JPH06250563A - Image forming device - Google Patents

Abstract

PURPOSE:To detect whether the temperature detecting element of a thermal fixing device is installed or not with a simple structure, minimize the number of input ports such as CPU for fixing temperature control, and simplify the wiring in a control base inner part in an electrophotographic device such as a laser beam printer having the thermal fixing device. CONSTITUTION:An analog switch 36 which is a semiconductor element is connected to both end sides of a thermistor 22 which is the temperature detecting element of a thermal fixing device. The output of a pull-up resistor 33 of short line for detecting the presence of the thermistor unit is inputted to the analog switch 35, and not to a CPU 32 for fixing temperature control. When the thermistor 22 is not installed to a thermal fixing device unit 22, or a connector 25 having the thermistor 22 mounted thereon is not installed, both end sides of the thermistor 22 is short-circuited by the output of the pull-up resistor 33.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic image forming apparatus having a heat fixing device.

[0002]

2. Description of the Related Art Conventionally, as an electrophotographic image forming apparatus of this type, a laser beam is modulated in accordance with input information,
A laser beam printer is known in which an electrostatic latent image is formed by exposing and scanning a photoconductor with this laser light, and the electrostatic latent image is developed with a developer and visualized to be transferred onto a recording paper.

FIG. 3 schematically shows a schematic structure of this laser beam printer. In the figure, 1 is a photosensitive drum rotatably supported in the housing H,
It has a semiconductor layer such as selenium or cadmium sulfide on its surface and rotates in the direction of arrow A during printing (image formation).
Reference numeral 2 denotes a semiconductor laser that emits a laser beam L, and the emitted laser beam L is incident on the beam expander 3 and becomes a laser beam having a predetermined beam diameter.

Reference numeral 4 denotes a polyhedral mirror which reflects the laser light and has a plurality of reflecting mirror surfaces. 5 is a polyhedral mirror 4
Is rotated at a low speed, 6 is an imaging lens for focusing the laser light reflected by the polyhedral mirror 4 on the photosensitive drum 1, and 7 is an imaging lens 6 reflected by the reflecting mirror 8.
The beam detector for detecting the laser light emitted from the semiconductor laser 2 determines the timing of the modulation operation of the semiconductor laser 2 for obtaining desired optical information on the photosensitive drum 1 by the detection signal of the beam detector 7.

Reference numeral 9 is a developing device, 10 is a cassette accommodating the recording paper 11, 12 is a thermal fixing device, and 13 is a charging device for uniformly charging the photosensitive drum 1.

In the laser beam printer having the above structure, the laser light L emitted from the semiconductor laser 2 passes through the beam expander 3 as described above and becomes a laser light having a predetermined beam diameter to become a polyhedron. It is incident on the mirror 4. At this time, since the polyhedral mirror 4 is rotating at a predetermined speed, the laser light reflected by the polyhedral mirror 4 is scanned substantially horizontally. Then, an image is formed as spot light on the photosensitive drum 1 which is charged to have a predetermined polarity by the charger 13 by the imaging lens 6 having a predetermined f-θ characteristic.

On the other hand, the photosensitive drum 1 is rotating in the direction of arrow A, and the surface of the photosensitive drum 1 is electrostatically charged by the image formation of the spot light, that is, the laser light image-formed and scanned according to the input information. A latent image is formed. This latent image is visualized by the developer in the developing device 9, and then transferred to the recording paper 11 housed in the cassette 10. Then, by passing through the thermal fixing device 12, the image is fixed on the recording paper 11 and discharged to a discharging device (not shown).

In this type of printer, heat fixing is adopted for fixing as described above. That is,
A heater (not shown) is provided inside the thermal fixing device 12, and heat is generated by energizing the heating device, and the heat is used to fix the developer on the recording paper 11. Has become.

In the above heat fixing, when the temperature of the heater is not an appropriate value, for example, a microprocessor (CPU)
To turn this on to an appropriate value, turn on the power to the heater (O
N), off (OFF) is controlled. However, when the CPU knows the temperature of the thermal fixing device 12 by the temperature detecting element (thermistor) and turns on and off the energization,
If it is determined that the temperature has not risen despite the absence of the temperature detecting element and the energization is continued to be turned on, the temperature of the thermal fixing device 12 may rise abnormally, which may cause a fire in the worst case. Therefore, in this type of printer, it is necessary to surely detect the presence or absence of the temperature detecting element of the thermal fixing device to judge whether or not the temperature currently measured is a correct value.

FIG. 4 is a diagram showing an example of the configuration around the temperature control of a conventional heat fixing device. In the figure, reference numeral 21 is a thermal fixing unit, which is composed of the following. That is, reference numeral 22 is a thermistor which is a temperature detecting element and detects the temperature of the thermal fixing device. 23 is a heater, which is a heater, 24 is a semiconductor relay (SSR) that turns on and off electricity to the heater 23, and 25 is a thermistor unit connector. Is the thermistor unit securely set in the heat fixing unit 21? The CPU 32 has a connector including a short line that passes through the inside of the thermal fixing unit for confirmation. 26 is A for supplying power
It is a C outlet.

Reference numeral 31 denotes a DC controller board for controlling the engine portion of the laser beam printer, which is composed of the following. That is, 32 is a CPU (microprocessor) that controls each part of the engine.
Therefore, the thermal fixing temperature control is also performed here. 33 is a pull-up resistor of the short line for detecting the presence or absence of the thermistor unit. When the point B is "1" (High), it is detected that the thermistor unit is not present, and when it is "0" (Low), the thermistor unit is present. The CPU 32 detects it. 34 is a pull-up resistor for temperature detection.

FIG. 5 shows an example of the relationship between temperature and voltage at point C in FIG. As shown in the figure, by appropriately selecting the characteristics of the thermistor and the value of the resistor 34, it is possible to make the temperature-voltage relationship of, for example, about 120 ° C. to 200 ° C. necessary for the thermal fixing temperature control linear.

The CPU 32 fetches the signal voltage at the point C into, for example, an 8-bit A / D conversion (analog-digital conversion) port and draws a table (not shown) for converting the A / D conversion value into temperature. By this, the current temperature of the heat fixing device is known. Then, the CPU 32 turns on / off the heater 23 by turning on / off the control line connected to the semiconductor relay 24 based on the detected temperature.
Control to the set temperature.

In the above-mentioned conventional structure, for example, only the thermistor 22 of the thermal fixing unit 21 fails, the connector of the thermistor portion is removed in order to replace it, and the connector of the thermistor portion is disconnected by a serviceman or a user. If it is forgotten to set, the control of the heater 23 does not converge, and in the worst case, there is a possibility of causing a fire as described above. Therefore, the heat fixing unit 21
It is necessary to detect the thermistor unit in order to confirm that the thermistor part of is securely set.

[0015]

However, in the conventional image forming apparatus having the thermal fixing device as described above, information on the points B and C is input to the input port of the CPU for controlling the fixing temperature. Since it is inputting, the wiring inside the board increases and the number of input ports increases. For example, it is necessary to add 8 points (1 byte) of CPU input ports because there is not 1 bit input port left. There is a problem that the situation occurs in the worst case and the cost increases. Also, in the internal operation of the CPU, points B and C
Since the points must be constantly monitored, the operation for detecting the temperature is complicated and time-consuming.

The present invention has been made by paying attention to the above-mentioned problems, and has a simple structure, and even if the temperature detecting element of the thermal fixing device is not attached at the time of inspection, the presence or absence thereof is surely ensured. An object of the present invention is to obtain an image forming apparatus that can detect the number of input ports such as a CPU for fixing temperature control and has a simple wiring inside a control board.

[0017]

An image forming apparatus according to the present invention comprises a heat fixing device, a temperature detecting element for detecting the temperature of the heat fixing device, and a detection output of the temperature fixing device. It is provided with a temperature control means for controlling the fixing temperature and a semiconductor element for short-circuiting both ends of the temperature detecting element when the temperature detecting element is not mounted on the thermal fixing device.

Further, the semiconductor element is an analog switch or a bipolar transistor.

[0019]

In the image forming apparatus of the present invention, when the temperature detecting element is absent, both ends of the temperature detecting element are short-circuited by the semiconductor elements. The presence or absence of the temperature detection element can be reliably detected by determining the signal of the detection line of the element.

[0020]

1 is a block diagram showing an embodiment of the present invention, and the same reference numerals as those in FIG. 4 denote the same components. In the figure, 21 is a thermal fixing unit, 22 is a thermistor (temperature detecting element) for detecting the temperature of the thermal fixing unit, and 23.
Is a heater for heating, 24 is a semiconductor relay for turning on / off the heater 23, 25 is a thermistor unit connector for attaching / detaching the thermistor 22, and 26 is an AC outlet for supplying power.

Further, 31 is a DC controller board, 32
Is a CPU provided on the substrate 31, and the thermistor 22
The temperature control means for controlling the fixing temperature of the thermal fixing device by inputting the detection output of 33 is a pull-up resistor for detecting the presence or absence of the thermistor unit, 34 is a pull-up resistor for temperature detection, and 35 is the thermistor 22 when the thermistor 22 is not attached to the thermal fixing unit 21.
Is an analog switch provided as a semiconductor element that short-circuits both ends of the pull-up resistor 33.
It is not input to 32, but is input to this analog switch 35.

Next, the operation will be described. The analog switch 35 is turned on when the point B in FIG. 1 is "1" (High), that is, when there is no thermistor unit, and both ends of the thermistor 22 are short-circuited. Here, when the value of the pull-up resistor 34 to which the control voltage Vcc is supplied is R1 and the on-resistance value of the analog switch 35 is Ron, the voltage Vc at the point C when the thermistor unit is not present is
Vc = Vcc · Ron / (R1 + Ron).

For example, Vcc = 5V, R1 = 10KΩ,
If Ron = 100Ω, Vc≈0.5V, and C
The input value of the PU32 8-bit A / D converter is
(03) hex. This value corresponds to a temperature of the heat fixing device of 300 ° C. or higher as shown in FIG. Therefore, for example, when the input value of the 8-bit A / D converter detects (10) hex or less, the CPU 32 can determine that the thermistor unit is not present.

On the contrary, when the thermistor unit is provided, the off resistance value of the analog switch 35 is sufficiently larger than the resistance value of the thermistor 22.
The temperature detection voltage can be obtained by the resistance value of. This allows
Even if the CPU 32 does not capture the output of the thermistor unit presence / absence detection sensor, for example, when (10) hex or less, it is determined that there is no thermistor unit, and when (11) hex or more, it is determined that the thermistor unit is present, and the A / D converter is determined. Table for converting the converted values in to temperature (not shown)
Can be used to know the temperature of the thermal fuser.

As described above, when at least the thermistor unit is not provided, the temperature detection voltage is shifted to a voltage value which is impossible in the control operation by a simple structure in which both ends of the thermistor 22 are short-circuited by the analog switch 35 which is a semiconductor element. However, it becomes possible to detect the presence or absence of the thermistor unit. Therefore, since it is necessary to input only the analog information of the point C to the input port of the CPU 32, the wiring inside the board is reduced and the number of input ports can be reduced.

In particular, in the case where the number of input ports of the CPU 32 needs to be increased by, for example, 8 points (for 1 byte) because there is not enough 1-bit input port left, it works effectively and the cost can be reduced. Also, in the internal operation of the CPU 32, it is sufficient to monitor only the point C, and the operation for detecting the temperature becomes simple.

FIG. 2 is a block diagram showing another embodiment of the present invention, and the same reference numerals as those in FIG. 1 denote the same components. In the figure, 36 is a semiconductor element N which short-circuits both ends of the thermistor 22 when the thermistor 22 is not mounted.
This is a PN bipolar transistor whose collector and emitter are connected to both ends of the thermistor 22 and whose base is connected to a pull-up resistor 33.

In this embodiment, the analog switch 35 in the above embodiment is replaced with a bipolar transistor 36, and when the point B in FIG. 2 is "1" (High), that is, when the thermistor unit is not provided, this transistor is used. Three
6 is turned on, and similarly both ends of the thermistor 22 are short-circuited. Here, the saturation voltage of the transistor 36 is Vce
Then, the voltage Vc at the point C when there is no thermistor unit is Vc = Vce.

For example, if Vc = Vce = 0.2V, the input value of the 8-bit A / D converter of the CPU 32 is (0A) hex. This value corresponds to 300 ° C. or higher as shown in FIG.
The voltage equivalent to the above is likewise impossible in control operation.
Therefore, for example, when the input value of the 8-bit A / D converter detects (10) hex or less, the CPU 32 can determine that the thermistor unit is not present.

On the contrary, when the thermistor unit is provided, the transistor 36 becomes non-conductive, so that the temperature detection voltage based on the resistance value of the thermistor 22 can be obtained. As a result, the CPU 32 determines that there is no thermistor unit when (10) hex or less, even if the output of the thermistor unit presence / absence detection sensor is not captured, and (11)
When x or more, it is judged that the thermistor unit is present and A / D
The temperature of the thermal fixing device can be known by using a table (not shown) for converting the converted value in the converter into the temperature.

Therefore, even with this configuration, the same operational effects as those of the above-described embodiment can be obtained, and even if the temperature detecting element of the heat fixing device is not attached at the time of inspection, the presence or absence thereof is the same as the above configuration. Can be reliably detected, the number of input ports such as a CPU for controlling the fixing temperature is small, and the wiring inside the control board can be simplified.

[0032]

As described above, according to the present invention, when the temperature detecting element of the thermal fixing device is not mounted, both ends of the temperature detecting element are short-circuited by the semiconductor elements, which is simple. With the configuration, even if the temperature detecting element of the thermal fixing device is not attached at the time of inspection, the presence or absence can be surely detected, and the number of input ports such as CPU for fixing temperature control is small, and the wiring inside the control board is This has the effect of simplifying the temperature detection operation.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of the present invention.

FIG. 2 is a configuration diagram showing another embodiment of the present invention.

FIG. 3 is a perspective view schematically showing a schematic configuration of a laser beam printer.

FIG. 4 is a configuration diagram showing a conventional example.

FIG. 5 is a characteristic diagram showing the relationship between temperature and voltage of the thermistor.

[Explanation of symbols]

 21 Thermal Fixer Unit 22 Thermistor (Temperature Detection Element) 23 Heater 25 Thermistor Unit Connector 32 CPU (Temperature Control Unit) 35 Analog Switch (Semiconductor Element) 36 Bipolar Transistor (Semiconductor Element)

Claims (3)

[Claims] 1. A thermal fixing device, a temperature detecting element for detecting the temperature of the thermal fixing device, and temperature control means for controlling the fixing temperature of the thermal fixing device by inputting the detection output thereof.
An image forming apparatus comprising: a semiconductor element that short-circuits both ends of the temperature detecting element when the temperature detecting element is not attached to a thermal fixing device. 2. The image forming apparatus according to claim 1, wherein the semiconductor element is an analog switch. 3. The image forming apparatus according to claim 1, wherein the semiconductor element is a bipolar transistor.