EP1591985A2

EP1591985A2 - Electromagnetic display panel

Info

Publication number: EP1591985A2
Application number: EP05007969A
Authority: EP
Inventors: Milan Bavec; Franc Justin; Janez Ropret; Janez Pirs
Original assignee: Iskra Mehanizmi Industrija mehanizmov aparatov in sistemov dd
Current assignee: Iskra Mehanizmi Industrija mehanizmov aparatov in sistemov dd
Priority date: 2004-04-28
Filing date: 2005-04-12
Publication date: 2005-11-02
Also published as: RU2004134001A; SI21768A; CN1691096A; EP1591985A3

Abstract

A novel construction, of an electromagnetic display, which allows for the significant reduction of the fabrication costs is described. The construction is adapted to a batch processing of the electromagnetic display panel pixels (P), which can optionally use novel electromagnetic driving as well as illumination concept. According to the described construction concept the display pixels (P) are integrated into smaller functional groups - segments, within which all static parts of the display pixels are joined in a monolithic block (1), which can be mass-produced in an automatic process. Due to the monolithic design the number of constituent parts is reduced to minimum and the mechanical tolerances can be kept tighter. This in turn allows the other operations like solenoid (5) winding, pixel flaps (2) insertion, contacting/mounting pins (4a + 4b) injection, etc to be performed simultaneously for all pixel elements joint in the said basic display segment. The described display panel design also applies a novel concept of display pixel illumination in low ambient light conditions based on the use of UV light luminescent paints replacing the discrete pixel illumination by light sources associated with each display pixel (for example: LED,...) as well as novel electromagnetic display pixel driving, reducing the crosstalk between neighboring display pixels based on the use of plasto-magnets built-in in the display flaps during the injection molding production process.

Description

OBJECTIVE OF THE INVENTION

The objective of the invention are display elements for relatively large medium information content flat display panels, with high contrast, excellent visibility, wide viewing angle and inherent memory for traffic signs, buses' and trains' destination displays, large information display panels in airports, bus and railway stations, sporting events, etc.

TECHNICAL FIELD OF THE INVENTION

According to the international patent classification, the patent application is classified in the groups G09F 3/4 and G09F 9/37.

The bistable electromagnetic display panels comply very well with the above objectives. Using visually highly contrasting surfaces on the selected picture elements and on the nonselected areas, these displays feature good contrast and excellent angular visibility in high ambient light conditions.

The electromagnetic displays are typically made as large matrix arrays of preferably square display pixels with movable flaps and built-in solenoids. The "on" and "off" state of the flaps is indicated by visually highly contrasting colors. By rotating the flap around the axis by means of the magnetic field one can display arbitrary patterns. The magnetic driving of the pixels provides for the inherent memory, which is essential for keeping the power consumption within the required limits. In poor lighting conditions these displays need and additional illumination either by a standard light source (illuminating the entire display panel) or selective one illuminating each selected display pixel either through fiber optic network or by light emitting diodes built-in each display pixel.

TECHNICAL PROBLEM

The technical problem solved by the present invention is to provide a novel, low production cost construction, of an electromagnetic display, which allows significant reduction of the fabrication costs.

BACKGROUND OF THE INVENTION

The electromagnetic display panels have been known for over two decades and are playing an important role in niche applications, where relatively large size, medium information content display panels, with high contrast and excellent visibility in rather high ambient lighting conditions are required. The bistable electromagnetic display panels (US 3,871,945, US 4,577,427, US 4,860,470, EP 0 084 959, EP 0 731 435 A1, US 4,243,978, US 5,771,616, US 6,272,778, US 6,025,825, US 5,898,418, US 6,603,458,...), used for traffic signs, buses' and trains' destination displays, large information display panels in airports, bus and railway stations and sporting events seem to comply very well with the above requirements. Using bright reflective paints on the selected picture elements and mate black on the nonselected areas, these displays feature good contrast and excellent angular visibility in high ambient light conditions.

The operating principle of the present state-of-the-art solutions is predominantly based on the movable pixel flap rotating around the pivoting axis for typically ≤ 180° just inward the mechanical limiting positions and having the size of the entire display pixel. The flap is painted on its front and rear side with visually highly contrasting colors (EP 0327250, US 6,272,778, US 6,025,825, US 5,898,418,...). In order to switch between the "on" and "off" state of the display pixel, these solutions typically use one fixed permanent magnet inserted in the movable pixel flap and a built-in solenoid wound around either straight (EP 0327250, US 6,603,458, US 6,272,778,...) or U-shaped magnetic core (US 4,243,978, US 6,025,825, US 5,898,418, US 5,005,305,...). Some technical solutions use an additional fixed permanent magnet to improve the stability of the bistable positions of the flaps (US 4,243,978, US 4,531,318).

There is yet another, substantially different operation principle known, based on display 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. The tilting flap covers one of the two portions of the panel surface in the pixel zone, when the flap lies in each of its two stable positions. The side of the tilting flap facing the front side of the panel and the portion of the panel in the pixel zone covered by it are painted in one and the opposite side of the flap and the remaining part of the pixel zone are printed with different, highly contrasting color to the first one (US 6,603,458, DE 3501912C2, DE 3601018A1). In order to switch between the "on" and "off" state of the display pixel these solution uses a permanent magnet inserted in each tilting flap in close proximity to the rotational axis. The tilting flap is rotated from a first bistable position into a second bistable position by an electromagnet (3s+5) with a straight magnetic core, which is located on the reverse side of each display pixel. Such a construction has a certain advantage over the other state of the art solutions, as the entire construction can be noticeable thinner (only one half of the pixel surface rotates around the pivoting axis!) than with the technical solutions as described before.

In order to extend the operation in the situations, where the ambient light is rather poor or not present at all (night), a number of technical solutions have been developed in order to improve the "night" visibility of these displays typically using additional light sources in each of the display picture elements. Most of these solutions use LED diodes (US 5,050,325, WO 00/62274, DE 189 02 218 A1, EP 0 731 435 A1,...) or other light sources (US 4,914,427, GB 2,297,185 A, US 5,642,130,...) built into every pixel element directly or via optical fibers (US 5,055,832).

The present state-of-the-art electromagnetic displays require a very complicated production process, difficult for automation and therefore expensive. The Patent US 5,771,616 teaches that a number of display pixels are bound together with joint, rigid sidewalls connecting a plurality of pixel elements together in a kind of a mainframe in order to make the assembling in larger display panels easier and with less demanding mechanical tolerances. However, for example the U-shaped solenoids of particular display pixels are each of them constructed out of two magnetic wires inserted into the mainframe and only after the coils are wound around both of them, the said magnetic cores are joined in a final U-shaped magnetic yoke with additional ferromagnetic bar - a complex and hence expensive construction. Finally the rigid joint sidewall does not provide adequate support for the LEDs adjacent to each pixel element and an additional support is necessary for each LED.

The technical solution described in the Patent US 6,603,458 also tends to join a plurality of display pixels in order to make the assembling of larger display panels easier. According to the solution, proposed by the said patent, the constituent parts of the display pixels to be joined in a larger functional groups are joined by the integrated top pixel mask for the entire functional group with the bearings for the pivoting axes for the pixel flaps and the bottom integrated support for the entire functional group, while the rest of the display pixel constituent parts are inserted individually between the above mentioned bottom an top functional group plate - a complicated and mechanically rather unstable construction requiring very strict mechanical tolerances.

SUMMARY OF THE INVENTION

The object of this invention is to provide display elements for an electromagnetic display allowing a low cost fabrication of the display.

The object is achieved with the display element according to claim 1. The proposed concept is based on the display pixel integration in larger functional, basically monolithic blocks (Fig. 1a, b, c) joining several display pixels (preferably 5 or 7) in a display panel segment that can be mass-produced in an automatic process. They include all static plastic constituent parts of the display pixels joint in the above-mentioned monolithic blocks. They can be produced in a single production step using the injection molding process. The said monolithic basic blocks include the segment pixel plate with pivoting axis bearings, solenoid body, driving PC board electrical contatcts' and mounting receptacles, etc. The proposed concept reduces the number of constituent parts to minimum and also allows the other operations like solenoid winding, pixel flaps insertion, contacting/mounting pins injection, etc to be performed simultaneously for all pixel elements joint in the said basic display segment S. The complete display panel (Fig. 2) can be later assembled from such display segments S, which keep a stable compact form with adequate dimensional tolerances allowing for easy assembling. To summarize - such an "integration" of the static mechanical constituent parts in a monolithic block results in the following advantages:

Significant reduction of the constituent parts - from minimum 8/display pixel in the sate-of-the-art technical solutions (US 4,243,978), to only 5/display pixel in the solution according to the proposed invention; furthermore the production process steps are reduced accordingly.
Significantly smaller number of expensive injection molding tools (only two compared to ~ 5 in the case of standard solutions (for example US 6,603,458)
Significantly cheaper injection molding tools manufacturing and hence noticeably easier variations and adaptations of the display panel design according to the specific customer requirements
The solenoids are part of the "monolithic" block of the display panel segment and the coils of the said segment are wound simultaneously in one single process,
No additional assembling of individual pixels in the functional building blocks for final display panel assembling,
Significantly less demanding mechanical tolerances for the constituent parts, as most of the tolerances are determined by a monolithic plastic body of the display segment S,
Mechanical rigidity of the said display segment S allows for easier final display panel assembling,
Lower production costs.

Further reduction of the constituent parts is optionally achieved by painting the display pixels according to the invention with the luminescent paint absorbing light in the near UV light range and upon absorbing the UV light reemitting the light in the visible spectral range. Such a solution replaces the use of discrete light sources for each display pixel, therefore strongly reducing the complexity of such a display panel. The further advantage of the new concept is that the reflected light, used for the display panel illumination, is hardly visible to the human eye and so the direct reflections from the dark, nonactivated background as well as from the outer transparent display panel protective cover is extremely low. This in turn results in extremely high display panel contrast in poor lighting conditions. As the light emitted from the display pixels is emitted in random directions, the angular visibility of such a display is excellent.

Finally the efficiency of the electromagnetic system, used for selecting the "on" and "off" state of the individual display pixels, is according to the invention increased by two rather than one Nd-Fe-B plasto-ferrite permanent magnets built-in each of the flaps during the flap manufacturing injection molding process. The said permanent magnets are magnetized in the opposite directions perpendicularly to the pivoting axes of the movable display pixel flaps. The driving electromagnets for the said two permanent magnets have to be oriented in the opposite directions perpendicularly to the display pixel flap's surface. The driving electromagnets for the said two permanent magnets have to be oriented in the opposite directions and can be efficiently replaced by a single U-shaped electromagnet, which is oriented along the pivoting axes of the flaps (see Fig. 4b) - unlike any other technical solution using U-shaped electromagnets (US 6,603,458, US 6,025,825, US 5,898,418, US 5,005,305). The above-described novel configuration results in:

Increased stability of the two bistable positions of the display pixel movable flaps
Significantly smaller crosstalk between the neighboring display pixels, which is in particular severe with technical solutions using rod-like electromagnets (US 6,603,458, DE 3501912, DE 3601018,...) - because of the crosstalk problem these sate-of-the-art solutions require a very specific orientation of the permanent magnets built-in the movable pixel flaps, characterized by the permanent magnets of all neighboring display pixel flaps being oriented antiparalelly to the permanent magnets of all neighboring display pixel flaps. Such a requirement significantly complicates the production process.
Significantly smaller magnetic stray fields and hence smaller magnetic resistivity, as compared to the present state-of-the-art solutions (US 6,603,458, DE 3501912, DE 3601018,...)
More efficient use of the display area (maximized display pixel size) and more compact design (effectively thinner display pixel elements) compared to the present state-of-the-art solutions (US 6,603,458, US 6,025,825, US 5,898,418, US 5,005,305,...).

DESCRIPTION OF DRAWINGS

This invention may be better understood and its objectives and advantages will become apparent to those skilled in the art by reference to the annexed drawings as follows:

Fig. 1.

a. - Display panel segment showing "monolithic" basic display block 1 (seven pixels) with two display pixel semi-surfaces 1a, 1b painted with two highly contrasting colors, mounting

pin receptacles

1c, 1d,

solenoid bodies

1e, flap's pivoting axes bearings 1f, 1g and additional parts such as flaps 2 with the two sides (2a, 2b) painted with two highly contrasting colors and with a built-in permanent magnet 2c (respectively 2c ₁ , 2c ₂), magnetic cores 3s (respectively 3u) and mounting

pins

4a, 4b.
b. - Monolithic display block 1 section for display panels using LED illumination of individual display pixels
c. - Monolithic display block 1 section for display panels using U-shaped driving electromagnets according to the invention

Fig. 2.

- Large matrix display panel composed of the basic display segments S, as shown in detail on Fig. 1a,b,c, comprising plurality of display segments S, mounted on the basic PC board 6 with the complete driving electronics 7, connected to the switching solenoids 5 of each of individual display pixels (1a+1b) via the mounting

pins

4a, 4b the said assembly being finally built-in the display panel mainframe 8.

Fig. 3.

- UV illumination principle - parts of the display pixels and one side of the movable flaps 2 are covered with UV luminescent paint 1a; display panel is illuminated with the near UV black ray light source 9 and the light intensity equalizing filters 10 can be optionally added to equalize the overall display panel illumination.

Fig. 4.

a - Magnetic switching system using a single rod-like electromagnet (3s + 5) including:

Rotatable typically triangular flap 2 with a built-in plasto-ferrite magnet 2c and a pivoting axis 2d; The two surfaces of the flap 2a and 2b are painted with highly contrasting colors,
Solenoid 5
Straight magnetic core 3s

b. - Magnetic switching system using a U-shaped electromagnet (3u+5) including

Rotatable typically triangular flap 2 with a built-in plasto- ferrite magnets 2c ₁ , 2c ₂ and a pivoting axis 2d; The two surfaces of the flap 2a and 2b are painted with highly contrasting colors,
Solenoid 5
U-shaped magnetic core 3u

Fig. 5.

- Display pixel flap production concept

Fig. 6.

a - Display pixel flap design - detail
b - Display pixel flap bearing - detail

DETAILED DESCRIPTION OF THE INVENTION Electromagnetic display panel according to the invention is described in detail using Figures 1 - 6:

Electromagnetic display panel is composed of plurality of substantially square display pixels organized in MxN display matrix. The display pixels are designed to provide visually highly contrasting surfaces in their bistable "ON" and "OFF" positions. The current positions of the pixels are controlled by the built-in electromagnets allocated to each display pixel. The pixels are shaped to conform generally to the square outline of the display panel matrix. In order to optimize the effective display area and minimize the required thickness of the display panel, the pixels are divided in two parts. Each pixel is provided with a rotatably mounted, bistable tilting flap, which is asymmetrical in relation to its rotational axis (see Fig. 6a,b). The tilting flap covers one of the two portions of the panel surface in the pixel zone, when the flap lies in each of its two stable ("ON" and "OFF") positions. The side of the tilting flap facing the front side of the panel and the portion of the panel in the pixel zone, which is covered by the tilting flap are painted with one color, which is highly contrasting to the color painted on the opposite side of the pixel flap and the other half of the pixel zone. A permanent magnet is fitted to the tilting flap in close proximity to the rotational axis. The tilting flap is displaced from a first stable position into a second stable position by an electromagnet, which is located on the reverse side of the panel and is allocated to the pixels.

As shown on the Fig. 2, the display panel is built from monolithic blocks 1 of multitude of display pixels → "display panel segments" S that can be mass-produced in an automatic process. The complete display panel can be later assembled from such display segments S, which keep a stable compact form with adequate dimensional tolerances allowing for easy assembling into the final matrix display panel built on the main PC board 6 with the complete driving and display control electronics 7. The static plastic constituent parts of the individual display pixels (including the segment pixel plates each of them being composed of two

complementary surface areas

1a, 1b covered with highly contrasting colors, with pivoting axis bearings 1f, 1g,

solenoid body

1e, driving PC board electrical contatcts' and mounting

receptacles

1c, 1d, ...) joint in the above-mentioned display segments S are produced in a form of a "monolithic" block 1 using the injection molding process. In order to further simplify the final assembling process of the display segment S, the pivoting axis bearings 1f, 1g on the monolithic block 1 have a special "snap in" design, as shown in detail on the Fig. 6b, which allows for easy insertion of the flap pivoting axis 2d. According to the invention the shape of the movable flaps deviates from formally ideal triangular form, having rounded-off corners, as shown on the Figures 4 and 6. The corners at the two "bearing" positions are rounded off just enough to simplify the molding tools manufacturing and increase of the yield of the production process (r > 1mm). The third corner opposite to the pivoting axis is rounded off more (typically 10% → r > 3mm) in order to reduce the moment of inertia of the flap and increase its switching dynamics.

The above-described moving flaps 2, magnetic cores 3s (respectively 3u) and electric contacts 4a + 4b of course have to be produced separately in parallel standard mass production processes in two rows of seven flaps (see Fig. 5). The moving flaps are connected together with spacers 19, which keep them positioned at exactly the same place/distance, as determined by the 14 pivoting axes' bearings 1f, 1g on the monolithic block 1 in order to optimize final display segment (7 pixels) assembling process. In the case of the moving flaps 2 the use of the plasto-ferrite materials allows the permanent magnet 2c (respectively 2c ₁ , 2c ₂ ) built-in the pixel flaps 2, to be produced as integral part of the said flaps 2 in a two-component injection molding process. In order to optimize the efficiency and/or compact design of the electromagnetic system (see Fig 4a, 4b), used for selecting the "ON" and "OFF" state of the individual display pixels, the permanent magnets 2c (respectively 2c ₁, 2c₂) built-in the pixel flaps 2 are oriented perpendicularly to the surfaces of the

flaps

2a, 2b and are slightly displaced off the axial position (see Fig. 4a, 4b), while the core 3s (respectively 3u) of the driving electromagnet (3s, respectively 3u+5) is oriented perpendicularly to the

display pixel surface

1a, 1b and located exactly under and as close as possible to the pivoting axis 2d.

The described configuration is more or less identical in the case of the above-described rod-like driving electromagnets 3s with corresponding single permanent magnets 2c in the pixel flaps (see Fig. 4a), as well as in the case of the U-shaped core 3u driving electromagnet (3u+5) according to the invention with corresponding dual

permanent magnets

2c ₁ , 2c ₂ in the pixel flaps 2, which is as follows: The construction and the shape of the pixel flaps as well as their pivoting system are the same except that two

permanent magnets

2c₁, 2c₂ oriented antiparalelly with respect to each other are built-in each display pixel flap (see Fig. 4b). The U-shaped core 3u electromagnet (3u+5) is located under the display pixel flap pivoting axis 2d as close as possible to the flap and parallel to the display pixel flap pivoting axis 2d. The core 3u is inserted in the solenoid body 1e of the monolithic block 1 with a single solenoid 5 so that both ends of the U-shaped core 3u are located as close as possible to the

permanent magnets

2c ₁ , 2c ₂ . Such a configuration increases the stability of the two bistable positions (increased magnetic force) of the display pixel movable flaps and reduces magnetic stray fields and hence magnetic resistivity of the magnetic driving system. Furthermore such a configuration reduces the crosstalk between the neighboring display pixels. Because of the antiparallel orientation of the permanent magnets on the display pixel as well as the magnetic field in both legs of the U-shaped core 3u electromagnet, the crosstalk problem between neighboring display pixels is significantly reduced compared to the sate-of-the-art solutions (US 6,603,458, DE 3501912, DE 3601018...). Therefore the orientation of the magnets on the display pixel flaps as well as the U-shaped core 3u electromagnets can be kept the same for all display pixel elements, which in turn results in important simplification of the production process.

Both configurations of the pixel flaps, either the one using single permanent magnets and rod-like driving electromagnet (3s+5), as well as the one using dual permanent magnets and U-shaped core 3u based driving electromagnet (3s+5) according to the invention, finally result in increased efficiency of the display area (maximized display pixel size) and more compact design (effectively thinner display pixel elements) as compared to the technical solution US 5,771,616 and the like.

The "ON" positions of the display pixels - flap sides 2a, as well as the adjacent pixels surfaces 1a - are according to the invention optionally painted with the luminescent paint absorbing the light in the near UV light range and upon absorbing the UV light reemitting the light in the visible spectral range. The color of the complementary flap sides 2b as well as the pixel sides 1b is chosen to be highly contrasting to the color of the said luminescent pixel side 2a and flap side 1a - preferably mate black color. Such a solution replaces the use of discrete light sources (LEDs, fiber optic illumination,...) for each display pixel therefore strongly reducing the complexity of such a display panel, as only a small number of near UV light sources 9 are necessary to illuminate the entire display panel (Figs. 2, 3). The further advantage of the new concept is that the reflected light, used for the display panel illumination, is hardly visible to the human eye and so the direct reflections from the dark, nonactivated background as well as from the outer transparent display panel protective cover is extremely low. This in turn results in extremely high display panel contrast in poor lighting conditions. As the light emitted from the display pixels is emitted in random directions, the angular visibility of such a display is excellent.

After the display pixels have been painted with said photo luminescent paint, the electrical contacts 4a + 4b are inserted into the adequate receptacles in the monolithic block 1 each of them in a simultaneous automatic process step for each monolithic block 1. Following the insertion of the

electrical contacts

4a, 4b the coils of the solenoids 5 are wound on the solenoid bodies 1e of the "monolithic" display segment 1 simultaneously for all display pixels of the said segment 1. Finally, after the magnetic cores 3s (respectively 3u) are inserted into the receptacles 1e in the monolithic block 1, the pixel flaps' pivoting axes 2d are inserted in the bearings 1f, 1g simultaneously for the complete display segment S.

The complete display panel is assembled using the above described "monolithic display segments" S on the display panel main PC board 6 with the display panel driving and control electronic 7, which is finally built-in the display panel mainframe 8 as shown on the Fig. 2. As mentioned above the said mainframe 8 can optionally contain additional light sources 9 and illumination equalizing filters 10 and/or 11 to allow for the display panel operation in low ambient lighting conditions (see Fig. 3). The additional light sources preferably operate in the near UV light spectral range (in combination with the UV luminescent paint) as for example the "black-ray" lights or similar.

EXAMPLE 1

The use of the proposed technical solutions can be best demonstrated by their application in medium large display panels typically used for bus destination displays. As already explained, the bistable electromagnetic display panels due to their excellent visibility, high contrast and wide viewing angle as well as their resistivity to widely variable environmental conditions, are almost ideal for this kind of application. The only problem related to the use of these display panels is their mechanical complexity and as a consequence high production costs.

Electromagnetic bus destination display panel is typically composed of 1792 substantially square display pixels organized in 16 x 112 display matrix. Due to a reasonably large number of display pixels, the standard production concepts, based on assembling the constituent parts of individual display pixels directly on the display panel main PC board, turns out to be a complex and expensive operation. The following is a description of the display panel manufacturing out of the monolithic blocks comprising 7 display pixels corresponding to one column of the 5x7 display pixel matrix for a single α-numeric character (Examples 1, 2, 3, patent claims). In order to make the final assembling of the display panel easier, the said display segments S have to keep a stable compact form with adequate dimensional tolerances. According to the invention the latter is achieved by manufacturing all the static plastic constituent parts of the 7 display pixels in a single monolithic block 1 (see Fig 1a,b,c), which contains:

7 pixel plates each of them being composed of two complementary surface areas 1a, 1b covered with highly contrasting colors
14 pivoting axes' "snap-in" bearings 1f, 1g
7 solenoid bodies 1e with openings for the magnetic cores 3s (respectively 3u)
14 receptacles for the metal pins 1c, 1d, used for electrical contacts 4a, 4b and mechanical mounting on driving PC board 6 using the injection molding process.

The above-specified monolithic block 1 is manufactured in mass production injection molding process using standard black mate plastic material for injection molding typically in car industry. The

display pixel areas

1a, 1b of monolithic block 1 are further painted so that one half of each display pixel area 1a is painted with bright fluorescent paint while the other half 1b is kept unpainted - mate black original plastic surface.

The rotatable flaps 2 cannot be made in the same injection molding process and have to be manufactured separately. As the flaps 2 have to have built-in permanent magnets 2c (respectively 2c ₁ , 2c ₂) the latter are made using plasto-ferrite materials in a two-component injection molding process. Just like with the monolithic block 1 one side 2a of the flaps is painted with the same bright fluorescent paint, while the other half 2b is kept unpainted - mate black original plastic surface.

In order to achieve the most economic production, 14 flaps are injection-molded at the same time in two rows of seven flaps (see Fig. 5), connected together with spacers 19, which keep them positioned at exactly the same place/distance, as determined by the 14 pivoting axes' bearings 1f, 1g on the monolithic block 1 in order to optimize final display segment (7 pixels) assembling process. Furthermore, unlike with the previous art like for example US 6,603,458, the flaps 2 are designed (see Fig. 6a) to have a predominantly triangular shape however without sharp corners (rounded out). Such a design makes the injection molding tool manufacturing easier and results in higher production yields (no voids in the corners of the flaps!). Just like with the monolithic block 1 one side 2a of the flaps is painted with the same bright fluorescent paint, while the other half 2b is kept unpainted - mate black original plastic surface. After the flaps 2 are painted, the spacers 19 are simultaneously cut away and the two rows of 7 flaps 2 are simultaneously "snapped-in" the 14 pivoting axes' bearings 1f, 1g on the monolithic block 1.

The final assembling of the display segments S (7 pixels) of the electromagnetic display panel is accomplished by simultaneous insertion of 7 magnetic cores 3s (respectively 3u) made of "semi-hard magnetic materials" into the adequately shaped solenoid bodies 1e on the monolithic block 1, which is followed by simultaneous insertion of 14

metal contacts

4a, 4b in the contacting/ mounting

receptacles

1c, 1d in the monolithic block 1 and simultaneous winding of all 7 solenoids 5 on the solenoid bodies 1e on the monolithic block 1. Finally, after the magnetic cores 3s (respectively 3u) are inserted into the receptacles 1e, the 7 rotatable pixel flaps 2 are inserted in the 14 pixel flap bearings 1f, 1g on the monolithic block 1 from the other side.

The complete display panel is assembled using the above described "monolithic display segments" S on the display panel main PC board 6 with the display panel driving and control electronics 7, which is finally built-in the display panel mainframe 8 as schematically shown on the Fig. 2.

As mentioned before, the said mainframe 8 can optionally contain additional light sources 10 and illumination equalizing filters 11 to allow for the display panel operation in low ambient lighting conditions (see Fig. 3).

In a preferred embodiment the standard bright fluorescent paint, used for covering the display pixel sections indicating the "ON" state of the display pixel 1a, is replaced with the luminescent paint absorbing light in the near UV light range and upon absorbing the UV light reemitting the light in the visible spectral range. Replacing at the same time the standard visible light sources with the near UV light emitting ones (for example the "black-ray" lights or similar), results in important increase of the contrast of the display panel in low ambient lighting conditions. The fact is that the reflected UV light, used for the display panel illumination, is hardly visible to the human eye and so the direct reflections from the dark, nonactivated background as well as from the outer transparent display panel protective cover is extremely low. This in turn results in extremely high display panel contrast in poor lighting conditions. As the light emitted from the display pixels is emitted in random directions, the angular visibility of such a display is excellent.

EXAMPLE 2

In some specific cases like for example train destination displays the latter have to be visible also from longer distances. In the case of poor lighting conditions the simple illumination of the electromagnetic train destination display, as described in the EXAMPLE 1, is not very applicable. Basically the technical requirements/manufacturing for such display panels are very similar to the EXAMPLE 1 except for the fact that these display panels have to have active light sources like LED for each pixel element.

In view of the above the monolithic block 1 (see Fig 1b) has to have an additional receptacle for the LED diode and therefore contains:

7 pixel plates, each of them being composed of two complementary surface areas 1a, 1b covered with highly contrasting colors and each of them having spacers 1h necessary to stop the flap at the optimal distance above the pixel surface
7 receptacles for the LED diodes 1i
14 pivoting axis bearings 1f, 1g
7 solenoid bodies 1e with openings for the magnetic cores 3s (respectively 3u)
14 receptacles for the metal pins 1c, 1d, used for electrical contacts 4a, 4b and mechanical mounting on driving PC board 6 using the injection molding process.

The manufacturing process for the monolithic block 1 as well as the rotatable flaps 2 is identical to EXAMPLE 1.

The final assembling of the display segments S (7 pixels) of the electromagnetic display panel is however a little bit different, as it has to take into account also additional LED diodes built-in each display pixel. The latter are inserted simultaneously during the last assembling step in manufacturing of the display segment S.

The complete display panel is assembled very much like in the EXAMPLE 1, except that the display panel main PC board 6 has to have additional leads for connecting the LED diodes built-in the display pixels and that the display panel driving and control electronic 7 has to have additional electronic drivers for LEDs.

EXAMPLE 3

Quite often the mechanical stability of both bistable positions of the display pixel flaps on the electromagnetic display panels can be critical (-display panel subjected to severe mechanical vibrations). Under such conditions the simple single rod-like electromagnet (3s+5) based driving of the display pixel flaps 2, as described in the EXAMPLE 1, may not be very applicable. As explained before, the magnetic force stabilizing both bistable positions of the display pixel flaps 2 can be increased by basically doubling the driving electromagnetic system of the display pixel flap. This can be realized by adding the second permanent magnet on the display pixel flap 2, while the second rod-like electromagnet (3s+5) can be joined with the first one in a single U-shaped core 3u electromagnet (3u+5) using the same driving solenoid 5. The two

permanent magnets

2c₁, 2c₂ are oriented antiparalelly with respect to each other and are built-in each display pixel flap 2 (see Fig. 4b) during the flap manufacturing two component injection molding process. The U-shaped core 3u electromagnet (3u+5) is located under the display pixel flap pivoting axis 2d as close as possible to the flap and parallel to the display pixel flap pivoting axis 2d. The core 3u is inserted in the solenoid body 1e of the monolithic block 1 with a single solenoid 5 so that both ends of the U-shaped core 3u are located as close as possible to the

permanent magnets

2c ₁ , 2c ₂ .

As already described before such a configuration not only increases the stability of the two bistable positions (increased magnetic force) of the display pixel movable flaps but also reduces magnetic stray fields and hence magnetic resistivity of the magnetic driving system as well as significantly reduces the crosstalk between the neighboring display pixels.

Basically the technical requirements/manufacturing for such display panels are very similar to the EXAMPLE 1: The general display panel construction, manufacturing process for the monolithic block 1, movable flaps, painting system with highly contrasting paints, display pixel flaps pivoting system, solenoid winding, electrical contacts, mounting on the electronic driving board, display panel or individual display pixel illumination systems are identical to the description already given in Examples 1 and 2

Some modifications however have to be made in order to apply the novel electromagnetic display pixel flap-driving concept:

The solenoid bodies 1e on the monolithic block 1 have to be displaced from the center of the flap pivoting axis 2d so that both legs of the U-shaped core 3u electromagnet (3u+5) are positioned under the pivoting axis symmetrically with respect to the permanent magnets 2c ₁ , 2c ₂ built-in the movable display pixel flaps 2 (See Fig 4b)
Display pixel flaps 2 are produced very much like with EXAMPLE 1 except that two plasto-ferites magnets are built-in instead of one and the magnetization processes is modified in order to allow for the antiparallel magnetization of both permanent magnets

It should be however emphasized, that the described examples represent only three feasible working embodiment of the electromagnetic display panel according to the invention. Various modifications and variations can be made within the scope of this invention, especially in the choice of number of display pixels joint in the monolithic block, individual display pixel construction as well as external illumination and magnetic driving concept.

Claims

Display element (S) for an electromagnetic display panel, said display panel consisting of lines of pixels (P), each of the pixels (P) having an asymmetric rotating flap (2) with two bistable positions, which in both of its bistable positions covers one or another half of a pixel surface (1a respectively 1b),
one side of the said flap (2a), when pointing towards a front side of the plate and part of the pixel surface (1a) covered by said flap (2) in this position, being painted with one color, while another side of the said flap (2b) and a corresponding part of the pixel surface (1b) being covered with another, highly contrasting color compared to the first one,
the said flap (2) having a built-in permanent magnet (2c respectively 2c₁, 2c₂) near the rotation axis (2d) of the flap (2) and
each of the pixels (P) having a built-in solenoid (5) allowing moving the flap (2) from one bistable position to the other by means of electric current pulses,
characterized in that
the display element (S) is formed by a plurality of display pixels (P), preferably 7, physically joint into a monolithic display segment block (1) including segment pixel plates (1a, 1b) with display flaps pivoting axis bearings (1f, 1g), solenoid bodies (1e) being positioned under the display pixel flap pivoting axis (2d) and mounting receptacles (1c, 1d)
and allowing solenoids (5) to be wound simultaneously on the solenoid bodies (1e) of the monolithic display segment block (1) in a single production step and electrical contacts (4a + 4b) as well as magnetic cores (3s respectively 3u) of the solenoids (5) to be inserted simultaneously in a single production step.
Display element (S) according to claim 1, characterized in that
the magnetic cores (3s) of the solenoids (5) have rod-like shapes, which are aligned perpendicularly to the display pixel surfaces (1a, 1b) and are preferably positioned under the center of the display pixel flap (2) pivoting axis (2d) and
that a permanent magnet (2c) built-in the display pixel flap (2) is magnetized perpendicularly to the display pixel flap surface (2a + 2b).
Display element (S) according to the claim 1, characterized in that the magnetic cores (3u) of the solenoids (5) of the display pixel driving magnets have a U shaped magnetic cores (3u) as shown on the Fig. 4b, which are aligned along the pivoting axis (2d) of the display pixel flap (2) and
that the permanent magnets (2c₁, 2c₂) built-in the display pixel flap (2) are magnetized antiparallely and oriented perpendicularly to the pivoting axis (2d) as well as display pixel flap (2) planes (2a, 2b).
Display element (S) according to one of the claims 1 and 2 or 3, characterized in that
the pivoting axes' bearings (1f, 1g) on the monolithic display segment block (1) have a "snap-in" design, which in turn allows for easy insertion of the flaps (2) into their positions on the monolithic display segment block (1).
Display element (S) according one of the claims 1, 2 or 3 and 4 characterized in that
first halves of the display pixels (1a) and adjacent flap sides (2a) are painted with a color heavily doped with a luminescent dye absorbing near UV light and emitting visible light, while second halves of the display pixels (1b) and adjacent flap sides (2b) are colored with highly contrasting light absorbing mate black color.
Electromagnetic display panel made of display elements (S) according one of the claims 1 and 2 or 3, 4 and 5 characterized in that a standard "black-ray" lamp (9) emitting light in the near UV light range of the spectrum is arranged for illuminating the display elements from at least one side.
Electromagnetic display panel according to the claim 6, characterized in that an additional grey level filter (10) is arranged between the lamp (9) and the display elements to homogenize the UV light intensity on the display surface.
Electromagnetic display panel according to the claim 6 or 7, characterized in that said lamp (9) is a standard "spot-light" UV A light source having an additional optical filter (11), the spectral dependence of which is centered to the peak absorption of the luminescent dye used for the display elements arranged between the lamp (9) and the display pixels.
Electromagnetic display panel according to the claims 1 through 8, characterized in that the bearings of the flaps have a snap-in design, as shown on the Fig. 6a and b.
Electromagnetic display panel according to the claims 1 through 9, characterized in that the shape of the flaps deviates from the triangular shape having rounded-off corners, the radius of the corners at the "bearing" positions being bigger than 1 mm and the radius of the corner opposite to the pivoting axis being bigger than 3 mm.
Method of manufacturing a display element (S) for an electromagnetic display panel according to claims 1 to 5, wherein said monolithic display segment block (S) is manufactured from plastic in a single step injection molding process.
Method of claim 11, wherein the solenoids (5) are wound simultaneously on the solenoid bodies (1e) of said monolithic display segment block (S) in a single production step.
Method of claim 11 or 12, wherein the electrical contacts (4a + 4b) as well as the magnetic cores (3s) or (3u) of the solenoids (5) are inserted simultaneously in a single step production process.