Abstract:
An ink ribbon positioning system of a color printer for identifying various positions of a color ink ribbon of the color printer. The ink ribbon includes a plurality of sequentially arranged color frames for storing different color dyes. The color printer includes a thermal print head for printing the color dyes onto an object and a driving device for scrolling the ink ribbon relative to the thermal print head. The ink ribbon positioning system includes first and second light sources for emitting light beams through the ink ribbon, an optical sensor for detecting the light beams penetrating through the ink ribbon, and an identification device electrically connected to the first and the second light sources. When the driving device scrolls the ink ribbon relative to the thermal print head, the identification device will control the first and the second light sources and identify the position of each of the color frames of the ink ribbon according to an output voltage generated by the optical sensor.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to an ink ribbon positioning system, and more particularly, to an ink ribbon positioning system for identifying various positions of a color ink ribbon of a color printer, such as a thermal printer. 
     2. Description of the Prior Art 
     Please refer to FIG.  1 . FIG. 1 is a perspective view of a prior art ink ribbon positioning system  10 . The ink ribbon positioning system  10  is used for identifying the position of a color ink ribbon  11  of a color printer (not shown). The ink ribbon  11  comprises a plurality of sequentially arranged transparent color frames  14 ,  16 ,  18  for storing yellow, magenta, and cyan dyes. The ink ribbon  11  further comprises a plurality of sequentially arranged strip areas  20 ,  22 ,  24  separately installed next to each of the color frames  14 ,  16 ,  18 . The strip area  20  is an opaque area installed between the yellow and cyan color frames  14 ,  18 . The strip area  22  has a top transparent portion and a bottom opaque portion and is installed between the yellow and magenta color frames  14 ,  16 . The strip area  24  also has a top transparent portion and a bottom opaque portion and is installed between the magenta and cyan color frames  16 ,  18 . 
     The ink ribbon positioning system  10  further comprises two light sources  26 ,  28  arranged along the way perpendicular to scrolling direction on one side of the ink ribbon  11 , and two corresponding sensors  30 ,  32  installed on another side of the ink ribbon  11 . The position of the ink ribbon  11  is identified through the strip areas  20 ,  22 ,  24 . The detection of the strip area  20  by the sensors  30 ,  32  corresponds to the beginning of a new yellow color frame  14  of the ink ribbon  11 . The detection of the partially opaque area  22  or  24  by the sensors  30 ,  32  corresponds to the beginning of the magenta or cyan color frame  16 ,  18  of the ink ribbon  11 . Because the ink ribbon positioning system  10  is installed with two sets of light sources  26 ,  28  and sensors  30 ,  32  for detecting the position of the ink ribbon  11 , it&#39;s production cost is very high. In addition, the light sources  26 ,  28  must be always on together so that the position of the ink ribbon  11  can be detected by the sensors  30 ,  32 . This makes the system not very flexible. 
     SUMMARY OF THE INVENTION 
     It is therefore a primary objective of the present invention to provide an ink ribbon positioning system to solve the above mentioned problem. 
     Briefly, in a preferred embodiment, the present invention provides an ink ribbon positioning system of a color printer for identifying various positions of a color ink ribbon of the color printer. The ink ribbon comprises a plurality of sequentially arranged color frames for storing different color dyes. The color printer comprises a thermal print head for printing the color dyes onto an object and a driving device for scrolling the ink ribbon relative to the thermal print head. The ink ribbon positioning system comprises: 
     a first light source for emitting a first light beam through the ink ribbon; 
     a second light source for emitting a second light beam through the ink ribbon; 
     an optical sensor for detecting the first and second light beams penetrating through the ink ribbon and generating an output voltage; and 
     an identification device electrically connected to the first and the second light sources; 
     wherein when the driving device scrolls the ink ribbon relative to the thermal print head, the identification device will control the first and the second light sources and identify the position of each of the color frames of the ink ribbon according to the output voltage generated by the optical sensor. 
     It is an advantage of the present invention that the ink ribbon positioning system only comprises one optical sensor. Thus, the number of components of the color printer is reduced and the production cost is lowered. In addition, it is not necessary for the light sources to be always on together. This substantially makes the system flexible. 
     These and other objectives and advantages of the present invention will no doubt become obvious to those of ordinary skill in the art after having read the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a prior art ink ribbon positioning system. 
     FIG. 2 is a perspective view of an ink ribbon positioning system according to the present invention. 
     FIG. 3 is a block diagram of a present invention color printer. 
     FIG. 4 is a time sequence diagram of the ink ribbon positioning system shown in FIG  2 . 
     FIG. 5 is a time sequence diagram of a present invention second embodiment according to the ink ribbon positioning system shown in FIG.  2 . 
     FIG. 6 is a time sequence diagram of a present invention third embodiment according to the ink ribbon positioning system shown in FIG.  2 . 
     FIG. 7 is a time sequence diagram of a present invention fourth embodiment according to the ink ribbon positioning system shown in FIG.  2 . 
     FIG. 8 is a time sequence diagram of a present invention fifth embodiment according to the ink ribbon positioning system shown in FIG.  2 . 
     FIG. 9 is a time sequence diagram of a present invention sixth embodiment according to the ink ribbon positioning system shown in FIG.  2 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Please refer to FIGS. 2 and 3. FIG. 2 is a perspective view of an ink ribbon positioning system  40  according to the present invention. FIG. 3 is a functional block diagram of a present invention color printer  54 . The ink ribbon positioning system  40  is used to identify the position of a color ink ribbon  42  of the color printer  54 . The ink ribbon  42  comprises a plurality of sequentially arranged color frames  46 ,  48 ,  50  for separately storing yellow, magenta, and cyan dyes. 
     The color printer  54  comprises a thermal print head  74  that uses the color dyes stored in the color frames to form color images onto the receiver. It also comprises a driving device  72  for scrolling the ink ribbon  42  related to the thermal print head  74 . 
     The ink ribbon positioning system  40  comprises a green light source  62  and a red light source  64  installed on one side of the ink ribbon  42 , an optical sensor  66  installed on the opposite side of the ink ribbon  42 , and an identification device  68  electrically connected to the two light sources  62 ,  64  and the optical sensor  66 . The two light sources  62 ,  64  emit two light beams  63 ,  65  of different colors towards the ink ribbon  42 . The optical sensor  66  (photosensor) detects the two light beams  63 ,  65  that pass through the ink ribbon  42  and generates a corresponding output voltage. The identification device  68  will control the state (on or off) of the two light sources  62 ,  64 , and thereby identify the current position of the color frames of the ink ribbon  42  by the output voltage generated by the optical sensor  66 . The identification device  68  will then generate the corresponding position signal. The two light beams  63 ,  65  emitted by the two light sources  62 ,  64  have different penetration rates for the three color frames  46 ,  48 ,  50 . Therefore, when the color frames pass by the optical sensor  66 , the optical sensor  66  will generate different output voltages according to which color frame is in front of the optical sensor  66  and the states of the two light sources  62 ,  64 . The identification device  68  comprises a comparator  70 . The comparator  70  compares the output voltages induced by the optical sensor  66  with a threshold voltage which is defined to identify the state during the ribbon positioning process, and generates comparison signals. Then the identification device  68  identifies the position of the color frames of the ink ribbon  42  according to these comparison signals, and generates the corresponding position signals offering to the control circuit  75 . 
     Please refer to FIG.  4 . FIG. 4 is a time sequence diagram of the ink ribbon positioning system  40  shown in FIG.  2 . When the ink ribbon  42  is scrolled along a predetermined direction by the driving device  72 , the identification device  68  will compare the output voltage generated by the optical sensor  66  with a threshold voltage to identify the position of the color frames of the ink ribbon  42 . Green light has a higher penetration rate for the yellow color frame  46  and a lower one for the magenta and cyan color frames  48 ,  50 . Hence, the light beam  63  through the ink ribbon  42  emitted by the green light source  62  can be used by the identification device  68  to identify the position of the yellow color frame  46  and the following magenta color frame  48 . Similarly, since red light has a higher penetration rate for the yellow and magenta color frames  46 ,  48  and a lower one for the cyan color frame  50 , the light beam  65  through the ink ribbon  42  emitted by the red light source  64  can be used by the identification device  68  to identify the position of the magenta color frame  48  and the following cyan color frame  50 . When the identification device  68  has identified the position of the yellow color frame  46 , the identification device  68  will keep the green light source  62  ON and the red light source  64  OFF. Thus, only the green light beam  63  penetrates through the ink ribbon  42 , and the identification device  68  can identify the position of the magenta color frame  48  that follows the yellow color frame  46  by comparing the output voltage of the optical sensor  66  to the threshold voltage. From this comparison, the identification device  68  generates the corresponding position signal. When the identification device  68  recognizes the presence of the magenta color frame  48 , it will turn off the green light source  62  and turn on the red light source  64 . Thus, only the red light beam  65  penetrates through the ink ribbon  42 , and the identification device  68  can identify the position of the cyan color frame  50  that follows the magenta color frame  48  by again comparing the output voltage from the optical sensor  66  to the threshold voltage. From this comparison the corresponding position signals are generated. The detailed operating time sequence is described as following: 
     1. Turn on the green light source  62 , detect the output voltage generated by the optical sensor  66 , and scroll the ink ribbon  42 . When the output voltage goes from low to high the initialization step is complete. These events occur around the time marked t 1 . 
     2. Continually scroll the ink ribbon  42  to make the color frames pass by the optical sensor  66 . When the ink ribbon  42  moves from the yellow color frame  46  to the magenta  48  with respect to the optical sensor  66 , because the green light has a lower penetration rate for the magenta color frame  48 , the output voltage will go from high to low. Interpret the output voltage drop as the magenta color frame  48  arrival signal. These events occur around the time marked t 2 . 
     3. At time t 3 , turn on the red light source  64 . Since the red light has a higher penetration rate for the magenta color frame  48 , the output voltage of the optical sensor  66  will go from low to high. This variation of the output voltage is caused by a change of light source rather than a change of color frame. Hence, the variation of the output voltage will not be regarded by the identification device  68  as a color frame arrival signal. 
     4. At time t 4 , turn off the green light source  62 . The output voltage of the optical sensor  66  will remain high. 
     5. When the ink ribbon  42  is moved from the magenta color frame  48  to the cyan one  50  with respect to the optical sensor  66 , because the red light has a lower penetration rate for the cyan color frame  50 , the output voltage will go from high to low. Interpret the output voltage drop as the cyan color frame  50  arrival signal. These events occur around the time marked t 5 . 
     6. At time t 6 , turn on the green light source  62 . The output voltage of the optical sensor  66  will remain low. 
     7. At time t 7 , turn off the red light source  64 . The output voltage of the optical sensor  66  will remain low. 
     8. When the ink ribbon  42  shifts from the cyan color frame  50  to the yellow one  46  with respect to the optical sensor  66 , the green light beam  63  again penetrates through the yellow color frame  46 , and the output voltage of the optical sensor  66  goes from low to high. Interpret the output voltage rise as the yellow color frame  46  arrival signal. These events occur around the time marked t 8 . 
     9. An identification cycle has been completed. Follow the same steps 2 through 8 repeatedly. 
     By the above-mentioned sequence of events, every time a new color frame arrives, the color frame arrival signal is compared to the threshold voltage and interpreted according to the present state of the identification device  68 . In this manner, the position of the ink ribbon  42  is identified. 
     Please refer to FIG.  5 . FIG. 5 is a time sequence diagram of a present invention second embodiment according to the ink ribbon positioning system  40  shown in FIG.  2 . The main difference between this second embodiment to the previous one is the arrangement of the color frames on the ink ribbon. On an ink ribbon  78  used in this embodiment, the color dyes stored in the sequentially arranged color frames  80 ,  82 ,  84 , and  86  are yellow, magenta, cyan, and black. In addition, there is a blank portion  88  between the cyan frames  84  and the black frame  86 . In this second embodiment, the green and red light sources  62 ,  64  are also used. Green light has a higher penetration rate for the yellow color frame  80  and the blank portion  88 ; a lower one for the magenta, cyan, and black color frames  82 ,  84 ,  86 . The red light has a higher penetration rate for the yellow and magenta color frames  80 ,  82  and the blank portion  88 ; a lower one for the cyan and black color frames  84 ,  86 . Thus, the identification process can be described as follows: 
     1. Turn on the green light source  62 , scroll the ink ribbon  78 , and detect the output voltage generated by the optical sensor  66 . When the output voltage goes from low to high, and if the time period that the output voltage remains high is longer than the time period required for the blank portion  88  to shift by, then interpret the output voltage change as the yellow color frame  80  arrival signal. The initialization step is complete. These events occur around the time marked t 11 . 
     2. Continually scroll the ink ribbon  78 . When the ink ribbon  78  is moved from the yellow color frame  80  to the magenta one  82 , because the green light has a lower penetration rate for the magenta color frame  82 , the output voltage will go from high to low. Interpret the output voltage drop as the magenta color frame  82  arrival signal. These events occur around the time marked t 12 . 
     3. At time t 13 , turn on the red light source  64 . Since the red light has a higher penetration rate for the magenta color frame  82 , the output voltage of the optical sensor  66  will go from low to high. This variation of the output voltage is caused by a change in light source rather than a change of color frame, and so the variation of the output voltage will not be regarded by the identification device  68  as a color frame arrival signal. 
     4. At time t 14 , turn off the green light source  62 . The output voltage of the optical sensor  66  will remain high. 
     5. When the ink ribbon  78  moves from the magenta color frame  82  to the cyan one  84 , because the red light has a lower penetration rate for the cyan color frame  84 , the output voltage will go from high to low. Interpret the output voltage drop as the cyan color frame  84  arrival signal. These events occur around the time marked t 15 . 
     6. When the ink ribbon  78  moves from the cyan color frame  84  to the blank portion  88 , the output voltage goes from low to high. This variation of the output voltage will not be regarded by the identification device  68  as a color frame arrival signal. These events occur around the time marked t 16 . 
     7. When the ink ribbon  78  moves from the blank portion  88  to the black color frame  86 , the output voltage goes from high to low. Interpret the output voltage drop as the black color frame  86  arrival signal. These events occur around the time marked t 17 . 
     8. At time t 18 , turn on the green light source  62 . The output voltage of the optical sensor  66  will remain low. 
     9. At time t 19 , turn off the red light source  64 . The output voltage of the optical sensor  66  will remain low. 
     10. When the ink ribbon  78  shifts from the black color frame  86  to the yellow one  80 , the green light beam  63  again penetrates through the yellow color frame  80 , and the output voltage of the optical sensor  66  goes from low to high. Interpret the output voltage rise as the yellow color frame  80  arrival signal. These events occur around the time marked t 20 . 
     11. An identification cycle has been completed. Follow the same steps repeatedly. In this manner, every color frame&#39;s arrival signal is obtained so that the position of the ink ribbon  78  can be identified. 
     In addition, in this second embodiment, because the red light has a higher penetration rate for both the yellow and magenta frames, the blank portion  88  could be replaced by either a yellow color frame or a magenta color frame. What is important is that there is a frame following the cyan frame  84  that the red light can penetrate to make the sensor voltage go high. 
     Please refer to FIG.  6 . FIG. 6 is a time sequence diagram of a present invention third embodiment according to the ink ribbon positioning system  40  shown in FIG.  2 . An ink ribbon  90  used in the third embodiment also comprises a plurality of sequentially arranged color frames  92 ,  94 ,  96  that store yellow, magenta, and cyan dyes respectively. However, there is an additional overcoating frame  98  that follows the cyan color frame  96 . In the third embodiment, green and blue light sources  62 ,  102  are used. Green light has a higher penetration rate for the yellow color frame  92  and the overcoating frame  98 ; a lower one for the magenta and cyan color frames  94 ,  96 . Blue light has a higher penetration rate for the cyan color frame  96  and the overcoating frame  98 ; a lower one for the yellow and magenta color frames  92 ,  94 . Thus, the identification process can be described as follows: 
     1. Turn on the blue light source  102 , detect the output voltage generated by the optical sensor  66 , and scroll the ink ribbon  90 . When output voltage goes from high to low, interpret the output voltage drop as the yellow color frame  92  arrival signal. The initialization step is then complete. These events occur around the time marked t 21 . 
     2. At time t 22 , turn on the green light source  62 , and the output voltage of the optical sensor  66  will go from low to high. This variation of the output voltage is caused by a change of light source rather than a change of color frame, so the variation of the output voltage will not be regarded by the identification device  68  as the color frame arrival signal. 
     3. At time t 23 , turn off the blue light source  102 . The output voltage of the optical sensor  66  will remain high. 
     4. When the ink ribbon  90  moves from the yellow color frame  92  to the magenta color frame  94 , because the green light has a lower penetration rate for the magenta color frame  94 , the output voltage will go from high to low. Interpret the output voltage drop as the magenta color frame  94  arrival signal. These events occur around the time marked t 24 . 
     5. At time t 25 , turn on the blue light source  102 . The output voltage of the optical sensor  66  will remain low. 
     6. At time t 26 , turn off the green light source  62 . The output voltage of the optical sensor  66  will remain low. 
     7. When the ink ribbon  90  moves from the magenta color frame  94  to the cyan color frame  96 , because the blue light has a lower penetration rate for the magenta color frame  94  and a higher one for the cyan color frame  96 , the output voltage will go from low to high. Interpret the output voltage rise as the magenta color frame  96  arrival signal. These events occur around the time marked t 27 . 
     8. At time t 28 , turn on the green light source  62 . The output voltage of the optical sensor  66  will remain high. 
     9. At time t 29 , turn off the blue light source  102 . The output voltage of the optical sensor  66  will go from high to low. This variation of the output voltage is caused by a change of light source rather than a change of color frame, so the variation of the output voltage will not be regarded by the identification device  68  as the color frame arrival signal. 
     10. When the ink ribbon  90  moves from the cyan color frame  96  to the overcoating frame  98 , because the green light has a lower penetration rate for the cyan color frame  96  and a higher one for the overcoating frame  98 , the output voltage will go from low to high. Interpret the output voltage rise as the overcoating frame  98  arrival signal. These events occur around the time marked t 30 . 
     11. At time t 31 , turn on the blue light source  102 . The output voltage of the optical sensor  66  will remain high. 
     12. At time t 32 , turn off the green light source  62 . The output voltage of the optical sensor  66  will remain high. 
     13. When the ink ribbon  90  is scrolled from the overcoating frame  98  to the yellow color frame  92 , because the blue light has a higher penetration rate for the overcoating frame  98  and a lower one for the yellow color frame  92 , the output voltage of the optical sensor  66  goes from high to low. Interpret the output voltage drop as the yellow color frame  92  arrival signal. These events occur around the time marked t 33 . 
     14. An identification cycle has been completed. Follow the same steps repeatedly. In this manner, every color frame&#39;s arrival signal is obtained so that the position of the ink ribbon  90  can be identified. 
     Please refer to FIG.  7 . FIG. 7 is a time sequence diagram of a present invention fourth embodiment according to the ink ribbon positioning system  40  shown in FIG.  2 . An ink ribbon  104  used in the fourth embodiment comprises a plurality of sequentially arranged color frames  106 ,  108 ,  110  that store yellow, magenta, and cyan dyes respectively, and an overcoating frame  112  following the cyan color frame  110 . The difference between this fourth embodiment and the previous third embodiment is that there is an opaque region  114  following the overcoating frame  112 . In the fourth embodiment, the green light source  62  and the red light source  64 , rather than the expensive blue one, are used. The green light has a higher penetration rate for the yellow color frame  106  and the overcoating frame  112 ; a lower one for the magenta and cyan color frames  108 ,  110  and the opaque region  114 . The red light has a higher penetration rate for the yellow and magenta color frames  106 ,  108  and the overcoating frame  112 ; a lower one for the cyan color frame  110  and the opaque region  114 . Thus, the identification process can be described as follows: 
     1. Turn on the green light source  62 , scroll the ink ribbon  104 , and detect the output voltage generated by the optical sensor  66 . When the output voltage goes from high to low, briefly turn on the red light source  64 . If the output voltage remains low then the position of the ink ribbon  104  is in the opaque region  114 . The initialization step is then complete. However, if the output voltage goes from low to high when the red light source  64  is briefly turned on, then the position of the ink ribbon  104  is in the magenta color frame  108 . The ink ribbon  104  must be scrolled, and the initialization step will be complete when the ink ribbon  104  is in the opaque region  114 . 
     2. When the ink ribbon  104  is scrolled from the opaque region  114  to the yellow color frame  106 , the output voltage goes from low to high. Interpret the output voltage rise as the yellow color frame  106  arrival signal. These events occur around the time marked t 41 . 
     3. When the ink ribbon  104  is moved from the yellow color frame  106  to the magenta color frame  108 , the output voltage goes from high to low. Interpret the output voltage drop as the magenta color frame  108  arrival signal. These events occur around the time marked t 42 . 
     4. At time t 43 , turn on the red light source  64 . The output voltage of the optical sensor  66  will go from low to high. This variation of the output voltage is caused by a change of light source rather than a change of color frame, so the variation of the output voltage will not be regarded by the identification device  68  as a color frame arrival signal. 
     5. At time t 44 , turn off the green light source  62 . The output voltage of the optical sensor  66  will remain high. 
     6. When the ink ribbon  104  moves from the magenta color frame  108  to the cyan color frame  110 , the output voltage goes from high to low. Interpret the output voltage drop as the cyan color frame  110  arrival signal. These events occur around the time marked t 45 . 
     7. When the ink ribbon  104  is moved from the cyan color frame  110  to the overcoating frame  112 , the output voltage goes from low to high. Interpret the output voltage rise as the overcoating frame  112  arrival signal. These events occur around the time marked t 46 . 
     8. At time t 47 , turn on the green light source  62 . The output voltage of the optical sensor  66  will remain high. 
     9. At time t 48 , turn off the red light source  64 . The output voltage of the optical sensor  66  will remain high. 
     10. When the ink ribbon  104  moves from the overcoating frame  112  to the opaque region  114 , the output voltage goes from high to low. Interpret the output voltage drop as the opaque region  114  arrival signal. These events occur around the time marked t 49 . 
     11. When the ink ribbon  104  is moved from the opaque region  114  to the yellow color frame  106 , the output voltage goes from low to high. Interpret the output voltage rise as the yellow color frame  106  arrival signal. These events occur around the time marked t 50 . 
     12. An identification cycle has been completed. Follow the same steps repeatedly. In this manner, every color frame&#39;s arrival signal is obtained so that the position of the ink ribbon  104  can be identified. 
     In addition, in this embodiment, since both the red and green lights have lower penetration rates for the cyan color frame, the opaque region  114  could be replaced by a cyan color frame. In this manner, the production process of the ink ribbon  104  can be simplified and the production cost of the ink ribbon  104  can be lowered. Actually, not only a cyan color frame, but any color or material can be used as the opaque region  114  if both of the light sources have lower penetration rates for the adopted color or material. 
     Please refer to FIG.  8 . FIG. 8 is a time sequence diagram of a present invention fifth embodiment according to the ink ribbon positioning system  40  shown in FIG.  2 . The ink ribbon  42  used in the fifth embodiment is the same as the one used in the first embodiment shown in FIG. 3, and the green and red light sources  62 ,  64  are also used in this embodiment. The main difference between this embodiment and the previous embodiments is the initialization step. The initialization step used in the previous embodiments is to find the yellow color frame  46 , but the initialization step in the fifth embodiment involves finding the cyan color frame  50  first. When the ink ribbon positioning system is started, the position of the ink ribbon may happen to be in the yellow color frame, and thus the previous embodiments may find an incomplete yellow color frame  46 . This embodiment ensures that the yellow color frame  46  found is complete. In addition, in this embodiment, the two light sources  62 ,  64  are turned on in a non-overlapping matter to save energy and prolong the life of light sources. The green light has a higher penetration rate for the yellow color frame  46 ; a lower one for the magenta and cyan color frames  48 ,  50 . The red light has a higher penetration rate for the yellow and magenta color frames  46 ,  48 ; a lower one for the cyan color frame  50 . Thus, the identification process can be described as follows: 
     1. Turn on the red light source  64 , scroll the ink ribbon  42 , and detect the output voltage generated by the optical sensor  66 . If the output voltage is initially low, then the position of the ink ribbon  42  is in the cyan frame  50 . Continually scroll the ink ribbon  42 . When the output voltage goes from low to high, the ink ribbon  42  is in the yellow color frame  46  and the initialization step is complete. However, if the output voltage is initially high, then continually scroll the ink ribbon  42 ; when the output voltage goes from high to low, followed by a low to high, the ink ribbon  42  is then in the yellow color frame  46 . These events occur around the time marked t 51 . 
     2. At time t 52 , turn off the red light source  64 , and the output voltage of the optical sensor  66  will go from high to low. The variation of the output voltage is caused by a change of light source rather than a change of color frame, so the variation of the output voltage will not be regarded by the identification device  68  as the color frame arrival signal. 
     3. At time t 53 , turn on the green light source  62 , and the output voltage of the optical sensor  66  will go from low to high. The variation of the output voltage is caused by a change of light source rather than a change of color frame, so the variation of the output voltage will not be regarded by the identification device  68  as the color frame arrival signal. 
     4. When the ink ribbon  42  is moved from the yellow frame  46  to the magenta color frame  48 , the output voltage goes from high to low. Interpret the output voltage drop as the magenta color frame  48  arrival signal. These events occur around the time marked t 54 . 
     5. At time t 55 , turn off the green light source  62 . The output voltage of the optical sensor  66  will remain low. 
     6. At time t 56 , turn on the red light source  64 , and the output voltage of the optical sensor  66  will go from low to high. This variation of the output voltage will not be regarded by the identification device  68  as the color frame arrival signal. 
     7. When the ink ribbon  42  moves from the magenta frame  48  to the cyan color frame  50 , the output voltage goes from high to low. Interpret the output voltage drop as the cyan color frame  50  arrival signal. These events occur around the time marked t 57 . 
     8. At time t 58 , turn off the red light source  64 . The output voltage of the optical sensor  66  will remain low. 
     9. At time t 59 , turn on the red light source  64 . The output voltage of the optical sensor  66  will remain low. 
     10. When the ink ribbon  42  is moved from the cyan color frame  50  to the yellow color frame  46 , the output voltage goes from low to high. Interpret the output voltage rise as the yellow color frame  46  arrival signal. These events occur around the time marked t 60 . 
     11. An identification cycle has been completed. Follow the same steps repeatedly. In this manner, every color frame&#39;s arrival signal is obtained so that the position of the ink ribbon  42  can be identified. 
     Please refer to FIG.  9 . FIG. 9 is a time sequence diagram of a present invention sixth embodiment according to the ink ribbon positioning system  40  shown in FIG.  2 . The different colored light sources of the present invention are replaced by two light sources with the same color. The ink ribbon  42  used in the sixth embodiment is the same as the one used in the first embodiment shown in FIG. 3. A first white light source  122  and a second white light source  124  are used in this embodiment rather than the green and red light sources  62 ,  64 . In the first mode, only one white light source is on, and in the second mode both of the white light sources are on. Consequently, in the first more, the light is of a lower intensity, whereas in the second mode the intensity of the light is higher. Thus, the white light in the first mode has a higher penetration rate for the yellow color frames  46 ; a lower one for the magenta and cyan color frames  48 ,  50 . The white light in the second mode has a higher penetration rate for the yellow and magenta color frames  46 ,  48 ; a lower one for the cyan color frames  50 . The identification process can be described as follows: 
     1. Turn on the first white light source  122 , scroll the ink ribbon  42 , and detect the output voltage generated by the optical sensor  66 . When the output voltage goes from low to high, interpret the output voltage rise as the yellow color frame  46  arrival signal. The initialization step is then complete. These events occur around the time marked t 61 . 
     2. When the ink ribbon  42  is moved from the yellow color frame  46  to the magenta color frame  48 , because the white light in the first mode has a lower penetration rate for the magenta color frame  48 , the output voltage goes from high to low. Interpret the output voltage drop as the magenta color frame  48  arrival signal. These events occur around the time marked t 62 . 
     3. At time t 63 , turn on the second white light source  124 . Since the white light in the second mode has a higher penetration rate for the magenta color frame  48 , the output voltage of the optical sensor  66  will go from low to high. This variation of the output voltage is caused by a change of mode rather than a change of color frame, so the variation of the output voltage will not be regarded by the identification device  68  as the color frame arrival signal. 
     4. When the ink ribbon  42  is moved from the magenta color frame  48  to the cyan color frame  50 , the output voltage will go from high to low. Interpret the output voltage drop as the cyan color frame  50  arrival signal. These events occur around the time marked t 64 . 
     5. At time t 65 , turn off the first white light source  122 . The output voltage of the optical sensor  66  will remain low. 
     6. When the ink ribbon  42  is moved from the cyan color frame  50  to the yellow color frame  46 , the output voltage will go from low to high. Interpret the output voltage rise as the yellow color frame  46  arrival signal. These events occur around the time marked t 66 . 
     7. An identification cycle has been completed. Follow the same steps repeatedly. In this manner, every color frame&#39;s arrival signal is obtained so that the position of the ink ribbon  42  can be identified. 
     The sixth embodiment uses two white light sources  122 ,  124 . In fact, a light source of any color that has two operational intensities can achieve the same result. An adjustable red light source, for example, would satisfy this requirement if the red light in the low-intensity mode had a higher penetration rate for the yellow color frames  46 ; a lower one for the magenta and cyan color frames  48 ,  50 , and the red light in the high-intensity mode had a higher penetration rate for the yellow and magenta color frames  46 ,  48 ; a lower one for the cyan color frames  50 . 
     The embodiments mentioned in this invention only describe cases in which the light source and the optical sensor are installed on opposite sides of the ink ribbon. However, the light source and the optical sensor may be installed on the same side of the ribbon if a reflector is installed on the opposite side of the ink ribbon to reflect the light beam emitted from the light source back to the optical sensor for generating output voltages. In addition, in these mentioned embodiments, the ink ribbon may or may not be installed in an ink ribbon cassette, as both types of products can be found in the present market. 
     Compared with the prior art ink ribbon positioning system, the ink ribbon positioning system  40  only comprises one optical sensor. Thus, the number of components of the color printer is reduced and the production costs are lowered. However, it should be noted that the present invention method identifies the position of the ink ribbon by controlling the luminosity of the light sources at different times, and by detecting the light beams that pass through the ink ribbon. According to the disclosure, more than one optical sensor can surely be used to achieve the same goal. 
     Those skilled in the art will readily observe that numerous modifications and alterations of the device may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.