U.S. patent application number 17/362626 was filed with the patent office on 2021-10-21 for planar rotary air bearing stage.
The applicant listed for this patent is DWFritz Automation, Inc.. Invention is credited to Nathan Lyons Brown, Quinn Matthew Wolf.
Application Number | 20210324912 17/362626 |
Document ID | / |
Family ID | 1000005685221 |
Filed Date | 2021-10-21 |
United States Patent
Application |
20210324912 |
Kind Code |
A1 |
Brown; Nathan Lyons ; et
al. |
October 21, 2021 |
PLANAR ROTARY AIR BEARING STAGE
Abstract
Various embodiments of the present technology generally relate
to precise rotary motion control systems. More specifically, some
embodiments relate to systems, methods, and means for providing
pressure to a non-contact rotary system. In some embodiments, the
rotary system comprises a rotary shaft that can rotate three
hundred and sixty degrees continuously. In order for the rotary
system to be entirely non-contact with any surfaces of surrounding
components or housing, pressure must be supplied to a rotary air
bearing that floats the rotary unit above a surface. In some
examples, the bottom air bearing is a vacuum preloaded (VPL) air
bearing. As such, the VPL air bearing requires a supply of positive
pressure and a supply of negative pressure to stabilize the rotary
unit. The present technology provides a mechanism for providing
pneumatic air to the air bearing without a physical connection to
the rotary shaft or air bearing.
Inventors: |
Brown; Nathan Lyons;
(Littleton, CO) ; Wolf; Quinn Matthew; (Arvada,
CO) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
DWFritz Automation, Inc. |
Wilsonville |
OR |
US |
|
|
Family ID: |
1000005685221 |
Appl. No.: |
17/362626 |
Filed: |
June 29, 2021 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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16519331 |
Jul 23, 2019 |
11067124 |
|
|
17362626 |
|
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|
|
62701900 |
Jul 23, 2018 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F16C 32/0614 20130101;
F16C 32/0696 20130101; F16C 29/025 20130101; F16C 32/0603 20130101;
F16C 2322/39 20130101; F16C 2233/00 20130101; G01B 5/0009 20130101;
F16C 41/007 20130101 |
International
Class: |
F16C 32/06 20060101
F16C032/06; F16C 41/00 20060101 F16C041/00; F16C 29/02 20060101
F16C029/02 |
Claims
1. A frictionless rotary union comprising: a bearing comprising: a
first port that provides a first pressure to a first aperture of a
rotary unit, wherein the frictionless rotary union is non-contact
with the rotary unit; and a second port that provides a second
pressure to a second aperture of the rotary unit.
2. The frictionless rotary union of claim 1, further comprising the
rotary unit, wherein the rotary unit is a vacuum preloaded air
bearing.
3. The frictionless rotary union of claim 1, wherein: the first
pressure is a positive pressure; and the second pressure is a
negative pressure.
4. The frictionless rotary union of claim 3, wherein the first
pressure and the second pressure are used by the rotary unit to
maintain a vertical stability of the rotary unit.
5. The frictionless rotary union of claim 1, wherein the
frictionless rotary union is mounted to a housing, the housing
comprising at least one radial air bearing that maintains stability
of the rotary unit in an x direction and a y direction.
6. The frictionless rotary union of claim 1, wherein: the first
aperture of the rotary unit is located within a first groove of the
rotary unit; the second aperture of the rotary unit is located
within a second groove of the rotary unit; and the frictionless
rotary union creates a first air seal between the first port and
the first aperture, wherein the first air seal enables the first
pressure to be provided to the first aperture.
7. The frictionless rotary union of claim 1, wherein: the
frictionless rotary union creates a first air seal between the
first port and the first aperture, wherein the first air seal
enables the first pressure to be provided to the first aperture
without leaking; and the frictionless rotary union creates a second
air seal between the second port and the second aperture, wherein
the second air seal enables the second pressure to be provided to
the second aperture without leaking.
8. An assembly comprising: a first air bearing that maintains
stability of a rotary air bearing in an x direction and a y
direction; and a second air bearing comprising at least one port,
wherein the at least one port provides a first pressure to an
aperture of the rotary air bearing.
9. The assembly of claim 8, further comprising the rotary air
bearing, wherein the rotary air bearing rotates about a vertical
axis without contacting either one of the first air bearing and the
second air bearing.
10. The assembly of claim 9, further comprising: a housing, wherein
the housing comprises the first air bearing and the second air
bearing; and a base, wherein the rotary air bearing rotates about
the vertical axis without contacting the base.
11. The assembly of claim 8, wherein: the rotary air bearing is a
positive pressure air bearing; and the first pressure is a positive
pressure.
12. The assembly of claim 8, wherein the rotary air bearing is a
vacuum preloaded air bearing and the first pressure is a positive
pressure.
13. A method comprising: providing, via a first port of a
frictionless rotary union, a first pressure to a first aperture of
a rotary unit, wherein providing the first pressure to the first
aperture comprises creating a first air seal between the first port
of the frictionless rotary union and the first aperture of the
rotary unit; and providing, via a second port of the frictionless
rotary union, a second pressure to a second aperture of the rotary
unit, wherein providing the second pressure to the second aperture
comprises creating a second air seal between the second port of the
frictionless rotary union and the second aperture of the rotary
unit.
14. The method of claim 13, further comprising, via at least one
rotary air bearing, maintaining a horizontal stability of the
rotary unit.
15. The method of claim 13, further comprising: floating the rotary
unit above a base using the first pressure provided to the first
aperture of the rotary unit, wherein the first pressure is a
positive pressure; and holding the rotary unit directly above the
base using the second pressure provided to the second aperture of
the rotary unit, wherein the second pressure is a negative
pressure.
16. The method of claim 13, wherein the rotary unit is a vacuum
preloaded air bearing.
17. A system comprising: a means for providing a first pressure to
a first aperture of a rotary unit without contacting the rotary
unit; a means for maintaining a horizontal stability of the rotary
unit; and a means for maintaining a vertical stability of the
rotary unit.
18. The system of claim 17, further comprising a means for
providing a second pressure to a second aperture of the rotary unit
without contacting the rotary unit.
19. The system of claim 17, wherein the rotary unit is a vacuum
preloaded air bearing.
20. The system of claim 17, wherein the first pressure, at least in
part, is used to maintain a vertical stability of the rotary unit.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of and claims priority to
and benefit from U.S. Non-Provisional patent application Ser. No.
16/519,331, filed on Jul. 23, 2019, by the same title, which claims
priority to and benefit from U.S. Provisional Patent Application
No. 62/701,900, filed on Jul. 23, 2018, by the same title, both of
which are expressly incorporated by reference herein.
TECHNICAL FIELD
[0002] Various embodiments of the present technology generally
relate to systems, methods, and means for providing pressure to a
rotary stage without a physical connection to the rotary stage.
More specifically some embodiments relate to a low-friction rotary
motion platform, wherein the rotary motion platform requires at
least one pressure be supplied to the rotary motion platform
without contact.
BACKGROUND
[0003] Rotary stage systems are utilized for precision motion in
angular and linear directions and are commonly used in
manufacturing processes, measurement processes, and similar motion
processes that require precise movement. Motion systems are
mechanical systems that are used to hold and position a part, such
as in manufacturing, machining, industrial processes, or part
analysis, for example. Motion systems used to position a part
typically require a high degree of accuracy in order to achieve a
highly precise positioning of the part. In order to achieve a large
number of working positions, a motion system may employ multiple
actuators, motors, and other devices coupled together to position a
platform or system on which a part or workpiece is mounted.
Complicated systems lead to additive tolerances and therefore
reduce positional accuracy. Furthermore, complicated interactions
between components can lead to poor stability within the
system.
[0004] A drawback of existing motion systems with a large number of
actuators, motors, and other motion devices is the inability to
provide a high level of positional accuracy due to an accumulation
of error tolerances. The result of this drawback is complicated
motion systems that cannot provide a high level of positional
accuracy. Prior art motion systems may provide micron order
performance, at best, due to additive tolerance errors from
multiple moving hardware axes.
[0005] Friction may be an additional source of error tolerance in
many systems. Systems have trended towards reducing error via
low-friction or non-contact systems. Air bearings are sometimes
used and utilize a thin film of pressurized gas to create an
interface between two surfaces. By reducing the number of
components that touch in a system, many traditional bearing-related
errors from sources such as friction, wear, heat, backlash, and
lubricant handling are reduced or eliminated.
BRIEF SUMMARY OF THE INVENTION
[0006] This Summary is provided to introduce a selection of
concepts in a simplified form that are further described below in
the Detailed Description. This Summary is not intended to identify
key features or essential features of the claimed subject matter,
nor is it intended to be used as an aid in determining the scope of
the claimed subject matter.
[0007] Various embodiments herein relate to systems, methods, and
means for providing pressure to a non-contact rotary system. In
some embodiments, the rotary system comprises a rotary shaft that
can rotate three hundred and sixty degrees continuously. That is,
the rotary shaft is not limited by a number of times it can make a
full rotation because it does not require connective components for
supplying pneumatic air. In order for the rotary system to be
entirely non-contact with any surfaces of surrounding components or
housing, pressure must be supplied to a bottom air bearing,
floating the rotary shaft above a surface. In some examples, the
bottom air bearing is a vacuum preloaded (VPL) air bearing. As
such, the VPL air bearing requires a supply of positive pressure to
hover the air bearing above the surface in addition to a supply of
vacuum pressure to hold the air bearing down. The opposing forces
on the VPL air bearing due to the positive and negative pressures
create vertical stability without friction between any
surfaces.
[0008] In some embodiments, a rotary stage comprises a base and a
housing. An exemplary embodiment of a base may be a granite block.
The housing comprises at least one air bearing that maintains x and
y stability of a rotary shaft comprising a VPL air bearing that
sits directly above the base. The housing further comprises at
least one air bushing. The air bushing is a cylindrical air bearing
that fits around the circumference of the rotary shaft. In the
present example, the air bushing is mounted to the housing and fit
to the rotary shaft. The air bushing is mounted to the housing such
that the housing does not constrain the motion of the air bushing
or the rotary shaft in the x-y plane. The x and y motion of the
rotary shaft is intended to be solely constrained radially by the
at least one air bearing. In order to provide a positive pressure
to the VPL air bearing, the air bushing has a first port that
provides a positive pressure to a first aperture of the rotary
shaft. The first aperture supplies pressure to the VPL air bearing.
The positive pressure supplied by the first aperture is used by the
VPL air bearing to float the rotary shaft above the base. The air
bushing further comprises a second port that provides a negative
(i.e., vacuum) pressure to a second aperture of the rotary shaft.
The second aperture supplies the vacuum to the VPL air bearing. The
vacuum pressure creates a vacuum between the VPL air bearing and
the base, stabilizing the rotary shaft directly above the base.
[0009] The rotary shaft can rotate about a z-axis, where the z-axis
is a vertical axis up the center of the rotary shaft. The rotary
shaft and the VPL air bearing can rotate three hundred and sixty
degrees continuously and are non-contact with any other components.
In the present example "continuously" means that once the rotary
shaft and VPL air bearing reach three hundred and sixty degrees, or
a full rotation, it can continue to rotate in the same direction.
The term continuously in the present example is not intended to
limit the technology to continuously rotate in time. However, the
present technology enables frictionless, non-contact, three hundred
and sixty degree continuous rotation by not requiring the positive
and negative pressures be supplied through a mechanical seal by a
direct connection with the rotary shaft using a physical connection
such as tubing, hosing, mechanical seals, a conventional rotary
union, or any other link to supply the positive and negative
pressures.
[0010] In some examples, the rotary shaft comprises a groove around
its circumference at the height of each of the apertures and each
of the grooves comprises an aperture. Furthermore, in certain
examples, the rotary shaft comprises a grated ring that an optical
encoder coupled to the housing can read to determine an angular
position of the rotary components. In yet another example, the air
bushing comprises a third port that provides a pressure to a third
aperture of the rotary shaft and the third aperture provides the
pressure to a top of the rotary shaft. Furthermore, the housing may
comprise at least one additional air bearing for translation of the
housing in the x direction and the y direction in the x-y
plane.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] Many aspects of the disclosure can be better understood with
reference to the following drawings. The components in the drawings
are not necessarily drawn to scale. Moreover, in the drawings, like
reference numerals designate corresponding parts throughout the
several views. While several implementations are described in
connection with these drawings, the disclosure is not limited to
the implementations disclosed herein. On the contrary, the intent
is to cover all alternatives, modifications, and equivalents.
[0012] FIG. 1 illustrates an exemplary embodiment of a rotary stage
in accordance with some embodiments of the present invention;
[0013] FIG. 2 illustrates an exemplary embodiment of a rotary stage
in accordance with some embodiments of the present invention;
[0014] FIG. 3 illustrates an exemplary embodiment of a rotary stage
in accordance with some embodiments of the present invention;
[0015] FIG. 4 illustrates an exemplary embodiment of a rotary stage
in accordance with some embodiments of the present invention;
[0016] FIG. 5 illustrates an exemplary embodiment of a rotary shaft
in accordance with some embodiments of the present invention;
[0017] FIG. 6 illustrates an exemplary embodiment of a rotary shaft
in accordance with some embodiments of the present invention;
and
[0018] FIG. 7 illustrates a top-down view of a rotary stage in
accordance with some embodiments of the present invention.
DETAILED DESCRIPTION
[0019] The following description and associated figures teach the
best mode of the invention. For the purpose of teaching inventive
principles, some conventional aspects of the best mode may be
simplified or omitted. The following claims specify the scope of
the invention. Note that some aspects of the best mode may not fall
within the scope of the invention as specified by the claims. Thus,
those skilled in the art will appreciate variations from the best
mode that fall within the scope of the invention. Those skilled in
the art will appreciate that the features described below can be
combined in various ways to form multiple variations of the
invention. As a result, the invention is not limited to the
specific examples described below, but only by the claims and their
equivalents.
[0020] The embodiments described herein are not limited in their
application to the details of construction, arrangement of
components, or illustrations in the following drawings. Embodiments
may be practiced or carried out in various ways. Additionally, the
phraseology and terminology used herein is for the purpose of
description and should not be regarded as limiting. The use of
"including." "comprising," or "having" and variations thereof is
meant to encompass the items listed thereafter and equivalents
thereof as well as additional items. The terms "vertical plane,"
"vertical axis," "z axis," and equivalents thereof may be used
interchangeably and are herein considered to generally refer to the
vertical direction in reference to the present technology.
Similarly, "x-y plane" "x and y," "x, y," "horizontal plane," and
equivalents thereof may be used interchangeably and are herein
considered to generally refer to the horizontal directions.
Furthermore, the term "air bearing" generally refers to bearings
that utilize a thin layer of pressurized gas to create a low
friction interface between surfaces. Air bearings may be utilized
in several different forms in the present invention and the general
term is not to be limited to a specific shape or embodiment.
[0021] Modern motion system technology including
coordinate-measuring machines (CMMs) require increasingly high
precision with increasingly smaller tolerances. In order to
accommodate these demanding requirements, motion control systems
must reduce errors wherever possible. Friction can be a significant
source of error and imprecision. Thus, motion control systems may
require as much reduction of friction in the system as possible.
Complicated systems with multiple actuators, motors, and other
moving parts can lead to additive tolerances further reducing
positional accuracy. Therefore, a non-contact rotary stage can
reduce frictional errors with the use of air bearings to avoid
contact on any surfaces. However, for a rotary stage to be entirely
non-contact with a three hundred and sixty degree continuous
rotation, a pneumatic system supplying pressurized gas to the
bearings is required. Direct connections such as tubes, pipes,
O-ring rotary unions, and other connections prohibit a rotary
platform from being non-contact and inhibit the ability to rotate
freely and continuously. Thus, a non-contact, frictionless rotary
union capable of receiving pressurized air or vacuum implemented
within a high-precision rotary stage is disclosed herein.
[0022] Various embodiments of the present technology generally
relate to systems, methods, and means for providing pressure to a
rotary stage without a physical connection to the rotary stage.
More specifically some embodiments relate to a low-friction rotary
motion platform, wherein the rotary motion platform requires at
least one pressure be supplied to the rotary motion platform
without contact. In some examples, the present invention is a
rotary stage comprising a base, a housing, and a rotary shaft. The
housing comprises a set of air bearings that maintains stability of
the rotary shaft in an x-direction and a y-direction in an x-y
plane. The housing may additionally include at least one air
bearing for translation of the housing, and therefore the rotary
shaft, in the x direction and the y direction in the x-y plane. In
some examples the rotary shaft comprises a rotary air bearing,
while in other embodiments the rotary shaft and rotary air bearing
may be separate components coupled together. The rotary air bearing
may be a vacuum preloaded (VPL) air bearing located directly above
the base of the rotary stage. The housing also includes an air
bushing having a first port that provides a positive pressure to a
first aperture of the rotary shaft and a second port that provides
a negative pressure to a second aperture of the rotary shaft.
[0023] The positive pressure in the present example is provided to
the VPL air bearing through the first aperture of the rotary shaft
and floats the rotary shaft above the base. The negative pressure
is provided to the VPL air bearing through the second aperture of
the rotary shaft and holds the rotary shaft down to the base. The
opposing forces generated by the negative pressure and the positive
pressure between the VPL air bearing and the base vertically
stabilize the rotary shaft, constraining its movement along the
z-axis, where the z-axis is the vertical axis normal to the x-y
plane.
[0024] In some examples, the first aperture of the rotary shaft is
located within a first groove of the rotary shaft and the second
aperture is located within a second groove. The present technology
supplies various pressures to the rotary shaft without contact via
the air bushing. The air bushing provides a pressure to the space
made by a groove, where an aperture is located within the groove.
The non-port surfaces of the air bearing provide a constant supply
of air that create an air barrier for the pressure to travel
through without escaping. The grooves therefore provide space for
the pressure to exist between the air bushing and the rotary shaft.
Thus, a path of pressure can be supplied to the aperture no matter
what degree of rotation the rotary shaft is at in relation to the
port on the air bushing in the housing.
[0025] In the present example, the rotary shaft and the VPL air
bearing can rotate three hundred and sixty degrees continuously.
The term "continuously" is intended to mean they can continue to
rotate past three hundred and sixty degrees infinitely many times,
not that they constantly rotate. On the contrary, the rotary shaft
could also rotate for a continuous period of time. Because the
rotary shaft can rotate continuously, the present example includes
an encoder feedback ring on the rotary shaft or air bearing that
can be read by an optical encoder coupled to the housing. Thus, the
optical encoder can be aware of the angular position of the rotary
shaft at any time.
[0026] In some examples, the air bushing may comprise a third port
that provides a pressure to a third aperture of the rotary shaft.
The third aperture may provide the pressure to the top surface of
the rotary shaft, according to the needs of a user.
[0027] In another embodiment, a system for non-contact rotary
motion comprises a rotary air bearing that rotates about a vertical
axis and a non-rotary air bearing. The rotary air bearing comprises
a first aperture that receives a first pressure and a second
aperture that receives a second pressure. The non-rotary air
bearing comprises a first port that provides the first pressure to
the first aperture of the rotary air bearing and a second port that
provides the second pressure to the second aperture of the rotary
air bearing.
[0028] In an additional example, a method of supplying pressure to
a rotary unit is provided. The method comprises maintaining
horizontal stability of a rotational air bearing, providing a first
pressure to a first aperture of the rotational air bearing without
a physical connection between the air bushing and the rotational
air bearing, and providing a second pressure to a second aperture
of the rotational air bearing without a physical connection between
the air bushing and the rotational air bearing.
[0029] In yet another embodiment, a system for providing pressure
to a non-contact rotary unit includes a means for providing a
positive pressure to a first aperture of the rotary unit without
contacting the rotary unit and a means for providing a vacuum
pressure to a second aperture of the rotary unit without contacting
the rotary unit. The present example also includes a means for
maintaining a horizontal stability of the rotary unit without
contacting the rotary unit and a means for maintaining a vertical
stability of the rotary unit without contacting the rotary
unit.
[0030] FIG. 1 demonstrates an exemplary embodiment of a rotary
stage in accordance with the present technology. In some examples,
the rotary stage of FIG. 1 is located within a CMM, or a similar
rotary motion system. FIG. 1 includes housing 105, where housing
105 includes air bearing 110, radial air bearing 115 mounted on
joint 120, and air bushing 125. Within housing 105 is rotary shaft
130, which includes VPL air bearing 135, shaft cylinder 140,
encoder feedback ring 145, groove 150, groove 155, groove 160, and
mounting surface 165. Rotary shaft 130 and VPL air bearing 135 are
coupled to one another in the present example and can rotate
non-contact with any components of housing 105. Rotary shaft 130
and VPL air bearing 135 rotate about a theoretical z-axis that runs
vertically through the coaxial centers of rotary shaft 130 and VPL
air bearing 135 and is normal to a base of the housing that VPL air
bearing 135 is held directly above. The base may be any bottom
surface that the VPL air bearing is held directly above.
[0031] In the present example, rotary shaft 130 comprises a large
diameter air bearing, VPL air bearing 135 that rides on the base.
The base may be a bottom surface made of granite, in some examples.
The VPL air bearing vertically supports the rotating mass of the
rotary shaft and any payload mass that may be mounted on mounting
surface 165. VPL air bearing 135 uses a positive pressure to float
itself on the base. The air bearing of the rotary shaft allows the
rotary shaft to rotate without constraining the rotary shaft's
z-axis in any horizontal direction. Thus, rotary shaft 130 can move
laterally in an x-direction and a y-direction of an x-y plane
parallel to the base. VPL air bearing 135 also has a vacuum applied
to it to hold it down to the base. In the present example, an inner
diameter of the base of VPL air bearing 135 is hollowed out such
that enough room is provided to create a sufficient vacuum space to
hold down rotary shaft 130.
[0032] In some cases, a positive pressure air bearing may be used
in the place of VPL air bearing 135. The positive pressure air
bearing may use only a single pressure source, without a vacuum
pressure supply and without a vacuum chamber to hold the air
bearing down to the base. Alternatively, two sources of positive
pressure may be supplied to VPL air bearing 135, wherein the second
positive pressure is used in a vacuum generator located within the
rotary shaft. The vacuum generator may then use the second positive
pressure to generate vacuum in the rotary shaft.
[0033] Rotary shaft 130 further comprises shaft cylinder 140. Shaft
cylinder 140 is a steel shaft cylinder in the present example,
where the steel shaft cylinder is a stainless-steel cylinder with
modifications according to the needs of the present technology.
Rotary shaft 130 also includes a motor rotor assembly. In the
present example, the motor rotor assembly comprises a magnetic ring
that is permanently fixed to the shaft. The motor rotor assembly,
however, could be any motor capable of rotating the rotary shaft,
including a frameless torque motor magnetic ring.
[0034] Rotary shaft 130 includes a high-accuracy encoder feedback
ring 145, in the present example. Encoder feedback ring 145 is
coupled to the outer diameter of rotary shaft 130 and has grating
around the outer diameter of the ring. In some examples, encoder
feedback ring 145 is permanently fixed to the rotary shaft, but may
be removable, movable, or the like in other examples. In the
present example, encoder feedback ring 145 is a ground disk encoder
ring that can be mounted flat and mechanically adjusted to be
within less than 10 micrometers of coaxial to rotary shaft 130.
However, encoder feedback ring could be any rotary encoder feedback
product that is non-contact with the encoder.
[0035] Housing 105 is a non-rotary housing that includes a motor
stator, an encoder system, a set of kinematically mounted radial
air bearings, a set of translational air bearings, and air bushing
125. In some cases, air bushing 125 is mounted to housing 105 via a
set of O-rings. The couple air bushing 125 to housing 105, helping
position air bushing 125. However, the O-rings enable flexibility
in that they can be compressed, allowing air bushing 125 to float
slightly laterally, ensuring no resistance against the radial
constraint provided by the radial air bearings. The motor stator is
an electric coil wound to interface with the magnetic ring of
rotary shaft 130. The motor stator is a part of the frameless
torque motor that enables rotary shaft 130 to rotate. In the
present example, the frameless torque motor specifically uses
ironless coils to eliminate radial forces between rotary shaft 130
and the non-rotating electric coil.
[0036] A typical motor can have cyclical radial forces associated
with the magnetic pattern on the rotor. These cyclical forces
acting on the bearing add to runout error and greater precision
degradation of the rotation. The motor of the present example is
frameless alternating current (AC) servo torque motor that is
designed to minimize radial forces in order to minimize the
degradation of the rotational precision, including effects such as
runout and wobble. However, other motor designs that have similar
levels of precision are anticipated. The rotary stage itself can be
run by many types of controllers and amplifiers, but control
systems that enable high precision and high constant velocity
performance are preferred to maintain a precise system. The encoder
system utilizes encoder feedback ring 145 to determine an angular
position of rotary shaft 130. The encoder system reads the grating
on the encoder ring. In some examples, the encoder system may
comprise only one encoder head. In other examples, more than one
encoder head may be used, such as a dual-head encoder system where
the signals are averaged to remove eccentricity from the angular
position data.
[0037] Housing 105 comprises three kinematically mounted radial air
bearings, including radial air bearing 115, that are non-rotating
and coupled to the housing. In other examples, housing 105 may
comprise a different number of radial air bearings providing
horizontal stability to the rotary shaft. The air bearings of the
present example are mounted on ball and socket joints, such as
joint 120. The ball and socket joints allow each of the radial air
bearings to self-align and mate with the outer diameter of rotary
shaft 130. All three radial air bearings may be preloaded to a
kinematic arrangement constraining rotary shaft 130 in the x and y
directions relative to the housing. In the present example, a four
to ten micrometer air gap exists between each of the radial air
bearings and rotary shaft 130. The air gap allows rotary shaft 130
to rotate on high pressure air between the air bearings and the
rotary shaft. Because the three air bearings are kinematically
mounted, they define the location of the z-axis, as three points
acting radially constrain the round cylinder to be stationary in x
and y. Thus, when housing 105 moves in x and y, rotary shaft 130
precisely follows the housing in the x and y plane.
[0038] Housing 105 may move in x and y on a combination of
mechanical and air bearings that translate housing 105 precisely in
the x-y plane, where the translation is enabled by set of air
bearings including air bearing 110. Air bearing 110 vertically
holds the housing down to a base, assisting in precise translation
of the housing. The translational air bearings allow low-friction
translation of housing 105 and rotary shaft 130 in the x and y
plane. For example, if housing 105 is used in a CMM, the job may
require both translational and angular positioning of a part on
mounting surface 165 in order to properly measure and analyze the
part.
[0039] Air bushing 125 is a hollow, cylindrical air bearing that is
coupled to housing 105 and fits around rotary shaft 130. Air
bushing 125 acts as a frictionless rotary union to feed high
pressure air to VPL air bearing 135. Rotary shaft 130 requires a
pneumatic system that provides high pressure air supplied to it
such that VPL air bearing 135 riding on the base can be
pressurized. Thus, air bushing 125 supplies the pressurized air to
rotary shaft 130 and subsequently to VPL air bearing 135. Air
bushing 125 has multiple pressurized surfaces that are composed of
a porous media. Because of the porous media of these surfaces, they
can supply a limited amount of pressure and act as flow
restrictors. Rotary shaft 130 has grooves (groove 150, groove 155,
and groove 160) that are not pressured and line up with
corresponding ports of air bushing 125. The ports of air bushing
125 can be pressurized and supply the pressure to the corresponding
grooves in rotary shaft 130. In order for each of the ports to
supply pressure to the corresponding groove and the corresponding
aperture of rotary shaft 130, the adjacent air bearing surfaces act
as a seal to each pressure supplied by the ports. Thus, the
adjacent air bearing surfaces seal and restrict flow, limiting the
escape of the pressure.
[0040] By restricting the escape of pressure, a first pressure can
be supplied from a first port of air bushing 125 into a first
groove and into a first aperture of rotary shaft 130, where the
first aperture is a cross-drilled hole that has an opening in the
first groove and supplies the first pressure to VPL air bearing
135. For example, the first pressure may be the positive pressure
required to float rotary shaft 130 off the base. In a similar
manner, additional grooves in rotary shaft 130 can feed in vacuum
to VPL air bearing 135. Due to the pressure supplied by the air
bushing, there is high pressure adjacent to the grooves of rotary
shaft 130. However, because the high-pressure source is limited in
flow, if there is enough evacuation flow from the vacuum pump, the
pressure leakage can be exhausted, creating a net vacuum (relative
to atmosphere) in the groove and port. Thus, the vacuum pressure
can be ported to the vacuum supply necessary for the VPL air
bearing. Thus, a second pressure may be supplied through a second
port of air bushing 125 into a second groove and thus into a second
aperture of rotary shaft 130, where the second pressure is the
negative (vacuum) pressure required by VPL air bearing 135 to hold
rotary shaft 130 down to the base.
[0041] In some scenarios, additional ports supply pressure to
additional apertures of rotary shaft 130, which may then be
supplied to components of rotary shaft 130 according to the needs
of a specific application. In some examples, a third port of air
bushing 125 supplies a third pressure to a third groove of rotary
shaft 130, and a third aperture provides the pressure to mounting
surface 165. Some scenarios may require that vacuum is ported to
the mounting surface of the rotary shaft to act as a vacuum supply
for any rotating device, vacuum chuck, or the like that a user may
require from the system.
[0042] Air bushing 125 is mounted to housing 105 such that it has
some radial compliance in regards to its mounting. In this way, air
bushing 125 does not over constrain the rotational axis and the
rotational axis is defined purely by the three kinematically
mounted radial air bearings. Air bushing 125 should not provide any
x, y constraint and is able to move slightly in x and y within the
housing such that it can self-align to the axis location, coaxial
with rotary shaft 130.
[0043] The system of the present rotary stage example provides for
an exceptionally high level of precision. Precision and accuracy of
a rotary stage are achieved at least partially through angular
accuracy, the mitigation of runout, and the mitigation of wobble.
These features are achieved, in the present technology, primarily
using precise components including the rotary shaft, VPL land
surface, and base and secondarily using precise dual encoder heads,
ironless stator, and large diameter VPL air bearing. Furthermore,
the strategic placement of components relative to one another and
precise mounting mechanisms and housings are also integral to
building a precise system.
[0044] In some examples, the rotary stage of FIG. 1 is located
within a CMM, or a similar rotary motion system. In an exemplary
embodiment of the present invention, a preferred order of
components of the rotary stage from the bottom up is: rotary air
bearing, motor, air bushing, radial air bearings, encoder, and
customer mounting surface. By having the encoder near the top of
the rotary shaft and the radial air bearings just below the
encoder, optimal angular positioning accuracy and runout
performance is achieved. The order provided lends to optimum
performance in the present example, but other arrangements may be
used and are anticipated.
[0045] FIG. 2 demonstrates a rotary stage including apertures for
providing pressure to the rotary shaft in accordance with certain
embodiments of the present invention. The rotary stage of FIG. 2
comprises housing 105, radial air bearing 115, joint 120, air
bushing 125, rotary shaft 130, rotary air bearing 135, shaft
cylinder 140, encoder feedback ring 145, mounting surface 165,
aperture 205, aperture 210, aperture 215, vacuum area 220, air
bearing land 225, motor rotor 230, and motor stator 235. Air
bushing 125 supplies pressure to apertures 205, 210, and 215.
[0046] As previously discussed, air bushing 125 comprises three
ports in the present example. A first port feeds a first pressure
to aperture 205 and aperture 205 provides the pressure to mounting
surface 165. According to the present technology, the first port of
air bushing 125 and aperture 205 are optional and may be based on
the needs of a user. In some scenarios, a user may require a vacuum
supply to mounting surface 165. In the present example, air bushing
125 comprises a second port that feeds a second pressure to
aperture 210. In the present example, the second port of air
bushing 125 supplies a positive pressure and aperture 210 provides
the positive pressure to air bearing land 225 of VPL air bearing
135. Air bearing land 225 then uses the positive pressure to float
on an air gap above a base or bottom surface at a fly height. In
this manner, VPL air bearing 135 can rotate without friction
between it and the base or bottom surface. VPL air bearing 135, in
some examples, is rotated by an electric torque motor. The electric
torque motor includes motor rotor 230 (i.e., magnetic ring) and
motor stator 235. In the present example, the frameless torque
motor specifically uses ironless coils to eliminate radial forces
between rotary shaft 130 and the non-rotating electric coil.
[0047] Air bushing 125 also includes a third port that supplies a
third pressure to aperture 215. In the present example the third
pressure is a negative (vacuum) pressure. In FIG. 2, aperture 215
supplies the vacuum pressure to vacuum area 220 of VPL air bearing
135. The vacuum pressure is then used by VPL air bearing to create
a vacuum in vacuum area 220 in order to maintain vertical stability
of VPL air bearing 135 as it floats on the air gap between it and
the base or the surface below. By supplying both a positive
pressure for the air bearing and a vacuum pressure, the fly height
and air gap stiffness can be precisely controlled. The precise
control over the vertical position of rotary shaft 130 is an
important component of a low-friction rotary stage capable of
meeting tolerance needs of modern motion system technology.
[0048] FIG. 3 provides further detail related to the delivery of
pressure to the rotary shaft of FIG. 2. FIG. 3 comprises air
bushing 125, vacuum area 220, air bearing land 225, as well as
aperture exit 305, aperture exit 310, and aperture exit 315. As
previously described, a port of air bushing 125 provides a vacuum
pressure to a hole of a rotary unit. The vacuum pressure is then
provided to a vacuum area via cross-drilled holes within the rotary
unit. The aperture meets vacuum area 220 at aperture exit 305. Via
aperture exit 305, pressure can be evacuated from vacuum area 220
to create sufficient force to hold the rotary unit at a controlled
fly height. Similarly, an additional port of air bushing 125
supplies a positive pressure to an additional hole of the rotary
unit. The rotary unit includes a second set of cross-drilled holes
through which the pressure is supplied to air bearing land 225. The
positive pressure reaches air bearing land 225 via aperture exit
310.
[0049] The forces created at the base of the VPL air bearing in the
present example provide a means to precisely control the size of an
air gap that exists between a base and the VPL air bearing. In some
examples, the base is a granite base. By maintaining precise
control over the size of the air gap, the rotary unit can precisely
rotate thus providing precise positioning for a component mounted
on the rotary stage. Furthermore, by eliminating friction due to
contact between a rotary bearing and a base, precision can be
better maintained.
[0050] Due to the porous nature of air bearing land 225, there is
limited flow through the air gap. The vacuum preloaded air bearing
uses this to the advantage; with enough evacuation flow being drawn
from vacuum area 220 via aperture exit 305, the pressure leakage
can be exhausted to create a net vacuum in the vacuum area,
aperture, and port. Thus, the vacuum is ported to the vacuum supply
necessary for the rotary air bearing.
[0051] FIG. 4 illustrates an additional example of a rotary stage
in accordance with the present technology. The rotary stage of FIG.
4 includes translational frame 405 and rotational unit 440.
Translational frame 405 includes air bearing 410, air bearing 415,
radial air bearing 420, radial air bearing 425, encoder head 430,
encoder head 435, and air bushing 465. Rotational unit 440 includes
rotational cylinder 445, rotational air bearing 450, mounting plate
455, and encoder ring 460. The rotary stage of FIG. 4 may be
implemented in a variety of motion control systems. Mounting plate
455 can be set up in a variety of ways such that it can be used to
control motion and position for a wide variety of applications. In
some examples, a part is mounted to mounting plate 455 using, at
least in part, vacuum supplied by air bushing 465 for any rotating
device or vacuum chuck that may be required in a system.
[0052] Translational frame 405, in the present example, includes
three air bearings, such as air bearing 410 and air bearing 415,
that allow for precise translational movement in the x, y plane of
the rotary stage. Translational frame 405 may take on other
embodiments as well, such as including non-air bearings for
translational movement. However, in the present example, air
bearings are used for translational frame 405 because of the
limited friction created between them and a surface on which the
stage may translate. Because of the precise rotational movement
allowed by the low-friction rotational unit, it may be advantageous
to include low-friction translation equipment as well, such as air
bearings 410 and 415.
[0053] The translational frame of the present example includes
three radial air bearings, including radial air bearing 420 and
radial air bearing 425. Each of the three radial air bearings are
kinematically mounted, non-rotating, and fixed to the translational
frame. The three radial air bearings are each mounted on a ball and
socket joint that allow them to self-align and mate with the outer
diameter of rotational unit 440. The three radial air bearings
horizontally constrain rotational unit 440, defining a center axis,
or z-axis, of the rotary unit. An air gap between rotational unit
440 and each of the radial air bearings allow rotational unit 440
to rotate on the high-pressure air. In this way, when translational
frame 405 moves in the x, y plane, rotational unit 440 follows it
precisely in the x, y plane.
[0054] Translational frame 405 also includes an encoder system that
reads encoder ring 460 in order to determine the rotational
position of rotational unit 440. The encoder system utilizes two
encoder heads, encoder head 430 and encoder head 435, to determine
a precise position of rotational unit 440. The dual-head encoder
system averages the signal of each encoder head to remove
eccentricity from the rotational position data. Each of encoder
heads 430 and 435 is lined up to and nearby encoder ring 460. The
positioning within the rotary stage system of encoder heads 430 and
435 as well as encoder ring 460 in the present example is optimal
for angular positioning accuracy and runout performance.
[0055] Rotational unit 440 includes rotational air bearing 450. In
some examples, rotational air bearing 450 is a vacuum preloaded air
bearing. Rotational unit 440 can precisely rotate about a z-axis
using rotational air bearing 450. In order to supply pressurized
air to rotational air bearing 450, air bushing 465 is mounted to
translational frame 405 and includes at least one port through
which pressurized air can be supplied to rotational air bearing
450. Air bushing 465 is a cylindrical air bearing that fits around
rotational until 440. The ports of air bushing 465 each line up
with an aperture of rotational unit 440, via which the pressure is
supplied to rotational air bearing 450.
[0056] FIG. 5 illustrates an example of a pneumatic rotary unit in
accordance with some embodiments of the present technology. Rotary
shaft 505 rotates about axis 510 and is located within air bushing
535. Rotary shaft 505 includes aperture 515, aperture 520, groove
525, and groove 530. Air bushing 535 comprises port 540 and port
545. A first pressure is depicted as being supplied by port 540 and
a second pressure is depicted as being supplied by port 545. In
some examples, the first pressure is a positive pressure and the
second pressure is a negative pressure (i.e., less than atmospheric
pressure). Alternatively, both the first pressure and the second
pressure may be positive pressures. If port 540 and port 545 both
supply positive pressures, the second positive pressure may be used
in a vacuum generator located within the rotary shaft. The vacuum
generator may then use the second positive pressure to generate
vacuum in the rotary shaft. In yet another scenario, rotary shaft
505 may comprise only a single port, wherein the single port
provides positive pressure to a rotary air bearing.
[0057] Rotary shaft 505 may be located within one of the rotary
stages of the previous examples, or rotary shaft 505 may be used in
an alternative setting that requires the supply of pressure to a
pneumatic rotary unit without contact.
[0058] Air bushing 535 is an air bearing that fits around the outer
perimeter of rotary shaft 505. There is an air gap between air
bushing 535 and rotary shaft 505. Air bushing 535 has an inner
layer of porous media that supplies high pressure to fill the air
gap between air bushing 535 and rotary shaft 505. Air bushing 535
has multiple pressurized surfaces that ride on rotary shaft 505.
Due to the porous media of these surfaces, they can only supply a
certain amount of flow, causing them to serve as a flow restrictor.
Thus, these air bearing surfaces of air bushing 535 act as a seal
and flow restrictor, limiting the escape of pressure. In this way,
pressure can be supplied from each of the ports into their
respective grooves. For example, port 540 supplies high pressure to
groove 525, and the pressure does not escape in the gap between air
bushing 535 and rotary shaft 505 because it is already
high-pressure on both sides. Similarly, port 545 can supply vacuum
to groove 530 as long as there is sufficient evacuation flow to
exhaust the restricted pressure leakage.
[0059] Groove 525 includes an opening to aperture 515 and because
the groove continues three hundred and sixty degrees around rotary
shaft 505, it can continue to feed pressure through the aperture at
any angular position. Groove 530 includes an opening to aperture
520 and because the groove also continues three hundred and sixty
degrees around rotary shaft 505, it can continue to feed pressure
through aperture 520. In some examples, apertures 515 and 520
deliver pressure to a rotary air bearing, or a rotary VPL air
bearing.
[0060] Although demonstrated as being cut into rotary shaft 505 in
the present example, grooves 525 and 520 are optional. In some
embodiments, rotary shaft 505 may not include grooves at all.
Furthermore, grooves may be cut into the air bushing instead of
rotary shaft 505, creating a three hundred and sixty degree space
in which a pressure can be fed to an aperture of rotary shaft 505.
In some embodiments, grooves may not be necessary in either
component if enough pressure can be supplied to the apertures
through the space between air bushing 535 and rotary shaft 505.
[0061] FIG. 6 illustrates an alternative example of a rotary shaft
in accordance with some embodiments of the present technology.
Rotary shaft 605, contrary to rotary shaft 505, includes three
grooves and three apertures. Air bushing 645 also includes an
additional port for supplying pneumatic air to the additional
groove and aperture. Rotary shaft 605 rotates about axis 610 while
air bushing 645 remains stationary. Air bushing 645 and rotary
shaft 605 are non-contact. In some examples, rotary shaft 605
rotates entirely non-contact with any other parts. For example,
rotary shaft 605 may supply the pneumatic air via apertures 620 and
625 to a rotational air bearing that provides vertical support for
the rotary unit to rotate above a surface without contact.
Furthermore, rotary unit 605 may be horizontally stabilized with at
least one air bearing. By not requiring a physical connection to
rotary shaft 605, the rotary shaft is capable of rotating three
hundred and sixty degrees continuously, i.e., when it reaches three
hundred and sixty degrees of rotation, it can continue to rotate in
the same direction as many times as necessary. Previous technology
would require connective components which restrict how far a rotary
shaft can rotate or mechanical seals that add significant amounts
of friction.
[0062] In order to supply pneumatic air to each of aperture 615,
aperture 620, and aperture 625 without air bushing 645 contacting
rotary shaft 605 and without physical connective components between
them, air bushing 645 supplies high pressure air through its inner
surface. Air bushing 645 uses the high-pressure air like an air
bearing to create an air gap between its inner surface and rotary
shaft 605. The porous media of the inner surface of air bushing 645
acts as a flow restrictor. Thus, when enough pressure is supplied
through the air bearing surface around each of ports 650, 655, and
660, positive or negative pressures can be supplied from each of
the ports into each of the grooves and therefore into each of the
apertures without loss of pressure between air bushing 645 and
rotary shaft 605. The air bearing pressure around each of the ports
thus creates an air barrier, sealing the pneumatic supply to travel
directly from the air bushing port to its respective groove and
aperture.
[0063] For example, port 650 supplies pneumatic air to aperture 615
via groove 630. In order for the pneumatic supply to travel from
port 650 into groove 630 and remain in groove 630 as it is fed to
aperture 615, the inner wall of air bushing 645 provides an air
barrier around port 650 that fills the air gap between air bushing
645 and rotary shaft 605. Enough pressure is supplied to the air
gap that the flow is restricted and the pneumatic air cannot escape
through the air barrier. The pneumatic air supplied by port 650 may
be vacuum pressure in some scenarios. Aperture 615 may provide the
vacuum pressure to the mounting surface of rotary shaft 605, which
can be utilized for various mounting techniques. In other
embodiments, more than one pressure may be supplied to the mounting
surface of the rotary shaft. In addition to the present example,
two ports, three ports, and more than three ports are anticipated
by the present example.
[0064] The other apertures, aperture 620 and aperture 625, are
supplied pneumatic air by ports 655 and 660, respectively. In the
same manner, the inner surface of air bushing 645 creates enough
pressure within the air gap that flow is restricted, allowing
pneumatic air to be supplied without physical contact. In some
embodiments, port 655 supplies positive pressure to aperture 620
and port 660 supplies vacuum to aperture 625. In other embodiments,
port 655 provides vacuum to aperture 620 and port 660 provides
positive pressure to aperture 625. In additional embodiments, ports
655 and 660 may both provide positive or negative pressure, or
there may be only a single port that provides pneumatic air to a
single aperture. Alternatively, both the first pressure and the
second pressure may be positive pressures. If port 540 and port 545
both supply positive pressures, the second positive pressure may be
used in a vacuum generator located within the rotary shaft. The
vacuum generator may then use the second positive pressure to
generate vacuum in the rotary shaft. In yet another scenario,
rotary shaft 505 may comprise only a single port, wherein the
single port provides positive pressure to a rotary air bearing.
[0065] In the present example, aperture 615, aperture 620, and
aperture 625 are formed from two cross-drilled holes having similar
diameters. However, in other examples the apertures may take on
different embodiments such as having different diameters, varying
diameters, or, instead of cross drilled holes, may take a different
path such as a curved path, a straight path, and similar paths
capable of porting pneumatic air through rotary shaft 605. In some
examples, ports 650, 655, and 660 have a diameter of equal size or
a smaller size than the width of grooves 630, 635, and 640,
respectively. Additionally, apertures 615, 620, and 625 may have
diameters of the same size or a smaller size than the width of
grooves 630, 635, and 640, respectively.
[0066] FIG. 7 illustrates an example of a rotary stage, as viewed
from above, in accordance with some embodiments of the present
technology. FIG. 7 shows a top-view, wherein three radial air
bearings, radial air bearing 705, radial air bearing 710, and
radial air bearing 715 and their relative positions are
illustrated. In the present example, the three radial air bearings
are used to stabilize the rotary shaft in the x-y plane. The three
radial air bearings are kinematically mounted on ball and socket
joints, enabling them to adjust such that the rotary shaft is
constrained properly. Alternative examples may use fewer air
bearings or more air bearings to horizontally stabilize the rotary
shaft may be used and are anticipated herein.
[0067] It should be emphasized that the above-described embodiments
are merely possible examples of implementations, merely set forth
for a clear understanding of the principles of this disclosure.
Many variations and modifications may be made to the
above-described embodiments without departing substantially from
the principles of the disclosure. All such modifications and
variations are intended to be included herein within the scope of
this disclosure.
* * * * *