A linear motor-driven X-Y table includes a base and an intermediate saddle mounted on the base through linear bearings so as to be linearly reciprocatable in an X-axis direction. A table body is mounted on the intermediate saddle through linear bearings so as to be movable in a Y-axis direction perpendicular to the X-axis direction. A first linear motor is provided between the intermediate saddle and the base so as to be able to move the saddle linearly relative to the base, and a second linear motor is provided between the table body and the intermediate saddle so as to be able to move the table body linearly relative to the saddle.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to an X-Y table employing linear motors as 
its drive source. 
2. Description of the Prior Art 
A typical conventional X-Y table has heretofore been arranged such that a 
table body mounted on a base through an intermediate saddle can slide in 
both the X-and Y-axis directions, orthogonal to each other. The feed 
mechanism of the X-Y table has been constituted by a combination of ball 
screw and nut assemblies and rotary motors such as a servomotor or 
stepping motor (see the specification of Japanese patent application laid 
open to public inspection under No. 214015/1983). 
More specifically, a ball screw shaft is rotatably disposed on the upper 
side of the base so as to extend in an X-axis direction, and a ball nut, 
which is screwed onto the screw shaft, is secured to the intermediate 
saddle. A rotary motor is operably connected to one end of the ball screw 
shaft so that the intermediate saddle is fed in the X-axis direction along 
the ball screw shaft by the rotation of the motor. Similarly, a ball screw 
shaft is disposed on the upper side of the intermediate saddle so as to 
extend in the Y-axis direction perpendicular to the longitudinal axis of 
the first ball screw shaft, and a ball nut screwed onto the second ball 
screw shaft is secured to the lower side of the table body. A rotary motor 
is operably connected to one end of this ball screw shaft so that the 
table body is fed in the Y-axis direction relative to the intermediate 
saddle by the rotation of the corresponding motor. 
A feed apparatus has also been known in which, when a ball screw shaft is 
rotated, the associated ball nut is also rotated by a rotary motor 
relative to the ball screw shaft, thereby allowing the table body to be 
selectively moved in a large-feed mode in accordance with the sum of the 
movements of the ball screw shaft and the ball nut or in a fine-feed mode 
in accordance with the difference therebetween, respectively. 
In the last-mentioned conventional X-Y table, however, the feed of the 
table body in the X- and Y-axis directions is controlled by controlling 
the rotation of the respective rotary motors, and the table body, which is 
one of the movable members, is equipped with a motor, a ball screw shaft 
and the like and therefore has a relatively large inertia, so that the X-Y 
table has a poor response at the start and end of the feed operation, thus 
resulting in an unfavorably low degree of accuracy in the positioning of 
the table body. 
The employment of ball screw and nut assemblies involves the disadvantages 
that a ball screw shaft may be twisted by rotational torque, and that 
backlash may occur between a ball screw shaft and a ball nut, resulting in 
a poor response. This also makes it impossible to increase the degree of 
positioning accuracy. 
Furthermore, the above-described prior art commonly requires a relatively 
large space for mounting of the rotary motors and the ball screw and nut 
assemblies, resulting in an increase in the overall size of the X-Y table. 
Similarly, the prior art arrangement, which enables the X-Y table to be 
selectively fed in a fine-feed mode and a large-feed mode, needs a motor 
for rotating each ball nut and another motor for rotating each ball screw 
shaft, that is, it needs two motors for each of the feed operations in the 
X- and Y-axis directions. In consequence, the overall weight and hence 
inertia of the table body increases to reduce the positioning accuracy 
thereof as well as enlarge the overall size of the X-Y table. 
SUMMARY OF THE INVENTION 
In view of the above, it is a primary object of the present invention to 
increase the degree of accuracy in positioning the table body by reducing 
the weight of movable members such as the table body and its related 
parts, and thereby improve the response at the start and stop of feed 
operations. 
It is another object of the present invention to provide an X-Y table which 
has a reduced weight and is capable of being selectively fed in a 
fine-feed mode and a large-feed mode. 
To these ends, the present invention provides a linear motor-driven X-Y 
table comprising: a base; an intermediate saddle mounted on the base 
through linear bearings so as to be linearly reciprocatable in the X-axis 
direction; a table body mounted on the intermediate saddle through linear 
bearings so as to be movable in a direction perpendicular to the X-axis 
direction; a first linear motor provided between the intermediate saddle 
and the base for driving the saddle linearly relative to the base; and a 
second linear motor provided between the table body and the intermediate 
saddle for driving the table body linearly relative to the saddle. 
These and other objects, features, and advantages of the present invention 
will become apparent from the following description of the preferred 
embodiment thereof, taken in conjunction with the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
The present invention is described hereinunder by way of one embodiment 
thereof, with reference to the accompanying drawings. 
Referring first to FIGS. 1 to 6, which show a linear motor-driven X-Y table 
in accordance with one embodiment of the present invention, a table body 3 
is mounted on a base 1 through an intermediate saddle 2. 
Assuming that the longitudinal direction of the base 1 represents the 
X-axis and the direction which is parallel to the upper surface of the 
base 1 and perpendicular to the X-axis represents the Y-axis, a pair of 
parallel track rails 4 are disposed on the upper surface of the base 1 so 
as to extend in the X-axis direction. These track rails 4 are clamped by 
four linear bearings 5 which are mounted on the lower surface of the 
intermediate saddle 2, so that the saddle 2 can move in the axial 
direction of the track rails 4. Also mounted on the upper surface of the 
intermediate saddle 2 are another set of four linear bearings 5 which 
clamp track rails 6 disposed on the lower surface of the table body 3 
along the Y-axis direction, so that the table body 3 can move in the 
Y-axis direction relative to the base 1. 
Each of the linear bearings 5, as shown in FIG. 3A to 3C, comprises a 
bearing block 5c having two ball-rolling grooves 5a provided on one side 
thereof and two ball-recirculating holes 5b formed therein, a retainer 5d 
which retains two trains of loaded balls, and end plates 5e each providing 
communication between the ball-rolling grooves 5a and the corresponding 
ball-recirculating holes 5b so that balls 5f circulate through the 
ball-rolling grooves 5a and the corresponding ball-recirculating holes 5b. 
The angle of contact .alpha. between each ball-rolling groove 5a and the 
loaded balls 5f is set at about 45 degrees in this embodiment, but the 
angle .alpha. is not necessarily limited to about 45 degrees, and may be 
set within the range of 30 to 60 degrees. The clearance between the track 
rails 4,4 and each of its associated linear bearings 5 interposed between 
the base 1 and the intermediate saddle 2, and the clearance between the 
track rails 6,6 and each of its associated bearings 5 interposed between 
the saddle 2 and the table body 3 are adjusted by means of 
clearance-adjusting bolts 7. More specifically, tightening the bolts 7 
presses the corresponding bearings 5 at one side toward the corresponding 
track rails 4,6. At the same time, a counterforce to the pressure force 
applied by the clearance-adjusting bolts 7 acts on the linear bearings 5 
on the opposite side through the intermediate saddle 2 so as to press 
these bearings 5 toward the associated track rails 4,6 thereby preloading 
the balls 5f. 
Linear motors are interposed between the intermediate saddle 2 and the base 
1 and between the saddle 2 and the table body 3, respectively. In this 
embodiment, each of the linear motors is a linear pulse motor which is 
constituted by a combination of movable members 8 and a fixed member 9. 
The linear motor is actuated by inputting pulses to the movable members 8 
from a pulse generator (not shown). 
More specifically, first and second fixed members 9a and 9b, each 
constituted by a flat plate-like magnetic member, are disposed on the base 
1 so as to extend in the X-axis direction parallel to the track rails 4. 
On the other hand, two pairs of movable members 8 are mounted on the lower 
surface of the intermediate saddle 2 in such a manner as to face the first 
and second fixed members 9a and 9b, respectively. Each movable member 8 is 
constituted by a permanent magnet 8a and two magnetic cores facing each 
other across the magnet 8a. One of the magnetic cores is formed so as to 
have first and second magnetic poles 8b and 8c magnetized to N polarity by 
the magnet 8a, while the other core is formed so as to have third and 
fourth magnetic poles 8d and 8e magnetized to S polarity by the magnet 8a. 
Each of the first and second fixed members 9a and 9b is, as shown in FIG. 
6, provided with teeth 10 of a rectangular cross-section which extend in 
the Y-axis direction, the teeth 10 being spaced from each other at a 
constant pitch P over substantially the whole length of each fixed member. 
Each of the magnetic poles 8b, 8c, 8d, and 8e is also formed so as to have 
pole teeth at the same pitch as that of the first and second fixed members 
9a and 9b. 
First and second coils 11a and 11b are respectively wound around the first 
and second magnetic poles 8b and 8c on the N-pole side and are connected 
in series so that when current flows through the coils 11a and 11b, 
magnetic fluxes extending in opposite directions are produced. The first 
and second coils 11a and 11b are electrically connected to a pulse 
generator (not shown). Similarly, third and fourth coils 11c and 11d 
connected in series are respectively wound around the third and fourth 
magnetic poles 8d and 8e on the S-pole side, and are connected to the 
pulse generator. 
The following description is made under the assumption that the pole teeth 
of the second magnetic pole 8c are a 1/2 pitch out of phase from those of 
the first magnetic pole 8b, and the pole teeth of the fourth magnetic pole 
8e are also a 1/2 pitch out of phase from those of the third magnetic pole 
8d. In addition, the pole teeth of the third and fourth magnetic poles 8d 
and 8e on the S-pole side are a 1/2 pitch out of phase from those of the 
first and second magnetic poles 8b and 8c on the N-pole side, 
respectively, and the first and second fixed members 9a and 9b are an 1/8 
pitch out of phase from each other. 
The operational principle of the linear pulse motors in accordance with 
this embodiment will be described first. 
Referring to FIGS. 7A to 7D, which schematically show the operational 
principle of one of the linear pulse motors, pulses are input to the first 
and second coils 11a and 11b through terminals a, while pulses are input 
to the third and fourth coils 11c and 11d through terminals b. FIG. 7A 
shows the state wherein pulses are input to the terminals a in a direction 
such that the first magnetic pole 8b is excited (Mode (1)); FIG. 7B shows 
the state wherein pulses are input to the terminals b in a direction such 
that the fourth magnetic pole 8e is excited (Mode (2)); FIG. 7C shows the 
state wherein pulses are input to the terminals a in a direction such that 
the second magnetic pole 8c is excited (Mode (3)); and FIG. 7D shows the 
state wherein pulses are input to the terminals b in a direction such that 
the third magnetic pole 8d is excited (Mode (4)). 
Table 1 shows the magnetic force generation conditions of each magnetic 
pole in Modes (1) to (4). 
TABLE 1 
______________________________________ 
Stable 
Mode Magnetic force generation conditions 
position 
______________________________________ 
(1) First pole: 
flux from magnet 8a + 
First pole 
flux from coil 11a 
Second pole: 
flux from magnet 8a - 
flux from coil 11b = 0 
Third and magnetic forces balanced 
Fourth poles: 
by magnet 8a 
(2) First and magnetic forces balanced 
Fourth pole 
second poles: 
by magnet 8a 
Third pole: 
flux from magnet 8a - 
flux from coil 11c = 0 
Fourth pole: 
flux from magnet 8a + 
flux from coil 11d 
(3) First pole: 
flux from magnet 8a - 
Second pole 
flux from coil 11a = 0 
Second pole: 
flux from magnet 8a + 
flux from coil 11b 
Third and magnetic forces balanced 
Fourth poles: 
by magnet 8a 
(4) First and magnetic forces balanced 
Third pole 
second poles: 
by magnet 8a 
Third pole: 
flux from magnet 8a + 
flux from coil 11c 
Fourth pole: 
flux from magnet 8a - 
flux from coil 11d = 0 
______________________________________ 
As is clear from Table 1, in Mode (1), the first magnetic pole 8b on the 
N-pole side has the strongest magnetic force, so that the movable member 8 
is held in a stable state by the attraction force acting between the first 
magnetic pole 8b and the corresponding tooth of the fixed member 9. On the 
other hand, the third and fourth magnetic poles 8d and 8e on the S-pole 
side are each a 1/4 pitch out of phase from the corresponding teeth of the 
fixed member 9. In Mode (2), the magnetic force of the first magnetic pole 
8b produced by the coil 11a disappears, and the magnetic force of the 
fourth magnetic pole 8e on the S-pole side becomes the strongest instead, 
so that the movable member 8 moves in the direction in which the fourth 
magnetic pole 8e comes into phase with the corresponding tooth of the 
fixed member 9, thereby advancing the movable member 8 by a 1/4 pitch. At 
this time, the first and second magnetic poles 8b and 8c on the N-pole 
side are each a 1/4 pitch out of phase from the corresponding teeth of the 
fixed member 9. 
In Mode (3), the second magnetic pole 8c on the N-pole side has the 
strongest magnetic force, so that the movable member 8 advances by a 1/4 
pitch in the direction in which the second magnetic pole 8c comes into 
phase with the corresponding tooth of the fixed member 9. At this time, 
the third and fourth magnetic poles 8d and 8e on the S-pole side are each 
a 1/4 pitch out of phase from the corresponding teeth of the fixed member 
9. In Mode (4), the third magnetic pole 8d on the S-pole side has the 
strongest magnetic force, so that the movable member 8 advances by a 1/4 
pitch in the direction in which the third magnetic pole 8d comes into 
phase with the corresponding tooth of the fixed member 9. Thereafter, the 
operation mode returns to Mode (1) in which the first magnetic pole 8b on 
the N-pole side has the strongest magnetic force, so that the movable 
member 8 advances by a 1/4 pitch to reach the position shown in FIG. 7A. 
In this way, the movable member 8 is moved a 1/4 pitch per pulse by the 
sequential repetition of Modes (1) to (4). 
In this embodiment, each motor is constituted by a combination of one fixed 
member 9 and two movable members 8. However, the operational principle of 
this motor is similar to that of the motor described above, which is 
constituted by a combination of one fixed member and one movable member. 
Therefore, the motor in accordance with this embodiment moves by a 1/4 
pitch per pulse. The employment of two movable members for one fixed 
member doubles the propulsion force. 
Linear pulse motors are also provided between the intermediate saddle 2 and 
the table body 3 in the following manner. Third and fourth fixed members 
9c and 9d are disposed on the lower side of the table body 3 so as to 
extend in the Y-axis direction parallel to the track rails 6, and movable 
members 8 are mounted on the upper side of the intermediate saddle 2. Each 
of the movable members 8 has first and second magnetic poles 8b and 8c 
magnetized by a permanent magnet 8a so as to serve as N-poles, and third 
and fourth magnetic poles 8d and 8e magnetized by the magnet 8a so as to 
serve as S-poles, similar to the movable members 8 described above. First 
to fourth coils 11a to 11d are respectively wound around the first to 
fourth magnetic poles 8b to 8e. The first to fourth coils 11a to 11d are 
electrically connected to the pulse generator so that the table body 3 is 
moved in the Y-axis direction relative to the intermediate saddle 2 by 
means of pulses supplied from the pulse generator. 
It must be noted that the reference numeral 13 in FIG. 6B denotes a bobbin. 
The following is a description of the operation of the linear motor-driven 
X-Y table in accordance with this embodiment. 
First, to feed the table body 3 in the X-axis direction in a large-feed 
mode, pulses are selectively input from the pulse generator to the movable 
members 8 which face either the first or second fixed member 9a or 9b 
disposed on the base 1, thereby driving the table body 3 by a combination 
of the selected fixed member and the associated movable members. In this 
case, the energized movable members move relative to the associated fixed 
member by a 1/4 pitch per pulse, so that the table body 3 is fed in the 
X-axis direction by a 1/4 pitch per pulse through the intermediate saddle 
2 equipped with the movable member 8. 
To feed the table body 3 in the X-axis direction in fine-feed mode, pulses 
are alternately input to the movable members 8 facing the first fixed 
member 9a and those facing the second fixed member 9b. In this case, the 
table body 3 moves by a 1/4 pitch per pulse for each of the first and 
second fixed members 9a and 9b. However, since the teeth of the first 
fixed member 9a and those of the second fixed member 9b are an 1/8 pitch 
out of phase from each other, the table body 3 is finely fed in the X-axis 
direction by an 1/8 pitch per pulse by alternately inputting pulses to the 
two pairs of coils of the movable members in the manner described above. 
Thus, it is possible to obtain a resolution half as large as that obtained 
when one fixed member is used. 
The feed of the table body 3 in the Y-axis direction is carried out by the 
linear motors provided between the table body 3 and the intermediate 
saddle 2 in a manner similar to that of the feed in the X-axis direction. 
It is similarly possible to select a large-feed mode of a 1/4 pitch or a 
fine-feed mode of an 1/8 pitch by inputting pulses to a pair of movable 
members 8 facing either one of the third and fourth fixed members 9c and 
9d, or by alternately inputting pulses to two pairs of movable members 8 
facing the two fixed members 9c and 9d, respectively. 
It must be noted that the rate of feed of the table body 3 is increased by 
raising the frequency of the pulses and decreased by lowering the 
frequency. The distance by which the table body 3 is fed is adjusted by 
varying the number of input pulses. 
Even when a load is imposed on the table body 3, no play or chatter is 
produced between the table body 3 and the intermediate saddle 2, or 
between the saddle 2 and the base 1, since the linear bearings 5 are 
appropriately preloaded. In addition, since the angle of contact between 
each ball-rolling groove 5a and the loaded balls 5f is set at about 45 
degrees, it is possible for the bearings 5 to uniformly bear any load 
applied thereto vertically and/or horizontally, so that the clearance 
between the movable and fixed members of each linear motor is kept at a 
constant value, and the propulsion force is thereby maintained at a 
constant level at all times. Even when a load is imposed on the table body 
3, there is no interference between the movable and fixed members. 
Accordingly, the clearances between the movable and fixed members can be 
minimized, so that it is possible to obtain a large propulsion force and a 
large force for stopping the movable table 3 and retaining it in a stopped 
state. 
It must be noted that, although two parallel fixed members are employed for 
each linear motor in this embodiment, three or more parallel fixed members 
may be used. If there are three parallel fixed members, they need only be 
out of phase from one another by 1/3 of a 1/4 pitch, that is, by a 1/12 
pitch; and if there are four parallel fixed members, it is only necessary 
for them to be out of phase from one another by 1/4 of a 1/4 pitch, that 
is, by a 1/16 pitch. This can provide a three-fold or four-fold 
resolution. 
Although this embodiment employs a linear pulse motor in which each movable 
member moves by a 1/4 pitch of the teeth of the corresponding fixed member 
per pulse, this type of motor is not necessarily limitative, and any type 
of linear pulse motor may be employed, provided that each movable member 
of the motor employed moves by a predetermined amount per pulse. In 
addition, linear pulse motors are not necessarily exclusive; other types 
of motor may be employed, such as linear DC motors or linear synchronous 
motors. 
The linear motor-driven X-Y table according to the present invention, which 
features the arrangement and operation described above, offers the 
following various advantages. The employment of linear bearings enables 
the table body to move smoothly, and the employment of linear motors 
eliminates the need to use ball and nut assemblies or the like, resulting 
in a reduction in the overall weight of the apparatus. In consequence, 
inertia is reduced to improve response at the start and stop of the feed 
of the table body, and hence increase the degree of accuracy in 
positioning the same. 
Since the present invention is free from problems such as twisting of ball 
screw shafts and backlash between each ball screw shaft and its ball nut, 
which are experienced in the prior art, the positioning accuracy is 
further improved. 
Since there is no need to provide space for rotary motors or the like, it 
is possible to obtain an X-Y table which is slim and compact, and thus has 
improved general-purpose properties. 
Moreover, since the number of parts required can be reduced, it is possible 
to reduce the production costs and increase the degree of accuracy in the 
assembly of the apparatus. In addition, the simplification of the 
structure of the apparatus makes it possible to prevent the occurrence of 
failures. 
By alternately inputting pulses to movable members facing corresponding 
fixed members, it is possible to feed the table body by an amount per 
pulse which is smaller than that obtained by employing a single fixed 
member. Accordingly, the table body can be selectively fed in fine-feed 
mode or large-feed mode as required; and it is possible to position the 
table body with an extremely high accuracy. 
If the angle of contact between the loaded balls and each ball-rolling 
groove of each of the linear bearings is set at about 45 degrees, any load 
applied to the bearings vertically or horizontally can be born 
substantially uniformly. Also, the clearance between the movable and fixed 
members of each linear motor can be thus maintained at a constant and 
limited value irrespective of loads applied to the table body in any 
direction so that the magnetic forces between the movable and fixed 
members, being in inverse proportion to the square of the distance between 
the movable and fixed members, may increase greatly. It is therefore 
possible for the linear motor to provide an increased propulsion force and 
force for stopping the table body and retaining the same in a stopped 
state, which further increases the degree of accuracy in the positioning 
of the table body. 
Although the present invention has been described in specific terms, it 
must be noted here that the described embodiment is not exclusive, and 
various changes and modifications may be imparted thereto without 
departing from the scope of the invention which is limited solely by the 
appended claims.