Patent Publication Number: US-6217278-B1

Title: Turbomolecular pump

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a turbomolecular pump for exhausting a gas by an interaction between a rotor and a stator and/or by an action of threaded rotor rotating at a high speed. 
     A general construction of a conventional turbomolecular pump is illustrated in FIG.  4 . The turbomolecular pump comprises a rotor R including a main shaft  10  and a rotary cylinder  12  rotating integrally therewith, a stator S including a fixed cylinder  14  surrounding the shaft  10 , and a cylindrical casing  16  surrounding the rotary cylinder  12 , which are assembled on a base B. A conductance adjusting valve  100  and a gate valve  110  are provided between the pump and an apparatus A to be evacuated in the upstream of the turbomolecular pump. 
     In the conventional turbomolecular pump as described above, however, driving mechanisms  101 ,  102  for the individual valve units are provided in the proximity of the valves near the turbomolecular pump. This has posed a problem of scaling-up of the valve units, resulting in a larger overall structure of the turbomolecular pump including the valves. 
     SUMMARY OF THE INVENTION 
     In view of the problem described above, the present invention was made and has an object to provide a turbomolecular pump which enables a compact construction of the overall apparatus to be realized including the valve units. 
     To achieve the above object, according to a first aspect of the invention a turbomolecular pump is provided which comprises a rotor and a stator housed in a casing and an exhaust mechanism is formed between the rotor and the stator; wherein the turbomolecular pump has a valve body for opening and closing a suction port provided in the casing, and a valve driving mechanism for opening/closing driving the valve body, wherein the valve driving mechanism is provided integrally with the turbomolecular pump. This makes it possible to achieve a compact overall construction including the valve units. 
     According to a second aspect of the invention, in a turbomolecular pump according to the first aspect, the valve driving mechanism is so constructed that it drives the valve body in the axial direction of the rotor. By this arrangement, it is possible to achieve a simple construction of the entire valve unit which does not require a large space for installation thereof, since the valve body is opened or closed by lifting or lowering the valve body relative to the suction port. 
     According to a third aspect of the invention, in a turbomolecular pump according to the first aspect, the valve driving mechanism is provided outside the stator. 
     According to a fourth aspect of the invention, in a turbomolecular pump according to the first aspect, the valve driving mechanism is provided at the center portion of the suction port. 
     According to a fifth aspect of the invention, in a turbomolecular pump according to any one of the above aspects, the valve driving mechanism is provided so as to make the degree of opening of the valve body adjustable. This permits simultaneous functioning of valve units as a gate valve and a conductance adjusting valve, thus allowing further simplification and space saving. 
     According to the present invention, as described above, since the valve driving mechanism is provided integrally with the turbomolecular pump, it is possible to connect the suction port of the turbomolecular pump directly to a duct or the like of an apparatus to be evacuated. In addition, because the valve driving unit can drive a valve supporting member which supports the valve body in the axial direction of the rotor, the structure of the valve unit and the valve driving mechanism can be made far simpler. It is therefore possible to provide a turbomolecular pump having a compact overall construction, including the valve units. 
     The above and other objects, features and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings in which preferred embodiments of the present invention are shown by way of illustrative examples. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a sectional view illustrating a turbomolecular pump of a first embodiment of the invention; 
     FIG. 2 is a sectional view illustrating a turbomolecular pump of a second embodiment of the invention; 
     FIG. 3 is a sectional view illustrating a turbomolecular pump of a third embodiment of the invention; and 
     FIG. 4 is a sectional view illustrating a conventional turbomolecular pump. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Preferred embodiments of the present invention will now be described with reference to the drawings. The turbomolecular pump of a first embodiment of the invention shown in FIG. 1 comprises a rotor R including a main shaft  10  and a rotary cylinder  12  fixed thereto for rotating integrally with the main shaft, a stator S including a fixed cylinder  14  surrounding the main shaft  10 , and a cylindrical casing  16  surrounding the rotary cylinder  12  and fixed to the stator S which, in turn, is fixed to a base B. A disk-shaped valve body  20  is provided on a suction port  18  of the casing  16  for opening and closing the suction port  18 . 
     A driving motor  22  is provided between the main shaft  10  and the fixed cylinder  14  for rotaing the shaft. An upper radial bearing  24  and a lower radial bearing  26  are provided on an upper and lower side of the driving motor  22 , respectively, for rotatably supporting the shaft. In the lower portion of the main shaft  10 , a target disk  28  is fixed at the lower end of the main shaft, and an axial bearing  32  is formed by the target disk  28  and upper and lower coils  30  fixed to the stator S. By this arrangement the rotor R can rotate at a high speed under active control along the axis by the action of the driving motor  22 . 
     Rotary blades  34  are formed integrally with the rotary cylinder  12  on the outer periphery of the upper portion thereof so as to form impellers  36 . On the inner surface of the casing  16 , on the other hand, fixed blades  38  are provided alternately with the rotary blades  34 , with a spacer interposed therebetween. There is therefore formed a blade exhaust section  40  between the rotary blades  34  and the fixed blades  38  and gas exhaust action is accomplished through interaction of the rotary blades  34  rotating at high speed and the stationary blades  38 . 
     A cylindrical screw thread portion  42  extending downward along the outer periphery of the fixed cylinder  14  is integrally formed with the rotary cylinder  12 , and a screw thread  44  is formed on the outer peripheral surface of the screw thread portion  42 . A thread spacer  46  surrounding the outer periphery of the screw thread portion  42  is provided on the stator S. As a result, a screw-thread exhaust section  48  which performs gas exhaust action under drag action created by the screw thread  44  of the screw thread portion  42  rotating at a high speed is formed between the blade exhaust section  40  and an exhaust port  49 . 
     Valve driving units  70  for driving the valve body  20  in the axial direction of the rotor R are attached to fixing members  74 , which extend from a flange  72  of the cylindrical casing  16  and are arranged circumferentially at equal intervals. Throughholes  76  are formed circumferentially spaced around the flange  72 . A plurality of valve rods  78  connecting the peripheral portion of the valve body  20  and the valve driving units  70  are inserted into the throughhole  76 . An O-ring  56  is provided on the flange surface to maintain air-tightness when the valve body  20  is closed against the suction port  18 . Actuators for the valve driving units  70  may comprise a piston cylinder unit operated by hydraulic pressure or pneumatic pressure or a ball screw unit driven by a motor. 
     According to the construction and arrangement as described above, the valve body  20  can be operated to open or close the suction port  18  under operation of the actuator of the driving unit  70 , and conductance can be adjusted by controlling the valve opening of the valve body  20 . As illustrated, the turbomolecular pump can be directly attached to a duct  58  or the like of the apparatus A to be evacuated without interposing valve unit therebetween as shown in FIG.  4 . Since the actuator of the valve driving units  70  drives the valve body  20  in the axial direction of the rotor R, the construction of the valve units and the driving mechanism can be made far simpler. It is therefore possible to provide a more compact turbomolecular pump as a whole, and use it effectively in a narrow space such as a clean room. 
     FIG. 2 illustrates a second embodiment of the invention wherein only one valve rod  50  is provided at the center thereof, and a valve driving unit  70   a  is supported at the center portion of a suction port  18  by an arm or arms  82  extending from the casing  16 . In an ordinary turbomolecular pump, the center portion of the suction port is provided with a space into which the rotor R does not extend. In this embodiment, this space is used to house the valve driving unit  70   a.  In this case, however, since the valve driving unit  70   a  is installed within a vacuum evacuating system, the valve driving unit  70   a  is required to have as small sliding portion as possible to avoid contamination. Thus, an electromagnetic driving means could be preferably used. 
     FIG. 3 illustrates a third embodiment of the invention. In this embodiment, an actuator for a valve driving unit  70   b  is formed into a cylindrical shape forming a part of a casing, and a plurality of valve rods  50  are attached thereto. The valve rods  50  are housed in a space between an inner casing  16   a  and an outer casing  16   b.  In this embodiment, since the actuator of the valve driving unit  70   b  has a large capacity, it is possible to perform stable and positive opening/closing operations. 
     As described above, according to the present invention, since the valve driving mechanism is provided integrally with the turbomolecular pump, it is possible to connect the suction port of the turbomolecular pump directly to a duct or the like of an apparatus to be evacuated. In addition, since the valve driving unit drives the valve supporting member supporting the valve body in the axial direction of the rotor, the structure of the valve unit and the valve driving mechanism can be made far simple. It is therefore possible to provide a turbomolecular pump having a compact overall construction including the valve units.