JP2002169414A - Heater control method for fixing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To decrease flickering by a simple and low cost constitution. SOLUTION: In a fixing device provided with a multiple number of heaters 2 and 8 for heating, the multiple number of heaters are controlled to be turned on and off independently and control is differentiated according to whether the total duty ratio of each heater is <=100% or greater.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixing device having a plurality of heaters, and more particularly to a heater control method for a fixing device for preventing voltage fluctuations and flicker caused by an inrush current generated at the start of lighting of the heater.

[0002]

2. Description of the Related Art In an image forming apparatus, a toner image held on a transfer material such as recording paper is heated and fused by a heating roller fixing device. At this time, if the fixing temperature is too low, toner fixing failure occurs. If the fixing temperature is too high, paper wrinkles, wrapping of the paper around the heat roller, high temperature offset (fixed toner adheres to a heating body such as a roller or a belt and the subsequent paper (A phenomenon in which an image of the previous paper is formed), and the fixing temperature must be controlled to a predetermined temperature. For this reason, the fixing temperature is detected by a thermistor or the like, and the temperature control of the heating roller is performed by changing the duty ratio of the heater drive pulse based on the difference between the target temperature and the current fixing temperature.

[0005] As shown in FIG.
When temperature control is performed by changing the ratio (duty ratio) of the N period to the control cycle (FIG. 5A), when the drive pulse rises, a large current flows due to a small resistance because the heater is cold. Eventually, as the heater temperature increases, the resistance increases and the current decreases (FIG. 5).
(B)), and the voltage changes accordingly (FIG. 5)
(C)). The differentiated waveform of this voltage changes in a complicated manner as shown in FIG. 5C, so that a high frequency is generated, which causes flicker in a surrounding fluorescent lamp and causes malfunction of surrounding electronic devices.

Conventionally, as a countermeasure against this, in a fixing device having a plurality of heaters (fixing lamps), it is necessary to prevent a plurality of fixing lamps from starting to light at the same time in order to prevent a large rush current from overlapping at the start of lighting. Lighting is started one time at a time, and the O
Japanese Patent Application Laid-Open No. H11-5278 proposes reducing the number of N / OFF times to reduce flicker at the rise and fall of the lighting pulse.
No. 2).

[0005]

However, in the above-mentioned proposal, only the overlap of the rush current at the start of lighting is prevented, and the shift of the lighting start time is a fixed time. There is a problem that the control circuit is not sufficient and a control circuit for reducing flicker is complicated and expensive.

The present invention has been made to solve the above problems,
An object is to reduce flicker by a simple and inexpensive configuration.

[0007]

According to the present invention, in a fixing device having a plurality of heaters, the plurality of heaters are independently turned on / off, and the sum of the duty ratio of each heater is 100% or less. It is characterized in that the control is made different depending on whether it is larger. Also, the present invention
When the sum of the duty ratios of the heaters is 100% or less, the lighting times of the heaters do not overlap and the heaters are continuously turned on. Also, the present invention
When the sum of the duty ratios of the respective heaters is greater than 100%, the respective heaters are illuminated by shifting the lighting start timing by a predetermined time. Further, the present invention is characterized in that the predetermined time for shifting the lighting start timing is changed according to the heater temperature. In addition, the present invention sets the heater to ON / OF.
In the fixing device that controls the temperature by applying the temperature, the heater OFF time is set within a predetermined time. Further, the invention is characterized in that the heater is a halogen lamp and the predetermined time is 400 ms. The present invention also provides
The control cycle is changed according to the duty ratio.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram illustrating an example of a fixing device according to the present invention. The heating roller 1 is heated by an HR (heating roller) heater 2, and the temperature is detected by an HR thermistor 3. A belt 4 made of a flexible resin having a large thermal resistance such as an aramid film is wound between the heating roller 1 and the fixing roller 6, and a pressure roller 7 is pressed against the fixing roller 6 to form a fixing portion. ing. The belt 4 is heated by being brought into contact with the heating roller 1, radiates heat to the paper at the fixing unit, and the temperature is detected by a BB (belt back) thermistor 5 disposed on the back of the belt. The pressure roller 7 is heated by a PR (pressure roller) heater 8, and its surface temperature is detected by a PR thermistor 9. The sheet 11 onto which the toner image has been transferred is conveyed to a fixing unit, where it is heated and fixed. The heat capacity of the pressure roller is larger than that of the heating roller 1, and the HR heater 2 and the PR heater 8 are temperature controlled by changing the duty ratio.

FIG. 2 is a diagram for explaining a heater control method according to the present invention. Here, the heaters A and B correspond to, for example, the HR heater 2 and the PR heater 8 in FIG.
Power is supplied to the heaters A and B from the same power supply circuit, and the ratio of the ON time Aon, Bon to the same control cycle T (duty A = Aon × 100 / T, duty B = Bon × 1)
00 / T), the heater control is performed.

In the present invention, when duty A + duty B ≦ 100%, as shown in the figure, control is performed so that the lighting times of the heaters A and B do not overlap and the heater B is turned on at the OFF timing of the heater A. I do. As described above, since the lighting times of the heaters A and B do not overlap with each other, a change in voltage is small. Further, since a voltage does not fluctuate when the heater A is turned off and when the heater B is turned on, generation of high frequency is reduced and flicker is reduced. Can be prevented. In the case of duty A + duty B> 100%, as shown in the figure, it is inevitable that the lighting times of the heaters A and B overlap, so that the lighting start timing is shifted to reduce the inrush current at the start of lighting to reduce flicker. Is to be reduced.

When the temperature of the roller is cold, the resistance is small because the filament is also easy to cool, and it takes time until the rush current at the time of lighting becomes large and the current becomes normal. It is desirable to change according to the roller temperature. For example, the time to be displaced when the roller temperature is low is increased, and the time for which the roller temperature is not increased is decreased.

An example in which the heater control method shown in FIG. 2 is applied to the fixing device shown in FIG. 1 is described below. The heating roller heater 700W and the pressure roller heater 230W are in a state of monochrome printing, color printing and standby. Table 1 shows the duty ratio of each heater.

[0013]

[Table 1]

When the sum of the duty ratio of the HR heater and the duty ratio of the PR heater does not exceed 100%, that is, when the HR heater is turned off during standby, the PR heater is turned on. When the sum of the duty ratios of both heaters exceeds 100%, that is, at the time of monochrome printing and color printing, H
After a predetermined time from the start of turning on the R heater, for example, 500 m
After sec, the PR heater is turned on.

In the above example, the lighting start timing of the heaters A and B is controlled. However, flicker is reduced even if only one of the heaters A and B is turned on so that the lighting times of the heaters A and B do not overlap. It is possible to For example, in a 4-cycle color machine, H
Only the R heater is turned on, and the HR heater is used for color printing.
Duty control is performed so that lighting of the PR heater does not overlap. As a result, high-speed printing is possible during monochrome printing, and the temperature stability is increased during color printing, so that high image quality can be maintained.

Further, in the present invention, in the fixing device of FIG. 1, FR warm-up and PR warm-up are performed when the power is turned on. This point will be schematically described with reference to FIG. When the power is turned on, the fixing roller warm-up (FRWup) is performed. At this time, the HR for the HR is set so that the target temperature T _{2 of the} belt 4 (198 ° C. by the BB thermistor 5 in FIG. 4 and 193 ° C. on the belt surface) is reached. The heater 2 is turned on to control the duty, the belt is idled, and heat is supplied to the pressure roller 7 through the belt. If the belt temperature reaches the target temperature T _2, FR warm-up is finished, it allows printing at this time, thereby enabling small printing of sheets at an early timing after power.

Subsequently, the pressure roller is warmed up (PR
Wup). PR warm-up is target temperature T
_The heater 8 for PR is turned on so that the temperature becomes ₁ (180 ° C.), duty control is performed, and idling of the belt is also performed. At this time, PR heater duty = control cycle−duty of HR heater. The control cycle is set as appropriate. This control can be large pressure roller 7 of the heat capacity is increased at a faster rate toward the target temperature T _1. The PR warm-up is performed following the FR warm-up,
Since heating is performed toward the target temperature from power-on, the heating is started at the same time as the FR warm-up. In the present embodiment, at the time of the PR warm-up, the target temperature of the belt surface is set to 185 ° C., which is lower than that at the time of the FR warm-up. Therefore, the belt temperature gradually decreases from the end of the FR warm-up toward 185 ° C. Thus, FR
By changing the target temperature of the belt temperature between the warm-up and the PR warm-up, it is possible to quickly start the temperature, prevent the temperature of the fixing unit from excessively rising, and reduce paper wrinkles, high-temperature offset, Preventing winding and the like, and extending the life of the fixing roller and the belt.

If continuous printing is performed at the end of the PR warm-up, the paper loses heat and the belt temperature, P
Although the R temperature decreases, the pressure roller 7 having a large heat capacity is at a high temperature of 180 ° C., so that even if high-speed printing such as 40 ppm is performed, it is calculated based on the belt temperature and the pressure roller temperature. The temperature does not fall below the lower limiter, printing is not interrupted, and high-speed printing is possible. Further, even when printing is started during warm-up of the pressure roller, a sufficient amount of heat is stored near the surface of the fixing roller, so that high-speed printing can be maintained. 4
When 0 ppm printing is performed, the fixing roller surface temperature becomes 10 to 2
The lowermost point is reached at about 0 sheets, then the surface temperature gradually rises, and reaches the target temperature after printing about 1000 sheets.

In the above example, the case where the number of the heaters is two has been described. However, the control method of the present invention is also applicable when the number of heaters is three or more. When the sum of the duty ratios of all the heaters approaches 100%, the flicker value decreases, and flicker can be suppressed by an inexpensive device. For example, in order to stabilize the temperature distribution, two heaters may be arranged in the HR, and both may be turned on at a staggered time during monochrome printing, and only one may be turned on during color printing. In this case, one of the two heaters in the HR is a first heater of high power and the other is a second heater of low power. At the time of printing, only the second heater may be turned on. At this time, for example, the first heater may be kept on, and the second heater may be duty-controlled to control the temperature. Low power heater ON / O
This is because flicker does not occur even if the FF is performed.

FIG. 4 is a diagram for explaining the OFF time dependency of the inrush current. The horizontal axis in the figure is the OFF time, and the vertical axis is the rush current (relative value). As described above, when the filament of the heater cools, the inrush current becomes extremely large. As can be seen from this figure, the filament of the halogen lamp cools less until about 400 msec, the filament does not cool down during such an OFF time, the inrush current is almost the same as the current at the time of normal lighting, and flickering occurs. Can be reduced. However, if it exceeds 400 msec,
Since the inrush current increases, flicker increases. Therefore, the duty control may be performed such that the OFF time is about 400 msec or less. In addition, 400 msec
Is different depending on the configuration of the fixing device of the heater,
The OFF time dependency of the inrush current may be experimentally obtained for each device, and duty control may be performed so that the OFF time is equal to or less than the value.

Table 2 shows the relationship between the duty and the control cycle so that the OFF time is 400 msec or less.

[0022]

[Table 2]

Don (ms) is the heater ON time, Doff
(Ms) indicates the OFF time. In Table 2, in the initial stage of warm-up, the heater is fully lit (duty = 1).
00%), and as the roller temperature approaches the target temperature,
Duty decreases. D when the duty is 96%
On is 3840 msec and Doff is 160 msec. When the duty goes below 90%, Don becomes 3600ms
ec, the control cycle is reduced so that Doff becomes 400 msec. Even if the duty is further reduced, Doff is maintained at 400 msec so that the filament does not cool, the inrush current is reduced, and flicker is not generated.

[0024]

As described above, according to the heater control method of the present invention, it is possible to reduce voltage fluctuations, eliminate temperature ripples, reduce inrush current, and reduce flicker.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating an example of a fixing device according to the present invention.

FIG. 2 is a diagram illustrating a heater control method according to the present invention.

FIG. 3 is a diagram illustrating warm-up according to the present invention.

FIG. 4 is a diagram illustrating the OFF time dependency of an inrush current.

FIG. 5 is a diagram illustrating a cause of flicker generation due to heater driving.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Heating roller 1, 2 ... HR heater, 3 ... HR thermistor, 4 ... Belt, 5 ... BB thermistor, 6 ... Fixing roller, 7 ... Pressure roller, 8 ... PR heater, 9 ... PR thermistor, 11 ... Paper.

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Keiichi Taguchi 3-3-5 Yamato, Suwa-shi, Nagano F-term in Seiko Epson Corporation (reference) 2H033 AA21 AA41 BA30 BB17 CA07 CA23 CA27 CA46 CA48 3K058 AA04 AA30 AA46 AA53 BA18 CA16 CA23 CB02 CB14 CB19 CE23 DA02 GA06

Claims (7)

[Claims] In a fixing device having a plurality of heaters, ON / OFF control of the plurality of heaters is independently performed, and control is made different depending on whether the sum of duty ratios of the respective heaters is equal to or less than 100% or more. A heater control method for a fixing device, characterized in that the method is as described above. 2. The sum of the duty ratio of each heater is 100%.
2. The heater control method according to claim 1, wherein the lighting times of the heaters do not overlap and the heaters are continuously turned on in the following cases. 3. The sum of the duty ratio of each heater is 100%
2. The heater control method according to claim 1, wherein when it is larger than the predetermined time, the lighting start timing of each heater is shifted by a predetermined time. 4. The heater control method according to claim 3, wherein the predetermined time for shifting the lighting start timing is changed according to the heater temperature. 5. A heater control method for a fixing device, wherein a heater OFF time is within a predetermined time in a fixing device that controls a temperature by turning on / off a heater. 6. The heater control method according to claim 5, wherein the heater is a halogen lamp, and the predetermined time is 400 ms. 7. The heater control method according to claim 5, wherein the control cycle is changed according to the duty ratio.