JP2001228925A - Temperature control device and image forming device - Google Patents

Abstract

(57) An object of the present invention is to provide a temperature control device which performs accurate and stable temperature control by suppressing a temperature ripple of a heating means, and is provided with a means for correcting a lighting duty calculated by PID control. It is an object to provide an image forming apparatus. In order to solve the above problem, a typical configuration of a temperature control device and an image forming apparatus according to the present invention is to supply electric power to a plurality of heating units and to allow an output voltage to be slowed up / down. Power supply means, temperature detection means for detecting the temperature of the heating means, and control means for controlling the heating means, the control means having a predetermined conversion table, the temperature detection It is characterized in that the detected value by the means is corrected to a value that changes linearly or to the actual temperature, and that the lighting time that cannot be performed due to the slow-up / down is corrected to a lighting time that can be performed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic image forming apparatus and, more particularly, to a fixing means temperature control apparatus.

[0002]

2. Description of the Related Art Generally, electrophotographic image formation is performed according to processes such as charging, exposure, development, transfer and fixing. The fixing process is a process in which heat and pressure are applied to the transferred image transferred to the recording medium to fuse the transferred image to the recording medium, and the fixing means includes a heater 51 as shown in FIG. It has a heating roller 50, a pressure roller 52 pressed against the heating roller 53 by an urging means 53, and a thermistor 54 for detecting the temperature of the heater 51.

At the time of fixing, the recording medium P on which an image has been transferred is held between the nip portion of the heating roller 50 and the pressing roller 52 by the urging force of the urging means 53, and is conveyed with the rotation of these rollers. Is done. At this time, the heat of the heater 51 built in the heating roller 50 is applied to the recording medium P via the heating roller 50, and the transfer effected earlier by the heating action and the pressing action by the urging force of the urging means 53. The image is fixed on the recording medium P.

However, if the entire heating roller 50 is configured to be uniformly heated in an image forming apparatus corresponding to a large-sized recording medium P, when the small-sized recording medium P is conveyed, only the recording-medium passage area is provided. Is taken by the recording medium P. For this reason, the surface temperature of the heating roller 50 is biased, which may cause a failure or deteriorate the fixing property. Therefore, as shown in FIG. 10, a plurality of heaters 51a and 51b having different light distributions are provided, and the ratio of the lighting time of the heater 51b to the lighting time of the heater 51a is changed depending on the size of the recording medium P. The surface temperature is controlled to be uniform.

[0005] In such a control device, previously, only the analog / digital conversion (hereinafter referred to as A / D) value corresponding to the target temperature value is held in the control means.
If the fuser temperature input from the D port is low, heat it,
If it was high, the heating was controlled to stop. However, such control has a problem in that when a thermal time constant is large due to a large heat capacity of the fixing device or the like, a temperature ripple (a temperature fluctuates periodically) becomes large.

Therefore, in general, in order to suppress the temperature ripple, the lighting duty (time to be turned on) is controlled by using proportional / integral control (hereinafter referred to as PI control) or proportional / integral / differential control (hereinafter referred to as PID control). There is a way to determine In actual control, a PID control is used to determine the difference between the target temperature value and the current temperature at regular intervals, and to determine the lighting duty in the next cycle. The expression is as follows.

D (t) = D (t−1) + α × (1 + 1 / i) × e (t) −α × e (t-1) D (t): lighting duty D (t) in the next cycle -1): Previous lighting duty e (t): Current temperature difference e (t-1): Previous temperature difference α: Arbitrary coefficient 1 i: Arbitrary coefficient 2 On the other hand, depending on the method of power supply to the heater Also, the temperature ripple can be prevented. That is, a constant power is supplied to the heater irrespective of the voltage fluctuation of the AC power supply, and the power consumption of the heater is always kept constant, thereby preventing overshoot and temperature ripple of the surface temperature of the heater.

In this method, a constant voltage output circuit for the heater is provided, and a halogen heater is used as a heat source. Also, if there is a lighting device that is supplied with power from the same outlet as the recording device, a flicker phenomenon such as the flickering of the lighting device may occur due to a sudden increase or decrease of the current when the halogen heater is turned on / off depending on the power supply impedance. is there. Therefore, the output of the constant voltage output circuit is slowed up / down with a constant time constant, thereby preventing a sudden increase and decrease of the current and preventing the flicker phenomenon.

[0009]

However, when a thermistor is used as the temperature detecting means, the rate of change of the thermistor resistance value with respect to the detected temperature is not linear, and the thermistor resistance value is converted into a voltage by resistance division. Therefore, the temperature of the heating roller 50 and the input value from the A / D port did not change linearly, and the PI control and the PID control could not be performed accurately.

If the result D (t) of the above-mentioned formula is used as it is when performing PID control, the on-duty (actual lighting time) within a certain time is expressed. Since it is 100%, it is necessary to determine the upper and lower limits. Here, when a constant voltage output circuit is used, since the slow-up / down operation is performed when the heater is switched, there is a problem in how to handle the on-duty during that time. The simplest is to assume that the heater is turned off during slow-up / down, but in such a case, an unusable lighting duty is generated.

Specifically, one cycle is defined as one second,
100ms slow-up time, 100ms slow-down time
ec, one slow-up / down during one cycle
Assuming that the heater is turned on each time, the maximum time during which the heater can be turned on during one cycle is 1- (0.1 + 0.1) = 0.8. Therefore 80
This means that the operation can be performed only up to 0 msec, that is, up to the on-duty of 80%, and a lighting duty of more than 80% becomes practically impossible.

Therefore, the present invention suppresses the temperature ripple of the heating means, performs accurate and stable temperature control,
An object of the present invention is to provide a temperature control device and an image forming apparatus provided with a means for correcting a lighting duty calculated by ID control.

[0013]

In order to solve the above-mentioned problems, a typical configuration of a temperature control apparatus and an image forming apparatus according to the present invention is to supply electric power to a plurality of heating means and increase output voltage. Power supply means capable of turning on / down, a temperature detecting means for detecting a temperature of the heating means, and a control means for controlling the heating means, wherein the control means has a predetermined conversion table. And correcting the detected value by the temperature detecting means to a linearly changing value or an actual temperature, and correcting the lighting time that cannot be performed due to the slow-up / down to a practicable lighting time. I do.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment A first embodiment of an electrophotographic image forming apparatus according to the present invention will be described with reference to the drawings. 1 is an overall configuration diagram of an image forming apparatus according to the present embodiment, FIG. 2 is a diagram illustrating a configuration of a heating unit in a fixing unit, FIG. 3 is a block diagram illustrating a configuration of a heater temperature control device, and FIG. FIG. 5 is a flowchart illustrating an operation of acquiring a detection value by the detection unit, FIG. 5 is a diagram illustrating a conversion table of the detection value by the temperature detection unit, and FIG. 6 is a flowchart illustrating an operation of temperature control.

(Overall Configuration) The image forming apparatus 1 shown in FIG. 1 employs an electrophotographic system. In the image forming apparatus 1, after the surface of the image carrier 2 is uniformly charged by the charging unit 3, the optical unit 4 scans a light beam to form an electrostatic latent image, and the latent image is developed by the developing unit 5. Thereby, a developer image is formed.

At the lower part of the apparatus, a cassette 6 for stacking and storing sheets as recording media is arranged. When sheets are separated and fed one by one by a feeding means 7, a skew is corrected by a pair of retard rollers 8 and The developer is conveyed in synchronization with the image carrier 2, and the developer image on the image carrier 2 is transferred to a sheet by the transfer unit 9. The developer remaining on the image carrier is removed by the cleaning means 10, and the image carrier 2 is used for the next image formation.

The sheet onto which the developer image has been transferred is fixed to fixing means 11.
Transported to The fixing unit 11 includes a heating roller 12 having a heater 13 as a heating unit therein, and a pressing roller 14 pressed against the heating roller 12 by an urging unit 15. Heating roller 12
Is provided with a thermistor 16 as temperature detecting means, and performs temperature control. These heating roller 12 and pressure roller 14
The developer image is fixed on the sheet by nipping and transporting the sheet while heating and pressurizing the sheet, and the sheet is discharged and stacked on a discharge tray 18 on the upper portion of the apparatus by a discharge roller pair 17, thereby completing the image formation.

(Temperature Control Device) As shown in FIG. 2, a plurality of heaters 13 having different light distributions are provided inside the heating roller 12.
a, 13b, and the heater 13a depending on the size of the recording medium.
The surface temperature of the heating roller 12 is controlled to be uniform by changing the ratio of the lighting time of the heater 13b to the lighting time of. FIG. 3 is a block diagram showing a configuration of the heater temperature control device.

As shown in FIG. 3, the heaters 13a and 13b are connected to a heater power supply 19 as power supply means, and the heater power supply 19 is connected to a heater control circuit 20 as control means. The heater power supply 19 is configured so that the output can be slowed up / down with a certain time constant in order to prevent a flicker phenomenon of another device sharing the power supply source. The heater control circuit 20 takes in the detected value of the thermistor 16 from the A / D port 21 and controls the heater power supply 19 based on the detected value to supply necessary power to one or both of the heaters 13a and 13b as heating means. This controls the temperature. Further, the heater control circuit 20 has a target temperature value.

In this embodiment, the heater control circuit uses a multitask system, and reads a value from one of the plurality of A / D ports 21 each time each task is switched. That is, as shown in FIG. 4, each time the task is switched, first, the number of the A / D port 21 from which the input value is read in the current switching is checked (S
1) A detection value is read from the A / D port 21 corresponding to each number (S2).

On the other hand, the heater control circuit 20 has a conversion table shown in FIG. 5, and converts the detected value into the temperature itself detected by the thermistor (S3). The conversion table is specified according to the characteristics of the thermistor used.
With this, the detected value is converted to the detected temperature and the PI
Control and PID control can be performed. In addition to the conversion into the detected temperature itself, accurate control can be performed by converting into a linear value that changes in proportion to the temperature.

Then, the converted values are stored in a storage area provided inside the heater control circuit 20 (S4). The storage area is A /
A plurality of D ports 21 are provided corresponding to the number. At this time, when storing the thermistor voltage, the A / D conversion value is used as a subscript of the array, and the value of the conversion table is stored in the storage area. Next, the variable indicating the number of the A / D port is updated (S5), and it is determined whether the number of A / D ports 21 is exceeded (S6). If the number is exceeded, the number is initialized (S7). To end. The above processing is executed every time the task is switched, and the detected temperature corresponding to the detected value is obtained.

Next, based on the obtained detected temperature, PI
The processing shown in FIG. 6 is executed in order to calculate the lighting duty by the D control and to apply an appropriate correction thereto.

First, from the acquired current detected temperature, the target temperature value held in the heater control circuit 20, and the lighting duty in the previous cycle, the above-described PID control formula D (t) = D (t-1 ) + Α × (1 + 1 / i) × e (t) −α × e (t-1), the next lighting duty D (t) is calculated at regular intervals (S10). The lighting duty D (t) is represented as an on-duty (actual lighting time) in one cycle.

Then, it is determined whether the calculated lighting duty D (t) is a feasible on-duty. In this embodiment, one cycle is set to 1 second, the slow-up time is set to 100 msec, and the slow-down time is also set to 100 msec as in the conventional example. The maximum time during which the heater can be turned on is 1- (0.1 + 0.1) = 0.8. Therefore, the operable on-duty is 0 to 80%.

The lighting duty D (t) calculated first
Is determined to be less than or equal to the upper limit (80%) that can be implemented (S1).
1) If it is outside the feasible range, the lighting duty D (t) is corrected to 100% (S12). Next, it is determined whether the lighting duty D (t) is equal to or more than a practicable lower limit (0%) (S13). If the lighting duty D (t) exceeds the practicable range, the lighting duty is corrected to 0%, that is, all lights are turned off. (S14). By executing the above processing every time the lighting duty is calculated, the calculation value by the PID control can be corrected to eliminate the lighting duty that cannot be implemented.

[Second Embodiment] In the first embodiment described above, the judgment was made by the conditional expression in order to correct the calculated value calculated by the PID control. However, the heater control circuit 20 is provided with a correction table. Correction can also be made based on this table. FIG. 7 is a view for explaining a correction table for correcting the calculated value of the lighting duty to a feasible value, and FIG.
Is a flowchart for explaining the operation of temperature control,
The same parts as those in the first embodiment will be denoted by the same reference numerals, and description thereof will be omitted.

When the next lighting duty D (t) is calculated from the detected temperature, the target temperature value, and the lighting duty in the previous cycle in the same manner as in the first embodiment (S10), the calculated value is used as a subscript in FIG. The correction value is extracted from the correction table shown in (1) (S15). Note that the correction table is held in the heater control circuit 20.

With this configuration, as shown in FIG. 8, S11 to S11 required for determination in the first embodiment are performed.
Since the step of S14 can be processed by one step S15, the temperature control processing can be simplified.

[0030]

As described above, the temperature control device and the image forming apparatus according to the present invention have a predetermined conversion table and correct the value detected by the temperature detecting means to a value which changes linearly or an actual temperature. However, by calculating the lighting time based on this correction value, it is possible to suppress temperature ripple and overshoot of the heating means, and to perform accurate and stable temperature control.

If the calculated lighting time is a value that cannot be implemented due to slowing up / down of the power supply means, it is determined whether or not the implementation is possible by a conditional expression or by correction using a correction table. It can be corrected to a possible lighting time.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram of an image forming apparatus according to a first embodiment.

FIG. 2 is a diagram illustrating a configuration of a heating unit inside the fixing unit.

FIG. 3 is a block diagram illustrating a configuration of a heater temperature control device.

FIG. 4 is a flowchart illustrating an operation of acquiring a detection value by a temperature detection unit.

FIG. 5 is a diagram illustrating a conversion table of a detection value by a temperature detection unit.

FIG. 6 is a flowchart illustrating an operation of temperature control.

FIG. 7 is a diagram illustrating a correction table for correcting a calculated value of a lighting duty to a practicable value according to the second embodiment.

FIG. 8 is a flowchart illustrating the operation of temperature control.

FIG. 9 is a diagram illustrating a fixing unit according to a conventional example.

FIG. 10 is a diagram illustrating a configuration of a heating unit inside the fixing unit.

[Explanation of symbols]

 P ... recording medium 1 ... image forming apparatus 2 ... image carrier 3 ... charging means 4 ... optical means 5 ... developing means 6 ... cassette 7 ... feeding means 8 ... retard roller pair 9 ... transfer means 10 ... cleaning means 11 ... fixing Means 12: Heating roller 13: Heater 14: Pressure roller 15: Urging means 16: Thermistor 17: Discharge roller pair 18: Discharge tray 19: Heater power supply 20: Heater control circuit 21: A / D port 50: Heating roller 51 … Heater 52… pressure roller 53… biasing means 54… thermistor

Claims (8)

[Claims] A power supply unit for supplying power to the plurality of heating units; a temperature detection unit for detecting a temperature of the heating unit; and a control unit for controlling the heating unit. The temperature control device, wherein the control means corrects a value detected by the temperature detection means to a linearly changing value or an actual temperature. 2. The temperature control device according to claim 1, wherein the control means has a predetermined conversion table for converting a value detected by the temperature detection means into a value that changes linearly or an actual temperature. 3. A power supply means for supplying power to a plurality of heating means and capable of increasing / decreasing an output voltage, a temperature detection means for detecting a temperature of the heating means, and controlling the heating means. The control means calculates the lighting time of the heating means based on the value detected by the temperature detecting means, and executes the lighting time which cannot be performed due to the slow-up / down. A temperature control device, wherein the temperature is corrected to a possible lighting time. 4. The temperature control device according to claim 3, wherein the control unit corrects the lighting time that cannot be performed to a lighting time that can be performed by a conditional expression. 5. The temperature control device according to claim 3, wherein the control unit has a predetermined correction table for correcting the lighting time that cannot be performed to a lighting time that can be performed. 6. The temperature control device according to claim 1, wherein said temperature detecting means is a thermistor. 7. The temperature control device according to claim 1, wherein said power supply means is a constant voltage output circuit. 8. An image carrier for carrying a developer image, transfer means for transferring the developer image to a recording medium, conveying means for conveying the recording medium, and a plurality of heating means for heating the recording medium An image forming apparatus, comprising: a fixing unit having: a heating unit of the fixing unit is controlled by the temperature control device according to claim 1.