Abstract:
An assembly for connecting a measuring head to a measuring robot, the assembly having a flange integral with a supporting member of the measuring robot; isostatic supporting elements interposed between the measuring head and the flange; and a rotary ring nut carried by the flange and movable between an angular position permitting insertion of the head, and an angular position locking the head; the ring nut having elastic elements generating a preload on the isostatic supporting elements; and the isostatic supporting elements defining respective switches of an electric circuit forming part of a safety system for detecting shock on the head.

Description:
The present invention relates to an assembly for connecting a measuring head to a measuring robot. 
     In the following description and in the Claims, the term “measuring head” is used in the widest sense to indicate any unit featuring a measuring stylus, regardless of configuration or number of axes. Similarly, the term “robot” is used to indicate any unit for moving a measuring head along a number of coordinate axes, regardless of configuration or number of axes. 
     The invention may be used conveniently, but not exclusively, for connecting a two-axis articulated head (sometimes referred to as “wrist”) to a measuring robot. 
     BACKGROUND OF THE INVENTION 
     A measuring head is normally connected to a measuring robot using a connecting assembly comprising a first and a second flange respectively integral with a supporting member of the measuring robot and with the measuring head, and which rest one on the other; and locking means for locking the flanges to each other. 
     The locking means may comprise straightforward screws or more complex locking members requiring a special wrench for assembly and disassembly. Whichever the case, known connecting assemblies require the use of tools to lock and release the head, so that assembling and disassembling the head are relatively long, painstaking jobs. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a connecting assembly permitting maximum positioning precision and repeatability, and which at the same time is fast and easy to use and, in particular, provides for assembling and disassembling the measuring head rapidly with no tools required. 
     According to the present invention, there is provided an assembly for connecting a measuring head to a supporting member of a measuring robot, of the type comprising: 
     a first connecting member integral with said supporting member of said measuring robot; 
     first supporting means carried by said first connecting member; 
     a second connecting member integral with said measuring head; 
     second supporting means carried by said second connecting member and cooperating with said first supporting means; and 
     locking means interposed between said first and said second connecting member to keep said first supporting means and said second supporting means contacting each other; 
     characterized in that said first and said second supporting means define a substantially isostatic constraint between said first and said second connecting member; said locking means comprising a ring nut carried by one of said first and second connecting members and rotating about a respective axis between a first release position permitting relative movement between said first and said second connecting member along said axis of said ring nut, and a second angular lock position; said assembly comprising elastic means interposed between said ring nut and said second connecting member in said second angular lock position of said ring nut to generate an elastic load to keep said first and said second supporting means in contact with each other. 
     According to a preferred embodiment of the present invention, said first and said second supporting means define a number of electric switches connected in series and normally closed in the assembly position of the measuring head, so as to define a safety or anticrash system for detecting any collision of the measuring head. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A preferred, non-limiting embodiment of the present invention will be described by way of example with reference to the accompanying drawings, in which: 
     FIG. 1 shows an elevation of a measuring head with a connecting assembly in accordance with the teachings of the present invention; 
     FIG. 2 shows a larger-scale, partially sectioned view of the connecting assembly according to the invention, and of an associated portion of the measuring head; 
     FIG. 3 shows a section along line III—III in FIG. 2, with parts removed for clarity; 
     FIG. 4 shows a section along line IV—IV in FIG. 2, with parts removed for clarity; 
     FIG. 5 shows a detail of FIG. 3 in a different operating position; 
     FIG. 6 shows a section along line VI—VI in FIG. 5; 
     FIG. 7 shows a partial section along line VII—VII in FIG. 3; 
     FIG. 8 shows, schematically, an emergency circuit associated with the FIG. 2 assembly. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Number  1  in FIG. 1 indicates as a whole a measuring head for a measuring robot  2 , of which is shown partially a supporting portion  3 . 
     Head  1  comprises in known manner a substantially tubular first body  4 , of axis A, which is connected to supporting portion  3  of robot  2  by an assembly  5  forming the object of the present invention. 
     Head  1  also comprises a second body  6 , which is supported in projecting manner by the first body and is rotated with respect to the first body and about axis A by a first known actuating and control device housed inside first body  4  and not shown by not forming part of the present invention. 
     The second body in turn carries a measuring tool  8  having a stylus  9 . The measuring tool is supported in projecting manner, and is rotated with respect to second body  6  and about an axis B perpendicular to axis A by a second actuating and control device (not shown) housed inside second body  6 . 
     The connecting assembly  5  (FIG. 2) substantially comprises a fixed annular flange  10  connected rigidly to supporting portion  3  of robot  2  by means of screws  11 ; an annular wall  12  of first body  4  cooperating with fixed flange  10  by means of three angularly equally spaced supports  13 ; and a ring nut  14  carried by fixed flange  10  and rotating between a release position (FIG. 3) —enabling head  1  to be fitted to and removed from supporting portion  3  —and a lock position. 
     Each support  13  is defined by two balls  15  fitted to flange  10  and spaced circumferentially; and by a cylinder  16 , which is fitted to annular wall  12  of first body  4 , with its own axis oriented radially with respect to first body  4 , and which cooperates with and defines respective contact points with the two balls. 
     Balls  15  and cylinders  16  are housed partly inside respective locating seats formed respectively on flange  10  and on wall  12 , and are conveniently fixed by means of adhesive. 
     The three supports  13  combine to define a substantially isostatic constraint between wall  12  and flange  10 , and prevent any movement (translation and rotation) in a plane perpendicular to axis A. 
     At each support  13 , wall  12  has a respective radial appendix  20 ; and each appendix  20  carries a supporting cylinder  21  having a radial axis and housed partly inside a respective seat  22 . In this case, too, cylinder  21  is conveniently fixed by means of adhesive. 
     Ring nut  14  (FIG. 3) has a substantially cylindrical lateral wall  23  with outer impressions  24  for easy handling; and an inner annular end wall  25  extending from the axial end of lateral wall  23  opposite the end facing flange  10 . Wall  25  has three cavities  26  (FIG. 4) for the passage of appendixes  20  when head  1  is fitted to flange  10 . 
     Ring nut  14  and flange  10  are secured axially to each other by means of respective inner and outer radial toothings shown more clearly in FIG.  3 . 
     More specifically, flange  10  comprises an external toothing consisting of a number of, e.g. three, teeth  28  forming gaps  29 , each of a circumferential extension equal to that of each tooth (60° in the example shown). Flange  10  also comprises a continuous circumferential projection  30  (FIG. 2) spaced axially with respect to teeth  28  so as to form, with teeth  28 , seats  31  for the teeth of ring nut  14 . 
     The innner toothing of ring nut  14  comprises a number of teeth  34  equal in number to teeth  28  (e.g. three) but of a smaller circumferential extension to enable ring nut  14  to be fitted axially onto flange  10  by inserting teeth  34  of ring nut  14  through gaps  29  between teeth  28  of flange  10 , and then rotating ring nut  14  so that teeth  34  are superimposed axially on teeth  28  (FIG.  3 ). 
     Following assembly, two threaded pins  35  (only one shown in FIG. 2) are screwed through flange  10 , and interfere with teeth  34  of ring nut  14  to limit the angular travel of teeth  34  between a release position and a lock position and prevent ring nut  14  from being positioned with teeth  34  aligned with gaps  29  and so withdrawn axially. 
     Ring nut  14  has three bend springs  36  for producing the axial load by which to lock head  1  to supports  13 . 
     Springs  36  (FIG. 4) are leaf springs of curved elongated shape, so as to be housed along annular wall  25  of ring nut  14 . More specifically, each spring  36  has one end  37  fitted to wall  25  by two screws  38  at a supporting region  39  substantially half-way between two cavities  26 , projects along wall  25 —provided, for the purpose, with a respective sunken portion  41 —and terminates with a free end  40  located close to a respective cavity  26  and which, in use, cooperates elastically with a respective supporting cylinder  21  as described in detail later on. 
     Ring nut  14  also has an antirelease device  44 —shown in FIGS.  5  and  6 —substantially comprising a pin  45  with its axis parallel to axis A and fitted in axially-sliding manner adjacent to lateral wall  23  of ring nut  14 . Pin  45  has a circular head  46  of such a diameter as to project radially through a milled portion  47  of lateral wall  23  of ring nut  14 , and is loaded axially by a spring  48  towards flange  10  against which head  46  rests axially. 
     Flange  10  has a circular sunken seat  54  into which head  46  of pin  45  clicks to define the angular lock position of ring nut  14  with respect to flange  10 . 
     Finally, connecting assembly  5  comprises a safety system  55  shown schematically in FIG.  8 . 
     System  55  substantially comprises an electric circuit  56  in turn comprising a voltage source  57  for generating a direct reference voltage; three normally-closed switches  58  in series with one another; and a voltage sensor  59  connected to the robot control unit (not shown) and for generating an open-circuit logic 0 signal  60  in the event at least one of switches  58  is open. 
     Each switch  58  is defined by balls  15  and respective cylinder  16  of a respective support  13 . More specifically, balls  15  define a pair of fixed contacts of each switch, and respective cylinder  16 —which is made of conducting material—defines a bridge-contact element for closing the circuit between the respective pair of balls when resting correctly on each ball. 
     Balls  15  are connected electrically by electric cables  61 , which are soldered to the balls and extend through respective holes  62  in flange  10  (FIG.  2 ). 
     Balls  15  are made of conducting material and conveniently insulated with respect to flange  10 , e.g. by means of nonconducting paint only applied to the supporting region and not, obviously, to the region contacting cylinder  16 . 
     Sensor  59  is subjected to the reference voltage and generates a logic 0 signal  60  when all three switches  58  are closed, and is subjected to zero voltage and generates a logic 1 signal when at least one of switches  58  opens. 
     Operation of connecting assembly  5 —which is partly self-explanatory from the foregoing description—is as follows. 
     Head  1  is fitted to flange  10  already fitted beforehand with ring nut  14 , which is set to the release position—that is, the position enabling insertion of head  1 —in which cavities  26  of ring nut  14  face respective pairs of balls  15 , so that, as head  1  is inserted, radial appendixes  20  of wall  12  fit axially through cavities  26  of wall  25  of ring nut  14 . 
     Upon cylinders  16  of s supports  13  contacting respective pairs of balls  15 , ring nut  14  may be rotated manually about 15° clockwise with reference to the FIG. 3 position , so that head  46  of pin  45  clicks inside seat  54  to lock ring nut  14  angularly with respect to flange  10  (FIG.  5 ). In this position, the respective free ends  40  of springs  36  contact respective supporting cylinders  21 , and the springs bend elastically to transmit an elastic load to first body  4  to maintain contact between pairs of balls  15  and respective cylinders  16  of supports  13 . 
     In the event of shock on head  1  in use, at least one of supports  13  loses contact (FIG.  8 )—this being permitted by the flexible axial lock provided for by assembly  5  by virtue of the flexibility of springs  36 —and the interruption in the circuit is detected by sensor  59  which sends an emergency signal  60  to the control unit. 
     Head  1  is disassembled equally rapidly by backing head  46  of pin  45  manually out of seat  54  (operation which can be easily carried out by means of the thumb while gripping ring nut  14 ) and rotating the ring nut in the opposite direction to previously. 
     The advantages of connecting assembly  5  according to the present invention will be clear from the foregoing description. 
     In particular, head  1  is fitted to and removed from the measuring robot quickly and easily by hand with no tools required. 
     Moreover, supports  13  define an isostatic constraint for ensuring maximum repeat positioning of head  1  with respect to supporting member  3 . 
     Finally, supports  13  themselves define respective switches of an emergency anticrash circuit, which function is therefore achieved simply, using a minimum number of dedicated components. 
     Clearly, changes may be made to assembly  5  without, however, departing from the scope of the accompanying claims.