Method of controlling ribbon motor for colour printing system

Abstract: There is disclosed a method of controlling the operation of a ribbon motor for a colour printing system, including the step of rotating a ribbon (102) in reverse by one colour pitch so as to prevent the deterioration of print quality due to dust particulates on a surface of the ribbon after the completion of the printing operation. The above method further includes the steps of counting the time of the printing system being in a standby mode after the completion of the printing operation; and presetting a critical point in the printing system in order to compare a count of the time of the printing system being in a standby mode with the critical point.

Description: The present invention relates generally to a method of controlling a ribbon motor for a colour printing system. A ribbon driving control portion of a conventional sublimation-type thermal printing system may be divided into four blocks: a colour detector 106; a central processing unit CPU 107; a ribbon motor driving controller 108; and a ribbon motor 109, as shown in Figure 1. Once the printing operation starts, the CPU 107 controls the ribbon motor driving controller 108 to make a ribbon 102 travel until the colour detector 106 detects yellow. When the colour detector 106 detects yellow, a thermal print head 103 (TPH) is pressed onto the ribbon 102 and paper 101 and generates heat to output a corresponding image on the paper 101. Once the "yellow" printing operation is completed, the CPU 107 returns the TPH 103 to its original position, and makes the ribbon 102 travel until the colour detector 106 detects the next colour, magenta. When the colour detector 106 detects magenta, the TPH 103 is pressed onto the ribbon 102 and paper 101 to imprint data corresponding to the colour on the paper 101. The above-described process is executed with respect to the printing of data corresponding to the colours of yellow, magenta, cyan and black. Figure 2 illustrates a ribbon used for a sublimation-type printing system. If three- or four-colour printing operation is completed, the conventional ribbon motor driving controller 108 holds the ribbon ready until there is a command to print. As a long period of time elapses after printing, dust particulates may lay on the surface of the ribbon, and when the printing operation is carried out in this state, the dust on the ribbon and the colours of the ribbon are transferred to paper to cause the poor print quality. As shown in Figure 3, after the printing operation, in case of the three- or four-colour ribbon, the end of the ribbon's cyan/black part (the last printing colour) is placed right under the TPH 103, and the dust adversely affects a region A of the ribbon so the dust particulates on the ribbon's yellow part negatively affect a region B of the ribbon during subsequent printing to thereby deteriorate the print quality. As described above, in such a sublimation-type thermal printing system, the dust on the ribbon and paper surface may deteriorate the print quality, and it is necessary to avoid waste of ribbons and paper due to poor print quality by providing the high standards of print quality, reliability, and performance. As a long period of time elapses after printing, the dust may lay on the surface of the ribbon and cause the poor print quality. JP-61209183 (OKI) discloses a single colour printing system where the printing ribbon is reversely rotated after a printing operation to align the leading edge of the unused portion of the printing ribbon with a print head. GB-A2289444 (Eastman Kodak) discloses a colour thermal printer which rotates the printing ribbon in a forward and a reverse direction in order to accurately align the leading edge of each colour frame with the print head before printing of that colour begins. Preferred embodiments of the present invention are directed to a method of controlling a ribbon motor for a colour printing system which substantially obviates the above-described problem due to limitations and disadvantages of the related art. According to a first aspect of the present invention there is provided a method of controlling the operation of a ribbon motor for a colour printing system, including the step of rotating a ribbon in reverse so as to prevent the deterioration of print quality due to dust particulates on a surface of the ribbon after the completion of the printing operation. Preferably, the ribbon is rotated in reverse by a length corresponding to one colour pitch. Embodiments of the above method also include the steps of counting the time of the printing system being in a standby mode after the completion of the printing operation; and presetting a critical point in the printing system in order to compare a count of the time of the printing system being in a standby mode with the critical point. Preferably, said step of rotating the ribbon in reverse is performed if the time of the printing system being in a standby mode is larger than the critical point. Preferably, said count of the time is cleared when the printing operation starts. For a better understanding of the invention, and to show how embodiments of the same may be carried into effect, reference will now be made, by way of example, to the accompanying diagrammatic drawings, in which: Figure 1 is a block diagram of a conventional ribbon driving control portion; Figure 2 illustrates a ribbon used for a sublimation-type printing system. Figure 3 shows a region of the ribbon where image degradation is created by dust on the ribbon surface; Figure 4 is a block diagram of a ribbon driving control portion in accordance with an embodiment of the present invention; Figure 5 shows the position of a ribbon that has been rotated in reverse by one colour pitch in accordance with an embodiment of the present invention; and Figure 6 is a flow chart of the control sequence of a ribbon driving cycle in accordance with an embodiment of the present invention. Reference will now be made in detail to the preferred embodiment of the present invention, examples of which are illustrated in the accompanying drawings. Figure 4 is a block diagram of the inventive ribbon driving control portion of a thermal printing system. As shown in Figure 4, contrary to the conventional art, the present invention employs first and second ribbon motors 201 and 202 and a predetermined control program of a central processing unit 107. Once the first ribbon motor 201 starts operating, a first reel 105 turns to rotate a ribbon forward, and when the second ribbon motor 202 operates, a second reel 111 turns to rotate the ribbon in reverse. The direction of the respective forward and reverse rotations is determined as shown in the drawings. Figure 5 shows the ribbon in a position where it has been rotated in reverse by one colour pitch. and Figure 6 is a flow chart of the control sequence of a ribbon driving cycle in accordance with the present invention. The flow chart of Figure 6 is divided into two parts: Step 601 of carrying out the printing operation of a three- or four-colour ribbon with respect to the colours of yellow, magenta, and cyan/black when a command to start printing is input to the system; and Step 602 of rotating the ribbon in reverse by one colour pitch if the time of the printing system being in standby mode exceeds a critical point. The first preferred embodiment of the present invention will now be described in detail with reference to Figures 4, 5 and 6. Referring first to Figure 4, the first ribbon motor 201 operates the first reel 105 to rotate the ribbon in the direction which is the same as that of the printing operation (forward rotation), and the second ribbon motor 202 actuates the second reel 111 to rotate the ribbon in the direction opposite to that of the forward rotation. Figure 5 shows the ribbon in a position where it has been rotated in reverse by one colour pitch. The cyan or black part of the ribbon whose colour has been transferred to paper during the preceding printing operation is shown, and the yellow part used for the next printing is wound around a ribbon cartridge 111. Accordingly, even if the dust lays on the ribbon surface, it affects adversely the cyan or black part of the ribbon, not the yellow part at all. Turning to Figure 6, the ribbon motor driving control program will now be described. The flow chart of Figure 6 may be divided into two parts: Step 601 of counting the time of the printing system being in standby mode and rotating the ribbon in reverse; and Step 602 of performing the printing operation when a command to print is input. When the printing system is in printing mode at Step 6a, the CPU 107 counts (Step 602) the time of the system being in standby mode (standby time) before it starts printing. Before counting, the CPU 107 checks (Step 6b) if the ribbon has previously rotated in reverse. When the ribbon has already rotated in reverse, there is no need to count the standby time, and the CPU 107 returns to the first stage to check if there is a command to print. On the contrary, if the ribbon has not rotated in reverse yet, the CPU 107 goes on counting the standby time. When there is a command to print during the CPU's counting, the CPU 107 clears the count of the standby time. If the count of the standby time exceeds a critical point M at Step 6d, the CPU 107 actuates (Step 6e) the second ribbon motor 202 to rotate the second reel 111 in reverse. Simultaneously with this, the CPU 107 checks (Step 6f) if a colour detector 106 produces an output. When an output of the cyan/black part of the three- or four-colour ribbon is input at Step 6g, the CPU 107 stops the second ribbon motor 202 to thereby stop the reverse rotation of the ribbon at Step 6h. As shown in Figure 5, the front end of the cyan/black part of the ribbon is placed on the colour detector 106. Accordingly, even if dust particulates lay on that part, they do not negatively affect the yellow part of the ribbon so that the good print quality can be achieved during the next printing operation. The CPU 107 clears (Step 6i) the count of the standby time T after stopping the ribbon, and, returning to the first stage, repeats the above procedure until a command to print is input. When a command to print is input to the system, the printing system operates at Step 6a. The CPU 107 clears (6j) a count of the standby time T, and performs the three- or four-colour printing operation. What is important at this stage is that the CPU 107 operates (Step 6k) the first ribbon motor 201 to turn the first reel 105 so that the ribbon rotates forward and the second reel motor 202 operates, contrary to the reverse rotation of the ribbon at Step 6e. Once the printing operation with respect to the last colour is completed, the CPU 107 returns to the first stage and repeats the above procedures, waiting for a command to print. The critical point M of Step 6d may be set up for sixty minutes or else at the factory, and the smaller the critical point is, the more the amount of the dust laying on the yellow part of the ribbon becomes decreased. According to the conventional printing system, as a long period of time elapses after the printing operation, dust particulates may accumulate on the ribbon surface, and they are mixed with the colours of the ribbon and transferred to paper during the next printing operation, resulting in the poor print quality. Therefore, if the standby time of the printing system exceeds a critical point after the last printing operation, embodiments of the present invention make the ribbon rotate in reverse by one colour pitch to prevent the dust from accumulating on a region of the ribbon used for the next printing. In other words, when the yellow part of the ribbon to be used for the next printing is exposed to the dust particulates, the print quality may be deteriorated due to the dust. Thus, by allowing the ribbon to rotate in reverse toward the cyan/black part that has been already used during the previous printing operation, the yellow part of the ribbon is free from dust to thereby prevent the print quality from being deteriorated due to the dust. Thus, the advantages of ensuring the best possible print quality and avoiding waste of ribbons and paper may be achieved.

Claims: A method for controlling the operation of a ribbon motor for a colour printing system, characterised by the step of rotating a ribbon (102) in reverse in order to prevent the deterioration of print quality due to dust particulates on a surface of the ribbon (102) after the completion of the printing operation. A method according to claim 1, wherein said ribbon (102) is rotated in reverse by a length corresponding to one colour pitch. A method according to claim 1 or 2, further comprising the step of counting the time of the printing system being in a standby mode after the completion of the printing operation. A method according to claim 3, further comprising the step of presetting a critical point in the printing system in order to compare a count of the time of the printing system being in a standby mode with said critical point. A method according to claim 4, wherein said step of rotating the ribbon (102) in reverse is performed if the time of the printing system being in a standby mode is larger than the critical point. A method according to any of claims 3 to 5, wherein said count of the time is cleared when the printing operation starts.

Inventors: SONG JUN-PIL, SONG, JUN-PIL
Applicants: SAMSUNG ELECTRONICS CO LTD, SAMSUNG ELECTRONICS CO. LTD.
Application year: 1997
Main classification: B41J17
IPC codes: B41J33, B41J17, B41J35, B41J5