Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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AN ELECTRO-OPTIC CE~L FOR ANIMATED DISPLAYS AND INDICATORS
David Makow
Backqround of the Invention
~LField of t.he invention
This invention relates to meters, monitors and indicator
instruments designed to measure or to indicate a voltage or
another physical quantity that can be displayed in the form of a
voltage. It also relates to animated displays used in signage
advertising, merchandising and instructional fields designed to
illustrate the movement of images or flow of air, liquids,
matter or energy, graphically depicted on a front-or backlighted
screen or in projection. It is related to liquid crystal,
electrochromic, electrophoretic, dipole suspension, ferro-
electric, electroluminescent, Plasma Discharge and other flat
panel displays which are designed to selectively illuminate
and/or animate areas on a screen. This invention is hased on a
novel and simple structure and design of an electro-optical
cell, for example a liquid crystal cell, that permits conversion
and the display of a time dependent variable as a spatial
coordinate variable on a two dimensional screen. The
indicating or metering function and/or the animation effects can
be achieved by simple means and can include linear, curved,
pulsating accelerating decelerating, blinking and wavelike
effects, and the effects can be limited to the parts of the
display screen of interest. Information in form of pictures,
artwork, symbols, letters, alphanumerics that is fixed or
changed as a function of a measured quantity can form a part of
the animated display. It can also form a separate display
device such as in an indicator, meter or monitor of any physical
quantity that may or may not include an animated symbol such as
an arrow to draw attention. This invention also relates to
coloured displays animated and/or stationary in which the
control of the hue or saturation of the colour is obtained
through the interaction of polarised light with a chromatic
polariser or optical retarder.
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2) pçscription Qf Prior Art
In the prior art meters, monitors and indicators were often
based on the electrodynamic or the electrostatic mechanism many
forms of which were invented by Faraday, Kelvin, Harris, Weston
and others in the l9th century. The electrodynamic mechanism is
based on the rotation of a current carrying coil placed in a
magnetic field. The electrostatic mechanism is based on the
torque resulting from the attraction between a fixed and movable
plate when a voltage is applied between them. Both these
mechanisms, designed for the purpose of measuring electrical
quantities, require moving parts. In this invention the
indication and/or measurement of a voltage or another derived
quantity is accomplished in a novel structure of an
electro~optical cell, such as in that of a liquid crystal cell;
and do not have any moving mechanical parts.
In the prior art animated displays have been generally
characterised by the presence of a light source, a ratable
polariser, manually or motor driver interacting with another set
of polarisers. One such display device is disclosed in the
patent by Yates and another, which might be considered an
improvement on the former, is disclosed in the patent to A.
Siksal, cited. Both show a motor driven polariser disc being an
integral and necessary part of the system. In the prior art
devices capable of selectively illuminating parts of a dark
screen, using the light polarisation phenomena applied to
indicators or advertising panels, also relied on rotating parts
as disclosed for example in the patent to Dreyer. In the prior
art production of animated colour effects or selectively
illuminated coloured parts on the viewing screen has been
obtained by placing suitably oriented and shaped birefringent or
dichroic plastic material between two polarisers (the second
being often referred to as the analyzer), one of them being
usually a motor driven polariser disc. An example of such a
display is disclosed in the patent to Burchell.
The presence of mechanical often motor driven parts in the
prior art indicators and displays, discussed in the foregoing,
gives rise to a number of undesirable side effects. In addition
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to the bulky design and wear and tear, that calls for reqular
maintenance, it is sometimes necessary to control noise,
vibration and heat generation due to the operation of an
electric motor. Also, since a rotating disc is usually circular
in shape and the display panel usually square or rectangular, a
common problem arising is that of illuminating the corners and
edges of the panel with rotating polarised light. Additional
pulleys and discs have to be provided for the corners; they do
not solve the problem completely and add to the complexity of
the design. Although the speed of the motor is controllable, it
cannot be changed quickly enough to produce certain desired
animation effects. The range of possible animation effects
could be greatly enlarged and the process could be simplified
were it possible to animate individually the desired portions of
the display. However the speed of the motor in such displays
often determines the rate of change of the animation effects
throughout the whole display panel. Some aspects of these
limitations have been overcome and disclosed in the patent by
Makow and further advantages and simplifications can be obtained
by the present invention.
In the prior art multiplexed liquid crystal and other
displays have also been used having a grid-like column and row
structure of the electrodes. These electrodes were excited from
the output of a electronic circuit or computer programmed to
display alphanumeric, or animated image information. Also in
the prior art indicator or animated displays have been used that
comprise a large number of light emitt-ing diodes placed side by
side in columns and rows and individually excited from suitable
electronic circuit or computers. In both the multiplexed liquid
crystal and light emitting diode designs such systems are
relatively complex and expensive for the applications mentioned
in the foregoing. These limitations can be overcome and a
number of advantages and new effects can be realised by the
present invention.
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~Summarv of the Invention
1) _Brief Descript.ion Qf the ~La~lngs
The drawings which illustrate the principles of the
embodiments of the invention, may be modified and changed as
regards the immediate illustration, all within the true intent
and scope of the invention, hereinafter defined and Claimed.
Figure 1 is a cross section of the basic embodiment of the
invention showing slanted confining walls of the electro-optic
cell for viewing in transmitted light.
Figure 2 shows the embodiment of the invention of Figure 1
in addition comprising a reflector for viewing in reflected
light.
Figure 3 shows the embodiment of the invention of Figure 1
in addition comprising two polarisers as used in a twisted or
supertwisted nematic liquid crystal electro-optic cells.
igure 4 shows the embodiment of the invention of Figure 3
in addition comprising an optical retardation plate and a
protective, masking or image carrying transparent screen.
Figure 5 shows a plane view of a rectangular slanted cell,
having the cross section shown in any one of the preceding
Figures exited by a voltage V, < Vx < V2 and the area AK through
which light transmission takes place.
Figure 6 is a plane view of the rectangular cell shown in
any of the preceding Figures in which one of the polarisers or
electrodes is shaped to form an arrow or is masked off by an
arrow shaped image depicted on the screen.
Figure 7 is a plane view of the rectangular cell shown in
any of the Figures 3 or 4 in which one polariser consists of a
plurality of linear polariser sections assembled side by side
and having different directions of polarisation.
Figure 8 shows one typical relationship between the
intensity~ I of transmitted or reflected light in a twisted
nematic cell, and the voltage V applied to its electrodes.
Figure 9 shows examples of waveforms of the voltage that
could be applied to the electrodes of the slanted cell in order
to produce an animated image effect.
Figure 10 is another embodiment of the invention showing
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the cross section of a rectangular cell in which one of the
glass plates with its deposited electrode is concave; thus the
angle of the slant being variable and the spacing dK being a
nonlinear function of the dimensions of the cell.
Figure 11 is still another embodiment of the invention
showing the cross sections of a rectangular cell in which one of
the glass plates is shaped to provide a step-like discontinuous
change of the slant angle and of the spacing dx.
Figure 12 is a plane view of the rectangular cell shown in
Figure 10 exited by a voltage Vl < Vx ~ V2 and the areas Ax
through which light transmission takes place.
Figure 13 shows the plane view of a circular equivalent of
Figures 10 and 12, in which at least one of the electrodes
deposited on the glass plates is circular.
Figure 14 shows the embodiment of Figure 3 comprising an
additional conventional twisted or supertwisted nematic cell and
a chromatic polariser placed in the same optical path for the
production and control of hue or saturation of the colour.
Figure 15 shows an embodiment of the invention to produce
an animated image flow effect comprising of an assembly of
slanted cells shown in Figures 3 or 4, placed side by side and
an additional conventional twisted or supertwisted nematic cell
placed in the same optical path with the assembly of slanted
cells.
Figure 16 shows an embodiment of the invention to produce
an animated image flow effect as i.n Figure 15, wherein the
assembly of slanted cell has been substituted by a single
slanted cell having separately excited sections of the
electrodes.
Figure 17 shows a diagramic explanation of the animated
image flow effect of the embodiment of Figure 15 when the
slanted cells are excited by saw-tooth voltage waveforms and the
conventional cell is excited by a square voltage waveform.
The above shown embodiments basically comprise the new
slanted electro-optical cell alone or in combination with a
reflector, retardation plate or screen or suitable polarisers to
be used as a meter, monitor, indicator or an animated display or
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in combination with additional conventional cells to produce an
animated image flow or colour effects. The operation of these
devices and its possible variations of modifications will now be
described in greater detail.
2) Description of the Invention
This invention utilises as its basic distinguishing element
a novel form of a electro-optical cell. The conventional form
that has been used to date in many displays mentioned in the
foregoing consists of two confining parallel walls, at least one
being transparent and made out of a glass or plastic plate. On
at least a part of the inside surface of the walls there are
deposited, or attached to, transparent conducti~e electrode
structures. These are treated, coated, covered or attached to
by layers of materials as required for the functioning of the
cell. A suitable electro-optical compound is sandwiched between
them. The compound is protected from the external environment
and leakage by a seal around the edges of the walls. Such basic
cell structures have been used as a basic element in liquid
crystal (LCD), in electrochromic (ECD), electrophoretic (EPD)
electroluminescent (EL), plasma discharge (PD) and dipolar
suspension (DSD), and other displays. The sandwiched compound
has been respectively a liquid crystal material, an electrolyte,
a dyed suspending medium, phosphor, gas and dipoles in liquid
suspension. Among the various types of liquid crystal displays
such cell structure has been used as its basic element ir
Dynamic Scattering Mode (DSM), Twisted Nematic (TN),
Supertwisted Nematic (STN), Fluorescent LCD's, Cholesteric-
nematic LCD's, tunable birefringence LCD's, LCD's with external
retardation sheet, Guest-host LCD's known as Dichroic LCD's.
Dye Phase Change LCD's, Smectic A LCD's, Ferroelectric LCD's,
Multiplexed LCD's and other recently proposed displays.
The common feature of the cell structure in the presently
used displays mentioned above is that the confining walls are
parallel to each other. In the proposed novel form these two
walls with their deposited electrodes are non-parallel and are
slanted with respect to each other at a small angle usually much
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smaller than a degree. The slant angle can be also variable or
discontinuous. All other features of the respective electro-
optical displays remain the same. The slant of the walls
introduces a new effect which permits the display of a time-
dependent variable f(t) as a two dimensional space coordinate
variable f(x,y) on the surface of the cell and on the attached
to it screen.
The operation of the novel cell form to be referred to in
the following as the slanted cell will be explained using the
example of a conventional Twisted Nematic (TN) cell, being
utilised in the majority of liquid crystal displays. Any other
type of electro-optical display cell mentioned in the foregoing
can be shown to acquire similar properties when their confining
walls are slanted. This is the case wherever the respective
electro-optical effect is dependent on the electric field
strength. The structure and the function of the Twisted Nematic
cells has been first described by Schadt et al in 1971 and has
been since used widely in a variety of display applications. A
brief description of this cell will facilitate the understanding
of the slanted cell.
The conventional twisted nematic cell consists of the
nematic liquid crystal Electro-optical compound confined between
the two parallel glass plates sealed together at the boundaries.
On the inside of the glass plates are deposited thin conducting
transparent electrodes having the spacing do. On the outside of
the cell, on the side away from the viewer, there is attached
and parallel to the glass plate one interior linear polariser
and on the side facing the viewer, there is attached an exterior
polariser rotated at a 90 degree angle with respect to the first
one. The inside surfaces of the electrodes facing the compound
are coated with blocking layer and then with an aligning layer
to facilitate the parallel alignment of the liquid crystal
molecules in the required relation with the direction of the
respective polariser. In the presence of a zero or small
electric field, that is when a voltage V < VO (VO = threshold
voltage) is applied to the electrodes, the polarised light is
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rotated by 90 degrees by the twisted molecular alignment and
emerges from the other side of the cell. When a suitable
voltage V = Vs (usually the saturation voltage V9 = 2 to 6
volts), giving rise to an electric field Es is applied to the
electrodes, the twisted alignment of the molecules is destroyed
and the light which is linearly polarised by the interior
polariser is not rotated and thus is blocked by the exterior
polariser. In the alternative arrangement the exterior polariser
is not rotated and thus makes a zero angle with the direction of
the first polarizer. The results are then reversed. For
intermediate values of the voltage V = Vx, where VO < Vx < V9~
the twisted alignment of the molecules is not fully destroyed
and part of the light is emerging, thus permitting a gray scale.
In the case of a supertwisted nematic (STN) cell the alignment
of the molecules can be as much as 270 degrees and more. The
electric field Es required to almost fully destroy the twisted
alignment of the molecules is given, in the first approximation,
V,
by the ratio Es > d f the applied voltage Vs to the spacing do
between the electrodes. Thus for greater spacings do~ the
voltage Vs has to increase to satisfy this equation.
The novel structure and new properties of twisted or
supertwisted nematic cell and the other cells mentioned in the
foregoing are obtained when one glass plate with the electrode
deposited on it is slanted by a suitable small angle, in the
direction of at least one spatial coordinate, with respect to
the other electrode deposited on the other glass plate. Thus
the electrodes are no longer parallel to each other, and have a
spacing dx that varies across the cell from the smallest value
d1, at the location x1 to its largest value d2 at the location x2
(see Figure 4). The application of a voltage Vx = EsdX to the
electrodes, dx being the spacing at the location x would result
in transmission of light through the area Ax of the cell for
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which dl < dx (see Figure 5). This effect can be used in a new
form of meter, monitor or indicator. In particular if the shape
of the voltage is a function of time such as for example a saw-
tooth waveform, (see Figure 9a), light transmission would be
observed through the area A which is increasing from the area A
= O to the total area A2 of the cell, as the voltage Vx f the
saw-tooth waveform varies from Vl to V2. Thus a function of time
f(t) is converted into a function of the coordinates x and y on
the face of the cell. The change of the voltage is visualised
as a movement of the illuminated area and can be used in novel
forms of animated displays for signage, advertising,
instructional and other displays.
~he spacing dx can be also a non-linear or discontinuous
function of the coordinates x and/or y of the cell dimensions.
This can be the case for example when the center of one
confining wall with its deposited electrode is bent upward with
respect to its edges (see Figure 10), or if there are steplike
transitions between the smallest and largest spacing (seeOFigure
11) .
It will be appreciated that depending on the shape of the
voltage waveforms, different effects and forms of animated
movement of the lighted area Ax can be obtained using a single
cell. In order to obtain an animated continuous flow movement
more than one cell will be required as will be explained later.
Animated colour effects can be obtained by placing chromatic
polarisers, retardation plates or additional cells with
chromatic polarisers in the same optical path with the system
described in the foregoing.
It will be apparent to a person skilled in the art that
most of the previously mentioned drawbacks of mechanical
elements will be eliminated using the described slanted cell.
In addition, distinct advantages will become apparent such as
complete freedom with regard to the placement of the animated
details on the panel, including the corners and edges. Each
detail could be animated from a separate electronic circuit at
its own rate and speed or can be stationary or slowly changing
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to supply information only. Thus new effects and effect
distribution and control, until now not possible, can be
realised by such electro-optical means. These and other
desirable objects and properties of the invention will become
evident to a person skilled in the art as they are discussed in
the following sections.
Descri~tion of the Preferred Embodiments
The basic embodiment of the invention is shown
diagrammatically in Figure 1 for viewing in transmitted light
and in Figure 2 for viewing in reflected light. Refinements of
design which might be required, such as for example an
enclosure, a transparent, protective, image carrying or masking
sheet or screen, light directing or modifying means such like
lenses or light diffusers or absorbers and the like, will be
evident to people skilled in the art and may not be shown for
the sake of clarity. The embodiment consists of a uniform
suitable incandescent, fluorescent electroluminescent or natural
light source 7 with or without a light diffuser, illuminating
the cell on the side away from the viewer which will be referred
to in the following as the interior side. The cell has two
glass walls 1 at least one transparent and slanted with respect
to the other at a small angle. On their inside are deposited or
attached transparent conductive electrodes 2 out of, for example
ITO or In302, which are connected to the voltage source 6. The
electrodes are treated coated covered or have attached to at
least one layer 3 of suitable material as requi~ed for the
operation of the cell or protection of the surface of the
electrodes. The walls are confining the compound 4 and the
interior space is fixed by spacers and is sealed at the edges
with the spacer 5 to prevent contamination and leakage of the
compound 4. The compound 4 varies depending on the type of the
cell, as discussed in the section summarizing the invention.
The desired angle of the slant of one wall with respect to the
other is obtained by using slanted separating spacers 5 at the
boundaries of the cell or by glass or other transparent fibres
or beads distributed uniformly across the cell and having a
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progressively increasing or decreasing diameter. The cell is
viewed from the side facing the viewer 8; this side to be
referred to in the following as the exterior side. Such basic
cell structure as shown in Figure 1 can be used for example in
electrochromic displays (ECD). Here one ITO transparent
electrode 2 can have a W03 layer 3 deposited on it, the second
ITO electrode has a Pd layer charged with hydrogen. The
internal compound 4 is an electrolyte with TIO2. When the basic
slanted cell is used in electrophoretic displays (EPD) the
compound 4 is a suspension of TIO2 charged particle in a black
fluid. When used in Dipolar Suspension displays (DSD) the
compound q is a suspension of dichroic particles. For the
electroluminescent (EL) and plasma discharge (PD) displays the
compound 4 is for example phosphor and neon-argon gas
respectively. The same basic structure of Figure 1 has been
used in Liquid Crystal Displays (LCD) where the conductive
electrode 2, often out of In203 or ITO, is coated with a blocking
and alignment layers 3 and the compound 4 is a liquid crystal.
Depending on the type of the cell, as discussed in the ~summary
of the invention, the compound 9 can be a nematic, quest host,
cholesteric, cholesteric-nematic, smectic or a ferroelectric
liquid crystal. Depending on the mode of operation one interior
or one exterior or both polarisers might be added to the basic
cell, and when viewed in reflected light a reflector is placed
on the interior side of the cell.
For viewing in reflected light, for example in suitably
illuminated rooms or in day light, the basic embodiment as shown
in Figure 2 also comprises a reflector 9 placed on the interior
side of the slanted cell. The reflector, well known in the art,
can be opaque, semitransparent and may also comprise any one of
the means to enhance, spectrally modify or diffuse the incident
light. Such means may include suitably treated fluorescent or
coloured foils made out of metals or other material, replacing
or complementing the light source. The light source 7 is now on
the same side as the viewer 8. All the effects desc~ibed in the
foregoing can be now observed in reflection as the polarisation
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of light is not lost as a result of reflection.
Further preferred embodiments of the invention are shown in
Figures 3 and 4 illustrating the mode of operation of a twisted
or supertwisted nematic liquid crystal display. In Figure 3 the
light is linearly polarised in the interior polariser 10 facing
away from the viewer 8 and the plane of polarisation is rotated
by 90 degrees or more in the slanted liquid crystal cell which
comprises the transparent electrodes 2 with a blocking and
aligning layer 3 deposited on the glass plates (1) which confine
the nematic LC material 4. The rotated polarised light is
emerging or is blocked by the exterior polariser 11 facing the
viewer 8 dependi~g on the orientation of the two polarizers with
respect to each other. The voltage which is applied to the
electrodes is generated in an electronic circuit, transducer or
manual voltage controller, 6 the latter such as a variac or
potentiometer to which the electrodes are connected to. In
Figure 9 an image carrying screen 12 and a retardation sheet 13
are shown in addition to the parts shown in Figure 3. One or
the other or both can be incorporated as an additional ,option.
The slanted cell in Figure 4 has the two confining walls 1 with
its deposited electrodes 2 and blocking and aligning layers 3.
The slanted walls, as described previously, permit the display
of a time dependent quantity on at least one space coordinate on
the face of the cell. The angle of the slant and the spacing
dl and d2 of the electrodes at its minimum and maximum values
respectively (see Figure 4) are in the first approximation
linearly related to the respective voltages V1 and V2 required
for maximum or minimum (depending on the angle of the two
polariser directions with respect to each other) light
transmission to satisfy the equation
Vl V2
Es = - = - = constant
which occurs at the electric field strength Es~ In a practical
case of a 2 x 6 inches cell the spacing required for dl and d2
were about 8 and 12 ~m (micrometers) for the voltages Vl and V2
of about 3 and 4.5 V or for another TN-LC mixture 12 and 18 ~m
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for voltages of 4.0 and 6 Volts respectively. Figure 8 shows a
typical relationship between voltage V and transmitted light
intensity I of a TN liquid crystal cell when the angle of the
interior to the exterior polariser direction is zero, thus the
directions being parallel to each other. For smaller spacings d
the maximum is reached at lower voltages Vs~ Figure 9 shows
examples of voltage waveforms that can be used to obtain various
animation effects.
The embodiment or the invention shown in Figure 4
comprises in addition to the parts shown in Figures 1 to 3 an
optical retardation plate 13 consisting of a solid birefringent
sheet which permits the display of two complementary colours
when the device is switched between the voltage values VO and Vs~
the colours being governed by the thickness of the sheet. Thus
by suitable choice of voltages the animation or indicating
effect can be combined with a colour change effect in order to
evoke an enhanced alerting response In addition an image
carrying screen 12 is shown in Figure 4, which can carry for
example numerals, or symbols indicating a value, a condition a
warning sign or an actual image to be animated. Figure 5 shows
the light distribution across the face of the cell shown in
Figure 9. Observe that light is transmitted through the area
Ax, from the location x1 corresponding to the smallest spacing
d1, to the location x corresponding to the spacing dx for which
the applied voltage Vx satisfies the equation Vx = EsdX. Thus
the location x or the area Ax shown on the screen is a measure
of the voltage Vx. This mode of operation can be used in the
application as a voltage indicator, meter or monitor. Figure 6
shows the plane view of the face of the cell shown in Figure 4
in which the image carrying screen is masking off the face or
the cell àccept for a arrow shaped symbol. This symbol could be
alternately obtained by shaping the exterior polariser or one of
the electrodes in the same manner. Of interest is the animation
of this arrow symbol which can be obtained by applying a saw-
tooth waveform shown in Figure 9 graph (a), to the electrodes.
As the voltage increases from the value V1 towards the peak
776
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value v2, the area Ax through which light is transmitted will be
increasing from zero to a maximum when the whole érrow is
visible, following which there will be a fast return to zero.
This periodic reciprocating animation of the arrow symbol will
help to draw the attention of the viewer as for example in the
case of the direction indicator light of a car or traffic sign.
The application of a triangular waveform to the electrode will
result in a symmetrical increase and decrease of the errow size
and the application of a square waveform will result in a
blinking mode. Figure 7 shows an example of the exterior
polariser consisting of polariser sections oriented at different
directions of polarisation. These sections are assembled side
by side and form a one layer polariser mosaic, which can also be
obtained by an embossing process described by Siksai. The use
of such a polarising mosaic makes it possible to incorporate
additional gray scale effects. Here the transmission of light
will be reduced in those sections whose directions differ from
the direction of the plane polarized light emerging from the
slanted cell.
In a further embodiments of the invention the spacing dx is
a~non-linear function of the dimensions of the cell as shown in
Figures 10 and 11. In the embodiment shown in Figure 10 the
exterior wall of the cell with its deposited electrode is
curved, for example concave. Following the same reasoning as in
the description of the slanted cell it is evident that there
will now be two areas Ax as shown in Figure 12 through which
light transmission will take place as there will be two
symmetrical locations having equal electrode spacing. These
areas will move symmetrically towards the center with increasing
voltage. A reverse effect can be obtained by reversing the
polarity of the saw-tooth waveform or when the curvature of the
exterior wall is convex. The curvature of the glass plate of
the cell can be obtained by a variety of means such as for
example by slightly bending the plate using a center post
determining the spacing in the center of the cell or by shaping
the surface of the glass plate with tools. A variation of a
concave or convex shape of one wall is a V or an inverted V
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shape which results in similar operational characteristics. The
face of the same cell having a circular electrode, and a cross
section that of Figure 10 is shown in Figure 13. The operation
of this cell is analogous to that of the rectangular cell. The
circular shape of the electrodes results in a concentric radial
change of the area through which light is transmitted and will
be found advantageous in certain indicator or animated image
applications in preference to the unidirectional movement in a
rectangular slanted cell. In the embodiment shown in Figure 11
the interior side of the exterior wall with its deposited
electrode is shaped in a discontinuous stair-like manner.
Following the same reasoning as in the foregoing it will be
appreciated that this configuration will permit the display of
the change of the area Ax in discrete steps.
In an extension of the basic embodiment of the invention
colour can be introduced by the addition of at least one
conventional TN or STN liquid crystal cell having parallel
electrodes in combination with a chromatic, sometimes referred
to as spectral polariser or in combination with a chromatic
linear retarder, well known in the art (and described by Shanks
and Shurcliffe, cited), which are commercially available. This
permits the production and independent control of colour effects
in an indicator or animated display using a slanted cell. In
Figure 14 the upper portion of such an embodiment is similar to
that of Figure 4 that produces the indicator or animation
effects. It consists of the picture carrying screen 12, the
slanted cell walls 1 with its transparent electrodes 2,
energised and controlled from the output (a) of the voltage
source 21 such as an electronic circuit transducer or manual
voltage controller, the blocking and alignment layers 3 and
exterior polariser 11. This upper portion receives plane
polarised coloured light from the chromatic or spectral
polariser 20 but its function is identical to the embodiment
shown in Figure 4 without the retardation plate 13. The
chromatic polariser 20 may represent a dyed linear polarizer
which absorbs a part of the visible spectrum and thus produces
coloured light in transmission. In such a case the change of
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angle of the plane of polarised achromatic light entering such
polariser from the conventional additional TN or STN cell,
changes the saturation of the transmitted coloured light. The
interior side of the chromatic polariser 20 is illuminated by
the conventional additional TN or STN cell with its glass walls
19, deposited transparent electrodes 17, blocking and aligning
layer 16, linear polariser 14 and nematic LC compound 18. The
degree of saturation can be controlled electronically from the
output (b) voltage source 21. The chromatic polariser 20 may
also consist, of two dyed linear polarisers, say one passing
blue light and the other red light, bonded together with their
polarisation axis at 90 degrees to each other and forming one
sheet. In such a case the change of angle of the plane of
polarised achromatic light entering this polariser from the
cell, which is aligned at 45 degrees to the direction of the
dyed polarisers changes the hue of the coloured light. The hue
of the coloured light can be thus controlled from the output
(b) of the voltage source 21. The chromatic polariser 20 may
also consist of a solid linear retarder plate of birefringent
material and a linear polariser which in this case will also
permit the control of hue in a manner as outlined in the
foregoing. A still further method of controlling the colour of
the emerging light is by substituting the said linear retarder
by one or more layers of a birefringement film (such as
polyvinyl alcohol film or cellulose film or polyvinyl fluoride
film). It will be evident to a person skilled in the art that
in addition to the slanted cell a serial assembly of said two
conventional cell configurations described in the foregoing one
controlling the saturation and the other the hue of the colour
light will result in the control of both.
A still further embodiment of the invention comprises at
least two slanted cells and a conventional cell having parallel
walls in order to obtain a continuous flow-like image animation
effect. An example of such an embodiment is shown in Figure 15
consisting of an assembly of 3 slanted cells 1, 2, 3 each having
a structure as in Figure 4, but without the retardation plate 13
and the interior polariser 10, connected in parallel to the same
~.Q~ 7~;
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output (a~ of the voltage source 22 which generates a saw-tooth
waveform shown in Figure 9, graph (a). In addition, on the
interior side of these cells a conventional large nematic cell
but without its exterior polariser, having parallel electrodes
17, deposited on parallel glass plates 19 is placed in the same
optical path with the three slanted cells; the electrodes being
connected to the second output (b) of the voltage source 22
generating a square voltage waveform. An equivalent embodiment
is shown in Figure 16 where only one larger slanted cell is used
having three separate electrodes deposited side by side on the
inside of the exterior wall of the cell and exited by three
different voltages. The voltages are related to each other, in
the first approximation, in the same ratio as the ratio of the
electrode spacings at the center of each of the three
electrodes.
The flow-like animation effect will be explained with the
help of the diagrams in Figure 17, graphs (a) to (e) showing the
plane view of the cells as a f~nction of time and the graphs (f)
and (g) showing respectively the voltage waveforms available at
the output (a) and (b) of the voltage source 22. The graph (a)
at the time t=O shows the cells 1 and 3 transmitting light and
appearing white while the cell 2 appearing dark as its exterior
polariser is turned 90 degrees with respect to the exterior
polarisers of the cell 1 and 3. The slant of the cells l, 2 and
3 and the value and slope of the rising saw-tooth voltage shown
in graph ~f) are chosen so that at the time t=0,5 the first
half of the cells 1 and 3 become dark and that of cell 2 become
white as shown in graph (b). At the time t<1, graph (c), just
before the drop of the voltage the cells 1 and 3 will be totally
dark and the cell 2 will be white. At the time t=1, the voltage
drops to zero and then continues rising. The situation would
repeat itself were it not for the conventional cell placed in
the same optical path. This cell being excited by the square
voltage waveform shown in graph (g) at the time t21 introduces a
degree rotation of the plane of polarized light which
illuminates the cells 1, 2 and 3. As a result the cells 1 and 3
remain dark and the cell 2 remains white but as the saw-tooth
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- 20 -
voltage is increasing a white area on the left side of the cell
1 and 3 and the dark area of the cell 2 begins to grow, as shown
in graph (d). Following this reasoning for t=2 and t>2 in graph
(e) it is seen that the white and dark areas would shift and
move in a wave-like manner animating a flow movement of the
image depicted on the screen 12.
While the preferred embodiments of the inventions have been
explained and illustrated it will be appreciated that the
invention is not restricted to these specific forms but it may
consist of further embodiments as a result of adding or omitting
some of its elements or combining or varying these forms and is
of broader scope as defined in the Claims.
