U.S. patent application number 11/606015 was filed with the patent office on 2008-06-05 for vacuum pump.
This patent application is currently assigned to SHIMADZU CORPORATION. Invention is credited to Junichiro Kozaki.
Application Number | 20080131288 11/606015 |
Document ID | / |
Family ID | 39475977 |
Filed Date | 2008-06-05 |
United States Patent
Application |
20080131288 |
Kind Code |
A1 |
Kozaki; Junichiro |
June 5, 2008 |
Vacuum pump
Abstract
A vacuum pump exhausting gas by rotating a rotor relative to a
stator includes a rotor having a ferromagnetic body provided on a
rotational axis on, or near, a rotational axis of the end face of a
rotational axis direction of a rotational body. The ferromagnetic
body's Curie temperature is approximately equal to an allowable
temperature of the rotor. A detecting portion disposed opposite the
ferromagnetic body is configured to detect a change in magnetic
permeability of the ferromagnetic body based upon a change in
inductance. A revolution sensor target and an inductance-type
revolution sensor are disposed in such a way as to detect both a
revolution of the rotor and a change in the magnetic permeability
of the ferromagnetic body. A control device halts rotor rotation
when a change in magnetic permeability of the ferromagnetic body is
detected and/or when a predetermined integrated time is
exceeded.
Inventors: |
Kozaki; Junichiro;
(Kyoto-shi, JP) |
Correspondence
Address: |
KANESAKA BERNER AND PARTNERS LLP
1700 DIAGONAL RD, SUITE 310
ALEXANDRIA
VA
22314-2848
US
|
Assignee: |
SHIMADZU CORPORATION
Kyoto
JP
|
Family ID: |
39475977 |
Appl. No.: |
11/606015 |
Filed: |
November 30, 2006 |
Current U.S.
Class: |
417/32 ;
417/44.1 |
Current CPC
Class: |
F04D 19/042 20130101;
F04D 29/058 20130101; F04D 27/0292 20130101 |
Class at
Publication: |
417/32 ;
417/44.1 |
International
Class: |
F04B 49/06 20060101
F04B049/06 |
Claims
1. A vacuum pump configured to exhaust gas by rotating a rotor
relative to a stator, comprising: a ferromagnetic body provided on
or near a rotational axis of an end face of a rotational axis
direction of a rotational body including said rotor, the
ferromagnetic body having a Curie temperature approximately equal
to an allowable temperature of said rotor; and a detecting portion
provided in such a way as to be opposed to the ferromagnetic body
and configured to detect a change in magnetic permeability of the
ferromagnetic body based upon a change in inductance.
2. A vacuum pump configured to exhaust gas by rotating a rotor
relative to a stator, comprising: a revolution sensor target
provided near a rotational axis of an end face of a rotational axis
direction of a rotational body including said rotor; a
ferromagnetic body provided in a position wherein a radial
directional distance from the rotational axis of said rotor is
approximately equal to a radial directional distance of said
revolution sensor target, and a Curie temperature of the
ferromagnetic body is approximately equal to an allowable
temperature of said rotor; and an inductance-type revolution sensor
disposed in such a way as to be opposed to said revolution sensor
target and said ferromagnetic body, said revolution sensor being
configured to detect a revolution of said rotor and a change in
magnetic permeability of said ferromagnetic body as a detected
inductance change.
3. A vacuum pump according to claim 1, wherein said ferromagnetic
body is provided on the end face of said rotor in such a way that a
detected inductance when said detecting portion and said
ferromagnetic body are opposed to each other, becomes smaller than
a detected inductance when said detecting portion and the end face
of said rotor are opposed to each other, when the temperature of
said rotor is lower than the Curie temperature.
4. A vacuum pump according to claim 1, further comprising control
means for reducing speed of rotation of said rotor or halting the
rotation of said rotor when change in the magnetic permeability of
said ferromagnetic body is detected.
5. A vacuum pump according to claim 1, further comprising control
means for halting rotation of said rotor when an integrated time,
wherein change of the magnetic permeability of said ferromagnetic
body is detected, exceeds a predetermined allowable time based on a
creep life design of said rotor.
6. A vacuum pump according to claim 4, further comprising alarm
means for presenting alarm information regarding abnormality of the
vacuum pump when the change of the magnetic permeability of said
ferromagnetic body is detected.
7. A vacuum pump configured to exhaust gas by rotating a rotor
relative to a stator, comprising: a first ferromagnetic body
provided on or near a rotational axis of an end face of a
rotational axis direction of a rotational body including said
rotor, the first ferromagnetic body having a Curie temperature
approximately equal to an allowable temperature of said rotor; a
second ferromagnetic body provided on or near the rotational axis
of the end face of the rotational axis direction of said rotor, the
second ferromagnetic body having a Curie temperature higher than
the Curie temperature of the first ferromagnetic body; a detecting
portion provided in such a way as to be opposed to said first and
said second ferromagnetic bodies, and configured to detect a change
in the magnetic permeability of said first and said second
ferromagnetic bodies as an inductance changes respectively; and
control means for halting rotation of said rotor when at least one
of the change in the magnetic permeability of said second
ferromagnetic body is detected, and when an integrated time,
wherein the change of the magnetic permeability of said first
ferromagnetic body is detected, exceeds a predetermined allowable
time based on a creep life design of said rotor.
Description
BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT
[0001] The present invention relates to vacuum pumps, and more
specifically, relates to vacuum pumps that use the change in the
magnetic permeability of a ferromagnetic body to determine a rotor
temperature and/or control rotor rotation.
[0002] In a turbo-molecular pump used for example in semiconductor
manufacturing equipment, as the flow rate or molecular weight of
the gas exhausted by the turbo-molecular pump increases, the rotor
temperature increases due to heat generated in association with an
increase in motor electricity or frictional heat associated with
gas exhaust. Also, even in a case wherein the gas with little
thermal conductivity is exhausted, the rotor temperature increases.
Generally, the higher the number of rotor revolutions, flow rate,
pressure, temperature of exhaust gas, and pump ambient temperature,
the higher the rotor temperature.
[0003] Since the rotor of a turbo-molecular pump rapidly rotates,
centrifugal force results in large tension stress. Therefore, an
aluminum alloy having an excellent specific strength is generally
used as the rotor material. However, an allowable temperature of
creep deformation for an aluminum alloy is relatively low
(approximately 110.degree. C..about.120.degree. C.). Therefore, an
operating pump must be constantly monitored to verify that the
rotor temperature stays below the allowable temperature.
[0004] A contactless method for detecting rotor temperature is
known and uses the fact that the magnetic permeability of the
ferromagnetic body greatly changes at the Curie temperature.
[0005] For example, Japanese Patent Publication No. H7-5051
discloses a device in which a ring-shaped ferromagnetic body is
disposed around a rotor. The changes in magnetic permeability of
the ferromagnetic body is detected by a coil as the temperature
reaches the Curie temperature.
[0006] However, because the ring-shaped ferromagnetic body is
installed around the rotor, a high degree of tension stress, due to
a centrifugal force, acts on the ferromagnetic body, and may
possibly damage the ferromagnetic body.
[0007] The present invention has been made to solve the above
conventional problems.
SUMMARY OF INVENTION
[0008] A first aspect of the invention includes a vacuum pump
exhausting gas by rotating a rotor relative to a stator and
includes a ferromagnetic body provided on a rotational axis or near
the rotational axis of an end face of the rotational axis direction
of a rotational body that includes a rotor whose Curie temperature
is approximately equal to an allowable temperature of the rotor. A
detecting portion is provided in such a way as to oppose the
ferromagnetic body and detects changes in magnetic permeability of
the ferromagnetic body as the inductance changes.
[0009] A second aspect applies to a vacuum pump exhausting the gas
by rotating the rotor relative to the stator and includes a
revolution sensor target provided near the rotational axis of the
end face of the rotational axis direction of the rotational body,
the rotational body including a rotor. A ferromagnetic body is
provided in a position wherein a radial directional distance from
the rotational axis of the rotor is approximately equal to the
radial directional distance of the revolution sensor target. The
Curie temperature of the rotor is approximately equal to the
allowable temperature of the rotor and an inductance-type
revolution sensor is disposed in such a way as to be opposed to the
revolution sensor target and the ferromagnetic body. The revolution
sensor detects the number of revolutions of the rotor and the
change in the magnetic permeability of the ferromagnetic body, as
the inductance changes.
[0010] A third aspect includes the vacuum pump as disclosed in the
first aspect, wherein the ferromagnetic body is provided on the end
face of the rotor in such a way that the inductance, when the
detecting portion and the ferromagnetic body are opposed to each
other, becomes smaller than the inductance when the detecting
portion and the end face of the rotor are opposed to each other,
when the temperature of the rotor is lower than the Curie
temperature.
[0011] A fourth aspect includes the vacuum pump of the first aspect
and further includes a control means that reduces the rotational
speed of the rotor, or halts the rotation of the rotor, when the
change of the magnetic permeability of the ferromagnetic body is
detected.
[0012] A fifth aspect includes the control means halting the
rotation of the rotor when an integration of time wherein the
change of the magnetic permeability of the ferromagnetic body is
detected, exceeds a predetermined allowable time based on the creep
life design of the rotor.
[0013] A sixth aspect includes an alarm means for presenting alarm
information that indicates an abnormality of the pump when a change
of the magnetic permeability of the ferromagnetic body is
detected.
[0014] A seventh aspect includes a detecting portion provided in
such a way as to be opposed to the first and second ferromagnetic
bodies, wherein the Curie temperature of the second ferromagnetic
is high than the Curie temperature of the first ferromagnetic. The
detecting portion detects the change in magnetic permeability of
the first and second ferromagnetic bodies as inductance changes. In
addition, a control means is included that halts the rotation of
the rotor when a change in magnetic permeability of the second
ferromagnetic body is detected, and/or when the integration time of
when the change of the magnetic permeability of the first
ferromagnetic body is detected exceeds a predetermined allowable
time based on the creep life design of the rotor.
[0015] Because the ferromagnetic body is provided on or near the
rotational axis of the end face of the rotational axis direction of
the rotational body, a tension stress acting on the ferromagnetic
body can be controlled and durability of the ferromagnetic body can
be improved. Moreover, because the revolution sensor detects the
change of the magnetic permeability of the ferromagnetic body as
the inductance changes, an increase in the number of parts and an
increase in cost may be prevented.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 is a drawing of one embodiment of a vacuum pump
according to the present invention;
[0017] FIGS. 2A and 2B are drawings showing portions of a nut,
wherein FIG. 2A is a cross sectional view and FIG. 2B shows the
bottom face of the nut;
[0018] FIG. 3 is a drawing depicting inductance changes of a gap
sensor;
[0019] FIG. 4 is a drawing showing a relationship between a Curie
temperature Tc and magnetic permeability;
[0020] FIG. 5 is a block diagram of a detecting portion;
[0021] FIGS. 6A-6C show signal waveforms based upon the block
diagram of FIG. 5;
[0022] FIG. 7 is a modified first example of the vacuum pump;
[0023] FIG. 8 is a cross sectional view of the pump, wherein a
target is provided on the upper end face of a rotor;
[0024] FIGS. 9A and 9B illustrates a second embodiment of the
vacuum pump, wherein FIG. 9A is a cross sectional view of the nut
and a gap sensor, and FIG. 9B is a view taken along 9B of the
nut;
[0025] FIG. 10 is a block diagram of a detecting portion according
to the modified second example of FIGS. 9A and 9B;
[0026] FIGS. 11A-11E illustrates signal waveforms based upon the
block diagram of FIG. 10;
[0027] FIGS. 12A and 12B illustrate a third embodiment of the
vacuum pump, wherein FIG. 12A is a cross sectional view of a nut
and gap sensor, and FIG. 12B shows the bottom face of the nut;
[0028] FIG. 13 is a block diagram of a detecting portion according
to the third example; and
[0029] FIGS. 14A-14C show waveforms according to the block diagram
of FIG. 13.
DETAILED DESCRIPTION OF EMBODIMENTS
[0030] FIG. 1 is a drawing showing an embodiment of a vacuum pump
according to the present invention, and shows a schematic structure
of a pump main body 1 of a magnet-bearing type turbo-molecular pump
and a controller 30.
[0031] A shaft 3 comprising an attached rotor 2 contactlessly
supported by electric magnets 51, 52, 53 is provided on a base 4.
The floating position of the shaft 3 is detected by radial
displacement sensors 71, 72 disposed on the base 4 in addition to
an axial displacement sensor 73. Electric magnets 51, 52 each
comprise a radial magnet bearing further comprising five
axis-control magnet bearings. The electric magnet 53 constitutes an
axial magnet bearing and displacement sensors 71-73.
[0032] At a lower end of the shaft 3, a circular disk 41 is
provided, and the electric magnet 53 is provided in such a way as
to sandwich the disk 41 from above and below. The shaft 3 is
floated in an axial direction by operation of the disk 41 being
attracted by the electric magnet 53. The disk 41 is fixed to the
lower end portion of the shaft 3 by a nut 42.
[0033] As shown in FIGS. 2A, 2B, a ring-shaped ferromagnetic body
target 43 is provided on the lower end face of the nut 42. The
target 43 is embedded in the nut 42 by adhesion, or fixed to the
nut 42 by heating the nut 42 side and carrying out shrinkage
fitting. When the nut 42, along with shaft 3, is rapidly rotated, a
centrifugal force acts on the target 43 in a horizontal direction,
as shown in the drawings. However, since the target 43 is provided
in the end face portion of a rotational body, the target 43 may be
provided near the axis, so that the effect of the centrifugal force
may be reduced. Moreover, since the side face of the target, which
is the direction of centrifugal action, is retained by a retaining
portion 42a of the nut 42, tension stress generated in the target
43 may be controlled, improving durability of the target 43.
[0034] Especially in the case wherein the target 43 is shrunk fit,
because compressive stress acts on the target 43, the effect of the
centrifugal force can be reduced. Also, the target 43 is provided
on the end face of the shaft 3, so that the outward form of the
target 43 can be reduced regardless of the diameter of the shaft 3,
and the target 43 can be provided near the axis of the shaft 3.
Hereby, the effect of the centrifugal force may be reduced.
[0035] On the stator side, an inductance-type gap sensor 44 is
provided in such a way as to be opposed to the target 43 provided
in the nut 42. As described below, the gap sensor 44 detects the
change of the magnetic permeability, e.g., an inductance change, of
the target 43 when the rotor temperature is increased more than an
allowable temperature.
[0036] In the pump shown in FIG. 1, the target 43 is provided on
the end face of the lower side of the disk 41 provided in the shaft
3. However, as shown in FIG. 8, the upper end face of the rotor 2
may be also provided with the target 43 on the axis of the rotor.
In this case, the target 43 may be discoidal and not ring-shaped,
and the side face of the target 43, upon which the centrifugal
force acts, is retained by the rotor 2. More specifically, the
rotor 2 functions as the retaining portion of the target 43. A gap
sensor 44B is retained on the axis of the rotor by a support 45
fixed to a spacer 10 on the highest level. The gap sensor 44B has a
structure wherein coils 401 are rolled around in the center of the
projection of a core 400. Because the target 43 in FIG. 8 is
provided on the rotor axis, the target 43 in FIG. 8 may reduce the
effect of the centrifugal force more than the target 43 shown in
FIG. 1.
[0037] In the rotor 2 in FIG. 1, rotating wings 8 with multiple
levels are formed along a direction of a rotational axis. Fixed
wings 9 are respectively provided between the rotating wings 8
lined up above and below. Durbin wing levels of the pump main body
1 are formed by the rotating wings 8 and fixed wings 9. Each fixed
wing 9 is retained by spacers 10 in such a way as to be clamped
above and below. The spacers 10 maintain gaps between the fixed
wings 9 at predetermined intervals and function to maintain the
position of the fixed wings 9.
[0038] Moreover, screw stators 11 are provided in back levels
(below in the figure) of the fixed wings 9, and comprise drag pump
levels. Gaps are formed between inner circumferential surfaces of
the screw stators 11 and a cylinder portion 12 of the rotor 2. The
fixed wings 9 retained by the rotor 2 and the spacers 10 are housed
inside a casing 13 wherein an inlet 13a is formed. The shaft 3 is
contactlessly supported by electric magnets 51.about.53. When the
shaft 3, to which the rotor 2 is attached, is rotated by a motor 6,
gas on an inlet 13a side is exhausted to a back-pressure side
(space S1) in the manner of an arrow G1. The gas exhausted to the
back-pressure side is exhausted through an auxiliary pump connected
to an outlet 26.
[0039] The turbo-molecular pump main body 1 is controlled by the
controller 30. Controller 30 comprises a magnet-bearing drive
control portion 32 controlling the magnet bearings; and a motor
drive control portion 33 controlling the motor 6. A detecting
portion 31 detects whether the magnetic permeability of the target
43 is changed or not, based on an output signal of the gap sensor
44.
[0040] The output signal of the gap sensor 44 is input into the
detecting portion 31, and a rotor temperature monitor signal is
output into the motor drive control portion 33 and an alarm portion
34. In some embodiments, an output terminal configured to output
the rotor temperature monitor signal to the outside of the
controller 30 may be provided. The alarm portion 34 is an alarm
means presenting alarm information, such as an abnormal rotor
temperature, etc., to an operator, and may comprise a display unit
displaying a warning message or may comprise a speaker releasing a
warning sound, or a warning and so on.
[0041] FIG. 3 illustrates an inductance change of the gap sensor
44, and a pattern diagram of a magnetic circuit that may be made by
the gap sensor 44 and the target 43. The gap sensor 44 is formed by
furling a coil around a core with large magnetic permeability such
as a silicon steel plate. A high-frequency voltage with constant
frequency and a constant voltage may be applied to the coil of the
gap sensor 44 as a carrier wave, and a high-frequency magnetic
field may be formed between the gap sensor 44 and the target
43.
[0042] The material that comprises the ferromagnetic body includes
a Curie temperature Tc that is approximately the same temperature
as the allowable temperature Tmax of the rotor 2, or near the
allowable temperature Tmax of the rotor 2, and comprises the
material of the target 43. In the case of the rotor 2, the
allowable temperature Tmax which generates a creep deformation in
the rotor material, is used. In the case of aluminum, the allowable
temperature Tmax is approximately 110.degree. C..about.120.degree.
C. Nickel and zinc ferrite, or manganese and zinc ferrite and so on
are used for materials of the ferromagnetic body wherein a Curie
temperature Tc is approximately 120.degree. C.
[0043] FIG. 4 illustrates wherein the magnetic permeability of a
target 43 rapidly decreases to approximately a vacuum magnetic
permeability .mu..sub.o when the temperature of the target 43
increases to a temperature near the Curie temperature Tc. Such an
increase may be due, for instance, to an increase of the rotor
temperature. When the magnetic permeability of the target 43
changes as a result of the magnetic field formed by the gap sensor
44, the inductance of the gap sensor 44 changes. As a result, the
carrier wave is amplitude-modulated, and the amplitude-modulated
carrier wave that is output from the gap sensor 44 is detected and
rectified. Therefore, a signal change corresponding to the change
of the magnetic permeability can be detected.
[0044] The ferromagnetic body, such as ferrite, etc., may be used
as the core material of the gap sensor 44. However, in the case
wherein the magnetic permeability is larger than the magnetic
permeability of the air gap, it may be possible to ignore the
magnetic permeability of the air gap. Furthermore, in the case
wherein the leakage flux can be ignored, the relationship between
inductance L and dimensions d, d.sub.1 are shown approximately in
the following formula (1), wherein N represents the furled number
of the coil, S represents a cross-sectional area of the core
opposed to the target 43, d represents the air gap, d.sub.1
represents the thickness of the target 43, .mu..sub.1 represents
the magnetic permeability of the target 43, and the magnetic
permeability of the air gap is equivalent to the vacuum magnetic
permeability .mu..sub.o.
L=N.sup.2/{d.sub.1/(.mu..sub.1S)+d/(.mu..sub.oS)} (1)
[0045] When the rotor temperature is lower than the Curie
temperature Tc, the magnetic permeability of the target 43 is
sufficiently large compared to the vacuum magnetic permeability
.mu..sub.o. As a result, d.sub.1/(.mu..sub.1S) decreases to the
degree of being able to be ignored compared to d/(.mu..sub.oS), so
that formula (1) can approximate to the following formula (2):
L=N.sup.2.mu..sub.oS/d (2)
[0046] On the other hand, when the rotor temperature rises more
than the Curie temperature Tc, approximately
.mu..sub.1=.mu..sub.o.
[0047] Therefore, in this case, formula (1) is represented in the
following formula (3):
L=N.sup.2.mu..sub.oS/(d+d.sub.1) (3)
[0048] More specifically, the air gap has changed from d to (d
+d.sub.i), and the inductance of the gap sensor 44 changes
accordingly. Whether or not the rotor temperature exceeds the Curie
temperature Tc may be monitored by detecting the inductance change
at the detecting portion 31 of the controller 30.
[0049] FIG. 5 is a block diagram of the detecting portion 31, and
FIGS. 6A-6E illustrate signal waveforms A-E generated based upon
the block diagram of FIG. 5. When the carrier wave as shown in FIG.
6A is applied to the gap sensor 44 by a power source 60, gap sensor
44 outputs modulation waves, as shown in FIG. 6B. When the rotor
temperature T exceeds the Curie temperature Tc at time tc, the
magnetic permeability .mu..sub.1 of the target 43 decreases such
that .mu..sub.1 approximately equals .mu..sub.o. Accordingly, the
inductance L decreases from a value shown in the formula (2) to a
value shown in the formula (3), decreasing the amplitude of the
carrier wave.
[0050] By inputting the signal in FIG. 6B into a detection circuit
61, a signal shown in FIG. 6C may be obtained. Moreover, by
processing the signal in FIG. 6C, e.g., by a rectification circuit
62, a smooth signal as shown in FIG. 6D may be obtained that may
serve as an input into a comparator 63. The comparator 63 compares
an input signal with the threshold Vo, and when the level of the
input signal exceeds the threshold Vo, the comparator 63 outputs a
signal of v=H. When the level of the input signal is decreased to
be less than the threshold Vo, the comparator 63 outputs a signal
of v=L (refer to FIG. 6E). A signal output from the comparator 63
is output to the motor drive control portion 33 and the alarm
portion 34 as the rotor temperature monitor signal.
Pump Operation
[0051] A method for safely operating a turbo-molecular pump by
using a rotor temperature monitor signal t output from a detecting
portion 31, is disclosed below.
OPERATION EXAMPLE 1
[0052] The operation example 1 is the easiest operation. When the
rotor temperature monitor signal v becomes v=L, the motor drive
control portion 33 immediately reduces the speed of the rotation of
a rotor 2, stopping the rotor 2. An alarm portion 34 informs
abnormality of the rotor temperature. When the rotor temperature T
becomes the allowable temperature Tmax and there are significant
creep deformations, the generation of the above-mentioned creep
deformations may be prevented by stopping the rotation of the
rotor, improving the safety of the pump.
OPERATION EXAMPLE 2
[0053] In the operation example 1, the rotor temperature monitor
signal is v=L and the rotation of the rotor is stopped. However,
the revolution of rotor 2 may be decreased only during the signal
of v=L, and may be returned to the rated speed again at a time
wherein the rotor temperature monitor signal becomes v=H. When the
rotor temperature T exceeds the Curie temperature Tc, creep
deformation of the rotor 2 due to the centrifugal force may be
controlled by decreasing the number of revolutions. In addition,
when the number of revolutions is decreased to be less than the
rated speed, not only is the increased rotor temperature
information displayed, but the operator may be alerted by
displaying the number of decreased revolutions in the alarm portion
34.
[0054] Also, when the turbo-molecular pump is used to etch
equipment and so on, a reaction product may be easily attached to
the inside of the pump. As the temperature of the pump decreases,
the pump main body may be heated by a heater and the like, helping
to prevent reaction product from being attached. Consequently,
instead of a decrease of the rotor revolution, or with a decrease
of the rotor revolution, a heating means such as a heater and the
like, may be halted only during the signal of v=L.
OPERATION EXAMPLE 3
[0055] In the operation examples 1, 2, when the rotor temperature
monitor signal becomes v=L, the rotation of the rotor may be
stopped, or the rotor revolution may only be decreased when the
signal of v=L. However, there is a case wherein the rotation of the
rotor cannot be changed due to being in the middle of the process
on a semiconductor equipment side. As an example, when an
integrated value of the time when the signal is v=L becomes the
predetermined criterion time, the rotor 2 is halted and the
generation of the abnormality is informed by the alarm portion
34.
[0056] Therefore, even when temperature T become wherein
T.gtoreq.Tc during the process, if the integrated time is within
the criterion time, the process can be continued without
change.
[0057] The criterion time is the time to reach allowable
deformation volume of the rotor 2 and is obtained beforehand by the
creep life design of the rotor. However, since the creep
deformation differs depending, for example, on the temperature, the
criterion time may be calculated based upon the condition that the
rotor temperature T is the Curie temperature Tc, or may be a
shorter time than the previously-described time.
MODIFIED EXAMPLE 1
[0058] FIG. 7 is a cross sectional view of a nut 42 comprising the
turbo-molecular pump. Other than nut 42, the structure of the pump
main body 1 of FIG. 7 is the same as the structure shown in FIG. 1.
In the modified example 1, in addition to the target 43, a target
43B with a high Curie temperature is added to the nut 42, as a
target of the gap sensor 44. In this case, formula (4) shown below
may be approximately replaced by the above-described formula (1).
The thickness of the target 43B may be d.sub.2, the magnetic
permeability is .mu..sub.2, and the Curie temperature is Tc',
wherein Tc'>Tc.
L=N.sup.2/{d.sub.1/(.mu..sub.1S)+d.sub.2/(.mu..sub.2S)+d/(.mu..sub.0S)}
(4)
[0059] When the rotor temperature T exceeds the Curie temperature
Tc, approximately .mu..sub.1=.mu..sub.2=.mu..sub.0, so that the
inductance L of the gap sensor 44 changes as follows depending on
the rotor temperature T.
(T<Tc) L=N.sup.2.mu..sub.0S/d
(Tc.ltoreq.T<Tc') L=N.sup.2.mu..sub.oS/(d+d.sub.1)
(T.gtoreq.Tc') L=N.sup.2.mu..sub.oS/(d+d.sub.1+d.sub.2)
[0060] In the case of the modified example 1, by conducting the
following control action, the pump can be more safely operated.
More specifically, the time wherein the inductance is L1 is
integrated, and in the case wherein the integrated time is within
the criterion time, the operation is continued, and when the
integrated time exceeds the criterion time, the rotation of the
rotor 2 is halted. However, in the case wherein the rotor
temperature T exceeds the Curie temperature Tc' of the target 43B,
even if the integrated time is within the criterion time, the
rotation of the rotor 2 is halted. This is because the creep
deformation also becomes significant, such as when the rotor
temperature T becomes the Curie temperature Tc', which is
furthermore higher than the allowable temperature Tmax.
Accordingly, the rotor 2 is immediately halted for safety. Motor
drive control portion 33 is configured to calculate the integrated
time.
MODIFIED EXAMPLE 2
[0061] FIGS. 9A and 9B illustrate a modified example 2 of the
turbo-molecular pump. FIG. 9A is a cross sectional view of the nut
42 and a gap sensor 44B. FIG. 9B is a view taken along B of the nut
42. The structure of the pump main body 1, other than the nut 42
and the gap sensor 44B, is the same as the structure shown in FIG.
1, and the structure of the gap sensor 44B is the same as the
structure shown in FIG. 8.
[0062] On the bottom face of the nut 42, a target 43C for
monitoring the rotor temperature and a depression 42b, which is a
revolution sensor target for monitoring the rotor rotation, are
provided relative to one gap sensor 44B. The discoid target 43C has
a thickness d.sub.1, and a circular depression 42b, with a depth
d.sub.3, is provided in a position of rotational symmetry through
180 degrees relative to the central axis of the nut 42, and when
the nut 42 rotates. The target 43C and the depression 42b are
alternately opposed relative to the gap sensor 44B. More
specifically, in the modified example 2, the gap sensor 44B
functions as a revolution sensor and as a sensor that monitors the
rotor temperature. D.sub.1 and d.sub.3 are set such that
d.sub.3>d.sub.1. Although the target 43C is described as a disk
and the depression 42b is disclosed as a circle, the target 43C and
the depression 42b are not limited to the above-mentioned
shapes.
[0063] FIG. 10 is a block diagram of the detecting portion 31
according to FIG. 1, and FIG. 11 illustrates the signal waveforms
a-e, referenced in the block diagram of FIG. 10. In FIG. 11, the
reference tc represents a time wherein the temperature of the
target 43C exceeds the Curie temperature Tc. Before time tc (shown
in the left side of the figures) the rotor temperature T is defined
wherein T<Tc. After time tc (shown in the right side of the
figures), the rotor temperature T is wherein T.gtoreq.Tc.
[0064] A carrier wave signal as shown as FIG. 6A, is applied to the
gap sensor 44B, as signal (b) of FIG. 5. The carrier wave is
modulated by the gap sensor 44B, and modulation waves shown as in
FIG. 11 are output from the gap sensor 44B. The inductance L of the
gap sensor 44B differs depending on which part of the nut 42 is
opposed to the gap sensor 44B. When the rotor temperature T fulfils
the equation wherein T<Tc relative to the Curie temperature Tc
of the target 43C, the inductance L changes as the following
formula.
(Opposed to Bottom Face of Nut 42) L=N.sup.2.mu..sub.oS/d
(Opposed to Depression 42b) L1=N.sup.2.mu..sub.oS/(d+d.sub.3)
(Opposed to Target 43C) L=N.sup.2.mu..sub.oS/d
[0065] On the other hand, when the rotor temperature T is where
T>Tc, the inductance L changes as the following formula, wherein
the relative sizes of the inductances L, L1, L2 are L>L2>L1.
In other words, sizes d.sub.1 and d.sub.3 are set in order to meet
the condition of L>L2>L1.
(Opposed to Bottom Face of Nut 42) L=N.sup.2.mu..sub.oS/d
(Opposed to Depression 42b) L1=N.sup.2.mu..sub.oS/(d+d.sub.3)
(Opposed to Target 43C) L2=N.sup.2.sub.oS/(d+d.sub.1)
[0066] Therefore, in signal of FIG. 11A, on the left side of the
time tc, portions of signal levels D1 and signal levels D2
corresponding to the inductances L, L1 appear on the modulation
waves. On the other hand, in the field of the right side of the
time tc wherein the time tc becomes T.gtoreq.Tc, portions of signal
levels D3 corresponding to the inductance L2 appear on the
modulation waves in addition to the signal levels D1, D2. The
signal levels D2 are generated each time the nut 42 makes one
revolution, and an interval between each signal level D2 and each
signal level D3 corresponds to a one-half revolution.
[0067] If the modulation waves (a) shown in FIG. 11A are passed
through the detection circuit 61 shown in FIG. 10, signals as shown
in FIG. 11B can be obtained. Moreover, by processing signal of FIG.
11B at the rectification circuit 62, signal of FIG. 11C can be
obtained. The signal (c) of FIG. 10 is output from the
rectification circuit 62 and is divided into two sections. The
signals serve as respective inputs to a comparator 64 for detecting
a rotational signal and a window comparator 65 for detecting a
temperature monitor signal.
[0068] The comparator 64 compares input signal of FIG. 11C with the
threshold V.sub.1, and when the signal level is below the threshold
V.sub.1, a signal of FIG. 11D, having a signal level H, is output.
When the signal level is larger than the threshold V.sub.1, a
signal L is output. In this case, the signal H is output only at
the time of the signal level D2, and in other cases, the signal L
is output. Accordingly, pulse signals of FIG. 11D are output at the
motor drive control portion 33 in FIG. 1 from the comparator 64, as
a revolution signal.
[0069] Pulses as shown in signal of FIG. 11D are output when the
signal level is D2, i.e., when the gap sensor 44B is opposed to the
target 43C. Accordingly, each time the rotor 2 rotates once, pulses
are output. These pulses are constantly output, regardless that the
rotor temperature T is higher or lower than the Curie temperature
Tc. In the motor drive control portion 33, the rotor revolution can
be obtained by counting these pulses.
[0070] The window comparator 65 that detects the temperature
monitor signal compares the input signal (c) with the threshold
Vmax and Vmin. When the signal level is over Vmin and below Vmax, a
signal level H is output, and when the signal level is smaller than
the threshold Vmin or greater than the threshold Vmax, the signal L
is output (see signal of FIG. 11E) . Therefore, pulse signals as
shown in FIG. 11F are output at the motor drive control portion 33
and the alarm portion 34 from the window comparator 65, as the
rotor temperature monitor signal.
[0071] As signal of FIG. 11C shows, the signals of level D3 are
output only when the rotor temperature T exceeds the Curie
temperature Tc. Accordingly a pulse is generated only at the time
of T.gtoreq.Tc, regardless of whether or not the rotor temperature
T, where T.gtoreq.Tc can be determined by detecting the pulse.
[0072] Conventionally, there was no device able to be used for both
the gap sensor and the revolution sensor of the ferromagnetic body
for detecting the temperature; however, in the above-mentioned
modified example 2, gap sensor 44B is provided as a revolution
sensor and is used for detecting the rotor temperature. As a
result, costs based on additional components can be controlled.
Furthermore, there is no need for providing a new space for a
sensor for detecting the rotor temperature.
MODIFIED EXAMPLE 3
[0073] FIGS. 12A, 12B refer to a modified example 3 of the
turbo-molecular pump. FIG. 12A is a cross sectional view of the nut
42 and the gap sensor 44B and FIG. 12B is bottom face of the nut
42. The structure of the pump main body 1, other than the nut 42
and the gap sensor 44B, is the same as that shown in FIG. 1. Of
target 43C, only an exposed surface having a size d4 is depressed,
rather than the bottom face of the nut 42. As a result, in the case
of T<Tc, when the nut 42 rotates, the inductance L changes
according to the position of the gap sensor 44B as the following
formula.
(Opposed to Bottom Face of Nut 42) L=N.sup.2.mu.oS/d
(Opposed to Target 43c) L3=N.sup.2.mu.oS/(d+d.sub.4)
[0074] On the other hand, in the case wherein the rotor temperature
T is T.gtoreq.Tc, the inductance L changes as the following
formula. At this time, sizes of the inductances L, L3, L4 are
L>L3>L4.
(Opposed to Bottom Face of Nut 42) L=N.sup.2.mu.oS/d
(Opposed to Target 43C) L4=N.sup.2.mu.oS/(d+d.sub.1+d.sub.4)
[0075] FIG. 13 shows a block diagram of the detecting portion 31.
The window comparator 65 in the block diagram shown in FIG. 10 is
replaced with a comparator 66. FIG. 14 show signal waveforms
(a)-(c) referenced in FIG. 13. In signal (a) of FIG. 14, a level D4
is output when the inductance is L3, and signals of levels D5 are
output when the inductance is L4.
[0076] The comparator 64 compares an input signal with the
threshold V.sub.1, and when the level of the signal exceeds the
threshold V.sub.1, the comparator 64 outputs a signal of level H,
and when the level of the input signal is decreased less than the
threshold V.sub.1, the comparator 64 outputs a signal L. Since both
signal levels D4, D5 are smaller than the threshold V.sub.1, pulse
signals corresponding to the signal levels D4, D5 are generated in
the revolution signal which is output from the comparator 64, as
shown in FIG. 14B. These pulses are generated every time when the
rotor 2 makes one rotation.
[0077] On the other hand, the comparator 66 that detects the
temperature monitor signal compares the input signal with the
threshold V.sub.2 which is lower than the threshold V.sub.1, and
when the signal levels exceed the threshold V.sub.2, the signal
level H is output, and when the signal levels are smaller than the
threshold V.sub.2, the signal level L is output. In this case, as
shown in signal (c) of FIG. 14, the signals of level D5 are output
only when the rotor temperature T exceeds the Curie temperature Tc.
As a result, a pulse is also generated only at the time of
T.gtoreq.Tc. More specifically, whether or not the rotor
temperature T is T.gtoreq.Tc can be determined by detecting the
pulse.
[0078] Even in the modified example 3, since the gap sensor 44B is
used as the revolution sensor and also the rotor temperature
monitor sensor, the modified example 3 can have the same effects of
the modified example 2.
[0079] In the above-mentioned modified example 1, the ring-shaped
targets 43, 43B are overlapped in an axial direction. However as
shown in the relationship between the target 43C and the depression
42b shown in FIGS. 9A, 9B, the targets 43, 43B may be arranged
separately in an axisymmetric position.
[0080] The technique shown in the modified example 1 wherein two
kinds of ferromagnetic bodies, whose Curie temperatures differ are
the targets for a temperature monitor, or in the modified examples
2 and 3, wherein the gap sensor is also used for a sensor detecting
the change of the magnetic permeability of a temperature monitor
target and revolution, is not limited to the vacuum pump wherein
the target for the temperature monitor is provided in the end face
as described in the above. A conventional ferromagnetic body ring
can be also applied to a device with a type of being provided
around the rotor. Furthermore, provided that the above disclosed
features are provided, the present invention is not limited to the
above-mentioned embodiment.
[0081] Non-limiting, the motor drive control portion 33 comprises a
control means for controlling the operation of the motor; the
target 43 in FIG. 7 comprises the first ferromagnetic body; and the
target 43B comprises the second ferromagnetic body,
respectively.
[0082] The disclosure of Japanese Patent Application No.
2004-271680 filed on Sep. 17, 2004 is incorporated by reference in
its entirety.
[0083] While the invention has been explained with reference to the
specific embodiments of the invention, the explanation is
illustrative and the invention is limited only by the appended
claims.
* * * * *