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Description  |
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FIELD OF THE INVENTION
This invention relates to a table device, and more particularly to a table
device suitable for driving tables in two right-angled directions.
BACKGROUND OF THE INVENTION
A table device was proposed some years ago, which is adapted to move a
table, on which a material to be processed or measured is placed, in two
directions which cross each other at right angles, so as to position such
a material accurately in a machining tool or a measuring apparatus. The
driving means for this table device include a driving means disclosed in
Japanese Patent Laid-open No. 18711/1983 dated Feb. 3, 1983 and entitled
"XY table", which driving means consists of a linear motor connected to a
table via a joint; and a driving means disclosed in "These Published in
the Spring Science Lecture Meeting Held by the Learned Circle of Precision
Machines in 1982" published on Mar. 22, 1982, pages 207-209, "Finely
Positioning Mechanism for Static Pressure Air-Floated Stages", which
consists of cross guides extending at right angles to each other and
connected to a table, and a linear motor operated on the cross guides.
In the former table driving means, the driving force of a linear motor is
transmitted to a table through a joint having backlash. Therefore, the
transmission of the driving force is delayed due to the backlash of the
joint. In the latter table driving means, the driving force of a linear
motor is applied to the cross guide which is positioned away from a table.
Accordingly, when a material to be processed is placed on the table or on
an eccentric portion thereof, the cross guide yaws, so that it takes time
to stabilize the cross guide. As may be clear from the above, these two
table driving means require a long settling time in which the table is set
in a predetermined position. Hence, it is very difficult to attain the
speedup of a positioning operation by these table driving means.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a table device which is
capable of reducing the settling time for positioning a material to be
processed.
To achieve this object, the present invention provides a table device
having a first table provided on a fixed base so that the first table can
be moved in one of two directions which cross each other at right angles,
and a second table provided on the first table so that the second table
can be moved in the other direction, characterized in that linear motors
for directly driving these tables are provided between the fixed base and
first table and between the fixed base and second table.
According to the present invention, each table can be driven directly by
the relative linear motor, so that the settling time for setting each
table in a predetermined position can be reduced. This enables the
efficiency of an operation using this table device to be improved.
BRIEF DESCRIPTION OF THE DRAWINGS:
FIG. 1 is a perspective view of an embodiment of the table device according
to the present invention;
FIG. 2 is a horizontal section of a linear motor used for the table device
of FIG. 1;
FIG. 3 is a sectional view taken along the line III--III in FIG. 2;
FIG. 4 is a sectional view taken along the line IV--IV in FIG. 2;
FIG. 5 is a front elevation of a position detector used for the table
device of FIG. 1;
FIG. 6 is a perspective view of another embodiment of the table device
according to the present invention; and
FIG. 7 is a plan view of another example of the linear motor used in the
present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to FIG. 1, reference numeral 1 denotes a fixed base, 2 a lower
table provided on the fixed base 1 so that the lower table 2 can be moved
in one (Y-direction) of two directions crossing each other at right
angles, and 3 an upper table provided on the lower table 2 so that the
upper table 3 can be moved in the other direction (X-direction). The fixed
base 1 is provided with two guide portions 4 extending in Y-direction.
These guide portions 4 are provided on their upper and inner side surfaces
4A, 4B with ball-and-roller bearings 5A, 5B. The lower portions of the
lower table 2 which are opposed to the upper and inner side surfaces 4A,
4B, in which the ball-and-roller bearings 5A, 5B are provided, of the
guide portions 4 are provided with guide surfaces 6A, 6B which are guided
by these bearings 5A, 5B. The lower table 2 is provided on its upper
surface with two guide portions 7 similar to the guide portions 4 on the
fixed base 1 and extending in X-direction. The guide portions 7 are
provided on their upper and inner side surfaces 7A, 7B with
ball-and-roller bearings 8A, 8B. The lower portions of the upper table 3
which are opposed to the guide portions 7 are provided with guide surfaces
9A, 9B which are guided by these ball-and-roller bearings 8A, 8B. The
linear motors 10, 11 and position detectors 12, 13 are provided between
the fixed base 1 and lower table 2 and between the lower table 2 and upper
table 3. The linear motors 10, 11 and position detectors 12, 13 have the
same construction, respectively. The linear motor 11 is constructed so
that a fixed portion 11A thereof is set firmly on the lower table 2 so as
to extend in X-direction with a movable portion (movable coil portion) 11B
fixed to the central portion of the lower surface of the upper table 3.
The position detector 13 is provided in parallel with the fixed and
movable portions 11A, 11B of the linear motor 11.
The construction of a control system for the table device will now be
described. Reference numeral 14 denotes a Y-direction object position
setter for the lower table 2, 15 a comparator for determining a difference
between an object value from the setter 14 and a detected value from the
position detector 12, 16 an amplifier adapted to amplify a difference
signal from the comparator 15 and supply the signal to the movable portion
11B of the linear motor 11, 17 an X-direction object position setter for
the upper table 3, 18 a comparator for determining a difference between an
object value from the setter 17 and a detected value from the position
detector 12, and 19 an amplifier adapted to amplify a difference signal
from the comparator 18 and supply the signal to the movable portion of the
linear motor 10.
Referring to FIGS. 2-4, the reference numerals which are the same as those
in FIG. 1 denote the same parts.
An outer yoke 102' is attached to the upper surface of each of the fixed
base 1 and lower table 2, and outer yokes 102 on both end portions of the
outer yoke 102' so that the outer yokes 102 extend in parallel with each
other and at right angles to the outer yoke 102'. The outer yokes 102 are
provided on their inner side surfaces with permanent magnets 104 in an
opposed state.
A movable portion of each of the linear motors 10, 11 consists of a coil
106 wound around a hollow body 111 of a coil bobbin having a flange
portion 105. A center yoke 101 is passed through the central portion of
the coil bobbin 111 via a clearance 108. At both end portions of the outer
yokes 102, side yokes 103 are provided so as to extend at right angles to
the center yoke 101 and outer yokes 102, the side yokes 103 being fixed at
their bottom surfaces to the upper surface of each of the fixed base 1 and
lower table 2. The upper end portion 109 of the coil 106 is attached to
the lower surface of each of the lower and upper tables 2, 3 via a
mounting portion 110.
Each of the position detectors 12, 13 consists of a member 121 secured to
each of the fixed base 1 and lower table 2 and having a slit 120, a
sensor-mounting frame 122 fixed to each of the lower and upper tables 2, 3
and a light-emitting element 123 and a light-receiving element 124
provided on the frame 122. The member 121 consists, for example, of glass,
and the slit 120 a plurality of evaporation films of chromium provided on
the member 121 so that these films extend in the direction of advancement
of the linear motor and at right angles to the upper surface of each of
the fixed base 1 and lower table 2. The light from the light-emitting
element 123 is sent to the light-receiving element 124 through a
transparent portion of the member 121.
When voltage signals, which correspond to object values in Y- and
X-directions of the tables 2, 3, are outputted from the object position
setters 14, 17, they are compared in the comparators 15, 18 with voltage
signals of positions from the position detectors 12, 13 to determine the
differences therebetween. The signals representative of these differences
are converted into electric currents and amplified by the amplifiers 16,
19 to be supplied to the coils 106 of the linear motors 10, 11.
Consequently, a magnetic circuit is formed between the center yoke 101,
outer yokes 102, permanent magnets 104 and coil 106, so that the force for
driving the lower and upper tables 2, 3 in the Y- and X-directions is
generated in the coils 106. As a result, the lower and upper tables 2, 3
are moved in the mentioned directions by object distances. During the
movement of the lower and upper tables 2, 3, they are driven directly by
the coils 106 of the linear motors 10, 11 provided in the central portions
thereof. Accordingly, the tables 2, 3 can be set to their object positions
with an accuracy of .+-.0.04 .mu.m in a short period of time, and settled
therein with an accuracy of 0.3 sec/15 mm step in a short period of time.
This enables, for example, the cycle of an operation for processing a
material placed on a table to be shortened, and the operation efficiency
to be improved. According to this embodiment, the linear motors 10, 11 can
be provided between the fixed base 1 and lower table 2 and between the
lower and upper tables 2, 3. Therefore, the linear motor-installing spaces
can be minimized, and a large space-saving effect can be obtained.
Referring to FIG. 6, the reference numerals which are the same as those in
FIG. 1 denote the same or equivalent parts. In the embodiment of FIG. 6,
the number of coils 106 of linear motors 10, 11 is increased in Y- and
X-directions so as to increase the table-driving force. If the table
device is constructed in this manner, the same effect as in the
previously-described embodiment can be obtained in addition to the driving
force-increasing effect.
The construction of each of the linear motors 10, 11 may be other than that
described previously, i.e., it may be as shown in FIG. 7, which shows a
linear motor having permanent magnets 107 provided in a spaced manner on a
center yoke 101. If the linear motors are constructed in this manner, the
leakage magnetic flux can be reduced, and the table-driving force can
further be increased. Moreover, a ratio of the length of coil generating
thrust by the magnetic force to a total length of coil increases, and the
motor can be miniaturized. Also, the energy loss can be minimized, and the
useless generation of heat can be suppressed.
The guide means for the tables 2, 3 are not limited to ball-and-roller
bearings; plain bearings and static pressure bearings can also be used.
The position detector used in this invention may also consist of a Hall
device and a laser measuring instrument.
As is clear from FIGS. 4 and 7, a plurality of permanent magnets attached
to the inner side surfaces of the outer yokes or center yoke are arranged
so that the adjacent poles have different polarities.
According to the present invention, the force-transmitting member used in a
known table device can be omitted, so that the settling time for
positioning a table can be reduced. The present invention also enables the
efficiency of an operation using the table device according to the present
invention to be improved.
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