JP2007057563A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve image quality. <P>SOLUTION: The image forming apparatus includes: an image forming part 10; a fixing device; a slack detection part to detect the slack of a medium; a driving part driven to convey the medium at first speed and second speed; a fixing device driving processing means to drive the driving part by switching the first speed and the second speed; a driving time calculating processing means to calculate first driving time when the driving part is driven at the first speed and second driving time when the driving part is driven at the second speed; and a speed setting processing means to set the first speed and the second speed based on the first driving time and the second driving time. Even though variance is found in the dimension of a component, slack amount is held in an appropriate range. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus.

  2. Description of the Related Art Conventionally, in an image forming apparatus such as an electrophotographic printer, a copying machine, a facsimile machine, and a multi-function machine, the surface of a photosensitive drum uniformly and uniformly charged by a charging roller is applied to an LED head or a laser beam. An electrostatic latent image is formed by exposure by a generator, the electrostatic latent image is developed by a developing unit to form a toner image, the toner image is transferred onto a sheet by a transfer roller, and is fixed by a fixing unit. Thus, an image is formed.

  In the image forming apparatus, a toner image is formed on the photosensitive drum, and the speed of the sheet transported through the image forming unit composed of a portion that transfers the toner image onto the sheet, that is, the transport speed of the image forming unit, On the downstream side of the image forming unit in the paper transport direction, the speed of the paper transported in the fixing device, that is, the transport speed of the fixing device cannot be completely matched. Therefore, the conveyance speed of the fixing device is slightly lower than the conveyance speed of the image forming unit, and slack is formed on the paper between the image forming unit and the fixing device.

Then, the amount of sag, that is, the amount of sag is detected, and the conveyance speed of the fixing device is controlled according to the detected amount of sag so that the amount of sag falls within a certain range (see, for example, Patent Document 1). .)
JP 2004-233437 A

  However, in the conventional image forming apparatus, the parts forming the image forming unit, the fixing device, and the like that form a toner image on the photosensitive drum have the dimensions at the time of manufacture depending on the manufacturing lot, material, manufacturer, etc. Not only there are variations, but also there are variations in the dimensions after manufacture, so that variations occur in the conveyance speed of the fixing device and the conveyance speed of the image forming unit, and the amount of sag varies for each image forming apparatus.

  When the amount of sag increases beyond the adjustment range (dynamic range), the paper before the toner image is fixed comes into contact with some part in the image forming apparatus, and the toner image is disturbed. Further, when the amount of sag is eliminated, the paper is pulled between the image forming unit and the fixing device, and the transferred or fixed toner image is disturbed. As a result, the image quality is degraded.

  It is an object of the present invention to provide an image forming apparatus that can solve the problems of the conventional image forming apparatus and improve the image quality.

  Therefore, in the image forming apparatus of the present invention, an image forming unit that forms a developer image on a medium, a fixing device that fixes the developer image formed on the medium, and the image forming unit and the fixing device. And a sag detector that detects the sag of the medium, and is driven to convey the medium at a first speed and a second speed higher than the first speed in the fixing device. A driving unit that switches the first and second speeds according to a detection result of the sag detecting unit and drives the driving unit, and a first unit that drives the driving unit at the first speed. Drive time calculation processing means for calculating a drive time and a second drive time for driving the drive unit at the second speed, and the first and second speeds based on the first and second drive times. Speed setting processing means for setting

  According to the present invention, in the image forming apparatus, an image forming unit that forms a developer image on a medium, a fixing device that fixes the developer image formed on the medium, and the image forming unit and the fixing device. And a sag detector that detects the sag of the medium, and is driven to convey the medium at a first speed and a second speed higher than the first speed in the fixing device. A driving unit that switches the first and second speeds according to a detection result of the sag detecting unit and drives the driving unit, and a first unit that drives the driving unit at the first speed. Drive time calculation processing means for calculating a drive time and a second drive time for driving the drive unit at the second speed, and the first and second speeds based on the first and second drive times. Speed setting processing means for setting

  In this case, a first drive time for driving the drive unit at the first speed and a second drive time for driving the drive unit at the second speed are calculated, and based on the first and second drive times. Since the first and second speeds are set, the amount of sag can be kept within an appropriate range even if there are variations in the dimensions of parts constituting the image forming unit, the fixing device, and the like.

  Therefore, the medium before the developer image is fixed does not come into contact with any part in the image forming apparatus, or the medium is not pulled between the image forming unit and the fixing apparatus. The developer image that is transferred or fixed is not disturbed. As a result, the image quality can be improved.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In this case, an electrophotographic printer that performs printing as an image forming apparatus will be described.

  FIG. 1 is a schematic diagram of a printer according to a first embodiment of the present invention.

  As shown in the figure, the printer includes an image forming unit 10, a fixing device 20 as a fixing device, a sag sensor unit 30 as a sag detecting unit, and a control unit (CPU) 40 functioning as a computer, and as a developer. An image is formed using a toner (not shown). Reference numeral 50 denotes a sheet as a medium conveyed in the direction of arrow a.

  In the image forming unit 10, reference numeral 11 denotes a photosensitive drum as an image carrier arranged rotatably in the direction of arrow b, 12 denotes a transfer roller as a transfer device arranged rotatably in the direction of arrow c, 13 Is a motor (M) as a first drive unit, and 14 is a motor driver (DRV). In the fixing device 20, 21 is a heating roller as a first fixing element, 22 is a pressure roller as a second fixing element, 23 is a motor (M) as a second drive unit, and 24 is a motor driver ( DRV). The heating roller 21 is rotatably arranged in the arrow d direction, and the pressure roller 22 is rotatably arranged in the arrow e direction. The heating roller 21 incorporates a heater 25 as a heating body. When the heater 25 is energized, the surface temperature of the heating roller 21 is heated to a predetermined temperature.

  The sag sensor unit 30 is disposed between the image forming unit 10 and the fixing device 20 at the tip, and detects the sag of the paper 50 as a sag amount. For this purpose, the sag sensor unit 30 protrudes toward the conveyance path of the paper 50 and rotates in conjunction with the sag sensor lever 31 as a detection member that is slidably disposed. A shield plate 32 as an interlocking member, a photo interrupter 33 as a detection output element, and a spring 34 as an urging member are provided. The spring 34 urges the sag sensor lever 31 in a clockwise direction, that is, urges the tip of the sag sensor lever 31 toward a side where the sheet 50 enters the conveyance path of the sheet 50 with a predetermined urging force. The photo interrupter 33 outputs whether or not the shielding plate 32 is blocking the optical path of the photo interrupter 33 as an electric signal.

  In the printer configured as described above, when the surface of the photosensitive drum 11 is uniformly and uniformly charged by a charging roller (not shown) as a charging device and exposed by an LED head (not shown) as an exposure device, the photosensitive drum 11 is exposed. An electrostatic latent image is formed on the surface. When the electrostatic latent image is developed by a developing roller (not shown) as a developer carrier, a toner image as a developer image is formed. Next, the toner image is transferred onto a sheet 50 by a transfer roller 12 as a transfer device, and fixed by a fixing device 20 to form an image.

  That is, first, when the control unit 40 sends an instruction to the motor driver 14 and rotates the transfer roller 12 by driving the motor 13, the sheet 50 is sandwiched and conveyed by the photosensitive drum 11 and the transfer roller 12. . Then, the conveyed paper 50 is sent to the sag sensor unit 30, the amount of sag is detected, and sent to the fixing device 20.

  Further, when the control unit 40 sends an instruction to the motor driver 24 and rotates the heating roller 21 by driving the motor 23, the sheet 50 is sandwiched and conveyed by the heating roller 21 and the pressure roller 22.

  When the paper 50 on which the toner image is transferred is conveyed in the fixing device 20, the heater 25 is energized to heat the heating roller 21, and the toner image is pressurized by the pressure roller 22, and the heating roller 21. Is heated, melted, and fixed on the paper 50.

  In the drawing, the sheet 50 represented by a solid line is in a sagging state, and the sagging sensor lever 31 cannot be pushed down against the urging force of the spring 34, and as a result, the shielding plate 32 is not attached to the photo interrupter 33. It is placed at a position where the optical path is not shielded, that is, at a non-shielded position. On the other hand, the sheet 50 indicated by the broken line is in a state where there is little sag by being pulled, and the sag sensor lever 31 is pushed down against the urging force of the spring 34. As a result, the shielding plate 32 is placed at a position where the optical path of the photo interrupter 33 is shielded, that is, at the shielding position.

  A sag control processing unit (not shown) of the control unit 40 reads an output signal of the photo interrupter 33, calculates a sag amount of the paper 50, sends a control signal to the motor drivers 14 and 24, and rotates the transfer roller 12. In addition, the rotation speed of the heating roller 21 is controlled independently, the respective conveyance speeds when the paper 50 is conveyed in the image forming unit 10 and the fixing device 20 are controlled, and the sag amount is controlled.

  In this embodiment, the sag amount detected by the sag sensor unit 30 is set as σ, the target value of the sag amount is set as a threshold σth, the conveyance speed of the image forming unit 10 is fixed to V0, and fixing is performed. The conveyance speed of the paper 50 in the container 20 is changed by two values to V1 and V2, so that the sag amount σ falls within a predetermined range centered on the threshold σth. The first and second speeds are configured by the transport speeds V1 and V2.

  Next, the operation of the control unit 40 when the dimensions of the parts constituting the image forming unit 10, the fixing device 20 and the like are all standard and an appropriate sag amount σ can be achieved will be described.

  FIG. 2 is a time chart showing a change in the amount of sag when the average conveying speed of the fixing device and the conveying speed of the image forming unit are the same in the first exemplary embodiment of the present invention.

  In the figure, V0 is a transport speed at which the paper 50 is transported as the transfer roller 12 rotates, that is, a transport speed of the image forming unit 10 (FIG. 1). The image forming unit driving processing unit of the sag control processing unit performs an image forming unit driving process, and outputs a drive signal corresponding to the transport speed V0 to the motor driver 14 in order to transport the paper 50 at the transport speed V0. Then, the motor 13 is driven to rotate the transfer roller 12.

V1 and V2 are transport speeds at which the paper 50 is transported as the heating roller 21 rotates, that is, transport speeds of the fixing device 20. The transport speed V1 is lower than the transport speed V0 by a value ΔV,
V1 = V0−ΔV
The transport speed V2 is higher than the transport speed V0 by a value ΔV,
V2 = V0 + ΔV
The average value of the transport speeds V1 and V2 is set to the average transport speed Va.
Va = (V1 + V2) / 2
In this case, the transport speed V0 and the average transport speed Va are made equal.

  In the fixing device 20, the paper 50 is first transported at the transport speed V <b> 1 at timing t <b> 1. For that purpose, the fixing device driving processing means of the sag control processing means performs fixing device driving processing, outputs a driving signal corresponding to the conveying speed V1 to the motor driver 24, drives the motor 23, and heats the roller 21. Rotate.

  Further, since the paper 50 enters the fixing device 20 straight at the start of printing, the amount of sag σ of the paper 50 between the image forming unit 10 and the fixing device 20 is small.

And conveyance speed V0, V1 is
V1 <V0
Therefore, as the time elapses, the sag amount σ increases, the sag amount σ exceeds the threshold σth at the timing t2, and the output of the photo interrupter 33 (hereinafter referred to as “sag sensor output”) is off. Turn on.

  When the sag sensor output changes from off to on, the fixing device drive processing means switches the conveyance speed V1 to the conveyance speed V2 at timing t3.

And the conveyance speeds V0 and V2 are
V2> V0
Therefore, after the timing t3, the sag amount σ decreases as time elapses. A delay time ΔTn occurs from the time when the sag sensor output is turned on at timing t2 to the time t3 when the sag amount σ starts to decrease at timing t3. The delay time ΔTn indicates a mechanical delay until the shielding plate 32 crosses the optical path of the photo interrupter 33 due to a change in the sag σ, an electrical delay until the sag sensor output changes, and a change in the sag sensor output. A delay in the control unit 40 from when the control unit 40 detects until the conveyance speed of the fixing device 20 is changed is included, and the delay time ΔTn due to these is unavoidable. In order to convey the paper 50 at the conveyance speed V1 at the timings t1 to t3, the time for driving the motor 23 is defined as a first drive time T1.

  The sagging amount σ continues to decrease from the timing t3, and at the timing t4, the sagging amount σ becomes equal to or less than the threshold σth, and the sagging sensor output changes from on to off. The fixing device drive processing means detects that the sag sensor output has changed from on to off, and switches the conveying speed V2 of the fixing device 20 to V1 at timing t5.

The relationship between the conveyance speeds V0 and V1 is V1 <V0.
Therefore, after the timing t5, the sagging amount σ increases as time elapses. A delay time ΔTf occurs until the sag amount σ starts to increase at timing t5 after the sag sensor output changes from on to off at timing t4. In addition, in order to convey the paper 50 at the conveyance speed V2 at the timings t3 to t5, a time for driving the motor 23 is a second drive time T2.

  Then, after the sag amount σ starts to increase at timing t5, the operations at timings t1 to t5 are repeated.

  As described above, when the dimensions of the parts forming the image forming unit 10, the fixing device 20, and the like are all standard, the sag amount σ falls within an appropriate range.

  By the way, the difference between the conveyance speeds V0 and V1 and the difference between the conveyance speeds V0 and V2 are all the value ΔV, and the sag amount σ increases as time elapses at the timings t1 to t3. The slope and the slope at which the sagging amount σ decreases as time elapses at timings t3 to t5 are equal in absolute value, and the delay time ΔTn at timings t2 to t3 and the delay between timings t4 to t5. It is also equal to time ΔTf. Further, the first drive time T1 during which the paper 50 is transported at the transport speed V1 at the timings t1 to t3 is equal to the second drive time T2 during which the paper 50 is transported at the transport speed V2 at the timings t3 to t5.

  Next, a case where the average transport speed Va becomes higher than the transport speed V0 due to variations in the dimensions of the parts forming the image forming unit 10, the fixing device 20, and the like will be described.

  In this case, the image forming unit drive processing means outputs a drive signal corresponding to the transport speed V0 to the motor driver 14 in order to transport the paper 50 at the transport speed V0. Further, the fixing device drive processing means outputs drive signals corresponding to the transport speeds V1 and V2 to the motor driver 24 in order to transport the paper 50 at the transport speeds V1 and V2.

The transport speeds V0 to V2 at this time are set values, and the speed at which the paper 50 is actually transported, that is, the actual transport speed, varies depending on the influence of variations in the dimensions of the parts. In this case, if the average transport speed Va is higher than the transport speed V0 by a value ΔV0 due to the variation in the dimensions of the parts,
Va = V0 + ΔV0
become.

Therefore, the conveyance speed V1 is
V1 = Va-ΔV
= V0 + ΔV0−ΔV
The transport speed V2 is
V2 = Va + ΔV
= V0 + ΔV0 + ΔV
It becomes.

  FIG. 3 is a time chart showing changes in the amount of sag when the average transport speed of the fixing device in the first embodiment of the present invention is higher than the transport speed of the image forming unit.

In this case, the process is started from a state where the amount of sag σ of the sheet 50 conveyed between the image forming unit 10 (FIG. 1) and the fixing device 20 is small, that is, from timing t11. And conveyance speed V0, V1 is
V1 <V0
Therefore, as time passes, the sag amount σ increases, the sag amount σ exceeds the threshold σth at timing t12, and the sag sensor output changes from OFF to ON.

  When the sag sensor output changes from OFF to ON, the fixing device drive processing means sets the conveyance speed to V2 at timing t13.

And the conveyance speeds V0 and V2 are
V2> V0
Therefore, after the timing t13, the sag amount σ decreases as time elapses. The sagging amount σ continues to decrease from the timing t13, and at the timing t14, the sagging amount σ becomes equal to or less than the threshold σth, and the sagging sensor output changes from on to off. The fixing device drive processing means detects that the sag sensor output has changed from on to off, and changes the conveyance speed of the fixing device 20 to the conveyance speed V1 at timing t15.

  In addition, after the sag amount σ starts to increase after the timing t15, the operations at the timings t11 to t15 are repeated.

  By the way, since the difference between the conveyance speeds V0 and V1 is small, the inclination of increase of the sag amount σ at timings t11 to t13 is small, and the first driving time T1 of the motor 23 for conveying the paper 50 at the conveyance speed V1 is standard. Longer than typical cases. Further, the sag amount σ becomes the maximum value at the timing t13 when the delay time ΔTn has elapsed from the timing t12, but the maximum value is smaller than that in the standard case.

  On the contrary, since the difference between the conveyance speeds V0 and V2 is large, the inclination of the decrease in the sag amount σ at the timings t13 to t15 is large, and the second drive time T2 of the motor 23 for conveying the paper 50 at the conveyance speed V2 is Shorter than the standard case. Further, the sag amount σ becomes the minimum value at the timing t15 when the delay time ΔTf has elapsed from the timing t14, but the minimum value is smaller than that in the standard case.

  That is, it can be seen that when the average transport speed Va becomes higher than the transport speed V0 due to variations in the dimensions of the parts, the sag amount σ changes while maintaining a small state as a whole. Further, when the dimensional variation of the parts is further increased and the average transport speed Va is further higher than the transport speed V0, the sag amount σ is further decreased, and the minimum value at the timing t15 is 0, that is, the sag amount σ is completely eliminated. Is estimated.

  In this case, the paper 50 is pulled between the image forming unit 10 and the fixing device 20, and the toner image is disturbed.

  Next, a case where the average transport speed Va becomes lower than the transport speed V0 due to variations in the dimensions of the parts will be described.

In this case, the average transport speed Va is lower than the transport speed V0 by a value ΔV0,
Va = V0−ΔV0
And

And the conveyance speed V1 is
V1 = Va-ΔV
= V0-ΔV0-ΔV
The transport speed V2 is
V2 = Va + ΔV
= V0-ΔV0 + ΔV
It becomes.

  FIG. 4 is a time chart showing changes in the amount of sag when the average transport speed of the fixing device in the first embodiment of the present invention is lower than the transport speed of the image forming unit.

In this case, the process is started from a state where the amount of sag σ of the sheet 50 conveyed between the image forming unit 10 (FIG. 1) and the fixing device 20 is small, that is, from timing t21. And conveyance speed V0, V1 is
V1 <V0
Therefore, as time passes, the sag amount σ increases, the sag amount σ exceeds the threshold σth at timing t22, and the sag sensor output changes from OFF to ON.

  When the sag sensor output changes from off to on, the fixing device drive processing unit sets the conveyance speed to V2 at timing t23.

And the conveyance speeds V0 and V2 are
V2> V0
Therefore, after the timing t23, the sagging amount σ decreases as time elapses. The sagging amount σ continues to decrease from the timing t23, and at the timing t24, the sagging amount σ becomes equal to or less than the threshold σth, and the sagging sensor output changes from on to off. The fixing device drive processing means detects that the sag sensor output has changed from on to off, and changes the conveyance speed of the fixing device 20 to the conveyance speed V1 at timing t25.

  Further, after the sag amount σ starts to increase after timing t25, the operation from timing t21 to t25 is repeated.

  By the way, since the difference between the conveyance speeds V0 and V1 is large, the inclination of the increase in the amount of sag σ at timings t21 to t23 is large, and the first drive time T1 of the motor 23 for conveying the paper 50 at the conveyance speed V1 is standard. It is shorter than the typical case. Further, the sag amount σ becomes the maximum value at the timing t23 when the delay time ΔTn has elapsed from the timing t22, but the maximum value is larger than that in the standard case.

  On the contrary, since the difference between the conveyance speeds V0 and V2 is small, the inclination of the decrease in the sag amount σ at the timing t23 to t25 is small, and the second drive time T2 of the motor 23 for conveying the paper 50 at the conveyance speed V2 is Longer than standard case. Further, the sag amount σ becomes the minimum value at the timing t25 when the delay time ΔTf has elapsed from the timing t24, but the minimum value is larger than that in the standard case.

  That is, it can be seen that when the average transport speed Va becomes lower than the transport speed V0 due to variations in the dimensions of the parts, the sag amount σ changes while maintaining a large state as a whole. Further, when the dimensional variation of parts further increases and the average transport speed Va becomes lower than the transport speed V0, the sag amount σ further increases, and the maximum value at the timing t23 becomes larger than necessary, and the toner image is fixed. The unprinted paper 50 comes into contact with the components inside the printer and the toner image is disturbed.

  Note that when the average transport speed Va becomes higher than the transport speed V0 due to the variation in the dimensions of the parts, the sag amount σ decreases as a whole because the difference between the transport speeds V0 and V2 increases. Depending on the degree of the difference, the sag amount σ is completely eliminated, and the sheet 50 is pulled between the image forming unit 10 and the fixing device 20, and the toner image is disturbed.

  In addition, when the average transport speed Va is lower than the transport speed V0, the overall amount of sagging σ increases because the difference between the transport speeds V0 and V1 increases. Depending on the degree of the speed difference, The amount of sag σ becomes larger than necessary, and the paper 50 on which the toner image is not fixed comes into contact with the components inside the printer and the toner image is disturbed.

  Therefore, the correction processing means of the sag control processing means performs correction processing, and corrects the transport speeds V1 and V2 so that the difference is eliminated when the average transport speed Va and the transport speed V0 are different due to variations in the dimensions of parts. To do. When the transport speed V0 is corrected, the transport speed V0 of the image forming unit 10 is not constant during the printing operation, and the toner image is disturbed. Therefore, the transport speed V0 is not corrected.

By the way, the difference between the average transport speed Va and the transport speed V0 cannot be directly detected. However, as described in FIGS. 2 to 4, when the average transport speed Va and the transport speed V0 are equal, the first and second drive times T1 and T2 are equal, and the average transport speed Va is higher than the transport speed V0. In this case, the first driving time T1 is longer than the standard case, and the second driving time T2 is shorter than the standard case.
T1> T2
When the average transport speed Va is lower than the transport speed V0, the first drive time T1 is shorter than the standard case, and the second drive time T2 is longer than the standard case. ,
T1 <T2
become.

Therefore, the correction processing means compares the first and second drive times T1, T2, and
T1> T2
In this case, it can be seen that the average transport speed Va is higher than the transport speed V0, so that the transport speeds V1 and V2 are corrected to be low,
T1 <T2
In this case, it can be seen that the average transport speed Va is lower than the transport speed V0, so that the transport speeds V1 and V2 are corrected to be higher,
T1 = T2
In this case, since it can be seen that the average transport speed Va and the transport speed V0 are equal, the current transport speeds V1 and V2 are maintained.

  FIG. 5 is a flowchart showing the operation of the correction processing means in the first embodiment of the present invention.

  First, the drive time calculation processing means of the correction processing means performs a drive time calculation process to calculate first and second drive times T1 and T2 for driving the motor 23 (FIG. 1). Therefore, when printing is started, the drive time calculation processing unit sets the conveyance speed of the image forming unit 10 to V0, and adds the accumulated values of the first and second drive times T1 and T2. 1. Reset the integration timer values τ1, τ2 of the second integration timer. The integration timer value τ1 is a value obtained by integrating the individual first drive times T1 when the paper 50 is conveyed at the conveyance speed V1 in the fixing device 20 while the set printing length is printed. The value τ2 is a value obtained by integrating the individual second driving times T2 when the sheet 50 is conveyed at the conveyance speed V2 in the fixing device 20 while the printing length is printed.

  Then, the driving time calculation processing means reads the sag sensor output, determines whether or not the sag amount σ is smaller than the threshold value σth, and when the sag amount σ is smaller than the threshold value σth, the timing timer value t1 of the first timing timer. Is reset, the conveying speed of the fixing device 20 is set to V1, and the time measurement of the first time measuring timer is started. The first timekeeping timer is for counting each first driving time T1.

  When the sag amount σ is equal to or greater than the threshold σth, the drive time calculation processing means adds the timed timer value t1 to the integrated timer value τ1. Note that the operations from the reset of the timer value t1 to the addition of the timer value t1 to the integrated timer value τ1 are the timings t1 to t3 when the conveying speed of the fixing device 20 is V1 in FIGS. It corresponds to t11-t13 and t21-t23.

  Then, the drive time calculation processing means determines whether or not printing of a predetermined length, for example, 1 [m], is completed. Here, a description will be given on the assumption that only a few centimeters have been printed immediately after the start of printing. Subsequently, the drive time calculation processing means resets the time count value t2 of the second time count timer, sets the conveyance speed of the fixing device 20 to V2, and starts time count of the second time count timer. The second clock timer is for clocking each second drive time T2.

  Next, when the sag amount σ becomes smaller than the threshold value σth, the drive time calculation processing means adds the timed timer value t2 to the integrated timer value τ2. The operation from the reset of the timer value t2 to the addition of the timer value t2 to the integrated timer value τ2 is the timing t3 to t5 when the conveying speed of the fixing device 20 is V2 in FIGS. This corresponds to t13 to t15 and t23 to t25.

  Then, it is determined whether or not the predetermined length of printing is completed, and the above-described operation is repeated until the predetermined length of printing is completed.

  Then, when printing of a predetermined length is completed, the speed setting processing means of the correction processing means performs speed setting processing, compares whether or not the integration timer values τ1 and τ2 are equal, and the integration timer values τ1 and τ2 Is equal, the average transport speed Va is equal to the transport speed V0, and the current transport speeds V1 and V2 are maintained.

  When the integration timer value τ1 is larger than the integration timer value τ2, the average conveyance speed Va is higher than the conveyance speed V0, so the speed setting processing means lowers the conveyance speeds V1 and V2 by the speed α. When the integration timer value τ1 is equal to or less than the integration timer value τ2, since the average conveyance speed Va is lower than the conveyance speed V0, the speed setting processing unit increases the conveyance speeds V1 and V2 by the speed α.

  By repeating such an operation, when the average transport speed Va is higher than the transport speed V0, the transport speeds V1 and V2 are gradually lowered, and the average transport speed Va and the transport speed V0 are gradually made equal. When the average transport speed Va is lower than the transport speed V0, the transport speeds V1 and V2 are gradually increased, and the average transport speed Va and the transport speed V0 are gradually made equal.

  In this way, the conveyance speeds V1 and V2 are corrected by comparing the first and second drive times T1 and T2, so that the components constituting the image forming unit 10, the fixing device 20 and the like are used. Even if there is a variation in the dimensions at the time of manufacturing or after manufacturing due to differences in manufacturing lots, materials, manufacturers, etc., the amount of slack σ can be kept within an appropriate range.

  Therefore, the paper 50 before the toner image is fixed does not come into contact with any part in the printer, and the paper 50 is not pulled between the image forming unit 10 and the fixing device 20. The toner image that is transferred or fixed is not disturbed. As a result, the image quality can be improved.

Next, a flowchart will be described.
Step S1: Printing is started.
Step S2: The conveyance speed of the image forming unit 10 is set to V0.
Step S3: The integration timer values τ1, τ2 are reset.
Step S4: Determine whether the amount of slack σ is smaller than the threshold σth. When the sag amount σ is smaller than the threshold σth, the process proceeds to step S5, and when the sag amount σ is equal to or larger than the threshold σth, the process proceeds to step S11.
Step S5: The clock timer value t1 is reset.
Step S6: The conveyance speed of the fixing device 20 is set to V1.
Step S7: Timing is started.
Step S8 Wait until the sag amount σ becomes equal to or greater than the threshold σth. If the sagging amount σ is equal to or greater than the threshold σth, the process proceeds to step S9.
Step S9: The time measuring timer value t1 is added to the integration timer value τ1.
Step S10: It is determined whether printing of a predetermined length has been completed. If printing of a predetermined length is completed, the process proceeds to step S17, and if not completed, the process proceeds to step S11.
Step S11: The clock timer value t2 is reset.
Step S12: The conveyance speed of the fixing device 20 is set to V2.
Step S13: Timing is started.
Step S14 Wait until the sag amount σ becomes smaller than the threshold value σth. If the sagging amount σ is smaller than the threshold σth, the process proceeds to step S15.
Step S15: The timed timer value t2 is added to the integrated timer value τ2.
Step S16: It is determined whether printing of a predetermined length has been completed. If printing of a predetermined length is completed, the process proceeds to step S17, and if not completed, the process returns to step S5.
Step S17: It is determined whether or not the integration timer value τ1 and the integration timer value τ2 are equal. If the integration timer value τ1 and the integration timer value τ2 are equal, the process ends. If the integration timer value τ1 and the integration timer value τ2 are not equal, the process proceeds to step S18.
Step S18: It is determined whether the integration timer value τ1 is greater than the integration timer value τ2. If the integration timer value τ1 is greater than the integration timer value τ2, the process proceeds to step S19. If the integration timer value τ1 is less than or equal to the integration timer value τ2, the process proceeds to step S20.
Step S19 The conveyance speeds V1 and V2 are subtracted by the speed α, and the process is terminated.
Step S20 The transport speeds V1 and V2 are added by the speed α, and the process is terminated.

  By the way, in the first embodiment, when the average transport speed Va and the transport speed V0 are different, the transport speeds V1 and V2 are changed so that the average transport speed Va and the transport speed V0 are equal. However, in this case, the transport speeds V1 and V2 are uniformly changed regardless of how much the average transport speed Va and the transport speed V0 are different.

  Therefore, a second embodiment of the present invention will be described in which values for changing the transport speeds V1 and V2 are made different according to the average transport speed Va and the transport speed V0. The structure of the printer in this embodiment is the same as that of the printer in the first embodiment, and will be described with reference to FIG.

  FIG. 6 is a flowchart showing the operation of the correction processing means in the second embodiment of the present invention, and FIG. 7 is a diagram showing a correction amount table for the conveyance speed of the fixing device in the second embodiment of the present invention.

  In this case, the operation from the start of printing until the integration timer values τ1 and τ2 are compared is the same as the operation in the first embodiment, and a description thereof will be omitted.

  The speed setting processing means of the correction processing means performs speed setting processing and compares whether or not the accumulated timer values τ1 and τ2 are equal. If the accumulated timer values τ1 and τ2 are equal, the average conveying speed Va and the conveying speed V0 are set. Are equal, the current transport speeds V1 and V2 are maintained.

Further, when the integration timer values τ1, τ2 are different, the difference calculation processing means of the speed setting processing means performs a difference calculation process, and a difference Δτ between the integration timer values τ1, τ2.
Δτ = | τ1-τ2 |
The correction amount calculation processing means of the speed setting processing means performs correction amount calculation processing, and calculates correction amounts for the transport speeds V1 and V2 according to the magnitude of the difference Δτ. For this purpose, a correction amount table is set in a memory (not shown), and the difference Δτ and the correction amount index β are recorded in correspondence with each other in the correction amount table. In this case, the time required to perform printing of a predetermined length is, for example, 2.0 [sec], and the difference Δτ is 0 <Δτ ≦ 0.5 [sec]
0.5 <Δτ ≦ 1.0 [sec]
1.0 <Δτ ≦ 1.5 [sec]
1.5 <Δτ ≦ 2.0 [sec]
The correction amount index β corresponding to the four stages is 0.1 [%], 0.2 [%], 0.3 [%], and 0.4 [%], respectively.

Then, the correction amount calculation processing means reads the correction amount index β corresponding to the difference Δτ with reference to the correction amount table, and corrects the correction amounts A1 and A2 of the transport speeds V1 and V2.
A1 = 0.01 · β · V1
A2 = 0.01 ・ β ・ V2
Is calculated.

  The speed change processing means of the speed setting processing means performs a speed change process. When the integrated timer value τ1 is greater than the integrated timer value τ2, the average transport speed Va is higher than the transport speed V0, so the transport speed V1, V2 is lowered by correction amounts A1 and A2.

  When the integration timer value τ1 is smaller than the integration timer value τ2, the average transfer speed Va is lower than the transfer speed V0, so the speed change processing means increases the transfer speeds V1 and V2 by correction amounts A1 and A2.

  By repeating such an operation, the correction amounts A1 and A2 of the transport speeds V1 and V2 are increased as the difference between the average transport speed Va and the transport speed V0 is larger. Therefore, the average transport speed Va and the transport speed V0 are set as follows. It can be made equal in a short time.

Next, a flowchart will be described.
Step S21: Printing is started.
Step S22: The conveyance speed of the image forming unit 10 is set to V0.
Step S23: The integration timer values τ1, τ2 are reset.
Step S24: It is determined whether the sag amount σ is smaller than the threshold value σth. When the sag amount σ is smaller than the threshold σth, the process proceeds to step S25, and when the sag amount σ is equal to or larger than the threshold σth, the process proceeds to step S31.
Step S25: Reset the clock timer value t1.
Step S26: The conveyance speed of the fixing device 20 is set to V1.
Step S27 Timekeeping is started.
Step S28 Wait until the sag amount σ becomes equal to or greater than the threshold σth. If the sagging amount σ is equal to or greater than the threshold σth, the process proceeds to step S29.
Step S29 The timer value t1 is added to the accumulated timer value τ1.
Step S30: It is determined whether printing of a predetermined length has been completed. If printing of a predetermined length has been completed, the process proceeds to step S37, and if not, the process proceeds to step S31.
Step S31: The timer value t2 is reset.
Step S32: The conveyance speed of the fixing device 20 is set to V2.
Step S33 Timekeeping is started.
Step S34 Wait until the sag amount σ becomes smaller than the threshold value σth. If the sagging amount σ is smaller than the threshold σth, the process proceeds to step S35.
Step S35: The timed timer value t2 is added to the integrated timer value τ2.
Step S36: It is determined whether printing of a predetermined length has been completed. If printing of the predetermined length is completed, the process proceeds to step S37, and if not completed, the process returns to step S25.
Step S37: It is determined whether or not the integration timer value τ1 and the integration timer value τ2 are equal. If the integration timer value τ1 and the integration timer value τ2 are equal, the process ends. If the integration timer value τ1 and the integration timer value τ2 are not equal, the process proceeds to step S38.
Step S38: It is determined whether or not the integration timer value τ1 is greater than the integration timer value τ2. If the integration timer value τ1 is greater than the integration timer value τ2, the process proceeds to step S39, and if the integration timer value τ1 is less than or equal to the integration timer value τ2, the process proceeds to step S40.
Step S39: The difference Δτ between the integration timer value τ1 and the integration timer value τ2 is calculated, the correction amounts A1 and A2 are determined from the correction amount table, the conveyance speeds V1 and V2 are subtracted by the correction amounts A1 and A2, and the process is terminated. To do.
Step S40: The difference Δτ between the integration timer value τ1 and the integration timer value τ2 is calculated, the correction amounts A1 and A2 are determined from the correction amount table, the transport speeds V1 and V2 are added by the correction amounts A1 and A2, and the process is terminated. To do.

  In each of the above embodiments, an electrophotographic printer has been described. However, the present invention can be applied to other printers such as an ink jet printer. Further, in the present embodiment, a single color printer is described, but the present invention can also be applied to a color printer.

  In addition, this invention is not limited to the said embodiment, It can change variously based on the meaning of this invention, and does not exclude them from the scope of the present invention.

1 is a schematic diagram of a printer according to a first embodiment of the present invention. 6 is a time chart showing a change in sag amount when the average conveyance speed of the fixing device and the conveyance speed of the image forming unit are the same in the first exemplary embodiment of the present invention. 6 is a time chart showing changes in the amount of sag when the average conveyance speed of the fixing device in the first embodiment of the present invention is higher than the conveyance speed of the image forming unit. 6 is a time chart showing changes in the amount of sag when the average conveyance speed of the fixing device in the first embodiment of the present invention is lower than the conveyance speed of the image forming unit. It is a flowchart which shows operation | movement of the correction | amendment process means in the 1st Embodiment of this invention. It is a flowchart which shows operation | movement of the correction | amendment process means in the 2nd Embodiment of this invention. FIG. 10 is a diagram illustrating a correction amount table for a conveyance speed of a fixing device according to a second embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Image forming part 20 Fixing device 23 Motor 30 Slack sensor part 40 Control part 50 Paper

Claims (2)

(A) an image forming unit that forms a developer image on the medium;
(B) a fixing device for fixing a developer image formed on the medium;
(C) a sag detection unit that is disposed between the image forming unit and the fixing device and detects sag of the medium;
(D) a driving unit driven to convey the medium at a first speed and a second speed higher than the first speed in the fixing device;
(E) a fixing device drive processing unit that drives the drive unit by switching the first and second speeds according to the detection result of the sag detection unit;
(F) drive time calculation processing means for calculating a first drive time for driving the drive unit at the first speed and a second drive time for driving the drive unit at the second speed;
(G) An image forming apparatus comprising speed setting processing means for setting the first and second speeds based on the first and second driving times. The speed setting processing means calculates a difference calculation processing means for calculating a difference between the first and second driving times, and a correction amount calculation for calculating a correction amount for the first and second speeds corresponding to the difference. The image forming apparatus according to claim 1, further comprising a processing unit.

Images