Patent Description:
<CIT> discloses an image forming apparatus including an image forming unit that forms an image, a sheet reversing unit used to perform double-sided printing, a guide unit used to retain the position of a paper sheet in the sheet reversing unit, and a sheet-position retaining unit. A paper sheet whose length in a transporting direction thereof is longer than the length of a transport passage in the sheet reversing unit may be transported into the transport passage. In such a case, the sheet-position retaining unit continuously retains the position of the paper sheet with the guide unit from when the paper sheet has entirely entered the transport passage and when the transportation of the paper sheet is stopped so that a trailing edge of the paper sheet is at a reversing start position. Then, when the next image forming operation is ready to be started, the sheet-position retaining unit stops retaining the position of the paper sheet and releases the paper sheet.

<CIT> discloses a sheet-length measurement device including a rotating body that rotates in contact with a sheet material, a measurement mechanism that measures an amount of rotation of the rotating body, and position sensing mechanisms disposed upstream and downstream of the rotating body in a transporting direction of the sheet material. Each of the position sensing mechanisms includes a sensing member line including plural sensing members arranged in a line. Each position sensing mechanism is disposed to cross side edges of the sheet material in a width direction, and is at an angle with respect to the transporting direction of the sheet material. A sheet length of the sheet material is determined based on the amount of rotation of the rotating body measured by the measurement mechanism and positions of edge portions of the sheet material sensed by the position sensing mechanisms. <CIT> discloses a sheet transport device including a sheet transport unit, a detector, and a releasing unit. The sheet transport unit transports a sheet by nipping the sheet in a nip between multiple pairs of transport rollers arranged in a sheet width direction intersecting a sheet transport direction. The detector detects a size of the transported sheet. The releasing unit releases the nip of one or more of the pairs of transport rollers outside a transport region of the sheet based on the size of the sheet detected by the detector. <CIT> discloses a sheet carrying device including: first detection means that detects an end in a carrying direction of a sheet; width detection means that is installed on the upstream side in the carrying direction of the sheet of the first detection means and detects positions of both ends in a width direction orthogonal to the carrying direction of the sheet; and second detection means that is installed on the upstream side in the carrying direction of the sheet of the width detection means and detects a position of an end in the carrying direction of the sheet. <CIT> discloses an image forming apparatus including an image forming unit that forms an image on a recording medium; a fixing unit that fixes the image formed on the recording medium by the image forming unit by applying heat; a first detector unit that detects a length of the recording medium in a transport direction, the first detector unit being disposed upstream of the fixing unit in the transport direction; and a second detector unit that detects the length of the recording medium in the transport direction. <CIT> discloses a medium carrying device in which a skew angle of a medium is obtained by skew detection sensors right after the medium is taken in a carriage passage, and the length of the medium in the carrying direction is calculated based on a detection signal of the skew detection sensor and a detection signal of a medium detection sensor.

Accordingly, it is an object of the present disclosure to enable a detection of positions of both edge portions of a medium in a direction orthogonal to a transporting direction of a medium while the medium is being transported. The detection is performed with increased accuracy compared to a case in which a length of the medium in the direction orthogonal to the transporting direction is estimated based on a length of the medium in the transporting direction determined by detecting a leading edge portion and a trailing edge portion of the medium while the medium is being transported.

According to a first aspect of the present disclosure, there is provided a detection device according to claim <NUM>.

According to a second aspect of the present disclosure, the second detection unit is disposed downstream of the abutting unit in the transporting direction.

According to a third aspect of the present disclosure, the second detection unit is divided into a section that detects one edge portion of the medium in the orthogonal direction and a section that detects other edge portion of the medium in the orthogonal direction, the sections facing each other in the orthogonal direction.

According to a fourth aspect of the present disclosure, at least one of the sections into which the second detection unit is divided in the orthogonal direction detects an amount of displacement of the medium in the orthogonal direction.

According to a fifth aspect of the present disclosure, the first detection unit includes a leading edge sensing unit that senses the leading edge portion of the medium while the medium is being transported and a trailing edge sensing unit that includes a plurality of sensing elements arranged in the transporting direction and that senses the trailing edge portion of the medium while the medium is being transported, a distance between one of the plurality of sensing elements that is disposed most upstream in the transporting direction and the leading edge sensing unit being less than a transporting-direction dimension of the medium when the medium has a maximum size.

According to a sixth aspect of the present disclosure, the first detection unit includes two pairs of sensing units, each pair including the leading edge sensing unit and the trailing edge sensing unit that overlap when viewed in the transporting direction.

According to an seventh aspect of the present disclosure, the transport unit transports the medium at a constant transport speed that is lower than a transport speed at which the medium is transported in a region upstream of the leading edge sensing unit in the transporting direction. The leading edge sensing unit and the trailing edge sensing unit respectively sense the leading edge portion and the trailing edge portion of the medium while the medium is being transported by the transport unit.

According to a eighth aspect of the present disclosure, the detection device further includes an upstream transport unit that is disposed upstream of the transport unit in the transporting direction and that is movable between a nipping position at which the upstream transport unit nips the medium and a separated position at which the upstream transport unit is separated from the medium, the upstream transport unit transporting the medium while the upstream transport unit is at the nipping position. The leading edge sensing unit and the trailing edge sensing unit respectively sense the leading edge portion and the trailing edge portion of the medium while the upstream transport unit is at the separated position.

According to a ninth aspect of the present disclosure, there is provided a program according to claim.

According to an tenth aspect of the present disclosure, there is provided a detection method according to claim <NUM>.

According to the first, ninth, and tenth aspects of the present disclosure, the positions of both edge portions of the medium in a direction orthogonal to the transporting direction of the medium can be more accurately detected while the medium is being transported.

According to the second aspect of the present disclosure, the second detection unit detects both edge portions of the medium with increased accuracy compared to a case in which the second detection unit is disposed upstream of the abutting unit in the transporting direction.

According to the third aspect of the present disclosure, unlike a case in which the second detection unit is composed of a single detection unit that extends from one edge portion to the other edge portion of the medium in the orthogonal direction and is not divided, the detection unit does not occupy a region unnecessary for the detection of both edge portions of the medium in the orthogonal direction.

According to the fourth aspect of the present disclosure, the number of components can be reduced compared to a case in which a detection unit that detects an amount of displacement of the medium in the orthogonal direction is provided in addition to the second detection unit.

According to the fifth aspect of the present disclosure, the influence of the detection by the first detection unit on the medium after the position of the medium has been adjusted by the abutting unit can be reduced compared to a case in which the first detection unit is disposed downstream of the abutting unit in the transporting direction.

According to the fifth aspect of the present disclosure, a load (that is, stress) applied to the medium is reduced compared to a case in which the leading and trailing edge sensing units sense the leading and trailing edge portions of the medium while the upstream transport unit is at the nipping position.

An exemplary embodiment of the present disclosure will now be described with reference to the drawings.

The structure of an image forming apparatus <NUM> according to the exemplary embodiment will be described. <FIG> is a schematic diagram illustrating the structure of the image forming apparatus <NUM> according to the present exemplary embodiment.

In the drawings, arrow UP shows an upward (vertically upward) direction of the apparatus, and arrow DO shows a downward (vertically downward) direction of the apparatus. In addition, arrow LH shows a leftward direction of the apparatus, and arrow RH shows a rightward direction of the apparatus. In addition, arrow FR shows a forward direction of the apparatus, and arrow RR shows a rearward direction of the apparatus. These directions are defined for convenience of description, and the structure of the apparatus is not limited to theses directions. The directions of the apparatus may be referred to without the term "apparatus". For example, the "upward direction of the apparatus" may be referred to simply as the "upward direction".

In addition, in the following description, the term "up-down direction" may be used to mean either "both upward and downward directions" or "one of the upward and downward directions". The term "left-right direction" may be used to mean either "both leftward and rightward directions" or "one of the leftward and rightward directions". The left-right direction may also be referred to as a lateral direction or a horizontal direction. The term "front-rear direction" may be used to mean either "both forward and rearward directions" or "one of the forward and rearward directions". The front-rear direction corresponds to a width direction described below, and may also be referred to as a lateral direction or a horizontal direction. The up-down direction, the left-right direction, and the front-rear direction cross each other (more specifically, are orthogonal to each other).

In the figures, a circle with an X in the middle represents an arrow going into the page, and a circle with a dot in the middle represents an arrow coming out of the page.

The image forming apparatus <NUM> illustrated in <FIG> is an apparatus that forms an image. More specifically, the image forming apparatus <NUM> is an inkjet image forming apparatus that forms an image on a medium P by using ink. Still more specifically, as illustrated in <FIG>, the image forming apparatus <NUM> includes an image forming apparatus body <NUM>, a medium storage unit <NUM>, a medium output unit <NUM>, an image forming unit <NUM>, a heating unit <NUM>, a transport mechanism <NUM>, a detection device <NUM>, and a control device <NUM>.

The medium P, components of the image forming apparatus <NUM>, an image forming operation performed by the image forming apparatus <NUM>, etc., will now be described.

The medium P is an object on which an image is formed by the image forming unit <NUM>. The medium P may be, for example, a paper sheet or a film. The paper sheet may be, for example, a sheet of cardboard paper or coated paper. The film may be, for example, a resin film or a metal film. In the present exemplary embodiment, a paper sheet, for example, is used as the medium P. The type of the medium P is not limited to the above-described types, and various types of media P may be used.

The size of the medium P may be, for example, greater than A3, and sizes such as A2, A1, A0, and B series may be used. The size of the medium P is not limited to the above-described sizes, and media P having various sizes may be used.

A length of the medium P in a transporting direction will be referred to as a transporting-direction dimension. A direction that crosses (more specifically, that is orthogonal to) the transporting direction of the medium P will be referred to as a width direction, and a length of the medium P in the width direction will be referred to as a width-direction dimension. The width direction is an example of an orthogonal direction. In the figures, the transporting direction is shown by arrow H as appropriate.

In the present exemplary embodiment, an upstream edge portion of the medium P in the transporting direction may be referred to as a trailing edge portion or an upstream edge portion. A downstream edge portion of the medium P in the transporting direction may be referred to as a leading edge portion or a downstream edge portion. Edge portions of the medium P in the width direction may be referred to as side edge portions.

As illustrated in <FIG>, components of the image forming apparatus <NUM> are disposed in the image forming apparatus body <NUM>. More specifically, for example, the medium storage unit <NUM>, the image forming unit <NUM>, the heating unit <NUM>, the transport mechanism <NUM>, and the detection device <NUM> are disposed in the image forming apparatus body <NUM>.

The detection device <NUM> is removably disposed in the image forming apparatus body <NUM>. In other words, the detection device <NUM> is detachably attached to the image forming apparatus body <NUM>.

The medium storage unit <NUM> is a unit that stores media P in the image forming apparatus <NUM>. The media P stored in the medium storage unit <NUM> are supplied to the image forming unit <NUM>.

The medium output unit <NUM> is a unit of the image forming apparatus <NUM> to which each medium P is output. The medium output unit <NUM> receives the medium P having an image formed thereon by the image forming unit <NUM>.

The image forming unit <NUM> illustrated in <FIG> is an example of an image forming unit that forms an image on the medium P transported thereto. More specifically, the image forming unit <NUM> forms an image on the medium P by using ink. Still more specifically, as illustrated in <FIG>, the image forming unit <NUM> includes discharge portions 15Y, <NUM>, 15C, and <NUM> (hereinafter denoted by 15Y to <NUM>), a transfer body <NUM>, and a facing member <NUM> that faces the transfer body <NUM>.

In the image forming unit <NUM>, the discharge portions 15Y to <NUM> discharge ink droplets of respective colors, which are yellow (Y), magenta (M), cyan (C), and black (K), toward the transfer body <NUM> to form images on the transfer body <NUM>. In addition, in the image forming unit <NUM>, the images of respective colors formed on the transfer body <NUM> are transferred to the medium P that passes through a transfer position TA between the transfer body <NUM> and the facing member <NUM>. As a result, an image is formed on the medium P. The transfer position TA may be regarded as an image formation position at which the image is formed on the medium P.

An example of the image forming unit does not necessarily have the structure of the image forming unit <NUM>. For example, an example of the image forming unit may instead be structured such that the discharge portions 15Y to <NUM> discharge ink droplets directly toward the medium P instead of the transfer body <NUM>.

As illustrated in <FIG>, an example of the image forming unit may instead be an electrophotographic image forming unit <NUM> that forms an image on the medium P by using toner.

As illustrated in <FIG>, the image forming unit <NUM> includes toner image forming units 215Y, <NUM>, 215C, and <NUM> (hereinafter denoted by 215Y to <NUM>), a transfer body <NUM>, and a transfer member <NUM>.

In the image forming unit <NUM>, the toner image forming units 215Y to <NUM> perform charging, exposure, developing, and transfer processes to form toner images of respective colors, which are yellow (Y), magenta (M), cyan (C), and black (K), on the transfer body <NUM>. The transfer member <NUM> transfers the toner images of the respective colors formed on the transfer body <NUM> to the medium P that passes through a transfer position TA between the transfer body <NUM> and the transfer member <NUM>. As a result, an image is formed on the medium P. Thus, an example of the image forming apparatus may instead be an electrophotographic image forming apparatus.

An example of the image forming unit may instead be structured such that, for example, the toner image forming units 215Y to <NUM> form the toner images directly on the medium P instead of the transfer body <NUM>.

The heating unit <NUM> illustrated in <FIG> is an example of a heating unit that heats the medium P on which an image is formed by the image forming unit <NUM>. For example, the heating unit <NUM> heats the medium P by using a heating source (not illustrated) in a contactless manner to dry the image formed of ink.

An example of the heating unit is not limited to the above-described heating unit <NUM>. An example of the heating unit may instead be, for example, a device that heats the medium P by coming into contact with the medium P without affecting the image. Various types of heating units may be used.

In the electrophotographic image forming apparatus including the image forming unit <NUM>, the heating unit <NUM> functions, for example, as a fixing device that fixes the toner images by applying heat.

The transport mechanism <NUM> is a mechanism that transports the medium P. For example, the transport mechanism <NUM> transports the medium P by using a transport member <NUM> including, for example, transport rollers. The transport member <NUM> may instead be, for example, a transport belt. The transport member <NUM> may be any member capable of transporting the medium P by applying transporting force to the medium P.

The transport mechanism <NUM> transports the medium P from the medium storage unit <NUM> to the image forming unit <NUM> (more specifically, to the transfer position TA). The transport mechanism <NUM> further transports the medium P from the image forming unit <NUM> to the heating unit <NUM>. The transport mechanism <NUM> further transports the medium P from the heating unit <NUM> to the medium output unit <NUM>. The transport mechanism <NUM> also transports the medium P from the heating unit <NUM> to the image forming unit <NUM>.

Thus, the image forming apparatus <NUM> includes a transport path <NUM> from the medium storage unit <NUM> to the image forming unit <NUM>, a transport path <NUM> from the image forming unit <NUM> to the heating unit <NUM>, and a transport path <NUM> from the heating unit <NUM> to the medium output unit <NUM>. The image forming apparatus <NUM> also includes a transport path <NUM> from the heating unit <NUM> to the image forming unit <NUM>.

The transport path <NUM> is a transport path along which the medium P having an image formed on one side thereof is returned to the image forming unit <NUM> (more specifically, to the transfer position TA). The transport path <NUM> also serves as a transport path that reverses the medium P having an image formed on one side thereof.

The transport path <NUM> and the transport path <NUM> include a common portion (more specifically, a downstream portion in the transporting direction). Accordingly, a transport path <NUM> along which the medium P is transported from the medium storage unit <NUM> may be regarded as being connected to the transport path <NUM> and configured to supply the medium P from the medium storage unit <NUM> to the transport path <NUM>. Therefore, a position at which the transport path <NUM> is connected to the transport path <NUM> may be regarded as a supply position 25A at which a new medium P fed from the medium storage unit <NUM> is supplied to the transport path <NUM> and transported toward the image forming unit <NUM>. In other words, according to the present exemplary embodiment, the medium P is supplied from the supply position 25A toward the image forming unit <NUM> through the transport path <NUM>.

In the image forming apparatus <NUM>, the medium P is transported from the medium storage unit <NUM> to the image forming unit <NUM> (more specifically, to the transfer position TA) along the transport path <NUM>, and the image forming unit <NUM> forms an image, which may hereinafter be referred to as "front image", on one side (i.e., the front side) of the medium P. When an image is to be formed only on one side of the medium P, the medium P having the front image formed on one side thereof is transported through the heating unit <NUM> and output to the medium output unit <NUM>.

When images are to be formed on both sides of the medium P, the medium P having the front image formed on one side thereof is transported through the heating unit <NUM> and then along the transport path <NUM>, so that the medium P is reversed and returned to the image forming unit <NUM> (more specifically, to the transfer position TA). Then, the image forming unit <NUM> forms an image on the other side (i.e., the back side) of the medium P. After that, the medium P is transported through the heating unit <NUM> and output to the medium output unit <NUM>. Thus, one and the other surfaces of the medium P are image forming surfaces on which images are formed.

As illustrated in <FIG>, the medium storage unit <NUM> is disposed below the transport path <NUM>. Therefore, each of the media P stored in the medium storage unit <NUM> is supplied to the supply position 25A of the transport path <NUM> from below.

As illustrated in <FIG>, the medium storage unit <NUM> may instead be disposed on a side of the transport path <NUM>. In this case, each of the media P stored in the medium storage unit <NUM> is supplied to the supply position 25A of the transport path <NUM> in a sideways direction (from the right side in <FIG>). In the structure illustrated in <FIG>, the medium storage unit <NUM> is disposed on a side of the image forming unit <NUM> (more specifically, the transfer position TA). Accordingly, each medium P is supplied to the image forming unit <NUM> (more specifically, to the transfer position TA) in a sideways direction. In <FIG>, the image forming apparatus body <NUM> is omitted.

The detection device <NUM> illustrated in <FIG> is an example of a detection device that detects edge portions of the medium P. In <FIG>, the detection device <NUM> is simplified.

<FIG> is a side sectional view illustrating the structure of the detection device <NUM>. <FIG> is a plan view illustrating the structure of the detection device <NUM>. In <FIG> and <FIG>, the left-right direction of the apparatus is reversed from that in <FIG>. More specifically, in <FIG> and <FIG>, the left and right sides of the apparatus are opposite to the left and right sides of the figures.

With regard to the detection device <NUM>, the expression "detect (or sense) an edge portion" does not necessarily mean that the edge of the medium P itself is directly detected (or sensed), and may also mean that a mark (for example, a trim mark) on the edge portion of the medium P, for example, is detected (or sensed). The mark is at a predetermined distance from the edge of the medium P so that the distance from the edge of the medium P is known.

As illustrated in <FIG>, the detection device <NUM> includes a first support <NUM>, a second support <NUM>, a transport mechanism <NUM>, detection units <NUM> and <NUM>, and a leading edge sensor <NUM>. The structures of components of the detection device <NUM> will now be described.

The first support <NUM> illustrated in <FIG> has a function of supporting components (more specifically, driving rollers <NUM>, <NUM>, <NUM>, <NUM>, and <NUM> described below) of the transport mechanism <NUM>.

As illustrated in <FIG>, the first support <NUM> constitutes a lower portion of the detection device <NUM>. The first support <NUM> has, for example, a flat shape that is thin in the up-down direction and extends in the front-rear and left-right directions.

The first support <NUM> includes a guide plate <NUM> that guides the medium P. The guide plate <NUM> faces the lower surface of the medium P and guides the medium P downstream in the transporting direction when the medium P is transported by the transport mechanism <NUM>.

The second support <NUM> illustrated in <FIG> and <FIG> has a function of supporting other components (more specifically, driven rollers <NUM>, <NUM>, <NUM>, <NUM>, and <NUM> described below) of the transport mechanism <NUM>.

As illustrated in <FIG>, the second support <NUM> constitutes an upper portion of the detection device <NUM>. The second support <NUM> has, for example, a flat shape that is thin in the up-down direction and extends in the front-rear and left-right directions.

The second support <NUM> includes a guide plate <NUM> that guides the medium P. The guide plate <NUM> faces the upper surface of the medium P and guides the medium P downstream in the transporting direction when the medium P is transported by the transport mechanism <NUM>.

The transport mechanism <NUM> illustrated in <FIG> and <FIG> is a mechanism that transports the medium P in the detection device <NUM>. As illustrated in <FIG> and <FIG>, the transport mechanism <NUM> includes transport roller units <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>. The transport roller units <NUM>, <NUM>, <NUM>, <NUM>, and <NUM> are arranged in that order toward the downstream side in the transporting direction. The transport roller units <NUM>, <NUM>, <NUM>, <NUM>, and <NUM> each have a function of transporting the medium P and include a pair of rollers, as illustrated in <FIG>. More specifically, the transport roller units <NUM>, <NUM>, <NUM>, <NUM>, and <NUM> include the driving rollers <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>, respectively, and the driven rollers <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>, respectively.

The driving rollers <NUM>, <NUM>, <NUM>, <NUM>, and <NUM> are disposed below the driven rollers <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>, respectively, and are rotated to apply transporting force to the medium P.

The driven rollers <NUM>, <NUM>, <NUM>, <NUM>, and <NUM> are disposed above the driving rollers <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>, respectively, and are rotated by the rotations of the driving rollers <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>.

The driven rollers <NUM>, <NUM>, <NUM>, <NUM>, and <NUM> are supported by the second support <NUM> such that the driven rollers <NUM>, <NUM>, <NUM>, <NUM>, and <NUM> are movable between nipping positions (positions shown by the solid lines in <FIG>) at which the medium P is nipped between the driven rollers <NUM>, <NUM>, <NUM>, <NUM>, and <NUM> and the driving rollers <NUM>, <NUM>, <NUM>, <NUM>, and <NUM> and separated positions (positions shown by the two-dot chain lines in <FIG>) at which the driven rollers <NUM>, <NUM>, <NUM>, <NUM>, and <NUM> are separated from the medium P. The transport roller units <NUM>, <NUM>, <NUM>, <NUM>, and <NUM> transport the medium P while the driven rollers <NUM>, <NUM>, <NUM>, <NUM>, and <NUM> are at the nipping positions.

The transport roller unit <NUM> is an example of a transport unit and has a function of transporting the medium P to the transport roller unit <NUM>.

The transport roller unit <NUM> is disposed downstream of the transport roller unit <NUM> in the transporting direction. The transport roller unit <NUM>, which is an example of an abutting unit, is an abutting roller unit that abuts against the leading edge of the medium P. In the following description, the transport roller unit <NUM> may be referred to as an abutting roller unit <NUM>. The abutting roller unit <NUM> has a function of correcting an inclination (i.e., skewing) of the medium P by abutting against the leading edge of the medium P transported by the transport roller unit <NUM>.

The transport roller unit <NUM> is disposed downstream of the transport roller unit <NUM> in the transporting direction. The transport roller unit <NUM> is a correction roller unit that corrects a displacement of the medium P in the width direction. In the following description, the transport roller unit <NUM> may be referred to as a correction roller unit <NUM>. The correction roller unit <NUM> corrects the displacement of the medium P in the width direction by moving in the width direction while nipping the medium P based on a detection result obtained by the detection unit <NUM>. In the present exemplary embodiment, two roller units, which are the abutting roller unit <NUM> and the correction roller unit <NUM>, serve a function of an adjustment unit that corrects skewing and displacement of the medium P. The medium P is transported to the image forming unit <NUM> (more specifically, the transfer position TA) after the position, for example, of the medium P is adjusted by the adjustment unit.

The transport roller units <NUM> and <NUM> are disposed upstream of the transport roller unit <NUM> in the transporting direction. The transport roller units <NUM> and <NUM> are examples of an upstream transport unit, and transport the medium P toward the transport roller unit <NUM>.

In the present exemplary embodiment, the transport roller unit <NUM> transports the medium P at a constant transport speed that is lower than a transport speed at which the medium P is transported in a region upstream of leading edge sensors <NUM> (612A and 612B), which will be described below, in the transporting direction. More specifically, the transport roller unit <NUM> transports the medium P at a constant transport speed that is lower than a transport speed at which the medium P is transported in a region upstream of the transport roller unit <NUM> in the transporting direction.

Although the transport mechanism <NUM> includes the transport roller units <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>, the transport mechanism <NUM> is not limited to this. For example, the transport roller units <NUM>, <NUM>, <NUM>, <NUM>, and <NUM> may be replaced by transport members, such as transport belts. More specifically, an example of a transport unit and an example of an upstream transport unit are not limited to the transport roller units <NUM>, <NUM>, and <NUM>, and transport members, such as transport belts, may instead be used. In addition, an example of the abutting unit is not limited to the abutting roller unit <NUM>, and a transport member, such as a transport belt, may instead be used. The abutting unit may be any unit that abuts against the leading edge of the medium P transported from a region upstream of the transport roller unit <NUM> in the transporting direction.

The detection unit <NUM> illustrated in <FIG> and <FIG> is an example of a first detection unit and has a function of detecting the leading and trailing edge portions of the medium P that is being transported. As illustrated in <FIG> and <FIG>, the detection unit <NUM> includes the leading edge sensors <NUM> (612A and 612B) and trailing edge sensors <NUM> (614A and 614B).

The leading edge sensors <NUM>, which are examples of a leading edge sensing unit, sense the leading edge portion of the medium P that is being transported. More specifically, the leading edge sensors <NUM> are non-contact sensors that sense the leading edge portion of the medium P without coming into contact with the medium P. Still more specifically, the leading edge sensors <NUM> are optical sensors that use light emitted toward the medium P. Still more specifically, the leading edge sensors <NUM> are reflective optical sensors that sense the leading edge portion of the medium P by sensing light emitted toward and reflected by the medium P. The leading edge sensors <NUM> may instead be transmissive optical sensors.

The trailing edge sensors <NUM>, which are examples of a trailing edge sensing unit, sense the trailing edge portion of the medium P that is being transported. As illustrated in <FIG>, the leading edge sensors <NUM> and the trailing edge sensors <NUM> overlap when viewed in the transporting direction. More specifically, the leading edge sensors <NUM> and the trailing edge sensors <NUM> are arranged in the transporting direction (more specifically, left-right direction). Here, the expression "viewed in the transporting direction" means that the leading edge sensors <NUM> and the trailing edge sensors <NUM> are viewed in a direction from one of the upstream and downstream sides of the transporting direction toward the other side. In addition, the term "overlap" does not necessarily mean a complete overlap, and may instead be a partial overlap.

In the present exemplary embodiment, as illustrated in <FIG> and <FIG>, the detection unit <NUM> is disposed upstream of the abutting roller unit <NUM> in the transporting direction. More specifically, the leading edge sensors <NUM> are disposed upstream of the abutting roller unit <NUM> and downstream of the transport roller unit <NUM> in the transporting direction. The trailing edge sensors <NUM> are disposed upstream of the transport roller unit <NUM> in the transporting direction.

The trailing edge sensors <NUM> are non-contact sensors that sense the trailing edge portion of the medium P without coming into contact with the medium P. More specifically, the trailing edge sensors <NUM> are optical sensors that use light emitted toward the medium P. Still more specifically, as illustrated in <FIG>, the trailing edge sensors <NUM> are line sensors which each extend in the transporting direction and include plural sensing elements <NUM> (more specifically, light emitting elements and light receiving elements) arranged in the transporting direction. Still more specifically, the trailing edge sensors <NUM> are, for example, contact image sensors (CISs). The trailing edge sensors <NUM> may instead be line sensors other than contact image sensors.

The trailing edge sensors <NUM> each have a detection region 614R that extends from a sensing element 616X disposed most upstream in the transporting direction to a sensing element 616Y disposed most downstream in the transporting direction and in which the trailing edge portion of the medium P is sensed.

Each trailing edge sensor <NUM> determines the position of the trailing edge portion of the medium P based on a boundary between the sensing elements <NUM> in a sensing state and the sensing elements <NUM> in a non-sensing state in the detection region 614R. Position information represented by the coordinate of the determined position (more specifically, the number of pixels counted from the downstream end of the detection region 614R in the transporting direction) is transmitted to, for example, the control device <NUM>.

Referring to <FIG>, the detection unit <NUM> is structured such that a distance D1 between the sensing element 616X disposed most upstream in the transporting direction in each trailing edge sensor <NUM> and the corresponding leading edge sensor <NUM> is less than a transporting-direction dimension D2 of the medium P having the maximum size. In other words, when the leading edge portion of the medium P having the maximum size is sensed by the leading edge sensor <NUM>, the trailing edge portion of the medium P projects upstream from the detection region 614R in the transporting direction. The detection region 614R is disposed so that the trailing edge portion of the medium P enters the detection region 614R before the leading edge portion of the medium P having the maximum size reaches the abutting roller unit <NUM> that is downstream of the leading edge sensor <NUM> in the transporting direction.

In the present exemplary embodiment, two pairs of leading and trailing edge sensors <NUM> and <NUM> are provided, as indicated by the letters A and B added to the reference numerals thereof in <FIG>. More specifically, the pairs of leading and trailing edge sensors <NUM> and <NUM> are disposed in front and rear regions of the detection device <NUM>.

As illustrated in <FIG>, in the detection unit <NUM>, the leading and trailing edge sensors <NUM> and <NUM> sense the leading and trailing edge portions of the medium P that is being transported by the transport roller unit <NUM> while the driven rollers <NUM> and <NUM> of the transport roller units <NUM> and <NUM> are at the separated positions.

Although the detection unit <NUM>, which is an example of a first detection unit, may have the above-described structure, the structure of an example of a first detection unit is not limited to this. For example, an example of a first detection unit may instead include one pair of leading and trailing edge sensors <NUM> and <NUM>. In addition, an example of a first detection unit may instead be structured such that the leading and trailing edge sensors <NUM> and <NUM> are displaced from each other in the width direction. An example of a first detection unit may be any unit that detects the leading and trailing edge portions of the medium P that is being transported.

The leading edge sensor <NUM> illustrated in <FIG> and <FIG> has a function of sensing the leading edge portion of the medium P detected by the detection unit <NUM> while the medium P is being transported. More specifically, the leading edge sensor <NUM> is disposed downstream of the correction roller unit <NUM> in the transporting direction.

The leading edge sensor <NUM> senses the leading edge portion of the medium P that is being transported by the correction roller unit <NUM> while the driven rollers <NUM>, <NUM>, <NUM>, and <NUM> of the transport roller units <NUM>, <NUM>, and <NUM> and the abutting roller unit <NUM> are at the separated positions.

More specifically, the leading edge sensor <NUM> is a non-contact sensor that senses the leading edge portion of the medium P without coming into contact with the medium P. Still more specifically, the leading edge sensor <NUM> is an optical sensor that uses light emitted toward the medium P. Still more specifically, the leading edge sensor <NUM> is a reflective optical sensor that senses the leading edge portion of the medium P by sensing light emitted toward and reflected by the medium P. The leading edge sensor <NUM> may instead be a transmissive optical sensor.

The detection unit <NUM> illustrated in <FIG> and <FIG> is an example of a second detection unit and has a function of detecting both edge portions in the width direction (i.e., a pair of side edge portions) of the medium P detected by the detection unit <NUM> while the medium P is being transported. As illustrated in <FIG>, the detection unit <NUM> includes a pair of side edge sensors <NUM> (628A and 628B).

The pair of side edge sensors <NUM> detect one and the other edge portions of the medium P in the width direction. In addition, the pair of side edge sensors <NUM> are positioned to face each other in the width direction (see <FIG> and <FIG>). Thus, the detection unit <NUM> is divided into a section that detects one edge portion of the medium P in the width direction and a section that detects the other edge portion of the medium P in the width direction, and these sections are disposed to face each other in the width direction.

In the present exemplary embodiment, as illustrated in <FIG>, the pair of side edge sensors <NUM> include a side edge sensor 628A disposed adjacent to the front of the apparatus and a side edge sensor 628B disposed adjacent to the rear of the apparatus, and sense the pair of side edge portions of the medium P that is being transported. The pair of side edge sensors <NUM> overlap when viewed in the width direction. More specifically, the pair of side edge sensors <NUM> are arranged in the width direction (more specifically, the front-rear direction).

In the present exemplary embodiment, the detection unit <NUM> is disposed downstream of the abutting roller unit <NUM> in the transporting direction. More specifically, the detection unit <NUM> is disposed downstream of the leading edge sensor <NUM> in the transporting direction.

The pair of side edge sensors <NUM> are non-contact sensors that sense the pair of side edge portions of the medium P without coming into contact with the medium P. More specifically, the pair of side edge sensors <NUM> are optical sensors that use light emitted toward the medium P. Still more specifically, as illustrated in <FIG>, the pair of side edge sensors <NUM> are line sensors which each extend in the width direction and include plural sensing elements <NUM> (more specifically, light emitting elements and light receiving elements) arranged in the width direction. Still more specifically, the pair of side edge sensors <NUM> are, for example, contact image sensors (CISs). The pair of side edge sensors <NUM> may instead be line sensors other than contact image sensors.

The pair of side edge sensors <NUM> each have a detection region 628R that extends from a sensing element 629X at one end in the width direction to a sensing element 629Y at the other end in the width direction and in which a side edge portion of the medium P is sensed.

Each of the pair of side edge sensors <NUM> determines the position of the corresponding side edge portion of the medium P based on a boundary between the sensing elements <NUM> in a sensing state and the sensing elements <NUM> in a non-sensing state in the detection region 628R. Position information represented by the coordinate of the determined position (more specifically, the number of pixels counted from the front end of the detection region 628R) is transmitted to, for example, the control device <NUM>.

The pair of side edge sensors <NUM> of the detection unit <NUM> sense the pair of side edge portions of the medium P that is being transported by the correction roller unit <NUM> while the driven rollers <NUM>, <NUM>, <NUM>, and <NUM> of the transport roller units <NUM>, <NUM>, and <NUM> and the abutting roller unit <NUM> are at the separated positions.

Although the detection unit <NUM>, which is an example of a second detection unit, may have the above-described structure, the structure of an example of a second detection unit is not limited to this. For example, plural pairs of side edge sensors <NUM> may be provided. In addition, an example of a second detection unit may instead be structured such that the pair of side edge sensors <NUM> are displaced from each other in the transporting direction. In addition, although an example of a second detection unit is disposed downstream of the first detection unit in the transporting direction, an example of a second detection unit may instead be disposed upstream of the detection unit <NUM> in the transporting direction. An example of a second detection unit may be any unit that detects both edge portions of the medium P detected by the detection unit <NUM> in an orthogonal direction that is orthogonal to the transporting direction while the medium P is being transported.

The structure of the control device <NUM> will now be described. The control device <NUM> has a function of controlling the operations of components of the image forming apparatus <NUM> including components of the detection device <NUM>. The control device <NUM> also has a function of determining the length of the medium P based on the detection results obtained by the detection units <NUM> and <NUM>. More specifically, as illustrated in <FIG>, the control device <NUM> includes a processor <NUM>, a memory <NUM>, a storage <NUM>, and a timer <NUM>.

The term "processor" refers to hardware in a broad sense. Examples of the processor <NUM> include general processors (e.g., CPU: Central Processing Unit) and dedicated processors (e.g., GPU: Graphics Processing Unit, ASIC: Application Specific Integrated Circuit, FPGA: Field Programmable Gate Array, and programmable logic device).

The storage <NUM> stores various programs including a control program 163A (see <FIG>) and various data. The storage <NUM> may be realized as a recording device, such as a hard disk drive (HDD), a solid state drive (SSD), or a flash memory.

The memory <NUM> is a work area that enables the processor <NUM> to execute various programs, and temporarily stores various programs or various data when the processor <NUM> performs a process. The processor <NUM> reads various programs including the control program 163A into the memory <NUM> from the storage <NUM>, and executes the programs by using the memory <NUM> as a work area. The timer <NUM> is a measurement unit used to measure elapsed times X and Y described below.

In the control device <NUM>, the processor <NUM> executes the control program 163A to realize various functions. A functional configuration realized by cooperation of the processor <NUM>, which serves as a hardware resource, and the control program 163A, which serves as a software resource, will now be described. <FIG> is a block diagram illustrating the functional configuration of the processor <NUM>.

As illustrated in <FIG>, in the control device <NUM>, the processor <NUM> executes the control program 163A to function as the acquisition unit 161A, the measurement unit 161B, and the control unit 161C.

The control unit 161C controls the transport mechanism <NUM>, the detection units <NUM> and <NUM>, and the leading edge sensor <NUM> to execute a detection operation described below.

As illustrated in <FIG>, for example, the transport roller units <NUM> and <NUM> of the transport mechanism <NUM> transport the medium P at a predetermined transport speed <NUM>, and further transport the medium P while reducing the transport speed to a transport speed <NUM> that is lower than the transport speed <NUM>. Then, for example, the transport roller unit <NUM> of the transport mechanism <NUM> receives the medium P from the transport roller units <NUM> and <NUM> and transports the medium P while maintaining the transport speed constant at the transport speed <NUM>. When the transport roller unit <NUM> transports the medium P, the driven rollers <NUM> and <NUM> of the transport roller units <NUM> and <NUM> are moved to the separated positions. In other words, the transport roller unit <NUM> alone transports the medium P toward the abutting roller unit <NUM> while maintaining the transport speed constant at the transport speed <NUM> (see <FIG>). The constant speed is not necessarily strictly constant as long as the speed is substantially constant.

The leading edge sensors <NUM> of the detection unit <NUM> sense the leading edge portion of the medium P transported by the transport roller unit <NUM>. After a predetermined time (hereinafter referred to as an elapsed time X) from the sensing of the leading edge portion, the trailing edge sensors <NUM> sense the trailing edge portion of the medium P. At this time, the leading edge of the medium P is positioned upstream of the abutting roller unit <NUM> in the transporting direction (see <FIG>). In other words, the trailing edge portion is sensed before the leading edge of the medium P abuts against the abutting roller unit <NUM>. The leading edge sensors <NUM> and the trailing edge sensors <NUM> respectively sense the leading and trailing edge portions of the medium P while the transport roller unit <NUM> alone transports the medium P.

When the medium P has the maximum size, the trailing edge portion is positioned upstream of the detection region 614R of each trailing edge sensor <NUM> in the transporting direction (see <FIG>) at the time of sensing of the leading edge portion by each leading edge sensor <NUM>. Then, after the predetermined elapsed time X, the trailing edge portion is positioned in the detection region 614R of each trailing edge sensor <NUM> (see <FIG>). When the medium P has the minimum size, the trailing edge portion is positioned in the detection region 614R of each trailing edge sensor <NUM> both at the time of sensing of the leading edge portion by each leading edge sensor <NUM> and the time after the predetermined elapsed time X.

The transport roller unit <NUM> continues to transport the medium P for a predetermined time period from when the medium P abuts against the abutting roller unit <NUM>, so that the leading edge of the medium P abuts against the abutting roller unit <NUM> from one end to the other end thereof in the width direction. Then, the transport roller unit <NUM> stops transporting the medium P.

After that, the abutting roller unit <NUM> transports the medium P. When the abutting roller unit <NUM> transports the medium P, the driven rollers <NUM>, <NUM>, and <NUM> of the transport roller units <NUM>, <NUM>, and <NUM> are moved to the separated positions. Accordingly, the abutting roller unit <NUM> alone transports the medium P toward the correction roller unit <NUM>.

After that, the correction roller unit <NUM> transports the medium P. When the correction roller unit <NUM> transports the medium P, the driven rollers <NUM>, <NUM>, <NUM>, and <NUM> of the transport roller units <NUM>, <NUM>, and <NUM> and the abutting roller unit <NUM> are moved to the separated positions. Accordingly, the correction roller unit <NUM> alone transports the medium P downstream in the transporting direction.

The leading edge sensor <NUM> of the detection unit <NUM> senses the leading edge portion of the medium P transported by the correction roller unit <NUM>. After a predetermined time (hereinafter referred to as an elapsed time Y) from the sensing of the leading edge portion, the pair of side edge sensors <NUM> sense the pair of side edge portions of the medium P. The leading edge sensor <NUM> and the pair of side edge sensors <NUM> sense the leading edge portion and the pair of side edge portions of the medium P while the correction roller unit <NUM> alone transports the medium P.

The correction roller unit <NUM> moves in the width direction based on an amount of displacement (described below) detected by the detection unit <NUM> to correct the displacement of the medium P in the width direction.

When the image forming unit <NUM> is used as an image forming unit, the abutting roller unit <NUM> starts to transport the medium P again so that the time at which the toner image formed on the transfer body <NUM> reaches the transfer position TA is synchronized with the time at which the medium P reaches the transfer position TA.

The acquisition unit 161A acquires detection information obtained by the detection units <NUM> and <NUM> that detect the leading and trailing edge portions and the pair of side edge portions of the medium P. The detection information of the trailing edge portion and the pair of side edge portions includes position information representing the positions of the trailing edge portion and the pair of side edge portions of the medium P. More specifically, the position information of the trailing edge portion of the medium P represents a position in the transporting direction, and the position information of the side edge portions of the medium P represents positions in the width direction of the medium P.

More specifically, for example, each trailing edge sensor <NUM> determines the position of the trailing edge portion of the medium P based on the boundary between the sensing elements <NUM> in a sensing state and the sensing elements <NUM> in a non-sensing state in the detection region 614R thereof. Then, the acquisition unit 161A acquires position information represented by the coordinate of the determined position (more specifically, the number of pixels counted from the downstream end of the detection region 614R in the transporting direction).

In addition, for example, each of the pair of side edge sensors <NUM> determines the position of the corresponding side edge portion of the medium P based on the boundary between the sensing elements <NUM> in a sensing state and the sensing elements <NUM> in a non-sensing state in the detection region 628R thereof. Then, the acquisition unit 161A acquires position information represented by the coordinate of the determined position (more specifically, the number of pixels counted from the front end of the detection region 628R).

The measurement unit 161B determines the transporting-direction dimension of the medium P based on the position information acquired by the acquisition unit 161A, for example, as follows.

For example, the measurement unit 161B determines a distance LA (see <FIG>) from the downstream end of the detection region 614R of each trailing edge sensor <NUM> in the transporting direction (i.e., the sensing element 616Y disposed most downstream in the transporting direction) to the trailing edge of the medium P based on the position information.

More specifically, the distance LA is determined from Equation (<NUM>) given below based on the overall number of pixels P1 (pixels/mm) in the sensing elements <NUM> of each trailing edge sensor <NUM> and the number of pixels P2 (pixels) in a range from the downstream end of the detection region 614R of the trailing edge sensor <NUM> in the transporting direction to the trailing edge of the medium P.

A distance LB (see <FIG>) from the downstream end of the detection region 614R of each trailing edge sensor <NUM> in the transporting direction to each leading edge sensor <NUM> is known. A distance LC (see <FIG>) from each leading edge sensor <NUM> to the leading edge of the medium P may be determined in advance as a known value by multiplying the transport speed <NUM>, which is known, by the elapsed time X, which is also known. The measurement unit 161B determines the transporting-direction dimension L1 of the medium P from Equation (<NUM>) given below.

In the present exemplary embodiment, as illustrated in <FIG>, the transporting-direction dimension L1 is measured at one and the other sides of the medium P in the width direction based on the sensing results obtained by the two leading edge sensors 612A and 612B and the two trailing edge sensors 614A and 614B. In <FIG>, the two leading edge sensors 612A and 612B and the two trailing edge sensors 614A and 614B are illustrated schematically.

When, for example, the medium P is a paper sheet, the transporting-direction dimension L1 at one side of the medium P in the width direction may differ from that at the other side due to a cutting error, as illustrated in <FIG>. This cutting error may be determined. The transporting-direction dimension of the medium P may be determined as, for example, the average, minimum, or maximum value of the transporting-direction dimensions L1 at one and the other sides of the medium P in the width direction.

Referring to <FIG>, in the present exemplary embodiment, skewing of the medium P may be detected based on the difference between the sensing times of the two leading edge sensors 612A and 612B. When the medium P is skewed, there may be an error between the calculated transporting-direction dimension L1 and the actual transporting-direction dimension Lm.

The above-described error may be corrected by determining the amount of skewing based on the transport speed <NUM> (v) of the medium P, the difference Δt between the times at which the medium P passes the leading edge sensors 612A and 612B, and a distance WX between the leading edge sensors 612A and 612B, and determining the actual transporting-direction dimension Lm from Equation (<NUM>) given below.

The measurement unit 161B determines the width-direction dimension W1 of the medium P based on the position information acquired by the acquisition unit 161A, for example, as follows.

For example, the measurement unit 161B determines a distance WA (see <FIG>) from the front end of the detection region 628R of the side edge sensor 628A (i.e., the sensing element 629Y disposed at the front end) to one side edge of the medium P (more specifically, the side edge adjacent to the front of the apparatus) based on the position information.

More specifically, the distance WA is determined from Equation (<NUM>) given below based on the overall number of pixels P3 (pixels/mm) in the sensing elements <NUM> of the side edge sensor 628A and the number of pixels P4 (pixels) in a range from the front end of the detection region 628R of the side edge sensor 628A to one side edge (more specifically, the side edge adjacent to the front of the apparatus).

In addition, for example, the measurement unit 161B determines a distance WB (see <FIG>) from the front end of the detection region 628R of the side edge sensor 628B (i.e., the sensing element 629Y disposed at the front end) to the other side edge of the medium P (more specifically, the side edge adjacent to the rear of the apparatus) based on the position information.

More specifically, the distance WB is determined from Equation (<NUM>) given below based on the overall number of pixels P5 (pixels/mm) in the sensing elements <NUM> of the side edge sensor 628B and the number of pixels P6 (pixels) in a range from the front end of the detection region 628R of the side edge sensor 628B to the other side edge (more specifically, the side edge adjacent to the rear of the apparatus).

A distance WC from the front end of the detection region 614R of the side edge sensor 628A to the front end of the detection region 614R of the side edge sensor 628B is known. The measurement unit 161B determines the width-direction dimension W1 of the medium P from Equation (<NUM>) given below.

In addition, for example, the measurement unit 161B determines the amount of displacement of the medium P in the width direction based on the position information acquired by the acquisition unit 161A as follows.

For example, as described above, the measurement unit 161B determines the distance WA (see <FIG>) from the front end of the detection region 628R of the side edge sensor 628A (i.e., the sensing element 629Y disposed at the front end) to one side edge of the medium P (more specifically, the side edge adjacent to the front of the apparatus) based on the position information.

A distance WM (see <FIG>) from the front end of the detection region 628R of the side edge sensor 628A (i.e., the sensing element 629Y disposed at the front end) to one side edge of the medium P (more specifically, the side edge adjacent to the front of the apparatus) when the medium P is disposed at a reference position is determined in advance as a known value.

The reference position of the medium P is a position in the width direction set in advance as a position at which the medium P is to be located when the medium P is transported.

The measurement unit 161B determines the amount of displacement WN of the medium P in the width direction based on the difference between the distance WM and the distance WA. Thus, the amount of displacement of the medium P in the width direction is determined based on the detection result obtained by one side edge sensor 628A, which is an example of one of the sections into which the detection unit <NUM> is divided.

The measurement unit 161B may instead determine the amount of displacement of the medium P in the width direction based on the distance WB from the front end of the detection region 628R of the side edge sensor 628B (i.e., the sensing element 629Y disposed at the front end) to the other side edge of the medium P (more specifically, the side edge adjacent to the rear of the apparatus). The amount of displacement of the medium P in the width direction may instead be determined based on both the distance WA and the distance WB.

In the present exemplary embodiment, the pair of side edge sensors <NUM> may sense the pair of side edge portions at the downstream side of the medium P in the transporting direction (see <FIG>) and at the upstream side of the medium P in the transporting direction (see <FIG>). The sensing results may be used to determine the width-direction dimension W1 at the upstream and downstream sides of the medium P in the transporting direction.

More specifically, for example, the pair of side edge sensors <NUM> sense the pair of side edge portions of the medium P after the elapsed time Y from when the leading edge portion of the medium P transported by the correction roller unit <NUM> is sensed by the leading edge sensor <NUM> of the detection unit <NUM>. Accordingly, as illustrated in <FIG>, the pair of side edge portions are sensed at the downstream side of the medium P in the transporting direction.

In the example illustrated in <FIG>, the pair of side edge portions of the medium P are sensed after the leading edge portion of the medium P has been transported from the leading edge sensor <NUM> by a distance M1 obtained by multiplying the transport speed of the correction roller unit <NUM> by the elapsed time Y.

In addition, the pair of side edge sensors <NUM> sense the pair of side edge portions of the medium P after an elapsed time Z, which is longer than the elapsed time Y, from when the leading edge portion of the medium P transported by the correction roller unit <NUM> is sensed by the leading edge sensor <NUM> of the detection unit <NUM>. Accordingly, as illustrated in <FIG>, the pair of side edge portions are sensed at the upstream side of the medium P in the transporting direction.

In the example illustrated in <FIG>, the pair of side edge portions of the medium P are sensed after the leading edge portion of the medium P has been transported from the leading edge sensor <NUM> by a distance M2 obtained by multiplying the transport speed of the correction roller unit <NUM> by the elapsed time Z. The distance M2 is longer than the distance M1.

When, for example, the medium P is a paper sheet, the width-direction dimension W1 at the upstream side of the medium P in the transporting direction may differ from that at the downstream side due to a cutting error. This cutting error may be measured. The width-direction dimension of the medium P may be determined as, for example, the average, minimum, or maximum value of the width-direction dimensions W1 at the upstream and downstream sides of the medium P in the transporting direction.

In addition, in the present exemplary embodiment, an error between the calculated width-direction dimension W1 and an actual width-direction dimension caused by skewing of the medium P may be corrected based on the sensing results obtained by the pair of side edge sensors <NUM> that sense the pair of side edge portions at the downstream side of the medium P in the transporting direction (see <FIG>) and at the upstream side of the medium P in the transporting direction (see <FIG>).

In <FIG>, the leading edge sensor <NUM> and the pair of side edge sensors <NUM> are illustrated schematically.

In the present exemplary embodiment, the detection unit <NUM> detects both edge portions (pair of side edge portions) of the medium P detected by the detection unit <NUM> in the width direction while the medium P is being transported.

Accordingly, compared to a case in which the length of the medium P in the width direction is estimated based on the length of the medium P in the transporting direction determined by detecting the leading and trailing edge portions of the medium P while the medium P is being transported, the positions of the pair of side edge portions of the medium P can be more accurately detected while the medium P is being transported.

In the present exemplary embodiment, as illustrated in <FIG> and <FIG>, the detection unit <NUM> is disposed downstream of the abutting roller unit <NUM> in the transporting direction. Therefore, the detection unit <NUM> is capable of detecting the pair of side edge portions of the medium P after the medium P is abutted against the abutting roller unit <NUM> so that the position thereof is adjusted. As a result, the detection unit <NUM> detects both edge portions (that is, the pair of side edge portions) of the medium P with increased accuracy compared to a case in which the detection unit <NUM> is disposed upstream of the abutting roller unit <NUM> in the transporting direction.

In the present exemplary embodiment, the detection unit <NUM> is divided into a section that detects one edge portion of the medium P in the width direction and a section that detects the other edge portion of the medium P in the width direction, and these sections are disposed to face each other in the width direction.

Therefore, unlike a case in which the detection unit <NUM> is composed of a single detection unit that extends from one edge portion to the other edge portion of the medium P in the width direction and is not divided, the detection unit does not occupy a region unnecessary for the detection of both edge portions of the medium P in the width direction.

In the present exemplary embodiment, the side edge sensor 628A, which is an example of one of the sections into which the detection unit <NUM> is divided, detects the amount of displacement of the medium P in the width direction.

Accordingly, the number of components is reduced compared to a case in which a detection unit that detects the amount of displacement of the medium P in the width direction is provided in addition to the detection unit <NUM>.

In the present exemplary embodiment, as illustrated in <FIG> and <FIG>, the detection unit <NUM> is disposed upstream of the abutting roller unit <NUM> in the transporting direction.

A configuration in which the detection unit <NUM> is disposed downstream of the abutting roller unit <NUM> in the transporting direction is hereinafter referred to as configuration A. In configuration A, since the detection unit <NUM>, which is long in the transporting direction, is disposed downstream of the abutting roller unit <NUM> in the transporting direction, the abutting roller unit <NUM> is disposed in an upstream region of the transport passage along which the medium P is transported through the detection device <NUM> in the transporting direction. As a result, the distance between the transfer position TA and the abutting roller unit <NUM> is increased, and skewing of the medium P may recur after the medium P has been abutted against the abutting roller unit <NUM> to adjust the position thereof.

In contrast, in the present exemplary embodiment, the detection unit <NUM> is disposed upstream of the abutting roller unit <NUM> in the transporting direction. Therefore, the abutting roller unit <NUM> is disposed closer to the downstream end of the transport passage along which the medium P is transported through the detection device <NUM> in the transporting direction. As a result, the distance between the transfer position TA and the abutting roller unit <NUM> is reduced. Accordingly, the influence of the detection by the detection unit <NUM> on the medium P after the position of the medium P has been adjusted by the abutting roller unit <NUM> is reduced compared to the case of configuration A.

In addition, in the present exemplary embodiment, as illustrated in <FIG> and <FIG>, the detection unit <NUM> is disposed upstream of the correction roller unit <NUM> in the transporting direction.

A configuration in which the detection unit <NUM> is disposed downstream of the correction roller unit <NUM> in the transporting direction is hereinafter referred to as configuration X. In configuration X, since the detection unit <NUM>, which is long in the transporting direction, is disposed downstream of the correction roller unit <NUM> in the transporting direction, the correction roller unit <NUM> is disposed in an upstream region of the transport passage along which the medium P is transported through the detection device <NUM> in the transporting direction. As a result, the distance between the transfer position TA and the correction roller unit <NUM> is increased, and the displacement of the medium P may recur after the displacement has been corrected by the correction roller unit <NUM>.

In contrast, in the present exemplary embodiment, the detection unit <NUM> is disposed upstream of the correction roller unit <NUM> in the transporting direction. Therefore, the correction roller unit <NUM> is disposed closer to the downstream end of the transport passage along which the medium P is transported through the detection device <NUM> in the transporting direction. As a result, the distance between the transfer position TA and the correction roller unit <NUM> is reduced. Accordingly, the influence of the detection by the detection unit <NUM> on the medium P after the displacement of the medium P has been corrected by the correction roller unit <NUM> is reduced compared to the case of configuration X.

In the present exemplary embodiment, as illustrated in <FIG>, the distance D1 between the sensing element 616X disposed most upstream in the transporting direction in each trailing edge sensor <NUM> and the corresponding leading edge sensor <NUM> is less than the transporting-direction dimension D2 of the medium P having the maximum size.

Therefore, the size of the detection device in the transporting direction can be reduced compared to a case in which the distance D1 between the sensing element 616X disposed most upstream in the transporting direction in each trailing edge sensor <NUM> and the corresponding leading edge sensor <NUM> is longer than the transporting-direction dimension D2 of the medium P having the maximum size.

In the present exemplary embodiment, two pairs of leading and trailing edge sensors <NUM> and <NUM> that overlap when viewed in the transporting direction are provided, as indicated by the letters A and B added to the reference numerals thereof in <FIG>.

Accordingly, the leading and trailing edge portions of the medium P can be detected with increased accuracy compared to a case in which one pair of leading and trailing edge sensors <NUM> and <NUM> that overlap when viewed in the transporting direction are provided.

In addition, in the present exemplary embodiment, as illustrated in <FIG>, the leading and trailing edge sensors <NUM> and <NUM> respectively sense the leading and trailing edge portions of the medium P while the medium P is being transported by the transport roller <NUM> that transports the medium P at a constant transport speed that is lower than a transport speed at which the medium P is transported in a region upstream of the leading edge sensors <NUM> in the transporting direction.

A configuration in which the leading and trailing edge sensors <NUM> and <NUM> sense the leading and trailing edge portions of the medium P while the medium P is being transported by a transport unit that transports the medium P at a gradually decreasing transport speed is hereinafter referred to as configuration B. The transport speed gradually decreases from the transport speed at which the medium P is transported in the region upstream of the leading edge sensors <NUM> in the transporting direction. In configuration B, the leading and trailing edge portions of the medium P are sensed while the transport speed of the medium P varies. Therefore, according to the above-described configuration, the leading and trailing edge portions of the medium P can be detected with increased accuracy compared to the case of configuration B.

In the present exemplary embodiment, as illustrated in <FIG>, the leading and trailing edge sensors <NUM> and <NUM> sense the leading and trailing edge portions of the medium P while the driven rollers <NUM> and <NUM> of the transport roller units <NUM> and <NUM> are at the separated positions.

Therefore, a load (that is, stress) applied to the medium P is reduced compared to a case in which the leading and trailing edge sensors <NUM> and <NUM> sense the leading and trailing edge portions of the medium P while the driven rollers <NUM> and <NUM> of the transport roller units <NUM> and <NUM> are at the nipping positions.

In the present exemplary embodiment, as illustrated in <FIG> and <FIG>, the detection unit <NUM> is disposed downstream of the abutting roller unit <NUM> in the transporting direction. However, the detection unit <NUM> is not limited to this. For example, the detection unit <NUM> may instead be disposed upstream of the abutting roller unit <NUM> in the transporting direction.

In the present exemplary embodiment, the detection unit <NUM> is divided into a section that detects one edge portion of the medium P in the width direction and a section that detects the other edge portion of the medium P in the width direction, and these sections are disposed to face each other in the width direction. However, the detection unit <NUM> is not limited to this. For example, the detection unit <NUM> may be composed of a single detection unit that extends from one edge portion to the other edge portion of the medium P in the width direction and is not divided.

In the present exemplary embodiment, the side edge sensor 628A, which is an example of one of the sections into which the detection unit <NUM> is divided, detects the amount of displacement of the medium P in the width direction. However, the detection unit <NUM> is not limited to this. For example, a detection unit that detects the amount of displacement of the medium P in the width direction may be provided in addition to the detection unit <NUM>.

In the present exemplary embodiment, as illustrated in <FIG> and <FIG>, the detection unit <NUM> is disposed upstream of the abutting roller unit <NUM> in the transporting direction. However, the detection unit <NUM> is not limited to this. The detection unit <NUM> may instead be disposed downstream of the abutting roller unit <NUM> in the transporting direction.

In the present exemplary embodiment, as illustrated in <FIG>, the distance D1 between the sensing element 616X disposed most upstream in the transporting direction in each trailing edge sensor <NUM> and the corresponding leading edge sensor <NUM> is less than the transporting-direction dimension D2 of the medium P having the maximum size. However, the distance D1 is not limited to this. The distance D1 may instead be longer than the transporting-direction dimension D2 of the medium P having the maximum size.

In the present exemplary embodiment, as illustrated in <FIG>, the leading and trailing edge sensors <NUM> and <NUM> respectively sense the leading and trailing edge portions of the medium P while the medium P is being transported by the transport roller <NUM> that transports the medium P at a constant transport speed that is lower than a transport speed at which the medium P is transported in a region upstream of the leading edge sensors <NUM>. However, the leading and trailing edge sensors <NUM> and <NUM> are not limited to this. For example, the leading and trailing edge sensors <NUM> and <NUM> may instead sense the leading and trailing edge portions of the medium P while the medium P is being transported by a transport unit that transports the medium P at a transport speed that gradually decreases from the transport speed at which the medium P is transported in the region upstream of the leading edge sensors <NUM> in the transporting direction. In addition, it is not necessary that the transport speed of the medium P be constant as long as at least the deceleration of the medium P at and during the detection of the leading and trailing edge portions of the medium P by the detection unit <NUM> is less than the deceleration of the medium P before and after the detection of the leading and trailing edge portions of the medium P by the detection unit <NUM>.

In the present exemplary embodiment, as illustrated in <FIG>, the leading and trailing edge sensors <NUM> and <NUM> sense the leading and trailing edge portions of the medium P while the driven rollers <NUM> and <NUM> of the transport roller units <NUM> and <NUM> are at the separated positions. However, the leading and trailing edge sensors <NUM> and <NUM> are not limited to this. For example, the leading and trailing edge sensors <NUM> and <NUM> may instead sense the leading and trailing edge portions of the medium P while the driven rollers <NUM> and <NUM> of the transport roller units <NUM> and <NUM> are at the nipping positions.

The present disclosure is not limited to the above-described exemplary embodiment, and various modifications, alterations, and improvements are possible without departing from the present disclosure. For example, the above-described modifications may be applied in combinations with each other as appropriate.

Claim 1:
A detection device (<NUM>), comprising:
a first detection unit (<NUM>) configured to detect a leading edge portion and a trailing edge portion of a medium while the medium is being transported;
a second detection unit (<NUM>) configured to detect both edge portions of the medium in an orthogonal direction that is orthogonal to a transporting direction of the medium while the medium is being transported; and
a transport unit (<NUM>) configured to transport the medium; the detection device (<NUM>) being characterized by further comprising:
an adjustment unit (<NUM>, <NUM>) configured to correct skewing and configured to correct displacement of the medium in the orthogonal direction, wherein the adjustment unit (<NUM>, <NUM>) is disposed downstream of the transport unit (<NUM>) in the transporting direction and comprises an abutting unit (<NUM>) against which a leading edge of the medium transported by the transport unit (<NUM>) is abutted to correct skewing, wherein the first detection unit (<NUM>) is disposed upstream of the abutting unit (<NUM>) in the transporting direction.