Printing – Selective or progressive – Bed and platen machines
Patent
1982-08-27
1985-12-10
Burr, Edgar S.
Printing
Selective or progressive
Bed and platen machines
101 9334, 4001572, 335263, B41J 904
Patent
active
045571937
DESCRIPTION:
BRIEF SUMMARY
The present invention refers to a printing device for use in printers and typewriters and of the kind having an axially translatable elongate cylindrical hammer with an impact surface which acts upon a type character. Rotation of the hammer is prevented by a guide pin disposed in a guide slot extending in the direction of translation of the hammer. The guide pin is mounted on the hammer or in a housing in which the hammer translates, and the guide slot is provided in the other of the hammer and the housing.
A printing device of the kind referred to comprises, preferably, a type carrier in the shape of a type disc which is rotatably mounted for the selection of a desired one of a number of type characters disposed along the disc periphery. The type disc cooperates with a hammer which preferably is driven electromagnetically. The easiest way of making the hammer is by using a circular rod. This shape, however, involves the possibility for the hammer to turn around its length axis which in certain cases may unfavourably influence the appearance of the print on a document made by the printing device.
In typewriters having a printing device comprising a type disc it has been suggested to have the hammer center the type at impact. For this purpose the hammer can be provided with an impact surface in the shape of a wedge-type recess which cooperates with a similarly shaped projection on the back of each type. The described shape of the impact surface and of the types causes the type at impact to be forced into a print position determined by the hammer.
If in a printing device having impact centered types as described above the hammer should turn slightly around its length axis, also the impact surface of the hammer will turn. Accordingly, the type at impact will turn correspondingly and the character will be obliquely reproduced on a recording medium. It may be noted that a turning of the hammer through an angle of about 1/2 degree will result in an oblique reproduction of the character that is detectable by the human eye.
In order to guide the hammer and thereby to reduce the undesired turning the hammer can be provided with a longitudinal slot in which engages a fixedly mounted guide pin.
However, the slot and the guide pin have to be carefully dimensioned so that on one hand the possible turning is minimized while on the other hand the inevitable friction between the cooperating guide parts are kept within reasonable bounds. The demand for narrow tolerances in a printing device of this kind calls for frequent replacement of the hammer and/or the guide pin due to wear.
Another way of preventing rotation is to give the hammer and the parts surrounding it a section that differs from the cylindrical shape. For instance, the hammer along part of its length may have a half-circular section and may be journalled in a similarly shaped slide bearing. Here a certain amount of play between the bearing and the hammer has to be accepted in order for the hammer to move under low friction. The said play may cause a turning of the hammer that equals 1/2 degree or is even greater. Hence, the printed characters will be obliquely reproduced in an unacceptable way. Moreover, the asymmetric hammer and bearing shape requires additional machining which increases the production costs.
The object of the invention is to overcome the drawbacks indicated above and to provide a printing device of the kind referred to in which a hammer of cylindrical shape has been provided with a guiding device that reduces the maximal turning of the hammer to a value far below the above limit of 1/2 degree. Moreover, the guiding device according to the invention operates mainly without any friction that might influence the movement of the hammer.
The object is achieved in a printing device having the features stated in the appended claims.
The invention will now be described in detail with reference to the accompanying drawing in which:
FIG. 1 is a front elevation of a print hammer in accordance with the invention; and
FIG. 2 is a section along the line
REFERENCES:
patent: 269151 (1882-12-01), Woolley
patent: 2295068 (1942-09-01), Woodin
patent: 2792779 (1957-05-01), Toeppen et al.
patent: 4308794 (1982-01-01), Adamoli et al.
Burr Edgar S.
Facit Aktiebolag
Pearson Charles A.
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