JPH09258601A - Method for controlling temperature for heating fixing device and device therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To quickly start up to control target temperature when power supply is once stopped by shortening warm-up time and making overshooting and temperature ripple small. SOLUTION: When a relation between a detected temperature value T and switching temperature values T1 , T2 ...Tn is T1 >T, a PID control circuit makes a heater perform totally energizing continuous heating operation, and when the relation is T2 >T>=T1 , the PID control circuit makes the heater perform PID control operation using a P value (proportional value) Kp2, an I-value(integrated value) Ti2 and a D-value(derivation) Td2, and when the relation is ...Tn >T>=Tn-1 , the PID control circuit makes the heater perform the PID control operation using the P-value Kpn, the I-value Tin and the D-value Tdn. Then, when the relation is T0 (control temperature target value)>T>=Tn , the PID control circuit makes the heater perform the PID control operation using the P value KpO, the I-value TiO and the D-value TdO, and moreover, when the relation is T>=T0 , it starts fixing operation while making the heater perform the PID control operation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a temperature control method and apparatus of a heat fixing device for heating and fixing a toner image transferred on a recording medium in an electrophotographic image forming apparatus.

[0002]

2. Description of the Related Art An electrophotographic image forming apparatus, for example, charges a photosensitive drum and then exposes it to record image information as an electrostatic latent image, and develops the electrostatic latent image with toner to visualize it. After that, it is transferred to a recording medium such as recording paper, and the transferred toner image is passed through a heat fixing device to be heat fixed, and then the paper is discharged. The heat fixing device is composed of, for example, a fixing roller heated by a heater and a pressure roller arranged opposite to the fixing roller, and the recording medium is passed between the rollers to perform heat fixing.

As an energy-saving measure, such an image forming apparatus has a standard of the United States Environmental Protection Agency (EPA) that requires a function of reducing the power consumption of the entire apparatus to a reference value or less when not used for a certain period of time. In order to comply with the International Energy Star Program (Energy Star standard), reduction of power consumption when not in use is a technical issue. Further, in the image forming apparatus, 80% of the power consumption is consumed by the heat fixing device. Therefore, the power supply of the heat fixing device is turned off to reduce the power consumption to 0 W when not in use, and the power supply is turned on to use the operation command. There is a demand for an on-demand type heat fixing device that can perform a fixing operation without requiring a waiting time after sending.

The temperature characteristic of the heating temperature (the surface temperature of the fixing roller) in the heat fixing device has a transient phenomenon and becomes a graph as shown in FIG. That is, there is a warm-up time from when the power is turned on to when the heating temperature reaches the control target temperature T0 (fixable temperature), and when the temperature rises, an overshoot, which is the difference between the control target temperature T0 and the maximum reached temperature, is set. And has an undershoot that is the difference between the control target temperature T0 and the minimum attainable temperature.
It has a temperature ripple that is the variation of the temperature above and below 0.

The on-demand type heat fixing device is required to have a short warm-up time, and in order to shorten the warm-up time, the heat capacity of the fixing device must be reduced to reduce the heat generation amount per unit time. I won't. However, when the heat capacity is reduced, there is a problem that overshoot and temperature ripple increase. Further, the heat fixing device requires a certain temperature to heat and fix the toner on the recording medium, but there are various kinds of recording media, and printing paper, postcards, plastic films (OH
P) etc. are used. In a relatively thick recording medium such as a postcard, the amount of heat taken from the fixing roller by the recording medium also increases, so control is performed to prevent an increase in temperature ripple and a decrease in the fixing roller temperature from a temperature suitable for fixing. It is necessary to set the target temperature high. Further, the hygroscopicity of the recording medium also varies depending on the environmental temperature, and the temperature required for fixing changes. In order to obtain a stable fixing property, the overshoot and the undershoot are reduced, and the control target temperature is smoothly shifted and maintained, that is, the temperature ripple is reduced. The temperature of the heater must be controlled.

An on-demand type heat fixing device, in particular, a direct heating type fixing device having a sheet heating element built-in as a heater, continuously heats the heater by energizing it when the heating temperature of the heater is lower than a control target temperature. When the temperature is higher than the control target temperature, the binary control method is adopted to keep the heating temperature constant by stopping the energization of the heater. The binary control method has an advantage that the warm-up time is short because the temperature rising rate is fast, but has a problem that the temperature ripple and the overshoot increase. To reduce the temperature ripple, P
(Proportion) control, I (Integral) control and D (Diff
However, if PID control is adopted from the start of heating the heater, the heating rate is slow and the warm-up time becomes long. Therefore, when the power is turned on, the control system is employed in which the heater is continuously energized and continuously heated, and after reaching a predetermined temperature, the heater is energized by switching to the PID control system.

For example, in Japanese Patent Laid-Open No. 58-38972, after the heating is started, the heater is fully energized and continuously heated until the heating temperature of the heater reaches a switching temperature lower than the control target temperature. After reaching, the heater energization is controlled by I (integration) control. Further, in Japanese Patent Laid-Open No. 60-163102, after the heating is started, the heater is fully energized and continuously heated until the heating temperature of the heater reaches a switching temperature lower than the control target temperature.
After the switching temperature is reached, PID control is used to control the energization of the heater. Furthermore, JP-A-3-11
In the Japanese Patent No. 6208, after the heating is started, the heater is continuously energized continuously until the heating temperature of the heater reaches a switching temperature lower than the control target temperature, and after reaching the switching temperature, P (proportional) control is performed. Is configured to control the energization of the heater.

[0008]

However, in each of the publications, the I control, the PID control, and the P control are performed after the switching temperature is reached, but since the switching temperature value is one, the overshoot occurs. However, it was impossible to control the temperature to be sufficiently small and to shift to the control target temperature in a short time. For example, in the case of a direct heating type fixing device with a built-in sheet heating element, the thermal conductivity is good and the heat capacity is small, so the temperature change due to heat generation when power is supplied or heat generation when the transfer medium passes. Is large and the overshoot is large. Therefore, if the switching temperature is set low so as to suppress overshoot, for example, P
Since the control shifts to the ID control, the warm-up time becomes long, and low-temperature fixing results in insufficient fixing. Further, when the switching temperature is set high, the PID control is performed while the overshoot is large, so that the followability to the control target temperature is deteriorated.

The on-demand type heat fixing device is
After the printing operation is finished, the surface temperature of the fixing roller changes to a temperature lower than the control target temperature because the power supply to the heater is stopped, but when there is an operation command, the power supply to the heater is restarted and the fixing is performed rapidly. The fixing temperature must be maintained by raising the temperature to a temperature that is possible. However, in the conventional device, as shown in FIG.
As shown in 0, when the surface temperature of the fixing roller is raised from the room temperature to the control target temperature T0, the heater is controlled so that the heater is fully energized and continuously heated up to the switching temperature Tc in the middle, so that a rapid rise is possible and a relatively short worm is used. Although the up time t1 is sufficient, if the operation command is issued again after the printing operation is completed and the surface temperature of the fixing roller is between the control target temperature T0 and the switching temperature Tc, the PID control is performed from the beginning to fix the image. There is a problem that the amount of heat applied to the roller is insufficient, and it takes a relatively long time T2 to bring the surface temperature of the fixing roller back to the control target temperature T0.

As a temperature control method during fixing operation, I
When (integration) control is performed, the temperature ripple is large, and
When the P (proportional) control is performed, the temperature ripple is greatly reduced, but there is a problem that the temperature is shifted to a temperature lower than the control target temperature T0 due to heat absorption by the recording medium and the pressure roller.
In addition, since the energization control to the heater is performed by the switching operation of the switching element, this switching operation causes the fluctuation of the power supply voltage and causes flickering of the fluorescent lamp, that is, flicker. This flicker amount depends on the number of times of switching, the switching control cycle, the amount of applied electric power, the inrush current, etc., but by using the PID control, the switching control cycle is shortened until the control target temperature T0 is reached. After reaching T0, the flicker amount is reduced by lengthening the switching control cycle. However, if the amount of input electric power is increased in order to increase the temperature rising rate, there is a problem that the amount of flicker cannot be suppressed to a small value even if the switching control cycle is lengthened by PID control.

Therefore, the invention according to claims 1 to 3 can shorten the warm-up time at the time of rising from the room temperature to the control target temperature, can reduce the overshoot and the temperature ripple, and can temporarily supply the electric power to the heater. (EN) A temperature control method for a heat fixing device, which can quickly raise the temperature to a control target temperature when stopped and performed again, and is particularly suitable for an on-demand type heat fixing device.

Further, according to the invention of claim 4, the warm-up time at the time of rising from the room temperature to the control target temperature can be shortened, the overshoot and the temperature ripple can be reduced, and the power supply to the heater is temporarily stopped. (EN) A temperature control device for a heat fixing device, which can quickly raise the temperature to the control target temperature when the process is performed again, and is particularly suitable for an on-demand type heat fixing device.

Further, according to the invention of claim 5, the warm-up time when rising from the room temperature to the control target temperature can be shortened, overshoot and temperature ripple can be reduced, and the power supply to the heater is temporarily stopped. A temperature control device for a heating and fixing device that can quickly raise the temperature to the control target temperature when it is again used, is particularly suitable for an on-demand type heating and fixing device, and can suppress the occurrence of flicker to a minimum. provide.

[0014]

According to the first aspect of the present invention,
In a heat fixing device that heat-fixes the transferred toner image, the switching temperature value for switching the energization control of the heater is set in multiple stages at a temperature value lower than the control target temperature value, and the heater is set to the lowest first switching temperature value. 1st with continuous heating control
After reaching the switching temperature value of, the heater is subjected to PID control to increase the temperature to the control target temperature value, and the control target temperature value is controlled to be substantially constant, and the control parameter of PID control is proportional to each switching temperature value. At least one of value, integral value, and derivative value
There is a temperature control method that changes the two.

According to a second aspect of the present invention, in the temperature control method according to the first aspect, the first switching temperature value is controlled such that the heater is continuously energized continuously until the control target temperature value is reached, and then the energization is stopped. This is because the temperature is set lower than the control target temperature value by a temperature value corresponding to the difference between the maximum temperature value of the overshoot that occurs in some cases and the control target temperature value.

According to a third aspect of the present invention, in the temperature control method according to the first or second aspect, the integral value and the differential value from the first switching temperature value to the final switching temperature value are set to 0, and substantially. The purpose is to control the electric power supply of the heater by proportional control.

According to a fourth aspect of the present invention, in a heat fixing device for heating and fixing the transferred toner image, a heater lighting circuit for controlling energization of the heater, a temperature detector for detecting the heating temperature by the heater, and a heating temperature The control target temperature value generator that generates the control target temperature value and the control target temperature value from this control target temperature value generator and the detected temperature value detected by the temperature detector are taken in and proportional to the difference between each temperature value. PID control circuit for controlling the heating temperature of the heater to match the control target temperature value by performing the operation, the integral operation proportional to the integral value of the difference between the temperature values, and the derivative operation proportional to the differential value of the difference between the temperature values. And a switching temperature value generator that generates multiple switching temperature values that are lower than the control target temperature value, and the detected temperature value detected by the temperature detector and the switching temperature value that the switching temperature value generator generates. Do Consists of a 較器, the proportional value of the PID control circuit based on the comparison result of the comparator, and the integral value and optionally switch the switching controller a control parameter of the differential value,
The PID control circuit drives and controls the heater lighting circuit so that the heater operates in a continuous energization continuous heating mode until the temperature detected by the temperature detector reaches the lowest first switching temperature value. After the temperature reaches, the temperature control device drives and controls the heater lighting circuit by PID control.

According to a fifth aspect of the present invention, in a heat fixing device that heat-fixes a transferred toner image, a heater lighting circuit that controls energization of the heater by alternating current and a phase angle of the alternating current through which the heater lighting circuit energizes the heater. A phase control circuit for controlling, a temperature detector for detecting the heating temperature by the heater,
The control target temperature value generator that generates the control target temperature value for the heating temperature and the control target temperature value from this control target temperature value generator and the detected temperature value detected by the temperature detector are taken in, and the difference between each temperature value is calculated. Performs proportional proportional operation, integral operation proportional to the integrated value of the difference between the temperature values, and differential operation proportional to the differential value of the difference between the temperature values to control the heating temperature of the heater to match the control target temperature value. PID control circuit, switching temperature value generator for generating a plurality of switching temperature values lower than the control target temperature value, detection temperature value detected by the temperature detector and switching temperature value generated by the switching temperature value generator A comparator that compares the values, a switching controller that arbitrarily switches the control parameters of the proportional value, the integral value, and the differential value of the PID control circuit based on the comparison result of this comparator, and within a fixed period from the output of the PID control circuit. Average power of And a pulse generator that generates a pulse that determines the timing of phase angle control with respect to the phase control circuit so that the phase control circuit performs AC phase angle control of energizing the heater with an electric energy equal to this average electric energy. The PID control circuit sends an output so that the heater performs a continuous heating operation with full energization until the detected temperature value from the temperature detector reaches the lowest first switched temperature value. After that, the temperature control device outputs the PID control output.

[0019]

Embodiments of the present invention will be described below with reference to the drawings. (First Embodiment) In FIG. 1, 1 is a heater for heating a fixing roller (not shown), 2 is a temperature detector for detecting the surface temperature of the fixing roller, which is the heating temperature by the heater 1,
Reference numeral 3 is a heater lighting circuit for controlling energization of the heater 1. The heater 1 is formed by sandwiching a plate-shaped heating element such as FeCr or NiCr patterned to have an arbitrary temperature distribution with an insulator such as PI or PBI so as to be closely attached to the inside of a heat roller made of Al. It is formed by arranging at. Then, on the surface of the heat roller, P
A fixing layer is formed by forming a release layer such as FA or PTFE. A pressure roller (not shown) is pressed against the fixing roller so as to face the fixing roller, and a recording medium such as a recording paper on which a toner image is transferred is passed between the fixing roller and the pressure roller, so that the heat of the fixing roller is generated. The toner is melted and heat-fixed. That is, this heat fixing device is an on-demand type fixing device.

A control target temperature value generator 4 for generating a control target temperature value T0 for setting the surface temperature of the fixing roller to a temperature suitable for fixing is provided, and the control target temperature value generator 4 controls the control target temperature value T0. The temperature value T0 and the detected temperature value from the temperature detector 2 are supplied to the PID control circuit 5. The PID control circuit 5 takes in the control target temperature value T0 from the control target temperature value generator 4 and the detected temperature value from the temperature detector 2 to obtain a P value (proportional value) as a control parameter,
Using I value (integral value) and D value (differential value) respectively, proportional action proportional to the difference of each temperature value, integral action proportional to the integral value of the difference of each temperature value, and differentiation of the difference of each temperature value The control is performed to make the heating temperature of the fixing roller by the heater 1 coincide with the control target temperature value T0 by performing a differential operation proportional to the value. The heater lighting circuit 3 is driven and controlled by the output of the PID control circuit 5.

The detected temperature value from the temperature detector 2 is also supplied to the comparator 6. This comparator 6 has a plurality of switching temperature values Tn (n = 1, n = 1, which are lower than the control target temperature value T0).
2, 3, ...) is generated, the switching temperature value Tn from the switching temperature value generator 7 is compared with the detected temperature value, and the comparison result is switched by the switching controller 8.
To supply. The switching controller 8 arbitrarily selects the control parameters of the P value Kp, the I value Ti and the D value Td generated by the control parameter generator 9 based on the comparison result of the comparator 6 to select the PID control circuit 5. It is designed to be supplied to. Each value of this control parameter is given by a generally known limit sensitivity method or step response method, and is determined by experimental data, simulation, or the like.

FIG. 2 shows the PID control circuit 5 and the comparator 6.
Also, in the flow chart showing the control operation of the switching controller 8, the power supply to the heater 1 is stopped (OF
F) and it is in a standby state. When an operation start command is generated in this state, the temperature detector 2 supplies the detected temperature value T detected in a constant cycle to the PID control circuit 5 and the comparator 6. The comparator 6 compares the switching temperature value Tn from the switching temperature value generator 7 with the detected temperature value T.

First, if T1> T with respect to the lowest first switching temperature value T1, the temperature rise (UP) 1 state is established,
The output of the switching controller 8 causes the PID control circuit 5 to drive and control the heater lighting circuit 3 so that the heater 1 operates in the full-energization continuous heating mode. When T2> T≥T1, the temperature rise (UP) 2 state is entered, and the switching controller 8 receives the P value Kp2, the I value Ti2 and the D value T from the control parameter generator 9.
d2 is selected and supplied to the PID control circuit 5. Accordingly, the PID control circuit 5 drives and controls the heater lighting circuit 3 so that the heater 1 operates in a predetermined PID control mode. Similarly, when Tn> T ≧ Tn−1, the temperature rise (U
P) The state becomes n, and the switching controller 8 selects the P value Kpn, the I value Tin, and the D value Tdn from the control parameter generator 9 and outputs the P value.
It is supplied to the ID control circuit 5. Accordingly, the PID control circuit 5 drives and controls the heater lighting circuit 3 so that the heater 1 operates in a predetermined PID control mode.

When T0> T ≧ Tn, the temperature rise (UP) becomes 0, and the switching controller 8 selects the P value Kp0, the I value Ti0 and the D value Td0 from the control parameter generator 9 to perform the PID control. Supply to the circuit 5. As a result, the PID
The control circuit 5 drives and controls the heater lighting circuit 3 so that the heater 1 operates in a predetermined PID control mode. And
The detected temperature value T is equal to or higher than the control target temperature value T0, that is, T
When ≧ T0, a fixing start command is generated and the fixing operation is started. The above control is shown in Table 1 as shown in Table 1.

[0025]

[Table 1]

This control is further performed by setting the control target temperature value T0 to 165 ° C., the three-stage switching temperature values T1, T2, and T3 to 140 ° C., 155 ° C., 159 ° C., and the P value in the heating (UP) 2 state. Kp2 = 11.1, I value Ti2 = 0 and D value Td2
= 0, P value in temperature rise (UP) 3 state Kp3 = 15.0, I
Value Ti3 = 0 and D value Td3 = 0, P value Kp0 = 5.29, I value Ti0 = 6 and D value Td0 = 28 in the temperature rising (UP) 4 state.
A concrete example will be described. Note that these values are examples and are not limited to these. As shown in FIG. 3, when the detected temperature value T is lower than the first switching temperature value T1, that is, when 140 ° C.> T, the temperature rise (UP) 1 state is entered, and the PID is output by the switching controller 8. The control circuit 5 drives and controls the heater lighting circuit 3 so that the heater 1 operates in the full-energization continuous heating mode.

When the temperature rises and the detected temperature value T is equal to or higher than the first switching temperature value T1 and lower than the second switching temperature value T2, that is, when 155 ° C.> T ≧ 140 ° C., the temperature rises. The (UP) 2 state is entered, and the switching controller 8 receives the P value Kp2 = 11.1 and the I value Ti2 = from the control parameter generator 9.
0 and the D value Td2 = 0 are selected and supplied to the PID control circuit 5. As a result, the PID control circuit 5 controls the heater 1 substantially in the proportional mode because the I value Ti2 and the D value Td2 are both 0. Further, when the temperature rises and the detected temperature value T is equal to or higher than the second switching temperature value T2 and lower than the third switching temperature value T3, that is, when 159 ° C.> T ≧ 155 ° C., the temperature is raised (UP). 3 states are entered, and the switching controller 8 outputs the P value Kp3 = 15.0 and the I value Ti3 = from the control parameter generator 9.
0 and the D value Td3 = 0 are selected and supplied to the PID control circuit 5. As a result, the PID control circuit 5 drives and controls the heater lighting circuit 3 so that the heater 1 operates substantially in the proportional mode because the I value Ti2 and the D value Td2 are both 0.

Further, when the temperature rises and the detected temperature value T is higher than the third switching temperature value T3 and lower than the control target temperature value T0, that is, when 165 ° C.> T ≧ 159 ° C.,
The temperature rises (UP) 4 state, and the switching controller 8 selects the P value Kp0 = 5.29, the I value Ti0 = 6 and the D value Td0 = 28 from the control parameter generator 9 and supplies them to the PID control circuit 5. . Accordingly, the PID control circuit 5 causes the heater lighting circuit 3 to operate the heater 1 in a predetermined PID control mode.
Drive control. Then, when the detected temperature value T becomes equal to or higher than the control target temperature value T0 of 165 ° C., a fixing start command is generated and the fixing operation is started. Then, during the fixing operation, the PID control circuit 5 keeps the heater 1 at a predetermined P
The heater lighting circuit 3 is drive-controlled to operate in the ID control mode. The above control is shown in Table 2 as shown in Table 2.

[0029]

[Table 2]

In this control, the first switching temperature value T1
Is the maximum overshooting temperature value of the overshoot and the control target temperature value T0 that occur when the heater 1 is controlled to continuously energize until the control target temperature value T0 is reached and then the energization is stopped.
It is desirable to set the temperature lower than the control target temperature value T0 by a temperature value corresponding to the difference between That is, the setting of the first switching temperature value T1 to 140 ° C. means that the heater 1 reaches the control target temperature value T0 and the continuous overheating control for all energization is performed, and the energization is stopped after that. Was 190 ° C.

By the way, the overshoot occurs because the surplus of the amount of heat accumulated by the electric power supplied when the surface temperature of the fixing roller is raised to the control target temperature T0 at which the fixing can be performed is released. Target temperature T0
By reducing the power supply to the heater 1 at a temperature lower than the overshoot, the surface temperature of the fixing roller is raised to the control target temperature T0 due to the surplus of the accumulated heat amount, and the control target is controlled while suppressing the overshoot. Temperature T
The power consumption can be reduced to 0 and the power consumption at startup can be reduced.

Further, the detected temperature value T is the first switching temperature value T
Until the temperature reaches 1, the heater 1 performs the continuous heating operation with full energization that can raise the temperature most rapidly, and from the first switching temperature value T1 through the second switching temperature value T2 to the third switching temperature value T3. The heater 1 is heated by the proportional control, and the heater 1 is heated by the PID control until the control target temperature value T0 is reached from the third switching temperature value T3. By the way, PI
Since the D control samples the temperature change within a fixed time and feeds it back to the next temperature control change timing, it works in the direction of suppressing the temperature change and maintains a constant temperature in opposition to the change in the heat capacity of the recording medium. However, it is not suitable as a control method during the temperature rise because it sensitively detects the temperature rise and suppresses it. In this regard, since the I value Ti and the D value Td are both set to 0 and the heater 1 is heated by the proportional control from the first switching temperature value T1 to the third switching temperature value T3, for example, the control is performed. The power consumption at the target temperature value T0 is 50
%, The output power is changed in accordance with the temperature difference with the control target temperature value T0 before and after the power consumption, so that only the surplus heat amount for overshoot is mitigated without greatly suppressing the temperature rise.

FIG. 4A shows a current waveform when the PID control is performed. In the PID control, the ratio of the ON time and the OFF time is variably controlled every control cycle A according to the surface temperature of the fixing roller. It 4B is a partially enlarged view of FIG. 4A, and an AC current of, for example, 50 Hz flows to the heater 1 during the ON time. Figure 4 (c) shows the power waveform, PID
In the control period, the output changes every control cycle A. FIG.
(D) is a graph showing changes in the surface temperature of the fixing roller.

FIG. 5 shows a graph g1 showing a change in the surface temperature of the fixing roller when the heater 1 is heated in this embodiment, and a graph g2 showing a change in the surface temperature of the fixing roller by the conventional temperature control. As can be seen from this graph, it is possible to shorten the warm-up time when rising from the room temperature to the control target temperature T0 and reduce the overshoot and the temperature ripple.

Further, in the on-demand type fixing device, the operation start command is generated because the surface temperature of the fixing roller is not always at room temperature and it takes a long time after the previous fixing operation is completed. The operation start command may be generated when is not elapsed. For example, as shown by a point P1 in FIG. 6, the surface temperature of the fixing roller, that is, the temperature detector 2
When the detected temperature value T is T2>T> T1, an operation start command is generated, or the detected temperature value T is
Immediately after the operation start command is generated when T3>T> T2, the PID control circuit 5 drives and controls the heater lighting circuit 3 so that the heater 1 is heated by the proportional control. The proportional control is continued until the detected temperature value T reaches the third switching temperature value T3, and then the heater 1 is heated by the PID control. The warm-up times in this case are t2 and t3, respectively, which are sufficiently shorter than the warm-up time t1 at the time of rising from the room temperature to the control target temperature value T0. As described above, when the power supply to the heater 1 is once stopped and then restarted, the control target temperature T0 can be quickly raised, which is extremely suitable for an on-demand type heat fixing device in which quick start fixing is desired. Suitable temperature control is possible.

(Second Embodiment) The same parts as those of the first embodiment are designated by the same reference numerals and detailed description thereof will be omitted. This is as shown in FIG.
A pulse generator 10 and a phase control circuit 11 are interposed between the heater lighting circuit 3 and the heater lighting circuit 3. The phase control circuit 11 controls the phase angle of the alternating current in which the heater lighting circuit 3 energizes the heater 1, and the pulse generator 10 obtains the average electric energy within a certain period from the output of the PID control circuit 5, The control circuit 11 generates a pulse for determining the timing of the phase angle control for the phase control circuit 11 so as to perform the AC phase angle control for energizing the heater 1 with the electric energy equal to the average electric energy.

That is, the PID control circuit 5 inputs the detected temperature value T from the temperature detector 2 for detecting the surface temperature of the fixing roller, and determines the ON time within the constant control period A according to the temperature state of the fixing roller. It outputs a signal to change.
This output signal is determined by predicting the temperature change state based on the temperature of the fixing roller fed back, that is, the deviation between the detected temperature value T and the control target temperature value T0 and the transfer function. The ON time of the heater 1 within the control cycle A, that is, the amount of electric power supplied to the heater 1 is given. In the pulse generator 10, in order to be able to supply the same amount of electric power as the amount of electric power obtained by this to the heater 1 by phase control, from the ON time within the constant control period A output from the PID control circuit 5 to the average amount of electric power within the period. Is calculated, the control angle of the phase control is determined to be equal to this, and a timing pulse for turning on the switching element in the phase control circuit 11 is generated and output. The phase control circuit 11 adjusts the amount of electric power supplied to the heater 1 with time by the timing pulse from the pulse generator 10.

FIG. 8 (a) shows a current waveform when PID control and phase control are combined, and FIG. 8 (b) shows a current waveform obtained by partially enlarging (a) in the power supply cycle. That is,
The output from the phase control circuit 11 is ON during the constant control period A.
It is not an output that determines the time, but an output that controls the conduction control angle in the power supply cycle, whereby the heater lighting circuit 3 controls the AC conduction control angle in each power supply cycle.
Energization control is performed. The power waveform at this time is as shown in FIG. 8 (c), and the maximum input power at the time of PID control can be reduced to about 1/3 of that when the phase control is not performed. Further, the surface temperature change of the fixing roller is as shown in FIG. 8D, and the same temperature characteristic as that of the first embodiment can be obtained.

Since the maximum input power can be reduced in this way, the number of times of switching is increased because it is performed twice every power supply cycle, but flicker such as flicker of the surrounding fluorescent lamp can be suppressed. Of course, in this embodiment as well as in the first embodiment, the warm-up time when rising from room temperature to the control target temperature T0 can be shortened, overshoot and temperature ripple can be reduced, and the power to the heater 1 can be reduced. It is possible to quickly raise the temperature to the control target temperature T0 when the supply is once stopped and then performed again, and it is possible to perform temperature control extremely suitable for an on-demand type heat fixing device in which quick start fixing is desired.

[0040]

As described above, according to the first to third aspects of the present invention, the warm-up time at the time of rising from the room temperature to the control target temperature can be shortened, overshoot and temperature ripple can be reduced, and the heater It is possible to quickly raise the control target temperature when power supply is once stopped and then performed again, and it is possible to obtain a temperature control method particularly suitable for an on-demand type heat fixing device.

Further, according to the invention described in claim 4, the warm-up time at the time of rising from the room temperature to the control target temperature can be shortened, the overshoot and the temperature ripple can be reduced, and the power supply to the heater is once provided. It is possible to quickly raise the temperature to the control target temperature when stopped and performed again, and it is possible to obtain a temperature control device particularly suitable for an on-demand type heat fixing device.

According to the fifth aspect of the present invention, the warm-up time at the time of rising from room temperature to the control target temperature can be shortened, overshoot and temperature ripple can be reduced, and the power supply to the heater is once provided. To obtain a temperature control device capable of promptly rising to a control target temperature when stopped and performed again, particularly suitable for an on-demand type heat fixing device, and further capable of suppressing the occurrence of flicker. You can

[Brief description of drawings]

FIG. 1 is a block diagram showing a first embodiment of the present invention.

FIG. 2 is a flowchart showing a control operation in the same embodiment.

FIG. 3 is a flowchart showing a specific example of a control operation in the same embodiment.

FIG. 4 is a graph showing a current waveform, a power waveform, and a temperature characteristic of a fixing roller during a heating operation of a heater according to the same embodiment.

FIG. 5 is a graph showing the temperature characteristic of the fixing roller and the temperature characteristic of the fixing roller according to the conventional temperature control method in the embodiment.

FIG. 6 is a graph showing rising temperature characteristics of the fixing roller in each temperature state in the embodiment.

FIG. 7 is a block diagram showing a second embodiment of the present invention.

FIG. 8 is a graph showing a current waveform, a power waveform, and a temperature characteristic of the fixing roller during the heating operation of the heater according to the same embodiment.

FIG. 9 is a graph for explaining general temperature characteristics of a fixing roller.

FIG. 10 is a graph showing rising temperature characteristics of the fixing roller from various temperature states when the conventional temperature control method is used.

[Explanation of symbols]

 1 ... Heater 2 ... Temperature detector 3 ... Heater lighting circuit 4 ... Control target temperature value generator 5 ... PID control circuit 6 ... Comparator 7 ... Switching temperature value generator 8 ... Switching controller 9 ... Control parameter generator

Claims (5)

[Claims] 1. In a heat fixing device for heating and fixing a transferred toner image, a switching temperature value for switching heater energization control is set in multiple stages at a temperature value lower than a control target temperature value, and the lowest first switching temperature value is set. Until the first switching temperature value is reached, PID control is performed on the heater to increase it to the control target temperature value, and the heater is controlled to a control target temperature value at a substantially constant level. Proportional value, integral value, which is a control parameter of PID control, at each switching temperature value
A temperature control method for a heat fixing device, characterized in that at least one of the differential values is changed. 2. The first switching temperature value is a maximum overshoot temperature value and a control target temperature value of an overshoot that occurs when the heater is continuously heated to full control until the heater reaches a control target temperature value and then the energization is stopped. 2. The temperature control method for a heat fixing device according to claim 1, wherein the temperature is set to be lower than the control target temperature value by a temperature value corresponding to the difference. 3. The integrated value and the differential value from the first switching temperature value to the final switching temperature value are set to 0, and the heater is substantially energized by proportional control. Alternatively, the temperature control method of the heat fixing device according to the item 2. 4. A heating fixing device for heating and fixing a transferred toner image, a heater lighting circuit for controlling energization of a heater, a temperature detector for detecting a heating temperature by the heater, and a control target temperature value of the heating temperature. The control target temperature value generator to be generated, the control target temperature value from this control target temperature value generator and the detected temperature value detected by the temperature detector are taken in, and a proportional operation proportional to the difference between each temperature value, each temperature A PID control circuit for performing control to match the heating temperature by the heater with a control target temperature value by performing an integral operation proportional to the integral value of the difference between the values and a differential operation proportional to the differential value of the difference between the respective temperature values; A switching temperature value generator that generates a plurality of switching temperature values lower than a target temperature value, and a detection temperature value detected by the temperature detector and a switching temperature value generated by the switching temperature value generator are compared. ratio A comparator and a switching controller that arbitrarily switches control parameters of the proportional value, integral value, and derivative value of the PID control circuit based on the comparison result of the comparator, and the PID control circuit includes the temperature detector. The heater lighting circuit is drive-controlled so that the heater performs a continuous heating operation with full energization until the detected temperature value from 1 reaches the lowest first switched temperature value, and after reaching the first switched temperature value, the PID is reached. A temperature control device for a heat fixing device, wherein the heater lighting circuit is driven and controlled by control. 5. In a heat fixing device for heating and fixing a transferred toner image, a heater lighting circuit for controlling energization of a heater by an alternating current, and a phase control for performing an alternating phase angle control for energizing the heater by the heater lighting circuit. A circuit, a temperature detector for detecting a heating temperature by the heater, a control target temperature value generator for generating a control target temperature value of the heating temperature, a control target temperature value from the control target temperature value generator and the temperature Taking in the detected temperature value detected by the detector, proportional operation proportional to the difference of each temperature value, integral operation proportional to the integral value of the difference of each temperature value, and differential operation proportional to the differential value of the difference of each temperature value A PID control circuit that performs control to match the heating temperature of the heater with a control target temperature value; a switching temperature value generator that generates a plurality of switching temperature values lower than the control target temperature value; A comparator for comparing the detected temperature value detected by the temperature detector and the switching temperature value generated by the switching temperature value generator, and the PID based on the comparison result of this comparator.
A switching controller that arbitrarily switches the control parameters of the proportional value, the integral value, and the differential value of the control circuit, and an average power amount within a fixed period is calculated from the output of the PID control circuit, and the phase control circuit determines the average power amount. The PID control circuit includes a pulse generator that generates a pulse that determines a timing of the phase angle control with respect to the phase control circuit so as to perform an AC phase angle control for energizing the heater with an equal amount of electric power.
Until the detected temperature value from the temperature detector reaches the lowest first switching temperature value, the heater outputs an output so that the heater performs a full energization continuous heating operation, and after reaching the first switching temperature value, the PID is reached. A temperature control device for a heat fixing device, which is characterized in that a control output is sent out.