JP2004265650A - Heater control device and image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To start power feed to a heater to heat it promptly without waiting for the completion of initialization of a software controlling computer. <P>SOLUTION: A triac 43 performs switching on/off of the current from the commercial AC power supply 66 to the heater 66. A hardware control circuit 65 controls the switching on/off of the triac 43 by hardware. The CPU 33 controls the switching on/off of the triac 43 by software. While the CPU is in initialization process, the triac 43 is controlled by the hardware control circuit 65. When the initialization is completed, the CPU 33 masks the control signal output from the hardware control circuit 65 to the triac 43 and performs the software control of the triac 43 in place of the hardware control. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a heater control device for controlling energization of a heater and an electrophotographic image forming apparatus including the heater control device.
[0002]
[Prior art]
Patent Literature 1 discloses a technique for shortening the recovery time of a digital copying machine by omitting unnecessary processing during initialization processing when the power of the digital copying machine is turned on. ing.
[0003]
[Patent Document 1]
JP 2000-10436 A
[0004]
[Problems to be solved by the invention]
In recent years, with respect to an electrophotographic image forming apparatus that copies an image based on image data input from a network or image data of a document read by an image input device, demands for energy saving have been increasing. There is a strong demand for a reduction in power consumption in a standby state where image formation is not being performed. Therefore, these devices are provided with an energy saving mode for saving power in a standby state in which image formation is not performed. As a means of power saving, in an image forming apparatus having a fixing device for fixing toner to transfer paper by heat, power supply to the fixing device is stopped in a standby state to reduce power consumption. ing.
[0005]
Further, as a measure for further reducing power consumption, power is supplied only to a specific control unit having an interface for communicating with the outside, and power supply is stopped for other control units. I have.
[0006]
On the other hand, in some areas, public regulations require that the time required to return from the energy-saving mode to the image forming operation be shortened, and contradict the demands of low power consumption during standby and a shorter time required for the return time. Is required.
[0007]
Further, in an image forming apparatus having a configuration in which a fixing unit is heated by a heater which receives power supply from a commercial power supply, when power is supplied to the heater at an arbitrary timing when power is supplied to the heater, voltage ripple of the commercial power supply is performed. And may affect other luminaire lights that draw power from the same commercial power source. In some cases, the effect on commercial power is limited by public regulations, and the usual countermeasure is to synchronize the heater lighting timing with the commercial power voltage waveform by software control. It is carried out.
[0008]
However, since software is interposed, it is difficult to start energization control of the heater of the fixing unit until the initialization operation of the control unit is completed, which is a major obstacle to shortening the time required to return from the energy saving mode.
[0009]
On the other hand, the technique disclosed in Patent Document 1 attempts to shorten the return time by omitting processes other than the minimum control required when starting up the apparatus. Since the operation and the like are indispensable processes for realizing stable control, there is a problem that the return time from the energy saving mode becomes long by the time required for the initialization of the control unit.
[0010]
SUMMARY OF THE INVENTION It is an object of the present invention to start energization of a heater and to quickly heat the heater without waiting for completion of initialization of a computer which controls energization of the heater by software.
[0011]
Another object of the present invention is to safely control the energization of the heater in this case.
[0012]
[Means for Solving the Problems]
According to the first aspect of the present invention, there is provided a heater, a first switching element for turning ON / OFF a power supply from a power supply for heating the heater, and a first hardware for controlling ON / OFF of the switching element by hardware. A hardware control circuit, a computer that operates based on a predetermined program, and software control of turning on and off the switching element by processing executed by the computer instead of the hardware control after the computer has completed initialization. And a control unit for executing the above.
[0013]
Therefore, when the computer is performing initialization, the first hardware control circuit controls the energization of the heater by hardware, and after the initialization is completed, the control is replaced by software control executed by the computer. The power supply to the heater is started without waiting for the end, and the heater can be quickly heated.
[0014]
According to a second aspect of the present invention, in the heater control device according to the first aspect, a second switching element for turning on and off the energization and a duration of the hardware control are detected. A second hardware control circuit that performs hardware control to turn off the second switching element when the duration becomes longer than a predetermined reference value.
[0015]
Note that the second switching element may be implemented as the same element as the first switching element, or may be implemented as another element.
[0016]
Therefore, during the period before the software control of the heater and the detection of the occurrence of an abnormality by the control become possible, the heater energization time is monitored by the second hardware control circuit, and the hardware control is performed for a longer time than the reference time In the case of continuous operation, the power supply to the heater is stopped, so that the power supply to the heater can be safely controlled.
[0017]
According to a third aspect of the present invention, in the heater control device according to the second aspect, the second hardware control circuit notifies the computer when the duration is longer than the reference value. introduce.
[0018]
Therefore, since the detection of the occurrence of the abnormality is transmitted from the second hardware control circuit to the computer, the history of the occurrence of the abnormality can be held in a form that can be detected by the computer. When the occurrence of an abnormality in energization is detected, re-lighting of the heater when hardware control is switched to software control can be prevented, and safety can be improved.
[0019]
According to a fourth aspect of the present invention, there is provided a printer engine for forming an image on a medium by electrophotography, a fixing device for fixing a toner image after the image formation on the medium, An image forming apparatus, comprising: a heater control device according to any one of claims 1 to 3, wherein the heater heats the fixing device.
[0020]
Therefore, the heater for heating the fixing unit can be controlled by the heater control device according to any one of the first to third aspects.
[0021]
The image forming apparatus may further include an image input device for reading an image of the document, and the printer engine may form the image based on the read image data.
[0022]
BEST MODE FOR CARRYING OUT THE INVENTION
[First Embodiment of the Invention]
One embodiment of the present invention will be described as a first embodiment of the present invention.
[0023]
FIG. 1 is a schematic configuration diagram showing a configuration of a digital copying machine according to the present embodiment. This digital copier implements the image forming apparatus of the present invention, and includes a scanner unit 1 and a printer unit 2.
[0024]
First, the scanner unit 1 will be described. The scanner unit 1 includes a contact glass 3 for placing a document. The original is irradiated with light by a light source 4, and the reflected light forms an image on a light receiving surface of a CCD image sensor 7 via a mirror 5 and a lens 6. The light source 4 and the mirror 5 are mounted on an optical scanning device 8 that moves the lower surface of the contact glass 3 in the sub-scanning direction in parallel with the contact glass 3, and the optical scanning device 8 is driven by a stepping motor 9. The mirrors 61 and 62 are mounted on the optical scanning device 10 that moves in the sub-scanning direction at half the speed in conjunction with the optical scanning device 8. The scanning in the main scanning direction is performed by scanning the CCD, and the original image is read by the CCD image sensor 7 and the entire original is scanned by moving the optical system as described above.
[0025]
Next, the printer unit 2 will be described. The printer unit 2 serves as a printer engine for forming an image on a medium such as transfer paper in an electrophotographic system, and includes a laser writing system, an image reproducing system, and a paper feeding system. The laser writing system includes a laser output unit 11, an imaging lens 12, and a mirror 13. Inside the laser output unit 11, a polygon mirror (polygon mirror) which is rotated at high speed by a laser diode (LD) as a laser light source and an electric motor is provided (not shown).
[0026]
Laser light output from such a laser writing system is applied to a photoreceptor drum 14 of an image reproducing system for forming an image on a medium such as transfer paper by an electrophotographic method. Around the photosensitive drum 14, a charging charger 15, an eraser 16, a developing unit 17, a transfer charger 18, a separation charger 19, a separation claw 20, a cleaning unit 21, and the like are provided.
[0027]
The image reproducing process in the printer unit 2 will be briefly described. The peripheral surface of the photosensitive drum 14 is uniformly charged to a high potential by the charging charger 15. When the laser light is irradiated around the area, the potential of the irradiated part decreases. Since the laser light is ON / OFF controlled in accordance with the recording / reproduction black / white, the potential distribution corresponding to the recorded image, that is, the electrostatic latent image is formed on the peripheral surface of the photosensitive drum 14 by the irradiation of the laser light. You. When the portion on which the electrostatic latent image is formed passes through the developing unit 17, toner adheres according to the level of the potential, and the electrostatic latent image becomes a visualized toner image. At a predetermined timing, a medium such as transfer paper is fed from the cassette 22 to the portion where the toner image is formed, and overlaps the toner image. This toner image is transferred to the medium by the transfer charger 18, and thereafter separated from the photosensitive drum 14 by the separation charger 19 and the separation claw 20. The separated transfer paper is transported by a transport belt 23, heated by a fixing device 25 including a fixing roller having a heater 24 (see FIG. 2) therein, and then discharged to a discharge tray 26.
[0028]
Further, in this digital copying machine, as shown in FIG. 1, the printer unit 2 has two paper feeding systems. One of the paper feed systems has an upper paper cassette 22a and a manual paper feed table 22b, and the transfer paper set in the upper paper cassette 22a and the manual paper feed table 22b is fed by a paper feed roller 27. . The other paper feeding system includes a lower paper cassette 22c, and the transfer paper in the lower paper cassette 22c is fed by a paper feed roller 28. Then, the transfer paper fed from one of the paper feed rollers 27 or 28 is temporarily stopped in a state of being in contact with the registration roller 29, and is sent to the photosensitive drum 14 at a timing synchronized with the progress of the recording process.
[0029]
FIG. 2 is a block diagram showing an electrical connection of the digital copying machine. As shown in FIG. 2, DC power consumed by the digital copying machine is supplied from a DC power supply unit 30 that obtains DC from a commercial AC power supply 66. The digital copying machine includes a power supply system (not shown) for operating the actuator in addition to the communication control unit 31 and the sequence control unit 32. The output control of the sequence control unit 32 and the power supply system for operating the actuator is controlled by communication control. This is performed by a signal from the unit 31.
[0030]
The sequence control unit 32 is a CPU 33 for centrally controlling each unit based on a control program, a ROM 34 containing the control program and the like, a RAM 35 serving as a work area of the CPU 33, and a nonvolatile memory. It is configured by an NVRAM 36 that retains even the state, a reset IC 37 that detects a voltage supplied to the sequence control unit 32, and outputs an initialization signal for the entire control unit. The ROM 34, the RAM 35, the NVRAM 36, and the like, centered on the CPU 33, constitute a computer that executes the software control of the present invention.
[0031]
The communication control unit 31 that controls data input from the network also includes a CPU 38, a ROM 39, and a RAM 40, like the sequence control unit 32. Further, an operation unit 42 for receiving an operation on the digital copying machine from a user, and an I / F logic 41 for connecting the digital copying machine to an external network or the like (in this example, a personal computer 64 is connected) are also mounted. Have been.
[0032]
The digital copier has an energy saving mode function that shifts to lower power consumption than in a normal standby state when a state in which a new job is not executed has passed for a predetermined period of time. In the energy saving mode, the communication control unit 31 is continuously energized and monitors data input from the network and a start command from the operation unit 42 by the user. On the other hand, in the energy saving mode, the supply of power is stopped in order to reduce power consumption.
[0033]
A heater drive circuit 63 for controlling the heater 24 provided in the fixing device 25 includes a first and a second switching element (a second switching element) for controlling ON and OFF of the power supply from the commercial AC power supply 66 to the heater 24. The elements may be implemented as the same element as the first switching element or may be implemented as another element, but are implemented as the same element in the present embodiment.) 44, a thermistor 45 for measuring the temperature of the fixing device 25, and a photocoupler 46 for detecting the 0 V point of the commercial AC power supply 66. When the applied control signal becomes L level, the triac 43 and the relay 44 conduct the circuit and start energizing the heater 24.
[0034]
The CPU 33 of the sequence control unit 32 A / D converts the detection signal (voltage) of the thermistor 45 and asserts the drive signals of the triac 43 and the relay 44 when the temperature measured by the thermistor 45 is lower than a preset reference value. Then, the heater 24 is energized, and if the measured temperature is higher than the reference value, the temperature of the fixing device 25 is maintained at a constant level by performing software control to turn off the triac 43. If the heater 24 of the fixing device 25 is turned on at an arbitrary timing, an excessive rush current is generated, which may adversely affect the commercial AC power supply 66 such as a voltage drop. For this reason, when turning on the heater 24, the CPU 33 repeats the control to turn on the heater 24 for a fixed time every half-wave time of the AC output from the commercial AC power supply 66. Then, at the start of the lighting control of the heater 24, the ON time is set to a very short time, and thereafter, the control for gradually increasing the ON time for each half-wave time of the alternating current is executed. On the other hand, a soft start control is executed to prevent an excessive rush current from being generated.
[0035]
When the digital copying machine is in the energy saving mode, power is supplied only to the communication control unit 31. When a communication command is input from an external personal computer 64 or the like or a start command is input by the user operating the operation unit 42, the communication control unit 31 issues a start signal to the DC power supply unit 30. . Upon receiving the activation signal, the DC power supply unit 30 activates the sequence control unit 32 and a power supply system for operating the actuator (not shown), and starts supplying power to the entire digital copying machine. After the power supply is started, after the reset period specified by the reset IC 37 has elapsed, the CPU 33 reads the control program from the ROM 34 to execute an initialization operation, reads various set values from the NVRAM 36, and reads the entire system. Start software control of.
[0036]
In the digital copying machine having this configuration, the sequence control unit 32 is activated by an external activation signal, and during the period in which the above-described initialization operation is being performed, the hardware control provided in the sequence control unit 32 is performed. The circuit 65 controls the heater 24 of the fixing device 25.
[0037]
FIG. 3 is a block diagram showing a circuit configuration of the hardware control circuit 65. As shown in FIG. 3, the hardware control circuit 65 is a first hardware control circuit that hardware-controls ON and OFF of the triac 43, and includes a period measurement counter 47, a clk generator 48, a latch circuit 49, a shift register 50, a subtractor 51, a one-shot timer 52, and the like. In addition, a comparator 53 for comparing a detection signal from the thermistor 45 with a predetermined reference voltage is provided.
[0038]
The cycle measuring counter 47 performs a count-up operation by the clk signal output from the clk generator 48. The latch circuit 49 latches the counter value by the edge of a signal (zero cross signal) indicating the 0 V point of the commercial power output from the photocoupler 46, and the counter 47 for period measurement clears the counter value. By executing, the cycle of the zero-cross signal is measured in units of the clk signal. The reset signal output from the reset IC 37 becomes an enable signal, and while the reset signal is at the L level, the latch operation is repeated in synchronization with the zero-cross signal. However, the operation stops when the reset signal is at the H level. And only retain the data.
[0039]
Here, as an example, it is assumed that the counter value of the period measurement counter 47 measured between the asserted edges of the zero-cross signal is 128, and the operation of the hardware control circuit 65 will be described below.
[0040]
The comparator 53 compares the reference voltage with the voltage value of the detection signal of the thermistor 45, and asserts the control signal of the triac 43 (the output of the comparator 53 is at L level) in a state where “reference voltage <thermistor voltage”. When the heater 24 is energized and the temperature rises above a certain value of the fixing device 25, "reference voltage> thermistor voltage" is satisfied, and the control signal of the triac 43 is negated (the output of the comparator 53 is at H level).
[0041]
The counter value latched by the latch circuit 49 is shifted by 2 bits by the shift register 50 and becomes a value of 1/4 of the counter value.
[0042]
The one-shot timer 52 outputs an H level signal in a steady state, and when a start signal (zero cross signal) is asserted, starts counting from the edge thereof and counts up a value set in a built-in Duty setting register. Switch the output signal to the L level. Therefore, as the value set in the duty setting register is larger, the delay from the edge of the zero-cross signal to the assertion of the counter output signal is delayed. When the value of the duty setting register is 0, the L level signal is continuously output. When the activation signal from the subtractor 51 is negated, the output is fixed at the H level.
[0043]
When detecting the falling edge of the output of the comparator 53, the subtractor 51 takes in data from the latch circuit 49 and the shift register 50. When the output of the comparator 53 is at the L level and a falling edge of the zero-cross signal is detected, the activation signal of the one-shot timer 52 is asserted, and the value of the shift register 50 is subtracted from the counter value of the latch circuit 49. The result is transferred to the duty setting register of the one-shot timer 52. The result and the value of the shift register 50 are also stored in a register (not shown) built in the subtractor 51. When the output signal of the comparator 53 is at the H level, the activation signal to the one-shot timer 52 is negated.
[0044]
The mask signal output from the CPU 33 is held at the L level during the reset period by the reset IC 37 and during the initialization operation of the sequence control unit 32, and is in a state in which the control of the triac 43 by the hardware control circuit 65 is permitted. . When the initialization operation is completed and the CPU 33 starts controlling the triac 43 by software according to the control program stored in the ROM 34, the signal logic is switched to the H level, and the influence of the hardware control circuit 65 on the control of the triac 43 is changed. To eliminate.
[0045]
When the DC power supply unit 30 starts supplying power to the sequence control unit 32 in response to an external start signal, the reset IC 37 detects a rise in voltage and outputs an H level for a predetermined time. While the reset signal is at the H level, the cycle measuring counter 47 counts the number of clk signals output from the clk generator 48 and latches the count result at each falling edge of the zero cross signal. When the reset signal is negated, if the output voltage of the thermistor 45 is higher than the reference voltage, the output of the comparator 53 is at the H level, and the subtractor 51 that has detected this output sets the set value in the Duty setting register of the one-shot timer 52. Forward. Until the first zero-cross signal is input, a value of 128 is set in the duty setting register in advance, and the value of the shift register 50 is subtracted from the counter value of the latch circuit 49 as the set value by the assertion of the first zero-cross signal. "128-32 = 96", which is the result of the above, is set, and if the interval of the zero-cross signal is, for example, 10 ms, from the assertion of the zero-cross signal, "7.5 ms" is calculated as "10 ms × (96/128) = 7.5 ms". Later, the heater 24 is turned on. Then, in the subsequent input of the zero-cross signal, the value of the shift register 50 is subtracted from the previous subtraction result stored in the register of the subtractor 51, and the result is output to the duty setting register. Store in a register. That is, the duty setting value is further reduced by 32 by the input of the next zero-cross signal, and the ON time of the heater 24 is lengthened for each zero-cross signal. After the fourth zero-cross signal is input, the value of 0 is stored in the duty setting register. Since this is set, the energization control of the heater 24 is performed at 100% duty.
[0046]
The subtractor 31 stops when the value stored in the duty setting register becomes 0, and reloads the value from the latch circuit 49 and the shift register 50 every time the output of the comparator 53 switches to the H level. After the reset signal from the reset IC 37 is negated, the CPU 33 completes initialization operations such as initialization of the CPU 33, initialization of peripheral devices, and reading of control data. Thereafter, the CPU 33 outputs a mask signal, the AND circuit 67 takes the AND of the mask signal and the Duty set value of the one-shot timer 52 by the AND circuit 67, and outputs a control signal ( The triac control signal) is invalidated by the OR circuit to which the output of the AND circuit 67 is output, and thereafter, the temperature control of the fixing device 25 is executed only by executing the software by the CPU 33 (outputting the software control signal).
[0047]
FIG. 4 shows a timing chart of each signal. As the duty setting value set in the duty setting register of the one-shot timer 52 decreases from the initial value of 128 to 64, 32, 0, It can be seen that the duty of the control signal of the triac 43 increases, and thus the energization time of the heater 24 increases. After that, due to the falling edge of the comparator output 53 generated when the temperature of the fixing device 25 once rises, the Duty setting value set in the Duty setting register of the one-shot timer 52 returns to the initial value of 128 again. It can be seen that the operation of is repeated. By changing the shift amount of the shift register 50, it is also possible to realize a more detailed soft start.
[0048]
By the way, in the digital copying machine having this configuration, if the temperature control of the fixing unit 25 is executed only by executing the software by the CPU 33 without using the hardware control circuit 65 or the like, the system initialization operation of the CPU 33 is completed. Cannot start the temperature control of the fixing device 25, and waits for the time corresponding to the initialization operation from the time when the communication control unit 31 receives the start signal to the time when the printer unit 2 can perform the image forming operation. There is a disadvantage that the raising time is long.
[0049]
However, in the digital copying machine having this configuration, when the CPU 33 is performing the system initialization operation, the temperature control of the fixing device 25 must be started by a hardware configuration control circuit such as the hardware control circuit 65. And the start-up time described above can be reduced. Also, by realizing soft start by the hardware control circuit 65, it is possible to reduce the rush current to the heater 24, and it is possible to minimize the adverse effect on the commercial AC power supply 66.
[0050]
[Embodiment 2]
Another embodiment of the present invention will be described as a second embodiment of the present invention.
[0051]
The following description focuses on the differences between the digital copying machine of the present embodiment and the digital copying machine of the first embodiment, and common members and circuit elements are denoted by the same reference numerals as those of the first embodiment. And new illustrations and descriptions are omitted.
[0052]
The difference between the digital copying machine of the present embodiment and the first embodiment is that, as shown in FIG. 5, a hardware control circuit 65 first includes a fixing device protection counter 54 serving as a second hardware control circuit. The point is.
[0053]
The fixing device protection counter 54 is a counter for integrating the clk signal output from the clk generator 48 after the reset signal of the reset IC 37 is negated. The fixing device protection counter 54 holds a reference value (timeout setting) set by hardware, and outputs an overflow signal to the AND circuit 67 when the integrated value of the clk signal matches the above-described reference value. . The time-out setting based on the reference value is equal to or longer than the time from the release of the reset to the start of the temperature control of the fixing device 25 by the CPU 33. If the sequence control unit 33 normally starts up, the counter 54 is not sufficiently generated before the overflow signal is generated. Clearing is possible, and when the heater 24 is continuously energized for a time corresponding to the reference value, a time is set for the fixing device 25 to rise to a temperature at which the image forming operation can be performed. The count value of the fixing device protection counter 54 is cleared by the counter clear signal output by the CPU 33 and the output of the H level signal of the comparator 53 (see FIG. 6).
[0054]
When the reset signal of the reset IC 37 is negated and the output of the comparator 53 is at H level, the heater 24 is energized by the hardware control circuit 65, and the counter 54 for the fixing device protection starts counting up. If this counter value exceeds the timeout setting, an overflow signal (active H) is output. This signal is latched by the counter 54 and output to the AND circuit 67 to negate the control signal of the triac 43. Even if the counter value is cleared, the overflow signal is held once set, and can be released only by the counter reset signal. Therefore, the case where the hardware control circuit 65 can control the energization of the heater 24 means that the CPU 33 clears the counter value within the timeout period, or the temperature of the fixing device 25 is within the timeout period. Until the temperature rises to a certain temperature, the output of the comparator 53 is inverted, and the counter value is cleared.
[0055]
With the above-described configuration, when the paper jam occurs in the fixing unit 25, or when an abnormality such as a state in which the temperature of the fixing unit 25 cannot be measured normally due to an abnormality of the thermistor 45 occurs, the hardware control circuit 65 Even if the heater 24 is continuously energized, the energization of the heater 24 can be stopped before the apparatus reaches a dangerous state. As described above, while the start-up time of the digital copying machine is reduced, the system Security can be maintained.
[0056]
Third Embodiment of the Invention
Another embodiment of the present invention will be described as a third embodiment of the present invention.
[0057]
The following description focuses on the differences between the digital copying machine of the present embodiment and the digital copying machine of the second embodiment, and common members and circuit elements are denoted by the same reference numerals as those of the second embodiment. And new illustrations and descriptions are omitted.
[0058]
The difference between the digital copying machine of the present embodiment and the second embodiment is that, as shown in FIG. 7, an overflow signal of a fixing device protection counter 54 for realizing a second hardware control circuit is used for fixing device fixing. That is, the signal is latched by the counter 54, this signal is output to the CPU 33, and this can be detected by the CPU 33.
[0059]
With such a configuration, when the fixing protection counter 54 overflows, the overflow signal is latched and output to the CPU 33, so that after the CPU 33 completes the initialization operation, the temperature of the fixing device 25 becomes low. Before the control is started, an overflow signal is detected. If the overflow signal is asserted, it is determined that the fixing unit 25 may be in an abnormal state. The power supply is stopped, and a user is notified of the abnormal state of the device on the operation unit 42 by a predetermined means, for example.
[0060]
With this configuration, it is possible for the CPU 33 to detect the continuous energization of the heater 24 that occurs before the operation of the system is started by software control, thereby reducing the start-up time of the digital copying machine as described above. In addition, the security of the system can be maintained.
[0061]
【The invention's effect】
According to the first aspect of the present invention, energization of the heater is started without waiting for the initialization of the computer to be completed, and the heater can be quickly heated.
[0062]
According to a second aspect of the present invention, in the first aspect of the present invention, the heater power-on time is set to the second hardware until software control of the heater and detection of an abnormality occurrence by the control become possible. Monitoring by the control circuit, when the hardware control is continued for a longer time than the reference time, by stopping the power supply to the heater, the power supply control of the heater can be executed safely.
[0063]
According to a third aspect of the present invention, in the second aspect of the present invention, it is possible to hold a history of occurrence of an abnormality detected by the second hardware control circuit in a form detectable by a computer. When the control detects the occurrence of an abnormality in the long-time energization of the heater, the heater can be prevented from being turned on again when hardware control is switched to software control, and safety can be improved.
[0064]
According to the fourth and fifth aspects of the present invention, the heater for heating the fixing device can be controlled by the heater control device according to any one of the first to third aspects.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram illustrating an overall configuration of a digital copying machine according to an embodiment of the present invention.
FIG. 2 is a block diagram showing electrical connections of a control system of the digital copying machine.
FIG. 3 is a block diagram of electrical connection of a hardware control circuit.
FIG. 4 is a timing chart of each signal in a control system of the digital copying machine.
FIG. 5 is a block diagram of an electrical connection of another configuration example of the hardware control circuit;
6 is a timing chart of each signal in a control system in the configuration example of FIG. 5;
FIG. 7 is a block diagram of electrical connection of another configuration example of the hardware control circuit;
[Explanation of symbols]
2 Printer engine
33 Computer
25 Fixing unit
43 First and second switching elements
54 Second Hardware Control Circuit
65 First Hardware Control Circuit

Claims (5)

A heater,
A first switching element for turning ON / OFF a power supply from a power supply for heating the heater;
A first hardware control circuit that hardware-controls ON and OFF of the switching element;
A computer that operates based on a predetermined program;
Control means for executing software control of ON and OFF of the switching element by processing executed by the computer in place of the hardware control after the computer completes initialization;
A heater control device comprising: A second switching element for turning on and off the energization;
A second hardware control circuit that detects a duration during which the hardware control is being performed and performs hardware control to turn off the second switching element when the duration is longer than a predetermined reference value; When,
The heater control device according to claim 1, further comprising: 3. The heater control device according to claim 2, wherein the second hardware control circuit, when the duration time becomes longer than the reference value, notifies the computer of the fact. A printer engine for forming an image on a medium by an electrophotographic method,
A fixing device for fixing the toner image after the image formation on the medium,
A heater control device according to any one of claims 1 to 3,
With
The heater is for heating the fixing device,
Image forming device. Equipped with an image input device that reads the image of the original,
The printer engine forms the image based on the read image data,
The image forming apparatus according to claim 4.

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