GB2241043A

GB2241043A - Pneumatic vibration isolation systems

Info

Publication number: GB2241043A
Application number: GB9100537A
Authority: GB
Inventors: Richard P Eddy; Jr Worthington Bowie Houghton
Original assignee: Newport Corp USA
Current assignee: Newport Corp USA
Priority date: 1990-01-12
Filing date: 1991-01-10
Publication date: 1991-08-21
Anticipated expiration: 2011-01-10
Also published as: DE4100271B4; GB9100537D0; DE4100271A1; GB2241043B; JPH0552231A; JP2936238B2

Abstract

Pneumatic vibration isolation systems (10, 100) displace an operating piston (15) by vibrations relative to a compliance chamber (16) containing compressed gas (17) of a volume predetermined in terms of natural vibration isolation frequency. The need for an external damping chamber is eliminated by closely fitting the operating piston (15) with a permeable pressure barrier (18) in the compliance chamber (16), and effecting damping by displacing gas (20) with that operating piston (15) through that pressure barrier (18) in the compliance chamber (16). Laminar flow (19) is preferably imparted to the gas (20) displaced with the operating piston (15) through the pressure barrier (18) in the compliance chamber (16), the pressure barrier (18) having flow restrictions (21) of sintered metal. A second embodiment (Fig. 2) includes self-levelling means (51-68). <IMAGE>

Description

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23 24 25 26 27 28 29 30 31 32 PNEUMATIC VIBRATION ISOLATION SYSTEMS The subject invention relates to isolation of loads and other objects from vibration and to pneumatic vib-ration isolation systems.

A modern pneumatic vibration isolation system is disclosed in the NEWPORT CATALOG (Newport Corporation, 1989), pp. A-2 to A-33. As seen, for instance, at A-4 and A-22 of that NEWPORT CATALOG, such state-of-the-art pneumatic vibration isolator has a spring chamber or spring reservoir relative to which the vibrating piston is displaced, and a damping chamber or damp ing reservoir which is external to the spring chamber or reservoir.

The spring chamber or reservoir, also known as compliance chamber, contains compressed gas, typically air, of a volume predetermined in terms of natural vibration isolation frequency, as may, for instance, be seen from the equations on page A-4 and the text about the Spring Reservoir on page A-22. That text also emphasizes the importance of the Damping Reservoir as "a secondary chamber which. is connected to the spring reservoir by an orifice or other device which restricts the flow and provides the damping necessary to reduce the amplification at resonance."

The best devices for such purpose are laminar flow restrictors, as may be seen from the paper entitled "Design of Laminar Flow Restrictors for Damping Pneumatic vibration isolators," presented by Professor Daniel B. DeBra at the CIRP 34th General Assembly, August 1984, showing also the damping chamber in addition to the compliance chamber in Fig. 5 thereof.

b r 1 2 3 4 6 7 8 9 11 12 13 14 16 17 18 19 discloses a horizontal vibration isolation system and also 21 provides-for each pneumatic vibration isolator a large air 22 housing relative to which the operating piston assembly 23 is displaced by vibrations.

Such damping chamber or reservoir occupies considerable space, shown larger than the compliance chamber in that Fig. 5 of the CIRP Paper, and shown as large as the spring chamber or reservoir at A-4 and A-22 of the NEWPORT CATALOG. This not only adds to the bulk of the system,-but imposes other limitations as well. Looking at the prior-art illustrations so far mentioned, it should be recognized that the pressure variations imposed by the vibrating piston in the spring reservoir or compliance chamber are very small given the large volume of that reservoir or chamber relative to the cross-section of the vibrating piston. The resulting pressure differential between the compliance and damping chambers results in minimal gas flow through the laminar or other flow restrictor and inefficient damping. This gives the designer little to work with at the laminar or other flow restrictor and in the damping reservoir or chamber. Reference may in this respect also be had to U.S. Patent 3,784,146, by John W. Matthews, Ph.D.r issued January 8, 1947, for Horizontal Vibration Isolation System. That patent 1 h V4 1 2 3 4 6 7 8 9 10 11 12 13 14 is 16 17 18 19 21 22 23 24 25 The invention is applicable to pneumatic vibration isolation methods and apparatus wherein an operating piston is displaced by vibrations relative to a compliance chamber containing compressed gas of a volume predetermined in terms of natural vibration isolation frequency. From a first aspect thereof, the invention resides in the improvement of eliminating the need for an external damping chamb-er by sufficiently closely fitting the operating piston with a permeable pressure barrier in the compliance chamber, and effecting damping by displacing gas with that operating piston through that pressure barrier in that compliance chamber.

From a related aspect thereof, the invention resides in the improvement of eliminating the need for an external damping chamber, comprising, in combination, a pressure barrier in the compliance chamber permeable to gas displaced by the operating piston and closely fitting that operating piston. Preferably, such pressure barrier is as close to that piston as permitted by operating piston travel.

Isolator efficiency and efficacy preferably are further improved by imparting laminar flow to the gas displaced with the operating piston through the pressure barrier in the compliance chamber.

Other aspects of the invention will become apparent in the further course of this disclosure, and no restriction is intended by the above summary.

a 1 1 For a better understanding of the invention and to show how the same may be carried into effect, reference will now be made, by way of exanple, to the acconpanying draw ings,. in which like-reference nufferalsdesignate like or -equivalent parts, -and in which:

2 3 4 5 6 7 8 9 10 11 12 13 Fig. 1 is a vertical section through a pneumatic vibration isolator according to one embodirm_nt; and Fig. 2 is a view similar to Fig. 1 illustrating a second enbodin-ent.

4 1 2 3 4 5 6 7 8 11 12 13 14 is 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 The drawings show pneumatic vibration isolators 10 and 100 which may, for instance, be employed to isolate a load, mass, machinery or table 12 from vibrations of a floor 13, or to isolate the floor from vibrations of machinery. A table typically would have thre e or more of such vibration isolators as legs for this purpose.

The vibration isolators 10 and 100 are of a type wherein an operating piston 15 is displaced by vibrations relative to compliance chamber 16 containing compressed gas 17 of a volume predetermined in terms of natural vibration isolation frequency. For a determination of a suitable gas volume reference may be had to equation (1) and its accompanying text on page 2 of the above mentioned CIRP Paper and to the tutorial on pages 2-A et seq. of the NEWPORT CATALOG.

However, unlike that prior art, the embodin-ents eliminate. the need for an external damping chamber or external damping chamber volume by closely fitting the operating piston 15 with a permeable pressure barrier 18 in the compliance chamber 16, and effecting damping by displacing gas 20 with the operating piston 15 through that pressure barrier in that compliance chamber, providing an integrated damping control.

According to a preferred embodiment laminar flow 19 is imparted to the gas 20 displaced by the operating piston 15. Laminar flow damping orifices or restrictors 21 may be used for that purpose and may be of a type as disclosed in the above mentioned CIRP Paper for vibration-induced air flow into a damping chamber, and being preferably made of sintered metal held, for instance, by a sealing grommet 22. Contrary to that CIRP Paper and other prior art, this eiffent, however, eliminates such a damping chamber or reservoir. Rather, all gas 17 of the volume in the compliance chamber is prevented from leaving that compliance chamber 16 due to displacement by the operating piston 15. In other words, the compliance chamber is sealed as seen also at 29 against any gas 17 leaving that compliance chamber 16 due to displacement of such gas by the operating piston 15.

a 1 As indicated at 23, gas may be admitted to the compli 2 ance chamber 16 via a port 24 and may be removed from such 3 chamber for leveling purposes, as indicated by a dotted arrow 4 25. A muffler (not shown) may be associated with the port 24.

Acoustical damping may be effected inside the compliance 6 chamber 16. In this manner, isolation of the mass 12 from low 7 er level acoustic wave propagation may be achieved. The com 8 pliance chamber may be lined with acoustic damping material 26.

9 Acoustical damping may be effected inside the pressure barrier 18, which may be lined with acoustic material 28 for that purpose.

11 By fitting the pressure barrier 18 as close to the 12 piston 15 as practical g, this einient insures that 13 maximum amounts of gas 20 will pass through the orifices 21 14 for each piston movement, for greatest efficiency and efficacy of the isolator. The pressure barrier 18 is fitted as closely 16 to the piston 15 as permitted by operating piston travel.

17 As in state-of-the-art equipment, the piston 15 may 18 be sealed relative to the compliance chamber 16 by a diaphragm 19 seal 31. Within this embodiment, the pressure barrier 18 is fitted as closely to the piston 15 as permitted by 21 operation of that diaphragm seal and operating piston travel.

22 one or more cushioned mechanical stops 32 may be positioned 23 between the load support plate 35 and the top of the piston 24 to limit"the vertical motion of the piston. According to the illustrated embodiment, the stop is in the 26 form of a mechanical stop ring 32 which extends around the 27 inner edge of a stop plate 33 between a conically contoured 28 centering guide 46 and the top of piston 15 to limit the 29 vertical and the horizontal motion of the operating piston.

The piston 15 is advantageously fitted with a pendulum 31 isolation system to isolate horizontal components of vibration.

32 Such pendulum isolation system 36 may be of a type shown 33 in the above mentioned U.S. Patent 3,784,146 and NEWPORT 34 CATALOG, pp. A-5 and A-22 and showing the top piston plate 44, internal plate 62 with rod 74 and suspension cables 36 84. The piston 15 may also be provided with damping oil 37 37 at least about plate 62.

1 1 1 A 1 2 3 4 5 6 7 8 9 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 7 - If a horizontal vibration isolation system is used, such as at 36, the pressure barrier 18 is fitted as closely to the piston 15 as permitted by such horizontal vibration isolation and needed operating piston travel.

In the illustrated preferred embodiment,the piston is fitted with a pendulum isolation system 36 to isolate horizontal components of vibration, and that piston 15 is sealed relative to the compliance chamber 16 by a rolling diaphragm seal 31. The pressure barrier 18 is fitted as closely to the piston 15 as permitted by operation of the rolling diaphragm seal, horizontal vibration isolation and other needed operating piston travel.

As illustrated in the upper portions of Figs. 1 and 2, the isolator automatically centers the operating piston 15 prior to each inflation of the compliance chamber with compressed gas 17 or during deflation of that compliance chamber, such as through the port 24. Means for effecting such automatic centering may comprise the illustrated contoured centering guide 46 on the operating piston 15 or on the top plate 44 thereof. That contoured centering guide has a slanted conical area 48 which contacts the stop 32, when the piston 15 settles downwardly as the vibration isolator 10 or 100 is deflated or decompressed by letting the compressed gas 17 flow out of the compliance chamber 16, such as through por-t 24 as indicated by the dotted arrow 25. Portions of this slanted area 48 slide along the upper corner of stop 32, until the deflating piston 15 is centered within the lateral confines of the pressure barrier 18 and rolling diaphragm 31 or other seal.

Accordingly, if the isolator 10 or 100 or compliance chamber is reinflated, such as by compression of gas 17 as indicated by the arrow 23 through the port 24, the piston 15 already is in a centered condition, which prevents faulty operation, especially if three or more isolators 10 or 100 are involved as legs of a table or other mass 12.

A 1 2 3 4 5 6 7 8 9 10 11 12 13 14 is 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 Thanks to the contoured centering guide 4 6, or other automatic centering, the Dressure barrier 18 can can be fitted closer -to the piston 15 and seal 31, inasmuch as such automatic centering prevents the piston 15 from contacting any side of the pressure barrier by canting or otherwise, when the compliance chamber is reinflated or recompressed.

- The Contoured cehtering guide 46 or other automatic centering also enhances the utility of the horizontal vibration isolation suspension 36, inasmuch as such suspension then always starts its operation from a centered condition when the compliance chamber 16 is reinflated or recompressed.

Within the scope of another- aspect of the invention, the piston 15 may be centered by fitting into a tapered stop in a design constituting the opposite of the design shown at 32 and 48. Such a centering guide within that scope could be fixed to the isolator body, with the descending position then centering itself at that fixed centering guide.

The contoured centering guide 46 or other automatic centering system has utility apart from the pressure barrier 18. In practice, such centering even has utility beyond a horizontal vibration isolation suspension 36, since such automatic centering is also beneficial to the operation of the prior-art pneumatic vibration isolator system in which an external damping-chamber was connected to the spring or compliance chamber through an orifice, as shown, for instance, in the above mentioned NEWPORT CATALOG and-in the above mentioned CIRP Paper.

The same applies to the additional feature shown in Fig. 2, even though it is shown therein in the context of both a pressure barrier 18 and a horizontal vibration isolation suspension 36.

In particular, that additional feature disclosed in Fig. 2 at 51, senses the distance of the piston 15 to the pressure barrier 18, and adjusts such distance by adjusting the pressure of the compressed gas 17.

2 ú 4 2 3 4 5 6 7 8 9 10 11 12 13 14 is 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 Fig. 2 in particular shows a valve 52 coupled to the compliance chamber, such as by a compressed gas line 53 through the port 24 for adjusting the pressure of the-compressed gas 17. Fig. 2 also shows an actuator 54 for that valve 52 including a linkage 55 extending from the piston is to the valve 52 in a direction of operating piston travel. In Fig. 2, such piston travel direction is vertical as shown. However, horizontal or other arrangements are also within the scope of the invention.

Accordingly to the embodiment illustrated in Fig. 2, the rod or linkage 55 is attached to the bottom of the piston 15 by a ball joint or swivel connection 56. The lower end of that rod is attached to a second or secondary piston 57 which is also sealed to the compliance chamber 16 by a rolling diaphragm seal 58, but which is much smaller in cross section and otherwise than the first or primary piston 15. The linkage also includes a second ball joint or swivel connection 59 associated with the secondary piston 57.

A barrier tube 61 encloses the connecting rod 55 between the pressure barrier 18 and secondary piston 57, and seals the compliance chamber volume 17 between the top and bottom of the compliance chamber 16.

The linkage 55 or secondary piston 57 thus actson the valve actuator 54 and thereby on the valve 52. By way of example, the valve 52 may be a spool type valve which connects the compliance chamber port 24 alternatively to a gas exhaust line 63, as indicated by a symbolic solid line 64, and to a gas supply line 65, as indicated by a symbolic dotted line 66. Spool type valves and their construction are well known per se. If linkage 55 and secondary piston 57 indicate that the piston 15 is too high for a given application, then the valve 52 1 ' ets gas 17 escape from the compliance chamber 16, as indicated by the arrow 67 in Fig. 2.

a c i Conversely, if such linkage and secondary piston indicate that the primary piston 15 is too low or too close to the pressure barrier 18, then the valve 52, as indicated by the arrow 68, admits compressed gas via port 24 to the compliance chamber 16, whereby the operating-piston 15 is adjusted upwardly as seen in Fig. 2. Adjustment of the height of the primary piston 15 or isolation system 100 is accomplished by adjusting the relative position of the spool to the valve ports in the valve 52, as indicated by the double arrow 69 in Fig. 2. The housing of the valve 52 may be vertically adjustable for that purpose.

The location of the valve 52 in direct line with the motion of the piston 15 ensures a minimum crosstalk in the feedback of the leveling control exerted by the valve 52 and its adjustment 69.

The subject extensive disclosure will render apparent or suggest to those skilled in the art various modifications and variations within the spirit and scope of the subject invention and equivalents thereof.

2 3 4 5 6 7 8 9 10 11 12 13 14 is 16 17 18 19 1

Claims

Claims: -

1. A DnexL-,.a-lic vibration isolator (10, 100) wherein an operating piston (15) is disola3eable by vibrations relative to a compliance chamber (16) containing compressed gas (17) of a volume nredetermined in terms of natural vibration isolation frequency, there being a pres.sure barrier (18) in said compliance chamber (16) permeable to gas (20) displaced by the operating piston and -closely fitting that operating piston (15) to eliminate the need for an external damping chamber.

2. An isolator as claimed in claim 1, includinc:

r-neans (29) for sealing said compliance chamber (16) any gas (17) of said volume leaving said cc.-.,=)1-4ance chamber due to displace.ment by said operating pist= (15).

3. An isolator as claimed in claim 1 or 2, includinc: means (21) for imparting laminar flow (19) to gas (20) d-i--=)laced by the operating piston (15) through the pressure barrier (18) in the compliance chamber (16).

4..','n isolator as in claim 1, 2 or 3, includinip:

5. claims, including:

acoustic damping material (26) inside the compliance chaz-aber (16).

An isolator as claimed in any of the preceding acoustic damping material (28) inside the pressure barrier (18).

k

6. claims, wherein:

7.. including:

An isolator as claimed in any of the preceding said pressure barrier (18) is as close to the piston (15) as permitted by operating piston travel.

An isolator as claimed in claim 6,- means (36) coupled to said piston (15) for isolating horizontal components of vibration, the pressure barrier (18) being as close to the piston (15) as permitted by horizontal components of vibration isolation and operating piston travel.

8. An isolator as claimed in any one of the preceeding claims wherein said Diston has a diaphragm seal (31).

9. An isolator as claimed in claim 8, ein said pressure barrier (18) is as-close to sald.piston (15) as permitted by operation of that diaphragm, seal and operating piston travel.

-

10. An isolator as claimed in any of the preceding claims, including: means (32,46) for automatically centering the operating piston (15) prior to each inflation of the compliance chamber (16) with compressed gas (17).

11. An isolator as claimed in claim 10, including:

a contoured centering guide (46) on the operating piston (15).

1 1 1 A

12. claims, including:

An isolator as claimed in any of the preceding means (51, Fig. 2) for sensing the distance of the piston (15) to the pressure barrier (18); and valve means (52) coupled to these sensing means for adjusting the pressure of the compressed gas (17).

13. An isolator as claimed in claim 12 including: an actuator (54) for said valve means (52) including a linkage (55) extending from the piston (15) to said valve means in a direction of operating piston travel.

14. A pneurratic vibration isolaor (10, 100) comprising a co.-mliance chamber, means (24) for supplying said chamber with compressed gas (17), and an operating piston displaceable by vibrations relative to said chalTber, the chr containing a pressure barrier (18) perpeable to gas displaced by the piston in use.

15. A pnei-rre-Lic'vibration isolator (10,100) comprising a carmliance chamber, means (24) fror supplying said chamber with compressed gas (17), and an operating piston displaceable by vibrations relative to said chr, there being rreans (32,46) for automatically centering the operating Diston (15) prior to each inflation of the compliance chamber (16) with compressed gas (17).

16. A pnewn--tic vibration isolator (10, 100) con-prising a compliance chamber, means (24) for supplying said chamber with corrpressedgas- (17), and an operating piston displaceable by vibrations relative to said chamber, there being means (51) for sensing the piston position and valve means (52) coupled to these sensing means for adjusting the pressure of the compressed gas (17).

17. An isollia-tor substantially as hereinbefore described with reference to the accompanying drawings.

Published 1991 at Ile Patent Office. State House. 66171 High Holborn, UndonWC1 R 41P. Further copies rnay be obtained from Sales Branch. Unit 6, Nine Mile Point Cvjrnfehnfach. Cross Keys. Newport. NPI 7HZ. Printed by Multiplex techniques ltd, St Mary Cray. Kent.