JP2016175718A - Medium conveyance device and image formation apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a medium conveyance device capable of accurately detecting skew of a medium, and an image formation apparatus having the same.SOLUTION: A medium conveyance device comprises: a conveyance part which conveys a medium along a conveyance path; a first sensor which detects the medium conveyed in the conveyance path; a second sensor which is arranged on the upstream side with respect to the first sensor in the conveyance path, arranged so as to be apart in the width direction of the conveyance path by a prescribed distance from the first sensor, and detects the medium conveyed in the conveyance path; a third sensor which detects the conveyance state of the medium in the conveyance path; and a control part which derives a skew amount of the medium on the basis of the respective detection results by the first to third sensors.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a medium conveying apparatus that conveys a medium such as paper and an image forming apparatus including the medium conveying apparatus.

  2. Description of the Related Art Conventionally, in an image forming apparatus, for example, image formation is performed on a medium fed out from a paper feed cassette, and then fixing and paper discharge are performed (see, for example, Patent Document 1).

JP 2013-044937 A

  In such an image forming apparatus, it is generally required to accurately detect the skew of the medium.

  The present invention has been made in view of such problems, and an object of the present invention is to provide a medium transport apparatus capable of detecting skew of a medium with high accuracy and an image forming apparatus including the medium transport apparatus.

  A medium transport apparatus according to an embodiment of the present invention includes: a transport unit that transports a medium along a transport path; a first sensor that detects a medium transported along the transport path; A second sensor that is disposed upstream of the sensor and that is separated from the first sensor by a predetermined distance in the width direction of the transport path, and that detects a medium transported on the transport path; A third sensor that detects the conveyance state of the medium and a control unit that derives the amount of skew of the medium based on the detection results of the first to third sensors.

  An image forming apparatus according to an embodiment of the present invention includes the medium conveying apparatus according to the embodiment of the present invention and an image forming unit that forms an image on a medium conveyed from the medium conveying apparatus. It is a thing.

  According to the medium conveying apparatus and the image forming apparatus as one embodiment of the present invention, it is possible to accurately detect the skew of the medium.

1 is a schematic diagram illustrating a schematic configuration example of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a schematic diagram illustrating a planar configuration example of a conveyance / slanting regulation mechanism illustrated in FIG. 1. FIG. 2 is a waveform diagram illustrating an example of an output of a conveyance / skewing regulation mechanism shown in FIG. 1 and an example of an operation of a pulse counter based on an output of the conveyance / skewing regulation mechanism shown in FIG. FIG. 2 is a schematic diagram illustrating a planar configuration example when a downstream sensor is disposed outside a central region of a transport path in the transport / slant regulation mechanism illustrated in FIG. 1. It is a schematic diagram showing an example of the relationship between a conveyance distance and the distance for the half circumference of a photosensitive drum. It is a schematic diagram showing the detailed structural example of the sensor which detects the conveyance state shown in FIG. It is a wave form diagram showing an example of operation | movement in the sensor shown in FIG. FIG. 2 is a block diagram illustrating an example of a control mechanism of the image forming apparatus illustrated in FIG. 1. 6 is a flowchart illustrating an example of a printing processing procedure. 10 is a flowchart showing an example of a detailed procedure in the skew amount derivation process shown in FIG. 9. It is a wave form diagram for demonstrating correction | amendment of the reference | standard pulse number shown in FIG. It is a schematic diagram showing the example of a structure in the image forming apparatus which concerns on the modification of this invention.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The following description is one specific example of the present invention, and the present invention is not limited to the following embodiment. Further, the present invention is not limited to the arrangement, dimensions, dimensional ratios, and the like of the components shown in the drawings. The description will be given in the following order.

1. Embodiment (example of direct image transfer)
2. Modification (example in which image transfer is indirect)
3. Other variations

<1. Embodiment>
[Constitution]
FIG. 1 schematically illustrates an overall configuration example of an image forming apparatus 1 according to an embodiment of the present disclosure. The image forming apparatus 1 is a printer that forms an image (for example, a color image) on a medium PM1 such as paper using an electrophotographic method, and is a so-called direct transfer type image forming apparatus in the present embodiment. ing. The image forming apparatus 1 includes a paper feeding unit 10, a conveyance / skew regulation unit 30, an image forming unit 40, a transfer unit 50, a fixing unit 60, and a discharge unit 70. The paper feeding unit 10, the conveyance / skew regulation unit 30, the image forming unit 40, the transfer unit 50, the fixing unit 60, and the discharge unit 70 are provided inside the housing 100 except for a part thereof.

  The conveyance / skew regulation unit 30 corresponds to a specific example of “medium conveyance device” of the present invention. The image forming apparatus 1 corresponds to a specific example of “an image forming apparatus” of the invention. In the present specification, a path through which the medium PM1 is transported is referred to as a transport path (for example, transport paths PW1, PW3, PW4 described later). In the transport path, a direction toward the paper feeding unit 10 as viewed from an arbitrary component or a position closer to the paper feeding unit 10 is referred to as upstream. In the transport path, a direction opposite to the direction toward the sheet feeding unit 10 when viewed from an arbitrary component or a position further away from the sheet feeding unit 10 is referred to as downstream. A direction in which the medium PM1 travels in the transport path (that is, a direction from upstream to downstream) is referred to as a transport direction F. A direction (for example, the X-axis direction in FIG. 1) that is parallel to the medium PM <b> 1 being conveyed on the conveyance path and orthogonal to the conveyance direction F is referred to as a width direction W. The width direction W corresponds to a specific example of “width direction” of the present invention. The dimension in the conveyance direction F is called a length, and the dimension in the width direction W is called a width.

  In the following, the conveyance path that connects the paper feeding unit 10 and the conveyance / skew regulation unit 30, the conveyance path of the medium PM1 in the conveyance / skew regulation unit 30, and the conveyance / skew regulation unit 30 and the transfer unit 50 are coupled. The conveyance path is referred to as a conveyance path PW1. The transport path PW1 corresponds to a specific example of “transport path” of the present invention. A conveyance path in the transfer unit 50, a conveyance path that connects the transfer unit 50 and the fixing unit 60, a conveyance path in the fixing unit 60, and a conveyance path that connects the fixing unit 60 and the discharge unit 70 are referred to as a conveyance path PW3. The conveyance path in the discharge part 70 is called conveyance path PW4.

(Configuration of paper feed unit 10)
The paper supply unit 10 supplies the medium PM1 to the conveyance path PW1 one by one. The sheet feeding unit 10 includes, for example, a sheet feeding tray 11, a driving unit 12, a pickup roller 13, a feed roller 14, a retard roller 15, and a sensor 16. A plurality of media PM1 are accommodated in the paper feed tray 11 in a stacked state. The paper feed tray 11 is built in the image forming apparatus 1 and is detachably attached to the lower part of the image forming apparatus 1, for example. The paper feed tray 11 has a mechanism that mechanically adjusts the position of the medium PM1 so that the medium PM1 is conveyed in a central alignment. The paper feed tray 11 has a mounting plate 11A that is rotatably supported by an axis AX1 provided on the bottom surface. The drive unit 12 includes a lift-up lever 12A that is rotatably supported by the shaft AX2, and a motor 12B that rotationally drives the shaft AX2. The lift-up lever 12A is disposed on the feeding side of the paper feed tray 11 from which the medium PM1 is fed, and is in contact with the bottom surface of the mounting plate 11A. The motor 12B rotates the lift-up lever 12A about the axis AX2 to push up the placement plate 11A in contact with the lift-up lever 12A so as to raise the medium PM1 on the placement plate 11A to a predetermined height. It has become. The motor 12B stops rotation of the lift-up lever 12A based on the output of the sensor 16, for example. The sensor 16 detects that the mounting plate 11A is sufficiently pushed up to a predetermined height and the upper surface of the uppermost medium PM1 is in contact with the pickup roller 13. By controlling the height of the medium PM1 by the sensor 16, a state where the upper surface of the uppermost medium PM1 is in contact with the pickup roller 13 is ensured.

  The pickup roller 13, the feed roller 14, and the retard roller 15 are configured to supply the medium PM 1 accommodated in the paper feed tray 11 to the conveyance / skew regulation unit 30. The pickup roller 13 and the feed roller 14 are controlled to rotate in the direction in which the medium PM1 is fed out to the transport path PW1 under the control of the control unit 101 described later. The pickup roller 13 and the feed roller 14 incorporate a one-way clutch mechanism, for example, and can idle in the direction in which the medium PM1 is fed out to the transport path PW1. The pickup roller 13 is arranged at a position where it can come into contact with the upper surface of the uppermost medium PM1. The feed roller 14 is disposed downstream of the pickup roller 13. The retard roller 15 prevents a plurality of media PM1 from being overlapped and fed out to the transport path PW1. The retard roller 15 is controlled to rotate in the opposite direction to the feed roller 14 under the control of the control unit 101. The retard roller 15 is disposed at a position facing the feed roller 14.

(Configuration of Conveyance / Slanting Control Section 30)
The conveyance / skew regulation unit 30 conveys the medium PM1 from the paper supply unit 10 to the transfer unit 50 along the conveyance path PW1 while regulating the skew. The conveyance / skew regulation unit 30 includes, for example, registration roller pairs 31 and 32 and sensors 33, 34, 35, and 36. Hereinafter, the conveyance / skewing regulation mechanism including the registration roller pair 32 and the sensors 34, 35, 36 is referred to as a conveyance / skewing regulation mechanism 30A. The registration roller pair 32 and the motor 112 (described later) for driving the registration roller pair 32 correspond to a specific example of “conveying unit” of the present invention. The sensor 34 corresponds to a specific example of the “second sensor” of the present invention, the sensor 35 corresponds to a specific example of the “first sensor” of the present invention, and the sensor 36 corresponds to the “second sensor” of the present invention. This corresponds to a specific example of “third sensor”.

  The registration roller pair 31 is disposed upstream of the registration roller pair 32, and specifically, is disposed between the paper feed tray 11 and the sensor 34. When the medium PM1 is transported from the paper feed tray 11, the registration roller pair 31 performs a butting process on the medium PM1 transported through the transport path PW1, and then transports the medium PM1 along the transport path PW1 in the transport direction. It is to be conveyed to F. The abutting process in the registration roller pair 31 refers to abutting the front end of the medium PM1 conveyed from the paper feeding unit 10 against the registration roller pair 31 whose rotation is stopped. During the abutting process, the power of a motor 112 (described later) controlled by the control unit 101 is not transmitted to the registration roller pair 31. That is, the registration roller pair 31 stops rotating while the abutting process is performed. In addition, when the medium PM1 is conveyed, the registration roller pair 31 is rotated in a direction in which the medium PM1 is conveyed in the conveyance direction F under the control of the control unit 101.

  The sensor 33 is disposed upstream of the registration roller pair 31. The sensor 33 detects the position of the medium PM1 in order to adjust the drive timing of the registration roller pair 31. The sensor 33 detects, for example, the medium PM1 transported along the transport path PW1 (specifically, the front end in the transport direction F of the medium PM1).

  FIG. 2 schematically illustrates an example of a planar configuration of a conveyance / skew regulation mechanism 30 </ b> A provided at a subsequent stage of the conveyance / skew regulation unit 30. FIG. 2 illustrates a state in which the medium PM1 is transported without being skewed, a state in which the medium PM1 is transported in the right advance, and a state in which the medium PM1 is transported in the left advance. Has been.

  As described above, the conveyance / skew regulation mechanism 30A includes the registration roller pair 32 and the sensors 34, 35, and 36. The registration roller pair 32 is disposed downstream of the registration roller pair 31. Further, the registration roller pair 32 is disposed between the sensor 34 and the sensor 35. This is because the medium PM1 (specifically, the front end of the medium PM1) is accurately detected by the sensor 35 while the medium PM1 is firmly held by the registration roller pair 32.

-Sensors 34, 35-
The sensor 35 is disposed downstream of the sensors 34 and 36 in the transport path PW1. The sensor 35 is further disposed in the central region CR in the width direction W of the transport path PW1, and is preferably disposed at the approximate center CL in the width direction W of the transport path PW1. A center line in the width direction W of the center region CR is located at the center CL of the transport path PW1. The width of the central region CR is, for example, a size corresponding to 10% of the width of the minimum width medium that can be used as the medium PM1. The sensor 35 detects the position of the medium PM1 in order to adjust the timing of image formation in the image forming unit 40. The sensor 35 detects the medium PM1 (specifically, the front end E in the transport direction F of the medium PM1) transported through the transport path PW1. The sensor 35 is arranged in the central region CR, so that the average position of the front end E of the medium PM1 can be detected. The sensor 35 is a transmissive or reflective component including a photodiode, for example.

  The sensor 34 is disposed upstream of the registration roller pair 32, the sensor 35, and the sensor 36 in the transport path PW1. The sensor 34 is further disposed away from the sensor 35 in the width direction W by a predetermined distance Δd. That is, the sensors 34 and 35 are arranged on a line segment that obliquely intersects the line segment parallel to the width direction W in the transport path PW1. The sensor 34 may be disposed within the central region CR, or may be disposed outside the central region CR. However, the sensor 34 needs to be disposed at a position where the front end E of the medium PM1 having the minimum width can be detected. The sensor 34 detects the position of the medium PM1 in order to adjust the drive timing of the registration roller pair 32. The sensor 34 detects the medium PM1 (specifically, the front end E of the medium PM1) conveyed along the conveyance path PW1. The sensor 34 is a transmissive or reflective component including a photodiode, for example.

  The transport / slant regulation mechanism 30A also detects skew of the medium PM1 transported on the transport path PW1. When the medium PM1 is transported from the paper feed tray 11, the registration roller pair 32 transports the medium PM1 along the transport path PW1 without performing an abutting process on the medium PM1. The registration roller pair 32 rotates in the direction in which the medium PM1 is conveyed in the conveyance direction F under the control of the control unit 101 when conveying the medium PM1. The sensors 34 and 35 are always arranged at the same position when the medium PM1 is conveyed from the paper feed tray 11. That is, the sensors 34 and 35 are fixed at a fixed position with respect to the transport path PW1.

  The sensors 34 and 35 are configured to detect the position of the medium PM1 transported along the transport path PW1. Specifically, the sensor 34 detects a portion of the medium PM1 transported along the transport path PW1 that passes through a region facing the sensor 34. The sensor 35 detects a portion of the medium PM1 transported along the transport path PW1 that passes through a region facing the sensor 35. Of the medium PM1, a part detected by the sensor 34 (for example, part E1 in FIG. 2) and a part of the medium PM1 detected by the sensor 35 (for example, part E2 in FIG. 2) are different from each other. Yes. Therefore, the sensors 34 and 35 are configured to detect two different places (for example, different parts E1 and E2 of the front end E of the medium PM1) among the media PM1 transported along the transport path PW1. . That is, the sensors 34 and 35 output information related to the skew of the medium PM1.

  FIG. 3 is a waveform diagram showing an example of the outputs of the sensors 34 and 35 and an example of the operation of a pulse counter 118A (described later) based on the outputs of the sensors 34 and 35. FIG. 3A is a waveform diagram when the medium PM1 is transported right ahead, and FIG. 3B is a waveform diagram when the medium PM1 is transported without being skewed, FIG. 3C is a waveform diagram when the medium PM1 is transported in the left front. The sensors 34 and 35 change the output when the medium PM1 is detected. The pulse counter 118A measures the number of pulses for a predetermined period T determined based on the outputs of the sensors 34 and 35. Here, the number of pulses refers to the number of pulses of a driving pulse signal output to the motor 112 when the driving circuit 111 (described later) controls the motor 112 that rotates the registration roller pair 31 and 32. ing. The pulse number (measurement pulse number Nm) obtained by measuring by the pulse counter 118A during the predetermined period T corresponds to a specific example of “measurement pulse number” of the present invention.

  The sensors 34 and 35 are configured to switch the output from high (HIGH) to low (LOW) when, for example, the medium PM1 is detected. For example, the pulse counter 118A measures the number of pulses from when the output of the sensor 34 changes from high to low until when the output of the sensor 35 changes from high to low. For example, the pulse counter 118A starts measuring the number of pulses when the output of the sensor 34 changes from high to low, and ends the measurement of the number of pulses when the output of the sensor 35 changes from high to low. It is like that.

  The sensors 34 and 35 may switch the output from low to high when, for example, the medium PM1 is detected. In this case, for example, the pulse counter 118A measures the number of pulses from when the output of the sensor 34 changes from low to high until when the output of the sensor 35 changes from low to high. It may be. At this time, for example, the pulse counter 118A starts measuring the number of pulses when the output of the sensor 34 changes from low to high, and measures the number of pulses when the output of the sensor 35 changes from low to high. Is supposed to end.

  The number of pulses is proportional to the length of the period during which the pulse counter 118A is executing measurement. The time from when the medium PM1 reaches the sensor 34 until it reaches the sensor 35 is referred to as “elapsed time”. Here, it is assumed that the sensor 34 is arranged on the left side in the width direction W as compared with the sensor 35. In this case, the elapsed time T2 when the medium PM1 is transported in the left front is longer than the elapsed time T0 when the medium PM1 is transported without being skewed. Further, the elapsed time T1 when the medium PM1 is conveyed right ahead is shorter than the elapsed time T0 when the medium PM1 is conveyed without being skewed. Therefore, the number of measurement pulses Nm when the medium PM1 is transported with the left leading is larger than the number of measurement pulses Nm when the medium PM1 is transported without skew. Further, the number of measurement pulses Nm when the medium PM1 is conveyed right ahead is smaller than the number of measurement pulses Nm when the medium PM1 is conveyed without being skewed. From the above, the number of pulses measured by the pulse counter 118A when the medium PM1 is transported without being skewed is used as a reference value, and the number of measurements of the pulse counter 118A is compared with the reference value to thereby determine the medium PM1. It can be seen that whether or not is skewed to the left or skewed to the right. It can also be seen how much the medium PM1 is skewed to the left or right. The reference value may be a predicted value that can be measured by the pulse counter 118A when the medium PM1 is transported without being skewed. The skew detection based on the number of measurement pulses Nm will be described in detail later.

  Next, the significance of arranging the sensor 35 in the central region CR of the transport path PW1 will be described.

  FIG. 4 schematically illustrates a planar configuration example when the sensor 35 is disposed in the central region CR and outside the central region CR of the transport path PW1. In FIG. 4, the sensor 35 disposed in the central region CR of the transport path PW1 and the medium PM1 detected by the sensor 35 are indicated by solid lines. In FIG. 4, the sensor 35 arranged outside the central region CR of the transport path PW1 and the medium PM1 detected by the sensor 35 are indicated by broken lines. In addition, FIG. 4 illustrates a state where the medium PM1 is transported in the left front.

  FIG. 5 schematically shows an example of the relationship between the transport distance L2 and the distance L1 corresponding to a half circumference of a photosensitive drum 41Y (described later). The transport distance L2 indicates the distance between the transfer point P2 and the portion corresponding to the center CL of the transport path PW1 in the front end E of the medium PM1 when the medium PM1 is detected by the sensor 35. When viewed in a plan view, the transport distance L2 is a portion corresponding to the center CL of the transport path PW1 in the front end E of the medium PM1 when the medium PM1 is detected by the sensor 35, and the image forming unit 40. The distance from the rotation center axis AX3 of the drum 41Y is indicated. Hereinafter, of the front end E of the medium PM1 detected by the sensor 35 disposed in the central region CR of the transport path PW1, the portion corresponding to the center CL of the transport path PW1 and the photosensitive drum 41Y of the image forming unit 40 are described. A distance from the rotation center axis AX3 is defined as a conveyance distance La. Further, of the front end E of the medium PM1 detected by the sensor 35 disposed outside the central region CR of the transport path PW1, the portion corresponding to the center CL of the transport path PW1 and the rotation of the photosensitive drum 41Y of the image forming unit 40. A distance from the central axis AX3 is defined as a conveyance distance Lb. The transfer point P2 indicates a place where the photosensitive drum 41Y and the medium PM1 are in contact with each other. The distance L1 indicates the distance from the location (latent image point P1) where the electrostatic latent image is performed by the LED head 43 to the transfer point P2 on the peripheral surface of the photosensitive drum 41Y. The photosensitive drum 41 </ b> Y is a photosensitive drum arranged on the most upstream side in the image forming unit 40. In FIG. 5, the medium PM1 detected by the sensor 35 arranged in the central region CR of the transport path PW1 is indicated by a solid line. In FIG. 5, the medium PM1 detected by the sensor 35 (the broken line sensor 35 in FIG. 4) arranged outside the central region CR of the transport path PW1 is indicated by a broken line. Note that FIG. 5 illustrates a state in which the medium PM1 is transported in the left front.

  As described above, the sensor 35 is a sensor for detecting the position of the medium PM1, and is used for adjusting the timing of image formation in the image forming unit 40. That is, the image forming unit 40 starts image formation based on the output of the sensor 35. Therefore, if the output timing of the sensor 35 is delayed from the original schedule, there is a possibility that the image formation start from the writing position defined in the specification may not be in time. Therefore, normally, even if the output timing of the sensor 35 is delayed from the original schedule, it is necessary to set a margin for the start of image formation from the writing position specified in the specification as the transport distance L2. . However, when the transport distance L2 is increased, the apparatus becomes large.

  For example, as shown by the solid line in FIG. 4, it is assumed that the sensor 35 is disposed in the central region CR of the transport path PW1. Here, when some processing time is not required before the exposure is started, the transport distance L2 (= La) may not have a margin. Accordingly, in this case, the transport distance La is equal to the distance L1 corresponding to the half circumference of the photosensitive drum 41Y. When some processing time is required before the exposure is started, the transport distance La needs to have a margin corresponding to the processing time. Accordingly, in this case, the transport distance La is longer than the distance L1.

  On the other hand, for example, as shown by the broken line in FIG. 4, it is assumed that the sensor 35 is disposed outside the central region CR of the transport path PW1. Furthermore, it is assumed that the transport distance La is longer than the distance L1. At this time, as shown in FIGS. 4 and 5, since the transport distance L2 (= Lb) is shorter than the transport distance La, the sensor 35 is compared with the case where the sensor 35 is disposed in the central region CR of the transport path PW1. The position of the medium PM1 at the start of exposure is closer to the photosensitive drum 41Y. Therefore, the margin included in the transport distance Lb is reduced by the distance Δy where the medium PM1 is shifted closer to the photosensitive drum 41Y. At this time, if the transport distance Lb is shorter than the distance L1, it becomes difficult to start image transfer from a desired position of the medium PM1.

  Therefore, in order to prevent such a problem from occurring when the sensor 35 is disposed outside the central region CR of the transport path PW1, the distance Δy is added to the margin included in the transport distance L2. It is possible. However, as the margin is increased, the conveyance / skew regulation mechanism 30A is disposed at a position away from the photosensitive drum 41Y, and the apparatus is increased in size. From the above, by arranging the sensor 35 in the central region CR of the transport path PW1, an increase in the size of the apparatus can be avoided.

-Sensor 36-
The sensor 36 shown in FIGS. 1, 2, 4, and 5 is a sensor that detects the transport state of the medium PM1 transported through the transport path PW1. The “transport state” in the present specification means, for example, the amount of slip of the medium PM1 (with respect to the transport path PW1) during transport. For example, the transport speed and transport time of the medium PM1 It is designed to be used. In the present embodiment, although details will be described later, based on the detection result of the medium PM1 by the two sensors 34 and 35 and the detection result of the conveyance state of the medium PM1 by the sensor 36, the inclination of the medium PM1 is determined. The line quantity is derived.

  Such a sensor 36 is disposed between the two sensors 34 and 35 described above (in this example, downstream of the sensor 34 and upstream of the sensor 35), for example, as shown in FIG. The reason why the sensor 36 is preferably arranged between the sensors 34 and 35 is as follows, for example. That is, by arranging the sensor 36 as close as possible to the upstream side of the sensor 35, the conveyance state of the medium PM1 that is closest to the image formation start timing is reflected in the skew correction or the like. is there.

  However, if the sensor 36 is too close to the sensor 35, the conveyance state of the medium PM1 detected by the sensor 36 cannot be reflected in the skew correction or the like (it may not be in time or the medium by the sensor 36). There is a risk that the transport state of PM1 cannot be detected). Therefore, for example, as shown in FIG. 2, it is desirable for the sensor 36 to set a margin of a distance L <b> 6 upstream of the sensor 35. The distance L6 satisfies, for example, n times (n: an integer equal to or greater than 2) of spec A (distance that can be skewed) unique to the image forming apparatus 1 described later, that is, L6 = (A × n). It is desirable to set as follows. This is because before the detection of the medium PM1 by the sensor 35, sampling of a later-described transmission / light-shielding period by the sensor 36 can be performed n times. A specific example of the distance L6 is L6 = about 10 to 30 mm (for example, 20 mm) using an example of A = 1 to about 3 mm (for example, 2 mm) and n = 10.

  Further, for example, as shown in FIG. 2 and the like, the sensor 36 is disposed in a central region CR (preferably in the center) in the width direction W of the transport path PW1. The reason why the sensor 36 is preferably disposed in the central region CR in the width direction W is, for example, for the following reason. That is, a difference (variation) does not occur as much as possible in the detection result of the conveyance state of the medium PM1 according to the presence / absence of the skew of the medium PM1, the skew direction (right leading or left leading), the degree of skew, and the like. It is to make it.

  In addition, about the arrangement position of the sensor 36, it is not restricted to the above arrangement examples, Other arrangement positions may be sufficient. That is, for example, the sensor 36 may be arranged outside the central region CR in the width direction W of the conveyance path PW1 on the upstream side of the sensor 34 or the downstream side of the sensor 35.

  Here, the sensor 36 will be described in detail with reference to FIGS. 6 and 7. FIG. 6 schematically illustrates a detailed configuration example of the sensor 36. FIG. 7 is a waveform diagram showing an example of the operation of the sensor 36 shown in FIG. FIG. 7A is an output waveform diagram by the sensor 36 when the medium PM1 is in a normal conveyance state (reference state), and FIG. 7B is a sensor when the medium PM1 is in a “slip” conveyance state. 36 is an example of an output waveform diagram according to FIG.

  First, for example, as shown in FIG. 6, the sensor 36 includes a roller-shaped rotating body 360, a light emitting unit 361, and a light receiving unit 362. The rotating body 360 is configured to be rotatable in the rotation direction R along the transport path PW1 in conjunction with the transport of the medium PM1 on the transport path PW1. Specifically, the rotating body 360 rotates with the medium PM1 due to friction with the medium PM1. Further, as shown in FIG. 6, the rotating body 360 has an opening S (in this example, a cross-shaped slit-shaped opening) formed on the rotating surface thereof. The light emitting unit 361 is a member that emits light L61 (emitted light) toward the rotating body 360 (the opening S), and is configured using various light emitting elements. The light receiving unit 362 is a member that receives light L62 (transmitted light) emitted from the light emitting unit 361 and passed through the opening S of the rotating body 360, and is configured using various light receiving elements. In such a light receiving unit 362, it is possible to detect (sampling) the transmission / light shielding period of the light L62 corresponding to the rotation speed of the rotating body 360 (that is, the conveyance state of the medium PM1 and the slip amount).

  Specifically, for example, as shown in FIG. 7, the result of light reception by the light receiving unit 362 in the sensor 36 (length of transmission / light shielding period (pulse width): shown in FIGS. 7A and 7B. The period of conveyance of the medium PM1 is defined on the basis of the periods T10 and T10). More specifically, in this example, the period T12 in the “slip” conveyance state shown in FIG. 7B is delayed with respect to the period T10 in the normal conveyance state (reference state) shown in FIG. It is longer by the amount ΔT (corresponding to the slip amount) (T12 = T10 + ΔT). This is because, as shown in FIG. 7, in the “slip” transport state, the rotation speed of the rotating body 360 is reduced according to the “slip” of the medium PM1, and each pulse width defining the transmission / light shielding period is increased. is there. As described above, in the sensor 36, the length (pulse width) of the transmission / light shielding period in the output waveform (measurement waveform) increases as the slip amount of the medium PM1 increases.

  It is desirable that the period of the transmission / light shielding period is, for example, a period less than the spec A (distance that allows skewing) unique to the image forming apparatus 1 described above. This is because when the cycle of the transmission / light-shielding period is equal to or greater than the specification A, the image forming apparatus 1 cannot adjust the skew feeding exceeding the specification A.

(Configuration of the image forming unit 40)
The image forming unit 40 forms an image on the medium PM1 transported from the transport / skew regulation mechanism 30A. For example, as shown in FIG. 1, the image forming unit 40 includes image forming units 40Y, 40M, 40C, and 40K. Each of the image forming units 40Y, 40M, 40C, and 40K uses toners of corresponding colors, that is, yellow toner, magenta toner, cyan toner, and black toner. Image). For example, the image forming units 40Y, 40M, 40C, and 40K are arranged in the order of the image forming unit 40Y, the image forming unit 40M, the image forming unit 40C, and the image forming unit 40K in the transport direction F. The image forming units 40Y, 40M, 40C, and 40K include, for example, a photosensitive drum 41, a charging roller 42, an LED (Light Emitting Diode) head 43, a developing roller 44, a supply roller 45, a transfer roller 46, a cleaning blade 47, and toner. A cartridge 48 is provided.

  The photosensitive drum 41 is a cylindrical member capable of carrying an electrostatic latent image on the surface (surface layer portion), and is configured using a photosensitive member (for example, an organic photosensitive member). Specifically, the photosensitive drum 41 has a conductive support and a photoconductive layer covering the outer periphery (surface) thereof. The conductive support is made of, for example, a metal pipe made of aluminum. The photoconductive layer has, for example, a structure in which a charge generation layer and a charge transport layer are sequentially stacked. Under the control of the control unit 101, the photosensitive drum 41 rotates at a predetermined peripheral speed in a direction in which the medium PM1 is transported in the transport direction F.

  The charging roller 42 is a member (charging member) that charges the surface (surface layer portion) of the photosensitive drum 41, and is disposed in contact with the surface (circumferential surface) of the photosensitive drum 41. The charging roller 42 has, for example, a metal shaft and a semiconductive rubber layer (for example, a semiconductive epichlorohydrin rubber layer) covering the outer periphery (surface) thereof. The charging roller 42 is rotated in the direction opposite to that of the photosensitive drum 41 under the control of the control unit 101.

  The LED head 43 is an exposure device that forms an electrostatic latent image on the surface (surface layer portion) of the photosensitive drum 41 by exposing the surface of the photosensitive drum 41. The LED head 43 has a plurality of LED light emitting units arranged in the width direction W with respect to one photosensitive drum 41. Each LED light emitting unit includes, for example, a light source such as a light emitting diode that emits irradiation light, and a lens array that forms an image of the irradiation light on the surface of the photosensitive drum 41.

  The developing roller 44 is a member that carries toner for developing an electrostatic latent image on the surface, and is disposed so as to be in contact with the surface (circumferential surface) of the photosensitive drum 41. The developing roller 44 has, for example, a metal shaft and a semiconductive urethane rubber layer covering the outer periphery (surface) thereof. The developing roller 44 is rotated in the direction opposite to the photosensitive drum 41 at a predetermined peripheral speed under the control of the control unit 101.

  The supply roller 45 is a member (supply member) for supplying toner to the developing roller 44 and is disposed in contact with the surface (circumferential surface) of the developing roller 44. The supply roller 45 has, for example, a metal shaft and a foamable silicone rubber layer covering the outer periphery (surface) thereof. The supply roller 45 rotates under the direction opposite to the developing roller 44 under the control of the control unit 101.

  The transfer roller 46 is a member for electrostatically transferring the toner image formed in each of the image forming units 40Y, 40M, 40C, and 40K onto the medium PM1. The transfer roller 46 is disposed to face the photosensitive drum 41 via a transfer belt 51 described later in each of the image forming units 40Y, 40M, 40C, and 40. The transfer roller 46 is made of, for example, a foaming semiconductive elastic rubber material.

  The cleaning blade 47 scrapes off the toner remaining on the surface of the photosensitive drum 41. The cleaning blade 47 is made of, for example, a flexible rubber material or a plastic material.

  The toner cartridge 48 is a container in which the toner of each color described above is stored. In the image forming unit 40Y, the toner cartridge 48 contains yellow toner. Similarly, magenta toner is stored in the toner cartridge 48 in the image forming unit 40M, cyan toner is stored in the toner cartridge 48 in the image forming unit 40C, and black toner is stored in the toner cartridge 48 in the image forming unit 40K. Is housed.

(Configuration of transfer unit 50)
The transfer unit 50 is also called a transfer belt unit. The transfer unit 50 includes a transfer belt 51, a driving roller 52 that drives the transfer belt 51, and an idle roller 53 that is a driven roller. Each of the driving roller 52 and the idle roller 53 is a substantially cylindrical member that can rotate around a rotation shaft portion extending in the width direction W. The transfer unit 50 transports the medium PM1 transported from the transport / skew regulating unit 30 along the transport direction F, and transfers the toner images formed in the image forming units 40Y, 40M, 40C, and 40K to the medium PM1. It is a mechanism that sequentially transfers to the surface.

  The transfer belt 51 is an endless elastic belt made of a resin material such as polyimide resin. The transfer belt 51 is stretched (strung) by a drive roller 52 and an idle roller 53. The driving roller 52 is rotationally driven in a direction in which the medium PM1 is transported in the transport direction F by a motor controlled by the control unit 101, and circulates and rotates the transfer belt 51. The drive roller 52 is disposed upstream of the image forming units 40Y, 40M, 40C, and 40K. The idle roller 53 adjusts the tension applied to the transfer belt 51 by the urging force of the urging member. The idle roller 53 rotates in the same direction as the drive roller 52, and is disposed downstream of the image forming units 40Y, 40M, 40C, and 40K.

(Configuration of the fixing unit 60)
The fixing unit 60 is a member for fixing the toner image onto the medium PM1 by applying heat and pressure to the toner image transferred onto the medium PM1 that has passed through the transfer unit 50. For example, the fixing unit 60 includes an upper roller 61 and a lower roller 62.

  Each of the upper roller 61 and the lower roller 62 includes a heat source (a fixing device heater 114 described later) that is a heater such as a halogen lamp, and applies heat to the toner image on the medium PM1. Functions as a heating roller. The upper roller 51 is configured to rotate in the direction in which the medium PM1 is transported in the transport direction F under the control of the control unit 101. The heat sources in the upper roller 61 and the lower roller 62 are supplied with a bias voltage controlled by the control unit 101, and control the surface temperatures of the upper roller 61 and the lower roller 62. The lower roller 62 is disposed to face the upper roller 61 so that a pressure contact portion is formed between the lower roller 62 and functions as a pressure roller that applies pressure to the toner image on the medium PM1. To do. The lower roller 62 may have a surface layer made of an elastic material.

(Configuration of discharge unit 70)
The discharge unit 70 discharges the medium PM1 on which the toner image is fixed by the fixing unit 60 to the outside. The discharge unit 70 includes, for example, conveyance roller pairs 71, 72, 73 and a sensor 74. The pair of transport rollers 71, 72, and 73 are configured to discharge the medium PM1 to the outside via the transport path PW4 and stock it on the external stacker 100A. The transport roller pairs 71, 72, and 73 are configured to rotate in a direction in which the medium PM <b> 1 is transported in the transport direction F under the control of the control unit 101. The pair of transport rollers 71, 72, 73 further discharges the medium PM1 to the outside, for example, face down.

  The sensor 74 is disposed upstream of the conveying roller pair 71, 72, 73. The sensor 74 detects the position of the medium PM1 in order to adjust the drive timing of the transport roller pair 71, 72, 73. The sensor 74 detects, for example, the medium PM1 (specifically, the front end E of the medium PM1) conveyed along the conveyance path PW4.

(Control mechanism)
Next, the control mechanism of the image forming apparatus 1 will be described with reference to FIG. 8 in addition to FIG. FIG. 8 is a block diagram illustrating an example of a control mechanism of the image forming apparatus 1.

  As shown in FIGS. 1 and 8, the image forming apparatus 1 includes, for example, a control unit 101, an image processing circuit 102, a display unit 103, a ROM 104, a RAM 105, and a nonvolatile memory 106 as control mechanisms. The image forming apparatus 1 further includes, for example, an I / O port 107, sensors 16, 33, 34, 35, 36, and 74, a video processing circuit 108, four LED heads 43, a DRAM 109, and an I / O port as control mechanisms. 110, a plurality of drive circuits 111, a plurality of motors 112, a drive circuit 113, a fixing device heater 114, a timer 115, and a high-voltage power supply 116. The image forming apparatus 1 further includes, for example, a comparison unit 117, a pulse counter 118A, a reference pulse number correction unit 118B, and a skew control unit 119 as control mechanisms. The control unit 101, the drive circuit 111, the comparison unit 117, the pulse counter 118A, the reference pulse number correction unit 118B, and the skew control unit 119 correspond to a specific example of the “control unit” of the present invention. Control unit 101, image processing circuit 102, display unit 103, ROM 104, RAM 105, nonvolatile memory 106, I / O port 107, video processing circuit 108, I / O port 110, timer 115, high voltage power supply 116, comparison unit 117, The pulse counter 118A, the reference pulse number correction unit 118B, and the skew control unit 119 are connected to the control line 120, for example.

  For example, the control unit 101 controls various controlled components in the image forming apparatus 1 via the control line 120. The image processing circuit 102 takes in image data sent from an external image transfer apparatus connected to the image forming apparatus 1 and converts it into a printable data format. The display unit 103 displays, for example, the state of the image forming apparatus 1 or information for prompting the user to act. The ROM 104 is a storage unit for storing a control program for operating the image forming apparatus 1. The RAM 105 is a storage unit for storing a work necessary for operating the image forming apparatus 1. The non-volatile memory 106 is a non-volatile storage unit for storing information that should be stored even when the power is turned off when the image forming apparatus 1 is operated. The non-volatile memory 106 stores, for example, a reference pulse number Ns used when calculating a skew amount ΔK (described later) of the medium PM1. The reference pulse number Ns is measured by the pulse counter 118A during a period T (= T0) determined based on the outputs of the sensors 34 and 35 obtained when the medium PM1 moves on the transport path PW1 without skew. The number of pulses generated. The reference pulse number Ns may be a predicted value that can be measured by the pulse counter 118A when the medium PM1 is moving without skew. The nonvolatile memory 106 may further store a threshold value TH described later, for example.

  The I / O port 107 is configured to monitor the status of the sensors 16, 33, 34, 35, 36, 74, and the like, for example. The sensors 34 and 35 not only detect the position of the medium PM1 being conveyed, but also detect the skew amount ΔK of the medium PM1 as described above. Further, as described above, the sensor 36 detects the conveyance state of the medium PM1. The video processing circuit 108 outputs the image data obtained by the data conversion in the image processing circuit 102 to each LED head 43 and simultaneously counts how many on-dots are output. The DRAM 109 is a storage unit for storing image data once before being output from the video processing circuit 108. The I / O port 110 outputs control signals for driving various driving motors 112 to various driving circuits 111. The I / O port 110 further outputs a control signal for driving the fixing device heater 114 to the drive circuit 113. The drive circuit 111 controls the motor 112 that rotates various rollers. The drive circuit 111 for the registration roller pair 31 and 32 controls the motor 112 that rotates the registration roller pair 31 and 32 in pulses. The drive circuit 113 performs pulse control of the fixing device heater 114. The fixing device heater 114 is provided inside each of the upper roller 61 and the lower roller 62, and heats the upper roller 61 and the lower roller 62. The fixing device heater 114 is a heater such as a halogen lamp. The timer 115 performs timer processing necessary for control. The high-voltage power supply 116 outputs a high voltage necessary for image formation, and outputs, for example, a charging CH voltage, a development DB voltage, a supply SB voltage, and a transfer TR voltage. It is like that.

  The pulse counter 118A measures the number of pulses for a predetermined period T determined based on the outputs of the sensors 34 and 35.

The reference pulse number correction unit 118B corrects (recalculates) the reference pulse number Ns when deriving the skew amount of the medium PM1 using the conveyance state of the medium PM1 detected by the sensor 36. . Specifically, the reference pulse correction unit 118B, for example, the period T10 in the normal conveyance state (reference state) and the period T12 in the “slip” conveyance state (T10, T12: predetermined transmission) illustrated in FIG. 7 described above, for example. / Corresponding to the pulse width in the light shielding period), the corrected reference pulse number Ns ′ is derived by the following equation (1). As can be seen from the equation (1), the reference pulse number Ns is corrected so that the corrected reference pulse number Ns ′ increases as the slip amount as the conveyance state of the medium PM increases. It has come to be.
Ns ′ = (T12 / T11) × Ns (1)

  The comparison unit 117 compares the reference pulse number Ns read from the nonvolatile memory 106 with the number of pulses newly measured by the pulse counter 118A (measurement pulse number Nm). However, in detail, the comparison unit 117 according to the present embodiment compares the reference pulse number Ns ′ after the correction by the reference pulse number correction unit 118B with the measurement pulse number Nm.

  The comparison unit 117 derives the skew amount ΔK of the medium PM1 based on the comparison result between the corrected reference pulse number Ns ′ and the measured pulse number Nm. Specifically, for example, the comparison unit 117 derives a difference between the reference pulse number Ns ′ and the measurement pulse number Nm, and sets the derived difference as the skew amount ΔK. In this way, based on the detection results of the three sensors 34, 35, 36 (the detection result of the medium PM1 by the two sensors 34, 35 and the detection result of the transport state of the medium PM1 by the sensor 36), The skew amount ΔK of the medium PM1 is derived.

  Further, the skew control unit 119 determines whether or not the medium PM1 is skewed based on the skew amount ΔK derived in this way. Specifically, the skew controller 119 has an absolute value of a difference (for example, the skew amount ΔK described above) between the measurement pulse number Nm and the reference pulse number Ns ′ larger than a predetermined threshold TH (the absolute value of the difference). >> Threshold TH), it is determined that the medium PM1 is skewed. That is, for example, when the threshold value TH is 0 (zero), the medium PM1 is skewed when the absolute value of the difference is larger than 0 (a value other than 0) as described below. It is determined that On the other hand, the skew controller 119 determines that the medium PM1 is not skewed when the absolute value of the difference is equal to or less than the threshold value TH. That is, for example, when the threshold value TH is 0, when the absolute value of this difference is 0, it is determined that the medium PM1 is not skewed. Further, when the skew control unit 119 determines that the medium PM1 is skewed, the skew control of the medium PM1 depends on whether the difference is a positive value or a negative value. The direction is further determined.

  More specifically, as an example, it is assumed that the skew amount ΔK is obtained by a mathematical formula: skew amount ΔK = reference pulse number Ns′−measurement pulse number Nm. At this time, when the skew amount ΔK is a negative value, the skew control unit 119 determines that “the end of the medium PM1 closer to the sensor 34 precedes”. Yes. When the skew amount ΔK is a positive value, the skew control unit 119 indicates that “the end of the medium PM1 opposite to the end near the sensor 34 precedes the end”. It comes to judge.

  Accordingly, when the sensor 34 is disposed on the left side in the width direction W in the positional relationship with the sensor 35, when the skew amount ΔK is a negative value, the skew control unit 119 determines that “the left end of the medium PM1. Part (end Ea) precedes "(see FIG. 2). Further, when the sensor 34 is arranged on the left side in the width direction W in the positional relationship with the sensor 35, when the skew amount ΔK is a positive value, the skew control unit 119 displays “medium PM1. It is determined that the right end portion (end portion Eb) of the head is leading "(see FIG. 2). Further, when the sensor 34 is disposed on the right side in the width direction W in the positional relationship with the sensor 35, when the skew amount ΔK is a negative value, the skew control unit 119 reads “the right end of the medium PM1”. Part (end Eb) precedes ". Further, when the sensor 34 is disposed on the right side in the width direction W in the positional relationship with the sensor 35, when the skew amount ΔK is a positive value, the skew control unit 119 displays “medium PM1. It is determined that the left end portion (end portion Ea) is preceded.

  As another example, it is assumed that the skew amount ΔK is obtained by a mathematical formula of skew amount ΔK = measurement pulse number Nm−reference pulse number Ns ′. At this time, when the skew amount ΔK is a negative value, the skew control unit 119 indicates that “the end of the medium PM1 opposite to the end near the sensor 34 precedes the end”. It comes to judge. When the skew amount ΔK is a positive value, the skew control unit 119 determines that “the end portion closer to the sensor 34 is ahead of both ends of the medium PM1”. .

  Accordingly, when the sensor 34 is disposed on the left side in the width direction W in the positional relationship with the sensor 35, when the skew amount ΔK is a negative value, the skew control unit 119 determines that “the right end of the medium PM1” Part (end Eb) precedes ". Further, when the sensor 34 is arranged on the left side in the width direction W in the positional relationship with the sensor 35, when the skew amount ΔK is a positive value, the skew control unit 119 displays “medium PM1. It is determined that the left end portion (end portion Ea) is preceded. Further, when the sensor 34 is disposed on the right side in the width direction W in the positional relationship with the sensor 35, when the skew amount ΔK is a negative value, the skew control unit 119 determines that “the left end of the medium PM1” Part (end part Ea) precedes ". Further, when the sensor 34 is disposed on the right side in the width direction W in the positional relationship with the sensor 35, when the skew amount ΔK is a positive value, the skew control unit 119 displays “medium PM1. It is determined that the right end portion (end portion Eb) is preceded.

  Here, when the absolute value of the skew amount ΔK is very small, it can be considered that the medium PM1 is not substantially skewed. Therefore, when the skew amount ΔK is obtained by any of the above formulas, if the absolute value of the skew amount ΔK is smaller than the above-described threshold value TH (a value other than 0), the skew control unit 119 , It may be determined that “medium PM1 is not skewed” and skew correction is not performed.

  Note that the comparison unit 117 may derive the skew amount ΔK by a method other than the difference in the number of pulses. That is, the comparison unit 117 may derive the skew amount ΔK using a ratio such as the number of measurement pulses / the number of reference pulses Ns ′ or the number of reference pulses Ns ′ / the number of measurement pulses.

  Further, the skew control unit 119 may derive a correction amount ΔC1 for reducing skew of image data printed on the medium PM1, for example, based on the skew amount ΔK. At this time, for example, the control unit 101 outputs the correction amount ΔC1 derived by the skew control unit 119 to the video processing circuit 108. Further, the video processing circuit 108 corrects the image data based on the correction amount ΔC1 so that the skew of the image data printed on the medium PM1 is reduced.

  Further, the skew control unit 119 may derive a correction amount ΔC2 for reducing the skew of the medium PM1 itself based on the skew amount ΔK, for example. At this time, for example, the control unit 101 inputs a control signal corresponding to the correction amount ΔC2 derived by the skew control unit 119 to the drive circuit 111 via the I / O port 110. Further, the drive circuit 111 drives the motor 112 based on the input control signal, thereby controlling the rotation operation of the skew correction roller so that the skew of the medium PM1 is reduced. . The skew correction roller is disposed, for example, in a section of the transport path PW1 between the sensor 35 and the transfer unit 50.

[Operation]
Next, the operation of the image forming apparatus 1 will be described. In the image forming apparatus 1, a toner image is formed on the medium PM1 as follows. When a print job is supplied from the image transfer apparatus connected to the image forming apparatus 1 to the control unit 101 via the communication line, the control unit 101 executes each item in the image forming apparatus 1 based on the print job. The printing process is performed so that the member performs the following operation.

  FIG. 9 is a flowchart illustrating an example of a print processing procedure for the medium PM1.

  In this print processing procedure, first, the medium PM1 stored in the paper feed tray 11 is separated and taken out one by one from the top by the pickup roller 13, the feed roller 14, and the retard roller 15, and fed out to the transport path PW1. (Step S11 in FIG. 9). Next, the skew of the medium PM1 is corrected by the abutting process in the registration roller pair 31 (step S12). Thereafter, the medium PM1 is conveyed to the registration roller pair 32 side.

(Derivation processing of skew amount ΔK)
Subsequently, when the medium PM1 is transported in the transport direction F, the skew amount ΔK of the medium PM1 is derived based on the outputs of the sensors 34, 35, and 36 (results of detection by the sensors 34, 35, and 36). (Step S13).

  Here, with reference to FIG. 10, the derivation process of the skew amount ΔK (step S13 in FIG. 9) will be described in detail. FIG. 10 is a flowchart showing an example of a detailed procedure in the process of deriving the skew amount ΔK.

  In the process of deriving the skew amount ΔK, first, when the medium PM1 (specifically, the front end E of the medium PM1) passes through a region facing the sensor 34, the medium PM1 is detected by the sensor 34 ( Step S131 in FIG. Thereby, measurement of the number of pulses mentioned above is started.

  Subsequently, the medium PM1 is conveyed in the conveyance direction F by the registration roller pair 32 along the conveyance path PW1. At this time, when the medium PM1 passes through the area facing the sensor 36, the sensor 36 detects the above-described transport state (transport state in the transport path PW1) of the medium PM1 (step 132).

  Next, when the medium PM1 (specifically, the front end E of the medium PM1) passes through an area facing the sensor 35, the sensor PM detects the medium PM1 (step S133). Thereby, the measurement of the number of pulses described above is completed. In this manner, the number of pulses is measured by detecting two different locations (for example, the portions E1 and E2) of the medium PM1 transported along the transport path PW1 by the sensors 34 and 35.

  That is, during a predetermined period T determined based on the outputs of these sensors 34 and 35, the pulse counter 118A measures the number of pulses (derivation of the number of measurement pulses Nm) (step S134).

  Next, using the transport state of the medium PM1 detected in step S132, the reference pulse number Ns is corrected (recalculated) by the above-described method (using the above-described equation (1)) (step S1). S135). Thereby, the corrected reference pulse number Ns ′ is derived.

  Then, the measurement pulse number Nm thus obtained is compared with the corrected reference pulse number Ns ′ (step S136). Based on the comparison result, the skew amount of the medium PM1 is determined by the above-described method. ΔK is derived (step S137).

  Subsequently, using the skew amount ΔK thus derived, the presence or absence of skew in the medium PM1 (and the direction of skew when skew is present) is determined by the method described above. Specifically, in this example, it is determined whether or not there is no skew using the skew amount ΔK (step 14 in FIG. 9). If it is determined that there is no skew (step S14: Y), skew correction described below (steps S15 and S16) is not performed, and step S17 described later (transfer of the toner image onto the medium PM1). Proceed to

  On the other hand, if it is determined that there is skew (step S14: N), then correction amounts ΔC1, ΔC2 are derived based on the derived skew amount ΔK (step S15). Specifically, for example, a correction amount ΔC1 for reducing skew of image data printed on the medium PM1 is derived based on the skew amount ΔK. Further, instead of deriving the correction amount ΔC1, a correction amount ΔC2 for reducing the skew of the medium PM1 itself may be derived based on the skew amount ΔK.

  Next, the skew of the image D or the medium PM1 is corrected based on the correction amounts ΔC1 and ΔC2 derived in this way (step S16). Specifically, for example, based on the correction amount ΔC1, the image data is corrected so that the skew of the image D printed on the medium PM1 is reduced. Further, instead of correcting the image data, the motor 112 is driven based on a control signal corresponding to the correction amount ΔC2 to rotate the skew correction roller (not shown) so that the skew of the medium PM1 is reduced. May be controlled.

  Thereafter, the medium PM1 is conveyed to the transfer unit 50. The medium PM1 is transported along the transport direction F by the transfer belt 51. Further, the toner images formed in the image forming units 40Y, 40M, 40C, and 40K as described below are sequentially transferred onto the medium PM1 (step S17). As a result, the image D with reduced skew is printed on the medium PM1, or the skew of the medium PM1 is reduced by the rotation operation of the skew correction roller.

(Formation of toner image by electrophotographic process)
Here, in the image forming units 40Y, 40M, 40C, and 40K, toner images of respective colors are formed by the following electrophotographic processes.

  That is, first, the surface (surface layer portion) of the photosensitive drum 41 is uniformly charged by the charging roller 42 to which the charging CH voltage is supplied from the high voltage power source 116. Next, irradiation light is emitted from the LED head 43 toward the surface of the photosensitive drum 41 and the surface of the photosensitive drum 41 is exposed, so that the electrostatic latent image according to the print pattern defined by the print job described above is obtained. An image is formed on the photosensitive drum 41. At this time, when the correction amount ΔC1 is derived, an electrostatic latent image corresponding to the print pattern corrected based on the correction amount ΔC1 is formed on the photosensitive drum 41.

  On the other hand, the supply roller 45 supplied with the SB voltage for supply from the high voltage power supply 116 is in contact with the developing roller 44 supplied with the DB voltage for development from the high voltage power supply 116, and the supply roller 45 and the development roller 44 are Each rotates at a predetermined peripheral speed. As a result, the toner is supplied from the supply roller 45 to the surface of the developing roller 44. Subsequently, the toner on the developing roller 44 is charged by friction with a toner regulating member (not shown) in contact with the developing roller 44. Here, the thickness of the toner layer on the developing roller 44 is determined by an applied voltage to the developing roller 44, an applied voltage to the supply roller 45, a pressing force of the toner regulating member (an applied voltage to the toner regulating member), and the like.

  Further, since the developing roller 44 is in contact with the photosensitive drum 41, the development DB voltage is supplied from the high voltage power source 116 to the developing roller 44, so that the electrostatic latent image on the photosensitive drum 41 is applied. On the other hand, toner adheres from the developing roller 44. Thereafter, the toner (toner image) on the photosensitive drum 41 is transferred onto the medium PM1 by an electric field between the photosensitive drum 41 and the transfer roller 46. The toner remaining on the surface of the photosensitive drum 41 is removed by being scraped off by the cleaning blade 47.

  In this manner, toner images of respective colors are formed in the image forming units 40Y, 40M, 40C, and 40K, and sequentially transferred onto the medium PM1 along the transport direction F. Specifically, in each of the image forming units 40Y, 40M, 40C, and 40K, a layer composed of toner images of each color (image layer) using the corresponding color toners (yellow toner, magenta toner, cyan toner, and black toner). ) Is formed.

  Subsequently, the fixing unit 60 fixes the toner on the medium PM1 conveyed from the transfer belt 51 by applying heat and pressure. For example, the fixing operation is performed by applying heat and pressure to the medium PM1 while the medium PM1 being conveyed in the conveyance direction F is sandwiched between the upper roller 61 and the lower roller 62.

[effect]
Next, effects of the image forming apparatus 1 will be described.

  2. Description of the Related Art Conventionally, in an image forming apparatus, for example, image formation is performed after skew correction is performed by abutting on a medium fed out from a paper feed cassette (see, for example, paragraph 0031 of Patent Document 1). However, skew correction may be insufficient before image formation starts due to the stiffness of the medium and the load on the transport route.

  Therefore, in the image forming apparatus 1, skew detection of the medium PM1 is performed using the two sensors 34 and 35 described above. Specifically, in the image forming apparatus 1, the two sensors 34 and 35 are arranged on a line segment that obliquely intersects the line segment parallel to the width direction W in the transport path PW 1. Based on the outputs of these two sensors 34 and 35, the skew amount ΔK of the medium PM1 is derived.

  However, even if the medium PM1 is not actually skewed at this time, as described above with reference to FIG. 7, for example, the medium PM1 is caused by the conveyance state (“slip” conveyance state) of the medium PM1. In some cases, the medium PM1 may be erroneously determined to be skewed.

  Specifically, for example, as in the example of the waveform diagram shown in FIG. 11A, the delay amount ΔT = ΔT0 described above with reference to FIG. 7 although the medium PM1 is not actually skewed. Due to (corresponding to the slip amount), there may occur a case where the period Tm of the measurement pulse becomes longer than the period T0 when there is no skew (Tm> T0). In such a case, for example, as shown in FIG. 11B, the period Tm corresponding to the number of measured pulses Nm is longer than the period T0 corresponding to the original number of reference pulses Ns. If it is left as it is, it is erroneously determined that there is a skew (in this example, the “left preceding” skew shown in FIG. 3C).

  In view of this, in the conveyance / skew regulation unit 30 of the present embodiment, in addition to the detection results by the two sensors 34 and 35 described above, the detection result by the sensor 36 that detects the conveyance state of the medium PM1 is also taken into consideration. The skew amount ΔK of PM1 is derived. Specifically, first, the reference pulse number Ns is corrected using the conveyance state of the medium PM1 detected by the sensor 36 (using the above-described equation (1)), and the corrected reference pulse number Ns is corrected. 'Is derived. The skew amount ΔK of the medium PM1 is derived based on the comparison result between the measured pulse number Nm thus obtained and the corrected reference pulse number Ns ′, and based on the derived skew amount ΔK. The skew is judged.

  Specifically, in the case described above, for example, as shown in FIG. 11C, the period T0 ′ (= T0 + delay amount ΔT0) corresponding to the reference pulse number Ns ′ after the correction indicated by the arrow P is performed. ) And a period Tm corresponding to the number of measurement pulses Nm are equal to each other. That is, in the present embodiment, by adopting the above-described method, it is possible to derive the skew amount ΔK in consideration of the transport state of the medium PM1, and the skew of the skew caused by the transport state of the medium PM1 as described above can be obtained. Incorrect determination is prevented.

  As described above, in the present embodiment, since the skew amount ΔK of the medium PM1 is derived based on the detection results of the two sensors 34 and 35 and the detection result of the sensor 36, the conveyance of the medium PM1 is performed. It is possible to prevent an erroneous determination of skew due to the state. Therefore, it is possible to accurately detect the skew of the medium PM1.

  In the image forming apparatus 1, the sensor 35 is disposed on the downstream side of the sensor 34 in the transport path PW1, and is further disposed in the central region CR in the width direction W of the transport path PW1. In addition, the sensor 34 is arranged in the width direction W by a predetermined distance Δd from the sensor 35 in the transport path PW1. As a result, the distance between the conveyance / skew regulation mechanism 30A and the image forming unit 40 can be reduced compared to the case where the sensor 35 is disposed outside the central region CR of the conveyance path PW1, and the image forming apparatus 1 can be reduced. It can be downsized.

  Further, in the image forming apparatus 1, the registration roller pair 32 is disposed between the sensor 34 and the sensor 35. As a result, the medium PM1 can be firmly pressed down by the registration roller pair 32. Therefore, when the sensor 35 detects the medium PM1 (specifically, the front end of the medium PM1), the trajectory (specifically, the medium PM1 passes) Can suppress variation in the trajectory in the thickness direction of the medium PM1. As a result, even when the difference between the measurement pulse number Nm and the reference pulse number Ns ′ is very small, the skew amount ΔK can be derived with high accuracy.

  In addition, in this image forming apparatus 1, since the sensor 36 is disposed between the sensor 34 and the sensor 35, the conveyance state of the medium PM1 that is closest to the timing of the image formation start is oblique. It will be reflected in line correction. Therefore, the skew of the medium PM1 can be detected with higher accuracy.

  In the image forming apparatus 1, since the sensor 36 is arranged in the central region CR in the width direction W of the transport path PW1, the presence / absence of the skew of the medium PM1, the skew direction, Depending on the degree or the like, a difference (variation) can be prevented from occurring as much as possible in the detection result of the conveyance state of the medium PM1. Therefore, also in this respect, the skew of the medium PM1 can be detected with higher accuracy.

  Further, in the image forming apparatus 1, the sensor 35 is disposed in the central region CR in the width direction W of the transport path PW1, and the two sensors 34 and 35 are parallel to the width direction W in the transport path PW1. It is arranged on a line segment that obliquely intersects the line segment. Since the two sensors 34 and 35 are arranged in this way, the performance regarding printing is not inferior to the case where the two sensors 34 and 35 are not arranged in this way. Therefore, by adding a new function of “medium skew detection of the medium PM1” to the transport / skew regulation mechanism 30A, there is no possibility that the conventional function such as printing is deteriorated.

<2. Modification>
Below, the modification of the image transfer apparatus 1 of the said embodiment is demonstrated. In the following, components that are the same as those in the above embodiment are denoted by the same reference numerals as those in the above embodiment. In addition, the description of the components different from the above embodiment will be mainly given, and the description of the components common to the above embodiments will be omitted as appropriate.

  In the above embodiment, the image transfer is a direct method, but may be an indirect method. This modified example described below corresponds to a so-called indirect transfer type image forming apparatus in which the sensors 34, 35, and 36 described in the above embodiments are applied.

  FIG. 12 is a schematic diagram illustrating a configuration example of the image forming apparatus according to the present modification. Specifically, an example of the relationship between the transport distance L3 and the distance L4 between the toner image TP and the transfer point P3 in the above-described indirect transfer method is schematically shown. The transport distance L3 indicates the distance between the front end E of the medium PM1 and the transfer point P3 when the medium PM1 is detected by the sensor 35. The transfer point P3 indicates a location where the intermediate transfer belt 54 (described later) and the medium PM1 come into contact with each other.

  In this modification, the transfer unit 50 includes, for example, an intermediate transfer belt 54, a driving roller 52 that drives the transfer belt 54, an idle roller 53 that is a driven roller, a backup roller 55, and a secondary transfer roller 56. Have. The transfer unit 50 sequentially transfers the toner images formed in the image forming units 40Y, 40M, 40C, and 40K onto the surface of the intermediate transfer belt 54, and then conveys and skews the toner images on the intermediate transfer belt 54. This is a mechanism for transferring to the medium PM1 conveyed from the regulating unit 30.

  The intermediate transfer belt 54 is an endless elastic belt made of a resin material such as polyimide resin. The intermediate transfer belt 54 is stretched (strung) by a drive roller 52 and an idle roller 53. The driving roller 52 is rotationally driven by a motor controlled by the control unit 101 so that the toner image on the intermediate transfer belt 54 runs parallel to the medium PM1 in the vicinity of the backup roller 55, and circulates and rotates the intermediate transfer belt 54. Is. The drive roller 52 is disposed upstream of the image forming units 40Y, 40M, 40C, and 40K. The idle roller 53 adjusts the tension applied to the transfer belt 51 by the urging force of the urging member. The idle roller 53 rotates in the same direction as the drive roller 52, and is disposed downstream of the image forming units 40Y, 40M, 40C, and 40K.

  Each of the backup roller 55 and the secondary transfer roller 56 is a substantially cylindrical member that can rotate around a rotation shaft portion extending in the width direction W. The backup roller 55 and the secondary transfer roller 56 are arranged to face each other and sandwich the intermediate transfer belt 54. The secondary transfer roller 56 includes, for example, a metal core material and an elastic layer such as a foam rubber layer formed so as to be wound around the outer peripheral surface of the core material. The sensor 35 detects the position of the medium PM1 in order to two-dimensionally transfer the toner image TP on the intermediate transfer belt 54 to a specified position of the medium PM1 conveyed along the conveyance path PW1.

  In this modification, when the medium PM1 (specifically, the front end E of the medium PM1) is detected by the sensor 35, the user can control the speed of the medium PM1 without changing the speed of the intermediate transfer belt 54. The toner image TP is two-dimensionally transferred to the designated position. Therefore, a period for adjusting the speed of the medium PM1 is required. However, if the output timing of the sensor 35 is delayed from the initial schedule, the speed adjustment of the medium PM1 may not be completed within a predetermined period, and may not be in time for the start of image formation from the writing position specified in the specification. There is. Therefore, normally, even if the output timing of the sensor 35 is delayed from the original schedule, it is necessary to set a margin for the start of image formation from the writing position defined in the specification as the transport distance L3. . However, when the transport distance L3 is increased, the size of the apparatus is increased. However, similarly to the above-described embodiment, the sensor 35 can be disposed in the central region CR of the transport path PW1 to avoid an increase in size of the apparatus.

<3. Other variations>
Hereinafter, other various modifications will be described.

  For example, in the embodiment and the modification described above, a method of detecting the transport state (slip amount) of the medium PM1 by detecting the transport speed (transport time) of the medium PM1 using the sensor 36 will be described as an example. However, it is not limited to this method. That is, for example, the conveyance state of the medium PM1 may be detected using a sensor that can directly detect the slip amount of the medium PM1.

  In the above-described embodiment and the like, the four color image forming units 40Y, 40M, 40C, and 40K are used. However, in the above-described embodiment and its modifications, for example, an image forming unit of 3 colors or less or 5 colors or more may be used.

  Furthermore, the LED head 43 is used in the above embodiment and the like. However, in the above-described embodiment and the like, a laser element or the like may be used instead of the LED head 43 or together with the LED head 43.

  In addition, the series of processing described in the above-described embodiments and the like may be performed by hardware (circuit) or software (program). When the above-described series of processing is performed by software, the software is configured by a group of programs for causing each function to be executed by a computer. Each program may be used by being incorporated in advance in the computer, for example, or may be used by being installed in the computer from a network or a recording medium.

  In the above-described embodiment and the like, an embodiment of the present invention has been described by taking a color electrophotographic printer as an example. However, the present invention is not limited to application to a color machine or a printer, but can be applied to all image forming apparatuses that form images on a conveyed medium. That is, the present invention can be applied to, for example, a monochrome copier, a color copier, a monochrome MFP, a color MFP, and the like.

  Further, in the above-described embodiment and the like, an image forming apparatus having a printing function has been described as a specific example of the “image forming apparatus” in the present invention. However, the present invention is not limited to application to an image forming apparatus having a printing function, and can also be applied to, for example, an image forming apparatus that functions as a multifunction peripheral having a scanning function and a fax function.

  DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 10 ... Paper feed part, 11 ... Paper feed tray, 11A ... Loading plate, 12 ... Drive part, 12A ... Lift-up lever, 12B ... Motor, 13 ... Pick-up roller, 14 ... Feed roller, 15 ... retard roller, 16, 33, 34, 35, 36, 74 ... sensor, 30 ... conveyance / skew regulation part, 30A ... conveyance / skew regulation mechanism, 31,32 ... registration roller pair, 360 ... rotating body, 361 ... light emitting part, 362 ... light receiving part, 40 ... image forming part, 40Y, 40M, 40C, 40K ... image forming unit, 41, 41Y ... photosensitive drum, 42 ... charge roller, 43 ... LED head, 44 ... developing roller, 45 Supply roller 46, 46Y Transfer roller 47 Cleaning blade 48 Toner cartridge 50 Transfer unit 51 Transfer belt 52 Drive roller DESCRIPTION OF SYMBOLS 3 ... Idle roller 54 ... Intermediate transfer belt 55 ... Backup roller 56 ... Secondary transfer roller 60 ... Fixing part 61 ... Upper roller 62 ... Lower roller 70 ... Discharge part 71, 72, 73 ... Conveyance Roller pair, 100 ... casing, 100A ... stacker, 101 ... control unit, 102 ... image processing circuit, 103 ... display unit, 104 ... ROM, 105 ... RAM, 106 ... non-volatile memory, 107, 110 ... I / O port , 108 ... Video processing circuit, 109 ... DRAM, 111, 113 ... Drive circuit, 112 ... Motor, 114 ... Fixer heater, 115 ... Timer, 116 ... High-voltage power supply, 117 ... Comparison unit, 118A ... Pulse counter, 118B ... Reference Pulse number correction unit, 119 ... skew control unit, 120 ... control line, AX1, AX2 ... axis, AX3 ... central axis of rotation, CL ... center, CR Central region, E ... front end, E1, E2 ... site, F ... transport direction, L1, L4, L6 ... distance, L2, L3, La, Lb ... transport distance, L61, L62 ... light, S ... opening, R ... rotation Direction, Nm ... Number of measurement pulses, Ns, Ns '... Number of reference pulses, P1 ... Latent image point, P2 ... Transfer point, PM1 ... Medium, PW1, PW3, PW4 ... Transport path, T, T0, T0', T1, T2, T10, T12, Tm ... period, W ... width direction, TH ... threshold, ΔT, ΔT0 ... delay amount, Δd ... distance, ΔK ... skew amount, ΔC1, ΔC2 ... correction amount.

Claims (15)

A transport unit for transporting the medium along the transport path;
A first sensor for detecting the medium transported along the transport path;
The transport path is disposed upstream of the first sensor, and is disposed away from the first sensor by a predetermined distance in the width direction of the transport path, and is transported through the transport path. A second sensor for detecting the medium;
A third sensor for detecting a conveyance state of the medium in the conveyance path;
And a control unit for deriving a skew amount of the medium based on the detection results of the first to third sensors. The controller is
While controlling the pulse of the transport unit,
Measuring the number of measurement pulses, which is the number of pulses output to the transport unit in a period from when the medium is detected by the second sensor to when the medium is detected by the first sensor;
The medium conveying apparatus according to claim 1, wherein the skew feeding amount is derived based on a comparison result between the measurement pulse number and a reference pulse number. The controller is
Using the transport state of the medium detected by the third sensor, correcting the reference pulse number,
The medium conveying apparatus according to claim 2, wherein the skew feeding amount is derived using the corrected reference pulse number as the reference pulse number. The control unit corrects the reference pulse number so that the corrected reference pulse number increases as the slip amount of the medium as the medium conveyance state increases. The medium conveying apparatus as described. The controller is
When the absolute value of the difference between the number of measurement pulses and the number of reference pulses is greater than a threshold, it is determined that the medium is skewed;
The medium transport apparatus according to claim 2, wherein when the absolute value of the difference is equal to or less than the threshold value, it is determined that the medium is not skewed. The controller is
If it is determined that the medium is skewed,
The medium conveying apparatus according to claim 5, wherein the skew feeding direction of the medium is further determined according to whether the difference is a positive value or a negative value. The medium transport apparatus according to claim 5, wherein the threshold value is 0 (zero). The medium conveyance device according to any one of claims 1 to 7, wherein the third sensor is disposed between the first sensor and the second sensor. The medium conveyance device according to any one of claims 1 to 8, wherein the third sensor is disposed in a central region in a width direction of the conveyance path. The medium conveyance device according to any one of claims 1 to 9, wherein the first sensor is disposed in a central region in a width direction of the conveyance path. The medium conveyance device according to any one of claims 1 to 10, wherein the conveyance unit is disposed between the first sensor and the second sensor. The third sensor is
A rotating body configured to rotate along the conveyance path in conjunction with the conveyance of the medium, and having an opening on a rotation surface thereof;
A light emitting unit that emits light toward the opening of the rotating body;
The medium transport device according to any one of claims 1 to 11, further comprising: a light receiving unit that receives light emitted from the light emitting unit and having passed through the opening of the rotating body. The medium transport apparatus according to claim 12, wherein a transport state of the medium is defined based on a light reception result by the light receiving unit. The medium transport apparatus according to any one of claims 1 to 13, wherein the transport state of the medium is a transport speed of the medium. A medium conveying device for conveying the medium;
An image forming unit that forms an image on the medium conveyed from the medium conveying device;
The medium conveying device is:
A transport unit that transports the medium along a transport path;
A first sensor for detecting the medium transported along the transport path;
The transport path is disposed upstream of the first sensor, and is disposed away from the first sensor by a predetermined distance in the width direction of the transport path, and is transported through the transport path. A second sensor for detecting the medium;
A third sensor for detecting a conveyance state of the medium in the conveyance path;
An image forming apparatus comprising: a control unit that derives a skew amount of the medium based on each detection result by the first to third sensors.

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