and off the 100 V commercial power supplied through the indoor breaker, the power supply sub key for switching between a power supply state during use and a standby state is provided.
In the case of a copying machine, a scanner (reading) unit for photoelectrically converting a document image and generating a document image signal in an apparatus body, and image processing for converting and processing the read image signal into a data form usable on the output side A unit (IPU: Image Processing Unit) and an image forming unit for forming an image on a recording medium (paper) by an electrophotographic process based on image data are provided. The electrophotographic process performed here is basically based on the following well-known process. That is, an electrostatic latent image is generated on the surface of a photoreceptor by optical writing based on image data, toner (developer) is adhered to the latent image, developed with toner, and the toner image is transferred to recording paper. This is a process in which the transferred toner image is fixed on recording paper by fusing and pressing.
[0015]
Next, the fixing unit in the image forming apparatus (copier) of the present embodiment will be described in more detail.
FIG. 1 is a block diagram illustrating a configuration related to a heater circuit of a fixing unit according to an embodiment of the present invention.
Here, the configuration and operation related to the heater circuit for realizing the temperature control function of the fixing unit will be described in detail with reference to FIG.
In the fixing section, the fixing roller heated to a high temperature is brought into contact with the transfer paper, and the toner image placed on the transfer paper by the electrophotographic process is melted and fixed on the transfer paper by heat from the roller and pressure from the pressing means. . The fixing roller has a built-in heating means 14 made of a resistor which generates heat when energized, and a temperature detecting means 16 for detecting the surface temperature of the roller heated by the heating means 14 in the vicinity of the roller. The control means 17 controls the DC power generation circuit 20 in accordance with the difference between the temperature required for fixing and the detected temperature, thereby changing the DC power supplied to the heating means 14 and changing the roller surface temperature to a predetermined value. Maintain to be.
In the present embodiment, for example, an infrared heater can be used as the heating unit 14, and a thermistor can be used as the temperature detection unit 16, for example.
In the vicinity of the heating means 14, a temperature fuse 15 for disconnecting the circuit when the temperature reaches an abnormal temperature is provided to prevent a situation such as abnormal heating due to a failure of the heater circuit or the like, and smoking and ignition. When the control unit 17 determines that the detection value from the temperature detection unit 16 is abnormal, the control unit 17 turns off the relay 3 provided at the input stage of the AC power supply 1 to cut off the power supply to the heating unit 14. .
[0016]
The AC power supply 1 is provided with a filter circuit 2 so that noise from the DC power generation circuit 20 does not affect the AC power supply 1.
The output of the filter circuit 2 passes through a relay 3 and is subjected to full-wave rectification by a full-wave rectification circuit 4 as first rectification means. FIG. 2 shows an AC voltage waveform input to the full-wave rectifier circuit 4, and FIG. 3 shows a full-wave rectified output voltage waveform from the full-wave rectifier circuit 4.
The positive side of the full-wave rectifier circuit 4 is connected to a noise absorbing capacitor 6, an input voltage detection circuit 7, and a choke coil 8 via a transistor 5 as a second switch. The other ends of the noise absorbing capacitor 6 and the input voltage detecting circuit 7 are connected to the negative side of the full-wave rectifier circuit 4. The other end of the choke coil 8 is connected to the collector or drain of the transistor 9 as the first switch and the anode of the diode 11 as the second rectifier. The emitter or the source of the transistor 9 is connected to the negative side of the full-wave rectifier circuit 4. The cathode of the diode 11 is connected to the smoothing capacitor 12, the output voltage detecting means 13 and the heating means 14, and the other end of the smoothing capacitor 12 and the output voltage detecting means 13 is connected to the negative side of the full-wave rectifier circuit 4. . Note that the second rectifier using the diode 11 may be a transistor.
The other end of the heating means 14 is connected to the negative side of the full-wave rectifier circuit 4 via the thermal fuse 15.
Current detection means 10 is provided between the emitter side of the transistor 9 as the first switch means and the negative side of the full-wave rectifier circuit 4. The current detection means 10 uses a resistance of 0.1Ω or less or a current detection coil.
The input voltage detecting means 7 and the output voltage detecting means 13 are connected to the control circuit 17 as a voltage stepped down by resistance division, or are once insulated by a photocoupler and connected to the control circuit 17.
[0017]
The DC power generation circuit 20 having the above configuration is a so-called step-up chopper. When the transistor 9 is ON, energy is stored in the choke coil 8, and when the transistor 9 is OFF, the capacitor 12 is connected via the diode 11. Charge.
Here, assuming that the average voltage E of the capacitor 12 is T, the switching period of the transistor 9 is Toff, the OFF time is Toff, the average voltage E of the capacitor 12, and the input voltage Vin.
E = k (T / Toff) × Vin × √2
It becomes. Note that k in the above equation is a coefficient determined by the impedance of the circuit, the resistance value of the heating device serving as a load, and the like. When this is set to 1, and T = 5 μsec and Vin = 100 V, Toff = 2.5 μsec , E become 282V. According to the above equation, it is likely that E can be increased as much as possible by reducing Toff, but the actually obtained boost ratio (E / Vin) is about five times.
By controlling Toff in this manner, the output voltage can be arbitrarily changed to, for example, the rated voltage value of the heating unit 14.
In addition, it is also possible to implement by the circuit configuration which does not use the smoothing capacitor 12. In this case, the output of the diode 11 flows directly to the heating means 14, and a voltage waveform having a large ripple with a switching cycle of 5 μsec (20 KHz) is applied to the heating means 14. Since the period is longer than the period of the AC voltage, the influence of the ripple on the heat output is suppressed, so that there is no problem. In this case, for example, when the fixing temperature rises to the target value, the temperature of the heating unit 14 is detected by the temperature detecting unit 16 and the Toff is increased or decreased according to the difference between the target temperature and the detected temperature ( DUTY ratio is changed), and the temperature is controlled so as to be a target temperature. In this example, elimination of the smoothing capacitor 12 enables low cost and miniaturization.
In the case where the smoothing capacitor 12 is provided, it is possible to perform flexible control using both information of the temperature of the heating means 14 and the output voltage detected by the output voltage detecting means 13, thereby achieving high functionality. be able to.
[0018]
In the DC power generation circuit 20 forming the boosting chopper, when T / Toff = 1, Emin = Vin × √2, so that Emin is applied to the heating means 14 as it is. Therefore, a transistor 5 serving as a second switch is provided at the output of the full-wave rectifier circuit 4 serving as a first rectifier, and the transistor 5 is turned off when the temperature of the heating means 14 becomes a predetermined value or more. Cut off the power supply.
Conventionally, for example, when the input voltage is 100 V, the rated voltage of the heater is also 100 V (AC), and an infrared heater having the maximum power required by the fixing unit has been used. Further, for example, a method is provided in which a heater of 650 W and a heater of 350 W are provided, and when the fixing device is started up, two of them are turned on at the same time, and only one or two are controlled during the fixing operation. Further, even when the fixing operation is not performed, the heater is turned on and off to control the temperature because there is a heat loss. In electronic equipment, allowable input power is determined by the Electricity Safety Law and the like, and the power outlets of general offices and homes in Japan are 100V and have a maximum rating of 15A.
When the AC input is directly supplied to the heater, the maximum power that can be supplied to the heater is 1500 W even if the power other than the heater is set to 0. In this example, since the output stage of the step-up chopper 20 is provided with the smoothing capacitor 12, the power of 1500 W or more can be instantaneously supplied to the heater, and the fixing temperature can be rapidly raised. Becomes possible.
[0019]
Next, the heater check function in the heater circuit (FIG. 1) will be described in detail.
The present invention monitors the change over time of the heater characteristics, so that the heater circuit is provided with a check function for properly managing the usable limit until the heater is disconnected, and the device itself can perform the check. Conventionally, if the characteristics of each device do not vary and the checks by management personnel are not performed in a timely manner, the heaters are approaching the operating limit, and even if the characteristics are degraded, there is no improvement even if the disconnection occurs. Therefore, it is intended to prevent a problem such as a failure to promptly respond to replacement maintenance of the heater or secure parts.
In the present embodiment, as means for realizing the check function in the heater circuit, in the present embodiment, a heater current when a supply voltage to the heater is set to a predetermined value (here, a rated voltage value of the heater) is detected, and the heater current is detected. The change with time of the current is captured as a change in the current reduction rate, and it is determined whether the current reduction rate has reached a predetermined allowable limit value (a value determined based on the current reduction rate at which the disconnection of the heater is predicted). Use means for performing the procedure.
The above-described current reduction rate is obtained by calculating a ratio of a detected value of a current actually flowing through the heater during operation to an initial current value when the heater is newly used. This initial current value can be implemented by a method that prepares in advance values experimentally obtained from many samples of the same type of heater, but also by a method using a value detected by a circuit in an actual machine. Is also possible.
When obtaining the initial current value, it is necessary to determine the current value for the heater bulb in consideration of the following properties. That is, the luminous flux gradually increases after lighting and increases to about 10 to 15%, reaches a maximum value and stabilizes, whereas the current gradually decreases but stabilizes at about 1 to 3%. This occurs in about a dozen minutes after lighting, and the new filament gradually becomes more stable. This is called withering, and it is known that a withered heater bulb has a larger luminous flux and a smaller current than that immediately after production. Therefore, it is necessary to determine, as the initial current value, a current value in a stable state after a sudden change in the current that occurs during the dozens of minutes when the heater bulb is manufactured.
[0020]
Further, regarding the setting of the allowable limit value, it is possible to determine the allowable limit value based on a working curve indicating how the current changes with time after the heater is turned on.
FIG. 4 exemplifies a working curve showing a change in a current reduction rate with respect to a time after the infrared heater is turned on. As shown in FIG. 4, the characteristic shows that the current gradually decreases with the initial value being 100%. The current gradually decreases over time, and then the filament breaks. The rate of decrease in the current at the time of the break is approximately constant for a specific type of heater, and varies depending on the type of heater. % And about 3% for gas-filled light bulbs, such values are used as predicted values.
The permissible limit value of the reduction rate is determined by the type of heater, taking into account an appropriate margin for the predicted current reduction rate at the time of disconnection. If a heater is used beyond that, the heat output will be insufficient and the problem of disconnection may occur. Is to determine the limit at which The permissible limit value of the reduction rate actually used is set by a certain empirical value that can be known in advance according to the type of heater to be used, or by referring to the saved prediction model while actually taking the data of the working distance during operation. It is possible to use a method of predicting and setting an optimum value. In order to adopt the latter method, it is necessary to accumulate the data of the current reduction rate obtained when the heater check is performed and make it available as history data. Also, by accumulating data of the heater current value detected when the heater check is performed or the current reduction rate calculated at the same time at the same time, a malfunction of the circuit or an abnormal input may occur. An error check of a detected value is performed to avoid a malfunction or to analyze a cause of a failure such as a disconnection.
[0021]
FIG. 5 is a diagram showing a processing flow when the heater check function in the heater circuit (FIG. 1) operates.
In the heater check process of this example, the heater current when the supply voltage to the heating means (heater) 14 is set to a predetermined value is detected, the current reduction rate is calculated from the detected heater current, and the current reduction rate is determined in advance. It is determined whether the allowable limit value has been reached, and when the allowable limit value has been reached, the operator is notified of the fact. This procedure is executed by the system control unit (not shown) that controls the entire copying machine or the control unit 17 that constitutes a control unit under the control in the embodiment of the copying machine of this example. Here, the control unit 17 has a CPU and a storage unit, and the storage unit stores a program (software) for executing processing / operation for controlling each unit of the copying machine or a heater circuit-related unit. The program includes a program for executing a heater check process of the heating unit (heater) 14 of the fixing unit described below. The CPU of the control means 17 reads a program for executing the heater check process of the present embodiment from a storage unit storing various programs, and executes a control operation according to the program.
The execution timing of the heater check process is set to an appropriate time while a predetermined supply voltage (normally, the voltage supplied during normal operation is the rated voltage value of the heater) is supplied to the heating means 14. You can choose.
[0022]
The heater check process executed by the control unit 17 will be described with reference to FIG. 5. First, the supply voltage to the heating unit 14 detected by the output voltage detection unit 13 is set to a predetermined value (heater rated voltage value) or a predetermined value. It is determined whether or not the voltage value is substantially equal to the voltage value (Step 11). If the voltage value is not the predetermined voltage value, the process is terminated. This Step 11 is performed to detect a heater current when a predetermined (rated) voltage is supplied, and to check whether a prerequisite condition is satisfied in a subsequent Step in which a heater use limit is checked based on a change in the heater current. , A predetermined (rated) voltage is not supplied, and it is possible to prevent a check error that may occur if this precondition is not met.
If it is confirmed that a predetermined (rated) voltage is supplied to the heating means 14 (Step 11-YES), the above-described precondition for the heater check is satisfied. The heater current value detected by the means 10 is fetched (Step 12).
Here, the current reduction rate of the acquired heater current is calculated (Step 13). This calculation calculates the ratio of the current detection current value to the current value stored as the initial current value of the heater (a current value in a stable state after a sudden change in the current generated at the beginning of the heater production). The calculation is performed, and the calculated current reduction rate is stored in the storage unit in the control unit 17. At the time of accumulation, an error check is performed on the calculated current reduction rate, and only normal data is accumulated. As a method of the error check, an existing method of comparing with accumulated past data can be adopted.
[0023]
Next, it is determined whether the calculated current reduction rate has reached a predetermined allowable limit value (Step 14). As the allowable limit value, as described above, a value obtained by an experiment in advance according to the type of the heater to be used, or a predicted value obtained from a work actually obtained in the operation so far is used. Here, if the current reduction rate does not reach the allowable limit value, the processing flow ends.
On the other hand, if the current reduction rate has reached the allowable limit value, if the heater continues to be used as it is, a trouble will occur, and the operator is warned that "the heater has reached the use limit" (Step 15). This alarm can be performed by displaying a message or the like on an operation panel (not shown) where the operator performs an input operation. The operator who sees this message display can take an action for replacing the heater, and smooth maintenance can be performed.
Further, even when the current reduction rate reaches the allowable limit value, it may be caused by various abnormalities such as sudden disconnection of the heater. Even in such a case, it is possible to present information to the operator, analyze the cause of the failure, and take appropriate measures by displaying accumulated history data so far.
[0024]
The above-described heater check process (see FIG. 5) is repeatedly performed so that an appropriate check effect can be obtained. For example, an implementation method is used in which this processing is started at a certain timing, managed by a clock.
Further, the above embodiment does not show an example in which a plurality of heaters are used. However, when a plurality of heaters are used, the respective operating states are different. Is applied to properly manage the heater.
[0025]
【The invention's effect】
(1) Effects corresponding to the first aspect of the invention
When the voltage output from the DC power supply to the heating means (heater) is controlled to a predetermined target value, the reduction rate of the current flowing through the heating means is calculated, and the obtained value is compared with the current reduction rate expected as the usage limit. As a result, the means for judging whether the heating means has reached the use limit is provided in the apparatus, so that the use limit can be known before the heating means becomes unusable due to disconnection or the like in each apparatus. And appropriate management of the heating means such as quick response to maintenance such as heater replacement.
(2) Effects corresponding to the second aspect of the invention
In addition to the effect of the above (1), by controlling to the rated voltage value of the heating means (heater) and performing the determination processing based on the current reduction rate obtained at that time, the heater with higher accuracy can be obtained. It becomes possible to know the usable limit.
[0026]
(3) Effects corresponding to the inventions of claims 3 and 4
In addition to the effects of the above (1) and (2), the usability determination processing is performed at regular intervals, and data relating to the determination is stored as history data. A check can be made, and more appropriate processing can be performed. In addition, since the history data is presented, by referring to this data, it is possible to determine whether the disconnection is due to an early accident such as breakage of parts (base) due to sudden external force, vibration, etc. Can be clarified.
(4) Effects corresponding to the invention of claim 5
In addition to the effects of the above (1) to (3), when it is determined that the use limit of the heating means has been reached, a notification to that effect is given, so that a prompt response by the operator is enabled. Provide effective means.
(5) Effects corresponding to the invention of claim 6
By using the heating device according to any one of claims 1 to 5 for heating the fixing portion of the toner image in the image forming unit, the effects (1) to (4) are realized in the image forming apparatus. Its performance can be improved.
[Brief description of the drawings]
FIG. 1 is a block diagram illustrating a configuration related to a heater circuit of a fixing unit according to an embodiment of the present invention.
FIG. 2 shows an AC voltage waveform input to a full-wave rectifier circuit of the heater circuit (FIG. 1).
FIG. 3 shows a full-wave rectified output voltage waveform from a full-wave rectifier circuit of the heater circuit (FIG. 1).
FIG. 4 exemplifies a working curve showing a change of a current reduction rate with respect to a time after lighting of an infrared heater.
FIG. 5 shows a processing flow when the heater check function in the heater circuit (FIG. 1) operates.
[Explanation of symbols]
1: AC power supply, 3: Relay,
4 Full-wave rectifier circuit 5 Transistor (second switch means)
8 choke coil 9 transistor (first switch means)
10 current detecting means 13 output voltage detecting means
14 heating means (heater) 15 thermal fuse
16 temperature detection means 17 control means
20 DC power generation circuit.

Claims (6)

In a heating device having a heating unit having a resistor as an element, a DC power supply for supplying DC power to the heating unit, and a power supply control unit for controlling a voltage output from the DC power supply to the heating unit, the heating unit is supplied to the heating unit. Current detection means for detecting a current flowing from the DC power supply to a heating means, and a voltage detected by the current detection means when the voltage output from the DC power supply to the heating means is controlled to a predetermined target value. A heating device comprising a usability judging means for judging whether or not the heating means has reached a use limit by comparing the current decrease rate with a predicted current decrease rate at a use limit. 2. The heating device according to claim 1, wherein the predetermined target value controlled by the power supply control means is a rated voltage value of the heating device. 3. The heating device according to claim 1, wherein the usability determination unit includes a unit that performs a determination process at regular intervals and stores data relating to each determination as history data. 4. Heating equipment. 4. The heating device according to claim 3, further comprising: a unit that presents the accumulated history data when the availability determination unit determines that the heating unit has reached a use limit. Heating equipment. The heating device according to any one of claims 1 to 4, further comprising means for notifying when the usability judging means judges that the heating means has reached a use limit, when the judgment is made. Heating equipment. An image forming apparatus having an image forming unit by an electrophotographic process, wherein the heating unit according to any one of claims 1 to 5 is used to heat a fixing portion of a toner image in the image forming unit. Image forming device.

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