Abstract:
A method and apparatus for mounting a calibration sphere to a calibration fixture for Coordinate Measurement Machine (CMM) calibration and qualification is described, decreasing the time required for such qualification, thus allowing the CMM to be used more productively. A number of embodiments are disclosed that allow for new and retrofit manufacture to perform as integrated calibration sphere and calibration fixture devices. This invention renders unnecessary the removal of a calibration sphere prior to CMM measurement of calibration features on calibration fixtures, thereby greatly reducing the time spent qualifying a CMM.

Description:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0001]    This invention was made with Government support under Contract No. DE-AC52-06NA25396 awarded by the U.S. Department of Energy. The Government has certain rights in this invention. 
     
    
     CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0002]    Not Applicable 
       INCORPORATION-BY-REFERENCE OF MATERIAL SUBMITTED ON A COMPACT DISC 
       [0003]    Not Applicable 
       BACKGROUND OF THE INVENTION 
       [0004]    1. Field of the Invention 
         [0005]    This invention pertains generally to fixtures and calibration spheres used for the calibration and accuracy verification of coordinate measurement machines (CMMs), and more particularly to integrated fixtures comprising a calibration sphere permanently or removably attached to a stepped calibration fixture reference for improved CMM qualification and calibration. 
         [0006]    2. Description of Related Art 
         [0007]    Coordinate measurement machines (CMMs) are widely used in industry for dimensional verification of miscellaneous parts. CMMs easily have measurement precision in the 0.0001 inch range (2.54 μm) or better. However, such measurements must be traced to dimensional standards in order to validate their accuracies. This process is known as calibration. 
         [0008]    A simplistic non-CMM calibration occurs when one measures a precision one inch steel gage block (here the measurement reference) with a micrometer or vernier caliper, which in turn reads 1.000 inches indicated on the device when in calibration. CMMs are much more complicated, able to render coordinate measurements in three dimensions with much higher precision. 
         [0009]    Precision is typically used in the science and engineering communities to describe the repeatability of a set of measurements. Accuracy, however, is the degree in which a measurement reflects a correct value. Typically, engineering measurements are described as a number plus or minus a tolerance. For high precision designs, one may turn to even more complex tolerance annotations, such as ANSI Y14.5. 
         [0010]    U.S. Pat. No. 5,430,948, entitled “Coordinate Measuring Machine Certification System”, was issued on Jul. 11, 1995, and is hereby incorporated by reference in its entirety (hereinafter referred to as the &#39;948 patent). The &#39;948 patent provides a method and apparatus for certifying a coordinate measuring machine that includes a certified ballbar, having a pair of spherical surfaces connected with a bar and having certified diameters separated by a certified distance, that is positioned with a positioning device. The positioning device includes a bar support that supports the ballbar at a midpoint of the bar between the balls, wherein the ballbar is supported free of attachment to the balls. The positioning device includes a first rotational assembly for rotatably supporting the ball support for rotation motion about a horizontal axis and a second rotational assembly for rotatably supporting the bar support about a vertical axis. The first rotational assembly provides rotation of the bar support in a clockwise direction to position the ballbar in a first set of angular orientations and in a counterclockwise direction to position the ballbar in a second set of angular orientations. The second rotational assembly provides rotation of the bar support in substantially a complete revolution. While the &#39;948 patent may allow for manual or computer programmed measurement operations, it does not allow for quick calibrations using calibration bars having precisely stepped features at calibrated locations so as to calibrate a CMM over an entire length of distance. 
         [0011]    Typical methods of CMM calibration a distance involve a sequence of steps first measuring a stand-alone calibration sphere, removing the calibration sphere, then attaching a stepped calibration fixture along one or two dimensions, and finally measuring the calibration fixture at one or more of the prescribed calibrated surfaces. Should an error occur during the calibration fixture measurement process, the calibration fixture must then be removed, and then the entire calibration sequence repeated with replacement of the calibration sphere. Such iteration step requires on average about 30 minutes for experienced measurement scientists, a significant time in the day of a work shift on an expensive CMM. 
       BRIEF SUMMARY OF THE INVENTION 
       [0012]    An aspect of the invention is an integrated calibration sphere and qualification fixture. In one embodiment, the fixture comprises: a calibration sphere; a calibration fixture comprising a plurality of calibration features; and means for attaching the calibration sphere to the qualification fixture. The calibration features may be planes, or cylindrical or spherical surfaces. The calibration feature is typified by a well known geometry leading to accurate measurement of the feature. In some calibration features, various basic calibration features may be combined to permit even more measurement information to be conveyed, for instance, intersecting planes may be used to convey perpendicular surfaces or other fixed angles of intersection. Typically, sets of calibration features are repeated in sets to provide for measurement patterns easily input into a CMM. 
         [0013]    The means for attaching the calibration sphere to the calibration fixture may be either removable or non-removable. By removable, it is understood that the calibration fixture may be removed and reused without recalibration or re-measurement, e.g., it is not destroyed by distorting any of its calibration features during the process of removal. 
         [0014]    In one embodiment, the removable means for attaching the calibration sphere may comprise a mount removably attaching to the calibration fixture wherein the calibration sphere is either a fixed or removable attachment to the mount. 
         [0015]    In one embodiment, the means for attaching the calibration sphere to the calibration fixture may comprise a clamp, whereby the calibration fixture measurement surfaces are not substantially deflected by attachment to the clamp. Typically, railing that appears sections of solid bars are not significantly deflected by a mere light compression force that is opposed on two opposite sides of the bars that are evenly matched, i.e., no net torque is generated from the attachment of the clamp beyond the clamp attachment features. 
         [0016]    In one embodiment, the means for attaching the calibration sphere to the calibration fixture may comprise a clamp that provides a removable attachment to the calibration fixture. In this embodiment, the clamp also provides attachment to the calibration sphere. The clamp may directly attach to the calibration sphere, or may directly attach to a pedestal, which in turn attaches to the calibration sphere. 
         [0017]    In one embodiment, the means for attaching the calibration sphere to the calibration fixture (or pedestal) may also comprise a threaded portion threaded into a receiving portion of the calibration sphere, wherein the calibration sphere is removable. Other typical means for attachment could include mortise and tenon connections, Morse taper fits, or an adhesive disposed between the calibration sphere and the calibration fixture when the calibration sphere is removable. In the latter embodiment, the adhesive would be chosen so as to make the calibration sphere removable (e.g. this would not be a high strength waterproof epoxy). 
         [0018]    In another embodiment, an integrated calibration sphere and calibration fixture comprises: a calibration sphere; a calibration fixture comprising a plurality of calibration features; and a mount, disposed between and attaches to, each of the calibration sphere and the calibration fixture. 
         [0019]    The mount may comprise either a removable attachment of the calibration sphere, or a removable attachment of the calibration fixture. In either implementation, the calibration sphere is ultimately able to be removed from the vicinity of the calibration fixture as needed. 
         [0020]    The mount may also non-removably attach to the calibration sphere and to the calibration fixture. Thus, the mount may comprise removable or nonremovable attachments to one or both of the attachments of the group consisting essentially of an attachment of the calibration sphere, and an attachment of the calibration fixture. 
         [0021]    In one embodiment, the mount may comprise a clamp, whereby the calibration fixture calibration features are not substantially deflected by attachment to the clamp; and means for attaching the mount to the calibration sphere, wherein the means for attaching causes a deformation of the mounted calibration sphere by less than an allowable tolerance of the calibration sphere prior to being mounted. Alternatively speaking, the means for attaching fails to cause a deformation of the mounted calibration sphere by more than an allowable tolerance of the unmounted calibration sphere. 
         [0022]    In one embodiment, the amount of allowed attachment deflection may comprise a deflection of the calibration fixture calibration features measured to be within an original tolerance of the calibration fixture prior to being mounted. 
         [0023]    In various embodiments, the mount attachment of the calibration sphere to the calibration fixture may be selected from one or more of a group consisting essentially of a threaded portion that projects from the mount, threaded into a receiver portion of the calibration sphere; a precision ground pin that projects from the mount into a close-fit receiver portion of the calibration sphere; and a flat region on the mount, to which the calibration fixture is glued to the mount via an adhesive. 
         [0024]    A still further aspect of the invention is a method of coordinate measurement machine calibration using an integrated calibration sphere and calibration fixture. In one embodiment, the method comprises: 
         [0025]    (a) providing an integrated calibration sphere mounted to a calibration fixture; 
         [0026]    (b) qualifying a coordinate measurement machine (CMM) by measuring the calibration sphere; then 
         [0027]    (c) measuring a plurality of calibrated features on the calibration fixture; 
         [0028]    (d) determining whether the CMM measures within an allowable tolerance zone:
       (i) if within the tolerance zone, then completing the CMM calibration; otherwise,   (ii) returning to step (b) without removal of the calibration sphere.       
 
         [0031]    An integrated calibration sphere and calibration fixture is a device capable of being used in any of the preceding methods. 
         [0032]    The integrated calibration sphere and calibration fixture above may be described where the integrated calibration sphere mounted to the calibration fixture is removable. 
         [0033]    Still another aspect of the invention is an improved calibration fixture for integrated calibration sphere and calibration fixture coordinate measurement machine (CMM) calibration. 
         [0034]    In one embodiment, the improvement comprises a calibration sphere mounted to the calibration fixture to allow CMM measurement of the calibration sphere and the calibration fixture without removal of either the calibration sphere or the calibration fixture from the CMM. 
         [0035]    The improved calibration fixture may be characterized by having the calibration sphere removably mounted to the calibration fixture. Further aspects of the invention will be brought out in the following portions of the specification, wherein the detailed description is for the purpose of fully disclosing preferred embodiments of the invention without placing limitations thereon. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S) 
         [0036]    The invention will be more fully understood by reference to the following drawings which are for illustrative purposes only: 
           [0037]      FIG. 1  is a perspective view of an idealized coordinate measurement machine (CMM) with the principal working elements shown. 
           [0038]      FIG. 2  is a perspective view of a simplified calibration fixture with several potential calibration surfaces shown. 
           [0039]      FIG. 3  is a perspective view of a calibration sphere assembly, showing a typical mounting technique. 
           [0040]      FIG. 4A  is a perspective view of a hold-down fixture for the calibration fixture previously described in  FIG. 2 . 
           [0041]      FIG. 4B  is a perspective view of a stand to which is mounted the calibration fixture previously described in  FIG. 2 . 
           [0042]      FIG. 5  is a perspective view of an integrated calibration sphere and calibration fixture mount showing an improvement of the hold-down fixture of  FIG. 4  allowing for simultaneous calibration sphere and calibration fixture mounting. 
           [0043]      FIG. 6A  is a perspective view of the integrated calibration sphere and calibration fixture mount of  FIG. 5  shown mounted to the calibration fixture previously shown in  FIG. 2  with the calibration sphere attached. 
           [0044]      FIG. 6B  is a perspective view of another improved integrated calibration sphere and calibration fixture mount shown mounted to the stand of  FIG. 4B  retaining the calibration fixture previously shown in  FIG. 2  with the calibration sphere attached. 
           [0045]      FIG. 7  is a perspective view of another embodiment of the calibration sphere directly mounted to the calibration fixture previously shown in  FIG. 2 . 
           [0046]      FIG. 8  is a perspective view of the  FIG. 1  CMM with the integrated calibration sphere and calibration fixture of  FIG. 6A . 
           [0047]      FIG. 9  is a flow chart illustrating an embodiment of a calibration method according to the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0048]    Referring more specifically to the drawings, for illustrative purposes the present invention is embodied in the apparatus generally shown in  FIG. 1  through  FIG. 8  and the method generally shown in  FIG. 9 . It will be appreciated that the apparatus may vary as to configuration and as to details of the parts, and that the method may vary as to the specific steps and sequence, without departing from the basic concepts as disclosed herein. 
       DEFINITIONS 
       [0049]    The following definitions are provided to facilitate understanding terminology used herein. It is intended that those terms be given their plain meaning except as otherwise defined herein. 
         [0050]    Calibration Sphere means an object with at least a portion of its surface substantially spherical to a very high degree. These spherical surfaces may typically be ceramic or finely finished stainless steel, and may have extremely low coefficients of thermal expansion. Typically, these are balls with tapped or bored holes for mounting; they are highly round, with dimensions traceable to well-regarded national or international dimensional standards. The organizations which have developed their standards throughout the world are the International Standards Organization (ISO) which is worldwide, the Anti-Friction Bearing Manufacturer Association (AFBMA) which is in North America, the Japanese Industrial Standards (JIS) in Japan, and the Deutsche Industrial Normen (DIN) in Germany. For instance an AFBMA grade 3 ball has an allowable ball diameter variation of 3μ″ (micro-inches) or 0.0762 μm (microns), thus a one inch (1″) ball would have a dimension of 1.000000±0.000003. 
         [0051]    Calibration fixture means a device with specific surface features that has dimensions traceable to well-regarded national or international standards. Without limitation, these may be perimeters of holes, surface ledges, or the like, in a repeated array in one, two, or three dimensions. This device is useful for calibrating the linearity of measurement accuracy of a CMM or other measurement device. 
         [0052]    Improved fixture means the invention disclosed herein, where a single qualification sphere has been attached (either permanently or removably) to a calibration fixture for ease of CMM calibration. 
       Introduction 
       [0053]    This invention allows for a calibration sphere to either temporarily or permanently) become an integral part of a coordinate measurement machine (CMM) calibration fixture for the calibration of a probe tip on a CMM. A calibration fixture typically has a pre-determined set of steps (a spaced apart distance from one to another) that performs a verification of how well a CMM is capable of measuring a known artifact. Spatial-location-based compensation factors that are built into the CMM may be adjusted based on the readings resulting from the measurement of the steps of the calibration fixture, allowing one to obtain accurate readings within a given spatial volume calibrated on a CMM. 
         [0054]    CMM calibrations are disclosed in various national testing standards, such as the American National Standards Institute/American Society of Mechanical Engineers (ANSI/ASME) B89.1.12m-1985. These calibrations insure that CMM devices do in fact make accurate measurements over a volume of space to be measured. 
         [0055]    Refer now to an idealized CMM depicted in  FIG. 1 . The CMM  100  typically sits on vibration isolators  102  to minimize environmentally induced vibrations. The CMM  100  is further isolated through the use of a heavy granite slab base  104 , whose upper surface  106  may have a plurality or pattern of recessed tie down points  108 . These tie down points  108  are typically threaded, and may be used to either directly mount a fixture to the CMM  100  bed  106 , or may hold down other potential fixtures that in turn hold down an object to be measured. Traversing this base upper surface  106  in one dimension (here arbitrarily chosen to be shown as X) is an X axis translation stage  110 . This is indicated as fairly massive, since the dimensions to be measured are exceedingly small, where even leaving a small light-weight object on the translation stage  110  could otherwise unacceptably deflect a measurement. 
         [0056]    The Y axis translation stage  112  in turn translates in the Y axis along a top portion  114  of the X axis translation stage  110 . 
         [0057]    A Z axis translator  116  moves in yet a third linearly independent direction. At the tip of the Z axis translator  118 , one finds the actual CMM probe tip  120  that actually performs the measurement. 
         [0058]    Not shown on the CMM are an array of (typically digital) readouts that monitor movements of the X  110 , Y  112 , and Z  116  axes, as well as the associated controllers, cabling, and a computer controlling movement of the CMM probe tip  120  through a set of coordinated motions and thus measure a complex part. 
         [0059]    Refer now to  FIG. 2 , which is a perspective view of a simplified calibration fixture  200 . Such fixture may be made of metal or ceramic, or both, with the important considerations being dimensional stability and ease of fabrication. Typically, there is a base  202  for mounting the calibration fixture  200  to a CMM bed ( 106  in  FIG. 1 ). From the base  202  may be a plurality of calibrated features, such as a top surface  204 , top lands  206 , and side holes  208 . An end hole  210  may be present at one or both ends. An end surface  212  is typically precision ground to a high degree of flatness, and is perpendicular to the top surface  204  and sides  214 . The top land  206  may also have a precision edge surface  216  parallel to the end surface  212 , and may also have a precision lengthwise edge surface  218  parallel to the sides  214 . By knowing the accuracy of theses various features, a CMM may be calibrated. 
         [0060]    Although not shown in the figures, one such example of a calibration fixture that may be used for CMM  100  calibration is a bar with accurately machined surface features manufactured by Kolb &amp; Baumann GmbH &amp; Co. KG, Daimlerstraβe 24, D-63741 Aschaffenburg, Germany. The Kolb &amp; Baumann bar is referred to typically as a “Koba Bar”; Kolb &amp; Baumann refer to it as a “Koba step”, or “Koba mini step” in its smaller sized incarnation. 
         [0061]    A calibration fixture has a predetermined set of calibration features, most commonly flat-surfaced (or other well known geometry, such as cylindrical or spherical) steps (at a spaced apart distance from one to another) that allows one to perform a verification of how well a CMM is capable of measuring the know artifact. 
         [0062]    Refer now to  FIG. 3 , which is a calibration sphere assembly  300  comprising a calibration sphere  302  with a base  304 . There may or may not be present a calibration sphere platform  306  that provides attachment between the base  304  and the calibration sphere  302 . 
         [0063]    Typical Coordinate Measurement Machine (CMM) Calibration Methods 
         [0064]    Refer now to  FIGS. 1-3 . In typical CMM calibration, a calibration sphere assembly  300  is attached to the bed  106  of the CMM  100  and a series of measurements of the CMM calibration sphere is done. This qualification procedure determines how well the CMM probe tip  120  is able to measure the know diameter and roundness of the calibration sphere  302 , whose diameter and roundness are known to exceedingly high levels that typically originate from a dimensional standards laboratory. If the series of measurements of the calibration sphere  302  by the CMM probe tip  120  agree with the known dimensions of the calibration sphere  302  as determined by a dimensional standards laboratory then the CMM  100  is said to have been qualified by the calibration sphere  302 . 
         [0065]    Once the CMM  100  has been qualified by the calibration sphere  302 , then the calibration sphere assembly  300  is then removed from the CMM bed  106 , and replaced by a calibration fixture  200  mounted on the CMM  100  bed  106  for calibrated fixture  200  measurements. 
         [0066]    The calibration fixture  200  typically has a series of calibration features as described above, whose dimensions are known with great accuracy. When such a calibration fixture  200  is positioned on the bed  106  of the CMM  100 , then measurement of the known features in the calibration fixture  200  is then performed. If, for whatever reason, it appears that the measurements of the known calibration fixture  200  features are incorrect as compared with their known values and tolerances, then the calibration fixture  200  must be removed from the CMM  100  bed  106 , and the qualification sphere assembly  300  reattached to the bed  106  of the CMM  100  yet again, and the above process is repeated. 
         [0067]    It is important to note that the calibration sphere  302 , while extremely dimensionally accurate in and of itself, may be randomly positioned on the CMM  100  bed  106  due to the lack of any mechanism to repeatably locate the calibration sphere  302  relative to the CMM bed  106  to extremely high accuracy. 
         [0068]    Each time the calibration fixture  200  is slightly moved on the bed  106  of the CMM  100 , measurements are taken with CMM probe tip  120  and recorded in the CMM computer memory. Since these measurements are resident in the CMM computer memory, a predetermined set of measurements on the calibration fixture  200  mounted on the CMM  100  may be made. Once there is a set of measurements in the CMM computer memory, remeasuring may occur with greater rapidity to reduce statistical measurement inaccuracies by the CMM computer simply stepping through the prior measurement list. This can occur over and over if, and only if, the calibration fixture  200  is not moved or shifted in position from the CMM  100  bed  106 . 
         [0069]    When the calibration fixture  200  is moved to an entirely new orientation, the calibration feature measurements have previously been recorded by the CMM computer software. With this information, the CMM computer software may calculate from a few initial measurements where the remaining calibration fixture  200  measurement locations are likely to be in the new orientation. Thus, the remaining measurements of the well-known (certainly well-known within ˜0.050″ or ˜2 mm for gross random mounts on the CMM bed  106 ) calibration features on the calibration fixture  200  may be made automatically. 
         [0070]    The time required from the initial set up of the calibration sphere assembly  300 , qualification of the CMM  100  with the calibration sphere  302 , to the measurement to specific calibrated features of the calibration fixture  200  may take on the order of approximately 30 minutes. 
         [0071]    Each time the calibration fixture  200  is removed to requalify the probe tip  120  on the calibration sphere  302  the time lost is about 30 minutes. For complete CMM calibration throughout its measurement volume, the calibration fixture  200  is positioned at a minimum of seven different positions. Thus, if the calibration fixture  200  is moved, time is wasted. 
         [0072]    Referring now to  FIG. 4A , we see the hold-down  400  for the traditional calibration fixture  200  previously described in  FIG. 2 . A base  402  connects to two L-shaped pieces  406  to hold down the calibration fixture  200  between them. Not shown here are the various hold-down  400  indexing and alignment dowels used to align the various part and minimize movement after attachment. 
         [0073]    Refer now to  FIG. 4B , where we see a stand  408  assembled with one of the hold-downs  400 . This method is one way to retain the calibration fixture  200  to the hold-down base  402 . The stand  408  may be secured to the CMM  100  base  106  through one or more retention holes  108  in the CMM  100  base  106 . 
       An Improved CMM Calibration Fixture 
       [0074]    Refer now to  FIG. 5 . An integrated calibration sphere and calibration fixture  500  mount is shown. This integrated fixture eliminates the loss of time due to frequently removing the calibration fixture and the calibration sphere by mounting them on an integrated calibration sphere and calibration fixture  500  hold down. In the integrated sphere and calibration fixture  500  mount, the base  502  has been extended and projected vertically with extension  504 . There, a calibration sphere  506  may either be directly mounted to the extension  504 , or may be vertically extended further by means of a riser  508  as indicated. The riser  508  may be a press fit dowel pressed at both ends to keep the calibration sphere  506  firmly attached to the extension  504 . Alternatively, the riser  508  may be merely a very close sliding lapped connection at the calibration sphere  506  to allow for the calibration sphere  506  to be removable. Still other means of attachment to allow for either removable or irremovable assembly may be readily discerned by practitioners in the art. 
         [0075]    Referring now to  FIGS. 6A and 6B , the integrated calibration sphere and calibration fixture  600  is shown, with the major components of the calibration fixture  200 , the integrated calibration sphere  506  and calibration fixture  200  mount  500 . 
         [0076]      FIG. 6B  shows an improved integrated calibration sphere and calibration fixture mount shown mounted to a traditional calibration fixture previously shown in  FIG. 2  with the calibration sphere attached  602 . This is improved from a machining efficiency and cost standpoint because, rather than removing a large percentage of a block of metal to form the extension support post ( 504  shown in  FIG. 5 ), a post  510  is attached to the base extension region  512  to form that function. This is more efficient, and less costly due to decreased machining time and material due to reduced material removal. Additionally, post  510  may be readily manufactured on numerically controlled lathes. The post  510  may or may not be tapered  514  at the top  516  to provide relief from the calibration sphere  506  as it is measured in various orientations with the CMM probe tip  120  (shown previously in  FIG. 1 ). The post  510 , any taper  514 , and top  516  may be referred to as a pedestal  518 . 
         [0077]    Alternate embodiments may also be formed by attaching the calibration sphere to the calibration fixture in other ways as described below. 
         [0078]    Refer now to  FIG. 7 . This embodiment of the calibration sphere mounted to a calibration fixture  700  comprises an initial calibration fixture  200 , to which a calibration sphere  702  is attached to a calibration fixture mount  704 . Here the calibration fixture mount  704  may have a pressure bearing plate  706  that receives the tips of set screws  708  threaded though the calibration fixture mount  704  so as to hold the calibration fixture mount  704  to the calibration fixture  200  through a clamping effect. 
         [0079]    The calibration fixture mount  704  may be designed to mount to a plurality of common CMM calibration fixtures, thus enabling providing an integrated capability to both original and retrofit devices. 
       An Improved CMM Calibration Fixture Application 
       [0080]    Any of the embodiments above may be used for integrated CMM calibration, which is greatly simplified by having a calibration sphere attached to the calibration fixture that does not require prior removal for CMM measurement of either the calibration sphere or calibration fixture. 
         [0081]    Refer now to  FIG. 8 , which is essentially an overlay of  FIGS. 1 and 6A . Also refer to typical sequence for CMM  100  qualification using the improved device  600  follows: 
         [0082]    (1) An integrated calibration sphere  506  mounted to a calibration fixture  200  (known as an integrated calibration fixture  600 ) is provided  902  (note, this may require attaching a calibration sphere, if not already connected); 
         [0083]    (2) The integrated calibration fixture  600  is positioned at one of the positions required for verification and calibration  904  of the CMM  100  on the CMM bed  106 . 
         [0084]    (3) When the measured dimensions of the known calibration features of the integrated fixture  600  exceed the tolerances stated by the manufacturer, requalification begins  904 . Here, the CMM probe tip  120  is requalified  908  with the calibration sphere  506  that is already attached to the integrated fixture  160 . 
         [0085]    (4) After requalification of the CMM probe tip  120  the integrated fixture  600  may be automatically remeasured without relocating the calibration fixture  200  (by using the previous measurement steps already stored as historical measurements in the CMM software memory). Since the calibration sphere  506  is already attached to the integrated fixture  600 , the calibration sphere  506  does not need to be moved to requalify the CMM probe tip  120 , because the coordinates of the calibration fixture  200  are roughly known to the CMM software, which can be stepped though its previous measurement sequence again to remeasure the calibration features on the calibration fixture  200 . 
         [0086]    (5) The sequence of steps above are repeated in the X, Y, Z, or diagonal positions as required to completely qualify the CMM  100  within a spatial volume. 
         [0087]    Restating the previous process,  FIG. 9  shows a flowchart  900  of the process steps described above in steps 1-5. Initially, the calibration sphere is mounted to the calibration fixture  902  using one of the many methods described above. The calibration fixture, with the calibration sphere attached, is positioned for calibration  904 . Then, the calibration fixture is measured  908 . If the calibration fixture is within tolerances  910 , then measurement is either  912  done  914 , or may be repeated  916 . 
       CONCLUSION 
       [0088]    Although the description above contains many details, these should not be construed as limiting the scope of the invention but as merely providing illustrations of some of the presently preferred embodiments of this invention. Therefore, it will be appreciated that the scope of the present invention fully encompasses other embodiments which may become obvious to those skilled in the art, and that the scope of the present invention is accordingly to be limited by nothing other than the appended claims, in which reference to an element in the singular is not intended to mean “one and only one” unless explicitly so stated, but rather “one or more.” All structural, chemical, and functional equivalents to the elements of the above-described preferred embodiment that are known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed by the present claims. Moreover, it is not necessary for a device or method to address each and every problem sought to be solved by the present invention, for it to be encompassed by the present claims. Furthermore, no element, component, or method step in the present disclosure is intended to be dedicated to the public regardless of whether the element, component, or method step is explicitly recited in the claims. No claim element herein is to be construed under the provisions of 35 U.S.C. 112, sixth paragraph, unless the element is expressly recited using the phrase “means for.”