Patent Publication Number: US-8540241-B2

Title: Sheet end detection device, image recording apparatus including the sheet end detection device, and a method for detecting position of sheet

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims priority from Japanese Patent Application No. 2007-310043 filed on Nov. 30, 2007, the entire contents of which are incorporated herein by reference. 
     TECHNICAL FIELD 
     This invention relates to a sheet end detection device for detecting an end of a sheet such as a recording sheet to be conveyed, an image recording apparatus including the sheet end detection device, and a method for detecting an end position of a conveyed sheet using the sheet end detection device. 
     BACKGROUND 
     An image recording apparatus for forming an image on a recording sheet, such as an ink jet printer needs to precisely keep track of the position of a sheet end to form an image at any desired position on the plane (space) of the recording sheet. Particularly, there has been a need for more precisely keeping track of the position of a sheet end in borderless printing of a photo, etc., needed increasingly in recent years. That is, in the borderless printing, a predetermined margin is provided from the sheet end of a recording sheet, and a slightly wider print area is set than the area of the recording sheet, thereby forming an image with no blank at the sheet ends. At this time, since the print area which is set for the borderless printing includes an outside area of the recording sheet, ink is also ejected to the outside area of the recording sheet and is not supplied to image formation, which goes to waste and makes dirt the periphery of a platen for supporting the recording sheet, etc. For the image formed on the recording sheet, the surrounding image is lost. In contrast, it the position of a sheet end can be kept track of more precisely, the margin size can be decreased, and the area of the recording sheet and the set print area can be more matched with each other. Therefore, waste of ink, occurrence of peripheral contamination, loss of the surrounding image, and the like as described above can be suppressed. 
     To detect an end part of a recording sheet, a method of providing a moving arm at a midpoint in a conveying passage of a recording sheet, detecting fluctuation of the moving arm caused by contact with the conveyed recording sheet with an infrared sensor, and detecting the leading end of the recording sheet has been known. However, when the recording sheet is conveyed in a floating attitude from the conveying passage in a direction normal to the sheet plane, a timing of contacting with the arm varies, and the thickness and the material of the recording sheet, etc., have an influence on the detection accuracy. Therefore, it is difficult to improve the detection accuracy. Further, in the method, the sheet end in the direction orthogonal to the conveying direction of the recording sheet (side end) cannot be detected. 
     JP-A-7-215528 (especially,  FIG. 10  of this reference) describes a configuration wherein a roller-shaped conductive electrode and a piezoelectric element group provided on a conveying passage of a recording sheet. The piezoelectric element group includes a plurality of piezoelectric elements facing the electrode and arranged along the sheet width direction and being independent of one another. In this configuration, when the conveyed recording sheet enters the space between the electrode and the piezoelectric element group, a signal is output from the piezoelectric element group in response to the width dimension of the recording sheet, and the position of a side end of the recording sheet can be detected. 
     However, in the configuration according to JP-A-7-215528, the piezoelectric element group including six piezoelectric elements is disclosed in an embodiment, and thus the position of a side end of the recording sheet can be detected in only six ways and the detection accuracy is low. Although the detection accuracy can be improved by increasing the number of arranged piezoelectric elements, a considerable number of minute piezoelectric elements independent of one another need to be provided to realize the detection accuracy at a level demanded in the borderless printing as described above; it is not realistic considering the labor and the cost at the manufacturing time. 
     Such circumstances is applied not only to the ink jet printer, but also to other printers such as a thermal printer, etc., and a copier and a facsimile machine. Further, in addition to a recording sheet to record an image, to detect the position of a sheet with an image recorded thereon in a scanner for reading an image and converting it into an electric signal, it is also necessary to precisely detect an end position of the sheet; similar circumstances to those described above exist. 
     SUMMARY 
     It is therefore an object of the invention to provide a sheet end detection device that can be easily manufactured and can suppress the manufacturing cost while more precisely detecting the end position (particularly, side end position) of a sheet to be conveyed such as a recording sheet, an image recording apparatus including the sheet end detection device, and a method for detecting an end position of a sheet using the sheet end detection device. 
     According to a first aspect of the invention, there is provided A sheet end detection device comprising: a cylindrical roller rotatable around an axis with conveying of a sheet to be conveyed in a state in which a peripheral surface of the roller contacts one face of the conveyed sheet; and a phase detection unit configured to detect a phase in a circumferential direction of the roller, wherein a first piezoelectric element band is provided on the peripheral surface of the roller and extending in the circumferential direction and the axial direction, the first piezoelectric element band being configured to detect a contact of the sheet and extending in an axial direction of the roller over an inside and an outside of a contact area to be contacted with the conveyed sheet on the peripheral surface, and wherein a position of an arbitrary point of the first piezoelectric element band in the axial direction of the roller corresponds one-to-one with the phase in the circumferential direction of the roller. 
     According to a second aspect of the invention, there is provided an image recording apparatus comprising: a sheet end detection device according to the first aspect of the invention; and a recording head for ejecting ink to a recording sheet as the conveyed sheet to form an image, wherein the roller is provided at a midpoint in the conveying passage of the sheet to be conveyed. 
     According to a third aspect of the invention, there is provided a method for detecting an end position of a sheet using the sheet end detection device according to the first aspect, said method comprising: detecting the phase of the roller by the phase detection unit; detecting a contact state indicating whether the first piezoelectric element band with the sheet; detecting the end position of the sheet in a direction orthogonal to the conveying direction by, when the first piezoelectric element band detects change in the contact state, a position of the roller in the axial direction at which the contact state is changed based on the phase of the roller detected by the phase detection unit. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view to show the external configuration of an image recording apparatus according to an embodiment of the invention; in the embodiment,  FIG. 1  shows a multifunction device as the image recording apparatus; 
         FIG. 2  is a schematic sectional view to show the configuration of a printer unit included in the image recording apparatus; 
         FIG. 3  is a front view to show the configuration of a sheet end detection unit when seen from the front of a conveying roller pair; 
         FIG. 4  is a developed view of a peripheral surface of a conveying roller and shows the peripheral surface developed at a point where the phase detected by an encoder becomes zero; 
         FIG. 5  is a fragmentary sectional view of the conveying roller and shows the configuration of a first piezoelectric element band and the vicinity thereof as a cross section orthogonal to the extension direction of the first piezoelectric element band; 
         FIG. 6  is a functional block diagram of the image recording apparatus and shows only the configuration involved mainly in the sheet end detection unit; 
         FIG. 7  is a drawing to describe a detection method of a side end position of a recording sheet by the sheet end detection unit and shows the positional relationship between the developed peripheral surface of the conveying roller and a recording sheet for coming in contact with the peripheral surface and a signal output from the first piezoelectric element band; 
         FIG. 8  is a flowchart to show the operation when the side end position of the recording sheet is detected using the sheet end detection unit shown in  FIG. 3 ; 
         FIG. 9  is a drawing to show a sheet end detection unit having another configuration;  FIG. 9(   a ) is a front view and  9 ( b ) is a drawing of developing a peripheral surface of a conveying roller that the sheet end detection unit has; 
         FIG. 10  is a drawing to describe a detection method of a side end position of a recording sheet by a sheet end detection unit according to example 2 and shows the positional relationship between a developed peripheral surface of a conveying roller  61  and the recording sheet for coming in contact with the peripheral surface and a signal output from a first piezoelectric element band; 
         FIG. 11  is a flowchart to show the operation when the side end position of the recording sheet is detected using the sheet end detection unit shown in  FIG. 10 ; 
         FIG. 12  is a drawing to show a sheet end detection unit having another configuration;  FIG. 12(   a ) is a front view and  12 ( b ) is a drawing of developing a peripheral surface of a conveying roller that the sheet end detection unit has; 
         FIG. 13  is a drawing to show a sheet end detection unit having another configuration;  FIG. 13(   a ) is a front view and  13 ( b ) is a drawing of developing a peripheral surface of a conveying roller that the sheet end detection unit has; 
         FIG. 14  is a drawing to show a sheet end detection unit having another configuration;  FIG. 14(   a ) is a front view and  14 ( b ) is a drawing of developing a peripheral surface of a conveying roller that the sheet end detection unit has; 
         FIG. 15  is a drawing to describe a detection method of a side end position of a recording sheet by the sheet end detection unit shown in  FIG. 14  and shows the positional relationship between the developed peripheral surface of the conveying roller and a recording sheet for coming in contact with the peripheral surface and a signal output from the first piezoelectric element band; 
         FIG. 16  shows a development view of a peripheral surface of the conveying roller of a still another embodiment; and 
         FIG. 17  shows a development view of a peripheral surface of the conveying roller of a still another embodiment. 
     
    
    
     DESCRIPTION 
     An image recording apparatus including a sheet end detection device according to an embodiment of the invention will be discussed specifically below with reference to the accompanying drawings. 
     (Image Recording Apparatus) 
       FIG. 1  is a perspective view to show the external configuration of an image recording apparatus  1  according to the embodiment of the invention. In the embodiment, a multifunction device is shown as the image recording apparatus  1 . As shown in  FIG. 1 , the image recording apparatus  1  is a multifunction device including a printer unit  2  for recording an image according to an ink jet system in a lower part of a cabinet  1   a  shaped roughly like a rectangular parallelepiped and a scanner unit  3  in an upper part of the cabinet  1   a  and has a printer function, a scanner function, a copy function, and a facsimile function. 
     The image recording apparatus  1  is connected to an external information machine such as a personal computer and records an image of text, a photo, a paint graph, etc., on a recording sheet P as a recording sheet based on data transmitted from the computer, etc. To connect a digital camera, etc., to the image recording apparatus  1 , the image recording apparatus  1  can also record a photo on a recording sheet P based on data output from the digital camera, etc.; to place any storage medium of a memory card, etc., in the image recording apparatus  1 , the image recording apparatus  1  can also record an image on a recording sheet P based on data recorded on the storage medium. To record an image of a photo, etc., borderless printing with no blank in a margin of a recording sheet P can be executed. 
     As shown in  FIG. 1 , the printer unit  2  included in the image recording apparatus  1  has an opening on the front and a lower sheet feed tray  5  and an upper sheet discharge tray  6  are provided at two stages in the opening  4 . A plurality of recording sheets P can be housed in the sheet feed tray  5 ; for example, a plurality of recording sheets P of various sizes of A4 size and the smaller sizes can be housed. 
     A door  7  is provided in the lower right portion of the front of the printer unit  2  as it can be opened and closed. Provided inside with the door  7  open is a housing room in which a main tank (ink cartridge)  9  (see  FIG. 2 ) can be installed. The housing rooms are provided in a one-to-one correspondence with ink colors to be used; in the printer unit  2 , they are provided in a one-to-one correspondence with the main tanks of five color inks, namely, cyan (C), magenta (M), yellow (Y), and photo black (PBk) of dye ink and black (Bk) of pigmented ink. 
     The scanner unit  3  provided in the upper part of the image recording apparatus  1  is implemented as a flatbed scanner. That is, as shown in  FIG. 1 , a document cover  10  that can be opened and closed as a top plate of the image recording apparatus  1  is provided on the top face of the image recording apparatus  1 . Platen glass on which a document is to be placed, an image sensor for reading an image of a document, and the like are disposed below the document cover  10 . 
     An operation panel  11  for operating the printer unit  2  and the scanner unit  3  is provided on the front top of the image recording apparatus  1 . The operation panel  11  includes various operation buttons and a liquid crystal display and the image recording apparatus  1  can operate based on a command output from the operation panel  11  as the user operates the operation panel  11 . If the image recording apparatus  1  is connected to an external computer, the image recording apparatus  1  also operates based on a command transmitted from the computer through a printer driver or a scanner driver. 
     A slot unit  12  is provided in the upper left portion of the front of the image recording apparatus  1 . Any of various small memory cards of storage media can be placed in the slot unit  12 . The user performs predetermined operation through the operation panel  11 , whereby data stored on the small memory card placed in the slot unit  12  can be read. The read data can also be displayed on the liquid crystal display of the operation panel  11  and any image selected based on the display can be recorded on a recording sheet P on the printer unit  2 . 
       FIG. 2  is a schematic sectional view to show the configuration of the printer unit  2 . As shown in  FIG. 2 , the sheet feed tray  5  is provided in the proximity of the bottom of the image recording apparatus  1  and a platen  18  is provided above the sheet feed tray  5 . An image recording unit  22  having a recording head  20  for ejecting ink toward a recording sheet P, a subtank  21 , etc., mounted on a carriage  19  is provided above the platen  18 . A conveying passage  23  of a recording sheet P is extended from the rear portion of the sheet feed tray  5 . The conveying passage  23  includes a bend path  24  going upward from the rear portion of the sheet feed tray  5 , bending toward the front, and extending to an upstream position of the image recording unit  22  and a straight path  25  extending from the end point of the bend path  24  to the front; it is formed of an outer guide wall and an inner guide wall opposed to each other with a predetermined spacing in any other portion than the disposition place of the image recording unit  22 . 
     A sheet feed roller  26  for feeding a recording sheet P in the sheet feed tray  5  to the conveying passage  23  is provided just above the sheet feed tray  5 . A conveying roller pair  29  including a conveying roller  27  and a driven roller  28  described later is provided so as to sandwich the conveying passage  23  from up and down between the rollers  27  and  28  in the proximity of the downstream portion of the bend path  24  in the conveying passage  23 . The conveying roller pair  29  forms apart of a sheet end detection unit  40  for detecting an end part position of a recording sheet P as described later (also see  FIG. 3 ). 
     Further, a sheet discharge roller pair  32  including a sheet discharge roller  30  and a pinch roller  31  is provided so as to sandwich the conveying passage  23  from up and down between the rollers  30  and  31  in the proximity of the downstream portion of the straight path  25  in the conveying passage  23 . The recording head  20  and the platen  18  are provided so as sandwich the straight path  25  from up and down between the conveying roller pair  29  and the sheet discharge roller pair  32 . 
     Therefore, a recording sheet P in the sheet feed tray  5  is fed to the conveying passage  23  by the sheet feed roller  26  and subsequently is conveyed from the bend path  24  to the straight path  25  on the conveying passage  23  by the conveying roller pair  29 . An image is recorded on the space of the recording sheet P arriving at the straight path  25  in ink ejected from the recording head  20  and upon completion of the recording, the recording sheet P is ejected from the straight path  25  by the sheet discharge roller pair  32  and is housed in the sheet discharge tray  6  (see  FIG. 1 ). 
     As shown in  FIG. 2 , the printer unit  2  according to the embodiment adopts a station supply system wherein a joint valve  36  provided at the tip of a tube  35  extending from the main tank  9  and a refill port valve  37  provided in the subtank  21  are joined as required in response to the ink remaining amount in the subtank  21 , etc., and the subtank  21  is replenished with ink from the main tank  9 . However, the ink supply system is not limited to the station supply system and a system such as a tube supply system wherein the recording head  20  and the main tank  9  are connected at all times through a tube may be adopted. 
     In the image recording apparatus  1  as described above, the conveying roller pair  29  provided at a midpoint in the conveying passage  23  includes the function of conveying the conveyed recording sheet P further to the downstream portion; in addition, in the embodiment, the conveying roller pair  29  forms a part of the sheet end detection unit  40  for detecting an end part position of the recording sheet P. The configuration of the sheet end detection unit  40  will be discussed below: 
     (Sheet End Detection Unit) 
     EXAMPLE 1 
       FIG. 3  is a front view to show the configuration of the sheet end detection unit  40  when seen from the front of the conveying roller pair  29 . As shown in  FIG. 3 , the sheet end detection unit  40  includes the conveying roller  27  and the driven roller  28  disposed up and down and making up the conveying roller pair  29 , and is provided with an encoder  41  for detecting a phase around an axis  27   a  of the conveying roller  27  in one end part of the upper conveying roller  27 . More particularly, the encoder  41  can detect a phase (angle) difference between a point on the peripheral surface of the conveying roller  27  in contact with the recording sheet P at any point in time (in other words, a point opposed to the driven roller  28 ) and a reference point set at a predetermined position around the axis  27   a.    
     The conveying roller  27  is provided on a-peripheral surface  27   b  with a first piezoelectric element band  42 .  FIG. 4  is a developed view of the peripheral surface  27   b  of the conveying roller  27  and shows the peripheral surface  27   b  developed at a point where the phase detected by the encoder  41  becomes zero. As shown in the developed view, an outer peripheral dimension L 1  (Y axis direction dimension in  FIG. 4 ) of the conveying roller  27  is a half or less of a conveying direction dimension L 2  (Y axis direction dimension) of the recording sheet P. The first piezoelectric element band  42  extends linearly so as to incline relative to a circumferential direction (Y axis direction in  FIG. 4 ) of the conveying roller  27 . Therefore, as shown in  FIG. 3 , the first piezoelectric element band  42  extends so as to make one round around the axis  27   a  while going in the direction along the axis  27   a  (X axis direction in  FIG. 3 ,  4 ) on the peripheral surface  27   b  of the cylindrical conveying roller  27  and consequently is provided so as to become spiral around the axis  27   a . According to the configuration, at an arbitrary point in the extension direction of the first piezoelectric element band  42 , the position in the direction along the axis  27   a  and the phase around the axis  27   a  are in a one-to-one correspondence with each other. 
     When the recording sheet P conveyed on the conveying passage  23  goes as it is sandwiched between the conveying roller  27  and the driven roller  28 , it passes through a position to one side in the direction of the axis  27   a  and a contact area  43  (area surrounded by the alternate long and two short dashes line in  FIG. 4 ) between the conveying roller  27  and the recording sheet P exists at the position. In contrast, the first piezoelectric element band  42  is provided at a position to an opposite side in the direction of the axis  27   a . the first piezoelectric element band  42  according to example 1 is formed so that a position on the first piezoelectric element band  42  opposed to the conveying passage  23  makes a transition from an outer portion of the contact area  43  to an inner portion with rotation of the conveying roller  27 . In other words, as the phase detected by the encoder  41  becomes larger, the first piezoelectric element band  42  extends from the outer portion of the contact area  43  toward one side in the direction of the axis  27   a  to the inner portion of the contact area  43 , as shown in  FIG. 4 . In this embodiment, the contact area  43  is set such that an error (e.g., an assumed error caused during the conveyance of the recording sheet) is added to the standard size of recording sheet. 
       FIG. 5  is a fragmentary sectional view of the conveying roller  27  and shows the configuration of the first piezoelectric element band  42  and the vicinity thereof as a cross section orthogonal to the extension direction of the first piezoelectric element band  42 . As shown in  FIG. 5 , the first piezoelectric element band  42  according to the embodiment includes piezoelectric elements provided by forming a ceramic material of lead-zirconate-titanate (PZT), etc., like a layer having a predetermined thickness dimension on the peripheral surface of the conveying roller  27 . Of the conveying roller  27 , the peripheral surface  27   b  at least coming in contact with the back of the first piezoelectric element band  42  contains metal and forms one electrode  44   a  of the first piezoelectric element band  42 . 
     A surface electrode extending along the first piezoelectric element band  42  shaped like a metal band is deposited on the surface of the first piezoelectric element band  42  and forms an opposite electrode  44   b  of the first piezoelectric element band  42 . Further, an insulating thin film cover  45  containing alumina, etc., is provided so as to cover the first piezoelectric element band  42  and the electrode  44   b . Therefore, if any point of the first piezoelectric element band  42  is pressed through the cover  45  and the electrode  44   b , an electromotive force occurs at the pressed point because of the piezoelectric effect and a pulse signal formed by the electromotive force is output through the electrode  44   a ,  44   b . Such a pulse signal and a detection signal from the encoder  41  are input to a controller  50  included in the image recording apparatus  1 . 
     The first piezoelectric element band  42  containing piezoelectric elements described above can be formed easily on the peripheral surface  27   b  of the conveying roller  27  by an aerosol deposition method (AD method). An outline of the forming method of the first piezoelectric element band  42  by the AD method is given below: The peripheral surface  27   b  of the conveying roller  27  is covered with a mask so as to expose only the area to form the first piezoelectric element band  42 , the conveying roller  27  in this state is held in a chamber, and this chamber is decompressed. Next, ceramics material powder entered in a storage vessel is mixed with a carrier gas to produce aerosol material, which is then introduced into a nozzle provided in the decompressed chamber. The aerosol ceramics material powder is ejected at high speed toward the conveying roller  27  from the nozzle using a pressure difference between the chamber inside and the nozzle inside and is brought into collision with the peripheral surface  27   b  to form a film. 
     The conveying roller  27  is rotated around the axis  27   a  using appropriate drive means while the ceramics material powder is ejected to the conveying roller  27 , whereby the ceramics material powder can be brought into collision with the full face of the peripheral surface  27   b  and the first piezoelectric element band  42  can be formed over the overall length where it is required. 
       FIG. 6  is a functional block diagram of the image recording apparatus  1  and shows only the configuration involved mainly in the sheet end detection unit  40 . As shown in  FIG. 6 , the controller  50  includes a processor  51  and memory  52  including RAM, ROM, etc., connected to the processor  51 . The external image recording unit  22  is also connected to the processor  51 . The memory  52  temporarily stores a signal from the processor  51  and an external input signal and also stores a previously created program. The processor  51  operates in accordance with the program, whereby the image recording apparatus  1  drives the image recording unit  22 , etc., and functions as a printer, a scanner, a copier, and a facsimile. Further, the memory  52  includes table data  52   a  associating the phase indicated by the detection signal of the encoder  41  and the side end position of the recording sheet P with each other. 
     A drive unit  53  including a motor, a driver circuit, etc., is connected to the processor  51 . The drive unit  53  drives in accordance with a command from the processor  51 , whereby the conveying roller  27  rotates around the axis  27   a  for conveying the recording sheet P along the conveying passage  23 . Further, the encoder  41  and the first piezoelectric element band  42  described above are connected to the processor  51 . A detection signal from the encoder  41  and a pulse signal from the first piezoelectric element hand  42  are input to the processor  51 . 
     The sheet end detection unit  40  included in the image recording apparatus  1  having the configuration as described above inserts the recording sheet P conveyed along the conveying passage  23  into the nip between the conveying roller  27  and the driven roller  28  and further conveys the recording sheet P downstream. At this time, the sheet end detection unit  40  detects the side end position of the recording sheet P. The detection method will be discussed below; 
       FIG. 7  is a drawing to describe the detection method of the side end position of the recording sheet P by the sheet end detection unit  40  and shows the positional relationship between the developed peripheral surface  27   b  of the conveying roller  27  and the recording sheet P for coming in contact with the peripheral surface  27   b  and a signal output from the first piezoelectric element band  42 . As shown in  FIGS. 7(   a ) and ( b ), the contact between the recording sheet P and the first piezoelectric element band  42  involves two modes; one is a mode in which the “leading end” of the recording sheet P initially comes in contact with the first piezoelectric element band  42  as shown in  FIG. 7(   a ) and the other is a mode in which a “side end” of the recording sheet P initially comes in contact with the first piezoelectric element band  42  as shown in  FIG. 7(   b ). 
     To begin with, the case shown in  FIG. 7(   a ) will be discussed in detail. When the conveying roller  27  becomes phase A 1  at the first revolution, the recording sheet P is inserted into the nip between the conveying roller  27  and the driven roller  28  and at the same time, the leading end of the recording sheet P comes in contact with the first piezoelectric element band  42  and a signal from the first piezoelectric element band  42  makes an off (noncontact state) to on (contact state) transition. Then, at the time of the end of the first rotation of the conveying roller  27  (phase 2π), the recording sheet P and the first piezoelectric element band  42  are once brought out of contact with each other (noncontact state) and thus the signal from the first piezoelectric element band  42  makes an on to off transition. Subsequently, when the conveying roller  27  becomes phase A 2  (≦A 1 +2π) at the second revolution, side end position P 2  of the recording sheet P comes in contact with the first piezoelectric element band  42  and the signal from the first piezoelectric element band  42  again makes an off to on transition. Therefore, in the contact mode shown in  FIG. 7(   a ), when the signal from the first piezoelectric element band  42  makes a second off to on transition, the first piezoelectric element hand  42  and the side end of the recording sheet P come in contact with each other. 
     In the case shown in  FIG. 7(   b ), when the conveying roller  27  becomes phase A 3  at the first revolution, side end position P 3  of the recording sheet P comes in contact with the first piezoelectric element band  42  and a signal from the first piezoelectric element band  42  makes an off to on transition. 
     Then, at the time of the end of the first rotation of the conveying roller  27  (phase 2π), the recording sheet P and the first piezoelectric element band  42  are once brought out of contact with each other (noncontact state) and thus the signal from the first piezoelectric element band  42  makes an on to off transition. Subsequently, when the conveying roller  27  becomes phase A 4  (≦A 3 +2π) at the second revolution, side end position P 4  of the recording sheet P comes in contact with the first piezoelectric element band  42  and the signal from the first piezoelectric element band  42  again makes an off to on transition. Therefore, also in the contact mode shown in  FIG. 7(   b ), when the signal from the first piezoelectric element band  42  makes a second off to on transition, the first piezoelectric element band  42  and the side end of the recording sheet P come in contact with each other. 
     Thus, in the sheet end detection unit  40  according to example 1, in both the contact modes in  FIGS. 7(   a ) and  7  ( b ), when the signal from the first piezoelectric element band  42  makes a second off to on transition within 2πin phase change of the conveying roller  27 , the first piezoelectric element band  42  and the side end of the recording sheet P come in contact with each other. Therefore, the side end position of the recording sheet P can be acquired from the phase A 2 , A 4  of the conveying roller  27  when the signal thus makes a transition. 
       FIG. 8  is a flowchart to show the operation when the side end position of the recording sheet P is detected based on the above-described method using the sheet end detection unit  40 . As shown in  FIG. 8 , the controller  50  determines whether or not the signal from the first piezoelectric element band  42  makes a second off to on transition within 2πin phase change of the conveying roller  27  (S 1 . If the controller  50  does not determine at step  1  that the signal makes a second off to on transition within 2π (NO at S 1 ), the controller  50  repeats the determination at step  1 . If the controller  50  determines that the signal makes a second off to on transition within 2π (YES at S 1 ), the controller  50  acquires the phase of the conveying roller  27  at the detecting time of the signal making the transition according to a signal from the encoder  41  (S 2 ). The controller  50  references the table data  52   a  ( FIG. 6 ) in the memory  52  (S 3 ) and acquires information stored in association with the phase of the conveying roller  27  indicated by the signal acquired from the encoder  41 , namely, information concerning the side end position of the recording sheet P (S 4 ). 
     Thus, the sheet end detection unit  40  according to example 1 can detect the side end position of the recording sheet P. As for the detection accuracy, the side end position is detected based on the phase of the conveying roller  27  at the contact time between the first piezoelectric element band  42  and the recording sheet P, so that the side end position can be detected with very high accuracy as compared with the related arts. 
     There is a possibility that the signal may make a second off to on transition at the second revolution of the conveying roller  27  since the conveying roller  27  and the recording sheet P started to come in contact with each other as shown in  FIG. 7 . However, the conveying direction dimension L 2  of the recording sheet P is twice the outer peripheral dimension L 1  of the conveying roller  27  or more as previously described and thus the recording sheet P and the first piezoelectric element band  42  reliably come in contact with each other even at the second revolution and no problem arises. 
     It is desirable that a plurality of recording sheets P conveyed consecutively on the conveying passage  23  should be conveyed with a spacing of the outer peripheral dimension L 1  of the conveying roller  27  or more from each other. In so doing, after completion of detection of the side end position about the first recording sheet P, it is confirmed that a signal indicating change in the contact state is not input from the first piezoelectric element band  42  during one revolution of the conveying roller  27 , whereby it can be determined that the first recording sheet P has passed through the conveying roller pair  29 . Therefore, then, if a signal indicating change in the contact state from the first piezoelectric element band  42  is detected, the signal is assumed to be the signal first making an off to on transition (signal occurring in phase A 1 , A 3  in  FIG. 7 ), and detection of the side end position of the second recording sheet P can be started. This point also applies to the following examples. 
     EXAMPLE 2 
       FIG. 9  is a drawing to show a sheet end detection unit  60  having another configuration;  FIG. 9(   a ) is a front view and  9 ( b ) is a drawing of developing the peripheral surface of a conveying roller  61  that the sheet end detection unit  60  has. The sheet end detection unit  60  shown in  FIG. 9  differs from the sheet end detection unit  40  described above only in that it has a first piezoelectric element band  62  provided in a different manner from the first piezoelectric element band  42  that the sheet end detection unit  40  shown in  FIG. 3  has. 
     Therefore, only the first piezoelectric element band  62  will be discussed and components identical with or similar to those of the sheet end detection unit  40  previously described with reference to the accompanying drawings are denoted by the same reference numerals and will not be discussed again. 
     As shown in the developed view of  FIG. 9(   b ), the first piezoelectric element band  62  according to example 2 is formed so that a position on the first piezoelectric element band  62  opposed to the conveying passage  23  makes a transition from an inner portion of a contact area  43  to an outer portion with rotation of the conveying roller  27 . In other words, as the phase detected by the encoder  41  becomes larger, the first piezoelectric element band  62  extends from the inner portion of the contact area  43  toward an opposite side in the direction of an axis  27   a  to the outer portion of the contact area  43 . Therefore, the first piezoelectric element band  62  is provided so as to become spiral making a round in the opposite direction to the first piezoelectric element band  42  shown in  FIG. 3 . 
       FIG. 10  is a drawing to describe the detection method of the side end position of the recording sheet P by the sheet end detection unit  60  according to example 2 and shows the positional relationship between a developed peripheral surface  27   b  of the conveying roller  61  and the recording sheet P for coming in contact with the peripheral surface  27   b  and a signal output from the first piezoelectric element band  62 . As shown in  FIGS. 10(   a ) and ( b ), the contact between the recording sheet P and the first piezoelectric element band  62  involves two modes; one is a mode in which the “leading end” of the recording sheet P initially comes in contact with the first piezoelectric element band  62  as shown in  FIG. 10(   a ) and the other is a mode in which a “side end” of the recording sheet P initially comes in contact with the first piezoelectric element band  62  as shown in  FIG. 10(   b ). 
     To begin with, the case shown in  FIG. 10(   a ) will be discussed in detail. When the conveying roller  61  becomes phase A 5  at the first revolution, the recording sheet P is inserted into the nip between the conveying roller  61  and a driven roller  28  and at the same time, the leading end of the recording sheet P comes in contact with the first piezoelectric element band  62  and a signal from the first piezoelectric element band  62  makes an off (noncontact state) to on (contact state) transition. Subsequently, when the conveying roller  61  becomes phase A 6 , side end position P 6  of the recording sheet P comes in contact with the first piezoelectric element band  62  and the signal from the first piezoelectric element band  62  makes an on to off transition. Therefore, in the contact mode shown in  FIG. 10(   a ), when the signal from the first piezoelectric element band  62  makes an on to off transition (namely, initially makes an on to off transition) after the signal once makes an off to on transition, the first piezoelectric element band  62  and the side end of the recording sheet P come in contact with each other. 
     In the case shown in  FIG. 10(   b ), when the conveying roller  61  becomes phase A 7  at the first revolution, the recording sheet P comes in contact with the peripheral surface of the conveying roller  61 ; at this point in time, however, the first piezoelectric element band  62  and the recording sheet P do not come in contact with each other and thus change in the contact state does not occur in the signal from the first piezoelectric element band  62 . Then, when the conveying roller  61  becomes phase A 8 , an inner position P 8  of the recording sheet P comes in contact with the first piezoelectric element band  62  and the signal from the first piezoelectric element band  62  makes an off to on transition. Subsequently, when the conveying roller  61  becomes phase A 9  at the second revolution, side end position P 9  of the recording sheet P comes in contact with the first piezoelectric element band  62  and the signal from the first piezoelectric element band  62  makes an on to off transition. Therefore, also in the contact mode shown in  FIG. 10(   b ), when the signal from the first piezoelectric element band  62  makes an on to off transition (namely, initially makes an on to off transition) after the signal once makes an off to on transition, the first piezoelectric element band  62  and the side end of the recording sheet P come in contact with each other. 
     Thus, in the sheet end detection unit  60  according to example 2, in both the contact modes in  FIGS. 10(   a ) and  10 ( b ), when the signal from the first piezoelectric element band  62  initially makes an off to on transition, the first piezoelectric element band  62  and the side end of the recording sheet P come in contact with each other. Therefore, the side end position of the recording sheet P can be acquired from the phase A 6 , A 9  of the conveying roller  61  when the signal thus makes a transition. 
       FIG. 11  is a flowchart to show the operation when the side end position of the recording sheet P is detected based on the above-described method using the sheet end detection unit  60 . As shown in  FIG. 11 , the controller  50  determines whether or not the signal from the first piezoelectric element band  62  makes an off to on transition within 2πin phase change of the conveying roller  61  (S 11 ). If the controller  50  does not determine at step  11  that the signal makes an off to on transition within 2π (NO at S 11 ), the controller  50  repeats the determination at step  11 . If the controller  50  determines that the signal makes an off to on transition within 2π (YES at S 11 ), the controller  50  acquires the phase of the conveying roller  61  at the detecting time of the signal making the transition according to a signal from the encoder  41  (S 12 ). The controller  50  references the table data  52   a  ( FIG. 6 ) in the memory  52  (S 13 ) and acquires information stored in association with the phase of the conveying roller  61  indicated by the signal acquired from the encoder  41 , namely, information concerning the side end position of the recording sheet P (S 14 ). 
     Thus, the sheet end detection unit  60  according to example 2 can also detect the side end position of the recording sheet P. As for the detection accuracy, the side end position is detected based on the phase of the conveying roller  61  at the contact time between the first piezoelectric element band  62  and the recording sheet P, so that the side end position can be detected with very high accuracy as compared with the related arts, as with the configuration of example 1. 
     EXAMPLE 3 
       FIG. 12  is a drawing to show a sheet end detection unit  70  having another configuration;  FIG. 12(   a ) is a front view and  12 ( b ) is a drawing of developing the peripheral surface of a conveying roller  71  that the sheet end detection unit  70  has. The sheet end detection unit  70  shown in  FIG. 12  differs from the sheet end detection unit  40  described above only in that it includes a second piezoelectric element band  72  in addition to the first piezoelectric element band  42  that the sheet end detection unit  40  of example 1 shown in  FIG. 3  has. Therefore, only the second piezoelectric element band  72  will be discussed and components identical with or similar to those of the sheet end detection unit  40  previously described with reference to the accompanying drawings are denoted by the same reference numerals and will not be discussed again. 
     As shown in  FIG. 12 , the second piezoelectric element band  72  is shaped like a band and is provided so as to make a round around the axis  27   a  of the conveying roller  71  in the contact area  43 . The cross-sectional shape of the second piezoelectric element band  72  and the proximity thereof is similar to that of the first piezoelectric element band  42  and the proximity thereof shown in  FIG. 5 , and the second piezoelectric element band  72  also includes piezoelectric elements. The second piezoelectric element band  72  can detect the leading end position of a recording sheet P because it comes in contact the recording sheet P at the same time as the recording sheet P conveyed along the conveying passage  23  is inserted into the nip between the conveying roller  71  and the driven roller  28 . 
     Thus, the sheet end detection unit  70  including the second piezoelectric element band  72  in addition to the first piezoelectric element band  42  can detect not only the side end position of the recording sheet P according to the first piezoelectric element band  42 , but also the leading end position of the recording sheet P according to the second piezoelectric element band  72 . Therefore, the four corner positions of a general recording sheet P shaped like a rectangle on a plan view can be detected precisely. 
     In  FIG. 12 , the configuration of adding the second piezoelectric element band  72  for detecting the leading end position of the recording sheet P to the sheet end detection unit  40  shown in example 1 is described, but the second piezoelectric element band  72  may be added to the sheet end detection unit  60  (see  FIG. 9 ) shown in example 2, as shown in  FIG. 13 . In so doing, a sheet end detection unit  80  shown in  FIG. 13  can detect not only the side end position of the recording sheet P according to the first piezoelectric element band  62 , but also the leading end position of the recording sheet P according to the second piezoelectric element band  72 . 
     EXAMPLE 4 
       FIG. 14  is a drawing to show a sheet end detection unit  90  having another configuration;  FIG. 14(   a ) is a front view and  14 ( b ) is a drawing of developing the peripheral surface of a conveying roller  91  that the sheet end detection unit  90  has. The sheet end detection unit  90  shown in  FIG. 14  differs from the sheet end detection unit  40  described above only in that it has a first piezoelectric element band  92  provided in a different manner from the first piezoelectric element band  42  that the sheet end detection unit  40  shown in  FIG. 3  has. Therefore, only the first piezoelectric element band  92  will be discussed and components identical with or similar to those of the sheet end detection unit  40  previously described with reference to the accompanying drawings are denoted by the same reference numerals and will not be discussed again. 
     As shown in  FIG. 14 , the first piezoelectric element band  92  shown in example 4 is formed so that it extends linearly and a position on the first piezoelectric element band  92  opposed to the conveying passage  23  makes a transition from an outer portion of a contact area  43  to an inner portion with rotation of the conveying roller  91  like the first piezoelectric element band  42  previously described and further extends and again makes a transition from the inner portion to the outer portion. In other words, as the phase detected by the encoder  41  becomes larger, the first piezoelectric element band  92  extends from the outer portion of the contact area  43  toward one side in the direction of an axis  27   a  to the inner portion of the contact area  43  and further extends so as to reach the outer portion of the contact area  43 , as shown in  FIG. 14(   b ). 
       FIG. 15  is a drawing to describe the detection method of the side end position of a recording sheet P by the sheet end detection unit  90  according to example 2 and shows the positional relationship between a developed peripheral surface  27   b  of the conveying roller  91  and the recording sheet P for coming in contact with the peripheral surface  27   b  and a signal output from the first piezoelectric element band  92 . As shown in  FIGS. 15(   a ) and ( b ), the contact between the recording sheet P and the first piezoelectric element band  92  involves two modes; one is a mode in which the “leading end” of the recording sheet P initially comes in contact with the first piezoelectric element band  92  as shown in  FIG. 15(   a ) and the other is a mode in which a “side end” of the recording sheet P initially comes in contact with the first piezoelectric element band  92  as shown in  FIG. 15(   b ). 
     To begin with, the case shown in  FIG. 15(   a ) will be discussed in detail. When the conveying roller  91  becomes phase A 11  at the first revolution, the recording sheet P is inserted into the nip between the conveying roller  91  and a driven roller  28  and at the same time, the leading end of the recording sheet P comes in contact with the first piezoelectric element band  92  and a signal from the first piezoelectric element band  92  makes an off (noncontact state) to on (contact state) transition. Subsequently, when the conveying roller  91  becomes phase A 12 , side end position P 12  of the recording sheet P comes in contact with the first piezoelectric element band  92  and the signal from the first piezoelectric element band  92  makes an on to off transition. Therefore, in the contact mode shown in  FIG. 15(   a ), when the signal from the first piezoelectric element band  92  makes an on to off transition (namely, initially makes an on to off transition) after the signal once makes an off to on transition, the first piezoelectric element band  92  and the side end of the recording sheet P come in contact with each other. 
     In the case shown in  FIG. 15(   b ), when the conveying roller  91  becomes phase A 13  at the first revolution, the recording sheet P comes in contact with the peripheral surface of the conveying roller  91 ; at this point in time, however, the first piezoelectric element band  92  and the recording sheet P do not come in contact with each other and thus change in the contact state does not occur in the signal from the first piezoelectric element band  92 . Then, when the conveying roller  91  becomes phase A 14 , one side end position P 14  of the recording sheet P comes in contact with the first piezoelectric element band  92  and the signal from the first piezoelectric element band  92  makes an off to on transition. Subsequently, when the conveying roller  91  becomes phase A 15  at the second revolution, opposite side end position P 15  of the recording sheet P comes in contact with the first piezoelectric element band  92  and the signal from the first piezoelectric element band  92  makes an on to off transition. Therefore, also in the contact mode shown in  FIG. 15(   b ), when the signal from the first piezoelectric element band  92  makes an on to off transition (namely, initially makes an on to off transition) after the signal once makes an off to on transition, the first piezoelectric element band  92  and the side end of the recording sheet P come in contact with each other. 
     Thus, in the sheet end detection unit  90  according to example 4, in both the contact modes in  FIGS. 15(   a ) and  15 ( b ), when the signal from the first piezoelectric element band  92  initially makes an off to on transition, the first piezoelectric element band  92  and the side end of the recording sheet P come in contact with each other. Therefore, the side end position of the recording sheet P can be acquired from the phase A 12 , A 15  of the conveyinq roller  91  when the signal thus makes a transition. 
     The mode in which the signal from the first piezoelectric element band  92  initially makes an off to on transition, the first piezoelectric element band  92  and the side end of the recording sheet P come in contact with each other is similar to that of the sheet end detection unit  60  in example 2. Therefore, the operation of the controller  50  based on the method described above using the sheet end detection unit  90  according to example 4 is similar to the operation previously described with reference to the flowchart of  FIG. 11 . 
     In the above-described example 1 to 4, one first piezoelectric element band is provided on the peripheral surface  27   b  of the roller  27 . However, as shown in  FIGS. 16 and 17 , a plurality of first piezoelectric element bands may be provided on the peripheral surface  27   b  of the roller  27 . 
     In the example shown in  FIG. 16 , first piezoelectric element hands  142   a ,  142   b ,  142   c  and  142   d  are provided on the peripheral surface  27   b  of the roller  27  and arranged along the X-axis direction (i.e., the axial direction of the roller  27 ). Further, the first piezoelectric element bands  142   a  to  142   d  are separated one another. In other words, the first piezoelectric element bands  142   a  to  142   d  output the signals independently. 
     The range of each of the first piezoelectric element bands  142   a  to  142   d  in the X-axis direction may be set according to the size of the recording sheet to be conveyed. In this case, the first piezoelectric element bands  142   a  to  142   d  are provided for detecting the end positions of the recording sheets of first to fourth sizes, respectively. For example, the first piezoelectric element band  142   a  is provided for detecting the end position of the recording sheet of A4 size, and the first piezoelectric element band  142   b  is provided for detecting the end position of the recording sheet of B5 size. In other words, the first piezoelectric element bands  142   a  to  142   d  are provided on the peripheral surface inside and outside the contact area to the recording sheets of respective sizes. One example of the end positions of the recording sheets of the respective sizes is shown by chain lines “a” to “d.” 
     The method for detecting the end position of the recording sheet using each of the piezoelectric element bands  142   a  to  142   d  are similar to the above-described examples. Further, when the size of the recording sheet to be conveyed is designated by the operation panel  11 , only one of the piezoelectric element bands  142   a  to  142   d  corresponding to the designated size may be used for detecting the end position of the recording sheet. For example, if A4 size is designated, the controller  50  may detect the end position of the recording sheet based on only the output from the piezoelectric element band  142   a . On the other hand, the controller  50  may detect the end position of the recording sheet based on the combination of the signals output from the piezoelectric element bands  142   a  to  142   d . For example, when the controller  50  detects the ON signals output from the piezoelectric element bands  142   b  to  142   d  and does not detect the ON signal from the piezoelectric element bands  142   a , the controller  50  determines the recording sheet is B5 size and detects the end position by using the signal output from the piezoelectric element band  142   b.    
       FIG. 17  shows a still another example of the arrangement of the first piezoelectric element band. As shown in  FIG. 17 , the plurality of the first piezoelectric element bands may be provided in the Y-axis direction, in addition to the X-direction. In this example, four groups “A” to “D” of the first piezoelectric element bands are provided along the X-axis direction, and three first piezoelectric element bands are provided in the Y-axis direction for each of the groups of the first piezoelectric element bands. The first piezoelectric-element bands  162   ax  to  162   az ,  162   bx  to  162   bz ,  162   cx  to  162   cz ,  162   dx  to  162   dz  are separately provided. The first piezoelectric element bands in the same group do not overlap one another in the Y-axis direction but continuously provided in the Y-axis direction. The controller  50  detects the end position using the first piezoelectric element bands arranged in the Y-axis direction (i.e., the first piezoelectric element bands in a same group) for the corresponding size of the recording sheet. In the above-described examples, the end position can be detected during two rotations of the roller  27  (i.e., 720° in phase) at maximum. In contrast, according to this arrangement, the end position can be detected during a rotation of the roller  27  up to 240° in phase. 
     Although the example of  FIG. 17  shows plural first piezoelectric element bands are provided along the X-axis and Y-axis directions, a plurality of the first piezoelectric element bands is arranged only in the Y-axis direction (that is, only one first piezoelectric element band is arranged in the X-axis direction). 
     By the way, in examples 1 to 4 described above, the sheet end detection unit  40 ,  60 ,  70 ,  80 ,  90  provided in the printer unit  2 , namely, the sheet end detection unit  40 , etc., for detecting the position of a recording sheet when the image recording apparatus  1  executes the printer function, the copy function, or the facsimile function has been described, but can also be adopted for detecting the position of a sheet fed in a scanner having an automatic sheet feed function. 
     The first piezoelectric element band  42 ,  62 ,  92  need not be linear as shown in the developed view and may be any other form if the position in the direction along the axis  27   a  of the conveying roller  27 , etc., and the phase around the axis  27   a  are in a one-to-one correspondence with each other about an arbitrary point in the extension direction of the first piezoelectric element band  42 , etc. Further, the positions of the start point and the end point of the second piezoelectric element band  72 ,  82  as shown in  FIGS. 12 and 13  in the direction along the axis  27   a  need not match; for example, it may be provided like a spiral around the axis  27   a  if it extends in the contract area  43  of the peripheral surface  27   b.    
     In the examples described above, the first piezoelectric element band  42 ,  62 ,  72 ,  82 ,  92  including piezoelectric elements has been described, but the invention is not limited to the mode. For example, a pressure sensitive capacity change material involving correlation between given pressure and output potential can also be used even if it is a material different from piezoelectric elements. As the material, for example, a pressure sensitive material manufactured by EMFIT with a large number of air bubbles formed in a resin of polypropylene (PP), etc., can be adopted. If the material is formed of a film and the film is pressurized from both faces, a charge move occurs in the material and a potential difference occurs between both the faces. Thus, change in the potential difference is detected, whereby an end part of a recording sheet P can be detected. 
     As a material capable of detecting pressure change on a different principle from piezoelectric elements, a pressure sensitive conductive material involving correlation between given pressure and conductivity (resistance value) can also be used. As the material, a material called inustomer (registered trademark) with conductive particles dispersed and mixed into an insulating polymer can be adopted. If the material is formed of a film and the film is pressurized from both faces, the conductive particles in the material come in contact with or are brought close to each other, whereby the electric resistance value between both the faces lowers. Thus, change in the electric resistance value is detected, whereby an end part of a recording sheet P can be detected. 
     Each piezoelectric element adopted in the embodiment has high rigidity as compared with the pressure sensitive material manufactured by EMFIT and inustomer (trade name) and thus has the advantage that when it comes in contact with a recording sheet P, deformation of the element is small and the influence on conveying the recording sheet P is small. 
     The invention can be applied to a sheet end detection device that can be easily manufactured and can suppress the manufacturing cost while detecting the end position (particularly, side end position) of a conveyed sheet such as a recording sheet, an image recording apparatus including the sheet end detection device, and an end position detection method of a recording sheet using the sheet end detection device. 
     In the above embodiment, a sheet end detection device includes a cylindrical roller being provided at a midpoint in a conveying passage of a conveyed sheet and capable of rotating around an axis with conveying of the conveyed sheet in a state in which a peripheral surface comes in contact with one face of the conveyed sheet and a phase detection unit for detecting a phase around the axis of the roller, wherein the roller is provided on the peripheral surface with a first piezoelectric element band shaped like a band for detecting contact with the conveyed sheet so as to make a round around the axis while extending in the axial center direction over the inside and the outside of a contact area with the conveyed sheet on the peripheral surface, and wherein the first piezoelectric element band is formed so that the axis direction position of the roller at an arbitrary point in the extension direction of the first piezoelectric element band and the phase around the axis of the roller are in a one-to-one correspondence with each other. 
     In an end position detection method of a conveyed sheet according to the embodiment using the sheet end detection device, based on the phase of the roller indicated by the phase detection unit when the first piezoelectric element band detects change in a contact state with the conveyed sheet, the axis direction position of the roller is acquired about the change position of the contact state with the conveyed sheet, thereby detecting the end position in a direction orthogonal to the conveying direction of the conveyed sheet. 
     With the sheet end detection device as described above, to detect contact with the conveyed sheet, the first piezoelectric element band shaped like a band is provided on the peripheral surface of the roller for rotating with conveying of the conveyed sheet, so that it is not necessary to provide a considerable number of piezoelectric elements and the sheet end detection device can be easily manufactured and the manufacturing cost can also be suppressed. The end part in the direction orthogonal to the conveying direction of the conveyed sheet (side end) can also be detected with high accuracy. 
     That is, according to the end position detection method of a conveyed sheet using the sheet end detection device described above, the contact position with the conveyed sheet in the first piezoelectric element band, more particularly, the axis direction position of the roller can be detected, so that the side end position of the conveyed sheet can be detected. The first piezoelectric element band can detect change in the contact state with the end part of the conveyed sheet (change from contact state to noncontact state and change from noncontact state to contact state) with good accuracy and thus the side end position of the conveyed sheet can also be detected with good accuracy. 
     The first piezoelectric element band may be provided so as to make only one round around the axis of the roller like a spiral along the peripheral surface of the roller. According to the configuration, the appearance of the first piezoelectric element band becomes geometrically simple and thus it becomes easier to manufacture the first piezoelectric element (band sheet end detection device). The angle between the extension direction of the first piezoelectric element and the side end of the conveyed sheet, namely, the angle between the direction in which the first piezoelectric element extends when the peripheral surface of the roller is developed and the direction in which the side end of the conveyed sheet extends has an influence on the detection accuracy of the side end of the conveyed sheet. In contrast, as for the first piezoelectric element band provided like a spiral, the extension direction of the first piezoelectric element is roughly the same at any position in the axis direction of the roller. Therefore, the angle between the extension direction of the side end of any of various conveyed sheets different in size and the extension direction of the first piezoelectric element becomes roughly uniform, so that variation in the detection accuracy caused by the size difference of the conveyed sheet is suppressed and the side end position can be detected with stable accuracy. 
     The first piezoelectric element band may be formed so that a position opposed to the conveying passage of the conveyed sheet makes a transition from an outer portion of the contact area to an inner portion with rotation of the roller. According to the configuration, the first piezoelectric element band detects change from the noncontact state to the contact state with the conveyed sheet, whereby the side end position of the conveyed sheet can be detected. 
     The first piezoelectric element band may be formed so that a position opposed to the conveying passage of the conveyed sheet makes a transition from an inner portion of the contact area to an outer portion with rotation of the roller. According to the configuration, the first piezoelectric element band detects change from the contact state with the conveyed sheet to the noncontact state, whereby the side end position of the conveyed sheet can be detected. 
     The roller may have an outer peripheral dimension being a half or less of a conveying direction dimension of the conveyed sheet. According to the configuration, while the roller makes one revolution while the conveyed sheet is being conveyed in a state in which the roller and the conveyed sheet are in contact with each other, if the side end of the conveyed sheet does not come in contact with the first piezoelectric element band on the peripheral surface of the roller, the first piezoelectric element band and the side end of the conveyed sheet will come in contact with each other at the second revolution of the roller and thus the side end of the conveyed sheet can be detected reliably. 
     The first piezoelectric element band may be formed so that a position opposed to the conveying passage of the conveyed sheet makes a transition from an outer portion of the contact area to an inner portion and further to the outer portion with rotation of the roller. According to the configuration, the first piezoelectric element band detects change from the noncontact state to the contact state with the conveyed sheet or change from the contact state with the conveyed sheet to the noncontact state, whereby the side end position of the conveyed sheet can be detected. 
     The roller may have an outer peripheral dimension equal to or less than a conveying direction dimension of the conveyed sheet. According to the configuration, the first piezoelectric element band and the side end of the conveyed sheet reliably come in contact with each other during one revolution of the roller and the side end of the conveyed sheet can be detected. 
     The peripheral surface of the roller may contain metal and comes in contact with the back of the first piezoelectric element band to form one electrode and on the surface of the first piezoelectric element band, an opposite electrode is extended along the first piezoelectric element band. According to the configuration, the peripheral surface of the roller can be used as one electrode and one electrode need not be formed additionally. 
     An insulating cover may be provided so as to cover the first piezoelectric element band and the opposite electrode. According to the configuration, the first piezoelectric element band can be protected from contact with the conveyed sheet. 
     The roller may be provided on the peripheral surface with a second piezoelectric element band shaped like a band for detecting contact with the leading end of the conveyed sheet in a conveying direction thereof so as to make a round around the axis in a contact area with the conveyed sheet. According to the configuration, while the first piezoelectric element band detects the side end of the conveyed sheet, the second piezoelectric element band can detect the end part of the conveyed sheet in the conveying direction thereof (leading end). 
     That is, in an end position detection method of a conveyed sheet using the sheet end detection device described above, using the sheet end detection device, based on the phase of the roller indicated by the phase detection unit when the first piezoelectric element band detects change in a contact state with the conveyed sheet, the axis direction position of the roller is acquired about the change position of the contact state with the conveyed sheet, thereby detecting the end position in a direction orthogonal to the conveying direction of the conveyed sheet, and based on the phase of the roller indicated by the phase detection unit when the second piezoelectric element band detects change in the contact state with the conveyed sheet, the end position of the conveyed sheet in the conveying direction thereof is detected. 
     Accordingly, the positions of the side end and the leading end (and the trailing end as required) of the conveyed sheet can be detected with high accuracy. Moreover, each of the first piezoelectric element hand and the second piezoelectric element band can be formed without providing a considerable number of piezoelectric elements independent of each other, so that it is easy to manufacture the first and second piezoelectric elements (band sheet end detection device) and the cost can also be reduced. 
     An image recording apparatus according to the embodiment includes any of the sheet end detection devices described above and a recording head for ejecting ink to a recording sheet as the conveyed sheet to form an image. 
     According to the configuration, the side end position of the conveyed sheet can be detected with good accuracy. Thus, for example, to execute borderless printing of a photo, etc., the space area and the print area to be set can be roughly matched with each other, so that waste ink can be suppressed, peripheral ink contamination can be decreased, and image loss in the space surrounding can be suppressed. 
     According to the sheet end detection device of the embodiment, the image recording apparatus including the sheet end detection device, and the end position detection method of a recording sheet using the sheet end detection device described above, it is made possible to facilitate manufacturing and suppress the manufacturing cost while the end position (particularly, side end position) of a conveyed sheet such as a recording sheet is detected more precisely.