Abstract:
What is disclosed: is a media width detecting apparatus comprising: a first media detecting section to detect media, a second media detecting section put downward from said first media detecting section, to detect media; wherein said second detecting section decide range to detect media according to result of detection by said first media detecting section.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to a media width detecting apparatus provided in a printer, for example, serial impact dot matrix (SIDM) printer, so as to detect width of print media.  
         [0003]     2. Description of Related Art  
         [0004]     In conventional art, for example, of SIDM printer, there provided is an apparatus having a function of detecting media width as well as having a function of canceling skew of print media. In this kind of apparatus, an inserted print medium is conveyed by rollers with comparatively small coefficients of friction. And, the print medium is pressed to a shutter. Then, every front edge portion of the print medium pressed to the shutter, so as to cancel skew.  
         [0005]     Moreover, in order to detect position of every portion of print medium inserted in the apparatus, that is, left end position and right end position; sheet width sensors are provided on a carriage conducting a spacing motion. Thereby, the left end position and right end position of print medium are detected by the sheet width sensor, with moving carriage; in occasion when the print medium is inserted.  
         [0006]     Each point of detecting sheet width of medium is set at position of ¼ inch for example apart from front edge of medium. And, as for sheet width detecting sensors, optical sensors of reflection type are used. Then, light is emitted to surface of print medium. And, reflecting light from medium is received by the sensor. Thereby, it is detected whether a medium exists or not. This kind of media width detecting apparatus is disclosed in, for example, JP11-208928.  
         [0007]     However, in the conventional apparatus mentioned above, sheet width sensors provided on carriage, move across range of whole width of media conveying path, so as to detect side end portions of a print medium. Therefore, if there is something, for example, dust or piece of sheet etc. on platen which is provided confronting with carriage; the dust or piece of sheet etc. can be detected as print medium by mistake. In this occasion, medium width is not detected properly. And, print starting position can be outside of medium. As a result, printing cannot be performed properly. Moreover, printing is performed directly on the platen. Then, the platen and print head is damaged.  
         [0008]     Moreover, as mentioned above, the conventional apparatus detects sheet width at a prescribed position (for example, position of ¼ inch apart from front end) by using optical sensors of reflection type as sheet width detecting sensors. Therefore, the sheet width sensors can detect the prescribed portion of medium as portions where medium does not exist, in occasion when the prescribed position is already printed so as to be a pre-printing portion. Since, the pre-printing portion is becoming black, in the occasion when it is already printed. As a result, there is a possibility of detecting end portion of the pre-printing portion as an end portion of print medium.  
       SUMMARY OF THE INVENTION  
       [0009]     For the purpose of solving problems mentioned above, according to one aspect of the present invention, there is provided a media width detecting apparatus comprising: a first media detecting section to detect media, a second media detecting section put downward from said first media detecting section, to detect media; wherein said second detecting section decide range to detect media according to result of detection by said first media detecting section.  
         [0010]     According to another aspect of the present invention, there is provided a media width detecting apparatus comprising: plural first media detecting section provided in a media conveying path, at least a second media detecting section put on a moving body moving over media conveyed along said media conveying path; wherein said second detecting section decide range to detect medium according to result of detection of existence of medium by said first media detecting section, and judge that positions where said second media detecting section detected changes of said result of detection at extreme left and extreme right in said range to detect media, are end portions of said medium. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]      FIG. 1  is a sketched diagram showing a media width detecting apparatus according to Embodiment 1;  
         [0012]      FIG. 2  is a side view showing a media width detecting apparatus according to Embodiment 1;  
         [0013]      FIG. 3  is a block diagram showing a media width detecting apparatus according to Embodiment 1;  
         [0014]      FIG. 4  is a flow chart showing an outline of operation of Embodiment 1;  
         [0015]      FIG. 5  is a flow chart showing operation of Embodiment 1;  
         [0016]      FIG. 6  is a sketched diagram showing a media width detecting apparatus according to Embodiment 2;  
         [0017]      FIG. 7  is a flow chart showing an outline of operation of Embodiment 2;  
         [0018]      FIG. 8  is a flow chart showing operation of Embodiment 2;  
         [0019]      FIG. 9  is a sketched diagram showing a media width detecting apparatus according to Embodiment 3;  
         [0020]      FIG. 10  is a flow chart showing an outline of operation of Embodiment 3;  
         [0021]      FIG. 11  is a sketched diagram showing a media detecting apparatus according to Embodiment 4;  
         [0022]      FIG. 12  is a block diagram showing a control system of a printer according to Embodiment 4;  
         [0023]      FIG. 13  is a plan view showing operation of Embodiment 4;  
         [0024]      FIG. 14  is a plan view showing operation of Embodiment 4;  
         [0025]      FIG. 15  is a flow chart showing operation of Embodiment 4;  
         [0026]      FIG. 16  is a plan view showing operation of Embodiment 5;  
         [0027]      FIG. 17  is a plan view showing operation of Embodiment 5;  
         [0028]      FIG. 18  is a flow chart showing operation of Embodiment 5;  
         [0029]      FIG. 19  is a plan view showing operation of Embodiment 6;  
         [0030]      FIG. 20  is a plan view showing operation of Embodiment 6;  
         [0031]      FIG. 21  is a flow chart showing operation of Embodiment 6;  
         [0032]      FIG. 22  is a plan view showing operation of Embodiment 7;  
         [0033]      FIG. 23  is a plan view showing operation of Embodiment 7;  
         [0034]      FIG. 24  is a flow chart showing operation of Embodiment 7;  
         [0035]      FIG. 25  is a plan view showing operation of Embodiment 8;  
         [0036]      FIG. 26  is a plan view showing operation of Embodiment 8;  
         [0037]      FIG. 27  is a plan view showing operation of Embodiment 8;  
         [0038]      FIG. 28  is a flow chart showing operation of Embodiment 8;  
         [0039]      FIG. 29  is a block diagram of Embodiment 9;  
         [0040]      FIG. 30  is a flow chart showing operation of Embodiment 9;  
         [0041]      FIG. 31  is a flow chart showing operation of Embodiment 9. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0042]     Hereafter, Embodiments of present invention are described, referring to the drawings mentioned above. In each Embodiment, a media width detecting apparatus provided in SIDM printer is described as an example of present invention. And, in the description, same elements shown in different drawings are designated with same symbols.  
       Embodiment 1  
       [heading-0043]     &lt;Configuration&gt; 
         [0044]      FIG. 1  is a sketched diagram showing a media width detecting apparatus according to Embodiment 1; and  FIG. 2  is a side view showing a media width detecting apparatus according to Embodiment 1.  
         [0045]     In  FIG. 1  and  FIG. 2 , a SIDM printer has a carriage  9  where a print head  10  is mounted. And, this carriage  9  is moved by driving means not shown in the drawings. A platen  8  is provided under the carriage  9 . And, a shutter  51  able to move up and down, is provided along the platen  8 . A sheet width sensor  52  for detecting side end portions of printing sheet  2 , is provided in a lower portion of carriage  9 .  
         [0046]     Along the shutter  51 , skew sensors  53  of plural number (ten in  FIG. 1  as  53   a  to  53   j ) are provided at prescribed positions with equal intervals in a direction perpendicular to conveying direction of sheet  2 . The skew sensors  53  are sensors for detecting whether printing sheet  2  inserted is skew or not. Each skew sensor  53  comprises a light emitting element and a light receiving element. Moreover, a roller shaft  54  is provided in same direction. And, plural skew rollers  55  and plural feed rollers  56  are mounted on the roller shaft  55 . Surface of each skew roller  55  is formed of material having comparatively low friction coefficient. Each feed roller  56  has a diameter smaller than diameter of skew roller  55 . And, it is able to move up and down. Surface of it is formed of material having friction coefficient higher than skew roller  55 . And, each feed roller  57  is provided confronting with each skew roller  55  and feed roller  56 . The feed roller  56  is able to convey sheet  2  with feed roller  57  when the skew roller is pressed to shrink.  
         [0047]     Along the roller shaft  54 , table sensors  58  of plural number (ten in  FIG. 1  as  58   a  to  58   j ) are provided at prescribed positions with equal intervals. The table sensors  58  are arrayed in a direction perpendicular to conveying direction of sheet  2 . And, each of table sensors  58  correspond each of skew sensors  53 . That is, table sensor  58   a  is arrayed with skew sensor  53   a  in direction of conveying sheet  2 , table sensor  58   b  is arrayed with skew sensor  53   b  in direction of conveying sheet  2 , and so on. The table sensors  58  are sensors for detecting whether printing sheet  2  inserted skews or not, as well as skew sensors  53 . And, they comprise light emitting elements and light receiving elements.  
         [0048]      FIG. 3  is a block diagram of media width detecting apparatus of Embodiment 1. In  FIG. 3 , CPU  61  is what controls overall operation of apparatus. This CPU  61  is connected with LSI  62  by way of signal lines. And, LSI  62  is connected with LF motor driver  63  and mode changing motor driver  64  respectively by way of signal lines. The LF motor driver  63  is connected with LF motor  65  by way of drive lines φ A, φ B. The mode changing motor driver  64  is connected with mode motor  66  by way of drive lines φ A, φ B.  
         [0049]     An output of sheet width sensor  52  is connected with an input port of CPU  61  by way of a signal line. Each output of skew sensor  53  is connected with each input port of skew selector  67  by way of each signal line. And, output of skew selector  67  is inputted to CPU  61  by way of signal line. Each output of table sensor  58  is connected with each input port of table selector  68  by way of each signal line. And, output of table selector  68  is inputted to CPU  61  by way of signal line. Further, CPU  61  puts out control signals to skew selector  67  and to table selector  68  by way of signal lines.  
         [heading-0050]     &lt;Operation&gt; 
         [0051]     Subsequently described is an operation of Embodiment 1. Here, chiefly described is an operation of detecting width of sheets. However, an outline of operation is described referring to  FIG. 4 , beforehand.  FIG. 4  is a flow chart showing an outline of operation of Embodiment 1.  
         [0052]     In  FIG. 4 , whole process comprises three processes. First process is a skew detecting process. This process includes a process (step  41 ) of reading all table sensors  58   a  to  58   j  arrayed, and a process (step  42 ) of reading all skew sensors  53   a  to  53   j  arrayed. Following process is a sheet width detecting process. The sheet width detecting process comprises a process (step  43 ) of selecting sensors which detected sheet  2  and selecting each of both sides of a series of sensors detecting sheet  2 , a process (step  44 ) of moving carriage  9  (print head  10 ) across whole range, and a process (step  45 ) of reading sheet width sensor  52  in area of skew sensors selected at step  43 . Moreover, third process is a process (step  46 ) of reading all skew sensors  53 , so as to perform control of managing media.  
         [0053]     Succeedingly described is a detailed operation referring to flow chart of  FIG. 5 .  FIG. 5  is a flow chart showing an operation of Embodiment 1. At first, a power unit of printer is turned on (step  51 ). Then, the printer performs an initial operation. And, it waits for an operator to insert sheet  2 .  
         [0054]     When sheet  2  is inserted by an operator (step  52 ), the table sensors  58  detect the sheet  2  (step  53 ). Here, among the table sensors  58 , what actually detected sheet  2  are table sensors  58   d  to  58   f  as shown in  FIG. 1 . So, each output of the table sensors  58   d  to  58   f  are sent to the table selector  68  as sheet existing signal. CPU  61  is always watching each sensor to judge which sensor is becoming on. That is, CPU  61  is detecting, at input port, on/off state of each sensor, which is put out from the table selector  68  selecting each output of sensors one by one at prescribed time interval.  
         [0055]     When either of the table sensors become on, CPU  61  puts out indication to LSI  62 , to drive LF motor  65 , so as to roll skew rollers  55  to press sheet  2  at shutter  51  (step  54 ). LSI  62 , according to the indication, puts out control signal to LF motor driver  63 . And, LF motor driver  63 , according to the control signal, puts out drive current φ A, φ B, so as to drive LF motor  65 . When LF motor is driven, skew rollers  55  and feed rollers  56  roll in direction of conveying sheet  2  to print head  10 .  
         [0056]     In this occasion, feed rollers  56  do not contact with sheet  2 . Only skew rollers  55  contact with sheet  2 . Surface of each skew roller  55  is formed with material of low friction coefficient. Therefore, in the occasion when skew of sheet  2  occurred, some of the skew rollers  55  slip on the sheet  2  after either left or right end portion of sheet  2  pressed at shutter  51 . On the other hand, other of the skew rollers  55  forward the sheet  2 . Thereby, after rolling skew rollers  55  for a prescribed time, the other end portion of sheet  2  comes at the shutter  51  as well. Therefore, skew is canceled.  
         [0057]     Subsequently, CPU  61  reads all sensors  53   a  to  53   j  of skew sensors  53 . That is, it reads in range C 1  shown in  FIG. 1 . Thus, range where sheet  2  exist is detected. And, CPU  61  compares the range with range where the table sensors  58  are detecting sheet  2 . Then, as a result, if both of ranges are same, CPU  61  judges that skew of sheet  2  is not occurring (step  55 ).  
         [0058]     Subsequently, CPU  61  puts out indication to LSI  62 , to drive mode motor  66 , so as to let down shutter  51  and feed roller  56  (step  56 ). LSI  62 , according to the indication, puts out control signal to mode changing motor driver  64 . And, mode changing motor driver  64 , according to the control signal, puts out drive current φ A, φ B, so as to drive mode motor  66 . When mode motor  66  is driven, shutter  51  gets down as well as feed roller  56  gets down. Then, the feed rollers  56  clips the sheet  2  with the lower feed roller  57 .  
         [0059]     Subsequently, CPU  61  puts out indication to LSI  62 , to drive LF motor  65 , so as to feed sheet  2  with feed rollers  56  and  57  (step  57 ). LSI  62 , according to the indication, puts out control signal to LF motor driver  63 . And, LF motor driver  63 , according to the control signal, puts out drive current φ A, φ B, so as to drive LF motor  65 . When LF motor is driven, feed rollers  56  and  57  roll in direction of conveying sheet  2  to print head  10 . Thereby, sheet  2  is conveyed to printing position through space between printing head  10  and platen  8 . Then, the sheet  2  stays at the printing position.  
         [0060]     Subsequently, CPU  61  moves carriage  9  (print head  10 ) across whole range able to move the carriage  9  (A 1  shown in  FIG. 1 ) (step  58 ). In this occasion, it is already detected that the sheet  2  exists between the skew sensor  53   c  and the skew sensor  53   g  (range of B 2  shown in  FIG. 1 ) by the result of detection with skew sensors  53 . Therefore, in order to detect both side portions of sheet  2 , to search in this range B 2  is enough for the sheet width sensor  52  to detect them. That is, CPU  61  reads output of sheet width sensor  52  while the sheet width sensor  52  on the carriage  9  is moving in this range B 2 . Thereby, both side portions of sheet  2  are detected. And, sheet width D 2  shown in  FIG. 1  is obtained.  
         [0061]     Therefore, even if there is a piece of sheet  69  on platen  8 , as shown in  FIG. 1  for example; the piece of sheet  69  is not detected as a portion of sheet  2 , because the portion of sheet  69  is out of the range of reading by sheet width sensor  52 . Thus, wrong detection can be avoided. After all, CPU  61  waits for printing to start (step  59 ). And, printing is performed in the range D 2  detected, when preparation of printing is completed.  
         [0062]     In Embodiment 1 mentioned above, in the occasion of moving carriage  9 , carriage  9  can be moved rapidly, in a range where the sheet width sensor  52  does not perform reading (a range in region A 1  excluding the range B 2 ). And, the carriage  9  can be moved rapidly, when the carriage  9  with the sheet width sensor  52  returns after detecting sheet width. Thus, throughput of printing can be increased.  
         [heading-0063]     &lt;Effects&gt; 
         [0064]     As described above, according to Embodiment 1, width of sheet  2  is detected by reading the sheet width sensor  52 , in a range where the sheet  2  is detected by sheet width sensor  52 . Therefore, reading can be performed only in the range near positions where the sheet  2  exists. And, width of the sheet  2  is detected exactly, even when dust or piece of sheet exists on the platen.  
       Embodiment 2  
       [heading-0065]     &lt;Configuration&gt; 
         [heading-0066]     &lt;Operation&gt; 
         [0067]     Subsequently described is Embodiment 2. Configuration of Embodiment 2 is same as that of Embodiment 1. Therefore, the same description of configuration is omitted. Here, an operation of detecting sheet width of Embodiment 2 is described, referring to  FIG. 6 ,  FIG. 7  and  FIG. 8 .  FIG. 6  is an outline configuration showing a media width detecting apparatus according to Embodiment 2.  FIG. 7  is a flow chart showing an outline operation of Embodiment 2. And,  FIG. 8  is a flow chart showing an operation of Embodiment 2. At first, an outline of operation is described referring to  FIGS. 4 and 5 . In the description, elements of Embodiment 1 are used.  
         [0068]     In  FIGS. 6 and 7 , whole process comprises, as same as Embodiment 1, three processes of a skew detecting process, a sheet width detecting process, and a process of managing media after above processes. The skew detecting process includes a process (step  71 ) of reading all table sensors  58   a  to  58   j  arrayed, and a process (step  72 ) of reading all skew sensors  53   a  to  53   j  arrayed. Following process of a sheet width detecting process comprises a process (step  73 ) of selecting sensors which detected sheet  2  and selecting each of both sides of a series of sensors detecting sheet  2 , a process (step  74 ) of moving carriage  9  (print head  10 ) across area decided by positions of sensors selected at step  73 , and a process (step  75 ) of reading sheet width sensor  52  in area of skew sensors selected at step  73 . Moreover, third process of managing media is a process (step  76 ) of reading all skew sensors  53 , so as to perform control of managing media.  
         [0069]     Succeedingly described is a detailed operation referring to flow chart of  FIG. 8 . Steps  81  to  87  shown in  FIG. 8  are steps  51  to  57  of Embodiment 1. At step  87 , it is already detected that the sheet  2  exists between the skew sensor  53   c  and the skew sensor  53   g  (range of B 2  shown in  FIG. 6 ) by the result of detection with skew sensors  53 .  
         [0070]     At step  88 , side end portions of sheet can be detected in a range sensors ( 53   c  to  53   g ) which are decided by sensors neighboring outside of sensors ( 53   d  to  53   f ) detecting existence of sheet in sheet detection by skew sensors  53 . Therefore, CPU  61  moves carriage  9  (print head  10 ) across a range from right end position shown in  FIG. 6  to a position corresponding to skew sensor  53   g  (range A 2  shown in  FIG. 6 ) (step  88 ). In this occasion, the sheet width sensor  52  reads a range between the skew sensor  53   c  and the skew sensor  53   g  (range of B 2  shown in  FIG. 1 ). That is, CPU  61  reads output of sheet width sensor  52  while the sheet width sensor  52  on the carriage  9  is moving in this range B 2 . Thereby, both side portions of sheet  2  are detected. And, sheet width D 2  shown in  FIG. 1  is obtained.  
         [0071]     Therefore, as same as Embodiment 1, even if there is a piece of sheet on platen  8  for example, the piece of sheet  69  is not detected as a portion of sheet  2 . Thus, wrong detection can be avoided. After all, CPU  61  waits for printing to start (step  89 ). And, printing is performed in the range D 2  detected, when preparation of printing is completed (step  90 ).  
         [0072]     In Embodiment 2 as well as Embodiment 1, in the occasion of moving carriage  9 , carriage  9  can be moved rapidly, in a range where the sheet width sensor  52  does not perform reading (a range in region A 1  excluding the range B 2 ). And, the carriage  9  can be moved rapidly, when the carriage  9  with the sheet width sensor  52  returns after detecting sheet width. Thus, throughput of printing can be even increased.  
         [heading-0073]     &lt;Effects&gt; 
         [0074]     As described above, according to Embodiment 2, wrong detection can be prevented as well as Embodiment 1, time to detect width of sheet  2  can be shortened and throughput of printing can be even increased, because range to move carriage is made narrow.  
       Embodiment 3  
       [heading-0075]     &lt;Configuration&gt; 
         [heading-0076]     &lt;Operation&gt; 
         [0077]     Subsequently described is Embodiment 3. Configuration of Embodiment 3 is same as that of Embodiment 1. Therefore, the same description of configuration is omitted. Here, an operation of Embodiment 3 is described, referring to  FIG. 9  and  FIG. 10 .  FIG. 9  is an outline configuration showing a media width detecting apparatus according to Embodiment 3. And,  FIG. 10  is a flow chart showing an outline operation of Embodiment 3. An outline of operation is described referring to  FIGS. 9 and 10 . In the description, elements of Embodiment 1 are used.  
         [0078]     In  FIGS. 9 and 10 , whole process comprises three processes of a skew detecting process, a sheet width detecting process, and a process of managing media after above processes. The skew detecting process includes a process (step  101 ) of reading all table sensors  58   a  to  58   j  arrayed, and a process (step  102 ) of reading all skew sensors  53   a  to  53   j  arrayed. Following process of a sheet width detecting process comprises a process (step  103 ) of selecting sensors which detected sheet  2  and selecting each of both sides of a series of sensors detecting sheet  2 , a process (step  104 ) of moving carriage  9  (print head  10 ) across area decided by positions of sensors selected at step  103 , and a process (step  105 ) of reading sheet width sensor  52  in area of skew sensors selected at step  103 .  
         [0079]     Moreover, third process of managing media is, in the occasion of detecting sheets by skew sensors  53  hereafter, a process (step  106 ) of reading skew sensors  53  in area of skew sensors selected at step  103 , so as to perform control of managing media.  
         [heading-0080]     &lt;Effects&gt; 
         [0081]     As mentioned above, in process of detecting sheets hereafter, range to read skew sensors is set to a range between sensors  53   c  and  53   g  which are decided by sensors neighboring outside of sensors  53   d  to  53   f  which primarily detected a sheet. And, this reading range is applied to all media management of detecting lower end of sheet after it is inserted, or issuing of sheets etc. Thereby, it is not necessary to read all skew sensors  53  to detect sheets at each line changing. As a result, throughput is increased.  
         [0082]     Incidentally, in each Embodiment mentioned above, reading range of sheet width sensor  52  is set to a range between sensors  53   c  and  53   g  which are neighboring outside of sensors  53   d  to  53   f  which detected a sheet. However, they are not limited to the neighboring outside of sensors  53   d  to  53   f  of  53   c  and  53   g  . They can be next neighboring of  53   b  and  53 h. Or, they can be further next to them of  53   a  and  53   i . They are decided adequately according to interval between sensors arrayed.  
         [0083]     Moreover, in each Embodiment mentioned above, a media width detecting apparatus of printer having a function of canceling skew, was described. However, the present invention can be applied to printing apparatus of an electro-photographic printer or facsimile, or copying machine etc. Further, the present invention can be applied to an apparatus of detecting width of bankbook. For example, in printing apparatus of an electro-photographic printer or copying machine, plural sensors are provided at positions confronting with sheet cassette containing sheets. And, the plural sensors detect movement of sheet guide mounted on the sheet cassette. Thereby, size of sheet in sheet cassette is detected. And, a range of detecting sheet by sheet detecting sensors in a conveying route, is decided according to the sheet size detected.  
       Embodiment 4  
       [heading-0084]     &lt;Configuration&gt; 
         [0085]     Subsequently described is Embodiment 4.  FIG. 11  is a sketched diagram showing a media detecting apparatus according to Embodiment 4. Incidentally, in each Embodiment hereafter described, a media detecting apparatus provided in SIDM printer is described as an example.  
         [0086]     In  FIG. 11 , shown is an SIDM printer  1  having a function of correcting skew. In front side of the SIDM printer, provided is a table  3  where print sheet  2  of a single leaf is set. front feed rollers  4  to convey print sheet  2 , skew correcting rollers  5  to push print sheet  2  to the front feed rollers  4  and to correct skew. In front of the front feed rollers  4 , plural table sensors  6  (seven in  FIG. 11 ) are provided along an axis  4   a  of front feed rollers  4 . The table sensors  6  comprise optical sensors of reflection type. Then, light ray is cast at lower face of print sheet  2  conveyed. And, the table sensors  6  receive light reflected. Thereby, existence of sheet is detected. The range where table sensors  6  provided, is set to a range able to detect whole of sheet  2  without fail wherever the sheet  2  of different sizes are set on the table  3 .  
         [0087]     Moreover, in back side of front feed roller  4 , plural front edge detecting/paper end sensors  7   a  to  7   g  (seven sensors) are provided along the axis of front feed rollers  4 . The front edge detecting/paper end sensors  7   a  to  7   g  comprise optical sensors of reflection type. And, they receive light reflected from sheet  2 . Thereby, existence of sheet is detected. However, they comprise sensors  7   a ,  7   c ,  7   e ,  7   g  which receive light ray cast at lower face of print sheet  2  and reflected. And, they comprise sensors  7   b ,  7   d ,  7   f  which receive light ray cast at upper face of print sheet  2  and reflected. Thus, sensors which receive light ray cast at lower face, and sensors which receive light ray cast at upper face, are provided alternately. Thereby, even in the occasion when there is a black portion on either of both faces of print sheet  2 , existence of sheet can be detected without fail. The range where front edge detecting/paper end sensors  7   a  to  7   g  provided, is set to a range able to detect whole of sheet  2  without fail wherever the sheet  2  of different sizes are set on the table  3 .  
         [0088]     In back side of front edge detecting/paper end sensors  7   a  to  7   g , a platen  8  is provided. Moreover, a carriage  9  is provided able to move along the platen  8 . The carriage  9  has a print head  10  mounted. And, the print head  10  with carriage  9  moves along the platen  8 . Thereby, printing is performed by print head  10 , to a print sheet  2  conveyed between platen  8  and print head  10 . On the carriage  9 , sheet width detecting sensors  11 ,  12  are mounted. A left sheet width detecting sensor  11  is a sensor for detecting left edge of sheet  2 . And, right sheet width detecting sensor  12  is a sensor for detecting right edge of sheet  2 . They both are optical sensors of reflection type.  
         [0089]     Further, in back side of platen  8 , rear feed rollers  13  are provided. The rear feed rollers  13  are rollers for letting out print sheet completed printing from the apparatus.  
         [0090]      FIG. 12  is a block diagram showing a control system of a printer of Embodiment 4. In  FIG. 12 , a printer control section  21  is a main control section of apparatus. It controls a data receiving section  22 , a data analyzing section  23 , a print data generating/outputting section  24 , mechanical control section  25  and an operation panel section  26 . The data receiving section  22  inputs print data etc. from a host device  27 . The data analyzing section  23  analyzes data received by the data receiving section  22  The print data generating/outputting section  24 , according to result obtained from analysis of the data analyzing section  23 ; generates print data expanded as a bit map data, and sends out print data generated, to a print control section  28 .  
         [0091]     The mechanical control section  25  comprises a print control section  28 , a sheet position detecting control section  29 , a skew detecting control section  30 , a sheet front end/rear end detecting control section  31 , and a feed control section  32 . The print control section  28  moves carriage  9  by driving a space motor of print mechanical section not shown in the drawings. And, it performs print control of print data expanded as a bit map by print data generating/outputting section  24 .  
         [0092]     The sheet position detecting control section  29  is connected with sheet width sensors  11 ,  12 . And, it detects positions of edges of sheet by signals received from the sheet width sensors  11 ,  12 , while it moves carriage  9  by driving a space motor of print mechanical section not shown in the drawings. The skew detecting control section  30  detects front edge portion of print sheet  2 , by plural front edge detecting/paper end sensors  7  when a sheet  2  is fed. And, it detects skew of sheet  2  by measuring difference of feed quantity until each of plural front edge detecting/paper end sensors  7  detect front edge portions of sheet  2  respectively.  
         [0093]     The sheet front end/rear end detecting control section  31  is connected with front edge detecting/paper end sensors  7 . And, it performs detection of front edge, detection of rear edge, and detection of end of sheet; by signals from plural front edge detecting/paper end sensors  7 . The feed control section  32  performs control of sheet feeding operation, of sheet issuing operation, of line changing operation, and of page changing operation; by driving a feed motor of print mechanical section not shown in the drawings.  
         [0094]     The operation panel section  26  performs detection of turning on state of switches on a operation panel, and presentation to a presenting section (LCD or LED) not shown in the drawings.  
         [heading-0095]     &lt;Operation&gt; 
         [0096]     Subsequently described is an operation of detecting sheet width according to Embodiment 4.  FIG. 13  is a plan view showing operation of Embodiment 4. Printing operation is started, by operation of an operator or by indication from a host device  27 . At first, front feed rollers  4  and skew correcting rollers  5  are revolved with indication of feed control section  32  of mechanical control section  25 . Then, print sheet  2  set on table  3  is fed in direction indicated by an arrow “a” shown in  FIG. 13 . Length of feeding, is equal to a distance L (¼ inch for example) that front edge of sheet  2  reaches to a position separated from position of sheet detecting sensors  11 ,  12  on carriage  9 .  
         [0097]     Incidentally, it is provided that there is a pre-printing portion  35 , that is, a black portion on surface of print sheet  2 . Moreover, existence of print sheet  2  is detected by each of front detecting/PE sensors  7  respectively, in the occasion when print sheet  2  is fed. For example, in the occasion when print sheet  2  is fed as shown in  FIG. 13 , existence of print sheet  2  is detected by each of front detecting/PE sensors  7   c ,  7   d ,  7   e ,  7   f  respectively. And, absence of print sheet  2  is detected by each of the other front detecting/PE sensors  7   a ,  7   b ,  7   g  respectively. The pre-printing portion  35  on carriage  9  passes through where light of sensor  7   d  is cast. However, there are white portions before and after the pre-printing portion  35 . Therefore, at these white portions, the sensor  7   d  detects existence of sheet.  
         [0098]     After the print sheet  2  is fed by a prescribed distance L, a space motor of print mechanical section  33  is driven by sheet position detecting control section  29 . The carriage  9  is moved from left to right, or from right to left. Thereby, detection of position of sheet  2  is performed according to signals outputted from sheet detecting sensors  11 ,  12  moved with carriage  9 .  
         [0099]      FIG. 13  shows an occasion when carriage  9  is moved from left to right. In  FIG. 13 , in the occasion when carriage  9  is moved from left to right; the sheet detecting sensors  11 ,  12  is moved; from a position of sensor  7   g , that is, a sensor neighboring at left side of left end sensor  7   f  among sensors ( 7   c ,  7   d ,  7   e ,  7   f ) of front detecting/PE sensors  7  which detected existence of sheet; to a position of sensor  7   g , that is, a sensor neighboring at right side of right end sensor  7   c  among sensors ( 7   c ,  7   d ,  7   e ,  7   f ) of front detecting/PE sensors  7  which detected existence of sheet. Then, detection of left end portion and right end portion of sheet  2 , is performed.  
         [0100]     In Embodiment 4, a sheet width detecting sensor  11  is used for detection of left end portion of print sheet  2 . And, a sheet width detecting sensor  12  is used for detection of right end portion of print sheet  2 . Therefore, at first, carriage  9  is moved positioning the sheet width sensor  11  at the position of sensor  7   g . And, detection of sheet position and sheet width, start from this position. Thereafter, carriage  9  moves to right, for the sheet width detecting sensor  12  to come up to the position of sensor  7   b . In the meantime, operation of detection is performed.  
         [0101]     Thus, a sheet width detecting sensor  11  is used for detection of left end portion of print sheet  2 . And, a sheet width detecting sensor  12  is used for detection of right end portion of print sheet  2 . Thereby, range of moving carriage  9  for detection, is shortened. And, this enables detecting both end portions of sheet having broader width. In operation described hereafter; carriage  9  moves from left to right. However, similar operation can be performed by moving carriage  9  from right to left.  
         [0102]     A state of positioning sheet width detecting sensor  11  at a position slightly left from the position of sensor  7   g , is shown in  FIG. 14 . The carriage  9  moves from this state. Then, a position where existence of sheet is detected at first, is made left end position of sheet. And, a position where existence of sheet is detected at last, and where absence of sheet is detected at first, is made right end position of sheet. When sheet is fed, there can be an occasion when there is not any sensor outside of range where existence of sheet is detected by front detecting/PE sensor  7 . In this occasion, position of extreme left end or position of extreme right end, is made, position to start moving or position to end moving.  
         [0103]     Hereafter described in detail, is an operation of detecting left end position and right end position of sheet  2 , referring to flow chart shown in  FIG. 15 . A sheet position detecting control section  29  reads output of sheet width detecting sensors  11 ,  12  at each prescribed interval. And, process shown in  FIG. 15 , is performed. The prescribed interval is set to, for example, {fraction (1/180)} inch of moving carriage  9 . The process shown in  FIG. 15  is performed while carriage  9  is moving.  
         [0104]     At first, the sheet position detecting control section  29  checks whether carriage  9  moved to an end position of detecting sheet width (step  501 ). Here, the end position is decided by front detecting/PE sensor  7 . And, it is a position where sheet width detecting sensor  12  came up to sensor  7   b . If carriage  9  moved to the end position of detecting sheet width, then the process of detecting ends.  
         [0105]     If carriage has not yet moved to the end position of detecting sheet width, then, the sheet position detecting control section  29  reads output information of sheet width detecting sensors  11 ,  12  (step  502 ). In this occasion, it checks whether left end of sheet  2  has been detected or not (step  503 ). This check is performed by checking whether a flag indicating completion of detection mentioned later, is put out or not. If it is judged that the left end of sheet has already been detected, then, the process proceeds to an operation of detecting right end of sheet  2 . If the left end of sheet has not yet been detected, then, the sheet position detecting control section  29  checks whether sheet width detecting sensor  11  read at step  502  has detected existence of sheet or not (step  504 ).  
         [0106]     At step  504 , if sheet width detecting sensor  11  for detecting left end, has already detected existence of sheet, then sheet existence detecting number ( 1   c ) of sheet width detecting sensor  11  for detecting left end is renewed by adding one (step  505 ). Subsequently at step  506 , checked whether sheet existence detecting times ( 1   c ) have become a prescribed value ( 1   x ). If sheet existence detecting times ( 1   c ) have become a prescribed value ( 1   x ), then it is judged that sheet existence has been detected across a prescribed length from left end position of sheet  2 . And, sheet existence detecting times ( 1   c ) detected by sheet width detecting sensor  11  is subtracted from reading times by sheet width detecting sensor  11  being read from starting time point of moving carriage  9  until present time point. Thereby, left end position of sheet  2  is calculated. And, the calculated value ( 1   p ) is set to RAM (step  507 ).  
         [0107]     If left end position ( 1   p ) of sheet  2  is calculated, information ( 1   pf ) indicating that the left end has been detected is set (step  508 ). This information is used in the occasion when whether left end has been detected or not is checked at step  503 .  
         [0108]     At step  506 , detecting times ( 1   c ) of sheet width detecting sensor  11  has not yet reached to a prescribed value, the process proceeds to process of detecting right end of sheet.  
         [0109]     Moreover, at step  504 , the sheet width sensor  11  for detecting left end does not detect existence of sheet, again left end position of sheet is detected. Therefore, detecting times of sheet existence by sheet width detecting sensor  11  is cleared (step  518 ). And, the process proceeds to process of detecting right end of sheet.  
         [0110]     In the occasion of detecting right end position of sheet  2 , the sheet position detecting control section  29  checks whether sheet width detecting sensor  12  for detecting right end has detected existence of sheet or not (step  509 ). If it has detected existence of sheet, then sheet existence detecting number by sheet width detecting sensor  12 , information of detecting changing point (sheet existence changes to no existence) by sheet width detecting sensor  12 , and information of completion of detecting right end is cleared (step  519  to  521 ). By clearing these of information, in the occasion when right end is wrongly detected owing to existence of pre-printing portion, information wrongly detected is cleared. And, at last it becomes possible to detect changing point from existence of sheet to no existence of sheet.  
         [0111]     At step  509 , in the occasion when sheet width detecting sensor  12  is detecting no existence of sheet, the control section  29  checks whether right end of sheet  2  has been detected or not (step  510 ). This check is performed by checking whether a flag indicating completion of detection mentioned later, is put out or not. If the right end of sheet has already been detected, then the process of detecting right end, ends. If the right end of sheet has not yet been detected, then it checks whether sheet width detecting sensor  12  has detected point of changing (sheet existence to no existence of sheet) (step  511 ).  
         [0112]     If sheet width detecting sensor  12  has not yet detected point of changing from sheet existence to no existence of sheet, sheet width detecting sensor  12  detects point of changing from sheet existence to no existence of sheet (step  512 ). If sheet width detecting sensor  12  detects point of changing, information of point changing completion (rpc) is set (step  513 ). The check whether sheet width detecting sensor  12  has detected point of changing or not, at step  511 , is performed by using this data of information (rpc). If point of changing is not detected, then the process of detecting right end, ends.  
         [0113]     If sheet width detecting sensor  12  detects point of changing, then sheet absence detecting number (rc) of sheet width detecting sensor  12  is renewed by adding one (step  514 ). If sheet absence detecting times (rc) exceeded a prescribed value (rx) (step  515 ), then it is judged that sheet absence has been detected across a prescribed length from right end position of sheet  2 . And, sheet absence detecting times (rc) detected by sheet width detecting sensor  12  is subtracted from reading times by sheet width detecting sensor  12  being read from starting time point of moving carriage  9  until present time point. Thereby, right end position of sheet  2  is calculated. And, the calculated value (rp) is set to RAM (step  516 ).  
         [0114]     If right end position (rp) of sheet  2  is calculated, information (rpf) indicating that the right end has been detected is set (step  517 ). This information is used in the occasion when whether right end has been detected or not is checked at step  510 . If sheet absence detecting times (rc) does not exceed a prescribed value (rx) at step  515 , then process of detecting right end ends.  
         [0115]     The processes mentioned above are performed at each prescribed interval ({fraction (1/180)} inch) in range M shown in  FIG. 14 , that begins at position where sheet width detecting sensor  11  confronts with sensor  7   g , and that ends at position where sheet width detecting sensor  12  passes by sensor  7   b . Then, left end position and right end position of sheet  2  are decided.  
         [0116]     As described above, carriage  9  is moved between sensors neighboring outside of left end sensor and right end sensor among front detecting/PE sensor  7  detecting sheet existence, so as to detect sheet width. Therefore, left end position and right end position of sheet  2  are detected exactly.  
         [heading-0117]     &lt;Effects&gt; 
         [0118]     As described above, according to Embodiment 4, carriage  9  is moved in maximum range where the carriage is able to move on sheet, so as to scan sheet width. And, right end position and left end position are made of extreme changing points. Thereby, right end position and left end position are detected exactly, in the occasion when pre-printing portion (black portion) is on the sheet, provided that a prescribed amount of white portion is at each of left end position and right end position on sheet  2 . And, wrong detection owing to existence of pre-printing portion can be avoided. Moreover, according to Embodiment 4, left end position of sheet  2  is detected by sheet width detecting sensor  11  equipped at left side of carriage  9 . And, right end position of sheet  2  is detected by sheet width detecting sensor  12  equipped at right side of carriage  9 . Therefore, it is not necessary to move carriage  9  across distance between a sensor neighboring outside of left end sensor detecting sheet existence and a sensor neighboring outside of right end sensor detecting sheet existence among front detecting/PE sensors  7 , in order to detect both end portions of sheet  2 .  
         [0119]     Incidentally, in Embodiment 4 mentioned above, front detecting/PE sensors  7  are used as means for detecting existence of sheet in the occasion when a sheet is fed. However, not limited to this, can be used, table sensors  6  detecting sheet with reflected light obtained by casting ray of light at one side of sheet.  
       Embodiment 5  
       [heading-0120]     &lt;Configuration&gt; 
         [0121]     Subsequently described is Embodiment 5. In Embodiment 4 mentioned above, it is provided that an amount of white portion exists at each of left and right end portions of sheet. However, Embodiment 5 is what enables to detect an end portion exactly even when a black portion exists at the end portion. Embodiment 5 is what is added a function of detecting left and right end portions of sheet again, to the sheet position detecting control portion  29  of Embodiment 4 shown in  FIG. 12 . That is, it performs detection of left end position end right end position of sheet, prescribed times with changing lines separated by a prescribed distance. Other configuration is same as Embodiment 1.  
         [heading-0122]     &lt;Operation&gt; 
         [0123]     Operation of Embodiment 5 is described referring to  FIG. 16  to  18 .  FIGS. 16, 17  are plan views showing operation of Embodiment 5;  FIG. 18  is a flow chart showing operation of Embodiment 5. In  FIG. 16 , a pre-printing portion  35  is formed at right end portion of sheet  2 .  
         [0124]     Left end position and right end position of print sheet  2  are detected by process same as Embodiment 4 (step  701 ). As shown in  FIG. 16 , in the occasion when a pre-printing portion  35  is formed at right end portion of sheet  2 , by using a method of detecting end positions according to Embodiment 4, left end position of sheet detected is position A. But, right end position is position B. Therefore, left end position is detected exactly. But, as for right end position, left end position of pre-printing position is detected as right end position of sheet. In Embodiment 5, after this, following process is performed.  
         [0125]     After detecting sheet width, left end position and right end position of sheet detected, are compared with, positions of sensor  7   f  of extreme left and sensor  7   c  of extreme right among sensors  7   c ,  7   d ,  7   e ,  7   f  detecting existence of sheet, among front detecting/PE sensors  7  in the occasion of feeding sheet (step  702 ,  703 ). That is, left end position of sheet detected is compared with position of sensor  7   f . At the same time, right end position of sheet detected is compared with position of sensor  7   c .  
         [0126]     Here, in the occasion when the left end position of sheet detected is located at left side of position of sensor  7   f , at the same time, the right end position of sheet detected is located at right side of position of sensor  7   c ;  
         [0127]     sheet position detecting control section  29  judges that both left and right end portions of sheet was normally detected, and it ends process of detecting sheet position.  
         [0128]     In the occasion when the left end position of sheet detected is located at right side of position of sensor  7   f , or the right end position of sheet detected is located at left side of position of sensor  7   c ; sheet position detecting control section  29  compares left end position (lp) of sheet detected this time, with extreme left end position (slp) of sheet until last time. In case that left end position (lp) of sheet detected this time, is located at left side of extreme left end position (slp) of sheet until last time (step  704 ); left end position (lp) of sheet detected this time, replaces extreme left end position (slp) of sheet until last time (step  705 ).  
         [0129]     Subsequently, sheet position detecting control section  29  compares right end position (rp) of sheet detected this time, with extreme right end position (srp) of sheet until last time. In case that right end position (rp) of sheet detected this time, is located at right side of extreme right end position (srp) of sheet until last time (step  706 ); right end position (rp) of sheet detected this time, replaces extreme right end position (slp) of sheet until last time (step  705 ).  
         [0130]     In Embodiment 5, detection of sheet width at step  701  is performed at every line changing of a prescribed quantity (1/m inch). And, whether detection of sheet width is performed a prescribed times or not, is checked (step  708 ). In case that it is performed a prescribed times; the extreme left and right end positions detected until present time, are respectively set as the extreme left and right end positions (step  710   711 ).  
         [0131]     Then, the process ends.  
         [0132]     In case that detection of sheet width is not performed a prescribed times; sheet  2  is fed by a prescribed quantity (1/m inch)(step  709 ). Then, detection of sheet width is performed again.  
         [heading-0133]     &lt;Effects&gt; 
         [0134]     As described above, detection of sheet width is performed at every time when a prescribed quantity is fed. Then, left and right end positions of sheet are detected plural times. And, left end position located at extreme left is set as left end position of sheet. Right end position located at extreme right is set as right end position of sheet. Therefore, as shown in  FIG. 17 , even in case that pre-printing portion  35  exists at right end of sheet, right end position C detected after pre-printing portion  35  passed is set as right end position of sheet. Thus, it becomes possible to detect exact left and right end positions of sheet.  
       Embodiment 6  
       [heading-0135]     &lt;Configuration&gt; 
         [0136]     Subsequently described is Embodiment 6. Embodiment 6 is also what is able to detect end portions of sheet exactly, even when black portions exist at end portions. Embodiment 6 is what is added to mechanical control section  25  of Embodiment 4 shown in  FIG. 12 , a function of delaying detection of left and right end portions of sheet until print sheet is fed to printing position of first line. That is, it is made up for performing detection of left and right end positions after printing position on sheet came to position confronting with sheet width detecting sensor. The other configuration is same as Embodiment 4.  
         [heading-0137]     &lt;Operation&gt; 
         [0138]     Operation of Embodiment 6 is described referring to  FIG. 19  to  21 .  FIGS. 19 and 20  are plan views showing operation of Embodiment 6, FIG.  21  is a flow chart showing operation of Embodiment 6. In  FIGS. 19 and 20 , pre-printing portions  35   a ,  35   b  are formed at right end portion of sheet  2 .  
         [0139]     Between the pre-printing portions  35   a ,  35   b , there are some printing lines.  
         [0140]     As being fed, a print sheet  2 , which width is detected to some extent by front detecting/PE sensor  7 , proceeds to a position for detecting front end. In this state, the printer waits for print data to come from host device  27 . As received print data and print start command from the host device  27 , start of printing occurs (step  901 ). And, printing position in direction of first line is established.  
         [0141]     Subsequently, the sheet  2  is conveyed to printing position  36  of first line established (step  902 ). As finished feeding, before printing at first line, sheet width detecting (detecting left and right ends of sheet) mentioned in Embodiment 4, is performed (step  903 ). Left end position A and right end position B detected, are set as left and right end positions of sheet. And, print position control hereafter is performed (step  904 ).  
         [0142]     At printing position, usually, pre-printing portion does not exist. Therefore, sheet width is detected at printing position of first line. Thereby, it becomes possible to detect left and right end positions of sheet accurately and quickly. Incidentally, more accurate detection can be possible, if the detection is performed at printing line filled with print data, provided that such printing line is detected.  
         [heading-0143]     &lt;Effects&gt; 
         [0144]     As mentioned above, according to Embodiment 6, it becomes possible to detect left and right end positions of sheet without feeding sheet in vain. Therefore, effect of increasing throughput of printing process, can be obtained.  
       Embodiment 7  
       [heading-0145]     &lt;Configuration&gt; 
         [0146]     Subsequently described is Embodiment 7. Embodiment 7 is also what is able to detect end portions of sheet exactly, even when black portions exist at end portions. It is what is added to feeding control portion  32  of Embodiment 4 shown in  FIG. 12 , a function of performing detection of left and right end positions of sheet between front portion of sheet and printing position. The other configuration is same as Embodiment 4.  
         [heading-0147]     &lt;Operation&gt; 
         [0148]     Operation of Embodiment 7 is described referring to  FIG. 22  to  24 .  FIGS. 22 and 23  are plan views showing operation of Embodiment 7.  FIG. 24  is a flow chart showing operation of Embodiment 7. In  FIG. 22 , pre-printing portions  35   a ,  35   b  are formed at right end portion of sheet  2 . Moreover, as same as Embodiment 4, table sensors  6  ( 6   a ,  6   b ,  6   c ,  6   d ,  6   e ,  6   f ,  6   g ) are provided confronting with front detecting/PE sensors  7  ( 7   a ,  7   b ,  7   c ,  7   d ,  7   e ,  7   f ,  7   g ).  
         [0149]     At first, print sheet  2  being set on table, front detecting/PE sensors  7  ( 7   d ,  7   f ), which are positioned in same range with table sensors ( 6   b ,  6   c ,  6   d ,  6   e ,  6   f ) detecting sheet existence, and which receive light reflected from sheet  2  cast light from upward, are selected (step  1101 ).  
         [0150]     After starting operation of feeding sheet, feeding control portion  32  reads data detected by front detecting/PE sensors  7  ( 7   d ,  7   f ) selected at above step  1101  (step  1102 ). And, front detecting/PE sensors  7  ( 7   d ,  7   f ) selected, all detected sheet existence or not, is checked (step  1103 ).  
         [0151]     In case that front detecting/PE sensors  7  ( 7   d ,  7   f ) selected, all detected sheet existence; counter of line changing quantity of detecting sheet existence (dvp), is renewed (step  1104 ). And, it is checked whether line changing quantity of detecting sheet existence (dvp) reached to width (dw) of portion  36  shown in  FIG. 22  without pre-printing (step  1105 ). Here, the width (dw) is wide enough for enabling detection of sheet width. In case that the sheet existence (dvp) reached to width (dw) wide enough for enabling detection of sheet width; middle position of width (dw) of portion  36  without pre-printing, in direction of changing lines (in direction of feeding sheet), is calculated from present position data and counter value of changing lines of sheet existence in direction of changing lines. And, the middle position is set as position data of detecting sheet width (vp) (step  1106 ).  
         [0152]     After this step; counter of line changing quantity of detecting sheet existence (dvp), is cleared (step  1107 ). And, following portion able to detect sheet width without pre-printing is detected until sheet comes to a prescribed end position of sheet feeding (step  1108 ). In case that portion able to detect sheet width without pre-printing has not detected at step  1105 , portion able to detect sheet width without pre-printing is detected until sheet comes to a prescribed end position of sheet feeding (step  1108 ).  
         [0153]     In case that either of front detecting/PE sensors  7  ( 7   d ,  7   e ) has detected absence of sheet at step  1103 ; counter of line changing quantity of detecting sheet existence (dvp), is cleared (step  1107 ). And, following portion able to detect sheet width without pre-printing is detected until sheet comes to a prescribed end position of sheet feeding (step  1108 ).  
         [0154]     After feeding sheet  2  until it comes to a prescribed end position of feeding; whether sheet width detecting position is detected or not, is checked by sheet width detecting position data (vp) (step  1109 ). In case that sheet width detecting position has been detected; according to sheet width detecting position data, as shown in  FIG. 23 , sheet  2  is fed in inverse direction (a direction designated with arrow b), so as to locate sheet  2  at sheet width detecting position (step  1110 ). After locating sheet  2  at sheet width detecting position, sheet width detecting process mentioned in Embodiment 1 is performed.  
         [heading-0155]     &lt;Effects&gt; 
         [0156]     As described above, at feeding sheet, portion able to detect sheet width without pre-printing is detected by front detecting/PE sensors  7 . And, sheet width is detected at the portion without pre-printing. Thereby, even when pre-printing portion exists at end portion of sheet, it becomes possible to detect left and right end portions of sheet certainly. Moreover, Embodiment 7 is able to detect left and right end portions of sheet exactly, especially about sheet with discontinuous pre-printing portion existing between front end and printing position.  
       Embodiment 8  
       [heading-0157]     &lt;Configuration&gt; 
         [0158]     Subsequently described is Embodiment 8. Embodiment 8 is also what is able to detect end portions of sheet exactly, even when black portions exist at end portions. It is what is added to sheet position detecting control portion  29  of Embodiment 4 shown in  FIG. 12 , a function of setting slice level again in area of pre-printing portion, and function of detecting sheet width again. The other configuration is same as Embodiment 4.  
         [heading-0159]     &lt;Operation&gt; 
         [0160]     Operation of Embodiment 8 is described referring to  FIG. 25  to  28 .  FIGS. 25, 26  and  27  are plan views showing operation of Embodiment 8.  
         [0161]      FIG. 28  is a flow chart showing operation of Embodiment 8. In  FIG. 25 , a pre-printing portion  35  is formed at right end portion of sheet  2 .  
         [0162]     At first, left end position and right end position of print sheet  2  are detected by process same as Embodiment 4 (step  1701 ). As shown in  FIG. 25 , in the occasion when a pre-printing portion  35  is formed at right end portion of sheet  2 , by using a method of detecting end positions according to Embodiment 4, left end position of sheet detected is position A. But, right end position is position B. Therefore, left end position is detected exactly. But, as for right end position, left end position of pre-printing position is detected as right end position of sheet.  
         [0163]     In order to confirm that pre-printing portions exist at left end position of sheet, left end position A detected at step  1701  mentioned above, is compared with, position of sensor  7   f  of extreme left among front detecting/PE sensors  7  (step  1702 ). In case that left end position A is left side of front detecting/PE sensor  7   f , it is judged that left end position of sheet is correctly detected. And, check of existence of pre-printing portion at right end position, begins.  
         [0164]     In case that left end position A is right side of front detecting/PE sensor  7   f , it is judged that pre-printing portion exists at left end position. And, the pre-printing portion at left side is calculated (step  1703 ). The pre-printing portion at left side is calculated by subtracting position of front detecting/PE sensor  7   f  from left end position A of sheet.  
         [0165]     Subsequently, position to move carriage  9  is set; so that sheet width detecting sensor  11  for detecting left end, enters in pre-printing range at left side calculated (step  1705 ). The position to move (cp) carriage  9  is calculated as follows. A value is calculated by subtracting sheet width position from center position of print head. The position to move (cp) carriage  9  is obtained by adding the value to a half of pre-printing range at left side.  
         [0166]     Subsequently, in order to adjust slice level which is set at sheet width detecting sensor  11  for detecting left end, sensor data for adjusting slice level such as setting value of slice data etc. is set (step  1707 ). And, slice level is adjusted by slice level adjusting process (step  1708 ), so as to adjust slice level to a level able to detect pre-printing portion.  
         [0167]     Here, described is adjusting process of slice level. At first, at step  1719 , carriage  9  is moved to a position appointed. And, sheet width detecting sensor  11  for detecting left end is moved into pre-printing range. Then, slice level of sensor appointed (sheet width detecting sensor  11 ) is let down with one step (step  1720 ). And, slice level lowered with one step is put out (step  1721 ). Then, sensor data of sheet width detecting sensor  11  is read (step  1722 ).  
         [0168]     It is judged whether the sheet width detecting sensor  11  detected existence of sheet (step  1723 ). In case that existence of sheet is detected, slice level outputting now is set as an adjusted value (step  1725 ). In case that existence of sheet is not detected, it is judged whether slice level outputting now is minimum in range able to set (step  1724 ). In case that slice level outputting now is minimum in range able to set, slice level outputting now is set as an adjusted value (step  1725 ).  
         [0169]     Slice level is usually divided into plural levels. And, at each level output voltage of sensor to slice, is decided. Then, setting value of slice level is adjusted minutely. And, output voltage of sensor to slice, is changed. Thereby, it becomes to be able to detect existence of sheet at pre-printing portion.  
         [0170]     After adjusting slice level, slice level of sheet width detecting sensor  11  at left side is changed to the adjusted value (step  1709 ).  
         [0171]     Subsequently, in order to confirm that pre-printing portions exist at right end position of sheet, right end position B detected at step  1701  mentioned above, is compared with, position of sensor  7   c  of extreme right among front detecting/PE sensors  7  (step  1710 ). In case that right end position B is right side of front detecting/PE sensor  7   c , it is judged that right end position of sheet is correctly detected. And, second process of detecting sheet width (step  1718 ), begins.  
         [0172]     As shown in  FIG. 26 , in case that right end position B is left side of front detecting/PE sensor  7   c , it is judged that pre-printing portion exists at left end position. And, as same as adjustment of sheet width detecting sensor  11  at left side; slice level of sheet width detecting sensor  12  at right side, is adjusted (step  1711  to  1717 ).  
         [0173]     When adjustment of slice level of sheet width detecting sensor  11 ,  12  at left and right side, are finished; process of detecting sheet width is performed again by process same as Embodiment 4.  
         [heading-0174]     &lt;Effects&gt; 
         [0175]     As described above, each slice level of sheet width detecting sensor  11 ,  12  is adjusted so as to enable detecting existence of sheet, at pre-printing portion. Therefore, whether pre-printing portion exists or not, it is possible to detect left and right end positions of sheet exactly. As for an example shown in  FIG. 27 , even when pre-printing portion  35  exists at right end portion of sheet, right end portion is detected exactly at position C.  
       Embodiment 9  
       [heading-0176]     &lt;Configuration&gt; 
         [0177]     Subsequently described is Embodiment 9.  FIG. 29  is a block diagram of Embodiment 9. Embodiment 9 is what is added to Embodiment 4 shown in  FIG. 12 , a nonvolatile memory control section  40 . The nonvolatile memory control section  40  controls writing each kind of data to a nonvolatile memory  40  and reading each kind of data from a nonvolatile memory  40  according to indication of printer control section  21 . The other configuration is same as Embodiment 4.  
         [heading-0178]     &lt;Operation&gt; 
         [0179]     Subsequently, operation of Embodiment 9 is described referring to flow charts of  FIG. 30  to  31 . In  FIG. 30 , processes of steps  1306  to  1323  are same as processes of steps  501  to  518  of Embodiment 4 shown in  FIG. 15 .  
         [0180]     At step  1314 , in case that sheet width detecting sensor  12  for detecting right end, detected existence of sheet; whether right end position of sheet has been detected or not, is checked (step  1324 ). In case that right end position of sheet has been detected, it is conceived that pre-printing portion has been detected. Therefore, starting position of pre-printing portion (left end position) and ending position of pre-printing portion (right end position) are saved in the nonvolatile memory  41  (step  1325 ). After this step or in case that right end position of sheet has not been detected; as same as Embodiment 4, sheet existence detecting times by sheet width detecting sensor  12 , changing point detecting data (change sheet existing to not existing) by sheet width detecting sensor  12 , and data of right end detected, are cleared (step  1326  to  1328 ).  
         [0181]     In  FIG. 31 , step  2001  is a process of steps  1306  to  1328  shown in  FIG. 30 . As a result of sheet width detecting process of step  2001 ; sheet width (right end position and left end position), starting/ending position of pre-printing portion, and sheet data indicating whether pre-printing portions exist at left and right ends of sheet or not, are set in working memory (step  2002 ).  
         [0182]     Subsequently, sheet width, starting/ending position of pre-printing portion, and whether pre-printing portions exist at left and right ends of sheet or not, comprising sheet data (sheet data about sheet fed last time or ever), are set in working memory (step  2003 ). And, these are compared with the sheet data obtained this time. Then, whether they accord or not is checked (step  2004 ). In case that they do not accord, reading address of nonvolatile memory  41  is renewed to next address of sheet data contained (step  2005 ). And, sheet data of this time is compared with all sheet data contained in the nonvolatile memory  41  (step  2006 ).  
         [0183]     Even after comparing with all sheet data contained in the nonvolatile memory  41 , there is none that accords with sheet data of this time. In this case, processes of steps  1701  to  1718  of Embodiment 8 shown in  FIG. 28  are performed. Then, sheet width detection and adjustment of slice level of sheet width detecting sensor  11 ,  12 , are performed (step  2007 ). Thereafter, whether there is vacancy in containing area of nonvolatile memory  41 , is checked (step  2008 ). In case that there is vacancy, sheet width, starting/ending position of pre-printing portion, whether pre-printing portions exist at left and right ends of sheet or not, and adjusting data of slice level of sheet width detecting sensors  11 ,  12 , are contained in the nonvolatile memory  41  (step  2009 ).  
         [0184]     In case that any sheet data contained in the nonvolatile memory  41  accorded with sheet data of this time, slice level value contained in the nonvolatile memory  41  is set to sheet width detecting sensors  11 ,  12  of left and right sides (step  2010 ). Further, whether there is a pre-printing portion at left end position of sheet or not, is checked (step  2011 ). In case that there is a pre-printing portion; slice level of front detecting/PE sensors  7  existing left side of end position (right end position) of pre-printing portion, are set to same level as slice level of sheet width detecting sensors  11  of left (step  2012 ).  
         [0185]     Subsequently, whether there is a pre-printing portion at right end position of sheet or not, is checked (step  2013 ). In case that there is a pre-printing portion; slice level of front detecting/PE sensors  7  existing right side of start position (left end position) of pre-printing portion, are set to same level as slice level of sheet width detecting sensors  12  of right (step  2014 ).  
         [0186]     After setting all sheet data, process of detecting sheet width is performed with same method as Embodiment 4, so as to settle left and right positions of sheet (step  2015 ).  
         [heading-0187]     &lt;Effects&gt; 
         [0188]     As mentioned above, sheet data are contained in nonvolatile memory. And, in case that either of sheet data already contained accords with data of sheet being fed now, adjustment of slice level of sheet width detecting sensors  11 ,  12  is not performed. Then, process of detecting position of sheet is performed by using sheet data contained in nonvolatile memory  41 . Therefore, process of slice level adjustment etc. can be omitted. And, throughput can be increased. Moreover, sheet data contained in nonvolatile memory  41  is data which accomplished detection of sheet position. Therefore, left and right end positions of sheet can be detected certainly, by using data which accomplished detection.