Two-phase excitation linear motor

Details Two-phase excitation linear motor Two-phase excitation linear motor

2002-02-08

2003-12-09

Ramirez, Nestor (Department: 2834)

Electrical generator or motor structure

Dynamoelectric

Linear

C310S013000

Reexamination Certificate

active

06661128

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a two-phase excitation linear motor.
2. Description of the Related Art
A linear motor has a simple structure, comprises a small number of parts, and drives a moving body linearly, and its drive is precise and quick. The linear motor is widely applied to linear driving devices and positioning devices in all fields such as exposing devices for manufacturing semiconductors, and highly precise machine tools.
In a general liner motor, as shown in
FIG. 8
, a current is allowed to flow through a coil unit (a moving body in this example) Ci placed between magnet rows Mg opposing to each other (fixed body in this example), and a Lorentz force generated drives the coil unit Ci. The magnet rows Mg are arranged such that the direction of a pair of an N pole and an S pole opposing to each other is altered one by one as shown in
FIG. 9. A
distance between the closest pairs of N/S poles facing in the same direction is referred as a magnetic pole pitch. A sinusoidal magnetic flux density distribution is generated between the magnet rows Mg where the magnetic pole pitch is one cycle. The magnetic pole pitch after normalization is represented as 2&pgr;.
The individual single coils
2
for constituting the coil unit Ci are in an approximately rectangular ring-like shape (a racetrack shape) as a whole as shown in FIG.
10
. Two sides of the four sides of this rectangle opposing to each other in a direction perpendicular to a traveling direction function as a pair of effective conductors
4
a
and
4
b
for contributing to generating a thrust force for a moving body in a linear motor. The other two sides opposing to each other form a pair of connecting conductors
6
a
and
6
b
for connecting between the effective conductors
4
a
and
4
b,
and these parts do not specifically contribute to generating a thrust force for the linear motor.
When a current is allowed to flow through the single coil
2
, the directions of the current are opposite to each other between the effective conductors
4
a
and
4
b
(indicated as U and U macron). Thus, because the signs of the magnetic fluxes are opposite to each other, when the distance T
1
between the effective conductors
4
a
and
4
b
is set to a distance corresponding to &pgr;, the thrust force becomes twice as much as that generated on one effective conductor
4
a
or
4
b.
It is necessary to provide a constant thrust force wherever the single coil
2
may be positioned along the magnet rows Mg for operating the linear motor smoothly. Because the magnetic flux density has the sinusoidal distribution, it is impossible to use one single coil for providing a constant thrust force in whatever way the current may be adjusted. It is necessary to connect the multiple single coils placed with intervals as one pole.
Three phases of (three) single coils
2
U,
2
V, and
2
W are arranged such that their positional phases are displaced by an amount corresponding to (⅔)&pgr; to one another for using them as one pole in a three-phase excitation motor as shown in FIG.
11
. Then, when a current with a phase matching the phases of the magnetic flux densities at the effective conductors
4
a
and
4
b
of the individual single coils
2
U,
2
V, and
2
W is allowed to flow therethrough as shown in
FIG. 12
, a constant thrust force can be obtained even if the positions of the three single coils
2
U,
2
V, and
2
W (a coil unit Ci
3
as a whole) move.
On the other hand, two single coils
2
A and
2
B are displaced by an amount corresponding to &pgr;/2 as a positional phase to form one pole for a two-phase excitation motor as shown in
FIG. 13. A
distance between the two single coils
2
corresponds to &pgr;, and the single coil itself is identical to that for the three-phase excitation motor. Then, when a current with a phase matching the phases of the magnetic flux densities at the effective conductors
4
a
and
4
b
is allowed to flow through the individual single coils
2
A and
2
B as shown in
FIG. 14
, a constant thrust force can be obtained even if the positions of the two single coils
2
A and
2
B (a coil unit Ci
2
as a whole) move.
Because three-phase excitation motors can maintain a motor constant (N/W: a thrust force provided with an equivalent current) high, three-phase excitation motors are used more than two-phase excitation motors in general.
However, the two-phase excitation motors can be applied to an area of the applications where the three-phase excitation motors cannot meet a dimensional requirement.
When the three-phase excitation motor or the two-phase excitation motor is structured such that multiple single coils for the individual phases are simply piled up as shown in
FIG. 11
or
FIG. 13
, the distance M
3
or M
2
between the magnet rows opposing to each other increases, thereby decreasing the magnetic flux density. It is necessary to arrange the effective conductors for the individual phases in a single row, thereby minimizing the distance M
2
or M
3
between the magnet rows Mg, resulting in constituting an effective linear motor. However, a simple racetrack shape as in
FIG. 10
prevents arranging the effective conductors
4
a
and
4
b
in a single row because of the existence of the connecting conductors
6
a
and
6
b.
There have been different types of proposals for the arrangement while the mutual interference between the connecting conductors
6
a
and
6
b
is avoided as much as possible.
Because it is primarily required for the two-phase excitation motors to reduce the size as described before, a method to arrange two single coils
2
A and
2
B corresponding to the A phase and the B phase separately in the same row while the coils are maintained to have the racetrack shape as shown in
FIG. 15
is adopted especially to maintain the distance between the magnet rows as short as possible.
When the two single coils
2
A and
2
B are separated while their phases in the magnetic flux density are being maintained, they can function as a two-phase excitation motor; A form where single coils are arranged separately is referred as a “separate type” two-phase excitation motor for convenience in the present specification. Though
FIG. 15
shows a case where two single coils are separated by (2k+½)&pgr;(k=1, 2, 3, . . .), the phases of the individual single coils
2
A and
2
B should be opposed to each other when they are separated by (2k−{fraction (
1
/
2
)})&pgr; as shown in FIG.
16
.
FIG. 17
shows an: example of the applications.
A main motor is indicated as a symbol
12
in
FIG. 17
, and is constituted with a conventional three-phase excitation motor. Because a coil unit
12
Ci for the main motor
12
is used with multiple poles in general, a wiring harness
14
for wiring the coil unit
12
Ci becomes thick and heavy, and becomes a resistance when the coil unit
12
Ci for the main motor
12
travels. Then, a separate type two-phase excitation motor
16
is separately provided such that the motor
16
strides across the main motor
12
to drive the wiring harness
14
in synchronization with the main motor
12
as shown in
FIG. 17
(B). Gaps are provided between a case
12
a
for the main motor
12
and a case
16
a
for the two-phase excitation motor
16
to prevent a contact between these cases when there is a difference between their travels. Thus, the two-phase excitation motor
16
does not affect the travel of the main motor
12
at all (while the motor
16
moves in synchronization with the motion of the main motor
12
). Because the wiring harness
14
is attached to the two cases
16
a
for the two-phase excitation motor
16
, and the wiring harness
14
does not affect the travel of the main motor
12
at all (while the harness
14
moves in synchronous with the motion of the main motor
12
).
When a separate type two-phase excitation motor is applied in this way, the separated single coils do not cause any problems, and the separate existence becomes an advantage on the contrary.
Though placing two

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