CH622637A5 - Display device for presenting characters - Google Patents

Description

The invention will now be explained in more detail with reference to the accompanying drawing. The figures have the following content:

Fig. 1 shows the rough structure of a matrix screen using a fluorescent plate as an embodiment of the

The invention relates to a display device for the device according to the invention;

3rd

FIG. 2 shows the detailed structure of a pixel of the matrix from FIG. 1;

3 shows the control of the fluorescent light emission at a pixel;

Fig. 4 schematically and electrical addressing of the screen 5;

5 shows a further embodiment of the device according to the invention, in which the fluorescent light emission is controlled by expansion of a ferroelectric ceramic plate as a function of the remanent electrical polarization.

We look at a flat plexiglass plate with a smooth surface, a few millimeters thick, in which a fluorescent substance is dissolved in such a concentration that, for example, the blue portion is fully absorbed by the incident daylight 15 and converted into green fluorescent light. Furthermore, this plate should have end faces running perpendicular to the plate plane, which should ideally be light-reflecting, so that no fluorescent material can escape at the edges of the plate. The reflection on the thinner medium is decisive for the re-emergence of the fluorescent light from the plate. To a good approximation, one can count as if all light that emerges on the surface at an angle atot (atot = angle of total reflection) leaves the plate and the light of the remaining angular range remains trapped in the plate as a result of total reflection. The angle of the total reflection results from the relationship n-sin atot = 1 (for the calculation index n of 1.49 for Plexiglas there is atot = 42 °). The proportion of the non-totally reflected fluorescent light - referred to here as loss factor V - is 30

V = 1- cos = n- j / n2-l '

n

(in example n = 1.49, V = 25%) 35

All light emitted within the angle of total reflection (75% in the example) is guided by continuous loss-free total reflection in the plate plane.

The fluorescent light captured in the fluorescence plate as a result of total reflection can now be brought out by deflection on light-scattering surfaces (hereinafter referred to as exit window for short), which can be brought into optical contact with the fluorescence plate in an electrically controllable manner, and in this way can be brought out optical representation of characters of all kinds can be used. Under 45 neglect of inevitable re-emergence losses and assuming that there are no other losses in the plate, is the "brightness gain factor", i.e. the factor which indicates the increase in the luminance of the exit windows of the fluorescent plate compared to the luminance 50 of a line of color with the same fluorescent substance, essentially given by the ratio of the light-absorbing area of the arrangement to the total area of the exit windows of the fluorescent light.

As an exemplary embodiment of the arrangement according to the invention, the rough structure of the matrix screen using a fluorescence plate is shown in an exploded view in FIG. 1.

A plastic plate (plexiglass) 3 carries back electrodes 1 and webs 2. A second plexiglass plate (fluorescent plate) 5 ao contains the dissolved fluorescent substance and has mirrored front edges 6, indicated by hatching. This second plexiglass plate, which is referred to here as a fluorescent plate, carries front electrodes 8 and webs 7 in an identical arrangement to the plexiglass plate 3. Between these 65 web systems there are strip-shaped plastic membranes 4 which are provided with conductive coatings and a pigment and an insulating layer. The detailed structure of the image

622 637

screen is shown in FIG. 2 on the basis of an enlarged detail of a pixel. 5 mean the fluorescent plate and 9 the light-scattering pigment layer, which serves to couple out the fluorescent light. 11 and 12 denote conductive layers. These layers are located on both sides of the plastic membrane 4 and are electrically connected to one another; they are called membrane electrodes in the following. 13 is an insulating layer, 3 is the other plastic plate, 1 is a strip-shaped back electrode, 8 is a strip-shaped front electrode, 10 is a contact film for optical contacting, e.g. a suitable liquid film in very flat circular depressions, and 7 are the mentioned ridges.

If an electrical voltage is applied between the membrane electrode 11, 12 and the front electrode 8, the plastic membrane 4 is pulled towards the front electrode due to the electrical field forces and finally comes into contact with the optical contact film 10, which provides the optical contact between the fluorescent plate 5 and the produces light-scattering layer 9. By applying an electrical voltage between the back electrode 1 and the membrane electrodes 11, 12, the membrane is pulled in the direction of the back electrode and brought into optical contact with the plastic plate 3. Due to surface tension, the contact film 10 causes the membrane to adhere in these two states of deflection.

In Fig. 3 the control of the fluorescent light emission at a pixel is shown in detail. In (a) the membrane position is shown at a pixel in position "on"; Fluorescent light emerges at the pixel. In (b) the membrane is shown in the detachment stage during the "erasure". The tear-off of the liquid contact film is indicated. In (c) the membrane position is drawn at a pixel in the “off” position: no fluorescent light emerges at the pixel.

4 shows a diagram of the electrical control of the screen. In the example shown, two marked pixels are switched “on” by the voltage pulse scheme shown. This diagram shows that electric field forces on the membrane only occur at the two marked points, i.e. the crosstalk problem that otherwise occurs in the usual matrix arrangements is completely eliminated in the matrix structure discussed here. For clarification, it should be pointed out that the front and rear electrodes are rigidly coupled to one another with regard to their electrical control: equivalent electrodes receive the same voltage pulses only with the opposite sign. The matrix is therefore still controlled via two independent crossed electrode rows.

Some qualitative information on the structure and function of the screen follows briefly.

- Aluminum or silver electrodes are advantageous as conductor tracks because of their high conductivity, high reflectivity for fluorescent light and compatibility with plastic; transparent electrodes made of SnÛ2 or In203 are also possible.

- If the plastic plates and plastic membranes have the same coefficient of expansion, the influence of temperature on the membrane voltage and thus on the electrical characteristics is eliminated.

- The production of sufficiently flat Plexiglas plates (e.g. flatness of optically polished glass 0.2 (im / cm) is very cheap, in contrast to glass plates of the same flatness.

- The structure outlined has the advantage that no membrane vibrations occur with the resulting complications.

- Coupling by pressure pulses is avoided by evacuating the interior of the display to about 10

622637

4th

Torr, which is easy because of the dense web system.

Due to the external air pressure, the membranes are fixed to the webs by pressing, which saves fixing with an adhesive.

- In the worst case, the total area of the display for alphanumeric 5 graphic representations of the usual type is far more than an order of magnitude higher than the area occupied by the pixels of the characters (light exit window). This ensures a sufficiently high image brightness.

The fact that when the number of 10 activated pixels becomes very low, the fluorescent light propagation time and thus the absorption loss at the mirrored end faces increases rapidly, as desired, has a strong effect on leveling the pixel brightness depending on the number of activated pixels . It has been empirically ensured that the pixel brightness, which is moderately dependent on the total amount of information, is completely problem-free for an observer.

- The optical contact means should be permanently fixed in place at the pixels. This is achieved by the small depressions 10 in FIG. 2 and by the contacting agent wetting the plexiglass surface (small contact angle), but not wetting the pigment layer or the insulating layer on the membranes (contact angle> 90 °). However, non-wetting of the membrane does not mean that the membrane cannot adhere to the plastic plates.

- By specifying the shape of the recess, the shape and size of the pixels is reproducibly determined. Furthermore, the course of redissolving of the membrane is thereby made reproducible. 30th

- In the contacting or detaching process, no significant spreading of the contacting agent in the image plane is necessary.

- During the addressing, the membrane can receive a power surge from a voltage pulse, which is sufficient to make an element respond, even if with a time delay. This means that a mechanical pulse can be stored in the membrane, an additional increase in the writing speed is possible.

- The light-scattering layer on the membranes must meet the condition that it scatters the fluorescent light by large angles (> about 40 °), which is the case, for example, with pigment layers. Electrically controlled light-scattering liquid crystal layers or ferroelectric ceramic layers with electrically controlled light scattering do not meet this condition 45 and are therefore out of the question as a control medium.

Here are some quantitative details of how the screen works using typical examples:

1. Attraction K of two electrode plates due to an electric field

Web distance b = 1 mm modulus of elasticity E = 3 * IO4 kp / cm2 membrane thickness d = 10 um ôfa2jim

3. Assuming that the inertia determines the switching time t, the following applies

-1UMa

6E o ^

Mass density p = 1 g cm3

t-10-5s

4. Adhesion work If a liquid is brought into contact with a solid, energy is obtained on the one hand because a solid and a liquid surface disappear, on the other hand energy has to be applied to create a new interface. The difference between the energy gained per unit area and the free energy used is the adhesion work Wsf.

Ws, f = <js + crf-ySif

<ys = surface tension of the solid body <jf = surface tension of the liquid ySif = surface tension between the solid and the liquid body

WSif can be both positive and negative for a solid / liquid interface.

The separation work to remove the membrane at one pixel is now

Separation work = Wsf • pixel area = 2-10_4dyncm with pixel area «* 2-10-3 cm2 and Wsf = 0.1 dyn cm

To simplify, assume that approximate separation work applies

Separation force =

Separation path

50

rF

Electrode distance D = 4.10-4 cm voltage U = 30 volts

Electrode area F = 1 mm x 0.1 mm = 10-7 m2 K = 2.5-l ~ 6kp

Field force «* 5-103 applies to a membrane element.

Gravity

This may be a criterion for ensuring that mechanical shocks have no effect on the display. 2. Maximum deflection 8 of the elastic membrane

</ = 1 K ♦ b2

3rd

60

Ed-

(Separation path 1 µm), the necessary separation force is 2 '10-6 kp.

The separating force generated by the electrical field is dimensioned such that, taking into account all manufacturing tolerances and the weak temperature dependence of the surface tensions, the threshold for separating the membranes is not fallen below. The electrical field can be made arbitrarily large, since there are no crosstalk effects.

A further exemplary embodiment of the arrangement according to the invention uses the surface formation of ferroelectric ceramics as a function of the remanent electrical polarization for local control of the fluorescent light emission instead of electromechanically controlled membranes. The polarization of the ferroelectric ceramic is directly linked, namely its expansion in the direction of polarization, i.e. perpendicular to the surface. If the state of polarization varies across the ceramic surface, a flat relief is formed on the ceramic surface as an image (see: C.E. Land, W.D. Smith, Digest of Techn. Papers p. 26, Soc. Inform. Display 1973). Optical contact with the fluorescent plate is made at the elevations of the relief. The image content can be changed by locally changing the remanent polarization via conductor arrangement on both sides of the ferroelectric ceramic. Here too, the image content is saved permanently.

5

622637

In this example, the screen, as shown in cross section in FIG. 5, consists of the fluorescent plastic plate 5 and a ferroelectric ceramic plate (for example made of lead zirconate / lead titanate with 7 atom% lanthanum additive) 14 of approximately 250 (in thickness, connected by spacers

ter 19. The conductor tracks 15, 16 in a crossed arrangement carrying ceramic plate is coated on the side facing the fluorescent plastic plate with a light-scattering layer 9 and a contact film 18 for optical contacting.

G

2 sheets of drawings

Claims (9)

622637 2 PATENT CLAIMS of characters, with a normally totally reflective 1.Display device for displaying characters, with a display surface that has a layer at freely selectable raster points of a normally totally reflective display surface, with an element that has a layer on its side facing the display surface at freely selectable raster points with an element that a 5 can be placed on its side facing the display surface in such a way that it has on the contacted layer, can be brought into optical contact, raster dots no more total reflection takes place, and in such a way that no total electrode system on the contacted raster dots electrical control of the reflection takes place more, and with an electrode system for clocking. electrical control of the contacting, thereby characterized. Such a display is known from US Pat. No. 3,376,092, This display device works as follows: Light-reflecting, reflecting fluorescent plastic plate (5), in the rays are sent into a prism, namely under the following fluorescent plate 5, which is called Chen angles that a total light trap for the fluorescent light acts on the rear wall of the prism so that the layer (9) experiences reflection and is reflected back towards the front. The element (4, 14) is light-scattering and that the back of the prism has a grid of stamp-optical contacting via a contact film (10, 18), 15 like elements. These elements have a very smooth pre-so that the fluor surface at the optically contacted grid points and, when controlled, approach the prism light by deflection or scattering on the back of the layer down to fractions of a light wavelength. This (9) emerges from the fluorescent plate (5). short distance between the prism and the stamp 2. Display device according to claim 1, characterized in that it causes, based on wave-optical laws, that the element made of strip-shaped plastic 20 the light on the area of the back of the prism, which consists of membranes (4) that pass through the pixel grid. the front of the moving stamp is opposite, the total speaking double web system (2.7) is no longer tensioned and which is reflected, but is coupled out to the rear. In this way, on both sides electrically conductive layers (11, 12) and above, an optically non-conductive coating (9, 13) against a background can be built, of which the fluorescent-staring image is built up. plate facing the light-scattering layer (9), wear, 25 In the above-described display device is disadvantageous, the webs on one side of the membranes on which one needs concentrated, intensive artificial light that without fluorescent plate (5) and the webs on of the other additional membrane precautions, only a very limited viewing angle is applied to a second plate (3), and that the kel range is available and that the display device Between the webs on both plates, the conductor tracks need a stamp for each pixel, which is also applied (1,8), which can be designed and moved very precisely with the conductor tracks (11,12) on the 30. In addition, membranes (4) form a cross-lattice pattern. that the display device the information entered 3. Display device according to claim 2, characterized can not save. is characterized in that the light-scattering layer (9) consists of a colored pigment. ment layer exists. according to it, based on the display 4. Display device according to claim 2 or 3, characterized in 35 device, a display device for displaying pointers, that the contact film (10) is in flat surfaces with good optical qualities, low power wells, which, according to the pixel grid, may and is simpler To create a design that is crosstalk-free on both plates (5.3). uncj has good switching and storage properties. 5. Display device according to one of claims 2 to 4, This object is achieved according to the invention in that the characterized in that the contact film (10) wets the display surface 40 to a mirror surface on its end faces, the light-scattering layer (9) or the isotene, fluorescent plastic plate, which does not wet the membrane as a light trapping layer (13). for the fluorescent light that acts the layer of the element 6. Display device according to one of claims 2 to 5, is designed to be light-scattering and in that the optical contact is characterized in that the surface tensions occur via a contact film, so that 45 make contact with the optical substances between which the optical contact is made The dots of the fluorescent light are matched to one another in such a way that membrane elements, the deflection or scattering on the layer, emerge from the fluorescence by applying appropriate voltage pulses to the plate. electrodes in question by field forces in optical contacts. The display device according to the invention is characterized by being brought into tact with the plates when the field is switched off by a number of advantages: the structural forces remain mechanically adherent. 50 is easy; the parts of the display device need 7. Display device according to one of claims 2 to 6, not to be worked particularly dimensionally; it is possible, characterized in that the plates (5, 3) and plastic display device have essentially of easily processable coefficients. rem plastic. A special light source is 8. Display device according to one of claims 2 to 7, not required. The power consumption is extraordinarily characterized in that the 55 containing the membranes is low. The representation has a good contrast and the space between the two plates (5,3) can be read airtightly even from oblique directions, is sealed and that the space is evacuated. In addition, the display device switched quickly 9. A display device according to claim 1, can be characterized by an almost unlimited storage capacity, that the element has a ferroelectric ceramic and in a wide temperature range is functional plate (14), the expansion of which is perpendicular to the upper surface is. Crosstalk problems cannot occur. Area controlled by the remanent electrical polarization. Advantageous refinements and developments of the present invention are the subject of additional claims.