JP7091682B2 - Image forming device and control method - Google Patents

Description

The present invention relates to an image forming apparatus including a fuser and a control method thereof.

In the temperature control of the fuser, those using PI control or PID control are known. In these controls, integral control is performed using the integrated value of the deviation between the target temperature and the current temperature. Therefore, for example, the integrated value becomes large when the temperature rises, and the overshoot in which the temperature of the heating part greatly exceeds the target temperature occurs. May occur. Therefore, for example, in Patent Document 1, the proportional coefficient of the calculation formula of the PID calculation is changed according to the temperature at the start of heating of the fixing belt detected by the temperature detector, whereby the fixing belt is over-heated at the time of temperature rise. Techniques for reducing the size of the shoot are disclosed.

Japanese Unexamined Patent Publication No. 2005-257945

As described above, in the temperature control of the fuser, it is desired that the overshoot at the time of raising the temperature is small. Furthermore, it is desired that the temperature fluctuation of a heating portion such as a fixing belt or a heating roller, including overshoot at the time of temperature rise, is small.

The present invention has been made in view of the above background, and an object of the present invention is to provide an image forming apparatus and a control method capable of reducing temperature fluctuations in a heating unit.

In order to achieve the above object, the image forming apparatus of the present invention has a developing agent image forming portion for forming a developing agent image on a sheet, a heating portion for heating the sheet, and a heater for heating the heating portion. It includes a fuser for fixing a developer image on a sheet, a temperature detection unit for detecting the temperature of the heating unit, and a control unit.
The control unit uses the calculation process to calculate the operation amount including the sum of the proportional term proportional to the deviation between the target temperature and the detection temperature and the integral term proportional to the integral value of the deviation, and the operation amount calculated by the calculation process. Based on this, the energization process of energizing the heater is executed, and the deviation used in the integration term in the calculation process is limited within a predetermined range.

According to such a configuration, since the absolute value of the deviation used in the integration term does not become too large, it is possible to suppress the sudden increase or decrease of the integral value calculated from the deviation. As a result, overshoot can be suppressed when the temperature of the heating unit is raised, and undershoot in which the temperature of the heating unit is significantly lower than the target temperature can be suppressed when the temperature of the heating unit is lowered. That is, the temperature fluctuation of the heating unit can be reduced.

In the image forming apparatus described above, in the calculation process, when the detected temperature is less than the switching temperature lower than the target temperature, the control unit calculates the operation amount including the proportional term and not including the integral term, and the detected temperature is determined. When the switching temperature is equal to or higher than the switching temperature, the operation amount including the sum of the proportional term and the integral term can be calculated.

According to this, when the temperature of the heating unit is raised, it is possible to suppress the sudden increase in the integrated value of the deviation, so that it is possible to suppress the sudden increase in the operation amount, and it is possible to suppress the sudden increase in the operation amount of the heating unit. It is possible to further suppress the rapid increase in temperature. As a result, overshoot at the time of temperature rise can be satisfactorily suppressed.

In the image forming apparatus described above, the control unit may be configured to reset the integrated value when the target temperature is changed to a new target temperature different by a predetermined value or more.

According to this, when the target temperature is changed to a lower target temperature, the temperature of the heating unit can be quickly brought closer to the new target temperature by resetting the integrated value. Further, when the target temperature is changed to a high target temperature, it is possible to suppress the temperature of the heating portion from rapidly increasing by resetting the integrated value, so that overshoot can be suppressed.

In the image forming apparatus described above, the control unit may be configured to calculate the manipulated variable by adding the differential term proportional to the differential value of the deviation in the calculation process.

According to this, since the response can be made faster, the temperature fluctuation of the heating unit can be made smaller.

In the image forming apparatus described above, the control unit uses a value obtained by subtracting the detected temperature from the target temperature as the deviation in the calculation process, and integrates when the detected temperature is equal to or less than the target temperature and the deviation is equal to or more than the first limit value. When the first limit value is used as the deviation used in the term and the detection temperature is equal to or higher than the target temperature and the deviation is equal to or less than the second limit value, the second limit value can be used as the deviation used in the integration term.

In the image forming apparatus described above, the first limit value and the second limit value may have an absolute value of 2 to 8 ° C.

In the image forming apparatus described above, the first limit value and the second limit value can be configured to have the same absolute value.

In the image forming apparatus described above, in the energization process, the control unit energizes the heater at a duty ratio corresponding to the operation amount by controlling the number of waves in units of half waves of AC sinusoidal waves, and the operation amount is equal to or more than the predetermined operation amount. When the duty ratio is 100% and the operation amount is 0 or less, the duty ratio can be set to 0%.

Further, the control method of the present invention for achieving the above-mentioned object includes a developer image forming unit for forming a developer image on a sheet, a heating unit for heating the sheet, and a heater for heating the heating unit. , A fixing device for fixing a developer image on a sheet, and a control method for an image forming apparatus.
This control method was calculated by a calculation process for calculating an operation amount including a sum of a proportional term proportional to the deviation between the target temperature and the temperature of the heating unit and an integral term proportional to the integral value of the deviation, and a calculation process. Including the energization process of energizing the heater based on the operation amount, the deviation used in the integration term in the calculation process is limited within a predetermined range.

According to such a method, since the absolute value of the deviation used in the integration term does not become too large, it is possible to suppress the sudden increase or decrease of the integral value calculated from the deviation. As a result, overshoot can be suppressed when the temperature of the heating section is raised, and undershoot can be suppressed when the temperature of the heating section is lowered, so that the temperature fluctuation of the heating section can be reduced.

According to the present invention, the temperature fluctuation of the heating unit can be reduced.

It is a figure which shows the schematic structure of the image forming apparatus which concerns on one Embodiment of an invention. It is a figure which shows the structure for controlling a fuser. It is a figure which shows the change of various temperature, the integral value and the flag when the target temperature is set to the first target temperature, and then is set to the second target temperature lower than the first target temperature. It is a figure which shows the change of various temperature and a flag when the target temperature is set to the first target temperature, and then is set to the third target temperature higher than the first target temperature. It is a figure for demonstrating wave number control. It is a map showing the relationship between the operation amount and the duty ratio. It is a flowchart which shows the operation of a control part. It is a time chart which shows the change of the detection temperature and the integral value at the time of limiting the magnitude of the integral term deviation which concerns on embodiment. It is a time chart which shows the change of the detection temperature and the integral value when the magnitude of the integral term deviation is not limited which concerns on a comparative example.

Hereinafter, an embodiment of the invention will be described in detail with reference to the drawings as appropriate.
As shown in FIG. 1, a laser printer 1 as an example of an image forming apparatus includes a main body housing 2, a sheet supply unit 3, an exposure apparatus 4, a developer image forming unit 5, a fixing device 8, and a temperature. It mainly includes a detection unit 9 and a control unit 100.

The sheet supply unit 3 is provided in the lower part of the main body housing 2, and mainly has a sheet tray 31 for accommodating a sheet S such as paper, a pressure plate 32, and a sheet supply mechanism 33. The sheet S housed in the sheet tray 31 is moved upward by the pressure plate 32, and is supplied by the sheet supply mechanism 33 toward between the photoconductor drum 61 and the transfer roller 63 of the developer image forming unit 5.

The exposure device 4 is arranged in the upper part of the main body housing 2 and has a light source device, a polygon mirror, a lens, a reflector, and the like (not shown). In the exposure device 4, a light beam (see two-dot chain line) based on image data emitted from the light source device is scanned at high speed on the surface of the photoconductor drum 61 to expose the surface of the photoconductor drum 61.

The developer image forming unit 5 is a member that forms a developer image on the sheet S, and is arranged below the exposure apparatus 4. The developer image forming unit 5 is configured to be detachably attached to the main body housing 2 from an opening formed when the front cover 21 provided on the front portion of the main body housing 2 is opened as a process cartridge. ing. The developer image forming unit 5 has a photoconductor cartridge 6 and a developing cartridge 7.

The photoconductor cartridge 6 mainly includes a photoconductor drum 61, a charger 62 which is a corona charger, and a transfer roller 63. The developing cartridge 7 is detachably configured with respect to the photoconductor cartridge 6, and includes a developing roller 71, a supply roller 72, a layer thickness regulating blade 73, an accommodating portion 74 for accommodating a developer made of dry toner, and an agitator. It mainly has 75.

In the developer image forming unit 5, the surface of the photoconductor drum 61 is uniformly charged by the charger 62 and then exposed by the light beam from the exposure device 4, so that the image data is displayed on the photoconductor drum 61. An electrostatic latent image is formed based on. Further, the developer in the accommodating portion 74 is supplied to the supply roller 72 while being stirred by the agitator 75, and is supplied from the supply roller 72 to the developing roller 71. Then, as the developing roller 71 rotates, it enters between the developing roller 71 and the layer thickness regulating blade 73 and is supported on the developing roller 71 as a thin layer having a constant thickness.

The developer supported on the developing roller 71 is supplied from the developing roller 71 to the electrostatic latent image formed on the photoconductor drum 61. As a result, the electrostatic latent image is visualized and a developer image is formed on the photoconductor drum 61. After that, the sheet S passes between the photoconductor drum 61 and the transfer roller 63, so that the developer image on the photoconductor drum 61 is transferred onto the sheet S.

The fuser 8 is arranged behind the developer image forming unit 5, and mainly has a heating unit 81, a pressurizing unit 82, and a heater 83.

The heating unit 81 is a cylindrical heating roller made of metal, and is configured to heat the sheet S.
The pressurizing portion 82 is a pressurizing roller provided with an elastic layer around the core metal, and is arranged in a state of being pressed in contact with the heating portion 81.
The heater 83 is a halogen lamp that heats the heating unit 81, and is arranged inside the heating unit 81.

In the fuser 8, the developer image transferred onto the sheet S is heat-fixed while the sheet S passes between the heating unit 81 and the pressurizing unit 82. The sheet S on which the developer image is heat-fixed is discharged onto the paper output tray 22 by the transport rollers 23 and 24.

The control unit 100 is a device that controls each unit of the laser printer 1, such as a fuser 8, and is composed of a single electric circuit or a plurality of electric circuits. The control unit 100 executes control of each unit by outputting a control signal and a drive voltage to each unit of the laser printer 1. Specifically, as shown in FIG. 2, the control unit 100 includes a CPU 110, a ROM 120, a RAM 130, a heater controller 140, a switching circuit 150, and the like.

The ROM 120 stores data such as a program for controlling each part of the laser printer 1 and various setting information.
The RAM 130 is used as a work area when the CPU 110 executes various programs and as a temporary storage area for data.

The CPU 110 performs a process of instructing the operation timing of each part of the laser printer 1 and sending a command value as a target temperature TT to the heater controller 140.
The heater controller 140 sets the duty ratio of the switching circuit 150 based on the target temperature TT and the detection temperature T detected by the temperature detection unit 9. In this embodiment, the CPU 110 and the heater controller 140 are integrated as a single semiconductor element.
The switching circuit 150 energizes the heater 83 by switching the AC voltage at the set duty ratio.

The temperature detection unit 9 is a sensor for detecting the temperature of the heating unit 81, and is arranged facing the surface of the heating unit 81 with a predetermined distance from the surface of the heating unit 81. .. The temperature detection unit 9 outputs a signal corresponding to the temperature of the heating unit 81 to the control unit 100. The control unit 100 acquires a detected value (detection temperature T) of the surface temperature of the heating unit 81 from the signal output from the temperature detection unit 9. As the temperature detecting unit 9, for example, a thermistor whose electric resistance changes according to the temperature can be used.

When controlling the fuser 8, the control unit 100 mainly executes a calculation process for calculating the operation amount U of the heater 83 and an energization process for energizing the heater 83 based on the operation amount U calculated in the calculation process. .. Specifically, the control unit 100 drives the switching circuit 150 so that the heater controller 140 calculates the operation amount U and energizes the heater 83 with the duty ratio corresponding to the calculated operation amount U.

The control unit 100 sets the target temperature TT of the heating unit 81 in the calculation process, and the heater so that the detection temperature T, which is the temperature of the heating unit 81 detected by the temperature detection unit 9, follows the set target temperature TT. The operation amount U of 83 is set. Specifically, the control unit 100 calculates an operation amount U including a sum of a proportional term proportional to the deviation ΔT between the target temperature TT and the detected temperature T and an integral term proportional to the integrated value of the deviation ΔT.

Specifically, the control unit 100 calculates the manipulated variable U including the proportional term and not including the integral term after the target temperature TT is set and before the detected temperature T reaches the switching temperature TS. Further, the control unit 100 calculates the manipulated variable U including the sum of the proportional term and the integral term after the detected temperature T reaches the switching temperature TS after setting the target temperature TT. The switching temperature TS is a temperature equal to or lower than the currently set target temperature TT.

In the present embodiment, the control unit 100 calculates the manipulated variable U by the following equation (1) including the proportional term K _p ΔT after the target temperature TT is set and before the detected temperature T reaches the switching temperature TS. ..
Un ₌ K _p ΔT _n ... (1)
Here, K _p is a proportional gain as a preset fixed value, and is a positive value. Further, n attached to each variable indicates that the variable is the current value, and n-1 indicates that the value is the previous value.

In the present embodiment, the value obtained by subtracting the detected temperature T from the target temperature TT represented by the following equation (2) is used as the deviation ΔT.
ΔT _n = TT _n −T _n・ ・ ・ (2)

Further, after the detection temperature T reaches the switching temperature TS after setting the target temperature TT, the control unit 100 uses the following equation (3) including the sum of the proportional term K _p ΔT and the integral term K _i I. The operation amount U is calculated.
_{Un =} K _p ΔT _n + K _i In ... (3)
Here, K _i is an integral gain as a preset fixed value, and is a positive value.

Further, I is an integral value of the deviation ΔT, and can be calculated by the following equation (4) as an example.
In ₌ In _-1 + tsΔTi _n ... (4)
Here, ts is a sampling time interval. Further, ΔTi is a deviation used in the integral term K _i I (hereinafter, referred to as “integral term deviation”). The integral term deviation ΔTi will be described later.

Further, when the target temperature TT (TT _n-1 ) is changed to a new target temperature TT (TT _n ) different by a predetermined value TTth or more, the control unit 100 resets the integrated value I to the first value. In the present embodiment, the first value is 0, and when the reset is performed, the value of the integral term K _i I becomes 0. Further, the predetermined value TTth is preferably 10 ° C. or higher, and can be set to 15 to 20 ° C. as an example.

To explain the control by the control unit 100 more specifically, as shown in FIG. 3, the control unit 100 sets the target temperature TT to, for example, the first target temperature TT1, and the detection temperature T is the first. Before reaching the switching temperature TS1, that is, when the detected temperature T is less than the first switching temperature TS1, the above equation (1) includes the proportional term K _p ΔT and does not include the integral term K _i I. The P control for calculating the operation amount U is executed.

The first switching temperature TS1 is set as a temperature lower than the first target temperature TT1. As an example, the first switching temperature TS1 can be set as a temperature 10 to 40 ° C. lower than the first target temperature TT1. In this case, it is desirable that the first switching temperature TS1 is set to a temperature 15 to 20 ° C. lower than the first target temperature TT1.

After setting the target temperature TT to the first target temperature TT1, the control unit 100 reaches the first switching temperature TS1 after the detection temperature T reaches the first switching temperature TS1, that is, the detected temperature T becomes the first switching temperature TS1 or higher. If this is the case, then PI control for calculating the operation amount U by the above equation (3) including the sum of the proportional term K _p ΔT and the integral term K _i I is executed.

Further, when the control unit 100 changes the target temperature TT from the first target temperature TT1 to a new second target temperature TT2 lower than a predetermined value TTth (satisfying TT1-TT2 ≧ TTth), the integrated value I Is reset to 0. The control unit 100 sets the target temperature TT to the second target temperature TT2, and before the detection temperature T reaches the second switching temperature TS2, that is, when the detection temperature T is higher than the second switching temperature TS2. Executes P control for calculating the operation amount U by the above equation (1).

The second switching temperature TS2 is set as a temperature equal to or lower than the second target temperature TT2. In the present embodiment, the second target temperature TT2 and the second switching temperature TS2 are set to the same temperature. The first target temperature TT1, the first switching temperature TS1, the second target temperature TT2, and the second switching temperature TS2 are set to values satisfying the following equation (5).
TT1-TS1> TT2-TS2 ... (5)

After setting the target temperature TT to the second target temperature TT2, the control unit 100 reaches the second switching temperature TS2 after the detection temperature T reaches the second switching temperature TS2, that is, the detection temperature T becomes the second switching temperature TS2 or less. If this is the case, then PI control for calculating the operation amount U is executed by the above equation (3).

Further, as shown in FIG. 4, the control unit 100 raises the target temperature TT from the first target temperature TT1 to a new third target temperature TT3 higher than a predetermined value TTth (satisfying TT3-TT1 ≧ TTth). When changed, the integrated value I is reset to 0 (not shown). The control unit 100 sets the target temperature TT to the third target temperature TT3, and before the detection temperature T reaches the third switching temperature TS3, that is, when the detection temperature T is less than the third switching temperature TS3. , P control for calculating the operation amount U by the above equation (1) is executed.

The third switching temperature TS3 is set as a temperature lower than the third target temperature TT3. As an example, the third switching temperature TS3 can be set as a temperature 10 to 40 ° C. lower than the third target temperature TT3. In this case, it is desirable that the third switching temperature TS3 is set to a temperature 15 to 20 ° C. lower than the third target temperature TT3.

After setting the target temperature TT to the third target temperature TT3, the control unit 100 reaches the third switching temperature TS3 after the detection temperature T reaches the third switching temperature TS3, that is, the detected temperature T becomes the third switching temperature TS3 or higher. If this is the case, then PI control for calculating the operation amount U is executed by the above equation (3).

As shown in FIGS. 3 and 4, when the control unit 100 changes the target temperature TT (TT1) to a new target temperature TT (TT2 or TT3) different by a predetermined value TTth or more and resets the integrated value I to 0. The flag FL is set to 0. Further, the control unit 100 sets the flag FL to 1 when the detection temperature T reaches the switching temperature TS after setting the target temperature TT. When the flag FL is 0, the control unit 100 executes P control for calculating the operation amount U by the above equation (1), and when the flag FL is 1, the operation amount U is calculated by the above equation (3). Perform PI control. The initial value of the flag FL is 0.

The control unit 100 limits the integral term deviation ΔTi within a predetermined range in the PI control for calculating the manipulated variable U by the above equation (3). Specifically, when the detection temperature T is equal to or lower than the target temperature TT (that is, ΔT ≧ 0) and the deviation ΔT is equal to or higher than the first limit value L1 (ΔT ≧ L1), the control unit 100 sets the integral term deviation ΔTi. The first limit value L1 is used. Further, the control unit 100 determines that the detection temperature T is equal to or higher than the target temperature TT (that is, ΔT ≦ 0) and the deviation ΔT is equal to or less than the second limit value −L2 (ΔT ≦ −L2 (L2 is a positive value). .)), The second limit value −L2 is used as the integral term deviation ΔTi.

Further, when the deviation ΔT is larger than the second limit value −L2 and is less than the first limit value L1 (−L2 <ΔT <L1), the control unit 100 uses the deviation ΔT as the integral term deviation ΔTi. In this way, the control unit 100 limits the integral term deviation ΔTi within the range of the first limit value L1 or less and the second limit value −L2 or more (−L2 ≦ ΔTi ≦ L1).

In the present embodiment, the first limit value L1 and the second limit value −L2 are values indicating a preset temperature difference. It is desirable that the absolute values L1 and L2 of the first limit value L1 and the second limit value −L2 are 2 to 8 ° C. Further, in the present embodiment, the first limit value L1 and the second limit value −L2 are set to values in which the absolute values L1 and L2 are equal (L1 = L2). As an example, the absolute values L1 and L2 of the first limit value L1 and the second limit value −L2 are 5 ° C.

As shown in FIG. 2, in the energization process, the control unit 100 sets a duty ratio corresponding to the operation amount U calculated in the calculation process, and controls energization to the heater 83 based on the set duty ratio. As shown in FIG. 5, the control unit 100 energizes the heater 83 at a set duty ratio by controlling the wave number in units of the half-wave HW of the AC sine wave SW.

As an example, when the duty ratio is 33%, the control unit 100 energizes with one half-wave HW out of three continuous half-wave HWs and does not energize with the other two half-wave HWs. When the duty ratio is 40%, energization is performed by two half-wave HWs out of five continuous half-wave HWs, and energization is not performed by the other three half-wave HWs. Further, when the duty ratio is 43%, the control unit 100 energizes with three half-wave HWs out of seven continuous half-wave HWs and does not energize with the other four half-wave HWs. When the duty ratio is 50%, energization is performed by one half-wave HW of two consecutive half-wave HWs, and energization is not performed by the other half-wave HW.

The heater controller 140 of the control unit 100 drives the switching circuit 150 by a map as shown in FIG. As shown in FIG. 6, when the operation amount U calculated by the calculation process is equal to or more than the predetermined operation amount Uth, the control unit 100 sets the duty ratio to 100%. Further, when the operation amount U is less than the predetermined operation amount Uth, the control unit 100 sets the duty ratio to a stepwise smaller value based on the map of FIG. Further, when the operation amount U is 0 or less, the control unit 100 sets the duty ratio to 0%.

Next, the operation of the control unit 100 (control method of the laser printer 1) will be described. The control unit 100 repeatedly executes the operation shown in FIG. 7 every predetermined control cycle (time ts).
As shown in FIG. 7, the control unit 100 determines whether or not the target temperature TT _n is equal to or higher than the predetermined value TTth with respect to the target temperature TT _n-1 (S11).

When the target temperature TT _n is equal to or higher than the predetermined value TTth with respect to the target temperature TT _n-1 (S11, Yes), that is, when the target temperature TT _n-1 is changed to a new target temperature TT _n different from the predetermined value TTth. , The control unit 100 resets the integrated value In to 0 ( _S12 ) and sets the flag FL to 0 (S13). After that, the control unit 100 proceeds to step S15.

Further, when the target temperature TT _n is not equal to or higher than the predetermined value TTth with respect to the target temperature TT _n-1 (S11, No), specifically, when the target temperature TT _n is not changed from the target temperature TT _n-1 . When the target temperature TT _n is changed from the target temperature TT _n-1 but the change width is less than the predetermined value TTth, the control unit 100 determines whether or not the flag FL is 1. (S14). Then, when the flag FL is not 1 (S14, No), that is, when the flag FL is 0, the control unit 100 proceeds to step S15.

In step S15, the control unit 100 determines whether or not the detected temperature T _n has reached the switching temperature TS (S15). Then, when the detected temperature T _n has not reached the switching temperature TS (S15, No), the control unit 100 proceeds to step S23, and since the integrated value _{In is} 0, the operation is performed by the above equation (1). _A calculation process for calculating the quantity Un is executed (S23).

On the other hand, in step S15, when the detection temperature T _n reaches the switching temperature TS (S15, Yes), the control unit 100 sets the flag FL to 1 (S16) and proceeds to step S17. If the flag FL is 1 in step S14 (S14, No), the control unit 100 proceeds to step S17.

In step S17, the control unit 100 determines whether or not the deviation ΔT _n is equal to or greater than the first limit value L1 (S17). Then, when the deviation ΔT _n is equal to or greater than the first limit value L1 (S17, Yes), the control unit 100 sets the integral term deviation ΔTi _n to the first limit value L1 (S19), and the deviation ΔT _n is the first limit value. When it is not L1 or more (S17, No), it is determined whether or not the deviation ΔT _n is equal to or less than the second limit value −L2 (S18). When the deviation ΔT _n is equal to or less than the second limit value −L2 (S18, Yes), the control unit 100 sets the integration term deviation ΔTi _n to the second limit value −L2 (S21), and the deviation ΔT _n is the second limit value. When it is not -L2 or less (S18, No), the deviation of the integration term ΔTi _n is defined as the deviation ΔT _n (S20).

After determining the integral term deviation ΔTi _n in steps S19 to S21, the control unit 100 calculates the integral value In ₍ S22). Then, the control unit 100 executes a calculation process for calculating the operation amount _Un by the above equation (3) (S23).

After executing the calculation process, the control unit 100 sets the duty ratio from the calculated operation amount _Un and the map of FIG. 6 (S24). Then, the control unit 100 executes the energization process of energizing the heater 83 at the duty ratio set by the wave number control (S25), and ends the current operation.

According to the present embodiment described above, by limiting the integral term deviation ΔTi within a predetermined range (−L2 ≦ ΔTi ≦ L1), for example, when the temperature of the heating unit 81 is raised as shown in FIG. Since the integral term deviation ΔTi does not become too large, it is possible to suppress a rapid increase in the integral value I calculated from the integral term deviation ΔTi. Note that FIG. 9 is a simulation result in the case where the deviation ΔT is used as the integral term deviation ΔTi and the integral term deviation ΔTi is not limited, but the integral value I is larger than that in the case of the embodiment shown in FIG. There is. In the present embodiment, since the integral value I can be suppressed from increasing rapidly, overshoot (particularly) as compared with the case where the integral term deviation ΔTi shown in FIG. 9 is not limited when the temperature of the heating unit 81 is raised. The very first overshoot) can be suppressed.

Further, in the present embodiment, when the detected temperature T is less than the switching temperature TS lower than the target temperature TT, the operation amount U is calculated by the above equation (1) not including the integral term _{Ki I} , so that the heating unit 81 It is possible to suppress the sudden increase in the integrated value I when the temperature of the above is raised. As a result, it is possible to suppress the sudden increase in the operation amount U, so that it is possible to further suppress the sudden increase in the temperature of the heating unit 81, and it is possible to satisfactorily suppress the overshoot at the time of temperature rise. be able to.

Although not shown, the integral term deviation ΔTi is within a predetermined range (−L2 ≦ ΔTi ≦ L1) even when the target temperature TT is set to a new low target temperature TT to lower the temperature of the heating unit 81. By limiting to, since the absolute value of the integral term deviation ΔTi does not become too large, it is possible to suppress a sharp decrease in the integral value I calculated from the integral term deviation ΔTi. As a result, undershoot can be suppressed when the temperature of the heating unit 81 is lowered. As described above, according to the present embodiment, the temperature fluctuation of the heating unit 81 can be reduced regardless of whether the temperature of the heating unit 81 is raised or lowered.

Further, in the present embodiment, the integral value I is reset when the target temperature TT is changed to a new target temperature TT different by a predetermined value TTth or more. Therefore, when the target temperature TT is changed to a lower target temperature TT, the integral value I is reset. By resetting the value I, the temperature of the heating unit 81 can be quickly brought closer to the new target temperature TT. Further, when the target temperature TT is changed to a high target temperature TT, it is possible to suppress the temperature of the heating unit 81 from rapidly increasing by resetting the integrated value I, so that overshoot can be suppressed. can.

Although one embodiment of the invention has been described above, the present invention is not limited to the above embodiment. The specific configuration can be appropriately changed as described below without departing from the spirit of the invention.

For example, the control unit 100 may be configured to calculate the manipulated variable U by adding the differential term K _d D proportional to the differential value of the deviation ΔT in the calculation process.

Specifically, the control unit 100 executes PD control for calculating the operation amount U by the following equation (1)'before the detection temperature T reaches the switching temperature TS after setting the target temperature TT. That is, the control unit 100 calculates the manipulated variable U including the sum of the proportional term K _p ΔT and the differential term K _d D.
_Un = K _p ΔT _n + K _d D _n ... (1)'
Here, K _d is a differential gain as a preset fixed value, and is a negative value.

Further, D is a differential value of the deviation ΔT, and can be calculated by the following equation (6) as an example.
D _n = (T _n −T _n-1 ) / ts ・ ・ ・ (6)

Further, after the detection temperature T reaches the switching temperature TS after setting the target temperature TT, the control unit 100 executes PID control for calculating the operation amount U by the following equation (3)'. That is, the control unit 100 calculates the manipulated variable U including the sum of the proportional term K _p ΔT, the integral term K _i I, and the differential term K _d D.
_{Un =} K _p ΔT _n + K _i In + K _d D _n・ ・ ・ (3)'

According to such a configuration, the response can be made faster, so that the temperature fluctuation of the heating unit 81 can be made smaller.

Further, in the above embodiment, the absolute values L1 and L2 of the first limit value L1 and the second limit value −L2 are equal values, but the first limit value and the second limit value are not limited to this. The absolute values may be different.

Further, in the above embodiment, the second target temperature TT2 and the second switching temperature TS2 are equal to each other, but the temperature is not limited to this, and the second switching temperature TS2 is higher than the second target temperature TT2. It may be at a low temperature.

Further, in the above embodiment, when the target temperature TT is changed to a new target temperature TT different by a predetermined value TTth or more, the integrated value I is reset to 0, but the present invention is not limited to this. For example, it may be reset to a value other than 0. Also, even if the target temperature is changed to a new target temperature that differs by a predetermined value or more, the integrated value at that time is retained as it is without resetting, and is retained when the next PI control is started. The operation amount may be calculated using the integrated value.

Further, in the above embodiment, the temperature detecting unit 9 is provided so as to directly detect the temperature of the heating unit 81, but the present invention is not limited to this. For example, the temperature detection unit is arranged facing the pressurizing unit, and by detecting the temperature of the pressurizing unit to which heat is transferred from the heating unit, the temperature of the heating unit is indirectly measured via the pressurizing unit. It may be something to detect. Further, the temperature detection unit may be provided so as to directly detect the temperature of the heater. Further, the temperature detection unit may be a temperature sensor other than the thermistor. The temperature sensor may be a non-contact type temperature sensor or a contact type temperature sensor.

Further, in the above embodiment, the heating roller is exemplified as the heating unit 81, but the heating roller is not limited to this, and the heating unit may be, for example, an endless fixing belt provided in a belt fixing type fixing device. .. Further, in the above embodiment, the pressure roller is exemplified as the pressure unit 82, but the pressure roller is not limited to this, and the pressure unit may be, for example, a belt-shaped member or the like.

Further, in the above embodiment, the halogen lamp utilizing radiant heat is exemplified as the heater 83, but the present invention is not limited to this, and for example, a ceramic heater or a carbon heater utilizing heat generated by the resistor may be used. Further, the heater may be an IH heater or the like that induces and heats the heating portion. Further, the heater may be arranged outside the heating unit instead of inside the heating unit.

Further, in the above-described embodiment, the laser printer 1 that forms a monochrome image on the sheet S is exemplified as the image forming apparatus, but the present invention is not limited to this, and for example, a printer configured to be able to form a color image on the sheet. May be. Further, the image forming apparatus is not limited to a printer, and may be, for example, a copying machine or a multifunction device provided with a document reading device such as a flatbed scanner.

Further, in the above embodiment, the process cartridge is exemplified as the developer image forming unit 5, but the present invention is not limited thereto. For example, an image forming apparatus can form a color image on a sheet, and a process unit having a plurality of arrayed photoconductor drums and a developer image formed on the plurality of photoconductor drums are transferred to the sheet. When a transfer unit having a transfer belt or the like is provided, the developer image forming unit can be configured to include a process unit and a transfer unit.

In addition, the elements described in the above-described embodiments and modifications can be combined and implemented as appropriate.

1 Laser printer 5 Developer image forming unit 8 Fuser 9 Temperature detection unit 81 Heating unit 83 Heater 100 Control unit S sheet

Claims (10)

A developer image forming unit that forms a developer image on the sheet,
A fuser having a heating unit for heating the sheet and a heater for heating the heating unit to fix the developer image on the sheet.
A temperature detection unit that detects the temperature of the heating unit,
With a control unit,
The control unit
Calculation processing to calculate the operation amount of the heater and
The energization process of energizing the heater based on the operation amount calculated in the calculation process is executed.
In the calculation process
P-control that calculates an operation amount that includes a proportional term proportional to the deviation between the target temperature and the detected temperature and does not include an integral term proportional to the integral value of the deviation.
It is possible to execute PI control for calculating an operation amount including the sum of the proportional term and the integral term.
The deviation used in the integration term is limited to a predetermined range, and the deviation is limited to a predetermined range.
The target temperature is changed from the first target temperature to a second target temperature lower than a predetermined value, the PI control is executed at the second target temperature, and the temperature of the heating unit is set to the second target. If you want to keep the temperature
When the detected temperature is higher than the switching temperature equal to or lower than the second target temperature, the P control is executed.
An image forming apparatus, characterized in that the PI control is executed when the detected temperature becomes equal to or lower than the switching temperature . The control unit is in the calculation process.
The target temperature is changed from the first target temperature to a third target temperature higher than a predetermined value, the PI control is executed at the third target temperature, and the temperature of the heating unit is changed to the third target temperature. When maintaining the target temperature,
If the detected temperature is less than the switching temperature lower than the third target temperature, the P control is executed.
The image forming apparatus according to claim 1, wherein when the detected temperature becomes equal to or higher than the switching temperature, the PI control is executed. The control unit is in the calculation process.
When the target temperature is set to the first target temperature and the PI control is executed at the first target temperature to maintain the temperature of the heating unit at the first target temperature.
If the detected temperature is less than the switching temperature lower than the first target temperature , the P control is executed .
The image forming apparatus according to claim 1 or 2 , wherein when the detected temperature becomes equal to or higher than the switching temperature, the PI control is executed . The image forming according to any one of claims 1 to 3 , wherein the control unit resets the integrated value when the target temperature is changed to a new target temperature different by a predetermined value or more. Device. The image forming according to any one of claims 1 to 4 , wherein the control unit calculates an operation amount obtained by adding a differential term proportional to the differential value of the deviation in the calculation process. Device. The control unit is in the calculation process.
As the deviation, a value obtained by subtracting the detected temperature from the target temperature is used.
When the detected temperature is equal to or lower than the target temperature and the deviation is equal to or greater than the first limit value, the first limit value is used as the deviation used in the integration term.
Any of claims 1 to 5 , wherein when the detected temperature is equal to or higher than the target temperature and the deviation is equal to or less than the second limit value, the second limit value is used as the deviation used in the integration term. The image forming apparatus according to claim 1. The image forming apparatus according to claim 6 , wherein the first limit value and the second limit value have an absolute value of 2 to 8 ° C. The image forming apparatus according to claim 6 or 7 , wherein the first limit value and the second limit value have the same absolute value. The control unit is used in the energization process.
The heater is energized at a duty ratio corresponding to the amount of operation by controlling the wave number in units of half an AC sine wave.
When the operation amount is equal to or more than the specified operation amount, the duty ratio is set to 100%.
The image forming apparatus according to any one of claims 1 to 8 , wherein when the operation amount is 0 or less, the duty ratio is set to 0%. It is provided with a developer image forming section for forming a developer image on the sheet, a heating section for heating the sheet, and a fixing device having a heater for heating the heating section and fixing the developer image on the sheet. It is a control method of the image forming apparatus.
Calculation processing to calculate the operation amount of the heater and
The energization process of energizing the heater based on the operation amount calculated in the calculation process is included.
In the calculation process
P-control that calculates an operation amount that includes a proportional term proportional to the deviation between the target temperature and the detected temperature and does not include an integral term proportional to the integral value of the deviation.
It is possible to execute PI control for calculating an operation amount including the sum of the proportional term and the integral term.
The deviation used in the integration term is limited to a predetermined range, and the deviation is limited to a predetermined range.
The target temperature is changed from the first target temperature to a second target temperature lower than a predetermined value, the PI control is executed at the second target temperature, and the temperature of the heating unit is set to the second target. If you want to keep the temperature
When the detected temperature is higher than the switching temperature equal to or lower than the second target temperature, the P control is executed.
A control method comprising executing the PI control when the detected temperature becomes equal to or lower than the switching temperature .

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