Patent Publication Number: US-8537187-B2

Title: Thermal transfer printing device

Description:
FIELD OF THE INVENTION 
     The present invention relates to a printing device, and more particularly to a thermal transfer printing device. 
     BACKGROUND OF THE INVENTION 
     Printing devices are peripherals for printing characters and/or graphics on papers or other kinds of printing media. Generally, the printing devices are classified into two types: ordinary printing devices and thermal transfer printing devices. The configurations of the thermal transfer printing devices are substantially identical to those of the ordinary printing devices except for the printing way. For example, the ordinary printing device supplies ink or toner onto a paper. Whereas, a thermal transfer printing device has a thermal transfer printing module for outputting the image. The thermal transfer printing module has a thermal print head (TPH) to heat a coating and allow the coating to be adsorbed on a thermal transfer paper, so that the image is printed out. The widely-used thermal transfer printing devices include for example faxing machines, POS (Point of Sale) printers and barcode printers. 
       FIG. 1  is a schematic side view illustrating a conventional thermal transfer printing device. As shown in  FIG. 1 , the conventional thermal transfer printing device  1  comprises a casing  10 , a thermal transfer paper  11 , a thermal transfer printing module  12 , a transport roller assembly  13 , and an ejecting roller assembly  14 . Generally, the thermal transfer paper  11  is wound as a paper roll for storage, and disposed within the casing  10 . The thermal transfer paper  11  has a first end  111  in contact with the transport roller assembly  13 . The transport roller assembly  13  is contacted with the thermal transfer paper  11  for transporting the thermal transfer paper  11  to the thermal transfer printing module  12 . The thermal transfer printing module  12  is arranged downstream of the transport roller assembly  13  for printing an image on the thermal transfer paper  11 . The thermal transfer printing module  12  comprises a thermal print head  121  and a print roller  122 . The thermal print head  121  is used for heating a coating (not shown) and allowing the coating to be adsorbed on the thermal transfer paper, thereby printing out the image. The print roller  122  is disposed under the thermal print head  121 . The print roller  122  is used for transporting the thermal transfer paper  11  and pressing the thermal transfer paper  11 . Consequently, the thermal transfer paper  11  is smoothly transported across the region under the thermal print head  121  while maintaining the printing performance. The ejecting roller assembly  14  is arranged downstream of the thermal transfer printing module  12  for ejecting the thermal transfer paper  11  out of the casing  10 . 
     A process of printing the thermal transfer paper  11  by the thermal transfer printing module  12  will be illustrated as follows. Firstly, the first end  111  of the thermal transfer paper  11  is transported across and printed by the thermal transfer printing module  12 . After the first end  111  of the thermal transfer paper  11  has been printed, the first end  111  of the thermal transfer paper  11  is continuously transported to the ejecting roller assembly  14 , and a middle segment  112  of the thermal transfer paper  11  is continuously printed by the thermal transfer printing module  12 . At this moment, the first end  111  of the thermal transfer paper  11  is transported by the ejecting roller assembly  14 , and the middle segment  112  of the thermal transfer paper  11  is transported by the print roller  122 . Moreover, the middle segment  112  of the thermal transfer paper  11  is transported by the print roller  122  at a first speed, and the first end  111  of the thermal transfer paper  11  is transported by the ejecting roller assembly  14  at a second speed. Ideally, the transporting speeds of the print roller  122  and the ejecting roller assembly  14  are equal. In practice, since the components of the thermal transfer printing device  1  have respective allowable tolerances, the accumulated allowable tolerance of the combined components will be increased. Consequently, the thermal transfer paper  11  is transported by ejecting roller assembly  14  at the second speed, which is slightly slower than the first speed. 
     Since the speed of transporting the first end  111  of the thermal transfer paper  11  is slower than the speed of transporting the middle segment  112  of the thermal transfer paper  11 , the portion of the thermal transfer paper  11  between the first end  111  and the middle segment  112  is readily upturned during the printing process (see  FIG. 1 ). Since the thermal transfer paper  11  is upturned, the thermal transfer paper  11  fails to be smoothly transported. Under this circumstance, the printing performance of the thermal transfer printing device  1  is deteriorated. 
     Therefore, there is a need of providing a thermal transfer printing device with enhanced printing performance. 
     SUMMARY OF THE INVENTION 
     The present invention provides a thermal transfer printing device with enhanced printing performance. 
     In accordance with an aspect of the present invention, there is provided a thermal transfer printing device. The thermal transfer printing device includes a thermal transfer printing module and a paper ejecting module. The thermal transfer printing module is for printing a thermal transfer paper. The paper ejecting module is arranged downstream of the thermal transfer printing module for outputting the thermal transfer paper. The paper ejecting module includes a D-shaped ejecting roller, a driving gear, a switching roller, a spring, and a stopper. The D-shaped ejecting roller is used for transporting the thermal transfer paper. The driving gear is connected with the D-shaped ejecting roller. The driving gear is not synchronously rotated with the D-shaped ejecting roller. The driving gear is driven to be rotated in a first rotating direction or a second rotating direction. The switching roller is connected with the D-shaped ejecting roller and synchronously rotated with the D-shaped ejecting roller for controlling whether the D-shaped ejecting roller is contacted with the thermal transfer paper or not. The spring is connected with the driving gear and the switching roller. In response to rotation of the driving gear, the spring provides a friction force to the switching roller, so that the switching roller is synchronously rotated with the driving gear. The stopper is disposed beside the switching roller. During the thermal transfer paper is printed by the thermal transfer printing module and the driving gear is rotated in the first rotating direction, the switching roller is stopped by the stopper from being rotated in the first rotating direction, so that the D-shaped ejecting roller is not contacted with the thermal transfer paper. After the thermal transfer paper has been printed and the driving gear is driven in the second rotating direction, in response to the friction force, the switching roller and the D-shaped ejecting roller are rotated in the second rotating direction, so that the D-shaped ejecting roller is contacted with the thermal transfer paper to output the thermal transfer paper. 
     In an embodiment, the D-shaped ejecting roller includes a D-shaped wheel and a transmission shaft. The D-shaped wheel is selectively contacted with the thermal transfer paper. When the D-shaped wheel is contacted with the thermal transfer paper, the thermal transfer paper is transported by the D-shaped wheel. The transmission shaft is penetrated through the D-shaped wheel, the driving gear and the switching roller. 
     In an embodiment, the D-shaped wheel includes a flat surface and an arc-shaped surface. When the D-shaped ejecting roller stops rotation with the switching roller, the flat surface is not contacted with the thermal transfer paper. When the D-shaped ejecting roller is rotated in the second rotating direction in response to the friction force, the arc-shaped surface is contacted with the thermal transfer paper to output the thermal transfer paper. 
     In an embodiment, the paper ejecting module further includes an upper cover and an ejecting idler assembly. The transmission shaft and the driving gear are covered by the upper cover, but the D-shaped wheel is exposed outside the upper cover. The ejecting idler assembly is disposed under the D-shaped ejecting roller for assisting in outputting the thermal transfer paper. When the D-shaped ejecting roller stops rotation with the switching roller, a gap is defined between the D-shaped ejecting roller and the ejecting idler assembly. 
     In an embodiment, the ejecting idler assembly includes an idler wheel and an idler spring. The idler wheel is disposed under the D-shaped ejecting roller for contacting the thermal transfer paper. The idler spring is used for providing an elastic force to the idler wheel, so that the thermal transfer paper is pressed by the idler wheel. 
     In an embodiment, the stopper includes a pivotal shaft and an extension arm. The pivotal shaft is disposed on the upper cover, and rotatable relative to the upper cover. The extension arm is extended from the pivotal shaft and permitted to be swung relative to the upper cover by using the pivotal shaft as a fulcrum. When the switching roller is rotated in the first rotating direction in response to the friction force, the extension arm is contacted with the switching roller to hinder rotation of the switching roller. When the switching roller is rotated in the second rotating direction, the extension arm is pushed by the switching roller, so that the extension arm is swung relative to the upper cover without hindering the switching roller from being rotated in the second rotating direction. 
     In an embodiment, the switching roller includes an outer surface and a notch. The outer surface is disposed on an outer periphery of the switching roller. When the switching roller is rotated in the second rotating direction, the stopper is pushed by the outer surface, so that the stopper is swung. During the stopper is swung, the stopper does not hinder the D-shaped ejecting roller from outputting the thermal transfer paper. The notch is disposed beside the outer surface. When the switching roller is rotated in the first rotating direction, the notch is contacted with the stopper, so that the switching roller is stopped by the stopper. 
     In an embodiment, a first terminal of the spring is sheathed and connected with the driving gear, and a second terminal of the spring is sheathed and connected with the switching roller. 
     In an embodiment, the thermal transfer printing device further includes an electrical energy storage element, a driving device, a transmission gear set, and a transport roller assembly. The electrical energy storage element is used for providing electricity. The driving device is connected with the electrical energy storage element. By acquiring the electricity from the electrical energy storage element, the driving device provides a motive power. The transmission gear set is connected with the driving device and the paper ejecting module for transmitting the motive power to the driving gear, so that the driving gear is rotated in the first rotating direction or the second rotating direction. The transport roller assembly is arranged upstream of the thermal transfer printing module for contacting the thermal transfer paper, thereby transporting the thermal transfer paper to the thermal transfer printing module. 
     In an embodiment, the thermal transfer printing module includes a thermal print head and a print roller. The thermal print head is used for heating the thermal transfer paper, thereby printing the thermal transfer paper. The print roller is disposed under the thermal print head. During the thermal transfer paper is printed by the thermal transfer printing module, the thermal transfer paper is transported and pressed by the print roller. 
     The above objects and advantages of the present invention will become more readily apparent to those ordinarily skilled in the art after reviewing the following detailed description and accompanying drawings, in which: 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic side view illustrating a conventional thermal transfer printing device; 
         FIG. 2  is a schematic side view illustrating a thermal transfer printing device according to an embodiment of the present invention, in which the thermal transfer printing device is in a printing status; 
         FIG. 3  is a schematic perspective view illustrating a paper ejecting module of a thermal transfer printing device according to an embodiment of the present invention; 
         FIG. 4  is a schematic exploded view illustrating the paper ejecting module of  FIG. 3 ; and 
         FIG. 5  is a schematic side view illustrating a thermal transfer printing device according to an embodiment of the present invention, in which the thermal transfer printing device is in a paper-ejecting status. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     For obviating the drawbacks encountered from the prior art, the present invention provides a thermal transfer printing device with enhanced printing performance. 
       FIG. 2  is a schematic side view illustrating a thermal transfer printing device according to an embodiment of the present invention, in which the thermal transfer printing device is in a printing status. As shown in  FIG. 2 , the thermal transfer printing device  2  comprises a thermal transfer printing module  21 , a paper ejecting module  22 , a driving device  23 , a transmission gear set  24 , a transport roller assembly  25 , and an electrical energy storage element  26 . The thermal transfer printing module  21  is disposed within the thermal transfer printing device  2  for printing an image on a thermal transfer paper  20 . The thermal transfer paper  20  is wound as a paper roll, and disposed within the thermal transfer printing device  2 . The paper ejecting module  22  is arranged downstream of the thermal transfer printing module  21  for ejecting the thermal transfer paper  20  out of the thermal transfer printing device  2 . The electrical energy storage element  26  is used for providing electricity. The driving device  23  is connected with the electrical energy storage element  26  through a power wire (not shown). By acquiring the electricity from the electrical energy storage element  26 , the driving device  23  provides a motive power. The transmission gear set  24  is connected with the driving device  23  and the paper ejecting module  22 . Through the transmission gear set  24 , the motive power from the driving device  23  is transmitted to the paper ejecting module  22 . In this embodiment, the electrical energy storage element  26  is a battery, and the driving device  23  is a driving motor. The transport roller assembly  25  is arranged upstream of the thermal transfer printing module  21 . The transport roller assembly  25  is contacted with the thermal transfer paper  20  for transporting the thermal transfer paper  20  to the thermal transfer printing module  21 . 
     Please refer to  FIG. 2  again. The thermal transfer printing module  21  comprises a thermal print head  211  and a print roller  212 . The thermal print head  211  is used for heating a coating (not shown) and allowing the coating to be adsorbed on the thermal transfer paper  20 , thereby printing out the image. The print roller  212  is disposed under the thermal print head  211 . During the thermal transfer paper  20  is printed by the thermal transfer printing module  21 , the print roller  212  is used for transporting the thermal transfer paper  20  and pressing the thermal transfer paper  20 . Consequently, the thermal transfer paper  20  can be smoothly transported across the region under the thermal print head  211  while maintaining the printing performance. The paper ejecting module  22  is arranged downstream of the thermal transfer printing module  21  for outputting the thermal transfer paper  20 . 
     Hereinafter, the paper ejecting module  22  will be illustrated in more details with reference to  FIG. 3 .  FIG. 3  is a schematic perspective view illustrating a paper ejecting module of a thermal transfer printing device according to an embodiment of the present invention. The paper ejecting module  22  comprises a D-shaped ejecting roller  221 , a driving gear  222 , a switching roller  223 , a spring  224  (see  FIG. 4 ), a stopper  225 , an upper cover  226 , and an ejecting idler assembly  227 . The driving gear  222  is connected with the D-shaped ejecting roller  221 . Moreover, the driving gear  222  is not synchronously rotated with the D-shaped ejecting roller  221 . The switching roller  223  is connected with the D-shaped ejecting roller  221 , and synchronously rotated with the D-shaped ejecting roller  221 . The spring  224  is arranged between the driving gear  222  and the switching roller  223 , and connected with the driving gear  222  and the switching roller  223 . The D-shaped ejecting roller  221  and the driving gear  222  are covered by the upper cover  226 . The stopper  225  is disposed on the upper cover  226 , and disposed beside the switching roller  223 . The stopper  225  may be swung relative to the upper cover  226 . The ejecting idler assembly  227  is disposed under the D-shaped ejecting roller  221 . The ejecting idler assembly  227  comprises an idler wheel  2271  and an idler spring  2272 . 
     As shown in  FIG. 3 , the driving device  23  is connected with the transmission gear set  24 . In addition, the transmission gear set  24  is engaged with the driving gear  222 , so that the motive power from the driving device  23  may be transmitted to the driving gear  222 . In such way, the driving gear  222  may be rotated in a first rotating direction C 1  or a second rotating direction C 2 . 
     Hereinafter, the detailed structures of the paper ejecting module  22  will be illustrated with reference to  FIG. 4 .  FIG. 4  is a schematic exploded view illustrating the paper ejecting module of  FIG. 3 . The D-shaped ejecting roller  221  is used for transporting the thermal transfer paper  20 . The D-shaped ejecting roller  221  comprises a D-shaped wheel  2211  and a transmission shaft  2212 . The D-shaped wheel  2211  is selectively contacted with the thermal transfer paper  20 . Once the D-shaped wheel  2211  is contacted with the thermal transfer paper  20 , the thermal transfer paper  20  is transported by the D-shaped wheel  2211 . The transmission shaft  2212  is penetrated through the D-shaped wheel  2211 , the driving gear  222  and the switching roller  223 . The switching roller  223  is fixed on the transmission shaft  2212 , so that the switching roller  223  is synchronously rotated with the D-shaped ejecting roller  221 . The driving gear  222  is not fixed on the transmission shaft  2212 , so that the driving gear  222  is rotatable relative to the transmission shaft  2212 . The transmission shaft  2212  of the D-shaped ejecting roller  221  is covered by the upper cover  226 , but the D-shaped wheel  2211  is exposed outside the upper cover  226 . 
     Please refer to  FIGS. 3 and 4  again. The switching roller  223  is used for controlling whether the D-shaped ejecting roller  221  is contacted with the thermal transfer paper  20  or not. In response to rotation of the driving gear  222 , the spring  224  is twisted to provide a friction force to the switching roller  223 . In response to the friction force, the switching roller  223  is synchronously rotated with the driving gear  222 . The operating mechanism of generating the friction force by the spring  224  will be illustrated as follows. Firstly, a first terminal  2241  of the spring  224  is sheathed and connected with the driving gear  222 , and a second terminal  2242  of the spring  224  is sheathed and connected with the switching roller  223 . Upon rotation of the driving gear  222 , the spring  224  is correspondingly twisted. As the spring  224  is twisted, a friction force between the second terminal  2242  of the spring  224  and the switching roller  223  is generated. In response to the friction force, the switching roller  223  is rotated. 
     The stopper  225  is disposed on the upper cover  226  and contacted with the switching roller  223  for stopping the switching roller  223  from being rotated in the first rotating direction C 1 . The stopper  225  comprises a pivotal shaft  2251  and an extension arm  2252 . The stopper  225  is disposed on the upper cover  226  through the pivotal shaft  2251 . Moreover, the pivotal shaft  2251  is rotatable relative to the upper cover  226 . The extension arm  2252  is extended from the pivotal shaft  2251 . In addition, the extension arm  2252  may be swung relative to the upper cover  226  by using the pivotal shaft  2251  as a fulcrum. In this embodiment, the pivotal shaft  2251  and the extension arm  2252  are integrally formed. 
     Please refer to  FIG. 4  again. The switching roller  223  comprises an outer surface  2231  and a notch  2232 . The outer surface  2231  is disposed on an outer periphery of the switching roller  223 . In a case that the switching roller  223  is rotated in the second rotating direction C 2 , the stopper  225  is pushed by the outer surface  2231  of the switching roller  223 , so that the extension arm  2252  of the stopper  225  is swung. Moreover, during the extension arm  2252  is swung, the extension arm  2252  is not contacted with the switching roller  223 . Consequently, the rotation of the switching roller  223  and the rotation of the D-shaped ejecting roller  221  will not be hindered by the extension arm  2252 . The notch  2232  is disposed beside the outer surface  2231 . In a case that the switching roller  223  is rotated in the first rotating direction C 1 , the notch  2232  is contacted with the extension arm  2252  of the stopper  225 . Under this circumstance, since the switching roller  223  is stopped by the stopper  225 , the rotation of the switching roller  223  and the rotation of the D-shaped ejecting roller  221  are stopped. 
     The D-shaped wheel  2211  of the D-shaped ejecting roller  221  comprises a flat surface  2211 A and an arc-shaped surface  2211 B. In a case that the D-shaped ejecting roller  221  stops rotation with the switching roller  223 , the flat surface  2211 A of the D-shaped wheel  2211  and the ejecting idler assembly  227  under the D-shaped wheel  2211  are separated from each other by a gap G (see  FIG. 3 ). Whereas, in a case that the D-shaped ejecting roller  221  is rotated in the second rotating direction C 2  in response to the friction force, the arc-shaped surface  2211 B is contacted with the thermal transfer paper  20  to output the thermal transfer paper  20 . The ejecting idler assembly  227  is used to assist in outputting the thermal transfer paper  20 . The idler wheel  2271  of the ejecting idler assembly  227  is disposed under the D-shaped ejecting roller  221  for contacting the thermal transfer paper  20 . The idler spring  2272  is used for providing an elastic force to the idler wheel  2271 . When the D-shaped ejecting roller  221  is contacted with the thermal transfer paper  20 , the elastic force causes the idler wheel  2271  to press the thermal transfer paper  20 , thereby smoothly outputting the thermal transfer paper  20 . 
     The operations of the thermal transfer printing device will be illustrated as follows. Please refer to  FIGS. 2 and 3  again. For printing the thermal transfer paper  20  by the thermal transfer printing module  21 , a first end  201  of the thermal transfer paper  20  is firstly contacted with the transport roller assembly  25 , so that the thermal transfer paper  20  is transported to the thermal transfer printing module  21  by the transport roller assembly  25 . Then, the first end  201  of the thermal transfer paper  20  is pressed by the print roller  212 . Consequently, the first end  201  of the thermal transfer paper  20  is smoothly transported by the print roller  212 , and the first end  201  of the thermal transfer paper  20  may be printed by the thermal print head  211 . At the moment when the first end  201  of the thermal transfer paper  20  is printed by the thermal transfer printing module  21 , the motive power generated by the driving device  23  is transmitted to the driving gear  222  through the transmission gear set  24 , so that the driving gear  222  is rotated in the first rotating direction C 1 . As the driving gear  222  is rotated in the first rotating direction C 1 , the spring  24  connected with the driving gear  222  is twisted, so that the spring  24  provides a friction force to the switching roller  223 . In response to the friction force, the switching roller  223  is synchronously rotated with the driving gear  222  in the first rotating direction C 1 . Similarly, the D-shaped ejecting roller  221  and the switching roller  223  are synchronously rotated in the first rotating direction C 1 . 
     In a case that the switching roller  223  is rotated in the first rotating direction C 1 , the notch  2232  is contacted with the extension arm  2252  of the stopper  225 . Since the D-shaped ejecting roller  221  and the switching roller  223  are hindered by the extension arm  2252  from being continuously rotated in the first rotating direction C 1 , the rotation of the D-shaped ejecting roller  221  and the rotation of the switching roller  223  are stopped. Since the switching roller  223  is hindered by the extension arm  2252  from being continuously rotated, the spring  24  on the switching roller  223  results in idle running. Moreover, the driving gear  222  is continuously rotated in the first rotating direction C 1 . Under this circumstance, the flat surface  2211 A of the D-shaped ejecting roller  221  is rotated to face the underlying ejecting idler assembly  227 . Meanwhile, a gap G is defined between the flat surface  2211 A and the ejecting idler assembly  227 . After the first end  201  of the thermal transfer paper  20  has been printed, the first end  201  of the thermal transfer paper  20  is continuously transported to the paper ejecting module  22 . Meanwhile, a middle segment  202  of the thermal transfer paper  20  is transported to the thermal transfer printing module  21  by the transport roller assembly  25 . At the same time, the first end  201  of the thermal transfer paper  20  is transported across the gap G between the flat surface  2211 A and the ejecting idler assembly  227 , but is not contacted with the D-shaped wheel  2211 . On the other hand, since the middle segment  202  of the thermal transfer paper  20  is pressed by the print roller  212 , the middle segment  202  of the thermal transfer paper  20  can be smoothly transported by the print roller  212 . 
     During the process of printing the middle segment  202  of the thermal transfer paper  20 , since the first end  201  of the thermal transfer paper  20  is not contacted with the D-shaped wheel  2211 , the first end  201  of the thermal transfer paper  20  is not transported by the D-shaped wheel  2211 . In other words, the middle segment  202  of the thermal transfer paper  20  is only transported by the print roller  212  in order to be printed. Under this circumstance, since the problem of resulting in the speed difference of different rollers is eliminated, the printing performance will not be deteriorated. 
       FIG. 5  is a schematic side view illustrating a thermal transfer printing device according to an embodiment of the present invention, in which the thermal transfer printing device is in a paper-ejecting status. Please refer to  FIGS. 4 and 5 . After the middle segment  202  of the thermal transfer paper  20  has been printed, the driving device  23  is reversely rotated to output the motive power. The motive power is transmitted to the driving gear  222  through the transmission gear set  24 , so that the driving gear  222  is rotated in the second rotating direction C 2 . As the driving gear  222  is rotated in the second rotating direction C 2 , the spring  24  connected with the driving gear  222  is twisted, so that the spring  24  provides a friction force to the switching roller  223 . In response to the friction force, the switching roller  223  is synchronously rotated with the driving gear  222  in the second rotating direction C 2 . Similarly, the D-shaped ejecting roller  221  and the switching roller  223  are synchronously rotated in the second rotating direction C 2 . 
     In a case that the switching roller  223  is rotated in the second rotating direction C 2  and the outer surface  2231  of the switching roller  223  is contacted with the extension arm  2252  of the stopper  225 , the extension arm  2252  is pushed by the outer surface  2231 . Consequently, the extension arm  2252  is swung relative to the upper cover  226  by using the pivotal shaft  2251  as a fulcrum. In addition, the extension arm  2252  is swung to the location where the outer surface  2231  is not contacted with the extension arm  2252 . Consequently, the rotation of the switching roller  223  in the second rotating direction C 2  is not hindered by the extension arm  2252 . That is, the rotation of the D-shaped ejecting roller  221  is not hindered. 
     Under this circumstance, the arc-shaped surface  2211 B of the D-shaped ejecting roller  221  is rotated to face the underlying ejecting idler assembly  227 . Consequently, the arc-shaped surface  2211 B of the D-shaped ejecting roller  221  is contacted with the first end  201  of the thermal transfer paper  20 , and the first end  201  of the thermal transfer paper  20  is transported and outputted by the D-shaped ejecting roller  221 . At the same time, the ejecting idler assembly  227  assists in outputting the first end  201  of the thermal transfer paper  20 . The D-shaped ejecting roller  221  is continuously rotated in the second rotating direction C 2  until the middle segment  202  of the thermal transfer paper  20  is outputted. 
     For printing the subsequent segment of the thermal transfer paper  20 , the driving gear  222  is reversely rotated in the first rotating direction C 1  again. As the driving gear  222  is rotated in the first rotating direction C 1 , the spring  24  connected with the driving gear  222  is twisted, so that the spring  24  provides a friction force to the switching roller  223 . In response to the friction force, the switching roller  223  is synchronously rotated with the driving gear  222  in the first rotating direction C 1 . Similarly, the D-shaped ejecting roller  221  is also rotated in the first rotating direction C 1 . As shown in  FIG. 4 , the extension arm  2252  of the stopper  225  has a curvy profile. Consequently, as the switching roller  223  is rotated in the first rotating direction C 1 , the notch  2232  of the switching roller  223  will be contacted with the curvy extension arm  2252 . Consequently, the extension arm  2252  is swung relative to the upper cover  226  by using the pivotal shaft  2251  as a fulcrum. In addition, the extension arm  2252  is swung to a location where the notch  2232  is stopped by the extension arm  2252 . Until the notch  2232  is contacted with the extension arm  2252  again, the extension arm  2252  is stopped by the extension arm  2252 . Under this circumstance, the D-shaped wheel  2211  is not contacted with the thermal transfer paper  20 , so that the thermal transfer paper  20  is printed by the thermal transfer printing module  21 . 
     From the above description, the present invention provides a thermal transfer printing device. The operations of the driving gear, the switching roller, the stopper and the D-shaped ejecting roller are controlled according to the friction force generated by the spring. In a case that the thermal transfer printing device of the present invention is in the printing status, the D-shaped ejecting roller is not contacted with the thermal transfer paper. Since the printing task of the subsequent segment of the thermal transfer paper is not adversely affected, the printing quality is enhanced. In a case that the thermal transfer printing device of the present invention is in the paper-ejecting status, the D-shaped ejecting roller is switched to be contacted with the thermal transfer paper in order to output the thermal transfer paper. As a consequence, the thermal transfer printing device of the present invention can provides enhanced printing performance in order to meet the user&#39;s demand. 
     While the invention has been described in terms of what is presently considered to be the most practical and preferred embodiments, it is to be understood that the invention needs not be limited to the disclosed embodiment. On the contrary, it is intended to cover various modifications and similar arrangements included within the spirit and scope of the appended claims which are to be accorded with the broadest interpretation so as to encompass all such modifications and similar structures.