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STUT-ME
Vibration Control for Precision
Machinery
王永鵬
南台科技大學 機械工程系
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STUT-ME
Outline
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Introduction
Passive Vibration Isolation System
Active Vibration Isolation System
Conclusions
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STUT-ME
Introduction
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Vibration Sources of Precision Equipment:
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Environmental Vibrations
On-board Disturbances
Objective of Vibration Control for Precision
Equipment:
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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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STUT-ME
Introduction
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Vibration Control Techniques:
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Passive Isolation System
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Rubber Pad
Air Spring
Spring
Active Isolation System
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Soft-Mounted System
Hard-Mounted System
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Passive Vibration Isolation System
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
 

1   2
x
n 

T 
2
2
2
u
   
 
1  2    2

 n   n 
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Passive Vibration Isolation System

Transmissibility of
Passive Isolation
System
=0.10

Transmissibility (x/u,
(x1/df)dB)
Transmissibility

=0.01
=0.50
=1.00










Frequency (w/wn)
Frequency
(/n)
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


STUT-ME
Passive Vibration Isolation System
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A second-order mechanical filter
Eliminate vibration from the crossover
frequency onward
Drawbacks:
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Sensitive to payload forces
Vibration amplification around the natural
frequency
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Passive Vibration Isolation System
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Passive Isolation System
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Rubber Pad
Air Spring
Spring
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Active Vibration Isolation System
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Motion sensor
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Actuator
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Displacement, Velocity, Acceleration, Force
Electromagnetic type, Piezoelectric type,
Magnetostrictive type
Control
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Feedforward, Feedback
PID, Lead/Lag Compensator, LQG, Adaptive
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Active Vibration Isolation System
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Active Isolation System
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Soft-Mounted System (SMS)
Hard-Mounted System (HMS)
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Active Vibration Isolation System
Hard-Mounted System
Soft-Mounted System
x1
m1
x1
m1
cp
kp
x2
m2
kp
cp
actuator
actuator
f
f
(a)
(b)
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STUT-ME
Soft-Mounted System
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Soft-Mounted System (SMS)
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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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STUT-ME
Hard-mounted System
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Hard-Mounted System (HMS)
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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 passiveactive compromise and never is able to come up
to the performance of SMS.
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Modified Hard-Mounted Isolation System
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In order to improve the performance of hardmounted 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
d
x1
m1
kp
cp
fd
m2
VCM
x2
ka
f
PZT
c
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STUT-ME
Modified Hard-Mounted Isolation System
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Equations of Motion:
 m1x1  k p ( x1  x2 )  c p ( x1  x2 )  f d  d
 
m2 x2  ka ( x2   c   f )  k p ( x1  x2 )  c p ( x1  x2 )  f d

Control Laws:
 c ( S )  k3 X 2 ( S )  k4 SX 1 ( S )

 Fd ( S )  k1 X 1 ( S )  k2 X 2 ( S )
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Modified Hard-Mounted Isolation System
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Closed-Loop System:
X 1 (S )  H 5 (S ) f (S )  H 6 (S ) D(S )
where
 H 5 ( S ) : Vibration Transmissi bility

H 6 ( S ) : System Compliance
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Modified Hard-Mounted Isolation System
G4(S)
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Block Diagram of
Modified HardMounted Isolation
System

f
D
G3(S)
+
+
G6(S)
X2
+
+
G1(S)
X1
+
-
+
G2(S)
G7(S)
Fd
k2
-
k3
C
G5(S)
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-
k4 S
-
k1
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Modified Hard-Mounted Isolation System
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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
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System Compliance
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Modified Hard-Mounted Isolation System
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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 hardmounted isolation system.
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