JP2012126479A - Sheet-end detecting device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sheet-end detecting device having a low-cost configuration, detecting the position of the end of a sheet without performing a complicated operation such as a retreat operation.SOLUTION: The sheet-end detecting device is a detecting means 100 detecting the position of the end of the sheet during transportation, The sheet-end detecting device includes: a light emitting part 101 disposed in a direction perpendicular to the sheet transportation direction; and a light receiving part 102 which is independently arranged at a distance from the light emitting part 101 across the sheet, and is movable with respect to the light emitting part 101. The light receiving part 102 moves along the light emitting part 101 in the direction perpendicular to the sheet transportation direction, and detects a changing point showing whether the light emitted from the light emitting part 101 is shielded by the sheet or not, consequently detects the position of the sheet-end.

Description

  The present invention relates to a sheet edge detection device that detects the position of the edge of a sheet being conveyed, and an image forming apparatus such as a copying machine, a facsimile, a printer, or a multifunction machine including the sheet edge detection device. is there.

  In the conventional image forming apparatus, sheets are fed one by one from the sheet cassette to the image forming unit by a feeding roller. The fed sheet is inclined with respect to the sheet conveying direction due to various influences such as a difference in outer diameter of the conveying roller, a difference in conveying speed due to wear of the roller, and a rubbing resistance between the conveying guide member for guiding the sheet and the sheet. (Hereinafter referred to as skew).

  When the sheet is conveyed while being skewed and the toner image on the photosensitive drum is transferred to the sheet in the image forming unit, the image is inclined with respect to the sheet. Therefore, in the image forming apparatus, in order to suppress the skew of the sheet, a shutter member is provided on the registration roller pair or the conveyance roller pair, the sheet leading edge is brought into contact and locked, and the image is aligned after the sheet leading edge is aligned. A configuration for conveying to the forming unit is used.

  However, the configuration in which the skew is corrected by abutting the leading edge of the sheet may cause a positional deviation in a direction orthogonal to the sheet conveying direction when the leading edge of the sheet is abutted. In this case, the relative position between the sheet and the image is shifted. Also, the positional deviation in the direction perpendicular to the sheet conveyance direction is regulated by the sheet width direction regulating member in the sheet cassette, but the positional deviation occurs due to backlash of the regulating member or variations in the sheet itself. End up.

  Further, in the configuration in which double-sided printing is performed, after the image is formed on one side, the sheet is reversed and the image is formed on the back side again. The transport route to the end becomes longer. Therefore, the second surface (back surface) is more affected by various rollers and the conveyance guide than the first surface (front surface), and the sheet may be skewed or misaligned during conveyance. Further, the sheet that has passed through the fixing unit contracts due to the heat and pressure of the fixing unit, and the sheet size on the second side becomes smaller than the sheet size on the first side, and the end position of the sheet may be different.

  In order to correct such a misalignment between the image and the sheet, a configuration for detecting the position of the end of the sheet parallel to the sheet conveyance direction is provided. There exists patent document 1 as this structure. In this configuration, a line sensor is arranged as a detection unit at a position where the sheet end of the conveyed sheet can be detected from the minimum size to the maximum size, and light is emitted from a light emitting member such as an LED from one side of the sheet. The position of the sheet edge is detected by the brightness of the light.

  Further, as a configuration for detecting a sheet end position parallel to the sheet conveyance direction, there is a configuration described in Patent Document 2. In this configuration, a photo interrupter in which a light emitting element and a light receiving element are arranged at a predetermined interval moves across the sheet end, and detects the sheet end position based on the distance from the reference position to the optical path blocking position.

JP2003-223088 JP-A-5-132193

  However, as in Patent Document 1, a configuration using a line sensor in the detection unit requires a plurality of light receiving sensor elements in order to cover all the sheet sizes that can be conveyed. For this reason, the cost of a detection part becomes high.

  In addition, as in Patent Document 2, the configuration using the photo interrupter is such that the light receiving unit and the light emitting unit are integrated, so it is necessary to avoid collision with the sheet, and the sheet end must be detected and stopped immediately. I must. In addition, when the sheet is skewed, a retreat operation in accordance with the skew must be performed so as not to touch the sheet. Further, when the sheet is continuously conveyed or when the sheet edge is detected a plurality of times during conveyance of one sheet, it is necessary to repeat the sheet edge detection operation and the retreat operation.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a sheet end detection device that can detect the position of the end of a sheet without performing a complicated operation such as a retracting operation with an inexpensive configuration.

  The present invention for achieving the above object is a sheet edge detection device for detecting the position of the edge of a conveyed sheet, a light emitting section provided in a direction intersecting the sheet conveyance direction; A light receiving portion that is arranged independently with a gap to the light emitting portion so as to sandwich the sheet, and is movably provided with respect to the light emitting portion, and the light receiving portion is disposed on the light emitting portion. The position of the edge of the sheet is detected by detecting a change point of whether or not light is blocked by the sheet from the light emitting unit. .

  According to the present invention, since the light receiving unit moves with respect to the light emitting unit to detect the end of the sheet, at least one light receiving unit is sufficient, and the configuration is inexpensive. Furthermore, since the moving light receiving unit is independent of the light emitting unit, there is no need to stop at the sheet end position, and there is no need to retreat from the sheet conveyance area during skew feeding. That is, the position of the end portion of the sheet can be detected with an inexpensive configuration without performing a complicated operation such as a retracting operation.

It is a perspective view which shows the outline | summary of the principal part of a sheet | seat edge part detection apparatus. 1 is a schematic cross-sectional view showing an outline of a main part of an image forming apparatus. FIG. 6 is a diagram illustrating a sheet edge detection operation according to the first exemplary embodiment. FIG. 6 is a diagram illustrating an edge detection operation for continuously conveyed sheets according to the first exemplary embodiment. FIG. 10 illustrates a sheet width detection operation according to the second exemplary embodiment. FIG. 10 is a diagram illustrating an operation for detecting a skew amount of a sheet according to a third exemplary embodiment. FIG. 10 illustrates a sheet size detection operation according to the fourth exemplary embodiment.

  Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the drawings. However, the dimensions, materials, shapes, and relative arrangements of the components described in the following embodiments should be appropriately changed according to the configuration of the apparatus to which the present invention is applied and various conditions. Therefore, unless specifically stated otherwise, the scope of the present invention is not intended to be limited thereto.

  First, the configuration of an image forming apparatus having a sheet edge detection device will be described with reference to FIG. FIG. 2 is a schematic cross-sectional view showing an outline of a main part of the image forming apparatus.

  As shown in FIG. 2, the image forming apparatus 200 according to the present embodiment includes an optical unit 201 including a laser diode, a polygon mirror, a lens, and a reflection mirror, and a laser is formed according to image information obtained from the optical unit 201. Irradiate light. As a result, an electrostatic latent image corresponding to the image information is formed on the photosensitive drum 202 which is a drum-shaped electrophotographic photosensitive member. The latent image is developed by a developing unit configured inside the process cartridge 203.

  The sheet S is conveyed from the lower feeding cassette 204 along the conveyance guide member. The sheet S forms an image by passing through a conveyance nip formed by the process cartridge 203 and the transfer roller 205.

  When the sheets S in the feeding cassette 204 are fed by the respective sheet feeding devices 206, they are first sent to the conveying roller pair 209. Next, based on the image information, the sheet is sent by the conveying roller pair 209 in time with the latent image formed on the photosensitive drum 202 constituting the image forming unit. A transfer roller 205 as a transfer unit is disposed at the transfer position, and a toner image on the photosensitive drum 202 is transferred to the sheet S by applying a voltage.

  Thereafter, the sheet S that has received the transfer of the toner image is sent to the fixing unit 210, where a fixing process for fixing the transferred toner image on the paper surface is performed. The fixing unit 210 includes a driving roller 211 and a fixing roller 212 having a built-in heater, and fixes the transferred toner image on the sheet S by applying heat and pressure to the passing sheet S.

  The image forming apparatus includes a duplex printing mode for performing duplex printing on the sheet S and a simplex printing mode. In the single-sided print mode, the sheet S after the fixing process is discharged onto a discharge tray 215 outside the apparatus by the inner discharge roller pair 213 and the outer discharge roller 214. In the double-sided printing mode, the paper is temporarily stacked and stored on the intermediate tray 219 via the refeed path 217 and the double-sided conveyance path 218 by the internal discharge roller pair 213 or the switchback roller pair 216. Then, the sheet S stored on the intermediate tray 219 is conveyed again for image formation by the re-feeding device 220, and thereafter discharged outside the apparatus through the same process as single-sided printing.

  Here, the configuration of the controller that controls the entire image forming apparatus will be briefly described. The image forming apparatus 200 includes control means (not shown) that is a controller. The control means has a CPU circuit unit. The CPU circuit unit includes a CPU, a ROM, and a RAM, and comprehensively controls each unit constituting the image forming apparatus by a control program stored in the ROM. The control unit controls the image forming unit based on information detected by a sheet edge detection device described later. This control content will be described later. The RAM temporarily stores control data and is used as a work area for arithmetic processing associated with control.

  Next, the configuration of the sheet edge detection device in the image forming apparatus will be described with reference to FIG. FIG. 1 is a perspective view showing an outline of a main part of the sheet edge detection device.

  As shown in FIG. 1, a detection unit 100 as a sheet edge detection device includes a light emitting unit 101 and a light receiving unit 102. Here, a configuration in which the detection unit 100 is provided in the refeed path of the image forming apparatus 200 is illustrated, but the present invention is not limited to this (see FIG. 2).

  The light emitting unit 101 constituting the detection unit 100 is provided on the upper part of the conveyance guide member 103 constituting the sheet conveyance path. The light receiving unit 102 constituting the detecting means is arranged at an interval so as to sandwich the sheet with respect to the light emitting unit 101. The light receiving unit 102 is disposed independently of the light emitting unit 101 below the conveyance guide member 104 constituting the sheet conveyance path, and is provided so as to be movable with respect to the light emitting unit 101.

  The light emitting unit 101 is provided in a direction intersecting the sheet conveyance direction so that the end positions of sheets of various sizes can be detected. Specifically, the light emitting unit 101 conveys the plurality of light emitting elements 101a using a plurality of light emitting elements (for example, LEDs) so that light is irradiated to the edge of the sheet having the minimum size to the maximum size. They are arranged side by side in a direction that intersects the direction.

  In the light receiving unit 102, the substrate on which the light receiving element 105 is attached is engaged with the sensor holder 106. The light receiving unit 102 includes a gear unit that meshes with a pinion attached to the stepping motor 107. When the stepping motor 107 rotates forward and backward, the light receiving unit 102 reciprocates in the directions of arrows A and B in the drawing. Since the light receiving unit 102 corresponds to various sheet sizes, the light receiving unit 102 reversibly moves in a direction crossing the sheet conveyance direction so as to detect the edge of the sheet of the maximum size from the minimum size.

  Since the sheet blocks the optical path formed by the light emitting unit 101 and the light receiving unit 102, light brightness is generated, and the end position of the sheet can be detected by the light receiving unit 102 movable in the width direction intersecting the sheet conveying direction. . That is, the light receiving unit 102 can detect the position of the end portion of the sheet by detecting the change point of whether or not the light from the light emitting unit 101 is blocked by the sheet. It should be noted that the reference position of the detecting means 100 and the initial value of the drive pulse of the stepping motor 107 are set by known means outside the sheet conveyance area. The reference position of the detection means 100 is a position that serves as a reference for knowing the amount of positional deviation from the position detected by the detection means 100, and is set in advance.

  Here, the light emitting unit 101 is provided above the conveyance guide member 103 and the light receiving unit 102 is provided below the conveyance guide member 103. However, the arrangement is not limited to this, and the arrangement may be reversed. Moreover, although the structure which uses LED as a light emitting element of the light emission part 101 was illustrated, it is not restricted to this, What is necessary is just a light emitting member which can detect a sheet | seat edge part by the light-receiving part 102. FIG. Further, although the stepping motor is used for driving the detection means, the present invention is not limited to this, and any configuration that can detect the movement distance may be used.

  As described above, since the light receiving unit 102 moves with respect to the light emitting unit 101 and detects the edge of the sheet, it is sufficient that at least one light receiving unit 102 is provided, and the configuration is inexpensive. Further, since the moving light receiving unit 102 is independent of the light emitting unit 101, it is not necessary to stop at the sheet end position, and it is not necessary to retreat from the sheet conveyance area during skew feeding. That is, the position of the end portion of the sheet can be detected with an inexpensive configuration without performing a complicated operation such as a retracting operation.

[Example 1]
The sheet edge detection operation according to the first exemplary embodiment will be described with reference to FIGS. FIG. 3 is a diagram illustrating a sheet edge detection operation according to the first exemplary embodiment. FIG. 4 is a diagram illustrating the edge detection operation for continuously conveyed sheets according to the first exemplary embodiment.

  The sheet edge detection operation when a sheet is conveyed will be described with reference to FIG. When the sheet S is fed in the direction of arrow Z as shown in FIG. 3A, the sheet S eventually passes through a part of the light path of the light emitting unit (dotted line position in the figure) as shown in FIG. It reaches the blocking position. In this way, when the sheet S is in a state of blocking a part of the light path of the light emitting unit, the light receiving unit 102 crosses the end parallel to the conveying direction of the sheet S so that the sheet It moves in a direction (arrow A direction) that intersects the transport direction. When the light receiving unit 102 crosses the end in the width direction orthogonal to the sheet conveyance direction, the state of the output signal changes. The time of this change is detected, and the distance to the end of the sheet is detected by calculating based on the reference position and the number of driving pulses of the stepping motor to the change detection point.

  In FIG. 3, the light receiving unit 102 moves from the outside to the inside of the sheet so as to cross the sheet end and detects the position of the end in the width direction of the sheet. You can stand by either inside or outside. When the sheet is in a state where the sheet blocks the light path of the light emitting unit, the light receiving unit 102 may move along the light emitting unit so as to cross the end in the width direction orthogonal to the sheet conveying direction. The light receiving unit 102 may stop and wait at a predetermined position after detecting the sheet end position, but may be configured to continue the reciprocating motion without stopping so as not to complicate the operation.

  Based on the sheet edge position detected by the detection unit 100, the image forming unit is controlled by a control unit included in the image forming apparatus. Specifically, the control unit obtains the amount of misalignment of the sheet from the position detected by the detection unit 100 and a preset reference position, and corrects the position of the image formed on the sheet by the image forming unit accordingly. To do. Thereby, the position shift of the image with respect to the sheet can be suppressed.

  With reference to FIG. 4, the sheet edge detection operation when sheets are continuously conveyed will be described. When the sheets are continuously conveyed, the detection operation is continuously performed to detect the position of the end portion of the sheet.

  For example, the detection of the second sheet edge may be configured to move in the direction opposite to the first movement direction (second movement direction) moved when the first sheet edge is detected. In this case, after detecting the end position of the first sheet S (see FIG. 4A), the light receiving unit 102 slightly waits for the end of the sheet S and waits (FIG. 4B). reference). Then, the movement is performed in the direction opposite to the direction moved when the first sheet edge is detected (see FIG. 4C), and the position of the edge of the second sheet S is detected (FIG. 4D). reference). Here, the overrun amount of the light receiving unit 102 is set to be slightly larger than the variation amount of the sheet end portion position.

  As described above, the light receiving unit 102 has a first movement direction that intersects the sheet conveyance direction and a second movement direction that is opposite to the first movement direction during the conveyance of successive sheets. Reciprocally move in two directions, and sequentially detect the position of the end of the sheet conveyed continuously.

  This eliminates the need for the conventional retreat operation and reference position detection for each sheet conveyed continuously. Further, even if the interval between the previous sheet and the next sheet is clogged, the end of the sheet can be detected even when the sheet is conveyed at high speed by performing detection from two directions. By performing the detection operation from two directions in this way, it is possible to cope with the small paper, leading to an increase in the number of printed sheets of the image forming apparatus.

[Example 2]
The sheet edge detection operation of the second embodiment will be described with reference to FIG. FIG. 5 is a diagram illustrating a sheet width detection operation according to the second exemplary embodiment.

  The light receiving unit 102 moves in a direction intersecting the sheet conveyance direction during conveyance of one sheet, and is positioned at one end in the width direction intersecting the sheet conveyance direction. Is detected. Further, it moves in the same direction to detect the position of the other end in the width direction of the one sheet. Thereby, the length in the width direction of the one sheet is detected.

  When the sheet S is fed in the direction of the arrow Z, the sheet S eventually reaches a position where a part of the light path of the light emitting portion (dotted line position in the drawing) is blocked as shown in FIG. When the sheet S fed in this way is in a state of blocking a part of the light path of the light emitting unit (dotted line position in the figure), the light receiving unit 102 intersects the sheet conveyance direction along the light emitting unit. Move in the width direction (arrow A direction). When the light receiving unit 102 moves so as to cross one end in the width direction of the sheet, the state of the output signal changes, and a change point (first change detection point) of whether or not light from the light emitting unit is blocked is detected. To do. By calculating based on the reference position and the number of drive pulses of the stepping motor 107 up to the first change detection point, the distance to one end in the width direction of the sheet can be detected.

  Further, the light receiving unit 102 continues to move in the same direction (arrow A direction). As shown in FIG. 5B, when the light receiving unit 102 moves across the other end in the width direction of the sheet, the state of the output signal changes, and the change point of whether or not the light from the light emitting unit is blocked. (Second change detection point) is detected. The time point of this change is detected, the control means calculates based on the number of drive pulses of the stepping motor from the first change detection point to the second change detection point, and the first change detection point and the second change detection point are calculated. Detect the distance of a point. This detected distance becomes the length (sheet width) in the width direction orthogonal to the sheet conveyance direction.

  As described above, it is not necessary to provide a configuration for detecting the sheet width in the sheet cassette by detecting the sheet width. Further, the end position of the sheet with respect to the reference position is detected from the first change detection point or the second change detection point. In FIG. 5, the light receiving unit 102 moves from the outside to the inside of the sheet, but may be located anywhere when the sheet is conveyed. The sheet width can be detected by moving the light receiving unit 102 across both ends in the direction intersecting the sheet conveyance direction within the time when one sheet blocks the optical path from the light emitting unit. is there. As described above, the position of the edge of the sheet is detected, and the position of the image formed on the sheet is corrected based on the position of the edge, thereby suppressing the positional deviation of the image with respect to the sheet.

Example 3
The sheet edge detection operation of the third embodiment will be described with reference to FIG. FIG. 6 is a diagram illustrating an operation of detecting the skew amount of the sheet according to the third embodiment.

  During the conveyance of one sheet, the light receiving unit 102 is in two directions: a first movement direction that intersects the sheet conveyance direction and a second movement direction that is opposite to the first movement direction. Reciprocally move and detect the position of one end of the one sheet a plurality of times. Thus, the inclination of the one sheet is detected from each detection position.

  When the sheet S is fed in the arrow Z direction, the sheet S reaches a position where a part of the light path of the light emitting unit is blocked. When one sheet S fed in this way is in a state where a part of the light path of the light emitting unit is blocked, the light receiving unit 102 extends in the width direction intersecting the sheet conveying direction along the light emitting unit. It reciprocates in the direction of an arrow A and in the direction of arrow B, which is the opposite direction.

  First, when the light receiving unit 102 moves in the arrow A direction (first movement direction) so as to cross one end in the width direction of the sheet during conveyance of the single sheet S, the state of the output signal changes. A change point (first change detection point) of whether or not light from the light emitting unit is blocked is detected. By calculating based on the number of driving pulses of the stepping motor from the reference position to the first change detection point, the first distance from the reference position to one end in the sheet width direction can be detected.

  Further, during conveyance of the one sheet, the light receiving unit 102 moves in a direction indicated by an arrow B (second movement direction) opposite to the direction indicated by the arrow A after moving a predetermined distance from the first change detection point. To start. If the sheet moves in the direction of the arrow B so as to cross the end on the same side of the sheet during the conveyance of one sheet, the state of the output signal changes, and the change point of whether or not light is blocked from the light emitting unit (second Change detection point). By calculating based on the number of driving pulses of the stepping motor from the reference position to the second change detection point, the second distance from the reference position to one end in the sheet width direction can be detected.

  Thereby, the one side edge part of one sheet | seat can be detected twice. Then, the positional deviation of the sheet from the reference position and the position of the first change detection point is detected, and the distance between the detection timing of the first change detection point and the second change detection point and the sheet conveyance speed is two points in the sheet conveyance direction. Is calculated, the skew amount (slope) of the sheet is detected.

  Then, by correcting the position of the image formed on the sheet based on the positional deviation of the sheet from the reference position and the skew amount of the sheet, the positional deviation of the image with respect to the sheet can be reduced. Here, an example in which one side end portion of one sheet is detected twice has been described, but detection may be performed a plurality of times while the sheet passes through the optical path. By detecting multiple times, it is possible to detect the skew amount with higher accuracy.

Example 4
The sheet edge detection operation of the fourth embodiment will be described with reference to FIG. FIG. 7 is a diagram illustrating a sheet size detection operation according to the fourth embodiment.

  As shown in FIG. 7A, the light receiving unit 102 is positioned inside the sheet S to be conveyed before the timing when the leading end of the sheet S blocks the optical path of the light emitting unit. This position is a position where the light receiving unit 102 faces the light emitting unit, and is a position that is inside (in the conveyance area) of the minimum size sheet. As shown in FIG. 7B, when the leading end portion of the conveyed sheet S crosses between the light receiving portion 102 and the light emitting portion, the state of the output signal changes, and the detection means is the leading end portion in the sheet conveying direction. Is detected (first change detection point).

  After detecting the first change detection point, as shown in FIG. 7C, the light receiving unit 102 crosses one end in the width direction intersecting the sheet conveyance direction during conveyance of the sheet S. Next, the sheet moves in the sheet width direction (arrow B direction). Then, the state of the output signal of the detection means changes, and the light receiving unit 102 detects a change point (second change detection point) of whether or not light from the light emitting unit is blocked.

  After moving a predetermined distance from the second change detection point, as shown in FIG. 7D, the light receiving unit 102 moves in a direction (arrow A direction) opposite to the aforementioned direction (arrow B direction). When the light receiving unit 102 moves in the direction of arrow A so as to cross the end on the same side of the sheet S, as shown in FIG. 7E, the state of the output signal changes and the light from the light emitting unit is blocked. A change point (third change detection point) of the presence or absence of is detected.

  Even after detecting the third change detection point, the light receiving unit 102 continues to move in the same direction (arrow A direction) so as to cross the other end in the width direction of the sheet S. Then, the state of the output signal of the detection means changes, and as shown in FIG. 7 (f), the light receiving unit 102 detects a change point (fourth change detection point) of whether or not light from the light emitting unit is blocked. .

  After moving a predetermined distance from the fourth change detection point, the light receiving unit 102 moves in a direction (arrow B direction) opposite to the aforementioned direction (arrow A direction), as shown in FIG. Then, as shown in FIG. 7H, the light receiving unit 102 is positioned inside the conveyed sheet S before the rear end portion in the sheet conveying direction is removed from the optical path of the light emitting unit. Note that, similarly to the above-described position, this position is a position where the light receiving unit 102 is opposed to the light emitting unit, and is a position inside the sheet of the minimum size (within the conveyance region). When the rear end portion of the conveyed sheet S crosses between the light receiving portion 102 and the light emitting portion, the state of the output signal changes, and the detecting means detects the position of the rear end portion in the sheet conveying direction (fifth). Change detection point).

  The length in the sheet conveyance direction can be detected from the time from the detection timing of the first change detection point to the detection timing of the fifth change detection point and the sheet conveyance speed. The edge position of the sheet can be detected by counting and calculating the number of driving pulses of the stepping motor from the reference position of the second change detection point, the third change detection point, and the fourth change detection point. From the position of the second change detection point or the third change detection point and the fourth change detection point, the width (length) in the direction intersecting the sheet conveyance direction can be detected. By detecting the distance from the second change detection point to the detection timing of the third change detection point and the distance of the two sheet conveyance directions from the sheet conveyance speed, the second change detection point and the third change detection point are detected. The skew amount (inclination) of the sheet is detected from the position of the change detection point. Here, the second change detection point and the third change detection point are used in order to detect the skew amount of the sheet, but the sixth change detection point is between the fourth change detection point and the fifth change detection point. The change amount detection point may be provided, and the skew amount may be detected from the fourth change detection point and the sixth change detection point.

  With these operations, it is possible to detect the sheet size, the posture (tilt), and the position (position shift) of the sheet regardless of the regular shape or the irregular shape. Here, in order to cope with an irregular sheet, the positions of both side ends in the width direction intersecting the conveyance direction are detected. However, when only a regular sheet such as A4 is conveyed, the fourth change detection is performed. The point may be abolished and only the end position on one side may be detected. In the case of a regular sheet, the type of the sheet is narrowed down by detecting one end of the sheet in the width direction, and the sheet is limited to one sheet by detecting the length of the sheet. Further, the standard sheet size and the positional deviation of the sheet can be detected even if the third change detection point and the fourth change detection point are eliminated. Accordingly, by correcting the position of the image formed on the sheet based on the detected posture of the sheet, it is possible to suppress the positional deviation of the image with respect to the sheet. In addition, by disposing the sheet edge detection device upstream of the image forming unit, the sheet size detection mechanism in the sheet cassette can be eliminated, and the cost of the product can be reduced.

[Other Embodiments]
In the above-described embodiment, one image forming unit is used. However, the number used is not limited, and may be set as needed.

  In the above-described embodiment, the printer is exemplified as the image forming apparatus, but the present invention is not limited to this. For example, the image forming apparatus may be another image forming apparatus such as a copying machine or a facsimile machine, or another image forming apparatus such as a multi-function machine combining these functions. The same effect can be obtained by applying the present invention to these image forming apparatuses.

DESCRIPTION OF SYMBOLS S ... Sheet | seat 100 ... Detection means 101 ... Light-emitting part 101a ... Light-emitting element 102 ... Light-receiving part 103,104 ... Conveyance guide member 105 ... Light-receiving element 106 ... Sensor holder 107 ... Stepping motor 200 ... Image forming apparatus

Claims (7)

A sheet edge detection device that detects the position of the edge of a conveyed sheet,
A light emitting unit provided in a direction intersecting the sheet conveying direction;
A light receiving part that is arranged independently with a gap to sandwich the sheet with respect to the light emitting part, and is provided so as to be movable with respect to the light emitting part;
Have
The light-receiving unit moves along the light-emitting unit in a direction crossing the sheet conveyance direction, and detects a change point of the presence or absence of light blocking from the light-emitting unit by the sheet, thereby detecting the end of the sheet. A sheet edge detection device that detects a position. A light-receiving unit that moves in a direction that intersects the sheet conveyance direction along the light-emitting unit detects a change point of the presence or absence of light from the light-emitting unit by the sheet, so that the sheet intersects the sheet conveyance direction. Detect the position of the edge,
The light receiving unit located at a position in the sheet conveyance region facing the light emitting unit detects a change point of whether or not the light from the light emitting unit is blocked by the sheet, so that the end of the sheet in the conveyance direction is detected. The sheet edge detection device according to claim 1, wherein the position is detected.   The light receiving unit is configured to move in two directions, a first movement direction intersecting the sheet conveyance direction and a second movement direction opposite to the first movement direction during conveyance of one sheet. 3. The tilt of the one sheet is detected from each detection position by reciprocating and detecting the position of one end of the one sheet a plurality of times. A sheet edge detection device according to claim 1.   The light receiving unit moves to a position in a sheet conveyance region facing the light emitting unit before the front end of the sheet in the conveyance direction reaches the light emitting unit during conveyance of one sheet, and the sheet The front end of the sheet in the conveying direction is detected, and before the rear end of the sheet in the conveying direction passes through the light emitting unit, the sheet moves to a position in the sheet conveying region facing the light emitting unit, The length of the conveyance direction of the said 1 sheet is detected by detecting the position of the rear-end part of the conveyance direction of a sheet | seat, The any one of Claim 1 thru | or 3 characterized by the above-mentioned. Sheet edge detection device.   The light receiving unit moves in a direction intersecting the sheet conveyance direction during conveyance of one sheet, and positions one end in a direction intersecting the sheet conveyance direction. A direction that crosses the conveying direction of the single sheet by detecting the position of the other end of the direction that intersects the conveying direction of the single sheet by detecting the position of the other sheet. The sheet edge detection device according to any one of claims 1 to 4, wherein the length of the sheet is detected.   The light-receiving unit reciprocates in two directions, a first movement direction intersecting the sheet conveyance direction and a second movement direction opposite to the first movement direction during conveyance of successive sheets. The sheet edge detection device according to claim 1, wherein the sheet edge detection apparatus moves and sequentially detects positions of edges of the continuous sheets. Conveying means for conveying the sheet;
An image forming unit for forming an image on a sheet;
A sheet edge detection device according to any one of claims 1 to 6,
Control means for controlling the image forming unit based on information detected by the sheet edge detection device,
The control unit corrects a position of an image formed on the sheet by the image forming unit according to a positional deviation between a position detected by the sheet edge detection device and a preset reference position. Image forming apparatus.

Images