Typewriting machines – Typing by other than type-face or type-die – Character formation by impact
Patent
1986-08-19
1988-03-22
Sewell, Paul T.
Typewriting machines
Typing by other than type-face or type-die
Character formation by impact
101 9305, B41J 312
Patent
active
047324988
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a needle matrix printer comprising a set of needles each of which is mounted to be longitudinally slidable and is associated with an electrical lead which is flexible over at least part of its length and is situated in a plane containing said needle, a part of which is in engagement with the central part of said lead, at least one segment of the said lead being situated in the air-gap of a permanent magnet having a homogeneous magnetic field perpendicular to said plane, a lateral force being exerted on said lead when a current passes through it.
G.B.-A-1,423,518 already proposes actuating an electrodynamic matrix printer needle, for which purpose a loop is formed along a needle portion spaced laterally from its guidance axis. Current pulses are passed through said needle, said loop being disposed opposite the end of a magnetic bar which produces a magnetic field diverging in the direction of the needle loop. When a current pulse passes through said loop, it tends to embrace the maximum magnetic flux leaving the magnetic bar so that the loop is attracted towards the end of the bar.
A solution of this kind has considerable disadvantages. More particularly, it does not allow a plurality of needles to be stacked, because of the presence of the loops, so that a matrix printer comprising a plurality of needles is practically impossible to construct. Also, this solution actuates the needle by pushing it from its centre. Since, on the one hand, said needle must be capable of undergoing deformation easily to allow the movement of its free end towards the printing surface and, on the other hand, it must be sufficiently rigid to withstand compression, two contradictory requirements have to be satisfied simultaneously. It must also be noted that this type of actuation moves the needle at a speed which tends towards zero and a compression force which increases so that the kinetic energy in turn tends towards zero. This type of actuation is therefore unsuitable for a printing method in which the ink is transferred following an impact, from its support to the sheet for printing.
JP-A-58 145 467 describes a printer in which each needle is mounted slidably and its rear end bears against a segment of an electrical lead immersed in a homogeneous magnetic field. One end of said lead is fixed while its other is mounted to be longitudinally slidable so that when a current passes through said lead a lateral force is exerted thereon. This force produces lateral deformation of this lead by longitudinal sliding of its end. This laterally deformed lead part acts on the rear end of the needle and thus moves it longitudinally.
This solution has one important disadvantage. Since the needle is axially thrust by the laterally deflected lead portion, the force exerted on said needle is limited by the inherent flexibility of said lead. As soon as the needle meets any resistance in its movement, the lead deflects in the opposite direction so that the striking force and/or compression force of the needle can be only low and in any case does not exceed the force required to deflect the lead, which must obviously be as low as possible. This solution therefore combines two contradictory conditions.
Another electrodynamic solution is described in U.S. Pat. No. 3,918,567, which proposes a stack of hammers formed by plates having elastic tongues formed by cut-outs and intended to allow transverse movement of said plates, which are immersed in a magnetic field perpendicular to their planes, when a current is fed longitudinally along said plates.
Practical problems which are very difficult to solve arise in embodying such a solution. Each plate has a length equivalent to the width of the printing surface. This means a very long magnet and sufficient rigidity of the plates, hence a width and thickness proportional to said length, and hence a high mass, which necessitates a considerable current to actuate the plate at high speed. The example given indicates 40 watts so that it is easy to calculate that each plate must be fed
REFERENCES:
patent: 3754199 (1973-08-01), Lisinski
patent: 4493568 (1985-01-01), Estabrooks
Joyeux Didier
Vermot-Gaud Jacques
Battelle (Memorial Institute)
Sewell Paul T.
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