US 3563335 A
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United States Patent  Inventors John F. Holmes Andover, Mass; Lawrence C. Frederick, Nashua, N.l-l. [21 1 App]. No. 807,821  Filed Mar. 17, 1969  Patented Feb. 16, 1971  Assignee Sanders Associates, Inc.
Nashua, NH. a corporafion of Delaware  TUNED MECHANICAL STABILIZER 10 Claims, 1 Drawing Fig.
 US. Cl l8l/0.5,
' 114/122, 340/5, 340/8  Int. Cl B63b 45/08  Field ofSearch 181/05;
 References Cited UNITED STATES PATENTS 2,407,697 9/1946 Williams 181/05 Primary ExaminerRichard A. Farley Attorney-Louis Etlinger ABSTRACT: There is herein disclosed a tuned mechanical stabilizer for suspension of transducers from ships. The transducer is affixed to one end ofa shaft, the other end of which is provided with a fixed counterweight and an adjustable tuning weight whereby the natural period of the transducer-stabilizer assembly may be tuned such as to substantially exceed the roll-pitch period of the vessel and thereby isolate the transducer from vessel pitch and roll.
Patented Feb. 16, 1971 IN VE N TORS LAWRENCE C. FREDERICK JOHN F. HOLMES AGENT TUNED MECHANICAL STABILIZER BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates generally to the field of mechanics and more specifically to mechanically stabilized platforms for isolating transducers from rotational motion of the vessel to which they are secured.
2. Description of the Prior Art A variety of relatively narrow beam acoustic transducers has been developed to permit narrow beam depth soundings from floating vessels and have come into rather widespread use in the commercial shipping and fishing industries as well as in military applications. It will be apparent that when rigidly mounted transducers having beam widths on the order of 2 to 5 degrees are used significant errors may be introduced into depth soundings when the vessel pitches and rolls. In order to permit narrow beam depth soundings from a rolling or pitching vessel, mechanically stabilized platforms have been developed to provide roll and pitch corrections to the transducer. Typical platforms of this type comprise a vertical reference sensing element with pitch and roll error signals being applied to a servocontrol amplifier. The amplifier output controls a hydraulic servosystem for applying corrective position adjustments to the transducer. Electrohydraulic platforms are active in their operation and require relatively sophisticated electronic and hydraulic components. These requirements in turn result in expensive equipment which requires skilled maintenance personnel to maintain the platform in operating condition. The complexity of the apparatus also involves a concomitant decrease in its reliability in use in an operation environment.
OBJECTS AND SUMMARY OF THE INVENTION It is therefore a primary object of the present invention to provide a new and novel method and apparatus for isolating a transducer from rotational motion.
It is another object of the present invention to provide apparatus of the above described character which may be mounted through the hull of a floating vessel.
It is a further object of the present invention to provide apparatus of the above described character which is purely mechanical in its operation.
It is an additional object of the present invention to provide apparatus of the above described character which is tuned to a natural period of oscillation which is substantially greater than the oscillations to which the apparatus is subjected.
These as well as other objectives of the present invention are achieved by providing a coupling member between the transducer to be isolated and a counterweight whereby the assembly is balanced about a preselected center of rotation. A tuning weight is disposed about the coupling member such as to be adjustable in position along the member such that the natural period of oscillation of the apparatus about the center of rotation may be adjusted to a preselected value in excess of the natural roll and pitch period of the vessel in which it is to be installed.
The foregoing as well as other objects, features and advantages of the present invention will become more apparent from the following detailed description taken in conjunction with the appended drawing.
BRIEF DESCRIPTION OF THE DRAWING The attached drawing is a schematic illustration of one embodiment of the present invention adapted for through-thehull mounting on a floating vessel.
DESCRIPTION OF PREFERRED EMBODIMENT Turning now to FIG. 1 there is illustrated an embodiment of the present invention whereby transducer may be suspended through the hull 12 of a ship. The transducer head 10 is attached to a preferably hollow rigid coupling member 14 of calculated length which has a counterweight 16 attached to its opposite end. The member 14 is mounted such that it is free to rotate about a predetermined center of rotation 18 preferably located at the point where the coupling member 14 passes through the hull 12. The coupling member 14 passes through the ship hull 12 at the center of a conical well hole 20 and the hole is sealed about the member 14 by a watertight flexible diaphragm 22 which permits freedom of movement for the member 14 about its center of rotation 18. A tuning weight 24 of predetermined size is disposed on the coupling member 14 toward the counterweight end and is adjustable in position along the longitudinal axis 15.
Mechanically, the foregoing arrangement yields opposed point masses; i.e. the transducer head 10 and counterweight 16, which are separated from a center of rotation 18 on a relatively massless shaft 14 at predetermined distances. The distances are chosen such that the center of gravity of the mechanical system coincides with the center of rotation 18 and the moments about this point are:
M L M L 1 where the acceleration due to gravity is omitted and:
M is the transducer mass; M is the counterweight mass; L is the distance from the transducer 10 center of mass to the center of rotation 18; and L is the distance from the counterweight 16 center of mass to the center of rotation. The moment of inertia, l, of this mechanical system is thus:
The relatively small tuning or restoring weight 24 provides an elastic restoring torque when the otherwise balanced system is disturbed in rotation and, since the tuning weight mass is much less than the combined mass of the transducer and counterweight, the contribution to the total system moment of inertia is negligible. This restoring torque may be described as:
R= W L. unit radian where:
R is the restoring torque W is the weight ofthe tuning weight 24, and
L is the distance from the tuning weight center of mass to the center of rotation 18.
Thus the apparatus so arranged acts as a compound pendulum having a natural period of oscillation, T, determined by the relationship 1 :21 .i a a By selecting appropriate combination of values for the tuning weight mass and distance between the tuning weight center of mass and the center of rotation the apparatus is tuned to a natural period of oscillation which is well beyond the oscillation period of the vessel into which the system is to be installed. The transducer thus is made substantially insensitive to rotational ship motion. By way of illustration, if a 4500 pound transducer head is suspended 1 foot from the center of rotation of the shaft it may be counter balanced by a 1500 pound weight at three feet from the center of rotation. This assembly may then be tuned to a natural period of 30 seconds by a 12.2 pound tuning weight positioned at approximately 2 feet from the center of rotation.
The foregoing description allows for rotational stabilization in a single plane; e.g. pitch or roll. As a practical matter, however, it is generally desirable to provide stabilization of the transducer head 10 in both pitch and roll. This feature may easily be provided by a gimbal 26 attached to shaft 14 and disposed such that its axis of rotation 28 passes through the center of rotation 18. The shaft 14 is thus free to rotate about the center of rotation 18 in the orthogonal planes of pitch and roll.
In the embodiment of the present invention, whereby an acoustic transducer is to be suspended through the hull of a floating vessel, an acoustic dome 30 filled with a low specific viscosity (i.e. no greater than water) fluid is provided in order to reduce flow noise which would otherwise degrade the acoustic performance of the transducer. Bottoming cushions 32 may also be provided to absorb shock if a particularly severe pitch or roll forces the tilt angle 9 of the vessel beyond the anticipated free angular limits of the apparatus.
The natural period of the system is adjusted under quiescent conditions by adjusting the position of the small tuning weight 24 along the shaft while perturbing the system manually. When the natural period is observed to exceed the roll and pitch period of the vessel by any desired margin the tuning weight 24 is secured in position by locking means 34.
Although the foregoing description is directed to the stabilized suspension of a transducer head through the hull of a floating vessel, it will be readily apparent that the present invention is equally applicable to a wide variety of stabilized platforms. For example, the apparatus may simply be inverted and used to support optical or radio frequency sensors in air since the apparatus and the underlying principles of operation remain the same in either orientation.
If it is desired that the transducer be capable of tracking a given target (acoustic, optical or microwave) azimuth and zenith control motors may be disposed in and form part of the mass counterweight 16. Such motors which are illustrated schematically at 36 and 38 may operate to rotate 20 the transducer 10 at the end of the shaft 14 without changing the tuning period of the apparatus during tracking operation.
It will thus be apparent that the Applicants have conceived a purely mechanical stable platform which substantially isolates a transducer from rotational motion of the vessel or vehicle on which the apparatus is mounted. This stabilization is provided without any requirement for sophisticated electronics or hydraulics to be maintained or powered. Thus the objectives set forth hereinabove among those made apparent from the preceding discussion, are efficiently attained and since certain changes may be made in the above construction without departing from the scope of the invention, it is intended that all matter contained in the above description or iilustrated in the appended drawing shall be interpreted as illustrative and not in a limiting sense.
Having described what is new and novel and desired to secure by Letters Patent, what is claimed is:
1. Apparatus for isolating a transducer from rotational oscillations comprising:
a rigid member coupling said transducer to said counterweight;
means for supporting said coupling member such that it is free to rotate about a preselected center of rotation; and
a tuning weight disposed at a preselected position on said coupling member such as to tune said apparatus to a preselected period of oscillation greater than that of oscillations from which said transducer is to be isolated.
2. Apparatus as recited in claim 1 wherein:
said tuning weight is adjustably disposed on said coupling member such that said natural period of oscillation may be adjusted'according to the relationship weight and said center of rotation. 3. Apparatus as recited 1n claim 1 wherein:
said supporting means comprises a gimbal assembly having orthogonal axes of rotation which pass through said center of rotation.
4. Apparatus as recited in claim 1 wherein:
said transducer is rotatably coupled to said coupling member; and
further including means for rotating said transducer about said coupling member.
5. Apparatus as recited in claim 4 wherein:
said rotating means comprises azimuth and zenith control motors disposed in said counterweight and coupled to said transducer through said coupling member.
6. Apparatus for suspending an acoustic transducer from a floating vessel comprising:
a rigid member coupling said transducer to said counterweight and disposed through the hull of said vessel;
means for supporting said coupling member from said vessel such that it is free to rotate within angular limits about a preselected center of rotation; and
a tuning weight disposed at a preselected position on said coupling member such as to tune said apparatus to a preselected period of oscillation greater than the natural pitch and roll period of said vessel.
7. Apparatus as recited in claim 6 wherein:
said supporting means comprises a gimbal assembly having orthogonal axes of rotation which pass through said center of rotation.
8. Apparatus as recited in claim 6 wherein:
said center of rotation is disposed in the plane at which said coupling member passes through said hull of said vessel.
9. Apparatus as recited in claim 6 further including:
acoustically transmissive protective means affixed to said hull wherein said acoustic transducer is free to move within said angular limits.
10. Apparatus as recited in claim 9 wherein:
said protective means comprises an acoustically transmissive dome filled with an acoustically transmissive medium having a specific viscosity of no greater than water.
UNITED STATES PATENT OFFICE PEI-1050 (5/69) CERTIFICATE OF CORRECTION Patent No. 3, 563 335 Dated February 16, 1971 In John F, Holmes. et 211 It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:
Column 2, line 31 Change M to yMl) o Column 3, line 31 Delete the number "20".
EDWARD M.FI.ETCHER,JR. Attesting Officer C. MARSHALL DANN Commissioner of Patents