JP2009069371A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus that ensures the long life of a halogen heater and excellent durability, the apparatus having in a fixing means the halogen heater in which supply of electric current is controlled by PWM control. <P>SOLUTION: The image forming apparatus includes: the fixing means using the halogen heater; a power supply means for supplying an electric current to the halogen heater; and a control means for controlling the fixing means by exerting the PWM control, thereby controlling the supply of electric current to the halogen heater. The control means calculates an amount of power supplied to the halogen heater for each PWM control period and controls the supply of electric current to the halogen heater by the PWM control so that the calculated amount of power is equal to or greater than a predetermined lower limit specific to the halogen heater. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus provided with a fixing unit using a halogen heater.

  2. Description of the Related Art Conventionally, there is a fixing heater drive used in an electrophotographic image forming apparatus that uses control based on PWM (Pulse Wide Modulation) lighting. The PWM lighting method has an advantage that input power can be controlled moderately. In addition, it is already known that PWM lighting involves full-wave rectification of AC input, conversion to DC voltage, and inverter driving.

  As a technique using such PWM lighting (drive), for example, a power supply voltage obtained by rectifying the output of an AC power supply is connected in series with a load and a switching element provided in the main body of the image forming apparatus. In a power control apparatus that applies power to a load circuit and performs power control of the load by on / off operation of the switching element, first resonance means connected in series with the load, and the first resonance means Second resonance means connected in parallel to a series circuit with the load, and the first resonance means, the second resonance means, and the load are integrally provided and electrically detachable from the main body (For example, refer to Patent Document 1).

  In such a power control device, switching by the switching element is soft switching, and a region where the voltage applied to the switching element and the current flowing through the switching element intersect at the time of switching of the switching element is reduced, so that switching loss can be reduced. . In addition, the waveform of the current flowing from the AC power supply to the load becomes a sine wave, and the power factor of the power supply is improved and the high-frequency current is reduced. Furthermore, the switching frequency of the switching element is reduced, switching loss can be reduced, and noise generated by a change in voltage and current due to switching can be reduced. Moreover, the path | route through which the charging / discharging electric current at the time of switching can be shortened, and the noise radiated | emitted from the electric wire which connects a load and a part of electric power control apparatus can be reduced.

  FIG. 9 is a schematic diagram for explaining the halogen cycle of the halogen heater used for the fixing heater. The tungsten 102 evaporated from the high-temperature tungsten filament 101 during lighting reacts with the halogen gas, and a compound of the tungsten 102 and the halogen 103 (hereinafter referred to as a tungsten-halogen compound) is generated. The tungsten-halogen compound 104 maintains its state at about 250 ° C. to 1400 ° C. Therefore, if the valve is at about 250 ° C. or higher, it will not adhere to the inner wall of the valve and blackening (deterioration) will not occur. This tungsten-halogen compound 104 is decomposed again into tungsten 102 and halogen 103 due to the high temperature when it is carried to the vicinity of the filament by thermal convection, and the tungsten 102 is regenerated into a filament. Repeat the reaction.

Japanese Patent No. 3545877

  However, in the above conventional electrophotographic PWM lighting method, when the set temperature of the fixing unit in a standby state or the like is low, the duty cycle of the halogen heater is controlled to be low. There was a possibility that it could not be made normal. The halogen heater is filled with a halogen gas having a concentration corresponding to the filament temperature (color temperature) so that the optimum halogen cycle works at the rated voltage. Therefore, when the bulb temperature is lower than about 250 ° C., there is a problem that the filament is eroded and tends to have a short life.

  The present invention has been made in view of the above, and in an image forming apparatus in which a fixing unit includes a halogen heater in which energization of an input current is controlled by PWM control, the life of the halogen heater is long and has excellent durability. An object is to obtain an image forming apparatus.

  In order to solve the above-described problems and achieve the object, an image forming apparatus according to the present invention includes a fixing unit using a halogen heater, an energizing unit for energizing the halogen heater, and the halogen heater. Control means for controlling the temperature of the fixing means by controlling the energization of current by PWM control, and the control means calculates the amount of electric power supplied to the halogen heater for each control period of the PWM control. The current supply to the halogen heater by the PWM control is controlled such that the calculated electric energy is equal to or greater than a predetermined lower limit value specific to the halogen heater.

  According to the present invention, it is possible to prevent the life of the halogen heater from becoming shorter than the life of the image forming apparatus by operating the halogen cycle normally, and the life of the halogen heater is long and excellent in durability. There is an effect that an image forming apparatus can be obtained.

  Embodiments of an image forming apparatus according to the present invention will be described below in detail with reference to the drawings. In addition, this invention is not limited to the following description, In the range which does not deviate from the summary of this invention, it can change suitably.

Embodiment 1 FIG.
FIG. 1 is a diagram illustrating a schematic configuration of a printer that is an example of an image forming apparatus according to a first embodiment of the present invention. The printer according to the present embodiment includes an image forming unit 1, a writing unit 2, a fixing unit 3, an operation unit 4, a ROM (Read Only Memory) 5, a RAM (Random Access Memory) 6, and a communication interface. (I / F) 7 and a control unit 8.

  The image forming unit 1 includes a plurality of photosensitive drums as a plurality of image carriers, a toner supply unit, and the like, and forms images of different colors on the photosensitive drums, and images of the colors on the photosensitive drums. Is superimposed on a recording paper as a recording material and transferred to form a color image on the recording paper. The optical writing unit 2 serving as an exposure unit modulates and drives a laser diode with an image signal of each color, and irradiates the plurality of photosensitive drums with laser light modulated with the image signal of each color from the laser diode. By exposing, an electrostatic latent image corresponding to the image signal of each color is formed on each photosensitive drum.

  That is, in the image forming unit 1, each of the plurality of photosensitive drums is driven to rotate by the driving unit and uniformly charged by the charging unit, and then modulated by the image signal of each color from the optical writing unit 2. Exposure with light forms an electrostatic latent image corresponding to the image signal of each color. The electrostatic latent images corresponding to the image signals of the respective colors on the respective photosensitive drums are developed with the respective color toners by the developing means including the toner supply unit to become the respective color toner images. The recording paper is fed from the paper feeding device, and the recording paper is transferred by superimposing the toner images of the respective colors on the respective photosensitive drums by the transfer means, thereby forming a color image.

  The fixing unit 3 includes a fixing heater, and the recording paper on which the color image is formed by the image forming unit 1 is conveyed to fix the image (toner) on the recording paper to the recording paper. In the fixing unit 3, for example, a fixing roller (or a fixing belt) as a fixing member that is rotationally driven by a driving source and a pressure roller as a pressure member heat and press the recording paper passing through the nip portion. A fixing device is used in which the image (toner) is fixed by heating and at least one of the fixing roller (or fixing belt) and the pressure roller is heated by a fixing heater.

  The operation unit 4 is a part that a user or an operator operates to set the state of the printer. The ROM 5 stores and holds programs for controlling the printer and fixed parameters. The RAM 6 stores and holds the initial settings of the printer and is backed up by a battery. The communication I / F 7 is connected to a host via a LAN or the like, and controls external I / F and controls input / output data such as image data from the outside. The control unit 8 is a part that controls the printer, includes a CPU (Central Processing Unit), and controls each unit of the printer via the bus B.

  FIG. 2 is a diagram illustrating an example of a fixing heater driving circuit included in the fixing unit 3. The configuration of the fixing heater driving circuit will be described. An AC (Alternating Current) power source 9 is connected to the input side of the noise filter 10. The output side of the rectifier DB1 is connected to the inverter circuit 11 via a noise filter composed of capacitors C1, C2, and L2.

  In the inverter circuit 11, L2 as the first resonance unit and a halogen heater 13 as a load as a fixing heater of the fixing device in the image forming apparatus are connected in series, and a series circuit of L2 and the halogen heater 13 is connected. A series-parallel circuit is configured by connecting C3 as the second resonance means in parallel. This series-parallel circuit is connected to the output side of the rectifier DB (the output side of the noise filter composed of the capacitors C1 and C2 and the coil L1) via the FET transistor as the switching element Q1 in series.

  An output terminal of the FET drive circuit 12 is connected to a gate to which the drive signal of the switching element Q1 is input, and the PWM drive signal for turning on / off the halogen heater 13 according to the operating condition of the machine is connected to the FET drive circuit 12. A line is connected from the control unit 8 as a control means. The thermistor 14 is a temperature detection unit that detects the temperature of the fixing unit 3 and inputs a signal to the control unit 8 with the detected temperature information.

  Next, the operation of the fixing heater driving circuit will be described. The output of the AC power source 9 is input to the noise filter 10. The noise filter 10 removes noise from the AC line. The output from the noise filter 10 is supplied to the rectifier DB and full-wave rectified. The output of the rectifier DB is input to a noise filter composed of capacitors C1, C2 and a coil L1, and noise is removed.

  The capacitors C1 and C2 of the noise filter are provided to prevent high frequency noise of the pulse current flowing through the switching element Q1 from leaking to the AC power source 9 side, and the capacitance is set to a small value. . Therefore, the voltage waveform of the output of the noise filter is a voltage Vdb obtained by full-wave rectifying the output of the AC power supply 9 as shown in FIG. The output of this noise filter is input to the inverter circuit 11.

  In this state, when it is time to supply power to the halogen heater 13, a PMW signal for turning on the halogen heater is input from the control unit 8 to the FET drive circuit 12. The FET drive circuit 12 is turned on when the PWM signal from the control unit 8 is HI to generate the drive signal Vb of the switching element Q1, and this signal causes the switching element Q1 to have a frequency (much higher than the output frequency of the AC power source). For example, 20 KHz).

  Thus, when the switching element Q1 is turned on, the output Vin of the noise filter is applied to the series-parallel circuit of the halogen heater 13, the coil L2, and the capacitor C3 through the switching element Q1, and the halogen heater 13, the coil L2, and the capacitor are applied. A load current Ic flows through the series-parallel circuit of C3, electric power is supplied to the halogen heater 13, and energy is stored in the coil L2.

  Here, an AC (Alternating Current) power supply 9, a noise filter 10, a rectifier DB1, a noise filter composed of capacitors C1, C2, and L2, a switching element Q1, a halogen heater 13, a coil L2, and a capacitor C3 are connected in series and parallel. Thus, energizing means for energizing the halogen heater 13 is configured.

  When the switching element Q1 is turned off, energy is released from the coil L2 in the series-parallel circuit of the halogen heater 13, the coil L2, and the capacitor C3, the capacitor C3 is charged, and a current flows through the halogen heater 13. By performing the above-described operation, the current supplied to the halogen heater 13 has a current waveform close to a sine wave as indicated by Iht in FIG. 3, and the power factor is improved and the high-frequency current is reduced. . In addition, since the input current of the halogen heater 13 can be controlled by increasing or decreasing the PWM duty, the power consumption can also be accurately controlled by the PWM duty, and the power ripple can be accurately controlled, thereby reducing the temperature ripple of the fixing unit. It becomes possible. By reducing the temperature ripple of the fixing unit, there is an advantage that it is possible to stabilize color development such as color printing.

  On the other hand, in the halogen heater 13, as shown in the schematic diagram of the halogen cycle in FIG. 9, tungsten evaporated from the high-temperature filament during lighting reacts with the halogen gas to form a compound of tungsten and halogen (tungsten-halogen). Compound) is produced. The tungsten-halogen compound maintains its state at about 250 ° C to 1400 ° C. Therefore, if the valve temperature is about 250 ° C. or higher, it does not adhere to the inner wall of the valve and blackening (deterioration) does not occur. When this compound is transported to the vicinity of the filament by thermal convection, it is decomposed again into tungsten and halogen due to the high temperature, and tungsten is regenerated into a filament, and the liberated halogen repeats the next reaction again.

  As described above, the halogen heater 13 is filled with a halogen gas having a concentration corresponding to the filament temperature (color temperature) so that the optimum halogen cycle works at the rated voltage. Therefore, under conditions where the halogen cycle does not become normal, for example, when the voltage is lowered or the input current is lowered, the bulb temperature is lowered. When the bulb temperature is about 250 ° C. or lower, the tungsten-halogen compound is cooled by the bulb temperature when the tungsten-halogen compound contacts the bulb. It is known that the tungsten-halogen compound cannot be maintained as a compound and is decomposed into tungsten molecules and a halogen gas, and the tungsten molecules adhere to the inner wall of the bulb and cause a blackening phenomenon. Furthermore, it is generally known that a deterioration phenomenon such that the tungsten filament is thinned due to such a state being continued and eventually becomes disconnected.

  In the prior art, in printers and copiers equipped with the above-described image forming apparatus, the operation mode is an operation mode that maintains a state where the fixing temperature is used low, such as low power standby, standby, and energy saving standby. Sometimes. In such a case, since the temperature of the fixing unit may be maintained with a small amount of electric power, it may be used for a long time with a low PWM duty, and there is a possibility that deterioration of the halogen heater may be accelerated. There is a possibility that a failure such as a shortened life of the halogen heater may occur with respect to the life of the forming apparatus.

  When the halogen heater is turned on, a current is passed through the halogen heater so that the lower limit temperature (approximately 250 ° C., hereinafter referred to as Tf) of the bulb in which a normal halogen cycle is performed is reached in a short time. Rapid deterioration can be suppressed.

  By turning on the PWM duty at 100%, it is possible to shift to the normal halogen cycle in the shortest time. However, in recent years, in response to a request for shortening the time of first printing, etc. In addition, the fixing unit mechanism component having a small heat capacity is mounted, and there are conflicting problems such as a reduction in temperature ripple of the fixing unit. Therefore, a lower limit Duty that sets the lifetime of the halogen heater to be equal to or longer than that of the image forming apparatus without generating temperature ripple is set, and current supply control to the halogen heater is not performed above the lower limit Duty. Thus, the life of the halogen heater can be made longer than the life of the apparatus, and the temperature ripple of the fixing unit can be reduced.

  An example of a method for determining A% will be described, where the apparatus life is L (hours) and the lower limit value of PWM Duty that makes the halogen heater life longer than the apparatus life L is A%. The life when a halogen heater is used under rated input conditions is Lht (hours). Here, Lht is a characteristic unique to the halogen heater used in the apparatus. FIG. 4A is a diagram illustrating a relationship between a relative life of a general halogen heater and a bulb temperature.

  The worst state of the use form of the image forming apparatus in the present embodiment is to start energization of current from the normal temperature and to stop energization when it reaches 250 ° C. As for the temperature rise of the valve temperature, if the PWM duty is constant, the slope of the temperature rise is constant. Therefore, the lifetime when the valve temperature is 250 ° C. or less is about 50% from FIG. 4-1. The lifetime can be extended by more than about 50% by separately setting the PWM duty for starting the energization of the current or by controlling the temperature so that the valve temperature does not drop to room temperature.

  FIG. 4B is a diagram illustrating the temperature transition of the fixing unit and the valve temperature transition when the image forming apparatus is used in the worst manner with respect to the life of the halogen heater. For example, in the low power standby mode, the fixing unit target temperature is set lower than the fixing unit temperature at the time of printing, and since recording paper does not pass through the fixing unit, a large amount of power is not required to maintain the temperature. The transition between the fixing unit and the valve temperature of the image forming apparatus at the time may be assumed that the valve temperature and the fixing unit temperature are generally in the relationship shown in FIG. it can.

  In FIG. 4B, ton is a time during which current is supplied to the halogen heater 13 at PWM Duty: A%. In FIG. 4B, toff is a state in which the current supply to the halogen heater 13 is stopped. The gradient of ton differs depending on the PWM duty, but toff is specific to the heat capacity of the fixing unit 3 and the like of the image forming apparatus. In addition, because of low power standby, this state is continued unless there is a state transition such as printing. When there is no state transition, current is supplied to the halogen heater 13 in a cycle of t1, so that the life of the image forming apparatus: L and the current supply to the halogen heater 13 are (L / t1). ) Times. At this time, the energization time of the total current by PWM Duty: A% is ton × (L / (ton + toff)).

On the other hand, it is sufficient if the life of the halogen heater 13 is long. Therefore,
0.5 × Lth> ton × (L / (ton + toff))
ton <(0.5 × Lht × toff) / (L−0.5 × Lht)
Ton can be set such that

  Accordingly, if the rated power consumption of the halogen heater mounted in the image forming apparatus is W, the temperature of the fixing unit of the image forming apparatus is maintained by the amount of power W × A × ton, and the life of the image forming apparatus is reduced. Thus, the life of the halogen heater can be extended. PWM Duty: A% and continuous energization time: ton are stored in advance in the ROM 5 of the image forming apparatus.

  The relationship between the continuous energization time: ton, the fixing unit temperature control cycle: F (time, hereinafter referred to as control cycle: F), and PWM Duty: B% (value calculated by temperature control) will be described. For each control period F, the fixing unit temperature obtained by sampling the fixing unit temperature is compared with the fixing unit target temperature, and PWM duty to the halogen heater: B% is determined. In the control cycle F, the control cycle interval is predetermined with a fixed value in order to maintain the fixing unit target temperature against temperature fluctuations such as during printing.

  In the image forming apparatus of ton ≦ F, since W × A × ton ≦ W × A × F, it is possible to supply an amount of electric power that reaches a temperature at which the bulb temperature can normally perform the halogen cycle. By setting, the life of the halogen heater can be extended with respect to the life of the image forming apparatus.

  Further, in the image forming apparatus of ton> F, W × A × ton> W × A × F, and it is impossible to supply the amount of power that reaches the temperature at which the bulb temperature can normally perform the halogen cycle in one control cycle. Therefore, it is necessary to calculate and control the amount of electric power with PWM Duty: B% and control cycle: F.

  When B ≦ A, the control unit 8 resets the PWM duty to the lower limit PWM duty: A%, and performs control to turn on the halogen heater 13 continuously for ton time. When B> A and W × A × ton> W × B × F, the control unit 8 controls to turn on the halogen heater 13 continuously for (A × ton) / B time at PWM Duty: B. To do. When B> A and W × A × ton ≦ W × B × F, the control unit 8 controls the halogen heater 13 with PWM Duty: B and control cycle: F. In addition, since the temperature rise of the valve is affected by fluctuations in the ambient temperature of the fixing unit, the input voltage, and the input current, the life of each fluctuation is not affected.

  In the present embodiment, the energization of current to the halogen heater 13 provided in the fixing unit 3 is controlled by PWM control, and the amount of power supplied to the halogen heater 13 in the control cycle is calculated for each control cycle that is the PWM control cycle. The control unit 8 performs a function of a control unit that controls energization of the current to the halogen heater 13 by PWM control so that the calculated supply power amount is equal to or more than a predetermined lower limit value unique to the halogen heater 13.

  Next, the operation will be described with reference to FIG. FIG. 5 is a flowchart for explaining the operation of the printer according to the first embodiment. First, the thermistor 14 measures the temperature (fixing temperature) of the fixing unit 3 and inputs the temperature information signal to the control unit 8. Based on this temperature information signal, the control unit 8 determines whether or not the temperature detected by the thermistor 14 is lower than the fixing unit target temperature and it is necessary to raise the fixing temperature (step S101).

  If it is determined that there is no need to raise the fixing temperature (No at Step S101), the control unit 8 repeats the determination based on the temperature information signal as it is. Further, when it is determined that the temperature detected by the thermistor 14 is lower than the fixing unit target temperature and the fixing temperature needs to be increased (Yes at Step S101), the control unit 8 executes a process for determining the output PWM Duty. . The control unit 8 calculates PWM Duty: B% by using, for example, a PID calculation formula (step S102).

  Next, the control unit 8 compares the calculated PWM Duty: B% with the lower limit PWM Duty: A% stored in the ROM 5, and determines whether or not B% is larger than A% (Step S103). ). If B%> A% is determined as a result of the determination (Yes at Step S103), the control unit 8 calculates the power amount and compares the power amounts, and W × A × ton ≦ W × B × F. Whether or not (step S104).

  Here, when it is determined that W × A × ton ≦ W × B × F (Yes in Step S104), the control unit 8 sets a PWM signal with PWM Duty: B% and control cycle: F, and PWM Duty An output process is executed (step S105). If it is determined that W × A × ton> W × B × F (No in step S104), the control unit 8 calculates a continuous energization time: (A × ton) / B at PWM Duty: B ( Step S107), PWM duty output processing is executed (step S105).

  Returning to step S103, if it is determined that B ≦ A (No in step S103), the control unit 8 resets the PWM duty: A% and the continuous energization time: ton (step S106), and proceeds to the PWM duty output process. move on. In the PWM duty output process, the set PWM duty and the set continuous lighting time are output.

  Next, an example of a correction method when the environmental temperature of the fixing unit 3 is low will be described. When the detected temperature T from the thermistor 14 is equal to or lower than a specified temperature T1, the control unit 8 resets the lower limit PWM Duty: A% to (A + α)% and stores it in the RAM 6. T1 is the ambient temperature when the set values of A% and N stored in the ROM 5 are determined. Α may be a constant value or a value variable by (T−T1) so that the valve temperature Tf is reached at continuous energization time M = A / N.

  With reference to FIG. 6, the correction method when the environmental temperature of the fixing unit 3 is low will be specifically described. FIG. 6 is a flowchart for explaining the operation of the printer according to the first embodiment. First, the thermistor 14 measures the temperature (fixing temperature) of the fixing unit 3 and inputs the temperature information signal to the control unit 8. Based on this temperature information signal, the control unit 8 determines whether or not the temperature detected by the thermistor 14 is lower than the fixing unit target temperature and it is necessary to raise the fixing temperature (step S201).

  If it is determined that there is no need to raise the fixing temperature (No at Step S201), the control unit 8 repeats the determination based on the temperature information signal as it is. Further, when it is determined that the detection temperature in the thermistor 14 is lower than the fixing unit target temperature and the fixing temperature needs to be raised (Yes in step S201), the control unit 8 detects the thermistor temperature T: It is determined whether or not the specified temperature is equal to or higher than T1 (T1 ≦ T) (step S202).

  If T1 ≦ T as a result of the determination (Yes at Step S202), the control unit 8 starts the process of starting energization of the current to the halogen heater 13 and executes the process of determining the output PWM duty. The control unit 8 calculates PWM Duty: B% by using, for example, a PID calculation formula (step S203).

  Next, the control unit 8 compares the calculated PWM Duty: B% with the lower limit PWM Duty: A% stored in the ROM 5 and determines whether B% is larger than A% (B%> A%). Is determined (step S204). If B%> A% is determined as a result of the determination (Yes in step S204), the control unit 8 calculates the power amount and compares the power amounts, and W × A × ton ≦ W × B × F. Whether or not (step S205).

  Here, when it is determined that W × A × ton ≦ W × B × F (Yes in Step S205), the control unit 8 sets a PWM signal with PWM Duty: B% and control cycle: F, and PWM Duty An output process is executed (step S206). If it is determined that W × A × ton> W × B × F (No in step S205), the control unit 8 calculates a continuous energization time: (A × ton) / B at PWM Duty: B ( Step S208), PWM Duty output processing is executed (Step S206).

  Returning to step S204, if it is determined that B% ≦ A% (No in step S204), the control unit 8 resets the PWM duty: A% and the continuous energization time: ton (step S207), and outputs the PWM duty. Proceed to processing. In the PWM duty output process, the set PWM duty and the set continuous lighting time are output.

  Returning to step S202, if the detection temperature: T of the thermistor is less than the specified temperature: T1 (T1> T) as a result of determination (No at step S202), the control unit 8 is stored in the ROM 5. The correction value: α is added to the lower limit PWM Duty: A%, and (A + α)% is stored in the RAM 6 as the minimum PWM Duty (step S209).

  Next, the control unit 8 starts a process for starting energization of the halogen heater 13 and executes a process for determining the output PWM duty. The control unit 8 calculates PWM Duty: B% by using, for example, a PID calculation formula (step S210).

  Next, the control unit 8 compares the calculated PWM Duty: B% with the lower limit PWM Duty: (A + α)% stored in the RAM 6, and B% is larger than (A + α)% (B%> ( A + α)%) is determined (step S211). As a result of the determination, if B%> (A + α)% (Yes at Step S211), the control unit 8 calculates the power amount and compares the power amount, and W × (A + α) × ton ≦ W × B. It is determined whether or not xF (step S212).

  Here, when it is determined that W × (A + α) × ton ≦ W × B × F (Yes in step S212), the control unit 8 sets the PWM signal with PWM Duty: B% and control cycle: F. PWM Duty output processing is executed (step S213). If it is determined that W × A × ton> W × B × F (No in step S212), the control unit 8 calculates the continuous energization time: ((A + α) × ton) / B at PWM Duty: B. (Step S215), and PWM Duty output processing is executed (Step S213).

  Returning to step S211, if it is determined that B% ≦ (A + α)% (No in step S211), the control unit 8 resets the PWM duty: (A + α)% and the continuous energization time: ton (step S214). ), The process proceeds to PWM Duty output processing. In the PWM duty output process, the set PWM duty and the set continuous lighting time are output.

  With the above processing, when the halogen heater is turned on, the amount of electric power supplied to the halogen heater does not fall below a certain lower limit specific to the halogen heater due to the PWM duty when the current is applied and the continuous energization time. Since it is possible to suppress the occurrence of a state below the lower limit temperature of the bulb where normal halogen cycles are performed, for example, about 250 ° C. or less, the life of the halogen heater is longer than the life of the image forming apparatus. Can be prevented from becoming shorter.

  As described above, according to the image forming apparatus according to the present embodiment, when the current is supplied to the halogen heater 13, the amount of electric power at the time of supply is constant depending on the PWM duty at the time of energization and the continuous energization time. It can be controlled not to be less than the value. Thereby, since the occurrence of a state where the bulb temperature is about 250 ° C. or less can be suppressed, it is possible to prevent the life of the halogen heater from becoming shorter than the life of the image forming apparatus. Therefore, according to the image forming apparatus according to the present embodiment, in the image forming apparatus provided with the fixing unit with the halogen heater whose current is controlled by the PWM control, the halogen heater has a long life and excellent durability. An image forming apparatus can be obtained.

Embodiment 2. FIG.
FIG. 7 is a diagram illustrating another example of the fixing heater driving circuit included in the fixing unit 3 of the image forming apparatus according to the second embodiment. Since the configuration of the image forming apparatus according to the second embodiment is the same as that of the second embodiment except for the fixing heater driving circuit, the description thereof is omitted here. The fixing heater driving circuit shown in FIG. 7 further includes an input voltage detection circuit 15 and an input current detection circuit 16 in addition to the fixing heater driving circuit shown in FIG.

  The input voltage detection circuit 15 is a circuit that functions as a voltage detection unit that detects input power supplied to the fixing unit 3. The input current detection circuit 16 is a circuit that functions as a current detection unit that detects an input current supplied to the fixing unit 3. In this example, the input voltage detection circuit 15 and the input current detection circuit 16 are mounted at the same time, but only one of them may be mounted.

  The input voltage supplied to the fixing unit 3 may fluctuate depending on the power situation of the user, and the rated input voltage value (specified value: V) of the halogen heater 13 held in the ROM 5 may not be supplied. . Assuming that the halogen heater rated input voltage is V, the power: Win of the halogen heater 13 when the input voltage is Vin is Win = W × (Vin / V) ^ (1 / 0.65). Here, assuming that the rated power of the halogen heater is W, the same amount of power can be supplied by correcting the minimum PWM Duty from A% to (A × Win / W)%. As a result, it is possible to suppress the occurrence of a state below the lower limit temperature of the bulb where normal halogen cycle is performed, for example, about 250 ° C. or less, so that the life of the halogen heater is longer than the life of the image forming apparatus. Shortening can be prevented.

  Similarly, the input current supplied to the fixing unit 3 may fluctuate depending on the power situation of the user, and the rated input current value of the halogen heater 13 held in the ROM 5 may not be supplied. Assuming that the halogen heater rated input current is I and the halogen heater resistance is R, the power of the halogen heater when the input voltage is Iin: Win is Win = W × ((Iin × R) / (I × R)) ^ (1 / 0.65). Here, assuming that the rated power of the halogen heater is W, the same amount of power can be supplied by correcting the minimum PWM Duty from A% to (A × Win / W)%. As a result, it is possible to suppress the occurrence of a state below the lower limit temperature of the bulb where normal halogen cycle is performed, for example, about 250 ° C. or less, so that the life of the halogen heater is longer than the life of the image forming apparatus. Shortening can be prevented.

  Next, a correction method when the input voltage supplied to the fixing unit 3 fluctuates will be described with reference to FIG. First, the thermistor 14 measures the temperature (fixing temperature) of the fixing unit 3 and inputs the temperature information signal to the control unit 8. Based on this temperature information signal, the control unit 8 determines whether or not the temperature detected by the thermistor 14 is lower than the fixing unit target temperature and it is necessary to raise the fixing temperature (step S301).

  If it is determined that there is no need to raise the fixing temperature (No at Step S301), the control unit 8 repeats the determination based on the temperature information signal as it is. If it is determined that the detection temperature of the thermistor 14 is lower than the fixing unit target temperature and the fixing temperature needs to be increased (Yes at step S301), the control unit 8 detects the input voltage using the input voltage detection circuit 15. It is determined whether the input voltage Vin to be applied is equal to or higher than the specified value V (V ≦ Vin) (step S302).

  As a result of the determination, if the input voltage: Vin is equal to or higher than the specified value: V (V ≦ Vin) (Yes in step S302), the control unit 8 starts a process of starting energization of the current to the halogen heater 13, An output PWM duty determination process is executed. The control unit 8 calculates PWM Duty: B% by using, for example, a PID calculation formula (step S303).

  Next, the control unit 8 compares the calculated PWM Duty: B% with the lower limit PWM Duty: A% stored in the ROM 5 and determines whether B% is larger than A% (B%> A%). Is determined (step S304). If B%> A% is determined as a result of the determination (Yes at Step S304), the control unit 8 calculates the power amount and compares the power amounts, and W × A × ton ≦ W × B × F. Whether or not (step S305).

  Here, when it is determined that W × A × ton ≦ W × B × F (Yes in Step S305), the control unit 8 sets a PWM signal with PWM Duty: B%, control cycle: F, and PWM Duty. An output process is executed (step S306). When it is determined that W × A × ton> W × B × F (No in step S305), the control unit 8 calculates a continuous energization time: (A × ton) / B with PWM Duty: B ( Step S308), PWM duty output processing is executed (step S306).

  Returning to step S304, if it is determined that B% ≦ A% (No in step S304), the control unit 8 resets the PWM duty: A% and the continuous energization time: ton (step S307), and outputs the PWM duty. Proceed to processing. In the PWM duty output process, the set PWM duty and the set continuous lighting time are output.

  Returning to step S302, if the input voltage: Vin detected by the input voltage detection circuit 15 is less than the specified value: V (V> Vin) as a result of the determination (No in step S302), the control unit 8 corrects the lower limit PWM Duty: A% stored in the ROM 5 and stores it in the RAM 6 as (A × Win / W)% as the minimum PWM Duty (Step S309).

  Next, the control unit 8 starts a process of starting energization of the current to the halogen heater 13 and executes a process for determining the output PWM duty. The control unit 8 calculates PWM Duty: B% by using, for example, a PID calculation formula (step S310).

  Next, the control unit 8 compares the calculated PWM Duty: B% with the lower limit PWM Duty: (A × Win / W)% stored in the RAM 6, and B% is (A × Win / W)%. Is greater than (B%> (A × Win / W)%) (step S311). If B%> (A × Win / W)% is determined as a result of the determination (Yes in step S311), the control unit 8 calculates a power amount and compares the power amounts, and W × (A × Win / W). It is determined whether or not W) × ton ≦ W × B × F (step S312).

  Here, when it is determined that W × (A × Win / W) × ton ≦ W × B × F (Yes in step S312), the control unit 8 performs PWM at PWM Duty: B%, control cycle: F. The signal is set, and the PWM duty output process is executed (step S313). When it is determined that W × (A × Win / W) × ton> W × B × F (No in step S312), the control unit 8 uses PWM Duty: B and the continuous energization time: ((A × Win / W) × ton) / B is calculated (step S315), and PWM duty output processing is executed (step S313).

  Returning to step S311, if it is determined that B% ≦ (A × Win / W)% (No in step S311), the control unit 8 sets PWM Duty: (A × Win / W)%, continuous energization time: Ton is reset (step S314), and the process proceeds to the PWM duty output process. In the PWM duty output process, the set PWM duty and the set continuous lighting time are output.

  The correction when the input current supplied to the fixing unit 3 fluctuates can be performed by changing the voltage detection to current detection in the correction method when the input voltage supplied to the fixing unit 3 fluctuates. Therefore, detailed description is omitted here.

  As described above, according to the image forming apparatus according to the present embodiment, when the current is supplied to the halogen heater 13, the amount of electric power at the time of supply is constant depending on the PWM duty at the time of energization and the continuous energization time. It can be controlled not to be less than the value. Thereby, since the occurrence of a state where the bulb temperature is about 250 ° C. or less can be suppressed, it is possible to prevent the life of the halogen heater from becoming shorter than the life of the image forming apparatus. Therefore, according to the image forming apparatus according to the present embodiment, in the image forming apparatus provided with the fixing unit with the halogen heater whose energization is controlled by the PWM control, the image formation with a long life of the halogen heater and excellent durability. A device can be obtained.

  As described above, the image forming apparatus according to the present invention is useful for applications requiring durability.

1 is a diagram illustrating a schematic configuration of a printer that is an example of an image forming apparatus according to a first embodiment of the present invention; FIG. 3 is a diagram illustrating a fixing heater driving circuit included in the fixing unit 3 of the printer according to the first embodiment of the present invention. FIG. 4 is a diagram illustrating control characteristics of a fixing heater driving circuit included in the fixing unit 3 of the image forming apparatus according to the first embodiment of the present invention. It is a figure which shows the relationship between the relative lifetime of a general halogen heater, and valve | bulb temperature. It is the figure which illustrated the temperature transition of a fixing part, and valve temperature transition. 3 is a flowchart for explaining the operation of the printer according to the first embodiment of the present invention; 4 is a flowchart for explaining the operation of the printer according to the first embodiment; It is a figure which shows the fixing heater drive circuit which the fixing | fixed part 3 of the printer concerning Embodiment 2 of this invention has. 6 is a flowchart for explaining an operation of the printer according to the second embodiment; It is a schematic diagram for demonstrating the halogen cycle of the halogen heater used for a fixing heater.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image creation part 2 Optical writing part 3 Fixing part 4 Operation part 8 Control part 9 Power supply 10 Noise filter 11 Inverter circuit 12 Drive circuit 13 Halogen heater 14 Thermistor 15 Input voltage detection circuit 16 Input current detection circuit 101 Tungsten filament 102 Tungsten 103 Halogen 104 Halogen compound

Claims (5)

Fixing means using a halogen heater;
An energizing means for energizing the halogen heater;
Control means for controlling the temperature of the fixing means by controlling energization of the current to the halogen heater by PWM control;
With
The control means calculates the amount of power supplied to the halogen heater for each control period of the PWM control, and the PWM control so that the calculated amount of power is equal to or greater than a predetermined lower limit value specific to the halogen heater. Controlling the energization of the current to the halogen heater by
An image forming apparatus. In the case of the first duty which is a lower limit value of the duty in the PWM control determined in advance so that the amount of electric power supplied to the halogen heater is equal to or higher than the lower limit value, and the first duty in the PWM control Storage means for storing a predetermined reference energization time which is an energization time for energizing the halogen heater so that the amount of electric power supplied to the halogen heater is equal to or greater than the lower limit;
With
The control means calculates a second duty for the PWM control, and based on a magnitude relationship between the first duty and the second duty, a duty used for the PWM control or a current to the halogen heater Controlling the energization time to energize
The image forming apparatus according to claim 1. A temperature detecting means for detecting the temperature of the fixing means;
The control means controls energization of the current to the halogen heater based on temperature information detected by the temperature detection means;
The image forming apparatus according to claim 1. Voltage detecting means for detecting a voltage supplied to the fixing means;
The control means controls energization of the current to the halogen heater based on voltage information detected by the voltage detection means;
The image forming apparatus according to claim 1. A current detection means for detecting a current supplied to the fixing means;
The control means controls the energization of the current to the halogen heater based on the current information detected by the current detection means;
The image forming apparatus according to claim 1.

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