GB2321969A

GB2321969A - Rotary coupling alignment

Info

Publication number: GB2321969A
Application number: GB9801354A
Authority: GB
Inventors: Alan Pratt
Original assignee: Renold PLC
Current assignee: Renold PLC
Priority date: 1997-02-05
Filing date: 1998-01-23
Publication date: 1998-08-12
Anticipated expiration: 2018-01-23
Also published as: GB2360596A; GB9801354D0; GB2321969B; GB2360596B; GB0111682D0

Abstract

A rotary coupling assembly has first and second coupling halves (1) that are mounted on a pair of rotary shafts of two machine components to be coupled. A first coupling half has a fixing bore (5) that receives a stud (12) that supports a permanent magnet (14). An aligned fixing bore (4) in the second coupling half receives a sensing unit (13). The sensing unit has a compartment (16) in which the permanent magnet is freely received and comprises at least one Hall-effect sensor that detects the intensity of the magnetic field generated by the magnet. Misalignment of the coupling shafts results in movement of the magnet relative to the sensing unit and a corresponding fluctuating output signal from the Hall-effect sensor. The output signal is processed and the amount of misalignment is calculated. The invention provides a non-contacting, high resolution and high frequency response misalignment detector which may be used whilst the coupling is in operation. The arrangement may also be used in the measurement of torque (Figures 9-11).

Description

ROTARY COUPLING ALIGNMENT The present invention relates to (l Inethod and device for sensing the alignment or misalignment of rotary shafts that arc connected together by a coupling comprising two rotary coupling halves each connected to a rotary shaft.

Power transmission drives for a particular driven machine generally comprise a collocation of individual drive components such as for example. a motor, a gearbox and an input shaft of the driven machine. The rotary shafts of the individual components are connected together be flexible couplings. It is imperative during installation and service or the lrallslllissioll drives that the individual shafts and therefore the couplings are correct} aligned in order to avoid problems such as premature coupling wear. noise. vibration and excess loading on the component shafts and bearings. Even if the shafts are initially aligned they can become offset as a result of loads applied during use poor maintenance or deterioration of a structure on which the components are mounted. Shaft misalinment can be radial in which the shafts remain parallel but are offset radially indoor angularly in which the shafts are not parallel. Checking misalignment in-situ under site conditions can be X ery difficult and often impossible whilst the transmission drive is in operation.

Conventional shaft misalignment measurement is achieved by attaching a mechanical dial indicator to one coupling half. The indicator has a radially extending probe that is biased into contact with the periphery (or a suitable concentric circumferential surface) of the other coupling half and generates a reading indicative of the linear movement of the plebe. ()ne or both ol the coupling halves is then rotated and any radial misalignment will be manifested in movement of the probe. The difference between the maximum and minimum dial indicator measurements generally represents twice the parallel radial misalignment of the shafts.

The angular misalignment of the shafts is measured by mounting the dial indicator to the face of one of the coupling halves such that the probe contacts the opposed face of the other coupling half: The misalignment is calculated from the difference between the maximum and minimum readings and the radius at which the dial indicator is mounted.

A disadvantage of dial indicators ot this kind is that it is only possible to take measurements at low shaft speed revolulioll. Moreover it is often difficult to read the dial indicator because of its attitude during rotation and the proximity of other equipment. Furthermore. in some instances there is not sufficient clearance from peripheral equipment (e.g. brake callipers) for the coupling to make a full revolution with the dial indicator in place.

The use of Hall-effect position sensors is well known to detect the presence or position of one component in relation to another. particularly in automated processes.

The Hall effect results from applying a DC voltage to a semiconductor Hall-effect device and bringing the device into the proximity of a magnetic field. The device generates an output voltage in proportion to the strength of the magnetic field. In position sensor devices one or more permanent magnets are mounted on the component to be sensed and a magnetic field detecting device comprising a Halleffect device is moved relative thereto. When the component is in proximity to the detecting device the latter outputs a voltage representative oi the proximity of the component.

Such an arrangement is described in US patent No. 5493216 which discloses a magnetic position detector comprising three longitudinally axially aligned magnets attached to a component to be examined. The magnets are arranged in alternate polarities and with inter-magnet gaps. The Hall-effect device is adjustable so that it generates an output signal of alternating polarity as it passes over the inter-magnet gaps. The arrangement permits accurate detection of the fixed position of a component.

It is an object of the present invention to obviate or mitigate the aforesaid disadvantages of coupling alignment.

According to the present invention there is provided a rotary coupling assembly having first and second coupling halves that are mountable on a pair of rotary shafts of two components to be coupled. wherein a magnetic field generator is connected to the first coupling half and a sensing unit is connected to said second coupling half, the sensing unit comprising a magnetic field intensity detecting device that provides an output signal indicative of the relative movement magnetic field generator to the sensing unit during rotation of the coupling.

The output signal is therefore representative of the (axial or radial) misalignment of the rotary shafts or of the relative rotation of the coupling halves to one another.

The coupling halves may each conveniently have fixing apertures in which the magnetic field generator and the sensing unit may be fitted. The magnetic field generator is conveniently supported in an aperture in one coupling half whereas the sensing unit is fitted in an aperture in the other coupling half.

The magnetic field intensity detecting device may comprise a relative radial movement sensor, a relative angular movement sensor, a relative circumferential movement sensor or a combination of two or more of these.

Preferably the magnetic field generator projects from the first coupling half and is received in an open compartment of the sensing unit at a location adjacent the magnetic field intensity detecting device.

The magnetic field generator Is preferably a permanent magnet and the magnetic field intensity detecting device preferably comprises a Hall-effect sensor.

Each movement sensor may comprise a pair of Hall-effect sensors, one of each pair being positioned adjacent each pole of the magnet.

The orientation of the magnet may conveniently be adjusted to permit a change from one form of relative movement detection to another.

The magnet may be mounted on the end of a stud that is received in the fixing aperture of the coupling half.

In a preferred embodiment the sensing unit comprises a cylindrical housing at least a portion of which is received in and is lockable within the fixing aperture of the respective coupling half. It may be lockable by means of a rotary locking pin fitted in the wall of the housing. the pin having a cam that engages a wall of the fixing aperture when in a locking pOsition.

The sensing unit may further comprise a photocell that faces an opening in the housing, the opening being positioned such that it is outside the portion of the housing that is received in the bore. A light source is preferably provided in axial alignment with the opening so that as the coupling rotates the light is incident on the photocell once every revolution.

The measured magnetic field intensity is conveniently processed by a signal processing circuit and a coded signal is transmitted from a transmitter in the sensing unit to a receiver remote from the coupling.

A specific embodiment of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 is a sectioned side elevation of ci conventional coupling, the section being along line 1-1 of figure 2: Figure 2 is an end elevation of a conventional coupling; Figure 3 is a sectioned side elevation of part of the coupling of the present invention showing a conventional fixing arrangement: Figure 4 is a sectioned vieu- of the coupling of figure 3 in a plane inclined to the sectioned view of figure 4 and SllOU/illg a sensor assembly: Figure 5 is an end elevation of part of the sensor assembly: Figure 6 is a sectioned side elevation along line 6-6 of the sensor assembly of figure 5; Figure 7 is a section side elevation along line 7-7 of the sensor assembly of figure 5; Figure 8 is a circuit diagram for the sensor assembly. shown in tigures 5 to 7.

Figure- 9 is a sectioned side elevation of an alternative embodiment of the present invention; Figure 10 is an end view of part of the sensor assembly of figure 9; Figure 11 is a sectioned side elevation along line 1 - 1 of figure 10; and Figure 12 shows diagrammatically an alternative magnet arrangement of the sensor assembly in side and end views.

Referring now to the drawings. figures 1 and 2 show a conventional coupling assembly comprising two coupling halvcs I each having a central bore 2 by which it is connected to a respective machine shaft (not shown) and radially outward extending flanges 3 by which the coupling halves 1 are connected together. Each of the flanges 3 has axial bores 4, 5 equi-angularly- spaced therearound. the diameter of the bores 4 in one coupling half being larger than those (D) in the other.

The coupling halves I are connected together by a plurality of fixing assemblies 6, such as the one shown in figure 3 and described below. that pass through aligned bore pairs 4.5 in the coupling halves 1.

Each of the fixing assemblies 6 comprises a resilient sleeve 7 that is received coaxially in the larger bore 4 of the aligned bore pair and has a cylindrical metallic lining 8, a fixing bolt 9 that passes through the smaller bore 5 and the metallic lining 8, and a nut 10 that secures the bolt 9 in place.

The coupling of the present invention makes use of the above described conventional coupling assembly but replaces one of the fixing assemblies 6 with a sensor assembly that is mounted in an aligned bore pair 4.5 as shown in figure 4.

Alternatively the sensor assembly can be fitted in a vacant bore pair 4.5 if there is one available.

The sensor assembly (indicated generally by reference numeral 11) comprises a stud 12 that is received in the smaller bore 5 and a sensing unit 13 that is housed in the larger bore 4. The stud 12 protrudes at both ends of the smaller bore 5, the end proximate the sensing unit 13 supporting a permanent magnet 14 and the end distal from the sensing unit 13 being threaded and secured in place by a nut 15. The permanent magnet 14 is freely received in an end compartment 16 of the sensing unit 13 so that any movement of the magnet 14 relative to the sensing unit 13 is not impeded.

Figures 5 to 7 show the sensing unit 13 in more detail. In each of the figures the permanent magnet 14 is shown in the compartment 16 but the supporting stud 12 has been removed for clarity.

The sensing unit 13 comprises a cylindrical plastics housing 1 7 with a coaxial metallic ring 18 (constructed from magnetic material) connected at one end by means of a sliding interference fit and a radially outward extending flange 19 at the other end to which there is connected a rear section 20 (shown removed in figure 7). The metallic ring 18 and the contiguous portion of the housing 1 7 fit tightly in the larger bore 4 with the flange 1 9 and rear section 20 located outside the bore 4 (see figure 4) The wall of the housing 17 has an axial blind bore 21 in which there is received a pin 22 with an eccentric locking cam 23 that in a locking configuration projects from a radial opening in housing 17 to engage the internal surface of the coupling bore 4 thereby securing the sensing unit 13 in place. The sensing unit 1 3 is maintained stable within the coupling bore 5 by means ol an During 24 that is seated in an annular groove 25 defined in the exterior surface o the metallic ring I The rear section 20 may be used to house a power supply battery (not shown) and a status indicating LED (not shown).

The magnet receiving compartment 16 is defined between the metallic ring 18 and two axially spaced printed circuit boards 26. 27 seated at each end of the metallic ring 18. A main circuit board 26 is of circular configuration and is mounted on a rear edge of the metallic ring 18 adjacent the plastics housing 1 7. whereas a subsidiary circuit board 27 of D-shaped cont)urc'ition pal-tiall! closes an end opening of the compartment 16.

The main circuit board has three Hall-effect sensors 29. 30. 31 mounted on it.

A radial sensor 29, 30 is mounted at diametrically opposite locations at the periphery of the circuit board 26 and a single axial sensor 31 is mounted radially inward from one of the radial sensors 29 . The subsidiary' circuit board 27 has a single Hall-effect axial sensor 32 mounted opposite that on the main circuit board 96. When the coupling halves 1 are connected together the magnet 14. which is of parallelepiped configuration, is oriented such that its poles are each facing a respective radial sensor 29, 30 and the axial sensors 31. 32 are positioned at each side of one of the magnet poles. The radial sensors 29. 30 afford a clearance from the poles of approximately 2mum, thereby permitting relative radial displacement of the magnet 14. A similar clearance is provided in an axial direction between the magnet 14 and the axial sensors 31, 32.

The magnet 14 is inserted into the compartment 16 b) orienting it so that it passes through the compartment 1 6 opening that is partially closed bqi the subsidiary circuit board 27 and rotating it through 90 degrees to the position shown in figures 5 to 7 so that the circuit board 27 prevents its withdrawal.

The metallic ring 18. being of magnetic material. acts to focus the magnetic flux of the magnet 14 and shield the sensors 29 to 32 from magnetic field changes when the sensor assembly 11 is inserted into the aligned bores 4. 5 of the coupling.

The sensor unit 13 is fitted with a photocell 33 that faces in a radially outward direction towards an aperture (not shown) formed in the housing wall.

The Hall-effect sensors 29-39 are connected in an electronic circuit depicted in figure 8 which provides energising X voltage to the sensors and signal processing for the Hall voltage generated by each sensor.

The circuit is controlled bx a microprocessor 40 that ensures battery power is supplied to the Hall-effect sensors 2')-32 in pulsed form via switched regulators. The output of each pair of (axial or radial) Hall-effect sensors 29.30 or 31.32 are connected to the inputs of a differential amplifier 41 or 42. The amplified differential voltages are each passed to the same two channel A/D converter 43 that operates under the control of the microprocessor 40. Obviously a multiple channel A/D converter could be used if more than two data channels are to be transmitted simultaneously.

The Hall-effect sensors 29-32 each generate an output voltage that is proportional to the magnetic field intensity and therefore to the proximity of the magnet pole to the sensor. As the coupling rotates. any misalignment of the shafts will result in relative movement between the coupling halves 1 and therefore relative movement between the magnet 14 and the respective Hall-effect sensors 29-32. As the magnet 14 moves between the sensors 99-,2 their outputs are in antiphase and are amplified by means of a differential amplifier 41 or 42. The microprocessor 40 generates a digital pulse long enough for the A/D to take a sample from the relevant channel and the sampled voltage is converted to a digital value. If there is misalignment the digital value on the appropriate channel will fluctuate as the shafts rotate and resulting approximately sinusoidal signal can be related to the angular or radial misalignment to enable corrective action to be taken.

The measured digital value can be measured in a variety of known ways. In a simple embodiment a multimeter (not shown) can be directly' connected to the analogue output of the differential amplifiers 41. 42. The coupling is rotated at slow speed through one or two revolutions alloy ins the connecting wires to the multimeter to twist. For continuous measurement OX CI extended periods of time or at high speeds of shaft revolution a physical electrical connection is not possible and a radio telemetry link may be used. The sampled digital values are coded in serial form by the microprocessor and are transmitted hy an FM transmittel- to a receiver. The microprocessor feeds the transmitter with a coded signal of bits comprising the measured data. a channel identification bit to indicate to which of the sensor pairs each packet of measured data relates. a battery condition indicator bit and an angular position marker (generated by the photocell as discussed below).

The transmitted data is received bv an FM receiver module and a second microprocessor decodes the data and interfaces with a computer. The data is separated into the two channels of information and is displayed graphically and numerically.

In order to take corrective action it is necessary' to identify the angular position where the measured value is a maximun. This is achieved by shining light from a fixed location towards photocell aperture in the sensor unit 13. During revolution the photocell 33 will only detect light for a very short angle of rotation thereby providing an angular position reference point. The signal from the photocell 13 is included in the transmitted coded signal and a marker can be superimposed on the graphically displayed image to enable the r elationship between maximum misalignment and angular position to be deduced.

In an alternative embodiment not shown in the figures the magnet and sensors are repositioned so that they are disposed at 90 degrees to the position shown in figures 5 to 7. In this configuration it is possible to detect relative rotational movement of the coupling halves. This permits measurement of the compression of the resilient sleeve under loading. detection of sleeve wear and measurement of the torque.

In figures 9-11 there is shown an alternative embodiment in which parts corresponding to those of figures 5 to 7 are indicated by the same reference numerals increased by 100 and are not further described except insofar as they differ from their counterparts in figures 5 to 7.

The alternative embodiment differs from the embodiment of figures 5 to 7 only in that the positions of the axial Hall-effect sensors 131. 1 32 have been changed so that they are now adjacent the same face of the magnet 114 but at opposite ends thereof. This arrangement greatly simplifies installation of the sensor assembly as it obviates the need for the subsidiary circuit board 27. the presence of which in the previous embodiment meant careftil manoeuvring of the magnet 1 4 so that it could occupy the compartment 16.

The range and linearity of measurement is determined to some extent by the size and relative proportions of available rectangular magnets. In an alternative embodiment shown in figure 12 the rectangular magnet 14. 114 is replaced by a cluster of separate magnets 214 on ci non-magnetic support block 250. This arrangement provides for more control in that it permits measurements in the radial, axial and tangential directions without the need for repositioning of the magnet.

By using two Hall-effect sensors the measuring sensitivity of the equipment is doubled as compared with a single sensor. Moreover. two sensors provide compensation for errors introduced bql thermal drift of the sensors and ambient magnetic fields. However, it is to be understood that a single sensor could be used and is intended to be included within the scope of the present invention.

If necessary a dummy sensor assembly is inserted into a diametrically opposite pair of aligned bores to ensure that the coupling is balanced during rotation.

The present invention provides for non-contacting. infinite resolution, high frequency response misalignment measurement equipment that is operational whilst the coupling is in use. Not only can the initial radial or angular misalignment be measured but also any changes in these alignments as a result of loading or operating temperature, as well as relative rotation between the coupling. can be detected during running.

The equipment is easy to install and configure for use. The large measuring range and high resolution means that little or no adjustment is necessary before measurement is commenced.

The software used to generate a misalignment measurement from the measured digital data can include mathen7atical correction algorithms to take account of non-linearities in the response of the Hall effect sensors.

It will be appreciated that numerous modifications to the above described design may be made without departing from the scope of the invention as defined in the appended claims. For example. the clearance between the poles of the magnets can be selected according to the size of the coupling and the anticipated range of misalignment.

Claims

C;AlMS

1. A rotary coupling assembly having first and second coupling halves that are mountable on a pair of rotary shafts oF two components to be coupled, wherein a magnetic field generator is connected to the first coupling half and a sensing unit is connected to said second coupling half. the sensing unit comprising a magnetic field intensity detecting device that provides an output signal indicative of the relative movement of the magnetic field generator to the sensing unit during rotation of the coupling.

2. A rotary coupling assembly according to claim 1. wherein the coupling halves each have fixing apertures in which the magnetic field generator and the sensing unit are fitted, the magnetic field generator being supported in an aperture in one coupling half and the sensing unit being fitted in ciii aperture in the other coupling half.

3. A rotary coupling assembly according to claim 1 or 2. wherein the magnetic field intensity detecting device comprises a relative radial movement sensor. a relative angular movement sensor. or a relative circumferential movement sensor or a combination of two or more of these.

4. A rotary coupling assembly according to any preceding claim wherein the magnetic field generator projects from the first coupling half and is received in an open compartment of the sensing unit at a location adjacent the magnetic field intensity detecting device.

5. A rotary coupling assemble according to claim 3. wherein the or each movement sensor is a Hall-effect sensor.

6. A rotary coupling assembly according to claim 5. wherein the magnetic field generator is a permanent magnet.

7. A rotary coupling assembly according to claim 6. wherein each movement sensor comprises a pair of Hall-effect sensors. each one positioned adjacent a pole of the permanent magnet.

8. A rotary coupling assembly' according to claim 7. wherein the outputs of each pair of Hall-effect sensors are connected to a differential amplifier.

9. A rotary coupling assembly according to any one of claims 6 to S. wherein the magnet is mounted on the end of a stud that is received in a fixing aperture of the coupling half.

10. A rotary coupling assembly according to claim 2. wherein the sensing unit comprises a cylindrical housing at least a portion of which is received in and is lockable to the fixing aperture in the respective coupling half.

11. A rotary coupling assembly according to claim 1 0. wherein the housing is lockable by means of a rotary locking pin fitted in a wall of the housing

12. A rotary coupling assembly according to claim 1 I 11 wherein the pin has a cam that engages a wall of the fixing aperture to lock the housing in place.

13. A rotary coupling assembly according to any one of claims 10 to 12 wherein the sensing unit further comprises a photocell that faces an opening in the housing, the opening being positioned such that it is outside the portion of the housing that is received in the bore.

14. A rotary coupling assembly according to claim 13. wherein a light source is provided in axial alignment with the opening so that as the coupling rotates the light is incident on the photocell once every revolution.

15. A rotary coupling assembly according to any preceding claim. wherein the measured value of magnetic field intensity is conveniently processed by a signal processing circuit and a coded signal is transmitted fi-om a transmitter in the sensing unit to a receiver remote from the coupling.

16. A rotary coupling assembly substantially' as hereinbefore described with reference to figures 3 to S. tigtllcs 9 lo li and ligure 12 owl tile accompanying drawings.

17. A method for detecting the misalignment of shafts in a rotary' coupling according to claim 1. wherein the misalignment the shafts is calculated from the output signal indicative of the relative movement of the magnetic field generator to the sensing unit.

18. A method for detecting the misalignment of shafts in a rotary coupling substantially as hereinbefore described with reference to the accompanying drawings.

19. A method for measuring the torque in a rotary coupling according to claim 1, wherein the output signal is indicative of the relative movement of the magnetic field generator and the sensing unit in ci ro1atiollal direction of the coupling.

20. A method for measuring the torque in a rotary coupling substantially as hereinbefore described with reference to figures 3 to 8. figures 9 to 11 and figure 12 of the accompanying drawings.