United States Patent [19J
`Trago et al.
`
`[54]
`
`[76]
`
`METHOD OF FABRICATING AN INJECTED
`MOLDED MOTOR ASSEMBLY
`
`Inventors: Bradley A. Trago, 922 Cerasus Dr.,
`Rockford, Ill. 61108; Edward J.
`Byrnes, 116 Woodland Ct., #lD,
`Carpentersville, Ill. 60110; Griff D.
`Neal, 2600 N. Southport Ave., Unit 31,
`Chicago, Ill. 60614
`
`[21]
`
`Appl. No.: 415,639
`
`[22]
`
`Filed:
`
`Apr. 3, 1995
`
`[51]
`[52]
`
`[58]
`
`[56]
`
`Int. Cl.6
`..................................................... H02K 15/04
`U.S. Cl. ........................... 29/596; 264/272.2; 310/42;
`310/43; 310/90
`Field of Search ........................ 29/596, 598; 310/42,
`310/43, 90, 71; 264/272.2, 272.19
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`2,916,642 12/1959 Macks ....................................... 310/90
`3,046,604
`7/1962 Graham et al. .
`3,156,076 11/1964 Origoni et al.
`........................... 29/596
`3,258,624
`6/1966 Turk ........................................ 310/261
`3,433,986
`3/1969 Arutunoff .................................. 310/90
`4,015,154
`3/1977 Tanaka et al. ............................ 29/596
`4,029,977
`6/1977 Chai et al. ................................ 310/49
`4,200,344
`4/1980 Binns et al.
`.............................. 310/90
`4,382,199
`5/1983 Isaacson .................................... 310/90
`4,538,084
`8/1985 Kawada et al. ......................... 310/217
`.................. 310/43 X
`4,549,105 10/1985 Yamamoto et al.
`4,626,725 12/1986 Kawada et al. ........................... 310/89
`9/1987 Nitt ....................................... 29/596 X
`4,696,631
`4,712,028 12/1987 Horber ...................................... 310/49
`4,713,570 12/1987 Mastromattei .......................... 310/154
`4,763,034
`8/1988 Gamble ................................... 310/181
`4,781,610 11/1988 Mercer ...................................... 310/71
`
`I IIIII IIIIIIII Ill lllll lllll lllll lllll lllll lllll lllll lllll 111111111111111111
`US005806169A
`[11] Patent Number:
`[45] Date of Patent:
`
`5,806,169
`Sep. 15, 1998
`
`4,841,190
`4,922,604
`5,008,572
`5,073,735
`5,191,698
`5,331,237
`5,333,957
`
`6/1989 Matsushita et al. .................... 310/257
`5/1990 Marshall et al. .......................... 29/598
`4/1991 Marshall et al. .......................... 310/45
`12/1991 Takagi ................................... 310/43 X
`3/1993 Sumi et al.
`............................... 29/596
`7/1994 Ichimura ................................... 310/44
`8/1994 Yip et al. ................................ 385/484
`
`FOREIGN PATENT DOCUMENTS
`
`0553811
`0562146
`56-094952
`59-105864
`59-220051
`31120
`WO 91/09441
`
`8/1993
`2/1959
`7 /1981
`6/1984
`12/1984
`1/1995
`6/1991
`
`European Pat. Off ..
`Italy .................................... 264/272.2
`Japan.
`Japan.
`Japan.
`Japan.
`WIPO.
`
`Primary Examiner-Carl E. Hall
`Attorney, Agent, or Firm----Leydig, Voit & Mayer
`
`[57]
`
`ABSTRACT
`
`An electrical motor and the process for forming that motor
`utilizes injection molding techniques to unitize the stator
`assembly. The stator assembly includes a stator lamination
`stack and preferably a metal front end cap which is secured
`to the lamination stack after the lamination stack is insulated
`and wound. The windings are terminated at a plurality of
`conductive pins fusion welded to the terminating ends of the
`windings. The stator assembly with front end cap in place is
`positioned in an injection molding die. Pressure is applied to
`the die, and molten plastic is injected under pressure to fill
`voids in the stator assembly, and also to form a plastic mass
`which will serve as the rear end cap. The rear end cap is also
`molded with a connector portion which fixes the conductive
`pins in place as a part of the connector. A bore formed in the
`stator assembly provides mounting surfaces for bearings on
`a rotor assembly.
`
`28 Claims, 10 Drawing Sheets
`
`95
`
`25
`
`31
`
`26
`67
`98
`
`32
`
`Mitsuba - 1010
`Page 1 of 21
`
`

`

`f~ 1
`
`I
`
`20
`
`Sep. 15, 1998
`Sep. 15, 1998
`
`5,806,169
`
`U.S. Patent
`U.S. Patent
`
`Sheet 1 of 10
`Sheet 1 of 10
`
`5,806,169
`
`26
`
`40
`
`Mitsuba - 1010
`Page 2 of 21
`
`Mitsuba - 1010
`Page 2 of 21
`
`

`

`U.S. Patent
`
`Sep. 15, 1998
`
`Sheet 2 of 10
`
`5,806,169
`
`H'EL,P .J"?;,tfTI.JA'
`LA,#. .J' .7;4C,,f'
`
`---105
`
`l#cl.£Cl70...V MOL.I)
`REAR £#1) CAP
`
`~.4tf'A//A/L"
`.---112
`CE#.TML 4&>.IPE
`
`100""'
`
`101'--
`
`102
`
`103
`
`115
`
`116
`
`Mitsuba - 1010
`Page 3 of 21
`
`

`

`U.S. Patent
`
`Sep. 15, 1998
`
`Sheet 3 of 10
`
`5,806,169
`
`52
`
`54
`
`53
`
`22
`
`/
`
`50
`
`=mmwwm&
`
`61
`
`60
`
`51
`
`,,-22
`
`63
`
`50
`
`awwwwm a
`
`23
`
`51
`
`24
`
`Mitsuba - 1010
`Page 4 of 21
`
`

`

`Sep. 15, 1998
`Sep. 15, 1998
`
`Sheet 4 of 10
`Sheet 4 of 10
`
`5,806,169
`
`U.S. Patent
`U.S. Patent
`
`70
`
`5,806,169
`
`~-70
`~~---J.~ 67
`69
`
`\
`- _.,l
`
`te::>,...~!<N'
`
`Mitsuba - 1010
`Page 5 of 21
`
`Mitsuba - 1010
`Page 5 of 21
`
`

`

`U.S. Patent
`
`Sep. 15, 1998
`
`Sheet 5 of 10
`
`5,806,169
`
`25
`
`31
`
`----26
`67
`98
`
`32
`
`II
`11
`-t..::.Ll,....::=-=--=:~iimr.-__;;::=::;;;::=-:----nmll,j-,=I - __ .....,.._ ......... _
`
`Mitsuba - 1010
`Page 6 of 21
`
`

`

`U.S. Patent
`U.S. Patent
`
`Sep. 15, 1998
`Sep. 15, 1998
`
`Sheet 6 of 10
`Sheet 6 of 10
`
`5,806,169
`5,806,169
`
`
`
`94'
`
`
`
`z
`
`Mitsuba - 1010
`Page7 of 21
`
`—
`—
`
`=~
`
`
`
`
`
` a
`UGae
`
`
`
`<2VA
`
`
`
`;:~ 11
`
`a[
`
`iS
`
`Mitsuba - 1010
`Page 7 of 21
`
`

`

`U.S. Patent
`U.S. Patent
`
`Sep. 15, 1998
`Sep. 15, 1998
`
`Sheet 7 of 10
`Sheet 7 of 10
`
`5,806,169
`5,806,169
`
`68
`
`71'
`
`
`
`
`
`73
`
`
`AWARE STOLL
`PELE (stEPSYSY.
`
`
`
`
`f:t, 12
`
`
`
`
`
`98
`
`68
`68
`
`71'
`71
`
`
`
`
`
`
`Io0BlastWeKeii hi y 2
`
`
`
`
`
`85
`
`
`
`
`Fiwg, 43
`
`f:t, 1.J
`
`73
`
`82
`
`Mitsuba - 1010
`Page8 of 21
`
`
`lg
`p
`
`LY
`
`1G
`
`.U
`
`Mitsuba - 1010
`Page 8 of 21
`
`

`

`U.S. Patent
`
`Sep. 15, 1998
`
`Sheet 8 of 10
`
`5,806,169
`
`- __ ,
`
`107
`
`27
`
`I I
`I I
`I I
`I I
`I I
`I I
`1,
`
`I I
`
`1•
`
`~
`I
`I
`
`104a
`
`104b
`
`108
`, ,
`----------~---------
`- - - - - - - - - - - - - - - - - , r- -
`11
`J ~
`'
`, ,..
`'
`I
`, , ' '
`' '
`109
`, ,.
`I
`I
`' , '
`I
`( -L./- -
`- ~.....
`, l
`/
`I
`I
`,---U~-----~-~7-~-------,
`I
`I
`,--,
`'-,•r--41
`:
`I
`I
`,,
`,,
`'t'-'
`I
`I
`I
`,,
`,,
`,,
`,,
`••
`, ,
`,,
`,,
`,,
`,.
`,,
`, ,
`,,
`,,
`,•
`, ,
`, ,
`, , ,1
`,,
`,,
`I I
`I
`,,
`,,.,,
`, ....... - .J-,- -:
`--11
`L-
`I r-l
`... ,.aJ
`,, ir ,,
`..
`ll ..J' -",z : I
`I
`t!
`'-ao
`/
`1
`26
`\
`i 105
`
`-
`
`""'
`
`I
`t
`I
`
`'94
`
`I I
`11
`I I
`
`I I
`I I
`I I
`
`110
`
`I
`
`106
`
`120
`
`Mitsuba - 1010
`Page 9 of 21
`
`

`

`U.S. Patent
`U.S. Patent
`
`Sep. 15, 1998
`Sep. 15, 1998
`
`Sheet 9 of 10
`Sheet 9 of 10
`
`5,806,169
`5,806,169
`
`
`
`111
`
`11
`
`f~ 1S
`
`---+++-+- 106
`
`~ : ,
`,,, :I
`
`''I
`
`Mitsuba - 1010
`Page 10 of 21
`
`Mitsuba - 1010
`Page 10 of 21
`
`

`

`U.S. Patent
`U.S. Patent
`
`Sep. 15, 1998
`Sep. 15, 1998
`
`Sheet 10 of 10
`Sheet 10 of 10
`
`5,806,169
`5,806,169
`
`156
`
`156
`
`155 _ 156
`
`158
`
`157
`
`
`
`a 154
`154 150
`152
`f~ fJ
`3.077
`
`150
`
`150
`
`150 wl 47
`._j 17
`
`f~ 16
`fg. 16
`
`172
`172
`
`170
`170
`
`73
`173
`
`171
`
`171 Fig 19
`f~ ti
`
`189
`189~
`
`190
`190
`180
`|
`299 181
`185
`180 185
`I
`I
`
`I
`aioeiee
`
`193
`193
`
`183
`190 44, 120 1939 196
`1 20 1~3a
`196
`
`PRISE _ -
`
`
`
`
`
`
`BS ICOZ
`
`
`Y OY fn Eos
`SSye)KZ
`
`
`
`
`
`
`
`
`
`
`Ss
`
`
`
`
`
`~~*"-202
`206
`E=3t---m..._ 192
`
`mras
`
`
`204
`
`ir bare F.
`
`
`"~-184
`
`wa) a, Orn, THD EE, WE.SE.WE
`
`
`
`
`
`
`
`Mitsuba - 1010
`Page 11 of 21
`
`Mitsuba - 1010
`Page 11 of 21
`
`

`

`5,806,169
`
`1
`METHOD OF FABRICATING AN INJECTED
`MOLDED MOTOR ASSEMBLY
`
`BACKGROUND OF THE INVENTION
`
`5
`
`2
`'604 references, an insulator having connectors is seated
`against the rear end of the stator lamination stack. The
`terminating ends of the stator windings are brought out to the
`connectors, and a printed circuit board is configured to plug
`into connectors, establishing electrical continuity between
`the stator windings and conductive traces on the printed
`circuit. A second connector having conductive pins electri(cid:173)
`cally connected to the conductive traces on the printed
`circuit, is provided in conjunction with the printed circuit
`10 board to accommodate remote access to the stator windings
`by way of a complementary external connector. In this way,
`external signals are readily connected to the stator windings
`for controlling the motor operation.
`This second connector is nested within the rear stator end
`cap. As previously described, both end caps are attached to
`the lamination stack by means of several through bolts,
`before the potting compound is applied. To prevent any
`potting compound from leaking between the rear end cap
`and the second connector, a sealing means is provided
`20 around the second connector. Although the aforementioned
`structure provides an effective means for connecting exter(cid:173)
`nal motor drive signals to the stator windings, a simpler and
`therefore more cost-effective solution is desired.
`In short, improvements are sought which will more effi-
`25 ciently address the aspects described above, while maintain(cid:173)
`ing the benefits and advantages in the motor assembly and
`method as described in the '572 and '604 references.
`
`SUMMARY OF THE INVENTION
`
`1. Field of the Art
`The present invention relates to electric motors, and more
`particularly to a fabrication method and related assembly of
`potted electrical motors.
`2. Discussion of the Related Art
`U.S. Pat. Nos. 4,922,604 to Marshall et al. and 5,008,572
`to Marshall et al., both assigned to an assignee of the present
`invention and hereby incorporated by reference, describe an
`electrical motor and fabrication method for achieving pre(cid:173)
`cise bearing registration of an internally disposed rotor 15
`assembly. As described more fully in the aforementioned
`references, an electrical motor comprising stator and rotor
`assemblies is fabricated by utilizing a potting compound to
`both unitize the stator assembly and provide improved
`thermal characteristics.
`More particularly, the stator assembly is formed from a
`stack of stator laminations having inwardly projecting poles
`that define the walls of an unfinished internal chamber for
`housing a rotor assembly. Through-bolts attach front and
`rear aluminum end caps to the lamination stack, and this
`entire stator assembly is potted to unitize the lamination
`stack and fill voids between the stator poles with potting
`compound. The internal chamber is then finished by machin(cid:173)
`ing a continuous, cylindrical bore substantially coincident
`with the sidewalls defined by the inwardly projecting stator 30
`poles. Precision registration of the rotor assembly is
`achieved by aligning end bearings on the rotor shaft with
`internal receiving surfaces machined in the stator end caps;
`the receiving surfaces being part of the cylindrical bore.
`While the motor and fabrication method described in the
`'604 and '572 references achieve substantial advances over
`the prior art, further improvements are still desired. In this
`regard, various features of the assembly and method
`described in the '604 and '572 references were identified for
`improvement.
`One area sought to be improved relates to the potting of
`the stator assembly. Specifically, it has been determined
`empirically that a double cure cycle is desired for the potting
`compound; the second cure cycle improves the rigidity of
`the stator assembly, thereby yielding more efficient opera(cid:173)
`tion over the life of the motor. When only a single cure cycle
`is employed it has been found that, after a period of use, the
`rotor assembly occasionally locks within the stator
`assembly, thereby limiting the useful life of the motor. 50
`Adding a second cure cycle, however, undesirably increases
`manufacturing costs.
`A related aspect sought to be improved is the removal of
`air pockets formed within the potting compound. As dis(cid:173)
`cussed in the '572 and '604 references, air is a poor thermal 55
`conductor. Filling the otherwise open space between the
`stator poles with potting compound, improves thermal con(cid:173)
`ductivity and, accordingly, improves dissipation of the heat
`developed within the motor. The process used in potting the
`stator assembly, however, is known to leave an air pocket 60
`under the rear end cap. This impedes the flow of heat from
`the rear end cap. Therefore, further improvements in the
`thermal characteristics of the motor assembly are sought by
`eliminating the air pocket.
`Another area sought to be further improved relates to 65
`providing external electrical connections to the stator wind(cid:173)
`ings within the motor assembly. As described in the '572 and
`
`35
`
`40
`
`In view of the foregoing, it is a primary aim of the present
`invention to simplify and, thereby, achieve a lower cost
`motor assembly and fabrication method, than that presently
`known.
`Another object of the present invention is to provide an
`electrical motor assembly having improved thermal charac(cid:173)
`teristics.
`In more detail, it is an object of the present invention to
`eliminate the small air gap between the potted windings and
`the metal of the aluminum end cap. In even greater detail, an
`object of the present invention is to provide high dielectric
`paths of good thermal conductivity between the electrical
`conductor and pole structure and the exterior of the motor,
`in order to increase the capacity of the motor to dissipate
`45 heat.
`Another object of the present invention is to provide an
`electrical motor fabrication method that simplifies the
`method previously known and used by eliminating the cost
`and time demanded by a second potting compound cure
`cycle, while maintaining the structural integrity of the final
`motor assembly.
`Still another object of the present invention is to provide
`an electrical motor assembly having a simplified and thus
`improved electrical connection between the internal stator
`windings and an external connector.
`Additional objects, advantages and other novel features of
`the invention will be set forth in part in the description that
`follows and in part will become apparent to those skilled in
`the art upon examination of the following or may be learned
`with the practice of the invention. The objects and advan(cid:173)
`tages of the invention may be realized and obtained by
`means of the instrumentalities and combinations particularly
`pointed out in the appended claims.
`To achieve the foregoing and other objects, one aspect of
`the present invention is directed to a method of producing an
`electrical motor, wherein an intermediate or unfinished
`
`Mitsuba - 1010
`Page 12 of 21
`
`

`

`5,806,169
`
`10
`
`3
`stator assembly is formed by compiling a stack of stator
`laminations and stator windings. The intermediate stator
`assembly is then placed into a mold, and molten plastic is
`injected under pressure into the mold, whereby the molten
`plastic is forced into and fills interior voids between poles of 5
`the intermediate stator assembly. The molten plastic also
`forms a rear end cap for the stator assembly. The plastic used
`in this invention may be any thermoplastically processible
`resin, or blends of such resins. The resin may optionally
`include additives such as flame retardants, reinforcements,
`colored pigments, fillers, plasticizers, heat or light stabiliz(cid:173)
`ers. Next, a continuous bore is machined through the center
`of the molded stator assembly to produce a concentric bore
`for housing a rotor assembly; the bore also providing
`mounting surfaces for receiving rotor assembly bearings.
`Finally, the rotor assembly is mounted into the stator assem- 15
`bly by inserting the rotor assembly into the continuous bore
`and engaging the rotor bearings with the mounting surfaces.
`A related aspect of the present invention is directed to the
`injection molded electrical motor assembly, which includes
`a rotor assembly having a central rotor portion on a rotor 20
`shaft, and a rotor bearing disposed near each end of the rotor
`shaft. A unitary stator assembly includes a stator lamination
`stack which forms stator poles that carry stator windings,
`and front and rear end caps. The stator poles and windings
`are substantially encapsulated by an injection molded plastic 25
`mass, which fills the space between the stator poles. The
`molded plastic also integrally forms the rear end cap. A
`continuous bore formed in the stator assembly through the
`front end cap, the stator lamination stack, and the rear end
`cap, forms mounting surfaces in the end caps for receiving 30
`the rotor bearings; the rotor assembly being carried within
`the bore by an engagement between the rotor bearings and
`the mounting surfaces in the end caps.
`Having summarized the present invention above, the
`discussion will now be directed to a preferred embodiment 35
`of the invention. As an intermediate step of the fabrication
`process of a preferred embodiment, a matrix of conductive
`pins is fusion welded to the stator windings. The rear end cap
`is formed by the injection molded molten plastic to surround
`the matrix of pins and form a connector housing about the 40
`conductive pins. In this way, the motor assembly provides a
`connector that is readily adapted for electrical connection to
`an external or remote source for controlling the motor. The
`injection molded end cap is an extension of the injection
`molded mass in the stator, and thus provides an efficient 45
`continuous path for dissipation of heat generated in the
`windings.
`
`4
`FIG. 6 is an elevational view of an individual stator
`lamination, illustrating the inwardly directed stator poles
`and pole teeth;
`FIG. 7 is a perspective view showing an assembled stator
`lamination stack made up of individual laminations as
`illustrated in FIG. 6;
`FIG. 8 is a perspective view of the front end of the stator
`lamination stack of FIG. 7 with insulators and stator wind(cid:173)
`ings in place;
`FIG. 9 is the cut-away view as illustrated by arrows in
`FIG. 6, illustrating a wound stator assembly within the caps
`and connector in place;
`FIG. 10 is a perspective view of the rear end of the
`unfinished stator assembly, showing the insulators, stator
`windings, and matrix of connector pins in place;
`FIG. 11 is a partial view illustrating the matrix of con(cid:173)
`nector pins as disposed in relation to the stator lamination
`stack;
`FIG. 12 is a partial view illustrating the partially com(cid:173)
`pleted stator assembly of FIG. 9 after injection molding;
`FIG. 13 is a view similar to FIG. 12 illustrating the
`injection molded assembly after it has been machined and is
`thus ready for insertion of the rotor assembly;
`FIG. 14 is a side elevational view showing a mold fixture
`used in fabricating the motor assembly of the present
`invention;
`FIG. 15 is a perspective view with a partial cut-away of
`the mold fixture shown in FIG. 14;
`FIG. 16 is a partly broken away side view, and FIG. 17 is
`an axial section taken along the line 17-17 of FIG. 16,
`respectively, showing an alternative construction of motor
`adapted for practice of the present invention;
`FIG. 18 is an elevational view of a rotor assembly for the
`motor of FIGS. 16 and 17; and
`FIGS. 19 and 20 are an elevational cross section and an
`axial cross section taken along the line 20-20 at FIG. 19,
`respectively, showing a permanent magnet motor adapted
`for practice of the present invention.
`Reference will now be made in detail to various presently
`preferred embodiments of the invention, examples of which
`are illustrated in the accompanying drawings.
`
`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODIMENTS
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`The accompanying drawings incorporated in and forming
`a part of the specification, illustrate several aspects of the
`present invention, and together with the description serve to
`explain the principles of the invention. In the drawings:
`FIG. 1 is a perspective view illustrating a completely
`assembled motor constructed in accordance with one
`embodiment of the present invention;
`FIG. 2 is a partially exploded view showing a motor
`according to the invention with the rotor assembly removed
`from the stator assembly;
`FIG. 3 is a process flow chart illustrating the steps of
`constructing a motor in accordance with the preferred
`embodiment of the present invention;
`FIG. 4 is an elevational view illustrating a partially
`assembled rotor, including a partial cut-away view;
`FIG. 5 is an elevational view illustrating a rotor assembly
`with bearings and bushing in place and ready for insertion
`into a stator assembly;
`
`Turning now to the drawings, FIG. 1 shows a perspective
`view of a hybrid permanent magnet stepping motor, and
`50 FIG. 2 a partly exploded view showing the rotor and rotor
`retaining elements removed from the stator assembly. It will
`be noted at the outset, however, that while the invention will
`be described in connection with a hybrid stepping motor, it
`is also applicable to other motor types. For example, the
`55 invention is applicable to brushless variable reluctance step(cid:173)
`ping motors, permanent magnet brushless motor designs,
`switched reluctance motors, enhanced variable reluctance
`motors, as well as enhanced and unenhanced stepping
`motors of the hybrid stepping type. Finally, induction motors
`60 could also utilize the present invention as could other motor
`types as will be apparent to those skilled in the art upon
`reading the following detailed description.
`Referring to FIGS. 1 and 2, there is shown a hybrid
`stepping motor generally designated by reference numeral
`65 20 comprised of a stator assembly 21 and a rotor assembly
`22. The rotor assembly is fitted with bearings 23, 24 which
`in turn mount in end caps 25, 26 that support the rotor
`
`Mitsuba - 1010
`Page 13 of 21
`
`

`

`5,806,169
`
`5
`assembly 22 for rotation in the stator assembly 21. The end
`caps 25, 26, sandwich a central stator lamination stack 27
`that forms stator poles which carry stator windings (not
`shown in FIGS. 1 and 2). In the presently preferred
`embodiment, the stator laminations are aligned in registry 5
`and initially secured by weld joints 70 (See FIG. 7) along the
`corners of the lamination stack. As will be described in
`greater detail below, the lamination stack is further secured
`by means of a high-strength injection molded plastic which
`completely encapsulates the interior of the lamination stack 10
`and preferably projects partly into a central bore 30 after
`molding. The bore 30 is then machined as by honing to form
`bearing surfaces 31, 32 (See FIG. 9) in the end caps 25, 26
`and also to form a smooth bore 30 through the lamination
`stack 27, contiguous with the bearing surfaces 31, 32.
`In the illustrated embodiment of FIG. 2, retaining rings 36
`secure the rotor assembly 22 in the stator assembly 21. In
`another embodiment, the rotor assembly 22 is retained in the
`stator assembly by a press-fit engagement between bearings
`23, 24 and receiving surfaces 31, 32. The front end cap 26 20
`has a flange 37 which in turn has a machined surface 38 with
`a mounting boss 39 to locate the motor in a mounting
`bracket. Mounting holes 40 provide means for mounting the
`motor to its bracket (not shown). The rear end cap 25
`includes an integral electrical connector 41 for supplying 25
`power to the stator windings.
`As shown in FIG. 2, the rotor assembly 22 includes a rotor
`shaft 50 which supports a rotor section 51, (i.e., the portion
`of the rotor which is magnetically active) and outboard
`bearings 23, 24. In the illustrated embodiment, the rotor 30
`comprises toothed lamination sections 52, 53 separated by a
`permanent magnet 54. The magnet is positioned to provide
`the lamination sections 52, 53 with opposite magnetic
`polarities making, for example, lamination section 52 a
`north pole and lamination section 53 a south pole. In one 35
`embodiment, the laminations are formed with external teeth,
`of the same pitch as the teeth associated with the stator poles
`of the stator assembly. Other ratios of stator/rotor pitch can
`also be used such as 52/50 or 48/50. As is known in the art,
`the teeth of section 53 are offset by about one half pitch with 40
`respect to the teeth of the section 52 in order to form a hybrid
`permanent magnet rotor. Thus, when the stator windings are
`energized by a drive current coupled through the pins of
`connector 41, the rotating magnetic field which is produced
`in the stator tends to successively align the teeth of rotor 45
`lamination sections 52, 53, with the field of the stator teeth,
`causing the motor to step in sequence. Control of the
`rotational rate and direction of the stator field thus allows
`control of the rate and direction of rotor rotation.
`Turning now to FIG. 3, there is illustrated the process for
`fabricating a motor in accordance with the present invention.
`Concentrating first on the rotor assembly, it is seen that the
`primary raw materials which go to make up the rotor are
`brought together at process step 100, and include rotor
`shafts, rotor laminations (or prestacks) and magnets. Those 55
`items are assembled at a step 101 and the assembled rotor
`which results is best illustrated in FIG. 4. There is shown a
`rotor shaft 50 having a pair of lamination stacks 52, 53
`disposed thereon, with a permanent magnet 54 interposed
`between the lamination stacks forming a rotor section 51
`intended to be driven by the rotating magnetic field pro(cid:173)
`duced by the stator. In a hybrid permanent magnet stepping
`motor, the rotor laminations 52 and 53 have alternate teeth
`and valleys of a given pitch related to ( as described above)
`the pitch of the teeth on the stator poles. Moreover, the teeth
`in the sections 52 and 53 are offset with respect to each other
`by one-half pitch. The magnet 54 serves to magnetically
`
`6
`polarize the stacks 52, 53 with, for example, the stack 52
`being a north pole and the stack 53 being a south pole.
`The shaft 50 has a pair of machined sections 60, 61
`adapted to receive the inner race of bearings 23, 24 (FIG. 5)
`for support of the rotor within the stator assembly. The shaft
`50 can have its output end keyed as illustrated, unkeyed if
`desired, or with any other adaptor configuration. The motor
`can also be configured with an output shaft on the rear end
`to form a double-ended motor. Such constructional details
`form no part of the present invention and will not be
`emphasized herein.
`Having assembled the rotor 22 in step 101 (FIG. 3), the
`rotor is then passed to a grinding station where step 102 is
`performed to grind the rotor outer diameter. Such grinding
`15 tends to produce teeth in the lamination stacks 52, 53 which
`have relatively sharp corners. In addition, the grinding step
`produces a rotor which is substantially concentric and there(cid:173)
`fore can operate in a carefully machined stator bore with a
`relatively small air gap.
`Having thus configured the rotor magnetic section 51, and
`after machining debris is cleaned from the rotor, a step 103
`is then performed in which bearings 22, 23 are assembled
`onto the bearing support surfaces 60, 61 of the rotor. In the
`exemplary embodiment, spacer bushings 62, 63 are inter(cid:173)
`posed between the bearings 23, 24 and the lamination stacks
`52, 53 respectively. The bushings ride between the lamina-
`tion stack and the inner race of the bearings to form a spacer
`element to properly locate the bearings on the shaft. The
`bearings are press fit on the shaft, preferably in an appro(cid:173)
`priate fixture, in the step 103.
`Referring to FIG. 5, there is shown the rotor assembly
`including bearings 23, 24 and the spacing bushings 62, 63,
`providing a rotor assembly which is ready for insertion into
`a stator assembly. FIG. 5 illustrates, in somewhat exagger(cid:173)
`ated fashion, the fact that the outer diameter of the bearings
`23, 24 is slightly greater than the outer diameter of the rotor
`section 51. It was previously noted that the stator bore is a
`continuous straight through bore formed in a single opera(cid:173)
`tion after assembly of the stator. Thus, providing the bear(cid:173)
`ings 23, 24 with a slightly greater outer diameter than the
`rotor section 51 allows the entire rotor assembly to be
`inserted into the bore, with the outer race of the bearing 23,
`24 seating in the bearing surfaces of the end caps while the
`rotor section 51 has a sufficient, although a very small,
`clearance for rotation. The precision thereby achieved
`allows the motor to be configured with a relatively small air
`gap, thus providing higher torque and efficient operation.
`As illustrated in FIG. 3, the initial raw material compo(cid:173)
`nent for the stator assembly procedure is individual stator
`50 laminations which are assembled in a step 105. An indi(cid:173)
`vidual lamination 27a is illustrated in FIG. 6. it is seen that
`each lamination, which can be formed by stamping, has a
`series of poles 66a with a plurality of teeth 67a formed on
`each of the poles. The poles 66a are separated by gaps 68a
`which provide an area for receiving the stator windings. The
`laminations also have punched clearance holes 69a through
`which alignment bolts can pass for initially registering the
`stator assembly. Preferably a clearance hole 69a is associ(cid:173)
`ated with each pole 66a such that the stator laminations are
`60 symmetrical and can be installed in any of eight orientations.
`Thus, it is possible in assembly to turn the stator laminations
`with respect to each other such that the grain of the steel
`from which the laminations are made is not in a single
`direction, allowing the magnetic properties of the lamination
`65 stack due to grain to be averaged.
`As illustrated in FIG. 7, the step 105 (FIG. 3) is imple(cid:173)
`mented by assembling a stack of laminations of a predeter-
`
`Mitsuba - 1010
`Page 14 of 21
`
`

`

`5,806,169
`
`7
`mined height and affixing the laminations together, in the
`illustrated embodiment by means of welds 70. Alternatively,
`prestacks (i.e., groups of laminations joined by stamped
`dimples formed during the laminations stamping operation)
`may be used. Using the welding technique, preferably a
`stack of laminations is placed under pressure, and automatic
`machinery gauges that the laminations stack is of the appro(cid:173)
`priate height before the welds are made. If it is not lamina(cid:173)
`tions are either added or removed until the desired height is
`obtained at which point automatic welding equipment pref(cid:173)
`erably applies four welds 70 at corners of the lamination
`stack displaced 90 degrees from each other. As seen in FIG.
`7, the assembled lamination stack thereupon provides a pole
`structure 66 separated by inter-pole winding gaps 68, each
`pole structure having axially disposed teeth 67 of a prede- 15
`termined pitch. It is also seen that the anchor holes 69 are
`aligned such that an alignment bolt or injection molding
`needle can pass through the lamination stack at the appro(cid:173)
`priate point in the assembly process.
`After the lamination stack is assembled, and in the 20
`optional case where an "enhanced" motor is to be produced,
`in a step 105 elongate magnetic strips 85 are inserted in each
`gap between stator teeth 67 (See FIG. 12). As will be
`described below, the magnets which are inserted between
`stator teeth tend to enhance the magnetic properties of 25
`certain classes of motor. The magnetic strips have sufficient
`frictional engagement with and magnetic attraction for the
`gaps into which they are inserted to temporarily maintain the
`strips in place during subsequent manufacturing steps until
`they are firmly secured in their gaps by means of injection 30
`molded plastic material.
`Following the magnet insertion step 105 if performed, or
`the simple welding of the lamination stack 105 for a non(cid:173)
`enhanced motor, as shown in FIG. 3 subsequent operations
`are performed on the assembled lamination stack to associ- 35
`ate the stator electrical components with the stack and to
`magnetize the stator poles. In this regard, the stack is
`insulated, wound, and the windings are terminated. In FIG.
`3 the insulation step is indicated at 106. Preferably, discrete
`insulators are supplied along with the welded stator lami- 40
`nation stack in order to provide appropriate insulation
`between the stator windings and the lamination stack. Turn(cid:173)
`ing briefly to FIG. 8, one end of the insulator assembly is
`illustrated at 71 and is shown to completely line the slot 68
`as well as to cover the face 72 of each pole 66. Upstanding 45
`insulator sections 71' help retain the stator windings, and
`will interface with the end cap when they are juxtaposed.
`Bolt protectors 71" insulate the fasteners 28 and prevent
`contact between the fasteners and the windings. A mating
`end for the insulat