Note: Descriptions are shown in the official language in which they were submitted.
21401Cl
~,
Technical Field
S
The present invention relates generally to an apparatus and method for
interacting with a computer terminal and other instrumentation, and in par-
ticular to a touchscreen-type data input apparatus and to a signal transmission
apparatus.
Ba~ u-ld Art
Touchscreen interfaces which enable a user to interact with a computer
display, terminal, etc. are found in many applications. In a touchscreen-type
apparatus, the user touches areas of a video screen with his or her finger in
order to activate control functions displayed on the video screen, to select a
menu item from list of items displayed on the video screen, etc. In one type of
touchscreen technology, the location on the video screen contacted by the user
is detected using an array of emitters and associated detectors positioned alongthe perimeter of the video screen. In most, if not all applications, the video
screen perimeter is square or rectangular. Emitters are positioned along on
vertical and one horizontal side of the perimeter, and the corresponding
detectors are positioned on the opposite vertical and horizontal sides across
from and in alignInent with an associated emitter. With this arrangement, the
touchscreen is divided into multiple touch zones, the number of zones being
determined by the number of emitter/detectorpairs. For example, if four
vertical emitter/detectorpairs and four horizontal emitter/detectorpairs are
used, the video screen is divided into a matrix of 16 zones. The position
touched by a user is determined by which horizontcll an(l verlical l~eL~m p~
are blocked by the user's finger.
In explosive environments, data display terminals and/orinstrumentation
must be contained within explosion-proof housings. Data entry devices ena-
bling an operator to interact with instrumentation, data terminals, etc. that are
located in an explosion-proof environment are not readily available, and what
is available can be extremely costly. In many hazardous environments,
~ 21gO161
interactiLng with process instrumentation and controls is done in a secured
control room environment that is sealed and isolated from the process
~llvilo.. ~-~t In order to interact with or access process instrumentation and
controls, the operator must leave the process environment and enter the
S isolated control room.
It has been found desirable for some applications to be able to access
and interact with terminals and other instrumentation located in the process
e~viro~ .ent. For example, being able to interact with a display terminal on
the process floor in order to display process parameters and/orto change
process parameters would enable an operator to more quickl-y modify process
conditions because it would obviate the need for leaving the processing
el,vi~olllllent to enter a separate control room. Apparatus enabling an
operator to directly interact with instrumentation contained within an
explosion-proof housing, is not readily available, and what is available is
concidered to be prohibitively expensive for many applications.
It is also desirable in some applications to be able to transmit a signal
across a barrier which at least partially defines an explosion-proof room or
enclosure. In this type of signal tr~nsmicsion it is not necessary that an
operator be able to interact with the signal. However, it is very important thatsignal quality and integrity be maintained during the tr~n~mission.
Disclosure of the Invention
The present invention provides a new and improved touch input device
that is especially adapted for use in an explosive environment or other
ellvirol~ ents where it is desirable to isolate electronic components from the
surroundir~es. According to the preferred and ill~lslraled eml)odilllcl~ e
invention includes an enclosure that defines a view port inclu(lin~ a window
defined in part by a touch detecting region located adjacent an outside surface
of the window. A display, such as a cathode ray tube (CRT) liquid crystal
display (LCD), etc. is viewable in the view port by an operator.
In one embodiment, the touch input device comprises a frame
~tt~ch~ble to an axial end of a housing. A transparent window is receivable in
2140161
the frame for securement to the housing. The frame and window define a view
port for viewing the display device through. An interface between the window
and the frame defines a flame suppressing path extending continuously about
the periphery of the interface. The flame suppressing path has a length taken
in a plane eYtçntling normal to a surface of the frame defining the view port.
A light ernitting device is located within the enclosure for directing a beam oflight outwardly through the window. A first reflector is loc~ted on a side of the
window opposite the light emitting device for reflecting the beam of light
across the view port. A second reflector is located on the same side of the
window as the first reflector and is spaced therefrom to reflect the beam of
light from the first reflector through the window and back into the enclosure.
A light r~c~,ivi,lg device is located within the enclosure on the same side of the
window as the light emitting device. The light receiving device detects the
presence of the beam of light or the absence of the beam of light reflected
from the second reflector.
Each of the first and second reflectors comprises a prism located
between the window and the frame. Each prism has a surface adapted to be
in~line~l at an acute angle relative to a plane defining a surface of the window.
The light emitting device includes a plurality of emitters arranged in a linear
array. Each emitter is supported so a series of spaced apart and parallel
bearns of light are directed through the window towards the first reflector. Thelight receiving device includes a plurality of photoreceptors arranged in a linear
array. Each of the plurality of photoreceptors receives a respective one of the
beams of light reflected from the second reflector.
Each of the plurality of emitters and detectors includes a lens for
focusing a beam of light, a fiber optic c~lhlc h.lvillg one cn(J ~upl)orlcd .Idj.lcc
a respective lens for light communication therebetweell ancl the olher en(l of
the fiber optic cable being coupled to a respective one of an emitler all(J a
photoreceptor. The flame suppressing path in the illustrated embo(limellt
extends for at least 1.5 inches.
In another embodiment of the invention an apparatus transmits a light
signal through a barrier which at least partially defines an enclosed and
2140161
eYrlosion resistent room. The apparatus comprises a body with an opening
eYte~din~ therethrough. .Att~çhment structure fixes the body in an opening in
the barrier and maintains the explosion proof characteristics of the barrier. A
light ~ Ssive member is closely fit in the opening of the body to inhibit
S flame propagation on one side of the barrier from re~rhing the other side of
the barrier through a flame suppressing path clearance between the body and
the light tr~ncmicsive member. Retention structure retains the li~ht
tr~ ",;ss;ve member in the opening in the body. The retention structure
cormects a pair of fiber optic members to ends of the body for light
tr~n~mittin~ communication with ends of the light tr~nsmissive member.
A flame suppression path between the light tr~nsTTlissive member and
the body in the illustrated embodiment extends for a length of at least 1.5
inches taken in a direction along the extent of the body. The ~tt~hment
structure includes an external thread formed on an end portion of the body
and an internally threaded member for threaded engagement with the external
thread on the body. The retention structure includes an internal thread
formed in an end portion of the body and an externally threaded lens stop
member for threaded engagement with the internal thread in the body. The
lerls stop member has an internally threaded portion for threaded connection
with a threaded connector end of the fiber optic member.
The light tr~ncmis.cive member is a glass rod. A light transmitting
coupler sphere is located between the light tr~nsmissive member and the fiber
optic member to enable light communication between different sizes of the
light tr~n.cmis~ive member and the fiber optic member. The coupling sphere is
located in the retention structure. A first annular elastomeric member is
located between the couplinL~ sphere an(l ~I shoul(lcr Or lhe rclcnlioll slruclllre.
A second ~nnul~r elastomeric member is located between the retention
structure and the light transmissive member.
Additional features of the invention will become apparen~ an(l a fuller
understanding obtained by reading the following detailed description made in
connection with the accompanying drawings.
2I40161
s
Brief Description of the Drawings
Figure 1 is a perspective view of an explosion-proof enclosure containing
a video display terminal constructed in accordance with a preferred
embodiment of the invention;
S Figure 2 is a sectional view of the enclosure as seen from the plane
indicated by line 2-2 in Figure 3;
Figure 3 is a sectional view of the enclosure as seen from the plane
indicated by line 3-3 in Figure 2 with interior components shown schematically;
Figure 4 is an exploded view of a frame assembly that mounts eight
emitter/detectorpairs;
Figure S is a sectional view of the frame shown in Figure 4;
Figure 6 is a fragmentary, sectional view of a mounting assembly that
mounts the components of an emitter element to the frame shown in Figures 4
and S;
Figure 7 is a sectional view of an enclosure according to another
embodirnent of the invention;
Figure 8 is a plan view of a portion of the enclosure illustrated in Figure
7 taken al,~ro~;",~tely along a plane indicated by line 8-8 in Figure 7;
Figure 9 is a cross-sectional view of the enclosure illustrated in Figure 9
taken along a plane indicated by line 9-9 in Figure 7;
Figure 10 is an enlarged cross-sectional view of a portion of the
enclosure illustrated in Figure 7; and
Figure 11 is a cross-sectional view of another embodiment of the
present invention illustrating signal tr~ncmission through a barrier which is
explosion-resistant.
Best Mode for Carrying Out the Invention
Figure 1 illustrates the overall construction of an explosion-proof
enclosure 10 constructed in accordance with the preferred embodimen~ of tlle
invention. In the preferred embodiment, the enclosure 10 is intended to
enclose a video display terminal, the video screen being visible through a view
port indicated generally by the reference character 12. Referring also to
- 2140161
Figures 2 and 3, the enclosure 10 includes a housing member 14 in which the
electronic components are mounted, including a peripheral flange 16 to which
a m~qting, cover plate 18 is rigidly bolted by a plurality of bolts 19. The housing
14 and cover plate 18, as is known, may be made from cast aluminllm or other
S suitable materials.
The housing 12 in the illustrated embodiment includes integrally cast
mounting lugs 20 by which the enclosure is mounted to a wall, frame member,
etc. Conduits (not shown) extending from the housing 12 interconnect the
instnlment~tion contained within the housing to other instrumentation or other
process control equipment, such as a central process control computer (not
shown).
As is known, instrumentation electronics used in explosive environments
must be enclosed in such a way that a spark occurring within the enclosure is
contained and eYtin~lished within the enclosure and does not produce a flame
that leaks from the housing into the outside environment.
As seen best in Figure 3, the view port 12 is defined by a central
opening 22 formed in the cover. In the exemplary embodiment, the central
opening includes an outer, outwardly tapered portion 22a which merges with
an open ng portion defined by orthogonal walls æb.
The interior of the housing 12 is isolated from the opening æ by a glass
view plate 30 which is carried by a frame assembly indicated generally by the
reference character 32.
As seen best in Figure 3, the frame assembly 32 includes a perimeter
member 34 bolted directly to the rear of the front cover plate by a plurality
bolts 35. An O-ring seal 36 seals the interface between the back of the front
cover plate 18 and the perime~er mellll)cr 34. Thc glas~i view pl.lLc 3() i~ hcld
in a recess 38 formed in the frame member by a retaining plate 4(). The
retaining plate 40 includes a central opening 42 aligned with, and in the
illustrated embodiment, larger than, the opening 22 formed in the cover plate
18, and clamps the glass view plate 30 against the base of the recess 38. A
plurality of bolts 44 hold the retaining plate 40 to the frame member 34.
2190161
A square, central opening 46 formed in the frame member 34, which is
aligned with the opening 22 in the cover plate 18 defines a touch detecting
region. In particular, a sensing arrangement (to be described) detects locationson the glass view plate 30 touched by an operator. To achieve this feature, an
array of fiber optic "emitters" and "sensors" are spaced around the inside
perimeter of the frame member opening 46. An "emitter" fiber optic cable
transmits light from a conventional emitter located within the housing 14 to theinside perimeter of the frame member opening 46. The ends of the fiber optic
cables are captured within threaded, multi-diameter throughbores 48 formed in
the frame member 34. The bores 48 extend through the frame member 34.
Details of the bore construction will be described below.
A lens 49 at the end of the fiber optic cable forms a beam of light
aimed at the end of a "detector" fiber optic cable located on the opposite side
of the view port and directly across and aligned with the "emitter" fiber optic
1S cable. Referring to Figure 2, as an example, fiber optic cable 50 forms the
"emitter" of the "emitter/detector"pair and emits a light beam aimed and
aligned with the "detector" fiber optic cable 52 located on the oppositè side ofthe view port. Similarly, a fiber optic cable 54 defines the "emitter" and
conveys light from a conventional emitter located within the housing to the
inner perimeter of the view port. A beam of light is formed which is
tr~nsmitted across the view port to the "detector" fiber optic 56. The use of
three horizontal and three vertical fiber optic emitter/detectorpairs defines a
grid which divides the view port into nine zones. For purposes of explanation,
digits 1-9 are shown within the view port. It should be understood that the
video screen located within the enclosure and aligned with the view port may
be display digits, icons, text, legends, etc., clepencling On the applica~it)ll. In ~ny
event, the six emitter/detectorpairs define nine separate detectable zones. lf
the operator, as an example, touches zone 1 of the view port, the beams Bl,
B2 (see Figure 2) emitted by fiber optic cables 50, 54 are blocked. The
absence of light detected by the associated fiber optic detectors 52, 56 is
processed by the instrumentation contained within the enclosure (or alternately
by equipment connected to the enclosure) by which it is determined that zone
2140161
-
1 has been touched by the operator. Depending on the application, the
detection of the touch by the operator may invoke a control function, change
the display, signal the process computer that action needs to taken, etc. In
general, system control software will be programmed to effect an action when a
S particular zone in the view port is touch by an operator.
According to a feature of the invention, emitter and detector elements
are alternated along a given side of the view port. For example, fiber optic
element 54 as indicated above, is an "emitter," adjacent fiber optic element 58
is arranged as a 'Idetector~'' and fiber optic element 60 is formed as an
"emitter." The elements are similarly arranged along the vertical sides of the
view port. For example, fiber optic element 64 is a detector, whereas fiber
optic elements 66, 68 are emitters. By alternating emitters and detectors, the
elements may be more closely spaced.
According to another feature of the invention, the number of
ernitter/detectorpairs can be changed for a given enclosure without
neces~i~ating substantial modiffcations to the enclosure itself. This feature ismade possible by the frame assembly 34. If eight emitter/detectorpairs are
desired for a given application (as opposed to the six emitter/detectorpairs
illustrated in Figure 3), the frame assembly shown in Figure 3 is simply
replaced with one that includes four through bores in each wall of the frame
member opening 46. With this feature, the housing 14 and cover plate 18 need
not be modified at all to accept a touchscreen having 16 detectable zones (as
opposed to nine detectable zones). With the disclosed arrangement, an
enclosure can be changed from a "9-zone" touchscreen to a "16-zone" touch-
screen in the field. This enables the hardware to be readily upgraded when a
software upgrade is implemented wllich changes lhe inrorma~ioll or ~Oncs
defined on the video screen itself. With the disclosed invention, in many
applic~tion~, the display electronics, housing and cover plate remained
unchanged as a result of an upgrade. Only the emitter/detectorframe 34 an(l
the electronics associated with the fiber optic elements needs to be replaced.
Returning to Figure 3, the electronics for processing signals from the
emitter/detectorsis schematically illustrated. Each fiber optic cable that forms
2140161
a e~utter/detectorpair is connected to a module 70. The module includes a
light emitting element and a light detecting element that are coupled to the
ends of the respective fiber optic cables. For example, fiber optic cable 50,
which forms an emitter, is coupled to a light emitting element located within its
associated module 70a. Similarly, fiber optic emitter cable 54 is connected to
module 70f, fiber optic cable detector 58 is connected to module 70e, emitter
fiber optic cable 60 is connected to module 70d and emitter fiber optic cable
68 is connected to module 70b. Suitable modules 70 for processing signals
conveyed by the emitter/detectorfiber optic cables are available from Opcon of
Evert, Washington under part no. 15100A6517.
In the illustrated embodiment, a relatively flat display panel 72 is
depicted. This panel may comprise a CRT or LCD panel. In the illustrated
configuration, the panel 72 is shown as an LCD panel and is held to the frame
member by retaining clamps 74 which are also held by the bolts 44 which
secure the clamping plate 40. The LCD panel is connected to a conventional
display bus 80 which may be connected to an internal CPU mounted within the
housing 14 or to a remote CPU. In addition, the modules 70a-70f may also be
connected to a conventional input/outputbus 82 forming part of the overall
computer system. A 12 volt power supply 84 which may be internal to the
housing 14 provides power to the fiber optic sensor modules 70 and other
support circuitry (not shown). The modules 70a-70f may form part of an
overall circuit module mounted to the housing 14 by a bolt 86.
As indicated above, the frame assembly 34 may be replaced with
alternate configurations to provide a different number of touch zones in the
view port. Figures 4, 5 and 6 illustrate a frame assembly 34' which mounts
eight pairs of emitter/detectorsto provide lfi touch (Je~ec~al)le ~ones. I xcc
for the number of emitter/detectorelements, the construction of the frame
assembly 34' is substantially identical to the assembly 34 shown in Figure 2 andmay be mounted to the cover plate 18 of the enclosure 10.
Figure 5 illustrates a more preferred mounting for the emitter/detectors
in the detecting region 46'. In this embodiment, the multi-diameter
throughbores 48' mount a threaded ferrule 90 (best shown in Figure 6) which
2140161
~,
in~hldes a large diameter threaded portion 90a, a narrow uniform diameter
portion 90~ and a small diameter threaded portion 90c. The lens 49 is
threaded onto the threaded portion 90c of the ferrule 90. The large diameter
threaded portion 90a is threaded into the bore 48'. In this preferred
S embodiment, a light transmitting rod 94 (see Figure S) extends between the
lens 49 and the end of a fiber optic cable 96. The rod 94 is preferably held
within the ferrule by a suitable adhesive. The end 96 of the fiber op~ic cable is
threadedly received by a threaded internal bore 98 formed in the ferrule. With
the disclosed construction, a substantial flame path, FP (shown in Figure 5), isestablished between an inside surface 34a and an outside surface 34b of the
frame 34'. This ~lame path reduces a chance of flame propagation from inside
the enclosure 10 to the outside by way of the emitter/detectormountings.
It has been found that suitable fiber optic cable for use as part of the
emitter/detectorsis available from the Mitsubishi Company under part no.
ESKA SH4001. The lens 49 is available from SurLx, also of Japan, under part
no. FX-LE1.
It should be noted here that in the disclosed apparatus "fiber optic"
cables are utilized. It should be understood, that other light conducting
con~ it~ such as light pipes, optical fibers, etc. may be used, and are
contemplated, by the present invention.
The apparatus has been illustrated with a relatively flat display panel 72
located adjacent the view plate 30. It should be understood that the invention
also contemplates a construction in which the display panel may be directly
adjacent the touch detecting region 46, if the application permits, eliminating
the need for the separate view plate 30. The display panel 72 may comprise
other forms of technology including video monitors, plasm~ ~iispi~y p~nel~, c~c.The glass view plate 30 is "transparent" in the system described. lt
should be understood however that translucent or partially transparent
elements constructed of materials other than glass are also contemplate~i by
the invention. Any element used, must have sufficient light transmissivity to
allow an operator to see the information displayed by the display device 72.
2140161
11
Another explosion-resistant enclosure 120 embodying the invention is
illustrated in Fig. 7. The enclosure 120 is intended to house a video display
device læ. The display device 122 and other electronic components are
located within the enclosure 120. It is intended that the enclosure 120
S sul~r~sses any spark or flame emanating from the electronic components
within the enclosure. Thus, the enclosure 120is suitable for use in
enviromnents which are susceptible to explosion or which may be flammable.
The enclosure 120 includes a housing 124 for supporting the display
device 122 and other electrical and electronic components. The housing 124
includes a peripheral flange 126. A frame 142 and a transparent window 144
are connected to an axial end of the housing 124 to form an axial end of the
enclosure 120. ne window 144 is made of a suitable thickness and width to
withstand an explosion or flame according to an industry standard, such as
NEC Class I, Division I, Groups B, C, D, E, F and G Hazardous Locations.
lS Such industIy standard specifies that an enclosure has a specified minimum
flame path ~u~ressing length for a given volume enclosure. The enclosure
120 of the present invention can be constructed to meet this flame path
standard as a function of the volume in the enclosure. By way of example, a
specific size enclosure 120 is disclosed but does not serve to limit the invention
to the disclose example.
The frame 142 has a surface 146 defining a view port or touch region of
about 8.6 inches by 6.5 inches through which the display device 122 can be
viewed from outside of the enclosure 120. A flange 148 on the frame 142
extends around the entire peripheIy of the frame and attaches the frame to the
flange 126 of the housing 124. The housing 124 and the frame 142 are made
from a suitable metal material, such as casl alull~
An O-ring 150 is located in a peripheral chamlel extending about the
entire face of the flange 148 of the frame 142. The O-ring 150 compresses
upon engagement with the flange 126 to form an environmental seal which
keeps moisture and fl~mm~ble material outside the enclosure 120. The length
of the engaged flanges 126, 148 taken in a direction normal to the O-ring 150
is sufficient to meet industry standards for a flame path or flame propagation
2140161
12
s~ ession clearance that may exist between the flanges 126, 148. Such
irldustry standard flame suppression path length is a minimllm 1.5 inches for a
volume of the enclosure 120 of about 1,700 cubic inches and preferably 1,728
cubic inches.
S The frame 142 has a m~çhined-away portion defining a recess 162 for
receiving the window 144 in a close fitting relationship. The window 144 in the
recess provides a flame suppression path having a length of at least 1.5 inches
for the volume of the enclosure. The flame suppression path length is
deterrnined by adding the length of the interface between the window 144 and
frame 142. The interface is taken in a plane, such as that viewed in Fig. 10,
which is normal to the surface 146 defining the view port.
A frontal interface length L1 (Fig. 10) is the length of engagement or
close fit clearance, either of which suppresses flame propagation, between a
surface 162 definin~ the recess of the frame 142 and the window 144. The side
interf~ce length I~ is defined as the length of engagement or close fit
cleararlce, either of which suppresses flame propagation, between a side
surface 164 of the recess in the frame 142 and the window 144. The total
interface length or flame suppression path is the sum of the frontal interface
length L1 plus the side interface length L2. The total interface length (L1 plus1~) is preferably at least 1.5 inches. Thus, any flame or spark occurring withinthe enclosure 120 is prevented from communicating outwardly of the enclosure
by the flame suppression path lengths between the flanges 126, 148 and
between the recess in the frame 142 and the window 144.
Prisms 182, 184 (Figs. 7, 9 and 10), made from ISOPLAST
Thermoplastic Resin and available from Dow Plastics, are located between the
window 144 and the frame 142. E~ch of the four prisms 182, IX4 are localcd
along a respective side of the surface 146 defining the view port. A gasket IX6
is compressible and is located in a channel formed around the entire peripheral
surface 146 defining the view port in the frame 142. The gasket 186 is
compressible when the window 144 and prisms 182, 184 are forced in a
direction upwardly, as viewed in Fig. 10, by a retainer plate 188 attaching the
window to the frame 142 by screws 190.
2140161
The prisms 182, 184 are arranged in pairs. For example, a first one of
the pair of prisms 182, viewed in cross-section in Fig. 7, is intended to reflect
beams B (Fig. 10) of light, emitted from a light emitting device 198 from withinthe enclosure 120 outwardly through the window 144, across the longer
S ~limension of the view port defined by the surface 146. When the beam B of
light is reflected across the view port, it can be blocked by an operator or an
object. Such blocking of the beam B of light usually is indicative of an
instruction desired to be communicated to a controller.
The beam B of light extending across the view port is then reflected by
a second one of the pair of prisms 182 at the other axial end of the view port
back through the window 144 and to a light receiving device 260 located within
the enclosure 120. It will be equally understood that, as illustrated in Fig. 9, a
first one of the pair of prisms 184 is intended to reflect beams B of light,
en~itted from a light emitting device 198 within the enclosure 120 through the
window 144, across the shorter dimension of the view port defined by the
surface 146 to a second one of the pair of prisms 184 back through the window
and to a light receiving device 260 within the enclosure.
Preferably, light is generated from within the enclosure 120 (Fig. 7)
from the light emitting device 198 located within the enclosure on a first side of
the window 144. The light from the light émitting device 198 is directed
through a lens 202 to form a focused beam B of light. The beam B of light is
.,c~ ed through the window 144. The beam B of light (Fig. 10) is then
tr~n~mitted to a first one of thë prisms 182 on a second side of the window 144
opposite the side of the window that the light emitting device 198 is located.
The beam B of light is reflected by a reflective surface 204 of the prism. The
reflective surface 204 extends at an acute angle of about 45 relative to a
subst~nti~lly planar outer surface 206 of the window 144. The beam of light B
is reflected by the surface 204 of the first prism 182 on the right, as viewed in
Fig. 7, across the view port defined by the surface 146 in a direction
substantially parallel to the planar surface 206 of the window 144. It is at this
time that the beam B of light may be interrupted.
2140161
14
Each light emitting device 198 preferably has a plurality of individual
light emitters 2æ arranged in a linear array on a printed circuit board within
the enclosure 120. In the preferred embodiment, the light emitting device 198
which eYtenll~ in a direction parallel to the prisms 182 includes twenty-five
S ernitters 2æ, each of which can be selectively ~ctu~ted by circuitry on the
printed circuit board to emit light. Thus, twenty-five individual beams B of
light are tr~n~mitted by the light emitting device 198, through the window 144
and reflected by the first one of the pair of prisms 182 across the larger
~lim~ncion of the view port defined by the surface 146. The light emitting
dev~ce 198 tbat extends in a direction parallel to the prism 184 contains thirty-
t~vo emitters 222 to transmit light so thirty-two individual beams B of light bythe first one of the pair of prisms 184 are reflected across the shorter
(lim~nsion of the view port defined by the surface 146. These reflected beams
B of light eYtentlin~ across the view port are arranged in an orthogonal eight
hundred point matrix so that any of the beams being disrupted is indicative of
a particular location of an object, such as an operator's finger, within the view
port and relative to a particular location of the display dev~ce 122.
The second one of the cooperating pair of prisms 182, 184 on the
secorld side of the window 144 receives an uninterrupted beam B of light
eYten~lin~ across the view port. A reflective surface 204 of the prism 182, 184
exten-ls at an acute angle of about 45 relative the outer surface 206 of the
window 144 and reflects the beam B of light through the window and into the
enclosure 120. A light receiving device 260 on the first side of the window 144
detects the absence or presence of a particular beam B of light reflected into
the enclosure 120. Thus, each light receiving device 260 extending in a
direction parallel to the extent of the prism 182 contains twenty-five individual
photoreceptors 262 (Fig. 7). The light receiving device 260 extending in a
direction parallel to the prism 184 includes thirty-two individual photoreceptors
262 (Fig. 9). A lens 202 is located between the window 146 and each light
receiving device 260.
Each individual photoreceptor is sensitive to the absence or presence of
light from an associated emitter 222. Thus, a controller can communicate with
214~161
-
each photoreceptor 262 to detect where an object or objects are during any
particular dIsplay sequence of the display device 122. The light emitting
devices 198 and the light receiving devices 260 are available as a printed circuit
board assembly from Carroll Touch, Inc. of Round Rock, Texas.
S An explosion-proof barrier 302 such as an al~lmin-lm, steel or concrete
wall is illustrated in Fig. 11. In another embodiment of the present invention,
a sig~ lh~g device 320 is provided to transmit a signal from one side
of the barrier 302 from a signal emitter 3æ to another side of the barrier to a
signal receiver 324. Such a signal transmitting device 320 is suitable for use in
an e~vi-~nlllent in which a spark on one side of the barrier 302 could ignite
fl~mm~ble material on the other side of the barrier. For example, the signal
emitting device 322 could be electrical circuitry to actuate a light emitter andthe signal receiver 324 could be a photoreceptor.
In order to get the signal from the signal ernitter 322 and m~int~in the
e~plosion-proof characteristics of the barrier 302 to the signal receiving device
324, the signal transmitting device 320 is provided. The signal transmitting
device 320 includes a tube 342 preferably made from metal with axially
opposite end portions 344 having external threads. A pair of internally
threaded ~tt~chment members 346 are threaded onto the end portions 344 of
the tube 342 to hold the tube in the barrier 302 and maintain the explosion-
resist~nt characteristics of the barrier. The length of the tube 342 is greater
than the thickness of the barrier 302 to assure that the threaded end portions
344 of the tube 342 are located outside of the barrier 302.
A light tr~nsmissive member 360 is located within a central opening 348
in the tube 342. The light transmissive member 360 is preferably a gl~ss rod.
An elastomeric O-ring 362 is located at each axial end of the light tr~lncmi~sion
member 360 and partially within the central opening 348 of the tube 342. The
light tr~ncmicsive member 360 closely fits within the central opening 348 in thetube 342.
A flame suppression path length L3 extends between the light
tr~ncmissive member 360 and the central opening 348 of the tube 342. The fit
between the light tr~ncmicsive member 360 and the central opening 348 is tight
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so that either engagement or a very small clearance exists therebetween and
flame propagation through the interface of the light tr~nsmicsive member and
the central opening is inhibited. The flame suppression path has a length L3
which extends for at least 1.5 inches and preferably 2.03 inches.
S An externally threaded retention member 364 is located in each axial
end of the tube 342 in threaded engagement with internally threaded portions
366 of the tube. Each retention member 364 is threaded axi~lly into
engagement against the O-ring 362. The retention members 364 and O-rings
362, thus, retain the light tr~nsmicsive member 360 within the central opening
348 of the tube 342 and prevent any relative axial movement of the light
tr?ncmissive member within the tube. The O-rings 362 act to accommodate, by
compression or expansion, any difference in the rates of expansion or
contraction of the light tr~nsmissive member 360 and the tube 342.
Each retention member 364 has an internally threaded end portion 382
and a chamber 384. A light transmitting coupler sphere 386 is located in the
chamber 384 of the retention member 364. The spheiical coupling member
386 is spaced apart slightly *om the end of the light tr~ncmicsive member 360.
An elastomeric O-ring 388 is located between the spherical coupling member
386 aIld a shoulder 390 at an axial end of the chamber 384. The other axial
end 392 of the chamber 384 is deformed over the spherical coupling member
386 to retain the coupling member within the chamber 384. The O-ring 388
accornmodates differential rates of expansion or contraction of the coupling
member 386 and ~tt~chment member 364.
The internally threaded end portion 382 receives a threaded connector
400 for attaching a fiber optic cable 402 to the signal transmitting device 320.The fiber optic cable 402 is locatecl so its en~ 404 is adj~centtlle light
tr~ncmissive spherical coupling member 386. The coupling member 386
transmits light between the fiber optic cable 402 and light transmissive member
360.
Thus, when a light signal is generated within the signal emitting device
322, the light is transmitted through the fiber optic cable 402 to the left
spherical coupling member 386, as viewed in Fig. 11, to the light transmissive
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member 360, to the right spherical coupling member 386, to the right fiber
optic cable 402 and then to the signal receiving device 324. The light signal
has been transmitted through the barrier 302 without allowing a spark or flame
to propagate between the opposite sides of the barrier 302.
S Although the invention has been described with a certain degree of par-
ticularity, it should be understood that those skilled in the art can make various
changes to it without departing from the spirit or scope as hereina~ter claime(J.
