FIELD OF THE INVENTION
The present invention relates to electric motors and
more specifically to the reduction of harmonics
occurring in motors and the adverse effects caused by
these harmonics
BACKGROUND OF THE INVENTION
Electric motors convert electrical energy into
mechanical energy In electric motors of normal
construction, the basic parts, such as a rotor with a
shaft fitted to rotate, a stationary stator, bearings
and end shields, can be distinguished The rotor is
situated so as to be supported by the bearings.
Generally a small air gap is left between the rotor
and the stator
The operation of multiphase alternating-current
rotating machines, such as a multiphase synchronous
and asynchronous motor, is based on a magnetic field
circulating inside the machine A multiphase stator
winding is formed such that a sinusoidal voltage is
fed into the phase windings, with the voltages fed
into the windings being at a 360 / in angle to each
other in the phase shift, where in is the number of
phases, the currents passing through the stator
windings thus creating a magnetic field that
circulates the air gap in the machine, said magnetic
field interacting with the magnetic field of the rotor
windings thereby making the rotor rotate The magnetic
field in the rotor winding of synchronous machines is
typically formed from either a permanent magnet or
with direct current fed into the excitation winding of
the rotor Magnetization of the rotor winding in
asynchronous machines is generally implemented via the

voltages and currents induced in the rotor winding
caused by the magnetic flux of the stator current
The aim is for the distribution of the magnetic flux
density of the air gap to be as purely sinusoidal as
possible The rotating motion of the rotor is achieved
by means of the fundamental sinusoidal wave of the
magnetic flux density, but in practice the magnetic
field affecting a motor also contains harmonic terms,
1 e harmonic components of the pure wave.
The harmonics of the magnetic flux density cause extra
force components between the stator and the rotor
Furthermore, the magnitude of the torque fluctuates
(torque ripple) and additional losses occur in the
motor If the frequency and form of fluctuation of the
of the force caused by a magnetic field containing
harmonics are close to the mechanical natural
frequencies of the motor, a loud noise and vibration
of the machine can occur as a result of the harmonics
Further, constrained vibration is possible In
constrained vibration, forces are exerted on a
component that cause it to vibrate, although the
frequency of the excitation is not the natural
frequency of the component Additionally, harmonics
can lead to faulty operation of measuring and
protective equipment, to overvoltages and to overload
situations
In three-phase electric motors only odd harmonic terms
of the magnetic field occur Prior-art solutions have
attempted to minimize the effect of harmonics by
changing the basic winding of the stator, with a
fractional-pitch winding, with slot wedges and with
dispersed placement of the magnets In modern motors,
however, vibration and noise caused by the force
components occurring at 6 times and 12 times the
frequencies with respect to the frequency of the motor

current have been evident, said force components
resulting especially from the 5th, 7th, 11th and 13th
harmonic terms of the flux density-
Harmonic components occur in the air gap flux density
in a rotating electrical machine owing to both
discontinuity of the windings on the rims of the
stator and rotor and from fluctuations in the
permeance in the air gap The stator winding is
generally concentrated in slots and coil groups, in
which case the magnetomotive force produced in the air
gap is not sinusoidally distributed Permeance
fluctuation in the air gap is caused by, among other
things, possible slotting of the stator and rotor,
salient poles and magnetic saturation The harmonics
of the magnetic field of an electric motor can be
divided into harmonics caused by the rotor and
harmonics caused by the stator
Torque ripple occurs in other rotating field machines
also, but the following addresses in particular
permanent magnet synchronous motors, which can be
axial flux or radial flux machines In an axial flux
machine the magnetic flux of the air gap of the
machine is situated mainly in the direction of the
shaft of the machine In a radial flux machine, on the
other hand, the magnetic flux of the air gap of the
machine passes mainly in the radial direction with
respect to the shaft
Reduction of torque ripple caused by the rotor of
permanent magnet machines is addressed, for example,
in patent application US2004/0070300 In the solution
presented in this publication the magnetic field
caused by the rotor magnets is made as purely
sinusoidal as possible by making the rotor magnets
pole shaped and by skewing their placement Solutions
for reducing torque ripple caused by the rotor are

also presented in, for instance, publications
US6380658 and US5886440 Prior-art solutions also
include reducing torque ripple caused by the rotor by-
dispersed placement of the magnets
The publication written by Y Akiyama et al , "Slot
Ripple of Induction Motor and FEM Simulation on
Magnetic Noise", Proceedings of the IEEE IAS 31st
Annual Meeting, San Diego, USA, 1996, p 644-651,
addresses random placement of the slots of the rotor
The publication presents the reduction of the magnetic
noise of induction motors by using non-equidistant
distribution of the rotor slots Three different types
of rotor slotting principles (methods A, b and C) are
presented. In methods A and B the rotor slots are
situated completely randomly The simulation result
showed that the motor was very susceptible to
saturation at the location of very thin teeth In
method C the slotting of the rotor is divided into
quarters of the rim, and in each quarter the distance
between slots is constant Between adjacent quarters
is a small displacement. Rotor A gives the best result
in terms of interference components
As previously stated, torque ripple is also caused by
the stator, as a result of both harmonics caused by
the discrete distribution of current in the
circumferential direction of the stator and permeance
fluctuation in the air gap caused by the stator
slotting, for which the aforementioned publications do
not offer a solution.
Prior-art solutions have attempted to reduce harmonics
caused by distribution of the stator current with,
among other things, a fractional-pitch winding or by
using skewed slots A fractional-pitch winding can
eliminate slot harmonics of a certain order, but it
cannot affect slotting harmonics Skewed slots also

distribute permeance on the rim more evenly, but using
skewed slots complicates the process of manufacturing
the motor and also reduces the torque available from
the motor It is known that using a magnetic slot
wedge at the mouth of slots reduces permeance
fluctuations caused by the slotting By means of a
slot wedge the permeance fluctuations can be made more
even and the amplitude of certain harmonics reduced
For example, publication FI 112412 presents a method
for manufacturing the winding of an electrical
machine In this method the winding coils are formed
into their final shape before being placed in the
slots. The winding coils are then placed so that they
overlap, one coil being disposed at the base of the
slot and the other coil placed on top of it
Additionally, in the method the slots are closed after
placement of the winding coils with ferromagnetic slot
wedges By means of the slot wedges and by using
fractional-pitch winding the harmonic terms can be
damped to about one-quarter of the magnitude compared
to a motor without slot wedges.
Publication US 628510J, presents a solution for
reducing torque ripple wherein a different number of
conductors can be placed in the stator slots such that
the current vector fed smusoidally into each slot is
formed as similarly to the current vectors of the
other slots as possible In this method the width of
the stator slot is determined by the number of
conductors contained in the slot The method also
presents moving the rotor magnets in the direction of
the circumference with respect to the stator One
drawback in the solution presented is, among other
things, that it makes the process of manufacturing the
stator and stator winding more difficult

In prior-art solutions mechanical vibrations occurring
in the motor are damped, as presented in eg
publication WO 9826643 According to this publication
a second voltage is fed into the current supply of the
motor, the frequency of which is a certain multiple of
the fundamental frequency The frequency depends on
the number of phases and on the number of stator slots
per phase
Based on publication FI 950145, it is a prior-art
technique to manufacture the magnetic core (stator) of
an axial motor as a cylmdrically-shaped stack of
plates in the following manner A ribbon-like
ferromagnetic plate is coiled into a cylindrical stack
of plates either spirally or annularly Before coiling
into a roll, the exact positions of the stator slots
on the plate are calculated and the slots are punched
while the plate is in a straight plane with a special
punching and slotting machine The punching locations
are not positioned equidistantly because the radius of
the plate mass accumulating around the centre axis of
the plate stack changes during the coiling. When the
plate stack is fully coiled, the stator slots in the
stack are located in the desired positions and are of
the desired depth, and the walls of the slots are
even
The problem with this prior-art solution is that the
vibration and noise caused by harmonics are not
reduced in the best possible way with the prior-art
methods For example, the vibration caused by torque
ripple in an electric motor in elevator usage can
still be noticed as vibration and jerky motion of the
elevator car The noise caused by harmonics can also
reduce passenger ride comfort
PURPOSE OF THE INVENTION

The purpose of the present invention is to achieve a
motor in which the harmonics caused by the stator
winding and the stator slotting are smaller than in prior-art electric motors, and in which the adverse
effects on the operation of the electric motor caused
by harmonics are minimized
SUMMARY OF THE INVENTION
The method of the invention is characterized by what
is disclosed in the characterization part of claim 1
The motor of the invention is characterized by what is
disclosed in the characterization part of claim 10
Other embodiments of the invention are characterized
by what is disclosed in the other claims
Some inventive embodiments are also discussed in the
descriptive section and drawings of the present
application The inventive content of the application
can also be defined differently than in the claims
presented below The inventive content may also
consist of several separate inventions, especially if
the invention is considered in the light of
expressions or implicit sub-tasks or from the point of
view of advantages or categories of advantages
achieved In this case, some of the attributes
contained in the claims below may be superfluous from
the point of view of separate inventive concepts. The
features of the various embodiments can be applied
within the framework of the basic inventive concept in conjunction with other embodiments The features
presented in conjunction with the method and equipment
can be applied in conjunction with each other such
that the equipment of the invention can comprise
features presented in conjunction with the method of
the invention and vice versa The procedural phases
presented in conjunction with the method are not
however necessarily bound to those appliances that are

described in conjunction with the equipment, but can
also be more general
The method according to the invention is for forming
an electric motor, said motor comprising a rotor, a
stator, and a support structure for the rotor and
stator, as well as an output for transmitting rotary
movement out of the motor, such that the stator slots
or pole cores, possibly containing slots, are situated
on the rim of the stator in a placement differing from
equidistant distribution The method of placement of
the stator slots and/or pole cores can be called
dispersed placement of the stator slots and/or stator
poles The aim of placing the slots and/or poles at
non-equidistant intervals is to reduce the harmonics
caused by the stator winding and stator slotting,
which in turn achieves reduced vibration, noise and
losses of the motor A stator slotted in the manner
according to the invention can also be called a VSP
(Variable Slot Pitch) stator. Deviating from
equidistant placement preferably follows a certain
symmetry between the different portions of the stator.
The motor formed according to the invention can be an
axial flux motor, wherein the stator of the motor is
manufactured by coiling a ribbon-like ferromagnetic
plate into a cylinder-shaped stack of plates around
the centre axis of the plate stack, and in which
method, before coiling the plate stack, notches are
punched in the plate with a punching machine to form
the slots
In the electric motor of the invention a plurality of
stator slots and/or pole cores are arranged on the rim
of the stator in a placement diverging from
equidistant distribution Preferably the divergence
from equidistant distribution is implemented in one
portion of the stator such that the divergence from

equidistant placement of the slots and/or poles
situated in that portion are essentially symmetrical
with the divergences of another portion of the stator
The inventive concept also includes a method for
manufacturing a stator, wherein the poles and/or slots
of the stator are deployed dispersed in accordance
with the method of the invention The slots can be
made by e g punching, in other words by stamping a
notch in the plate using an appliance suited to this
perforating One method of manufacturing a stator is
to stamp slots in a planar ferromagnetic plate and
then coil the plate spirally into a stack of plates
One advantage of the solution according to the
invention is that the harmonics caused by the stator
of the motor are damped even to one-tenth compared to
equidistantly distributed slotting In this way, by
means of the invention a motor is achieved that has a
lower vibration and noise level, that has smaller
power losses and that produces a more even torque than
a prior-art motor All prior-art arrangements and
techniques can be used in the manufacture of the coils
and windings of the motor of the invention, because
the modifications made to the structure of the stator
compared to equidistant placement can be made so small
that they do not affect the manufacture of the coils
or the winding process The fundamental wave of the
magnetic field important from the viewpoint of the
operation of the motor thus remains in practice
unchanged Instead, the amplitude of the harmonics, of
which with a three-phase machine the 5th, 7th, 11th
and 13th harmonic terms are most essential from the
viewpoint of vibration and noise, is substantially
reduced
LIST OF FIGURES

Fig 1 presents an example of a prior-art radial
flux machine equipped with a permanent magnet
rotor,
Fig 2 presents an example of a prior-art axial flux
machine equipped with a permanent magnet
rotor,
Fig 3 presents a cross-section of stator and rotor
frames slotted in accordance with prior-art
techniques,
Fig 4 presents part of the rim of a stator in
accordance with prior-art techniques opened
out into a straight plane,
Fig 5a presents a cross-section of a prior-art
stator frame provided with equidistantly
distributed slotting,
Fig 5b presents a cross-section of a part of the
stator frame provided with slotting according
to the invention opened out into a straight
plane,
Fig 5c presents a cross-section of a stator frame
provided with slotting according to the
invention, and
Fig 6 shows a diagrammatic representation of
parameters that can be varied according to
the invention.
DETAILED DESCRIPTION OF THE INVENTION
The method according to the invention is for forming
an electric motor, said motor comprising a rotor, a
stator, and a support structure for the rotor and
stator, as well as an output for transmitting rotary-
movement out of the motor, and in which stator is a

plurality of slots and/or poles, said plurality of
stator slots and/or stator poles being positioned in a
manner differing from equidistant distribution.
A winding for the stator of a multiphase electric
motor can be arranged by e g making slots in the rim
of the stator and by placing in the slots coils
comprising insulated conductor loops, which are
connected together to achieve the desired type of
winding The slot winding is typically formed as
distributed such that the stator frame is divided into
the number of zones determined by the number of phases
(m) and the number of poles (2p) of the motor, and in
e g three-phase motors, the phases of which are
called A-, B- and C-phases, one coil side of the coil
of phase A belonging to the positive zone of phase A
and the other coil side belonging to the negative zone
of phase A The coil sides of phases B and C are
generally positioned between said coil sides in such a
case A winding can also be arranged as a centralized
pole winding, wherein poles are formed on the stator
rim by placing coils around the pole body, so that
coil sides belonging to another phase are not left
between the coil sides of one pole Hereafter the term
pole core is used to refer to the coil body and to any
pole shoe that is part of it Slotting may also be
added to a pole core, in which case the pole winding
can be formed from both coils placed around the pole
body and placed in the slotting of the pole core
In prior-art stators the slots or pole cores, in which
the winding is formed, are typically distributed
equidistantly on the stator rim The construction of
the stator causes harmonics owing to both the discrete
distribution of current on the stator rim and to
changes in permeance on the stator rim caused by the
stator geometry In the present invention the

placement locations of the stator slots on the stator
rim are moved from the conventional equidistantly
distributed placement This can be called dispersed
placement of the stator slots The same inventive
concept includes the fact that when using pole
windings the poles of the stator can be positioned at
non-equidistant intervals This can be implemented
either by non-equidistant placement of the pole cores
or their associated slots, and the non-equidistant
placement can apply not only to the mechanical pole
core but also to the magnetic axis of the pole
The magnetic field caused by the stator winding is
formed from the effect of the current passing through
the winding The current in the slot winding is
centralized in the slots, so that the magnetomotive
force produced in the air gap by the winding changes in jumps at the location of the slots The aim is to
design the winding so that the magnetomotive force
produced is as purely sinusoidal as possible, because
it is by means of exactly this fundamental frequency
component that achieves the rotary movement of the
rotor The wave of a magnetomotive force that changes in jumps also however contains harmonics The
proportion of harmonic components can be examined by
presenting the waveform of the magnetomotive force by
means of a Fourier series, 1 e by presenting the
waveform as the sum of the sine waves and cosine
waves. Changing the placement of the slots can affect
the harmonics content of the magnetomotive force
produced In the solution of the invention the
positions of the slots are shifted from equidistant
placement so that the harmonic composition of the
waveform of the magnetomotive force produced changes
such that a reduction is achieved in the proportion of
the 5th, 7th, 11th and 13th harmonic terms, which have
been noticed to be detrimental in an electrical

machine Non-equidistant placement of the slots also
achieves dispersal of the permeance fluctuation in the
air gap caused by the stator teeth thus damping the
slot harmonic components of the magnetic field
The non-equidistant placement according to the
invention is preferably implemented such that despite
the dispersed placement of the slots or poles there
are at least two portions of the stator in which the
deviations from equidistant placement of the slots
and/or poles are symmetrical to each other The
symmetry can be e g mirror-image symmetry or the
placement of the slotting and/or pole cores can be
identically repeated in the two portions A portion as
referred to here means any part whatsoever of the
stator in which the condition for symmetry is
fulfilled, and which at its simplest can be e g a
half section of the stator rim Between the portions,
however, can be parts of the stator in which the
condition for symmetry is not fulfilled, and the
portion meeting zhe symmetry requirement does not need
to be an equidistantly distributed part of the stator
By means of a certain symmetry the winding can be
implemented in non-equidistantly formed stator
slotting or pole cores such that non-equidistant
distribution of the winding does not caused
undesirable force components between the stator and
the rotor
The placements of the slots and/or pole cores on the
stator rim can according to the invention be
determined by means of a shape function, which is
formed by adding a so-called conversion function to
the placement function describing the placement of
slots of a stator that is slotted at equidistant
intervals The stator is formed such that the slots

and/or poles are positioned essentially in accordance
with the shape function
Fig 4 presents part of a prior-art stator that for
the sake of graphical clarity has been opened out from
its circular shape into a straight plane The stator
slots in Fig 4 are situated at horizontally
equidistant intervals, 1 e the distance between slots
40, 42 is the same as the distance between slots 42,
44 , and likewise the distances between teeth 41, 43
and between teeth 43, 45 are of the same magnitude
The placement of each slot on the rim of a stator rim
with equidistantly distributed slotting in relation to
a selected reference point can be presented by means
of the placement function f (Formula 1)
f(k) = (k - 1) * L / Q (1)
Here Q is the number of stator slots, k is the ordinal
number of the slot (1, 2, , Q) , and L is the length
of the stator rim Presented in the form of Formula 1
f(k) indicates the position of slot k as the distance
from the reference point, which here is the slot with
the ordinal number 1 With reference to Fig. 4 the
symbol f(k) of Formula (1) can be considered the
central point of the slot, I e the location point on
the symmetry axis of the slot Placement function f
can also be formed such that the position of slot k is
presented as an angle, in which case symbol L of
Formula 1 is replaced with the value 3 60° The
positions of pole cores can correspondingly be
addressed in place of the aforementioned positions of
slots In this case in placement function f the
ordinal number of the slot is substituted by the
ordinal number of the pole core in relation to the
selected reference point and the number of slots Q is
substituted by the number of poles 2pm of the machine,

where p is the number of pole-pairs of the machine and in is the number of phases
The shape function expressing the placement of the
slot or pole core is formed by adding the conversion
function for varying the slotting to the placement
function for equidistantly distributed slotting
Slot placement in the solution is thus achieved
according to Formula 2
M(k) = f(k) + H(k) (2)
where M(k) indicates the placement of the slot for
ordinal number k Also the values of the shape
function and the conversion function can be presented
either as distances or as degrees of angle
By means of Formula (2) information about placement of
the teeth can also be obtained by using the ordinal
number of the tooth in place of k, because the
positions of the slots and the teeth are linked to
each other The fact that the widths of the teeth vary in dispersed placement of the slots must be taken into
account, however
Conversion function H can be e g a sine function in
accordance with Formula (3)
H(k) = a*sin(s*2n*f(k)/L) (3)
where s is the symmetry number of the conversion
function, which determines the number of symmetrical
portions in the stator rim and a is the amplitude,
which determines the magnitude of the change If, for
example, s = 3, then three closer groupings and three
sparser groupings are observed on the stator rim
Symmetry number s and amplitude a can be selected with
the desired method

The interval length of the sine function is preferably-
selected such that no discontinuity in the slotting
seen in the cross-section occurs, 1 e the length of
the inner rim of the stator is an exact multiple of
the interval length of the sine function The inner
rim of the stator frame refers here generally to the
rotor side of the rim The conversion function can
also be the sum of a number of sine functions. By
means of Fourier expansion any continuous function
whatsoever is achieved for this shape Thus in the
method of the invention a generally non-equidistant
placement for the slots and/or poles on the stator
frame is determined
Figures 5a, 5b and 5c show a diagrammatic
representation of the modification to equidistant
distribution of the slotting for the slotting to
accord with the invention Fig 5a shows a cross-
section of the stator, wherein the slots 51 are
positioned at equidistant intervals in accordance with
prior-art technology Fig 5c presents a cross-section
of a stator 54 in accordance with the invention. The
positions of the slots 55 diverge slightly from those
presented in Fig 5a It can be seen from Fig 5c that in three points in the area of the cross-section there
is denser slotting than the average and
correspondingly in three points there is sparser
slotting than the average One of the three points in which the slotting is sparser is marked as point b in the diagram From this point the minimum and maximum
points of the distances between adjacent slots follow
alternately at 60-degree intervals It is thus
possible to select angles a 56 and (3 57 on the rim of
the stator 54, which meet the condition a > (3 The
difference between the angles can be e g in the order
of magnitude of one degree The positioning of the
slots in this example is determined using the

sinusoidal conversion function, the symmetry number of
which is three The position of each slot 55 diverges
from the values according to Fig 5a by the amount of
the values indicated by the conversion function In
the present example one interval of the sine function
corresponds to one-third of the complete circle of the
stator, 1 e 120 degrees, in other words the stator
contains three symmetrical portions of 120 degrees
One-sixth of the stator rim could also be selected as
a portion meeting the condition of symmetry in this
example
Fig 5b presents one-third of the stator according to
Fig 5c, opened out into a straight plane and with the
non-equidistant placement of the slots 53 accentuated
for the sake of clarity
In one preferred embodiment of the invention the slots
are kept as standard width slots, and dispersed
placement of the slots means the variation in the
distances between the standard width slots This is a
simple solution in terms of manufacturing technique
Reduction of harmonics according to the invention is
however also possible using stator slots of non-
standard width
The concept of the invention can be applied to
windings formed using prior-art techniques, such as
e.g lap windings, in which the coil ends in the
finished winding are positioned overlapping each
other, and concentric windings, in which the coil ends
are positioned on the same level
Dispersed displacement of the poles can be implemented
by e g modifying the angles between the standard
width pole cores, by modifying the width of the pole
cores keeping the angles between the pole cores
constant, or by modifying both the aforementioned

widths and angles Any variables that can be varied in a pole winding of a stator according to the invention
are graphically presented in Fig 6 Fig 6 presents
the stator frame 60 of an axial flux machine and four
slotted pole cores 61 arranged in it In the solution
according to the invention the divergence from
equidistant placement can be implemented in the angles
62 between the pole cores, in the widths 63 of the
pole cores, in the angles 64 between the slots and in
the positioning of the slots 65 in the pole core 61
The pole cores can also be unslotted, in which case of
course the variable parameters are the angles 62
between the pole cores and the widths 63 of the poles
In the solution according to the invention the
divergence from equidistant placement can focus on one
or more of the aforementioned parameters. Thus in the
method according to the invention it is possible to
e g select the required width of the pole core and
after this determine the non-equidistantly distributed
positions of the poles on the stator rim, or
alternatively to first select the value for the angles
between the poles and after this determine a slightly
differing width for each pole core Further, non-
equidistantly distributed positioning for the slots in
the pole cores can be determined The widths and
positions of the pole cores and slots can be expressed
either as a length measurement or as an angular value
The invention can be applied to a radial flux machine, in which case the slotting or pole cores according to
the invention can be implemented eg in the
manufacturing process of the stator plates, or to an
axial flux machine, in which case the slotting and/or
pole cores according to the invention can be
implemented eg in the manufacturing process of the
stator strip

The electric motor of the invention coprises a stator, in which there are slots and/or poles, a rotor, a
support structure for these as well as an output for
transmitting rotary movement out of the motor, and the
stator slots and/or poles are arranged in a placement
differing from equidistant distribution Preferably
the divergence from equidistant distribution is made
such that the divergences from equidistant placement
of the slots and/or poles in at least one portion of
the stator are symmetrical with at least one other
portion of the stator Examples of the types of
electric motors to which the invention can apply are
presented in Figs 1-3 Fig 1 presents an example of
the active parts of a permanently magnetized radial
flux machine The rotor 2 0 of the machine is
manufactured from e g steel or from electrical plate
The permanent magnets 21 are disposed on the surface
of the rotor The stator 22 can also be manufactured
from electrical plate The stator of the example is
made from two halves The coils 23, which can be
formed from e g insulated copper conductor, are
disposed on the stator 22 meg. a ring-like fashion
as shown in the figure The main direction of the
magnetic flux between the rotor and the stator is
radial as viewed from the shaft.
Fig 2 presents an example of the active parts of a
permanently magnetized axial flux machine. The stator
of the machine contains slotting, but an axial flux
machine can also be implemented with pole windings In
the machine shown as an example in the figure
permanent magnets are positioned on the rotor 26, and
the winding of the stator 24 is made in the slots 2 5
Three stator coils 27, 28, 29 are marked in the
figure The direction of the magnetic flux of the
machine in the air gap between the rotor and the

stator is mainly in the direction of the shaft of the
machine
Fig 3 presents a cross-section of the stator and
rotor frames of a motor slotted in accordance with
prior-art techniques The inner rim of the stator 3 0
has slots 31 and teeth 32 between said slots. The
rotor 33 also has slots 34 and teeth 35, and a narrow
air gap is located between the rotor 33 and the stator
30, in which air gap the magnetic flux passes from the
stator 30 to the rotor 33 and back Windings are
disposed in the slots 34, 31 of both the rotor 33 and
the stator 30. In this type of motor it is also
possible if necessary to apply dispersed placement of
the slots according to the invention to the rotor side
to reduce harmonics originating from the rotor.
In one preferred embodiment of the invention the
deviations from equidistant placement of the slots or
poles formed with the conversion function are so small
that changing the normal equidistant placement to
accord with the invention does not affect the
manufacture of the stator coils or the winding The
new placement of the slots according to the method can
be implemented by making a software adjustment to the
machinery with which the slots are made in the stator
strip or electric plate
In one preferred embodiment of the invention the
divergence from equidistant placement of the slot
and/or pole is formed by means of at least one sine
function to be the same magnitude as the value of the
conversion function In one preferred embodiment the
symmetry number of the conversion function is selected
as s = 2 It is characteristic for the method
according to the invention that by using a larger s
value a larger a value is also needed to achieve the
same effect of damping harmonics

In another embodiment of the invention the symmetry-
number s of the conversion function is selected to be
at least as large as s = 2 In certain embodiments
even s values are preferred to odd ones, because with
odd pole-pair numbers of the conversion function the
composite force exerted on the rotor diverges from
zero, which can cause wear on the bearings Odd
symmetry numbers, including the symmetry number 1, are
however possible and meg slowly rotating axial
flux machines these can be preferable
The inventive concept of the present invention also
includes a concept for manufacturing a stator with
dispersed placement of slots or pole cores One
manufacturing method is to notch slots in the stator
plate or stator strip and form a stator stack from the
notched plates or notched strip The different layers
of the stator structure can be fastened together e g
by welding In the case of a stator strip, e g when
an axial flux machine is the case in question, it is
preferable to first calculate the location points of
the stator slots or stator poles, and after this punch
the slots in the strip and finally coil the slotted
plate into a spiral shape eg in accordance with the
method presented in publication FI 950145 Slots can
be made in the plate stack also after coiling into a
spiral In this case it is preferable to use laser
cutting for slotting, because if punching of the slots
is done to the finished plate stack there is a danger
that harmful short-circuits form between the different
layers of the plate as a result of fraying caused by
the punching
The inventive concept further includes a manufacturing
method for the stator of an electric motor, wherein
dispersed placement of the slots according to the
invention is achieved by using the shape function and

conversion function of the invention in determining
the positions of notches in the ferromagnetic plate to
be coiled into a ribbon-like plate stack Publication
FI 950145 presents a method and an apparatus, with
which a cylinder-shaped stator with equidistantly
positioned slotting can be formed by punching notches
in the ferromagnetic plate or stator strip such that
the final slots are aligned on the cylindrical plate
stack despite the fact that the distance between two
notches on the stator strip increases as the diameter
of the plate stack grows By increasing the distance
between two notches in accordance with a correction
factor dependent, among other things, on the diameter
of the plate stack, the notches are positioned such
that when the strip is coiled, equidistant stator
slotting has been formed in the stator According to
the present invention a conversion function is added
to the slot placement function describing equidistant
slotting, from which a shape function describing the
shape of the slotting is obtained The stator is
manufactured such that notches are punched in
ferromagnetic plate, increasing the distance between
two notches by a correction factor dependent on the
radius of the plate stack so that non-equidistant
slotting according to the shape function forms in the
finished plate stack The method of the invention can
be implemented by making a software modification to
the appliance presented in publication FI 950145, with
which the placement describing equidistant slotting is
modified with a conversion function Because the
stator slotting according to the invention can be
implemented such that the changes in the positions of
the slots with respect to a stator having a
corresponding number of equidistant slots are very
small, stator coils similar to each other and
manufactured for equidistant stator slotting can be
used in a stator according to the invention

Especially in elevator motors the largest possible
torque is desired from the motor, but the outer
diameter of the motor should be small because of
restricted space. This means in practice that the aim
is to make the outer diameter of the stator of an
elevator motor as large as possible with respect to
the diameter of the motor, so it is preferable to keep
the space remaining for the ends of coils as small as
possible In accordance with the invention stator
coils of the same size as each other can be placed in
non-equidistantly positioned slots to form a winding
such that the wound stator can still be fitted into
the same sized motor frame as a stator having a
corresponding number of equidistant slots and wound in a corresponding manner For example in a stator, which
is provided with a double-layer lap winding, of a
permanently magnetized axial flux motor designed for
elevator use, the diameter of the outer rim of which
is 320 mm and the largest divergences in the distances
between two adjacent slots is less than a millimeter,
a stator wound with stator coils of the same size as
each other can be fitted into a stator frame with an
inner diameter of 3 80 mm Adopting the method of the
invention thus does not require any change in the
manufacture of the stator coils Further, using coils
of the same size as each other in a stator with non-
equidistant placement of its slotting gives the
advantage that the winding process remains just as
simple as in manufacturing a stator having equidistant
slotting, as the position of an individual coil on the
stator rim is not established on the basis of the
divergence of its width from the other coils One
advantage in making small changes to the slotting with
respect to equidistant placement is also that that the
selected harmonics of the flux can be damped without
this having a significant effect on the fundamental
wave

In one embodiment of the invention the placement
function, conversion function and shape function of
equidistant slots are formed as measurement lengths on
the inner rim of the plate stack Punching of the
plate stack starts from the end of the strip that will
be on the inner rim of the plate stack and as the
punching progresses to the points of the strip that
will be on a larger diameter in the plate stack,
increasing the distance between two slots by a
correction factor dependent on the diameter of the
plate stack
In one embodiment of the invention the positions on
the stator rim of the slots of equidistant slotting,
the conversion function and the shape function are
presented as angular values When implementing in practice the placement of the invention for the slots
or pole cores as determined by the shape function, the
values of the shape function or conversion function
must often be rounded up or down, which slightly
affects the symmetry of the resultant stator The
slotting or pole cores according to the invention are
preferably implemented such that the actual position
of the slot and/or pole do not diverge substantially
from the value given in Formula 3 despite the rounding
up or down For example a divergence between the
actual position and the position described by the
shape function corresponding to ten per cent of the
amplitude of the conversion function can however be
regarded as a sufficiently small divergence from the
viewpoint of meeting the symmetry condition
As one application of the present invention the slots
and teeth of the stator of the motor can be measured
e g such that the width of a tooth is 5 millimeters

In one embodiment of the invention the placement
function, conversion function and shape function of
equidistant slots are formed as measurement lengths on
the inner rim of the plate stack Punching of the
plate stack starts from the end of the strip that will
be on the inner rim of the plate stack and as the
punching progresses to the points of the strip that
will be on a larger diameter in the plate stack,
increasing the distance between two slots by a
correction factor dependent on the diameter of the
plate stack.
In one embodiment of the invention the positions on
the stator rim of the slots of equidistant slotting,
the conversion function and the shape function are
presented as angular values When implementing in practice the placement of the invention for the slots
or pole cores as determined by the shape function, the
values of the shape function or conversion function
must often be rounded up or down, which slightly
affects the symmetry of the resultant stator The
slotting or pole cores according to the invention are
preferably implemented such that the actual position
of the slot and/or pole do not diverge substantially
from the value given in Formula 3 despite the rounding
up or down For example a divergence between the
actual position and the position described by the
shape function corresponding to ten per cent of the
amplitude of the conversion function can however be
regarded as a sufficiently small divergence from the
viewpoint of meeting the symmetry condition
As one application of the present invention the slots
and teeth of the stator of the motor can be measured
e g such that the width of a tooth is 5 millimeters

in magnitude and the width of a slot is 7 millimeters in magnitude
One application of the present invention is a motor in which the stator winding is a fractional-pitch
winding, using e g a fractional pitch of 5/6
In one preferred embodiment of the present invention
one sine function is used as the conversion function,
for which an amplitude of 0 3 millimeters is selected
When the symmetry number of the shape function is two,
substantial damping of the fifth, seventh, eleventh
and thirteenth harmonic is achieved At the same time
however the amplitude of the fundamental wave does not
in practice change
In a second preferred embodiment 0 3 millimeters is
selected as the amplitude of the conversion function
and three as the symmetry number In a third preferred
embodiment 0 2 millimeters is selected as the
amplitude of the conversion function and two as the
symmetry number In both the second and third
preferred embodiments substantial damping of
particularly the 11th and 13th harmonic is achieved
One application of the present invention is the flat
type of motor used as the power source for elevator
systems, such as that described in publication EP
676357 The motor contains a laminar stator and a
laminar rotor Permanent magnets are disposed on the
surface of the rotor plate The essential parts of the
motor have been rendered very flat in shape in a
solution according to EP 676357, as a result of which
the motor can be deployed directly in the elevator
shaft and no separate machine room is then needed
The invention is not however limited to an individual
application, but can be applied to electric motors m

general Another preferred application is the drive
machineries of escalators
It is obvious to the person skilled in the art that
the invention is not limited to the embodiments
described above, in which the invention is described
using examples, but that many adaptations and
different embodiments of the invention are possible
within the frameworks of the inventive concept defined
by the claims presented below

WE CLAIM:
1 A Method for forming an electric motor, said electric motor comprising a rotor,
a stator, and a supporting structure for the rotor and the stator as well as an output
for transmitting rotary movement out of the motor, and in which stator is a
plurality of slots and/or poles, characterized in that in the method the plurality of
stator slots and/or poles are placed in a manner diverging from equidistant
distribution, and which method further includes the phases of
defining a conversion function, which comprises a sine function or the sum
of a number of sine functions,
defining a shape function for the placement positions of the stator slots
and/or poles by summing the values of the conversion function for the
placement positions of the slots and/or poles according to equidistant
slotting, and
forming a stator, in which the slots and/or poles are positioned essentially
in accordance with the shape function
2 The method as claimed in claim 1 wherein the method additionally includes
the phase of
making in at least one portion of the stator the divergences of the
placement of the slots and/or poles from equidistant placement
symmetrical with the divergences made in another portion
3 The method as claimed in claim 1 or 2 wherein changes to the structure of the
stator with respect to equidistant placement are made so small that they do not
affect the manufacturing of the coils or the winding process
4 The method as claimed in any of claims 1-3 wherein the method additionally

includes the phase of
defining the non-equidistant positioning for the slots on the stator rim
5 The method as claimed in any of claims 1-4 wherein the method additionally
includes the phase of
defining the non-equidistant positioning for the slots in the pole cores
6 The method as claimed in any of claims 1-5 wherein the method additionally
includes the phase of
defining the non-equidistant positioning for the poles on the stator rim
7 The method as claimed in any of claims 1-6 wherein the method additionally
includes the phase of
defining widths that differ slightly from each other for the pole cores
8 The method as claimed in any of claims 1-7 wherein the symmetry number of
the conversion function is at least two
9 The method as claimed in any of claims 1-8 wherein the symmetry number of
the conversion function is an even number
10 The method as claimed in any of claims 1-9 wherein the motor formed is an
axial flux motor, and in which method the stator of the motor is manufactured by
coiling a ribbon-like ferromagnetic plate into a cylindrical stack of plates around
the centre axis of the of the plate stack, and in which method before coiling into a

plate stack notches are punched in the plate with a punching appliance to form the
slots
11 An Electric motor, in which there is a stator (22, 26, 30, 50, 52, 54, 60), and in
which there is also a plurality of slots (31, 40, 42, 44, 51, 53, 55, 65) and/or poles
(61), a rotor (20, 24, 33), and a support structure for the rotor and the stator, as
well as an output for transmitting rotary movement out of the motor characterized
in that the plurality of slots (31, 40, 42, 44, 51, 53, 55, 65) and/or poles (61) are
arranged in the stator in a manner diverging from equidistant distribution such that
the divergence of the positioning of the slot (31, 40, 42, 44, 51, 53, 55, 65) and/or
pole (61) from equidistant positioning is the same magnitude as the value of the
conversion function, formed by means of at least one sine function
12 The electric motor as claimed in claim 11 wherein the divergences of the
positioning of the slots (31, 40, 42, 44, 51, 53, 55, 65) and/or poles (61) from
equidistant positioning are in at least one portion of the stator (22, 26, 30, 50, 52,
54, 60) symmetrical with the divergences in at least one other portion of the stator
13 The electric motor as claimed in claim 11 or 12 wherein changes to the
structure of the stator with respect to equidistant placement are made so small that
they do not affect the manufacturing of the coils or the winding process
14 The electric motor as claimed in any of claims 11-13 wherein the rotor (20,
24, 33) of the electric motor is permanently magnetized

15 The electric motor as claimed in any of claims 11-14 wherein the electric
motor is an axial flux machine
16 The electric motor as claimed in any of claims 11-15 wherein the electric
motor is a radial flux machine
17 The electric motor as claimed in any of claims 11 - 16 wherein the winding of
the stator (22, 26, 30, 50, 52, 54, 60) is a fractional-pitch winding
18 The electric motor as claimed in any of claims 11-17 wherein the electric
motor is used as the power source of an elevator system
19 The electric motor as claimed in any of claims 11 — 18 wherein the stator (22,
26, 30, 50, 52, 54, 60) is slotted by punching slots in the stator plate or stator strip
and by forming the stator stack from the slotted plate or the slotted strip

ABSTRACT

METHOD FOR FORMING AN ELECTRIC MOTOR AND ELECTRIC
MOTOR THEREOF
In the present invention the positions of the slots or poles of the
stator of an electric motor are changed in order to reduce the harmonics caused
by the stator winding and any vibration caused by these harmonics In the present
invention a shape function is defined according to the new placement positions
for the stator slots and/or stator poles A conversion function sums for the slot
placement positions to be given to equidistant statot slotting placement In one
embodiment of the invention the conversion function is the sum of sinusoidal
functions and in its amplitude small in relation to the distance between the slots