Patent Application
20090280244
This invention relates in general to coating techniques and, more particularly, to techniques for supporting workpieces during a coating process.
When fabricating optical components such as lenses, it is very common to form a coating on an optical surface of the component, where the coating provides desired optical or physical properties. For example, the coating may provide an anti-reflective (AR) characteristic, a filtering characteristic, physical protection for the component, some other characteristic, or a combination of two or more characteristics. These coatings often include multiple layers of different materials that collectively provide the desired characteristic(s).
It is often desirable that a coating completely cover an optical surface that is being coated. However, as discussed in more detail later, conventional workpiece support fixtures often support a workpiece in a manner that obstructs at least part of a peripheral portion of the optical surface, and these covered regions do not end up being coated. Consequently, although conventional support fixtures have been generally adequate for their intended purposes, they have not been entirely satisfactory in all respects.
A better understanding of the present invention will be realized from the detailed description that follows, taken in conjunction with the accompanying drawing, in which:
The support part 19 rotatably supports two workpiece support members 21 and 22. More specifically, two additional vertical axles 23 and 24 are rotatably supported on the support part 19. These additional axles are spaced circumferentially from each other about the primary axle 17, and each rotate about a respective additional vertical axis 26 or 27. The two support members 21 and 22 are each supported on a respective one of the axles 23 and 24 for rotation therewith about the associated axis 26 or 27. In the disclosed embodiment, the support members 21 and 22 are disk-shaped, but they could each alternatively have any other suitable shape. Although
A drive mechanism 31 such as an electric motor is coupled to the axle 17, in order to effect rotation of the axle 17 and the support part 19. A not-illustrated planetary gearing mechanism of a well-known type is provided and, in response to rotation of the support part 19 with respect to the housing 12, effects rotation of the additional axles 23 and 24 with respect to the support part 19. Thus, the workpiece support numbers 21 and 22 each undergo planetary movement about the primary axis 18 with respect to the housing 12. Each of the workpiece support members 21 and 22 has thereon a respective workpiece support fixture 36 or 37. The workpiece support fixtures 36 and 37 will be described in more detail later. The primary axle 17, the support part 19, the additional axles 23 and 24, the workpiece support members 21 and 22, and the workpiece support fixtures 36 and 37 collectively serve as a workpiece support mechanism. For simplicity and clarity,
Each of the workpiece support fixtures 36 and 37 is configured to removably support a respective workpiece 41 or 42. The workpieces 41 and 42 each have a surface 43 or 44 on a lower side thereof. The apparatus 10 is used to form respective coatings 51 and 52 on the surfaces 43 and 44 of the workpieces 41 and 42, in a manner discussed later. In the disclosed embodiment, the workpieces 41 and 42 with the coatings 51 and 52 are each an optical component of a well-known type, such as a lens. Therefore, they are described here only briefly, to the extent necessary to facilitate an understanding of various aspects of the present invention. Further, it should be understood that the coating apparatus 10 is not limited to use for coating optical components, but instead can be used for coating any of a wide variety of other types of workpieces.
It would be possible for each of the coatings 51 and 52 to be only a single layer of a single material. But in the disclosed embodiment, the coatings 51 and 52 each happen to include a plurality of different layers, involving the use of one material for some layers, another material for other layers, and so forth. By interleaving different layers of different materials in a known manner, the coatings 51 and 52 can each be given certain desired optical characteristics. For example, the coatings 51 and 52 may each provide an anti-reflective (AR) characteristic that causes little or no reflection of a selected range of wavelengths, such as a range corresponding to visible light.
In some cases, the multi-layer coatings 51 and 52 will be configured in a known manner to provide a combination of two or more desired optical characteristics. For example, a given coating might provide an anti-reflection characteristic as to one range of wavelengths, such as visible light, while also filtering out wavelengths in a different range of wavelengths, such as a range associated with laser energy.
As another example, if the optical workpiece 41 or 42 happens to be made of a relatively soft material that was selected because it provides certain desirable optical properties, the coating 51 or 52 may be configured to be physically harder than the associated workpiece 41 or 42, in order to help physically protect the material of the workpiece 41 or 42. Thus, a given coating 51 or 52 may provide an anti-reflection characteristic, while also being physically harder than the material of the associated workpiece 41 or 42, in order to help physically protect the workpiece. The discussion here of anti-reflection characteristics, filtering characteristics and hardness characteristics is merely exemplary. The coatings 51 and 52 may each provide some or all of these characteristics, and/or any of a variety of other characteristics, separately or in combination.
The coating apparatus 10 includes a source 62 within the housing 12, in a lower portion of the chamber 13. The source 62 is spaced downwardly from the support part 19. The source 62 and the drive mechanism 31 are both controlled by a control unit 64 of a known type. Although
The source 62 is a device of a type well known in the art, and is therefore described here only briefly. In the disclosed embodiment, the source 62 is a type of device commonly referred to as an electron beam evaporator. However, the source 62 could alternatively be any other suitable type of device. The source 62 contains two or more different materials that will be used to form respective layers in each of the multi-layer coatings 51 and 52, and the source can selectively evaporate any of these different materials. At any given point in time, the source 62 will typically be evaporating only one of the multiple materials that it contains. But in some situations, the source may simultaneously evaporate two or more of these different materials.
When the source 62 is evaporating a material, a plume of the evaporated material travels upwardly, as indicated diagrammatically by arrows 71-74. The plume 71-74 has a dispersion angle 91. The plume 71-74 from the source 62 coats the surfaces 43 and 44 on the workpieces 41 and 42 as the workpieces pass above the source 62.
As discussed above, the flange 102 on the workpiece support fixture 36 has an inside diameter 107. The workpiece surface 122 that is to be coated has a diameter 131 that is greater than the diameter 107. Consequently, when a coating is formed on the surface 122, the coating has a diameter 107, and does not cover the peripheral edges of the surface 122.
In the case of the lens or workpiece 121, there is a further consideration. As noted above, the workpiece 121 is relatively thin. The material of the workpiece 121 may have a coefficient of thermal expansion (CTE) that is different from the CTE of the workpiece support fixture 36. If the interior of the chamber 13 is heated during a coating operation, the workpiece 121 may expand faster than the fixture 36, causing compressive forces to be exerted on the workpiece 121 by the fixture 36, and thereby causing the workpiece 121 to shatter. Similarly, if the interior of the chamber 13 is cooled during a coating operation, and if the fixture 36 contracts more rapidly than the workpiece 121, the fixture 36 may exert compressive forces on the workpiece 121 that cause it to shatter.
The support wires are provided at circumferentially spaced locations about the workpiece 41. Each has a vertical central portion 206 or 207, and an upper end portion 208 or 209 that is bent to extend horizontally outwardly at a right angle to the associated central portion 206 or 207. The workpiece support fixture 201 includes a clamping mechanism having two annular clamping elements 211 and 212 that are capable of a small amount of relative vertical movement. The upper end portions 208 and 209 of the wires 203 and 204 are each removably clamped between the clamping elements 211 and 212.
The support wires 203 and 204 each also have a lower end portion 216 or 217 that is bent to extend at approximately a right angle to the associated central portion 206 or 207, and approximately parallel to an outwardly-facing cylindrical side surface 218 of the workpiece 41. In this regard,
With reference to
Although
The workpiece support fixture 251 also includes a piece of flexible, vacuum-compatible tape 271 that extends around both the workpiece 41 and the lower end of the support member 256, in engagement with each. The tape includes an elongate flexible strip or carrier 273, with an adhesive layer 274 on the inner side thereof. The lower portion of the adhesive layer 274 engages the side surface 218 on the workpiece 41, and the upper portion of the adhesive layer engages the lower portion of the outwardly facing side surface on the support member 256. In the disclosed embodiment, the tape 271 is a product obtained commercially under the trademark KAPTON® from C.S. Hyde Company, Inc. of Lake Villa, Ill. KAPTON® tape is commercially available in a variety of widths and with a variety of different levels of adhesion, and the particular tape selected for use at 271 will depend on factors such as the size and weight of the particular workpiece that is to be supported. Although the disclosed embodiment uses KAPTON® tape, it would alternatively be possible to use any other suitable part.
Although
It will be noted from
Although a selected embodiment has been illustrated and described in detail, it should be understood that a variety of substitutions and alterations are possible without departing from the spirit and scope of the present invention, as defined by the claims that follow.
