JP2545390B2 - 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:
The heat-sensitive elements provided at predetermined positions corresponding to each of the independent heating elements and having the same set temperature are used for detection, and energy is independently supplied to the independent heating elements according to the detected temperature. The temperature is controlled to keep the effective area of the peripheral surface of the roller 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 when the temperature finally drops to a certain temperature, there is a power shortage to stop the copying operation. If this technique is applied to a machine that is operating, the number of heaters W in the non-sheet-passing portion cannot be fully utilized when passing a small-sized sheet (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. 4 shows a temperature characteristic diagram for performing such control, in which the temperature T of the fixing roller is plotted on the vertical axis and the time t is plotted on the horizontal axis.

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 above-mentioned heater power for the non-paper portion can be used for the paper feeding portion, it becomes 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-mentioned object, a fixing temperature control device according to the present invention is a fixing temperature control device for a fixing device, which causes a fixing roller heated by a heater to pass a recording sheet and fix the transferred image on the sheet. First and second heaters arranged in the paper passing width region of the small size sheet in the fixing roller, and a third heater arranged in a difference portion of the paper passing width region of 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 and second heaters and the installation portion of the third heater, and the roller surface temperature of the installation portion of the third heater is the first A control means is provided for de-energizing the third heater and energizing the second heater when the temperature is higher than the roller surface temperature of the installation portion of the second heater.

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 one embodiment of the present invention.

FIG. 2 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. 2, the fixing device 1 has a hollow fixing roller 2 and a first heater 4 and a second heater having a length corresponding to the paper width of a small size (for example, A4 size) sheet 3. 9, the third heater 6 (6a + 6b) disposed at a position corresponding to the paper width difference between the large size sheet 5 (for example, A3 size) and the sheet 3, and the surface temperature of the fixing roller 2 by the heaters 4 and 9 And a thermistor 8 for measuring the surface temperature of the fixing roller 2 by the heater 6a.
And a pressure roller 20 described later.

The wattages of the second heater 9 and the third heater 6 are set to the same value, and the energization of each is controlled based on the temperature measurement results of the thermistors 7 and 8.

FIG. 3 is a cross-sectional view showing an outline of the entire structure of the fixing device. The pressure roller 20 is rotatably pressed against the fixing roller 2, and the sheet 50 having the transfer image 51 attached between the rollers is the transfer image 51.
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, the temperature Ta of the non-sheet passing portion is detected by the thermistor 8,
When the measured temperature Tb of the thermistor 7 in the paper passing portion is compared, when Ta> Tb, the heaters 6a and 6b are turned off and the heater 9 is turned off.
It is intended to energize.

In this case, since the non-sheet passing portion hardly takes heat by the sheet 3, the non-sheet passing portion hardly changes from the off state to the on state.

Next, taking the fixing device 1 shown in FIG. 2 as an example, the structure of the control unit shown in FIG. 1 for controlling the heater will be described.

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

I / O port 14 has three ports (PA0, PA1, PA2),
Each port corresponds to each of the heaters 4, 6 and 9.

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) 16-18 are connected to the heaters 4, 6 and 9.

still. Between the common connection point of each heater and each common connection point of the SSR and the power source, relay contacts 19A and 19B that are opened / closed in conjunction with a power switch (not shown) are provided.

[Effect] As described above, according to the fixing temperature control device of the present invention, a plurality of heaters arranged according to the sheet size to be continuously supplied are switched and controlled according to the sheet size. It is possible to minimize the amount of electric power, and it is possible to utilize surplus electric power (use for insufficient circuits, etc.).

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, FIG. 2 is a front sectional view showing a constitution of a fixing roller of a fixing device in the present invention, and FIG. 3 is an outline of an entire constitution of the fixing device. FIG. 4 is a cross-sectional view showing a general temperature characteristic of the fixing device. Explanation of symbols 1 …… Fixer, 2 …… Fixing rollers 4,6 (6a, 6b), 9 …… Heater 7,8 …… Thermistor 10 …… Control section, 15 …… Driver 16-18 …… SSR ( Solid state relay) 20 ... Pressure roller

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, and a transfer image on the sheet is fixed, in a sheet passing width range of a small size sheet in the fixing roller. First and second heaters arranged, a third heater arranged at a difference in sheet passing width region between the small size sheet and the large size sheet, an installation portion of the first and second heaters, and Temperature detecting means for detecting the roller surface temperature of each of the third heater installation portions, and the roller surface temperature of the third heater installation portion is the roller surface temperature of the first and second heater installation portions. A fixing temperature control device comprising: a control unit that deenergizes the third heater and energizes the second heater when the temperature is higher.