JPH01158513A - Temperature control circuit - Google Patents

Abstract

PURPOSE:To suppress the voltage fluctuation of an alternating current power source due to a heater conducting action and to suppress an favorable influence for other electronic equipment connected to a power source by 2-step controlling a heater temperature and chopping-controlling the voltage impressed to a heater at the time of a heater conducting action. CONSTITUTION:The title circuit is provided with a switching circuit 3 inserted into the conducting path of a heater 2, a temperature detector 6 of a heater, a first voltage comparator 12 to send a first conducting signal while the detecting temperature is lowered to a second setting temperature or below, a second voltage comparator 13 to send a second conducting signal while the temperature is lowered to a second setting temperature or below, a control part 14 to send a chopping conducting control signal to the switching circuit during the period from a first conducting signal sending start up to a second conducting signal sending start and send the continuous conducting control signal to the switching circuit during the second conducting signal sending period and an AND gate 9 to calculate the AND of respective control signals and a first conducting signal. Thus, the voltage fluctuation of the alternating current power source due to a heater conducting interrupting action can be suppressed and the unfavorable influence for other electronic equipment connected to the power source can be suppressed.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a humidity control circuit that controls the temperature of a heater to a constant temperature, and in particular, the present invention relates to a humidity control circuit that controls the temperature of a heater to a constant temperature, and in particular, the present invention relates to a humidity control circuit that controls the temperature of a heater to a constant temperature, and in particular, the present invention relates to a humidity control circuit that controls the temperature of a heater to a constant temperature. Regarding control circuits.

[Prior Art] For example, in a dry electrophotographic apparatus, an image formed on the outer circumferential surface of a photosensitive drum is transferred onto paper by a transfer device, and the image transferred to the paper is thermally fixed in a heat fixing section. This heat fixing section is composed of a pair of heat fixing rollers, and each heat fixing roller has a built-in heater, and the temperature of the heater is required to be controlled to a constant temperature.

A temperature control circuit for such a heater is configured as shown in FIG. 4, for example. A heater 2 and a thyristor circuit 3 as a switching circuit are connected in series to an AC power source 1. The temperature of the heater 2 is detected as the voltage at the connection point between the thermistor 4 and the resistor 5 in the temperature detector 6, which consists of the thermistor 4 and resistor 5, which are inserted between the control TLL voltage terminal and the ground, and the voltage of the voltage comparator 7 ( −) are input to the input terminals. A reference voltage V1 is applied to the (+) input terminals of the voltage comparator 7 by a battery 8, for example. This reference voltage v1 is 180°C in terms of the detected temperature of the temperature detector 6.
is set to the voltage value corresponding to.

Therefore, when the detected temperature is below the set temperature of 180° C., the voltage comparator 7 outputs an H-level heater-on signal, and when the detected temperature exceeds 180° C., it outputs an L-level heater-off signal. The output signal a of this voltage comparator 7 is input to one input terminal of an AND gate 9.

The other input terminal of the AND gate 9 receives an operation signal from an output terminal P1 of a microprocessor (MPU) 10 serving as a control section. The output signal of the AND gate 9 is inputted to the control terminal of the thyristor circuit 3 via the inverter 11. This thyristor circuit 3 is connected to the control terminal
It becomes conductive when a high level signal is input, and shuts off when an H level signal is input.

The MPU 10 controls various electronic components of the dry electrophotographic apparatus in addition to the operation signals to the heater 2. In addition to the heater 2, the AC power supply 1 also supplies control power to various electronic members constituting the dry electrophotographic apparatus.

In such a temperature control circuit, when the device is powered on, an H-level operation signal is output from MPtJlo. In this state, since the heater 2 is not energized, the temperature of the heater is naturally below the set temperature of 180°C. Therefore, the detected temperature detected by the temperature detector 6 is also below the set temperature. Therefore, H from the voltage comparator 7
The heater-on signal of the level is sent out, the AND gate 9 is established, and the L level signal is input to the control terminal of the thyristor circuit 3. Therefore, the thyristor circuit 3 becomes conductive, and the heater 2 starts being energized by the AC power source 1.

When the temperature of the heater 2 rises and exceeds the set humidity of 180° C., the voltage comparator 7 sends out an L-level heater-off signal, and the AND gate 9 no longer holds true. Therefore, the thyristor circuit 3 is cut off, and the heater 2 is also cut off.

When the temperature of the heater 2 once rises above the set temperature and then falls to the set temperature again, the output signal a of the voltage comparator 7 becomes H level again, and the heater 2 starts to run 1R.

[Problems to be Solved by the Invention] However, the humidity control circuit configured as shown in FIG. 4 still has the following problems.

That is, FIG. 5 shows the energization/cutoff of the heater 2 and the energization/cutting
Current fluctuations in heater current Is due to interruption, and AC? 5 is a time chart showing voltage fluctuations in the power supply voltage ACV of Ifi1. As is clear from this time chart, since the heater 2 consumes a large current compared to other electronic components constituting the dry electrophotographic apparatus, when the heater 2 starts energizing for a specified current value of about 15A, A large current of up to 3OA flows, and the power supply voltage ACV temporarily drops significantly. In the fifth factor, the peak voltage drops to about 110V for a peak voltage of about 141V.

Therefore, each time the heater 2 is energized or cut off in order to control the heater 2 to a constant temperature, a large voltage fluctuation occurs.
There is a concern that other electronic components connected to this AC power source 1 will be adversely affected.

Particularly in CRT devices, there is a problem in that the image being displayed fluctuates greatly due to the voltage fluctuation.

The present invention controls the heater temperature in two stages and performs chopping control on the voltage applied to the heater when the heater is energized, thereby suppressing voltage fluctuations in the AC power supply caused by the heater energization operation. It is an object of the present invention to provide a temperature control circuit that can suppress adverse effects on other electronic devices as much as possible.

[Means for Solving the Problems] The humidity control circuit of the present invention includes a switching circuit inserted in the energizing path of the heater, a temperature detector that detects the temperature of the heater, and a temperature detected by the temperature detector. A first voltage comparator that sends out a first energization signal when the detected humidity has dropped below a first set temperature; The second voltage comparator sends out the second energization signal, and the chopping energization control signal is sent to the switching circuit during the period from the start of sending out the first energization signal to the start of sending out the second energization signal, and jF!
a control section that sends continuous energization control signals to the switching circuit during the second energization signal sending period; and an AND gate that calculates the AND of .

Further, in another invention, in addition to the above-mentioned means, the control unit is provided with a switching circuit during a period from the end of sending out the second energizing signal to the end of sending out the first energizing signal, in addition to the above two functions. A function is added to send a chopping energization control signal to the

[Operation] With the temperature control circuit configured in this way, when the humidity of the heater that has reached a certain temperature decreases to, for example, the first set temperature, the first voltage comparator turns on the first energization. A signal is sent, and the heater starts to be energized under chopping control. Then, when the detected temperature drops to the second set temperature, the heater is continuously energized.

Note that if you turn on the power when the temperature of the heater is below the second set temperature, such as when starting the device, the heater will be energized with the first and second energization signals being output, and chopping control will be almost impossible. This is not done, but only once when the power is turned on.

Therefore, once the temperature has reached the vicinity of the set temperature, a specified current will not suddenly start flowing through the heater. Therefore, the power supply voltage does not momentarily drop when the heater starts energizing, and other electronic devices are not adversely affected.

Furthermore, even if some abnormality occurs in the control section and a continuous energization control signal is sent from the control section regardless of the state of each energization signal from each voltage comparator, the AND gate will control the M connection. Energization control signals are blocked. Therefore, the safety of the circuit can be improved.

Further, in another invention, in addition to the above-mentioned effect, the heater is subjected to chopping energization control when the temperature of the heater rises to the second set temperature, and is completely shut off when the temperature rises to the first set temperature. . Therefore, even when the heater is shut off, fluctuations in the power supply voltage can be suppressed.

[Example] An embodiment of the present invention will be explained below with reference to the drawings.

FIG. 1 is a circuit diagram showing a temperature control circuit according to an embodiment. Components that are the same as those in FIG. 4 are given the same reference numerals, and explanations of the overlapping portions will be omitted.

In the temperature control circuit of this embodiment, the thermistor 4.
The temperature detected by the temperature detector 6 consisting of a resistor 5 is converted into a voltage and sent to a first voltage comparator 12 and a second voltage comparator 13.
is being input to the (-) side input terminal. The (+) side input terminals of the first and second voltage comparators 12 and 13 are connected to the first and second voltage comparators, respectively.
Reference voltage corresponding to the set temperature of 180℃ ■1 and 2
A reference voltage (2) corresponding to a set temperature of 160° C. is applied. 1st. Each output signal c, d of the second voltage comparison 112.13 is connected to each input terminal P2 of the MPU 14 as a control section.
．． Input to P3.

Therefore, as shown in FIG. 3, when the temperature detected by the temperature detector 6 falls below the first set temperature 180'C, the first voltage comparator 12 input to the input terminal P2 of the MPU 14 The output signal C becomes the first energization signal at H level. Further, when the detected temperature exceeds the first set temperature of 180° C., the output signal C becomes L level.

Further, the detected temperature of the temperature detector 6 is set to the second set temperature 16.
When the temperature drops below 0° C., the output signal d of the second voltage comparator 13, which is input to the input terminal P3 of the MPU 14, becomes the second energization signal at H level. Furthermore, when the detected temperature exceeds the second set temperature of 160°C, the output signal d becomes L.
level.

The output signal C of the first voltage comparator 12 is input to one input terminal of an AND gate 9 serving as an AND gate. The other input terminal of this AND gate 9 has the MPL
The energization control signal e sent from J14 is input.

The output signal of the AND gate 9 is inputted via the inverter 11 to the control terminal of the thyristor circuit 3 as a switching circuit.

Then, the MPLJ 14 executes temperature control processing for the heater 2 according to the main routine shown in FIG.

When the flowchart starts, the output signal C of the first voltage comparator 12 inputted to the input terminal P2 at Sl rises to H level. When the output signal C changes to the H level, the detected temperature drops below the first set temperature of 180° C. and the first energization signal is input, so the heater input chopping process is started in S2. That is, a heater-on chopping energization control signal whose on time gradually increases as shown in FIG. 3 is sent from the output terminal P1 to the AND gate 9. Then, since the first energization signal of H level is sent from the first voltage comparator 12, MPtJ
The heater-on chopping energization control signal output from 14 is input to the control m+ terminal of thyristor circuit 3 via AND gate 9 and inverter 11. Therefore, the thyristor circuit 3 is turned on and off in response to the heater on/off chopping energization control signal. As a result, heater 2
A current IH corresponding to the heater-on chopping energization control signal flows through. Therefore, the current IH is subjected to chopping control.

Then, in S3, when the output signal d of the second voltage comparator 13 input to the input terminal P3 changes to H level,
The detected temperature drops to the second set temperature of 160°C, and the second
Since the energization signal has been sent, continuous energization to the heater 2 is started in S4. That is, from output terminal P1 to H
AND gate 9. Continuous energization control signal with constant level. It is sent to the thyristor circuit 3 via the inverter 11.

Thus, the thyristor circuit 3 becomes conductive, and the heater 2 is continuously energized.

The temperature of heater 2 rises, and input terminal P3 becomes L at S5.
When the detected temperature changes to the second set temperature 160
It is determined that the temperature has reached ℃. Then, since the sending of the second energization signal has been completed, the heater cutoff chopping process is started in S6. That is, a heater cutoff chopping energization control signal whose on time gradually decreases as shown in FIG. 3 is sent from the output terminal P1 to the AND gate 9. Then, the heater cutoff chopping energization control signal is transmitted to the thyristor circuit 3 via the AND gate 9 and the inverter 11.
is input to the control terminal of Therefore, the thyristor circuit 3 responds to the heater cutoff chopping energization control signal,
Continuity/cutoff occurs. As a result, a current IN corresponding to the heater cutoff chopping energization control signal flows through the heater 2 . Therefore, the current IN is subjected to chopping control.

Then, when the input signal of the input terminal P2 changes to the L level in S7, the first energization signal transmission has ended, so the control signal e output from the output terminal P1 is set to the L level, and the heater 2 is completely shut off. do.

Then, the process returns to Sl, and the temperature of the heater 2 becomes lower than the first set temperature of 180° C. again.

In the temperature control circuit configured in this way, the temperature of the heater 2 is at room temperature when the power switch is initially turned on, so the temperature of the heater 2 is at room temperature. Second voltage splitter 12.13 to H
Level 1. A second energization signal is being sent. Therefore, chopping control is not executed and heater 2
is started to be energized. Then, the temperature becomes the second set temperature 16
When the temperature reaches 0°C, the heater cutoff chopping operation is started, and when the temperature reaches the first set temperature of 180°C,
Heater 2 is completely shut off.

Even if the heater 2 is shut off, the temperature does not drop immediately, but starts to drop when it slightly exceeds the first set temperature of 180°C. Then, when the temperature falls again to the first set temperature of 180° C. or lower, as shown in FIG. 3, the heater 2 starts to be energized under chopping control. Then, the temperature further decreases to the second set temperature 160.
℃ or below, the heater 2 becomes continuously energized. Then, when the state shifts to a continuous energization state, the heating power of the heater 2 increases, and the temperature starts to rise. Then, the second set temperature 1
When the temperature rises to 60° C., the heater 2 shifts to chopping control. When the temperature rises to the first set temperature of 180° C., the heater 2 is completely shut off. Then, when the temperature falls again to the first set temperature of 180° C., the heater 2 starts to be energized under chopping control. This cycle is then repeated until the power switch is turned off.

In this way, only when the power is turned on for the first time, the heater 2 starts energizing without chopping control, but once it transitions to the temperature control state, the heater 2 always starts energizing or shuts off under chopping control. be done.

Therefore, during normal operation when the heater 2 is controlled to a constant temperature, the current 1) Iffifi flowing through the heater 2 does not increase dramatically. As a result, it is possible to suppress the voltage fluctuation of the AC power supply 1 due to the heater energization/opening operation, so that the adverse effects on other electronic devices connected to the AC power supply 1 can be suppressed to a minimum.

Note that when the power is turned on, the heater is energized without any chopping control, but the device incorporating this temperature control circuit is in a standby state until the heater reaches a certain temperature. Power supply voltage fluctuations due to startup do not pose a particular problem.

In this embodiment, as shown in FIG. 3, the maximum value of the heater current IN can be suppressed to about 20 A, and voltage fluctuations in the power supply voltage ACV can be significantly suppressed compared to the conventional characteristics shown in FIG. Ta.

Further, since chopping control is performed even when the heater 2 is shut off, fluctuations in the power supply voltage ACV can be suppressed to a minimum, and the above-mentioned effects can be further improved.

Further, even if some program abnormality occurs in the MPU 14 and a continuous energization control signal of H level is always sent from the output terminal P1, the temperature will not reach the first set temperature 180.
℃, the output signal C of the first voltage comparator 12 becomes L.
Since the current level changes, AND gate 9 no longer holds true. Therefore, the heater 2 is forcibly shut off. Therefore, the reliability of this temperature control circuit can be improved.

Although the humidity control circuit of the embodiment is applied to a heat fixing section incorporated in a dry electrophotographic apparatus, it can also be applied to other apparatuses using a heater.

Furthermore, the on/off period and pulse width during chopping control can be changed arbitrarily by program operation.

[Effects of the Invention] As explained above, according to the temperature control circuit of the present invention, the temperature is controlled in two stages, and the voltage applied to the beater during the heater pass and cut-off operations is subjected to chopping control.

Therefore, it is possible to suppress the voltage fluctuation of the AC power source due to the heater energization/cutoff operation, and to minimize the adverse effects on other electronic devices connected to the power source.

[Brief explanation of the drawing]

1 to 3 show a temperature control circuit according to an embodiment of the present invention. FIG. 1 is an overall circuit diagram, FIG. 2 is a flowchart showing the operation, and FIG. 3 is a flowchart showing the operation. FIG. 4 is a circuit diagram showing a conventional temperature control circuit, and FIG. 5 is a time chart showing the operation of the conventional temperature control circuit. DESCRIPTION OF SYMBOLS 1... AC M source, 2... Heater, 3... Thyristor circuit, 4... Thermistor, 6... Temperature detector, 9
...AND gate, 12...First voltage comparator, 13...Second voltage comparator, 14...M
P.U. Applicant's agent Patent attorney Takekin Suzue 2 Figure

Claims (2)

[Claims] (1) A switching circuit inserted in the energizing path of the heater, a temperature detector that detects the temperature of the heater, and a first a first voltage comparison device that sends out an energization signal; and a second voltage comparison device that sends out a second energization signal when the detected temperature is lower than a second set humidity that is lower than the first set temperature.
a voltage comparator, and transmitting a chopping energization control signal to the switching circuit during a period from the start of sending out the first energization signal to the start of sending out the second energization signal,
a control section that sends a continuous energization control signal to the switching circuit during the second energization signal sending period; and a control section that is inserted in a signal path of each of the control signals from the control section to the switching circuit, A temperature control circuit comprising: an AND gate that calculates an AND with the first energization signal. (2) a switching circuit inserted in the energizing path of the heater; a temperature detector for detecting the temperature of the heater; a first voltage comparator that sends out an energization signal; and a second voltage comparator that sends out a second energization signal when the detected temperature is lower than a second set temperature that is lower than the first set temperature.
a voltage comparator, and transmitting a chopping energization control signal to the switching circuit during a period from the start of sending out the first energization signal to the start of sending out the second energization signal,
Sending a continuous energization control signal to the switching circuit during the second energization signal transmission period, and chopping energization control to the switching circuit during the period from the end of the second energization signal transmission to the end of the first energization signal transmission. a control section that sends out a signal; and an AND gate that is inserted in a signal path of each of the control signals from the control section to the switching circuit and that calculates the AND of each of the control signals and the first energization signal. A temperature control circuit comprising: