Typewriting machines – Platen or platen-moving mechanism – Cylindrical platen
Reexamination Certificate
2002-02-12
2003-09-30
Colilla, Dan (Department: 2854)
Typewriting machines
Platen or platen-moving mechanism
Cylindrical platen
C400S088000, C347S220000
Reexamination Certificate
active
06626597
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
The present invention relates to a printer assembly (printing assembly) and a printer for printing on a thermosensible (thermal) paper.
2. Description of the Related Art
In recent years, various types of computers have been developed and used that includes a portable type such as a notebook type and a portable or mobile type such as a PDA which can be put in a pocket. As the Internet becomes popular, applications of computers have been spread in various fields including information service and communication, and the population of users has also been spread from a specialist to a general user. Accordingly, computers will be daily used in ordinary homes in the future. In addition, the application handling daily works with a computer at home, by introducing computerized account settlement, electronic commerce.
According to increase of mobile computers and other mobile devices, user will require printout whenever they are required even if they are using mobile computer. However, in a case that computers are used for daily works such as electronic transaction, an amount of prints is not so many and the frequency of printing is also not so many. Accordingly, one style or aspect of a printer which is demanded in the future for the above mobile computer will surely be thin, compact, light-weight and low-cost type and it can be carried together with a portable information processing device and/or portable terminal such as a PDA, a portable telephone or the like, by being built in the device and/or being connected to the device.
A printer for printing on a thermosensible paper or thermal paper using a thermal head does not require ink or ribbons. Therefore, its printing mechanism becomes compact. Specifically, a line thermal printer having a line thermal head extending in a paper width direction (scanning direction or line direction) does not require a mechanism for moving a thermal head in the scanning direction. Hence the line thermal printer becomes much compact and the printer meets the above demand.
However, a mechanism for pressing a printing paper on a thermal head is an obstacle to realize a very thin printer having a thickness of, for example, about 10 mm or less. In the thermal printer, a mechanism for feeding a thermal paper or sheet has a platen roller. The platen roller presses the paper on the thermal head by holding the paper between the thermal head and feeds the thermal paper by rotating. In order to realize a thin printer having a thickness of 10 mm or less, a diameter of the platen roller shall be smaller than that of the conventional printer. When the diameter of the platen roller becomes small, a contacting area or surface between the roller and the printing paper is reduced, so that the platen roller must be pressed on the paper with stronger force in order to keep a sufficient contacting force for pressing the thermal paper to the thermal head. However, when the diameter of the platen roller becomes 10 mm or less, the roller lacks in strength. Therefore, when pressing force is increased for compensating for the lack of contacting area, flexure or bending tends to occur in the platen roller.
Particularly, when the diameter becomes 5 mm or less, flexure occurs over the entire length of the platen roller. Accordingly, when the platen roller is supported only at both ends, it becomes impossible to press the printing paper on the thermal head by the platen roller with sufficient force for printing. Particularly when the line thermal head is used and the force for pressing the thermal paper is deviated along the direction of the paper width, the pressing forces are lost in some portion of the paper. Therefore, printing quality deteriorates so that it becomes impossible to perform practical printing.
For preventing the platen roller from flexing, the platen roller may be divided along its longitudinal direction so that the shaft of roller is exposed and is supported by a bearing. However, for printing along the thermal head without missing of data, the pressure must be continuously applied by the platen roller along the scanning direction. Therefore, the platen roller cannot be divided along its longitudinal direction. It is also possible to support the entire platen roller from a side opposed to the thermal head by a member extending in the longitudinal direction. However, for feeding the paper smoothly, the surface of the platen roller is formed of material having a high coefficient of friction, such as a rubber. For this reason, in a pressed or pressurized state, a frictional force between such a supporting member and the platen roller is excessively large so that driving force of a motor for rotating the platen roller becomes too large and such a large capacity motor cannot be installed in thin and small printer.
It is also possible to install several sub rollers along the longitudinal direction of the platen roller to prevent the platen roller from flexing. However, if we applied the sub rollers supported by a shaft and bearings, it is necessary to make an additional space for arranging the sub rollers and their bearings including some clearances between the sub rollers and the housing of printer. Therefore, the above solution cannot be applied for the extremely thin printer of this invention.
Hence, an object of this invention is to solve the above problems about the platen rollers that are the neck of realizing a very thin printer and to provide a thin printer that can achieve a high printing quality. In addition, in the present invention, it is an object to provide a very thin printing mechanism or printer assembly and a very thin line thermal printer by the printer assembly that has a thickness about 10 mm or less, and further about 5 mm or less.
SUMMARY OF THE INVENTION
For achieving the object, in a printer assembly of the present invention, a platen roller is supported by thin rollers (shafts) of a small diameter having a surface of small or low coefficient of friction. In addition, a plate-shaped member supports or bears the supporting rollers so that flexure of the platen roller is prevented via the supporting plate and supporting rollers. Therefore, in this invention, if the diameter of the platen roller is small, stronger pressure or force can be applied between the platen roller and a thermal head. That is, the printer assembly of the invention comprises a line thermal head, a platen roller having a surface of high or large coefficient of friction, which holds a printing paper between the line thermal head and the platen roller and feeds the printing paper, supporting rollers having a surface of small or low coefficient of friction respectively, which are disposed at a front and a rear of the platen roller in a paper feeding direction so as to support the platen roller from a side opposed to the line thermal head, a supporting plate extending along the supporting rollers for supporting or bearing the supporting rollers from a side opposed to the line thermal head, and pressurizing or pressing means for applying pressure between the supporting rollers and the line thermal head.
The platen roller made of a metal member whose surface is processed for increasing a coefficient of friction or the platen roller made of a resin material with a high coefficient of friction such as phenol resin may be used, but the platen roller covered by the rubber materials having some elasticity and a high coefficient of friction is the most suitable. On the other hand, a member made of resin having a low coefficient of friction, for example, nylon, polyethylene or the like is suitable for the supporting rollers. A rod-shaped member made of fluororesins is the most suitable for the supporting rollers since it has so smaller coefficient of friction that becomes several tenths, or one or more digits smaller than that of rubber material.
In this printer assembly, the supporting rollers having a small coefficient of friction support the platen roller having a large coefficient of friction, and the supporting plate extending along the
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