Patent Publication Number: US-6666600-B1

Title: Printer having detection and correction of tilt using skew correction

Description:
BACKGROUND OF THE INVENTION 
     Some conventional printers perform a recording operation by feeding recording paper in the direction of the width of the same in a recording section while moving it in a paper feed direction. In particular, when a recording operation is performed on a cut form that is manually fed such as an envelope or cut paper, it is necessary for preferable recording to move the recording paper in a feeding direction such that it is not tilted in the direction of the width thereof. Referring to the prior art, for example, JP-A-1-267075 has disclosed an example in which a plurality of pinch rollers are provided side by side in the direction of the width of paper; means is provided for obtaining a correction amount for a pressure to be applied from each of the pinch rollers to a capstan roller when recording paper is moved in a feeding direction; and a pressure correction controller for controlling the applied pressure based on the correction amount. 
     For example, according to JP-A-5-155086, a paper feed roller and a separating roller are rotated in a forward direction and an inserter driving roller is rotated in the reverse direction when paper is fed. When the leading edge of the paper is located above a sensor, a control circuit detects that the output of the sensor has been turned on and feeds the paper further by the distance between the sensor and the inserter driving roller plus an overfeed amount. The overfeed amount is set at a great value for thick paper and at a smaller value for thinner paper. In the example disclosed, the inserter driving roller is then rotated in the forward direction to put the paper feed roller and the separating roller in an idle state. 
     However, in the first example of the prior art, there is a need for special mechanisms, i.e., the means for obtaining correction amounts for respective pressures to be applied by the pinch rollers to the capstan roller and the pressure correction controller for controlling the applied pressures based on the correction amounts, which has resulted in the problem of a cost increase. In the second example of the prior art, when paper is deflected by overfeeding the same, the thickness of the paper and the amount of deflection may not be in an appropriate relationship, and a problem has arisen in such a case in that a tilted state cannot be corrected. 
     Under such circumstances, the invention provides an apparatus which allows correction to be performed to prevent paper from being fed in a tilted state without a need for any special mechanism. 
     SUMMARY OF THE INVENTION 
     A printer according to the invention is characterized in that it has head driving means for moving a printing head along a platen in the direction of the width of paper that is orthogonal to a paper feed direction, paper feed means for feeding paper into a gap between said printing head and said platen, paper detecting sensors for detecting the position of the leading edge of said paper in a plurality of positions in the direction of the width of the paper when said paper is fed, a moving mechanism for moving said printing head toward and away from said platen; and gap adjusting means for driving said moving mechanism in the direction in which said printing head moves toward said platen to urge said printing head against said paper and for spacing said printing head from said platen a predetermined amount with said position serving as a reference, thereby adjusting the gap between said printing head and said platen, and skew correcting means for detecting the direction and amount of a tilt of said paper based on signals output by said paper detecting sensors when said the paper is fed and for driving said head driving means and said moving mechanism such that an edge of said paper in the direction of the width thereof is sandwiched between said printing head and said platen when said amount of the tilt exceeds a predetermined range and driving said paper feed means such that the paper is rotated about the sandwiched portion depending on the direction of the tilt, thereby correcting the amount of the tilt such that it stays in the predetermined range. Since the skew correcting means operates by sandwiching paper using the head driving mechanism for moving the printing head along the platen, the moving means for moving the printing head toward and away from the platen, and the gap adjusting means and by rotating the paper with the paper feed means, a tilted state of paper can be easily corrected without a need for any special mechanism other than those of a printer. 
     Said skew correcting means preferably controls the driving of said head driving means and said paper feed means such that said sandwiched portion is always said edge of the paper in the direction of the width thereof regardless of said direction of tilt and such that said feeding direction of the paper is switched depending on said direction of the tilt. 
     Said skew correcting means preferably switches the sandwiched portion between the edge of the paper in the direction of the width thereof and another edge of the same depending on said direction of the tilt and controls the driving of said head driving means and the paper feed unit such that the feeding direction of the paper is always a constant direction regardless of said direction of the tilt. 
     Said paper detecting sensors are preferably disposed in positions in which they face both edges of said paper in the direction of the width thereof. This maximizes the amount of the tilt of the paper to allow accurate correction of a tilted state. 
    
    
     A mode for carrying out the invention will now be described with reference to the accompanying drawings. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram illustrating a configuration according to the invention. 
     FIG. 2 is a sectional view showing a mode for carrying out the invention. 
     FIG. 3 is an enlarged perspective view of a major part of the same. 
     FIG. 4 is a flow chart for explaining an operation of detecting a tilted state of paper. 
     FIG. 5 is a flow chart for explaining an operation of correcting a tilted state of paper. 
     FIG. 6 is a flow chart for explaining another operation of correcting a tilted state of paper. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A printer according to the invention is primarily aimed at recording on a cut form that is manually fed such as an envelope or cut paper as recording paper, and a description will now be made on a configuration of a mechanical section for such a purpose with reference to FIGS. 1 to  3 . 
     As shown in FIG. 1, a carriage motor (motor) driving circuit  10 , a paper feed motor (LF motor) driving circuit  20 , a gap adjusting circuit  30 , a printing head pin driving circuit  40 , and a skew detecting circuit  50  are provided in a control section of a printer. The carriage motor  11  is driven under the control of the carriage motor driving circuit  10  to configure head driving means A for moving a printing head on a carriage to be described later in the direction of the width of paper. The paper feed motor  21  is driven under the control of the paper feed motor driving circuit  20  to configure paper feed means B for feeding paper to a printing section. The gap adjusting motor  31  is driven under the control of the gap adjusting circuit  30  to configure a moving mechanism C 1  for moving the printing head toward and away from a platen and to configure gap adjusting means C 2  for adjusting a gap between the printing head and the platen. A printing signal is supplied to a printing head  41  under the printing head pin control circuit  40  to configure printing means D for performing printing on paper. The skew detecting circuit  50  constitutes skew detecting means F that detects the direction and amount of a tile of paper based on signals output by an edge sensor  51  and a skew sensor  52  that constitute paper detection sensors E. 
     FIG.  2  and FIG. 3 show a mechanical section of the printer. An outer case  1  is provided with a front cover  2  that can be opened and closed on a front side (left side) thereof; a partition cover  3  that can be opened and closed is provide inside the front cover  2 ; and a top cover  4  that can be opened and closed is provided on a top side thereof. Behind a bottom end of the front cover  2  about which the cover is swung, a front tractor  5  is provided such that it can be swung about a shaft  5   a . Paper is manually supplied from the front side of the printer to be fed into the printing section when the front cover  2  is opened with the front tractor  5  in a horizontal position. The paper is advanced by a forward rotation of the paper feed motor  21  to the printing section where it is printed and, after printing, the paper is advanced as it is by a forward rotation of the paper feed motor  21  to be ejected from a rear side of the printer or an opening provide by opening the top cover  4 . Alternatively, the paper feed motor  21  may be rotated in the reverse direction after printing to retract the paper and eject it from the front side of the printer. 
     A platen  42  is provided in a face-to-face relationship with the printing head  41  at the printing section inside the outer case  1 , and an ink ribbon which is not shown is transported in one direction between the printing head  41  and the platen  42 . The printing head  41  is carried by a carriage  8  that can be moved under the guidance of upper and lower guide shafts  6  and  7 . Both ends of the guide shafts  6  and  7  are supported by both of side plates that are provided in a face-to-face relationship in the vicinity of both sides of the outer case  1 ; the lower guide shaft  7  penetrates through the carriage  8  to guide the printing head  41  in the direction of the width of paper; and the upper guide shaft  6  guides the carriage  8  while allowing it to move upward and downward. Therefore, the printing head  41  can be moved by the head driving means A in the direction of the width of paper and can be moved by the moving mechanism C 1  toward and away from the platen  42 . 
     The paper feed means B for paper manually supplied from the front side of the printer will now be described. A paper guide  9  is provided horizontally such that it extends from the neighborhood of an inner end of the front tractor  5  to a paper ejecting section through the gap between the printing head  41  and the platen  42 . Paper feed rollers  22  and  23  are disposed at front and rear ends of the paper guide  9 . A turning force of the paper feed motor  21  is transmitted to the paper feed rollers  22  and  23  through a gear train which is not shown to drive each of the paper feed rollers  22  and  23  for cooperative rotation. Driven rollers  22   a  and  23   a  provided on the printing head  41  side of the paper feed path are in elastic contact with the paper feed rollers  22  and  23 , and paper is fed by the feed rollers  22  and  23  and the driven rollers  22   a  and  23   a  that are paired respectively. A paper transport path  25  is formed such that it extends backward and upward from the rear end of the paper guide  9  through a switch lever  24  that can be swung. The paper can be ejected backward by swinging the switch lever  24  to a horizontal position and can alternatively be guided onto the top cover  4  and ejected therefrom by swinging the switch lever  24  to a tilted position to open the top cover  4 . 
     A description will now be made on the skew detecting means F for detecting whether manually supplied paper has been fed in a tilted state. As shown in FIG. 3, a paper sensor  53  is disposed at the front end of the paper guide  9 . An edge sensor  51  and a skew sensor  52  that are paper detecting sensors E are incorporated in the paper guide  9  behind the paper sensor  53 . The edge sensor  51  and the skew sensor  52  are disposed in a plurality of positions which are spaced from each other in the direction of the width of paper; the edge sensor  51  is disposed leftward in the direction in which paper is advanced; and the skew sensor  52  is located on the right side of the edge sensor  51 . Signals output by the edge sensor  51  and the skew sensor  52  are supplied to the skew detecting circuit  50  to constitute the skew detecting means F. 
     When the amount of a tilt detected by the skew detecting means F exceeds a predetermined range, it is corrected by skew correcting means G. 
     As shown in the flow chart in FIG.  4  and FIG. 5, a judgment is made by the paper sensor  53  as to whether a cut form of paper has been inserted into the printer or not (f 1 ). The judging operation is repeated while no paper is detected by the paper sensor  53  and, when paper is detected, the paper feed means B sets 0 in an LF counter of the paper feed motor  21  and rotates the paper feed motor  21  in the forward direction (f 2 ). When paper is fed by the paper feed motor  21 ; it is judged whether the paper has reached the position of the edge sensor  51  (f 3 ); it is judged whether paper has been detected by the skew sensor  52  when no paper is detected by the edge sensor  51  (f 4 ); and the judgments are continued until paper is detected by either of the paper detecting sensors E. When it is judged that the edge sensor  51  has first detected paper (f 3 ), the value in the LF counter of the paper feed motor  21  at that time is set in an edge counter of the edge sensor  51  (f 5 ). The forward rotation of the paper feed motor  21  continues, and it is judged whether the paper has reached the position of the skew sensor  52  (f 6 ). When paper is detected by the skew sensor  52 , the value in the LF counter of the paper feed motor  21  at that time is set in a skew counter of the skew sensor  52 ; and S is set at “0” (f 7 ). Then, the value in the edge counter of the edge sensor  51  is subtracted from the value in the skew counter of the skew sensor  52  to calculate a value X (f 8 ). The value X is then compared with a maximum value A of allowable skew in a predetermined range (f 9 ). When the value X is smaller than the predetermined range A (X&lt;A), the process of locating the head of paper is terminated (f 10 ), and the process then enters a normal printing operation. 
     The above-described state of the paper can be summarized as follows. Since the paper was inserted upward from a lower part in FIG.  3  and first detected by the edge sensor  51 , the paper was inserted with the left edge thereof in the lead. The value X indicates the state of a delay of the subsequent detection of the paper with the skew sensor  52 , i.e., the amount of a tilt of the paper. That is, when S=0, it indicates the direction of a tilt at which the paper is inserted such that the left edge thereof leads. Further, the relationship expressed by X&lt;A indicates that the amount of the tilt of the paper is in a predetermined range and that it is an allowable amount of tilt, and it is therefore judged that a printing operation can be performed in a normal manner in the same state. 
     Further, when the paper is detected by the skew sensor  52  before it is detected by the edge sensor  51  (f 4 ), the value in the LF counter of the paper feed motor  21  at that time is set in the skew counter of the skew sensor  52  (f 11 ). The forward rotation of the paper feed motor  21  continues, and it is judged whether the paper has reached the position of the edge sensor  51  (f 12 ). When the paper is detected by the edge sensor  51 , the value in the LF counter of the paper feed motor  21  at that time is set in the counter of the edge sensor  51 ; and S is set at “1” (f 13 ). Then, the value in the skew counter of the skew sensor  52  is subtracted from the value in the edge counter of the edge sensor  51  to calculate the value X (f 14 ). The value X is then compared with the maximum value A of allowable skew (f 9 ). When the value X is smaller than the maximum value A of allowable skew (X&lt;A), the process of locating the head of paper is terminated (f 10 ), and the process then enters a normal printing operation. 
     The above-described state of the paper can be summarized as follows. Since the paper was first detected by the skew sensor  52 , the paper was inserted with the right edge thereof in the lead. The value X indicates the state of a delay of the subsequent detection of the paper with the edge sensor  51 , i.e., the amount of a tilt of the paper. That is, when S=1, it indicates the direction of a tilt at which the paper is inserted such that the right edge thereof leads. Further, the relationship expressed by X&lt;A indicates that the amount of the tilt of the paper is in the predetermined range and that it is an allowable amount of tilt, and it is therefore judged that a printing operation can be performed in a normal manner in the same state. 
     While the process directly proceeded to a printing operation because X&lt;A in the above examples, a printing operation cannot be performed in a normal manner when X&gt;A because the amount of the tilt is greater than the predetermined range or the allowable maximum value A. In this case, it is therefore necessary to correct the skew of the paper. 
     The skew correcting means G will be described with reference to the flow chart in FIG.  5 . In this example, the sandwiched portion is always one edge of paper in the direction of the width thereof regardless of the direction of a tilt of the paper, and the feeding direction of the paper is switched depending on the direction of the tilt. Then, the printing head  41  is first moved to the position of the left edge of the paper with the head driving means A (f 21 ). Specifically, the carriage motor  11  is driven to move the printing head  41  to the left edge; the gap adjusting motor  31  is driven for forward rotation (f 22 ); the printing head  41  is lowered by the moving mechanism C 1 ; and it is judged whether the printing head  41  has detected the paper (f 23 ). When the printing head  41  is lowered into contact with the paper with a predetermined pressure, an HA sensor  32  such as a micro-switch (shown in FIG. 1) generates an output, and the output signal is supplied to the gap adjusting circuit  30 . The printing head  41  is thus urged against the platen  42 , and it is possible to detect that the paper has been tightly sandwiched between the printing head  41  and the platen  42 . The gap adjusting motor  31  is then stopped (f 24 ). Next, the gap adjusting means C 2  rotates the gap adjusting motor  31  in the reverse direction for B pulses with that position used as a reference (f 25 ). The printing head  41  is elevated by reversing the gap adjusting motor  31 , and the B pulses set here are a number of pulses that cause the printing head  41  to be elevated very slightly. Specifically, the printing head  41  is very slightly elevated from the state in which the printing head  41  has been lowered to tightly sandwich the paper between the platen  42  and itself to sandwich the paper more gently with a slight gap such that it can be rotated in the sandwiched state. The B pulses are a learned value and are a value that is preset by repeating a test. As a result of the operations up to this point, the paper is rotatably sandwiched by the printing head  41  and the platen  42  at the left edge thereof. 
     Next, it is judged which of S=1 and S=0 is true before the skew correcting means G is entered (f 26 ). Since the state expressed by S=1 is a state in which paper is inserted in a direction that is tilted such that the right edge thereof leads as described above, the paper feed motor  21  is rotated in the reverse direction for Y pulses (f 27 ). Y=C·Y+D is true, and the paper is retracted as a result of the reverse rotation of the paper feed motor  21 . Since the left edge of the paper is gently sandwiched, the paper is rotated clockwise about the left edge thereof, which causes the right edge to be retracted to mitigate the tilted state. The value C and the value D are learned values and are preset by repeating a test. Since the state expressed by S=0 is a state in which paper is inserted in a direction that is tilted such that the left edge thereof leads as described above, the paper feed motor  21  is rotated in the forward direction for Y pulses (f 28 ). Y=C·Y+D′ is true, and the paper is advanced as a result of the forward rotation of the paper feed motor  21 . 
     Since the left edge of the paper is gently sandwiched, the paper is rotated counterclockwise about the left edge thereof, which causes the right edge to be advanced to mitigate the tilted state. The value C′ and the value D′ are learned values and are preset by repeating a test. Since this operation temporarily corrects the tilted state, the gap adjusting motor  31  is rotated in the reverse direction to move the printing head  41  upward with the moving mechanism C 1 , thereby returning the same to a home position thereof (f 29 ). 
     The paper feed motor  21  is then rotated in the reverse direction by the paper feed means B (f 30 ) to retract the paper. When the edge sensor  51  judges that there is no paper (f 31 ) and the skew sensor  52  also judges that there is no paper (f 32 ), the paper feed motor  21  is stopped (f 33 ). The process then returns to the flow in FIG. 4 again to check the state of tilting of the paper through the same operations. When it is judged that X&lt;A (f 9 ), the process of locating the head of the paper is terminated, and printing is then performed on the paper according to a normal procedure. 
     The skew correcting means is not limited to FIG. 5, and skew correcting means G 2  as shown in the flow chart in FIG. 6 may be employed. The operation of the same will now be described. In this example, a sandwiched position of paper is changed depending on the direction in which the paper is tilted, and the paper is fed always in a constant direction regardless of the tilting direction. Specifically, it is first judged which of S=1 and S=0 is true (f 41 ). The state expressed by S=1 is a state in which paper is inserted in a direction that is tilted such that the right edge thereof leads as described above, the head driving means A drives the carriage motor  11  to move the printing head  41  to the position of the left edge of the paper (f 42 ). The state expressed by S=0 is a state in which paper is inserted in a direction that is tilted such that the left edge thereof leads as described above, the carriage motor  11  is driven to move the printing head  41  to the position of the right edge of the paper (f 43 ). The moving mechanism C 1  then drives the gap adjusting motor  31  for forward rotation (f 44 ) to lower the printing head  41  close to the paper. The sensor  32  judges whether the printing head  41  has detected the paper (f 45 ). If yes, the gap adjusting motor  31  is stopped (f 46 ), and that position is then used as a reference. This state is a state in which the paper is tightly sandwiched between the printing head  41  and the platen  42  as described above. Next, the gap adjusting means C 2  rotates the gap adjusting motor  31  in the reverse direction for B pulses (f 47 ) to elevate the printing head  41  very slightly as described above. The paper is then put in a gently sandwiched state in which the paper can be rotated while it is sandwiched. 
     Next, the skew correcting means G 2  rotates the paper feed motor  21  in the reverse direction for Y pulses (f 48 ). The paper is retracted as a result of the reverse rotation of the paper feed motor  21  as described above. However, since the left edge or right edge of the paper is gently sandwiched, the paper is rotated clockwise or counterclockwise about the left edge or right edge thereof, which retracts the right edge or left edge to mitigate the tilted state. Since this operation has temporarily corrected the tilted state in which the paper is inserted at an angle, the gap adjusting motor  31  is rotated in the reverse direction as described above (f 49 ) to elevate the printing head  41  with the moving mechanism C 1 , thereby returning it to a home position thereof. 
     Next, the paper feed motor  21  is rotated in the reverse direction by the paper feed means B (f 50 ) to retract the paper. When the edge sensor  51  judges that there is no paper (f 51 ) and the skew sensor  52  also judges that there is no paper (f 52 ), the paper feed motor  21  is stopped (f 53 ). The process then returns to the flow in FIG. 4 again to check the state of tilting of the paper through the same operations. When it is judged that X&lt;A (f 9 ), the process of locating the head of the paper is terminated, and printing is then performed on the paper according to a normal procedure. 
     While the edge sensor  51  and the skew sensor  52  are disposed on the paper guide  9  in the above-described examples, the same effects can be achieved by disposing the edge sensor  51  and the skew sensor  52  on a ribbon guide  43 . 
     As described above in detail, in a printer according to the invention, skew is corrected by sandwiching paper with a head driving mechanism for moving a printing head along a platen, a moving mechanism for moving the printing head toward and away from the platen, and gap adjusting means and by rotating the paper with paper feed means. It is therefore possible to correct a tilted state of paper with a simple configuration without a need for any special mechanism other than those of a printer and to provide an apparatus that can preferably perform printing by preventing paper from being transported in a tilted state. 
     DESCRIPTION OF REFERENCE NUMERALS AND SIGNS 
     
       
         
           
               
               
               
             
               
                   
                   
               
             
            
               
                   
                 A: 
                 head driving means 
               
               
                   
                 B: 
                 paper feed means 
               
               
                   
                 C1: 
                 moving mechanism 
               
               
                   
                 C2: 
                 gap adjusting means 
               
               
                   
                 E: 
                 paper detecting sensor 
               
               
                   
                 G, G2: 
                 skew correcting means 
               
               
                   
                 41: 
                 printing head 
               
               
                   
                 42: 
                 platen