Work holders – With fluid means – Vacuum-type holding means
Reexamination Certificate
2002-07-03
2003-12-02
Wilson, Lee D. (Department: 3723)
Work holders
With fluid means
Vacuum-type holding means
C269S020000
Reexamination Certificate
active
06655672
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to air bearing drive systems, and more particularly, it relates to a mechanism of the drive system for controlling a gap of an air film (hereinafter, a gap of an air film is simply referred to as an air film gap) formed by an air bearing.
2. Description of the Related Art
Roundness testers are conventionally used for obtaining a variety of data about geometrical round precision of a cylindrical form such as roundness, concentricity, and coaxiality. By placing a workpiece on a turntable, rotating the workpiece by the turntable, and detecting a profile of the workpiece by a detection head, the roundness testers collect data about the profile of the workpiece, and then measure and calculate the geometrical round precision of the workpiece.
As disclosed, for example, in Japanese Unexamined Patent Application Publication Nos. 2000-120686 and 2000-348429, air bearings producing dramatically less frictional resistance, heat generation, and rotating vibration than ball bearings and the like are widely used for a variety of accurate drive systems, for example, for achieving a rotary motion of the turntable and a linear feed motion of the detection head of the roundness testers.
In general, a rotary drive system
10
using an air bearing shown in
FIG. 1
has a stator (also referred to as base)
12
, a rotor
14
, an upper plate (also referred to as moving portion)
16
, and a lower plate
18
. The rotor
14
is formed integrally with the upper plate
16
and lower plate
18
and supported by the stator
12
.
By supplying air
26
, the lower surface of the upper plate
16
and the upper surface of the stator
12
have an upper air film gap
20
formed therebetween, the lower surface of the stator
12
and the upper surface of the lower plate
18
have a lower air film gap
22
formed therebetween, and the outer peripheral surface of the rotor
14
and the inner peripheral surface of the stator
12
have a tubular air film gap
24
formed therebetween. Thus, these gaps
20
,
22
, and
24
allow the rotor
14
to rotate smoothly together with the upper and lower plates
16
and
18
relative to the stator
12
.
The drive system using the foregoing conventional air bearing has an air film gap generally formed between the base and each of the moving parts facing the base. For example, in the rotary drive system
10
shown in
FIG. 1
, the air flows in these three gaps
20
,
22
, and
24
. In order to achieve an accurate rotation of the rotor
14
together with the upper and lower plates
16
and
18
while maintaining all the air film gaps, between the base and the moving parts facing the base, at respectively fixed amounts of spacing, all the foregoing upper and lower gaps
20
and
22
and tubular gap
24
are required to satisfy a large area of extremely strict precision, as described below, for example.
Within currently attainable levels of geometrical precision, for example, the stator
12
is required to satisfy flatness of its upper and lower surfaces, parallelism between the opposing surfaces (hereinafter, also referred to as surface-to-surface parallelism), squareness of the axis of its inner peripheral surface relative to the above surfaces, cylindricity of the inner peripheral surface, and so forth. Also, the rotor
14
is required to satisfy flatness of its upper and lower surfaces, parallelism between these surfaces, squareness of the axis of its outer peripheral surface relative to the above surfaces, cylindricity of the outer peripheral surface, and so forth. In addition, the upper plate
16
is required to satisfy flatness of its upper and lower surfaces and the like, and the lower plate
18
is required to satisfy flatness of its upper surface and the like.
However, since satisfying the foregoing variety of extremely strict geometrical precision requires a large amount of work and time for processing and finishing these components, and accordingly incorporates an increased cost of the drive system, a new drive system which can achieve a reduced cost has been strongly desired without deteriorating accurate and stable driving features required.
Furthermore, when the center of rotation and the center of gravity of a rotating workpiece placed on the upper plate
16
for measuring its roundness do not coincide with each other, an eccentric load is exerted on the rotating upper plate
16
, causing the air film between the lower surface of the upper plate
16
and the upper surface of the stator
12
to vary in accordance with the rotation of the rotating workpiece, giving rise to a problem in that it is difficult to accurately measure geometrical round precision of the workpiece because the axis of the rotation center of the workpiece is tilted.
SUMMARY OF THE INVENTION
In view of the above-described problems of the related art, it is an object of the present invention to provide an air bearing drive system that offers a reduced cost and achieves accurate and stable driving performances.
The present invention is made to achieve the above object. An air bearing drive system according to the present invention comprises (a) a moving portion performing a rotational motion or a linear motion, (b) a base for supporting the moving portion, (c) an air bearing having an air film gap, for supporting the moving portion on the base, between the base and the moving portion, (d) at least one air nozzle, (e) air supplying means, (f) at least one suction inlet, (g) attracting means, and (h) two adjusting means.
The air nozzle is formed on the base and faces the moving portion, for forming the air film gap by blowing air toward the moving portion and exerting a levitation force on the moving portion. The air supplying means supplies air to the air nozzle.
The suction inlet is formed on the base and faces the moving portion, for exerting an attraction force on the moving portion so as to attract the moving portion toward the base. The attracting means attracts the moving portion toward the base via the suction inlet.
The two adjusting means adjust the levitation force produced by the air blowing from air nozzle and the attraction force from the suction inlet.
According to the present invention, by adjusting the thickness of the air film between the moving portion and the base by using the air nozzle and the suction inlet, the thickness of the air film can be fine-tuned or adjusted without making increasing the size of the air bearing.
Further, in the air bearing drive system according to the present invention, it is preferable that the moving portion comprises a cylindrical rotor and a moving flat surface orthogonal to the axial center of the rotor, the base comprises at least one thrust flat surface facing the moving flat surface, and the thrust flat surface comprises the air nozzle and the suction inlet formed thereon so that the moving flat surface is levitated, at a prescribed height via the air film, relative to the thrust flat surface.
According to the present invention, the moving portion can be easily positioned in a non-contact manner since the moving portion has a levitation height controlled in the thrust direction thereof.
Further, in the air bearing drive system according to the present invention, the thrust flat surface is preferably a single surface disposed on one side of the stator.
Since the air bearing drive system according to the present invention has a smaller number of elements of components requiring precise processing, unskilled workers can process the components. Accordingly, a reduced processing cost of the components is achieved without a risk of deteriorating rotation accuracy of the drive system.
Further, in the air bearing drive system according to the present invention, the base may have a cylindrical opening therein for supporting the rotor in the radial direction of the rotor. Also, the base may comprise a plurality of the air nozzles disposed on the peripheral surface of the cylindrical opening so that the rotor is positioned in the center of the cylindrical opening.
According
Mitutoyo Corporation
Rankin, Hill Porter & Clark LLP
Wilson Lee D.
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