Patent Publication Number: US-6698955-B2

Title: Method and apparatus for adjusting print positions of dot line printer

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a method and an apparatus for adjusting the print positions of a dot line printer. 
     A method and an apparatus for adjusting the print positions of a dot line printer in the prior art will be described in detail with reference to the drawings. 
     FIG. 1 is a perspective view for explaining a first prior-art example (refer to, for example, Japanese Unexamined Patent Publication (JP-A) No. 244282/1996). 
     The dot line printer is constructed of a hammer bank  2  in which a large number of printing hammers  1  are arrayed in one row, a shuttle mechanism  8  which vibrates the hammer bank  2  laterally at a predetermined amplitude, a sheet feed mechanism  12 , and so forth. 
     In the shuffle mechanism  8 , the hammer bank  2  supported by right and left parallel flat springs  7  is connected to an eccentric cam  6  of a shuttle drive motor  5  through a connecting rod  4 . When the shuttle drive motor  5  is rotated, the hammer bank  2  is vibrated in an approximate sinusoidal wave rightwards and leftwards. The sheet feed mechanism  12  is constituted by a platen  9  for transporting a printing sheet  13 , and a sheet feed motor  11  for driving the platen  9  through a belt  10 , thereby to transport the sheet  13  every dot line very exactly. While the hammer bank  2  is vibrated, the respective printing hammers  1  are operated to print dots at predetermined intervals, so that one row of dots is formed by the one-way operation (forward printing) Subsequently, when the hammer bank  2  is turned back (for reverse printing), the sheet  13  is transported the interval of one dot line, and the next dot line is printed. Further, the sheet  13  is transported one dot line immediately before forward printing. Characters are printed by repeating such operations. Incidentally, numeral  3  designates an inking ribbon. 
     FIG. 2 is a waveform diagram showing the printing timing signals of the prior-art dot line printer. A hammer bank leftmost-end signal  30  and a hammer bank rightmost-end signal  31  indicating the arrivals of the hammer bank  2  at the leftmost end and rightmost end thereof start a forward printing timing signal  32  for executing the forward printing and a reverse printing timing signal  33  for executing the reverse printing, respectively. Both the forward printing timing signal  32  and the reverse printing timing signal  33  are generated substantially at the time when hammer bank speed  36  is a set value. Since the printing is performed by reciprocally moving the hammer bank  2  by means of the shuttle mechanism  8 , the printing of the identical printing hammer  1  must not allow a misalignment or shear between the lateral printing of the forward printing mode and that of the reverse printing mode. It is difficult, however, to avoid the lateral print shear of the identical printing hammer  1  between the forward and reverse printing modes merely by keeping the mechanical balance of the shuttle mechanism  8  which reciprocally moves the hammer bank  2 . In the prior-art dot line printer, therefore, a reverse printing timing signal  35  as shown in FIG. 2 is generated after a delay of a time period after the transmission of the pulse of the hammer bank rightmost-end signal  31 . The printing of the identical printing hammer  1  can be freed from the lateral print shear between in the forward printing mode and in the reverse printing mode by adjusting the time period t. 
     Besides, the line feed of the dot line of the sheet  13  is started by the final pulse of both the forward printing timing signal  34  and the reverse printing timing signal  35 . 
     With the method for adjusting the print positions of the dot line printer in the first prior-art example, it is intended to compensate for the lateral print shear of the identical printing hammer  1  by shifting the reverse printing timing signal  35  in the reciprocal motion. On the other hand, the sheet line feed operation is started by the final pulse of both the forward printing timing signal  34  and the reverse printing timing signal  35 , so that decrease or increase in the time period of the line feed is incurred. Accordingly, the sheet  13  does not cease moving before the start of the printing as shown by the sheet line feed speed  37  in FIG. 2, and hence, print dot positions become disordered to degrade print quality. 
     FIG. 3 is a waveform diagram showing a second prior-art example. Here in the second prior-art example, a dot line printer itself is supposed the same as shown in FIG. 1. A hammer bank leftmost-end signal  20  and a hammer bank rightmost-end signal  21  indicating the arrivals of the hammer bank  2  at the leftmost end and rightmost end thereof start a forward printing timing signal  22  for executing the forward printing and a reverse printing timing signal  23  for executing the reverse printing, respectively. Both the forward printing timing signal  22  and the reverse printing timing signal  23  are substantially generated at times when hammer bank speed  26  is a predetermined value. 
     Since the printing is performed by reciprocally moving the hammer bank  2  by means of the shuttle mechanism  8 , in the printing of the identical printing hammer  1  shear or misalignment between the lateral print of the forward printing mode and that of the reverse printing mode is not allowable. It is difficult, however, to avoid the lateral print shear of the identical printing hammer  1  between in the forward printing mode and in the reverse printing mode merely by keeping the mechanical balance of the shuttle mechanism  8  which reciprocally moves the hammer bank  2 . 
     Therefore, a forward printing timing signal  24  as shown in FIG. 3 is generated after a delay of a time period t 1  following generation of the pulse of the hammer bank leftmost-end signal  20 . 
     Subsequently, a reverse printing timing signal  25  as shown in FIG. 3 is generated after a delay of a time period t 2  following generation of the pulse of the hammer bank rightmost-end signal  21 . The printing of the identical printing hammer  1  can be freed from the lateral print shear between the forward printing mode and the reverse printing mode by adjusting the time periods t 1  and t 2 . 
     The line feed of the dot line of the sheet  13  is started by the final pulse of both the forward printing timing signal  24  and the reverse printing timing signal  25 . In this embodiment, the forward printing timing signal  24  and the reverse printing timing signal  25  are both adjusted by the predetermined adjustment time periods t 1  and t 2  relatively to the hammer bank leftmost-end signal  20  and the hammer bank rightmost-end signal  21 , respectively. As shown by a sheet line feed speed  27  in FIG. 3, therefore, decrease or increase in the time period of the line feed is not incurred, to eliminate the drawback that the sheet  13  does not come to a stop before the start of the printing, causing print dot positions to become disordered to degrade print quality. Further, the adjustment can be facilitated more by equalizing the adjustment time periods t 1  and t 2 . 
     With the method and apparatus for adjusting the print positions of the dot line printer in the second prior-art example, only one printing element assembly is concerned, and hence, the print shear can be avoided by adjusting the forward and reverse printing timing signals. However, in a case where a dot line printer includes a plurality of printing element assemblies and where the relative positions of the printing element assemblies in the extending direction thereof (in the line direction of a printing sheet) are not exactly in alignment, the relative positions of the print dots of the printing element assemblies cannot be corrected merely by the pair of printing timing signals in the forward and reverse modes. 
     Further, even in case of a known dot line printer whose printing mechanism module has a plurality of printing element assemblies, only one drive circuit is included, and only one printing timing signal is generated by a control circuit. Besides, while the printing element assemblies are mechanically coupled, the relative positions of these printing element assemblies in the extending direction thereof sometimes fail to meet designed values on account of discrepancy in the dimensions of the individual printing element assemblies. On this occasion, since only one printing timing signal is generated, the positions of installed printing elements are directly reflected on print dots formed, and the relative positions between the print dots in the extending direction (in the line direction of a printing sheet) fall outside designed values. 
     In a case where the relative positions between the print dots in the line direction misalign by a large amount due to the plurality of printing element assemblies, these assemblies must be mechanically regulated, and the magnitude of the regulation is a level of several tens μm. Accordingly, there have hitherto been the disadvantages that the regulation is difficult and that the number of the stages of the adjusting work enlarges. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to provide a method and an apparatus for adjusting the print positions of a dot line printer according to which the relative positions between print dots in the line direction of a printing sheet can be brought to appropriate relative positions without performing any mechanical regulation. 
     Another object of the present invention to provide a method and an apparatus for adjusting the print positions of a dot line printer according to which the number of the stages of adjusting work is small. 
     According to the present invention, in a dot line printer having a printing mechanism module which includes a plurality of printing element assemblies each having at least one printing element and which are mechanically coupled, and there is provided a method for adjusting print positions of the dot line printer characterized the adjustment steps of assigning drive circuits to the respective printing element assemblies, and generating a plurality of printing timing signals and individually sending them to said respective printing element assemblies by means of a control circuit, thereby to compensate a misalignment of relative positions between print dots of the printing element assemblies in opposing directions of printing, the misalignment being attendant upon a misalignment of relative positions between the printing element assemblies in opposing line directions. 
     Also, according to the present invention, in a dot line printer having a printing mechanism module which includes a plurality of printing element assemblies each having at least one printing element and which are mechanically coupled, there is provided an apparatus for adjusting print positions of the dot line printer, characterized by adjustment means for assigning drive circuits to the respective printing element assemblies, and generating a plurality of printing timing signals and individually sending them to the respective printing element assemblies by means of a control circuit, thereby to compensate a misalignment of relative positions between print dots of the printing element assemblies in opposing directions of printing, the misalignment being attendant upon a misalignment of relative positions between the printing element assemblies in opposing line directions. 
     Further, according to the present invention, in a dot line printer having a printing mechanism module which includes a plurality of printing element assemblies each having at least one printing element and which are mechanically coupled, there is provided an apparatus for adjusting print positions of the dot fine printer, characterized by comprising a detector which detects a position of the printing mechanism module, and a control circuit which generates two sorts of printing timing signals on the basis of an output signal of the detector. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS: 
     FIG. 1 is a perspective view for explaining a method and an apparatus for adjusting the print positions of a dot line printer in a first prior-art example; 
     FIG. 2 is a waveform diagram for explaining the operation of the method and apparatus shown in FIG. 1; 
     FIG. 3 is a waveform diagram for explaining the operation of a method and an apparatus for adjusting the print positions of a dot line printer in a second prior-art example; 
     FIG. 4 is a block diagram showing a method and an apparatus for adjusting the print positions of a dot line printer in an embodiment of the present invention; and 
     FIG. 5 is a waveform diagram for explaining the operation of the method and apparatus shown in FIG.  4 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT; 
     In a dot line printer having a printing mechanism module which includes a plurality of printing element assemblies, the present invention is intended to avoid that misalignment of print dots in the line direction of a printing sheet which is ascribable to the misalignment of the relative positions of the printing element assemblies mechanically combined, and it consists of separately disposing drive circuits for the respective printing element assemblies and individually sending printing timing signals from a control circuit to the respective assemblies, thereby to adjust the print dot positions of the printing element assemblies. 
     Now, an embodiment of the present invention will be described in detail with reference to the drawings. 
     FIG. 4 is a block diagram showing one embodiment of the present invention. The embodiment concerns a dot line printer which includes, for example, two printing element assemblies  107 ,  108 . A detector  101  detects the position of a printing mechanism module. A control circuit  102  generates two sorts of printing timing signals  103 ,  104  on the basis of the detected position, and the generated signals  103 ,  104  are respectively sent to drive circuits  105 ,  106 . Herein, the printing mechanism module is configured of the two printing element assemblies  107  and  108  each of which has a plurality of printing elements  109 , and both of which are mechanically coupled. The drive circuits  105 ,  106  taking charge of the printing element assemblies  107 ,  108  respectively supply the printing elements  109  to-be-driven with printing input signals on the basis of the received printing timing signals  103 ,  104 , respectively. Accordingly, the relative positions between the print dots of the printing element assemblies  107 ,  108  can be adjusted in the line direction of a printing sheet by changing the difference between the times of the printing timing signals  103 ,  104 . 
     FIG. 5 is a waveform diagram showing the printing timing signals for explaining the operation of the embodiment of the present invention. When the printing mechanism module has arrived at a predetermined position during its horizontal reciprocating rectilinear motion due to a shuttle mechanism module, the sensor  101  detects the arrival and generates a reference position signal  110 . The printing timing signal  111  of the printing element assembly  107  is generated after a predetermined time period t 1  on the basis of the reference position signal  110 . 
     Subsequently, in a case where the dot position of the printing element assembly  108  is to be shifted in, for example, a forward printing direction relatively to that of the printing element assembly  107 , the printing timing signal  112  of the printing element assembly  108  is generated with the delay of a time period t 2  in the forward printing mode thereof. The time period t 2  is determined from the moving speed and dot pitch deviation amount of the printing mechanism module. 
     In the reverse printing mode of the printing element assembly  108 , the generation of the printing timing signal  112  is advanced a time period t 3  equal to the time period t 2 , relatively to that of the printing timing signal  111  contrariwise to the operating aspect in the forward printing mode. The print dot positions of the printing element assembly  108  can be adjusted as required by controlling the time periods t 2 , t 3 . 
     With the method and apparatus of the present invention for adjusting the print positions of a dot line printer, the optimum print positions can be attained by adding the procedure or means for adjusting the relative positions between the printed dots in lines facing each other, without performing any mechanical regulation. Moreover, the number of the stages of an adjusting work can be decreased.