CA1063696A

CA1063696A - Damped pendulum angular position

Info

Publication number: CA1063696A
Application number: CA243,386A
Authority: CA
Inventors: Robert J. Armstrong; Boyd S. Cook
Original assignee: BP Trading Ltd
Current assignee: BP Trading Ltd
Priority date: 1975-01-27
Filing date: 1976-01-09
Publication date: 1979-10-02
Also published as: NL7600814A; NL183907C; DE2601177A1; NO760217L; FR2298785A1; FR2298785B1; NL183907B; US4027399A; JPS5199559A

Abstract

ABSTRACT OF THE DISCLOSURE
An angular positional sensor comprises a housing in which is mounted rotary sensing device including a shaft which mounts a pendulum having relatively low inertia and a balance member having relatively high inertia and rotatably mounted within the housing adjacent the pendulum member. At least the part of the housing containing the pendulum and the balanced member also contains a liquid to provide a viscous coupling between the pendulum and the balanced member. The arrangement is such, that in use, angular movement of the housing about the longitudinal axis of the shaft causes movement of the rotary sensing device relative to the shaft which is retained stationary by the pendulum which in turn is damped by the balanced member, to produce a signal representative of such angular movement from the rotary sensing device.

Description

~3~
The invention relates to angular positional sensors, more particularly, although not exclusively, to sensors for use in determining the deflection of a riser pipe during underwater drilling.
According to one aspect of the present invention there is provided an angular positional sensor comprising:

(a) a housing; : .
(b) a rotary sensing device, the rotary sensing device ~-having a freely rotatable shaft and being mounted in the housing, said sensing device being operative to .-produce a signal representative of the relative :.
angular movement between the device and said shaft;
~c) a pendulum, the pendulum being mounted on the shaft ~
of the rotary sensing device in the housing and having low inertia;
~d) a balanced member, the balanced member having high inertia relative to said pendulum inertia and being rotatably mounted within the housing adjacent the : pendulum;

2~ ~e) a liquid, the liquid being contained in at least the part of the housing containing the pendulum and the balanced member to provide a visaous coupling between the pendulum and the balanced member, the -arrangement being such, that in use, angular move- .
ment of the housing about the longitudinal axis of the shaft causes movement of the rotary sensing de- .
vice relative to the shaft which ~.s retained ~
stationary by the pendulum which in turn is damped :-by the balanced Member, whereby a signal represent- - -

3~ ativ~ of such angular movementis produced by the rotary sensing device. ~: :
The ratio of the inertia of the balanced member to .
the inertia of the pendulum should be as high as possible - 2 ~

such as in the order o~ 40:1. lhe pendulosi-ty of -the pendul~
is preferably 50 gram centimetres minimum, or sufficient to overcome the bearing breakaway frictional torque within the angular accuracy allowanceO
Conveniently, the pendulum is cylindrical and has a closed end by which it is mounted coaxially on the shaft of the rotary sensing device with a weight being attached thereto. With such a pendulum9 the balanced member is also cylindrical9 having a closed end by which it is mounted coaxially with the pendul~ and the shaft of the rotary sensing device, the open end of the balanced member inter-fitting with the open end o~ the pendulum. ~he open ends of the pendulum and balanced members may each be formed or carry3 coaxial with said sha~t, cylindrical ~ormations or members which are interfitting to increase the viscous coupling between the pendulum and balanced member.
~he part of the housing containing the pendulum and ~ -balanced member may be completely filled with liquid 9 and a relatively small proportion may be removed, and the ratio of ~the spacing between the radially outer surface of the balanced member and a surrounding inner surface of the housing, on the one hand 9 and between the radially inner surface of the balanced member and the radially outer surface of the pend-ulum9 on the o-ther hand 9 may be of the order of 12:1 or more.
~he housing may be substantially filled with liquid which may be a silicone fluid9 with a member of closed cell, cellular synthetic pla,stics material, e.g. neoprene 9 also located in the housing to facilitate expansion of the liquid with increase of tempera-ture. ~ -, 19,12.75 tgs.rp ~ 3 --- - , . . . ... . . . ...

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1~63696 BP-7 ~he rotary sensing de~ice may comprise a rotary A.C. induc-tive pick-off.
According to a still further aspect of the invention a positional sensing module comprises an outer casing con-taining two angular positional sensors as defined in any of the next preceding se~en paragraphs located within the outer casing with the axes of rotation of said shafts normal to one ano-ther.
~he outer casing ma~ also be substantially filled with liquid, which may be a silicone fluid, with a member of closed cell, cellular synthetic plastics material~ e.g.
neoprene, also located in the casing to ~acilitate expansion of the liquid with increase in tempera-ture, According to yet a further aspect of the invention an angular positional sensing sys-tem comprises a-t least two -positional sensing modules each connected via respective resolvers and demodulators to indicator means.
lhe indicator means may comprise a ca-thode ray -tube display device. In addition or alternativel~ the~ demodul-ators may be connected via an attenuator and an arithmetic unit for operating audible and/or visible warning devices.
According to yet a still further aspect of the invention, a method of monitoring the deflection from vert- -ical or a riser during underwater drilling comprises locat-ing a separate angular positional sensing module9 as defined hereinabove at a required position on the riser and at the top of the BOP stack9 and comparing the outputs from such positional sensing modules to define the deflec-tion angle in the ball or flexible joint between the riser and ~OP
stack.

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i3696 The foregoing and further features of the invention may be more readily unders-tood from the following descrip~
tion of two preferred embodiments thereof, by way o:E example9 with reference to the accompanying drawings9 in which:-~ig.1~ is a side sectional view of a positional sensor9 Fig,1B is a side sectional view of an alternative positional sensor9 Fig.2 is a side elevational view9 part in section of a positional sensing module including two sensors as shown in ~ig.1A or ~ig~1B 9 Fig.3 is a diagrammatic perspective view of a sending module as shown in ~ig.2 located ln position on a riser9 and Fig.4 is a block schematic diagram of a positional sensing system.
Referring flrstly to Fig.1A there is shown a positional sensor comprising a generally T-shaped section ;
housing 10 with a sensing device 11 comprising a rotary h.C.
.
lnductive pick-off located with its body housed in the hollow leg of the housing 10. lhe device 11 is attached by screws 12 to an interior wall 13 of housing 10 with a sensing shaft 14 projecting through an aperture 15 in wall 1~ and into a hollow body 16 of housing 10. A light weight cylindrical pendulurn member 17, carrying at least one weight 18 on it~ radially inner surface, is rigialy mounted on, and coaxially with shaft 1~ for rotation therewith by way of a closed end of the member 17. ~he pendulum is arranged to have a pendulosity of 50 gram centimetres.
~he hollow body 16 is closed by a circular end 19.12.75 tgs.rp .. . . . . . . .
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10~3~36 cap 19 retained by screws 20 and sealed by an 0-ring seal 21. lhe end cap 19 is formed with an inwardly projecting, central nose portion 22 which carries deep grooved~ instru-ment quality, bearings 23 for rotatably mounting a wheel 24 coaxially with the pendulum 17 and shaft 1~. ~he wheel 24 carries a relatively heavy annular weight 25 such -tha-t there is an inertia ratio of the order of 4001 between the wheel 24 and pendulum 17. lhe wheel 24 is bo-th statically and dynamically balanced and fits over the pendulum 17.
The hollow leg of housing 10 is closed by an end cap 26, retained by screws 27 and sealed by an 0-ring seal 28. ~ tubular member 29 of closed cell, cellular synthetic plastics materlal9 such as neoprene9 is located in -the holl~
leg of housing 10.
~he interior of housing 10 i9 filled with a liquid9 ,such as a silicone fluid, by initially locating end cap 19 horizontal and introducing llquid through an aperture subsequently closed by screw 30 in end cap 26. ~he housing 10 is then rotated to the position sho~m ln ~ig.1 when a screw 31 is removed to bleed any entrapped air from hollow body 169 such body is then filled with the liquid. ~he, tubular member 29 allows for expansion of the liquid with increase of temperature.
The internal ~iameter of wheel 249 where it surrounds pendulum 179 is sligh-tly larger than -the external diameter of the pendulum 17, e.g. 1 millimetre larger for a device with a pendulum 17 having an external diameter of 60 millimetres. The external diameter of weight 25 is such that the gap between it and the inner surface of the wall of ~0 housing 10 is about twelve -times9i.e. 12 millime-tres9 tha-t of 19.12.75 tgs.rp - 6 -:; , . . . . -~ . . .

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~63~96 BP-7 the gap between pendulum 17 and wheel 24.
In use, when the housing 10 is tilted about the longitudinal axis of shaft 1~ the sensing device 11 moves with the housing 10 but the pendulum 17 remains vertical.
Hence there is rotation of device 11 relative -to its shaft 14 and a corresponding electrical output is produced from device 11. ~he sensor is particularly suitable for use in environments such as for sensing the deviation from vertical of a riser used in underwater drilling. In such an environ-ment there is considerable vibration and therefore the pendulum 17 is reciuired to be damped so as to minimise the ~ -effects of such vibrations which might otherwise cause the pendulu~ to oscillate. Ihis is achieved by the provision of the inertial wheel 249 the particular parameters of the pendulum 17 and wheel 24 referred to9 and the silicone fluid.
When the housing is tilted about the longi-tuclinal axis of the shaft the combined effects of the high inertia wheel 9 its low fric-tion bearings 9 and light viscous couple to the case allows the inertia wheel to remain stationary. ~he high viscous couple between the wheel 25 and pendulum 17 assists the pendulum to remain ver-tical. ~he pendulurn isg of course9 sensitive to la-terally applied accelera-tions such as those due to drilling. ~he effects of these are mini-mised by the high viscous couple with -the inertial wheel 24 which does not react to such conditions.
Re~erring now to Fig.1~ there is shown an alter-native positional sensor which is similar to the sensor of Fig.1A. In this sensor the pendulurn 17' extends around the radiall~ outer surface of weight 25 so as to increase the viscous coupling between wheel 24' and the pendulum. In 19.12075 tgs.rp 7 - . .. ~ - . : . : .:

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~;3~;96 addition the open ends of pen~ulum 17' and wheel 24' are formed with cylindrical portions 17a and 24a respectively9 which are coaxial with shaft 14 and which inteEfit so as to increase the viscous coupling between pendulum 17' and wheel 24'. The clearance spaces between each portion 17a and adj~cent por-tion 24a is of the order of ten -to fifteen thousandths of an inch. ~he weight 18' for pendulum 17' is in the form of a heavy disc located on the rear of the closed end of pendulum 17lo In addition in this embodiment the member 29 m~y ~e omitted and a sm~ll amount~ e. g~ 12 cc of . ....
a total of 200 ccO 9 of fluid removed~ to allow for temper-ature expansion9after filling. ~his also further reduces the viscous couple between the pen~lulum and the case and provides a measure of compensation for fluid viscosity variation with temper~tureO Bleed holes 17b are provided in the u ?per half of pendulum 17' to preven-t air locks when filling with damping flu.id.
~he sensor of Fig.1B oper~tes in similar manner to that described for Figo 1Ao ~ . .
A suitable sensing device for sensor 11 is :~ commercially ava.ilable from the Sperry Gyroscope Division of Sperry Rand :Limitedj :3s Sperry Part No.211~2-0.
Referring now to Figu 2 there i.s shown a positional sensing module comprising a cylindrical casing 32 with octag-onaI end caps 33 attached and sealed t1l.ereto. 1~ separate sensor as shown in ~ig.1A or 1B is attached by a respective :~ bracket 34 to the interior surface of each end cap 330 ~he ; operational axes of the two sensors (i.e. the longitudinal axes OI shafts 14 of devices 11) are ~rranged normal to one another to provlde signals representative of a defledtion 19.12.75 tgs.rp - ~ -. - . . .. 1 .. ~ ; .
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1~636~6 BP-7 ~rom vertical o~ casin~ 32 in any dircc-tionO The casing 32 is also filled with a silicone oil and a member (not shown) similar to member 29 of Figo 1~ is ?~lSO located in casing Referring now to ~ig.3 9 a sensing module as shown in Fig~ 2 is shown attached to a riser 35 by way of a bracket 36 having two pairs of arms 37, 3~ with respective cross members 3~ he bracket 36 is attached to the riser 35 by a tensioned strap 39 having its ends associated with respec-tive cross members 3~'. lhe bracket 36 further includes two angled faces 40 into contact with which corres-ponding faces of the oc~agonal end caps 33 o~ the casin~ 32 are drawn by tensioning a strap 41 whichh~s a quick-release device (not shown) intermediate its ends. ~he bracket 36 is attached at a specific position on the riser 35 using a loeation reference (not shown) which may be an h~draulic line9 for example9 extending generally parallel to, and alongside, the riser. With this specific positioning of the bracket 36 on the riser 35 and, in -turn, the position-ing of the module on the bracket9 the operational axes of the two sensors of the module are oriented in the desired .
manner relatlve to the corresponding axes of the riser 35 whieh latter axes are reference~ to the meridian or other datum. ~he upper end cap 33 fits under a corner pla-te 42 of the bracket 36, the eorner plate having a notch or reeess 43 formed therein to aecommodate -the sensor cables 44 whieh ~enter the module through the upper end eap. ~hus9 it is not possible incorreetly to orientate the module when offering it to the bracket 36 for attaehment thereto by the strap ~1. -~he sensing module is a~tached to the riser 35 elose to -tlle usual flexible or ball joint provided at the ~' ' 19 12.75 tgs.rp . ... .... .

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1063~96 BP-7 point where the riser is attached to the blow-of~-preventer (BOP) stack (not shown). Ano-ther module is attached to the top of the BOP stack in a manner similar to that described and such that the operational axes of that module are orient&d in the sarne ~ay as those of the riser module.
Referring now to ~ig.4 the outputs from the two sensor modules or uni~s 45a and 45b comprising A.C~ signals representati~e of an angle are fed to respective resolvers 46a and 46b ~hich align the sensor signals9 i.e. they orient in azimuth the sensor signals with respect either to a geographic reference or a heading referenceO ~he ~.C. out- ;~
puts from the resolvers 46a and 46b are fed to respective demodulators 47a and 47b. The outputs from the demodulators ~7a and 47b are in terms of Cartesian co-ordinates and are fed to a cathode ray tube control device 48 in which the signals from the respecti~e sensor devices are subtracted and fed to a cathode ray tube display 49.
The outputs from demodulators 47a and 47b are also fed via an attenuator 50 into an arithmetic unit 51 which functions first to con~ert the inputs thereto ~rom Cartesian to polar co-ordina-tes9 then to sub-tract one sensor unit angle from the other sensor uni-t angle9 and then to compare the final angle with predetermined reference angles. The reference angles are derived from a frequency divider (not shown) and i~ the measured angle exceeds a lowest predeter-mined angle (e.g. 6) then a lamp ~P1 is illumin~ted and a Sonalert*52 sounded ~ith a lo~ ~requency "bleep". Should the measured angle increase to a second prede-termined angle (e.g. 8) then lamp ~P2 is illuminated and the frequency of ;
~0 the "bleep'~ from Sonalert* 52 increased. Should -the measured ~Trade Mark 19.12.75 tgs.rp ' : ' , ' ' ~:' .' . ' ,, ' ., . . ', :,. :

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angle increase to a fur-ther predetermined angle (e.g. 10 ) then lamp ~P3 is illurninated and the output from Sonalert*
is changed -to a continuous note.
The angle resolvers ~6a and 46b not Qnly allow the apparent sensor axes to be rotated in azimuth to perrnit alignrnent to the meridian or other riser datum, but also relative to each other as between the riser module and BOP
stack module to allow for v~riations in the mounting there-of.
Alternative applications of -the present lnvention are to the control loop of a dynamic ship positioning system as the main or back-up term, to a pitch and roll sensor for a vessel, to an oil drilling rig to sense its inclination when being tilted from a towed position to an operative position9 and for monitoring the angle of inclination of a wire from which a dredger bucket is suspended.

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Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. An angular positional sensor comprising:
(a) a housing;
(b) a rotary sensing device, the rotary sensing device having a freely rotatable shaft and being mounted in the housing, said sensing device being operative to produce a signal representative of the relative angular movement between the device and said shaft;
(c) a pendulum, the pendulum being mounted on the shaft of the rotary sensing device in the housing and having low inertia;
(d) a balanced member, the balanced member having high inertia relative to said pendulum inertia and being rotatably mounted within the housing adjacent the pendulum;
(e) a liquid, the liquid being contained in at least the part of the housing containing the pendulum and the balanced member to provide a viscous coupling between the pendulum and the balanced member, -the arrangement being such, that in use, angular move-ment of the housing about the longitudinal axis of the shaft causes movement of the rotary sensing de-vice relative to the shaft which is retained stationary by the pendulum which in turn is damped by the balanced member, whereby a signal represent-ative of such angular movement is produced by the rotary sensing device.

2. An angular positional sensor as claimed in claim 1 wherein the ratio of the inertia of the balanced member to the inertia of the pendulum is in the order of 40:1.

3. An angular positional sensor as claimed in claim 1 wherein the pendulosity of the pendulum is fifty gram centi-meters minimum.

4. An angular positional sensor as claimed in claim 1, wherein the pendulum is cylindrical and has a closed end by which it is mounted coaxially on the shaft of the rotary sensing device with a weight being attached thereto.

5. An angular positional sensor as claimed in claim 4, wherein the balanced member is also cylindrical, having a closed end by which it is mounted coaxially with the pendulum and the shaft of the rotary sensing device, the open end of the balanced member interfitting with the open end of the pendulum.

6, An angular positional sensor as claimed in claim 5, wherein the open ends of the pendulum and balanced members each have, coaxial with said shaft, cylindrical formations which are interfitting to increase the viscous coupling be-tween the pendulum and balanced member.

7. An angular positional sensor as claimed in claim 1, wherein the part of the housing containing the pendulum and balanced member is substantially filled with liquid.

8. An angular positional sensor as claimed in claim 7, wherein the ratio of the spacing between the radially outer surface of the balanced member and a surrounding inner surface of the housing, on the one hand, and between the radially inner surface of the balanced member and the radially outer surface of the pendulum, on the other hand, is of the order of at least 12:1.

9. An angular positional sensor as claimed in claim 1, wherein the housing is substantially filled with liquid with a member of closed cell, cellular synthetic plastics material also located in the housing to facilitate expansion of the liquid with increase of temperature.

10. An angular positional sensor as claimed in claim 1, wherein said liquid comprises a silicone oil.

11. An angular positional sensor as claimed in claim 1, wherein the rotary sensing device comprises a rotary A. C.
inductive pick-off.

12. An angular positional sensor as claimed in claim 1, further comprising an outer casing containing said sensor and a second angular positional sensor, said two sensors being located within the outer casing with the axes of rotation of said shafts normal to one another, thereby forming a positional sensor module.

13. A positional sensing module as claimed in claim 12, wherein the outer casing is substantially filled with liquid, with a member of closed cell, cellular synthetic plastics material also located in the casing to facilitate expansion of the liquid with increase of temperature.

14. A positional sensing module as claimed in claim 13, wherein said liquid is silicone oil and said cellular synthetic plastics material is neoprene.

15. An angular positional sensing system comprising at least two positional sensing modules as claimed in claim 12, each connected via respective resolvers and demodulators to indicating means.

16. An angular positional sensing system as claimed in claim 15, wherein said indicator means comprises a cathode ray tube display device.

17. An angular positional sensing system as claimed in claim 15, wherein the demodulators are connected via an atten-uator and an arithmetic unit for operating at least one warming device.