Indeposition hinge joint

Abstract

The invention relates to an indexable articulation joint. An indexable articulated wrist (10) for redirecting a metrology tool mounted on a positioning platform (45) includes an improved Hertz coupling in which several teeth are omitted to simplify construction and reduce its cost. An improved Hertz coupler has: a toothed crown (310) having a reduced number of teeth spaced apart by a plurality of indexing pitches; and a second crown having a plurality of toothed sections (370), each toothed section having a plurality of teeth (371) spaced apart by a pitch angle, the toothed sections being separated by non-engaging sections.

Description

TECHNICAL FIELD

[0001] The present invention relates to a swivelling articulation joint for a measuring device such as a coordinate positioning apparatus or coordinate measuring machine. The swivelling articulation joint of the invention is particularly suitable for use in a wrist or probe holder mounted on a positioning platform of an apparatus and supports a metrology tool in a re-orientable manner so that the metrology tool can be positioned and oriented relative to a workpiece being measured. The swivelling articulation joint of the invention is also suitable for use in a swivelling rotary table supporting a workpiece to be measured. However, the invention can be applied in other fields such as machine tools and robots. BACKGROUND

[0002] A coordinate measuring machine (CMM) is a coordinate positioning apparatus that uses various probes attached to a movable position platform to provide the coordinates of points on the surface of a workpiece being measured. In known bridge-type coordinate machines, the positioning platform is part of a precise Cartesian positioning system and its position relative to the machine's reference table is read by precise linear encoders. Wrist-type coordinate machines and industrial robots, which are sometimes equipped with coordinate probes for measurement purposes, have a kinematic chain of rotating axes in series and determine the coordinates of a positioning platform derived from the rotation angles, read by angular encoders. The rotating axes can alternatively or complementarily be provided by a probe holder with a rotating adapter for a measurement probe or by a rotary table supporting a workpiece to be measured.

[0003] Contact coordinate probes are used with coordinate measuring machines for inspecting the dimensions or surfaces of machined parts and capturing the three-dimensional shape of a workpiece, for example to reproduce or model them. Contact coordinate probes usually have a mobile stylus designed to come into contact with the surface of the workpiece being measured. A sensor reacts to the smallest displacement of the stylus and provides an electrical signal which is sent to an operator or an automatic controller. The sensor can be a trigger circuit which produces an electrical transition each time contact occurs, or a deflection transducer which produces a deflection measurement in one, two or three coordinates. Contact probes with deflection sensors are also known as scanning or analogue probes and can be used by sliding their stylus along the surface of a workpiece, while the more common former type of contact probes are also known as trigger probes and are usually used by tapping the surface in discrete points and collecting information about a set of discrete points on the surface of the workpiece being measured.

[0004] Non-contact coordinate probes are also known in the art. They use non-contact sensors to determine the distance between, for example, the tip of the probe and the surface of the object being measured without contacting it. Such probes include laser interferometric probes, chromatic confocal probes, ultrasonic probes, cameras, line scanners, etc.

[0005] A coordinate machine can be equipped with other tools than coordinate probes, such as surface quality probes that measure roughness or imaging devices for inspection and control. For the present disclosure, these tools are equivalent to coordinate probes and are interchangeable with them.

[0006] Coordinate probes can also be used in the art for mobile parts of machine tools, such as milling machines, lathes and machining centers.

[0007] Many measurements require changing the orientation of the coordinate probe to measure the workpiece completely and satisfactorily. It is very useful to be able to align the axis of the probe with the axis of the hole, for example, when measuring features at the blind end of a hole. Many movable platforms do not provide this ability and coordinate probes are usually mounted on articulated wrists to overcome this lack. Usually, articulated wrists used in these applications have two independent orthogonal axes in series, but implementations with fewer or more degrees of freedom are possible.

[0008] The rotation axes of the reorientable wrists are usually indexed, which means that they can be locked in a precise and repeatable number of predetermined positions. This usually requires a locking mechanism with indexing elements or parts such as periodic joints or Hirth couplings, with a periodic arrangement of radial grooves on the rings, forming crowns that intermesh. In the locked state, also denoted in the present disclosure as locked configuration, the indexed axes are blocked by pushing the two halves of the joint so that one rests against the other, while in the free state, or free configuration, they are separated and one is free to rotate with respect to the other, the transition between the rotated and locked state and the free state can be manual or automatic. Indexing pitches of 1°, 2.5°, 5°, 7.5°, 10° or 15° are known.

[0009] Hirth couplings provide precise indexing and fine pitch angles in small spaces, but their production requires high-precision grinding and is expensive.

[0010] Documents EP1666832 B1, EP1666833 A1, EP0392660 A1, EP1672309 B1, EP2889573 B1, EP3184960 B1, EP3179203 B1, US10557702 B2, WO2024 / 033613 A1, EP3129750 B1, US2015 / 176958 A1 describe articulated devices for coordinate measurement probes. GB1411331 A discloses an indexing mechanism involving a superimposed toothed disc device.

[0011] Some measurements can benefit from changing the single orientation of the coordinate probe and / or workpiece about an axis. In this case, the coordinate probe can be a mount of a probe holder, which has a rotary adapter for supporting the probe. Alternatively or complementarily, the apparatus can comprise a rotary stage for orienting the workpiece about an axis. The re-orientable probe holder and the rotary axis of the rotary stage can be indexed, meaning that they can be locked in a large, but finite number of predetermined, precisely repeatable positions. SUMMARY

[0012] It is an object of the present invention to provide an indexed articulated joint for articulated arms that provides fine pitch indexing at a lower cost.

[0013] According to the invention, these objects are achieved by an indexed articulated joint for articulated arms for re-orienting a metrology tool mounted on a positioning platform. The articulated arm comprises a support element mountable on the positioning platform, a re-orientable element rotatably connected to the support element so that the re-orientable element is rotatable about a first rotation axis relative to the support element between a plurality of indexable orientations equally spaced by a pitch angle and lockable in one of the plurality of indexable orientations, wherein the support element and the re-orientable element comprise a modified Hirth coupling having a pair of intermeshing components that can be unlocked by spreading them apart along the first rotation axis to effect a change from one indexable orientation to another indexable orientation and locked together by pushing them against each other to provide any one of the indexable orientations, characterized in that a first component of the intermeshing components is a ring of teeth having a plurality of teeth equally spaced by a multiple of the pitch angle, i.e. an integer greater than 1, and a second component of the intermeshing components has three or more toothed sections separated by non-toothed sections, each toothed section comprising a plurality of radial teeth spaced by the pitch angle, the plurality of radial teeth being configured so that, when the first component and the second component are locked together in any one of the index positions, each toothed section intermeshes with at least one tooth of the first component and there is a gap between the non-toothed section and the first component.

[0014] Embodiments of the invention can present the same number of equidistant teeth in each section. These highly symmetrical configurations provide a joint with a plurality of indexable orientations with (substantially) uniform joint stiffness and load capacity.

[0015] The present invention also includes embodiments in which the teeth are not present in equal numbers in the different segments, and / or the non-engaging segments can have different angular dimensions (i.e., different multiples of the pitch angle), such that the segments are unequally spaced apart. These embodiments can exhibit an enlarged and / or reduced contact area between the pair of intermeshing components, particularly for locally modifying the joint stiffness and / or load capacity.

[0016] The use of the Hirth coupling structure enables to achieve a finer pitch indexing than what can be obtained with other known periodic couplings (e.g. pin ball type), while the modified Hirth coupling also allows to reduce the cost by limiting the number of costly operations required to machine the modified Hirth coupling with respect to a conventional Hirth coupling.

[0017] The integer ratio between the angular spacing of adjacent teeth in the first component and the pitch angle can be denoted by K. For symmetry, K will be an exact divisor of the total number of teeth, K being greater than 1. The inventors determined that K teeth in each toothed segment are necessary and sufficient to ensure that for all indexing positions, each toothed segment intermeshes with at least one tooth of the first component. However, in this case and in some indexing positions, the intermeshing involves two different teeth on the first component, each tooth being in contact with the second component with one flank, while in other indexing positions, each toothed segment intermeshes with exactly one tooth of the first component with two flanks. However, the former configuration is slightly less ideal because the contact forces on each tooth of the first component are unbalanced in the horizontal plane and deflection can occur.

[0018] To avoid this, it can be advantageous to increase the number of teeth in each toothed segment to K+1 or even K+2. In this case, always one tooth of the first component is in contact with the toothed segment with two flanks.

[0019] The arrangement of the present invention provides a reliable positioning because at each indexing position, the two components intermesh at several positions equally spaced apart circumferentially, one component per toothed segment. However, the number of teeth is much lower than for a complete Hirth coupling. To provide some numerical examples, a complete Hirth joint with a 2.5° pitch would require to grind 144 teeth in each of the two components, the incomplete tooth profile of the present invention can greatly reduce the number of teeth and correspondingly save manufacturing costs. In theory, three toothed segments equally spaced apart (at 120°, i.e. providing a joint of a triquetral coupling) are sufficient for a precise positioning, but more preferred. Configurations with four (i.e. a quadrangular coupling), five (i.e. a pentagonal coupling), six (i.e. a hexagonal coupling) or more toothed segments can be advantageous, although above six toothed segments, the sought reduction in the number of teeth is less pronounced.

[0020] Depending on each given angular pitch and number of toothed segments, there will be a value (or two adjacent K values) that minimizes the total number of teeth and production costs. In embodiments, the second component can have exactly four, five or six toothed segments and the ratio K can be exactly four, six or eight. The pitch angle can be 5°, 2.5°, 2°, 1 ° or other.

[0021] The toothed segments are configured to provide a desired number of index positions. In each of these, each toothed segment intermeshes with at least one of the teeth of the other component of the improved Hirth coupling. This can be achieved, for example, by spacing the toothed segments evenly around the circumference and having at least K teeth in each segment that are spaced apart by a pitch angle. However, this is not the only possibility. For example, a coupling with a pitch angle Θ = 2.5° and five toothed segments will have the segments slightly offset from a symmetrical position, since 72° is not an exact multiple of the pitch angle. A non-symmetrical variant can require more than K teeth per segment to ensure correct intermeshing in all index positions.

[0022] The invention does not limit the profile of the teeth in the two components, as long as they reliably intermesh. A triangular profile is possible, the angle at the vertex line where the two slanted sides of each tooth meet can be less than 90°, for example 60°. According to the invention, a tooth is any (radial) protrusion designed to facilitate intermeshing movement between the first and second components of the improved Hirth coupling (e.g. a conical protrusion, i.e. a protrusion with a narrow distal tip), the sides of the protrusion are designed to provide at least partial contact (e.g. point contact, line contact, patchy contact) with the sides of the opposing tooth that intermeshes. The teeth of different components can have different shapes if they are able to intermesh with at least partial contact between the sides of the opposing tooth. However, the teeth can be manufactured by machining (in particular milling or grinding) a metal (e.g. stainless steel) cylindrical piece, other materials and manufacturing processes are possible (e.g. additive manufacturing, injection molding), in particular to reduce costs. Additional processes can be used, for example for reducing wear and / or facilitating intermeshing, such as tooth coating and / or lubrication.

[0023] The rotation of the wrist and / or its locking and unlocking can be provided by an automatic actuator, for example an electric motor, or a manual mechanism. In both cases, more advantageously in the former, the wrist can comprise an angular encoder to measure the relative rotation from which the orientation of the probe can be inferred. In addition, the joint can alternatively or complementarily comprise a sensor that senses the relative 6 degrees of freedom position of the two intermeshing components of the modified Hirth coupling, i.e. the relative position along 3 orthogonal linear axes and around 3 orthogonal rotation axes. This 6 degrees of freedom sensor can thus be used not only as an angular encoder, but also as a sensor supporting collision detection and / or measurement error correction. In one embodiment, the reader of the 6 degrees of freedom sensor can be fixed on one of the two intermeshing components, while the associated scale can be fixed on the other of the two intermeshing components. A second orthogonal index rotation axis can be included in series with the first orthogonal index rotation axis to increase the possible orientations of the probe in space. To this end, the articulated wrist can have an additional reorientable element rotatably connected to the first element, so that the orientation of the additional element relative to the reorientable element can be changed between a plurality of indexable orientations around a second axis and locked in one of the plurality of indexable orientations. In this case, the tool will be fixed to the additional reorientable element.

[0024] The indexable articulated joint of the invention can also be used in a probe holder with a rotary adapter in the form of an indexable reorientation adapter, the probe holder being mounted on a positioning stage of a measuring device, ultimately supported by an articulated wrist. The indexable articulated joint of the invention can also be used alternatively or complementarily in a rotary stage providing indexable reorientation of a support workpiece within a measuring volume of a measuring device. The rotary stage is configured to be mounted on and / or its surface of a reference stage of a measuring device.

[0025] The preferred use of the invention is in an articulated wrist for a coordinate measuring machine, to reorient a coordinate probe, such as a contact probe, or a non-contact coordinate probe, or a camera, and / or to reorient a workpiece to be measured, and this use case will be given special space in the detailed description below. However, other applications are also possible. BRIEF DESCRIPTION OF DRAWINGS

[0026] Exemplary embodiments of the invention are disclosed in the specification and shown in the drawings, in which:

[0027] Figure 1 A coordinate measuring machine with an automatically reorientable wrist of the invention is schematically shown, which measures a workpiece under the supervision of a numerical controller,

[0028] Figure 2 A reorientable wrist as used in the invention is schematically shown,

[0029] Figure 3 shows a variant of the improved Hirth coupling for use in the present invention,

[0030] Figure 4 a to d of the figure show in an idealized manner the relative positions of the intermeshing components in four indexable positions,

[0031] Figure 5a similar to Figure 4 d of the figure and representing a variant of the present invention, in which the teeth are arranged differently in one of the intermeshing components, and

[0032] Figure 5b is Figure 5a an enlarged view of detail "C" in

[0033] In the drawings, significant elements are identified by reference numbers repeated in the text. Identical, similar, or technically equivalent different elements can be identified by the same reference numbers. When there are many identical, similar, or equivalent elements in a figure, some reference numbers can be omitted to avoid the figure being overly crowded.

[0034] Reference numbers in the drawings

[0035] 10 articulated wrist

[0036] 25 machine controller

[0037] 30 workpiece

[0038] 40 coordinate measuring machine, CMM

[0039] 41 bridge

[0040] 42 carriage

[0041] 43 table

[0042] 45 Z-piston, sleeve shaft, positioning stage

[0043] 60 "A" axis (horizontal)

[0044] 70 "B" axis (vertical)

[0045] 100 support element

[0046] 103 connector

[0047] 200 reorientable element

[0048] 220 visual indicator

[0049] 300 additional reorientable element

[0050] 310 first intermeshing component

[0051] 321 equidistant teeth on a first intermeshing component

[0052] 360 second intermeshing component

[0053] 370 equidistant toothed segments

[0054] 371 teeth on a second intermeshing component

[0055] 375 non-intermeshing segments

[0056] 400 stylus, end sensor

[0057] 415 contact tip DETAILED DESCRIPTION

[0058] Figure 1 A coordinate measuring system is shown comprising a coordinate measuring machine 40 of the known type. The coordinate measuring machine 40 has a water table 43 on which a workpiece 30 to be measured rests. A bridge 41 moves along a first linear axis Y on the table 43 and a carriage 42 moves along a second linear axis X orthogonal to the first linear axis. A vertical spindle 45 (also known as sleeve shaft or Z-plunger according to different conventions) moves on a third orthogonal axis Z so that the end tip of the spindle 45 is a positioning platform that can be positioned at any desired point in the measuring volume of the machine (i.e. in the volume in which the CMM is able to provide surface measurements of an object). Suitable encoders (not shown) read the positions of the bridge 41, carriage 42 and spindle 45 along the measuring axes X, Y, Z. Most coordinate measuring machines are automatic, the movements of the bridge 41, carriage 42 and spindle 45 being determined by electric motors, but there are also manual machines. The machine controller 25 is programmed to command the motors according to a predetermined measurement plan designed taking into account the shape of the workpiece 30.

[0059] Figure 1 A contact probe 400 is also shown, having a spherical tip 415 designed to contact the workpiece 30 at a desired point. The contact probe 400 is typically a trigger probe, configured to generate an electrical signal upon contact. The controller 25 uses this signal to store the instantaneous values of X, Y and Z and calculates the corresponding coordinates of the point of contact by known methods.

[0060] The trigger probe 400 can be replaced by another type of coordinate probe, for example an optical non-contact probe, a scanning probe, a "hard" probe, etc., without departing from the scope of the invention. The shape and length of the stylus are also not limited.

[0061] Although it is common, Figure 1The bridge structure shown is not the only one possible. The invention is not limited to this implementation, but includes all the various shapes and structures found in coordinate measuring systems. The invention expressly includes systems in which the carriage slides along a cantilevered horizontal beam rather than being supported at both ends, articulated arm machines based on rotational degrees of freedom only, rather than linear articulated arm machines such as articulated arm coordinate machines and robots, parallel robots such as delta robots and Stewart platforms, etc.

[0062] The size of the machine can also vary from a benchtop machine to a large device for measuring a vehicle, aircraft, or turbine, without departing from the scope of the invention. The articulated wrist can be mounted vertically or horizontally on the positioning platform of the system. The invention expressly includes systems that include a movable stage, such as a rotary stage, for movably supporting a workpiece during an operation, such as a measurement.

[0063] The precision and accuracy range of a CMM varies from sub-micron precision in laboratory equipment to 5-100 pm in some industrial applications. The invention applies to all variations disclosed herein, and generally to any kind of moving platform that can be moved with suitable repeatability and precision.

[0064] The use of the reorientable wrist of the invention is not limited to its installation on a coordinate measuring machine, although this is the preferred and important use case. The wrist can be used on a machine tool, an industrial robot, a machine vision system, or any time accurate reorientation of an instrument is needed.

[0065] Figure 2 The overall structure of an articulated wrist as used in conjunction with a general purpose coordinate measuring machine is shown. The wrist includes a support element 100 that is configured to be fixed to a positioning platform of a coordinate measuring machine. In many implementations, including Cartesian coordinate machines, the support element 100 will be translated by the coordinate machine along a desired trajectory without rotation, and the articulated wrist is used to reorient the measurement probe as needed, for example to insert the probe into a hole or between aerodynamic blades of a turbine. In other cases, the motion of the positioning platform to which the wrist is fixed can include rotation, and in these cases the wrist can be used to compensate for them. The connection between the wrist and the positioning platform can be obtained in any suitable way.

[0066] The wrist has a connector 103 to power and control internal actuators responsible for re-orienting the probe and for powering and reading the coordinate probe itself. In the simple case where the coordinate probe is a contact trigger probe, the only connection needed is a current loop that is opened once the probe contacts the workpiece (i.e. the trigger event), but more complex power and signaling modes can be used, the connector 103 can also include a fiber optic connection, for example in combination with an optical probe, measuring the distance to the workpiece by interferometry, triangulation, time of flight, chromaticity, focus variation or in any other suitable way. This does not mean that the connector 103 is necessary. For example, the wrist of the invention can work entirely with a battery and some form of wireless data transmission to handle the connector 103. The connector 103 can include an optical channel, or the wrist can have an additional connector for optical signals. Alternatively, an optical probe equipped on the wrist can be connected to a dedicated measurement device through a fiber that bypasses the wrist.

[0067] The support element 100 is pivotably connected with a re-orientable element that can be turned about an axis "B" relative to the support element. The axis "B" is drawn vertically in the figures and this is its normal orientation; it can therefore also be called "vertical rotation axis", although the wrist can be used in any orientation in space.

[0068] It is important that the rotation axis "B" has a permutational kind, which means that in addition to a "free" state in which the re-orientable element can be turned about the axis "B", the wrist also has a locked state in which the relative position of the first rotor 200 relative to the support element is determined by an internal periodic joint. In the locked state, the rotor is fixed relative to the support 100 in one of a predetermined plurality of precise and repeatable angles. The angle of rotation about the axis "B" is preferably adjustable by an internal actuator in the wrist and controlled by a digital signal, but the invention also encompasses manually actuated wrists that are unlocked, re-oriented and locked again in another permutational position by hand.

[0069] Preferably, the wrist also comprises an additional re-orientable element 300 that is pivotably attached to the first element. The additional re-orientable element 300 is able to turn about a second axis "A" that is preferably orthogonal to the first axis "B" and is therefore generally horizontal. As in the case of the other axis, the rotation of the additional re-orientable element 300 is preferably permutational.

[0070] The coordinate probe 400 is attached to the additional re-orientable element (when present). This figure illustrates a contact probe that generates a contact signal each time the sphere 415 contacts the workpiece or a deflection signal when the sphere sliding on the surface of the workpiece moves away from its rest position. The wrist can be equipped with any kind of contact or non-contact based coordinate probe, or with other probes, such as surface quality probes or cameras.

[0071] By successive composition of the angles of rotation around the axes "B" and "A", the probe 400 can be aligned with any desired direction in space, with precision and granularity provided by the indexing. Preferably, the rotation around the axis "B" spans more than one turn, and even more preferably it is boundless. The rotation of the additional re-orientable element around the axis "A" can have upward forbidden segments, which are of little importance when the wrist is attached below the positioning platform, as is usually the case.

[0072] Optionally, the re-orientable wrist can have one (or more) visual indicators 220, which can be activated by the controller of the coordinate machine or autonomously by the wrist controller circuit. For example, this can be used to signal contact of the contact probe 415. Complementarily or alternatively, the visual indicators 220 can be activated by the controller of the wrist, for example the operational configuration of the wrist (for example) and / or the operational state or configuration of the wrist and / or sensed environmental factors (for example the locked or free configuration of the wrist, below / above given humidity or temperature levels, operational anomalies of active components of the wrist such as actuators).

[0073] Figure 3 An improved Hirth coupling for providing the indexing in the present invention is shown, the support element 100 and the re-orientable element 200 comprising each one of a pair of intermeshing components 310, 320.

[0074] The intermeshing components 310, 320 are coaxially arranged with respect to the rotation axis 70 and are unlocked by separating them along the rotation axis 70 to effect a change from one indexable orientation to another indexable orientation, and are locked together by pushing them axially against each other to provide any one indexable orientation.

[0075] The first intermeshing component 310 is a crown having a plurality of teeth 321 equally spaced by integer multiples of a pitch angle, oriented towards the second intermeshing component 360. As mentioned above, the ratio between the pitch angle of the teeth 321 and the spacing, which is an integer value, can be denoted by K hereinafter.

[0076] The second intermeshing component 360 has various toothed sections 370 separated by non-toothed sections 375. In this example, the second intermeshing component 360 has four toothed sections and an equal number of non-toothed sections arranged in a four-fold symmetry pattern. The number of toothed sections in the present invention is not prescribed. However, three toothed sections are sufficient to provide stability of the coupling when the intermeshing components are locked together (i.e., a tripod-based coupler), with more toothed sections preferred for increased stability (particularly a four-, five-, or six-pronged coupler).

[0077] The improved Hirth coupler of this embodiment provides 144 index positions spaced apart by a pitch angle Θ = 2.5° with reduced tooth counts. However, finer and coarser index pitches are also possible. The first (upper) component 310 is a crown having teeth 321 equally spaced apart by an angle equal to K x Θ, where K is an integer greater than 1. In this case, K = 4, so that the angle is equal to 10°. Looking along the circumference and downward, toward the complementary intermeshing component. The second (lower) component 360 is also shaped as a circular crown having six toothed sections 370 around the circumference. Each toothed section has K = 4 teeth 371 spaced apart by a pitch angle Θ = 2.5°.

[0078] In each indexed position, each toothed section 370 is in contact with one or two upper teeth 321 and precisely determines the relative position of the intermeshing components. However, Figure 3 The combination of sixty teeth on both components in comparison to the 288 teeth of a Hirth coupler that would normally be required with a 2.5° pitch.

[0079] In other, unrepresented variations, the number of teeth in each toothed section 370 can be different from four, such as two, three, five, six, or more. The spacing of the teeth in the first component should not be greater than the width of the toothed sections to ensure intermeshing in all index positions. Thus, combinations with a small number of teeth in each section 370 can be less desirable because they must have more teeth in the opposing component.

[0080] The inventors have identified advantageous combinations that provide precise intermeshing in all index positions with reduced tooth counts. For an index pitch Θ = 2.5°, they include:

[0081]

[0082] Table 1

[0083] Figure 4Figures a to d of the application show the intermeshing of the improved Hirth coupling, in the example of four segments each having four teeth, with a ratio K equal to 4. These figures are conceptual representations of the device, not realistic representations: the two parts have been flattened to allow a two-dimensional representation, and the teeth extend radially rather than axially. Their purpose is to show how a reduced number of teeth produces a complete set of indexing positions as in a full Hirth coupling.

[0084] Figure 4 Figure a of the application shows the modified Hirth coupling in one indexing position. The first part 310 has four teeth intermeshing with the first and second teeth of each segment 370 of the second part 360. The other teeth of the first part are on the face of non- meshing segments 375 and do not participate in the indexing. The positioning is stable and reliable since the contact points between the two parts are distributed symmetrically around the circumference of the crown.

[0085] Figure 4 Figure b of the application shows the next indexing position of the first part 310, rotated clockwise by θ = 2.5° with respect to the configuration of figure a. Figure 4 Figure a of the application shows the modified Hirth coupling in one indexing position. The first part 310 has four teeth intermeshing with the first and second teeth of each segment 370 of the second part 360. The other teeth of the first part are on the face of non- meshing segments 375 and do not participate in the indexing. The positioning is stable and reliable since the contact points between the two parts are distributed symmetrically around the circumference of the crown. Figure 4 Figure c of the application shows the configuration resulting from another step of θ = 2.5°, and figure d of the application shows the configuration resulting from another step of θ = 2.5°. Figure 4 Figure c of the application shows the configuration resulting from another step of θ = 2.5°, and figure d of the application shows the configuration resulting from another step of θ = 2.5°. Figure 4 In this illustrated configuration of figure d of the application, the left face of the first tooth and the right face of the last tooth in each segment 370 contact the corresponding side faces of two consecutive teeth in the first part 301. In this case too, the positioning is symmetrical and reliable.

[0086] After a further rotation of θ = 2.5°, the first part 310 has turned through an angle equal to the spacing between its teeth, and the configuration of figure a of the application is repeated. Figure 4 Figure a of the application shows the modified Hirth coupling in one indexing position. The first part 310 has four teeth intermeshing with the first and second teeth of each segment 370 of the second part 360. The other teeth of the first part are on the face of non- meshing segments 375 and do not participate in the indexing. The positioning is stable and reliable since the contact points between the two parts are distributed symmetrically around the circumference of the crown.

[0087] Figure 5a Figures a to d of the application show the intermeshing of the improved Hirth coupling, in the example of four segments each having four teeth, with a ratio K equal to 4. These figures are conceptual representations of the device, not realistic representations: the two parts have been flattened to allow a two-dimensional representation, and the teeth extend radially rather than axially. Their purpose is to show how a reduced number of teeth produces a complete set of indexing positions as in a full Hirth coupling. Figure 5b Figure a of the application shows the modified Hirth coupling in one indexing position. The first part 310 has four teeth intermeshing with the first and second teeth of each segment 370 of the second part 360. The other teeth of the first part are on the face of non- meshing segments 375 and do not participate in the indexing. The positioning is stable and reliable since the contact points between the two parts are distributed symmetrically around the circumference of the crown. Figure 4 In this illustrated configuration of figure d of the application, the left face of the first tooth and the right face of the last tooth in each segment 370 contact the corresponding side faces of two consecutive teeth in the first part 301. In this case too, the positioning is symmetrical and reliable.

[0088] In this illustrated configuration of figure d of the application, the left face of the first tooth and the right face of the last tooth in each segment 370 contact the corresponding side faces of two consecutive teeth in the first part 301. In this case too, the positioning is symmetrical and reliable. Figure 4 Figure a of the application shows the modified Hirth coupling in one indexing position. The first part 310 has four teeth intermeshing with the first and second teeth of each segment 370 of the second part 360. The other teeth of the first part are on the face of non- meshing segments 375 and do not participate in the indexing. The positioning is stable and reliable since the contact points between the two parts are distributed symmetrically around the circumference of the crown. Figure 5a andFigure 5b In the illustrated embodiment, the second intermeshing member 360 comprises four toothed sections 370 regularly separated by non-intermeshing sections 375 of the same length (i.e. a length corresponding to the same multiple of the pitch angle), each toothed section 370 comprising the same number of teeth 371. These joint embodiments provide a plurality of indexable orientations with (substantially) constant joint stiffness and load capacity.

[0089] Alternatively, one or more toothed sections 370 can have a different number of radial teeth and / or one or more toothed sections 370 can be unequally spaced by one or more non-intermeshing sections of different lengths. This alternative embodiment thus provides one or more relatively enlarged and / or reduced contact areas between the pair of intermeshing members, in particular for locally modifying the joint stiffness and / or load capacity of the joint.

[0090] The relative rotation between the first member 310 and the second member 360 of the partial Hooke joint can be driven, preferably, by an automatic actuator such as an electric motor or by a manual mechanism. In both cases, the joint can comprise an angular encoder configured to measure the relative angular position during re-orientation (unlocked Hooke joint) and / or upon re-positioning (locked Hooke joint). In the case of an electrically articulated wrist, the wrist of the CMM 40 or the machine controller 25 can be configured to read the relative angular position provided by such an encoder for driving the re-orientation by the actuator and / or for confirming the correct locking at the desired index angle position.

[0091] In a possible variant of the application, the encoder is a six degrees of freedom sensor (6D) providing the position and orientation of the second member 360 relative to the first member 310. This information can be used for collision detection, correction of measurement errors when the Hooke joint is locked or in any other useful way. The machine controller 25 of the CMM 40 can be configured to read the sensor periodically (e.g. every millisecond) when the Hooke joint is locked. Fast scanning times are particularly useful when the encoder is used for detecting collisions.

[0092] The 6D sensor can comprise a reader fixed to the first member 310 and a scale fixed to the second member 360, or other ways.

[0093] The swivel articulation joint can include an axially extending perimeter guard for protecting the improved Hirth coupling from dust and / or fluid penetration (not shown). The guard can include a cylindrical flange that is circumferentially secured to one of the first and second components 310, 360 while extending toward the other to enclose its perimeter side in both the locked and unlocked configurations. Complementarily, the other component can include an additional peripheral flange or joint configured to mate with such a flange to increase the tightness. Alternatively, the extending perimeter guard can include a bellows secured to both perimeters of the first and second components 310, 360 to provide the required tightness.

[0094] In addition to the axis (or axes) provided by the wrist (e.g., the "C" axis), the modified Hirth coupling can also be used in a probe holder (not shown) to provide reorientation of the probe 400 about one single axis (e.g., the "S" axis). In this case, one of the first and second components 310, 360 is secured to a support element of a rotary adapter of the probe holder, which is mountable to the positioning stage 45 of the CMM 40, alternatively or complementarily to the first or second reorientable elements 200, 300 of the wrist 10. The other of the first and second components 310, 360 is then secured to a probe support on which the probe can be mounted, or directly to the probe.

[0095] The improved Hirth coupling of the present invention can also be used in a rotary table in order to provide swivelable reorientation of a workpiece to be measured. Thus, one of the first and second components 310, 360 can be attached to a support element configured to secure the rotary table on the reference table 43, or to another surface of the measuring apparatus 40. The other of the first and second components 310, 360 can then be connected to a workpiece support configured to hold a workpiece for measurement.

Claims

1. A repositioning hinge joint for reorienting a workpiece within the measuring volume of a measuring instrument and / or a measuring device, the repositioning hinge joint comprising: A support element, which can be mounted on the measuring equipment or a component of the measuring equipment. A reorientable element, rotatably connected to the support element, wherein the reorientable element is capable of rotating relative to the support element about a first rotation axis among a plurality of indexable orientations equally separated by pitch angles, and of being locked in one of the plurality of indexable orientations. An improved Hertz coupling has two interlocking parts, one in the support element and the other in the reorientable element, wherein... The first component of the improved Hertzspar connector has a plurality of teeth spaced equally at multiples of the pitch angle, and the second component of the improved Hertzspar connector has three or more toothed sections separated by non-engaging sections, each toothed section comprising a plurality of teeth spaced apart at the pitch angle, wherein each of the toothed sections engages with at least one tooth of the first component when the first component and the second component are locked together in any indexed position, and there is a gap between the non-toothed sections and the first component.

2. The indexable hinge joint according to claim 1, wherein, Each toothed segment includes at least K teeth, where K represents the integer ratio between the angular spacing of adjacent teeth in the first component and the pitch angle.

3. The indexable hinge joint according to claim 2, wherein, Each toothed section includes K+1 teeth or K+2 teeth.

4. The indexable hinge joint according to claim 1, wherein, The toothed sections are equidistant from each other at an angle.

5. The indexable hinge joint according to claim 1, wherein, At least one of the toothed sections is composed of a different number of teeth and / or is spaced unequally at an angle.

6. The indexable hinge joint according to claim 2, wherein, The second component has exactly three, four, or six toothed sections, and the ratio K is exactly four, six, or eight.

7. The indexable hinge joint according to claim 1, wherein, The pitch angle is 5°, 2.5°, 2° or 1°.

8. The indexable hinge joint according to claim 1, wherein, The teeth have oblique surfaces that intersect at an angle of less than or equal to 90°.

9. The indexable hinge joint according to claim 1, the indexable hinge joint comprising an automatic actuator for driving the reorientable element to rotate about the first rotation axis and / or for locking the support element and the reorientable element together by pushing the support element and the reorientable element against each other.

10. The indexable hinge joint of claim 1, wherein the indexable hinge joint includes an angle encoder configured to measure the rotation angle of the reorientable element relative to the support element about the first rotation axis.

11. The indexable hinge joint according to claim 1, the indexable hinge joint comprising an axially extending peripheral protection member fixed to the first component and / or the second component for protecting the improved Hertz coupling from dust and / or fluid infiltration, the peripheral protection member being, in particular, a bellows.

12. A hinged wrist or probe holder for reorienting a measuring tool mounted on a positioning platform of a measuring device, the hinged wrist or probe holder comprising the indexing hinge joint according to claim 1, wherein the support element is mountable on the positioning platform.

13. The articulated wrist of claim 12, wherein the articulated wrist includes an additional reorientable element rotatably connected to the reorientable element such that the orientation of the additional reorientable element relative to the reorientable element can be changed among a plurality of indexable orientations about a second rotation axis orthogonal to the first rotation axis and locked in one of the plurality of indexable orientations, the tool being fixed to the additional reorientable element.

14. A rotary table for reorienting a workpiece within the measuring volume of a measuring device, the rotary table comprising the indexing hinge joint according to claim 1, wherein the support element is mountable on a reference table or surface of the measuring device.

15. The use of the articulated wrist according to claim 12 in a coordinate measuring machine for reorienting a coordinate probe.

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