JP2545391B2 - Fixing temperature control device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixing temperature control device in a fixing device for fixing a transfer image on a sheet by passing a recording sheet through a fixing roller heated by a heater. The present invention relates to a fixing temperature control device for increasing the number of sheets guaranteed for fixing during continuous copying of small-size paper.

[Prior art]

As a conventional fixing temperature control device used in a copying machine, there is, for example, Japanese Patent Application Laid-Open No. 50-138838, and a roller for heating the sheet while contacting and rotating the sheet to convey the sheet in a fixed direction. Is heated by an independent heating element at each of the central portion and the end portion in the axial direction, and the temperature in the effective region corresponding to the width of the sheet on the peripheral surface of the roller is applied to each of the independent heating elements. The heat-sensitive elements provided at corresponding predetermined positions and having the same set temperature are used for detection, and the energy supply to the independent heating elements is independently controlled according to the detected temperatures, and the circumference of the roller is controlled. The effective area of the surface is kept within a predetermined temperature range.

However, in such a fixing temperature control device, when continuous copying is performed, the surface temperature of the fixing roller decreases, and finally, when the temperature drops to a predetermined temperature, the power is insufficient to stop the copying operation. If this technique is used in a machine that performs the operation, there is a problem that the number of heaters W in the non-sheet passing portion cannot be fully utilized when the small size sheet is passed (at the time of fixing).

That is, in the heat roller fixing device, when the machine is on standby,
The fixing roller is maintained at a certain set temperature.

Then, the transfer paper sent by the copy start signal is held between the rollers and heat is applied to fuse and fix the toner on the transfer paper.

Therefore, since the heat of the fixing roller is taken away by the transfer paper, the temperature of the fixing roller continues to decrease during continuous copying (fixing), and finally falls below the feasible temperature.

Therefore, the copying operation is stopped, and after the fixing temperature is restored to the set temperature, the copying operation is restarted.

FIG. 12 shows a temperature characteristic diagram for performing such control, in which the ordinate represents the temperature T of the fixing roller and the abscissa represents the time t.

T ₁ is the standby temperature and T ₂ is the lower limit fixing temperature.

In addition, t ₁ and t ₄ indicate standby, t ₂ indicates copying, and t ₃ indicates temperature recovery.

As shown in this characteristic diagram, continuous copying (fixing)
Fixing roller temperature between lowered and the recovery time t ₃ to T ₂ are the copy impossible.

In order to eliminate such recovery time t ₃ may be caused to increase the power supplied to the heater, but this power consumption of the entire copying machine and to increases, the difficulties generally use household power Become.

Therefore, if the heater power for the non-sheet passing portion can be used for the sheet passing portion, it is possible to use a household power source.

However, in the conventional device, the heater of the non-sheet-passing portion does not take away the heat from the sheet, so that the heater is hardly energized, but this margin is insufficient. There is a problem that it is not used for departments.

〔Purpose〕

SUMMARY OF THE INVENTION The present invention has been made in view of the above, and an object of the present invention is to provide a fixing device in which electric power for a non-sheet passing portion is diverted to a sheet passing portion and the number of continuous copies of small size sheets can be increased. It is to provide a temperature control device.

〔Constitution〕

In order to achieve the above object, in a fixing temperature control device of a fixing device for passing a recording sheet through a fixing roller heated by a heater and fixing a transfer image on the sheet, a small-sized sheet in the fixing roller is A first heater disposed in the sheet passing width region, and a second heater disposed in a difference in sheet passing width region between the small size sheet and the large size sheet,
Temperature detecting means for detecting the roller surface temperature of each of the installation portion of the first heater and the installation portion of the second heater,
If the roller surface temperature of the installation portion of the second heater is the first
When the temperature is higher than the roller surface temperature of the heater installation portion, the control means for cutting off the power supply to the second heater and increasing the power supply current to the first heater is provided.

Hereinafter, an embodiment of a fixing temperature control device according to the present invention will be described with reference to the accompanying drawings.

FIG. 1 is a circuit diagram showing an embodiment of the present invention.
3 is a circuit diagram showing details of the control unit, and FIG. 3 is a detailed circuit diagram of the zero-cross detector shown in FIG.

FIG. 4 is a front sectional view showing the structure of the fixing roller of the fixing device according to the present invention.

As shown in FIG. 4, the fixing device 1 includes a rotatable fixing roller 2 having a hollow structure, a first heater 4 having a length equivalent to the paper width of a small-sized (for example, A4 size) sheet 3, and a large-sized ( A second heater 6 (6a + 6b) disposed at a position corresponding to a sheet width difference between the sheet 5 and the sheet 3 (for example, A3 size).
The thermistor 7 measures the surface temperature of the fixing roller 2 by the heater 4, the thermistor 8 measures the surface temperature of the fixing roller 2 by the heater 6a, and the pressure roller 20 described later.

FIG. 5 is a cross-sectional view showing the outline of the overall structure of the fixing device. A pressure roller 20 is rotatably pressed against the fixing roller 2, and a sheet 70 with a transfer image 71 adhered between the rollers is transferred image 71.
The sheet is passed with the sheet facing the fixing roller 2.

In the above configuration, when passing a large-sized sheet 5 continuously, the heater 4 and the heater 6 are energized to raise the surface temperature of the fixing roller 2 to T ₁ .

 In this state, the sheet 5 is continuously passed.

The surface temperature of the fixing roller 2 begins to drop after passing t ₁ as shown in FIG.
The copying operation is stopped when t ₂ has elapsed.

Next, when the small-sized sheet 3 is continuously passed, the energization of the heaters 6a and 6b results in extra heating with respect to the sheet width, and wastes energy.

Therefore, in the present invention, the temperature Ta of the non-sheet passing portion is set by the thermistor 8.
Is detected and the measured temperature Tb of the paper passing portion is detected by the thermistor 7, the two are compared, and when Ta> Tb, the heater 6 is turned off, and at the same time, for example, 66.7% duty is turned on. Heater 4 to 10
Energize with 0% duty.

As a result, the amount of energy held in the non-energized part is increased,
It enables efficient heater control regardless of the sheet size.

Next, taking the fixing device 1 shown in FIG. 4 as an example, the configuration of the control unit in FIG. 1 for controlling the heater will be described.

The control unit 10 combines an A / D converter (converter) 11 for A / D converting the outputs of the thermistors 7 and 8 and a CP for executing heater control based on the thermistor output and each control of the copying machine.
It is composed of a U12, a ROM 13 in which a program for operating the CPU 12 in a predetermined procedure is stored, and an I / O port 14 for outputting the calculation result of the CPU 12 at a predetermined timing.

The I / O port 14 has two ports (PA0, PA1), and each port corresponds to each of the heaters 4, 6.

A driver 15 is connected to the I / O port 14 to perform voltage amplification corresponding to each port.

Each output of the I / O port 14 is used as a gate voltage and is a kind of semiconductor switch element SSR (Solid State Switch)
Relays 16 and 17 are connected to heaters 4 and 6, respectively.

still. Between the common connection point of each heater and each common connection point of the SSR and the power source, relay contacts 18A and 18B that are opened and closed in conjunction with a power switch (not shown) are provided.

FIG. 2 shows the details of the control unit 10. For example, an 8-bit 8085 is used for the CPU 12, and its address (A 0 to 7) and data (D 0 to 7) are separated by the latch 21.

4 Line to 16 line decoder 22 for addresses A12 to A15
Are connected, and each IC and controller of the I / O port 14 are selected by the memory mapped method.

The ROM 13 has a capacity of, for example, 32 Kbytes, is connected to an address bus and a data bus, and is connected to the CPU 12 via a programmable timer 23 (for example, 8253A) to enable an interrupt.

In addition, RAM2 for temporarily storing the temperature measurement results, etc.
4 is connected to each bus, and, for example, addresses OFOOOH to OF7FFH are assigned.

The I / O port 14 has I / O port ICs 14A to 14C (for example, 825
5) is provided and selected by the decoder 22, and each has a 24-bit I / O of PA0 to PA7, PB0 to PB7, PC0 to PC7.
It has an O port.

In addition, PA0 to PA3 of the I / O port IC 14A are A / D converters 25 that convert the outputs of the thermistors 7 and 8 into digital signals.
Is connected.

In addition, there are keys for setting reference values and LEDs for displaying the operating status and key settings.
LED matrix 27 and each bus, decoder 22 and ▲
A keyboard / display controller 26 (for example, 8279) is provided between the ▼ and ▲ ▼ terminals to control the timing of the key input display.

Further, in order to control the duty of the heaters 4 and 6, a zero cross detector 28 as shown in FIG. 3 is used.

The zero-cross detector 28 includes a transformer 400 for converting AC 100 V to a predetermined low voltage, diodes 401 to 404 constituting a diode bridge for performing double-wave rectification of the secondary winding output of the transformer 400, and the diode bridge. 405, a voltage dividing resistor 406, 407 and 408 inserted between the DC power supply (+ 15V), a resistor 409 connected in series to the output terminal of the diode bridge, and an output of the resistor 409. It comprises a comparator 410 for comparing the voltage with the output voltage (reference voltage) of the resistor 408, and an inverter 411 for inverting and outputting the output voltage of the comparator 410.

FIG. 6 shows the operating voltage waveform of each part of the zero-cross detector 28 of FIG. 3, the waveform a is the secondary side output voltage of the transformer 400, and the waveform b is the output voltage waveform of the diode bridge.

The voltage generated at the point b changes in the range of 0 to 12 V. When this voltage exceeds the reference voltage (0.8 V) output from the resistor 408, the comparator 410 generates a voltage as shown in waveform C.

This voltage is inverted by the inverter 411, and a voltage like the waveform d is output.

The output voltage of the inverter 411 is connected to the interrupt pin (R
It is applied to ST6.5) and interrupt operation is performed at the zero point of AC input.

 Next, the operation in the above configuration will be described.

In FIG. 1, when a main switch (not shown) of the copying machine is turned on, the relay contacts 18A,
18B closes.

When the detected temperature T _th8 of the thermistor 8 _becomes T _th8 > T _th7 with _respect to the detected temperature T _th7 of the thermistor 7, the duty ratio of the heater 4 and the heater 6 as shown in FIG. As shown in the figure, the heater 6 is turned off and the duty of the heater 4 is set to 10
Increase to 0%.

Next, a processing example by the CPU 12 will be described with reference to FIG.

FIG. 9 is a flowchart showing a subroutine process of fixing control.

First, the temperature detection values of the thermistors 7 and 8 are read into the CPU 12 (steps 30 and 31).

Next, during non-copying (standby), the temperature T _th7 detected by the thermistor 7 is _compared with the reference temperature T _S (180 ° C.) (step 33).

When T _S > T _th7, the temperature detected by the thermistor 8 T _th8 and the thermistor 7
The detected temperature T _th7 is compared (step 34).

When T _th7 > T _th8 , the 1-byte register contents are set to (RHEAT1 ← 4) and (RHEAT2 ← 2) (step S35), and the heaters 4 and 6 are energized at a duty ratio of 2: 1.

When T _th8 > T _th7 , (RHEAT1 ← 6) and (RHEAT2 ← 0) are set (step 36), the heater 4 is fully energized, and the heater 6 is turned off.

On the other hand, in step 33, if T _th7 > T _S , T _th8 and T _S are compared (step 37), and if T _S > T _th8 , set (RHEAT1 ← 0) and (RHEAT2 ← 6) ( Step 38), as shown in FIG. 11, the heater 4 is turned off and the heater 6 is energized 100%.

If T _th8 > T _S , (RHEAT1 ← 0) and (RHEAT2 ← 0) are set (both heaters 4 and 6 are off), and the process returns (RET) (step 39).

RHEAT1 and RHEAT2 indicate the operation contents of the heaters 4 and 6, and the heater control as shown in Table 1 is performed depending on how to take numerical values.

This numerical value indicates the number of half-wave waveforms in which the heater is continuously turned on.

FIG. 10 is a flowchart showing an interrupt control process by the zero-cross detector 28.

Here, CHEAT1 and CHEAT2 are RHEAT1 and RHEAT2 counters set in the fixing control routine.

First, save the register (step 52), then
It is determined whether or not CHEAT1 is 0 (step 53).

If CHEAT1 = 0, it is determined whether CHEAT2 is 0 (step 54).

If CHEAT2 = 0, both heaters 4 and 6 are turned off (step 55), and further (CHEAT1 ← RHEAT1) and (CHEAT2
← Set to RHEAT2) (step 56).

After that, interrupt disable release is executed (step 57),
The register restoration process is executed (step 58) and the process returns (RET).

On the other hand, if the value of CHEAT1 is not 0 in step 53, the value of CHEAT1 is reduced by one count (step 59).
Is turned on and the heater 6 is turned off (step 6
0).

 Thereafter, the processing enters into the processing after step 57.

If CHEAT2 is not 0 in step 54, CHE
The AT2 is decreased by one count (step 61), the heater 4 is turned off, and the heater 6 is turned on (step 62).

Next, it is determined whether or not CHEAT2 is 0. If 0, the process returns to step 56; if not, the process returns to step 57 to repeatedly execute the above-described processing.

〔effect〕

As described above, according to the fixing temperature control device of the present invention, the control is performed by changing the ON / OFF of each heater and the duty ratio based on the surface temperature state of the fixing roller. Electric power can be supplied to the paper section.

As a result, the limited electric power can be operated efficiently, the continuous passing of small size sheets becomes possible, and the number of continuous copies can be increased.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, FIG. 2 is a circuit diagram showing details of a control unit, and FIG. 3 is a detailed circuit diagram of the zero-cross detector shown in FIG. FIG. 4 is a front sectional view showing the constitution of the fixing roller of the fixing device according to the present invention, FIG. 5 is a sectional view showing the outline of the entire constitution of the fixing device, and FIG. 6 is each part of the zero-cross detector. 7 is a voltage waveform diagram of duty ratio energization control for the heaters 4 and 6, and FIG.
FIG. 9 is a voltage waveform diagram when 0% electricity is supplied and the heater 6 is turned off. FIG. 9 is a flowchart showing a subroutine process of fixing control in the present invention, and FIG. 10 is a flowchart showing an interrupt control process by zero-cross detection. FIG. 11 is a voltage waveform diagram when the heater 4 is off and the heater 6 is 100% energized, and FIG. 12 is a general fixing roller surface temperature characteristic diagram in fixing temperature control. Explanation of symbols 1 ... Fixing device, 2 ... Fusing roller 4,6 (6a, 6b) ... Heater 7,8 Thermistor 10 ... Control section, 15 ... Driver 16,17 ... SSR (solid State relay) 20 …… Pressure roller 28 …… Zero cross detector

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-61-204666 (JP, A) JP-A-53-76288 (JP, A) JP-A-59-177581 (JP, A) JP-A-57- 211180 (JP, A) JP 58-87575 (JP, A) JP 58-105180 (JP, A)

Claims (1)

(57) [Claims] 1. A fixing temperature control device of a fixing device, wherein a recording sheet is passed through a fixing roller heated by a heater to fix a transfer image on the sheet, in a sheet width range of a small size sheet in the fixing roller. The first heater is provided, the second heater is provided at a difference between the sheet passing width regions of the small size sheet and the large size sheet, the installation portion of the first heater and the second heater are provided. Temperature detecting means for detecting the roller surface temperature of each of the installation parts, and the roller surface temperature of the installation part of the second heater is the first
When the temperature of the roller surface of the heater installation portion is higher than that of the roller, the fixing temperature control is provided with a control means for cutting off the power supply to the second heater and increasing the power supply current to the first heater. apparatus.