JP2583235B2 - 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 or the like, there is, for example, Japanese Patent Application Laid-Open No. Sho 50-138838. The central part and the end part in the axial direction are heated by independent heating elements, and the temperature in the effective area corresponding to the width of the sheet on the peripheral surface of the roller is determined by:
Detected by thermosensitive elements provided at predetermined positions corresponding to the independent heating elements and having the same set temperature, and independently supply energy to the independent heating elements in accordance with the detected temperature. By controlling, the inside of the effective area on the peripheral surface of the roller is maintained in 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 vertical axis represents the temperature T of the fixing roller and the horizontal axis represents time t.

T ₁ is the standby temperature, T ₂ represents a lower limit fixing temperature.

Also, 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 of the non-sheet passing portion can be used for the sheet passing portion, a home power supply can be used.

However, in the conventional apparatus, since the heater in the non-sheet passing portion is not deprived of the heat by the sheet, 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, a fixing temperature control device according to the present invention provides 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 first heater disposed in the paper width region of the size sheet, a second heater disposed in a difference portion between the paper width region of the small size sheet and the large size sheet, and fixing of the installation portion of the first heater Temperature detecting means for detecting the roller surface temperature, and changing the duty ratio of the first and second heaters when the temperature detected by the temperature detecting means is lower than a preset reference temperature when a small-size sheet is passed. And control means for energizing the battery.

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).
And a thermistor 7 for measuring the surface temperature of the fixing roller 2 by the heater 4, and a pressure roller 20 shown in FIG.

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 paper is passed in a state where is directed to the fixing roller 2 side.

In the above construction, when fed the sheet 5 having a large size in a continuous, energizing the heater 4 and the heater 6, thereby the surface temperature of the fixing roller 2 is heated to T _1.

 In this state, the sheet 5 is continuously passed.

Surface temperature of the fixing roller 2 with the sheet passing progresses begins to drop from t ₁ after passing, as shown in FIG. 12 in the entire area, time
the copying operation is stopped upon elapse of t _2.

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, according to the present invention, the thermistor 7 _controls the temperature T _th
Is detected, and when the detected temperature is equal to or lower than the reference temperature, the heater 6 is controlled at a predetermined duty ratio, and extra power generated by the control is supplied to the heater 4.

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

The control unit 10 includes an A / D converter (converter) 11 for A / D-converting the output of the thermistor 7, a CPU 12 for executing various controls of the copying machine in addition to the heater control based on the thermistor output,
It comprises a ROM 13 in which a program for operating the CPU 12 according to a predetermined procedure is stored, and an I / O port 14 for outputting a 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, and performs 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. Relay contacts 18A and 18B that open and close in conjunction with a power switch (not shown) are provided between the common connection point of each heater and each of the common connection points of the SSR and the power supply.

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.

Addresses A12 to A15 have 4-line to 16-line decoder 22
Are connected, and each IC and controller of the I / O port 14 are selected by a 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 addresses of, for example, OFOOOH to OF7FFH are assigned.

The I / O port 14 is an I / O port IC 14A to 14C (for example, 8255)
Are selected by the decoder 22, and each has a 24-bit I / O port of PA0 to PA7, PB0 to PB7, and PC0 to PC7.

An A / D converter 25 for converting the output of the thermistor 7 into a digital signal is connected to PA0 to PA3 of the I / O port IC 14A.

In addition, a key for setting a reference value and the like and an LED for displaying an operation state and key setting contents are provided.
LED matrix 27, each bus, decoder 22, and ▲
A keyboard / display controller 26 (for example, 8279) is provided between the ▼ and ▲ ▼ terminals to perform key input and display timing control.

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 in FIG. 3, where 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 having a waveform d is output.

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

In the case of a small-sized sheet, if the temperature detected by the thermistor 7 is lower than the reference temperature, the CPU 12 sets PA0 of the I / O port 14A to “1”, turns on the SSR 16 via the driver 15, and turns on the heater 4 (At this time, the port PA1 is set to “0” and the SSR17 is in the off state).

On the other hand, in the case of a large-size sheet, PA0 and PA1 are set to “1” based on the output of the thermistor 7,
The SSRs 16 and 17 are turned on, and the heaters 4 and 6 are energized.

At this time, as shown in FIG. 7, the duty ratio of the heaters 4 and 6 is set to, for example, 2: 1.

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

FIG. 8 is a flowchart showing a subroutine process of the fixing control.

First, the temperature detection value of the thermistor 7 is read into the CPU 12 (step 30), and it is determined whether or not copying is in progress (step 31).

If copying is in progress, the process proceeds to the process of FIG. 9, and during non-copying (during standby), the detected temperature T _th of the thermistor 7 and the reference temperature T
_s (180 ° C.) (step 32).

Next, the content of the register (1 byte) indicating the operation content of the heater is changed based on the relationship of T _s > T _th or T _th > T _s .

The numerical values set in the registers RHEAT1 and RHEAT2 are heater non-energization (0), 100% energization (6), and energization by duty ratio (2 or 4). Is the number of half-wave waveforms.

If T _s > T _{th in} step 32, (RHEAT1 ← 4) and (R
HEAT2 ← 2), and the heaters 4 and 6 are energized at a duty ratio of 2: 1 (step 33).

On the other hand, when T _th > T _s , (RHEAT1 ← 0) and (RHEAT2
← 0), and the heaters 4 and 6 are turned off (step 34).

Next, processing during copying shown in FIG. 9 will be described.

First, it is determined whether or not the sheet to be passed is a small size sheet (step 41). If the sheet is a small size sheet, T _th7 is compared with T _s (step 42). If T _s > T _th7 , (RHEAT1 ← 6) and (RHEAT2 ← 0) are set (step 43), and the heater 4 is set to 100 as shown in FIG.
%, And the heater 6 is turned off.

If T _th7 > T _s (step 42) (RHEAT1 ← 0)
And (RHEAT2 ← 0) (step 44), and both heaters 4 and 6 are turned off.

Next, the heater control when a large-size sheet is passed as shown in FIG. 10 will be described.

First, the detection temperature T _th of the thermistor 7 and the reference temperature T _s (177
C.) are compared (step 45).

If T _s > T _th , (RHEAT1 ← 4) and (RHEAT2 ← 2) are set, and power is supplied to each of the heaters 4 and 6 at a duty ratio of 2: 1 (step 46).

If T _th > T _s , (RHEAT1 ← 0) and (RHEAT2 ← 0) are set, and the heaters 4 and 6 are turned off (step 47).

Table 1 shows the relationship between RHEAT1 and RHEAT2 and the heaters 4 and 6 described above.

FIG. 11 is a flowchart showing the interrupt processing 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 or not CHEAT2 is 0 (step 54).

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

After that, interrupt disable release is executed (step 57),
A register return 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 other than 0 in step 54, CHEA
T2 is reduced by one count (step 61), and 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 the 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 a zero cross detector shown in FIG. 4 is a front sectional view showing the structure of the fixing roller of the fixing device according to the present invention, FIG. 5 is a sectional view showing an outline of the whole structure of the fixing device, and FIG. FIG. 7 is a voltage waveform diagram of duty ratio energization control for heaters 4 and 6, FIG. 8 is a flowchart showing a subroutine process of fixing control in the present invention, and FIG. FIG. 10 is a flowchart showing processing during copying in the present invention. FIG. 10 is a flowchart showing heater control processing when a large-size sheet is passed in the present invention, and FIG. 11 is a flowchart showing interrupt control processing by zero-cross detection. FIG. 12 is a general fixing roller surface temperature characteristic diagram in fixing temperature control. DESCRIPTION OF SYMBOLS 1 ... Fixing device 2 ... Fixing roller 4,6 (6a, 6b) ... Heater 7 ... Thermistor 10 ... Control unit 15 ... Driver 16,17 ... SSR (Solid state relay) 20 …… Pressure roller 28 …… Zero cross detector

Claims (1)

(57) [Claims] In 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 first sheet is provided in a sheet passing width area of a small-sized sheet in the fixing roller. A heater; a second heater disposed at a difference between the sheet passing width areas of the small-sized sheet and the large-sized sheet; a temperature detecting means for detecting a surface temperature of a fixing roller at an installation portion of the first heater; When the temperature detected by the temperature detecting means is lower than or equal to a preset reference temperature when a sheet is passed, the first and the second
A fixing means for energizing the heater by changing a duty ratio of the heater.