Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
2002-08-26
2004-05-04
Lam, Thanh (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S012060
Reexamination Certificate
active
06731029
ABSTRACT:
TECHNICAL FIELD
The invention relates to a linear motor, and in particular a canned linear motor, used for, for example, feeding in electronic component inspection apparatuses and machine tools, etc., in which an increase in temperature is suppressed and constant-rate feeding accuracy is required.
PRIOR ARTS
In a canned linear motor provided with three-phase armature winding at its stator and a permanent magnet, used as a field system, at its mover, the armature winding is directly cooled by a coolant, wherein an increase in the surface temperature of the linear motor can be suppressed to be low.
However, according to the conventional art, since there is completely no problem if a structure in which a mover and a stator are replaced with each other is employed, such a type in which the mover is provided with armature winding has been frequently used in applications where the stroke is long.
Herein, a description will be given mainly of a canned linear motor in which an armature winding formed of a plurality of coil groups is made into a mover, and a plurality of permanent magnets of which used field systems, which have different polarities from each other are juxtaposed adjacent to a stator. However, the canned linear motor is not limited to this specification.
FIG. 8
is a perspective view showing the entirety of a linear motor in a conventional art. In
FIG. 8
, reference number
80
denotes a mover, reference number
81
denotes a mover base, reference number
84
denotes a can, reference number
31
denotes a coolant discharge port, reference number
32
denotes a coolant supply port, reference number
33
denotes a cable, reference number
90
denotes a stator, reference number
91
denotes a stator base, reference number
92
denotes a field system yoke, and reference number
93
denotes a permanent magnet.
The mover
80
is formed to be T-shaped as described later, wherein its longitudinal member (armature) is supported by a linear guide, an air slider, and a slider guide, etc., between the permanent magnets
93
disposed between the field system yokes
92
and
92
of the stator
90
, and by causing an appointed current to flow into the armature winding, the longitudinal member operates with a magnetic field produced by the permanent magnets
93
to generate a thrust in the mover
80
, by which the motor
80
is movable in the directions of travel shown by the arrows.
FIG.
1
(
b
) is a cross-sectional view of a conventional art linear motor of
FIG. 8
when observing the same from the front side thereof. In the drawing, the mover
80
is formed to be T-shaped. The mover
80
is composed of a mover base
81
, a can
84
supported in a depression of the mover base
81
downward, a header
84
′ (See
FIG. 5
) to seal the can
84
, a winding fixing frame
82
disposed in a gap produced by the can
84
and the header
84
′, a coreless type three-phase armature winding
83
, which is fixed at the winding fixing frame
82
, and a coolant passage
87
passing through the can
84
.
FIG.
5
(
a
) shows a side elevational view of the mover, and
FIG. 6
shows a view of arranging an armature winding when being observed from the mover side. Herein, as shown in
FIG. 6
, the armature winding
83
is formed of three phases and is thin plate-shaped. By adhering the same to both the right and left sides of the winding fixed frame
82
, the entirety of the armature winding is constructed, and the strength thereof is improved. Also, since the winding fixing frame
82
itself needs strength, the winding fixing frame
82
is frequently made of stainless steel.
The can
84
is rectangular-tubular, for which a stainless steel thin plate is bent to be channel-shaped and welded together. Two headers
84
′ (
FIG. 5
) made of stainless steel casting are provided with a coolant supply port
32
and a coolant discharge port
31
, through which a coolant is permitted to pass. The can
84
and headers
84
′ are welded together at the conjunction plane.
Also, by causing a coolant to be supplied through the coolant supply port
32
and to be discharged through the coolant discharge port
31
, the coolant flows through a coolant passage
87
(FIG.
1
(
b
)) located between the armature winding
83
and the can
84
.
On the other hand, as shown in FIG.
1
(
b
), the stator
90
is recess-shaped so that it can wrap the armature portion of the mover
80
. The stator
90
is composed of a permanent magnet
93
disposed at both sides of the can
84
and header
84
′ of the mover
80
with a gap, a field system yoke
92
made of a magnetic body that causes a magnetic flux produced by the permanent magnet
93
to pass through, and a stator base
91
to support the same. Also, a plurality of permanent magnets
93
juxtaposed in the direction of travel are disposed so that the same have a different polarity from each other at each polarity pitch &lgr; (FIG.
8
).
The canned linear motor thus constructed operates with a magnetic field produced by the permanent magnet of the stator by causing an appointed current appropriate to a position of the mover to flow into the armature winding, wherein a thrust is generated at the mover, and the armature winding heated due to a copper loss is cooled by the coolant, and a temperature rise at the surface of the mover can be suppressed to be low.
However, in the conventional art, there are the following problems.
The can
84
, winding fixing frame
82
, header
84
′, etc., are made of stainless steel as described above. The members made of stainless steel materials generate an eddy current ie at each polarity pitch &lgr; by passing between the permanent magnets
93
of the stator
90
. FIG.
5
(
b
) shows a view of an occurrence of the eddy current ie. As has been made clear in FIG.
5
(
b
), the eddy current ie of the conventional art device flows, depicting a large loop, so that the flow passage extends entirely in the vertical direction of the can
84
and header
84
′. And, a viscous damping force is generated by vertical direction constituents of the eddy current ie. The viscous damping force crosses the magnetic flux produced by the eddy current ie and permanent magnet
93
and is generated in a reverse direction of the direction of travel of the mover
80
. The intensity thereof is almost proportionate to the thickness and width of stainless steel, travel speed of the mover
80
, number of points where the eddy current ie occurs, and square of the magnetic flux density. The following problems further occur due to generation of such a viscous damping force.
(1) Where a certain thrust is attempted to be gained, the thrust is decreased equivalent to the size of the viscous damping force even if an appointed armature current is caused to flow, wherein it becomes necessary to cause a greater armature current to flow than is usually necessary. Resultantly, the copper loss of the armature winding is increased, temperature of the can and the surface of the header is accordingly increased.
(2) The eddy current is converted to heat as a so-called eddy current loss at a point where an eddy current is generated. That is, the can, winding fixing frame and header where the eddy current is generated are heated, resulting in a further rise in temperature. In applications where the temperature is remarkably limited, there may be a case where no expected specification can be satisfied by the heating.
(3) Recently, a viscous damping force has tended to be further increased in line with a request for increasing the speed, and further the viscous damping force is generated in a reverse direction of the travel direction of the mover, wherein the speed of a linear motor is subjected to fluctuations due to fluctuations of the viscous damping force. Since influences of the viscous damping force onto fluctuations in the speed of the linear motor are comparatively slight in comparison with a thrust generated, the influences are not highly emphasized. However, in recent years, requests to decrease fluctuations in the speed have increased in line with r
Irie Nobuyuki
Shikayama Toru
Yoshida Shusaku
Yu Jian-Ping
Kabushiki Kaisha Yaskawa Denki
Lam Thanh
Westerman Hattori Daniels & Adrian LLP
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