GB2105827A - Anti-vibration mountings - Google Patents

Abstract

An anti-vibration mounting for protecting structure against impulses generated by a reciprocating mechanism, where the mount is for use with automatic guns installed in aircraft, comprises a carriage (12) guiding a gun (13) on a pair of parallel rods (11) by means of swinging telescopic arms (14) each containing a compression spring (not shown) and by an axially-acting compression spring (15, 16). In operation, ratchets (20) engage flange (18) on spring casing (16) in a position where it exerts a force on the carriage (12). As the carriage (12) recoils from the position at (21) where the gun is fixed, the spring (15) acts as a positive rate spring, while the springs in arms (14) act as negative rate springs, the strengths of the springs being such that they combine to operate as a zero-rate spring. At the end of a firing sequence, the ratchets (20) are disengaged and the recoil is resisted only by the springs in arms (14) so that the carriage (12) moves beyond its operational maximum recoil position and ratchets (19) engage a further flange (17) on the carriage (12). <IMAGE>

Description

SPECIFICATION Gun mountings The present invention relates to anti-vibration mountings, and especially to such mountings for use with automatic guns installed in military aircraft.

Automatic guns installed in aircraft have high rates of fire and generate high recoil forces. Conventional recoil buffers transmit these forces to aircraft structure in a cyclic manner which is potentially damaging to the structure, and from which sensitive aircraft equipment must be isolated.

The present invention provides an anti-vibration mounting which reduces the effect of the recoil forces.

According to the present invention an antivibration mounting for protecting structure against a mechanism cyclically generating a series of impulses includes means for locking the mechanism in a position beyond a maximum recoil position, means incorporating a negative rate spring for moving the mechanism from the locked position to a position where an impulses is generated, and means incorporating a positive rate spring for cooperating with the negative rate spring to provide a zero rate spring system during generation of impulses.

The negative rate spring can conveniently be in the form of at least one swinging telescopic arm containing a Hookean compression spring and the positive rate spring can conveniently be a Hookean compression spring acting along the line of motion of the mechanism.

One embodiment of the invention has a mechanism connected to structure by a negative rate spring including at least one swinging telescopic arm containing a Hookean compression spring, a positive rate spring secured to the mechanism, first locking means for locking the mechanism, in a non-operational mode of the mechanism, in a position beyond an operational maximum recoil position such that the positive rate spring is substantially unstressed and the negative rate spring is stressed, second locking means for locking the positive rate spring to the structure in an operational mode of the mechanism, means for releasing the first locking means at the initiation of an operational mode of the mechanism to allow the negative rate spring to move the mechanism to a position where an impulse is generated and means for locking the second locking means so that recoil of the mechanism stresses the positive rate spring, means for releasing the second locking means at the end of an operational mode of the mechanism so that a recoil of the mechanism after a final impulse drives the mechanism to the position beyond the operational recoil position and means for locking the first locking means with the mechanism in this position, the strengths of the positive and negative rate springs being such that in an operational mode of the mechanism they combine to form a zero rate spring system.

There are preferably two swinging telescopic arms. The locking mans can conveniently include ratchets.

In a one form or the invention position and velocity transducers are used to sense the optimum position of the mechanism for the generation of eac impulse.

One embodiment of the invention will now be described, by way of example only, with reference to the accompanying diagrammatic drawings, of which Figure 1 is a view of a gun mounted in an anti-vibration mounting according to the invention.

Figure 2 is a graph of gun displacemet against time, and Figure 3 is a graph of force against time.

A gun cradle, of which parts are illustrated at 10 in Figure 1, has a pair of parallel guides 11 on which a gun carriage 12 is slideably mounted.

A gun 13 is mounted in the carriage 12.

A pair of swinging telescopic arms 14 each of which contains a Hookean compression spring (not shown) are secured between the cradle 10 and the carriage 12, and a Hookean compression spring 15 is secured to the carriage 12 with its line of action aligned with the direction of motion of the carriage 12. The compression spring 15 has a body 16 to which are secured a first flange 17 and a second flange 18. Mounted on the cradle 10 are a first pair of ratchets 19, moveable between positions as shown at 19 where they engage flange 17 positions as shown at 1 9a where they disengage flange 17, and a second pair of ratchets 20 moveable between positions as shown at 20 where they engage flange 18 and positions as shown at 20a where they disengage flange 18.

In operation the ratchets 19 are in disengaged position 19a and ratchets 20 engage flange 18 holding compression spring 15 in a position where it exerts a force on the carriage 12. As the carriage recoils from a position indicated at 21 where the gun 13 is fired, the force exerted by spring 15 increases as the spring is compressed - that is, it operates as a positive rate spring. In contrast, the force acting on carriage 12 along its line of motion due to the spring in telescopic arms 14 decreases as the springs are compressed, due to the change in angle between the line of action of these springs and the line of motion.

The swinging telescopic arms 14 therefore act as negative rate springs. The strengths of the springs in telescopic arms 14 and of the spring 15 are so adjusted that over the range of movement experienced by the carriage 12 during firing of gun 13 the combination operates substantially as a zero rate spring, in which the force exerted on carriage 12 remains constant irrespective of the position of the carriage.

At the end of a firing sequence the ratchets 20 are moved to position 20a to disengage flange 18 on the final firing. The recoil from this final firing is thus resisted only by the springs in swinging telscopic arms 14, so the carriage 12 will move beyond its usual maximum recoil position. The strength of the springs in arms 14 is such that the energy of the final recoil is absorbed by the time the arms are substantially normal to the line of motion of carriage 12, as indicated at 22 in Figure 1. Ratchets 19 are then moved to engage flange 17.

At the start of a firing sequence ratchet 19 are disengaged from flange 17, the springs in telescopic arms 14 move the carriage 12 and gun to the firing position 21 and the ratchets 20 are brought into engagement with flange 18.

The position of a datum point of the carriage 12 relative to a non-firing locked position 0 during a sequence of firings 23 is illustrated in Figure 2. The force exerted on the cradle 10, and hence on structure supporting the cradle, rises (Figure 3) steadily from zero to a level Fwherethe gun 13 is first fired, remains constant to a point S where the gun is last fired, and then drops steadily back to zero.

This arrangement avoids shock loads.

It will be realised that, in practice, with telescopic arms 14 normal to the line of motion of carriage 12 there will be no force tending to move the carriage.

Some means must be provided to intiate movement upon retraction of ratchets 19 from flange 17. Also care must be taken in design to ensure that the moving system will travel back far enough on the final recoil to enable ratchets 19 to engage flange 17.

Suitable means to accomplish these requirements for example the use of a buffer spring, or the use of a plunger, acting on flange 17, and "overshoot" against a buffer spring on final recoil, will be readily apparent to one skilled in the art. As such means do not constitute part of the invention they will not, therefore, be further discussed. Though the means may well result in loads other than those shown in Figure 3, these will be very small compared with the load F of Figure 3.

As a zero rate spring is unstable it is preferable that the optimum position of the gun for each firing be determined by position and velocity sensing transducers.

Claims (9)

1. An anti-vibration mounting for protecting structure against a series of impulses generated by a reciprocating mechanism, including means for locking the mechanism in a position beyond a maximum recoil position, means incorporating a negative rate spring for moving the mechanism from the locked position to a position where an impulse is generated, and means incorporating a positive rate spring for co-operating with the negative rate spring to provide a zero rate spring system during generation of impulses.

2. An anti-vibration mounting as claimed in Claim 1 wherein the negative rate spring is in the form of at least one swinging telescopic arm containing a Hookean compression spring.

3. An anti-vibration mounting as claimed in Claim 1 or in Claim 2 wherein the positive rate spring is a Hookean compression spring acting alone the line of motion of the mechanism.

4. An anti-vibration mounting having a mechanism connected to structure by a negative rate spring including at least one swinging telescopic arm containing a Hookean compression spring, a positive rate spring secured to the mechanism, first locking means for locking the mechanism, in a non-operational maximum recoil position such that the positive rate spring is substantially unstressed and the negative rate spring is stressed, second locking means for locking the positive rate spring to the structure in an operational mode of the mechanism, means for releasing the first locking means at the initiaion of an operational mode of the mechanism to allow the negative rate spring to move the mechanism to a position where an impulse is generated and means for locking the second locking means so that recoil of the mechanism stresses the positive rate spring, means for releasing the second locking means at the end of an operational mode of the mechanism so that a recoil of the mechanism after a final impulse drives the mechanism to the position beyond the operational recoil position and means for locking the first locking means with the mechanism in this position, the strengths of the positive and negative rate springs being such that in an operational mode of the mechanism they combine to form a zero rate spring system.

5. An anti-vibration mounting as claimed in Claim 4 wherein there are two swinging telescopic arms.

6. An anti-vibration mounting as claimed in Claim 4 or in Claim 5 wherein the first and second locking means include ratchets.

7. An anti-vibration mounting as claimed in any one of claims 1 to 6 including position and velocity transducers to sense an optimum position of the mechanism forthe operation of each impulse.

8. An anti-vibration mounting as claimed in any one of Claims 1 to 7 wherein the mechanism includes a gun.

9. An anti-vibration mounting substantially as herein described with reference to the accompanying drawings.