Abstract:
A probe head for a coordinate measuring machine has a coupling part having a retaining pin, on which a probe tool is detachably arranged. The probe tool has at least one stylus for touching a measurement object, and a rotary plate. The rotary plate is coupled to the coupling part by means of the retaining pin in one of a plurality of defined rotation angle positions. Moreover, the rotary plate has a latching mechanism including at least one adjustable latching element and a detector. The latching element has a latching position in which it fastens the rotary plate on the retaining pin, and it has a release position in which it releases the retaining pin. The detector generates a signal which is representative of at least one from the latching position and the release position.

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of international patent application PCT/EP2011/056305 filed on Apr. 20, 2011 designating the U.S., which international patent application has been published in German and claims priority from German patent application DE 10 2010 020 654.7 filed on May 7, 2010. The entire contents of these prior applications are incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The present invention relates to a probe head for a coordinate measuring machine for determining spatial coordinates on a measurement object, and to a probe tool for such a probe head. 
         [0003]    Coordinate measuring machines are typically used for determining geometrical dimensions and/or the shape of workpieces. In general, the coordinate measuring machine has a measurement head which can be moved relative to the workpiece (hereafter measurement object). Depending on the position of the measurement head relative to the workpiece, spatial coordinates are determined which represent the position of defined measurement points on the workpiece within a measurement volume. If a plurality of spatial coordinates are determined for a plurality of measurement points, the geometrical dimensions and/or the shape of the measurement object can be checked with the aid of the spatial coordinates. 
         [0004]    In many cases, the probe head of a coordinate measuring machine has a probe tool with which the desired measurement points on the measurement object are touched (physical contact). Accordingly, the probe head may be referred to as a touch probe head. 
         [0005]    The probe tool often has a stylus with a free end, on which a touch ball is arranged. The desired measurement points on the measurement object are touched with the touch ball. In order to reach all measurement points in the case of complex workpieces, it is often desirable to hold the stylus in different orientations relative to the probe head. Furthermore, it is often desirable to use probe tools with different styli or styli combinations on a probe head, in order to optimally reach all desired measurement points. 
         [0006]    DE 101 14 126 A1 discloses a probe head having a replaceable probe tool. The probe tool has a stylus which is angled in an L-shape and can be fastened on the probe head in different rotation angle positions. A rotary plate of the probe tool is arranged in a defined rotation angle position on the probe head by means of a kinematic three-point bearing. In order to change the rotation angle position, the rotary plate is disengaged from the three-point bearing by means of a pneumatically actuated push-rod and subsequently rotated on the push-rod by means of a rotary drive arranged in the probe head. The rotary plate is then re-engaged into the defined three-point bearing. The rotation angle position of the rotary plate and of the stylus arranged thereon is determined by a sensor, which at the same time also delivers signals for the rotary drive. In order to prevent the rotary plate from falling when the stylus is being rotated, the rotary plate is fastened on the push-rod by a hook-shaped connection. Further safeguarding of the rotary plate against falling during the rotation process is not disclosed. 
         [0007]    The known probe head makes it possible to use different probe tools with different orientations. It is therefore suitable for flexible measurements on complex measurement objects. Disadvantages are the rotary drive integrated in the probe head and the pneumatically actuated push-rod, which are required in addition to the probe head sensors with which displacements of the stylus relative to the probe head are determined. Depending on the frequency of use, the rotary drive generates heat which can have an unfavorable effect on the measurement accuracy of the probe head. Furthermore, integration of the additional components into the probe head leads to heavier weight. 
         [0008]    In U.S. patent application Ser. No. 13/198,845, published as US 2012/0079731 A1, the assignee has described a probe head for a coordinate measuring machine, in which the probe tool can be rotated using measurement force generators and a so-called roll motion projection. Measurement force generators are actually used in so-called active probe heads to adjust and ensure a defined sampling force when a measurement point is being touched. They are present in active probe heads, and according to the concept described in US 2012/0079731 A1, they are also used for rotating the probe tool. Accordingly, this probe head avoids the disadvantages of the probe head of DE 101 14 126 A1. 
         [0009]    In the case of the probe head of US 2012/0079731 A1, the rotary plate of the probe tool is fastened on a retaining pin, by means of which the rotary plate can be disengaged from its kinematic bearing for the rotational movement. In test operation, it has been found that the fastening of the rotary plate on the retaining pin is a critical point. If the retaining pin and/or the rotary plate are contaminated, for example, it is possible that the fastening of the rotary plate on the retaining pin will be insufficient and the probe tool can loosen and fall during rotation on the roll motion projection. This may cause damage to the probe tool and/or the measurement object. 
         [0010]    DE 10 2005 043 454 B3 discloses a change device for replaceable reception of a probe tool on a coordinate measuring machine, a safety cable ensuring that the probe tool does not fall out of the holder even in the event of collision, even though the probe tool can detach from the holder in the event of a collision in order to avoid damage. A similar safety mechanism is also described in the aforementioned prior application US 2012/0079731 A1. This safety mechanism, however, does not offer protection against the probe tool falling out when the fastening of the probe tool on the retaining pin is already insufficient. 
         [0011]    EP 0 523 906 A1 discloses a further probe head having a rotatable probe tool. The probe tool is in this case retained magnetically on the probe head. A retaining magnet for holding the probe tool is connected to a shaft which can be rotated by means of a motor specially provided therefor. In order to rotate the probe head, the retaining magnet is moved forward together with the shaft, so that the probe tool is disengaged from its working position. With the aid of the motor, the probe tool is then rotated. Subsequently, the shaft is pulled back into its original position, the retaining magnet being released from the probe tool. Here again, no particular security is provided against the probe tool falling during rotation. 
       SUMMARY OF THE INVENTION 
       [0012]    Against this background, it is an object of the present invention to provide a probe head, wherein the probe tool is better protected against damage due to falling particularly during rotation. Preferably, the new probe head is intended to function without a special rotary drive for rotating the probe tool, although the invention is generally not restricted thereto. 
         [0013]    According to one aspect of the invention, there is provided a probe head for a coordinate measuring machine for determining spatial coordinates on a measurement object, comprising a coupling part having a retaining pin, on which a probe tool is arranged; a body part on which the coupling part is moveably mounted; at least one measurement force generator configured to effect a defined movement of the coupling part relative to the body part; and a roll motion projection formed on the body part; wherein the probe tool comprises at least one stylus for touching the measurement object and a rotary plate coupled to the coupling part by means of the retaining pin, said rotary plate being configured to be rolled along the roll motion projection as a result of the defined movement of the coupling part relative to the body part in order to set a rotation angle position of the at least one stylus, wherein the rotary plate comprises a latching mechanism having at least one adjustable latching element and a detector, the latching element having a latching position in which it secures the rotary plate on the retaining pin, and at least one release position in which it releases the retaining pin, and wherein the detector is configured to generate a signal which is representative of at least one from the latching position and the release position. 
         [0014]    According to a further aspect, there is provided a probe tool for a probe head having a retaining pin for holding the probe tool, said probe tool comprising at least one stylus for touching a measurement object and comprising a rotary plate designed to be coupled to the probe head by means of said retaining pin in one of a plurality of defined rotation angle positions, wherein the rotary plate comprises a latching mechanism having at least one adjustable latching element and a detector, the latching element having a latching position in which it fastens the rotary plate on the retaining pin, and at least one release position in which it releases the retaining pin, and wherein the detector is configured to generate a signal which is representative of at least one of the latching position and the release position. 
         [0015]    According to yet another aspect, there is provided a probe head for a coordinate measuring machine for determining spatial coordinates on a measurement object, the probe head comprising a coupling part having a retaining pin, on which a probe tool is detachably arranged, the probe tool comprising at least one stylus for touching the measurement object and a rotary plate, which is coupled to the coupling part by means of the retaining pin in one of a plurality of defined rotation angle positions, wherein the rotary plate comprises a latching mechanism having at least one adjustable latching element and a detector, the latching element having a latching position in which it fastens the rotary plate on the retaining pin, and at least one release position in which it releases the retaining pin, and the detector generating a signal which is representative of at least one of the latching position and the release position. 
         [0016]    The new probe head and the new probe tool have a latching mechanism, which is arranged on the rotary plate of the probe tool. Fastening of the probe tool on the probe head is thus at least partially achieved by the rotary plate, and is not merely subject to the receptacle for the rotary plate in the probe head. Furthermore, the rotary plate has a detector, with the aid of which the function of the latching mechanism is monitored. The detector generates a signal which is representative of the latching position and/or the release position of the latching element. Accordingly, the signal is designed to indicate the respective position of the latching element. Preferably, the detector signal is evaluated in the probe head in order to detect insufficient fastening of the rotary plate on the retaining pin as early as possible, and to deliver a warning signal to the user of the machine and/or to trigger an operational shutdown as a function thereof. It is furthermore preferred, if an evaluation and control unit, which may optionally be arranged in the probe head or separately from the probe head, prevents disengagement of the rotary plate and a change in the rotation angle position, as the case may be, as a function of the signal of the detector. 
         [0017]    The new probe head and the new probe tool thus have a dedicated detector, which allows monitoring of the latching mechanism with the aid of a dedicated monitoring signal. As an alternative or in addition to this, the latching mechanism could be formed so as to be failsafe, for example by a mechanical design which rules out fastening of the probe tool with insufficient latching. The use of a detector to generate a dedicated monitoring signal, however, simplifies the mechanical design of the interface between the rotary plate and the coupling part. Furthermore, the detector allows alterations of the mechanical interface between the rotary plate and the coupling part to be taken into account. Alterations which have an effect on the function of the latching mechanism, and which do not occur until during operation of the coordinate measuring machine, may for instance be a result of contamination, wear and/or incorrect operation. The detector allows very reliable and economical monitoring of the latching function. Furthermore, integration of the detector in the probe tool is advantageous in order to simplify retrofitting of older coordinate measuring machines. 
         [0018]    As will be explained below with respect to preferred exemplary embodiments, the new probe head may advantageously be produced without a special rotary drive for rotating the probe tool by using one or more measurement force generators in the probe head, in order to generate a desired rotational movement using a roll motion projection. The detector, integrated in the probe tool, for monitoring a latching element integrated in the probe tool may, however, also be used advantageously in probe heads which have a special rotary drive for rotating the probe tool. 
         [0019]    In a preferred refinement, the rotary plate has at least one identification circuit, and the coupling part has a sensor for reading the at least one identification circuit. 
         [0020]    An identification circuit in the context of this refinement is a—preferably electronic—circuit, which contains encoding that identifies the rotary plate. A preferred identification circuit comprises a memory in which the encoding is digitally stored. In principle, however, the identification circuit could comprise mechanical encoding which can be read mechanically, electrically and/or optically by a suitable sensor in the coupling part. The preferred refinement has the advantage that the probe head can recognize the identity and properties of the probe tool in a simple and automated fashion, for example in order to determine the number of possible rotation angle positions and/or the presence of the new detector. 
         [0021]    In another refinement, the detector is designed to prevent the identification circuit from being read by the sensor depending on the latching position and/or the release position. 
         [0022]    This refinement allows very simple, economical and compact production of the detector, by the detector using the encoding delivered anyway by the identification circuit, in order to generate the monitoring signal for the latching mechanism. In a preferred exemplary embodiment, the detector prevents the identification circuit from being read when the latching element is not in its latching position, i.e. it is in a release position of whatever type. The “signal” of the detector consists in this case in the sensor receiving no signal from the identification circuit. The detector may therefore be a passive element, which causes no additional heat generation in the probe head. 
         [0023]    In a further refinement, the detector comprises an electrical switch, which is arranged electrically in series with the at least one identification circuit. 
         [0024]    This refinement allows very simple, economical and reliable production of the detector. The electrical switch is preferably a mechanically actuated microswitch, which is closed only when the latching element is in its latching position. Such a switch can be integrated well in the small installation space of a rotary plate, and it can prevent reading of the identification circuit very efficiently. 
         [0025]    In a further refinement, the rotary plate has a plurality of identification circuits, with each identification circuit being representative of one of the defined rotation angle positions, and the detector is designed to prevent the identification circuit from being read by the sensor depending on the latching position and/or the release position. 
         [0026]    Preferably, in this refinement, an individual identification circuit is provided for each defined rotation angle position. The probe head can determine the current rotation angle position of the rotary plate very efficiently in this refinement with the aid of the individual identification circuit, which is read by the sensor. It is advantageous for the detector to be formed so as to prevent reading of the plurality of identification circuits, since in this case only one detector is required. In a preferred exemplary embodiment, the detector comprises the aforementioned switch, which is arranged in series with the plurality of identification circuits. The refinement allows reliable monitoring of the latching function in each rotation angle position and a compact structure. 
         [0027]    In a further refinement, the rotary plate has a plurality of rotary plate latching elements, which define the rotation angle positions, and the at least one identification circuit has a number of electrical contacts which are arranged radially with respect to at least one of the rotary plate latching elements. Preferably, arranged radially with respect to each rotary plate latching element, there is a pair of electrical contacts which are respectively connected to an identification circuit, each identification circuit identifying precisely one rotary plate latching element. It is furthermore preferred that, on the coupling part, a contact pair is arranged which reads precisely one identification circuit in each rotation angle position via the electrical contacts which are assigned to this identification circuit. 
         [0028]    The refinement allows rapid and very reliable determination of each defined rotation angle position. The radial arrangement of the electrical contacts furthermore contributes to a compact and clear structure. In addition, this refinement simplifies the preferred production of the detector in the form of a switch electrically arranged in series with all the identification circuits. 
         [0029]    In a further refinement, the coupling part comprises a plurality of coupling plate latching elements and a further sensor, the further sensor being designed to detect mechanical contact between at least one coupling plate latching element and at least one rotary plate latching element. Preferably, the coupling plate latching element is formed as a ball or roller pair which forms an intermediate space in which precisely one rotary plate latching element can engage. It is, however, also conceivable for each rotary plate latching element to be a ball or roller pair between which precisely one coupling plate latching element can engage. 
         [0030]    The refinement produces a second, independent signal path which can advantageously be used to detect the bearing of the rotary plate on the coupling part. The further sensor does not, however, replace the detector described above, since by itself it does not offer any information in relation to the latching element. Nevertheless, the further sensor allows better monitoring of the latching function since the detector of the rotary plate can deliver the above-described signal to the probe head only when the rotary plate is arranged in the region of the coupling part. The further sensor thus delivers additional information, which is advantageously used to distinguish between various possible configurations. Furthermore, the further sensor makes it readily possible to establish whether the rotary plate is coupled to the coupling part in a kinematically uniquely defined rotation angle position and/or whether it is disengaged from the kinematic bearing for rotation. 
         [0031]    In a further refinement, the latching mechanism comprises two, preferably spring-loaded, sliding members, which can be displaced counter to one another in order to bring the at least one latching element into the release position. 
         [0032]    Two counter-running sliding members allow simple and reliable opening and closing of the latching mechanism. Furthermore, a latching mechanism comprising at least two counter-running latching elements is robust and tolerant to slight positioning inaccuracies when fitting the rotary plate. Such inaccuracies are compensated for by the counter-running elements. Spring-loaded sliding members have the advantage that they ensure a defined resting position, in which the rotary plate is preferably latched on the retaining pin. 
         [0033]    The preferred sliding members each have a free end, the free ends lying diametrically opposite one another in the resting position and protruding radially beyond the rotary plate edge. This refinement allows simple manual activation and highly reproducible machine actuation of the latching mechanism. 
         [0034]    In a further refinement, the probe head has a body part on which the coupling part is moveably mounted, and at least one measurement force generator which is designed to effect a movement of the coupling part relative to the body part. 
         [0035]    This refinement involves an active probe head comprising at least one measurement force generator, which is capable of displacing the probe tool arranged on the coupling part in a defined direction, or generating a defined measurement force when the probe tool abuts on a measurement point. Preferably, the probe head has at least three measurement force generators, which can displace the coupling part in three mutually orthogonal directions. The refinement allows very accurate adjustment of a measurement force and it simplifies automatic path control during the continuous scanning of a measurement object. 
         [0036]    In a further refinement, a roll motion projection, on which the rotary plate can be rolled by movement of the coupling part, is formed on the body part. 
         [0037]    This refinement uses the concept described in above mentioned US 2012/0079731 A1, which is incorporated by reference herewith, for bringing the rotary plate into a desired rotation angle position with the aid of measurement force generators. The new latching mechanism which is monitored with the aid of the new detector allows reliable fastening of the rotary plate especially in this case, and it avoids in particular damage due to the probe tool falling when the rotary plate is rotated on the roll motion projection. Precisely in this situation, the rotary plate experiences lateral forces which can cause falling when there is fastening but it is not sufficient. 
         [0038]    In a further refinement, the roll motion projection is a sleeve, which is arranged essentially concentrically with the rotary plate. Preferably, the sleeve is a cylindrical sleeve which is arranged concentrically with a circular rotary plate. 
         [0039]    This refinement allows a very compact structure as well as rapid and position-independent rotation of the rotary plate on the roll motion projection. 
         [0040]    In a further refinement, a traction element is arranged between the rotary plate and the roll motion projection. In a preferred variant, the traction element is a rubber-like ring which is arranged on the outer circumference of the rotary plate and which increases the static friction and sliding friction between the rotary plate and the roll motion projection. In a further variant, the traction element has a sandpaper-like surface on the roll motion projection and/or on the outer circumference of the rotary plate. In a further variant, the traction element produces a form fit between the rotary plate and the roll motion projection. For example, the traction element may contain gearing, for instance by the rotary plate comprising outer teeth on the outer circumference which are formed so as to mesh with inner teeth on the roll motion projection. 
         [0041]    Such a traction element improves the driving force between the rotary plate and the roll motion projection. Slip is reduced, even if not entirely avoided. The traction element therefore contributes to bringing the rotary plate rapidly and accurately into a desired rotation angle position. 
         [0042]    In a further refinement, a stop, by which the retaining pin can be fixed relative to the coupling part, is arranged on the body part. 
         [0043]    In the preferred refinements, the retaining pin is arranged on the coupling part in such a way that it can be moved parallel to the rotation axis of the rotary plate. In a first position (latching position), the retaining pin draws the rotary plate into the preferred kinematic three-point bearing. In a second position (rotation position) the retaining pin disengages the rotary plate from the kinematic bearing, in order to permit rotation of the rotary plate. Preferably, the pin is mounted in the rotation position without play in a roller bearing, in order to permit slight rotation of the rotary plate. In the latching position, the retaining pin is preferably arranged at a distance from the bearing element, i.e. it has play inside the bearing element in order to avoid mechanical clamping when touching measurement objects. 
         [0044]    The preferred stop has the advantage that the retaining pin can be moved very efficiently relative to the coupling part with the aid of a measurement force generator, by displacing the coupling part parallel to the rotation axis of the rotary plate with the aid of the measurement force generator, while the retaining pin is fixed on the stop. The configuration allows very smooth disengagement and engagement of the rotary plate, wherein use is again made of an integrated measurement force generator in an advantageous manner. 
         [0045]    In a further refinement, the coupling part is arranged between the stop and the rotary plate. 
         [0046]    This refinement contributes to a particularly compact structure and allows advantageous encapsulation of all the probe head components except for the replaceable probe tool. 
         [0047]    It is to be understood that the features mentioned above and those yet to be explained below may be used not only in the respectively indicated combination but also in other combinations or separately, without departing from the scope of the present invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0048]    Exemplary embodiments of the invention are illustrated in the drawing and are explained in more detail in the description which follows. 
           [0049]      FIG. 1  shows a coordinate measuring machine comprising a probe head according to one exemplary embodiment of the invention, 
           [0050]      FIG. 2  shows a simplified representation of the probe head comprising a probe head sensors and a measurement force generator, 
           [0051]      FIG. 3  shows a preferred exemplary embodiment of the probe head in a view on to the coupling part, 
           [0052]      FIG. 4  shows the probe head of  FIG. 3  in a sectional view along the line IV-IV, 
           [0053]      FIG. 5  shows a preferred exemplary embodiment of a probe tool for coupling to the coupling part of  FIG. 3 , 
           [0054]      FIGS. 6   a  and  6   b  show a first and a modified second exemplary embodiment of the latching mechanism of the probe tool of  FIG. 5 , 
           [0055]      FIG. 7  shows a simplified representation of the preferred probe head during rotation of the probe tool, and 
           [0056]      FIGS. 8 to 10  show the coupling part of the probe head of  FIGS. 3 and 4  in various operating positions. 
       
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0057]    In  FIG. 1 , a coordinate measuring machine with the new probe head is denoted overall by reference number  10 . The coordinate measuring machine  10  in this case has a base  12 , on which a gantry  14  is arranged so that it can be moved in the longitudinal direction. The movement direction of gantry  14  relative to the base  12  is typically denoted as the y axis. On the upper crossbar of the gantry  14 , a carriage  16  is arranged which can be moved in the transverse direction. The transverse direction is typically denoted as the x axis. The carriage  16  carries a quill  18 , which can be moved in the z direction, i.e. perpendicularly to the base  12 . The reference numbers  20 ,  22 ,  24  denote measuring instruments, with the aid of which the position of the gantry  14 , the carriage  16  and the quill  18  can be determined. Typically, the measuring instruments  20 ,  22 ,  24  are glass measuring scales, which are read with the aid of suitable sensors. 
         [0058]    A probe head  26 , which holds a probe tool  27 , is arranged on the lower free end of the quill  18 . The probe tool  27  in this case comprises three styli  28 , each of which has a ball  29  on its free end. The ball is used to touch a measurement point on a measurement object  30 . With the aid of the measuring instruments  20 ,  22 ,  24 , it is possible to determine the position of the probe head  26  within the measurement volume when the measurement point is touched. As a function of this, spatial coordinates of the sampled measurement point can then be determined. 
         [0059]    Reference number  32  denotes an evaluation and control unit, which is connected via lines  34  and  36  to the drives and sensors on the gantry. The control unit  32  is used to operate the motor drive for the movement of the probe head  26  along the three coordinate axes x, y and z. The evaluation and control unit  32  furthermore reads in the measurement values from the measuring instruments  20 ,  22 ,  24 , and as a function thereof and as a function of displacements of the probe tool  27 , it determines the current spatial coordinates of the measurement point and further geometrical values of the measurement object  30 . 
         [0060]    In a highly simplified schematic representation,  FIG. 2  shows the basic functionality of the probe head  26 . The probe head  26  has a body part  38  and a coupling part  40 , which are in this case connected to one another by means of two leaf springs  42  and  44 . The leaf springs  42 ,  44  form a spring parallelogram, which in this case permits movement of the coupling part  40  in the direction of arrow  46  (and back in the direction of the arrow  46 ′). The probe tool  27  with the styli  28  can therefore be deployed from its resting position through a distance D. The references  28 ′ and  29 ′ show one of the styli  28  with a ball  29  in the deployed position. 
         [0061]    The displacement of the probe tool  27  relative to the body part  38  may be the result of touching the measurement object  30  at a measurement point. Advantageously, the displacement of the probe tool  27  is taken into account when determining the spatial coordinates. Furthermore, the displacement of the probe tool  27  may in the preferred exemplary embodiments be generated with the aid of a measurement force generator  56 , as explained in more detail below. A limb  48 ,  50  is in this case respectively arranged on the body part  38  and on the moving part  40 . The limbs  48 ,  50  are in this case parallel to the leaf springs  42 ,  44 . Between the limbs  48 ,  50 , a displacement detector  52  (here represented by a scale  54 ) and the measurement force generator  56  are arranged. The displacement detector  52  in this case comprises a measurement coil  53  in the form of a plunger coil. As an alternative or in addition, a Hall sensor, a piezoresistive sensor or another sensor may be envisioned as displacement detector  52 , with the aid of which the spatial displacement of the probe tool  27  relative to the body part  38  (or more precisely the displacement of the spring parallelogram which is formed by the leaf springs  42 ,  44 ) can be determined. The measurement force generator  56  is in this case likewise formed as a plunger coil. With the aid of it, the two limbs  42  and  50  can be drawn together or pushed apart, by attracting or repelling a core  59  with the aid of a magnetic field generated in the coil. 
         [0062]    In the highly simplified representation of  FIG. 2 , the probe head  26  only allows displacement of the probe tool  27  in the direction of the arrow  46 . It is, however, clear to the person skilled in the relevant art that such a probe head  26  typically allows corresponding displacement in two further orthogonal spatial directions. This may, for example, be achieved with further spring parallelograms and/or with a diaphragm spring. The invention is not, however, restricted to this special probe head and may also be carried out with other probe heads which have a body part  38  and a coupling part  40  movable relative thereto. 
         [0063]      FIG. 3  shows a preferred exemplary embodiment of the probe head  26  of  FIG. 2  in a view from below (without the probe tool  27 ).  FIG. 4  shows a simplified section of the probe head of  FIG. 3  along a section line IV-IV. 
         [0064]    The body part  38  holds the coupling part  40 , which is preferably movable in three orthogonal spatial directions on the body part  38 . For the sake of simplicity only two spring elements  42 , which permit the three orthogonal movement directions, are shown in  FIG. 4 . The coupling part  40  in this case comprises a pin  57 , which is guided in a perpendicularly mobile fashion in the coupling part  40  (this will be explained in more detail below with the aid of  FIGS. 8 to 10 ). In the edge region of the coupling part  40 , three pairs of latching balls  58  are arranged uniformly distributed in the circumferential direction. The arrangement is selected in such a way that the latching ball pairs respectively have the same radial distance from pin  57 . The coupling part  40  furthermore has a magnet  60 , here for example in the form of an annular electromagnet. As an alternative, the magnet may be a permanent magnet, which is strengthened or weakened by an additional electromagnet. The magnet  60  is in this case arranged concentrically with the pin  57  on the coupling part  40 . The coupling part  40  in this case furthermore has a sensor  64  with two contacts  66 , and a sensor  65 . A roll motion projection  68  in the form of a cylindrical sleeve with an internal wall  72  is formed on the body part  38 . The roll motion projection  68  in this case extends concentrically with the pin  57 . 
         [0065]    As already mentioned with reference to  FIG. 2 , the position of the coupling part  40  relative to the body part  38  can be modified with the aid of measurement force generators  56 . These are conventionally used in order to generate a defined measurement force when sampling the measurement object. In order furthermore to permit advantageous movement of the pin  57  relative to the coupling part  40 , in the preferred exemplary embodiment a stop  62  is provided which is formed here on the body part  38  or at least rigidly connected thereto. The stop  62  cooperates with a plate  63  which is formed on the upper end of the pin  57 . In  FIG. 4 , the upper end of the pin  57  extends upward beyond the stop  62  and the plate  63  is arranged above the stop  62 . When the coupling part  40  is pressed downward with the aid of measurement force generator  56 , pin  57  follows this movement until the plate  63  encounters the stop  62  from above. Beyond this position, the pin  57  is blocked against further movement downward. The coupling part  40 , on the other hand, can be pressed further downward with the aid of the measurement force generator  56 . After the moment when the pin  57  is blocked on the stop  62  by means of the plate  63 , the measurement force generator continues to move only the coupling part  40  downward, and no longer the pin  57 . In other words, the measurement force generator  56  pushes the coupling part  40  downward relative to pin  57 . Since pin  57  is formed with its lower free end holding a probe tool (as explained in more detail with reference to  FIGS. 8 to 10 ), the distance between the coupling part  40  and the probe tool  27  can be varied, and in particular reduced, using the measurement force generator  56  and the stop  62 . This is advantageously used in exemplary embodiments of the new coordinate measuring machine in order to move the coupling part  40  “smoothly” onto the probe tool  27  and subsequently fasten it with the magnet  60 . 
         [0066]      FIG. 5  shows a preferred exemplary embodiment of the probe tool  27  in a plan view of the interface, by which the probe tool is coupled to the coupling part  40 . The probe tool  27  has a rotary plate  74 , which is formed circularly in this case. Arranged on the outer circumference of the rotary plate  74 , there is a traction element  76 , here by way of example in the form of an O-ring. Instead of an O-ring, in other exemplary embodiments a flat belt of a rubber-elastic material is arranged on the outer edge of the rotary plate. The rotary plate  74  in this case comprises a plurality of latching rollers  80 , each of which is radially aligned. The latching rollers  80  are uniformly distributed in the circumferential direction of the rotary plate  74 . Radially inward of each latching roller  80 , two contacts  82  are arranged. The contacts  82  in this case lie behind one another in the radial direction of the rotary plate  74 , so as to provide an arrangement of radial contact pairs distributed in the circumferential direction. Each pair is part of an alignment determination element  84 , which cooperates with the sensor  64  on the coupling part  40  (cf.  FIG. 8 ). 
         [0067]    In the preferred exemplary embodiments, each alignment determination element  84  includes an identification circuit, for example in the form of a memory chip, in which an individual encoding is stored. Each identification circuit therefore represents a unique item of information. The sensor  64  can, by means of the contacts  66 , only read one identification circuit  84  at a time and determine the rotation angle position of the probe tool relative to the coupling part with the aid of the encoding which it reads. Preferably, at least one identification circuit contains further information items which represent the identity and/or properties of the probe tool  27  as a whole. 
         [0068]    A reception element  90  in the form of a circular opening is arranged at the center of the rotary plate  74 . In this case, two latching elements  92  are arranged in the reception element  90 , by which the rotary plate  74  can be fastened on the lower free end of the pin  57 . In the exemplary embodiment in  FIG. 5 , the latching elements  92  are two bars which are formed so as to engage in a groove on the lower free end of the  57  (cf.  FIG. 9 ). 
         [0069]    The probe tool  27  in this case carries the three styli  28  according to  FIG. 1 . The styli  28  are arranged below the rotary plate  74 . The configuration of the probe tool is not restricted to the manner shown in  FIG. 5 . It is possible to use styli of different length and/or geometries. The number of styli used and/or the number of latching rollers may also differ from the exemplary embodiment represented. 
         [0070]      FIG. 6   a  shows a latching mechanism  86  with which the latching elements  92  can be opened or closed, in order to fasten the rotary plate  74  on the pin  57 . The latching mechanism  86  is integrated in the rotary plate  74  in the preferred exemplary embodiments. Preferably, the latching mechanism  86  is arranged between the upper side of the rotary plate  74 , which is shown in  FIG. 5 , and the stylus  28 . 
         [0071]    In the preferred exemplary embodiment, the latching mechanism  86  has two sliding members  87   a ,  87   b  movable counter to one another. Each sliding member  87   a ,  87   b  is biased into a resting position by means of a spring element  88 . In the preferred exemplary embodiments, the spring elements  88  bias the sliding members  87  in a resting position in which the latching elements  92  clamp the rotary plate  74  on the pin  57 . In the preferred exemplary embodiment, each sliding member  87  is respectively connected to a clamping piece  89   a ,  89   b . The latching elements  92  are arranged on the clamping pieces  89   a ,  89   b.    
         [0072]    By pressing the sliding members  87   a ,  87   b  against one another in the direction of the arrows shown in  FIG. 6   a , the clamping pieces  89  can be pressed apart from one another. The effect of releasing the sliding members  87  is that the spring elements  88  press the latching elements  92  together again. In order to open the latching mechanism  86 , each sliding member  87  has a free end  91  which protrudes outward beyond the outer circumference of the rotary plate  74 . In the preferred exemplary embodiments, the free ends  91   a ,  91   b  of the sliding members  87   a ,  87   b  lie diametrically opposite one another on the outer circumference of the rotary plate  74 . 
         [0073]      FIG. 6   b  shows the latching mechanism  86 ′ in an operating position in which the latching elements  92  are in a release position, i.e. the latching mechanism  86 ′ is opened. Conversely,  FIG. 6   a  shows the latching mechanism  86  in the closed state, i.e. the latching elements  92  are in their latching position. 
         [0074]    Furthermore,  FIG. 6   b  represents a variant comprising latching elements  92 ′. The latching elements  92 ′ are tooth-like projections on the clamping pieces  89 , which engage radially in a groove on pin  57 . Conversely, the latching elements  92  according to  FIG. 6   a  are bar-shaped elements which are placed tangentially into the groove (cf.  FIG. 9 ). In some exemplary embodiments, the tooth-like projections  92 ′ are preferred since they break more easily in the event of a collision of the probe tool with the measurement object and therefore permit emergency unlatching of the probe tool. Conversely, the bar-shaped latching elements  92  according to  FIG. 6   a  are preferred when particularly secure retention of the probe tool on the probe head is desired. 
         [0075]    In the preferred exemplary embodiments, the latching mechanism  86  comprises a detector  93  designed to detect the latching position and/or the release position of the latching element  92 . In the exemplary embodiments according to  FIG. 6 , the detector  93  is a microswitch comprising a switching contact  95 , which is arranged in series with all the contact pairs  92  of the rotary plate  74 . The switching contact  95  may be a mechanical contact or an electronic switch, for instance in the form of a transistor. The switching position of the switch  93  is influenced by means of the sliding member  87   a . In the position shown in  FIG. 6   a , a lug  89  of the sliding member  87   a  touches the switch  93 . The switching contact  95  is closed by means of the lug  98 . In this position, the sensor  64  in the probe head  27  can read that identification circuit  84  whose contacts  82  are in contact with the contacts  66  on the coupling part (cf.  FIG. 4  and  FIG. 10 ). In the position shown in  FIG. 6   b , on the other hand, the lug  98  is separated from the switch  93 . The switching contact  95  is consequently opened and the sensor  64  cannot read any of the identification circuits  84 . The absence of an identification signal of one of the identification circuits  84  is a signal with which the detector  93  reports that the latching mechanism  86  is not closed properly. 
         [0076]    In other words, the detector  93  delivers a signal of one of the identification circuits  84  to the sensor  64  only when rotary plate  74  bears on the contacts  66  and the latching mechanism  86  is closed. 
         [0077]      FIG. 7  shows the probe head  26  of  FIG. 3  or  4  and the rotary plate  74  of  FIG. 5  in a simplified representation from below. The probe head  26  is in this case shown merely by the outer contour of the body part  38  and the roll motion projection  68 . The rotary plate  74  is shown here with a reception unit  94  for styli  28  and the traction element  76 . In order to move the rotary plate  74  relative to the probe head, the measurement force generators  56  are used in this case, which generate movements in the direction of the double arrows  96  and  97 . The directions  96  and  97  are mutually orthogonal and correspond here to the movement directions x and y of the coordinate measuring machine  10 . With the aid of the movements  96 ,  97 , it is possible to move the rotary plate  74  inside the roll motion projection  68 . In the position represented, the rotary plate  74  with the traction element  76  bears on the inner surface  72  and forms a friction fit on the roll motion projection  68 . As an alternative, the rotary plate  74  could also enter into a form fit with the roll motion projection  68 . For example, the rotary plate  74  could be formed as a gearwheel on the outer circumference, which meshes with matching teeth on the roll motion projection. 
         [0078]    By a circular movement (arrow  100 ) of the rotary plate  74 , which in this case takes place concentrically with the roll motion projection  68 , rotation of the rotary plate  74  in the direction of the arrow  102  is achieved. The circular movement is generated by corresponding control of the measurement force generators along the arrows  96  and  97 . The movement  102  is carried out until the stylus has reached a desired rotation position. Subsequently, the rotary plate  74  can be moved back into its central resting position. Preferably, the resting position lies centrally with respect to the roll motion projection  68 . Owing to the different radii of the roll motion projection and of the traction element  76 , these elements form a friction drive  104  which, with appropriate dimensioning, determines the rotational speed of the rotary plate  74 . 
         [0079]      FIG. 8  shows a sectional view of the coupling part  40  and of the rotary plate  74  in a first operating position. For the sake of simplicity, pin  57  is not shown over its entire length here. In particular, omitted in this case is the upper end comprising the plate  63 , which can be retained on the stop  62  ( FIG. 4 ), in order to move the coupling part  40  relative to the pin  57 . 
         [0080]    The coupling part  40  comprises the ring magnet  60 , which concentrically encloses the retaining device  106 . The retaining device  106  in this case comprises two bearing elements  108  in the form of rolling bearings, which are configured annularly and are arranged concentrically with the pin  57 . 
         [0081]    The pin  57  is arranged inside the retaining device  106 . It has two conical sections  112  and  114 . In the represented position of the pin  57 , the conical sections  112 ,  114  bear on the bearing elements  108  without play. That end of the centering pin  57  which lies inside the coupling part  40  forms a retaining projection  116 , which secures the centering pin  57  inside the retaining device  106  against high tensile forces. That section  118  which lies outside the coupling part  40  is essentially formed conically. The section  118  comprises a groove  120 , which is formed in the circumferential direction of the centering pin  57 . That wall  122  of the groove  120  which faces the coupling part  40  forms a further conical section  124 , which is oriented opposite to the conical sections  112  and  114 . The free end of the centering pin  57  forms a further conical section  126 , the orientation of which corresponds to the orientation of the conical sections  112 ,  114 . Furthermore, one of the latching balls  58  and the contacts  66  can be seen here. 
         [0082]    The rotary plate  74  carries the traction element  76 . On that side of the rotary plate  74  which faces the coupling part  40 , two of the latching rollers  80  and two associated identification circuits  84  are represented. The reception element  90  is essentially formed conically, so that secure seating of the pin  57  inside the reception element  90  and automatic centering are ensured. Inside the reception element  90 , there is a cylindrical recess  128 , inside which the latching elements  92  can be moved. The rotary plate  74  holds the reception unit  94 . Styli  28  are not represented for the sake of clarity. 
         [0083]      FIG. 9  shows the coupling part  40 , the pin  57  and the rotary plate  74  in a second operating position. In contrast to  FIG. 8 , the rotary plate  74  is in this case fastened on the pin  57 . The latching elements  92  are in their latching position. The pin  57  is fitted into the reception element  90 , so that the latching elements  92  engage in the groove  120 . The conical section  124  therefore forms a support for the latching elements  92 , and the groove  120  forms a closure with the latching elements  92 . 
         [0084]    In the position of the rotary plate  74  as represented in  FIG. 9 , a distance remains between the latching ball  58  and the latching roller  80  lying closest. It is therefore possible to rotate the rotary plate  74  with the centering pin  57 . The conical sections  112  and  114  in this case rest without play on the bearing elements  108 . The pin  57  is therefore in a rotation position  134  which allows rotation of the rotary plate  74 . 
         [0085]    By virtue of an axial movement of the coupling part  40  in the direction of the movement arrows  136  (i.e. in the longitudinal direction of the axle and therefore parallel to the rotation axis of the rotary plate  74 ), the rotary plate  74  can be brought from the position shown in  FIG. 9  into a position close to the coupling part  40 . Advantageously, the coupling part  40  is pressed downward with the aid of the measurement force generator  56  from the body part  38  to such an extent that the plate  63  ( FIG. 4 ) at the upper end of the pin  57  moves against the stop  62  and thereafter no longer alters its position relative to the body part  38 . The coupling part  40 , on the other hand, is pressed further downward with the aid of the measurement force generator  56  and therefore moves toward the rotary plate  74  at the lower end of the pin  57 . 
         [0086]      FIG. 10  shows the coupling part  40 , the pin  57  and the rotary plate  74  of  FIGS. 8 and 9  in a corresponding third operating position. Furthermore, the electromagnet  60  is now magnetized in order to fix the rotary plate  74  in the position close to the coupling part  40 . In this proximal position, the latching balls  58  cooperate with the latching rollers  80  lying closest and form a kinematically determined three-point bearing. The contact of the latching balls  58  with the latching rollers  80  is advantageously detected with the aid of the sensor  65  ( FIG. 4 ). 
         [0087]    Owing to the fact that the pin  57  has been displaced upward relative to the coupling part  40 , the conical sections  112  and  114  are now arranged at a distance  138  from the bearing elements  108 . Owing to these distances  138 , the pin  57  now has play inside the retaining device  106 . This prevents the pin  57  from generating undesired counter-forces, which work against the alignment of the rotary plate  74  by the latching. The pin  57  is therefore in a defined latching position  140 .