JP2010217789A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce the number of components to reduce manufacturing costs with simple structure in which no temperature detection means or active control means is used. <P>SOLUTION: Timing in which a paper tip passes through a predetermined position is measured from a detection result of a paper passage sensor 71. When the paper is conveyed at conveyance speed, difference is obtained between ideal timing of passage of the paper tip in which the paper tip should pass through the predetermined position so that the paper tip can reach a transfer position in scheduled timing when an image reaches the transfer position, and the timing of passage of the paper tip. An error with the transfer position of a paper tip position in the scheduled timing is predicted from the time difference and the conveyance speed. The conveyance speed is changed so as to eliminate the error with the transfer position of the paper tip position in the scheduled timing on the basis of a prediction result. A detected position of the paper passage sensor 71 is moved from the predetermined position to the direction in parallel with the paper conveyance direction according to temperature change in the image forming apparatus. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image forming apparatus that forms and outputs an image on a sheet using an electrophotographic system.

  In an electrophotographic image forming apparatus, an electrostatic image is first formed on a photoconductor based on a signal corresponding to image information, and developed into a toner image by a developing unit. Next, the toner image is transferred to an image carrier such as an intermediate transfer belt or directly to a sheet. In the former case, the toner image on the image carrier is further transferred to a sheet (secondary transfer). Thereafter, the toner image transferred onto the paper is fixed by the fixing unit, and the paper on which the image is formed is output.

  In such an image forming apparatus, in order to convey a sheet to a transfer position that is a position for transferring a toner image to the sheet, a sheet conveyance unit such as a registration roller is provided upstream from the transfer position in the conveyance direction. If the timing at which the toner image reaches the transfer position and the timing at which the paper reaches the transfer position are shifted, the image position on the paper is shifted from the target position, and the width of the margin is also shifted. The quality of the (printed material) is degraded. Therefore, conventionally, the timing at which the toner image reaches the transfer position is calculated in advance with reference to the start of the formation of the electrostatic image on the photoconductor, and the sheet reaches the transfer position in accordance with the calculated timing. It controls the drive timing and roller rotation speed of the rollers of the paper transport unit.

  However, slips between the rollers of the paper transport unit and the paper, slips between the intermediate transfer belt that is the image carrier and the rollers that drive the intermediate transfer belt, or deformation of parts due to changes in temperature and humidity, etc. The relative timing at which the toner image and the paper arrive at the transfer position may be shifted due to factors such as the length of the conveyance path and the change in the distance that the toner image moves to the transfer position. Therefore, many mechanisms and methods for adjusting the timing at which the toner image reaches the transfer position or the timing at which the paper reaches the transfer position are disclosed.

  For example, a means for detecting a change in the circumference of the image carrier belt or the peripheral speed of the belt or a means for predicting and detecting a change in the circumference of the image carrier belt from the temperature detection result in the image forming apparatus by the temperature detection means is provided. By controlling the paper conveyance and image formation based on the detection results by these means, the timing at which the toner image reaches the transfer position without using a sensor for detecting the position of the image on the image carrier is provided. An image forming apparatus that matches the timing at which a sheet reaches a transfer position is disclosed (see Patent Document 1).

  In addition, for example, a change in the diameter and circumference of the roller of the paper conveyance unit is directly measured, or a change in the diameter and circumference of the roller is calculated from the measurement result of the ambient temperature of the paper conveyance unit, and the measurement result or the calculation result An image forming apparatus is disclosed in which the sheet conveyance is controlled on the basis of the toner image and the deviation of the timing at which the toner image and the sheet arrive at the transfer position due to a change in the outer shape of the sheet conveying unit due to environmental changes and changes with time (see FIG. Patent Document 2).

  In addition, for example, the temperature of the registration roller of the paper transport unit or the ambient temperature thereof is measured, and based on the measured temperature, the driving of the registration roller is controlled so as to cancel the influence of the temperature change, or exposure to the photosensitive member is started. An image forming apparatus is disclosed in which the timing at which the toner image reaches the transfer position and the timing at which the paper reaches the transfer position are matched by controlling the timing (see Patent Document 3).

  However, in the image forming apparatuses disclosed in Patent Documents 1 to 3, in order to suppress errors caused by environmental changes (temperature and humidity changes) inside the image forming apparatus, the ambient temperature, roller diameter, circumferential length, etc. Is measured, and the start timing of forming the electrostatic image on the photosensitive member is controlled so as to cancel the influence of the temperature change based on the measured temperature. For this reason, since components such as actively controlling means and temperature detecting means have to be mounted, there is a problem that the number of parts increases and the manufacturing cost increases.

  The present invention has been made in view of the above, and has a simple configuration that does not use a temperature detection unit or an active control unit, and thus toner caused by environmental changes (changes in temperature and humidity) inside the image forming apparatus. An object of the present invention is to obtain an image forming apparatus capable of reducing the number of parts and reducing the manufacturing cost by suppressing the deviation between the timing at which the image reaches the transfer position and the relative timing at which the paper reaches the transfer position.

  In order to solve the above-described problems and achieve the object, an image forming apparatus of the present invention includes an image forming unit that forms an image, and an image in which the image formed by the image forming unit is transferred to the surface and moves endlessly. A carrier, a transfer unit that transfers an image on the image carrier onto a sheet at a transfer position, a conveyance unit that conveys the sheet to a transfer position of the transfer unit, and a transfer unit between the transfer unit and the conveyance unit. In order to reach the transfer position at the scheduled timing when the image formed by the image forming means reaches the transfer position of the transfer means and the paper passage detection means that is in a predetermined position and detects the passage of the paper tip A setting unit that presets the timing at which the leading end of the sheet should pass through the predetermined position as an ideal timing for passing the leading end of the sheet, and the conveying unit conveys the sheet to the transfer position at a predetermined predetermined conveying speed. The measurement timing is measured when the leading edge of the paper passes through the predetermined position from the detection result of the paper passage detection means, and the paper is conveyed at the conveyance speed. A time difference from the timing is obtained, and an error between the time difference and the transfer speed of the paper front end position at the scheduled timing is predicted from the time difference. Based on the prediction result, the transfer position of the paper front end position at the scheduled timing is determined. The conveyance speed is changed so that the error with respect to 0 is zero, and the conveyance means controls the sheet conveyance operation of the conveyance means so that the conveyance speed becomes a predetermined speed until the sheet reaches the transfer position. The detection position of the paper passage detection means is changed from the predetermined position to the paper conveyance direction in response to a temperature change in the image forming apparatus. Characterized in that it comprises a sheet passage detecting position moving means for moving the row direction, a.

  According to the present invention, it is possible to suppress a difference between the timing at which the toner image reaches the transfer position and the relative timing at which the paper reaches the transfer position due to environmental changes (temperature and humidity changes) inside the image forming apparatus. In addition, a simple configuration can be realized without using temperature detecting means and active control means, and the manufacturing cost can be reduced by reducing the number of parts.

FIG. 1 is a schematic diagram showing the mechanism of the image forming apparatus according to the present embodiment. FIG. 2 is a diagram illustrating an example of a mechanism for adjusting the timing at which the paper reaches the transfer position. FIG. 3 is an explanatory diagram showing the leading end position of the sheet when the mechanism of FIG. 2 operates. FIG. 4 is a diagram illustrating the front end position of the sheet when the diameter of the transport roller is expanded. FIG. 5 is an explanatory diagram of a method for moving the paper passage sensor when the diameter of the transport roller expands. FIG. 6 is an explanatory diagram of a method of moving the sheet passing sensor when the endless moving speed of the intermediate transfer belt is increased due to the expansion of the diameter of the driving roller. FIG. 7 is a schematic diagram of an intermediate transfer belt drive control system in the prior art. FIG. 8 is an explanatory diagram of a method of moving the sheet passage sensor when the conveyance speed and the endless moving speed of the intermediate transfer belt are increased. FIG. 9 is an explanatory diagram showing an example in which a paper passage sensor fixing member is used as a mechanism for moving the position of the paper passage sensor. FIG. 10 is an explanatory diagram illustrating an example in which an opening forming member is used as a mechanism for moving the position of the paper passage sensor. FIG. 11 is an explanatory diagram illustrating another example in which an opening forming member is used as a mechanism for moving the position of the paper passage sensor.

  Exemplary embodiments of an image forming apparatus according to the present invention will be explained below in detail with reference to the accompanying drawings. The image forming apparatus of the present invention includes a printer, a copier, a facsimile machine, a scanner device, and an MFP (multifunction device, multifunction machine, Multi Function Peripherals) in which a plurality of functions such as a copy, a fax machine, and a printer are housed in one casing. Etc.) and can be applied to a device having an output function.

  FIG. 1 is a schematic diagram showing the mechanism of the image forming apparatus according to the present embodiment. This image forming apparatus is a tandem type color image forming apparatus having four image forming units. In the image forming apparatus, the apparatus main body 1 is placed on a paper feed table 2. A scanner 3 is mounted on the apparatus body 1 and an automatic document feeder (ADF) 4 is mounted thereon. In the apparatus main body 1, a transfer device 20 having an intermediate transfer belt 10 that is a belt-like endless moving member is provided at substantially the center. The intermediate transfer belt 10 includes a driving roller 9 and two driven rollers 15 and 16. In FIG. 1, the drive roller 9 is rotated by a driving force from a driving force transmission unit such as a motor so as to rotate in the clockwise direction.

  The intermediate transfer belt 10 is configured so that residual toner remaining on the surface after image transfer is removed by a cleaning device 17 provided on the left side of the driven roller 15. Above the linear portion spanned between the drive roller 9 and the driven roller 15 of the intermediate transfer belt 10, yellow (Y), cyan (C), magenta along the moving direction of the intermediate transfer belt 10. Four drum-shaped photoconductors 40Y, 40C, 40M, and 40K (hereinafter simply referred to as photoconductors 40 unless otherwise specified) of (M) and black (K) are arranged at predetermined intervals. . In addition, four primary transfer rollers 62 are provided inside the intermediate transfer belt 10 so as to face the respective photoreceptors 40 and sandwich the intermediate transfer belt 10 therebetween.

  Each of the four photoconductors 40 can be rotated in the counterclockwise direction in FIG. 1, and around each photoconductor 40, a charging device 60, a developing device 61, the above-described primary transfer roller 62, and a photoconductor. A body cleaning device 63 and a charge removal device 64 are provided, and each constitutes an image forming unit 18. A common exposure device 21 is provided above the four image forming units 18. Each image (toner image) formed on each photoconductor is successively transferred onto the intermediate transfer belt 10 in a superimposed manner.

  On the other hand, on the lower side of the intermediate transfer belt 10, a secondary transfer device 22 serving as a transfer unit that transfers an image on the intermediate transfer belt 10 to a sheet of recording paper is provided. The secondary transfer device 22 is a belt in which a secondary transfer belt 24 that is an endless belt is stretched between two rollers 23 and 23, and the secondary transfer belt 24 is driven by a driven roller 16 via an intermediate transfer belt 10. It comes to be pressed against.

  The secondary transfer device 22 collectively transfers the toner images on the intermediate transfer belt 10 at a transfer position A (see FIG. 2) onto a sheet fed between the secondary transfer belt 24 and the intermediate transfer belt 10. A fixing device 25 that fixes the toner image on the paper is located downstream of the secondary transfer device 22 in the paper conveyance direction, and a pressure roller 27 is pressed against the fixing belt 26 that is an endless belt. .

  Note that the secondary transfer device 22 also functions to convey the sheet after image transfer to the fixing device 25. Further, the secondary transfer device 22 may be a transfer device using a transfer roller or a non-contact charger. Below the secondary transfer device 22, a paper reversing device 28 is provided for reversing the paper when images are formed on both sides of the paper. As described above, the apparatus main body 1 constitutes an indirect transfer tandem color image forming apparatus.

  When making a color copy with this color image forming apparatus, the document is set on the document table 30 of the automatic document feeder 4. When the document is manually set, the automatic document feeder 4 is opened, the document is set on the contact glass 32 of the scanner 3, and the automatic document feeder 4 is closed and pressed.

  When a start key (not shown) is pressed, when the document is set on the automatic document feeder 4, the document is fed onto the contact glass 32. When the document is manually set on the contact glass 32, the scanner 3 is immediately driven, and the first traveling body 33 and the second traveling body 34 start traveling. Then, light is emitted from the light source of the first traveling body 33 toward the document, and reflected light from the document surface is directed to the second traveling body 34, and the light is reflected by the mirror of the second traveling body 34. The light enters the reading sensor 36 through the imaging lens 35 and the content of the original is read.

  Further, when the start key is pressed, the intermediate transfer belt 10 starts to rotate. At the same time, the photoconductors 40Y, 40C, 40M, and 40K start to rotate, and yellow (Y), cyan (C), magenta (M), and black (K) monochromatic toners on the photoconductors. The operation for forming an image is started. The toner images of the respective colors formed on the respective photoreceptors are sequentially transferred while being superimposed on the intermediate transfer belt 10 that rotates in the clockwise direction in FIG. 5, and a full-color composite color image is formed there. It is formed.

  On the other hand, when the start key described above is pressed, the paper feed roller 42 of the selected paper feed stage in the paper feed table 2 rotates, and the sheet (see FIG. 1) is fed out, and is separated into one sheet by the separation roller 45 and conveyed to the sheet feeding path 46. The sheet is conveyed by a conveyance roller 47 to a sheet feeding path 48 in the apparatus main body 1, hits a registration roller 49 and temporarily stops.

  In the case of manual paper feeding, the paper set on the manual tray 51 is fed out by the rotation of the paper feeding roller 50, and is separated into one sheet by the separation roller 52 and conveyed to the manual paper feeding path 53. Then, it hits the registration roller 49 and temporarily stops. The registration roller 49 starts to rotate at an accurate timing in accordance with the composite color image on the intermediate transfer belt 10, and feeds the temporarily stopped paper between the intermediate transfer belt 10 and the secondary transfer device 22. . Then, a color image is transferred onto the paper by the secondary transfer device 22. Note that the sheet may be temporarily stopped by a stopper instead of the registration roller 49.

  The sheet on which the color image has been transferred is conveyed to the fixing device 25 by the secondary transfer device 22 that also functions as a conveying device, where the transferred color image is fixed by applying heat and pressure. Thereafter, the sheet is guided to the discharge side by the switching claw 55, discharged onto the discharge tray 57 by the discharge roller 56, and stacked there. When the double-sided copy mode is selected, the sheet on which an image is formed on one side is conveyed to the sheet reversing device 28 side by the switching claw 55, reversed there and guided again to the transfer position A, and this time the image is printed on the back side. After the formation, the paper is discharged onto a paper discharge tray 57 by a discharge roller 56.

  Next, adjustment of the timing at which the paper reaches the transfer position A will be described. FIG. 2 is a diagram illustrating an example of a mechanism for adjusting the timing at which the paper reaches the transfer position. FIG. 3 is an explanatory diagram showing the leading edge position of the sheet when the mechanism of FIG. 2 operates. After the leading edge of the sheet is brought into contact with the registration roller 49 or a stopper (not shown) to temporarily stop the sheet, the registration roller 49 is restarted at a predetermined timing based on the start of electrostatic image formation on the photosensitive member 40 or the like. Resume paper conveyance by driving or releasing the stopper. The conveyed sheet reaches the conveyance roller 70 in FIG. 2 and is further conveyed to the transfer position A of the secondary transfer device 22. The conveyance speed Vref is set to a speed that is a predetermined ratio to the endless moving speed of the intermediate transfer belt 10, but is substantially the same speed as the endless moving speed Vref_belt of the intermediate transfer belt 10. This ratio varies depending on the type of paper, and is determined in advance so that the paper conveyance speed is slower than the endless movement speed. By controlling the conveyance speed at a ratio corresponding to the paper, the transferability of the image from the intermediate transfer belt 10 to the paper can be improved. However, even if the conveyance speed is controlled to be the same as the endless movement speed, No problem.

  A paper passage sensor 71 is provided at a predetermined position between the conveyance roller 70 and the transfer position A of the secondary transfer device 22 to detect passage of the front end of the paper when the paper is conveyed. When the conveyance control unit 72 starts forming an electrostatic image on the photosensitive member 40, the conveyance control unit 72 starts counting the timer from zero. Thereafter, the value (passing timing) of the timer when the passage of the leading end of the sheet is detected by the sheet passing sensor 71 is measured. Here, in the case of a tandem color machine, there are a plurality of photoconductors 40. If the photoconductor on the most downstream side (photoconductor 40K in the present embodiment) is used as a reference, the distance from the photoconductor 40K to the transfer position A will be described. Since the length between them is the shortest compared to the length from the other photoconductors (40M, 40C, 40Y) to the transfer position A, in this embodiment, the most downstream photoconductor 40K is used as a reference. Suppose that Therefore, the electrostatic image formation start timing on the photoreceptor 40 is the electrostatic image formation start timing on the reference photoreceptor 40K. However, another photoconductor may be used as a reference.

  The conveyance control unit 72 is configured to convey the sheet at the measured timer value (passing timing) when the passage of the leading end of the sheet is detected and the preset ideal timing of passing the leading end of the sheet, that is, the conveying speed Vref. The predetermined position where the sheet passage sensor 71 is provided for the leading edge of the sheet to reach the transfer position A at the scheduled timing when the image formed on the photoreceptor 40 reaches the transfer position A of the secondary transfer device 22 A time difference Δt with respect to the timing at which to pass is calculated.

  The conveyance control unit 72 determines, based on the time difference Δt and the conveyance speed Vref, between the leading edge position of the sheet and the transfer position A at the scheduled timing when the image formed on the photoconductor 40 reaches the transfer position A of the secondary transfer device 22. An error Δd is predicted. Then, based on the prediction result, the conveyance control unit 72 increases the conveyance speed so that the error between the paper leading edge position and the transfer position A at the timing when the image reaches the transfer position A is 0 (zero). Alternatively, the driving of the conveying roller 70 is controlled so that the ratio of the conveying speed to the endless moving speed of the intermediate transfer belt 10 becomes a predetermined value until the sheet reaches the transfer position A (position control is performed). Do).

  Next, a case where the temperature in the image forming apparatus rises will be described. FIG. 4 is a diagram illustrating the front end position of the sheet when the temperature in the image forming apparatus rises and the diameter of the transport roller expands. When the temperature in the image forming apparatus (particularly the temperature around the conveyance roller 70) rises, the material of the conveyance roller 70 is thermally expanded, and the diameter D_rol of the conveyance roller 70 increases.

  For example, when the diameter of the conveyance roller 70 is increased by α times, the circumference of the conveyance roller having a relationship of π · D_rol is also increased (π · α · D_rol). Here, the drive speed of the transport roller 70 is controlled by keeping the transport roller rotation angular velocity constant based on the detection result of the transport roller rotation angular speed detection unit (not shown) that detects the rotation angular speed of the transport roller 70. If the method of controlling to the predetermined target value Vref is taken, even if the conveyance roller rotation angular velocity is kept constant, the conveyance speed will be increased by the increase of the circumference by α times (α · Vref).

In this case, after the sheet reaches the conveyance roller 70, the sheet is conveyed at the conveyance speed α · Vref, and reaches a predetermined position (position of the sheet passage sensor 71) earlier by Δt in FIG. Further, if the position correction is not performed as it is, ΔL [= (α−1) · (L ₁ + L ₂ ) at the scheduled timing when the image reaches the transfer position A than the transfer position A of the secondary transfer device 22. ] Just go ahead.

  Here, the conveyance control unit 72 performs position correction by calculating the positional deviation Δd (= Vref · Δt) of the leading end of the sheet from the deviation Δt of the timing when the leading end of the sheet passes through the predetermined position. Since it is impossible to grasp that the conveyance speed is increased due to the thermal expansion of the sheet, the leading edge position of the sheet and the position of the image are shifted by d_error = ΔL−Δd.

  Therefore, in the image forming apparatus of the present embodiment, the position error of the paper passage sensor is corrected when the temperature in the image forming apparatus rises and the diameter of the transport roller expands. FIG. 5 is an explanatory diagram of a method for moving the sheet passage sensor for correcting a position error when the temperature in the image forming apparatus rises and the diameter of the conveying roller expands.

In order to set the above d_error = ΔL−Δd to 0 (zero), the position correction amount in the conveyance control unit 72 is set to ΔL [= (α−1) · (L ₁ + L ₂ )]. It will be good. If the value of the conveyance speed (Vref) used for the position correction by the conveyance control unit 72 is not changed, the apparent position can be obtained by moving the position of the paper passage sensor 71 from a predetermined position (movement amount: d_adj). In addition, there can be considered a method in which the leading edge of the sheet passes through a predetermined position early. At this time, the time difference from the ideal timing is Δt ′.

△Ｌ：用紙を搬送速度α・Ｖrefで搬送した場合の予定タイミングにおける用紙先端位置と転写位置Ａの距離
△ｄ´：用紙を搬送速度α・Ｖrefで搬送した場合の理想タイミングにおける用紙先端位置と所定位置の距離
Ｖref：用紙の搬送速度
α：搬送ローラ７０の熱膨張倍数
Ｌ₁：転写位置Ａと所定位置との距離
Ｌ₂：所定位置と搬送ローラ７０との距離
△ｔ：用紙を搬送速度α・Ｖrefで搬送した場合の用紙先端位置が所定位置を通過するタイミングと理想タイミングとの差 The amount of movement d_adj from the predetermined position of the sheet passage sensor 71 for generating the time difference Δt ′ from the ideal timing can be calculated from the following relational expressions (Expression 1) to (Expression 4).

ΔL: distance between the leading edge position and the transfer position A at the scheduled timing when the sheet is conveyed at the conveying speed α · Vref Δd ′: the leading edge position at the ideal timing when the sheet is conveyed at the conveying speed α · Vref Distance of predetermined position Vref: Paper conveyance speed α: Thermal expansion multiple of conveyance roller L ₁ : Distance between transfer position A and predetermined position L ₂ : Distance between predetermined position and conveyance roller 70 Δt: Paper conveyance speed The difference between the ideal timing and the timing when the leading edge of the paper passes the specified position when transported with α ・ Vref

From the above relational expressions (Expression 1) to (Expression 4), when the movement amount d_adj is solved, the following relational expression (Expression 5) is obtained.

Further, when the linear expansion coefficient of the transport roller 70 is a and the change amount of the ambient temperature of the transport roller 70 is ΔT ₁ , the thermal expansion multiple α of the transport roller 70 is expressed by the following (formula 6).

  Similarly to the thermal expansion of the transport roller 70, in the image forming apparatus of the present embodiment, the endless moving speed of the intermediate transfer belt 10 is increased by the temperature of the image forming apparatus rising and the diameter of the drive roller 9 expanding. The position error of the sheet passage sensor 71 is corrected when the timing at which the image reaches the transfer position becomes earlier. FIG. 6 shows the correction of the position error when the temperature inside the image forming apparatus rises and the endless moving speed of the intermediate transfer belt is increased due to the expansion of the diameter of the driving roller and the timing at which the image reaches the transfer position is advanced. It is explanatory drawing of the movement method of the paper passage sensor for doing.

  Similarly to the conveyance roller 70, the driving roller 9 of the intermediate transfer belt 10 is heated when the temperature in the image forming apparatus (particularly the ambient temperature of the driving roller 9 that moves the intermediate transfer belt 10) increases. The diameter D_belt of the driving roller expands due to expansion.

  For example, when the diameter of the drive roller 9 is increased by a factor of β, the circumference of the drive roller having a relationship of π · D_belt is also increased (π · β · D_belt). Here, drive control of the drive roller 9 is performed by a drive roller rotation angular velocity detection unit (not shown) that detects the rotation angular velocity of the drive roller by drive control of the drive force transmission unit by an intermediate transfer belt drive control unit (not shown). If the method of controlling the endless moving speed of the intermediate transfer belt 10 to the predetermined target value Vref_belt by keeping the driving roller rotational angular velocity constant based on the detection result, the driving roller rotational angular velocity was kept constant. However, the endless moving speed is increased by the increase of the circumference by β times (β · Vref_belt).

  In this case, the image reaches the transfer position A of the secondary transfer device 22 earlier by Δt in the figure. Even if the paper is being transported at the transport speed target value Vref, at the timing when the image reaches the transfer position A of the secondary transfer device 22, the front end of the paper is the transfer position A by ΔL (= Vref · Δt). Located on the side of the conveying roller 70.

  Therefore, as in FIG. 5, if the position correction amount in the transport control unit 72 is ΔL, the position error can be set to 0 (zero). Assuming that the sheet is conveyed at the conveyance speed target value Vref, as shown in FIG. 6, the timing at which the sheet passes through the position of the sheet passage sensor 71 is delayed by the time Δt that the image quickly reaches the transfer position A. As described above, by moving the position of the sheet passage sensor 71 from the predetermined position (movement amount: d_adj), the position correction amount in the transport control unit 72 can be set to ΔL.

△Ｌ：中間転写ベルトを無端移動速度β・Ｖrefで移動した場合に画像が転写位置Ａに到達するタイミングに搬送速度Ｖrefで搬送した用紙の用紙先端位置と転写位置Ａの距離
Ｖref：搬送速度
△ｔ：中間転写ベルトを無端移動速度β・Ｖrefで移動した場合に画像が転写位置Ａに到達するタイミングと予定タイミングとの差 The amount of movement d_adj from the predetermined position of the sheet passage sensor 71 at this time can be calculated from the following relational expression (Expression 7).

ΔL: Distance between the leading edge position of the sheet conveyed at the conveyance speed Vref at the timing when the image reaches the transfer position A when the intermediate transfer belt is moved at the endless movement speed β · Vref Vref: the conveyance speed Δ t: Difference between the timing at which the image reaches the transfer position A and the scheduled timing when the intermediate transfer belt is moved at the endless moving speed β · Vref

Ｌ_belt：感光体４０Ｋから中間転写ベルト１０にトナー像を転写する一次転写の位置から二次転写装置２２の転写位置Ａの長さ
Ｖref_belt：中間転写ベルト１０の無端移動速度
β：駆動ローラ９の熱膨張倍数 Here, the direction in which the position of the paper passage sensor 71 is moved is opposite to the direction in FIG. Further, the time Δt for the image to reach the transfer position A of the secondary transfer device 22 quickly because the peripheral length of the drive roller 9 is extended and the endless moving speed is increased is expressed by the following relational expression (formula 8). It can be calculated from

L_belt: length of the transfer position A of the secondary transfer device 22 from the primary transfer position at which the toner image is transferred from the photoreceptor 40K to the intermediate transfer belt 10 Vref_belt: endless moving speed of the intermediate transfer belt 10 β: heat of the driving roller 9 Expansion factor

Then, by substituting the relational expression (Expression 8) for Δt into Δt in the relational expression for d_adj (Expression 7), d_adj is expressed by the following relational expression (Expression 9).

Further, when the linear expansion coefficient of the drive roller 9 is b and the change in the ambient temperature of the drive roller 9 is ΔT ₂ , the thermal expansion multiple β of the drive roller 9 is expressed by the following (Equation 10).

  Here, a method of driving control of the intermediate transfer belt will be described. FIG. 7 is a schematic diagram of an intermediate transfer belt drive control system in the prior art. The method of driving control of the intermediate transfer belt is described in, for example, Japanese Patent Application Laid-Open No. 2006-139217 and Japanese Patent Application Laid-Open No. 2006-160512. As shown in FIG. 7, two marks are formed on the intermediate transfer belt 1000 ( (Or two or more) mark sensors 1001 detect the endless moving speed of the intermediate transfer belt 1000 with high accuracy without being affected by the expansion and contraction of the intermediate transfer belt 1000, and control the intermediate transfer belt 1000 with high accuracy. There is also a method. In this case, since the expansion / contraction amount of the intermediate transfer belt 1000 is corrected based on the length of the interval between the two (or more) mark sensors 1001, if the interval between the mark sensors 1001 is thermally expanded, The endless moving speed of the transfer belt 1000 cannot be detected correctly, and the controlled endless moving speed of the intermediate transfer belt 1000 also has a deviation from the target speed. Japanese Patent Application Laid-Open No. 2008-51801 describes a method of suppressing the thermal expansion amount of the length of the sensor interval.

このように、中間転写ベルトの駆動制御方法によって、上記のd_adjの関係式のβをγで置き換えることができる。 Here, when the length L_sens of the interval between the mark sensors 1001 is γ times, the endless moving speed of the intermediate transfer belt 1000 is also γ times (γ · Vref_belt). Assuming that the linear expansion coefficient of the sensor fixing member fixing two (or two or more) mark sensors 1001 is c and the change in ambient temperature of the sensor fixing member is ΔT ₃ , γ is expressed by )become that way.

In this way, β in the relational expression of d_adj can be replaced with γ by the intermediate transfer belt drive control method.

  Next, in the image forming apparatus according to the present embodiment, when the temperature in the image forming apparatus rises and the conveyance speed and the endless moving speed of the intermediate transfer belt increase, the position error of the paper passage sensor is corrected. Yes. FIG. 8 is an explanatory diagram of a sheet passing sensor moving method for correcting a position error when the temperature in the image forming apparatus rises and the conveying speed and the endless moving speed of the intermediate transfer belt increase. In particular, a case will be described in which the influence due to the increase in the endless moving speed of the intermediate transfer belt is large.

  When both the conveying speed and the endless moving speed of the intermediate transfer belt are increased, the influences of the respective movements cancel each other, and the shift between the position of the image and the leading edge of the sheet becomes smaller than the influence of each of them. Further, by moving the paper passage sensor 71 by Δd ′ in the figure from the predetermined position to the transfer position A side, the position correction amount in the transport control unit 72 is set to 0 (zero) for the reason described above. Therefore, it is possible to further bring out the effect of canceling each other due to the increase in the conveyance speed. However, if the influence of the increase in the endless moving speed of the intermediate transfer belt is great, the image and the leading edge of the sheet still remain (Δd "in the figure).

  Therefore, the position of the paper passage sensor 71 is further moved by Δd ′ ″ so as to delay the paper detection timing of the paper passage sensor 71 by the time required to move Δd ″ by the target value Vref of the conveyance speed. Thus, the position correction amount in the conveyance control unit 72 can be set to Δd ″, and the deviation between the position of the image and the front end of the sheet can be set to 0 (zero).

Here, the total amount d_adj of the movement amount of the sheet passing sensor 71 from the predetermined position can be calculated from the following relational expressions (Expression 12) to (Expression 15).

From the above relational expressions (Expression 12) to (Expression 15), the total movement amount d_adj is obtained as the following relational expression (Expression 16).

The intermediate transfer belt 10 obtained in the description of FIG. 6 is d_adj_paper, which is the amount of movement to move the paper passage sensor 71 so as to cancel the position error when only the conveyance speed is increased, which is obtained in the explanation of FIG. Assuming that d_adj_belt is the amount of movement by which the sheet passage sensor 71 is moved so as to cancel out the position error when only the endless moving speed of the intermediate transfer belt 10 becomes d_adj_belt, The amount of movement d_adj of the sheet passing sensor 71 required to cancel the position error when the influence due to the increase in the endless moving speed of the intermediate transfer belt 10 is large is expressed by the following (Equation 17).

Further, when the influence due to the increase in the conveyance speed is large, the movement amount d_adj of the sheet passage sensor 71 necessary for canceling the position error is obtained in the same manner as (Equation 18) below.

  Next, a mechanism for moving the position of the paper passage sensor 71 will be described. FIG. 9 is an explanatory diagram showing an example in which a paper passage sensor fixing member is used as a mechanism for moving the position of the paper passage sensor.

  The paper passage sensor fixing member 73 fixes the paper passage sensor 71 to a support member (not shown) such as a housing of the image forming apparatus by fixing the paper passage sensor 71. Specifically, the detection position of the paper passage sensor 71 is parallel to the paper conveyance direction in accordance with the change in the external dimension (length) in the direction parallel to the paper conveyance direction due to the thermal expansion of the paper passage sensor fixing member 73. The paper passage sensor 71 is fixed to a support member such as a housing of the image forming apparatus via the paper passage sensor fixing member 73 so as to move in a proper direction.

ｘ：用紙通過センサ固定部材７３の線膨張係数
ｌ：用紙通過センサ固定部材７３の支持部材との固定位置７３ａと用紙通過センサ７１の検出位置の長さ The fixing position 73a of the sheet passing sensor fixing member 73 to the support member such as the housing of the image forming apparatus is shifted to the downstream side or the upstream side in the direction parallel to the sheet conveying direction with respect to the detection position of the sheet passing sensor 71. Position. Depending on the combination of thermal expansion of each component, the same position as the detection position of the paper passage sensor 71 may be used for the direction component parallel to the paper conveyance direction. The selection of fixing the fixing position 73a of the sheet passage sensor fixing member 73 to the support member to either the upstream side or the downstream side is based on the degree of influence of the error of the conveyance speed and the error of the endless moving speed of the intermediate transfer belt 10. To do. Further, the moving amount d_adj of the position of the paper passage sensor 71 is expressed by the following (Equation 19) when the ambient temperature of the paper passage sensor fixing member 73 is ΔT ₁ ′.

x: Linear expansion coefficient of the paper passage sensor fixing member 73 l: Length of the fixing position 73a of the paper passage sensor fixing member 73 with the support member and the detection position of the paper passage sensor 71

Further, since the positions of the transport roller 70 and the paper passage sensor fixing member 73 are relatively close, ΔT ₁ ≈ΔT ₁ ′ may be set. Note that ΔT ₁ is the amount of change in the ambient temperature of the conveyance roller 70.

  Next, another mechanism for moving the position of the paper passage sensor 71 will be described. FIG. 10 is an explanatory diagram illustrating an example in which an opening forming member is used as a mechanism for moving the position of the paper passage sensor.

  The paper passage sensor 71 is a transmissive optical sensor 710 in which a light emitting unit 711 that projects parallel light and a light receiving unit 712 that outputs an electric signal corresponding to the amount of light received by receiving light are opposed to each other. is there. In the case of this transmissive sensor, the passage of the front end of the paper is detected from the change in the amount of light received by the light receiving portion 712 due to the paper blocking light from the light emitting portion 711.

  The opening forming member 74 has an opening 74 b that allows only a part of the light from the light emitting part 711 to pass to the light receiving part 712 side. The opening forming member 74 is fixed to a support member such as a casing of the image forming apparatus so that the opening 74 b is disposed on the optical path of the paper passage sensor 71. Further, the opening forming member 74 causes the detection position of the paper passage sensor 71 to be parallel to the paper transport direction in accordance with the position change of the opening 74b in the direction parallel to the paper transport direction due to the thermal expansion of the opening forming member 74. It is fixed to a support member such as a casing of the image forming apparatus so as to move in the direction.

ｙ：開口部形成部材７４の線膨張係数
ｌ：開口部形成部材７４の支持部材との固定位置７４ａと開口部７４ｂ（用紙通過センサの検出位置）の長さ The fixing position 74a of the opening forming member 74 to the support member such as the housing of the image forming apparatus is shifted to the downstream side or the upstream side in the direction parallel to the paper transport direction with respect to the detection position of the paper passage sensor 71. Position. Depending on the combination of thermal expansion of each component, the same position as the detection position of the paper passage sensor 71 may be used for the direction component parallel to the paper conveyance direction. The selection of fixing the fixing position 74a of the opening forming member 74 to the support member to either the upstream side or the downstream side depends on the degree of influence of the error of the conveyance speed and the error of the endless moving speed of the intermediate transfer belt 10. Do. Further, the moving amount d_adj of the position of the paper passage sensor 71 is expressed by the following (Equation 20) when the ambient temperature of the opening forming member 74 is ΔT ₁ ″.

y: Linear expansion coefficient of the opening forming member 74 l: Length of the fixing position 74a of the opening forming member 74 and the opening 74b (detection position of the paper passage sensor) with the support member

Further, since the positions of the conveying roller 70 and the opening forming member 74 are relatively close, ΔT ₁ ≈ΔT ₁ “may be set. This ΔT ₁ is a change in the ambient temperature of the conveying roller 70. Amount.

  Further, another mechanism for moving the position of the paper passage sensor 71 will be described. FIG. 11 is an explanatory diagram illustrating another example in which an opening forming member is used as a mechanism for moving the position of the paper passage sensor.

  The paper passage sensor 71 is a transmissive optical sensor in which a light emitting unit that projects parallel light and a light receiving unit that outputs an electric signal according to the amount of light received by receiving the light are opposed to each other, or a reflective type This is an optical sensor. In the case of a transmissive optical sensor, the passage of the leading edge of the paper is detected from the change in the amount of light received by the light receiving portion due to the light from the light emitting portion being blocked by the paper. In the case of a reflection type optical sensor, the passage of the leading edge of the paper is detected from the change in the amount of light received by the light receiving part due to the reflection of the light from the light emitting part.

The first opening forming member 75 has a rectangular opening 75b that allows only a part of the light from the light emitting part to pass to the light receiving part side, and the second opening forming member 76 is for the light from the light emitting part. It has a rectangular opening 76b that allows only a part of the light to pass to the light receiving unit.
In addition, the first opening forming member 75 and the second opening forming member 76 are arranged so that the respective openings 75b and 76b overlap with each other on the optical path of the paper passage sensor 71, and light from the light emitting part is transmitted through the respective openings. It is fixed to a support member such as a casing of the image forming apparatus so as to pass through 75b and 76b and reach the light receiving unit.

  The first opening forming member 75 and the second opening forming member 76 are fixed at positions shifted in a direction perpendicular to the sheet transport direction in a plane parallel to the sheet surface, and each opening 75b, 76b is formed such that the direction perpendicular to the sheet conveying direction from the fixing positions 75a and 76a of the first opening forming member 75 and the support member of the second opening forming member 76 is reversed.

  The rectangular opening 75b of the first opening forming member 75 is provided such that a line parallel to the long side of the opening 75b intersects with a line parallel to the paper transport direction at an angle θ other than a right angle. The rectangular opening 76b of the second opening forming member 76 has a shape inverted with respect to a plane perpendicular to the sheet surface and parallel to the sheet conveyance direction. Thereby, the position change of the opening in the direction perpendicular to the sheet conveying direction due to the thermal expansion of the first opening forming member 75 and the second opening forming member 76 (the moving directions of the respective openings 75b and 76b are opposite to each other). Accordingly, the position where the respective openings 75b and 76b intersect moves in a direction parallel to the paper transport direction, thereby moving the detection position of the paper passage sensor 71 in a direction parallel to the paper transport direction.

ｚ：第１開口部形成部材７５と第２開口部形成部材７６の線膨張係数
ｌ：第１開口部形成部材７５と第２開口部形成部材７６の支持部材との固定位置７５ａ、７５ｂと検出位置の長さ（用紙搬送方向と直角な方向成分） The amount of movement d_adj of the detection position of the paper passage sensor 71 is approximately expressed by the following (formula 21) when the ambient temperature of the opening forming members 75 and 76 is ΔT ₁ ″ ″.

z: Linear expansion coefficient of the first opening forming member 75 and the second opening forming member 76 l: Fixing positions 75a and 75b between the first opening forming member 75 and the support member of the second opening forming member 76 and detection Position length (direction component perpendicular to the paper transport direction)

Further, since the positions of the transport roller 70, the first opening forming member 75, and the second opening forming member 76 are relatively close, ΔT ₁ ≈ΔT ₁ '''may be set. Note that ΔT ₁ is the amount of change in the ambient temperature of the conveyance roller 70.

  As described above, the image forming apparatus according to the present embodiment is based on a change in the sheet conveying speed due to the expansion of the conveying roller 70 in the image forming apparatus and a change in the endless moving speed of the intermediate transfer belt 10 due to the expansion of the driving roller 9. Thus, by moving the position of the paper passage sensor 71 in a direction parallel to the paper conveyance direction, the timing at which the paper passes a predetermined position can be apparently shifted. As a result, the conveyance control unit 72 corrects the conveyance speed and position of the sheet based on the apparent timing shift, and therefore “the toner image and the sheet reach the transfer position due to the environmental change in the image forming apparatus. Relative timing shift ”can be suppressed.

  Further, as described above, the sheet is passed through the members (the sheet passing sensor fixing member 73, the opening forming member 74, the first opening forming member 75, and the second opening forming member 76) that fix the sheet passing sensor 71. By fixing the passage sensor 71 to the housing or the like of the image forming apparatus, the thermal expansion of the member that fixes the sheet passage sensor 71 can be used as a force for moving the sheet passage sensor 71. It is possible to cancel the “deviation of relative timing at which the toner image and the paper reach the transfer position” due to the environmental change.

DESCRIPTION OF SYMBOLS 1 Apparatus body 2 Paper feed table 3 Scanner 4 Automatic document feeder (ADF)
DESCRIPTION OF SYMBOLS 9 Drive roller 10 Intermediate transfer belt 15 Drive roller 16 Drive roller 17 Cleaning device 18 Image forming unit 20 Transfer device 21 Exposure device 22 Secondary transfer device 23 Roller 24 Secondary transfer belt 25 Fixing device 26 Fixing belt 27 Pressure roller 28 Paper Inversion device 30 Document table 32 Contact glass 33 First traveling body 34 Second traveling body 35 Imaging lens 36 Sensor 40 (40Y, 40C, 40M, 40K) Photosensitive body 42 Paper feed roller 43 Paper bank 44 Paper feed cassette 45 Separating roller 46 paper feed path 47 transport roller 48 paper feed path 49 registration roller 50 paper feed roller 51 tray 52 separation roller 53 paper feed path 55 switching claw 56 discharge roller 57 paper discharge tray 60 charging device 61 developing device 62 primary transfer roller 63 photoconductor Cleaning device 64 Static eliminator 70 Conveying roller 71 Paper passage sensor 72 Conveyance control unit 73 Paper passage sensor fixing member 73a Fixed position 74 Opening portion forming member 74a Fixed position 74b Opening portion 75 First opening forming member 75a Fixed position 75b Opening portion 76 Second Opening forming member 76b Opening 710 Optical sensor 711 Light emitting part 712 Light receiving part

JP 2000-238931 A JP 2000-351472 A JP 2007-206406 A

Claims (19)

An image forming means for forming an image;
An image formed by the image forming means is transferred to the surface, and an image carrier that moves endlessly;
Transfer means for transferring an image on the image carrier onto a sheet at a transfer position;
Conveying means for conveying the sheet to a transfer position of the transfer means;
A paper passage detection means that is in a predetermined position between the transfer means and the transport means and detects the passage of the leading edge of the paper;
The ideal timing for passing the leading edge of the paper is the timing at which the leading edge of the paper should pass through the predetermined position in order for the leading edge of the paper to reach the transfer position at the scheduled timing when the image formed by the image forming means reaches the transfer position of the transferring means. Setting means preset as:
A measurement timing that is a timing at which the leading edge of the sheet passes through the predetermined position based on a detection result of the sheet passage detection unit by controlling the conveying unit to convey the sheet to a transfer position at a predetermined predetermined conveyance speed. When the paper is transported at the transport speed, a time difference between the measurement timing and the ideal timing is obtained, and an error between the time difference and the transfer speed of the front end position of the paper at the scheduled timing is determined from the transport speed. Based on the prediction result, the conveyance speed is changed so that the error from the transfer position of the front end position of the paper at the scheduled timing becomes zero, and the conveyance speed is set in advance until the paper reaches the transfer position. A transport control means for controlling a paper transport operation of the transport means so as to have a predetermined speed;
A paper passage detection position moving means for moving the detection position of the paper passage detection means from the predetermined position in a direction parallel to the paper transport direction in response to a temperature change in the image forming apparatus;
An image forming apparatus comprising:   The paper passage detection position moving means is a paper passage detection means fixing member for fixing the paper passage detection means to a support member such as a casing of the image forming apparatus, and the paper due to thermal expansion of the paper passage detection means fixing member. The paper passage through the paper passage detection means fixing member is moved so that the detection position of the paper passage detection means is moved in a direction parallel to the paper conveyance direction in accordance with a change in the outer dimension in a direction parallel to the conveyance direction. The image forming apparatus according to claim 1, wherein the detection unit is fixed to a support member such as a casing of the image forming apparatus.   The paper passage detection means fixing member is a position shifted to a direction component parallel to the paper conveyance direction with respect to the detection position of the paper passage detection means fixed to the paper passage detection means fixing member, and downstream of the paper conveyance direction. The image forming apparatus according to claim 2, wherein the image forming apparatus is fixed to a support member such as a casing of the image forming apparatus on the side.   The paper passage detection means fixing member is a position shifted to a direction component parallel to the paper conveyance direction with respect to the detection position of the paper passage detection means fixed to the paper passage detection means fixing member, and upstream of the paper conveyance direction. The image forming apparatus according to claim 2, wherein the image forming apparatus is fixed to a support member such as a casing of the image forming apparatus on the side. The transport means includes a pair of transport rollers that transport by sandwiching and rotating the paper,
The conveyance control unit includes a conveyance roller rotation angular velocity detection unit that detects a rotation angular velocity of the conveyance roller, and controls the conveyance speed to a predetermined target value based on a detection result of the conveyance roller rotation angular velocity detection unit,
The first factor that determines the amount of thermal expansion of the transport roller, the length between the pair of transport rollers and the transfer position, and the second factor that determines the amount of thermal expansion of the paper passage detection means fixing member are the heat of the transport roller. 4. The image forming apparatus according to claim 3, wherein the image forming apparatus is set to a combination that cancels a deviation in timing at which the paper reaches the transfer position due to a paper conveyance speed error due to a change in diameter due to expansion. The image carrier is an endless belt stretched around a plurality of rollers,
One roller in the plurality of rollers is a driving roller that moves the endless belt endlessly,
Driving force transmitting means for transmitting a driving force to the driving roller;
Drive roller rotation angular velocity detection means for detecting the rotation angular velocity of the drive roller;
Image carrier drive control means for driving and controlling the drive force transmission means so that the endless moving speed of the image carrier becomes a predetermined speed based on the detection result of the drive roller rotation angular velocity detection means,
A third factor that determines the amount of thermal expansion of the drive roller, a distance between a position at which an image is transferred from the image forming unit to the image carrier, and a position at which the image is transferred to a sheet by the transfer unit; The two factors are set in such a combination that cancels the deviation in the timing at which the image due to the endless moving speed error of the image carrier due to the change in diameter due to the thermal expansion of the driving roller reaches the transfer position. The image forming apparatus according to claim 4. The transport means includes a pair of transport rollers that transport by sandwiching and rotating the paper,
The conveyance control unit includes a conveyance roller rotation angular velocity detection unit that detects a rotation angular velocity of the conveyance roller, and controls the conveyance speed to a predetermined target value based on a detection result of the conveyance roller rotation angular velocity detection unit,
The image carrier is an endless belt stretched around a plurality of rollers,
One roller in the plurality of rollers is a driving roller that moves the endless belt endlessly,
Driving force transmitting means for transmitting a driving force to the driving roller;
Drive roller rotation angular velocity detection means for detecting the rotation angular velocity of the drive roller;
Image carrier drive control means for driving and controlling the drive force transmission means so that the endless moving speed of the image carrier becomes a predetermined speed based on the detection result of the drive roller rotation angular velocity detection means,
The second factor is due to a shift in the timing at which the paper reaches the transfer position due to a paper conveyance speed error due to a change in diameter due to thermal expansion of the transport roller, and a change in diameter due to thermal expansion of the drive roller. 5. The image forming apparatus according to claim 3, wherein the image forming apparatus is set to a combination that cancels out a difference in timing at which an image caused by an endless moving speed error of the image carrier reaches a transfer position. .   A length between the pair of conveying rollers and a transfer position, a distance between a position at which an image is transferred from the image forming unit to the image carrier and a transfer position of an image onto a sheet by the transfer unit, and the first Factor and the third factor are the difference in timing at which the paper reaches the transfer position due to the conveyance speed error of the paper due to the change in diameter due to the thermal expansion of the conveyance roller, and the diameter due to the thermal expansion of the driving roller. 8. The image processing apparatus according to claim 7, wherein the image carrier is set to include a combination that cancels out a difference in timing at which an image due to an endless moving speed error of the image carrier due to a change in the position reaches a transfer position. Image forming apparatus. The transport means includes a pair of transport rollers that transport by sandwiching and rotating the paper,
The conveyance control unit includes a conveyance roller rotation angular velocity detection unit that detects a rotation angular velocity of the conveyance roller, and controls the conveyance speed to a predetermined target value based on a detection result of the conveyance roller rotation angular velocity detection unit,
The image carrier is an endless belt provided with a plurality of marks that are spanned by a plurality of rollers and that are continuous at a predetermined interval in the endless movement direction.
One roller in the plurality of rollers is a driving roller that moves the endless belt endlessly,
Driving force transmitting means for transmitting a driving force to the driving roller;
First endless movement detecting means for outputting a signal corresponding to the presence or absence of a mark due to endless movement of the endless belt by detecting a plurality of marks provided on the endless belt;
By detecting a plurality of marks provided on the endless belt, a signal corresponding to the presence / absence of a mark due to endless movement of the endless belt is output, and the first endless movement detecting means outputs the signal of the endless belt. A second endless movement detecting means installed at a predetermined distance in the endless movement direction,
The first endless movement detection means and the second endless movement detection means are fixed by an endless movement detection means fixing member which is the same fixing member,
Based on the signal output from the first endless movement detection means and the second endless movement detection means, and the value of the predetermined distance between the first endless movement detection means and the second endless movement detection means A speed / position control means for performing drive control of the drive force transmission means, thereby performing speed control or position control of the endless belt,
The length between the conveying roller pair and the transfer position, the first factor, the second factor, the position at which the image is transferred from the image forming means to the image carrier, and the image on the paper by the transfer means The fourth factor that determines the thermal expansion amount of the distance between the transfer positions and the distance between the first endless movement detection means and the second endless movement detection means is a change in diameter due to the thermal expansion of the transport roller. The endlessness of the image carrier due to the deviation of the timing at which the sheet reaches the transfer position due to the sheet conveyance speed error due to the thermal expansion of the distance between the first endless movement detection means and the second endless movement detection means The image forming apparatus according to claim 3, wherein the image forming apparatus is set to include a combination that cancels out a difference in timing at which an image caused by a moving speed error reaches a transfer position. The paper passage detection means is a transmission type or reflection type in which a light emitting unit that projects parallel light and a light receiving unit that outputs an electric signal corresponding to the amount of light received by facing the light are arranged to face each other. In the case of the transmissive type, the light receiving unit changes the amount of light received by the light receiving unit when the paper blocks the light from the light emitting unit. In the case of the reflective type, the light receiving unit reflects the light from the light emitting unit. Detects the passage of the leading edge of the paper from the change in the amount of received light,
The paper passage detection position moving means is an opening forming member having an opening through which only a part of light from the light emitting part passes to the light receiving part side, and the opening on the optical path of the paper passage detection means And is fixed to a support member such as a casing of the image forming apparatus so that the opening portion is disposed, and further, the opening portion in a direction parallel to the paper conveyance direction due to thermal expansion of the opening portion forming member. The opening forming member is fixed to a support member such as a casing of the image forming apparatus so that the detection position of the paper passage detection means is moved in a direction parallel to the paper transport direction in accordance with a change in position. The image forming apparatus according to claim 1. The paper passage detecting means is a reflection type optical sensor in which a light emitting unit that projects parallel light and a light receiving unit that outputs an electric signal corresponding to the amount of light received by receiving the light face each other. A reflection member that reflects the light from the light emitting part to the light receiving part, and detects the passage of the front end of the paper from the change in the amount of light received by the light receiving part due to the light blocking the light from the light emitting part,
The paper passage detection position moving means is an opening forming member having an opening through which only a part of light from the light emitting part passes to the light receiving part side, and the opening on the optical path of the paper passage detection means And is fixed to a support member such as a casing of the image forming apparatus so that the opening portion is disposed, and further, the opening portion in a direction parallel to the paper conveyance direction due to thermal expansion of the opening portion forming member. The opening forming member is fixed to a support member such as a casing of the image forming apparatus so that the detection position of the paper passage detection means is moved in a direction parallel to the paper transport direction in accordance with a change in position. The image forming apparatus according to claim 1.   The opening forming member is a position shifted to a direction component parallel to the paper transport direction with respect to the position of the opening, and is fixed to a support member such as a casing of the image forming apparatus on the downstream side in the paper transport direction. The image forming apparatus according to claim 10, wherein the image forming apparatus is an image forming apparatus.   The opening forming member is a position shifted to a direction component parallel to the paper transport direction with respect to the position of the opening, and is fixed to a support member such as a casing of the image forming apparatus on the upstream side in the paper transport direction. The image forming apparatus according to claim 10, wherein the image forming apparatus is an image forming apparatus. The paper passage detection means is a transmission type or reflection type in which a light emitting unit that projects parallel light and a light receiving unit that outputs an electric signal corresponding to the amount of light received by facing the light are arranged to face each other. In the case of the transmissive type, the light receiving unit changes the amount of light received by the light receiving unit when the paper blocks the light from the light emitting unit. In the case of the reflective type, the light receiving unit reflects the light from the light emitting unit. Detects the passage of the leading edge of the paper from the change in the amount of received light,
The paper passage detection position moving means includes a first opening forming member having a rectangular opening that allows only part of the light from the light emitting part to pass to the light receiving part, and one of the light from the light emitting part. A second opening forming member having a rectangular opening that allows only the part to pass to the light receiving part side,
The first opening forming member and the second opening forming member are arranged so that the respective openings overlap each other on the optical path of the paper passage detecting means, and the light from the light emitting part passes through each opening. Is fixed to a support member such as a casing of the image forming apparatus so as to reach the light receiving unit.
The first opening forming member and the second opening forming member are further fixed at positions shifted in a direction perpendicular to the paper transport direction in a plane parallel to the surface of the paper. It is formed so that the direction perpendicular to the paper transport direction from the fixed position with the support member of the part forming member is reversed,
The rectangular opening of the first opening forming member is provided such that a line parallel to the long side of the opening intersects with a line parallel to the paper transport direction at an angle other than a right angle.
The rectangular opening of the second opening forming member has a shape that is inverted with respect to a plane that is perpendicular to the plane of the sheet and parallel to the sheet conveyance direction,
As the position of the opening changes in a direction perpendicular to the paper transport direction due to thermal expansion of the first opening forming member and the second opening forming member, the position where each opening intersects is the paper transport direction. 2. The image forming apparatus according to claim 1, wherein the detection position of the paper passage detection means is moved in a direction parallel to the paper transport direction by moving in a direction parallel to the paper transport direction. The transport means includes a pair of transport rollers that transport by sandwiching and rotating the paper,
The conveyance control unit includes a conveyance roller rotation angular velocity detection unit that detects a rotation angular velocity of the conveyance roller, and controls the conveyance speed to a predetermined target value based on a detection result of the conveyance roller rotation angular velocity detection unit,
The first factor, the fifth factor that determines the length between the conveying roller pair and the transfer position, and the amount of thermal expansion of the opening forming member, or the first opening forming member and the second opening forming member The sixth factor that determines the amount of thermal expansion of the sheet is set to a combination that cancels the deviation of the timing at which the sheet reaches the transfer position due to the sheet conveyance speed error due to the change in diameter due to the thermal expansion of the conveyance roller. The image forming apparatus according to claim 12, wherein the image forming apparatus is an image forming apparatus. The image carrier is an endless belt stretched around a plurality of rollers,
One roller in the plurality of rollers is a driving roller that moves the endless belt endlessly,
Driving force transmitting means for transmitting a driving force to the driving roller;
Drive roller rotation angular velocity detection means for detecting the rotation angular velocity of the drive roller;
Image carrier drive control means for driving and controlling the drive force transmission means so that the endless moving speed of the image carrier becomes a predetermined speed based on the detection result of the drive roller rotation angular velocity detection means,
The third factor, the distance between the position at which the image is transferred from the image forming means to the image carrier and the transfer position of the image onto the sheet by the transfer means, the fifth factor, or the sixth factor. Is set in such a combination as to cancel the deviation in the timing at which the image due to the endless moving speed error of the image carrier due to the change in diameter due to the thermal expansion of the driving roller reaches the transfer position. The image forming apparatus according to claim 13 or 14. The transport means includes a pair of transport rollers that transport by sandwiching and rotating the paper,
The conveyance control unit includes a conveyance roller rotation angular velocity detection unit that detects a rotation angular velocity of the conveyance roller, and controls the conveyance speed to a predetermined target value based on a detection result of the conveyance roller rotation angular velocity detection unit,
The image carrier is an endless belt stretched around a plurality of rollers,
One roller in the plurality of rollers is a driving roller that moves the endless belt endlessly,
Driving force transmitting means for transmitting a driving force to the driving roller;
Drive roller rotation angular velocity detection means for detecting the rotation angular velocity of the drive roller;
Image carrier drive control means for driving and controlling the drive force transmission means so that the endless moving speed of the image carrier becomes a predetermined speed based on the detection result of the drive roller rotation angular velocity detection means,
As for the fifth factor or the sixth factor, the deviation of the timing at which the paper reaches the transfer position due to the paper transport speed error due to the change in the diameter due to the thermal expansion of the transport roller, and the thermal expansion of the drive roller. 15. The combination is set so as to cancel a difference in timing at which an image due to an endless moving speed error of the image carrier due to a change in diameter at a transfer position reaches a transfer position. The image forming apparatus according to any one of the above.   A length between the pair of conveying rollers and a transfer position, a distance between a position at which an image is transferred from the image forming unit to the image carrier and a transfer position of an image onto a sheet by the transfer unit, and the first Factor and the third factor are the difference in timing at which the paper reaches the transfer position due to the conveyance speed error of the paper due to the change in diameter due to the thermal expansion of the conveyance roller, and the diameter due to the thermal expansion of the driving roller. 18. The image processing apparatus according to claim 17, wherein the image carrier is set to include a combination that cancels out a difference in timing at which an image caused by an endless moving speed error of the image carrier due to a change in the position reaches a transfer position. Image forming apparatus. The transport means includes a pair of transport rollers that transport by sandwiching and rotating the paper,
The conveyance control unit includes a conveyance roller rotation angular velocity detection unit that detects a rotation angular velocity of the conveyance roller, and controls the conveyance speed to a predetermined target value based on a detection result of the conveyance roller rotation angular velocity detection unit,
The image carrier is an endless belt provided with a plurality of marks that are spanned by a plurality of rollers and that are continuous at a predetermined interval in the endless movement direction.
One roller in the plurality of rollers is a driving roller that moves the endless belt endlessly,
Driving force transmitting means for transmitting a driving force to the driving roller;
First endless movement detecting means for outputting a signal corresponding to the presence or absence of a mark due to endless movement of the endless belt by detecting a plurality of marks provided on the endless belt;
By detecting a plurality of marks provided on the endless belt, a signal corresponding to the presence / absence of a mark due to endless movement of the endless belt is output, and the first endless movement detecting means outputs the signal of the endless belt. A second endless movement detecting means installed at a predetermined distance in the endless movement direction,
The first endless movement detection means and the second endless movement detection means are fixed by an endless movement detection means fixing member which is the same fixing member,
Based on the signal output from the first endless movement detection means and the second endless movement detection means, and the value of the predetermined distance between the first endless movement detection means and the second endless movement detection means A speed / position control means for performing drive control of the drive force transmission means, thereby performing speed control or position control of the endless belt,
The length between the conveying roller pair and the transfer position, the first factor, the fifth factor, or the sixth factor, the position at which the image is transferred from the image forming means to the image carrier, and the transfer The distance between the transfer position of the image to the sheet by the means and the fourth factor are the timing of the arrival of the sheet due to the sheet conveyance speed error due to the change in diameter due to the thermal expansion of the conveyance roller. The difference between the deviation and the timing deviation of the image due to the endless movement speed error of the image carrier due to the thermal expansion of the distance between the first endless movement detection means and the second endless movement detection means The image forming apparatus according to claim 12, wherein the image forming apparatus is set to be included in a combination that cancels the image.

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