Probe head for a coordinate measuring machine for determining spatial coordinates on a measurement object

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.

BACKGROUND OF THE INVENTION

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.

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.

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.

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.

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.

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.

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.

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.

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.

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

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

In a further refinement, the detector comprises an electrical switch, which is arranged electrically in series with the at least one identification circuit.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

This refinement allows a very compact structure as well as rapid and position-independent rotation of the rotary plate on the roll motion projection.

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.

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.

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.

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.

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.

In a further refinement, the coupling part is arranged between the stop and the rotary plate.

This refinement contributes to a particularly compact structure and allows advantageous encapsulation of all the probe head components except for the replaceable probe tool.

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.

DESCRIPTION OF PREFERRED EMBODIMENTS

InFIG. 1, a coordinate measuring machine with the new probe head is denoted overall by reference number10. The coordinate measuring machine10in this case has a base12, on which a gantry14is arranged so that it can be moved in the longitudinal direction. The movement direction of gantry14relative to the base12is typically denoted as the y axis. On the upper crossbar of the gantry14, a carriage16is arranged which can be moved in the transverse direction. The transverse direction is typically denoted as the x axis. The carriage16carries a quill18, which can be moved in the z direction, i.e. perpendicularly to the base12. The reference numbers20,22,24denote measuring instruments, with the aid of which the position of the gantry14, the carriage16and the quill18can be determined. Typically, the measuring instruments20,22,24are glass measuring scales, which are read with the aid of suitable sensors.

A probe head26, which holds a probe tool27, is arranged on the lower free end of the quill18. The probe tool27in this case comprises three styli28, each of which has a ball29on its free end. The ball is used to touch a measurement point on a measurement object30. With the aid of the measuring instruments20,22,24, it is possible to determine the position of the probe head26within 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.

Reference number32denotes an evaluation and control unit, which is connected via lines34and36to the drives and sensors on the gantry. The control unit32is used to operate the motor drive for the movement of the probe head26along the three coordinate axes x, y and z. The evaluation and control unit32furthermore reads in the measurement values from the measuring instruments20,22,24, and as a function thereof and as a function of displacements of the probe tool27, it determines the current spatial coordinates of the measurement point and further geometrical values of the measurement object30.

In a highly simplified schematic representation,FIG. 2shows the basic functionality of the probe head26. The probe head26has a body part38and a coupling part40, which are in this case connected to one another by means of two leaf springs42and44. The leaf springs42,44form a spring parallelogram, which in this case permits movement of the coupling part40in the direction of arrow46(and back in the direction of the arrow46′). The probe tool27with the styli28can therefore be deployed from its resting position through a distance D. The references28′ and29′ show one of the styli28with a ball29in the deployed position.

The displacement of the probe tool27relative to the body part38may be the result of touching the measurement object30at a measurement point. Advantageously, the displacement of the probe tool27is taken into account when determining the spatial coordinates. Furthermore, the displacement of the probe tool27may in the preferred exemplary embodiments be generated with the aid of a measurement force generator56, as explained in more detail below. A limb48,50is in this case respectively arranged on the body part38and on the moving part40. The limbs48,50are in this case parallel to the leaf springs42,44. Between the limbs48,50, a displacement detector52(here represented by a scale54) and the measurement force generator56are arranged. The displacement detector52in this case comprises a measurement coil53in 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 detector52, with the aid of which the spatial displacement of the probe tool27relative to the body part38(or more precisely the displacement of the spring parallelogram which is formed by the leaf springs42,44) can be determined. The measurement force generator56is in this case likewise formed as a plunger coil. With the aid of it, the two limbs42and50can be drawn together or pushed apart, by attracting or repelling a core59with the aid of a magnetic field generated in the coil.

In the highly simplified representation ofFIG. 2, the probe head26only allows displacement of the probe tool27in the direction of the arrow46. It is, however, clear to the person skilled in the relevant art that such a probe head26typically 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 part38and a coupling part40movable relative thereto.

FIG. 3shows a preferred exemplary embodiment of the probe head26ofFIG. 2in a view from below (without the probe tool27).FIG. 4shows a simplified section of the probe head ofFIG. 3along a section line IV-IV.

The body part38holds the coupling part40, which is preferably movable in three orthogonal spatial directions on the body part38. For the sake of simplicity only two spring elements42, which permit the three orthogonal movement directions, are shown inFIG. 4. The coupling part40in this case comprises a pin57, which is guided in a perpendicularly mobile fashion in the coupling part40(this will be explained in more detail below with the aid ofFIGS. 8 to 10). In the edge region of the coupling part40, three pairs of latching balls58are 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 pin57. The coupling part40furthermore has a magnet60, 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 magnet60is in this case arranged concentrically with the pin57on the coupling part40. The coupling part40in this case furthermore has a sensor64with two contacts66, and a sensor65. A roll motion projection68in the form of a cylindrical sleeve with an internal wall72is formed on the body part38. The roll motion projection68in this case extends concentrically with the pin57.

As already mentioned with reference toFIG. 2, the position of the coupling part40relative to the body part38can be modified with the aid of measurement force generators56. 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 pin57relative to the coupling part40, in the preferred exemplary embodiment a stop62is provided which is formed here on the body part38or at least rigidly connected thereto. The stop62cooperates with a plate63which is formed on the upper end of the pin57. InFIG. 4, the upper end of the pin57extends upward beyond the stop62and the plate63is arranged above the stop62. When the coupling part40is pressed downward with the aid of measurement force generator56, pin57follows this movement until the plate63encounters the stop62from above. Beyond this position, the pin57is blocked against further movement downward. The coupling part40, on the other hand, can be pressed further downward with the aid of the measurement force generator56. After the moment when the pin57is blocked on the stop62by means of the plate63, the measurement force generator continues to move only the coupling part40downward, and no longer the pin57. In other words, the measurement force generator56pushes the coupling part40downward relative to pin57. Since pin57is formed with its lower free end holding a probe tool (as explained in more detail with reference toFIGS. 8 to 10), the distance between the coupling part40and the probe tool27can be varied, and in particular reduced, using the measurement force generator56and the stop62. This is advantageously used in exemplary embodiments of the new coordinate measuring machine in order to move the coupling part40“smoothly” onto the probe tool27and subsequently fasten it with the magnet60.

FIG. 5shows a preferred exemplary embodiment of the probe tool27in a plan view of the interface, by which the probe tool is coupled to the coupling part40. The probe tool27has a rotary plate74, which is formed circularly in this case. Arranged on the outer circumference of the rotary plate74, there is a traction element76, 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 plate74in this case comprises a plurality of latching rollers80, each of which is radially aligned. The latching rollers80are uniformly distributed in the circumferential direction of the rotary plate74. Radially inward of each latching roller80, two contacts82are arranged. The contacts82in this case lie behind one another in the radial direction of the rotary plate74, so as to provide an arrangement of radial contact pairs distributed in the circumferential direction. Each pair is part of an alignment determination element84, which cooperates with the sensor64on the coupling part40(cf.FIG. 8).

In the preferred exemplary embodiments, each alignment determination element84includes 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 sensor64can, by means of the contacts66, only read one identification circuit84at 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 tool27as a whole.

A reception element90in the form of a circular opening is arranged at the center of the rotary plate74. In this case, two latching elements92are arranged in the reception element90, by which the rotary plate74can be fastened on the lower free end of the pin57. In the exemplary embodiment inFIG. 5, the latching elements92are two bars which are formed so as to engage in a groove on the lower free end of the57(cf.FIG. 9).

The probe tool27in this case carries the three styli28according toFIG. 1. The styli28are arranged below the rotary plate74. The configuration of the probe tool is not restricted to the manner shown inFIG. 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.

FIG. 6ashows a latching mechanism86with which the latching elements92can be opened or closed, in order to fasten the rotary plate74on the pin57. The latching mechanism86is integrated in the rotary plate74in the preferred exemplary embodiments. Preferably, the latching mechanism86is arranged between the upper side of the rotary plate74, which is shown inFIG. 5, and the stylus28.

In the preferred exemplary embodiment, the latching mechanism86has two sliding members87a,87bmovable counter to one another. Each sliding member87a,87bis biased into a resting position by means of a spring element88. In the preferred exemplary embodiments, the spring elements88bias the sliding members87in a resting position in which the latching elements92clamp the rotary plate74on the pin57. In the preferred exemplary embodiment, each sliding member87is respectively connected to a clamping piece89a,89b. The latching elements92are arranged on the clamping pieces89a,89b.

By pressing the sliding members87a,87bagainst one another in the direction of the arrows shown inFIG. 6a, the clamping pieces89can be pressed apart from one another. The effect of releasing the sliding members87is that the spring elements88press the latching elements92together again. In order to open the latching mechanism86, each sliding member87has a free end91which protrudes outward beyond the outer circumference of the rotary plate74. In the preferred exemplary embodiments, the free ends91a,91bof the sliding members87a,87blie diametrically opposite one another on the outer circumference of the rotary plate74.

FIG. 6bshows the latching mechanism86′ in an operating position in which the latching elements92are in a release position, i.e. the latching mechanism86′ is opened. Conversely,FIG. 6ashows the latching mechanism86in the closed state, i.e. the latching elements92are in their latching position.

Furthermore,FIG. 6brepresents a variant comprising latching elements92′. The latching elements92′ are tooth-like projections on the clamping pieces89, which engage radially in a groove on pin57. Conversely, the latching elements92according toFIG. 6aare bar-shaped elements which are placed tangentially into the groove (cf.FIG. 9). In some exemplary embodiments, the tooth-like projections92′ 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 elements92according toFIG. 6aare preferred when particularly secure retention of the probe tool on the probe head is desired.

In the preferred exemplary embodiments, the latching mechanism86comprises a detector93designed to detect the latching position and/or the release position of the latching element92. In the exemplary embodiments according toFIG. 6, the detector93is a microswitch comprising a switching contact95, which is arranged in series with all the contact pairs92of the rotary plate74. The switching contact95may be a mechanical contact or an electronic switch, for instance in the form of a transistor. The switching position of the switch93is influenced by means of the sliding member87a. In the position shown inFIG. 6a, a lug89of the sliding member87atouches the switch93. The switching contact95is closed by means of the lug98. In this position, the sensor64in the probe head27can read that identification circuit84whose contacts82are in contact with the contacts66on the coupling part (cf.FIG. 4andFIG. 10). In the position shown inFIG. 6b, on the other hand, the lug98is separated from the switch93. The switching contact95is consequently opened and the sensor64cannot read any of the identification circuits84. The absence of an identification signal of one of the identification circuits84is a signal with which the detector93reports that the latching mechanism86is not closed properly.

In other words, the detector93delivers a signal of one of the identification circuits84to the sensor64only when rotary plate74bears on the contacts66and the latching mechanism86is closed.

FIG. 7shows the probe head26ofFIG. 3or4and the rotary plate74ofFIG. 5in a simplified representation from below. The probe head26is in this case shown merely by the outer contour of the body part38and the roll motion projection68. The rotary plate74is shown here with a reception unit94for styli28and the traction element76. In order to move the rotary plate74relative to the probe head, the measurement force generators56are used in this case, which generate movements in the direction of the double arrows96and97. The directions96and97are mutually orthogonal and correspond here to the movement directions x and y of the coordinate measuring machine10. With the aid of the movements96,97, it is possible to move the rotary plate74inside the roll motion projection68. In the position represented, the rotary plate74with the traction element76bears on the inner surface72and forms a friction fit on the roll motion projection68. As an alternative, the rotary plate74could also enter into a form fit with the roll motion projection68. For example, the rotary plate74could be formed as a gearwheel on the outer circumference, which meshes with matching teeth on the roll motion projection.

By a circular movement (arrow100) of the rotary plate74, which in this case takes place concentrically with the roll motion projection68, rotation of the rotary plate74in the direction of the arrow102is achieved. The circular movement is generated by corresponding control of the measurement force generators along the arrows96and97. The movement102is carried out until the stylus has reached a desired rotation position. Subsequently, the rotary plate74can be moved back into its central resting position. Preferably, the resting position lies centrally with respect to the roll motion projection68. Owing to the different radii of the roll motion projection and of the traction element76, these elements form a friction drive104which, with appropriate dimensioning, determines the rotational speed of the rotary plate74.

FIG. 8shows a sectional view of the coupling part40and of the rotary plate74in a first operating position. For the sake of simplicity, pin57is not shown over its entire length here. In particular, omitted in this case is the upper end comprising the plate63, which can be retained on the stop62(FIG. 4), in order to move the coupling part40relative to the pin57.

The coupling part40comprises the ring magnet60, which concentrically encloses the retaining device106. The retaining device106in this case comprises two bearing elements108in the form of rolling bearings, which are configured annularly and are arranged concentrically with the pin57.

The pin57is arranged inside the retaining device106. It has two conical sections112and114. In the represented position of the pin57, the conical sections112,114bear on the bearing elements108without play. That end of the centering pin57which lies inside the coupling part40forms a retaining projection116, which secures the centering pin57inside the retaining device106against high tensile forces. That section118which lies outside the coupling part40is essentially formed conically. The section118comprises a groove120, which is formed in the circumferential direction of the centering pin57. That wall122of the groove120which faces the coupling part40forms a further conical section124, which is oriented opposite to the conical sections112and114. The free end of the centering pin57forms a further conical section126, the orientation of which corresponds to the orientation of the conical sections112,114. Furthermore, one of the latching balls58and the contacts66can be seen here.

The rotary plate74carries the traction element76. On that side of the rotary plate74which faces the coupling part40, two of the latching rollers80and two associated identification circuits84are represented. The reception element90is essentially formed conically, so that secure seating of the pin57inside the reception element90and automatic centering are ensured. Inside the reception element90, there is a cylindrical recess128, inside which the latching elements92can be moved. The rotary plate74holds the reception unit94. Styli28are not represented for the sake of clarity.

FIG. 9shows the coupling part40, the pin57and the rotary plate74in a second operating position. In contrast toFIG. 8, the rotary plate74is in this case fastened on the pin57. The latching elements92are in their latching position. The pin57is fitted into the reception element90, so that the latching elements92engage in the groove120. The conical section124therefore forms a support for the latching elements92, and the groove120forms a closure with the latching elements92.

In the position of the rotary plate74as represented inFIG. 9, a distance remains between the latching ball58and the latching roller80lying closest. It is therefore possible to rotate the rotary plate74with the centering pin57. The conical sections112and114in this case rest without play on the bearing elements108. The pin57is therefore in a rotation position134which allows rotation of the rotary plate74.

By virtue of an axial movement of the coupling part40in the direction of the movement arrows136(i.e. in the longitudinal direction of the axle and therefore parallel to the rotation axis of the rotary plate74), the rotary plate74can be brought from the position shown inFIG. 9into a position close to the coupling part40. Advantageously, the coupling part40is pressed downward with the aid of the measurement force generator56from the body part38to such an extent that the plate63(FIG. 4) at the upper end of the pin57moves against the stop62and thereafter no longer alters its position relative to the body part38. The coupling part40, on the other hand, is pressed further downward with the aid of the measurement force generator56and therefore moves toward the rotary plate74at the lower end of the pin57.

FIG. 10shows the coupling part40, the pin57and the rotary plate74ofFIGS. 8 and 9in a corresponding third operating position. Furthermore, the electromagnet60is now magnetized in order to fix the rotary plate74in the position close to the coupling part40. In this proximal position, the latching balls58cooperate with the latching rollers80lying closest and form a kinematically determined three-point bearing. The contact of the latching balls58with the latching rollers80is advantageously detected with the aid of the sensor65(FIG. 4).

Owing to the fact that the pin57has been displaced upward relative to the coupling part40, the conical sections112and114are now arranged at a distance138from the bearing elements108. Owing to these distances138, the pin57now has play inside the retaining device106. This prevents the pin57from generating undesired counter-forces, which work against the alignment of the rotary plate74by the latching. The pin57is therefore in a defined latching position140.