Abstract:
A kinematic optical mount comprising a frame supporting an optical element; a base member having first and second surfaces and providing magnetic attraction to seat the frame against first, second, and third point contacts. The kinematic optical mount further includes threaded yaw and pitch adjustment cavities extending through the base member from the first surface to the second surface, together with threaded yaw and pitch adjustment inserts that can be inserted into the yaw and pitch adjustment cavities from either the first or second surfaces of the base member enabling adjustment of two of the point contacts from the direction of the either the first or second surfaces.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present invention is related to commonly assigned U.S. patent application Ser. No. 12/432,856 filed Apr. 30, 2009, entitled “Digital Projector using Arrayed Light Sources” by Harland et al., and to commonly assigned U.S. patent application Ser. No. 12/432,999 filed Apr. 30, 2009, entitled “Beam Alignment Chamber Providing Divergence Correction” by Silverstein et al. 
     FIELD OF THE INVENTION 
     This invention generally relates to an apparatus for precision mounting and positioning of a component and more particularly relates to an apparatus for mounting and adjusting the position of a mirror or other reflective optical element. 
     BACKGROUND OF THE INVENTION 
     Proper alignment of mirrors and other types of reflective optical surfaces is of particular value in optical systems that require accurate redirection of light. This can be a particularly important requirement for a system that uses laser light. Without high-precision alignment, for example, minor deviation of a laser beam for a measurement instrument or for an imaging apparatus can seriously compromise system performance. 
     Conventional approaches for mirror mounting and adjustment often require precision machining and a complex arrangement of actuators for making slight adjustments to mirror position. This approach may be justifiable for precision alignment of larger mirrors that may be used with higher-power lasers, using solutions such as that taught in U.S. Pat. No. 5,004,205 entitled “High-Range and Resolution Determinate Mount and Positioner” to Brown et al., for example. However, with the advent of solid-state lasers and laser arrays, used for various types of instrument, communications, illumination, and imaging systems, there is a demand for more compact mounting mechanisms with fewer parts and allowing lower cost fabrication and assembly. 
     In general, for proper alignment of an optical component with respect to an optical axis, a mount mechanism for a mirror must allow the capability for precision adjustment about each of two orthogonal axes. In some systems, the use of a fixture for alignment may be advantageous. This approach is taught, for example, in U.S. Pat. No. 6,053,469 entitled “Low-Cost 2-Axis Mirror Mount” to Burgarella. However, fixturing can be impractical for some systems, particularly where heat or vibration can be a factor. In addition, fixturing is less satisfactory where a light source may need to be replaced. 
     Compact spacing can be another requirement for a mirror mount. The need for compact packaging not only affects the size, weight, and other physical attributes of the mirror mount, but can also constrain access to adjustment actuators. Conventional solutions that allow access to mirror adjustments once the mirror mount is installed tend to work against the requirements to constrain the overall profile and mechanical footprint of the mirror mount. 
     Thus, it is seen that there is a need for a compact mirror mount that allows precision adjustment of mirror alignment from multiple directions and uses a small number of component parts. 
     SUMMARY OF THE INVENTION 
     The present invention addresses the need for improved mounting of mirrors and other reflective, refractive, or light conditioning optical components by providing a kinematic optical mount comprising: 
     a reflective optical element; 
     a frame supporting the reflective optical element; 
     a base member having first, second, and third point contacts, the base member having a first surface configured for fastening to a chassis and a second surface opposite and substantially parallel to the first surface; 
     an attraction means providing an attractive force to attract the frame to the base member seating the frame against the first, second, and third point contacts; 
     a threaded yaw adjustment cavity extending through the base member from the first surface to the second surface; 
     a threaded yaw adjustment insert that enables adjustment for re-positioning the first point contact from the direction of the first surface when inserted in the threaded yaw adjustment cavity in a first orientation and enables adjustment for re-positioning the first point contact from the direction of the second surface when inserted in the threaded yaw adjustment cavity in an opposite orientation; 
     a threaded pitch adjustment cavity extending through the base member from the first surface to the second surface; and 
     a threaded pitch adjustment insert that enables adjustment for re-positioning the second point contact from the direction of the first surface when inserted in the threaded pitch adjustment cavity in a first orientation and enables adjustment for re-positioning the second point contact from the direction of the second surface when inserted in the threaded pitch adjustment cavity in an opposite orientation. 
     It is an advantage of the present invention that it provides an apparatus and method for optical component mounting that can be configured to allow adjustment from either of two opposite directions. 
     It is another advantage of the present invention that it provides an optical mount that is compact, uses a small number of component parts, and is readily adapted to mounting from either of two opposite surfaces. The flexibility in the adjustment direction and the mounting surface allows the optical mount to be used in a wide variety of system configurations. 
     These and other features, and advantages of the present invention will become apparent to those skilled in the art upon a reading of the following detailed description when taken in conjunction with the drawings wherein there is shown and described an illustrative embodiment of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an exploded perspective of an optical mount according to an embodiment of the present invention; 
         FIG. 2A  is a partial cutaway view showing pitch adjustment components in one embodiment; 
         FIG. 2B  is a partial cutaway view showing pitch adjustment components in an alternate embodiment; 
         FIGS. 3A and 3B  show optical mount configurations allowing pitch and yaw adjustment from either the top surface or the bottom surface of the optical mount, respectively; 
         FIG. 4  is a perspective of an alternate embodiment in which a pair of optical mounts are installed back-to-back against a chassis; 
         FIG. 5  is a perspective of a beam combiner assembly using a number of optical mounts for alignment of light beams from multiple sources; and 
         FIGS. 6A and 6B  are schematic diagrams showing the use of springs for providing kinematic loading force in alternate embodiments. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present description is directed in particular to elements forming part of, or cooperating more directly with, apparatus in accordance with the invention. It is to be understood that elements not specifically shown or described may take various forms well known to those skilled in the art. 
     Figures shown and described herein are provided to illustrate principles of operation according to the present invention and may not be drawn with intent to show actual size or scale. Because of the relative dimensions of the component parts for the mirror mount of the present invention, some exaggeration is necessary in order to emphasize basic structure, shape, and principles of operation. 
     The terms “bottom” and “top” are used to indicate opposite surfaces or other features of components as described and illustrated herein, but are not intended to limit a component to a vertical orientation. One advantage of the mirror mount of the present invention relates to its adaptability for orientation in other than vertical directions, such as in a horizontal direction. For ease of description and reference, only the vertical orientation is shown in the examples given herein. 
     Embodiments of the present invention address the need for an optical mount that is compact, has a relatively small parts count, and is adaptable for mounting singly or in an array in any of various types of optical systems. Kinematic design enables an optical mount to maintain a component in a fixed position without over constraint. This component can be an optical element such as a mirror or other reflective element, a polarizer, a lens or other type of refractive element, an optical grating, or some other light-redirecting, measurement, or light-conditioning component, for example. 
     Referring to  FIG. 1 , there is shown, in an exploded view presentation, component parts of a kinematic optical mount  200  for a reflective element  202 . A frame  204  supports the reflective element  202  and is kinematically secured against a base member  210  by a magnet  212  that provides an attractive force against a 3-point contact. Magnet  212  is seated within a cavity  222 . Pitch adjustment ball  214   a , fixed ball  214   b , and yaw adjustment ball  214   c  are seated in sockets formed on a surface of base member  210  to provide three contact points for the 3-point contact. The magnet  212  should be mounted so that its force is concentrated within the triangle formed by the three contact points. 
     In the embodiment shown in  FIG. 1 , base member  210  has two alternate mounting surfaces  218   a  and  218   b , either of which can be used for securing base member  210  to a chassis or other body. 
     The design of base member  210  allows optical mount  200  to be configured so that it allows pitch and yaw adjustment from either top mounting surface  218   a  or bottom mounting surface  218   b , depending on the orientation from which the adjustment hardware is installed. A yaw adjustment cavity  220  extends through base member  210  between top mounting surface  218   a  and bottom mounting surface  218   b  and is threaded over at least a portion of its length. Similarly, a pitch adjustment cavity  224  also extends through base member  210  between surfaces  218   a  and  218   b  and is threaded over at least a portion of its length. 
     A threaded yaw adjustment insert  228  is provided for fitting into the yaw adjustment cavity  220 , either from top mounting surface  218   a  or bottom mounting surface  218   b . Likewise, a threaded pitch adjustment insert  230  is provided for fitting into the pitch adjustment cavity  224 , either from top mounting surface  218   a  or bottom mounting surface  218   b  Both threaded yaw adjustment insert  228  and threaded pitch adjustment insert  230  are adjustment screws in one embodiment. 
     In a preferred embodiment of the present invention, the adjustment screws will have a conical taper, typically on the end of the adjustment screws. The partial cutaway view of  FIG. 2A  shows an embodiment of threaded pitch adjustment insert  230  having a tapered end  238  that sits in contact with pitch adjustment ball  214   a  to force it outward against frame  204  in a direction D. In this configuration, threaded pitch adjustment insert  230  is installed from the top mounting surface  218   a . As the threaded yaw adjustment insert  228  and the threaded pitch adjustment insert  230  are turned in or out, the conical tapers push the pitch adjustment ball  214   a , and the yaw adjustment ball  214   c  in or out accordingly, thereby providing the pitch and yaw adjustment for the reflective element  202 . 
     Alternately, the conical taper may be provided in the midsection of the adjustment screws, resulting in hour-glass-shaped interior portions. This alternate configuration is shown in the embodiment of  FIG. 2B , in which threaded pitch adjustment insert  230  has a tapered section  242 . In this embodiment, threaded pitch adjustment insert  230  can be installed from either top or bottom mounting surfaces  218   a  or  218   b . An advantage of this arrangement is that the threaded pitch adjustment insert  230  can be adjusted from either top or bottom mounting surfaces  218   a  or  218   b  without needing to remove the threaded pitch adjustment insert  230  and insert it from the other direction. To enable this feature, both ends of the threaded pitch adjustment insert  230  are provided with an adjustment means, such as a screwdriver slot or an Allen wrench head, which can be used to turn the threaded pitch adjustment insert  230  within the pitch adjustment cavity  224 . 
     In an alternate embodiment of the present invention, the conical or tapered slugs are inserted into the yaw adjustment cavity  220  and the pitch adjustment cavity  224  between the adjustment screws and the balls. The adjustment screws push on the conical or tapered slugs, which in turn push the pitch adjustment ball  214   a , and the yaw adjustment ball  214   c  in or out accordingly. 
     The yaw adjustment cavity  220  and the pitch adjustment cavity  224  may have a uniform diameter all the way through the base member  210 . Alternately, the yaw adjustment cavity  220  and the pitch adjustment cavity  224  can have a larger diameter near one or both mounting surfaces to provide easier access to the yaw adjustment insert  228  and the pitch adjustment insert  230  using adjustment tools such as Allen wrenches. It is particularly advantageous to use a larger diameter cavity when the adjustment inserts are positioned a relatively large distance from the mounting surface. For the example shown in  FIG. 1 , it can be seen that the yaw adjustment cavity  220  has a larger diameter toward the bottom mounting surface  218   b  and the pitch adjustment cavity  224  has a larger diameter toward the top mounting surface  218   a.    
     Only the portions of the yaw adjustment cavity  220  and the pitch adjustment cavity  224  near the pitch adjustment ball  214   a  and the yaw adjustment ball  214   c , respectively, need to be threaded to engage the threads on the yaw adjustment insert  228  and the pitch adjustment insert  230 . 
     In one embodiment of the present invention, the axes of yaw adjustment cavity  220  and the pitch adjustment cavity  224  can be offset relative to the bores for the pitch adjustment ball  214   a  and the yaw adjustment ball  214   c . This will force the adjustment ball to one side of the bore, thereby eliminating possible “hunting” or lost motion during adjustment as the adjustment ball wanders from one side of the bore to another. 
     Threaded yaw adjustment insert  228  is shown in both of its possible orientations as it would be threaded into threaded yaw adjustment cavity  220 ; only one orientation would be used for any single optical mount  200 . In similar fashion, a threaded pitch adjustment insert  230  is shown in both of its possible orientations. 
     Mounting holes  240  are also provided on the top mounting surface  218   a  and the bottom mounting surface  218   b . These holes can be used to fasten the optical mount  200  to an external chassis from either the top or bottom directions. Typically, the mounting holes  240  are threaded and the optical mount  200  is fastened to the external chassis using threaded screws. 
     For yaw adjustment, or rotation about the y-axis using the axes designations of  FIG. 1 , threaded yaw adjustment insert  228  adjusts the position of yaw adjustment ball  214   c  in its socket. This repositioning causes a slight change in the position of the plane formed by the 3-point contact, effecting a slight shift in yaw for frame  204  and the optical component that it supports, here, reflective element  202 . 
     For pitch adjustment, or rotation about the x-axis using the axes designations of  FIG. 1 , threaded pitch adjustment insert  230  adjusts the position of ball pitch adjustment ball  214   a  in its socket. This repositioning also causes a slight change in the position of the plane formed by the 3-point contact, effecting a slight shift in pitch for frame  204  and the optical component that it supports. 
     The position of fixed ball  214   b  is not adjusted for the mirror mount embodiment shown in  FIG. 1 . Fixed ball  214   b , seated in a socket  232 , provides a pivot point for both pitch and yaw adjustments. A V-channel  234  extending lengthwise along frame  204  provides low-friction contact for yaw rotation of frame  204 . 
       FIGS. 3A and 3B  show how optical mount  200  can be configured to allow pitch and yaw adjustment from either top surface  218   a  or bottom surface  218   b , respectively. For the configuration of  FIG. 3A , the threaded yaw adjustment insert  228  and the threaded pitch adjustment insert  230  are inserted from top surface  218   a , and the pitch and yaw adjustments can therefore be accessed from the top surface  218   a . For the configuration of  FIG. 3B , the threaded yaw adjustment insert  228  and the threaded pitch adjustment insert  230  are inserted from bottom surface  218   b , and the pitch and yaw adjustments can therefore be accessed from the bottom surface  218   b.    
     Reflective element  202  is adhesively bonded to frame  204  in one preferred embodiment. Alternatively, some other method of coupling or attachment can be provided for the optical component, including the use of a bracket or fastener, for example. In an alternate embodiment, reflective element  202  is formed directly onto frame  204 , rather than being a separate component. 
     The perspective view of  FIG. 4  shows an alternate embodiment in which a pair of optical mounts  200  are installed back-to-back against a chassis  236  within an optical assembly. In this embodiment, base member  210  has a broadened mounting surface  218   c  that has a broadened area for mounting. However, as with the  FIG. 1  embodiment, access for pitch and yaw adjustment can be from the direction of the top surface  218   a , as viewed in  FIG. 3A , or from bottom surface  218   c , as viewed in  FIG. 3B , again depending on the orientation of threaded yaw adjustment insert  228  and the threaded pitch adjustment insert  230 . 
     Optical mount  200  of the present invention is particularly suited for use in an array configuration, such as that shown in cutaway perspective in  FIG. 5 . A beam alignment chamber  100  has a number of optical mounts  200  installed along a base  110  and along a top cover (removed for clarity). Beam alignment chamber  100  redirects light beams from multiple sources (not shown), each beam source coupled with a corresponding reflector in an optical mount  200 , to provide light along an output path A. With this type of arrangement, a separate adjustment is provided for each beam, simplifying the beam alignment task. 
     Using optical mount  200  of the present invention, pitch and yaw adjustment for an optical component does not require fixturing and can be configured to be performed from either of two directions without the need for fabricating different sets of components for the different configurations. Adjustment of pitch and yaw can be made over a few degrees in each orthogonal direction and the position maintained due to the magnetic force and three-point mounting that is provided. 
     The use of magnetic loading for this kinematic mount helps to reduce the parts count and provides a kinematic loading force that is sufficiently robust for mounting and accurately positioning a mirror or other optical component. In another embodiment of the present invention, the base member  210  can be magnetized to provide the attraction force, thereby eliminating the need for magnet  212 . In yet another embodiment of the present invention, the magnet  212  can be replaced by a spring or other type of attraction means that provides the kinematic loading force needed to hold the frame  204  tightly against the three contact points. It can be appreciated that other attraction means could be employed in various embodiments, such as gravity, elastic tension, or fluid pressure, for example. 
     An alternate embodiment of the present invention using a spring as the attraction means is shown in the partial cutaway view of  FIG. 6A , in which an extension spring  244  extends from base member  210  to provide a kinematic loading force F. Another arrangement using a spring is shown in the partial cutaway view of  FIG. 6B . In this case, a compression spring  246  cooperates with an arm  248  that is coupled to frame  210  to provide the loading force F that attracts frame  204  toward base member  210 . This configuration has the added advantage that it can limit the excursion of the frame  204  during a shock event. This can also prevent the pitch adjustment ball  214   a , the fixed ball  214   b  and the yaw adjustment ball  214   c  from becoming dislodged during such shock events. 
     Base member  210  and frame  204  can be formed of various types of steel or other metals or from ceramics or other materials having suitable magnetic permeability and other properties. Base member  210  need not have a high magnetic permeability, but this characteristic can be advantageous for providing an improved flux distribution for providing the kinematic loading when a magnetic attraction means is used. Electrical-Discharge Machining (EDM) can be used to fabricate either or both of base member  210  and frame  204 . Other automated or manual machining methods such as die casting or extrusion can alternately be employed. 
     The invention has been described in detail with particular reference to certain preferred embodiments thereof but it will be understood that variations and modifications can be effected within the spirit and scope of the invention. For example, 
     base member  210  can be a magnetic or magnetized material, rather than housing a separate magnet. Optical mount  200  can also be configured to support other types of optical elements beside the simple reflective element  202  shown in the preceding examples. For example, optical mount  200  can also be configured to support a partially reflective element such as a beam splitter, or a refractive element or some other type of optical element that transmits light. The optical mount of the present invention can be used for accurate positioning of an optical component that redirects, filters, reflects, blocks, or transmits light or otherwise conditions incident light. Thus, what is provided is an apparatus and method for mounting an optical element. 
     PARTS LIST 
     
         
           100  Beam alignment chamber 
           110  Base 
           200  Optical mount 
           202  Reflective element 
           204  Frame 
           210  Base member 
           212  Magnet 
           214   a  Pitch adjustment ball 
           214   b  Fixed ball 
           214   c  Yaw adjustment ball 
           218   a  Top mounting surface 
           218   b  Bottom mounting surface 
           218   c  Broadened mounting surface 
           220  Yaw adjustment cavity 
           222  Cavity 
           224  Pitch adjustment cavity 
           228  Threaded yaw adjustment insert 
           230  Threaded pitch adjustment insert 
           232  Socket 
           234  V-channel 
           236  Chassis 
           238 . Tapered end 
           240  Mounting holes 
           242 . Tapered section 
           244 . Extension spring 
           246 . Compression spring 
           248 . Arm 
         A. Output path 
         F. Loading force 
         x, y. Axis