DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

[0121] Various examples (preferred embodiments) of the present invention will be explained hereinafter with reference to the drawings. The scope of the present invention, however, is not limited to the following preferred embodiments.

[0122] (Embodiment 1)

[0123] FIG. 1 is a vertical cross-sectional view of a first embodiment of a multiple-type vacuum pump, according to the present invention. FIG. 2 is a cross-sectional view of FIG. 1 along the line II-II, illustrating the path of air evacuation in the same embodiment.

[0124] In FIG. 1, a multiple-type vacuum pump P includes a base 1. The base 1 has a cylindrical bearing support member 3 which protrudes upward from the middle section of a flange 2. Formed within flange 2 is an air outlet 2a, an electricity supply cable insert hole 2b and a casing support surface 2c. The air outlet 2a has a downstream side air outlet 2a₁, which extends in the direction of a shaft of the cylindrical bearing support member 3, and a downstream side air outlet 2a₂, which extends in a radial direction of the shaft. An exhaust pipe connecting member 4 is connected to an outer edge of the downstream side air outlet 2a₂, and a connector 5 is connected to an outer edge of the electricity supply cable insert hole 2b.

[0125] A cylindrical casing 6 is fixed to the casing support surface 2c. An upper bearing 8 is supported by the upper edge of the cylindrical bearing support member 3 via an upper bearing support member 7. A thrust displacement sensor 12 is supported by a lower edge of the cylindrical bearing support member 3 via a thrust displacement sensor 11. A lower bearing support member 13 is supported by an upper surface of the thrust displacement sensor support member 11, and a lower bearing 14 is supported by the lower bearing support member 13. A thrust magnetic bearing lower portion 16a is supported by an upper surface of the lower bearing support member 13.

[0126] An upper bearing support member 17, which supports a thrust magnetic bearing upper portion 16b, is supported on an inner surface of the cylindrical bearing support member 3 located above the lower bearing support member 13 with a certain spacing therefrom.

[0127] A thrust magnetic bearing 16 is made up of the thrust magnetic bearing lower portion 16a and the thrust magnetic bearing upper portion 16b.

[0128] A magnetic generation member for a motor 18 is mounted on the inner surface of the cylindrical bearing support member 3 at a middle vertical portion thereof. The magnetic generation member for the motor 18 is comprised of four electromagnets 18a and 18b which have four iron cores 18a disposed circumferentially at equal intervals and coils 18b which are wrapped around the circumference of each of the four iron cores 18a, and generate a rotative magnetic field and causes a rotor H to rotate, as mentioned below.

[0129] A pair of radial magnetic bearings 19 are mounted on the cylindrical bearing support member 3 by upper and lower portions of the magnetic generation member for a motor 18. The radial magnetic bearings 19, 19 are comprised of four electromagnets 18a and 18b which have four iron cores 19a disposed circumferentially at equal intervals and coils 19b which are wrapped around the circumference of each of the iron cores 19a. By virtue of magnetic force, radial magnetic bearings 19 control a radial position of the rotor H vis-a-vis the rotary shaft.

[0130] Radial displacement sensors 20, 20 are mounted at an upper side of the upper radial magnetic bearing 19 and at a lower side of the lower radial magnetic bearing 19, respectively. The magnetic force of the radial magnetic bearings 19 is controlled, by the detection signal of radial displacement sensors 20, such that the rotor H rotates at a predetermined position. Such control of the rotary position of the rotor is well known, and a variety of conventional art can be used for the application of this embodiment as well.

[0131] The rotor H is disposed inside of an inner circumferential surface of the cylinder of the casing 6. The rotor H has a shaft J and an air transfer member K. The air transfer member K has a disc-shaped shaft connecting portion K1, which is connected to the shaft J, and a cylinder portion K2, which is formed integrally with the shaft connecting portion K1.

[0132] The shaft J has a larger diameter portion 22, a tapered portion 23, which is located at an upper edge portion of the shaft J and the outer diameter of which grows smaller as it goes toward its upper edge, and a smaller diameter portion 24, which is located at the lower edge portion of the shaft J. The upper edge portion of the larger diameter portion 22 is rotatably supported by the upper bearing 8. The smaller diameter portion 24 is rotatably supported by the lower bearing 14. A circular plate 26, made from magnetic material, is supported by the upper edge portion of the smaller diameter portion 24. This circular plate 26 is disposed within a space between the lower portion 16a and the upper portion 16b of the thrust magnetic bearing 16. Stainless cylinder members 27 and steel (magnetic material) cylinder members 28 are installed alternately on the outer circumference of the larger diameter portion 22 in the direction of the shaft. Each of the multiple steel cylinder members 28 is placed at a location facing the iron cores 18a, 19a.

[0133] The shaft J is thus constructed with the elements indicated by the reference numericals 23-28.

[0134] A shaft insertion hole 31, whose inner diameter grows smaller as it progresses toward its upper edge, is formed in the central portion of the disc-shaped shaft connector K, and the tapered portion 23 of the shaft J is inserted into the shaft insertion hole 31. A connecting plate 32 is mounted onto an upper surface of the shaft connector portion K. A connecting bolt 33 passes through the connecting plate 32 from above and is screwed into an upper edge screw hole of the shaft J. Since the tapered portion 23 of the shaft J, through the connecting bolt 33, presses against the shaft insertion hole 31 of the shaft connector K, the shaft connector K and the upper edge of shaft J are connected.

[0135] A ring-shaped air outlet space G, as seen from the rotary shaft of rotor H, is formed between the lower edge of the rotor H and the flange 2, and communicates with the upstream edge of the air outlet hole upstream portion 2a₁, formed at the flange 2.

[0136] FIG. 3 is a drawing showing the rotor shown in FIG. 1. FIG. 3A is a drawing of the rotor viewed from the upstream side in the direction of air transfer; FIG. 3B is the side view of the rotor, FIG. 3C is an expanded drawing of the outer surface of the rotor; and FIG. 3D is drawing which magnifies the essential elements in FIG. 3C.

[0137] In FIG. 1 and FIG. 3, an air transfer portion S is formed at the outer surface of the air transfer member K. The air transfer portion S has a screw type pump air transfer portion S1 on a downstream side thereof in the air transfer direction, and a turbo-molecular type pump air transfer portion S2 on a downstream side thereof.

[0138] The screw type pump air transfer portion S1 has multiple screw threads 36 which have set widths, are spiral in shape and are formed toward the circumference at prescribed intervals, and screw grooves 37 which are formed between each of the screw threads 36. The screw type pump air transfer portion S1 takes in the air from the upstream edge at the time of rotation, and transfers it to the downstream side.

[0139] The turbo-molecular type pump air transfer portion S2 has multiple vanes 41, which are disposed at the circumference at prescribed intervals in the upstream portion of the outer surface of the rotor H, which are tilted in the axial direction of the rotary shaft J, and air transfer grooves 42, which are formed in between each of the multiple vanes 41. A vane angle of the vane 41 is θ=30° which equals a tilt angle of screw α(=30°) of the upper edge of the screw type pump air transfer portion S1. A vane width W1 of the upstream edge of the vane 41 is 2 mm, the width of which gets wider as it goes downstream in order for the downstream edge of the vane 41 to be smoothly connected to the upstream edge of the screw threads 36. The vane width of the downstream edge (the connecting portion of screw threads 36) of the vane 41 equals the thread width d of the screw threads 36; d=5.65.

[0140] Furthermore, the downstream edge of the base of the air transfer grooves 42 is formed as to be smoothly connected to the upstream edge of the base of the screw grooves 37. The turbo-molecular type pump air transfer portion S2 takes the air that has been brought in from the upstream edge of the rotor H at the time of rotation, and compresses it and then transfers it to the upstream edge of the screw type pump air transfer portion S1. The following section explains the meaning of φ, r, r 0^˜r 2 that appear in FIG. 1 and refers to the measurements of the rotary shaft (J).

[0141] φ: Outer diameter of the rotary shaft (J).

[0142] r: Radius of a circle touching the base (a connecting portion of the vanes 41 and the air transfer grooves 42) or that of the base of the screw threads 36 (a connecting portion of the screw threads 36 and screw grooves 37), within a cross-section perpendicular to the axial direction of the rotary shaft J.

[0143] r 0: Base radius of the bases of either the upstream edge of the screw type pump air transfer portion S1 or the downstream edge of the turbo-molecular type pump air transfer portion.

[0144] r 1: Base radius of the downstream edge of the screw type pump air transfer portion S1.

[0145] r 2: Base radius of the upstream edge of the turbo-molecular type air transfer portion.

[0146] The base radius r 0 of the upstream edge of the screw type air transfer portion S1 and the base radius r 0 of the downstream edge of the turbo-molecular type air transfer portion, have the same value. For this reason, the bottom of the downstream edge of the air transfer grooves 42 of the turbo-molecular type air transfer portion S2 run smoothly together with the base of the upstream edge of screw grooves 37 of the screw type pump air transfer portion S1. Further, the base diameter (2×base radius r), which is the diameter of the circle that is in contact with the base of the vanes 41 in the cross-section which is perpendicular to the axial direction of the rotary shaft J, is formed as to be on top of a conical plane whose outer diameter gets smaller as it makes its way up to its upstream side. For this reason, the air transfer grooves 42 of the turbo-molecular type air transfer portion S2 become deeper lineally as they make their way upstream.

[0147] In the multiple-type vacuum pump P, according to the first embodiment of the present invention, described above, when there is a big difference between the cubical flow volume (air intake volume) of the upstream edge of the screw type pump air intake portion S1 and the cubical flow volume (air exhaust volume) at the downstream edge of the turbo-molecular air transfer portion S2, the system as a whole could experience a decrease in air exhaust performance. The downstream edge of the turbo-molecular type pump air transfer portion S2 and the upstream edge of screw type pump air transfer portion S1 are, therefore, constructed in such a way that their cubical flow volumes are identical. It is possible to apply the screw type pump design theory to the design of the screw type pump air transfer portion S1, and, in the same manner, to apply the turbo-molecular pump design theory to the design of turbo-molecular type pump air transfer portion S2.

[0148] Using the screw type pump and the turbo-molecular pump design theories makes it easy to design the multiple-type vacuum pump P in which the cubical flow volume of the downstream edge of the turbo-molecular type air transfer portion S2 equals that of the upstream edge of the screw type pump air transfer portion S1.

[0149] The following procedure, for example, can be used when designing the multiple-type vacuum pump using the screw type pump and turbo-molecular pump design theories.

[0150] (Example of Design Method)

[0151] First, one establishes standard shape parameters which will serve as the design standards for the screw type pump air transfer portion S1. Once the aforementioned standard shape parameters are established, other shape parameters can be established using the same procedure as used in ordinary screw type pump design methods. For example, the aspect ratio (a/e) at the upstream edge (air intake edge) of the screw type pump air transfer portion S1 is set at 3 or more, the groove width ratio (a/a+d) is set at approximately 0.9, and the screw tilt angle α is set, as appropriate, within the 30°^˜40° range.

[0152] In other words, the initial values of the above-mentioned standard shape parameters are established, for example, as follows: while other shape parameters are adjusted and determined on the basis of the initial values, adjustments can also be made to the initial values of standard shape parameters. Further, adjustments to the other shape parameters result in changes to the standard shape parameters, as well. For example, even if the initial value of intake volume (cubical flow volume) (V) were to be V=300 L/s (liters/sec), once one reaches the stage where groove width and the groove width ratio are determined in concrete terms, the aforementioned value of (V) will change.

[0153] (1) r 0=(174/2) mm=87 mm

[0154] r 0: the base radius of the upstream edge of the screw type pump air flow portion S1

[0155] (2) the intake flow volume (cubical flow volume) (V): V=300 L/s (liters/sec)

[0156] (3) the diameter of the rotor (H) (rotor diameter) φ=200 mm

[0157] (4) aspect ratio (a/e) at the cross-section of the groove=4.0

[0158] (a: groove width at the cross-section of the groove; e: groove depth measured from the inner surface of the casing, i.e., the distance between the inner surface of the casing and the base of the grooves 37)

[0159] (5) groove width ratio (a/a+d)=0.91

[0160] (a: groove width at the cross section of the groove; d: thread width at the cross section of the groove)

[0161] (6) upstream edge tilt angle of screw α1=30°

[0162] (α1=the tilt angle of screw of the upstream edge of the screw type pump air transfer portion S1)

[0163] (7) clearance coefficient β (=e/δ)=23

[0164] (e: the groove depth measured from the inner surface of the casing; δ: radial clearance, i.e., the distance between the inner surface of the casing and the surface of the screw threads;

[0165] e=δ+b, b=groove depth)

[0166] (8) Number of rotations N=24,000 rpm

[0167] Once the above-mentioned standard shape parameter values are set, the other shape parameters of screw type pump air transfer portion S1 (inner diameter of the casing, screw thread width (d=5.65 mm), groove depth, groove width ratio, and the like) are set on the basis of screw type pump design theory. When undertaking this, the groove width ratio gets smaller as it goes toward the downstream side in the direction of air transfer, and is as much as 0.5^˜0.6 at the downstream edge. Also determined are the tilt angle of screw α, which gets smaller as it makes its way to the downstream side, as well as the optimum depth, width, and the number of screw threads, etc. for the screw groove.

[0168] The following parameters are set for this embodiment:

[0169] (11) Number of screw threads=5

[0170] (12) groove width a=57.18 mm

[0171] (13) thread width d=5.65 mm

[0172] (14) groove depth e=14.29 mm

[0173] (15) square opening area of the screw groove portion=41 cm²

[0174] (16) the inner diameter of the casing 6=201.24 mm

[0175] (Based on the above-mentioned (7), δ=(e/23)=(14.29/23)=0.62 (=radial clearance), inner diameter of the casing=diameter of the rotor H(rotor diameter)+0.62×2=200+1.24=201.24 mm)

[0176] (17) The designed air intake velocity V as the screw type pump=282 L/s (liters/sec)

[0177] When the shape parameters are set, the air intake velocity (V) is expressed as follows:

[0178] Air intake velocity=groove width a×groove depth e×π×number of rotations N×number of grooves 5×diameter r 0×pump efficiency/2

[0179] It is noted that the pump efficiency is determined by the relationship to geometric shape, circumferential velocity and clearance, etc.

[0180] Next is determined the necessary standard shape parameters for the design of the turbo-molecular type pump air transfer portion S2. The constructional elements (the vanes 41, the air transfer grooves 42, etc.) of the turbo-molecular type pump air transfer portion S2, according to the example 1, are members which have the same air intake function as dynamic vanes at the upstream edge (first-stage) of ordinary turbo-molecular pumps. The standard shape parameter values for the constructional elements (the vanes 41, the air transfer grooves 42, etc.) of the turbo-molecular type pump air transfer portion S2 can, therefore, be determined in the same manner as for the upstream edge of the conventional turbo-molecular pumps.

[0181] After the standard shape parameters are determined, it is possible to determine the other shape parameters using ordinary turbo-molecular pump design theory. In other words, the downstream edge values of the turbo-molecular type pump air transfer portion S2, such as cubical flow volume (air exhaust volume) (V), compression ratio (R), spacing chord ratio (So/b), vane angle θ, etc., can be determined as the standard shape parameters as follows, for example:

[0182] (21) Air exhaust volume (cubical flow volume) (V): V=282 (L/s=liters/s)

[0183] Providing that V={cubical flow volume (air exhaust volume) of the downstream edge of the turbo-molecular type pump air transfer portion S2}={the air exhaust volume of the screw type pump air transfer portion S1, i.e., air intake volume at the upstream edge of the screw type pump air transfer portion S1}.

[0184] (22) compression ratio (R): R=2.63

[0185] (In this case, designed air exhaust velocity at the upstream edge of the turbo-molecular type pump air transfer portion S2 is=V×2.6=282×2.63=742 (L/=liters /s))

[0186] It is noted that the compression ratio R is the initially set value, which is variable when the other multiple shape parameter values are determined while they are adjusted during the actual design process. In such a case, the final air exhaust velocity, too, becomes different from its initially set value.

[0187] (23) Spacing chord ratio (So/f) (So/f)=1.0

[0188] (The spacing chord ratio is a value calculated using (So/f), with f being the length of the vanes 41 from their upstream edge to their downstream edge, and So being the spacing between two adjacent vanes 41, 41. Providing that So=the average value of the upstream edge spacings of the adjacent vanes 41, 41 and the downstream edge spacings of the same. It is possible to set the spacing chord ratio of the vanes 41 of the upstream edge of the turbo-molecular type pump air transfer portion S2 within the 1±0.2 range, just like in the dynamic vanes of the air intake side of run-of-the-mill turbo-molecular pumps. In this first embodiment, the spacing chord ratio is set at 1.0, the value used generally for the upstream edge of ordinary turbo-molecular pumps.

[0189] (24) vane angle θ=30°

[0190] (Ordinarily, the vane angle θ to the tilt angle of screw α of the upstream edge of the screw type pump air transfer portion S1, is θ≧α. Further, the air exhaust efficiency value is set in the θ=30°^˜40° range. Since there is no big difference in the air exhaust efficiency value between θ=30° and θ=40°, and the compression capacity decreases when the value nears 40°, θ=30° is used in this embodiment.

[0191] (25) the upstream edge vane width (W1)=2 mm

[0192] (It is desirable to make the upstream edge vane width (W) as thin as possible so long as its strength can be maintained, because the air intake opening has a larger square area. For this reason, the upstream vane width is set at W1=2 mm. As mentioned above, the vane width (W2) of the downstream edge of the vanes 41 is identical to the thread width of the screws 36 (d=5.65 mm). In other words, W2=5.65 mm. Since the vanes 41, according to this first embodiment, a flat plate shape, the average value (W a) of the vane width (W) is W a=(W 1+W 2)/2=3.33 mm.)

[0193] (26) the number of vanes 41=5

[0194] (The number of vanes (41)=5 is determined in accordance with the number of the screw grooves 37 (=5) of the screw type pump air transfer portion S1 on the downstream side of the vane 41.)

[0195] After the initial values for the above-mentioned standard shape parameters are determined, the approximate values for the other shape parameters of the turbo-molecular type pump air transfer portion S2 are determined based on the turbo-molecular design theory under the condition that the air exhaust volume of the turbo-molecular type air transfer portion S2 equals the air intake volume at the upstream edge of the screw type pump air transfer portion S1. Nevertheless, in reality, a variety of parameter values are changed little by little as calculations are done repeatedly until each of the appropriate values are determined. When calculations are being performed on values using the above-mentioned design theory, as, for example, when the average value of the vane width W a=(W1+W2)/2 is used for the value of the different vane width of the vane 41 at the upstream and downstream edges thereof, even should the vane pitch (the space of the adjacent vanes) at the upstream and downstream edges be different, the average value of all the pitches, from the upstream edge pitches to the downstream edge pitches, is used.

[0196] Calculated in this manner, the shape parameter value for the turbo-molecular type air transfer portion S2 is, for example, the following (31) to (35).

[0197] (31) vane circumferential length=46 mm

[0198] (32) length of the vanes in the axial direction=46 mm

[0199] (33) square area of the air intake opening=213 mm²

[0200] (34) designed air exhaust velocity of vane at the edge portion of the air intake side=742 L/s

[0201] The air exhaust velocity value here was calculated according to the formula (see below) used for high vacuum zones (molecular flow zones).

[0202] Air exhaust velocity =square area of vane opening×11.6×efficiency =(the square area per one thread)×the number of threads (=5)×11.6×0.618=(4.6×4.5)×5×11.6×0.618=742 Providing that the above-mentioned 11.6 (L/(s/cm²) ) represents the air volume of the air molecules passing through the square area of 1 cm² per second, and the above-mentioned efficiency is a value determined by variables such as the number of rotations, the vane angle, the vane length and the base diameter, etc.

[0203] (35) r 2=45 mm

[0204] Providing that r 2 is the base radius of the upstream edge of the vanes 41 of the turbo-molecular type pump air transfer portion S2. The groove depth of the aforementioned edge is calculated based on its shape elements, and is determined based on the relationship between the compression capacity and the air exhaust velocity. Although (r 0−r 1)/(length of S2 in the direction of shaft) corresponds to the average tilt angle of the air transfer grooves 42, the compression efficiency is lowered if the average tilt angle is large, and the required length of the turbo-molecular type pump air transfer portion S2 becomes long if the average tilt angle is small. Thus, such being the case, the optimum values for the above-mentioned r 2 should be determined in view of the above. The multiple-type vacuum pump (P) is thus designed in this manner and made on an experimental use thereafter, experiments and tests are conducted by using the experimental multiple-type vacuum pump (P), followed by a number of revisions of the shape, until the optimum shape is determined. In this way, it becomes easy to design and manufacture the multiple-type vacuum pump P with the desired high-volume air evacuation capacity.

[0205] (Operation of First Embodiment)

[0206] In the multiple-type vacuum pump P, according to the embodiment 1, having the abovementioned construction, since the vanes 41 are used at the upstream edge of turbo-molecular type pump air transfer portion S2, similar to the first stage dynamic vanes used at the upstream edge in the ordinary turbo-molecular pumps, it is possible to enlarge the square area of the air intake opening to a great extent as compared to the conventional screw type vacuum pumps. The result: By virtue of the geometric shape of the vanes 41, not only can the air exhaust velocity be significantly increased within the free molecule zone, which determines the probability of air molecule influx, but the compression capacity can also be maintained.

[0207] The downstream edge (the edge on the discharge side) of the vanes 41 of the turbo-molecular type pump air transfer portion S2 is connected to the screw type pump air transfer portion S1, which performs air evacuation with great velocity even in the slip flow zone (low vacuum zone). Since the thread widths d of the screw threads 36 of the screw type pump air transfer portion S1 are larger than the vane widths W1 of the vanes 41 at the upstream edge of the turbo-molecular type pump air transfer portion S2, the widths of the vanes 41, as shown in FIG. 3C, gradually get larger as they go from the upstream edge to the downstream edge, and are connected to the upstream edge of screw threads 36.

[0208] Disturbances created in the stream of air due to sudden changes at the connecting portion of the vanes 41 and the screw threads 36, which would result in a decrease in air evacuation efficiency, are solved by this invention.

[0209] In this embodiment, since the vane angle θ and the screw tilt angle α of the vane 41 is θ=α=30°, it is possible to make a smooth connection between the flat plate shaped vanes 41 and the upstream edge of the screw threads 36. And this, in turn, prevents any disturbances created in the connecting portion of the downstream edge of the vanes 41 and the upstream edge of the screw threads 36.

[0210] Furthermore, according to the first embodiment, the base radius of a downstream portion S2b of the vanes 41 of the turbo-molecular type pump air transfer portion S2, is made larger (i.e., gets smaller as it goes toward the upstream edge), thereby making a smooth transition in the changes in shape from the turbo-molecular type pump air transfer portion S2 to the screw type pump air transfer portion S1, making it possible to prevent disturbances from occurring in the air being transferred.

[0211] Further, the multiple-type vacuum pump P of the first embodiment takes in air molecules through the turbo-molecular type pump air transfer portion S2 situated at the upstream side of the multiple-type vacuum pump, then compresses this air to the predetermined pressure. Because the cubical volume of this compressed air has become small, the cubical air volume taken in at the subsequent screw type pump air transfer portion S2, ends up being even less than in the turbo-molecular type pump air transfer portion S2. Because the air continues to be even more compressed in the screw type pump air transfer portion S1, the cubic volume of the screw grooves 37 also continues to get smaller. In the first embodiment, the screw type pump air transfer portion S1, which meets the requirement of the pressure and volume of the air discharged from the turbo-molecular type pump air transfer portion S2, is designed as described above. Thus, the air evacuation capacity (compression capacity and air evacuation velocity) of the multiple-type vacuum pump on the whole can be improved.

[0212] Further, because the air that flows through the air transfer grooves 42 and the screw grooves 37 of the multiple-type vacuum pump P is transferred smoothly, heat generation is reduced and deterioration of the strength of material of the rotor H is lowered, allowing the pump to be operated in even high pressure zones.

[0213] FIG. 4 is a comparative diagram of multiple-type vacuum pump P, according to the first embodiment, and a conventional screw type vacuum pump, regarding an example of measurements taken on the air evacuation speed relating to the pressure of the air intake opening. As will be understood from the graph in FIG. 4, the distinct air evacuation characteristics in the multiple-type vacuum pump P of the first embodiment were improved in the high vacuum zone. Further, the air evacuation velocity in the low vacuum zone is maintained at the same level as that of the conventional screw type vacuum pumps.

[0214] (Second embodiment)

[0215] FIG. 5 illustrates a rotor of the multiple-type vacuum pump in a second embodiment according to the present invention, which corresponds to FIG. 3 in the above-mentioned first embodiment. FIG. 5A is a top plan view of the rotor as viewed from the upstream side in the air transfer direction; FIG. 5B is a side view of the rotor; FIG. 5C is a development elevation of the outer surface of the rotor; and FIG. 5D is an enlarged part of the FIG. 5C.

[0216] In the description of this second embodiment, the same reference numbers are given to the corresponding parts of the above-mentioned first embodiment to eliminate repetitive explanation. The second embodiment is different from the above-mentioned first embodiment in the following features, but is constructed similarly in other features.

[0217] As shown in FIG. 5, the turbo-molecular type pump air transfer portion S2 has an upstream portion S2a and a downstream portion S2b.

[0218] The depth of the air transfer groove 42 of the upstream portion S2a, according to the turbo-molecular type pump air transfer portion S2, becomes smaller in a straight line as it goes towards the upstream in the rotary shaft direction. The downstream portion S2b is curved to form a convex shape on an outer surface with respect to the rotary shaft so as to connect smoothly the bottom surface of the air transfer groove 42 of the upstream portion S2a to the bottom surface of the screw groove 37.

[0219] The vane 41 includes a flat plate portion 41a mounted on the upstream portion S2a and a curved plate portion 41b mounted on the downstream portion S2b. A vane angle θ of the flat plate portion 41a is 40°. The upstream edge of the curved plate portion S2b is connected to the downstream edge, having the vane angle of 40°, of the flat plate portion S2a. The downstream edge of the curved plate S2b is connected to the upstream edge, having a tile angle of screw of α1, of the screw type pump air transfer portion S1. When the tilt angle α1 is greater than the vane angle θ (as in the case of the second embodiment, the angles are: θ=40° and α130°), the downstream portion S2b is curved so as to be smoothly connected to the flat plate portion S2a on its upstream side and to the screw type pump air transfer portion S1 on its downstream side.

[0220] (Operation of the Second Embodiment)

[0221] When the rotor H rotates, the turbo-molecular type pump air transfer portion S2 compresses the air which had been taken in from its upstream edge, and transfers the air into the upstream edge of the screw type pump air transfer portion S1. In the second embodiment, the vane angle θ is 40° which is greater than the vane angle, θ=30°, in the first embodiment. Therefore, it is possible to increase the air outlet velocity in the high vacuum region.

[0222] In the second embodiment, the downstream portion S2b is curved to form a convex shape on the outer surface with respect to the rotary shaft so as to smoothly connect the bottom surface of the air transfer groove 42 of the upstream portion S2a to the bottom surface of the screw groove 37. This makes it difficult to cause a disturbance on the air flow at the connecting portion between the bottom surface of the air transfer groove 42 and the bottom surface of the screw groove 37.

[0223] (Third Embodiment)

[0224] FIG. 6 illustrates a rotor of the multiple-type vacuum pump in a third embodiment according to the present invention, which corresponds to FIG. 5 in the above-mentioned second embodiment. FIG. 6A is a top plan view of the rotor as viewed from the upstream side in the air transfer direction; FIG. 6B is a side view of the rotor; FIG. 6C is a development elevation of the outer surface of the rotor; and FIG. 6D is an enlarged part of the FIG. 6C.

[0225] In the description of this third embodiment, the same reference numbers are given to the corresponding parts of the above-mentioned second embodiment to eliminate repetitive explanation.

[0226] As shown in FIG. 6, the upstream edge portion 41c of the vane 41 of the turbo-molecular type pump air transfer portion S2 is slightly curved toward the downstream side in the direction of the air transfer. (see FIG. 6D). Except for this feature, the third embodiment is constructed similar to the above-mentioned second embodiment.

[0227] By changing the degree of the curvature of the upstream edge, curved toward the downstream side in the direction of the air transfer, portion 41c of the vane 41, it is possible to control the compression performance of the turbo-molecular type pump air transfer portion.

[0228] (Fourth Embodiment)

[0229] FIG. 7 illustrates a rotor of the multiple-type vacuum pump in the fourth embodiment according to the present invention, which corresponds to FIG. 5 in the above-mentioned second embodiment. FIG. 7A is a top plan view of the rotor as viewed from the upstream side in the air transfer direction; FIG. 7B is a side view of the rotor; FIG. 7C is a development elevation of the outer surface of the rotor; and FIG. 7D is an enlarged part of the FIG. 7C.

[0230] In the description of the fourth embodiment, the same reference numbers are given to the corresponding parts of the above-mentioned second embodiment to eliminate repetitive explanation. The fourth embodiment is different from the above-mentioned second embodiment in the following features, but is constructed similarly in other features.

[0231] As shown in FIG. 7, the upstream portion S2c of the turbo-molecular type pump air transfer portion S2 has a plurality of additional vanes 43 in the shape of flat plates, respectively, which are mounted between the vanes 41.

[0232] The thickness t of the additional vane 43 is uniform from the upstream edge to the downstream edge and the value of t is 2 mm. The vane angle θ′ of the additional vane 43 is 40° (θ′=40°), and the same as the vane angle θ of the upstream side of the flat plate portion 41a of the vane 41 (θ=40°). It is preferable that the thickness t of the additional vane 43 be as thin as possible as long as its strength can be maintained. The vane angle θ′ of additional vane 43 is set in the range of θ′≧0, while the range of the vane angle θ of the vane is θ≧α1.

[0233] (Operation of the Fourth Embodiment)

[0234] In the fourth embodiment of the multiple-type vacuum pump, according to the present invention, which comprises the above-mentioned structure, it is possible to control the volume of the sucked air and the air compression ratio, by setting up properly the vane angle θ′, the vane thickness t, and the length of the additional vanes 43 which are mounted respectively between the plurality of vanes 41 of the upstream portion S2c of the turbo-molecular type pump air transfer portion S2. Furthermore, since the additional vanes 43 are made of flat plates, they are easier to be designed and manufactured.

[0235] (Fifth Embodiment)

[0236] FIG. 8 illustrates a rotor of the multiple-type vacuum pump in a fifth embodiment according to the present invention, which corresponds to FIG. 3 in the above-mentioned first embodiment. FIG. 8A is a top plan view of the rotor as viewed from the upstream side in the air transfer direction; FIG. 8B is a side view of the rotor; FIG. 8C is a development elevation of the outer surface of the rotor; and FIG. 8D is an enlarged part of the FIG. 8C.

[0237] In the description of this fifth embodiment, the same reference numbers are given to the corresponding parts of the above-mentioned second embodiment to eliminate repetitive explanation.

[0238] As shown in FIG. 8, the upstream portion S2a of the vane 41 of the turbo-molecular type pump air transfer portion S2 is made in the form of a flat plate, and the downstream portion of the vane 41 of the downstream portion S2b is of a curved plate. The tilt angle of screw α1 of the upstream edge of the screw type pump air transfer portion S1 is 30°, and the vane angle θ of the vane 41 of the upstream portion S2a of the turbo-molecular type pump air transfer portion S2 is 40°. The curved plate portion of the downstream portion of the vane 41 is curved so as to smoothly connect to the upstream edge of the screw thread 36 of the screw type pump air transfer portion S1.

[0239] In the first to fourth embodiments of the turbo-molecular type pump air transfer portion S2, as shown in the foregoing FIGS. 3C, 5C, 6C and 7C, the downstream edge of a vane 41 of the turbo-molecular type pump air transfer portion S2 and the upstream edge of an adjacent vane 41 are located at the same longitude in a circumferential direction. In the fifth embodiment, however, as shown FIG. 8, the downstream edge of a vane 41 and the upstream edge of the adjacent vane 41 are spaced from each other in a circumferential direction.

[0240] Depending on the rotation speed of the rotor H and values of the parameter, such as a vane shape, a multiple-type vacuum pump P, as shown in FIG. 8, is constructed. It is also possible to construct a multiple-type vacuum pump P which has a function similar to that of the abovementioned first embodiment.

[0241] (Sixth Embodiment)

[0242] FIG. 9 illustrates a rotor of the multiple-type vacuum pump in a sixth embodiment according to the present invention, which corresponds to FIG. 8 in the above-mentioned fifth embodiment. FIG. 9A is a top plan view of the rotor as viewed from the upstream side in the air transfer direction; FIG. 9B is a side view of the rotor; FIG. 9C is a development elevation of the outer surface of the rotor; and FIG. 9D is an enlarged part of the FIG. 9C.

[0243] In the description of this sixth embodiment, the same reference numbers are given to the corresponding parts of the above-mentioned second embodiment to eliminate repetitive explanation.

[0244] As shown in FIG. 9, five vanes 41, which are similar to those of the fifth embodiment, are mounted on the downstream portion S2d of the turbo-molecular type pump air transfer portion S2, and five additional flat-plate-shape vanes 44 are mounted on the upstream portion S2e. The five additional vanes 44 provided on the upstream side are located at the midpoints, in a circumferential direction, of the five vanes 41 provided on the downstream side.

[0245] The tilt angle of screw a 1 of the upstream edge of the screw type pump air transfer portion SI is 30°. The vane angle of the vane 41 of the downstream portion S2d of the turbo-molecular type pump air transfer portion S2 is 30°. The vane angle θ of the additional vane 44 of the upstream portion S2e is 40°. It is also possible to construct a multiple-type vacuum pump P, as shown FIG. 9, by setting up a proper compression ratio of the turbo-molecular type pump air transfer portion S2. It is possible to construct a multiple-type vacuum pump P which has the same function as that of the first embodiment.

[0246] (Seventh Embodiment)

[0247] FIG. 10 shows a vertical section of the multiple-type vacuum pump of a seventh embodiment according to the present invention. FIG. 11 shows a section along the line XI-XI of the FIG. 10.

[0248] In the description of the seventh embodiment, the same reference numbers are given to the corresponding parts of the above-mentioned first embodiment to eliminate repetitive explanation. The seventh embodiment is different from the above-mentioned first embodiment in the following features, but is constructed similarly in other features.

[0249] As shown in FIG. 10, a female screw thread 46 is formed at the upstream edge of the turbo-molecular type pump air transfer portion S2. A straightening member 47 has a male screw 48, which is screwed into the female screw thread 46. The straightening member 47 has an airflow guide surface 49, which is made of a curved surface and symmetric with respect to the axis protruding towards the upstream side. The downstream edge of the airflow guide surface 49 is constructed so as to be smoothly connected to the upstream edge of the base surface of the air transfer groove 42 of the turbo-molecular type pump air transfer portion S2. This straightening member thus guides the airflow to the base surface of the upstream edge of the air transfer groove of the turbo-molecular type pump air transfer portion.

[0250] Therefore, an air intake efficiency increases especially in a low vacuum region where an air density is high.

[0251] The flange 2 of the seventh embodiment has an air outlet 2d instead of the air outlet 2a of the first embodiment. The air outlet 2d has an air circulation groove 2d1 and a tangential air outlet 2d2, the first being located in an upstream portion and maintains a uniform depth and the latter being located in a downstream portion. The air circulation groove 2d1 is made of a cylindrical wall of smaller diameter and a cylindrical wall of larger diameter, and forms a ring shape viewed in the axial direction of the rotary shaft of the rotor H. The upstream edge of the ring-shaped air circulation groove 2d1 is connected to the air outlet space G which is created between the downstream edge of the rotor H and the upstream edge of the flange 2.

[0252] The tangential air outlet 2d2 is formed in a tangential direction extended from the outer peripheral wall of the cylindrical walls which constitutes the air circulation groove 2d1. The tangential air outlet 2d2 is disposed at the lower end of the air circulation groove 2d1 whose depth is uniform, and the base wall of the air circulation groove 2d1 and the bottom portion of the inside surface of the tangential air outlet 2d2 are formed on the same plane. Air is discharged from the downstream edge of the rotor H, circulating through the ring-shaped air outlet space G, and moves downwardly circulating through the ring-shaped air circulation groove 2d1. Then the air is discharged from the lower end of the air circulation groove 2d1 into the tangential air outlet 2d2.

[0253] Therefore, the air discharged from the downstream edge of the rotor H is smoothly discharged from the multiple-type vacuum pump P.

[0254] (Eighth Embodiment)

[0255] FIG. 12 shows a vertical section of the multiple-type vacuum pump of an eighth embodiment of the current invention. FIG. 13 shows a section along the line XIII-XIII of the FIG. 12. FIG. 14 is a perspective view describing the construction of the air outlet.

[0256] In the description of the eighth embodiment, the same reference numbers are given to the corresponding parts of the above-mentioned seventh embodiment to eliminate repetitive explanation. The eighth embodiment is different from the above-mentioned seventh embodiment in the following features, but is constructed similarly in other features.

[0257] As shown FIGS. 12 to 14, the flange 2 of the eighth embodiment has an air outlet 2e instead of the air outlet 2d of the seventh embodiment. The air outlet 2e has an air circulation groove 2e1 and a tangential air outlet 2e2, the first being located in the upstream portion and the latter being in the downstream portion. The tangential air outlet 2e2 is constructed in the same way as the tangential air outlet 2d2 of the seventh embodiment. The air circulation groove 2e1 is different from the air circulation groove 2d1 of the seventh embodiment in that the base surface of the air circulation groove 2e1 becomes deeper as it spirals downward, whereas the air circulation groove 2d1 maintains a uniform depth. The deepest point of the air circulation groove 2e1 is connected to the upstream edge of the tangential air outlet 2e2.

[0258] Air is discharged from the downstream edge of the rotor H, circulating through the ring-shaped air outlet space G, and moves downwardly circulating along the spiral-shaped base surface of the air circulation groove 2e1. The air is then discharged from the downstream edge of the air circulation groove 2e1 into the tangential air outlet 2e2.

[0259] Therefore, the air discharged from the downstream edge of the rotor H is smoothly discharged from the multiple-type vacuum pump P.

[0260] (Ninth Embodiment)

[0261] FIG. 15 shows a vertical section of the multiple-type vacuum pump of a ninth embodiment according to the present invention.

[0262] FIG. 16 illustrates the rotor of the embodiment 15. FIG. 16A is a top plan view of the rotor as viewed from the upstream side in the air transfer direction; FIG. 16B is a side view of the rotor; FIG. 16C is a development elevation of the outer surface of the rotor; and FIG. 16D is an enlarged part of the FIG. 16C.

[0263] In the description of this ninth embodiment, the same reference numbers are given to the corresponding parts of the above-mentioned first embodiment to eliminate repetitive explanation. The ninth embodiment is different from the above-mentioned first embodiment in the following features, but is constructed similarly in other features.

[0264] As shown in FIGS. 15 and 16, according to the ninth embodiment, the multiple-type vacuum pump P has a turbo-molecular pump zone S3 on the upstream side of the turbo-molecular type pump air transfer portion S2 of the multiple-type vacuum pump P of the first embodiment. The turbo-molecular pump zone S3 has a turbo molecule pump 50, where dynamic vanes and static vanes are alternately mounted in the air transfer direction.

[0265] The rotor H of the ninth embodiment has a first stage dynamic vane wheel 51, having a plurality of dynamic vanes 51a, and a second stage dynamic vane wheel 52, having a plurality of dynamic vanes 52a, on the upstream side of the upstream edge of the turbo-molecular type pump air transfer portion S2.

[0266] The casing 6 has an inner cylinder 6a and an outer cylinder 6b. A first stage static vane wheel 53, having a plurality of static vanes 53a, and a second stage static vane 54, having a plurality of static vanes 54a, are supported by the inner cylinder 6a.

[0267] The vane wheels 51 to 54 are mounted alternately from the upstream side of the air transfer direction, beginning with the dynamic vane wheel 51, the static vane wheel 53, the dynamic vane wheel 52, and the static vane wheel 54.

[0268] The turbo molecule pump 50 is constructed by the vane wheels 51 to 54.

[0269] (Operation of the Ninth Embodiment)

[0270] Compared with the first embodiment, the multiple-type vacuum pump P of the ninth embodiment, having the aforementioned structure, especially by using the turbo molecule pump 50, obtains a higher compression rate and can achieve higher discharge performance in a superhigh vacuum region.

[0271] By combining the vane 41 and the groove 42 of the turbo-molecular type pump air transfer portion S2 with the turbo molecule pump 50, which is mounted on the upstream side of the turbo-molecular pump zone S2, even if the number of the stages of the vane wheels of the turbo molecule pump 50 is reduced, it is possible to achieve the same discharge performance as that of the turbo molecule pump which has more numbers of stages of the vane wheels. That is, the multiple-type vacuum pump P can achieve a high performance in spite of its smaller number of the stages of the vane wheels and lower costs.

[0272] Embodiments of the present invention are not limited to those whose detailed explanation has been made above. It is possible to make various modifications on embodiments of the present invention within the scope of the present invention which is described in the claims. Examples of modifications of the present invention will be described as follows:

[0273] In the sixth embodiment, another additional vane can be mounted on the upstream side of the additional vane 44. That is, multiple stages of vanes can be mounted on the turbo-molecular type pump air transfer portion S2. In this case, it is possible to increase the compression performance of the turbo-molecular type pump air transfer portion S2.

[0274] It is possible to place a turbo molecule pump having dynamic vanes and static vanes mounted, alternately and in the air transfer direction, on the upstream side of the turbo-molecular type pump air transfer portion S2 of the above-mentioned embodiments 1 to 8.

[0275] It is possible to bend the upstream edge portions of each of the vanes, according to the respective embodiments as described above, towards the upstream side in the air transfer direction instead of bending them towards the downstream side. In this case, by adjusting the bending degree, it is also possible to control the compression performance and discharge velocity of the turbo-molecular type pump air transfer portion.

[0276] It is possible to use other bearings, such as a kinetic pressure bearing, instead of the magnetic bearing used in the above mentioned embodiments. The air transfer groove 42 of the turbo-molecular type pump air transfer portion S2 is constructed such that the air transfer groove 42 becomes deeper as it goes to the upstream edge. The air transfer groove 42, however, can be constructed such that the air transfer groove 42 could maintain the same depth from the upstream edge to a certain point at the downstream side, and become shallower as it goes beyond that point towards further downstream side.

[0277] The structure of the air outlets 2d and 2e of the seventh and eighth embodiments can be applied not only to the multiple-type vacuum pump P of these embodiments, but also to the air outlet of the screw type pump.