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Description  |
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FIELD OF THE INVENTION
The present invention relates to laminated ferromagnetic structures, and
more particularly to such structures for use in conjunction with linear
motors in which the structures are laminated in mutually perpendicular
directions to reduce eddy currents in both of said directions.
BACKGROUND OF THE INVENTION
Laminated stators have been used for decades to improve the performance of
electromagnetic devices such as motors. The elimination or significant
reduction of eddy currents through the use of insulating laminations
yields significant performance gained in devices having such laminated
designs. One-dimensional linear motors are becoming more popular as a
drive source for machinery requiring linear motion. The linear motors are
typically provided with laminated stators to improve performance. A
special class of linear motors permits motion in two orthogonal directions
across a planar stator (i.e. platen). Systems of this type have not been
designed with laminated platens because of the difficulties in eliminating
eddy currents while maintain flux paths in two orthogonal directions.
BRIEF DESCRIPTION OF THE INVENTION
The present invention provides a novel laminated platen design and method
for manufacture, which design is based on the merging of two laminants
into a single platen and which provides flux paths in two orthogonal
directions while eliminating eddy current circulation.
The present invention includes a substrate laminate comprised of
ferromagnetic and insulator plates arranged in alternating fashion. The
major surface thereof is machined to provide elongated slots which extend
in the direction perpendicular to the planes of the plates making up the
substrate laminate. Each of said elongated channels is fitted with a
transverse laminate comprised of alternating ferromagnetic and insulator
plates preferably arranged so that the outside plates are both insulator
plates. The transverse laminations are preferably expoxied into position.
The working surface is then machined to form a grid-like pattern of
grooves which is filled with a suitable insulating material to provide a
smooth operating surface. The grid-like pattern cooperates with
electromagnets in the linear motor to effect movement of the linear motor
in mutually perpendicular directions along the working surface. The size
and spacing of the grooves in the grid-like pattern determine the
resolution of linear motor movement.
A method is disclosed for producing the laminated platen in which the
insulator plates determine the spacing between adjacent ferromagnetic
plates. Each insulator plate is preferably provided with a plurality of
openings having at least one dimension extending beyond the width of the
adjacent ferromagnetic plates to assure that sufficient adhesive has been
introduced into said openings by means of an elongated hollow tube for
dispensing adhesive into each opening in a sequential fashion.
The transverse laminations are preferably cut from the initially produced
substrate laminate to conserve both material costs and fabrication costs.
OBJECTS OF THE INVENTION AND BRIEF DESCRIPTION OF THE FIGURES
It is therefore one object of the present invention to provide a novel
laminated platen for use with linear motors and the like and having
laminations in mutually perpendicular directions.
Another object of the present invention is to provide a novel method for
forming a laminated structure having mutually perpendicular laminations
for reducing eddy currents in said mutually perpendicular directions.
Still another object of the present inventin is to provide a novel method
for producing laminated platens for use with linear motors and the like in
which insulator members interspersed with ferromagnetic members have
openings therein filled in a sequential fashion with a suitable adhesive
for adhering the plates making up the laminate to one another and to
assure adequate introduction of suitable adhesive material while
preventing the adhesive material from affecting the spacing of the plates
making up the lamination.
Still another object of the present invention is to provide a novel method
for producing a platen for use with linear motors, said platen having
laminations in mutually perpendicular directions wherein the laminations
are joined by introducing adhesive into sequential openings provided in
insulator plates making up the laminate structure by means of elongated
hollow tubular members, the openings in said insulator plates having at
least one dimension which is greater than the width of adjacent
ferromagnetic plates to permit the release of air captured in the openings
and thereby assure that the openings are completely filled with adhesive
while preventing the adhesive from altering the spacing between
ferromagnetic plates.
The above, as well as other objects of the present invention, will become
apparent when reading the accompanying description and drawing in which:
FIG. 1 is a perspective view showing a laminated platen structure designed
in accordance with the principles of the present invention.
FIG. 2 shows an exploded perspective view of the elements utilized to
produce the substrate laminate.
FIG. 2a is a perspective view showing one end of the tubular adhesive
injector member of FIG. 2 shown in greater detail.
FIG. 2b is a perspective view showing a portion of the laminate structure
of FIG. 2 in the assembled condition to facilitate an understanding of the
assembly steps.
FIG. 3 is an enlarged perspective view showing a portion of the laminated
structure of FIG. 1 and which is useful in providing a better
understanding of the invention.
DETAILED DESCRIPTION OF THE INVENTION
Before going into a detailed description of the present invention, a brief
description of the manner of use of the device and a statement of the
problem will be presented.
Two dimensional stepping motors are utilized for providing movement in
mutually perpendicular directions and comprise two main elements, namely a
moving member ("forcer") and a fixed member ("platen").
In operation, the forcer is magnetically propelled along the working
surface of the platen. One typical two-dimensional forcer is the dual axis
X-Y motor produced by Xynetics Products of Santa Clara, California. The
forcer is magnetically propelled along the platen by means of selectively
controlling the power provided to a plurality of electromagnets within the
forcer. The electromagnets magnetize themselves to a grid array machined
into the working surface of the platen. The forcer further incorporates
permanent magnets which maintain an uninterrupted attraction between the
platen and the forcer to maintain the forcer in close proximity to the
working surface of the platen. Either an air bearing or ball bearing
system respectively provide either a frictionless or low friction
operation of the forcer upon the platen.
The movement of the magnetic forcer along the steel platen causes eddy
currents to be generated within the platen. The eddy currents are
proportional to the forcer's velocity and generate resistance to motion in
the direction of travel in the forcer. The resistance to travel reduces
the forcer's performance in terms of both peak velocity and acceleration.
As forcer velocities increase, the net force available for acceleration is
reduced.
It is well known to provide electric motors with laminated stators to
reduce the effects of eddy currents on motor performance. Typically,
however, such motors are generally of the type having a rotating shaft
which rotates in a single plane vector. Such "one-dimensional" motion
allows the motor designer to create a lamination stack which eliminates
circulating eddy currents (normal to the rotor's magnetic fields) while
still providing adequate flux paths between the rotor magnets. Laminated
platens have also been provided for use with one-dimensional linear motors
and generally result in doubling of both peak acceleration and velocity.
To date, however, there are no platens which eliminate eddy currents and
yet allow two-dimensional motion.
In the case of a two-dimensional motor, it is important to eliminate
circular paths for eddy currents in the plane of a platen. However, flux
paths between magnetic elements in two orthogonal directions parallel to
the plane of the platen must be provided.
The solution to the problem achieved by the present invention is the
provision of a laminated platen which promotes flux paths in two
orthogonal directions parallel to the plane of the platen while
eliminating the circular path for eddy currents in the plane of the
platen.
FIG. 1 shows a two-directional laminate platen structure 10 which is
constructed of ferromagnetic plates 14 and insulator plates 12 arranged in
alternating interspersed fashion. The plates are held together by a
suitable adhesive preferably using the technique employed in FIG. 2 as
will be more fully described. The assembled ferromagnetic and insulator
plates 14 and 12 are machined or otherwise formed to provide elongated
substantially U-shaped slots S, which slots receive transverse laminate
structures 20 comprised of insulator plates 22 and ferromagnetic plates 24
arranged in an interspersed fashion similar to the insulator 14 and
ferromagnetic 12 plates forming the substrate laminate 10 but differing in
the sense that these plates are of significantly reduced height compared
with plates 12 and 14.
FIG. 2 shows one technique for assembly of the alternating steel 12 and
insulating 14 sheets. As can be seen from the figure, the insulator plates
12 have a plurality of openings which may be stamped or otherwise formed
therein and identified as 12a. The height of the openings 12a is greater
than the height of the steel plates 14 (measured in the vertical
direction). Each of the steel plates 14 is provided with a plurality of
preferably circular-shaped openings 14a arranged at spaced intervals along
each plate, each aligned to coincide with one of the insulator openings
12a. The insulator openings allow for the receipt of adhesive, such as an
epoxy or cyanoacrylate to bond the steel plates to one another. The
insulator plates serve to maintain accurate (plus or minus 0.0001 inch)
spacing between the steel plates and the structure does not have to rely
upon the thickness of the adhesive to establish the spacing. In addition,
the accuracy is selected so that the system has high repeatability for
positioning the linear motors whereby the distance between any plate and a
reference point lies within a cumulative tolerance of no greater than
0.001 inch. It is preferred that an assembly fixture is employed to
assemble the entire lamination stack before injecting adhesive. The
assembly fixture may, for example, be comprised of a first assembly member
16 with a pair of rods 18, 18 extending therethrough and extending through
openings 12b, 12b in each of the insulator plates 12, as well as the end
openings 14b, 14b of the steel plates 14. The opposite end member of the
fixture may be a second fixture member (not shown) or one of the steel
plates 14. The entire assembly is firmly pressed together with the steel
and insulator plates in intimate engagement by tightening nuts 19, 19
which threadedly engage the threaded portions 18a,18a of elongated rods
18, 18.
The openings 14a, as well as the openings 16a in the assembly fixture 16,
allow for insertion of an adhesive injector 17 which is extended through
the openings in the assembled lamination stack to sequentially fill the
hollow region defined by the opening 12a in each insulator plate 12 and
the steel plates 14, 14 on opposite sides thereof.
The adhesive injector 17 is a hollow tubular member, a portion of which is
shown in FIG. 2a in greater detail. The right-hand end of tube 17 is
sealed at 17a and annular-shaped slots 17b, 17 are provided in the wall of
tube 17b. Tube 17 is moved into the opening 16a', for example, and is
moved in the axial direction to align annular-shaped slots 17b with the
first opening 12a' in the first plate 12 adjacent to the assembly fixture
member 16. With the adhesive injector 17 aligned in this manner, adhesive
is dispensed in a radial direction and is introduced into the hollow
tubular injector 17. Since end 17a is sealed, adhesive is caused to move
in the outward radial direction through slot 17b in order to fill the
region defined by opening 12a' and the plates on opposite sides thereof.
As the adhesive is introduced into the hollow region defined by opening
12a', air contained therein is vented through the upper and lower portions
12a'-1 and 12a'-2 of opening 12a' which portions extend above and below
the upper and lower surfaces of adjacent ferromagnetic plates 14, 14 as
shown in FIG. 2b. Eventually, when the hollow region defined by opening
12a' is filled, epoxy passes out of the top and bottom portions 12a'-1 and
12a'-2 of opening 12a' providing a positive indication that the opening is
suitably filled with epoxy (i.e. adhesive material).
The injector tube 17 is then axially moved to the opening in the next
insulator plate. Each of the openings are thus filled in a sequential
fashion. If desired, all of the openings 12a within the same insulator
plate may be simultaneously filled by simultaneous operation of injector
tubes introduced into each of the five openings 12a. If desired, the
injector tubes may begin to introduce adhesive into the left-hand-most
insulator plate and move incrementally toward the right-hand direction or,
alternatively, the injector tubes may be extended all the way through the
laminate assembly so that the ejector slot 17b is aligned with the opening
in the right-hand-most insulator plate and the injector tube is thereafter
drawn toward the left in incremental fashion to fill each of the openings
of the insulator plates. Using the latter method, the injector tube avoids
coming into contact with the adhesive in each of the filled openings in
the insulator plates. Linear motors may be employed as the means for
stepping the adhesive tube from one opening 12a to the next.
As another possible alternative, the injector tube may be provided with
more than one slot for ejecting the epoxy into two or more openings in
adjacent insulator plates in a simultaneous fashion.
When the adhesive has been properly introduced in the manner described
hereinabove, at least the portions of the insulator plates extending
beyond the upper surfaces 14c of the steel plates are removed to provide a
smooth planar surface. The planar surface is then machined or otherwise
formed to provide the slots S for receipt of the transverse laminate
structures 20. The transverse laminate structures 20 can be manufactured
in the same way as the substrate laminates. Since the transverse laminates
are preferably only 0.075 inches thick, many such laminates can be sliced
from a substrate laminate. Each sliced transverse laminate is then
precision ground to guarantee a proper fit within the associated slot S
provided in the substrate laminate so that no air gaps are provided
between the engaging surfaces of the substrate laminate and the transverse
laminate, as shown best in FIG. 3.
Once the transverse laminates 20 are ground and the substrate laminate has
been ground to accept the transverse laminate, the transverse laminate is
pressed and glued in place. It is important that no adhesive be allowed to
separate those portions of the top surfaces of the plates 12 and 14 which
form the base of each slot S from the bottom surfaces of the plates 22 and
24 which comprise the transverse laminate although adhesive is permitted
to be introduced between the exposed sides of the plates in the transverse
laminate which comprise the outer plates of the transverse laminate and
the engaging surfaces of the plates 12 and 14 forming the sidewalls of the
slots S.
After insertion of the transverse laminate structures 20 into associated
slots 10 of the substrate laminate 10, the upper surface of the resulting
laminate is ground flush to form a planar surface having an accuracy
sufficient to maintain the consistency and smooth operation of the air
bearing. This planar surface is then machined to form grooves for creating
the magnetization teeth, said grooves G forming a grid-like pattern, as
well as defining the teeth T.
It is important that the teeth T must be created relative to the
laminations as shown best in FIG. 3 and the grooves G must be accurately
positioned with respect to each other. Inaccuracies in the machining
process will have an adverse effect on the acceleration limits and
positioning accuracy of the forcer member utilized with the dual laminated
platen.
After creation of the magnetization teeth T by formation of the grooves G,
the entire grooved surfaces forming the grid-like pattern is filed with
epoxy. The epoxy is then ground flush with the top of the magnetization
teeth to form a smooth, planar surface for receipt of one or more forcers.
A latitude of modification, change and substitution is intended in the
foregoing disclosure, and in some instances, some features of the
invention will be employed without a corresponding use of other features.
Accordingly, it is appropriate that the appended claims be construed
broadly and in a manner consistent with the spirit and scope of the
invention herein.
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