US3856267A

US3856267A - Vibration isolator

Info

Publication number: US3856267A
Application number: US00323038A
Authority: US
Inventors: W Flannelly
Original assignee: Kaman Aerospace Corp
Current assignee: Kaman Aerospace Corp
Priority date: 1973-01-12
Filing date: 1973-01-12
Publication date: 1974-12-24
Anticipated expiration: 1991-12-24

Abstract

A vibration isolator is disclosed in a winch structure for damping vibratory tension loads in a winch cable. A winch drum is driven through a speed reduction unit by a motor mounted on the winch frame. The speed reduction unit has a very high reduction ratio and, as a consequence, reacts substantially all of the torque applied by the tensioned cable to the winch frame. The housing of the speed reduction unit which reacts the torque is mounted for free rotation relative to the winch frame and an isolation spring is connected between the frame and the housing to resiliently react the torque loads against the winch frame. An inertial mass rotatably mounted to the winch frame is also driven through a mechanical motion amplifier by the rotational motions of the speed reduction unit as the torque loads are resiliently reacted through the spring. By appropriate tuning of the inertial mass and the spring, it is possible to generate an antiresonance condition in which the isolator exhibits a zero impedance or transmissibility characteristic for vibratory forces originating at either end of the cable at a particular frequency.

Description

[4 1 Dec. 24, 1974 United States Patent [191 Flannelly VIBRATION ISOLATOR [57] ABSTRACT A vibration isolator is disclosed in a winch structure for damping vibratory tension loads in a winch cable.

[75] Inventor: William G. Flannelly, South Windsor, Conn.

73 Assi nee: Kaman Aeros ace Cor orat'on 1 g p p l A winch drum is driven through a speed reduction unit by a motor mounted on the winch frame. The

Bloomfield, Conn.

Jan. 12, 1973 [22] Filed:

speed reduction unit has a very high reduction ratio and,

as a consequence, reacts substantially all of the torque applied by the tensioned cable to the winch frame. The housing of the speed reduction unit which reacts the torque is mounted for free rotation relative to the winch frame and an isolation spring is connected between the frame and the housing to resiliently react the torque loads against the winch frame. An inertial mass rotatably mounted to the winch frame is also driven through a mechanical motion amplifier by the rotational motions of the speed reduction unit as the torque loads are resiliently reacted through the spring. By appropriate tuning of the inertial mass and the spring, it is possible to generate an antiresonance condition in which the isolator exhibits a zero impedance or transmissibility characteristic for vibratory forces originating at either end of the cable at a particular frequency.

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PATENIED DEC 2 4 [5174 saw 2 95 3 BACKGROUND OF THE INVENTION The present invention relates to tuned vibration isolators which exhibit antiresonance characteristics at a given frequency. More particularly, the present invention relates to a vibration isolator integrally embodied in a winch structure to eliminate the coupling of vibratory motions at a given frequency to or from a cablesupported load.

The inventor has disclosed in a previously issued US. Pat. No. 3,322,379 entitled Dynamic Antiresonant Vibration lsolator issued May 30, 1967, a coupling device which exhibits antiresonance characteristics at a tuned frequency. The transmissibility characteristics of this device are said to be of zero or low impedance because it prevents or substantially reduces the level at which vibrations are transmitted by the device between the coupled bodies.

In a related co-pending application by the inventor, Ser. No. 249,131, filed May 1, 1972, entitled Vibration lsolator, a coupling device employing the antiresonance principles is disclosed in series with a winch cable and a suspended load. Although the isolator of the present invention employs the antiresonance principles, its structure is substantially different and it is incorporated directly in the winch structure.

Low impedance couplers are particularly useful in winch systems employed by aircraft carrying suspended loads. In particular, a helicopter which frequently carries loads having weights comparable to that of the helicopter itself can encounter serious stability problems if the load becomes unmanageable in flight due to vibratory bouncing. The bouncing may be induced at critical excitation frequencies related to the rotor system. Such frequencies are generally relatively low, between two to six cycles per second. If the generation of vibratory loads at the critical frequencies is not prevented, the results may be catastrophic. It is for this reason that tuned vibration isolators providing zero impedance characteristics at the critical frequencies are so valuable in aircraft installations.

The vibration isolators of the above-referenced patent and application are passive isolators which neither absorb nor dissipate energy. Because power requirements and heat dissipation problems may be critical in aircraft, passive isolators are particularly desirable in this environment. The isolators may be self-contained units. Furthermore, in the passive isolator there are no feedback devices which might fail and cause phase reversal instability, a situation more critical than if no isolator were used at all.

Another important feature of passive isolators exhibiting zero impedance characteristics is that they can be tuned to a critical frequency and will exhibit the zero impedance characteristics at that frequency regardless of the size of the masses joined by the isolator. In other words, the characteristics of a passive antiresonant isolator of the type described in the above-referenced patent and application and in the present application are independent of the mass characteristics of the interconnected bodies.

It is a general object of the present invention to disclose a passive, antiresonant vibration isolator which may be integrally installed in a winch system.

SUMMARY OF THE INVENTION The present invention resides in a vibration isolator for reducing the transmission of vibrations through a winch between the winch load and a supporting structure. The winch drum is driven rotatably relative to the supporting structure through a torque-reaction member such as a housing enclosing a speed reduction unit. The reduction unit is in turn driven by a high-speed motor. The torquereaction housing is mounted for free rotation relative to the supporting structure. Resilient means are connected between the housing and the supporting structure to resiliently restrain the rotational movements of the housing relative to the supporting structure as torques applied to the winch drum are reacted through the housing and the resilient means to the structure. An inertial mass is mounted for movement on the supporting structure and connecting means between the mass and the housing cause the mass to be displaced relative to the supporting structure in accordance with the rotational movements of the housing relative to the structure. The combined resilient means and inertial mass form a mass-spring system which can be tuned to a particular anti-resonance frequency and establish a zero impedance or transmissibility characteristic insofar as vibratory forces at either end of the cable are concerned. In other words, at the antiresonant frequency, the load suspended on the winch cable is effectively isolated from the supporting structure or the winch. Excitation forces originating in either the load or supporting structure at the antiresonant frequency are, therefore, not transmitted through the winch system.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side elevation view of a winch system having dual winches for supporting a common load and each winch incorporates the vibration isolator of the present invention.

FIG. 2 is a partially sectioned view of one of the winches in the winch system as viewed along the line 22 of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 1, a winch system, generally designated 10, is shown with the components forming a vibration isolator in accordance with the present invention. The winch system shown is a tandem unit having two separate winches 12 (letter subscripts being used where appropriate to distinguish corresponding parts of the winches), each of which includes a vibration isolator. The winch system may be used in various environments where a suspended load is to be isolated from the structure supporting the load and the winch system. For example, isolation may be desired in an elevator system in which the lifting winches isolate the elevator cabin from the building, or isolation may be needed where a suspended load includes delicate instruments. As mentioned above, the antiresonant isolator has particular utility in the aircraft field where loads suspended beneath helicopters must be isolated from the airframes to avoid instabilities at dominant excitation frequencies originating in the lifting rotors.

The winch system 10 includes a structural mounting frame 20 on which both of the winches 12 are supported for installation in an airframe or other platform.

A cable 22 from each of the winches extends downwardly through a central opening in the frame to an equalizing beam 24 to which a cargo hook 26 is attached for connection with the suspended load L. Each of the winches 12 is driven by means of a high speed motor 28, such as an air turbine or hydraulic motor, mounted at the upper portion of the frame 20 between the two winches 12. The power train between the motor and the winches is divided between two shrouded bevel gear drive mechanisms 30 which extend from the motor 28 to the respective winches 12.

The following description is limited to the construction and operation of the winch 12b; however, it will be understood that the winch 120 has corresponding parts and its operation is essentially the same. The rotation of the two winches are coordinated to cause the cables 22 to be reeled in and out together.

Referring now to both FIGS. 1 and 2, it will be seen that the winch 12b is comprised of a rotatably mounted drum 40 and a drum support structure 42 which is fixedly secured to the mounting frame 20. The drum 40 has on its outer surface a continuous helical groove in which the reeled portion of the cable 22 is wrapped. The drum 40 is not only rotatable relative to the support structure 42 in the frame 20, but also shifts axially of itself as the cable is paid in and out in order to maintain a single point payout station at a central point within the frame 20. The single point payout feature avoids a shifting suspension point which in an aircraft can be critical to attitude stability. Since the mechanism which shifts the drum laterally forms no part of the present invention and is not essential to the invention, it is not shown or described.

The drive mechanism 30b between the motor 28 and the winch 12b extends to the axis 44 of the drum 40 where a set of bevel gears 46 drive a speed reduction unit 50. A typical reduction ratio within the unit 50 might be 500:1. With such a ratio, there is a corresponding increase in torque between the power input shaft 52 and the power output shaft 54 interconnected by the gear set 56, the idler shaft 58 and gear set 60. The output shaft 54 extends through the drum support 42 and has a splined end which engages the drum 40 in driving relationship. Since the shaft 54 is splined to the drum 40, the torquing carried by the shaft 54 is equal to the torque produced by the portion of the load L suspended on the cable 22b. Since the value of the torque in the input shaft 52 is comparatively negligible because of the high reduction ratio of the unit 50, substantially all of the torque produced in the shaft 54 by the load on the cable 22b must be reacted through the housing 62 of the unit 50 to the mounting frame 20.

It will be observed that the housing 62 of the speed reduction unit 50 is journaled within the drum support structure 42 by bearings 64 for rotation about the axis 44 of the drum 40. None of the drive torque, therefore, will be reacted directly into the support structure 42 from the housing 62. lnstead, an offset lever arm 70, seen most clearly in FIG. 1, projects radially from the housing 62 and a resilient compression spring 72 is connected between the arm 70 and a reaction pad 74 fixed to the frame 20. Static loads on the cable 22b, therefore, generate a torque in the shaft 54 which is reacted to the frame 20 through the arm 70, spring 72 and the pad 74.

Although the spring 72 is represented in the drawings as a coil spring, in high capacity winch systems, the spring would very possibly be formed by other resilient means such as a fluid spring having a pneumatic or hydraulic cylinder providing the desired compliance. As discussed in greater detail below, the spring 72 forms one of the dynamic components of the vibration isolator which prevents the transmission of vibratory loads through the winch and cable between a suspended load and the structure supporting the winch system 10.

Connected to the exposed end of the speed reduction housing 62 is a gear sector 80. The sector is centered on the drum axis 44 and rotates with the housing 62 as the housing rotates relative to the drum support structure 42 due to the bearings 64 and the compliance of the spring 72.

Fixed to the frame 20 immediately below the gear sector is a pivot pin 82. An inertial mass is mounted by means of a radius arm 92 on the pin 82 to rotate about the pin relative to the frame 20. The mass 90 is supported on an end of the radius arm 92 opposite an end carrying a gear sector 94. The gear sectors 80 and 94 are in mesh so that the rotations of the speed reduction housing 62 relative to the frame 20 cause the inertial mass 90 to be rotated about the pin 82 in conjunction with the deflection of the spring 72. The mass 90 and the spring 72 form the principal tuning elements of the passive antiresonant vibration isolator.

The gear sectors 80 and 94 have radii which effectively amplify the motion of the inertial mass 90 as the spring 72 deflects and the housing 62 rotates relative to the frame 20. The gear sectors, therefore, form a mechanical motion amplifier which is considered to be particularly useful in the vibration isolator employed with the winches because it permits the size of the mass 90 and consequently the weight of the isolator to be reduced due to the larger displacements and accelerations produced by the amplifier.

When a static load is initially applied to the cargo hook 26, the resulting torque produced on the drum 40 is reacted through the housing 62 and causes the spring 72 to be compressed. The compression of the spring 72 is accompanied by a slight rotation of the housing 62 relative to the frame 20 so that the gear sector 80 causes the inertial mass 90 to move from an unloaded static position shown in phantom to the solid-line static position. lf vibratory loads originate in either the platform supporting the frame 20 or the suspended load L, the resulting vibratory torques produced on the housing 62 will produce small amplitude oscillations of the housing and cause the inertial mass 90 to oscillate with the amplitude D. By appropriate tuning of the spring and mass characteristics, an antiresonant condition is established at a particular forcing frequency. The isolator at that frequency exhibits zero impedance characteristics and the vibratory forces will not be transmitted through the winch 12 between the frame 20 and suspended load L.

The dynamics of the vibration isolator can be studied more thoroughly with a simplified mathematical analysis. By setting up the equations for the kinetic and the potential energy of the interconnected load and winch supporting systems and using Lagranges equation to obtain the steady state equations of motion, it can be established that the transfer impedances for forces originating in either the supporting platform or the load are the same. Furthermore, it can be shown that the transfer impedance of an isolator becomes zero and provides zero transmissibility characteristics at an antiresonant frequency given by the expression where k spring constant of spring 72 R radius of lever arm 70 from axis 44 m mass of mass 90 r length of radius arm 92 1,, moment of inertia of radius arm 92 including gear sector 94 A amplification factor equal to radius of sector 80/radius of sector 94 1,, moment of inertia of housing 62 The mass of the drum 40 in a typical helicopter installation is found to have little effect on A due to the negligible drum rotations in the pertinent range of frequencies.

While the present invention has been described in a preferred embodiment, it will be understood that numerous modifications and substitutions can be made in the apparatus without departing from the spirit of the invention. For example, although the vibration isolator has been disclosed in a dual winch system it is readily apparent that there are effectively two isolators, each associated with one of the respective winches independent of the other and, therefore, capable of operation on a single winch system. The structure employed to react the drum torque to the frame includes the speed reduction housing 62; however, other means are also available. For example, if a drive motor is connected directly to the drum, the motor housing might be employed to react the drum torque to the winch frame. Also, it may be possible to couple other torque reaction members such as a brake or locking member to the winch drum when the drum has stopped at a static position and to connect the spring 70 to such member. The advantage, however, of reacting the torque through the speed reduction unit is that the rotation of the unit in response to vibratory loads does not appreciably affect cable position and the isolator is at all times coupled to the drum and operative to produce the zero impedance characteristics even while the drum is being rotated to pay out or reel in the winch cable. It is, of course, possible to reposition the spring 72 and mass 90 and to utilize other means for connecting the mass to the torque reaction housing. Accordingly, the present invention has been described in several preferred embodiments by way of illustration rather than limitation.

I claim:

1. A vibration isolator for reducing the transmission of vibrations from a winch cable through a winch drum to a supporting structure, the drum being driven rotatably relative to the supporting structure, comprising: a torque-reaction housing rotatably mounted on the supporting structure, the drum being rotatably driven relative to the supporting structure through the housing whereby the driving torque applied to the drum is reacted through the housing to the supporting structure, resilient means connected between the torque-reaction housing and the supporting structure for resiliently restraining rotational movements of the torque-reaction housing relative to the supporting structure; an inertial mass mounted for movement on the supporting structure; and connecting means between the mass and the torque-reaction housing for displacing the mass relative tional movements of the housing relative to the supporting structure.

2. A vibration isolator for reducing the transmission of vibrations as defined in claim 1 wherein a pivot member is connected to the supporting structure; the inertial mass is mounted on the pivot member for rotation about the pivot member relative to the supporting structure; and the connecting means causes the mass to be rotatably displaced relative to the supporting structure about the pivot member.

3. A vibration isolator for reducing the transmission of vibrations as defined in claim 1 wherein the connecting means comprises a mechanical motion amplifier connected between the torque-reaction housing and the inertial mass to amplify the movements of the mass relative to the supporting structure.

4. A vibration isolator as defined in claim 3 wherein the inertial mass is rotatably mounted on the supporting structure; and the mechanical motion amplifier comprises gear means for transforming the rotational movements of'the housing into rotational movements of the inertial mass.

5. A vibration isolator as defined in claim 4 wherein the gear means includes a gear sector fixed to the torque-reacting housing for rotation with the housing relative to the supporting structure, and a gear sector attached to the inertial mass for rotation with the mass relative to the supporting structure and engaged with the gear sector fixed to the housing.

6. A vibration isolator for reducing the transmission of vibrations as defined in claim 1 wherein a lever arm projects from the torque-reacting housing; and the resilient means is connected between the lever arm and the supporting structure.

7. A vibration isolator as defined in claim 6 wherein: a pivot member is mounted to the supporting structure adjacent the torquereacting housing; the inertial mass is rotatably mounted to the pivot member; and the connecting means comprises gear means interconnecting the housing and the rotatable inertial mass for rotating the inertial mass on the pivot member as the housing rotates relative to the supporting structure.

8. A vibration isolator as defined in claim 1 wherein:

the resilient means and the inertial mass are tuned to a given antiresonant frequency inhibiting cable vibrations at that frequency.

9. A vibration isolator for damping vibratory tension loads in the support cable reeled on and off of a winch drum rotatably driven in a winch frame comprising: a rotatable torque-reaction member mounted to the winch frame and coupled to the winch drum for reacting torque produced on the drum by the tension in the winch cable; an inertial mass also movably mounted on the winch frame and coupled to the rotatable torquereaction member for simultaneous movement therewith; and resilient load reaction means connected between the winch frame and the torque-reaction member for reacting the torque to the frame and tuned with the inertial mass for dynamically restraining vibratory relations of the torque-reaction member produced by the loads in the support cable.

10. A vibration isolator for damping as defined in claim 9 wherein the rotatable torque-reacting member comprises the housing of a speed reduction unit in the winch drum drive mechanism, the housing being rotatably mounted to the winch frame.

11. A vibration isolator for damping as defined in claim 10 wherein the resilient load reaction means comprises a lever arm extending from the rotatable housing, and a resilient element between the lever arm and the winch frame.

12. A vibration isolator as defined in claim 10 wherein the inertial mass is rotatably mounted on the winch frame; and a gear set connects the housing to the rotatable inertial mass.

13. A vibration isolator as defined in claim 9 wherein rotational coupling means are connected between the torque-reaction member and the mass for rotating the mass simultaneously with the rotations of the member.

14. In apparatus for supporting a load on a cable in isolated relationship from a frame, the improvement comprising: a cable drum rotatably mounted in the frame and having a reeled portion of the cable wrapped about the drum; compliant means coupled between the drum and the frame for resiliently reacting to the frame the torque produced on the drum by a load connected to the unreeled portion of the cable; an inertial mass also rotatably mounted on the frame; and connecting means also coupling the inertial mass to the drum to cause the mass to rotate on the frame in response to the deflection of the compliant means as loads are resiliently reacted to the frame.

15. The improvement of claim 14 wherein the connecting means comprises a mechanical motion amplifier coupled between the drum and the rotatable iner-

Claims

1. A vibration isolator for reducing the transmission of vibrations from a winch cable through a winch drum to a supporting structure, the drum being driven rotatably relative to the supporting structure, comprising: a torque-reaction housing rotatably mounted on the supporting structure, the drum being rotatably driven relative to the supporting structure through the housing whereby the driving torque applied to the drum is reacted through the housing to the supporting structure, resilient means connected between the torque-reaction housing and the supporting structure for resiliently restraining rotational movements of the torque-reaction housing relative to the supporting structure; an inertial mass mounted for movement on the supporting structure; and connecting means between the mass and the torque-reaction housing for displacing the mass relative to the supporting structure in accordance with rotational movements of the housing relative to the supporting structure.

4. A vibration isolator as defined in claim 3 wherein the inertial mass is rotatably mounted on the supporting structure; and the mechanical motion amplifier comprises gear means for transforming the rotational movements of the housing into rotational movements of the inertial mass.

7. A vibration isolator as defined in claim 6 wherein: a pivot member is mounted to the supporting structure adjacent the torque-reacting housing; the inertial mass is rotatably mounted to the pivot member; and the connecting means comprises gear means interconnecting the housing and the rotatable inertial mass for rotating the inertial mass on the pivot member as the housing rotates relative to the supporting structure.

8. A vibration isolator as defined in claim 1 wherein: the resilient means and the inertial mass are tuned to a given antiresonant frequency inhibiting cable vibrations at that frequency.

9. A vibration isolator for damping vibratory tension loads in the support cable reeled on and off of a winch drum rotatably driven in a winch frame comprising: a rotatable torque-reaction member mounted to the winch frame and coupled to the winch drum for reacting torque produced on the drum by the tension in the winch cable; an inertial mass also movably mounted on the winch frame and coupled to the rotatable torque-reaction member for simultaneous movement therewith; and resilient load reaction means connected between the winch frame and the torque-reaction member for reacting the torque to the frame and tuned with the inertial mass for dynamically restraining vibratory relations of the torque-reaction member produced by the loads in the support cable.

15. The improvement of claim 14 wherein the connecting means comprises a mechanical motion amplifier coupled between the drum and the rotatable inertial mass.