JPH0748125B2 - Image forming device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus provided with various heating devices such as a heat fixing device, a condensation preventing device, a photoconductor heating device, and a transfer paper heating device. In particular, the present invention relates to a so-called wide-range power supply image forming apparatus in which the power supply voltage used varies greatly and the temperature of the heating device also varies correspondingly.

2. Description of the Related Art Conventionally, in an image forming apparatus such as an electrophotographic copying apparatus, a toner image formed on an image carrier is transferred onto a transfer material such as transfer paper, and then the toner image is transferred onto the transfer material. In order to fix as a permanent image, a heating device using an electric heating element, that is, a device having a heating fixing device is generally used.

An example of an electrophotographic copying machine using a heat fixing device is shown in FIG. The photosensitive drum 11 as an image carrier is a charger 12
An electrostatic latent image is formed by scanning a laser beam emitted from a laser light source 13 based on an image signal with a laser scanning device 14 so that the electrostatic latent image is uniformly charged. Photosensitive drum 11
The electrostatic latent image on the top is visualized by toner made of thermoplastic resin or the like in the developing device 15, and the paper feeding device 16 is timed.
It is transferred by the transfer device 17 onto the transfer paper fed by the transfer device 17. The photosensitive drum 11 is cleaned by the cleaner 18 and is used again for image formation. After the transfer paper is transferred, it proceeds to the heat fixing device 10, where the toner image is fixed on the transfer paper as a permanent image. The heat fixing device generally includes an electric heating element, that is, a heating roller 19 including an electric heater 5, and
It is configured by a pressure roller 20 that is driven by pressure contact with this,
The surface temperature of the heating roller 19 is a temperature detector (thermistor) 7
Is maintained at a predetermined temperature. The heat-fixed transfer paper is then discharged outside the machine.

Since the electric heater 5 of the heat fixing device 1 has a significantly different amount of heat generation depending on the power supply voltage of the apparatus, an abnormality detecting means is provided as a safety device in this kind of heating apparatus in order to prevent accidents due to heating. ing. As an abnormality detection means,
Abnormality detection means with a hardware configuration such as a thermostat and temperature fuse, and the thermal characteristics of the heating device, such as the temperature rise rate of the heating roller and the factor such as the energization time to the electric heater are digitized to a predetermined target area. Is set, and when a numerical value different from the set area is detected, there is a software-like abnormality detecting means for determining an abnormality.

The hardware abnormality detecting means is often set as the final means at the time of heating, and when the abnormality detecting means operates, the image forming apparatus may be significantly damaged. On the other hand, the soft abnormality detecting means has a small effect on the image forming apparatus main body even if the abnormal means acts in the unlikely event of an abnormality depending on the setting method, and is excellent in safety,
Its importance is great.

However, the soft abnormality detecting means is often based on the thermal characteristics of the heat fixing device as described above, and when the calorific value fluctuates, it is necessary to set a wide setting area to cope with the fluctuation. Therefore, safety inevitably decreases in case of an abnormality. In recent years, in particular, an image forming apparatus having a wide usable power supply voltage range, for example, an image forming apparatus capable of being shared by 100V and 200V is desired, and the safety due to the soft abnormality detecting means further decreases, which is a problem. ing.

OBJECT OF THE INVENTION An object of the present invention is to provide an image forming apparatus which can be used for a wide range of power supply voltages and has high safety.

Means for Solving Problems The above object is achieved by the image forming apparatus according to the present invention.
In summary, the present invention sets a predetermined target area by digitizing a heating device that is heated up to a predetermined temperature by an electric heating element that generates a different amount of heat according to a power supply voltage. However, it has an abnormality detecting means for judging an abnormality when a numerical value different from the target setting area is detected, and a means for changing the target setting area of the abnormality detecting means according to a power supply voltage. Image forming apparatus.

Embodiment Next, the image forming apparatus according to the present invention will be described in more detail with reference to the drawings. In this embodiment, the image forming apparatus is embodied in the electrophotographic copying apparatus shown in FIG. 2, the heat fixing device 10 has a heating roller 19 and a pressure roller 20, and the heating roller is a heating roller. 19 has an electric heating element 5 such as an electric heater inside, and the surface temperature of the heating roller 19 is a temperature detector,
That is, it is assumed that the thermistor 7 detects it.

FIG. 1 is an electric block diagram showing the operation and control relationship of the heat fixing device 10. In FIG. 1, a power source 1 is a power source that can take a wide range of voltage and is input to an image forming apparatus including a heat fixing device 10. The voltage detection circuit 2 detects the power supply voltage of this device and sends the measured voltage detection signal to the CPU 3. The electric heating element provided in the heat fixing device 10, that is, the electric heater 5, is connected to the power source through the heater control circuit 4, and generates heat in response to a signal from the CPU 3. Further, the roller surface temperature is detected by the temperature detector 7 provided on the heating roller 19 of the heat fixing device 10, and the temperature detection signal is sent to the CPU 3
Sent to.

The heating roller 19 is mechanically connected to the drive source 6 whose drive is controlled by a signal from the CPU 3, and its rotation is controlled.
The display and operation unit 8 is connected to the CPU 3 and can display and operate the state of the image forming apparatus.

The heating and fixing device 10, which is particularly important in the image forming apparatus of the present invention, will be described in more detail. Heat fixing device of this embodiment
10 is effective fixing width 212 mm, fixing processing speed 50 mm / S (A4 size 8 sheets / minute), fixing processing temperature 180 ° C, fixing processing temperature upper limit 2
It has a performance of 00 ℃ and the same lower limit of 170 ℃. Heating roller 19
Is a base made of an aluminum cylinder with an outer diameter of 20 mm and a wall thickness of 1 mm, a heat resistant black coating on the inner peripheral surface, and a release layer on the outer peripheral surface, such as a fluorine resin layer such as PFA or PTFE. Is a roller having a total length of 252 mm, and is drive-transmitted from the drive source 6 at the end portion and is rotatably supported. In addition, inside the heating roller 19, a halogen lamp heater 5 having a heating portion length of 226 mm, which shows an electric power of 350 W when turned on at 115 V.
Is provided as an electric heating element (electric heater), and heat is generated by the heater control circuit 4 controlled by the CPU 3 based on the detection value of the thermistor 7 which is a temperature detector provided on the outer circumference of the heating roller. Controlled. Heating roller 19
Is a pressure roller 20 having an outer diameter of 20 mm and an overall length of 226 mm in which an elastic layer made of silicone rubber or the like is provided on a metal core material with a thickness of 5 mm, and has a pressure contact width of 2.5 mm. The fixing process is performed by the co-rotation of the and.

Currently, the power supply voltage used in each country is 100V, 120V,
There are many types such as 220V and 240V, and an image forming apparatus having a heat fixing device using an electric heater as a heat source is also manufactured using a plurality of voltages. Also, various power supply voltages have a fluctuation tolerance with respect to the rated voltage, and it is considered that there is a fluctuation of about 10 to 15%.

Table 1 shows the effective power of the electric heater and the temperature rise characteristics of the heating roller in the image forming apparatus in which the power supply used varies in the range of 85V to 115V. The effective power P ₁ of the halogen lamp heater 5 used in this embodiment is a rated voltage V ₀ , a rated power P ₀ ,
Regarding the power supply voltage V _1, there is a relation of P ₁ = P ₀ (V ₁ / V ₀ ) ^1.54 , and as shown in Table 1, at 85V 219
The maximum power is 350 W at W and 115 V, and the power fluctuates about 1.6 times. The temperature rising characteristics of the heating roller include temperature rise per unit time (temperature rising rate; ° C / s) and the time required to reach the fixing processing temperature of 180 ° C from room temperature of 20 ° C (temperature rising time; s )showed that. For the temperature rising characteristics, the actual temperature of the heating roller was measured with a thermocouple. The thermistor 7 is
The time (response time) until a 63.2% change in the predetermined resistance value is shown by pressing a thermistor at room temperature (20 ° C) onto a 180 ° C constant temperature cylinder has a response of about 3 seconds. is there.

FIG. 3 and FIG. 4 show the temperature of the heating roller when the temperature is raised from 20 ° C. with the power supply voltage of 85V, 100V, 115V, 127V without pre-rotating the heating roller in this embodiment. When,
It shows changes in the temperature detected by the thermistor.
Since the temperature control of the heating roller is performed based on the temperature detected by the thermistor as described above, the actual temperature of the heating roller surface is higher than the thermistor detected temperature when the temperature rises due to the response delay of the thermistor, which causes overshoot. As described above, the overshoot is related to the rate of temperature rise of the heating roller and the response of the thermistor. The greater the rate of temperature rise and the longer the response time, the greater the overshoot. Although various improvements have been made to the response of the thermistor, a protective layer such as a sliding layer or an air layer for the purpose of protecting the thermistor and the heating roller is interposed between the thermistor element 7 and the heating roller 19. Therefore, good results have not been obtained.

According to the present invention, in order to solve the above-mentioned problem, paying attention to the energization time to the electric heater, and when the electric heater is continuously energized for a predetermined time (T seconds) or more, the energization signal causes There is provided software-like abnormality detecting means for judging that the heating device is abnormal, stopping the power supply to the electric heater, and displaying a warning.

The energization time to the electric heater is detected by a timer circuit, the signals are integrated for each heater energization signal, and the heater energization signal is cleared. According to the present invention, such an abnormal situation is detected when the temperature of the heating roller does not rise due to the disconnection of the electric heater, or even when the temperature of the heating roller is sufficiently raised, it is detected that the temperature of the heating roller has risen due to the thermistor failure It occurs when you cannot.

The constant T, which is the predetermined time, can be set as follows.

The longest energization of the heater occurs at low power, that is, in the heating roller in a low temperature state where the power supply voltage used is 85 V, and referring to FIG. 4, the energization time is 63 seconds.
If the margin of 5 seconds is taken into consideration when the room temperature is lower, the energization time constant T becomes 68 seconds.

Here, for example, when the heater is continuously turned on from 20 ° C for 68 seconds due to a thermistor failure, the heating roller rises to about 230 ° C at 85V as shown in Fig. 5, but
Since the heat resistant temperature of the heating roller is usually 260 ° C, the heating roller itself is not damaged and the heating device, that is, the heating fixing device can be repaired by replacing the thermistor.
There is no problem. However, at 100V and 115V, the temperature rises to 300 ° C and 380 ° C, respectively, the heating roller becomes hot, is damaged, and the heat fixing device itself must be replaced.
Also, at a temperature of 380 ° C, smoke may be emitted from the heat fixing device or the transfer paper.

Therefore, according to the present invention, the energization time constant T can be changed according to the power supply voltage used. For example, as shown in FIG. 4, the energization time constant T is 68 V as described above at 85V.
Seconds, 55 seconds at 100V, 46 seconds at 115V. Therefore, in FIG. 1, when the voltage is detected by the voltage detection circuit 2,
The detection signal is transmitted to the CPU 3, and the constant T of the timer circuit in the heater control circuit 4 is determined according to the power supply voltage as described above.

According to the configuration of the present invention, even when the thermistor fails and the electric heater is continuously turned on from 20 ° C., the maximum temperature of the heating roller is 85V, 100V, 115V as shown in FIG.
At 230 ℃, 240 ℃ and 260 ℃ respectively, the heating roller is not damaged, and the thermistor can be used for the heat fixing device by simply sliding the steel pipe.

In the above description, the description has been made in relation to three voltages of 85V, 100V, 115V, but the heater energization maximum energization time is 1: 1 to the power.
Therefore, the appropriate energization constant T can be set with other voltages. Alternatively, the energization constant T may be set by dividing the voltage into two or three regions such as when the power is high and when the power is low.

Next, another embodiment of the present invention will be described. In the image forming apparatus of this embodiment, in the first embodiment, the heating roller has an outer diameter of 25 mm, a wall thickness of 2.5 mm, and a power supply voltage of 8
The difference is that it is an image forming device that can be used in the range of 5V to 264V, and the electric heater is 400W when used at 115V.
Was shown. Table 2 shows the temperature rising characteristics of the heating device, that is, the heating roller used in the heating and fixing device. In the image forming apparatus that can be used in a wide voltage range as in this embodiment, the temperature rising rate of the heating roller greatly changes depending on the power supply voltage used. The temperature rise characteristics at 100 V and 240 V are shown in Fig. 7, and the thermistor detection temperature is shown in Fig. 8.

In the present embodiment, as shown in FIG. 8, in order to reduce the overshoot during the temperature rise, the heater energization is forcibly interrupted for 2 seconds at the time of detecting 150 ° C. during the temperature rise. If the heating roller has not reached 180 ° C. after the interruption, the heater is energized again.

In the present embodiment, the pressure roller 20 that is in pressure contact with the heating roller 19 is used, and when the heat generation of the electric heating element is stopped, both rollers 1
By spinning the 9, 20 idle, that is, the heating roller 19
The overshoot can be further reduced by substantially increasing the heat capacity of the.

In the image forming apparatus of this embodiment, the power supply voltage used is 85V to 264V.
Since it can be used in the above range, the fluctuation range of the temperature rising rate becomes larger than that of the first embodiment, and the present invention becomes more effective.

In the present embodiment, the abnormality detection is performed at an early stage after a lapse of a predetermined time after the start of energization of the heater. When the heating means is normal, the temperature of the heating roller is detected by a thermistor after a lapse of a predetermined time after the power is turned on, and if the temperature of the heating roller does not reach the predetermined temperature, it is judged as abnormal and the heater is energized. Stop and display a warning.

More specifically, referring to FIG. 8, when the power supply voltage is 240 V and the heating and fixing device is operating normally, it is found that the temperature of the heating roller rises by about 40 ° C. in 10 seconds after the power is turned on. Have been detected in. Therefore, the minimum ambient temperature used is 10 ° C.
If so, at least the heating roller must reach 50 ° C. after 10 seconds. Therefore, in the case of 240V, if the temperature detected by the thermistor is less than 50 ° C 10 seconds after the power is turned on, it is determined that the heat fixing device is abnormal. Similarly, 10
In the case of 0V, the temperature rises by 30 ° C in 30 seconds, so if the minimum environment temperature for use is 10 ° C, at least the heating roller must reach 40 ° C after 10 seconds. Therefore, if the temperature detected by the thermistor is less than 40 ° C 30 seconds after the power is turned on, it is determined that the heating and fixing device is abnormal. In the case of other voltages, similarly, the abnormality of the heat fixing device is determined by setting the elapsed time after the power is turned on and the thermistor detection temperature. Of course, it may be set stepwise according to the voltage region.

Compared to the first embodiment, in this embodiment, the abnormality can be detected relatively early by making a determination based on two values, that is, the elapsed time after the power is turned on and the temperature. In this embodiment, the elapsed time after the power is turned on is detected by adding a timer circuit to the CPU shown in FIG.

Further, in the present invention, the heating device is not limited to the heat fixing device, and various heating devices such as a dew condensation preventing device, a photoconductor heating device, a transfer paper heating device, and the like can be used.

Further, even if the special power source detection circuit 2 is not used as in this embodiment, the user makes a judgment and sends a signal to the CPU 3 by, for example, a voltage switching switch (not shown) provided in the operation unit 8. You may do it.

Furthermore, although the halogen lamp heater is used as the heating element, that is, the electric heater, the present invention is not limited to this, and the heating value changes depending on the power supply voltage even in the case of another electric heating element such as a nichrome wire heater. If so, the present invention is effectively implemented.

EFFECTS OF THE INVENTION As described above, the image forming apparatus according to the present invention is an image forming apparatus that determines the abnormality of the heating means when the thermal characteristics of the heating device are digitized and a value different from the predetermined setting area is detected. By changing the above-mentioned setting area according to the power supply voltage, it is possible to enhance the safety against the thermal abnormality of the heating means and to use it safely in a wide range of power supply voltage.

[Brief description of drawings]

FIG. 1 is a main electric block diagram of the heating device of the image forming apparatus of the present invention. FIG. 2 is a main sectional view of an image forming apparatus embodying the present invention. FIG. 3 is a temperature change diagram of the heating roller showing an overshoot state of the heating fixing device when the present invention is not adopted. FIG. 4 is a temperature change diagram showing the detected temperature state of the thermistor of the heat fixing device according to the present invention. FIG. 5 is a temperature change diagram of the heating roller showing an overshoot state of the heating fixing device when the present invention is not adopted. FIG. 6 is a temperature change diagram of the heating roller showing an overshooting state of the heat fixing device according to the present invention. FIG. 7 is a temperature change diagram of the heating roller showing an overshoot state of the heat fixing device according to the present invention. FIG. 8 is a temperature change diagram showing a thermistor detected temperature state of the heat fixing device according to the present invention. 5: Electric heating element (electric heater) 10: Heat fixing device 19: Heating roller 20: Pressure roller

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-53-39136 (JP, A) JP-A-54-92748 (JP, A) JP-A-60-55373 (JP, A) JP-A-62- 173484 (JP, A) JP 59-77526 (JP, A) JP 59-77525 (JP, A) JP 58-144868 (JP, A) JP 56-40874 (JP, A) Actually open 62-123671 (JP, U) Actually open 62-186172 (JP, U)

Claims (5)

[Claims] 1. A heating device which is heated to a predetermined temperature by an electric heating element having a different heating value corresponding to a power supply voltage, and a predetermined target region is set by digitizing thermal characteristics of the heating device.
An image characterized by having an abnormality detecting means for judging an abnormality when a numerical value different from the target setting area is detected, and a means for changing the target setting area of the abnormality detecting means according to a power supply voltage. Forming equipment. 2. The image forming apparatus according to claim 1, wherein the thermal characteristic of the heating device is the time for which electricity is supplied to the electric heating element. 3. The image forming apparatus according to claim 1, wherein the thermal characteristics of the heating device are the time of energizing the electric heating element and the temperature of the heating device. 4. A heating device has a heating roller containing an electric heating element and a pressure roller that comes into contact with the heating roller to rotate, and a temperature detector for detecting the temperature of the heating roller. The image forming apparatus according to claim 1, wherein the image forming apparatus comprises: 5. The image forming apparatus according to claim 4, wherein the heating roller and the pressure roller are rotated at least when the heat generation of the electric heating element is stopped.