Byron Knapp, Dave Arneson, Dan Oss, and Mel Liebers
Professional Instruments CompanyHopkins, Minnesota, USA
Ultra Precision Oil Hydrostatic Spindle Design and Metrology
1
A presentation given at the 10th International Symposium of Measurement Technology and Intelligent Instruments
KAIST, Daejeon, Korea 01 July 2011
2
Professional Instruments CompanyHopkins, Minnesota, USA
Byron [email protected]
Professional Instruments Company7800 Powell Road
Hopkins, Minnesota, USA
3
Snow-covered Professional Instruments headquarters, January 2011.
Ultra precision oil hydrostatic spindle
Some industrial applications
demand high precision and high
load capacity spindles.
A bi-conic oil hydrostatic spindle is
ideal for the rigorous demands of
precision machining and grinding.
This presentation describes an oil
hydrostatic spindle that features:
• nanometer-level error motion• high load capacity• excellent dynamics• high crash resistance
Background
Design
Metrology
4
Benefits of oil hydrostatic spindles
Machine tool spindles commonly
use rolling element bearings.
Some potential advantages of oil
hydrostatic bearings (compared to
rolling element bearings):
• lower error motions• high damping• no wear
Background5
K Wasson. “A Comparison of rolling element and hydrostatic bearing
spindles for precision machine tool applications.” Proceedings of ASPE
Conference Precision Bearings and Spindles. June 2007.
Photo credit: SKF
rolling elements
oil hydrostatic
Comparison of two types of compensation
6
Hale, L, Donaldson, R, Edson, S, and R Thigpen. “Hydrostatic bearings
designed for POGAL.” Proceedings of ASPE Conference Precision
Bearings and Spindles. June 2007.
orifice compensation
with pockets
step
compensation
Design
Step at the outer edge of the
bearing area provides restriction.
• higher average pressure• tighter clearances• high stiffness• shear film heating
Orifice or slit prior to bearing
pocket provides restriction.
• average bearing pressure less than half of supply pressure
• pockets affect error motion
Comparison of two rotor configurations
7
“H” style rotor
bi-conic rotor
Design
“H” style uses basic geometric
elements with separated axial and
radial bearings.
Bi-conic design offers several
potential advantages:
• high bearing efficiency (load capacity for a given volume)
• high structural stiffness• balance of radial, axial and tilt
load capacities• design simplicity
Bi-conic design with ring restrictor and pockets
8
Kane, NR, Sihler, J. and AH Slocum. “A hydrostatic rotary bearing with angled
surface self-compensation.” Precision Engineering, 2003;27(2): 125-139.Design
Bi-conic with step compensation
Bi-conic with step compensation:
• no pocket “print-through” to error motion
• higher oil film pressure• increased bearing area• improved bearing stability• high stiffness• no complicated up-stream
restrictors
9Design
20 µm
oil films
10
Non-influencing, non-contact air seals
Design
Bi-conic modal analysis
11
• Kistler 2,000 N modal hammer• Kistler 50 g K-shear accelerometer• HP Dynamic Signal Analyzer
Metrology
12Metrology
Outstanding dynamic response!
Ideal axis of rotation
An axis of rotation with pure
rotation θ about the Z reference
axis.
Rotation θ is the intended function
of the spindle.
Five other basic degrees of freedom
exist: 3 linear and 2 angular.
ANSI/ASME B89.3.4M-2010. “Axes of Rotation: Methods
for Specifying and Testing.” ASME: New York (2010).Metrology
13
Radial motions
Pure radial degrees of freedom as a
function of θ in the X and Y
directions.
ANSI/ASME B89.3.4M-2010. “Axes of Rotation: Methods
for Specifying and Testing.” ASME: New York (2010).Metrology
14
Tilt motions
Angular degrees of freedom as a
function of θ about the X and Y axes.
ANSI/ASME B89.3.4M-2010. “Axes of Rotation: Methods
for Specifying and Testing.” ASME: New York (2010).Metrology
15
Axial motion
One degree of freedom as a function
of θ in the Z direction.
ANSI/ASME B89.3.4M-2010. “Axes of Rotation: Methods
for Specifying and Testing.” ASME: New York (2010).Metrology
16
Radial motion measurement
Measurement of the pure radial and
tilt at a particular axial location.
ANSI/ASME B89.3.4M-2010. “Axes of Rotation: Methods
for Specifying and Testing.” ASME: New York (2010).Metrology
17
Tilt motion measurement
Can be calculated from two radial
measurements at specified axial
locations…
or two face measurements at
specified radial locations.
ANSI/ASME B89.3.4M-2010. “Axes of Rotation: Methods
for Specifying and Testing.” ASME: New York (2010).Metrology
18
Axial motion measurement
Sensor placed collinear with the axis
of rotation.
ANSI/ASME B89.3.4M-2010. “Axes of Rotation: Methods
for Specifying and Testing.” ASME: New York (2010).Metrology
19
Separating ball and spindle error
Radial motion measurements include out-of-roundness of the master and radial motion of the axis of rotation.
For nanometer-level spindles, the ball out-of-roundness can be significant.
Without separation of ball out-of-roundness, the spindle error can appear better or worse.
Ball: 9 nm Spindle: 8 nm
Ball and spindle: 14 nm
Metrology20
Reversal
Reversal techniques are theoretically the simplest way to remove artifact error.
Donaldson reversal for radial motion measurements; Estler reversal for face measurements.
Both require exact artifact reversal.
Potential errors from debris, handling, and remounting.
Metrology21
Multiprobe method
Sensor orientation angles affect harmonic suppression.
Asymmetric orientated measurements reduce harmonic suppression.
Orientation angles of 0.000°, 99.844°, and 202.500° give good separation results to 225 UPR. xEm ArtifactA
sincos yxEm ArtifactB
sincos yxEm ArtifactC
E Marsh. Precision Spindle Metrology. 2nd Edition.
Destech Publications: Lancaster, PA (2010).Metrology
22
Lapped master
25 mm diameter ball of monolithic design for uniform circular stiffness.
Provision for balancing.
Flat mounting flange with six mounting screws.
Out-of-roundness is 9 nm as measured with a capacitive sensor and 150 UPR filter.
23Metrology
jig-ground locating
hole (3x)
jig-ground indexing
hole (4x)
toroidal
pilot
24Metrology
Error separation tooling
Bi-conic spindle error measurement
MCS brushless DC motor with cooling jacket and 1,024 line count encoder
Fixed displacement pump provides inlet pressures up to 70 bar with light spindle oils.
Uses 2 lpm oil (Mobile Velocite #6, viscosity 10 cSt) at 40 bar.
25Metrology
Spindle metrology setup
26
• Lion Precision SEA software
• Lion capacitive sensor
• Lion Elite amplifier
• Custom target and error separation
• Stiff structural loop for testing
Metrology
Radial error measurement
27Metrology
Axial error measurement
28Metrology
Machining results
29Metrology
Retrofit workhead of CNC cylindrical grinder (Parker Liberty) :
• Hardened 440C test piece, 75 mm diameter• Better than 0.25 µm out-of-roundness
0.22 µm
Conclusions
Conclusions30
• Design and metrology techniques of an ultra-
precision oil hydrostatic spindle are described.
• This spindle ideal for the rigorous demands of
precision machining, hard turning, and grinding.
• Nanometer-level error motions, high load
capacity, excellent dynamics, and high crash
resistance are realized.
Byron [email protected]
Professional Instruments CompanyHopkins, Minnesota, USA
Sewon Eng. LTDwww.sewoneng.net
Seoul, Korea
Contact information:
31
10th International Symposium of Measurement Technology and Intelligent Instruments
32
Bonus features.
Bonus
33Bonus
34
Grinding wheelhead
Bonus
35
Grinding the cone
Bonus
36
Continuing work: lathe retrofit
Bonus
Goals: demonstrate advantages of precision hydrostatic
spindle retrofitted into a standard lathe for hard turning.
37Bonus
38
Stiffness and load capacity (40 bar bearing inlet pressure).
Bonus
39Bonus
3 decimal places on the angle?
Zeiss Contura G2 Inspection Report
40Bonus
Top Related