Note: Descriptions are shown in the official language in which they were submitted.
PHN 10.126 1 1.7.1982
The invention relates to a self-starting
brushless d.c. motor comprising a stator, a rotor and a
commutating device. In brushless motors commutation is
effected electronically. Rotor-position information can
then be ob-tained by means o~ detectors, such as Hall
elements. ~or polyphase motors satisfactory commutation and
starting charac-teristics are obtained by the use of one
detector per phase, which detectors are circum~erentially
1 spaced in conformity with the number of phases o~ the
motor. The disadvantage of this is tha-t such motors are
comparatively expensive. There~ore, the aim is to ~se only
one Aetector. Single-phase motors obviously employ one
detector. However, these motors have the inherent dis~
advantage that the direction of rotation is unde~ined.
Moreover, the starting situation may be such that, -upon
energization, the rotor is in a stable position, which
problem may also occur in polyphase motors. The two
problems can be overcome by mechanical means, such as -the
zO provision of a "detent position", ~or example by ensuring
by means of an au~iliary magnet that the motor stops in a
position in ~hich starting is possible in a predetermined
direction. ~owever~ the drawback of mechanical and/or
magnetic means is that such means also adversely a-~fect
the steady-state behaviour o~ the motor. In order to
permit the use o~ only one detector in polyphase motors,
specifically three-phase motors, it has therefore been
proposed to start the motor by means of a rota-ting auxili-
ary ~ield. This has the disadvantage that, during starting,
the motor is not self-commutating and consequently
exhibits unfavourable starting characteris-tics.
The invention aims at providing a brushless
motor which is self-commutating during starting, thereby
PHN 10 126 2 1.7.1982
enabling it to be started by purely electronic means.
To this end the invention is characterized in
that the sta-tor is of a two-phase type and that the commu-
tative device comprises
- a detec-tion device having only one detec-tor ~or
distinguishing towards which of the two sta-tor phases the
rotor is mainly directed~
- a prese-ttable energizing circuit ~or the commutated
energization o~ -the stator phases, and
_ a presetting circuit adapted to be control.led by the
detection device for, a-t least when the rotor is
sta-tionary, se-tting the energizing circuit to one o~ the
two states which correspond to energization of the stator
phase other than that towards which the rotor is mainly
directed~
This combination of charac-teristic features
results in a motor which comprises only one detector, which
is self-commutating during starting, and which does not
require any non-electronic starting means.
The invention is based on the insight that,
although in a polyphase motor the rotor position cannot be
detec-ted unambiguously by means o~ only one detector~ in a
two~phase motor the two rotor positions that cannot be
distinguished by means of one detector always corresponcl
to one speci~ic sta-tor phase, so that self-commutating
starting is possible using only one detector~
A motor in accordance with the invention, which
comprises p pole-pairs, may ~urther be characterized in
that the detection device comprises a permanent-magne-tic
30 member having 2p pole-pairs, which member is rotable in
synchronism with the rotor~ and in that the detector
comprises a magneto-sensitive element, speci~ically a Hall
elementO
This embodiment may ~urther be characterized in
that the presetting circuit comprises a polarity detector
~or detecting the polarity o~ the magne-tic ~ield sensed by
the magneto-sensitive element and a gate circuit ~or compa-
4~38
PHN 10.126 3 1.7,1982
ring the detected polarity with the state of theenergizing circuit.
The undefined starting direction of some mo-tors
in accordance wi-th the invention is not a problem for some
uses. If a specific direction of rotation is required~ an
additional advantage of a solution in accordance with the
invention will become apparent: in the motor in accordance
with the invention the correct direction of rotation can be
guaranteed in a simple manner~ For this purpose a preferred
embodiment of the invention may further be characteri2ed
in -that the presettable energizing circuit is preset to the
switching sequence corresponding to the desired direction
of rotation of the rotor and can be switched, in accordance
with a cyclic permutation, under command of commutation
signals, regardless of the actual direction of rotation of
the rotor. This further characteristic feature is based on
the insight that when the motor is started commutating
pulses are generated as a result of the self-commutating
starting behaviour of the motor in accordance with the
invention. By electronically laying down the switching
sequence of the motor phases it is achieved that the phases
are consecutively energized in the correct sense, e~en in
the case of an incorrect starting direction. In the case
of such an incorrect starting direction the rotating stator
field and the rotor ~ich rotates in the opposite sense
~'mee-t" each other and the rotor locks in after a maximum
of two commutations. In the case of a p-pole motor the
maximum rotation in the incorrect dircction is equal to
substantially ~ . For many uses, such as motors in
p
cassette recorders, such an incorrect starting motion
presents no problem at all. It may then be advantageous
that the presettable energizing circuit comprises a control
input and is adapted to preset the switching sequence to
one of the two possible directions as a function of a
signal on said control input in order to render the direc~
tion of rotation of the motor reversible~
This preferred embodimerlt may further be
~4~
Pl~ 10.126 4 1.7,1982
charac-terized in that the detection device comprises a
permanent-magnetic rnember having 2p pole-pairs9 which
member is rotatable in synchronism with the rotor, in that
the detector comprises a magneto-sensitive element, specifi-
cally a Hall element, and in that there is provided acommutating-signal generator for genera-ting commutating
signals for -the energizing circuit in synchronism with
the magnetic-field polarity changes detected by the
detector.
l ~ firs-t version o~ said preferred embodimen-t may
be characterized in that the presetting circuit comprises
a polarity detector for detecting the polarit~ of the
magnetic field sensed by the magneto-sensitive element and
a first gate circuit for comparing the detected polarity
with the state of the energizing circu-t.
.~ further characteristic feature is than -that
the comparator circui-t is adapted to supply additional
commutating signals to the energizing circui-t, In said
first version of the preferred emdobiment of the invention
an incorrect rotor position is corrected by supplying an
additional commutating pulse,
~ second alternative version o~ the preferred
embodiment of -the invention may be characterized in that
the commutating-signal generator comprises a polarity
detector for detecting the polarity of the magnetic field
sensed by the magneto-sensitive element and a gate circuit
for comparing the detected polarity with the sta-te of
-the energizing circui-t and generating a commutating signal
if said state does not correspond to the detected polari-ty.
In this version -the commutating signal is supplied by the
presetting circuit, This version is based on the insigh-t
that each commutation is in fact preceded by an "incorrect"
energizing condition. Indeed, the output signal of the
position detector changes, a-t the commutation instant, ~hilst
the energizing condition of the stator changes only shortly
afterwards, This means that the rotor posi-tion and the
energizing condition briefly do not correspond to each
PlrN 10.126 5 1.7.1982
other, which non-correspondence can be signalled by
the preset-ting circuit. In -the present version this is
utilized byhaving the presetting circuit generate the
commutating pulses in the case of these apparently incor-
rect rotor positions, so that a separate commutating-pulse
generator may be dispensed with.
In said first and second version the cletected
rotor position is compared with the energizing condition
a-t the ins-tant of star-ting. However~ regardless o-~ the
energizing condition which would occur up on starting o~
the motor, it is alternatively possible to set the
energizing circuit to one of the two possible correct
states depending on the detected rotor position during
build-up o~ the supply voltage. ~or this purpose a third
version of the preferred embodiment of the invention is
characterized in that there are provided means for detec-
ting the application of a supply voltage, in that the
presetting circuit comprises a polarity detector for
detecting the polarity of the magnetic field sensed by the
magneto sensitive element, and a first gate circuit ~or
comparing the detected polarity with the state of the
energizing circuit and, after detection of the applica-tion
of a supply voltage, setting the energizing circuit to a
state which is in conformity wi-th the detected polarity.
In this third version these steps also ensure
correct starting. ~ince the commutation may be disturbed
by spurious pulses and -this is not readily corrected as in
the first and second versions, it is advantageous if
appropriate steps are taken in this third version. A
3~ suitable solution is then characterized in that there is
provided a second gate circuit for suppressing the next
commu-tating signal under command o~ the comparator circuit.
By suppressing the ne~t commutating pulse in,
stead o~ generating an additional commutating pulse it is
achieved that -the commutation is corrected immediately.
Indeed a spurious impulse will practically always give
rise to an additional commutation instead of suppressing a
PHN 10.126 6 1.7.1982
commutation, so that it is more favourable to suppress a
commutating pulse than to generate an additional pulse.
It is advantageous if the energizing circuit
of the motor in accordance with the invention comprises a
shift register. A further characteristic feature is that the
shift register has an adjustable shifting direction. Thus,
the direction of rotation o~ the motor can be selected in
a simple manner. With respect ~ its construction~ the motor
in accordance with the invention may further be charac-
terized by
- a rotor having a cylindrical permanent magnet which
is magnetized to have substantially 2p poles,
a s-tator having two-phase windings, arranged coaxially
with the rotor inside the cylindrical permanent magnet~
_ a wiring support secured to the stator, to ~hich
support the stator winding~ are connected, and
- a substra-te arranged on the wiring support9 on which
substrate at least the magneto-sensitive element is
arranged in such a way tha-t said element is disposecL within
the magnetic range of influence of the end face of the
cylindrical permanent magnet which faces said suppor-t, the
permanent magnet being provided with a 4p-pole magnetiza-
tion at the location of said end face.
The invention will now be describcd in more
detail with reference to the drawings, in which
Figure 1 schematically represents the principle
of the motor in accordance with the invention,
Figure 2 is a diagram to explain the operation
of the motor of Figure 1,
Figure 3 shows a first version of the circuit
4 in t~e motor of Figure 19
Figure 4 shows an alternative to a part of the
circuit o~ Figure 3,
Figure 5 shows a second -version of said circuit
4~
Figure 6 shows a third version of said circuit
4,
and
PHN 10.126 7 1.7.1982
Figure 7 is a sectional view of a preferred
embodiment of the invention.
Figure 1 schematically represents a motor with
energizing circuit in accordance with the invention. The
motor has a :rotor 1~ which in the present example is
magnetized to have two poles (N, S). The rotor position is
specified by an angle ~ , which in the conclition sho1~n is
zero. The stator comprises four coils L1, L2, L3 and Ll~ wi-tl
connections 5, 6, 7 and ~ respectively. A position encoder
- lO 2, which i5 magnetized to have four poles, is mechanically
coupled to - or arranged on - the rotor 1. A ~i.eld sensor
H~ specifically a Hall element, is in magnetic contac-t with
said position encoder 20 The position of the position
encoder 2 and sensor H relative to the rotor position is
such that the sensor H dètects polarity changes via the
position encoder 2 at those rotor positions ~ where commu-
tation of the energization of the stator coils L1~ L2~ L3
and L4 is most app~opriate, tha-t is, appro~imatsly at the
positions ~ = L~5 , 135 , 225 and 315. The output signal
20 of the ~ield sensor H is applied to an input 3 o~ an
energizing circuit 4, which energizing circuit 4 in turn
energizes each of the stator coils L1, L2, L3 and Ll~.
Figure 2 shows the variation TL1, TL2, TL3 and
TL4 of the torque T e~erted on the rotor 1 as a function
25 of the rotor position ~ upon energization of the coils
Ll 9 L2, L3 and Ll~ respectively, and the field ( N, S)
of the position encoder 2 sensed b-~ the field sensor H as a
function of said rotor position ~ .
If upon starting of the motor - after applica-
30 tion of a supply voltage or after blocking of the rot~r -
a specific coil is energized, the rotor will or will not
begin to revolve depending on the instantaneous position
~ , If, for e~ample, coil LL~ is energized, the diagram of
Figure 2 shows that the torque e~erted on the rotor is zero
35 at ~ = 270. An unstable position of equilibrium for
which T _ 0 is found at ~ = 90, in which position the
motor will not start in the loaded condition~ ~or rotor
positions ~ between 270 and 315 ancl those between 225
PHN 10.126 S 1.7.19~2
and 270 the rotor will be drawn to~ards the position of
equilibrium ~ = 270 . Outside this range of 225 - 315
the rotor will also be attracted to~ards ~ = 270, but
commutation is effected at the appropriate instan-t when
at ~ _ 225 or ~ = 315 the field sensor 1I senses a field
change via -the position encoder 2.
Irhen the ro-tor positions for WiliCil ~nergization
o~ the sta-tor coil L4 gives rise to star-ting problems are
compared with the positions of the positionencoder 2 coupled
thereto, it is found that s-tarting is problematic when -the
field sensor H senses an S-magnetization of -the position
encoder 2. A similar comparison carried out for energiza-
tion of the stator coils L1, L2 and L3 sho~is that 1~Then
the field sensor H senses an S-magnetization starting is
lS problematic upon energization of coil L2 or L4 and that when
the field sensor H senses an N-magnetization starting is
problematic when coil L1 or L3 is energized. In accordance
with the i~ntion starting can be guaranteed by cons-truc-
ting the energizing circuit 4 so that the said combinations
20 Of energization of one of the coils L1 to L4 and -the polari-
ty of the field from the position encoder 2 sansed by the
field sensor H for which s-tarting gives rise to problems
are excluded. Ths motor will then always start though with
an undefined direction of rota-tion.
A specific direction of rotation can be obtained
by designing the energizing circuit 4 so tha-t the energi-
zing sequence of the coils L1 to Ll~ is fi~ed~ far e~ample
-t~le secLuence L1, L2~ L3~ L4 *or clockwise rotation,
switching to the next coil in said sequence being e~fected
30 under command of the field sensor H. Thus, after starting
a ro-tating *ielcl is obtained in a specified direction,
regardless of the starting direction of the rotor 1y so
that upon starting of the rotor in the incorrect direction
the rotor position will be in conformity with the energi-
35 zation and the rotor locks in to the rotating field andbegins to rota-te in the corract direction after half a
revolution a-t most. If, for example, coil L4 in the confi-
PHN 100126 9 -1.7.1982
guration shown in Figure 1 is energized ~hen the position
of -the rotor 1 is as shown~ the energizing circuit 4 bei~g
set to cloekwise energization, the rotor 1 ~ill begin
to revolve in the anticlockwise direetion ~t y = - 45
commuta-tion i5 effeeted under eommand of the sensor ll and
coil L1 is energized, so that the rotor motion is brakec1
and -the direction is reversed. The rotor then eon-tinues to
the position ~ 5, at whieh instan-t eoil L~ is
energized and the rotor locks in to the cloclcwise rotating
~ield. The maximum rotation in -the ineorrect direction is
less than 180, namel~ -the rotation ~rom ~ < ~ 45 to
~ ~ - 135. For many uses sueh as in eassette recorders
this ineorrect rotation upon starting presents no problem.
~igure 3 shows an example of the energizing
lS circuit 4 (see Figure 1), whieh together ~ith the field
sensor ~ may be ineorporated in one integrated circuit.
The eireuit comprises a eircuit 12 which is cyelically
s1~itched under eommand of a pulse on an input 13, for
example a 4-bit shift register 1~hieh is coupled end-around
20 and in which one logic "one" and three logic "zeros" are
stored. Thus, one o~ the four outputs Q1 to ~4 o~ the
cireuit 12 is all~ays energized di~ferently. The four out-
puts Q1 to Ql~ are eonnected to the terminals 5 to 8 of the
coils L1 to L4t as the ease may be via buffer amp~ifiers 14
to 17, so that al1~ays one of the eoils L1 to L4 is energi-
zed. The shift register 12 has a fixed shifting direction~
which is for example optionally presettable by the applica-
tion of one of two possible logic levels -to an inpu-t 24.
This ensures that the eoils L1 to L4 are energized in a
30 predeterminecl sequenee. By making -the shifting direetion of
the shift register 12 adjustable it is possible to select
the direetion of rotation of the motor by applying the
logle level whieh eorresponds to the desired direc-tion of
rotation to the input 24.
The shift register 12 is advaneed under control
of pulses on input 13. In order to synchronize this shif-ting
~ith the rotor motion the signal supplied by the field
~4~39~3
Pl~ 1o.1Z6 10 I.7.1902
sensor H is applied to a pulse shaper 9 ~ia input 3,
~rhich pulse shaper produces a pulse on input 13 upon the
occurrence of each field transition which is d~tected,
~that is at the desired commutation instants when the
rotor position ~ is 45, 135j 225 or 315, so that
self-commutating operation of the motor is possible,
In order to prevent the stator coils ~rom
being energizecl in such a way that the mo-tor does no-t
start, the polarity of the field sensed by the fielcl
sensor ~I is compared wi-th -the position of the shift regis-
ter 12, as has been explained with reference to Figure 2.
For this purpose the signal from the field sensor H is
applied, via input 3, to a detector 10 which detects a
signal eorresponding to N-magnetization, and to a detector
lS 11 which deteets a signal eorresponding to S-magnetization.
I~hether eoil L1 or eoil L3 is energized is deteeted by
means of an OR-gate 18 eonnected to outputs Q1 and Q3 and
whether coil L2 or coil L4 is energized is deteeted by
means of an OR-gate 19 connected to outputs Q2 and Q4.
The output signals of the c~teetor 10 and OR-gate 18 are
applied to an ~D-gate 20 and the signals from detector 11
and OR-ga-te 19 are applied to an ~ND-gate 21. The output
signals of the AND-gates 20 and 21 are c~mbined, for
example by means of an OR-gate or, as is shown in Figure
3, by interconnecting the outpu-ts ("wired-ort'). This com-
bined output signal is an indication of an impermissible
energizing eondition, -that is a eondi-tion in which -the
energization ean keep the rotor in a position in wh:Lch the
torqlle T = O, so that the rnotor does no-t start. ~ me-thod
o~ eliminating the impermissible energizing condit.ion is
then, for example, to set the shift regis-ter 12 to a
position corresponding to a permissible eondition, which in
the example of Figure 3 is achieved by advancing -the shi.ft
register 12 by one adclitional position. For this purpose
the combined output signal of the ~ND-gates 20 and 21 is
applied to a pulse shaper 22 which, upon the occurrence of
such an impermissible eondition, supplies a pulse whieh is
PHN '10.'12~ 11 1.7.1g~2
adcled -to the ou-tput signal of -t'he pulse shaper 9 by
means o~ an OR-gate 23, so tha-t an aclcli-tional shifting pulse
appears on inpu-t 13 o~ the shi~'t register l2.
An al-terna-tive -to this method is ob-tained by
for example, -.removing the pulse shaper 22 (and OR gate
~3) from -the circuit of ~igure 3 and by completing the
remainder 1~ith -the circuit sec-tion sho~n in Figure 4 The
outputs Q1~ Q2~ Q3 and Q~ of the shift register 12 are -then
connected to switches S1, S2~ S3 and SL; respectively,
lO ~hich switches may be formed by means of logic gates. In
the positions of the switches S1 to SL~ sho1rn, the si-tuation
is then as shown in Figure 3, whils-t in the other positions
of said swi.tches (the positions shown dotted) the ou-tputs
Q1' Q2~ Q3 and ~4 are connected to the bu~fer amplifiers 15
15 16J 17 and 14, respectively, so that the energizing
condition i.s shi~ted by one position in the specif'ied
direction, The switches S1 to S~ are controllecl by th.e ou-t-
put sign.als of AND-ga-tes ZO and 21, which signa.Ls are com-
bined by means of the OR-gate ~
In the c:Lrcui.t arrangernent o:~'.F:igurc 3 steps
must be taken to prevent an undesircd pulse ~`rom bei:ng ~ormecl
by the pulse shaper 22 as a result of' -t:he non-simul-taneous
change-over of the shift register 12 and the detectors lO and
11. This is for example possible 'by the use of cl.ocked loglc.
25 Another possibility is to utilize this situation by removing
the pulse shaper 9 and the OR~gate 23 -from the circuit of
Figure 3 and connecting the pulse shaper 22 to the input 13
of the shif-t register 12, ~hich alternative is shown in
Figure ~, The circuit then operates in the same way as
30 regards undesired rotor positions. ~s regards the commuta-
tion the circuit then operates iIl that ~t the instant that
the polarity of the signal on input 3 changes the shift
regis-ter remains in the same state. This is detected by AND~
gate 20 or 21 in the same way as is an incorrect position
35 o~ the shift regis-ter and a pulse is applied to input 13 of
the shift register 12 by pulse shaper 22.
In the circuit arrangement and the alternatives
~b 3~
PIIN 100126 12 1.7.1982
described in the ~oregoing an addi-ti.olla:L pulse which
advances the shift regis-ter 1Z by one position is appl:ied
to the shift register each time -that a spllrious pulse
appears Since spur:ious pulses are generally addi-tional
pu]ses ancl do not suppress a desired pulse, this results in
the shift register 12 being advanced by two steps in total,
which temporarily gives rise to the same si-tuation as
described in the case of start:ing in the wrong direc-tion.
This may not be a problem if the risk of spurious pulses
lO occurring is minimi~ed~ for examplc by electronic means -
such as generating time windows for blocking pulses during
time intervals in which no commutating pulse can occur.
However~ in cases in which such a situation must be preclu.-
decl, the circuit arrangement of Figure 3 may be modif`ied
15 to suppress the next pulse supplied b~ the pulse shaper 9,
instead of generating an additional pu.Lse, uncler comman(l of
the AND-ga-tes 20 ancl Z'l~ which modi.~lcation i9 shown in
Figure 6.
:Ln comparison w:Lth the ~ersi.on o~ :igurc 3 the
20 0~-g~ate 23 has been rep:Laced by an ~ND-gate ~5 having arl
inverting inp~lt which :L~ driven 'by t'he output signal o:f the
AND_gates 20 ancl 21 'However~ this method :~a:ils during
starting when the motor is still statlonary. If` the initial
energi~ing condition is a condition in whlch the rotor is in
25 a stable positi.on, the pulse shaper 9 initially cloes not
supply a pulse, so that said pulse cannot be suppressed. A
solution to this is to se-t the shift register to a position
which corresponds to a desired position under control of the
detectors 10 and 11 during the build-up o~ the supply
3n voltage. If during the build-up of the supply voltate the
detector 10 is activated, the shif-t register 12 should 'be
set so that output Q2 or Q4 goes high whereas if the
detector 11 is activated the shift register 12 should be
set so that outpu-t Q1 or Q3 goes high-
In oomparison with the circuit of Figure 3, the
circuit o~ ~igure 6 therefore also comprises a supply-
voltage de-tector 46, which supplies a pulse at -the instant
:PElN l0.'126 13 1.7.19~2
that -the supp:Ly voltage appears on -terminal 'VB, Thi,s
pulse :i5 compared with -the ou-tput signals of the
de-tectors 10 and 11 by AND-ga-tes ~7 and 48 respec-ti-vely.
The outpu-t signals of the ga-tes 47 and l~8 are applie~l to
respec-tive se-t inputs S1 and S2 o:~ -the shift register to
energize outpu-t Q1 or Q2 respectively. This ensures that,
wllen -the detector 10 i5 actuated during application oi` the
supply voltage~ the shif-t register is set so -that output 6
is energi~ed and, when the detec-tor 11 is ac-tuated, so that
output 5 is energized.
The circuit of Figure 3 - in so far as alreacly
described - as well as o-ther versions may be provicled with
a use~ul extension~ especially when these circuits are
in-tegrated. This extension utilizes the ~`act tha-t -the si~na:L
generated by -the fiel<l sensor M can also be used as a tac:ho-
s:ignal. For this purpose said s:i.gnal or~ a.s is shown in
F.igure 3, -the output s:ignal o:~ pulse shap2r 9 may i~e
appl:ied to a contro:L circuit 3~ to wh:Lc:h a cont-rol, s:igrl.l'L
can 'be applied v:La an input ~O. I5specially -i,n t,he casc o.t'
speed control the :rrequency of`-t:he pu:l.s~s supp:liecl by tho
pwlse shaper 9 can be de-termined :iIl the circuit 39 us:ing,
~'or example, a frequency-voltage converter arld rnay be com-
parod wi-th a cl.c. control signal ~hic'h is, ~or examp:Le,
supplied by a reference source 42 lncorporated in -the same
integrated circuit. I:n particular in the case of phase
control the phase o~f -the pulse train supplied by -th.e pulse
shaper 9 ma.y be compared with a reference~p~lse train
applied to input ~OO Other servo~control circllits are also
possible, Th~ output signal of the serw-control circuit 39
can influence the speed and/or phase of the motor, for
example by controlling the magnitude of the drive, for
~ example by control o~ the amplitude of the output signals
,~ of the buffer amplifiers 14 to 17 by the contr~ol circui-t 3g,
which is represented syrn'bolically by arrow~ ~ in Figure 3,
or for example by the use of pulse-width control.
Figure 7 shows an example of a rnotor in accor-
dance with the invention in a~ial cross-section~ Said mo-tor
YIIN 10.12~ 1.'7.19~2
comprises a mounting pla-te 25, whlch may t`or e~ample f`orrn
par-t of an enclosure, The ro-tor shaf-t 27 is secured -to
the pla-te 25 -via a 'bearlng arrangement 26. The ro-tor 1
i5 cup-shaped and eomprises a magnetically conductive cup
28 which is provided with a cyllndrical permanent magnet
29 on the inside of' its cylindrical portion~ The stator ls
secured -to said bottom plate 25 inslcle sald cup and magne-t
28, 29 and eomprlses a larninatlon assembly (30, 30')
formlng poles, and coils (32, 33). A prlnted clrcuit board
34 in l~hich plns, such as the pln 37 shown in -the presen-t
cross-sectlon3 are mounted is secured to -the stator. 'rhe
stator coils are eonnected -to these pins (connection 36).
The prin-ted cireuit 'board also accommoda-tes an :in-tegrated
circuit 35, which comprises the energl7.lng clrcu:i-t l1 and
the field sensor H (in the present ease a Mall element).
In orcler to arrange sa:id Hall elcment as noar as
posslble to the rotor magnet 29 the integratecl c:irc1lit 35
ls arranged ln an open-Lng ln the p.o.'boarcl 3~ projoc-ting
part 3'1 of' sald printecl clrcult 'boarcl comprlses connec-1;ion
~acilities ~or the 9upply voltage and, as the ease may be,
an inp-ut 24 (f'or ad~ustlng the dlrection of' rotation)
and/or 40 (f'or adjusting -the speed) (see Figure 3). The
magnet 29 is radially magnetized~ The position encoder 2
is ~ormed 'by providing the side of the permanent magne-t
29 which f'aees the printed cireuit board 34 with loeally
differen-t magne-ti~ltions~ which does no-t slgnlfleantly
inf'luence -the mo-tor operation whilst the main f'ield o-
~magnet 29 does not perceptibly inf'luence the output signal
of the Hall element. In a particular example -the mo-tor
eomprised 6 poles and the position encoder consequently
12 poles.
In general the invention may be used in a two-
phase rnotor having p pole-pairs and a position encoder wi-th
2p pole-pairs~ It is -to be noted tha-t a motor as is shown
sehematically in Figure 1 is sometimes referred -to as a
f'our-phase motor, the motor being a two-phase motor when -the
coils L1 and L3 as ~ell as the coils L2 and L4 are eonnee-
n~
PIIN 10.126 15 1.7.19~2
-ted in serie~. Each o~ the -two serle,s arrangemen-ts can
-then be energ:ized in both scnses. In this application -the
-term appliecl ~two-phase~ relates to both -types of' mo-tor.
'~urthermore i-t will 'be appreciated that a permanent-
magnetic rotor i9 not esselltial.
lU
