Note: Descriptions are shown in the official language in which they were submitted.
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THERMAL IMAGING DEVICE WITH SELECTIVELY REPLACEABLE
TELESCOPIC LENSES AND AUTOMATIC LENS IDENTIFICATION
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention is in the field of imaging
devices. More particularly, the present invention relates
to devices for receiving invisible infrared light from a
scene, and for providing a visible-light image replicating
the scene.
Related Technoloav
Night vision devices have been available for many
years. One category of these conventional night vision
devices uses image intensifier technology. This
technology is effected using a device generally known as
an image intensifier tube. The image intensifier tube is
essentially a frequency-shifting and amplifying device
receiving ambient light, which light may include visible
light too dim to provide natural vision (i.e., so-called
~ "Star Light" scopes), or invisible near-infrared light, in
a first frequency band and responsively providing a
2o greatly intensified visible image in a phosphorescent
monochrome yellow-green light.
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Such an image intensifier night vision device
converts available low-intensity ambient light to a
visible image which a human user of the device may use for
surveillance or weapon aiming, for example, under lighting
conditions of too dim to allow a scene to be viewed with
the natural vision. These image intensifier night vision
devices require some residual light, such as moon or star
light, in which to operate. This light is generally rich
in infrared radiation, which is invisible to the human
eye. The present generation of night vision scopes use a
photoelectrically responsive "window", referred to as a
photocathode; which is responsive to the dim or invisible
ambient light focused on this "window" from an invisible
scene to provide a pattern of photo-electrons flowing as
a space charge moving under the influence of an applied
electrostatic field, and replicating the scene being
viewed. This pattern of photo-electrons is provided to a
microchannel plate, which amplifies the electron pattern
to a much higher level. To accomplish this amplification
at the microchannel plate, the pattern of photo-electrons
is introduced into a multitude of small channels (or
microchannels) which open onto the opposite surfaces of
the plate. By the secondary emission of electrons from
the interior surfaces of these channels a shower of
electrons in a pattern corresponding to the low-level
image is produced. The shower of electrons, at an
intensity much above that produced by the photocathode, is
then directed onto a phosphorescent screen, again by the
application of an electrostatic field. The phosphors of
3o the screen produce an image in visible light which
replicates the low-level image.
Image intensifier tubes have evolved from the
so-called "Generation I" tubes through the more recent '
"Generation III" tubes, which provide greater
amplification of available light and greater sensitivity
to infrared light somewhat deeper into the infrared
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portion of the spectrum. However, these image intensifier
devices are limited with respect to the depth into the
infrared portion of the spectrum to which they can
operate.
Another category of conventional night vision device
is represented by the cryogenically cooled focal plane
array thermal imaging devices. These devices use a
photoelectrically responsive detector which is cooled to
a temperature in the cryogenic range to reduce unwanted
thermal noise. The detector includes a pluralltlT of
detector elements, or "pixels", each of which provides
an
electrical signal indicative of the flux of infrared light
falling on the detector element. Some such devices use
a
staring focal plane array: while others have a linear
focal plane array of detector elements, and require the
use of a scanner to sequentially move portions of the
viewed scene across the detector. In either case, because
the detector is cooled to cryogenic temperatures, it can
proved an electrical response to invisible infrared light
much deeper into the infrared part of the spectrum than
is
possible with the image intensifier devices. The
electrical signal provided by such a detector must be
processed and converted to a visible image. For this
purpose, many such devices of this category have used
cathode ray tubes, liquid crystal displays, and other such
display technologies to provide a visible image to the
user of the device.
A significant disadvantage of this category of night
vision device is the requirement for cryogenic cooling
of
the detector. Early devices of this category used a Dewar
' vessel into which a supply of a cryogenic fluid (such a
liquid nitrogen) had to be provided by the user of the
device. The utility of such devices was severely limited
by their requirement for occasional replenishment of the
cryogenic coolant. Later devices of this type have used
cryogenic cooling developed by reverse Sterling-cycle
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coolers. However, such coolers require a considerable
amount of power, are not without their own maintenance and "
reliability problems, and are generally noisy.
Generally, some of the image intensifier type of
night vision devices may be used with add-on telescopes
and other types of accessory lenses (i.e., wide-angle
lenses, etc.). These telescopic lenses have the effect of
bringing far away scenes apparently closer to the user of
the device. However, the imaging device itself does not
adapt to the telescopic lens mounted to it. That is, if
the night vision device is equipped with an aiming
reticle, this reticle does not adapt to the enlarged image
of the scene being viewed through the telescopic lens.
Moreover, the angular size of the reticle cross hairs or
other aiming indicia may be larger that desired when the
image is enlarged by a telescopic lens. Similarly, if
equipped with range estimation stadia lines in the field
of view, the apparent spacing between these lines will not
change when a telescope is used with the imaging device.
Thus, the range estimation lines may not be useable with
a telescopic lens mounted to the viewing device.
Alternatively, a dual set of stadia lines may be provided,
one for use without and one for use with the add-on
telescopic lens. However, this extra set of stadia lines
is always present in the field of view of the device, and
can prove distracting or can obstruct part of the viewed
scene.
A conventional thermal infrared imaging device (known
under its military designation of AAWS-M) allowed for use
of the device with a variety of telescopic and or
wide-angle lenses. However, the user of the device had to
manually provide control input commands allowing the
device to alter its display parameters to accommodate the
installed lens. This expedient is undesirable because of
the time and complexity involved for the user of such a
device.
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SUMMARY OF THE INVENTION
In vie;w of the deficiencies of the conventional technology, a primary
object for this invention is to overcome one or more of these deficiencies.
Another object for this invention is to provide a thermal infrared
imaging device having selectively replaceable telescopic or wide angle lenses,
for
example, and which automatically recognized which of the several lenses is
installed,
changing display parameters for the device accordingly.
Accordingly, in one aspect the present invention provides a thermal
imaging device comprising:
a device housing sealingly defining a chamber therein, said device
housing having at least a ;portion which is magnetically-permeable to allow
penetration of an exl;ernal magnetic field into said chamber; and said device
housing
defining an optical aperture allowing admission of infrared thermal radiation
into said
chamber, said optical aperture being sealingly closed by a window member which
is
transparent to thermal radiation;
a lens assembly having an optical axis, and a respective lens housing
removably attachable to said device housing at said optical aperture to align
said
optical axis with said optical aperture, thus to direct infrared thermal
radiation from a
viewed scene into said chamber via said optical aperture, said lens assembly
including
a movable power-adjustment portion movement of which changes a power of
telescopic magnification for said lens assembly;
a magnet fixedly positioned on said lens housing, when said lens
housing is attached to said device housing, said magnet being in juxtaposition
to said
magnetically-permeable portion of said device housing;
a second magnet moving between a first position and a second position
dependent upon the I>osition of said power-adjustment portion, said second
magnet in
only one of said first and second positions providing a magnetic field which
penetrates into said chamber v:ia said magnetically-permeable portion of said
device
housing;
a ma~;netically-responsive sensor disposed within said chamber in
juxtaposition to said magnetically-permeable portion of said device housing;
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whereby said magnetically-responsive sensor indicates the presence of
said lens assembly ao said optical aperture; and
another magnetically-responsive sensor responding to said magnetic
field of said second magnet in said one of said first and second positions to
uniquely
identify the power seating of said lens assembly.
These and additional objects and advantages of the present invention
will be appreciated from a reading of the following detailed description of at
least one
preferred exemplary embodirrient of the invention, taken in conjunction with
the
appended drawing Figures, in which the same reference numeral indicates the
same
feature, or features v~~hich are analogous in structure or function to one
another.
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DESCRIPTION OF THE DRAWING FIGURES
Figure 1 provides a diagrammatic representation of
the functionally cooperating physical components of a
thermal imaging device embodying the invention;
Figure 2 is a schematic block diagram of a thermal
imaging device according to the present invention;
Figures 3a and 3b respectively provide an external
view and an exploded perspective view of a thermal imaging
device embodying the invention, which is shown with one of
to the accessory telescopic lenses which may be mounted to
the device;
Figures 4a and 4b collectively show other accessory
lenses which may be used with the present thermal imaging
device; and
Figure 5 provides a tabulation of the telescopic
magnification and field of view setting of the various
accessory lenses usable with the present thermal imaging
device, along with applicable magnetic position-code
entries allowing the device to automatically identify each
lens as well as the field of view setting of each
particular lens, if applicable.
DETAILED DESCRIPTION OF AN EXEMPLARY
PREFERRED EMBODIMENT OF THE INVENTION
An overview
Viewing Figure 1, a thermal imaging device l0 is
diagrammatically depicted with its functionally
cooperative physical components suspended in space without
the depiction of a supporting housing (which housing is,
of course, included by a physical embodiment of the
device), so that these components and a ray-tracing '
diagram for light rays in the device can also be
presented. Viewing Figure 1 in detail, the thermal '
imaging device includes an objective optics group,
generally indicated with the numeral 12. This objective
optics group includes several lenses (indicated with
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reference numerals 12', 12", 12"', etc.), which lenses are
transparent to light in the spectral band of interest (but
not necessarily transparent to visible light). The
objective optics group 12 is pointed toward a scene to be
viewed, so that infrared light from this scene (indicated
with the arrowed numeral 14) can be received and focused
by this optics group. It will be understood that the
objective optics group 12 seen in Figure 1 is
representative only, and that this optics group may be
removed and replaced with objective optics of differing
configurations, as will be further described. The
objective optics group 12 concentrates and columnates
received light through a window 16, which window is a
permanent part of a basic sensor portion 18 of the device
l0. In conjunction with the housing (to be described
below) of this basic sensor portion 18, this window 16
bounds a sealed chamber 2o in which are received almost
all of the remaining components of the device 10 as
illustrated in Figure 1. '
Within the housing chamber 20 is received a scanner,
generally referenced with the numeral 22. This scanner 22
includes a scanner frame 24, which is generally of
triangular or tripod configuration in plan view. The
scanner frame 24 includes a generally triangular upper
wall portion 26, and three depending leg portions 28, only
two of which are visible in Figure 1. Carried by the wall
portion 26 is a scanner motor, generally indicated with
the numeral 30. This scanner motor 30 includes a
generally vertically extending rotational drive shaft (not
visible in the drawing Figures) drivingly carrying a
disk-like circular multi-faceted scanning mirror 32. The
scanning mirror 32 includes plural outwardly and
circumferentially disposed adjacent facets or faces 32a,
32b, etc. only a few facets of which are seen in any one
of the drawing Figures. This scanning mirror 32 rotates
in a generally horizontal plane to reflect light 14
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received via the window 16 and objective optics group 12
to an image optics group, generally indicated with the '
numeral 34. It will be noted that because of rotation of
the scanning mirror 32, the facets 32a, 32b, etc.,
continually change their angulation in the horizontal
plane with respect to the scene viewed via the objective
optics group 12.
Considering the image optics group 34 in greater
detail, it is seen that light (arrow 14) reflected from a
facet of the scanning mirror 32 passes through a lens 36
and to a pair of vertically spaced angulated mirrors 38,
and 40. The mirror 40 reflects this light through an
additional pair of lenses 42, and 44 toward a window 46
carried by a Dewar vessel 48. The Dewar vessel 48
includes a thermally insulative housing, generally
indicated with the dashed line and the reference numeral
48'. This Dewar vessel 48 houses a linear focal plane
infrared detector 50 having a linearly arrayed multitude
of small infrared detector elements, indicated
collectively on Figure 1 with the vertical line 50' on
detector 50. Each of the detector elements 50' of the
detector 5o provides a corresponding one of a like
multitude of electrical signals each of which is
indicative of the flux level of infrared light falling on
the particular detector element. These electrical signals
are provided outwardly of the Dewar vessel 48 by an
electrical interface (to be further described), and
indicated on Figure 1 with the dashed line 52.
In order to cool the detector 50 to a sufficiently
low temperature that thermally excited electrons (as
opposed to electrons excited by photons of infrared light
falling on the detector 50) do not cause an undesirably
high level of electrical noise which would hide the
desired photoelectric image signal, the Dewar vessel 48
includes a multi-stage reversed Peltier-effect (i.e.,
thermoelectric) cooler 54. The thermoelectric cooler 54
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has a chilling face to which the detector 5o is mounted
to
- be cooled, and a heating face in heat transfer
relationship with a heat sink schematically indicated with
the numeral 56. In the physical embodiment of the imaging
device 10, the heat sink 56 is defined by a metallic
portion of the housing for the device 10 as will b
e seen.
It will be understood that because of the continuous
change in angulation of each facet 32a, 32b, etc., of the
scanning mirror 32 as this mirror rotates in a horizontal
plane, the scene reflected frori each particular facet
sweeps horizontally across the linear array of detector
elements 50' (i.e., perpendicularly to the vertical linear
array of these detector elements). The detector elements
50' responsively provide electrical signals (via interface
52) which are indicative of the flux levels of infrared
light falling on corresponding ones of the plural detector
elements 50' from a particular part of the scene during
any one sweep of a scene portion across the detector 50.
In order to provide a visible image to be viewed by
a user of the imaging device 10, a light emitting diode
(LED) projection array module 58 is carried by an
apertured flange portion 60 of the scanner frame 26. This
LED projection array module 58 includes a linear LED array
62, which array includes a multitude of individual LED's
(not visible in Figure 1, but indicated with the arrowed
numeral 62'), each individually emitting visible light
when energized. The LED's 62' of the array 62 are arrayed
linearly along a vertical line similarly to the linear
arrangement of the detector elements 50' of the detector
50. The LED's 62' provide respective portions of a
visible image, as will become apparent. Light from the
LED' s 62 ' is columnated and proj ected by a proj ection
lens
' group, generally indicated with the numeral 64, onto a
facet of the mirror 32, and as indicated by the arrowed
reference numerals 14'. The numerals 14 and 14' are used
intentionally with respect to the invisible infrared light
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carrying image information from a scene, and the visible
light replicating the scene for viewing by a user of the '
device 10.
From the mirror 32 (i.e., from a particular facet 32' '
5 of this mirror) the visible light from the LED's 62' is
reflected to an ocular lens group, generally indicated
with the numeral 66. The ocular lens group 66 includes
several individual lenses, indicated with the respective
reference numerals 66', 66", etc. Along with these lenses
10 66', 66", etc., a status d~..splay unit 68 is interposed in
the ocular lens group 66. This status display unit 68
defines an aperture through which the visible image is
perceived, and includes several individual LED's which
when illuminating are peripherally visible to the user of
the device 10. These individual LED's are indicated with
the numerals 68', 68", etc. Finally, the imaging device
10 includes a pair of eyepiece shutters 70. These
shutters 70 are biased closed to prevent light emanations
from the device 10 when a user's face is not pressed
against a movable eyepiece member (to be described below).
When the user presses against the movable eyepiece member,
the shutters 70 open to allow the user to view the visible
light image provided by the LED projection display module
and the spinning mirror 32.
Viewing now Figure 2, a schematic functional block
diagram of the thermal imaging device 10 is presented.
This thermal image device 10 is divided into functionally
modular portions, as is indicated by the dashed-line boxes
encircling the various components of the device, with some
of the modules including several sub-modules or
components. The module 72 manages both invisible and '
visible light, and includes the objective optics group 12
receiving the invisible infrared light 14 from a scene to
be viewed, the scanner 22, and image optics group 34
directing this invisible light to the detector 50. This
light management module 72 also receives visible light
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from the LED array 62 , and includes the proj ection lens
group 64 projecting this light to the scanner 22, and
ocular lens group 66 providing the image to a user of the
d device.
Detection module 74 is enclosed within the Dewar
vessel 48, and receives the focused invisible infrared
light 14 from the scene to be viewed. This module 74
includes the detector 50, along with a readout circuit
76
providing multiple channels of electrical image signal
78
(one channel for each detector elemQnt of the linear
detector array '50, recalling the description above) to
a
multiplexer circuit (MUX) 80. The MUX 80 provides the
electrical interface output 52 in the form of a serial
analog image signal. Detector module 74 also includes a
driver circuit 82 providing control commands to the
readout circuit 76. An electrically erasable programmable
read-only memory (EEPROM) 84 is included in the detection
module 74 to locally store and provide data on the
operation of the readout circuit 76, providing
compensation factors locally for a number of gain-control
and non-uniformity compensations in connection with the
infrared detector 50. As can be seen from Figure 2, the
various circuits of the module 74 have electrical
interface with other modules of the device 10.
The serial analog image signals 52 provided by module
74 are received by an analog signal processor (ASP) 86
which is located in a process-and-control (P&C) module
88.
A processed serial analog image signal 90 is provided by
the ASP 86 to a analog-to-digital converter (ADC) 92. A
resulting processed serial digital image signal 94 is
' provided to a timing generator 96. This timing generator
96 has an interface with the multiplexer circuit 80 to
' control the timing of operation of this circuit. A frame
memory 98 is interfaced with the timing generator so that
image information which is global to the scene being
viewed may be stored and retrieved for use in providing
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gain adjustment, contrast, and other compensation factors
for use in processing the image signals obtained from the '
detection module 74. Timing generator 96 also provides a
system-wide timing control signal, indicated with the
reference numeral 100. This timing control signal is used
to operate several other features of the imaging device
10, including control of the rotational speed and position
of the mirror 32 so as to achieve time-correlation of the
operation of the detector 50, mirror 32, and LED array 62.
A serial digital image signal 102, compensated and
time-correlated, is provided by the timing generator 96 to
a display module 104. This display module 104 includes
the LED projection array module 58, along with a driver
circuit 106 for receiving the signal 102 and driving the
individual LED's 62' in response to this signal. An
electrically erasable programmable read-only memory
(EEPROM) 108 has an interface with the driver circuit 106
for receiving and storing for future use values to be used
in the operation of the device 10. For example, EPROM 108
may be used to store stadia line spacing information,
which would allow the device l0 to be used to estimate
ranges to personnel or vehicles of known sizes. In order
to provide a user of the imaging device 10 with additional
useful image information, such as spaced apart
comparative-size lines for humans and various types of
vehicles so that ranges can be estimated, or with a
reticle of various kinds and sizes in accord with the
range to an object being viewed and the use being made of
the device 10 at a particular time, the display module 102
also includes another electrically erasable programmable
read-only memory (EEPROM) 110 for storing such image '
information. This image information, as selected by the
user of the device 10, is provided to a symbology
generator circuit 112, which in turn provides a symbology
signal 114 to the LED array 62. The array 62 includes
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separate light emitting diodes (LED's) for receiving the
signal 114.
In order to complete this description of the imaging
device l0 as illustrated in Figure 2, it should be noted
that the device 10 includes an input-output (I/O) module
116. This I/O module 116 allows a user of the device 10
to input commands via a set of externally-accessible
controls 118, such as a set of momentary contact push
button switches which may be operated from outside the
l0 housing of the device 10. The controls 118 have an
interface with a microprocessor 118 , which is part of a
distributed control system also including another
microprocessor 122 in the P&C module 88. The
microprocessors 120 and 122 have an interface with the
EEPROM's 84, 108 and 110, along with the circuits served
by the data and commands stored in these EEPROM' s . The
microprocessor 120 has an externally-accessible data
interface port 120' so that all of the data and
programming stored in the microprocessors 120, 122, and
the EEPROM's interfaced with these microprocessors, and
the circuits served, may be inserted and changed by access
to the port 120'. Finally, it is seen that the P&C module
88 provides power input to the system from a power source,
such as from a battery pack 124. A DC/DC power converter
126 provides power to various modules and components of
the device l0 at appropriate voltage and current levels.
One of the circuits powered from converter 126 is a
controller 128 for the thermoelectric cooler 54.
Turning now to Figures 3a and 3b, a physical
embodiment of the imaging device 10 is presented in
' external view and in exploded perspective view,
respectively. The imaging device 10 includes a two-piece
' chambered housing 130. This housing includes two pieces
130a and l3ob which sealingly cooperate (via an
intervening sealing member 132) to bound the chamber 20
within this housing. The part 130a of the housing 130 is
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fabricated of cast non-magnetic metal (of aluminum, for
example), is somewhat L-shaped in transverse cross '
section, and provides a lower wall portion 134, a side
wall portion 136, and an apertured pair of opposite front
(138), and rear (140) wall portions. This housing part
130a provides a heat sink for the thermoelectric cooler
54, and a base (i.e., in effect, an optical bench) to
which the optical and other components of the device 10
are mounted, as will be seen.
The front wall portion 138 of housing part 130a
defines a reentrant portion 142 which forwardly defines a
somewhat conical recess (not visible in the drawing
Figures, but referenced on Figure 3a with the arrowed
numeral 142'), and which at its aft end carries the window
16 in the aperture 144 of this wall. The objective optics
group 12 is carried at this front wall 138 by a lens
housing 146 which at its aft end defines a conical portion
148 for receipt into the front. recess of the housing part
130a. The conical portion 148 centrally defines an
aperture 148' within which the most rearward of the lens
elements 12', 12", etc., 'is received, and defines an
optical aperture (also referenced 148') at which thermal
infrared radiation received by the objective lens 12' is
delivered to the device 10. The housing 146 is removably
engageable with the housing part 130 to connect the
objective optics group 12 in its proper location, and is
also removable so that optics of different power may be
fitted to the sensor portion 18. At the aperture 150 of
the rear wall portion 140, the ocular lens group 66 is
sealingly carried in a housing portion 152.
Within the chamber 20 of the housing 130, the scanner
24 is secured to the lower wall 134 by a trio of screws
154 which each pass through a respective vertically
extending hole defined centrally of a corresponding one of
the three legs 28 of the scanner frame 24. These screws
threadably engage respective bores defined by the lower
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wall 134. Captured between the lower ends of the legs of
the scanner frame 24 and the lower wall 134 of the housing
130 is an electronics assembly 156. This electronics
,, assembly 156 includes a circuit board and many of the
5 discreet and integrated circuit devices including
micro-controller 122, which are necessary in order to
effect the functions explained with respect to Figures 1
and 2. Also mounted to the lower housing part l3oa, in
addition to the already identified components and modules,
to which are indicated on Figure 3b wa_th their
previously-introduced reference numerals, is an electronic
cable assembly 158. This cable carries
externally-accessible data interface port 120, the
connector for which extends sealingly through a hole
15 provided in the housing portion 130b, as is seen in this
drawing Figure.
A Control electronics module 160 with its own cable
assembly also mounts in the housing 130 and provides the
control input momentary-contact switches 118 and
micro-controller 120 identified with respect to Figure 2.
Finally, received in the housing 130 and circumscribing
the reentrant portion 142 of the front wall 138 is a
magnetic reed switch and cable assembly 162. This cable
assembly with its several magnetically-responsive reed
switches is responsive to one or more magnets carried in
respective locations by various ones of the objective
optics groups which can be used with the basic sensor 18.
These magnets are located in particular locations (i.e.,
in a position code) on each objective lens set in order
to
provide a user both with differing levels of magnification
of a distant scene, and differing symbology appropriate
for the particular use for which the objective lens set
adapts the sensor 18. When the basic sensor responds to
the installation of a particular lens group, the user is
provided with symbology and other internal adjustments of
the operation of the sensor 18 automatically. The reed
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switches are able to sense the particular locations of the
magnets on the lens groups (thus identifying the
particular lens group) through the non-magnetic front wall
portion 138 of the housing 130. Thus, no physical input
is necessary from an operator to identify a particular
lens group to the sensor 18, and the chamber 20 remains
sealed.
Viewing now the housing portion 130b, it is seen that
this housing portion defines a battery compartment recess
164 at an aft portion of the housing 130. This recess
opens both upwardly and rearwardly on the housing part
130b. Battery 124 is received into the recess 164, and is
covered sealingly in this recess by a hinged door member
166 with an intervening sealing member 168. The door 166
is somewhat L-shaped in side view, and is hinged adjacent
to its rear edge to the housing part 130b. A latching
device 170 is carried by the door 166 adjacent to its
forward end, and is removably engageable with a recess
feature of this housing part to retain the door 166 in its
closed position, as is seen in Figure 3a.
Identification of Accessory Lenses
Still viewing Figure 3b it will be appreciated that
if the thermal imaging device 10 is used without the
objective optics group 12, then the image optics group 34
internal to the housing 130 will focus an image on the
detector 50. In this configuration, the thermal imaging
device 10 has the widest possible field of view (FOV), and
has a unity power. That is, the image presented to the
user of the device 10 is the same size as would be seen
through a unity power telescope, except that the presented
image is a replication in visible light of the invisible
thermal infrared light from the viewed scene. If the user
chooses to employ a telescopic objective lens group 12
with the device 10, the housing 146 for this telescopic
lens group is inserted at its conical rear portion 148
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into the matching cavity at the from of the housing 130,
as was explained above. Figure 3 shows that the conical
rear portion 148 of the housing 146 carries a flat feature
- 172 defined on the conical portion so that the housing can
be fully seated into the device 10 in only one relative
rotational position. An internally threaded retaining
ring 174 rotationally carried by the housing 146
threadably engages a threaded annular boss (not visible in
the drawing Figures) on the front of housing 13o to
releasably retain the telescopic lens.
The telescopic accessory lens seen in Figure 3 is one
of three alternative telescopic lenses which may be used
with the device 10. The other two alternative telescopic
lenses are seen as a group in Figure 4. Viewing Figure 3,
it is seen that this accessory lens has on the housing 146
a magnet carried on the housing portion 148 iri a location
indicated with the numbered arrow 176. This magnet is
uniquely positioned relative to the feature 172. The
magnet 176 of this lens aligns with and actuates only one
of the magnetic reed switches 178 carried on reed switch
assembly 162. The one of the reed switches 178 actuated
by the magnet 176 uniquely identifies the installed
telescopic lens. Each of the other two lenses seen in
Figures 4 likewise has a magnet (176', 176") differently
positioned relative to the flat feature 172 of that lens
so as to actuate only a corresponding one of the four reed
switches of the reed switch assembly 176.
Turning now to Figures 4, it is seen more
particularly that each of the other two accessory
telescopic lenses also has a similar magnet (176', and
' 176") uniquely located on the respective portion 148 of
the lens. The two of these three lenses seen in Figures
' 4 also include a two-position variable-power (and variable
field of view) feature. It will be understood that
greater magnification (greater power) results in the user
of the device 10 being provided with a narrower field of
CA 02207408 1997-06-09
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18
view. Conversely, if the user desires a wider field of
view, a lower power setting for the lens will be used. '
This variable power feature is actuated by the user
manually rotating a power-select ring 180 between either
one of two possible rotational positions for this ring.
In one of the two positions for ring 180, an additional
internal magnet (not directly seen on the drawing Figures,
but indicated by reference to its magnetic field area, as
explained below) is spaced from the conical portion 148,
and does not outwardly present a signif.ic~.nt magnetic
field. In the other position for the power-select ring
180, the additional internal magnet moves axially to a
position adjacent to an inner surface of the portion 148.
In this position, the magnet presents an additional area
of magnetic field area on the portion 148 of the lens
housing 146, which magnet, magnet position, and magnetic
field area on the exterior surface 148 are all indicated
on Figures 4 with the dashed line area and arrowed numeral
. 182. The magnetic field area 182 aligns with the forth
magnetic reed switch 178 of the device 10. Thus, the
device 10 can identify not only which one (if any) of the
lenses 12 is installed by a user of the device, but also
identifies which power setting is enabled by the user for
those lenses have a variable power level.
Table 5 provides a depiction of the locations of the
magnets 176, 176', 176°' on the various lenses 12, and the
presence or absence of magnetic field at area 182 on the
conical portion 148 of the lenses and the telescopic power
level provided by these lenses to the user of the device
10, dependent upon the rotational position of the ring
180. The first row of this tabulation is for the device '
10 alone with no installed accessory lens. It is seen
from this tabulation that the three lenses use only a
single-position magnetic code to indicate the installed
lens. Thus, it is apparent that additional lenses can be
provided for use with the device 10 without necessitating
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19
any internal structural changes to the device. The
- addition of lenses using a two-position magnetic would
allow three additional lenses to be uniquely identified.
An additional lens (for a total of seven accessory lenses)
can be identified by using a magnetic field at all three
of the magnetic reed switch positions used for lens
identification. The device 10 can be programmed as
necessary to recognize the installed accessory lenses, and
to provide symbology to the user of the device as
appropriate to the installed lens. The table of Figure 5
also shows whether a magnetic field is present or absent
at area 182 dependent upon the power level (and field of
view) selected by the user of the device 10. From an
inspection of Figure 5, it will be apparent that lenses #1
and #2 are depicted in Figures 4, while the lens seen in
Figures 3 is lens #3 and does not have a variable power or
power select ring 180.
While the present invention has been depicted,
described, and is defined by reference to a particularly
preferred embodiment of the invention, such reference does
not imply a limitation on the invention, and no such
limitation is to be inferred. The invention is capable of
considerable modification, alteration, and equivalents in
form and function, as will occur to those ordinarily
skilled in the pertinent arts. The depicted and described
preferred embodiment of the invention is exemplary only,
and is not exhaustive of the scope of the invention.
Consequently, the invention is intended to be limited only
by the spirit and scope of the appended claims, giving
full cognizance,to equivalents in all respects.
