Patent Publication Number: US-6712536-B2

Title: Printer

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to printers, and more specifically, to apparatus and methods for printing on a card with high precision. 
     Thermal printers are used for printing various documents including personal identification cards. Typically, these identification cards have images on their surfaces printed in various colors. Some cards have images printed in metallic color. Further, some cards have a lenticular lens thereon so that a user can see different images depending on the viewing angle with respect to the normal direction of the surface of the card. 
     In the prior art, when an image sheet having printed images thereon is affixed onto a plastic sheet having a lenticular lens thereon, alignment of these two sheets requires high precision. Misalignment of the image sheet and the lenticular lens sheet would result in mixed or blurred images of the two separate images. In a normal lenticular card, only one of the two images can be seen if the user fixes the point of view. In order to align the image sheet with the lenticular sheet, the prior art technique requires a skilled worker to manually align the two sheets. This is a time-consuming task, and thus incurs cost. Besides, due to the manual alignment, the yield of the resulting product is low. 
     In view of these and other issues, it would be desirable to have a technique allowing a printer to print images with high precision. 
     SUMMARY OF THE INVENTION 
     According to various embodiments of the present invention, a printer prints images on a printing medium having a mark. The printer includes an optical sensor, a feeding section, a controller, and a printing section. The optical sensor is operable to generate a signal based on a position of the mark of the printing medium with respect to the optical sensor. The feeding section is operable to perform feeding of the printing medium. The controller is operable to control the feeding of the printing medium based on the signal. The printing section is operable to print images on the printing medium. 
     In a specific embodiment, the sensor is a linear optical sensor which is operable to detect the mark provided on the printing medium. Based on a signal output from the sensor, the controller aligns the printing medium with the images printed on the medium using the feeding section. 
     In some embodiments, the mark is a line or a stripe drawn on the printing medium diagonally with respect to the line. 
     In some specific embodiments, the printing section includes an intermediate transfer film, a print head, and an intermediate transfer roller. The print head has a plurality of resistance heating elements for transfer of the ink from the ink film to the intermediate transfer film. The intermediate transfer roller is operable to heat the ink on the intermediate transfer film for transfer of the ink from the intermediate transfer film to the printing medium. 
     A further understanding of the nature and advantages of the present invention may be realized by reference to the remaining portions of the specification and the drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     The invention, together with further objects and advantages thereof, may best be understood by reference to the following description taken in conjunction with the accompanying drawings in which: 
     FIG. 1 is a cross-sectional view of a thermal transfer printer of a specific embodiment according to the present invention. 
     FIG. 2 is a cross-sectional view of a thermal transfer printer of an alternative embodiment according to the present invention. 
     FIG. 3 is a cross-sectional view of a card after the printing process utilizing a specific embodiment of the apparatus and methods according to the present invention. 
     FIG. 4 is a plain view of the printing medium and the sensor used for specific embodiments of the apparatus and methods according to the present invention. 
     FIG. 5 is a plain view of the printing medium and the sensor used for specific embodiments of the apparatus and methods according to the present invention where the sensor transverses a mark. 
     FIG. 6 is a plain view of the printing medium and the sensor used for alternative embodiments of the apparatus and methods according to the present invention where the sensor transverses a mark. 
     FIG. 7 is a plain view of the printing medium and the sensor in an alternative configuration used for specific embodiments of the apparatus and methods according to the present invention where the sensor transverses a mark. 
    
    
     DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS 
     Various embodiments of the present invention will now be described in detail with reference to the drawings, wherein like elements are referred to with like reference labels throughout. 
     As described in detail below, various embodiments of the present invention include an optical sensor which is operable to generate a signal based on a position of mark provided on a printing medium. Thus, the embodiments of the present invention are capable of aligning the printing medium with high precision, thereby avoiding misalignment of images printed on the medium with respect to the medium. 
     In this specification, “regular color ink” means any ink other than the metallic ink, which includes, for example, cyan ink, magenta ink, yellow ink, black ink, and white ink. A “regular color ink film” includes any film which carries regular color ink thereon. In this specification, “ink” includes regular color ink and metallic ink which presents metallic color. An “ink film” includes any ink film which carries metallic ink or regular color ink. Thus, the ink film includes regular color ink films  140  and  240 , and an intermediate transfer film  148  described in detail below referring to FIGS. 1 and 2. 
     FIG. 1 is a cross-sectional view of a thermal transfer printer  100  of a specific embodiment according to the present invention. The thermal transfer printer  100  includes a thermal transfer printing section  104 , and a controller  106  within a housing  108 . A printing medium  110  is fed along a medium flow path  112  from left to right in FIG.  1 . FIG. 1 shows two locations of the printing medium  110  in the thermal transfer printer  100 . 
     Suitable polymers for the printing medium  110  include polyvinylchloride (PVC), polycarbonate (PC), acrylonitrile-butadiene-styrene (ABS), polypropylene sulfate (PPS), and polyethylene terephthalate glycol (PETG). Circles shown in FIG. 1 represent rollers or platens, and elongated rectangles  110  in FIG. 1 represent cards or plate-like materials used as the printing medium  110 . 
     The thermal transfer printing section  104  is operable to heat regular color ink on the regular color ink film  140  for transfer the regular color ink from the regular color ink film  140  to the printing medium  110 . The regular color ink film  140  includes at least one of a cyan color layer, a magenta color layer, a yellow color layer, a black color layer, and a white color layer on a base film. The base film is made from plastic materials including polyethylene terephthalate (PET). 
     The thermal transfer printing section  104  includes a printing head  142  having a plurality of resistance heating elements  144 , and a platen  146 . The resistance heating elements  144  apply heat to the regular color ink film  140  based on electric drive pulses representing image data. The printing head  142  presses the regular color ink film  140  and the intermediate transfer film  148  against the platen  146 , thereby transferring the regular color ink to the intermediate transfer film  148  by heat and pressure. The intermediate transfer film  148  constitutes a closed loop, which rotates counterclockwise in FIG. 1 supported by feeding rollers  150 ,  152 ,  154  and  156 . 
     The regular color ink transferred from the regular color ink film  140  to the intermediate transfer film  148  is carried counter clockwise to a point where an intermediate transfer roller  158  and a platen  160  contact the printing medium  110 . In order to determine the exact position of the printing medium  110 , the thermal transfer printing section  104  includes a sensor  162  which detects a predetermined point, e.g., a mark  161 , provided on the printing medium  110  by utilizing, for example, an optical sensing technique. A light emitting device  163  emits light toward the sensor  162  through the printing medium  110  during detection of the location of the printing medium  110 . The light emitting device  163  may be any device which supplies sufficient intensity and wavelength of light for the sensor  162  such as an light emitting diode, a lamp, an electroluminescent lamp, or the like. 
     In the specific embodiment shown in FIG. 1, the light emitting device  163  is positioned on the opposite side of the sensor  162  with respect to the medium flow path  112  because the sensor  162  generates signal based on the light intensity through the printing medium  110 , and the mark  161  on the printing medium  110  varies the transmissivity of the printing medium  110  compared to other part of the printing medium  110 . Conversely, when the reflection of the printing medium  110  is varied by the mark  161 , the light emitting device  163  is positioned on the same side of the sensor  162  with respect to the medium flow path  112 . 
     Feeding rollers  164  and  166  feed the printing medium  110  onto the intermediate transfer roller  158  and the platen  160  along the medium flow path  112 . The controller  106  controls rotational speeds and directions of the feeding roller  164  appropriately. 
     The printing medium  110  is positioned on a predetermined point on the medium flow path  112  by using the sensor  162  and the feeding roller  164  controlled by the controller  106 . Then, the feeding rollers  164  and  166  feed the printing medium  110  onto the intermediate transfer roller  158  and the platen  160  along the medium flow path  112 . The intermediate transfer roller  158  presses the intermediate transfer film  148  and the printing medium  110  against the platen  160 , thereby transferring the regular color ink from the intermediate transfer film  148  to the printing medium  110  by pressure. Feeding rollers  170  and  172  feed the printing medium  110  out of the housing  108  of the thermal transfer printer  100  along the medium flow path  112 . The controller  106  controls rotational speeds and directions of the feeding rollers  170  and  172  appropriately. 
     FIG. 2 is a cross-sectional view of a thermal transfer printer  200  of an alternative embodiment according to the present invention. The thermal transfer printer  200  includes a thermal transfer printing section  204 , and the controller  106  within the housing  108 . The differences between the embodiments shown in FIGS. 1 and 2 mainly reside in the thermal transfer printing section  204 . Thus, it should be appreciated that elements in FIG. 2 which are assigned the same reference labels as shown in FIG. 1 have the same functionalities as those of FIG. 1 with the exception that the elements are designed to be coordinated with the thermal transfer printing section  204 . 
     The thermal transfer printing section  204  is operable to heat regular color ink on the regular color ink film  240  for transfer the regular color ink from the regular color ink film  240  to the printing medium  110 . The regular color ink film  240  includes at least one of a cyan color layer, a magenta color layer, a yellow color layer, a black color layer, and a white color layer on a base film, which is made from plastic materials including PET. 
     The thermal transfer printing section  204  includes a printing head  242  having a plurality of resistance heating elements  244 , and a platen  246 . The resistance heating elements  244  apply heat to the regular color ink film  240  based on electric drive pulses representing image data. The printing head  242  presses the regular color ink film  240  and the printing medium  110  against the platen  246 , thereby transferring the regular color ink from the regular color ink film  240  to the printing medium  110  by heat and pressure. 
     FIG. 3 is a cross-sectional view of a card  300  after the printing process utilizing a specific embodiment of the apparatus and methods according to the present invention. Before the printing process utilizing the thermal transfer printers  100  and  200 , the card  300  includes only the printing medium  110 . The printing medium  110  in the card  300  used for a specific embodiment of the present invention includes parallel ridge portions  302  on one side thereof, which may be used as lenticular lenses. In a specific embodiment, the pitch p between the immediately neighboring parallel ridge portions  302  is, for example, 0.254 mm (i.e., 100 line per inch). 
     After the printing process performed by one of the thermal transfer printing sections  104  and  204 , images  310 - 315  and  320 - 325  are printed on the printing medium  110 . In this specific embodiment, the images  310 - 315  and  320 - 325  compose first and second pictures, respectively, where the first and second pictures can be seen from different angles with respect to the normal direction of the card  300 . As described in detail below, this specific embodiment of the present invention having the sensor  162  capable of detecting the location of the card  300  with high precision is advantageous especially when the printing medium  110  has the lenticular lenses thereon because aligning the images  310 - 315  and  320 - 325  with the ridge portion  302  becomes an issue. 
     However, it should be appreciated that other images including a plain, single image rather than stripes of images similar to the images  310 - 315  and  320 - 325  may be printed on the top surface of the printing medium  110 . Furthermore, the printing medium  110  may be any other suitable planar printing medium without including parallel ridge portions  302 . 
     FIG. 4 is a plain view of the printing medium  110  and the sensor  162  used for specific embodiments of the apparatus and methods according to the present invention. As described above referring to FIGS. 1 and 2, the printing medium  110  has the mark  161  thereon. The mark  161  has a different transmissivity rate or a reflection rate compared to other part of the printing medium  110 . In a specific embodiment, the mark  161  is provided on the printing medium  110  by printing a black stripe having the width w. However, it should be appreciated that the color and the width w of the mark  161  may be any other suitable color and width. Also, the mark  161  may be provided by any other suitable way such as etching, abrasion, scratching or the like. In the embodiment shown in FIG. 4, the width w ranges from about 0.5 mm to about 1.0 mm. However, in this specification, the term “stripe” covers (i) the mark  161  of which width w is not negligible compared to the size of each of the sensor cells  410 ,  411 ,  412 , . . . , and (ii) a fine line of which width is substantially negligible compared to the size of each of the sensor cells  410 ,  411 ,  412 , . . . as described in detail below referring to FIG.  6 . 
     In the specific embodiments shown in FIGS. 1,  2  and  4  of the printer according to the present invention, the sensor  162  is a charge coupled device (CCD) line sensor which has a plurality of sensor cells  410 ,  411 ,  412 , . . . It should be appreciated that any other suitable linear optical sensor may be used for the sensor  162 . In some embodiments, the mark  161  and the longitudinal direction of the sensor  162  intersect at an angle which is substantially non-perpendicular, where a line  460  in FIG. 4 is parallel to the mark  161 . In more specific embodiments, the angle  450  at which the mark  161  and the longitudinal direction of the sensor  162  intersect is between about 3 degrees and about 30 degrees. The printing medium  110  is fed along a feeding direction  470  by the feeding rollers  164  and  166 . The medium flow path  112  can be a curved line. In such a case, the feeding direction  470  is a direction along which the printing medium  110  is fed in the vicinity of the sensor  162 . 
     FIG. 5 is a plain view of the printing medium  110  and the sensor  162  used for specific embodiments of the apparatus and methods according to the present invention where the sensor  162  transverses the mark  161 . During the process of feeding the printing medium  110  toward the thermal transfer printing sections  104  and  204  along the feeding direction  470 , the sensor  162  transverses the mark  161 . In a specific embodiment shown in FIG. 5, the sensor cells  410 - 413  and  419 - 422  output a HIGH level signal corresponding to a high intensity of the incident light, and the sensor cells  414 - 418  output a LOW level signal corresponding to a low intensity of the incident light. It should be appreciated that the level of the output signal from the sensor  162  may be inverted or shifted depending on the characteristics of the sensor  162  and output circuitry associated with the sensor  162 . The controller  106  receives the output signal from the sensor  162  and calculates the distance between the mark  161  on the printing medium  110  and the sensor  162 , i.e., the location of the printing medium  110  with respect to the sensor  162 , based on the output signal from each of the sensor cells  410 - 422 . 
     FIG. 6 is a plain view of the printing medium  110  and the sensor  162  used for specific embodiments of the apparatus and methods according to the present invention where the sensor  162  transverses a mark  661 . In this specific embodiment, the mark  661  is a fine line of which width is negligible compared to the size of the each of the sensor cells  410 - 422 . 
     Similar to the operation described referring to FIG. 5, during the process of feeding the printing medium  110  toward the thermal transfer printing sections  104  and  204  along the feeding direction  470 , the sensor  162  transverses the mark  661 . In a specific embodiment shown in FIG. 6, the sensor cells  410 - 412  and  415 - 422  output a HIGH level signal corresponding to a high intensity of the incident light, and the sensor cells  413  and  414  output a LOW level signal corresponding to a low intensity of the incident light. It should be appreciated that the level of the output signal from the sensor  162  may be inverted or shifted depending on the characteristics of the sensor  162  and output circuitry associated with the sensor  162 . The controller  106  receives the output signal from the sensor  162  and calculates the distance between the mark  661  on the printing medium  110  and the sensor  162 , i.e., the location of the printing medium  110  with respect to the sensor  162 , based on the output signal from each of the sensor cells  410 - 422 . 
     FIG. 7 is a plain view of the printing medium  110  and the sensor  162  used for specific embodiments of the apparatus and methods according to the present invention where the sensor  162  transverses a mark  661 . In this specific embodiment, the mark  661  and the longitudinal direction of the sensor  162  intersect at an angle which is substantially perpendicular. In other words, the angle  450  in FIG. 7 is substantially 90 degrees. 
     Similar to the operation described referring to FIG. 5, during the process of feeding the printing medium  110  toward the thermal transfer printing sections  104  and  204  along the feeding direction  470 , the sensor  162  transverses the mark  661 . In a specific embodiment shown in FIG. 7, the sensor cells  410 - 414  and  416 - 422  output a HIGH level signal corresponding to a high intensity of the incident light, and the sensor cell  415  outputs a LOW level signal corresponding to a low intensity of the incident light. It should be appreciated that the level of the output signal from the sensor  162  may be inverted or shifted depending on the characteristics of the sensor  162  and output circuitry associated with the sensor  162 . The controller  106  receives the output signal from the sensor  162  and calculates the distance between the mark  661  on the printing medium  110  and the sensor  162 , i.e., the location of the printing medium  110  with respect to the sensor  162 , based on the output signal from each of the sensor cells  410 - 422 . 
     The embodiments described above referring to FIGS. 4-6 where the sensor  162  is provided so that the angle  450  is substantially non-perpendicular are advantageous especially when higher detection resolution of the sensor  162  is necessary. Suppose that the sensor  162  has a longitudinal length of 25 mm, having 500 sensor cells, and the angle  450  is 11.5 degrees. Then, the detection resolution of the sensor  162  is improved up to 0.01 mm (=25×sin 11.5/500). Here, the detection resolution is defined as a resolution along the feeding direction  470  while actual resolution of the sensor  162  is defined as a resolution along the longitudinal direction of the sensor  162 . 
     It should be appreciated that the angle  450  which is substantially 90 degrees may be applied to the embodiment illustrated in FIGS. 4 and 5. In the specific embodiments described above, the sensor  162  is a CCD line sensor. However, the sensor  162  may be a two-dimensional CCD sensor as long as the sensor  162  traverses the mark on the printing medium  110  during the feeding of the printing medium  110 . Alternatively, the sensor  162  may be any suitable sensor which is capable of detecting the location of the printing medium  110 . 
     The specific embodiments of the present invention described referring to FIGS. 1 and 2 utilize the roller printing section  102 . However, it should be appreciated that the sensor  162  may be used with only one of the thermal transfer printing sections  104  and  204 , i.e., without employing the roller printing section  102 . The thermal transfer printing sections  104  and  204  may be replaced by any other suitable printing mechanism such as an ink jet print engine, a bubble jet print engine, an electrophotographic print engine, a dot impact print engine or the like. 
     The specific embodiment of the apparatus and methods according to the present invention described above referring to FIG. 1 can be implemented by utilizing the thermal transfer printer  200  illustrated in FIG. 2 in a similar manner except that the regular color printing is performed by the thermal transfer printing section  204  rather than the thermal transfer printing section  104 . Thus, further detail is omitted. 
     In the specific embodiments described above, the regular color printing by the thermal transfer printing sections  104  and  204  can be implemented by a single thermal head. However, it should be appreciated that a plurality of thermal heads can be used for the regular color printing. 
     In the specific embodiments described above, the image layer printing by the thermal transfer printing sections  104  and  204  can be implemented by a single thermal head. However, it should be appreciated that a plurality of thermal heads can be used for the regular color printing. For example, five separate thermal heads can be used for five colors (e.g., cyan, magenta, yellow, and black and white) for the thermal transfer printing sections  104  and  204 . 
     In the above-described specific embodiments of the thermal transfer printer according to the present invention described referring to FIGS. 1 and 2, the feeding rollers  164 ,  166 ,  170  and  172  are appropriately positioned along the medium flow path  112  so that the position of the printing medium  110  is controlled to go back and forth along the medium flow path  112  based on a specific printing process which is applied to the printing medium  110 . 
     In the above embodiments of the thermal transfer printer according to the present invention described referring to FIGS. 1 and 2, the controller  106  can be implemented by any combination of software and/or hardware. For example, the controller  106  can be implemented by a microprocessor, a memory device which stores instruction codes and data, and an interface which drives external devices such as the feeding rollers, the transfer roller, and the intermediate transfer roller. 
     Although only a few embodiments of the present invention have been described in detail, it should be understood that the present invention may be embodied in many other specific forms without departing from the spirit or scope of the invention. For example, although the illustrated embodiments have been described primarily in the context of a thermal transfer printer for printing images on a plastic card, it should be appreciated that various materials may be used for embodiments of the thermal transfer printer according to the present invention. Therefore, it should be apparent that the above described embodiments are to be considered as illustrative and not restrictive, and the invention is not to be limited to the details given herein, but may be modified within the scope of the appended claims.