Typewriting machines – Including interposed inking device for record-medium – Ribbon-feeding mechanism
Reexamination Certificate
1999-10-13
2001-11-13
Colilla, Daniel J. (Department: 2854)
Typewriting machines
Including interposed inking device for record-medium
Ribbon-feeding mechanism
C400S223000, C400S120010, C347S172000, C347S217000
Reexamination Certificate
active
06315471
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATION
This application claims the priority benefit of Taiwan application serial no. 88114314, filed Aug. 21, 1999, the full disclosure of which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to an apparatus for controlling ribbon tension and a method for controlling the same. More particularly, the present invention relates to an apparatus for controlling ribbon tension in a thermal printer and a method for controlling the same.
2. Description of Related Art
In a thermal printer, a ribbon is used as a medium for transferring image. To obtain high print quality, a uniform ribbon tension should be maintained during the printing process. If ribbon tension is too low in the printing process, ribbon tension cannot lead the ribbon forward; the ribbon may even become slack, resulting in a torn ribbon by mechanism. If ribbon tension is too high, the ribbon may wrinkle and lower the print quality, and the ribbon may be deformed.
In general, the ribbon is unwound from a supply reel and collected on a take-up reel. The take-up reel in the thermal printer is usually driven by a step motor or a direct current motor, which provides a constant torque. The supply reel is not connected to a motor; thus, ribbon tension on the supply reel is only maintained by the frictional force between the supply reel and the ribbon. During the printing process, for a constant torque provided by the motor connected to the take-up reel, ribbon tension is governed by the equation:
tension=torque/radius of take-up reel
Consequently, ribbon tension is varied during the operation of the thermal printer by a change in the radius of the take-up reel.
Furthermore, to improve the print quality, the thermal print head is usually directly in contact with the ribbon during the printing process; thus, the frictional force between the thermal print head and the ribbon and the frictional force between the ribbon and the paper are both tremendously increased. Ribbon tension is also needed to be boosted up.
In addition, different functions are performed by the ribbon during the operation of the thermal printer, and these functions are achieved by controlling ribbon tension and the direction in which the ribbon moves. For example, in the preparation process, the ribbon should lead the paper into an engagement position between the capstan roller and the pinch roller. During the printing process, the ribbon should overcome the friction between the ribbon and the thermal print head and the friction between the ribbon and the paper. After a certain color panel is printed, the ribbon should run reversely to conduct the paper back into the back-feed path smoothly.
In U.S. Pat. No. 5,138,335, a spring is directly in contact with the supply reel and the take-up reel to control ribbon tension. In U.S. Pat. No. 5,529,410, ribbon tension is controlled by using pulse width of the motor connected to the take-up reel; thus, ribbon tension on the take-up reel is maintained uniform during the printing process. However, the structures in these patents mentioned above are complex, and their operations obviously do not satisfy the extra functions performed by nowaday thermal printing system.
SUMMARY OF THE INVENTION
The invention provides an apparatus for controlling ribbon tension in a thermal printer and a method for controlling the same to obtain high print quality.
As embodied and broadly described herein, the invention provides a thermal printer. In the thermal printer, ribbon tension is maintained uniform during the printing process to obtain high print quality.
As embodied and broadly described herein, the invention provides an apparatus for controlling ribbon tension in a thermal printer. The apparatus includes a supply reel, a take-up reel and a pair of motors. Each motor connects with the supply reel and the take-up reel, respectively. A detecting apparatus detects parameters of a ribbon and the reels while initializing the thermal printer. A control apparatus stores a transform relationship between a radius of the supply reel, a radius of the take-up reel, ribbon tension and pulse width of each motor.
In accordance with this invention, a thermal printer having a supply reel, a take-up and a pair of motors is provided. Each motor connects with the supply reel and the take-up reel, respectively. A detecting apparatus detects parameters of a ribbon and the reels, while initializing the thermal printer. A memory in the thermal printer stores a transforming table which was established beforehand. And the transforming table describes the relationship between a radius of the supply reel, a radius of the take-up reel, ribbon tension and pulse width of each motor. A control apparatus drives each motor with different pulse width according to parameters detected by the detecting apparatus and the transforming relationship. Hence, the tension of the ribbon either in take-up reel end or in supply reel end can be easily operated throughout the whole printing process. The front-end of paper also can be easily conducted into the moving path by the moving ribbon in back or forward direction.
The invention provides a method for controlling ribbon tension, which is applied in a thermal printer. The thermal printer includes a supply reel and a take-up reel, and each reel connects to a motor. A predetermined relationship table between ribbon tension and pulse width of each motor is established and stored in the thermal printer. While the thermal printer performs an initializing process, a radius of the supply reel and a radius of the take-up reel are calculated. Each motor is driven by different pulse width in accordance with the radius of the supply reel, the radius of the take-up reel and the transforming table.
In the invention, the initializing process is performed to obtain the radius of the supply reel and the radius of the take-up reel before the printing process. In accordance with the transforming table, the motor connecting with the supply reel and the motor connecting with the take-up reel are respectively driven by different pulse widths to obtain different ribbon tension during processes such as the preparation process, the printing process or the overprinting process. Additionally, the direction in which the ribbon moves can be changed during the above-mentioned processes.
It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.
REFERENCES:
patent: 4661826 (1987-04-01), Saitou
patent: 4788558 (1988-11-01), Caldwell et al.
patent: 6010258 (2000-01-01), Tomita et al.
patent: 6-312568-A (1994-11-01), None
patent: 8-2078-A (1996-01-01), None
patent: 63-4984-A (1988-01-01), None
patent: 5-58014-A (1993-03-01), None
Chung Chuan-Yuan
Hsieh Chu-Cheng
Colilla Daniel J.
Huang Jiawei
Industrial Technology Research Institute
J. C. Patents
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