NL2034497B1

NL2034497B1 - Vacuum coupling with integrated vibration insulator.

Info

Publication number: NL2034497B1
Application number: NL2034497A
Authority: NL
Inventors: Kluijtmans Ton; Van Der Mast Karel
Original assignee: Phe Nx Knowledge B V
Priority date: 2023-04-04
Filing date: 2023-04-04
Publication date: 2024-03-05

Abstract

Vacuum pumps, such as Turbo Molecular Pumps (TMP), are used to evacuate vacuum apparatuses, such as electron microscopes. A problem is that many pumps introduce vibrations. Such vibrations have a negative impact on, for example, the image quality of an electron microscope. European Patent Application EP1580477A1 addresses this problem. |t describes a corrugated bellow with flanges at each end, one flange to be connected to, for example, a TMP using an O-ring or a copper ring (Conflat® flange), the other flange likewise to be connected to, for example, an electron microscope. An elastomeric body at the outside of the bellow keeps the flanges at a constant distance from each other and fills the outside of the grooves of the bellow to absorb energy. A drawback of EP1580477A1 is that corrugated bellows are quite expensive, resulting in high Cost of Goods and is rather lumpy. The invention offers an improved solution. A vacuum coupling according to the invention comprises: o A central body (102, 402) with an evacuable cavity (104) connecting to a vacuum port (106), the central body showing a first perforation (108) and a second perforation (110) opposing each other and in contact with the cavity, each perforation surrounded by a flange (120, 122), o Two elastomeric sealings (116, 118), each sealing forming a sealing on a flange, 0 One or more spacers (124, 430) keeping the flanges (120, 122) at a constant distance from each other such, that the elastomeric sealings are slightly compressed, thereby forming vacuum tight sealings, 0 one flange (122) equipped to mount the vacuum pump thereby forming a pump port (126), the pump port in vacuum contact with a vacuum port (106) for connecting to an electron microscope.

Description

Vacuum coupling with integrated vibration insulator.

Technical field of the invention.

[0001] The invention relates to a vacuum coupling with integrated vibration insulator for use with a vacuum apparatus and a vacuum pump.

Background of the invention.

[0002] Vacuum pumps, such as Turbo Molecular Pumps (TMP), are used to evacuate vacuum apparatuses, such as electron microscopes. A problem is that many pumps introduce vibrations. Such vibrations have a negative impact on, for example, the image quality of an electron microscope. Therefore, there is a need for vibration insulators that reduce the vibrations transferred to the vacuum apparatus.

[0003] European Patent Application EP1988320A2 describes such a vacuum coupling with integrated vibration insulator. It describes a corrugated bellow with a flange at each end, one flange to be connected to, for example, a TMP using an

O-ring or a copper ring (Conflat® flange), the other flange likewise to be connected to, for example, an electron microscope. For further reduction of the vibration elastomeric rings (O-rings) are placed in the outside grooves of the bellow to absorb energy.

[0004] An improved solution is described in European Patent Application

EP1580477A1. It describes a corrugated bellow with flanges at each end, one flange to be connected to, for example, a TMP using an O-ring or a copper ring (Conflat® flange), the other flange likewise to be connected to, for example, an electron microscope. An elastomeric body at the outside of the bellow keeps the flanges at a constant distance from each other and fills the outside of the grooves of the bellow to absorb energy.

[0005] A drawback of both applications is that corrugated bellows are quite expensive, resulting in high Cost of Goods.

Also, the length of the vibration insulator, typically much more than the diameter of the flange, results in a much increased length of the assembly of pump and vibration insulator, as well as an increased length from the pump to the rest of the vacuum apparatus, resulting in lower pump conductance.

[0006] A further drawback of the EP1580477A1 is that the outer diameter is even larger than the diameter of the flanges due to the elastomeric body, resulting in a bulky object.

Also, the weight of the vibration insulator or more specifically the vacuum coupling is quite high: as an example of an insulator using EP1580477A1, sold by Pfeiffer with order number PM 016 600 -U, with a flange diameter of 100 mm (DN100ISO) weights 10.3 kg.

[0007] The invention intends to provide a low-cost solution with reduced size and weight.

Summary of the invention.

To that end the vacuum coupling comprises: e A central body with a cavity, the cavity in working evacuated, the cavity connecting to a vacuum port, the vacuum port for connecting to the vacuum apparatus, the central body showing a first perforation and a second perforation, the two perforations opposing each other and in contact with the cavity, each perforation surrounded by a smooth area for forming a vacuum sealing,

Two elastomeric sealings, each sealing on the smooth area of a corresponding perforations, each forming a sealing on one of the smooth areas, e Two flanges, each flange sealing on one of the elastomeric sealings, e One or more spacers keeping the flanges at a constant distance from each other such, that the elastomeric sealings are slightly compressed, thereby forming vacuum tight sealings, e one flange equipped to mount the vacuum pump thereby forming a pump port, the pump port in vacuum contact with the vacuum port.

[0008] The central body, for example a hollow box, has two perforations at opposite sides. Through the perforations one or more spacers are placed, keeping the flanges at a constant distance such, that, together with the elastomeric sealings, vacuum tight sealings are formed on the smooth surfaces. The force on the perforations is not large, even when the pump port has a large diameter, as the flanges are kept at a constant distance by the one or more spacers, thereby cancelling the vacuum force of the pump port with the force of the opposing (sealed) port. Therefore, the vibrations, causing movements with a small deflection, result in small forces on the central body (and the vacuum apparatus attached to it) and thus strongly reduced vibrations.

It is noted that TMP’s are known to rotate with 90.000 rpm (although other rotation speeds are known to be used), thus introducing vibrations with a frequency of 1500 Hz plus harmonics. it is also noted that normal O-ring sealings compress the O-ring typically until the two metal parts meet, thereby transferring much larger forces.

[0009] In an embodiment the smooth surfaces are flat surfaces.

[0010] The use of flat, smooth surfaces around the perforations enables the use of standard O-rings and O-ring flanges.

[0011] In another embodiment the two smooth surfaces are two annul.

[0012] Sealing on an annulus is common practice when sealing with an elastomer, such as an X-ring, an O-ring, a C-rings, or an annulus of flat (vacuum compatible) elastomeric material.

[0013] In yet another embodiment the one or more spacers take the form of a hollow tube, the tube after assembly connecting to the two flanges, the tube showing a penetration in its wall contacting the tube showing a penetration in its wall in contact with the cavity is, thereby in working connecting the pump port to the vacuum port.

[0014] Here the spacer is placed in the cavity of the central body. A penetration of the wall of the tube connects the pump port to the vacuum port. The placing of the tube in the cavity implies that at least one flange must be connected to the tube after that the tube is inserted in the cavity.

[0015] In yet another embodiment one or more spacers take the form of several pillars.

[0016] Instead of a hollow cylinder, as mentioned before, the spacers take the form of pillars. The pillars can be (partly) threaded to simplify mounting them.

[0017] In yet another embodiment the one or more spacers take the form of one or more plates,

[0018] Instead of a hollow cylinder or pillars, as mentioned before, the spacers take the form of plates.

[0019] In yet another embodiment the one or more spacers (124) surround the central body.

[0020] Instead of placing the spacer inside the central body the spacer can also be formed to surround the central body.

[0021] In yet another embodiment the elastomeric sealings are sealings from the group of X-rings, O-rings, C-rings, or annuli of flat elastomeric material.

[0022] It is well-known to use elastomers, such as Viton®, in the form of X-rings,

O-rings, C-rings, or annuli of a flat elastomeric material.

[0023] In yet another embodiment the two elastomeric sealings have slightly different diameters to compensate for the weight of the vacuum pump.

[0024] When the weight of the vacuum pump results in a different compression of the elastomeric sealings, the diameter of the two sealings can be varied to compensate for the weight.

[0025] In yet another embodiment the two elastomeric sealings are each formed as two concentric elastomeric sealings, and the area between each of the two elastomeric sealings is in working connected to a vacuum pump.

[0026] In “Vacuum Technology, Practice for Scientific Instruments”, Yoshimura,

N., 2008, ISBN: 978-3-540-74432-0, at page 148 it is mentioned that (per)fluoroelastomer O-rings are used as sealings in the high-vacuum system of an electron microscope. Water vapor molecules from the atmosphere permeate through the elastomer O-rings, and as a result, water molecules become the main residual gas in high vacuum systems using elastomer sealings.

This book then proceeds at page 150 to mention that a solution to this problem was formulated in 1967 by L. de Csernatony and D. J. Crawley. The solution involves the use of 2 concentric O-rings, the volume between the O-rings evacuated to a pressure of, for example, 10 mbar. As the gas between the O- rings is pumped away, water is pumped away with it, resulting in a lower partial 5 water pressure of the remaining gas. Due to the lower partial water pressure in the intermediate volume less water permeates through the O-ring to the high vacuum.

[0027] By executing each of the two elastomeric sealings as two concentric sealings and pumping the space between the sealings with a pump, the leakage over the inner sealing is minimal. Each of the sealings are, for example, O-rings and the space between the O-rings is, for example, connected to a pre-vacuum pump. It is noted that typically a pump system is a series connection of a pre- vacuum pump (for example a rotary pump or a diaphragm pump) and a main vacuum pump (for example a Turbo Molecular Pump) and that the pre-vacuum pump may also be used as pre-vacuum pump for the main vacuum pump

[0028] In yet another embodiment the two elastomeric sealings are each formed as two concentric elastomeric sealings, and the area between each of the two elastomeric sealings is filled with a dry gas.

[0029] As described in US patent application US2013313783A1 the use of a dry gas, such as dry nitrogen, ensures that the partial water vapor pressure is much reduced, and thus the permeation of water through the O-rings as well. By filling the volume between the two concentric sealings with a dry gas, such as with dry nitrogen will thus lower the permeation of water through the O-rings.

[0030] In yet another embodiment the flange opposing the pump port is a blind flange.

[0031] Although many utensils such as vacuum sensors and/or indicators may be used, a blind flange is most appropriate.

[0032] In an aspect a vacuum apparatus is equipped with a vacuum coupling according to the invention, the vacuum apparatus further equipped with a vacuum pump.

[0033] In a further aspect the vacuum pump is a Turbo Molecular Pump.

[0034] If a high vacuum, for example better than 1x10 Pa, is needed, often a

Turbo Molecular Pump (TMP) is used.

[0035] In another aspect the vacuum apparatus is a vacuum apparatus from the group of scanning electron microscopes, transmission electron microscopes, scanning transmission electron microscopes, electron microprobes, ion microscopes or ion microprobes.

[0036] These apparatuses are prone to interference by vibrations, and typically need a high vacuum of better than 10-8 Pa, and are thus often equipped with a

TMP.

Detailed description of the invention.

[0037] The invention is now elucidated using figures, in which identical reference signs indicate corresponding features. To that end:

Figure 1 schematically shows a cross-section of a vacuum coupling with integrated vibration insulator,

Figure 2 schematically shows a cross-section of a vacuum coupling with integrated vibration insulator.in which the one or more spacers surround the central body.

Figure 3 schematically shows a cross-section of a sealing using two concentric O- rings for low leakage.

Figure 4 schematically shows another cross-section of a vacuum coupling with integrated vibration insulator.

Detailed description of the invention.

Figure 1 schematically shows a cross-section of a vacuum coupling with integrated vibration insulator.

[0038]A central body 102 with a cavity 104 shows a vacuum port 106 to which a vacuum apparatus can be coupled. The port 106 can be a so-called ISO-KF (preferably mounted via a tube to the central body), a Conflat® flange, or another type of vacuum coupling, even oval, square or any other form. The central body,

for example a box-like body, has two perforations 108, 110 at opposite sides of the central body. These perforations are typically round perforations, although also other forms can be used. The perforations are surrounded with smooth, and preferably round and flat, areas 112, 114 that are used to form a sealing surface.

On the two smooth surfaces two elastomeric sealings, for example O-rings, are placed. Two flanges 120, 122 are also in contact with the elastomeric sealings 116, 118. Thereby the smooth surfaces 112,114, the elastomeric sealings 116, 118 and the flanges 120, 122 form two vacuum sealings.

[0039] It is noted that the flange can form a sealing to the inner diameter of the elastomer (O-ring), or to the side opposite to the smooth surface, as long as a vacuum sealing is formed.

[0040] Typically for a vacuum sealing the elastomer is compressed with a large force, and the smooth surface and the flange are in contact with each other. In this case that would imply that vibrations from the flange are transferred via the central body 102 and vacuum port 106 to the vacuum apparatus.

[0041] The invention is based on the insight that typically elastomeric sealings are highly compressed to limit the leakage over the sealing. However, this implies a high stiffness of the sealing, resulting in a limited vibration insulation. By reducing the stiffness while keeping the leakage over the sealings low, the vibration insulation is improved. This is achieved by choosing an elastomer with low hardness, and one or more spacers that limit the force with which the elastomer is loaded (resulting in a low stiffness and thus high vibration insulation) and sufficient force to have a reliable low leakage over the sealings.

[0042] Preferably the smooth areas (112, 114) are flat and circular areas.

[0043] Although not necessarily flat, flat areas are more easily machined.

[0044] Typically, a TMP has a circular pump opening. Therefore, it is most appropriate to form the pump port 106 as a circular opening as well so that the pump port 106 and the vacuum port of the vacuum pump match.

[0045] The one or more spacers can take the form of a cylinder with its wall perforated by one or more holes. The holes bring the vacuum port in contact with the pump port. Another solution is to use several pillars, for example several thread endings. Still another solution is the use of several plates. The skilled person can think up many solutions. These spacers can be inside the cavity of the central body. This typically implies that at least one of the flanges must be mounted in a surface that is in working exposed to vacuum.

[0046] Preferably the one or more spacers are adjustable so that the distance between the flanges 120 and 122 can be tuned for low stiffness and reliable vacuum performance.

[0047] Figure 2 schematically shows a cross-section of a vacuum coupling with integrated vibration insulator in which the one or more spacers surround the central body.

[0048]Figure 2 can be thought to be derived from figure 1. In this solution a spacer 202 surrounds the central body 102, and (blind) flange 120 is connected to the spacer with bolts 204A and 204B. Likewise flange 122 is connected to the spacer by bolt 206. Optional distance rings 208 between spacer 202 and flange 120 are used to tune the stiffness of the vibration insulator by increasing or decreasing the distance between spacer and flange.

[0049] Figure 3 schematically shows a cross-section of a sealing using two concentric O-rings for low leakage.

[0050] In this example a flange 306 is welded to the central body with a tube 308.

The tube shows rotational symmetry around axis 302. Two concentric O-rings 310 and 312 are placed between flanges 306 and 304, flange 304 taking the form of a blind flange {comparable to blind flange 120 shown in figures 1 and 2). Flange 304 is connected to a spacer 320 using bolt 322, while spacer ring 324 is used to tune the compression of the O-rings, as explained in the text accompanying figure 2.

[0051] The volume 314 is connected to a nipple 316 by a channel 318. Tubing (not shown) connects said nipple 316 to a dry gas reservoir or a pre-vacuum pump.

[0052]In a first embodiment the volume 314 is filled with a dry gas, such as dry nitrogen. Thereby the partial pressure of water in volume 314 is lowered, and thus the permeation of water through the O-rings as well. As described in US patent application US2013313783A1 this is typically the main reason for leakage through an O-ring. Tubing connects nipple 316 to a dry gas reservoir, preferably with a low overpressure of for example 10 mbar.

[0053] In a second embodiment the volume 314 is pumped by a pre-vacuum pump to a low pressure of, for example, 1 mbar. This lowers the partial pressure of water vapor and other gasses and lowers leakage through damages of the surface where the O-rings form a sealing (scratches etc). Tubing connects nipple 316 to the pre-vacuum pump.

[0054] It is noted that in the second embodiment the volume 314 is preferably pumped by a pre-vacuum pump that also acts as a pre-vacuum pump for the

TMP.

[0055] It is further noted that the O-rings 310 and 312 do not need to show rotational symmetry around axis 302, but can be eccentric or even, seen along axis 302, rectangular.

[0056] Flange 306 is connected to the central body 102 via a tube 308. The skilled artisan will recognize that likewise the smooth areas can be part of flanges mounted on tubes.

[0057] Figure 4 schematically shows another cross-section of a vacuum coupling with integrated vibration insulator.

[0058] The central body 402 takes the form of a manifold with three or more vacuum ports. A first vacuum port is formed by a first tube 404 and a fixed flange 406.

In this context “fixed” means that the flange is rigidly and vacuum tight connected to the tube, for example by welding.

A second vacuum port opposite to the first vacuum port is formed by a tube 408 and a fixed flange 410. A third vacuum port is formed by a tube 412 and a fixed flange 414.

A flange 416 forms a sealing with flange 406 using O-ring 418. Likewise flange 420 forms a sealing with flange 410 using O-ring 422. Flanges 416 and 420 are rigidly connected to perforated disks or strips 432 and 436, for example using welding spots. These disks or strips are also connected to a spacer in the form of a threaded end 430. The threaded end is connected to perforated disk or strip 432 by nuts 432A and 432B. Likewise the threaded end is connected to perforated disk or strip 436 by nuts 438A and 438B. Hereby the distance of flanges 416 and

420 is fixed and thus the force with which the O-rings 418 and 422 are compressed, resulting in the required stiffness, as earlier explained.

On flange 420 a blind flange 424 is mounted. An O-ring 426 is used to form a sealing between the blind flange 424 and flange 420. The O-ring 426 is highly compressed by bolts 428A and 428B to ensure low leakage. This

[0059] It is noted that the strips 432 and 436 can be flat strips or, for example, U strips, showing increased strength and stiffness.

[0060] It is mentioned that the O-rings 418 and 422 should have comparable diameters as otherwise one of them is compressed more than the other due to the difference surface area of the O-ring, resulting in different (atmospheric) forces.

[9061]It is further noted that the manifold can have 3, 4, 5 or more ports, but that two ports opposite to each other are used for the vibration insulation. The ports preferably have a similar diameter, and also a diameter similar to that of the vacuum pump.

Claims

Conclusions.

1. A vacuum coupling with integrated vibration isolator for use with a vacuum device and a vacuum pump, where the vacuum pump exhibits vibrations, the vacuum coupling consisting of: e A central body (102, 402) with a cavity (104), the cavity evacuated during work, the cavity connecting to a vacuum port (106), the vacuum port for connection to the vacuum device, the central body having a first perforation (108) and a second perforation (110), the two perforations opposite each other and in contact with the cavity, each perforation surrounded by a smooth area (112, 114) to form a vacuum seal, e Two elastomeric seals (116, 118, 422, 426), each seal forming a seal on the smooth area, e Two flanges (120, 122 , 416, 420), each flange seal on one of the elastomeric seals, e One or more spacers (124, 430) that keep the flanges a constant distance apart so that the elastomeric seals are slightly compressed, forming vacuum-tight seals, e one flange (122) equipped to mount the vacuum pump forming a pump port (126), the pump port being in vacuum contact with the vacuum port (106).

The vacuum coupling of claim 1, wherein the smooth areas (112, 114) are planar areas.

The vacuum coupling according to claim 1 or claim 2, wherein the two smooth areas (112, 114) are two rings.

A vacuum coupling according to claim 3, wherein the smooth areas form part of fixed flanges which are rigidly connected to and form part of the central body by tubes, the central body taking the form of a manifold.

A vacuum coupling according to any one of the preceding claims, wherein the one or more spacers (124) are in the form of a hollow tube, the tube being connected to the two flanges after mounting, the tube having a penetration (128) in its wall is in contact with the cavity, connecting the pump port (126) to the vacuum port (106).

A vacuum coupling according to any one of the preceding claims, wherein the one or more spacers (124) are in the form of one or more multiple pillars (430).

A vacuum coupling according to any one of the preceding claims, wherein the one or more spacers (124) are in the form of one or more plates.

A vacuum coupling according to any preceding claim, wherein the one or more spacers (124) surround the central body.

A vacuum coupling according to any one of the preceding claims, wherein the elastomeric seals (118, 118, 422, 426) are seals from the group of X-rings, O-rings, C-rings or annuli of flat elastomeric material. A vacuum coupling according to any one of the preceding claims, wherein the two elastomeric seals (116, 118) have slightly different diameters to compensate for the weight of the vacuum pump.

A vacuum coupling according to any one of the preceding claims, wherein the two elastomeric seals (116, 118) have slightly different diameters to compensate for the weight of the vacuum pump.

A vacuum coupling according to any one of the preceding claims, wherein the two elastomeric seals (116, 118, 418, 422) are each formed as two concentric elastomeric seals (310, 312), and the volume between each of the two elastomeric seals is in operation connected to a vacuum pump.

A vacuum coupling according to any one of the preceding claims, wherein the two elastomeric seals (116, 118, 418, 422) are each formed as two concentric elastomeric seals (310, 312), and the volume between each of the two elastomeric seals is filled with a dry gas.

A vacuum coupling according to any preceding claim, wherein the flange (120, 424) opposite the pump port (126) is a blind flange.

A vacuum device equipped with a vacuum coupling according to any one of claims 1-12, wherein the vacuum device is further equipped with a vacuum pump.

A vacuum device according to claim 14, wherein the vacuum pump is a molecular turbopump.

A vacuum apparatus according to any one of claims 14 to 15, wherein the vacuum apparatus is a vacuum apparatus from the group of scanning electron microscopes (SEM), transmission electron microscopes (TEM), scanning transmission electron microscopes (STEM), electron microprobe, ion microscopes or ion microprobes.