CA1194098A - Self-starting brushless d.c. motor using only one magneto-sensitive element - Google Patents
Self-starting brushless d.c. motor using only one magneto-sensitive elementInfo
- Publication number
- CA1194098A CA1194098A CA000409798A CA409798A CA1194098A CA 1194098 A CA1194098 A CA 1194098A CA 000409798 A CA000409798 A CA 000409798A CA 409798 A CA409798 A CA 409798A CA 1194098 A CA1194098 A CA 1194098A
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- motor
- circuit
- rotor
- self
- polarity
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Abstract
ABSTRACT:
A motor is self-starting using only one magneto-sensitive element because the motor is of a two-phase type and is provided with a detection device which detects towards which of the two phases the rotor is mainly directed. A presetting circuit compares the detected rotor position with the state of an energizing circuit in order to set this circuit so that the energiz-ing circuit energizes the stator phases for said specific rotor position in such a way that starting of the motor is guaranteed, although initially with an undefined direction of rotation. By presetting the commutating direction of the energizing circuit the rotor subsequently locks the field which rotates in the correct direction if it has started in the incorrect direction.
A motor is self-starting using only one magneto-sensitive element because the motor is of a two-phase type and is provided with a detection device which detects towards which of the two phases the rotor is mainly directed. A presetting circuit compares the detected rotor position with the state of an energizing circuit in order to set this circuit so that the energiz-ing circuit energizes the stator phases for said specific rotor position in such a way that starting of the motor is guaranteed, although initially with an undefined direction of rotation. By presetting the commutating direction of the energizing circuit the rotor subsequently locks the field which rotates in the correct direction if it has started in the incorrect direction.
Description
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
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
Claims (14)
IS CLAIMED ARE DEFINED AS FOLLCWS:
1. A self-starting brushless d.c. motor comprising a stator, a rotor and a commutating device, characterized in that the stator is of a two-phase type and that the commutating device comprises - a detection device having only one detector for distin-guishing towards which of the two stator phases the rotor is mainly directed, - presettable energizing circuit for the commutated ener-gization of the stator phases, and - a presetting circuit adapted to be controlled by the detection device for, at least when the rotor is stationary, setting the energizing circuit to one of the two states which correspond to energization of the stator phase other than that towards which the rotor is mainly directed.
2. A self-starting brushless d.c motor as claimed in Claim 1, characterized in that the presettable energi-zing circuit is preset to the switching sequence corres-ponding 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.
3. A self-starting brushless d.c. motor asclaimed in Claim 2, characterized in that the presettable energi-zing 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 direction of rotation of the motor reversible.
4. A self-starting brushless d.c. motor as claimed in Claim 1, comprising p pole pairs, characterized in that the detection device comprises a permanent-magnetic member having 2p pole-pairs, which member is rotatable in synchro-nism with the rotor, and the detector comprises a magneto-sensitive element, specifically a Hall element.
A self-starting brushless d.c. motor as claimed in Claim 4, characterized 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 gate circuit for comparing the detected polarity with the state of the energizing circuit.
6. A self starting brushless d.c. motor as claimed in Claim 2, comprising p pole pairs, characterized in that the detection device comprises a permanent-magnetic member having 2 p pole-pairs, which member is rotatable in synchro nism with the rotor, the detector comprises a magneto-sensitive element, specifically a Hall element, and there is provided a commutating-signal generator for generating com-mutating signals for the energizing circuit in synchronism with the magnetic field polarity changes detected by the detector.
7. A self-starting brushless d.c. motor as claimed in Claim 6, characterized 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 for comparing the detected polarity with the state of the energizing circuit.
8. A self-starting brushless d.c. motor as claimed in Claim 7, characterized in that the presetting circuit is adapted to supply additional commutating signals to the energizing circuit.
9. A self-starting brushless d.c. motor as claimed in claim 6, characterized in that there are provided means for detecting the application of a supply voltage 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 for comparing the detected polarity with the state of the energizing circuit and after detection of the application of a supply voltage setting the energizing circuit to a state which is in conformity with the detected polarity.
10. A self-starting brushless d.c. motor as claimed in Claim 7 or 9, characterized in that there is provided a second gate circuit for suppressing the next commutating signal under command of the presetting circuit.
11. A self-starting brushless d.c. motor as claimed in Claim 6, 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 state of the energizing circuit and generating a commutating signal each time that said state does not correspond to the detected polarity.
12. A self-starting brushless d.c. motor as claimed in Claim 2, characterized in that the energizing circuit comprises a shift register.
13. A self-starting brushless d.c. motor as claimed in Claim 12, characterized in that the shift register has an adjustable shifting direction.
14. A self-starting brushless d.c. motor as claimed in Claim 1, 2 or 3, characterized by -a rotor having a cylindrical permanent magnet which is magnetized to have substantially 2 p poles, -a stator having two-phase windings arranged coaxially with the rotor inside the cylindrical permanent magnet, -a wiring support secured to the stator, to which support the stator windings are connected, and -a substrate arranged on said wiring support, on which substrate at least the magneto-sensitive element is arranged in such a way that said element is disposed within magnetic range of influences of the end face of the cylin-drical permanent magnet which, faces said support, the permanent magnet being provided with a 4p-pole magnetiza-tion at the location of said end face.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000409798A CA1194098A (en) | 1982-08-19 | 1982-08-19 | Self-starting brushless d.c. motor using only one magneto-sensitive element |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000409798A CA1194098A (en) | 1982-08-19 | 1982-08-19 | Self-starting brushless d.c. motor using only one magneto-sensitive element |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1194098A true CA1194098A (en) | 1985-09-24 |
Family
ID=4123446
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000409798A Expired CA1194098A (en) | 1982-08-19 | 1982-08-19 | Self-starting brushless d.c. motor using only one magneto-sensitive element |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1194098A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN106707163A (en) * | 2016-12-29 | 2017-05-24 | 上海奥波电子有限公司 | Detection system and method of brush motor |
-
1982
- 1982-08-19 CA CA000409798A patent/CA1194098A/en not_active Expired
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN106707163A (en) * | 2016-12-29 | 2017-05-24 | 上海奥波电子有限公司 | Detection system and method of brush motor |
| CN106707163B (en) * | 2016-12-29 | 2023-08-25 | 上海奥波智能科技有限公司 | Detection system and method for brush motor |
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| Date | Code | Title | Description |
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| MKEX | Expiry |