Note: Descriptions are shown in the official language in which they were submitted.
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Electromagnetic Display Device
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The invention relates to an electromagnetic display
device, comprising a panel which consists of a number
of substantially square pixels which are divided into
two parts. Each pixel is provided with a rotatably
mounted bistable tilting flap, which is asymmetrical
in relation to its rotational axis. Said tilting flap
covers orie of the two portions of the panel surface
iri the pixel zone when the flap lies in each of its
two stable positions. The side of the tilting flap
facirig the front side of the panel and the portion of
the panel in the pixel zone which is covered by the
tilting flap in this position has a first colour and
the other side of the tilting flap and the other
portion of the panel in the pixel zone has a second
colour. A permanent magnet is fitted to the tilting
flap in close proximity to the rotational axis. The
tilting flap is displaced from a first position into
a second position by an electromagnet which is
located on the reverse side of the panel and is
allocated to the pixels, and which has a coil body,
with coil head and coil base, and core.
Electromagnetic display devices of this kind are used
for the construction of display boards, in which the
displayed information can be changed, that is to say
exchanged or adapted, in a simple manner. To this
end, the display board comprises a multiplicity of
individual picture elements, the pixels, which are
arranged in the form of a matrix and can be switched
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back and forth between two different states, such
that they appear, for exainple, in a light or dark
colour. These pixels may be used to compose any
appropriate letters, numerals or other characters, a
matrix comprising seven cells of five pixels each
being sufficient for the display of most characters.
Patent specifications DE 35 01 912 C2 and DE 36 01
018 C2 disclose an electromagnetic display device of
this generic type which consists of a matrix of
square pixels arranged on a panel, each pixel being
equipped with a bistable tilting flap which is
rotatably mounted in two bearing brackets and is in
the form of a right-angled triangle, the rotational
axis being congruent with the hypotenuse of the
triangle. In both of its stable positions, the
tilting flap covers one half in each case of that
portion of the panel associated with the square
pixel, the respective visible portions of the panel
and tilting flap being coloured uniformly, and
differently for the two positions of the tilting
flap, for example black and white. The changeover
between the two display states of the pixel is
carried out by means of an electromagnet arranged
below the pixel, which comprises a coil body and pin-
shaped core, and the tilting flap equipped with a
permanent magnet tilting back and forth between the
two positions on the application of a corresponding
voltage. This construction of the individual pixel
allows almost complete utilization of the display
surface, with virtually no interspaces, by the
picture elements, which are only somewhat impaired by
the recesses required in the vicinity of the bearing
brackets. The result of this good area filling is
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good legibility of the letters, numerals and other
c:har.,acl.c,rs represente<1 by means of Lhe display
device, provided that they are sufficiently
illuminated by daylight or artificial light. At
poorly illuminated places or in darkness, on the
other harid, this type of display can only be used in
conjunction with an additional light source, which
lights up its front surface.
Patent specification EP 0 401 980 B1 describes a
display device that can also be read in darkness and
whose individual pixels each consists of a circular
disc, which has a radially extending slit and is
rotatably mounted on the rotational axis extending
perpendicular to the s].it on the diameter of the
circular disc. The circular disc can be rotated
through an angle of about 180 between two stops by
means of a permanent magnet located next to said
circular disc on the rotational axis and an
electromagnet arranged behind said permanent magnet.
As a consequence, in one position the light-coloured
front side of the circular disc is directed towards
the observer and the end of a fibre-optic light guide
in the slit becomes visible, whereas in the other
position the dark side of the circular disc faces
forwards and covers the fibre-optic light guide.
Patent specification EP 0 463 725 B1 discloses a
similarly constructed display device, in which the
circular disc is only rotated through 90 , so that,
in one position, the light-coloured front side and,
in the other position, the dark edge of the circular
disc, faces forwards. The light sources used to
illuminate the pixel, in particular light-emitting
diodes, are, in the first position of the pixel,
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visible through a circular opening in the circular disc and,
with the changeover of the pixel, are disconnected by means
of a reed contact.
The last-mentioned display devices possess, by virtue of the
light-coloured sources integrated into the pixel, the
advantage that they can also be operated and read in
darkness. However, this is countered by the disadvantage
that the portions of the pixel used for the display are
circular and, because of the electromagnetic display device
arranged next to the circular disc, are spaced from one
another. This results in a comparatively small area density
and therefore an impairment of the legibility of these
display devices. In addition, in the case of circular
pixels, the discs, at least in one of their switching
states, are not disposed parallel to the display plane, so
that the pixel has a different appearance when observed from
different directions. A particular disadvantage of pixels
formed as circular discs can be seen in the fact that the
light source is usually arranged behind the disc, which
leads to partial attenuation of the emitted light and
significantly impairs the legibility of the corresponding
display device from the side.
On this basis, it is a feature of an embodiment of the
present invention to provide an electromagnetic display
device that ensures good legibility of the information
presented both under light conditions and in darkness.
In accordance with one embodiment of the present invention
there is provided an electromagnetic display device,
comprising a base plate and a panel having a plurality of
substantially square pixels divided into two parts. Each
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pixel has an opening in the panel and is provided with a
rotatably mounted bistable tilting flap. The tilting flap
is asymmetrical in relation to its rotational axis. The
5 tilting flap covers one of two portions of the panel surface
in the pixel zone when the flap lies in each of its two
stable positions. A pin for each pixel is located on the
base plate and faces in a direction of the opening. A light
emitting diode is mounted on the pin. A first side of the
tilting flap faces a front side of the panel and the first
portion of the panel in the pixel zone is covered by the
tilting flap in this position and has a first colour. A
second side of the tilting flap and the second portion of
the panel in the pixel zone has a second colour. A
permanent magnet is fitted to the tilting flap in close
proximity to the rotational axis and the tilting flap is
displaced from a first position into a second position by an
electromagnet which is located on the reverse side of the
panel and is allocated to the pixels. The electromagnet has
a coil body and a coil base. The coil base is inserted into
the base plate and the coil head is fastened on the panel.
The present invention is based on the idea of forming the
electromagnetic display device with pixels that are readily
legible in daylight and are switchable back and forth by
means of bistable tilting flaps between two colours, for
example a light colour such as white or yellow, which may be
embodied as a reflective film, and a dark colour such as
black, and by providing each pixel with at least one light-
emitting diode (LED), which is preferably arranged in the
light-coloured region and promotes the legibility of the
display device in failing light and ensures good legibility
even in darkness. To this end the electromagnetic display
device is to be provided with square pixels, which are
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switchable between two colours, preferably a light and a
dark colour, by means of bistable tilting flaps, which
assume one of two possible positions on the pixel depending
on the switching state. For their movement, the tilting
flaps are fitted, in close proximity to their rotational
axis, with a permanent magnet which, depending on the
position of the tilting flap, is arranged with either its
north or south pole in the direction of the electromagnet,
which is arranged on the reverse side of the panel, is
allocated to the respective pixel and comprises a coil body
and a pin-shaped core, which is introduced into said coil
body and composed of electromagnetically soft or retentive
material. The use of a retentive material here has
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the advantage that, for triggering a switching
operation, magnetic reversal of the core is
sufficient, the current pulse on the coil can
therefore be considerably shorter than the actual
changeover operation of the tilting flap. At the same
time, the magnetization of the retentive core ensures
reliable holding of the tilting flap in the position,
once this has been set. To enstare the recognizability
of the display device according to the invention even
in darkness, each pixel is provided on its reverse
side with a light-emitting diode, which shines
through an opening introduced into the light-coloured
region of the pixel. In this application, the light-
emitting diode can be operated with such a low
current that its lifetime is virtually unlimited. A
base plate arranged behind the panel serves for
fixing the electromagnet and light-emitting diode in
defined positions and distances corresponding to the
grid dimensions of the pixels. To this end, the coil
bases are inserted into the base plate, which is
equipped with pins directed towards the openings in
the pixels, said pins receiving the light-emitting
diodes and, in this manner, ensuring a uniform
distance from the openings in the individual pixels,
which results in good legibility of the display
device in darkness.
A particularly simple and therefore preferred
rotational mounting of the tilting flaps is obtained
by integral moulding of corresponding bearing
brackets on the panel, which receives bearing pins
disposed at the ends of the rotational axis of the
tilting flap.
The tilting flap is, in its two stable positions,
required to cover in each case one half of the square
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pixel. This can be achieved, for example, by means of
a tilting flap desigiled in the form of a rectangle,
in which the rotational axis passes through one of
the long sides of the rectangle. A more favourable
weight distribution with respect to the rotational
axis, and therefore a lower moment of inertia,
however, is obtained by designing said tilting flap
in the form of a right-angled isosceles triangle, in
which the rotational axis is congruous with the
hypotenuse of the triangle. Greater switching speeds
and the possibility of 90 rotation of the display
without changing its physical properties are the
advantages or this design of the tilting flaps. For a
good area filling of the display board, the corners
adjacent to the rotational axis, and possibly other
corners, may also have to be provided with recesses
for receiving the bearing brackets.
The permanent magnet necessary for moving the tilting
flaps can, in the simplest case, be bonded onto the
tilting flap in the vicinity of the tilting axis.
In a further development of the invention, the
permaiient magnet is inserted into a recess introduced
into the tilting flap, which is subsequently closed,
for example glued up or welded. In this manner, the
permanent magnet is reliably protected against
harmful environmental effects and neither runs the
risk of corroding, falling off or moving.
In an advantageous embodiment of the invention,
attachment of the electromagnet to the panel and base
plate is carried out by means of detachable snap
connections which can be formed in recesses of the
panel and base plate with utilization of the
elasticity of the material, and in which a coil head
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and coil base can be engaged. This results in an
easier-to-repair, modular construction of the display
device according to the invention, in which
electromagnets and light-emitting diodes, but in
particular the panel with the tiiting flaps, can be
easily exchanged.
In a preferred embodiment, the base plate of the
display device is formed such that the coil base of
the electromagnet can be easily inserted and engaged
in the base plate from the side in a radial
direction, a bead on the base plate engaging in a
groove on the coil base so as to fix the
electromagriet against axial displacement. An
advaritage of this desigri of the display device lies
in the facilitat:ion of its assembly by means of
automatic means, which can simply slide in the
electromagnet in a radial direction, while the light-
emitting diode must be inserted axially.
Since the light-emitting diodes of the tilting flap
are exposed in one position and covered in the other,
the display device according to the invention can
readily be operated with permanently lit light-
emitting diodes. To reduce power consumption and
operating costs, however, it is recommended that the
light-emitting diodes be connected so that they are
switched on and off with the movements of the
associated tilting flap, that is to say only
illuminate when they are exposed by the associated
tilting flap.
For good legibility of the display device in
darkness, a larger angle of spread for the light
emitted from the individual pixels is desirable. To
this end the height of the pin, disposed on the base
plate, for the light-emitting diodes of the
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individual pixels is chosen such that the upper end
of the light-emitting diode terminaLes flush with the
front side of the panel, that is to say is in the
same plane-with the panel front side, and
consequently the attenuation of the light emitted by
the light-emitting diode by the side wall of the
opening is kept to a minimum, without impairment of
the moveinent of the tilting flaps. This flush method
of installation of the light-emitting diodes results
in a large reading angle, which permits rapid
apprehension of the picture element by the eye. In an
advantageous further development of the invention,
the individual pixels are equipped with a transparent
front pane, which is illuminated from its reverse
side by the light-emitting diode allocated to the
pixel and diffuses the transmitted light as a
diffuser. With this design of the pixels, it is
expedient for good illumination of the transparent
covering to design the opening in the panel such that
the light of the light-emitting diode can pass
through as large as possible a part of that portion
of the pixel that is not covered by the tilting flap.
In a further development of the invention, both
portions of each pixel are equipped with, in each
case, one or more light-emitting diodes, different
coloured light-emitting diodes being expediently used
on the two pixel portions, the colour of which is
matched to the respective coloration of those
portions of the pixel to which they are allocated. In
this manner, display devices can be provided which,
even in darkness, can display coloured characters
against a differently coloured background and are
therefore ideally suited for information or
advertising purposes.
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In an expedient embodiment of the invention, the
individual pixels on the panel can be arranged in the
form of a matrix, which, for example, may contain
seven lines with five pixels each, that is to say a
total of 35 pixels, it being possible to display
numerals, letters and other characters. From a
multiplicity of such display devices, display boards
for the representation of a plurality of characters
can be constructed, whose size can be flexibly
matched to need, depending on the particular purpose
of the panel. It is also conceivable, instead of the
matrix-like arrangement of pixels on the panel to
choose a strip-shaped arrangemerit, the strips being
arranged in columns or strips also forming a matrix
for the display of numerals, letters and characters.
Good space utilization of the area available on the
display board, and good legibility of the information
represented there requires, as far as possible,
complete utilization of the pixel area for the
display and the least possible interspace between the
areas used for the display, not only the immediately
adjacent pixels on a panel but also pixels arranged
side-by-side on adjacent panels. Here, the
accommodation of the bearing brackets becomes a
problem since, on one hand they should be arranged as
far as possible towards the outside at the pixel edge
in order not to impair the useful display area of the
pixel, but on the other hand this undesirably
increases the interspace between adjacent pixel rows.
As an expedient compromise solution to this problem,
the invention provides for arranging the bearing
brackets of a tilting flap so far towards the outside
that they partly project over the square pixel
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surface and, together with the bearing bracket of the
respective adjacent pixel, are arranged in the region
of recesses introduced at the corners of the square
pixel. To allow the continuation of this design even
over adjacent panels, the invention recommends that
the edges of each panel be provided with recesses in
the region of the bearing brackets, which recesses
can receive the projecting bearing brackets of the
adjacent panel. In this manner, a defined arrangement
of the pixels of adjacent panels with very small
interspaces is obtained, which is to the benefit of
the space utilization on the display board and the
legibility of the information displayed.
The field distribution of the magnetic field
generated by the electromagnet can be influenced by
the precise shape of the pin-shaped coil core. For
rapid and reliable tilting over of the tilting flaps,
it is desirable to have a high field intensity, and
thus a focusing of the field lines in the region of
the permanent magnet above the coil head. To this
end, the invention recommends extending the coil core
in an axial direction through the coil base, which
intensifies the focussing of the lines of force at
the coil head and at the same time reduces
undesirable leakage fields in the region of
neighbouring coils. The lower ends of the coil cores
can be inserted through bores in the circuit board,
to which the electrical connections of light-emitting
diodes and electromagnets are soldered for the power
supply. By this means, a guide, which facilitates the
assembly of the circuit board, and increased
mechanical stability of the entire arrangement are
obtained.
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Further details, features and advantages of the
invention according to the invention can be obtained
from the following descriptive part, in which a
typical embodiment of the invention is described in
greater detail by means of two drawings, wherein
Figure 1 shows a p_lan view of a display device
according to the invention, consisting of a
strip of pixels, and
Figure 2 shows a side view of a pixel of a display
device according to the invention, which is
partly drawn in section.
Figure 1 shows a plan view of an electromagnetic
display device according to the invention, which
consists of 5 pixels arranged on a strip. Each of the
pixels possesses an essentially square form with
recesses at the four corners and is divided into two
parts along its diagonal, each part being covered by
a tilting flap (1). The tilting flaps (1) possess the
form of right-angled isosceles triangles with
recesses at the corners, the hypotenuse (2) of the
triangles being congruent with the rotational axis of
the tilting flap. At both ends of the rotational axis
are arranged bearing pins (3), with which the tilting
flap is rotatably mounted in bearing brackets (4). At
the bottom right-hand side of each pixel, the panel
(5) is provided with an opening, through which a
light-emitting diode (6) can be seen. At the second
pixel from the left, the tilting flap (1) is
represented in a position in which it covers the
light-emitting diode (6). The upward facing side of
the tilting flap (1) and the visible part of that
portion of the panel (5) associated with the pixel
are coloured a dark colour, shown here as hatch
marks. The other four pixels shown in the drawing, on
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the other hand, are in the other possible switching
state, in which the tilting flap assumes a position
in whi.ch the pixel appears in a light colour and the
light-emitting diode (6) can be seen. The switchover
between the two positions is carried out by means of
an electromagnet arranged below each pixel, which
acts on the permanent magnet (7) fastened to the
tilting flap. The panel (5) is provided on its sides
with recesses (8), which are contiguous with the
bearing brackets (4) and permit a plurality of lines
of the electromagnetic display device according to
the invention to be arranged adjacently in a defined
position without interspace between the pixels, and
thus form, for example, a matrix of seven such lines,
with which letters, numerals and other characters can
be easily represented.
Figure 2 shows a pixel of the display device
according to the invention in side view, drawn partly
in sectional view. A section through the panel (5),
shown extending partly through the centre plane of
the pixel and partly through the plane of the light-
emitting diode, with the tilting flap and the opening
with the light-emitting diode (6) can be seen, the
upper end of the light-emitting diode (6) being in a
plane with the front side of the panel (5). Below the
pixel centre, an electromagnet is arranged, which
consists of a coil body (9) with coil head (11)
arranged above and coil base (12) arranged below, and
a pin-shaped core (10) consisting of retentive
material. Coil head (11) and coil base (12) engage in
corresponding recesses in panel (5) and base plate
(16), where they engage in detachable snap
connections. To facilitate the exchange of the panel
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(5), only two of the pixels, for example the second
and fourth, are here equipped with snap connections
for the spool head (11). On the base plate (16),
there is arranged a pin (13) to be directed to the
opening for the light-emitting diode (6) in the panel
(5), which pin has on its upper end face a recess in
which a light-emitting diode (6) is held in a well
defined position. Axial grooves on its surface
extending in an axial direction serve to receive the
electrical connections (14) of the light emitting
diode (6). For power supply to the pixel, they and
the electrical connections (15) of the electromagnet
are firmly soldered to a circuit board, which
additionally receives the lower end of the pin-shaped
core (10) in a bore, whereby the position of the
pixel is reliably fixed on the circuit board.
As a result, an electromagnetic display device is
obtained, which is characterized by high area
coverage and is recognisable and legible equally well
by day and night.
