Patent Description:
Quality imaging optical components are made from crystalline and glass materials, which are very brittle and sensitive to stress concentrations and tensile stresses. Mounting of elements made from these materials for survival under high gravitational forces such as unmanned air vehicles, rockets, and gun launches can be very challenging due to catastrophic failure modes of these brittle materials. Any existing or new stress concentration can cause a fracture initiation point and the optical element can be prone to shattering. This can happen, for example, after longterm storage and transport, when the adhesive holding optical elements in place breaks down and regular vibrations cause contact between one or more optical elements and the housing holding them in place.

<CIT> discloses a camera objective having at least: one lens mount for fixing to a camera housing, at least one lens held in the lens mount with a front lens face, a rear lens face and a preferably cylindrical lateral lens face for bearing against a preferably cylindrical internal face of the lens mount. The invention provides for a positively locking connection to be provided between the lateral lens face and the internal face of the lens mount, which connection is in the form of, for example, a groove in one of the components and protrusion or lug in the other of the components, or is formed by an additional positively locking means, such as an O ring.

From a first aspect, the present disclosure provides an optical assembly as claimed in claim <NUM>.

The optical assembly of the preceding paragraph can optionally include any one or more of the following features, configurations and/or additional components:
A further embodiment of the foregoing optical assembly, wherein the mounting structure includes a cylindrical body and a central bore defined by the inner surface.

A further embodiment of the foregoing optical assembly, wherein a width of the central bore increases stepwise along an optical axis between the open end and the receiving end.

A further embodiment of the foregoing optical assembly, wherein corresponding ones of the plurality of optical elements have a diameter increasing stepwise along the optical axis.

A further embodiment of the foregoing optical assembly, wherein the conformal filler material, or a precursor thereof, is selected from a group consisting of: epoxy, silicone, urethane resin, solder material, braze material, frit glass, ceramic cement, and combinations thereof.

A further embodiment of the foregoing optical assembly, further comprising: a full-range image sensor disposed at a receiving end of the optical assembly.

A further embodiment of the foregoing optical assembly, wherein the image sensor is connected to a wireless communication system for transmitting a sensed image to an external location.

A further embodiment of the foregoing optical assembly, wherein the plurality of optical elements including alternating ones of a convex optical element and a concave optical element.

A further embodiment of the foregoing optical assembly, further comprising: a plurality of spacers disposed between adjacent ones of the convex optical element and the concave optical element.

From a further aspect, the present disclosure is directed to a method for making an optical assembly as claimed in claim <NUM>.

The method of the preceding paragraph can optionally include any one or more of the following features, configurations and/or additional components:
A further embodiment of the foregoing method, further comprising: after the inserting step, inserting a plurality of axially spaced optical elements into the bore of the mounting structure, each of the plurality of axially spaced optical elements having an undercut in a perimeter edge surface.

A further embodiment of the foregoing method, further comprising: aligning the undercut in the perimeter edge of each of the plurality of optical elements with corresponding ones of the plurality of recessed undercuts in the inner surface of the mounting structure to define a plurality of axially spaced voids; casting a conformal filler material in place in each of the plurality of voids to create a mechanical lock between the optical element and mounting structure.

A further embodiment of the foregoing method, wherein the plurality of optical elements including alternating ones of a convex optical element and a concave optical element.

A further embodiment of the foregoing method, further comprising: assembling a plurality of spacers between adjacent ones of the plurality of optical elements.

A further embodiment of the foregoing method, wherein a width of the central bore increases stepwise along an optical axis between the open end and the receiving end.

A further embodiment of the foregoing method, wherein corresponding ones of the plurality of optical elements have a diameter increasing stepwise along the optical axis.

A further embodiment of the foregoing method, wherein the conformal filler material, or a precursor thereof, is selected from a group consisting of: epoxy, silicone, urethane resin, solder material, braze material, frit glass, ceramic cement, and combinations thereof.

A further embodiment of the foregoing method, further comprising: installing a full-range image sensor at a receiving end of the optical assembly.

The present disclosure relates to an optical assembly and method of its assembly. This assembly includes a mounting structure that houses a plurality of axially spaced optical elements. Both the mounting structure and the optical elements have circumferential undercuts that are aligned when the optical elements are installed. These undercuts together define voids between each optical element and the mounting structure. Conformal filler material is cast in place into each void, thereby creating a resilient mechanical lock between each optical element and the mounting structure.

<FIG> schematically depicts an air vehicle <NUM> in transit to a ground location <NUM>. Air vehicle <NUM> can be an unmanned air vehicle (UAV), rocket, missile, or other munitions, though the disclosure is not so limited.

Air vehicle <NUM> is outfitted with an imaging system (not visible) at or near nose <NUM>. The imaging system provides still images and/or video of some or all of view range <NUM>. These images or videos are taken by a full-range imaging sensor <NUM>, which is in communication with on-board controller <NUM>. On-board controller <NUM> can, for example, use and process data from imaging sensor <NUM> for guidance purposes, and/or can include a wireless radio configured to communicate with external location <NUM>, e.g. to transmit images or video to external location <NUM>.

To provide the desired or optimal resolution for imaging sensor <NUM>, the imaging system can include an embodiment of an optical assembly according to the present disclosure. One such non-limiting embodiment is shown in <FIG>.

<FIG>, <FIG>, and <FIG> depict optical assembly <NUM>, an ordered series of lenses used for optical conditioning of light received by imaging sensor <NUM> of air vehicle <NUM>. <FIG> is a perspective view of optical assembly <NUM> (illustrating section plane <NUM>-<NUM>), <FIG> is a sectional view of optical assembly <NUM> through section line <NUM>-<NUM>, and <FIG> is an exploded perspective view of optical assembly <NUM>. <FIG>, <FIG>, and <FIG> illustrate optical assembly <NUM> with mounting structure <NUM> and a plurality of optical elements <NUM> axially spaced in inner bore <NUM>. <FIG> and <FIG> depict additional details of mounting structure <NUM>, optical elements <NUM>, and bore <NUM>, including ports <NUM>, undercuts <NUM> in perimeter edge surface <NUM> of optical elements <NUM>, and circumferential recessed undercuts <NUM> in inner surface <NUM> of mounting structure <NUM>.

In the illustrated embodiment, mounting structure <NUM> is a substantially cylindrical structure that supports and retains several optical elements <NUM> at set axial positions within bore <NUM>, a central axial passage extending through mounting structure <NUM>. Inner surface <NUM> defines an inner surface of mounting structure <NUM> along bore <NUM>. In the illustrated embodiment, inner surface <NUM> is generally cylindrical except where interrupted by circumferential recessed undercuts <NUM>. Circumferential recessed undercuts <NUM> are annular grooves or channels disposed at axial locations along inner surface <NUM> corresponding to assembly locations of optical element <NUM>. In at least some embodiments, inner surface <NUM> can have one or more circumferential recessed undercuts <NUM> for each optical element <NUM>.

Optical elements <NUM> are lenses, prisms, mirrors, or other elements of an optical assembly. Each optical element <NUM> has a perimeter edge surface <NUM> defining an outer perimeter of the optical element. Undercuts <NUM> are annular grooves or channels disposed circumferentially about at least some optical elements <NUM>, within perimeter edge surfaces <NUM>. In some embodiments, each optical element <NUM> has at least one undercut <NUM>. In other embodiments, some optical elements <NUM> may not include undercuts. During assembly of optical array <NUM>, optical elements <NUM> are inserted into bore <NUM> of mounting structure <NUM> and aligned such that undercuts <NUM> face circumferential recessed undercuts <NUM>. In this assembled state of optical assembly <NUM>, alignment of each undercut <NUM> with a matching circumferential recessed undercut <NUM> in inner surface <NUM> defines voids <NUM>.

Voids <NUM> are annular passages formed by and between perimeter edge surfaces <NUM> and inner surface <NUM>. Voids <NUM> are filled with conformal filler material <NUM> (not shown in <FIG>, <FIG>, or <FIG>, but discussed below with respect to <FIG> and <NUM>). In the depicted embodiment, when each optical element <NUM> is situated at its installation location within mounting structure <NUM>, the optical element is surrounded by a single void <NUM>. Voids <NUM> are accessible via ports <NUM>, which in this embodiment extend fully and radially through mounting structure <NUM> and provide communication between an outer surface of mounting structure <NUM> and at least one circumferential recessed undercut <NUM>. Each void <NUM> can be accessible via multiple ports <NUM>; in the depicted embodiment (see <FIG>), four radial ports <NUM> feed each void <NUM>, though the ports could be of any suitable shape or direction. In certain embodiments, one or more ports <NUM> can be provided with a longitudinal component as well, either through mounting structure <NUM> and/or through one or more optical elements <NUM>.

Radial ports <NUM> are used to inject conformal filler <NUM> into voids <NUM> to resiliently secure optical elements <NUM> within mounting structure <NUM>. Generally, depending on the exact application and required properties, conformal filler material <NUM>, or a precursor thereof, can include polymers (such as injection molded materials), elastomers, cements, or adhesives such as epoxies, urethane, and polysulfides. Additionally and/or alternatively it can also include potting materials, hot melt adhesives, plasters, or other suitable materials that can be cast or injected into the void then subsequently cured or hardened. In certain embodiments, conformal filler material <NUM>, or a precursor thereof, is selected from a group consisting of: epoxy, silicone, urethane resin, solder material, braze material, frit glass, ceramic cement, and combinations thereof.

The exploded view of <FIG> illustrates a method for making optical assembly <NUM>. A first of the plurality of optical elements <NUM> is inserted into bore <NUM> of mounting structure <NUM>, and positioned at its installation location (as discussed above) so as to define void <NUM>. This optical element <NUM> is then secured within bore <NUM> by injection of conformal filler material <NUM> into void <NUM> via port(s) <NUM>. This process can be repeated to successively install all optical elements <NUM> into mounting structure <NUM>.

<FIG> and <FIG> further illustrate spacers <NUM>. Spacers <NUM> are situated between adjacent optical elements <NUM>, and are sized to provide a desired relative axial spacing or positioning of each optical element <NUM>. In some embodiments, optical assembly <NUM> can be formed by stacking all optical elements <NUM> and spacers <NUM> within bore <NUM>, then injecting conformal filler material <NUM> to lock optical elements <NUM> in place.

<FIG> respectively show convex optical element <NUM> and concave optical element <NUM>, each with undercut <NUM>. In the non-limiting example embodiment shown in <FIG>, alternating ones of convex optical element <NUM> and concave optical element <NUM> are inserted into bore <NUM>. As discussed above, optical elements <NUM> can be separated by spacers <NUM>, which are assembled between adjacent optical elements <NUM>. In other embodiments, optical elements <NUM> can be spaced via steps or shelves of inner surface <NUM>, as discussed below with respect to <FIG>.

<FIG> illustrate two embodiments of optical assembly <NUM>, in a final (assembled) state. <FIG> substantially parallel <FIG> (described above), but additionally illustrate conformal filler material <NUM> in place within voids <NUM>.

<FIG> illustrates an embodiment wherein optical elements <NUM> are positioned axially by means of spacers <NUM>. Spacers <NUM>, as discussed above, determine an axial offset between adjacent optical elements <NUM> so as to align undercuts <NUM> with circumferential recessed undercuts <NUM>. In the embodiment of <FIG>, mounting structure <NUM> includes a cylindrical body and a central bore defined by a cylindrical inner surface <NUM>. In some embodiments, spacers <NUM> can particularly be situated between adjacent convex optical elements <NUM> and concave optical elements <NUM>.

<FIG> illustrates an alternative embodiment that eschews spacers <NUM> (see <FIG>) in favor of steps <NUM>. As illustrated in <FIG>, optical elements <NUM> have decreasing diameter as a function of axial/longitudinal position, from top to bottom. In this embodiment of optical assembly <NUM>, inner surface <NUM> of bore <NUM> has steps <NUM> at axial locations selected to support optical elements <NUM> with undercuts <NUM> facing circumferential recessed undercuts <NUM>. Accordingly, the width of bore <NUM> increases in a stepwise fashion along the optical/longitudinal axis of optical assembly <NUM>, between its open end and a receiving end. During assembly, successively largerdiameter optical elements <NUM> are placed into bore <NUM>, and allowed to settle onto a step <NUM> of inner surface <NUM>, such that the diameter of successive optical elements <NUM> increases in a matching stepwise fashion along the optical axis. Conformal filler material <NUM> locks optical elements <NUM> into place, once cured.

As shown in both <FIG>, voids <NUM>/<NUM> (and in some embodiments at least a portion of ports <NUM>/<NUM>) are filled with conformal filler material <NUM>/<NUM>. Each undercut <NUM>/<NUM> in optical elements <NUM>/<NUM> is aligned with corresponding ones of the plurality of undercuts <NUM>/<NUM> in mounting structure <NUM>/<NUM>, the aligned circumferential undercuts <NUM>/<NUM> and <NUM>/<NUM> defining axially spaced voids <NUM>/<NUM>. Conformal filler material <NUM>/<NUM> is cast in place in void(s) <NUM>/<NUM> to create a mechanical lock between each optical element <NUM>/<NUM> and inner surface <NUM>/<NUM> of mounting structure <NUM>/<NUM>. This mechanical lock is a compressive force independent of any adhesive properties that may or may not be provided by the selected filler material <NUM>/<NUM>. For example, many installations utilizing such a system may be stored for long periods of time, exposed to extreme environmental and thermal variation, as well as vibrations from transport. Over time, any adhesive properties which may be present at the time of manufacture are prone to breaking down but the mechanical lock can remain for a much longer time period, extending the life of the product.

The conformal material selection for a gun hard application will be a mechanically stable structural material that also possesses properties to address CTE mismatches between the optical elements and the mounting structure. The filled void will create a mechanical lock between the optical element and mounting structure with high surface area in contact, so stress concentrations will be minimized with this configuration. This configuration will not need to rely on bond strength of the conformal material with either the optical element or the mounting structure. The undercut shapes in both components can also be "tuned" in size, location, and geometry to impart compressive stresses on the more vulnerable locations of the optical elements during high acceleration environments like a gun launch.

Optical array <NUM> is formed by inserting optical elements <NUM> within mounting structure <NUM>, then performing a casting step wherein conformal filler material <NUM> is injected into resulting voids <NUM> and cured or otherwise allowed to harden into rigid locking elements disposed between inner surface <NUM> of mounting structure <NUM> and perimeter edge surface <NUM> of optical elements <NUM>. To position optical elements <NUM>/<NUM> at appropriate axial locations within bore <NUM>/<NUM>, optical assembly <NUM>/<NUM> can include spacers <NUM> disposed between adjacent optical elements (see <FIG>), or can have steps <NUM> along inner surface <NUM> (see <FIG>). In some embodiments, optical array <NUM> may include both steps and spacers to position optical elements <NUM>.

The aforementioned casting step comprises injecting a curable filler material into a plurality of ports, such as a radial port providing communication between an outer surface of the mounting structure and at least one of the circumferential recessed undercuts; and curing the filler material to form the mechanical lock. The mechanical lock includes a residual compressive force between the mounting structure and the optical element independent of any adhesive bond which may exist. As noted above, the conformal filler material, or a precursor thereof, is selected from a group consisting of: epoxy, silicone, urethane resin, solder material, braze material, frit glass, ceramic cement, and combinations thereof.

As disclosed herein, optical assembly <NUM>/<NUM> includes a plurality of optical elements <NUM>/<NUM> locked into mounting assembly <NUM>/<NUM> by the injection and curing of conformal filler material <NUM>/<NUM> to form a durable structure capable of withstanding heavy acceleration loads with minimal crack initiation or other damage to sensitive imaging components.

Claim 1:
An optical assembly (<NUM>; <NUM>) comprising:
a mounting structure (<NUM>; <NUM>) including a plurality of axially spaced circumferential recessed undercuts (<NUM>; <NUM>) formed into an inner surface of the mounting structure (<NUM>; <NUM>);
a plurality of optical elements (<NUM>; <NUM>) axially spaced in the mounting structure (<NUM>; <NUM>), at least one of the plurality of optical elements (<NUM>; <NUM>) including an undercut (<NUM>; <NUM>) in a perimeter edge surface (<NUM>; <NUM>) of the optical element (<NUM>; <NUM>), the undercut (<NUM>; <NUM>) in the perimeter edge (<NUM>; <NUM>) aligned with one of the plurality of undercuts (<NUM>; <NUM>) in the mounting structure (<NUM>; <NUM>), the aligned circumferential undercuts defining a void (<NUM>; <NUM>); and
a cured or hardened conformal filler material (<NUM>; <NUM>) cast in place in the void (<NUM>; <NUM>) to create a mechanical lock between the optical element (<NUM>; <NUM>) and mounting structure (<NUM>; <NUM>),
wherein the mechanical lock is a residual compressive force between the mounting structure (<NUM>; <NUM>) and the optical element (<NUM>; <NUM>) independent of any adhesive bond which may exist,
characterised in that the optical assembly comprises a plurality of ports (<NUM>; <NUM>) providing communication between an outer surface of the mounting structure (<NUM>; <NUM>) and at least one of the circumferential recessed undercuts (<NUM>; <NUM>),
wherein the plurality of ports (<NUM>; <NUM>) are configured to be used to inject the curable or hardenable conformal filler material (<NUM>; <NUM>) into the void (<NUM>; <NUM>) to resiliently secure the optical element (<NUM>; <NUM>) within the mounting structure (<NUM>; <NUM>).