JP4177138B2 - Heater control device and image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a heater control device that controls energization of a heater and an electrophotographic image forming apparatus including the heater control device.
[0002]
[Prior art]
Patent Document 1 discloses a technique for shortening the recovery time of an apparatus by omitting the initialization process when there is an unnecessary process in the digital copying machine when the power is turned on. ing.
[0003]
[Patent Document 1]
JP 2000-10436 A
[0004]
[Problems to be solved by the invention]
In recent years, for electrophotographic image forming apparatuses that copy image data based on image data input from a network or image data of a document read by an image input apparatus, there has been an increasing demand for energy saving. There is a strong demand to reduce power consumption in a standby state in which image formation is not performed. Therefore, these devices have an energy saving mode for saving power in a standby state in which image formation is not performed. As a means for saving power, an image forming apparatus having a fixing device that fixes toner onto transfer paper by heat stops power supply to the fixing device in a standby state to reduce power consumption. ing.
[0005]
In addition, as a measure to further reduce power consumption, power is supplied only to a specific control unit having an interface for communication with the outside, and power supply is stopped for other control units. Yes.
[0006]
On the other hand, in some areas, it is also required to reduce the return time from the energy saving mode to the image forming operation due to official regulations, so that the conflicting demands of low power consumption during standby and shortening the return time are compatible. It is demanded.
[0007]
In addition, in an image forming apparatus having a configuration in which a fixing unit is heated by a heater that is supplied with electric power from a commercial power source, when the heater is energized at an arbitrary timing when power is supplied to the heater, the voltage ripple of the commercial power source, etc. May affect other luminaire lights that are taking power from the same commercial power source. The impact on commercial power supply may be limited by public regulations. In general, countermeasures are taken by synchronizing the heater lighting timing with the commercial power supply voltage waveform by software control. It is carried out.
[0008]
However, since software is involved, it is difficult to start the energization control of the heater of the fixing unit until the initialization operation of the control unit is completed, which is a great obstacle to shortening the return time from the energy saving mode.
[0009]
On the other hand, in the technique disclosed in Patent Document 1, it is attempted to shorten the recovery time by omitting processes other than the minimum necessary control when starting up the apparatus. Since the operation and the like are processes indispensable for realizing stable control, there is a problem that the return time from the energy saving mode becomes longer by the time required for initialization of the control unit.
[0010]
An object of the present invention is to start energization of a heater and quickly heat the heater without waiting for completion of initialization of a computer that controls the energization of the heater with software.
[0011]
Another object of the present invention is to safely perform energization control of the heater in this case.
[0012]
[Means for Solving the Problems]
The invention according to claim 1 is a heater, a switching element for turning on / off power from a power source for heating the heater, and a first hardware control circuit for hardware-controlling on / off of the switching element. And a computer that operates based on a predetermined program, and after the computer finishes initialization, executes software control of ON / OFF of the switching element by processing executed by the computer instead of the hardware control And a second hardware control for detecting a duration during which the hardware control is executed and performing a hardware control for turning off the switching element when the duration exceeds a predetermined reference value. And the reference value is a normal temperature control start by the computer Is the time or more in, and, Continuous energization of the heater The temperature is set to a time at which the temperature rises to a temperature at which an image forming operation can be performed.
[0013]
Therefore, when the computer is performing initialization Ha Hardware control of the heater is controlled by the hardware control circuit, and instead of software control executed by the computer after the initialization is completed, power supply to the heater is started without waiting for the completion of the computer initialization. Can be heated.
[0016]
Therefore, during the period until the software control of the heater and the occurrence of the abnormality by the control can be detected, the energization time of the heater is monitored by the second hardware control circuit, and the hardware control is performed for a longer time than the reference time. When continuous, the power supply to the heater can be safely executed by stopping the power supply to the heater.
[0017]
Claim 2 The invention described in Claim 1 In the heater control device described in (1), when the duration time becomes longer than the reference value, the second hardware control circuit notifies the computer to that effect.
[0018]
Accordingly, since the detection of the occurrence of abnormality is transmitted from the second hardware control circuit to the computer, the history of occurrence of abnormality can be maintained in a form that can be detected by the computer, and the heater control can be performed for a long time. When the occurrence of an abnormality in energization is detected, the heater can be prevented from being turned on again when switching from hardware control to software control, and safety can be improved.
[0019]
Claim 3 The invention described in (1), a printer engine that forms an image on a medium by electrophotography, a fixing device that fixes the toner image after the image formation on the medium, Claim 1 or 2 The heater control device according to claim 1, wherein the heater heats the fixing device.
[0020]
Therefore, about the heater that heats the fixing device Claim 1 or 2 Control by the described heater control device can be executed.
[0021]
The image forming apparatus may further include an image input device that reads an image of a document, and the printer engine may perform the image formation based on the image data after the reading ( Claim 4 ).
[0022]
DETAILED DESCRIPTION OF THE INVENTION
Embodiment 1 of the Invention
One embodiment of the present invention will be described as Embodiment 1 of the present invention.
[0023]
FIG. 1 is a schematic configuration diagram showing the configuration of the digital copying machine according to the present embodiment. This digital copying machine 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 the light source 4, and the reflected light forms an image on the light receiving surface of the CCD image sensor 7 via the mirror 5 and the 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 parallel to the contact glass 3 in the sub-scanning direction, 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, 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 by an electrophotographic method, 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 laser diode (LD) that is a laser light source and a polygon mirror (polygon mirror) that is rotated at high speed by an electric motor are provided (not shown).
[0026]
Laser light output from such a laser writing system is applied to a photosensitive drum 14 of an image reproducing system that forms 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 reproduction 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 laser light is irradiated around the periphery, the potential of the irradiated portion decreases. Since the laser light is ON / OFF controlled in accordance with black / white for recording / reproduction, 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 laser light irradiation. The When the portion where 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. A medium such as transfer paper is fed from the cassette 22 to the portion where the toner image is formed at a predetermined timing, and overlaps the toner image. This toner image is transferred to a medium by a transfer charger 18 and then separated from the photosensitive drum 14 by a separation charger 19 and a separation claw 20. The separated transfer paper is transported by a transport belt 23, heated by a fixing device 25 using a fixing roller incorporating a heater 24 (see FIG. 2), and then discharged to a paper discharge tray 26.
[0028]
In this digital copying machine, as shown in FIG. 1, the printer unit 2 has two paper feeding systems. One paper feed system has an upper paper feed cassette 22a and a manual paper feed tray 22b, and the transfer paper set on the upper paper feed cassette 22a and the manual paper feed tray 22b is fed by a paper feed roller 27. . The other paper feed system includes a lower paper feed cassette 22 c, and the transfer paper in the lower paper feed cassette 22 c is fed by a paper feed roller 28. Then, the transfer paper fed from any of the paper feed rollers 27 or 28 is temporarily stopped in contact with the registration roller 29 and 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 electrical connections of the digital copying machine. As shown in FIG. 2, the 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. This digital copying machine includes a power supply system (not shown) for actuator operation in addition to the communication control unit 31 and sequence control unit 32. The output control of the power supply system for operation of the sequence control unit 32 and 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 that centrally controls each unit based on a control program, a ROM 34 that contains this control program, a RAM 35 that serves as a work area for the CPU 33, and a non-volatile memory. The configuration includes an NVRAM 36 that is held even in a 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, RAM 35, NVRAM 36, etc. centered on the CPU 33 constitute a computer that executes software control of the present invention.
[0031]
Further, the communication control unit 31 that controls data input from the network is provided with a CPU 38, a ROM 39, and a RAM 40, similar to the sequence control unit 32. In addition, an operation unit 42 that receives an operation on the digital copying machine from a user, and an I / F logic 41 that connects the digital copying machine to an external network or the like (in this example, a personal computer 64 is connected) are also mounted. Has been.
[0032]
This digital copying machine has an energy saving mode function that shifts to a lower power consumption than the normal standby state when a new job has not been executed for a certain period of time. In this energy saving mode, the communication control unit 31 continues to be energized, and monitors data input from the network and activation commands from the operation unit 42 by the user. On the other hand, in the energy saving mode, the sequence control unit 32 stops supplying power in order to reduce power consumption.
[0033]
A heater driving circuit 63 for controlling the heater 24 provided in the fixing device 25 is provided with first and second switching elements (second switching) for controlling ON / OFF of energization from the commercial AC power supply 66 to the heater 24. The element may be implemented as the same element as the first switching element, or may be implemented as another element, but is implemented as the same element in the present embodiment) and the triac 43 and the relay 44, a thermistor 45 that measures the temperature of the fixing device 25, and a photocoupler 46 that detects the 0V point of the commercial AC power supply 66. The triac 43 and the relay 44 both conduct the circuit and start energization to the heater 24 when the given control signal becomes L level.
[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 signal for 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 when the measured temperature is higher than the reference value, the temperature of the fixing device 25 is kept at a constant level by performing software control to turn off the triac 43. Further, when the heater 24 of the fixing device 25 is turned on at an arbitrary timing, an excessive inrush current is generated, which may adversely affect the commercial AC power supply 66 such as a voltage drop. For this reason, when the heater 24 is turned on, the CPU 33 repeats the control to turn on the heater 24 for a predetermined time every half-wave time of the alternating current output from the commercial alternating-current power supply 66. Then, at the time of starting the lighting control of the heater 24, the ON time is set to a very short time, and thereafter, the control is performed to gradually increase the ON time for each half-wave time of the alternating current. On the other hand, soft start control is performed to prevent excessive inrush current.
[0035]
When the digital copying machine is in the energy saving mode, only the communication control unit 31 is energized. When a start command is input by inputting a communication command from an external personal computer 64 or the like or when the user operates the operation unit 42, the communication control unit 31 issues a start signal to the DC power supply unit 30. . The DC power supply unit 30 that has received the start signal starts the sequence control unit 32 and a power supply system for actuator operation (not shown), and starts supplying power to the entire digital copying machine. After the reset period specified by the reset IC 37 elapses, the sequence control unit 32 that has started supplying power reads the control program from the ROM 34 and executes an initialization operation, and reads various setting values from the NVRAM 36 to read the entire system. Start software control.
[0036]
In the digital copying machine of this configuration, the sequence control unit 32 is activated by an activation signal from the outside, and the hardware control provided in the sequence control unit 32 is performed during the period in which the above-described initialization operation is performed. The circuit 65 controls the heater 24 of the fixing unit 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 serves as a first hardware control circuit for hardware control of ON / OFF of the triac 43, and includes a period measurement counter 47, a clk generator 48, and a latch circuit. 49, a shift register 50, a subtractor 51, a one-shot timer 52, and the like. In addition, a comparator 53 that compares the detection signal from the thermistor 45 with a predetermined reference voltage is provided.
[0038]
The period measurement counter 47 performs a count-up operation according to the clk signal output from the clk generator 48. The latch circuit 49 latches the counter value by the edge of the signal (zero cross signal) indicating the 0V point of the commercial power supply output from the photocoupler 46, and the counter 47 for period measurement clears the counter value. When executed, the period of the zero cross signal is measured in units of the clk signal. In addition, the reset signal output from the reset IC 37 becomes an enable signal, and the latch operation is repeated in synchronization with the zero cross signal while the reset signal is at the L level, but the operation is stopped when the reset signal is at the H level. Only hold data.
[0039]
Here, as an example, it is assumed that the counter value by the period measurement counter 47 measured between the assert 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 in the state where “reference voltage <thermistor voltage” (the output of the comparator 53 is L level). When the heater 24 is energized and the temperature rises above a certain value of the fixing unit 25, “reference voltage> thermistor voltage” is established, and the control signal of the triac 43 is negated (the output of the comparator 53 is 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 quarter value 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 a count operation from that edge and counts up the value set in the built-in duty setting register. The output signal is switched to L level. For this reason, as the set value of 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 the subtractor 51 detects the falling edge of the output of the comparator 53, it takes in data from the latch circuit 49 and the shift register 50. Further, when the falling of the zero cross signal is detected while the output of the comparator 53 is at the L level, the start 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 becomes H level, the start signal for the one-shot timer 52 is held in the negate.
[0044]
The mask signal output from the CPU 33 is held at the L level during the reset period of the reset IC 37 and the initialization operation of the sequence control unit 32, and is in a state of permitting control of the triac 43 by the hardware control circuit 65. . When the initialization operation is completed and the CPU 33 starts to control 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 effected. To eliminate.
[0045]
When the DC power supply unit 30 starts to supply power to the sequence control unit 32 by an activation signal from the outside, the reset IC 37 detects the rise of the voltage and outputs the H level only for a predetermined time. While the reset signal is at the H level, the period measurement 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 it outputs a set value to 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 advance in the duty setting register, and when the first zero cross signal is asserted, the value of the shift register 50 is subtracted from the counter value of the latch circuit 49 as the setting value. When “128−32 = 96”, which is the result of the above, is set and the interval between the zero cross signals is, for example, 10 ms, from the assertion of the zero cross signal, “10 ms × (96/128) = 7.5 ms” is approximately 7.5 ms. The heater 24 is turned on later. 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 register. That is, when the next zero cross signal is input, the duty setting value is further subtracted by 32, and the ON time of the heater 24 becomes longer for each zero cross signal, and after the fourth zero cross signal is input, the duty setting register has a value of 0. Since it is set, the energization control of the heater 24 is performed with 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 is switched to the H level. In addition, after the reset signal from the reset IC 37 is negated, the CPU 33 can start the control of the fixing device 25 when initialization operations such as initialization of the CPU 33, initialization of peripheral devices, and reading of control data are completed. Thereafter, the CPU 33 outputs a mask signal, takes an AND of the mask signal and the duty setting value of the one-shot timer 52 by the AND circuit 67, and outputs a control signal (to the triac 43 by the hardware control circuit 65). The triac control signal) is invalidated in the OR circuit that is the output destination of the AND circuit 67, and thereafter, the temperature control of the fixing device 25 is executed only by the execution of software (output of the software control signal) by the CPU 33.
[0047]
FIG. 4 shows a timing chart of each signal. The duty setting value set in the duty setting register of the one-shot timer 52 decreases from the initial 128 to 64, 32, 0. It can be seen that the duty of the control signal of the triac 43 increases, and therefore the energization time of the heater 24 increases. Thereafter, due to the falling edge of the comparator output 53 that occurs once the temperature of the fixing device 25 becomes high, the duty setting value set in the duty setting register of the one-shot timer 52 again returns to the initial value 128, and It can be seen that the above operation is repeated. It is also possible to realize a finer soft start by changing the shift amount of the shift register 50.
[0048]
By the way, in the digital copying machine of this configuration, if the temperature control of the fixing device 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 the time from when the communication control unit 31 receives the start signal until the printer unit 2 can perform the image forming operation for the time corresponding to the initialization operation. There is a disadvantage that the raising time becomes longer.
[0049]
However, in the digital copying machine having this configuration, the temperature control of the fixing device 25 is started by a control circuit having a hardware configuration such as the hardware control circuit 65 when the CPU 33 is executing the system initialization operation. This makes it possible to reduce the aforementioned startup time. In addition, by realizing the soft start by the hardware control circuit 65, the inrush current to the heater 24 can be reduced, and the adverse effect on the commercial AC power supply 66 can be minimized.
[0050]
[Embodiment 2 of the Invention]
Another embodiment of the present invention will be described as a second embodiment of the present invention.
[0051]
In the following description, the digital copying machine of the present embodiment will be described mainly with respect to differences from the digital copying machine of the first embodiment, and common members, circuit elements, and the like are denoted by the same reference numerals as in the first embodiment. The new illustration and explanation are omitted.
[0052]
As shown in FIG. 5, the digital copying machine of the present embodiment is different from that of the first embodiment. First, as shown in FIG. 5, the hardware control circuit 65 is provided with a fixing device protection counter 54 serving as a second hardware control circuit. It is a point that has.
[0053]
The fixing device protection counter 54 is a counter that integrates 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 in hardware, and outputs an overflow signal to the AND circuit 67 when the integrated value of the clk signal matches the reference value. . The time-out setting based on this reference value is equal to or more than the time from the reset release to the start of temperature control of the fixing device 25 by the CPU 33. If the sequence control unit 33 starts up normally, the counter 54 is sufficiently set before the overflow signal is generated. When the heater 24 is continuously energized for a time corresponding to the reference value, the fixing device 25 is set to a time for raising the temperature to a temperature at which an image forming operation can be performed. Further, the count value of the fixing device protection counter 54 is cleared by the output of the counter clear signal output from the CPU 33 and 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 the H level, the heater 24 is energized by the hardware control circuit 65, and at the same time, the fixing device protection counter 54 starts counting up. When 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, thereby negating the control signal of the triac 43. Even if the counter value is cleared, the overflow signal is retained once set, and can be canceled only by the counter reset signal. For this reason, the case where the hardware control circuit 65 can control the energization of the heater 24 means that the temperature of the fixing unit 25 can perform the image forming operation until the counter value is cleared within the timeout time by the CPU 33 or within the timeout time. Until the counter value is cleared and the output of the comparator 53 is inverted.
[0055]
With the configuration described above, the hardware control circuit 65 causes a paper jam in the fixing device 25 or an abnormality such as a state in which the temperature of the fixing device 25 cannot be measured normally due to an abnormality in the thermistor 45. Even if continuous energization of the heater 24 occurs, it becomes possible to stop the energization of the heater 24 before the apparatus reaches a dangerous state. As described above, while reducing the startup time of the digital copying machine, the system It becomes possible to maintain the safety of.
[0056]
Embodiment 3 of the Invention
Another embodiment of the present invention will be described as a third embodiment of the present invention.
[0057]
In the following description, the digital copying machine according to the present embodiment will be described with a focus on differences from the digital copying machine according to the second embodiment. Common members, circuit elements, and the like are denoted by the same reference numerals as those in the second embodiment. The new illustration and explanation are omitted.
[0058]
The digital copying machine of the present embodiment is different from that of the second embodiment in that the overflow signal of the fixing device protection counter 54 that realizes the second hardware control circuit is used for the fixing device protection as shown in FIG. It is latched by the counter 54 and this signal is output to the CPU 33 so that the CPU 33 can detect it.
[0059]
By adopting 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 is reached. When the overflow signal is detected before the control is started and the overflow signal is asserted, it is determined that there is a possibility that the fixing device 25 is already in an abnormal state. While stopping the energization, the user is notified of the abnormal state of the device on the operation unit 42 by a predetermined means.
[0060]
By adopting this configuration, it becomes possible to detect the continuous energization of the heater 24 generated before the CPU 33 starts the operation of the system by software control, while reducing the start-up time of the digital copying machine as described above. It is also possible to maintain the safety of the system.
[0061]
【The invention's effect】
According to the first aspect of the present invention, energization of the heater can be started without waiting for completion of initialization of the computer, and the heater can be heated quickly.
[0062]
According to the first aspect of the present invention, the heater energization time is monitored by the second hardware control circuit during the period until the software control of the heater and the detection of the occurrence of abnormality by the control become possible. If hardware control continues for a longer time than Before the equipment is in danger By stopping energization to the heater, While reducing the startup time of digital copiers, The energization control of the heater can be executed safely.
[0063]
Claim 2 The invention described in Claim 1 In the invention described in (2), it is possible to maintain the history of occurrence of abnormality detected by the second hardware control circuit in a form that can be detected by a computer, and the occurrence of abnormality in the energization of the heater for a long time by hardware control. When detected, the heater can be prevented from being turned on again when switching from hardware control to software control, and safety can be improved.
[0064]
Claims 3 and 4 The invention described in 1 relates to a heater for heating the fixing device. Claim 1 or 2 Control by the described heater control device can be executed.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram showing an overall configuration of a digital copying machine according to an embodiment of the present invention.
FIG. 2 is a block diagram showing electrical connection 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 the control system of the digital copying machine.
FIG. 5 is a block diagram of electrical connection of another configuration example of the hardware control circuit.
6 is a timing chart of each signal in the control system in the configuration example of FIG.
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 computers
25 Fixing device
43 First and second switching elements
54 Second hardware control circuit
65 First hardware control circuit

Claims (4)

A heater,
A switching element for turning ON / OFF the energization from a power source for heating the heater;
A first hardware control circuit for hardware control of ON / OFF of the switching element;
A computer that operates based on a predetermined program;
Control means for performing software control of ON / OFF of the switching element by processing executed by the computer instead of the hardware control after the computer has completed initialization;
A second hardware control circuit that detects a duration time during which the hardware control is executed and performs hardware control to turn off the switching element when the duration time is longer than a predetermined reference value;
With
The heater control apparatus, wherein the reference value is set to a time that is equal to or longer than a time until normal temperature control is started by the computer and rises to a temperature at which an image forming operation can be performed by continuous energization of the heater. .   2. The heater control device according to claim 1, wherein when the duration time is longer than the reference value, the second hardware control circuit notifies the computer to that effect. A printer engine for forming an image on a medium by electrophotography;
A fixing device for fixing the toner image after the image formation on the medium;
The heater control device according to claim 1 or 2,
With
The heater heats the fixing device.
Image forming apparatus. It has an image input device that reads the image of the document,
The printer engine performs the image formation based on the image data after reading.
The image forming apparatus according to claim 3.

Images