stut-me 1 vibration control for precision machinery 王永鵬 南台科技大學 機械工程系
TRANSCRIPT
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Vibration Control for Precision Machinery
王永鵬南台科技大學 機械工程系
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Outline
Introduction Passive Vibration Isolation System Active Vibration Isolation System Conclusions
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Introduction Vibration Sources of Precision Equipment:
Environmental Vibrations On-board Disturbances
Objective of Vibration Control for Precision Equipment: Isolate sensitive equipment from a vibrating
environment, e.g. floor-induced vibration. Isolate vibration equipment from on-board
disturbances, e.g. payload-induced vibration.
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Introduction Vibration Control Techniques:
Passive Isolation System Rubber Pad Air Spring Spring
Active Isolation System Soft-Mounted System Hard-Mounted System
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Passive Vibration Isolation System
22
2
2
2
21
21
nn
n
u
xT
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Passive Vibration Isolation System
Frequency (w/wn)
Tra
nsm
issi
bilit
y (x
1/df
)
=0.01
=0.50
=0.10
=1.00
Frequency (/n)
Tra
nsm
issi
bili
ty (
x/u,
dB
)
Transmissibility of Passive Isolation System
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Passive Vibration Isolation System
A second-order mechanical filter Eliminate vibration from the
crossover frequency onward Drawbacks:
Sensitive to payload forces Vibration amplification around the
natural frequency
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Passive Vibration Isolation System
Passive Isolation System Rubber Pad Air Spring Spring
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Active Vibration Isolation System Motion sensor
Displacement, Velocity, Acceleration, Force Actuator
Electromagnetic type, Piezoelectric type, Magnetostrictive type
Control Feedforward, Feedback PID, Lead/Lag Compensator, LQG, Adaptive
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Active Vibration Isolation System
Active Isolation System Soft-Mounted System (SMS) Hard-Mounted System (HMS)
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Active Vibration Isolation System
Soft-Mounted System
Hard-Mounted System
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Soft-Mounted System Soft-Mounted System (SMS)
The system’s overall performance predominantly from the passive element.
The active feedback system uses contactless electrodynamic force to overcome the weakness of the passive isolators.
The system remains inherently soft. SMS are insensitive to resonance in the main
structure below the isolators. SMS are sensitive to resonance in the
payload. (require adaptive control to ensure optimal performance)
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Hard-mounted System Hard-Mounted System (HMS)
HMS relies mainly on the control system for isolation.
HMS have a much higher closed-loop bandwidth than SMS by using a piezoactuator.
SMS needs for higher frequency isolation with a passive spring that is tuned to 10-20 Hz. Hence, HMS is extremely stiff and allows for large payload forces without excessive motion.
The major drawback of a HMS is that vibration isolation performance suffers from the passive-active compromise and never is able to come up to the performance of SMS.
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Modified Hard-Mounted Isolation System
In order to improve the performance of hard-mounted isolation system, a voice-coil motor (VCM) is placed between the payload mass and intermediate mass.
The VCM is used to eliminate the effects of onboard disturbances on the payload mass.
The piezoactuator is used to isolate the floor vibration from the payload mass.
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Modified Hard-Mounted Isolation System
VCM
PZT
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Modified Hard-Mounted Isolation System
dppfca
dpp
fxxcxxkxkxm
dfxxcxxkxm
)()()(
)()(
2121222
212111
)()()(
)()()(
2211
1423
SXkSXkSF
SSXkSXkS
d
c
Equations of Motion:
Control Laws:
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Modified Hard-Mounted Isolation System
Compliance System :)(
bilityTransmissiVibration :)(
6
5
SH
SH
Closed-Loop System:
where
)()()()()( 651 SDSHSSHSX f
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Modified Hard-Mounted Isolation System
Block Diagram of Modified Hard-Mounted Isolation System
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Modified Hard-Mounted Isolation System
Case (a): Without feedback Case (b): Single-loop hard-mounted
isolation system Case (c): Double-loop hard-mounted
isolation system Case (d): Modified hard-mounted
isolation system with absolute displacement feedback
Case (e): Modified hard-mounted isolation system with relative displacement feedback
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Modified Hard-Mounted Isolation System Vibration Transmissibility
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Modified Hard-Mounted Isolation System System Compliance
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Modified Hard-Mounted Isolation System When the absolute displacement of the payload
mass is used as the feedback signal to the VCM, the system is capable of eliminating the effects of onboard disturbances for the whole frequency range and the transmissibility can also be improved in the lower frequency range.
When the relative displacement between the payload mass and intermediate mass is used as the feedback signal to the VCM, the system is capable of eliminating the effects of onboard disturbances for the range of higher frequencies but the transmissibility is indistinguishable from that of hard-mounted isolation system.