VACUUM PUMP AND ROTATING BODY FOR VACUUM PUMP

A vacuum pump which can reduce a stress generated in a connected part between a rotating body and a rotating shaft is provided. A rotating body is provided having rotor blades provided on an outer periphery of a rotor-blade forming portion, and fastened to the rotor shaft by a bolt, and rotatable with the rotor shaft. At least either one of a fitting hole portion fitted with the rotating shaft and a through hole portion, through which a bolt penetrates, in the rotating body is a stress-reduction target portion, and a groove portion that reduces stress generated in the stress-reduction target portion during rotation of the rotating body is provided.

FIELD

The present invention relates to a vacuum pump such as a turbo molecular pump and a rotating body for the vacuum pump, for example.

BACKGROUND

In general, a turbo molecular pump is known as one type of a vacuum pump. This turbo molecular pump is configured such that a rotor blade is rotated by conduction to a motor inside a pump main-body so as to flick off gas molecules of a gas (process gas) sucked into the pump main-body, whereby the gas is exhausted. Moreover, in this type of the turbo molecular pump, a rotating shaft (rotor shaft) is connected to the rotating body, on which the rotor blade is formed, so that the rotating shaft and the rotating body are rotated by the motor and perform exhaustion.

SUMMARY

By the way, in the vacuum pump such as various turbo molecular pumps as described above, in general the more a rotation number of the rotor blade is increased, the higher the exhaust performance becomes. However, as a result of structural analysis by the inventor and the like by paying attention to a connected part between the rotating body and the rotating shaft, it has been found out that stress concentration can easily occur at the connected part.

In order to reduce such stress generated at the connected part between the rotating body and the rotating shaft, setting of a rotation number at low during a rated operation can be considered, but if the rotation number is lowered, improvement of the exhaust performance becomes difficult. On the other hand, if the rotation number is increased in order to improve the exhaust performance without considering a measure against the stress concentration as above, a high stress is generated at the connected part between the rotating body and the rotating shaft, which lowers reliability. And since the connected part between the rotating body and the rotating shaft is a part which considerably influences reliability of the vacuum pump, a large design change of the connected part is not easy.

An object of the present invention is to provide a vacuum pump and a rotating body for the vacuum pump which can reduce stress concentration generated in the rotating body or particularly the stress generated at the connected part between the rotating body and the rotating shaft.

(1) In order to achieve the aforementioned object, the present invention is, in a vacuum pump having a rotor blade on an outer periphery of a cylinder part and including a rotating body fastened to a rotating shaft by a fastening means and rotatable together with the rotating shaft, characterized in that

in the rotating body, at least one of a fitting hole portion fitted with the rotating shaft and a through hole portion, through which the fastening means penetrates, is a stress-reduction target portion, and a groove portion that reduces stress generated in the stress-reduction target portion during rotation of the rotating body is provided in the rotating body.

(2) Moreover, in order to achieve the aforementioned object, another present invention is a vacuum pump described in (1), characterized in that the groove portion is provided closer to an outer peripheral side than the fitting hole portion or the through hole portion.
(3) Moreover, in order to achieve the aforementioned object, another present invention is a vacuum pump described in (1) or (2), characterized in that the groove portion is provided on at least one of an inner peripheral surface and an outer peripheral surface of the rotating body.
(4) Moreover, in order to achieve the aforementioned object, another present invention is a vacuum pump described in any one of (1) to (3), characterized in that, in the groove portion, at least an inner peripheral side has a gentle inclination structure.
(5) Moreover, in order to achieve the aforementioned object, another present invention is a vacuum pump described in any one of (1) to (4), characterized in that the groove portion is disposed on a fastened surface of the rotating body or on an extended surface thereof.
(6) Moreover, in order to achieve the aforementioned object, another present invention is a vacuum pump described in any one of (1) to (5), characterized in that the rotating body is applied with surface treatment and has a counterbore portion, which avoids contact with the rotating shaft, on a peripheral edge part of at least one of the fitting hole portion and the through hole portion.
(7) Moreover, in order to achieve the aforementioned object, another present invention is, in a rotating body for a vacuum pump having a rotor blade on an outer periphery of a cylinder part and fastened to the rotating shaft by a fastening means, characterized in that

at least one of a fitting hole portion fitted with the rotating shaft and a fastened part, to which the fastening means is fastened, is a stress-reduction target portion, the rotating body including a groove portion which reduces a stress generated in the stress-reduction target portion during rotation.

According to the present invention, the vacuum pump and the rotating body for the vacuum pump which can reduce stress generated in the connected part between the rotating body and the rotating shaft can be provided.

DETAILED DESCRIPTION

Hereinafter, a vacuum pump according to an embodiment of the present invention will be explained on the basis of the drawings.FIG.1illustrates a turbo molecular pump100as a vacuum pump according to the embodiment of the present invention. This turbo molecular pump100is configured to be connected to a vacuum chamber (not shown) of a target device such as a semiconductor manufacturing device, for example.

A vertical sectional view of this turbo molecular pump100is shown inFIG.1. InFIG.1, the turbo molecular pump100has an inlet port101formed in an upper end of a cylindrical outer cylinder127. And inside the outer cylinder127, a rotating body103with a plurality of rotor blades102(102a,102b,102c, . . . ), which are turbine blades for sucking/exhausting a gas, formed on a peripheral part radially and in multiple stages is provided. At a center of this rotating body103, a rotor shaft113(rotating shaft) is mounted, and this rotor shaft113is floated/supported in the air and position-controlled by a magnetic bearing of 5-axis control, for example. The rotating body103is constituted by metal such as aluminum or an aluminum alloy in general.

Regarding an upper-side radial electromagnet104, four electromagnets are disposed by forming a pair on an X-axis and a Y-axis. Four upper-side radial sensors107are provided in the vicinity of the upper-side radial electromagnets104and correspondingly to each of the upper-side radial electromagnets104. As the upper-side radial sensors107, an inductance sensor, an eddy current sensor or the like having a conductive winding is used, and a position of the rotor shaft113is detected on the basis of a change in inductance of this conductive winding changing in accordance with the position of the rotor shaft113. This upper-side radial sensor107is configured to detect radial displacement of the rotor shaft113, that is, the rotating body103fixed thereto and to send it to a control device200.

In this control device200, a compensation circuit having a PID adjustment function, for example, generates an excitation control-instruction signal of the upper-side radial electromagnet104on the basis of a position signal detected by the upper-side radial sensor107, and an amplifier circuit150(which will be described later) shown inFIG.2excites and controls the upper-side radial electromagnet104on the basis of this excitation control-instruction signal, whereby an upper side radial position of the rotor shaft113is adjusted.

And this rotor shaft113is formed of a material with high magnetic permeability (such as iron and stainless) and the like and is attracted by a magnetic force of the upper-side radial electromagnet104. Such adjustment is performed independently in each of an X-axis direction and a Y-axis direction. Moreover, a lower-side radial electromagnet105and a lower-side radial sensor108are disposed similarly to the upper-side radial electromagnet104and the upper-side radial sensor107and adjust a radial position on a lower side of the rotor shaft113similarly to the radial position on the upper side.

Moreover, axial electromagnets106A,106B are disposed by vertically sandwiching a disc-shaped metal disc111provided on a lower part of the rotor shaft113. The metal disc111is constituted by a material with high magnetic permeability such as iron. In order to detect axial displacement of the rotor shaft113, the axial sensor109is provided, and it is configured such that an axial position signal thereof is sent to the control device200.

And in the control device200, the compensation circuit having the PID adjustment function, for example, generates an excitation control-instruction signal for each of the axial electromagnet106A and the axial electromagnet106B on the basis of the axial position signal detected by the axial sensor109, and the amplifier circuit150excites and controls the axial electromagnet106A and the axial electromagnet106B, respectively, on the basis of these excitation control-instruction signals, whereby the axial electromagnet106A attracts the metal disc111upward by the magnetic force, while the axial electromagnet106B attracts the metal disc111downward, and the axial position of the rotor shaft113is adjusted.

As described above, the control device200adjusts the magnetic force by which the axial electromagnets106A,106B affect the metal disc111as appropriate, magnetically floats the rotor shaft113in the axial direction, and holds it in a space in a non-contact manner. Note that, the amplifier circuit150which excites and controls the upper-side radial electromagnet104, the lower-side radial electromagnet105, and the axial electromagnets106A,106B will be described later.

On the other hand, a motor121includes a plurality of magnetic poles disposed in a peripheral state so as to surround the rotor shaft113. Each of the magnetic poles is controlled by the control device200so as to rotate and drive the rotor shaft113via an electromagnetic force acting between it and the rotor shaft113. Moreover, rotation speed sensors such as a Hall element, a resolver, and an encoder, not shown, for example, are incorporated in the motor121such that a rotation speed of the rotor shaft113is detected by a detection signal of this rotation speed sensor.

Furthermore, a phase sensor, not shown, is mounted in the vicinity of the lower-side radial sensor108, for example, so as to detect a phase of rotation of the rotor shaft113. The control device200is configured to detect a position of the magnetic pole by using the detection signals of this phase sensor and the rotation speed sensor together.

A plurality of stator blades123(123a,123b,123c, . . . ) are disposed with a slight gap from the rotor blades102(102a,102b,102c, . . . ). The rotor blades102(102a,102b,102c, . . . ) are formed with inclination only by a predetermined angle from a plane perpendicular to an axis of the rotor shaft113in order to transfer molecules of an exhaust gas downward by collision, respectively. The stator blades123(123a,123b,123c, . . . ) are constituted by metal such as aluminum, iron, stainless, copper, for example, or an alloy containing these metals as components.

Moreover, the stator blades123are also formed with inclination only by a predetermined angle from a plane perpendicular to the axis of the rotor shaft113similarly and are disposed alternately with stages of the rotor blades102toward the inside of the outer cylinder127. And an outer peripheral end of the stator blade123is supported in a state fitted and inserted between a plurality of stator-blade spacers125(125a,125b,125c, . . . ) stacked in stages.

The stator-blade spacer125is a ring-shaped member and is constituted by metal such as aluminum, iron, stainless, copper, for example, or an alloy containing these metals as components. On an outer periphery of the stator-blade spacer125, the outer cylinder127is fixed with a slight gap. A base portion129is disposed on a bottom part of the outer cylinder127. An outlet port133is formed in the base portion129and is made to communicate with the outside. The exhaust gas entering the inlet port101from the chamber (vacuum chamber) side and transferred to the base portion129is sent to the outlet port133.

Moreover, depending on an application of the turbo molecular pump100, the threaded spacer131is disposed between the lower part of the stator-blade spacer125and the base portion129. The threaded spacer131is a cylindrical member constituted by metal such as aluminum, copper, stainless, iron or an alloy having these metals as components, and a plurality of spiral thread grooves131aare engraved in an inner peripheral surface thereof. A spiral direction of the thread groove131ais a direction in which, when molecules of the exhaust gas move in a rotating direction of the rotating body103, the molecules are transferred toward the outlet port133. At a lowest part continuing to the rotor blades102(102a,102b,102c, . . . ) of the rotating body103, a cylinder portion102dis suspended. An outer peripheral surface of this cylinder portion102dis cylindrical and is extended toward the inner peripheral surface of the threaded spacer131and is in the vicinity of the inner peripheral surface of this threaded spacer131with a predetermined gap. The exhaust gas having been transferred to the thread groove131aby the rotor blade102and the stator blade123is sent to the base portion129while being guided by the thread groove131a.

The base portion129is a disc-shaped member constituting a base part of the turbo molecular pump100and is constituted by metal in general such as iron, aluminum, and stainless. The base portion129physically holds the turbo molecular pump100and also functions as a heat conduction path and thus, metal with rigidity and high heat conductivity such as iron, aluminum, and copper is preferably used.

In the configuration as above, when the rotor blade102is rotated and driven by the motor121together with the rotor shaft113, the exhaust gas is sucked from the chamber through the inlet port101by actions of the rotor blade102and the stator blade123. A rotation speed of the rotor blade102is normally 20000 rpm to 90000 rpm, and a peripheral speed at a distal end of the rotor blade102reaches 200 m/s to 400 m/s. The exhaust gas sucked from the inlet port101passes between the rotor blade102and the stator blade123and is transferred to the base portion129. At this time, a friction heat generated when the exhaust gas is brought into contact with the rotor blade102and conduction of the heat generated in the motor121raise a temperature of the rotor blade102, and this heat is transmitted by radiation or conduction by gas molecules of the exhaust gas and the like to the stator blade123side.

The stator-blade spacers125are joined to each other on the outer peripheral parts, and the heat received by the stator blade123from the rotor blade102or the friction heat generated when the exhaust gas contacts the stator blade123or the like is transmitted to the outside.

Note that, in the explanation described above, the threaded spacer131is disposed on the outer periphery of the cylinder portion102dof the rotating body103, and the thread groove131ais engraved in the inner peripheral surface of the threaded spacer131. However, to the contrary, the thread groove is engraved in the outer peripheral surface of the cylinder portion102d, and the spacer having a cylindrical inner peripheral surface is disposed in the periphery thereof in some cases.

Moreover, depending on the application of the turbo molecular pump100, an electric component portion is covered with a stator column122on the periphery, and inside this stator column122is kept at a predetermined pressure by a purge gas in some cases so that the gas sucked from the inlet port101does not intrude into the electric component portion constituted by the upper-side radial electromagnet104, the upper-side radial sensor107, the motor121, the lower-side radial electromagnet105, the lower-side radial sensor108, the axial electromagnets106A,106B, the axial sensor109and the like.

In this case, a piping, not shown, is disposed in the base portion129, and the purge gas is introduced through this piping. The introduced purge gas is sent out to the outlet port133through gaps between a protective bearing120and the rotor shaft113, between a rotor and a stator of the motor121, and between the stator column122and the inner-peripheral side cylinder portion of the rotor blade102.

Here, the turbo molecular pump100requires control based on specification of a model and individually adjusted specific parameters (characteristics corresponding to the model, for example). In order to store the control parameters, the turbo molecular pump100includes an electronic circuit portion141inside the main body thereof. The electronic circuit portion141is constituted by a semiconductor memory such as EEP-ROM, and electronic components such as semiconductor elements for access thereof, a board143for mounting them and the like. This electronic circuit portion141is accommodated in a lower part of a rotation speed sensor, not shown, in the vicinity of a center of the base portion129, for example, constituting the lower part of the turbo molecular pump100and is closed by an airtight bottom lid145.

By the way, in a manufacturing process of a semiconductor, some of process gases introduced into the chamber have such a nature that becomes a solid when its pressure becomes higher than a predetermined value or when its temperature becomes lower than a predetermined value. Inside the turbo molecular pump100, a pressure of the exhaust gas is the lowest at the inlet port101and the highest at the outlet port133. If the pressure of the process gas becomes higher than the predetermined value or the temperature thereof becomes lower than the predetermined value in the middle of transfer from the inlet port101to the outlet port133, the process gas becomes a solid state, which adheres and deposits inside the turbo molecular pump100.

When SiCl4 is used as the process gas in an Al etching device, for example, at a low vacuum (760 [torr] to 10-2 [torr]) and at a low temperature (approximately 20 KA it is known from a steam pressure curve that a solid product (AlCl3, for example) precipitates, adheres and deposits inside the turbo molecular pump100. As a result, if the precipitates of the process gas deposit inside the turbo molecular pump100, the depositions narrow a pump channel and causes lowering of performances of the turbo molecular pump100. And the product described above was in such a state that easily solidifies and adheres at a part in the vicinity of the outlet port133or in the vicinity of the threaded spacer131where the pressure is high.

Therefore, in order to solve this problem, conventionally, a heater or an annular water-cooling pipe149, not shown, is wrapped around an outer periphery of the base portion129and the like, a temperature sensor (thermistor, for example), not shown, is embedded in the base portion129, for example, and control of heating of the heater or cooling by the water-cooling pipe149is executed so as to keep the temperature of the base portion129at a certain high temperature (set temperature) on the basis of a signal of this temperature sensor (hereinafter, called TMS. TMS: Temperature Management System).

Subsequently, regarding the turbo molecular pump100configured as above, the amplifier circuit150that excites and controls the upper-side radial electromagnet104, the lower-side radial electromagnet105, and the axial electromagnets106A,106B will be explained. A circuit diagram of this amplifier circuit150is shown inFIG.2.

InFIG.2, an electromagnet winding151constituting the upper-side radial electromagnet104and the like has one end thereof connected to a positive pole171aof a power source171through a transistor161and the other end connected to a negative pole171bof the power source171through a current detection circuit181and a transistor162. And the transistors161,162are so-called power MOSFET and have a structure in which a diode is connected between source-drain thereof.

At this time, the transistor161has a cathode terminal161aof the diode thereof connected to the positive pole171aand an anode terminal161bconnected to one end of the electromagnet winding151. Moreover, the transistor162has a cathode terminal162aof the diode thereof connected to the current detection circuit181and an anode terminal162bconnected to the negative pole171b.

On the other hand, a diode165for current regeneration has a cathode terminal165athereof connected to one end of the electromagnet winding151and an anode terminal165bthereof connected to the negative pole171b. Moreover, similarly, a diode166for current regeneration has a cathode terminal166athereof connected to the positive pole171aand an anode terminal166bthereof connected to the other end of the electromagnet winding151through the current detection circuit181. And the current detection circuit181is constituted by a Hall sensor-type current sensor or an electric resistance element, for example.

The amplifier circuit150constituted as above corresponds to one electromagnet. Thus, in a case where the magnetic bearing is 5-axis control and there are ten pieces in total of the electromagnets104,105,106A,106B, the similar amplifier circuit150is constituted for each of the electromagnets, and ten units of the amplifier circuits150are connected to the power source171in parallel.

Moreover, an amplifier control circuit191is constituted by a digital-signal processing portion (hereinafter referred to as a DSP portion), not shown, of the control device200, for example, and this amplifier control circuit191switches on/off of the transistors161,162.

The amplifier control circuit191compares a current value detected by the current detection circuit181(a signal reflecting this current value is called a current detection signal191c) with a predetermined current instruction value. And on the basis of this comparison result, a size of a pulse width (pulse width time Tp1, Tp2) generated within a control cycle Ts, which is one cycle by PWM control, is determined. As a result, gate drive signals191a,191bhaving this pulse width are output from the amplifier control circuit191to gate terminals of the transistors161,162.

Note that, when passing a resonant point during an acceleration operation of a rotation speed of the rotating body103or when disturbance occurs during a constant-speed operation and the like, position control of the rotating body103needs to be performed at a high speed and with a strong force. Thus, a high voltage such as50Y, for example, is used for the power source171so that the current flowing in the electromagnet winding151can rapidly increase (or decrease). Moreover, between the positive pole171aand the negative pole171bof the power source171, an ordinary capacitor is connected (not shown) for stabilization of the power source171.

In the configuration as above, when both the transistors161,162are turned on, the current flowing through the electromagnet winding151(hereinafter, referred to as an electromagnet current iL) increases, while when the both are turned off, the electromagnet current iL decreases.

Moreover, when one of the transistors161,162is turned on, while the other is turned off, a so-called flywheel current is held. And by causing the flywheel current to flow through the amplifier circuit150as above, a hysteresis loss in the amplifier circuit150is decreased, and power consumption of the circuit as a whole can be kept low. Moreover, by controlling the transistors161,162as above, a high frequency noise such as a higher harmonic wave generated in the turbo molecular pump100can be reduced. Furthermore, by measuring this flywheel current by the current detection circuit181, the electromagnet current iL flowing through the electromagnet winding151can be detected.

That is, if the detected current value is smaller than the current instruction value, both the transistors161,162are turned on only for a period of time corresponding to the pulse width time Tp1only once in the control cycle Ts (100 μs, for example) as shown inFIG.3. Thus, the electromagnet current iL during this period increases toward a current value iLmax (not shown) that can flow from the positive pole171atoward the negative pole171bthrough the transistors161,162.

On the other hand, if the detected current value is larger than the current instruction value, both the transistors161,162are turned off only for a period of time corresponding to the pulse width time Tp2only once in the control cycle Ts as shown inFIG.4. Thus, the electromagnet current iL during this period decreases toward a current value iLmin (not shown) that can be regenerated from the negative pole171btoward the positive pole171athrough the diodes165,166.

And in the both cases, after elapse of the pulse width time Tp1, Tp2, either one of the transistors161,162is turned on. Thus, during this period, the flywheel current is held in the amplifier circuit150.

In the turbo molecular pump100having the basic configuration as above, an upper side inFIG.1(the side of the inlet port101) is a sucking portion connecting to the side of the target device, and a lower side (the side provided on the base portion129so that the outlet port133protrudes to the left side in the drawing) side is an exhaust portion connecting to an auxiliary pump (back pump for roughing), not shown, and the like. And the turbo molecular pump100can be used in an inverted attitude, a horizontal attitude, an inclined attitude other than a perpendicular attitude in a vertical direction as shown inFIG.1.

Moreover, in the turbo molecular pump100, the outer cylinder127described above and the base portion129are combined to constitute a single case (hereinafter, both are combined and called a “main-body casing” and the like in some cases). Moreover, the turbo molecular pump100is connected to a box-shaped electric component case (not shown) electrically (and structurally), and the electric component case incorporates the control device200described above.

An internal constitution of the main-body casing (combination of the outer cylinder127and the base portion129) of the turbo molecular pump100can be separated into a rotation mechanism portion that rotates the rotor shaft113and the like by the motor121and an exhaust mechanism portion rotated/driven by the rotation mechanism portion. Moreover, the exhaust mechanism portion can be considered separately as a turbo-molecular-pump mechanism portion constituted by the rotor blade102, the stator blade123and the like and a groove-exhaust mechanism portion (which will be described later) constituted by the cylinder portion102d, the threaded spacer131and the like.

Moreover, the purge gas (protective gas) described above is used for protection of the bearing part, the rotor blade102and the like and prevents corrosion caused by the exhaust gas (process gas) and cools the rotor blade102and the like. Supply of this purge gas can be performed by a general method.

For example, though not shown, a purge gas channel extending linearly in the radial direction is provided at a predetermined part (a position separated approximately by 180 degrees with respect to the outlet port133and the like) of the base portion129. And to this purge gas channel (more specifically, a purge port to be an inlet of the gas), a purge gas is supplied via a purge-gas bomb (N2 gas bomb or the like), a flow-rate controller (valve device) and the like from the outer side of the base portion129.

The aforementioned protective bearing120is also called a “touchdown (T/D) bearing”, “backup bearing” and the like. By means of these protective bearings120, even in the case of a trouble in an electric system or a trouble such as atmospheric entry or the like, for example, a position or an attitude of the rotor shaft113is not largely changed, or the rotor blade102or its peripheral part is not damaged.

Note that, in each of the drawings (FIG.1,FIGS.5to10,FIG.13,FIG.14) showing the structure of the turbo molecular pump100, depiction of hatching illustrating a section of a component is omitted in order to avoid complexity of the drawings.

Subsequently, a stress distribution function and the like of the rotating body103described above will be explained. As described above, the rotor shaft113is mounted at the center of the rotating body103. The rotating body103has a disc portion212having a fitting hole211at the center as shown inFIG.5in an enlarged manner, and the fitting shaft portion241of the rotor shaft113is fitted in a fitting hole211.

On one end part in the axial direction of the rotor shaft113(upper end part inFIG.1andFIG.5, here), a relatively small-diameter protruding end portion242and the aforementioned fitting shaft portion241are formed. The protruding end portion242and the fitting shaft portion241are formed with diameters different from each other, and the diameter of the fitting shaft portion241is larger than the diameter of the protruding end portion242.

Furthermore, the fitting shaft portion241and the protruding end portion242constitute a stepped shape. And the fitting shaft portion241is coaxially inserted into the fitting hole211of the rotating body103and is brought into contact with an inner peripheral surface of the fitting hole211with a pressure generated by a predetermined method (here, quenching). Though not shown clearly, a length in the axial direction acting as the fitting part of the fitting shaft portion241substantially matches a thickness H of the disc portion212shown inFIG.5. Moreover, the protruding end portion242of the rotor shaft113is located outside the disc portion212of the rotating body103.

In the disc portion212of the rotating body103, a plurality of (6 spots or 8 spots, for example) bolt through holes213are formed and disposed in the periphery of the fitting hole211. In the bolt through holes213, a bolt214(fastening means) such as a bolt with a hexagonal hole or the like is inserted. These bolts214are threaded into the rotor shaft113. And the rotating body103and the rotor shaft113are coupled with each other by a fastening force of the bolt214.

In the following, as shown inFIG.6, the fitting hole211and the parts around the fitting hole211in the disc portion212of the rotating body103are assumed to be a fitting hole portion215(stress-reduction target portion). Moreover, the bolt through hole213and the part around the bolt through hole213in the disc portion212are assumed to be a through hole portion216(similarly, the stress-reduction target portion). Moreover, when the fitting hole portion215and the through hole portion216are adjacent to each other, an area where the fitting hole portion215, which is the stress-reduction target portion, and the through hole portion216, which is the stress-reduction target portion, overlap each other is assumed to be generated. And the overlap area in this case is also assumed to be the stress-reduction target portion. Here, in this embodiment, the explanation is made such that the fitting hole portion215includes the fitting hole211, and the through hole portion216includes the bolt through hole213, but this is not limiting, and it may be configured such that the fitting hole portion215does not include the fitting hole211, and the through hole portion216does not include the bolt through hole213.

Moreover, between the disc portion212and the head part of the bolt214, a disc-shaped and annular washer220is sandwiched. Furthermore, on an outer peripheral part on the bottom part in the recessed portion223in which the washer220is disposed in the disc portion212, as shown inFIG.6, a groove portion (groove portion in recessed portion)223afacing a plate surface of the washer220is formed. Moreover, though reference numerals are omitted, a plurality of through holes capable of preventing collecting of a gas between the disc portion212and itself is formed in the washer220.

On the outer peripheral part of the disc portion212in the rotating body103, as shown inFIG.5, a rotor-blade forming portion217(cylinder part) is integrally formed continuously. This rotor-blade forming portion217is integrally formed continuously also on the cylinder portion102ddescribed above of the rotating body103. Moreover, at a boundary part224between disc portion212and the rotor-blade forming portion217, a groove portion218is formed.

This groove portion218is formed in an inner peripheral surface219of the disc portion212and is opened in the inner peripheral surface219. Moreover, in this embodiment, the groove portion218extends over the entire circumference of the inner peripheral surface219and has a constant sectional shape over the entire circumference. Note that the invention according to this embodiment is not limited to the formation of the groove portion218over the entire circumference of the inner peripheral surface219, but the groove portion218may be formed so as to be intermittently disposed along the peripheral direction of the inner peripheral surface219.

The groove portion218has, as shown inFIG.7, an inclined portion221and a curved portion222. The inclined portion221in them is inclined so as to be deeper from a center side toward an outer peripheral side of the rotating body103, and the curved portion222is curved in an arc shape so as to become shallow from the center side toward the outer peripheral side of the rotating body103. Furthermore, the inclined portion221is positioned on the center side of the rotating body103, and the curved portion222is positioned on the outer peripheral side of the inclined portion221.

The inclined portion221is formed at a part adjacent to the inner peripheral surface219of the disc portion212and continues from the inner peripheral surface219via an inclination angle α1with the inner peripheral surface219as a reference. Moreover, the inclination angle α1is substantially constant from the inner peripheral side to the outer peripheral side of the inclined portion221. Note that this is not limiting, and the inclination angle of the inclined portion221may be configured to be changed in the middle from the inner peripheral side toward the outer peripheral side.

The curved portion222is formed so as to have a tangent angle of α2with the inner peripheral surface219of the disc portion212as a reference. InFIG.7, the tangent angle α2is an angle of a tangent at a position where the curved portion222intersects an extension219aof the inner peripheral surface219. Moreover, the inclination angle α1and the tangent angle α2have a relationship of α1<α2. That is, in a relationship between the tangent angle α2and the inclination angle α1in the groove portion218, the inclination angle α1has a gentler inclination structure as compared with the tangent angle α2, and the tangent angle α2has a larger and steeper inclination structure than the inclination angle α1.

Moreover, the inclination angle α1preferably has an acute-angle structure (α<45 degrees).

In the turbo molecular pump100having the rotating body103as above, the more the rotation number of the rotating body103is raised, the higher the exhaust performance becomes. However, when the rotating body103is designed, a shape and a dimension of each part need to be determined so that an excessive stress is not generated by a centrifugal force during rotation.

Moreover, spots where the stress concentration can easily occur in the rotating body103include the connected part between the rotating body103and the rotor shaft113. And the connected part between the rotating body103and the rotor shaft113includes the through hole portion216around the bolt through hole213and the fitting hole portion215around the fitting hole211.

If the stress generated in these spots can be reduced and an excessive rise of the stress generated in other spots can be prevented, strength of the rotating body103and the reliability of the turbo molecular pump100are improved. Moreover, since a room for the stress generation can be increased, the rotation number of the rotating body103can be raised, and the exhaust performance of the turbo molecular pump100can be improved.

From these viewpoints, the inventor and the like have made researches on the stress reduction in the through hole portion216and the fitting hole portion215and acquired an idea of purposely adding an irregular part to the disc portion212in the rotating body103so as to increase the stress generated in the disc portion212. And by forming the groove portion218as described above as the irregular part, the stress generated in the parts in the vicinity of the through hole portion216and the fitting hole portion215can be increased. As a result, the stress can be distributed in the rotating body103(particularly in the disc portion212), the stress in the through hole portion216and the fitting hole portion215can be reduced, and reliability and performances of the turbo molecular pump100can be improved.

Moreover, the inventor and the like conducted simulations for a structural model in which the groove portion218is formed in the rotating body103and experiments using an actual one, the stress generated in the through hole portion216and the fitting hole portion215was actually lowered. It can be considered that the groove portion218forms a so-called “escape” of the stress, and the stress was averaged.

Moreover, even if the stress generated in the through hole portion216and the fitting hole portion215can be reduced as described above, an excessive stress in the groove portion218is not preferable. Furthermore, excessive increases in the number of processes and costs for machining the rotating body103by providing the groove portion218are not preferable, either. Thus, the inventor and the like examined the optimal shape and machining method for the groove portion218and reached the conclusion that such a shape is preferable that the inclined portion221that inclines gently is disposed on the inner peripheral side and that a relatively steep part (the curved portion222, here) is disposed on the outer peripheral side. By forming the groove portion218having the shape as above on the rotating body103, the stress distribution can be distributed more averagely.

FIG.9(a)models and schematically illustrates deformation at rotation of the rotating body103in the case where the groove portion218is not provided (conventional structure). Moreover,FIG.9(b)similarly models and illustrates the deformation at the rotation of the rotating body103in the case where the groove portion218is provided. At the rotation of the rotating body103, a centrifugal force acts on the rotating body103, and a load F acts on the rotor-blade forming portion217to the outer peripheral side. Moreover, on the connected part between the rotating body103and the rotor shaft, a moment by the load F acts.

And the rotating body103is deformed with the fastened part with the rotor shaft113(here, it is considered as the through hole portion216) as a fulcrum, and the closer it gets from the fulcrum toward the outer peripheral side, the larger it is deflected and displaced to the sucking side (Upper sides inFIGS.9(a),9(b)). InFIGS.9(a),9(b), it is assumed that displacement amounts in the axial direction on the outer peripheral side of the disc portion212are δa, δb, respectively, and displacement amounts in the radial direction on the exhaust side in the rotor-blade forming portion217(lower sides inFIGS.9(a),9(b)) are γa, γb.

When the groove portion218is provided as shown inFIG.9(b), in the displacement amounts δa, δb of the disc portion212, δb becomes smaller than δa for the reason described below. In the displacement amounts γa, γb of the rotor-blade forming portion217whose lower side is not restricted, γb becomes larger than γa. That is, in the case ofFIG.9(b)in which the groove portion218is provided, the stress generated in the vicinity of the groove portion218becomes higher than the case ofFIG.9(a)in which the groove portion218is not provided, and the deformation of the rotor-blade forming portion217becomes larger on the outer peripheral side than the groove portion218. And the stress corresponding to a part by which the deformation amount increases is generated on and around the groove portion218, and the stress caused by the load F is distributed not only to the fastened part (fulcrum) but also to the groove portion218.

And by distributing the stress caused by the load F to the groove portion218, the stress generated at the fastened part (fulcrum) can be reduced. And by keeping the stress generated in the groove portion218appropriate and by preventing the excessive rise of the stress generated in the groove portion218, the strength of the rotating body103and the reliability of the turbo molecular pump100are improved as a whole. Moreover, since a room for stress generation can be increased, the rotation number of the rotating body103can be raised, and the exhaust performance of the turbo molecular pump100can be improved.

Subsequently, when the groove portion218as above is to be fabricated, a work as shown inFIG.10can be performed. For example, while a base material230of the rotating body103is rotated around a shaft center, a cutting tool (cutting tool)231is made to advance to the inner peripheral side of the base material230. Here, what is indicated by a reference character C inFIG.10is the shaft center of the base material230, and at the fabrication of the groove portion218, the base material230is rotated around this shaft center C. InFIG.10, only a part of the half in the base material230is shown with the shaft center C as a boundary.

a distal end of the cutting tool231, a tip (blade edge)232for lathe is mounted. At the distal end of the tip232, cutting-edge surfaces234a,234bare formed by sandwiching an angle portion233. The tip232is mounted on the cutting tool231with the distal end side directed to the outer peripheral side (outer side in the radial direction) of the disc portion212in the base material230.

The cutting tool231performs forward/backward movement along the shaft center C of the base material230or vertical/lateral movement on an orthogonal plane to the shaft center C by a feeding mechanism, not shown. And the tip232is brought into contact with the base material230in a state where the one cutting-edge surface234adiagonally directed to the inner peripheral side (inner side in the radial direction) and gradually cuts the rotating base material230while performing the forward/backward movement and the vertical/lateral movement as necessary. The cutting tool231is guided so that the closer the tip232goes to the outer peripheral side, the deeper it cuts the base material230, whereby the inclined portion221is formed.

Moreover, the cutting tool231is made to go backward with respect to the disc portion212while moving to the outer peripheral side. And the tip232moves so as to reach the side of the rotor-blade forming portion217from the disc portion212, whereby the curved portion222is formed. The movement of the cutting tool231as above is performed in a narrow width in the radial direction as compared with the formation of the inclined portion221. As a result, between the inclined portion221and the curved portion222, as shown inFIG.7, a width in the radial direction (width of an annular part) W1in the inclined portion221becomes larger than a width in the radial direction (width of the same annular part) W2in the curved portion222.

As described above, by setting the inclination angle α1related to the inclined portion221smaller than the tangent angle α2related to the curved portion222, the groove portion218can be formed as smoothly as possible. Moreover, at a part on the outer peripheral side of the disc portion212, the base material230can be machined by disposing the cutting tool231closer to the inner peripheral side, which is the side where there is no rotor-blade forming portion217.

And the fabrication of the groove portion218, the space (inner space) on the inner peripheral surface side of the base material230can be effectively utilized. Moreover, such machining can be realized that the tip232does not interfere with the rotor-blade forming portion217. As a result, when the groove portion218is fabricated, such a work of changing a direction of the cutting tool231is not necessary any more, and the groove portion218can be fabricated easily with a smaller number of processes. Moreover, the groove portion218can be fabricated with the general cutting tool231without preparing a dedicated tool.

Subsequently, a stress control function exerted between the rotating body103and the rotor shaft113will be explained.FIG.11illustrates a part surrounded by a one-dot chain line circle D inFIG.1in an enlarged manner. Here, inFIG.11, the fitting shaft portion241of the rotor shaft113is not cut vertically but a part on the lower side in the figure of the fitting shaft portion241is cut vertically.

In the example inFIG.11, at a root part in the fitting shaft portion241of the rotor shaft113, a stress-control recess portion251(counterbore portion) is formed. This stress-control recess portion251is formed with a certain depth (approximately 0.1 to 0.5 mm, for example) by counterboring an opening portion of a female screw portion252into which the bolt214is screwed in the periphery of the root part in the fitting shaft portion241. Moreover, the stress-control recess portion251is formed so as to face a peripheral edge part of the opening portion of the bolt through hole213in the rotating body103.

This stress-control recess portion251is configured to receive a protruding portion (not shown), if it is present on a surface opposed to the rotating body103and the rotor shaft113, in a space in the inner side so that the opposed surface does not contact (is not contacted) or press the protruding portion. And the stress-control recess portion251prevents the stress generated in the disc portion212from increasing by application of a stress generated in the protruding portion or a contact surface with the protruding portion.

As a result, collapse of a relationship between the stress generated in the fitting hole portion215or the through hole portion216and the stress generated in the groove portion218by the pressing of the protruding portion can be prevented. And the stress distribution function of the groove portion218is exerted as designed without being affected by the pressing of the protruding portion. Moreover, by providing the stress-control recess portion251, the stress distribution function by the groove portion218can be made to function more reliably.

Here, as the protruding portion, a substance generated after applying surface processing (electroless nickel plating or the like) (so-called plating drip) to the inner peripheral surfaces of the fitting hole211and the bolt through hole213for improving resistance against an erosive gas, unexpected protruding part generated on the fitting hole portion215and the through hole portion216and the like can be exemplified. And even if the protruding portion as above is generated at a part close to the fitting hole211or the bolt through hole213, by preventing or suppressing stress generation by the stress-control recess portion251, the function of the groove portion218can be exerted to the maximum.

Note that, inFIG.11, the example in which the stress-control recess portion251is provided on the rotor shaft113is illustrated, but this is not limiting, and as shown inFIG.12, the stress-control recess portion254(counterbore) may be provided on the side of the rotating body103, for example. In the example inFIG.12, by counterboring the opening portion of the bolt through hole213, it is formed with a certain depth (approximately 0.1 to 0.2 mm, for example). If the stress-control recess portion254is formed on the side of the rotating body103as above, the working effects of the invention similar to that in the example inFIG.11can be exerted.

As components forming the stress-control recess portions251,254, a component on the side where the protruding part is not generated (or difficult to be generated) can be considered. For example, in the rotating body103and the rotor shaft113, since the rotor shaft113is rarely plated, the stress-control recess portion251may be formed on the rotor shaft113.

According to the turbo molecular pump100of this embodiment as described above, the stress on the through hole portion216and the fitting hole portion215can be distributed by the groove portion218provided on the rotating body103at rotation of the rotating body103. Thus, the stress that can be generated in the through hole portion216and the fitting hole portion215is increased and as a result, reliability and performances of the rotating body103and the turbo molecular pump100can be improved.

The averaging of the stress by the groove portion218does not change energy relating to the stress generated in the through hole portion216, the fitting hole portion215, and the rotating body103as a whole. However, if the groove portion218is not provided, stress at a part where stress exceeding the average could be generated can be lowered.

Moreover, the groove portion218has the inclined portion221with the inclination angle α1and the curved portion222with the tangent angle α2, and the inclination angle α1and the tangent angle α2have the relationship of α1<α2. And it can be also described that the inclined portion221is gentler than the curved portion222, and the curved portion222is steeper than the inclined portion221. Thus, the stress can be distributed appropriately for the through hole portion216and the fitting hole portion215by the gentle inclined portion221and the steep curved portion222.

Note that the both inclination angle α1and the tangent angle α2can similarly have gentle angles. In that case, the similar stress distribution can be generated in the both inclined portion221and the curved portion222. On the other hand, by causing the curved portion222to have a structure steeper than that of the inclined portion221as described above, the radial width (width of the annular part) W2in the curved portion222can be made smaller.

Moreover, in the example inFIG.7, since the inclined portion221is formed on the inner peripheral side away from the rotor-blade forming portion217, and the curved portion222is formed on the outer peripheral side close to the rotor-blade forming portion217, the internal space of the base material230can be effectively utilized at machining of the inclined portion221, and the groove portion218can be machined while preventing interference of the base end side of the tip232in the cutting tool231with the rotor-blade forming portion217. And the machining of the groove portion218can be performed with a lower cost.

Here, in the example inFIG.7, the sectional shape of the groove portion218is constituted by combining the inclined portion221and the curved portion222, but this is not limiting, and a groove portion228may be formed by combining a first inclined portion226and a second inclined portion227as shown inFIG.8, for example. In the example inFIG.8, the first inclined portion226is formed similarly to the inclined portion221in the example inFIG.7, but the second inclined portion227is constituted not by an arc-shaped surface but a substantially flat inclined surface with an inclination angle α3. Moreover, in the example inFIG.8, the first inclined portion226and the second inclined portion227continue to each other through a connecting curved-surface portion229having an arc-shaped sectional shape.

In the example inFIG.8, too, it can be described that the first inclined portion226on the inner peripheral side is gentler than the second inclined portion227on the outer peripheral side and that the second inclined portion227is steeper than the first inclined portion226. And the groove portion228can be machined while effectively utilizing the internal space of the base material230.

The embodiment of the present invention has been explained as above, but the present invention is not limited to the aforementioned embodiment but is capable of various variations. For example, the disposition of the groove portion218is not limited to the boundary part224with respect to the rotor-blade forming portion217in the disc portion212as shown inFIG.5, but it may be disposed on any of parts closer to the inner peripheral side than the boundary part224(part on the outer peripheral side of the fitting hole portion215or the through hole portion216and on the inner peripheral side of the boundary part224). Moreover, a plurality of the groove portions218may be provided in a space between the boundary part224and the fitting hole211.

Moreover, the groove portion218can be provided on at least either one of the inner peripheral surface and the outer peripheral surface of the rotating body103. And the disposition of the groove portion218can be configured such that it is opened in the outer peripheral surface of the rotating body103. As the outer peripheral surface of the rotating body103, an outer peripheral surface225of the disc portion212can be exemplified. Moreover, as the inner peripheral surface and the outer peripheral surface of the rotating body, the inner peripheral surface and the outer peripheral surface of the cylinder portion102d(FIG.1) closer to the exhaust side than the rotor blade102in the rotating body103can be cited. Furthermore, regarding distinction between the inner peripheral surface and the outer peripheral surface of the rotating body103, a surface facing the internal space of the rotating body103can be distinguished as the inner peripheral surface from the other as the outer peripheral surface, for example.

Here, the stress distribution function by the groove portion218is considered to be exerted more easily by disposing the groove portion218closer to the outer peripheral side of the connected part (the fitting hole portion215and the through hole portion216) between the rotating body103and the rotor shaft113and a part closer to the connected part. And as the part as above, in the example ofFIG.5, a part closer to the outer peripheral side than the through hole portion216in the inner peripheral surface219or the outer peripheral surface225of the disc portion212can be cited.

Moreover, the groove portion218can be provided on both of the inner peripheral surface219and the outer peripheral surface225of the disc portion212. In the analysis by the inventor and the like, the stress generated in the fitting hole portion215and the through hole portion216was smaller in the case where the groove portion218was provided on the inner peripheral surface219than the case of being provided on the outer peripheral surface225. Moreover, when the groove portion218was provided on the both inner peripheral surface219and the outer peripheral surface225of the disc portion212as described above, the stress was averaged, and the effect of the stress distribution was further improved.

Moreover, according to analysis by the inventor and the like, when the thickness H of the disc portion212(FIG.5) is made smaller, the effect of the stress distribution by provision of the groove portion218is prominent. Furthermore, in the examples inFIG.1andFIG.5, the groove portion223afacing the plate surface of the counterbore220is formed on the outer peripheral part of the bottom part in the recessed portion223, and this groove portion223acan be also considered to have the stress distribution function.

Moreover, inFIG.1,FIG.5and the like, with regard to the connection relationship between the rotating body103and the rotor shaft113, such a type that the rotor shaft113is inserted so as to penetrate the fitting hole211of the rotating body103is exemplified, but the present invention is not limited to that, and as shown inFIGS.13(b) to13(d), for example, it can be also applied to various types of rotating bodies103bto103das shown in partially vertical sections.

For example,FIG.13(a)illustrates a part of the rotating body103according to the embodiment shown inFIG.5(disc portion212) in an enlarged manner as a partially and vertical section, but this is not limiting, and as shown inFIG.13(b), the present invention can be applied also to the type of the rotating body103bwhich does not include the fitting hole (reference numeral211inFIG.5) and to which the rotor shaft113bis connected. The rotor shaft113bshown inFIG.13(b)is the one not including the fitting shaft portion241or the protruding end portion242in the example shown inFIG.13(a). As described above, for the structure in which the rotor shaft113babuts against the rotating body103bso as to fasten the both, the groove portion218is disposed on the fastened surface of the rotating body103b(an inner peripheral surface219bagainst which the rotor shaft113babuts) or an extended surface thereof.

Moreover, the one shown inFIG.13(c)is a type of the rotating body103cnot having the bolt hole around the fitting hole211cin the disc portion212c. This type of the rotating body103cis connected to the rotor shaft113csuch that a nut256is attached to a protruding end portion242cin the rotor shaft113c, and the counterbore220is pressed onto the rotating body103cby fastening the nut256.

Furthermore, the one shown inFIG.13(d)is the type of the rotating body103din which the fitting hole211ddoes not penetrate the disc portion212dand is closed at a part in the middle of the thickness direction of the disc portion212d. When this type of rotating body103dis employed, the rotor shaft113dis fixed to the rotating body103dby the bolt214in a state where the rotor shaft113ddoes not penetrate the disc portion212d. Note that the rotating body103dand the rotor shaft113dshown inFIG.13(d)can be considered as the one in which a protruding portion257formed on an end part in the axial direction of the rotor shaft113dis inserted into a recess portion (reference numeral omitted) of the rotating body103dso as to engage the rotor shaft113dwith the rotating body103d.

Moreover, the one shown inFIG.14(a)is a rotating body103e, which is similar to the rotating body103bof the type shown inFIG.13(b)but is different in a point that it has an engagement structure by a protrusion258between it and a counterbore220e. In the example inFIG.14(a), the protrusion258is formed on the counterbore220e, and this protrusion258enters a recess part (reference numeral omitted) of the rotating body103e. As described above, the structure which causes the rotor shaft113bto abut against the rotating body103bso as to fasten the both, too, similarly to the example inFIG.13(b), the groove portion218is disposed on the fastened surface of the rotating body103e(an inner peripheral surface219eagainst which the rotor shaft113eabuts) or on the extended surface thereof.

Furthermore, the one shown inFIG.14(b)is a type of a rotating body103fhaving a protruding portion259and engaged with a rotor shaft113fby inserting this protruding portion259into a recess part (reference numeral omitted) of the rotor shaft113f.

Furthermore, the one shown inFIG.14(c)is a type of a rotating body103ghaving a protrusion260and the protruding portion259, the protrusion260is caused to enter a recess part of the counterbore220g, and the protruding portion259is inserted into a recess part (reference numeral omitted) of the rotor shaft113gsimilarly to the example inFIG.14(b).

In the turbo molecular pump including these various types of the rotating bodies103bto103gand the rotor shafts113bto113gand the like as described above, too, by providing the groove portions218and223aat appropriate positions, the stress distribution function can be exerted similarly to the turbo molecular pump100shown inFIG.1,FIG.5and the like.

Note that the present invention is not limited to the aforementioned embodiment but is capable of many variations by ordinary creative capabilities of a person ordinarily skilled in the art as long as they are within the technical scope of the present invention.