JPH01291309A - Temperature controller - Google Patents

Abstract

PURPOSE:To exactly execute the detection of abnormality and to prevent the overheat of a heater by varying the time for detecting a disconnection of a temperature detecting element in accordance with a non-electric conduction (service interruption) time after the power source has been turned on. CONSTITUTION:After the power source has been turned on, an MPU (microcomputer) 7 inputs a terminal voltage VA of a timer use capacitor 11 and calculates a service interruption time (tb). Subsequently, by subtracting that which has multiplied a service interruption time tb by a prescribed coefficient, from a total electric conduction time ta of a heater 2 which has been stored in a built-in RAM, tc is obtained. When tc is positive, a roller is heated already, therefore, by shortening a thermistor disconnection detection time, a voltage Vc of a thermistor 5 is checked after a tB (normal time) - tC time. In such a way, a disconnection check time is shortened after the restart in accordance with the service interruption time, therefore, the disconnection of a temperature detecting element (thermistor) can be detected exactly, and the overheat of the heater caused by the disconnection of the temperature detecting element is prevented.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a temperature control device.

(Prior Art) Conventionally, a recording device having a heat roller fixing device is known.This type of recording device is equipped with a heat roller fixing device heated by a halogen heater. A thermistor is applied to the surface to detect the temperature, the temperature is determined by receiving the detection output of the thermistor with a microcomputer (hereinafter referred to as MPU) with an A/D converter, and the heat roller surface temperature is controlled by on/off control of the halogen heater. are doing.

[Problems to be Solved by the Invention] In such a heating device, the thermistor that detects the temperature may be disconnected. A thermistor has a very large resistance value when the temperature is low, but if the thermistor is disconnected, the same state will occur, and the MPtJ will issue a command to the heater to raise the temperature. In this way, the heater overheats,
Eventually it will lead to a fire.

Therefore, conventionally, a disconnection check has been performed by checking the value of the thermistor after a certain period of time after the heater starts being energized. However, if the power switch of the recording apparatus is turned off before the disconnection check is performed, the MPU is cleared and the thermistor disconnection detection will be restarted from the beginning when the power is turned on next time. However, the heater has already been heated by the previous energization, and since it is further energized from there, the temperature increases even more. If this operation is repeated several times, the heater will overheat and become dangerous.

[Means for solving problems]

In order to solve the above-mentioned problems, the present invention operates a timer to measure the non-energizing time before turning off the power switch, and after turning on the power, detects disconnection of the temperature sensing element according to the non-energizing time. It changes the time.

〔Example〕

FIG. 1 shows the circuit configuration of the first embodiment, and FIG. 2 is a flowchart showing its operation. 1 is by heater 2,
1 shows a heating device that heats a fixing roller of a recording device. 3 is an AC power supply, and 4 is a semiconductor relay 5SR15, which is a temperature detection element that measures the surface temperature of the fixing roller, and uses a thermistor.

This element has the characteristic that the resistance decreases as the temperature increases. Therefore, when the resistor 6 pulls up the voltage to Vcc2, the voltage across the thermistor 5 will decrease as the temperature increases. Reference numeral 7 denotes a one-chip microcomputer MPU (for example, μPD78C14 manufactured by NEC Corporation) incorporating a read-only memory ROM, a random access memory RAM, and an analog-to-digital converter A/D. A/D receives the voltage across the thermistor 5 from the analog boat AN2.
Convert it to a digital value using a converter.

When the voltage value of the thermistor 5 is high, the MPU 7 determines that the temperature of the heat roller of the fixing device is low, and outputs the voltage from the output terminal 02 to 5SR4.
is turned on, and the heater 2 is energized. 8 is a reset circuit that resets the MPU 7 when the power is turned on, and 9 is a battery backup battery that applies a voltage to maintain the contents of the built-in RAM of the MPU 7 when the power is turned off. This battery 9 is connected to the power supply terminal of the MPU 7 through a diode 10.
. Connected to D. Note that this power supply terminal VDD is connected to a power supply VCC independent from other control elements.

Reference numeral 11 designates a timer capacitor for measuring the non-current (power outage) time when the power is turned off, reference numeral 12 a resistor for discharging the timer, and reference numeral 13 a transistor for charging the capacitor 11.

When the terminal 01 of the MPU 7 becomes a high level °H°, the transistor 13 is turned on and the capacitor 11 is charged.

This transistor 13 turns on after the power is turned on.
7 completes initialization, takes in the voltage of capacitor 11 from analog port ANI, and finishes checking. The transistor 13 remains on until the power is turned off.

Next, the operation of the MPU 7 will be explained according to the flowchart of FIG. 2-1. When the initialization is completed after the power is turned on, the terminal voltage vA of the capacitor 11 is fetched from the analog boat ANI in step 101, and the terminal voltage vA of the capacitor 11 is
The power outage time tb is calculated using the time constant of the resistor 12.

In step 102, it is checked whether an error in the temperature control system is stored in the built-in RAM of the MPU 7. If there is no error, energization of the heater is started in step 103, but if there is an error, it is checked in step 104 whether the power outage time tb was longer than the time tA for the fixing roller to cool down sufficiently. If a sufficiently long time has elapsed, energization of the heater is started, but if not, energization of the heater is prohibited in step 105, a heater error is displayed on a display (not shown) in step 106, and the recording device is restarted. It also prohibits startup.

Also, when heater energization is started in step 103, output port 01 is set to H' in step 107, and transistor 1 is turned on.
3 is turned on to charge the capacitor 11 to the maximum voltage.

Next, in step 108, the total energization time of the heater stored in the built-in RAM is 1. (This is data that is the cumulative count of the time during which the heater is energized) is checked to see if it is within the thermistor disconnection detection time tBB. When tll<t, thermistor disconnection detection has not yet been completed, so a thermistor disconnection check is performed.

When checking the thermistor for disconnection, first in step 109, a constant coefficient m is set from the total energization time t3 to the power outage time tb.
Subtract what you multiply. Let it be tc. This constant coefficient m varies depending on the power outage time. This is because the decrease in temperature of the heat roller when the heater is turned off becomes an exponential function as shown below. If the roller temperature is T, the roller temperature when the heater is off is To, and the time constant when the roller temperature falls is t, then b T = T Oe x p - (-) d Therefore, by examining the coefficient m for t, the MPU's Save it in the ROM. Then, calculate the necessary m for t.

When tc becomes zero or negative, the power outage time is sufficiently long compared to the roller cooling time, so it is only necessary to check the voltage V of the thermistor after the regular time t6 has elapsed. Now, when tC in step 111 is positive, the roller is already heated, so it is necessary to shorten the thermistor disconnection detection time. Therefore, after the ta-tc period, the voltage of the thermistor is ■. Check. This is step 112.

In step 113, step 111 or step 11
■I took it in 2. The data is the voltage when the thermistor is normal. If it is higher, it is determined that the wire is broken, and the heater current supply is immediately stopped in step 114.

FIG. 3 shows the relationship between the heat roller temperature and the voltage VA of the capacitor 11. Turn off the power after t hours after the first power supply, and turn on the power after a power outage time tb.

Note that when calculating the coefficient m, the accuracy can be further improved if the temperature T0 before the power is turned off is stored in the RAM and m is determined based on the values of To and t.

As shown in Fig. 2-2, data indicating that paper is jammed in the recording device is stored in the built-in RAM and backed up by a battery, and checked between steps 101 and 102. Immediately disabling the heater energization prevents the paper remaining in the fixing device from burning. When this function is added, it is necessary to provide a jam reset switch 16 on the input board of the MPU to erase the jam data in the RAM when the jammed paper is removed.

[Other Examples]

In the embodiment described above, the heater energization time until the power is turned off is stored in a battery-backed memory. However, in such an application, it is sufficient to hold the contents of the memory until the heat roller cools down after the power switch is turned off, so it is sufficient to hold the power to MPtl only during that period. Therefore, in the second embodiment (FIG. 4), a capacitor backup is used as a battery backup.

Furthermore, the third embodiment (fifth embodiment) uses a common capacitor for capacitor backup and a timer capacitor.
Figure).

In the second embodiment, as shown in FIG. 4, a capacitor 14 is used in place of the battery 9 for battery backup.

The diode 15 is provided to prevent the charge in the capacitor from flowing out. The heater temperature control section is the same as in FIG. 1, so it is omitted.

Further, in the third embodiment, as shown in FIG. 5, the capacitor 14 and the capacitor 11 in FIG. 4 are combined into one. The heater temperature control section is the same as in FIG. 1, so it is omitted.

As described above, according to this embodiment, 1. Even if the power switch is turned off while the temperature sensing element is being checked for disconnection, or the MPU is cleared due to a momentary power interruption, the MPU will be cleared after rebooting depending on the duration of the power outage. By shortening the disconnection check time, disconnection of the temperature sensing element can be accurately detected, and overheating of the heater due to disconnection of the temperature sensing element can be prevented.

2. The effect described in 1 above can now be achieved by using the error memory capacitor, which was previously used only to prohibit restart after turning off the power switch for a certain period of time when a temperature control abnormality is detected. .

3. Paper jam information can also be saved when the power is turned off, so restarting the heating device can be prohibited when the power is turned on again, and paper jammed between the heat rollers will not catch fire.

Although the above embodiment has been described using a recording device that performs thermal fixing, the present invention is not limited to this, and the temperature can be controlled by controlling power supply to a heater using a temperature sensing element such as a thermistor. It can be applied to anything.

(Effects of the Invention) As explained above, according to the present invention, even if the power is turned off and then immediately turned on again before an abnormality is detected in the temperature sensing element, the abnormality can be detected in a short time after being turned on again. , it becomes possible to accurately detect abnormalities and prevent overheating of the heater.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of the first implementation of the present invention, FIG. 2-1,
Fig. 2-2 is a flowchart showing the operation of the MPU, Fig. 3 is a time chart showing the heat roller temperature and the voltage of the capacitor 11, Fig. 4 is a circuit diagram showing the second embodiment, and Fig. 5 is the third embodiment. It is a circuit diagram showing an example of. 1 is a heating device for the fixing device, 7 is an MPU, 9 is a battery backup battery, 11 is a timer capacitor, and 12 is a timer resistor.

Claims (1)

[Scope of Claims] A heater that generates heat when energized; a temperature detection element that detects the temperature of the heater; energization control means that controls energization of the heater in accordance with an output signal from the temperature detection element; a measuring means for measuring the non-energizing time of the heater; and an abnormality determining means for determining an abnormality in the temperature sensing element after a predetermined time after the power is turned on; A temperature control device characterized in that the predetermined times are different.