JP6004929B2 - Image heating control device - Google Patents

Description

  The present invention relates to an image heating control apparatus used in an image forming apparatus employing an image forming process such as an electrophotographic system or an electrostatic recording system, such as a copying machine or an LBP. Examples of such an image heating control device include a fixing device that heats and fixes an unfixed toner image formed on a recording material as a fixed image, and increases the glossiness of the image by heating the image fixed on the recording material. Examples include a glossiness increasing device.

  2. Description of the Related Art Conventionally, image forming apparatuses such as printers, copiers, and facsimiles have used a method of fixing an image by heating and melting a toner image formed on a recording sheet as an image forming unit using a fixing device.

  In general, a fixing device that fixes a toner image on a sheet supplies power to a heater, which is a heating source, to heat a member in the fixing unit, and the toner is melted and fixed on the sheet by the heat. The output of the heater can be varied by controlling the lighting time (duty) of the heater within a predetermined control time, and a desired output value can be obtained.

  As a duty control method, PI control, PID control, or the like is used, and the temperature of the fixing member detected by the temperature detection element, which is a temperature detection unit provided in the fixing device, is set to a predetermined target temperature (fixing temperature). ) To control the heater duty.

Control parameters used for these controls (for example, proportional coefficient K _P used in PID control) are designed based on a nominal model that does not take into account variations in the components of the control system. However, the environment in which the image forming apparatus is actually used is not uniform, and the constituent elements vary. For this reason, the control parameters determined at the design stage are not always optimal parameters under actual use conditions due to variations in the power supply conditions and the physical property values of the fixing members.

  For example, the power supply environment in which the image forming apparatus is used is different from the environment assumed at the time of design, and a high voltage exceeding the intended input voltage range may be input. In this case, if the heater start-up control is performed with the control parameters determined at the time of design, excessive power is applied to the heater, the fixing member is excessively warmed, and uneven glossiness and density unevenness appear in the initial recording sheet image. There was a fear.

  In order to solve such a problem, Patent Document 1 calculates the heater temperature-time characteristic when returning from the energy saving mode, predicts the input voltage based on the rate of temperature rise, corrects the duty operation, and optimizes the heater output. Is going on.

JP 2005-338634 A

  However, the temperature change of the fixing member in the vicinity of the fixing temperature is affected not only by the input voltage but also by variations in the physical property values of the fixing member (for example, the thermal conductivity of the fixing member). In particular, in a fixing device (on-demand fixing device) using a low heat capacity member for the purpose of quick start, a temperature change near the fixing temperature reacts sensitively to variations in physical property values of members constituting the fixing device. In addition, the temperature rise rate at the start-up is mainly influenced by the power consumed by the heater, that is, the heater resistance and the input voltage, and it is difficult to detect the difference in the physical property value of the fixing member only from the temperature rise rate.

  Therefore, in the on-demand fixing device, it is difficult to accurately estimate the temperature change of the fixing member from the temperature increase rate as in Patent Document 1, and it is difficult to predict the behavior in the vicinity of the fixing temperature such as the overshoot amount with respect to the target temperature. . Certainly, it is possible to improve the prediction accuracy by providing voltage detection means in the image forming device or measuring the physical property value of each fixing member at the time of shipment from the factory, but the system complexity and cost increase etc. There is a concern about the harmful effects.

  An object of the present invention is to simplify the generation of uneven glossiness and density unevenness of an image for the next job based on the maximum temperature detected during the start-up period while performing PI control or PID control on a heating rotator. It is in providing the image heating control apparatus which can be suppressed by.

  In order to achieve the above object, an image heating control device according to the present invention is formed between a heating rotator heated and rotated by a heating source, and the heating rotator facing the heating rotator. PI control or PID control is performed corresponding to the difference between the target temperature of the heating rotator and the detected temperature of the temperature detecting means, and the detected temperature is set to the pressure member for nipping and conveying the recording material carrying the image in the nip portion. A temperature control system for controlling the temperature to the target temperature, an initial duty corresponding to each temperature control initial temperature in the temperature control system, and a proportional coefficient in the temperature control corresponding to each temperature control initial temperature, In the start-up period using the storage means for storing at least one data as data and the data in the storage means corresponding to the temperature control initial temperature detected by the temperature detection means, the temperature detection means detects the data. Whether the maximum temperature to be detected exceeds the first allowable range as the target temperature, or the time integral value of the difference between the maximum temperature detected by the temperature detecting means and the target temperature exceeds the second allowable range And determining means for determining whether or not the data in the storage means corresponding to the initial temperature adjustment temperature is appropriate data for the next job when the first allowable range or the second allowable range is exceeded. Data rewriting means for rewriting.

  According to the present invention, while PI control or PID control is performed on a heating rotator, the occurrence of uneven glossiness and density unevenness of an image for the next job is simplified based on the maximum temperature detected during the start-up period. Can be suppressed.

(A) is a flowchart for explaining an optimization method of the initial duty I ₀ in the image heating control apparatus according to the first embodiment of the present invention, and (b) is for heating of the image heating control apparatus according to the first embodiment. It is the schematic explaining the control circuit of a heater. (A) is a schematic sectional drawing showing the image forming apparatus carrying the image heating control apparatus which concerns on 1st Embodiment, (b) is a schematic sectional drawing showing the image heating control apparatus which concerns on 1st Embodiment. Is a table showing the initial duty I ₀ for temperature control initial temperature of each of the image heating control apparatus according to the first embodiment. It is a figure which shows the thermistor temperature profile in the conditions from which input voltage and the heat conductivity (lambda) of a pressure roller differ. From the difference between the maximum value T _max and the target temperature of the thermistor temperature is a table for obtaining the amount of change of the initial duty I _0.

Is a table showing the initial duty I ₀ for temperature control initial temperature of each of the image heating control apparatus according to the second embodiment. It is a table for obtaining a uniform change amount of the initial duty I ₀ from the difference between the maximum value T _max of the thermistor temperature and the target temperature at the time of the first printing after initialization.

<< First Embodiment >>
(Image forming device)
FIG. 2A is a schematic cross-sectional view showing an image forming apparatus equipped with the image heating control apparatus according to the first embodiment. Reference numeral 1 denotes a photosensitive drum, and a photosensitive material such as OPC, amorphous Se, or amorphous Si is formed on a cylindrical substrate such as aluminum or nickel. The photosensitive drum 1 is rotationally driven in the direction of the arrow, and first, the surface thereof is uniformly charged by a charging roller 2 as a charging device. Next, scanning exposure is performed with a laser beam L which is ON / OFF controlled according to image information by the laser scanner 3 to form an electrostatic latent image. This electrostatic latent image is developed and visualized by the developing device 4 using toner (developer).

  The toner image visualized from the photosensitive drum 1 is transferred to the recording paper P conveyed from the paper feed cassette 6 at a predetermined timing in a transfer nip portion which is a pressure contact portion between the transfer roller 5 and the photosensitive drum 1. Here, the top sensor 8 detects the leading edge of the recording sheet conveyed by the conveying roller 9 so that the image forming leading edge position of the toner image on the photosensitive drum 1 and the writing position of the leading edge of the recording sheet coincide with each other. Are combined.

  The sheet P conveyed to the transfer nip portion at a predetermined timing is nipped and conveyed by the photosensitive drum 1 and the transfer roller 5 with a constant pressure. The paper P on which the toner image has been transferred is conveyed to the fixing device 7, where it is fixed as a final image, and then discharged onto a paper discharge tray.

(Image heating control device)
Next, the fixing device 7 will be described in detail with respect to the image heating control device in the present embodiment. The image heating control apparatus according to the present embodiment includes a temperature control system, a storage unit, a determination unit, and a data rewriting unit, which will be described later, in addition to a heating rotator and a pressure member, and constitutes an image forming apparatus as a whole. In this case, both the case where the fixing device is configured as a whole are included.

  As shown in FIG. 2B, the fixing device 7 includes a heating member 10 as a rotatable heating rotator, and a nip portion N that faces the heating member 10 and is formed between the heating member 10. It has a pressurizing member 20 that pressurizes so as to heat the image by sandwiching and conveying the recording material P carrying the image. As the pressure member 20, a pressure roller 21 made of an elastic layer formed by foaming heat-resistant rubber such as silicon rubber or fluorine rubber or silicon rubber on the outside of a metal core bar such as Al was used.

  The heating member 10 includes a heater 12 as a heating source, a heater holder 13 that fixes the heater 12, and a cylindrical heat-resistant film 11 that is loosely fitted to the heater holder 13. The heating member 10 is sufficiently pressurized to form nip portions N necessary for heat fixing from both ends in the longitudinal direction by a pressing means (not shown) in the direction of the pressing member 20. And it is rotationally driven in the direction of the arrow by a rotational drive (not shown) through the metal core of the pressure roller 21 from the end in the longitudinal direction. As a result, the heat-resistant film 11 is driven to rotate on the outside of the heater holder 13 in the direction of the arrow in the figure.

  In the heater 12, a heating element mainly composed of an Ag / Pd (silver palladium) alloy, RuO 2 (ruthenium oxide) alloy, or the like is formed on a ceramic substrate such as aluminum nitride by screen printing or the like. The one that is overcoated with a glass layer is used.

  Further, a temperature detection element 14 such as a thermistor is provided inside the heat resistant film 11 at appropriate positions such as the inner surface of the heat resistant film and the rear surface of the heater, and the temperature of the heat resistant film 11 becomes a predetermined target temperature based on the detected temperature. As described above, the temperature control is performed by the temperature control system shown below.

(Temperature control system)
1) Configuration of temperature control system that performs PID control (including calculation means)
FIG. 1B shows a configuration of a temperature control system 31 including a calculation unit, along with configurations of a storage unit 100, a determination unit 200, and a data rewrite unit 300, which will be described later, regarding the control of the heater output in the present embodiment. . In FIG. 1B, the heater 12 is connected to a commercial power source 33 via a bidirectional switching element 32 such as a triac.

  In the temperature control system 31, as will be described below, calculation is performed based on the difference between the detected temperature of the heat-resistant film 11 that is a fixing member detected by the thermistor 14 that is a temperature detecting means and a preset target temperature, The ratio (duty) of the heater that is turned on at a certain time is determined. Then, based on the determined duty, the wave number control or phase control of the triac 32 is performed, and the power supplied to the heater 12 is controlled so that the heat-resistant film 11 as a fixing member is controlled to have a desired temperature.

2) Determination of duty in PID control 2-1) Initial setting (initial duty called from storage means)
Here, the determination of the duty in the temperature control system 31 will be described. First, when the start-up control of the heater 12 is started, an initial duty I ₀ (data storage in the storage unit 100 described later) that is a fixed lighting duty corresponding to the detected temperature adjustment initial temperature is set. If the set value of the initial duty I ₀ is large, the power duty is supplied to the high becomes the heater at start up is higher. On the contrary, when the set value of the initial duty I ₀ is small, the power supplied to the heater at the time of start-up becomes low.

2-2) Calculation control (subsequent duty determined by calculation)
In the present embodiment, the duty of the heater output is calculated and determined on the assumption of PID control. Specifically, P component, I component, and D component calculated as described below are added (increased or decreased) to the above-described initial duty I ₀ . As a result, it is possible to improve the followability to the target temperature and to shorten the heater rise time. That is, the duty is, the P component obtained by multiplying the difference in proportional coefficient K _P of the temperature and the target temperature thermistor 14 detects the I component weighted by the time integral of the difference multiplied by a proportionality factor K _I, the difference Is determined by the sum of the time derivative of _D and the D component multiplied by KD.

The design of control parameters such as K _P , K _I , K _D , and I ₀ is designed and optimized based on a nominal model that does not consider the variation of each component. However, since there are variations in the environment in which the image forming apparatus is actually used and the physical property values of the fixing member, the control parameters determined in the design stage are not necessarily optimal parameters in the environment in which they are actually used. Absent. Therefore, in the present embodiment, the value of the control parameter is optimized to a suitable value in the operating environment in which the image forming apparatus is installed.

(Optimization of control parameters)
Here, the control parameter optimization method will be described in detail with reference to the flowchart of FIG. In the present embodiment, optimization of the initial duty I ₀ that is one of the control parameters will be described.

Simultaneously with the start of the temperature control, first, the initial duty I ₀ is determined as follows. That is, as shown in the table of FIG. 3, the initial duty I ₀ having a different value corresponding to the thermistor temperature (temperature adjustment initial temperature) T ₀ at the start of temperature adjustment is stored in the storage means 100 (FIG. 1B). The initial duty I ₀ corresponding to the detected temperature control initial temperature is set (S101).

In the data of the table of FIG. 3, the value of the initial duty I ₀ is reduced as the thermistor temperature T ₀ (temperature adjustment initial temperature) at the start of temperature adjustment is higher. The amount of power required for the startup in the cold state after a long time has passed since the previous printing and the startup in the hot state after a large amount of printing are different. The temperature can reach the target temperature. The table in FIG. 3 is a value optimized with respect to the nominal model that does not consider the variation of each component. When the image forming apparatus operates for the first time as a product, the initial duty I ₀ is the _value of the table in FIG. Follow the value.

After the initial duty I _{0 is} determined, heater driving is started at a duty determined based on the above-described PID control (S102). Then, after the heater driving is started, the thermistor temperature is monitored, and the maximum value T _max of the thermistor temperature from the start of the temperature control until the recording paper reaches the fixing nip portion N (start-up period) is recorded (S103). .

When this T _max is higher than the target temperature, the difference between the T _max and the target temperature indicates the overshoot amount, and the larger this overshoot amount, the more power is required when starting up and the fixing member becomes excessive. It shows that it was warming up. On the other hand, when T _max is lower than the target temperature, it indicates that the fixing member temperature was insufficiently raised because the input power was reduced too much.

Therefore, the value of the control parameter is appropriate based on whether or not the maximum value (maximum temperature) T _max of the thermistor temperature at the time of startup exceeds the allowable range (first allowable range) as the target temperature. Is determined by the determination means 200 (FIG. 1B). That is, it is determined whether the maximum temperature _Tmax is within a range between a preset upper limit temperature (allowable maximum temperature) _TH and a lower limit temperature (allowable minimum temperature) _TL (S104).

The maximum temperature T _H, when the thermistor temperature exceeds the temperature overshoot, is set as a threshold which image defects such as uneven gloss and unevenness in image density may occur. On the other hand, the lower limit temperature _TL is set as a threshold at which a fixing failure occurs at the leading edge of the recording paper if the thermistor temperature is lower than this temperature when the recording paper reaches the fixing nip.

If T _max is not within the allowable range, it is determined that the used initial duty I ₀ is not an optimum value in the current operating environment, and the initial duty corresponding to the initial thermistor temperature T ₀ in the table of FIG. The value of _I0 is corrected (S105). When T _max is greater than T _H lowers the value of the initial duty I _0, to reduce the duty of the heater output during start-up. On the contrary, when T _max is smaller than _TL , the value of the initial duty I ₀ is increased, and the duty of the heater output at the time of starting is increased.

In the start-up control in the next print job, by using the corrected table, the fixing member temperature can be quickly reached the target temperature without causing unnecessary overshoot. As described above, it is determined whether the value of the initial duty I ₀ corresponding to the initial thermistor temperature T ₀ is optimal for each print, and if necessary, the table of FIG. 3 is replaced with appropriate data. Modify the table to be optimal for the operating environment.

The physical property value of the fixing member is an inherent value when the image forming apparatus is shipped as a product, and the input voltage hardly fluctuates extremely once the installation location is determined. Therefore, once the initial duty I ₀ is corrected, it is highly possible that the corrected initial duty I ₀ remains at an optimal value in subsequent printing. However, in the present embodiment, the optimization of the initial duty I ₀ is always performed every time the start-up control is performed.

  This is because by always monitoring the thermistor temperature at the start-up, even if the control parameter is not the optimum value due to a temporary irregular factor such as a voltage drop, it can be immediately corrected in the next print. Further, it is possible to cope with a change in physical property value of the fixing unit member with time.

(Comparison result)
Next, a comparison result between the optimization control of this embodiment and the optimization control of the conventional example is shown. Incidentally, in the conventional example to be compared this time, the initial duty I ₀ is changed based on the temperature increase rate in the section where the thermistor temperature is 50 ° C. to 100 ° C.

4, the fixing device having a different pressure roller heat conductivity lambda, was when charged with different input voltages V _in, it shows a thermistor temperature profile. Incidentally, at this time, the start-up is started at the initial thermistor temperature T ₀ = 55 ° C., and the initial duty I ₀ = 45% is selected based on the table of FIG. The result using optimization control is shown for each condition.

The thermal conductivity λ = 0.2 W / m · K of the pressure roller and the input voltage V _in = 120 V (condition 1) are the same conditions as the nominal model in the image forming apparatus of the present embodiment. In the start-up under this condition, the thermistor temperature reaches the target temperature = 200 ° C. without overshooting. The _{T max} as _1, if _{T max} is within the allowable range, the initial duty _I 0 = 45% of the current value is determined to no problem, changing the value of the initial duty _{I 0} is not performed.

On the other hand, when the thermal conductivity λ = 0.2 W / m · K of the pressure roller and the input voltage V _in = 130 V (condition 2) are high, the thermistor temperature overshoots the target temperature. Specifically, the maximum value T _max 2 greatly exceeded the allowable upper limit temperature T _H = 207 ° C. (target temperature + 7 ° C.). In this case, the control of this embodiment, T _max from higher than T _H, determines the duty at the time of start-up is too high, changing the value of the initial duty I ₀ to a small value. In the present embodiment, the original value of 45% is reduced to 43%.

In the present embodiment, the subtraction value of the initial duty I ₀ is changed according to the overshoot amount (T _max −target temperature). When the overshoot amount is 8 ° C. or more and less than 13 ° C., the subtraction value of the I ₀ value is −2%, and when the overshoot amount is 13 ° C. or more, the subtraction value is −4%. In this way, the initial duty I ₀ is optimized quickly by changing the subtraction value of the initial duty I _{0 in accordance} with the overshoot amount. FIG. 5 shows the amount of change in the initial duty I ₀ value according to (T _max −target temperature). When printing is performed at the initial thermistor temperature T ₀ = 50 to 74 ° C. after the next job, the start-up is performed with the initial duty I ₀ = 43%.

  Also, under such conditions where the input voltage is high, the rate of increase of the thermistor temperature is high even in the conventional example, so that it can be detected that there is too much input power at startup, and the control parameters can be corrected. Can do.

Next, although the input voltage is the same at V _in = 120 V, the result is shown for the case where the heat conductivity λ of the pressure roller is different. Under such conditions, as shown in FIGS. 1, 3, and 4, the rate of temperature increase at the initial stage of startup is substantially constant, but the behavior of the thermistor temperature near the target temperature changes.

For example, if λ = 0.3 W / m · K (Condition 3) and the thermal conductivity is large, the amount of heat taken away by the pressure roller during startup is large, so that the temperature of the heating member does not easily rise, and the thermistor temperature Becomes lower. In particular, in a high temperature state near the target temperature, the temperature difference between the heating member temperature and the pressure roller temperature is large, and the amount of heat taken away by the pressure roller increases, so that the temperature rise greatly slows down. For this reason, the fixing member does not sufficiently warm up until the paper enters the fixing nip, the maximum value T _max 3 of the thermistor temperature is lower than the lower limit temperature T _L = 195 ° C., and a slight fixing failure occurs at the leading edge of the paper. Occurred.

In this case, in this embodiment, it is determined that the duty at the time of start-up is too low from the result of T _max 3 < _TL , and the value of the initial duty I ₀ is changed to a large value. In the present embodiment, the original value of 45% is increased to 47% according to the table of FIG. When printing is performed at the initial thermistor temperature T ₀ = 50 to 74 ° C. after the next job, the start-up is performed with the initial duty I ₀ = 47%. On the other hand, in the conventional example, since the rate of increase of the thermistor temperature is substantially equal to the rate of temperature increase under the conditions of the nominal model, the initial duty I ₀ is not changed.

Conversely, when the thermal conductivity is as small as λ = 0.1 W / m · K (Condition 4), the amount of heat taken away by the pressure roller is small, so the temperature inside the heating member tends to rise, and the thermistor temperature overshoots. To do. Therefore, the maximum value T _{max 4} of the thermistor temperature is above the maximum temperature T _H of the allowable range, minor concentrations, uneven gloss paper tip has occurred. In this case, in this embodiment, it is determined that the duty at the time of startup is too high, and the value of the initial duty I ₀ is changed to a small value. In the present embodiment, the original value of 45% is reduced to 43%.

Then, when printing is performed at the initial thermistor temperature T ₀ = 50 to 74 ° C. after the next job, the start-up is performed with the initial duty I ₀ = 43%. Even under this condition, in the conventional example, since the rate of increase in the thermistor temperature is substantially equal to the rate of temperature increase under the conditions of the nominal model, the initial duty I ₀ is not changed.

  As described above, as for the thermistor temperature profile, the energy consumed by the heater is dominant in the initial behavior of the start-up, and if the resistance of the heater and the input voltage are the same, the rate of increase of the thermistor temperature is almost the same. On the other hand, in the high temperature state near the target temperature, the influence of the physical property value of the fixing member cannot be ignored, and the thermistor temperature depends on the thermal conductivity of each member and other variations in contact thermal resistance (fixing nip width, etc.) between members. The behavior of changes.

  In particular, in an on-demand fixing device using a low heat capacity member as employed in this embodiment, the influence of the physical property value of the fixing member is significant. For this reason, it is difficult to determine the temperature change in the vicinity of the target temperature such as the overshoot amount only from the rate of increase of the thermistor temperature as in the conventional example.

Next, Table 1 below shows the printing results when printing is performed again under the same conditions. This is because when printing is performed under conditions 1 to 4, (1) when optimization is not performed on the initial duty I ₀ that is a control parameter, (2) when the optimization method of the conventional example is used, and ( 3) This is a case where the optimization method of this embodiment is used.

When the target temperature is reached without overshooting as in Condition 1, both the conventional example and the present embodiment determine that there is no problem with the current initial duty I ₀ value, and the initial duty I ₀ is not changed. Subsequently, a good image can be obtained. Under the condition where the input voltage is high as in condition 2, (1) the initial duty I ₀ is not changed when optimization is not performed. Therefore, when printing under the same condition, the fixing member is always excessively warmed. , Density unevenness and gloss unevenness continue to occur in the image.

On the other hand, (2) in the conventional optimization method, it is determined that the rate of increase of the thermistor temperature is large, and the value of the initial duty I ₀ is subtracted. Therefore, when printing under the same conditions, a good image can be obtained because the duty at startup is suppressed.

Further, (3) In the present embodiment, since it is determined as the maximum value T _{max 2} of the thermistor temperature is above the upper limit T _H tolerance, subtracting the value of the initial duty I _0, printed under the same conditions In doing so, a good image is obtained.

Under the condition where the thermal conductivity of the pressure roller is low as in Condition 3, (1) If the optimization is not performed, the initial duty I ₀ is not changed. Therefore, when printing under the same conditions, power is always insufficient. Thus, fixing failure continues to occur at the leading edge of the image. Further, (2) even in the optimization method of the conventional example, the rate of increase in the thermistor temperature is not different from the rate of temperature increase in the nominal model, so the value of the initial duty I ₀ is not changed. For this reason, when printing under the same conditions, power is always insufficient, and fixing failure continues to occur at the leading edge of the image.

On the other hand, (3) in the present embodiment, it is determined that the maximum value T _max 3 of the thermistor temperature is below the lower limit value _TL of the allowable range, and the value of the initial duty I ₀ is added. Therefore, when printing under the same conditions, the duty at startup is increased and a good image can be obtained.

In addition, under the condition where the thermal conductivity of the pressure roller is high as in condition 4, (1) the initial duty I ₀ is not changed when optimization is not performed. The fixing member is excessively warmed, and density unevenness and gloss unevenness continue to occur in the image. Further, (2) even in the optimization method of the conventional example, the rate of increase in the thermistor temperature is not different from the rate of temperature increase in the nominal model, so the value of the initial duty I ₀ is not changed. For this reason, when printing under the same conditions, the fixing member is always excessively warmed, and density unevenness and gloss unevenness continue to occur in the image.

On the other hand, (3) In the present embodiment, it is determined that the maximum value T _{max 4} of the thermistor temperature is above the upper limit T _H tolerance, subtracting the value of the initial duty I _0. Therefore, when printing under the same conditions, the duty at startup is suppressed and a good image can be obtained.

As described above, the optimization method according to the present embodiment can cope with not only the difference in the input voltage but also the variation in the physical property value of the fixing member, and the initial duty I ₀ value is corrected to the optimum value in the operating environment of each image forming apparatus. To do. As a result, the fixing member temperature can be quickly reached the target temperature without causing unnecessary overshoot, and uneven glossiness and density unevenness of the image can be prevented.

(Effect of this embodiment)
According to the present embodiment, the heater output control parameter is corrected to an optimum value in the operating environment of each image forming apparatus using a simple optimization method. As a result, even in different operating environments, the fixing member temperature can reach the target temperature quickly and without causing unnecessary overshoot, and gloss unevenness and density unevenness of the image can be prevented.

<< Second Embodiment >>
Next, a second embodiment of the present invention will be described. Since the configuration of the image forming apparatus and the control circuit in the present embodiment are the same as those shown in the first embodiment, the description thereof is omitted. As a feature of the present embodiment, when determining the initial duty I ₀ of the control parameter, not only the initial thermistor temperature T ₀ but also the warm-up count value α including the print history of the fixing device is considered. The purpose of introducing the warm air count value α is to estimate the hot state of the fixing device more accurately.

In the optimization control of the present invention, correction is performed based on the past print result. Therefore, in order to increase the reliability of the optimization control, it is possible to determine in what state the print performed in the past was performed. Need to know exactly. For example, even with a fixing device having the same initial thermistor temperature T ₀ = 100 ° C., when the thermistor temperature slowly drops to 100 ° C. after printing 500 sheets, and when it reaches 100 ° C. immediately after printing 10 sheets And the hot state of the fixing device is different. In the former, the heat storage amount of the entire fixing device is larger, and the atmospheric temperature in the device is also higher.

Thus, it is difficult to predict the heat storage amount of the entire fixing device and the ambient temperature in the device only from the thermistor temperature installed on one fixing member. For this reason, even if the start-up is performed from the same initial thermistor temperature T _{0 with} the same initial duty I ₀ , a slight difference may occur in the behavior of the thermistor temperature due to a difference in print history. Although it is possible to increase the number of thermistors installed in the fixing device and to make a prediction based on the temperature of a plurality of fixing members, there is a concern that the fixing device may become complicated and costly.

Therefore, in this embodiment, the initial duty I ₀ is determined in consideration of not only the initial thermistor temperature T ₀ but also the warm air count α. The warm air count α is a value obtained from the print history and the standby time, and is a value corresponding to the heat storage amount of the entire fixing device and the ambient temperature in the device.

  Below, the management method of a warm-up count is demonstrated. The warm-up count value α is incremented by 1 every time a sheet of paper is printed, and the count value α increases as the number of printed sheets increases. Also, under printing conditions where the amount of heat stored in the fixing device during printing is large, the count addition value is increased. For example, since the fixing temperature is high in the printing mode for thick paper / rough paper, +2 is added to the warm-up count α every time one sheet is printed. On the other hand, in the standby state after the end of printing, the warm-up count α is also counted down with the passage of time in response to the natural cooling of the fixing device.

  Specifically, the cooling characteristics of the fixing device are examined in advance, and the warm-up count is subtracted using an arithmetic expression having a function of elapsed time. By managing the warm air count α in this way, it is possible to predict the heat storage amount of the entire fixing device and the atmospheric temperature in the device.

In this embodiment, the table of the initial duty I ₀ is set as shown in FIG. 6, and different values are selected for each initial thermistor temperature T ₀ and warm-up index α. Even at the same initial thermistor temperature, the value of the initial duty I ₀ is reduced when starting up in a state where the warm-up count is high. For example, even if the initial thermistor temperature is 50 ° C., the initial duty I ₀ is 45% when the warm air count α is 0, but is 42% when the warm air count α is 500.

As in the first embodiment, each time printing is performed, it is determined whether or not the maximum value T _max of the thermistor temperature at the start-up is within an allowable range (T _H ≧ T _max ≧ T _L ). To do. If the value is outside the allowable range, the values of the initial duty I ₀ corresponding to each initial thermistor temperature T ₀ and warm-up index α are corrected.

As described above, in the optimization method according to the present embodiment, the reliability of the optimization control is improved by rewriting the appropriate data for each initial thermistor temperature T ₀ and warm-up index α (correcting to the optimal initial duty I ₀ ). Can be improved.

<< Third Embodiment >>
Next, a third embodiment of the present invention will be described. A feature of the present embodiment is that, when a user performs printing for the first time after initial setting (initialization) of the image forming apparatus, the following is performed. That is, when the _Tmax of the thermistor temperature at the time of startup is out of the preset temperature range, all values in the initial duty I ₀ table are uniformly changed. The objective is to quickly optimize the initial duty ₁₀ table and reduce the number of image defects.

In the second embodiment, the initial duty I ₀ is determined by the state (initial thermistor temperature T ₀ and warm-up index α) at the start-up control start, and is corrected to be an optimum value for each state. Since the thermistor temperature profile depends on the state of the fixing device at the start of control, the more accurately the state at the start of control, that is, the value of the initial duty I _{0 in} the table of FIG. Sex goes up.

However, the more frequently the state of the fixing device is classified, inevitably, the number of times of starting up with the initial duty I ₀ before correction increases. Therefore, when the operating environment of the image forming apparatus is far from the nominal model conditions, the number of image defects is increased.

Therefore, in the present embodiment, when printing is performed for the first time after initialization by the user, for example, when the printing operation is performed for the first time after the image forming apparatus is installed in the operating environment, a threshold value with an overshoot amount at startup is set. If so, do as follows. That is, it is predicted that there is a high possibility that overshoot will occur in other states (other initial thermistor temperature T ₀ and warm air index α), and the value of initial duty I ₀ in other states is also reduced uniformly. By doing so, after the next printing, even if printing is performed in another state, the possibility of image failure is reduced.

Conversely, when the printing operation is performed for the first time after initialization, if the maximum value T _max of the thermistor temperature falls below a certain threshold value, it is predicted that there is a high possibility that start-up shortage will occur even in other states. The value of the initial duty I _{0 in} the state is increased uniformly. For example, when a print operation is performed for the first time after initialization, the print start state is the initial thermistor temperature T ₀ = 20 ° C. and the warm-up count α = 0, and the start-up control is performed with the initial duty I ₀ = 50% according to the table of FIG. Consider the case where

At this time, when the maximum value T _max of the thermistor temperature at startup is 210 ° C. or higher, that is, when the overshoot amount (T _max −target temperature) is 10 ° C. or higher, the following is performed. That is, the value of 50% of the initial duty I ₀ corresponding to the starting state (initial thermistor temperature T ₀ = 20 ° C., warm air count α = 0) is reduced to 48%. In addition, the value of the initial duty I ₀ in other states (other initial thermistor temperature T ₀ , warm air count α) is also uniformly reduced by 2%. As a result, when printing is performed under other conditions after the next printing, the power at startup is reduced, and the possibility of image defects such as density unevenness and gloss unevenness is reduced.

On the contrary, when the maximum value T _max of the thermistor temperature at the time of start-up is 195 ° C. or less, that is, when the difference (T _max −target temperature) is −5 ° C. or less, the following is performed. That is, the initial duty I ₀ value 50% corresponding to the start-up state (initial thermistor temperature T ₀ = 20 ° C., warm air count α = 0) is increased to 52%. In addition, the value of the initial duty I ₀ in other states (other initial thermistor temperature T ₀ , warm air count α) is also increased by 2%.

As a result, when printing is performed in another state after the next printing, the possibility of an image failure such as a fixing failure is reduced by increasing the power at startup. FIG. 7 shows a table summarizing the difference (T _max -target temperature) at the first printing after initialization and the uniform change amount of the initial duty I ₀ .

Thus, when the image forming apparatus performs a printing operation for the first time after initialization, if the thermistor temperature T _max at the time of start-up is out of the preset temperature range, all values in the initial duty I ₀ table are uniformly set. change. Thus, it is possible to quickly optimize the initial duty I ₀ table, reducing the number of occurrences of image defects.

However, even when the values of the initial duty I ₀ table are uniformly changed, the maximum value T _max of the thermistor temperature at the time of startup is always within the allowable range (T _H ≧ T _max ≧ T _L ) when performing printing. Judge whether there is. If it is out of the allowable range, only the initial duty I ₀ value corresponding to each state (each initial thermistor temperature T ₀ and warm-up index) is corrected (rewritten).

In addition, when the user performs initialization when the fixing device is replaced or when the installation environment of the image forming apparatus is changed, the initial duty I ₀ table described in the present embodiment is uniformly changed after initialization. Judge whether or not to do so. However, at the time of initialization, the initial duty I ₀ table is reset to an initial value designed based on the nominal model.

(Modification 1)
In the embodiment described above, the control parameters for optimizing was the initial duty I _0, control parameters to optimize is not limited to the initial duty I _0, may be another control parameter such as the proportional coefficient K _P.

(Modification 2)
In the above-described embodiment, whether or not the value of the control parameter is appropriate is determined based on whether or not the maximum value T _max of the thermistor temperature exceeds the first allowable range as the target temperature. Instead, it is determined whether the value of the control parameter is appropriate based on whether or not the time integral value of the difference between the maximum temperature detected by the temperature detecting means and the target temperature exceeds the second allowable range. May be.

(Modification 3)
In the above-described embodiment, the temperature control system performs the PID control. However, the temperature control system also performs the PI control.

(Modification 4)
Further, the heat-resistant film as the heating rotator is not limited to the one heated by the heater described in the above-described embodiment, and the heat-resistant film includes a current-carrying portion and self-heats, or the heat-resistant film generates heat by electromagnetic induction. It may be a thing.

(Modification 5)
Further, in the above-described embodiment, the pressure roller as the driving roller is used as the pressure member. However, when the heat-resistant film that is the heating rotator is mounted on another driving roller and can be rotated, A fixed pressure pad may be used as the pressure member.

11. Heat resistant film (heated rotating body) 12. Heater for heating (heating source), 14 Thermistor (temperature detection means), 21 Pressure roller (pressing member) 31, Temperature control System, 100 ... storage means, 200 ... discrimination means, 300 ... data rewrite means

Claims (8)

A heating rotator heated and rotated by a heating source;
A pressurizing member that faces the heating rotator and sandwiches and conveys a recording material carrying an image in a nip formed between the heating rotator, and
A temperature control system that performs PI control or PID control corresponding to the difference between the target temperature of the heating rotator and the detected temperature of the temperature detector, and controls the detected temperature to the target temperature;
Storage means for storing at least one of an initial duty corresponding to each temperature adjustment initial temperature in the temperature control system and a proportional coefficient in the temperature control corresponding to each temperature adjustment initial temperature as data;
In the start-up period using the data of the storage unit corresponding to the temperature adjustment initial temperature detected by the temperature detection unit, the maximum allowable temperature detected by the temperature detection unit is a first allowable range as the target temperature. Determining means for determining whether or not the time integral value of the difference between the maximum temperature detected by the temperature detecting means and the target temperature exceeds a second allowable range;
Data rewriting means for rewriting the data in the storage means corresponding to the temperature control initial temperature to appropriate data for the next job when the first allowable range or the second allowable range is exceeded;
An image heating control device comprising:   The image heating control apparatus according to claim 1, wherein the determination unit determines whether or not a maximum temperature detected by the temperature detection unit is out of a range between an allowable maximum temperature and an allowable minimum temperature. .   The image heating control apparatus according to claim 1, wherein the temperature control system calculates a duty after the initial duty based on the temperature control initial temperature and the proportional coefficient.   When the data rewriting means exceeds the allowable range, only the data of the storage means corresponding to the detected temperature control initial temperature is rewritten to the appropriate data that differs depending on the amount exceeding the allowable range. The image heating control apparatus according to any one of claims 1 to 3.   4. The image heating control apparatus according to claim 1, wherein the data rewriting unit rewrites the appropriate data that is different depending on a heat storage amount or an ambient temperature in the apparatus. 5.   The image heating control apparatus according to claim 5, wherein the heat storage amount or the ambient temperature is determined from a temperature detected by the temperature detection unit and a print history.   When the data rewriting means exceeds the allowable range, only the data of the storage means corresponding to the detected temperature control initial temperature is rewritten to the appropriate data that differs depending on the amount exceeding the allowable range and the warm-up index. The image heating control apparatus according to claim 6. When the data rewriting means exceeds the allowable range, as an initial setting,
4. All of the data of the said memory | storage means corresponding to the said temperature control initial temperature as well as the data of the said memory | storage means corresponding to the detected said temperature control initial temperature are rewritten. 2. The image heating control device according to item 1.