Patent Application
20170055731
When attaching large mirrors (i.e., greater than ˜0.5 meter diameter) to a mounting or external support structure, the goal is to do so in a way that does not disturb the “figure” or shape of the optical surface of the mirror. Surface distortion of a mirror's optical surface, or “figure error,” is typically held to very tight tolerances (e.g., a fraction of a millionth of an inch). The larger the mirror the more difficult it is to avoid distortion and meet the tolerance requirements. Adhesive is typically used to attach the mirror to an external support structure because other ways (e.g., fasteners) result in excessive distortion of the mirror. In some cases, a large mirror will have a relatively large mass of material at a mount location to reduce stress at the mount location, and therefore reduce distortion of the optical surface. A metal fitting is bonded or screwed to the mirror at this location for attachment to an external support structure. Another approach is to bond a metal insert into a cylindrical hole in the mirror, often at an intersection of support ribs on a back side of the mirror.
Features and advantages of the invention will be apparent from the detailed description which follows, taken in conjunction with the accompanying drawings, which together illustrate, by way of example, features of the invention; and, wherein:
Reference will now be made to the exemplary embodiments illustrated, and specific language will be used herein to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended.
As used herein, the term “substantially” refers to the complete or nearly complete extent or degree of an action, characteristic, property, state, structure, item, or result. For example, an object that is “substantially” enclosed would mean that the object is either completely enclosed or nearly completely enclosed. The exact allowable degree of deviation from absolute completeness may in some cases depend on the specific context. However, generally speaking the nearness of completion will be so as to have the same overall result as if absolute and total completion were obtained. The use of “substantially” is equally applicable when used in a negative connotation to refer to the complete or near complete lack of an action, characteristic, property, state, structure, item, or result.
As used herein, “adjacent” refers to the proximity of two structures or elements. Particularly, elements that are identified as being “adjacent” may be either abutting or connected. Such elements may also be near or close to each other without necessarily contacting each other. The exact degree of proximity may in some cases depend on the specific context.
An initial overview of technology embodiments is provided below and then specific technology embodiments are described in further detail later. This initial summary is intended to aid readers in understanding the technology more quickly but is not intended to identify key features or essential features of the technology nor is it intended to limit the scope of the claimed subject matter.
Although providing a relatively large mass of material at a mount location may effectively support a mirror with acceptable levels of distortion, this approach is not lightweight and may not be feasible for some applications, such as for mirrors that must be launched into space. While a metal insert bonded in a hole may not introduce weight concerns, this approach can result in unacceptable figure error due to the shrinkage of the adhesive in the hole as the adhesive cures, which can “print through” a deformation to the mirror's optical surface causing distortion that can exceed tolerances. In addition, a coefficient of thermal expansion (CTE) differential between any of the metal insert, the adhesive, and the mirror substrate can also cause figure error, which can be exacerbated when the temperature decreases as the mirror is transported to space. Furthermore, large lightweight mirrors often have a lot of weight concentrated at the mirror mount locations because the load transfer between the external support structure and the mirror is not structurally efficient and/or because adding material to the mirror substrate reduces the thermo-elastically induced figure error caused by the metal insert, adhesive, and the mirror substrate CTE differential. Thus, mounting of large, lightweight mirrors can be improved by reducing print through to the optical surface due to curing of the adhesive and by being thermally tolerant while not increasing weight.
Accordingly, a mirror mount system is disclosed that can limit print through to the optical surface due to curing of the adhesive to acceptable levels while being able to accommodate temperature changes without excessive distortion of the optical surface in a manner that does not increase weight. The mirror mount system can include a rib forming a support structure of a mirror, the rib having an attachment portion. The mirror mount system can also include an attachment fitting bonded to the attachment portion of the rib with an adhesive. The attachment portion can be sufficiently isolated from other portions of the rib structure such that loading in the other portions of the rib structure tending to distort the mirror, which is generated internal to the attachment fitting and the attachment portion, is minimized while providing adequate structural support for the mirror.
A mirror support structure is also disclosed that can include a rib forming a portion of a support structure of a mirror. The rib can have an attachment portion to bond to an attachment fitting with an adhesive. The attachment portion can be sufficiently isolated from other portions of the rib structure such that loading in the other portions of the rib structure tending to distort the mirror, which is generated internal to the attachment fitting and the attachment portion, is minimized while providing adequate structural support for the mirror.
One example of a mirror mount system 100 is illustrated in
As shown in the detailed cross-sectional view of
In one aspect, the attachment fitting 130 can include one or more adhesive injection ports 132a, 132b. The adhesive injection ports 132a, 132b can be configured to deposit adhesive on the adhesive interface surfaces 114a, 114b of the attachment portion 113. Typically, a circular-shaped injection bond spot will result, but other configurations are possible. The attachment fitting 130 can also include one or more witness holes 133 to view the progression of adhesive as it is injected to ensure that a sufficiently large bond spot is achieved. In one aspect, the attachment fitting 130 can be bonded to the rib 110 and then the strut 120a can be attached to the attachment fitting 130.
With continued reference to
In contrast, the attachment portion 113 can be isolated from other portions of the rib structure, such as by being located on a “lobe” of the rib 110, which can be defined, at least in part, by a protrusion 115 of the rib 110 having a profile identified by reference no. 105. As illustrated in
A rib profile identified by reference no. 106 illustrates another example of a lobe or protrusion 115′ of a rib in which the lobe or protrusion 115′ is undercut 117 to even further isolate the attachment portion of the rib compared to the profile identified by reference no. 105. It should be recognized that a lobe or protrusion of a rib can be of any suitable configuration that isolates the attachment portion from other portions of the rib structure sufficient to adequately reduce loading tending to cause distortion of the mirror, while providing adequate structural support for the mirror. Typically, the degree of mirror distortion due to the stresses originating at the lobe or protrusion can be balanced against the structural support provided by the lobe, which serves as the attachment location for the strut and is subjected to loading (e.g., operating loads) from the strut. In other words, the amount of isolation of the attachment portion can be configured to provide adequate joint strength while minimizing or reducing distortion of the mirror due to bond shrinkage and/or CTE mismatch to acceptable tolerances. Thus, the attachment portion can be further isolated to reduce mirror distortion with a trade-off in joint strength.
In one aspect, illustrated in
In one aspect, illustrated in
In one aspect, the attachment fitting 130 and the rib 110 can have approximately the same coefficient of thermal expansion (CTE). For example, the rib 110 can be constructed of silicon carbide (SiC) and the attachment fitting 130 can be constructed of Invar® (a nickel-iron alloy known for having a low CTE), although any suitable material can be used for either component, such as aluminum for both the attachment fitting and the rib. In one aspect, the attachment fitting 130 can be designed to have flexion in the direction of rib thickness, which can further reduce the impact that differential CTE will have on figure.
Ribs are a typical feature of many mirror supports, so incorporating the principles disclosed herein should not add any extra weight to a mirror.
Typically, the bond spots 213a, 231b will be circular, as illustrated in
In accordance with one embodiment of the present invention, a method for facilitating mounting a mirror is disclosed. The method can comprise providing a rib that forms a support structure of a mirror, the rib having an attachment portion. The method can also comprise facilitating bonding of an attachment fitting to the attachment portion of the rib with an adhesive, wherein the attachment portion is sufficiently isolated from other portions of the rib structure such that loading in the other portions of the rib structure tending to distort the mirror, which is generated internal to the attachment fitting and the attachment portion, is minimized while providing adequate structural support for the mirror. It is noted that no specific order is required in this method, though generally in one embodiment, these method steps can be carried out sequentially.
It is to be understood that the embodiments of the invention disclosed are not limited to the particular structures, process steps, or materials disclosed herein, but are extended to equivalents thereof as would be recognized by those ordinarily skilled in the relevant arts. It should also be understood that terminology employed herein is used for the purpose of describing particular embodiments only and is not intended to be limiting.
Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment.
As used herein, a plurality of items, structural elements, compositional elements, and/or materials may be presented in a common list for convenience. However, these lists should be construed as though each member of the list is individually identified as a separate and unique member. Thus, no individual member of such list should be construed as a de facto equivalent of any other member of the same list solely based on their presentation in a common group without indications to the contrary. In addition, various embodiments and example of the present invention may be referred to herein along with alternatives for the various components thereof. It is understood that such embodiments, examples, and alternatives are not to be construed as de facto equivalents of one another, but are to be considered as separate and autonomous representations of the present invention.
Furthermore, the described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. In the description, numerous specific details are provided, such as examples of lengths, widths, shapes, etc., to provide a thorough understanding of embodiments of the invention. One skilled in the relevant art will recognize, however, that the invention can be practiced without one or more of the specific details, or with other methods, components, materials, etc. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of the invention.
While the foregoing examples are illustrative of the principles of the present invention in one or more particular applications, it will be apparent to those of ordinary skill in the art that numerous modifications in form, usage and details of implementation can be made without the exercise of inventive faculty, and without departing from the principles and concepts of the invention. Accordingly, it is not intended that the invention be limited, except as by the claims set forth below.
