JPH0745091Y2 - Temperature control device - Google Patents

Description

TECHNICAL FIELD OF THE INVENTION The present invention relates to a temperature control device used in a fixing device of an image forming apparatus.

[Prior art]

As a heated object, for example, a fixing roll (fixing device) used in an image forming apparatus such as an electrophotographic printer holds a surface temperature at a predetermined temperature. Therefore, a temperature sensitive element such as a thermistor is provided on the fixing roll surface, A temperature control device is provided to control energization of the heater provided in the fixing roll according to the temperature detected by the temperature sensitive element.

FIG. 4 is a circuit diagram of a conventional temperature control device. A heater H, which is a heating source, is built in the fixing roll (not shown).
The temperature sensitive element R _TH composed of a thermistor is arranged on the surface of the fixing roll. Resistor R ₁ , variable resistor VR and resistor R ₂ are connected in series, one end of resistor R ₁ is connected to the power supply + V _CC , one end of resistor R ₂ is grounded, and further resistor R ₃ and temperature sensor R _TH and resistor R _A bridge configuration is formed by connecting ₄ in series and connecting in parallel with a series circuit composed of the resistor R ₁ and the variable resistor VR. Then, the reference voltage generated at the connection point between the resistor R ₁ and the variable resistor VR
V _{TH +} is supplied to the non-inverting input terminal of the comparator 1 via the resistor R _5, and the voltage V _TH- generated at the connection point between the resistor R ₃ and the temperature sensing element R _TH is input to the inverting input of the comparator 1 via the resistor R _6. Supply to the terminal. A resistor R ₇ is connected between the output terminal and the non-inverting input terminal of the comparator 1, and the output of the comparator 1 is connected to the power supply + V _CC via the pull-up resistor R ₈ and the heater drive circuit (hereinafter referred to as SSR) 2 Is supplied to. A heater driving power source is supplied to the SSR2 from an AC power source (not shown), and voltage application to the heater H is controlled according to the output of the comparator 1.

In the above structure, the temperature-sensitive element R _TH mounted on the surface of the fixing roll changes its resistance value according to the temperature of the heater H built into the fixing roll, so that the voltage V _TH- also changes and this voltage V _TH-
And the reference voltage V _{TH +} are compared by the comparator 1 to extract the difference output, and the temperature of the heater H is controlled by supplying or not supplying the current to the heater H via SSR2 based on the difference output. .

Then, the reference voltage of the comparator 1 is appropriately adjusted by the above-mentioned variable resistor VR in consideration of variations in the resistance values of the resistors R _{1 to} R ₈ in this control circuit, variations in the output of the power supply, variations in voltage, etc. Temperature control.

[Problems of conventional technology]

In the conventional temperature control device as described above, in order to correct the variation in the resistance value and the variation in the power supply voltage, the variable resistor
The reference voltage V _{TH +} must be adjusted for each device by VR. For this adjustment, for example, in a production process of an electrophotographic printer, an operator manually adjusts each device. However, this is a very time-consuming work because the adjustment value varies depending on the operator and is performed for each machine.

[Purpose of device]

In view of the above conventional drawbacks, the present invention automatically adjusts the reference voltage V _{TH +} to the comparator in the temperature control device to eliminate the variation in the adjustment value due to the artificial adjustment,
In addition, the purpose is to reduce the time required for the adjustment work.

[Key points of device]

In order to achieve the above object, the present invention provides a pulse signal generating means for generating a pulse signal having a width corresponding to given pulse width setting information, and a reference voltage for smoothing the pulse signal output from the pulse signal generating means. A smoothing circuit that generates
A temperature control device comprising: a comparison unit that compares a detection potential generated by a temperature-sensitive element with the reference voltage and outputs a signal according to the magnitude relationship between the two, and controls the energization of a heater according to the output signal of the comparison unit. A jig for applying a detection potential generated by the temperature sensitive element to the comparing means under a set temperature condition to be controlled, a pulse width changing means for sequentially giving different pulse width setting information to the pulse signal generating means, and the pulse Pulse width setting information applied when a reference voltage generated from a pulse signal corresponding to the width varying means and an output voltage of the jig are applied to the comparing means, and the comparing means outputs an inverted signal of magnitude relation. And a storage unit that stores the current, and that controls the energization of the heater by generating the reference voltage by a pulse signal generated according to the pulse width setting information stored in the storage unit. The features.

[Example of device]

Hereinafter, embodiments of the invention will be described in detail with reference to the drawings.

FIG. 1A shows a circuit diagram of the temperature control device of the present embodiment, and the temperature control device of the present embodiment is provided in an electrophotographic printer (not shown). Further, in the circuit of FIG. 1 (a), portions corresponding to those of FIG. In the figure, the circuit of this embodiment has a resistor R ₉ in the adjustment jig 3 connected to the connectors I ₁ and I ₂ in addition to the comparator 1, SSR 2 and heater H described in FIG. CPU (central processing unit) 4 that outputs the adjustment signal or reference signal to the comparator 1, EEPROM that stores the reference signal
(Electrical, Erasable, Programmable RO
M) 5 etc.

The CPU 4 controls each part of the electrophotographic printer in addition to the control circuit of the temperature control device of this embodiment, and controls according to the system program stored in the ROM 6. Further, the RAM7 has an area for storing the data generated during the above-mentioned control operation by the CPU4 and the data read from the EEPROM5 as described later, and the count value of the timer described later. The data storage operation is performed according to the reading and writing control of. The CPU 4 is connected to a dip switch (not shown), and the dip switch sets the adjustment mode or the normal print mode, which will be described later in detail. The CPU4 is shown in the figure (b) in the adjustment mode.
The adjustment signal B in which the T _on time is gradually increased is output to the integrating circuit 8. In addition, the CPU 4 uses the reference signal B'in the normal print mode.
Is output to the integrating circuit 8. This reference signal B'is a signal based on the data stored in the EEPROM 5 as will be described later in detail at the end of the adjustment mode.

The integrating circuit 8 is composed of a resistor R ₁₀ and a capacitor C, smoothes the pulse included in the adjustment signal B or the reference signal B ′, and inverts the voltage value corresponding to the pulse width of the comparator 1 via the resistor R _6. Output to the input terminal. The connection point of the series circuit of the resistor R ₁₁ and the thermistor R _TH is connected to the non-inverting input terminal of the comparator 1. Also, the thermistor R
_At both ends of _TH , connectors I ₁ and I ₂ are provided.
Both ends of a resistor R ₉ provided on the adjustment jig 3 are connected to I ₁ and I ₂ . Moreover, when the resistor R ₉ of the adjusting jig 3 is connected to the connectors I ₁ and I ₂ , the connection circuit of the thermistor R _{TH to} the resistor R ₁₁ is cut off (not shown), but the series circuit of the resistors R ₁₁ and R ₉ is disconnected. Is formed. Therefore, when the resistance R ₉ of the adjusting jig 3 is connected to the connectors I ₁ and I ₂ ,
The voltage V _{A1 at} the connection point between R ₉ and R ₁₁ is constant. Also, the resistance R ₉
Uses a highly accurate resistor.

As described in FIG. 4 above, the comparator 1 compares the voltage input to the inverting input terminal and the voltage input to the non-inverting input terminal, and when the voltage input to the inverting input terminal is high, outputs a low signal to SSR2 and outputs the non-inverting signal. This circuit outputs a high signal to SSR2 when the voltage input to the input terminal is high. SSR2 is a circuit which controls the current supply of the heater H according to the above-mentioned high or low signal.

In the temperature control device for the fixing device having the above circuit configuration,
The circuit operation will be described below. First, the connectors I ₁ , I ₂
Connect the resistor R ₉ of the adjustment jig 3 to. The resistance value of the resistor R ₉ is one having a value equal to the resistance value setting temperature of the fixing roll (e.g. 190 ° C.) thermistor R _TH is generated across the thermistor R _TH upon detection.

Next, a dip switch (not shown) connected to the CPU4 is pressed to set the CPU4 in the adjustment mode and the power is turned on. In the adjustment mode, the power supply to the heater H is forcibly cut off even if the power is turned on. When the power is turned on, the voltage V _{A1 obtained} by dividing the power supply voltage V _CC by the resistors R ₉ and R ₁₁ is supplied to the non-inverting input terminal of the comparator 1. This voltage V _A1 is the heater H
It is a voltage corresponding to the temperature (that is, the resistance value of the thermistor) at which ON / OFF of is switched. On the other hand, the CPU 4 reads the adjustment program from the ROM 6 and executes it. This program controls the output of the adjustment signal B to the integrating circuit 8. According to this program, the CPU 4 executes the processing of the flowchart shown in FIG. That is, first, CPU 4 is set to "0" pulse width ratio within one period T (hereinafter indicated by PDR (pulse duty ratio)) included in the adjustment signal B shown in FIG. 1 (b), T _ON time Is calculated (T × PDR) (steps S1 and S2). This T _ON time indicates a high level time of the pulse signal included in the adjustment signal B. Next, the CPU 4 outputs a high signal to the integrating circuit 8 to start the timer (S3, S4). Therefore, at this time (first), the high signal is always output once.

After that, the timer time T ₁ is compared with the T _ON time (S5). If the timer time T ₁ is longer than the T _ON time, the adjustment signal B is lowered to a low level, and if the timer time T ₁ is shorter than the T _ON time. to sustain the high level of the adjusting signal _{B (S 6, S 7)} .
Therefore, at the initial stage, the result of the above-mentioned calculation process (S ₂ ) is T _ON.
= "0" because it is (T × "0") (the S ₅ Y), the adjustment signal B was high immediately becomes a low level. After that, the timer time T ₁ is compared with _one cycle T (S ₈ ), and when they are equal, the timer T ₁ is reset (S ₉ ). During this time (time T-T _ON ), the adjustment signal B maintains the low level. Then CPU4 determines whether there is an input of the detection signal A to be described later, if there is no input of the detection signal A (S ₁₀ is N), the value of the PDR + and delta, the PDR value is smaller than or determines 1 (S ₁₁ ,
S ₁₂ ). If it is normal, the detection signal A is input before PDR becomes larger than 1, so the determination (S ₁₂ ) becomes Y and the processing (S ₂ )
Return to. Therefore, by executing the first flow, the adjustment signal B output from the CPU 4 is the signal of the part a shown in FIG. 1 (b).

Next, in the process (S ₂ ), T _{ON is} again calculated based on the value of PDR + Δ.
Time calculation (T × (PDR + Δ)) is performed, a high signal is output to the integrating circuit 8, and the timer is started (S ₂ ~
S ₄ ). After that, the timer time T ₁ is compared with the T _ON time as in the above (S ₅ ). In this comparison (S ₅ ), the T _ON time is + Δ minutes longer than the initial time, so the high level is set to T ×
Maintain only Δ (S ₇ ). After that, the timer time T ₁ is T ₁ ≧
When T _ON , the adjustment signal B output from the CPU 4 is set to low level, the timer time T ₁ is compared with _one cycle T, and when they are equal, the timer T ₁ is reset. Further determines whether there is an input in the same way as described above the detection signals A, if there is no input of the detection signal A (S ₁₀ is N), and further + delta value of PDR, PDR value is smaller than or determines 1 (S ₈ ~ S ₁₂ ). Therefore, by executing this second flow, the signal output from the CPU 4 is the signal of the portion b shown in FIG. 1 (b).

Then, by repeating the same processing, c in FIG.
, An adjustment signal B whose pulse width is gradually increased is output to the integrating circuit 8.

In the flow of FIG. 2, the PDR is changed every cycle (T), but a stable smoothed voltage level may not be obtained depending on the time constant of the integrating circuit 8. Therefore, the pulse signal of the same PDR is used. May be changed after a plurality of cycles are repeated. In this case it Rure to change the flow to repeat a plurality of times the processing of S ₂ to S _9.

In the integrating circuit 8, when a signal whose pulse width becomes longer as described above is input, the pulse is smoothed by the resistor R ₁₀ and the capacitor C, and a signal whose voltage level becomes higher sequentially is supplied to the inverting input terminal of the comparator 1. Comparator 1 is
The reference voltage V _A2 that gradually increases in voltage level is compared with the above-mentioned voltage V _A1 supplied to the non-inverting input terminal, and the reference voltage V _A2
Becomes higher than the voltage V _A1 , the low signal (detection signal A) becomes C
Output to PU4 (S ₁₀ is Y). The reference voltage V _A2 supplied to the comparator 1 when the detection signal A is output from the comparator 1 is a voltage equal to the divided voltage value V _A1 of the resistors R ₉ and R ₁₁ . That is, it corresponds to the resistance R ₉ equivalent to the resistance value when the thermistor R _TH detects 190 ° C. Therefore,
When the detection signal A is input, the CPU 4 latches the PDR data at this time, stores the PDR data in the EEPROM 5 (S ₁₃ ) and displays the adjustment completion display (S ₁₄ ).

Next, according to the circuit operation described above, the PDR stored in the EEPROM 5 is
The circuit operation in the case of controlling the temperature control device in accordance with the above data will be described with reference to the flowchart of FIG. In this case, the adjustment jig 3 is not connected to the connectors I ₁ and I ₂ , but the thermistor R _TH is connected. First, the operator presses a dip switch (not shown)
Is set so that a normal program such as a print operation is executed (normal print mode). Then, when the power is turned on, the initialization program read from ROM6 is executed, and the PDR set from the EEPROM5 in the adjustment mode described above is executed.
Data is read out and set in RAM 7 (step ST
1). Based on this PDR data, the CPU 4 performs a calculation (T × PDR) to set the T _ON time (ST2), and outputs a high signal to the integrating circuit 8 (ST3). After that, the timer T ₁ is started (ST 4), the timer time T ₁ is compared with the T _ON time, and T ₁
Time outputs a high signal to reach T _ON time, when the T _ON time reaches ₁ hour T, outputs a low signal to the integrating circuit 8,
After that, when the timer time T ₁ becomes the same as the time T, the timer T ₁
Reset (ST5 to ST8). By this processing, the reference signal B'output from the CPU 4 is the reference voltage V _{A2 of the} temperature control circuit.
Is a signal having an optimum pulse width for outputting.

Through the above processing, the reference signal B ′ output to the integrating circuit 8 is smoothed by the integrating circuit 8 and the above-described reference voltage V ′ is obtained.
It is supplied to the comparator 1 as _A2 . This reference voltage V
_A2 is a reference voltage set on the basis of the resistance R ₉ provided on the adjusting jig 3 as described above, and is a reference voltage value having no variation in circuit components or variation in power supply voltage. Therefore,
The temperature change of the heater H is detected by the thermistor R _TH, it is possible to control the optimum temperature of the heater by comparing the reference voltage V _A2 of uniform above the voltage V _A1 which varies according to the resistance value of the thermistor R _TH.

[Effect of device]

As described in detail above, according to the present invention, the reference temperature can be automatically set during temperature control, and the operator does not need to adjust the variable resistance to set the reference temperature. It is possible to prevent the variation of and to eliminate the working time for temperature adjustment.

[Brief description of drawings]

FIG. 1 (a) is a circuit diagram showing an embodiment of the present invention, FIG. 1 (b) is a waveform diagram of an adjustment signal B according to an embodiment of the present invention, and FIGS. 2 and 3 are present embodiments. 4 is a circuit diagram of a conventional temperature control device. 1 …… Comparator, 2 …… SSR, 3 …… Adjustment jig,
4 ... CPU, 5 ... EEPROM, 8 ... Integrator circuit, R _{1 to} R ₁₁ ...
… Resistance, R _TH …… Thermistor, H …… Heater.

Claims (1)

[Scope of utility model registration request] 1. A pulse signal generating means for generating a pulse signal having a width corresponding to given pulse width setting information, and a smoothing circuit for smoothing a pulse signal output from the pulse signal generating means to generate a reference voltage. A temperature control device that has a comparison unit that compares the detection potential generated by the temperature-sensitive element with the reference voltage and outputs a signal according to the magnitude relation between the two, and controls the energization of the heater according to the output signal of the comparison unit. A jig for applying a detection potential generated by the temperature sensitive element to the comparing means under a set temperature condition to be controlled, a pulse width changing means for sequentially giving different pulse width setting information to the pulse signal generating means, The reference voltage generated from the pulse signal according to the pulse width varying means and the output voltage of the jig are applied to the comparing means, and the comparing means outputs an inverted signal of magnitude relation. Storage means for storing the applied pulse width setting information, and controls the energization of the heater by generating the reference voltage by a pulse signal generated according to the pulse width setting information stored in the storage means. A temperature control device characterized by the above.