JP2000305409A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent such a state that an image is not immediately formed because the temperature of a fixing unit rises by the runaway of a microprocessor so that a thermistor is actuated and to prevent a mechanism member from being thermally damaged by the temperature rise of the fixing unit, as for an image forming device actuated by the program control of the microprocessor. SOLUTION: The output of the thermistor TH is inputted to the microprocessor 14 and also inputted to a comparator 16. The OR signal of a control signal S1 from the microprocessor 14 and a control signal S2 from the comparator 16 is inputted to a heater energizing circuit 15 so as to control the energizing circuit 15. Then, temperature (θ2) controlled by the comparator 16 is set to be higher than temperature (θ1) controlled by the microprocessor 14. Thus, the energizing circuit 15 is controlled by the comparator 16 after the runaway of the microprocessor 14 is caused.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus provided with a fixing device for fixing a toner image on a recording medium by heat. It is an object of the present invention to provide an image forming apparatus for controlling a temperature.

[0002]

2. Description of the Related Art In recent years, an electrophotographic image forming apparatus is often used in printers, copiers and facsimile machines. The outline of the image forming apparatus will be described with reference to FIG. The image forming apparatus 1 includes a sheet cassette 2, a pickup roller 3, a transport roller 4, a registration roller 6, a developing device 7, a transfer roller 8, a photosensitive drum 9, a cleaner blade 10, a charging roller 11, an LED array head 12, a fixing device. It comprises a vessel 13 and the like.

[0005] The paper feed cassette 2 stores recording media such as paper and OHP sheets. In the following description, a sheet will be described as an example of a recording medium. The pickup roller 3 feeds out the paper from the paper feed cassette 2 and sends out the paper to the transport roller 4. The transport roller 4 transports a sheet along a guide 5. The registration rollers 6
The sheet conveyed along the guide 5 is sent to the photosensitive drum 9 at a proper timing.

The photosensitive drum 9 has a photoconductive film formed on the surface of a grounded aluminum pipe. The photosensitive drum 9 rotates clockwise in FIG. 5, and a charging roller 11, an LED array head 12, a developing unit 9, a transfer roller 8, and a cleaner blade 10 are arranged around the photosensitive drum 9 along the rotation direction. I have. The charging roller 11 is made of a fur brush, conductive rubber, or the like, and charges the surface of the photosensitive drum 9 to a predetermined potential while rotating.

[0005] The LED array head 12 comprises an LED array 12a and a rod lens 12b. LE
The D array 12a is driven based on image data, and the rod lens 12b irradiates light from the LED array 12a to the surface of the photosensitive drum 9 to form an electrostatic latent image. The developing device 7 adheres toner to the electrostatic latent image on the surface of the photosensitive drum 9 to form a visible toner image.

The developing device 7 includes a developing roller 7a, a doctor blade 7b, and a toner hopper 7c. Powder toner is stored in the toner hopper 7c. The toner in the toner hopper 7c is formed as a layer having a predetermined thickness on the developing roller 7a by the action of the doctor blade 7b. A predetermined voltage is applied to each of the developing roller 7a and the doctor blade 7b, and the toner on the developing roller 7a is controlled to have an appropriate charge amount.

The transfer roller 8 is made of a conductive rubber, and is applied with a predetermined transfer voltage. Transfer roller 8
Are in contact with the photosensitive drum 9 with the sheet interposed therebetween, and the toner visual image on the photosensitive drum 9 is transferred to the sheet P by the transfer voltage. The cleaner blade 10 is used to transfer the photosensitive drum 9 after the transfer.
The toner remaining on the top is removed to prepare for the next charging.

[0008] The fixing device 13 comprises a heating roller 13a, a nip roller 13b, a separation claw 13c, a thermistor TH, and a thermostat TS. Heating roller 13a
Has a rod-shaped halogen lamp HL inserted as a heating element in a metal tube. On the other hand, the nip roller 13b is made of heat-resistant rubber. A nip roller 13b is in contact with the heating roller 13a at a predetermined pressure, and the heating roller 13a rotates clockwise in FIG. 5 and the nip roller 13b rotates counterclockwise. The toner image on the sheet is fixed on the sheet by the heat from the heating roller 13a and the pressure by the nip roller 13b.

The separation claw 13c separates the sheet from the heating roller 13a so that the sheet can be smoothly transported downstream. A thermistor TH for temperature control and a thermostat for shutting off the power supply of the halogen lamp HL when abnormal heat is generated are arranged near the heating roller 13a.

Next, temperature control of a fixing device of a conventional image forming apparatus will be described with reference to FIG. A signal from the thermistor TH is supplied to a microprocessor (hereinafter, MPU).
) Analog / digital (A / D) port. The signal input from the A / D port is MPU1
The digital signal is converted into a digital signal in Step 4, and compared with a digital threshold value corresponding to the fixing temperature θ1 based on a program. The MPU 14 outputs a control signal S1 to the heater energizing circuit 15 based on the result of the comparison. In addition, MPU
Reference numeral 14 denotes a high voltage generation circuit that applies a high voltage to the transfer roller 8, the charging roller 11, and the developing device 7, and the LED array head 1
2. A motor and the like (not shown) are controlled, but are omitted because they are not related to the present invention.

The heater energizing circuit 15 receives the control signal S1
, The current flowing through the halogen lamp HL is turned on / off. Note that a thermostat TS is connected in series to the halogen lamp HL. This thermostat T
S is set so that the contacts are separated at a temperature θts higher than the fixing temperature θ1.

FIG. 4 shows an example of temperature control by the circuit of FIG. When the power of the apparatus is turned on or a print command is given, the temperature of the fixing unit 13 is lower than the fixing temperature θ1, so the MPU 14 outputs a control signal S1 to the heater energizing circuit 15 to turn it on. The halogen lamp HL is energized to generate heat. When the MPU 14 determines from the signal from the thermistor TH that the temperature of the fixing unit 13 has risen and has reached the fixing temperature θ1, the MPU 14
Turns off the control signal S1, and the heater energizing circuit 15 stops energizing the halogen lamp HL.

When the temperature of the fixing unit 13 decreases and falls below the fixing temperature θ1, the MPU 14 detects this by a signal from the thermistor TH, turns off the heater energizing circuit 15 and turns on the halogen lamp HL. When the temperature of the fixing unit 13 rises, the MPU 14 outputs a control signal S1 to the heater energizing circuit 15, and turns off the halogen lamp HL again. MPU1
As long as 4 is normal, this process is repeated and the temperature of the fixing device 13 is maintained at the fixing temperature θ1.

When MPU 14 runs away at time t1 and control signal S1 continues to be turned on, the temperature of fixing unit 13 continues to rise. As the temperature of the fixing device 13 rises, the thermostat TS operates at time t2 to open the contact, and the halogen lamp HL is turned off. This prevents the image forming apparatus from smoking or firing.

[0015]

As described above, in the conventional image forming apparatus, when the MPU 14 runs away and the fixing unit 13 continues to generate heat, the heat generation of the halogen lamp HL is stopped by the thermostat TS. Has become. However, since the thermostat TS is provided at a slight distance from the heating roller 13a, the thermostat T
When S reaches the operating temperature θts, the heating roller 13
a is at a much higher temperature. For this reason,
Even if smoke or ignition does not occur, there is a problem in that the components in the apparatus are deteriorated or deformed. In particular, in recent years, so-called engineering plastics have been frequently used as mechanical parts, so this problem has become more remarkable.

After the thermostat TS operates, an image cannot be formed naturally.
If U14 runs away, there is a problem that an image cannot be formed immediately even if other parts are operating normally.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an image forming apparatus capable of forming an image safely even when the temperature control of the fixing unit of the MPU runs away.

[0018]

According to a first aspect of the present invention, there is provided an image forming apparatus, wherein a microprocessor controls a temperature of a fixing unit by program control based on a temperature detection signal from a temperature detecting unit. In the image forming apparatus, hardware control means for controlling the temperature of the fixing device by hardware based on the temperature detection signal is provided, and when control of the fixing device by program control is disabled, the fixing device is controlled by the hardware control means. Is characterized in that the temperature is controlled.

According to a second aspect of the present invention, there is provided an image forming apparatus comprising: a heat generating means for heating a toner image and fixing the toner image on a recording medium; a power supply control means for controlling power supply to the heat generating means; In an image forming apparatus including a detection unit and a microprocessor that outputs a control signal to an energizing unit to control the temperature of the heating unit based on an output signal of the temperature detection unit, the output signal of the temperature detection unit is compared with a reference signal. And a logic means for controlling the energization control means by an output signal of the comparison means when the temperature control by the microprocessor becomes impossible.

Further, in the image forming apparatus according to a third aspect, in the image forming apparatus according to the second aspect, the microprocessor controls the heat generating means to a first temperature, and the comparison means controls the heat generating means to the first temperature. In addition to controlling to a high second temperature, the heat generating means is provided with a thermostat, and the thermostat operates between the first temperature and the second temperature.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An image forming apparatus according to an embodiment of the present invention will be described with reference to FIGS. The mechanical structure of this image forming apparatus is the same as that shown in FIG. 5 and will not be described again.

FIG. 1 shows a main part of a circuit configuration of the image forming apparatus. The thermistor TH, the MPU 14, the heater energizing circuit 15, and the halogen lamp HL are the same as in the conventional case of FIG. The heater energizing circuit 15 turns on the halogen lamp HL when a signal of L is given to the input terminal of the control signal (low active). Regarding the thermostat TS, the insertion position is the same as the conventional one, but the operating temperature is specially set as described later.

The signal from the thermistor TH is
Of the comparator 16 and also to one terminal of the comparator 16. A reference voltage Vref is input to another terminal of the comparator 16.
The resistors R1 and R2 are voltage dividing resistors for setting the reference voltage Vref.

Assuming that the thermistor TH has a negative characteristic, when the temperature rises, the resistance value of the thermistor T decreases,
The voltage Vth increases. When the voltage Vth is Vre
When f is lower than f, the signal S2 output from the comparator 16 becomes L, and when the voltage Vth becomes equal to or higher than Vref, the signal S2 output from the comparator 16 becomes H. The temperature θ2 when the signal S2 output from the comparator 16 is inverted from L to H is set to a temperature slightly higher than the temperature θ1 controlled by the MPU 14.

The control signal S1 from the MPU 14 and the signal S2 from the comparator 16 are input to both input terminals of the OR gate 17. The signal S3 output from the OR gate 17 is input to a control signal input terminal of the heater energizing circuit 15. Therefore, when the signals S1 and S2 both become L, the heater energizing circuit 15 turns on the halogen lamp HL. Also, the temperature θts at which the thermostat TS operates
Is set to be between the temperatures θ1 and θ2.

Next, the operation of the image forming apparatus will be described with reference to FIG. When the power is turned on or the print command is turned on, the MPU 14 sets the control signal S1 to L. At this time, since the temperature of the fixing device 11 is low, the signal S2 of the comparator 16 is also low. Therefore, the signal output from the OR gate 17 also becomes L, and the heater energizing circuit 15 turns on the halogen lamp HL.

When the halogen lamp HL is turned on, the temperature of the fixing unit 11 rises. When the temperature of the fixing unit 11 reaches θ1, the MPU 14 inverts the control signal S1 from L to H according to a program based on the signal Vth from the thermistor TH. Therefore, the signal S3 output from the OR gate 17 is inverted from L to H, and the heater energizing circuit 15 turns off the halogen lamp HL.

When the temperature of the fixing unit 11 is lowered by turning off the halogen lamp HL, the MPU 14 detects this from the output Vth of the thermistor TH, and returns the control signal S2 from H to L again. The signal S3 of the OR gate 17 also becomes L, and the heater energizing circuit 15 turns on the halogen lamp HL again. This process is repeated, and the MPU 14
Is controlled to θ1.

At time t1, when the temperature control of the MPU 14 begins to run out of control and the control signal S1 remains at L, the temperature of the fixing unit 11 starts to rise. When the temperature reaches θ2, the signal S2 of the comparator 16 is inverted from L to H. Therefore, the signal S3 of the OR gate 17 changes from L to H.
And the heater energizing circuit 15 turns off the halogen lamp HL.

When the temperature of the fixing device 11 decreases, the signal S2 of the comparator 16 returns from H to L, and the signal S3 of the OR gate 17 also changes to L, so that the heater energizing circuit 15 turns on the halogen lamp HL again. This process is repeated, and the temperature of the fixing device 11 is controlled to θ2. As described above, the temperature θ2 is set to a temperature slightly higher than the temperature θ1, and at the temperature θ2, there is no danger of smoking or ignition. However, it is not preferable to control the fixing device 11 at the long-term temperature θ2 because the mechanical parts also deteriorate and deform.

Therefore, in this image forming apparatus, the operating temperature θts of the thermostat TS is between the temperatures θ1 and θ2. That is, there is a relationship of θ1 <θts <θ2 between these temperatures. The thermostat TS has a heating roller 13
a, the fixing device 1
Even if 1 is controlled by the temperature θ2, the temperature does not immediately rise and the operation is not performed. At a time point t2 when the predetermined time has elapsed, the temperature of the thermostat TS starts to be θts
, The thermostat TS operates here, and the halogen lamp HL is turned off.

Since there is some time between the times t1 and t2, the image forming apparatus can form an image. After that, since the heat generation of the fixing device 11 is stopped, unnecessary mechanical stress is not applied to the mechanical parts and the like around the fixing device 11.

In the above embodiment, the control by the hardware is performed by the analog circuit, but it is needless to say that the control by the hardware may be performed by the digital circuit by the wire logic. Further, although the control of the halogen lamp is performed only by switching on / off, the control of the heat generation amount may be performed stepwise by voltage control or firing angle control.

As the heating means, various heaters such as a ceramic heater can be used instead of the halogen lamp. Further, the image forming process is not limited to a process having a cleaner, and the present invention can be applied to an image forming process called a cleanerless process.

[0035]

As described above, the image forming apparatus of the present invention continues to control the temperature of the fixing unit by hardware even when the microprocessor becomes uncontrollable and the temperature control of the fixing unit becomes impossible. The image formation is not immediately disabled, and the thermal damage to the mechanical members and the like is not greatly caused.

The relationship of θ1 <θts <θ2 is set between the first temperature θ1 controlled by the microprocessor, the second temperature θ2 controlled by hardware, and the operating temperature θts of the thermostat. Therefore, the control by the hardware is prevented from continuing for a long time, and the thermal damage to the fixing device and its peripheral mechanism is prevented.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a control circuit of an image forming apparatus according to an embodiment of the present invention.

FIG. 2 is a diagram illustrating temperature control of the image forming apparatus.

FIG. 3 is a diagram illustrating a control circuit of a conventional image forming apparatus.

FIG. 4 is a diagram illustrating temperature control of the image forming apparatus.

FIG. 5 is a diagram illustrating a mechanism of a general image forming apparatus.

[Explanation of symbols]

 13: Fixing unit 14: Microprocessor (MPU) 15: Heater energizing circuit 16: Comparator 17: OR gate TH: Thermistor HL: Halogen lamp TS: Thermostat

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H027 DA12 EA12 EE07 EK00 EK11 EK15 EK17 2H033 AA25 BB00 CA06 CA07 CA34 CA44 CA45 3K058 AA22 AA41 BA18 CA23 CA61 CA71 CB02 CB22 GA06 5H323 AA36 BB17 CA08 FF01 DA03FF GG04 KK05 MM02 NN04 TT10 9A001 HH34 JJ35 KK42 LL05

Claims (3)

[Claims] 1. An image forming apparatus in which a microprocessor controls the temperature of a fixing device by program control based on a temperature detection signal from a temperature detecting means, wherein the temperature of the fixing device is controlled by hardware based on the temperature detection signal. An image forming apparatus, comprising: a hardware control unit that controls the temperature of the fixing unit by the hardware control unit when control of the fixing unit by program control is disabled. 2. A heating means for heating a toner image and fixing the toner image on a recording medium, an energization control means for controlling energization to the heating means, a temperature detection means for detecting a temperature of the heating means, and an output of the temperature detection means. An image forming apparatus comprising: a microprocessor for outputting a control signal to the power supply means for controlling the temperature of the heat generating means by a signal; and a comparison means for comparing an output signal of the temperature detection means with a reference signal. An image forming apparatus, comprising: logic means for controlling the power supply control means by an output signal of the comparison means when the temperature control becomes impossible. 3. The microprocessor controls the heating means to a first temperature, the comparison means controls the heating means to a second temperature higher than the first temperature, and the heating means includes a thermostat. 3. The image forming apparatus according to claim 2, wherein the thermostat operates between a first temperature and a second temperature.