JPH0786729B2 - Fixing device safety device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixing device safety device, and more particularly to overheat protection control of a fixing device in an electrophotographic printer or the like.

[Conventional technology]

As shown in FIG. 2, the electrophotographic printing apparatus faces the outer peripheral surface of the photosensitive drum 1 which is rotationally driven at a constant speed, and sequentially comprises a charger 2, a laser beam exposure device 3, a developing device 4, and a transfer device 5. The cleaner 6 and the eraser 7 are arranged.

An electrophotographic process in which a uniform charge is applied to the surface of the photosensitive drum 1 and then exposed according to image information to be printed to form a latent charge image, and the latent charge image is developed to obtain a toner image. To execute.

The printing paper 8 is extracted from the paper feed cassette 9 by the extraction roller 10 and is controlled by the registration roller 11 so that the timing is aligned with the toner image on the surface of the photosensitive drum. Is supplied to. The transfer device 5 brings the printing paper 8 into contact with the surface of the photosensitive drum 1 and applies a transfer charge to the back surface thereof to electrostatically transfer the toner image on the surface of the photosensitive drum 1 to the surface of the printing paper 8.

After transferring the toner image, the photosensitive drum 1 removes the toner and charges remaining on its surface by the eraser 7 of the cleaner 6, and reuses the surface of the photosensitive drum for the next electrophotographic process.

The fixing device 12 heats the printing paper 8 on which the toner image is transferred by the transfer device 5 to a heating roller 12a and a back-up roller 12b.
And the toner image is fixed to the surface of the printing paper 8 by welding. The paper discharge roller 13 discharges the printing paper 8 having the toner image fixed to the outside of the machine.

The controller 14 controls the rotation of the photosensitive drum 1 and the charging function of the charger 2 while exchanging information with the host 15.
The exposure function control of the laser beam exposure device 3, the development function control of the developing device 4, the rotation control of the extraction roller 10, the register roller 11 and the discharge roller 13, the transfer function control of the transfer device 5, and the fixing function control of the fixing device 12 are performed. Run.

In such an electrophotographic printing apparatus, the fixing device 12
As shown in FIGS. 3 and 4, the heating roller 12a is detected by the temperature detecting element 12c provided in the vicinity of the surface of the heating roller 12a in a non-contact state to detect the surface temperature of the heating roller 12a. 12a is controlled to a predetermined temperature, and temperature fuse 12d
Therefore, the power supply is cut off during heating. A heater 12e such as an infrared lamp that heats the heating roller 12a is arranged at the center of the heating roller 12a.

FIG. 5 shows a control circuit therefor, which includes the heater 12e.
Is an interlock relay contact 14a provided in the control device 14, an AC power control element 14b, and the temperature fuse 12d.
Is connected to the AC power supply 16 via. The interlock relay contact 14a is opened / closed by the interlock relay coil 14c controlled by the maintenance door switch 17. The first comparator 14d compares the temperature detection signal V corresponding to the heating roller surface temperature detected by the temperature detection element 12c with a reference value V _0, and based on the comparison result, the ignition control circuit 14e. By controlling the conduction angle of the AC power control element 14b, the amount of power supplied to the heater 12e is controlled so that the surface temperature of the heating roller 12a becomes a predetermined value.

In this fixing device 12, the prevention of burns and electric shock when the operator opens the maintenance door by a printing paper jam or the like is performed by shutting off the current of the interlock relay coil 14c by the maintenance door switch 17 to interlock. This is done by cutting off the supply power by opening the relay contact 14a. Further, prevention of heating deterioration of components during heating, such as when the AC power control element 14b falls into uncontrollable state due to a short circuit due to malfunction of the ignition control circuit 14e or destruction of the AC power control element 14b, To prevent smoke and fire,
The power supply is cut off by melting the temperature fuse 12d.

[Problems to be Solved by the Invention]

However, as described above, when the temperature fuse 12d is arranged in a non-contact state with the heating roller 12a, an error occurs in the fusing time of the temperature fuse 12d due to the heat transfer gradient and the temperature fuse installation position error. To do. That is, as shown in FIG. 6, the temperature T acting on the temperature fuse 12d greatly changes according to the change of the installation position (distance from the heating roller surface to the temperature fuse) 1 of the temperature fuse 12d,
As shown in FIG. 7, the fusing time t of the temperature fuse 12d also tends to greatly change according to the temperature T acting on it. Therefore, if there is an error Δl in the installation position 1 of the temperature fuse 12d, an error Δt also occurs in the fusing time t, and the heat generation amount and the heating action time change due to this error Δt, and the heating deterioration of the components is prevented. It was difficult to reliably prevent smoke, smoke and fire. This difficulty is magnified if the temperature fuse 12d itself has variations in fusing characteristics.

SUMMARY OF THE INVENTION An object of the present invention is to provide a simple supporting means capable of reliably preventing heating deterioration of components and smoking / ignition by accurately detecting heating of a fixing device and cutting off power supply. .

[Means for Solving the Problems]

The present invention relates to a fixing device that heats a toner image formed on a printing paper sheet and fuses the toner image onto the printing paper sheet. The fixing device is provided with an opening / closing contact of an interlock relay and a temperature control device controlled by a temperature detecting means in series. In a safety device of a fixing device having a control circuit connected to an electric power control means, the control circuit is responsive to a detected temperature to open an opening / closing contact of the interlock relay when the detected temperature reaches a predetermined value. Is provided with a protection circuit.

[Action]

The protection circuit opens the opening / closing contact of the interlock relay in response to the temperature detection signal from the temperature detecting means for temperature control. Since the temperature detection error by the temperature detection means can be corrected by a simple electric signal processing, the open / close contact of the interlock relay is opened in response to the predetermined detected temperature accurately, and the heating is surely stopped. You can

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings. The mechanical structure of the fixing device is the same as that described above with reference to FIGS. 3 and 4.

As shown in FIG. 1, the electrical control circuit compares the temperature detection signal V output from the temperature detection element 12c with the heating roller surface temperature with a predetermined reference value Va for preventing heating. Comparator 14f and a microcomputer 14g responsive to the comparison result signal output from the second comparator 14f.
And an AND logic circuit 14h, further including a transistor 14i controlled by an output signal of the AND logic circuit 14h,
The transistor 14i is also configured to cut off the current of the interlock relay coil 14c. Other configurations are the same as those of the conventional device described with reference to FIG.

In the above configuration, in a state where the control circuit is operating normally, AC power is supplied to the heater 12e from the AC power supply 16 through the interlock relay contact 14a, and the surface temperature of the heating roller 12a is a predetermined value. The amount of electric power supplied to the heater 12e is controlled by the AC power control element 14b so that the set value is obtained. For this reason, the temperature detecting element 12c is connected to the heating roller 1
The surface temperature T of 2a is converted into a temperature detection signal V and output, and the first comparator 14d compares the temperature detection signal V with a reference value V ₀ corresponding to a predetermined set temperature T ₀ to determine whether it is larger or smaller. A conduction angle control signal is supplied to the firing control circuit 14e. That is, the first comparator 14d outputs a low-level conduction angle control signal while the temperature detection signal V is smaller than the reference value V ₀ corresponding to the set temperature T ₀ , and this low-level conduction angle control signal is given. The ignition control circuit 14e thus controlled controls the AC power control element 14b to supply AC power to the heater 12e. And
When the temperature detection signal V reaches the reference value V ₀ or more, the first comparator 14d outputs a high level conduction angle control signal,
The ignition control circuit 14e to which the high-level conduction angle control signal is applied controls the AC power control element 14b so as to limit (decrease or cut off) the AC power supplied to the heater 12e. By this control operation, the surface temperature T of the heating roller 12a is maintained substantially equal to the set temperature T ₀ as shown in FIG.

If the AC power control element 14b falls out of control due to a short circuit for some reason, the power supply to the heater 12e is continuous, resulting in abnormal overheating, as shown in FIG. The temperature rise at this time is converted into a temperature detection signal V by the temperature detection element 12c. The second comparator 14f compares the temperature detection signal V with a predetermined reference value Va for preventing abnormal overheating. The predetermined reference value Va for preventing abnormal overheating is set to a value corresponding to a predetermined temperature which is lower than the heat resistant temperature Tm of the fixing device constituent parts and lower than the smoke / ignition temperature Tp of the printing paper 8, and the above temperature. It is set almost equal to the melting temperature of fuse 12d.

The second comparator 14f outputs a low-level conduction angle control signal when the temperature detection signal V becomes equal to or higher than the reference value Va. AND
When the logic level 14h receives the low-level conduction angle control signal, the logic circuit 14h turns off the transistor 14i to cut off the exciting current of the interlock relay coil 14c. As a result, the interlock relay contact 14a is opened to cut off the AC power supplied to the heater 12e. Since the power supply cutoff at the time of abnormal overheating is performed by signal processing of the temperature detection signal V obtained from the temperature detection element 12c, assembly adjustment (for example, the magnitude of the temperature detection signal V itself with respect to temperature is adjusted by a variable resistor). The error can be minimized by adjusting the reference value Va with a variable resistor.

On the other hand, as shown in FIG. 10, the microcomputer 14g starts to set the output port (which gives a logic processing signal to the AND logic circuit 14h) to a high level, and then the conduction angle given to the input port. The control signal is monitored for low level. When the conduction angle control signal goes low, the output port goes low. As a result, once abnormal overheating occurs and the interlock relay contact 14a is opened, the safety control state is maintained even if the temperature drops thereafter due to the opening. This safety control state can be released by a maintenance switch (not shown) or the like.

Even if the safety control function of the interlock relay circuit is lost, if the melting time of the temperature fuse 12d is reached, the temperature fuse 12d melts and the power supplied to the heater 12e can be cut off. .

Further, although the temperature control is in a normal state, when the operator opens the maintenance door by a printing paper jam or the like, the maintenance door switch 17 is opened and the interlock relay contact 14a is opened. The power supply is cut off, ensuring the safety of the operator.

〔The invention's effect〕

As described above, the present invention utilizes the temperature detection signal by the temperature detection means for temperature control and the interlock relay for ensuring safety during maintenance operation, and the interlock relay of the interlock relay based on the temperature detection signal at the time of abnormal overheating. Since the on / off contact is opened to cut off the power supplied to the heater with high accuracy, it is possible to reliably prevent overheating deterioration of the fixing device components and smoke / ignition with a relatively simple structure. .

[Brief description of drawings]

FIG. 1 is a control circuit diagram of a fixing device in an electrophotographic printing device according to the present invention, FIG. 2 is a vertical sectional side view of a conventional electrophotographic printing device, and FIG. 3 is a schematic perspective view of the fixing device. Is a vertical side view thereof, FIG. 5 is a control circuit diagram for the fixing device, and FIG. 6 is a temperature characteristic diagram which acts on temperature fuse.
FIG. 7 is an operating characteristic diagram of the temperature fuse, FIG. 8 is a temperature control characteristic diagram of the fixing device according to the present invention when the fixing device is normal, and FIG. 9 is a temperature control characteristic diagram of the fixing device according to the present invention when the fixing device is abnormal. Figure 10 shows the control flow chart. 12 ... Fixing device, 12a ... Heating roller, 12b ... Back up roller, 12c ... Temperature detecting element, 12d ... Temperature fuse, 12e ... Heater, 14 ... Control device, 14a ... Interlock relay contact , 14b …… AC power control element, 14c ……
Interlock relay coil, 14d ...... first comparator, 1
4f …… Second comparator, 14g …… Microcomputer, 1
4h …… AND logic circuit, 14i …… Transistor.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Shoji Saito, 1-1 1-1 Higashitaga-cho, Hitachi-shi, Ibaraki Hitachi Ltd. Taga factory (56) Reference JP-A-63-212975 (JP, A) JP 61-211979 (JP, A) JP 60-176076 (JP, A) JP 60-25562 (JP, A) JP 56-154777 (JP, A)

Claims (2)

[Claims] 1. A fixing device for heating and fixing a toner image formed on a printing sheet by welding to the printing sheet, which comprises an interlock relay that opens and closes in series with a heater in response to a door switch for maintenance. In the safety device of the fixing device having a control circuit connecting the opening / closing contact and the temperature control power control means controlled by the temperature detecting means, the maintenance door switch is connected in series with an interlock relay coil, The control circuit responds to the temperature detecting means and controls the detected temperature to be a first set temperature; and the interlock coil when the detected temperature reaches a second set temperature. 2. A fixing device comprising a protection circuit having a switch means for cutting off the exciting current of the fixing device. 2. A fixing device for heating and fixing a toner image formed on a printing sheet by welding to the printing sheet, the fixing device comprising an interlock relay which opens and closes in series with a heater in response to a maintenance door switch. In a safety device of a fixing device, which comprises a control circuit connecting an opening / closing contact, a temperature fuse, and a temperature control power control means controlled by a temperature detection means, the maintenance door switch includes an interlock relay coil and a series circuit. And a temperature control means for controlling the detected temperature to reach a first set temperature in response to the temperature detection means, and the control circuit when the detected temperature reaches a second set temperature. A protection circuit for opening a switch means provided in series with the interlock relay coil, wherein the second preset temperature is substantially equal to the fusing temperature of the thermal fuse. A fixing device characterized by being set to a new value.