CA1081756A - Synchronous motor - Google Patents
Synchronous motorInfo
- Publication number
- CA1081756A CA1081756A CA281,663A CA281663A CA1081756A CA 1081756 A CA1081756 A CA 1081756A CA 281663 A CA281663 A CA 281663A CA 1081756 A CA1081756 A CA 1081756A
- Authority
- CA
- Canada
- Prior art keywords
- stator
- teeth
- systems
- annular
- magnetic
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02K—DYNAMO-ELECTRIC MACHINES
- H02K21/00—Synchronous motors having permanent magnets; Synchronous generators having permanent magnets
- H02K21/38—Synchronous motors having permanent magnets; Synchronous generators having permanent magnets with rotating flux distributors, and armatures and magnets both stationary
- H02K21/44—Synchronous motors having permanent magnets; Synchronous generators having permanent magnets with rotating flux distributors, and armatures and magnets both stationary with armature windings wound upon the magnets
Abstract
ABSTRACT:
A synchronous motor, in particular a stepping motor, with two coaxial stator sections which are each provided with a ring coil and with two circular systems of teeth, which are shifted by half a tooth pitch relative to each other. The two stator sections are shifted by a quarter tooth pitch relative to each other.
In addition the motor comprises means, in parti-cular an axially magnetized permanent-magnetic ring which is disposed between the two stator systems, for magnetizing the two systems of teeth of the stator sections with mutually the same polarity. The two systems of teeth of each stator section are constituted by annular parts which are provided with teeth at the inner circumference, which annular parts form part of the magnetic circuit which surrounds the annular coil and which annular parts are disposed concentrically in such a way that the axial distance between the teeth of both systems is at least a few times greater than the air gap between stator and rotor.
A synchronous motor, in particular a stepping motor, with two coaxial stator sections which are each provided with a ring coil and with two circular systems of teeth, which are shifted by half a tooth pitch relative to each other. The two stator sections are shifted by a quarter tooth pitch relative to each other.
In addition the motor comprises means, in parti-cular an axially magnetized permanent-magnetic ring which is disposed between the two stator systems, for magnetizing the two systems of teeth of the stator sections with mutually the same polarity. The two systems of teeth of each stator section are constituted by annular parts which are provided with teeth at the inner circumference, which annular parts form part of the magnetic circuit which surrounds the annular coil and which annular parts are disposed concentrically in such a way that the axial distance between the teeth of both systems is at least a few times greater than the air gap between stator and rotor.
Description
Pl-iN ~ !~5 IIC
5.5. 1977 17'Sf~
Synchronous motor.
The invention relates to a synchronous motor comprising at least two coaxial stator sections which are each provided with at least one annular coil, which annular coil is surroun-ded by a magnetic circuit of a soft ferro~agnetic - material, which circuit i5 constituted by a rotor section with toothings and by the stator section which surrounds the relevant annular coil, ~hich . - 10 stator section terminates in two systems of s:tator teeth which are arran~ed in a circle, and .
which co-operate with the rotor teeths across air gaps in such a manner that at any time the ~ position of one o~ both systems of stator teeth ~ 15 of each stator section relati~e to t-he co-operating~
: rotor tee-th dif~ers half a tooth pitch fro~l the : po3ltl0n of tlle other system of stator teeth of tllat stator section rela-~ive to the co-operating rotor teeth, meaRs bei~ provided for each stator .
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PfIN 8l15llC
10817S6 ~.5.1977 teeth with mutually the same polarity.
Sucha motor is particular~y suitable as stepping motor and :is known from Germ~l Patent Application 25 14 503, Fig. 3, which has been laid open for public inspection. In this motor the said means are constituted by an axially magne-tized annular permanent magnet which is coaxial with two stator sections and is disposed between these two stator sections. This permanent magnet magnetizes the two systems of teeth of each stator section with the same polarity, whilst the annular coil assoclated with said stator section magnetizes the two systems of teeth with opposite polarity. As a result of this the rotor exhibits a preferred position relative to the teeth of one of the two systems of teeth depending on the sense of energization of said annular coil. These two positions are offset by half a tooth pitch relative to each other. The other stator section is shifted by a quarter tooth pitch relative to the one stator section, so that there are pre-ferred positions. If the two stator coils are energized in the correct sequence, the rotor perfor=s a rotary movement in a synchronous or ste~-wise fashlon, depending on the nature of the ener-gization.
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.10~1~5i6 PHN 8 45 4C
In this known motor both systems of stator teeth of each stator section are consti-tuted by axially e~xtending teeth, the teeth of both systems interdigita-te, i.e at any time one tooth of the one sy3tem being disposed between two teeth of the other system. It is found that the electromagnetic properties of this motor deteriorate substantially when the stepping angle, ; which is related to the number of poles per circumference, is reduced, for example to 1.8 . which corresponds to 50 teeth per ~ystem.
It is an object of the invention to pro~ide a motor of the type mentionsd in the preamble which is extremely suitable to be equipped with a large number of stator teeth per ~ system of stator teeth.
.~ Forthis~purpose the invention is characterized in that the two systems of teeth o~
each stator section are constituted b~ annular - 20 parts which are provided with teeth at the inner .
circumference, which annular parts both form part : o~ the magnetic circuit which surrounds the annu-lar coil and which annular parts are disposed concentricall~ in such a way that the axial dis-: ~ 25 tanoe between the teeth~of the two syste~ls is at ~ ~ least a ~ew times greater than the air gap between : the systems of stator teeth and the rotor.
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PIIN 81~5I~C
5.5- 1977 75~
Thestep in accordance with the invention readily enables a construction to be realized with a large number of teeth per system of stator teeth, without giving rise to impermissible stray fields 5 in the air gap.
Itis found that the torque produced by this motor as a function of the rotor position is non-symmetrical, i.e. it is not the same for both current directions which are possible in the stator coils. This asymmetry also results from the fact that the magnetic resistance constituted by the air gap formed by the permanent magnetic ring is not infinite, so that via the permanent - magnetic ring magnetic circuits are formed for the : 15 fields produced by the stator coils. As the direc-tions of these fields depend on the direction of : the energizing current through these coils, the working point of said permanent magnetic rîng depends on this direction of energization, which also causes said asymmetric t~rquc.
Said asymmetry may also result from the fact that the magnetic resistances from said means ...
for magnetizing the systems of stator teeth to each:of the two systems of teeth are unequal for saoh stator section. Other typesof asymmetry also 1sad to asymmetric torques, depending on the design of the motor in accordance with the invention.
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' PHN 8~54C
5.5.1977 5~ii These asymmetries can be compensated for in that the stator sections are divided into an even number of segments along axial surfaces, the stator teeth for each stator secti.on being mutually shifted by half a tooth pitch relative to the rotor teeth of each time two adjacent segments and said means for each stator section magnetizing the two systems of each time two adjacent segments with opposite polarities.
Asowing to said means the magnetization .of two adjacent segments is oppositely directed and the teeth are shifted by half a tooth pitch relati~e to each other, the asymmetries in the torque owing to each of these segmen$s are in 15 phase opposition and do not appear in the total torque produced by the rotor.
: . The asymmetries in the torque of a motor in accordance with the invention may also be compensated for by a step which is characteri~ed - .
- 20 in that the motor comprises at least one compensa-tion coil whose magnetic circuit 1~ in parallel with the magnetic circuit of said means.
This compensation coil may increase or reduce the influence of said means. By energizing this compensation coil depending on the energiza-tlon of the stator coils a symmetrical torque can be obtained. The correct method of energizing the compensation coil can readily be det~rmined em~rically.
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If said ~neans are constituted by an axially magnetized ring which is coaxially disposed between two stator sections, it is advantageous that said compensation coil is annular and is disposed between the two stator sectlons coaxially with the permanent~magnetic ring.
: - For said steps in accordance with the invention it is advantageous to avo-d air gaps in the magnetic stator circuits which surround the annular coils. This is suitably achieved in that the magnetic stator circuits surrounding the ring coils comprise integrally manufactured laminations which are substantially disposed in axial planes.
: ~ These laminations can be arranged cor-rectly in a simple manner when the ring coils ars surrounded by a coil former provided with posi-tioning means for the alignment of the said l;aminations.
~ For forming the stator toothings in the .. . oase that the said laminations are used, it is of ~ ad~antage that said laminatir~ns are U~shaped, - the limbs of the laminations extending within the 25~ airgap between stator and rotor for the formation of the. systems o~ stator teeth, whilst said posi-tioning means are such that in 1;he air gap, the end .~ .
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PHN 8 l~5 l~C
of the one limb of e~ch U-shaped la~ination is shifted by half a tooth pitch relative to -the end of the other limb.
In this motor, which employs an axially magnetized permanent-magnetic ring, i-t - i9 of advantage for a minimal dispersion o~ the flux of this permanent magnet that the laminations at the side facing the permanent-magnetic ring are provided with a folded portion which is disposed in a plane which is substantially perpendicular to the axis for the conduction o~ the flux of the permanent magnet.
With a synchronous motor in accordance with the invention in which the per~anent magnetic ring is situated between the two stator sections , anasymmetry may occur in that the magnetic resistances of the permanent magnetic rings to each of the two systems of teeth are unequal per stator section. An ad~antageous construction which eliminates this, i~ oharacterized în that the two magnetic stator circuits of the two stator sections, which circuits surround the ring coils, each time consist o~ two parallel annular plates : :
~ ~ which are disposed in planes subs-tantially perpen~
`~ ~ 25 dicular o the rotor axis, at whose inner circum-~erence said systems of teeth are formed and ~hose outer circumference each time adjoins the inner . .
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P~N 8454C
5.5.1977 ~0817~6 surface of a cylindrical ring belonging to said stator section, between which plates and the cylindrical ring the ring coil is interposed, the two cylindrical rings extending as far as the permanent magnetic ring and being provided with means for catching the flux of the permanent mag-netic ring,so that be-tween the two annular plates facing the permanent magnetic ring and the perma-nent magnetic ring spaces are obtained with a magnetic resistance which i5 comparatively high relative to the magnetic resistance between the permanent magnetic ring and the cylindrical rings.
Inthis construction the flux of the permanent magnet passes via said catching means to the cylindrical ring and hence, via a transition, to the two annular plates, so that the - paths to the two systems of teeth are identical.
The last-mentioned construction neces-~ sarily results in spaces between stator sections - 20 ~nd permanent maenet. These spaces are utilized eff~ctively if in said spaces annular coaxially - ~ disposed compensation coils are accommodated.
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Th,se coils then have a similar function as the pre~iously mentioned compensation coil.
The invention will now be described in more detail with reference to the drawing, in which: -' ':
: " _g_ PHN 8ll5L~C
7l3~
Figure 1 shows an aYial cross-section of a motor in accordance with the inventioll, Figure2 is an exploded view correspon-ding to said axial cross-section, Figure 3 schematically shows the posi--- tions of the stator and rotor teeth relative to each other, Figure 4 is an energizing diagram for the mo$or in accordance with Figures 1, 29 5, 6 Figure 5 shows an alternative vers.on of the motor of Figure 1 in axial cross~section, . . .
Figure 6 is a plan view of an e~bodiment of a motor in accordance with the invention with segmen$ed stator9 : Figure7 shows an axial cross-section :~ of the motor in acoordance with Figure 6 taken : on the line VII-VIIJ
.
. : Figure 8 schematically shows the .: 20 positions of the stator and rotor teeth of the motor ~ in accordance with Figures 6 and 7relative to each . ~ :
other, Figure 9 is a perspective view of a lamination in accordance with a I~ur~her charac-teristic feature of the invention, .. . .
~ Figure 10 shows the construction of a .
~; stator section with lami.nations in accordance .- ~ .
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,, --1 0--P~-IN 845'lC
with Figure 9.
Figure 11 shows a motor in accordance with Figure 1 provided with a compensation coil, Figure 12 shows a suitable ~ariant of the motor in accordance with Figure 11, and Figure 13 shows a suitable variant of the motor in accordance with Fig. 1.
Figure 1 is an axial cross-section of a motor to which the steps in accordance with the invention may be applied, Figure 2 being an axial cross-section of the motor in perspective. The ~ motor is rotation-symmetrical about the axis A-A~.
- It comprises a rotor 1, which consists of a cylin-;~ drical body with four circular discs 2 which are disposed in a plane perpendicular to the axis A-A~, which discs are provided with a regular pattern of rotor teeth 3 along the oircumference.
The rotor~is made of a soft ferro-magnetic material.
~The stator comprises two sections 4 and 5 which each consists of an annular coil 6 and 7 respecti~ely, which are surrounded by a yoke 8 and : ~
9 respectively9 of a soft ferromagnetic material, " :
which yokes terminate in annular systems of toothings 10, 11 and 12, 13 respectively.
~-! 25 These toothings are disposed in the same plane :,i : , .. . .
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PHN 8ll54c 5.5-1977 .
- as the rotor disc 2 and all comprise an equal number of teeth. A stepping motor with a stepping angle of 1.8 requires 50 teeth per circumference.
Per stator segment the toothings in the two systems are shifted by half a tooth pitch rela$ive to each other, whilst the two sections are shifted by a quarter tooth pitch relative to each other.
The two stator sections are axially separated by a ring 14 of a permanent magnetic material, which ring is 'axially magnetized.
The permanent magnet 14 gives rise to a magnetic field, which is represented in the left half of Figure 1 by a dashed line 16 with arrows.
For this field the two stator sections 4 and 5 and the rotor 1 are in series, whilst per stator section the two air gaps near the toothings 10, 11 and 12, 13 respectively are in parallel. As a result of this the magnetic potential difference across every pair of air gaps is substantially equal and e~ually directed owing to the permanent magnet.
For a certain energi2ation the ring coils 6 and 7 produce a field as represented in ~; the right half of Figure 1 by dashed lines 17 and 18 provided with arrows. The magnetic circuit for this field per stator s~ction comprises the yokes 8 and 9 respecti~ely, the two systems of teeth 10, .
; ' ' ' .
5-5~1977 11 and 12, 13 respectively and the rotor. Owing to this the magneti.c potential difference across the air gaps near the systems of teeth 10, 11 and 12, 13 respectively is alternately of different polarity, so that per stator section when the coils are energized the magnetic potential difference across one of the air gaps is reduced and the magnetic potential difference across the other air gap is increase~ so that one of the two systems of teeth of a stator section is activated as if it were dependent-on the sense of energization of the coils. If a certain coil is not energized, the two systems of teeth of said stator section are equally active and because the two systems.are shifted by half a tooth pitch relative to each other, no force is exerted on the rot.~r.
In order to explain the operation of :. the motor in accordance with Fig. 1 and 2, . ~ 20 Figure 3 schematically shows the mutual position :
o:~ -the systems of stator teeth 10, 11, 12 and 13 and~the rotor toothing 3 for five different~posi-t:ions P1 through P$ relative to the stator toothings and ~igure 4 shows an energizing diagram for the ~25 coils 6 ~(Fig. 4a) and 7 (Fig. 4b).
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PllN 8!l5~C
S.5.1977 ~8~ S~
current (+I) the magnetic potential difference across the air gaps near the stator toothings 10 . and 12 is greater than the magnetic poten-tial difference across the air gaps near the stator toothings 11 and 13 respectively.
If it is assumed that at the instant : ` ~0 the rotor teeth 3 are disposed slightly before the stator teeth 10, the rotor will move, upon energization o~ ring coil 6 whilst ring coil : 10 is unenergized, until the rotor teeth 3 are disposed exactly opposite the stator teeth 10.
: This is the position with the smallest magnetic - resistance for that air gap with the greatest : magnetlc potential difference. This position is positioned P1 in Figure 3. If at the instant t1 the coil 7 is now energized with a positive current +I and coil 6 is de-energized, the magne-tic pot~tial diffe~ence across the air gap near the stator toothing 12 will be greatest, whilst :
. 20 the rotor toothing 3 will be disposed a quarter ' ~- tooth~pitch before the stator toothing 12. The rotor~is then a-ttracted until the rotor teath 10 are opposite the stator taeth 12, this is . ~ ~
: : position P2. Similarly, after the instant t2, after which coil 6 is energized with a negati~e , current and coil 7 is de-energized, the rotor will ; move to position P3, this is with its teeth 3 . . .
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- 1 4- , PllN 8454C
opposite the stator t~e-th 11, and after the - instant t3, after which coil 7 is energized with a negative cur:rent and coil 6 is de-energized?
to position Pl~, this opposite the stator toothing 13. The rotor now assumes a similar position relative to the stator toothing as jus-t before the - instant to ~ld a full stepping cycle is completed.
A displacement by one tooth pitch is consequently performed in four steps. If the total number of teeth equals 50 m the stepping angle will be 1.8. --Figures1 and 2 show that per stator section the two systems of teeth are shifted by half a tooth pitch relative to each other and that two stator sections are shifted by a ~uarter tooth pltch relative to each otner. It is also possible to give all the systems of stator teeth the same position relative to each other and to rotate the systems at rotor teeth by 0, -~9 ~ and 3/4 tooth pitch relative to each other, or a combination thereof. For a correct operation of th,e motor the position of -the one system of stator teeth relative to the corresponding system ~, of rotor teeth per stator section should be shifted ~25 by half a tooth pitch relative to the position of the other system of stator teeth relative to the - corresponding system of rotor teeth.
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P~IN 8l~54c 5.5.1977 ,r56 The motor may consist o~ more than two stator sections. T]hese sections are then always separated by a ring magnet which is axially magnetized in the appropriate direction.
It is possible to replace the ring magnet 14 by a ring coil.
It is also possible to include the permanent msgnet in the rotor in such a way that the field line pattern is maintained, for example an axially magnetized magnet, or a ring coil, at the location indicated by the dash-dot line 15 in Fig. 1. At the location where the magnet 14 is shown in Fig. 1 a connection with good magne-:
ticconduction must then be provided.
For the purpose of illustration Fig. 5 - shows a longitudinal section of a rnotor whose operation is the same as that the motor o~ Fig.1.
The various parts are numbered in accordance ~th - ~ Fig. 1 and the description is also applied to it.
The motor in accordance with Fig. 5 has been ; ~ obtained by axially compressing the rotor o~ the :: ~
motor in accordance with Figure 1 to one disc and by increasing the tooth depth. The two stator :,- ' : :
sections are now disposed above and u~derneath ; 25 the~diso and co-operate with one and the same system 3~o~ rotor teeth. The various magnetic circuits are represented by dashed arrows in ., .
. .
.,.
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.~., . -PHN 845LIc ~.5~1977 - the same way as in P`ig. 1.
In prac-tice the motor of Fig. 1 is found to produce asymtnetrical torques for various reasons, inter alia owing to the difference in magnetic resistance from the permanent magnet 1l~
to for example the system of teeth 10 and the system of teeth 11 and the difference in magnetic~
resistance of the air gaps belonging to these systems of teeth viewed through the field of the coil 6, owlng to the difference in the directions of the fields in these ~r gaps. A solution to this problem is the axial di~ision of the stator section into an even number segment whose toothings are shifted relative to each other by half a tooth pitch, the polarity of the corresponding segment of the magnetic ring 14 being also reversed.
Figure 6 is a plane view of the motor in accordance with Fig. 1 to which this step is applied (which may for example also be used ln - 20 the motor of Figure 5)O The Figure 6hows the top Burface of the yoke 8 of stator section 4 with tator tee-th 10 and the rotor 1 with rotor teeth 3. The stator is divided into four segments, designated a, b, c, d. The segments b and d 25 ~ as well as the segments a and c are identical, whllst the toothings 10a and 10c are shifted by hal~ a tooth pitch relative to the toothings 10b ' ',: . ',.
' PHN 8ll5LIC
5.5.1977 and 10d. As Q result of this the toothings 10b and 10d are shifted by half a tooth pitch - relative to the rotor teeth 3 when the teeth - . of the toothings 10a and 10c are exactly opposite the rotor teeth. The to~hings 11, not shown, are again shifted by half a tooth pitch per segment - relative to the toothings 109 whilst the other : stator section 5 is shifted by a quarter tooth pitch relati~e to the stator sectinn 4. I'he four segments are separated from each other by means of air gaps in order not to short-circuit the field of the permanent magnet.
Figure7 is a cross-section of the motor in accordance with Figure 6 taken on the line VII-VII and i.5 numbered in a similar way as the motor of ~igure 1 with the addition of the indexes a and b. The magnetic ring 14 at the . location of segment a is magnetized oppositely : _ to the magnetization and the location o~ segment b, which is indicated b~ the arrows 19 and ~0.
If for a certain energi~ing current +I
through coil 6 the:magnetia potential difference across the air gap near system of teeth 10a and 10c is large relative to the magnetic potantial ;"
di~ference across the air gaps near the systems of te~th 11a and 11c, the same applies withlres-pect to the systems of teeth 11b and 11d relative ., .
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5.5.1977 to the systems of teeth 10b and 10do The same applies to the systems of teeth 12 and 13 in a corresponding manner.
Figure 8 schema-tically shows the position of the systems of stator teeth 10, 11, 12 and 13, of which only the segments a and b are shown. The seg~ents c and d occupy the same positions relative to the rotor teeth 3 as the segments a and b respectively. The rotor toothing 3 is shown in ~ive positions P1 ; through P5, which positions are always shifted by a quarter tooth pitch relati~e to each other.
Thecoils are energized in accordance with the energizing diagr~ of Figure 4, the polarities of the currents being defined relative to the stator segment a in the same manner as for the motor in accordance with Figure 1.
It is assumed that at the instant to the rotor teeth 3 are disposed slightly before the stator teeth 10a and 10c, and thus slightly before - . ..
~ ~ the stator teeth 11b and 1ld, the rotor will mae :
until~ the rotor teeth 3 are exactly opposite said stator teeth upon energization of the ring coil 6 whilst ring coil 7 is unenergized. This is the position P1 in Fig. o. If at the instant t1 coil 7 is energi~ed with a positi~e current ~I and coil 6 is~de-energized,~ the magnetic potential difference ~:
1: : , . . .
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PII~ 8~l54C
5.5.1977 across the air gap near the stator toothings 12a, 12c, 13b and 13d will be greatest, whilst the rotor toothing 3 is disposed a quarter tooth ~tch before said stator toothings. The rotor will then be attracted until the rotor teeth are opposite the last-mentioned stator teeth, this is position B2.
Similarly, after the instant t2, after which coil 6 is energized with a negative current and coil 7 is de-energized, the rotor will move to position P3, i.e. with its toothing 3 opposite the stator toothings 11a, 11c, 10 b and 10d, and after instant t3, after which coil 7 is energized irith a negative current and coil 7 is de-energized, to position P~, this is opposite the rotor toothings 13a, 13cg 12b a~d 12d. The rotor now has again assumed the same position relative to the stator toothing as j~st before the instant to and a full cycle has been completed.
. ~ . , .
` ~ Although Figs. 6 and 7 show a division into four axial segments~ any axial division into an even number of segments is possible, though a division lnto two segments is unfavourable because in that case unbalanced radial forces will be exerted on the rotor. In a similar way as with , :
~`~ 25 the motor in accordance with Fig. 1 it is possible to arrange the toothings 10, 11, 12 and 13 in the same posltion and to arrange the various rotor `~ toothings at 0, ~ 3/4 tooth pitch from each - .
~ other.
- - 2~-PIIN 8ll54C
5.5.1977 .7~6 It is also possible to use a plurality . of stator sections.
In the s~gmented motor of Figs. 6 and 7 the permanent magnetic rin~ 14 may be replaced by permanent magnets which are disposed in the two stator sections between the segments at the locations 35, 36, 37 and 38 indicated in Fig. 6.
These magnets should then be magnetized tangen-tially relative to the rotor, the direction of magnetization of the magnets: at the locations . 35 and 37 being opposite to the direction of magnetization of the magnets at the locations 36 and 38, as is indicated by the dashed arrows in Fig. 6.
The stator section for a motor in accordance with the in~ention can be manufactured - simply by enclosing the ring coil 6, 7 between two parallel annular plates 30 and 21 (Figo 2) ~ and a cylindrical ring 22. This results in two transi-tions 23 and 24 in the yoke 8. However, it is .: ~ . fo~nd that in the case of motors with a small air .
~ gap between stator and rotor this gives rise to an . ~
asymmetrlcal torque, because the magnetic resis-tance in the circuit via plate 21 to the rotor ~iewed from the p~rmanent magnetic ring 14, lS
~: then too small relative to the magnetic resistance i.n the circuit via plates 22 and 30.
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N. 8454C.
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A solution to this problem is to construct the yoke 8 (and 9) from U-shaped laminations which are placed over the ring coil in substantially axial planes. Figure 9 shows an example of such a U-shaped lamination and Fig. 10 shows the construction of a stator section with such laminations.
The laminations can be made of a flat sheet material and bent in such a way that one of the limbs 25 is shifted by half a tooth pitch ~/2 relative to the other limb 26. Similarly a portion 27 can be bent at right angles. This portion 27 may adjoin the adjacent lamination and also serves as a contact face with the permanent-magnetic ring 14.
Figure 10 shows the stator section 5. It comprises the ring coil 7 in a former 28 of for example a plastic. During manufacture suitable slots may be f~rmed in this former into which slots the laminations can be slido By bending the laminations the one system of teeth is always shifted by half a 2n tooth pitch relative to the other system of teeth.
It is alternatively possible to use non-bent laminations and to slide these onto the coil former in an oblique position relative to the axial planes, or to slip -~
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them onto the coi1 former in axial plane and shift corresponding systems of rotor teeth by half a tooth pitch, Furthermore, the bent portion 27 may be dispensecl with when between the magnetic ring 14 and the stator section 5 and 4 respectively a disc of a soft-magnetic material is included. Instead of slots in the coil former it i9 alternatively possible to use projections and the like for positioning.
It is very advantageous to construct the stator sections in accordance with Fig. 10 f'dr a motor in accordance with Figure 6, because the shift of the teeth of the segments b and d rela-tive to the segments a and c by half a tooth pitch can simply be obtained by suitably arran-ging the slots or projections of the coil former 28. The same laminations may then be used for nll segments.
~or ~e motor of Fig~ 1 it is found that the torque as a function of the rotor position is not symmetrical, i.e. not the same for bo$h possible directions of the current in the coil 6 and 7 respectively. This asymmetry is produced as a result of the magnetic resistance constituted by Z5 the air gap formed by the permanent magnet t4 not being infinite so that for the fields produced by the coils 6 and 7 respectively magnetic circuits , ~ , ' ~ :
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PHN 84~4C
! , 5.5.1977 ~:98~
are formed via the permanent magnet 14. As the direction of these fieldsdepends on the direction of the energizing current through the coils 6 and 7 respectively, the working point of the permanent magnet 14 depends on this direction, which causes the said asymmetrical torque.
Figure 11 is an axial cross-section of a motor in accordance with Fig. 1 in which steps have been taken to mitigate the said asymmetry.
These steps include the incorporation of a coaxial ring coil 30' between the two stator sections 4 and 5. By energizing this ring coil 30~ in such a way that the field of this ring coil in the perma-nent magnet 14 is directed oppositely to the field of the ring coils 6 and 7, the working point of the permanent magnet 14 c~ be maintained substantially constant.
In the ease that each time one phase is energized the number of amp~re-t~rns (this is the p:roduct of the current through the coil and the number of turns of said coil) of coil 30' should be approximately half the number of ampère-turns .
of the energlzed coil 6 or 7.
As has already been remarked with respect to the motor in accordance with Fig. 2, the stator sections 4 and 5 for a motor in accordance with the invention can be manufactured in a simple :~: ~ , . . , ~. .
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.
PHN 8454c , 5.5.1977 7C~6 : manner by enclosing the ring coils 6 an.d 7 : respectively between two parallel annular toothed plates 20 and 21 (Fig. 2, Fig. 12) and a cylin-drical ring 22 which may surround the pla-tes 20 and 21 (Fig. 12). In that case and also with other methods of manufacture, transitions 23 and 24 are formed in the yoke 20, 21~ 22. As previ-ously stated, this also leads to an asymmetry in the torque.
Fig. 12 shows an axial cross-section of a motor in accordance with Fig. 2, for which the last mentioned-problem has been solved. Be-tween the st~Dr systems 4 and 5 and the permanen-t magnet 14 comparatively large air gaps are formed . 15 tin.Fig~ 12 filled by the coils 32 and 33 respec~
: tively). Said cylindrical ring 22 then extends as : far as the permanent magnet 14, the flux of said permanent magnet 14 being caught by an annular disc .. 31 which is surrounded by the cylinder 22. Thus the magnetic path from the permanent magnet 14 to the system of teeth 10 has the same magnetic resistance as the path to the system of teeth 11~ The sarne applies to the stator section 5.
The space which has become available owing to the use of addi~ional airgaps may be used e~fectively by choosing two ring coils 32 and 33 ~` instead of the compensation coil 30 in the motor of . : . .
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5..5. 1977 s ~ 756 ~ig. 11 and to place these ring coils in these two spaces. The ring coils 32 and 33 may then be energi~ed simultaneously ~or alternately).
The compensation coils in the motors in accordance with Figs. 11 and 12, in respect of the energization of one or both stator coils 6 and 7, should be energized so that the magnetic potential difference across the permanent magnet is independent o~ the energizing condition of the coils 6 and 7.
Fig. 13 is an axial cross-section of a variant of the motor of Fig. 1. Corresponding parts bear the same reference numerals. The parts on which the stator teeth 10, 11, 123 13 are provided in the motor of Fig. 13 are widened in comparison with the motor of Fig. 1. The two stator sections 8 and 9 consist of two annular parts 40, 41 and - 42, 43 respectively, between which the annular coil 6 or 7 i9 disposed. These parts can be manu-factured simply, for example from sintered iron7 and provided with teeth7 for example by milling the inner circumference, and subsequently assembled with the permanent-magnetic ring 14 shifted through angles of 0, 180, 90 and 270 relative to each other.
The rotor 1 comprises a shaft on which :
two annular parts 2 are mounted, each with an axial length in accordance with that of the stator ':
i: :
~- -26-PHN 845~1C
5.5.1977 P ~81'7~t;
sections 8 and g and constricted near the shaft so as to reduce the mass moment of inertia. These rings 2 are provided with teeth 3 at least opposite the stator teeth 10, 11, 12 and 13, which may ~or example be formed by milling the outer circumfe-rence of the parts 2. The operation of the rnotor further corresponds to that of the motor of Fig.1.
- The invention is not limited to the embodiment shown. A multiplicity of variants to be basic principle described with reference to Fig.1 are posslble.
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5.5. 1977 17'Sf~
Synchronous motor.
The invention relates to a synchronous motor comprising at least two coaxial stator sections which are each provided with at least one annular coil, which annular coil is surroun-ded by a magnetic circuit of a soft ferro~agnetic - material, which circuit i5 constituted by a rotor section with toothings and by the stator section which surrounds the relevant annular coil, ~hich . - 10 stator section terminates in two systems of s:tator teeth which are arran~ed in a circle, and .
which co-operate with the rotor teeths across air gaps in such a manner that at any time the ~ position of one o~ both systems of stator teeth ~ 15 of each stator section relati~e to t-he co-operating~
: rotor tee-th dif~ers half a tooth pitch fro~l the : po3ltl0n of tlle other system of stator teeth of tllat stator section rela-~ive to the co-operating rotor teeth, meaRs bei~ provided for each stator .
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PfIN 8l15llC
10817S6 ~.5.1977 teeth with mutually the same polarity.
Sucha motor is particular~y suitable as stepping motor and :is known from Germ~l Patent Application 25 14 503, Fig. 3, which has been laid open for public inspection. In this motor the said means are constituted by an axially magne-tized annular permanent magnet which is coaxial with two stator sections and is disposed between these two stator sections. This permanent magnet magnetizes the two systems of teeth of each stator section with the same polarity, whilst the annular coil assoclated with said stator section magnetizes the two systems of teeth with opposite polarity. As a result of this the rotor exhibits a preferred position relative to the teeth of one of the two systems of teeth depending on the sense of energization of said annular coil. These two positions are offset by half a tooth pitch relative to each other. The other stator section is shifted by a quarter tooth pitch relative to the one stator section, so that there are pre-ferred positions. If the two stator coils are energized in the correct sequence, the rotor perfor=s a rotary movement in a synchronous or ste~-wise fashlon, depending on the nature of the ener-gization.
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.10~1~5i6 PHN 8 45 4C
In this known motor both systems of stator teeth of each stator section are consti-tuted by axially e~xtending teeth, the teeth of both systems interdigita-te, i.e at any time one tooth of the one sy3tem being disposed between two teeth of the other system. It is found that the electromagnetic properties of this motor deteriorate substantially when the stepping angle, ; which is related to the number of poles per circumference, is reduced, for example to 1.8 . which corresponds to 50 teeth per ~ystem.
It is an object of the invention to pro~ide a motor of the type mentionsd in the preamble which is extremely suitable to be equipped with a large number of stator teeth per ~ system of stator teeth.
.~ Forthis~purpose the invention is characterized in that the two systems of teeth o~
each stator section are constituted b~ annular - 20 parts which are provided with teeth at the inner .
circumference, which annular parts both form part : o~ the magnetic circuit which surrounds the annu-lar coil and which annular parts are disposed concentricall~ in such a way that the axial dis-: ~ 25 tanoe between the teeth~of the two syste~ls is at ~ ~ least a ~ew times greater than the air gap between : the systems of stator teeth and the rotor.
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PIIN 81~5I~C
5.5- 1977 75~
Thestep in accordance with the invention readily enables a construction to be realized with a large number of teeth per system of stator teeth, without giving rise to impermissible stray fields 5 in the air gap.
Itis found that the torque produced by this motor as a function of the rotor position is non-symmetrical, i.e. it is not the same for both current directions which are possible in the stator coils. This asymmetry also results from the fact that the magnetic resistance constituted by the air gap formed by the permanent magnetic ring is not infinite, so that via the permanent - magnetic ring magnetic circuits are formed for the : 15 fields produced by the stator coils. As the direc-tions of these fields depend on the direction of : the energizing current through these coils, the working point of said permanent magnetic rîng depends on this direction of energization, which also causes said asymmetric t~rquc.
Said asymmetry may also result from the fact that the magnetic resistances from said means ...
for magnetizing the systems of stator teeth to each:of the two systems of teeth are unequal for saoh stator section. Other typesof asymmetry also 1sad to asymmetric torques, depending on the design of the motor in accordance with the invention.
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' PHN 8~54C
5.5.1977 5~ii These asymmetries can be compensated for in that the stator sections are divided into an even number of segments along axial surfaces, the stator teeth for each stator secti.on being mutually shifted by half a tooth pitch relative to the rotor teeth of each time two adjacent segments and said means for each stator section magnetizing the two systems of each time two adjacent segments with opposite polarities.
Asowing to said means the magnetization .of two adjacent segments is oppositely directed and the teeth are shifted by half a tooth pitch relati~e to each other, the asymmetries in the torque owing to each of these segmen$s are in 15 phase opposition and do not appear in the total torque produced by the rotor.
: . The asymmetries in the torque of a motor in accordance with the invention may also be compensated for by a step which is characteri~ed - .
- 20 in that the motor comprises at least one compensa-tion coil whose magnetic circuit 1~ in parallel with the magnetic circuit of said means.
This compensation coil may increase or reduce the influence of said means. By energizing this compensation coil depending on the energiza-tlon of the stator coils a symmetrical torque can be obtained. The correct method of energizing the compensation coil can readily be det~rmined em~rically.
' ' ' ' , . --6-- -PHN 8lf51~C
t75;~6~
If said ~neans are constituted by an axially magnetized ring which is coaxially disposed between two stator sections, it is advantageous that said compensation coil is annular and is disposed between the two stator sectlons coaxially with the permanent~magnetic ring.
: - For said steps in accordance with the invention it is advantageous to avo-d air gaps in the magnetic stator circuits which surround the annular coils. This is suitably achieved in that the magnetic stator circuits surrounding the ring coils comprise integrally manufactured laminations which are substantially disposed in axial planes.
: ~ These laminations can be arranged cor-rectly in a simple manner when the ring coils ars surrounded by a coil former provided with posi-tioning means for the alignment of the said l;aminations.
~ For forming the stator toothings in the .. . oase that the said laminations are used, it is of ~ ad~antage that said laminatir~ns are U~shaped, - the limbs of the laminations extending within the 25~ airgap between stator and rotor for the formation of the. systems o~ stator teeth, whilst said posi-tioning means are such that in 1;he air gap, the end .~ .
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PHN 8 l~5 l~C
of the one limb of e~ch U-shaped la~ination is shifted by half a tooth pitch relative to -the end of the other limb.
In this motor, which employs an axially magnetized permanent-magnetic ring, i-t - i9 of advantage for a minimal dispersion o~ the flux of this permanent magnet that the laminations at the side facing the permanent-magnetic ring are provided with a folded portion which is disposed in a plane which is substantially perpendicular to the axis for the conduction o~ the flux of the permanent magnet.
With a synchronous motor in accordance with the invention in which the per~anent magnetic ring is situated between the two stator sections , anasymmetry may occur in that the magnetic resistances of the permanent magnetic rings to each of the two systems of teeth are unequal per stator section. An ad~antageous construction which eliminates this, i~ oharacterized în that the two magnetic stator circuits of the two stator sections, which circuits surround the ring coils, each time consist o~ two parallel annular plates : :
~ ~ which are disposed in planes subs-tantially perpen~
`~ ~ 25 dicular o the rotor axis, at whose inner circum-~erence said systems of teeth are formed and ~hose outer circumference each time adjoins the inner . .
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P~N 8454C
5.5.1977 ~0817~6 surface of a cylindrical ring belonging to said stator section, between which plates and the cylindrical ring the ring coil is interposed, the two cylindrical rings extending as far as the permanent magnetic ring and being provided with means for catching the flux of the permanent mag-netic ring,so that be-tween the two annular plates facing the permanent magnetic ring and the perma-nent magnetic ring spaces are obtained with a magnetic resistance which i5 comparatively high relative to the magnetic resistance between the permanent magnetic ring and the cylindrical rings.
Inthis construction the flux of the permanent magnet passes via said catching means to the cylindrical ring and hence, via a transition, to the two annular plates, so that the - paths to the two systems of teeth are identical.
The last-mentioned construction neces-~ sarily results in spaces between stator sections - 20 ~nd permanent maenet. These spaces are utilized eff~ctively if in said spaces annular coaxially - ~ disposed compensation coils are accommodated.
~ .
Th,se coils then have a similar function as the pre~iously mentioned compensation coil.
The invention will now be described in more detail with reference to the drawing, in which: -' ':
: " _g_ PHN 8ll5L~C
7l3~
Figure 1 shows an aYial cross-section of a motor in accordance with the inventioll, Figure2 is an exploded view correspon-ding to said axial cross-section, Figure 3 schematically shows the posi--- tions of the stator and rotor teeth relative to each other, Figure 4 is an energizing diagram for the mo$or in accordance with Figures 1, 29 5, 6 Figure 5 shows an alternative vers.on of the motor of Figure 1 in axial cross~section, . . .
Figure 6 is a plan view of an e~bodiment of a motor in accordance with the invention with segmen$ed stator9 : Figure7 shows an axial cross-section :~ of the motor in acoordance with Figure 6 taken : on the line VII-VIIJ
.
. : Figure 8 schematically shows the .: 20 positions of the stator and rotor teeth of the motor ~ in accordance with Figures 6 and 7relative to each . ~ :
other, Figure 9 is a perspective view of a lamination in accordance with a I~ur~her charac-teristic feature of the invention, .. . .
~ Figure 10 shows the construction of a .
~; stator section with lami.nations in accordance .- ~ .
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,, --1 0--P~-IN 845'lC
with Figure 9.
Figure 11 shows a motor in accordance with Figure 1 provided with a compensation coil, Figure 12 shows a suitable ~ariant of the motor in accordance with Figure 11, and Figure 13 shows a suitable variant of the motor in accordance with Fig. 1.
Figure 1 is an axial cross-section of a motor to which the steps in accordance with the invention may be applied, Figure 2 being an axial cross-section of the motor in perspective. The ~ motor is rotation-symmetrical about the axis A-A~.
- It comprises a rotor 1, which consists of a cylin-;~ drical body with four circular discs 2 which are disposed in a plane perpendicular to the axis A-A~, which discs are provided with a regular pattern of rotor teeth 3 along the oircumference.
The rotor~is made of a soft ferro-magnetic material.
~The stator comprises two sections 4 and 5 which each consists of an annular coil 6 and 7 respecti~ely, which are surrounded by a yoke 8 and : ~
9 respectively9 of a soft ferromagnetic material, " :
which yokes terminate in annular systems of toothings 10, 11 and 12, 13 respectively.
~-! 25 These toothings are disposed in the same plane :,i : , .. . .
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PHN 8ll54c 5.5-1977 .
- as the rotor disc 2 and all comprise an equal number of teeth. A stepping motor with a stepping angle of 1.8 requires 50 teeth per circumference.
Per stator segment the toothings in the two systems are shifted by half a tooth pitch rela$ive to each other, whilst the two sections are shifted by a quarter tooth pitch relative to each other.
The two stator sections are axially separated by a ring 14 of a permanent magnetic material, which ring is 'axially magnetized.
The permanent magnet 14 gives rise to a magnetic field, which is represented in the left half of Figure 1 by a dashed line 16 with arrows.
For this field the two stator sections 4 and 5 and the rotor 1 are in series, whilst per stator section the two air gaps near the toothings 10, 11 and 12, 13 respectively are in parallel. As a result of this the magnetic potential difference across every pair of air gaps is substantially equal and e~ually directed owing to the permanent magnet.
For a certain energi2ation the ring coils 6 and 7 produce a field as represented in ~; the right half of Figure 1 by dashed lines 17 and 18 provided with arrows. The magnetic circuit for this field per stator s~ction comprises the yokes 8 and 9 respecti~ely, the two systems of teeth 10, .
; ' ' ' .
5-5~1977 11 and 12, 13 respectively and the rotor. Owing to this the magneti.c potential difference across the air gaps near the systems of teeth 10, 11 and 12, 13 respectively is alternately of different polarity, so that per stator section when the coils are energized the magnetic potential difference across one of the air gaps is reduced and the magnetic potential difference across the other air gap is increase~ so that one of the two systems of teeth of a stator section is activated as if it were dependent-on the sense of energization of the coils. If a certain coil is not energized, the two systems of teeth of said stator section are equally active and because the two systems.are shifted by half a tooth pitch relative to each other, no force is exerted on the rot.~r.
In order to explain the operation of :. the motor in accordance with Fig. 1 and 2, . ~ 20 Figure 3 schematically shows the mutual position :
o:~ -the systems of stator teeth 10, 11, 12 and 13 and~the rotor toothing 3 for five different~posi-t:ions P1 through P$ relative to the stator toothings and ~igure 4 shows an energizing diagram for the ~25 coils 6 ~(Fig. 4a) and 7 (Fig. 4b).
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PllN 8!l5~C
S.5.1977 ~8~ S~
current (+I) the magnetic potential difference across the air gaps near the stator toothings 10 . and 12 is greater than the magnetic poten-tial difference across the air gaps near the stator toothings 11 and 13 respectively.
If it is assumed that at the instant : ` ~0 the rotor teeth 3 are disposed slightly before the stator teeth 10, the rotor will move, upon energization o~ ring coil 6 whilst ring coil : 10 is unenergized, until the rotor teeth 3 are disposed exactly opposite the stator teeth 10.
: This is the position with the smallest magnetic - resistance for that air gap with the greatest : magnetlc potential difference. This position is positioned P1 in Figure 3. If at the instant t1 the coil 7 is now energized with a positive current +I and coil 6 is de-energized, the magne-tic pot~tial diffe~ence across the air gap near the stator toothing 12 will be greatest, whilst :
. 20 the rotor toothing 3 will be disposed a quarter ' ~- tooth~pitch before the stator toothing 12. The rotor~is then a-ttracted until the rotor teath 10 are opposite the stator taeth 12, this is . ~ ~
: : position P2. Similarly, after the instant t2, after which coil 6 is energized with a negati~e , current and coil 7 is de-energized, the rotor will ; move to position P3, this is with its teeth 3 . . .
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- 1 4- , PllN 8454C
opposite the stator t~e-th 11, and after the - instant t3, after which coil 7 is energized with a negative cur:rent and coil 6 is de-energized?
to position Pl~, this opposite the stator toothing 13. The rotor now assumes a similar position relative to the stator toothing as jus-t before the - instant to ~ld a full stepping cycle is completed.
A displacement by one tooth pitch is consequently performed in four steps. If the total number of teeth equals 50 m the stepping angle will be 1.8. --Figures1 and 2 show that per stator section the two systems of teeth are shifted by half a tooth pitch relative to each other and that two stator sections are shifted by a ~uarter tooth pltch relative to each otner. It is also possible to give all the systems of stator teeth the same position relative to each other and to rotate the systems at rotor teeth by 0, -~9 ~ and 3/4 tooth pitch relative to each other, or a combination thereof. For a correct operation of th,e motor the position of -the one system of stator teeth relative to the corresponding system ~, of rotor teeth per stator section should be shifted ~25 by half a tooth pitch relative to the position of the other system of stator teeth relative to the - corresponding system of rotor teeth.
.
.. . . ~ , , . , , . . . . : .
P~IN 8l~54c 5.5.1977 ,r56 The motor may consist o~ more than two stator sections. T]hese sections are then always separated by a ring magnet which is axially magnetized in the appropriate direction.
It is possible to replace the ring magnet 14 by a ring coil.
It is also possible to include the permanent msgnet in the rotor in such a way that the field line pattern is maintained, for example an axially magnetized magnet, or a ring coil, at the location indicated by the dash-dot line 15 in Fig. 1. At the location where the magnet 14 is shown in Fig. 1 a connection with good magne-:
ticconduction must then be provided.
For the purpose of illustration Fig. 5 - shows a longitudinal section of a rnotor whose operation is the same as that the motor o~ Fig.1.
The various parts are numbered in accordance ~th - ~ Fig. 1 and the description is also applied to it.
The motor in accordance with Fig. 5 has been ; ~ obtained by axially compressing the rotor o~ the :: ~
motor in accordance with Figure 1 to one disc and by increasing the tooth depth. The two stator :,- ' : :
sections are now disposed above and u~derneath ; 25 the~diso and co-operate with one and the same system 3~o~ rotor teeth. The various magnetic circuits are represented by dashed arrows in ., .
. .
.,.
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.~., . -PHN 845LIc ~.5~1977 - the same way as in P`ig. 1.
In prac-tice the motor of Fig. 1 is found to produce asymtnetrical torques for various reasons, inter alia owing to the difference in magnetic resistance from the permanent magnet 1l~
to for example the system of teeth 10 and the system of teeth 11 and the difference in magnetic~
resistance of the air gaps belonging to these systems of teeth viewed through the field of the coil 6, owlng to the difference in the directions of the fields in these ~r gaps. A solution to this problem is the axial di~ision of the stator section into an even number segment whose toothings are shifted relative to each other by half a tooth pitch, the polarity of the corresponding segment of the magnetic ring 14 being also reversed.
Figure 6 is a plane view of the motor in accordance with Fig. 1 to which this step is applied (which may for example also be used ln - 20 the motor of Figure 5)O The Figure 6hows the top Burface of the yoke 8 of stator section 4 with tator tee-th 10 and the rotor 1 with rotor teeth 3. The stator is divided into four segments, designated a, b, c, d. The segments b and d 25 ~ as well as the segments a and c are identical, whllst the toothings 10a and 10c are shifted by hal~ a tooth pitch relative to the toothings 10b ' ',: . ',.
' PHN 8ll5LIC
5.5.1977 and 10d. As Q result of this the toothings 10b and 10d are shifted by half a tooth pitch - relative to the rotor teeth 3 when the teeth - . of the toothings 10a and 10c are exactly opposite the rotor teeth. The to~hings 11, not shown, are again shifted by half a tooth pitch per segment - relative to the toothings 109 whilst the other : stator section 5 is shifted by a quarter tooth pitch relati~e to the stator sectinn 4. I'he four segments are separated from each other by means of air gaps in order not to short-circuit the field of the permanent magnet.
Figure7 is a cross-section of the motor in accordance with Figure 6 taken on the line VII-VII and i.5 numbered in a similar way as the motor of ~igure 1 with the addition of the indexes a and b. The magnetic ring 14 at the . location of segment a is magnetized oppositely : _ to the magnetization and the location o~ segment b, which is indicated b~ the arrows 19 and ~0.
If for a certain energi~ing current +I
through coil 6 the:magnetia potential difference across the air gap near system of teeth 10a and 10c is large relative to the magnetic potantial ;"
di~ference across the air gaps near the systems of te~th 11a and 11c, the same applies withlres-pect to the systems of teeth 11b and 11d relative ., .
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5.5.1977 to the systems of teeth 10b and 10do The same applies to the systems of teeth 12 and 13 in a corresponding manner.
Figure 8 schema-tically shows the position of the systems of stator teeth 10, 11, 12 and 13, of which only the segments a and b are shown. The seg~ents c and d occupy the same positions relative to the rotor teeth 3 as the segments a and b respectively. The rotor toothing 3 is shown in ~ive positions P1 ; through P5, which positions are always shifted by a quarter tooth pitch relati~e to each other.
Thecoils are energized in accordance with the energizing diagr~ of Figure 4, the polarities of the currents being defined relative to the stator segment a in the same manner as for the motor in accordance with Figure 1.
It is assumed that at the instant to the rotor teeth 3 are disposed slightly before the stator teeth 10a and 10c, and thus slightly before - . ..
~ ~ the stator teeth 11b and 1ld, the rotor will mae :
until~ the rotor teeth 3 are exactly opposite said stator teeth upon energization of the ring coil 6 whilst ring coil 7 is unenergized. This is the position P1 in Fig. o. If at the instant t1 coil 7 is energi~ed with a positi~e current ~I and coil 6 is~de-energized,~ the magnetic potential difference ~:
1: : , . . .
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PII~ 8~l54C
5.5.1977 across the air gap near the stator toothings 12a, 12c, 13b and 13d will be greatest, whilst the rotor toothing 3 is disposed a quarter tooth ~tch before said stator toothings. The rotor will then be attracted until the rotor teeth are opposite the last-mentioned stator teeth, this is position B2.
Similarly, after the instant t2, after which coil 6 is energized with a negative current and coil 7 is de-energized, the rotor will move to position P3, i.e. with its toothing 3 opposite the stator toothings 11a, 11c, 10 b and 10d, and after instant t3, after which coil 7 is energized irith a negative current and coil 7 is de-energized, to position P~, this is opposite the rotor toothings 13a, 13cg 12b a~d 12d. The rotor now has again assumed the same position relative to the stator toothing as j~st before the instant to and a full cycle has been completed.
. ~ . , .
` ~ Although Figs. 6 and 7 show a division into four axial segments~ any axial division into an even number of segments is possible, though a division lnto two segments is unfavourable because in that case unbalanced radial forces will be exerted on the rotor. In a similar way as with , :
~`~ 25 the motor in accordance with Fig. 1 it is possible to arrange the toothings 10, 11, 12 and 13 in the same posltion and to arrange the various rotor `~ toothings at 0, ~ 3/4 tooth pitch from each - .
~ other.
- - 2~-PIIN 8ll54C
5.5.1977 .7~6 It is also possible to use a plurality . of stator sections.
In the s~gmented motor of Figs. 6 and 7 the permanent magnetic rin~ 14 may be replaced by permanent magnets which are disposed in the two stator sections between the segments at the locations 35, 36, 37 and 38 indicated in Fig. 6.
These magnets should then be magnetized tangen-tially relative to the rotor, the direction of magnetization of the magnets: at the locations . 35 and 37 being opposite to the direction of magnetization of the magnets at the locations 36 and 38, as is indicated by the dashed arrows in Fig. 6.
The stator section for a motor in accordance with the in~ention can be manufactured - simply by enclosing the ring coil 6, 7 between two parallel annular plates 30 and 21 (Figo 2) ~ and a cylindrical ring 22. This results in two transi-tions 23 and 24 in the yoke 8. However, it is .: ~ . fo~nd that in the case of motors with a small air .
~ gap between stator and rotor this gives rise to an . ~
asymmetrlcal torque, because the magnetic resis-tance in the circuit via plate 21 to the rotor ~iewed from the p~rmanent magnetic ring 14, lS
~: then too small relative to the magnetic resistance i.n the circuit via plates 22 and 30.
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N. 8454C.
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A solution to this problem is to construct the yoke 8 (and 9) from U-shaped laminations which are placed over the ring coil in substantially axial planes. Figure 9 shows an example of such a U-shaped lamination and Fig. 10 shows the construction of a stator section with such laminations.
The laminations can be made of a flat sheet material and bent in such a way that one of the limbs 25 is shifted by half a tooth pitch ~/2 relative to the other limb 26. Similarly a portion 27 can be bent at right angles. This portion 27 may adjoin the adjacent lamination and also serves as a contact face with the permanent-magnetic ring 14.
Figure 10 shows the stator section 5. It comprises the ring coil 7 in a former 28 of for example a plastic. During manufacture suitable slots may be f~rmed in this former into which slots the laminations can be slido By bending the laminations the one system of teeth is always shifted by half a 2n tooth pitch relative to the other system of teeth.
It is alternatively possible to use non-bent laminations and to slide these onto the coil former in an oblique position relative to the axial planes, or to slip -~
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:. , : : . ., 5.5.1977 ~ t7~ ~
them onto the coi1 former in axial plane and shift corresponding systems of rotor teeth by half a tooth pitch, Furthermore, the bent portion 27 may be dispensecl with when between the magnetic ring 14 and the stator section 5 and 4 respectively a disc of a soft-magnetic material is included. Instead of slots in the coil former it i9 alternatively possible to use projections and the like for positioning.
It is very advantageous to construct the stator sections in accordance with Fig. 10 f'dr a motor in accordance with Figure 6, because the shift of the teeth of the segments b and d rela-tive to the segments a and c by half a tooth pitch can simply be obtained by suitably arran-ging the slots or projections of the coil former 28. The same laminations may then be used for nll segments.
~or ~e motor of Fig~ 1 it is found that the torque as a function of the rotor position is not symmetrical, i.e. not the same for bo$h possible directions of the current in the coil 6 and 7 respectively. This asymmetry is produced as a result of the magnetic resistance constituted by Z5 the air gap formed by the permanent magnet t4 not being infinite so that for the fields produced by the coils 6 and 7 respectively magnetic circuits , ~ , ' ~ :
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PHN 84~4C
! , 5.5.1977 ~:98~
are formed via the permanent magnet 14. As the direction of these fieldsdepends on the direction of the energizing current through the coils 6 and 7 respectively, the working point of the permanent magnet 14 depends on this direction, which causes the said asymmetrical torque.
Figure 11 is an axial cross-section of a motor in accordance with Fig. 1 in which steps have been taken to mitigate the said asymmetry.
These steps include the incorporation of a coaxial ring coil 30' between the two stator sections 4 and 5. By energizing this ring coil 30~ in such a way that the field of this ring coil in the perma-nent magnet 14 is directed oppositely to the field of the ring coils 6 and 7, the working point of the permanent magnet 14 c~ be maintained substantially constant.
In the ease that each time one phase is energized the number of amp~re-t~rns (this is the p:roduct of the current through the coil and the number of turns of said coil) of coil 30' should be approximately half the number of ampère-turns .
of the energlzed coil 6 or 7.
As has already been remarked with respect to the motor in accordance with Fig. 2, the stator sections 4 and 5 for a motor in accordance with the invention can be manufactured in a simple :~: ~ , . . , ~. .
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;, ' .. . .
.
PHN 8454c , 5.5.1977 7C~6 : manner by enclosing the ring coils 6 an.d 7 : respectively between two parallel annular toothed plates 20 and 21 (Fig. 2, Fig. 12) and a cylin-drical ring 22 which may surround the pla-tes 20 and 21 (Fig. 12). In that case and also with other methods of manufacture, transitions 23 and 24 are formed in the yoke 20, 21~ 22. As previ-ously stated, this also leads to an asymmetry in the torque.
Fig. 12 shows an axial cross-section of a motor in accordance with Fig. 2, for which the last mentioned-problem has been solved. Be-tween the st~Dr systems 4 and 5 and the permanen-t magnet 14 comparatively large air gaps are formed . 15 tin.Fig~ 12 filled by the coils 32 and 33 respec~
: tively). Said cylindrical ring 22 then extends as : far as the permanent magnet 14, the flux of said permanent magnet 14 being caught by an annular disc .. 31 which is surrounded by the cylinder 22. Thus the magnetic path from the permanent magnet 14 to the system of teeth 10 has the same magnetic resistance as the path to the system of teeth 11~ The sarne applies to the stator section 5.
The space which has become available owing to the use of addi~ional airgaps may be used e~fectively by choosing two ring coils 32 and 33 ~` instead of the compensation coil 30 in the motor of . : . .
' , .. ~ Z5~
~, .
5..5. 1977 s ~ 756 ~ig. 11 and to place these ring coils in these two spaces. The ring coils 32 and 33 may then be energi~ed simultaneously ~or alternately).
The compensation coils in the motors in accordance with Figs. 11 and 12, in respect of the energization of one or both stator coils 6 and 7, should be energized so that the magnetic potential difference across the permanent magnet is independent o~ the energizing condition of the coils 6 and 7.
Fig. 13 is an axial cross-section of a variant of the motor of Fig. 1. Corresponding parts bear the same reference numerals. The parts on which the stator teeth 10, 11, 123 13 are provided in the motor of Fig. 13 are widened in comparison with the motor of Fig. 1. The two stator sections 8 and 9 consist of two annular parts 40, 41 and - 42, 43 respectively, between which the annular coil 6 or 7 i9 disposed. These parts can be manu-factured simply, for example from sintered iron7 and provided with teeth7 for example by milling the inner circumference, and subsequently assembled with the permanent-magnetic ring 14 shifted through angles of 0, 180, 90 and 270 relative to each other.
The rotor 1 comprises a shaft on which :
two annular parts 2 are mounted, each with an axial length in accordance with that of the stator ':
i: :
~- -26-PHN 845~1C
5.5.1977 P ~81'7~t;
sections 8 and g and constricted near the shaft so as to reduce the mass moment of inertia. These rings 2 are provided with teeth 3 at least opposite the stator teeth 10, 11, 12 and 13, which may ~or example be formed by milling the outer circumfe-rence of the parts 2. The operation of the rnotor further corresponds to that of the motor of Fig.1.
- The invention is not limited to the embodiment shown. A multiplicity of variants to be basic principle described with reference to Fig.1 are posslble.
. , .
, '~
~ s -,~
:
'~
:~ :
j~: : ' . , .,': ~ : ' ', ' ~ 27-.~ .
: '
Claims (10)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A synchronous motor comprising at least two coaxial stator sections which are each pro-vided with at least one annular coil, which annular coil is surrounded by a magnetic circuit of a soft ferromagnetic material, which circuit is constituted by a rotor section with toothings and by stator section which surrounds the relevant annular coil, which stator section terminates in two systems of stator teeth which are arranged in a circle, and which co-operate with the rotor teeth across air gaps in such a manner that at any time the position of one of both systems of stator teeth of each stator section relative to the co-operating rotor teeth differs half a tooth pitch from the position of the other system of stator teeth of that stator section relative to the co-operating rotor teeth, means being provided for each stator section for magnetizing both systems of stator teeth with the same polari-ty, characterized in that the two systems of teeth of each stator section are constituted by annular parts which are provided with teeth at the inner circumference, which annular parts both form part of the magnetic circuit which surrounds the annular coil and which annular parts are disposed concentrically in such a way that the axial distance between the teeth of the two systems is at least a few times greater than the air gap between the systems of stator teeth and the rotor.
2. A synchronous motor as claimed in Claim1, characterized in that the stator sections are divided into an even number of segments along axial surfaces, the stator teeth for each stator section being mutually shifted by half a tooth pitch relative to the rotor teeth of each time two adjacent segments and said means for each stator section magnetizing the two systems of each time two adjacent segments with opposite polarities.
3. A synchronous motor as claimed in Claim 1, characterized in that the motor comprises at least one compensation coil whose magnetic cir-cuit is in parallel with the magnetic circuit of said means.
4. A synchronous motor as claimed in Claim 3, said means being constituted by an axially magnetized ring which is coaxially disposed between two stator sections, characterized in that said compensation coil is annular and is disposed be-tween the two stator sections coaxially with the permanent-magnetic ring.
5. A synchronous motor as claimed in Claim 1, characterized in that the magnetic stator circuits which surround the annular coils consist of integrally manufac-tured laminations which are disposed in substantially axial planes.
6. A synchronous motor as claimed in Claim 5, characterized in that the annular coils are surrounded by a coil former provided with positioning means for locating said laminations.
7. A synchronous motor as claimed in Claim 6, characterized in that the laminations are U-shaped, the limbs of the laminations extending in the air gap between the stator and rotor for the formation of the systems of stator teeth and said positioning means being such that the end of the one limb of each U-shaped lamination inside the air gap is shifted by half a tooth pitch relative to the end of the other limb.
8. A synchronous motor as claimed in Claim 7, the means for magnetizing the two systems of stator teeth of each stator section with equal polarity being constituted by an axially magnetized permanent-magnetic ring disposed between two stator sections, character-ized in that the laminations at the side which faces the permanent magnetic ring are provided with a folded portion, which is disposed in a plane which is sub-stantially perpendicular to the axis, for receiving the flux of the permanent magnet.
9. A synchronous motor as claimed in Claim 3, the means for magnetizing the two systems of stator teeth of each stator section with equal polarity being consti-tuted by an axially magnetized permanent-magnetic ring which is disposed between two stator sections, character-ized in that the two magnetic stator circuits surrounding the annular coils of both stator sections each consist of two parallel annular plates which are disposed in planes substantially perpendicular to the rotor axis, at the inner circumference of which said systems of teeth are formed and whose outer circumference adjoins the inner surface of a cylindrical ring belonging to said stator section, between which plates and the cylindrical ring the annular coil is included, both cylindrical rings extending as far as the permanent-magnetic ring and being provided with means for receiving the flux of the permanent-magnetic ring, so that between the two annular plates which face the permanent magnetic ring and the permanent magnetic ring spaces are obtained with a magnetic resistance which is comparatively high relative to the magnetic resistance between the permanent-magnetic ring and the cylindrical ring.
10. A synchronous motor as claimed in Claim 9, characterized in that annular coaxially disposed compensation coils are accommodated in said spaces.
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| NL7607381 | 1976-07-05 | ||
| NL7607381A NL7607381A (en) | 1976-07-05 | 1976-07-05 | Sync. motor with two part coaxial stator - has stator poles whose positioning within motor air gap can be adjusted |
| NL7701510 | 1977-02-14 | ||
| NL7701510A NL7701510A (en) | 1977-02-14 | 1977-02-14 | Sync. motor with two part coaxial stator - has stator poles whose positioning within motor air gap can be adjusted |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1081756A true CA1081756A (en) | 1980-07-15 |
Family
ID=26645230
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA281,663A Expired CA1081756A (en) | 1976-07-05 | 1977-06-29 | Synchronous motor |
Country Status (11)
| Country | Link |
|---|---|
| US (1) | US4206374A (en) |
| JP (2) | JPS535714A (en) |
| BE (1) | BE856441A (en) |
| CA (1) | CA1081756A (en) |
| CH (1) | CH625366A5 (en) |
| DE (1) | DE2727450A1 (en) |
| ES (1) | ES460352A1 (en) |
| FR (1) | FR2358046A1 (en) |
| GB (1) | GB1586513A (en) |
| IT (1) | IT1076074B (en) |
| SE (2) | SE433419B (en) |
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| NL7904816A (en) * | 1979-06-20 | 1980-12-23 | Philips Nv | STEPPER MOTOR. |
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-
1977
- 1977-06-18 DE DE19772727450 patent/DE2727450A1/en not_active Ceased
- 1977-06-22 US US05/808,784 patent/US4206374A/en not_active Expired - Lifetime
- 1977-06-29 CA CA281,663A patent/CA1081756A/en not_active Expired
- 1977-07-01 SE SE7707643A patent/SE433419B/en not_active IP Right Cessation
- 1977-07-01 GB GB27648/77A patent/GB1586513A/en not_active Expired
- 1977-07-01 IT IT25335/77A patent/IT1076074B/en active
- 1977-07-01 SE SE7707643D patent/SE7707643L/en not_active Application Discontinuation
- 1977-07-02 ES ES77460352A patent/ES460352A1/en not_active Expired
- 1977-07-04 CH CH819977A patent/CH625366A5/de not_active IP Right Cessation
- 1977-07-04 BE BE179051A patent/BE856441A/en not_active IP Right Cessation
- 1977-07-05 JP JP8035177A patent/JPS535714A/en active Pending
- 1977-07-05 FR FR7720560A patent/FR2358046A1/en active Granted
-
1984
- 1984-01-19 JP JP1984004677U patent/JPS59132379U/en active Granted
Also Published As
| Publication number | Publication date |
|---|---|
| IT1076074B (en) | 1985-04-22 |
| FR2358046A1 (en) | 1978-02-03 |
| ES460352A1 (en) | 1978-04-01 |
| JPS59132379U (en) | 1984-09-05 |
| SE433419B (en) | 1984-05-21 |
| FR2358046B1 (en) | 1983-03-11 |
| DE2727450A1 (en) | 1978-01-12 |
| JPS535714A (en) | 1978-01-19 |
| GB1586513A (en) | 1981-03-18 |
| US4206374A (en) | 1980-06-03 |
| BE856441A (en) | 1978-01-04 |
| JPS6122476Y2 (en) | 1986-07-05 |
| SE7707643L (en) | 1978-01-06 |
| CH625366A5 (en) | 1981-09-15 |
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