Abstract:
An apparatus includes a workpiece support, a source that is spaced from the workpiece support and can emit a plume of coating material toward the workpiece support, and plume adjusting structure that, between the source and workpiece support, can influence a plume of material flowing from the source. A different aspect involves a method that includes emitting from a source a plume of coating material that flows toward a workpiece support, and adjusting, between the source and the workpiece support, a plume of material flowing from the source.

Description:
FIELD OF THE INVENTION 
     This invention relates in general to techniques for coating surfaces and, more particularly, to techniques for coating curved surfaces. 
     BACKGROUND 
     While fabricating optical components such as lenses, it is very common to form a coating on a 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). 
     One problem with conventional coating techniques is that any given layer in the coating may have a thickness that is not uniform throughout the layer. For example, where a coating is on a relatively highly curved surface, it is not unusual for a given layer within the coating to have a peripheral region that is as much as 30% to 50% thinner than a central region of that layer, or even more than 50% thinner. Further, different layers in the same coating often have different variations in thickness. For example, one layer may be 30% thinner in a peripheral region than in a central region, while another layer may be 50% thinner in the peripheral region than in the central region. Consequently, the ratios of thicknesses of different layers in the peripheral region can be different from the ratios of the thicknesses of those same layers in the central region. 
     Thus, even assuming that the layers of a coating all have the proper thicknesses or ratios of thickness in the central region, the thicknesses in the peripheral region will typically not be correct and, moreover, the ratios of thicknesses in the peripheral region will typically not be correct. As a result, the coating may provide the desired characteristics in the central region, but may fail to provide the desired characteristics in the peripheral region, or may at least exhibit a degradation of the desired characteristics in the peripheral region. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A better understanding of the present invention will be realized from the detailed description that follows, taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a diagrammatic sectional side view of a coating apparatus that embodies aspects of the present invention. 
         FIG. 2  is a diagrammatic sectional side view of a coating apparatus that is an alternative embodiment of the coating apparatus of  FIG. 1 , and that embodies aspects of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  is a diagrammatic sectional side view of a coating apparatus  10  that embodies aspects of the present invention. The coating apparatus  10  includes a housing  12  with a chamber  13  therein. The housing  12  supports a primary axle  17  for rotation about a primary vertical axis  18 . A disk-shaped support part  19  is supported on the axle  17  for rotation with the axle about the axis  18 . 
     The support part  19  rotatably supports two disk-shaped 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 . Although  FIG. 1  shows two additional axles  23  and  24  and two workpiece support members  21  and  22 , it would alternatively be possible to have one or more further workpiece support members that each have an additional axle, wherein all the additional axles are spaced circumferentially from each other about the primary axle  17 . 
     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 members  21  and  22  each undergo planetary movement about the primary axis  18  with respect to the housing  12 . The primary axle  17 , the support part  19 , the additional axles  23  and  24 , and the workpiece support members  21  and  22  collectively serve as a workpiece support mechanism. 
     Each of the workpiece support members  21  and  22  is configured to removably support a respective workpiece  41  or  42 . The workpieces  41  and  42  each have on the lower side thereof a relatively highly curved surface  43  or  44 . The apparatus  10  is used to form respective coatings  51  and  52  on the respective curved surfaces  43  and  44  of the workpieces  41  and  42 , in a manner discussed in more detail later. The coating apparatus  10  is not limited to use for coating highly curved surfaces, and in fact can be used to coat surfaces having a variety of different shapes. However, the coating apparatus  10  is very effective when used to coat highly curved surfaces such as those shown at  43  and  44 . In the disclosed embodiment, the workpieces  41  and  42  with the coatings  51  and  52  thereon are each an optical component of a type well known in the art, such as a lens. Therefore, they are described here only briefly, to the extent necessary to facilitate an understanding of the structure and operation of the coating apparatus  10 . Further, it should be understood that the coating apparatus  10  is not limited to use for coating optical components, but instead can alternatively be used for coating 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 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 be anti-reflective (AR) coatings that provide 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 may provide an anti-reflection characteristic as to one range of wavelengths, such as visible light, while also filtering out wavelengths in a different range, 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  thereon 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  may provide an anti-reflection characteristic, while also being physically harder than the material of the 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. 
     In the multi-layer coatings  51  and  52 , the layers may all have the same thicknesses, or some layers may be intentionally thicker than other layers. Ideally, it is desirable that the thickness of each layer be relatively uniform throughout the layer. As a practical matter, that is not always possible. But even if the thickness of a given layer varies somewhat, it is desirable that, as between any two layers, the ratio of their thicknesses remain relatively uniform across the entire surface  33  or  34 . The disclosed coating apparatus  10  is configured to achieve good uniformity of the ratios of thicknesses within the coatings  51  and  52 . 
     The apparatus  10  includes two spaced sources  61  and  62  in a lower portion of the housing  12 . In the disclosed embodiment, the sources  61  and  62  are each spaced radially from the primary axis  18 , and are each positioned approximately below the path of travel of the workpiece support members  21  and  22 , at locations spaced circumferentially about the primary axis  18 . Alternatively, however, it would be possible for the sources  61  and  62  to be positioned at various other locations within the housing  12 . The sources  61  and  62  are each a device of a type well known in the art, and are therefore described only briefly here. In the disclosed embodiment, the sources  61  and  62  are each a device commonly referred to as an electron beam evaporator. However, either or both of the sources  61  and  62  could alternatively be any other suitable type of device. Although  FIG. 1  shows two sources  61  and  62 , it would alternatively be possible to provide three or more sources in the apparatus  10 . 
     The source  61  contains one material that will be used to form one or more layers in each of the multi-layer coatings  51  and  52 , and the source  62  contains a different material that will be used to form one or more other layers in each of the multi-layer coatings  51  and  52 . The sources  61  and  62  are both controlled by a control unit  64 . Typically, only one of the sources  61  and  62  will be active at any given point in time, but there can be circumstances under which the sources  61  and  62  will both be active at the same time. 
     The sources  61  and  62  each evaporate the coating material provided therein, so that a plume of the evaporated material travels upwardly, as indicated diagrammatically by arrows  71 - 74  for the source  61 , and by arrows  81 - 86  for the source  62 . It will be noted that the plume  71 - 74  of material from the source  61  has a flow pattern that is different from the plume  81 - 86  of material from the source  62 . For example, the dispersion angle  91  of the plume  71 - 74  is less than the dispersion angle  92  of the plume  81 - 84 . This can result from any of various different factors, including differences between the sources  61  and  62 , differences in the materials that are being evaporated, or other factors. 
     The narrower plume  71 - 74  from the source  61  basically coats the workpieces  41  and  42  as they pass directly above the source  61 . In this regard, when one of the workpieces  41  and  42  is above the source  61 , and due to the significant curvature of the surfaces  43  or  44  thereon, the plume  71 - 74  will impinge on the central region of the curved surface approximately perpendicular thereto, but will impinge on the peripheral regions of the curved surface at a relatively steep angle. Consequently, the resulting coating will tend to be thicker in the central region that in the peripheral regions of the highly curved surface. 
     In contrast, the wider plume  81 - 86  from the source  62  will exhibit a similar coating effect on highly curved surfaces that are passing above it, but also has the potential to simultaneously coat peripheral edges of other workpieces that are not above it. For example, arrow  81  in  FIG. 1  represents a peripheral portion of the plume  81 - 86 , and a broken-line arrow  96  represents a potential path of travel of the evaporated material in this peripheral portion  81  of the plume  81 - 86 . As indicated by arrow  96 , in the absence of any preventative measure, the peripheral portion  81  of the plume  81 - 86  would tend to travel to and be deposited on a peripheral portion of the surface  43  of a workpiece  41  that is not currently above the source  62 . 
     Thus, when source  62  is being used to form a layer in each of the coatings  51  and  52 , that layer would potentially receive proportionally more coating material in its peripheral regions than a layer formed by the source  61 . Stated differently, a layer formed with the source  61  might have a peripheral region that is 50% thinner than its central region, while a layer formed with the source  62  could potentially have a peripheral region that is only 30% thinner than its central regions. Consequently, in the absence of preventative measures, the various different layers of a coating could all have the desired thicknesses and desired ratios of thicknesses in the central region of the coating, but the same layers could have different ratios of thicknesses in the peripheral regions of the coating. As a result, the central region of the coating could accurately provide desired optical (such as anti-reflection or filtering), whereas peripheral regions of the same coating might fail to provide these optical characteristic, or might provide them with reduced performance. 
     In order to improve the quality and performance of the coatings  51  and  52 , the apparatus  10  in  FIG. 1  includes a shield  101  that is supported by a shield support  103 . The position of the shield  101  is selected to provide an appropriate degree of influence on a peripheral portion of the plume  81 - 86  of material from the source  62 . In particular, the shield  101  influences a peripheral portion  81  of the plume  81 - 86 , so that this portion  81  of the plume is diverted away from the original path  96  that it otherwise would have followed toward peripheral portions of workpieces that are not located approximately above the source  62 . Instead, due to shield  101 , the relatively wide plume  81 - 86  from the source  62  is adjusted so that material therein is limited to coating workpieces that are located approximately above the source  62 . 
     The shield  101  thus serves to avoid an undesired increase in thickness in the peripheral regions of layers formed with the source  62 , which in turn results in greater uniformity in the ratios of thicknesses of different layers. As a result, the intended characteristics of the coatings  51  and  52  are significantly more uniform throughout these coatings than would be the case if the shield  101  was not present in the apparatus  10 . 
       FIG. 2  is a diagrammatic sectional side view of a coating apparatus  210  that is an alternative embodiment of the coating apparatus  10  of  FIG. 1 , and that embodies aspects of the present invention. In  FIG. 2 , equivalent parts are identified with the same reference numerals used in  FIG. 1 , and these parts are not described again in detail here. The following discussion focuses on differences between the apparatus  210  of  FIG. 2  and the apparatus  10  of  FIG. 1 . 
     The coating apparatus  10  of  FIG. 1  includes two separate sources  61  and  62 , and each of these sources evaporates a respective different material. In contrast, the coating apparatus  210  of  FIG. 2  includes a single source  262 . The source  262  is a device of a type well known in the art, and can selectively evaporate any one of two or more different materials. In  FIG. 2 , the source  262  is shown evaporating the material that produces the plume  81 - 86 , or in other words the same material that was evaporated by the source  62  in  FIG. 1 . But the source  262  can alternatively evaporate other materials. For example the source  262  contains and can evaporate the same material that was in the source  61  of  FIG. 1 . Thus, the source  262  can produce the plume  81 - 86  that is shown in  FIG. 2 , can alternatively produce a plume that is equivalent to the plume  71 - 74  in  FIG. 1 , or can alternatively produce yet another plume of still some other material. 
     In  FIG. 2 , the shield support  103  can move the shield  101  between an operational position  101 A, a retracted position  101 B, and an intermediate position  101 C. In the position  101 A, the shield  101  influences the plume  81 - 86  in the manner discussed above in association with  FIG. 1 . In the retracted position  101 B, the shield  101  does not influence the material of any of the various different plumes that the source  262  can generate. In the intermediate position  101 C, the shield  101  influences a plume of material emitted by the source  262 , other than either of the plumes  71 - 74  and  81 - 86 . The influence exerted by the shield in position  101 C is different than the influence exerted by the shield in position  101 A. The movement of the shield  101  between the positions  101 A,  101 B, and  101 C may be effected manually, or may be effected in an automated manner by the shield support  103 , under control of the control unit  64 . 
     Although the embodiment of  FIG. 2  has only a single source  262  that can selectively evaporate any of two or more different materials, it would alternatively be possible to provide one or more additional sources that can each selectively evaporate one or more different materials. In addition, although the disclosed embodiments are discussed in regard to the formation of coatings on optical components, they can also be alternatively used to form coatings on parts other then optical components. 
     Although selected embodiments have 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.