JPH1195611A - Method for controlling fixing heater and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for controlling a fixing heater and an image forming device adopting the same, capable of reducing a drastic current change caused by the fixing heater, without depending on the phase control. SOLUTION: Right after the start of applying an AC power source voltage when the heater temp. falls to fellow a target temp., in order to reduce the heater current, by regarding 3 halfwave lengths as a period of the AC power source voltage applied to the fixing heater, the thinning number is decreased from a large number to a small one. When the device is provided with two heaters, the same method is successively applied to each of the heater (states a, b, c and d). Subsequently, application of voltage is performed with the thinning number 0. At this time too, by regarding the successive 3 halfwave lengths as one period, power is applied to a first heater by thinning the waveform of one halfwave length or two halfwave lengths out of 3 halfwave lengths for one period, while the power having the waveform of only halfwave lengths which are used for thinning the first heater is applied to a second heater, which is a state (f) of applying a first energizing pattern. The state (f) and the state (e) of energizing only one of the heaters (or state of reversing the relation between both heaters in the state (f)) are alternately repeated, until the heater temp. reaches the desired temp.

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 an electrostatic copying machine or a printer, and more particularly to a heater control for reducing a fluctuation of a current including an inrush current due to ON / OFF of a fixing heater. It is about the method.

[0002]

2. Description of the Related Art Conventionally, a halogen lamp which consumes a relatively large amount of current is used in this type of fixing heater, and when the lamp is turned on, a very large inrush current is generated. Especially,
Due to the characteristics of the halogen heater, when the temperature of the halogen heater itself is high, its resistance is large, and when it is low, the resistance is small. Usually, when the heater temperature becomes lower than a predetermined temperature, the halogen heater is turned on, so that a large inrush current flows immediately after lighting.

FIG. 5 is a diagram for explaining voltage fluctuation. Typically,
When the power supply is viewed from the power outlet side, a relatively small power supply impedance (Rs) 7 exists. For this reason, when the current consumption I of the device connected to the power supply (here, the copying machine) changes greatly and suddenly, the power supply voltage V fluctuates. Then, the rapid power fluctuation can be evaluated as ΔV = Rs × ΔI. For example, if the lighting equipment 9 is connected to this outlet line, a sudden voltage change appears as flickering of the lighting.

[0004]

The object of the present invention will now be described with reference to a specific configuration of the fixing device.

FIG. 1 is a schematic view of a fixing device to which the present invention is applied, where 1 represents a heater roller and 2 represents a pressure roller. By passing the paper 3 on which the toner image has been developed between the rollers 1 and 2, the toner image can be thermally fused onto the paper 3. In the heater roller 1, a main heater 4 and a sub-heater 5 are mounted in the form shown.

That is, as shown in FIG. 2, the heat generation intensity distribution of the main heater 4 has a peak near the center (FIG. 2).
A) On the other hand, the sub-heater 5 has peaks at both ends (FIG. 2B). By turning on these two heaters alternately and adjusting the lighting time of each heater, the temperature distribution on the roller surface is made uniform (FIG. 2C).

FIG. 3 shows a waveform of a current flowing through the heater at the time of standby, in which P1 is a portion where a large current change occurs. As described above with reference to FIG. 5, this change in current has caused a voltage change in the power supply itself, and has caused adverse effects such as flickering of lighting and the like connected to the same power supply. In recent years, there has been a growing social demand to reduce voltage fluctuations due to current changes in such devices.

The present invention provides a method for reducing a sudden current change caused by a halogen heater used in a fixing device of an image forming apparatus.
This is to alleviate the following rapid current change portions shown in the above.

1. Inrush current section of halogen heater (FIG. 3)
(P1, P2 section in FIG. 3) Current fluctuation section when heaters are alternately switched in a fixing device having two or two heaters (P3, P4 in FIG. 3) In order to solve such a problem, FIG. It is possible to energize the heater by the phase control as shown in FIG. Heater ON
In order to prevent a sudden voltage fluctuation such as when an inrush current occurs immediately afterward, the effective magnitude of the voltage may be gradually increased. For example, the waveform shown in the energization waveform to the main heater 4 in FIG. First, the energizing time within one half-wave is defined as tm1, tm
It should be expanded gradually to 2, tm3, ..., tmc.
Similarly, for the sub-heater 5, ts1, ts2, ts3,.
tsc. Among them, tmc corresponding to the steady-state conduction phase angle of the main heater 4 and tsc of the sub-heater 5 are constant values.

Returning to this switching waveform in FIG. 3, the power supplied to the main heater 4 in this case is Tm
Since / T and the sub-heater have a ratio of Ts / T, it is possible to adjust tmc and tsc according to this value.

With such a configuration, in fact, it is also possible to make a near-ideal gentle current change. But,
This method also has the following disadvantages.

1. The hardware such as a timer mechanism for determining the phase angle (that is, the time such as tmc and tsc) is complicated, and the control complexity such as setting and activation is also required. It is expected to be similarly high.

2. Regions with different power supply frequencies (50 Hz,
(60 Hz regional difference), it is necessary to make different settings for each, and the management of the separation becomes complicated.

As is clear from FIG. 4 and FIG. 4, the power supply to the heater is not at the zero crossing starting point but at the middle of the half wavelength.
Since it is N, a problem of generation of a harmonic current is produced. This harmonic current is higher than the power supply frequency (several times
(Several tens of times), which may interfere with other devices connected through the power supply line as noise, causing malfunction and failure. Therefore, in the case of phase control, it is necessary to take measures such as inserting a large-capacity choke coil separately in order to reduce the power supply harmonic current.

The present invention has been made in view of the above problems, and proposes a method that can overcome the problems. That is, the present invention provides a fixing heater control method capable of reducing a sudden current change caused by the fixing heater without using phase control, and an image forming apparatus employing the same.

[0016]

A method for controlling a fixing heater according to the present invention is characterized in that at least three consecutive half-wavelengths of an AC power supply voltage applied to the fixing heater are cycled, and one or more half-wavelengths of the waveform are provided. Adopt control to thin out
Immediately after the start of the application of the AC power supply voltage to the fixing heater, a thinning waveform by the thinning control is applied to the fixing heater, and then a transition to application of a waveform without thinning is performed.

This makes it possible to prevent the occurrence of an inrush current immediately after the start of application of the AC power supply voltage to the fixing heater. Further, since the heater current is applied from the zero-cross starting point regardless of the phase control, generation of power supply harmonics on the power supply line can be almost eliminated, and the control hardware can be relatively simplified.

More specifically, immediately after the start of the application of the AC power supply voltage with a period of three half wavelengths, application of a plurality of periods is performed as the thinning number 2, and thereafter, the process proceeds to the application of the zero number.

According to another aspect, in the method of the present invention, the decimation number is changed from large to small immediately after the start of the application of the AC power supply voltage, and then the decimation number is reduced to zero.

For example, immediately after the start of the application of the AC power supply voltage with a period of three half wavelengths, application of a plurality of periods is performed as a decimation number 2, then application of a plurality of periods is performed with a decimation number of 1, and thereafter, The process proceeds to the application of the decimation number 0.

When the fixing heater is composed of a first heater and a second heater, when the first heater and the second heater are energized alternately, a cycle of three consecutive half wavelengths is used. The first heater is energized by thinning out a waveform of one half wavelength or two half wavelengths out of three half wavelengths in one cycle, and the second heater is energized by only the half wavelength thinned out by the first heater. Apply a waveform.

In this case, for example, the first energizing pattern for the first and second heaters and the second energizing pattern in which the relationship between the first and second heaters is reversed are alternately switched. .

More specifically, 2Ns-control is equivalent to control in which Nm half-wavelength continuous application to the first heater and Ns half-wavelength continuous application to the second heater are alternately repeated. The first and second heaters are energized by the first energization pattern for Nm half wavelengths, and then the first and second energization are performed by the second energization pattern by 2Nm-Ns half wavelengths. The energization of the heater is alternately repeated.

As another method, a method of alternately switching between the above-described first energizing pattern to the first and second heaters and energizing only one of the first and second heaters with a decimation number of 0 is used. Conceivable.

An image forming apparatus according to the present invention is an image forming apparatus having a fixing device for fixing a toner image on a sheet, wherein first and second heaters as fixing heaters of the fixing device are provided. First and second switching means for independently controlling the application of the AC power supply voltage to the second and second heaters, and first and second switching means for controlling the switching of the first and second switching means. Temperature detecting means for detecting a heater temperature of the fixing heater, zero-cross detecting means for detecting a zero-crossing point of the AC power supply voltage, and when the temperature detected by the temperature detecting means falls below a predetermined temperature, Each time a zero cross is detected by the zero cross detection means,
Determining whether to apply the power supply voltage in half-wavelength units to the first and second heaters in a predetermined procedure,
Control means for controlling the first and second switching means based on the determination result.

In this image forming apparatus, preferably,
The first heater and the second heater have different heat intensity distributions.

[0027]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below in detail.

The schematic configuration of the fixing device to which the present invention is applied is as described above with reference to FIGS. That is, the two heaters of the main heater 4 and the sub-heater 5 as the fixing heaters are turned on in principle alternately, and the lighting time of each heater is adjusted, so that the temperature distribution on the surface of the heater roller is made uniform.

Although the energizing pattern for both heaters shown in FIG. 3 is not according to the present invention, the significance of using two heaters using this energizing pattern will be briefly described.

At the time of standby without paper passing, as shown in FIG. 3, the energization of the main heater 4 is shorter than that of the sub-heater 5, and both heaters are turned on alternately. In addition, when the paper is passed, if the paper is of a small size, the latent heat near the center of the heater roller is taken away, so that the lighting time of the main heater 4 is lengthened. In this way, the alternate lighting time is switched for each mode such as a standby mode and a copying mode so that the heat distribution on the heater roller is made uniform. That is, unnecessary temperature rise (parts close to both sides) is prevented, and damage due to excessive temperature rise of the bearing at the end of the heater roller and the drive gear portion is prevented.

In the present embodiment, it is intended to obtain a result equivalent to the heat control of the two heaters while suppressing a rapid change in the average current.

FIG. 6 shows an example of "wave number control" according to the present invention. This is performed for the inrush current portion of the halogen heater. The inrush current portion is a rising portion immediately after the heater is turned on, and it is preferable that the current gradually increases on average. Therefore, in this example, the main heater is turned on.
, First, as shown in the period a, the half-wavelength is energized once every three half-cycles (this is called “１ ／ half-wave”).
). Next, as shown in period b, 2 in 3 half cycles
A half-wave period is energized periodically (this is called “２ half-wave”). Subsequently, the main heater may be energized for the required period for the entire period (this is referred to as “entire period”, not shown). After that, the main heater 4 is turned off, and the energization of only the sub-heater 5 is continued. Similarly, first, a period c of 1/3 half-wave, a period d of 2/3 half-wave, and thereafter, no thinning is performed. This is the period e of the entire cycle.

In other words, this means that the average current is switched stepwise (in this case, three steps) from the smaller one to the larger one at the time of rising, and finally the whole cycle is shifted. In other words, since the inrush current is the largest at the beginning of the startup, the inrush current is reduced by subtracting two half wavelengths out of the three half wavelength periods (period a or period c), and then the heater wire is slightly warmed up. For this reason, one half wavelength of the three half wavelength periods is subtracted (period b or period d). Finally, the application is switched to the application of all the cycles of the decimation number 0.

Here, the reason why it is preferable to perform the wave number thinning based on the three half-wave periods will be described. For example, if two half wavelengths (one normal cycle) are used as a reference, if one half wavelength is subtracted from this, the DC component becomes the same as the half-wave rectified waveform. This results in DC lighting, and such driving is not recommended for the halogen heater. In addition, thinning out at a cycle longer than the three-half wavelength cycle is more likely to be perceived as flickering by the human eye due to the nature of flickering of lighting and the like. Therefore, it is most appropriate to consider the shortest cycle other than the two-half wavelength, that is, the three-half wavelength cycle. In fact, in the thinning of the three half-wave periods, when flickering was actually observed with the illumination connected, almost no flickering was felt experimentally.

However, the effect of the thinning out in the cycle longer than the three-half wavelength cycle can be recognized as compared with the conventional technique, so that the present invention does not exclude this as will be described later.

Next, when the two halogen heaters are switched,
That is, the current change that occurs when switching from one of the main heater 4 and the sub-heater 5 to the other (P3, P3 in FIG. 3)
Part 4) will be described.

Conventionally, two heaters are periodically switched.
As shown in FIG. 3, one cycle is performed at a relatively large period (about several hundred mSec to several Sec). In the present invention, this switching is performed with the idea of making the switching as fast as possible.

FIG. 7 shows a switching method in this embodiment. First, as shown in a state M1, control is performed such that the main heater 4 is energized by a half wavelength, and the subsequent two half wavelengths are energized only by the sub-heater 5 as shown in a state S2. As shown in the state M1 + S2, the combined current thus obtained has a form in which the current fluctuation due to the switching of the two heaters is finely resolved every three half-wave periods. Since the power supply voltage fluctuation due to the fluctuation of the three-half wavelength cycle occurs at a minute time interval, it is practically not perceived as a flicker of illumination or the like.
In fact, if such a concept is applied, the switching of the two heaters is conventionally performed as shown in FIG.
After applying Nm continuous half-waves (M3) to the
Is performed by repeating the application of Ns continuous half-waves (S3), the heater switching every three half-wave periods equivalent to this is performed by the three half-wavelengths of the main heater 4 as shown in FIG. 7 is a pattern in which energization for one half wavelength (state M1 in FIG. 7) and energization for two half wavelengths within three half wavelengths of the sub-heater (state S2 in FIG. 7), that is, the state M1 + S2 in FIG. It becomes an energization pattern. This energization pattern is 2Ns-
Nm half wavelengths (part A in FIG. 9) continue.

Next, the main heater 4 is energized for two half-waves (M2 state in FIG. 7), and the sub-heater 5 is energized for one-half wavelength (FIG.
7), that is, M2 in FIG.
In the energization pattern shown in the + S1 state, application of 2Nm-Ns half wavelengths (part B in FIG. 9) is performed. Such repetition of the portions A and B in FIG. 9 is equivalent to the conventional switching pattern (FIG. 8). The reason is that (1) When A and B in FIG. 9 are regarded as one cycle, the repetition cycle is Nm + Ns half wavelengths, which is the same as that of the conventional pattern (FIG. 8).

(2) The main heater 4 in the portions A and B in FIG.
Is Nm, and that of the sub-heater 5 is Ns.
It is the same as the energized half-wave number within one cycle of the conventional pattern.

(3) From (1) and (2), the amount of heat generated by each heater is clearly equal in each cycle as compared with the conventional pattern application.

Further, considering that the variation within three half-wavelength periods inside A and B in FIG. 9 does not matter, the average current difference between the portions A and B in FIG. It becomes a problem. However, when this amount is evaluated, the average current in the portion A is (1/3) Im + (2/3) Is, and the average current in the portion B is (2/3) Im + (1/1). 3) It becomes Is. Therefore, the difference between the A and B portions is ((1/3) Im + (2/3) Is)-((2/3) Im + (1 /
3) Is) = (1/3) (Is-Im), which indicates that it is 1/3 that of the conventional case. (Here, Im is a steady-state current value when the entire period is applied to the main heater 4, and Is is that of the sub-heater.) Consider the above special case where 2Nm ≦ Ns. In this case, the half wave number of the portion B in FIG. 9 becomes negative.
Therefore, as shown in FIG. 10, the sub-heater 5 is applied in the S2 state for 3Nm half wavelength, the main heater 4 is applied with the waveform applied in the M1 state, and then the S3 state of only the sub-heater 5 is changed to (Ns-2Nm) half wave. Apply. Even in this case, the repetition period is T = Nm + Ns (the number of half waves)
The half-wave number applied to the main heater 4 within the period T is Nm, and the half-wave number applied to the sub-heater is Ns, which is the same as in the conventional switching. Further, the average current difference between the A 'and B' portions in FIG. 10 is ((1/3) Im + (2/3) Is) -Is = (1/3) (Im-
Is), which is １ ／ of the conventional case (FIG. 8).

The same applies to the case of 2Ns ≦ Nm.
That is, although not shown, the portion A ′ in FIG.
The 2 state and the B ′ part are considered to be the M3 state. In this case, the half-wave number of the part A 'is set to 3Ns, and the half-wave number of the part B' is set to Nm-2.
Ns. In this case, the difference in the average current between the A 'and B' parts is ((1/3) Is + (2/3) Im) -Im =-(1 /
3) (Im-Is), and the sign is inverted, but it can be seen that the absolute value of the current difference is still 1/3 of the conventional case.

In short, according to the present embodiment, in the period of three half wavelengths, the waveform is thinned when the heater is started, so that the average current is started from a low state. When the main heater 4 and the sub-heater 5 are switched at a rate of one half-wave and the following two half-waves (1 cycle) within the cycle of the power supply, the power supply fluctuation frequency caused by the current difference between the two heaters increases, and as a result, It can be said that it utilizes the fact that the flicker of lighting or the like connected to the power supply is not felt by human eyes.

FIG. 11 is a circuit diagram for realizing the "wave number control" described above.

In this figure, TH is a temperature sensor (FIG. 1) such as a thermistor for detecting the temperature of the heater roller (1 in FIG. 1).
6>, which is connected to the resistor R1, and the divided potential is input to the analog input terminal A / D in the CPU. The signal given to the A / D terminal is converted from analog to digital and processed in the CPU. CPU INT
A zero cross pulse (see FIG. 13) corresponding to a zero cross point of the AC power supply voltage is input to the input terminal. This zero-cross pulse is generated by the photocoupler PC1 and the comparator COM based on the AC voltage input of the power supply.

In response to the falling of the zero cross pulse, C
An interrupt routine (described later) inside the PU is started, and immediately after the zero-cross signal falls, signals OUT1 and OUT2 for turning on the main heater 4 and the sub-heater 5, respectively, are output at a predetermined timing.

For example, when the OUT1 output is at the H level, the transistor TR1 is turned off, and the light emitting side of the phototriac PT1 is turned off. Since the light-receiving side phototriac of PT1 is also OFF, the gate current of TRIAC T1 does not flow, so TRIAC T1 is OFF.
The main heater 4 is turned off. In the present embodiment, the transistor TR1, the phototriac PT1, and the triac T1 constitute "switching means".

On the other hand, when OUT1 is at the L level, the operation is the reverse of the above, the transistor TR1 is turned on, the light emitting diode of the phototriac PT1 is turned on, and the light receiving phototriac is turned on. The gate of the triac T1 is supplied with the gate current limited by the resistor R2 or R4 because the light receiving side of the PT1 is conductive. Accordingly, the triac T1 becomes conductive and the main heater 4
Lights up.

The connection between the resistor R6 and the capacitor C1 connected in parallel to the triac T1 is a so-called snubber circuit, and when there is a sudden change in the power supply voltage due to the influence of external noise or the like, the triac T1 turns on independently. (The same applies to the resistor R7 and the capacitor C2).

The flow of the OUT2 output for controlling the lighting of the sub-heater 5 is the same as described above.

An example of the control performed by the above-described circuit will be described. Here, the two energization patterns at the time of switching between the main heater 4 and the sub-heater 5 correspond to the states A ′ and B ′ in FIG. 10, but depending on the application target and the like, as shown in FIG. Another combination of energization patterns can be used.

As shown in FIG. 12, the CPUA in FIG.
When the / D input value, that is, the signal corresponding to the temperature of the heater roller 1 is higher than the target temperature (when the roller temperature is high), the main heater 4 and the sub heater 5
Both are OFF. On the other hand, when it falls below, as shown in FIG. 12, the states a → b → c → d → e to f → e → f →
By repeating step e, heater lighting control is performed until the roller temperature exceeds the target temperature value. State a in this state is, as described above, a state in which the main heater 4 shown in FIG. 7 is energized by M1 (one half wavelength out of three half wavelengths) and the sub heater 5 is off. In state b, the main heater 4 is energized for M2 (S2 in FIG. 7).
(2 waveforms), the sub-heater 5 is OFF. In state c, the main heater is OFF and the sub-heater 5 is S1. State d
Indicates that the main heater 4 is OFF and the sub heater 5 is S2.

As described above, in the states a, b, c, and d, the current change of each heater with respect to the rush current is reduced. Since this is the same as the content shown in FIG. 6, it is as described above. As for the subsequent repetition of the states e and f, in the state e, the main heater 4 is OFF and the sub-heater 5 is ON for the entire cycle (S3). In state f, the main heater 4 is Ml energized and the sub-heater 5 is combined energization of S2. This pattern is the same as the pattern shown in FIG. 7, and has also been described above. In short, this consists of a main heater 4 and a sub heater 5
This is an operation for reducing a change in the switching current that occurs at the time of switching.

FIG. 14 is a flowchart showing an example of a software procedure for implementing the above control.

Interrupt input I to CPU (FIG. 11)
It has already been described that the zero cross pulse shown in FIG. 13 is given to NT. Due to the fall of the zero cross pulse, an interrupt operation is applied to the processing in the CPU, and the procedure shown in the flow of FIG. 14 is executed.

First, when the A / D input value is higher than the target temperature, the process proceeds to the N side in decision S141, and the respective initial values 0 are set in the counters a, b, c, d, e and f. Is performed (S142). Further, OUT1 and OUT2 are each set to 1 (S143), whereby both the main heater 4 and the sub-heater 5 are turned off. The counters a, b, c, d, e, and f are the counters that determine the duration of each of the states a, b, c, d, e, and f when the heater is ON as shown in FIG. number,
That is, it is managed by the number of power supply half waves.

The processing when the roller temperature is higher than the target has been described above. If the A / D input value indicates a value lower (lower temperature) than the target temperature, the flow S141 is executed every time an interrupt is issued. This time, the process flows to the Y side. At that time, 1 is added to the thinning counter TO (S144). This thinning counter TO is 0
Each time the interrupt passes through this part of the flow in the order of → 1 → 2 → 0 → 1 → 2, the state advances by one and continues to cycle through the three states. When the counter value becomes 3 in the judgment S145, the initial value is reset to 0 (S146). This counter TO serves as an instruction pointer indicating which half wavelength of the three half wavelengths indicates the half wavelength in the subsequent processing.

In the judgment S147, the state of the a counter is checked, and if the predetermined value A is not reached, that is, if the state is the state a in FIG. It is raised (S138). Here, the specified value A is the number of half waves in the state a (the same applies to other specified values described later). Next, in step S149, the value of the thinning counter TO is confirmed. If this value is 0, the main heater 4 is turned on (S150). If the value is other than 1 or 2, the main heater 4 and the sub heater 5 are turned on.
Both are turned off (S151).

When the heater temperature is lower than the target temperature and the falling edge of the zero-cross pulse is input to the INT input, the thinning counter TO goes round (0 → l → 2 → 0 →).
...), And if the a-counter does not reach the specified value A, it passes through the determination unit S149 each time, and the main heater 4 is periodically turned on for only one half wave to three half waves. . It can be said that the determination unit S149 creates the energized state M1 shown in FIG. a counter is the specified value A
Is reached, the state a shown in FIG.
Move to That is, the state of the b counter is confirmed in S152 in the flow, and if the value does not reach the specified value B, N
The processing proceeds to the side and the b counter is counted up by 1 (S1
53), in decision S154, the value of the thinning counter TO becomes 0
Or, the main heater 4 is turned ON only when the value is 1 (S1
55, S156). This corresponds to the energized state M2 shown in FIG.
It can be said that is realized.

As described above, similarly, the judging section S157 checks whether or not the state is the state c in FIG.
At 58, the c counter is incremented by one, and the thinning counter TO is viewed (S159). When the thinning counter TO is 0, only the sub-heater 5 is turned on to realize the S1 state (in FIG. 7) (S160, S161). Then, the next judgment S16
In step 2, the d state is determined, and after the d counter is counted up by one (S163), only the sub heater 5 is set to the S2 state in determination S164 (S165, S166). Further, in the next determination S167, the e state is determined, and after the e counter is counted up by one (S168), only the sub heater 5 is set to the S3 state (S169).

Thus, the states a, b, c, d, and e in FIG. 12 are completed. That is, a series of the rising portion sequence shown in FIG. 6 has been completed.

In the next determination step S170, it is determined whether or not the state is f in FIG. While the f-counter does not reach the specified value F, the process proceeds to the N side, the f-counter is counted up by 1 (S171), and the thinning-out counter TO is checked in the judgment S172. 4
ON only (S174), otherwise, the sub-heater 5
Only ON is performed (S173). As a result, the state M1 in which the state of the main heater M1 and the state of the sub-heater S2 are combined.
+ S2 (see FIG. 7).

When the f-counter has reached the specified value F, the process proceeds to the Y side in a judgment S170, and the initial value 0 is reset in the e-counter and the f-counter. As a result, in the next INT interrupt, the arrival of the specified value of the e-counter in the determination S167 is released, so the e-state is again performed, that is, the sub-heater 5 is turned ON (S3 state), and f → e → f → These two states are repeated.

It has been shown that the lighting state of the heater shown in FIG. 12 can be realized in this way.

The a to f counters are different from the above,
After setting these specified values A, B, C, D, E, and F as initial values, it is also possible to check whether or not each counter value has reached 0 by decreasing the number.

According to the above embodiment, the following special effects can be obtained.

(1) The control hardware is relatively simple. For example, as a means for suppressing the heater current, a phase control method is generally mentioned as described above. In this case, a timer is set from the zero-cross point of the power supply voltage to turn on the heater by a phase angle (half-wavelength). It is necessary to generate a pulse which specifies a time interval that is sufficiently shorter than the time interval. These have the disadvantage that the control itself is complicated and hardware such as a timer mechanism must be prepared.
In the case of “wave number control” as in the present invention, the heater is only turned on at the zero-cross starting point, and therefore, a timer for determining the phase is not required. In addition, the complexity of the control such as setting, starting, and the like is reduced accordingly.

(2) Another advantage when compared with the phase control is that in the case of the “wave number control”, since the heater current is applied from the zero-cross starting point, the current change at a higher frequency of the power supply frequency on the power supply line. That is, there is almost no generation of so-called power supply harmonics. Usually, it is necessary to insert a large-capacity inductance (choke coil) in series with the heater in order to suppress the generation of such power supply harmonics, but this increases the cost due to the addition of extra electric components. In addition, the demand for securing the installation location hindered the downsizing of the machine.

Although the typical example relating to “wave number control” of the present invention has been described above, the following modifications are also conceivable.

FIG. 6 shows an example for reducing the inrush current. For example, even if there is no state b or d in this, even if the transition is from one-third half-wave to a full-period waveform, there is still a certain effect in the sense of reducing the magnitude of the current fluctuation.
Similarly, the same is true when there is no state a or c and only state b or d.

In short, all the combinations that can reduce the average current value and reduce the magnitude of the inrush current by subtracting one or two half wavelengths from the cycle of three half wavelengths at the time of the start-up are described. The invention includes.

FIG. 9 shows a main heater 4 and a sub-heater 5.
In the above, an example of the case of alternate lighting, so-called flickering lighting, is shown, but this is also a form using a waveform obtained by thinning one or two half wavelengths out of a cycle of three half wavelengths. The present invention is within the scope of the present invention as long as it reduces the switching current difference due to the conventional full-cycle application among all possible combinations of the main heater 4.

For example, in the above description, the case where mainly the three-half wavelength is used as a reference has been described. However, as shown in FIG. 15, the four-half wavelength cycle, the five-half wavelength cycle, the seven-half wavelength cycle,
Wave number control as shown in FIGS. 6 and 7 is also possible for each of the 11 half-wave periods and the like.

Further, even when only a single heater is used, the control for gradually increasing the wave number as shown in FIG. 6 is effective.

[0076]

According to the present invention, abrupt current change due to the halogen heater can be reduced irrespective of the phase control, so that control hardware can be relatively simplified. Further, since the heater current is applied from the zero-cross starting point, generation of power supply harmonics on the power supply line can be almost eliminated.

[0077]

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a fixing device to which the present invention is applied.

2 is a graph showing a heat intensity distribution of a main heater and a sub heater of the fixing device of FIG. 1;

FIG. 3 is a timing chart showing an example of an energized state of a main heater and a sub-heater of the fixing device of FIG.

FIG. 4 is a timing chart for explaining energization of a heater by phase control.

FIG. 5 is a circuit diagram for explaining a voltage fluctuation caused by electric current of a device.

FIG. 6 is a current waveform diagram illustrating an example of wave number control at the time of starting a heater according to the embodiment of the present invention.

FIG. 7 is a current waveform diagram showing an energization pattern used when switching between a main heater and a sub heater in the embodiment of the present invention.

FIG. 8 is an explanatory diagram showing a conventional method of switching between a main heater and a sub heater.

FIG. 9 is an explanatory diagram showing the energized state of the main heater and the sub-heater in the embodiment of the present invention equivalent to FIG.

FIG. 10 is an explanatory diagram showing a modification of the energized state of the main heater and the sub-heater of FIG. 9;

FIG. 11 is a circuit diagram showing a circuit for realizing an energized state of a main heater and a sub-heater in the embodiment of the present invention.

FIG. 12 is an explanatory diagram of an actual example of control performed by the circuit of FIG. 11;

13 is an explanatory diagram of a zero-cross pulse of a power supply voltage detected by the circuit of FIG.

FIG. 14 is a flowchart illustrating an example of an interrupt process executed by the CPU of FIG. 11;

FIG. 15 is a waveform chart showing a modification of the embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Heater roller, 2 ... Pressure roller, 3 ... Paper, 4 ... Main heater, 5 ... Sub heater, 6 ... Temperature sensor.

Claims (10)

[Claims] 1. A method in which at least three consecutive half-wavelengths of an AC power supply voltage applied to a fixing heater are used as a cycle.
Or, a control for thinning out waveforms for a plurality of half wavelengths is employed. Immediately after the start of application of the AC power supply voltage to the fixing heater, a thinning waveform by the thinning control is applied to the fixing heater, and then a waveform without thinning is applied. A control method for the fixing heater, characterized by shifting to the application of the fixing heater. 2. The method according to claim 1, wherein a cycle of three half wavelengths is set immediately after the start of application of the AC power supply voltage.
A method of controlling a fixing heater in which a plurality of cycles are applied as the thinning number 2 and then the process shifts to the application of the thinning number 0. 3. The method according to claim 1, wherein the number of thinnings is changed from large to small immediately after the start of application of the AC power supply voltage, and then the number of thinnings is reduced to zero. 4. The method according to claim 3, wherein a period corresponding to three half wavelengths is set immediately after the start of the application of the AC power supply voltage.
A method of controlling a fixing heater in which a plurality of cycles are applied as a thinning number 2, then a plurality of cycles are applied with a thinning number of 1, and the process proceeds to the application of a thinning number 0. 5. The method according to claim 1, wherein the fixing heater includes a first heater and a second heater, and the first heater and the second heater are energized alternately. In this case, the first heater is energized by thinning out a waveform of one half wavelength or two and a half wavelengths out of three half wavelengths of one cycle, with a period of three consecutive half wavelengths. A fixing heater control method for applying a waveform corresponding to only a half wavelength thinned out by the first heater. 6. The method according to claim 5, wherein the method comprises:
3. A fixing heater control method for alternately switching between a first energizing pattern to the first and second heaters and a second energizing pattern in which the relationship between the first and second heaters is reversed. 7. The method according to claim 6, wherein Nm half-wavelength continuous application to the first heater and Ns half-wavelength continuous application to the second heater are alternately repeated. Control equivalent to 2Ns-Nm half wavelengths,
The first and second heaters are energized in the first energization pattern, and then the second and the second heaters are half-wavelength of 2Nm-Ns.
A method of controlling the fixing heater, wherein the energization of the first and second heaters is alternately repeated with the energization pattern of (1). 8. The method according to claim 5, wherein the method comprises:
A fixing heater control method for alternately switching between a first energization pattern to the first and second heaters and an energization of only one of the first and second heaters with a decimation number of 0. 9. An image forming apparatus having a fixing device for fixing a toner image on a sheet, comprising: a first heater and a second heater as fixing heaters of the fixing device; First and second switching means for independently controlling the application of an AC power supply voltage, first and second switching means for controlling the switching of the first and second switching means, and a heater for the fixing heater Temperature detection means for detecting a temperature, zero-cross detection means for detecting a zero-cross point of the AC power supply voltage, and, when the temperature detected by the temperature detection means falls below a predetermined temperature, zero-crossing by the zero-cross detection means. The application of the power supply voltage in half-wavelength units to the first and second heaters sequentially in a predetermined procedure. Determined, the image forming apparatus characterized by comprising a control means for controlling said first and second switching means based on the determination result. 10. The image forming apparatus according to claim 9, wherein
An image forming apparatus, wherein the first heater and the second heater have different heat intensity distributions.