Abstract:
An apparatus for providing feedback to the operator of a portable coordinate measurement machine which comprises an articulated arm having jointed arm segments is presented. The apparatus includes sensing deformation of a portion of the articulated arm when the arm is placed under a load, the deformation being an indication of the magnitude of the external force being applied to the arm, and providing feedback to the operator of the CMM in response to the sensed external forces.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]     This application claims the benefit of provisional application Nos. 60/357,599 filed Feb. 14, 2002 and 60/394,908 filed Jul. 10, 2002, all of the contents of both provisional applications being incorporated herein by reference and is a continuation of application Ser. No. 10/642,427, which is a continuation-in-part of application Ser. No. 10/366,589 filed Feb. 13, 2003. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The invention relates in general to coordinate measurement machines (CMMs) and in particular to portable CMMs having an articulated arm.  
         [0004]     2. Prior Art  
         [0005]     Currently, portable articulated arms are provided as a measurement system with a host computer and applications software. The articulated arm is commonly used to measure points on an object and these measured points are compared to computer-aided design (CAD) data stored on the host computer to determine if the object is within the CAD specification. In other words, the CAD data is the reference data to which actual measurements made by the articulated arm are compared. The host computer may also contain applications software that guides the operator through the inspection process. For many situations involving complicated applications, this arrangement is appropriate since the user will observe the three-dimensional CAD data on the host computer while responding to complex commands in the applications software.  
         [0006]     An example of a prior art portable CMM for use in the above-discussed measurement system is disclosed in U.S. Pat. No. 5,402,582 (&#39;582), which is assigned to the assignee hereof and incorporated herein by reference. The &#39;582 patent discloses a conventional three-dimensional measuring system composed of a manually operated multi-jointed articulated arm having a support base on one end thereof and a measurement probe at the other end. A host computer communicates to the arm via an intermediate controller or serial box. It will be appreciated that in the &#39;582 patent, the arm will electronically communicate with the serial box which, in turn, electronically communicates with the host computer. Commonly assigned U.S. Pat. No. 5,611,147 (&#39;147), which is again incorporated herein by reference, discloses a similar CMM having an articulated arm. In this patent, the articulated arm includes a number of important features including an additional rotational axis at the probe end thus providing for an arm with either a two-one-three or a two-two-three joint configuration (the latter case being a 7 axis arm) as well as improved pre-loaded bearing constructions for the bearings in the arm.  
         [0007]     Still other relevant prior art CMMs include commonly assigned U.S. Pat. No. 5,926,782 (&#39;782), which provides an articulated arm having lockable transfer housings for eliminating one or more degrees of freedom and U.S. Pat. No. 5,956,857 (&#39;857) which provides an articulated arm having a quick disconnect mounting system.  
         [0008]     More current portable CMMs of the type described herein do not necessitate the use of an intermediate controller or serial box since the functionality thereof is now incorporated in the software provided by the host computer. For example, commonly assigned U.S. Pat. No. 5,978,748 (&#39;748), which is incorporated herein by reference, discloses an articulated arm having an on-board controller which stores one or more executable programs and which provides the user with instructions (e.g., inspection procedures) and stores the CAD data that serves as the reference data. In the &#39;748 patent, a controller is mounted to the arm and runs the executable program which directs the user through a process such as an inspection procedure. In such a system, a host computer may be used to generate the executable program. The controller mounted to the arm is used to run the executable program but cannot be used to create executable programs or modify executable programs. By way of analogy to video gaming systems, the host computer serves as the platform for writing or modifying a video game and the arm mounted controller serves as the platform for playing a video game. The controller (e.g., player) cannot modify the executable program. As described in the &#39;748 patent, this results in a lower cost three dimensional coordinate measurement system by eliminating the need for a host computer for each articulated arm. U.S. application Ser. No. 09/775,236 (&#39;236), assigned to the assignee hereof and incorporated herein by reference, discloses a method and system for delivering executable programs to users of coordinate measurement systems of the type disclosed in the &#39;748 patent. The method includes receiving a request to create an executable program from a customer and obtaining information related to the executable program. The executable program is then developed which guides an operator through a number of measurement steps to be performed with the three dimensional coordinate measuring system. The executable program is delivered to the customer, preferably over an on-line network such as the Internet.  
         [0009]     Commonly assigned U.S. Pat. No. 6,131,299 (&#39;299), (all the contents of which is incorporated herein by reference), discloses an articulated arm having a display device positioned thereon to allow an operator to have convenient display of positional data and system menu prompts. The display device includes for example, LEDs which indicate system power, transducer position status and error status. U.S. Pat. No. 6,219,928 (&#39;928), which is assigned to the assignee and incorporated herein by reference, discloses a serial network for the articulated arm. The serial network communicates data from transducers located in the arm to a controller. Each transducer includes a transducer interface having a memory which stores transducer data. The controller serially addresses each memory and the data is transferred from the transducer interface memory to the controller. Commonly assigned U.S. Pat. Nos. 6,253,458 (&#39;458) and 6,298,569 (&#39;569) both disclose adjustable counter balance mechanisms for articulated arm portable CMMs of the type described herein.  
         [0010]     While well suited for their intended purposes, there is a continued and perceived need in the industry for improved portable CMMs that are easier to use, more efficient to manufacture, provide improved features and can be sold at a lower cost.  
       SUMMARY OF THE INVENTION  
       [0011]     In accordance with the present invention, a portable CMM comprises an articulated arm having jointed arm segments. In one embodiment, the arm segments include bearing/encoder cartridges which are attached to each other at predetermined angles using a dual socket joint. Each cartridge contains at least one, and preferably two, preloaded bearing assemblies and an encoder, preferably an optical encoder, all assembled in a cylindrical housing. Preferably, two or more encoder read heads are used in each joint so as to cause cancellation effects that can be averaged. The arm segments may be threadably interconnected with the arm tapering from a wider diameter at its base to a narrower diameter at the probe end.  
         [0012]     In accordance with another embodiment of the present invention, one or more of the jointed arm segments of the articulated arm includes replaceable protective coverings and/or bumpers to limit high impact shock and abrasion as well as to provide an ergonomically and aesthetically pleasing gripping location.  
         [0013]     In still another embodiment of this invention, the articulated arm includes an integrated, internal counter balance in one of the hinge joints. This counter balance utilizes a coil spring having relatively wide end rings and narrower internal rings machined from a metal cylinder. The spring further includes at least two (and preferably three) posts for locking into the hinge structure of the arm as well as a spring adjustment mechanism.  
         [0014]     In still another embodiment of this invention, the articulated arm includes a measurement probe at one end thereof. This measurement probe has an integrally mounted touch trigger probe which is easily convertible to a conventional hard probe. The measurement probe also includes improved switches and a measurement indicator light. In one embodiment, the switches have an arcuate, oblong shape and are easily arctuatable by the operator. The improved switches include differing color, surface texture and/or height which allow the operator to easily distinguish between them while the indicator light preferably is color-coded for ease of operation.  
         [0015]     Another embodiment of the present invention includes an articulated arm having an integral, on-board power supply recharger unit. This power supply/recharger unit allows for a fully portable CMM and makes it far easier to use the CMM at a remote location and/or without the need for a directly cabled articulated arm.  
         [0016]     Still another embodiment of the present invention includes an articulated arm having a measurement probe at one end. The measurement probe includes a rotatable handle cover and switch assembly which surrounds the measurement probe. The rotatable handle cover and switch assembly allows the measurement probe to be more easily held and activated regardless of hand position. The use of the rotatable handle cover further precludes the necessity for having a third axis of rotation at the probe end thus allowing for a lower cost and more easily constructed portable CMM (relative to 7 axis CMMs or CMMs having a third angle of rotation at the measurement probe).  
         [0017]     In another embodiment of this invention, a portable CMM includes an articulated arm having jointed arm segments with a measurement probe at one end thereof and a base at the other end thereof. In accordance with a novel feature of this embodiment, the base has an integrated magnetic mount therein for attaching the arm to a magnetic surface. This integrated magnetic mount is preferably threadably connected to the articulated arm and has an on/off lever for ease of use (which lever preferably automatically engages when the mount is positioned onto a magnetic surface).  
         [0018]     The above-discussed and other features and advantages of the present invention will be appreciated and understood by those skilled in the art from the following detailed description and drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0019]     Referring now to the drawings wherein like elements are number alike in the several FIGURES:  
         [0020]      FIG. 1  is a front perspective view of the portable CMM of the present invention including an articulated arm and attached host computer;  
         [0021]      FIG. 2  is a rear perspective view of the CMM of  FIG. 1 ;  
         [0022]      FIG. 3  is a right side view of the CMM of  FIG. 1  (with the host computer removed);  
         [0023]      FIG. 3A  is a right side view of the CMM of  FIG. 1  with slightly modified protective sleeves covering two of the long joints;  
         [0024]      FIG. 4  is a partially exploded, perspective view of the CMM of the present invention depicting the base and the first articulated arm section;  
         [0025]      FIG. 5  is a partially exploded, perspective view of the CMM of the present invention depicting the base, first arm section and partially exploded second arm section;  
         [0026]      FIG. 6  is a partially exploded, perspective view of the CMM of the present invention depicting the base, first arm section, second arm section and partially exploded third arm section;  
         [0027]      FIG. 7  is an exploded, perspective view depicting a pair of encoder/bearing cartridges being assembled between two dual socket joints in accordance with the present invention;  
         [0028]      FIG. 8  is a front elevation view of the bearing/encoder cartridges and dual socket joints of  FIG. 7 ;  
         [0029]      FIG. 9  is an exploded, perspective view of a short bearing/encoder cartridge in accordance with the present invention;  
         [0030]      FIG. 9A  is an exploded, perspective view similar to  FIG. 9 , but showing a single read head;  
         [0031]      FIG. 9B  is an exploded, perspective view, similar to  FIG. 9 , but showing four read heads;  
         [0032]      FIG. 9C  is a perspective view of  FIG. 9B  after assembly;  
         [0033]      FIG. 9D  is an exploded, perspective view, similar to  FIG. 9 , but showing three read heads;  
         [0034]      FIG. 9E  is a perspective view of  FIG. 9D  after assembly;  
         [0035]      FIG. 10  is a cross-sectional elevation view of the cartridge of  FIG. 9 ;  
         [0036]      FIG. 11  is an exploded, perspective view of a long bearing/encoder cartridge in accordance with the present invention;  
         [0037]      FIG. 11A  is an exploded, perspective view similar to  FIG. 11 , but showing a single read head;  
         [0038]      FIG. 12  is a cross-sectional elevation view of the cartridge of  FIG. 11 ;  
         [0039]      FIG. 12A  is a cross-sectional elevation view of the cartridge of  FIG. 12  depicting the dual read heads being rotatable with the shaft;  
         [0040]      FIG. 13  is an exploded, perspective view of still another bearing/encoder cartridge in accordance with the present invention;  
         [0041]      FIG. 13A  is an exploded, perspective view similar to  FIG. 13 , but showing a single read head;  
         [0042]      FIG. 14  is a cross-sectional elevation view of the cartridge of  FIG. 13 ;  
         [0043]      FIG. 15  is an exploded, perspective view of a bearing/encoder cartridge and counter balance spring in accordance with the present invention;  
         [0044]      FIG. 15A  is an exploded, perspective view similar to  FIG. 15 , but showing a single read head;  
         [0045]      FIG. 16  is a cross-sectional elevation view of the cartridge and counter balance of  FIG. 15 ;  
         [0046]      FIG. 17  is a top plan view of a dual read head assembly for a larger diameter bearing/encoder cartridge used in accordance with the present invention;  
         [0047]      FIG. 18  is a cross-sectional elevation view along the line  18 - 18  of  FIG. 17 ;  
         [0048]      FIG. 19  is a bottom plan view of the dual read head assembly of  FIG. 17 ;  
         [0049]      FIG. 20  is a top plan view of a dual read head assembly for a smaller diameter bearing/encoder cartridge in accordance with the present invention;  
         [0050]      FIG. 21  is a cross-sectional elevation view along the line  21 - 21  of  FIG. 20 ;  
         [0051]      FIG. 22  is a bottom plan view of the dual read head assembly of  FIG. 20 ;  
         [0052]      FIG. 23A  is a block diagram depicting the electronics configuration for the CMM of the present invention using a single read head and  FIG. 23B  is a block diagram depicting the electronics configuration for the CMM of the present invention using a dual read head;  
         [0053]      FIG. 24  is a cross-sectional elevation view longitudinally through the CMM of the present invention (with the base removed);  
         [0054]      FIG. 24A  is a cross-sectional elevation view of the CMM of  FIG. 3A ;  
         [0055]      FIG. 25  is an enlarged cross-sectional view of a portion of  FIG. 24  depicting the base and first long joint segment of the CMM of  FIG. 24 ;  
         [0056]      FIG. 25A  is a perspective view of the interconnection between a long and short joint in accordance with an alternative embodiment of the present invention;  
         [0057]      FIG. 25B  is a cross-sectional elevation view longitudinally through a portion of  FIG. 25A ;  
         [0058]      FIG. 26  is an enlarged cross-sectional view of a portion of  FIG. 24  depicting the second and third long joint segments;  
         [0059]      FIGS. 26A  and B are enlarged cross-sectional views of portions of  FIG. 24A  depicting the second and third long joints as well as the probe;  
         [0060]      FIG. 27A  is an exploded side elevation view depicting the first short joint/counter balance assembly in accordance with the present invention;  
         [0061]      FIG. 27B  is a perspective view depicting the components of  FIG. 27A ;  
         [0062]      FIG. 28  is a cross-sectional elevation view depicting the internal counter balance of the present invention;  
         [0063]      FIG. 29  is a cross-sectional, side elevation view through a first embodiment of the measurement probe in accordance with the present invention;  
         [0064]      FIG. 29A  is a side elevation view of another embodiment of a measurement probe in accordance with the present invention;  
         [0065]      FIG. 29B  is a cross-sectional elevation view along the line  29 B- 29 B of  FIG. 29A ;  
         [0066]      FIG. 29C  is a perspective view of a pair of “take” or “confirm” switches used in FIGS.  29 A-B;  
         [0067]     FIGS.  30 A-C are sequential elevation plan views depicting the integrated touch probe assembly and conversion to hard probe assembly in accordance with the present invention;  
         [0068]      FIG. 31  is a cross-sectional, side elevation view through still another embodiment of a measurement probe in accordance with the present invention;  
         [0069]      FIG. 32  is an exploded, perspective view of the integrated magnetic base in accordance with the present invention;  
         [0070]      FIG. 33  is a cross-sectional elevation view through the magnetic base of  FIG. 32 ;  
         [0071]      FIG. 34  is a top plan view of the magnetic mount of  FIG. 32 ;  
         [0072]      FIG. 35  is a cross-sectional elevation view of a CMM joint from Raab &#39;356 with dual read heads;  
         [0073]      FIG. 36  is a cross-sectional elevation view of a CMM joint from Eaton &#39;148 with dual read heads;  
         [0074]      FIG. 37  is a side elevation view of a measurement probe with a seventh axis transducer;  
         [0075]      FIG. 38  is a side elevation view, similar to  FIG. 37 , but including a removable handle;  
         [0076]      FIG. 39  is an end view of the measurement probe of  FIG. 38 ;  
         [0077]      FIG. 40  is a cross-sectional elevation view of the measurement probe of  FIG. 38 ;  
         [0078]      FIG. 41  is a top plan view of a bearing/encoder cartridge employing a read head combined with a plurality of sensors in accordance with the present invention;  
         [0079]      FIG. 42  is a perspective view of the cartridge of  FIG. 41 ; and  
         [0080]      FIG. 43  is an enlarged view of the upper portion of the cartridge of  FIG. 42 . 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0081]     Referring first to  FIGS. 1-3 , the CMM of the present invention is shown generally at  10 . CMM  10  comprises a multijointed, manually operated, articulated arm  14  attached at one end to a base section  12  and attached at the other end to a measurement probe  28 . Arm  14  is constructed of basically two types of joints, namely a long joint (for swivel motion) and a short joint (for hinge motion). The long joints are positioned substantially axially or longitudinally along the arm while the short joints are preferably positioned at 90° to the longitudinal axis of the arm. The long and short joints are paired up in what is commonly known as a 2-2-2 configuration (although other joint configurations such as 2-1-2, 2-1-3, 2-2-3, etc. may be employed) Each of these joint pairs are shown in  FIGS. 4-6 .  
         [0082]      FIG. 4  depicts an exploded view of the first joint pair, namely long joint  16  and short joint  18 .  FIG. 4  also depicts an exploded view of the base  12  including a portable power supply electronics  20 , a portable battery pack  22 , a magnetic mount  24  and a two-piece base housing  26 A and  26 B. All of these components will be discussed in more detail hereinafter.  
         [0083]     Significantly, it will be appreciated that the diameters of the various primary components of articulated arm  14  will taper from the base  12  to the probe  28 . Such taper may be continuous or, as in the embodiment shown in the FIGURES, the taper may be discontinuous or step-wise. In addition, each of the primary components of articulated arm  14  may be threadably attached thereby eliminating a large number of fasteners associated with prior art CMMs. For example, and as will be discussed hereafter, magnetic mount  24  is threadably attached to first long joint  16 . Preferably, such threading is tapered threading which is self-locking and provides for increased axial/bending stiffness. Alternatively, as shown in  FIGS. 25A and 25B , and as discussed hereafter, the primary components of the articulated arm may have complimentary tapered male and female ends with associated flanges, such flanges being bolted together.  
         [0084]     Referring to  FIG. 5 , the second set of a long and short joint is shown being attached to the first set. The second joint set includes long joint  30  and short joint  32 . As is consistent with the attachment of magnetic mount  24  to long joint  16 , long joint  30  is threadably attached to threading on the interior surface of long joint  16 . Similarly, and with reference to  FIG. 6 , the third joint set includes a third long joint  34  and a third short joint  36 . Third long joint  34  threadably attaches to threading on the interior surface of second short joint  32 . As will be discussed in more detail hereinafter, probe  28  threadably attaches to short joint  36 .  
         [0085]     Preferably, each short joint  18 ,  32  and  36  is constructed of cast and/or machined aluminum components or alternatively, lightweight stiff alloy or composite. Each long joint  16 ,  30  and  34  is preferably constructed of cast and/or machined aluminum, lightweight stiff alloy and/or fiber reinforced polymer. The mechanical axes of the three aforementioned joint pairs (i.e., pair  1  comprises joint pairs  16 ,  18 , pair  2  comprises joint pairs  30 ,  32  and pair  3  comprises joint pairs  34 ,  36 ) are aligned with respect to the base for smooth, uniform mechanical behavior. The aforementioned tapered construction from base  12  to probe  28  is preferred to promote increased stiffness at the base where loads are greater and smaller profile at the probe or handle where unobstructed use is important. As will be discussed in more detail hereinafter, each short joint is associated with a protective bumper  38  on either end thereof and each long probe is covered with a protective sleeve  40  or  41 . It will be appreciated that the first long joint  16  is protected by the base housing  26 A, B which provides the same type of protection as sleeves  40 ,  41  provide for the second and third long joints  30 ,  34 .  
         [0086]     In accordance with an important feature of the present invention, each of the joints of the articulated arm utilizes a modular bearing/encoder cartridge such as the short cartridge  42  and the long cartridge  44  shown in  FIGS. 7 and 8 . These cartridges  42 ,  44  are mounted in the openings of dual socket joints  46 ,  48 . Each socket joint  46 ,  48  includes a first cylindrical extension  47  having a first recess or socket  120  and a second cylindrical extension  49  having a second recess or socket  51 . Generally, sockets  120  and  51  are positioned 90 degrees to one another although other relative, angular configurations may be employed. Short cartridge  42  is positioned in each socket  51  of dual socket joints  46  and  48  to define a hinge joint, while long cartridge  44  is positioned in socket  120  of joint  46  (see  FIG. 25 ) and long cartridge  44 ′ (see  FIG. 26 ) is positioned in socket  120  of joint  48  to each define a longitudinal swivel joint. Modular bearing/encoder cartridges  42 ,  44  permit the separate manufacture of a pre-stressed or preloaded dual bearing cartridge on which is mounted the modular encoder components. This bearing encoder cartridge can then be fixedly attached to the external skeletal components (i.e., the dual socket joints  46 ,  48 ) of the articulated arm  14 . The use of such cartridges is a significant advance in the field as it permits high quality, high speed production of these sophisticated subcomponents of articulated arm  14 .  
         [0087]     In the embodiment described herein, there are four different cartridge types, two long axial cartridges for joints  30  and  34 , one base axial cartridge for joint  16 , one base cartridge (which includes a counter balance) for short joint  18  and two hinge cartridges for joints  32  and  36 . In addition, as is consistent with the taper of articulated arm  14 , the cartridges nearest the base (e.g., located in long joint  16  and short joint  18 ) have a larger diameter relative to the smaller diameters of joints  30 ,  32 ,  34  and  36 . Each cartridge includes a pre-loaded bearing arrangement and a transducer which in this embodiment, comprises a digital encoder. Turning to  FIGS. 9 and 10 , the cartridge  44  positioned in axial long joint  16  will now be described.  
         [0088]     Cartridge  44  includes a pair of bearings  50 ,  52  separated by an inner sleeve  54  and outer sleeve  56 . It is important that bearings  50 ,  52  are pre-loaded. In this embodiment, such preload is provided by sleeves  54 ,  56  being of differing lengths (inner sleeve  54  is shorter than outer sleeve  56  by approximately 0.0005 inch) so that upon tightening, a preslected preload is generated on bearings  50 ,  52 . Bearings  50 ,  52  are sealed using seals  58  with this assembly being rotatably mounted on shaft  60 . At its upper surface, shaft  60  terminates at a shaft upper housing  62 . An annulus  63  is defined between shaft  60  and shaft upper housing  62 . This entire assembly is positioned within outer cartridge housing  64  with the shaft and its bearing assembly being securely attached to housing  64  using a combination of an inner nut  66  and an outer nut  68 . Note that upon assembly, the upper portion  65  of outer housing  64  will be received within annulus  63 . It will be appreciated that the aforementioned preload is provided to bearings  50 ,  52  upon the tightening of the inner and outer nuts  66 ,  68  which provide compression forces to the bearings and, because of the difference in length between the inner and outer spacers  54 ,  56 , the desired preload will be applied.  
         [0089]     Preferably, bearings  50 ,  52  are duplex ball bearings. In order to obtain the adequate pre-loading, it is important that the bearing faces be as parallel as possible. The parallelism affects the evenness of the pre-loading about the circumference of the bearing. Uneven loading will give the bearing a rough uneven running torque feel and will result in unpredictable radial run out and reduced encoder performance. Radial run out of the modularly mounted encoder disk (to be discussed below) will result in an undesirable fringe pattern shift beneath the reader head. This results in significant encoder angular measurement errors. Furthermore, the stiffness of the preferably duplex bearing structure is directly related to the separation of the bearings. The farther apart the bearings, the stiffer will be the assembly. The spacers  54 ,  56  are used to enhance the separation of the bearings. Since the cartridge housing  64  is preferably aluminum, then the spacers  54 ,  56  will also preferably be made from aluminum and precision machined in length and parallelism. As a result, changes in temperature will not result in differential expansion which would compromise the preload. As mentioned, the preload is established by designing in a known difference in the length of spacers  54 ,  56 . Once the nuts  66 ,  68  are fully tightened, this differential in length will result in a bearing preload. The use of seals  58  provide sealed bearings since any contamination thereof would effect all rotational movement and encoder accuracy, as well as joint feel.  
         [0090]     While cartridge  44  preferably includes a pair of spaced bearings, cartridge  44  could alternatively include a single bearing or three or more bearings. Thus, each cartridge needs at least one bearing as a minimum.  
         [0091]     The joint cartridges of the present invention may either have unlimited rotation or as an alternative, may have a limited rotation. For a limited rotation, a groove  70  on a flange  72  on the outer surface of housing  64  provides a cylindrical track which receives a shuttle  74 . Shuttle  74  will ride within track  70  until it abuts a removable shuttle stop such as the rotation stop set screws  76  whereupon rotation will be precluded. The amount of rotation can vary depending on what is desired. In a preferred embodiment, shuttle rotation would be limited to less than 720°. Rotational shuttle stops of the type herein are described in more detail in commonly owned U.S. Pat. No. 5,611,147, all of the contents of which have been incorporated herein by reference.  
         [0092]     As mentioned, in an alternative embodiment, the joint used in the present invention may have unlimited rotation. In this latter case, a known slip ring assembly is used. Preferably, shaft  60  has a hollow or axial opening  78  therethrough which has a larger diameter section  80  at one end thereof. Abutting the shoulder defined at the intersection between axial openings  78  and  80  is a cylindrical slip ring assembly  82 . Slip ring assembly  82  is non-structural (that is, provides no mechanical function but only provides an electrical and/or signal transfer function) with respect to the preloaded bearing assembly set forth in the modular joint cartridge. While slip ring assembly  82  may consist of any commercially available slip ring, in a preferred embodiment, slip ring assembly  82  comprises a H series slip ring available from IDM Electronics Ltd. of Reading, Berkshire, United Kingdom. Such slip rings are compact in size and with their cylindrical design, are ideally suited for use in the opening  80  within shaft  60 . Axial opening  80  through shaft  60  terminates at an aperture  84  which communicates with a channel  86  sized and configured to receive wiring from the slip ring assembly  82 . Such wiring is secured in place and protected by a wire cover  88  which snaps onto and is received into channel  86  and aperture  84 . Such wiring is shown diagrammatically at  90  in  FIG. 10 .  
         [0093]     As mentioned, modular cartridge  44  include both a preloaded bearing structure which has been described above as well as a modular encoder structure which will now be described. Still referring to  FIGS. 9 and 10 , the preferred transducer used in the present invention comprises a modular optical encoder having two primary components, a read head  92  and a grating disk  94 . In this embodiment, a pair of read heads  92  are positioned on a read head connector board  96 . Connector board  96  is attached (via fasteners  98 ) to a mounting plate  100 . Disk  94  is preferably attached to the lower bearing surface  102  of shaft  60  (preferably using a suitable adhesive) and will be spaced from and in alignment with read heads  92  (which is supported and held by plate  100 ). A wire funnel  104  and sealing cap  106  provide the final outer covering to the lower end of housing  64 . Wire funnel  104  will capture and retain wiring  90  as best shown in  FIG. 10 . It will be appreciated that the encoder disk  94  will be retained by and rotate with shaft  60  due to the application of adhesive at  102 .  FIGS. 9 and 10  depict a double read head  92 ; however, it will be appreciated that more than two read heads may be used or, in the alternative, a single read head as shown in  FIG. 9A  may be used. FIGS.  9 B-E depict examples of modular cartridges  44  with more than two read heads. FIGS.  9 B-C show four read heads  92  received in a plate  100  and spaced at 90 degree intervals (although different relative spacings may be appropriate). FIGS.  9 D-E show three read heads  92  received in a plate  100  and spaced at 120 degree intervals (although different relative spacing may be appropriate).  
         [0094]     In order to properly align disk  94 , a hole (not shown) is provided through housing  64  at a location adjacent disk  94 . A tool (not shown) is then used to push disk  94  into proper alignment whereupon adhesive between disk  94  and shaft  66  is cured to lock disk  94  in place. A hole plug  73  is then provided through the hole in housing  64 .  
         [0095]     It is important to note that the locations of disk  94  and read head  92  may be reversed whereby disk  94  is attached to housing  56  and read head  92  rotates with shaft  60 . Such an embodiment is shown in  FIG. 12A  where board  96 ′ is attached (via adhesive) to shaft  60 ′ for rotation therewith. A pair of read heads  92 ′ are attached to board  96 ′ and thus will rotate with shaft  60 ′. The disk  94 ′ is positioned on a support  100 ′ which is attached to housing  64 ′. In any event, it will be appreciated that either the disk  94  or read head  92  may be mounted for rotation with the shaft. All that is important is that disk  94  and read head  92  be positioned in a cartridge (or joint) so as to be rotatable with respect to each other while maintaining optical communication.  
         [0096]     Preferably, the rotational encoder employed in the present invention is similar to that disclosed in U.S. Pat. Nos. 5,486,923 and 5,559,600, all of the contents of which are incorporated herein by reference. Such modular encoders are commercially available from MicroE Systems under the trade name Pure Precision Optics. These encoders are based on physical optics that detect the interference between diffraction orders to produce nearly perfect sinusoidal signals from a photo detector array (e.g., read head(s)) inserted in the fringe pattern. The sinusoidal signals are electronically interpolated to allow detection of displacement that is only a fraction of the optical fringe.  
         [0097]     Using a laser light source, the laser beam is first collimated by a lens and then sized by an aperture. The collimated size beam passes through a grating that diffracts the light into discrete orders with the 0 th  and all even orders suppressed by the grating construction. With the 0 order suppressed, a region exists beyond the diverging 3 rd  order where only the ±1 st  orders overlap to create a nearly pure sinusoidal interference. One or more photodetector arrays (read heads) are placed within this region, and produces four channels of nearly pure sinusoidal output when there is relative motion between the grating and the detector. Electronics amplify, normalize and interpolate the output to the desired level of resolution.  
         [0098]     The simplicity of this encoder design yields several advantages over prior art optical encoders. Measurements may be made with only a laser source and its collimating optics, a diffractive grating, and a detector array. This results in an extremely compact encoder system relative to the bulkier prior art, conventional encoders. In addition, a direct relationship between the grating and the fringe movement desensitizes the encoder from environmentally induced errors to which prior art devices are susceptible. Furthermore, because the region of interference is large, and because nearly sinusoidal interference is obtained everywhere within this region, alignment tolerances are far more relaxed than is associated with prior art encoders.  
         [0099]     A significant advantage of the aforementioned optical encoder is that the precision of the standoff orientation and distance or the distance and orientation of the read head with respect to the encoder disk is far less stringent. This permits a high accuracy rotational measurement and an easy-to-assemble package. The result of using this “geometry tolerant” encoder technology results in a CMM  10  having significant cost reductions and ease of manufacturing.  
         [0100]     It will be appreciated that while the preferred embodiment described above includes an optical disk  94 , the preferred embodiment of the present invention also encompasses any optical fringe pattern which allow the read head to measure relative motion. As used herein, such fringe pattern means any periodic array of optical elements which provide for the measurement of motion. Such optical elements or fringe pattern could be mounted on a rotating or stationary disk as described above, or alternatively, could be deposited, secured or otherwise positioned or reside upon any of the relatively moving components (such as the shaft, bearings or housing) of the cartridge.  
         [0101]     Indeed, the read head and associated periodic array or pattern does not necessarily need to be based on optics (as described above) at all. Rather, in a broader sense, the read head could read (or sense) some other periodic pattern of some other measurable quantity or characteristic which can be used to measure motion, generally rotary motion. Such other measurable characteristics may include, for example, reflectivity, opacity, magnetic field, capacitance, inductance or surface roughness. (Note that a surface roughness pattern could be read using a read head or sensor in the form of a camera such as a CCD camera). In such cases, the read head would measure, for example, periodic changes in magnetic field, reflectivity, capacitance, inductance, surface roughness or the like. As used herein therefore, the term “read head” means any sensor or transducer and associated electronics for analysis of these measurable quantities or characteristics with an optical read head being just one preferred example. Of course, the periodic pattern being read by the read head can reside on any surface so long as there is relative (generally rotary) motion between the read head and periodic pattern. Examples of the periodic pattern include a magnetic, inductive or capacitive media deposited on a rotary or stationary component in a pattern. Moreover, if surface roughness is the periodic pattern to be read, there is no need to deposit or otherwise provide a separate periodic media since the surface roughness of any component in communication with the associated read head (probably a camera such as a CCD camera) may be used.  
         [0102]     As mentioned,  FIGS. 9 and 10  depict the elements of the modular bearing and encoder cartridge for axially long joint  16 .  FIGS. 11 and 12  depict the bearing and encoder cartridge for axial long joints  30  and  34 . These cartridge assemblies are substantially similar to that shown  FIGS. 9 and 10  and so are designated by  44 ′. Minor differences are evident from the FIGURES relative to cartridge  44  with respect to, for example, a differently configured wire cap/cover  88 ′, slightly differing wire funnels/covers  104 ′,  106 ′ and the positioning of flange  72 ′ at the upper end of housing  64 ′. Also, the flanges between housing  64 ′ and shaft upper housing  62  are flared outwardly. Of course, the relative lengths of the various components shown in  FIGS. 11 and 12  may differ slightly from that shown in  FIGS. 9 and 10 . Since all of these components are substantially similar, the components have been given the same identification numeral with the addition of a prime.  FIG. 11A  is similar to  FIG. 11 , but depicts a single read head embodiment.  
         [0103]     Turning to  FIGS. 13 and 14 , similar exploded and cross-sectional views are shown for the bearing and encoder cartridges in short hinge joints  32  and  36 . As in the long axial joints  44 ′ of  FIGS. 11 and 12 , the cartridges for the short hinge joints  32  and  36  are substantially similar to the cartridge  44  discussed in detail above and therefore the components of these cartridges are identified at  44 ″ with similar components being identified using a double prime. It will be appreciated that because cartridges  44 ″ are intended for use in short joints  32 ,  36 , no slip ring assembly is required as the wiring will simply pass through the axial openings  78 ″,  80 ″ due to the hinged motion of these joints.  FIG. 13A  is similar to  FIG. 13 , but depicts a single read head embodiment.  
         [0104]     Finally, with reference to  FIGS. 15 and 16 , the modular bearing/encoder cartridge for short hinge joint  18  is shown at  108 . It will be appreciated that substantially all of the components of cartridge  108  are similar or the same as the components in cartridges  44 ,  44 ′ and  44 ″ with the important exception being the inclusion of a counter balance assembly. This counter balance assembly includes a counter balance spring  110  which is received over housing  64 ″ and provides an important counter balance function to CMM  10  in a manner which will be described hereinafter with reference to FIGS.  26  to  28 .  FIG. 15A  is similar to  FIG. 15 , but depicts a single read head embodiment.  
         [0105]     As mentioned, in a preferred embodiment, more than one read head may be used in the encoder. It will be appreciated that angle measurement of an encoder is effected by disk run out or radial motion due to applied loads. It has been determined that two read heads positioned at 180° from each other will result in run out causing cancellation effects in each read head. These cancellation effects are averaged for a final “immune” angle measurement. Thus, the use of two read heads and the resultant error cancellation will result in a less error prone and more accurate encoder measurement.  FIGS. 17-19  depict the bottom, cross-sectional and top views respectively for a dual read head embodiment useful in, for example, a larger diameter cartridge such as found in joints  16  and  18  (that is, those joints nearest the base). Thus, a cartridge end cap  100  has mounted thereto a pair of circuit boards  96  with each circuit board  96  having a read head  92  mechanically attached thereto. The read heads  92  are preferably positioned 180° apart from each other to provide for the error cancellation resulting from the run out or radial motion of the disk. Each board  96  additionally includes a connector  93  for attachment of the circuit board  96  to the internal bus and/or other wiring as will be discussed hereinafter.  FIGS. 20-22  depict substantially the same components as in  FIGS. 17-19  with the primary difference being a smaller diameter cartridge end cap  100 . This smaller diameter dual read head embodiment would be associated with the smaller diameter cartridges of, for example, joints  30 ,  32 ,  34  and  36 .  
         [0106]     The use of at least two read heads (or more such as the three reads heads shown in FIGS.  9 D-E and the four read heads shown in FIGS.  9 B-C) is also advantageously employed in more conventional coordinate measurement machines to significantly reduce the cost and complexity of manufacture thereof. For example, a coordinate measurement machine described in U.S. Pat. No. 5,794,356 (hereinafter “Raab &#39;356”), incorporated herein by reference, includes a relatively simple construction for each joint including a first housing that remains stationary with one joint half, and a second housing that remains stationary with the second joint half, the first and second housings having pre-loaded bearings that allow them to rotate with each other. The first housing retains a packaged encoder and the second housing includes an axially-disposed internal shaft that extends into the first housing and mates with the encoder shaft protruding from the packaged encoder. The prior art packaged encoder required that there be no loads applied thereto and that the motion of the second housing be accurately transmitted to the encoder despite small misalignments of the axis of the internal shaft and the axis of the packaged encoder to maintain the highly accurate rotational measurements. To accommodate manufacturing tolerances in axial misalignment, a special coupling device is connected between the encoder shaft and the internal shaft. Such a structure can be seen in  FIG. 7  of Raab &#39;356.  
         [0107]     In contrast,  FIG. 35  shows a modified structure  400  in which the coupling device and packaged encoder from the Raab &#39;356 CMM are removed and replaced with encoder disk  96  and end cap  100 . Here, two joints are positioned at 90° to each other, each joint having a first housing  420  and a second housing  410 . Internal shaft  412  extends from second housing  420  into first housing  410 . As shown, encoder disk  96  is attached, e.g., using adhesive, to the end of internal shaft  412  while end cap  100  is fixed within first housing  420 . However, it will be understood that encoder disk  96  may be fixed within first housing  420  and end cap  100  be fixed to internal shaft  412  without affecting the operation of the joint.  
         [0108]     As previously described, the use of two (or more) read heads and the resultant error cancellation will result in a less error prone and more accurate encoder measurement despite small axial misalignments. In addition, a direct relationship between the grating and the fringe movement desensitizes the encoder from environmentally induced errors to which prior art devices are susceptible. Furthermore, because the region of interference is large, and because nearly sinusoidal interference is obtained everywhere within this region, alignment tolerances are far more relaxed than is associated with prior art encoders as previously described.  
         [0109]     In another example, U.S. Pat. No. 5,829,148 to Eaton (hereinafter “Eaton &#39;148”), incorporated herein by reference, describes a prior art CMM in which a packaged encoder forms an integral part of each joint by providing primary rotational bearings, therefore avoiding any need to compensate for axial misalignments as required in Raab &#39;356 discussed above. However, because the encoder provides primary rotational bearings, it is important that the encoder be structurally rugged and able to be subjected to various loadings without affecting its performance. This adds to the cost and bulkiness of the encoder. Such a structure can be seen in  FIG. 4  of Eaton &#39;148.  
         [0110]     In contrast,  FIG. 36  shows a modified structure  450  in which the packaged encoder and connecting shaft of one joint from the Eaton &#39;148 CMM is removed and replaced by end cap  100  and encoder disk  96 . Here a first housing  470  retains end cap  100  and retains internal shaft  462  of second housing  460  by bearings  472 . Internal shaft  462  is extended to terminate proximate end cap  100  and encoder disk  96  is attached, e.g., using adhesive, at the end of internal shaft  462 . As in the embodiment shown in  FIG. 35 , the use of two (or more) read heads significantly reduces the cost and complexity of the joint without sacrificing accuracy.  
         [0111]     It will be appreciated that non-circularity of the motion of the periodic pattern is the primary cause for inaccuracies in a rotational transducer of the types described herein. This non-circularity of motion can be due to a number of phenomena including assembly imperfections and external deformations. External deformations can occur anywhere in the CMM and most generally occur with respect to the bearing structure and/or the joint tubing. For example, such external deformation can result from non-repeatable bearing run-out, bearing wobble, bearing deformation, thermal affects and bearing play. As discussed with respect to  FIGS. 17-21 , in one embodiment of this invention, the inaccuracies of the rotational transducers are corrected for using at least two read heads, preferably mounted at 180° apart from each other. However, in still another embodiment of this invention shown in  FIGS. 41-43 , the possible error derived from deformations to the CMM and/or assembly imperfections are corrected using a combination of at least one read head with one or more sensors, preferably a plurality of proximity sensors (or any other sensor which measures displacement).  
         [0112]     It will be appreciated that in any given cartridge of the type described herein, there are six degrees of freedom between the shaft and the housing of the cartridge. That is, the shaft includes six degrees of freedom, namely X, Y and Z axis displacement and X, Y, and Z axis rotation. Turning now to  FIGS. 41-43 , a cartridge of the type described above is shown at  600 . Cartridge  600  includes an internal shaft  602  rotationally mounted on bearings (not shown) within a housing  606 . Read head plate  604  secures an encoder read head  610  and sensors S 1 -S 5  to housing  606 . An encoder disk  608  having an optical fringe pattern thereon is attached to shaft  602  for rotation therewith. Encoder read head  610  (attached to read head plate  604 ) is mounted above optical fringe pattern  608  and preferably functions to measure Z axis rotation of shaft  602 . In addition to read head  610 , cartridge  600  includes five additional sensors, all of which are fixed to housing  606  through read head plate  604 ; and all of which are intended to measure relative movement between the shaft  602  and housing  606 . These additional sensors include a displacement sensor S 1  for measuring Y axis displacement of shaft  602  (with respect to housing  606 ) and a displacement sensor S 2  for measuring X axis displacement of shaft  602  (with respect to housing  606 ). Thus, shaft  602  has associated with it three sensors, namely read head  610  and sensors S 1  and S 2  for respectively measuring the Z axis rotation and the X and Y axis displacement thereof. Preferably, the shaft  602  includes three additional sensors associated with it for measuring X and Y axis rotation and Z axis displacement. Specifically, sensors S 3 , S 4  and S 5  in combination measure the X and Y axis of rotation as well as the Z axis displacement. In the embodiment shown in  FIGS. 41-43 , the S 3 , S 4  and S 5  sensors are spaced along the read head plate  604  at 120° intervals. The measurements from these equidistantly spaced three sensors are combined in a known manner to determine the combined X and Y axis rotation and Z axis displacement.  
         [0113]     Thus, these additional five sensors S 1 -S 5  measure and correct for any deformations in the CMM including the joint tubes or the bearing structure and these sensors can be used to correct for such error in measurement. These additional sensors are therefore used to measure relative motions between the shaft and housing to determine movements other than the rotary movement of the disk and therefore correct for any errors caused by these “other” movements. Any suitable type of sensor for carrying out these displacement measurements may be used in accordance with the present invention. Preferably the sensors are proximity sensors such as proximity sensors using Hall effects, or proximity sensors based on magneto, resistive, capacitive or optical characteristics.  
         [0114]     It will be appreciated that, when for example, a joint is placed under load and the bearing structure deforms (and as a result of such deformation, the shaft  602  carrying the optical pattern  608  and the housing  606  with the read head  610  will move with respect to each other), the angular measurement which will be affected by such movement will be “corrected” using the displacement information from the additional sensors S 1 -S 5  (it being appreciated that the present invention contemplates the use of all or less than all of the sensors S 1 -S 5  and moreover further contemplates the use of sensors in addition to S 1  through S 5 ). This correction results in substantially improved accuracy for the portable CMM. It will further be appreciated that while the invention contemplates at least one of the joint cartridges including additional sensors S 1 -S 5 , in a preferred embodiment, all of the cartridges would include such additional sensors. Also, while the  FIGS. 41-43  embodiment is shown with a rotary encoder having an optical grating disk, any of the alternative rotary encoders described previously which detect and analyze a periodic pattern of a measurable characteristic including those employing measurable characteristics such a reflectivity, opacity, magnetic field, capacitance, inductance or surface roughness, may be utilized with the sensors S 1 -S 5  as described herein. Also, while the FIGS.  41 - 43  embodiment depict an embodiment wherein the optical disk rotates with the shaft  602 , the multiple sensors S 1 -S 5  may also be used with an embodiment such as that shown in  FIG. 12A  where the optical disk is stationary.  
         [0115]     While, as discussed above, the additional sensors could be used to correct for errors caused by bearing and other arm deformations, the additional sensors may also be used to calculate and measure the external forces directed at the joint which are actually causing such structural deformation. These measurements may be advantageously utilized so as to provide sensory feedback to the user. For example, certain ranges of external forces can be tolerated on a particular bearing structure or joint; however, the sensing of external forces by deformation of the bearing arrangement can be used to indicate that these ranges have been exceeded and thereafter provide sensory feedback to the user so as to take remedial action to alleviate such external forces. That is, the user can then modify the handling of the CMM in order to improve the measurement. This sensory feedback may be in the form of auditory and/or visual feedback; and may be indicated by software controlling the CMM. Thus, the additional sensors S 1 -S 5  described above can act as overload sensors and prevent the user from overstressing the arm and thereby maintain optimum precision so as to insure precise measurement. Indeed, the measurement of the external force on a given joint may be utilized not only with the embodiment of  FIGS. 41-43  (wherein additional sensors S 1 -S 5  are employed) but also with the above-discussed embodiments wherein two or more read heads are employed. In the case of the two read head arrangement, the angular measurement is derived from the average of the two read heads. The force of deformation can then be obtained by measuring the difference between the two read head readings. In the case of the  FIGS. 41-43  embodiments, the deformation can be measured in the direction of each of the two proximity sensors. This provides additional directional information. Using all six sensors (S 1 -S 5  and the read head) will provide a total description of the deformations in each of the joints due to the measurement of all six degrees of freedom.  
         [0116]     In addition to the improvements in the angular accuracy of the transducer provided by either the use of two read heads or the use of a single read head together with one or more proximity sensors, the information derived from measuring the force of deformation can also be used to correct the kinematics of the arm by using such deformation information to change the dimension of the arm in real time and thereby improve the accuracy of the measurement. Thus, for example, if the bearings are deformed, this deformation will cause a change in the length of a segment of the arm. By measuring this deformation using the sensors and read heads as described herein, this change in the length of the arm can be taken into account in the measurement software associated with the CMM and then used as a correction to improve the ultimate measurement accuracy of the arm.  
         [0117]     Turning now to  FIG. 23A , a block diagram of the electronics is shown for the single read head embodiment of  FIGS. 9A, 11A ,  13 A and  15 A. It will be appreciated that CMM  10  preferably includes an external bus (preferably a USB bus)  260  and an internal bus (preferably RS-485)  261  which is designed to be expandable for more encoders as well as either an externally mounted rail or additional rotational axes such as a seventh axis. The internal bus is preferably consistent with RS485 and this bus is preferably configured to be used as a serial network in a manner consistent with the serial network for communicating data from transducers in a portable CMM arm as disclosed in commonly assigned U.S. Pat. No. 6,219,928, all of the contents of which have been incorporated herein by reference.  
         [0118]     With reference to  FIG. 23A , it will be appreciated that each encoder in each cartridge is associated with an encoder board. The encoder board for the cartridge in joint  16  is positioned within base  12  and is identified at  112  in  FIG. 25 . The encoders for joints  18  and  30  are processed on a dual encoder board which is located in the second long joint  30  and is identified at  114  in  FIG. 26 .  FIG. 26  also depicts a similar dual encoder board  116  for the encoders used in joints  32  and  34 , board  116  being positioned in third long joint  34  as shown in  FIG. 26 . Finally, the end encoder board  118  is positioned within measurement probe handle  28  as shown in  FIG. 24  and is used to process the encoders in short joint  36 . Each of the boards  114 ,  116  and  118  are associated with a thermocouple to provide for thermal compensation due to temperature transients. Each board  112 ,  114 ,  116  and  118  incorporates embedded analog-to-digital conversion, encoder counting and serial port communications. Each board also has read programmable flash memory to allow local storage of operating data. The main processor board  112  is also field programmable through the external USB bus  260 . As mentioned, the internal bus (RS-485)  261  is designed to be expandable for more encoders which also includes either an externally mounted rail and/or seventh rotation axis. An axis port has been provided to provide internal bus diagnosis. Multiple CMMs of the type depicted at  10  in these FIGURES may be attached to a single application due to the capabilities of the external USB communications protocol. Moreover, multiple applications may be attached to a single CMM  10  for the very same reasons.  
         [0119]     Preferably, each board  112 ,  114 ,  116  and  118  includes a 16-bit digital signal processor such as the processor available from Motorola under the designation DSP56F807. This single processing component combines many processing features including serial communication, quadrature decoding, A/D converters and on-board memory thus allowing a reduction of the total number of chips needed for each board.  
         [0120]     In accordance with another important feature of the present invention, each of the encoders is associated with an individualized identification chip  121 . This chip will identify each individual encoder and therefore will identify each individual bearing/encoder modular cartridge so as to ease and expedite quality control, testing, and repair.  
         [0121]      FIG. 23B  is an electronics block diagram which is similar to  FIG. 23A , but depicts the dual read head embodiment of  FIGS. 10, 12 ,  14  and  16 - 22 .  
         [0122]     With reference to  FIGS. 24-26 , the assembly of each cartridge in the articulated arm  14  will now be described (note that  FIG. 24  depicts arm  10  without base  12 . Note also that  FIGS. 24-26  employ the single read head embodiments of  FIGS. 9A, 11A ,  13 A and  15 A). As shown in  FIG. 25 , the first long joint  16  includes a relatively long cartridge  44 , the upper end of which has been inserted into a cylindrical socket  120  of dual socket joint  46 . Cartridge  44  is securely retained within socket  120  using a suitable adhesive. The opposite, lower end of cartridge  44  is inserted into an extension tube, which in this embodiment may be an aluminum sleeve  122  (but sleeve  122  may also be comprised of a stiff alloy or composite material). Cartridge  44  is secured in sleeve  122  again using a suitable adhesive. The lower end of sleeve  122  includes a larger outer diameter section  124  having internal threading  126  thereon. Such threading is outwardly tapered and is configured to threadably mate with inwardly tapered threading  128  on magnetic mount housing  130  as is clearly shown in  FIG. 4 . As has been discussed, all of the several joints of CMM  10  are interconnected using such tapered threading. Preferably, the tapered thread is of the NPT type which is self-tightening and therefore no lock nuts or other fastening devices are needed. This threading also allows for and should include a thread locking agent.  
         [0123]     Turning to  FIG. 26 , as in first long joint  16 , long cartridge  44 ′ is adhesively secured in the cylindrical opening  120 ′ of dual socket joint  46 ′. The outer housing  64 ′ of cartridge  44 ′ includes a shoulder  132  defined by the lower surface of flange  72 ′. This shoulder  132  supports cylindrical extension tube  134  which is provided over and surrounds the outer surface of housing  64 ′. Extension tubes are used in the joints to create a variable length tube for attachment to a threaded component. Extension tube  134  thus extends outwardly from the bottom of cartridge  64 ′ and has inserted therein a threaded sleeve  136 . Appropriate adhesive is used to bond housing  44 ′ to extension tube  134  as well as to bond sleeve  136  and tube  134  together. Sleeve  136  terminates at a tapered section having outer threading  138  thereon. Outer threading threadably mates with internal threading  140  on connecting piece  142  which has been adhesively secured in opening  144  of dual socket joint  48 . Preferably, extension tube  134  is composed of a composite material such as an appropriate carbon fiber composite while threadable sleeve  136  is composed of aluminum so as to match the thermal properties of the dual socket joint  48 . It will be appreciated that PC board  114  is fastened to a support  146  which in turn is secured to dual socket joint support  142 .  
         [0124]     In addition to the aforementioned threaded connections, one, some or all of the joints may be interconnected using threaded fasteners as shown in FIGS.  25 A-B. Rather than the threaded sleeve  136  of  FIG. 26 , sleeve  136 ′ of  FIG. 25B  has a smooth tapered end  137  which is received in a complimentary tapered socket support  142 ′. A flange  139  extends circumferentially outwardly from sleeve  136 ′ with an array of bolt holes (in this case 6) therethrough for receiving threaded bolts  141 . Bolts  141  are threadably received in corresponding holes along the upper surface of socket support  142 ′. An extension tube  134 ′ is received over sleeve  136 ′ as in the  FIG. 26  embodiment. The complimentary tapered male and female interconnections for the joints provide improved connection interfaces relative to the prior art.  
         [0125]     Still referring to  FIG. 26 , long cartridge  44 ″ of third long joint  34  is secured to arm  14  in a manner similar to cartridge  44 ′ of long joint  30 . That is, the upper portion of cartridge  44 ″ is adhesively secured into an opening  120 ″ of dual socket joint  46 ″. An extension tube  148  (preferably composed of a composite material as described with respect to tube  134 ) is positioned over outer housing  64 ″ and extends outwardly thereof so as to receive a mating sleeve  150  which is adhesively secured to the interior diameter of extension tube  148 . Mating sleeve  150  terminates at a tapered section having outer threading  152  and mates with complimentary interior threading  153  on dual socket joint support  154  which has been adhesively attached to a cylindrical socket  156  within dual socket joint  148 ′. Printed circuit board  116  is similarly connected to the dual socket joint using the PCB support  146 ′ which is secured to dual socket joint support  154 .  
         [0126]     As discussed with respect to  FIGS. 7 and 8 , the short cartridges  44 ′ in  FIGS. 13 and 14  and  108  of  FIG. 15  are simply positioned between two dual socket joints  46 ,  48  and are secured within the dual socket joints using an appropriate adhesive. As a result, the long and short cartridges are easily attached to each other at right angles (or, if desired, at angles other than right angles).  
         [0127]     The modular bearing/transducer cartridges as described above constitute an important technological advance in portable CMMs such as shown, for example, in the aforementioned Raab &#39;356 and Eaton &#39;148 patents. This is because the cartridge (or housing of the cartridge) actually defines a structural element of each joint which makes up the articulated arm. As used herein, “structural element” means that the surface of the cartridge (e.g., the cartridge housing) is rigidly attached to the other structural components of the articulated arm in order to transfer rotation without deformation of the arm (or at most, with only de minimis deformation). This is in contrast to conventional portable CMMs (such as disclosed in the Raab &#39;356 and Eaton &#39;148 patents) wherein separate and distinct joint elements and transfer elements are required with the rotary encoders being part of the joint elements (but not the transfer elements). In essence, the present invention has eliminated the need for separate transfer elements (e.g., transfer members) by combining the functionality of the joint and transfer elements into a singular modular component (i.e., cartridge). Hence, rather than an articulated arm comprised of separate and distinct joints and transfer members, the present invention utilizes an articulated arm made up of a combination of longer and shorter joint elements (i.e., cartridges), all of which are structural elements of the arm. This leads to better efficiencies relative to the prior art. For example, the number of bearings used in a joint/transfer member combination in the &#39;148 and &#39;582 patent was four (two bearings in the joint and two bearings in the transfer member) whereas the modular bearing/transducer cartridge of the present invention may utilize a minimum of one bearing (although two bearings are preferred) and still accomplish the same functionality (although in a different and improved way).  
         [0128]     FIGS.  24 A and  26 A-B are cross-sectional views, similar to  FIGS. 24-26 , but showing the dual read head embodiments of  FIGS. 10, 12 ,  14  and  16 - 22  and are further cross-sections of the CMM  10 ′ shown in  FIG. 3A .  
         [0129]     The overall length of articulated arm  14  and/or the various arm segments may vary depending on its intended application. In one embodiment, the articulated arm may have an overall length of about 24 inches and provide measurements on the order of about 0.0002 inch to 0.0005 inch. This arm dimension and measurement accuracy provides a portable CMM which is well suited for measurements now accomplished using typical hand tools such as micrometers, height gages, calipers and the like. Of course, articulated arm  14  could have smaller or larger dimensions and accuracy levels. For example, larger arms may have an overall length of 8 or 12 feet and associated measurement accuracies of 0.001 inch thus allowing for use in most real time inspection applications or for use in reverse engineering.  
         [0130]     CMM  10  may also be used with a controller mounted thereto and used to run a relatively simplified executable program as disclosed in aforementioned U.S. Pat. No. 5,978,748 and application Ser. No. 09/775,226; or may be used with more complex programs on host computer  172 .  
         [0131]     With reference to  FIGS. 1-6  and  24 - 26 , in a preferred embodiment, each of the long and short joints are protected by an elastomeric bumper or cover which acts to limit high impact shock and provide ergonomically pleasant gripping locations (as well as an aesthetically pleasing appearance). The long joints  16 ,  30  and  34  are all protected by a rigid plastic (e.g., ABS) replaceable cover which serves as an impact and abrasion protector. For the first long joint  16 , this rigid plastic replaceable cover comes in the form of the two-piece base housing  26 A and  26 B as is also shown in  FIG. 4 . Long joints  30  and  34  are each protected by a pair of cover pieces  40  and  41  which, as shown in  FIGS. 5 and 6  may be fastened together in a clam shell fashion using appropriate screws so as to form a protective sleeve. It will be appreciated that in a preferred embodiment, this rigid plastic replaceable cover for each long joint  30  and  34  will surround the preferably composite (carbon fiber) extension tube  134  and  148 , respectively.  
         [0132]     Preferably, one of the covers, in this case cover section  41 , includes a slanted support post  166  integrally molded therein which limits the rotation at the elbow of the arm so as to restrict probe  28  from colliding with base  12  in the rest position. This is best shown in  FIGS. 3, 24  and  26 . It will be appreciated that post  166  will thus limit unnecessary impact and abrasion.  
         [0133]     As will be discussed with respect to  FIGS. 29 and 31 , probe  28  may also include a replaceable plastic protective cover made from a rigid plastic material.  
         [0134]      FIGS. 3A, 24A  and  26 A-B depict alternative protective sleeves  40 ′,  41 ′ which also have a clam shell construction, but are held in place using straps or spring clips  167  rather than threaded fasteners.  
         [0135]     Each of the short joints  18 ,  32  and  36  include a pair of elastomeric (e.g., thermoplastic rubber such as Santoprene®) bumpers  38  as previously mentioned and as shown clearly in  FIGS. 1-3  and  5 - 6 . Bumpers  38  may either be attached using a threaded fastener, a suitable adhesive or in any other suitable manner. Elastomeric or rubber bumper  38  will limit the high impact shock as well as provide an aesthetically pleasing and ergonomically pleasant gripping location.  
         [0136]     The foregoing covers  40 ,  41 ,  40 ′,  41 ′ and bumpers  38  are all easily replaceable (as is the base housing  26 A,  26 B) and allow arm  14  to quickly and inexpensively be refurbished without influencing the mechanical performance of CMM  10 .  
         [0137]     Still referring to  FIGS. 1-3 , base-housing  26 A, B includes at least two cylindrical bosses for the mounting of a sphere as shown at  168  in  FIG. 3 . The sphere may be used for the mounting of a clamp type computer holder  170  which in turn supports a portable or other computer device  172  (e.g., the “host computer”). Preferably, a cylindrical boss is provided on either side of base housing  26 A, B so that the ball and clamp computer mount may be mounted on either side of CMM  10 .  
         [0138]     Turning now to  FIGS. 15, 16 ,  27 A, B and  28 , the preferred counter balance for use with CMM  10  will now be described. Conventionally, portable CMMs of the type described herein have utilized an externally mounted coil spring which has been mounted separately in outrigger fashion on the outside of the articulated arm for use as a counter balance. In contrast, the present invention utilizes a fully integrated internal counter balance which leads to a lower overall profile for the articulated arm. Typically, prior art counter balances have utilized wound coil springs in the counter balance mechanism. However, in accordance with an important feature of the present invention, the counter balance employs a machined coil spring (as opposed to a wound coil spring). This machined spring  110  is shown in FIGS.  16  and  27 A-B and is formed from a single cylinder of metal (steel) which is machined to provide a pair of relatively wide rings  174 ,  176  at opposed ends of the coil and relatively narrower rings  178  forming the intermediate coils between end coils  174 ,  176 . It will be appreciated that the wider end rings  174 ,  176  engage with the respective side surfaces  180  of shaft  62 ′ and  182  of housing  64 ″ thereby preventing lateral movement of spring  110 . The wider, solid end rings  174 ,  176  act as an anti-twist device and provide superior function relative to prior art wound springs. End ring  174  preferably includes a pair of locking posts  184 ,  186  (although only one locking post may be employed) while end ring  176  includes a locking post  188 .  
         [0139]     With reference to  FIG. 27B , each dual socket joint  46 ,  48  includes channels such as shown at  190  and  191  in dual socket joint  46  for receiving a respective post  184 ,  186  or  188 . With reference to  FIG. 28 , while pins  184 ,  186  will remain in a fixed position within the appropriate channel or groove of dual socket joint  48 , the location of pin  188  may be changed so as to optimize the overall wind-up on spring  110  and provide the most efficient counter balance force. This is accomplished using a threaded hole  192  which receives threaded screw  194 . As shown in  FIG. 28 , screw  194  may be operated on to contact pin  188  and move pin  188  circumferentially in a clock-wise direction along interior channel  696  which is shown in  FIG. 27B  as being perpendicular to pin access groove  190 . Screw  194  is preferably positioned to optimize spring  110  in the factory.  
         [0140]     It will be appreciated that during use of articulated arm  14 , the encoder/bearing cartridge  108  will act as a hinge joint and once inserted and adhesively secured within the sockets of dual socket joints  46 ,  48 , pins  184 ,  186  and  188  will be locked in their respective grooves. When socket joint  48  is rotated relative to socket joint  46  (via the hinge joint of cartridge  108 ), spring  110  will wind-up. When it is desired that socket joint  48  rotate back to its original position, the wound forces of spring  110  will unwind providing the desired counter balance force.  
         [0141]     In the event that it is desired that articulated arm  14  be mounted upside down such as on a grinder, beam or ceiling, the orientation of spring  110  may similarly be inverted (or reversed) so that the proper orientation for the necessary counterbalance may be achieved.  
         [0142]     Turning now to  FIGS. 29 and 30  A-C, a preferred embodiment of the measurement probe  28  will now be described. Probe  28  includes a housing  196  having an interior space  198  therein for housing printed circuit board  118 . It will be appreciated that housing  196  constitutes a dual socket joint of the type described above and includes a socket  197  in which is bonded a support member  199  for supporting circuit board  118 . Preferably, handle  28  includes two switches, namely a take switch  200  and a confirm switch  202 . These switches are used by the operator to both take a measurement (take switch  200 ) and to confirm the measurement (confirm switch  202 ) during operation. In accordance with an important feature of this invention, the switches are differentiated from each other so as to minimize confusion during use. This differentiation may come in one or more forms including, for example, the switches  200 ,  202  being of differing height and/or differing textures (note that switch  202  has an indentation as opposed to the smooth upper surface of switch  200 ) and/or different colors (for example, switch  200  may be green and switch  202  may be red). Also in accordance with an important feature of this invention, an indicator light  204  is associated with switches  200 ,  202  for indicating proper probing. Preferably, the indicator light  204  is a two-color light so that, for example, light  204  is green upon taking of a measurement (and pressing the green take button  200 ) and is red for confirming a measurement (and pressing the red button  202 ). The use of a muticolored light is easily accomplished using a known LED as the light source for light  204 . To assist in gripping, to provide improved aesthetics and for impact resistance, an outer protecting covering of the type described above is identified at  206  and provided over a portion of probe  28 . A switch circuit board  208  is provided for the mounting of buttons  200 ,  202  and lamp  204  and is supported by support member  199 . Switch board  208  is electrically interconnected with board  118  which houses components for processing the switches and light indicator as well as for the processing of short hinge joint  36 .  
         [0143]     In accordance with another important feature of the present invention, and with reference to both  FIG. 29  as well as FIGS.  30 A-C, probe  28  includes a permanently installed touch trigger probe as well as a removable cap for adapting a fixed probe while protecting the touch trigger probe. The touch probe mechanism is shown at  210  in  FIG. 29  and is based on a simplified three point kinematics seat. This conventional construction comprises a nose  212  which contacts a ball  214  biased by a contact spring  216 . Three contact pins (one pin being shown at  218 ) are in contact with an underlying electric circuit. Application of any forces against the probe nose  212  results in lifting of any one of the three contact pins  218  resulting in an opening of the underlying electric circuit and hence activation of a switch. Preferably, touch trigger probe  210  will operate in conjunction with the front “take” switch  200 .  
         [0144]     As shown in  FIG. 30B , when using touch trigger probe  210 , a protective threaded cover  220  is threadably attached to threading  222  surrounding trigger probe  210 . However, when it is desired to use a fixed probe rather than the touch trigger probe, the removable cap  220  is removed and a desired fixed probe such as that shown at  224  in  FIGS. 29 and 30 A-C is threadably attached to threading  222 . It will be appreciated that while fixed probe  224  has a round ball  226  attached thereto, any different and desired fixed probe configuration may be easily threadably attached to probe  28  via threading  222 . Touch trigger probe assembly  210  is mounted in a housing  228  which is threadably received into threaded connector  230  which forms a part of probe housing  196 . This threadable interconnection provides for the full integration of touch trigger probe  210  into probe  28 . The provision of a fully integrated touch probe represents an important feature of the present invention and is distinguishable from prior art detachable touch probes associated with prior art CMMs. In addition, the permanently installed touch trigger probe is also easily convertible to a hard probe as described above.  
         [0145]     FIGS.  29 A-C disclose yet another preferred embodiment for a measurement probe in accordance with the present invention. In FIGS.  29 A-C, a measurement probe is shown at  28 ′ and is substantially similar to measurement probe  28  in  FIG. 29  with the primary difference residing in the configuration of the “take” and “confirm” switches. Rather than the discrete button type switches shown in  FIG. 29 , measurement probe  28 ′ utilizes two pairs of arcuate oblong switches  200   a - b  and  202   a - b.  Each respective pair of oblong switches  202   a - b  and  200   a - b  correspond respectively to the take switch and the confirm switch as described above with respect to  FIG. 29 . An advantage of the measurement probe  28 ′ embodiment relative to the measurement probe  28  embodiment is that each pair of oblong switches  202  and  200  surround virtually the entire circumference (or at least the majority of the circumference) of the measurement probe and therefore are more easily actuatable by the operator of the portable CMM. As in the  FIG. 29  embodiment, an indicator light  204  is associated with each switch with the light  204  and switches  200 ,  202  being mounted on respective circuit boards  208 ′. Also, as in the  FIG. 29  embodiment, switches  200 ,  202  may be differentiated using for example, different heights, different textures and/or different colors. Preferably, switches  200 ,  202  have a slight float such that the button may be actuated when pressed down in any location therealong. As in the  FIG. 29  embodiment, an outer protective covering of the type described above is used at  206  and provided over a portion of probe  28 ′.  
         [0146]     Referring now to  FIG. 31 , an alternative measurement probe for use with CMM  10  is shown generally at  232 . Measurement probe  232  is similar to measurement probe  28  of  FIG. 29  with the primary difference being that probe  232  includes a rotating handle cover  234 . Rotating cover  234  is mounted on a pair of spaced bearings  236 ,  238  which in turn are mounted on an inner core or support  240  such that cover  234  is freely rotatable (via bearings  236 ,  238 ) about inner core  240 . Bearings  236 ,  238  are preferably radial bearings and minimize the parasitic torques on the arm due to probe handling. Significantly, the switch plate  208 ′ and corresponding switches  200 ′,  202 ′ and LED  204 ′ are all mounted to rotating handle cover  234  for rotation therewith. During rotation, electrical connectivity to processing circuit board  118 ′ is provided using a conventional slip ring mechanism  242  which comprises a known plurality of spaced spring fingers  242  which contact stationary circular channels  244 . In turn, these contact channels  244  are electrically connected to circuit board  118 ′. The rotating handle cover  234  and switch assembly is thus electrically coupled to the inner core or probe shaft  240  and electronics board  118 ′ using the slip ring conductor  242 . The rotation of the probe handle  234  permits switches  200 ′,  202 ′ to be oriented conveniently for the user. This allows the articulated arm  14 ′ to measure accurately during handling by minimizing undocumented forces. The cover  234  is preferably comprised of a rigid polymer and is provided with appropriate indentations  246  and  248  to allow easy and convenient gripping and manipulation by the probe operator.  
         [0147]     It will be appreciated that the remainder of probe  232  is quite similar to probe  28  including the provision of a permanently and integrally installed touch probe  210  in cover  220 . Note that switches  200 ′,  202 ′ are of differing heights and surface textures so as to provide ease of identification.  
         [0148]     The rotating cover  234  is a significant advance in the CMM field in that it can alleviate the need for a seventh axis of rotation at the probe such as disclosed in aforementioned U.S. Pat. No. 5,611,147. It will be appreciated that the addition of a seventh axis leads to a more complex and expensive CMM as well as the addition of possible error into the system. The use of the rotatable probe  232  alleviates the need for a “true” seventh axis as it permits the probe to provide the rotation needed for handle position at the probe end without the complexity of a seventh transducer and associated bearings, encoder and electronics.  
         [0149]     In the event that it is desired to utilize a measurement probe having a “true” seventh axis, that is, having a measurement probe with a seventh rotary encoder for measuring rotary rotation, such a measurement probe is shown in  FIGS. 37-40 . With reference to such FIGURES, a measurement probe  500  is shown with such measurement probe being substantially similar to the measurement probe in  FIG. 29  with the primary difference being the insertion of a modular bearing/transducer cartridge  502  of the type described above, the presence of the take and confirm switches  504 ,  506  on the sides of the measurement probe and the inclusion of a removable handle  508 .  
         [0150]     It will be appreciated that the modular bearing/transducer cartridge  502  is substantially similar to the cartridges described in detail above and include a rotatable shaft, a pair of bearings on the shaft, an optical encoder disk, at least one and preferably two optical read heads spaced from and in optical communication with the encoder disk and a housing surrounding the bearings, optical encoder disk, read head(s) and at least a portion of the shaft so as to define the discrete modular bearing/transducer cartridge. A circuit board  503  for the encoder electronics resides in an opening  505  with probe  500 . Pairs of take and confirm buttons  504 ,  506  are positioned on either side of a downwardly projected housing portion  510  of probe  500  with the buttons being connected to an appropriate PC board  512  as in the measurement probe of the  FIG. 29  embodiment. Similarly, an indicator light  513  is positioned between buttons  504 ,  506  as in the previously discussed embodiments. A pair of threaded openings  514  in housing  510  receive fasteners for removable attachment of handle  508  which provides for ease of rotary manipulation during use of measurement probe  500 .  
         [0151]     In all other substantial respects, measurement probe  500  is similar to measurement probe  28  of  FIG. 29  including the preferred use of permanently installed touch trigger probe at  516  as well as a removable cap for adapting a fixed probe  518  while protecting the touch trigger probe. It will be appreciated that the seventh rotary encoder  502  included in measurement probe  500  facilitates the use of CMM  10  in connection with known laser line scanners and other peripheral devices.  
         [0152]     Turning now to  FIGS. 2-4 ,  23  and  25 , in accordance with an important feature of the present invention, a portable power supply is provided to power CMM  10  thus providing a fully portable CMM. This is in contrast to prior art CMMs where power supply was based only on an AC cord. In addition, CMM  10  may also be powered directly by an AC cord through an AC/DC adapter via a conventional plug-in socket. As shown in  FIGS. 2, 3  and  25 , a conventional rechargeable battery (e.g., Li-ion battery) is shown at  22 . Battery  22  is mechanically and electrically connected into a conventional battery support  252  which in turn is electrically connected to a conventional power supply and battery recharger circuit component  254  located on circuit board  20 . Also communicating with board  20  is an on/off switch  258  (see  FIG. 3 ) and a high-speed communication port  259  (preferably a USB port). The joint electronics of arm  14  is connected to board  20  using an RS-485 bus. Battery  22  can be charged on a separate charger, or charged in place in cradle  252  as is commonly found in conventional video cameras. It will be appreciated that portable computer  172  (see  FIG. 2 ) can operate for several hours on its built-in batteries and/or in the alternative, may be electrically connected to the power supply unit  254  of CMM  10 .  
         [0153]     The on-board power supply/recharger unit in accordance with the present invention is preferably positioned as an integral part of CMM  10  by locating this component as an integral part of base  12  and more specifically as a part of the plastic base housing  26 A, B. Note also that preferably, base housing  26 A, B includes a small storage area  260  having a pivotable lid  262  for storing spare batteries, probes, or the like.  
         [0154]     Turning now to  FIGS. 4, 25  and  32 - 34 , the novel magnetic mounting device for use with CMM  10  will now be described. This magnetic mounting device is shown generally at  24  in  FIGS. 4, 25 ,  32  and  33 . Magnetic mount  24  includes a cylindrical non-magnetic housing  266  which terminates at its upper end in a threaded section  268 . As with all of the preferred threading used in CMM  10 , threading  268  is a tapered thread which is intended to be threadingly connected to threading  126  of first long joint  16  as best shown in  FIG. 25 . Non-magnetic housing  266  has a substantially cylindrical configuration with the exception of two longitudinal extensions  270 ,  272  which are opposed from each other at 180° and extend outwardly and downwardly from housing  266 . Attached on either side of longitudinal extensions  270 ,  272  are a pair of semi-cylindrical housings  274 ,  276 , each of which is formed from a “magnetic” material, that is, a material capable of being magnetized such as iron or magnetic stainless steel. Together, “magnetic” housing halves  274 ,  276  and longitudinal extensions  270 ,  272  form an open ended cylindrical enclosure for receiving and housing a magnetic core  278 . Magnetic core  278  has an oblong shape with a non-magnetic center  280  sandwiched between a pair of rare earth magnets (e.g., neodymium-iron-boron)  282 ,  284 . An axial opening  286  is provided through non-magnetic center  280 . A circular cover plate  288  is positioned beneath magnetic core  278  and located within the lower housing formed by elements  274 ,  276  and longitudinal extensions  270 ,  272 . A shaft  290  is positioned through a circular opening  291  in housing  266  and extends downwardly through axial opening  286  of magnetic core  278 . Shaft  290  is supported for rotation by an upper bearing  292  and a lower bearing  294 . Upper bearing  292  is received by an internal cylindrical recess in housing  266  and lower bearing  294  is received by a similar cylindrical recess in cover plate  288 . A lever  296  extends outwardly and perpendicularly from shaft  290  and, as will be described hereafter, provides an on/off mechanism for the magnetic mount  264 . Lever  296  extends outwardly of housing  266  through a groove  297  through housing  266  (see  FIG. 25 ).  
         [0155]     This entire assembly of lever  296 , shaft  290  and bearings  292 ,  294  is secured together using an upper threaded fastener  298  and a lower retaining ring  300 . It will be appreciated that the various components of magnetic mount  264  are further secured by, for example, threaded fasteners  302  which connect housing  266  to “magnetic” material housing portions  274 ,  276  and threaded fasteners  304  which interconnect housing portions  274 ,  276  to cover  288 . In addition, threaded fasteners  306  attached longitudinal extensions  270 ,  272  of housing  266  to cover  288 . A pin  308  is received by a lateral opening in core  278  and a lateral opening in shaft  290  so as to lock shaft  290  to core  278 . In this way, as lever  296  is rotated, shaft  290  will rotate core  278  via shaft connection  208 .  
         [0156]     As shown in  FIGS. 1, 3  and  25 , lever  296  is connected to a handle  310  which is easily accessible on the exterior of base  12  and is used to actuate magnetic mount  264 . To accomplish such actuation, handle  296  is simply moved (from the right to the left in  FIG. 1 ). Movement of handle  310  will in turn rotate lever  296  which in turn will rotate shaft  290  which will then rotate rare earth magnets  282 ,  284  from their non-operative position (wherein magnets  282 ,  284  are aligned with non-magnetic extensions  270 ,  272 ) into an actuated position where magnets  282 ,  284  are aligned with magnetic material  274 ,  276 . When the magnets are aligned with the magnetic material as described, a magnetic field (flux) is formed. Similarly, when the magnets  282 ,  284  are out of alignment with the magnetic material  274 ,  276 , the flux path is interrupted. In this state, the magnetic base can be separated from the table upon which it sits. Note however that even in the non-aligned position, there will be some residual magnetic flux. This small residual magnetic flux in the “off” position is a positive feature of this invention as a small amount of magnetic flux acts to react with the magnet and automatically rotate lever  296  back to the “on” position when replaced on the table. It will be appreciated that when the magnets are in alignment with the magnetic material, a strong magnetic field will be established and semi-circular elements  274 ,  276  will be magnetically adhered to the annular surface formed at the bottom thereof as shown at  312  in  FIGS. 25 and 33 .  
         [0157]     The magnetic mount  264  of the present invention provides a fully integrated yet removable mounting device since it is detachably mounted (via threading  268 ) and may be replaced by other attachments such as a screw mount or vacuum mount. Of course, in order to be properly used, magnetic mount  264  must be placed on a magnetizable surface and be activated (via lever  296 ) in order to operate. In the event that mounting is required to a non-magnetic surface (e.g., granite), then interface plates or other suitable mechanisms must be used between the magnetic base and the non-magnetic surface.  
         [0158]     While preferred embodiments have been shown and described, various modifications and substitutions may be made thereto without departing from the spirit and scope of the invention. Accordingly, it is to be understood that the present invention has been described by way of illustrations and not limitation.