Electricity: motive power systems – Positional servo systems – Adaptive or optimizing systems including 'bang-bang' servos
Reexamination Certificate
2000-08-09
2002-12-03
Nappi, Robert E. (Department: 2837)
Electricity: motive power systems
Positional servo systems
Adaptive or optimizing systems including 'bang-bang' servos
C318S562000, C318S563000, C318S564000, C318S565000, C318S566000, C318S568100, C318S568110, C318S568120, C318S568130, C318S568140, C318S568150, C318S568160, C318S568170, C318S568200, C318S568210
Reexamination Certificate
active
06489741
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to substrate handling robots.
2. Description of Related Art
In the semiconductor and other industries, robots are called upon to perform a variety of tasks requiring high repeatability and precision. For example, in semiconductor wafer processing, cassettes containing a plurality of semiconductor wafers are loaded and unloaded into a micro-environment in which the wafers are to undergo processing. The loading and unloading functions involve automated motions performed by a robot, also serving to variously transport the wafers between different processing stations in the micro-environment. Such a robot is disclosed in co-pending U.S. patent application Ser. No. 09/079,850, entitled “Robot Having Multiple Degrees of Freedom”, incorporated herein by reference in its entirety.
The robot in the aforementioned patent application is of the type known as a Global Positioning Robot (GPR) and, as seen in
FIG. 1
, comprises a base unit
12
having one or more telescoping platforms
14
atop of which is mounted a robot arm
16
with an end effector
18
for handling the substrates. The telescoping motion constitutes motion in the Z axis, with the robot further adapted to tilt about the Z axis. Tilting is effected by independently actuating Z motion along means such as motors (not shown). Other tilting mechanisms are also known and may be used to effect the tilting along the Z axis.
The robot arm
16
is additionally capable of motion in a plane defined by R and &thgr; coordinates in a conventional cylindrical coordinate system such that the end effector
18
can move anywhere about a predetermined region in the plane, taking a variety of possible paths including both linear and non-linear paths. This motion is effected using appropriate actuation means such as motors and associated belt-pulley linkages (not shown) as described in the aforementioned patent application. Other motions include yaw and roll motion of the end effector
18
, permitting the robot to achieve six or more degrees of freedom and possibly kinematic redundancy. The actuation means are controlled using a suitable control means such as a microprocessor adapted to issue the appropriate commands to achieve the desired motion trajectories.
The amount of precision which can be realized in robotic applications is dependent upon various factors and is limited by for example the geometry and stiffness of the moving components such as the robot arm. The weight of the substrate being manipulated by the robot also imparts certain deflections on the system, and with the advance of the semiconductor and LCD technology fields requiring the handling of larger and larger substrates, this factor becomes increasingly significant. As the substrate is transported between different positions by the robot, deviations from the intended path inevitably occur, compromising the accuracy of the system and imposing undesirable constraints, such as for example the need to increase spacing between the wafers in a cassette in order to accommodate expected deviations. Problems can thus arise due to inaccuracies or deflection of the robot arm, deflection of the end effector of the robot arm or of the manipulated substrate, or to misalignment of the substrate and/or cassette.
To better explain the problems encountered, an ideal situation will first be discussed.
FIG. 2A
shows the ideal case in which the substrate, in this case a semiconductor wafer
24
having a substantially planar shape and an object axis P lying in its primary plane, is centered within its designated slot
28
in cassette
22
. The orientation of the wafer
24
and the orientation of the slot
28
are identical. The robot arm (not shown) is assumed to be perfectly manufactured and therefore the wafer
24
remains in the same plane during its transport to and from slot
28
. Since the plane of motion of wafer
24
, depicted in
FIG. 2B
, is coincident with the plane of the wafer itself (and more particularly with the object axis P) and the plane of the slot
28
, no obstructions in the travel path are encountered and motion of the wafer
24
between the approach position and the pickup position is unhampered. For clarity, the approach position is defined with respect to the cassette and is to be understood as the position at which the end effector and/or end effector-wafer combination approach or retract from the cassette, while the pickup position is defined with respect to the wafer itself and is the position at which the end effector is just about to engage or disengage from the wafer.
In a first non-ideal situation encountered in practice and depicted in
FIG. 3A
, the orientation of the wafer
24
is different from that of slot
28
which it occupies, with object axis P being transverse to the axis of the slot
28
. Since the wafer
24
cannot be withdrawn from the cassette
22
in this transverse position, either the cassette
22
must be rotated while the orientation of the wafer
24
is maintained until parallelism of the two is achieved (FIG.
3
B), or the robot itself must be rotated while supporting wafer
24
(FIG.
3
C). The rotation of the cassette is a disruptive intervention which must be performed manually and detracts from system throughput and efficiency, while rotation of the wafer-end effector combination can only be performed using GPR-type robots.
A worse situation, depicted in
FIGS. 4A and 4B
, occurs when the wafer
24
, initially properly aligned within slot
28
(FIG.
4
A), changes its orientation and vertical position during motion due to for example geometric inaccuracies of the arm. Equally undesirable is for the wafer
24
to approach the slot
28
in the displaced orientation and vertical position during the reverse, insertion process into the cassette
22
. A manifestation of this is the tilt of object axis P with respect to the direction of motion a such that the orientation of wafer
24
is transverse to the direction of motion a.
FIGS. 6A-6C
show the motion of a semiconductor wafer
24
during retraction from a slot
28
of a misaligned cassette
22
. As can be seen from the drawing figure, because the direction of motion of wafer
24
is not coincident with object axis P of wafer
24
, an object shadow
29
is created which the wafer
24
, over the course of the transport duration, necessarily occupies. This object shadow
29
exceeds the slot width shown in
FIGS. 6A and 6B
and imposes the requirement of an expanded width on slot
28
as shown in
FIG. 6C
in order to permit unobstructed retraction or insertion of the wafer
24
into the cassette
22
. Accordingly, wafer pitch and cassette capacity are reduced.
Conventional non-GPR robots cannot obviate this situation because they are unable to change the orientation of the end effector about its longitudinal axis and because they lack adequate algorithmic resources to implement the necessary combination of motions. GPR robots, on the other hand, can compensate for the undesirable deviations because these robots can for example be tilted along the Z axis, as shown in FIG.
5
.
FIG. 5
schematically shows two positions of a wafer-carrying GPR robot: compensated position
30
and uncompensated position
30
′. The compensation in this case is effected in order to maintain a horizontal position of the wafer
24
, although other positions can of course also be achieved. As can be seen, in the uncompensated position
30
′, with the arm
16
′ extended, the position of the end effector
18
′ and the wafer
24
′ deviate from the horizontal, exhibiting a sag due to for example the weight of wafer
24
′, arm
16
′ and end effector
18
′, and to the geometry and stiffness of arm
16
′ and end effector
18
′. In order to compensate for this deviation, platform
14
is tilted a predetermined angle &agr; and lowered an amount dZ while arm
16
is extended by a predetermined amount. The resultant tilt re-aligns wafer
24
to a horizontal orientation.
Because the above sit
Bonev Eugene
Genov Genco
Genov Mila
Sotirov Zlatko M.
Genmark Automation, Inc.
Genov Mila
Krebs Robert E.
Nappi Robert E.
Smith Tyrone
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