Patent Application
20110286833
The present invention claims the priority of German Patent Application no. DE 10 2010 021 241.5 filed on May 21, 2010, the disclosures of which are incorporated herein by reference.
1. Field of the Invention
The invention refers to a vacuum pump, in particular a turbo-molecular pump.
2. Description of the Prior Art
Vacuum pumps are used, for example, to evacuate chambers of an installation serving the optical or electronic examination of samples. These installations may be, for instance, mass spectrometers, electron microscopes, installations for coating processes, etc. Such installations frequently have a very high resolution of 1 to 2 nm, for instance. The vacuum pump may transmit vibrations to the installation, resulting in a corruption of the measurement results. Resonances may be excited as well, which may, for example, generate noises or cause structural damages. Such vibrations may be due, for example, to an imbalance of the rotating pump elements. Even with pump elements that are balanced very precisely, there is always a risk that undesired vibrations are still transmitted to the installation. Further, vibrations and movements in the pump can be caused by the pump being asymmetrically connected with connection elements or attachments. These may be electronic control elements connected to the pump, other pumps connected, such as pre-vacuum pumps, or electric lines which, for turbo-molecular pumps, may have a diameter of about 1 cm and more and are therefore rather heavy. Asymmetric attachments or connection elements may cause a tumbling or swaying of the pump in a direction substantially perpendicular to the longitudinal axis. Such a swaying or tumbling movement has a further disadvantage in that, independent of the transmission of vibrations to the installation, a relative movement occurs between the fast rotating rotor and the housing. With mechanically supported pumps, this causes high loads on the bearings. With electromagnetically supported pumps, this causes loads on the electronics of the magnetic bearings. The forces and moments thus acting on the pumping elements, such as the rotor, may lead to permanent damage to the pumping elements. The service life of the bearings and/or the pumping elements is thereby compromised.
For the purpose of damping the vibrations transmitted from the vacuum pump to the installation, it is known to provide mechanical damping elements between the vacuum pump and the installation. However, this can only result in a reduction of the vibrations transmitted. In particular the transmission of low-frequency vibrations, especially in the range of up to 200 Hz, can be damped thereby only to a limited degree. Further, such damping elements are difficult to adapt to the installation condition of the vacuum pump. Moreover, it is known to actively dampen vibrations. For this purpose, phase-shifted vibrations are induced into the vacuum pump by a vibration generator, so that the vibrations cancel each other. Such components are costly and do not allow the suppression of low-frequency vibrations.
It is an object of the invention to provide a vacuum pump, in particular a turbo-molecular pump in which the transmission of critical, especially low-frequency vibrations to an installation is avoided and/or the service life thereof is prolonged by reducing relative movement between pumping elements and the housing.
The vacuum pump of the present invention, which preferably is a turbo-molecular pump, comprises a suction chamber formed by a pump housing. At least one pumping element is arranged in the suction chamber, which element specifically is a rotor of a turbo-molecular pump. For the purpose of a reduction of vibrations, which may be caused, for example, by a remaining imbalance of the pumping element and/or by components asymmetrically connected with the pump housing, the invention provides for the connection of at least one retaining element with the pump housing. The retaining element serves to accommodate at least one mass element. By providing at least one, preferably a plurality of mass elements moving together with the pump housing it is possible, depending on the arrangement and/or the weight of the mass elements, to suppress critical vibrations or to avoid their occurrence. In particular, this allows suppressing the especially critical vibrations in the low-frequency range up to 200 Hz.
Preferably, several different mass elements can be connected with the pump at respective different positions. This allows an adaptation of the pump. Accordingly, it becomes possible in a simple manner to adapt the vacuum pump, depending on the application, to a respective field of application or a respective installation, with consideration to the connections and attachments used. According to the invention, this is achieved in a simple manner by arranging and/or exchanging mass elements correspondingly. A complex and costly special structure depending on the application of the vacuum pump or the installation, to which the vacuum pump is connected, can thus be omitted owing to the invention. Rather, identical pumps can be used for different applications and can be readily adapted to the respective given application.
Preferably, the retaining element has a plurality of recesses or compartments to accommodate a plurality of in particular different mass elements. The mass elements may be inserted into the same, for instance. Since the mass elements are preferably removably retained in the recesses or compartments, the mass elements can be changed in a simple manner. The mass elements are also retained, for instance, by friction occurring between the mass element and the recess or compartment, or by providing fixing elements. Thus, the vacuum pump can be readily adapted to the respective application. Vibrations occurring can be measured and be changed by replacing and/or arranging the mass elements in other recesses or compartments.
The recesses or compartments are arranged with respect to the longitudinal axis of the vacuum pump, which for a turbo-molecular pump is the rotational axis of the rotor, such that it is possible to asymmetrically arrange different mass elements at a plurality of positions.
Preferably, the mass elements used have different weights. Varying the weights can be achieved by using mass elements of different sizes and/or different materials.
The mass elements are rod-shaped, for instance, and are thus easily be inserted into recesses or compartments.
In another preferred embodiment of the invention, it is further possible to provide mass elements in bulk. The corresponding bulk, which may be spherical bulk, for instance, may be provided in the different compartments. A very fine adjustment of the mass provided at a certain location can be achieved by using a bulk containing spheres of different materials and/or different sizes, for instance.
Likewise, it is possible to use liquids as mass elements, which in particular have different viscosities. These may also be provided in the compartments.
A movement of the bulk or the liquids in the compartments can be avoided by making the compartments variable in size so that a respective compartment is always filled completely with the liquid or the bulk. For that purpose, a side wall and/or a lid of the compartment may be slidable, for example.
In a further preferred embodiment, the at least one retaining element is rod-shaped and serves to receive disc-shaped, in particular round mass elements. These can be set on the retaining element and be fixed using a nut or the like. In this context it is also possible to arrange asymmetric discs as mass elements on the retaining elements.
Of course, the above described embodiments can also be combined with each other at will.
The retaining element, which preferably comprises a plurality of recesses, compartments and/or pin-shaped protrusions, is preferably arranged at a front end side of the pump housing. In particular, the front end side of the pump housing is a surface extending perpendicularly to the longitudinal axis of the pump. It is preferred that the retaining element has the same dimensions as the front end side and thus extends across all of the front end side.
In another preferred embodiment the retaining element surrounds the vacuum pump at least partially. Preferably, the retaining element is annular and in particular symmetrical to the longitudinal axis. With such a retaining element it is possible to arrange mass elements around the vacuum pump, if need be also at different distances from the longitudinal axis. Such a retaining element allows arranging mass elements at different distances from the longitudinal axis of the vacuum pump and at different positions. For this purpose, a preferred embodiment of the retaining element has a plurality of recesses or compartments extending parallel to or under an angle with the longitudinal axis.
Of course, it is also possible to connect retaining elements of different designs with one and the same vacuum pump.
Likewise, it is possible to use a retaining element to arrange at least one mass element symmetrically to the longitudinal axis of the vacuum pump. Here, the at least one mass element may be arranged on the in particular rod-shaped retaining element such that the relative position of the mass element to the retaining element can be changed. For example, this is possible by providing the mass element with a bore through which the retaining element projects and by providing the bore asymmetrically in the mass element. In particular, the mass element may be a parallelepiped, the connection with the retaining element preferably being made at a distance from the centre of gravity of the parallelepiped. Thereby, simply turning the mass element around the retaining element allows setting which vibrations are to be suppressed by the mass element. This makes it possible to suppress critical vibrations that particularly occur in the low-frequency range up to 100 Hz.
It is of course possible to arrange additional elements such as vibration dampers and the like between individual mass elements. Further, it is possible to provide spacer elements in order to vary the distance of the individual mass elements to the pump housing or to the longitudinal axis of the pump housing.
A full and enabling disclosure of the present invention including the best mode thereof, enabling one of ordinary skill in the art to carry out the invention, is set forth in greater detail in the following description, including reference to the accompanying drawing in which
A vacuum pump 10, such as a turbo-molecular pump, is arranged at a housing 14 of an installation, e.g. via a flange 12, so that a medium, especially gases, can be drawn by the pump from a chamber of the installation, as indicated by an arrow 16. The vacuum pump 10 has an outlet 18 from which the medium pumped is discharged in the direction of an arrow 20. The outlet 18 may be connected to a pre-vacuum pump, for instance. The outer side 22, such as the shell surface of the housing 24 of the vacuum pump 10, a control means 26 as well as a cable 28 may be connected.
Inside the pump housing 24 of a turbo-molecular pump, a pumping element 30 in the form of a rotor is arranged within the suction chamber 32 defined by the pump housing 24. The rotor 30 rotates at high speeds about a longitudinal axis 34.
Due to imbalances in the rotor 30, remaining in spite of complex and precise balancing methods, and/or to elements fastened asymmetrically to the housing with respect to the longitudinal axis 34, vibrations occur in all of the vacuum pump. On the one hand, these are transmitted to the installation 14 and may, on the other hand, cause relative movements between the rotor 30 and the pump housing 24.
To suppress these vibrations, especially in low-frequency ranges of up to 200 Hz, the invention provides to connect retaining elements 36, 38 with the pump housing 24. In the embodiment illustrated a first retaining element 36 is connected all over a front end face 40 of the pump housing 24 so that the entire front end face 40 is covered by the retaining element 36. In the embodiment illustrated the second retaining element 38 is of annular design and surrounds the pump housing 24.
As can be seen in the detail illustrated in
For the sake of clarifying the various embodiments of the invention,
Correspondingly, the retaining element 46 illustrated in
In another embodiment (
Although the invention has been described and illustrated with reference to specific illustrative embodiments thereof, it is not intended that the invention be limited to those illustrative embodiments. Those skilled in the art will recognize that variations and modifications can be made without departing from the true scope of the invention as defined by the claims that follow. It is therefore intended to include within the invention all such variations and modifications as fall within the scope of the appended claims and equivalents thereof.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2010 021 241.8 | May 2010 | DE | national |
