Patent Application
20210231843
The present invention relates to materials for making fast steering optical mirrors for laser deflection, and more specifically to a composite material based on carbon fibers, into the manufacturing of fast steering optical mirrors.
For fast moving mirrors, e.g., as used for galvanometer scanners (Galvos) or single pivot-point mirrors, fast steering mirrors (FSM), all users are looking for lightweight mirrors with a maximum stiffness. A typical value used for the specification of mirrors is E/ρ2, with E: Young modulus and p: density.
Table 1 shows the typical values for actually used materials:
As can be seen from Table 1, carbon fiber reinforced polymer (CFRP) shows clear benefits compared to SiC and SiO2 and is not toxic as Beryllium.
Carbon fibers (CF) are fibers composed mostly of carbon atoms. Carbon fibers have several advantages including high stiffness, high tensile strength, low weight, high chemical resistance, high temperature tolerance and low thermal expansion. These properties have made carbon fiber very popular in aerospace, civil engineering, military, and motorsports, as well as other sports equipment. However, carbon fiber composite has not been incorporated into optical equipment, such as high-speed mirrors. There is little knowledge about suitable components (correct fibers and orientation, resins for composite and top coating) required for the composite material in the fast steering optical mirror, and the additional problem of outgassing at the coating for high reflectivity. Presently, in the optical community, carbon fiber composite is considered not suitable for fast steering mirrors.
Therefore, there is a long-felt need for suitable components in fast steering optical mirrors made of carbon fiber composite material and a method of introducing a composite material based on carbon fibers into the manufacturing of optical mirrors.
An embodiment of the present disclosure provides a fast steering optical mirror for laser beam deflection, moved by at least one rotational axis, including: a plate containing a plurality of carbon fiber layers laid up in a resin, wherein the plate includes a front face, at least a portion of the front face being polished and coated for laser light reflection; and wherein a surface normal of the front face is aligned orthogonal to the at least one rotational axis.
In a further embodiment, where the above mirror has one rotational axis, the plate includes a section for mounting to a driving motor; wherein the plate is aligned so that its centroid coincides with the one rotational axis and wherein the surface normal of the front face is aligned preferable orthogonal to the one rotational axis. One example application of this embodiment is a Galvo mirror.
In another further embodiment, where the above mirror has two orthogonal rotational axes, the plate includes a section for mounting to an electromagnetic drive; and wherein the surface normal of the front face is aligned orthogonal to one of the two orthogonal rotational axes. One example application of this embodiment is a 2-axes FSM.
An embodiment of the present disclosure provides a method of manufacturing a fast steering optical mirror for laser beam deflection including: forming a plate having a front face and a back face by laying up a plurality of carbon fiber layers in a resin; aligning the plate so that a surface normal of the plate is orthogonal to at least one rotational axis of the mirror; and polishing and coating at least a portion of the front face for light reflection.
The description of illustrative embodiments according to principles of the present invention is intended to be read in connection with the accompanying drawings, which are to be considered part of the entire written description. In the description of embodiments of the invention disclosed herein, any reference to direction or orientation is merely intended for convenience of description and is not intended in any way to limit the scope of the present invention. Relative terms such as “lower,” “upper,” “horizontal,” “vertical,” “above,” “below,” “up,” “down,” “top” and “bottom” as well as derivative thereof (e.g., “horizontally,” “downwardly,” “upwardly,” etc.) should be construed to refer to the orientation as then described or as shown in the drawing under discussion. These relative terms are for convenience of description only and do not require that the apparatus be constructed or operated in a particular orientation unless explicitly indicated as such. Terms such as “attached,” “affixed,” “connected,” “coupled,” “interconnected,” and similar refer to a relationship wherein structures are secured or attached to one another either directly or indirectly through intervening structures, as well as both movable or rigid attachments or relationships, unless expressly described otherwise. Moreover, the features and benefits of the invention are illustrated by reference to the exemplified embodiments. Accordingly, the invention expressly should not be limited to such exemplary embodiments illustrating some possible non-limiting combination of features that may exist alone or in other combinations of features; the scope of the invention being defined by the claims appended hereto.
This disclosure describes the best mode or modes of practicing the invention as presently contemplated. This description is not intended to be understood in a limiting sense, but provides an example of the invention presented solely for illustrative purposes by reference to the accompanying drawings to advise one of ordinary skill in the art of the advantages and construction of the invention. In the various views of the drawings, like reference characters designate like or similar parts.
CFRPs are composite materials. In this case the composite consists of two parts: a matrix and a reinforcement. In CFRP the reinforcement is carbon fiber, which provides the strength. The matrix is usually a polymer resin, such as epoxy, to bind the reinforcements together. Because CFRP consists of two distinct elements, the material properties depend on these two elements.
Reinforcement gives CFRP its strength and rigidity; measured by stress and elastic modulus respectively. Unlike isotropic materials like steel and aluminum, CFRP has directional strength properties. The properties of CFRP depend on the layouts of the carbon fiber and the proportion of the carbon fibers relative to the polymer.
In optical application, there are several components required for the composite material. And the composition of the best fibers, the orientation of the fibers and especially the resin, are selected so as to fulfill all requirements of the post processing (especially for the optical coating: heat resistance and outgassing) and the final application (maximum stiffness by using the correct fibers and the orientation of fibers for each layer in the composite structure).
The required stiffness is achieved by an orientation of the fibers in appropriate directions, depending on the design of each mirror.
The standard thickness for fibers is about 0.2 mm to 0.25 mm. The fiber component may be a gauze made by such fibers, or single fibers. In one embodiment, the composite is a mixture of both. In one embodiment, the single fibers are quite fine with a thickness of 100-120 μm. By using the finer fibers, more layers may be built up for a plate of fixed thickness. A typical example for a flat mirror can lay up according to
Here, UD (unidirectional) refers to a layer with fibers arranged in only one direction. Mesh correspond to bi-directional fiber layers. Fibers in two directions are weaved together to form a mesh, gauze, or twill. A specific lay-up scheme may be selected to provide more rigidity in certain desired directions that is suitable for a specific optical mirror design. In one embodiment, all fiber layers form a symmetrical stack with respect to its center (symmetrical axis).
For the coating process it is very important to find a suitable resin, which is heat resistant (more than 160° C.) and does not outgas in vacuum. An additional aging process can improve these properties. In one example embodiment, the resin used is ER405.
In one embodiment, an additional layer of pure resin is added to help to improve the results of the polishing process and can be also used to compensate distortion after manufacturing of the composite material. Also, it is very important to find a suitable resin, which is heat resistant (more than 160° C.) and does not outgas in vacuum. Typical materials used in some example embodiments include: RenLam LY5210 and Aradur 2954.
This additional layer (Top Coat) can be added either at one side or from both sides to compensate shrinkage and distortion. Typical thickness is between 0.1 mm and 1.0 mm. In one embodiment, the final optical coating can be a Silver-coating, an Aluminum-coating, a dielectric HR coating or any other coating, which is common for optical mirrors. Note that the carbon fiber material is sensitive to humidity. At the edges of the plate, the open fiber ends will absorb moisture, which will result in distortion. To avoid or reduce this effect, in one embodiment, a resin coating is applied to the cutting edges of the plate that have the open fiber ends. The resin is heat resistant and shows no outgassing at the coating process, similar to or the same as the resin, which is used in the top coating discussed above.
In one embodiment shown in
As the material is good to be milled, in one embodiment, the complete or a partial clamping unit can also be included in the design of the CF mirror. Note that typical mirror sizes start at an aperture of 6 mm can go easily up to 100 mm. However, designs according to embodiments of the present disclosure, there are no limitations by the material.
The optical mirrors made of carbon fiber composite material according to various embodiments of the present invention satisfy the long-felt need for suitable components in fast steering optical mirrors. The use of a composite material based on carbon fibers for making fast steering optical mirrors that meet the lightweight and stiffness requirements is an unexpected result, because carbon fiber composite is considered not suitable for fast steering mirrors by the optical community presently.
While the present invention has been described at some length and with some particularity with respect to the several described embodiments, it is not intended that it should be limited to any such particulars or embodiments or any particular embodiment, but it is to be construed so as to provide the broadest possible interpretation in view of the prior art and, therefore, to effectively encompass the intended scope of the invention. Furthermore, the foregoing describes the invention in terms of embodiments foreseen by the inventor for which an enabling description was available, notwithstanding that insubstantial modifications of the invention, not presently foreseen, may nonetheless represent equivalents thereto.
This application claims the benefit of U.S. Provisional Patent Application No. 62/966,781 filed on Jan. 28, 2020. The disclosure of U.S. Provisional patent Application 62/966,781 is hereby incorporated by reference.
| Number | Date | Country | |
|---|---|---|---|
| 62966781 | Jan 2020 | US |
