Note: Descriptions are shown in the official language in which they were submitted.
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1 Back~round of the Invention
2 This invention relates to variable reluctance step-
3 per motors and a method of making such stepper motors.
4 Variable reluctance stepper motors are characterized
by a plurality of pole members having windings associated
6 therewith and an additional magnetic structure cooperating
7 with the pole members to close the various flux paths in re-
8 sponse to the selective energization of the windings. The
9 pole members include pole faces having magnetic discontinui-
ties therein which cooperate with similar magnetic discon-
11 tinuities in the additional magnetic structure so as to permit
12 the poles and the adtitional magnetic structure to move in dis-
13 crete steps relative to one another in response to the selec-
14 tive energization of the windings.
Some variable reluctance stepper motors have pole
16 structure which require that the windings be wrapped around
17 the pole members with the magnetic structure in placeO The
18 wrapping of such pole members, particularly in the case of a
19 rotary stepper motor, can be very expensive since it is diffi-
cult to ~utomate such winding and the motors must therefore
21 be made, in large measure, by hand.
22 SummarY of the Invention
23 Advantages of this invention are to provide for
24 ease, cost effectiveness and automation in ~he fabrication of
a stepper motor.
26 In accordance with the invention there is provided
27 a stepper motor of the variable reluctance type comprising a
28 plurality of poles having a plurality of magnetic discontinui-
29 ties at a plurality of pole faces is formed by adhesively
bonding one portion of a pole structure having windings
31 wrap?ed around pole members to another portion of the pole
32 structure.
33 In accordance with one important aspect of the inven-
34 tion, the windings may be preformed on bobbins and placed on
the pole members before the adhesive bonding.
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1 In a particularly preferred embodiment of the inven-
2 tion~ the other portion of the pole structure comprises pole
3 faces which are adhesively bonded to the pole members. The
4 pole faces are preformed from a continuous member and subse-
quently adhesively bonded to the portion of the pole struc-
6 ture carrying the windings. After adhesive bonding, the con-
7 tinuous member is cut into the separate pole faces associated
8 with the various pole members. Magnetic discontinuities are
9 formed in the continuous member before adhesive bonding.
In the preferred embodiment, the one portion of the
11 pole structure is formed by grinding the pole members into a
12 lamination to a depth so as to leave a connecting segment be-
13 tween the pole members. In the alternative, the pole members
14 may be separately formed with or without the pole faces
attached and subsequently adhesively bonded to a connective
16 member. Where the pole members are formed without the pole
17 faces, the pole faces are also adhesively bonded to the pole
18 members.
19 In one embodiment of the invention described in de-
tail hereinafter, the pole structure forms the stator of an
21 axial air gap rotary stepper motor. The windings are wrapped
22 around the pole members such that the axes of the windings ex-
23 tend in a direction parallel to the axis of the motor. The
24 pole members comprise a substantially uniform cross-sectional
area.
26 Brief Description of the Drawin~s
27 Fig. 1 is a perspective view of a blank utilized in
28 forming a portion of the pole structure of this invention;
29 Fig. la is an enlarged view of a portion of the
blank shown in Fig. l;
31 Fig. 2 is a perspective, partially schematic illus-
32 tration of the blank of Fig. 1 being formed into pole members;
33 Fig. 3 is a perspective view of a preformed winding
34 being placed on a pole member formed by the step of Fig. 2;
Fig. 4 is a perspective view of a blank from which
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1 the pole faces will be formed;
2 Fig. 5 is a perspective view of the blank of Fig. 4
3 after the magnetic discontinuities or teeth of the pole faces
4 have been ~ormed;
Fig. 6 is a perspective view of the ring of Fig. 5
6 after adhesive bonding to the pole structure of Fig. 3;
7 Fig. 7 is a perspective view of the structure of
8 Fig. 6 after the ring has been cut so as to form separate pole
9 faces;
Fig. 8 is a plan view of the pole faces of Fig. 7;
11 Fig. 9 is a side view of the pole structure of Fig.
12 8;
13 Fig. 10 is a sectional view of the pole structure of
14 Fig. 8 taken along line lO-10 thereof in combination with addi-
tional magnetic structure including a rotor and an inactive
16 stator portion;
17 Fig. ll is a perspective view of an alternative
18 method of fabricating the pole structure of Figs. l-lO; and
l9 Fig. 12 is a perspective view of yet another altern-
ative method of fabricating the pole structure of Figs. 1-10.
21 Detailed DescriPtion of Preferred ~mbodiments
22 Referring to Fig. 1, the annular member lO which is
23 adapted to form one portion of a stator pole structure for a
24 variable reluctance stepper motor is shown. The annular mem-
ber 10 comprises a high permeability magnetic material, e.g.,
26 iron, in the form of a plurality of laminations 12 which may
27 be wound in the form of a coil as shown in Fig. la.
28 In Fig. 2, the annular member 10 is being ground by
29 a crush grinding wheel 14 so as to preform pole members 16.
The pole members 16 are ground from the member 10 to a depth
31 so as to leave a continuous annular support segment 18.
32 In accordance with this invention and as shown in
33 Fig. 3, the pole structure as formed in Fig. 2 is now ready
34 for application of the windings of the variable stepper motor.
As shown in Fig. 3, one of these windings 20 is preformed on
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1 a bobbin 22 having an opening 24 therein so as to be placed
2 down over the pole members 16. In this regard, it will be
3 noted that the pole members 16 are of substantially uniform
4 cross-sectional area so as to permit the pole members 16 to
freely pass through the opening 24 and substantially conform
6 with the area of that opening. Having now described the for-
7 mation of the one portion of the stator pole structure with
8 reference to Figs. 1-3, the formation of the pole face portion
9 of the stator structure will now be described with reference
to Figs. 4 and 5.
11 As shown in Fig. 4, a continuous member or ring 26
12 is provided. This ring which is also formed from a high per-
13 meability magnetic material is adapted to have discrete mag-
14 netic discontinuities in the form of teeth 28 as shown in Fig.
5 formed therein. The teeth 28, as shown in Fig. 5, are
16 located at four different pole face positions. The exact
17 location of the teeth 28 in accordance with stepper motor de-
18 sign may be readily achieved by utilizing a coining or electro-
19 chemical etching technique to form the teeth 28.
In accordance with this invention, the ring 26 with
21 the teeth 28 is then a & esively bonded to one end of the pole
22 members aæ shown in Fig. 6 with the winding 20 already on the
23 pole members as a result of the step shown in Fig. 3. It is
24 important to appropriately place the teeth 28 at the various
pole positions with respect to the pole members enclosed with-
26 in ~he windings 20 in accordance with standard stepper motor
27 design techniques. The ad~esive bonding agent may comprise
28 an epoxy resin or other agent capable of assuring an appropri-
29 ate bonding strength without substantially affecting the flux
paths.
31 After the ring 26 is adhesively bonded to the pole
32 members, the individual pole faces 30 are formed in the ring
33 by cutting the ring at four different locations between the
34 pole members and the windings 20. This cutting of the ring 26
may be achieved by grinding.
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Reference will now be made to Figs. 8-10 for a
description of the stator pole construction of Figs. 1-8 in
a variable reluctance stepper motor. As shown in Figs. 8 and
9 twithout the rotor or the inactive stator portion), the
motor includes a sleeve 32 having a flange 34 attached to the
segment 18 of the pole structure. Referring to Fig. 10, the
sleeve 32 includes a bearing support area 36 which is adapted
to receive a shaft which supports a rotor 38 in the stator-to-
stator air gap 40 between the pole faces 30 and an inactive
stator portion 42 having similar pole faces 44. For more de-
tails concerning the actual stepper motor assem~ly, reference
is made to copending Canadian Patent Application 303,683,
filed May 18, 1978 and to U. S. Patent No. 4,198,582 granted
April 15, 1980 on an application filed in the United States
on June 24, 1977.
In the embodiment of Figs. 1-8, the pole members
were ground from an annular laminated structure and the pole
faces were adhesively bonded to the pole members so formed.
In Fig. 11, the pole members 16a are integrally formed with
the pole faces 30a having teeth 28a at one end and the other
end of the pole members 16a are adhesively bonded to an annu-
lar support segment 18a. In Fig. 12, the pole mem~ers 16b
are adhesively bonded to the pole faces 30b as well as an
annular support segment 18b at both ends thereof.
As shown in both Figs. 11 and 12, the pole faces
30a and 30b are individually and separately formed and do not
form a continuous ring as shown in Fig. 6. It will, however,
be appreciated that the pole faces 30a and 30b may be formed
in a continuous ring and severed after the adhesive bonding
is completed.
Although the invention has been described in terms
of a pole structure for the stator of a rotary stepper motor,
it will be understood that the method and the product formed
by the method is equally applicable where the pole structure
forms a moving member in the stepper motor and/or the motor is
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linear rather than rotary. In other words, this invention is
equally applicable to moving or stationary pole structures
and/or linear or rotary stepper motors.
Various stepper motors of various designs which
could benefit from the principles of this invention are dis-
closed in a book entitled "Theory and Applications of Step
Motors" by Benjamin C. Kuo, West Publishing Co., 1974. Ref-
erence is also made to this book for a full and complete ex-
planation of the manner in which stepper motors operate.
Although particular embodiments of the invention
have been shown and described, it will be appreciated that
other embodiments and modifications will occur to those of
ordinary skill in the art and such embodiments and modifi-
cations will fall within the true spirit and scope of the in-
vention as set forth in the appended claims.
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