JPH09101716A - Fixing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixing device which allows stable fixing by preventing an overtshoot phenomenon which occurs at the time of bringing a heat roller to a set temperature. SOLUTION: The output of the power source 8 of the heater lamp 3 of the fixing heat roller is controlled to be opened and closed by a switching circuit 7. A control circuit 6 sets the ratio of switch-on time of the power source output to control the switching circuit 7 based on the temperature information supplied from a temperature sensor 4 which detects the temperature of the heat roller. In this case, the percentage of the switch-on time during the warm-up period immediately after the start of printing is set to exceed 80%. When the temperature information that a prescribed temperature lower than the set temperature is reached is recognozed, the percentage of the switch-on time is set at 10 to 80%.

Description

DETAILED DESCRIPTION OF THE INVENTION

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a printing apparatus such as a printer, a facsimile, and a copying machine using an electrophotographic process, and more particularly to a fixing apparatus for heating and melting and fixing a toner image on a recording medium.

[0001]

2. Description of the Related Art Conventionally, an electrophotographic printing apparatus uniformly charges the surface of an image carrier having photoconductivity, then forms an electrostatic latent image by light from a semiconductor laser or the like, and develops the charged toner by a developing device. To form a toner image. Next, in the electrophotographic printer, the toner image on the image carrier is transferred onto the recording medium by using a conductive elastic roller or the like, and then the toner image on the recording medium is heated and melted by the fixing device to fix the toner image. And obtain an image with good storability.

A conventional fixing device uses a heat roller made of a metal tube having a high heat conductivity such as aluminum and a pressure roller, and is provided with a heater lamp such as a halogen lamp inside the heat roller. The pressure roller contacts the surface of the heat roller and is rotated. The recording medium passes between the heat roller and the pressure roller to fix the toner image.

Since the temperature at which the toner melts is constant, the temperature of the surface of the heat roller is detected by a temperature sensor. If the detected temperature is lower than the set temperature, a voltage is applied to the heater lamp to heat it with constant power. However, when the detected temperature is higher than the set temperature, the control of turning off the voltage of the heater lamp and waiting for the temperature to drop by natural cooling is performed.

In recent years, from the viewpoint of energy saving, a so-called energy saving mode is generally used in which temperature control is not performed during normal printing standby, the heater lamp is always turned off, and the heat roller is heated each time a printing operation is started. Has become. However, it usually takes one minute or more for the temperature of the heat roller to reach the temperature required for fixing, resulting in the inconvenience that required printing cannot be performed immediately. Therefore, it has become common to reduce the size and thickness of the heat roller and reduce the heat capacity to accelerate the temperature rise without increasing the power consumption.

[0005]

In the above-mentioned conventional fixing device, the heat capacity of the heat roller is small. Therefore, if the heater lamp is always heated with a constant power, the actual temperature when the heat roller is set to the preset temperature is set. Since there is a time lag between the temperature detected by the temperature sensor and the temperature detected by the temperature sensor, an overshoot phenomenon may occur in which the temperature temporarily exceeds the set temperature.
Even if the temperature is kept constant, there is a problem that the temperature rises and falls around the set value and the temperature ripple becomes large.

An object of the present invention is to provide a fixing device which prevents an overshoot phenomenon that occurs when the heat roller is set to a preset temperature and enables stable fixing.

[0007]

According to the present invention, in a fixing device that heats and fuses a toner on a sheet by heating a heat roller having a heating element therein, a voltage is supplied to the heating element. Set the power supply, the switching circuit that turns the power supply output on and off, the temperature sensor that detects the temperature of the heat roller, and the ratio of the power supply output on time based on the temperature information from the temperature sensor. A fixing device including a control unit that controls the opening / closing circuit is obtained.

As a result, stable fixing is possible.

In particular, the control means sets the ON time ratio of the open / close circuit to 80% or more in the warm-up period immediately after the start of printing, recognizes the temperature information from the temperature sensor, and when a predetermined temperature lower than the set temperature is reached. , The on-time ratio is set to 10 to 80%. As a result, overshoot that occurs during temperature control can be prevented, and since the heater lamp operating duty during normal printing is reduced to 10-80%, it is possible to perform stable temperature control while reducing the amount of heat generated by the heater lamp. .

[0010]

Next, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a perspective view showing a fixing device according to a first embodiment of the present invention. In the figure, the heat roller 1
The cylinder is made of a metal such as aluminum having a high thermal conductivity, and the surface of the cylinder is coated with a toner that does not easily adhere to the cylinder. The cylinder is rotated by a motor (not shown).
The pressure roller 2 is composed of a metal cored bar made of a heat-resistant elastic material such as silicon rubber, and is pressed against the heat roller 1 by a pressure spring 5 and rotatably supported while maintaining a predetermined pressure. ing.

The heater lamp 3 is composed of a resistor having a heat generating function such as a halogen lamp, and is connected to a power source 8 via an opening / closing circuit 7. The temperature sensor 4 is attached so as to be in contact with the heat roller 1, and is composed of an element having a thermocouple function whose resistance value changes depending on the temperature in order to measure the surface temperature. The output from the temperature sensor 4 is
A / D conversion is performed by the control circuit 9 and the temperature data is determined.

FIG. 2 is a detailed circuit diagram of an electric circuit system including the control circuit 6 of FIG. A commercial AC power supply signal is input to the power supply 8, and the heater lamp 3 passes through the opening / closing circuit 7.
AC voltage is supplied to.

The control circuit 6 detects the point where the voltage becomes 0 from the AC phase of the power supply, and A / A which converts the temperature information from the temperature sensor 4 into digital data.
D converter 17, I / O port 11, microprocessor 12, ROM (Read Only Memory) 13 in which a program for temperature control is written, and RAM 14
And a timer 15, and controls the switching circuit 7 based on the temperature control program by using the AC phase of the power supply and the output of the temperature sensor 4 as external inputs.

The detection circuit 10 generates a timing signal of a zero cross point at which the AC voltage becomes 0 and supplies it to the microprocessor 12 through the I / O port 11. A
The output of the / D converter 17 is also supplied to the microprocessor 12 via the I / O port 11.

FIG. 3 shows the microprocessor 1 of the control circuit 6.
3 is a flowchart showing temperature control by 2. At the start of printing, the opening / closing circuit 7 is fully opened, the heater lamp operation duty (ratio of ON time) is set to 100% (step S1), and the heat roller 1 is heated with the maximum heat amount (step S2). FIG. 4A is a waveform diagram showing the waveform (50 or 60 Hz) of the voltage supplied to the heater lamp 3 when the heater lamp operating duty is 100%.

When the microprocessor 12 recognizes the temperature from the temperature sensor 4 (step S3) and the temperature reaches 140 ° C. (step S4), a control signal is sent to the switching circuit 7 in order to prevent overshoot due to a time delay of temperature detection. Is output, and the heater lamp operating duty is set to 60% (step S5). At this time, the switching circuit 7 sets the heat generation amount to 60% of the rated value by the chopper control described below. That is, the on-time ratio for supplying power is set to 60%.

FIG. 4B is a waveform diagram showing the waveform of the voltage supplied to the heater lamp 3 when the operation duty of the heater lamp is set to 60%. In the figure, the shaded portion is the waveform when voltage is applied, and the waveform in the broken portion is cut off. The temperature of the microprocessor 12 is 140 ° C.
When it is recognized that the timer 15 is operated, the timing signal generated at the zero cross point from the detection circuit 10 is counted, the switching circuit 7 is turned on until the timing signal is counted three times, and then the timing signal is counted twice. Switching circuit 7
By repeating the operation of turning off, the switching circuit 7 is turned on / off at a ratio of 3: 2 in synchronization with the timing signal, and the heater lamp operation duty is set to 60%.

The microprocessor 12 recognizes the temperature (step S6), and when it exceeds 150 ° C (step S6).
7) The switching circuit 7 is closed to turn off the heater lamp 3 (step 8). When the temperature drops below 150 ° C due to heat consumption due to natural cooling and paper passage (step S10), the opening / closing circuit 7 is controlled to set the heater lamp operating duty to 40% and the heater lamp 3 is turned on. (Steps 11 and 12). The setting method of 40% is
As in the case of 60%, the timer 15 counts the timing signal generated at the zero cross point from the detection circuit 10, turns on the switching circuit 7 until the timing signal is counted twice, and then turns the switching circuit 7 until counting three times. By repeating the operation of turning off, the switching circuit 7 is turned on / off at a ratio of 2: 3 in synchronization with the timing signal, and the heater lamp operation duty is set to 40%.

Thereafter, similarly, the temperature of the heat roller 1 is set to 150.
The operation is repeated to control the temperature at a heater lamp operating duty of 40% so as to maintain the temperature around ° C.

As described above, the opening / closing circuit 7 is fully opened at the start of driving the heater lamp 3, and the target temperature of 150 is reached.
When the temperature reaches 140 ° C before reaching ° C, the heater lamp operating duty is set to 60% to prevent overshoot that occurs during temperature control, and the heater lamp operating duty during normal printing is Since it is reduced to 40%, the amount of heat generated by the heater lamp can be reduced to enable stable temperature control.

The values of the heater lamp operating duty and the set temperature are not limited to the values described above, and other values can sufficiently exert the above effect as long as they satisfy the requirements of the claims. be able to.

Further, the control circuit 6 counts the timing signal from the detection circuit 10 to control the opening / closing circuit 7, and the detection signal from the temperature sensor 4 at 140 ° C.
First and second comparison circuits that compare with the first and second reference voltage signals corresponding to 50 ° C are used, and the counter circuit is switched by the output of each comparison circuit to control the on / off time of the switching circuit. It may be done. In this case, no software is needed.

Also in FIG. 2, the microprocessor 1
2 does not turn on / off at the value by counting the timing signal of the zero cross of the AC waveform as shown in FIG.
The heater lamp operation duty may be set by executing control for turning on only for a predetermined time from the rise or fall from the zero cross time. In this case, a thyristor chopper circuit is used for the switching circuit 7. However, a circuit that turns on / off the AC power supply at the zero cross point like the circuit of FIG. 2 is superior in that it can prevent the generation of electromagnetic noise and does not require the addition of noise countermeasure components. .

In another embodiment of the present invention, the amount of heat required for fixing differs depending on the size of the paper passing through the fixing device and the type of paper, so that the heater lamp operating duty during printing is set to the paper size. It may be appropriately set according to For example, the operation duty is 40% for A4 size, and 30% for small size paper such as postcards and envelopes.
The operation duty of. In this case, in FIG. 2, the type of paper is input from another input circuit, and the microprocessor 12 recognizes it and controls the operation duty. As a result, stable fixing can be performed according to the type of paper.

[0026]

As described above, according to the present invention,
The warm-up time can be shortened by maximizing the amount of heat generated by the heater lamp at the start of printing operation.By changing the amount of heat generated before reaching the target temperature, the surface temperature of the heat roller keeps rising. Can be suppressed. Therefore, it is possible to prevent the wrinkle of the sheet during fixing. Further, there is an effect that stable temperature control can be performed by reducing the amount of heat generated by the heater lamp during normal printing.

Further, as in the invention of claim 4, the zero cross point of the AC power source is detected, and the on-point is turned on at that point.
When the control for turning off is performed, it is possible to prevent generation of electromagnetic noise, and there is an effect that no noise countermeasure component is required.

According to the fifth aspect, stable fixing can be performed according to the type of paper.

[Brief description of the drawings]

FIG. 1 is a schematic perspective view showing a fixing device according to a first embodiment of the present invention.

FIG. 2 is a circuit diagram showing details of an electric circuit system of the fixing device in FIG.

3 is a flowchart showing a temperature control operation of a control circuit of the electric circuit system of FIG.

FIG. 4 is a waveform diagram showing an opening / closing operation of a voltage signal of a power supply.

[Explanation of symbols]

 1 Heat roller 2 Pressure roller 3 Heater lamp 4 Temperature sensor 6 Control circuit 7 Open / close circuit 8 Power supply

Claims (5)

[Claims] 1. A fixing device for heating and fixing a toner on a sheet by heating a heat roller having a heating element therein, and turning on a power supply for supplying a voltage to the heating element and an output of the power supply. Control means for controlling the switching circuit by setting the ratio of the ON time of the power supply output on the basis of the temperature information from the temperature sensor that detects the temperature of the heat roller and the switching circuit that is turned off. A fixing device including and. 2. The control means sets the ratio of the on-time to 80% or more in the warm-up period immediately after the start of printing, and when the temperature information is recognized and a predetermined temperature lower than the set temperature is reached, the on-time is reached. Ratio is 10 to 80%
The fixing device according to claim 1, wherein the fixing device is set to. 3. The phase detecting circuit for detecting a predetermined phase of the power supply output, and the control means determines the ratio of the on-time based on temperature information from the temperature sensor, and detects the detected phase. The fixing device according to claim 1, further comprising an opening / closing control circuit that controls the opening / closing circuit in accordance with the determined ratio at a timing synchronized with. 4. The phase detection circuit detects the phase of a zero-cross voltage and generates a timing signal at that phase,
The opening / closing control means changes a count value of the timing signal and a count value thereof based on temperature information from the temperature sensor, and outputs the power supply in synchronization with the timing signal according to the count value. The fixing device according to claim 3, further comprising a control circuit for controlling ON / OFF of the fixing device. 5. The control means further comprises means for varying the on-time ratio according to the type of the recording medium after the temperature information from the temperature sensor reaches the predetermined temperature. The fixing device according to claim 2.