Card – picture – or sign exhibiting – Changing exhibitor – Alphanumeric device
Reexamination Certificate
1999-08-16
2001-08-14
Silbermann, Joanne (Department: 3628)
Card, picture, or sign exhibiting
Changing exhibitor
Alphanumeric device
C340S815620, C040S452000
Reexamination Certificate
active
06272778
ABSTRACT:
The invention relates to a display element for an electromagnet display device. Such display devices are normally formed by an array of display elements which collectively produce indicia or signs. They are used for numerous purposes, e.g. as destination signs in public transportation vehicles such as busses.
Each display element or “dot” generally has a disc which is mounted to a frame in such a manner that it can turn between two operating positions limited by stops of the frame. In a first of the operating positions an ON-side of the disc which normally has a yellow or white color (and in any case contrasts with respect to the background color of the display frame) is directed towards the viewing direction. In the second operating position the disc presents its OFF-side to the viewing direction which has essentially the same (non-contrasting) color as the background of the frame.
The disc of each display element is moved from its ON-position to its OFF-position and vice versa by an electromagnetic drive system comprising a permanent magnet attached to the disc and an electromagnet fixed to the frame. The disc operating position is determined by an electric current running through the coil of the electromagnet.
Display elements of the type to which the invention refers are subject to substantial development work with the aim to provide best possible visibility and reliable operation at least possible cost. An important factor with respect to this development work refers to the operation of the electromagnetic disc drive system. It is important to minimize the consumption of electric power, mainly where the displays are battery operated. To this end it is standard practice to use for the ferromagnetic core of the electromagnet a material which has a high magnetic remanence and simultaneously allows changing of the magnetic polarity in an electromagnetic field with relatively little electric power. Such a ferromagnetic core retains its magnetic field when the electric current in the surrounding coil is switched off. Therefore electric power is consumed only for changing the operating positions of the dots. No electric current is needed as long as the indicia which are to be displayed remain unchanged.
In most commercially available displays the electromagnetic drive system uses two electromagnets which are located in such a manner that the permanent magnet attached to the disc extends essentially along a line connecting two tips of the magnets having opposed polarity. This allows reliable operation, because in each operating position each of the poles of the permanent magnet is attracted by a closely located tip of an electromagnet which tip has an opposed polarity. Examples of this standard design are shown in U.S. Pat. No. 4,577,427 and EP 0731435 A1. This design, however, is costly, because on the one hand the high remanence material of the core of the electromagnet suitable for providing the above explained function is expensive and on the other hand the labour cost associated with making and assembling two coils is substantial.
There have been numerous efforts in the prior art to reduce this cost while simultaneously allowing reliable operation.
A simple possibility is to use a U-shaped ferromagnetic rod with only one coil. An example of this approach is shown in U.S. Pat. No. 5,005,305. It does, however, not achieve a cost reduction, because a large amount of the costly high remanence core material is needed and the assembly of the U-shaped electromagnet is difficult.
In another prior art design (shown for example in EP 0247045 B1) the display disc is shaped as a triangular flap which pivots about an axis running along an edge of the triangle. Here the magnet is positioned in the flap with its magnetic axis perpendicular to the surface of the flap. In one of the operating positions the magnet sits essentially on a tip of the ferromagnetic rod of the electromagnet. It is attracted thereby if the neighbouring poles are of different polarity and it is repulsed when the polarity of the electromagnet is switched over. This design, however, is limited to displays using the flap type triangular disc which is disadvantageous concerning other factors, such as production cost and visibility.
A further prior art approach to operate with only one electromagnet is shown for example in U.S. Pat. Nos. 4,914,427 and 5,055,832. Here a cylindrical permanent magnet is mounted on one of the pins about which the disc pivots. It has the shape of a thin cylinder centered on the pivoting pin and is magnetized transverse to the median plane of the disc. This design is suitable only for large sizes of displays such as highway signs. The assembly of the required parts is not feasible at tolerable cost for small signs which have surface areas of the discs of less than 3 cm
2
or even less than 2 cm
2
.
On this basis the instant invention is concerned with the problem to provide a display element which allows reliable operation at reduced cost.
To this end the invention proposes a display element having a main viewing direction and comprising a frame and a disc mounted to the frame by means of a rotation bearing for pivoting of the disc about a pivoting axis, the pivoting axis running essentially in a display main plane which extends perpendicular to the main viewing direction, the disc having two differently colored sides, an ON-side the color of which contrasts against the background color of the frame and an OFF-side having a non-contrasting color, the bearing allowing pivoting of the disc about the pivoting axis between two operating positions, an ON-position where it rests against a first stop and its ON-side is directed towards the main viewing direction and an OFF-position where it rests against a second stop and its OFF-side is directed towards the viewing direction, an electromagnetic drive system for driving the disc from one of the operating positions to the other of the operating positions and comprising a permanent magnet attached to the disc and an electromagnet attached to the frame and having a high remanence core and a coil surrounding the core, wherein two portions of the disc extend in a disc plane on both sides of the pivoting axis, the permanent magnet is attached to the disc with its polar axis running essentially parallel to the disc and extending across the pivoting axis whereby its poles are located on differing sides thereof, the turning angle of the disc between the operating positions is less than 180°, the magnetic drive system has a single electromagnet and a driving tip of the ferromagnetic core is located sidewise of the pivoting axis such that in each of the operating positions one of the poles of the permanent magnet is directed towards the driving tip and the driving tip is in one of the operating positions rearward and in the other of the operating positions forward relative to the disc plane
38
.
Experimental studies in the context of the instant invention have shown, that, by maintaining the mentioned conditions concerning the relative position of the disc, the permanent magnet and the electromagnet, a highly reliable operation of electromagnet display elements can be achieved with a single electromagnet which has a non-U-shaped, preferably straight, core. Thereby a substantial reduction of cost can be achieved, while maintaining the required operation and good visibility.
Further improvement of the operation is achieved by preferred features which are set forth in the subclaims and in the following detailed description of the invention. These preferred features can be used individually or in any suitable combination.
The invention is further explained with reference to a preferred embodiment represented in the drawings, wherein
FIG. 1
shows a front plane view of a display element in the ON-position,
FIG. 2
shows a front plane view of a display element in the OFF-position,
FIG. 3
shows a cross-sectional view of the display element of
FIG. 1
,
FIG. 4
shows a cross-sectional view of the display element of FIG.
2
.
REFERENCES:
patent: 3295238 (1967-01-01)
Chadbourne & Parke LLP
Lite Vision, Inc
Silbermann Joanne
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