JPH03267987A - Fixing device - Google Patents

Abstract

PURPOSE:To recognize the disconnection of a thermistor by software by connecting a switching part for checking the disconnection of the thermistor to the thermistor and a potential division resistor which are serially connected in series and connecting a resistor to the potential division resistor and the switching part in parallel. CONSTITUTION:The switching part 4 for checking the disconnection of the thermistor 1 is connected to the thermistor 1 and the potential division resistor 2 which are electrically serially connected in series, and the resistor 3 is connected to the resistor 2 and the switching part 4 in parallel. Thus, the heating device of a fixing device is prevented from being kept in an on-state even when a connector is off by a mistake in a wiring operation or by an accident in an electric wire connected to the thermistor 1 or the electric wire is disconnected.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention provides reliability and reliability in temperature control of a fixing device.
Regarding ensuring safety.

[Conventional technology 1] In the conventional temperature control of the fuser, if the electric wire connected to the thermistor is left disconnected or the wire is disconnected due to a wiring error or an accident, the fuser The device's heating device was left on.

[Problem to be Solved by the Invention 1] Therefore, in the case where the fixing device is equipped with a temperature fuse to prevent ignition, it becomes impossible for the user to restore the fixing device. Even if a temperature switch is used, the temperature setting of the switch varies, and the temperature may become higher than the setting, which may damage parts such as the coating on the fixing roller or the separation claw. Conventional fixing devices have had such problems.

The present invention is intended to solve these problems, and its purpose is to detect when the wire connected to the thermistor is disconnected or the connector is disconnected, and to stop the temperature heating device. To provide a fixing device having a temperature control means capable of easily returning the fixing device.

[Means for Solving the Problems] The fixing device of the present invention includes a thermistor whose resistance value changes depending on the temperature by detecting a temperature change of the fixing device, and a thermistor whose resistance value changes into a voltage change. is installed electrically in series with the thermistor, and 1! A fixing temperature measuring means constituted by a voltage dividing resistor that divides the pressure, a voltage detecting means for detecting the voltage generated by the fixing temperature measuring means, and a temperature control of the fixing unit by the voltage detected by the voltage detecting means. In a fixing temperature control device consisting of a temperature control section that generates a signal, and a fixing temperature heater control means that turns on and off a constant @ temperature heater according to the signal generated by the temperature control section, the fixing temperature controller is electrically connected in series. A switch section for checking disconnection of the thermistor was further connected in series to the thermistor and the voltage dividing resistor, and a resistor was connected in parallel to the voltage dividing resistor and the switch section.

[Example] Fig. 2 is a circuit diagram showing a specific example of the present invention.
is attached to the fuser and measures the temperature. The characteristics of the thermistor are approximately 3M ohm at 10 degrees Celsius (low temperature environment).
At 180 degrees Celsius (control temperature) it is approximately 3.7 ohms
The voltage dividing resistor 2 divides Vcc approximately 5V. Voltage divider resistor 2 is approximately 3.7 ohms. The transistor 4 serves as a switch section, and a signal is output from the CPU 7 via the buffer 5 to turn it on or off. Resistor 3 is about 10M
It is an ohm resistance. When the transistor 4 is turned on, the voltage at the input part a of the A/D converter 6 remains VcC in an environment of 10 degrees Celsius, and becomes V c c / 2 = 2.5 ■ in an environment of 180 degrees Celsius. . When transistor 4 is turned off, the voltage at input part a is as follows in an environment of 10 degrees Celsius.
Approximately 3.8V, and approximately 5V under 180 degree control. At this time, if the thermistor wire is disconnected, the input section a indicates the ground level.

The A/D converter 6 converts the voltage into 8-bit digital data. If 5V is 256 and the ground is O, then the control voltage 2.5cm is 128. CPLI7
includes ROM8 and RAM9, and constitutes a temperature control unit IO. Depending on the content of the temperature control, a control signal is sent from the CPU 7 to a constant temperature heat control means 11 that turns on/off the current of the AC power supply 14 supplied to the fixing temperature heater 13.

The fixing temperature heater control means 11 is composed of a photocoupler 11 and a triac 15.

Next, the operation of the fixing device configured as described above will be explained using the flowchart shown in FIG.

At the same time as the power is turned on, the fixing temperature control program written in the ROM 8 starts. (Steps 32 and 33) When the power is turned on, first the fixing temperature heater is turned off. (Step 34) Turn off the transistor to check for disconnection of the thermistor. (Step 35) Determine whether the voltage at the input section is 2V or less. If it is at ground level, the wire is disconnected, if it is over 3.8V,
You can check if the wire is not broken, so if it is less than 2V, it is broken, 2
If it is more than V, it is determined that there is no disconnection. If it is 2V or less, error processing is performed in case the thermistor wire is disconnected. If the voltage is 2V or higher, the transistor 4 for checking disconnection is turned on and constant temperature control is started.

(Steps 36, 37, 38, and 39) When the fixing temperature reaches the set value, a timer is set to check for wire breakage at regular intervals, and a command to start printing can be accepted. (Step 40
．． 41.42) Continue constant @ temperature control. Fixing control continues until the timer set for checking for wire breakage reaches the set time. At the set time, if printing is in progress at that time, wait until printing is finished, and when printing is no longer in progress, repeat the disconnection check sequence. (Steps 43.44.45
) By following such a flowchart, it becomes possible to detect a thermistor disconnection using software.

[Effect of the Invention 1] Due to the above-mentioned reasons, the fixing device of the present invention can be used even if the connector remains disconnected or the wire connected to the thermistor is disconnected due to a wiring error or an accident. , the fuser heating device will not remain on. Furthermore, check whether there is a disconnection or not.
Because it is checked on the PU, it also has the advantage that it is possible to clearly inform the user of the cause of the error by displaying it on the front panel.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of a fixing device according to the present invention. FIG. 2 is an electrical circuit diagram of temperature control as an embodiment. Third
The figure is a flowchart showing an example of a program for temperature control Voltage detection means Temperature control means Switch control means Fixing temperature heater Control means Thermistor Partial voltage resistor Resistor Switch part Above l Figure 2

Claims (1)

[Claims] A thermistor that detects temperature changes in the fixing unit and whose resistance value changes depending on the temperature; and a thermistor that is installed electrically in series with the thermistor to convert the resistance change of the thermistor into a voltage change. , a fixing temperature measuring means constituted by a voltage dividing resistor that divides the voltage; a voltage detecting means for detecting the voltage generated by the fixing temperature measuring means; A fixing temperature control device comprising a temperature control section that generates a temperature control signal, and a fixing temperature heater control means that turns on and off the fixing temperature heater according to the signal generated by the temperature control section, electrically connected in series. Further, a switch section for checking disconnection of the thermistor is connected in series to the thermistor and the voltage dividing resistor connected to the voltage dividing resistor and the voltage dividing resistor, and a resistor is further connected in parallel to the voltage dividing resistor and the switch section. A fixing device characterized by: