JP2002050450A - Heater control method and image forming apparatus - Google Patents

Abstract

(57) [Problem] To provide finer temperature control during temperature adjustment and reduce current fluctuation (flicker value) by multi-value control different from binary control. A temperature of a heating target of a heater is set to three threshold values T.
It is divided into four temperature ranges divided by a, tb, and tc. On the other hand, an energization pattern having a period of three consecutive half-waves of the AC power supply voltage, a first energization pattern without half-wave thinning, a second energization pattern with half-wave thinning,
A third energization pattern for thinning out half-waves and a fourth energization pattern without energization are prepared, and these are respectively assigned to the four temperature ranges from the lower temperature side. During the control of the heater temperature adjustment, the temperature of the heater to be heated is sequentially detected, and it is determined which of the four temperature ranges the detected temperature belongs to. The heater is controlled by an energization pattern corresponding to the temperature range to which the heater belongs.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heater control for a fixing device incorporated in an image forming apparatus such as an electrostatic copying machine or a printer, and more particularly, to a rapid control when a heater is energized for temperature adjustment. The present invention relates to a heater control method and an image forming apparatus capable of reducing current fluctuation.

[0002]

2. Description of the Related Art Conventionally, a halogen lamp which consumes a relatively large amount of current has been used for this type of heater.
At the time of N, a large current fluctuation such as an inrush current occurs.

FIG. 1 is a schematic view of a fixing roller. The fixing roller has a heater roller 1 having a built-in heater 4 and a pressure roller 2 pressed against the heater roller 1. The toner image developed on the paper 3 is thermally fused onto the paper 3 by passing the paper 3 between the rollers 1 and 2.

FIG. 2 shows a heater current waveform during conventional ON / OFF control for adjusting the temperature of the heater roller 1. In this waveform, the P1 and P2 portions indicate the OF of the heater.
This is an abrupt current change portion corresponding to the switching point between the F state and the ON state. This current fluctuation has caused a voltage fluctuation of the power supply itself, and has caused flickering of lighting and the like connected to the same power supply. That is, as shown in FIG. 4, generally, when the power supply AC is viewed from the outside of the power outlet, the power supply impedance R is relatively small.
s exists. For this reason, when the current consumption of the device (here, the copying machine) D connected to the power supply AC changes greatly and suddenly, the power supply voltage fluctuates due to the voltage drop due to the power supply impedance Rs. Abrupt current change ΔI
Then, the rapid power supply voltage variation ΔV is expressed by the following equation.

ΔV = Rs × ΔI For example, if a lighting fixture L is connected to this outlet line, a sudden fluctuation in power supply voltage appears as flickering of lighting. In recent years, there has been an increasing demand for reducing power supply voltage fluctuations caused by rapid current changes in such devices.

[0006]

In order to prevent such flickering of the lighting equipment, it is necessary to make the current change gentle. That is, it is necessary to reduce an abrupt current change caused by a halogen heater used in a fixing device such as a copying machine. (This is also referred to as “reduction of flicker value” in the present specification.) Specifically, a rapid current change in P1 portion when the halogen heater energizing current is ON and P2 portion when OFF shown in FIG. It is necessary to relax the part.

A method for solving this problem is shown in FIG.
This is the energization of the heater by the phase control (conduction angle control) as shown in FIG. As described above, in order to prevent a sudden current change such as when an inrush current occurs immediately after the heater is turned on, the applied voltage may be gradually increased effectively. First, the energizing time within each half-wave of the AC power supply voltage is initially reduced and gradually increased (t1, t2, t3,... T).
n).

This method is well known, and it is possible to make a gentle current change which is almost ideal. However, the method also has the following disadvantages. 1. The hardware such as a timer mechanism for determining the phase angle is complicated, and the control complexity such as setting and activation of the hardware is considered to be similarly high. 2. Separate settings are required for regions with different power supply frequencies (regional difference between 50 Hz and 60 Hz), and there is complexity in the separation management. 3. As is clear from FIG. 3, the current to the heater is not turned on at the zero crossing start point but is turned on within a half wavelength, so that the harmonic current increases. This current is generated by a high-order wave (several times to several tens times) of the power supply frequency. This can interfere with other equipment connected through the power line as noise,
It may cause malfunction or 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 harmonic current.

[0009] Other than the method based on the phase control, Japanese Patent Application Laid-Open
No. 80961 discloses ON timing and OFF of a heater.
A technique is disclosed in which power is supplied to a heater so as to perform zero-cross lighting in an AC discontinuous pattern in which power is smaller than a rated energizing power by AC continuous lighting for at least a predetermined time from the ON timing of the timing. Japanese Patent Application Laid-Open No. H11-95611 discloses a technique of zero-cross lighting in a fixing device having two heaters. As a result, the rush current when the heater is turned on can be reduced, and the occurrence of noise can be reduced.

Usually, in the fixing device, continuous temperature adjustment is performed to maintain the temperature of the heater roller at a predetermined temperature. The predetermined temperature may vary depending on the operation mode such as copying or standby, but in any case, the heater is turned on / off by comparing the temperature of the heater roller with a predetermined value (threshold). That is, when the temperature falls below a predetermined value, the heater ON signal is output, and when the temperature exceeds the predetermined value, the heater OFF signal is output. In some cases, the threshold value at the time of temperature rise and the threshold value at the time of temperature fall are different (that is, hysteresis is provided), but in any case, the conventional heater control is basically a binary control.

On the other hand, an object of the present invention is to provide a novel heater control method and an image forming apparatus capable of performing finer temperature control during temperature adjustment and reducing current fluctuation (flicker value). And

[0012]

In order to achieve the above object, a heater control method according to the present invention is a heater control method for driving a heater with an AC power supply. Detecting, a step of determining which temperature range the detected temperature belongs to among the four temperature ranges divided by the three thresholds, and a cycle of three consecutive half-wavelengths of the power supply voltage. A first energizing pattern without thinning out half-waves, a second energizing pattern to thin out half-waves, a third energizing pattern to thin out half-waves, and a fourth energizing pattern without energizing Allocating the heaters to the four temperature ranges from the lower temperature side, respectively, and controlling the heater with an energization pattern assigned to the determined temperature range. .

As described above, by dividing the temperature range to be heated by the heater into four and allocating four different energizing patterns (four values) to each temperature range, the conventional ON-state is achieved.
It is possible to perform the temperature control with higher accuracy than the control of the / OFF2 value, and it is also possible to achieve the reduction of the flicker value by reducing the current fluctuation.

In this heater control method, it is preferable that the control of the heater by at least one of the second, third, and fourth power supply patterns be performed in at least one cycle without considering the temperature of the object to be heated. Continue for a long predetermined time. As a result, the flicker value can be further reduced as compared with a case where such time continuation is not performed.

In the above heater control method, the temperature threshold for shifting from the second energizing pattern to the first energizing pattern is Ta, the temperature threshold for shifting from the third energizing pattern to the second energizing pattern is Tb, and the fourth threshold is Tb. When a temperature threshold for shifting from the energizing pattern to the third energizing pattern is Tc, the relationship between these temperature thresholds is as follows:

It is assumed that Ta> Tb> Tc, and

Conversely, the temperature threshold for shifting from the first energizing pattern to the second energizing pattern is Ta ', the temperature threshold for shifting from the second energizing pattern to the third energizing pattern is Tb', and the third energizing pattern is Ta. When the temperature threshold for shifting from the pattern to the fourth energization pattern is Tc ′,

Ta ≧ Ta ′ Tb ≧ Tb ′ Tc ≧ Tc ′ (excluding the condition that all three equations have equal signs)
The relationship can also be used. This means that at least one of the thresholds at the boundaries of the four temperature ranges has a so-called hysteresis. This is also effective in reducing the flicker value.

Another heater control method according to the present invention is a heater control method when the heater is driven by an AC power supply, wherein the step of sequentially detecting the temperature of the object to be heated by the heater includes the steps of: 7 divided by 6 thresholds
Determining which temperature range of the two temperature ranges belongs to, and a first energization pattern having a period of three consecutive half-wavelengths of the power supply voltage and no half-wave thinning. Second energization pattern for thinning out half waves, 2
Among the third energization pattern for thinning out half-waves and the fourth energization pattern without energization, a first combination energization pattern combining the first energization pattern and the first energization pattern, a second energization pattern, A second combined energizing pattern combining the first energizing pattern, a third combined energizing pattern combining the second energizing pattern and the second energizing pattern, a third energizing pattern and the second energizing pattern, , A fifth combined energizing pattern combining the third energizing pattern and the third energizing pattern, and a sixth combined energizing pattern combining the fourth energizing pattern and the third energizing pattern. A combined energizing pattern, a seventh combined energizing pattern obtained by combining the fourth energizing pattern and the fourth energizing pattern, is referred to as “7” from the lower temperature side. Assigned to temperature ranges, characterized by comprising a step of controlling the heater in combination energization pattern assigned to the determined temperature range. This is also an example of another multi-value control, and the same effect as the above-described heater control method can be obtained.

According to another aspect, the heater control method according to the present invention is a heater control method for driving a heater by an AC power supply, wherein the step of sequentially detecting the temperature of the object to be heated by the heater, Temperature is (n-1)
Determining which temperature range belongs to n (n is an integer of 3 or more) temperature ranges divided by three threshold values, and for a continuous m half-wavelength (m is 3 or more) of the power supply voltage. One or a plurality of energization patterns having a cycle of (odd number) are set as unit energization patterns, and the first-order decimation number of the half-wave is sequentially increased.
To the n-th unit energization pattern from the lower temperature side to the n temperature ranges, respectively, and energizing the heater with the energization pattern allocated to the determined temperature range. And

An apparatus for carrying out the heater control method according to the present invention is an image forming apparatus having a fixing device for fixing a toner image on a sheet, comprising a fixing heater built in the fixing device, and a heater for the heater. Switching means for controlling the application of an AC power supply voltage; temperature detecting means for detecting the temperature of the fixing heater; and n number of the temperatures detected by the temperature detecting means divided by (n-1) thresholds. Means for determining to which temperature range the temperature range belongs to (n is an integer of 3 or more), and one or a plurality of cycles having a period of continuous m half wavelengths (m is an odd number of 3 or more) of the power supply voltage. The first to n-th unit energization patterns, in which the half-wave thinning-out numbers become sequentially larger, are assigned to the n temperature ranges from the lower temperature side, respectively, with the energization pattern of (a) as a unit energization pattern. Wherein the energization pattern assigned to temperature ranges and control means for controlling said switching means.

[0022]

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

First, the concept of the present invention will be described. The method of the present invention is to provide a heater control method capable of improving the control accuracy more than the conventional heater ON / OFF (binary) control, thereby effectively reducing the flicker value. it can. This heater control method will be referred to as “multi-value proportional control”.

One preferred embodiment has three half wavelengths, one
This is a 4-value proportional control using a 4-value (0, 1/3, 2/3, 3/3) energization pattern obtained by thinning out a different number of half waves from this 1 period. In this control, FIG.
As shown in (a), three boundary temperature values (thresholds) for switching the four values are set to Ta, Tb, and Tc, and the relationship among these is set to Ta>Tb> Tc. (For example, Tb is a target temperature at the time of printing or copying.) FIG. 5B shows four temperature ranges defined by these boundary temperature values.
As shown in (1), a one-cycle applied voltage pattern (energization pattern) obtained by thinning out half waves of different thinning numbers is assigned. Assuming that the temperature changes as shown in FIG. 5A, the four-valued energization pattern (the energization state) is sequentially 3
/ 3 → 2/3 → 1/3 → 0/3 → 1/3 → 2/3 → 3 /
It will change like 3. FIG. 5C shows the energization pattern of each of these four values.

FIG. 5A shows an actual heater roller 1.
It does not show the temperature change of (FIG. 1), but shows the correspondence with four energization patterns. However, since the temperature of the heater roller 1 changes relatively slowly, it may be considered that the change in the voltage application to the heater 4 occurs stepwise (by a difference of 1/3). Therefore, it can be said that a rapid change in current is reduced by this method.

By developing the above basic four-value proportional control,
It is also possible to apply an energization pattern divided into more values. For example, FIG. 6 shows a second embodiment of the present invention in which a combination energization pattern in which two half-wavelength periods are set is used as a unit energization pattern.
In this case, six half waves are one cycle of the unit energization pattern.

More specifically, the following seven values are shown. (1) Combination of non-energized (0/6) and (0/6) (0
/ 6) Combined energizing pattern, (2) Combined energizing pattern combining (1/3) and (0/3), (3) Energizing (1/3) and (1/3) (2/6) Combined energizing pattern, (4) Energized (2/3)
(3/6) combined energizing pattern combining (1/3) and (1/3), (5) (4/6) combined energizing pattern combining (2/3) and (2/3) energizing, (6) Energization (3/3)
(5/6) combined energizing pattern combining (2/3) and (2/3), (7) Combined energizing pattern combining (3/3) and (3/3), that is, (6/6) combined energizing pattern with full energization .

As described above, if two unit periods (three half wavelengths) of three half wavelength periods are used as the unit energization pattern, seven-value proportional control becomes possible. Similarly, if three sets of three half-wavelength periods (for nine half-wavelengths) are used as a set pattern, a stage of ten values can be obtained. By further increasing the period, more values can be obtained. Even in such a form in which a plurality of cycles (multiples of three half wavelengths) are used as the unit energization pattern, each current change is 1/3 as compared with simple full energization ON / OFF. It works in the direction of reducing sudden current change.

With further consideration, a method of avoiding a current change at a frequency (around 8 Hz) at which humans easily perceive flicker will be described as a first modification of the present embodiment. Change in energization described in FIG. 5 3/3 → 2/3 → 1/3 →
The frequency of switching from 0 to 1/3 to 2/3 to 3/3 may be shifted from around 8 Hz to a lower frequency direction. That is, the switching temperatures Ta and Tb for each energization pattern and the difference between Tb and Tc are set to be equal to or more than a predetermined value, and the time for staying in each state of each energization pattern (1/3), (2/3), (3/3) ( If the number of three half-wave periods is forcibly managed to be equal to or more than a predetermined value, the current change frequency can be reduced and the change frequency can be shifted to a lower frequency range. For example,
For a 230V, 800W halogen heater, Ta =
186 ° C., Tb = 185 ° C., and Tc = 184 ° C., and the minimum forced residence time (minimum duration) is changed from one cycle of three half wavelength cycles (three half waves) to eight cycles (24 cycles). In the experiment by the present inventor, the flicker value (Pst) measured by the flicker meter was 1.
It gradually decreased from 01 to 0.67. Here, Pst (P
eriod Short Time) is a short-time (10-minute) flicker evaluation value defined by the standard of EN61000-3-3, and is, for example, pages 35 to 35 of EMC 1995.10.5 (No. 90). It is described in “Voltage Fluctuation and Flicker Measurement” on page 41.

However, the longer the minimum duration, the worse the response of the temperature control, and the greater the fluctuation in the temperature of the heater roller. Therefore, the minimum duration is desirably two cycles (six half wavelengths) or more. However, in consideration of the responsiveness, about four cycles are preferable. That is, even if the temperature control fluctuation slightly increases as compared with the case where the minimum duration is one cycle, the flicker value can be further reduced by limiting the fluctuation to a range where the fixability is not impaired.

The actual switching frequency of the energized state is
The frequency is not determined by the minimum duration, but is lower than the frequency converted by the minimum duration because of the influence of the heat history of the heater.

As a second modification of the present embodiment, T
Consider a method of providing temperature hysteresis for a, Tb, and Tc. For example, from energization (1/3) to energization (0 /
The temperature threshold value when shifting to 3) is Ta, and the temperature threshold value is (2/3 → 1).
The temperature threshold of (/ 3) is Tb, and the temperature threshold of (3/3 → 2/3) is Tc, and (0/3 → 1 /
The temperature threshold of 3) is Ta ′, the temperature threshold of (1/3 → 2/3) is Tb ′, the temperature threshold of (2/3 → 3/3) is Tc ′,
Is determined. At this time,

Ta ≧ Ta ′, Tb ≧ Tb ′, Tc ≧ T
c ′ (except for the condition that all three expressions are equal signs).

In this way, by making the duration of each energization pattern easy to maintain, the frequency of fluctuation can be shifted in the low frequency direction. This second modification can be employed independently of the first modification,
It is also possible to use both modified examples together. Further, both modified examples can be employed together or alone in the second embodiment.

In the above examples, three half-wave periods were used as references. Here, the advantage of applying the wave number thinning based on three half-wave periods will be briefly described. For example, if one cycle of the energization pattern is considered to be two and a half wavelengths (one cycle of a sine waveform), if it is subtracted for one and a half wavelengths, it will have the same DC component as the half-wave rectified waveform. Is big. In addition, thinning out at a cycle longer than the three-half wavelength cycle tends to be perceived as flickering by human eyes due to the characteristics of flickering such as illumination. Therefore, it is appropriate to consider the shortest cycle other than the two-half wavelength cycle, that is, the three-half wavelength cycle. In fact, when the three half-wave periods were thinned out, when flickering was observed by actually connecting the illumination, almost no flickering was felt.

However, it is also possible to use an odd half wave such as 5, 7 as the reference period. In such a case, even if the effect is reduced in terms of flicker as compared with the three-half wavelength cycle, the effect of reducing the current fluctuation is still recognized. The number of temperature thresholds in the case of m half-wave periods (m is an odd number of 3 or more) is the same number m
Becomes

FIG. 7 is a circuit diagram of a control circuit for realizing "wave number control" of the present embodiment described above.

TH in the figure is a thermistor temperature sensor (5 in FIG. 1) for detecting the temperature of the heater roller (1 in FIG. 1). The sensor TH is connected to a resistor R1, and the divided potential is input to an analog input terminal A / D in the central processing unit CPU. The signal given to the A / D terminal is converted from analog to digital and processed in the CPU. A zero-cross pulse generated at a zero-cross point of the power supply voltage is input to an interrupt input terminal INT of the CPU. The circuit for generating the zero-cross pulse includes a photocoupler PC and a comparator COM at the top of FIG.
10. It is composed of a diode D.

The CPU responds to the falling edge of the zero cross pulse.
An internal interrupt routine (described later) is started, and immediately after the zero-cross signal falls, a signal OUT for turning on or off the heater HT (4 in FIG. 1) is output. For example, O
When the UT output is at the H level, the transistor TR
The light emitting side of the photo triac PT is turned off. At this time, the light receiving side of the photo triac PT is also OF
Since it is F, the gate current of the triac T does not flow. Therefore, the triac T is turned off, and the heater is turned off. Conversely, when OUT is at the LOW level, the above operation is reversed, TR is turned on, the PT light emitting diode is lit, and the phototriac PT light receiving side is turned on. To the gate of Triac T, Photo Triac P
Since the T light receiving side conducts, the gate current limited by the resistor R2 or R3 is supplied. Therefore, the triac T becomes conductive, and the heater is turned on. R4 and C1 connected in parallel to T are snubber circuits for preventing the triac T from turning on independently when there is a sudden change in the power supply voltage due to the influence of external noise or the like. is there.

The process of controlling the heater in this embodiment by the circuit of FIG. 7 will be described again with reference to FIG. First, as shown in the figure, three thresholds are set so that the control temperature has a relationship of Ta>Tb> Tc. When the temperature detection signal input to the A / D terminal in FIG. 7 is equal to or lower than Tc, a full energization pattern (3/3) is given to the heater, and the temperature becomes Tb ≧ T>
When the temperature falls within the range of Tc, an energization pattern (2/3) is given to the heater. Further, the temperature rises and Ta ≧ T> T
When the level becomes b, the heater energizing power is further reduced to apply the energizing pattern (３). Temperature is T ≧
In the case of Ta, a non-energized pattern (0/3) is given. When the temperature decreases, the reverse process is followed, and the power of the heater is increased by energizing (1/3) → energizing (2/3) → energizing (3/3) depending on the temperature. (The process of (b) in FIG. 5 is shown.)

FIG. 8 shows the state during standby and printing (copying).
The figure shows an actual temperature control (temperature adjustment) state in the middle. Assuming that the average power during standby is equal to or less than 1/3 of the total power of the heater, the temperature equilibrates in a reciprocating manner between energization (0/3) and energization (1/3). Further, if the average power during printing is between (1/3) and (2/3) of the total power of the heater, the power is switched between energization (1/3) and energization (2/3). , The temperature will equilibrate. As shown in the figure, when the switching frequency of the energized state is high, it works against the flicker value. Therefore, as an example of reducing this frequency, when entering a certain energized state, as described above, it is possible to reduce this frequency by determining the minimum duration that remains in that state.

As can be seen from FIG. 8, when the apparatus is first turned on to enter the standby state, it is energized (3/3), and an inrush current may occur. However, once the temperature reaches the maximum threshold value Ta, the current always reaches the current distribution (3/3) from the current distribution (0/3) via the current distribution (1/3) and the current distribution (2/3). That is, it can be said that the present invention is directed to heater control at the time of temperature control other than when the power of the apparatus is turned on. Equipment power supply O
In order to cope with the inrush current at the time of N, the above-described conventional method may be adopted only immediately after the power of the apparatus is turned on.

A software procedure for realizing the above control will be described with reference to a flowchart extending over FIGS. 9 and 10. Here, a case where the minimum duration is set to a predetermined value based on the three-half wavelength cycle is taken as an example.

Since a zero-cross pulse is supplied from the zero-cross pulse generation circuit to the interrupt input terminal INT to the CPU (FIG. 7), the processing in the CPU is interrupted every time this pulse is generated (falling pulse). (INT) and the flow procedure starting from FIG. 9 is executed.

First, in a judgment step S1, a temperature sample flag (hereinafter, a flag is indicated by F in FIGS. 9 and 10) indicating a timing to sample the heater roller temperature is checked. The setting and resetting of this flag are performed in steps described later. If this flag is set, the flow shifts to the Y side of S1, and the temperature T is sampled (S19). Next, the range to which the temperature T belongs is determined by the determination steps S2, S3, S4, and the process moves to the corresponding detailed flow.

Specifically, T> Ta in decision step S2
If so, the process proceeds to the Y side, and the energization state flag group 0/3
Of the F, 1 / 3F, 2 / 3F, and 3 / 3F, only the energized state flag 0 / 3F is set. Then, the process moves to the junction (d).

If Ta ≧ T> Tb in the judgment step S3, the flow shifts to the Y side, and it is checked whether or not the energization state flag 1 / 3F has already been set (S6). If not set, the continuation counter is started (S23). This continuation counter is for measuring the above-mentioned minimum continuation time. Then, the energization state flag 1 / 3F is set, and the other energization state flags (1 / 3F,
(2 / 3F, 3 / 3F) are all reset (S2
4). In the judgment step S6, the energization state flag 1 / 3F has already been set.
Is set in step S2 just in case
Execute Step 4.

If Tb ≧ T> Tc in the judgment step S4, the flow shifts to the Y side, and it is checked whether or not the energization state flag 2 / 3F has already been set (S7). If not set, the continuation counter is started (S25). Then, the energization state flag 2 / 3F is set, and the other energization state flags (0 / 3F, 1 / 3F, 3/3) are set.
F) are all reset (S26). Judgment step S
If the energization state flag 2 / 3F has already been set in step 7, the same step S26 is executed just in case.

If it is not Tb ≧ T> Tc in the judgment step S4, that is, if Tc ≧ T, the process shifts to the Y side,
It is checked whether the energization state flag 3 / 3F has already been set (S8). If not set, the continuation counter is started (S27). Then, the energization state flag 3 / 3F is set, and the other energization state flags (0
/ 3F, 1 / 3F, 2 / 3F) are all reset (S28). In the judgment step S8, the power supply state flag 3
Even when / 3F is set, the same step S28 is executed just in case.

If the temperature sample F has not been set in the aforementioned judgment step S1, or if the above-mentioned S22, S2
Following S4, S26 and S28, the thinning counter is incremented (S20). The thinning counter is incremented at each interruption, and when the value becomes 3 (S9),
It is reset to 0 (S21). Therefore, the value of the thinning counter is 0 → 1 → 2 → 0 →. . . It patrols in the form of. This decimation counter is for managing the wave number decimation timing by monitoring the value in the subsequent processing. That is, the judgment step S10 in FIG.
The process proceeds to S11, S12, and S13, and the interrupt is set to 3
Which half wave in the half wave corresponds to which half wave is to be turned ON in accordance with the setting state of each energization state flag at that time.
It is determined whether to perform FF, and an output of a control signal is instructed.

More specifically, in the judgment step S10, it is checked whether or not the energization state flag 0 / 3F has been set. If Yes, the output signal OUT is turned on and the heater is turned off regardless of the value of the thinning counter (S31). ).

In judgment step S11, it is checked whether or not the energization state flag 1 / 3F has been set. If Yes, the heater is turned off only when the thinning counter is 0 (Yes in S14).
N (S33); otherwise, it is turned off (S3).
2). Therefore, only one half wave of the three half waves is turned ON and the two half waves are thinned out.

In the judgment step S12, it is checked whether or not the energization state flag 2 / 3F is set. If Yes, the heater is turned off only when the thinning counter is 2 (S15, Yes).
FF is performed (S35), otherwise, the heater is turned on (S34). That is, one of the three half waves is thinned out (when the thinning counter is 2).

In the judgment step S13, it is checked whether or not the energization state flag 3 / 3F has been set. If Yes, the heater is turned on regardless of the value of the thinning counter (S3).
6). That is, the heater is fully energized. If the decision result in the decision step S13 is No, the temperature sample F is set (S37), and this interrupt processing is ended (return). Step S37 is for dealing with a case where none of the energization state flags is set at an initial time or for some reason.

ON / OFF of each heater in S31 to S36
In the determination step S16 following the setting, the thinning counter value is checked to determine whether it is the end of the three half-wave periods (the last half wave), that is, whether the thinning counter value is 2. If not, the temperature sample F is reset (S39) and the process returns.

In the judgment step S16, the thinning counter is set to 2
In other words, when it comes to the end of the three half-wave periods (the last half wave), it is checked in the next decision step S17 whether or not the continuation counter is counting. That the continuation counter is counting means that the continuation counter was started in any of the previous steps S23, S25, and S27. If counting is in progress, the continuation counter is incremented (S3
8). As described above, this continuation counter is set to forcibly maintain the energized state for a certain period of time (a multiple of three half-wave periods). If the continuation counter has not reached the predetermined value (S18, No), the process proceeds to the junction (g). Here, the temperature sample F is reset (S
39). Therefore, in the next interrupt cycle, the temperature sampling is not performed and the wave number thinning energization based on the thinning counter value is continued. In this way, the minimum duration of the energized state is managed by the continuation counter.

If the continuation counter has reached the predetermined value in S18, the continuation counter is stopped (S40). Also, by setting the temperature sample F (S4
1) A temperature sample is performed at the beginning of the next interrupt routine, and an instruction is made to switch the energization state according to the temperature sample.

At the beginning of the next interrupt routine after the temperature sample F is set in step S41 (FIG. 9),
Temperature T is sampled (S19), and Y is determined in step S1.
Side to check the temperature T. For example,
If the temperature is within Ta ≧ T> Tb, the flow proceeds to the Y side in decision step S3, and in step S6, the energization state flag which has been set previously is changed to the energization state flag 1 to be set.
It is determined whether it is the same as / 3F. In the case of the same, the continuation counter is kept stopped without starting, and
Only F is set (S24), and the process moves to the next junction (d). Thereafter, during the three-half wavelength period, the two-half-wave culling is performed, and at the end of the three-half wavelength period (Y side in S16), the continuation counter has already stopped, so the processing shifts to the N side in S17, and again. Temperature sample F is set (S4
1).

Similarly, at the start of the next interrupt routine, the flow goes to the Y side in the judgment step S1, for example, when the temperature is Tb ≧ T>
If it is determined in Tc that the power supply state F has passed through the determination step S4, the power supply state F immediately before was 1 / 3F.
The continuation counter is started (S25), and 2 / 3F
Is set (S26). This 2/3 energization lasts at least for the time indicated by the continuation counter.

In the determination step S2, the immediately preceding flag is not checked on the Y side, there is no instruction to start the continuation counter, and the minimum duration of the energization F (0 / 3F) set here is not specified. . That is, in the present embodiment,
For the 0/3 energized state, no continuation exceeding three half-wave periods is intentionally instructed. Since it is not desirable to keep the fixing heater completely turned off from the viewpoint of the fixability to the sheet, the forced continuity is intentionally left out.

The merits of the present embodiment based on three half wavelengths as described above include the following.

(1) Energization without thinning out half-waves (3/3) with a cycle of three consecutive half wavelengths of the power supply voltage and energization with thinning out one half-wave with a cycle of three half-waves (2/3) And 2
The conventional two-value control is performed by four-value control in which four-stage energization patterns of half-wave thinning (1/3) energization and no energization (0/3) are respectively associated with four divided ranges of the temperature to be heated by the heater.
It is possible to achieve finer and more precise temperature control than value control.

At the same time, in continuous temperature adjustment, the change (difference) in the energization state is always 1/3 (see FIG. 8), that is, a half-wave per cycle, so that a sharp current change in heater energization is effectively reduced. can do.

(2) The control hardware is relatively simple. For example, in the case of the above-described phase control method, it is necessary to set a timer from the zero-cross point of the power supply voltage and generate a pulse specifying a phase angle at which the heater should be turned on. These require the complexity of the control itself and hardware such as a timer mechanism. On the other hand, in the case of the “wave number control”, the heater is only turned on at the zero-cross starting point, so that the timer for determining the phase becomes unnecessary. In addition, the complexity of the control such as setting, starting, and the like is reduced accordingly.

(3) Further, since the heater current in the case of "wave number control" is applied from the zero-cross starting point, there is almost no change in the higher-order frequency current of the power supply frequency on the power supply line, that is, so-called power supply harmonics. . Usually, in order to suppress the generation of such power supply harmonics, a large-capacity inductance (choke coil) is inserted in series with the heater, thereby increasing the cost due to the addition of unnecessary electric components and securing the installation place. Although this has been an obstacle to downsizing the machine, the present embodiment solves such a problem.

While the preferred embodiment of the present invention has been described above, various modifications and changes are possible.

[0067]

According to the present invention, by performing multi-value control different from binary control, finer temperature control can be performed during temperature adjustment, and current fluctuation (flicker value) can be reduced.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a fixing roller as an example to which the present invention is applied.

FIG. 2 is a diagram showing a heater energizing current waveform at the time of conventional ON / OFF temperature control for adjusting the temperature of the heater roller of FIG.

FIG. 3 is an explanatory diagram of energization to a heater by conventional phase control (conduction angle control).

FIG. 4 is an explanatory diagram of generation of a power supply voltage variation caused by a device current variation.

5A and 5B are diagrams illustrating four temperature ranges (a) and energized states (b) with different thinning numbers and waveforms (c) in different energized states according to the embodiment of the present invention.

FIG. 6 is an explanatory diagram of an energization pattern according to another embodiment of the present invention, in which three half-wave periods are set for two periods and six half-waves are set as one new period.

FIG. 7 is a circuit diagram of a control circuit for implementing wave number control according to the embodiment of the present invention.

FIG. 8 is a waveform chart showing an example of an actual temperature control (temperature adjustment) state during standby and during printing (copying) according to the embodiment of the present invention.

FIG. 9 is a flowchart showing a software procedure for implementing wave number control in the embodiment of the present invention.

FIG. 10 is a flowchart following FIG. 9;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Heater roller 2 Pressure roller 3 Paper 4 Heater 5 Thermistor temperature sensor

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G05F 1/455 G05F 1/455 A F-term (Reference) 2H033 AA41 BA24 CA47 CA48 3K058 AA24 AA27 BA18 CA05 CA12 CA23 CA46 CA61 CB05 CB09 CB10 CB23 CB32 CD01 CD02 CE12 CE17 DA02 GA06 5H323 AA36 BB01 BB09 CB04 DA02 DB04 FF03 GG04 MM15 5H420 BB12 CC04 DD03 EA05 EB03 EB05 EB13 EB26 FF04 FF14 FF26 LL07

Claims (6)

[Claims] 1. A heater control method for driving a heater by an AC power supply, the method comprising: sequentially detecting a temperature of a heater to be heated by the heater; and dividing the detected temperature by three thresholds. Determining which temperature range belongs to one of the two temperature ranges; and a first energization pattern having a period of three consecutive half-wavelengths of the power supply voltage, wherein no half-wave thinning is performed.
A second energizing pattern for thinning out one half-wave, a third energizing pattern for thinning out half-waves, and a fourth energizing pattern without energization are respectively assigned to the four temperature ranges from the lower temperature side, and the determination is made. Controlling the heater with an energization pattern assigned to the selected temperature range. 2. The control of the heater by at least one of the second, third, and fourth energization patterns is continued for at least a predetermined period longer than one cycle without considering the temperature of the object to be heated. The heater control method according to claim 1, wherein: 3. The heater control method according to claim 1, wherein the temperature threshold for shifting from the second energization pattern to the first energization pattern is Ta, and the third energization pattern is the second energization pattern. Tb is the temperature threshold for shifting to
Assuming that Tc is a temperature threshold for shifting from the energizing pattern to the third energizing pattern, the relationship between these temperature thresholds is Ta>Tb> Tc, and conversely, the second energizing is performed from the first energizing pattern. The temperature threshold for shifting to the pattern is Ta ', the temperature threshold for shifting from the second energizing pattern to the third energizing pattern is Tb',
When the temperature threshold for shifting from the current-carrying pattern to the fourth current-carrying pattern is Tc ′, Ta ≧ Ta ′, Tb ≧ Tb ′, Tc ≧ Tc ′ (excluding the condition that all three equations are equal signs)
And a heater control method. 4. A heater control method for driving a heater with an AC power supply, the method comprising: sequentially detecting a temperature of a heating target of the heater; and dividing the detected temperature by six thresholds. Determining which temperature range belongs to one of the two temperature ranges; and a first energization pattern having a period of three consecutive half-wavelengths of the power supply voltage, wherein no half-wave thinning is performed.
Among the second energizing pattern for thinning out one half-wave, the third energizing pattern for thinning out two half-waves, and the fourth energizing pattern without energization, the first energizing pattern and the first energizing pattern are combined. 1, a second combined energizing pattern in which the second energizing pattern and the first energizing pattern are combined, a third combined energizing pattern in which the second energizing pattern and the second energizing pattern are combined,
A fourth combined energizing pattern combining the third energizing pattern and the second energizing pattern, a fifth combined energizing pattern combining the third energizing pattern and the third energizing pattern, a fourth energizing pattern, A sixth combined energizing pattern combining a third energizing pattern, a seventh combined energizing pattern combining a fourth energizing pattern and a fourth energizing pattern, and the seven temperature ranges from the lower temperature side, respectively. And controlling the heater with a combination energization pattern assigned to the determined temperature range. 5. A heater control method when a heater is driven by an AC power supply, the method comprising: sequentially detecting a temperature of a heater to be heated by the AC power source; Determining which of the n (n is an integer of 3 or more) temperature ranges the temperature range belongs to; dividing m continuous wavelengths of the power supply voltage (m is an odd number of 3 or more) One or a plurality of energized patterns having a cycle are set as unit energized patterns, and first to n-th unit energized patterns in which the number of half-wave thinning-outs are sequentially increased are assigned to the n temperature ranges from the lower temperature side. Energizing the heater with an energization pattern assigned to the determined temperature range. 6. An image forming apparatus having a fixing device for fixing a toner image on paper, comprising: a fixing heater built in the fixing device; a switching unit for controlling application of an AC power supply voltage to the heater; Temperature detecting means for detecting the temperature of the fixing heater; and (n-1) a temperature detected by the temperature detecting means.
Means for determining which temperature range belongs to the n (n is an integer of 3 or more) temperature ranges divided by the number of thresholds, and a continuous m half-wavelength (m is 3 or more) of the power supply voltage. One or a plurality of energization patterns having a cycle of (odd number) are set as unit energization patterns, and the first to n-th unit energization patterns in which the thinning-out number of the half-wave is sequentially increased are set as the n temperature values from the lower temperature side. An image forming apparatus comprising: a control unit configured to control the switching unit in accordance with an energization pattern allocated to the temperature range and the determined temperature range.