Abstract:
A mount  10  for a part to be measured (e.g. a tooth  20  which is to have its surface measured) has three locators  14  which allow repeatable positioning of the mount on a holder  12.  The mount  10  and its locators are manufactured in a low cost way e.g. by means of chemical etching, stamping, piercing, folding, embossing or moulding. The mount may be sheet material or a moulded plastics, and a support  22  for the part may be provided. The material of the mount may be magnetisable or have magnetic properties for its attraction and position securement to the holder  12.  A mount transit system is described (FIGS.  10  and  11 ) for placing and removing a mount on the holder.

Description:
FIELD OF THE INVENTION AND DESCRIPTION OF PRIOR ART  
         [0001]    This invention relates to a mount for parts to be measured dimensionally particularly but not exclusively a mount for small parts, especially teeth, impressions of teeth and other dental parts. The invention relates also to a transit system for the mount.  
           [0002]    Teeth, impressions etc can be measured for example by moving a scanning probe across their surface. A digital profile can be produced. This profile can be used to make a replacement tooth or tooth-part, for example it can be used to machine a ceramic filling.  
           [0003]    The part to be measured has to be held accurately and might need to be removed from a measuring machine and replaced. The mount will need to be moved around a measuring machine e.g. to automate the measurement of many parts. So, repeatable positioning of the mount when it is replaced on its holder, following removal, is desirable.  
           [0004]    Where low cost or disposable items like dental impressions are to be scanned or worked upon, it is often convenient and hygienic to dispose of the item together with its mount (particularly where the two are permanently affixed as by adhesive). So a low cost disposable mount is desirable also. More desirably such a mount would have the attributes mentioned in the preceding paragraph.  
         SUMMARY OF THE INVENTION  
         [0005]    According to a first aspect of the invention there is provided a mount for a part to be measured in a measuring machine, the mount comprising a plurality of locators for locating kinematically the mount to a holder, the mount at the locators being formed by means of one or more manufacturing techniques selected from a group consisting of etching, stamping, piercing, folding, embossing and moulding.  
           [0006]    According to a second aspect of the present invention there is provided a mount for a part to be measured in a measuring machine, the mount comprising a plurality of locators for locating kinematically the mount to a holder, the mount at the locators being formed from sheet or substantially planar material and the locators being in the form of material missing from the material of the mount.  
           [0007]    According to a third aspect of the present invention there is provided a mount for a part to be measured in a measuring machine, the mount comprising a plurality of locators for locating kinematically the mount to a holder, the mount at the locators being formed from sheet or substantially planar material and the locators being in the form of mount material which is deformed.  
           [0008]    According to a fourth aspect of the present invention, there is provided a mount for a part to be measured in a measuring machine, comprising a base, the base having a plurality of locators for locating kinematically the mount to a holder, and a support portion upstanding from the base, the support portion being adapted to support the part to be measured.  
           [0009]    Preferably the locators of the first and third aspect are formed as three slots of missing material in the mount/base.  
           [0010]    Preferably the locators of the first and third aspect are formed as three slots of material which is deformed.  
           [0011]    Preferably the mount according to the first to fourth aspects is formed from magnetic or magnetisable material.  
           [0012]    According to a fifth aspect of the invention there is provided a method of manufacturing a kinematic mount, the method comprising the steps of:  
           [0013]    providing a magnetic or magnetisable, mount material;  
           [0014]    forming a kinematic location in the material by a method selected from a group consisting of etching, stamping, piercing, folding, embossing, moulding, or combinations thereof.  
           [0015]    Preferably the method further includes the step of forming a support at the mount for supporting a part which is to be mounted, the support being formed by means of one of the techniques mentioned in the preceding paragraph.  
           [0016]    The invention provides also a mount transit system for moving mounts (e.g. of the type mentioned above), the system comprising a mount rest station and a movable mount holder, the rest station including at least one mount rest area, the or each area having a mount accepting part and protrusion for supporting a mount from below, the movable mount holder being adapted for movement in at least two paths, a first path approaching the station laterally then moving downwardly relative to the station, and a second path approaching the station in a relative upward direction and then moving away from the station, wherein in use movement of the mount along the first of the paths causes a mount held on the holder to be removed by abutment of the mount with the protrusion and thereby accepted into the mount accepting part.  
           [0017]    Preferably the or each mount accepting part comprises an open-ended first slot in a plate and the protrusion is formed by a ledge in the slot.  
           [0018]    Preferably the rest area comprises a device for allowing only one possible orientation of the mount at the rest area. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0019]    Various illustrative embodiments of the invention will now be described in detail. Reference will be made to the drawings, wherein:  
         [0020]    [0020]FIGS. 1 a  and  1   b  show a mount and a holder for the mount and also a section through the mount and holder about centre line A; all according to one embodiment of the invention;  
         [0021]    [0021]FIG. 2 shows the mount, the holder and in this case the mount holding a tooth;  
         [0022]    [0022]FIG. 3 shows an alternative form of mount holding a tooth in a different orientation;  
         [0023]    FIGS.  4 - 9  show variants of the mount; and  
         [0024]    [0024]FIGS. 10 and 11 show a mount, its holder, and a mount rest station, together forming a mount transit system. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0025]    In FIGS. 1 a  and  1   b  there is shown a sheet metal or other planar material mount  10  to which in use a small part for example a tooth may be mounted. The small part may then be dimensionally measured and a profile of its surface can be determined. The mount  10  is held to a holder  12 . A magnet  18  is, in this case, used to attract the mount  10  to the holder  12 . Magnet  18  may resiliently deflect the mount  10 , particularly if the mount  10  is manufactured from thin sheet metal. Such deflection would add to the magnetic attraction of the mount to the holder  12  and thereby give a more positive holding force between the two. The mount  10  is located positively and accurately on its holder  12  by means of three location slots  14  which co-operate with three spherical parts  16  fixed to holder  12 . The slots  14  are formed by generally masking the mount and chemically etching unmasked areas of the slots. In use, each spherical part  16  will touch either side of one of the slots  14  thereby giving six points of location for the mount  10 . The slots  14  can, with equal merit, be produced by stamping. Such location is referred to as a kinematic location. It is of course possible that other kinematic arrangements could be used, e.g. the three spheres  16  can engage with a triangular hole, a slot and a flat surface respectively.  
         [0026]    [0026]FIGS. 2 and 3 show how a tooth or other small part can be held on mount  10 . In the case of FIG. 2, tooth  20  is held on mount  10  by means of a support portion in the form of a post  22 . Likewise in FIG. 3, a support post  22  is shown holding tooth  20 .  
         [0027]    [0027]FIG. 4 shows open-ended slots  14 . This is an alternative method of producing the mount slots.  
         [0028]    [0028]FIG. 5 shows a support post  22  in the form of a pierced tab folded up from the material of the mount  10 .  
         [0029]    Similarly FIG. 6 shows a two-part support post pierced and folded from the material of the mount  10 . In this case a two-part piercing and folding is shown.  
         [0030]    It will be noted that FIGS. 3 and 6 show an additional lateral support  23 , which may enable a probe to reach areas of a supported part which are not possible to reach when the part is supported as illustrated in FIG. 2.  
         [0031]    [0031]FIG. 7 shows an alternative form of locator. In this case an elongate dimple  24  is embossed into the surface of mount  10 .  
         [0032]    Similarly FIG. 8 shows a flanged slot  26  stamped into the surface of the mount  10 . Again this provides a two-point location for ball  16 .  
         [0033]    [0033]FIG. 9 shows a plastics mount  10 . In this case a ferrite loaded plastics material has been moulded into the shape of the mount  10  having a tooth support  22  with strengthening webs  23  and three location recesses  14  (two of which only are illustrated), and which are positioned on the underside of the mount shown. These recesses can have edges which provide a total of six location points for balls  16  or may be vee grooves again providing six faces at which six contact points are made.  
         [0034]    The use of ferrite within the plastics enables the mount to be magnetically attractable to the holder  12 , as well as making the plastics harder. Consequently the contact points at the recess will be hard and therefore repeatable positioning of the mount on the holder is possible.  
         [0035]    The mounts illustrated in FIGS.  2 - 9  and described above have the advantage of being inexpensive to produce whilst providing kinematic positioning repeatability.  
         [0036]    Various other ways of producing a support on the mount for the part to be measured will be obvious to a skilled addressee, as would the various ways of producing locators in or on the surface of the mount  10 .  
         [0037]    The manufacturing techniques described could be used solely or in combination to produce the mount and/or the support.  
         [0038]    Kinematic locations have been described and illustrated which in use provide highly repeatable positioning of the mount to the holder. The kinematic elements at the mount and base provide generally six points of contact. Often these take the form of three pairs of contact points (as described and illustrated) but other arrangements are possible within the ambit of the term “a kinematic location”. The kinematic location should restrain the six possible degrees of freedom of the mount relative to the holder.  
         [0039]    Such a location or support is sometimes known as a Boys support, and is described in, for example, H. J. J. Braddick, “Mechanical Design of Laboratory Apparatus”, Chapman &amp; Hall, London, 1960, pages 11-30. Braddick also describes a functionally equivalent kinematic support, sometimes known as a Kelvin support, in which the six points of contact or constraints are provided three at a first area, two as a second spaced area, and one at a third spaced area. The terms “kinematic”, “kinematically constrained” and like terms, as used in this specification, encompass Boys supports, Kelvin supports and other kinematic and semi- or quasi-kinematic types of supports. An example of a quasi-kinematic location or support is a cone and ball, together with a vee and ball, and a flat and ball. Thus the vee and flat co-operate with their respective balls to provide 2+1 contact points and the cone and ball nominally provide a further  3  contact points.  
         [0040]    In this specification the term magnetic or magnetisable material is intended to embrace permanently magnetised materials as well as those materials which can be temporarily magnetised (e.g. soft iron or steel) and those which exhibit the properties of magnetism, permanently or temporarily. So if the mount were magnetised, the magnet  18  could be replaced by a soft iron insert or the like.  
         [0041]    [0041]FIGS. 10 and 11 show a rest station  30  for holding one or more mounts  10 . There is shown a rest area  32  for a mount which has a mount-accepting slot  34 . A protrusion in the form of ledge  36  in the slot holds the mount  10  in place. In use holder  12  is movable from a part scanning location to the rest station  30  and back (e.g. it may be mounted to a movable table or arm. FIG. 10 shows holder  12  with mount  10  approaching the rest station  30  in the direction of the arrow. Holder  12  will enter slot  34  in a lateral direction and as shown in FIG. 11 may move away from the station vertically downwardly. This downward movement causes the under-face of mount  10  to abut ledge  36  and mount  10  will be pulled off holder  12  as the holder moves downwardly. This action causes unloading of the mount  10  from holder  12 . Loading of holder  12  with a mount  10  may be carried out in an opposite manner to loading i.e. the holder may approach the station from below, move upwardly and accept a mount by magnetic attraction, then move away from the station  30  laterally.  
         [0042]    It can be seen that holder  12  and mount  10  are slightly modified in this embodiment. Holder  12  has flats  40  for entering slot  34  and clearing ledge  36 . Mount  10  has similar flats  38  which allow it to enter the slot  34  but which overhang the flats  40  so that they can rest on the ledge  36 . In this embodiment a device for allowing only one possible orientation of the mount in the slot  34  is illustrated. This device may take many forms but in this illustration a peg  42  co-operates with a hole  44  so complete acceptance of the mount  10  in the slot  34  will not be made if the mount is correctly orientated.  
         [0043]    Although only one mount rest area  32  is shown, a plurality of areas may be provided at the station  30 . Such a plurality might then allow automatic scanning of a series of parts each on a different mount and each being automatically loaded/unloaded onto/from the holder  12  for measuring. The mount holder and area(s) thus form a mount transit system.  
         [0044]    Whilst the description and drawings refer to use with teeth etc, this application is purely illustrative and it is not intended to limit the invention to such applications.