Brakes – Inertia of damping mass dissipates motion
Reexamination Certificate
1999-10-06
2002-04-30
Rodriguez, Pam (Department: 3613)
Brakes
Inertia of damping mass dissipates motion
C267S140140, C700S042000
Reexamination Certificate
active
06378672
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an active anti-vibration device used in a semiconductor exposure apparatus or liquid crystal substrate manufacturing apparatus for transferring and printing a circuit pattern on a reticle onto a semiconductor wafer, an electron microscope, or the like and, more particularly, to an anti-vibration device using a displacement generation element represented by a piezoelectric element or like, i.e., a displacement generation actuator active vibration isolation device comprising a versatile feedback process encompassing the prior art.
Also, the present invention relates to a hybrid active vibration isolation apparatus using an anti-vibration unit which integrates a displacement generation actuator (e.g., a piezoelectric element) and a force actuator (e.g., an electromagnetic motor).
In an electron microscope using an electron beam or a semiconductor manufacturing apparatus represented by a stepper, scanner, or the like, an X-Y stage is placed on an anti-vibration unit. The anti-vibration unit has a function of damping vibration by vibration absorbing means such as an air spring, coil spring, anti-vibration rubber, and the like. However, a passive anti-vibration unit having such vibration absorbing means can damp vibration that propagates from a floor to some extent, but cannot effectively damp vibration produced by the X-Y stage itself. That is, the counter force produced by high-speed movement of the X-Y stage itself vibrates the anti-vibration unit, and this vibration considerably impairs alignment settling performance of the X-Y stage.
Furthermore, the passive anti-vibration unit suffers a tradeoff between isolation of vibration (vibration isolation) that propagates from the floor, and suppression of vibration (vibration damping) produced upon generation of high-speed movement of the X-Y stage itself. To solve such problems, an active anti-vibration unit has been used more often in recent years. The active anti-vibration unit can eliminate the tradeoff between vibration isolation and vibration damping within the range of an adjustable mechanism, and can get performance that cannot be achieved by a passive anti-vibration unit by positively applying feedforward control.
However, in order to further suppress propagation of vibration to apparatuses that cannot tolerate vibration represented by a semiconductor manufacturing apparatus, vibration isolation is required for a still lower frequency range. For this purpose, attempts have been made to use an active vibration isolation device using a piezoelectric element, which can accurately control infinitesimal displacement, in vibration isolation of the entire semiconductor manufacturing apparatus. However, an anti-vibration device using an air spring or electromagnetic motor has been developed remarkably and has reached a practical level, but an active vibration isolation device using a piezoelectric element as an actuator stays at the level of laboratory study. The arrangement of its controller has not been examined extensively, and the performance of the piezoelectric element cannot be fully utilized.
The active vibration isolation device using a piezoelectric element that represents a displacement generation actuator includes three different types. The first type (type A) drives a piezoelectric element
1
on the basis of a signal output from a vibration detection means
9
b
on an intermediate plate
5
, as shown in FIG.
7
A. The second type (type B) drives a piezoelectric element
1
on the basis of outputs from vibration detection means
9
b
and
9
a
provided on an intermediate plate
5
and an object from which vibration is to be removed (to be referred as vibration damping subject)
4
, as shown in FIG.
7
B. The third type (type C) drives a force actuator
6
provided between an intermediate plate
5
and vibration damping subject
4
together with a piezoelectric element
1
on the basis of outputs from vibration detection means
9
a,
9
b,
and
9
c
mounted on the vibration damping subject
4
, the intermediate plate
5
, and a floor
10
, as shown in FIG.
7
C. Higher performance characteristics are assured in the order of
FIGS. 7A
,
7
B, and
7
C.
Skipping an analysis for the arrangement shown in
FIG. 7A
, the feedback arrangement in
FIG. 7B
will be explained first.
FIG. 8
shows a structure of an anti-vibration unit in which a piezoelectric element is built in as an actuator. Referring to
FIG. 8
, reference numeral
1
denotes a piezoelectric element;
2
, a leaf spring;
3
, laminated rubber;
4
, a stepper, for example, as a vibration damping subject; and
5
, an intermediate plate.
FIGS. 9A and 9B
respectively show a dynamics model of this structure and feedback control executed for this structure. This structure is disclosed in Japanese Patent Laid-Open No. 8-54039 (stiff actuator active vibration isolation system: U.S. Pat. No. 5,660,255). Using reference symbols in
FIGS. 9A and 9B
, equations of motion are given by:
M
P
s
2
x
=(
K
i
+C
i
s
)(
v−x
)+
f
p
(1)
M
S
s
2
v=K
S
(
z−v
)+(
K
i
+C
i
s
)(
x−v
) (2)
where M
P
is the mass of the vibration damping subject
4
, K
i
is the spring constant of the laminated rubber
3
, C
i
is the viscous damping coefficient of mainly the laminated rubber
3
between the vibration damping subject
4
and intermediate plate
5
, M
S
is the mass of the intermediate plate
5
, K
S
is the spring constant of the piezoelectric element
1
, x is the displacement of the vibration damping subject
4
, v is the displacement of the intermediate plate
5
, u is the displacement of floor vibration, z is the displacement of the piezoelectric element
1
, and f
p
is disturbance acting on the vibration damping subject
4
.
Analysis will be again given first considering the technical contents disclosed in Japanese Patent Laid-Open No. 8-54039 (stiff actuator active vibration isolation system: U.S. Pat. No. 5,660,255).
FIG. 9B
is a block diagram that explains the feedback arrangement of the active vibration insulation device which uses the piezoelectric element as an actuator, as given by equations (1) and (2). As illustrated in
FIG. 9B
, there are two feedback loops. Using symbols in
FIG. 9B
, a feedback equation is given by:
z=u−C
d
v−C
V
sx
(3)
where C
d
is the feedback gain of the absolute displacement, and C
v
is the feedback gain of the absolute velocity. From equations (1) to (3), the relationship among the displacement x of the vibration damping subject, the displacement u of floor vibration, and the disturbance f
p
is given by:
x
=
(
C
i
s
+
K
i
)
K
s
D
(
s
)
·
u
+
M
s
s
2
+
C
i
s
+
K
i
+
K
s
(
1
+
C
d
)
D
(
s
)
·
f
p
(
4
)
D
(
s
)=
M
P
M
s
s
4
+(
M
p
+M
S
)
C
i
s
3
+[M
P
{K
i
+K
s
(1
+C
d
)}+
M
S
K
i
+C
i
K
s
C
V
]s
2
{C
i
K
S
(1
+C
d
)+
K
i
K
S
C
V
}s+K
i
K
S
(1
+C
d
) (5)
From the above equations, the transmissibility from the displacement u of floor vibration to the displacement x of the vibration damping subject with the mass M
P
is defined by the first term of the right-hand side of equation (4). If s→0, the transmissibility in the DC range is given by:
x
u
=
1
1
+
C
d
<
0
[
dB
]
(
6
)
That is the transmissibility in the DC range can be set below 0 [dB] by adjusting the gain C
d
. This is a critical difference from an anti-vibration device using an air spring or electromagnetic actuator. Normally, in an active anti-vibration device using an air spring as an actuator, damping is given by a vibration control loop based on detection of acceleration (absolute acceleration), and the designated posture is maintained by a position control loop based on the relative displacement between a floor and anti-vibration base. Since the relative displacement is fed back, the transmissibility in the low-frequency range
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Rodriguez Pam
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