CA1065597A - Borehole sensor with motor driven direction-sensing gimbals - Google Patents

Abstract

A borehole sensor is presented including a three axis gimbal device for determining (1) a vertical plane, using the force of gravity as a reference, (2) a horizontal plane, using the force of gravity as a reference, and (3) the north direction, using the earth's magnetic field as a reference.
A motor drive system drives parts of the mechanism to desired positions about the three axes, and error transducers deter-mine the deviation from desired positions about the axes and provide feedback to the motor drive system to eliminate the error.

Description

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This inv~ntion relates to the field of parameter sensors.
More particularly, this invention rela~es to the field of borehole sensors where parameters in a borehole, particularly a gas or oil well, are sensed and transmitted to the surface.
In the field of oil and gas drilling, ~he usefulness of a system capable of detecting cer~ain parameters a~ the bot~om o~ the drill string and transmitting such data to the surface during the course of dril~ing has long been recognized.
Saveral systems have been proposed for accomplishing such sensing and data transmission. One of the principal types of such systems is ~he mud pulse telemetry system wherein pulses are generated in the mud column in the drill string ~or transmission of data to the surface. The present inven- -tion is particularIy adapted for use in mud pulse transmission systems.
While some proposals and systems for borehol~ telemetry have involved arrangements where se~sor packages are periodic-ally lowered into and raised from a well hole, by far ~he most preferred arrangement is ~o have the parame~er sensing apparatus permanently positioned at the bottom of the wall, preferably in a Lower segment of ~he drill string. The perma~ent down hole positîon of the parametar sensors d~es~
howe~er, make the factors of reliability, accuracy and .
repea~ab~lity of parame~er oper~tion a71 the more important.
O~herwLse, ~:he driller does not ha~e a truely accurate irl-dica~ion o tha direction of the well hole i~ the parameter sensors~are not highly accurate, or serious loss of time and

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expense may be involved if it is necessary to remove t~e drill str ~ at unscheduled times.
The downholP telemetry sensing device o~ the present invention includes:
(1) A three axis device for determining:
(a) a vertical plane, using the force of gravity as a reference, (b) a horizontal plane, using the force of gravity as a reference~ and :
1~ (c) ~he nor~h direc~ion, using the earth's m~gnetic ~ield as a r~ference.
(2) A motor drive system to drive parts o~ the mechanism to desired positions about the axes. ~ .

(3) Error transducers to determine deviation from the desired positions about ~he axes and provide ~eed-bark to the motor drive system. ~ ~ .
~4) A control and measuring system to measure the total ~ -movement of the motor drive system required to eliminate error.
ZO The sensor system is a thre~ gimbal system servo controlled ~ by two accelero~ters and one magnetometer. The accelérometers .
are used to establish the horiæontal and ver~ical planes by : inding the zero gravity posi~ion along two orthogonal axes, and ~he magn~tometer îs used ~o es~ablish the direction of : Z5 magnetic north in the horizon~al plane. : -An ou~er gim~al, known as the reference gimbal~ measures ~he re~erence angle (R) between a r~ference mark on the. drill ~ .... ....

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string and the ver~ical plane con~aining the drill a~is. The middle gimbal, or the inclination gimbal~ measures the angle of inclination of the drill axis with respect to the vertical.
The inner or magnetometer gimbal measures the angle between the horizontal projection of the drill a~is and magnetic north in the horiæontal plane. The sensor package is configured to be conta-ined within the drill string, and thus the design is compatible with a cylindrical form where diameter is xestricted ~-by the diameter of the dri11 string, but where there is no significant restriction on length.
The reference gimbal consists of a tubular s~ructwre free to rota~e coaxially with ~he drill string wi~hin a stationary tube in the drill string. An accelerometer is mounted on the re~erence gimbal with its sensiti~e axis perpendicular to t~e axis of rota~ion of the reference gimbal~
The reference angle is measured by determining the movement required to move the accelerometer from a HOME position to a position where the output of the accelerometer is zero. The ~-reerence angle is preerably measured by counting the number o steps required or a s~ep mokor to go from a known "HOME'I
position to a position where the reference accalerometer output is zero.
An inelinatio~ gLmbal or m~asuring ~he inclinatlon angle I) is mounted within the referance gimbal. The inclination gimbal algo has~an accelerometar whereby the inclina~ion angle iB measured by dete~mining the movement required to move the : : acaelerom~ter ~rom a HOME position to a posi~ion where ~he , 5~

output of the accelerometer is zero. The inclinatiun angle is preferably measured by coun~ing the number of s~eps required ~or a step motor to drive the incli~ation gimbal from a known "HOME" position to a position where the accelerometer output is zero~
Ano~her gimbal is also mou~ted within ~he reerenee gimbal parallel to the inclination gimbal and sla~ed to the inclina-tion gimbal. The third gimbal carrying the magnetometer is carried by this slaved additional gimbal. The azimuth angle ~A~ is also measured by determining the movement required to move the magnetometer from a HOME position to a position whare output of the magnetometer is zexo. The az~muth angle is pre~erably measured by counting the number of steps necessary for a stepping motor to drive the magnetometer ~o a null position whereby its relationship with r~spect to the ~arth's magnetic field is known.
One par~icular advan~age of ~he preferred steppi~g mo~or apparatus of the present invention is ~hat it elimina~es ~he need for separa~e angle transducers and the at~e~dant mechan-i~l or reliability problems such a~gle ~ransducers ~ypically present. Instead, angle measurement is determined s~lely by ~.-.
: ~ , . . .
counting the number o steps required to operate ~he stepping : motors to drive the respecti~e g~mbals ~o tha null positions.
Thus, since accura~e drive trains can be readily cons~ructed~ :
a system wi~h ex~ramely high accuracy is achieved.

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In accordance with one embodiment, a sensor apparatus for measuring directional parameters of a dri:Ll string in a bore-hole includes: :Eirst gimbal means mounted for rotation in a seg-men-t of a drill string, said first gimbal means being rotatable about the axis of -the drill string segment or an axis parallel to the drill string axis, first gravity responsive means mounted on said firs-t gimbal means for establishing a predetermined posi-tion of said first gimbal means with respect to the direction of the force of gravity, second gimbal. means mounted for rotation in said drill string segment, said second gimbal means being rotatable about an axis perpendicular to the axis of rotation of said first gimbal, second gravity responsive means mounted on said second gimbal means for generating inclination related sig- -nals as a function of gravity forces on said second gravity :
responsive means~ said inclination related signals varying as a function of the alignment of said second gravity responsive means with respect to the direction of the force of gravity, third gimbal means mounted for rotation in said drill string segment, said third gimbal means being rotatable about an axis perpen-dicular to an axis perpendicular to the axis of rotation of said first gimbal, magnetic responsive means mounted on said third gimbal means for generating azimuth related signals as a function of maynetic field forces on said magnetic responsive means, said azimuth related signals varying as a function of the alignment of said magnetic res~onsive means with respect to the direction of the earth's magnetic field, motor means for sai.d second gimbal means connected to said second gimbal means for driving said second gravit~ responsive means to a first predetermined position and then to a second position having a predetermined alignment wlth respect to the directlon of the force of gravity as determined by said inclination related signals, detector means for determining when said second gravity responsive means is at its first pre-- 5a - ~ :
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determined position and generating a home signal for said second gravity responsive means' control means for said second gimbal means for operating said second gimbal motor means, said second gimbal control means receiving said home signal for said second gravity responsive means to terminate the drive of said second gravity responsive means to the first predetermined position thereof, said second gimbal control means then driving said second gravity responsive means to said second position thereof, said .
second gimbal control means receiving said inclination related ~
signals to de-termine when said second position has been reached, ~.
the net movement of said second gxavity responsive means from .
said first position thereof to said second position thereof being commensurate with an inclination parameter of the drill string, motor means for said third gimbal means connected to .
said third gimbal means for driving said magnetic responsive means to a first predetermined position and then to a second position having a predetermined aIignment with respect to the .-.
direction o~ the earth's magnetic field as determined by said .
azimuth related signals, detector means for determining ~hen said magnetic responsive means is at its first predetermined position and generating a home signal for said magnetic re-sponsive means; and control means for said third gimbal means for operating said third gimbal motor means, said third gimbal :.
control means receiving said home signal for said magnetic responsive means to terminate the drive o~ said magnetic . : .
responsive means to the first predetermined position thereo.f, said third gimbal control means then driving said magnetic .
responsive means to said second position thereof, said third :
glmbal control means receiving said azimuth related signals to .
determine when said second position has been reached, the net movement of said magnetic responsive means from said first :
position thereo~ to said second position thereof being commensurate : -.
~ ~ - Sb -with an azimuth parameter of the drill string.
In a more specific embodiment, sensor apparatus for measuring directional parameters of a drill string in a bore hole includes: first gimbal means mounted for rotation in a seg-ment of a drill string, said first gimbal means being rotatable about the axis of the drill string segment or an axis parallel to the drill string axis, first gravity responsive means mounted on said first gimbal means for generating first alignment signals as a function of gravity forces on said first gravity responsive means, s-aid firs~ alignment signals varying as a function of the alignment o~ said first gravity responsive means with respect to the Eorce of gravity, second gimbal means mounted for rotation :
in said drill string segment, said second gimbal means being rotatable about an axis perpendicular to the axis of rotation of said first gimbal, second gravity responsive means mounted on said second gimbal means for generating second alignment signals as a function of gravity forces on said second gravity responsive means, sald second alignment signals varying as a function of the . .
~ alignment of said second gravity responsive means with respect :~ 20 to the force of gravity; third gimbal means mounted for rotation : in said drill string segment, said third gimbal means being rotatable about an axis perpendicular to an axis perpendicular to the axis of rotation of said first gimbal, magnetic responsive means~mounted on said third gimbal for generating third alignment signal.s as a ~unctlon of magnetic field forces on said magnetic ~.
respons.i~e means, said third alignment signals varying as a func-:tlon of the alignment o~ said magnetic responsive means with :.
: respect to the earth's magnetic field, first motor means connected ~ :
to said first gimbal for driving said first gravity responsive ...
30~ means~ to a~ first predetermined position and then to a second posi- ~ ~
tlon having a~predetermined alignment with respect to the force of .. ~ .

gra~7ity as determined by said first alignment signals, ~irst , ~ :.' ~:, : ' ~Sc- ~

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detector means for dete:rmining when said ~lrst gravity responsive means is at its first predetermined position and generating a first home signal, first con-trol means for operating said first motor means, said -first control means receiving said first home signal to terminate the drive of said first gravity responsive : ~
means to the first predetermined position thereo~ ~aid first .
control means then driving said first gravity responsive means to said second position thereof, said first control means receiving said first alignment signals to determine when said second posi-tion has been reached, the net angular movement of said first motor means being commensurate with a first directional parameter of the drill string, second motor means connected to said second . .-gimbal for driving said second responsive means to a first pre-determined position and then to a second position having a pre-determined aliynment with respect to the force of gravity as determined by said second alignment signals, second detector means for determining when said second gravity responsive means is at its first predetermined position and generating a second home sig-nal, second control means for operating said second motor means, said second control means receiving said second home signal to terminate the drive of said second gravity responsive means to ~ -the first predetermined position thereof, said second control means then driving said second gravity responsive means to said second position thereof, said second control means receiving ~ .
said second alignment signals~to determine when said second posi-tion has been reached, the net angular movement of said second .
: motor means belng commensurate with a second directional parameter of the drill string, third motor means connected to said third ~ .
gimbal for driving said ~irst magnetic responsive means to a .
irst predetermined position and then to a second posit:ion having a predetermined alignment with respect to the earth's magnetic ~.
fie~d as determined by said third alignment signals, third detector SC~

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means for determining when said first rnagnetic responsive means is at its first predetermined position and genera-ting a third home signal, and third control means for operating said third mo-tor means, said third control means receiving said third home signal to terminate the drive of said magnetic responsive means to the first predetermined position thereof, said third control means then driving said first magnetic responsive means to said second position thereof, said third contro] means receiving said third alignment signals to determine when said second posi-tion has been reached, the net angular movement of said thirdmotor means being commensurate with a third directional parameter of the drill string.
From a different aspect, an embodiment of the invention comprises the method of measuring directional parameters of a drill string in a borehole including the steps of: rotating first gravity responsive means in a segment of the drill string to establish a predetermined position of said firs-t gravity responsive means as a function of gravity forces on said first gra-vity responsive means, said first gravity responsive means being mounted on a first gimbal mounted for rotation in the drill string ~ -segment about the axis of the drill string segment or an axis ..
parallel to the drill string a~is, rotating second gravity responsive means:in said drill string segment for generating -.
ncl~nation related signals as a function of gravity forces on said second gravity responsive means~ said second gravity respon-~;~ : sive means being mounted for rotation on a second gimbal having . ::
an a~is of rotation perpendicular to the axis of rotation of the first gimbal, said inclination related signals varying as a func- :-; ~ ti~on of the alignment of said second gravity responsive means with ;.
respect to the direction of the force of gravity. rotating mag-netic responsive means in said drill string segment to obtain . .
azimuth related signals as a function of magnetic field forces on . .

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said magnetic responsive means, said magnetic responsive means being mounted on a third gimbal rotatable about an axis perpen-dicular to an axis perpendicular to the axis of rotation of the -:
first gimbal, and said azimuth related signals varying as a func- .
tion of the alignment of said magnetic responsive means with . .
respect to the direction of the earth's mag:netic field, operating a driving motor connected to said second gimbal to drive said : .
second gravity responsive means to a first predetermined position and then to a second position having a predetermined alignment with respect to the direction of the force of gravity as deter-mined by said inclination related signals, detecting when said second gravity responsive means is at its first predetermined position and generating a home signal for said second gravity responsive means, terminating the drive of said second gravity responsive means to the first position thereof upon receipt of said home signal for said second gravity responsive means, driving said second gravity responsive means to said second position after the flrst predetermined position thereof has been reached, .. ~ .
measuring the net movement of said second gravity responsive means ..
from said first predetermined position thereof to said second .. ..
position thereof to determine an inclination parameter of the :
drill string; operating a driving motor connected to said third gimbal to drive said magnetic responsive means to a first pre-determined position and then to a second position having a pre-determined alignment with respect to the direction of the earthls magnetic field as determined by said azimuth related signals; ~:.
detecting when said magnetic responsive means is at its first . .
predetermined position and generating a home signal for said ~: : magnetic responsive means, terminating the drive of said magne~ic ..~ -.
.
:responsive means to the first position thereof upon receipt of said home signal for said magnetic responsive means, driving said : magnetic~responsive means to said second position after the first s~

predetermined position thereof has been reached, and measuring the net movement of said magnetic responsive means from said first predetermined position thereof to said second position thereof to determine an azimuth parameter of the drill string.
In a more specific embodiment and in a second aspect, the method of measuring directional parameters of a drill string in a borehole includes the steps of: rotating first gravity responsive means in a segment of the drill string to generate first alignment signals as a function of gravity forces on said first gravity responsive means, said first gravity responsive means being mounted on a first gimbal mounted for rotation in the drill string segment about the axis of the drill string segment or an axis parallel to the drill string axis, and said first alignment signals varying as a function of the alignment of said first gravity responsive means with respect to the force of ~ .
gravlty, rotating second gravity responsive means in said drill .. -string segment for generating second alignment signals as a . :.
: function of gravity forces on said second gravity responsive means, said second gravity responsive means being mounted for - ~.
rotation on a second gimbal having an axis of rotation perpen- : .
dicular to the axis of rotation of the first glmbal, said second alignment signals varying as a function of the alignment of said second gravity responsive means wiih respect to the force of gravity; rotating magne-tic responsive means in said drill :string segment to obtain third alignment signals as a unc-tion ~ .
of magnetic field forces on said magnetic responsive means~ said .
magnetic responsive means being mounted on a third gimbal ro-tatable about an axis perpendicular to an axis perpendicular to .~ -: the axis of rotation of the first gimbal, and said thircl align- . :
: 30 ment signals varying as a function of the alignment of said ~ :
:magnetic responsive means with respect to the earth's magnetic field; operating à driving motor connected to said first gimbal - 5g ~

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to drive said first gravlty responsive means to a first pre-determined position and then to a second posltlon having a pre-determined alignment with respect to the force of gravity as de-termined by said first alignment signals, detecting when said first gravity responsive means is at its first predetermined position and generating a first home signal, terminating the drive of said first gravity responsive means to the first posi.-tion thereof upon receipt of said first home signal, driving said first gravity responsive means to said second position after the first predetermined position thereof has been reached, measuring the net movement of said first gravity responsive means from said first predetermined position thereof to said second ~ :
position thereof to determine a first directional parameter of ..
the drill string, operating a driving motor connected to said . ..
second gimbal to drive said second gravity responsive means to a first predetermined position and then to a second position having a predetermined alignment with respect to the force of gravity ~ :
as determined by said second alignment signals, detecting when said second gravity responsive means is at its first predetermined position and generating a first home signal, terminatlng the drive of said second gravity responsive means to the first posi-tion thereof upon receipt of said first home signal; driving said second gravity responsive means to said second position after :
: the first predetermined position thereof has been reached, measur-~: ing the net movement of said second gravity responsive means from :~
said first predetermined position thereof to said second position . .
thereof to deter~ine a second directional parameter of the drill ..

;~ string; operating a driving motor connected to said third gimbal : : to drive said magnetic responsive means to a first predetermined :
position and then to a second position having a predetermined alignment with respect to the earth's magnetic field as determined by said third alignment signals, detecting when said magnetic ~ X~ 5h ~:

65S~7 responsive means is at its first predetermined position and gen~
erating a first home signal, terminating the drive of said mag-netic responsive means to the first position thereof upon receipt of said first home signal, driving said magnetic responsive means to said second position after the first predetermined posi-tion thereof has been reached, and measuring the net movement of said magnetic responsive means from said first predetermined position thereof to said second position thereof to determine a third directional parameter of the drill string.

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- 5i -~ ,,' ~, ' In the drawings, wherein like elements are n~nbered al~:kc in the several figures:
FIGURE 1 is a g~oneralized schema~ic view o~ a borehole and drilling derrick showing the environment ~or ~he present invent ion .
FIGURE 2 is a view of a section o:E t:he drill string of FIGURE 1 showi~g, in schematic form, the dri:Ll s~ring environ-ment of the present inven~ion.
FIGURE 3 is a view~ par~ly in section, of a de~cail of FIGUR~ 2.
FIGURE 4 is a view of the flux magne~ometer of the rotation seDsor. ;~ ~
FIGURE 5 is a block diagram o the ro~ation sensor.
FI~URE 5A i~ a.schematic showing of ~he digi~al ~ilter :
o FIt~URE lOB.
FIGURES 6A~ 6B and 6C are curves showing outputs a~
var:ious stages of the rotatiloD sensor of FIGURE 5.
FIGI~ 7 is a schematic represen~tion of the sensor device for determining inclination, reference and azimuth 20 ~ angles.
.
FIGURE 8 is a repre~en~ative curve o~ the output of one ; o th~ acc~lerometers o~ FIG~ 7, FIGURE 9 is a repraæenta~ive curve of the ou~put of the magnetometer af FIGURE 7 ~ : FIGURES ;lOA and lOB consti~llte a block diagr~m o ~ha c on~ro l ~ ~ sys tem .

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FIGURES llA, llB and llC are a schernatic o~ the con~rol system shown in block diagram in FIGITRES lOA and lOB, FIGURE 12 is a schema~ic showing of the initiation cont:rol of FIGUE~E lOB~
FIGURE 13 is a schema~ic showing o the mas~er clock of FIGURE lOB. : -FIGURE 13A shows ~he outpu~ pulses of the master clock and divider circuit.
FIGURE 14A shows the output rom the s~:~er of FI~URE
lOA which is delivered to the sign and magnitude de~ector.
FIGURES 14B, 14C, 14D and 14E show outpu~s from the sign .
de~ector o~ FIGURE lOA.

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Referring now to FIGURE l, the general environment is shown in which the present inve~tion is employed. It will, however, be understood that the generalized showing o FIGURE 1 is only for ~he purpose of showing a representative environment in which the present inventîon may be used~ and there is no in~ention to lLmît applicability of the present invention ~o the speci~ic con~iguration o~ FIGURE 1.
The drilling apparatus shown in FIGURE 1 has a derrick 10 h w lch supports a drlll string or drill stem 12 which tlerminates in a drill bi~ 14. As i8 well known in ~he art, the entire drill string may ro~ate~ vr the drill string may be maintained s~ationary and only the drill bit rotated. The drill string 12 is made up of a series of interconnected segment~, with new segments being added as the depth of the well increases.
lS ~ The drill s~ring is suspended from a movable block 16 of a winch 18, and the entire drill string is driven in rotation by a square kelly 20 which slidably passes through but is rotatably driven by the rotary table 22 at the foot o the derrick. A motor assembly 24 is connected to both operat~
~: winch 18 and rotatably driva ro~ary ~able 22, The lower part of the drill string may contain one or more segments 26 of larger diame~er than other segmen~s of the :drill etring. As is well known:in the art, these larger segm~nts may con~aln sensors and el~ctronic cireuitry for :~
5 ~ ~ sensors;, and power sources~such as mud driven ~urbines which drive~generaeor6, to supply the electrical energy for the sensIng ~elements. A ~typical e~ample of a system in which a ~7 mud turbine, generator and sensor elements ara included in a lower segmen~ 26 is shown in U.S. Patent No. 3,693,428 to which reerence is hereby made.
Drill cu~tings produced by ~he operation of drill bit 14 are carried away by a large mud stream rising up through the free annular space 28 bctween the drill string and the wall 30 o~ the well. That mud is delivered via a pipe 32 to a filtering and decan~ing system, schematically shown as tank 34. The ~iltered mud is then sucked by a pump 36, provided wlth a pulsation absorber 38, and is delivered via line 40 : under pressurg to a revolving injector head 42 and thence ~o the interio~ of drill ~tring 12 to be delivered to drill bit 14 and the mud turbine if a mud turbine is included in ~he system. . . ~:
: 15 ~ The mud column in drill string 12 also serves as the~
; transmission m~dium ~or carrying signals of down the well : drilling parameters to the surace. This signal transmission ~:, is accomplished by the well known ~chnique of mud puls~ ~ -genera~ion whereby pressure puls~s are generated in the mud , .: .
- 20 ~ ~ calumn in drill string 12 representative of sensed parameters down the well. ~The drilliDg parameters are sensed in a sensor unit 44 ~see also FIGURE 2) i~ a drill collar unit 26 near or.
adjacent to the drill bit. Pressure puls~s ar~ cstablished in the mud ~s~ream in drill strîng 12~ and ~hese pressure ~-~:25~ pulses are receivad by a pre~sure ~ransducer 46 and.then trans-mitted~to~a signal receiving unit 48 which may record, display ;.
and/or perform~computations~on the signals to prvvide in~orma-, ~ion of various conditions down the well.
Re~erring briefly to FIGURE 2, a schematie system is shown of a drill string segment 26 in whi.ch the mud pul~es are generated. The mud ~lows through a variable flow orifica 50 and is delivered to drive a turbine 52, The turbine powers a generator 54 which del~vers electrical power to the sensors in sensor u~it 44. The output from sensor unit 44, which may be m the form of electrical or hydraulic or similar signals, operates a plunger 56 which varies thle size .
of variable orifice 50, plunger 56 havin~ a valve driv,er 57 which may be hydraulically or electrically operatecl. Varia-tions in the size of orifice 50 create pressure pulses in ~he mud stream which are transmitted ~o and sensed a~ ~he surface .~ to provide indications of various conditions sensed by sensor ~ . .
;15 ~ unit 44. M~d flow is i~dicated by the arrows.
For several classe~ o~ data or parame~ers to be sensed at the bottom of a well, it is quite unnecessary to sense the data and obtain readings more frequen~ly than once every ~hirty feet or so of depth. This corresponds to readings ~very one quarter ~20: : hour to one and oneohal~ hour at typical drilling rates o one hundred twenty feet per hour to twenty feet per h~ur. It there~
:fore becomes desirable to turn of the down hole sansing equipment during long periods of drilling, ~hereby minimizing ~::
wear of the sensox~ J transmitter and other parts o~ t:he tele- .
25~ metry system which would o~harwisa result ~rom contirluous operation.~ The~invention shown in FIGURES 3~6 is directed to this feature of ~ ~urning of th~ par~meter sensir~g equip-, . . .

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A~0~ ~59 7 m~nt by ~ensing and dis~inguishing b~tween periods o~ rotation and absence of rotation of the drill string. The invention requires a rotation sensor to de~ec~ drill. string ro~ation and interrup~ the delivery of electrical power to ~he well parameter sensors when the drill s~ring is rotated, and, conversely, to p~rmit ~he delive'ry of power to the well parameter sensors when the drill string is no~ ro~ated. A
magnetic deteeting device which sens~s the earth's magnetic flux is used as a rotation sensor to detec the presence or absenoe of ro~ation of the drill string. This rota~ion sensor contains no moving parts, and~ therefore, unlike other motion sensors which may contain moving elemen~s, offers high reliability notwithstanding exposur~ to mechanical shocks and vi~rations.
~ ReferriDg now to FIGUR~S 2 and 3~ some details o~ a drill s~ring segment 2~ are shown housing ~he rotation sensor 58 in accordance with this invention. Since both the rotation sensor : and on~ or more other sensors in sensor unit 44 are magne~ic- ~:
:~. ally sensitive,:the particular dril~ string segmen~ 26A which houses the rota~ing se~sor of this invention a~d the o~her :;
sensor elements must be a non-magnetic section o the drill string, preferably o~ s~ainle~s steal or monel. The rotation sensor 58 may b~ incorporated in sensor unit 44 ox ~ay be separately package~, and for the sake of convenienca it is !Z5~ shown as part o~ sensor uni~ 44 in FIGURE 3. S~nsor unit 44 i further encased~.wi~hin a non-magnetic pressur~ vessel 60 to oro~ect~and i6018t-~the sensor unl~ from pr~s6ures down in .
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5~'7 the well.
Referring to FIGURE ~, the rotation sensor 58 is a rincJ-Core fluxgate magnetometer which is used to determine the dixection of the earth's magnetic field. Although theoretically many other killds of flux detecting devices could be used, the ring core fluxgate magnetometer is used ~lecause of its low power consumption and its rugged physical constructlon. Operation of the ring-core fluxgate magnetometer is ~ased on the non-linear or asymmetric characteristics of the magnetically :~
saturable transformer which is used in the sensing element. As seen in FIGURE 4, the device has a toroi.dal or annular core 62 which is appropriately wound (winding details not shown), an input .
or primary winding 64 and an output or secondary or sensing winding 64 and an output or secondary or sensing winding 66. Core 62 is made of a magnetic material with a square B-H hysteresis curve.
The characteristic of this device is such that when the core is saturated by appropriate AC energizing of the primary winding in the absence of an external magnetic field, the ou-tput of :~:
, the secondary windings, i.e~, the voltage induced in the secondary w.indings is symmetrical, i.er, contains only odd harmonics of :-the fundamental of the driving current. However, in the presence of an external magnetic signal field such as the earth's magnetic field, the output voltage o~ the secondary windings becomes ~: asymmetrical with second and other even harmonics of the primary frequency appearing at the output o~ the secondary windings. This asymmetry is related in direction and magnitude to the signal field and can be ~ ' ~
,,', ~,," . ' detected by se~eral known techniques. Discussions of such fluxgate magnetometers can be found in the artlcle by Gorclon and Brown, IEEE Transactions on Magnetics, Vol. Mag-8, No. 1, March 1972, and the article by Geyer, Electronics, June 1, 1962 and in the article by R. Munoz, AA-3.3, 1966 National Tele-metering Conference'Proceedings.
As employed in the present invention, the input to the primary windings 64 drives core 62 to saturate twice for each cycle of the primary winding input. The moment in time that the core saturates is related to the ambient external magnetic field that biases the drive field in the core. That is, saturation of the core varies as a function of the intensity and direction of the earth's magnetic field, which ~ield is indicated diagrammatically by the flux lines in FIGURE 4.
Sensor 58 is physically supported on a sha~t 68 which is fixed in drill string segment 26A and is on or pa~allel to the axis of rotation of drill string segment 26A. While the drill string is being rotated, rotation sensor 58 is also being rotated in thè ambient magnetic field of the earth. As rotation sensor 58 is rotated, the combined action of the input to primary windings 64 and the ambient magnetic fie~d of the earth result in a varying phase shift in the second harmonic output . . .
at secondary windings 66~

Referring now to FIGURE 5, a block diagram of the ' ' .
,"",' , .
' ' -)~ :

s~
ro~ation sensor outpu~ signal processing is illustrated. The input to primary winding 64 emanates rom an oscillator 61, the output requency of which is divided in half by divider 63 a~ld then delivered to ampli~ier 65 and then delivared ~o primary winding 64. The output ~rom secondary winding~ 66, which is tuned to the second,harmo~ic of the primary winding input by capaci~or 67, is delivered to a buffer amplifier 69 and then to phase detector 70A o~ de~ector 70. D~tec~or 70 also includes low pass filter 70B and amplifier 70C. The ; 10 output of oscillator 61 (which is equal in requency to ~he second harmonic ou~put of secondary winding 66) i9 also .
delivered to phase detector 70A. The phase angle of the second harmonic output of secondary windings 66 is a func~ion : of the rate vf rotation of magne~ome~er 58, and that phase 15~ ~ angle varies as a function of changes in ~he rate o rotation o~ magnetometer 58, The output of secondary windings 66 is ~ .
compared wi~h the output of oscillator 61 in phase detector 70A, wher~ the~ di~ference ~n phase betw~en the two is detected and delivered to low pass ilter 70B. The output from filter 70B (when the drill string is ~otating) is an alternating signal~which ~aries in frequency as a function of the rate of ehange of thq phase angle o the second harmonic ou put of secondary wlndi~g 66; i.e. ~he ou~put of fil~er 70B varies ~n frequency as a ~unc~ion o~ changes in the ra~e of ro~ation ., ~ ,~; , .
25~ the drill stri~g`~: The ou~put from ~il er 70B i~ ampliied : n amplLfier 70C and is ~hen del~ver~d ~o a zero cros~ing det~ctor 72 wh~ch produce~ an ~ou~put pulse each k~me th~

" , : ~ :
.

alternating signal from detector 70 crosses ~hrough the zero value. The pul~ses generated by crossing detector 72 (which are also a func~ion o~ ~he rate of rotat:ion of the drill string) are delivered to a digi~al ~llter 74 which produces ou~put sig~als commensurate with states of rotation and no rotatiorl . .
Referring also to FIGUR~ 5A, digi~al filter 74 includes counter-divider 75, an S-R type flip-flop 76, J-K type ~ flip-flops 7~ and 78, and an AND gate ~9 connected as shown.
:~ 10 The outpu~ puls~s from zero crossing detector 72 are delivexed to the C input o counter-divider 75. Assuming the drill string is normally rotating, the pulses delivered to counter 75 cause counter 75.to overflow before being reset by a clock pulse : CPN (which may be any selected subdivision of a clock pulse : :: comm~nsura~e with a predetermined minimum ra~e of rota~cion), :
whereby ~he Q output of counter 75 goes high. Th~ Q ou~pu~
o~ counter 75 is connec~ed to ~he S input of flip-flop 76 and the high state of the Q output of counter 75 ~e~s ~lip-flop 76~ whereby the Q output of flip~flop 76 goes high and the 20 ~ Q output goes low. .The Q output of flip -10p 76 is connect~d ; .
to~ the J input of ~lip-flop 77. Flip-flop 77 is initially -; cleared by a reset pulse ICLEAR which may be obtairled from ;any convenient place in ~he system upon the initia~ion of : power in the con~rol sys~em. The J inpu~ of flip-flop 77 is ` ~ 25;;~ examined by the l~ading edge of each pulse CPN delivered to the C~Lnput of ~flip flop 77 ~hereby the J input is delivered o the ~ Q output. Thus ~ ~hen the drill string is normally , .
~ o~a~ing,: coun~r 75 r~peate~ly over~lows and is theln ~ ::

`L06S597 s reset by clock pulses CPN; ~lip-flop i6 is repeatedly set.by the Q output from countar 75 and reset by the uppar level o clock pulses CPN; and the J input of flip-flop 77 is low each time it is examined by the leading edge of the CPN pulse at ~he C inpu~ o~ ~llp-~lop 77. The Q output of flip-~lop 77 is thus also low ~hen the drill string is ~o~mally rota~ing; and a first ou~put leYel indica~lng rotation is deli~er~d from fil~er 74 (see LeYel X3 FIGUR~ 6C).
Reerring again to FIGUR~ 6, the various signa~s discuss-~.d above are shown graphically. The abscissa in each graph is time, and the ordina~e ln çach graph ls signal amplitude.
FIGU~E 6A shows ~he second ~armonic outpu~ o detector 70, FIGURE 6B shows th~ pulse outpu~ f~om zero crossing de~ec~or 72, and FIGURE 6C shows ~hc outpu~s ~rom digital filter 74.
From tine Tl tc T2 in all ~he graphs, the drill string is rot~ting at cons~ant speed. As ~he drill s~ring sl ws down when approaching a state o~ no rotation (ater t~e T2~, ~he freque~cy o ~h~ al~erna~ing outpu~ of detector 70 decxeases, thus resulting in a ~ow~r rcquency output ~rom zero cross~ng . det~ctor 72.
When the rota~ion of ~h~ drill 6~ g cease~, or the ~a~e of rota~ion d~ops ~o a ~ery lo~ ra~c on th~ way ~o a : ~ state of no rota~ on, the pulses from z~ro crossing de~ector 72 drop below a prede~ermined mi~mum frequency corresponding :: 25 to a pra~et~rmin~d lo~ ra~e o rotation o~ ~he drill~ Sinca the angular velocity o~ the drill s~rlng mus~ go ~hrough decreasing le~el~ in going ~rom normal to zero rotation, a , .
, ' ' , ' ' - ~s predetermined low rate (on the order o~ 3 rpm or les~) can b~ used as a signal o~ no rotation, in that ro~ation is abou~
to cease and will have ceased within the time required ~o iniciatc opexation of desired sensors which operate when S rotation has ceased.
When ro~ation ceases or drops below the predetermined low xate, which signals the ~ nence o the state o~ no rotation, ;~
counl:ar 75 doe~ not overflo;r be~ore being reset by the cloc~
pulse CP~i!, Thus the Q output o~ coun~er 7~ stays low~ and ~lip-flop 76 does no~ get s~t. Since 1ip-~lop 76 does not set, th~ Q ou~cput of 1ip-flop 76 is high and the ~ inp~t o~
flip-flop 77 ~s high. Th~ leading edge of clock pulse CPN ~ .-then set3 flip-~lop 77 whereby the Q output o~ ~lip-flop 77 is high (see le~el Y o~ FIGURE 6C) indicating the s~ate of no .:
` lS xo~ation. Thus, when the predetermined minimum ~requenc~
ou~ut from æe~o crossing detec or 72 is main~ained for a given ~ime period from T2 tO T3 (e.g. ten seconds)~ the digital filtar outpu~ (i.e. ~he Q level of flip-~lop 77) is switched, as shown in PIGURE 6C, to a second level indicating a state o~ no rotation (see lavel Y o~ FIGURE 6C). This second output ~ev~19 commensurate with a condition o no ~otat~on, is then used as a control slgnal ~or ar~ing or powering che oth~r senso~ elements in sensor uni~ 44. Pxior to ~;eneration o this coIl~rol signal, the other sensor ~l~ments In uni~ 44 are not powered, The oontrol sigr~al e. ~che second Gutpue level ~rom digi~al ~ er 74) is used .as a signal to arm or deliver ~he power from genera~or 54 ~o ~ -:

.. . ..
' '.

' '. , ,' .

valve driver 57 and to those other sensor elements, such as by opera~ing flip-flops or arming gates to enable power to be delivered to the other scnsor eleman~s in sensor unit 44 or în any o~her desired fashion to that end.
Referring now ~o ~IGURE 7, ~he invention of the param0ter sensing elements in sensor unit~44 and operation thereof are sho~n, i.e. th~ sensor units for se~lng the various ~o~n the well parame~ers whîch are to be sensed af~er rotation has ceased and transmi~ted to ~he surfac~ periodically to provide a measurement and indica~ion o c~rtain directional charac~er-istics at the bottom of the well.
The characteristics to'be measured and determined in thc present i~vention are directional characteristics o~ the drillin~ line, especially a drilling line which is s1anted ei~her from its point of origin or ~rom an intenmediate poin~ in the well. ~s is k~own in the art (for example ~ee U.S. Patent No. 3,657,637 to Claret), the parameters of ~:
incli~a~ion ang;le, azim~th angle and ref~enee angla must be known in order to h~ve ~o~al ~n~ormation about ~he posi~ion : ~ ~ 20 and direction o~ a drilling line. For purposes of clarifica- :
ion, the fo~lowing definitio~s of the several angles are ;presented:
Inclination angle (i) is the angle of inclination of the drill axis wi~h respec~ to the v~rtical ~V) w~ere , ~ , ,, ~25~ .bot~ ~he drill axis snd the vertical ar~ contain~d : .
in a common vertical plane. Re~erri~g to FI ~ 7, ~- ~
the drill mg axis~ s XIXg and I - ~ngl~ XOV, ~ ~ .

~ .
: : :

;5~ 7 -2, Azimu~h tA) is a magne~ic aæimuth. It is de~ined as the dihedral angle formed by the vertical plane which con~ains the horizontal projection of the drill axis and ~he ver~ical plane con~aining the horizontal projsc~ion of the local terrestrial - :~
magnetic field. R~erring to FIGURE 7, it is the angle A as shown in connection with the ri~g core 1uxgate magnetometer.
3. The reference angle R is the dihedral angle d,efined ::
by the intarsection be~ween a first plane containing .the drill axis and a line (commo~ly referred ~o as the scribe line) on ~he drill s~ring parallel to the drill axis and a second plane containing the : ~ . . . .
~:: drill axis and.the v~rtical projec~ion o~ the 15~ drillîng axis. The reference angle R is shown at :
the top of the unit in FI~URE 7.
Ge~erally speaking, ~he ~ensor system, shown in FIGURE
7, includes:
. ~
A mechanical devie~ with three axes ~or determining 20~ (a) A~va~ical plan~ using the force o~ gravity a~ a r~erence, and b~ A~horizontal plane, using the force of gravity 6 ~ referen~e, and a)~ The north direction, using the earth'~ magnetic :
25~ d as ~ r~er~ce.
2. ~A~mo~or:drive 5y8t~mito ~iV2 par~s o~ ~he:mecha~i~m ~ -to desired~position6 a~out the axa~

.

~ ~ SS ~ 7 3. Error transducers to determine devia~ion ~rom the desired positions about the axe,s and provide feed-back ~o the motor drive sys~em.

4. A control and a measuring system to m~asure ~he total movement of the motor drive sy~;tem requlred to eliminate the error.
FIGUR~ 7 schematica1ly shows the mechanism of the sys~em and the in~eraction wi~h the motor drives and error trans-:~ ducers. The sensor is a multi-axis or multi-gimbal syste~
servo eontrolled by error transducers. More speci~ically, the sensor consists of a three gimbal system, servo controlled by two error transducing accelerometers and one error trans-ducing magnetometerO The accelerometers are used to establish horizontal and vertical planes, and the magnetometer is used .~ .
15 ~ to e~tablish a direc~ion of magnetic north in a horizontal plane.
The ~ensor includes an outer frame lO0 which is rotatably mounted in sensor unit 44 i~ pressure vess~l 60 with non-, ~ , ~ : magnetic drill collar sec~ion 26A (see FIGURE 3). Fri~m~ lO0 ~ .
. ~ , .
:~ 20 ~ is rotatably mounted on axis 102 which is ~he axis of the ; dril~l string at the bottom Q~ the well9 or ~rame lO0 may be :mounted ~or rotation about an axis parallel ~o axis 102.
Frame;~100 is mounted for such rotation by shafts 104 a~d 10~ :
which e~tendj~rom opposite~ends of the frame and are mounted 25 ~ in;bearin~s 108~and 110, respective1y, which arc, in ~urn, .:
conncct~d to sensor housing 44 by suppor~9 1l2 ~nd 114. Frame lOO~ is:shown as~a raetangulax ~tructure with sides parallel 20- :

~o axis 102 and ends perpe,ndicu1ar to axi~ 102; however, the ~rame can be of any shape symmetric about axis 102 or could be a surface of revo1ution about axi~ 102. Thus 3 in the embodiment being discussed, the axis of the ~rame, which is the axis o rotation o~ the frame~ coincides with or may be parallel to drill string axis 162. Frame 100 cons~itutes a first gimbal in the system.
A first acce1ero~e~er 116 ~sometimes referred to as the reference accelerome~er) is mounted on a p1atform 118 between the sides of frame 100 with its sensitive axis perpendicular to the direction of drill string axis 102 (as used throughout this specification9 the term "perpendicular" as used with lines or axes will be understood to mean a right angle rela~ionship regard1ess of whether ~he lines or axes inter-15 ~ ~ sect in a common plane or are in dlfferent planes. By definition, the sensitive axis is the axis along which : .
gravity forces will generate an output. Acce1erometer 116 is an error transducing de~ice of the type whose output goes ~ :
to zero when its sensi~ive a~is is perpendicular to the ~: 20; ~ ~ force of gra~ity (i.e.~ the null position~ and which has ~ `
.j .
maximum output when its sensi~ive a~is is parallel to the orce of gravi~ (see~FIGURE 8 where the ordi~a~e is acce1er- :
ometer~output ~nd the abscissa îs ~he angle of the ~ens~tiva ax1s:o$ the accelerome~er with respect to gravity). A

5;~ particul~rly accurate and des~irable type of such deYice is ; kno~n m the art ~s a force ba~ance accelerometer, of wh~ch several:~type6 are available. The ou~put from acca1erometer ::': ~ ~ ' ' . :
. ~ : . :

~ ~6~
.~
116 is delivered via a motor drive control 120 in control section 121 to a stepping servo motor 122 ~o rotate ~rame 100 until accelerometer 116 reaches a null posi~ion.
Aecelerometer 116 is used in deter,mining the re~erance angle R, and thus accelerome~er 116 may be reerred to aæ the re~erence accelerometer. Bearing in mind the previously : stated de~inition of ~he reference angle R, a r~erence line must first be established parallel to axis 102, and that reference line mus~ be fixed relative to the drill :10 string or drill collar segment 26A. That reference line is ;~ identified as scribe line 124, and it is arbitrarily located parallel to axis 102. The angle R is thus equal to the angle between scribe line 124 and ~he vertical plane contain-. ing drill axis 102, i.e. angle R is the angle between the :~
scribe line and ~he "high side" of the hole as that term is understood in drilling parlance~ Scribe line 124 ls also ` ~: :
representable by a light path in this invention.
:To determine ~he angle R in the present invention, on a signal from control 121 motor 122 first drives frame 100 and ~: -~;; 20 :~ accalerome~er 116 to a "start" or HOME position in which there are know~ angular relationships ~o scribe ~ine 124.
: Tha~ home po~it~ion is conveniently selected as alignment with the`scxibe line 124 i~self, and ~he ~tainment o~ Shat align-ment~is determinad photoelectrically by employment of a light : ;
5~ sour~ce 126 and~:a photo cell 128. ~Light source 126 and photo :cell:128 are;shown mounted direc~ly or i~direc~ly on support `114,~but it will be understood that ~hey may be mounted in 55~7 any way fixed relative to drill string segment 26A, The light path 130 from source 126 to photo ce~l 128 is in the plane defined by scribe line 124 and rot:ation axis 102 (thus path 130 is equivalent to scribe line 124). Two rotating dlscs, 132 and 134, are in the light path 130.
Each of these discs has an aperture, 136 and 138, respectively, and the light beam 130 is interrupted e~cept when apertures 136 and 138 are simultaneously aligned with the ligh~ beam to permit light ~o reach pho~o cell 128. Disc 132 is mounted directly on shaft 106 ~and is thus directly mounted on the first gimbal) and disc 134 is separately mounted on a shaf~
140 (the support for which is not shown for purposes of clarity) and is directly driven by a geared connection with disc 132. Disc 132 permits the l~ight ~o pass once for each , ~ 15 revoIution of frame lO0 and is sized to permit the light to ~ : .
.
~ pass over an ar of approximately 12 ; dise 134 makes one . ~ . .
revolu~ion for every 30 of rota~ion of frame 100 and is sized to pass the light over less than 1 o arc. Th~s, the light from light sou~rce 12~ can only reach photo cell 128 once in : ~a complete revolution of Erame 100, a~d then only in a band less than~l wid~. Whe~n th~ home position i8 reached~ a ~ ;
firæt plane is:defi~ed by scribe lîne 124 (or light beam 130) and axi~ 102.
Wh~n operation of tha s~nsor s~stem is initia~ed by ths 5~ control signal rom digital filter 74, a signal ~rom motor dri~e control 120 is delivered to stepping motor 122, which is dri~ingly conn~cted ~o shaf~ 106 throu~h gear ~rain 142, .. . .. , .. ~ .. . .. . . . I . ~ ,. . . . .

and mo~or 122 drives frame 100 in a firs~ direc~ion o~
rotation (assumed coun~arclockwise~ un~il the light is incident on photo cell 128. The ou~put from photo cell 128 is deli~
vered ~o con~rol 121 ~o terminate this operation o~ motor 122. Tha~ establishes the start or home position or reference accelerome~er 116 for measuring the reference angle. Assuming tha~ accel~rome~er 116 is now in any position other than its null position, the accelerometer, which m~y be considered an error transducer, will deliver ~n ou~put signal : :
~10 to motor drive control 120 in control section 121. Motor :~
drive control 120 then operates to deliver operating pulses to motor 122 to cause the frame or gim~al 100 to be rotated (clockwise or counterclockwise) until the ~ensiti~e axis o~ accelerome~er 116 has reached a horizon~al position, i.e., ~-perpendicular to the force of gravity, whereupon the ou~put : .
from accelerometer 116 reaches a null and causes drive control ~120 to terminate ro~a~ion o gimba~ 100. The sensi~ive axis ~ :
of accelerometer 116, in this null posi~ion, defines a ; vertical plane (a second plane) which includes axis 102.
~:~ 20 ~ This second plane and ~he ~irst plane, defined wi~h reference o the scrib~ line and axis 102 are the planes be~ween which rhe reference~angle R iB measured. Accordingly, the n~t n~umber and sig~ (corresponding to direc~ion of rvta~ion) of equal steps required to opera~e s~epping motor 122 ~o 25~ drive accelerometer 116 r~m i~s home position to the null posi~ion, and hence ~he nat number of pul~es deli~ered rom motor~control unit 1209 i~ a mgasure of referance angle R.

:. : . :

, The pulsed ou~pu~ from mo~or controller 120 is also delivered to a binary up-down counter 1440 The number of pulses counted by counter 144 constitutes data or information com~ensura~e with ~he reerence angle R, and ~his data is eventually ~ransmi~ted ~o ~he surface of the well through mud pulse techniques so that the angle R is known at ~he surface of the well.
A second error ~ransducing accelerometer 148 is ~ixedly~-mounted on a second gimbal in the form of shaft 150 (having axis of rotation 151) which is ro~atably moun~ed on the first gimbal 100 via bearings LS2 This second accelerome~er ; will sometimes be referred to as the inclina~ion accele~ometer . ~ :
The sensitive axis o inclination accelerometer 148 is arranged orthogonally with respect to th~ sensitiva axis of reference lS ~ accelerom~ter 116 Inclina~ion accelerometer 148 establishes a vertical plan~ perpendicular ~o the plane established by . ~
reference accelerometer 116, and, operating in conjunction with reference acceLerometer 1163 serves to deine a hori-zontal plane and determines the angle of inclination, I, of .~ , ~ 20 ~ drilling axis 102 ~ .
In operating inclination accelerometer 148, it is first d~i~en to a start or HOME position which is an arbitrarily preseLected and known position of the acceler~meter and shaft 150 wi~h rs~pec~ to rame 100 The accalerome~r's home 5 ~ position is detected through an optical sys~m similar to the system us d~or detecting the home posi~ion o acclel~rometer ;116; ~This optic~l~eystem ircLud-s a Iight sourc~ 154, a photo , . ~ ~ : , ..

- , . . . .. .

. ~Q~

cell 1569 light path 158, and rotating discs 160, 162 and 164 which have apertures 166, 168 and 170 therein, respectively. Disc 164 is rigidly mounted on a shaft 171, and disc 160 is dri~ingly connected to a stepping servo motor 174 by a gear ~rain as shown. The ~hree discs are also drivingly interconnec~ed by a gear train as shown. The gear train is sized so that the discs ~ravel at sligh~ly dif~erent rotational spe~ds relative to rotation o gimbal 150. A
preferred arrangement has disc 160 making one full revolu-: 10 ~ion for each 10 of rotation of gimbal 150 while discs 162 and 164 each make one complete rotation for each 9 and 8 of rotation of gimbal 150, respectively. Apertures 166, 168 and 170 hecome aligned only once for each 360 of ~ : . rotation of gimbal l50; ~hat alignment alway~ occurring along ; 15 : li~ht path 158 to permit the light beam to reach photo cell 156 once for any complete 360 rota~ion of gimbal 150.
rhe USB of the ~hree discs 160, 162 and 164 at slightly : ~ differen~ rotating speeds results from the fact that it is ~: ~ impractical to attach one of the discs directly to gimbal . .
~ 20 ~ :150 for the inclination measuring system. If one of the .
discs were attached direc~ly to gimbal 150, ~hen a two disc system could be used as in the case for ~he reference a~gle syst~m where one of the discs is attached dir2ctly to gim~al 100.
25 ~ When operation of ~he iniclination acc~laromatar is : ~ :
desir~d,~i~s motor driv~ con~rol 172 delivers a signal ~v : :
` stepping motor 174 to.drive the motor in a first direc~ion.
, . . .
, , ~ 26- ~

, , ::
.: ~

3~

The discs 160, 162 and 164 and shaft 171 are thus rotat~d, and shaft 171 drives through a worm and gear 174 to rotate gimbal 150 about its axis in a ~irst direc~ion (assumed counterclockwise). When the three apertures 166, 168 and 17n reach ~he posâtion of aligl~ment which permits ~he light beam to be delivared to photo cell lS6, the home position of accelerometer 148 is reached, and the output from the photo cell 156 is deliver~d to con~rol 121 to ~rminate the operatio~
of motor 174. Accelerometer 148 is thus in a known position relative to ~rame or gimbal 100.
Assuming that accelexometer 148 is in any position other than the position where its sensitive axis is perpendicular to ~he direction of gravity~ accelerometer 148 will function as an error transducer, and error signals will be deLivered to motor drive control 172 in control section 121. Motor dri~e :: : control unit 172 functions ~o generate output pulses which are delivered to steppîng mo~or 174 to dr;ve stepping ~otor 174 in a step by-s~ep manner in the direction to red~ce the error signal. Gimbal 150 and accelerometer 148 are thus ~ driven in a serîeB o~ steps until the sensitive axis of accelerome~er 148 is perpendicular to ~he direction of gravity9 i.e. until the sensîtiva axis is a line in a horizon~al position, which line defines a second vertical plane estab-lished by the reference accelerometer, Since accelerome~er 25 ~ 148 is:in ~he null position, furthar op~ration o~ ~he stepping motor is terminated.
Bearing ~n mind ~ha~ the ~ull posi~ion of r~erenc~
.
~: ` : :
~ 27- ~

.

accelerometer 116 da~ines a ~irst horizontal line ~the sensitive axis o~ arcelarome~er 116), and that the null position o~ inclination accelerometar 148 also defi.nes a second horizontal line (~he sensitive axis of accelerometer 148) which is orthogonal wi~h respec~ to the first horizontal line, these two orthogona~ horizontal lines cooperate to define a horizontal plane. This is so because a plane can be defined by two orthogonal lines or by one line and a directio~.
As applied to the presen~ inve~tion, the horizon~al l:Lna defined by the sensitive axis of either of the two accelerometers defines the direction o~ a plane which includes the horizontal line of the other accelerometer, Thus, ~he two sensitive axes o~ accelerometers 116 and 148 combine and cooperate to define a horiæon~al plane.
lS ~ The intersection of ~he ~irst ver~ical plane (es~ablished by the sensitive axis of accelerometer 116) and the second vertical plane (establiæhed ~y the sensitive axis of accelerometer 148) defines a vertical line which intersects the drill axis 102~ thus defining the inclination angle I.
20 ~ As with the maasurement of reference angle R, the output ~ -pulses ~x~m motor drive con~rol 172 are ~elivered to a binary up~down coun~er 176. trhe ne~ ~umber of s~eps o~ stepping ~-:
motor 1749 and hence the net number of pulses delivered to counter 176, n~ceBsary to drive accelerometer 148 to the null 5 ~ position~from the home station is direc~ly rela~ed ~o and a measuremene of ~he àngl~ of inclinat~on I of drilling axis 102 with. respect to the v~rtieal. The pul~es ~countecl by , . ' : -~ ~6 ~S~

coun~er 176 are even~ually ~ransmitted to the surface by mud pulse telemetry techniques ~o that ~he angle o~ inclination I is known at the surface.
The sensor system also includes an a imu~h sensor in the S form of a ring core flu~ga~e magnetome~er 178. Magnetometer 178 is the same type of device as magnetometer 58 disclosed and discussed above in FIGURE 4 with regard to ~he ro~ation sensor. Accordingly, no detailed discussion of the nature or construction of magnetometer 178 is nec~ssar~. Mk~gnetometer ~ 178 is fi~ed to a shaft 180 w~ich is a third gimbal in the . sensor sys~em, Gimbal 180 is ro~a~ably mounted in bearing 182 for ro~a~ion about the axis 183 of shaft 180, and bearing 182 is ~ixed to rotatable ~haft 184. Shaf~ 184 is parallel to shaft 150 and is rotatably moun~ed on rame 100 by bearings :
lS 186, and shaf~ 184 is rotatably driven about its axis:by shaf~ 171 through worm and gear 188. Thus, shaf~ 184 is slaved :: ~
to gimbal 150 which acts as a master ~or shaft 184. The toro-idal core of magnstometer 178 is arranged perpendicular to the axis I83 o gimbal 180, and the axis of gimbal 180 is . ~:
:~ positioned perpendicular to the sen i~ive axis of inclination acGelerome~er 1~8. Thus, when re~erence accelerome~er 116 and irlclination acceleroIne~er 148 reach their horlæon~al or ~, ~ . , , null posi~ions, gimbal 180 is in a vertical position and the toroidal core of magnetometex 178 is in a horizon~a:L plane.
29~ Gimbal ~180 is rotated about its axis through bevel gear : ::
assembly 190 and worm and gear 192. The gear of lg2 and one of the beveled gears:o~ 190 are connected ~ogether by sleev~

.

191 which is rotatably mounted on shaft 184. Worm and gear 192 are, in turn, driven by rotatable shaft 194 which is drivingly connect~d to an azimuth S8rV0 motor 196. A photo-elec~ric de~ection sys~em identical to l:hat previously des-cribed with respect to the inclination sensor system is arranged to operate as shown be~ween azimuth servo motor 196 and shaft 194. Since this optical system is iden~ical to that - previously described wi~h respect to the inclination sensor3 no further discussion of it should be required, ~d the parts : 10 of this azimuth optical system ar~ numbered ~o correspond with the similar parts of the inclination op~ical system with the addition o~ a prime (') superscript, The optical system associated with the azimu~h ~ensor is also used to de~ermine a start or HOME position for azimuth sensor 178.
; ~ .The azimuth sensor is employed to d~ermine the north direction by sensing the local horizontal componen~ o~ the earth's magnetic field. As is done with the reference and inclination sensors, the azimu~h sensor is ~irst driven to .~ ~ . .. .
a start or HOMæ posîtion which is a previously determined ~ and known position with axis 183 perpendicular to drill string . :; : , .
axis 102 and with ~he sensi~'ive axis of the magnetome~er orthogonal to drill stxing axis 102 a~d with the north seeking axis of the magnetometer (the north seeking axis being per- :
pendicular to ~he sensitive axis~ pointin~ in the direc~ion o~
25~ he drill bit (i.e. downhole). The azimuth sensor is drlven o this home.positio~ by a signal from mo~or dri~e eontrol 198 which is dellvered to a~muth servo ~vtor 196 to rotate . 30 .

~ ' gimbal 180 countercloclcwise about its axis until th~ home position is reached. The reaching of thl~ home position is, o~ course, determined by the incidence Oe ligh~ beam 158' on photo cell 156' whereupon the output fxom photo cell 156' S is delivered ~o control s~ction 121 to terminate this ~irst operation of motor 196.
Assuming ~hat magnetometer 178 is in any pOSitiOII other than its null position, an ~rror signal is generated which results in operating signals~ from motor drLve control 198 ~o stepping motor 196 to reduce the error signal gen~rated by the magnetometer. Magnetometer 178 ~unctions as an error transducer in that the phase angle o~ the second harmonic of . its output will rise and Eall epending on the orientation ; ~ of its sensitive axis with respect to the earth's mag~etic ~ield. The characteristic of this transducer is th~t this phase angle change varies as a func~ion of the orien~ation ::~
of its sensitive axis with ~he earth's magne~ic field, the variatîon being ~rom a maximum or minimum ou~pu~ when the sensitive axis is aligned with ~he earthls magne~ic field and falling to zero when ~he sensitive a~is is perpendicular to the earth~s magnetic field. This relationship is shown in FIGURE 9. The magnetome~er 178 func~io~s as an error ransducer in ~hat ~ts ou~put will go to ~ero as i~ is driven t;o~a position where its`sensitive axis is perpendicuLar ~o 25 ~ thR qar~h's magnetic field.
The error signal genera~ed by magne~ome~er 178; i.e.. ~he outpu~ ~ig~al generated wh~ ~he magne~ome~r is ~n a posi~ion :

:: : , ~ ; .

other ~han the null position, is delivered ~o mo~or drive unit 1~8 in control sectiun 121. Upon receip~ o~ khese error signals from magnetom~er 178, motor drive unl~ 198 generates ou~put pulsPs w~ich are delivered to s~epping mo~or 196 ~o drive s~epping motor 196 in a step-by s~ep mann~r ~o drive magnetometer 178 ~o i~s zero ou'tput or null posi~ion. M~g-netometer 178 and i~s gimbal 180 a~e ~hus driven in a series o~ steps u~til the sensitive axis o~ ~agnetom~$er 178 is ~rpendicular ~o the direc~ion o~ ~he ear~h's magnetic field~ n and further operation of the s~epping mo~or is terminated. ~.
The alge~raic sum of ~he output pulses ~om motor drive 198 and motor driva 172 are'delivered through "OR" gate syste~
199 to a binary up-down counter 200 in con~rol section 121.
OR gate systam 199 consists o~ OR ga~e 199~a~ o~ sign signals and OR gate l99(b) for number signals. The net number and sig~ o~ the said algebraic sum of pulses delivered to coun~
ter ~00, ~ecessary to dr~ve magne~ometer 178 ~o the null posi~ion from ~he home posit~on i~ a di~ect measurement of ~he axis of~ direction o ~che well axis wl~h respect ~o magnetic north, i.e. ~he angle A. Th~ pulses ~rom mo'cor . :
drive 198 arld 172 must be algebraically sus~n~d becauae gimbal 183 is driven both by its own motor 196 and ls also rotated : ~
one step ~or ~ach s~ep of mo~or 174 as sha~t 1~1 dri~es ~ -:: acceleromete~ 148 ~o i~s null posicion becaus2 o:E the Arive connec~ion between sha~ts 171 and 184 and bevel gears 190.
The pulses counted by countex 200 are eventually trcLnsmicted :~
.. . .
to ~he surfaae ~ mud pu}sa ~elemetry techniques so ~ha~

' ' ' .~ . . .

;s5~
the aæimu~h angle A is known at the s~r~ace.
The sensor sys~em described above ~hus consists of a three gimbal system servo con~rolled by two error trans-ducing accelerometers and one error transducing magne~ometer.
The accelerometers are used to establis;h horizontal and ver~
tical planes by finding zero gravity positions along two orthogonal axes, and the mag~e~ometar is used to establish the direction of magnetic north in the horizontal plane. The system measuxes the reference angle, R, the inclination angle, I, and the azimuth angle, A, those three items o angular i~formation being sufficient ~o define tha posi~i~n and direc- `~
~ion of the drill string at ~he bottom of the well.
will, of course, be understood that electrical inputs are required to each o~ the ~hree sensors, namely accelero~
; ~ 15 meter 116, accelerometer 148 and magnetometer 178 so ~hat these ::sensors can function as error transducers generating outputs which are deli~rered ~o their respec~ive motor drive eontrols.
These electrical inputs ca~ be supplied in any known and desired; fashion (including slip rings) from gen~rator 54, ~ and they havs been shown only schematically in FIGURE 7 as-,VO.
One particular adYantage of the sensor system of the present inven~ion is ~hat it eliminates ~he need ~or separate angl~ ~ransduoers and a~tendant mechanical or reliability ~ ~:problems such angle ~ran ducers typically present. Ins~ead ;- Q~ such~angla transdueers, angulax measuxement is accomplished in the present invention merely by counting ~he net rlumber of , - ~ .................................................................. .
~: -33-':

s~eps o~ the s~epping mo~ors or the net number o~ pulses delivered to the stapping motors ~o accompllsh each step.
The drive trains associated with each ~epping mo~or are highly accurate drive txains such ~hat each step of the s~epping motor resul~s in a known angular movemen~ o~ its associated gLmbal. Thus,,angular measurement is reduced to the simple proce~s of algebraically counting the pulses delivered to or the ~tPps of the stepping motor.
~ The entire sensor mechanism shown in FIGURE 7 may be immersed in a viscous silicone oil which entirely fills ~he:.
. sen60r housing 44. The oil serves both to protect the sensor mechani~m from vibration and shock damage while also serving to iubricat~ ~he bearings and gears and also act as a heat ~ ~ ~ransfer medium for ~he motors.
lS In order to pro~ec he precision and sensitLve gear trains which drive gimbals 150 and 180 in shaft 184 ~rom ~he effects of dif~erential ~hermal expansion, the drive worm ~;
gears o~ gear ~rains 174, 188 and 192 have been Lsolated ~y expansion bellows 202 and symmetrically supported wi~hin one :; 20 ~ piece hangers 204. Thus, shafts 171 and 194 are actually shaft segmPn~s joined together by the expansion bellows 202~ .
: which faithfully transmit the ro~ation o~ the shafts while accommoda~ing all ~hermally induc~d axial expansion o the shafts in both directions so that ~h~re will be no displaca-~ men~ of the poi~ts o contac~s between mating gears in thegaar~rains.
: If hard wired electrical inputs and/or outputs for the ~ . ~
~ acc~larome~ers.~are used, sa~0~y stops may nead ~o bP, employ~d~ .

~, . . . .

.
,:

~6 5~ ~ ~
Thus, re~erring to gimbal 150, a mechanical stop 206 ex~ends from gimbal 100 and is posi~ioned to be contacted by fiIlger 208 :Eixed to gimbal 150. Finger 208 andi stop 206 c~mbine to limit the ro~ation of gimbal 150 to 1.ess than 360 in any direction~ th~s preventing the breaking of hard wired electri~
cal lines. Similar steps could also be employed for the other gimbals if circums~ances warran~ed.
Referri~g now to FIGURES 10 and 11, a block diagram and a schematie, respec~ively, of the con~rol system of the present inYention is shown. FIGURE 10 is a block dia~ram of the entire control system, including the rotation sensor. ::
circuit o~ EIGURE 5`and ~he motor drive controls 120, 172 and 198 for ~he reference angle measuring circuit, the in- -clination angle measuring circuit and the azimuth angle mea~
suring circuit, r~sp~ctively. ~o~or drive controls 120 and 172 are identical, while motor drive con~rol 198 differs only to the extent that some of the components at the beginning of ~he circui~ are different due to the fact that the aæimu~h error signals are obtained ~rom magnetometer 178 while tha 20- reference and inclination s~gnals are ob~ained from error :transducing aecelerometers 116 and 148. The s hematic of EIGURE 11 shows one o~ the two iden~ical motor driva controls 120 and 17~, and the diferent structure found in mo~or drive ~ control`198 will b~ pointed out hereinater.
; ~25:~ Referring~to FIGURE 10,-~he rotation sensor is sho-~n, including~ma~netometer 58~ detector 70 (comprised o phas~
de~ec~or 70A,~low pass fil~ar 70B and:amplifier 7QC)~ zero ~ 35 .~,: .

.. , ... ..... ,.. . .. ~, , ,, - ~, ,. . , - . . .. ..

- ~6 crossing detector 72" a.nd digi~al ~ er 74 comprised oi~
clock 76, comparator 78 and ~lip-flop 80, see FIGURE SA
As described above wit:h respec~ to FIGURES 5 and 61 ~he sensing o the condi~ion o;E no ro~ation (ar a prede~ermined low rate o:E ro~ation of the dr~ll st:ring) results in fllp-~lop 77 being set. The rising edge of t:he Q outpu~ o~ ~lip-~lop 7~ is delivered to an ini~ia~ion con~rol unit 210 ~o condition and s~art the opera~ion o~ ~he control unit 121.
Ini~iat~on con~rol ~10 (se~ ~IGURE 12) is made up o~ t~o orle shot multivi.bxators 212 and 214, The rising edge o~ th~ Q
output of~ flip-flop 77 ~criggers one shot 212 to generate a pulse of lms du~a~ion at che Q ou~put o~ one shot 212, This output pulse at the Q ou~put o:~ one shot 212 is a cle~ring pulse (CLEARP) which, as will be described hPreinarCter ~ goes to ~he reset side o:E several devices in the cont~ol sys~em - :
to insure that: the entire control sys~em ~ ~1 is prepa~ed ~or a start command. The Q ou~put o~ one shot 212 :is connec~ed to the inp~t of one sho~ 214 whereby one shot 214 is triggered by the trailing ~dge of ~he pulse o:E one shot: 212 to generate a lms pulse which serves as a star~ command (ST~RTP) or the sys~em. AS Wi11 also be described hereinaf~er~ S~ TP is ; d~livered ~co variouæ comp~nents ~n the con rol system ~o initiate the operation o the con~rol system.
s addition.to th~ STARTP pulse which is delivered ~o ~:25~ he severa~ components i.n ~he ~ys~em, a mas~er clock 216 also :; .
delivers timing pulses or ~imin~ signals to the co~trol system.
Reerring to ~X~URI: 13, the ~aster clocl~ '.716 includes a :~re~ -. . . ~: .
3 6 ~
- "...

running astable multivibrator 218, the output of which is delivered to a counter/divider 220 where the multivibrator output is divided down to provide the basic timing pulses for delivery to various components in the system. FIGURE
13A shows the multivibrator output or frequency (f) and the output pulses CPI-CP10 from master clock 216 which are delivered to various components in the system for timing purposes.
The control system will now be described in connection with the determination of the reference angle R. It will be understood that the same description is applicable to the inclination angle I and, except as otherwise noted, also to the azimuth angle A. The description will be presented with joint reference to FIGURES 10 and 11. References to "high", "up" and logic "1" states of system components will be understood to be equivalents, as will "low", "down" and logic "O".
HOME MODE OPERATION
When initiation control 210 is triggered, the clearing pulse (CLEARP) is delivered to several components of START/STOP/RUN circuitry of pulse generator and control unit 222. Pulse generator and control unit 222 includes a start circuit 224, which has a home subcircuit 226 and a measure subcircuit 228, a run circuit 230, a done circuit 232 and a stop circuit 234.
Referring first to start circuit 224, in FIGURE 11, a clear pulse (CLEARP) from initiation control 210 is delivered s~
to an OR gate 236 and passes through the OR gate to a D type flip flop 238 ~o reset the ~lip-flop. Flip~10p 238 may also sometimes be referr~d to as the "home" ~l~p-flop since it i~
involved in detarmining the "home" position to which the S re~erence accelerometer 116 is first driven, as descri~ed above. The star~ pulse ~ST~RTP) ~rom initiation control 210 is then delivered to an OR ga~e 240 and passes ~hrough OR gate 240 to flip-flop 238, and ST~RTP is also delivered to 0~ gate 2440 The pulse STARTP is i~rted a~ the delivery to flip-flop 238, and hence the trailing edge o~ the STARTP
:: pulse sets flip-flop 238, since the D type ~lip-flop requires ......
a rising signal to set. When flîp-flop 238 is set, its Q
outpu~ goes high, and constitu~es a signal which will some- ~
times be referred to as HOMEF. The set condition of flip-flop ~-~ 15 238 is the home mode. The Q ~unction (HOMEF) of ~lip ~lop 238 is delivered ~o several places in tha sys~em. For one, HOMEF goes to a single sho~ multîvibrator 242 in the home circuît, but i~ does no~ trigger one shot 242 untîl ~he : : .
raîling edge o~ the HO~EF sîgnal appears, whieh :is la~er on 20 ~ în tha operatîon of the system when acceleromater 116 îs drîven~:home. The pulse HOMEF is also delivered to a magnitude detectîng cîrcuit 246 in a sign and magnîtude de~ec~or 245, and more partieularly to an OR gate 247 in magnitude detecting cîrcuit 246. This HOMEF signal overrîdes any o~her signal to 25~ OR ga~e 247, and it is delî~éred to an AND gate 249 ~o eon-stitute one o~ the two inputs to AND ga~e 24g. When the : :
second ~nput is d~liver~d ~o ~ND ga~e 249 along wi~h ~he : :

- . . ~.

~ . . . .

~ 5~3 ~

HOMEF signal 3 pulses will be gener~ted to drive the reference accelerometer to i~s home posi~ion~
The second inpu~ to AND ga~e 249 is delivered from run circuit 230 which has received an input from 0R gate 244, The input from OR gate 244 is the result of STARTP which passes through gate 244 and appears at the output of gate 244 as a RUNP signal, which is then delivered to the S input of a JK type flip-flop 248 in run circuit 230, Flip-~lop 248 (sometimes reerred to as the "run" flip~flop) was previously reset by a CLEARP pulse from the initia~ion control, so that the ~UNP signal a~ the S ~erminal of flip-flop 248 unconditionally sets flip-flop 248 so tha~ the Q output is high and is delivered to AND gate 249 as ~he second inpu~ to A~D gate 249. Upon ~he deLivery of the neccssary two input ;15 signals to A~D gate 249, an output signal is del~v~red from AND gate 249 to the D input of a D type flip~flop 250 in .:
~ pulse genera~or circui~ 252. The C input of ~lip-flop 250 .
receives clock pulses CPl from master clock 216, and Lip-flop 250 is set (D inpu~ transerred to Q) wh~n îts D
; input is at the logic 1 level ~the input from ga~ 249) in : the presence of the clock puLses CPl. Thus, flip-~Lop 250 is set at a frequency detarmined by the clock pulses GPl when i~s D input is at a logic 1~ At each setting of flip-flop 250, th~ Q outpu~ is deli~ered to an AND gate 254 in 25 ~ pulse generator 252 where it is ga~ed with a second signal , :, CP3 from~master clock 216. The two inputs to AND gate 254 resuLt ~n a paLsed outpu~ from gate 254. ~This pulsed output i~ . . .
~ 3~- .

:. " :~ , .
:~ ' :

,. , .. ... ,. . . . . - . . . . , .. . - -~ ~6 ~ 7 is delivered to several locations in ~he sys~em, one such loca~ion being motor sequence circui~ 256 to drive motor 122.
The output of AND gate 254, and hence the, output ~xom pulse generator 252, is ~hus a series o step pulses delivered to the motor sequ~nce circuit.
The HOMEF signal (resulting~when ~he Q output of ~lip flop 238 is high) is also delivered to the S input of a JK-type flip-flop 258 in sign and magnitude detector 245. The HOMEF
signal at the S input to flip-flop 258 sets flip-flop 258 so that the Q output is high. The high Q output o flip-flop 258 is.also delivered ~o motor sequence circuit 256 where it constitu~es and serves as a sign or direction indica~or to cause motor rotation in one predetermined direction (assumed coun~erclockwise) to drive reference accelerometer 116 to its home position.
From the foregoing i~ can be seen that two separate signals are delivered ~o mo~or sequence circuî~ 256. One of ~hese signals is the step pulses ~rom pulse generator 252, and the o~her of these signals is ~he sign or direction signals ~: 20 ~rom flip-flop 258 in sign and magnitude detec~or 245.
Motor sequence circuit 256 is a ~wo bit up/down counter 260. It receiv~s the step pulses from pulse genera~or 252 and - .
sign in~ormation from ~Iip-flop 258 in sign and magni~ude de~ector 245, and it converts these inputs into a our phase 25 ~ signal. That is, tha motor sequence circuit is a phase generator ~or a our phase motor. The ~our phase signal is delivered on separate lines to motor drive amplifier 262 which .~ , ~ 7 has separate ampliiers and level converters for converting the four phase signals from sequence circuit 256 Lnto an appropriate power level for driving ~he four phasa step motor 122. Before being delivered to the separate ampli~iers ln motor drive amplifier 262, each phase is delivered ko an AND
gate 2619 and the second or arming input to AND gate 261 is ~he Q output of flip-flop 77 o~ digital fil~er 74. Thus the drive mo~or 122 is not operated u~less there is present both a no rotation signal from digital ~ilter 74 and pulses - 10 from pulse generator 252. In the presence of both signals to AN~ gate 261, the reference arcelerometer îs thus driven toward the home position, and i~ will be noted that the direction o~ rotation to ~he home posi~ion is always the same (assumed counterclockwise) since the sign or di~ection infor-lS mation from fLip-flop 258 is always at th~ same level for ; a home mode operation. :;
Mo~or 122 runs until home detector 128 recei~es light : .
; from light source 126. Light en~ering home de~ector 128 is: :
amplified and converted to logic levels in an amplifier and -~
~20 Bquaring circuit 264, the output of which is delivered as the : second input to an AND ga~e 266 in s~op eircuit 234. The irst input eo AND gate 266 is already pres~nt ~n the form of the :HOMEF signal rom flip flop 238 of start circuit 224. The ; output of AND gate 266 go~s high upon ~he delivery of ~he : ~ signal rom amplifier and squaring circ~it 264, and this ou~pu~
is.deli~ered ~o and passaB through an OR ga~e 268 causing the : output o~R gate 26~ ~o go high. This resultant sig~al rom ~ 5~ ~ :
OR gate 268 is delivered to an AND gate 270 in run circuit 230 whare it is gated with clock signal CP9. The outpu~ ~rom AND gate 270 is inverted and delivered ~o the C input o JK type flip-10p 248 to reset ~lip-flop 248 on the trailing S edge o~ CP9, thus causing ~he Q output of ~lip-~lop 248 to go low. This resetting o~ flip-10p 248 removes one of the two inputs to AND ga~e 249 in magnitude detecting circuit 246 whereby the D input to flip-~lop 250 is removed so that flip~
flop 250 is reset and no fur~her pulses are generated from pulse genera~or 252, whereb~ motor 122 stops because the prede~ermined home posi~ion has been reached.
The above described home mode o~ operation takes pIace sLmultaneously ~or all three axes o~ reference, inelination .:
and azimuth. Each of ~he motor control circuits 120, 172 and ~ .
-L98 has a run flîp-flop 248. The Q ou~put of each run flip- ~ -lop 248 is connected to a three input AND gate 272 in a :: common done circuit 232. When each of the three run flip-flops 248 is reset, ~he Q output of each goes high. When the .
: Q output of each of ~he three 1ip-flops 248 is high~ ~he output of AND gate 272 goes high to constitute a DONE signal indicating that accelerometers 116 and 148 and magns~ometer L78 have all been dri~en to their respec~ive home positions.
miS DONE s ignal a~ ~he output of 8a~e 272 is delivered as one of ~he two inputs ~o a~ AND gate 274 in home subcircuit 25~ 226 of~start circuit 224, The second input ~0 AND ga~e 274 is provided by:the HOMEF signal, and ~hus a signal is passed through A~D gate 274 and is delivered~to OR gate 2360 The .

:
~:

5~
signal passes through OR ga~e 236 and is delivered to the R
inpu~ of flip-flop 238 to re~et flip-flop 238. When ~lip-10p 238 resets, i~s Q output goes ~o logic O and causes one shot 242 to fire for lms, i.e. one shot 2b~2 is triggered on the trailing edge of the HOMEF signal. The :Lms output pulse from one shot 242 is delivered to up/down counter 144 ~o reset counter 144 so that counter 144 is now c:Leared to receive : measuring pulses. The pulsed output from one shot 242 also causes a pulse to be pa~sed through OR ga~e 244 whereby the RUNP pulse again appears a~ the output of gate 244 and is delivered to again set run flip-flop 248 in run circuit 230 in the same manner as ~lip-flop 248 was sat during the home mode operation. When flip-~lop 248 is set, the Q outpu~ goes high -. : and is delivered again to AND gate 249 in magnîtude de~ector: 15 circuit 246 to enable ~ND gat~ 249, However, it will be ~oted that in this mode of operation ~he HOMEF signal has been removed, and ~hus no signal is passed through AND gate 243 until OR gate 247 receives an input from some other part of :~ . the circuitry o~ sign and magnitude detector 245. Thu~, ~he passing of the DONE signal from gate 272 ~erminates the HOMEF
signal in each of the motor control circuit~, 120, 172 and 198, whereby the pulse generator output is temporarily terminated . :
to ~wai~: further ac~ivation even ~hough the Q output ~rom run ;: 1ip-flop 248 is up and has ~een delivsred as one of the i~puts 25 ~ ~to~A~D ga~e 249. The home mode operation îs thus completed. . ~ -r~
The pulse ~rom one shot 242 i~ also i~v~r~ed ~nd delivered , : ~ , -:: : :
., ,.... ,,, .~ ,, , ., ~, .

r~7 to the C input of a D type flip-~lop 276, and ~lip-flop 276 is set on the trailing edge o~ the pulse from one shot 242, The Q ou~put of flip;~lop 276 ~h~ls goes high to constitute a MEASUREF signal and is delivered, inter alia, as one input to an A~D gate 278 in stop circui~ 234. Ga~es 278 and 266 and 268 combine to constitute an AND/OR'gate structure. The MEASUREF signal is also delivered to the D input of D ~ype flip-flop 310 to arm ~lip-~lop 310. The system is now se~
for operation i~ a measure mode as determined by error signals from accelerometer 116.
Assuming tha~ re~eren~e accelerometer 116 is now in any position other ~han its null'position, an error signal will be generated and delivered to amplifiar 280. As indicated in FIGURE 8, this error signal is a current whDse magnitudP is ::
a cosi~e function of the angle of the accelerometer's sansiti~e . -~ axis with respect to the ~orce of gravity. Amplifier 280 is a .. .
;~ high gain amplifier o~ the type LM107, and the ~mplifier ;:
circui~ can be found in l~n~ar pll~a }on~ Ha ~b~}, 1973 edi~ed by M. ~. Vander Kooi, Natio~al Semiconductor Applica~
~ion Note AN20-5, February 1969~ FIGURE 13. In this amplifiar circuit the current is ampli~ied and conver~ed to a volt~ge for further use in tha system.
The amplified signal from:ampli~ier circuit 280 is ~hen deli~ered to a ilter circuit 282 ~o remove high frequency ~ components on~he~signal which may be in~roduced by the step motors~and ambien~ vi~ra~ioDs. The ~ er is a two pole fil~er :: with a break ~r~quency of 3 her~z with a type LMl07..~pl.ifier, 4~
~: : :
;: , ' . ~
i - . :

- ~ \

and may be found in Linear Applications Handbook, 1973 edited by M. K. Vander Kooi, National Semiconductor, Inc. Note AN5~10, April 1968, FIGURE 25.
The filtered signal from filter circuit 282 is ~hen delivered to and integrat~d in an integrator circuit 284.
The amplifier in in~agrator circuit 284 is an LM107 type, switches Sl and S2 are semiconductor switches such as RCA
.
CD4016, and for ~urther de~ails of such integrator circuits see ~ ~ by Tobey, Graeme, and Hunlsman, FIGURE 6.15, McGraw-Hill, 1971. The ~: integrator func~ions to enlarge the error from accelerometer 116 as a function of time in order to examine and process small errors. The integra~or is reset by feeding back ~he output ~rom pulse generator 252 to semiconductor swi~ches S
~ and S:2 to reset ~he integrator to zero by alternately Glosing and opening switehes S and S with ~he signal rom the pulse : . 1 2 generator each time step motor 122 is stepped, one switch belng open when the other is closed.
: The filtered si~nal from filter 282 and the integrated 20 ~ ~ signal from integrator 284 are both delivered to a summing circuit 286 where the ~iltered signal and the integra~ed signal are.algebraically added. Thus, aven if the error signal rom~iLter 282~is small, ~he i~egra~d error signal will be `:
available ~or proce~slng in the rest of the system. For ~:~ further reference ~o ~he s~mmer circut, see National Semi-conductor,~Inc.~Notè A a~d 20-3, February 1969, FIGURE 3 1973 edited by M. K. Vander Kooi). .-45- :

- ~ . .
.. . ..

Tha output ~rom su~m~r circuit 286 is then delivered to sign and m~gnitude de~ec~or 245 to be examined ~or both sign and magnitude. The magni~ude is commensurate with the degree or magnitude of error between the instantaneous posi~ion o~ the re~erence accelerometer and the null posi~ion~ and ~ha sign is commensurate with the direction of rotation whlch is necessary in order to drive the reference accelero- :
meter to ~he null position. ~
Sign and magn~tude detector 245 has a comparator circuit ~:;
288A and a comparator cixcui~ 288B. Comparator circuit 288A
has a voltage divlder.290 comprised of resistors RlA and R2A
connected as show~ ~o amplifier 292; and compara~or circui~ :
288B has a similar voltage divider 294 comprised o~ resistors RlB and R2B connec~ed as shown ~o amplifier 296. Amplifiers 292 and 296 are both hi~h gain di~ferential amplifiers, The output ~rom summe~ 286 is delivered to amplifier 292 and the outpu~ from summer 286 is also delivered to ampli~ier 296.
Vol~age di~ider 290 establishes a ~irst reference voltage, reference A~ or di~feren~ial amplifier 292, and ~ol~age divider 294 establishes a second reerence voltage, re~erence B, for dif~erential amplifier 296. The comparator circui~
unctions ~o compare the o~tpu~ of summer 286 with the : reerencQ ~olkages~ Reerring ~o ~IGURES 14A~ 14B and 14G, when the outpu~ ~om summer 286 is more positive than the xe~erenc~ A voltage~ the ou~put (our~) ~rom ampli~ier 292 is n~gative. Similarly, whe~ the output from sun~ler 286 is more nega~ive than th~ vo.ltag~ level Qf re~erence B, then the .
~4~~

~,'' ' ' '. : ::
' '., ' '` , ' ~:

s~

outpu~ (OUTB) of amplifier 296 is positive. As the result of this oparation of comparator circuits 288A and 288B, OUTA
and OUTB are signals such as shown in FIGURES 14B and 14C.
The outputs from comparators 288A and 288B are fed to `inverting buffer 298 and non-inverting bu~er 300, respect-ively. The buffars serve ~o shift the levels o~ ~he voltages from the compara~ors to a voltage level compatible with flip-flop 258 to which the buffer outpu~s are delivered. The __.
signal OUTA (shown in FI&URE 14D) is delivered to tha J
term;nal of flip-flop 258, while the signal OUTB is delivered : to the K terminal of flip-flop 258, Also, the outputs of bu~f- -ers 298 and 300 are delivered ~o OR gate 247, OR gate 247 being in magnitude detector circuit 246. Thus, the s;gnals OUTB
and OUTA (see FIGURE 14E~ are delivered to OR ga~e 247.
Referring again to flip~lop 258, timing pulses CPl from master clock 216 are deliverad to ~he C input whereby which- .
_ ever of ~he signal OUT~ at ~he J input or the signal OUTB at the K input is present whenever a ~iming pulse CPl is received will be set into the flip-~lop. Thus, ~rom signal diagram~
14B ~hrough 14E, it can be seen that ~lip~flop 258 will set Q output high) when OUTA is negative ~OUT~ positive) in the presence o clock pulses CPl; and ~lip-flop 258 will b~ res~ :
;(Q outpu~ low) whenever OUTB is positive in the presence of clock pulses CPl. Resalling that the Q ou~put o~ flip-flop - .
~ 25~8 is~ d21ivered~to mo~or s~quence circuit 256 to con~rol the ~ .
direction o~ rota~ion of motor 122 depending on the le~el of ~ :
t~e~Q output~signal of flip-10p 258, it can thus be seen tha~
~ , ~
~47 ' :~: : ~:

~ 6 ~S~ 7 motor 12~ will be dri~en either clockwise or counterclockwise depending on ~he outputs o~ compara~ors ~88A and 288B, Thus, reerenca accelerometer 116 is driven in the appropria~e dirQction to reduc~ ~h~ error signal ~rom accelerometer 116 S and drive accelerometer 116 to i~s null position.
The OUTA signal (inver~ed to OUTA~ and the OUTB si.gnal delivered to OR gate 247 of magni~ude detector circu1t 246 serve to determ~nQ.the magn~tude of 'ch~ error signa'l frsr~
acceleromete~ 116. As illustra~ed in the signal diagrams 14A
~hrough 14E! whenever OUTB or OUTA is high, the signal from ~ummer 286 ~s outside the bounds defi~ed in ~IGURE 14A, i.e.
be~ow rcerence B and abo~e re~erence A. Hence, the area below reference A and above reference B in FIGU~E 14A defines a null band; and whenever the error is in excess o~ this null band, i.a. ~ above re~rence A or below reference B, a ~ignal is passed through OR gate 247 and is delivered to ~ND gat~ 249 to constitute the second input ~o AND ga~e 249. The first input to AND gate ~49 is already present in the ~orm o~ ~he high Q output ~rom run ~lip-10p 248. Thus, in the manner preYiously described, a sign~ passed by AND ga~e 249 ~o s~ ~lip-flop 250, ~lip-10p 250 be~ng set whe~ ~he D input iS 8t a logic 1 in the presence o~ the cl~ck pulses CPl. As ~:~
~ preYiously desc~ibed with respec~ ~o the home mode opexa~ion, ; ~ ~he s~ ~ out~u~ of flip-~lop 250 is ~hen ga~d with the :~
clock pulses CP3 in ~ND ga~e 254 whexeby step pulses are deli~red ~o motor sequence circui~ 2S6 to be ga~ed with ~he . . .
high Q output of flip-flop 77 at gate 261 to driv2 mo~or 122.

, . ..... . .

~r r~
~, ... .
Motor 122 will continue to drive as long as the s~ep pulses are received from pulse generator 25~, i.e., until aecelerome-ter 116 is driven ~o its null posi~ion at which poin~ the outpu~ from summer 286 is commensurate with the null described above.
, The outputs from ~lip-flop 258 of ~;ign and magnitude detector 245 and ~he pulsed output ~rom pulse genera~or 252 are also both delivered to up/down counter 144 for algebraic summing to d~termine the net number of stepping pulses deliv-, ered to motor 122 ~o drîve accelerometer 116 to i~s null position.
As will be apparent, the signal diagrams shown in FIGURES14A through 14E are only ~or purposes of illustration, and they approximate a eondition in which accelerometer 116 would , 15~ actually be hunting or oscillating back and forth across its null position. For oth~r conditions comm~nsurate with ~ .
error, an OUTA or OUTB signal would be present, but it would ~ --not be regular in time.

As previously described, run flip~flop 248 was resat 20 ~`~ upon delivery of a signal rom stop circui~ 234 ~o run circuit .
ga~e 270 in ~he pr~sence of clQck puIsé CP9 ~o gate 270.
As also previously described, the signal from stop circuit 234 occurred upon~the concurren~ delivery to gate 266 of a signal ~from home detector 128 (through amp1i~ier and squaring :25~ eir~uit ~264) ::and ~he HO~F signal :rom flip-flop 238. In the measure mode, the signal HOME:F has bean terminated, and thus ~ ~
the signal~rom stop circuit 234 to reset run flip-~lop 248 ~: -: : : . --~9_ . .

;. - , . . - ,. ,. . , .; ,, .

mus~ be generated in another manner. In the measure mode, ~lip-flop ~76 of measure circuit 228 has been se~ so that the sigllal MEASUREF is ~elivered to orm one inpu~ ~o AND
gate 278 in stop circuit 234! When a sqcond input is also present at AND gat~ 278, a signal will be passed through AND
gate 278 and throug~ OR ga~e 268 to be delivered to AND gate 270 where~y run flip-flop 248 will be reset on the concurrencie o~ clock pulse CP9. This second input to AND gate 278 is supplied from a counter 302 which delivers a signal ~o AND
ga~e 278 when the counter has ov~rflowed.
Thexe are two ways to load pulses into counter 302. First, : if there is a sign change from sign and magnitude detector 245, the Q outpu~ o flip-flop 258 will change between low and high.
The Q output of flip-flop 258 is connected as one of the inputs :~ 15 to an AND ga~e 304, and ~he other input to AND ga~e 304 is .obtained from the Q output of a flip-flop 306. Flip-~lop 306 ; wi~ have been reset by the RU~P pulse so that its Q outpu~ is ~:
high, and thus a signal wiIl pass through AND gate 304 each : time the Q output of 1ip-flop 2S8 goes high in aecordance ~: :
~: ~
~ 20 with a sign change.~ The output from-gate 304 passes through ~. :
an.OR gate 308 and is deli~ered to counter 302. When counter `:
302 o~er~lows,- a signal is delivere~ r~m counter 302 ~o AND
gate 278 which ~oincides with the MEASUR~F signal to ga~e 278 where~y~gate 278 passes a, $ignal to OR gate 268 and hence to 25~ : ga~e 270.~ The;signal ~hus delivered.~o gate 270 will, in the presenc2~0f:the~clock pulces CP9, re~et ~lip-flop 248 whereby the Q input~rom flip~ p 248 to gate 249 o~ ~he magnitude , ~ ~
~ 50 .

~o~

detec~or is removed. The removal o~ ~he input ~o ga~e 249 terminates the operation of pulse generator 252 whereby stepping of motor 122 is terminated. Thus, s~epping of motor 122 can be terminated in a "sign forcedl' stop mode when the sign of the error signal ~rom ac~celerome~er 116 changes a pre~
determined number of times. Tha~ would, of course, occur when accelerome~er 116 has reachqd and is hunting across its null position.
Flip-~lop 248 can also be reset and hen~e the stepping of motor 122 terminated, if no pulses are generated by pulse generator 252 for a prede~ermined period of time. This condition, which may be referred to as a "~ime forced" stop mode, is accomplished by means o~ D type flip-flop 306 (previously described~ and D ~ype flip flop 310. .The ::
. MEASUREF signal from flip~flop 276 is delivered to the D
input of flip-flop 310 to enable flip-flop 310. Also~ a ti~ing ~ stop signal CPN (a deriva~i~e of the master clock ou~put3 .
is delivered to ~he C inpu~ of ~lîp~flop 310 to clock the : flip-flop, and the R terminal o~ flip-flop 310 is connected ~ to receive ~he output pulses from pulse generator 252. Flip-flop 310 will set each time a zero ~o one transi~ion is re-. ceîved on ~he clock input termina~ C, and will rese~ each : ~ tIme a pulse is rec~i~ed at terminal R from pulse generator 252. The companio~ flip-~lop 306 is reset once at the :~ 25 ~beginning of the measure mode by the RUNP signal connected ~o the R ~erminal. The G termi~al of 1ip~flop 306 is also connected to receive the CPN slgnal rom ~h~ master clock3 and : :: : , : ~ ' w51- .

~ 7 flip-flop 306 will set on the leading edge of CPN if the D
enable input of flip-~lop 306 is high, a condition w~ich occurs if flip-flop 310 is set when ~lip-:Elop 306 rec~ives the leadin~ edge of CPN. When flip-flop 306 is set, it provides S one o~ the inputs to an AND gate 31~, ~he other input to which is in the ~orm of puls~s CPl from'the master clock. The pulses CPl are thus passed through ga~e 312 and through gatP 308 to counter 302. Thus, a burst of pulses are delivered~to counter 302 to cause counter 302 ~o overflow whereby ~ signal is passed through gate 278 and through gate 268 to be delivered to gate 270. The signal thus delivered to gate 270 coincides with the CP9 clock input tG reset flip-flop 248 whereby gate 249 is disabled and ~he output from pulse generator 252 is t~rminated. Thus, ~he stepping o motor ::~
~ 122 is terminat~d because accelerometer 116 is at i~s null position.
The Q output of flip-flop ~48 is oonnected to gate ~72 of done circuit 232. When 1ip-flop 248 is reset, commensur-. ~
a~e with the te~mination of ~he operation of mo~or 122, ~ ~the Q signal is d01i~er~d ~o gate 272. When similar Q signals have been delivered to gate 272 from all three axes (i~e.
the commensura~ç run flip-flops) and all three flip-flops have been rèA~et to terminate operation of their respective motors, ;a DONE signal will be passed ~hrough ga~e 272 and will be ~;2~ ~deli~ered to gate 274 in home segment circui~ 226 and also to three:input AND ~ate 314 in measure circuit 228. T~ree way AND~gate 314 is~also r~ceiving the MEASUREF signal, so that it is recei~ing two o~ the three inputs necessary ~o pass a 52~

,. ~ . , , signal. A first pass flip-.flop 316 o ~he JK~type in measure circuit 228 has previously be~n set by CLEARP
whereby the Q output of flip-flop 316 is high. The Q output of flip-~lop 316 is connected to and constitutes the third input to gate 314, whereby the DONE signal ~rom gate 272 will pass through gate 314 i~ this is the fir~t occurrsnce of ~he DONE signal since the start pulse STARTP was recs;ived.
The signal passed through AND gate 314 then passes through OR
gate 318 and is delivered to ~he R input of fl~ip~flop 276 to reset flip-~lop 276 and thus terminate the MEASUREF signal.
Upon the reset~ing of flip-1Op 276 the trailing edge of MEASUREF,triggers a one shot LOAD multivibrator 320 ~o generate a lms pulse from one shot 320, identified as LOADP. The LOADP
signal is delivered to shift register 331 to enable the jam inputs o~ the shift regis~er whereby the in~ormation stored in each of ~he up/down counters 144, 176 and 200 is parallel : transferred in~o the shift regis~er. The pulse LOADP is also : delivered ~o flip-flop 316 to reset flip-flop 316, and the LOADP pulse is also deli~erad through OR gate 240 to se~ home flip-flop 23~, The LOADP pulse pa~sing through OR ga~e 240 ., :~ ` . is also delivered to OR gate 244 to create another RUNP pulse.
This RUNP pulse.again se~s run flip-flop 248 to cause the system to again run i~ the home mod~ as previously described.
The control system will thus~repeatedly run through cycles ~ ~of~home moda and measure mode operation until opera~ion o the ~.
~: controL sys~em is terminated when ro~ation of ~he drill string : is again resumed. The repa~i~ive cycling through the home ~ ;: : ' , ' ~ ~ ~ 7 mode and measu~e mocles o operation will be as described above witll the exception that 1ip-10p 276 will not be xese~ on the subsequent cycling of the system by the DO~E
signal from gate 272 because the pul~e LOADP will have reset ~lip-flop 316 to produce a logic low at the Q output of gate 316, thus ~emoving one of ~he nécessary inputs a~ gate 314.
On these subsequent cyclings o~ ~he system, ~lip-~lop 316 will rese~ only upon r~celp~ 9f a comple~ion signal ~COMPP) fr~m a shif~ pulse genexator 330 delivered t~ OR gate 318.
Ope~a~ion o~ the shit pulsQ gene~ator ~s star~ed by the ~OADP pulse.
The first pass flip-~lop 316 is needed in the system because shift pulse generator 330 does not operat~ until.
completion o~ the first cycle of the system; and therefore a one time pulse is needed to r~cycle the sgs~em so a second se~ o measuremen~s can be taken while the first information loaded Into the shi~t register by the ~irst LOhDP si~nal is ~ransfer~ed ~o the surfac~. The shift pulse generator, which i~ merely a divider to subdivide master clock pulses, ~0 g~nerates pulses to move ~he in~orma~ion out of shift regi~ter 331 to ~alve driver 57 which operates plunger 56.
COMPP is ge~erated a~er each ~ pulses o~ pulse genera~or 330 equal th~ ~to~age capacl~y o~ shi~t register 331~
As pr~vi~usly ~oted, th~ above descrip~ion was for motor drive control 120, and the same description would also apply ~or ~he corresponding identical unit 172. Mo~or .. ..
drive con~rol unit 198 differs only in that arnpli~ier 280 -5.~-' ,' , ' ~ .. . .

' : . ',' ' . : :, , . ... : ' ' ' . '

6~g~
~;~
and filter 282 are replaced with a unit iden~ical to detector 70 (including phase detector 70A, filter 70B and amplifier 70C) in order to receive and process the output o:E magneto-meter 178. The output o de~ector 70 in motor drive control unit 198 is delivered to its associated integrator, and the antire remaining part of unit 198 is the same as and operates in the same way as motor drive control 120. A dif~erent set of clock pulses is delivered to and used in each of the three motor control units 120, 172 and 198 so that 6ach unit -~10 operates sequentially in its MEASURE mode rather than the units operating simultaneously which might result in cross talk or interference in signals from the three u~its. That ;
is, reference motor 122 is stepped one step, and then inclination motor 174 is stepped one step, and then azimuth motor 196 is s~epped on~ s~ep, and that sequential stepping process is ~hen repeated un~il all ~hree sensors have reached : their null posi~ions.
Each LOADP pulse is also dalivered to ~he S input of ; ~ flip-flop 78 (see FIGURE 5A) to set 1ip-flop 78 whereby the Q output of f~ip-flop 78 goes high and consti~utas one of the : r~quired inpu~s for AND gate 79. The other inpu~ ~or AND
gate 79 is the in~erted Q ou~pu~ of flip-10p 76. Thus, AND
gate 79 will pass a signal when flip-flop 76 is set (commen-~: ~ surate with à resumed s~ate of ro~a~ion~ and LOADP has been ~ ge~rated. This signal p~ssed by AND gate 70 causes ~he K
input~ of ~ip-flop 77 to go;high, whereby a rising edge of ~he : clock pulse C~ will res~t flip~lop 77 so tha~ ~h~ Q ou~pu~
=55-:
: ..

.

o~ 1ip~10p 77 goes low (level X o~ FIGURE 6C~ ~o signal re~urn to the s~ate o~ rotation. The recurrence of this low state of the Q output o~ flip-flop 77 ~hen terminates operation o~ the step motors 122, 174 and 196 by remvving one of the inpu~s to the ~ND gate 261 in each motor drive circuit 256 and also by disarming valve driver 57.
The HOME and MEASURE cycling described abov~ wil-l then - persist for each of r~ference accelerometer 116, inclination accelerometar 148 and azimuth magnetom~ter 178, until the ro~ation sensor logic de~ects drill string motion or power is removed ~rom the system due to loss of generator p~wer which, for example, could occur when mud flow is stopped.
While preferred embodiments have been shown and described9 various modi~ications and substitutions may be made thereto , ~ ~ 15 without departing from ~he spirit and scopes of th~ in~ention.
- .
Accordingly, it is ~o be ~nderstood that the present invention as been described by way o~ illustration and no~ limitation.
,~
, , : , :
: ~ :

.:

, . ~ :

-:
, ~ 56 , : : :
: ~ , .
::

Claims (112)

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

1. Sensor apparatus for measuring directional parameters of a drill string in a borehole, the sensor appara-tus including:
first gimbal means mounted for rotation in a segment of a drill string, said first gimbal means being rotatable about the axis of the drill string segment or an axis parallel to the drill string axis;
first gravity responsive means mounted on said first gimbal means for generating first alignment signals as a function of gravity forces on said first gravity responsive means, said first alignment signals varying as a function of the alignment of said first gravity responsive means with res-pect to the force of gravity;
second gimbal means mounted for rotation in said drill string segment, said second gimbal means being rotatable about an axis perpendicular to the axis of rotation of said first gimbal;
second gravity responsive means mounted on said second gimbal means for generating second alignment signals as a function of gravity forces on said second gravity responsive means, said second alignment signals varying as a function of the alignment of said second gravity responsive means with respect to the force of gravity;
third gimbal means mounted for rotation in said drill string segment, said third gimbal means being rotatable about 1. (continued) an axis perpendicular to an axis perpendicular to the axis of rotation of said first gimbal;
magnetic responsive means mounted on said third gimbal for generating third alignment signals as a function of magnetic field forces on said magnetic responsive means, said third alignment signals varying as a function of the alignment of said magnetic responsive means with respect to the earth's magnetic field;
first motor means connected to said first gimbal for driving said first gravity responsive means to a first pre-determined position and then to a second position having a predetermined alignment with respect to the force of gravity as determined by said first alignment signals;
first detector means for determining when said first gravity responsive means is at its first predetermined position and generating a first home signal;
first control means for operating said first motor means, said first control means receiving said first home signal to terminate the drive of said first gravity responsive means to the first predetermined position thereof, said first control means then driving said first gravity responsive means to said second position thereof, said first control means receiving said first alignment signals to determine when said second position has been reached, the net angular movement of said first motor means being commensurate with a first directional parameter of the drill string;

1. (continued) second motor means connected to said second gimbal for driving said second responsive means to a first predeter-mined position and then to a second position having a pre-determined alignment with respect to the force of gravity as determined by said second alignment signals;
second detector means for determining when said second gravity responsive means is at its first predetermined position and generating a second home signal;
second control means for operating said second motor means, said second control means receiving said second home signal to terminate the drive of said second gravity responsive means to the first predetermined position thereof, said second control means then driving said second gravity responsive means to said second position thereof, said second control means receiving said second alignment signals to determine when said second position has been reached, the net angular movement of said second motor means being commensurate with a second directional parameter of the drill string;
third motor means connected to said third gimbal for driving said first magnetic responsive means to a first pre-determined position and then to a second position having a predetermined alignment with respect to the earth's magnetic field as determined by said third alignment signals;
third detector means for determining when said first magnetic responsive means is at its first predetermined position and generating a third home signal; and

1. (continued) third control means for operating said third motor means, said third control means receiving said third home signal to terminate the drive of said magnetic responsive means to the first predetermined position thereof, said third control means then driving said first magnetic responsive means to said second position thereof, said third control means receiving said third alignment signals to determine when said second position has been reached, the net angular movement of said third motor means being commensurate with a third directional parameter of the drill string.

2. Sensor apparatus as in claim 1 wherein:
said first gravity responsive means is error trans-ducing accelerometer means having a sensitive axis with respect to the direction of gravity forces;
said second gravity responsive means is error trans-ducing accelerometer means having a sensitive axis with respect to the direction of gravity forces; and said magnetic responsive means is magnetometer means having a sensitive axis with respect to the earth's magnetic field.

3. Sensor apparatus as in claim 2 wherein:
said first gravity responsive means is a first force balance accelerometer having its sensitive axis perpendicular to the axis of the drill string segment in the second position thereof;

3. (continued) said second gravity responsive means is a second force balance accelerometer having its sensitive axis perpendicular to the sensitive axis of the sensitive axis of the first force balance accelerometer in the second position of each accelerometer; and said magnetic responsive means is a fluxgate magneto-meter having its sensitive axis perpendicular to the earth's magnetic field in the second position thereof.

4. Sensor apparatus as in claim 1 wherein:
said first directional parameter is the reference angle formed between a first plane containing the axis of the drill string segment and a known reference on the drill string segment and a second plane containing the drill axis and a vertical projection of the drill axis; and said second directional parameter is the angle of inclination of the axis of the drill string segment with respect to the vertical in a common vertical plane; and said third directional parameter is the azimuth angle between a vertical plane which contains the horizontal projec-tion of the axis of the drill string segment and the vertical plane containing the horizontal projection of the local terrestrial magnetic field.

5. Sensor apparatus as in claim 1 wherein each of said first, second and third detector means includes:
light generating means, photoelectric receiving means,

5. (continued) and light control means for delivering light from said light generating means to said photoelectric receiving means when the respective gravity or magnetic responsive means is in its first predetermined position.

6. Sensor apparatus as in claim 5 wherein:
said light control means includes apertured disc means positioned between said light generating means and said light receiving means, said disc means being drivingly connected to the motor means associated with the respective gravity or magnetic responsive means.

7. Sensor apparatus as in claim 1 wherein:
said first, second and third motor means are each stepping motors.

8. Sensor apparatus as in claim 7 wherein each of said first, second and third control means includes:
pulse generating means for delivering pulses to the step motor associated with the control means; and means for counting the net number of pulses delivered to the step motor to drive the associated gravity or magnetic responsive means from its home position to its second position, said net number of pulses being commensurate with the direc-tional parameter of the drill string to be measured by the gravity or magnetic responsive means.

9. Sensor apparatus as in claim 1 wherein:
said second gimbal means is rotatably mounted in said first gimbal means; and said third gimbal means is rotatably mounted on a rotatable shaft, said rotatable shaft being rotatably mounted in said first gimbal.

10. A sensor system as in claim 9 wherein:
said second gimbal means has an axis of rotation perpendicular to the axis of rotation of said first gimbal means; and said rotatable shaft has an axis of rotation parallel to the axis of rotation of said second gimbal means; and said third gimbal means has an axis of rotation perpendicular to the axis of rotation of said rotatable shaft.

11. A sensor system as in claim 10 wherein:
said first motor means is connected to said drill string segment;
said second motor means is mounted on said first gimbal and is drivingly connected to said second gimbal and to said rotatable shaft; and said third motor means is mounted on said first gimbal and is drivingly connected to said third gimbal.

12. A sensor system as in claim 1 wherein said first motor means is connected to said drill string segment and is drivingly connected to said first gimbal means;

12. (continued) said second motor means is mounted on said first gimbal and is drivingly connected to said second gimbal; and said third motor means is mounted on said first gimbal and is drivingly connected to said third gimbal.

13. A sensor system as in claim 12 including:
rotatable support means for said third gimbal; and means drivingly connecting said second motor means to said rotatable support means to coordinate the position of said magnetic responsive means with the position of said second gravity responsive means.

14. A sensor system as in claim 13 wherein:
the axis of rotation of said rotatable support means is parallel to the axis of rotation of said second gimbal; and the axis of rotation of said rotatable support means and the axis o rotation of said second gimbal means are perpendicular to the axis of rotation of said first gimbal; and the axis of rotation of said third gimbal means is perpendicular to the axis of rotation of said rotatable support means.

15. Sensor apparatus as in claim 1 wherein:
said drill string segment is non-magnetic.

16. Sensor apparatus as in claim 15 wherein:
said sensor apparatus is contained in a non-magnetic housing mounted in said drill string segment.

17. Sensor apparatus as in claim 1 including:
means for transmitting to the surface information representative of the directional parameters determined by the sensor system.

18. Sensor apparatus as in claim 17 wherein:
said transmitting means is acoustical transmitting means for generating acoustical signals in a liquid in the drill string.

19. The method of measuring directional parameters of a drill string in a borehole, including the steps of:
rotating first gravity responsive means in a segment of the drill string to generate first alignment signals as a function of gravity forces on said first gravity responsive means, said first gravity responsive means being mounted on a first gimbal mounted for rotation in the drill string segment about the axis of the drill string segment or an axis parallel to the drill string axis, and said first alignment signals varying as a function of the alignment of said first gravity responsive means with respect to the force of gravity;
rotating second gravity responsive means in said drill string segment for generating second alignment signals as a function of gravity forces on said second gravity respon-sive means, said second gravity responsive means being mounted for rotation on a second gimbal having an axis of rotation perpendicular to the axis of rotation of the first gimbal, said second alignment signals varying as a function of the 19. (continued) alignment of said second gravity responsive means with respect to the force of gravity;
rotating magnetic responsive means in said drill string segment to obtain third alignment signals as a function of magnetic field forces on said magnetic responsive means, said magnetic responsive means being mounted on a third gimbal rotatable about an axis perpendicular to an axis perpendicular to the axis of rotation of the first gimbal, and said third alignment signals varying as a function of the alignment of said magnetic responsive means with respect to the earth's magnetic field;
operating a driving motor connected to said first gimbal to drive said first gravity responsive means to a first predetermined position and then to a second position having a predetermined alignment with respect to the force of gravity as determined by said first alignment signals;
detecting when said first gravity responsive means is at its first predetermined position and generating a first home signal;
terminating the drive of said first gravity responsive means to the first position thereof upon receipt of said first home signal;
driving said first gravity responsive means to said second position after the first predetermined position thereof has bean reached;

19. (continued) measuring the net movement of said first gravity responsive means from said first predetermined position thereof to said second position thereof to determine a first directional parameter of the drill string;
operating a driving motor connected to said second gimbal to drive said second gravity responsive means to a first predetermined position and then to a second position having a predetermined alignment with respect to the force of gravity as determined by said second alignment signals;
detecting when said second gravity responsive means is at its first predetermined position and generating a first home signal;
terminating the drive of said second gravity respon-sive means to the first position thereof upon receipt of said first home signal;
driving said second gravity responsive means to said second position after the first predetermined position thereof has been reached;
measuring the net movement of said second gravity responsive means from said first predetermined position thereof to said second position thereof to determine a second directional parameter of the drill string;
operating a driving motor connected to said third gimbal to drive said magnetic responsive means to a first predetermined position and then to a second position having a predetermined alignment with respect to the earth's magnetic

19. (continued) field as determined by said third alignment signals;
detecting when said magnetic responsive means is at its first predetermined position and generating a first home signal;
terminating the drive of said magnetic responsive means to the first position thereof upon receipt of said first home signal;
driving said magnetic responsive means to said second position after the first predetermined position thereof has been reached; and measuring the net movement of said magnetic responsive means from said first predetermined position thereof to said second position thereof to determine a third directional parameter of the drill string.

20. The method of measuring directional parameters of a drill string in a borehole as in claim 19 wherein:
the step of rotating first gravity responsive means includes rotating error transducing accelerometer means having a sensitive axis with respect to the direction of gravity forces;
the step of rotating second gravity responsive means includes rotating error transducing accelerometer means having a sensitive axis with respect to the direction of gravity forces; and the step of rotating magnetic responsive means include es rotating magnetometer means having a sensitive axis with respect to the earth's magnetic field.

21. The method of measuring directional parameters of a drill string in a borehole as in claim 20 wherein:
the step of rotating first gravity responsive means includes rotating first force balance accelerometer means having a sensitive axis, the sensitive axis being aligned perpendicular to the axis of the drill string segment in the second position of said first force balance accelerometer means;
the step of rotating second gravity responsive means includes rotating second force balance accelerometer means having a sensitive axis, the sensitive axis being aligned perpendicular to the sensitive axis of the first force balance accelerometer means in the second position of each accelerometer means; and the step of rotating magnetic responsive means includes rotating fluxgate magnetometer means having a sensitive axis, the sensitive axis being aligned perpendicular to the earth's magnetic field in the second position of the magnetometer means.
22. The method of measuring directional parameters of a drill string in a borehole as in claim 19 wherein:
the step of measuring the net movement of the first gravity responsive means to determine a first directional parameter is the step of measuring the reference angle formed between a first plane containing the axis of the drill string segment and a known reference on the drill string segment and a second plane containing the drill axis and a vertical

22. (continued) projection of the drill axis;
the step of measuring the net movement of the second gravity responsive means to determine a second directional parameter is the step of measuring the angle of inclination of the axis of the drill string segment with respect to the vertical in a common vertical plane; and the step of measuring the net movement of the magnetic responsive means to determine a third directional parameter is the step of measuring the azimuth angle between a vertical plane which contains the horizontal projection of the axis of the drill string segment and the vertical plane containing the horizontal projection of the local terrestrial magnetic field.

23. The method of measuring directional parameters of the drill string in a borehole as in claim 19 wherein:
the step of detecting when said first gravity respon-sive means is at its first predetermined position includes passing a light from a light source to a photoelectric detector;
the step of detecting when said second gravity responsive means is at its first predetermined position includes passing a light from a light source to a photoelectric detector;
and the step of detecting when said magnetic responsive means is at its first predetermined position includes passing a light from a light source to a photoelectric detector.

24. The method of measuring directional parameters of a drill string in a borehole as in claim 23 wherein the step of passing light from each light source to each photo-electric detector includes:
rotating apertured disc means positioned between each light source and each photoelectric detector by driving connection between the apertured disc means and the driving motor associated with the respective gravity or magnetic responsive means.

25. The method of measuring directional parameters of the drill string in the borehole as in claim 19 wherein:
the step of operating each driving motor includes operating stepping motors.

26. The method of measuring directional parameters of a drill string in a borehole as in claim 25 wherein the steps of measuring the net movement of each of said first and second gravity responsive means and said magnetic responsive means includes:
generating and delivering pulses to the step motor associated with each of said gravity responsive means and magnetic responsive means; and counting the net number of pulses delivered to the step motor to drive each gravity responsive means or magnetic responsive means from its first predetermined position to its second predetermined position, said net number of pulses being commensurate with the directional parameter of the drill string

26. (continued) to be measured by the gravity or magnetic responsive means.

27. The method of measuring directional parameters of a drill string in a borehole as in claim 1.9 wherein:
the step of rotating said second gravity responsive means includes rotating said second gravity responsive means on a gimbal rotatably mounted in said first gimbal; and the step of rotating said magnetic responsive means includes rotating said magnetic responsive means on a gimbal rotatably mounted on a rotatable shaft mounted in said first gimbal.

28. The method of measuring directional parameters of a drill string in a borehole as in claim 27 wherein:
said second gimbal has an axis of rotation perpendicu-lar to the axis of rotation of said first gimbal;
said rotatable shaft has an axis of rotation parallel to the axis of rotation of said second gimbal; and said third gimbal has an axis of rotation perpendicu-lar to the axis of rotation of said rotatable shaft.

29. The method of measuring directional parameters of a drill string in a borehole as in claim 19 including the step of:
transmitting to the surface information representative of the directional parameters determined by the gravity respon-sive means and the magnetic responsive means.

30. The method of measuring directional parameters of a drill string in a borehole as in claim 19 including the step of:
transmitting to the surface information representative of the directional parameters determined by the gravity and magnetic responsive means by generating acoustical signals in a liquid in the drill string.

31. Sensor apparatus as in claim 8 wherein:
said first gravity responsive means is error transduc-ing accelerometer means having a sensitive axis with respect to the direction of gravity forces;
said second gravity responsive means is error transduc-ing accelerometer means having a sensitive axis with respect to the direction of gravity forces; and said magnetic responsive means is magnetometer means having a sensitive axis with respect to the direction of the earth's magnetic field.

32. Sensor apparatus as in claim 31 wherein:
said first gravity responsive means is a first force balance accelerometer having its sensitive axis perpendicular to the axis of the drill string segment in the second position thereof;
said second gravity responsive means is a second force balance accelerometer having its sensitive axis perpendicular to the sensitive axis of the first force balance accelerometer in the second position of each accelerometer; and said magnetic responsive means is a fluxgate magneto-meter having its sensitive axis perpendicular to the direction of the earth s magnetic field in the second position thereof.

33. Sensor apparatus as in claim 8 wherein:
said first directional parameter is the reference angle formed between a first plane containing the axis of the drill string segment and a known reference on the drill string segment and a second plane containing the drill axis and a vertical pro-section of the drill axis; and said second directional parameter is the angle of in-clination of the axis of the drill string segment with respect to the vertical in a common vertical plane; and said third directional parameter is the azimuth angle between a vertical plane which contains the horizontal projection of the axis of the drill string segment and the vertical plane con-taining the horizontal projection of the direction of the local terrestrial magnetic field.

34. Sensor apparatus as in claim 8 wherein each of said first, second and third detector means includes:
light generating means, photoelectric receiving means, and light control means for delivering light from said light generating means to said photoelectric receiving means when the respective gravity or magnetic responsive means is in its first predetermined position.

35. Sensor apparatus as in claim 34 wherein:
said light control means includes apertured disc means positioned between said light generating means and said light re-ceiving means, said disc means being drivingly connected to the motor means associated with the respective gravity or magnetic responsive means.

36. Sensor apparatus as in claim 8 wherein:
said second gimbal means is rotatably mounted in said first gimbal means; and said third gimbal means is rotatably mounted on a ro-tatable shaft, said rotatable shaft being rotatably mounted in said first gimbal means; and

37. A sensor system as in claim 36 wherein:
said second gimbal means has an axis of rotation perpen-dicular to the axis of rotation of said first gimbal means; and said rotatable shaft has an axis of rotation parallel to the axis of rotation of said second gimbal means; and said third gimbal means has an axis of rotation perpen-dicular to the axis of rotation of said rotatable shaft.

38. A sensor system as in claim 37 wherein said first motor means is mounted on said drill string segment and is drivingly connected to said first gimbal means;
said second motor means is mounted on said first gimbal means and is drivingly connected to said second gimbal means and to said rotatable shaft; and said third motor means is mounted on said first gimbal means and is drivingly connected to said third gimbal means.

39. A sensor system as in claim 8 wherein:
said first motor means is mounted on said drill string segment and is drivingly connected to said first gimbal means;
said second motor means is mounted on said first gimbal means and is drivingly connected to said second gimbal means; and said third motor means is mounted on said first gimbal means and is drivingly connected to said third gimbal means.

40. A sensor system as in claim 39 including:
a rotatable support means for said third gimbal means;
and means drivingly connecting said second motor means to said rotatable support means to coordinate the position of said magnetic responsive means with the position of said second gravity responsive means.

41. A sensor system as in claim 40 wherein:
the axis of rotation of said rotatable support means is parallel to the axis of rotation of said second gimbal means; and the axis of rotation of said rotatable support means and the axis of rotation of said second gimbal means are perpen-dicular to the axis of rotation of said first gimbal; and the axis of rotation of said third gimbal means is perpendicular to the axis of rotation of said rotatable support means.

42. Sensor apparatus as in claim 8 wherein:
said drill string segment is non-magnetic.

43. Sensor apparatus as in claim 42 wherein:
said sensor apparatus is contained in a non-magnetic housing mounted in said drill string segment.

44. Sensor apparatus as in claim 8 including:
means for transmitting to the surface information re-presentative of the directional parameters determined by the sensor system.

45. Sensor apparatus as in claim 44 wherein:
said transmitting means is acoustical transmitting means for generating acoustical signals in a liquid in the drill string.

46. Sensor apparatus as in claim 1 wherein each of said first, second and third control means includes:
measuring means for measuring the net movement of the motor means associated with the control means required to drive the associated gravity or magnetic responsive means from its first position to its second position, the net movement of each of said motor means being commensurate with a directional parameter of the drill string.

47. The method of measuring directional parameters of a drill string in a borehole as in claim 26 wherein:
the step of rotating first gravity responsive means in-cludes rotating error transducing accelerometer means having a sensitive axis with respect to the direction of gravity forces;

the step of rotating second gravity responsive means includes rotating error transducing accelerometer means having a sensitive axis with respect to the direction of gravity forces;
and the step of rotating magnetic responsive means includes rotating magnetometer means having a sensitive axis with respect to the direction of the earth's magnetic field.

48. The method of measuring directional parameters of a drill string in a borehole as in claim 47 wherein:
the step of rotating first gravity responsive means in-cludes rotating first force balance accelerometer means having a sensitive axis, the sensitive axis being aligned perpendicular to the axis of the drill string segment in the second position of said first force balance accelerometer means;
the step of rotating second gravity responsive means in-cludes rotating second force balance accelerometer means having a sensitive axis, the sensitive axis being aligned perpendicular to the sensitive axis of the first force balance accelerometer means in the second position of each accelerometer means; and the step of rotating magnetic responsive means includes rotating fluxgate magnetometer means having a sensitive axis, the sensitive axis being aligned perpendicular to the direction of the earth's magnetic field in the second position of the magnetometer means.

49. The method of measuring directional parameters of a drill string in a borehole as in claim 26 wherein:
the step of measuring the net movement of the first gravity responsive means to determine a first directional para-meter is the step of measuring the reference angle formed between a first plane containing the axis of the drill string segment and a known reference on the drill string segment and a second plane containing the drill axis and a vertical projection of the drill axis;
the step of measuring the net movement of the second gravity responsive means to determine a second directional para-meter is the step of measuring the angle of inclination of the axis of the drill string segment with respect to the vertical in a common vertical plane; and the step of measuring the net movement of the magnetic responsive means to determine a third directional parameter is the step of measuring the azimuth angle between a vertical plane which contains the horizontal projection of the axis of the drill string segment and the vertical plane containing the horizontal projection of the direction of the local terrestrial magnetic field.

50. The method of measuring directional parameters of the drill string in a borehole as in claim 49 wherein:
the step of detecting when said first gravity responsive means is at its first predetermined position includes passing a light from a light source to a photoelectric detector;
the step of detecting when said second gravity respon-sive means is at its first predetermined position includes passing a light from a light source to a photoelectric detector; and the step of detecting when said magnetic responsive means is at its first predetermined position includes passing a light from a light source to a photoelectric detector.

51. The method of measuring directional parameters of a drill string in a borehole as in claim 50 wherein the step of passing light form each light source to each photoelectric detector includes:

rotating apertured disc means positioned between each light source and each photoelectric detector by driving connection between the apertured disc means and the driving motor associated with the respective gravity or magnetic responsive means.

52. The method of measuring directional parameters of a drill string in a borehole as in claim 26 wherein:
the step of rotating said second gravity responsive means includes rotating said second gravity responsive means on a gimbal rotatably mounted in said first gimbal; and the step of rotating said magnetic responsive means includes rotating said magnetic responsive means on a gimbal rotatably mounted on a rotatable shaft mounted in said first gimbal.

53. The method of measuring directional parameters of a drill string in a borehole as in claim 52 wherein:
said second gimbal has an axis of rotation perpendicular to the axis of rotation of said first gimbal;
said rotatable shaft has an axis of rotation parallel to the axis of rotation of said second gimbal; and said third gimbal has an axis of rotation perpendicular to the axis of rotation of said rotatable shaft.

54. The method of measuring directional parameters of a drill string in a borehole as in claim 26 including the step of:
transmitting to the surface information representative of the directional parameters determined by the gravity responsive means and the magnetic responsive means.

55. The method of measuring directional parameters of a drill string in a borehole as in claim 26 including the step of:
transmitting to the surface information representative of the directional parameters determined by the gravity and magnetic responsive means by generating acoustical signals in a liquid in the drill string.

56. The method of measuring directional parameters of a drill string in a borehole as in claim 19 wherein the step of measuring the net movement of each of said first and second gravity responsive means and said magnetic responsive means includes:
measuring the net movement of the driving motor associated with each of said gravity responsive means and said magnetic responsive means, the net movement of each of said driving motors being commensurate with a directional parameter of the drill string.

57. Sensor apparatus for measuring directional parameters of a drill string in a borehole, the sensor apparatus including:
first gimbal means mounted for rotation in a segment of a drill string, said first gimbal means being rotatable about the axis of the drill string segment or an axis parallel to the drill string axis;
first gravity responsive means mounted on said first gimbal means for establishing a predetermined position of said first gimbal means with respect to the direction of the force of gravity;
second gimbal means mounted for rotation in said drill string segment, said second gimbal means being rotatable about an axis perpendicular to the axis of rotation of said first gimbal;
second gravity responsive means mounted on said second gimbal means for generating inclination related signals as a func-tion of gravity forces on said second gravity responsive means, said inclination related signals varying as a function of the alignment of said second gravity responsive means with respect to the direction of the force of gravity;

third gimbal means mounted for rotation in said drill string segment, said third gimbal means being rotatable about an axis perpendicular to an axis perpendicular to the axis of rota-tion of said first gimbal;
magnetic responsive means mounted. on said third gimbal means for generating azimuth related signals as a function of magnetic field forces on said magnetic responsive means, said azimuth related signals varying as a function of the alignment of said magnetic responsive means with respect to the direction of the earth's magnetic field;
motor means for said second gimbal means connected to said second gimbal means for driving said second gravity respon-sive means to a first predetermined position and then to a second position having a predetermined alignment with respect to the direction of the force of gravity as determined by said inclination related signals;
detector means for determining when said second gravity responsive means is at its first predetermined position and gen-erating a home signal for said second gravity responsive means;
control means for said second gimbal means for operating said second gimbal motor means, said second gimbal control means receiving said home signal for said second gravity responsive means to terminate the drive of said second gravity responsive means to the first predetermined position thereof, said second gimbal control means then driving said second gravity responsive means to said second position thereof, said second gimbal control means receiving said inclination related signals to determine when said second position has been reached, the net movement of said second gravity responsive means from said first position thereof to said second position thereof being commensurate with an inclination parameter of the drill string;
motor means for said third gimbal means connected to said third gimbal means for driving said magnetic responsive means to a first predetermined position and then to a second position having a predetermined alignment with respect to the direction of the earth's magnetic field as determined by said azimuth related signals;
detector means for determining when said magnetic responsive means is at its first predetermined position and gen-erating a home signal for said magnetic responsive means; and control means for said third gimbal means for operating said third gimbal motor means, said third gimbal control means receiving said home signal for said magnetic responsive means to terminate the drive of said magnetic responsive means to the first predetermined position thereof, said third gimbal control means then driving said magnetic responsive means to said second position thereof, said third gimbal control means receiving said azimuth related signals to determine when said second position has been reached, the net movement of said magnetic responsive means from said first position thereof to said second position thereof being commensurate with an azimuth parameter of the drill string.

58. Sensor apparatus as in claim 57 wherein:
said second gravity responsive means is error transducing accelerometer means having a sensitive axis with respect to the direction of gravity forces; and said magnetic responsive means is magnetometer means having a sensitive axis with respect to the direction of the earth's magnetic field.

59. Sensor apparatus as in claim 57 wherein:
said second gravity responsive means is a force balance accelerometer; and said magnetic responsive means is a fluxgate magnetometer having its sensitive axis perpendicular to the direction of the earth's magnetic field in the second position thereof.

60. Sensor apparatus as in claim 57 wherein:
said inclination parameter is the angle of inclination of the axis of the drill string segment with respect to the vertical in a common vertical plane; and said azimuth parameter is the azimuth angle between a vertical plane which contains the horizontal projection of the axis of the drill string segment and the vertical plane containing the horizontal projection of the direction of the local terrestrial magnetic field.

61. Sensor apparatus as in claim 57 wherein each of said detector means includes:
light generating means, photoelectric receiving means, and light control means for delivering light from said light generating means to said photoelectric receiving means when the respective gravity or magnetic responsive means is in its first predetermined position.

62. Sensor apparatus as in claim 61 wherein:
said light control means includes apertured disc means positioned between said light generating means and said light receiving means, said disc means being drivingly connected to the motor means associated with the respective gravity or magnetic responsive means.

63. Sensor apparatus as in claim 57 wherein:
each of said motor means are each stepping motors.

64. Sensor apparatus as in claim 63 wherein each of said control means includes:
pulse generating means for delivering pulses to the stepping motor associated with the control means; and means for counting the net number of pulses delivered to the stepping motor to drive the associated gravity or magnetic responsive means from its first position to its second position, said net number of pulses being commensurate with the directional parameter of the drill string to be measured by the gravity or magnetic responsive means.

65. Sensor apparatus as in claim 64 wherein:
said second gravity responsive means is error transducing accelerometer means having a sensitive axis with respect to the direction of gravity forces; and said magnetic responsive means is magnetometer means having a sensitive axis with respect to the direction of the earth's magnetic field.

66. Sensor apparatus as in claim 65 wherein:
said second gravity responsive means is a force balance accelerometer having its sensitive axis perpendicular to the sensitive axis of the first force balance accelerometer in the second position of each accelerometer; and said magnetic responsive means is a fluxgate magnetometer having its sensitive axis perpendicular to the direction of the earth's magnetic field in the second position thereof.

67. Sensor apparatus as in claim 64 wherein:
said inclination parameter is the angle of inclination of the axis of the drill string segment with respect to the vertical in a common vertical plane; and said azimuth parameter is the azimuth angle between a vertical plane which contains the horizontal projection of the axis of the drill string segment and the vertical plane containing the horizontal projection of the direction of the local terrestrial magnetic field.

68. Sensor apparatus as in claim 64 wherein each of said detector means includes:
light generating means, photoelectric receiving means, and light control means for delivering light from said light gen-erating means to said photoelectric receiving means when the respective gravity or magnetic responsive means is in its first predetermined position.

69. Sensor apparatus as in claim 68 wherein:
said light control means includes apertured disc means positioned between said light generating means and said light receiving means, said disc means being drivingly connected to the motor means associated with the respective gravity or magnetic responsive means.

70. Sensor apparatus as in claim 64 wherein:
said second gimbal means is rotatably mounted in said first gimbal means; and said third gimbal means is rotatably mounted on a rotatable shaft, said rotatable shaft being rotatably mounted in said first gimbal means.

71. A sensor system as in claim 70 wherein:
said second gimbal means has an axis of rotation per-pendicular to the axis of rotation of said first gimbal means;
and said rotatable shaft has an axis of rotation parallel to the axis of rotation of said second gimbal means; and said third gimbal means has an axis of rotation perpen-dicular to the axis of rotation of said rotatable shaft.

72. A sensor system as in claim 71 wherein:
said motor means for said second gimbal means is mounted on said first gimbal means and is drivingly connected to said second gimbal means and to said rotatable shaft; and said motor means for said third gimbal means is mounted on said first gimbal means and is drivingly connected to said third gimbal means.

73. A sensor system as in claim 64 wherein:
said motor means for said second gimbal means is mounted on said first gimbal means and is drivingly connected to said second gimbal means; and said motor means for said third gimbal means is mounted on said first gimbal means and is drivingly connected to said third gimbal means.

74. A sensor system as in claim 73 including:
rotatable support means for said third gimbal means;
and means drivingly connecting said second motor means to said rotatable support means to coordinate the position of said magnetic responsive means with the position of said second gravity responsive means.

75. A sensor system as in claim 74 wherein:
the axis of rotation of said rotatable support means is parallel to the axis of rotation of said second gimbal means; and the axis of rotation of said rotatable support means and the axis of rotation of said second gimbal means are perpendicular to the axis of rotation of said first gimbal; and the axis of rotation of said third gimbal means is perpendicular to the axis of rotation of said rotatable support means.

76. Sensor apparatus as in claim 64 wherein:
said drill string segment is non-magnetic.

77. Sensor apparatus as in claim 76 wherein:
said sensor apparatus is contained in a non-magnetic housing mounted in said drill string segment.

78. Sensor apparatus as in claim 64 including:
means for transmitting to the surface information re-presentative of the directional parameters determined by the sensor system.

79. Sensor apparatus as in claim 78 wherein:
said transmitting means is acoustical transmitting means for generating acoustical signals in a liquid in the drill string.

80. Sensor apparatus as in claim 57 wherein each of said control means includes:
measuring means for measuring the net movement of the motor means associated with the control means required to drive the associated gravity or magnetic responsive means from its first position to its second position, the net movement of each of said motor means being commensurate with a directional para-meter of the drill string.

81. Sensor apparatus as in claim 57 wherein:
said second gimbal means is rotatably mounted in said first gimbal means; and said third gimbal means is rotatably mounted on a rotatable shaft, said rotatable shaft being rotatably mounted in said first gimbal.

82. A sensor system as in claim 81 wherein:
said second gimbal means has an axis of rotation perpen-dicular to the axis of rotation of said first gimbal means; and said rotatable shaft has an axis of rotation parallel to the axis of rotation of said second gimbal means; and said third gimbal means has an axis of rotation perpen-dicular to the axis of rotation of said rotatable shaft.

83. A sensor system as in claim 82 wherein:
said motor means for said second gimbal means is mounted on said first gimbal means and is drivingly connected to said second gimbal means and to said rotatable shaft; and said motor means for said third gimbal means is mounted on said first gimbal means and is drivingly connected to said third gimbal means.

84. A sensor system as in claim 57 wherein:
said motor means for said second gimbal means is mounted on said first gimbal means and is drivingly connected to said second gimbal means; and said motor means for said third gimbal means is mounted on said first gimbal means and is drivingly connected to said third gimbal means.

85. A sensor system as in claim 84 including:
rotatable support means for said third gimbal means;
and means drivingly connecting said second motor means to said rotatable support means to coordinate the position of said magnetic responsive means with the position of said second gravity responsive means.

86. A sensor system as in claim 85 wherein:
the axis of rotation of said rotatable support means is parallel to the axis of rotation of said second gimbal means; and the axis of rotation of said rotatable support means and the axis of rotation of said second gimbal means are perpen-dicular to the axis of rotation of said first gimbal means; and the axis of rotation of said third gimbal means is perpendicular to the axis of rotation of said rotatable support means.

87. Sensor apparatus as in claim 57 wherein:
said drill string segment is non-magnetic.

88. Sensor apparatus as in claim 87 wherein:
said sensor apparatus is contained in a non-magnetic housing mounted in said drill string segment.

89. Sensor apparatus as in claim 57 including:
means for transmitting to the surface information re-presentative of the directional parameters determined by the sensor system.

90. Sensor apparatus as in claim 89 wherein:
said transmitting means is acoustical transmitting means for generating acoustical signals in a liquid in the drill string.

91. The method of measuring directional parameters of a drill string in a borehole, including the steps of:
rotating first gravity responsive means in a segment of the drill string to establish a predetermined position of said first gravity responsive means as a function of gravity forces on said first gravity responsive means, said first gravity responsive means being mounted on a first gimbal mounted for rotation in the drill string segment about the axis of the drill string segment or an axis parallel to the drill string axis;
rotating second gravity responsive means in said drill string segment for generating inclination related signals as a function of gravity forces on said second gravity responsive means, said second gravity responsive means being mounted for rotation on a second gimbal having an axis of rotation perpen-dicular to the axis of rotation of the first gimbal, said inclina-tion related signals varying as a function of the alignment of said second gravity responsive means with respect to the direc-tion of the force of gravity;
rotating magnetic responsive means in said drill string segment to obtain azimuth related signals as a function of magnetic field forces on said magnetic responsive means, said magnetic re-sponsive means being mounted on a third gimbal rotatable about an axis perpendicular to an axis perpendicular to the axis of rotation of the first gimbal, and said azimuth related signals varying as a function of the alignment of said magnetic responsive means with respect to the direction of the earth's magnetic field;
operating a driving motor connected to said second gimbal to drive said second gravity responsive means to a first pre-determined position and then to a second position having a pre-determined alignment with respect to the direction of the force of gravity as determined by said inclination related signals;
detecting when said second gravity responsive means is at its first predetermined position and generating a home signal for said second gravity responsive means;
terminating the drive of said second gravity responsive means to the first position thereof upon receipt of said home sig-nal for said second gravity responsive means;
driving said second gravity responsive means to said second position after the first predetermined position thereof has been reached;
measuring the net movement of said second gravity re-sponsive means from said first predetermined position thereof to said second position thereof to determine an inclination parameter of the drill string;
operating a driving motor connected to said third gimbal to drive said magnetic responsive means to a first predetermined position and then to a second position having a predetermined align-ment with respect to the direction of the earth's magnetic field as determined by said azimuth related signals;
detecting when said magnetic responsive means is at its first predetermined position and generating a home signal for said magnetic responsive means;
terminating the drive of said magnetic responsive means to the first position thereof upon receipt of said home signal for said magnetic responsive means;
driving said magnetic responsive means to said second position after the first predetermined position thereof has been reached; and measuring the net movement of said magnetic responsive means from said first predetermined position thereof to said second position thereof to determine an azimuth parameter of the drill string.

92. The method of measuring directional parameters of a drill string in a borehole as in claim 91 wherein:
the step of rotating second gravity responsive means includes rotating error transducer accelerometer means having a sensitive axis with respect to the direction of gravity forces; and the step of rotating magnetic responsive means includes rotating magnetometer means having a sensitive axis with respect to the direction of the earth's magnetic field.

93. The method of measuring directional parameters of a drill string in a borehole as in claim 92 wherein:
the step of rotating first gravity responsive means includes rotating first force balance accelerometer means having a sensitive axis, the sensitive axis being aligned perpendicular to the axis of the drill string segment in the second position of said first force balance accelerometer means;
the step of rotating second gravity responsive means includes rotating second force balance accelerometer means having a sensitive axis, the sensitive axis being aligned per-pendicular to the sensitive axis of the first force balance accelerometer means in the second position of each accelerometer means; and the step of rotating magnetic responsive means includes rotating fluxgate magnetometer means having a sensitive axis, the sensitive axis being aligned perpendicular to the direction of the earth's magnetic field in the second position of the magnet-ometer means.

94. The method of measuring directional parameters of a drill string in a borehole as in claim 91 wherein:
the step of measuring the net movement of the second gravity responsive means to determine an inclination related parameter is the step of measuring the angle of inclination of the axis of the drill string segment with respect to the vertical in a common vertical plane; and the step of measuring the net movement of the magnetic responsive means to determine an azimuth related parameter is the step of measuring the azimuth angle between a vertical plane which contains the horizontal projection of the axis of the drill string segment and the vertical plane containing the horizontal projection of the direction of the local terrestrial magnetic field.

95. The method of measuring directional parameters of the drill string in a borehole as in claim 91 wherein:
the step of detecting when said second gravity respon-sive means is at its first predetermined position includes passing a light from a light source to a photoelectric detector; and the step of detecting when said magnetic responsive means is at its first predetermined position includes passing a light from a light source to a photoelectric detector.

96. The method of measuring directional parameters of a drill string in a borehole as in claim 95 wherein the step of passing light from each light source to each photoelectric detector includes:
rotating apertured disc means positioned between each light source and each photoelectric detector by driving connection between the apertured disc means and the driving motor associated with the respective gravity or magnetic responsive means.

97. The method of measuring directional parameters of the drill string in the borehole as in claim 91 wherein:
the step of operating each driving motor includes operating stepping motors.

98. The method of measuring directional parameters of a drill string in a borehole as in claim 97 wherein the steps of measuring the net movement of each of said second gravity re-sponsive means and said magnetic responsive means includes:
generating and delivering pulses to the stepping motor associated with said second gravity responsive means and said magnetic responsive means; and counting the net number of pulses delivered to the stepping motor to drive said second gravity responsive means or magnetic responsive means from its first predetermined position to its second predetermined position, said net number of pulses being commensurate with the directional parameter of the drill string to be measured by the gravity or magnetic responsive means.

99. The method of measuring directional parameters of a drill string in a borehole as in claim 98 wherein:
the step of rotating second gravity responsive means includes rotating error transducing accelerometer means having a sensitive axis with respect to the direction of gravity forces;
and the step of rotating magnetic responsive means includes rotating magnetometer means having a sensitive axis with respect to the direction of the earth's magnetic field.

100. The method of measuring directional parameters of a drill string in a borehole as in claim 99 wherein:
the step of rotating first gravity responsive means includes rotating first force balance accelerometer means having a sensitive axis, the sensitive axis being aligned perpendicular to the axis of the drill string segment in the second position of said first force balance accelerometer means;
the step of rotating second gravity responsive means includes rotating second force balance accelerometer means having a sensitive axis, the sensitive axis being aligned perpen-dicular to the sensitive axis of the first force balance accelero-meter means in the second position of each accelerometer means;
and the step of rotating magnetic responsive means includes rotating fluxgate magnetometer means having a sensitive axis, the sensitive axis being aligned perpendicular to the direction of the earth's magnetic field in the second position of the magnetometer means.

101. The method of measuring directional parameters of a drill string in a borehole as in claim 98 wherein:
the step of measuring the net movement of the first gravity responsive means to determine a first directional para-meter is the step of measuring the reference angle formed between a first plane containing the axis of the drill string segment and a known reference on the drill string segment and a second plane containing the drill axis and a vertical projection of the drill axis;
the step of measuring the net movement of the second gravity responsive means to determine a second directional parameter is the step of measuring the angle of inclination of the axis of the drill string segment with respect to the vertical in a common vertical plane; and the step of measuring the net movement of the magnetic responsive means to determine a third directional parameter is the step of measuring the azimuth angle between a vertical plane which contains the horizontal projection of the axis of the drill string segment and the vertical plane containing the horizontal projection of the direction of the local terrestrial magnetic field.

102. The method of measuring directional parameters of the drill string in a borehole as in claim 101 wherein:
the step of detecting when said second gravity re-sponsive means is at its first predetermined position includes passing a light from a light source to a photoelectric detector;
and the step of detecting when said magnetic responsive means is at its first predetermined position includes passing a light from a light source to a photoelectric detector.

103. The method of measuring directional parameters of a drill string in a borehole as in claim 102 wherein the step of passing light from each light source to each photoelectric detector includes:
rotating apertured disc means positioned between each light source and each photoelectric detector by driving connection between the apertured disc means and the driving motor associated with the respective gravity or magnetic responsive means.

104. The method of measuring directional parameters of a drill string in a borehole as in claim 98 wherein:
the step of rotating said second gravity responsive means includes rotating said second gravity responsive means on a gimbal rotatably mounted in said first gimbal; and the step of rotating said magnetic responsive means includes rotating said magnetic responsive means on a gimbal rotatably mounted on a rotatable shaft mounted in said first gimbal.

105. The method of measuring directional parameters of a drill string in a borehole as in claim 104 wherein:
said second gimbal has an axis of rotation perpendicular to the axis of rotation of said first gimbal;

said rotatable shaft has an axis of rotation parallel to the axis of rotation of said second gimbal; and said third gimbal has an axis of rotation perpendicular to the axis of rotation of said rotatable shaft.

106. The method of measuring directional parameters of a drill string in a borehole as in claim 98 including the step of:
transmitting to the surface information representative of the directional parameters determined by the gravity responsive means and the magnetic responsive means.

107. The method of measuring directional parameters of a drill string in a borehole as in claim 98 including the step of:
transmitting to the surface information representative of the directional parameters determined by the gravity and magnetic responsive means by generating acoustical signals in a liquid in the drill string.

108. The method of measuring directional parameters of a drill string in a borehole as in claim 91 wherein the step of measuring the net movement of each of said second gravity responsive means and said magnetic responsive means includes:
measuring the net movement of the driving motor associated with each of said gravity responsive means and said magnetic responsive means, the net movement of each of said driving motors being commensurate with a directional parameter of the drill string.

109. The method of measuring directional parameters of a drill string in a borehole as in claim 91 wherein:
the step of rotating said second gravity responsive means includes rotating said second gravity responsive means on a gimbal rotatably mounted in said first gimbal; and the step of rotating said magnetic responsive means includes rotating said magnetic responsive means on a gimbal rotatably mounted on a rotatable shaft mounted in said first gimbal.

110. The method of measuring directional parameters of a drill string in a borehole as in claim 109 wherein:
said second gimbal has an axis of rotation perpendicular to the axis of rotation of said first gimbal;
said rotatable shaft has an axis of rotation parallel to the axis of rotation of said second gimbal; and said third gimbal has an axis of rotation perpendicular to the axis of rotation of said rotatable shaft.

111. The method of measuring directional parameters of a drill string in a borehole as in claim 91 including the step of:
transmitting to the surface information representative of the directional parameters determined by the gravity responsive means and the magnetic responsive means.

112. The method of measuring directional parameters of a drill string in a borehole as in claim 91 including the step of:
transmitting to the surface information representative of the directional parameters determined by the gravity and magnetic responsive means by generating acoustical signals in a liquid in the drill string.