Laterally flexible mounting structure

Abstract

A method and apparatus for a mounting structure including a first arm having a first stiffness and a second arm having a second stiffness, the first stiffness being less than the second stiffness in at least one degree of freedom. The first arm includes a flex region capable of deflecting in response to a load. In an embodiment, the mounting structure is capable of movably securing the antenna array to a pedestal.

Description

[Background technology]

[0001] Radar antennas mounted on a deployment mechanism typically require a means to manage thermal mismatch stresses and deflections between the antenna structure and the mechanism due to bulk temperature differences. The antenna may experience significantly higher temperatures than the deployment mechanism. For large span structures, a coaxial pin connection may provide the pivot for deployment. A common configuration to address thermal mismatch across large spans is for the mechanism to have degrees of freedom to allow the structures to expand and contract relative to one another without resistance. In some known systems, this is accomplished using two or more pin joint connections about which the radar antenna rotates from a stowed position to a deployed position for operation. It is common for a single pin joint to be axially constrained and therefore all loads act axially. The other pin joint(s) provide radial restraint but are allowed to float axially to allow differential movement between the structures due to bulk temperature and material mismatch. For applications with small spans and thermal mismatches, special treatment of a doubly fixed pivot cannot be used. In this configuration, thermal stresses and deflections are absorbed by the primary structure and must be designed accordingly. Summary of the Invention

[0002] An embodiment of the present disclosure provides a method and apparatus for a mounting structure having first and second support arms with different load response characteristics. In an embodiment, the first and second support arms connect a structure, such as an antenna array, to a dual elevation drive rotary actuator unit. The actuator output bearing defines the elevation pivot axis and can provide a structural load path from the antenna to the support structure. The first support arm provides a relatively flexible region that allows flexibility in a direction parallel to the rotation axis. The second support arm provides a relatively rigid connection in all degrees of freedom, directly coupling the antenna structure to one of the actuators. This flexibility provides a leakage path over large spans and reduces reaction forces generated by thermal mismatch between the antenna and the support structure.

[0003] In an embodiment, stiffness about the axis of rotation is approximately equal to reduce torsional deflection. Flexibility is achieved by utilizing a thin section in the first support arm that acts as a beam structure to allow for a lower spring rate in the narrow dimension while maintaining higher stiffness in the other two directions.

[0004] One or both of the support arms may comprise the same or different materials having properties that meet the needs of a particular application. In an exemplary embodiment, the first and second support arms comprise high strength alloy steel, providing high specific strength, allowing for thinner sections, resulting in increased flexibility while maintaining the required strength. Additionally, high toughness properties support many load cycles over the life of the system and resist fatigue failure.

[0005] In an exemplary embodiment, the flexible region of the first support arm is approximately 12:1 in length to thickness (e.g., 3.5 inches by 0.30 inches) and is sized to keep stresses below the endurance limit of the material. This configuration reduces load build-up due to thermal mismatch stresses while distributing the axial load between the two support arms. In an exemplary embodiment, the stiffer arm acts on the majority of the lateral load resulting in approximately 70 / 30% load sharing between the first and second support arms. This type of load sharing allows for more optimal loading of the elevation actuator bearings since 100% of the lateral load is not absorbed by a single actuator. This allows for a compact form factor and a more direct connection of the actuator torque path to the load.

[0006] In one aspect, a system includes a base, an instrument, and a mounting structure for movably securing the instrument to the base, the mounting structure including a first arm having a first stiffness and a second arm having a second stiffness, the first stiffness being less than the second stiffness in at least one degree of freedom.

[0007] The system may further include one or more of the following features: the base includes a pedestal, the device includes an antenna array, the pedestal and the mounting structure are configured to move the antenna array from a stowed position to a deployed position by pivoting the antenna array about an elevation axis, the at least one degree of freedom includes translational motion along the elevation axis or an axis parallel to the elevation axis, the first arm includes a flex region configured to flex in response to a lateral load, the flex region having a thickness less than a thickness of an adjacent region of the first arm, a length of the flex region being at least ten times the thickness of the flex region, the flex region deflects in response to a thermal mismatch between the pedestal and the antenna array, reaction forces at the mounting portion of the mounting structure due to an externally applied lateral load condition are distributed unevenly between the first and second sides, and / or reaction forces at the mounting portion of the mounting structure due to thermal expansion or contraction load conditions are distributed evenly between the first and second sides.

[0008] In one aspect, a method includes movably securing an apparatus to a base by a mounting structure, the mounting structure including a first arm having a first stiffness and a second arm having a second stiffness, the first stiffness being less than the second stiffness in at least one degree of freedom.

[0009] The method may further include one or more of the following features: the base includes a pedestal, the device includes an antenna array, the pedestal and the mounting structure are configured to move the antenna array from a stowed position to a deployed position by pivoting the antenna array about an elevation axis, the at least one degree of freedom includes translational motion along the elevation axis or an axis parallel to the elevation axis, the first arm includes a flex region configured to flex in response to a lateral load, the flex region having a thickness less than a thickness of an adjacent region of the first arm, a length of the flex region being at least ten times the thickness of the flex region, the flex region deflects in response to a thermal mismatch between the pedestal and the antenna array, reaction forces at the mounting portion of the mounting structure due to an externally applied lateral load condition are distributed unevenly between the first and second sides, and / or reaction forces at the mounting portion of the mounting structure due to thermal expansion or contraction load conditions are distributed evenly between the first and second sides.

[0010] The foregoing features of the present disclosure, as well as the disclosure itself, can be more fully understood from the following description of the drawings. [Brief description of the drawings]

[0011] [Figure 1A] 1 is a diagrammatic representation of a mounting structure for mounting the antenna array on a pedestal. [Figure 1B] 1 is a diagrammatic representation of a mounting structure for mounting the antenna array on a pedestal. [Figure 2A] FIG. 1 is a front view of a prior art mounting structure having a clamp joint. [Figure 2B] FIG. 1 is a front view of a prior art mounting structure having a floating joint. [Diagram 3] FIG. 2 is an isometric view of an exemplary first arm having a bend region, the first arm forming part of the mounting structure of FIGS. 1A and 1B. [Figure 3A] FIG. 4 is a side view of the first arm of FIG. 3. [Figure 3B] FIG. 4 is a top view of the first arm of FIG. 3. [Figure 3C]FIG. 4 is a front view of the first arm of FIG. [Figure 3D] 4 is a schematic diagram of the first arm of FIG. 3 showing deflected and undeflected configurations; FIG. [Figure 4] FIG. 2 is an isometric view of an exemplary second arm forming part of the mounting structure of FIGS. 1A and 1B. [Figure 5A] FIG. 2 shows a side view of the first and second arms under a positive lateral load. [Figure 5B] FIG. 1 illustrates a side view of the first and second arms under a negative lateral load. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] 1A and 1B illustrate an exemplary system 100 including a device 102, such as an antenna array, supported by a support structure 104, such as a pedestal. In an exemplary embodiment, the support structure 104 is capable of rotating the antenna array 102 from a stowed position to a deployed position. In the illustrated embodiment, the antenna array 102 is shown in the deployed position. The mounting structure may include a first arm 106 and a second arm 108 for securing the antenna array 102 to the support structure 104. As described more fully below, the first arm 106 is more flexible in at least one axis than the second arm 108. In an embodiment, the antenna array 102 pivots about an elevation axis 110. Lateral movement of the antenna array 102 is along the elevation axis 110. That is, lateral movement / load is laterally on the elevation axis 110.

[0013] The first and second arms 106, 108 provide unequal reaction loads to the support structure 104 due to externally applied loading conditions such as inertial transport loads or wind loads, because the first arm 106 is more flexible in response to lateral loads than the second arm 108. This arrangement compensates for the different thermal conditions and materials between the array assembly and the pedestal. During operation, especially in cold environments, the antenna array 102 is significantly warmer than the pedestal 104 and the mounting structures 106, 108. The first arm 106 is laterally flexible to prevent large thermal stresses from developing between the first and second arms due to mismatches between materials and bulk temperatures. Thermally induced reaction loads are distributed evenly between the support structures on either side of the pedestal 104. Under combined (external and thermally induced) loading conditions, the reaction forces and moments are distributed between the first arm 106 and the second arm 108, providing a structurally efficient configuration in which both structures act on a portion of the total load.

[0014] This is in contrast to conventional systems where substantially 100% of the lateral load is carried on one side by one arm while the other arm is free to float to accommodate thermal mismatch. FIG. 2A shows a prior art axis joint with a clamped bearing 200 that carries the lateral load. FIG. 2B shows a prior art axis joint with a floating bearing 202 that does not carry any lateral load. In this configuration, the elevation axis has two separate pivot joints along a common axis, one of which is axially constrained (FIG. 2A) and the other is "floating" (FIG. 2B). This allows a degree of freedom to allow for thermal mismatch between the array and the lifting structure, but forces all lateral loads to be acted on by a single side, i.e., the clamped side in FIG. 2A, which drives the structural design of that side such that the bearings of the pivot axis and support structure need to be sized to accommodate 100% lateral load.

[0015] 3, 3A, 3B, and 3C show a first arm 300 having a base portion 302 and an arm portion 304 extending from the base portion. The base portion 302 includes a series of holes 306 through which the arm can be secured to an antenna array (not shown) using an attachment mechanism such as bolts.

[0016] In an exemplary embodiment, the arm portion 304 includes a bending region 308 and a pivot region 310. In an embodiment, the bending region 308 has a thickness 312 that is less than at least a portion of an adjacent pivot region 310. In one particular embodiment, the height 314 of the bending region 308 is about 12 times the thickness 312 of the bending region 308.

[0017] In the illustrated embodiment, the arm portion 304 includes a series of holes 318 for mounting the first arm 300 to a pedestal that may include a rotational actuator (not shown). As described above, the pedestal is capable of pivoting the antenna array about an elevation axis from a stowed position to a deployed position.

[0018] The relaxed flex region 308 between the pivot region 310 and the base 302 provides increased flexibility in the lateral direction only. The flex region 300 acts as a beam with its ends fixed to the base portion 302 and the pivot region 310.

[0019] The second arm 400 has a base portion 402 and an arm portion 404 extending from the base portion. The base portion 402 includes a series of holes 406 through which the arm can be secured to an antenna array (not shown) using an attachment mechanism such as bolts.

[0020] The second arm 400 does not have a bend region like the first arm 300. To provide added strength, the second arm 400 may include a series of gussets 410 extending from the base 402.

[0021] The first and second arms 300, 400 together provide the structural strength and stiffness necessary to support the array. In the presence of inertial transport and / or motion loads, the complementary lateral stiffness of the first and second arms 300, 400 results in approximately 30 / 70% load sharing between the pedestal drive unit bearings. In addition, the laterally flexible configuration of the first arm 300 partially mitigates the build-up of thermally induced loads along the elevation axis. The advantages of lower bearing load requirements will be readily apparent to those skilled in the art.

[0022] The relative stiffness of each of the degrees of freedom depends on the structure of each arm, as shown for the first arm 300 in Figure 3 and for the second arm 400 in Figure 4. As shown in Figure 3, the flex region 308 provides low stiffness for relative translation between the base portion 302 and the pivot region 310 in the x-axis (referred to above as lateral movement). In contrast, the second arm 400, which includes the gusset 410 but does not include the flex region, has high stiffness in each of the listed degrees of freedom.

[0023] The structure of the first arm 300 provides high stiffness in y-axis and z-axis translation, as well as relative rotation about the x-axis, between the base portion 302 and the pivot region 310. The first arm 300 has low stiffness for relative rotation about the z-axis and medium stiffness for relative rotation about the y-axis.

[0024] In the illustrated embodiment, the length of the elongated beam with a triangular shape provides adequate stiffness in the longitudinal (z) and vertical (y) directions, high moment stiffness in Rx, moderate stiffness in Ry to allow for small magnitude torsion (Ry), and low moment stiffness in Rz to allow growth accommodation in the lateral (x) direction.

[0025] It is understood that low, medium, and high are relative terms used to facilitate understanding of the exemplary embodiments, and the use of these terms should not be construed as limiting in any way.

[0026] It is understood that the first and second arms 300, 400 can include any practical shape to meet the needs of a particular application. In an exemplary embodiment, the arms have a generally triangular shape to distribute the load of the antenna array mounted on the pedestal.

[0027] 3D, it can be seen that the bending region 308 of the first arm 300 can bend under a simple translational load. The first arm 308 initially has an undeflected shape with the base portion 302 perpendicular to the bending region 308. Upon application of a load, the bending region 308 bends and the first arm transitions to a deflected shape. As can be seen, the surface of the base portion 302 drops somewhat as the first arm 308 moves from the undeflected shape to the deflected shape. The base portion 302 also translates by some delta amount.

[0028] The magnitude of the drop is negligible in the actual value of the deflection. The drop can be nominally defined as:

number

[0029] FIG 5A shows a comparison of the deflection of the first arm 300 (FIG 3) and the second arm 400 (FIG 4) for a 1 kip load under a lateral load condition. As described above, the first arm 300 has a flex region 308 that can deflect in response to a lateral load. FIG 5B shows a comparison of the deflection of the first arm 300 and the second arm 400 for a -1 kip load under a lateral load condition.

[0030] It will be appreciated that the first and second arms 300, 400 can comprise any suitable material having desired stiffness characteristics. The first and second arms can comprise the same or different materials and can include combinations of the same or different materials. An example of a suitable material for the first and second arms includes ASTM A514 alloy steel plate.

[0031] It is further understood that the first and second arms and the connected system can be configured to distribute the load in a variety of ways to meet the needs of a particular application. In an exemplary embodiment, the lateral load is percent distributed 30 / 70. In alternative embodiments, other load distributions can be achieved.

[0032] Although exemplary embodiments of the present disclosure have been described, it will be apparent to one of ordinary skill in the art that other embodiments incorporating these concepts may be used. The embodiments contained herein should not be limited to the disclosed embodiments, but rather should be limited only by the spirit and scope of the appended claims. All publications and references cited herein are expressly incorporated herein by reference in their entirety.

[0033] Elements of different embodiments described herein can be combined to form other embodiments not specifically described above. Various elements that are described in the context of a single embodiment may also be provided separately or in any suitable subcombination. Other embodiments not specifically described herein are also within the scope of the following claims.

Claims

1. 1. A system comprising: A base including a pedestal; an apparatus including an antenna array; A mounting structure for movably fixing the device to the base, a first arm having a first stiffness, the first arm including a flex region configured to deflect in response to a thermal mismatch between the base and the antenna array; a second arm having a second stiffness, the first stiffness being less than the second stiffness in at least one degree of freedom; The mounting structure; Including, the system.

2. The system of claim 1 , wherein the base and the mounting structure are configured to move the antenna array from a stowed position to a deployed position by pivoting the antenna array about an elevation axis.

3. The system of claim 2 , wherein the at least one degree of freedom includes translation along the elevation axis or an axis parallel to the elevation axis.

4. The system of claim 3, wherein the flex region is configured to flex in response to a lateral load.

5. The system of claim 4 , wherein the bending region has a thickness less than a thickness of an adjacent region of the first arm.

6. The system of claim 5 , wherein the length of the bend region is at least 10 times the thickness of the bend region.

7. 7. The system of claim 6, wherein reaction forces at a mounting portion of the mounting structure due to an externally applied lateral load condition are distributed unevenly between the first side and the second side.

8. The system of claim 6 , wherein reaction forces at a mounting portion of the mounting structure due to thermal expansion or contraction loading conditions are evenly distributed between the first side and the second side.

9. 1. A method comprising: A mounting structure is used to movably fasten a device including an antenna array to a base including a pedestal, the mounting structure comprising: a first arm having a first stiffness, the first arm including a flex region configured to deflect in response to a thermal mismatch between the base and the antenna array; a second arm having a second stiffness, the first stiffness being less than the second stiffness in at least one degree of freedom; said fixing method.

10. 10. The method of claim 9, wherein the base and mounting structure are configured to move the antenna array from a stowed position to a deployed position by pivoting the antenna array about an elevation axis.

11. The method of claim 10 , wherein the at least one degree of freedom comprises translation along the elevation axis or an axis parallel to the elevation axis.

12. The method of claim 11, wherein the flex region is configured to flex in response to a lateral load.

13. The method of claim 12 , wherein the bend region has a thickness less than a thickness of an adjacent region of the first arm.

14. The method of claim 13 , wherein the length of the bend region is at least 10 times the thickness of the bend region.

15. 15. The method of claim 14, wherein reaction forces at a mounting portion of the mounting structure due to an externally applied lateral load condition are distributed unevenly between the first side and the second side.

16. 15. The method of claim 14, wherein reaction forces at a mounting portion of the mounting structure due to thermal expansion or contraction loading conditions are evenly distributed between the first side and the second side.

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