PNEUMATIC ACTUATOR AND METHOD FOR OPERATING AN ACTIVE VIBRATION ISOLATION SYSTEM

Abstract

A pneumatic actuator configured for a stationary vibration isolation system which serves to accommodate equipment for processing semiconductor devices. The pneumatic actuator comprises a working space with a piston which divides the working space into a first and a second pressure chamber, and the piston is spaced apart from an inner surface of the working space by a gap, and the piston is movable only in an axial direction.

Claims

1. A pneumatic actuator for a stationary vibration isolation system, comprising a working space with a piston that divides the working space into a first pressure chamber and a second pressure chamber, wherein the piston is spaced apart from the inner surface of the working space by a gap, wherein the piston is movable only in an axial direction.

2. The pneumatic actuator as claimed in claim 1, wherein the piston is guided axially by at least two leaf springs that are spaced apart from each other.

3. The pneumatic actuator as claimed in claim 2, wherein one leaf spring is arranged in the first pressure chamber and a further leaf spring is arranged in the second pressure chamber.

4. The pneumatic actuator as claimed in claim 1, wherein the first and second pressure chambers are each sealed by a membrane.

5. The pneumatic actuator as claimed in claim 4, wherein the membrane spans the piston.

6. The pneumatic actuator as claimed in claim 2, wherein the piston is connected to the leaf springs through a respective spacer protruding into the pressure chamber.

7. The pneumatic actuator as claimed in claim 1, wherein the piston has at least one extension protruding out of a lateral wall of the working space.

8. The pneumatic actuator as claimed in claim 1, wherein the piston has a plurality of laterally projecting extensions.

9. The pneumatic actuator as claimed in claim 1, wherein the pneumatic actuator comprises means for adding an isolation transversely to the axial direction.

10. The pneumatic actuator as claimed in claim 9, wherein the piston is connected to a load to be isolated or to a base via at least one bending rod, a bending pendulum, a cable, or a wire.

11. The pneumatic actuator as claimed in claim 9, wherein the means for adding an isolation transversely to the axial direction are arranged outside the working space.

12. The pneumatic actuator as claimed in claim 10, wherein the piston is connected to the load to be isolated or to a base through a plurality of bending rods, bending pendulums, cables, or wires distributed around the circumference of the piston.

13. An isolator for a vibration isolation system, comprising at least two pneumatic actuators according to claim 1, wherein the at least two pneumatic actuators are effective in different directions.

14. An active vibration isolation system, comprising isolators with pneumatic actuators according to claim 13.

15. A method for operating an active vibration isolation system, comprising: pneumatic actuators which are effective in at least one direction are driven by a control device which is connected to a valve for controlling the pressure in a working space of the pneumatic actuator; wherein the force exerted by the pneumatic actuators or the pressure in pressure chambers of the pneumatic actuators is measured; and wherein the control device controls the pneumatic actuators taking into account the non-linear characteristic of the fluid in the pressure chambers.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0063] The subject matter of the invention will now be described in more detail by way of a schematically illustrated exemplary embodiment and with reference to the drawings of FIGS. 1 to 8.

[0064] FIG. 1 shows a schematic sectional view of an exemplary embodiment of a pneumatic actuator according to the invention.

[0065] FIG. 2 is an elevational side view of the actuator, now illustrating additional means for providing an isolation transversely to the direction of action thereof.

[0066] FIG. 3 is a schematic diagram of a vibration isolation system with isolators comprising actuators according to the invention.

[0067] FIG. 4 shows a sectional view of an exemplary embodiment of an actuator according to the invention.

[0068] FIGS. 5 and 6 are exploded views of the actuator.

[0069] FIG. 7 is a perspective view of the actuator with bending rods already mounted thereto.

[0070] FIG. 8 is a perspective view of an isolator according to the invention with the actuator of FIGS. 4 to 7 installed therein.

DETAILED DESCRIPTION

[0071] FIG. 1 is a schematic sectional view of an exemplary embodiment of an actuator 1 according to the invention.

[0072] Pneumatic actuator 1 comprises a housing 2 enclosing a working space 3 in which a piston 5 is able to move. The working space defines a working volume into which compressed air can be directed.

[0073] Working space 3 is divided, by piston 5, into a first pressure chamber 4a and a second pressure chamber 4b.

[0074] Pressure chamber 4a comprises pneumatic port 13a, and pressure chamber 4b comprises pneumatic port 13b.

[0075] Compressed air can be introduced into the otherwise sealed pressure chambers 4a and 4b via ports 13a and 13b.

[0076] In this manner, a force can be produced in the axial direction, that is a force along axis 24, by means of piston 5.

[0077] In contrast to known pneumatic cylinders, a gap 6 is provided between the inner surface 7 of the housing 2 of working space 3 and the piston 5, and as a result thereof no friction forces will arise during a movement of the piston 5. Gap 6 has a width of at least 0.1 mm, preferably at least 0.5 mm, and most preferably at least 1 mm.

[0078] For sealing the pressure chambers 4a and 4b so as to prevent fluid from escaping through gap 6, a respective elastic membrane 12a, 12b is provided spanning at least the gap 6.

[0079] In the present exemplary embodiment, the membrane 12a, 12b spans the entire piston 5 while being connected to the piston 5 at the same time.

[0080] Furthermore, the membrane 12a, 12b is clamped along its edge in the lateral wall 25 of housing 2.

[0081] For guiding the piston 5 in the axial direction, a respective leaf spring 9a, 9b is provided in both the pressure chamber 4a and pressure chamber 4b and is connected to the piston 5 via a respective spacer 10a and 10b.

[0082] Leaf springs 9a and 9b are also fastened to the lateral wall 25 of working space 3, in particular clamped in lateral wall 25.

[0083] Preferably, the leaf springs 9a, 9b are fastened within pressure chambers 4a and 4b, respectively, in order to avoid otherwise necessary sealing means.

[0084] Leaf springs 9a and 9b extend perpendicularly to the axis 24 and may in particular be configured as a leaf spring having an inner ring and an outer ring.

[0085] Spacers 10a, 10b are respectively secured on either side of the piston 5, and in the present exemplary embodiment they additionally serve to fasten the membrane 12a, 12b to the piston 5.

[0086] In the present exemplary embodiment, the pneumatic actuator has an essentially rotationally symmetric shape with respect to the axis 24 which extends centrally through the pneumatic actuator 1 in the direction of action thereof.

[0087] Furthermore, the first and second pressure chambers 4a, 4b with leaf springs 9a, 9b and membranes 12a, 12b are substantially configured identically. Leaf springs 9a and 9b are installed in mirror-symmetric manner in terms of their shape and function.

[0088] The lateral wall 25 of housing 2 has an opening 11 from which an extension 8 is protruding perpendicularly to the axis 24.

[0089] It will be understood that the extension 8 has sufficient clearance within the opening 11 so that it will not engage on lateral wall 25 during operation of the pneumatic actuator 1.

[0090] In the present exemplary embodiment, extension 8 is configured as a circumferential ring. The extension 8 may have openings, with components extending therethrough, by means of which the two halves of the housing 2 are coupled (not shown).

[0091] Extension 8 serves to couple the piston 5 to the base or to the load to be isolated.

[0092] It will be understood that instead of a circumferential ring it is likewise possible that a plurality of extensions (not shown) are provided distributed around the circumference of the pneumatic actuator 1.

[0093] FIG. 2 is a schematic elevational side view of pneumatic actuator 1, and this view moreover shows the components which couple the piston 5 to the load 15 to be isolated (or to the base).

[0094] In this exemplary embodiment, three bending rods 14a to 14c on extension 8 are distributed uniformly around the circumference of extension 8 and are connected to the load 15 to be isolated.

[0095] Bending rods 14a to 14c provide isolation transversely to the effective axis of the pneumatic actuator 1.

[0096] Bending rods 14a to 14c exhibit high stiffness in the direction of action (axis 24 in FIG. 1), but yield to a force acting transversely thereto, thus decoupling the base and the load to be isolated transversely to the direction of action of the pneumatic actuator 1.

[0097] FIG. 3 is a schematic view of a vibration isolation system 16.

[0098] Vibration isolation system 16 comprises a table 17 mounted for vibration isolation, on which in particular lithography and metrology systems for processing semiconductor devices (not shown) can be arranged.

[0099] Table 17 rests on a plurality of isolators 18 which are coupled to the floor 19.

[0100] Isolators 18 can be configured as pneumatic or mechanical springs.

[0101] Isolators 18 comprise at least two of the pneumatic actuators 1 described above, one actuator that is effective in the horizontal spatial direction and one actuator that is effective in the vertical spatial direction.

[0102] It will be appreciated that the vibration isolation system may comprise further actuators, in particular magnetic actuators based on the voice coil principle.

[0103] In the present exemplary embodiment, seismic vibrations are detected by sensor 20, and vibrations of the load to be isolated, that is the table 17 with the assemblies arranged thereon, are detected by sensor 21.

[0104] A control device 22 generates compensation signals on the basis of the signals from sensors 21 and 20, thereby controlling valves 23 through which the pressure in the pressure chambers of the pneumatic actuators 1 is adjusted.

[0105] It goes without saying that a respective valve will be provided for each port of a pressure chamber, although only one respective valve 23 is schematically illustrated in this exemplary embodiment.

[0106] In order to take account of the fact that air is compressible, the actuators 1 may be controlled via a feed-forward control on the basis of the pressure in the pressure chambers or on the basis of a force measured by means of a sensor (not illustrated).

[0107] An exemplary embodiment of an actuator according to the invention will now be explained in more detail with reference to FIGS. 4 to 7.

[0108] FIG. 4 is a perspective cutaway view of a pneumatic actuator 1.

[0109] In this exemplary embodiment, the piston consists of the three parts 5a to 5c.

[0110] In this exemplary embodiment, again, the piston consisting of parts 5a to 5c divides the working space into two pressure chambers 4a, 4b.

[0111] Spacer 10a clamps the leaf spring 9a and the membrane 12a to the piston.

[0112] It goes without saying that the lower pressure chamber arranged in mirror symmetry thereto is configured similarly.

[0113] FIG. 5 is an exploded view of the actuator illustrated in FIG. 4.

[0114] The two parts of the housing (2 in FIG. 4) are now separated from each other and the piston 5 can be seen, consisting of three parts (5a to 5c in FIG. 4).

[0115] It can be seen that the piston 5 has three extensions 8a to 8c which protrude laterally outwards and which are distributed around the circumference of the piston 5 with a respective spacing of 120° in this exemplary embodiment.

[0116] FIG. 6 is a further exploded view in which the upper housing part and the piston are omitted.

[0117] Here, especially the spacer 10b can be seen, which is used to attach the leaf spring 9b and the membrane 12b to the piston.

[0118] Leaf spring 9b is substantially circular in shape and comprises an inner ring and an outer ring.

[0119] FIG. 7 shows the previously illustrated actuator 1, and now 3 respective bending bars 14a to 14c are mounted on either side, which serve to provide isolation perpendicularly to the direction of action of actuator 1.

[0120] It can be seen that the extension 8b protrudes laterally out of housing 2 of the actuator.

[0121] The extensions for bending rods 14a and 14c are located inside the housing. Accordingly, two bores are provided in the housing for extending the bending rods 14a and 14c therethrough.

[0122] FIG. 8 is a perspective view of an isolator 18 in which the actuator 1 illustrated in FIGS. 4 to 7 is installed for active vibration isolation.

[0123] The actuator 1 illustrated herein is used to generate compensation forces in the horizontal direction.

[0124] Isolator 18 comprises a housing 28 accommodating a spring that is preferably effective in both the vertical and the horizontal directions, for isolation purposes. The spring is preferably configured as a pneumatic spring (not shown).

[0125] The housing 28 is connected to a base part 26 which provides the connection to the ground.

[0126] The upper part 27 is supported in vibration isolated manner on the spring and is used for coupling to the load to be isolated.

[0127] The actuator 1 is mounted to the housing 28.

[0128] The upper part 27 has brackets 29 to which the bending rods 14a to 14b are mounted.

[0129] The bending rods 14a to 14c couple the upper part, that is the vibration isolated load, to the actuator 1.

[0130] In particular bending rods 14b which are connected to extension 8b are visible here.

[0131] Bending rods 14a to 14c are preloaded by means of screws 30.

[0132] During operation of the actuator, the bending rods 14a to 14c are only loaded by tension and decouple the actuator 1 in the vertical direction from the load that is supported in vibration isolated manner.

[0133] It will be understood that the isolator 18 preferably additionally comprises a further actuator 1 which is effective in the vertical direction (not visible).

[0134] The invention permits to provide a compact actuator which is capable of generating high forces and which is in particular suitable for replacing a magnetic actuator.

LIST OF REFERENCE NUMERALS

[0135] 1 Pneumatic actuator

[0136] 2 Housing

[0137] 3 Working space

[0138] 4a, 4b Pressure chamber

[0139] 5 Piston

[0140] 5a-5c Part

[0141] 6 Gap

[0142] 7 Inner surface

[0143] 8, 8a-8c Extension

[0144] 9a, 9b Leaf spring

[0145] 10a, 10b spacer

[0146] 11 Opening

[0147] 12a, 12b Membrane

[0148] 13a, 13b Port

[0149] 14a-14c Bending rod

[0150] 15 Load

[0151] 16 Vibration isolation system

[0152] 17 Table

[0153] 18 Isolator

[0154] 19 Floor

[0155] 20 Sensor

[0156] 21 Sensor

[0157] 22 Control device

[0158] 23 Valve

[0159] 24 Axis

[0160] 25 Lateral wall

[0161] 26 Base

[0162] 27 Upper part

[0163] 28 Housing

[0164] 29 Bracket

[0165] 30 Screw