Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
1998-04-28
2001-09-11
Enad, Elvin (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C361S143000, C219S648000
Reexamination Certificate
active
06288465
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a combined externally pressurized gas and magnetic bearing assembly in which an externally pressurized gas bearing and a magnetic bearing are combined together, and also to a spindle device employing the combined externally pressurized gas and magnetic bearing assembly. More particularly, the present invention relates to the combined externally pressurized gas and magnetic bearing assembly and the spindle device both suited for use in, for example, a high speed milling machine.
2. Description of the Prior Art
The magnetic bearing is known to have a feature in that because it has a relatively large bearing gap a loss of torque during rotation thereof is extremely small and it can exhibit a high static rigidity by an integral control.
FIG. 28
illustrates a longitudinal sectional view showing a prior art spindle device utilizing a magnetic bearing, which is used in a high-speed aluminum milling machine. This prior art spindle device includes a touch-down bearing
251
, a tool
252
, a displacement sensor
253
, a radial magnetic bearing
254
, an axial magnetic bearing
255
, a drive motor
256
, a radial magnetic bearing
257
, a displacement sensor
258
, and a main shaft
259
. The spindle device utilizing the magnetic bearings has a performance of a maximum rotation of 40,000 rpm, and a maximum output of 15 kW, a maximum machining capacity of 1,250 cm
3
/min, thus exhibiting an excellent performance for an aluminum milling work.
However, the spindle device utilizing the magnetic bearing is susceptible to influence brought about by a natural frequency of bending of the main shaft during the milling operation and, for this reason, requires the use of an extremely complicated control system. Accordingly, the known spindle device of the type discussed above is not suited as a spindle device for a versatile machine tool that is required to accommodate various processing conditions.
On the other hand, a non-contact bearing currently available other than the magnetic bearing includes an externally pressurized gas bearing. Although the externally pressurized gas bearing is known to have a high rotational accuracy and an excellent dynamic stability, the externally pressurized gas bearing has been little used in the versatile machine tool because of the compressivity and, hence, a low static rigidity and a low load bearing capacity.
In view of the foregoing, attempts have recently been made to use, as a spindle device for high speed machining purpose, a spindle device utilizing a composite bearing in which the externally pressurized gas bearing and the magnetic bearing are combined, such as shown in
FIG. 29
in a longitudinal sectional representation. Referring to
FIG. 29
, reference numeral
263
represents a displacement sensor; reference numeral
264
represents a radial magnetic bearing; reference numeral
265
represents an axial magnetic bearing; reference numeral
266
represents a drive motor; reference numeral
267
represents a radial magnetic bearing; reference numeral
268
represents a displacement sensor; reference numeral
270
represents a displacement sensor; reference numeral
271
represents a main shaft; and reference numerals
272
and
273
represent respective externally pressurized gas bearings.
However, the spindle device utilizing the composite bearing shown in
FIG. 29
has a problem in that since the magnetic bearings
264
and
267
and the externally pressurized gas bearings
272
and
273
are disposed one after another in an axial direction of the main shaft
271
, not only is a relatively long main shaft
271
required, but the natural frequency of bending tends to be lowered. Also, since the spindle device shown in
FIG. 29
makes use of a control system of a structure similar to that required in the spindle device utilizing solely the magnetic bearings, an additional problem has arisen that the dynamic stability of the externally pressurized gas bearing is impaired and it tends to function as a source of external disturbances.
Accordingly, the art has not yet been developed to the extent as to fulfill the objective of utilizing advantages of the externally pressurized gas bearing and also those of the magnetic bearing while counterbalancing demerits of those respective bearings.
SUMMARY OF THE INVENTION
Accordingly, the present invention has been devised with a view substantially eliminating the above discussed problems and is intended to provide a novel combined externally pressurized gas and magnetic bearing assembly which has an excellent dynamic rigidity, such as exhibited by the externally pressurized gas bearing, and also an excellent static rigidity, such as exhibited by the magnetic bearing, and which contributes to reduction in length of the main shaft, and an improved spindle device utilizing the novel combined externally pressurized gas and magnetic bearing assembly.
In order to accomplish the foregoing and other objects of the present invention, there is provided a novel combined externally pressurized gas and magnetic bearing assembly comprising an externally pressurized gas bearing and a magnetic bearing combined together in a predetermined relationship. Because of this, the bearing assembly can be obtained which can exhibit both the dynamic rigidity possessed by the externally pressurized gas bearing and the static rigidity possessed by the magnetic bearing.
While numerous combined externally pressurized gas and magnetic bearing assemblies of different constructions within the spirit of the present invention are disclosed, the combined externally pressurized gas and magnetic bearing assembly according to a first aspect of the invention is so designed as to combine the externally pressurized gas bearing and the magnetic bearing together by providing a magnetic bearing including an electromagnet having a core and a fluid restrictor defined in the core for supply of a gaseous medium under pressure into a bearing gap of the externally pressurized gas bearing.
The combined externally pressurized gas and magnetic bearing assembly according to a second aspect of the invention is of a design in which the magnetic bearing and the externally pressurized gas bearing are combined together with the magnetic bearing so as to have commonly shared component parts. It is to be noted that the combined externally pressurized gas and magnetic bearing assembly according to any one of the first to third aspects of the invention may be used as either a radial bearing or an axial bearing.
The combined externally pressurized gas and magnetic bearing assembly according to a third aspect of the invention is of a design in which a fluid restrictor is formed by a self-forming orifice or a normal orifice in a bearing stator of the magnetic bearing. The self-forming orifice performs a function as an orifice at a virtual cylindrical surface defined by and between a gas conduit and a bearing gap. The magnetic bearing includes a displacement measuring means for measuring a displacement of a rotor and is operable to support the rotor at a predetermined position by generating an electromagnetic force according to the displacement measured by the displacement measuring means. The displacement measuring means may be of a type capable of directly measuring the displacement of the rotor or of a type capable of indirectly measuring the displacement of the rotor, that is, of a type capable of measuring a different object to be measured that can eventually be converted into the displacement of the rotor.
The combined externally pressurized gas and magnetic bearing assembly according to a fourth aspect of the invention is a radial bearing and is of a design in which the externally pressurized gas bearing is accommodated within a width of the magnetic bearing in an axial direction.
The combined externally pressurized gas and magnetic bearing assembly according to a fifth aspect of the invention is a radial bearing and is of a design in which the magnetic bearing is accommodated within a widt
Suzuki Nobuyuki
Yamada Hiroyuki
Birch & Stewart Kolasch & Birch, LLP
Dinh Le Dang
Enad Elvin
NTN Corporation
LandOfFree
Combined externally pressurized gas-magnetic bearing... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Combined externally pressurized gas-magnetic bearing..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Combined externally pressurized gas-magnetic bearing... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2434956