JPH05313436A - Image forming device - Google Patents

Abstract

(57) [Summary] [Object] The present invention relates to an image forming apparatus such as a copying machine or a printer to which an electrophotographic process is applied, and in particular, the fixing roll is not wastefully heated and electric power is not wasted. An object of the present invention is to provide an image forming apparatus that does not need to switch the power saving mode switch. [Structure] The sensor 22 detects the presence / absence of mounting of the paper feed cassette 5 and outputs it to the CPU 23, so that the CPU 23 outputs a FULOW signal according to the presence / absence of mounting of the paper feed cassette 5 to the resistor bridge circuit 24, and the point A The reference voltage of the comparator 25, which is the electric potential of, is changed, and the control temperature of the heater H is switched between the fixing temperature and the power saving temperature to prevent waste of power during non-printing work in which the paper feed cassette 5 is not mounted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine or a printer device to which an electrophotographic process is applied.

[0002]

2. Description of the Related Art An image forming apparatus, such as a copying machine or a printer, which applies an electrophotographic process, transfers a toner image formed on a photoconductor onto a sheet and then fixes the toner image on the sheet by heat. A vessel is provided.

Conventionally, a fixing device used in such an image forming apparatus has, for example, a fixing roll provided in the fixing device, a heater is provided in the fixing roll, and energization of the heater is controlled to fix the fixing roll. Was controlled to a predetermined temperature. The temperature of the fixing roll is controlled by first heating the heater after the power is turned on to heat the fixing roll to a predetermined fixing temperature. After that, in order to maintain the set predetermined temperature, heating control of the heater is performed according to the temperature detected by a temperature detector such as a thermistor provided in the vicinity of the fixing roll to maintain the fixing roll at the predetermined temperature.

During the printing process in which the paper passes through the fixing roll, the heat of the fixing roll is absorbed by the paper and the temperature of the fixing roll sharply drops. However, on the contrary, when the printing process is not performed, the temperature drop of the fixing roll is small.Therefore, for example, by providing a power saving mode switch and letting the operator operate this switch, the power to the fixing roll is supplied while the printing work is not performed. A device that controls to reduce the supply amount has also been proposed.

[0005]

However, the conventional image forming apparatus as described above has the following problems. (A) First, in an image forming apparatus that controls the temperature of the fixing roll to a predetermined temperature regardless of the printing work, if the printing work is not performed for a long time even when the power of the apparatus is turned on, the heater is heated to control the fixing roll. Maintaining a high fusing temperature is a waste of power. In such a case, it is conceivable to turn off the main power source of the apparatus, but if the power source is turned off, it is time-consuming and inconvenient for the heating process of the fixing roll when the printing operation is desired to be performed immediately. (B) On the other hand, in the device provided with the power saving mode switch, the fixing roll is controlled to a low temperature when the printing operation is not performed, so the above-mentioned waste of power can be prevented, but the operator must operate the switch consciously. I won't. For example, when each operator finishes his / her printing work, he / she must confirm whether or not to use someone's device next and operate the switch. Therefore, the printing work becomes complicated.

[0006]

SUMMARY OF THE INVENTION In view of the above conventional problems, the present invention provides an image forming apparatus in which the fixing roll is not wastefully heated to waste electric power, and the operator himself does not have to switch the power saving mode switch. The purpose is to

[0007]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention detects the presence or absence of the paper cassette in an image forming apparatus that feeds paper from a paper cassette detachably attached to a main body device to perform printing. And a temperature switching control unit that switches the fixing temperature of the thermal fixing unit according to the output of the detecting unit.

[0008]

EXAMPLES An example of the present invention will be described below with reference to the drawings. FIG. 2 is an overall configuration diagram of the image forming apparatus of this embodiment. In FIG. 1, an image forming apparatus 1 includes a so-called image forming section 4 including a photosensitive drum 2, a print head 3, etc., a sheet conveying mechanism 7 including a sheet feeding cassette 5, a conveying roll 6, etc., and a control circuit section described later. It is configured.

The image forming section 4 includes a photosensitive drum 2 which is rotatable in the direction of the arrow, and a charger 9, a print head 3, a developing device 10, and a transfer device which are sequentially arranged near the peripheral surface of the photosensitive drum 2. 11 and a cleaner 12. The paper transport mechanism 7 includes the above-described paper feed cassette 5 that stores a predetermined amount of paper P, and the paper feed roller 1 that carries out the paper P from the paper feed cassette 5.
3, a transport roll 6 for transporting the sheet P, a standby plate 15 for temporarily suspending the sheet P, and re-feeding the sheet P at the same timing as the toner image formed on the photosensitive drum 2. ing. The fixing roll 16 is a device that conveys the paper P and heat-fixes the toner image transferred by the transfer device 11 onto the paper P. The paper discharge roll 17 ejects the paper after the fixing process out of the machine. This is a roll for discharging to the paper discharge tray 18.

Here, the above-mentioned fixing roll 16 as the heat fixing means is housed in the fixing device 19 (note that the fixing device 1
The paper discharge roll 17 described above is also housed in the sheet 9. The fixing roll 16 includes a heating roll 16 'and a pressure roll 1.
6 ", and a heater H is provided inside the heating roll 16 '.
Is provided, and a predetermined current is supplied to the heater H from an AC power supply described later. Also, heating roll 1
A thermistor for detecting the temperature of the heating roll 16 'is provided near the peripheral surface of 6'.

FIG. 1 is a diagram showing the configuration of the above-mentioned control circuit, which is a circuit having a function as temperature switching control means. In the figure, a CPU 23 is a central processing unit that controls the drive of the entire image forming apparatus 1, and performs various controls other than the temperature control of the fixing roll 16 of this embodiment.

A sensor 22 as a detection means is connected to the input I of the CPU 23, and a detection signal indicating whether or not the paper feed cassette 5 is attached is output from the sensor 22 to the CPU 23. That is, when the paper feed cassette 5 is attached to the main body of the apparatus, the convex portion 5 ′ provided at the front end of the paper feed cassette 5 becomes the sensor 22.
Is detected by and the signal indicating that the paper feed cassette 5 is attached to the apparatus main body is output to the CPU 23.

When the above-mentioned detection signal is input from the sensor 22, the CPU 23 outputs the FULOW signal from the output O as a high level to the resistance bridge circuit 24. The resistance bridge circuit 24 is composed of a thermistor TH arranged near the peripheral surface of the heating roll 16 'and three resistors R1 to R3. The thermistor T is provided at the point B of the resistor bridge circuit 24.
Based on the temperature change of the heating roll 16 'detected by H, a voltage according to the voltage division ratio with the resistor R1 is generated, and this voltage is output to the non-inverting input (hereinafter referred to as + input) of the comparator 25. In addition, the inverting input of the comparator 25 (hereinafter-
The voltage (voltage value at point A) determined by the resistance values of resistors R2 and R3 is output to (input), and the comparator 2
The standard value is 5. This reference value is a reference value for setting the heating roll 16 ′ to a predetermined temperature (fixing temperature, for example, 175 ° C.) when the temperature of the fixing roll 16 is controlled.

Also, a circuit 2 for changing the reference value, which is composed of a transistor Q1 and resistors R4 to R6, is connected in parallel with the resistor R2.
6 is connected. This circuit 26 uses the transistor Q in accordance with the above-mentioned FULOW signal output from the CPU 23.
It is a circuit for controlling ON / OFF of 1, for example, turning on the transistor Q1 when the FULOW signal is at a low level to change the potential at the point A and change the reference value output to the-input of the comparator 25. That is, the reference value of the comparator 25 is changed by outputting a low level FULOW signal when the paper feeding cassette 5 is not mounted, and the power saving temperature (for example, 100 ° C.) lower than the fixing temperature (175 ° C.) described above.
This is a circuit for setting the temperature of the fixing roll 16 in C).

The comparator 25 has a voltage higher than the reference value supplied to the minus input when the voltage supplied to the plus input is higher, that is, when the temperature of the fixing roll 16 is lower than a predetermined temperature (or a power saving temperature slightly lower than the predetermined temperature). When it is low, a high signal is output to the transistor Q2 via the resistor R8, and the transistor Q2 is turned on. On the contrary, when the voltage supplied to the + input is lower than the reference value, that is, when the temperature of the fixing roll 16 is higher than a predetermined temperature (or a power saving temperature slightly lower than the predetermined temperature), a low signal is output via the resistor R8. Transistor Q2
To turn off the transistor Q2.

A switch circuit 30 composed of a transistor Q2, an LED 27, a gate trigger circuit 28, and a triac 29 controls energization of a heater circuit 31 according to whether the transistor Q2 is on or off. For example, when the transistor Q2 is on, a current is supplied to the LED 27 through the resistor R10 to cause the LED 27 to emit light and sequentially drive the gate trigger circuit 28 and the triac 29 to energize the heater circuit 31. That is, the AC current output from the AC power supply 32 at this time is supplied to the heater H. On the other hand, when the transistor Q2 is off, the LED 27 is turned off and the gate trigger circuit 2
8. Turn off the triac 29 to stop energizing the heater H.

The resistor R7 shown in the figure is a so-called pull-up resistor, and the resistor R9 is a transistor Q together with the resistor R8.
This is a so-called bleeder resistance that sets the voltage value of the base voltage applied to 2.

The temperature control operation of the fixing roll 16 will be described below. FIG. 3 is a time chart for explaining the temperature control of the fixing roll 16. First, when the power of the image forming apparatus 1 is turned on, the temperature detected by the thermistor TH is low because the fixing roll 16 is initially at a low temperature (for example, 0 in FIG.
° C), the output of the comparator 25 becomes high level regardless of whether the paper feed cassette 5 is attached or not attached. That is, since the thermistor has a negative temperature-resistance one-time characteristic, when the temperature detected by the thermistor TH is low, the resistance value of the thermistor becomes high and the potential at the point B also becomes high, so that the output of the comparator 25 becomes high level. Becomes Therefore, the transistor Q2 is turned on to drive the triac 29 and supply the current from the AC power supply 32 to the heater H. Therefore, the heating roll 16 'is heated and the temperature of the fixing roll 16 including the pressure roll 16 "gradually rises. When the temperature of the fixing roll 16 rises to some extent, the temperature control is performed by mounting / non-mounting the paper feed cassette 5. Makes a difference.

If the paper feed cassette 5 is mounted in the main body of the apparatus, a cassette detection signal from the sensor 22 will be CP.
The signal is output to U23, and the CPU 23 outputs the FULOW signal to the resistance bridge circuit 24 as a high level based on this detection signal. Therefore, at this time, the transistor Q
1 is turned off, the potential at the point A is controlled to be high, and the reference voltage value of the comparator 25 is high.

This reference voltage value (potential at point A) is the same as the potential generated at point B when the thermistor TH detects 175 ° C. as the temperature of the fixing roll 16. That is,
The temperature of the fixing roll 16 rises, and the predetermined fixing temperature is 175 ° C.
The output of the comparator 25 will be inverted when the voltage reaches the threshold, and at this time the transistor Q2 is turned off and the triac 2
9 is turned off to stop energizing the heater H. After that, when the temperature of the fixing roll 16 becomes 175 ° C. or lower, the output of the comparator 25 is inverted again to heat the heater H, and the energization control of the heater H is performed for the period T1 shown in FIG. It is held at C (characteristic indicated by the solid line of the period T1). Thus, even if the temperature of the fixing roll 16 is kept at the normal heat fixing temperature during the period T1, the paper feed cassette 5 is still attached at this time, and there is a high probability that the printing operation will be performed. There is no problem such as waste of money.

On the other hand, during the period T1, if the paper feed cassette 5 is not attached to the main body of the apparatus, the sensor 22 does not output the cassette detection signal to the CPU 23, and the CPU 23 outputs F
The ULOW signal is output as a low level. Therefore, at this time, the transistor Q1 is on, the potential at the point A drops, and the reference voltage value of the comparator 25 becomes a voltage value corresponding to the power saving temperature of 100 ° C. which is a lower temperature than before. That is, the temperature of the fixing roll 16 is 100 ° C.
When the temperature reaches, the output of the comparator 25 is inverted, the transistor Q2 is turned off, the triac 29 is turned off, and the power supply to the heater H is stopped. After that, the heater H is energized for the period T1 shown in FIG.
Is maintained at 100 ° C. (characteristic indicated by the dotted line of period T1). As described above, by keeping the temperature of the fixing roll 16 at the power saving temperature while the paper feeding cassette 5 is not mounted, it is possible to prevent power consumption. In addition, while the paper feed cassette 5 is not mounted in this manner, the fixing roll 16
Even if the temperature is kept low, there is no possibility that the printing operation will be performed immediately unless the paper feed cassette 5 is attached, and there is no problem.

Further, a period T2 in the figure shows a temperature state of the fixing roll 16 when the sheet feeding cassette 5 mounted on the apparatus is removed. At this time, the detection signal of the cassette is not output from the sensor 22, so the CPU 23 switches the FULOW signal from the high level to the low level. Therefore, at this time, the transistor Q1 changes from off to on,
The potential at the point A decreases and is set to the same power saving temperature as the state shown by the dotted line in the figure during the period T1.

Further, a period T3 shown in the figure shows an example in which the sheet feeding cassette 5 is mounted again in the apparatus main body. At this time, the FULOW signal output from the CPU 23 becomes high level again, so that the reference voltage value of the comparator 25 becomes high again and the fixing temperature is set to a temperature at which the fixing roll 16 can be immediately thermally fixed. By controlling in this way, it is possible to control the temperature immediately so that the printing operation can be started immediately after the paper feed cassette 5 is attached to the apparatus main body.

In the above embodiment, whether or not the paper feed cassette 5 is attached to the main body of the apparatus is detected and the fixing roll temperature is switched to the power saving temperature in accordance with the detection. Of course, it may be configured to switch according to the detection of.

[0025]

As described above in detail, according to the present invention, the temperature of the fixing roll is controlled to the power saving temperature in a state where there is no possibility of performing the printing operation and the paper feeding cassette is not attached, which is wasteful. Power consumption can be prevented.

Further, the switching to the power saving temperature can be automatically performed by the sensor, and the operator does not need to perform a complicated switch switching operation as in the conventional case.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a temperature control circuit of a fixing roll used in an image forming apparatus according to an embodiment.

FIG. 2 is an overall configuration diagram of an image forming apparatus according to an embodiment.

FIG. 3 is a time chart illustrating a temperature control operation of a fixing roll.

[Explanation of symbols]

 1 Image Forming Apparatus 2 Photosensitive Drum 3 Print Head 4 Image Forming Section 5 Paper Feeding Cassette 5'Convex Section 7 Conveying Mechanism 16 Fixing Roll 16 'Heating Roll 16 "Pressurizing Roll 19 Fixing Device 22 Sensor 23 CPU 24 Resistance Bridge Circuit 25 Comparator 27 LED 28 Gate trigger circuit 29 Triac 30 Switch circuit 31 Heater circuit 32 AC power supply

Claims (1)

[Claims] 1. An image forming apparatus that feeds a sheet from a sheet cassette detachably attached to a main body device to perform printing, and a detection unit that detects the presence or absence of the sheet cassette, and fixes an image on the sheet. An image forming apparatus comprising: a heat fixing unit that causes the temperature change control unit to change a fixing temperature of the heat fixing unit according to an output of the detection unit.