JPS6218911B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a temperature switching device for a fixing device in a copying machine or the like.

Currently, there are two types of copy paper used in copiers: paper that is suitable for fixing at relatively high temperatures, such as plain paper, and paper that is suitable for processing at relatively low temperatures, such as tracing paper. Conventionally, these two set temperatures have been switched by turning the heater circuit on or off with a switch. However, simply shutting off or turning on the heater circuit like this takes time, especially when changing from a high set temperature to a low set temperature, and the operator has to wait several tens of minutes when switching from plain paper to tracing paper. If you copy without waiting, the fusing temperature will be too high.
Air bubbles and wrinkles occur in the paper, and in the case of roller fixing, it is inevitable that the paper will become wrapped.

The present invention aims to eliminate the above-mentioned drawbacks, and includes a cooling device, such as a fan, for forcibly cooling a fixing device, especially a fixing roller type fixing device, and a relatively high temperature setting circuit. When the temperature of the fixing roller of the fixing device that is at the first set temperature is switched to a relatively low second set temperature, the period until the temperature of the fixing roller falls to the second set temperature (low temperature transition period) In this system, the cooling device is activated only to shorten the low-temperature transition time, that is, the waiting time, and during this time, the insertion of original documents is prohibited to prevent inadvertent copying.

The present invention will be explained below with reference to the illustrated embodiments.

In the figure, 10 is a temperature setting circuit that can selectively switch between two different temperature settings, and includes a temperature sensor 11, such as a thermistor, installed in the fixing device section, and a set temperature changeover switch S-1. , and an operational amplifier 12, which provides a positive output when the fusing temperature is below the selected set point temperature. 2
0 is a heater control circuit, which includes a switch element 21 that is turned on by a positive output from the temperature setting circuit 10, and a fixing device section heater 22 that is connected to an AC power source via the switch element. In this embodiment, the switch element 21 is a solid state relay.
It uses so-called SSR. The SSR is a switching element that includes a light emitting diode, a zero volt switch, and a triax. When voltage is applied to the built-in light emitting diode and it emits light, the subsequent zero volt switch is activated and the built-in triax is ignited. It was designed so that 30 is a cooling device control circuit that operates a fan motor (cooling device) M that forcibly cools the fixing device only during the low temperature transition period, and a cooling device control circuit that operates a lamp, a buzzer, and other indicators 42 during the low temperature transition period, and issues a copy prohibition command X. This control circuit includes a copy permission command circuit that issues a copy permission command circuit. This circuit consists of temperature setting circuit 10
output signal and set temperature selector switch S-1
It is controlled by the opening and closing of switch S-2, which is linked to the switch S-2.

Now, set the set temperature changeover switch S-1 to the high temperature side, that is, the contact H side, and switch S-1.
Suppose that you turn on the power switch of the copying machine with 2 open. Since the temperature of _the fixing device is naturally lower than the set temperature, the resistance value of the thermistor ₁₁ , which is a heat-sensitive semiconductor, is also large. The output voltage of the pressure regulator is higher than the reference voltage applied to the amplifier 12, and the amplifier 12 operates to produce a positive output to the temperature setting circuit 10, which is applied to the input terminal (+) of the SSR. A light emitting diode 31 in the photocoupler PC is connected in series to the terminal (-) of the SSR in the same direction as the light emitting diode in the SSR, and both light emitting diodes emit light due to the positive output of the temperature setting circuit 10. When the light emitting diode in the SSR emits light, the triac in the SSR becomes conductive, thereby energizing the heater 22.
Therefore, the temperature of the fixing device begins to rise. When the fixing device reaches a predetermined first set temperature suitable for plain paper, the resistance value of the thermistor 11 changes,
The positive output of temperature setting circuit 10 disappears and the triac in the SSR becomes non-conductive. The triax controls the heater circuit on and off based on the first set temperature.

In the above-mentioned copying operation using plain paper, switch S-2 is open, so the input of the inverter 33 is at H level, and one of the AND circuits 34 connected to the output terminal of the inverter via a differentiating circuit. The input terminal B of is at L level. accordingly
The fan register 35 whose set input terminal is connected to the input/output terminal of the AND circuit 34 is connected to the input/output terminal of the AND circuit 34.
It is not set regardless of the output level of the photocoupler PC to which the other input terminal A of No. 4 is connected. That is, the relay RA connected to the output terminal Q of the fan resistor 35 via the amplifier 36 and the fan motor M connected to the power supply via the make contact RA-1 associated with the relay also do not operate.

When it is desired to switch from the first set temperature to a lower second set temperature and make a copy using tracing paper, the switch S-1 is first set to the low temperature side, that is, to the contact L side. As a result, the resistor R ₂ is cut off and only the resistor R ₁ is connected in series with the thermistor 11, the voltage division ratio changes and the positive output of the temperature setting circuit 10 disappears. The heater circuit is therefore cut off. Also, since the light emitting diode 31 does not emit light, the output of the photocoupler PC becomes H level, and the AND circuit 3
It is applied to input terminal A of 4. On the other hand, Switch S-
Since switch 2 is closed in conjunction with switch S-1, the input terminal of inverter 33 becomes L level. accordingly
Inverter 33 is also connected to input terminal B of AND circuit 34.
The differential waveform of the rising edge of is added, and the AND circuit 3
4, and the fan register 35 is set. Therefore, relay RA is activated, contact RA-1 is closed, fan motor M is activated, and the fixing device is forcibly cooled. Further, the copy permission command register 40 is reset by the output of the AND circuit 34, and a signal (copy prohibition command) The lamp 42 lights up to indicate that copying is prohibited.

The temperature of the fixing device is rapidly lowered by the fan motor M, and finally reaches a second set temperature suitable for fixing tracing paper, and the light emitting diode 31 of the photocoupler emits light again. photo coupler
The output of the PC becomes L level, and the fan register 35 is reset via the inverter 37, and the fan motor M is stopped. On the other hand, the heater 22 is energized by the light emitted from the light emitting diode in the SSR.

When the temperature of the fixing device becomes slightly higher than the second set temperature, the output of the temperature setting circuit 10 disappears and the output of the photocoupler PC becomes H level. Therefore, the output of the photocoupler PC and the fan resistor 35
NOR gate 3 with 2 inputs of reset output
8 changes to L level. This output change is applied to the set input terminal of the copy permission command register 40 via the differentiating circuit and inverter 39,
Set the same register. Therefore, the lamp 42 is turned off, the copy prohibition command is canceled, and the lamp 44 connected to the output terminal Q of the register 40 via the amplifier 43 is turned on instead. A lamp 44 indicates permission for copying with tracing paper.

As described above, according to the present invention, the fixing temperature can be lowered from a relatively high first set temperature to a lower second set temperature, such as when lowering the fixing temperature from plain paper to the appropriate temperature for tracing paper.
The waiting time when switching to the set temperature can be extremely shortened. Experiments have shown that when copying paper was switched from plain paper to tracing paper, the waiting time was reduced to approximately 1/10 of the conventional time. Moreover, there were no defective copies. Further, during the standby period, insertion of the original is not possible or a display prohibiting the insertion is activated, so that the occurrence of defective copies due to inadvertence is prevented.

[Brief explanation of the drawing]

The figure is an electric circuit showing a specific example of a temperature switching device for a fixing device according to the present invention. 10...Temperature setting circuit, 21...Switch element, 2
2... Heater, 30... Control circuit, S-1... Set temperature changeover switch, S-2... Switch, M... Fan motor (cooling device).

Claims (1)

[Scope of Claims] 1. A heater that heats the fixing roller; a cooling device that forcibly cools the fixing roller; a heater control circuit that turns on and off the heater; and a heater control circuit that is connected to the cooling device and controls opening and closing of a drive circuit of the cooling device. and a temperature setting circuit capable of selectively switching between high and low temperature settings, the temperature setting circuit comprising means for setting two temperatures, and means for setting the two temperatures. a temperature sensor that senses the temperature of the fixing roller; an electric signal corresponding to the temperature sensed by the temperature sensor; and an electric signal corresponding to one temperature selected by the switching means. the heater control circuit has a switching element that switches the heater on and off according to the output from the operational amplifier; and the cooling device control circuit has the switching means. a pulse generation circuit that generates an output of one pulse when the switch is switched in response to switching from the high set temperature to the low set temperature; a signal generating means that generates a signal when the signal generating means is set; an AND circuit that outputs an electric signal from the signal generating means and an electric signal from the pulse generating circuit; and the low setting of the AND circuit. a fan resistor connected so as to be set by the output when the temperature is selected and reset by the output from the inverter connected to the signal generating means when the temperature is not set by the output of the AND circuit; 1. A temperature switching device for a fixing device in a copying machine, characterized in that the cooling device is driven by setting a fan register, and the cooling device stops driving by being reset.