Note: Descriptions are shown in the official language in which they were submitted.
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LIGHT CONTROL DEVICE
Technical Field
This invention relates to an electrostatically
controllable electromechanical display device for use in
light transmissive and light reflective displays.
_ckground Art
The background art contains various examples of
electrostatic display elements. One type of device, such as
is shown in U.S. 1,984,683 and 3,553,364, includes light
~ valves having flaps extending parallel with the approaching
light, with each flap electrostatically divertable to an
oblique~angle across the light path for either a transmissive
or reflective display. U.S. 3,897,997 discloses an electrode
which is electrostatically wrapped about a curved fixed
15 electrode to affect the light reflective character of the
fixed electrode. Eurther prior art such as is described in
ELECTRONICS, 7 December 1970, pp. 78-83 and I.B~M. Technical
Disclosure Bulletln, Vol. 13, No. 3, August 1970, uses an
electron gun to electrostatically charge selected portlons of
20 a deformable material and thereby alter its light
transmissive or reflective properties.
Disclosure of the Invention
The present invention provides an electrostatically
controllable electromechanical display device for light
25 reflective or light transmissive display arrays. Each
display element i~ the array can be individually controlled
to enable the production of a variety of visual displays,
including black and ~lhite and multicolor digital and
pictorial displays.
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~ dispLay element of the invention has a
sta~;nnaryelectroc1e with an adjacent moveable electeode which
is electrostatically controllable between a curled position
removed from the stationary electrode and an uncurled
position overlying the stationary electrode. In a preferred
embodiment, the stationary electrode has a flat surface
normal to the light path, with the uncurled electrode lying
adjacent to and covering the stationary electrode flat
surface. The electrodes can control light transmission or
~ can affect light reflection qualitites for a light reflective
device.
Non-conductive means are provided between the
stationary electrode and the uncurled moveable electrode.
irhe non-conductive means can, for example, take the form of
15 an insulative layer on either the stationary or moveable
electrode. Particular embodiments of dielectric insulators
and external circuitry are provided to avoid operational
difficulties arising from residual electric polarization of
the dielectric insulators.
Embodiments of stationary electrodes having multiple
discrete conductive regions or segments are provided to
enable individual control of elements within a display array.
Each segment of an elec-trode can be addressed separately and
latched in an activated or unactivated state to cause, for
25 example, selected elements within an array to become
actuated, or to cause selected elements to remain actuated
while other elements are not.
Further information disclosing our invention is set
forth in the following portions of the specifications and in
~ the claims.
Brief Description of Drawings
Figure 1 is a perspective view of an embodiment of a
display element.
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Figure 2 is a perspective view of another embodiment
of a display element.
Figure 3 is a perspective view of a light reflective
embodiment.
Figure 4 is a perspective view of a light
transmissive embodiment.
Figure 5 i5 a schematic view of another embodiment.
Figure 6 is a perspective, exploded view illustrating
another embodiment of a stationary electrode in a display
element-
Figure 7 is a perspective, exploded view illustrating
another embodiment of a stationary electrode in a display
element.
- Figure 8 is a perspective, exploded view illustrating
15 another embodiment of a stationary electrode in a display
element
Figure 10 is a schematic view of an embodiment of a
display comprising an array of display elements.
Figure 11 is a plan view of various embodiments of
20 stationary electrodes.
Figure 12 is a perspective view of an embodiment used
to create grey scales and primary color scales.
Best Mode for Carrying Out the Invention
As shown in the drawings, the display elements of the
invention can be of several configurations which can be
incorporated into varied display arrays.
Figure 1 depicts a display element 10 of the
invention having a stationary electrode 12, to which is
attached a layer of insulative material 14. A moveable
80 electrode 16 has a portion 18 adjacent to one end fixed with
respect to the stationary electrode 12 and a free end 20
controllable between a curled position removed from the
stationary electrode -12 and an uncurled position adjacent to
the stationary electrode 12. The moveable electrode 16 is
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electrostatically controlled by means of a source of
electrical potential V and a control switch 24. When the
potential V is connected across the electrodes 12 and 16, the
resulting electrostatic forces cause the moveable electrode
16 to uncurl into a position overlying the stationary
electrode 12, as shown by dotted lines 26. When the
potential V is disconnected and the electrodes connected
together, the electrostatic orces decrease and the
restitution force of the moveable electrode 16 causes the
body portion 20 to curl to its relaxed, curled position
removed from the stationary electrode 12.
Figure 2 shows an embodiment in which the insulative
layer 14 is attached to the inner surface of the moveable
electrode.
The display element 10 of Figure 1 can be used for
either a light re1ective or light transmissive display
device. Use in a reflective device is illustrated in Figure
3. As seen in Figure 3, when the moveable electrode 16 is
curled away from the stationary electrode 12, the viewer sees
the light reflected from the area 32, consisting of
reflections off the exposed stationary electrode 12 and
insulative layer 14, as well as off the exposed portion of
inner surface 34 of the moveable electrode 16. When the
moveable electrode 16 is flattened to a position overlying
the stationary electrode, as shown by dotted lines 6, the
viewer sees only the light reflected from outer surface 36 of
the moveable electrode.
As a light reflective device, the element can be used
in a variety of displays such as in a black and white or a
multicolor array. For example, in a black and white display
the insulative material layer 14 can be black, the inner
surface 34 of the moveable electrode can be black, and the
outer surface 36 of the moveable electrode white. In the
curled state, no light is reflected and area 32 appears to be
black. When the moveable electrode is uncurled or 1attened,
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light is reflected ~rom the white surface. Similarly, in a
colored display the exposed surfaces in one state of the
device can be of one color with the exposed surfaces in the
other state of another color.
The element can also be part of a light transmissive
device. Use as such a device is shown in Figure 4 with the
light source 40 on the opposite side o the device from the
viewer who sees the transmitted light emanating from area 44.
As a light gate device, light is transmitted through a
` translucent stationary electrode 12 and translucent
insulative layer 14- In the flattened condition, an opaque
moveable electrode 16 blocks the light. In a multicolor
display, the curled condition reveals a color of light
transmitted through either a clear or colored stationary
electrode 12 and insulative layer 14. The moveable electrode
16 can be opaque, to constitute a color light gate device, or
translucent and colored to effect a change of color of the
transmitted light.
In addition, other embodiments of devices can be
constructed for other light conditions or display effects.
For example, a combination reflective and transmissive
display can be constructed for use in varying light
conditions by use of a translucent reflective coating on the
surfaces of the electrodes ].2 and 16 whereby the device can
be used in a reflective mode when the light source 40 is off,
or in a transmissive mode when the light source is on.
In constructing operating embodiments of the
invention, several operating variables are to be considered
in selecting the materials for use in the electrodes, the
insulative layer, and the further components of a display
device, such as the substrate. With respect to the moveable
electrode, the material used must be capable of being curled
to the correct curl size for the particular use. Other
considerations include the mass since a lower mass moveable
electrode will have a lower inertia and respond more quickly
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to a given electrostatic force. A further conslderation is
the stiffness of the rnaterial which affects the force needed
to bend the material to effect flattening.
In general, a moveable electrode can be formed either
of a metal or of a plastic laminate containing a conductive
material. In one embodiment, beryllium copper 25 (BeCu 25)
foil, 0.0001 inches thick, is curled by wrapping it about a
0.25 inch mandrel and heat treating it to set the curl. The
resulting curled sheet is chemically etched into an array of
10 0.5 inch by 0.5 inch moveable electrodes. Other materials
for use in opaque moveable electrodes include tin-alloys and
aluminum. Materials for use in translucent electrodes
include a translucent base material with a translucent
deposited thin conductive layer such as deposited gold,
15 indium oxide, or tin oxide. The materials for moveable
electrodes can be provided with the curl by heat forming or
can be a laminate of two or more plies bonded together while
stressed to form a curl.
Stationary electrodes can be formed of a conductive
~0 material such as metal foil for a reflective display, or of a
translucent layer of indium oxide or tin oxide on a
translucent substrate in a transmissive display.
The insulative layer 14 can also be chosen from many
materials. Materia]s having high dielectric constants are
~5 preferred. A polymeric film may be used. One problem
encountered in the use of certain materials arises in the
temporary retention of a residual electrical charge or
polarization after an electric potential has been removed.
For example, it has been found that in the embodiment of
~0 Figure 1, the application of sufficient potential to cause
the moveable electrode to flatten to a position adjacent to
the stationary electrode, may induce a temporary residual
.~ polarization in the dielectric insulative layer sufficient to
maintain the moveable electrode flattened for a time after
35 the electric potential has been removed or decreased.
Certain materials do not exhibit this effect or the effect is
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small. Cellulose, pol~propylene and polyethylene are
examples of such materials. Another solution is the use of
dielectrics which allow the residual charge to leak off. As
another solution to this residual polari~ation problem, a
preferred embodiment of this invention uses an electret
formed of material such as polyethylene terephthalate (MYLAR~
as the insulative layer. An electret material maintains a
relatively constant degree of residual polarization unaffectd
by the further application of an electric potential across
it. Since the residual charge is a constant, it can be
accurately accounted for in the design of the element. As an
illustration of the use of an electret in an element as shown
in Figure 1, the insulative layer 14 is the electret. Since
the electret provides a portion of the attractive force to
flatten the moveable electrode, the electric potential V can
be of a lower potential to add a further electrostatic force
sufficient to cause the moveable electrode 16 to uncurl to a
position adjacent to the stationary electrode 12. The
removal of the electric potential V results in the recurling
return of the moveable electrode to its original curled
position since the force provided by the electret is less
than the restorative force of the curl bias.
A further embodiment of the invention is illustrated
in Figure 5 where a biasing power source 54 and an
incremental drive power source 56 are used to control the
mcveable electrode 16. The biasing power source 54, set at V
volts, is at a voltage potential just below that needed to
effect the uncurling of the moveable eletrode 16. The
incremental drive source 56, set at ~V volts, adds sufficient
further voltage potential when added to the bias potential to
cause the moveable electrode to uncurl and overlie the
stationary electrode 12. The use of a bias voltage
continually applied across the electrode, requiring only the
switching of the ~V incremental voltage to effect a change of
position of the moveable electrode, can be highly
advantageous in a display system. For example, a high
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voltage power supply can provide the bias voltage for all
elements in the array. Only a small incremental potential is
necessary to control the elements which the attendant cost
savings resulting from the ability to use low voltage
5 switchiny hardware.
This biasing effect and results are also obtained by
the use of an electret as the insulative layer since the
charge of the electret serves the same biasing function as
bias power source 54. Therefore, only the incremental drive
voltage ~V is needed to actuate the moveable electrode.
The advantages of this biasing effect are also
realizable when a liquid layer is present between the
moveable and stationary electrodes. Surface tension forces
of the liquid provide a portion of the attractive force
15 acting on the moveable electrode. The liquid thus acts in a
manner similar to a bias voltage. Suitable liquids include
silicone oil and petroleum oils and derivatives.
The embodiment of Figure 5 can also be operated with
an excess of bias voltage sufficient by itself to maintain
the moveable electrode in a flattened position adjacent to
the stationary electrode. In this embodiment, the
incremental drive voltage 56 is of opposite polarity,
suf~icient to decrease the electrostatic charge to a level
allowing the moveable electrode to recurl to a position
25 removed from the stationary electrode. This embodiment can
also take the form of a sufficiently charged electret
insulative layer with the incremental drive source 56 of
reverse polarity. This embodiment is advantageous in that in
the quiescent state with no l~V potential applied, the
moveable electrode is adjacent to the stationary electrode,
rendering the moveable electrode less subject to accidental
physical damage.
Figure 6 illustrates a display element 60 having a
stationary electrode 62 with a plurality of discrete
~5 conductive regions 66-68, insulative layer 64, and moveable
electrode 65. This embodiment provides independently
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addressable conductive portions of the stationar~ electrode
62 to facilitate particular control of the display element 60
for use in a display array. In the illustrated embodiment of
a three region stationary electrode, for example, an
electrical potential can be applied independently to the X
electrode region 66, to the Y electrode region 67, or to the
hold-down electrode region 68. Only when the X, Y, and
hold-down regions are energized, will the moveable electrode
65 fully flatten. Once fully flattened, the hold-down
10 electrode region 68, when energized, provides sufficient
electrostatic force to latch the moveable electrode 65 in its
flattened state regardless of whether the X or Y electrode
regions are energized. To release the electrode 65 from its
flattened state, all of the hold-down regions 68 and the X
15 and Y electrode regions must be de-energized.
When only the X electrode region is energized, that
is the conductive region 66 proximate the fixed edge portion
61 of the moveable electrode 65, the moveable electrode will
partially uncurl. If, in addition to energization of the X
20 electrode region 66, the Y electrode region 67 is also
energized, the moveable electrode 65 will further uncurl.
Energization of hold-down electrode region 68, the conductive
region most remote from the fixed edge portion 61, will
complete the uncurling of moveable electrode 65 to a fully
~5 flattened condition.
It should be noted that uncurling can not be effected
by any conductive segment which is not immediately adjacent
to the curled end portion of the moveable electrode.
Therefore, the Y electrode region 67 cannot cause uncurling
~ until the X electrode region 66 has been energized to cause
partial uncurling.
In order that the moveable electrode be attracted by
the electrostatic field of a particular stationary electrode
region, the moveable electrode must sufficiently proximate to
~5 that region. This proximity can be achieved by causing the
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moveable electrode to partially overlie the particular
region. One manner of achieving the condition of partial
overlying is to shape the stationary regions such that the
demarcations between regions are not parallel to the curl
axis of the moveable electrode. A chevron shape of the
regions provides demarcations which are not parallel to the
curl axis such that the moveable electrode partially overlies
the adjacent electrode region and thereby is located within
the domain of the electrostatic field of that adjacent region
when it is subsequently energi~ed.
The operation of the X, Y, hold-down configuration of
Figure 6 is illustrated in Figure 7 where drive voltage V can
be applied between the moveable electrode 65 and any or all
of the regions of the stationary electrode, X region 66, Y
15 region 67, or hold-down region 68, by means of switches 70,
71 or 72 respectively. When switch 70 activates the X region
66, the moveable electrode 65 uncurls partially; activation
of the Y region 67 provides further uncurling of the moveable
electrode 65. Switch 72 activates the hold-down region 68 to
~ fully flatten and latch the moveable electrode 65 even if the
switches 70 and 71 subsequently deactivate the X and Y
regions 66 and 67.
Control of display elements such as are illustrated
in Figures 6 and 7 having segmented stationary electrodes
~5 provides for use of the elements in a display array in which
each element of the array can be selectively actuated without
affecting the state of the remainder of the elements in the
array. Such a display array is illustrated in Figure 8 in
which a plurality of display elements 81, 82, 83 and 84 are
~0 assembled in columns and rows to form a display array 80.
The moveable electrodes (not shown) are connected via a
common lead 90 to one side of a source of electrical poten-
tial 110. Each stationary electrode has an X region, a Y
region, and a hold-down region ~. All X regions in the first
~5 column are connected via a common lead to switch Xl, and all
X regions in the second column are connected to switch X2.
Similarly, all Y regions in the first row are connected
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to switch Yl and all Y regions in the second row are
connected to switch Y2. All hold-down regions are connected
in common to switch El. Thereby, each element 81-84 can be
selec.ively actuated by selection of the appropriate
switches, and latched down by the closure of hold-down switch
H.
As an example of the operation of the array in Figure
8, ln order to actuate element 83, hold-down switch H and
switch Xl are closed to connect the hold-down and the X
electrode regions in the first column to the potential 110,
and switch Y2 is closed to connect the Y electrode regions in
the second row to the potential llO. Since the element 83 is
the only element in the array with both its X and Y electrode
regions energized, it alone is caused to fully uncurl.
Hold-down switch El will latch element 83 in the flattened .
state when the X and Y electrode regions are subsequently
deactivated. The fact that a moveable electrode can be
affected only by a stationary electrode region immediately
adjacent the curled portion is of great value in simplifying
~0 the circuitry required to control an array of elements.
The display elements illustrated in Figures 6 and 7
have two independently controllable stationary electrode
conductive regions in addition to the hold-down region.
Increasing the number of independently controllable con-
25 ductive regions in each element permits a significantincrease in the number of elements in an array without a
concomitant increase in the number of switch devices
required. Specifically, in order to independently address an
element in an array having a number of elements N, each
3 element having a number of independently controllable
conductive regions d, the number of switch elements S
required is
S = d ~
For example, for an array of N = 390,625 individually
controlled picture elements, a single conductive region per
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element would requice 390,625 switches, or one switch per
element. If each element has two conductive regions, such as
in Figure 8, 1250 switches are needed to individually conteol
and address each element. If the elements have four regions,
only 100 switches are required. The switch devices and all
other switch devices referred to in this specification can be
mechanical or electeonic switches including semiconductor
elements which apply one of two potentials to the element to
be controlled.
Figure 9 illustrates an embodiment of an element
wherein moveable electrode 120 can be selectively controlled
to change its state from either a flattened to a curled
position, or ~rom a curled to a flattened position when in a
display array. The Figure 9 element has a stationary
e Lectrode formed of an X region 124, Y region 126 and two
hold-down regions, 122 and 128. Hold-down region 122
(proximate the fixed edge of the moveable electrode) is
partially beneath the moveable electrode 120 when it is fully
curled. The X and Y regions, 1~4 and 126 respectively, are
positioned between the hold-down regions. In other words,
the conductive regions are in a series progressing linearly
from the fixed edge.
In operation, in order to selectively cause the
moveable electrode 120 to change its state from a curled to a
fully flattened condition, hold-down regions 122 and 128 are
energized, as well as X regions 124 and Y regions 126, in the
manner explained in reference to Figure 8. In this
configuration, the hold-down region 122 lying underneath the
moveable electrode 120 in its fully curled state, must be
activated to partially uncurl the moveable electrode 120 to a
position partially overlying X region 124 to enable the X
region to cause further uncurling upon activation. When all
regions 122, 124, 126 and 128 are activated, the electrode
120 will fully flatten.
In order to selectively cause the moveable electrode
120 to go from a fully flattened condition to a fully curled
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condition without affecting ot:her display elements in an
array, the following operation is performed. At the start,
only those moveable electrodes which have their hold-down
portions energized are in a fully flattened condition. To
6 selectively release a moveable electrode first all Y regions
in the array are deactivated. All X regions are then
activated. The moveable electrodes thereby partially curl to
a position above the Y region. Deactivation of the X and Y
regions in the column and row of the desired element will
10 thereby release that specific moveable electrode and cause
that electrode to fully curl. The hold-down regions can then
be reactivated to secure the remaining flattened electrodes.
The response speed of an element is related to the
size of the element. Sub-dividing an element into a
15 plurality will promote increased response speed. Therefore,
the element at a particular address in an array advantage-
ously may be subdivided into two or more elements
electrically connected in common.
Figure lO illustrates the further use of a biasing
~ power source such as described with reference to Figure 5.
In the display array 240 of Figure lO, four display elements
comprise moveable electrodes 242, 243, 244 and 245 and
corresponding stationary electrodes having hold-down region
246, Xl row region 248, X2 row regions 250, Yl column regions
252, and Y2 column regions 254. Bias voltage Vl is con-
tinually applied to the electrodes of all elements. Further
bias voltage V2 can be selectively applied in series with V
via switch 247. Incremental drive voltage V3 can be
selectively applied in series with Vl and V2. In order to
cause a curled moveable electrode to change state, all three
potentials Vl, V2 and V3 must be applied. To release a
flattened electrode, the V2 and V3 potentials must be
removed. The Vl potential therefore represents a relatively
large bias voltage which can be applied across all elements.
85 The V2 potential reflects the residual polarization of the
insulative layer in each element. The V3 potential is of an
incremental level to drive an element already biased by Vl
and V2. The level of V3 potential is set to allow for the
inherent deviations in the amount of potential required to
cause a change in state in various individual display
elements stemming from manufacturing variations in such
element parameters as insulative layer thickness, dielectric
characteristics and curl diameter. It has been found that
the V3 potential may be in the order of ten percent of the V
~ V2 level. In the biasing configuration of Figure 10, the
10 curls can be controlled to selectively cause their change oE
state from a curled to an uncurled position by control of V3
alone, once the biasing voltages Vl and V2 have been applied.
The control switches required in a display array can be
operated at the lower V3 voltage, with fewer switches needed
15 at the higher Vl or V2 voltages, with attendant savings in
manufacturing cost.
The present invention can be used to create a
digitally controlled two color, or black and white, display
with desired gray scales, or a color display with desired
20 intensities of the three primary colors. Various procedures
for creating the gray scale and color shades are discussed
here. Figure 11 shows a plan view of element arrangements to
create gray scales. Figuee lla shows the use of curls 148
which have square or rectangular shapes in the plan view.
2$ Figures llb and llc, respectively, show the use of triangular
shapes. To create an 80% black gray scale, 20% of the
elements are curled. When the curled position represents
white, 60~ of the elements are curled to create 40~ black
gray scale. In all these examples, the dotted lines, 144
~ represent the curl axes of the elements and the straight
solid lines represent the element perimeters. The arrows 146
show the curl direct~on.
Various shade scales can be accomplished by grouping
plural elements. The number of shade combinations available
95 in a group is S = 2N where N is the number of differently
shaded elements. Thus, four elements will provide 16 shade
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cornbinations, ranging rom no actuation to all elements fully
actuated.
Another procedure for the creation of different two
color scales and primary color shades is through the control
of the duty (up and down) cycles of elements. Therefore, a
black and white element, (where white is the curled position)
when cycled faster than the ability of the eye to perceive
the movement, would appear to be the percentage of the dllty
cycle devoted to the coiled up state vs. the flat (black)
10 state. Where S is the number of different shade combinations
achieved from N different discrete and additive duty cycles,
then S = 2. Therefore, for four different discrete and
additive duty c~cles 16 different shades can be created.
Figure 12 shows another way to make use of the
- 15 present invention to create gray scales and primary color
scales shade. Separately driven X and Y electrode regions
150, 152 pull the selected moveable electrode 158 to the
first hold-down electrode 154 representing a gray or shade
scale. Additional separately driven regions X2 and X3, 156
2V and 157 are used to pull the selected electrode to the second
hold-down electrode region 154 to create another gray or
shade scale. Additional X, Y and hold-down electrode regions
to create additional selectable shades or gray scales can be
provided.
