JPS60198612A - Temperature controller - Google Patents

Abstract

PURPOSE:To detect easily a disconnection through a simple constitution by connecting a constant voltage element in series to a temperature detecting element. CONSTITUTION:The temperatures are detected by a series circuit of a bridge resistance R15 and a thermister TH serving as a temperature detecting element and bridge resistances R16-R18. The voltages VF and VG of unctures are supplied to a comparator Q2 for temperature control to obtain the ON/OFF signals of a heater. In this case, a constant voltage element ZD such as a Zener diode, etc. is connected in series to the thermistor TH to extract the voltage VH at the juncture between the element ZD and the TH as well as the voltage VI of the R18. These voltages are supplied to a comparator Q3 for detection of disconnection. If the TH has a disconnection, the VH is set at 0. The output of the comparator Q3 is inverted with VH<VI, and this inverted output is detected by a central controller to open a heater circuit or turn on an alarm display device, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a temperature control device, and particularly to a temperature control device such as a heat fixing device.

[Technology background]

In fusers such as copying machines, the temperature of the heat source is controlled using a temperature detection element such as a thermistor. The lead wires for the detection elements have also become extremely thin, and disconnection accidents of the temperature detection elements and the lead wires have become unavoidable. There is no good measure to prevent such a disconnection accident of the temperature detection element and the lead wire. If the above-mentioned temperature detection element and lead wire are disconnected, a change in the temperature of the heat source can be detected.If power is continuously supplied to the heat source, the temperature of the heat source will rise abnormally, causing thermal deformation of the fuser etc. near the heat source. causing harmful effects.

[Problems with conventional technology]

A conventional temperature control device for eliminating such adverse effects is shown in FIG. In the figure, Vcc is a voltage source, which constitutes a bridge with resistors R1, R2, R3, and capacitor C1. Provided to the inverting and non-inverting inputs of the disconnection detection prevention comparator Q1,
A Vcc voltage is applied to the connection point between resistors R1 and R3, and the connection point between resistor R2 and capacitor C1 is grounded to form a bridge. The output of the disconnection detection blocking comparator Q1 is applied to the base of a second disconnection detection activation transistor Q5, which will be described later, and the H (high) output is taken out as an off signal for the heater H. On the other hand, resistor R5, thermistor TH which is a temperature detection element, resistor R9,
A bridge is configured with RIG. Voltage ■ taken out from the connection point of resistor R5 and thermistor TH. and resistance R9
The voltage taken out from the connection point of and R+o ■.

is applied to the non-inverting and inverting inputs of a temperature adjusting comparator Q2, and the output of the temperature adjusting comparator is applied to the base of a switching transistor Q6 that turns on and off the heater I. Furthermore, the above resistor R5 and thermistor T
Add a bridge composed of H and resistors Re and Rv,
・Voltage V6 at the connection point of resistors R6 and R7 and the above-mentioned resistor R
Connection point voltage between 5 and thermistor TH ■. are added to the non-inverting and inverting inputs of the disconnection detection comparator Q3, and the output of the disconnection detection comparator Q3 is applied to the base of the first disconnection detection operating transistor Q4. Note that resistors R5 and R6
, R9 are commonly connected to vcc through resistor R4.
Connected to voltage source, thermistor TH, resistor R? , R1O are also commonly connected and dropped to ground potential.

The emitter of the first disconnection detection transistor Q4, the collector of the second disconnection detection transistor Q5, and the heater on/off switching transistor Q.
The collector of 6 is connected to the resistor R+ +, R+ from the VCC voltage source.
3. R+ s and the photodiode Q of the phototriac? The collector of the first disconnection detection activation transistor Q4 is connected to the base of the second disconnection detection activation transistor Q5, and the other end of the resistor R13 is also connected to the base of the switching transistor Q6. There is. The base of the second disconnection detection operating transistor Q5 is connected to the ground potential via the resistor Ra2, and the emitter is similarly grounded via the diode D1.

Further, the emitter of the switching transistor Q6 is lowered to the ground potential through a series circuit of a diode D2.03.

The photo triac Q7" is connected to the commercial power supply AC by connecting the fuse F and the fuser heater H in series, and is electrically separated from the temperature detecting means and optically coupled. To explain the operation in the above configuration.

In the above configuration, temperature control is performed by detecting whether or not the thermistor is disconnected after a certain period of time has elapsed after the start of heating of the heater H. Generally, if the heater H is left in a low temperature state without power being supplied for a long time, the thermistor T
H has a high resistance on the order of several MΩ, making it impossible to determine that the resistance is high when the thermistor TH is disconnected. Work is being done to solve this problem. That is, when the power is first turned on, charging of the capacitor C1 starts in the time determined by the resistor R1 and the time constant of Contin-'J"lc+. Initially, V
If A>VB, the output of comparator Q1 for preventing wire breakage detection is “
Since the voltage is L' (low), the second disconnection detection operating transistor Q5 is in the "off" state.

In this state, the resistance value of the thermistor TH shows a high resistance because the ambient temperature is low, and the input voltage relationship of the temperature adjustment comparator Q2 is vc>Vr, and the output of the temperature adjustment comparator Q2 is "11". It shows. On the other hand, by appropriately selecting the resistance ratio of resistors R6 and R7, the relationship with vc is selected so that vc>y, so the output of comparator Q3 for disconnection detection becomes "L", and the first disconnection detection is performed. The operating transistor Q4 is "on", but the second disconnection detection operating transistor Q5 is "off", so the photodiode Q of the phototriac Q7? Heat-on/off switching transistor Q connected to '
6 becomes “on” and triac Q7 is also “on”.
AC is supplied to the heater (2).

Here, if the thermistor TH is normal and not disconnected, after a predetermined time determined by the time constant of resistor R3 and capacitor c1, the relationship between ■^ and vB will be reversed from the above, and vA<
y, so the output of the disconnection detection prevention comparator Q1 becomes "H". However, before this, the resistors R5 and R
6. The relationship between voltage VC obtained by the bridge composed of R7 and thermistor TH and ■6 is ■. 〈■. Therefore, the disconnection detection comparator Q3 outputs "H", and the first disconnection detection activation transistor Q4 becomes "off".

The second disconnection detection operating transistor Q5 also becomes "off" and maintains this state. For this reason, the temperature adjustment comparator Q2 maintains H'' and the heater H continues to be energized.When the temperature adjustment point set by the resistors R5, R9, R1o and thermistor TH is reached, ■.〈■o is reached. The output of the temperature adjustment comparator Q2 becomes "'L", the second disconnection detection operation transistor Q6 is turned off, the phototriac Q7 is also turned off, and the power supply to the heater H is cut off.After that, the temperature is adjusted. "On" and "off" are controlled by the operation of the comparator Q2.

When the thermistor TH is disconnected, the disconnection detection blocking comparator Q+ is "H", the disconnection detection comparator Q3 is "L", and the first and second disconnection detection activation transistors Qa and Qs are in the "ON" state. Then the heater turns on,
The OFF switching transistor Q6 is brought into a 6 OFF state.

That is, according to the above operation, the temperature adjustment comparator Q
2 controls the heater H on and off, and when detecting a wire breakage with the wire breakage detection comparator Q3, the wire breakage detection comparator Q3 becomes active, and the first and second disconnection detection operating transistors Q a .

Q5 is activated, and the comparator Q1 for inhibiting disconnection detection prevents the operation of the comparator Q3 for disconnection detection. However, even with the above-described configuration and operation, the thermistor performs a fixing operation and the temperature rises sufficiently.

If the thermistor is disconnected during the transition to the next operation, i.e. when copying is complete and the thermistor temperature has not cooled sufficiently before the next copy operation is performed, the comparator QI for preventing disconnection detection is activated. However, there is a drawback that heating the heater H causes thermal damage to the fixing device.

Furthermore, according to the configuration shown in Fig. 1, not only is it impossible to detect a thermistor failure during the entire operating time, but also a comparator for preventing disconnection detection is required in addition to the comparator device for detecting disconnection, which increases the complexity of the circuit. , which will lead to an increase in costs.

(Object of the Invention) In view of the above-mentioned conventional drawbacks, an object of the present invention is to provide a temperature control device that can detect failures of temperature detection elements such as thermistors throughout the operating time of the temperature control device with a simple circuit configuration. That is.

[Structure of the invention]

According to the present invention, this object includes a temperature detection element for detecting temperature and a constant voltage element connected in series with the temperature detection element, and the temperature detection element is controlled by a change in the terminal voltage of the constant voltage element. This is achieved by providing a temperature control device characterized by detecting disconnection of the wire.

[Embodiments of the invention]

An embodiment of the present invention will be described in detail below with reference to the drawings.

FIG. 2 shows a circuit diagram of the temperature control device of the present invention.

In the same figure, a series circuit consisting of a bridging resistor R+a, a constant voltage element such as a thermistor TH and a Zener diode ZD, and a series circuit of bridging resistors R16°R+t and RIB are configured as a bridge, and the connection point of resistors Ra1I and Rye is connected to Vcc. Apply voltage.

The 7 note side of the Zener diode ZD and the connection point of one end of the resistor R+a are grounded, and the voltage V is applied from the connection point of the thermistor and the resistor R15, and the connection point of the resistor R16 and R+v, respectively.
11-. Take out V(, and mix it up for temperature adjustment.
2 non-inverting and inverting inputs. On the other hand, thermistor TH
and Zener diode ZD, and resistor R17,
Voltages V, , Vr are taken out from the connection points of RIB and applied to the non-inverting and inverting inputs of the disconnection detection comparator Q3. A resistor RI11 connected in parallel to the Zener diode 1'ZD is a protective resistor for dropping the voltage to the ground potential when the Zener diode is disconnected. Also, resistor R21,
R21 indicates a hysteresis resistor inserted between the input and output of the temperature adjustment comparator C2 and the disconnection detection comparator Q3. The temperature adjustment comparator Q2 outputs an "H" level when the relationship between the input voltage VF and v5 is VF>VG.

The input voltage for the disconnection detection comparator Q3 is ■.

> VI.

To explain the operation in the above configuration, first, the relationship between the input voltage VI: and VG of the temperature adjustment comparator Q2 is Vp>
If Ve, the output of the temperature network adjustment comparator Q2 is “H”.
”, this “H” level state is detected by a central control unit (CPU) or a detection means configured with a discrete circuit (not shown), and the heater H is energized as shown in FIG. 1.The heater H is energized. If the heater is heated and the resistance value of the thermistor TH decreases, the relationship between VF and VQ becomes Vp.
<V5, and the output of the temperature adjustment comparator Q2 becomes the "L" level, so the central control device described above only has to cut off the power to the heater. In this way, the temperature adjustment comparator Q2 turns the heater on and off. can be controlled.

On the other hand, VH applied to the disconnection detection comparator Q3,
The voltage relationship of VT is that if the thermistor TH is functioning in a compressive manner, ■, the Zener potential of the Zener diode ZD is (V 5 - Vz) $ and is added to the disconnection detection comparator Q3, and ■8> VI conditions. Select each resistor of the bridge so that

Therefore, the output of comparator Q3 for disconnection detection is ”
As soon as the H'' level is detected, it is detected that the wire is not disconnected, and the energization operation is performed.

Now, if the thermistor TH is disconnected, the Zener potential of the Zener diode is zero and VH is the protective resistor R19.
is grounded through the terminal, the voltage becomes zero volts, and the relationship of V H < V is established, and the output of the disconnection detection comparator Q3 is inverted and becomes “
This output is detected by the central control unit to open the heater circuit. Of course, the above L level signal can be used to stop the temperature control device or turn on the alarm display device. You may also do this.

Since the present invention is configured and operated as described above, it can be used as
The present invention is extremely effective in detecting temperature detection elements such as thermistors of the thermal coefficient type, which have a very high resistance value at room temperature, and it is impossible to determine whether the thermistor is disconnected at the time of startup.

In addition, in the present invention, since the Zener diode potential can be sufficiently secured with a relatively weak operating current of about 10-5 to 10-'A, disconnection of the temperature detection element can be detected simply by connecting the Zener diode in series with the thermistor. Therefore, it has the characteristic that a circuit can be constructed at an extremely low cost for detecting disconnection of a thermistor having a resistance of several MΩ at a temperature.

According to the present invention, disconnection of the temperature element can be reliably detected in a wide temperature range, whether in a cold state or a high temperature state.

〔Effect of the invention〕

As described above in detail, according to the temperature control device of the present invention, disconnection can be easily detected with a simple configuration in which a constant voltage element is connected in series with a temperature detection element.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of a conventional temperature control device, and FIG. 2 is a circuit diagram of a temperature control device of the present invention. R1, R2, R3, R5, R6, R7, R9゜RIO,
R11l, R+a, R17, R+5100 bridge resistor, R4, Rθ...resistance. R111RI2910 voltage dividing resistor, R13゜R+a...
・Bleeder resistance, R19...protective resistance, R2O,
R21... Hysteresis resistor, C1... Electrolytic capacitor. H...Heater, F...Fuse. AC...Commercial power supply, Q+...Comparator for disconnection detection prevention, C2...Comparator for temperature adjustment,
C3... Comparator for disconnection detection, C4, C5...
・First and second disconnection detection operation transistors, Qs
...Switching transistor for heater on/off,
Ql...Phototriac. Qv'...photodiode, C7"...triac, Vcc...voltage source. Patent applicant: Casio Computer Co., Ltd. Same as above Yoshiyuki Osuga, agent of ID Co., Ltd. Figure 1

Claims (2)

[Claims] (1) It has a temperature detection element that detects temperature and a constant voltage element connected in series with the temperature detection element, and detects disconnection of the temperature detection element based on a change in the terminal voltage of the constant voltage element. Features temperature control device. (2) A bridge is configured by a temperature detection element that detects temperature, a constant voltage element connected in series with the temperature detection element, and a bridge resistor, and the bridge output is added to a disconnection detection comparator. A temperature control device according to claim 1.