Feb. 2, 1971
`
`P. G. SPINK ET AL
`
`3,560,912
`
`Filed Feb. 3, 1969
`
`3 Sheets-Sheet 1
`
`CONTROL SYSTEM FOR A TOWED VEHICLE
`
`21
`
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`
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`
`ROLL
`AXIS
`
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`FIG.2A.
`
`277
`
`FIG.2C.
`
`FIG.2B.
`
`FIG.2D.
`~29
`TAIL SHAFT
`AXIS
`
`T
`
`FIG.4.
`
`:::::-31
`
`WESTERNGECO Exhibit 2145, pg. 1
`PGS v. WESTERNGECO
`IPR2014-01475
`
`

`
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`WESTERNGECO Exhibit 2145, pg. 2
`PGS v. WESTERNGECO
`IPR2014-01475
`
`

`
`Feb. 2, 1971
`
`P. G. SPINK ET AL
`
`3,560,912
`
`Filed Feb. 3, 1969
`
`CONTROL SYSTEM FOR A TOWED VEHICLE
`3 Sheets-Sheet ~
`
`WING
`ANGLE
`e
`
`T1
`
`T2
`I
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`
`FIG.7.
`
`29
`
`29'
`
`WESTERNGECO Exhibit 2145, pg. 3
`PGS v. WESTERNGECO
`IPR2014-01475
`
`

`
`United States Patent Office
`
`3,560,912
`Patented Feb. 2, 1971
`
`1
`
`3,560,912
`CONTROL SYSTEM FOR A TOWED VEHICLE
`Paul G. Spink, Severna Park, and James T. Malone, Ar(cid:173)
`nold, Md., assignors to Westinghouse Electric Corpora(cid:173)
`tion, Pittsburgh, Pa., a corporation of Pennsylvania
`Filed Feb. 3, 1969, Ser. No. 795,913
`Int. Cl. B63b 21 /00; B64d 3/00; GOls 9/68
`U.S. Cl. 340-3
`6 Claims
`
`ABSTRACT OF THE DISCLOSURE
`A towed underwater vehicle having rotatable wing and
`tail surfaces is maintained in a predetermined orientation
`at a constant height above the ocean bottom, or at a
`constant depth below the surface, by commanding a rate
`of rotation of the wing or tail surfaces when a deviation
`from the desired attitude occurs.
`
`BACKGROUND OF THE INVENTION
`
`Field of the invention
`The invention in general relates to a feedback control
`system, and particularly to a system carried by a towed
`vehicle for maintaining the vehicle at a predetermined
`constant distance from a reference and at a predetermined
`orientation.
`
`Description of the prior art
`
`2
`is a tow force from the cable, and tow force is dependent
`upon depth and speed, then a variable wing angle is
`needed to counteract that force. In order to have a wing
`angle, in accordance with the control statement, an alti-
`5 tude error is required so that in the prior art system of
`commanding a wing angle an accurate desired altitude
`or depth is seldom attained.
`In the prior art system of commanding a certain wing
`angle, in accordance with the vehicle deviation from a
`10 reference, a signal indicative of the actual wing angle is
`required for feedback control purposes. In a mechanical
`system where the wings are rotated by means of gears a
`feedback signal proportional to actual angle may be de(cid:173)
`veloped which includes a lot of noise or chatter compo-
`l:'i nents due to mechanical linkages to thus degrade the sig(cid:173)
`nal and reduce the efficiency of operation.
`Accordingly, it is an object of the present invention
`to provide a control system for a towed vehicle which
`enables the towed vehicle to accurately follow a bottom
`20 contour at a specified height above the contour or to
`accurately maintain a predetermined distance below a
`reference.
`A further object of the present invention is to provide
`a control system for a towed vehicle having rotatable con-
`25 trol surfaces which eliminates the need for measuring the
`angular orientation of the control surfaces.
`A further object is to provide an improved control sys(cid:173)
`tem of the type described which further stabilizes the
`vehicle with respect to rolling action.
`SUMMARY OF THE INVENTION
`A control system is provided for maintaining a towed
`vehicle in a desired orientation at a predetermined dis(cid:173)
`tance from a reference as the vehicle is being towed.
`35. The vehicle has rotatable control surfaces to vary its
`attitude and motive means are provided to rotate the con(cid:173)
`trol surfaces in accordance with a certain input signal.
`The control system includes circuit means which derives a
`control signal indicative of the difference between a de-
`40 sired rate of rotation of the control surfaces, with respect
`to a stationary inertial coordinate reference, and the
`actual rate of rotation of the control surfaces. The control
`signal thus derived is supplied to the motive means to
`command a certain rate of rotation of the controlled sur-
`4:i faces as opposed to commanding a certain control surface
`angle.
`
`30
`
`In data sensing and gathering operations, particularly
`in the field of oceanography, use is made of a cable towed
`vehicle which carries various instrumentation such as
`sensors, cameras, television and sonar equipment, to
`name a few. It is often desired that the vehicle be towed
`at a constant altitude from the ocean bottom to thereby
`follow its contours, or alternatively at a constant distance
`from the surface.
`A common method for controlling the altitude of a
`towed vehicle utilizes an active winch to vary the cable
`length, and thus the vehicle altitude. In this type of system,
`the maximum winching rate becomes a limiting factor
`when operating at high speeds over an irregular ocean
`bottom surface.
`Another system uses a ,fixed depressor surface to main(cid:173)
`tain a constant depth below the surface. For this type
`of system however, the operating depth becomes a func(cid:173)
`tion of the type of depressor, cable lengths and operating
`speed, and does not have a bottom contour following
`capability.
`In order to provide for depth or altitude variation and
`control one type of vehicle incorporates the use of ro(cid:173)
`tatable control surfaces, for example, rotatable wing sur(cid:173)
`faces which will 'vary the altitude of the vehicle if rotated
`while the vehicle is being towed. In such a system, a ccr- 55
`tain wing angle is commanded when there is an error (or
`tail control surface angle when there is a roll error), and
`the response of the vehicle will result in a known change
`of altitude for a certain speed or speed range. The vehicle
`carries a depth or altitude sensor for deriving a position 60
`signal which is compared with a reference, and if there
`is an error a certain wing angle will be commanded in
`accordance with the control statement; 11c=C1A.+C2A..,
`where Oc is the wing angle which is commanded when
`there is an altitude error A •. Ae is the rate of change 65
`of the altitude error and C 1 and C2 are constants for the
`particular system.
`To control a wing angle in accordance with the con(cid:173)
`trol statement means that a steady state error (Ae has some
`value and A.=O) is required to maintain a wing angle o 10
`to counteract any steady-state vertical forces, such as an
`upward force on the vehicle from the tow cable. If there
`
`50
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 illustrates a towed vehicle in an underwater
`environment demonstrating two possible "flight" paths;
`FIGS. 2A to 2D illustrate various portions of a towed
`vehicle such as in FIG. 1 and serve to define various terms
`utilized therein;
`FIG. 3 illustrates a block diagram of one embodiment
`of the present invention;
`FIG. 4 is a more detailed view of the towed vehicle
`of FIG. 1, with portions broken away;
`FIG. 5 is a curve to aid in an understanding of the
`operation of the present invention;
`FIG. 6 illustrates a block diagram for roll control of
`the vehicle of FIG. 4; and
`FIG. 7 illustrates a typical drive arrangement for the
`rotatable tail surfaces of the vehicle of FIG. 4.
`FIG. 1 illustrates by way of an example an underwater
`environment wherein vehicle 10 is towed by means of tow
`cable 12 connected to a surface craft 14, although it is to
`be understood that the towing craft may be any one of a
`number of different submerged, surface, or air varieties.
`The vehicle 10 is towed over the ocean bottom 17 and for
`one mode of operation it may be desired that the vehicle
`10 be maintained at a predetermined distrmce H above the
`
`WESTERNGECO Exhibit 2145, pg. 4
`PGS v. WESTERNGECO
`IPR2014-01475
`
`

`
`3,560,912
`
`3
`ocean bottom 17 reference so as to follow the contour
`thereof as illustrated by the dotted path 19. For other
`applications, it may be desired that the vehicle 10 maintain
`a constant distance D below the water surface 21 reference
`so as to follow the dashed path 23.
`Vehicle 10 has rotatable control surfaces to vary its
`vertical positioning and angular orientation about a roll
`axis. For convenience the control surfaces may be rotat(cid:173)
`able wing surfaces 25 located on either side of the body
`27 in addition to rotatable tail surfaces 29, 29' located on 10
`either side of the body 27.
`In order to maintain path 19, it is necessary that the al(cid:173)
`titude of the vehicle 10 above the ocean bottom 17 be
`known. The actual altitude may be determined by known
`sonar techniques whereby the time required for an emitted 15
`sonar signal 31 to hit the bottom and return to the vehicle
`10 is an indication of the height H. For maintaining oper(cid:173)
`ation along the path 23, a suitable pressme indicator
`indicative of depth may be utilized, or alternatively, an
`upward looking sonar system may be used.
`As the vehicle 10 is towed, it may pitch and roll and in
`maintaining a prescribed path the control surfaces may
`rotate. Various responses of the vehicle are set forth by
`way of explanation in FIGS. 2A to 2D to which reference
`is now made.
`FIG. 2A is a side view of the vehicle body 27. The body
`27 may oscillate about a pitch axis and the rate of this
`oscillation, or pitch rate, with respect to a stationary ref(cid:173)
`erence herein termed an inertial coordinate system, is de(cid:173)
`fined by the term q which therefore is a rate of rotation as 30
`opposed to a pitch angle.
`The body 27 may also rotate about a roll axis such as
`illustrated in FIG. 28 and the rate of rotation about the
`roll axis (as opposed to an angular displacement rp) is
`herein termed rp:
`FIG. 2C illustrates a side view of a rotatable wing
`surface. The wing surface 25 is rotatable about a wing
`shaft axis and the rate of rotation about that axis is given
`the designation w. In addition, the wing surface 25 is rotat(cid:173)
`able with respect to the inertial coordinate system. This
`latter rate of rotation is herein designated s. If the pitch
`rate q of the body 27 is zero, then the rate of rotation w
`is equal to the rate of rotation s.
`In the present invention, a rate of rotation for the con(cid:173)
`trol surfaces is commanded. The rate of rotation of the
`wing surfaces with respect to the stationary inertial coordi(cid:173)
`nate system is commanded in accordance with altitude
`error and the rate of change of altitude error (or depth
`error and rate of change of depth error). This statement
`of control may be expressed mathematically as:
`
`40
`
`25
`
`4
`FIG. 3 illustrates a block diagram of a control system
`operating in accordance with Equation 3.
`In the description of operation of the control system,
`reference is made to commanded, actual and error sig-
`5 nals. To aid in a reading of the description of the preferred
`embodiment the following Table I sets out definitions of
`various terms used throughout. Pitch or roll rate designa(cid:173)
`tions are additionally illustrated in FIGS 2A to 2D.
`TABLE I
`q 0 =actual rate of rotation (pitch) of body with respect
`to stationary inertial coordinate system.
`w0 =actual rate of rotation of wing surfaces with respect
`to body.
`w0 =commanded rate of rotation of wing surfaces with
`surfaces with respect to body.
`we=w .. -w~=error signal which drives servo if w,. is
`sensed and Equation 3 utilized.
`sa=actual rate of rotation of wing surfaces with respect
`20 to inertial coordinate system.
`s~=commanded rate of rotation of wing surfaces with
`respect to inertial coordinate system.
`Se=s,.-sc=error signal which drives servo if sa is
`sensed and Equation 1 utilized.
`Ae=altitude (or depth) error.
`Ae=rate of change of altitude (or depth) error.
`Ta=actual tail rate of rotation with respect to body.
`Tc=commanded tail rate of rotation with respect to
`body.
`Te=r .. -rc=error signal which drives servo.
`</>e=roll angle deviation from reference position.
`~e=rate of change <Pe·
`In FIG. 3, the block designated 25 represents the rotat-
`35 able wing surfaces driven, that is rotated, by a motive
`means. One suitable motive means, shown by way of ex(cid:173)
`ample, includes a gear train 36 driven by a servomotor
`38 supplied with a suitable input signal from amplifier
`means 40.
`Circuit means are provided for deriving a control sig-
`nal to drive the servomotor 38, which control signal is
`indicative of the difference between a desired rate of ro(cid:173)
`tation of the wing surfaces 25 with respect to a stationary
`inertial coordinate system and the actual rate of rotation
`·hi of the wing surfaces with respect to such coordinate sys(cid:173)
`tem. One way of deriving an indication of the actual rate
`of rotation of the wing surfaces with respect to the co(cid:173)
`ordinate system is to obtain an indication of the rate of
`rotation of the wing surfaces with respect to the body, and
`50 modify that indication by the rate of rotation of the body
`with respect to the coordinate system. In FIG. 3, means
`are provided for deriving a signal indicative of the rate
`of rotation of the wing surfaces with respect to the body
`such means being in the form of tachometer 45 which i~
`55 responsive to the shaft rotation of the servomotor 38 in
`a well known manner, to provide an output rotation sig(cid:173)
`nal herein disignated "'a·
`The rate of rotation of the body with respect to the
`st.ationary inertial coordinate system is obtained by a
`60 pitch rate sensor 47 the output signal of which is desig(cid:173)
`nated q ... Obviously other methods are available for ob(cid:173)
`taining q., such methods including the use of an ac(cid:173)
`celerometer to derive pitch acceleration and integrating
`such acceleration or alternatively obtaining an indication
`65 of pitch angle and differentiating such indication.
`The commanded rate of rotation is in accordance with
`Equation 3 which sets forth a relationship involving alti(cid:173)
`tude error Ae. Accordingly a position sensor 50 provides
`a position signal indicative of the vehicle's actual posi(cid:173)
`tion. Such position sensor 50 may include sonar means
`as previously described or a pressure indicator indicative
`of depth.
`In order to derive a positional error, and in the present
`example an altitude error, the position signal from the
`7.3 position sensor 50 is compared with a reference signal
`
`(1)
`where s0 is the commanded rate of rotation of the wing
`surfaces with respect to the inertial coordinates system,
`Ae is the altitude error, Ae is the rate of change of alti(cid:173)
`tude error, and K 1 and K2 are multiplication constants
`dependent upon vehicle response.
`The commanded rate of rotation s0 is compared with
`an actual rate of rotation sa (with respect to the inertial
`coordinate system) and any difference therebetween re(cid:173)
`sults in an error signal se which drives servomechanism
`apparatus controlling the wing surfaces. As a practical
`matter, an indication of the actual rate of rotation sa of
`the wing surfaces with respect to a stationary inertial co(cid:173)
`ordinate system is difficult to obtain. The actual rate of
`rotation s.. is related to the actual rate of rotation "'a
`of the wing surfaces with respect to the body by the
`expression:
`
`S 0 =wa+qa
`(2) 70
`Cfa is easily measured and "'• is easily measured so that the
`control statement of Equation 1 may be expressed in terms
`of easily measured quantities as follows:
`
`(3)
`
`WESTERNGECO Exhibit 2145, pg. 5
`PGS v. WESTERNGECO
`IPR2014-01475
`
`

`
`3,560,912
`
`5
`from a reference source 53, and which reference signal is
`indicative of a desired altitude. Such reference signal may
`be fixed, or may be varied during the course of travel of
`the vehicle by means of automatic circuitry, or by means
`of suitable connection to a towing craft.
`The position and reference signals are compared at
`summing means 56 and any difference therebetween re(cid:173)
`sults in an altitude error signal A 0 which is provided to
`circuits 58 and 59. The altitude error signal Ae is multi(cid:173)
`plied by a constant K 1 in the circuit 58 which provides
`an error signal K1K2A •. The derivative of A., that is, the
`rate of change of Ae is obtained and multiplied by a con(cid:173)
`stant K2 in the circuit 59 which provides a rate of change
`of error signal K21 •. The constants K 1 and K2 are func(cid:173)
`tions of the vehicle response and speed, and are chosen
`in accordance with well known techniques for a predeter(cid:173)
`mined speed or speed range. In order to vary the con(cid:173)
`stants K 1 and K2 to accommodate a different speed range,
`there may be provided a speed sensor circuit 62 which is
`operative to provide different output signals for different 20
`speed ranges to effect a predetermined change in K 1 and
`K2• Alternatively, with electrical connections to the tow-
`ing craft, K 1 and K2 may be varied from a remote posi(cid:173)
`tion.
`Circuit means are provided for implementing Equation
`3 to obtain an we. This is illustrated functionally in FIG.
`3 by the provision of a summing means 65 having a first
`summing point 66 which receives the signals K 1Ae, K 2Ae
`and qa to provide an output we· we is compared with the
`output of tachometer 45, that is signal w8 , at summing
`point 67, the comparison resulting in an error signal we
`which is also herein referred to as a control signal which
`forms the input to the motive means to drive the wing
`surf aces 25.
`FIG. 4 is a view of the vehicle 10, with portions
`broken away to illustrate some of the components shown
`in the block diagram of FIG. 3. The wing surfaces 25 are
`rotatable by means of shaft 72, connected to a quarter
`segment gear 36A intermeshed with gear 36B, and desig(cid:173)
`nated as the gear train 36 of FrG. 3. A servomotor 38 40
`drives the gear train and the tachometer 45 may be in(cid:173)
`cluded in the same housing as the servomotor.
`The sonar signal 31 is provided by means of a sonar
`transducer 50A forming a portion of the position sensor
`means 50 of FIG. 3, or the position signal may be ob-
`tained utilizing a pressure sensor SOB for a constant depth
`below the water surfaces to be maintained.
`The pitching of the body 27 is sensed by the pitch rate
`sensor 47 and the calculating, and other circuitry is lo(cid:173)
`cated in the electronic section 75.
`Rotatable tail surfaces 29 and 29' are provided in order
`to compensate for roll deviation from normal. When the
`tail surfaces are rotated they rotate differentially, that is,
`one will rotate upwards while the other rotates down(cid:173)
`wards and accordingly the starboard tail surface has been :,.-,
`given a primed designation and the operation with re(cid:173)
`spect to roll stabilization will be described subsequently
`with respect to FIGS. 6 and 7.
`FIG. 5 is a curve to illustrate the response of the wing
`surfaces 25 when an error in altitude is detected. To no
`change altitude,
`the wing surfaces 25 concurrently
`change their angle and FIG. 5 is a plot of wing angle
`as a function of time during operation of the circuitry of
`FIG. 3. Although wing angle is plotted it is to be re(cid:173)
`membered that there is no requirement to measure this n:;
`wing angle since the present invention commands a rate
`of rotation of the wing surfaces 25 to eliminate the need
`for a constant error and the need for a wing angle sensor.
`FIG. 5 will be described with respect to the operation
`of FIG. 3 where a rate of rotation is commanded as a 70
`function of an altitude error A. and a rate of change of
`altitude error A •. At time T 0 the vehicle erroneously in(cid:173)
`creases its altitude due to, for example, a tow force.
`K 1Ae and K 2A. act together to effect a rotation of the
`wing surface downward. This is represented in FIG. 5 75
`
`6
`by the curve from T 0 to T 1 representing an increase in the
`downward angle of the wing angle 8.
`In response to the commanded rate of rotation, the
`wing angle reaches a point wherein the vehicle no longer
`rises and accordingly the term K 2A.=0. This situation
`5 occurs in FIG. 5 at time T 1 where it is seen that the curve
`has a decreased slope but since K 1Ae is still positive,
`the wing is still commanded to rotate downward to cause
`the vehicle to decrease in altitude. When the vehicle com-
`l 0 mences to decrease in altitude, there is again a rate of
`change of error A., however, it is now in an opposite di(cid:173)
`rection so that in effect the quantity K2Ae is subtracted
`from K1A. as illustrated by the progressively decreasing
`slope of the curve between times T 1 and T 2• That is. as
`15 the vehicle decreases in altitude, K 2A. is negative which
`in effect is commanding the wing to rotate upwards. K 1Ae
`however is positive, commanding the wing to rotate down(cid:173)
`wards with the net effect being that the wing surfaces ro-
`tate downwardly at a slower rate.
`As the altitude error Ae gets progressively smaller, the
`rate of change term K2A. becomes greater than K 1Ae
`and the wings start rotating upwardly as indicated by
`the decrease in negative wing angle commencing past time
`T 2 (T2 is the point where K 1Ae just equals K 2A.).
`2'3 As the correct altitude is approached, Ae and A. go to
`zero values but since the wing surfaces were rotated down(cid:173)
`wardly faster for a greater time period than rotated up(cid:173)
`wardly there is a net down angle on the wings at time
`30 T 3 where A.=Ae=O. It is seen therefore that the control
`system operates to correctly position the vehicle by com(cid:173)
`manding a rate of rotation of the wing surfaces and the
`correct position is attained with a net downward wing
`surface angle such as Oa in FIG. 5.
`FIG. 6 illustrates the circuitry for roll compensation
`and is similar in many respects to the circuitry of FIG. 3
`in that a rate of rotation of the tail surfaces 29, 29' is
`commanded in accordance with the control statement
`Te=K~<Pe+K4¢e•
`A gear train 80 serves to rotate the tail surfaces when
`drive~ by a servomotor 82 receiving its input signal from
`amplifier means 84. An indication of the rate of rota(cid:173)
`tion of the tail surfaces is provided by means of tachom(cid:173)
`eter 86 the output signal of which is rotation signal Ta·
`Means are provided for obtaining indications of the
`values ¢e and ¢. These values can be obtained in any one
`of a number of ways such as by measurement of roll
`angle with appropriate differentiation, by measurement of
`roll angle and roll rate, or by measurement of roll ac-
`;,o celeration with suitable integration. In FIG. 6, a first
`sensor 88 is provided for obtaining an indication of the
`roll angle ¢. For normal operation, the desired ¢ is zero
`degrees and accordingly any output signal provided by
`the roll angle sensor 88 is an error signal indicating an
`angular deviation from normal. A second sensor. a roll
`rate sensor 90 is provided for deriving the rate of angu(cid:173)
`lar change ¢ •.
`First and second circuits 92 and 93 perform the re(cid:173)
`quired multiplication by constants K3 and K4 to provide
`error signal K3¢e and rate of change of error signal K4¢.,
`respectively. As was the case with respect to FIG. 3 a
`speed sensor 95 may be provided to vary the value of
`constants K3 and K4 in accordance with predetermined
`speed ranges.
`A summing means 97 combines all the signals provided
`thereto, to in turn provide a control or error signal To to
`the amplifier means 84. Functionally the summing means
`97 combines the signals K3¢e and K4¢.•to result in a
`signal Tc a commanded rate of rotation of the tail sur(cid:173)
`faces, in accordance with the control statement. The com-
`manded rate of rotation is compared with the actual rate
`of rotation Ta to result in an error signal .,.c·
`The error signal .,.. causes the tail surfaces to rotate
`differentially. This operation may be seen in FIG. 7 which
`
`35
`
`~:;
`
`WESTERNGECO Exhibit 2145, pg. 6
`PGS v. WESTERNGECO
`IPR2014-01475
`
`

`
`3,560,912
`
`5
`
`8
`(ii) a rate of change of error signal (K 2.\e);
`(c) first sensing means for providing a pitch rate sig(cid:173)
`nal (qa) indicative of the pitch rate of the vehicle
`with respect to the stationary inertial coordinate
`system;
`(d) second sensing means for providing a rotation
`signal (wa) indicative of the rate of rotation of said
`wing surfaces with respect to the vehicle;
`(e) means for combining said error, rate of change
`of error, pitch rate and rotation signals, to derive the
`control signal.
`3. Apparatus according to claim 2 which additionally
`includes:
`(a) means for modifying the valve of the error signal
`(K1Ae) and the rate of change of error signal (K2Ae)
`in accordance with vehicle speed.
`4. Apparatus according to claim 2 wherein:
`(a) the motive means includes a servomotor; and
`(b) the second sensing means is a tachometer opera(cid:173)
`tively connected to said servomotor for providing
`an output signal proportional to the rotation of ~aid
`servomotor.
`5. Apparatus according to claim 1 wherein the control
`surfaces are rotatable tail surfaces and wherein the cir-
`25 cuit means of clause (b) includes:
`(a) means for deriving
`(i) an error signal (K3</>e) indicative of the devia(cid:173)
`tion of the vehicle about a roll axis, with respect
`to a reference, and
`(ii) a rate of change of error signal (K 4¢e)
`(b) sensing means for providing a rotation signal ( ra)
`indicative of the rate of rotation of said tail 5ur(cid:173)
`faces with respect to the vehicle;
`(c) means for combining the error, rate of change
`of error and rotation signals to derive the control
`signal.
`6. Apparatus according to claim 5 which includes:
`(a) means for simultaneously and differentially rotat(cid:173)
`ing the tail surfaces to rotate in opposite directions.
`
`7
`illustrates the starboard tail surface 29', and the port tail
`surface 29 each connected by means of respective shafts
`99 and 100 to gears 102 and 103 which mesh with a third
`gear 105. Gears 102, 103 and 105 form the gear train
`80, which is driven by the servomotor 82. As the servo-
`motor 82 causes rotation as indicated by the arrow, the
`tail surfaces 29' and 29 will rotate differentially as indi(cid:173)
`cated by the respective arrows around shafts 99 and 100.
`If the vehicle is pitching, the rotation of tail surface 29'
`with respect to a stationary inertial coordinate system 10
`will have a vehicle pitch component. The other tail sur(cid:173)
`face 29 however rotates in an opposite direction than tail
`surface 29' and its rotation with respect to the stationary
`inertial coordinate system will have a vehicle pitch com(cid:173)
`ponent which is equal and opposite to the pitch compo- 15
`nent associated with the tail surface 29'. These compo(cid:173)
`nents cancel one another and there is no requirement for
`a vehicle pitch sensor to be included in the circuitry of
`FIG. 6.
`Although the present invention has been described with 20
`a certain degree of particularly, it should be understood
`that the present disclosure has been made by way of ex(cid:173)
`ample and that modifications and variations of the pres-
`ent invention are made possible in the light of the above
`teachings.
`We claim as our invention:
`1. A control system for maintaining a towed vehicle
`in a desired orientation at a predetermined distance from
`a reference, the towed vehicle having rotatable control
`surfaces to vary vehicle attitude as it is towed through a 30
`fluid medium, comprising:
`(a) motive means operative in response to an input
`signal for rotating said control surfaces;
`(b) circuit means for deriving a control signal indica-
`tive of the difference between a desired rate of rota-
`tion of said control surfaces with respect to a sta(cid:173)
`tionary inertial coordinate system and the actual rate
`of rotation of said control surfaces with respect to
`said coordinate system; and
`(c) means for supplying said control signal to said 40
`motive means.
`2. Apparatus according to claim 1, wherein the con(cid:173)
`trol surfaces are rotatable wing surfaces and wherein the
`circuit means of clause (b) includes:
`(a) a position sensor for providing a position signal 45
`indicative of the vehicle's actual position from a refer-
`ence;
`(b) means responsive to said position signal for pro-
`viding
`(i) an error signal (K 1Ae) indicative of the differ- 50 244---3; 114-235
`ence in the actual and desired position, and
`
`35
`
`References Cited
`UNITED STATES PATENTS
`3/1964
`Anderson ----------- 114-235
`III 1967
`Cupp et al. ------------ 340-3
`
`3,125,980
`3,351,895
`
`RICHARD A. FARLEY, Primary Examiner
`
`U.S. Cl. X.R.
`
`WESTERNGECO Exhibit 2145, pg. 7
`PGS v. WESTERNGECO
`IPR2014-01475