Abstract:
A damper mechanism for isolating vibrations from a vacuum pump constructed and adapted for coupling to a vacuum chamber, the damper mechanism including an elastomeric material, preferably an elastomer diaphragm, coupled between the pump and the vacuum chamber so as to permit the pump to move in six degrees of freedom, while transferring minimum force to the chamber.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to vibration isolation of high vacuum pumps, in general, and in particular, to devices for isolating vibrations of turbo pumps from vacuum chambers.  
       BACKGROUND OF THE INVENTION  
       [0002]     Turbo pumps are used to provide deep vacuum in sensitive inspection machines, such as scanning electron microscopes. As the pumps rotate, they produce vibrations which can prevent proper operation of the inspection machines. Accordingly, it is desired to provide vibration isolation of the pump from the vacuum chamber to which it is connected. In conventional systems, dampers are connected between the pump, which rotates at high speed, and the vacuum chamber. The purpose of these dampers is to isolate the sensitive equipment from the vibration of the pumps.  
         [0003]     One example of a known damper is shown in  FIG. 1 . A pump ( 1 A) is connected to a vacuum chamber (not shown) by a sealing mechanism. The sealing mechanism consists of a metal bellow ( 2 A), which connects the pump ( 1 A) and the vacuum chamber, and a damper ( 3 A) which is built around the bellow. Damper ( 3 A) is usually a rubber or elastomer ring that fits around the metal bellow.  
         [0004]     While this damper is able to absorb a large percentage of the vibrations from the pump, the metal bellow transfers vibrations, which can be sufficient to degrade the proper functioning of extremely sensitive instruments.  
         [0005]     Accordingly, there is a long felt need for an efficient mechanism for isolating vibrations from turbo pumps, and it would be very desirable if such mechanism were to provide a hermetic seal while permitting the pumps to vibrate without passing vibrations to the chamber.  
       SUMMARY OF THE INVENTION  
       [0006]     It is an object of this invention to provide vibration isolation of high vacuum pumps from a vacuum chamber. Since the pump vibrates, it is necessary to connect the pump to the vacuum chamber via a flexible, vacuum-tight material. A fiber-reinforced diaphragm is preferred at present. The elastomer diaphragm enables the pump to move in all six degrees of freedom, while transferring minimum force to the chamber. To minimize the gas permeation through the elastomer diaphragm, an intermediate pumping technique may be used. The mid-section between the diaphragms is connected to the roughing pump, the back up pump for the turbo. The diaphragm may be made out of any flexible, vacuum-tight material, or a very thin metal diaphragm whose ends are sealed by an elastomer.  
         [0007]     There is thus provided, is accordance with the present invention, a damper mechanism for isolating vibrations from a turbo pump to a vacuum chamber, the  
         [0008]     damper mechanism including an elastomeric diaphragm coupled between the pump and the vacuum chamber so as to permit the pump to move in six degrees of freedom, while transferring minimum force to the chamber. Preferably, the elastomeric diaphragm is fiber reinforced.  
         [0009]     According to one embodiment of the invention, the damping is provided by three elastomer dampers: an isolation mass is connected between two elastomer dampers. Alternatively, pneumatic integrated isolators may be utilized.  
         [0010]     According to a further embodiment, tuned dampers may be added to the elastomer damper. By measuring the tuned damper acceleration amplitude and maximizing it by changing the rotational speed of the pump, minimum transmissibility is achieved. The tuned dampers are tuned to the basic rotational speed of the pump.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]     The present invention will be further understood and appreciated from the following detailed description taken in conjunction with the drawings in which:  
         [0012]      FIG. 1  is a sectional illustration of a pump with a damper mechanism according to the prior art;  
         [0013]      FIG. 2A  is a sectional illustration of a pump with a damper mechanism constructed and operative in accordance with one embodiment of the present invention;  
         [0014]      FIG. 2B  is a sectional illustration of a pump with a damper mechanism constructed and operative in accordance with another embodiment of the present invention;  
         [0015]      FIG. 2C  is a sectional illustration of a pump with a damper mechanism constructed and operative in accordance with a further embodiment of the present invention;  
         [0016]      FIG. 2D  is a sectional illustration of a pump with a damper mechanism constructed and operative in accordance with another embodiment of the present invention; and  
         [0017]      FIG. 2E  is a sectional illustration of a pump with a damper mechanism constructed and operative in accordance with a further embodiment of the present invention.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0018]     The present invention relates to a vibration damper mechanism that connects a vacuum pump, particularly a turbo pump, to a vacuum chamber. The damper consists of a flexible elastomer diaphragm that connects the pump to the chamber and enables the pump to move in all directions. The elastomer diaphragm provides a vacuum-tight seal.  
         [0019]     According to a preferred embodiment, the damper mechanism consists of three or more dampers that carry the vacuum load and pump mass and isolate the pump vibration from the chamber. The dampers can utilize three or more different concepts of damping: the first, an elastomer damper with intermediate mass; the second, an integrated air or pneumatic damper, the third a tuned damper wherein the pump&#39;s main speed is tuned to the damper&#39;s resonance via a closed loop. These concepts will be described in more detail with reference to the Figures.  
         [0020]     Referring to  FIG. 2A , there is shown a sectional illustration of a pump ( 1 A) with a damper mechanism constructed and operative in accordance with one embodiment of the present invention. In this embodiment, vacuum pump ( 1 A) is connected to a base ( 2 ) via a standard vacuum-tight flange, ISO style or other.  
         [0021]     A sandwich of two elastomer diaphragms ( 3 ) is built with one side on the base ( 2 ). The other side of these diaphragms ( 3 ) is connected to a static flange ( 4 ), which is coupled to the vacuum chamber. These double diaphragms are vacuum-tight and sealed to base ( 2 ) and static flange ( 4 ). The static flange ( 4 ) is connected to a vacuum chamber ( 5 ) via a standard vacuum flange, ISO style or other.  
         [0022]     Since gas permeation through the elastomer diaphragms ( 3 ) may be large, the space between the two diaphragms is connected via a tube ( 9 ) to the outlet of the vacuum pump ( 10 ), which is connected to a roughing pump. This serves to reduce the pressure between the diaphragms ( 3 ), thereby providing a double seal with an intermediate pump.  
         [0023]     According to an alternative embodiment of the invention, illustrated in  FIG. 2D , the vacuum sealing may consist of a very thin metal diaphragm ( 31 ) whose ends are sealed by an elastomer, shaped, in this example, as two o-rings ( 32 ) on each side of the metal diaphragm. One side of the diaphragm  31  is mounted on the base ( 2 ) of the pump and the other side is mounted on a static flange ( 4 ) coupled to the vacuum chamber. In this way, the metal does not contact the vacuum chamber, and the elastomer serves to absorb the vibrations. In this option, only one diaphragm is required.  
         [0024]     Since the atmospheric pressure tends to pull the vacuum pump into the vacuum chamber, it is essential to connect additional dampers between the vacuum pump and the vacuum chamber. In the embodiment of  FIG. 2A , three additional dampers are provided. These dampers consist of two conventional elastomer dampers ( 6 ) with a damping mass ( 7 ) connected between the two elastomer dampers ( 6 ). A post ( 8 ), connected to the pump, supports the dampers.  
         [0025]     Another way to achieve damping is shown in  FIG. 2B , a sectional illustration of a pump ( 1 A) with a damper mechanism constructed and operative in accordance with another embodiment of the present invention. Pump ( 1 A) is connected to the vacuum chamber ( 5 ) via a double elastomer seal ( 3 ), substantially as shown and described in  FIG. 2A , and via a pneumatic vibration isolator ( 20 ) mounted between a static flange ( 4 ) coupled to the vacuum chamber and a post. The pneumatic damper ( 20 ) is connected to a pressurized air supply ( 21 ).  
         [0026]     Another way to achieve a pneumatic vibration damper is shown in  FIG. 2E . In this embodiment, the base ( 2 ) is connected to the static flange ( 4 ) by a flexible diaphragm ( 43 ), thus creating an annular volume ( 44 ). Pressurizing this volume ( 44 ) from a source of pressurized air ( 41 ) serves to create the force needed to overcome the vacuum forces, thus achieving a pneumatic vibration isolator.  
         [0027]     Still another way to achieve additional vibration isolation is shown in  FIG. 2C , a sectional illustration of a pump ( 1 A) with a damper mechanism constructed and operative in accordance with a further embodiment of the present invention. In this embodiment, a tuned damper is connected to the base of existing dampers. This embodiment can apply to the embodiment with elastomer dampers as well as to the embodiment having a pneumatic damper.  
         [0028]     The tuned damper consists of a spring ( 12 ) and a mass ( 13 ). The resonance frequency of the mass-spring system is roughly tuned to the pump main speed frequency. It is a particular feature of the present invention that this exact tuning is accomplished, not by adjusting the frequency of the tuned damper, as in conventional systems, but by adjusting the rotational speed of the pump to the frequency of the tuned damper. Thus, an accelerometer ( 15 ) is coupled to the mass of the tuned damper and the acceleration of the mass measured. Changing the rotational speed of the pump maximizes the acceleration measured by this accelerometer. When maximum acceleration of the mass is achieved, the rotational speed of the pump is exactly at the tuned mass frequency, which is optimal. It will be appreciated that the tuned damper frequency is designed to be at the desired rotational speed of the pump.  
         [0029]     It is a particular feature of the present invention that the damper mechanism is a horizontal system, not vertical as in conventional systems. Thus, the pump is closer to the chamber and the damper can be very short. In this way, the pumping speed that is achieved in the chamber is very similar to the basic pumping speed of the pump.  
         [0030]     While the invention has been described with respect to a limited number of embodiments, it will be appreciated that many variations, modifications and other applications of the invention may be made. It will further be appreciated that the invention is not limited to what has been described hereinabove merely by way of example. Rather, the invention is limited solely by the claims, which follow.