Flexible Structure Orientation Control

Abstract

Separated parts of a flexible structure are maintained in a predetermined desired orientation with respect to each other against the action of distorting forces by applying to selected part or parts of the structure inertially developed torques (e.g. from flywheels) to main the selected part in its desired orientation with respect to a selected reference part of the structure.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention pertains to the use of powered means to control the deflections of portions of flexible structures.

2. Description of the Prior Art

The oldest and most general approach to controlling the deflections of separated portions of flexible structures has been to make the structures more rigid, and thus less subject to deflection, either by making their members larger, or using materials of higher moduli of elasticity, or by altering their geometry to make them stiffer, or by a combination of any of these. A slightly more sophisticated approach is to modify the structure to cause smaller forces to be applied to them by the source of the deflecting force, as by shaping a mast to offer less resistance to the wind.

Specialized schemes have included provision of means to change the lengths of various members in order to restore the desired conformation which has been altered by distorting force.

The older schemes have the disadvantage that they add weight or cost to the structure, or restrict the permissible conformations which may be used. They in effect destroy any inherent great flexibility which may be a very useful characteristic of the structure at some time in its use other than the time when rigidity is desired.

SUMMARY OF THE INVENTION

Our invention provides for the application, to selected part or parts of the flexible structure whose deflection is to be controlled, of a torque appropriate to negate or damp that deflection. This we accomplish by inertial means, since the use of any means requiring some rigid reference frame against which to thrust would, as has been indicated, defeat our purpose. In general, we employ suitable deflection- or rate-sensing means to sense the deflection of a selected part, and cause the indications of such sensing means to continuously control the operation of an inertial torque producer, such as a controllably rotatable flywheel, which is attached to transmit torque to the selected part. Thus, if the sensor senses that the selected part has deflected in a clockwise direction around the axis of the flywheel, the flywheel is caused to rotate clockwise, producing counterclockwise torque reactions which reduce the deflection to zero. Since this action is localized at a given location, a number of locations may be thus equipped, as determined by the conditions of the given situation, providing correction over an entire structure.

In the most common situation, that a structure is elastically flexible, so that it tends to oscillate, the application of our invention provides damping of such oscillations. The theory of continuous beams teaches the benefit of applying to a continuous flexible structure at various discrete points torques tending to negate any deflection resulting from externally applied forces. That theory is, however, concerned primarily with continuously applied dead weight loading, and the torques envisaged are the reaction produced by holding the structure firm against rotation at selected points. However, the results it teaches, that stresses in and deflection of the structure are thus reduced in magnitude, appear as benefits in the practice of our invention also.

BRIEF DESCRIPTION OF THE DRAWINGS:

FIGS. 1 and 2 represent, in two views, schematically an embodiment of our invention;

FIG. 3 represents a more elaborate embodiment;

FIG. 4 represents an alternate device for inertially producing torque, for use in embodiments of our invention;

FIG. 5 represents schematically electrical means for use in the embodiment of FIGS. 1 and 2;

FIG. 6 represents schematically electrical means for controlling the operation of the device represented in FIG. 4;

FIG. 7 represents a modification of the embodiment represented in FIGS. 1 and 2;

FIG. 8 represents schematically electrical means for controlling the operation of the embodiment represented in FIG. 7; and

FIG. 9 represents generally the extension of the application of our invention to a two-dimensional structure.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1 and 2 represent a flexible mast 10, which may be an antenna, mounted upon a mobile vehicle 12, whose rolling while in motion will necessarily cause the mast to be oscillated at its base, which, in the absence of our invention, would produce shipping of large amplitude, as indicated generally by the dashed outline 10A in FIG. 2. At the tip of mast 10 there are represented a flywheel 14, and a gyroscopic rotation sensor 16, oriented to sense angular deflection of the mast tip in a plane normal to the axis of flywheel 14. A motor 18 supports and drives the flywheel 14 in a direction determined by and the same as the angular displacement sensed by sensor 16. Thus, if the mast 10, as a result of rolling of vehicle 12 while in transit, tended to sway as represented by dashed outline 10A of FIG. 2, sensor 16, upon sensing the beginning of the deflection clockwise, as represented, would (through a servoamplifier system) cause motor 18 to drive flywheel 14 clockwise, producing an inertially generated reaction torque on the frame of motor 18, and through it to the tip of mast 10 tending to turn it counterclockwise. This torque will bend the tip of mast 10 counterclockwise, causing it to assume a position similar to that represented by 10B. The total excursion of the middle of the mast is markedly reduced, and that of the tip rendered negligible by this operation of our invention; in effect, the mast appears stiffer than it is in fact, and the undesired deflection with respect to the base of mast 10 of the controlled tip is markedly reduced.

Since mast 10 is an extensive structure, more than one point on it may be selected for control. Thus FIG. 3 represents in outline the deflection to be expected by applying an additional flywheel 20, motor 22, and gyroscopic sensor 24 at the midpoint of 10, with the indicated result represented by 10B.

For simplicity, the control has been represented as affecting only transverse deflection of the mast 10 with respect to the long axis of vehicle 12. It is, of course, possible to provide another flywheel-motor-sensor combination with the respective axes of the various components orthogonal to those of the combination 14, 18, 16, to control fore-and-aft deflections as well, although the relatively greater length of the wheelbase of a conventional vehicle compared with its track width is likely to render such damping less necessary.

The use of a flywheel to produce torques inertially is convenient where it may be expected (as in the example represented by FIGS. 1, 2, and 3) that the time average of the torque required, averaged with due respect to sign, will be zero. However, where this condition does not exist, the device represented by FIG. 4 may be employed. Nozzles to serve as mass ejectors 26 and 28 are spaced apart by a lever arm distance and oppositely directed. Operation of solenoid valve 30 will permit discharge of compressed gas from source 32 through nozzles 26 and 28 into external space; the reaction produced upon the structure by the inertia of the gas being accelerated out of the nozzles will produce a counterclockwise torque. Similarly, nozzles 34 and 36, when caused to discharge gas by operation of solenoid valve 38, will produce a clockwise torque by reaction. Operation of one or the other of solenoid valves 30 and 38 will produce a torque in one or the other direction, just as will operation of motor 18 to accelerate flywheel 14 in one or the other direction. Since in the apparatus of FIG. 4 mass of the gas from source 32 may be continuously accelerated, a continuous torque in either direction may be produced; with the flywheel 14, there is a necessary limit to the obtainable time-acceleration (or, alternatively, time-torque) product at which the flywheel reaches its bursting angular velocity.

FIG. 5 represents schematically a general arrangement of known components which may be used to control the flywheel motor 18 responsively to the indications produced by gyroscopic sensor 16; and FIG. 6 represents a similar arrangement for controlling solenoid valves 30 and 38 represented in FIG. 4.

In FIG. 5, a potential divider 40 is represented as the sensor of the position of gyroscopic sensor 16, so that the setting of the moving arm of 40 is a measure of the angular displacement sensed by 16. Potential divider 40 has extreme ends of its resistor tied to the secondary of a transformer 42, the moving arm of 40 and the center tap of the secondary of 42 being connected to input terminals of amplifier 44, whose output is fed to phase-sensitive detector 46. The necessary reference voltage for operation of phase detector 46 is provided by transformer 48, whose primary, in parallel with the primary of transformer 42, is fed from an alternating source 50. Potential divider 40 is used conventionally as the position pickoff for gyroscopic sensor 16; as its moving arm is rotated to one side or the other of the midpoint of its resistor, the phase of the AC potential from transformer 42 which is applied to the input of amplifier 44 will change. Consequently the polarity of the output of phase detector 46 (which is provided with comparison potential from transformer 48 which is in phase with the output of transformer 42) which appears at terminal points marked T-T will depend upon the position of the moving arm of potential divider 40, and will thus cause the direction of rotation of motor 18 (here represented as a permanent-field commutator motor) to depend upon the position of the moving arm. Thus, if the central position of the moving arm of potential divider 40 corresponds to a vertical position of the tip of mast 10, the direction of rotation of motor 18 will depend upon the direction in which the end of mast 10 has tilted.

FIG. 6 represents simply an alternative to motor 18 as a load for connection to terminals T-T, comprising solenoid valves 30 and 38 of FIG. 4, tied in parallel respectively through diodes 52 and 54 to terminals T-T. The opposite poling of diodes 52 and 54 obviously has the effect that potential of one polarity applied to terminals T-T will open one valve, and potential of reversed potential will open the other valve.

It is not pretended that the control circuitry of FIGS. 5 and 6 represents sophistication; but it has the virtue that, with modern semiconductor devices, it can readily be built compactly enough to be housed in situ with the motor and gyroscopic sensor, requiring only DC supply.

FIG. 7 exemplifies the fact that various forms of displacement sensor may be employed in our invention. A projector 52 of a narrow beam of light is represented fixed at the base of mast 10, aimed vertically. Two photosensitive devices 54 and 56 are represented fixed on opposite sides of the tip of mast 10, so that when mast 10 is erect and aligned with the beam of light from projector 52, both 54 and 56 will be equally illuminated, but when the mast is deflected, one will be illuminated more than the other. FIG. 8 represents schematically a mode of connection of photosensitive devices 54 and 56 to the two inputs to a differential amplifier 58, whose output will depend in magnitude and polarity upon the difference in illumination of 54 and 56. This output appears at terminals marked T, T. Connection of these terminals to the similarly marked terminals of motor 18, as shown in FIG. 5, or of the solenoid valve system represented in FIG. 6, will result in inertially produced torques of the proper direction to negate deflection of the tip of mast 10, producing the same result as the arrangement represented by the use of gyroscopic sensor 16 in FIGS. 1 and 2.

The sensors employed have been described generically as deflection sensors; and the use, for example, of a freely rotatable gyroscope will cause the system to operate to cancel out deflections. It is well known in the art to cause a gyroscope to function as a rate sensor. This is described in Handbook of Automation, Computation and Control, Volume 3, editors Grabbe, Ramo, and Wooldridge, 1961, John Wiley and Sons, Inc., New York City, N.Y., Library of Congress Card 58-10800, Chapter 28, pages 07--09; the so-called rate-integrating or displacement gyroscope is described immediately thereafter on pages 09--10. If a rate sensor is employed in our invention, the effect of its operation will be more directly to damp out oscillations than to cancel deflections as such. Since, however, damping of oscillations will in general reduce deflections also, we have used the term displacement sensor to include both displacement rate sensors and displacment-rate-integrating sensors, since our invention may use either or both, according to the particular characteristics desired; and use "damping of deflections" generically to include reduction of their amplitude, as well as damping of oscillations.

For complete exemplification of the applicability of our invention, FIG. 9 represents a structure 62 which is extensive in two dimensions which is provided at various points with sensor-torque-producer units represented simply as rectangles 64 bearing the letter U to indicate that each is a unit comprising a suitable sensor which controls the operation of a source of inertially produced torque. It is, of course, evident that our invention may equally well be applied to a three-dimensional structure. While while we have taught and explained our invention in application to a long flexible mast, which is a practically useful form of the embodiments which we have constructed and demonstrated, it is evident that its principles are generally applicable to any flexible structure whose oscillations are to be damped or which is otherwise to be given a simulation of greater rigidity than in fact it possesses as a simple structure. It is also evident that, while we have for simplicity shown embodiments in which the sensor is located at substantially the same point as the torque-producing means, it would, for example, in FIG. 7, be possible to mount the projector 52 at the tip of mast 10 pointing downward, and mount the photosensitive cells 54 and 56 at the base of mast 10, so that the sensor device proper might be considered as being at least partially located away from this point whose deflection is controlled.

Claims

We claim:

1. Means for damping undesired deflections of an extensive structure with respect to a selected reference point of the structure comprising,

means for sensing the angular deflection of a controlled point of the structure with respect to the selected reference point, a source of inertially produced torque, said source including a mass, means for accelerating said mass to effect said inertially produced torque, said source providing a torque to said structure at the controlled point responsive to said sensing means to produce rotation in a direction opposed to said angular deflection.

2. The means claimed in claim 1 in which the said controllably operative source of inertially produced torque is a flywheel driven by a controllable motor.

3. The means claimed in claim 1 in which the said controllably operative source of inertially produced torque comprises ejectors which are adapted to produce torque by the reactions produced by ejection of mass from the ejectors into external space.