U.S. patent number 3,553,364 [Application Number 04/713,503] was granted by the patent office on 1971-01-05 for electromechanical light valve.
This patent grant is currently assigned to Texas Instruments Incorporated. Invention is credited to Ray H. Lee.
United States Patent |
3,553,364 |
Lee |
January 5, 1971 |
ELECTROMECHANICAL LIGHT VALVE
Abstract
An electromechanical light valve in an array of many such valves
for controlling the transmission of light in continuously changing
patterns. Each light valve consists of a housing having grounded
conducted walls for shielding the interior thereof from external
electrostatic forces produced by surrounding valves in the array or
from other external forces. Light from a source enters one end of
the housing through a light transparent and electrically insulating
panel coated with a conductive film to which is mounted one or more
electrostatically controlled leaf shutters. The leaf shutter and
the conductive housing walls form a capacitor; connecting a voltage
to the leaf shutter sets up a charge thereon thereby causing the
shutter to be attracted to the housing walls. Voltages for charging
the leaf shutters of all the valves in an array are generated by an
XY scanner. A slight modification changes valve from a light
transmissive device to a light reflective valve.
Inventors: |
Lee; Ray H. (Richardson,
TX) |
Assignee: |
Texas Instruments Incorporated
(Dallas, TX)
|
Family
ID: |
24866396 |
Appl.
No.: |
04/713,503 |
Filed: |
March 15, 1968 |
Current U.S.
Class: |
359/230;
348/795 |
Current CPC
Class: |
G09F
9/372 (20130101) |
Current International
Class: |
G09F
9/37 (20060101); H04n 005/74 () |
Field of
Search: |
;178/7.3D,7.5D,6A,6LMS
;350/17,266,269,160 ;315/169TV |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Richardson; Robert L.
Claims
I claim:
1. An electromechanical light valve for controlling the
transmission of light from a source comprising:
a housing having grounded conductive walls for shielding the
interior thereof from external electrostatic forces;
mounting means in said housing transmitting light from said source
and electrically insulating; and
at least one electrostatically controlled leaf shutter mounted to
said means and deflectable in said housing by means of an
electrostatic charge thereon generated by an applied voltage.
2. An electromechanical light valve for controlling the
transmission of light from a source as set forth in claim 1 wherein
said mounting means includes curved surfaces against which said
leaf shutter deflects thereby improving the response time of said
shutter.
3. An electromechanical light valve for controlling the
transmission of light from a source as set forth in claim 1
including means for charging said leaf shutters to a level slightly
less than the pull-in voltage of said shutters.
4. An electromechanical light valve for controlling the
transmission of light from a source as set forth in claim 1
including means for reducing the air drag on said leaf
shutters.
5. An electromechanical light valve for controlling the
transmission of light from a source as set forth in claim 1
including filter means at said housing to transmit to light waves
having only preselected wavelengths.
6. An electromechanical light valve for controlling the
transmission of light from a source comprising:
a housing including means for shielding the interior thereof from
external electrostatic forces;
a first set of electrostatically controlled leaf shutters
positioned at the inner walls of said housing and deflectable by
means of an electrostatic charge thereon; and
a second set of electrostatically controlled leaf shutters
positioned at the center of said housing opposite said first set of
shutters and deflectable by means of an electrostatic charge
thereon generated from an applied voltage, said sets of
electrostatically controlled shutters deflectable in a manner to
impede the transmission of light through said housing.
7. Apparatus for controlling the transmission of light from a
source in a continuously changing pattern comprising:
a plurality of electromechanical light valves each including a
housing having means for shielding the interior thereof from
external electrostatic forces and at least one electrostatically
controlled leaf shutter mounted to a panel at the light source end
of said housing and deflectable in said housing by means of an
electrostatic charge thereon;
scanning means for connecting a voltage to said electrostatically
controlled leaf shutters to generate the electrostatic charge
thereon in accordance with a changing program; and
an output panel covering said light valve housings at the end
opposite from said source having a conductive inner surface
connected to ground.
8. Apparatus for controlling the transmission of light from a
source as set forth in claim 7 including means for receiving a
video signal connected to said scanning means for programming the
operation of said electromechanical light valves.
9. An electromechanical light valve for controlling the reflection
of light from a source comprising:
a housing including means for shielding the interior thereof from
external electrostatic forces;
means for piping light into the interior of said housing; and
an electrostatically controlled leaf shutter mounted in said
housing and deflectable by means of an electrostatic charge
thereon, said leaf shutter blocking out light into said housing in
a first position and reflecting light from said housing transmitted
through said piping means in second position.
10. An electromechanical light valve for controlling the reflection
of light from a source as set forth in claim 9 wherein said piping
means includes an electrically conductive fiber optic panel for
mounting said leaf shutter.
11. Apparatus for controlling the transmission of light from a
source in a continuously changing pattern comprising:
a plurality of electromechanical light valves each including:
a housing including means for shielding the interior thereof from
external electrostatic forces;
a mounting frame forming a passage for transmitting light from said
source to an observer; and
at least one electrostatically controlled leaf shutter mounted
between said housing and said mounting frame and deflectable
therein by means of an electrostatic charge thereon generated from
an applied voltage.
12. An electromechanical light valve for controlling the
transmission of light from a source as set forth in claim 11
wherein said housing is of an electrically conductive material and
said leaf shutters are in electrical contact with said housing.
13. An electromechanical light valve for controlling the
transmission of light from a source comprising:
a housing including means for shielding the interior thereof from
external electrostatic forces;
a mounting frame forming a passage for transmitting light from said
source to an observer; and
at least one electrostatically controlled leaf shutter mounted
between said housing and said mounting frame and deflectable
therein by means of an electrostatic charge thereon generated from
an applied voltage; wherein said mounting frame is an electrically
conductive material in electrical contact with said leaf shutters
and wherein said housing is an electrically conductive material
coated on the inner walls with an electrically insulating
material.
14. An electromechanical light valve for controlling the
transmission of light from a source as set forth in claim 13
including means for reducing the air drag between said leaf
shutters and said electrically insulating coating.
Description
This invention relates to light transmission or light reflection
control, and more particularly to a light valve for controlling the
transmission or the reflection of light by means of an
electrostatic charge.
During the early development of television in the latter part of
the last century, a picture was generated on the retina of the eye
of an observer by the rapid movement and intensity fluctuation of a
narrow light beam. Because of persistence of vision of the human
eye, a picture was in fact generated although of a very low
quality. A method in vogue in panel displays, such as television,
during the first part of the present century built up a picture by
controlling the transmission of a high intensity light source by
means of light valves. Two patents which issued about this time on
light valves are U.S. Pat. No. 1,848,888 and U.S. Pat. No.
1,964,062. Both of these patents describe light valves reportedly
operated by means of electrostatic forces generated on a shutter
mechanism.
Earlier light valves such as described in the aforementioned
patents are extremely inefficient because of the large amount of
"crosstalk" or interference between adjacent valves. As a result,
the displays produced by earlier light valves were not acceptable
due to inferior picture resolution.
As a result of inferior picture quality, earlier efforts for
producing a picture by means of light valves were abandoned in
favor of its electron counterpart, the cathode ray tube. However,
it is now realized that the cathode ray tube displays have their
limitation especially when producing color pictures. Screen sizes
larger than a 25-inch diagonal measurement produces a picture that
lacks brightness as well as being difficult to handle (too bulky),
and smaller than a 21-inch diagonal measurement suffers in
resolution on account of tolerance requirements.
It is an object of this invention to provide a light valve isolated
from surrounding electrostatically generated forces, thereby
reducing "crosstalk."
A further object of this invention is to provide a light valve for
a panel display.
Yet another object of this invention is to provide a light valve
for a panel display using an ordinary light source.
A still further object of this invention is to provide a light
valve operable from a low voltage source and consuming small
amounts of power.
An additional object of this invention is to provide a light valve
not affected by the earth' s magnetic field.
Another object of this invention is to provide a light valve having
a response time well within present standards established for
television displays.
Still another object of this invention is to provide a light valve
for large area display systems with acceptable brightness and
resolution characteristics.
In accordance with a specific embodiment of this invention, an
electromechanical light valve is provided for controlling the
transmission of light from a source. The valve includes a housing
having a grounded conductive wall for shielding the interior
thereof from external electrostatic forces, and a light transparent
panel at the light source end of the housing mounting an
electrostatically controlled leaf shutter deflectable in the
housing by means of an electrostatic charge thereon generated by an
applied voltage.
In accordance with another embodiment of the invention, by properly
arranging the light source direction with respect to the
electrostatically controlled leaf shutter, the light valve produces
a display by means of light reflection. This valve includes an
electrostatically shielded housing, and an opaque panel supporting
electrostatically controlled leaf shutters reflecting light piped
into the housing from a light source.
A more complete understanding of the invention and its advantages
will be apparent from the specification and claims and from the
accompanying drawings illustrative of the invention.
Referring to the drawings:
FIG. 1 illustrates a picture receiving system employing a light
valve panel in accordance with the present invention;
FIG. 2 is an enlarged view in perspective of a single light valve
in the panel illustrated in FIG. 1;
FIGS. 3a and 3bare enlarged illustrations of the light valve of
FIG. 2 showing the operation thereof;
FIG. 4 is a plot of response time in milliseconds, applied voltage
in volts, and energy in nonowatt-seconds versus the thickness of a
nonmagnetic stainless steel light valve shutter;
FIG. 5 is a cross section, partially cutaway, of the panel of FIG.
1 showing parallel leaf shutter valves;
FIG. 6 is a perspective view of the light panel of FIG. 5,
partially cutaway, of the parallel leaf shutter valves;
FIGS. 7a and 7bshow schematically a charged-dark light valve;
FIG. 8 is a modification of the valve of FIG. 7 for a
charged-bright valve;
FIGS. 9a and 9billustrate a modification of the valve shown in FIG.
2 for improving the response time of the leaf shutters;
FIGS. 10a and 10b illustrate a light valve using fixed-at-both-end
leaf shutters; and
FIGS. 11a and 11b illustrate a two voltage source light valve.
Basically, the system illustrated in FIG. 1 consists of a light
valve panel 10 and an address scanner 12. The address scanner 12
performs XY scanning of the panel 10 as well as intensity
modulation (Z axis control) for each light valve of the panel
array. Many XY scanners are available that produce a variable
voltage for each XY position of an array. A video receiver 14
coupled to an antenna 16 controls the operation of the address
scanner 12 in the usual manner of present day video receiving
systems. To generate a visual display for an observer 18 on the
panel 10, a light source 20 produces a light beam 22 collimated by
a lens 24. A light panel may also be employed as a light source
replacing the source 20 and the lens 24. This panel would match the
size of the panel 10. By selectively opening and closing each light
valve in the panel 10 in accordance with the video signal received
by the antenna 16, the observer 18 sees a picture display.
Although this description will proceed to emphasize a television
system, it is not intended to be so limited. The scanner 12 may be
programmed from any one of many sources other than the receiver 14.
For example, a computer can be employed to program the scanner 12
to produce simulated environmental conditions, such as might be
encountered in space travel, to the observer 18.
In a typical television system in accordance with present day NTSC
(National Television Systems Committee) regulations, the panel 10
includes 525 scanning lines, a bandwidth chosen for equal area
resolution with an aspect ratio of 4:3, and there would be two
interlaced fields in one frame having a frame rate of 30 frames per
second. Accordingly, in order to fully utilize the NTSC
information, the panel 10 has 525 .times. (4/3.times. 525) =
367,500 light units (one light valve per unit for a monochrome
display, two light valves per unit for a bicolor display, and three
light valves per unit for a tricolor display). In terms of light
units, the video information received at the antenna 16 comes in at
a rate of 0.0906 microseconds per unit (roughly 0.1 microsecond).
Thus, for sequential addressing each valve in the panel 10 must be
able to be addressed within 0.1 microsecond and be updated once per
one-thirtieth second. However, other addressing schemes, such as
line sequential addressing, may be used.
Referring to FIGS. 2 and 3, there is shown an electromechanical
light valve 26 having two chargeable leaf shutters 28, 30 connected
to a battery 29 through a two-position switch 25. Typically, the
shutters 28 and 30 are made from a metallic material, such as
copper, but other materials can be used as will be explained
shortly. The light valve 26 includes a housing having sidewalls 34
and 36 along with front and back walls all of a reflective opaque
material either electrically conductive, such as aluminum, or
electrically insulating and covered with a conductive coating. An
insulating layer, as shown in FIGS. 3a and 3b, covers the
conductive coating to electrically insulate the housing walls from
the shutters. The housing or conductive coating is grounded by
means of a lead 38 to provide electrostatic shielding, thereby
eliminating electrostatic forces in the housing interior generated
externally thereof. One of the many advantages of the light valve
of this invention is that the housing need not be air sealed.
Although sealing and evacuating may be desirable in some
application, it is not a necessity as the valve operates in an air
environment. At the light source end of the valve 26, the top shown
in FIGS. 2 and 3, there is provided an electrically insulating
mounting panel 40 for the shutters 28 and 30 and for an
electrically conductive center plate 31. The panel 40 transmits
light wave energy produced by the source 20 and is covered with a
transparent electrically conductive film 33, except in the area of
lead 32, connected to ground through the lead 38. At the observer'
s end of the valve 26, the bottom of FIGS. 2 and 3, there is a
light transparent panel 42 having a light transmissive electrically
conductive film deposited thereon (schematically illustrated by a
heavy line) connected to ground through the lead 38. Thus, the
shutters 28 and 30 are shielded to eliminate "crosstalk." Both the
input panel 40 and the output panel 42 may have filtering
properties to pass only selected wavelengths of the light beam 22.
In addition, the output panel 42 may be processed to diffuse the
light transmitted to expand the viewing area.
Operationally, the light valve 26 uses the well-known electroscope
principle with each of the leaf shutters 28 and 30 considered one
plate of a capacitor with its respective sidewalls 34 and 36
forming the second plate. For the configuration shown in FIGS. 2
and 3, the capacitor plates are rectangular having a length L and a
width b. For purposes of this discussion, the leaf shutters 28 and
30 will be considered to have a uniform thickness h, a uniform
modulus of elasticity (Young' s modulus) E, and made from an
elastic material of uniform density d. It will be understood that
other shutter configurations are possible and materials with
nonuniform properties may be used.
Neglecting edge effects, the capacitance of a deenergized valve is
given by the equation: ##SPC1## where K is the dielectric constant
of the capacitor medium (unity for air) and s is the distance
between the undeflected leaf shutter 28 and the sidewall 34.
Considering only the leaf shutter 28 and its associated sidewall
34, these will be charged to + Q.sub.o and - Q.sub.o, respectively,
when a voltage of magnitude V.sub.o is applied to the lead 32 in
accordance with the equation Q.sub.o = C.sub.oV.sub.o. This charge
is uniformly distributed, neglecting edge effects, over the facing
surfaces, resulting in a uniformly distributed load on the leaf
shutter 28 and setting it in motion against both the inertia and
elastic properties of the shutter material.
Since electrical charging is a surface phenomena, the shutters 28
and 30 are not restricted to metallic materials but cover the broad
spectrum of all materials capable of storing a surface charge. This
permits a wide choice of materials in regards to the electrical,
mechanical, and optical characteristics.
To completely shut off the transmission of light to the observer
18, the leaf shutter 28 must be deflected to the sidewall 34. The
voltage connected to the lead 32 to deflect the shutter 28 to the
wall 34 is identified as the pull-in voltage, V.sub.s. A
conservative estimate of the pull-in voltage may be calculated from
the equation: ##SPC2## where V.sub.s is in volts. As a practical
matter, the valve 26 is designed to meet given panel requirements
and the pull-in voltage determined by actual measurement. The power
required to deflect the leaf shutter 28 to the wall 34 can now be
calculated from the expression: ##SPC3## where W.sub.s is given in
nanowatt-seconds. Again the value given by equation (3) will be
somewhat conservative estimate.
Referring to FIG. 4, there is shown two sets of curves calculated
from the above equations illustrating the pull-in voltage, the
pull-in energy, and the period of oscillation of the leaf shutters
28 and 30 in microseconds. The leaf shutters are separated from
their respective walls by 5 .times. 10.sup.-3 inches in the
undeflected condition. These curves are for nonmagnetic stainless
steel shutters having a Young's modulus of 30 .times. 10.sup.6
lbs./in..sup.2, a uniform density d of 0.283 lbs./in..sup. 3, a
shutter width of 30 mils and operating in air with K equal to one.
The solid line curves are for leaf shutters 50 mils long where the
valve has a capacitance, C.sub.o, of 0.135 pf. The dot-dash curves
are for leaf shutters 100 mils in length and valves having a
capacitance, C.sub.o, of 0.275 pf.
The description to this point has emphasized a valve for
controlling light transmission to produce an image display on the
panel 10. By a slight modification, the valve 26 of FIGS. 2 and 3
produces an image display on the panel 10 by means of reflected
light. The two chargeable leaf shutters 28 and 30 are made from a
light reflective material, such as chrome plated beryllium copper,
and mounted, as shown in FIG. 2, in a housing of an opaque
material. In addition to being electrically conductive, the center
plate 31 is now made of a material which also transmits light such
as a fiber optic material. The lower end of the center plate 31,
referring to FIG. 3a, not covered by the shutters 28 and 30 is made
opaque. Also, the input panel 40 will be of an opaque material
similar to the housing proper.
Light is piped into the valve housing by means of the light
transmissive center plate 31 from the source 20. With the shutters
28 and 30 in a discharged condition, shown in FIG. 3a, light
entering the center plate 31 will be blocked from being transmitted
through the output panel 42. However, charging the shutters 28 and
30 such that they assume a position as shown in FIG. 3b, permits
light to be reflected from the shutters through the output panel.
Thus, to the observer 18 a minimum brightness will be observed with
a valve operating as shown in FIG. 3a and a maximum brightness will
be observed when the valve is operating as shown in FIG. 3b. Other
than producing a charged-bright condition, that is, charging the
leaf shutters 28 and 30 reflects light to the observer 18, the
reflective light valve operates in a manner similar to the light
transmissive valve.
Referring to FIGS. 5 and 6, there is shown a portion of the light
panel 10 wherein light transmission valves are charged to produce a
light condition. Where the light transmission valve 26 of FIGS. 2
and 3 is a charged-dark configuration, that is, charging the leaf
shutters 28 and 30 cuts off light to the observer 18, the light
valves 44, 46 and 48 of FIG. 5 are a charged-bright configuration.
Operationally, the light valves 44, 46, and 48 are similar to the
light valve 26. Referring specifically to the light valve 46, with
the understanding that the valves 44 and 48 are similar, it
includes a leaf shutter 50 of an electrically conductive and opaque
material spaced from a fixed leaf 52 of an electrically conductive
and light transmissive material, both of which are connected to a
voltage source 54 through a two-position switch 56. With specific
reference to FIG. 1, the voltage source 54 and switch 56 are part
of the address scanner 12. The plate 52 and the leaf shutter 50 are
fastened to an input panel 58 of an electrically insulating and
light transmissive material. The panel 58 transmits light wave
energy produced by the source 20; it is covered with a transparent
electrically conductive film (again schematically illustrated by a
heavy line) connected to ground through metal sidewalls and
conductive films of adjoining units through a lead 60. Each of the
light valves 44, 46 and 48 shares a common wall with the adjoining
valve. These sidewalls are of an opaque material either
electrically conductive or covered with a conductive coating. An
output panel 62 covers the observer's side of the valves of FIGS. 5
and 6; it is coated with an optically transparent electrically
conductive layer connected to ground through the lead 60. This
conductive layer forms the second capacitor plate as previously
described with reference to FIGS. 2 and 3.
A video modulated voltage from the source 54 charges the leaf
shutter 50 and the conductive surface of the panel 62 thereby
generating a force on the shutter. This force causes the shutter 50
to be deflected to any "half-tone" position including in contact
with the panel 62. Half-tone positioning is the ability to control
the shading of the image display. Light from the source 20 will now
pass around the deflected shutter 50 and be transmitted to the
observer 18. A charge placed on the shutter 50 and the conductive
surface of the panel 62 will remain until the two-position switch
56 connects the shutter to ground.
Because the shutter 50 cannot be made close fitting with the
housing walls, a mask 64 extends over the input panel for each of
the valves. This mask prevents light from being transmitted around
the edge of the shutter 50 when in a noncharged condition.
Referring to FIGS. 7a and 7b, there is shown another configuration
for a light valve of the panel 10. A housing 66 of a reflective
opaque material either electrically conductive or covered with a
conductive coating is connected to ground through a lead 68. In
this configuration light is transmitted from the source 20 to the
observer 18 through a hollow port 70 of an opaque electrically
conductive material coated with an electrically insulating layer.
Typically, the port 70 may be anodized aluminum. The hollow port 70
connects to a voltage source 72 through a switch 74. A pair of leaf
shutters 76 and 78 are attached to the port 70 by means of an
elastic band 80. The lower ends of the shutters are bent around the
elastic band 80 to make electrical contact with the housing 66.
Thus, the shutters 76 and 78 are electrically connected to ground
in the embodiment shown in FIGS. 7a and 7b. Closing the switch 74
causes an electrostatic charge to be built up in the port 70 and on
the leaf shutters 76 and 78. As a result, the shutters 76 and 78
are attracted to the port 70, as shown in FIG. 7b, to block out
light from the source 20 to the observer 18. Although not shown,
input and output panels may enclose the end of the housing 66 to
prevent dirt and other foreign matter from obstructing the
operation of the valve and to provide electrostatic shielding for
shutter isolation.
In a model of the valve shown in FIGS. 7a and 7b, the overall valve
capacitance measured 30 picofarads. This is well below a limit
which permits addressing (charging the capacitor plates) within 0.l
microsecond. The time required for the shutters 76 and 78 to close
on the hollow port 70 after reaching a charged state was on the
order of 8 .times. 10.sup.-3 seconds. The shutters 76 and 78 moved
from a closed position to an open position, after being discharged,
in about 3 .times. 10.sup.-3 seconds. Thus, as discussed
previously, if a video display is updated once every 33
miliseconds, then about two-thirds of the display time is utilized
to produce a picture. Since very strong light sources may be used,
several orders of magnitude brighter than available phosphor
displays, a sufficiently bright display will be produced even in
bright ambient light conditions.
In FIG. 8 there is shown a modification of the valve of FIGS. 7a
and 7b for charged-bright operation. The valve of FIG. 8 includes a
housing 82 connected to ground and coated internally with an
electrically insulating layer 84. The hollow port 86 is of an
electrically conductive material tied to a voltage source 92
through a switch 94. Attached to the port 86 are leaf shutters 88
and 90. Closing the switch 94 causes the leaf shutters 88 and 90 to
be charged in one polarity and the housing 82 to be charged in the
opposite polarity. The leaf shutters move away from the port 86 to
the insulating layer 84. As illustrated, the insulating layer 84
contains a series of grooves in the area of the leaf shutters 88
and 90. These grooves provide air paths to minimize air drag
between the insulating layer 84 and the leaf shutters when the
switch 94 is closed thus enabling the shutter to operate in an air
environment. Thus, as soon as the leaf shutters 88 and 90 are
discharged, they begin to resume their normally biased position
against the curved surfaces of the housing 86 to block off light
from the source 20. In general, unless air paths are provided to
minimize air drag, the valve must be sealed and evacuated.
Referring to FIGS. 9a and 9b, there is shown another modification
of the valve of FIG. 2 to improve the response time of the leaf
shutters. A pair of light transmissive curved blocks 96 and 98
replace the input panel 40. These blocks have a curved inner
surface substantially conforming to the bending action of a
cantilever beam. The curved surfaces of the blocks 96 and 98 are
coated with a conductive layer (illustrated as a heavy line) and
then covered with an optically transparent, electrically insulating
layer 100. In the light transmitting position, a pair of leaf
shutters 104 and 106 are positioned against a center plate 108 all
of which are connected to a voltage source 110 through a switch
112. Closing the switch 112, as shown in FIG. 9b, causes the leaf
shutters 104 and 106 to conform to the curved inner surfaces of the
blocks 96 and 98.
Consider the leaf shutter 104 to be a cantilever beam rigidly
mounted at one end. This shutter has a certain moment of inertia
which must be overcome before it begins to move from the center
plate 108. After the initial movement of the leaf shutter 104, the
cantilever length is shortened since the upper end is now in
contact with the curved inner surface of the block 96. This reduces
the overall moment of inertia of the shutter and it begins to move
faster to a fully light blocking position. Similarly, when the
switch 112 is opened and the shutter 104 discharges, the shutter
104 opens first at the end with an increasing length thus improving
the response time of the shutter over that if the block 96 were not
used. Therefore, by including the blocks 96 and 98 in the valve of
FIG. 2, a faster responding valve results.
As mentioned previously, there is no limitation whereby the leaf
shutters must be of a metallic material. Referring to FIGS. 10a and
10b, there is shown a light valve wherein the leaf shutters 114 and
116 are of a flexible plastic material covered with an electrically
conductive coating. These shutters are positioned about a center
plate 118 and fastened in place by means of an input panel 120 and
an output panel 122. The housing 124 is again of electrically
conductive material connected to ground through a lead 126. A
second pair of flexible leaf shutters 128 and 130 are positioned
between the outer edge of the input and output panels and the inner
wall of the housing 124. These shutters are also coated with an
electrically conductive coating. Note that the electrically
conductive coating of the shutters 128 and 130 is in contact with
the housing 124.
Closing a switch 132 connects a voltage source 134 to the shutters
114 and 116, thereby positively charging shutters 114 and 116 and
negatively charging shutters 128 and 130. Since the shutters are of
a flexible material, they tend to "balloon" or expand, as shown in
FIG. 10b, thereby shutting off light from the source 20 to the
observer 18. Again it should be noted that the electrically
conductive coatings of the shutters 114 and 116 form an outer layer
and the coatings of the shutters 128 and 130 form an inner
layer.
Referring to FIGS. 11a and 11b, there is shown a light valve
coupled to a biasing voltage source 136 (shown schematically as a
battery) and to a control signal source 138 (shown as an
alternating current source). In this embodiment, the housing 140 is
of an electrically conductive material connected to ground and
coated on the inner surface with an electrically insulating
material 142. An input panel 144 and an output panel 146 again form
an enclosure which prevents external electrostatic forces from
interfering with the operation of a pair of leaf shutters 148 and
150. The leaf shutters 148 and 150, when in an uncharged state, are
positioned against an electrically conductive center plate 152
which is covered with a layer of electrically insulating material
154. The center plate 152 connects to the voltage source 136 and
the leaf shutters 148 and 150 are connected to the voltage source
138.
The source 136 is designed to generate a voltage equal to the
pull-in voltage, V.sub.s, described previously. When the control
signal 138 equals V.sub.s, the shutters 148 and 150 will be pulled
close to their respective walls as shown in FIG. 11 b. To return
the shutters 148 and 150 to a light transmission position, the
control signal 138 is lowered from the V.sub.s level. Using a two
electrostatic field system, the shutters 148 and 150 will be pulled
away from the walls before the control signal reaches ground
potential because they are closer to the center plate 152 than to
their respective walls. This narrowing of the control signal range
means an improvement in the drive sensitivity. Also, the existence
of two electrostatic fields enables the use of poor elastic
materials for the shutters 148 and 150. Of course, including the
panels 96 and 98 of the embodiment shown in FIGS. 9 a and 9b or the
hollow ports shown in FIGS. 7 and 8, will further enhance the
response time of the valve shown in FIGS. 11a and 11b.
In general, the shutters of the various valve configuration shown
are designed and oriented to minimize the effect of the earth's
gravitational field or external magnetic fields by using
nonmagnetic materials. Actually, the effect of the gravitational
field on the shutters is equivalent to a fixed brightness bias, as
discussed with respect to FIGS. 11a and 11b, and can be used to
return the shutters to an initial position. It is also contemplated
that a small permanent magnet may be positioned within the valve
housing to return a magnetic shutter made from a material having
poor elastic properties to an initial discharged position.
Because a leaf shutter is a mechanical member, it has lowpass
mechanical filtering properties and for this reason may be used in
applications where vibrations are encountered. This is an inherent
advantage of a light valve fast enough to operate at the display
frame rates discussed previously. Thus, the light valve of this
invention is not restricted to stationary applications.
Many variations can be made in the number of leaf shutters per
valve, the configuration and geometry of the shutters, and the
number and arrangement of housing walls to produce many desired
lighting effects. Referring again to FIGS. 5 and 6, a three color
display can be generated with this valve by merely dividing the
leaf shutter 50 into three equal segments and connecting each
segment to a separate charging source. In effect, each of the
valves 44, 46 and 48 would then be three valves, one for each of
the three primary colors. The input and output panels would include
filters to pass only the desired color.
Although several embodiments of the invention, together with
modifications thereof, have been described in detail herein and
shown in the accompanying drawings, it will be evident that various
further modifications are possible in the arrangement and
construction of its components without departing from the scope of
the invention.
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