Optical element mount and method thereof for a gun-launched projectile
원문보기
IPC분류정보
국가/구분
United States(US) Patent
등록
국제특허분류(IPC7판)
F42B-015/01
F42B-015/00
F42B-015/10
F41G-007/00
출원번호
UP-0761155
(2007-06-11)
등록번호
US-7547865
(2009-07-01)
발명자
/ 주소
Johnson, Gary H.
Beard, Douglas M.
Thomas, John A.
Perez, Rene D.
출원인 / 주소
Raytheon Company
대리인 / 주소
The Law Offices of Eric A. Gifford
인용정보
피인용 횟수 :
1인용 특허 :
8
초록▼
An optical element mount is effective in high G environments to protect brittle optical elements in which tensile stresses are generated on surface S2 without degrading optical performance. A flexible spacer formed of a relatively low-stiffness material supports an optical element having a tapered o
An optical element mount is effective in high G environments to protect brittle optical elements in which tensile stresses are generated on surface S2 without degrading optical performance. A flexible spacer formed of a relatively low-stiffness material supports an optical element having a tapered outer periphery in an optical seat having a complementary tapered surface. When the optical assembly is exposed to the high G environment, the inertial loading drives the optical element in the aft direction into the flexible spacer and seat. This puts the optical element into a plate bending condition thereby inducing tensile stress on S2 which is at least partially offset by a compressive stress caused by the reaction force normal to the tapered interface. The stresses, both compressive and tensile, placed on the optical element in the high G environment can be very large. In the absence of the tapered mount and flexible spacer, the tensile stress placed on S2 would likely fracture or shatter the brittle optical element. When the inertial loading is removed, the optical element returns to its initial unstressed position.
대표청구항▼
We claim: 1. A gun-launched projectile for use in a high G environment, comprising: a gun-launched projectile having a central axis along the length of the projectile; and an optical assembly on the projectile having an optical axis that is approximately parallel to the central axis at launch, said
We claim: 1. A gun-launched projectile for use in a high G environment, comprising: a gun-launched projectile having a central axis along the length of the projectile; and an optical assembly on the projectile having an optical axis that is approximately parallel to the central axis at launch, said assembly including, an optical element formed from a brittle material, said optical element comprising a forward facing surface, S1, an aft facing surface, S2, such that the diameter of S2 is smaller than the diameter of S1, with an outer tapered surface connecting S1 and S2; an optical seat having a complementary tapered surface around a clear optical aperture formed therethrough and configured to engage the outer tapered surface of said optical element; and a flexible material between the mating surfaces of the optical element and the optical seat that supports the optical element in an initial unstressed position, said optical assembly configured to react to the inertial load upon launch to deform the flexible material and drive the optical element into the seat thereby producing both a bending moment that places S2 under tensile stress and a force normal to the outer tapered surface that places S2 under compressive stress that at least partially offsets the tensile stress and to react to the removal of the inertial load to return the optical element to the initial unstressed position. 2. The gun-launched projectile of claim 1, wherein the optical assembly constitutes a portion of an electro-optical seeker. 3. The gun-launched projectile of claim 1, wherein the tensile stress in S2 of the optical element produced by the bending moment exceeds the tensile strength of the brittle material, said compressive stress being sufficiently large that the net tensile stress is less than the tensile strength. 4. The gun-launched projectile of claim 3, wherein a total compressive stress on S1 of the optical element caused by the bending moment and the normal force does not exceed the compressive strength of the brittle material. 5. The gun-launched projectile of claim 4, wherein the brittle optical element has a compressive strength at least two times greater than its tensile strength. 6. The gun-launched projectile of claim 1, wherein the flexible material has a stiffness given by its Young's modulus that is at most one-twentieth ( 1/20) the stiffness of the brittle optical element. 7. The gun-launched projectile of claim 1, wherein the flexible material is a gasket that deforms in reaction to the inertial loading but does not provide an opposing shear force except that due to friction. 8. The gun-launched projectile of claim 1, wherein the flexible material is an adhesive that deforms in reaction to the inertial loading and provides an opposing shear force. 9. The gun-launched projectile of claim 8, wherein the tapered surfaces of the optical element and optical seat form an angle to the optical axis greater than an angle at which the shear stress on the adhesive exceeds its failure point. 10. The gun-launched projectile of claim 9, wherein the angle of the outer tapered surfaces of the optical element and optical seat is also greater than an angle at which the compressive force is too small to sufficiently offset the tensile stress. 11. The gun-launched projectile of claim 1, wherein the tapered surfaces of the optical element and optical seat form an angle to the optical axis less than an angle at which the inertial loading causes shear cracking at the interface of the forward facing and outer tapered surfaces of the optical element. 12. The gun-launched projectile of claim 11, wherein the angle of the outer tapered surfaces of the optical element and optical seat is also less than an angle at which the compressive stress is too small to sufficiently offset the tensile stress. 13. The gun-launched projectile of claim 1, wherein the outer tapered surfaces of the optical element and optical seat form an angle to the optical axis that lies in a range defined by, an upper bound set by the minimum of the angle at which the inertial load causes shear cracking at the interface of the forward facing and outer tapered surfaces of the optical element and the angle at which the compressive stress is too small to sufficiently offset the tensile stress, and a lower bound set by the maximum of an angle at which the shear stress on the material exceeds its failure point and the angle at which the compressive stress is too small to sufficiently offset the tensile stress. 14. The gun-launched projectile of claim 1, wherein the optical seat only supports the optical element along its outer tapered surface and not on S2. 15. The gun-launched projectile of claim 1, wherein the shape of S2 is such that inertial loading places S2 under tensile stress that would otherwise exceed the tensile strength of the lens material. 16. The gun-launched projectile of claim 15, wherein S2 is planar. 17. An optical assembly for use in a high G environment, comprising: an optical element formed of a brittle material having a compressive strength at least two times its tensile strength, said optical element comprising a forward facing surface, S1, an aft facing surface, S2, such that the overall diameter of S2 is smaller than the overall diameter of S1, with an outer tapered surface connecting S1 and S2; an optical seat having a complementary tapered surface around a clear optical aperture formed there-through and configured to engage the outer tapered surface of said optical element; and a flexible spacer between the optical element and the optical seat that supports the optical element in an initial unstressed position, said spacer formed of a material having a Young's modulus that is at most one-twentieth that of said brittle material, said optical assembly configured to react to the inertial load of the high G environment to drive the optical element into the flexible spacer and seat thereby producing a net tensile stress does not exceed the brittle material's tensile strength and to react to the removal of the inertial load to return the optical element to its initial unstressed position. 18. The optical assembly of claim 17, wherein the flexible material is an adhesive that deforms in reaction to the inertial loading and provides an opposing shear force. 19. The optical assembly of claim 18, wherein the tapered surfaces of the optical element and optical seat form an angle to an optical axis that lies in a range defined by, an upper bound set by the minimum of the angle at which the inertial load causes shear cracking at the interface of the forward facing and outer tapered surfaces of the optical element and the angle at which the compressive stress is too small to sufficiently offset the tensile stress, and a lower bound set by the maximum an angle at which the shear stress on the material exceeds its failure point and the angle at which the compressive force is too small due to the sheer stress on the material to sufficiently offset the tensile stress. 20. The optical assembly of claim 17, wherein the shape of S2 is such that inertial loading places S2 under tensile stress that would otherwise exceed the tensile strength of the lens material. 21. A method of mounting an optical element for use in a high G environment of a gun-launched projectile, comprising: providing a projectile having a central axis along the length of the projectile; mounting an optical assembly on the projectile that is approximately parallel to the central axis of the projectile at launch, said assembly including, an optical element formed of a brittle material, said optical element comprising a forward facing surface, S1, an aft facing surface, S2, such that the diameter of S2 is smaller than the diameter of S1, with an outer tapered surface connecting S1 and S2; an optical seat having a complementary tapered surface around a clear optical aperture formed there-through and configured to engage the outer tapered surface of said optical element; and a flexible spacer between the optical element and the optical seat that supports the optical element in an initial unstressed position; launching the projectile from a gun whereby the inertial loads drive the optical element into the flexible spacer and seat thereby producing both a bending moment that places S2 under tensile stress that exceeds the brittle material's tensile strength and a normal force on the element's outer tapered surface that that places S2 under compressive stress that at least partially offsets the tensile stress so that the net tensile stress is less than the material's tensile strength; and when the inertial loads are removed after launch, returning the optical element to its initial unstressed position. 22. The method of claim 21, wherein the inertial loading on the optical element exceeds 1,000 Gs. 23. The method of claim 21, wherein the brittle material has a compressive strength at least two times greater than its tensile strength. 24. The method of claim 23, wherein a total compressive stress on S1 of the optical element caused by the bending moment and the normal force does not exceed the material's compressive strength. 25. The method of claim 23, wherein the flexible spacer is formed of a material whose stiffness given by its Young's modulus is at most one-twentieth ( 1/20) the stiffness of the brittle material. 26. The method of claim 25, wherein the spacer material is an adhesive that deforms in reaction to the inertial loading and provides an opposing shear force. 27. The method of claim 26, wherein the outer tapered surfaces of the optical element and optical seat form an angle to the optical axis that lies in a range defined by, an upper bound set by the minimum of the angle at which the inertial load causes shear cracking at the interface of the forward facing and tapered surfaces of the optical element and the angle at which the compressive stress is too small to sufficiently offset the tensile stress, and a lower bound set by the maximum an angle at which the shear stress on the material exceeds its failure point and the angle at which the compressive force is too small to sufficiently offset the tensile stress.
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