Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
1999-12-08
2001-05-29
Ramirez, Nestor (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S254100, C310S256000, C310S256000, C310S208000, C310S216006
Reexamination Certificate
active
06239528
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for coiling a wire around a slotless stator core of a motor.
2. Description of the Prior Art
Components of various precision apparatuses, such as optical and electronic apparatuses, require working accuracy of the nanometer order to meet the requirement for the development of higher-accuracy, higher-density, and higher-integration versions. A very high resolution is expected of a machine tool, stepper,. electron-beam exposure system, etc. that are used to work these high-precision components. In general, these machining and manufacturing apparatuses are provided with a positioning device. In many cases, the position control of the positioning device is effected by means of a rotary servomotor or linear motor that is controlled by means of a CNC. In order to increase the working accuracy of the components, therefore, the rotary servomotor or linear motor must be controlled with high accuracy.
FIG. 10
is a schematic sectional view for illustrating a magnetic circuit of a conventional servomotor. In this servomotor, slots
24
are formed in a stator core
21
, and a winding
23
formed of a coiled wire
22
is embedded in each slot
24
, whereby a magnetic circuit is formed. In this magnetic circuit, lines
27
of magnetic force pass through tooth portions
26
between the slots
24
. Thus, the lines
27
of magnetic force extend depending on the location and shape of the tooth portions
26
, and are not influenced by the way of coiling the winding
23
.
Usually, the rotary servomotor or linear motor is subject to torque ripples, which must be minimized in order to control the motor with high accuracy.
Torque ripples can be divided broadly into two categories; one based on structural condition and the other based on electromagnetic condition. In the case of the rotary servomotor, for example, frictional resistance produced in a bearing for the shaft of a rotor can be a torque ripple based on the structural condition. On the other hand, magnetostriction caused between the rotor and a stator can be a torque ripple based on the electromagnetic condition.
Conventionally, in order to restrain the occurrence of torque ripples based on the structural condition, a proposal is made to reduce frictional resistance by supporting the shaft in a noncontact manner by means of a pneumatic or magnetic bearing. Further, use of a slotless stator core is proposed to restrain the occurrence of torque ripples based on an electromagnetic condition.
In order to form a winding by coiling a wire around a stator core, in general, slots are formed in the stator core. The slots may produce cogging torque. In the case of the stator core having slots, electromagnetic action on the rotor depends on the slot shape, and is influenced little by the wire coiling mode. Accordingly, it is necessary only that the number of turns of the winding be equal to a set number, and the position and shape of the winding are not very important factors.
In the case of the motor that uses the slotless stator core, on the other hand, the positional accuracy and shape of the winding constitute essential factors that determine the electromagnetic action on the rotor.
FIG. 11
is a schematic sectional view for illustrating a magnetic circuit of a slotless motor, and
FIG. 12
is a schematic sectional view for illustrating positional errors of a winding.
As shown in
FIG. 11
, a winding
33
is pasted on the inner surface of a ring-shaped stator core
31
of the slotless motor that is opposed to a rotor
35
. The stator core
31
is formed having no slots or tooth portions. Since lines
37
of magnetic force are influenced by the location and the way of coiling of the winding
33
, the positional accuracy of the winding
33
pasted on the stator core
31
constitutes a factor that determines the incidence of torque ripples.
As shown in
FIG. 12
, the positional errors of the winding include (a) misalignment between turns of the wire in each block of the winding, (b) an error in the pasting position for the wire in the circumferential direction of the stator core, and (c) an error in the pasting position for the wire in the radial direction of the stator core. In some cases, torque ripples attributable to the positional errors of the winding are greater than in the case of a motor having slots.
A method for coiling a wire around a slotless stator core has already been proposed.
FIGS. 13 and 14
are views for illustrating this coiling method.
As shown in
FIGS. 13 and 14
, windings
52
in the form of a simple segment each are prepared in advance by coiling a wire like an array by means of a jig or the like. These segment-shaped windings
52
are pasted on a stator core
51
and then connected to one another through a connecting wire. By doing this, the positional accuracy of the windings during assembly can be improved.
According to this method for coiling the wire around the slotless stator core, however, the winding is pasted on only one side of the stator core, so that satisfactory strength cannot be obtained with ease. In the case where the entire structure is molded, therefore, the winding may come off as a molding agent undergoes cure shrinkage.
Since the segment-shaped windings overlap one another, moreover, they must have a complicated three-dimensional shape. More specifically, a first-phase winding segment
52
(e.g., segment of U-phase winding), second-phase winding segment
54
(e.g., segment of V-phase winding), and third-phase winding segment
55
(e.g., segment of W-phase winding) overlap partially one another, and are pasted continuously on the stator core
51
in the circumferential direction. In order to fix the height of a straight portion (which serves as a magnet) of each segment in the normal direction, therefore, the winding segment
52
is formed having a bent portion
53
.
The bent portion
53
is a portion in which the coating of the wire can be broken most easily, and is situated corresponding to an edge portion of the stator core. Therefore, a short circuit between lines or line-to-ground fault easily occurs in this portion. Accordingly, the wire is subjected to a substantial bending stress, so that its coating may be broken, possibly causing a short circuit between lines or line-to-ground fault. Besides, it is hard to arrange the winding segments with high positional accuracy, due to positional errors attributable to differences in shape and size between the segments or errors in the normal direction caused by adhesive bonding.
As shown in
FIG. 15
, showing stator
30
moreover, winding lugs
58
protrude in the axial direction of a motor shaft
56
from the stator core
51
. The lugs
58
have no electromagnetic effect on the rotor. If the number of turns increases, therefore, the motor size becomes larger, thus constituting a hindrance to miniaturization. In the example shown in
FIG. 16
, spot-faced grooves
59
are formed by cutting those portions of a housing
57
of a support member for the stator and the like which correspond to the lugs
58
, individually. If the motor is reduced in size in this manner, its mechanical rigidity lowers inevitably.
OBJECTS AND SUMMARY OF THE INVENTION
The object of the present invention is to provide a method for coiling a wire around a slotless stator core with high positional accuracy, thereby forming a winding capable of generating a uniform magnetic field.
In an aspect of the present invention, there is provided a method in which a winding is formed by toroidally coiling a wire like an array around a slotless stator core, whereby a stator of a rotary or linear motor is formed.
In the following explanation, “toroidal coiling” means a coiling method carried out in a manner such that wire is coiled without any intersecting turns in one direction for the formation of the winding as it is coiled rotating spirally. By using this coiling method, the accuracy of the position of the winding in the direction tangent to the surface of the stator core can be improved.
Further, “
Kawai Tomohiko
Sawada Kiyoshi
Suzuki Masaki
Fanuc Ltd.
Lam Thanh
Ramirez Nestor
Staas & Halsey , LLP
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