Abstract:
In one embodiment, a coordinate measurement apparatus includes an articulated arm having a first end and a second end with at least a first arm segment and a second arm segment therebetween. Further, the apparatus can comprise at least one ball and socket joint connecting the first arm segment to the second arm segment, with the ball and socket joint including a ball member and a socket member, and a measurement probe attached to the first end of said articulated arm.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application is a continuation of U.S. patent application Ser. No. 12/822,940, filed Jun. 24, 2010 and entitled “COORDINATE MEASUREMENT MACHINE WITH IMPROVED JOINT,” which is a continuation of U.S. patent application Ser. No. 11/943,463, filed on Nov. 20, 2007 and entitled “COORDINATE MEASUREMENT MACHINE WITH IMPROVED JOINT,” now issued as U.S. Pat. No. 7,743,524, which claims the benefit of U.S. Provisional Application No. 60/860,239, entitled “COORDINATE MEASUREMENT MACHINE WITH IMPROVED JOINT,” filed on Nov. 20, 2006, and the entirety each of these is hereby incorporated by reference. 
     
    
     BACKGROUND 
       [0002]    1. Field of the Invention 
         [0003]    The present application relates to measuring devices, and more particularly, articulated arm coordinate measurement machines for measuring the coordinates of three-dimensional objects. 
         [0004]    2. Description of the Related Art 
         [0005]    Rectilinear measuring systems, also referred to as coordinate measuring machines (CMM&#39;s) and articulated arm measuring machines including portable coordinate measuring machines (PCMM&#39;s) have been described for generating geometry information from various objects and areas. In general, these instruments capture the structural characteristics of an object for use in electronic rendering and duplication. One example of a conventional apparatus used for coordinate data acquisition comprises a support and a moveable measuring arm made up of hinged segments to which a contact-sensitive probe or remote scanning device is attached. 
         [0006]    Geometry information or three-dimensional coordinate data characterizing the shape, features, and size of the object may be acquired by tracing or scanning along the object&#39;s surface and contours. Probe or scanning device movement is typically tracked relative to a reference coordinate system resulting in a collection of data points and information that may be used to develop an accurate electronic rendering of the object. In conventional implementations, the acquired geometry information is processed by a computer capable of making use of the information to model the surface contours and dimensions of the object. 
       SUMMARY OF THE INVENTION 
       [0007]    In one embodiment, a coordinate measurement apparatus comprises an articulated arm having a first end and a second end with at least a first arm segment and a second arm segment therebetween. Further, the apparatus comprises at least one ball and socket joint connecting the first arm segment to the second arm segment, with said ball and socket joint including a ball member and a socket member, and a measurement probe attached to the first end of said articulated arm. In another embodiment, the ball member comprises at least one graphical pattern and the socket member comprises at least one optical reader device configured to read said graphical pattern. In other arrangements, the optical reader device comprises a camera. In yet another embodiment, the ball member is maintained adjacent to the socket member using at least one magnet member. In still another embodiment, the ball member is maintained adjacent to the socket member using at least one vacuum port. 
         [0008]    In another arrangement, a coordinate measurement apparatus further comprises a slip ring rotatably connected to the first arm segment. In other embodiments, the coordinate measurement apparatus includes one or more hardwired connections attached to the slip ring. Such hardwired connections are in electronic communication with the second arm segment, and are configured to transfer data between said first arm segment and said first arm segment. 
         [0009]    In some embodiments, a coordinate measurement apparatus comprises an articulated arm having a first end, a second end, at least a first arm segment and a second arm segment therebetween. Further, the coordinate measurement apparatus includes at least one joint connecting said first arm segment to said second arm segment, said joint configured to allow said first arm segment to pivot and rotate relative to said second arm segment, and a measurement probe attached to said first end of said articulated arm. In another arrangement, a coordinate measurement apparatus comprises an articulated arm having a first end, a second end, at least a first arm segment and a second arm segment therebetween. Further, at least one joint connects the first arm segment to the second arm segment, said joint comprising a first joint member and a second joint member. In addition, the coordinate measurement apparatus includes a measurement probe attached to said first end of said articulated arm, wherein either of said first joint member or second joint member comprises a generally convex surface and the other of either said first joint member or said second joint member comprises a rounded surface configured to generally mate with said convex surface of said first joint member so that said first arm segment is configured to pivot and rotate relative to said second arm segment. 
         [0010]    A method of operating a coordinate measurement apparatus to acquire coordinate data regarding a target surface comprises moving a first arm segment relative to a second arm segment using a first joint, said first joint configured to permit said first arm segment to pivot and rotate relative to said second arm segment and acquiring position data of the pivotal and rotational position of the first arm segment relative to the second arm segment from a data surface of the first joint. Further, the method includes moving a probe member connected to said first arm segment relative to said target surface. 
         [0011]    In some embodiments, a coordinate measurement apparatus is provided comprising an articulated arm, at least one joint, and a measurement probe. The articulated arm has a first end, a second end, and at least a first arm segment and a second arm segment therebetween. The at least one joint connects said first arm segment to said second arm segment. The joint comprises a first joint member and a second joint member. The measurement probe is attached to said first end of said articulated arm. Said joint is capable of movement in two or more degrees of freedom, and measurement of both degrees of freedom is done by measuring a single coded surface. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    Further objects, features and advantages of the invention will become apparent from the following detailed description taken in conjunction with the accompanying figures showing illustrative embodiments of the invention, in which: 
           [0013]      FIG. 1  is a perspective view of an embodiment of a coordinate measuring machine; 
           [0014]      FIG. 2  is a perspective view of an embodiment of a coordinate measuring machine including a ball and socket type articulation member; 
           [0015]      FIG. 3  is a cross-sectional view of an embodiment of a ball and socket type articulation member for use in a coordinate measuring device; 
           [0016]      FIG. 4  is a cross-sectional view of an embodiment of two-axis articulation member for use in a coordinate measuring device 
           [0017]      FIG. 5  is a front elevation view of a circular section of the ball portion of an articulation member depicting one embodiment of a graphical pattern; and 
           [0018]      FIG. 6  is a flowchart for obtaining coordinate data with a CMM that includes a ball and socket type articulation member according to one embodiment. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0019]      FIG. 1  illustrates one embodiment of a prior art coordinate measuring machine (CMM)  10 . In the illustrated embodiment, the CMM  10  comprises a base  20 , a plurality of rigid transfer members  24 ,  26 ,  28 , a coordinate acquisition member  30  and a plurality of articulation members  40 ,  42 ,  44 ,  46 ,  48 ,  50  connecting the rigid transfer members  24 ,  26 ,  28  to one another. Each articulation member is configured to impart one or more rotational and/or angular degrees of freedom. Through the various articulation members  40 ,  42 ,  44 ,  46 ,  48 ,  50 , the CMM  10  can be aligned in various spatial orientations thereby allowing fine positioning of the coordinate acquisition member  30  in three-dimensional space. 
         [0020]    The position of the rigid transfer members  24 ,  26 ,  28  and the coordinate acquisition member  30  may be adjusted using manual, robotic, semi-robotic and/or any other adjustment method. In one embodiment, the CMM  10 , through the various articulation members, is provided with seven rotary axes of movement. It will be appreciated, however, that there is no strict limitation to the number of axes of movement that may be used, and fewer or additional axes of movement may be incorporated into the CMM design. 
         [0021]    In various embodiments, the coordinate acquisition member  30  comprises a contact sensitive member or probe  32  configured to engage the surfaces of a selected object and generate coordinate data on the basis of probe contact. Alternatively, the coordinate acquisition member  30  may comprise a remote scanning and detection component that does not necessarily require direct contact with the selected object to acquire geometry data. In one embodiment, a laser coordinate detection device (e.g., laser camera) may be used to obtain geometry data without direct object contact. It will be appreciated that various coordinate acquisition member configurations including: a contact-sensitive probe, a remote-scanning probe, a laser-scanning probe, a probe that uses a strain gauge for contact detection, a probe that uses a pressure sensor for contact detection, a probe that used an infrared beam for positioning, and a probe configured to be electrostatically-responsive may be used for the purposes of coordinate acquisition. 
         [0022]    In other embodiments, one or more of the rigid transfer members  24 ,  26 ,  28  comprise a composite structure that includes an inner portion and an outer exoskeletal portion. In such an arrangement, the inner portion of the rigid transfer members  24 ,  26 ,  28  are interconnected to one another through articulation members that provide the ability to position the coordinate acquisition member  30  in a variety of different orientations in three dimensional space. The outer portions surrounding the various inner portions of the rigid transfer members  24 ,  26 ,  28  form an environmental barrier that at least partially encloses segments of the inner portions. In one aspect, the inner portions are configured to “float” inside the corresponding outer portions. 
         [0023]    As is known in the art, the position of the probe  32  in space at a given instant can be calculated by knowing the length of each member and the specific position of each of the articulation members  40 ,  42 ,  44 ,  46 ,  48 ,  50 . Each of the articulation members  40 ,  42 ,  44 ,  46 ,  48 ,  50  can be broken down into a singular rotational degree of motion, each of which may be measured using a dedicated rotational transducer. Each transducer outputs a signal (e.g., an electrical signal), which varies according to the movement of the  40 ,  42 ,  44 ,  46 ,  48 ,  50  in its degree of motion. The signal can be carried through wires or otherwise transmitted to a base  20 . From there, the signal can be processed and/or transferred to a computer for determining the position of the probe  32  in space. 
         [0024]    In one embodiment, the transducer can comprise an optical encoder. In general, each encoder measures the rotational position of its axle by coupling is movement to a pair of internal wheels having successive transparent and opaque bands. In such embodiments, light can be shined through the wheels onto optical sensors which feed a pair of electrical outputs. As the axle sweeps through an arc, the output of the analog encoder can be substantially two sinusoidal signals which are 90 degrees out of phase. Coarse positioning can occur through monitoring the change in polarity of the two signals. Fine positioning can be determined by measuring the actual value of the two signals at the instant in question. In certain embodiments, maximum accuracy can be obtained by measuring the output precisely before it is corrupted by electronic noise. Additional details and embodiments of the illustrated embodiment of the CMM  10  can be found in U.S. Pat. No. 5,829,148, the entirety of which is hereby incorporated by reference herein. 
         [0025]    While the above described CMM  10  has been proven to be particularly advantageous improvement can be made. For example, between the rigid transfer members  24 ,  26 ,  28 , the device  10  includes six articulation members  40 ,  42 ,  44 ,  46 ,  48 ,  50 . Thus, between each transfer member, there is one articulation member configured to provide rotational movement and another articulation member that provides hinge-like movement. Each articulation member includes a transducer. Thus, it can be advantageous to reduce the number of articulation members and thus the number of transducers between transfer members. 
         [0026]      FIG. 2  illustrates one embodiment of a CMM  10 B, which includes an articulation member  60  that is configured to provide two degrees of freedom between transfer members  24 B,  26 B. It should be appreciated that, while only one articulation member  60  with two degrees of freedom is shown in the CMM  10 B, in modified embodiments, the CMM  10 B can include 2, 3 or more articulation members  60  between other transfer members or components of the CMM  10 B. In the illustrated embodiment, the articulation member  60  comprises includes a ball and socket type joint that permits one rigid transfer member  26 B to swivel relative to another rigid transfer member  24 B. Consequently, the need for multiple articulation members between transfer members is eliminated, as single ball and socket type articulation member  60  provides two degrees of freedom. 
         [0027]    With continued reference to  FIG. 2 , a ball (or male) portion  62  of the articulation member  60  is positioned on the upper rigid transfer member  26 B and the socket (or female) portion  64  is positioned on the lower rigid transfer member  24 B. Alternatively, the articulation member  60  may be configured so that the orientation of the ball and socket portions  62 ,  64  is reversed. Further, as mentioned above, additional ball and socket type articulation members can be provided between rigid transfer members of a CMM  10 B to further simplify its overall design. In the embodiment illustrated in  FIG. 2 , the ball and socket type articulation member  60  also eliminates the need for a swiveling articulation member  40  at the base of the CMM (see  FIG. 1 ) while still providing hinge-like movement. 
         [0028]      FIG. 3  shows a cross-sectional view of the ball and socket type articulation member  60  of  FIG. 2 . In the illustrated embodiment, the ball portion  62  is positioned at the end of transfer member  26 B, and the corresponding socket portion  64  is located at the end of the adjacent transfer member  24 B. The ball and socket portions  62 ,  64  can be separate from the adjacent transfer members or they can be integrally formed as single bodies with the transfer members. It will be appreciated that if the articulation member components are separate from the adjacent transfer members, one or more connection methods are used to secure the back and socket portions  62 ,  64  to the transfer members. Non-limiting examples include threading, gluing, welding, snap fitting, using fasteners (e.g., bolts, screws, pins, etc.) and the like. 
         [0029]    In some preferred embodiments, the ball portion  62  can be maintained within the socket portion  64  by one or more magnets or an annular magnet  68  situated within the socket portion  64 . As illustrated in  FIG. 3 , the magnets  68  exert an attractive force on the ball portion  62 , urging the ball portion  62  towards the concave surface of the socket portion  64 . Thus, the ball portion  62  can advantageously include one or more magnetically responsive materials (e.g., metal) on which the magnetic force may act. 
         [0030]    As shown in  FIG. 3 , the annular magnet  68  can be situated at or near the concave mating surface of the socket portion  64 . Alternatively, the socket portion  64  can include one or more additional magnets to ensure that the ball portion  62  is adequately maintained within the socket portion  64 . As depicted in  FIG. 3 , the magnet  64  can be substantially flush with the adjacent surfaces of the socket portion  64  to form a continuous concave interface against which the ball portion  62  may move. However, it will be appreciated that the magnets  68  need not be flush with the adjacent surfaces of the socket portion  64 . For example, the magnets may be recessed or otherwise set back with respect to the concave surface of the socket portion  64 . Alternatively, the magnets may be located closer to the ball portion  62  than the adjacent non-magnetic surfaces of the socket portion  64 , forming all or part of the contact surface with the adjacent ball portion  62 . In other embodiments, the magnets may be positioned at more interior locations relative to the concave surface such that they are not directly exposed at the concave open end of the socket portion  64 . 
         [0031]    Preferably, the materials, size, shape, location, magnetic strength, orientation and other characteristics of the magnets are selected to ensure that the ball portion  62  is constantly maintained within the socket portion  64  during the entire range of motion of the articulation member  60  during operation. In addition, the magnets are preferably capable of resisting all anticipated forces and/or moments that may cause the ball portion  62  to separate from the socket portion  64 . In other embodiments, the ball portion  62  of the articulation member  60  may include one or more magnets, either in addition to or lieu of magnets positioned on the socket portion  64 . 
         [0032]    Other ways of maintaining the integrity of the ball and socket type articulation members  60  can be used, either in lieu of or in combination with magnets. For example, a vacuum can be used to urge the ball portion  62  within the socket portion  64 . One or more vacuum sources may be located on the ball portion  62 , socket portion  64  or both. Such vacuum sources may interface with the surfaces of the ball and/or socket portions  62 ,  64  through one or more vacuum ports. In other embodiments, the ball portion  62  may be secured within the socket portion  64  using springs or other biasing members. In other embodiments, the articulation member  60  can be configured to otherwise mechanically retain the ball portion  62  within the socket portion  60 . For example, in  FIG. 3 , the open end of the socket portion  64  may surround the ball portion  62  in a manner that prevents the ball portion  62  from being withdrawn from the inner concave portion of the socket portion  64 . In such an embodiment, the socket portion  64  may include an adjustable housing that can be used to clamp down on the ball portion  62 . 
         [0033]    Regardless of the methods used to retain the ball portion  62  within the socket portion  64 , the articulation member  60  is preferably configured for relatively simple and quick assembly and/or disassembly. For example, articulation members that utilize magnets may be separated by simply pulling the adjacent rigid transfer members  24 B,  26 B away from one another. Alternatively, the articulation member  60  may be configured so that the magnetic force that maintains the ball portion  62  within the socket portion  64  can be temporarily inactivated, permitting the transfer members  24 B,  26 B to be separated with greater ease. Such a feature is especially helpful when the magnetic forces maintaining the ball portion  62  within the socket portion  64  are relatively strong. In embodiments that utilize a vacuum to maintain the integrity of the articulation member, the ball portion  62  may be separated from the socket portion  64  by discontinuing the vacuum source (e.g., by actuation of a power switch or lever). Likewise, mechanical members used to join the ball and socket portions  62 ,  64  are preferably configured to be easily manipulated, allowing for easy connection and/or disconnection of the articulation member  60 . 
         [0034]    The features described in the above embodiments can provide CMMs with a desirable degree of modularity. For example, the relative ease with which ball and socket type articulation members may be connected and/or disconnected permits CMMs to be modified by either adding or removing transfer members. In addition, such modifications can be performed on-site where CMMs are being used. Thus, CMMs can be conveniently customized according to a particular application. Further, the simple assembly and disassembly features of the ball and socket type articulation members facilitate transportation and overall mobility of the CMM. 
         [0035]    Preferably, smooth and unobstructed three-dimensional pivoting movement is permitted between the ball and socket portions  62 ,  64  of the articulation member  60 . In one embodiment, the adjacent surfaces of the ball and socket portions  62 ,  64  are manufactured from one or more low friction materials, such as smooth metals, synthetic polymers and the like. One or more coatings, layers, lubricants and the like can be optionally applied to the ball portion  62  and/or the socket portion  64  to further reduce the effects of friction within the articulation member  60 . 
         [0036]    In preferred embodiments, the range of motion of the ball portion  62  relative to the socket portion  64  may be enhanced by the shape of the articulation member  60  and/or the rigid transfer members to which the articulation member  60  is joined. For example, in  FIG. 3 , transfer member  26 B includes a step  70  or recess at the interface with the ball portion  62 . Further, the open end  72  of the socket portion  64  may be angled away from the ball portion  62 . Consequently, the extent to which the adjoining transfer members  24 B,  26 B can swivel relative to one another can be increased by eliminating what would otherwise be interfering surfaces. 
         [0037]    As mentioned above, the position of a CMM probe in space at a given instant can be calculated, in part, by knowing the position of each of the articulation members. In the embodiment of  FIG. 3 , the specific angular position of the ball and socket type articulation member can be determined using optical imaging techniques. As shown, the surface of the ball portion  62  can include a graphical pattern  80 . The depicted graphical pattern  80  comprises a plurality of dots or points that are scattered across the surface area of the ball portion  62 . In the illustrated embodiment, the dots are interconnected by imaginary lines (i.e., the lines are illustrated for purposes of clarity in  FIG. 3 ), forming a plurality of adjacent triangles. As will be discussed in greater detail below, each triangle is preferably uniquely shaped, sized and/or otherwise configured, such that it may be correlated to a particular location of the ball portion surface. 
         [0038]    In  FIG. 3 , the socket portion  64  can include a bore  84  that is substantially coaxial to the center longitudinal axis  78  of the socket portion  64  and the attached transfer member  24 B. The bore  84 , which extends to the distal end of the socket portion  64 , is preferably sized and shaped to receive an optical camera  86  configured to read the graphical pattern  80  situated on the ball portion  62 . In the illustrated embodiment, both the bore  84  and the exterior of the camera  86  have a generally cylindrical shape. The camera  86  may be secured within the bore  84  using welds, adhesives, bolts, screws, pins, snap-fit members, engagement members, other fasteners and/or the like. Regardless of the exact attachment method used, the camera  86  is preferably statically connected to the socket portion  64  during operation of the CMM. In other embodiments, one or more additional cameras  86  may be used to read the graphical pattern  80 . In other embodiments, an optical encoder, such as a spherical encoder can be used to read the graphical pattern  80 . 
         [0039]    The bore  84  may additionally include a light element  88  to illuminate the section of the ball portion&#39;s outer surface visible through the bore  84 . In  FIG. 4 , the light element  88  comprises a light ring that is securely positioned between the camera  86  and the inside diameter of the bore  84 . Preferably, as described above in relation to the camera  86 , the position of the light element  88  is immovably attached to the socket portion  64  during operation of the CMM. Moreover, in some arrangements, additional light elements may be provided as required by the particular configuration. 
         [0040]    With continued reference to  FIG. 3 , power and/or data regarding the orientation or position of the various CMM components (e.g., articulation members, probe member, etc.) may be transmitted between adjoining rigid members  24 B,  26 B using a hardwired connection  90 . Preferably, such a hardwired connection  90  is equipped with a coupling  94  to optionally disconnect the two hardwired connection ends  92 A,  92 B. For example, the coupling  94  can be disconnected prior to separating the transfer members connected by the articulation member  60 . As illustrated in  FIG. 3 , at least one of the transfer members  26 B may preferably include a slip ring  96  to which the hardwired connection  90  attaches. The slip ring  96  rotates relative to the interior segments of the transfer member  26 B. Thus, the slip ring  96  ensures that the hardwired connection  90  does not interfere with the movement or operation of the ball and socket type articulation member  60 , regardless of how the ball and socket portions  62 ,  64  are moved relative to one another. 
         [0041]    Alternatively, a wireless connection can be used between adjacent transfer members to transmit coordinate data. Non-limiting examples of the types of wireless connections that may be used include infrared (IR), radio frequency (RF), Wi-Fi and others. 
         [0042]    With reference to  FIG. 4 , a cross-sectional view of an embodiment of two-axis articulation member  60 ′ including a ball  62 ′ is illustrated. The two-axis articulation member can be used in some embodiments of CMM as illustrated in  FIG. 2 . In the illustrated embodiment, the ball portion  62 ′ is positioned at the end of transfer member  26 B. A two-axis rotatable joint connects the transfer member  26 B to the adjacent transfer member  24 B. The ball  62 ′ can be separate from the transfer member  26 B or it can be integrally formed as single bodies with the transfer member  26 B. It will be appreciated that if the ball  62 ′ is separate from the adjacent transfer members, one or more connection methods can be used to secure the back and socket portions  62 ′ to the transfer members  26 B. Non-limiting examples include threading, gluing, welding, snap fitting, using fasteners (e.g., bolts, screws, pins, etc.) and the like. 
         [0043]    The ball  62 ′ can be rotatably coupled to a joint body  154  to define a first axis of rotation  152  of the two-axis rotatable joint. With continued reference to  FIG. 4 , the ball  62 ′ can have arms  150  extending therefrom and defining a first axis of rotation  152  of the joint. The arms  150  can be integrally formed with the ball  62 ′, or can be connected using one or more of the connection methods described above. The arms can be rotatably coupled to a joint body  154 , such as with bearings  156  to allow rotation of the joint body  154  about the first axis  152  relative to the ball  62 ′ and transfer member  26 B. In other embodiments, the ball  62 ′ does not have arms  150  extending therefrom. Instead, in these embodiments, the ball  62 ′ can be directly rotatably coupled to the joint body  154 . 
         [0044]    With continued reference to  FIG. 4 , the joint body  154  can be rotatably coupled to the adjacent transfer member  24 B with respect to its longitudinal axis  78 . In the illustrated embodiment, an endcap  158  for the transfer member  24 B can have flanged extensions  160  for rotatably coupling to the transfer member  24 B. Bearings  162  can rotatably couple the flanged extensions  160  of the endcap  158  to the joint body  154 . In some embodiments, the endcap  154  can be fastened to the transfer member  24 B such as by threaded coupling, adhesive, welding, or another suitable fastening technique. In other embodiments, the endcap  154  can be integrally formed with the transfer member  24 B. In other embodiments, the transfer member  24 B can have a flanged end to rotatably couple to the joint body  154 . 
         [0045]    With reference to  FIG. 4 , the endcap  158  can include a bore  164  that is substantially coaxial to the center longitudinal axis  78  of the endcap  158  and the attached transfer member  24 B. The bore  164 , which extends to a distal end of the endcap  158 , is preferably sized and shaped to receive an optical camera  86  configured to read the graphical pattern  80  on the ball portion  62 ′. In the illustrated embodiment, both the bore  164  and the exterior of the camera  86  have a generally cylindrical shape. The camera  86  may be secured within the bore  164  using welds, adhesives, bolts, screws, pins, snap-fit members, engagement members, other fasteners and/or the like. Regardless of the exact attachment method used, the camera  86  is preferably statically connected to the endcap  158  during operation of the CMM. In other embodiments, one or more additional cameras  86  may be used to read the graphical pattern  80 . In other embodiments, an optical encoder, such as a spherical encoder can be used to read the graphical pattern  80   
         [0046]    With reference to  FIG. 4 , in the illustrated embodiment, the first axis of rotation  152  is transverse to, E.g., substantially perpendicular to, the longitudinal axis  78  of the transfer member  24 B, which defines a second axis of rotation of the joint. Thus, the joint can be articulated about two axes of rotation. Advantageously, in the illustrated embodiment, the bearings  156 ,  162  rotatably coupling the joint can allow rotation while maintaining a known separation between the components of the joint. 
         [0047]    As mentioned above, the position of a CMM probe in space at a given instant can be calculated, in part, by knowing the position of each of the articulation members. In the embodiment of  FIG. 4 , the specific angular position of the two-axis joint type articulation member relative to the two axes of rotation  152 ,  78  can be determined using optical imaging techniques. As shown, the surface of the ball portion  62 ′ can include a graphical pattern  80 . The depicted graphical pattern  80  comprises a plurality of dots or points that are scattered across the surface area of the ball portion  62 . In the illustrated embodiment, the dots are interconnected by imaginary lines (i.e., the lines are illustrated for purposes of clarity in  FIG. 4 ), forming a plurality of adjacent triangles. As will be discussed in greater detail below, each triangle is preferably uniquely shaped, sized and/or otherwise configured, such that it may be correlated to a particular location of the ball portion surface. 
         [0048]    As discussed above with respect to  FIG. 3 , in some embodiments of two-axis joint, the bore  164  may additionally include a light element  88  to illuminate the section of the ball portion&#39;s outer surface visible through the bore  164 . In  FIG. 4 , the light element  88  comprises a light ring that is securely positioned between the camera  86  and the inside diameter of the bore  164 . In other embodiments, the joint can include more than one light element  88 . 
         [0049]    As discussed above with respect to  FIG. 3 , in some embodiments of two-axis joint, the power and/or data regarding the orientation or position of the various CMM components (e.g., articulation members, probe member, etc.) may be transmitted between adjoining rigid members  24 B,  26 B using a hardwired connection. Preferably, such a hardwired connection is equipped with a coupling to optionally disconnect two hardwired connection ends. As illustrated in  FIG. 4 , at least one of the transfer members  26 B may preferably include a slip ring  96  to which the hardwired connection attaches. The slip ring  96  rotates relative to the interior segments of the transfer member  26 B. Thus, the slip ring  96  ensures that the hardwired connection does not interfere with the movement or operation of the two-axis articulation member  60 ′, regardless of how the transfer members  24 B,  26 B are moved relative to one another. Alternatively, a wireless connection can be used between adjacent transfer members to transmit coordinate data. Non-limiting examples of the types of wireless connections that may be used include infrared (IR), radio frequency (RF), Wi-Fi and others 
         [0050]    The embodiment in  FIG. 5  illustrates a graphical pattern  80  as viewed from within the bore  84 ,  164  of the socket portion  64  or endcap  158 . Thus, this is the extent of the graphical pattern  80  that is detectable by the camera  86  at a particular angular orientation of the articulation member. Preferably each triangle or other shape included in the graphical pattern  80  is unique. For example, each triangle may vary according to size, dimensions, shape, angle of interior angles, ratio of sides and/or the like. Consequently, the camera  86  may correlate the area it has optically detected to a distinct position of the articulation member. In one embodiment, the camera  86  can determine the exact orientation of the articulation member by detecting only a single triangle or other graphical feature. However, in other arrangements, the camera  86  may need to read and identify two, three or more triangles or other features before accurately determining the position of the corresponding articulation member. Further, one or more algorithms may be used to correlate the pattern  80  detected by the camera  86  to a particular articulation member position. As described below with reference to  FIG. 6 , the acquired data relates the position of the various articulation members to determine the coordinates of the CMM probe member. 
         [0051]    With reference to  FIG. 6 , the light element may be initially activated  110  to illuminate the graphical pattern  80  on the exposed surface of the ball portion  62 ,  62 ′ of the articulation member  60 ,  60 ′. In one embodiment, the optical camera  86  may next determine which triangle is situated at the center of the exposed graphical pattern  80  and acquire its characteristics  112 . For example, the triangle&#39;s size, shape, area, interior angles and/or the like may be detected by the camera  86 . Such data may be used to identify the triangle and its exact orientation  114 , especially if each triangle in the graphical pattern  80  is unique. Further, information regarding the orientation of the identified triangle can be correlated to a unique position (e.g., bend, rotation, etc.) of the ball and socket type articulation member  116 . Finally, data collected from each articulation member in a CMM are used to calculate the exact coordinates of the probe member  118 . In alternative arrangements, the camera  86  may need to acquire information regarding two or more triangles or other graphical benchmarks within the graphical pattern  80  to determine the orientation of an articulation member. 
         [0052]    Those of skill in the art will appreciate that other graphical patterns, in addition to or in lieu of, triangles can be used. For example, in some embodiments, the graphical pattern may comprise dots, circles, rectangles and/or any other geometrical shape. In other embodiments, the surface may be color coded, and the camera configured to detect subtle differences in color shades, intensities, hues, etc. Furthermore, it is contemplated that different graphical patterns can be used in ball-and-socket articulation members  60 , which provide three axes of movement than are used in two-axis articulation members  60 ′. Preferably, the graphical elements included within a particular pattern can be reliably and accurately detected and distinguished from one another by the optical camera. The graphical pattern  80  can be placed on a surface of the articulation member (e.g., ball portion  62 ,  62 ′) using any suitable method. For example, the pattern  80  may be marked on a ball portion surface using a permanent dye, ink or other color pigment. Alternatively, the graphical pattern may be etched or shaped directly into a surface. In other non-limiting embodiments, the graphical pattern can placed on the surface as part of a coating and/or plating. 
         [0053]    In the embodiments of the ball and socket type articulation member described above, the graphical surface has been included on the ball portion  62 . However, it will be appreciated that the articulation member may be alternatively configured so that the graphical surface is positioned on the concave surface of the socket portion  64  or on an inner surface of the joint body  154 . In such embodiments, the camera or other detection member is preferably secured within the ball portion  62 . 
         [0054]    The various devices, methods, procedures, and techniques described above provide a number of ways to carry out the invention. Of course, it is to be understood that not necessarily all objectives or advantages described may be achieved in accordance with any particular embodiment described herein. Also, although the invention has been disclosed in the context of certain embodiments and examples, it will be understood by those skilled in the art that the invention extends beyond the specifically disclosed embodiments to other alternative embodiments, combinations, sub-combinations and/or uses and obvious modifications and equivalents thereof. Accordingly, the invention is not intended to be limited by the specific disclosures of preferred embodiments herein.