Radiant energy – Photocells; circuits and apparatus – With circuit for evaluating a web – strand – strip – or sheet
Reexamination Certificate
2001-05-09
2002-10-01
Dang, Hung Xuan (Department: 2873)
Radiant energy
Photocells; circuits and apparatus
With circuit for evaluating a web, strand, strip, or sheet
C365S042000, C702S153000
Reexamination Certificate
active
06459092
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a six degree-of-freedom (DOF) motion measuring apparatus, and more particularly, to a swing arm type optical system using the 6-DOF measuring apparatus to measure the motion of a slider in a hard disk drive (HDD).
2. Description of the Related Art
The position and orientation of an object (rigid body) in 3-dimensional (3-D) space can be measured by a variety of methods. As one of the methods extensively used, the position of an object is expressed as position vector in an orthogonal coordinate system, and the orientation of the object is expressed using Euler angles. The Euler angles are angles of rotation of an object about x, y, and z axes of the reference coordinate system, are referred to as rolling, pitching, and yawing angles, and are denoted by &ggr;, &bgr;, and &agr;, respectively.
FIG. 1
illustrates the concept of 6-DOF motion and symbols used for describing the motion. As shown in
FIG. 1
, coordinate system O
w
is a reference coordinate system used to express motion of an object
1
. Coordinate systems O
w
, and O
s
are defined on object
1
. Coordinate system O
s
is fixed to and moves along with object
1
. Coordinate system O
w
, has the same orientation as reference coordinate system O
w
and the same origin as coordinate system O
s
. The position of object
1
in coordinate system O
s
, is expressed by position vector {right arrow over (t)}
w
=[t
x
t
y
t
z
]
T
. T
s
w
is a matrix having elements which include the parameters t
x
, t
y
, t
z
, &ggr;, &bgr;, and &agr;, as below, and T
s
w
defines the position and orientation of object
1
in coordinate system O
s
with respect to the reference coordinate system O
w
:
T
s
w
=
[
c
α
c
β
c
α
s
β
s
γ
-
s
α
c
γ
c
α
s
β
c
γ
+
s
α
s
γ
t
x
s
α
c
β
s
α
s
β
s
γ
+
c
α
c
γ
s
α
s
β
c
γ
-
c
α
s
γ
t
y
-
s
β
c
β
s
λ
c
β
c
γ
t
z
0
0
0
1
]
(
1
)
where c and s denote cosine and sine, respectively.
The coordinate system O
s
is fixed to object
1
, and the position and orientation of object
1
are expressed using T
s
w
. To calculate the values of the six elements t
x
, t
y
, t
z
, &ggr;, &bgr;, and &agr; is to measure the position and orientation of object
1
in 3-D space.
According to conventional methods used to measure the position and orientation of object
1
, multiple degree-of-freedom displacement is measured using sensors mounted on each axis of coordinate system.
FIG. 2
illustrates the concept of measuring the coordinates and orientation of an object in a 2-D plane using conventional capacitance-type proximity sensors. As shown in
FIG. 2
, signals from x
1
and y
1
proximity sensors
21
and
25
are used to measure displacement in x- and y-axial directions. An x
2
proximity sensor
23
is installed parallel to the x
1
proximity sensor
21
to measure the angle of rotation. However, to measure 6-DOF motion in 3-D space, two proximity sensors are required for each direction. Thus, to measure 6-DOF displacement using the conventional method, a plurality sensors are needed for each axis, which causes many difficulties in actual applications. Also, when such capacitance-type proximity sensors are used, the material of object
1
to be measured is limited to metal. In addition, installation of the sensors may be difficult depending on the shape of object
1
. A small space must be maintained between object
1
and the proximity sensors
21
,
23
, and
25
.
On the other hand, a Mikelson interferometer can be used as an apparatus for measuring 6-DOF motion of an object.
FIG. 3
illustrates the structure of a conventional Mikelson interferometer applied to measure one-dimensional displacement. As shown in
FIG. 3
, a laser source
30
, a beam splitter
32
, and a cube corner reflector
34
are fixed in position, and another cube corner reflector
36
is affixed to the surface of object
1
whose motion is to be measured, so that optical paths are formed, as shown in FIG.
3
. This complex configuration is for measuring one-dimensional displacement, and six such interferometers must be used to measure 6-DOF displacement. In addition to a configuration of six interferometers being significantly complicated, it is difficult to keep the optical path of each interferometer aligned for 6-DOF displacement.
FIG. 4
illustrates the concept of measuring 6-DOF motion of an object by conventional four position-sensitive detectors (PSDs). The 6-DOF displacement measuring system of
FIG. 4
, which is suggested in an article in
Optical Engineering,
Vol. 36, No. 8, pp. 2287-2293 (1997), includes four beam splitters
45
,
46
,
47
, and
48
, which are mounted on an object
1
whose motion is to be measured, four PSDs
41
,
42
,
43
, and
44
, and two lenses
49
a
and
49
b
. Transitions and rotations in three axial directions of the object
1
are measured by this system with a resolution of 0.05 &mgr;m and 0.25 &mgr;rad, respectively. The 6-DOF measuring system is advantageous in that 6-DOF transitional and rotational motions are simultaneously measured. However, the object
1
should be large enough such that four beam splitters
45
,
46
,
47
, and
48
can be mounted thereon, and the 6-DOF measuring system is unsuitable for measuring high-speed motion.
FIG. 5
illustrates the concept of measuring 6-DOF displacement using a conventional apparatus in which a photodetector assembly is affixed to an object whose position and orientation are to be measured. The 6-DOF displacement measuring apparatus of
FIG. 5
is disclosed in U.S. Pat. No. 5,884,239 by Romanik. As shown in
FIG. 5
, vertical and horizontal planar laser beams
56
are emitted from a scanner
56
. The vertical planar laser beam scans in the horizontal direction and the horizontal planar laser beam scans in the vertical direction, so that a particular area within which the position and orientation of an object is to be measured is scanned with the laser beams. Four photodetectors
51
,
52
,
53
, and
54
are given a particular 3-D arrangement defining a shape. As this photodetector assembly is scanned with the vertical and horizontal planar laser beams, each of the photodetectors
51
,
52
,
53
, and
54
irradiated with the laser beams detects the intensity of the laser beams. The photodetectors
51
,
52
,
53
, and
54
detect the laser beams in a particular order according to the shape, position, and orientation of the photodetector assembly. Since the shape of the photodetector assembly is constant, the position and orientation of the photodetector assembly can be measured by measuring the timing of detecting laser beams by each of the photodetectors
51
,
52
,
53
, and
54
. Based on this principle, the position and orientation of an object (not shown) can be measured by mounting such a photodetector assembly on the object. A single external photodetector
55
, which is not one of the four photodetectors
51
,
52
,
53
, and
54
which form the photodetector assembly, is used for synchronization between a scanning system and sensor signals.
To increase precision in the measurement of 6-DOF motion with the apparatus of
FIG. 5
, it i
Byun Yong-kyu
Cho Hyung-suck
Ko Kuk-won
Park Noh-yeol
Park Won-shik
Burns Doane , Swecker, Mathis LLP
Dang Hung Xuan
Korean Advanced Institute of Science & Technology
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