Sheet feeding device and imaging apparatus

Abstract

Disclosed are a sheet feeding device and an imaging device, wherein the sheet feeding device comprises: a first feeding roller pair; an upstream feeding roller pair; a downstream feeding roller pair; a second feeding roller pair; a first detecting portion; a second detecting portion; a third detecting portion; and a controller. The controller calculates a sheet feeding speed based on a first time and a first distance. The controller calculates a length of the sheet relative to a sheet feeding direction based on the sheet feeding speed, a second time, and a second distance. The controller controls a sheet feeding timing of the second feeding roller pair based on information on the length of the sheet.

Description

Technical Field

[0001] The present invention relates to a sheet feeding device for feeding a sheet and an image forming apparatus including the sheet feeding device. Background Art

[0002] Conventionally, there is an imaging device having a function of printing an image on both sides (two surfaces) of a sheet. In such an imaging device, in the case where an image is formed on both sides of a sheet, first, an image is formed on a first surface (front surface) of the sheet. After that, the sheet having an image formed on its first surface is reversed, and then, an image is formed on a second surface (back surface) of the sheet. Usually, a folding type is used as a type of reversing the front and back sides of a sheet. However, in the case of the folding type, a positional deviation of an image occurs between the front and back sides of the sheet having an image formed thereon with respect to the sheet feeding direction.

[0003] In Japanese Patent Application Laid-Open (JP-A) 2007-4137, after the sheet is folded back, in the sheet feeding path, an upstream feed roller pair and a downstream feed roller pair are arranged at different positions relative to the sheet feeding direction. In addition, a plurality of sensors are arranged between the upstream feed roller pair and the downstream feed roller pair and at different positions relative to the sheet feeding direction.

[0004] In addition, the sheet feeding speed is calculated by measuring the time in which the sheet fed by the feed roller passes through the plurality of sensors, and thus the length of the sheet relative to the sheet feeding direction is calculated. Thus, a configuration is disclosed in which an image on the second surface can be formed in accordance with the sheet length and thus the positional deviation between the front and back surfaces (front and back surfaces) of the sheet can be corrected.

[0005] However, in the above configuration, after the rear end of the sheet passes through the upstream feed roller pair, the rear end of the sheet is detected by the sensor. When entering the nip portion of the downstream feed roller pair, the fed sheet receives an impact, and thereby, the sheet feeding speed may be temporarily reduced. In this case, when calculating the sheet length relative to the sheet feeding direction, the calculation of the sheet length is affected by the change in the sheet feeding speed, and thereby, the sheet length changes, which causes a positional deviation between the images formed on the front and back sides of the sheet to occur. Summary of the invention

[0006] A main object of the present invention is to provide a sheet feeding device capable of reducing the degree of positional deviation occurring between images formed on the front and back sides of a sheet by accurately calculating the length of a sheet fed in the sheet feeding direction.

[0007] According to one aspect of the present invention, there is provided a sheet feeding device, comprising: a first feed roller pair, the first feed roller pair being rotatable in a sheet clamping state and configured to feed the sheet; an upstream feed roller pair, the upstream feed roller pair being arranged upstream of the first feed roller pair relative to a sheet feeding direction and configured to feed the sheet; a downstream feed roller pair, the downstream feed roller pair being arranged downstream of the first feed roller pair relative to the sheet feeding direction and configured to feed the sheet; a second feed roller pair, the second feed roller pair being arranged downstream of the downstream feed roller pair relative to the sheet feeding direction and configured to feed the sheet; a second feed roller pair a detection portion, the first detection portion being arranged at a first detection position downstream of the first feed roller pair and upstream of the downstream feed roller pair with respect to the sheet feeding direction, and being configured to detect the passage of the leading end portion of the sheet fed by the first feed roller pair; a second detection portion being arranged at a second detection position different from the first detection position downstream of the first feed roller pair and upstream of the downstream feed roller pair with respect to the sheet feeding direction, and being configured to detect the passage of the leading end portion of the sheet fed by the first feed roller pair; a third detection portion being arranged at a second detection position downstream of the first feed roller pair and upstream of the downstream feed roller pair with respect to the sheet feeding direction, and being configured to detect the passage of the leading end portion of the sheet fed by the first feed roller pair; and The sheet feeding direction is set at a third detection position upstream of the first feed roller pair and downstream of the upstream feed roller pair, and is configured to detect the passage of the rear end portion of the sheet fed by the first feed roller pair; and a controller, the controller is configured to perform calculations in response to signals from the first detection portion, the second detection portion and the third detection portion, wherein the controller calculates the sheet feeding speed based on a first time and a first distance between the first detection position and the second detection position relative to the sheet feeding direction, the first time being the time when the front end portion of the sheet passes the first detection position The controller calculates the length of the sheet relative to the sheet feeding direction based on the sheet feeding speed, the second time and the second distance between the second detection position and the third detection position relative to the sheet feeding direction, the second time being the difference between the moment when the front end portion of the sheet passes the second detection position and the moment when the rear end portion of the sheet passes the third detection position, and wherein the controller controls the sheet feeding timing of the second feeding roller pair based on information on the length of the sheet.

[0008] According to another aspect of the present invention, there is provided a sheet feeding device, comprising: a first feed roller pair, the first feed roller pair being rotatable in a sheet clamping state and configured to feed the sheet; an upstream feed roller pair, the upstream feed roller pair being arranged upstream of the first feed roller pair relative to a sheet feeding direction and configured to feed the sheet; a downstream feed roller pair, the downstream feed roller pair being arranged downstream of the first feed roller pair relative to the sheet feeding direction and configured to feed the sheet; a second feed roller pair, the second feed roller pair being arranged downstream of the downstream feed roller pair relative to the sheet feeding direction and configured to feed the sheet; a first detection portion, the first detection portion being arranged at the upstream of the first feed roller pair relative to the sheet feeding direction a first detecting portion disposed at a first detecting position upstream of the first feed roller pair and downstream of the upstream feed roller pair, and configured to detect the passage of the rear end portion of the sheet fed by the first feed roller pair; a second detecting portion disposed at a second detecting position different from the first detecting position upstream of the first feed roller pair and downstream of the downstream feed roller pair with respect to the sheet feeding direction, and configured to detect the passage of the rear end portion of the sheet fed by the first feed roller pair; a third detecting portion disposed at a third detecting position downstream of the first feed roller pair and upstream of the upstream feed roller pair with respect to the sheet feeding direction, and configured to detect the passage of the front end portion of the sheet fed by the first feed roller pair;and a controller configured to perform calculation in response to signals from the first detection portion, the second detection portion, and the third detection portion, wherein when the leading end portion of the sheet fed by the first feed roller pair is detected by the third detection portion, the trailing end portion of the sheet passes through the upstream feed roller pair, and wherein when the trailing end portion of the sheet fed by the first feed roller pair is detected by the first detection portion and the second detection portion, the leading end portion does not reach the downstream feed roller pair, wherein the controller calculates a sheet feeding speed based on a first time and a first distance between the first detection position and the third detection position relative to the sheet feeding direction, The first time is the difference between the time when the rear end portion of the sheet passes the first detection position and the time when the rear end portion of the sheet passes the second detection position, wherein the controller calculates the length of the sheet relative to the sheet feeding direction based on the sheet feeding speed, the second time and the second distance between the second detection position and the third detection position relative to the sheet feeding direction, the second time is the difference between the time when the front end portion of the sheet passes the third detection position and the time when the rear end portion of the sheet passes the second detection position, and wherein the controller controls the sheet feeding timing of the second feeding roller pair based on information on the length of the sheet;

[0009] According to another aspect of the present invention, there is provided a sheet feeding device, comprising: a first feed roller pair, the first feed roller pair being rotatable in a sheet clamping state and configured to feed the sheet; an upstream feed roller pair, the upstream feed roller pair being arranged upstream of the first feed roller pair relative to a sheet feeding direction and configured to feed the sheet; a downstream feed roller pair, the downstream feed roller pair being arranged downstream of the first feed roller pair relative to the sheet feeding direction and configured to feed the sheet; a second feed roller pair, the second feed roller pair being arranged downstream of the first feed roller pair relative to the sheet feeding direction a first reading portion, the first reading portion being arranged to extend along the sheet feeding direction on a side downstream of the first feeding roller pair and upstream of the downstream feeding roller pair with respect to the sheet feeding direction, and being configured to read an image of a leading end portion of the sheet fed by the first feeding roller pair; a second reading portion being arranged to extend along the sheet feeding direction on a side upstream of the first feeding roller pair and downstream of the upstream feeding roller pair with respect to the sheet feeding direction, and being configured to read an image of a leading end portion of the sheet fed by the first feeding roller pair; and a second reading portion being arranged to extend along the sheet feeding direction on a side upstream of the first feeding roller pair and downstream of the upstream feeding roller pair with respect to the sheet feeding direction, and being configured to causing reading of an image of a rear end portion of the sheet fed by the first feed roller pair; and a controller configured to perform calculations based on the images read by the first reading portion and the second reading portion, wherein when the image of the front end portion of the sheet fed by the first feed roller pair is read by the first reading portion, the rear end portion of the sheet passes through the upstream feed roller pair, and wherein when the image of the rear end portion of the sheet fed by the first feed roller pair is read by the second reading portion, the front end portion does not reach the downstream feed roller pair, wherein the controller calculates a sheet feeding speed based on a fifth time being a difference between moments of a plurality of images read by the first reading portion and a fifth distance being a difference in positions of the front end portion of the sheet between the plurality of images, wherein the controller calculates a length of the sheet based on a sixth time being a difference in moments between the image read by the first reading portion and the image read by the second reading portion, and wherein the controller controls the sheet feeding timing of the second feed roller pair based on information on the length of the sheet.

[0010] Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 is a schematic structural diagram of the imaging device of Embodiment 1.

[0012] Figure 2: is a schematic diagram showing a configuration for calculating a sheet feeding speed and a length of a sheet with respect to a (sheet) feeding direction in a reference example.

[0013] Figure 3 is an output diagram of a signal in a configuration for detecting the passage of a sheet in a reference example.

[0014] 4A to 4D is a cross-sectional view for explaining the behavior of the sheet S in the reference example.

[0015] Figure 5 : is a top view (plan view) showing the structure of the sheet detection unit in Embodiment 1.

[0016] FIG. 6A to FIG. 6E is a schematic diagram showing the sheet feeding behavior of the sheet detection unit in Embodiment 1.

[0017] Figure 7 is a timing chart showing changes in signals in the sheet detection unit in Embodiment 1.

[0018] Figure 8 is a top view showing the structure of a sheet detection unit in a modified embodiment of Embodiment 1. FIG.

[0019] 9A to 9E is a schematic diagram illustrating a sheet feeding behavior of a sheet detection unit in a modified embodiment of Embodiment 1. FIG.

[0020] Fig.10 is a top view showing the structure of a sheet detection unit in Embodiment 2.

[0021] Fig.11 is a timing chart showing changes in signals in the sheet detection unit in Embodiment 2.

[0022] Fig.12 is a top view showing the structure of a sheet detection unit in Embodiment 3.

[0023] Fig.13 is a timing chart showing changes in signals in the sheet detection unit in Embodiment 3.

[0024] Fig.14 : is a top view showing the structure of the sheet detection unit in Embodiment 4.

[0025] Fig.15 is a top view showing a sheet feeding behavior in a modified embodiment of Embodiment 4.

[0026] Fig.16 : is a timing chart showing changes in signals in the sheet detection unit in a modified embodiment of Embodiment 4.

[0027] Fig.17 is a top view showing the structure of a sheet detection unit in Embodiment 5.

[0028] Fig.18A and Fig.18B 1 and 2 are schematic diagrams respectively showing one example and another example of reading an image by the first reading portion and the second reading portion in Embodiment 5, respectively.

[0029] Fig.19A is a graph showing the relationship between the reading timing of the first reading portion and the end portion of the sheet in Embodiment 5, and Fig.19B : is a graph showing the relationship between the reading timing of the second reading portion and the end portion of the sheet in Embodiment 5.

[0030] Fig. 20A and Fig. 20B 1 and 2 are top views respectively showing detection of a leading end portion and detection of a trailing end portion of a sheet in Embodiment 5.

[0031] Fig.21 is a control block diagram in embodiments 1 to 5. Specific embodiments

[0032] Hereinafter, embodiments for carrying out the present invention will be described with reference to the accompanying drawings.

[0033] [Example 1]

[0034] <Overall Structure of Imaging Apparatus>

[0035] First, a schematic structure of a printer 1 as an example of an image forming apparatus including a sheet feeding device according to Embodiment 1 will be described. Figure 1 is a schematic structural diagram of the printer 1. The printer 1 includes a controller for controlling the entire operation of the printer 1 based on image information input from an external PC or image information read from an original. The printer 1 is an apparatus in which an image is formed on a sheet used as a recording medium (material), such as a printer, a copier, a fax machine, a multifunction machine, etc. In addition, the printer 1 can meet printing other than printing for general business purposes, and can use various sheets as recording media (materials), including paper (such as forms or envelopes), glossy paper, plastic films (such as overhead projector (OHP) sheets), cloth, etc.

[0036] In the apparatus main assembly 100A of the printer 1, a feed cassette 51 for accommodating a sheet S and an image forming engine 513 for forming an image on the sheet S fed from the feed cassette 51 are accommodated. The image forming engine 513 as an example of an image forming device includes four image forming portions PY, PM, PC, and PK for forming toner images of yellow, magenta, cyan, and black, respectively, and an intermediate transfer belt 506. The image forming engine 513 forms an image on the sheet S by a tandem intermediate transfer type. The image forming portions PY to PK are electrophotographic units including photosensitive drums 1Y, 1M, 1C, and 1K, respectively, as photosensitive members.

[0037] The image forming parts PY to PK achieve commonality in their configuration except that the colors of the toners used for development are different from each other. In this embodiment, the structure of the image forming engine 513 and the toner image forming process will be described by using the image forming part PY for yellow as an example. In addition to the photosensitive drum 1Y, the image forming part PY includes an exposure device 511, a developing device 510, and a drum cleaner 509. The photosensitive drum 1Y is a drum-shaped photosensitive member including a photosensitive layer at the peripheral portion, and is rotated in the direction of rotation ( Figure 1 direction of arrow B in the figure) Figure 1 The photosensitive drum 1Y rotates in the direction of arrow A in FIG. 1 . The surface of the photosensitive drum 1Y is charged by being supplied with electric charge from a charging device (e.g., a charging roller). The exposure device 511 emits laser light modulated according to image information, so that the surface of the photosensitive drum 1Y is scanned with laser light by an optical system including a reflecting device 512 and the like, and thus an electrostatic latent image is formed on the surface of the photosensitive drum 1Y. The developing device 510 contains a developer containing a toner, and visualizes (develops) the electrostatic latent image into a toner image by supplying the toner to the surface of the photosensitive drum 1Y. The toner image formed on the photosensitive drum 1Y is transferred once onto the intermediate transfer belt 506 in a primary transfer portion, which serves as a clamping portion between the intermediate transfer belt 506 and the primary transfer roller 507. The residual toner remaining on the photosensitive drum 1Y after the transfer is removed by a drum cleaner 509.

[0038] The intermediate transfer belt 506 is extended and wound around the driving roller 504, the driven roller 505, the inner secondary transfer roller 503 and the primary transfer roller 507, and is connected by the driving roller 504 to the intermediate transfer belt 506. Figure 1The image forming process described above is carried out in parallel in the image forming parts PY to PK, and the toner images of four colors are transferred in a multiple transfer manner so that the toner images of four colors are superimposed on each other, so that a full-color image is formed on the intermediate transfer belt 506. These toner images for the full-color image are fed to the secondary transfer part 100C by being carried on the intermediate transfer belt 506. The secondary transfer part 100C is constructed as a clamping portion between an internal secondary transfer roller 503 and a secondary transfer roller 56 as a transfer device. A bias voltage having a polarity opposite to the charge polarity of the toner is applied to the secondary transfer roller 56. Thus, the toner image is secondarily transferred onto the sheet S. The residual toner remaining on the intermediate transfer belt 506 after the transfer is removed by the belt cleaner.

[0039] The sheet S on which the toner image is transferred is delivered to the fixing unit 58 through the pre-fixing feeding portion 57. The fixing unit 58 includes a fixing roller pair for feeding the sheet S while sandwiching the sheet S and a heat source (e.g., a halogen heater), and applies heat and pressure to the toner image carried on the sheet S. Thereby, the toner particles are melted and fixed, so that the toner image is fixed on the sheet S.

[0040] Next, the sheet feeding process for feeding sheets will be described. The sheet feeding system 100D as the sheet feeding device of this embodiment feeds the sheet S contained in the feed box 51 and discharges the sheet S with an image formed thereon to the outside of the main component 100A of the device. The sheet feeding system 100D includes a sheet feeding part 53, a sheet conveying part 54, a tilt movement correction part 55, a branch feeding (conveying) part 59, a reverse feeding (conveying) part 501 and a double-sided feeding (conveying) part 502. The feed box 51 is installed in the main component 100A of the device so that it can be pulled out, and the sheets S are contained in a stacked state on a lifting plate 52 that can rise and fall. The sheets S are fed one by one by the sheet feeding part 53. As the type of the feeding part 53, a belt type in which the sheet S is attracted to the belt member by a suction fan and then fed and a friction separation type in which a roller or a pad is used can be adopted. The sheet S fed from the feeding portion 53 is fed along a feeding path 54 a by a pair of feeding rollers of the sheet conveying portion 54 , and then, is delivered to the oblique movement correcting portion 55 .

[0041] The sheet S delivered to the tilt movement correction portion 55 is subjected to tilt movement correction and timing correction, and then, is fed toward the secondary transfer portion 100C. At this time, the registration roller pair 7 included in the tilt movement correction portion 55 sends the sheet S to the secondary transfer portion 100C at a timing synchronized with the degree of progress of the image forming process of the image forming portions PY to PK. The sheet S on which the toner image is transferred in the secondary transfer portion 100C and the image is fixed thereon by the fixing unit 58 is fed to a branch feeding portion 59 for branching the feeding path of the sheet S. In a case where the image forming on the sheet S is completed, the sheet S is discharged by the discharge roller pair onto a discharge tray 500 arranged outside the main assembly 100A of the apparatus. In a case where an image is formed on the back surface (back side) of the sheet S, the sheet S is delivered to the double-sided feeding portion 502 through the reverse feeding portion 501. The reverse feeding portion 501 includes a reverse roller pair that can rotate forwardly and reversely, and then delivers the sheet S to the double-sided feeding portion 502 in a state in which the front and back sides of the sheet S are reversed by a switchback in which both the front and back sides of the sheet S are reversed. The double-sided feeding portion 502 feeds the sheet S toward the tilt movement correction portion 55 again through the sheet feeding portion 54. After an image is formed on the back surface of the sheet S, the sheet S is discharged onto the discharge tray 500.

[0042] As described above, the image forming apparatus 1 operates the “image forming process” and the “sheet feeding process” in relation to each other, thereby achieving image formation on the sheet S.

[0043] <Configuration for Calculating Length of Sheet with Respect to Feeding Direction in Reference Example>

[0044] By the way, conventionally, the above-mentioned folding type has generally been used as a type in which the front and back sides of a sheet are reversed in an imaging device because the construction is easy and advantageous in terms of space. However, in the case of the folding type, the front end and the rear end of the sheet are switched with each other, and therefore, even when a mechanism for correcting the tilting movement of the sheet is provided, positional deviation of the image formed on the sheet on the front and back sides (front surface and back surface) occurs. This is due to the occurrence of a change in the size of the sheet due to a change in the cutting of the sheet, and fiber shrinkage, expansion, etc. of the sheet depending on the amount of moisture absorbed in the air. In particular, with respect to fiber shrinkage of the sheet, in the case where an image is formed on the back surface of the sheet after the image is formed on the front surface of the sheet, the sheet is heated and pressed once by the fixing unit, and thereby, sheet shrinkage is likely to occur. In this case, during the transfer of the image onto the back surface of the sheet, when the timing of the toner image and the leading end of the sheet coincide with each other only on the basis of the leading end (where the image is formed on the front surface of the sheet), positional deviation of the image formed on the sheet on the front and back surfaces occurs. Then, due to the occurrence of such positional deviation, the quality of the printed product is degraded due to the occurrence of image defects and blanks between subsequent pages in a processing step after printing (such as trimming or folding).

[0045] To solve this problem, Figure 2 As shown, the following structure is known, in which a sensor for detecting the passage of a sheet is provided to each of the two detection parts SN1A and SN2A in the double-sided feeding part of the imaging device, and the sheet feeding speed and the sheet length relative to the (sheet) feeding direction are calculated based on the signal sent from the sensor. After the sheet length is calculated, the controller controls the sheet feeding timing from the tilted movement correction part to the secondary transfer part based on the information of the calculated sheet length. Specifically, in the case where the controller determines that the calculated sheet length is shorter than the information of the sheet length, the sheet feeding timing from the tilted movement correction part to the secondary transfer part is delayed. On the other hand, in the case where the controller determines that the calculated sheet length is longer than the information of the sheet length, the sheet feeding timing from the tilted movement correction part to the secondary transfer part is advanced.

[0046] Therefore, the sheet length is detected and the timing of sheet feeding through the tilt movement correction portion is controlled, so that the reference position of the sheet end portion can be known during the image formation on the first surface (front surface), even if the front end and the rear end of the sheet are switched with each other when the image is formed on the second surface (back surface). Therefore, the position of the image formed on the first surface (front surface) is known, and thus, the image on the second surface (back surface) is formed in accordance with the reference position of the sheet end portion during the image formation on the first surface (front surface), so that the position deviation of the image formed on the sheet on the front and back surfaces can be prevented.

[0047] Figure 2 1 is a top view (plan view) illustrating a configuration for detecting the passage of a sheet in a conventional image forming apparatus as a reference example. Figure 2 , as a reference example, feed rollers 5 and 6 provided at a double-sided feeding portion of a conventional image forming apparatus, and detection portions SN1A and SN2A provided between the feed rollers 5 and 6 with respect to the feeding direction are shown. The detection portion SN1A arranged on the upstream side with respect to the feeding direction is provided with two sensors SN1 and SN2, which are provided at an interval d while sandwiching a center (hereinafter referred to as a feeding center C) with respect to a transverse direction perpendicular to the feeding direction in a sheet feeding passage. Similarly, the detection portion SN2A arranged downstream of the detection portion SN1A is provided with two sensors SN3 and SN4, which are provided at an interval d while sandwiching the feeding center C.

[0048] In addition, when Figure 2 When the sheet S fed in the direction of the arrow FX in FIG. 1 passes through the detection portions SN1A and SN2A, the outputs from the sensors SN1, SN2, SN3, and SN4 are as follows: Figure 3 The signal shown. Figure 3 is an output diagram of a signal in a configuration for detecting the passage of a sheet in a reference example. Figure 3 In the figure, T1 and T2 are the times when sensors SN1 and SN2 of the detection part SN1A detect the passage of the front end of the sheet. T3 and T4 are the times when sensors SN3 and SN4 of the detection part SN2A detect the passage of the front end of the sheet. T1' and T2' are the times when sensors SN1 and SN2 detect the passage of the rear end of the sheet. T3' and T4' are the times when sensors SN3 and SN4 detect the passage of the rear end of the sheet. Incidentally, in Figure 3 In the example, it is assumed that the sheet is made of Figure 2 The feed rollers 5 and 6 feed the sheet so that a straight line showing a feed center C and each of a leading end portion of the sheet and a rear end portion of the sheet are orthogonal to each other.

[0049] Here, when the time required for the leading end of the sheet S to pass between the sensors SN1 and SN3 is time F, time F=T3-T1 holds. On the other hand, when the time required for the leading end of the sheet S to pass between the sensors SN2 and SN4 is time E, time E=T4-T2 holds. In addition, the time required for the trailing end of the sheet S to pass between the sensors SN1 and SN3 is time H, and time H=T3'-T1' holds. On the other hand, the time required for the trailing end of the sheet S to pass between the sensors SN2 and SN4 is time G, and time G=T4'-T2' holds. In addition, based on the times E, F, G and H and the distance D between the detection parts SN1A and SN2A, the feeding speed of the sheet S is calculated. Incidentally, in order to average out the influence of the feed rollers 5, 6, etc., the average value Avg(E, F, G, H) of the times E, F, G and H is taken as the time for the sheet S to be fed a distance D, and the feeding speed VEX is calculated according to the following (Formula 1).

[0050] Feed speed VEX = D / Avg(E,F,G,H) (Formula 1)

[0051] In addition, when the time required from the front end of the sheet S to the rear end of the sheet S through the sensor SN1 is time AX and the time required from the front end of the sheet S to the rear end of the sheet S through the sensor SN2 is time BX, time AX=T1'-T1 and time BX=T2'-T2 hold. In addition, when the time required from the front end of the sheet S to the rear end of the sheet S through the sensor SN3 is time CX and the time required from the front end of the sheet S to the rear end of the sheet S (that is, the entire sheet S) through the sensor SN4 is time DX, time CX=T3'-T3 and time DX=T4'-T4 hold. In addition, in order to average out the effects of rollers 5, 6, etc., based on the average value Avg (AX, BX, CX, DX) and the feed speed VEX calculated in (Formula 1), the length L of the sheet S relative to the feed direction is calculated according to the following (Formula 2).

[0052] Length L = VEX × Avg (AX, BX, CX, DX) (Formula 2)

[0053] Next, we will refer to 4A to 4D The behavior of the sheet S when the sheet S passes through the feed rollers 5 and 6 in the reference example will be described. 4A to 4D 2 is a cross-sectional view for explaining the behavior of the sheet S in the reference example. Figure 4A As shown, when the end portions of the sheet S are detected by the detection portions SN1A and SN2A, the sheet S is fed toward the feed roller 6 in a state in which the sheet S is nipped by the feed roller (pair) 5. Figure 4BAs shown in FIG. 1 , when the sheet S enters the feed roller 6, a "bouncing behavior" is observed that causes the feed roller 6 to bounce in the direction indicated by the dotted line. Figure 4B , the position of the feed roller 6 that bounces due to the entry of the sheet S is indicated by a dotted line. Incidentally, this bouncing behavior becomes significant as the feed speed increases to ensure the productivity of the sheet feeding operation or as the thickness increases. In addition, when this bouncing behavior occurs, the sheet S and the feed roller 6 cause a slip between the sheet and the feed roller at the moment when the clamping pressure for clamping the sheet S by the feed roller 6 is released (eliminated). As a result of this slip, as shown in FIG. Figure 4C As shown, the feed roller 6 holds the sheet S at a position different from the position when no slip occurs in some cases. In addition, when the passage of the rear end portion of the sheet S is detected by the detection portions SN1A and SN2A, the sheet S is fed in a state where the slip occurs ( Figure 4D ). Therefore, positional deviation due to slippage between the sheet S and the feed roller 6 occurs. Therefore, when the passage of the rear end portion of the sheet S is detected, an error occurs, so that the measurement accuracy of the length of the sheet S with respect to the feeding direction is likely to be reduced. The measurement accuracy of the length of the sheet S has an influence on the timing when the tilt movement correction portion feeds the sheet S to the secondary transfer portion, and causes positional deviation of the image formed on the sheet S on the front and back sides (front surface and back surface).

[0054] <Configuration for Calculating Sheet Length with Respect to Feeding Direction in Embodiment 1>

[0055] Next, a configuration for detecting the sheet length with respect to the feeding direction in Embodiment 1 will be described. Figure 5 1 is a top view (plan view) showing the structure of the sheet detection unit 10 for detecting the length of the sheet with respect to the feeding direction in Embodiment 1. Regarding the sheet detection unit 10, description will be made assuming that the sheet detection unit 10 is arranged at the double-sided feeding portion 502, but when the sheet detection unit 10 is located on the feeding path on which the sheet S is fed in the printer 1, the sheet detection unit 10 may be arranged at a position other than the double-sided feeding portion 502.

[0056] The sheet detection unit 10 includes a feed roller pair 11 for feeding a sheet S, and a first detection portion S1, a second detection portion S2, and a third detection portion S3 for detecting the passage of end portions (front end portion and rear end portion) of the sheet S. With respect to the feed roller pair 11 in this embodiment, the peripheral surface of each roller that can contact the sheet S has been subjected to sandblasting, and metal is used as the material of the roller. Therefore, the change in outer diameter due to temperature and humidity is smaller than that of a commonly used rubber roller, and the sheet S is less likely to slip, so that the feeding of the sheet S can be accurately and stably controlled. In addition, with respect to the sheet feeding direction D1, the first detection portion S1 and the second detection portion S2 are arranged downstream of the feed roller pair 11. With respect to the (sheet) feeding direction D1, the third detection portion S3 is arranged upstream of the feed roller pair 11. In addition, an upstream feed roller pair 12 for feeding the sheet S is arranged upstream of the third detection portion S3, and a downstream feed roller pair 13 for feeding the sheet S is arranged downstream of the first detection portion S1.

[0057] The first detection portion S1 detects the passage of the end portions (the front end and the rear end) of the sheet S at a first detection position P1, which is located on the downstream side of the feed roller pair 11 with respect to the feed direction D1. In addition, the second detection portion S2 detects the passage of the end portions (the front end and the rear end) of the sheet S at a second detection position P2, which is located on the downstream side of the feed roller pair 11 with respect to the feed direction D1 and is different from the first detection position P1. In addition, the third detection portion S3 detects the end portions (the front end and the rear end) of the sheet S at a third detection position P3, which is located on the upstream side of the feed roller pair 11 with respect to the feed direction D1. Figure 5 , an example is shown in which each of the first detection position P1 , the second detection position P2 , and the third detection position P3 is arranged at the center of the sheet S with respect to the transverse direction perpendicular to the feeding direction D1 .

[0058] In addition, Figure 5, the distance between the first detection position P1 and the second detection position P2 with respect to the feeding direction D1 is represented as L12, and the distance between the second detection position P2 and the third detection position P3 with respect to the feeding direction D1 is represented as L23. Incidentally, the first detection portion S1 is constituted by including an optical sensor that outputs a low signal when the sheet S is not present and outputs a high signal when the sheet S is present. Moreover, with respect to the second detection portion S2 and the third detection portion S3, the same sensor as the first detection portion S1 is used. Therefore, due to the passage of the leading end portion of the sheet S, the signal output from the sensor of each of the first detection portion S1, the second detection portion S2, and the third detection portion S3 is switched from low to high. In addition, due to the passage of the rear end portion of the sheet S, the signal output from the sensor of each of the first detection portion S1, the second detection portion S2, and the third detection portion S3 is switched from high to low. Therefore, the controller 9 can identify the passing time of the leading end portion or the rear end portion of the sheet at the first detection position P1, the second detection position P2, and the third detection position P3 in response to the signals output from the sensors of the first detection portion S1, the second detection portion S2, and the third detection portion S3, respectively. In addition, the controller 9 can calculate the feeding speed V of the sheet S and the length of the sheet S relative to the feeding direction D1 based on the passing time of the leading end portion or the rear end portion of the sheet S at the first detection position P1, the second detection position P2, and the third detection position P3. In addition, in the case where the length of the sheet S is L, the length between the feed roller pair 11 and the upstream feed roller pair 12 is L (11-12), the length between the downstream feed roller pair 13 and the feed roller pair 11 is L (13-11), the length between the second detection portion S2 and the upstream feed roller pair 12 is L (2-12), and the length between the downstream feed roller pair 13 and the third detection portion S3 is L (13-3), and the feed roller pair and the detection portion are arranged to satisfy the following relationship:

[0059] L>L(11-12) and L>L(13-11) Formula (3)

[0060] L(2-12)>L and L(13-3)>L Formula (4)

[0061] With respect to the corresponding feed roller pair and the corresponding detection portion, by arranging the feed roller pair and the detection portion to satisfy the relationship of formula (3) and formula (4), the sheet detection unit 10 is capable of detecting the leading end portion and the trailing end portion of the sheet S through the first detection portion, the second detection portion, and the third detection portion in a state where the sheet S is not clamped by the upstream feed roller pair and the downstream feed roller pair during the feeding of the sheet S by the feed roller pair 11. That is, when calculating the sheet length, it becomes possible to calculate the sheet length before the leading end portion of the sheet is clamped by the downstream feed roller pair. That is, the vibration of the sheet caused by the clamping of the leading end portion of the sheet by the downstream feed roller pair can be suppressed, so that it becomes possible to accurately detect the sheet length.

[0062] Next, referring to FIG. 6 , the sheet feeding behavior of the sheet detection unit in this embodiment will be described. Fig. 6A 1 is a schematic diagram of a sheet having a sheet length L being nipped and fed by the upstream feed roller pair 12 . Figure 6B The timing when the leading end of the sheet is detected by the second detection portion S2 is shown. Incidentally, at this time, the trailing end of the sheet is in a state immediately after passing through the upstream feed roller pair 12. Although described later, in order to calculate the speed of the sheet fed at this time, the measurement of time is started (the start time of the first time). In addition, in order to calculate the length of the sheet, the measurement of time is started (the start time of the second time). Figure 6C 1 is a schematic diagram showing that a sheet is nipped and fed by the feed roller pair 11 . Figure 6C The moment when the leading end of the sheet is detected by the first detection portion S1 (the start moment of the third time) is shown. Incidentally, at this time, the trailing end of the sheet is in a state after passing through the upstream feed roller pair 12, and the third detection portion S3 is in a state where the third detection portion S3 detects the sheet. In addition, although described later, in order to calculate the speed of the sheet fed at this moment, the measurement of time is ended (the end moment of the first time). In addition, in order to calculate the length of the sheet, the measurement of time is started. Fig.6D 1 is a schematic diagram of a sheet being held and fed by the feed roller pair 11. The leading end of the sheet is in a state before reaching the downstream feed roller pair 13, and the trailing end of the sheet is in a state where the trailing end of the sheet is detected by the third detection portion S3. In addition, although described later, in order to calculate the sheet length at this time, relative to the start at Figure 6B and Figure 6C The time when the second time and the third time are measured is ended. Fig. 6E 1 is a schematic diagram showing the moment when the leading end of the sheet is clamped by the downstream feed roller pair 13. The trailing end of the sheet is in a state where the trailing end of the sheet is clamped and fed by the feed roller pair 11. As described above, the sheet detection unit in this embodiment detects the leading end and the trailing end of the sheet while feeding the sheet.

[0063] Next, refer to Figure 5 , Figure 6 and Figure 7 , a calculation method of the length of the sheet S with respect to the feeding direction D1 in this embodiment will be specifically described. Figure 7 It shows that when the sheet surface passes Figure 5 6 and the sheet detection unit 10 are respectively output from the first detection portion S1, the second detection portion S2 and the third detection portion S3. Figure 7 In the formula 1-1, the time when the leading end of the sheet S passes through the second detection position P2 and the first detection position P1 is represented as T2t and T1t, respectively. In addition, the time when the trailing end of the sheet S passes through the third detection position P3 is represented as T3h. First, based on the time T2t, T1t, T3h and the relative positions of the first detection position P1, the second detection position P2, and the third detection position P3 with respect to the feeding direction D1, the feeding speed V of the sheet S is calculated as shown in the following (Formula 1-1):

[0064] Feed speed V = L12 / (T1t-T2t) (Formula 1-1).

[0065] In (Formula 1-1), the feed speed V is calculated based on the distance L12 and the difference between the time T1t when the leading end of the sheet passes the first detection position P1 and the time T2t when the leading end of the sheet passes the second detection position P2. The difference between the time T1t when the leading end of the sheet passes the first detection position P1 and the time T2t when the leading end of the sheet passes the second detection position P2 is the first time in this embodiment, and the distance L12 is the first distance in this embodiment.

[0066] In addition, the length of the sheet relative to the feeding direction D1 is calculated as shown below (Formula 1-2):

[0067] Length L' = L23 + (T3h - T2T) × V,

[0068] Length L" = L23 + L12 + (T3h - T1t) × V, and

[0069] Length L = (L' + L") / 2 (Formula 1-2).

[0070] In (Formula 1-2), the length L' of the sheet relative to the feeding direction D1 is calculated based on the distance L23 and the difference between the time T2t when the leading end of the sheet passes the second detection position P2 and the time T3h when the trailing end of the sheet passes the third detection position P3. In addition, the length L" of the sheet relative to the feeding direction D1 is calculated based on the distance (L23+L12) and the difference between the time T1t when the leading end of the sheet passes the first detection position P1 and the time T3h when the trailing end of the sheet passes the third detection position P3.

[0071] The difference between time T2t when the leading end of the sheet passes the second detection position P2 and time T3h when the trailing end of the sheet passes the third detection position P3 is the second time in this embodiment, and the distance L23 is the second distance in this embodiment.

[0072] In addition, the difference between time T1t when the leading end of the sheet passes the first detection position P1 and time T3h when the trailing end of the sheet passes the third detection position P3 is the third time in this embodiment, and the distance (L23+L12) is the third distance in this embodiment.

[0073] In this embodiment, the sheet length L is calculated based on the average value of the length L' as the first length and the length L" as the second length in this embodiment. Thus, the variation in the detection of the end portion of the sheet S by the sensor of each of the first detection part S1, the second detection part S2, and the third detection part S3 is corrected, so that the calculation error of the sheet length can be reduced. Therefore, a construction in which the sheet length L relative to the feeding direction D1 is calculated based on only one of the length L' and the length L" may also be adopted. In this embodiment, for example, the feeding speed V of the sheet S calculated in (Formula 1-1) is substituted into (Formula 1-2), that is, length L"=L23+L12+(T3h-T1t)×V, and the sheet length L relative to the feeding direction D1 can also be calculated under the condition that length L=length L".

[0074] Therefore, in this embodiment, the length L is calculated using the sheet leading end portion passing time (T2t, T1t) after the sheet leading end portion passes the feed roller pair 11 and using the sheet trailing end portion passing time (T3h) before the sheet trailing end portion passes the feed roller pair 11. Therefore, the length L of the sheet S with respect to the feeding direction D1 can be accurately calculated without being affected by when the sheet S enters the downstream feed roller pair 13. That is, based on the sheet length L, the sheet feeding timing by the tilt movement correction portion is controlled so that it becomes possible to suppress the positional deviation between the front and back sides of the image formed on the sheet S.

[0075] Next, Figure 8FIG. 9 shows a modified embodiment of Embodiment 1. Regarding Figure 8 , assume a state in which the rear end portion of the sheet is detected by the third detection portion after the front end portion of the sheet is clamped by the downstream feed roller pair. That is, Figure 8 shows a case where the sheet length L is longer than the sheet length L in Embodiment 1 and the positional relationship between each feed roller pair and each detection portion is set to the following formula (4)':

[0076] L(2-12)<L and L(13-3)<L Formula (4)'.

[0077] As in Embodiment 1 above, an arrangement is formed in which the rear end portion of the sheet is detected by the third detection portion before the front end portion of the sheet is clamped by the downstream feed roller pair, so that the impact of clamping the front end portion of the sheet by the downstream feed roller pair can be reliably prevented. However, even when the position detection in the above formula (4)' in this modified embodiment is established, the length L of the sheet S can be accurately calculated for the following reasons. FIG. 9 includes a schematic diagram showing the sheet feeding behavior of the sheet detection unit in the Figure 8 arrangement, and the sheet feeding behavior will be described using FIG. 9. Fig. 9A is a schematic diagram in which a sheet having a length of L is clamped and fed by the upstream feed roller pair 12. Fig. 9A shows the moment when the front end portion of the sheet is detected by the third detection portion S3. Fig. 9B is a schematic diagram in which the sheet is clamped and fed by the feed roller pair 11. Fig. 9B shows the moment when the front end portion of the sheet is detected by the second detection portion S2. Incidentally, the rear end portion of the sheet at this time is in a state where the rear end portion of the sheet is clamped by the upstream feed roller pair 12. Fig. 9C is a schematic diagram of the sheet being clamped and fed by the feed roller pair 11. Fig. 9C shows the moment when the front end portion of the sheet is detected by the first detection portion S1. Incidentally, the rear end portion of the sheet at this time is in a state after the rear end portion of the sheet has passed the upstream feed roller pair 12, and the third detection portion S3 is in a state of detecting the sheet. In this modified embodiment, the sheet feeding speed is calculated at the moment when the front end portion of the sheet passes the second detection portion and the first detection portion. During the period when the front end portion of the sheet passes the second detection portion, the rear end portion of the sheet is in a state where the rear end portion of the sheet is clamped by the upstream feed roller pair 12. In addition, when the front end portion of the sheet passes the first detection portion, the rear end portion of the sheet is in a state where the rear end portion of the sheet has passed the upstream feed roller pair 12. Generally speaking, when the number of feed roller pairs clamping the sheet changes, in some cases the change in the sheet feeding speed becomes large, but in this modified embodiment, the front end portion of the sheet is clamped by the sandblasted feed roller pair 11, and thus, the influence of the change in the number of feed roller pairs clamping the sheet becomes small. Fig.9D 1 is a schematic diagram of the moment when the leading end of the sheet reaches the downstream feed roller pair 13. At this time, as described above, the leading end of the sheet receives an impact from the downstream feed roller pair 13. However, in this modified embodiment, the rear end of the sheet is clamped by the feed roller pair 11, and therefore, positional deviation of the sheet is less likely to occur on the upstream side of the feed roller pair 11. Incidentally, regarding the sheet between the feed roller pair 11 and the downstream feed roller pair 13, its influence is taken into consideration. Fig.9E The moment when the rear end of the sheet is detected by the third detection portion is shown. The rear end of the sheet is detected by the third detection portion while the rear end of the sheet is clamped and fed by the feed roller pair 11. That is, the rear end of the sheet can be detected without being affected by the impact when the front end of the sheet enters the downstream feed roller pair 13.

[0078] As described above, when the leading end portion of the sheet is clamped by the downstream feed roller pair 11, the sheet is subjected to impact, but the rear end portion of the sheet is clamped by the feed roller pair 11. In a state where the rear end portion of the sheet is clamped by the feed roller pair 11, the rear end portion of the sheet is detected by the third detection portion. Thus, with respect to the impact received by the leading end portion of the sheet from the downstream feed roller pair 13, the rear end portion of the sheet can be detected without being subjected to impact. That is, the feeding speed and length of the fed sheet can be accurately calculated. By the way, in the case of a configuration in which the rear end portion of the sheet is detected on the downstream side of the downstream feed roller pair as in the conventional example, the rear end portion of the sheet is detected in a state including the impact received by the leading end portion of the sheet from the downstream feed roller pair 13, and therefore, the detection accuracy naturally decreases.

[0079] [Example 2]

[0080] <Configuration for Calculating Sheet Length with Respect to Feeding Direction in Embodiment 2>

[0081] Next, a configuration for calculating the sheet length with respect to the feeding direction in Embodiment 2 will be described. Fig.10 1 is a top view (plan view) showing the structure of the sheet detection unit 10 for calculating the sheet length with respect to the feeding direction in Embodiment 2.

[0082] The difference from Embodiment 1 lies in the number of detection portions arranged on one side upstream and on one side downstream of the feed roller pair 11. Specifically, two detection portions are arranged on one side upstream of the feed roller pair 11 and downstream of the upstream feed roller pair 12, and a single detection portion is arranged on one side downstream of the feed roller pair 11 and upstream of the downstream feed roller pair 13. Incidentally, the configurations of the printer 1, the feed roller pair 11, the upstream feed roller pair 12, and the downstream feed roller pair 13 are similar to those in Embodiment 1, and therefore, redundant description thereof will be omitted. With regard to the sheet detection unit 10, the description will be made assuming that the sheet detection unit 10 is arranged at the double-sided feeding portion 502, but when the sheet detection unit 10 is located on a feeding path on which the sheet S is fed in the printer 1, the sheet detection unit 10 may also be arranged at a position other than the double-sided feeding portion 502.

[0083] The sheet detection unit 10 includes a feed roller pair 11 for feeding a sheet S, and a first detection portion S1, a second detection portion S2, and a third detection portion S3 for detecting the passage of an end portion of the sheet S. The first detection portion S1 and the second detection portion S2 are arranged upstream of the sheet feed roller pair 11 with respect to the sheet feeding direction D1. The third detection portion S3 is arranged downstream of the feed roller pair 11 with respect to the (sheet) feeding direction D1.

[0084] The first detection portion S1 detects the passage of the end portion of the sheet S at a first detection position P1, which is located on the side upstream of the feed roller pair 11 and downstream of the upstream feed roller pair 12 with respect to the feed direction D1. In addition, the second detection portion S2 detects the passage of the end portion of the sheet S at a second detection position P2, which is located on the side upstream of the feed roller pair 11 with respect to the feed direction D1 and is different from the first detection position P1. In addition, the third detection portion S3 detects the end portion of the sheet S at a third detection position P3, which is located on the side downstream of the feed roller pair 11 and upstream of the downstream feed roller pair 13 with respect to the feed direction D1. Figure 8 , an example is shown in which each of the first detection position P1 , the second detection position P2 , and the third detection position P3 is arranged at the center of the sheet S with respect to the transverse direction perpendicular to the feeding direction D1 .

[0085] In addition, Figure 8, the distance between the first detection position P1 and the second detection position P2 with respect to the feeding direction D1 is represented as L12, and the distance between the second detection position P2 and the third detection position P3 with respect to the feeding direction D1 is represented as L23. Incidentally, the first detection portion S1 is constituted by including an optical sensor that outputs a low signal when the sheet S is not present and outputs a high signal when the sheet S is present. Moreover, with respect to the second detection portion S2 and the third detection portion S3, the same sensor as the first detection portion S1 is used. Therefore, due to the passage of the leading end portion of the sheet S, the signal output from the sensor of each of the first detection portion S1, the second detection portion S2, and the third detection portion S3 is switched from low to high. In addition, due to the passage of the rear end portion of the sheet S, the signal output from the sensor of each of the first detection portion S1, the second detection portion S2, and the third detection portion S3 is switched from high to low. Therefore, the controller 9 can recognize the passing time of the leading end portion or the rear end portion of the sheet at the first detection position P1, the second detection position P2, and the third detection position P3 in response to the signals output from the sensors of the first detection portion S1, the second detection portion S2, and the third detection portion S3, respectively. In addition, the controller 9 can calculate the feeding speed V of the sheet S and the length of the sheet S relative to the feeding direction D1 based on the passing time of the leading end portion or the rear end portion of the sheet S at the first detection position P1, the second detection position P2, and the third detection position P3. In addition, in the case where the length of the sheet S is L, the length between the feed roller pair 11 and the upstream feed roller pair 12 is L (11-12), the length between the downstream feed roller pair 13 and the feed roller pair 11 is L (13-11), the length between the third detection portion S3 and the upstream feed roller pair 12 is L (3-12), and the length between the downstream feed roller pair 13 and the second detection portion S2 is L (13-2), and the feed roller pair and the detection portion are arranged to satisfy the following relationship:

[0086] L>L(11-12) and L>L(13-11) Formula (5)

[0087] L(3-12)>L and L(13-2)>L Formula (6)

[0088] With respect to the corresponding feed roller pair and the corresponding detection portion, by arranging the feed roller pair and the detection portion to satisfy the relationship of formula (5) and formula (6), the sheet detection unit 10 is capable of detecting the leading end portion and the trailing end portion of the sheet S through the first detection portion, the second detection portion, and the third detection portion in a state in which the sheet S is not clamped by the upstream feed roller pair and the downstream feed roller pair during the feeding of the sheet S by the feed roller pair 11. That is, when calculating the sheet length, it becomes possible to calculate the sheet length before the leading end portion of the sheet is clamped by the downstream feed roller pair. That is, the vibration of the sheet caused by the clamping of the leading end portion of the sheet by the downstream feed roller pair can be suppressed, so that it becomes possible to accurately detect the sheet length.

[0089] Next, refer to Fig.10 and Fig.11 , a calculation method of the length of the sheet S with respect to the feeding direction D1 in this embodiment will be described. Fig.11 It shows that when the sheet surface passes Fig.10 Schematic diagram of changes in signals output from the first detection section S1, the second detection section S2, and the third detection section S3 when the sheet detection unit 10 is in FIG. Fig.11 In the formula 2-1, the time when the rear end of the sheet S passes through the first detection position P1 and the second detection position P2 is represented as T1h and T2h, respectively. In addition, the time when the front end of the sheet S passes through the third detection position P3 is represented as T3t. First, based on the time T1h, T2h, T3t and the relative positions of the first detection position P1, the second detection position P2, and the third detection position P3 with respect to the feeding direction D1, the feeding speed V of the sheet S is calculated as shown in the following (Formula 2-1):

[0090] Feed speed V = L12 / (T2h-T1h) (Formula 2-1).

[0091] In (Formula 2-1), the feed speed V is calculated based on the distance L12 and the difference between the time T1h when the rear end portion of the sheet passes through the first detection position P1 and the time T2f when the rear end portion of the sheet passes through the second detection position P2. The difference between the time T1h when the rear end portion of the sheet passes through the first detection position P1 and the time T2h when the rear end portion of the sheet passes through the second detection position P2 is the first time in this embodiment, and the distance L12 is the first distance in this embodiment.

[0092] In addition, the length of the sheet relative to the feeding direction D1 is calculated as shown below (Formula 2-2):

[0093] Length L' = L12 + L23 + (T1h - T3t) × V,

[0094] Length L" = L23 + (T2h - T3t) × V, and

[0095] Length L = (L' + L") / 2 (Formula 2-2).

[0096] In (Formula 2-2), the length L' of the sheet relative to the feeding direction D1 is calculated based on the distance (L23+L12) and the difference between the time T1h when the rear end of the sheet passes the first detection position P1 and the time T3t when the front end of the sheet passes the third detection position P3. In addition, the length L" of the sheet relative to the feeding direction D1 is calculated based on the distance L23 and the difference between the time T2h when the rear end of the sheet passes the second detection position P2 and the time T3t when the front end of the sheet passes the third detection position P3.

[0097] The difference between time T1h when the sheet trailing end passes the first detection position P1 and time T3t when the sheet leading end passes the third detection position P3 is the third time in this embodiment, and the distance (L23+L12) is the third distance in this embodiment.

[0098] In addition, the difference between the time T2h when the sheet trailing end passes the second detection position P2 and the time T3t when the sheet leading end passes the third detection position P3 is the second time in this embodiment, and the distance L23 is the second distance in this embodiment.

[0099] In this embodiment, the sheet length L is calculated based on the average value of the length L' which is the first length and the length L" which is the second length in this embodiment. Thus, the variation in the detection of the end portion of the sheet S by the sensor of each of the first detection part S1, the second detection part S2, and the third detection part S3 is corrected, so that the calculation error of the sheet length can be reduced. Therefore, a construction in which the sheet length L relative to the feeding direction D1 is calculated based on only one of the length L' and the length L" may also be adopted. In this embodiment, for example, the feeding speed V of the sheet S calculated in (Formula 2-1) is substituted into (Formula 2-2), that is, length L'=L12+L23+(T1h-T3t)×V, and the sheet length L relative to the feeding direction D1 can also be calculated under the condition that length L=length L'.

[0100] Therefore, in this embodiment, the length L is calculated using the time when the rear end of the sheet passes before the front end of the sheet passes the feed roller pair 11 (time T1h, T2h) and the time when the rear end of the sheet passes after the front end of the sheet passes the feed roller pair 11 (time T3t). Therefore, the length L of the sheet S relative to the feeding direction D1 can be accurately calculated without being affected by when the sheet S enters the downstream feed roller pair 13. That is, based on the sheet length L, the timing of sheet feeding by the tilt movement correction part is controlled so that it becomes possible to suppress the position deviation between the front and back sides of the image formed on the sheet S. Incidentally, in addition, with regard to Embodiment 2, as a modified embodiment, a configuration similar to that of the modified embodiment of Embodiment 1 can also be adopted. That is, after the front end of the sheet is clamped by the downstream feed roller pair 13, the rear end of the sheet can also be detected by the second detection part.

[0101] [Example 3]

[0102] <Configuration for Calculating Sheet Length with Respect to Feeding Direction in Embodiment 3>

[0103] Next, a configuration for calculating the sheet length with respect to the feeding direction in Embodiment 3 will be described. Fig.12 1 is a top view (plan view) showing the structure of the sheet detection unit 10 for calculating the sheet length with respect to the feeding direction in Embodiment 3. FIG.

[0104] The difference from Embodiments 1 and 2 lies in the number of detection portions arranged on one side upstream and on one side downstream of the feed roller pair 11. Specifically, two detection portions are arranged on one side upstream of the feed roller pair 11 and downstream of the upstream feed roller pair 12, and two detection portions are arranged on one side downstream of the feed roller pair 11 and upstream of the downstream feed roller pair 13. Incidentally, the configurations of the printer 1, the feed roller pair 11, the upstream feed roller pair 12, and the downstream feed roller pair 13 are similar to those in Embodiment 1, and therefore, redundant description thereof will be omitted. With regard to the sheet detection unit 10, the description will be made assuming that the sheet detection unit 10 is arranged at the double-sided feeding portion 502, but when the sheet detection unit 10 is located on a feeding path on which the sheet S is fed in the printer 1, the sheet detection unit 10 may also be arranged at a position other than the double-sided feeding portion 502.

[0105] The sheet detection unit 10 includes a feed roller pair 11 for feeding a sheet S, and a first detection portion S1, a second detection portion S2, a third detection portion S3, and a fourth detection portion S4 for detecting the passage of an end portion of the sheet S. The first detection portion S1 and the second detection portion S2 are arranged upstream of the sheet feed roller pair 11 with respect to the sheet feeding direction D1. The third detection portion S3 and the fourth detection portion S4 are arranged downstream of the feed roller pair 11 with respect to the (sheet) feeding direction D1.

[0106] The first detection portion S1 detects the passage of the end portion of the sheet S at a first detection position P1, which is located on a side upstream of the feed roller pair 11 and downstream of the upstream feed roller pair 12 with respect to the feed direction D1. In addition, the second detection portion S2 detects the passage of the end portion of the sheet S at a second detection position P2, which is located on a side upstream of the feed roller pair 11 with respect to the feed direction D1 and is different from the first detection position P1. In addition, the third detection portion S3 detects the end portion of the sheet S at a third detection position P3, which is located on a side downstream of the feed roller pair 11 and upstream of the downstream feed roller pair 13 with respect to the feed direction D1. The fourth detection portion S4 detects the passage of the end portion of the sheet at a fourth detection position P4, which is located on a side downstream of the feed roller pair 11 with respect to the feed direction D1 and is different from the third detection position P3. Fig.10 , an example is shown in which each of the first detection position P1 , the second detection position P2 , the third detection position P3 , and the fourth detection position P4 is arranged at the center of the sheet S with respect to the transverse direction perpendicular to the feeding direction D1 .

[0107] In addition, Fig.12, the distance between the first detection position P1 and the second detection position P2 with respect to the feeding direction D1 is represented as L12, the distance between the second detection position P2 and the third detection position P3 with respect to the feeding direction D1 is represented as L23, and the distance between the third detection position P3 and the fourth detection position P4 with respect to the feeding direction D1 is represented as L34. In addition, the first detection portion S1 is constituted by including an optical sensor that outputs a low signal when the sheet S does not exist and outputs a high signal when the sheet S exists. Moreover, with respect to the second detection portion S2, the third detection portion S3, and the fourth detection portion S4, the same sensor as the first detection portion S1 is used. Therefore, due to the passage of the leading end portion of the sheet S, the signal output from the sensor of each of the first detection portion S1, the second detection portion S2, the third detection portion S3, and the fourth detection portion S4 is switched from low to high. In addition, due to the passage of the trailing end portion of the sheet S, the signal output from the sensor of each of the first detection portion S1, the second detection portion S2, the third detection portion S3, and the fourth detection portion S4 is switched from high to low. Therefore, the controller 9 can recognize the passing moment of the leading end portion or the rear end portion of the sheet at the first detection position P1 in response to the signal output from the sensor of the first detection portion S1. Incidentally, in addition, with respect to the second detection portion S2, the third detection portion S3, and the fourth detection portion S4, similarly to the first detection portion S1, the controller 9 can recognize the passing moment of the leading end portion or the rear end portion of the sheet at the second detection position P2, the third detection position P3, and the fourth detection position P4. In addition, the controller 9 can calculate the feeding speed V of the sheet S and the length of the sheet S relative to the feeding direction D1 based on the passing moment of the leading end portion or the rear end portion of the sheet S at the first detection position P1, the second detection position P2, the third detection position P3, and the fourth detection position P4. In addition, in the case where the length of the sheet S is L, the length between the feed roller pair 11 and the upstream feed roller pair 12 is L(11-12), the length between the downstream feed roller pair 13 and the feed roller pair 11 is L(13-11), the length between the third detection portion S3 and the upstream feed roller pair 12 is L(3-12), and the length between the downstream feed roller pair 13 and the second detection portion S2 is L(13-2), and the feed roller pairs and the detection portions are arranged to satisfy the following relationship:

[0108] L>L(11-12) and L>L(13-11) Formula (7)

[0109] L(3-12)>L and L(13-2)>L Formula (8)

[0110] With respect to the corresponding feed roller pair and the corresponding detection portion, by arranging the feed roller pair and the detection portion to satisfy the relationship of formula (7) and formula (8), the sheet detection unit 10 is capable of detecting the leading end portion and the trailing end portion of the sheet S through the first detection portion, the second detection portion, the third detection portion, and the fourth detection portion in a state in which the sheet S is not clamped by the upstream feed roller pair and the downstream feed roller pair during the feeding of the sheet S by the feed roller pair 11. That is, when calculating the sheet length, it becomes possible to calculate the sheet length before the leading end portion of the sheet is clamped by the downstream feed roller pair. That is, the vibration of the sheet caused by the clamping of the leading end portion of the sheet by the downstream feed roller can be suppressed, so that it becomes possible to accurately detect the sheet length.

[0111] Next, refer to Fig.12 and Fig.13 , a calculation method of the length of the sheet S with respect to the feeding direction D1 in this embodiment will be described. Fig.13 It shows that when the sheet surface passes Fig.12 Schematic diagram of changes in signals output from the first detection section S1, the second detection section S2, the third detection section S3 and the fourth detection section S4 respectively when the sheet detection unit 10 is in FIG. Fig.13 In the formula 3-1, the time when the rear end of the sheet S passes through the first detection position P1 and the second detection position P2 is represented as T1h and T2h, respectively. In addition, the time when the front end of the sheet S passes through the third detection position P3 and the fourth detection position P4 is represented as T3t and T4t, respectively. First, based on the time T1h, T2h, T3t, T4t and the relative positions of the first detection position P1, the second detection position P2, the third detection position P3 and the fourth detection position P4 with respect to the feeding direction D1, the feeding speed V of the sheet S is calculated as shown below (Formula 3-1):

[0112] Feed speed V' = L34 / (T4t-T3t)

[0113] Feed speed V" = L12 / (T2h-T1h)

[0114] Feed speed V = (V' + V") / 2 (Formula 3-1).

[0115] In (Formula 3-1), the feeding speed V" as the first speed in this embodiment is calculated based on the distance L12 and the difference between the moment T1h when the rear end of the sheet passes the first detection position P1 and the moment T2f when the rear end of the sheet passes the second detection position P2. The difference between the moment T1h when the rear end of the sheet passes the first detection position P1 and the moment T2h when the rear end of the sheet passes the second detection position P2 is the first time in this embodiment, and the distance L12 is the first distance in this embodiment. The difference between the moment T3t when the front end of the sheet passes the third detection position P3 and the moment T4t when the front end of the sheet passes the fourth detection position P4 is the fourth time in this embodiment, and the distance L34 is the fourth distance in this embodiment.

[0116] In addition, in (Formula 3-1), the speed V' as the second speed in this embodiment is calculated based on the distance L34 and the difference between the time T3t when the leading end of the sheet passes the third detection position P3 and the time T4t when the leading end of the sheet passes the fourth detection position P4. Here, by calculating the feed speed V based on the average value of the speed V' and the speed V", the calculation error caused by the change in the detection of the end portion of the sheet S by the sensor of each of the first detection part S1, the second detection part S2, the third detection part S3 and the fourth detection part S4 can be reduced.

[0117] In addition, the length of the sheet relative to the feeding direction D1 is calculated as shown below (Formula 3-2):

[0118] Length L' = L12 + L23 + L34 + (T1h - T4t) × V,

[0119] Length L" = L12 + L23 + (T1h - T3t) × V,

[0120] Length L"'=L23+L34+(T2h-T4t)×V,

[0121] Length L"" = L23 + (T2h - T3t) × V, and

[0122] Length L = (L'+L"+L"'+L"") / 4 (Formula 3-2).

[0123] In (Formula 3-2), the length L' of the sheet relative to the feeding direction D1 is calculated based on the distance (L12+L23+L34) and the difference between the moment T1h when the rear end of the sheet passes the first detection position P1 and the moment T4t when the front end of the sheet passes the fourth detection position P4. In addition, the length L" of the sheet relative to the feeding direction D1 is calculated based on the distance (L12+L23) and the difference between the moment T1h when the rear end of the sheet passes the first detection position P1 and the moment T3t when the front end of the sheet passes the third detection position P3. In addition, the length L"' of the sheet relative to the feeding direction D1 is calculated based on the distance (L23+L34) and the difference between the moment T2h when the rear end of the sheet passes the second detection position P2 and the moment T4t when the front end of the sheet passes the fourth detection position P4. In addition, the length L"" of the sheet with respect to the feeding direction D1 is calculated based on the distance L23 and the difference between the time T2h when the sheet trailing end passes the second detection position P2 and the time T3t when the sheet leading end passes the third detection position P3.

[0124] The difference between time T1h when the sheet trailing end passes the first detection position P1 and time T3t when the sheet leading end passes the third detection position P3 is the third time in this embodiment, and the distance (L23+L12) is the third distance in this embodiment.

[0125] In addition, the difference between the time T2h when the sheet trailing end passes the second detection position P2 and the time T3t when the sheet leading end passes the third detection position P3 is the second time in this embodiment, and the distance L23 is the second distance in this embodiment.

[0126] Here, the sheet length L is calculated based on the average value of the length L' as the first length and the length L", the length L"' and the length L"" as the second length in this embodiment. Thereby, the calculation error of the sheet length caused by the change in the detection of the end portion of the sheet S by the sensor of each of the first detection part S1, the second detection part S2, the third detection part S3 and the fourth detection part S4 can be reduced. Incidentally, it is also possible to adopt a structure in which the sheet length L relative to the feeding direction D1 is calculated based on only one of the length L' and the length L" or the average value of any two or more of the length L', the length L", the length L"' and the length L"". In this embodiment, for example, the feeding speed V of the sheet S calculated in (Formula 3-1) is substituted into (Formula 3-2), that is, the length L"=L12+L23+(T1h-T3t)×V, and the sheet length L relative to the feeding direction D1 can also be calculated under the condition that the length L=length L".

[0127] Therefore, in this embodiment, the length L is calculated using the time (T1h, T2h) at which the rear end of the sheet passes before the rear end of the sheet passes the feed roller pair 11 and the time (T3t, T4t) at which the front end of the sheet passes after the front end of the sheet passes the feed roller pair 11. Therefore, the length L of the sheet S relative to the feeding direction D1 can be accurately calculated without being affected by the time when the sheet S enters the downstream feed roller pair 13. That is, based on the sheet length L, the timing of sheet feeding by the tilt movement correction portion is controlled so that it becomes possible to suppress the positional deviation between the front and back sides of the image formed on the sheet S. Incidentally, in addition, with regard to Embodiment 3, as a modified embodiment, a configuration similar to that of the modified embodiments of Embodiments 1 and 2 can also be adopted. That is, after the front end of the sheet is clamped by the downstream feed roller pair 13, the rear end of the sheet can also be detected by the second detection portion.

[0128] [Example 4]

[0129] <Configuration for Calculating Sheet Length with Respect to Feeding Direction in Embodiment 4>

[0130] Next, a configuration for calculating the sheet length with respect to the feeding direction in Embodiment 4 will be described. Fig.14 1 is a top view (plan view) showing the structure of the sheet detection unit 10 for calculating the sheet length with respect to the feeding direction in Embodiment 4.

[0131] The difference from Embodiments 1, 2, and 3 is that each of the detection portions arranged on the upstream side and the downstream side of the feed roller pair 11 is provided with a plurality of sensors with respect to the lateral direction. Incidentally, the configurations of the printer 1, the feed roller pair 11, the upstream feed roller pair 12, the downstream feed roller pair 13, the first detection portion S1, the second detection portion S2, and the third detection portion S3 are similar to those in Embodiment 1, and therefore, redundant description thereof will be omitted. With regard to the sheet detection unit 10, the description will be made assuming that the sheet detection unit 10 is arranged at the double-sided feeding portion 502, but when the sheet detection unit 10 is located on the feeding path on which the sheet S is fed in the printer 1, the sheet detection unit 10 may be arranged at a position other than the double-sided feeding portion 502.

[0132] The first detection section S1 includes sensors S1A and S1B for detecting the passage of the end portion of the sheet at a first detection position P1, which is located on the side downstream of the feed roller pair 11 and upstream of the downstream feed roller pair 13 with respect to the feed direction D1. The sensors S1A and S1B are a sensor pair arranged at a certain interval with respect to the transverse direction perpendicular to the feed direction D1. In addition, the second detection section S2 includes sensors S2A and S2B for detecting the passage of the end portion of the sheet at a second detection position P2, which is located on the side downstream of the feed roller pair 11 with respect to the feed direction D1 and is different from the first detection position P1. The sensors S2A and S2B are a sensor pair arranged at a certain interval with respect to the transverse direction perpendicular to the feed direction D1. In addition, the third detection section S3 includes sensors S3A and S3B for detecting the passage of the end portion of the sheet at a third detection position P3 located on the side upstream of the feed roller pair 11 and downstream of the upstream feed roller pair 12 with respect to the feed direction D1. The sensors S3A and S3B are a sensor pair arranged at a certain interval with respect to the lateral direction perpendicular to the feed direction D1.

[0133] By the way, in Fig.14, the distance between the first detection position P1 and the second detection position P2 with respect to the feeding direction D1 is represented as L12, and the distance between the second detection position P2 and the third detection position P3 with respect to the feeding direction D1 is represented as L23. In addition, each of the sensors S1A and S1B constituting the first detection portion S1 is an optical sensor that outputs a low signal when the sheet S is not present and outputs a high signal when the sheet S is present. Moreover, with respect to the second detection portion S2 and the third detection portion S3, the same sensor as the first detection portion S1 is used. Therefore, due to the passage of the leading end portion of the sheet S, the signal output from each of the first detection portion S1, the second detection portion S2, and the third detection portion S3 is switched from low to high. In addition, due to the passage of the trailing end portion of the sheet S, the signal output from each of the first detection portion S1, the second detection portion S2, and the third detection portion S3 is switched from high to low. Therefore, the controller 9 can identify the passing moment of the leading end portion or the rear end portion of the sheet at the first detection position P1, the second detection position P2, and the third detection position P3 in response to the signals output from the first detection portion S1, the second detection portion S2, and the third detection portion S3, respectively. In addition, the controller 9 can calculate the feeding speed V of the sheet S and the length of the sheet S relative to the feeding direction D1 based on the passing moment of the leading end portion or the rear end portion of the sheet S at the first detection position P1, the second detection position P2, and the third detection position P3. In addition, in the case where the length of the sheet S is L, the length between the feed roller pair 11 and the upstream feed roller pair 12 is L (11-12), the length between the downstream feed roller pair 13 and the feed roller pair 11 is L (13-11), the length between the second detection portion S2 and the upstream feed roller pair 12 is L (2-12), and the length between the downstream feed roller pair 13 and the third detection portion S3 is L (13-3), and the feed roller pair and the detection portion are arranged to satisfy the following relationship:

[0134] L>L(11-12) and L>L(13-11) Formula (9)

[0135] L(2-12)>L and L(13-3)>L Formula (10)

[0136] With respect to the corresponding feed roller pair and the corresponding detection portion, by arranging the feed roller pair and the detection portion to satisfy the relationship of formula (9) and formula (10), the sheet detection unit 10 is capable of detecting the leading end portion and the trailing end portion of the sheet S through the first detection portion, the second detection portion, and the third detection portion in a state in which the sheet S is not clamped by the upstream feed roller pair and the downstream feed roller pair during the feeding of the sheet S by the feed roller pair 11. That is, when calculating the sheet length, it becomes possible to calculate the sheet length before the leading end portion of the sheet is clamped by the downstream feed roller pair. That is, the vibration of the sheet caused by the clamping of the leading end portion of the sheet by the downstream feed roller pair can be suppressed, so that it becomes possible to accurately detect the sheet length.

[0137] like Fig.14 As shown, the first detection section S1 is composed of sensors S1A and S1B arranged at overlapping positions with respect to the feeding direction D1 and arranged at different positions with respect to the lateral direction W. In addition, the sensors S2A, S2B, S3A, and S3B are in the same positional relationship as the sensors S1A and S1B. Therefore, it is possible to Fig.14 The sensors S1B, S2B, and S3B on the upper side and arranged in Fig.14 The feeding speed and the length of the sheet S with respect to the feeding direction D1 are acquired from sensors S1A, S2A, and S3A on the lower side of the sheet S.

[0138] Specifically, by applying the configuration of Example 1, based on the arrangement in Fig.14 The speed VB is calculated based on the signals of sensors S1B, S2B and S3B on the upper side, and the speed VA is calculated based on the signals of sensors S1A, S2A and S3A. In addition, the following (Formula 4-1) is calculated so that the feeding speed V of the sheet S is obtained based on the average value of the speed VA and the speed VB.

[0139] Feed speed V = (VA + VB) / 2 (Formula 4-1)

[0140] Next, the length LB of the sheet S is calculated based on the sheet feeding speed V obtained by calculation and the signals of the sensors S1B, S2B, and S3B arranged on the upper side. In addition, the length LB is calculated based on the sheet feeding speed V obtained by calculation and the signals of the sensors S1A, S2A, and S3A arranged on the lower side. Then, as shown in the following (Formula 4-2), calculation is performed so that the length L of the sheet S relative to the feeding direction D1 is obtained based on the average value of the length LA and the length LB.

[0141] Length L = (LA + LB) / 2 (Formula 4-2)

[0142] Therefore, in this embodiment, by arranging two sensors with respect to the lateral direction W, it becomes possible to use data that is twice as much as in the case of a single sensor, so that calculation errors caused by changes in sensor detection of the end portion can be further reduced.

[0143] <Modified Example of Example 4>

[0144] Next, refer to Fig.15 and Fig.16 As a modified embodiment of Embodiment 4, a calculation method of the length of the sheet S with respect to the feeding direction D1 will be described. Fig.15 1 is a top view showing a state in which a sheet S in a state of being tilted at an oblique movement angle θ is fed in the sheet detection unit 10. In addition, Fig.16 It is shown in Fig.15 Schematic diagram of changes in signals output from sensors S2A and S2B of the second detection portion S2 in the state of Fig.16 In FIG. 1 , the time when the leading end of the sheet S passes through the sensors S2A and S2B is represented as T2At and T2Bt, respectively. Fig.15 As shown, in the case where the sheet S is obliquely moved and fed, the length of the sheet S with respect to the feeding direction calculated in (Formula 4-2) is the length of the sheet (length L') measured along the feeding center C with respect to the transverse direction W. On the other hand, in this embodiment of the first detection portion S1, the second detection portion S2, and the third detection portion S3, for example, based on the change in the signal output from the sensors S2A and S2B, the oblique movement angle θ of the sheet S is calculated, so that the length of the sheet with respect to the feeding direction is acquired.

[0145] like Fig.15 As shown in FIG. 1 , in the case where the sheet S is fed while forming an oblique movement angle θ with respect to the feeding direction D1, as shown in FIG. Fig.16 As shown, the timings when the signals of sensors S2A and S2B become high are different from each other by time (T2Bt-T2At). The controller 9 calculates the tilt movement angle θ based on the feed speed V acquired from (Formula 4-1), the time (T2At-T2Bt), and the length W1 as the interval between sensor S2A and sensor S2B by performing calculations as shown in the following (Formula 4-3).

[0146] Tilt movement angle θ = tan^(-1){(T2Bt-T2At)×V / W} (Formula 4-3)

[0147] In addition, based on the oblique movement angle θ thus calculated, the length L′ calculated in (Formula 4-2) is corrected by the following (Formula 4-4), so that the length L of the sheet S with respect to the feeding direction D1 is obtained.

[0148] Length L = L'cosθ (Formula 4-4)

[0149] Therefore, in this embodiment, even in the case where the sheet S moves obliquely, the length L of the sheet S with respect to the feeding direction D1 can be accurately calculated without being affected by the time when the sheet S enters the downstream feed roller pair 13. In reality, the fed sheet moves slightly obliquely, and therefore, by executing this embodiment, the sheet feeding speed and the sheet length can be calculated more accurately. That is, based on the sheet length L, the timing of sheet feeding by the oblique movement correction portion is controlled, so that it becomes possible to suppress the positional deviation between the front and back sides of the image formed on the sheet S.

[0150] [Example 5]

[0151] <Configuration for Calculating Sheet Length with Respect to Feeding Direction in Embodiment 5>

[0152] Next, a configuration for calculating the sheet length with respect to the feeding direction in Embodiment 5 will be described. Fig.17 1 is a top view (plan view) showing the structure of the sheet detection unit 10 for calculating the sheet length with respect to the feeding direction in Embodiment 5. FIG.

[0153] The difference from Embodiments 1 and 4 lies in the kind of detection portions arranged on the upstream side and the downstream side of the feed roller pair 11. Specifically, a CIS (Contact Image Sensor) capable of reading the end portion of the sheet is arranged. Incidentally, the configurations of the printer 1, the feed roller pair 11, the upstream feed roller pair 12, and the downstream feed roller pair 13 are similar to those in Embodiment 1, and therefore, redundant description thereof will be omitted. With regard to the sheet detection unit 10, the description will be made assuming that the sheet detection unit 10 is arranged at the double-sided feeding portion 502, but when the sheet detection unit 10 is located on the feeding path in which the sheet S is fed in the printer 1, the sheet detection unit 10 may also be arranged at a position other than the double-sided feeding portion 502.

[0154] The sheet detection unit 10 includes a feed roller pair 11 for feeding a sheet S, and a first reading portion S10 and a second reading portion S20 extending along a feed direction D1. The first reading portion S10 is provided on either one of the upstream side and the downstream side of the feed roller pair 11 with respect to the feed direction D1, and reads an end portion of the sheet S fed in the sheet detection unit 10. The second reading portion S20 is provided on the other of the upstream side and the downstream side of the feed roller pair 11 with respect to the feed direction D1, and reads an end portion of the sheet S fed in the sheet detection unit 10. Incidentally, in Fig.17In the embodiment, the first reading section S10 is arranged downstream of the feed roller pair 11 and upstream of the downstream feed roller pair 13 with respect to the feed direction D1. In addition, the second reading section S20 is arranged upstream of the feed roller pair 11 and downstream of the upstream feed roller pair 12. Fig.17 , a distance from an upstream end of the first reading portion S10 to an upstream end of the second reading portion S20 with respect to the feeding direction D1 is represented as a distance L120. For example, a CIS is used as the first reading portion S10 and the second reading portion S20.

[0155] Fig.18A is a schematic diagram showing an example of a plurality of images read by the first reading portion S10. Fig.19A : is a graph that plots the relationship between the reading time T when each of the plurality of images is read by the first reading portion S10 and the position X of the end portion of the sheet for each of the plurality of images. Fig.18A and Fig.19A As shown, the first reading section S10 can read an image of an end portion of a sheet fed in the sheet detection unit 10 at regular intervals. Fig.18A and Fig.19A , the position X of the end portion of the sheet read by the first reading portion S10 is denoted by X11 at time T11, by X12 at time T12, . . . , and by X1m at time T1m.

[0156] in addition, Fig.18B is a schematic diagram showing an example of a plurality of images read by the second reading portion S20. Fig.19B : is a graph that plots the relationship between the reading time T when each of the plurality of images is read by the second reading portion S20 and the position X of the end portion of the sheet for each of the plurality of images. Fig.18B and Fig.19B As shown, the second reading section S20 can read an image of an end portion of a sheet fed in the sheet detection unit 10 at regular intervals. Fig.18B and Fig.19B , the position X of the end portion of the sheet read by the second reading portion S20 is denoted by X21 at time T21, by X22 at time T22, . . . , and by X2n at time T2n.

[0157] By the way, in Fig.18A and Fig.18B, the area where the sheet is detected is indicated by a white background, and the area where the sheet is not detected is indicated by a black background. Therefore, for each of the specific moments, the first reading section S10 and the second reading section S20 are able to read the change in the position of the end portion of the sheet as the end portion of the sheet passes through the sheet detection unit 10 as a plurality of continuous images. In addition, the images read by the first reading section S10 and the second reading section S20 are transmitted to the controller 9. The controller 9 calculates the sheet feeding speed and the sheet length relative to the feeding direction based on the images read by the first reading section S10 and the second reading section S20.

[0158] In addition, in the case where the length of the sheet S is L, the length between the feed roller pair 11 and the upstream feed roller pair 12 is L(11-12), the length between the downstream feed roller pair 13 and the feed roller pair 11 is L(13-11), the length between the upstream end of the first reading section S10 and the upstream feed roller pair 12 is L(10-12), and the length between the downstream feed roller pair 13 and the downstream end of the second reading section S20 is L(12-20), the feed roller pairs and the detection section are arranged to satisfy the following relationship:

[0159] L>L(11-12) and L>L(13-11) Formula (11)

[0160] L(10-12)>L and L(12-20)>L Formula (12)

[0161] With respect to the corresponding feed roller pair and the corresponding reading portion, by arranging the feed roller pair and the detection portion to satisfy the relationship of formula (11) and formula (12), the sheet detection unit 10 can detect the leading end portion and the trailing end portion of the sheet S through the first reading portion and the second reading portion in the state in which the sheet S is not clamped by the upstream feed roller pair and the downstream feed roller pair during the feeding of the sheet S by the feed roller pair 11. That is, when calculating the sheet length, it becomes possible to calculate the sheet length before the leading end portion of the sheet is clamped by the downstream feed roller pair. That is, it is possible to suppress the vibration of the sheet caused by the clamping of the leading end portion of the sheet by the downstream feed roller pair, so that it becomes possible to accurately detect the sheet length. Incidentally, in addition, with respect to this embodiment 5, as a modified embodiment, a configuration similar to the modified embodiments of embodiments 1 and 3 can also be adopted. That is, after the leading end portion of the sheet is clamped by the downstream feed roller pair 13, the trailing end portion of the sheet can also be detected by the second reading portion.

[0162] The controller 9 plots the relationship between the reading timing T of the plurality of images and the position of the end portion of the sheet for the plurality of associated images based on the images read by the first reading section S10 and the second reading section S20, and performs linear approximation by the least square method. Then, in the curve after the linear approximation, the slope of the straight line is used as the sheet feeding speed. Fig.19A As shown, the slope of the straight line obtained by plotting the difference between any two points in T11, T12, ..., T1m and the difference between the positions X11, X12, ..., X1m of the sheet end portion of the image read at each point in time is V1. Fig.19B As shown, the slope of the straight line obtained by plotting the difference between any two points in T21, T22, ..., T2n and the difference between the positions X21, X22, ..., X2n of the sheet end portion of the image read at each point in time is V2. Fig.19A The sheet feeding speed is determined as V1 by the slope of the straight line obtained in Fig.19B When the sheet feeding speed is determined as V2 by the slope of the straight line obtained in , the sheet feeding speed V is calculated as in the following (Formula 5-1).

[0163] Feed speed V = (V1 + V2) / 2 (Formula 5-1)

[0164] The difference in time between any two points in T11, T12, ..., T1m is an example of the fifth time in this embodiment. In addition, the difference in position X11, X12, ..., X1m of the sheet end portion of the image read at the associated time is an example of the fifth distance. In addition, the feed speed V1 is the third speed in this embodiment. In addition, the difference in time between any two points in T21, T22, ..., T2n is an example of the seventh time in this embodiment, and the difference in position X21, X22, ..., X2n of the sheet end portion of the image read at the associated time is an example of the seventh distance. In addition, the feed speed V2 is the fourth speed in this embodiment.

[0165] Next, a method of calculating the length L of the sheet with respect to the feeding direction D1 using the sheet feeding speed V will be described. Fig. 20A As shown, the position of the leading end portion of the sheet read by the first reading section S10 at time T=T1i is referred to as X1i. Fig. 20B As shown, the position of the rear end portion of the sheet read by the second reading portion S20 at time T=T2j is referred to as X2j. At this time, the distance the sheet is fed within time T=T1i to T2j can be expressed as (T2j-T1i)×V.

[0166] The sixth time in this embodiment corresponds to the time difference between the reading time T1i of the first reading section S10 and the reading time T2j of the second reading section S20. In addition, the sixth distance in this embodiment corresponds to the difference between the leading end position X1i of the sheet read by the first reading section S10 and the trailing end position X2j of the sheet read by the second reading section S20.

[0167] The controller 9 calculates the length Lij of the sheet calculated from the data of time T=T1i and time T=T2j as in the following (Formula 5-2) based on the distance ((T2j-T1i)×V), the distance L120, the leading end position X1i of the sheet, and the trailing end position X2j of the sheet.

[0168] Length Lij = (T2j-T1i) × V + L120 + X1i-X2j ​​(Formula 5-2)

[0169] Then, the controller 9 calculates the length L of the sheet with respect to the feeding direction D1 as in the following (Formula 5-3) based on all the images read by the first reading portion S10 and the second reading portion S20 .

[0170] Length L = Σ[i = 1 → m] Σ[j = 1 → n]

[0171] {(T2j-T1i)×V+L120+X1i-X2j} / m×n (Formula 5-3)

[0172] Therefore, in this embodiment, the sheet length L is calculated based on the position change in the rear end portion of the sheet before the leading end portion of the sheet passes through the downstream feed roller pair 13 and based on the position change in the rear end portion of the sheet after the leading end portion of the sheet passes through the feed roller pair 11. Therefore, the length L of the sheet S with respect to the feeding direction D1 can be accurately calculated without being affected by when the sheet S enters the downstream feed roller pair 13. That is, based on the sheet length L, the timing of sheet feeding by the tilt movement correction portion is controlled so that it becomes possible to suppress the positional deviation between the front and back sides of the image formed on the sheet S.

[0173] <Other embodiments>

[0174] The printer 1 of Embodiments 1 to 5 is an example of an image forming apparatus, and for example, may also be an image forming apparatus including an image forming device of an inkjet type instead of an electrophotographic type. In addition, there is an image forming apparatus including an auxiliary device (such as an optional feeder or sheet processing device) in addition to the main assembly of the apparatus including the image forming device, but the configuration corresponding to the sheet feeding device described according to Embodiments 1 to 5 may also be used to feed the sheet S in such an auxiliary device.

[0175] exist Fig.21, a control block diagram in embodiments 1 to 5 is shown. The controller 9 of embodiments 1 to 5 includes a central processing unit (CPU) and a memory. The CPU loads and executes a program stored in the memory, and performs integrated control of the printer 1 in cooperation with a corresponding functional part that exhibits a specific function. The memory includes a non-volatile storage medium such as a read-only memory (ROM) and a volatile storage medium such as a random access memory (RAM), and not only constitutes a storage place for programs and data, but also becomes a work area when the CPU executes the program. In addition, the memory is an example of a non-transient storage medium in which a program for controlling the printer 1 is stored. Incidentally, the controller 9 can also be installed on the circuit of the controller as independent hardware, and can also be installed in a software-like manner as a functional unit of a program executed by a CPU or other processing device.

[0176] The controller rotates the corresponding motor connected to the corresponding roller based on the information fragments of the first to fourth detection parts and the first and second reading parts. In addition, regarding the rotation of the motor, the rotation timing and the rotation speed can be controlled, and the rotation timing and the rotation speed are controlled based on the information fragments of the corresponding detection part and the corresponding reading part.

[0177] While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments.The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.

Claims

1. A sheet feeding device, comprising: a first feed roller pair, the first feed roller pair being rotatable in a sheet-holding state and configured to feed the sheet; an upstream feed roller pair disposed upstream of the first feed roller pair with respect to a sheet feeding direction and configured to feed the sheet; a downstream feed roller pair disposed downstream of the first feed roller pair with respect to the sheet feeding direction and configured to feed the sheet; a second feed roller pair disposed downstream of the downstream feed roller pair with respect to the sheet feeding direction and configured to feed the sheet; a first detection portion provided at a first detection position downstream of the first feed roller pair and upstream of the downstream feed roller pair with respect to the sheet feeding direction and configured to detect the passage of a leading end portion of the sheet fed by the first feed roller pair; a second detection portion disposed at a second detection position different from the first detection position, downstream of the first feed roller pair and upstream of the downstream feed roller pair with respect to the sheet feeding direction, and configured to detect the passage of the leading end portion of the sheet fed by the first feed roller pair; a third detection portion provided at a third detection position upstream of the first feed roller pair and downstream of the upstream feed roller pair with respect to the sheet feeding direction and configured to detect passage of a rear end portion of the sheet fed by the first feed roller pair; as well as a controller configured to perform calculations in response to signals from the first detection portion, the second detection portion, and the third detection portion, wherein the controller calculates the sheet feeding speed based on a first time and a first distance between the first detection position and the second detection position relative to the sheet feeding direction, the first time being a difference between a time when the leading end portion of the sheet passes through the first detection position and a time when the leading end portion of the sheet passes through the second detection position, wherein the controller calculates the length of the sheet relative to the sheet feeding direction based on the sheet feeding speed, a second time, and a second distance between the second detection position and the third detection position relative to the sheet feeding direction, the second time being a difference between a time when the leading end portion of the sheet passes through the second detection position and a time when the trailing end portion of the sheet passes through the third detection position, and The controller controls the sheet feeding timing of the second feeding roller pair based on the information of the length of the sheet.

2. The sheet feeding device according to claim 1, wherein: When the leading end portion of the sheet fed by the first feed roller pair is detected by the first detection portion and the second detection portion, the trailing end portion of the sheet passes through the upstream feed roller pair, and wherein, when the rear end portion of the sheet fed by the first feed roller pair is detected by the third detection portion, the front end portion has not reached the downstream feed roller pair.

3. The sheet feeding device according to claim 1, wherein: The calculated length of the sheet is a first length, wherein the controller calculates a second length of the sheet relative to the sheet feeding direction based on the sheet feeding speed, a third time, and a third distance between the first detection position and the third detection position relative to the sheet feeding direction, the third time being a difference between a time when the leading end portion of the sheet passes through the first detection position and a time when the trailing end portion of the sheet passes through the third detection position, and The controller calculates the length of the sheet relative to the sheet feeding direction based on the first length and the second length, and controls the sheet feeding timing of the second feeding roller pair based on information on the length of the sheet.

4. A sheet feeding device, comprising: a first feed roller pair, the first feed roller pair being rotatable in a sheet-holding state and configured to feed the sheet; an upstream feed roller pair disposed upstream of the first feed roller pair with respect to a sheet feeding direction and configured to feed the sheet; a downstream feed roller pair disposed downstream of the first feed roller pair with respect to the sheet feeding direction and configured to feed the sheet; a second feed roller pair disposed downstream of the downstream feed roller pair with respect to the sheet feeding direction and configured to feed the sheet; a first detection portion provided at a first detection position upstream of the first feed roller pair and downstream of the upstream feed roller pair with respect to the sheet feeding direction and configured to detect the passage of a rear end portion of the sheet fed by the first feed roller pair; a second detection portion which is disposed at a second detection position different from the first detection position and upstream of the first feed roller pair and downstream of the downstream feed roller pair with respect to the sheet feeding direction and is configured to detect the passage of the rear end portion of the sheet fed by the first feed roller pair; a third detection portion provided at a third detection position downstream of the first feed roller pair and upstream of the upstream feed roller pair with respect to the sheet feeding direction and configured to detect the passage of a leading end portion of the sheet fed by the first feed roller pair; as well as a controller configured to perform calculations in response to signals from the first detection portion, the second detection portion, and the third detection portion, wherein, when the leading end portion of the sheet fed by the first feed roller pair is detected by the third detection portion, the trailing end portion of the sheet passes through the upstream feed roller pair, and wherein, when the rear end portion of the sheet fed by the first feed roller pair is detected by the first detection portion and the second detection portion, the front end portion has not reached the downstream feed roller pair, wherein the controller calculates the sheet feeding speed based on a first time and a first distance between the first detection position and the third detection position relative to the sheet feeding direction, the first time being a difference between a time when the rear end portion of the sheet passes through the first detection position and a time when the rear end portion of the sheet passes through the second detection position, wherein the controller calculates the length of the sheet relative to the sheet feeding direction based on the sheet feeding speed, a second time, and a second distance between the second detection position and the third detection position relative to the sheet feeding direction, the second time being a difference between a time when the leading end portion of the sheet passes through the third detection position and a time when the trailing end portion of the sheet passes through the second detection position, and The controller controls the sheet feeding timing of the second feeding roller pair based on the information of the length of the sheet.

5. The sheet feeding device according to claim 4, wherein: The calculated length of the sheet is a first length, wherein the controller calculates a second length of the sheet relative to the sheet feeding direction based on the sheet feeding speed, a third time, and a third distance between the first detection position and the third detection position relative to the sheet feeding direction, the third time being a difference between a time when the leading end portion of the sheet passes through the third detection position and a time when the trailing end portion of the sheet passes through the first detection position, and The controller calculates the length of the sheet relative to the sheet feeding direction based on the first length and the second length, and controls the sheet feeding timing of the second feeding roller pair based on information on the length of the sheet.

6. The sheet feeding device according to claim 4 or 5, further comprising a fourth detection portion, the fourth detection portion being arranged at a fourth detection position different from the third detection position downstream of the first feed roller pair and upstream of the downstream feed roller pair with respect to the sheet feeding direction, and being configured to detect the passage of the leading end portion of the sheet fed by the first feed roller pair, in, The calculated sheet feeding speed is the first speed, wherein the controller calculates the second speed based on a fourth time and a fourth distance between the third detection position and the fourth detection position relative to the sheet feeding direction, the fourth time being a difference between a time when the leading end portion of the sheet passes through the third detection position and a time when the leading end portion of the sheet passes through the fourth detection position, and The controller calculates a sheet feeding speed based on the first speed and the second speed.

7. The sheet feeding device according to claim 1, wherein: Each of the first detection portion, the second detection portion, and the third detection portion includes a plurality of detection portions spaced apart with respect to a transverse direction of the sheet which is perpendicular to the sheet feeding direction, and wherein the controller calculates an inclination movement angle of the sheet based on a difference between a moment when the leading end portion of the sheet passes through one of the plurality of detection portions and a moment when the leading end portion of the sheet passes through another of the plurality of detection portions, and corrects a length of the sheet based on the inclination movement angle.

8. A sheet feeding device, comprising: a first feed roller pair, the first feed roller pair being rotatable in a sheet-holding state and configured to feed the sheet; an upstream feed roller pair disposed upstream of the first feed roller pair with respect to a sheet feeding direction and configured to feed the sheet; a downstream feed roller pair disposed downstream of the first feed roller pair with respect to the sheet feeding direction and configured to feed the sheet; a second feed roller pair disposed downstream of the downstream feed roller pair with respect to the sheet feeding direction and configured to feed the sheet; a first reading portion disposed so as to extend along the sheet feeding direction on a side downstream of the first feed roller pair and upstream of the downstream feed roller pair with respect to the sheet feeding direction and configured to read an image of a leading end portion of the sheet fed by the first feed roller pair; a second reading portion provided to extend along the sheet feeding direction on a side upstream of the first feed roller pair and downstream of the upstream feed roller pair with respect to the sheet feeding direction and configured to read an image of a rear end portion of the sheet fed by the first feed roller pair; as well as a controller configured to perform calculations based on the images read by the first reading portion and the second reading portion, wherein, when the image of the leading end portion of the sheet fed by the first feed roller pair is read by the first reading portion, the trailing end portion of the sheet passes through the upstream feed roller pair, and wherein, when the image of the rear end portion of the sheet fed by the first feed roller pair is read by the second reading portion, the front end portion does not reach the downstream feed roller pair, wherein the controller calculates the sheet feeding speed based on a fifth time which is a difference in timing between a plurality of images read by the first reading portion and a fifth distance which is a difference in position of a leading end portion of the sheet between the plurality of images, wherein the controller calculates the length of the sheet based on a sixth time that is a difference in timing between an image read by the first reading portion and an image read by the second reading portion, and The controller controls the sheet feeding timing of the second feeding roller pair based on the information of the length of the sheet.

9. The sheet feeding device according to claim 8, wherein: The calculated sheet feeding speed is the third speed, wherein the controller calculates a fourth speed based on a seventh time which is a difference in timing between the plurality of images read by the second reading portion and a seventh distance which is a difference in position of an end portion of the sheet between the plurality of images, and Wherein, the controller calculates the sheet feeding speed based on the third speed and the fourth speed.

10. The sheet feeding device according to claim 1 or 8, wherein: The first feed roller pair is subjected to sandblasting at peripheral surfaces thereof capable of contacting the sheet.

11. An imaging device comprising: The sheet feeding device according to claim 1 or 8; as well as An image forming device is configured to form an image on a sheet fed by the sheet feeding device.

12. The image forming apparatus according to claim 11, further comprising a double-sided feeding portion configured to reverse the sheet on which the image is formed by the image forming device and then feed the sheet to the image forming device again, and in, The sheet feeding device calculates the length of the sheet fed through the double-side feeding portion.

Images