Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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The invention relates to an electromagnet comprising two cylindri-
cal pole-shoes which are coaxially arranged end to end and which are made
of a magnetically conductive material, the pole-shoes being magnetically
separated from each other by an intermediate ring, a cylindrical armature
which is displaceable against the force of a spring being slidable in the
said pole-shoes when a coil arranged about the pole-shoes is energi7ed.
In a known electromagnet of the kind set forth (German Offenlegungs- ;
schrift 2.119.415) which is used in a printing device, the pole-shoes, the
intermediate ring and the electrical excitation coil are connected to the
upper side and the lower side of a cylindrical housing by means of a
clamping construction. The clamping action is obtained by means of a
construction consisting of nuts, bolts and flanges.
The known electromagnet has a drawback in that its assembly
requires a comparatively large number of operations.
The invention has for its object to provide an electromagnet which -
.~ requires fewer assembly operations. -
According to the present invention, then, there is provided an
electromagnet comprising two magnetically conductive pole-shoes coaxially -
arranged end to end; an intermediate ring magnetically separating one of
said pole-shoes from the other; a cylindrical armature slidably mounted
within said pole-shoes, said armature being actuatable in one direction
by energization of a coil arranged axially about said pole-shoes inter-
mediate ring; and a reset spring mounted within said pole-shoes adjacent
to the armature, said spring being compressed upon actuation of the
armature, wherein the pole-shoes, intermediate ring and coil are inter-
connected by a connecting member, composed of a suitab]e plastic material,
i the connecting member being situated between said pole-shoes and the coil.
Electromagnets in accordance with the invention are particularly
suitable for use in printing devices of the type where a character to
~, 30 be printed is composed of a number of dots. Printing devices of this -
kind are generally referred to as matrix printers. The printing member
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10675~;6
of these printing devices is formed by a wire-like recording pin which is
driven by an electromagnet.
An electromagnet in accordance with the invention which is parti-
cularly suitable for matrix printers is characterized in that a recording
pin is connected to the armature.
The invention will be described in detail hereinafter with reference
to the drawing.
Figure 1 is a longitudinal sectional view of a preferred embodiment
of an electromagnet for a matrix printer in accordance with the invention,
Figure 2 is partly a side elevation and partly a longitudinal
sectional view at an increased scale of an armature of the electromagnet
shown in Figure 1.
Figure 3 is a front view of the armature shown in Figure 2.
The electromagnet for a matrix printer shown in Figure 1 comprises
two cylindrical pole-shoes 1 and 3 which are coaxially arranged one in the
prolongation of the other and which are made of a suitably magnetically
conductive material. The inner diameter of the pole-shoes 1 and 3 are equal
in a preferred embodiment. The pole-shoes 1 and 3 are physically and
magnetically separated from each other by an intermediate ring 5 of a
magnetically non-conductive material such as, for example, brass. By way of
a cylindrical member 7 composed of thermoplastic synthetic matorial, the
pole-shoes 1 and 3 and the intermediate rlng 5 are connected to an electri-
cal excitation coil 9 which is coaxial with the pole-shoes 1 and 3.
Consequently, the connecting member 7 not only serves as a connecting mem-
ber but also as a coil-former. In the pole-shoes 1 and 3 a cylindrical
armature 11 is slidably arranged. When the coil 9 is energized, the arma-
ture 11 is displaced downwards against the force of a helical reset spring
13. The upper end of the reset spring 13 bears against the armature 11
and its lower end bears against a rigid cylindrical support 15 on the pole-
shoe 3.
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The armature 11 includes a support body made of a synthetic
material and comprising a cylindrical central portion 17 and two cylindrical
flanges 19 and 21. The diameter of the central portion 17 is smaller than
that of the two cylindrical flanges 19 and 21, so that a space remains
between the support body of synthetic material on the one hand and the pole-
shoes 1 and intermediate ring 5 on the other hand. This space accommodates
a hollow axial cylinder 23 composed of a suitably magnetically conductive
material. The outer diameter of the cylinder 23 is slightly smaller than
the inner diameter of the pole-shoes 1 and 3 and the intermediate ring 5.
Because the outer diameter of the flanges 19 and 21 substantially equals
the inner diameter of the pole-shoes and the intermediate ring, only the
outer circumference of the flanges 19 and 21 serves as a guide surface for ~ -~
the armature 11.
Because the armature 11 is partly made of a synthetic material, a
; saving is realized as regards weight as well as regards the comparatively
expensive magnetic material. Moreover, the friction on the armature is re-
duced.
In the non-energized condition of the coil 9, the armature 11 is
lightly biased by the reset spring 13 against a cylindrical abutment 25
which is rigidly provided in the pole-shoe 1.
A wire shaped recording pin 27 is connected to armature 11 by means
of a holder 29. The holdcr 29 ls rigidly connectod to thc recording pin
` 27. On the lower side of the flange 21 there is provided a flexible
edge 31 which serves to locate the holder 29 by allowing th~ holder to
be snapped into placo. Around the holder 29 there is provided a grommet
l 33 for supporting the reset spring 13. The holder 29 is preferably made
Z of brass, whilst the gromme~ 33 is preferably made of a synthetic material.
An elastic connection between armature and recording pin, having a damping
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. 10675~6
PHD. 75-033.
19-2-1976.
effect, is thus realized.
The pole-shoes 1 and 3 are provided with cir-
cumferential grooves 35 and 37, respectively, which have
a rectangular section and ~hich serve to anchor the con-
necting member 7. The connecting member 7 is cast or mould-
ed after the pole-shoes 1 and 3 and the intermediate ring
5 have been arranged on a mandril in the correct position
relative to each other. A casting die or mould is arrang-
; ed around this assembly on the mandril. The pre-manufactured
coil may form part of this mould. It is alternatively pos-
sible~ however, to wlnd the coil on the connecting member
; 7 only after the moulding or casting has been completad.
The thermoplastic material for the connecting member 7 is
pre~erably a fibreglass-reinforced polycarbonate or poly-
amide. Even though thermoplastic synthetic materia~s are
preferably used for the connecting member, thermosetting
materials are also feasible.
The synthetio part o~ the armature 11 i9 pro-
~erably made of polymer isate~ notably copolymerlsates
or homopolymerisates. In order to reduce the ~rictlon
between the armature and the pole-shoes and the inter~e-
diate ring~ polytetrafluoroethylene is preferably added
.. . . .
I to the said polymerisates.
As appears from the Figs. 2 and 3, the armature
11 can be provided with longitudinal grooves 41. The frict-
ion caused by particles which have become detached from
the armature and the pole-shoes is reduced by these groo~es,
1 5
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PHD. 75-33.
19-2-1976.
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because these particles collect therein.
Even though the invention has been described
with reference to an electromagnet for a printing device,
the invention is by no means restricted thereto. The arma-
ture can inter alia co-operate with hinge arms, levers etc.,
for example, for driving a step mechanism in a counting
device, The armature of an electromagnet in accordance
with the invention can be embodied in various ways. For
example, the entire armature can be made of a magnetically
conductive material.
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