JP2003149990A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To monitor the on / off cycle and the number of times of a sub-heater or a main and a sub-heater, and to feed back to a control of a heater, so that a flicker value is obtained irrespective of a change in conditions such as a paper size, a paper type, and an environmental temperature. Low. In an image forming apparatus for thermally fixing a toner image formed on a recording sheet by a heat roller, a means for detecting a temperature of the heat roller, at least two or more heaters for overheating the heat roller are provided. Having heater control means for turning on and off the heater independently,
An image forming apparatus that operates the heater control unit based on a detection result of the temperature detection unit, the image forming apparatus includes a detection unit that detects an operation state of the heater control unit, and turns on and off at least one heater based on the detection result. Change the control method of.

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 for forming an image by thermally fixing a toner image formed on a transfer sheet with a heat roller.

[0002]

2. Description of the Related Art Conventionally, in an image forming apparatus in which a toner image formed on a transfer paper is heat-fixed by a heat roller to form an image, the heater is turned on to prevent voltage fluctuation (countermeasure against flicker) due to inrush current when the heater is turned on. A slow start method is sometimes used, and the wattage balance of the main heater and sub-heater is adjusted, and the temperature control temperature of the main heater and the sub-heater are shifted so as to eliminate wasteful ON / OFF of the heater.

[0003]

However, the slow start method is effective as a measure against flicker, but has a demerit that harmonics are deteriorated. Therefore, in recent years, the method for adjusting the wattage balance of the heater and the temperature control sequence has been used. Due to the improvement of the image forming speed of the image forming apparatus and the diversification of the corresponding transfer paper materials, there are various conditions and it may not be possible to unambiguously determine.

For example, A4 size plain paper (80 g paper)
Even if the wattage of the heater and the temperature control sequence are determined in consideration of the balance, it is possible that the B4 and B5 size plain paper (80 g paper) loses the balance and increases the flicker value.

This will be described with reference to FIGS. 3 (A) to 3 (C).

FIGS. 3A to 3C show the main temperature of the fixing roller and the main temperature of the fixing roller when the temperature control is controlled during the image forming operation by the two heaters of the main heater having a large wattage and the sub heater having a small wattage. It is a figure showing the relation of ON / OFF control of a heater and a sub heater.

To control the heater, both the main heater and the sub heater are turned on from the temperature control lower limit to the temperature control center, only the main heater is turned on from the temperature control center to the temperature control upper limit, and when the temperature control upper limit is reached, the temperature control is performed. This is an example of the case where the heaters are turned off until the lower limit is reached.

FIG. 3A is a diagram when A4 size paper is fed, FIG. 3B is a B5 size paper, and FIG. 3C is a diagram when B4 size paper is fed.

In FIG. 3A, at A4, the amount of heat taken by the paper from the fixing roller in a unit time and the amount of heat supplied by the main heater to the fixing roller in a unit time are almost in equilibrium (the heat supply amount of the heater is slightly higher). For this reason, the flicker value is low because the on / off repetition cycle of the main heater and sub heater is long.

However, as shown in FIG. 3 (B), since the size of B5 size is smaller, the amount of heat that the main heater supplies to the fixing roller per unit time is larger than the amount of heat taken from the fixing roller per unit time by the paper. Therefore, the main heater alone reaches the temperature control upper limit temperature immediately, so that the on / off cycle of the main and sub heaters is shortened and the flicker value is increased.

Further, as shown in FIG. 3C, in the B4 size, since the size becomes smaller, the amount of heat that the main heater supplies to the fixing roller per unit time is insufficient for the amount of heat taken from the fixing roller per unit time by the paper. After the temperature reaches the center of temperature control, the power supply from only the main heater will not make it in time and the temperature will drop.When the temperature reaches the lower limit, the sub-heater will be lit up repeatedly, and the on-off cycle of the sub-heater will be shortened. , The flicker value becomes worse (the wattage of the sub-heater is sufficiently small, and the flicker value may not be affected even if the inrush current is small even when the on / off operation is repeated).

Although only the paper size has been described above,
It is considered that the flicker value also varies depending on the type of transfer paper (thick paper, thin paper) or the ambient temperature.

As described above, in order to keep the flicker value within the standard, it is necessary to consider various conditions such as the wattage balance of the heater, and it takes time to design and confirm.

[0014]

In an image forming apparatus for thermally fixing a toner image formed on a recording sheet with a heat roller, a means for detecting the temperature of the heat roller and at least two means for overheating the heat roller. An image forming apparatus which has one or more heaters and heater control means for turning the heaters on and off independently, and operates the heater control means based on a detection result of the temperature detection means,
It has a detection means for detecting the operating condition of the heater control means, and changes the on / off control method of at least one heater based on the detection result.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS (Embodiment 1) An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a cross-sectional structural view for explaining an example of the image forming apparatus of the present invention. 100 is a copying apparatus main body, 142 is a circulating automatic document feeder (hereinafter referred to as RD) for automatically feeding originals.
When a plurality of originals are piled upward, the originals are read in order from the bottom one.

The operation of the image forming apparatus of this embodiment will be described below.

In FIG. 1, reference numeral 101 is a document table glass as a document placing table, and 102 is a document illumination lamp which constitutes a scanner together with a scanning mirror 103. The scanner is reciprocally scanned in a predetermined direction by a motor (not shown), and the reflected light of the document is passed through the scanning mirrors 103 to 105 to the lens 10
After passing through 7, the image is formed on the CCD sensor 108.

Reference numeral 117 denotes a laser, which is an image sensor unit 10.
The photosensitive drum 110 is irradiated with a laser beam that is converted into an electric signal in 6 and modulated based on the image signal that has been subjected to predetermined image processing in the image controller 139.

Around the photosensitive drum 110, a primary charger 113, a developing device 118, a transfer charger 127, a separation charger 128, a cleaning device 111, and a pre-exposure lamp 112.
Is equipped with. In the image forming unit 126, the photoconductor drum 110 is rotated in the direction of the arrow shown in the figure by a motor (not shown), and after being charged to a desired potential by the primary charger 113, the image from the image control unit 139. Laser light is emitted from the laser 117 according to the data, and an electrostatic latent image is formed. The electrostatic latent image formed on the photoconductor drum 110 is developed by the developing device 118 and visualized as a toner image.

On the other hand, the transfer paper fed from the upper cassette 122 or the lower cassette 124 by the pickup rollers 123 and 124 is sent to the main body by the paper feed rollers 138 and 139, and is fed to the transfer belt by the registration rollers 126. The visualized toner image is transferred to the transfer charger 1.
It is transferred to the transfer paper by 27. After the transfer, the cleaning device 111 cleans the residual toner on the photosensitive drum, and the pre-exposure lamp 112 erases the residual charge.

The transfer paper after transfer is sent to the fixing device 130 by the conveyor belt 129. The fixing period device 130 is 2 above and below
Two heaters, a main heater 132 and a sub-heater 133, are inserted inside the upper roller, and a heater control unit (not shown) is output by the output of a thermistor 134 which is pressed against the surface of the upper roller. Thus, the main heater 132 and the sub heater 133 are controlled to be turned on / off to keep the temperature of the roller surface constant. It is fixed by pressure and heat in the fixing device 130, and is discharged to the outside of the main body by the discharge roller 131.

Next, the heater control of this embodiment will be described with reference to the block diagram of the heater control section shown in FIG.

In FIG. 2, 201 is a CPU, 202, 2
Reference numeral 03 is a heater control triac, 204 is a main heater, 205 is a sub heater, 206 is a temperature detecting thermistor, 207 is a voltage dividing resistor, and 208 is a commercial power supply (100 V). Here, the CPU 201 detects the temperature of the fixing roller from the divided voltage of the temperature detecting thermistor 206 and the resistor 207, and the triacs 202 and 203.
By controlling the operation of the main heater 204 and the sub heater 205, the temperature of the fixing roller is kept constant.

In this embodiment, the main heater is 800 W and the sub heater is 400 W. Main / sub heaters are selected and turned on according to the state of the copying machine. Also CP
U201 detects the ON / OFF cycle of the sub-heater and the presence / absence of ON / OFF of the main heater.

Next, referring to the flow chart shown in FIG. 4, the temperature change of the fixing device and the lighting timing chart of the main / sub heaters 204 and 205 shown in FIGS. 3, 4 and 5, the fixing heater control of this embodiment will be described. An example will be described.

In FIG. 4, description will be given corresponding to FIG. 3 and 5, the temperature upper limit, the temperature control center (sub-heater temperature control point), and the temperature lower limit are 2 in FIG. 4, respectively.
The temperature is set to 00 ° C, A ° C, and 196 ° C.

Next, the main heater is set so that the flicker value falls within the allowable range according to the maximum condition in which the heat supply amount of the heater is the relation of the heat supply amount of the heater with respect to the heat amount taken by the paper from the fixing device >> the heat amount taken by the paper. 204, sub heater 20
Set wattage of 5.

For example, if FIG. 3 (B) is set as the maximum condition, as the amount of heat supplied by the heater approaches the amount of heat taken by the paper, there are two stages, that is, FIG. 3 (A) and FIG. 3 (C).
How to turn on and off both heaters will change in two steps. As a difference between FIG. 3A and FIG. 3C, in FIG. 3A, the heat supply amount of the main heater 204 exceeds the heat amount taken by the paper, and in FIG. 3C, the heat supply amount of the main heater 204. Is less than the amount of heat taken by the paper.

As shown in FIG. 3A, while the amount of heat supplied by the main heater exceeds the amount of heat taken by the paper, the sub heater,
The on / off interval of the main heater is the maximum condition.
Since it is wider than in (B), the flicker value is low. However, if the heat supply amount of the main heater 204 is lower than the heat amount taken by the paper as shown in FIG. 3C, the on / off cycle of the sub heater may be shortened and the flicker value may be increased. In order to avoid this, an embodiment of the present invention will be described according to the flow shown in FIG.

After the copying operation is started, the CPU 201 clears the sub-heater cycle measurement counter (f4-
1). Next, the CPU 201 detects a signal from the thermistor 206 and determines whether the temperature of the fixing device is lower than or equal to the temperature control lower limit temperature of 196 ° C. (f4-2). Turn on (f4
-3). If it is 196 ° C. or higher, then the CPU 201 determines whether the temperature of the fixing device is the temperature control center temperature A ° C. or lower (f4-4). As for the temperature control center value A, the initial value at the start of copying is 198 ° C. If the fixing device temperature is equal to or lower than A = 198 degrees, the process returns to f4-2 and the above sequence of f4-2 to f4-4 is repeated until the fixing device temperature exceeds A = 198 ° C.

At f4-4, the temperature of the fixing device is A = 19.
When it is determined that the temperature is 8 ° C. or higher, the CPU 201 determines whether or not the sub heater is turned on (f4-5), and when the sub heater 205 is turned on, the sub heater 205 is turned off (f4-6) and turned on. If not, just f
Go to 4-7. At f4-7, the CPU 201 determines whether or not a predetermined time has elapsed. If the predetermined time has not elapsed, the process proceeds to f4-11.

When a predetermined time has elapsed, the count value of the sub-heater cycle count and the count value of the on / off number of the sub-heater are returned to 0 (f4-8), and then the sub-heater 20.
It is determined whether or not 5 has been turned off and on a predetermined number of times or more (f
4-9). If the sub heater is turned on and off a predetermined number of times or more, it is determined that the on / off cycle of the sub-heater is short, the value is changed to A = 199.5, and the process proceeds to f4-11 (f4-10). If it has not been turned on / off a predetermined number of times or more, the process directly proceeds to f4-11. f4-
At 11, it is determined whether the temperature of the fixing device is 200 ° C. or higher. If the temperature is 200 ° C. or higher, the main heater 204 is turned off (f
4-12), if the temperature is 200 ° C. or lower, the process directly returns to step f4-2. Here, the predetermined number of times is the sub-heater 2
The off-on period of 05 is set to be equal to or less than the maximum value within the flicker standard value.

By performing the above flow control, the flow chart shown in FIG.
In (C), since the number of times the sub-heater is turned on and off exceeds the predetermined number at f4-9, A = 1 at f4-10.
It will be changed to 99.5. Therefore, the main heater 204 and the sub heater 205 are turned on and off as shown in FIG. 5, and the flicker value is improved.

(Embodiment 2) In Embodiment 1, an example in which only the on / off cycle of the sub-heater is taken into consideration is shown, but in this embodiment, an example of control for reducing the flicker value is shown in consideration of the number of times the main heater is turned on / off.

As shown in FIGS. 3A and 3B, when the heat supply amount of the main heater 204 exceeds the heat amount taken by the paper, the heat generation amount of only the main heater 204 causes the temperature control upper limit 200. Sub heater 205 because it can reach ℃
No need to turn on. However, FIG. 3 (A) and FIG. 3 (B)
When the heater control is made common under all conditions as shown in, the sub heater 205 is turned on,
The on / off cycle of the main heater is shortened, and the sub heater is turned off / on unnecessarily, resulting in a large flicker value.

In order to avoid this, the number of times the main heater 204 is turned off and on is detected during the copy operation, and when the on and off times are repeated a predetermined number of times or more, the main heater 204 is turned on.
It is only necessary to control the sub heater so that the sub heater is always turned off when it is judged that the heat supply amount of is larger than the heat amount taken by the paper. The control method will be described with reference to FIGS. 3 and 7 according to the flow of FIG.

After the copy operation is started, the CPU 201 clears the sub-heater cycle measurement counter, the sub-heater on / off counter, the sub-heater control flag, and the main heater on-off counter to 0 (f6-
1).

Next, the CPU 201 detects the signal from the thermistor 206, and the temperature of the fixing device is controlled to the lower limit temperature of 196 ° C.
If it is 196 ° C. or lower, it is judged whether the sub heater control flag is 1 (f6-3). If it is 1, only the main heater is turned on (f6 -4), if 0, the sub heater and the main heater are turned on (f6-5).

If the temperature is 196 ° C. or higher, then the CPU 201 determines whether the temperature of the fixing device is the temperature control center temperature A ° C. or lower (f6-6). As for the temperature control center value A, the initial value at the start of copying is 198 ° C. If the fixing device temperature is A = 198 degrees or lower, the process returns to f6-2 and the fixing device temperature is A = 198 ° C.
The above-mentioned sequence of f6-2 to f6-5 is repeated until it exceeds.

At f6-6, the temperature of the fixing device is A = 19.
When it is determined that the temperature is 8 ° C. or higher, the CPU 201 determines whether or not the sub heater is turned on (f6-7). When the sub heater 205 is turned on, the sub heater 205 is turned off (f6-8) and turned on. If not, just f
Go to 6-9. At f6-9, the CPU 201 determines whether or not the sub-heater cycle counter 6-9 has counted a predetermined number, and if it has not counted the predetermined number, the process proceeds to f6-13. When the predetermined number is counted, it is determined whether the sub-heater 205 has been turned on or off a predetermined number of times or more (f6-1).
2).

When the sub heater is turned on and off a predetermined number of times or more, it is determined that the on / off cycle of the sub-heater is short and changed to A = 199.5, and the predetermined count value at f6-11 and the on / off number count value of the sub heater are returned to f6-13. Move (f6-
10). If it has not been turned off and on for the predetermined number of times or more, the predetermined count value and the on / off number count value of the sub-heater are returned to 0 (f6-11), and the process proceeds to f6-13. Here, the predetermined number of times is set so that the off-on cycle of the sub-heater 205 is equal to or less than the maximum value within the flicker standard value.

At f6-13, it is judged whether the temperature of the fixing device is 200 ° C. or higher.
Return to step -2. If the temperature is 200 ° C. or higher, the main heater 204 is turned off (f6-14), and it is determined whether or not the main heater is turned on / off a predetermined number of times (f6-1).
5). When the sub heater is turned on and off a predetermined number of times, the sub heater control flag is set to 1 and the control is changed so that the sub heater is not turned on (6-16).

If it has not been turned on and off a predetermined number of times, f6-
Return to 2 and repeat the control. By performing the above control, when the temperature of the main heater reaches the temperature control upper limit as shown in FIGS. 3A and 3B, the sub heater is not turned on. As shown in B, unnecessary ON / OFF of the sub-heater can be eliminated, and the ON / OFF cycle of the main heater can be extended, so that the flicker value can be improved.

[0045]

According to the present invention, by monitoring the ON / OFF cycle of the sub-heater or main and sub-heaters, and the number of times of ON and feeding them back to the control of the heater, flicker can be obtained regardless of changes in conditions such as paper size, paper type, and environmental temperature. The value can be kept low.

[Brief description of drawings]

FIG. 1 is a schematic diagram of an image forming apparatus.

FIG. 2 is a block diagram of the present invention.

FIG. 3 is a correlation diagram of ON / OFF control of a heater and a fixing temperature according to a conventional technique.

FIG. 4 is a flowchart of the first embodiment of the present invention.

FIG. 5 is a correlation diagram of heater on / off control and fixing temperature improved in the first embodiment of the present invention.

FIG. 6 is a flowchart of Embodiment 2 of the present invention.

FIG. 7 is a correlation diagram of heater on / off control and fixing temperature improved in the second embodiment of the present invention.

[Explanation of symbols]

201 CPU 204 Main heater 205 Sub heater 206 thermistor

Claims (8)

[Claims] 1. An image forming apparatus for thermally fixing a toner image formed on a recording sheet with a heat roller, a means for detecting the temperature of the heat roller, and at least two or more heaters for overheating the heat roller. When,
In an image forming apparatus that has a heater control unit that independently turns on and off the heater and that operates the heater control unit based on a detection result of the temperature detection unit, a detection unit that detects an operation state of the heater control unit. An image forming apparatus, characterized in that an on / off control method of at least one heater is changed based on the detection result. 2. The image forming apparatus according to claim 1,
An image forming apparatus, wherein the heater control means turns on at least one heater when the temperature detection means detects a temperature lower than a predetermined temperature, and turns off at least one heater when a temperature higher than a predetermined temperature is detected. . 3. The image forming apparatus according to claim 2, wherein at least two or more heaters included in the image forming apparatus can be turned on and off independently of each other. Image forming apparatus. 4. The image forming apparatus according to claim 3, wherein the temperature at which at least one heater is turned on and the temperature at which it is turned off are changed based on the detection result. 5. The image forming apparatus according to claim 1, wherein the time for turning on and off the at least one heater is changed to a fixed value based on the detection result. 6. The image forming apparatus according to claim 1, wherein the operation detecting unit detects an on / off cycle of at least one heater. 7. The image forming apparatus according to claim 6, wherein the heater for detecting the on / off cycle is a heater having the smallest wattage with respect to other heaters. 8. The image forming apparatus according to claim 6, wherein the operation detecting unit also detects whether or not another heater is on / off within the detected heater on / off cycle.