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Claims  |
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I claim:
1. Linear motor apparatus for driving a machine slide with respect to a
machine frame comprising:
means for supporting and guiding the machine slide for movement with
respect to the machine frame along a first axis;
magnetic field array means disposed along the first axis and fixedly
located with respect to the machine frame for providing a plurality of
magnetic poles which generate a magnetic field of periodic alternating
polarity, where the distance between adjacent poles of the plurality of
magnetic poles is equal to an inter-pole distance L, and further wherein
the magnetic field array means provide magnetic field lines parallel to a
second axis which is orthogonol to the first axis; and
a multiphase armature also disposed along the first axis but fixedly
located with respect to the machine slide, said multiphase armature having
a plurality of phases which are spaced successively along the first axis,
wherein each phase is formed of at lease a first coil, said first coil
having first and second active portions with center lines that are
separated from one another by a distance substantially equal to the
inter-pole distance L, and further wherein the first and second active
portions extend across the magnetic field array means in a direction
parallel to a third axis such that they are encompassed by the magnetic
field lines of the magnetic field array means, said third axis being
orthogonal to the second axis, and
further wherein, the first active portion of any one of the phases is
located relative to the first active portion of a successively positioned
phase at a distance equal to the inter-pole distance L divided by the
number of phases present in the multiphase armature and
further wherein any additional coils used in forming a phase are located,
with respect to the other coils that form the phase, at the inter-pole
spacing L.
2. A linear motor apparatus as in claim 1 wherein the magnetic field array
comprises a pair of ferromagnetic bars with an array of magnets arranged
so that north poled magnets alternate with south poled magnets an extend
along the first axis, and wherein the array of magnets is mounted on a
surface of a first one of the pair of ferromagnetic bars said surface
facing the second one of the ferromagnetic bars.
3. A linear motor apparatus as in claim 2 wherein the array of magnets is a
spaced array of magnets wherein each magnet of the spaced array of magnets
is spaced from the next magnet of the spaced array of magnets by a
distance equal to the inter-pole distance L divided by the number of
phases.
4. A linear motor, apparatus as in claim 3 wherein the magnets at each end
of the spaced array of magnets has a width one-half that of the other
magnets of the spaced array of magnets.
5. A linear motor apparatus as in claim 1 wherein the magnetic field array
means comprises
a pair of ferromagnetic bars;
two arrays of magnets each having alternate north poled magnets and south
poled magnets extending along the first axis, wherein each array of
alternate north poled and south poled magnets is mounted on the
ferromagnetic bars so that the two arrays of magnets are positioned such
that each north poled magnet of either array of magnets is located
opposite a south poled magnet of the other array of magnets.
6. A linear motor apparatus as in claim 5 wherein each array of magnets is
a spaced array of magnets wherein each magnet of each spaced array of
magnets is spaced from the next magnet of that spaced array of magnets by
a distance equal to the inter-pole distance L divided by the number of
phases.
7. A linear motor apparatus as in claim 6 wherein the magnets at the ends
of each spaced array of magnets are half the width of the other magnets of
that spaced array of magnets.
8. A linear motor apparatus as in claim 1, wherein the machine slide is
translatable over a length of travel, and further wherein the length of
the magnetic field array is equal to or longer than the length of the
multiphase armature plus the length of travel of the machine slide.
9. A linear motor apparatus as in claim 1 wherein the various coils
comprising the phases of the multiphase armature are interleaved and
staggered with respect to one another.
10. A linear motor apparatus as in claim 9 wherein width of the active
portions of each of the coils is equal to the inter-pole distance L
divided by the number of phases.
11. A linear motor apparatus as in claim 9 wherein the active portions of
each coil are located in different planes and joined together by end turns
which slope from an active portion of a coil to the other active portion
of the coil to accommodate the positioning of selected portions of the end
turns of the coils of a number of coils equal to the number of phases plus
one.
12. A linear motor apparatus as in claim 9 wherein each coil of the
multiphase armature is formed to have a pair of leads for receiving
energizing current and further wherein both leads emerge from outside
faces of the coil.
13. A linear motor apparatus as in claim 1 wherein the magnetic field of
the magnetic field array means alternates between a magnetic field forward
position and a magnetic field reversal position, including means for
commutating the phases of the multiphase armature, said commutating means
comprising a plurality of solid state switches that form connections
between each of the phases and an energizing source as the multiphase
armature moves spatially along the magnetic field array and further
wherein the commutating means reverses the connections of a phase as the
phase leaves a magnetic field reversal position between the magnetic field
array means.
14. A linear motor apparatus as in claim 13 wherein the commutating means
include an encoder strip mounted on the machine frame and having selected
bands of windows which sequentially enable and interrupt the passage of
light to an array of sensors mounted on the machine slide.
15. A linear motor apparatus as in claim 14 wherein the array of sensors
controls the state of each of the plurality of solid state switches that
form the connections to each of the phases of the multiphase armature of
the linear motor apparatus.
16. A linear motor apparatus as in claim 15 wherein the array of sensors
comprises a number of sensors equal to the number of solid state switches.
17. A linear motor apparatus as in claim 13 wherein the number of solid
state switches is equal to four times the number of phases of the
multiphase armature of the linear motor apparatus.
18. A linear motor apparatus as in claim 14 wherein the sensors are
phototransistors.
19. A linear motor apparatus as in claim 13 wherein the solid state
switches comprise two MOSFETs connected source-to-source with a common
gate connection, wherein the gate-to-source voltage is regulated by a
zener diode having a zener voltage so that the zener voltage is applied as
the gate-to-source voltage of the MOSFETs when the solid state switch is
in an "on" state and a reversed diode drop voltage is applied to the
MOSFETs when the solid state switch is in an "off" state.
20. A method of commutating the phases of the linear motor apparatus of
claim 1 as the multiphase armature moves spatially along the magnetic
field array wherein a phase is faulted as it approaches a magnetic field
reversal position between magnetic poles of the magnetic field array means
and then the connections of that phase are reversed as it leaves the
magnetic field reversal position.
21. Linear motor apparatus for driving a machine slide with respect to a
machine frame comprising:
means for supporting and guiding the machine slide for movement with
respect to the machine frame along a first axis;
a multiphase armature disposed along the first axis and fixedly located
with respect to the machine frame, said multiphase armature having at
least two phase which are spaced successively along the first axis.
wherein each phase comprises a plurality of coils, each coil having first
and second active portions with center lines that are separated from one
another by a distance substantially equal to an inter-pole distance L,
where the first and second active portions extend in a direction parallel
to a second axis, said phases being positioned such that adjoining first
and second active portions of successive phases are located relative to
one another at a distance equal to the inter-pole distance L divided by
the number of phases present in the multiphase armature, and the
additional coils in each of the phases are located at the inter-pole
spacing L with respect to each other; and
magnetic field array means disposed along the first axis and fixedly
located with respect to the machine slide, for providing a plurality of
magnetic poles which generate a magnetic field of periodic alternating
polarity wherein centers of each of the plurality of magnetic poles are
located at the inter-pole distance L, and further wherein the magnetic
field array means provide magnetic field lines parallel to a third axis
which is orthogonal to the second axis and encompass the active portions
of the coils located concomitantly along the first axis.
22. A linear motor apparatus as in claim 21 wherein the magnetic field
array means comprises a pair of ferromagnetic bars with an array of
magnets arranged so that north poled magnets alternate with south poled
magnets and extend along the first axis, and wherein the array of magnets
is mounted on a surface of a first one of the pair of ferromagnetic bars,
said surface facing the second one of the ferromagnetic bars.
23. A linear motor apparatus as in claim 22 wherein the array of is a
spaced array of magnets wherein each magnet of the spaced array of magnets
is spaced from the next magnet of the spaced array of magnets by a
distance equal to the inter-pole distance L divided by the number of
phases.
24. A linear motor apparatus as in claim 23 wherein the magnets at each end
of the spaced array of magnets have a width one half that of the other
magnets of the spaced array of magnets.
25. A linear motor apparatus as in claim 21 wherein said magnetic field
array means comprises
a pair of ferromagnetic bars;
two arrays of magnets each having alternate north poled magnets and south
poled magnets extending along the first axis, wherein each array of
alternate north poled and south poled magnets is mounted on a surface of
one of the ferromagnetic bars which faces a surface of the other one of
the ferromagnetic bars and wherein the two arrays of magnets are
positioned such that each north poled magnet of either array of magnets is
located opposite a south poled magnet of the other array of magnets.
26. A linear motor apparatus as in claim 25 wherein each array of is a
spaced array of magnets wherein each magnet of each spaced array of
magnets is spaced from the next magnet of that spaced array of magnets by
a distance equal to the inter-pole distance L divided by the number of
phases.
27. A linear motor apparatus as in claim 26 wherein the magnets at the ends
of each spaced array of magnets are half the width of the other magnets of
that spaced array of magnets.
28. A linear motor apparatus as in claim 21, wherein the machine slide is
translatable over a length of travel, and further wherein the length of
the multiphase armature is equal to or longer than the length of the
magnetic field array plus the length of travel of the machine slide.
29. A linear motor apparatus as in claim 21 wherein the various coils
comprising the phases of the multiphase armature are interleaved and
staggered with respect to one another.
30. A linear motor apparatus as in claim 29 wherein the width of each of
the two active portions of each of the coils is equal to the inter-pole
distance L divided by the number of phases.
31. A linear motor apparatus as in claim 29 wherein the active portions of
each coil are located in different parallel planes and joined together by
end turns which slope from an active portion of a coil to the other active
portion of the coil to accommodate the positioning of selected portions of
the end turns of the coils of a number of coils equal to the number of
phases plus one.
32. A linear motor apparatus as in claim 29 wherein each coil of the
multiphase armature is formed to have a pair of leads for receiving
energizing current and further wherein both leads emerge from outside
faces of the coil.
33. A linear motor apparatus as in claim 21 wherein the magnetic field of
the magnetic field array means alternates between a magnetic field forward
position and a magnetic field reversal position, including means for
commutating the phases of the multiphase armature, said commutating means
comprising a plurality of solid state switches that form connections
between each of the phases of the multiphase armature and an energizing
source as the magnetic field array moves spatially along the multiphase
armature, and further wherein the commutating means reverses the
connections of that phase as the magnetic field reversal position between
the magnetic poles of magnetic field array means leaves that phase.
34. A linear motor apparatus as in claim 33 wherein the commutating means
include an encoder strip mounted on the machine frame and having selected
bands of windows which sequentially enable and interrupt the passage of
light to an array of sensors mounted on the machine slide.
35. A linear motor apparatus as in claim 34 wherein the array of sensors
controls the state of each of the plurality of solid state switches that
form the connections to each of the phases of the multiphase armature of
the linear motor apparatus.
36. A linear motor apparatus as in claim 35 wherein the array of sensors
comprises a number of sensors equal to the number of solid state switches.
37. A linear motor apparatus as in claim 33 wherein an encoder strip
mounted on the machine slide and having selected bands of windows is
utilized to sequentially enable and interrupt the passage of light to an
array of sensors mounted on the machine frame for controlling said
commutation.
38. A linear motor apparatus as in claim 37 wherein the array of sensors
controls the state of each of the plurality of solid state switches that
form the connections to each of the phases of the multiphase armature of
the linear motor apparatus.
39. A linear motor apparatus as in claim 38 wherein the array of sensors
comprises a number of sensors equal to the number of solid state switches.
40. A linear motor apparatus as in claim 33 wherein the number of solid
state switches is equal to four times the number of phases of the ironless
multiphase armature of the linear motor apparatus.
41. A linear motor apparatus as in claims 34 or 37 wherein the sensors are
phototransistors.
42. A linear motor apparatus as in claim 33 wherein the solid state
switches comprise two MOSFETs connected source-to-source with a common
gate connection, wherein the gate-to-source voltage is regulated by a
zener diode having a zener voltage so that the zener voltage is applied as
the gate-to-surface voltage of the MOSFETs when the solid state switch is
in an "on" state and a reversed diode drop voltage is applied to the
MOSFETs when the solid state switch is in an "off" state.
43. A method of commutating the phases of the linear motor apparatus of
claim 21 as the magnetic field array moves spatially along the multiphase
armature wherein a phase is faulted as a magnetic field reversal position
between magnetic poles of the magnetic field array means approaches that
phase, and then the connections of that phase are reversed as the magnetic
field reversal position between the magnetic poles.
44. The linear motor apparatus of claim 12 wherein the commutating means
further includes means for faulting a phase as it approaches a magnetic
field reversal position of the magnetic field array means.
45. The linear motor apparatus of claim 21 wherein the commutating means
further includes means for faulting a phase as it approaches a magnetic
field reversal position of the magnetic field array means. |
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Claims |
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Description |
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TECHNICAL FIELD
This invention relates generally to linear motors of a type commonly
utilized in a servo controlled positioning system for driving a moving
element and positioning it with respect to a reference element and more
specifically, this invention relates to an improved solid state commutated
linear motor having an ironless multiphase armature with significantly
improved thrust capability.
BACKGROUND ART
This type of linear motor has a magnetic field array comprised of first and
second arrays of magnets. The magnets of each array are coupled
magnetically by way of a ferromagnetic bar for providing a magnetic field
of a selected geometrical pattern. The ferromagnetic bars are parallel to
one another. Typically the linear motor also has a solid state commutated
armature mounted for relative axial movement between the two bars and
providing thrust when energized by current in a selected manner.
Many linear motors of the type described above are disclosed in the patent
literature. Three examples of such linear motors are those shown in U.S.
Pat. No. 4,151,447 entitled LINEAR MOTOR and issued Apr. 24, 1979 to
Johann von der Heide and Georg F. Papst; U.S. Pat. No. 4,187,453 entitled
ELECTRIC MOTOR DRIVE SYSTEM and issued Feb. 5, 1980 to J. Kirkwood H.
Rough; and U.S. Pat. No. 4,396,966 entitled LOW MASS ACTUATOR SYSTEM FOR
MAGNETIC RECORDING DISKS WITH HALF STRENGTH END POLES and issued Aug. 2,
1983 to Robert A. Scranton, David A. Thompson and Thomas K. Worthington.
One problem common to all of the linear motors described in the above
cited U.S. Patents is their inefficient use of the space available within
their magnetic fields for generating thrust with the current in their
armatures. In two cases, a portion of the available magnetic field is cut
by current flowing the wrong way through a portion of the armature. Thus,
the applied current partially generates reverse thrust. The other case
shows an armature winding having a very low conductor stacking factor and
hence even poorer efficiency.
U.S. Pat. Nos. 4,151,447 and 4,396,966 show an array of magnets mounted on
each of two parallel ferromagnetic bars wherein the magnets are
sequentially oppositely poled and the bars are mounted with respect to one
another such that each magnet of each array of magnets is positioned
opposite an oppositely poled magnet of the other array of magnets. U.S.
Pat. Nos. 4,151,447 and 4,396,966 also show two coils spacially positioned
in quadrature with respect to the arrays of magnets wherein each coil is
wound such that when one side of the coil is positioned between a first
pair of magnets the other side of the coil is positioned between an
adjacent pair of magnets. Current is forced to flow through each coil at
all times. The direction of current flow in either coil is reversed as
that coil passes between the magnets of either array. Thus the current
flowing in that coil is wasted at that position because it is distributed
equally between opposing magnetic fields and has a net contribution of
zero thrust. For other positions a portion of the current flowing in each
coil is partly wasted depending on its spacial relationship with the
arrays of magnets.
Also, any back e.m.f. present due to relative velocity between the armature
and the magnetic field opposes only the net thrust producing portions of
the current flowing in each coil. Since the control shown in U.S. Pat. No.
4,151,447 is a voltage control, the coil of the linear motor disclosed
therein which produces the least thrust will always have the larger
current. When such a coil is positioned between the magnet poles at the
location where the direction of current flow is reversed, the net back
e.m.f. is zero and the current is limited only by the series resistance of
the coil and its drive amplifier.
U.S. Pat. No. 4,396,966 additionally shows end magnets of half strength.
This is said to have the advantage of reducing leakage flux emanating from
the linear motor. Also, it is evident that since only half of the flux
from each magnet flows between magnets in the ferromagnetic bars then the
ferromagnetic bars of the linear motor of U.S. Pat. No. 4,396,966 may be
made half the size of the ferromagnetic bars of the linear motor of U.S.
Pat. No. 4,151,447.
U.S. Pat. No. 4,187,453 shows two serpentine format windings formed via
printed circuit techniques and placed in quadrature with respect to arrays
of oppositely poled magnets similar to those of U.S. Pat. Nos. 4,151,447
and 4,396,966. The linear motor of U.S. Pat. No. 4,187,453 operates as a
stepping motor. However, that linear motor could be controlled as a servo
motor, as explained above, although it additionally shows a very low
conductor stacking factor, as also explained hereinabove. It is cited
herein both because it illustrates a method of constructing a multi-poled
linear motor armature and because it illustrates a "moving field"
configuration of linear motor wherein the linear motor has an elongated
armature and a foreshortened magnetic field array.
What is needed is a linear motor having an ironless multiphase armature
wherein no portion of the current flowing through any of the coils of the
ironless multiphase armature generates reverse thrust. Further, it is
desired that the coils of the ironless multiphase armature possess a high
conductor stacking factor. It would also be desirable to provide a "moving
field" configuration of a linear motor having an improved conductor
stacking factor. Also, what is needed is a solid state switching
arrangement for commutating the coils of the multiphase armature of the
linear motor wherein all current conducting coils of the armature are
connected in series so that each current conducting coil carries the same
current.
SUMMARY OF THE INVENTION
These and other problems of previous linear motors are overcome by the
present invention of an improved solid state commutated linear motor with
an ironless multiphase armature including an array of magnets mounted on
each of two parallel ferromagnetic bars wherein the magnets are
sequentially oppositely poled, the bars are mounted with respect to each
other such that each magnet of each array of magnets is positioned
opposite an oppositely poled magnet of the other array of magnets, the
axial length of the space between all magnets is equal to the ratio of the
inter-pole distance between full strength magnets of each array of magnets
divided by the number of phases and further wherein the axial length of
the end magnets of each array of magnets is half of the length of the full
strength magnets (and therefore of half strength); an ironless multiphase
armature with at least two phases each comprised of at least one coil
whose axial center-line span is equal to the inter-pole distance between
full strength magnets wherein the coils are wound in a multi-plane fashion
and are interleaved in a staggered manner when assembled and potted to
form the ironless multiphase armature; a " moving armature" configuration
wherein the poles of the armature are fewer in number than the poles of
the arrays of magnets and wherein the phases of the armature are series
connected so that each current conducting coil carries the same current; a
commutation program of solid state switching of the phases according to a
truth table wherein each phase is sequentially switched into a faulted
condition and then switched into a reverse connected state as it passes
opposite the space between magnets in the arrays of magnets; and a
switching circuit able to perform the desired switching in a
bi-directional manner between phases and output terminals of a servo
amplifier drive circuit.
An alternate embodiment of the present invention comprises an improved
solid state commutated linear motor with an ironless multiphase armature
including an array of magnets mounted on each of two parallel
ferromagnetic bars wherein the magnets are sequentially oppositely poled,
the bars are mounted with respect to each other such that each magnet of
each array of magnets is positioned opposite an oppositely poled magnet of
the other array of magnets, the axial length of the space between all
magnets is equal to the ratio of the inter-pole distance between full
strength magnets of each array of magnets divided by the number of phases
and further wherein the axial length of the end magnets of each array of
magnets is half of the length of the full strength magnets (and therefore
of half strength); an ironless multiphase armature with at least two
phases each comprised of multiple coils whose axial center-line span is
equal to the inter-pole distance between full strength magnets wherein the
coils are wound in a multi-plane fashion and are interleaved in a
staggered manner when assembled and potted to form the ironless multiphase
armature; a "moving field" configuration wherein the poles of the arrays
of magnets are fewer in number than the poles of the armature and wherein
the phases of the armature are series connected so that each current
conducting coil carries the same current; a commutation program of solid
state switching of the phases according to a truth table wherein each
phase is sequentially switched into a faulted condition and then switched
into a reverse connected state as it passes opposite the space between
magnets in the arrays of magnets; and a switching circuit able to perform
the desired switching in a bi-directional manner between phases and output
terminals of a servo amplifier drive circuit.
Accordingly, it is the principal object of this invention to provide an
improved solid state commutated linear motor having an ironless multiphase
armature wherein no portion of the current flowing through any of the
coils of the ironless multiphase armature generates reverse thrust.
Another object of this invention is to provide a method of fabrication for
the coils of the ironless multiphase armature of the linear motor wherein
the coils possess a high conductor stacking factor.
Another object of this invention is to provide a solid state commutated
linear motor with an ironless multiphase armature having a "moving
armature" configuration wherein an ironless multiphase armature moves
within an alternately poled magnetic field array whose length is at least
equal to the length of the ironless multiphase armature plus the length of
travel of the armature.
Another object of this invention is to provide a solid state commutated
linear motor with an ironless multiphase armature having a "moving field"
configuration wherein an alternately poled magnetic field moves over an
ironless multiphase armature whose length is at least equal to the length
of the alternately poled magnetic field plus the length of travel of the
moving field.
Another object of this invention is to provide a solid state commutated
linear motor with an ironless multiphase armature wherein the phases are
series connected so that each current conducting coil carries the same
current.
Another object of this invention is to provide a solid state commutated
linear motor with an ironless multiphase armature wherein the phases are
switched in polarity in accordance with a truth table which includes
overlap in the switching sequence so that transient open circuit
conditions are not possible.
Still another object of this invention is to provide a solid state
switching circuit able to switch current on-and-off in a bi-directional
manner between phases and output terminals of a servo amplifier drive
circuit.
These and other objectives, features and advantages of the present
invention will become more apparent upon consideration of the following
detailed description and accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an isometric drawing of a "moving armature" version of an
improved solid state commutated linear motor with an ironless multiphase
armature in accordance with the preferred embodiment of the present
invention.
FIG. 2 is a cutaway isometric drawing of an armature portion of the
improved solid state commutated linear motor with an ironless multiphase
armature of FIG. 1.
FIG. 3 is an isometric drawing of a coil portion of the armature shown in
FIG. 2 which is wound in a selected offset fashion.
FIGS. 4A and 4B are isometric drawings of a partially wound coil on a
winding mandrel which illustrate a method of winding the coil of FIG. 3.
FIG. 5 is a sectional view of the armature shown in FIG. 2 showing a
printed circuit board utilized for holding the coils of the armature in
place during a potting operation.
FIG. 6 is a plan view of the printed circuit board shown in FIG. 5.
FIGS. 7A, 7B and 7C are sectional views of the "moving armature" version of
the improved solid state commutated linear motor with an ironless
multiphase armature shown in FIG. 1 showing the spacial relationship of
the phases to the arrays of magnets before, during and after a switching
sequence.
FIG. 8 is a circuit diagram for the improved solid state commutated linear
motor with an ironless multiphase armature showing the disposition of
solid state switches required for armature commutation.
FIG. 9 is a truth table showing the state of each solid state switch with
respect to the spacial positioning of the armature.
FIGS. 10A and 10B are sectional and plan views of a first type of encoder
strip and diode array used for implementing the switching of each solid
state switch as called for in the truth table of FIG. 9.
FIG. 11 is a circuit diagram showing a solid state switch utilized for
switching in a bi-directional manner.
FIG. 12 is an isometric drawing of a "moving field" version of the improved
solid state commutated linear motor with an ironless multiphase armature
in accordance with an alternative embodiment of the present invention.
FIG. 13 is a plan view of a second type of encoder strip and diode array
used for implementing the switching of each solid state switch as called
for in the truth table of FIG. 9 wherein the encoder strip and diode array
are modified for use with a more efficiently switched ironless multiphase
armature of the "moving field" version of the improved solid state
commutated linear motor with an ironless multiphase armature shown in FIG.
12.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring now to FIG. 1, there is shown an improved solid state commutated
linear motor with an ironless multiphase armature 10 of a "moving
armature" configuration wherein a magnetic field array 11 comprising at
least one of two arrays of magnets 12 and 14 and two ferromagnetic bars 16
and 18 encompasses and interacts with an ironless multiphase armature 20.
In the "moving armature" configuration of the present invention, the
length of the magnetic field array 11 is at least equal to the length of
the ironless multiphase armature 20 plus the length of travel, relative to
the magnetic field array 11, of the ironless multiphase armature 20.
The arrays of magnets 12 and 14 each comprise alternate north poled magnets
22 and south poled magnets 24 which are spaced apart from one another by a
distance equal to the inter-pole distance, L, divided by the number of
phases in the ironless multiphase armature 20. The array of magnets 12 and
14 are positioned on the ferromagnetic bars 16 and 18 such that each north
poled magnet 22 on one of the ferromagnetic bars is located opposite a
south poled magnet 24 on the other of the ferromagnetic bars.
Each end magnet 26 is half the width of the non-end magnets. Thus the flux
from each end magnet 26 is conducted through its corresponding
ferromagnetic bar 16 or 18 and is returned via half of a neighboring north
poled magnet 22 or south poled magnet 24, crosses the air gap 28 provided
for passage of the multiphase ironless armature 20, passes through the
opposite magnets and ferromagnetic bar, and crosses the air gap 28 a
second time. See arrows 26a, FIG. 1. Since half of the flux from the
neighboring north poled magnet 22 or south poled magnet 24 must then be
returned to it in a similar fashion with respect to its next neighboring
magnet and so on down each array of magnets, it is apparent that the
ferromagnetic bars 16 and 18 can be sized for carrying half of the flux
coming from each non-end magnet 27. It is to be understood that in the
preferred embodiment of the present invention the magnets used in the
arrays of magnets 12 and 14 are of the type having their poles at their
broadest faces. Thus, as shown in FIG. 1, the faces of the magnets in
array 12 oppose faces of magnets in array 14. These opposing faces
comprise the poles of the magnets. As such, for a magnet having a north
pole face facing into the gap 28, such magnet has a south pole face
abutting the ferromagnetic bar.
The ferromagnetic bars 16 and 18 are mounted on a channel 30 which is in
turn mounted on a machine frame 32. The ironless multiphase armature 20 is
mounted on a machine slide 34 which is supported by guideway bearings 33
and thereby guided for linear movement along the magnetic field array 11.
The ironless multiphase armature 20 includes at least two phases. The
phases are selectively and equally spaced along a common axis with the
magnetic field array 11 such that each of the phases can be commutated in
sequence, as the magnetic field cutting portions 21 of the armature 20
pass the spaces between the north poled magnets 22 and south poled magnets
24, without perturbing the continuous thrust characteristics of the
present invention. The magnetic field cutting portions 21 are defined as
the portion of armature 20 whioh is positioned within gap 28. Each of the
phases includes at least one coil whose axial center-line span between its
magnetic field cutting portions 21 is equal to the inter-pole distance L,
so that each field cutting portion 21 is always identically positioned
with respect to each one of a neighboring set of a north poled magnet 22
and a south poled magnet 24.
The ironless multiphase armature 20 can include more than two phases and
each phase can include more than one coil, wherein the coils comprising a
phase are series connected as described below. FIG. 2 is a cutaway
isometric drawing showing details of a two coil per phase, three phase
armature 36 which may be utilized as the ironless multiphase armature 20
in the improved solid state commutated linear motor 10. The two coil per
phase, three phase armature 36 is comprised of six identical coils 38
wherein each coil 38 is interleaved with the other coils in a staggered
manner, wired together and potted, as described hereinafter. The coil
width W of each coil 38 is equal to the inter-pole distance L divided by
the number of phases (or L/3 for the two coil per phase, three phase
armature 36) while the axial center-line span, S, of each coil 38 (see
FIG. 3) is equal to the inter-pole distance L as described above. The
series connected pairs of individual coils 38 may be further identified by
phase as follows: Phase 1 is comprised of coils 40a and 40b, phase 2 is
comprised of coils 42 a and 42b, and phase 3 is comprised of coils 44a and
44b. Each of these pairs of coils overlap with -h other-to form the
interleaved and staggered eac assembly. Thus, it can be seen in FIG. 2
that the end portion of coil 44b which lies along the upper portion of
armature 36 is positioned above the end portion of coil 44a which lies
along the bottom portion of armature 36. Disposed between these end
portions of coils 44a and 44b are parts of the end portions of coils 42b
and 40b. See arrows 51, FIG. 2.
It is apparent that each of the pairs of coils which form a phase should be
series connected in counter fashion so that the current passing through
each will go in the same direction at each overlapping position, arrow 51,
as indicated by the arrows 46. It is also apparent that within the
overlapped region the two coil per phase, three phase armature 36 has the
maximum possible conductor stacking factor. An ironless multiphase
armature 20 comprising a large number of coils formed as described herein
would therefore have a very high average conductor stacking factor.
A particular coil configuration that can be used for the coil 38 is shown
in FIG. 3. Magnetic field cutting portions 48a and 48b, also referred to
as the active portions, are parallel but transversely offset from one
another by a stagger distance d. End-turn portions 50a and 50b should be
offset and sloped sufficiently to accommodate the interleaved and axially
spaced positioning of the coils 38 as shown in FIG. 3. This results in a
continuously offset stack of the coil end-turn portions 50a and 50b equal
in total thickness to at least the number of phases plus one. This means
that there is a nominal four high stacking of end-turn portions 50a and
50b in the two coil per phase, three phase armature as is shown in FIG. 2
at arrows 51. As such, there is provided a series of active portions 48b
from each of the coils 38, which active portions are abutted up against
one another to form a planar active portion face. This face lies along the
upper portion of armature 36 as it is oriented in FIG. 2. Similarly, there
is provided a series of active portions 48a from each of the coils 38,
which active portions are abutted against one another to form a planar
active portion face which lies along the bottom portion of armature 36 as
it is oriented in FIG. 2. Thus, from FIGS. 2 and 3 it can be appreciated
that the distance between center lines of abutted active portions of
successive phases (for example, phases 1 and 2) of the ironless multiphase
armature 20 is equal to the inter-pole distance (or intermagnet distance)
L divided by the number of phases present in the armature 20. It also
follows that the coils which form a phase are themselves separated from
one another by the inter-pole distance L.
Further, it is for leads 52a and 52b to be on the outside of each coil 38
because passage of one of the leads from the inside of the coil 38 to the
outside would further increase the thickness of the coil 38 at some
position along the coil. FIGS. 4A and 4B illustrate a method of winding
the coil 38 wherein both leads 52a and 52b will be on the outside of the
coil as desired. FIG. 4A shows a partially wound coil 38 on a winding
mandrel 54 wherein two central turns 56a and 56b of the coil 38 have been
placed on the mandrel 54 in counter-wound directions with respect to each
other by pulling wire ends 58a and 58b around the mandrel in counter
directions. Each pair of turns thereafter is wound directly over the
preceding pair as shown in FIG. 4B until finally the remaining wire ends
58a and 58b become the leads 52a and 52b as the final turns are completed
and the coil assumes its final form as shown in FIG. 3.
What is obtained is a coil 38 which has a thickness approximately equal to
two times the diameter of the wire being used. The width of coil is a
function of the number of turns of wire in the coil, e.g., the number of
turns divided by two in the example of FIGS. 4A and 4B, where the coil is
two wire diameters thick. It is to be noted that except for the first
turn, see region 38a, the successive turns of wire in the coil 38 are
stacked on top of one another in a parallel fashion and do not cross.
FIG. 5 is a sectional view showing further details of construction of the
ironless multiphase armature 20. Each coil 38 is positioned in a selected
position proximate to a printed circuit board 60 with its leads 52a and
52b projecting through plated through holes 62 formed in the printed
circuit board 60. The various leads 52a and 52b are soldered to pads 64
surrounding each end of the plated through holes 62 in order to provide
electrical connection and locate the coils 38 in their selected positions
proximate to the printed circuit board 60. The printed circuit board 60 is
then positioned in notches 66 in a mold 68 wherein potting compound 70 is
poured and cured to form the ironless multiphase armature 20.
For purposes of illustration, assume a vertical sectional view in FIG. 5 of
the ironless multiphase armature 20 positioned within the mold 68 taken,
for example at line A--A of FIG. 2. As such, what is shown are portions of
coils 40a, 42a, and 44a, as indicated in parenthesis.
FIG. 6 is a plan view of the printed circuit board 60 showing traces 72a,
72b and 72c which form the series interconnections between the coils 40a
and 40b 42a and 42b, and 44a and 44b, respectively. Also shown are
terminals 1a and 1b, 2a and 2b, and 3a and 3b which are connected to the
non-series connected ends of the coils 40a and 40b, 42a and 42b, and 44a
and 44b, respectively, and which are used for connecting solid state
switching circuitry to the phases 1, 2 and 3, respectively. For purposes
of illustration, the end turn portions of coils 40a and 40b, which form
phase one of the ironless multiphase armature 36, are drawn in dotted
lines to demonstrate the relative locations of the various coils. Thus,
current applied at terminal 1a flows into one lead of coil 40a and out the
other lead to trace 72 a. The current then flows from trace 72a into one
of the leads of coil 40b. The current then flows out of the other lead of
coil 40b and out to terminal 1b.
FIGS. 7A, 7B and 7C are sectional views showing the spacial relationship of
the active portions of coils 40a and 40b, 42a and 42b, and 44a and 44b
(phases 1, 2 and 3, respectively) to the arrays of the magnets 12 and 14
before, during and after a switching sequence, respectively, where the
terminals 3a and 3b are being switched. During the switching sequence
(when positioned as shown in FIG. 7B) phase 3 can be faulted as the
ironless multiphase armature moves spacially over a very short distance
.delta. (such as L divided by 100, for instance) with respect to the
arrays of magnets 12 and 14. Phase 3 is shown crosshatched in the figures.
This is because very few magnetic flux lines are cut by phase 3 over such
a short distance and any resulting thrust perturbations are minimal. For
purposes of illustration, the magnetic flux lines are drawn as arrows in
FIG. 7a. Thus the new connections can be made before the old ones are
broken and no momentary breaks in the series current flow through phases 1
and 2 during the switching of phase 3 will result.
The foregoing can be seen more clearly by referring to the improved solid
state commutated linear motor circuit diagram shown in FIG. 8. This
circuit diagram shows the terminals 1a, 1b, 2a, 2b, 3a and 3b as well as a
servo amplifier output terminal Ts and a ground terminal Tg. The circuit
diagram also shows solid state switches 74a and 74b for connecting the
servo amplifier output terminal Ts to the terminals 1a and 1b,
respectively; solid state switches 76a and 76b for connecting the terminal
1a to the terminals 2a and 2b, respectively; solid state switches 78a and
78b for connecting the terminal 1b to the terminals 2a and 2b
respectively; solid state switches 80a and 80b for connecting the terminal
2a to the terminals 3a and 3b, respectively; solid state switches 82a and
82b for connecting the terminal 2b to the terminals 3a and 3b,
respectively; and solid state switches 84a and 84b for connecting the
terminals 3a and 3b to the ground terminal Tg, respectively.
In FIG. 8, the solid state switches 74a, 78a, 82a and 84b are shown in a
closed position wherein the servo amplifier output terminal Ts is
connected to the terminal 1a, the terminal 1b is connected to the terminal
2a, the terminal 2b is connected to the terminal 3a, and the terminal 3b
is connected to the ground terminal Tg. The circuit is connected in this
manner at the end of the switching | | |
