U.S. patent number RE39,748 [Application Number 09/885,942] was granted by the patent office on 2007-07-31 for sealed actuator.
This patent grant is currently assigned to NSK, Ltd.. Invention is credited to Atsushi Horikoshi, Hayao Watanabe.
United States Patent |
RE39,748 |
Watanabe , et al. |
July 31, 2007 |
Sealed actuator
Abstract
A sealed actuator includes a motor stator having rotation-drive
magnetic poles; a motor rotor arranged so as to confront magnetic
pole surfaces of the motor stator while interposing a small
distance therebetween and rotatably supported through roller
bearings; and displacement detecting means for measuring
displacement of the motor rotor. A partition wall made of a
nonmagnetic metal is disposed in a clearance between the motor
stator and the motor rotor, so that the inner space where the motor
stator is disposed is hermetically covered. The bearings are
disposed at both sides of the partition wall in the axial direction
so that the load applied to the bearings are directly received by a
housing. At least a part of the partition wall is reinforced by
reinforcing members and a mold agent is charged into the space on
the motor stator side.
Inventors: |
Watanabe; Hayao (Gunma,
JP), Horikoshi; Atsushi (Gunma, JP) |
Assignee: |
NSK, Ltd. (Tokyo,
JP)
|
Family
ID: |
26577617 |
Appl.
No.: |
09/885,942 |
Filed: |
June 22, 2001 |
Related U.S. Patent Documents
|
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
Reissue of: |
08773180 |
Dec 27, 1996 |
05914548 |
Jun 22, 1999 |
|
|
Current U.S.
Class: |
310/88; 310/68B;
310/112 |
Current CPC
Class: |
H02K
7/20 (20130101); H02K 11/0141 (20200801); H02K
11/225 (20160101); H02K 5/128 (20130101) |
Current International
Class: |
H02K
5/10 (20060101); H02K 11/00 (20060101); H02K
7/20 (20060101) |
Field of
Search: |
;310/86,87,88,89,68B,112,114 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
2527854 |
|
Dec 1983 |
|
FR |
|
3-150041 |
|
Jun 1991 |
|
JP |
|
3-150042 |
|
Jun 1991 |
|
JP |
|
WO94/23911 |
|
Oct 1994 |
|
WO |
|
Other References
Translation of French Patent 2527854 by Jacquin "Direct Current
Motor Operating Submerged", Dec. 1983, 10 pages. cited by
examiner.
|
Primary Examiner: Tamai; Karl
Attorney, Agent or Firm: Sughrue Mion, PLLC
Claims
What is claimed is:
1. A sealed actuator comprising: a motor stator including a stator
magnetic pole excited by a rotation-drive coil; housings to which
said motor stator is attached; a motor rotor including a rotor
magnetic pole disposed opposite to a surface of said stator
magnetic pole through a gap; bearings for rotatably supporting a
rotation shaft of said motor rotor to said housing; displacement
measuring means for measuring displacement of said motor rotor; and
a hermetically sealing partition wall made of a nonmagnetic metal
material and disposed at the gap between said stator magnetic pole
and said rotor magnetic pole, a space where said motor rotor is
disposed being hermetically isolated from a space wherein said
motor stator is disposed; wherein said bearings are a plurality of
rolling bearings, said rolling bearings supporting said motor rotor
at positions on said housings at both sides of a member
constituting said sealing partition wall in a longitudinal
direction of said motor rotor so that said housings directly
receive a load applied to said bearings, wherein said displacement
measuring means comprises a resolver rotor made of a mass of
magnetic metal material, disposed at a side of said motor rotor,
and includes a salient tooth cut from said mass of magnetic metal
material; and a resolver stator including a detection coil magnetic
pole and disposed at a side of said motor stator.
2. A sealed actuator as claimed in claim 1, wherein said resolver
rotor is fixed to a member of a nonmagnetic substance.
3. A sealed actuator as claimed in claim 1, wherein said resolver
stator includes a differential circuit type winding.
4. A sealed actuator as claimed in claim 1, further comprising a
magnetic shield plate made of a magnetic metal material disposed
between said stator magnetic pole of said motor stator and said
detection coil magnetic pole of said resolver stator.
5. A sealed actuator as claimed in claim 1, wherein said resolver
rotor is fixed to a member of a nonmagnetic substance; wherein said
resolver rotor includes a differential circuit type winding; and
wherein said actuator further comprises a magnetic shield plate
made of a magnetic metal material disposed between said stator
magnetic pole of said motor stator and said detection coil magnetic
pole of said resolver stator.
6. A sealed actuator comprising: a motor stator including a stator
magnetic pole excited by a rotation-drive coil; a housing to which
said motor stator is attached; a motor rotor including a rotor
magnetic pole disposed opposite to a surface of said stator
magnetic pole through a gap; bearings for rotatably supporting a
rotation shaft of said motor rotor to said housing; displacement
measuring means for measuring displacement of said motor rotor; and
a hermetically sealing partition wall made of a nonmagnetic metal
material and disposed at the gap between said stator magnetic pole
and said rotor magnetic pole, a space where said motor rotor is
disposed being hermetically isolated from a space wherein said
motor stator is disposed; wherein said displacement measuring means
comprises a resolver rotor made of a mass of magnetic metal
material, disposed at a side of said motor rotor, and includes a
salient tooth cut from said mass of magnetic metal material; and a
resolver stator including a detection coil magnetic pole and
disposed at a side of said motor stator.
7. A sealed actuator as claimed in claim 6, wherein said resolver
rotor is fixed to a member of a nonmagnetic substance.
8. A sealed actuator as claimed in claim 6, wherein said resolver
stator includes a differential circuit type winding.
9. A sealed actuator as claimed in claim 6, wherein said
displacement measuring means includes a coarse resolver and a fine
resolver configured such that it is unnecessary to return to an
origin to detect the position of the motor rotor.
10. A sealed actuator as claimed in claim 6, wherein said motor
stator and said motor rotor constitutes a variable-reluctance
motor.
11. A sealed actuator as claimed in claim 6, further comprising a
magnetic shield plate made of a magnetic metal material disposed
between said stator magnetic pole of said motor stator and said
detection coil magnetic pole of said resolver stator.
12. A sealed actuator as claimed in claim 6, wherein said resolver
rotor is fixed to a member of a nonmagnetic substance; wherein said
resolver rotor includes a differential circuit type winding; and
wherein said actuator further comprises a magnetic shield plate
made of a magnetic metal material disposed between said stator
magnetic pole of said motor stator and said detection coil magnetic
pole of said resolver stator.
13. A sealed actuator comprising: a motor stator including a stator
magnetic pole excited by a rotation-drive coil; a housing to which
said motor stator is attached; a motor rotor including a rotor
magnetic pole disposed opposite to a surface of said stator
magnetic pole through a gap; bearings for rotatably supporting a
rotation shaft of said motor rotor to said housing; displacement
measuring means for measuring displacement of said motor rotor; and
a hermetically sealing partition wall made of a nonmagnetic metal
material and disposed at the gap between said stator magnetic pole
and said rotor magnetic pole, a space where said motor rotor is
disposed being hermetically isolated from a space where said motor
stator is disposed; wherein said sealed actuator further comprises
reinforcing means for reinforcing at least a part of said
hermetically sealing partition wall, said reinforcing means being
made of substantially the same nonmagnetic metal material as said
partition wall.
14. A sealed actuator as claimed in claim 13, wherein said
reinforcing means is at least one selected from a group consisting
of a reinforcing member and a molding agent.
15. A sealed actuator comprising a plurality of unit sealed
actuators connected in series to each other, each of said unit
sealed actuators comprising: a motor stator including a stator
magnetic pole excited by a rotation-drive coil; a housing to which
said motor stator is attached; a motor rotor including a rotor
magnetic pole disposed opposite to a surface of said stator
magnetic pole through a gap; bearings for rotatably supporting a
rotation shaft of said motor rotor to said housing; displacement
measuring means for measuring displacement of said motor rotor; and
a hermetically sealing partition wall made of a nonmagnetic metal
material and disposed at the gap between said stator magnetic pole
and said rotor magnetic pole, a space where said motor rotor is
disposed being hermetically isolated from a space where said motor
stator is disposed; wherein said bearings are a plurality of
rolling bearings, said rolling bearings supporting said motor rotor
at positions on said housings at both sides of a member
constituting said sealing partition wall in a longitudinal
direction of said motor rotor so that said housings directly
receive a load applied to said bearings; wherein said rotor
magnetic pole includes a salient pole tooth of a steel material of
a magnetic substance subjected to salient pole working; and wherein
said displacement measuring means comprises a resolver rotor made
of a magnetic metal material, disposed at a side of said motor
rotor, and include a salient pole tooth; and a resolver stator
including a detection coil magnetic pole and disposed at a side of
said motor stator.
16. A sealed actuator comprising a plurality of unit sealed
actuators connected in series to each other, each of said unit
sealed actuators comprising: a motor stator including a stator
magnetic pole excited by a rotation-drive coil; a housing to which
said motor stator is attached; a motor rotor including a rotor
magnetic pole disposed opposite to a surface of said stator
magnetic pole through a gap; bearings for rotatably supporting a
rotation shaft of said motor rotor to said housing; displacement
measuring means for measuring displacement of said motor rotor; and
a hermetically sealing partition wall made of a nonmagnetic metal
material and disposed at the gap between said stator magnetic pole
and said rotor magnetic pole, a space where said motor rotor is
disposed being hermetically isolated from a space where said motor
stator is disposed; wherein said bearings are a plurality of
rolling bearings, said rolling bearings supporting said motor rotor
at positions on said housings at both sides of a member
constituting said sealing partition wall in a longitudinal
direction of said motor rotor so that said housings directly
receive a load applied to said bearings.
17. A sealed actuator comprising a plurality of unit sealed
actuators connected in series to each other, each of said unit
sealed actuators comprising: a motor stator including a stator
magnetic pole excited by a rotation-drive coil; a housing to which
said motor stator is attached; a motor rotor including a rotor
magnetic pole disposed opposite to a surface of said stator
magnetic pole through a gap; bearings for rotatably supporting a
rotation shaft of said motor rotor to said housing; displacement
measuring means for measuring displacement of said motor rotor; and
a hermetically sealing partition wall made of a nonmagnetic metal
material and disposed at the gap between said stator magnetic pole
and said rotor magnetic pole, a space where said motor rotor is
disposed being hermetically isolated from a space where said motor
stator is disposed; wherein said displacement measuring means
comprises a resolver rotor made of a magnetic metal material,
disposed at a side of said motor rotor, and including a salient
tooth; and a resolver stator including a detection coil magnetic
pole and disposed at a side of said motor stator.
18. A sealed actuator as claimed in claim 17, wherein said resolver
rotor is fixed to a member of a nonmagnetic substance.
19. A sealed actuator as claimed in claim 17, wherein said resolver
stator includes a differential circuit type winding.
20. A sealed actuator as claimed in claim 17, wherein said
displacement measuring means includes a coarse resolver and a fine
resolver.
21. A sealed actuator as claimed in claim 17, wherein said motor
stator and said motor rotor constitutes a variable-reluctance
motor.
22. A sealed actuator as claimed in claim 17, further comprising a
magnetic shield plate made of a magnetic metal material disposed
between said stator magnetic pole of said motor stator and said
detection coil magnetic pole of said resolver stator.
23. A sealed actuator as claimed in claim 17, wherein said resolver
rotor is fixed to a member of a nonmagnetic substance; wherein said
resolver rotor includes a differential circuit type winding; and
wherein said actuator further comprises a magnetic shield plate
made of a magnetic metal material disposed between said stator
magnetic pole of said motor stator and said detection coil magnetic
pole of said resolver stator.
24. A sealed actuator as claimed in one of claims 15 to 22, wherein
said rotation shaft of said motor rotor is an extension shaft fixed
to said motor rotor.
.Iadd.25. A sealed actuator comprising: a motor stator including a
stator magnetic pole excited by a rotation-drive coil; a housing to
which said motor stator is attached; a motor rotor including a
rotor magnetic pole disposed opposite to a surface of said stator
magnetic pole through a gap; an encoder for measuring displacement
of said motor rotor; and a hermetically sealing partition wall made
of a nonmagnetic metal material and disposed at the gap between
said stator magnetic pole and said rotor magnetic pole, a space
where said motor rotor is disposed being hermetically isolated from
a space where said motor stator is disposed; wherein said sealed
actuator further comprises reinforcing means for reinforcing at
least a part of said hermetically sealing partition wall, said
reinforcing means being made of the same nonmagnetic metal material
as said partition wall, wherein said partition wall is disposed
between said reinforcing means and said motor rotor..Iaddend.
.Iadd.26. A sealed actuator as claimed in claim 25, wherein said
encoder is an optical encoder..Iaddend.
.Iadd.27. A sealed actuator as claimed in claim 25, wherein said
encoder is a magnetic encoder..Iaddend.
.Iadd.28. A sealed actuator comprising a plurality of unit sealed
actuators connected in series to each other, each of said unit
sealed actuators comprising: a motor stator including a stator
magnetic pole excited by a rotation-drive coil; a housing to which
said motor stator is attached; a motor rotor including a rotor
magnetic pole disposed opposite to a surface of said stator
magnetic pole through a gap; bearings for rotatably supporting a
rotation shaft of said motor rotor to said housing; an encoder for
measuring displacement of said motor rotor; and a hermetically
sealing partition wall made of a nonmagnetic metal material and
disposed at the gap between said stator magnetic pole and said
rotor magnetic pole, a space where said motor rotor is disposed
being hermetically isolated from a space where said motor stator is
disposed; wherein said bearings support said motor rotor at
positions on said housing at both sides of a member constituting
said sealing partition wall in a longitudinal direction of said
motor rotor so that said housing directly receives a load applied
to said bearings..Iaddend.
.Iadd.29. A sealed actuator as claimed in claim 28, wherein said
encoder is an optical encoder..Iaddend.
.Iadd.30. A sealed actuator as claimed in claim 28, wherein said
encoder is a magnetic encoder..Iaddend.
Description
BACKGROUND OF THE INVENTION
The present invention relates to sealed actuators, and more
particularly to a sealed actuator adapted for use in an ultra-high
vacuum environment in which even small amounts of contaminants and
impure gases are not admitted or in an environment in which
magnetic poles and coils of a motor become corroded, such as in a
corrosive gas environment.
For example, in semiconductor manufacturing, a workpiece is worked
in an ultra-high vacuum environment in order to eliminate
impurities to a possible extent. In an actuator employed in such a
case, a lubricant that contains volatile component such as ordinary
grease is not allowed to be used for bearings of a drive shaft of a
drive motor for, e.g., a workpiece positioning apparatus.
Therefore, the inner and outer races of such bearings are plated
with soft metal such as gold or silver. Further, the coil
insulators and wiring sheathes of the motor, the adhesives of
laminated magnetic poles, and the like are made of stable materials
having good heat resistance and discharging relatively small
amounts of gases.
On the other hand, as means for introducing rotational output into
an ultra-high vacuum vessel from outside, various types of
actuators such as a bellows type drive system, a magnetic coupling
drive system, a magnetic fluid seal drive system have heretofore
been known. These actuators are so constructed that the output end
of a rotating shaft supported by vacuum bearings is projected into
the vacuum environment and that rotating force is transmitted to
the input end by a drive apparatus disposed in the atmosphere. More
specifically, a bellows type drive system is designed as follows.
As shown in FIG. 6, an output end 101A of a rotating shaft 101 is
projected into a vacuum environment V while being supported by
vacuum bearings 102, and when an inclined-plate type oscillating
mechanism 103 on the other end 101B is driven to rotate by a
rotating apparatus 105 disposed in the atmosphere, a bellows 104
repeats expansion and contraction, so that the rotating shaft 101
is rotated.
In contrast thereto, a magnetic coupling drive system is designed
as follows. A rotor made of a magnetic substance is secured to the
input end of a rotating shaft with the outer circumference of the
rotor being hermetically sealed by a housing. A magnet is arranged
on the side of the atmosphere so as to surround the rotor while the
housing being interposed. The magnet is rotated to thereby rotate
the rotating shaft.
Further, a magnetic fluid seal drive system is designed as follows.
A housing made of a nonmagnetic substance is arranged so as to pass
through a partition wall disposed between the atmosphere side and
the vacuum side. Not only circular-ring-like pole pieces
sandwiching a permanent magnet therebetween are arranged between
bearings disposed in the housing, but also a clearance between the
outer circumferential surface of a rotating shaft passing through
the housing and the inner circumferential surface of the pole
pieces confronting the outer circumferential surface of the
rotating shaft is sealed with a magnetic fluid.
Recently, higher integration of semiconductors is accompanied with
higher density by miniaturizing IC pattern widths. In order to
fabricate wafers that can meet such miniaturization needs, a high
degree of consistency for wafer quality is required. To meet such
needs, it is important to reduce impure gas concentration in wafers
in a low-pressure gas processing chamber. Further, in order to
implement miniaturization as required, an extremely highly accurate
positioning apparatus must be employed.
From these viewpoints, the aforementioned conventional actuators
have the following problems.
In the case of a drive motor used for an ultra-high vacuum
apparatus:
(1) Even if highly heat-resistant, stable materials that discharges
relatively small amounts of gases are selected for the coils,
insulators, wiring sheathes, and the like of the drive motor, these
materials still impose problems as long as they are organic
insulating materials. Since an organic insulating material is
porous and has numerous holes over the surface when observed
microscopically. When such material is exposed to the atmosphere,
gas, moisture, and the like are adsorbed into the holes on the
surface thereof. It takes much time to degas such adsorbed impure
molecules by means of evacuation, which is most likely to reduce
production efficiency.
(2) In addition, no heat radiation by air convection occurs in a
vacuum. Therefore, if coil temperature increases locally,
resistance at such local part increases to accelerate heating,
which in turn makes the coil insulating film susceptible to
burning.
(3) On the other hand, it is conceivable to reduce adsorbed impure
molecules by using inorganic materials for coil insulators and
sheathed wires in stainless conduits for wiring. However, this
measure not only entails large costs, but also imposes the problem
that the motor capacity is reduced due to the fact that the rate of
conductors such as copper in the coil winding space is reduced to
increase electric resistance.
In contrast to the aforementioned problems imposed when an actuator
is disposed in an ultra-high vacuum apparatus, the following
problems arise in the cases where the drive section of an actuator
is disposed outside a vacuum apparatus as in the bellows type drive
system, the magnetic coupling drive system, the magnetic fluid seal
drive system, and the like.
In the bellows type drive system, large backlash occurs. In the
magnetic coupling drive system in which rotating force is
transmitted by the attracting force of a magnet, rigidity is
reduced. That is, highly accurate positioning requirements cannot
be met by these systems.
Further, in the magnetic fluid seal drive system, the magnetic
fluid has a heat resistance temperature of about 70.degree. C.,
which is a relatively low temperature. Therefore, the magnetic
fluid is not resistant to beating temperatures during a bake-out
process in an ultra-high vacuum vessel (the process of discharging
adsorbed gas and water molecules contained in an inner wall of a
vacuum vessel and the like). As a result, the magnetic fluid,
containing a small amount of volatile component, discharges gas
disadvantageously.
To overcome these problems of the conventional actuators, the
present applicant proposed a sealed actuator in Japanese Patent
Unexamined Publication Nos. Hei. 3-150041 and Hei. 3-150042. This
actuator is characterized by discharging no impure gas in an
ultra-high vacuum environment and achieving highly accurate
positioning. This actuator includes: a motor stator having
rotation-drive magnetic poles excited by rotation-drive coils; a
motor rotor arranged so as to confront the magnetic pole surfaces
of the motor stator while having a small clearance with respect to
the magnetic pole surfaces and rotatably supported through roller
bearings; and a resolver serving as a displacement detecting means
for measuring a displacement of the motor rotor. The actuator has a
partition wall made of a nonmagnetic metal between the motor stator
and the motor rotor so that the inner space within which the motor
stator is disposed is hermetically covered with the partition wall,
which in turn allows the motor stator side space to be isolated
from the motor rotor side space.
In the sealed actuator described above, since the motor stator is
isolated from the motor rotor by the partition wall made of a
nonmagnetic metal, even if the. actuator is used in a high vacuum
environment or reactive gas environment of a semiconductor
manufacturing apparatus, neither impure gases are discharged from
the coils and organic insulators of the actuator to contaminate the
environment nor are the coils and organic insulators eroded. In
addition, the formation of a magnetic circuit is not hindered
between the motor stator and the motor rotor. Moreover, highly
accurate positioning can be implemented by the resolver. Thus, such
actuator is highly useful in practical use.
However, the thickness of the partition wall made of a nonmagnetic
metal must be so limited as not to hinder the formation of a
magnetic circuit between the motor stator and the motor rotor in
particular. Thus, when exposed to an ultra-high vacuum, the
partition wall may be swollen.
Further, as a drive apparatus of a magnetic coupling drive system,
the configuration as shown in FIG. 7 is known. That is, an
attachment flange 201 is attached to an opening of a bottom wall
202 of a vacuum container. In the inside of housings 216 and 236
positioned outside of the vacuum container, two drive shafts of an
outer drive shaft 204 and an inner drive shaft 205 are coaxially
disposed and extend outside of the housing through the opening. The
outer drive shaft 204 positioned in the vacuum container is
supported by bearing 206 at the tip portion of the inner drive
shaft 205.
Further, a motor rotor 207 is supported on an outer surface of the
outer drive shaft 204. A motor stator 208 corresponding thereto is
supported on an outer housing 216 of the motor rotor 207.
Similarly, a motor rotor 209 is supported on an outer surface of
the inner drive shaft 205. A motor stator 210 corresponding thereto
is supported on an outer housing 236 of the motor rotor 209. The
motor rotors 207 and 209 are disposed in a vacuum state, and the
motor stators 208 and 210 are disposed outside of the vacuum
state.
The outer drive shaft 204 is supported on the housing 216 through
bearings 218 and 219, and the inner drive shaft 205 is supported on
the housing 236 through bearings 238 and 239. Between the motor
rotor 207 and the motor stator 208, and between the motor rotor 209
and the motor stator 210, thin nonmetal partition walls 216a and
236a extended from the housing 216 and the housing 236 are
respectively located to keep the vacuum state in the side of the
motor rotor 207 and 209.
In such a configuration, for the improvement of performance of a
motor, it is required to prevent the decrease in magnetic flux to a
possible degree between the motor rotor and the motor stator by the
nonmagnetic partition wall. For the purpose, the thickness of the
partition wall must be as thin as possible. Thus, since the outer
drive shaft 204 and the inner drive shaft 205 are supported by the
bearings disposed in the housings 216 and 236 including the thin
partition wall, the conventional drive apparatus has a problem that
supporting rigidity of the respective drive shafts to the housings
is lowered. If an arm or the like is attached to the tip of the
drive shaft of the drive apparatus having such a structure and a
load is applied to the tip, the force acting on the bearings acts
also on the partition wall so that such a possibility can not be
neglected that the partition wall is deformed or the partition wall
is broken, which is a problem of the conventional apparatus.
Further, since the support rigidity of the outer drive shaft 204
and the inner drive shaft 205 are low, there occurs a problem that
both the drive shafts are brought into contact with each other by
swing due to rotation of both the drive shafts. Accordingly, this
prior art overcomes the disadvantage of contact of both the drive
shafts by using the pilot bearings 206.
Moreover, high integration of semiconductors requires control of
higher accuracy and stability. Under such circumstances,
positioning control with a resolver becomes insufficient due to the
fact that magnetism from a motor stack surrounds the resolver.
SUMMARY OF THE INVENTION
The present invention has been made in view of the aforementioned
problems encountered by the prior art. An object of the invention
is therefore to provide a sealed actuator which does not discharge
impure gases in an ultra-high vacuum environment, which can achieve
highly accurate positioning, and which can maintain sufficient
strength.
According to a first aspect of the invention, a sealed actuator
comprises: a motor stator including a stator magnetic pole excited
by a rotation-drive coil; housings to which said motor stator is
attached; a motor rotor including a rotor magnetic pole disposed
opposite to a surface of said stator magnetic pole through a gap;
bearings for rotatably supporting a rotation shaft of said motor
rotor to said housing: displacement measuring means for measuring
displacement of said motor rotor; and a hermetically sealing
partition wall made of a nonmagnetic metal material and disposed at
the gap between said stator magnetic pole and said rotor magnetic
pole, a space where said motor rotor is disposed being hermetically
isolated from a space where said motor stator is disposed; wherein
said bearings are a plurality of rolling bearings, said rolling
bearings support said motor rotor at positions on said housings at
both sides of a member constituting said sealing partition wall in
a longitudinal direction of said motor rotor so that said housing
directly receives a load applied to said bearings.
According to a second aspect of the invention, a sealed actuator
comprises: a motor stator including a stator magnetic pole excited
by a rotation-drive coil; a housing to which said motor stator is
attached; a motor rotor including a rotor magnetic pole disposed
opposite to a surface of said stator magnetic pole through a gap;
bearings for rotatably supporting a rotation shaft of said motor
rotor to said housing; displacement measuring means for measuring
displacement of said motor rotor; and a hermetically sealing
partition wall made of a nonmagnetic metal material and disposed at
the gap between said stator magnetic pole and said rotor magnetic
pole, a space where said motor rotor is disposed being hermetically
isolated from a space where said motor stator is disposed; wherein
said displacement measuring means comprises a resolver rotor made
of a magnetic metal material, disposed at a side of said motor
rotor, and include a salient tooth; and a resolver stator including
a detection coil magnetic pole and disposed at a side of said motor
stator.
According to a third aspect of the invention, a sealed actuator
comprises: a motor stator including a stator magnetic pole excited
by a rotation-drive coil; a housing to which said motor stator is
attached; a motor rotor including a rotor magnetic pole disposed
opposite to a surface of said stator magnetic pole through a gap;
bearings for rotatably supporting a rotation shaft of said motor
rotor to said housing; displacement measuring means for measuring
displacement of said motor rotor; and a hermetically sealing
partition wall made of a nonmagnetic metal material and disposed at
the gap between said stator magnetic pole and said rotor magnetic
pole, a space where said motor rotor is disposed being hermetically
isolated from a space where said motor stator is disposed; wherein
said sealed actuator further comprises reinforcing means for
reinforcing at least a part of said hermetically sealing partition
wall.
According to a fourth aspect of the invention, a sealed actuator
comprises a plurality of unit sealed actuators connected in series
to each other, and each of said unit sealed actuators comprises: a
motor stator including a stator magnetic pole excited by a
rotation-drive coil; a housing to which said motor stator is
attached; a motor rotor including a rotor magnetic pole disposed
opposite to a surface of said stator magnetic pole through a gap;
bearings for rotatably supporting a rotation shaft of said motor
rotor to said housing; displacement measuring means for measuring
displacement of said motor rotor; and a hermetically sealing
partition wall made of a nonmagnetic metal material and disposed at
the gap between said stator magnetic pole and said rotor magnetic
pole, a space where said motor rotor is disposed being hermetically
isolated from a space where said motor stator is disposed; wherein
said bearings are a plurality of rolling bearings, said rolling
bearings supporting said motor rotor at positions on said housings
at both sides of a member constituting said sealing partition wall
in a longitudinal direction of said motor rotor so that said
housing directly receives a load applied to said bearings; wherein
said rotor magnetic pole includes a salient pole tooth of a steel
material of a magnetic substance subjected to salient pole working;
and wherein said displacement measuring means comprises a resolver
rotor made of a magnetic metal material, disposed at a side of said
motor rotor, and include a salient pole tooth; and a resolver
stator including a detection coil magnetic pole and disposed at a
side of said motor stator.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a side sectional view showing a sealed actuator of a
first embodiment of the invention;
FIG. 2 is a plan view for explanation of arrangement of magnetic
poles of a variable-reluctance resolver;
FIG. 3 is a circuit diagram of the resolver;
FIG. 4 is a side sectional view showing a sealed actuator of a
second embodiment of the invention;
FIG. 5 is a side sectional view showing a sealed actuator provided
with a second variable-reluctance resolver;
FIG. 6 is a sectional view showing an example of a conventional
sealed actuator; .[.and.].
FIG. 7 is a sectional view showing another example of a
conventional sealed actuator.[...]. .Iadd.;.Iaddend.
.Iadd.FIG. 8 is a side sectional view, similar to FIG. 1, showing a
sealed actuator having an encoder instead of a
resolver..Iaddend.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Preferred embodiments of the invention will now be described with
reference to the drawings.
A sealed actuator 10 shown in FIG. 1 is a so-called inner-rotor
direct-drive motor in which a motor rotor 12 rotates inside a motor
stator 11. More specifically, the sealed actuator 10 is a
variable-reluctance stepping motor.
The motor stator 11 is cylindrical and has motor stator magnetic
poles 15 formed on the inner circumferential surface thereof. Each
motor stator magnetic pole 15 serves as a rotation-drive magnetic
pole excited by a rotation-drive coil 14. The rotation-drive coil
14 is wound around the motor stator magnetic pole 15 through an
insulating member 13.
A plurality of teeth pitched. at a predetermined interval in
parallel with the rotating shaft of the motor rotor 12 are arranged
on the inner circumference of the motor stator magnetic poles 15,
though they are not shown in the drawing. These teeth are well
known and are generally called salient pole teeth. Also in the
following description, the teeth will be referred to as salient
pole teeth.
On the other hand, the motor rotor 12 is cylindrical and has a
hollow hole H that passes through the shaft. The motor rotor 12 is
rotatably disposed inside the motor stator 11 through vacuum roller
bearings 17 and 18. The vacuum roller bearings 17 and 18 are
arranged so as to be distant from each other and coaxial with
respect to the motor stator 11. Motor rotor magnetic poles 16 are
arranged around the outer circumferential surface of the motor
rotor 12 so as to confront the motor stator magnetic poles 15 of
the motor stator 11.
Each motor rotor magnetic pole 16 is made of a magnetic metal. A
plurality of salient teeth are arranged around the outer
circumferential surfaces of the motor rotor magnetic poles 16 so as
to be in parallel with the teeth on the inner circumferential
surfaces of the motor stator magnetic poles 15. A train of teeth of
the motor rotor magnetic poles 16 are pitched at the same interval
as that of the motor stator magnetic poles 15, but are arranged out
of phase with the train of teeth of the motor stator magnetic poles
15. Thus, by sequentially exciting the train of teeth of the motor
stator magnetic poles 15 in the circumferential direction while
controlling the supply of current to the rotation-drive coils 14,
the train of teeth of the motor rotor magnetic poles 16 are
attracted to the teeth of the motor stator magnetic poles 15, so
that the motor rotor 12 is rotated inside the motor stator 11.
The vacuum roller bearings 17 and 18 are such that the inner races
and outer races thereof are plated with soft metal such as gold or
silver for metal lubrication that is free from discharging gases.
An inner race 17a of the bearing 17 is fitted with the outer
surface on one end of the motor rotor 12, and an outer race 17b
thereof is fixed by a bearing press 21 to a housing member 23 on
one end of the motor stator 11 through an annular mounting member
22A.
An inner race 18a of the other bearing 18 is fitted with the outer
surface on the other end of the motor rotor 12, and an outer race
18b thereof is fixed to a housing member 24 on the other end of the
motor stator 11 through an annular mounting member 22B. A body to
be driven to rotate is bolted onto one end face 12A of the thus
rotatably supported motor rotor 12.
A collar portion 23a is disposed on the inner circumference of the
housing member 23 to which the outer race 17b of the bearing 17 is
fixed, the collar portion 23a annularly projecting toward the outer
circumferential surface of the motor rotor 12. A collar portion 24a
is disposed on the inner circumference of the housing member 24 to
which the outer race 18b of the bearing 18 is fixed, the collar
portion 24a annularly projecting toward the outer circumferential
surface of the motor rotor 12. These collar portions 23a and 24a
define the space in which the motor stator magnetic poles 15 are
accommodated.
A variable-reluctance resolver 26 is accommodated in a space S
located on one end of the motor stator magnetic pole 15 defined by
the collar portion 23a. The variable-reluctance resolver 26 is a
high-resolution rotation detector serving as a displacement
detecting means for detecting a relative displacement between the
motor stator 11 and the motor rotor 12 to position the motor with
high accuracy. A stator 28 of the resolver 26 having coils 27 is
secured to the inner circumferential surface of the motor stator
11. On the other hand, a rotor 29 of the resolver 26 is secured to
a stepped portion of the motor rotor 12 of nonmagnetic metal so as
to confront the stator 28.
A plurality of teeth pitched at a predetermined interval in
parallel with the rotating shaft of the motor rotor 12 are arranged
on the inner circumferential surface of the magnetic poles of the
stator 28 of the variable-reluctance resolver 26 in a manner
similar to the motor stator magnetic poles 15. The coils 27 are
wound around the respective magnetic poles. On the other hand, the
rotor 29 of the resolver 26 has a train of teeth pitched at the
same interval as that of the motor rotor magnetic poles 16 so as to
be out of phase with one another. The details of the
variable-reluctance resolver 26 and its control circuit will be
described later.
As the motor rotor 12 rotates, the rotor 29 of the resolver 26
rotates, and the reluctance with respect to the magnetic poles the
stator 28 varies. A reluctance change is detected by setting the
reluctance change so that the basic wave component of the
reluctance change equals an n cycle per one revolution of the rotor
29, and the detected value is digitized by a resolver control
circuit to be used as a position signal, so that the rotational
angle position (or rotational speed) of the motor rotor 12 can be
detected. Reference numeral 31 denotes a magnetic shield plate
fixed to the motor stator 11 so as to be interposed between the
motor stator magnetic pole 15 and the resolver 26. Reference
numeral 32 denotes a wiring hole passing through the motor stator
11, and a mold agent 42 is filled therein as described later.
A cylindrical partition wall 33 made of a nonmagnetic metal such as
nonmagnetic stainless steel SUS304 is disposed so as to separate
the motor stator 11 from the motor rotor 12 in a clearance 19
between the confronting surfaces of the motor stator 11 and the
motor rotor 12. On end of the partition wall 33 is welded onto the
inner circumferential surface of the collar portion 23a of the
housing member 23 that partitions the space S on one end of the
motor stator magnetic pole 15. The other end of the partition wall
33 is welded with the collar portion 24a of the housing member 24
that partitions the space on the other end of the motor stator
magnetic pole 15. The inner circumferential surface of the motor
stator magnetic pole 15 is brought into close contact with the
partition wall 33. In this embodiment, the two bearings 17 and 18
support the motor rotor 12 at positions of both sides of the member
33 constituting the partition wall in the longitudinal direction of
the motor rotor 12, so that loads applied to the bearings 17 and 18
are directly received by the housing member 23, the motor stator 11
and the housing member 24, which constitutes the housing of the
sealing actuator.
Thus, both ends of the partition wall 33 is hermetically integrated
with the housing. Hence, the space in which the rotation-drive
coils 14, the motor stator magnetic poles 15, the coils 27 and the
stator 28 of the resolver 26, and the like are accommodated is
completely hermetically isolated from the inside of the motor rotor
12 in the inner circumference of the motor stator 11.
Further, ring-shaped reinforcing members 40 and 41 made of a
nonmagnetic metal are attached closely without gap to a portion of
the partition wall 33 corresponding to the motor stator 11 and the
resolver 26. The reinforcing members 40 and 41 are made of the same
material as the nonmagnetic partition wall. Thus, since the
reinforcing members can receive the inner pressure deforming force
to the partition wall by expansion of the mold material having a
large expansion coefficient even when the mold agent is also used
as the reinforcing means and the stator is heated to a high
temperature at bake-out, the partition wall is not deformed. The
reinforcing members also serve to reinforce the partition wall 33
when it is subjected to a thinning process through cutting or
grinding an inner diameter side thereof.
Moreover, the mold agent 42 as reinforcing means is charged fully
into the space S in which the resolver 26, the rotation-drive coils
14 of the motor stator magnetic poles 15, and the like are
accommodated while partitioned by the collar portion 23a of the
housing member 23 on one side, into the space in which the
rotation-drive coils 14 are accommodated while partitioned by the
collar portion 24a of the housing member 24 on the other side, and
into the wiring hole 32. In this embodiment, although both the
reinforcing members and the mold agent are used as the reinforcing
means, only one of them may be used according to the
circumstances.
It may be noted that electron-beam welding or laser-beam welding,
which can restrict the rise of temperature to a local portion, is
employed to weld one end of the partition wall 33, because the
welding operation of the partition wall 33 is performed under the
state where the parts made of material that are relatively low heat
resistant, such as the rotation-drive coils 14, insulators thereof
13, and the coils 27 of the resolver 26, are contained.
A vacuum flange portion 35 having a vacuum seal 34 is formed by
extending the outer circumference of the housing member 23 on one
side of the motor stator 11. The vacuum flange portion 35 allows
the sealed actuator 10 to be mounted on a vacuum apparatus.
Further, an origin detector 60 is disposed on the housing member 24
on the other side. The origin detector 60 has a magnetic sensor 61
and a single magnet 62. The magnetic sensor 61 is embedded in a
recess formed in the outer circumferential surface of the
nonmagnetic housing member 24. The magnet 62 is attached to one
place on the end face of the other end of the motor rotor 12 on the
bearing 18 side so that the magnet 62 can confront the magnetic
sensor 61 through a thin wall of the housing member 24. The magnet
62 rotates together with the rotation of the motor rotor 12, and
the magnetic sensor 61 outputs a position signal in response to the
magnetism of the rotating magnet 62.
The above mentioned variable-reluctance resolver 26 will be
described. As the variable-reluctance resolver, one that is
disclosed in Japanese Patent Unexamined Publication No. Hei.
5-122916 can be preferably used. As shown in FIG. 2, this
variable-reluctance resolver is constructed so that the resolver
stator 28 has 3-phase 18-pole first magnetic poles A11 to C.sub.16,
B.sub.11, to B.sub.16, C.sub.11 to C.sub.16 formed with a
predetermined interval, and 3-phase 18-pole second magnetic poles
A.sub.21 to C.sub.26, B.sub.21 to B.sub.26, C.sub.21 to C.sub.26
formed with a predetermined distance at intermediate position of
the first magnetic poles A.sub.11 to C.sub.16, B.sub.11, to
B.sub.16, C.sub.11 to C.sub.16. The respective magnetic poles are
arranged in the order of
A.sub.11-C.sub.21-B.sub.11-A.sub.21-C.sub.11-B.sub.21-A.sub.12-C.sub.22
- - -. For the respective magnetic poles A.sub.11 to C.sub.26,
three teeth T.sub.S1 to T.sub.S3 are formed at end surfaces of the
inner circumference side, and exciting windings L.sub.A11 to
L.sub.C26 are wound around at the center portion. Thus, magnetic
poles at the position of 180.degree. are in the same phase to each
other.
The resolver rotor 29 includes a train of teeth with the phase
shifted from the teeth T.sub.S1 to T.sub.S3 of the resolver stator
28 and with the same pitch as those.
FIG. 3 shows the structure of a resolver control circuit. One end
of the exciting windings L.sub.A11 to L.sub.C26 is connected to a
single-phase AC power source 45, and the other end thereof is
grounded through resistors R.sub.A1 to R.sub.C2, so that i-phase
output signals fa1 (.theta.) to fc1 (.theta.) and fa2 (.theta.) to
fc2 (.theta.) in accordance with current change in response to
change of reluctance between the output terminals T.sub.A1 to
T.sub.C2 leading from a portion between the exciting winding and
the resistor and the slot tooth T.sub.R of the rotor 29, are output
to the terminals T.sub.A1 to T.sub.C1, and T.sub.A2 to T.sub.C2,
and input into differential amplifiers 46A to 46C. The differential
amplifications 46A to 46C calculate difference values, which are
converted into two-phase signal by a phase conversion circuit 47,
so that two-phase signal fC(.theta.) and FS(.theta.) are supplied
to a signal processing circuit 48.
The signal processing circuit 48 includes a multiplier, a
synchronous rectifier into which an AC voltage is input as a
synchronizing signal from an AC power source for excitation, and
the like. An output signal of the synchronous rectifier is output
as a speed signal and a digital value indicating a rotation speed
in output.
That is, when single-phase AC current is supplied to the exciting
windings L.sub.A11 to L.sub.C26 to excite, resolver signals
fa1(.theta.) to fc1 (.theta.) and fa2 (.theta.) to fc2 (.theta.)
generated in the exciting windings L.sub.A11, to L.sub.C26 are
expressed by the following equations (1) to (6). fa1(.theta.)=A0+A1
cos .theta.+A2 cos 2.theta.+A3 cos 3.theta.+A4 cos 4.theta. (1)
fb1(.theta.)=A0+A1 cos (.theta.-120.degree.)+A2 cos
2(.theta.-120.degree.)+A3 cos 3(.theta.-120.degree.)+A4 cos
4(.theta.-120.degree.) (2) fc1(.theta.)=A0+A1 cos
(.theta.+120.degree.)+A2 cos 2(.theta.+120.degree.)+A3 cos
3(.theta.+120.degree.)+A4 cos 4(.theta.+120.degree.) (3)
fa2(.theta.)=A0+A1 cos (.theta.+180.degree.)+A2 cos
2(.theta.+180.degree.)+A3 cos 3(.theta.+180.degree.)+A4 cos
4(.theta.+180.degree.) (4) fb2(.theta.)=A0+A1 cos
(.theta.-300.degree.)+A2 cos 2(.theta.-300.degree.)+A3 cos
3(.theta.-300.degree.)+A4 cos 4(.theta.-300.degree.) (5)
fc2(.theta.)=A0+A1 cos (.theta.+300.degree.)+A2 cos
2(.theta.+300.degree.)+A3 cos 3(.theta.+300.degree.)+A4 cos
4(.theta.+300.degree.) (6)
Since the respective resolver signals fa1 to fc1 and fa2 to fc2 are
supplied to the differential amplifiers 46A to 46C, output signals
da to dc of these differential amplifiers 46A to 46C are expressed
by the following equations (7) to (9). da=2A1 cos .theta.+2A3 cos
3.theta. (7) db=2A1 cos (.theta.-120.degree.)+2A3 cos
3(.theta.-120.degree.) (8) dc=2A1 cos (.theta.+120.degree.)+2A3 cos
3(.theta.+120.degree.) (9)
As is apparent from these equations (7) to (9), the differential
amplifiers 46A to 46C can produce three-phase signals da to dc in
which only third harmonic distortion remains among harmonic
distortion of permeance. These threephase signals da to dc are
converted through the phase conversion circuit 47 into two-phase
signals fc(.theta.) and fS(.theta.) in which the third harmonic
distortion is cancelled. The signal processing circuit includes the
multiplier, the synchronous rectifier into which an AC voltage is
input as a synchronizing signal from the AC voltage for excitation,
and the like. An output signal of the synchronous rectifier is
output as a speed signal, and a digital value indicating a rotation
speed is output. Japanese Patent Unexamined Publication No. Hei
5-122916 may be referred to for the details of the resolver and
resolver control circuit.
The attachment and operation of the sealed actuator will next be
described. The sealed actuator 10 is mounted by, for example,
fixing the flange portion 35 to a vessel wall 37 of a vacuum vessel
with a bolt 38. The front end portion of the motor rotor 12 of the
sealed actuator 10 is inserted, as an output shaft A, into the
vacuum vessel interior V from a mounting hole 39 arranged in the
vessel wall 37.
The space of the motor stator 11 hermetically sealed and isolated
from the motor rotor 12 with the partition wall 33 in the sealed
actuator 10 is completely isolated from the vacuum vessel interior
V. The hollow hole H passing through the motor rotor 12
communicates with the vacuum vessel interior V, but is isolated
from the atmosphere while sealed with a seal 36. As a result, gas
and moisture contained in rotation-drive coil 14 of the motor
stator 11, the coil 27 of the resolver 26, and their insulators 13
and the like are prevented from being dispersed in the vacuum
vessel interior V to contaminate the vacuum environment.
Therefore, the vacuum vessel interior V can not only be easily
discharged, but also be rapidly evacuated to a predetermined
ultra-high vacuum even during bake-out, achieving high production
efficiency. In addition, coil insulators are not necessarily be
made of expensive nonorganic materials. Moreover, in the case of
semiconductor manufacturing, there is no danger of etching the
aforementioned coils, insulators, and the like since they are
protected by the partition wall 33 made of a stainless steel from
etching reactive gas introduced into the vacuum vessel interior V
after evacuation.
Further, since the rotation-drive coils 14 are sealed without
clearance with the mold agent 42, heat can be radiated even if the
coils 14 are heated while being energized. This means that burning
of the coils due to local heat reserve can be prevented. It may be
noted that the rotation-drive coils 14 can be forcibly cooled
easily by flushing air or water into the motor stator 11 whenever
necessary since the coils 14 are located on the side of the
atmosphere.
Still further, not only the partition wall 33 is reinforced by the
reinforcing members 40 and 41, but also the spaces on both ends of
the motor stator 11 are reinforced by charging the mold agent 42.
Therefore, for example, even if the sealed actuator 10 is used for
an ultra-high vacuum apparatus, it is stable without occurrence of
such a trouble that the partition wall 33 exposed to vacuum is
deformed-by being swollen.
Further, in the case of the conventional inner rotoractuator of
this type, for example, the inner circumferential surface of the
partition wall 33 is cut or ground after the partition wall 33 has
been welded to the housing member, so that the partition wall 33 is
finished to a thickness of several tens .mu.m. Therefore, the
partition wall 33 escapes from a cutting (grinding) tool during
cutting or grinding operation, which in turn impairs concentricity
accuracy of the inner circumferential surface of the partition
wall, thereby causing the partition wall to come in contact with
the outer circumferential surface of the motor rotor magnetic poles
16. This results in a low yield. Unlike such conventional example,
this embodiment of the invention has greatly improved the yield by
reinforcing the partition wall 33 with the reinforcing members 40,
41 and the mold agent 42.
Still further, feedback control can guarantee high rotational
positioning accuracy of the motor rotor 12. That is, when the
rotation-drive coils 14 of the motor stator 11 are energized,
electromotive force is produced. As a result, the teeth of the
motor stator magnetic poles 15 are excited. Since the partition
wall 33 made of nonmagnetic metal is very thin, the magnetic fluxes
produced reach the motor rotor 12 through the partition wall 33.
Thus, a magnetic circuit is formed between the magnetic poles 15 of
the thus energized motor stator and the confronting motor rotor
magnetic poles 16, allowing the confronting teeth on both the
magnetic poles to attract each other strongly.
Motor current controlled through a not shown drive unit is applied
sequentially to the plurality of rotation-drive coils 14 that are
sequentially arranged in the circumferential direction. As a
result, the teeth of the motor stator magnetic poles 15 are
sequentially excited, which in turn causes the motor rotor 12 to
rotate. When the motor rotor 12 starts rotating, the rotor 29 of
the resolver 26 also rotates. As a result, reluctance between the
stator 28 and the teeth varies. Such variations are digitized by a
resolver control circuit of the not shown drive unit and utilized
as position signals. The thus obtained position signals permit
accurate feedback control of rotational angles of the rotor 29 and
hence of the rotational angles of the motor rotor 12. Therefore,
highly accurate positioning can be implemented.
In this case in particular, since the variable-reluctance resolver
in which a resolver rotor described later is attached to a
nonmagnetic substance, a differential circuit is adopted, a
magnetic shield plate is adopted, and so on, is used as the
rotation detecting resolver of the motor rotor 12, magnetism
surrounding the resolver from the motor stack can be cancelled out
to thereby stabilize the control, unlike an ordinary resolver in
which it is extremely difficult to control since the magnetism
generated from the motor stack surrounds the resolver.
A second embodiment of the invention will next be described. FIG. 4
shows the second embodiment of the invention. This embodiment is a
coaxial two-shaft actuator unit having two output shafts A and B.
Taking advantage of the hollowed inner rotor structure of the
sealed actuator 10 of the first embodiment of the invention and
using the sealed actuator of the first embodiment as a unit
actuator, this actuator unit is formed by coupling the two sealed
actuators 10 in series.
The output shaft A uses the motor rotor 12 of a first sealed
actuator 10A as it is. The output shaft B is formed by mounting an
extension shaft 50 to the motor rotor 12 of a second sealed
actuator 10B and allowing the extension shaft 50 to project from
the output shaft A by taking advantage of the hollow hole H passing
through the motor rotor 12 of the sealed actuator 10A.
This embodiment is a coaxial two-shaft sealed actuator in which the
first and second sealed actuators are coupled and the output shafts
A and B are coaxially arranged. However, the invention is not
limited to this arrangement, but may be applied to a sealed
actuator of coaxial three or more shafts in which three or more
sealed actuators are coupled and the output shafts are coaxially
arranged.
Other structural aspects and operation of this embodiment are
substantially the same as those of the first embodiment. Thus, the
same structural elements are designated by the same reference
characters and detailed description thereof will be omitted.
The necessity and effects of such a sealed actuator of coaxial two
or more shafts will be described. In an apparatus including a
plurality of wafer transport arms under vacuum such as scaler type
or frog leg type arms, a plurality of rotation motors are required.
Under a vacuum environment, in order to make a contact area to the
outside as small as possible, and to effectively use the space, the
attachment holes for the motors and the like are required to be as
small as possible. Further, in order to transport the wafer
horizontally and straight with as little vibration as possible, the
moment acting on the tip ends of the arms must be strongly kept by
the rotor support portion.
Then, a plurality of sealed actuators each described in FIG. 1 are
coupled coaxially at the housing portions, and the coupling
portions are closely connected (close contact by welding, O-ring,
metal gasket, etc.). The space where the motor rotor is disposed is
separated from the space outside the housing. The hollow output
shaft A of the motor rotor 12 of the first sealed actuator 10A is
coaxially arranged to the output shaft B extended through the
extension shaft 50 from the motor rotor 12 of the second sealed
actuator 10B, and they are protruded from the common opening
provided in the housing member 23. According to this, it is
possible to decrease the surface area in vacuum and to lessen the
number of the hole where the motor is attached to one.
In order to transport the wafer horizontally and straight with less
oscillation, it is necessary to hold the moment acting on the tip
end of the arm by the rotor support portion strongly. In this
sealed actuator, bearings are a plurality of rolling bearings, and
the rolling bearings are arranged such that they are located at
both sides of the member constituting the partition wall in the
axial direction to sandwich the partition wall constituting member
so that the force acting on the bearings are directly received by
the housing without intervening the partition wall. Accordingly, it
is possible to make a wide span of arrangement of the bearings even
to a moment load acting in the case where an arm or the like is
attached to the rotor and a load is put on the tip thereof, the
force acting on the bearings hardly act on the partition wall but
is applied directly to the housing, so that it is possible to
extremely decrease a fear that the partition wall is broken. Also,
it is not always necessary to keep concentricity of two output
shafts by using other auxiliary bearings.
As in the second embodiment, when the extension shaft 50 is fixed
to the motor rotor 12 of the second sealed actuator 10B, and the
extension shaft 50 is protruded from the output shaft A, the
materials of the motor rotors become common so that the cost of
part production can be reduced. Further, in FIG. 4, if the shape of
the motor rotor 12 of the second sealed actuator 10B is made equal
to that of the motor rotor 12 of the first sealed actuator 10A, a
flange portion is provided at the tip end of the extension shaft
50, and the motor rotor 12 of the second sealed actuator is
connected at the flange portion, the housings 24, 24 can be made
common, whereby the first and the second sealed actuators can be
made common. Accordingly, since the parts constituting the actuator
are made common, the cost of part production can be further
reduced, and exchange of parts at maintenance can be further made
easy.
Next, a second example of a variable-reluctance resolver will be
described with reference to FIG. 5.
When arms of a plurality of shafts are driven under vacuum
environment, if a rotation position of the present arm is not
recognized at switching of a power source, there is a possibility
that the arms collides with the wall of a vacuum chamber or with
the shutter between the vacuum chambers. Thus, in the first
embodiment described above, the origin detector 60 is provided (see
FIG. 1).
However, in the actuator including a plurality of shafts, there are
problems that the origin detector must be disposed for each of the
plurality of shafts, and if the positions of the plurality of
shafts at present can not be recognized, sequence of driving the
plurality of arms into the origin can not be specified. Further,
there is a problem that an absolute (absolute position detection)
sensor is not sufficient in resolution for smooth driving of arms
under vacuum environment, so that smooth driving can not be
made.
As a countermeasure to this, it is proposed to adopt a
variable-reluctance resolver including a coarse resolver for
detecting the absolute position of one rotation of a rotation shaft
and a fine resolver for detecting a rotation position in finer
resolution.
FIG. 5 is a sectional view showing a sealed actuator to which a
variable-reluctance resolver including a coarse resolver and a fine
resolver is attached.
The same parts as those in the first embodiment shown in FIG. 1 are
designated by the same reference numerals and detailed description
thereof will be omitted, but the resolver will be described.
In FIG. 5, reference numeral 60 denotes a coarse resolver, and 26
denotes a fine resolver. The fine resolver 26 is the same as the
resolver in the first embodiment. The coarse resolver 60 has almost
the same structure as that of the fine. resolver 26. A resolver
stator 61 including a coil 63 is attached to the inner
circumferential surface of the motor stator 11, and a resolver
rotor 62 is fixed to a stepped portion of the motor rotor 12 while
being opposite to the stator 61. A plurality of teeth with a
constant pitch are provided in the inner circumferential surface of
magnetic poles of the resolver stator 61 in parallel with the
rotation shaft of the motor rotator 12. The coil 63 is wound around
the respective magnetic poles. The resolver 62 includes a train of
teeth with the same pitch and shifted phase.
As a resolver control circuit for processing detection signals of
the coarse resolver 60 and the fine resolver 26, the resolver
control circuit shown in FIG. 3 may be used.
The coarse resolver 60 detects the absolute position of one
rotation of the rotation shaft. The fine resolver 26 detects the
rotation position of the rotation shaft with finer resolution.
Since the fine resolver 26 of rotation position detector with fine
resolution is disposed near the coarse resolver 60 for detecting
the absolute position of one rotation at the output shaft side,
when wafer transport arms in the vacuum, for example, a plurality
of arms of scaler type or frog leg type are driven by using a link
and the like, the angle of the present arm can be recognized by the
coarse resolver at switch-on of power source so that return. to the
origin becomes unnecessary. Further, when the arms are driven
smoothly and with high accuracy, the fine resolver 26 can detect
the position.
Since the coarse resolver and the fine resolver can be made same to
each other in the structure of resolver windings, it is not
necessary to provide a plurality of control circuits as shown in
FIG. 3. That is, at the switch-on of the power source, the coarse
resolver 60 is connected to the control circuit to recognize the
present position, and the fine resolver 26 is connected to the
control circuit at the subsequent driving to detect rotation
positions.
Next, the reason why the sealed actuator of this embodiment of the
invention adopts the variable-reluctance motor will be
described.
As kinds of motors, there is a inductive motor using a sliding
torque between an eddy current generated in the rotor by rotation
of a stator magnetic field and the stator magnetic field, or a
synchronous motor using attraction force between the rotor of a
permanent magnet and the stator magnetic field. In the case where
the motor is used under vacuum as in the present invention, the
inductive motor has problems that since it can not effectively
dissipate the heat generated by the eddy current in the rotor, the
temperature of the rotor rises, the shape of the motor is deformed,
the discharged gas is increased.
In the synchronous motor including the permanent magnet as the
rotor, the permanent magnet is generally made of sintered magnetic
powder so that the inside thereof is porous and the surface area is
very large. Thus, when the motor is used in ultra-high vacuum, it
has defects that gases remaining inside of the permanent magnet are
not easily discharged even if the outside of the magnet is made
vacuum so that a long time is required to attain the vacuum
state.
Thus, in this embodiment of the invention, magnetic substance
including salient pole teeth is disposed for the rotor, and the
structure of the motor is basically made into magnetic
variable-reluctance (VR type) stepping motor. Since this motor uses
magnetic attraction force, there is no heat generated in the rotor
by the eddy current as in the inductive motor. Also, since a
permanent magnet is not used as a rotor, there is no defect that it
takes a long time to attain the vacuum state.
Since the motor of the invention has the structure of the stepping
motor, it has a feature that the torque is large. However, if
laminated layers are adopted like a rotor of a general stepping
motor, since the surface area is increased like the aforementioned
permanent magnet, it is not preferable for use in vacuum. Then, in
this embodiment, a mass (for example, ring-shaped) of
steel-Material is cut and worked into salient pole teeth to form a
magnetic substance.
Further, since the magnetic metal is generally apt to rust, the
rotor is subjected to surface treatment such as plating of nickel
stable in vacuum environment to prevent rusting, so that increase
of a surface area due to rust, discharge of oxygen in high vacuum
due to oxidation, corrosion due to an inert gas, and the like are
prevented.
In this embodiment, although the magnetic variable-reluctance motor
is adopted as the kind of the motor, it is not restricted to this
motor type, but a permanent magnet may be assembled in the stator.
As an example of this type of motor, there is a hybrid type (HB
type) motor. Since the magnetic substance including salient pole
teeth may be disposed for the rotor, the same effects as the VR
type can be expected.
Next, the reason why the sealed actuator of the embodiment adopts
the variable-reluctance (VR type) resolver as detecting means for
detecting displacement of the rotor will be described.
In general, in a servo motor used for high accuracy positioning, an
optical encoder or a magnetic encoder using a magnetic resistance
element is used as position detecting means for high accuracy
smooth driving. .Iadd.A sealed actuator having an encoder is shown
in FIG. 8, which is similar to FIG. 1, but replaces resolver 26
with an encoder similar to that shown in FIG. 7. .Iaddend.The
optical encoder includes a disc with slits at the rotor side, and a
light emitting element and a light receiving element at the stator
side. The optical encoder detects the position by detecting the
amount of light passing through the optical slits during the
rotation of the rotor or the change of interference.
However, in the degas process of a step of reducing a discharged
gas performed to use the optical encoder in vacuum, since the light
emitting element and the light receiving element are made of
semiconductor, commonly performed high temperature bake-out at more
than 100.degree. C. is difficult. Further, since some insulator
must be used to prevent an electric circuit used in vacuum from
shortcircuiting and resin/print substrate used as the insulator
generally includes a large amount of impurities in the inside
thereof, the optical encoder has a defect that it is difficult to
be used in vacuum.
On the other hand, the electric encoder using the magnetic
resistance element has also the same defect as the optical encoder
since the element is made of semiconductor.
In this embodiment, it is necessary to provide a position detector
capable of detecting rotation position of the rotor in the state
that the sealing partition wall is interposed between the stator
and the rotor. Then, this embodiment adopts a variable-reluctance
(VR type) resolver in which a resolver rotor of magnetic metal
material provided with slot teeth on the surface, is disposed at
the motor rotor side, a resolver stator of magnetic poles of
magnetic substance including slot teeth similar to the
aforementioned slot teeth in shape and wound by detection coils, is
disposed at the motor stator side, and the change of magnetic
resistance (reluctance) passing through the nonmagnetic metal
partition wall during the rotation of the resolver, is detected
from the resolver stator side.
In general, the variable-reluctance resolver detects change of
reluctance in accordance with the rotation position .theta. of the
opposing slot teeth as change of inductance by applying AC voltage
to the detection coil. It is possible to detect the output
Vsin.theta. in which an exciting voltage component is removed, by
the synchronous rectifier, and to detect the rotation position of
the rotor. However, if a frequency of AC voltage exciting the
detection coil is high, the eddy current generated in the
nonmagnetic metal when magnetic flux passes through the sealing
partition wall, increases so that detection of rotation position of
the rotor becomes difficult.
Accordingly, in this embodiment, exciting is conducted by applying
AC of about 1 KHz to 10 KHz necessary to suppress the generation of
the eddy current in the sealing partition wall and to stably drive
and control the rotor. As materials constituting the resolver
rotor, a laminated steel plate is preferable in view of AC
characteristics to decrease the generation of eddy current.
However, lamination increases the surface area like the permanent
magnet. It is desirable to lessen the surface area to a possible
degree for use in vacuum. Thus, in this embodiment, the magnetic
substance is formed by cutting a mass of steel material to form the
salient pole teeth.
Further, as described before, since the magnetic metal is apt to
rust, the resolver rotor is subjected to surface treatment such as
plating of nickel stable in vacuum environment for preventing the
rust, so as to prevent the increase of surface area due to rust,
discharge of oxygen in ultra-high vacuum due to oxidation, and
corrosion due to an inert gas.
The magnetic variable-reluctance resolver adopted in this
embodiment in which the detection coil magnetic poles are disposed
at the motor stator side, has a feature that it can detect the
position even through the nonmagnetic partition wall. However, it
has problems as follows.
That is, in the resolver of the embodiment, the nonmagnetic metal
partition wall is intervened between the resolver stator and the
resolver rotor. Thus, the change of detected magnetism is apt to be
less. Although the improvement of S/N ratio is important, since the
sealed actuator of the embodiment is equipped with the motor, there
is a fear that high frequency magnetic flux of switching frequency
of a motor current supplied from the motor drive power source, or
leak magnetic flux from a rotating magnetic field generated from
the motor stator is mixed into the resolver to lower the S/N ratio
so that high accuracy position detection becomes impossible.
Accordingly, as a countermeasure to this, an attachment member of
the resolver rotor is made of a nonmagnetic substance to decrease
the mixture of leak magnetic flux through the driving shaft into
the rotor resolver rotor and to improve the S/N ratio so that high
accuracy position detection is made possible.
Further, to improve the S/N ratio, the winding of the resolver
stator constituting the variable-reluctance resolver may be made
into a differential circuit type so that the noise can be decreased
by making the winding into the differential circuit type. This
structure will be described below.
In the variable-reluctance resolver described with reference to
FIGS. 2 and 3, when AC current is supplied to an exciting winding
of the first magnetic pole of 3N phase in the resolver stator and
to an exciting winding of the second magnetic pole of 3N phase, the
current flowing through these exciting windings is changed by the
reluctance change generated in response to the change of position
between the first and second resolver stator magnetic poles and the
resolver rotor magnetic poles, so that the change of the position
is detected as the change of the exciting current.
Among these current detection values, difference values of the
first and second magnetic poles with the same phase are calculated
by three difference value detection means, so that three-phase
signals in which only third harmonic distortions remains, can be
obtained among harmonic distortions of permeance. Thus, a rotation
angle or rotation speed of the rotor can be detected without
influence of the harmonic distortions.
In this embodiment, since the exciting winding of the first
magnetic pole and the exciting winding of the second magnetic pole
of the 3N phase are configured as differential windings, effects of
noise reduction can be obtained as described below.
In the above-described resolver control circuit shown in FIG. 3,
since LA11 winding and LA21 winding are located at positions where
the phase is inverted 180.degree. with respect to the position of
the rotor, the resolver signals are as shown by equations (1) to
(6) described before. When magnetic noise of B sin .alpha.t (where,
.alpha. is a switching frequency, t is a time) is superimposed to
the respective resolver signals, the resolver signals are expressed
by the following equations (10) to (15). fa1(.theta.)=A0+A1 cos
.theta.+A2 cos 2.theta.+A3 cos 3.theta.+A4 cos 4.theta.+B sin
.alpha.t (10) fb1(.theta.)=A0+A1 cos (.theta.-120.degree.)+A2 cos
2(.theta.-120.degree.)+A3 cos 3(.theta.-120.degree.)+A4 cos
4(.theta.-120.degree.)+B sin .alpha.t (11) fc1(.theta.)=A0+A1 cos
(.theta.+120.degree.)+A2 cos 2(.theta.+120.degree.)+A3 cos
3(.theta.+120.degree.)+A4 cos 4(.theta.+120.degree.)+B sin .alpha.t
(12) fa2(.theta.)=A0+A1 cos (.theta.+180.degree.)+A2 cos
2(.theta.+180.degree.)+A3 cos 3 (.theta.+180.degree.)+A4 cos
4(.theta.+180.degree.)+B sin .alpha.t (13) fb2(.theta.)=A0+A1 cos
(.theta.-300.degree.)+A2 cos 2(.theta.-300.degree.)+A3 cos
3(.theta.-300.degree.)+A4 cos 4(.theta.-300.degree.)+B sin .alpha.t
(14) fc2(.theta.)=A0+A1 cos (.theta.+300.degree.)+A2 cos
2(.theta.+300.degree.)+A3 cos 3(.theta.+300.degree.)+A4 cos
4(.theta.+300.degree.)+B sin .alpha.t (15)
Since the respective resolver signals fa1 to fc1 and fa2 to fc2 are
supplied to the differential amplifiers 46A to 46C, the magnetic
noises Bsin at can be differentially removed because of the same
phase, and the output signals da to dc of the differential
amplifiers 46A to 46C can be expressed by the following equations
(16) to (18). da=2A1 cos .theta.+2A3 cos 3.theta. (16) db=2A1 cos
(.theta.-120.degree.)+2A3 cos 3(.theta.-120.degree.) (17) dc=2A1
cos (.theta.+120.degree.)+2A3 cos 3(.theta.+120.degree.) (18)
As is apparent from these equations (16) to (18), three-phase
signals da to dc in which only third harmonic distortion remains
among harmonic distortions of permeance, can be obtained from the
differential amplifiers 46A to 46C, and at the same time, the
noises generated from the motor are also effectively reduced. The
third harmonic distortion is cancelled in the phase conversion
circuit 47, and the two-phase signals fc(.theta.) and fs(.theta.)
can be obtained, as described before.
In order to further improve the S/N ratio, a magnetic shield plate
formed of a magnetic metal material may be interposed between the
motor stator magnetic pole and the detection coil magnetic pole of
the variable-reluctance resolver. This has an effect that magnetic
noises generated by the motor magnetic field are bypassed by the
magnetic substance superior in magnetic properties disposed between
the motor and the resolver, so that the magnetic flux does not act
on the resolver stator detection coil.
In this case, as the magnetic substance superior in the magnetic
properties, an electromagnetic steel plate, permalloy and the like
may be used.
As described above in detail, the invention relates to a sealed
actuator in which a sealing partition wall made of a nonmagnetic
metal material is provided between a stator magnetic pole of a
motor stator and a rotor magnetic pole of a motor rotor, and a
space where the motor rotor is disposed is hermetically isolated
from a space where the motor stator is disposed.
According to the first aspect of the invention, the bearings of the
sealed actuator for supporting the motor rotor are a plurality of
rolling bearings, and the rolling bearings support the motor rotor
at positions on the housings at both sides of a member constituting
the sealing partition wall in a longitudinal direction of the motor
rotor so that the housings directly receive a load applied to the
bearings. According to this, even if an arm or the like is attached
to the motor rotor and force such as bending moment caused in the
motor rotor is applied to the bearings, the force does not act on
the hermetically sealing partition wall, so that such a superior
effect as eliminates the fear that the sealing partition wall is
broken, can be obtained.
According to the second aspect of the invention, the sealed
actuator adopts a variable-reluctance resolver for detecting the
position of the motor rotor with respect to the motor stator. The
resolver comprises a resolver rotor made of a magnetic metal
material and including salient pole teeth at a side of the motor
rotor; and a resolver stator including a detection coil magnetic
pole at a side of the motor stator. According to this, there is
obtained such a superior effect that even if the partition wall
made of nonmagnetic material is interposed between both, the
position of the motor rotor can be accurately detected. Since such
a resolver rotor that magnetic salient poles (slot teeth) are
provided on the magnetic metal material is adopted to decrease the
surface area, it is made suitable for use in vacuum
environment.
According to the third aspect of the invention, since at least a
part of the partition wall disposed between the stator magnetic
pole of the motor stator and the rotor magnetic pole of the motor
rotor of the sealed actuators is reinforced by reinforcing means,
even if the actuator is used in a ultra-high vacuum apparatus,
there occurs no such a disadvantage that the partition wall exposed
to vacuum is expanded to be deformed. Further, there is obtained
such a superior effect that deformation of the sealing partition
wall at thinning working of the partition wall from the inner
diameter side of the motor rotor can be prevented to perform
accurate thinning working.
As the reinforcing means, there are adopted such means as the use
of reinforcing members, filling of a mold agent.
According to the fourth aspect of the invention, the sealed
actuator is used as a unit sealed actuator, a plurality of unit
sealed actuators are connected in series to each other, and a
plurality of output shafts of the motor rotors are coaxially
arranged. According to this, the following effects can be obtained.
That is, it is possible to easily construct the sealed actuator
having a plurality of coaxial shafts.
Further, when the actuator is mounted to a vacuum vessel or the
like, the plurality of shafts can be inserted into the inside of
the vacuum vessel or the like through one common opening, so that
the number of connection portions between the actuator and the
vacuum vessel or the like can be decreased.
Further, in the invention, since a variable-reluctance resolver is
provided as displacement detection means, there is obtained such an
effect that it is possible to prevent the magnetism from the motor
stack from surrounding so that stable and high accuracy positioning
control can be made.
* * * * *