Note: Descriptions are shown in the official language in which they were submitted.
11398~3
PERMANENT MAGNET FOR A BISTABLE ELEMENT AND BISTABLE
ELEMENT AND DATA DISPLAY UNITS l~ITH AT LEAST ONE SUCI~
ELEMENT
The invention relates to a permanent ~agnet for a bistable
element activated by magnetic means as well as such elements and
data display units provided with at least one unit.
In such a bistable element, data display is accomplished
by means of a rotor made up of a cylindrical body (U.S. patent
2,740,955), spherical body (U.S. patent 3,036,300) or even flat
body tU.S. patent 1,191,023) on one of whose surfaces--which for
each body form listed above are the halves of the lateral sur-
face, the hemispherical surfaces, or the opposite sides, respec-
tively--are found, in at least one area, an indication differing
from the one provided by the other surface.
For example, these different indications could be conven-
tional fields of color, such as white or yellow on the one hand
and black on the other hand,
Depending on which surface is visible, the body in question
makes it possible to provide an indication which is either suf-
ficient unto itself (U.S. patents 2,415,452 and 2,740J955~ or,
in combination with other e~ements, contributes to making up a
more compiicated sign, such as the formation of le~ers or
numbers (U.S. patents 1,1~1~023, 1,799,731 and 3,036,300).
These characters then make it possible,`among other applications,
to compose display panels showing schedules, train or airplane
times, sports results, etc.`
1139~13
As indicated above, in order to orient each rotor of a
bistable element correctly, it is possible to induce 180
rotation around its axis by magnetic means.
Such magnetic means are described in the patents noted above
and in numerous other documents, for example in U.S. patent
3,025,512 in which, exclllsive o~ the rotor, these Inea.ls include:
a ~ermanent magnet which interlccl:s in rotation with
the rotor it i5 attached to in a position such that the
axes passing through the NnRTH and SOUT~I poles of the per-
manent magnet are basically radial to the a~is of rotation
of the motor;
a stator constituting the support for the following
component;
an electromagnet attached to the stator and in a posi-
tion such that its North and South poles lie both more or
less symetrically to the axis of the rotation of the rotor
and in the plane in which, in conjunction with said rotor,
the poles of the rotor's permanent magnet turn;
a device for mobile connection of the electromagnet
to a direct current source with reversible polarlty,
It is known that:
on the one hand, two magnets placed in the presence of one
another combine to exercise forces of attraction between their
ends with different polarities and repulsion between their ends
with the same polarities; and
on the other hand, reversing the polarity of the direct
current feeding the electromagnet results in a reversal of the
magnetic field of that electromagnet.
1139813
Thus i1: can be seen that, depending on the magnetic field
created by the electromagnet of the stator, the permanent magnet
and consequently the rotor are:
either held in place if the permanent magnet was pro-
perly oriented;or caused to rotate 180 so that the permanent magnet
assumes the proper position.
The current feed to the electromagnet can be switched off
immediately because,the bars making up the North-South poles of
the electromagnet, even if they no longer have any remanent mag-
netismj are made of magnetic material and therefore would still
attract the poles of the permanent magnet, thus keeping the rotor
stabilized in the position determined by the latest command.
The principle of operation of such a bistable element is
thus quite simple.
But there would be a problem, however, if before a rotation
command was given the rotor was fixed in a position where thé
axis passing through the North-South poles of its permanent magnet
was perfectly in line with the axis through the North and South
poles of the electromagnet.
In such a case, the forces of repulsion would then produce
no rotational torque, and instead would offset each other.
In order to overcome this problem when using magnetic acti-
vating methods, one known approach is to use other devices which
intervene so that between commands, the North-South axes of the
electromagnet and of the permanent magnet are always out of line
with respect to one another.
Among these other devices principally are found mechanical
stops generally limiting the angle of the rotor's pivoting with
1139~3~ 3
respect to the stator to less than 180 (U.S. patent 3,025,512),
which obviously, in the event of a cylindrical or spherical body,
reduces the surface area usable for display purposes or, in the
case of a flat body, tilts the display surfaces, and tilts them
at a different angle depending upon which surface is exposed to
view; this, in at least one of the positions, might negati~ely
affect visibility.
In some variants which exist, some of which make it possible
to continue having complete 180 pivoting, the action of these
mechanical stops is combined with the action of a magnetic field
created by a supplementary permanent magnet mounted on the stator
(U.S. patent 2,740,955 and 3,518,661) and/or the action resulting
from a characteristic positioning of the permanent magnet of the
rotor, wherein this permanent magnet, when the rotor is stabi-
lized, may have the axis of North-South poles which, in relation
to the axis of the poles of the electromagnet, is offsot in
parallel ~U.S patent 2,740,955) or is tilted (U.S. patent 3,624,941).
With all these other methods, the distance of the poles of the
electromagnet from those of the permanent magnet decreases the
level of magnetic attraction in the resting state and therefore
has a negative effect on the stability of the rotor between
commands. Furthermore, by virtue of these mechanical methods
and/or magnetic methods other than those essential for the acti-
vation of the rotor, such a bistable element is both complex
and, especially, bulky and relatively expensive.
These defects are all the more serious as the element in
question is used rarely but, generally at least, in large quantities.
1139813
Por example, to make up only one changeable character,
there are systems currently in use which involve thirty-five of
these elements in five vertical rows of seven elements each.
Hence one result which is a goal of the invention is a
permanent magnet for a bistabl0 element of the type referred to
above which, in order than its rotor not become stabilized in
positions where the axes of the permanent magnet of the rotor
and of the electromagnet of the stator would not be in an un-
satisfactory position relative to each other, uses no means other
than those which are essential for activating the rotor, yielding
an element which accordingly is simple, not bulky and inexpensive
to manufacture.
One other result of this invention is such a bistable rotor
whose rotations may be 180 exactly, said rotations always taking
place in the same direction.
A further result of the invention is such an element whose
methods of activation involve high torque. at a low level of power
consumption and are fully protected from blows and dust and from
interference stemming from outside magnetic fields.
~ lso a result of the invention is an element which is very
stable in the resting state, even in gusty winds.
To accomplish this, the object of the invention is a per-
manent magnet for a bistable element of the type referred to above
which, when seen in profile, has its North and South poles on
the same radial line to the axis of rotation and has over those
areas where said poles are.located has contours which, in rela-
tion to said axis of rotation:
on the one hand, are diametrically opposed; and
on the other hand, situate fractions of the aforementioned
areas at different distances from that axis depending on whether
they are Oil gne ~.~.de Q~ t~e. ot~er of the radi~l line~
11391313 `~
Another object of the invention is these bistable elements
and data display units consisting of at least one such element.
The following description, provided as a nonlimitative
example and with reference to the attached drawing!;, Wl~ 1 help
make the invention easier to understand. The drawlngs are
schematic representations of the followlng:
Figure l. An element seen in cross section through the
axis of rotation of the rotor.
Figure 2. The element seen in cross section along II I~
in Figure l.
Figure 3. A permanent magnet of a known type.
Figure 4. A permanent magnet according to the invention
Figure 5. A large scale view of detail from Figure 4.
Figure 6. A row of elements making up a display unit.
Figure 7. Schematically, such a unit seen in profile.
Figure 8. Schematically, the front surface of such a unit.
With reference to Figures l and 2, it can be seen that the
element in question includes a rotor l formed by a cylindrical
body 2 which has, on its lateral surface and in a known manner,
two diametrically opposed zones 2a and 2b with dif~erent indica-
tions 3a and 3b, such as one reflectorized yellow patch 3a and
one flat black patch 3b.
The rotor l is borne on an axis 4 which rotates freely
within a bearing 5 which guides its rotation as well as stops
its movement in at least one direction as will be explained below.
To properly orient the rotor so that the indications 3a
and 3b which are suited for the time being are visible, the rotor
is caused to rotate by magnetic means including:
~139~1.3
a permanent magnet 6 rotating of a piece with the
rotor 1 to which it is attached in such a way that the ~
axis 7, passing through its North N 6 and South S 6 poles,
is radial to the axis of rotation of the rotor;
a stator 8 made up of one support 9 for an electro-
magnet 10;
the aforementioned electromagnet, attached to the
stator, and consisting of a bar 11 of magn~ ic n~aterial
bent into a U shape and a winding 12 connected with two
connecting studs 13;
a connecting circuit 14 for the studs 13, tying them
into a direct current source 15 through a reversing switch 16
allowing for short-term and reversible feeding of the -
winding 12.
The bar 11 may thus be temporarily magnetized in the sense
selected and the end of each of its branches 17, 1~, thus alter-
nately giving them a North pole N 10 and South pole S 10.
The branches 17, 18 of the bar 11 are arra~ged both in
parallel and symetrically with respect to the axis 4, and their
free ends are well within the P ~ within which the poles N 6,
S 6 of the permanent magnet 6 turn.
If the current feed is such that the poleg opposite one
another of the permanent magnet 6 and the electromagnet 10 are
of opposite polarity ~Figure 2), the reciprocal forces of attrac-
tion which result cause the permanent magnet to remain where
it is. On the other hand, if the poles in question are of the
same polarity, repulsive forces develop which, if they are not
offsetting, bring about a 180 rotation of the permanent magnet
6 until the conditions described above are achieved.
~ - 8 - 1139813
After the current.feed to the winding is switched
off, because of the remanent magnetism of the bar 11 or
simply because its branches 17, 18 are of a magnetic
material, the poles of the permanent magnet 6 are main-
tained near the branches 17, 18 and thus retain the last
position induced.
We shall now descr.ibe how, in accordance with the
invention and without any other mechanical and/or magnetic
means, the rotor 1 is kept from becoming stabilized in a
lQ position where the radial line 7 through the poles of the
permanent magnet 6 would be exactly the same as the one
19 through the poles of the electromagnet 10.
That situation, which would be possible with a
permanent magnet of a known type, would result in a situation
where, when the current is reversed (Figure 3), there would
be a balancing of the repulsion forces F and F' which would
not allow the permanent magnet 20 to rotate.
It is therefore quite necessary that in the resting
position the two lines 7 and 19 be out of phase by a given
angle A.
In accordance with one essential trait of the in-
vention, this~result is obtained by abrupt and sudden contours
or cuts 21, 22 ~Figure 4) in the permanent magnet 6, this in
areas 23, 24 which have the poles, and by the fact that these
cuts, in relation to the axis of rotation 4, are diametrically
opposed and located at different distances from the fractions
of areas 23a, 24a, on the one hand and 23b, 24b on the other
hand, delimited by radial line 7.
This result is attributable to the fact than in any
magnetic attraction between two bodies, the stable position
toward which the system tends is the one corresponding to
the maximum flux.
X
~1398~.3
In fact, the flux, and hence the magnetic force, increases
as the clearance E decreases; on the assumption that lines 7 and
19 are initially in line, the areas 23a, 24a would be subjected
to greater forces of attraction than those affecting fractions
23b, 24b, and the difference would therefore create a rotational
torque existing until the forces acting are in balance (see lines
of force in Figure 5).
The angle A of being out of phase is proportional to the
size o the cut and to the size of the branches of the electro-
magnet 10.
On the other hand, the permanent magnet 6 may have any
shape whatsoever, such as, for example~ the one represented by
a heavy line in Figure 4 or the one represented by fine dashes
and the cross-hatching also in Figure 4.
As ~he cut does not modify the actual position of the
~ e r~an~n~ fn~g~et
poles of the e~cc~romngnct, when the magnetic field is reversed
in the electromagnet 10, the situation is the same as if the
permanent magnet had been tilted by mechanical and/or magnetic
means.
Accordingly, every time the current changes, forces P and
F' are unequal and the rotor therefore pivots, this always in
the same direction, namely toward the cut out side, wh~ch dis-
tinguishes it from other known bistable elements which always
pivot a maximum of 180 and alternately~in one direction and
then the other.
It is quite obvious that, without going outside the scope
of the invention, this permanent magnet may be used to fit out
a bistable element in which the rotor body could be of any
shape, such as cylindrical, spherical or flat,
11398~3
-- 10 --
In one preferred method of manufacture, if only
because of its lack of sensitivity to the wind, the body
of the rotor is cylindrical or slightly arched and, in
accordance with one of the invention's characteristics,
completely covers the electromagnet 10 and the permanent
magnet, first to protect them from shocks, dust, and the
effects of outside magnetic fields, and second, to provide
the largest possible surface area for the indication~ to
be displayed.
In accordance with another characteristic, the
bearing 5 for the rotational axis of the rotor and hence
for the permanent magnet 6 is precisely positioned with
respect to the branches 17, 18 of the electromagnet, this
by inserting said branches in holes 25 drilled in the
rign 26 making up the bearing 5. Consequently, clearance E
~-~y be reduced to the lowest possible value, permitting
the obtaining of high rotational torque at very low levels
of power consumption.
The axis of rotation 4, part of the rotor, may be
anchored or simply placed in the bearing 5 until it butts
against the end 26 bearing 5 in ring 26, this without
there being any need to provide for a retaining device.
In fact, by virtue of the law of maximum flux referred to
above, the permanent magnet will be drawn toward the in-
side of the branches of the electromagnet and will not be
able to escape.
The support 9 for the electromagnet 10 is formed
by a radial plate which is the fictive extension of the
axis of rotation 4, and against which the end of the rotor
with the cylindrical overhang nearly abuts, thereby
improving airtightness.
'~-
~39E~ 3
The plate may also feature a small collar 27 or ring
capped by the body of the rotor in order to guide the rotor or
simply constituting a protective baffle.
For greater stability, the plate also has a base 28 providing
proper seating for the entire bistable element and/or studs 29
which will form positioning shims by pressing against similar
elements or other stops.
For the same reason, when constructing visual display units
made up of several rows of elements, the elements in the same
row or in the same unit could be supported by a single support 30.
For further protection of the bistable elements, in front
of the visual display unit could be a mask 31 which has, opposite
each body 2, cutouts 32 in the shape of the character or letter
to be shown, for example circular ones, which then makes it possible
to mount colored fields 3a, 3b with larger surfaces and in different
shapes.
