Incremental printing of symbolic information – Thermal marking apparatus or processes – Housing or mounting
Patent
1994-10-31
1996-11-26
Fuller, Benjamin R.
Incremental printing of symbolic information
Thermal marking apparatus or processes
Housing or mounting
B41J 1170
Patent
active
055790437
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a thermal printer in which inserting and removing the print medium are facilitated.
BACKGROUND OF THE INVENTION
The print medium for thermal printing is generally in the form of a roll of sheet material which is paid out beneath a print head by means of a drive roll (or capstan) and which is then cut into lengths to constitute separate sheets (or receipts, etc.).
One of the main drawbacks of that type of apparatus lies in the difficulty of threading the leading end of a roll through the print head and between the blades of the device for cutting the sheet into lengths.
Printers have already been proposed in which the print medium is installed from the side, i.e. after removing a cover that is perpendicular to the axes of the capstan and of the roll so that the medium can be slotted in parallel to said axes.
Printers also exist in which the print head is separated from the capstan so that they are moved apart from each other parallel to the axis of the capstan. The capstan is then secured to a chassis component that pivots on a fixed component carrying the print head. The pivoting cover moves in relatively complex manner in order to avoid rubbing contact between the capstan and the head when they are being brought together or moved apart. The capstan support therefore begins its separation movement substantially perpendicularly to the head and then moves parallel to the head for disengagement purposes once the capstan is no longer in contact with the head.
The present invention seeks to simplify the structure of thermal printers that are capable of being opened in order to facilitate insertion of the strip of paper; it also has the advantage of being simpler to use than existing printers.
SUMMARY OF THE INVENTION
To this end, the invention therefore provides a thermal printer for printing on a thermal paper type medium, the printer comprising a thermal print head that co-operates with a paper drive roll by bearing thereagainst, in which the print head is carried resiliently by a fixed chassis portion while the drive roll is carried by a moving chassis portion hinged to the fixed chassis and forming a cover giving access to the compartment in the printer for containing the roll of paper. According to one of the characteristics of the invention, when the cover is closed, the zone of contact between the paper drive roll and the row of heating points of the print head is situated behind the diameter of said roll that passes through the hinge between the moving chassis and the fixed chassis, where "behind" is as seen in the closure direction of the cover about its hinge. This disposition makes it possible to ensure enough pressure to hold the paper properly against the capstan, the print head forming a resilient latch on closure of the cover.
The portion of the print head situated in front of the row of heating points is shaped to offer a cam-forming surface for displacing the head against the force of a resilient member when the backing roll goes past in the cover-closing direction. In contrast to what could have been feared, this direct contact (with the strip of paper in between) gives rise to no premature damage or wear of the head or of the capstan, thereby making it possible to avoid installing cam devices external to the capstan and to the print head. The capstan rolls without slipping over said (paper-covered) cam surface and therefore without producing any rubbing between the head and the paper that could be driven by the roll. The absence of any complex cam mechanism means that the total bulk of the device is as small as possible.
In order to obtain maximum benefit from an opening thermal printer, the invention also proposes adding thereto a paper cutter member that is likewise capable of opening. To do this, the fixed chassis carries the rotary blade of the cutting member downstream from the print head in the paper travel direction, with the stationary blade being carried by the cover downstream from the backing roll. The stationary blade is secured to a support
REFERENCES:
patent: 4042939 (1977-08-01), Lloyd et al.
patent: 4297039 (1981-10-01), Lees
patent: 4663638 (1987-05-01), Hirose
Anderson Lynne
Axiohm
Fuller Benjamin R.
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