Indexed articulated joint

Abstract

To provide an indexed articulated wrist for reorientation of a measurement tool mounted on a positioning platform.SOLUTION: The present invention relates to an indexed articulated wrist including an improved Hirth coupling in which some teeth are omitted to simplify the structure and reduce the cost. The improved Hirth coupling includes: a toothed crown 310 having teeth spaced apart by a multiple of an index pitch due to a reduced number of teeth; and a second crown including a plurality of toothed sectors 370 each having a plurality of teeth 371 spaced apart by a pitch angle, the toothed sectors being separated by non-engaging sectors.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to an indexable articulated joint for a measuring apparatus, such as a coordinate positioning apparatus or coordinate measuring machine. The indexable articulated joint of the present invention is particularly adapted for use with a wrist or probe holder that is attached to the positioning platform of the apparatus and that reorientably supports a measuring tool so that the measuring tool can be positioned and oriented relative to a part to be measured. The indexable articulated joint of the present invention may also be adapted for use in an indexable rotary table that supports the part to be measured. However, the present invention may be applied in other areas, such as machine tools and robotics. [Background technology]

[0002] A coordinate measuring machine (CMM) is a type of coordinate positioning device that uses various probes mounted on a movable positioning platform to provide the coordinates of points on the surface of the part 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 a precise linear encoder. Wrist-type coordinate machines and industrial robots, which may also be equipped with coordinate probes for measurement purposes, have a kinematic chain of rotary axes in series to determine the coordinates of the positioning platform, which are inferred from the rotation angle read by an angle encoder. The rotation axis may alternatively or complementary be provided by a probe holder with a rotary adapter for the measurement probe, or by a rotary table supporting the workpiece to be measured.

[0003] Touch coordinate probes are used with coordinate measuring machines to check the dimensions or surface of machined parts and capture the part's three-dimensional shape, e.g., to reproduce or model them. Touch coordinate probes typically have a movable feeler designed to make contact with the surface of the part under test. A sensor responds to slight displacements of the feeler and provides an electrical signal that is sent to an operator or automated controller. The sensor can be a trigger circuit that generates an electrical transition each time contact occurs, or a deflection transducer that generates a deflection measurement in one, two, or three coordinates. Touch probes with deflection sensors, also known as scanning or analog probes, can be used by sliding their feeler along the part's surface, although the more common type of probe, also known as a trigger probe, is often used by tapping the surface at discrete points, collecting information about a set of discrete points on the surface of the part under test.

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

[0005] Coordinate machines may be equipped with other tools different from coordinate probes, for example surface quality probes to measure roughness, or imaging devices for inspection and control, which in this disclosure are equivalent to and interchangeable with coordinate probes.

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

[0007] Many measurements require the coordinate probe to be reoriented in order to fully and satisfactorily measure the workpiece. For example, when measuring a feature at the blind end of a hole, it is very useful to be able to align the probe axis with the axis of the hole. Many moving platforms do not provide this capability, and coordinate probes are often mounted on articulated wrists to overcome this shortcoming. Typically, the articulated wrists used in these applications have two independent, orthogonal axes in series, although implementations with fewer or more degrees of freedom are possible.

[0008] The axis of rotation of a reorientable wrist is often indexed, meaning that the wrist can be locked into a large but finite number of precisely repeatable predetermined positions. This typically requires a locking mechanism with an indexing element or component, such as a periodic joint, like a Hirth coupling, which has radial grooves periodically arranged on a ring forming a crown of interlocking teeth. In the locked state (also referred to in this disclosure as the locked configuration), the indexed axis is blocked by the two halves of the joint being pressed together; in the free state (or free configuration), the two halves are pulled apart and are free to rotate relative to one another. Rotation and the transition between the locked and free states can be manual or automatic. Index pitches of 1°, 2.5°, 5°, 7.5°, 10°, or 15° are known.

[0009] Although Hirth couplings provide precise indexing and fine pitch angles in a small space, their manufacture requires high-precision grinding, which is costly.

[0010] EP 1666832, EP 1666833, EP 0392660, EP 1672309, EP 2889573, EP 3184960, EP 3179203, U.S. Patent No. 10557702, WO 2024 / 033613, EP 3129750, and U.S. Patent No. 2015 / 176958 describe articulating devices for coordinate measuring probes. GB 1411331 discloses an indexing mechanism including an arrangement of superimposed toothed discs.

[0011] Some measurements can benefit from changing a single orientation of the coordinate probe and / or workpiece about an axis. In such cases, the coordinate probe may be mounted in a probe holder having a rotational adapter for supporting the probe. Alternatively, or complementary, the apparatus may include a rotary table for orienting the workpiece about the axis. The rotational axes of the reorientable probe holder and rotary table may be indexed, meaning that they can be locked into a large but finite number of predetermined, accurately repeatable positions. Summary of the Invention

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

[0013] According to the present invention, these objects are achieved by the objects of the appended claims, in particular by an indexable articulated joint for an articulated wrist for reorienting a measuring tool mounted on a positioning platform, the articulated wrist comprising a support element which may be mounted on the positioning platform, and a reorientable element rotatably connected to the support element such that it can rotate relative to the support element about a first axis of rotation between a plurality of indexable orientations equally separated by a pitch angle, and can be locked in one of the plurality of indexable orientations, the support element and the reorientable element being unlockable by separating them along the first axis of rotation to allow a change from one indexable orientation to another, and the articulated wrist being able to rotate relative to the support element about a first axis of rotation between a plurality of indexable orientations equally separated by a pitch angle, and can be locked in one of the plurality of indexable orientations The present invention includes an improved Hirth coupling having a pair of intermeshing components that can be locked together by biasing one toward the other to provide one intermeshing member, characterized in that a first one of the intermeshing components is a toothed ring having a plurality of teeth evenly spaced apart by a multiple of a pitch angle (i.e., an integer greater than one), and a second one of the intermeshing components has three or more toothed sectors separated by non-intermeshing sectors, each toothed sector including a plurality of radial teeth spaced apart by a pitch angle configured such that when the first and second components are locked together in any of the indexed positions, each of the toothed sectors intermeshes with at least one tooth of the first component and a gap exists between the non-toothed sector and the first component.

[0014] Embodiments of the present invention may present the same number of evenly spaced teeth in each sector. These highly symmetrical configurations provide joints with multiple indexable orientations with (substantially) uniform joint stiffness and load carrying capacity.

[0015] The present invention also encompasses embodiments in which teeth are not present in equal numbers in different sectors and / or in which non-intermeshing sectors may have different angular dimensions (i.e., different multiples of pitch angle) such that the sectors are unevenly spaced. These embodiments may exhibit enlarged and / or reduced contact zones between a pair of intermeshing components, particularly to locally modify joint stiffness and / or load-bearing capacity.

[0016] The use of the Hirth coupling design allows for finer pitch indexes than those available with other known periodic couplings, such as the pin-and-ball type, and the improved Hirth coupling further allows for cost savings by limiting the number of expensive operations required to machine the improved Hirth coupling compared to conventional Hirth couplings.

[0017] The integer ratio between the angular spacing of adjacent teeth on the first component and the pitch angle may be represented by K. For symmetry, K is a number that exactly divides the total number of teeth and is greater than 1. The inventors have determined that K teeth in each toothed sector are necessary and sufficient to ensure that, for all indexed positions, each toothed sector meshes with at least one tooth on the first component. However, in this case, at some indexed positions, the meshing involves two separate teeth on the first component, each of which contacts the second component on one side, while at other indexed positions, each toothed sector meshes with both sides of exactly one tooth on the first component. However, the former configuration is less desirable because the contact forces on each tooth on the first component are not balanced in the horizontal plane, potentially resulting in deflection.

[0018] To avoid this, it may be advantageous to increase the number of teeth in each toothed sector to K+1 or K+2, so that there is always one tooth of the first component contacting the toothed sector on both sides.

[0019] The inventive arrangement provides reliable positioning because, at each indexed position, the two components mesh at several evenly spaced locations (one for each toothed sector) around the circumference. Nevertheless, the number of teeth is significantly less than in a perfect Hirth coupling. To provide some numerical examples, a perfect Hirth coupling with a 2.5° pitch requires grinding 144 teeth on each of the two components. The incomplete teeth of the present invention can provide a significant reduction in the number of teeth and a corresponding savings in manufacturing costs. While three evenly spaced toothed sectors (at 120°, i.e., for a coupling providing a tripod-shaped coupling) are theoretically sufficient for accurate positioning, more may be preferable. Configurations with four (i.e., tetrapod-shaped couplings), five (i.e., pentapod-shaped couplings), six (i.e., hexapod-shaped couplings), or more toothed sectors may be advantageous, although the reduction in the required number of teeth is less significant beyond six toothed sectors.

[0020] For each given angular pitch and number of toothed sectors, there is one value (or two adjacent values ​​of K) that minimizes the total number of teeth and manufacturing costs. In embodiments, the second component may have exactly four, five, or six toothed sectors, and the ratio K may be exactly 4, 6, or 8. The pitch angle may be 5°, 2.5°, 2°, 1°, etc.

[0021] The toothed sectors are configured to provide the desired number of indexed positions. In each of these, each toothed sector meshes with at least one of the teeth of the other component of the modified Hirth coupling. This can be achieved, for example, by spacing the toothed sectors evenly around the circumference and providing at least K teeth in each sector, spaced apart by the pitch angle. However, this is not the only possibility. For example, a coupling with a pitch angle θ = 2.5° and five toothed sectors would result in the sectors being slightly shifted from their symmetrical positions because 72° is not an exact multiple of the pitch angle. Asymmetric variations may require more than K teeth per sector to ensure precise meshing at all indexed positions.

[0022] The tooth profiles of the two components are not limited by the present invention, as long as they interlock reliably. A triangular profile is possible, and the angle at the apex where the two oblique sides of each tooth meet may be less than 90°, for example, 60°. According to the present invention, the teeth are any (radial) protrusions (e.g., tapered protrusions, i.e., protrusions tapered at the distal end) designed to facilitate the interlocking movement between the first and second components of the improved hearth, and the protrusions have sides designed to provide at least partial contact (e.g., point-like, linear, or spot-like contact) with the sides of the mating tooth. The teeth of different components may have different shapes, as long as the sides of the teeth can interlock with each other and at least partially contact each other. The teeth can be manufactured by machining (particularly milling or grinding) cylindrical parts of metal (e.g., stainless steel), although other materials and manufacturing processes (e.g., additive manufacturing, injection molding) are possible, particularly to reduce costs. For example, additional processes such as tooth coating and / or lubrication may be used to reduce wear and / or facilitate engagement.

[0023] Rotation of the wrist and / or its locking and unlocking may be provided by an automatic actuator, such as an electric motor, or by a manual mechanism. In both cases, but more advantageously the former, the wrist may include an angular encoder for measuring relative rotation from which the probe's orientation can be deduced. Additionally, the joint may alternatively or complementary include a sensor for sensing the relative six-degree-of-freedom position (i.e., the relative position along three orthogonal linear axes and around three orthogonal rotational axes) of the two interlocking components of the modified Hartz. This six-degree-of-freedom sensor may therefore be used not only as an angular encoder but also as a sensor supporting collision detection and / or measurement error correction. In one embodiment, a six-degree-of-freedom sensor reader may be fixed to one of the two interlocking components, and an associated scale may be fixed to the other of the two interlocking components. A second orthogonal, indexed rotation axis may be included in series with the first rotation axis to increase the possible orientations of the probe in space. To this end, the articulated wrist may have an additional reorientable element rotatably connected to the first reorientable element, such that the orientation of the additional element relative to the reorientable element may be changed among and locked to one of a plurality of indexable orientations about the second axis, with the tool attached to the additional reorientable element.

[0024] The indexable articulation joint of the present invention may be used in a probe holder having a rotational adapter in the form of an indexable reorientation adapter, where the probe holder is attached to a positioning platform of a measuring device and ultimately supported by an articulating wrist. Alternatively or complementary, the indexable articulation joint of the present invention may be used in a rotary table that provides indexable reorientation of a workpiece supported within the measurement volume of the measuring device. The rotary table is configured to be attached to a reference table and / or a surface thereof of the measuring device.

[0025] A preferred application of the invention is in an articulating wrist for a coordinate measuring machine, for reorienting a coordinate probe such as a touch probe or a non-contact coordinate probe or a camera, and / or for reorienting a workpiece to be measured, and this use case will be given special space in the detailed description below, however other applications are possible.

[0026] Exemplary embodiments of the invention are disclosed herein and illustrated in the drawings. [Brief explanation of the drawings]

[0027] [Figure 1] 1 is a schematic diagram of a coordinate measuring machine with an automatically reorientable wrist of the present invention measuring a workpiece under the control of a digital controller; FIG. [Figure 2] FIG. 2 is a schematic diagram of a reorientable list for use in the present invention; [Figure 3] FIG. 10 shows a modified example of the improved Hirth coupling used in the present invention. [Figures 4a-4d] 10 is an idealized view showing the relative positions of mating components in four indexable positions. FIG. [Figure 5a] 4d is a view similar to FIG. 4d, showing a variant of the invention in which the teeth arrangement is different on one of the mating components. [Figure 5b] FIG. 5b is an enlarged view of detail "C" of FIG. 5a.

[0028] In the figures, notable elements are identified by reference numbers that are repeated in the text. The same reference numbers may be used to identify identical, similar, or technically equivalent separate elements. When there are many identical, similar, or equivalent elements in a drawing, some reference numbers may be omitted to avoid overcrowding the drawing. DETAILED DESCRIPTION OF THE INVENTION

[0029] FIG. 1 illustrates a coordinate measuring system including a known type of coordinate measuring machine 40. The coordinate measuring machine 40 has a horizontal table 43 on which the workpiece 30 to be measured is mounted. A bridge 41 moves along one first linear axis (Y) on the table 43, and a carriage 42 moves along a second linear axis (X) perpendicular to the first linear axis. A vertical spindle 45 (also called a quill or Z-ram, according to different conventions) moves on a third orthogonal axis (Z), providing a positioning platform that can position the end of the spindle 45 at any desired point within the machine's measurement volume (i.e., the volume within which the CMM can provide measurements of an object's surface). Suitable encoders (not shown) read the positions of the bridge 41, carriage 42, and spindle 45 along the measurement axes X, Y, and Z. Most CMM machines are automatic, with electric motors determining the movement of the bridge 41, carriage 42, and spindle 45, but manual machines also exist. 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 .

[0030] 1 also shows a touch probe 400 having a spherical tip 415 designed to contact the workpiece 30 at a desired point. The touch probe 400 is often a trigger probe configured to generate an electrical signal upon contact. This signal is used by the controller 25 to store the instantaneous X, Y, and Z values ​​and calculate the corresponding coordinates of the contact point by known methods.

[0031] The trigger probe 400 can be replaced by other types of coordinate probes without departing from the scope of the invention, for example, optical non-contact probes, scanning probes, "hard" probes, etc. The shape and length of the stylus are both unlimited.

[0032] The bridge structure of Figure 1, while typical, is not the only possible one. The invention is not limited to this embodiment and includes all the various shapes and configurations found in coordinate measuring systems. The invention expressly includes systems in which a carriage slides along a cantilevered horizontal beam rather than being supported at both ends, articulated arm machines that are based only on rotational degrees of freedom rather than linear degrees of freedom, such as articulated arm coordinate machines and robots, parallel robots such as delta robots and Stewart platforms, etc.

[0033] The size of the machine can also vary widely, from bench-top machines to large devices used to measure vehicles, aircraft, or turbines, without departing from the scope of the present invention. The articulating wrist can be mounted vertically or horizontally on the system's positioning platform. The present invention expressly includes systems that include a movable table, e.g., a rotary table, for movably supporting a workpiece during operation (e.g., measurement).

[0034] The precision and accuracy of CMMs range from sub-micron accuracy in laboratory setups to perhaps 5-100 μm in some industrial applications. The present invention is applicable to all variations disclosed herein and is generally applicable to any kind of mobile platform that can be moved with adequate repeatability and accuracy.

[0035] The use of the reorientable wrists of the present invention is not limited to their installation on coordinate measuring machines, although this is a preferred and important use case: wrists can be used on machine tools, industrial robots, machine vision systems, or whenever an implement needs to be precisely reoriented.

[0036] FIG. 2 shows the general structure of an articulated wrist for use in the present invention in combination with a general-purpose coordinate measuring machine. The wrist includes a support element 100 configured to be mounted on the positioning platform of the coordinate measuring machine. In many embodiments involving a Cartesian coordinate machine, the support element 100 is 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 bore or between the aerodynamic vanes of a turbine. In other cases, the movements of the positioning platform to which the wrist is mounted may include rotations, in which case the wrist can be used to compensate for them. The connection between the wrist and the positioning platform may be obtained in any suitable manner.

[0037] The wrist has a connector 103 for powering and controlling the internal actuators responsible for reorienting the probe and for powering and reading the coordinate probe itself. In the simple case where the coordinate probe is a touch-trigger probe, the only connection required is a current loop that opens as soon as the probe touches the workpiece (i.e., a trigger event), but more sophisticated powering and signaling schemes can be used. The connector 103 can include, for example, an optical fiber connection in combination with an optical probe that measures the distance to the workpiece by interferometry, triangulation, time-of-flight, chromaticity, focus variation, or any other suitable method. However, this does not mean that the connector 103 is essential. The wrist of the present invention can, in some cases, completely eliminate the connector 103, for example, by using a battery and some form of wireless data transmission. The connector 103 can include an optical channel, or the wrist can have an additional connector for the optical signal. Alternatively, an optical probe equipped with the wrist can be connected to a dedicated measurement device by an optical fiber that bypasses the wrist.

[0038] The support element 100 is pivotally connected to a reorientable element that can rotate relative to the support element about axis "B." Axis "B" is depicted vertically in the figures, which is its conventional orientation and is therefore sometimes referred to as the "vertical axis of rotation," although the wrist can be used in any orientation in space.

[0039] Importantly, axis of rotation "B" is of the indexed variety, meaning that in addition to a "free" state in which the reorientable element may rotate about axis "B," the wrist also has a locked state in which the relative position of first rotor 200 to the support element is determined by an internal periodic joint. In the locked state, the rotor is fixed at one of a plurality of predetermined, precise, and repeatable angles with respect to support 100. The angle of rotation about axis "B" is preferably adjustable by an internal actuator in the wrist and controlled by a digital signal, although the invention also contemplates a manually actuated wrist that can be manually unlocked, reoriented, and relocked to another indexed position.

[0040] Preferably, the wrist also includes an additional reorientable element 300 pivotally attached to the first reorientable element. The additional reorientable element 300 can be rotated about a second axis "A," which is preferably orthogonal to the first axis "B" and is therefore conventionally horizontal. As with the other axes, the rotation of the additional reorientable element 300 is preferably indexed.

[0041] Coordinate probe 400 is attached to additional reorientable elements, if present. The drawing shows a touch probe that generates a contact signal each time sphere 415 touches the workpiece, or a deflection signal when the sphere sliding over the surface of the workpiece moves away from its rest position. The wrist can be equipped with any kind of coordinate probe, either contact or non-contact, or other probes such as surface quality probes or cameras.

[0042] By serially configuring the rotation angles about axes "B" and "A", the probe 400 can be aligned with any desired direction in space with the accuracy and granularity provided by the index. Preferably, the rotation about axis "B" is over two or more revolutions, and even more preferably is unlimited. Rotation of additional reorientable elements about axis "A" may have a forbidden sector above, which is of little concern if the wrist is mounted below the positioning platform as usual.

[0043] Optionally, the reorientable wrist may have one or more visual indicators 220 that may be activated by the coordinate machine's controller or autonomously by the wrist controller circuitry. This may be used, for example, to indicate contact of the touch probe 415. Complementarily or alternatively, the visual indicators 220 may be activated by the wrist's controller, such as the wrist's operational configuration (for example) and / or the wrist's operational state or configuration, and / or sensed environmental factors (e.g., locked or free configuration of the wrist, below / above a given humidity or temperature level, malfunction of an active component of the wrist such as an actuator).

[0044] FIG. 3 illustrates a modified Hirth coupling used to provide indexing in the present invention, where the support element 100 and the reorientable element 200 each include a pair of interlocking components 310, 320, respectively.

[0045] The mating components 310, 320 are arranged coaxially relative to the axis of rotation 70 and are unlocked by separating them along the axis of rotation 70 to allow for changes from one indexable orientation to another, and locked together by axially biasing one toward the other to provide any indexable orientation.

[0046] The first mating component 310 is a toothed crown having a plurality of teeth 321 evenly spaced an integer multiple of the pitch angle oriented toward the second mating component 360. The ratio of the pitch angle to the spacing of the teeth 321 is an integer value as discussed above and may be represented hereinafter as K.

[0047] The second mating component 360 has various toothed sectors 370 separated by non-meshing sectors 375. In this example, the second mating component 360 has four toothed sectors and an equal number of non-meshing sectors arranged in a four-fold symmetrical pattern. The number of toothed sectors in this invention is not specified. Three toothed sectors are sufficient to provide stability to the coupling when the mating components are locked together (i.e., a tripod-based coupling), but more toothed sectors are preferred for increased stability (especially tetrapod-, pentapod-, or hexapod-based couplings).

[0048] The modified Hirth coupling of this embodiment provides 144 indexed positions, spaced apart by a pitch angle θ = 2.5°, due to the reduced number of teeth. However, finer and coarser index pitches are also possible. The first (top) component 310 is a crown with teeth 321 evenly spaced apart by an angle equal to K × θ, where K is an integer greater than 1. In this case, K = 4, so the angle is equal to 10°. Looking down the circumference, one faces the complementary mating component. The second (bottom) component 360 is also shaped as a circular crown with six toothed sectors 370 around its circumference. Each toothed sector has K = 4 teeth 371, spaced apart by a pitch angle θ = 2.5°.

[0049] At each index position, each of the toothed sectors 370 contacts one or two of the upper teeth 321, and the relative positions of the mating components are precisely determined. However, the combination of Figure 3 has a total of 60 teeth on both components, compared to the 288 teeth typically required by a Hirth coupling with a 2.5° pitch.

[0050] In other variations not shown, the number of teeth in each toothed sector 370 can be other than four, for example, two, three, five, six, or more. The spacing between the teeth of the first component should be equal to or less than the width of the toothed sector to ensure meshing at all indexed positions. Therefore, combinations with fewer teeth in each sector 370 may be less desirable because they necessarily require a larger number of teeth on the mating component.

[0051] The inventors have determined preferred combinations that provide accurate meshing at all indexed positions with a reduced number of teeth. These include, for an index pitch θ=2.5°: [Table 1]

[0052] 4a-4d show the meshing of the improved Hirth coupling of the present invention in an example with four sectors of four teeth each, with the ratio K equal to 4. These figures are conceptual rather than realistic views of the device, with the two components flattened to allow a two-dimensional representation, and the teeth extending radially rather than axially. The purpose is to show how a reduced number of teeth can achieve a full set of indexed positions like a complete Hirth coupling.

[0053] Figure 4a shows the improved Hirth coupling in one indexed position. The first component 310 has four teeth that mesh with the first and second teeth of each sector 370 of the second component 360. The other teeth of the first component face non-meshing sectors 375 and do not contribute to the indexing. The contact points between the two components are symmetrically distributed around the circumference of the crown, so positioning is stable and reliable.

[0054] Figure 4b shows the next index position, rotated clockwise by θ = 2.5 relative to the position of Figure 4a. Four teeth of the first component 310 mesh with the second and third teeth of sector 370. A further step of θ = 2.5 produces the configuration of Figure 4c, and another step of θ = 2.5 produces the configuration of Figure 4d. Since the number of teeth in each sector corresponds exactly to the ratio K, in this illustrated configuration of Figure 4d, the left side of the first tooth and the right side of the last tooth of each sector 370 contact the corresponding sides of two consecutive teeth of the first component 301. In this case, positioning is also symmetrical and reliable.

[0055] After a further rotation of θ=2.5, the first component 310 is rotated by an angle equal to its tooth-to-tooth spacing, and the configuration of FIG. 4a is repeated.

[0056] 5a and 5b show a variant of the invention in which the toothed sectors have one (or more) extra tooth (i.e., >K). In this case, the integer ratio K=4, the tooth-to-tooth spacing of the first component is K×θ=10°, and the toothed sectors each have K+1=5 teeth 371. As a result of this increase, at every indexed position, there is one of the teeth 371 of the first component inserted between two teeth 321 of the second component. The contact force on this contact tooth is symmetrical (which was not the case in the configuration of FIG. 4d) and the indexing is more accurate.

[0057] 4a-4d and 5a-5b, the second mating component 360 includes four toothed sectors 370 regularly separated by non-meshing sectors 375 of the same length (i.e., lengths corresponding to the same multiple of the pitch angle), each toothed sector 370 including the same number of teeth 371. These joint embodiments provide multiple indexable orientations with (substantially) constant joint stiffness and load-bearing capacity.

[0058] Alternatively, one or more of the toothed sectors 370 may have a different number of radial teeth, and / or one or more of the toothed sectors 370 may be unevenly spaced with one or more non-intermeshing sectors having different lengths. This alternative embodiment thus provides one or more relatively enlarged and / or reduced contact zones between a pair of intermeshing components, particularly for locally modifying joint stiffness and / or load-bearing capacity.

[0059] Relative rotation between the first and second components 310, 360 of the partial hearth may preferably be driven by an automatic actuator, such as an electric motor, or by a manual mechanism. In either case, the joint may include an angular encoder configured to measure the relative angular position during reorientation (unlocked hearth) and / or when repositioned (locked hearth). In the case of a powered articulated wrist, the wrist or machine controller 25 of the CMM 40 may be configured to read the relative angular position provided by such an encoder to drive reorientation via the actuator and / or to confirm correct locking at the desired indexed angular position.

[0060] In a possible variation of the invention, the encoder is a six-degree-of-freedom sensor (6 degrees of freedom) that provides the position and orientation of the second component 360 relative to the first component 310. This information can be used for collision detection, to correct for measurement errors when the hearth is locked, or in any other useful manner. The machine controller 25 of the CMM 40 can be configured to read the sensor periodically (e.g., every millisecond) when the hearth is locked. Fast scan times are particularly useful when encoders are used to detect collisions.

[0061] The six degrees of freedom sensor may include a reader attached to the first component 310 and a scale attached to the second component 360, or vice versa.

[0062] The indexed articulation joint may include an axially extending peripheral guard to protect the improved Hirth coupling from dust and / or fluid intrusion (not shown). The guard may include a cylindrical flange circumferentially fixed to one of the first and second components 310, 360 and extending toward the other to encircle its circumferential side in both the locked and unlocked configurations. Complementarily, the other component may include an additional peripheral flange or fitting configured to cooperate with such flange to enhance the gas-tightness. Alternatively, the extending peripheral guard may include a bellows fixed to the periphery of both the first and second components 310, 360 to provide the necessary gas-tightness.

[0063] The modified Hirth coupling may also be used in a probe holder (not shown) to provide for reorientation of the probe 400 about a single axis (e.g., the "S" axis), ultimately in addition to an axis provided by the wrist (e.g., the "C" axis). In such a case, one of the first and second components 310, 360 is fixed to a support element of a rotational adapter of the probe holder, which may be attached to the positioning platform 45 of the CMM 40 instead of, or complementary 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 fixed to a probe support to which the probe may be attached, or directly to the probe.

[0064] The improved Hirth coupling of the present invention may be used with a rotary table to provide indexable reorientation of a workpiece to be measured. Thus, one of the first and second components 310, 360 may be attached to a support element configured to secure the rotary table on the reference table 43 or to another surface of the measurement apparatus 40. The other of the first and second components 310, 360 may then be connected to a workpiece support configured to hold the workpiece for measurement. [Explanation of symbols]

[0065] 10 Joint List 25 Machine Controller 30 Work 40 Coordinate Measuring Machine, CMM 41 Bridge 42 Carriage 43 Table 45 Z-ram, quill, positioning platform 60 “A” axis (horizontal) 70 “B” axis (vertical) 100 Support Elements 103 Connector 200 Reorientable Elements 220 Visual Indicators 300 additional reorientable elements 310 first mating component 321 equally spaced teeth of first mating component 360 Second mating component 370 equally spaced toothed sectors 371 Teeth of second meshing component 375 non-meshing sectors 400 stylus, end sensor 415 Touch tip

Claims

1. An indexed articulation joint for reorienting a measuring tool of a measuring device and / or a workpiece within a measuring volume of the measuring device, a support element that can be attached to the measuring device or a component of the measuring device; a reorientable element rotatably connected to the support element, the reorientable element being capable of being rotated relative to the support element about a first axis of rotation between a plurality of indexable orientations equally separated by a pitch angle, and being locked into one of the plurality of indexable orientations; a modified Hirth coupling having two interlocking components, one within said support element and the other within said reorientable element; a first component of the modified Hirth coupling having a plurality of teeth evenly spaced apart by multiples of the pitch angle; a second component of the modified Hirth coupling having three or more toothed sectors separated by non-meshing sectors, each toothed sector including a plurality of teeth spaced apart by the pitch angle, wherein when the first component and the second component are locked together in any of the indexed positions, each of the toothed sectors meshes with at least one tooth of the first component, and there is a gap between the non-toothed sectors and the first component; Indexed articulated joint.

2. 2. The indexed articulation joint of claim 1, wherein each toothed sector includes at least K teeth, K representing an integer ratio between the angular spacing of adjacent teeth on the first component and the pitch angle.

3. 3. An indexed articulation joint according to claim 2, wherein each toothed sector comprises K+1 teeth or K+2 teeth.

4. 2. The indexable articulation joint of claim 1, wherein said toothed sectors are evenly spaced in angle.

5. 2. The indexed articulation joint according to claim 1, wherein at least one of said toothed sectors is configured with a different number of teeth and / or is unevenly angularly spaced.

6. 3. An indexed articulation joint according to claim 2, wherein the second component has exactly three, four or six toothed sectors and the ratio K is exactly four, six or eight.

7. The indexable articulation joint of claim 1 , wherein the pitch angle is 5°, 2.5°, 2°, or 1°.

8. 2. The indexable articulation joint of claim 1, wherein said teeth have sloping sides that meet at an angle of less than 90 degrees.

9. 2. The indexable articulation joint of claim 1, including an automatic actuator for driving the rotation of the reorientable element about the first axis of rotation and / or for locking the support element and the reorientable element together by biasing one toward the other.

10. The indexed articulation joint of claim 1 , including an angular encoder configured to measure an angle of rotation of the reorientable element relative to the support element about the first axis of rotation.

11. 2. The indexable articulation joint according to claim 1, comprising an axially extending peripheral protection, in particular a bellows, fixed to the first component and / or the second component to protect the improved Hirth coupling from the ingress of dust and / or fluids.

12. 10. An articulating wrist or probe holder for reorienting a measuring tool mounted on a positioning platform of a measuring device, said articulating wrist or probe holder comprising an indexed articulated joint according to claim 1, and wherein said support element can be mounted on said positioning platform.

13. 13. An articulated wrist according to claim 12, further comprising an additional reorientable element rotatably connected to said reorientable element such that an orientation of the additional reorientable element relative to said reorientable element can be changed among a plurality of indexable orientations about a second axis of rotation orthogonal to said first axis of rotation and locked in one of said plurality of indexable orientations, and said tool is attached to said additional reorientable element.

14. 10. A rotary table for reorienting a workpiece within a measurement volume of a measuring device, the rotary table comprising an indexed articulated joint according to claim 1, wherein the support element can be attached to a reference table or surface of the measuring device.

15. Use of an articulated wrist according to claim 12 in a coordinate measuring machine for reorienting a coordinate probe.

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