GB2597262A

GB2597262A - Monitoring misalignment of coupled rotary members

Info

Publication number: GB2597262A
Application number: GB2011004.5A
Authority: GB
Inventors: Gviniashvili Vladimir
Original assignee: John Crane UK Ltd
Current assignee: John Crane UK Ltd
Priority date: 2020-07-16
Filing date: 2020-07-16
Publication date: 2022-01-26
Also published as: GB202011004D0

Abstract

An apparatus 100 for monitoring alignment of a rotary coupling comprises a rotatable component of the rotary coupling having a rotation axis and a tangential surface carrying a marker region 150 and a signal provider 130 for providing a first signal indicating presence of the marker region at a first reference coordinate 133. The first reference coordinate defines a location with respect to a preferred axis of rotation of the rotatable component. The marker region is bounded by an axial datum edge aligned with the rotation axis of the rotatable component and a circumferential datum edge which extends circumferentially along the tangential surface. The axial extent of the marker region varies along the circumferential datum edge so that, during rotation of the rotatable component, a time between: (i) passing of the first reference coordinate by the axial datum edge; and (ii) passing of the first reference coordinate by the circumferential datum edge, indicates the axial position of the marker region. The signal provider may be a laser or other illumination source or optical detector.

Description

MONITORING MISALIGNMENT OF COUPLED ROTARY MEMBERS

FIELD

[0001]The present disclosure relates to methods and apparatus and more particularly to methods and apparatus for rotary couplings for use with rotating equipment, and still more particularly to methods and apparatus for sensing misalignment in a rotary coupling.

BACKGROUND

[0002]Rotary couplings are used for the transmission of 10 rotational energy from one machine to another (i.e., torque transmission). Thus connected by such a a coupling to a second shaft. This second, drive shaft from one machine can be driven, shaft in turn provides rotational drive to the second machine. This enables transmission of torque and/or rotational energy. The efficiency of the connection and transmission of energy from one machine to another may be significantly affected by this coupling.

[00031 The term "rotating equipment" is used in processing industries such as the oil and gas industry to describe mechanical apparatus having rotating parts. Examples of rotating equipment include engines, compressors, turbines, pumps, generators, blowers, and gearboxes. Alignment of rotary couplings, and components of those rotary couplings in rotating equipment is important, and particularly so in high speed applications. Misalignment can result in equipment malfunction leading to equipment downtime. This can be a critical and costly issue in many industries.

[0004]A variety of approaches are used to address this problem. For example, in order to accommodate misalignment and torque 30 transmission from one shaft to another, a flexible coupling may be employed between the rotatable shafts. In some configurations, based on the machines and/or installation thereof, the rotatable shafts may have fixed or variable misalignment (e.g., misalignment of axes, misalignment of end facings of shafts, etc.). The coupling may comprise one or more pieces that fixedly engage with each of the two shafts to provide a connection therebetween. Such couplings are typically connected about peripheral flanges of the shafts so as to transmit torque from one shaft to the other shaft while absorbing, and sometimes dissipating, the effects of misalignment.

mos] However, while configured for addressing misalignment between two shafts, conventional couplings may still have a limited degree of flexibility, and thus may not be able to accommodate some misalignments (e.g., variable, extreme angles, etc.). For example, for a given misalignment, the coupling is subjected to high stresses (e.g., from a drive shaft). Due to the high stresses, the coupling will respond with high reaction forces transmitted to the connected shaft (e.g., a driven shaft). If, during operation, the misalignment changes due to unforeseen circumstances, the coupling may fail due to fatigue fractures or other impacts. In addition, if the connected machines are modified to result in an increase in misalignment compared to the original set-up, the coupling may not be appropriate anymore and thus may require redesign or reconfigured to avoid costly failures.

SUMMARY

[0006] Aspects and examples of the invention are set out in the claims and aim to address at least a part of the above described technical problem, and other problems by providing a way to detect and or monitor alignment of one or more components of a rotary coupling.

N007]Embodiments of the disclosure aim to provide improved sensing of misalignment in rotary couplings. Embodiments may provide methods and apparatus for sensing alignment and/or misalignment of a rotating component with a preferred axis and/or plane of rotation. Embodiments may enable alignment to be sensed in a number of degrees of freedom, and may be able to operate at very high rotational speeds.

[0008]Embodiments of the disclosure may provide the ability to monitor misalignment of the rotating parts, and may aim to allow prediction of their failure before it occurs. The methods and apparatus described herein may allow measurement of complete orientation of the rotating object in the 3D space, such methods may use at least three detectors (e.g. sensors -optical, mechanical, magnetic etc.). These may be positioned conveniently from a radial direction towards the centre of the object whose alignment is to be monitored.

[0009j In an aspect there is provided a method of determining misalignment of a rotatable component rotating in a rotary coupling. The misalignment may be defined with respect to a reference position, e.g. a preferred axis of rotation of the rotary coupling and a preferred plane of rotation of the rotary coupling. The method comprises: operating a detector to provide at least one signal indicating interaction with a marker region at a plurality of reference coordinates disposed about the rotatable component. The marker region is carried by the rotatable component, and is configured so that said signal has a period corresponding to the rotation of the rotatable component. For example, the marker region may be disposed on a rotating surface such as a tangential surface or an axial face of the rotatable component. The method further comprises identifying a misalignment of the rotatable component based on said signal (s) [00101 In this aspect, the marker region is also configured so that the signal(s) provided by The detector has (have) a first characteristic which is invariant under axial displacement of the marker region. An example of such a first characteristic is the timing of a pulse edge of the signal. One way to provide a pulse edge which is invariant under axial translation is to provide the marker region with a straight axially aligned edge on a tangential surface of the rotatable component. This may be referred to herein as an axial datum edge. The marker region may be configured so that the first characteristic varies with radial position of the rotatable component. For example, during each revolution the time of arrival of the axial damm edge at each reference coordinate will depend upon the radial position of the rotatable component. The method may thus comprise identifying a radial displacement of the rotatable component based on a change in the first characteristic of each signal from each of a set of reference coordinates. For example, the delay or advancement of a pulse edge at each reference coordinate can be used to identify radial misalignment.

[0011] In this aspect, the marker region is also configured so that the signal(s) provided by the detector has (have) a second characteristic, which varies with axial posigion of the marker region. One example of such a characteristic is the duration of a pulse in the signal(s). One way to provide the variation in duration of the pulse is to provide a tapered marker region, in which the circumferential length of the marker region varies with axial displacement. Another example of such a characteristic is a frequency modulation of the signal. One way to provide this is to pattern the marker region so that the signal produced by the detector is modulated with a frequency which indicates axial displacement. A variety of other ways that such variability with axial displacement can be achieved will be appreciated in the context of the present disclosure.

Typically, however this second characteristic is provided, the marker region may be configured so that this second characteristic is invariant under radial displacement of the rotatable component, for example so that any variation with radial displacement is negligible as compared to the variation with axial displacement.

N0121 The "at least one signal" generally comprises a set of signals, each associated with a corresponding on of the reference coordinates. Axial displacement of the rotatable component may thus be identified based on a change in the second characteristic which is the same in each signal of the set of signals. This would represent a uniform axial displacement of the rotatable component as measured at each of the reference coordinates.

[0013] The method may comprise identifying a tilt of the rotatable component based on a difference in the second characteristic of at least two signals of the set of signals. For example, by identifying a different axial displacement of the rotatable component at each of two or three points, the tilt of the rotatable component can be inferred. The presence of tilt can be detected based on the presence of such differences, or the extent of tilt misalignment can be calculated.

[00141 The second characteristic may comprise information encoded in said signal. This information may encoded in any appropriate way -provided that it has a dependence upon axial displacement. For example, in the embodiment described with reference to the drawings, below, the information is encoded in pulse duration which arises from the tapered shape of the marker region. It may however be encoded in other ways. For example, rather than tapering the marker region, it may have a surface feature which causes any one or more of: * a change in the pulse amplitude, such as might be provided by parts of the marker region a reflectance which varies as a function of axial position on the tangential surface.

* a modulation frequency or a modulation phase such as might be provided by the marker region being marked with a particular pattern having a spatial frequency or phase which varies as a function of axial position on the tangential surface.

* a field strength of the signal such as might be provided by electric/magnetic field detection of a marker region in which the charge/flux density on the surface varies as a function of axial position on the tangential surface.

* a wavelength of the signal such as might be provided by parts of the marker region having a colour which varies as a function of axial position on the tangential surface.

[0015]Embodiments may monitor any type of misalignment, and/or load on bearings due to misalignment, and/or torque and rotational speed, and/or torsional vibration intensity.

[0016]Embodiments may provide control apparatus, such as 20 processors and or computer readable instructions configured to program a processor having signal acquisition capability to implement any one or more of the methods described herein.

[00171 In an aspect there is provided an apparatus for monitoring alignment of a rotary coupling, the apparatus comprising: a rotatable component of the rota:able coupling having a rotation axis and a tangential surface carrying a marker region, and a first signal provider for providing a first signal based on an interaction with the marker region at a first reference coordinate, wherein the first reference coordinate defines a location with respect to a preferred axis of rotation of the rotatable component; and the inueraction with the marker region at the first reference coordinaue varies as a function of axial position of the marker region.

[0018]The marker region may also be arranged so that a first 5 characteristic of the interacuion is invariant under axial translation of the marker region relative to the reference coordinate e.g. within an expected range of movement/misalignment of the rotatable component. One example of such a characteristic is the timing of a pulse of the signal during each revolution of the rotatable component. For example, the marker region may comprise an axial datum edge aligned with the rotation axis of the rotary member so that the timing of the signal provided by detection of this edge does not change with axial translation of the marker region.

[00]9]The marker region may also be arranged so that a second characteristic of the interaction varies (e.g. monotonically) with axial translation of the marker region with respect to the reference coordinate. One example of such a characteristic is its duration, or the amplitude, phase, or frequency content of a signal triggered by said interaction. For example, to provide a characteristic duration which varies in this way, the marker region may comprise a circumferential datum edge which extends circumferentially along the tangential surface wherein the axial extent of the marker region varies along the circumferential datum edge.

[0020] During rotation of the rotatable component, a time between: (i) passing of the first reference coordinate by the axial datum edge; and (ii) passing of the first reference coordinate by the circumferential datum edge may be used to determine the axial 30 position of the marker region. This may be done based on calibration data, and/or based on an indication of the speed of rotation of the rotatable component.

[00211 The circumferential datum edge of the marker region may be axially offset from a plane of rotation of the rotatable component by a displacement which varies along the circumferential datum edge with angular distance from the axial 5 datum edge. This variation may be monotonic -so that a one-to-one mapping is provided between the axial offset of the circumferential datum edge and the angular distance from the axial datum edge. This may be provided by the axial extent of the marker region tapering with circumferential distance from 10 the axial datum edge.

[0022]An aspect of the disclosure provides an apparatus for monitoring alignment of a rotary coupling, the apparatus comprising: a rotatable component for the rotary coupling the rotatable component having a rotation axis and a tangential surface carrying a marker region; and a first signal provider for providing a first signal indicating presence of the marker region at a first reference coordinate, wherein the first reference coordinate defines a location with respect to a preferred axis of rotation of the rotatable component; and, the marker region is bounded by: an axial datum edge aligned with the rotation axis of the rotatable componenc, and a circumferential datum edge which extends circumferentially along the tangential surface wherein the axial extent of the marker region varies along the circumferential datum edge so that, during rotation of the rotatable component, a time between: (1) passing of the first reference coordinate by the axial datum edge; and (ii) passing of the first reference coordinate by the circumferential datum edge, indicates axial position of the marker region. The circumferential datum edge may be axially offset from a plane of rotation of the rotatable component by a displacement which varies along the circumferential datum edge with angular distance from the axial datum edge.

[00231 In the above described aspects and embodiments, a second circumferential edge of the marker region on the tangential surface may be perpendicular to the axial datum edge. For example, the marker region may comprise at least one right angle triangle, the hypotenuse of which may provide the circumferential datum edge.

[0024]As noted above, the marker region may be arranged so that a second characteristic of the interaction varies (e.g. monotonically) with axial translation of the marker region with respect to the reference coordinate. A second example of such a characteristic is signal intensity e.g. amplitude. The marker region may comprise a set of sub-regions, e.g. arranged in a strip, an axial datum edge of which set may be aligned with the rotation axis of the rotary member. The properties of the sub- regions strip may be chosen based on their axial position such that a strength of interaction between the marker region at the first reference coordinate indicates axial position of the marker region. For example, the sub regions may each comprise an indicator, which is different from the other sub-regions -such as grey scale in the case of an optical detector that varies in shade between the sub-regions -such that axial position can be uniquely identified based on the detected indicator. Other such characteristics may be used such as the spatial frequency of a detectable pattern in the marker region.

[0025]The apparatus may comprise a second signal provider for providing a second signal indicating presence of the marker region at a second reference coordinate, differen:, from the first reference coordinate, so that during each revolution of the rotatable component: (a) a timing of the first signal varies with displacement of the rotation axis from the preferred axis of rotation of the rotatable component; and (b) a timing of the second signal varies with displacement of the rotation axis from the preferred axis of rotation of the rotatable component.

[00261 The apparatus may comprise a controller configured to determine, based on said timing a radial displacement of the rotation axis from the preferred axis of rotation of the rotatable component. In this context the term radial displacement may refer to displacement perpendicular to the preferred axis.

[0027]1n some embodiments, a difference in duty cycle between the first signal and the second signal may vary with tilt of the rotation axis from the preferred axis. The apparatus may comprise a controller configured to determine, based on said difference in duty cycle, a tilt of the rotatable component as compared to a reference position.

[0028]The apparatus may comprise a third signal provider for providing a signal indicating presence of the marker region at a third reference coordinate, different from the first reference coordinate and the second reference coordinate. Said reference coordinates may be defined with respect to the preferred axis of rotation of the rotatable component and each may comprise an axial displacement ordinate, z, and an azimuthal angle ordinate. The azimuthal angle ordinate of each of the reference coordinates may be different from the azimuthal angle ordinate of all of the other reference coordinates. Thus, the reference coordinates may be distributed about the periphery of the

rotatable component.

[00291 The signal provider may comprise a detector for detecting the marker region by at least one of an optical, electronic, or magnetic sensing channel, or by another type of sensing.

[003011n an aspect there is provided a method of determining misalignment of a rotatable component rotating in a rotary coupling with respect to a preferred axis of rotation of the rotary coupling and a preferred plane of rotation of the rotary coupling.

[0031]The method may comprise: obtaining a first signal indicating when, during a revolution of the rotatable component, a marker region carried by the rotatable component is present at a first reference coordinate; obtaining a second signal indicating when, during said revolution, the marker region is present at a second reference coordinate, different from the first reference coordinate; determining, based on the first signal and the second signal, whether a rotation axis of the rotatable component is displaced from the preferred axis of rotation and whether the rotatable component is displaced from the preferred plane of rotation.

[0032]The marker region may be bounded by an axial datum edge aligned with the rotation axis of the rotary member, or may otherwise be arranged so that a characteristic of the first signal and the second signal does not change in response to axial displacement of the marker region. The marker region may also be arranged so that a second characteristic of said signal varies in response to axial displacement of the marker region. This variation may be arranged uniquely to identify the axial position of the marker region. For example, the marker region may comprise a circumferential datum edge which extends circumferentially along the tangential surface wherein the axial extent of the marker region varies along the circumferential datum edge.

[00331 The first signal and the second signal may each comprise a periodic signal having a first edge timing determined by the axial datum edge passing the first sensor and the second sensor respectively, and a second edge timing determined by the circumferential datum edge passing the first sensor and the second sensor respectively.

[00341 The method may comprise determining the axial position of the rotatable component based on a delay between the first edge timing and the second edge timing of at least one of the first 10 signal and the second signal.

[0035] The first signal and the second signal may each have a respective reference timing, for example defined by a reference signal and/or other stored calibration data. A delay may be defined between a measured timing of the first signal and the second signal and the corresponding reference timing. The method may comprise determining a radial misalignment of the rotatable component based on a difference between the delay of the first signal and the delay of the second signal.

[0036]The first signal and the second signal each have a respective pulse duration comprising the time between the first edge timing and second edge timing of each respective signal, and the method may comprise determining a tilt of the rotatable component based on a difference in duration between the first signal and the second signal.

[0037]The method may comprise obtaining a third signal indicating when, during the rotation, the marker region is present at a third reference coordinate, different from the firs: reference coordinate and the second reference coordinate.

[0038]Embodiments of the disclosure provide a system for 30 determining misalignment of a rotatable component rotating in a rotary coupling, the system comprising a processor configured to perform any one or more of the methods described herein. The system may comprise a datum frame carrying: a first signal provider arranged for providing the first signal and a second signal provider arranged for providing the second signal. The signal providers may each comprise a detector for detecting characteristics of a marker region, carried on a tangential surface of the rotatable component.

[0039]It will be appreciated from the discussion above that the embodiments shown in the Figures are merely examples, and 10 include features which may be generalised, removed or replaced as described herein and as set out in the appended claims.

[0040] With reference to the drawings in general, it will be appreciated that schematic functional block diagrams are used to indicate functionality of systems and apparatus described herein. It will be appreciated however that the functionality need not be divided in this way, and should not be taken to imply any particular structure of hardware other than that described and claimed below.

[0041] The function of one or more of the elements shown in the drawings may be further subdivided, and/or distributed throughout apparatus of the disclosure. In some embodiments the function of one or more elements shown in the drawings may be integrated into a single functional unit.

BRIEF DESCRIPTION OF DRAWINGS

[0042]Some practical implementations will now be described, by way of example only, with reference to the accompanying drawings in which: [0043] Figure 1 shows a system including a rotary coupling between 30 two machines; [00441 Figure 2 shows some more detailed schematic views of parts of a rotary coupling such as that illustrated in Figure 1 and an apparatus for monitoring alignment of a rotatable component of that coupling; [0045]Figure 3 shows schematic views of two time series plots indicating sensor signals used by the apparatus shown in Figure 2 for determining axial misalignment; [0046]Figure 4 shows schematic views of two time series plots indicating sensor signals used by the apparatus shown in Figure 10 2 for determining tilt misalignment; and [0047] Figure 5 shows schematic views of two time series plots indicating sensor signals used by the apparatus shown in Figure 2 for determining tilt misalignment [0048]In the drawing like reference numerals are used to indicate 15 like elements

SPECIFIC DESCRIPTION

[00491 Figure 1 shows a system 1100 which includes a first machine 1102 and a second machine 1104 that are operably connect by a coupling system 1106. The first machine 1102 may be a driving machine that drives a first rotary member 1108 (e.g., a drive shaft). The second machine 1104 may be a driven machine that includes a second rotary member 1110 (e.g., driven shaft) that is driven by operation of the first machine 1102. The first rotary member 1108 is operably and fixedly connected to the second rotary member 1110 by the coupling system 1106. The coupling system 1106 comprises a first coupling member 1114 and a second coupling member 1112 and includes one or more other coupling components 1116, such as flanges, membranes, coupling extension members and so forth. The first coupling member 1114 connects the driven shaft 1114 to the coupling system 1106, and the second coupling member 1112 connects the drive shaft 1108 to the coupling system 1106. Thus, in operation, rotation force is transmitted from the drive shaft 1108 via the second coupling member and the other components 1116 of the coupling system 1106 and the first coupling member 1114 to the driven shaft 1110.

[0050]The coupling system 1116 can allow some degree of misalignment between the drive shaft 1108 and the driven shaft 1110. As an example, the coupling components 1116 shown in Figure 1 illustrate a radial misalignment (e.g. misalignment which is lateral, transverse to, the preferred axis of rotation of the coupling 1106. The coupling 1116 accommodates the misalignment through flexibility provided from one or both of the first coupling member 1114 and the second coupling member 1112, and the arrangement of the other components 1116 of the coupling.

The precise arrangement of these components can vary between implementations, but irrespective of the manner in which the components of the coupling system might he arranged, the present disclosure aims to provide a method and apparatus for sensing misalignments of the coupling between the coupled shafts 1108, 1110.

[0051] This may be based on alignment between one of the components 1116 of the coupling 1106 and the preferred axis of rotation of that coupling. According to the present disclosure, a rotatable component of the coupling 1116 has a rotation axis and a tangential surface carrying a marker region. A signal provider such as an optical detector, provides a signal indicating an interaction with the marker region at a first reference coordinate. The marker region and/or the signal provider are arranged so that a characteristic of this interaction with the marker region varies as a function of axial position of the marker region as it passes the reference coordinate during rotation of the rotatable component. The interaction may also vary with radial alignment of the rotatable component (lateral displacement, transverse to The axis of rotation of the coupling).

[0052]Radial, axial, and tilt misalignment of the rotatable component may be determined based on this interaction. A variety of implementations may be provided. The simplest being the detection of pure axial misalignment, which can be accomplished using a single detector at a single reference coordinate. More sophisticated implementations may use a greater number of detectors.

[0053]Misalignment may be defined with respect to a reference position associated with the coupling. Typically the reference position comprises a preferred plane of rotation and a preferred axis of rotation, such as a plane and axis defined with reference to the rotary coupling 1106. This may in turn be defined as the axis of either the drive shaft 1108, or the driven shaft 1110.

[0054]Figure 2 shows an apparatus 100 for monitoring the alignment of a rotatable component 110 in a rotary coupling system 120. Views of the apparatus 100 are shown in three insets -A, B and C. [0055]The coupling system 120 comprises rotary components 110, 116, 124 which may provide a coupling system 1106 of the type illustrated in Figure 1.

[0056]The apparatus 100 comprises a signal provider 130, and a marker region 150 disposed on a tangential surface 112 of one of the rotatable components 110 of the coupling system 120. The apparatus 100 may also comprise a controller 140 connected to the signal provider 130. The signal provider 130 may comprise a detector for interacting (e.g. by optical means) with the marker region 150 at a reference coordinate 133. It may also comprise a signal source 160 (such as a source of illumination, for example a laser).

[00571 In the coupling 120 illustrated in Figure 23 the drive shaft 122 is connected to the first rotatable component 110 of the coupling 120, e.g. by a flexible coupling member of the type described with reference to Figure 1 (but not shown in Figure 2). The driven shaft 126 may be similarly connected to a second rotatable component 124. The coupling 120 connects the first rotatable component 110 to the second rotatable component 120 to provide rotary coupling between the drive shaft 122 and the driven shaft 126.

[0O58]Misalignment of the shafts 122, 126 may be manifest as misalignment of one or more of the rotatable components 110, 116, 124 of the coupling system 120. Such misalignment can result in inefficient performance, and damage to or failure of the coupling 120.

P0591The rotatable components 110, 116, 124, may be circular e.g. disc shaped and the tangential surface 112 (radially outward facing edge) of one of the rotatable components 110 carries a marker region 150. The marker region 150 comprises a detectable (e.g. optically detectable) marking of the tangential surface 112. As Illustrated, the marker region 150 is in the shape of a right angled triangle on this curved tangential surface 112. A first cathetus of this right angle c,riangle is aligned axially across the tangential surface 112 and thus provides an axial edge 154 of the marker region, e.g. parallel to the axis of the rotatable component 110. The other cathetus of the right angle triangle provides a tangential edge 156 aligned circumferentially about the axis perpendicular to the axial edge, and along the tangential surface 112.

[0060] The axial edge 154 of the marker region may be positioned 30 such that it leads the hypotenuse and the tangential edge 156 of the right angle triangle in the direction of rotation 190 of the rotatable component 110. The hypotenuse of this triangle thus provides a circumferential edge which is diagonal across the surface, e.g. axially offset from a plane of rotation of the rotatable component by a displacement which varies with angular distance from the axial datum edge.

[0061]Alignment and misalignment of the rotatable component 110 is defined with respect to the preferred or reference position of the rotary coupling 100. This reference position may be defined by a preferred axis 170 of rotation of the rotary coupling 120, and a preferred plane 172 of rotation of the rotatable component 110 in The rotary coupling 120. The reference position may thus define both the location of the rotatable component and its orientation -for example when it is in the preferred plane of rotation, centered on and aligned with the preferred axis 170 it is properly aligned.

[0062]Seven types of misalignment may occur -three pure movements: radial 179, axial 175, and tilt 177 and four composite movements: radial with axial, radial with tilt, axial with tilt, and radial with both axial and [0063]To enable misalignment to be detected, the con:,roller 140 may be configured to store reference data indicating the signal associated with the rotatable component being aligned at the reference position. This signal may be measured in a calibration process when the rotatable component is installed or trued, and stored for comparison with later observed signals. This reference signal may be hard coded or otherwise stored in a memory device associated with the controller 140 to allow its use in determining misalignment. Thus misalignment of the rotatable component 110 may be determined by a comparison of an observed signal with such a reference signal. Other types of 30 calibration may be used.

[00641 For ease of understanding, as illustrated in Figure 23, the reference position of the rotatable component 110 may be defined in a three dimensional Cartesian coordinate system x-y-z 178, 174, 176. The origin of this coordinate system may be defined as the centre of rotation 171 for the rotatable component in its reference position. The x-z plane 172 is the preferred plane of rotation 172 and the y-axis 174 is the preferred axis of rotation 170 about which the rotatable component rotates in the reference position. Axial movement 175 may be defined as translation of the rotatable component 110 in the y direction, radial movement 179 as translation of the rotatable component 110 in the x-z plane 172 and tilt as rotation of the rotatable component 110 about the z-axis 176 and/or the x-axis 178.

[0065]As illustrated in Figure 1, the signal provider 130 may be arranged to interact with the marker region 150 at a first reference coordinate 133 thereby to provide a signal 144 to the controller 140 indicating the presence or absence of the marker region 150 at the reference coordinate. The controller is configured to take this signal 144 and to use it to provide an alignment signal 142, indicating the presence of and/or extent of misalignment. The alignment signal 142 may be used by a further device to control the coupling, e.g. to improve its alignment or to trigger an alert e.g. to cause corrective action.

[00661 During operation, the drive shaft 122 provides torque to rotate the rotatable component 110, which in turn drives second rotatable component 124 to rotate the driven shaft 126. When aligned with the reference position 170, 172, the rotatable component 110 rotates about the preferred axis of rotation 170 in, and parallel with, the preferred plane of rotation 172. The marker region 150 thus coincides with (is present at) the reference coordinate 131 for an interval during each revolution of the rotatable component 110. If the axial edge 154 of the marker region leads the region in the direction of rotation, this interval begins when the axial edge 154 reaches the reference coordinate 131, and continues until the hypotenuse 156 of the marker region passes the reference coordinate. This tapered marker region is thus arranged so that at least two fiducial points can be identified in the signal 164 obtained at each reference coordinate. A first fiducial point in the signal is provided by the arrival of the axial edge of the marker region at the reference coordinate, and this is invariant under axial displacement (within some defined range -e.g. the axial width of the marker region). A second fiducial point varies as a known function of the axial position of the marker region at the corresponding reference coordinate. For example, this second fiducial point in the signal may be provided by the arrival of the circumferential edge of the marker region 150.

[0067]The signal provider 130 may interact with the tangential surface by illuminating 162 the reference coordinate 131, and detecting the signal 164 reflected from the tangential surface 112 at the reference coordinate 133. The reflected signal 164 can thus indicate of the presence or absence of the optically detectable marker region at the reference coordinate 133. The signal provider 130 provides a signal 144, based on this, to the controller 140.

[0068]The controller 140 then determines the axial position of the marker region 150 based on the duration of the interval in which the marker region 150 is detected at the reference coordinate. For example this may be done based on the speed of rotation of the rotatable component 110 and the shape and size of the marker region, or based on comparison with reference data such as that described above. The interval occupies some known fraction of the period of revolution, but typically not all of that period.

[00691 Detection of the marker region at more than one such reference coordinate may be used. As illustrated in Inset B of Figure 2, the signal provider 130 may comprise a set of such detectors 132, 134, 136 or other means arranged about the periphery of the rotatable component 110 for providing a signal indicating the presence of the marker region at each of the set of corresponding reference coordinates 133, 135, 137. The reference coordinates 133, 135, 137 may comprise three separate angular positions about the periphery of the rotatable component (e.g. angularly spaced at some distance about the preferred axis of rotation in the preferred plane of rotation).

[00701 Operation to identify misalignment using three reference coordinates 133, 135, 137 will now be described with reference to Figure 3. Figure 3 comprises a graph 200 the x-axis 202 of which indicates time, and the y axis of which provides a schematic indication of a signal amplitude from the signal provider 130. A first plot 220 on this graph indicates the signal provided when the rotatable component is aligned with the reference position. The thumbnail sketch 260 beneath the first plot 220 indicates the correspondence between the marker region 152 and the signal shown in that plot 220. The signal illustrated in the first of these two plots 220 may be used as a reference signal.

[00711A second plot 240 on the same axes indicates the signal provided when the rotatable component 110 is misaligned with the reference position because it is axially displaced from that reference position (e.g. otherwise aligned, but axially offset from the preferred plane of rotation 172 -"axial misalignmentn). The thumbnail sketch 280 beneath the second plot 240 indicates the correspondence between the marker region 152 on the tangential surface 112 and the signal shown in that plot 240.0peration of the apparatus, shown in Figure 1 will now be described with reference to these plots 220, 240.

Detecting Axial Misalignment [0072]With the rotatable component aligned at the reference position, each revolution of the rotatable component causes the marker region to pass each of the three reference coordinates 133, 135, 137. At these coordinates, the passage of the marker region is detected by the detectors 132, 134, 136 giving rise to three pulses 222, 224, 226 shown in the upper plot 220. it can be seen from this plot that, with this type of marker region, the timing of a first edge of each pulse is set by the axial edge of the marker region 154 passing each reference coordinate, and the timing of the second edge is set by the hypotenuse. The timing of the first pulse edge is thus invariant under axial translation of the marker region at the reference coordinates. The timing of the second pulse edge however varies as a known function of such translation. The duration of each pulse thus indicates the axial position of the tangential surface of the rotatable component 110 at that reference coordinate. The detector 132, 134, 136 at each reference coordinate provides such a signal to the controller, indicating the time at which the marker region arrived at each reference coordinate and the time at which its passage of that coordinate completed.

[0073]In the case of axial alignment, the detectors 132, 134, 136 provide a sequence of three pulses, which match the reference signal. In the case of a pure axial misalignment, as illustrated in the plot 240, the duration of all the three pulses changes in the same way. If the rotatable component moves axially in one direction, the pulse duration is decreased, and it it moves axially in the other direction, the pulse duration is increased. The amount of increase or decrease being related to the axial shift by the shape of the marker region and the speed of rotation. Thus, the controller can determine axial displacements of the rotatable component from the reference position (axial misalignment) based on the pulse duration. For example, the controller may determine axial misalignment by comparing the duration of the pulses from the detectors with the duration of the pulses in the corresponding reference signal(s). The controller may thus detect a purely axial misalignment based on the presence of a uniform shift in axial position of the marker region (e.g. pulse duration) at each of the three reference coordinates.

Detecting Tilt Misalignment [0074]Where the rotatable component is tilted with respect to the reference position, the tangential surface of the rotatable component at each of the three reference coordinates will be at a different axial position. The duration of the pulses provided by the detectors at each location therefore differ from each other, but can be determined as outlined above. This enables the axial position of the rotatable component to be determined at each of three locations about its circumference, and hence enables tilt misalignment to be identified.

[0075] In Figure 2 the axial edge of the marker region spans the width of that marker region, so that the timing of one edge of each pulse (either leading edge or trailing edge) is invariant under axial displacement of the rotatable component whereas the other edge of the pulse changes with axial displacement due to the tapering of the marker region. Thus the axial edge provides a datum line and the time between the axial edge and the circumferential edge passing the reference coordinate indicates the axial position of the marker region.

[0076] It is possible to measure more than simple axial misalignment -e.g. to account for the possibility that other misalignments might be present. Other features of the waveform provided by the interaction between the marker region and the detectors can be used for this purpose.

[00771 Figure 3 comprises a graph 300 the x-axis 302 of which indicates time, and the y axis 304 of which provides a schematic indication of a signal amplitude from the signal provider 130. A first plot 320 on this graph indicates the signal provided when the rotatable component 110 is aligned with the reference position (e.g. a reference signal). The thumbnail sketch 360 beneath the first plot 320 indicates the correspondence between the marker region 152 and the signal shown in that plot 320. A second plot 340 on the same axes indicates the signal provided when the rotatable component 110 is misaligned with the reference position because it is tilted with respect to the preferred axis of rotation. The thumbnail sketch 360 beneath the second plot 340 indicates the correspondence between the marker region 152 and the signal shown in that plot 340.

[007811t can be seen that, when the rotatable component is tilted, the duration of the pulses will differ from each other. To identify the presence of tilt misalignment, when the rotatable component is revolving the controller obtains a pulse from each of the three detectors once per revolution. The controller then determines the duration of each pulse and, based on that duration determines the axial shift of the marker region at the corresponding reference coordinate as described above. The controller can thus determine an axial displacement of the tangential surface of the rotatable component at each reference coordinate by comparing the pulse duration associated with that location against the reference signal to identify the presence of differences between the pulse durations. The colmroller can thus detect tilt of the rotatable component based on differences in the pulse durations detected at the three reference coordinates. It may also be configured to determine the extent of tilt misalignment based on the axial displacement at each reference coordinate.

Detecting Radial Misalignment [0079]Although the first edge of each pulse is invariant under axial translation of the rotatable component, where the rotatable component is displaced radially (e.g. displacement transverse to the preferred axis of rotation) the timing of both the start and end of each the pulse is shifted equally with respect to that of the corresponding pulse in the reference signal. The duration of each pulse is however unchanged by such radial displacement.

[0080]When the rotatable component is rotating the controller receives a pulse from each detector during each revolution of the rotatable. The controller then determines the timing (e.g. based on the rising edge and falling edge) of each pulse, and may compare this timing with the timing of the corresponding pulse in the reference signal. The controller can thus determine whether radial misalignment is present based on whether a shift in timing of any of the three pulses, is different from the timing of the others.

[0081]As illustrated in plot 440 in Figure 5, in the case of radial misalignment the timing of the pulse 442 from the first detector 132 is shifted by a first delay, At'. The timing of the pulse from the second detector 136 is shifted by a second delay, At2, and the timing of the pulse from the third detector 134 is shifted by a third delay, At2. The controller may also be configured to determine the extent of radial misalignment based on the delay of the signals with respect to the reference signal. For example, this may be determined based on the angular position of each of the reference coordinates with respect to the preferred axis of rotation and the timing delay of the signals at each of the three reference co-ordinates as compared to the reference signal. The three reference coordinates are spaced at known angular intervals about the preferred axis of rotation 171, and the time delay of the pulse measured at each reference coordinate 133, 135, 137 corresponds to a displacement of the centre of the rotatable component. The direction of the displacement measured at each detector is perpendicular to a line to that detector 132, 134, 136 from the preferred axis of 5 rotation 171 (the origin of the x-z plane -see Figure 2, inset B). The controller can thus apply a geometric transformation (e.g. a projection) from these three measured displacements to determine the location (e.g. in the x-z plane) of the axis of rotation of the rotatable component thereby to determine radial 10 misalignment of the rotatable component.

[00821 It can thus be seen that axial, tilt and radial misalignment may all be detected by using this arrangement, and a greater or lesser number of detectors may be used according to the sophistication of the measurement required.

[00831A variety of different implementations may be used. For example, the possibility of using a marker region which as a right angled triangle has been described, but other types of marker region may be used. The right-angle triangle provides certain benefits, namely: * a first characteristic of the signal at each detector is invariant under axial translation of the marker region with respect to the detector.

* a second characteristic of that signal varies (e.g. monotonically) with axial translation of the marker region with respect to the detector.

* a third characteristic of that signal varies (e.g. monotonically) with radial translation of the rotatable component with respect to the detector.

[0084j However, any other marker region which provides signals 30 having these features may be used. As just a first example, the marker region and/or the detector may be arranged so that the rising and/or falling edge of the pulse at each detector is invariant under axial translation of the marker region with respect to the detector, while a second characterist_c of that pulse varies with axial translation of the marker region with respect to the detector.

[00851 Such properties could be provided by a region having a straight axially aligned edge, and a detectable characteristic which varies in the axial direction, for example monotonically.

This could be any detectable characteristic such as the circumferential length (as in the case described above), the intensity and/or strength of the marking, the spatial frequency of the marking and so forth. The characteristic which varies with radial translation may arise from the interaction range between marker region and detector, for example as would be constrained by the field of view of an optical detector, the aperture of an electrical (e.g. capacitive or inductive) detector, or of a magnetic detector.

[00861 It is mentioned with reference to Figure 1 that the signal provider 130 provides a signal 144 indicating the presence or absence of the marker region 150 at a particular reference coordinate. It will be appreciated however that it may also indicate the strength of interaction -e.g. in the event that marker regions which use other types of sensing (optical, magnetic, electrical etc.) to provide the characteristic which varies with axial displacement electric field strength.

[00871 It will also be appreciated that the different parts of the system described herein may be made and sold separately. For example the detectors themselves need not be included -all that is required is a rotatable coupling in which a component of the coupling carries a marker region on a tangential surface, and signal providers are located for sensing the marker region at reference coordinates disposed about the periphery of that component. These could simply be apertures to permi7_ detection of the marker region.

[0088]As such the signal providers described above may take different forms, in the example of optical interactions an optical detector such as a photodiode may be used. For magnetic interactions the signal provider could be configured to detect changes in the properties of a magnetic field such as changes in polarity and/or flux.

[0089]The interaction with the marker region at the reference coordinate may be an interaction of an active signal with the marker region such as the optical illumination described above and/or it could be passive interaction resulting from the properties of the marker region (such as a magnetic or electric field or other illumination originating from the marker region).

[0090]Characteristics other than duration and/or intensity could be measured by the signal provider and used to indicate axial position on the marker region -such as the phase, frequency and/or wavelength of the signal detected at each reference coordinate.

[0091]The marker region may comprise a material affixed to the tangential surface of the rotatable component, or it could be integrally formed in the rotatable component (e.g. molded, ground, cut, engraved, machined and/or etched into the rotatable component). The marker region may be more or less reflective than the tangential surface of the rotatable component.

[0092]More than one marker region may be arranged on the tangential surface, in which case the signal from each of the regions may be used as described above.

N0931A reference signal is not necessary to identify displacement in all cases -other types of calibration may be used. Differences between the first, second and/or third pulses and the differences in timing between the first, second and/or third pulses over a single revolution of the rotatable component are in some cases sufficient to identify displacement of the rotatable component.

[0094]In certain examples the controller may be configured to perform any of the methods described herein, or particular steps of said methods. For example the controller may comprise a signal acquisition interface for communicating with detectors disposed for detecting the marker region at the reference coordinates. The controller may be provided by fixed logic such as assemblies of logic gates or programmable logic such as software and/or computer program instructions executed by a processor. Other kinds of programmable logic which may be used include programmable processors, programmable digital logic (e.g., a field programmable gate array (FPGA), an erasable programmable read only memory (EPROM), an electrically erasable programmable read only memory (EEPROM)), an application specific integrated circuit, ASIC, or any other kind of digital logic, software, code, electronic instructions, flash memory, optical disks, CDROMs, DVD ROMs, magnetic or optical cards, other types of machine-readable mediums suitable for storing electronic instructions, or any suitable combination thereof. Embodiments of the disclosure provide computer programs and computer program products such as tangible, non transitory computer readable media carrying program instructions configured to program a programmable processor (such as the controller) to perform any of the methods described herein, or particular steps of said methods [0095]The above examples are to be understood as illustrative examples.

[00961 It is to be understood that any feature described in relation to any one example may be used alone, or in combination with other features described, and may also be used in combination with one or more features of any other of the examples, or any combination of any other of the examples.

[0097]Furthermore, equivalents and modifications not described above may also be employed without departing from the scope of the invention, which is defined in the accompanying claims.

Claims

Claims 1. An apparatus for monitoring alignment of a rotary coupling, the apparatus comprising: a rotatable component for the rotary coupling the rotatable component having a rotation axis and a tangential surface carrying a marker region; and a first signal provider for providing a first signal indicating presence of the marker region at a first reference coordinate, wherein the first reference coordinate defines a location with respect to a preferred axis of rotation of the rotatable component; and, the marker region is bounded by: an axial datum edge aligned with the rotation axis of the rotatable component, and a circumferential datum edge which extends circumferentially along the tangential surface wherein the axial extent of the marker region varies along the circumferential datum edge so that, during rotation of the rotatable component, a time between: (1) passing of the first reference coordinate by the axial datum edge; and (ii) passing of the first reference coordinate by the circumferential datum edge, indicates axial position of the marker region.
2. The apparatus of claim I wherein the circumferential datum edge is axially offset from a plane of rotation of the rotatable component by a displacement which varies along the circumferential datum edge 30 with angular distance from the axial datum edge.
3. The apparatus of claim 2 wherein the displacement varies monotonically.
4. The apparatus of claim 2 or 3 wherein the axial extent of the marker region tapers with circumferential distance from the axial datum edge.
5. The apparatus of any preceding claim wherein the marker region comprises at least one right angle triangle.
6. The apparatus of any preceding claim comprising a second signal provider for providing a second signal indicating presence of the marker region at a second reference coordinate, different from the first reference coordinate, so that daring rotation of the rotatable component: (a) a time delay between the fist signal and the second signal varies with displacement of the rotation axis from the preferred axis; and/or (b) a difference in duty cycle between the first signal and the second signal varies with tilt of the rotation axis from the preferred 15 axis.
7. The apparatus of claim 6 comprising a third signal provider for providing a signal indicating presence of the marker region at a third reference coordinate, different from the first reference coordinate and the second reference coordinate.
8. The apparatus of any preceding claim wherein said reference coordinates are defined with respect to the preferred axis of rotation of the rotatable component and each comprise an axial displacement ordinate, z, and an azimuthal angle ordinate, 4), for example wherein the azimuthal angle ordinate, 4), of each of the reference coordinates is different from the azimuthal angle ordinate of all of the other reference coordinates.
9. The apparatus of any of claims 1 to 8 wherein the signal providers each comprise a channel located for obtaining a signal from the tangential surface for the reference location of the corresponding signal provider.
10. The rotary apparatus of claim 9 wherein the channel comprises at least one of an optical, electronic, or magnetic sensing channel.
11. A method of determining misalignment of a rotatable component rotating in a rotary coupling with respect to a preferred axis of rotation of the rotary coupling and a preferred plane of rotation of the rotary coupling, the method comprising: obtaining a first signal indicating when, during the rotation, a marker region carried by the rotatable component is present at a first reference coordinate wherein the marker region is bounded by (i) an axial datum edge aligned with the rotation axis of the rotatable compnent, and (ii) a circumferential datum edge which extends circumferentially along the tangential surface wherein the axial extent of the marker region varies along the circumferential datum edge; obtaining a second signal indicating when, during the rotation, the marker region is present at a second reference coordinate, different from the first reference coordinate; determining, based on the first signal and the second signal, (a) whether a rotation axis of the rotatable component is displaced from the preferred axis of rotation and (b) whether the rotatable component is displaced from the preferred plane of rotation.
12. The method of claim 11, wherein the first signal and the second signal each comprise a periodic signal having a first edge timing determined by the axial datum edge passing the first sensor and the second sensor respectively, and a second edge timing determined by the circumferential datum edge passing the first sensor and the second sensor respectively.
13. The method of claim 12 comprising determining the axial position of the rotatable component based on a delay between the first edge timing and the second edge timing of at least one of the first signal and the second signal.
14. The method of claim 12 or 13 wherein the first signal and the second signal each have a respective reference timing, and a respective delay between their first edge timing and their reference timing, the method comprises determining a radial misalignment of the rotatable component based on a difference between the delay of the first signal and the delay of the second signal.
15. The method of claim 14 wherein the first signal and the second signal each have a respective duration comprising the time between the first edge timing and second edge timing of each respective signal, the method comprising determining a tilt of the rotatable component based on a difference in duration between successive pulses of at least one of the first signal and the second signal.
16. The method of any of claims 11 to 15 comprising obtaining a third signal indicating when, during the rotation, the marker region is present at a third reference coordinate, different from the first reference coordinate and the second reference coordinate.
17. A system for determining misalignment of a rotatable component rotating in a rotary coupling comprising a data processor configured to perform the method of any of claims 11 to 16, and a datum frame 20 carrying: a first signal provider arranged for providing the first signal and a second signal provider arranged for providing the second signal.
18. A rotatable component for a rotatable coupling and for use in the apparatus of any of claims 1 to 10 or the method of any of claims 11 to 16 and comprising a marker region bounded by (i) an axial datum edge aligned with the rotation axis of the rotatable component, and (ii) a circumferential datum edge which extends circumferentially along the tangential surface of the rotatable component wherein the axial extent of the marker region varies along the circumferential datum edge.
19. A method of determining misalignment of a rotatable component rotating in a rotary coupling with respect to a preferred axis of rotation of the rotary coupling and a preferred plane of rotation of the rotary coupling, the method comprising: operating a detector to provide a signal indicating interaction with a marker region at a plurality of reference 5 coordinates disposed about the rotatable component, wherein the marker region is carried by the rotatable component, and is configured so that said signal has a period corresponding to the rotation of the rotatable component and comprises: a first characteristic, invariant under axial displacement of the marker region; and a second characteristic, which varies with axial position of the marker region; and the method further comprises identifying a 15 misalignment of the rotatable component based on said signal.
20. The method of claim 19 wherein the first characteristic varies with radial position of the rotatable component.
21. The method of claim 19 or 20 wherein the second characteristic is invariant under radial displacement of the rotatable component.
22. The method of any of claims 19 to 21 wherein the at least one signal comprises a set of signals, each associated with a corresponding on of the reference coordinates.
23. The method of claim 22 wherein the method comprises identifying an axial displacement of the rotatable component based on a change in the second characteristic which is the same in each signal of the set of signals.
24. The method of claim 22 or 23 wherein the method comprises identifying a radial displacement of the rotatable component based on a change in the first characteristic of each signal of the set of signals.
25. The method of any of claims 22 to 24 wherein the method comprises identifying a tilt of the rotatable component based on a difference in the second characteristic of at least two signals of the set of signals.
26. The method of any of claims 19 to 25 wherein the first 10 characteristic comprises a timing of the at least one signal in said period, for example the timing of an edge of a pulse of the signal.
27. The method of any of claims 19 to 26 wherein the second characteristic comprises information encoded in said signal, wherein the information is encoded by at least one of a pulse duration, a pulse amplitude, a modulation frequency, a modulation phase, a field strength of the signal, and a wavelength of the signal.
28. A computer program product configured to program a programmable 20 processor to perform the method of any of claims 11 to 16 or 19 to 27.
29. A data processor configured to perform the method of any of claims 11 to 16 or 19 to 27.