Indexing articulated joint comprising sensor for establishing engaged state and associated metering device

Abstract

An apparatus includes a first relatively reorientable member and a second relatively reorientable member, and an indexer arrangement configured to provide a plurality of angularly indexed lockable positions of the first member and the second member about a first axis. The indexer arrangement includes: i) a series of features disposed on the first member, the series of features extending annularly about a first axis; and ii) at at least three discrete, annularly spaced-apart locations on the second member, engagement features are provided that are configured to engage with a subset of the features on the first member when in a locked state, a stable, repeatable relative rest position of the first and second members is provided at each indexing position. The apparatus further comprises at least a first non-contact sensor mounted to the second member, the non-contact sensor configured to sense an area on the first member and thereby provide a signal relating to the spatial configuration of the first and second members when in their locked state.

Description

[0001] The present invention relates to an indexing articulated joint, in particular an indexing articulated joint for use in high precision metrology equipment. For example, in a specific embodiment, the present invention relates to an indexing articulated joint for an articulated head configured to support a measurement probe on a coordinate positioning device so that the measurement probe can be arranged in a plurality of different rotational orientations.

[0002] As is well known in the field of coordinate positioning equipment, in particular in the field of coordinate measuring machines (CMMs), an articulating head (or a rotary table) for a measuring probe (or object) comprises articulatable members which facilitate reorienting the measuring probe (or object) mounted thereon about at least one axis of rotation. Typically, an articulating head will provide two orthogonal axes of rotation, but may also provide fewer or more axes of rotation. Typically, a rotary table will provide one axis of rotation.

[0003] US 5185936 describes an articulated head with one axis of rotation, and EP 2889573 and WO 2006 / 079794 describe articulated heads providing two orthogonal axes of rotation. As described in these documents, it is also known to provide an articulated head with an indexing arrangement that enables the relatively rotatable portion of the articulated head to be locked to a defined indexing position. The indexing arrangement can be provided by providing two sets of mutually meshing members (one set on each relatively rotatable member). When the mutually meshing members are engaged, they lock to present a relative rotation of the rotatable members. When the mutually meshing members are disengaged, the rotatable members are free to rotate relative to each other, so that they (and the measuring probes mounted thereon) can be repositioned to a new orientation (e.g., under the control of a potentiometer or encoder as described in WO 2006 / 079794) before reengaging, so as to lock the rotatable member (and the measuring probes mounted thereon) in the new orientation. Then the measuring operation can be performed with the measuring probes being held in a defined, known rotational orientation. Renishaw plc sells such an indexing articulated joint under the product name PH10, in which the indexing arrangement comprises a series of balls on one of the rotatable members and three pairs of cylindrical "rollers" on the other member. A potentiometer mounted to the member having the three cylindrical rollers engages (via a series of gear members) the member having the series of balls, and the output of the potentiometer is used when the members are unlocked so that the relative position of the members can be monitored and controlled to ensure that they are positioned in the desired relative orientation before they are locked together.

[0004] The present invention relates to an improved indexing articulated joint. In particular, the present invention has been found to be very useful in facilitating high performance indexing articulated joints, for example where the desired repeatability of the index position is 100 nm (nanometers) or less.

[0005] According to a first aspect of the invention, there is provided a device comprising a first relatively reorientable member and a second relatively reorientable member and an indexer arrangement, the indexer arrangement being configured to provide a plurality of angularly indexed lockable positions of the first and second members about a first (rotational) axis, wherein the indexer arrangement comprises: i) a series (e.g. a continuous series) of features provided on the first member, the series of features extending annularly about the first axis; and ii) engagement features provided at a plurality (e.g. at least three) discrete, annularly spaced (about the first axis) positions on the second member, the engagement features being configured to intermesh with a subset of the features on the first member when in a locked state, thereby providing a stable, (e.g. kinematically) repeatable relative rest position of the first and second members at each indexed position; wherein the device further comprises at least a first non-contact sensor mounted to the second member (i.e. so as to be rotationally fixed thereto), the first non-contact sensor being configured to sense an area on the first member and thereby provide a signal relating to the spatial configuration of the first and second members when in their locked state.

[0006] As described in more detail below in conjunction with specific embodiments of the present invention, the inventors have found that placing non-contact sensors (which measure the spatial configuration of the first and second members) on the second member as opposed to placing them on the first member can have significant advantages. In particular, the measurement of the spatial configuration of the first and second members can be less prone to error, or at least any error in the measurement can be more predictable and therefore easier to compensate for.

[0007] The first relatively redirectable member and the second relatively redirectable member may be referred to as a pair of relatively redirectable members, such as a first pair of relatively redirectable members.

[0008] The material of at least those portions of the first and second members that mechanically link the first non-contact sensor on the second member and the area on the first member at each indexed position and thereby govern their relative spatial configuration may have a CTE of at least 2 ppm / ° C. Although materials having a CTE of less than 2 ppm / ° C. are known and may be used, such materials may be expensive and / or may have other inappropriate properties that make it unsuitable for use in a desired application (e.g., the material may be too soft).

[0009] The first non-contact sensor can be positioned so that the radial line where its sensing window is located is within + / -15° of the radial line where the first one of the engaging features of the second component is located, preferably within + / -10° of the radial line where the first one of the engaging features of the second component is located, more preferably within + / -5° of the radial line where the first one of the engaging features of the second component is located, and especially preferably within + / -1° of the radial line where the first one of the engaging features of the second component is located.

[0010] The first non-contact sensor can be configured to measure the relative spatial configuration of the first member and the second member in only one dimension, or can be configured to measure the relative spatial configuration of the first member and the second member in at least two orthogonal dimensions (e.g., three orthogonal dimensions). The first non-contact sensor can be configured to measure the relative height / spacing of the first member and the second member (e.g., along the rotational axis / first axis).

[0011] Optionally, the first non-contact sensor can be configured to measure the relative configuration (e.g., lateral position and / or rotational orientation) of the first member and the second member in a plane perpendicular to the rotation axis (i.e., the first axis). For example, the first non-contact sensor can be configured to measure the relative lateral position of the first member and the second member (e.g., in at least one dimension perpendicular to the rotation axis, such as in two orthogonal dimensions perpendicular to the rotation axis). In particular, for example, the first non-contact sensor can be configured to measure the relative rotational orientation of the first member and the second member around the first axis. Optionally, the at least one first non-contact sensor can be configured to measure a combination of the above relative configurations.

[0012] As will be appreciated, the first contactless sensor may be configured to provide a measurement of the relative configuration of the first body and the second body (in a plane perpendicular to the axis of rotation) with a finer resolution than the graduation increments of the indexer arrangement, for example with a resolution of at least 5 times the graduation increments of the indexer arrangement, optionally at least 10 times the graduation increments of the indexer arrangement, for example at least 15 times the graduation increments of the indexer arrangement. Preferably, the first contactless sensor enables the relative position of the first body and the second body to be established within 50 μm, for example within 10 μm, optionally within 1 μm, for example within 100 nm, optionally within 10 nm, for example within 2 nm.

[0013] The area on the first member sensed by the first non-contact sensor may include a scale member (e.g., a rotating scale member). Accordingly, the non-contact sensor and the scale member may be what is commonly referred to as an "encoder device" or a "position encoder device". In this case, the non-contact sensor may be what is commonly referred to as a "readhead". The scale member may include a series of features that the first non-contact sensor / readhead may read to determine its relative position. The scale member may include an incremental scale track (with or without one or more reference marks). The incremental scale track typically includes a periodic series of features that form a signal at the non-contact sensor / readhead that varies with the relative movement of the non-contact sensor / readhead and the scale. In the case of an optical encoder device, the signal may be a fringe field (e.g., interference fringes) that moves with the relative movement of the non-contact sensor / readhead and the scale, or may be, for example, one or more spots of light that change intensity with the relative movement of the non-contact sensor / readhead and the scale. The scale member may include an absolute scale track. An absolute scale track typically includes a non-periodic series of features that encode unique position information along the length of the track. The scale member may comprise more than one scale track, and optionally a combination of incremental and absolute scale tracks. The scale member / series feature / one or more tracks thereof may extend about the first axis. A non-contact sensor / readhead may read the scale member to determine / provide a direct measurement of the relative position of the first and second members about the first axis.

[0014] The contactless sensor may sense the area by one or a combination of optical means, inductive means, magnetic means, and capacitive means. Accordingly, the contactless sensor may include an optical sensor, a magnetic sensor, an inductive sensor, and / or a capacitive sensor. Accordingly, in the case of an encoder device, the encoder device may include an optical encoder device, an inductive encoder device, a magnetic encoder device, or a capacitive encoder device (any of which may use a combination of sensing technologies, for example, known incremental optical encoder devices include magnetic reference marks).

[0015] The first non-contact sensor need not necessarily be part of the encoder device. More specifically, the first non-contact sensor need not necessarily sense the scale member, and may, for example, sense a structural portion of the first member. The first non-contact sensor may include a position sensitive device (PSD) whose output is related to the relative spatial position of the first member and the second member when locked together. In another embodiment, the first non-contact sensor may include a height / distance sensor (e.g., an inductive sensor, a magnetic sensor, and / or a capacitive sensor) that is configured to sense the height / distance of the sensor from the first body.

[0016] The device can be configured so that when the first member and the second member are locked together at the indexed position, the first non-contact sensor is used to establish information about the engagement state of the first body and the second body. For example, the signal provided by the first non-contact sensor can be used to establish information about the engagement state of the first member and the second member.

[0017] The first non-contact sensor can be used to obtain a ("current") measurement of the relative spatial configuration of the first member and the second member. The information obtained from the measurement can be compared with calibration information. The calibration information can be obtained from at least one other (in other words, previous) measurement of the relative spatial configuration of the first member and the second member when the first member and the second member were locked at the indexing position at an earlier point in time (in other words, when the first member and the second member were previously locked at the indexing position) (for example, performed by the first non-contact sensor). The comparison can be performed in order to establish information about the engagement state of the first member and the second member. Preferably, the calibration information is obtained from at least one other measurement of the relative spatial configuration of the first member and the second member performed by the first non-contact sensor (for example, when the first member and the second member were locked at the indexing position at an earlier point in time).

[0018] The first non-contact sensor can help verify that the first and second members have been properly locked together; for example, verifying that they have been locked together in substantially the same relative configuration as at a previous / earlier point in time, for example, during a calibration phase. Accordingly, the first non-contact sensor can help verify the repeatability of the indexed position at which the first and second members are locked together.

[0019] The device can be configured to react in a predetermined manner depending on the determined engagement state of the first member and the second member (e.g., depending on the result of the above-mentioned comparison). For example, if the determined engagement state (e.g., comparison) indicates that the first member and the second member are not properly locked together, the device can be configured to react by unlocking the first member and the second member. Optionally, the device can be configured to react by unlocking the first member and the second member and relocking at the same indexing position. Optionally, this can include relocking the first body and the second body from a slightly different position (e.g., from a slightly different relative rotational orientation). Reacting in a predetermined manner can additionally or alternatively include recording and / or reporting (e.g., outputting to a controller device) an error or warning state.

[0020] As will be understood, references to "previous measurements" and "previous locking at said indexed positions" do not necessarily refer to the latest or most recent measurements, or the latest or most recent time at which they were locked at said indexed positions. Rather, the terms "previous" and "previously" are used to mean at some earlier point in time. Accordingly, the first member and the second member may have been locked at said indexed positions multiple times between the current time and the time at which the calibration information was obtained.

[0021] The device can be configured so that if the comparison result indicates that the current relative spatial configuration of the first member and the second member in the indexed position differs from the relative spatial configuration of the first member and the second member represented by the calibration information by more than a predetermined threshold, it is determined that the first member and the second member are not correctly locked together. The predetermined threshold may be no greater than 100 μm (micrometers), such as no greater than 50 μm, optionally no greater than 20 μm, but may be, for example, as small as no greater than 1 μm, such as no greater than 100 nm (nanometers), no greater than 50 nm, or no greater than 10 nm.

[0022] As described above, the first non-contact sensor may be part of an encoder device (e.g. a readhead). As also described above, the scale track may include a series of features, such as a series of substantially periodic features. The scale track may have a characteristic pitch distance (or "characteristic pitch angle" for some rotating systems (e.g. a disk scale on which the scale features are radially arranged). The signal from the non-contact sensor / readhead may be used to interpolate between the scale pitch intervals to produce a position measurement with a much higher resolution than the scale pitch. (There are cases where the readhead produces a spatially periodic signal, and in some embodiments the signal period of the readhead has a higher frequency (shorter wavelength) than the scale period. In these cases, interpolation may still be used to produce a position measurement with a much higher resolution than the signal period). The "information obtained from the measurement" and the "calibration information" may include relative position information with a resolution much finer than the period of the scale. This relative position information may be referred to as a "phase reading"; because the information relates to the "phase" position between the periodic features of the scale. Accordingly, the "information obtained from the measurement" and the "calibration information" may include phase readings. Accordingly, in such an embodiment, the device can be configured such that, when the first member and the second member are locked together at the indexing position, the phase reading obtained from the first non-contact sensor is compared with the phase reading obtained by the first non-contact sensor when the first member and the second member were locked at the indexing position at an earlier point in time, so as to establish information about the engagement state of the first member and the second member.

[0023] It may be preferred that the device includes a second non-contact sensor configured to provide a signal related to the spatial configuration of the first and second members when they are in their locked state. Preferably, the second non-contact sensor is mounted to the second member and is configured to sense an area on the first member at an annular position different from the annular position sensed by the first non-contact sensor around the first axis (and thereby provide a signal related to the spatial configuration of the first and second members when they are in their locked state). As will be understood, an additional (e.g., third) non-contact sensor may be provided, which is configured to provide a signal related to the spatial configuration of the first and second members when they are in their locked state. Further, (e.g., third) non-contact sensors may be particularly beneficial if these non-contact sensors include a height / interval sensor for sensing the height / interval of the sensor and the first body. For example, in this case, it may be beneficial to provide three height / interval sensors equiangularly around the axis of rotation. Preferably, each height / interval sensor is configured such that its sensor window is located within + / -15° of the radial line where the engagement feature closest to it is located of the second member.

[0024] All statements made above with respect to the first non-contact sensor may also apply to the second non-contact sensor (and any additional non-contact sensors). Accordingly, the statements made above with respect to the type (e.g., whether it is a read head of an encoder device or another type of sensor, such as a height / spacing sensor), the position (e.g., its position relative to the engagement feature of the second member), and the purpose of the first non-contact sensor may also apply to the second non-contact sensor. Accordingly, for example, with respect to the purpose of the second non-contact sensor, in an embodiment in which at least the first non-contact sensor and the second non-contact sensor are provided, the device may be configured such that, in the case where the first member and the second member are locked together at the indexing position, the first non-contact sensor and the second non-contact sensor are used to sense the first member and thereby provide a signal related to the spatial configuration of the first member and the second member when they are in their locked state. The signals provided by the first non-contact sensor and the second non-contact sensor may be used to establish information about the engagement state of the first member and the second member. For example, the first non-contact sensor and the second non-contact sensor may be used to obtain a measurement of the relative spatial configuration of the first member and the second member. The information obtained from the measurement may be compared with calibration information obtained from at least one other (in other words, previous) measurement of the relative spatial configuration of the first and second members when the first and second members were locked together in the indexing position at an earlier point in time (in other words, when the first and second members were previously locked in the indexing position) (e.g., by the first non-contact sensor and the second non-contact sensor) in order to establish information about the state of engagement of the first and second members. Optionally, in accordance with the above description in which the non-contact sensor is part of the encoder device, the metrology device may be configured such that with the first and second members locked together in the indexing position, the first and second non-contact sensors may be configured to read the scale member (the same scale member or different scale members) and compare the first and second phase readings, respectively, obtained from the first and second readheads with the corresponding first and second phase readings obtained by the first and second readheads when the first and second members were locked together in the indexing position at an earlier point in time in order to establish information about the state of engagement of the first and second members.

[0025] It may be preferred that the second non-contact sensor is configured to sense the following area of ​​the first member, which is at a position less than 180° around the first axis from the position where the at least one first non-contact sensor senses the first member, for example, at a position between 45° and 135° from the position where the at least one first non-contact sensor senses the first member, for example, at a position between 115° and 125° from the position where the at least one first non-contact sensor senses the first member, for example, at a position 120° from the position where the at least one first non-contact sensor senses the first member. As described in more detail below, it may be preferred that the second non-contact sensor is configured to sense an area of ​​the first member at a position 90° from the position where the at least one first non-contact sensor senses the first member.

[0026] As described above, the statements about the position of the first non-contact sensor also apply to the second non-contact sensor. Accordingly, for example, the second non-contact sensor can be positioned so that the radial line where its sensing window is located is within + / -15° of the radial line where the second engagement feature in the engagement features of the second member is located, preferably within + / -10° of the radial line where the second engagement feature in the engagement features of the second member is located, more preferably within + / -5° of the radial line where the second engagement feature in the engagement features of the second member is located, and particularly preferably within + / -1° of the radial line where the second engagement feature in the engagement features of the second member is located. However, this does not necessarily have to be the case, and the second non-contact sensor can be intentionally placed so that the radial line where its sensing window is located is not within + / -15° of the radial line where any engagement feature in the engagement features of the second member is located. For example, it may be advantageous to position the second non-contact sensors substantially 90° from each other about the first axis so as to be able to extract the most accurate information about the spatial configuration of the first and second members in multiple (e.g., orthogonal) dimensions, and the second engagement feature may not be positioned at or near 90° about the first axis relative to the first engagement feature (e.g., they may be positioned 120° apart).

[0027] The area of ​​the first member sensed by the second non-contact sensor need not be the same area as the area sensed by the first non-contact sensor. For example, where the first non-contact sensor and the second non-contact sensor are part of an encoder device (e.g., a readhead) and the area includes a scale member, the second non-contact sensor may sense a different track on the scale member, or may even sense a different scale member. Furthermore, the first non-contact sensor may be part of an encoder device (and therefore sense a scale member), while the second non-contact sensor is not part of the encoder device (and therefore does not sense a scale member).

[0028] The indexer arrangement of the first and second members can be unlocked (or their mutually engaging features can be disengaged) by axial relative movement of the first and second members in a first direction along the first axis, so that the first and second members are free to rotate relative to each other about the first axis. The first and second members can be locked (or their mutually engaging features can be reengaged) by axial relative movement of the first and second members in a second direction along the axis.

[0029] The apparatus may further comprise a motor (eg an electric motor) for driving the first and second members about the first axis when they are unlocked.

[0030] The device may further include a main encoder device configured to monitor the relative rotational position of the first member and the second member around the first axis when unlocked. Optionally, in those embodiments where the non-contact sensor is part of an encoder device (labeled as a "secondary encoder device" herein), the main encoder device may be the same encoder device as the non-contact sensor / secondary encoder device. In other words, the non-contact sensor can be configured so that it can be used (and optionally used) to detect / monitor the relative rotational position of the first member and the second member around the first axis when unlocked. Optionally, the main encoder device can share some common parts with the non-contact sensor / secondary encoder device (for example, they can share the same scale, wherein the main encoder device includes a read head different from the first non-contact sensor / read head). However, it may be preferred that the main encoder device is an encoder device completely different from the non-contact sensor / secondary encoder device, including a different read head and a different scale.

[0031] The device may include a motor mechanism for actuating the first member and the second member between their locked state and / or unlocked state (a "lock / unlock" motor mechanism). The lock / unlock motor mechanism may include a member (e.g., a pillar) that can be actuated by a motor to unlock the first member and the second member (the indexer arrangement) (e.g., by separating them along a first axis). For example, the pillar can be actuated between a retracted configuration and an extended configuration, in which the first member and the second member are in their locked state, and in which the first member and the second member are held apart by the pillar along the first axis, so that the first member and the second member are unlocked, thereby allowing the first member and the second member to rotate relative to each other. For example, the member body may include a pillar, and the pillar and the second member may be magnetically biased toward each other to magnetically retain the first member and the second member. A supplementary biasing member (e.g., a magnetic material) may be configured to bias the pillar toward its retracted configuration.

[0032] For example, the first member (or in an alternative embodiment, the second member) may include a portion (e.g., a pillar) that is relatively rotatable about a first axis relative to the first (or second) member, at least when in an unlocked configuration, and is configured to engage the second (or first) member and be rotationally fixed relative thereto when the first and second members are unlocked and rotated relative to each other. The portion may be actuatable (e.g., by a motor) between a retracted configuration in which the first and second members are in their locked state and an extended configuration in which the first and second members are held apart along the first axis by the portion / pillar so that the first and second members are unlocked, thereby permitting relative rotation of the first and second members. The primary encoder device may include a readhead on one of the first (or second) member and the portion and a scale member on the other, so that the readhead provides a measurement of the relative rotational position of the first (or second) member and the portion. The device may be configured to control the rotation of the first and second members using the output of the primary encoder device when the first and second members are unlocked. The portion / strut can be coupled to a second member (or in an alternative embodiment, to a first member) when in its extended configuration (e.g., via corresponding engagement features as described in more detail below) and decoupled from the second (first) member when in its retracted configuration.

[0033] The metrology apparatus may include a rotary table including an indexing articulated joint on which the workpiece to be inspected is mounted. The metrology apparatus may include a probe head including an indexing articulated joint. The probe head may be configured to support a measurement probe on a coordinate positioning apparatus so that the measurement probe may be arranged in a plurality of different indexing rotational orientations. Suitable measurement probes include contact and non-contact measurement probes. Suitable measurement probes include probes for measuring dimensions of a workpiece. Suitable measurement probes include touch trigger measurement probes as well as scanning or "analog" measurement probes.

[0034] The metrology device (e.g., rotating table / probe head) may be configured to be mounted on a positioning device, in particular a coordinate positioning device, such as a coordinate measuring machine (CMM). The metrology device (e.g., rotating table / probe head) may be mounted on a positioning device, which is configured to facilitate repositioning of the metrology device in at least two, such as three orthogonal linear degrees of freedom. The metrology device (e.g., rotating table / probe head) may be removably mounted to a positioning device (e.g., to a z-column or quill of a CMM) via one or more releasable fasteners (e.g., one or more bolts).

[0035] The metrology device may comprise a memory device, the memory device comprising calibration information. The memory device may be located in a part of the device separate from the indexing articulated joint (e.g. in the controller). Preferably, a part of the indexing articulated joint (e.g. the first body or the second body) comprises the memory device. In embodiments where the device comprises a probe head (or a rotating stage), the probe head (or the rotating stage) may comprise the memory device.

[0036] The metrology device may include processing means configured to perform the above comparison. The processing means may be located in a portion of the device separate from the indexing articulated joint (e.g. within a controller). Optionally, a portion of the indexing articulated joint (e.g. the first member or the second member) includes the processing means. In embodiments where the device includes a probe head (or a rotating table), the probe head (or the rotating table) may include the processing means.

[0037] Accordingly, the apparatus may be configured such that the above-mentioned information about the state of the joint (eg the comparison) is performed within a portion of the metrology apparatus comprising the indexed articulated joint itself (eg within the probe head or the rotary table).

[0038] The calibration information may be stored in a lookup table. Optionally, the calibration information may be represented by a function. Accordingly, the above-mentioned memory device may include a lookup table and / or a function containing / representing the calibration information. The lookup table may include calibration information for each possible indexing position in at least a subset of the possible indexing positions of the first body and the second body. The lookup table may include calibration information for each possible indexing position of the first body and the second body. For example, the lookup table may include at least one element / data unit for each indexing position. Each element / data unit may include calibration information for the indexing position associated with the element / data unit. The lookup table may include multiple elements / data units for each indexing position. This may be helpful in the presence of more than one contactless sensor.

[0039] "Information obtained from the measurements" and "calibration information" may include relative position information (eg, as opposed to absolute position information).

[0040] Calibration information (e.g., a lookup table or function) can be updated over time. This can occur continuously or periodically. This can be done as part of a dedicated calibration process, or it can be done during a measurement operation. For example, each time the first member and the second member are locked together at any given indexing position and the comparison result indicates that the first member and the second member have been correctly locked together (e.g., the comparison result indicates that the current relative spatial configuration of the first member and the second member at the indexing position does not differ from the relative spatial configuration of the first body and the second body represented by the calibration information by no more than a predetermined threshold), the information obtained from the measurement of the current relative spatial configuration of the first member and the second member provided by the first (and optionally the second) non-contact sensor can be used to update (e.g., can be stored) the calibration information (e.g., can be used to update / replace the information stored in the lookup table in a specific element / data unit associated with the indexing position).

[0041] As will be understood, "information obtained from the measurement" may mean that the information is obtained from the measurement obtained by the contactless sensor itself, or may mean that the information is obtained from the measurement obtained by the contactless sensor and also from other data sources. Accordingly, the information does not necessarily have to be obtained / derived from or only from the measurement obtained by the contactless sensor. However, it may be preferred that "at least the information derived from the measurement" is only the measurement obtained by the contactless sensor. Accordingly, "information obtained from the measurement" may be the measurement obtained by the contactless sensor, for example it may be only the output from the contactless sensor.

[0042] Similarly, "calibration information obtained from at least one other measurement / previous measurement of the relative spatial configuration of the first member and the second member" may mean that the calibration information is obtained from at least one other / previous measurement result obtained by the non-contact sensor itself, or may mean that the calibration information is obtained from at least one other / previous measurement result obtained by the non-contact sensor and from other data sources. Accordingly, the calibration information does not necessarily have to be obtained / derived from or only from at least one other / previous measurement result obtained by the non-contact sensor. However, it may be preferred that the "calibration information" is only a measurement result obtained by the non-contact sensor at an earlier point in time. Accordingly, the "calibration information" may be a measurement result obtained by the non-contact sensor, for example it may be only an output from the non-contact sensor.

[0043] Accordingly, the device can be configured to compare current measurements of the relative spatial configuration of the first member and the second member obtained by the first (and optionally the second) non-contact sensor with other measurements / previous measurements of the relative spatial configuration of the first member and the second member performed by the first (and optionally the second) non-contact sensor when the first member and the second member were locked at the indexing position at an earlier point in time, so as to establish information about the engagement state of the first member and the second member.

[0044] As will be appreciated, the intermeshing features of the indexer arrangement may provide a plurality of predetermined angular indexing positions at which the first member and the second member may be locked relative to each other. The intermeshing features of the indexer arrangement may provide indexing increments of 10° or less, such as 5° or less, such as 4° or less. The intermeshing features of the indexer arrangement may provide indexing increments of at least 0.5°, such as at least 1°. For example, the intermeshing features of the indexer arrangement may provide indexing increments of about 2.5°.

[0045] The apparatus may include a motor (a "re-orienting" motor mechanism) configured to drive the first and second members about an axis of rotation (the first axis) when the first and second members are unlocked.

[0046] The series of features provided on the first member and being part of the indexer arrangement may include a series of teeth, preferably tapered teeth. The tapered teeth in the series may include projections having straight sides or curved sides. For example, the teeth may have a spherical (e.g., hemispherical) shape, a cylindrical (e.g., semi-cylindrical) shape, or a generally triangular shape. The series of teeth may provide a face spline member. The device may be configured such that when in a locked state (and for each possible indexing position), an engagement feature provided on another of the second members engages with a subset of the series of teeth of the first member at a plurality of (e.g., three) discrete, equiangularly spaced positions.

[0047] The engagement feature of the second member may include one or more teeth. The engagement feature of the second member may include only a single tooth. Optionally, the engagement feature of the second member may include a plurality of teeth arranged at different annular positions around the first axis, such as a group of teeth (e.g., a small series of teeth, the series extending annularly around the first axis). This group of teeth may include, for example, no more than 5 teeth, such as two teeth, three teeth or four teeth. Preferably, the angle of the arc defined by the first tooth and the last tooth in the group / series of teeth of the engagement feature is no more than 25°, more preferably no more than 20°, particularly preferably no more than 10°, for example no more than 5°.

[0048] As described above in conjunction with the teeth of the first member, the one / multiple teeth of the engagement feature of the second member may include one / multiple tapered teeth. Tapered teeth may include protrusions with straight sides or curved sides. For example, the tooth may have a spherical (e.g., hemispherical) shape, a cylindrical (e.g., semi-cylindrical) shape, or a generally triangular shape.

[0049] The device can be configured so that when in a locked state (and for each possible indexing position), the features of the indexer arrangement on the first member and the engagement features on the second member provide a kinematic mounting / positioning / connection / coupling between the first member and the second member. As will be understood, the kinematic mounting seat is a mounting seat below: the mounting seat has an element arranged to cooperate with an element on another part on one part to provide a highly repeatable positioning. These elements are arranged to cooperate with each other so as to preferably constrain the relative motion between these parts on all six degrees of freedom (i.e., three vertical linear degrees of freedom and three vertical rotational degrees of freedom) through six contact points or constraint points. In a specific embodiment, the features on one of the components can be arranged to provide a pair of mutually converging surfaces at each of three spaced-apart positions, thereby providing a total of six rigid contact points with the features on another component. This limits the six possible degrees of freedom of one part relative to another part. Such kinematic mounts are sometimes referred to as Boys supports and are described, for example, in HJJ Braddick, "Mechanical Design of Laboratory Apparatus", Chapman and Hall, London, 1960, pp. 11 to 30. Further details of example configurations for providing such kinematic mounting / positioning / connection are provided below.

[0050] The metering device may include a third member, and a second indexer arrangement may be provided, the second indexer arrangement being configured to provide a plurality of angular indexing positions of i) the third member and ii) the first member or the second member (regardless of which the third member is mounted) about a second axis (hereinafter referred to as the "second pair of relatively redirectable members"). The features described above in conjunction with the first member and the second member are equally applicable to the second pair of relatively redirectable members. Accordingly, for example, there may be provided: a) a series of features provided on one of the relatively redirectable members of the second pair of relatively redirectable members, the series of features extending annularly about the second axis; and b) engagement features provided at at least three discrete, annularly spaced positions on the other of the second pair of relatively redirectable members, the engagement features being configured to intermesh with a subset of the series of features when in a locked state, thereby providing a stable, repeatable relative idle position of the second pair of relatively redirectable members at each indexing position. In addition, a first non-contact sensor may be provided and configured to provide a measurement of the relative spatial configuration of the second pair of relatively reorientable members. Preferably, the first non-contact sensor is mounted on the member on which the engagement features are provided and is configured to sense an area on the other member (on which the series of features are provided) and thereby provide a signal related to the spatial configuration of the second pair of relatively reorientable members when in their locked state.

[0051] As will be appreciated, references herein to a "subset" refer to a "proper subset" in a mathematical sense (in that each engagement feature on the second component cannot engage and does not engage all features in the series of features on the first component).

[0052] Embodiments of the present invention will now be described, by way of example only, with reference to the following drawings, in which:

[0053] Figure 1 The indexing head according to the present invention mounted on a coordinate measuring machine (CMM) is shown;

[0054] Figure 2 Shown separately Figure 1 Dividing head;

[0055] Figure 3 Shown Figure 1 A cross-sectional view of the dividing head in its locked configuration;

[0056] Figure 4 Shown Figure 1 A cross-sectional view of the dividing head of FIG. 1 in its unlocked configuration;

[0057] Figure 5a Shown Figure 1The indexing arrangement of the dividing head;

[0058] Figure 5b Shown separately Figure 5a A portion of a graduated arrangement;

[0059] Figure 6 yes Figure 5a A detailed view of the indexing arrangement shown;

[0060] Figure 7a , Figure 7b and Figure 7c Shown Figure 5b a single tooth of the portion of the indexing arrangement shown;

[0061] Figure 8 yes Figure 1 Exploded view of the different parts of the indexing mechanism and unlocking mechanism of the indexing head.

[0062] Fig. 9 and Fig.10a Shows Figure 1 A cross-sectional view of different parts of an indexing mechanism and an unlocking mechanism of an indexing head;

[0063] Fig.10b Shows Figure 1 a bottom side of one of the hinged portions of the indexing arrangement of the indexing head;

[0064] Figures 11a to 11d Shows Figure 1 Schematic cross-sectional views of different parts of the indexing mechanism and the unlocking mechanism of the indexing head at different stages during the unlocking operation and the locking operation;

[0065] Figures 12 to 15 shows schematic cross-sectional views of different parts of an indexing mechanism and an unlocking mechanism according to an alternative embodiment, in particular with different magnet arrangements;

[0066] Fig.16 Is displayed for Figure 3 , Figure 4 and a graph of the support force and the holding force of the three ring magnet embodiments of FIG. 11 ;

[0067] Fig.17 Is displayed for Fig.12 A graph of the support force and the holding force of an embodiment of two ring magnets;

[0068] Fig.18 is a graph showing strut force and starting torque for an embodiment of two disk magnets;

[0069] Fig.19 yes Figure 1 A first isometric view of an indexing arrangement of an indexing head and an associated non-contact sensor;

[0070] Fig. 20 yes Figure 1 A second isometric view of an indexing arrangement of an indexing head and an associated non-contact sensor;

[0071] Fig.21 is a plan view of a first member of the articulated joint showing the relative positions of the non-contact sensor and the indexing arrangement of teeth;

[0072] Fig.22a and Figure 22b A side cross-sectional view of two different non-contact optical sensors for determining the spatial configuration of the first member 102 and the second member 104 is shown;

[0073] Fig.23a and Figure 23b A side cross-sectional view of a non-contact inductive sensor for determining the spatial configuration of the first member 102 and the second member 104 is shown;

[0074] Fig.24 a partial plan view of a first member of the articulated joint showing an engagement feature including a plurality of teeth in an indexed arrangement; and

[0075] Fig.25 is a cross-sectional view of the articulated head 100 taken in the ZX plane, wherein both the first axis “D” and the second axis “E” are in an unlocked configuration.

[0076] refer to Figure 1 , shows the articulated head 100 according to the present invention mounted on a positioning device 200.

[0077] The positioning apparatus 200 comprises a mobile structure, which in this case is in the form of a coordinate measuring machine ("CMM"). The CMM 200 comprises a base 202 supporting a frame 204, which in turn holds a carriage 206, which in turn holds a quill 208 (or "Z-column"). A motor (not shown) is provided to move the quill 208 along three mutually orthogonal axes X, Y and Z (e.g., by moving the frame along the Y axis, the carriage 206 along the X axis, and the quill 208 along the Z axis).

[0078] The quill 208 holds the articulating head 100, which in turn holds the probe 300. In this embodiment, the articulating head 100 facilitates repositioning of the probe 300 mounted thereon about the first rotation axis D and the second rotation axis E, as explained in more detail below.

[0079] The combination of the two rotational axes (D, E) provided by the articulating head 100 and the three linear translation axes (X, Y, Z) of the CMM 200 allows the probe 300 to be moved / positioned in five degrees of freedom (two rotational degrees of freedom and three linear degrees of freedom).

[0080] Although not shown, a measurement encoder may be provided for measuring the relative positions of the base 202, frame 204, bracket 206, quill 208 and portions of the articulating head 100 so that the position of the measurement probe 300 relative to a workpiece located on the base 202 may be determined.

[0081] A controller 220 is provided for controlling the operation of the CMM 200, such as controlling the position and orientation of the probe 300 within the CMM volume (manually, e.g., via an input device such as a joystick 216; or automatically, e.g., under control of an inspection program) and receiving information (e.g., measurement information) from the CMM 200. A display device 218 may be provided for assisting a user in interacting with the controller 220. The controller 220 may be, for example, a dedicated electronic control system and / or may include a personal computer.

[0082] In the illustrated embodiment, the probe 300 is a contact probe including a probe body 302 and a stylus 304. The stylus 304 has a spherical end 306 for contacting a workpiece to be inspected, and in this embodiment, the stylus 304 is deflectable relative to the probe body 302. The contact probe 300 may be a so-called touch trigger probe, or may be a scanning (or analog) probe. As will be appreciated, other types of probes, including non-contact probes, may also be mounted on the articulating head 100.

[0083] In the current embodiment, the articulating head 100 includes a probe mount 108 to facilitate the replacement of different probes thereon. In particular, this may be a mount that facilitates automatic replacement of the probe to or from the rack within the operating volume of the CMM. For example, the probe mount 108 and the probe body 302 may include magnets for holding the probe on the mount.

[0084] The articulating head 100 may include built-in sensor components for detecting deflection of a stylus 304 of a contact probe mounted thereon. However, in the present embodiment, all such sensor components are disposed within the body 302 of the probe 300 itself. The probe 300 is configured to send stylus deflection signals to the controller 220. As is common, this may be accomplished via a contact signal interface between the probe 300 and the probe mount 108, wherein such signals are then relayed to the controller 220 via the wiring of the articulating head 100 and the CMM 200. Such an interface may also be used to power the probe 300. Accordingly, as will be appreciated, the articulating head 100 itself will have a signal interface with the quill 208 (e.g., one or more corresponding electrical contacts on the articulating head and the quill), which may be used to relay probe signals and to receive power and motor control commands to control the articulating head 100 (e.g., to control the operation of the electric lock motors 190, 190' and drive motors 192, 192' described in more detail below). Accordingly, although not shown for simplicity of illustration, as will be understood, in the described embodiments, the CMM 200 and the articulated head 100 will include wires for relaying signals from the articulated head 100 (e.g., probe signals, position information, error messages, etc.) and / or for providing power and instructions / signals to the articulated head 100 (e.g., to control the motor of the articulated head and thus control the rotational position of the relatively rotatable member). As will be understood, in other embodiments, the articulated head may include one or more of its own power sources (e.g., one or more batteries) for powering the articulated head. It will also be understood that in other embodiments, the articulated head may communicate wirelessly with the controller 220.

[0085] Reference now Figures 2 to 24 , the articulated head 100 will now be described in more detail.

[0086] like Figure 2 As shown, the articulated head 100 includes a first member 102 or "mounting plate", a second member 104 that can be articulated / rotated relative to the first member 102 about a first rotation axis "D", and a third member that can be articulated / rotated relative to the second member 104 about a second rotation axis "E", which is in the form of a probe arm 106 in this embodiment. The second rotation axis "E" is orthogonal to the first rotation axis "D". In the described embodiment, the first rotation axis "D" is arranged to be parallel to the Z axis of the CMM, but this does not necessarily have to be the case.

[0087] The first member / mounting plate 102 comprises holes 103 through which bolts may pass to secure the articulating head 100 to a quill 208 of the CMM 200. The probe arm 106 comprises a probe mount 108 to which a probe, such as a contact probe 300, may be interchangeably mounted.

[0088] In an alternative embodiment, the probe arm 106 and its probe mount 108 may themselves be interchangeable components. For example, the probe arm 106 may be provided as part of the probe, rather than as part of the articulating head 100, so that it may be interchanged (e.g., automatically) with the probe. In this case, the third member of the articulating head 100 may include a mount member 106' for the probe / probe arm 106, the mount member 106' being articulated / rotatable relative to the second member 104 about the second axis of rotation "E". The mount member 106' and the probe arm 106 may be provided with cooperating mounting features to enable the probe arm 106 to be removably mounted to the mount member 106'. For example, such cooperating mounting features may include features 150 defining a kinematic mount (see Fig.25 ). One or more magnets may be provided to retain the probe arm 106 on the mount member 106'.

[0089] Figure 3 and Figure 4 shows a cross-sectional view of the articulated head 100 taken in the ZY plane, and Fig.25 A cross-sectional view of the articulated head 100 taken in the ZX plane is shown. Figure 3 and Figure 4 Essentially the same and common view of the same articulated head, but in Figure 3 FIG. 1 shows the hinge joint 100 when the first member / mounting plate 102 and the second member 104 are in their locked state, while FIG. Figure 4 1 shows the articulated joint 100 with the first member / mounting plate 102 and the second member 104 in their unlocked states. Figure 4 Many reference numerals are omitted to facilitate viewing of the various features of the articulating head 100 .

[0090] The locking / unlocking mechanism, rotating mechanism, and indexing arrangement of the first axis "D" and the second axis "E" (i.e., the first member / mounting plate 102 and the second member 104) will now be explained. In this embodiment, the locking / unlocking mechanism and indexing arrangement of the second axis "E" (i.e., the second member 104 and the third member 106 / 106') are substantially the same (but arranged to be perpendicular to the locking / unlocking mechanism and indexing arrangement of the first axis "D"). Accordingly, in this embodiment, the locking / unlocking mechanism, rotating mechanism, and indexing arrangement of the first axis "D" and the second axis "E" have substantially the same parts. For the sake of brevity and clarity, the following description focuses primarily on the first axis "D", but as will be understood, most of the description of the first axis "D" also applies to the second axis "E", and the parts of the second axis "E" that are the same as the first axis "D" are marked in the drawings with the same reference numerals as the first axis "D" but with a prime 'symbol suffix. In this embodiment, the locking / unlocking of the first axis "D" and the second axis "E" can be controlled / actuated independently of each other. In other words, the articulated head can be operated to unlock the first axis "D" but keep the second axis "E" locked, or vice versa. Of course, if desired, the articulated head can still be controlled to unlock the first axis "D" and the second axis "E" together / simultaneously. Moreover, as will be appreciated, other configurations are possible, including those in which the locking / unlocking of the first and second axes cannot be independently controlled / actuated, such as described in EP 2889573 or US7213344.

[0091] The indexing arrangement of the first axis "D" includes an arrangement of interengageable features provided on the first member / mounting plate 102 and the second member 104. In particular, a first annular member 110 having a continuous series of tapered teeth 112 is provided (e.g., see FIG. 1 for a detailed view). Figure 5a and Figure 6 ). The teeth 112 extend substantially radially in that the extent of the teeth extends primarily in a radial direction (relative to the radius of the first annular member; also relative to the first axis "D"). Accordingly, in this embodiment, the first annular member 110 is in the form of a "face spline member" and will be named as such hereinafter (particularly noting that in the described embodiment, the face spline member has the configuration of a Hirth joint member). The teeth of the face spline member 110 are radially elongated and have a generally conical cross-sectional profile (taken perpendicular to its length). In this embodiment, each side 111 of the tooth 112 is substantially flat / planar, but this need not necessarily be the case (for example, they may be curved or crowned, as with the crowned teeth 118 described below).

[0092] The indexing arrangement further includes a second annular member 114 having an engagement feature 117 configured to intermesh with the teeth 112 of the face spline member 110. The second annular member 114 has an engagement feature 117 configured to engage only a subset (i.e., a "proper subset" in a mathematical sense) of the continuous series of teeth provided on the face spline member 110 (see FIG. 1 for a detailed view). Figure 5b and Figure 6 ). Accordingly, instead of providing a continuous series of interengaging teeth for the second annular member 114, the second annular member 114 includes only engagement features 117 configured to intermesh with the teeth 112 of the face spline member 110 at three discrete, equiangularly spaced (120°) locations 116. In this particular embodiment, the engagement features 117 at each of the locations 116 include a single tooth 118, each of which is configured to be located between and engage two adjacent teeth 112 of the face spline member 110. Each tooth 118 is radially elongated and has a generally conical profile (taken perpendicular to its length) and thereby provides two curved engagement side surfaces 120 that are configured to engage the side surfaces 111 of the teeth 112 on the face spline member 110. Because the engagement side surfaces 120 are curved, the teeth 118 can be described as "crown" teeth 118.

[0093] like Figures 7a to 7c As shown, the engaging side surface 120 of the crown tooth 118 is substantially parallel to its length (in this embodiment, along the radial dimension, or along the X-axis, as shown in FIG. Figure 7a and Figure 7c as shown) and in their cross-sectional profiles (taken perpendicular to their length / radial dimension, as Figure 7bThis configuration (i.e., the crown teeth 118 engaging the flat / face teeth 112 on the face spline member 110) ensures that each engaging side surface 120 of the crown teeth 118 presents an apex region 122. It is this apex region 122 that will tend to engage the side surface 111 of the tooth 112 on the face spline member 110. It has been found that providing an apex region will provide a more repeatable seating position between the first annular member / face spline member 110 and the second annular member 114. This is because providing the apex region 112 means that for any given pair of teeth on the first annular member / end face spline member 110 and the second annular member 114, it is significantly more likely that the teeth in the pair will engage at the same area on their side surfaces 111, 120 each time they are brought together (compared to the case where the side surfaces 111, 120 of the teeth on both the first annular member / end face spline member 110 and the second annular member 114 are substantially flat / planar), thereby helping to ensure that the first annular member / end face spline member 110 and the second annular member 114 are positioned together in the same position each time they are brought together at a given angular orientation.

[0094] As will be appreciated, the teeth of the indexing arrangement can be provided by other types of features. For example, the teeth on the second member 104 can include a series of spherical members (e.g., a "ring of balls") extending annularly around the axis of rotation D, and the engagement features 117 can each include a pair of cylindrical members, such as described in WO 2006 / 079794 or US 5185936. However, it has been found that the configuration described in this embodiment provides an excellent kinematic connection between the first annular member / end spline member 110 and the second annular member 114 compared to other configurations. This is especially the case when the indexing increment becomes smaller (e.g., less than 7.5°, particularly less than 5°, such as close to 2.5°). This is because the smaller the indexing increment, the smaller the intermeshing features. Not only may it be difficult to accurately manufacture and assemble a ring of balls with a much smaller diameter, but also due to the very small contact points between the balls with very small diameters and the corresponding cylindrical members, the Hertzian contact pressure will be extremely high, causing them to be subjected to excessive pressure, and this in turn will cause excessive wear and / or failure of the indexing arrangement.

[0095] For example, in the presently described embodiment, the first annular member / face spline member 110 and the second annular member 114 have an outer diameter of 75 mm and are provided with teeth sized to provide 2.5° indexing increments, and the articulated head 100 is configured such that when in the locked position, the first annular member / face spline member 110 and the second annular member 114 will be held together by a force of approximately 120 N (Newtons). The crown teeth are in a plane perpendicular to their length (e.g., in Figure 7bThe radius of curvature R' of the crown tooth in a plane along its length (e.g., in the ZY plane) is 1.8 mm, and Figure 7c The radius of curvature R" (taken in the ZX plane of the embodiment of the present invention) is 23mm. In contrast, if a spherical ball is used instead of a crowned tooth, the ball will have to have a radius of curvature of <0.75mm in order to fit between the teeth 112 of the first annular member / end spline member. Not only will it be difficult to assemble such small balls into the articulated joint, but they will also provide a very small contact point, resulting in extremely high Hertzian contact pressures.

[0096] As will be appreciated, the same effect can be achieved by crowning the teeth 112 on the first annular member / face spline member 110 and providing flat sides for the teeth 118 on the second annular member 114, but this may be more difficult to manufacture. Alternatively, the teeth 112, 118 on both the first annular member / face spline member 110 and the second annular member 114 may be crowned, but with the added difficulty of manufacturing, the tooth size will need to be adjusted (particularly increased) to avoid undesirable Hertzian contact pressures.

[0097] In the above embodiment, the teeth 112 are provided on the annular member 110 which will then be attached to the body 105 / top surface 115 of the second member 104, and the teeth 118 are provided on the annular member 114 which will then be attached to the first member 102. However, this need not necessarily be the case; for example, the teeth 112 may be provided directly on the body 105 / top surface 115 of the second member 104, and / or the teeth 118 may be provided directly on the first member / mounting plate 102.

[0098] The mechanism for locking and unlocking the indexing arrangement of the first axis "D" will now be described. In summary, in the particular embodiment described, the locking / unlocking mechanism relies solely on magnets to provide a retaining force between the first annular member / end spline member 110 and the second annular member 114 having crown teeth 118, and uses a motor-driven actuator to push the first member / mounting plate 102 and the second member 104 away from each other in order to separate the first annular member / end spline member 110 and the second annular member 114 having crown teeth 118. This mechanism will be described in more detail below.

[0099] In the described embodiment, the locking / unlocking mechanism includes a set of three stacked magnets. In particular, a first ring magnet 140 is disposed on the top surface 115 of the housing 105 of the second member 104, a second ring magnet 142 is disposed on the contact plate 134 of the pillar 130 (described in more detail below), and a third magnet 144 is disposed on the first member / mounting plate 102. The first ring magnet 140, the second ring magnet 142, and the third ring magnet 144 are of the same shape and size, are stacked coaxially with each other, and are arranged so that both the first ring magnet 140 and the third ring magnet 144 attract the second magnet 142 sandwiched therebetween. The magnetic poles of the ring magnets are arranged axially (i.e., so that the two magnetic poles are located on the top and bottom of the flat surface of the ring). In particular, the ring magnets are configured so that the north pole of the first magnet 140 faces the south pole of the second magnet 142, and so that the north pole of the second magnet 142 faces the south pole of the third magnet 144. As explained in more detail below, the second member 104 is retained only by magnetic attraction, and in particular only by magnetic attraction between the third magnet 144 , the second magnet 142 , and the first magnet 140 , when in the locked and unlocked positions.

[0100] The locking / unlocking mechanism includes a post 130 including a shaft 132 and a "head" or "contact plate" 134. The shaft 132 of the post 130 is supported within a linear cylindrical bearing housing 107 provided by the top surface 115 member of the housing 105 of the second member 104. Bearings (in this case an array of ball bearings 109) are disposed between the shaft 132 and the cylindrical bearing housing 107 to facilitate relative linear and rotational movement (i.e., along and around the first axis "D") between the shaft 132 and the cylindrical bearing housing 107. The contact plate 134 includes a radially extending surface sandwiched between the body of the first member / mounting plate 102 and the body of the second member 104.

[0101] A motor driven lever 170 is provided to effectuate the described linear / axial movement of the shaft 132 along the first axis "D". The lever 170 is pivotally mounted toward its first end to a flexure 178, which is anchored to the housing 105 of the second member (in this embodiment anchored to the top plate 115) via a mounting block 179. The lever 170 is attached toward its second end to a lead screw mechanism 172, which is configured to raise and lower the second end of the lever 170. The lever is attached to the end of the shaft 132 away from the contact plate 134 via a spool 146 at a point between its first and second ends (which facilitates relative rotation of the shaft 132 and the lever 170). The electric lock motor 190 is configured to drive the lead screw mechanism 172. In particular, the lock motor 190 is configured to drive a first gear 171, which is configured to engage and rotate a second drive gear 173, which rotates the lead screw 174. As the lead screw 174 turns, it causes the nut 176 (which is attached to the lever 170 via the pin 175) to travel axially along the lead screw 174. The lead screw 174 is also anchored to the housing 105 of the second member (in this embodiment, to the cylindrical bearing housing 107) via the mounting bracket 177 and bearing 179, so that the lead screw can rotate about its axis of rotation, but so that the lead screw is fixed in the Z dimension relative to the housing 105 of the second member (e.g., Figure 3 and Figure 4 shown).

[0102] It may be advantageous that the drive mechanism for the support 130 resists back-driving (in other words, it is not easily manually back-driven), especially if the three-magnet design described below is not employed. This is because, if the net external force on the support 130 is low enough, a drive mechanism that is not easily manually back-driven will tend to maintain its position, even when the motor / power supply is not activated. This can avoid the need for a servo drive mechanism / motor to maintain a fixed position, and therefore can reduce the power consumption of the articulated head. Accordingly, this can reduce the heat generated by the drive mechanism / motor, which in turn can improve the metering performance of the articulated head by reducing thermal deformation. A lead screw mechanism with a high gear pitch is an example of a drive mechanism that is not easily back-driven.

[0103] As explained in more detail below, an electric drive motor 192 having a gear arrangement (not shown) is provided that is configured to engage a drive gear 148 disposed on the shaft 132 and drive the drive gear toward the end of the shaft distal from the contact plate 134, and can be operated to rotate / spin the housing 105 of the first member 104 (and everything anchored thereto) about the shaft 132 about a first axis "D". A first (or "primary") rotary encoder device 135 (e.g., a magnetic absolute rotary encoder device) is provided to measure / monitor the relative angular position of the housing 105 of the first member 104 and the shaft 132 about the first axis "D".

[0104] The contact plate 134 of the support and the first member / mounting plate 102 have corresponding engagement elements. In particular, the corresponding engagement elements include features configured such that, when engaged, they provide a repeatable, particularly kinematic, connection between the contact plate 134 of the support and the first member / mounting plate 102. In the described embodiment, the contact plate 134 of the support includes three engagement balls 152 positioned 120° apart from each other, and the first member / mounting plate 102 has three pairs of engagement balls 154, which are positioned 120° apart from each other (see Fig.10b Each pair of engagement balls 154 on the first member / mounting plate 102 defines a channel or recess for receiving one of the engagement balls 152 located on the contact plate 134 .

[0105] Also like Figure 3 and Figure 4 As shown, a second rotary encoder device is provided, which includes an annular scale 162 disposed on the top surface 115 of the housing 105 of the second member 104 and a first readhead 160 and a second readhead 161 ( Figure 4 5). In the described embodiment, the first readhead 160 and the second readhead 161 are annularly spaced 120° from each other. In the described embodiment, the second rotary encoder device is an incremental optical rotary encoder device. In the particular embodiment described, the second encoder device is a high resolution encoder that enables the relative position of the first member / mounting plate 102 and the body 105 of the second member 104 to be established within 10 nm (nanometers). The purpose of this will be described in more detail later in this document.

[0106] The unlocking / reorienting / locking process of the first member / mounting plate 102 and the second member 104 will now be described. Figure 3The first member / mounting plate 102 and the second member 104 are shown in a locked state. In the locked state, the probe 300 mounted on the probe mount 108 can be held in a stable and well-defined angular position so that it can be used to inspect the article during a measurement operation. However, it may be desirable to reorient the probe mounted on the probe mount 108, for example for access reasons. To do this, it will be necessary to unlock the first member / mounting plate 102 and the second member 104, reorient them relative to each other, and then lock them together in the new orientation.

[0107] Unlocking the first member / mounting plate 102 and the second member 104 involves driving the strut 130 axially along the first axis "D" toward the first member / mounting plate 102. In the described embodiment, this is facilitated by the controller 220 sending instructions to the articulating head 100 to operate the lock motor 190 to drive the lead screw 174 to drive the lead screw nut 176 upward in the Z dimension (in Figure 3 and Figure 4 In turn, the lever 170 (which is connected to and thus actuated by the lead screw nut 176) pushes the shaft 132 of the strut upward in the Z dimension (in the Figure 3 and Figure 4 102). After a short distance, the engagement balls 152 on the contact plates 134 of the struts 130 will contact and engage the paired engagement balls 154 on the first member / mounting plate 102, after which continued actuation of the lead screw 174 will cause the lever 170 and lead screw mechanism 172 to push the housing 105 (to which the lead screw 174 is anchored via the cylindrical bearing housing 107) axially downward, thereby causing the housing 105 of the second member 104 to separate from the first member / mounting plate 102. The lead screw 174 is operated to separate the second member 104 and the first member / mounting plate 102 by a controlled, predefined amount that is sufficient to cause the crown teeth 118 to disengage from the teeth 112, but not too much, as explained in more detail below, because it is desired that the first magnet 140 remain close enough to the second magnet so as to have a reasonable amount of pulling force on the second magnet 142 even in the unlocked state. Figure 4 The indexing head 100 is shown in this unlocked state. In this embodiment, the first axis "D" lock motor 190 can be operated independently of the second axis "E" electric lock motor 190' so that the second axis "E" can remain locked while the first axis "D" is unlocked.

[0108] Once the unlocked state has been reached, the lock motor 190 driving the lead screw mechanism 172 is stopped and the first axis "D" drive motor 192 engaged with the drive gear 148 of the shaft 132 is operated to achieve a change in the rotational position of the second member 105 of the articulated head 100. As described above, in the unlocked state, the support 130 is engaged with the first member / mounting plate 102 via the engagement balls 152, 154 and is therefore rotationally fixed relative thereto (in the unlocked state). Accordingly, when the drive motor 192 engaged with the drive gear 148 of the shaft 132 is operated, it causes the entire housing 105, 107, 115 of the second member 104 (and all components anchored thereto, including the above-mentioned motor) to be driven around the shaft 132 and thus causes the entire housing 105, 107, 115 of the second member 104 (and all components anchored thereto) to rotate around the first axis "D".

[0109] The relative rotational position of i) the housing 105, 107, 115 of the second member 104 and ii) the shaft 132 (and hence the first member / mounting plate 102) is known from the first ("master") encoder device 135. Accordingly, the controller 220 can use the output from the first encoder device 135 to control a motor (not shown) engaged with the drive gear 148 of the shaft to bring the first member / mounting plate 102 and the second member 104 to a desired relative orientation. As will be appreciated, the rotational position needs to be controlled with sufficient accuracy so that when in the new desired relative orientation, the crown teeth 118 on the second annular member 114 are opposite the valleys of the teeth 112 on the first annular member / face spline member 110 so that when they are locked together, the crown teeth 118 are perfectly located between two teeth 112 of the first annular member / face spline member 110.

[0110] The process of locking the first member / mounting plate 102 and the second member 104 will now be described. In the described embodiment, this is accomplished as follows: The lock motor 190 is operated to drive the lead screw 174 so as to drive the lead screw nut 176 downward (at Figure 3 and Figure 4102). This will cause the housing 105 of the second member 104 to be pulled upwardly toward the first member / mounting plate 102 until the crown teeth 118 on the second annular member 114 engage the teeth 112 of the face spline member 110, after which continued operation of the lock motor 190 will cause the strut 130 to retract away from the first member / mounting plate 102, thereby disengaging the engagement balls 152, 154 provided on the contact plate 134 and the first member / mounting plate 102. Accordingly, at the disengagement point of the engagement balls 152, 154, the first member / mounting plate 102 and the second member 104 are held via the kinematic constraints provided by the six rigid points between the three crown teeth 118 and the teeth 112 of the first annular member / face spline member 110.

[0111] Will refer to Figures 11a to 11d Describing the manner in which the first magnet 140, the second magnet 142 and the third magnet 144 interact with each other, these figures schematically show the shaft 132 and contact plate 134 of the support, the top plate 115 of the second member, the first member / mounting plate 102, the second annular member 114 (as three crown teeth 118), the first annular member / end spline member 110 (which has a continuous series of teeth 112), and the first ring magnet 140, the second ring magnet 142 and the third ring magnet 144. Fig.11a The first member / mounting plate 102 and the second member 104 are shown in a locked position; that is, when the teeth 112 on the first annular member / face spline member 110 are fully engaged with the teeth 118 on the second annular member 114 . Fig.11b The first member / mounting plate 102 and the second member 104 are shown in a locked position, but at this time the support post 130 has been actuated to the point where the engagement ball 152 on the contact plate 134 has engaged the engagement ball 154 on the first member / mounting plate 102 and is about to begin to separate the teeth 112 on the first annular member / end spline member 110 from the teeth 118 on the second annular member 114. Fig.11c The first member / mounting plate 102 and the second member 104 are shown wherein they have begun to separate, but have not yet reached their fully unlocked configuration. Fig.11d The first member / mounting plate 102 and the second member 104 are shown in an unlocked position, at which time the teeth 112 on the first annular member / end spline member 110 and the teeth 118 on the second annular member 114 are completely disengaged from each other, so that the housings 105 of the first member / mounting plate 102 and the second member 104 are free to rotate relative to each other about the first axis "D".

[0112] exist Fig.11aIn the configuration shown, the third magnet 144 is attracted to both the second magnet 142 and the third magnet 144, thereby pulling the first member / mounting plate 102 toward the pillar 130 and the housing 105 of the second member 104. In the described embodiment, the device is configured so that there is a total locking force of about 120N between the first member / mounting plate 102 and the second member 104 when in the locked position (this provides a starting torque of 2Nm in combination with appropriate head size, particularly the indexing arrangement and the diameter and position of the ring magnet). As will be understood, the starting torque is the moment that can be applied before the first body and the second body begin to peel off from each other. This may be important because the hinge joint is often subjected to eccentric loading. As will also be understood, the starting torque is related to factors other than the retention / holding / locking force, such as the diameter of the end spline member 110 or the diameter of this circle of engagement balls 152, 154.

[0113] To transition to the unlocked state, the post 130 needs to move towards the first member / mounting plate 102. While it would appear that the presence of the first magnet 140 would, at least initially, increase the work required by the lock motor 190 to do this (compared to the absence of the first magnet), it should be noted that the device is configured so that in Fig.11a In the locked state shown, the contact plate 134 of the pillar is held in a predetermined position, which places the second magnet 142 between the first magnet 140 and the third magnet 144. This ensures that the pull of the first magnet 140 on the second magnet 142 is significantly less than when they are in contact with each other. Moreover, the third magnet 144 has a certain degree of magnetic pull on the second magnet 142. Accordingly, the work / power required to move the second magnet (and therefore the contact plate 134) away from the first magnet 140 is significantly less than when the first magnet 140 and the second magnet 142 are in contact.

[0114] In particular, in the described and illustrated embodiment, the contact plate 134 of the pillar is held in a predetermined position, which places the second magnet 142 approximately midway between the first magnet 140 and the third magnet 144, but places the second magnet 142 slightly closer to the first magnet 140 than the third magnet 144. This means that the magnetic forces exerted on the second magnet by the first magnet 140 and the third magnet 144 are almost (but not completely) balanced. Accordingly, the lock motor 190 requires very little work / power to move the pillar 130 toward the first member / mounting plate 102. In fact, once the second magnet 142 has reached the midpoint between the first magnet 140 and the third magnet 144, the magnetic pull of the third magnet 144 on the second magnet 142 will be greater than the magnetic pull of the first magnet 140. As the contact plate 134 advances toward the first member / mounting plate 102, the magnetic pull of the third magnet 144 on the second magnet 142 gradually increases.

[0115] When the support 130 has moved to Fig.11b In the configuration shown, the lock motor 190 must then pull the teeth 118 on the body 105 / 115 of the second member 104 away from the teeth 112 on the first member / mounting plate 102. Although there is now a sufficient holding / retaining force (at least 160N) to hold the second member 104 on the first member / mounting plate 102 (via the engagement balls 152, 154), the lock motor 190 needs to apply less than this holding / retaining force because now only enough force (about 95N in this embodiment) needs to be applied to overcome the attraction of the first magnet 140 pulling the second magnet 142 and the third magnet 144.

[0116] The lock motor 190 continues to drive the strut 130 until the housing 105 of the second member 104 has moved away from the first member / mounting plate 102 by an amount sufficient to disengage the teeth 112 of the first annular member 110 from the teeth 118 on the second annular member 114, as shown in FIG. Fig.11d At this point, the holding force holding the support 130 and the housing 105 of the second member 104 to the first member / mounting plate 102 is about 160N. By controlling the gaps between the first magnet 140, the second magnet 142, and the third magnet 144, Fig.11a In comparison, Fig.11d The configuration shown achieves a higher holding force. In particular, despite Fig.11d In the unlocked state, there is a relatively large gap between the first magnet 140 and the second magnet 142, but there is a relatively small gap between the second magnet 142 and the third magnet 144 (compared to the Fig.11a In the locked state, the gap between the first magnet 140 and the second magnet 142 is compared), thereby achieving a higher total holding force. A higher total holding force is expected in the unlocked position because the diameter S of the ring of engagement balls 152, 154 is smaller than the diameter S' of the first annular member 110 and the second annular member 114, which means that they need a higher pulling force / holding force to ensure the same or similar starting torque of about 2Nm (Newton meters).

[0117] When in Fig.11dIn the unlocked state shown, the first member 102 and the second member 104 can be relatively rotated about the D axis to a new relative rotational position / orientation. As described above, this involves driving the drive motor 192 (not shown) that drives the drive gear 148 that engages the shaft to rotate the body 105 of the second member 104 about the shaft 132. The output of the first encoder device 135 is used to measure / monitor the relative position of the body 105 of the second member 104 and the shaft 132 (and therefore the first member / contact plate 102, which is fixed in rotational orientation about D). When the output of the first encoder device 135 indicates that the body 105 of the second member 104 is now in the desired indexing position, the drive motor 192 stops, and the first member 102 and the second member 104 are locked together, as described below.

[0118] In order to lock the first member 102 and the second member 104 in their new rotational position / orientation, the lock motor 190 is operated to drive the lead screw mechanism 172 so as to drive the lead screw nut 176 downward along the lead screw 174. This initially causes the housing 105 of the second member 104 to be pulled up toward the first member / mounting plate 102. As will be appreciated, the lock motor 190 requires very little power because the housing 105 of the second member 104 has already been pulled toward the first member / mounting plate 102 by the first magnet 140, the second magnet 142, and the third magnet 144. This continues until the teeth 112 of the first annular member 110 engage the teeth 118 of the second annular member 114 ( Fig.11b As shown in FIG. 1 , the lock motor 190 and the lead screw mechanism 172 must begin to push against the magnetic force to separate the contact plate 134 of the pillar from the first member / mounting plate 102. However, at this time, the first magnet 140 is much closer to the second magnet 142, so the first magnet exerts a relatively large force on the second magnet. In fact, at this time Fig.11b The net force on the second magnet 142 in the state shown is only 95 N. Accordingly, the lock motor 190 and the lead screw mechanism 172 are assisted by the magnets and can much more easily pull the second magnet 142 (and therefore the support post 130) away from the third magnet 144 (and therefore away from the first member / mounting plate 102) until the contact plate 134 reaches Fig.11a Predetermined axial position / Z position shown.

[0119] From the output of the first rotary encoder 135, it is known what indexed rotational position the first member / mounting plate 102 and the second member 104 are in. It may also be useful to check that the first member / mounting plate 102 and the second member 104 have been properly locked together. This can be achieved in various ways, such as by using one or more sensors that can check the spacing between the opposing faces of the first member / mounting plate 102 and the second body 105, and if the spacing is greater than a fixed threshold amount (which is the same for all indexed positions), corrective measures can be taken (for example, an error / warning can be reported and / or measures can be taken to try to correct the problem, such as by trying an unlocking operation / relocking operation, such as from a different position / direction, and / or requiring recalibration).

[0120] In the present embodiment described, the second rotary encoder device is configured to measure and provide information about the relative spatial configuration of the first and second bodies in their locked state. In particular, the outputs of the first and second readheads 160, 161 of the second rotary encoder device are used to ensure that the first member / mounting plate 102 and the second member 104 have been properly locked together. In particular, when locked, the outputs of the first and second readheads 160, 161 are transmitted to the electronics 400 within the readheads, which include, for example, a processing device 402 (such as a CPU (central processing unit), FPGA (field programmable gate array) or ASIC (application-specific integrated circuit) and the like) and a memory 404. The processing device 402 compares the values ​​received from the first and second readheads 160, 161 with the values ​​stored in the lookup table located in the memory 404. In particular, the processing device 402 compares the outputs of the first and second readheads 160, 161 to determine whether their outputs are substantially the same as those values ​​stored in the lookup table elements associated with a particular indexing position. If the output of either or both of the first readhead 160 or the second readhead 161 differs significantly from the value stored in the lookup table (e.g., the difference is greater than 100 nm), this may indicate that a problem has occurred; in particular, the teeth 112 / 118 of the first member / mounting plate 102 and the second body 105 are not properly locked together / engaged with each other, and are therefore not seated in substantially the same position as when the value stored in the lookup table associated with that particular indexing position was obtained. This may be because, for example: the teeth 112 / 118 have been knocked out; there is debris between the teeth 112 / 118; there is excessive wear between the teeth / 118, etc. Accordingly, the device (e.g., a controller) may then take corrective action in this situation. Such corrective action may include: unlocking and re-locking the first member / mounting plate 102 and the second body 105; outputting a warning signal to an operator and / or other processes; stopping the current operation, etc.

[0121] As described above, the second rotary encoder device is an incremental encoder device. Therefore, the outputs of the first readhead 160 and the second readhead 161 do not include any absolute position information. Accordingly, rather than comparing absolute position information, the processor 402 compares relative (position) data / information. In particular, for example, as will be appreciated by those skilled in the art of position measurement encoders, the scale of an incremental position encoder typically comprises an array of regularly spaced features arranged at a particular pitch or "period" (which in the described embodiment is 20 μm, but as will be appreciated, scales with other periods may be used). The readhead may read these features (e.g. optically, magnetically, inductively, depending on the technology used), and the readhead or its output is typically used to "calculate" the relative position of the readhead and the scale as they move relative to each other. It is also well known that the signals received by and / or output by the readhead may be interpolated to provide a measurement of the relative position of the readhead and the scale at a resolution much finer than the actual period of the scale. Such interpolated readings are typically referred to as "phase" readings. For example, typically, quadrature (e.g., SIN and COS) signals are generated from the scale signals and / or output by the readhead. Such quadrature (e.g., SIN and COS) signals may be interpolated to provide such "phase" readings. In the described embodiment, the processor 402 uses the interpolated or "phase" readings and compares them to pre-stored "phase" readings stored in a lookup table element associated with a particular value.

[0122] Accordingly, as the first 104 member / mounting plate 102 and the second body 105 move relative to each other as the indexing position changes, it is not necessary for the first readhead 160 or the second readhead 161 to read the scale 162 (although this may be done if the configuration permits). Rather, when the locking operation has been completed, the first readhead 160 and the second readhead 161 may take and output a single reading, and an interpolated or "phase" value of these readings may be compared to pre-stored "phase" readings stored in a lookup table element associated with a particular value. If one or both of the phase readings differ by more than a predetermined amount (e.g., 100 nm as per the above example), corrective action may be taken as described above.

[0123] Accordingly, the data elements in the lookup table may be said to be a "phase-signature" for each calibration index position, and if the values ​​of the phase readings of the first readhead 160 and the second readhead (not shown) differ sufficiently from the phase signature in the lookup table for a given index position, corrective action may be taken.

[0124] Prior to carrying out a measurement operation using the articulating head 100, the look-up table is populated (e.g. it may be populated during a calibration procedure). This may include the steps of locking the first 104 member / mounting plate 102 and the second body 105 in a given indexed position relative to each other and recording / storing the phase readings of the first readhead 160 and the second readhead (not shown) in the element / data cell associated with the given indexed position. This step is then repeated for each of the indexed positions of the articulating head (or at least for the indexed positions for which the head is to be used and for which such verification is desired).

[0125] Optionally, the lookup table may be updated over time to allow for a small degree of drift over time. This may occur continuously or periodically. This may be done as part of a dedicated calibration process, or may be done during a measurement operation. For example, each time the first member / mounting plate 102 and the second body 105 are successfully locked together at any given indexed position (e.g., they pass the 100 nm test described above), the phase readings output by the first readhead 160 and the second readhead (not shown) may replace the previous values ​​stored in the lookup table.

[0126] As will be appreciated, the lookup table may be replaced by a function describing the values ​​in the lookup table if desired. However, a lookup table may be preferred because it is easy to generate and because it is easy to keep up to date.

[0127] As will be appreciated, in addition to two readheads, a single readhead may be used, or more than two readheads may be used. The multiple readheads need not be placed 120° apart from each other around the scale 162. However, it has been found that providing multiple readheads that are not completely opposite each other (i.e. not 180° apart) is particularly advantageous because it can provide information about the spatial configuration of the first member / mounting plate 102 and the second body 105 in multiple dimensions. On the one hand, for reasons of efficiency and optimal performance, it may be preferred to arrange them substantially / approximately 90° apart from each other around the first axis, but for reasons discussed above, it may also be preferred to place them substantially on the same radial line as the engagement teeth 118 for different reasons. Accordingly, depending on the circumstances, when the engagement teeth are not 90° apart from each other (such as in the described embodiment, where they are placed 120° apart from each other), the benefits of placing each of the readheads on the same radial line as the corresponding engagement tooth may outweigh the benefits of placing the readheads 90° apart from each other.

[0128] The second rotary encoder device described above is an incremental encoder, but as will be appreciated it could be replaced by an absolute encoder device.

[0129] In the present embodiment described, the first readhead 160 (and optional second readhead 161) may be referred to as a "verification" sensor as it is used to check / verify that the first member / mounting plate 102 and the second body 105 have been properly locked together.

[0130] In the above-described embodiment, an optical rotary encoder device is used to determine the spatial configuration of the first member 102 and the second member 104 when they are in their locked state. However, this need not necessarily be the case. Other types of non-contact sensors may be used, such as a position sensitive device (PSD) mounted on the first member 102, the output of which is related to the relative spatial position of the first member / mounting plate 102 and the second body 105 when they are locked together. In this case, a lookup table may be filled during the calibration phase to record the PSD output for each indexing position of interest (e.g., which may be all indexing positions or only those indexing positions intended to be used during subsequent measurement operations). Subsequently, in use, when the first member / mounting plate 102 and the second body 105 are locked in a particular indexing position, the PSD may provide an output to the processor 402, which is then compared with the value stored in a particular element of the lookup table associated with the particular indexing position stored in the memory 404. If the output of the PSD differs by more than a threshold amount, corrective action may be taken.

[0131] In an alternative embodiment, the (so called "verification") contactless sensor is configured to measure only the relative height / separation of the first and second bodies (e.g. via a capacitive sensor, or an inductive sensor as explained in more detail below in conjunction with FIG. 23). Advantageously, when the first and second bodies are locked together, the output of the height sensor is compared with a pre-stored value in an element of the lookup table associated with a particular indexed position when the first and second bodies are locked together.

[0132] As will be appreciated, further variations and alternative embodiments of the above-described articulated joint are possible. For example, one or two of the first magnet 140, the second magnet 142 and the third magnet 144 may be replaced with a magnetically attractable (e.g. ferrous) material. This would provide a similar (albeit weaker) effect to that when three magnets are provided. Accordingly, the remaining one or two magnets would need to be stronger and therefore larger, which may also (depending on the configuration) mean that a greater peak motor force is required.

[0133] In another similar embodiment, the first magnet 140 is located elsewhere. For example, the first magnet 140 can be located at / towards the end of the shaft 132 away from the contact plate 134. Again, this will provide a similar effect in assisting the lock motor 190 during the locking / unlocking process, but because the first magnet 140 is located away from the first member / mounting plate 102, it will provide little holding force (if any), so it is necessary to provide a larger / stronger second magnet 142 and / or third magnet 144.

[0134] Fig.12 An alternative embodiment is schematically illustrated in which the first magnet 140 is omitted so that the second member 104 is magnetically retained on the first member / mounting plate 102 by only a pair of magnets (i.e., a third magnet 144 disposed on the first member / mounting plate 102 and a second magnet 142 disposed on the contact plate 134 of the pillar 132). While this is possible, the second magnet 142 and the third magnet 144 themselves need to provide all of the locking / holding force, so either or both of them would need to be much stronger than the above-described three magnet arrangement, which in turn would require the lock motor 190 to be pulled during the locking process when the contact plate 134 of the pillar is to be pulled away from the first member / mounting plate 102 (i.e., when the contact plate 134 of the pillar is to be pulled away from the first member / mounting plate 102). Fig.11b Transform to Fig.11a Also, without the first magnet 140, all of the forces holding the housing 105 of the second member 104 to the first member / mounting plate 102 must be carried by the struts 130, levers 170 and lead screw mechanisms 172 and associated bearings. This would require these parts to be larger / stronger and would ideally require a motor that prevents back-driving.

[0135] Fig.13 Another alternative embodiment is shown in which the third magnet 144 is omitted, so that the second member 104 is magnetically retained on the first member / mounting plate 102 by only a pair of magnets (i.e., a first magnet 140 disposed on the top plate 115 of the housing and a second magnet 142 disposed on the contact plate 134 of the pillar). In this case, the first member / mounting plate 102 (at least a portion thereof) must be made of a material that can be attracted by magnets (e.g., a ferrous material). A disadvantage of this embodiment is that the holding / retaining and starting torques are lower than if the third magnet is present (thus, if the same holding / retaining and starting torques are desired, a larger / stronger first magnet 140 and / or second magnet 142 is required).

[0136] Fig.14Another alternative embodiment is shown in which the second magnet 144 is omitted, so that the second member 104 is magnetically retained on the first member / mounting plate 102 by only a pair of magnets (i.e., a first magnet 140 disposed on the top plate 115 of the housing and a third magnet 144 disposed on the first member / mounting plate 102). A disadvantage of this embodiment is that the holding / retention and starting torques are lower than if the second magnet is present (thus, if the same holding / retention and starting torques are desired, a larger / stronger first magnet 140 and / or third magnet 144 are required). In this embodiment, the contact plate 134 can include a material that can be attracted to the magnet (e.g., a ferrous material) to assist in magnetic retention, but this is not as good as a contact plate 134 that includes a magnet.

[0137] Fig.15 Another alternative embodiment is shown. In this embodiment, it is shown that the magnets do not have to be stacked directly in line with each other. For example, Fig.15 Alternative positions for the first magnet 140 and / or the third magnet 144 140 are shown (eg, they may be located radially further away than the second magnet 142 ).

[0138] The magnets may also be used in an arrangement that repels each other in order to provide the necessary locking / holding force.

[0139] However, it has been found that the described Figure 1 to Figure 1 It may be advantageous for an embodiment of 1 to have an arrangement of at least three stacked magnets in an in-line arrangement (all arranged to attract each other). In particular, it has been found that this significantly reduces the work required of the lock motor 190 to control the linear position of the strut 130 when it is in its locked state, and may help reduce the peak work required of the lock motor 190 during the locking action. This may not only reduce the size of the lock motor 190 required and help keep the articulated head compact and lightweight, but may also reduce the heat output of the lock motor 190 (which in turn may improve the metering performance of the articulated head by reducing / avoiding thermal deformation). In fact, when Figure 1 to Figure 1 1 embodiment can be configured to provide 120N of pulling force when locked and 160N when unlocked (to provide a starting torque of 2Nm), and due to the three stacked magnets in a straight line, the lock motor 190 only needs to generate a peak force of 95N.

[0140] Fig.16 It is a display Figure 3 , Figure 4 and a graph of the support force and the holding force of the three magnet embodiment of FIG. 11 , Fig.17 It is a display Fig.12Graphs of the strut force and holding force for an embodiment of two magnets (identical in all respects except that the first magnet 140 is omitted). The holding force (also referred to above as the "holding force" or "locking force") is the net force pulling the first member 102 and the second member 104 together. The strut force is the net magnetic force experienced / applied to the strut 130. Accordingly, this is the magnetic force that must be overcome in order to hold the strut 130 in place. This force can be overcome by a combination of the force applied to the strut by the lock motor 190 and any friction in the gearing / motor / strut system (as will be appreciated, if friction in the gearing / motor / strut system is excluded, the strut force is proportional to the work required by the lock motor 190; for example, proportional to the motor current).

[0141] like Fig.16 As shown, when the first member / mounting plate 102 and the second member 104 are in their locked state, the strut force is very low (less than 10N). Accordingly, the force required to hold the strut 130 in place is low. In fact, it is so low that, depending on the gearing / motor / strut system, the friction force may be sufficient to hold the strut 130 in place (for example, if it is very resistant to backdrive). Accordingly, little or even no motor power is required to hold the strut 130 in place. In addition, as described above, Figure 1 to Figure 1 1 is arranged so that in the locked position, the post 130 is positioned so that the magnetic force biasing the second magnet 142 toward the first magnet 140 is greater than the magnetic force biasing the second magnet 142 toward the third magnet 144. Accordingly, even if the lock motor 190 that controls the linear position of the post 130 is turned off, and even if the friction force is insufficient to resist the magnetic bias to hold the post 130 in place, all that will occur is that the post 130 will be further retracted until the contact plate 134 abuts the housing top surface 115, which will not adversely affect the engagement of the teeth 112, 118 of the first member / mounting plate 102 and the second member 104.

[0142] This is similar to Fig.12 The support forces experienced by support 130 in the two magnet embodiments are contrasted. Fig.17 As shown, when in the locked state ( Fig.12104). When the lock motor 190 is in the locked position, there is a significant net magnetic force (approximately 110N) biasing the second magnet 142 toward the third magnet 144. Accordingly, in the locked position, the lock motor 190 requires significant work / power to hold the pillar 130 in place. In fact, the pillar force is so large that even the friction of the lead screw mechanism, which is very resistant to backdrive, is insufficient to overcome the pillar force, so if the lock motor 190 is powered off, the pillar 130 will creep toward the first member / mounting plate 102 until they are in contact, which will then interfere with the engagement of the teeth 112, 118 of the first member / mounting plate 102 and the second member 104.

[0143] As from Fig.16 and Fig.17 As can be seen from the graph in FIG. 1 , the three magnet embodiment has some disadvantages because there is a significant post force when the post 130 and the first member / mounting plate 102 are engaged. Accordingly, significant motor work / power is required to push the post force in order to separate the first member / mounting plate 102 from the second body 104 (e.g., in FIG. 1 ). Fig.11b and Fig.11d The first member / mounting plate 102 and the second body 104 are also held in their unlocked states (e.g., Fig.11d In contrast, for Fig.12 In the two magnet embodiment, the post force is zero, so once the post 130 and the first member / mounting plate 102 have been engaged, very little motor work / power is required to separate the first member / mounting plate 102 from the second body 104.

[0144] However, under normal circumstances, the amount of time the articulated head spends in its unlocked state is significantly less than the amount of time the articulated head spends in its locked state, so the benefit of the three magnet embodiment requiring significantly less (or even zero) motor power in the locked state outweighs the cost of having to work harder in the unlocked state.

[0145] Figure 1 to Figure 1The three magnet embodiment of 1 also has the following benefits: the peak motor work / power required by the lock motor 190 is less than the two magnet embodiment. In the two magnet embodiment, the greatest amount of work required by the lock motor 190 occurs when it re-locks the first member / mounting plate 102 and the second body 104, and in particular, the peak motor work / power is required when the teeth 112, 118 of the first member / mounting plate 102 and the second body 104 are engaged and the lock motor 190 attempts to separate the contact plate 134 of the pillar from the first member / mounting plate 102. At this time, the lock motor 190 must overcome the attractive pull of the second magnet 142 and the third magnet 144 all by itself (and overcome any friction in the gearing / motor / pillar system), so a force greater than 150N needs to be applied. In contrast, for the three magnet embodiment, during the locking operation, when the teeth 112, 118 of the first member / mounting plate 102 and the second body 104 are engaged and the lock motor 190 attempts to separate the contact plate 134 of the post from the first member / mounting plate 102 (i.e., when Fig.11b ), the first magnet 140 and the second magnet 142 are closer together (compared to when they are Fig.11d 140 is sufficiently close to the second magnet 142 to exert a significant amount of pulling force on the second magnet 142 and thus assist the lock motor 190 in separating the contact plate 134 of the pillar from the first member / mounting plate 102. This allows the lock motor 190 to apply only about 95N to achieve such separation (see Fig.16 point A).

[0146] As will be appreciated, alternative means may be provided to retain the first member / mounting plate 102 and the second member 104 and / or to retain the third member 106 / 106' and the second member 104. For example, a mechanical spring may be used to draw the housing 105 of the second member 104 and the first member / mounting plate 102 together, and / or a mechanical spring may be used to draw the third member 106 / 106' and the second member 104 together. In another embodiment, one or more mechanical levers (such as those described in US 7213344) may be used to draw the housing 105 of the second member 104 and the first member / mounting plate 102 together (i.e., to enable locking / unlocking of the axis D), and / or a mechanical lever (again, such as those described in US 7213344) may be used to draw the third member 106 / 106' and the housing 105 of the second member 104 together (i.e., to enable locking / unlocking of the axis E). However, it has been found that magnets are preferred over such mechanical solutions due to possible hysteresis issues caused by friction (magnets can avoid the need for any moving parts between the first member / mounting plate 102 and the second member 104 and / or between the third member 106 / 106' and the second member 104).

[0147] Advantageously, the above described embodiments rely on the use of ring magnets. It is possible that one or more of the ring magnets could be replaced by a disk magnet, but, somewhat counterintuitively, the inventors have found that ring magnets have a substantially different force / distance profile than disk magnets, which is significantly advantageous in the present case (particularly as ring magnets appear to provide a more efficient design for a given surface area than disk magnets). In fact, it has been found that in this configuration, the ring magnet can provide significantly greater force (approximately 50% more) than a disk magnet of the same outer diameter and depth (measured orthogonally to the diameter of the ring). Fig.18 is a graph showing the strut force and detent torque of an embodiment of two disk magnets, which is similar in all respects to the embodiment of the present invention except that the second magnet 142 and the third magnet 144 are disk magnets instead of rings (wherein the outer diameter of the disk magnet is the same as the outer diameter of the ring magnet). Fig.12 As shown, the strut force and critically the starting torque are significantly less than in the equivalent ring magnet embodiment.

[0148] This discovery enables them to provide very high holding / locking forces for articulated joints, which in turn enables the articulated joint to withstand higher loads / higher moments before the magnetic coupling fails. For example, it may be desirable to carry very heavy probes (such as camera / video probes) and / or it may be desirable to carry very long styluses that provide large moments on the magnetic coupling, especially during detection. In the past, the need for such large forces forced designers of articulated joints suitable for carrying large loads / moments to abandon the use of magnets. For example, the articulated joints disclosed in US 7263780 and US 9494403 use mechanical rods to provide locking forces. However, the inventors have found that the use of ring magnets can provide appropriately large holding loads without the need for physically larger magnets, and can therefore be appropriately assembled into an articulated joint to be mounted on a positioning device (such as a CMM).

[0149] As an alternative to a continuous ring magnet, a series of small disk magnets arranged in a ring shape may offer advantages over a single disk magnet having the same diameter as the ring shape, but it has been found that a continuous ring provides the most efficient design (for a given surface area).

[0150] As described above, the face teeth 112 of the first annular member / face spline member 110 and the crown teeth 118 of the second annular member 114 provide stable and repeatable positioning of the first member / mounting plate 102 and the second member 104. When in the locked state, the only physical / mechanical constraint between the first member / face spline member 102 and the second member 104 is the contact point between the face teeth 112 of the first annular member / face spline member 110 and the crown teeth 118 of the second annular member 114. The particular advantage of this configuration is that at each indexing position, the second member 104 is constrained in all six degrees of freedom relative to the first member / mounting plate 102 by the six contact points provided by the crown teeth 118 of the second annular member 114 and the face teeth 112 of the first annular member / face spline member 110, thereby providing a kinematic constraint. This is true for each possible indexing position. This provides maximum position repeatability for the probe 300 mounted on the articulated head 100 at each indexing position. It is also advantageous that the face spline member 110 and the second annular member 114 have a dual function as indexing elements and retaining elements.

[0151] If you can Figure 3 , Figure 4 and Fig.24 As seen in FIG. 1 , a safety catch 136 or "pin" is provided. The safety catch 136 is provided merely to act as a safety mechanism to prevent the first member 102 from completely disengaging from the second member 104 when the magnetic retention mechanism fails (e.g., due to overloading of the second member 104, such as due to a collision). One end of the safety catch 136 is fixed to the contact plate 134 of the pillar, and the other "head" end is loosely located within a gap 138 in the first member / mounting plate 102. Because it is loosely located within the gap in the first member / mounting plate 102, it does not act as a constraint between the first member / mounting plate 102 and the pillar 130 / second member 104 (and therefore does not interfere with the above-mentioned kinematic connection between the first member / mounting plate 102 and the second member 104 when in the locked configuration, nor does it interfere with the kinematic connection between the first member / mounting plate 102 and the pillar 130 when in the unlocked configuration). However, the safety catch 136 has an enlarged head member 137 which will engage a lug 139 in the gap in the event of a failure of the magnetic coupling between the second and third magnetic rings 142 , 144 , thereby preventing further separation of the first and second members / mounting plate 102 , 104 .

[0152] In the above described embodiment, the face spline member 110 is provided on the second member 104 of the hinge head and the crown teeth 118 are provided on the first member / mounting plate 102. However, this need not necessarily be the case and they may be provided in the opposite manner.

[0153] In the above-described embodiment, the first member / mounting plate 102 and the second member 104 are magnetically retained via the arrangement of magnets, which means that there is no need to use a mechanical device (e.g., an arm / lever) to pull and hold the first member / mounting plate 102 and the second member 104 together. Accordingly, when in a locked state, the only mechanical constraint between the first member / mounting plate 102 and the second member 104 is provided by the teeth of the face spline member 110 and the teeth of the second annular member 114. Therefore, when in a locked configuration, the pillar 130 is decoupled from the first member / mounting plate 102 so that the pillar 130 does not interfere with the above-mentioned kinematic connection of the first member / mounting plate 102 and the second member 104. However, this need not necessarily be the case. For example, in other embodiments, a mechanical push / pull lever arm mechanism may be provided, wherein one end of the arm is encapsulated in a bearing of the first member / mounting plate 102, and the other end of the arm is encapsulated in a bearing of the second member 104.

[0154] According to the present invention, the first readhead 160 and the second readhead 161 are provided on the first member 102; i.e. on the member having the crown teeth 118 located at three discrete, annularly spaced positions about the axis of rotation. This has been found to be particularly advantageous and, as explained in the following paragraphs, can help to improve the reliability of the information provided by the first and second readheads 160, 161.

[0155] The original design of the articulated head had non-contact ("verification") sensors (e.g., first readhead 160 and second readhead 161) disposed on the second member 104, i.e., on the member provided with the continuous series of tapered teeth. However, a problem was found in that the relationship between the position information provided by the first readhead 160 and second readhead 161 and the actual relative spatial configuration of the first member 102 and second member 104 was found to be affected by temperature variations. In other words, even if the teeth 112 / 118 of the first member / mounting plate 102 and second body 105 were in fact already in substantially the same position as when the value associated with the indexed position stored in the look-up table was obtained, if the current temperature of the articulated head is different from the temperature at the time the value associated with the indexed position stored in the look-up table was obtained, it was found that the readings provided by the first readhead 102 and / or second readhead 104 indicated that the teeth 112 / 118 of the first member / mounting plate 102 and second body 105 were not in substantially the same position as when the value associated with the indexed position stored in the look-up table was obtained. Furthermore, it has been found that such temperature-related effects are difficult to predict and vary in particular from one index position to another. Such adverse information from the readheads 102, 104 may result in two problems: i) the aforementioned "corrective action" being taken unnecessarily, and ii) "corrective action" being taken when it should be (e.g. because the teeth 112 / 118 are not actually seated correctly, so they are seated in different relative positions, but thermal effects offset this difference).

[0156] The inventors have found that the unpredictability of the temperature related effects described above can be significantly reduced if the readheads are instead provided on a component having engagement features 117 located at discrete, annularly spaced locations 116. This is believed to be because the positional relationship of the first readhead 160 (and second readhead 161) and the engagement features 117 on the first component 102 is the same regardless of the indexing position and therefore any temperature related effects can be repeatable and can therefore be calibrated / error mapped.

[0157] Furthermore, the inventors have discovered that the temperature-dependent effects described above can be substantially eliminated by placing the readhead on the same radial line as one of the engagement features 117 on the first member 102, or on a radial line close to the radial line on which one of the engagement features 117 is located. The presently described embodiment is configured such that the first readhead 160 is located on the same radial line 119 as one of the engagement features 117 of the first member 102, and the second readhead 161 is located on the same radial line 121 as another engagement feature 117 of the first member 102. This is in Figures 19 to 21 is most clearly shown in .

[0158] As will be appreciated, what is important here is the location of the sensing window / area of ​​the readhead relative to the radial line 119 / 121 where the engagement feature 117 lies. Fig.22a and Figure 22b , shows different first optical embodiments 160a and second optical embodiments 160b of the first reading head 160, wherein their sensors 163a / 163b and optical components 165a / 165b for forming optical signals on the sensors are schematically shown (these optical components may include, for example, one or more lenses and / or diffraction gratings). Fig.22a As shown, the sensor 163a of the read head 160a is positioned so that it is located on the same radial line 119 as one of the engagement features 117 on the first member 102. Figure 22b As shown, the read head 160b is nominally Fig.22a The readheads 160a, 160b are optically identical except that a mirror 169 is used to fold the optical scheme so that the sensor 163b is positioned to the side, which may be advantageous in minimising the height of the readhead, but results in the sensor 163b being positioned further away from the radial line 119 of the engagement feature 117. However, the effect of any temperature variation on their readings will be substantially the same because the angle between i) the radial line on which their sensing windows / areas 167a, 167b lie and ii) the radial line on which the teeth 118 lie is the same (and in the embodiment shown, this angle is substantially 0° and so the readings of both readheads 160a, 160b will be substantially unaffected by any temperature variation).

[0159] While optimal performance may be achieved by positioning the sensing windows / areas of the readhead on the same radial line as the radial line 119 / 121 where the engagement features 117 are located (i.e. such that the angle between i) the radial line where their sensing windows / areas 167a, 167b are located and ii) the radial line where the engagement features 117 are located is 0°), this need not necessarily be the case. As discussed above, there are benefits to mounting the readhead on a component (in this embodiment, component 102) having engagement features 117 located at discrete, annularly spaced locations, regardless of the position of the readhead relative to the engagement features 117. However, it has been found that the closer the sensing window 167 of the readhead is to the radial line 119 / 121 where the engagement features 117 are located, the less the temperature-related effects described above are. In particular, the inventors believe that positioning the readhead so that its sensing window 167 is located on a radial line that is within + / - 15° of the radial line 119 / 121 of the nearest engagement feature 117 (e.g., 0°). Fig.21The above temperature dependent effects should be sufficiently minimized (e.g. to the extent that any calibration / error mapping of temperature dependent effects will be unnecessary) as the sensing window 167 of the readhead is closer to the radial line 119 / 121 of the engagement feature 117, the magnitude of the above temperature dependent effects decreases, and it may therefore be particularly preferred that the angle between i) the radial line where the sensing window 167 of the readhead is located and ii) the radial line 119 / 121 where the engagement feature 117 is located is no greater than + / -5°, more preferably no greater than + / -1°.

[0160] In the above described embodiment, the first readhead 160 and the second readhead 161 are both arranged such that the angle between i) the radial line where its sensing window 167 lies and ii) the radial line 119 / 121 where its nearest engagement feature 117 lies is the same for both readheads (and in particular is 0° for both readheads), but as will be appreciated this need not necessarily be the case. For example, one of the readheads may be arranged such that the angle between i) the radial line where its sensing window 167 lies and ii) the radial line 119 / 121 where its nearest engagement feature 117 lies is 0°, while the other readhead may be arranged such that the angle between i) the radial line where its sensing window 167 lies and ii) the radial line 119 / 121 where its nearest engagement feature 117 lies is 5°.

[0161] Furthermore, as will be appreciated (and as mentioned above), it is not necessary to provide two read heads; one read head is sufficient, but two read heads may be advantageous.

[0162] In the above-described embodiment, the engagement feature 117 at each of the positions 116 includes only a single tooth 118 (and accordingly, the radial lines 119 / 121 of the engagement feature 117 can be the same as the radial lines of such a single tooth 118). However, this need not be the case, and the engagement feature 117 can include, for example, a plurality of teeth, in other words, a "set" of teeth, such as two teeth, three teeth, or four teeth. This can help distribute the load between the first member 102 and the second member 104 at each engagement position, but this may impair the repeatability of the connection. The teeth in a set of teeth of the engagement feature 117 can be arranged to engage the continuous teeth 112 of the face spline member 110, or they can be spaced apart to engage the non-continuous teeth 112. In those embodiments where the engagement feature 117 includes two teeth, the two teeth can be configured to engage opposite sides of the same tooth 112 on the second member 104.

[0163] Where the engagement feature 117 comprises a set of teeth, the radial line of the engagement feature may comprise a radial line falling midway between the first tooth and the last tooth in the set of teeth of the engagement feature. Fig.24, where the engagement feature 117 includes a set of three teeth 118a, 118b, 118c. As shown, the radial line 121 of the engagement feature is the radial line located midway between the first tooth 118 and the last tooth 118c in the set. In this embodiment, the radial line 121 happens to coincide with a tooth of the engagement feature 117 (i.e., the middle tooth 118b), but this need not be the case. For example, if the engagement feature 117 includes a set of teeth that only includes two teeth (e.g., 118a and 118c), then the radial line of such an engagement feature would not coincide with any of those teeth, but would instead be located between the two teeth.

[0164] Although the engagement feature may include a plurality of teeth, in this case it may be preferred that the angle subtended by the arc defined by the first and last teeth in a set of teeth of the engagement feature is no greater than 25°. Again, this is Fig.24 , which shows the angle α subtended by the arc defined by the first tooth 118a and the last tooth 118c in a set of teeth of the engagement feature 117.

[0165] It may be preferred that the indexing arrangement is configured to provide a kinematic connection between the first member 102 and the second member 104. Optionally, the engagement features may be configured such that when locked together at the indexing position, there are only six contact points between the first member 102 and the second member 104 in total. This may be achieved by providing only one tooth on the first member 102 at each of the three discrete positions 116 to contact the facing sides of the opposing tooth 112 on the second member 104 (according to the embodiment shown), or in another embodiment, this may be achieved by providing two teeth on the first member at each of the three discrete positions 116 to contact the opposite sides of the single tooth 112 on the second member (e.g., somewhat like the spherical ball and cylindrical roller embodiments described in WO 2006 / 079794 or US 5185936).

[0166] As mentioned above, the present invention is not limited to optical sensors. For example, inductive sensors or capacitive sensors may be used. Fig.23a and Figure 23b A non-contact ("verification") sensor 180 is shown having an inductive sensor 182 disposed on the first member 102 and arranged to sense an area of ​​the top surface 115 of the second member 104. The output of the inductive sensor 182 varies depending on the spacing 's' between the inductive sensor 182 and the top surface 115. Fig.23a and Figure 23bAs shown, the spacing 's' varies depending on the idle position of the tooth / teeth 118 of the first member 102 relative to the teeth 112 of the second member 104. Accordingly, the output of the inductive sensor 182 can be used in the same manner as described above in conjunction with the optical encoder embodiment, for example, by comparing the output of the inductive sensor 182 with a pre-stored value to verify that the first member 102 and the second member 104 have been locked together at a given indexing position in substantially the same spatial configuration as at an earlier point in time (e.g., during a calibration phase).

[0167] The material of at least those portions of the first and second members 102, 104 that mechanically link the readhead 160 / 161 on the first member 102 and the scale 162 on the second member at each indexed position and thereby control their relative spatial configuration has a CTE of at least 2 ppm / °C. In the described embodiment, the first member 102 and the top surface 115 are made of a metal having a CTE of 24 ppm / °C, particularly an aluminum alloy, and the first and second annular members 110, 114 (and the teeth 112, 118 disposed thereon) are made of a metal having a CTE of 10 ppm / °C, particularly stainless steel. Accordingly, those portions of the first and second members 102, 104 that mechanically link the readhead 160 / 161 on the first member 102 and the scale 162 on the second member at each indexed position and thereby control their relative spatial configuration have a CTE greater than 2 ppm / °C. Other suitable materials include ceramics (e.g., tungsten carbide, zirconium oxide, silicon nitride).

[0168] The unlocking and locking of the first axis "D" are described in detail above. In the described embodiment, the locking / unlocking mechanism and indexing arrangement of the second axis "E" (i.e., the second member 104 and the third member 106 / 106') are substantially the same as those of the first axis "D", and thus the above description of the first axis "D" also applies to the second axis "E". Accordingly, in summary, similar to the above-described first axis "D", the controller 220 may send instructions to the articulated head 100 to operate the lock motor 190' of the second axis "E" so as to drive the lead screw (not shown) to drive the lead screw nut 176' horizontally in the X dimension (in Fig.25 In turn, lever 170' (which is connected to and thus actuated by lead screw nut 176') pushes the shaft 132 of the strut upward in the Z dimension (in the Figure 3 and Figure 4106'). After a short distance, the engagement balls 152' on the contact plates 134' of the struts 130' will contact and engage the paired engagement balls 154' on the third member 106 / 106', after which continued actuation of the lead screw 174' will cause the lever 170' and lead screw mechanism 172' to push the third member 106 / 106' axially outward, thereby causing the housing 105 of the second member 104 to separate from the third member 106 / 106'. The lead screw 174' is operated to separate the second member 104 from the third member 106 / 106' by a controlled, predefined amount, which is sufficient to cause the crown teeth 118' of the third member 106 / 106' to disengage from the mating teeth 112' on the second member 104, but as explained above in conjunction with the first axis "D", the amount is not too large because it is expected that the first magnet 140' will still be close enough to the second magnet 142' so as to have a reasonable amount of pulling force on the second magnet 142' even in the unlocked state. Fig.25 The second axis "E" of the articulated head 100 is shown in this unlocked state.

[0169] Once the unlocked state has been reached, the lock motor 190' driving the lead screw mechanism 172' is stopped and the second axis "E" electric drive motor 192' engaged with the drive gear 148' of the shaft 132' is operated to achieve a change in the rotational position of the third member 106 / 106' relative to the second member 105. In the unlocked state, the support 130' is engaged with the third member 106 / 106' via the engagement balls 152', 154' and is therefore rotationally fixed relative thereto (in the unlocked state). Accordingly, when the second axis "E" drive motor 192' engaged with the drive gear 148' of the shaft 132' is operated, it causes the third member 106 / 106' to be driven around the rotational axis E defined by the shaft 132'.

[0170] The relative rotational positions of i) the housing 105, 107, 115 of the second member 104 and ii) the shaft 132' of the second axis "E" (and therefore the third member 106 / 106') are known from the first ("primary") encoder device 135' of the second axis "E". Accordingly, the controller 220 can use the output from the first encoder device 135' of the second axis "E" to control the second axis "E" drive motor 192' engaged with the drive gear 148' of the shaft to bring the second member 104 and the third member 106 / 106' to the desired relative orientation. As will be appreciated, it is necessary to control the rotational position with sufficiently high accuracy so that when in the new desired relative orientation, the crown teeth 118' on the third member 106 / 106' are opposite the valleys of the teeth 112 on the annular member / end spline member 110' of the second axis "E" so that when they are locked together, the crown teeth 118' are perfectly located between the two teeth 112' of the annular member / end spline member 110' of the second axis "E".

[0171] As with the first axis "D", the first magnet 140', the second magnet 142' and the third magnet 144' are disposed on the housing 105, the pillar 130' and the third member 106 / 106' of the second member 104 of the second axis "E" and therefore benefit from the magnetically assisted unlocking and locking arrangement of the first axis "D". Moreover, the indexing arrangement of the second axis "E" is similar to the indexing arrangement of the first axis "D" in that it includes a first annular member 110' having a continuous series of tapered teeth extending substantially radially (e.g., it is in the form of a "face spline member") and a second annular member 114' having three crown teeth, which are configured to engage a subset of the continuous series of teeth disposed on the face spline member 110' at three equiangularly spaced locations. Furthermore, as with the first axis "D", a second rotary encoder apparatus is provided for the second axis "E", comprising an annular scale 162' provided on the housing 105 of the second member 104, and a first readhead 160' and a second readhead (not shown) provided on the third member 106 / 106', and may be used in the same manner as described above in connection with the first axis "D" for verifying / checking that the second member 104 and the third member 106 / 106' have been correctly locked together.

[0172] In the above-described embodiment, separate lock motors are provided for the first axis "D" and the second axis "E". However, this need not necessarily be the case. For example, a "lock" motor may be provided, and a device may be provided for selecting which axis it will cause to separate. For example, a gear system (e.g., a gearbox) may be provided and configured so that the motor may be selected to control only the locking / unlocking of the first axis "D", or to control only the locking / unlocking of the second axis "E", or to control both the locking / unlocking of the first axis "D" and the second axis "E" together. However, for simplicity, it may be preferred to use a separate motor, and because if only one motor is provided, it needs to be large / powerful enough to cope with simultaneous unlocking of the two axes when necessary. Similarly, in the above-described embodiment, separate drive motors are provided for the first axis "D" and the second axis "E". However, this need not necessarily be the case. For example, a "drive" motor may be provided, and a device (e.g., a gearbox) may be provided for selecting which axis it will drive. Similarly, a separate drive motor may be preferred.

[0173] A two-axis articulated head is described above. However, as will be appreciated, the present invention is not limited to a two-axis articulated head. For example, the articulated head may be a three-axis articulated head, in which a fourth member is provided, which is connected to the third member so that the orientation of the fourth member relative to the third member around the third axis can be changed (for example, changed between a plurality of predefined gradable orientations and locked in one of the predefined gradable orientations). In this case, the above features may be applicable to the third member and the fourth member when appropriate. The first axis, the second axis and the third axis may be orthogonal to each other. In this case, the fourth member may include a tool mount for receiving a tool. In this case, the first axis of rotation, the second axis of rotation and the third axis of rotation may be orthogonal to each other. The present invention is also applicable to single-axis devices, such as a rotating table having one axis of rotation.

Claims

1. An apparatus comprising a first relatively reorientable member and a second relatively reorientable member and an indexer arrangement configured to provide a plurality of angularly indexed lockable positions of the first member and the second member about a first axis, wherein: The indexer arrangement comprises: i) a series of features provided on the first member, the series of features extending annularly about the first axis; and ii) engagement features provided on the second member at at least three discrete positions annularly spaced about the first axis, the engagement features being configured to interengage with a subset of the features on the first member when in a locked state to provide a stable relative rest position of the first and second members at each indexed position; Therein, the apparatus further comprises at least a first non-contact sensor mounted to the second member, the first non-contact sensor being configured to sense an area on the first member and thereby provide a signal related to a spatial configuration of the first member and the second member when in their locked state.

2. The device according to claim 1, wherein: The material of at least those portions of the first member and the second member that mechanically link the first non-contact sensor on the second member and the area on the first member at each indexing position and thereby control the relative spatial configuration of the first member and the second member has a CTE of at least 2 ppm / °C.

3. The device according to claim 1 or 2, wherein: The first non-contact sensor is positioned such that a radial line where a sensing window of the first non-contact sensor is located is within + / - 15° of a radial line where a first one of the engagement features of the second member is located.

4. The device as claimed in claim 3, wherein: The first contactless sensor is positioned such that a radial line where a sensing window of the first contactless sensor is located is within + / - 1° of a radial line where the first engagement feature is located.

5. Apparatus as claimed in any preceding claim, wherein: The area on the first member sensed by the first non-contact sensor includes a scale member including a series of features that can be read by the first non-contact sensor to determine the relative position of the scale member.

6. Apparatus as claimed in any preceding claim, configured such that, with the first and second members locked together in an indexed position, the first non-contact sensor is used to establish information about the state of engagement of the first and second bodies.

7. The device of claim 6, the device being configured to react in a predetermined manner depending on the determined engagement state of the first member and the second member.

8. The device of claim 7, wherein: Said reacting in a predetermined manner comprises causing said first member and said second member to unlock, and optionally re-lock at the same indexed position.

9. A device as claimed in any preceding claim, comprising a second non-contact sensor mounted to the second member, the second non-contact sensor being configured to sense an area on the first member at an annular position about the first axis that is different from the annular position sensed by the first non-contact sensor, and thereby provide a signal related to the spatial configuration of the first member and the second member when they are in their locked state.

10. The device of claim 9, wherein: The second non-contact sensor is positioned such that a radial line where a sensing window of the second non-contact sensor is located is within + / - 15° of a radial line where a second one of the engagement features of the second member is located.

11. A device as described in any preceding claim, wherein the device is configured so that at each indexing position, the engagement features on the second member are configured to engage with a subset of the features on the first member when in the locked state, thereby providing a kinematic connection between the first member and the second member.

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