JP2007030430A - Ribbon-end detecting unit of printer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a ribbon-end detecting unit of a printer, which eliminates the need for increasing a distance from a ribbon feeding shaft 2 to a printing section by detecting a ribbon end while adapting to high-speed printing. <P>SOLUTION: This ribbon-end detecting unit of the printer, which is provided with a pair of detectors 20 and 21 for detecting a slit 22 (a part to be detected), detects timing when a thermal transfer ribbon moves in a direction opposite to the direction of being paid out to a ribbon carrying passage. The ribbon-end detecting unit comprises: a rotating plate 16 to be detected, in which the plurality of parts 22 to be detected are circumferentially formed; and the pair of detectors 20 and 21 to detect the parts 22. When the rotation of the shaft 2 in the direction opposite to the pay-out direction of the thermal transfer ribbon is detected according to detection signals of the detectors 20 and 21, it is determined that the ribbon end of the thermal transfer ribbon is detected. The length of the part 22 in the circumferential direction of the rotating plate 16 is set almost equal to the total lengths 2G of the detectors 20 and 21 in the circumferential direction. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

The present invention relates to a ribbon end detection device for a printer, and more particularly to a ribbon end detection device for a printer compatible with high-speed printing.

In a printer such as a conventional thermal transfer type label printer, printing is performed by superimposing a thermal transfer ribbon on a printing paper such as a tag or a label in a printing unit having a thermal head and a platen roller.
A slit plate (detected rotating plate) for detecting the rotation is provided on the ribbon supply shaft of the thermal transfer ribbon, and a slit (detected portion) is formed on the slit plate and a single slit sensor (detector) is provided. In addition, a stepping motor that rotates the ribbon take-up shaft or the platen roller is provided, and the thermal transfer ribbon along with the remaining ribbon amount (ribbon diameter) depending on the number of stepping motor steps required to pass through the slit of the slit plate. The end or end of the ribbon (ribbon end) was detected.

    When detecting the ribbon end using the number of steps described above, a distance of a predetermined length is required from the ribbon supply shaft to the printing unit. In a label printer with a high printing speed, the end of the ribbon is printed. Since the ribbon end is detected after passing through the thermal head of the portion, there is a problem that printing failure occurs and the ribbon cannot be used for high-speed printing at a certain speed or higher.

    Furthermore, since the thermal transfer ribbon is thin, in order to prevent wrinkles in the ribbon transfer path, the ribbon supply shaft has a slight resistance in the direction opposite to the ribbon feeding direction (depending on the ribbon take-up shaft). Although a back tension mechanism that applies tension in the reverse direction by a force weaker than the winding force of the thermal transfer ribbon is also provided, when the ribbon end is reached, the ribbon supply shaft moves in the reverse direction by the back tension mechanism. At the same time, it vibrates in the feeding direction and in the reverse direction due to inertial force, so that the slit is detected when the vibration stops and the slit plate becomes stable. There is a possibility that printing defects may occur, and in particular, in high-speed printing, there is a problem that the possibility becomes higher.

JP-A-8-72373

    The present invention has been considered in view of the above problems, and an object of the present invention is to provide a ribbon end detection device for a printer capable of detecting a ribbon end in correspondence with high-speed printing.

    It is another object of the present invention to provide a ribbon end detection device for a printer that does not require a large distance from the ribbon supply shaft to the printing unit even when high-speed printing is performed.

    Another object of the present invention is to provide a ribbon end detection device for a printer that can detect a ribbon end at an appropriate timing even if a back tension mechanism for urging the thermal transfer ribbon in a direction opposite to the feeding direction is provided. To do.

    That is, according to the present invention, a pair of (two) detectors that detect slits (detected portions) in the ribbon supply shaft are provided, and a mechanism for detecting the rotation direction of the ribbon supply shaft is provided. Focusing on the fact that the ribbon end can be detected by detecting the timing when the thermal transfer ribbon is moved in the direction opposite to the feeding direction to the ribbon transfer path by the back tension mechanism. A ribbon supply shaft that can be held in a roll shape and can be fed out into a ribbon transfer path, the thermal transfer ribbon and the printing paper overlapped with each other, a printing unit that prints on the printing paper, and the printing that has been finished A ribbon take-up shaft for winding the thermal transfer ribbon into a roll shape, and the ribbon take-up shaft provided on the ribbon supply shaft of the thermal transfer ribbon A ribbon end detection device for a printer provided with a back tension mechanism that slightly biases in a direction opposite to the feeding direction of the thermal transfer ribbon with a force weaker than the winding force of the thermal transfer ribbon. A detected rotating plate that rotates in synchronization with the shaft and has a plurality of detected portions in the circumferential direction thereof, a pair of detectors that can detect these detected portions, and the pair of detectors And a controller that determines that the ribbon end of the thermal transfer ribbon has been detected when rotation of the ribbon supply shaft in the direction opposite to the feeding direction of the thermal transfer ribbon is detected based on the detection signal. The length of the detected portion in the circumferential direction of the detection rotating plate is substantially equal to the total length of the pair of detectors in the circumferential direction. A ribbon end detection apparatus of the printer.

    A second aspect of the invention is a printing method in which a ribbon supply shaft that holds a thermal transfer ribbon in a roll shape and can be fed out into a ribbon transfer path in a belt shape, and the thermal transfer ribbon and the printing paper are overlapped to perform printing on the printing paper. And a ribbon take-up shaft that winds up the thermal transfer ribbon that has been printed, and a ribbon supply shaft of the thermal transfer ribbon, and is weaker than the winding force of the thermal transfer ribbon by the ribbon take-up shaft A ribbon end detection device for a printer provided with a back tension mechanism that slightly biases the thermal transfer ribbon in a direction opposite to the feeding direction of the thermal transfer ribbon by force, and rotates in synchronization with the ribbon supply shaft. A rotating plate to be detected in which a plurality of detected portions are formed in the circumferential direction, a pair of detectors capable of detecting these detected portions, and detection signals of the pair of detectors And a controller for determining that the ribbon end of the thermal transfer ribbon has been detected when detecting the rotation of the thermal transfer ribbon on the ribbon supply shaft in the direction opposite to the feeding direction. A ribbon end detection device for a printer, wherein a length of the detected portion in the circumferential direction is substantially equal to a length of each of the pair of detectors in the circumferential direction.

    The detected parts can be formed at equal intervals in the circumferential direction of the detected rotating plate.

    The pair of detectors can be arranged at different positions in the circumferential direction of the detected rotating plate.

    The pair of detectors can be arranged at different positions in the diameter direction of the detected rotating plate.

    An interval between the adjacent detected portions can be made equal to the length of the detected portion in the circumferential direction of the detected rotating plate.

    The pair of detectors can be arranged to be closest to each other on the same diameter of the detected rotating plate in the circumferential direction of the detected rotating plate.

    The detected portion is formed in an arc shape along the rotation direction of the detected rotation plate, and the pair of detectors are arranged in an arc shape along the rotation direction of the detection rotation plate. can do.

    The pair of detectors can be displaced from each other in the diameter direction and the circumferential direction of the detected rotating plate.

    The detected portion can have a length in the diameter direction of the detected rotating plate larger than a length of the detected rotating plate in the circumferential direction.

    By increasing the number of detected parts, it is possible to shorten one cycle of detection signals from the pair of detectors.

In the ribbon end detection device for a printer according to the present invention, the back tension mechanism provided on the ribbon supply shaft detects the timing at which the thermal transfer ribbon moves in the direction opposite to the feeding direction to the ribbon transfer path, that is, Since the ribbon end is detected by providing a mechanism for detecting the rotation direction of the ribbon supply shaft, the ribbon supply shaft is moved by the back tension mechanism when the thermal transfer ribbon disappears and the ribbon end moves away from the ribbon supply shaft. By detecting the timing of rotating in the reverse direction, the ribbon end can be detected, so it becomes possible to immediately detect the ribbon end at the time of rotation of the ribbon supply shaft in the reverse direction. The thermal transfer ribbon moves the distance between the ribbon supply shaft and the printing unit. Without any, it is possible to detect that the thermal transfer ribbon is no longer, are particularly suitable for high-speed printing printer.
Further, the pair of detectors can be obtained by making the circumferential length of the detected portion of the rotating plate to be detected substantially equal to the circumferential length of the pair of detectors or by increasing the number of detected portions. By shortening one cycle of the detection signal by, detection of the ribbon end corresponding to high-speed printing becomes possible.

    In particular, according to the first invention, the length of the detected portion in the circumferential direction of the detected rotating plate is substantially equal to the total length of the pair of detectors in the circumferential direction. The configuration corresponding to the detector can be simplified, it is easy to ensure the necessary detection timing, and the arrangement and assembly of the pair of detectors are easy.

In particular, according to the second invention, the length of the detected portion in the circumferential direction of the detected rotating plate is substantially equal to the length of each of the pair of detectors in the circumferential direction. As a result, it is possible to secure a larger number of to-be-detected parts and to further shorten one cycle of detection signals from the pair of detectors.

    The present invention makes it possible to detect that the end of the thermal transfer ribbon has been reached by rotating the ribbon supply shaft in the reverse direction, and to detect the detection signal by making the relative sizes of the pair of detectors and the detected portion equal. Because one cycle is shortened, it is possible to detect in a short time, and even if the printing speed is high, the printer that can maintain the ribbon end detection function without causing defects such as defective printing Ribbon end detection device was realized.

Next, a ribbon end detection apparatus for a printer according to a first embodiment of the present invention will be described with reference to FIGS.
FIG. 1 is a schematic side view of a thermal transfer type label printer 1 (printer) provided with the ribbon end detection device. The thermal transfer type label printer 1 includes a ribbon supply shaft 2, a printing unit 3, and a ribbon winding. A take-up shaft 4, a paper supply shaft 5, a control unit 6, and a ribbon end detection device 7 are provided.

    The ribbon supply shaft 2 holds the thermal transfer ribbon R in a roll shape and can supply (feed out) the ribbon to the ribbon transfer path 8. The ribbon end detection device 7 according to the present invention (see FIGS. 2 and 3, which will be described later). ) And a back tension mechanism 9 (FIG. 2, which will be described later).

    The printing unit 3 includes a thermal head 10 and a platen roller 11. The platen driving motor 12 (stepping motor) is rotated by a predetermined number of steps to rotate the platen roller 11, and print information is given to the thermal head 10. By doing so, it is possible to print on the printing paper L (for example, label) from the paper supply shaft 5.

    The ribbon take-up shaft 4 is located on the downstream side of the printing unit 3 and rotates the take-up motor 13 (stepping motor or DC motor) to take up the thermal transfer ribbon R in a roll shape. The ribbon take-up shaft 4 can also be rotationally driven in conjunction with the platen roller 11 by the platen drive motor 12 without providing the take-up motor 13.

    The control unit 6 controls the thermal head 10, the platen drive motor 12, and the take-up motor 13, and from a pair of optical sensors (first sensor 20 and second sensor 21, described later) in the ribbon end detection device 7. The end portion (ribbon end) of the thermal transfer ribbon can be detected based on the detection signal.

    FIG. 2 is a schematic cross-sectional side view of the back tension mechanism 9 and the ribbon end detection device 7. As shown in the figure, the ribbon supply shaft 2 is rotatably attached to a mounting housing 14 and the ribbon supply shaft 2 Includes a circular flange plate 15, a slit plate 16 (detected rotating plate) of the ribbon end detection device 7, and a back tension mechanism 9 that can rotate integrally with the ribbon supply shaft 2 at predetermined intervals in the axial direction. The pressing plate 17 is fixedly attached.

The back tension mechanism 9 includes the pressing plate 17, a felt plate 18, and a coil spring 19.
The coil spring 19 presses the felt plate 18 with a predetermined pressing force in the direction of the holding plate 17 by the urging force between the mounting housing 14 and the holding plate 17, thereby causing sliding rotation between the holding plate 17 and the felt plate 18. And a predetermined tension in a direction opposite to the feeding direction of the thermal transfer ribbon fed from the ribbon supply shaft 2 (however, a reverse tension by a force weaker than the winding force of the thermal transfer ribbon R by the ribbon winding shaft 4) Can be granted.

    FIG. 3 is a plan view of the slit plate 16 in the ribbon end detection device 7. The ribbon end detection device 7 is a pair of optical elements arranged in the circumferential direction so as to face the slit plate 16 and its edge. It has a sensor (the 1st sensor 20 and the 2nd sensor 21), and the above-mentioned control part 6.

As shown in FIG. 3, the slit plate 16 has a plurality of rectangular (rectangular) slits 22 (detected portions) formed at equal intervals in the circumferential direction, and corresponds to the slit 22 portion. The first sensor 20 and the second sensor 21 that can detect the slit 22 are disposed at the positions where the slit 22 is to be detected.
The slit plate 16 can be rotated in the forward direction or in the feeding direction of the thermal transfer ribbon (clockwise in FIG. 3, solid arrow) and in the reverse direction (counterclockwise in FIG. 3, dotted arrow). .

The first sensor 20 and the second sensor 21 are, for example, light transmission type sensors for detecting the slit 22, and each light emitting element and light receiving element are fixedly arranged across the slit plate 16. At the same time, the slit plates 16 are arranged closest to each other on the same diameter at different positions in the rotation direction (circumferential direction) of the slit plate 16.
That is, the length of the slit 22 in the circumferential direction of the slit plate 16 is substantially equal to the total length of the first sensor 20 and the second sensor 21 in the circumferential direction.
More specifically, when the length in the circumferential direction of the slit plate 16 of the first sensor 20 and the second sensor 21 is G, the slit 22 has the length in the circumferential direction as the first length. This is approximately equal to the sum of the circumferential lengths of the sensor 20 and the second sensor 21 (that is, 2G). Further, the interval between the adjacent slits 22 is made equal to the circumferential length 2G of the slits 22, and the interval between the slits 16 is divided into eight equal parts with the interval between them being equally spaced. ing. The slit 22 has a length that can be detected by the first sensor 20 and the second sensor 21, and the length in the diameter direction of the slit plate 16 is less than the length 2 G in the circumferential direction of the slit plate 16. It is small.

FIG. 4 is a timing chart showing waveforms of detection signals of the first sensor 20 and the second sensor 21. FIG. 4A shows that the slit plate 16 (that is, the ribbon supply shaft 2) is in the forward direction. FIG. 4B is a timing chart when the thermal transfer ribbon is rotated in the feeding direction. FIG. 4B is a timing chart when the slit plate 16 (that is, the ribbon supply shaft 2) is rotated in the reverse direction. 3) is a timing chart showing an example of a waveform when an end portion (ribbon end) of the thermal transfer ribbon is detected.
As shown in FIG. 4 (1), in the normal operation state in which the slit plate 16 rotates in the forward direction and the thermal transfer ribbon R is fed out to the ribbon transfer path 8, the first sensor 20 has the end of the slit 22. First, the waveform rises, and after a short time (in the embodiment, when the first sensor 20 is rotated by the circumferential length G), the second sensor 21 makes the slit 22 open. Detect and the waveform rises.
Similarly, when the first sensor 20 is disengaged from the end portion of the slit 22, the waveform falls, and after a short time (in the embodiment, only the length G of the first sensor 20 in the circumferential direction). When rotated, the second sensor 21 is disengaged from the slit 22 and its waveform falls.

As shown in FIG. 4 (2), in the state where the slit plate 16 rotates in the reverse direction, the second sensor 21 first detects the end of the slit 22, and the waveform rises, with a slight delay. The first sensor 20 detects the slit 22 (when the second sensor 21 is rotated by the circumferential length G of the second sensor 21), and its waveform rises.
Similarly, when the second sensor 21 is disengaged from the end of the slit 22, the waveform falls, and after a short time (in the embodiment, only the length G of the second sensor 21 in the circumferential direction). When rotated, the first sensor 20 is disengaged from the slit 22 and its waveform falls.

    As shown in FIG. 4 (3), the portion up to the one-dot chain line shows the forward rotation state of the slit plate 16, and in the illustrated example, after the waveform of the first sensor 20 falls, the second sensor The waveform of the first sensor 20 rises again without falling, and the waveform of FIG. 4 (2) is drawn thereafter, indicating that the slit plate 16 has started to rotate in the reverse direction. Therefore, the rotation in the direction opposite to the feeding direction of the ribbon supply shaft 2 (slit plate 16) is detected based on the detection signals of the pair of optical sensors (first sensor 20 and second sensor 21). The controller 6 determines that the ribbon end of the thermal transfer ribbon R has been detected.

    FIG. 5 is a flowchart showing the ribbon end determination process by the control unit 6. In step S1, the step number P of the platen drive motor 12 (or the take-up motor 13) is set to zero. Then, the rotational direction (X) of the slit plate 16 (slit 22) is not determined.

In step S2, the platen drive motor 12 is fed by one step so that P = P + 1.
In step S3, it is determined whether the waveform of the first sensor 20 has been turned on from the off state (ie, has risen). It is determined whether or not the above number of steps has been exceeded. If not, the process returns to step S2 to further increment the number of steps.
When the number of steps P exceeds the number of steps Pmax, the ribbon supply shaft 2 stops rotating, for example, when the thermal transfer ribbon R reaches its end and does not leave the ribbon supply shaft 2. Is determined to be a ribbon end (step S11).

    If the waveform of the first sensor 20 changes from OFF to ON in step S3, the process proceeds to step S5 to determine the state of the second sensor 21, and if the waveform of the second sensor 21 is OFF, the current state in step S6. Is determined to be the forward direction (clockwise) CW, and if the waveform of the second sensor 21 is on, the current rotational direction (Y) is the reverse direction (counterclockwise) in step S7. While judging that it is CCW, it transfers to step S8.

    In step S8, it is determined whether or not the rotation direction (X) is fixed. If it is not fixed, in step S9, the rotation direction (X) = current rotation direction (Y) is set, and the process returns to step S2. If it is determined in step S8, it is determined in step S10 whether or not the rotation direction (X) = current rotation direction (Y). If they are correct, the process returns to step S2. Judge. .

    Thus, when the rotation direction of the ribbon supply shaft 2 (slit plate 16) is detected and rotated from the forward direction to the reverse direction, the thermal transfer ribbon R disappears and the thermal transfer ribbon R is separated from the ribbon supply shaft 2, that is, Since it can be immediately determined that the ribbon end has been detected, it is possible to detect the ribbon end before the thermal transfer ribbon R reaches the portion of the printing unit 3, which can cope with high-speed printing, and increase the size of the label printer 1. It can also be avoided.

In the present invention, the detection accuracy can be improved by devising the shape of the detected portion and the arrangement of the pair of detectors.
For example, the slit 22 is formed in an arc shape or a sector shape along the rotation direction of the slit plate 16 as indicated by a dashed line in the lower right part of FIG. The two sensors 21 are arranged in a circular arc shape or a sector shape along the rotation direction of the slit plate 16, and the slits 22 are aligned with the center lines of the slits 22, so that the slit 22 becomes the first sensor 20 and By passing through the center of the second sensor 21, detection errors are reduced, and detection with higher accuracy is possible.

Further, in the present invention, a light reflection type sensor may be used as the detector instead of the light transmission type sensor.
In the case of adopting a light reflection type sensor, a reflection rotating plate having an area having different light reflectivity instead of the slit 22 as a detected portion is adopted instead of the slit plate 16, but the detection responsiveness. From the possibility of responding to high-speed printing and the demand for downsizing, a light transmission type sensor is preferable.

In the present invention, the number of the slits 22 is further increased to further shorten one cycle of the detection signal from the pair of optical sensors (the first sensor 20 and the second sensor 21). It can also be used with a type label printer 1.
For example, FIG. 6 is a plan view of the slit plate 16 in the ribbon end detection device 30 according to the second embodiment of the present invention. The slit 31 divides the circumference of the slit plate 16 into 16 equal parts, and the slit 31 is The length G in the circumferential direction is made equal to the length G in the circumferential direction of the first sensor 20 and the second sensor 21, and the length 2D in the diameter direction of the slit plate 16 is determined from this length G. Is enlarged.
Further, the first sensor 20 and the second sensor 21 are displaced from each other in the diameter direction of the slit plate 16, and the length of the slit plate 16 in the diameter direction is D.
That is, the length G of the slit 31 in the circumferential direction of the slit plate 16 is substantially equal to the length G of each of the first sensor 20 and the second sensor 21 in the circumferential direction.
In other words, the first sensor 20 and the second sensor 21 are configured such that their positions are shifted in the diameter direction and the circumferential direction of the slit plate 16, and the slits 31 are detected at different positions in the diameter direction. Is.

In the ribbon end detection device 30 having the slit plate 16 and the plurality of slits 31 having such a configuration, the detection of the first sensor 20 and the second sensor 21 is performed similarly to the ribbon end detection device 7 (FIG. 3) described above. The ribbon end can be detected by quickly detecting the reverse rotation of the slit plate 16 (ribbon supply shaft 2) from the signal waveform.
Further, the circumferential length G of the slit 31 is made equal to the circumferential length G of the first sensor 20 and the second sensor 21, and the slit 31 is arranged in the circumferential direction of the slit plate 16. Compared to the case of (FIG. 3), more can be formed, so it is possible to secure more timing for detecting the rotation in the reverse direction as the slit plate 16 (ribbon supply shaft 2) rotates. Therefore, it is possible to cope with further high-speed printing.

Thus, according to the present invention, the number of detected parts such as the slit 22 (FIG. 3) and the slit 31 (FIG. 6) is increased, and one of the detection signals from the pair of first sensor 20 and second sensor 21 is detected. The cycle can be shortened, and the ribbon end can be detected promptly corresponding to the high-speed printing of the label printer 1.

1 is a schematic side view of a thermal transfer type label printer 1 provided with a ribbon end detection device 7 for a printer according to a first embodiment of the present invention. 2 is a schematic side cross-sectional view of the back tension mechanism 9 and the ribbon end detection device 7. FIG. FIG. 6 is a plan view of the slit plate 16 in the ribbon end detection device 7. FIG. 4 is a timing chart showing the waveforms of detection signals from the first sensor 20 and the second sensor 21. FIG. 4A shows the slit plate 16 (that is, the ribbon supply shaft 2) in the forward direction or the thermal transfer ribbon. 4 (2) is a timing chart when the slit plate 16 (that is, the ribbon supply shaft 2) is rotating in the reverse direction, and FIG. 4 (3). These are timing chart figures which show an example of a waveform at the time of detecting the terminal part (ribbon end) of a thermal transfer ribbon. FIG. 7 is a flowchart showing a ribbon end determination process by the control unit 6; It is a top view of the slit board 16 in the ribbon end detection apparatus 30 by the 2nd Example of this invention.

Explanation of symbols

1 Thermal transfer label printer (printer, Fig. 1)
DESCRIPTION OF SYMBOLS 2 Ribbon supply axis | shaft 3 Printing part 4 Ribbon take-up axis | shaft 5 Paper supply axis | shaft 6 Control part 7 Ribbon end detection apparatus of the label printer 1 (1st Example, FIG. 3)
8 Ribbon transfer path 9 Back tension mechanism 10 Thermal head 11 Platen roller 12 Platen drive motor 13 Winding motor 14 Mounting housing 15 Flange plate 16 Slit plate (Detected rotating plate)
17 Presser plate 18 Felt plate 19 Coil spring 20 First sensor (detector)
21 Second sensor (detector)
22 Slit (Detected part)
30 Ribbon end detection device of label printer 1 (second embodiment, FIG. 6)
31 Slit (Detected part)
R Thermal transfer ribbon L Printing paper (tags, labels, etc.)
G Lengths of the first sensor 20 and the second sensor 21 in the circumferential direction of the slit plate 16 (FIGS. 3 and 6)
2G The length of the slit 22 in the circumferential direction of the slit plate 16 (FIG. 3)
D Length of first sensor 20 and second sensor 21 in the diameter direction of slit plate 16 (FIG. 6)
The length of the slit 31 in the diameter direction of the 2D slit plate 16 (FIG. 6)

Claims (11)

A ribbon supply shaft that holds the thermal transfer ribbon in a roll shape and can be fed out into a ribbon transfer path in a strip shape;
A printing unit that superimposes the thermal transfer ribbon and printing paper and prints on the printing paper;
A ribbon take-up shaft that winds the thermal transfer ribbon after printing into a roll;
A back tension mechanism that is provided on the ribbon supply shaft of the thermal transfer ribbon, and is slightly biased in a direction opposite to the feeding direction of the thermal transfer ribbon with a force weaker than the winding force of the thermal transfer ribbon by the ribbon winding shaft; A ribbon end detection device of a printer provided with
Rotating in synchronization with the ribbon supply shaft, and a detected rotating plate in which a plurality of detected portions are formed in the circumferential direction;
A pair of detectors capable of detecting these detected parts;
A controller that determines that the ribbon end of the thermal transfer ribbon has been detected when the rotation of the ribbon supply shaft in the direction opposite to the feeding direction of the thermal transfer ribbon is detected based on the detection signals of the pair of detectors;
And providing
Ribbon end detection device for a printer, characterized in that the length of the detected portion in the circumferential direction of the detected rotating plate is substantially equal to the total length of the pair of detectors in the circumferential direction . A ribbon supply shaft that holds the thermal transfer ribbon in a roll shape and can be fed out into a ribbon transfer path in a strip shape;
A printing unit that superimposes the thermal transfer ribbon and printing paper and prints on the printing paper;
A ribbon take-up shaft that winds the thermal transfer ribbon after printing into a roll;
A back tension mechanism that is provided on the ribbon supply shaft of the thermal transfer ribbon, and is slightly biased in a direction opposite to the feeding direction of the thermal transfer ribbon with a force weaker than the winding force of the thermal transfer ribbon by the ribbon winding shaft; A ribbon end detection device of a printer provided with
Rotating in synchronization with the ribbon supply shaft, and a detected rotating plate in which a plurality of detected portions are formed in the circumferential direction;
A pair of detectors capable of detecting these detected parts;
A controller that determines that the ribbon end of the thermal transfer ribbon has been detected when the rotation of the ribbon supply shaft in the direction opposite to the feeding direction of the thermal transfer ribbon is detected based on the detection signals of the pair of detectors;
And providing
Ribbon end detection device for a printer, characterized in that the length of the detected portion in the circumferential direction of the detected rotating plate is substantially equal to the length of each of the pair of detectors in the circumferential direction . 3. The ribbon end detection device for a printer according to claim 1, wherein the detected portions are formed at equal intervals between each other in the circumferential direction of the detected rotating plate. 3. The ribbon end detection device for a printer according to claim 1, wherein the pair of detectors are arranged at different positions in the circumferential direction of the rotation plate to be detected. 3. The ribbon end detection device for a printer according to claim 1, wherein the pair of detectors are arranged at positions different from each other in a diameter direction of the detected rotating plate. 3. The printer according to claim 1, wherein an interval between adjacent detected portions is equal to a length of the detected portion in the circumferential direction of the detected rotating plate. Ribbon end detection device. 2. The printer ribbon according to claim 1, wherein the pair of detectors are arranged to be closest to each other on the same diameter of the detected rotating plate in the circumferential direction of the detected rotating plate. End detection device. The detected portion is formed in an arc shape along the rotation direction of the detected rotating plate,
2. The ribbon end detection device for a printer according to claim 1, wherein the pair of detectors are arranged in an arc shape along a rotation direction of the rotation plate to be detected. 3. The ribbon end detection device for a printer according to claim 2, wherein the pair of detectors are displaced from each other in the diameter direction and the circumferential direction of the rotation plate to be detected. 3. The ribbon end of a printer according to claim 2, wherein the detected portion has a length in a diameter direction of the detected rotating plate larger than a length of the detected rotating plate in the circumferential direction. Detection device. 3. The ribbon end detection device for a printer according to claim 1, wherein the number of the detected parts can be increased to shorten one cycle of detection signals from the pair of detectors.

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