JP5900236B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus that thermally fixes an image on a sheet by a fixing member.

In order to stabilize the image quality of the formed image, the image forming apparatus temporarily stops the image forming operation being executed at a predetermined timing and adjusts the charge amount and exposure amount of the photosensitive drum. Many of them have a function to execute control.
The image stabilization control includes, for example, density correction, a predetermined toner pattern is formed on the photosensitive drum, the density of the formed toner pattern is detected, and charging is performed based on the amount of deviation between the detected density and the target density. The amount and the exposure amount are adjusted. When the image stabilization control ends, the temporarily interrupted image forming operation is resumed.

In addition to the image stabilization control, there is also a function that executes a function called sheet number control for controlling the number of sheets that pass through the fixing unit per unit time.
The number control is the number of sheets conveyed per unit time when the temperature of the fixing member for heat fixing an unfixed image on the sheet is too low during the image forming operation for a large number of continuously conveyed sheets. Specifically, the image forming operation is controlled to temporarily reduce or increase the interval between conveyed sheets.

The reason why the temperature of the fixing member is lowered during the image forming operation is that the heat cannot be caught up by the heat of the fixing member being taken away by a large number of sheets passing through the fixing member.
In addition, the number control may be executed when the temperature of the fixing member is too high. That is, because the sheet size is small, the heat of the non-sheet passing region where the sheet does not pass at the end of the fixing member in the sheet width direction is not taken away by the sheet, and the temperature of the fixing member rises too much. In order to cool this, the number of conveyed sheets per unit time is reduced.

By controlling the number of sheets, the amount of heat per unit time by which the heat of the fixing member is taken by the sheet is reduced, and the temperature of the fixing member can be increased by heating the fixing member. Note that the sheet number control has the same meaning as so-called PPM control that limits the number of prints per unit time (PPM: print per minute), and is hereinafter referred to as PPM control.
Both the image stabilization control and the PPM control need to be executed while the image forming operation is temporarily interrupted. Since the image formation cannot be executed while these controls are executed, the productivity of the image forming operation is increased accordingly. Will drop.

  Therefore, in Patent Document 1, if the end temperature of the fixing member is within a range that is higher than the target temperature and lower than the upper limit at the execution timing of the image stabilization control during the image forming operation, The image forming operation is continued without executing the image stabilization control. When the upper limit is reached, the image forming operation is temporarily suspended (corresponding to PPM control) to lower the end temperature of the fixing member, and the image stabilization control is performed. Techniques to perform are disclosed.

By delaying the execution of the image stabilization control in accordance with the start of the PPM control, it is possible to shorten the interruption time of the image forming operation, and to improve the productivity accordingly.
Further, in Patent Document 2, when a downtime in which image formation cannot be performed due to needle replacement or the like in the post-processing device occurs, if the image stabilization control is scheduled thereafter, the schedule is advanced and the downtime is reduced. Discloses a technique for executing image stabilization control.

  If the downtime is replaced with PPM control, image stabilization control can be executed simultaneously with PPM control.

JP 2008-304781 A JP 2011-242710 A

However, since the image stabilization control is executed later than the original timing with the configuration of Patent Document 1, it is formed between the original timing and the time when the image stabilization control is actually executed. There is a problem that the image quality tends to be deteriorated.
Further, with the configuration of Patent Document 2, the image stabilization control is advanced from the original timing, so the image quality of the formed image does not deteriorate. However, if the number of times of advancement increases, the image per unit period is increased. This leads to an increase in the total number of executions of stabilization control.

Increasing the number of executions of image stabilization control is not desirable because it increases the amount of toner consumed for forming a toner pattern and the amount of power consumed for driving the photosensitive drum.
The present invention has been made in view of the above-described problems, and an image forming apparatus capable of preventing a decrease in productivity of an image forming operation while executing image stabilization control at an original timing. It is intended to provide.

  In order to achieve the above object, an image forming apparatus according to the present invention forms an image on a plurality of conveyed sheets, and fixes the image to each sheet by the heat of a heated fixing member. An image forming apparatus that performs an image forming operation, wherein the fixing member executes predetermined image stabilization control for stabilizing the image quality of the formed image by temporarily interrupting the image forming operation, and the fixing member. When the temperature of the fixing member changes with the image forming operation and reaches a threshold value lower or higher than the target temperature during the image forming operation, the number of sheets conveyed per unit time is reduced. Number control means for starting the number control, heating control means for controlling the heating amount to the fixing member so as to return to the target temperature when the temperature of the fixing member reaches the threshold, and N (plural) sheets If the image forming operation is continuously performed on the sheet, a prediction unit that predicts that the image stabilization control and the sheet number control are separately performed with a time shift, and the prediction is performed. Of the N sheets, the image forming speed of image formation for one or more sheets included in the P sheets scheduled to be executed by the image stabilization control until the temporary interruption is determined from the reference speed, and the predicted number of sheets Speed change means for changing to a speed satisfying a condition that the control start time enters the execution period of the predicted image stabilization control.

  The image forming operation for the P sheets is an operation for continuously executing a plurality of jobs when the image forming operation for one or more sheets is a single image forming job. When the image stabilization control is predicted to be executed earlier than the number control, the image forming speed of the job immediately before the predicted image stabilization control is started so as to satisfy the condition May be changed to a speed faster than the reference speed.

Here, when the high speed exceeds the upper limit speed, the speed changing unit selects a job to be changed to a high image forming speed as at least one preceding job and the immediately preceding job. The image forming speed for these jobs may be changed to a speed higher than the reference speed so as to satisfy the above conditions.
The image forming operation for the P sheets is an operation for continuously executing a plurality of jobs when the image forming operation for one or more sheets is a single image forming job. If the number control is predicted to be executed earlier than the image stabilization control, immediately before the predicted stabilization control is started among the plurality of jobs so as to satisfy the condition. The image forming speed of the current job may be changed to a speed faster than the reference speed, and the image forming speed of at least one job prior to the immediately preceding job may be changed to a speed slower than the reference speed.

  Here, when the high speed exceeds the upper limit speed, the speed changing unit selects a job to be changed to a high image forming speed as at least one preceding job and the immediately preceding job. The image forming speed for these jobs is changed to a speed higher than the reference speed, and the image forming speed of the job before the changed job is set to a speed lower than the reference speed. It may be changed.

  Here, the speed changing means increases the image forming speed as a result of increasing the image forming speed as a result of increasing the image forming speed by tsa, and decreasing the image forming speed as a result of increasing the image forming speed. When the formation execution time is tΔ2, the fast speed and the slow speed may be set so that the time obtained by adding the time tΔ2 to the time tsa is equal to the time tΔ1.

The speed changing unit may prohibit the speed change if it determines that the condition is not satisfied even if the image forming speed is changed for all jobs.
Further, the predicting means includes a first judging means for judging that the predetermined execution timing of the image stabilization control is reached during execution of image formation for the N sheets, and an image for the N sheets. A second determination unit that determines that the predicted temperature of the fixing member reaches the threshold value during the formation, and when the determination by both the first determination unit and the second determination unit is performed, The prediction may be performed.

  Here, the predicting unit includes a third determining unit that determines that the predicted temperature of the fixing member becomes a predetermined allowable temperature or less during execution of image formation on the N sheets, and the allowable temperature Among the N sheets, the width direction length of the first size sheet is CD1, and the width direction length of the second size sheet on which image formation is scheduled to be performed next to this is, When CD2 wider than CD1 is set, an allowable value of the temperature difference in the sheet width direction of the fixing member due to the difference is set in advance according to the difference in the CD length represented by (CD2-CD1). When the temperature of the fixing member is lower than the target temperature by a predetermined value and the determination by the third determination unit is made, the determination by the second determination unit is not performed. , By the first determination means If disconnection is performed, it may perform the prediction.

  If configured as described above, the number control that was scheduled to be executed separately from the image stabilization control will be performed in parallel with the image stabilization control. It is not necessary to execute the number control separately from the image stabilization control during the image forming operation of the sheet. The image stabilization control and the number of sheets can be performed without changing the execution timing of the image stabilization control from the original timing. Compared to a configuration in which the control is executed separately, the productivity of the image forming operation can be improved.

1 is a schematic diagram illustrating an overall configuration of a printer. It is a block diagram which shows the structure of a control part. It is a figure which shows the content of management information. It is a figure which shows the content of electric power control information. 10 is a timing chart illustrating a first example when it is predicted that stabilization control and PPM control are executed separately with a time shift between a plurality of jobs. 6 is a timing chart in the case of executing a process speed change process in the first example shown in FIG. 5. It is a timing chart which shows the 2nd example when it is predicted that PPM control will be performed earlier than stabilization control. It is a timing chart in the case of performing process speed change processing in the 2nd example shown in FIG. It is a figure which shows the example of the content of a PPM control parameter. It is a flowchart which shows the content of the process speed change necessity judgment process which a control part performs. It is a flowchart which shows the content of the subroutine of a PPM control necessity prediction process. It is a flowchart which shows the content of the subroutine of PPM control necessity judgment based on CD length. It is a flowchart which shows the content of the subroutine of a stabilization control schedule judgment process. It is a flowchart which shows the content of the subroutine of a process speed change process. It is a figure which compares and shows the difference by the presence or absence of a process speed change process of the total estimated execution time in the case of performing a some job.

Hereinafter, an embodiment of an image forming apparatus according to the present invention will be described by taking a tandem color printer (hereinafter simply referred to as “printer”) as an example.
<Overall configuration of printer>
FIG. 1 is a schematic diagram illustrating the overall configuration of a printer 1 according to the present embodiment.
As shown in the figure, the printer 1 forms an image by a well-known electrophotographic method, and includes an image processing unit 10, an intermediate transfer unit 20, a feeding unit 30, a fixing unit 40, and a control unit 50. And an IH power supply unit 60, and executes color image formation (printing) based on a job execution request from an external terminal device (not shown) via a network (for example, LAN).

The image processing unit 10 includes image forming units 10Y, 10M, 10C, and 10K corresponding to development colors of yellow (Y), magenta (M), cyan (C), and black (K). The image forming unit 10Y includes a photosensitive drum 11Y, a charging unit 12Y, an exposure unit 13Y, a developing unit 14Y, a cleaner 15Y, and the like disposed around the photosensitive drum 11Y.
The charging unit 12Y charges the peripheral surface of the photosensitive drum 11Y that rotates in the direction indicated by the arrow A. The exposure unit 13 exposes and scans the charged photosensitive drum 11Y with a laser beam to form an electrostatic latent image on the photosensitive drum 11Y.

  The developing unit 14Y develops the electrostatic latent image on the photoreceptor drum 11Y with Y color toner. As a result, a Y-color toner image is formed on the photosensitive drum 11 </ b> Y, and the formed Y-color toner image is primarily transferred onto the intermediate transfer belt 21 of the intermediate transfer unit 20. The cleaner 15Y cleans residual toner on the photosensitive drum 11Y. The other image forming units 10M to 10K have the same configuration as that of the image forming unit 10Y, and the reference numerals of members other than the photosensitive drum are omitted in FIG.

The intermediate transfer unit 20 includes an intermediate transfer belt 21 that is stretched around a driving roller 24 and a driven roller 25 and circulated in the direction of the arrow, and the photosensitive drums 11Y, 11M, 11C, and 11K across the intermediate transfer belt 21. There are provided primary transfer rollers 22Y, 22M, 22C, and 22K arranged to face each other and a secondary transfer roller 23 arranged to face the driving roller 24.
The feeding unit 30 is fed with two cassettes 31 a and 31 b that store sheets S as an example of sheets, and feeding rollers 32 a and 32 b that feed the sheets S from the cassettes 31 a and 31 b one by one to the conveyance path 39. Conveying rollers 33 and 34 for conveying the paper S are provided.

  The cassettes 31a and 31b are configured to be capable of accommodating different sizes, for example, A4 size paper S in the cassette 31a and B5 size paper S in the cassette 31b. Here, the paper S is set to a transport posture of either a vertical posture or a horizontal posture. The vertical posture refers to the transport posture when the paper S is transported with the long side of the short side and the long side of the paper S in the posture along the paper transport direction, and the horizontal posture refers to the short side of the paper S This means the transport posture when transported in a posture along the direction.

The fixing unit 40 is an electromagnetic induction heating type fixing device, and includes a fixing roller 41 having an electromagnetic induction heat generation layer, a pressure roller 42 that presses the fixing roller 41 and secures a nip between the fixing roller 41, and An exciting coil 43 that generates a magnetic flux for generating heat from the electromagnetic induction heat generating layer of the fixing roller 41 and a fixing temperature sensor 44 are provided.
The excitation coil 43 generates magnetic flux by the power supplied from the IH power supply unit 60, and the IH power supply unit 60 supplies the excitation coil 43 with power having a magnitude indicated by the control unit 50. The fixing temperature sensor 44 detects the temperature of the surface portion of the fixing roller 41 substantially at the center in the axial direction, and sends the detection result to the control unit 50. Since the position in the approximate center of the fixing roller 41 in the axial direction is included in the sheet passing area through which the sheet S passes, it is hereinafter referred to as detecting the fixing roller sheet passing portion temperature.

  In such a configuration, when a job is executed, a corresponding color toner image is formed on the photoconductive drums 11Y to 11K, and the formed toner images are electrostatically transferred to the primary transfer rollers 22Y to 22K. The primary transfer is performed on the intermediate transfer belt 21 by the action. The image forming operations for the respective colors Y to K are executed while shifting the timing from the upstream side to the downstream side so that the toner images of the respective colors are transferred to the same position on the traveling intermediate transfer belt 21. The

In synchronization with this image forming timing, the paper S is conveyed from the paper feed cassette toward the secondary transfer roller 23 from the paper feeding unit 30, and between the secondary transfer roller 23 and the intermediate transfer belt 21. When the paper S passes, the color toner images primarily transferred onto the intermediate transfer belt 21 are secondarily transferred collectively onto the paper S by the electrostatic action of the secondary transfer roller 23.
The sheet S after each color toner image is secondarily transferred is conveyed to the fixing unit 40 and heated and pressed when passing through the nip between the fixing roller 41 and the pressure roller 42 of the fixing unit 40. The toner on the surface is fused and fixed to the surface of the paper S. The paper S that has passed through the fixing unit 40 is discharged (output) onto the paper discharge tray 36 by the paper discharge roller 35. Hereinafter, forming an image on the paper S and outputting the paper S is referred to as printing.

The rotating members such as the photoconductive drums 11Y to 11K, the intermediate transfer belt 21, and the fixing roller 41 are rotated by the power of the process motor 18 as a driving source. The rotation speed of the process motor 18 can be switched between a reference (system) speed, a high speed faster than the reference speed, and a slow low speed in the process speed changing process described later.
When the rotation speed of the process motor 18 changes, the peripheral speed of the photosensitive drums 11Y to 11K and the intermediate transfer belt 21 and the conveyance speed of the paper S during image formation change.

Since the peripheral speeds of the photosensitive drums 11Y to 11K, the peripheral speed of the intermediate transfer belt 21, and the conveyance speed of the paper S are in the same relationship, the rotation of the process motor 18 is assumed to be the process speed (image forming speed). By changing the speed, the process speed changes, and the number of sheets that can be printed per unit time also changes.
An operation unit 70 is disposed at a position on the front side and the upper side of the apparatus main body and easy to be operated by the user. The operation unit 70 is a touch panel type that accepts input of setting of the size (A4, B5, etc.), type (plain paper, thin paper, etc.), conveyance posture (vertical and horizontal) of the paper S stored in the cassettes 31a, 31b from the user. A liquid crystal display unit and the like are provided, and information such as the accepted size is sent to the control unit 50.

Further, an in-machine temperature sensor 71 for detecting the temperature inside the main body and an in-machine humidity sensor 72 for detecting the humidity inside the main body are arranged inside the apparatus main body and around the fixing unit 40. The detection results of the temperature and humidity of these sensors are sent to the control unit 50.
<Configuration of control unit>
FIG. 2 is a block diagram illustrating a configuration of the control unit 50.

  As shown in the figure, the control unit 50 includes an I / F unit 101, an overall control unit 102, a job management table 103, a stabilization control unit 104, a stabilization execution prediction unit 105, and a fixing temperature adjustment control. Unit 106, power control information table 107, PPM control unit 108, PPM execution prediction unit 109, PPM control table 110, process speed change unit 111, storage unit 112, and the like.

  An I / F (interface) unit 101 receives job data from an external terminal device via a network, and stores the data in the storage unit 112. The job data includes job data specified by the user who requested the job, such as the number of sheets to be printed, the size, and the paper type, in addition to the print data used for image formation. The paper types include plain paper, thin paper, and thick paper.

The overall control unit 102 controls each unit such as the image forming unit 10 and the intermediate transfer unit 20 based on the job data stored in the storage unit 112 to execute a smooth image forming operation. Each time a job is accepted, management information 1031 for managing the job is written in the job management table 103.
<Management information>
FIG. 3 is a diagram showing the contents of the management information 1031.

As shown in the figure, the management information 1031 is associated with job number (No), job name, number of prints, paper size, paper type, and transport posture for each job.
The job number (No) indicates the order in which the jobs are received. As the number increases, the job has a later reception time. Each job is executed in order from the earlier reception order. When one job is newly accepted, the next number of the job with the latest acceptance order is numbered, management information for the job is added, and when one job is finished, the end information ( Management information is updated by writing (not shown). By referring to the presence / absence of end information, which job has not been executed and has been completed, and what job has been executed immediately before the completed job (number of prints, paper size, etc.) ) Can be known.

The job name is arbitrary information for identifying the job, and the number of printed sheets, the sheet size, and the sheet type are the number of sheets, the size, and the sheet type indicated by the job information included in the received job data.
The conveyance posture indicates whether the conveyance posture is vertical or horizontal when the paper indicated in the paper size column is conveyed. It is acquired from the setting of the operation unit 70 by the user whether the paper S shown in the paper size column is set in the cassette in the vertical posture or the horizontal posture, and the acquired information is the transport posture column. To be written.

By referring to the job management table 103, it is possible to know how many jobs are scheduled to be executed after the reference time, and know the number of prints for each job.
When a job is executed, the paper size, paper type, and transport attitude written in the job management table 103 are referred to for each job. Of the cassettes 31a and 31b, the referred paper size, paper type, and transport attitude are referred to. The sheet S is fed from the cassette in which the sheet S corresponding to is stored.

<Stabilization control>
Returning to FIG. 2, the stabilization control unit 104 stabilizes the image quality of the formed image at a predetermined execution timing, specifically, image stabilization control (hereinafter referred to as “stabilization” for maintaining a certain level or more). Abbreviated as “control”). Stabilization control includes so-called registration correction and γ correction. For example, the registration correction is performed as follows.

That is, (a) a toner pattern of each color having a predetermined shape is formed on the photosensitive drums 11Y to 11K, the formed toner pattern of each color is primarily transferred to the intermediate transfer belt 21, and each color of the color on the intermediate transfer belt 21 is transferred. The toner pattern is detected by an optical sensor (not shown).
(B) An interval in the sub-scanning direction of another color, for example, a Y toner pattern, with respect to a specific color, for example, a K color toner pattern, is obtained from the detection result by the optical sensor, and the deviation of the obtained interval from the reference value Find the amount. This shift amount is the shift amount of the image writing timing of the Y color to the photosensitive drum 11Y with respect to the K color.

(C) The image forming condition, here, the Y color image writing (exposure start) timing for K color is corrected so that the amount of deviation from the reference value is eliminated. The image writing timing is corrected in the same way for the other M and C colors.
The γ correction is to adjust the relative relationship between the gradation value of the input image (such as 256 gradations) and the gradation value of the actual output image, and is executed as follows.

That is, (a) a plurality of toner patterns having different gradations are formed on the photosensitive drum for each of the image forming units 10Y to 10K, and the density of each of the formed toner patterns is detected by an optical sensor (not shown).
(B) The amount of deviation from the target density is obtained for each detected toner pattern.
(C) For each gradation value, the image forming condition, here, the exposure amount is corrected so that there is no deviation from the target value.

The stabilization control is executed by temporarily suspending the job being executed each time the cumulative number of printed sheets Ps reaches a multiple of a predetermined number of sheets Pc (for example, 1000 sheets). The accumulated print number Ps is managed by the control unit 50.
The time required for the stabilization control is determined in advance. For example, the time Tr1 is used for registration correction, and the time Tr2 is used for γ correction. When the stabilization control is finished, the temporary suspension of the job is released and the suspended job is resumed.

If the stabilization execution prediction unit 105 executes all scheduled jobs, whether or not the stabilization control is executed by reaching the execution timing of the stabilization control during the job execution. Predict. This prediction is performed in the following manner.
That is, among the multiples of the predetermined number of sheets Pc, a value that is larger than the cumulative number of printed sheets Ps and is closest to Ps is set as the scheduled stabilization sheet number Pb (for example, 2000 sheets).

Then, J1, J2, J3,... Are added in order from the job with the earlier execution order, and a value obtained by adding the number of prints of J1 (for example, 30 sheets) to the current cumulative print sheet number Ps (for example, 1950 sheets) For example, 1980 sheets).
If P ≧ Pb, the execution timing of the stabilization control is reached during execution of J1, but if P <Pb, it is determined that it does not. In the above example, P = 1980 sheets and Pb = 2000 sheets are not reached.

Next, a value obtained by adding the number of prints J2 (for example, 50) to the current number P (1980 in the above example) is set as a new number P (for example, 2030), and P ≧ Pb again. It is determined whether or not. In the above example, since P = 2030 sheets and Pb = 2000 sheets, the condition of P ≧ Pb is satisfied, and it is predicted that the execution timing of the stabilization control will be reached during the execution of J2.
If the condition of P ≧ Pb is not satisfied, for the next J3, the number P is obtained by the same method as J2, and it is determined whether or not the condition of P ≧ Pb is satisfied. The same determination is performed for all remaining scheduled jobs until the condition of P ≧ Pb is satisfied.

Even if the same determination is repeated for all jobs, if the condition of P ≧ Pb is not satisfied, stabilization control will not be executed in the middle even if all scheduled jobs are executed sequentially. is expected.
The execution timing of the stabilization control is not limited to the cumulative number of printed sheets.
For example, if the past transition of the surrounding environment, specifically, the temperature or humidity in or around the device is detected and a scheduled job is executed, the job is executed based on the past change. If the temperature or humidity is predicted to reach the upper limit or the lower limit during, at the end or at the start, a configuration for predicting that the stabilization control execution timing is reached can be adopted. The present invention can be applied to a configuration that executes stabilization control according to changes in the surrounding environment.

<Fixing temperature control>
The fixing temperature adjustment control unit 106 instructs the IH power supply unit 60 to supply power to the exciting coil 43 so that the fixing roller sheet passing portion temperature is stabilized at the target temperature (temperature optimum for fixing) Tm. Execute adjustment control.
Specifically, (a) if the fixing roller sheet passing portion temperature T detected by the fixing temperature sensor 44 is lower than the target temperature Tm, the IH power source 60 is instructed to supply power to the exciting coil 43. The power supply value at this time is determined by referring to the power control information table 107. As a result, electric power is supplied from the IH power supply unit 60 to the exciting coil 43 (ON), and the fixing roller sheet passing portion temperature rises.

(B) If the fixing roller sheet passing section temperature T is equal to or higher than the target temperature Tm, the IH power supply section 60 is instructed to stop power supply. As a result, the power supply from the IH power supply unit 60 to the exciting coil 43 is cut off (off), the temperature increase of the fixing roller sheet passing unit temperature is stopped, and it starts to fall.
By repeatedly supplying and shutting off power to the exciting coil 43, the fixing roller sheet passing portion temperature can be stabilized in the vicinity of the target temperature Tm. Note that the fixing temperature control method is not limited to the above-described on / off. Another method may be used as long as the fixing roller sheet passing portion temperature falls within a range between an upper limit higher than this and a lower lower limit around the target temperature Tm.

The power control information table 107 is a table in which power control information indicating the magnitude of power supplied to the exciting coil 43 is written.
<Power control information>
FIG. 4 is a diagram showing the contents of the power control information 1071.
As shown in the figure, the power control information 1071 is information in which the power supply timing and the supplied power are associated with each other.

The power supply time indicates a time when power is supplied to the exciting coil 43, and includes normal and stabilization control. The normal time is a time when a job, PPM control (described later) is executed, and the stabilization control time is a time when the above-described stabilization control is executed.
The power supplied to the exciting coil 43 at normal time is Wa. The power value Wa is the maximum value that can be supplied to the exciting coil 43 among the power supplied from the power source, or a power value close thereto.

On the other hand, the supply power during the stability control is higher than the threshold Tz that is predetermined as a temperature lower than the target temperature Tm by a predetermined value at the fixing roller sheet passing portion temperature T at the start of the stabilization control. , Wb (<Wa), and when the fixing roller sheet passing portion temperature T is equal to or lower than the threshold Tz, Wa is set.
Here, the threshold value Tz is a temperature at which the fixing roller sheet passing portion temperature falls below this, which may cause a problem in fixability, and is a temperature value that is a starting condition for PPM control.

The power value Wb is significantly smaller than Wa, and is a power value that increases at a slight temperature increase rate so that the fixing roller sheet passing portion temperature does not decrease during the execution of the stabilization control. The target temperature Tm, the threshold value Tz, and the power values Wa and Wb are determined in advance through experiments or the like.
Depending on whether or not the fixing roller sheet passing portion temperature T is equal to or lower than the threshold Tz at the start of the stabilization control, the power supplied to the exciting coil 43 is switched between Wa and Wb that is significantly smaller than this. For the following reason.

That is, in the stabilization control, since the job is interrupted, it is not necessary to heat-fix the image on the paper S, and it is not necessary to supply electric power as large as the electric power value Wa.
On the other hand, if the power supplied to the exciting coil 43 is cut off, the fixing roller sheet passing portion temperature decreases to a low temperature during the execution of the stabilization control by the start of the job scheduled after the stabilization control. As a result, it takes time to return to the target temperature Tm after canceling the job interruption, and the restart of the job may be delayed, resulting in a decrease in productivity. This is particularly noticeable when the fixing roller sheet passing portion temperature is lowered to the threshold value Tz or less.

Therefore, if the fixing roller sheet passing portion temperature T> the threshold value Tz, if the electric power Wb that is assumed to be necessary at the minimum is supplied to the exciting coil 43, the fixing roller is suppressed during the execution of the stabilization control while suppressing the power consumption. A decrease in job productivity can be prevented without lowering the sheet passing portion temperature.
On the other hand, when the fixing roller sheet passing temperature T ≦ the threshold value Tz, if the power value remains as low as about Wb, it takes time to raise the fixing roller sheet passing part temperature. This is because the fixing roller sheet passing portion temperature can be raised as early as possible by setting the power supplied to the exciting coil 43 to Wa giving priority to the direction.

<PPM control>
Returning to FIG. 2, the PPM control unit 108 performs PPM control, that is, the number control (the number of sheets) for decreasing the number of prints (sheets) per unit time when the fixing roller sheet passing portion temperature decreases to the threshold Tz during job execution. Start (paper feeding interval control).
Here, the job is temporarily interrupted, and when the fixing roller sheet passing portion temperature rises during the interruption, the interruption is canceled and the job is resumed.

During the job execution, the fixing roller sheet passing portion temperature decreases to the threshold value Tz because the heat of the fixing roller 41 is deprived by a large number of sheets S that are continuously conveyed, thereby heating the fixing roller 41 by the exciting coil 43. Is due to the fact that no longer catch up.
Due to the temporary interruption of the job, the heat of the fixing roller 41 is not lost to the conveyed paper S, and the electric power Wa is continuously supplied to the exciting coil 43 by the fixing temperature control even if the job is temporarily interrupted. Therefore, the fixing roller temperature can be raised by heating the fixing roller 41.

When the PPM control is started, the fixing roller sheet passing portion temperature is set by interposing the interruption time between jobs, such as interruption for a certain period of time, job execution, interruption for a certain period of time, and execution of the next job. When the temperature rises to a predetermined temperature, for example, the target temperature Tm, while the job execution and interruption are repeated, the PPM control is released.
When the PPM control is started, the job is temporarily interrupted, so that the job productivity is lowered. Note that the PPM control method is not limited to this.

For example, the control may be performed so that the n-th and (n + 1) -th feeding interval (sheet passing interval) of the plurality of sheets S to be conveyed is wider than before the PPM control is started without interrupting the job.
Further, the temporary interruption is continued not for a fixed time but until the fixing roller sheet passing portion temperature reaches a predetermined temperature, for example, the target temperature Tm. When the temperature is raised to the predetermined temperature, the temporary interruption is canceled ( It is also possible to take a method of resuming a job that has been interrupted. In this case, it is assumed that one interruption time is longer than the above-mentioned fixed time, but the number of interruptions can be limited to one.

  If the PPM execution prediction unit 109 executes a scheduled job, whether or not the PPM control start timing is reached during the job execution, that is, the fixing roller sheet passing portion temperature decreases to the threshold Tz. Predict whether or not it will happen. This prediction is performed by calculating how many times the fixing roller passing portion temperature has decreased after the end of the job based on the number of prints, the paper size, the paper type, and the like. To do.

<Timing chart of stabilization control and PPM control (first example)>
FIG. 5 is a timing chart showing a first example in the case where it is predicted that the stabilization control and the PPM control are separately executed with a time lag between a plurality of scheduled jobs. (A) shows the names of jobs scheduled to be executed (jobs 1 to 5), (b) shows the transition prediction of the fixing roller sheet passing portion temperature, and (c) shows the process speed.

  As can be seen from FIG. 5A, in the first example, when the jobs 1 to 5 are scheduled to be executed in this order, the execution timing of the stabilization control is reached at the end of the job 3; The stabilization control is interrupted between jobs 3 and 4 and the fixing roller sheet passing portion temperature drops to the threshold Tz at the end of job 4, so that the next job 5 is subject to PPM control and the job is In the example, job 5 is started after being temporarily interrupted.

As shown in FIG. 5C, the process speed is constant at the reference speed Vs, and an example in which the process speed is not changed is shown.
In the first example, the transition prediction of the fixing roller sheet passing portion temperature is as follows.
That is, as shown in FIG. 5B, the fixing roller sheet passing portion temperature decreases from job 1 to job 3, but at the end of job 3 (time point ta), a threshold value that is a PPM control start condition Tz has not been reached, and stabilization control is started when job 3 ends.

  During the execution of the stabilization control, the job is temporarily interrupted, and the fixing roller temperature control causes the Wb (FIG. 4) power to be supplied to the exciting coil 43 when the fixing roller sheet passing portion temperature T> Tz. As a result, the fixing roller sheet passing portion temperature changes from a decrease to an increase. Since power value Wb is smaller than normal Wa, the temperature increase rate (gradient) is extremely small as shown between time points ta and tb in FIG.

When the stabilization control ends (time tb), the temporary suspension of the job is released and job 4 is started. The fixing roller sheet passing portion temperature has increased during the stabilization control. However, when the job 4 is started, the temperature starts to decrease again, and reaches the threshold value Tz at the end of the job 4 (time point tc).
As a result, the PPM control is started at time tc. During execution of PPM control, while the job is temporarily suspended, Wa power is supplied to the exciting coil 43 by fixing temperature control, so that the heat is not taken away by the sheet S, so that the fixing roller is more than during execution of the job. The amount of heat per unit time supplied to 41 increases, and the fixing roller sheet passing portion temperature starts to rise.

When the job interruption by the PPM control is completed (time td), the job 5 is started. When the job 5 is started, the fixing roller sheet passing portion temperature starts decreasing again and gradually decreases.
In FIG. 5B, when the transition of the fixing roller sheet passing portion temperature is compared between the execution of the stabilization control and the execution of the PPM control, the direction during the execution of the PPM control is greater than that during the execution of the stabilization control. Also, the magnitude of the temperature that rises per unit time (temperature rise rate) is large.

This is because, in the fixing temperature adjustment control, the power supplied to the exciting coil 43 is Wa at normal times including the PPM control, whereas at the time point ta, the fixing roller sheet passing portion temperature T> Tz. This is because the power supplied to the exciting coil 43 is reduced to Wb smaller than Wa.
In this way, in the first example, it is predicted that job interruption will occur twice between jobs 1-5, and if jobs 1-5 are executed as they are, twice as expected. Due to this job interruption, the number of prints (print productivity) that can be executed per unit time is reduced.

The PPM control is based on the condition that the fixing roller sheet passing portion temperature decreases to the threshold Tz during job execution. Therefore, if this start condition is not satisfied, PPM control is entered between jobs 4 and 5. This can be prevented.
In other words, it is sufficient that the fixing roller sheet passing portion temperature does not decrease to the threshold Tz during execution of jobs 4 and 5, but the fixing roller sheet passing portion temperature continues to decrease during job execution. . From this, if the temperature at the fixing roller sheet passing portion at the time tb at the start of the job 4, that is, at the end of the stabilization control, is higher than the temperature shown in FIG. Even if the fixing roller sheet passing portion temperature continues to decrease during the execution of the above, it should be possible to prevent the decrease to the threshold value Tz.

In order to make the temperature of the fixing roller passing portion at the time tb higher, it is only necessary to raise the fixing roller passing portion temperature as much as possible during the execution of the stabilization control, and the fixing roller passing portion temperature is increased as much as possible. In order to do this, the power supplied to the exciting coil 43 may be switched from the power value Wb for suppressing power consumption to a power value Wa larger than this.
In order to allow the power supplied to the exciting coil 43 to be switched to Wa during the stabilization control, from FIG. 4, the condition of the fixing roller sheet passing portion temperature ≦ the threshold Tz is satisfied at the start of the stabilization control, that is, PPM. It is sufficient that the control start condition is satisfied.

In order to satisfy the PPM control start condition at the start of the stabilization control, the fixing roller sheet passing section is executed during the execution of the job scheduled before the stabilization control, such as job 3 in the example of FIG. By increasing the temperature decrease rate (gradient), it is sufficient that the fixing roller sheet passing portion temperature just reaches the threshold value Tz at the start of the stabilization control (time point ta).
In order to increase the decrease rate of the fixing roller sheet passing portion temperature, it is sufficient that the amount of heat taken by the sheet S per unit time from the fixing roller 41 is increased, and in order to increase the amount of heat per unit time, The number of sheets S that pass through the fixing roller 41 per unit time may be increased.

In order to increase the number of sheets S passing through the fixing roller 41 per unit time, the process speed may be set higher than the normal reference.
Therefore, in the present embodiment, the fixing roller sheet passing portion temperature is set to the threshold value at the start of the stabilization control (time point ta) without changing the stabilization control execution timing (between jobs 3 and 4) from the original timing. Jobs 1 to 1 scheduled before the stabilization control so that the electric power Wa is supplied to the exciting coil 43 during the execution of the stabilization control when the start-up condition of the PPM control is satisfied. 3 is variably controlled. The variable control of the process speed is called process speed change processing.

6A and 6B are timing charts when the process speed change process is executed in the first example shown in FIG. 5, where FIG. 6A shows the name of a job scheduled to be executed, and FIG. Temperature transition prediction is shown, and (c) shows the process speed.
As shown in FIG. 6A, when the process speed changing process is executed, the stabilization control is interrupted between the jobs 3 and 4 with respect to the schedule shown in FIG. Although it does not change, it can be seen that the schedule is changed to that in which the PPM control is not executed between jobs 4 and 5.

Looking at the transition prediction of the fixing roller sheet passing portion temperature, as shown in FIG. 6B, the temperature decreases during execution of jobs 1 to 3, but the temperature decrease rate (temperature gradient) is based on jobs 1 and 2. However, job 3 is larger. This is due to the following reason.
That is, as shown in FIG. 6C, control is performed to increase the process speed to the first speed Va faster than the reference speed Vs only while the job 3 is being executed. As the process speed during job execution increases, the number of sheets S conveyed per unit time increases, and when the sheet S passes through the fixing roller 41, the unit time taken by the sheet S of the heat of the fixing roller 41 This is because the hit amount also increases, so that the rate of decrease in the fixing roller sheet passing portion temperature is larger in job 3 having a faster process speed than jobs 1 and 2.

Note that the process speed is changed from the reference speed Vs when the image writing timing by exposure on the photosensitive drums 11Y to 11K is changed to the reference speed Vs according to the magnitude of the speed change. Will be.
By increasing the process speed, as shown in FIG. 6B, the fixing roller sheet passing portion temperature reaches the threshold Tz at the time tf when the job 3 is completed.

The time point tf is the end time of the job 3, but is also the start timing of the stabilization control, and also corresponds to the time point that satisfies the start condition of the PPM control.
The job execution is temporarily interrupted by starting the stabilization control at the time point tf, but the temperature of the fixing roller sheet passing portion is raised in parallel during the execution of the stabilization control. The temperature increase rate (temperature gradient) at the time of temperature increase is equal to the increase rate at the time of PPM control in FIG.

This is because the fixing roller passing portion temperature at the start of the temperature rise is the same threshold Tz both in the case of the PPM control of FIG. 5 and in the case of the stabilization control of FIG. This is because the state in which the current does not pass is the same, and the power supplied to the exciting coil 43 is also set to the same Wa.
When the fixing roller sheet passing portion temperature rises during the execution of the stabilization control and the stabilization control is completed (time tg), the job execution temporary suspension is canceled and the job 4 is started. During the execution of job 4, the fixing roller sheet passing portion temperature starts to drop, but at the time point th when the job 4 ends, the threshold Tz is not reached and the PPM control start condition is not satisfied. Therefore, PPM control does not occur between jobs 4 and 5, and jobs 4 and 5 are continuously executed.

In order to execute the stabilization control with the jobs 1 to 5 in the schedule shown in FIG. 6, the start condition of the PPM control is satisfied at the time tf when the job 3 is finished, that is, the fixing roller sheet passing portion temperature is decreased to the threshold Tz. It is necessary to synchronize the timing when the job 3 is completed.
In order to satisfy this condition, the process speed of the job scheduled to be executed before the stabilization control, here, the job 3 is changed to the first speed Va. Therefore, it is necessary to determine the magnitude of the first speed Va before the start of the job 3 so as to decrease to the threshold value Tz.

The first speed Va is determined based on the value at which the process speed is set based on the number of printed sheets, the paper size, the paper type, and the like in the process speed changing process. This is done by calculating whether the end of job 3 is synchronized.
As shown in FIG. 6B, the time required to execute job 3 is shortened by increasing the process speed of job 3, so the start timing tf of stabilization control is shown in FIG. It is earlier than the indicated time point ta. The difference α between the time points tf and ta shown in FIG. 6B corresponds to this shortened time. As a result, the total time for executing jobs 1 to 5 is reduced by the time α if the process speed change process is executed.

That is, since the start timing of the PPM control is advanced to the stabilization control, the originally predicted PPM control is not executed between the jobs 4 and 5 scheduled after the stabilization control. The productivity of printing can be improved by reducing the time α while reducing job interruption to one time.
In the first example, the stabilization control is predicted to be executed earlier than the PPM control. The second example in which this order is reversed is shown in FIGS. 8 will be used for explanation.

<Timing chart of stabilization control and PPM control (second example)>
FIG. 7 is a timing chart showing a second example when it is predicted that the PPM control is executed earlier than the stabilization control. FIG. 7A shows the names of jobs scheduled to be executed (jobs 1 to 1). 6), (b) shows the transition prediction of the fixing roller sheet passing portion temperature, and (c) shows the process speed.

As shown in FIG. 7A, the jobs 4 and 5 are the targets of the PPM control, and the stabilization control interrupts between the jobs 5 and 6.
As shown in FIG. 7B, the transition prediction of the fixing roller sheet passing portion temperature is as follows.
That is, the fixing roller sheet passing portion temperature decreases during execution of job 3 (between time points ta and tb), reaches the threshold value Tz at the end of job 3 (time point tb), and the job is temporarily suspended due to the start of PPM control. When it is done, it starts to rise, and when the temporary interruption ends (time tc), it decreases with the execution of the job 4 started by releasing the interruption.

The fixing roller sheet passing portion temperature has not yet reached the target temperature Tm at the end of the job 4 (time point td). Therefore, when the job is temporarily interrupted due to the continuation of the PPM control, during that time (time points td to te). When the temporary interruption is completed by reaching the target temperature Tm (time te), the temperature decreases with the execution of the job 5 started by releasing the interruption.
When the job 5 is ended (time tf) and the job is temporarily interrupted for stabilization control, the fixing roller sheet passing portion temperature starts to rise. In this example, the PPM control is canceled when the fixing roller sheet passing portion temperature rises to the target temperature Tm during the stabilization control. When the stabilization control ends (time tg), the job 6 is started by canceling the interruption, and the fixing roller sheet passing portion temperature decreases as the job 6 is executed. The process speed is constant at the reference speed Vs as shown in FIG.

Also in the second example, as in the first example shown in FIG. 5, the PPM control and the stabilization control are executed separately with a time shift, so that the print productivity decreases accordingly. .
Even when the PPM control and the stabilization control are executed in this order as in the second example, as in the first example, the temperature at the fixing roller sheet passing portion is set at the start of the stabilization control (time point tf). Predicted PPM control can be achieved by variably controlling the process speed for a job to be executed (here, jobs 3 to 5 etc.) before the stabilization control so that the threshold Tz is reached, that is, the start condition for PPM control is satisfied. Will not be executed, and a decrease in print productivity should be prevented.

FIG. 8 is a timing chart when the process speed change control is executed in the second example shown in FIG. 7, where (a) shows the name of the job scheduled to be executed, and (b) shows the fixing roller sheet passing portion. Temperature transition prediction is shown, and (c) shows the process speed.
When process speed change control is executed as shown in FIG. 8A, stabilization control is interrupted between jobs 5 and 6 with respect to the schedule shown in FIG. However, it can be seen that the schedule is changed between jobs 3 and 4 and jobs 4 and 5 so as not to be interrupted by PPM control.

Looking at the transition prediction of the fixing roller sheet passing portion temperature, as shown in FIG. 8B, the temperature decreases during execution of jobs 3 to 4, but the rate of temperature decrease compared to jobs 1 and 2, It has become quite gradual. This is because, as shown in FIG. 8C, during the execution of jobs 3 and 4, control is performed to lower the process speed to the second speed Vb that is slower than the reference speed Vs.
As the process speed during job execution decreases, the number of sheets S transported per unit time decreases, and when the sheet S passes the fixing roller 41, the heat of the fixing roller 41 is deprived by the sheet S. Since the amount per time is reduced, the rate of decrease in the fixing roller sheet passing portion temperature is smaller in jobs 3 and 4 having a slower process speed than jobs 1 and 2.

For job 5, the rate of decrease of the fixing roller sheet passing portion temperature is significantly greater than that of jobs 1 and 2. This is because, as shown in FIG. 8C, during the execution of the job 5, the control for increasing the process speed to the first speed Va higher than the reference speed Vs is executed.
In this way, the process speed is changed to either the first speed Va that is faster than the reference speed Vs or the second speed Vb that is slower than the reference speed Vs in units of jobs when the job 5 ends (time tk). This is to synchronize the timing at which the paper part temperature reaches the threshold value Tz.

In the second example, the PPM control is predicted to be executed before the stabilization control, and in order to disable the previous PPM control, the timing satisfying the start condition of the PPM control, that is, the fixing roller passage. It is necessary to delay the timing at which the paper part temperature reaches the threshold value Tz until the subsequent stabilization control start timing.
In order to delay this timing, the process speed of the job scheduled to be executed before the stabilization control, in this case, any one of 1 to 5 may be reduced. However, if the speed is reduced, the temperature decrease rate becomes smaller. The transition of the roller sheet passing portion temperature tends to draw a descending line that gradually approaches the threshold value Tz and reaches the threshold value Tz as time elapses with little temperature difference from the threshold value Tz. In this state, immediately before reaching the threshold value Tz, if the fixing roller sheet passing portion temperature falls below the threshold value Tz due to fluctuation, the PPM control start condition is satisfied earlier than expected, and the PPM control start condition is set. The filling timing is likely to vary.

This is due to the fact that the temperature decrease rate of the fixing roller sheet passing portion temperature for the job 5 immediately before the stabilization control is small. To avoid this, in the example of FIG. The rate of decrease in the fixing roller sheet passing portion temperature is reduced to a low speed, and for the job 5 immediately before the stabilization control, the process speed is increased to increase the temperature decrease rate.
Note that if the second speed Vb, which is the process speed of the jobs 3 and 4, is set too low, the print productivity will be lower than when the process speed changing process is not executed. Therefore, the second speed Vb is It is desirable to be determined in the process speed changing process within a range where productivity is not lowered.

  In the example of FIG. 8, the time tp from the start time of job 3 (time point ta) to the start time of job 5 (time point tj) is the same as that of job 5 from the start time of job 3 (time point ta) in FIG. It is the same as the time tp until the start time (time te). As a result, the start time of the stabilization control (time tk) is earlier than the time tf shown in FIG. 7B because the time required to execute job 5 is shortened by increasing the process speed of job 5. . A difference β between the time points tk and tf shown in FIG. 8B corresponds to the shortened time.

Even in the case of the second example, the total time for executing the jobs 1 to 6 is shortened by the time β, and print productivity can be improved.
In FIGS. 5 to 8, the prediction example in which the PPM control and the stabilization control are interrupted at successive job and job breaks has been described. However, there may be a case where the interrupt occurs in the middle of the job. In this case, the PPM control can be configured such that the image forming operation for the remaining number of interrupted jobs is the target of the PPM control. In some cases, even if the PPM control start condition is satisfied, if the job is in the middle of execution, the job may not be subject to PPM control, and the next job may be subject to PPM control.

Returning to FIG. 2, the PPM control table 110 is a table in which PPM control parameters used when performing PPM control execution prediction are written.
FIG. 9 is a diagram showing an example of the contents of the PPM control parameter. (A) is the paper type information 121, (b) is the paper CD information 122, (c) is the paper FD information 123, and (d) is the paper type information 121. , Process speed information 124, (e) is temperature / humidity information 125, (f) is environment step information 126, (g) is the fixing roller warming condition information 127, and (h) is the CD length / temperature difference allowance. Value correspondence information 128 is shown, and these pieces of information are included in the PPM control parameter. How to use the PPM control parameter for the execution prediction of the PPM control will be described later.

Returning to FIG. 2, if the process speed change unit 111 determines that a change is necessary by the process speed change necessity determination process for determining whether or not the process speed needs to be changed, the process speed change unit 111 performs process speed change processing, that is, stabilization control. The process speed of the previously scheduled job is changed to one of the reference speed Vs, the first speed Va that is higher than this, and the second speed Vb that is lower than this.
The control unit 50 includes an internal timer (not shown) and measures various times, for example, an elapsed time tx from the end of warm-up. The warm-up is started when the power of the apparatus is turned on or the power switch is turned on. When the fixing roller 41 is heated and the temperature of the fixing roller passing portion reaches the target temperature Tm due to the temperature rise, the printable state is reached. This is a preparatory operation for transition to (ready state). Here, the elapsed time tx from the end of the warm-up is an elapsed time after the fixing roller sheet passing portion temperature reaches the target temperature Tm. Note that the warm-up is not limited to a configuration that starts when the power switch is turned on, and may start, for example, when a jam (paper jam) or recovery from a trouble occurs.

<Processing content by control unit>
FIG. 10 is a flowchart showing the contents of the process speed change necessity determination process executed by the control unit 50, and this process is executed every time a new job is received.
As shown in the figure, a PPM control necessity prediction process is executed (step S1). The PPM control necessity prediction process is a process for determining whether or not a PPM control start condition is satisfied during a plurality of jobs that are currently scheduled.

If it is determined that the PPM control start condition is satisfied (“YES” in step S2), then a stabilization control schedule determination process is executed (step S3). The stabilization control schedule determination process is a process for determining whether or not the execution timing of the stabilization control is reached in the meantime if a plurality of scheduled jobs are to be executed.
If it is determined that the execution timing of the stabilization control is reached (“YES” in step S4), the process speed change process is executed (step S5), and the process speed change necessity determination process is terminated. In this case, jobs executed after the processing are sequentially executed at the changed process speed.

  On the other hand, if it is determined that the PPM control start condition is not satisfied ("NO" in step S2), the process speed change process is skipped (not executed), and the process speed change necessity determination process is terminated. . If it is determined that the stabilization control execution time has not been reached ("NO" in step S4), the process speed change process is skipped, and the process speed change necessity determination process ends. In these cases, the process speed is not changed, and jobs executed after the process are sequentially executed at the reference speed Vs.

<Contents of PPM Control Necessity Prediction Process>
FIG. 11 is a flowchart showing the contents of a subroutine of PPM control necessity prediction processing. As shown in the figure, PPM control parameters are acquired (step S11). The PPM control parameter is acquired by referring to the PPM control table 110.
<1. Coefficient setting>
Based on the acquired PPM control parameters, the following coefficients C1 to C6 are set (steps S12 to S17). These coefficients C1 to C6 are used for temperature prediction in later-described steps S18 to S20.

First, the paper type coefficient C1 is set (step S12). That is, the paper type of the paper S used by the scheduled job is acquired from the job management table 103, and the coefficient corresponding to the acquired paper type is read from the paper type information 121 shown in FIG. Is set to the paper type coefficient C1.
For example, when the paper type is plain paper, referring to the paper type information 121, the coefficient corresponding to plain paper is 1, so the paper type coefficient C1 is set to 1. For thin paper, the paper type coefficient C1 is set to 0.9, and for thick paper, the paper type coefficient C1 is set to a value larger than 1 depending on the thickness. When there are a plurality of jobs, the paper type coefficient C1 is set for each job. This is the same for the coefficients C2 and C3.

The reason why the paper type coefficient C1 is made different depending on the paper type is to improve the prediction accuracy when the fixing roller paper passing part temperature during the job is predicted.
That is, the amount of heat per unit time taken by the sheet S from the fixing roller 41 varies depending on the sheet type, and the temperature decrease rate of the fixing roller sheet passing portion temperature also varies.
If the fixing roller passing portion temperature is predicted without considering the paper type, if a certain type of paper S is used, the prediction accuracy is high, but if another type of paper S is used. Depending on the difference in temperature decrease rate due to the paper type, a difference between the predicted temperature and the actual temperature may occur, and the prediction accuracy may be greatly reduced.

  Therefore, as the paper type, here, due to the difference in the thickness of the paper S, the temperature decrease rate of the fixing roller passing portion temperature increases as the thickness increases. By setting the value of the paper type coefficient C1 so that a larger temperature decrease rate is applied to the thick paper S than to the thin paper S, the prediction accuracy is improved compared to the case where the paper type coefficient C1 is not applied. It is a thing. Similarly, different values are prepared for the other coefficients C2 to C6 according to the respective conditions in order to improve the prediction accuracy.

Next, the paper CD coefficient C2 is set (step S13). Specifically, the paper size and transport posture of the paper S used by the scheduled job are acquired from the job management table 103, and the paper CD length (the length orthogonal to the transport direction) is determined from the acquired paper size and transport posture. : Paper width).
Since the length in the vertical direction and the length in the horizontal direction are defined in advance with respect to the paper size, the length in the vertical direction corresponds to the length in the transport direction (paper FD length), and the length in the horizontal direction is perpendicular to the transport direction. By determining that the length corresponds to the length (paper CD length), the paper CD length can be obtained if the paper size and the conveying posture are known. For example, if it is A4 size and vertical posture, it is 210 [mm], and if it is B5 size and vertical posture, it is 182 [mm]. In the case of A4 size and horizontal posture, the paper CD length is 297 [mm].

The coefficient corresponding to the obtained paper CD length is read from the paper CD information 122 shown in FIG. 9B, and the read coefficient is set as the paper CD coefficient C2. For example, in the case of A4 size and vertical orientation, the paper CD length is 210 [mm], so the paper CD coefficient C2 is set to 0.90. Similarly, the B5 size is set to 0.90.
When the paper S having a longer paper CD length passes through the fixing roller 41 than when the paper S is shorter, the amount of heat per unit time taken away from the fixing roller 41 by the paper S increases. Therefore, the paper CD coefficient C2 is set such that the paper S having a long paper CD length is applied to the paper S having a longer paper CD length than the paper S having a shorter length when the temperature of the fixing roller passing portion is predicted. By setting, the prediction accuracy can be improved as compared with the case where the paper CD coefficient C2 is not applied.

Subsequently, the paper FD coefficient C3 is set (step S14). Specifically, the paper FD length is obtained from the acquired paper size and transport posture. For example, if it is A4 size and vertical posture, it is 297 [mm], and if it is B5 size and vertical posture, it is 257 [mm].
A coefficient corresponding to the obtained sheet FD length is read from the sheet FD information 123 shown in FIG. 9C, and the read coefficient is set as the sheet FD coefficient C3. For example, in the case of A4 size and vertical posture, the paper FD coefficient C3 is set to 1.05. The same applies to the B5 size.

The reason why the paper FD coefficient C3 becomes larger as the paper FD length becomes longer is the same reason that the paper CD coefficient C2 becomes larger as the paper CD length becomes longer.
Then, a process speed coefficient C4 is set (step S15). Specifically, referring to the process speed information 124 shown in FIG. 9D, a coefficient corresponding to the process speed set for the job is read, and the read coefficient is set as the process speed coefficient C4. Here, the process speed for all jobs is set to 210 [mm / s], which is the reference speed Vs, and before execution of the process speed changing process, 1.0 is a coefficient corresponding to the reference speed Vs. The speed coefficient is set to C4.

Subsequently, an environmental step coefficient C5 is set (step S16). Specifically, the current temperature detection result by the in-machine temperature sensor 71 and the current humidity detection result by the in-machine humidity sensor 72 are acquired.
And the environmental step (0-6) corresponding to the acquired internal temperature and internal humidity is read with reference to the temperature / humidity information 125 shown in FIG.9 (e). For example, when the in-machine temperature is 25 ° C. and the in-machine relative humidity is 50%, the environmental step is 4, and when the in-machine temperature is 35 ° C. and the in-machine relative humidity is 85%, the environmental step is 6

Subsequently, referring to the environmental step information 126 shown in FIG. 9F, the coefficient corresponding to the environmental step is read, and the read coefficient is set as the environmental step coefficient C5. For example, when the environmental step is 4, the environmental step coefficient C5 is 0.9, and when the environmental step is 6, the environmental step coefficient C5 is 0.7.
The reason why the environmental step coefficient C5 is smaller when the in-machine temperature and the in-machine humidity are higher than when the in-machine temperature and the in-machine humidity are low is as follows. That is, normally, in a high-temperature and high-humidity environment, the temperature of the sheet S itself is higher than in a low-temperature and low-humidity environment, and when the sheet S passes through the fixing roller 41, the unit is deprived of the sheet S by the fixing roller 41. Less heat per hour. This means that the decreasing rate of the fixing roller sheet passing portion temperature is reduced.

Therefore, when the temperature / humidity environment changes, when predicting the temperature at which the fixing roller passes through, the temperature drop in the high-temperature, high-humidity environment is smaller than that in the low-temperature, low-humidity environment by the temperature and humidity difference. This is because by setting the environmental step coefficient C5 so that the rate is applied, the prediction accuracy can be improved as compared with the case where the environmental step coefficient C5 is not applied.
Next, the fixing roller warming coefficient C6 is set (step S17). Specifically, first, an elapsed time tx from the end of warm-up is acquired.

  The ratio of the acquired elapsed time tx to the reference time ty is obtained. For example, if the elapsed time tx is 55 seconds and the reference time ty is 1 minute, it is 92 [%]. Then, referring to the fixing roller warming condition information 127 shown in FIG. 9G, the coefficient corresponding to the obtained ratio is read, and the read coefficient is set as the fixing roller warming coefficient C6. For example, when the obtained ratio is 92 [%], the fixing roller warming coefficient C6 is 1.5.

The reason for obtaining the fixing roller warming coefficient C6 is as follows.
That is, the surface of the fixing roller 41 should have reached the target temperature Tm if the warm-up has been completed, but if the elapsed time tx from the end of the warm-up is short, the inside of the fixing roller 41 is heated. May not be widespread and may still be lower than the target temperature Tm.

  When the job is started in such a state, the heat generated from the electromagnetic induction heating layer provided on the surface of the fixing roller 41 is transferred to the inside of the fixing roller 41 while being taken away by the sheet S. It can be said that the heating roller cannot catch up, and the temperature at the fixing roller sheet passing portion is likely to decrease during job execution. This means that the decreasing rate of the fixing roller sheet passing portion temperature is increased.

  On the other hand, if the elapsed time tx from the end of the warm-up is long, the heat is sufficiently distributed inside the fixing roller 41, and the heat generated from the electromagnetic induction heating layer is used only for fixing the paper S. Then, compared to the case where a large amount of heat is transmitted to the inside of the fixing roller 41, the fixing roller sheet passing portion temperature is less likely to decrease. This corresponds to a small decrease rate of the fixing roller sheet passing portion temperature.

In other words, due to the length of the elapsed time tx from the end of the warm-up, the rate of decrease in the fixing roller sheet passing part temperature changes, and the change in the temperature decreasing rate has an effect on the prediction accuracy of the fixing roller sheet passing part temperature. Will give.
Therefore, as a measure of the length of the elapsed time tx from the end of the warm-up, a ratio with respect to the reference time ty (how the fixing roller is warmed) is obtained. This is because when the temperature is predicted, by setting the fixing roller warming coefficient C6 so that a large temperature decrease rate is applied, the prediction accuracy can be improved as compared with the case where the fixing roller warming coefficient C6 is not applied.

When the ratio of the elapsed time tx from the end of warm-up to the reference time ty exceeds 100 [%], it is regarded as 100 [%] and the fixing roller warming coefficient C6 is set.
<2. Temperature prediction>
Returning to FIG. 11, in step S <b> 18, the fixing roller sheet passing portion lowering temperature Ta is predicted using the set coefficients C <b> 1 to C <b> 6. Here, the fixing roller sheet passing portion drop temperature Ta indicates the amount of temperature drop when the fixing roller sheet passing portion temperature decreases from the start to the end if the job is executed.

The fixing roller sheet passing portion lowering temperature Ta is calculated by the following equation (1).
Ta [° C.] = Pn [sheet] × Tk [° C./sheet]×C1×C2×C3×C4×C5×C6 (Formula 1)
Here, Pn is the number of prints.
Tk is a fixing roller that decreases when a reference size sheet, that is, a sheet having a size in which both the sheet CD coefficient C2 and the sheet FD coefficient C3 are both 1, passes through the fixing roller 41. This is the sheet passing part temperature (fixed value), and here it is 0.3 [° C./sheet].

For example, the number of prints is 50 [sheets], the paper size is A4 (vertical posture), the paper type is plain paper, the process speed is 210 [mm / s], the environmental step is 5, and the temperature of the fixing roller is 92 [%]. C1 becomes 1, C2 becomes 0.9, C3 becomes 1.05, C4 becomes 1, C5 becomes 0.8, C6 becomes 1.. 5
Substituting these values into (Equation 1) yields Ta [° C.] = 17.01.

  Next, the fixing roller sheet passing portion recovery temperature Tb is predicted (step S19). Here, the fixing roller sheet passing portion recovery temperature Tb is such that the leading edge of the next (N + 1) th sheet S after the trailing edge of the Nth sheet S passes through the fixing roller 41 during job execution. The time until the fixing roller 41 is reached, that is, the amount of temperature increase when the temperature of the fixing roller sheet passing portion rises due to heating during the so-called paper is shown.

The fixing roller sheet passing portion recovery temperature Tb is calculated by the following equation (2).
Tb [° C.] = Q [number of times] × Th [° C./msec]×tq [msec] (Formula 2)
Here, Q is the number of times between sheets.
Th is an increase rate (fixed value) of the fixing roller sheet passing portion temperature per unit time when the power supplied to the exciting coil 43 is Wa between the sheets. Here, 0.005 [° C./msec] It has become. Note that msec is a unit of millisecond.

tq is the time (fixed value) between one sheet of paper when the process speed is 210 [mm / s], and is 20 [msec] here.
For example, when the number of prints is 50, there are 49 paper gaps, and if this is substituted into (Equation 2), Tb = 4.9 [° C.].
Next, the fixing roller sheet passing portion temperature Tc at the end of the job is predicted (step S20).

The prediction of the fixing roller sheet passing portion temperature Tc is calculated by the following (Equation 3).
Tc [° C.] = Td [° C.] − Ta [° C.] + Tb [° C.] (Formula 3)
Here, Td [° C.] is a temperature detected as the current fixing roller sheet passing portion temperature.
For example, in FIG. 5, if the execution conditions (paper size, type, and transport posture) of jobs 1 to 3 are the same and the total number of prints of jobs 1 to 3 is 50, the current job 1 is started. If the current fixing roller sheet passing portion temperature Td is 165 [° C.] and the threshold Tz is 150 [° C.] immediately before the time, the fixing roller sheet passing portion temperature Tc at the end of the job 3 is 152.89 [° C.]. It is predicted.

In this example, since the fixing roller sheet passing portion temperature at the end of the job 3 does not become the threshold value Tz (= 150 [° C.]) or less, the PPM control start condition is not satisfied and it is not necessary to execute the PPM control. Judgment can be made.
Further, for example, the number of prints is 30 [sheets], the paper size is A4, the horizontal posture, the paper type is plain paper, the process speed is 210 [mm / s], the environmental step is 3, the warming condition of the fixing roller is 85 [%]. ], C1 to C5 are each 1 and C6 is 2.

Therefore, from (Formula 1), Ta = 18 [° C.], from (Formula 2), Tb = 2.9 [° C.], and from (Formula 3), the predicted temperature Tc = 149.99 [° C.] become.
In this example, since the temperature at the fixing roller passing portion at the end of the job 3 is predicted to be equal to or lower than the threshold Tz (= 150 [° C.]), it is necessary to satisfy the PPM control start condition and execute the PPM control. Can be judged.

In the above description, an example in which a plurality of jobs are performed under the same conditions such as paper size and type has been described, but Ta to Tc can be similarly obtained even when different jobs are different.
For example, for the fixing roller sheet passing part drop temperature Ta, Ta1 for job 1, Ta2 for job 2, and Tan for job n are obtained for each job, and the obtained Ta1, Ta2, and Tan are added together. Ta can be used. The same applies to the fixing roller paper passing portion recovery temperature Tb, and Tb1 for job 1, Tb2 for job 2,... Tbn for job n are obtained for each job, and the obtained Tb1, Tb2,. Is Tb.

If the stabilization control is predicted to interrupt during the job, the stabilization control execution period is assumed to be the same as the interval between sheets, and the temperature is raised during the stabilization control execution period. The temperature Tbz may be incorporated into the fixing roller sheet passing portion recovery temperature Tb.
Specifically, assuming that the fixing roller sheet passing portion temperature T> Tz at the start of the stabilization control, the power supplied to the excitation coil 43 is Wb as described above during the execution of the stabilization control. Therefore, the increasing rate th1 of the fixing roller sheet passing portion temperature per unit time is smaller than the above th (= 0.005 [° C./msec]), for example, (th / 50).

If the execution period of the stabilization control is 60 seconds, the recovery temperature Tbz during the execution of the stabilization control is 6 [° C.] from 60 [seconds] × Th1 [° C./msec].
When jobs 1 to 3, stabilization control, and job 4 are scheduled to be executed in this order as in the example of FIG. 5, the fixing roller sheet passing portion drop temperature Ta is predicted to be a value obtained by (Ta 1 + Ta 2 + Ta 3 + Ta 4) and fixed. The roller sheet passing portion recovery temperature Tb is predicted to be a value obtained by (Tb1 + Tb2 + Tb3 + Tbz + Tb4). Can be sought.

If the example of FIGS. 5 and 7 is a graph showing the result of applying the calculation according to the above formula to a scheduled job, in FIG. 5, the fixing roller sheet passing portion temperature Tc ≦ threshold Tz is set at the end of job 4. In FIG. 7, it can be predicted that, at the end of job 3, the fixing roller sheet passing portion temperature Tc ≦ threshold value Tz is satisfied.
<3. Judgment of necessity of PPM control>
In step S21 in FIG. 11, it is determined whether or not the fixing roller sheet passing portion temperature Tc at the end of the job satisfies a threshold value Tz.

If Tc ≦ Tz is determined (“YES” in step S21), it is determined that the PPM control start condition is satisfied, a necessary flag indicating that PPM control is necessary is set (step S22), and then PPM control is scheduled. The start timing is determined (step S23), and the process returns.
In the present embodiment, since the fixing roller sheet passing portion temperature Tc at the end of the job is predicted for each job, among the plurality of scheduled jobs, Tc at the start of each job in order from the job with the earlier execution order. > Tz is satisfied and whether Tc ≦ Tz is satisfied at the end, and if there is a job that satisfies this, it is determined that the scheduled start timing of PPM control is entered between the start and end of the job it can.

In the example of FIG. 5, Tc = Tz at the end of job 4 (time tc), and in the example of FIG. 7, Tc = Tz at the end of job 3 (time tb). The scheduled start timing of PPM control is determined.
When Tc ≦ Tz is satisfied during the execution of the job, the drop temperature Ta and the recovery temperature Tb per sheet are calculated as to how many sheets S are passed for the job when Tc = Tz is satisfied. As a result, the scheduled start timing of the PPM control can be obtained.

On the other hand, if Tc> Tz is determined (“NO” in step S21), it is determined whether the CD length of the previous job and the sheet S is different (step S24).
Here, the previous job refers to a job immediately before one of scheduled jobs. For example, if the scheduled jobs are 1 to 5, the previous job for job 1 is a job that has been completed immediately before, the previous job for job 2 is job 1, and the previous job for job 5 is , Job 4.

For each scheduled job, it is determined whether the CD length differs from the previous job. This determination is made by referring to the management information 1031 (FIG. 3) of the job management table 103.
The reason why the CD lengths are different in this way is to determine that PPM control is necessary even if the fixing roller sheet passing portion temperature Tc ≦ threshold value Tz is not satisfied. The reason will be described below.

That is, since the CD length of the paper S is the length in the paper width direction, if the CD length of the paper S used for the previous job is small and the CD length of the paper S used for the subsequent job is large, the fixing is performed. Of the entire area of the roller 41 in the axial direction, there is a non-sheet passing area for the previous job, but there is a partial area that becomes the sheet passing area for the subsequent job.
The sheet passing area of the fixing roller 41 is controlled to be stabilized at the target temperature Tm by the heat of the induction heating layer while the sheet S is deprived of heat, but the sheet S is not deprived of heat in the non-sheet passing area. Therefore, it is likely to rise to some extent than the target temperature Tm.

In addition to this, if the fixing roller sheet passing portion temperature continues to decrease gradually during the previous job execution, the temperature of the sheet passing area (fixing roller sheet passing portion temperature) itself is lower than the target temperature Tm. Thus, the temperature difference between the paper passing area and the non-paper passing area becomes larger.
In this case, in a job following the previous job, the sheet passing area of the fixing roller 41 when one sheet S passes through the fixing roller 41 is more than the target temperature Tm in the axial direction (corresponding to the sheet width direction). The lower partial region and the partial region higher than the target temperature Tm coexist, and the portion fixed in the sheet width direction at a temperature lower than the target temperature Tm in the sheet S is fixed at the higher temperature. This causes a portion to be fixed, and tends to affect the fixing property due to fixing unevenness.

The decrease in fixability is likely to be noticeable when the temperature of the fixing roller 41 is low, and is difficult to appear when the temperature is high. That is, the fixing roller 41 is likely to appear when a portion lower than the target temperature Tm and a portion higher than the target temperature Tm coexist, but it is difficult to appear only when the portion is higher than the target temperature Tm.
That is, when the CD length of the paper S is different between the previous job and the subsequent job, the temperature of the paper passing area (fixing roller paper passing portion temperature) is lowered below the target temperature Tm. As a result, even if the entire axial direction is somewhat higher than the target temperature Tm, the influence of the fixing property due to uneven fixing can be reduced as compared with the case where the temperature of the sheet passing area is lower than the target temperature Tm.

PPM control may be performed to increase the fixing roller sheet passing portion temperature.
Therefore, in this embodiment, the CD length / temperature difference allowable value correspondence information in which the fixing roller temperature difference allowable value Tf, which affects the fixability due to the different CD lengths, is associated with the magnitude of the CD length difference D. If it is determined in advance at 128 (FIG. 9 (h)) and it is determined that the fixability is affected, the PPM control is required even if the fixing roller sheet passing portion temperature Tc ≦ the threshold Tz is not satisfied. Judging that there is.

If there is at least one job set having a different CD length from the previous job (“YES” in step S24), the necessity of PPM control based on the CD length is determined (step S25).
FIG. 12 is a flowchart showing the contents of a subroutine for determining the necessity of PPM control based on the CD length.
As shown in the figure, a CD length difference D is obtained (step S251). The difference D is obtained by subtracting the CD length (= CD1) of the paper S of the job A from the CD length (= CD2) of the paper S of the job B, where A is the previous job and B is the subsequent job. . For example, if the CD length of the paper S of the job B is 297 [mm] (corresponding to the A4 horizontal posture) and the CD length of the paper S of the job A is 210 [mm] (corresponding to the A4 vertical posture), the difference D = 87 [mm].

The fixing roller temperature difference allowable value Tf for the difference D is acquired from the CD length / temperature difference allowable value correspondence information 128 (step S252). In the example of the CD length / temperature difference allowable value correspondence information 128 shown in FIG. 9H, the allowable value Tf for the difference D = 87 [mm] is 6 [° C.].
Next, a temperature difference Te is obtained (step S253). The temperature difference Te is performed by subtracting the predicted temperature Tc from the target temperature Tm. If the target temperature Tm is 165 [° C.] and the predicted temperature Tc is 152.89 [° C.], the temperature difference Td = 12.11 [° C.].

It is determined whether or not the temperature difference Te ≧ allowable value Tf (step S254).
If it is determined that the temperature difference Te ≧ allowable value Tf (“YES” in step S254), the temperature difference between the fixing roller sheet passing portion temperatures increases due to the execution of jobs A and B, thereby affecting the fixability. It is determined that the PPM control start condition is satisfied and the PPM control is necessary (step S255), and the process returns.

On the other hand, if it is determined that the temperature difference Te <allowable value Tf (“NO” in step S254), there is no need to affect the fixability, and therefore the PPM control start condition is not satisfied and PPM control is not required. Judge (step S256) and return.
In the above description, the temperature difference Te and the allowable value Tf are compared. However, the present invention is not limited to this. For example, instead of the temperature difference, the fixing roller allowable temperature Tf1 for the difference D is obtained and compared with the predicted temperature Tc, the same result can be obtained. In this case, it is determined that PPM control is necessary when the predicted temperature Tc ≦ the fixing roller allowable temperature Tf1.

The fixing roller allowable temperature Tf1 can be obtained in advance as a value obtained by subtracting the allowable value Tf for the difference D from the target temperature Tm.
For example, in the above example, since the target temperature Tm is 165 [° C.] and the allowable value Tf for the difference D = 87 [mm] is 6 [° C.], the fixing roller allowable temperature Tf1 is 159 [° C.]. If the predicted temperature Tc is set to 152.89 [° C.], the condition of Tc ≦ Tf1 is satisfied, so that it is determined that PPM control is necessary.

  Returning to FIG. 11, in step S26, it is determined whether it is determined that PPM control is necessary. If it is determined that PPM control is necessary (“YES” in step S26), the process proceeds to step S22. In the case of passing through step S26, since it was not originally determined that Tc ≦ Tz (“NO” in step S21), the timing that satisfies Tc = Tz cannot be determined in step S23. For this reason, when going through step S26, the scheduled start timing of the PPM control is determined as the end time of the previous job, which is the time when the CD length is switched.

On the other hand, if it is determined that PPM control is not required (“NO” in step S26), an unnecessary flag indicating that PPM control is not required is set (step S27), and the process returns.
If it is determined in step S24 that the CD length is the same as the previous job ("NO" in step S24), the process proceeds to step S27. In this case, an unnecessary flag is set.

<Contents of stabilization control schedule determination processing>
FIG. 13 is a flowchart showing the contents of the subroutine of the stabilization control schedule determination process. As shown in the figure, the current accumulated print number Ps is acquired (step S31).
Among the scheduled jobs, the job number of the job with the earliest execution order is set in the variable n (step S32). The job number is read from the job number (No) column included in the management information 1031. Here, n = 1 will be described as an example.

The number of prints Pn of the n (= 1) th job is acquired (step S33). This acquisition is performed by reading the number of sheets for the n (= 1) th job written in the print number column included in the management information 1031.
The total number of prints P is obtained by adding the number of prints Pn to the total number of prints Ps (step S34).

The number Pb of prints scheduled to be subjected to the next stabilization control is acquired (step S35).
In the above example, since a multiple of the predetermined number Pc (1000 sheets or the like) is the number of prints scheduled for execution of the stabilization control, the multiple that is larger than the current cumulative print number Ps and closest to the cumulative print number Ps is scheduled. The number of prints is Pb. For example, if the cumulative print number Ps is 1950, the planned print number Pb is 2000.

It is determined whether or not the total print number P ≧ the planned print number Pb (step S36).
When P ≧ Pb (“YES” in step S36), if the n (= 1) th job is executed, it is determined that the execution timing of the stabilization control is reached, and the stabilization control is necessary. After setting the necessary flag indicating this (step S37), the scheduled number of prints Pb is determined as the scheduled execution timing of the stabilization control (step S38), and the process returns. In the above example, there are 2000 sheets.

On the other hand, if P <Pb (“NO” in step S36), it is determined whether n is the last (step S39). “n is the last” means that the variable “n” is equal to the job number of the last job among the scheduled jobs included in the management information 1031.
If it is determined that it is not the last ("NO" in step S38), a value obtained by incrementing the current variable n by "1" is reset to a new variable n (step S41). If n = 1, the new variable n is 2.

The number of prints Pn of the reset variable n (= 2) th job is acquired (step S42). This acquisition is performed by the same method as step S33.
The number of prints Pn added to the current total number of prints P is reset to a new total number of prints P (step S43).
Then, it is determined whether or not the reset total print number P is equal to or greater than Pb (step S36).

When P ≧ Pb (“YES” in step S36), if the n (= 2) th job is executed, the execution timing of the stabilization control is reached midway, and the process moves to step S37.
On the other hand, if P <Pb (“NO” in step S36), it is determined whether n is the last (step S39). If n is not the last, the process returns to S36 via steps S41 to S43. As a result, the total print number P is set again. A series of processes from steps S36, S39, and S41 to S43 are repeated until P ≧ Pb is satisfied.

If n is determined to be the last ("YES" in step S39), an unnecessary flag indicating that the stabilization control is unnecessary is set (step S40), and the process returns.
<Contents of process speed change processing>
FIG. 14 is a flowchart showing the contents of a subroutine for process speed change processing.
As shown in the figure, it is determined whether or not the scheduled start timing of the PPM control and the scheduled execution timing of the stabilization control are the same (step S50).

The scheduled start timing of the PPM control is determined in the above step S23, and the scheduled execution timing of the stabilization control is determined in the above step S38. Therefore, it is determined whether or not they are the same according to the determined timing. be able to.
The same timing (“YES” in step S50) means that the start condition of the PPM control is satisfied at the scheduled start of the stabilization control, and the process speed does not need to be changed. In this case, the process speed is not changed.

On the other hand, when the timing is not the same, that is, when the PPM control and the stabilization control are executed with a time lag ("NO" in step S50), the process proceeds to step S51. In this sense, when executing step S50, it can be said that the process speed changing unit 111 functions as a means for predicting that the PPM control and the stabilization control are executed separately with a time shift.
In step S51, it is determined whether or not the scheduled start timing of the PPM control is later than the scheduled execution timing of the stabilization control.

If it is determined that the scheduled start timing of PPM control is later than the scheduled execution timing of stabilization control (“YES” in step S51), a job scheduled immediately before stabilization control (hereinafter referred to as “job”). The process speed V is calculated for “Ja”) (step S52). In the example of FIG. 5, job 3 is job Ja.
The process speed V of the job Ja is calculated by the following method.

Tu− (Tap × Cp) + (Tbp / Cp) ≦ Tz (Formula 4)
V = Cp × Vs (Formula 5)
Here, Tu is the predicted temperature of the fixing roller sheet passing portion at the start of the job Ja.
If there is only one job scheduled before the stabilization control, the fixing roller sheet passing portion temperature Tc at the end of the job obtained by (Equation 3) becomes equal to Tu.

When there are two or more, when the one or more jobs excluding the immediately preceding job Ja are executed, the fixing roller sheet passing portion temperature Tc at the end of the job is obtained by (Equation 3), and the obtained temperature Tc is Tu. become. In the example of FIG. 5, since jobs 1 to 3 are scheduled, the temperature at the start (time point tu) of the immediately preceding job 3 becomes Tu.
Tap is the temperature at which the fixing roller sheet passing portion drops when it is assumed that only job Ja is executed, and can be obtained from the above (Equation 1).

Tbp is a fixing roller sheet passing portion recovery temperature when it is assumed that only job Ja is executed, and can be obtained by the above (Equation 2).
Tz is a threshold value indicating the start condition of PPM control.
Cp is a process rate coefficient. Since other than Cp can be obtained by (Equation 1) or the like, (Equation 4) is an equation for calculating the range of Cp.

Vs is a reference speed Vs, here 210 [mm / s].
A speed obtained by multiplying the reference speed Vs by Cp calculated by (Expression 4) is calculated as the process speed V of the job Ja (Expression 5).
The left side of (Expression 4) is equal to the value obtained by applying the coefficient Cp to Ta and Tb when it is assumed that only job Ja is executed in (Expression 3). In this case, (Expression 3) Since the formula for obtaining the fixing roller paper passing portion temperature Tc at the end of Ja is obtained, the range of Cp obtained by (Equation 4) is that when the fixing roller paper passing portion temperature at the end of the job is equal to or lower than the threshold Tz. It can be said that it shows conditions.

Specifically, for example, the fixing roller sheet passing part drop temperature Tap = 6.75 [° C.], the fixing roller sheet passing part recovery temperature Tbp = 1.4 [° C.], the fixing roller sheet passing part temperature Tu = 157 [° C.], Assuming that the threshold value Tz = 150 [° C.], in (Expression 3), the fixing roller sheet passing portion temperature Tc at the end of the job Ja is 151.65 [° C.], which exceeds the threshold value Tz.
If (Expression 4) is used, Cp ≧ 1.21, and if Cp = 1.21, the process speed V of job Ja is calculated as 254 [mm / s] from (Expression 5).

Accordingly, if the process speed V of the job Ja is increased from the reference speed Vs (= 210 [mm / s]) to 254 [mm / s], the fixing roller sheet passing portion temperature decreases to the threshold Tz at the end of the job Ja. Can be predicted.
Increasing the process speed as described above means that the number of sheets S transported per unit time increases, so that the amount of heat per unit time taken away from the fixing roller 41 by the sheet S increases accordingly. Accordingly, the temperature decrease rate of the fixing roller sheet passing portion temperature is increased, and the timing at which the fixing roller sheet passing portion temperature is decreased to the threshold value Tz is accelerated.

In the example of FIG. 6, if the job 3 is the job Ja, the process speed is increased to the first speed Va only in the case of the job 3, as shown in FIG. This corresponds to the process speed V calculated in 5).
In addition, the time tf at which the rate of decrease of the portion of job 3 in the transition graph of the fixing roller sheet passing portion temperature in FIG. 6B becomes larger than jobs 1 and 2 (slope is steep) and reaches the threshold value Tz is When the process speed is not changed (FIG. 5), it is earlier by the time α than the time ta, which corresponds to an earlier timing for the fixing roller sheet passing portion temperature to be lowered to the threshold value Tz.

Returning to FIG. 14, in step S53, it is determined whether or not the obtained process speed V is within a settable range.
Within the settable range is within a range that is equal to or lower than the upper limit speed of the process speed that can be varied by the own apparatus, and is determined in advance. In this embodiment, it is 330 [mm / s] as shown in FIG. 9 (d), but it is needless to say that it is not limited to this, and a suitable range is determined by experiments or the like according to the device configuration. It is done. In the case where no restriction on the upper limit speed is imposed, a configuration in which it is not determined whether or not it is within the settable range can be adopted.

If it is determined that the obtained process speed V is within the settable range (“YES” in step S53), the obtained process speed V is determined as the process speed for the corresponding job, here job Ja (step S56). ), Return. The process speed determined in step S56 is used as the process speed at the time of actual job execution.
In the above description, an example of the schedule in the case where the stabilization control interrupts at a break between the job and the next job has been described in FIGS. 5 to 8, but the stabilization control is predicted to interrupt during the execution of the job. In this case, the job is divided into a partial job in the first half and a partial job in the second half with the interruption of the stabilization control, and the first partial job is regarded as the job Ja immediately before the stabilization control, and the process speed V Can be requested.

For example, in FIG. 5, if a stabilization control interrupt occurs in the middle of job 3, the first half job of job 3 becomes the immediately preceding job, job 2 becomes the previous job, and job 1 becomes the previous job. Become a job.
Assuming that the total number of prints of jobs 1 to 5 is N, the number of prints in job 1 is N1, the number of prints in job 2 is N2, the number of prints in the first half of job 3 is N3, and the total number of (N1 + N2 + N3) Assuming P, at least one or more sheets included in P (<N) scheduled to be executed before the temporary suspension by the stabilization control among N sheets, here (N3) sheets The image forming process speed is changed from the reference speed Vs to a higher speed Va.

If it is determined that the obtained process speed V is not within the settable range, that is, exceeds the upper limit speed (“NO” in step S53), it is further determined whether there is a previous job (step S54).
Further, the previous job is a job for which the process speed V is determined not to be within the settable range, here, the job immediately preceding the previous job Ja.

In the example of FIG. 5, if the immediately preceding job Ja is job 3, the further previous job is job 2. Hereinafter, the previous job is referred to as job Jb.
Then, the process speed V for all jobs from the job Ja to the previous job Jb is obtained (step S55). That is, the job Ja and the job Jb are regarded as one job, and (Expression 4) and (Expression 5) are applied. In this case, Tu in (Expression 4) is the predicted temperature of the fixing roller sheet passing portion at the start of the job Jb, and in the example of FIG. 5, it is replaced with the temperature Tv at the start of job 2 (time tv). .

The fixing roller sheet passing portion lowering temperature Tap is calculated when the job Ja is assumed to be executed, and when the fixing roller sheet passing portion falling temperature is calculated according to (Expression 1) and when the job Jb is assumed to be executed (equation). The temperature is replaced with the temperature obtained by adding the temperature at which the fixing roller sheet passing portion is obtained in 1). The same applies to the fixing roller sheet passing portion recovery temperature Tbp.
Since the target job whose process speed V is to be changed is expanded to both jobs Ja and Jb, if the rate of decrease of the fixing roller sheet passing portion temperature is substantially the same between jobs Ja and Jb, The process speed V is smaller than when only the job Ja is targeted.

It is determined whether or not the obtained process speed V is within a settable range (step S53).
When it is determined that the process speed V is within the settable range (“YES” in step S53), the process proceeds to step S56. In this case, the process speeds of the two jobs Ja and Jb are determined as the obtained speeds.
On the other hand, if it is determined that the process speed V is not within the settable range (“NO” in step S53), the process proceeds to step S54.

In step S54, it is determined whether there is a previous job. Here, the previous job means a job immediately preceding the job Jb. In the example of FIG. 5, job 1 is the previous job. Hereinafter, this is referred to as job Jc.
The process speed V for all jobs from the previous job Ja to the previous job Jc is obtained (step S55), and the process returns to step S53. Here, the jobs Ja, Jb, and Jc are regarded as one job, and (Expression 4) and (Expression 5) are applied. The application method is the same as the two cases of jobs Ja and Jb. In the example of FIG. 5, since there are only 1 to 3 jobs scheduled before the stabilization control, when applying (Equation 4), Tap and Tbp are replaced with Ta and Tb used in (Equation 3). be able to.

The processes in steps S53 to S55 are repeated until the obtained process speed V falls within the settable range. Each time this is repeated, the number of target jobs for which the process speed V is to be changed to high increases by one, and the calculation of the process speed V for those target jobs is repeated each time.
In the meantime, if the obtained process speed V falls within the settable range (“YES” in step S53), the process proceeds to step S56 and returns, and if it is determined that there is no previous job (“NO” in step S54). )), The process speed is forbidden to be changed. In this case, since the job cannot be executed at the obtained process speed V, the scheduled job is executed without changing the process speed, that is, at the reference speed Vs.

In the above description, an example has been described in which the scheduled start timing of PPM control is later than the scheduled execution timing of stabilization control (“YES” in step S51), but the opposite, that is, the scheduled start of PPM control is performed. When the timing is earlier than the scheduled execution timing of the stabilization control (“NO” in step S51), the process proceeds to step S57.
In step S57, process speeds V for all jobs from job Jp immediately before PPM control to job Ja immediately before stabilization control are provisionally determined. The reason for the provisional decision is that the processing method is adopted in which the speed temporarily decided here is decided in step S56 after this.

In the example of FIG. 7, the job Jp immediately before the PPM control is the job 3, the job Ja immediately before the stabilization control is the job 5, and all the jobs are the jobs 3, 4, and 5. .
The process speed V is calculated by the following method.
Tw− (Taq × Cp) + (Tbq / Cp)> Tz (Expression 6)
V = Cp × Vs (Expression 7)
Here, Tw is the predicted temperature of the fixing roller sheet passing portion at the start of the job Jp.

If there is only one job scheduled before the PPM control, the fixing roller sheet passing portion temperature Tc at the end of the job obtained by (Equation 3) becomes equal to Tw.
When there are two or more, when the one or more jobs excluding the job Jp are executed, the fixing roller sheet passing portion temperature Tc at the end of the job is obtained by (Equation 3), and the obtained temperature Tc becomes Tw. . In the example of FIG. 7, since jobs 1 to 3 are scheduled, the temperature at the start (time point ta) of the immediately preceding job 3 is Tw.

Taq is the temperature at which the fixing roller sheet passing portion drops when all the jobs Jp to Ja are executed in order. The fixing roller sheet passing part drop temperature is obtained for each job by (Equation 1), and the value obtained by adding the obtained total drop temperature is defined as the fixing roller sheet passing part drop temperature Taq.
Tbq is a fixing roller sheet passing portion recovery temperature when it is assumed that all of the jobs Jp to Ja are sequentially executed. The fixing roller sheet passing portion recovery temperature for each job is obtained by (Equation 2), and a value obtained by adding the obtained total recovery temperatures is defined as a fixing roller sheet passing portion recovery temperature Tbq.

The threshold Tz indicating the start condition of PPM control and the process speed coefficient Cp are the same as Tz and Cp in (Expression 4), and (Expression 7) is the same as (Expression 5).
(Equation 6) indicates that fixing from the job Jp (corresponding to the job 3) to the job Ja immediately before the stabilization control (corresponding to the job 5) is executed in order, and fixing at the end of the last job Ja. This is an equation for obtaining the range of the coefficient Cp when the roller sheet passing portion temperature becomes larger than the threshold value Tz. By obtaining the coefficient Cp, the process speed V for all jobs is provisionally determined using (Equation 7). .

Specifically, for example, the fixing roller sheet passing part lowering temperature Taq = 15 [° C.], the fixing roller sheet passing part recovery temperature Tbq = 4.9 [° C.], the fixing roller sheet passing part temperature Tw = 157 [° C.], the threshold Tz Assuming = 150 [° C.], in (Expression 3), the fixing roller sheet passing portion temperature Tc at the end of the job Ja is 146.9 [° C.], which is lower than the threshold value Tz.
If (Expression 6) is used, Cp <0.85, and if Cp = 0.85, the process speed V is calculated as 178 [mm / s] from (Expression 7). This is provisionally determined as the process speed V from job Jp to Ja. In this case, it is predicted that the temperature at the fixing roller sheet passing portion does not decrease to the threshold value Tz at the end of the job Ja under the condition that the PPM control is not performed between the jobs Jp and Ja.

Decreasing the process speed from the reference speed Vs means that the number of sheets S transported per unit time is reduced, and the amount of heat per unit time taken by the sheet S from the fixing roller 41 is reduced accordingly. This is because the temperature drop rate of the paper part temperature is reduced and the timing at which the fixing roller paper passing part temperature is lowered to the threshold value Tz is delayed.
Then, the process speed for the job Ja immediately before the stabilization control is obtained (step S52). This calculation method is basically the same as that described above, but since the process speed V is provisionally determined in step S53, it is included in (Expression 1) when calculating Tap in (Expression 4). The process speed coefficient C4 is replaced from 1 to 0.85 described above.

Further, when obtaining Tbp of (Expression 4), the time tq included in (Expression 2) is replaced with a time corresponding to the temporarily determined process speed V.
The process speed calculated in step S52 is faster than the reference speed Vs as described above, but the process speed V provisionally determined in step S57 is slower than the reference speed Vs. The processing in the order of S52 requires the process speed V of the temporarily determined job Ja to be obtained again at a higher speed.

  It is determined whether or not the obtained process speed V is within the settable range (step S53). The settable range here is within the range of the upper limit speed and the lower limit speed of the process speed because the process speed V is provisionally determined to be slower than the reference speed Vs in step S57. The lower limit speed can be set to, for example, 50 [mm / s], but is not limited thereto, and a suitable value is determined in advance according to the apparatus configuration. In the case where no upper limit and lower limit speed restrictions are imposed, it is possible to adopt a configuration in which it is not determined whether the speed is within the settable range.

If it is determined that it is within the settable range (“YES” in step S53), the determined process speed V is determined as the process speed V for the job Ja (step S56).
In this case, among the jobs Jp to Ja scheduled before the stabilization control, for the jobs other than the job Ja, the temporarily determined process speed is changed to the final determination.
In the example of FIG. 8C, the process speed V of job 3 (corresponding to job Jp) and job 4 is the second speed Vb that is lower than the reference speed Vs, and this second speed Vb is temporary. Corresponding to the determined speed, the process speed V of job 5 (corresponding to job Ja) is the first speed Va higher than the reference speed Vs, and this first speed Va is obtained in step S52. Corresponds to speed.

By changing the process speed of jobs 3 to 5, the rate of decrease in the portions of jobs 3 and 4 in the transition graph of the fixing roller paper passing portion temperature in FIG. 8B is smaller than that of jobs 1 and 2 (gradient is gentler). Therefore, the rate of decrease in the portion of job 5 becomes larger than that of jobs 1 and 2 (the gradient is steep).
Here, the time tp from the start of job 3 (time ta) to the end of job 5 (start of stabilization control) (time tf) without changing the process speed in FIG. 7 and the process in FIG. If the time tp from the start time of job 3 (time point ta) to the start time of job 5 (time point tj) in the case of changing the speed is the same, the process speed of job 5 is increased as shown in FIG. As a result, the time required for execution of job 5 is shortened, so that the predicted execution timing (time tk) of the stabilization control is earlier than the execution timing (time tf) of the stabilization control shown in FIG. Accordingly, stabilization control can be started earlier, and the total time required for executing jobs 1 to 6 can be reduced.

  Returning to FIG. 14, if it is determined in step S53 that the calculated process speed V of the job Ja is not within the settable range (“NO” in step S53), the processing after step S54 is executed. In this case, the process speed V is obtained again for both the job Ja and the previous job (step S55). The method for obtaining the process speed V is the same as in step S52.

  The steps S53 to S55 are repeatedly executed until the determined process speed V falls within the settable range. This is the same as described above. Each time this repetition is performed, one step back from the job Ja, The number of jobs for which the process speed is to be changed increases, and the process speed provisionally determined in step S57 is obtained again in step S55 as a higher speed.

Since the time required for job execution can be shortened by increasing the process speed V, the time required for executing the total job can be shortened compared with the case where only the slow process speed V that is provisionally determined is used. Print productivity can be improved.
FIG. 15 is a diagram showing a comparison of differences in total estimated execution time depending on the presence or absence of process speed change processing when a plurality of jobs are executed. (A) to (c) execute process speed change processing. The example in the case of not performing is shown, (d)-(f) shows the example in the case of performing a process speed change process.

FIG. 15A is a diagram showing that six jobs 1 to 6 are scheduled as a plurality of jobs, and it is assumed that jobs 1 to 6 are sequentially executed without PPM control and stabilization control being entered. The total estimated job execution time is indicated by ts.
In FIG. 15B, the jobs 3 to 5 are targeted for PPM control based on the predicted transition of the fixing roller sheet passing portion temperature shown in FIG. 15C, and the stabilization control is interrupted between the jobs 5 and 6. It is a figure showing becoming a schedule. 15A to 15C show conditions when the process speed is constant.

It can be seen that the total job predicted execution time ts1 is significantly longer than ts in FIG. 15A by the PPM control and the stabilization control.
On the other hand, when the process speed changing process is executed, as shown in FIG. 15F, for jobs 1 and 2, the process speed V becomes the second speed Vb that is lower than the reference speed Vs, and jobs 3 to 5 are executed. Is changed to the first speed Va higher than the reference speed Vs.

  Due to this change in the process speed, as shown in FIG. 15 (e), the rate of decrease in the fixing roller sheet passing portion temperature is the execution of jobs 1 and 2 shown in FIG. 15 (c) during the execution of jobs 1 and 2. The rate of decrease is smaller (gradient), and the jobs 3 to 5 are larger (slope is steep). At the end of job 5, the fixing roller sheet passing portion temperature reaches the threshold Tz. It can be seen that the PPM control start condition is satisfied.

  Since the timing satisfying the start condition of the PPM control is delayed (shifted) until the end of the job 5, the jobs 3 to 5 are excluded from the target of the PPM control, and the job is not interrupted by the PPM control. Moreover, although the job execution time becomes longer due to the reduction in the process speed of jobs 1 and 2, the longer time can be offset by the time reduced by increasing the process speed of jobs 3-5.

Depending on the method of changing the process speed, the total job predicted execution time ts2 shown in FIG. 15 (f) should be the same as the total job predicted execution time ts shown in FIG. 15 (a) without performing the stabilization control. You can also. That is, the time tsa required for the stabilization control may be allocated to a job for reducing the process speed and a job for increasing the speed.
Specifically, the following (Formula 8) can be used.

(FDy / Vu) − (FDx / Vd) = tsa (Equation 8)
Here, FDy [mm] is a length obtained by converting the number of prints Py of the target job y of PPM control y (jobs 3 to 5 in the example of FIG. 15B) into the paper FD length.
Vu [mm / s] is a speed increased with respect to the reference speed Vs when the process speed of the job y is increased, and corresponds to the difference between Va and Vs in FIG.

FDx [mm] is a length obtained by converting the number of prints Px of job x (jobs 1 and 2 in the example of FIG. 15B) before the start of PPM control into the paper FD length.
Vd [mm / s] is a speed decelerated with respect to the reference speed Vs when the process speed of the job x is reduced, and corresponds to the difference between Vs and Vb in FIG.
(FDy / Vu) is the amount of time the job execution time decreases with respect to the reference speed Vs as a result of increasing the process speed from the reference speed Vs (the job execution time decreasing as a result of the process speed increase). tΔ1 is shown.

(FDx / Vd) is a result of decelerating the process speed from the reference speed Vs. As a result, the job execution time is increased for the reference speed Vs (the job execution time increased as a result of the process speed deceleration) tΔ2. Show.
In (Expression 8), if (FDx / Vd) is shifted to the right side, (Expression 8) adds the job execution time tΔ2 [= FDx / Vd] that increases due to deceleration to the time tsa required for stabilization control. It can be said that the time is equal to the job execution time tΔ1 [= FDy / Vu] that decreases due to the speed increase.

  Since the time tsa required for the stabilization control is constant regardless of the change of the process speed, if the speeds Vu and Vd satisfying the condition that the left side and the right side of (Equation 8) are equal are obtained, FIG. The total predicted execution time ts2 of the job shown in FIG. 15 (f) can be made the same as the total predicted execution time ts shown in FIG. 15 (a) in the example in which the stabilization control is not performed.

This improves the image quality through stabilization control without causing the user to feel that extra time is being spent on job execution, as well as fixing performance by increasing the temperature of the paper feed section during the stabilization control. Improvements can be made.
In the above description, the process speed change necessity determination process shown in FIG. 10 is executed every time a new job is received. However, the present invention is not limited to this. For example, each time a scheduled job ends, the process speed change necessity determination process may be executed for a job scheduled to be executed at that time. If the processing is executed immediately before the job to be executed, the transition of the fixing roller sheet passing portion temperature is predicted more accurately, and the accuracy of the determination as to whether or not the condition for the start timing of PPM control is satisfied is further improved. Is possible.

  As described above, in the present embodiment, when it is predicted that the stabilization control and the PPM control are executed while being shifted in time during a plurality of scheduled jobs, the PPM control is executed. The process speed for the job scheduled before the stabilization control is changed so that the start condition (the fixing roller sheet passing portion temperature decreases to the threshold Tz) satisfies the scheduled start timing of the stabilization control. It has a configuration.

Thereby, the productivity of the job (print) can be improved as compared with the configuration in which the PPM control and the stabilization control are separately performed without changing the process speed.
The present invention is not limited to an image forming apparatus, and may be a method of changing an execution speed (process speed) of an image forming operation, for example. The method may be a program executed by a computer. Furthermore, the program according to the present invention is a computer-readable program such as a magnetic disk such as a magnetic tape or a flexible disk, an optical recording medium such as a DVD-ROM, DVD-RAM, CD-ROM, or CD-R, or a flash memory recording medium. It can be recorded on various possible recording media, and may be produced, transferred, etc. in the form of the recording medium, and various wired and wireless networks including the Internet in the form of programs, broadcasting, telecommunications In some cases, the data is transmitted and supplied via a line or satellite communication.

(Modification)
As described above, the present invention has been described based on the embodiment. However, the present invention is not limited to the above-described embodiment, and the following modifications may be considered.
(1) In the above-described embodiment, while the rotation of the fixing roller 41 is continued during the stabilization control, power is supplied to the excitation coil 43 to heat the fixing roller 41 and the fixing roller sheet passing portion temperature is increased. However, it is not limited to this.

For example, if the fixing roller sheet passing portion temperature at the start of the stabilization control is equal to or higher than a predetermined value higher than the threshold value Tz, the heating of the fixing roller 41 may be stopped from the start of the execution of the stabilization control. . This is because during the execution of the stabilization control, some that do not require the fixing roller 41 to be heated, such as registration correction, are included.
With this configuration, even when the stabilization control is being performed, the fixing roller sheet passing portion temperature may reach the threshold value Tz due to a decrease. Reaching the threshold value Tz means that the start condition for PPM control is satisfied. Taking this condition as an opportunity, the fixing roller 41 passes the temperature of the fixing roller when the heating of the fixing roller 41 is resumed during the stabilization control. Therefore, the fixing roller sheet passing portion temperature does not drop too much, and it is possible to prevent the job scheduled after the stabilization control from being affected.

In the middle of the stabilization control (between the start and the end), the PPM control start condition may occur. This means that the fixing roller sheet passing portion temperature reaches the threshold Tz at a time slightly delayed from the start of the stabilization control. Thus, it is possible to take a method for obtaining the process speed V in the process speed changing process.
Specifically, Tz in the above (Expression 4) is replaced with a value (150 + Δ) [° C.] that is higher than the original value (150 [° C.] in the above example) by a time that shifts the timing at which the threshold Tz is reached. For example, at the start of the stabilization control, the fixing roller sheet passing portion temperature is reduced to (150 + Δ) [° C.], and when the shift time elapses from the start of the stabilization control, the fixing roller sheet passing portion temperature is 150 [° C. ] Can be predicted. However, the present invention is not limited to this method, and another equation may be used in which the time when the threshold value Tz is reached is delayed from the start of the stabilization control.

  As described above, the job process speed V for at least one sheet S among a plurality of jobs (including the partial job) scheduled to be executed before the stabilization control is predicted from the reference speed Vs. The condition that the start timing of PPM control enters the predicted stabilization control execution period (ie, does not deviate), specifically, (a) the start timing of PPM control is the same as in the embodiment. Synchronize with the start timing of the stabilization control, (b) The start timing of the PPM control is a little later than the start time of the stabilization control as in this modification, or (c) Start of the PPM control If the time is changed to a speed satisfying that the stabilization control is being executed, at least the PPM control and the stabilization control are produced at a time higher than the configuration in which the control is executed separately in time. Sex It is possible to above.

  (2) In the above embodiment, the scheduled print (image formation) operation is managed in units of jobs. However, the present invention is not limited to this, and for example, it may be managed in units of the number of sheets (sheets). Specifically, the first to Mth sheets S are A4 size plain paper, the (M + 1) th to Zth sheets S are B5 size, thick paper, etc. Are associated and managed.

In this way, when the execution timing of the stabilization control is reached on the U-th sheet that is larger than M and smaller than Z, the printing operation is temporarily interrupted on the U-th sheet and the stabilization control is interrupted. Can do.
(3) In the above embodiment, the coefficients such as C1 to C6 are applied in (Equation 1). However, the present invention is not limited to the configuration using all of them, and one or more required coefficients may be applied.

  For example, in the case where the fixing roller sheet passing portion temperature is hardly affected by the environmental temperature or the like, a configuration in which C5 is not applied can be employed. Further, in a configuration in which the paper size used is fixed to one, a configuration in which C2 and C3 are not applied may be taken. In some cases, a configuration in which no coefficient is applied may be employed. Note that the temperature, humidity, threshold value, speed, coefficient, number of sheets (sheets), size, type, and the like are not limited to those described above, and values and the like according to the apparatus configuration are determined in advance through experiments or the like. Further, the present invention is not limited to the above equations, and other equations may be used as long as the temperature to be calculated can be calculated.

(4) In the above-described embodiment, the PPM control start condition is that the fixing roller sheet passing portion temperature reaches the threshold value Tz that is smaller than the target temperature Tm by a predetermined value, but is not limited thereto.
For example, the start condition of the PPM control is a case where the threshold Tz1 that is larger than the target temperature Tm by a predetermined value due to a rise in the temperature of the non-sheet-passing area where the sheet S does not pass on the edge side in the sheet width direction of the fixing roller 41 You can also

  Specifically, the paper S used for the job is a small size, and the temperature of the paper S passing area of the fixing roller 41 (fixing roller paper passing portion temperature) does not decrease during job execution. (The target temperature Tm is substantially maintained), but the heat of the non-sheet passing area of the fixing roller 41 is not taken away by not contacting the sheet S, and the temperature of the non-sheet passing area of the fixing roller 41 increases. This is a case where the threshold value Tz1 is reached, that is, the temperature rises excessively.

If the PPM control is performed when the temperature of the non-sheet passing area of the fixing roller 41 is too high, the sheet conveyance interval is increased accordingly. As a result, the amount of heat applied to the fixing roller 41 is also reduced, so that the temperature of the non-sheet passing area of the fixing roller 41 also changes from rising to lowering, and an excessive temperature rise in the non-sheet passing area of the fixing roller 41 is prevented. Can do.
Also in this case, when the PPM control is started, the print productivity is lowered. Therefore, if the start condition of the PPM control is that the threshold value Tz1 is reached, the same effect as in the above embodiment can be obtained. it can. The prediction that the temperature of the non-sheet passing area of the fixing roller 41 rises to the threshold value Tz1 is based on how much the temperature rises per sheet and how much the temperature falls between sheets to recover. If it is obtained by experiment or the like, it can be carried out by calculating the temperature rise for each job or for each sheet based on the obtained value.

In order to satisfy the PPM control start condition, the printing speed may be increased so that the temperature of the non-sheet passing area of the fixing roller 41 rises to the threshold value Tz1 at the start timing of the stabilization control.
(5) In the above embodiment, an example in which the image forming apparatus according to the present invention is applied to a tandem type color printer has been described. However, the present invention is not limited to this. Any image forming apparatus capable of executing stabilization control and number control regardless of color or monochrome can be applied to, for example, a copying machine, a facsimile machine, an MFP (Multiple Function Peripheral), and the like.

In addition, although an example using an electromagnetic induction heating type fixing unit has been described, the present invention is not limited to this method. For example, a heating method using a halogen heater, a heating method using a resistance heating element that energizes a resistance heating element to generate Joule heat, and the like are used. Also good.
Further, although an example in which a fixing roller is used as a fixing member has been described, the present invention is not limited to this, and for example, a fixing belt or the like can also be used. Furthermore, the type of sheet is not limited to paper such as plain paper, and may include a resin film such as an OHP sheet. In addition, the configuration in which the processing in the above embodiment is performed by software may be used, or the configuration may be performed by using a hardware circuit.

  Further, the contents of the above-described embodiment and modification examples may be combined.

  The present invention can be applied to an image forming apparatus that performs image stabilization control and number control.

DESCRIPTION OF SYMBOLS 1 Printer 10 Image forming part 18 Process motor 20 Intermediate transfer part 30 Feeding part 40 Fixing part 41 Fixing roller 43 Excitation coil 44 Fixing temperature sensor 50 Control part 60 IH power supply part 104 Stabilization control part 105 Stabilization execution prediction part 106 Fixing Temperature control unit 108 PPM control unit 109 PPM execution prediction unit 111 Process speed change unit S Paper Tz threshold V Process speed (image forming speed)
Va 1st speed (fast speed)
Vb 2nd speed (slow speed)
Vs reference speed

Claims (9)

An image forming apparatus that performs an image forming operation of forming an image on a plurality of conveyed sheets, and fixing the image to the sheet by heat of a heated fixing member for each sheet,
Stabilization control means for executing predetermined image stabilization control for stabilizing the image quality of the formed image by temporarily interrupting the image forming operation;
Detecting means for detecting the temperature of the fixing member;
A sheet number control means for starting sheet number control for reducing the number of sheets conveyed per unit time when the temperature of the fixing member changes with the image forming operation and reaches a threshold value lower or higher than the target temperature during the image forming operation; ,
When the temperature of the fixing member reaches the threshold value, a heating control means for controlling a heating amount to the fixing member so as to return to the target temperature;
Predicting means for predicting that the image stabilization control and the sheet number control are separately performed with a time lag if the image forming operation is continuously performed on N (plurality) sheets;
When the prediction is performed, an image forming speed of image formation for one or more sheets included in P sheets scheduled to be executed before the temporary suspension by the image stabilization control among N sheets is set as a reference speed. From the speed change means for changing to a speed satisfying a condition that the predicted start timing of the number control enters the execution period of the predicted image stabilization control,
An image forming apparatus comprising: The image forming operation for the P sheets is as follows.
When an image forming operation for one or more sheets is a single image forming job, the operation is to continuously execute a plurality of jobs.
The speed changing means is
When the image stabilization control is predicted to be executed earlier than the number control,
The image forming apparatus according to claim 1, wherein an image forming speed of a job immediately before the predicted image stabilization control is started is changed to a speed higher than a reference speed so as to satisfy the condition. . The speed changing means is
When the fast speed exceeds the upper limit speed,
The job for which the image forming speed is to be changed at a high speed is expanded to the immediately preceding job and at least one preceding job so that the image forming speed for these jobs satisfies the above condition. 3. The image forming apparatus according to claim 2, wherein the image forming apparatus is changed to a speed faster than a reference speed. The image forming operation for the P sheets is as follows.
When an image forming operation for one or more sheets is a single image forming job, the operation is to continuously execute a plurality of jobs.
The speed changing means is
When the number control is predicted to be executed earlier than the image stabilization control,
In order to satisfy the condition, among the plurality of jobs, the image forming speed of the job immediately before the predicted stabilization control is started is changed to a speed faster than the reference speed, and more than the immediately preceding job. The image forming apparatus according to claim 1, wherein the image forming speed of at least one previous job is changed to a speed slower than a reference speed. The speed changing means is
When the fast speed exceeds the upper limit speed,
The job for which the image forming speed is to be changed at a high speed is expanded to the immediately preceding job and at least one preceding job, and the image forming speed for these jobs is set to a speed higher than the reference speed. 5. The image forming apparatus according to claim 4, wherein the image forming speed is changed to a speed slower than a reference speed. The speed changing means is
When tsa is the time required for the image stabilization control, tΔ1 is the execution time of the image formation that is decreased as a result of increasing the image formation speed, and tΔ2 is the execution time of the image formation that is increasing as a result of decreasing the image formation speed. ,
The image forming apparatus according to claim 5, wherein the fast speed and the slow speed are set so that a time obtained by adding the time tΔ2 to the time tsa is equal to the time tΔ1. The speed changing means is
The image forming apparatus according to claim 2, wherein even if the image forming speed for all jobs is changed, if it is determined that the condition is not satisfied, the speed changing is prohibited. The prediction means includes
First determination means for determining that the predetermined execution timing of the image stabilization control is reached during execution of image formation on the N sheets;
Second determination means for determining that the predicted temperature of the fixing member reaches the threshold during execution of image formation on the N sheets,
The image forming apparatus according to claim 1, wherein the prediction is performed when the determination by both the first determination unit and the second determination unit is performed. The prediction means includes
A third determination unit configured to determine that the predicted temperature of the fixing member is equal to or lower than a predetermined allowable temperature during the execution of image formation on the N sheets;
The allowable temperature is
Of the N sheets, the length in the width direction of the first size sheet is CD1, and the length in the width direction of the second size sheet on which image formation is scheduled next is CD1. When the width of the CD2 is wider, the temperature difference in the sheet width direction of the fixing member is set in advance according to the difference in the CD length represented by (CD2-CD1). , A temperature lower than the target temperature of the fixing member by a predetermined value,
If the determination by the third determination means is performed, the prediction is performed if the determination by the first determination means is performed even if the determination by the second determination means is not performed. The image forming apparatus according to claim 8.

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