Electrical generator or motor structure – Dynamoelectric – Linear
Reexamination Certificate
2002-12-17
2004-09-14
Lam, Thanh (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Linear
Reexamination Certificate
active
06791214
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a moving-magnet, linear motor, an aligner provided therewith, and a method for manufacturing devices, for example, semiconductor devices, using the aligner.
2. Description of the Related Art
In various types of equipment, such as machine tools and semiconductor manufacturing apparatuses, linear motors have been used to achieve accurate positioning control. In machine tools, semiconductor manufacturing apparatuses, and the like, in addition to achieving accurate positioning control, linear motors are required to produce a large thrust force for improving productivity and to have a light-weight mover.
FIGS. 9A
,
9
B, and
9
C are a top view, a side view, and an illustration of the configuration of a known moving-magnet, linear motor, respectively, by way of example. The linear motor includes a stator
800
and a mover
810
. The stator
800
includes a base
801
, a toothed-armature, iron-core
802
(sometimes referred to herein as “toothed iron-core” and iron-core) having a plurality of teeth, and a plurality of coils
803
respective coils of which are wound around respective teeth
802
a
of the iron-core
802
. The iron-core
802
and the plurality of coils
803
are fixed on the base
801
. The mover
810
has magnet rows, i.e., magnet units, formed of a plurality of permanent magnets
811
, which are orderly disposed along the traveling direction of the mover
810
, i.e., in the thrust direction of the linear motor, so as to face the upper surface of the stator
800
with a gap therebetween, and a back yoke
812
so as to provide an improved magnetic flux coupling (hereinafter, referred to as “flux linkage”) of the rows of the magnets with the coils
803
. The mover
810
is fixed to a stage (not shown) guided by a guide (not shown) and the stage is driven in the thrust direction of the linear motor.
The coils
803
along with the iron-core
802
allow the linear motor to produce a large thrust force.
Also, in the linear motor, the mover
810
is formed of magnet units so as to have a light weight. If the mover
810
is formed of coil units, the greater the number of wire turns, that is, the heavier the weight of the coils on the mover
810
so as to produce a larger thrust force, the heavier the mover
810
becomes. On the contrary, the number of wire turns, that is, the weight of the coils
803
fixed to the base
801
of the stator
800
is irrelevant to the weight of the mover
810
formed of magnet units.
In the linear motor, the length of 11 magnets
811
is equal to those of 12 stator iron-core teeth
802
a
and 12 stator iron-core slots
802
b
in the traveling direction of the mover
810
. These 12 teeth
802
a
and 12 slots
802
b
form a unit of the linear motor having a three-phase configuration. That is, this linear motor has a so-called “11-pole, 12-slot configuration”.
The stator coils
803
are connected so as to form a three-phase configuration, i.e., a U, V, and W phase configuration. The two adjacent coils in each phase are connected either in series or in parallel.
In the linear motor shown in
FIGS. 9A
to
9
C, the stator
800
has 36 slots
802
b
forming three units of three U, V, and W phase configurations. For ease of understanding, the coils in the U phase are taken as an example, and the coils in the first, second, and third units are referred to as U1, U2, and U3 coils, respectively. The U1 to U3 coils are connected to each other either in an in-phase or an opposite-phase mode with respect to the electrical degrees thereof, and are energized only when they face the magnets
811
. That is, the U1 to U3 coils are switched over in accordance with the travel of the magnets
811
. The foregoing discussion also applies to the coils
803
in the V and W phases.
The magnet rows have 14 poles, that is, 14 magnets. Among these 14 magnets, 11 magnets mainly contribute to producing a thrust force, and the remaining 3 magnets are provided so as to switch over the coils
803
.
FIGS. 10A
to
10
J illustrate the positional relationships between the moving magnets
811
and the coils
803
to be energized. In these figures, the coils
803
marked x are to be energized. In this linear motor, basically, although no two pairs of coils
803
in the same phase are energized at the same time, the two pairs of coils
803
, i.e., 4 coils=2 coils×2 pairs, are energized at the same time when these coils
803
face the moving magnets
811
at the same time. However, these coils are not energized at the instant of switch-over. The energizing currents are controlled by using sinusoidal currents so as to make the vectors of the flux linkages orthogonal to the vectors of the currents. This control is generally known as “sinusoidal driving”. The linear motor produces a thrust force by performing the sinusoidal driving and the switch-over of the coils at the same time.
Although the U1 to U3 coils are connected either in an in-phase or an opposite-phase mode to each other in the previous explanation, the U1 and U3 coils are connected in an in-phase mode to each other, and are in an opposite-phase mode with respect to the U2 coils in this example, because the linear motor has a configuration formed of 11 poles and 12 slots and the number of the poles is odd. Since one pole corresponds to 180 electrical degrees (180°), when the number of poles is odd, the three-phase coils in a unit are in an opposite-phase mode with respect to the corresponding three-phase coils in the neighboring unit.
The linear motor provided with the iron-core produces a so-called “cogging force” caused by an attractive force between the permanent magnets and the iron-core. The cogging force occurs regardless of the existence of the energizing current, and deteriorates the positioning accuracy of the linear motor. Also, the cogging force requires additional energizing current for the linear motor to produce a necessary thrust force and thereby causes the amount of heat produced by the linear motor to increase.
To solve these problems, some methods have been proposed. For example, the moving magnets may have an additional compensation pole so as to compensate for an apparent cogging force, and a plurality of linear motors may be used so as to shift the phases of the coils of one linear motor from those of the corresponding coils of the other linear motors. However, these methods only remove specific harmonic components of the cogging force and have not managed to completely eliminate the cogging force, including the harmonic components thereof.
SUMMARY OF THE INVENTION
The present invention has been made in view of the above-described background. Accordingly, it is an object of the present invention to provide a moving-magnet, linear motor, which has reduced cogging force, preferably nearly zero.
In accordance with a first aspect of the present invention, a moving-magnet, linear motor comprises a mover and at least one stator. The mover comprises a plurality of permanent magnets orderly disposed along the traveling direction thereof. The stator comprises a toothed iron-core with a plurality of teeth and a plurality of coils wound around the teeth of the iron-core. The two longitudinal ends of at least one permanent magnet among the plurality of permanent magnets are skewed with respect to each other substantially by a positive, integral multiple of a tooth pitch of the toothed iron-core.
Also, another moving-magnet, linear motor comprises a mover and at least one stator. The mover comprises a plurality of permanent magnets orderly disposed along the traveling direction thereof. The stator comprises a toothed iron-core with a plurality of teeth and a plurality of coils wound around the teeth of the iron-core. A cogging force produced by at least one permanent magnet among the plurality of permanent magnets has a phase changing from 0 to 360 degrees (0° to 360°) in a continuous or multistep manner along the length direction of the permanent magnet.
In the moving-magnet, linear motor according to the present inv
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Jones Judson H.
Lam Thanh
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