Electrical generator or motor structure – Dynamoelectric – Linear
Reexamination Certificate
1999-09-10
2001-10-23
Ramirez, Nestor (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Linear
C318S135000
Reexamination Certificate
active
06307284
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an ultra-precision positioning technique and, more particularly, to a high-speed, high-precision positioning apparatus which is required to have, for example, a positioning resolution on the submicron order or less. The present invention also relates to an information recording/reproducing apparatus and inspection apparatus which are used in the semiconductor manufacturing industry and the fields associated with the manufacture of high-density recording media such as hard disks and information write/read operation.
2. Related Background Art
FIG. 8
shows a conventional direct-acting positioning apparatus.
An object (not shown) is mounted on a table
521
. The table
521
can move in the X direction. A gravity guide
523
supports the table
521
on a horizontal X-Y reference surface in the gravity direction (Z direction). A yaw guide
522
has an X-Z guide surface perpendicular to the X-Y reference surface of the gravity guide
523
and parallel to the moving direction of the table
521
, and supports the table
521
in the Y direction. That is, the table
521
is moved in the X direction by “two-surface restraint guiding” by means of the gravity guide
523
and yaw guide
522
.
A feed screw driving unit
524
drives the table
521
in the X direction in a noncontact state by converting the rotating motion transferred from a motor into a translating motion. The feed screw driving unit
524
has a motor and feed screw which are substantially integrated with the gravity guide
523
, and a nut (not shown) integrated with the table
521
to convert a rotating motion into a translating motion.
An optical encoder
525
measures the position of the table
521
in the X direction. A head is fixed on the yaw guide
522
. The encoder
525
measures the position of the table
521
in the X direction at a position near the yaw guide
522
. The driving amount of the feed screw driving unit
524
is feedback-controlled by using the position information about the table
521
which is measured by the encoder
525
, thereby positioning the table
521
.
FIG. 9
shows a model indicating a positional relationship when the conventional stage unit is viewed from the Z direction.
The table
521
has a barycentric position
531
. At a yawing restraining position
532
, the table
521
is supported by the guide surface of the yaw guide
522
to be restrained in the yawing direction. At a driving position
534
, the table
521
is driven by a thrust F from the feed screw driving unit
524
. At a measuring position
535
, the encoder
525
measures the position of the table
521
.
As shown in
FIG. 9
, the driving position
534
of the thrust F from the feed screw driving unit
524
is set to pass through the barycentric position
531
of the table
521
.
In addition, as shown in
FIG. 9
, the measuring position
535
at which the position of the table
521
is measured is relatively near the yawing restraining position
532
. By setting the measuring position
535
near the yawing restraining position
532
, even if the table
521
undergoes posture variations in the yawing direction, a disturbance due to the yawing posture variations is prevented from affecting measurement of the position of the table
521
in the translating direction.
In a positioning apparatus for driving a motor by feeding back the position of a table, the transfer function of a system has a great influence on the positioning time and the stability of a feedback system. When, for example, the gain of a feedback loop compensator is increased, hunting occurs in the worst case. If the gain is set low to improve the stability of the system, a necessary steady-state precision cannot be ensured. In addition, if a rotation/translation conversion element such as a feed screw driving unit is inserted in the system, nonlinearity such as hysteresis or lost motion occurs. As a result, a phase delay occurs in the transfer function, and the responsivity deteriorates.
SUMMARY OF THE INVENTION
In general, the productivity of machine tools and inspection devices using such direct-acting positioning apparatuses increases as the positioning performance of the direct-acting positioning apparatuses improves. A direct-acting positioning apparatus is therefore required to have high-speed, high-precision table positioning performance.
It is an object of the present invention to realize a positioning apparatus having a control system with high responsivity at a low cost.
In order to achieve the above object, a positioning apparatus of the present invention is characterized by comprising a movable member which can move, an actuator for driving the movable member in a moving direction, a first guide having a reference surface for supporting the movable member in a gravity direction, a second guide for guiding the movable member from one side thereof in the moving direction by means of a guide surface perpendicular to the reference surface, and a measuring device for measuring a position of the movable member in the moving direction, wherein a distance from a measuring position at which the measuring device measures the position of the movable member to the guide surface is longer than a distance from a driving position at which the actuator drives the movable member to the guide surface.
In addition, in order to achieve the above object, another positioning apparatus of the present invention is characterized by comprising a movable member which can move, an actuator for driving the movable member in a moving direction, a first guide having a reference surface for supporting the movable member in a gravity direction, a second guide for guiding the movable member from one side thereof in the moving direction by means of a guide surface perpendicular to the reference surface, and a measuring device for measuring a position of the movable member in the moving direction, wherein a distance from a driving position at which the actuator drives the movable member to the guide surface is shorter than a distance from the center of gravity of the movable member to the guide surface.
The movable member is preferably supported to the guides by static pressure bearings.
Preferably, this apparatus further comprises a pre-pressurizing mechanism for pre-pressurizing the static pressure bearings, and the pre-pressurizing mechanism comprises a magnet.
The actuator preferably comprises a linear motor.
The actuator for driving the movable member in the moving direction is preferably one in number.
The measuring device preferably comprises an encoder.
The measuring device is preferably one in number.
Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof.
REFERENCES:
patent: 4579320 (1986-04-01), Gladish
patent: 4616960 (1986-10-01), Gladish
patent: 5228358 (1993-07-01), Sakino et al.
patent: 5917294 (1999-06-01), Mitarai
patent: 2329521A (1999-03-01), None
Hisamoto Kenji
Mitarai Reiji
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Jones Judson H.
Ramirez Nestor
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