Optics: measuring and testing – By light interference – For dimensional measurement
Reexamination Certificate
2000-10-21
2003-08-05
Kim, Robert H. (Department: 2882)
Optics: measuring and testing
By light interference
For dimensional measurement
C356S399000
Reexamination Certificate
active
06603562
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
This invention relates to two-dimensional positioning apparatus, and more particularly, to such apparatus wherein components thereof and methods used therein are improved.
2. Description of the Prior Art
A two-dimensional positioning apparatus is disclosed, for example, in Japan unexamined patent application No. 2000-65970, and shown in
FIG. 1
, wherein a platen
10
, which is made of a magnetic material, is provided with teeth formed at fixed spacings in the X-axis and Y-axis directions. Only part of the teeth are shown for simplicity of description. An object to be positioned is placed on slider
11
. Levitating means
12
causes slider
11
to be disposed or levitated above platen
10
. Nozzles are provided on the surface of slider
11
facing platen
10
Jets of compressed air are directed through the nozzles by levitating means
12
to produce a levitating force.
A Y-axis motor
13
is mounted on slider
11
and teeth
132
are formed on Y-axis motor
13
at fixed spacings in the Y-axis direction. Y-axis motor produces magnetic attractive force between teeth
132
and teeth
101
of platen
10
to cause slider
11
to move in the Y-axis direction.
X-axis motors
14
and
15
are mounted on slider
11
to be symmetrically opposite to each other in relation to the center point of slider
11
. Teeth
141
and
151
are formed on X-axis motors
14
and
15
at fixed spacings in the X-axis direction. X-axis motors
14
and
15
provide magnetic attractive force between teeth
141
and
101
and between teeth
151
and
101
to cause slider
11
to move in the X-axis direction. Connecting members
111
and
112
connect X-axis motor
13
to both X-axis motors
14
and
15
.
An X-axis mirror
16
is attached to one side of platen
10
, and a mirror surface is formed in the Y-axis direction. A Y-axis mirror
17
is attached to another side adjacent to the side of platen
10
, and a mirror surface is formed in the X-axis direction.
A Y-axis position sensor
18
, which is mounted on Y-axis motor
13
, is a laser interferometer that emits light beams to imping Y-axis mirror
17
, receives catoptric light beams from Y-axis mirror
17
, and detects Y-axis position of slider
11
by means of optical interference.
X-axis position sensors
19
and
20
, which are mounted on the X-axis motors
14
and
15
, respectively, are laser interferometers that emit light beams to X-axis mirror
16
, receive catoptric light beams from X-axis mirror
16
, and detect X-axis position of slider
11
by means of optical interference.
A Y-axis controller
21
feedback controls the position of slider
11
according to the deviation of a Y-axis directive position from a position detected by Y-axis position sensor
18
.
X-axis controllers
22
and
23
feedback control the position of slider
11
according to deviations of X-axis directive positions from positions detected by X-axis position sensors
19
and
20
.
A rotational error may occur around an axis perpendicular to the X and Y axes of slider
11
. This phenomenon is referred to as yawing and the angle of rotational error, i.e. the yaw angle, is assumed to be &thgr;.
In the apparatus shown in
FIG. 1
, the X-axis and &thgr;-axis positions are controlled by supplying the same position command to X-axis controllers
22
and
23
. The state in which any yawing in slider
11
is eliminated is defined as &thgr;=0.
For light beams emitted by Y-axis position sensor
18
and X-axis position sensors
19
and
20
toward mirrors to be able to correctly return to their respective sensors, the yaw angle must be maintained at nearly zero, i.e. &thgr;=0. If the yaw angle &thgr; deflects the light in a large measure, the light beams emitted by Y-axis position sensor
18
and X-axis positions sensors
19
and
20
will fail to return to the sensors. Thus, the position of slider
11
will be unknown, and hence, the position and speed of slider
11
cannot be feedback controlled. Since the position sensors are optical sensors using laser interferometers, even a small rotational error of slider
11
can result in lack of control.
In the
FIG. 1
apparatus, it is difficult to adjust angle &thgr; to be close to 0 for the following reasons: First, it is not possible to separately set the control characteristics of the &thgr;-axis and X-axis directions. To be able to effect control and satisfy the angle &thgr;=0, the servomechanical rigidity of angle &thgr; may be increased. However, the servomechanical ridigity in the &thgr;-axis direction is uniquely fixed when the control methods and bandwidths of the X-axis controllers
22
and
23
are fixed. Second, control in the &thgr;-axis direction becomes difficult or impossible when acceleration in the X-axis direction is at its maximum.
The output torque T of slider
11
is represented by the following equation:
T=Fx
2
·
Lx
2
−
Fx
1
·
Lx
1
wherein, Fx
1
is the propulsion force of X-axis motor
14
; Fx
2
is the propulsion force of X-axis motor
15
; Lx
1
is the Y-axis distance from the center of gravity of slider
11
to the center point of X-axis motor
4
; and Lx
2
is the Y-axis distance from the center point of X-axis motor
15
to the center of gravity of slider
11
.
If the load on slider
11
is large and the value of an acceleration/deceleration command signal for the X-axis direction is also large, the propulsion force Fx
1
and Fx
2
of X-axis motor
14
and
15
are at a maximum. Assuming the maximum values of Fx
1
and Fx
2
are Fx
1
max and Fx
2
max, then the output torque T of slider
11
is
T=Fx
2
max·
Lx
2
−
Fx
1
max·
Lx
1
.
If Fx
1
max·Lx
1
≠Fx
2
max·Lx
2
holds true for reasons of manufacturing variations, for example, then angle &thgr; will also increase. Even when Fx
1
max·Lx
1
=Fx
2
max·Lx
2
is true, angle &thgr; will also increase and servo control becomes difficult if not impossible when a disturbing torque Td is applied.
As discussed, in the
FIG. 1
apparatus, propulsion force is consumed only for control in the X-axis-direction and no consideration is provided for consuming propulsion force for control in the &thgr;-axis direction. This approach results in an unbalanced maximum propulsion force being applied to the two X-axis motors, or angle of yaw &thgr; increasing when, for example, a disturbing torque interferes. Hence, servo control is difficult if not impossible.
SUMMARY OF THE INVENTION
Accordingly, an object of the invention is to overcome the aforementioned and other problems, disadvantages and deficiencies of the prior art.
The foregoing and other objects are attained by the invention which encompasses a two-dimensional positioning apparatus that provides for position control even when rotational errors occur in the slider of the apparatus by performing control separately in the X-axis and &thgr;-axis directions.
In other aspects of the invention, an interferometer is used with angular frequency being modulated according to amount of movement by an object and multiplied by a reference signal so that a high frequency signal is provided even when the slider is stopped or moved at a low speed; and a motor drive circuit is provided having a feedback control loop that employes a compensation for signals near a zero crossing point so that a deadband near the zero crossing is eliminated; and a return to origin slip plate having two slits arranged in the Y-axis and X-axis directions is provided to detect the position of the slider with the two sliders detecting an interference of laser light, so that a change in wavelength of the laser light, such as due to aging, is detected.
REFERENCES:
patent: 3715599 (1973-02-01), Marcy
patent: 5506684 (1996-04-01), Ota et al.
patent: 5633720 (1997-05-01), Takahashi
patent: 5638179 (1997-06-01), Masuyuki
patent: 5708505 (1998-01-01), Sogard et al.
patent: 6331885 (2001-12-01), Nishi
patent: 6414742 (2002-07-01), Korenaga et al.
patent: 63-242187 (1988-10-01), None
patent: 04-166718 (1992-06-01), None
patent: WO 99/16113 (1999-04-01), None
Hashida Shigeru
Jimbo Ryuichi
Kaiho Fumio
Kimura Atsufumi
Koizumi Yutaka
Kao Chih-Cheng Glen
Kim Robert H.
Kojima Moonray
Yokogawa Electric Corporation
LandOfFree
Two-dimensional positioning apparatus and method for... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Two-dimensional positioning apparatus and method for..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Two-dimensional positioning apparatus and method for... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3107899