JPH0535147A - Excessive temperature rise preventing device for image forming device - Google Patents

Abstract

PURPOSE:To secure safety before the damage of a member to be heated is caused and to facilitate postprocessing such as repair even when the imperfect contact of a temperature sensor to the member to be heated occurs. CONSTITUTION:This device is provided with the temperature sensor 5 for detecting the temperature of the member to be heated 2 whose temperature is raised by a heater 1. Besides that, it is provided with a heater power control part 6 which controls input power to the heater 1, a timer which counts the on-time of the heater, and a heater control part & abnormality decision part 7 which decides whether the control of the temperature of the member to be heated is abnormal or not. Then, the on-time of the heater 1 after the temperature of the member 2 attains a target value previously set is counted by the timer for every mode of an image forming device (each mode such as warm-up, standby or image forming), and when the on-time counted is equal to or above the previously set time which is supposed at a normal state, the decision part 7 decides that the control is abnormal, so that the heater 1 is turned off.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an overheat preventing device for an image forming apparatus.

[0002]

2. Description of the Related Art Generally, an image forming apparatus such as a copying machine has a heat fixing device and becomes high temperature. Therefore, safety measures are essential. Thus, for example, when the copier warms up and the reloading (standby state) does not occur even after a preset time (for example, 5 minutes) elapses (normally, 1
It takes about 25 seconds to reload), and it is judged to be abnormal, and the power to the heater is turned off.

[0003]

As a safety measure, the temperature of the fixing heat roller with a heater is brought into contact with the thermistor to detect its temperature, and when the target temperature is reached, the heater is turned off. ing. However, when the thermistor is not in contact with the surface of the fixing roller during standby or during copying, or when the connector between the thermistor and the controller has a high resistance due to poor contact, the controller does not cover the surface. Assuming that the temperature of the heating member, that is, the fixing roller, is still low, the electric power is continuously supplied to the heater. As a result, the temperature of the fixing roller or the pressure roller facing the fixing roller may rise excessively, resulting in damage or smoke generation. In this case, if a thermal fuse is used, accidents such as ignition can be prevented, but repairing will take time.

[0004]

According to a first aspect of the present invention, a heater, a member to be heated whose temperature is raised by the heater, a temperature sensor for detecting the temperature, and a control for controlling input power to the heater. Unit, a timer that measures the ON time of the heater, and an abnormality determination unit that determines whether the temperature control of the heated member is abnormal, the temperature of the heated member for each mode of the image forming apparatus. The on time of the heater after reaching the preset target value is measured by the timer, and when the on time becomes equal to or longer than the preset time, the abnormality determining unit determines that the heater is abnormal and I turned it off.

In this case, according to the second aspect of the invention, the preset time is made different for each mode of the image forming apparatus.

According to a third aspect of the present invention, a heater, a member to be heated whose temperature is raised by the heater, a temperature sensor for detecting the temperature, a control unit for controlling the input power to the heater, and the heater. It is composed of a ratio calculation unit that calculates the ratio of on / off time and an abnormality determination unit that determines whether the temperature control of the heated member is abnormal, and is calculated by the ratio calculation unit for each mode of the image forming apparatus. The ratio of ON / OFF time is compared with a preset ratio, and the presence / absence of an abnormality is determined by the abnormality determining unit, and the heater is turned off when the abnormality occurs.

[0007]

In the image forming apparatus, in each mode, the maximum value of the time during which the heater should be continuously turned on until the heated member reaches the target temperature under normal conditions, or the ratio of the on / off time is measured in advance. Or it can be calculated. Therefore, based on the values measured and calculated in advance, determine the heater ON continuous time or ON / OFF time ratio for abnormality determination in each mode, and if it exceeds these set values, it is determined to be abnormal. By turning off the heater, safety can be secured before damage to the member to be heated and post-processing such as repair becomes easy.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described with reference to FIGS. This embodiment is applied to the temperature control of a heat fixing device of a copying machine, for example, and its schematic configuration is shown in FIG. First, a fixing roller 2 which is a member to be heated and which has a built-in heater 1 is provided in a pressure contact state with a pressure roller 3, and a transferred transfer paper 4 is passed between both rollers 2 and 3 to heat and fix it. It is a thing. A thermistor 5 serving as a temperature sensor is provided in contact with the surface of the fixing roller 2. Further, a heater power control section 6 for controlling on / off of the input power of the heater 1 is provided. Further, a heater control section & abnormality determination section 7 connected to the thermistor 5 and the heater power control section 6 is provided. A display unit 8 is also provided and is connected to the main control unit 9 that controls the entire image forming apparatus together with the heater control unit and the abnormality determination unit 7 and the like.

In such a structure, first, a basic operation in a normal state will be described. When the main switch is turned on, normally, the fixing roller 2 is judged by the heater control unit 7 to have not reached the target temperature T ₁ , a heater ON signal is given to the heater power control unit 6, and the heater 1 is turned on. Be heated. After that, when the surface temperature of the fixing roller 2 detected by the thermistor 5 reaches the target temperature T ₁ , the heater 1
Is turned off. When the heater 1 is turned off, the fixing roller 2
Since the surface temperature decreases, the heater 1 is turned on again.
Here, the target temperature T _{1 in} the warm-up mode immediately after the main switch is turned on is set higher than the target temperature T ₂ during the subsequent standby or copying, as shown in FIG. This is because, immediately after the main switch is turned on, the temperature of the pressure roller 3 and the internal temperature of the apparatus are lower than those at the time of standby and copying, so that it is corrected.

The surface temperature of the fixing roller 2, which is the basis of such control operation, is detected by the thermistor 5 having the temperature characteristic shown in FIG. That is, the fixing roller 2
When the temperature rises, the resistance value of the thermistor 5 decreases, and when the temperature decreases, the resistance value increases.

Here, the on / off time of the heater 1 will be considered. The on / off time of the heater 1 is the fixing roller 2
Temperature, whether the rollers 2 and 3 are rotating, the transfer paper 4
Between the rollers 2 and 3 depends on the environmental temperature and the like. Considering this point, considering the mode of the copying machine, immediately after the main switch is turned on, it is in the warm-up mode, and the temperature inside the fixing roller 2 and inside the machine is low.
The target temperature T _{1 is} also high, and the ON time of the heater 1 is long. There is no heater off time unless there is a machine abnormality. Next, in the standby mode (from the end of warming up to the start of copying, or between copy modes), the temperature inside the fixing roller 2 and inside the machine becomes high, and the roller 2
Since the heater 3 is stopped and there is no transfer paper 4 between the rollers 2 and 3, the heat dissipation is small. Therefore, the heater 1 has a short ON time and a long OFF time. Further, in the copy mode, the rollers 2 and 3 rotate together, and the transfer paper 4 also passes between the rollers 2 and 3, so that the heat of the fixing roller 2 is gradually removed, so that the heater 1 has a long ON time. The off time becomes shorter and the on / off operation is repeated. Therefore, when the heater 1 is turned on and off depending on the mode, as shown in FIG.
The situation is as shown in. However, each state changes depending on the environment, temperature, paper type of the transfer paper 4, and the like.

Considering an abnormal state in which the thermistor 5 is separated from the fixing roller 2 and is out of contact with the normal operating state, the heater control section 7 determines that the temperature of the fixing roller 2 is still low. It is considered to be low, and the heater 1 is kept on. Here, the maximum time during which the heater 1 is continuously turned on during normal operation varies depending on each mode, but can be known in advance for each mode by measurement or the like.
For example, the maximum time t ₁₀ in the warm-up mode is 8
The maximum time t ₂₀ in the standby mode is 20 seconds, and the maximum time t _{30 in the} copy mode is 1 minute.

Therefore, in this embodiment, based on these maximum times t ₁₀ , t ₂₀ and t ₃₀ , the abnormality determination times t ₁ , t ₂ and t.
₃ (however, t ₁ > t ₁₀ , t ₂ > t ₂₀ , t ₃ > t ₃₀ ) is set in advance. Then, in each mode, the timer is started when the heater 1 is turned on, and the time during which the heater 1 is continuously turned on is measured. Measured time t is in the warm-up mode is t> t _1, in the standby mode t> t _2, In the copy mode t> t
_{In the case of 3} , the abnormality determination unit 7 determines that the heater 1 detects an abnormality, regardless of the temperature detected by the thermistor 5.
Is turned off and the fact is displayed on the display unit 8 to inform the user.

FIG. 4 is a flowchart showing such processing.

By the way, the above-mentioned heater power control section 6,
FIG. 5 shows a specific configuration example of the heater control section & abnormality determination section 7 and the display section 8. These share the CPU 10 with an A / D converter that is connected to the main control unit 9, and the display unit 8 is connected to this CPU 10 via an inverter 11 and is configured by an LED 12 that indicates an abnormality when an abnormality is determined. . Further, the heater power control unit 6 uses the commercial power supply AC.
For 100V, a thermal fuse 13 and an SSR (solid state relay) 14 connected in series with the heater 1 are connected to the CPU 10 via an inverter 15. Further, the heater control section & abnormality determination section 7 includes an OP amplifier 16,
It is composed of a transistor 17, resistors R _{1 to} R ₆ , and a capacitor C. First, a resistor R ₁ and a capacitor C for removing high frequency noise are connected to the A / D converter port of the CPU 10. Then, the voltage dividing resistance of the thermistor 5 and the resistor R ₂ is input to the + terminal of the OP amplifier 16 via the resistor R _3, and the voltage dividing resistance of the resistors R ₄ and R ₆ is inputted to the OP amplifier 16 via the resistor R _5. If the temperature detected by the thermistor 5 exceeds the value preset by the resistors R ₄ and R ₆ , the OP amplifier 16 turns on the transistor 17 to control the SSR 14 +. The power is turned off and the heater 1 is turned off. At this time, the resistance change of the thermistor 5 is returned to the voltage by the voltage division of the thermistor 5 and the resistor R ₂ and is taken into the CPU 10 with the A / D converter.
The power source side of the SSR 14 is also controlled via the, and the heater 1 is turned on and off.

Next, a second embodiment of the present invention will be described with reference to FIG. The same parts as those shown in the above-mentioned embodiment are designated by the same reference numerals. In the present embodiment, for example, when the heater 1 is in the standby mode, the time during which the heater 1 is turned on and the time during which the heater 1 is turned off are measured, the ratio of the on / off times is calculated, and the on / off time measured during normal operation If you exceed the ratio,
The heater 1 is determined to be abnormal and the heater 1 is turned off.

That is, in the normal operation, the heater 1 is continuously turned on and is not turned off in the warm-up mode. The heater 1 is turned on almost continuously even in the copy mode, although it is intermittent. On the other hand, in the standby mode, for example, the on time is 5 to 20 seconds and the off time is 10 to 25 seconds. Therefore, the ratio of on / off time R
Is 0.2 (= 5 seconds / 25 seconds) to 2 (= 20 seconds / 10 seconds)
Becomes Therefore, the actual on / off time ratio is monitored by the abnormality determination unit 7, and the ratio is out of the range of 0.1 to 3 (the upper limit and the lower limit have a margin with respect to 0.2 to 2). When it is judged to be abnormal, the heater 1 is turned off.

FIG. 6 shows a control process in the case of this embodiment.
Here, the time measured by the timer 1 in the standby mode is the standby heater on time t ₂₁ , the time measured by the timer 2 is the standby heater off time t _22, and the time measured by the timer 1 in the copy mode is the copy time. When the heater on time is t _31, and the time measured by the timer 2 is the heater off time during copying t ₃₂ , they are stored in the registers 1 and 2, respectively, and the ratios R ₂ and R ₃ are respectively R ₂ = t ₂₁ / t. ₂₂ , R ₃ = t ₃₁ / t ₃₂ , and compared with the predetermined normal reference values R ₂₂ and R ₃₃ (determined by the CPU 10 using the values of the registers 1 and 2) and exceeded. If so, it will be determined to be abnormal.

Even in the present embodiment, the circuit configuration shown in FIG. 5 can be applied as it is.

[0020]

As described above, according to the present invention, in the image forming apparatus, in each mode, the maximum value of the time during which the heater should be continuously turned on until the heated member reaches the target temperature in normal mode, or Focusing on the fact that the on / off time ratio can be measured or calculated in advance, determine the heater on continuous time or the on / off time ratio for abnormality determination in each mode based on the value measured and calculated in advance. It should be noted that when the heater is in the ON state that exceeds these set values, it is judged to be abnormal and the heater is turned off. Therefore, even if the temperature sensor is installed incorrectly, the heated member will not be damaged. Safety can be ensured and post-processing such as repairs can be facilitated.

[Brief description of drawings]

FIG. 1 is a schematic block diagram showing a first embodiment of the present invention.

FIG. 2 is a characteristic diagram showing a relationship between a fixing roller temperature, a heater on / off state, and a mode.

FIG. 3 is a temperature characteristic diagram of the thermistor.

FIG. 4 is a flowchart showing an abnormality detection process.

FIG. 5 is a circuit diagram showing a specific configuration example.

FIG. 6 is a flowchart showing a second embodiment of the present invention.

[Explanation of symbols]

1 heater 2 Heated member 5 Temperature sensor 6 control unit 7 Abnormality judgment part

Claims (3)

[Claims] 1. A heater, a member to be heated whose temperature is raised by the heater, a temperature sensor for detecting this temperature, a control unit for controlling the input power to the heater, and a timer for measuring the ON time of the heater. And an abnormality determination unit that determines whether the temperature control of the heated member is abnormal, and the temperature of the heated member reaches a preset target value for each mode of the image forming apparatus. An image forming method characterized in that the ON time of the heater is clocked by the timer, and when the ON time is equal to or longer than a preset time, the abnormality is judged by the abnormality judging section and the heater is turned OFF. Device to prevent overheating of equipment. 2. The overheat prevention device for an image forming apparatus according to claim 1, wherein the preset time is made different for each mode of the image forming apparatus. 3. A heater, a member to be heated whose temperature is raised by the heater, a temperature sensor for detecting this temperature, a control unit for controlling the input power to the heater, and a ratio of the on / off time of the heater. Of the on / off time calculated by the ratio calculation unit for each mode of the image forming apparatus. An excessive temperature rise prevention apparatus for an image forming apparatus, characterized in that a ratio is compared with a preset ratio, and whether or not there is an abnormality is determined by the abnormality determination unit, and the heater is turned off when the abnormality occurs.