CA2038257A1 - Full-wave feedback speed control for hand mixer - Google Patents
Full-wave feedback speed control for hand mixerInfo
- Publication number
- CA2038257A1 CA2038257A1 CA 2038257 CA2038257A CA2038257A1 CA 2038257 A1 CA2038257 A1 CA 2038257A1 CA 2038257 CA2038257 CA 2038257 CA 2038257 A CA2038257 A CA 2038257A CA 2038257 A1 CA2038257 A1 CA 2038257A1
- Authority
- CA
- Canada
- Prior art keywords
- motor
- scr
- transistor
- control circuit
- speed control
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
Links
- 239000003990 capacitor Substances 0.000 claims description 20
- 238000010304 firing Methods 0.000 claims description 7
- 230000035945 sensitivity Effects 0.000 claims description 3
- 238000010586 diagram Methods 0.000 description 8
- 239000004020 conductor Substances 0.000 description 3
- 230000001276 controlling effect Effects 0.000 description 3
- 241000272470 Circus Species 0.000 description 2
- PBAYDYUZOSNJGU-UHFFFAOYSA-N chelidonic acid Natural products OC(=O)C1=CC(=O)C=C(C(O)=O)O1 PBAYDYUZOSNJGU-UHFFFAOYSA-N 0.000 description 2
- 235000013305 food Nutrition 0.000 description 2
- 230000001105 regulatory effect Effects 0.000 description 2
- 235000014676 Phragmites communis Nutrition 0.000 description 1
- 241001296096 Probles Species 0.000 description 1
- 241000290149 Scapteriscus didactylus Species 0.000 description 1
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 description 1
- 241000011102 Thera Species 0.000 description 1
- 238000013459 approach Methods 0.000 description 1
- 230000002238 attenuated effect Effects 0.000 description 1
- 238000010009 beating Methods 0.000 description 1
- 235000014510 cooky Nutrition 0.000 description 1
- 230000001066 destructive effect Effects 0.000 description 1
- 235000014103 egg white Nutrition 0.000 description 1
- 210000000969 egg white Anatomy 0.000 description 1
- 238000001914 filtration Methods 0.000 description 1
- 230000001939 inductive effect Effects 0.000 description 1
- 239000000203 mixture Substances 0.000 description 1
- 239000002674 ointment Substances 0.000 description 1
- 230000000630 rising effect Effects 0.000 description 1
- 229910052710 silicon Inorganic materials 0.000 description 1
- 239000010703 silicon Substances 0.000 description 1
- 241000894007 species Species 0.000 description 1
- 238000004804 winding Methods 0.000 description 1
Classifications
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
- H02P7/00—Arrangements for regulating or controlling the speed or torque of electric DC motors
- H02P7/06—Arrangements for regulating or controlling the speed or torque of electric DC motors for regulating or controlling an individual dc dynamo-electric motor by varying field or armature current
- H02P7/18—Arrangements for regulating or controlling the speed or torque of electric DC motors for regulating or controlling an individual dc dynamo-electric motor by varying field or armature current by master control with auxiliary power
- H02P7/24—Arrangements for regulating or controlling the speed or torque of electric DC motors for regulating or controlling an individual dc dynamo-electric motor by varying field or armature current by master control with auxiliary power using discharge tubes or semiconductor devices
- H02P7/28—Arrangements for regulating or controlling the speed or torque of electric DC motors for regulating or controlling an individual dc dynamo-electric motor by varying field or armature current by master control with auxiliary power using discharge tubes or semiconductor devices using semiconductor devices
- H02P7/285—Arrangements for regulating or controlling the speed or torque of electric DC motors for regulating or controlling an individual dc dynamo-electric motor by varying field or armature current by master control with auxiliary power using discharge tubes or semiconductor devices using semiconductor devices controlling armature supply only
- H02P7/292—Arrangements for regulating or controlling the speed or torque of electric DC motors for regulating or controlling an individual dc dynamo-electric motor by varying field or armature current by master control with auxiliary power using discharge tubes or semiconductor devices using semiconductor devices controlling armature supply only using static converters, e.g. AC to DC
- H02P7/295—Arrangements for regulating or controlling the speed or torque of electric DC motors for regulating or controlling an individual dc dynamo-electric motor by varying field or armature current by master control with auxiliary power using discharge tubes or semiconductor devices using semiconductor devices controlling armature supply only using static converters, e.g. AC to DC of the kind having one thyristor or the like in series with the power supply and the motor
Landscapes
- Engineering & Computer Science (AREA)
- Power Engineering (AREA)
- Control Of Direct Current Motors (AREA)
- Control Of Ac Motors In General (AREA)
- Control Of Motors That Do Not Use Commutators (AREA)
Abstract
ABSTRACT
A speed control circuit for a permanent magnet motor utilizing full wave rectified current and including an SCR controlled by a circuit responsive to the counter EMF of the motor during the period the SCR is shut off which is compared to a reference voltage produced in a transistor circuit.
A speed control circuit for a permanent magnet motor utilizing full wave rectified current and including an SCR controlled by a circuit responsive to the counter EMF of the motor during the period the SCR is shut off which is compared to a reference voltage produced in a transistor circuit.
Description
-' 2038257 FULL-WAVE FEE~A~ SPEED CONTROL FOR HAND MIX~
1 0 , ~, , :', ~ ' ' .
BACKGROUND OF ~11E INVENTION
~ he present invention relates to a variable speed control for a permanent maqnet electric motor and more speci~ically relates to a ~eedbac~ type o~ variable speed control for tho motor in an electric rood mixer.
In the field o~ electric household mixers, it has always been r~garded as important to provide variable ~peed controls for such mixers. The many types of mixing chores to which a household mixer is applied reguire beater speeds from several hundred rpms to over laoo, depending on whether one might be mixing cookie dough or beating egg whites. More recently, domestic food mixers have been sold with various alternative mixing implements such as whippers or dough hooks, the Iatter requiring ~ubstant~al power at ;~ low speeds.
The simplest type of speed control still used on s~ome mixers involveq a tapped field and a series wound electric motor. The principal problem with such an ap-proach is the ~act that the lower speed windings for the ~;series motor provide less power when under load conditions.
Substantial power i9 often required at lower speeds.
Accordingly,~the tapped ~ield type o~ spEed control is generally regarded as unsatisfactory for miXers that are to 35 be oper~ted under substantial power at low spo~ds. ;~;
- .' " .
` 2~2~7 Another type of speed control commonly used on electric food mixers is a governor type control uslng a mechanical centrifugal governor or tachometer ~eedback which may be adjusted to control the speed of the mixer over a wide range of speeds. This type o~ governor control is reasonably expensive but has the advantage of beinq able to provide high power at low speeds. There are also available more sophi~ticated electronic controls which utilize pulse generating tachometers associated with the motor to sense speed accurately and adjust power to compen-sate ~or variation~ of the actual ~peed ~rom the required speed. These more sophisticated electronic controls are fairly expensive and are unsuitable ~or lower priced electric mixers.
There have also been available electronic con-trols which utilize the counter electromagnetic voltage produced by the motor to sense whether the motor is operat-ing at the proper speed and make suitable ad~ustment~ to control the speed accurately in the ~ace o~ a varying load.
Wh~le the general theory of operation of such feedback controls is well Xnown, there has been conslderable dif~i-culty in providing operating circuits which are simple enough to bc competitively priced and at the same time serve the desired function. Various problems have been encountered which render such controls generally unsatis-actory. They are ensitive to line voltage changes, have a tendency to provide cyclical swings in ~peed, someti~es called ~cogqlng~, which is objectionable to th~ user since it at least creates the impression that the mixer is unable ~0 to settle down and oparate at the selected speed level. It would,~ thera~ore, be desirable to provide a ~eedback control utillzing the counter EM~ o~ the motor to accurate~
ly contro} the speed under ~arying load conditions utiliz-; ing a simple circuit having little filtering of the control signal.BRIEF DESCRIPTION OF THE INVENTIO~
~ , g~7 The present invention involves a feedback control ~or ~ permanent magnet or equivalent motor op~rating on recti~ied unfiltered ~C current which is controlled by an SC~. The gate of the SCR is regulated by a signal which is inver~ely proportional to the fsedbac~ voltage and which is applied to an RC circuit associated with the gate of the SCR. A comparison is made between a re~erence voltage and a signal proportional to the back EMF by mean~ Or a tran-sistor circuit in which the base o~ the transistor is connected to a voltage divider which i~ set according to the speed desired and thus provide~ the voltag~ which i5 a predetermined portion o~ the back EMF. The emitter o~ the transistor is connected to a zener diode which provides ~
re~erence voltage to control the conduction Or the tran~is-tor depending on magnitude o~ the portion of the ~eedback : voltaqe applied to the base. By ty$ng the emitter o~ the transistor to ground through a zener diode and a resistor, :~ a speed stabiIity is achieved which i9 reasonably lnsensi-tive to variations o~ line voltage. In addition, the resistor in circuit with the tran~istor permit~ the circuit to be designed with the constant slope on ths ~peed torque : curve which improves the speed stability and the control ensitivlty.
: It is an object of the present invention to provide an improved variable speed control rOr use with a : permanent magnet motor.
It~is another object o~ the preaent invention to provide;an improved ~eedback control circuit rOr varying the speed of a permahent magnet motor utilizing the back or counter ~MF produced during the portion of the cycle in ; which the:power to the motor is shut of~.
:It is another object of the present invention to provide a ~speed control circuit for a permanent magnet motor utilizing ~ull-wave rectified AC curren~ and an SCR
: 3~ ~controlled by a circuit responsive to the counter EMF of t~e motor during th~ period in which the SC~ is shut off , , - . .
~ i,, , .
~\ 2~38257 ~ `
and includinq a voltage divider which may he set for a -~desired speed to produce a signal proportional to the counter EMF to be compared with a standard ~or regulating the char~ing o~ an RC circult associated with the gate S circuit o~ the SCR.
It is still another ob~ect of the present inven- -tion to provide a speed control circuit for a permAnent maqnet ~otor utilizing ~ull-wave recti~ied AC current controlled by an SCR in which the counter EMF o~ the motor is compared to a reference voltage in a transistor circuit having means in the emitter circuit of the transistor to regulate the slope o~ the spead torque curve for the motor and its control circuit.
Further objects and advantages o~ the instant invention will become apparent to one skilled in the art as the ~ollowing deRcription proceeds, and the ~eaturas of novelty which characterize the invent~on will be pointed -out in the claims annexed to and ~orming a part o~ the specification.
BRI~F DESC~I~TION OF THE DRAWINGS
Fig. 1 is a schematic diagram of the ~peed control circuit embodying my invention:
Fig~. 2a and 2b are diagrams o~ the voltage acro~R the motor and SCR o~ the control circuit embodying 25 my invention under conditions o~ light and heavy load: `~
Flg~. 3a and 3b are diagrams o~ the voltage acros~ the permanent magnet motor under light and heavy loads, respectively;
~Yigs. 4a and 4b are diagra~s o~ the voltage ; 30 acro~ the gate and cathod~ Or the SCR in the motor control circuit undar the ~ama load condîtions a~ Figs. 2 and 3:
Fig~. 5a and 5b are diagram~ o~ the voltages across the conden~er in the ~ate circuit o~ the SC~ which controls the ~ir~ng o~ the SCR under the same lo~d condi-tions as Figs. 2 - 4:
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- ~382~7 ~
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Figs. 6a and 6b are diagra~s o~ the voltage across the base of the transistor in the motor control circuit under the same 1O2d conditions as in Figs. 2 - 5;
and Figs. 7a and 7b are diagrams of the voltage across tha emitter o~ the transistor control circu~t to ground under the same load conditions as in FigY. ~ - 6.
Re~erring to Fig. 1 of the drawinq~, there is shown a schematic diagram of the control circuit embodying ~y invention. The speed control circuit of the instant invent~on i8 applicable to a permanent magnet type motor operating on AC current. The motor is shown in Fig. 1 schematically and desi~nated by reference numeral 20.
The motor control circuit is designated generally by re~erenCQ numeral 22 and ~ncludes a ~ull-w~ve recti~ier 24 connected to a line cord 26. The output o~ the ~ull~
wave rectifier 24 is connected at one output terminal by a conductor 28 to an SCR 30 and the other ~ide of the recti-fier output is connected through a conductor 32 through a line switch 34 and by conductor 36 to the motor :20. The other terminal of the motor 20 is connected by~a lead 38 to the ca~hode 30a o~ the SCR 30. The SC~ 30 al~o has an anode 30~ to which the lead 28 connects and a gate 30c to which a lead 40 connects to one terminal oY a resistance 42, capacitor 54, and diode 80.
In~order to regulate the ~peed o~ the motor 20, 'there~ iY provided in the circuit 22 a potentiometer 44 havinq one end connectad to the lead 36 by lead 46 with the other end connected by lead 48 to an adjust~blo resistor 50. Also connected:in se~ies with potentiomQter 44 and reY~is~or 50 ~i~ a r~stor 52.~ Connected between resistor 52:~and the le~d 40 o~ the gate or the SCR circu~t is a capacitor 54.
The purpose o~ the re$istancQR 50, 52 and potentiom2ter 44 i~ to provide a portion of ths ~otor ~eed back voltaga to use ln controlling the oper~tion o~ the SC~
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30. Interconnected between the potentiometer 44 and the resistance S0 i~ a lead 56 which connects to a tranqistor 58 at its base term~nal 58a. The transistor 58 i3 ~urth~r provided with a collector terminal 58b which is connected by a lead 60 to a resistance 62 which in turn is connected by lead 64 to the input lead 28. The transistor 58 is further provided with an emitter terminal 58c which is connected to a resistance 66 and a zener diode 68 and lead 70 which is connected to the other input lead 36. Connect-ed in parallel with the zener diode ~8 and the resistance66 is a capacitor 72. The resistance 62 and the resistance 42 are interconnected by lead 74 which also connects to one terminal o~ a capacitor 76, the other terminal of which is connected to the base terminal 58a of the transistor 58.
Thus, the capacitor 76 is connected across tha collector t~rminal 58b and base terminal 58a o~ tha transistor 58.
The motor ~ack EMF signal i9 supplied to the resistance 52 by a lead 78 connected to the motor lead 38.
Interconnecting the lead 78 to the lead 40 of the gate of the SCR 30 is a diode 80. There is also a diode 82 inter-connecting the other motor lead 36 to the lead 78. To explain the operation o~ the mot~r control circuit forming my invention a review will first be made of the functions performed by the variou~ elements of the circuit described above and then reference will be made to the aurves forming : Figs. 2 through 7 of the drawing~ to explain the dynamicoperation o~ the circuit and its function~ in controlling : speed at various load levels.
: : :
: In a preferred embodiment of my circuit, the SCR
30 comprised a model T-106Dl silicon controlled rectifier which requires a positive gate ~o cathode voltage o~ on the .
: order o~ .25 to l.o volts to trigqer the iring Or the SCR
30. In the gate c~rcuit Oe the SCR 30, there is ~n RC
network comprlsing the resistan¢e 42 and the c~pacitor 54. .-~ In my prePerred embodiment, the resi~tor 42 had a value of 22k ohms and the capacitor 54 was a .22 microfarad ~: :
2~3~2~7 capacitance. The power for chargin~ the ~C network on the gate circuit ~or the SCR is supplied through the re~istance 62 which is a 30k ohm resistance. ~he rate at which the capacitor 54 i5 charqed depends to a large extent on the conductlon through the transistor 58. Thus the transistor 58 determines how soon in the cycle the SCR begins to conduct. If the transistor 58 diminishes conducting, the capacitor 54 will charge more rapidly.
The diode 80 allows the back EMF ~rom the motor lo to provide voltage through the load resistor 42 to the collector Or transistor 58 when the unfiltered full-wave voltage on busg 28 is below tho motor back EMF This maintain~ transistor 58 operational ~or bo~h short and lonq delay angles, i.e., near zero crosslng and lmprovao stabil-ity o~ the ramp voltages in Fiqs. 4 and 5.
In general terms the circuit 22 may be descri~adas a speed control circuit which utilizes a back EMF signal indicative o~ motor speed to control on each half cycle the point at which the SCR fires. The ~snsing of t~e b~ck EMF
~s performed on each half cycle prior to the firing Or th~
SC~. Since the back EM~ voltage i8 quite high, on the order of 100 volts, the network including the re~istances 44;, 50 and 52 are used as a voltage divider to pick off a portion o~ the reed bacX signal which is then compared to a 2 re~erence signal appearing acros~ the resistor 66 and the zener 68.~ The resistance 52 is a fixed 130k ohms resis-tance, whereas the resi~tance 50 is an adjustable resis-tance having a maxi~um o 250k ohms. Resistance 50 is adjustable ~o that the low speed setting o~ the speed ; control 22 may be accomplished accurately as a factory setting. The ~resistancq o~ the potentiometer 44 may be v~ri~d ~rom 0 at the high speed setting to a maximum of sak ohms at tho low speQd setting. At the low speed sQtting o~
the potentiometer 44, about a fi~th o~ the voltaqe across the network of resistances 46, 50 and 52 ~would appear across the base o~ the transistor S8. Wit~ a low speed ~ : , ', ~:
- : --- 2~382~7 : ,~
setting on the potentiometer 44, the voltage produced bythe back EMF would produce a hiqher voltage on the transis~
tor base 58a causing the transistor 58 to conduct ~rlier in the cycle and, there~ore, inCreasQ the time ~or the current through the resistor 62 to charge tha RC network including the resistor 42 and the capacitor 54. On the high speed setting one would get a smaller voltage on the base of the transistor 58~ Therefore, the transistor 58 would begin conducting later in the cycle causing the capacitor 54 to charge to the firing voltage oP the SCR 30 earlier in the cycle. With the earlier ~iring o~ the SCR
more power would be delivered to th~ motor 20.
~ n considering the ~unction o~ the transistor 58, lt. should bs noted that one o~ the proble~s ~rsquently 15 encountered in the less complex type ~eed bac~ circuits is the lack Or stability and the sensitivity o~ th~ circuits to varlations in lin~ voltage. Through the u~o Or the zener 68 to provide a rixed voltage re~erence o~ about 5.1 volts and the resistance 66 to vary the re~erence in a predetermined manner, we have ach~eved the ob~ect of increa~ed stability and lack o~ voltags sensitivity. I~
tha resistance 6~ were made largar, the regulation o~ the speed ~or v~rious chanqes in the load would in theory be more precise. However, it has been ~ound that the precise regulation produces an undesirable instability which is eliminated by the use Or a 3k ohm resistance 66 to provide slope to the speed torque curve to achievQ greater stabili-ty. While this r-~ults in some speed changa~ with varia-tions in load, thi~ relatlvely sm~ll chango i5 acceptabl~
; 30 to achieve the desired stability.
Th~ capacitor 72 in parallel with the zener 68 and~ resistor 66 ~ilters t~e commutation no~s~ and any :suddsn changes in the re~erence voltage to again add to the stab~lity o~ the cirCuit in controlling thQ ~peed Or the motor 20. The capacitor ~6 i8 similar in runctlon in that it redu~e~ the gain Or high ~requency tran~ient and keeps ::
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noise ~rom de-stabilzing the control 22 and serves to bypass the transients ~rom the colle~tor to the base circuit. Capacitor 72 IS 1.0 micro~arad and capacitor 76 is .01 micro~arad.
S The capacitor 54 $8 a .22 micro~arad capacitor, and along with thQ 22K ohm re~istor 42, Porms the RC
network which controls the ~iring o~ the SCR 30. The resistor 42 not only controls the rate at which the'capaci-tor 54 is charged but also serves tc limit th~ current from lo t~e motor ~0 through the transistor 58 after the SC~ 30 has fired.
The diode 80 limits the negative voltage on the capacitor 54 to 1 volt when the cathode o the SCR is at a higher voltage than the collector on the transistor 58 The diode 82 is for the purpose o~ commutating the induc-tive energy in the motor 20 such that it is used as motor output power rather than as destructive high voltage energy.
Turn~ng now to the curves shown in Figs. 2 through 7, we are better able to understand the manner in which the control circuit 22 functions. $he curves o~
Figs. 2a and 2b show the voltage-across the output o~ the ~ull-wave rect~ier during condition~ of light load and heavy load. T~is voltage has been shown as Vs on the schematic diagram o~ Fig. 1 and in the diagram~ o~ Figs 2a and 2b~ Under both load c,onditions ths voltage is approxi-mately the same w~th the arc shaped curves ~eing spaced by periods o~ sub~tantially constant voltage which represents the result o~ the bac~ EMF of the motor 20. ~n the curves o~ Fig. 3 we note the change~ in the firing o~ the SCR as the load is increased from the li~ht load to the heavy load. Figs. 3a and 3b represent the voltaqe across the motor as the load is varied. Under the light load condi-tion, the SC~ fires past the peak of the input voltaqe curYe~ wherea~, in the heavy load ~ondition, the SCR 30 fires as the rising voltaqe approaches about 150 volt~.
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2~3~257 - 10 ~
The curves o~ Fig~. 4a and 4b represent t~e gate to cathode voltage on t~e SCR 30, or the voltage across the terminals 3 Oa to 3 Oc . To best understand the manner in which the back EMF affects the charging of the cap~citor 54 and the firing o~ the SCR 30, reference should be made to the curves o~ Figs. 6 and 7. Fig. 6 shows the voltage on the base o~ the transistor 58 which is principally a result o~ the bac~ EMF of the motor 20 attenuated through the re~istance network 44, 50 and 52. Under light load condi-lo tions the back EMF i8 greatest and decreas~s slightly as the load i8 increased ~rom Fig. 6a to 6b. Figs. Sa and 5bshow the voltage to the collector terminal S8b which is essentially the charging voltage ~or the ~C network, including the resistor 42 and the condenser S4. AB thi~
charging voltage, as shown in Figs. 5a and 5b, lncreases with lo~d, the SCR 30 fires earlier and earlier in each hal~ cycle o~ power, the firing point being shown by the curves o~ Figs. 3a and 3b. Fiq~. 4a and 4b show the voltage across the gate 30c and cathode 30a oP the SCR 30 which voltage determines when firing occurs. Th~ firinq point is a~ected by the charge on the capacitor 54 a~ well a~ the back EMF which, as shown by Figs, 3a and 3b is reduced as load increases.
:In considering the change in the voltage at the b~se o~ 58a o~ the transistor 58 in going ~rom ~ light load to a heavy load, we note that the higher voltage in Fig. 6a : as compared to Fig. 6b re~ult3 in conduction in the tran~istor 58 that lower~ the charging voltag~ at the collector terminal 58b thereby delaying the point as shown in F~g~ 4 when the gate to cathode voltago ~or SC~ 30 reache~ a level required ~or ~iring.In Fig. 4b, the charq~
ing complete~ rapidly and the SCR 30 rires early in the hal~ cycle.
: In claiming the speed control circuit 22, re~er-ence is made to the charging circuit which i9 connected to the RC network that controls the ~iring o~ tho S~R in 2~3~2~7 series with the motor across the full wave power supply.
This charging circuit includes the transistor 58, and the voltage divider comprised o~ the resistances 44, So and 52.
The speed control circuit 22 described above 5provides excellent speed control for motors in dome~t~c appliances, particularly mixers, giving good control under varying loads at ~peeds ~rom 500 to 1000 revolution~ per minute ~or mixinq element~ driven through g~ar reduction~ , o~ on the order o~ 20 to l.
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1 0 , ~, , :', ~ ' ' .
BACKGROUND OF ~11E INVENTION
~ he present invention relates to a variable speed control for a permanent maqnet electric motor and more speci~ically relates to a ~eedbac~ type o~ variable speed control for tho motor in an electric rood mixer.
In the field o~ electric household mixers, it has always been r~garded as important to provide variable ~peed controls for such mixers. The many types of mixing chores to which a household mixer is applied reguire beater speeds from several hundred rpms to over laoo, depending on whether one might be mixing cookie dough or beating egg whites. More recently, domestic food mixers have been sold with various alternative mixing implements such as whippers or dough hooks, the Iatter requiring ~ubstant~al power at ;~ low speeds.
The simplest type of speed control still used on s~ome mixers involveq a tapped field and a series wound electric motor. The principal problem with such an ap-proach is the ~act that the lower speed windings for the ~;series motor provide less power when under load conditions.
Substantial power i9 often required at lower speeds.
Accordingly,~the tapped ~ield type o~ spEed control is generally regarded as unsatisfactory for miXers that are to 35 be oper~ted under substantial power at low spo~ds. ;~;
- .' " .
` 2~2~7 Another type of speed control commonly used on electric food mixers is a governor type control uslng a mechanical centrifugal governor or tachometer ~eedback which may be adjusted to control the speed of the mixer over a wide range of speeds. This type o~ governor control is reasonably expensive but has the advantage of beinq able to provide high power at low speeds. There are also available more sophi~ticated electronic controls which utilize pulse generating tachometers associated with the motor to sense speed accurately and adjust power to compen-sate ~or variation~ of the actual ~peed ~rom the required speed. These more sophisticated electronic controls are fairly expensive and are unsuitable ~or lower priced electric mixers.
There have also been available electronic con-trols which utilize the counter electromagnetic voltage produced by the motor to sense whether the motor is operat-ing at the proper speed and make suitable ad~ustment~ to control the speed accurately in the ~ace o~ a varying load.
Wh~le the general theory of operation of such feedback controls is well Xnown, there has been conslderable dif~i-culty in providing operating circuits which are simple enough to bc competitively priced and at the same time serve the desired function. Various problems have been encountered which render such controls generally unsatis-actory. They are ensitive to line voltage changes, have a tendency to provide cyclical swings in ~peed, someti~es called ~cogqlng~, which is objectionable to th~ user since it at least creates the impression that the mixer is unable ~0 to settle down and oparate at the selected speed level. It would,~ thera~ore, be desirable to provide a ~eedback control utillzing the counter EM~ o~ the motor to accurate~
ly contro} the speed under ~arying load conditions utiliz-; ing a simple circuit having little filtering of the control signal.BRIEF DESCRIPTION OF THE INVENTIO~
~ , g~7 The present invention involves a feedback control ~or ~ permanent magnet or equivalent motor op~rating on recti~ied unfiltered ~C current which is controlled by an SC~. The gate of the SCR is regulated by a signal which is inver~ely proportional to the fsedbac~ voltage and which is applied to an RC circuit associated with the gate of the SCR. A comparison is made between a re~erence voltage and a signal proportional to the back EMF by mean~ Or a tran-sistor circuit in which the base o~ the transistor is connected to a voltage divider which i~ set according to the speed desired and thus provide~ the voltag~ which i5 a predetermined portion o~ the back EMF. The emitter o~ the transistor is connected to a zener diode which provides ~
re~erence voltage to control the conduction Or the tran~is-tor depending on magnitude o~ the portion of the ~eedback : voltaqe applied to the base. By ty$ng the emitter o~ the transistor to ground through a zener diode and a resistor, :~ a speed stabiIity is achieved which i9 reasonably lnsensi-tive to variations o~ line voltage. In addition, the resistor in circuit with the tran~istor permit~ the circuit to be designed with the constant slope on ths ~peed torque : curve which improves the speed stability and the control ensitivlty.
: It is an object of the present invention to provide an improved variable speed control rOr use with a : permanent magnet motor.
It~is another object o~ the preaent invention to provide;an improved ~eedback control circuit rOr varying the speed of a permahent magnet motor utilizing the back or counter ~MF produced during the portion of the cycle in ; which the:power to the motor is shut of~.
:It is another object of the present invention to provide a ~speed control circuit for a permanent magnet motor utilizing ~ull-wave rectified AC curren~ and an SCR
: 3~ ~controlled by a circuit responsive to the counter EMF of t~e motor during th~ period in which the SC~ is shut off , , - . .
~ i,, , .
~\ 2~38257 ~ `
and includinq a voltage divider which may he set for a -~desired speed to produce a signal proportional to the counter EMF to be compared with a standard ~or regulating the char~ing o~ an RC circult associated with the gate S circuit o~ the SCR.
It is still another ob~ect of the present inven- -tion to provide a speed control circuit for a permAnent maqnet ~otor utilizing ~ull-wave recti~ied AC current controlled by an SCR in which the counter EMF o~ the motor is compared to a reference voltage in a transistor circuit having means in the emitter circuit of the transistor to regulate the slope o~ the spead torque curve for the motor and its control circuit.
Further objects and advantages o~ the instant invention will become apparent to one skilled in the art as the ~ollowing deRcription proceeds, and the ~eaturas of novelty which characterize the invent~on will be pointed -out in the claims annexed to and ~orming a part o~ the specification.
BRI~F DESC~I~TION OF THE DRAWINGS
Fig. 1 is a schematic diagram of the ~peed control circuit embodying my invention:
Fig~. 2a and 2b are diagrams o~ the voltage acro~R the motor and SCR o~ the control circuit embodying 25 my invention under conditions o~ light and heavy load: `~
Flg~. 3a and 3b are diagrams o~ the voltage acros~ the permanent magnet motor under light and heavy loads, respectively;
~Yigs. 4a and 4b are diagra~s o~ the voltage ; 30 acro~ the gate and cathod~ Or the SCR in the motor control circuit undar the ~ama load condîtions a~ Figs. 2 and 3:
Fig~. 5a and 5b are diagram~ o~ the voltages across the conden~er in the ~ate circuit o~ the SC~ which controls the ~ir~ng o~ the SCR under the same lo~d condi-tions as Figs. 2 - 4:
; .
. . , -, :: .
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''"""'''"':'~'' ~''''' '''''' '''`''''" ' "";. ''.' '"' "'''' .. .. . . . . . . . . . . ..
- ~382~7 ~
: .
Figs. 6a and 6b are diagra~s o~ the voltage across the base of the transistor in the motor control circuit under the same 1O2d conditions as in Figs. 2 - 5;
and Figs. 7a and 7b are diagrams of the voltage across tha emitter o~ the transistor control circu~t to ground under the same load conditions as in FigY. ~ - 6.
Re~erring to Fig. 1 of the drawinq~, there is shown a schematic diagram of the control circuit embodying ~y invention. The speed control circuit of the instant invent~on i8 applicable to a permanent magnet type motor operating on AC current. The motor is shown in Fig. 1 schematically and desi~nated by reference numeral 20.
The motor control circuit is designated generally by re~erenCQ numeral 22 and ~ncludes a ~ull-w~ve recti~ier 24 connected to a line cord 26. The output o~ the ~ull~
wave rectifier 24 is connected at one output terminal by a conductor 28 to an SCR 30 and the other ~ide of the recti-fier output is connected through a conductor 32 through a line switch 34 and by conductor 36 to the motor :20. The other terminal of the motor 20 is connected by~a lead 38 to the ca~hode 30a o~ the SCR 30. The SC~ 30 al~o has an anode 30~ to which the lead 28 connects and a gate 30c to which a lead 40 connects to one terminal oY a resistance 42, capacitor 54, and diode 80.
In~order to regulate the ~peed o~ the motor 20, 'there~ iY provided in the circuit 22 a potentiometer 44 havinq one end connectad to the lead 36 by lead 46 with the other end connected by lead 48 to an adjust~blo resistor 50. Also connected:in se~ies with potentiomQter 44 and reY~is~or 50 ~i~ a r~stor 52.~ Connected between resistor 52:~and the le~d 40 o~ the gate or the SCR circu~t is a capacitor 54.
The purpose o~ the re$istancQR 50, 52 and potentiom2ter 44 i~ to provide a portion of ths ~otor ~eed back voltaga to use ln controlling the oper~tion o~ the SC~
. ".' - 2038257 ;;
30. Interconnected between the potentiometer 44 and the resistance S0 i~ a lead 56 which connects to a tranqistor 58 at its base term~nal 58a. The transistor 58 i3 ~urth~r provided with a collector terminal 58b which is connected by a lead 60 to a resistance 62 which in turn is connected by lead 64 to the input lead 28. The transistor 58 is further provided with an emitter terminal 58c which is connected to a resistance 66 and a zener diode 68 and lead 70 which is connected to the other input lead 36. Connect-ed in parallel with the zener diode ~8 and the resistance66 is a capacitor 72. The resistance 62 and the resistance 42 are interconnected by lead 74 which also connects to one terminal o~ a capacitor 76, the other terminal of which is connected to the base terminal 58a of the transistor 58.
Thus, the capacitor 76 is connected across tha collector t~rminal 58b and base terminal 58a o~ tha transistor 58.
The motor ~ack EMF signal i9 supplied to the resistance 52 by a lead 78 connected to the motor lead 38.
Interconnecting the lead 78 to the lead 40 of the gate of the SCR 30 is a diode 80. There is also a diode 82 inter-connecting the other motor lead 36 to the lead 78. To explain the operation o~ the mot~r control circuit forming my invention a review will first be made of the functions performed by the variou~ elements of the circuit described above and then reference will be made to the aurves forming : Figs. 2 through 7 of the drawing~ to explain the dynamicoperation o~ the circuit and its function~ in controlling : speed at various load levels.
: : :
: In a preferred embodiment of my circuit, the SCR
30 comprised a model T-106Dl silicon controlled rectifier which requires a positive gate ~o cathode voltage o~ on the .
: order o~ .25 to l.o volts to trigqer the iring Or the SCR
30. In the gate c~rcuit Oe the SCR 30, there is ~n RC
network comprlsing the resistan¢e 42 and the c~pacitor 54. .-~ In my prePerred embodiment, the resi~tor 42 had a value of 22k ohms and the capacitor 54 was a .22 microfarad ~: :
2~3~2~7 capacitance. The power for chargin~ the ~C network on the gate circuit ~or the SCR is supplied through the re~istance 62 which is a 30k ohm resistance. ~he rate at which the capacitor 54 i5 charqed depends to a large extent on the conductlon through the transistor 58. Thus the transistor 58 determines how soon in the cycle the SCR begins to conduct. If the transistor 58 diminishes conducting, the capacitor 54 will charge more rapidly.
The diode 80 allows the back EMF ~rom the motor lo to provide voltage through the load resistor 42 to the collector Or transistor 58 when the unfiltered full-wave voltage on busg 28 is below tho motor back EMF This maintain~ transistor 58 operational ~or bo~h short and lonq delay angles, i.e., near zero crosslng and lmprovao stabil-ity o~ the ramp voltages in Fiqs. 4 and 5.
In general terms the circuit 22 may be descri~adas a speed control circuit which utilizes a back EMF signal indicative o~ motor speed to control on each half cycle the point at which the SCR fires. The ~snsing of t~e b~ck EMF
~s performed on each half cycle prior to the firing Or th~
SC~. Since the back EM~ voltage i8 quite high, on the order of 100 volts, the network including the re~istances 44;, 50 and 52 are used as a voltage divider to pick off a portion o~ the reed bacX signal which is then compared to a 2 re~erence signal appearing acros~ the resistor 66 and the zener 68.~ The resistance 52 is a fixed 130k ohms resis-tance, whereas the resi~tance 50 is an adjustable resis-tance having a maxi~um o 250k ohms. Resistance 50 is adjustable ~o that the low speed setting o~ the speed ; control 22 may be accomplished accurately as a factory setting. The ~resistancq o~ the potentiometer 44 may be v~ri~d ~rom 0 at the high speed setting to a maximum of sak ohms at tho low speQd setting. At the low speed sQtting o~
the potentiometer 44, about a fi~th o~ the voltaqe across the network of resistances 46, 50 and 52 ~would appear across the base o~ the transistor S8. Wit~ a low speed ~ : , ', ~:
- : --- 2~382~7 : ,~
setting on the potentiometer 44, the voltage produced bythe back EMF would produce a hiqher voltage on the transis~
tor base 58a causing the transistor 58 to conduct ~rlier in the cycle and, there~ore, inCreasQ the time ~or the current through the resistor 62 to charge tha RC network including the resistor 42 and the capacitor 54. On the high speed setting one would get a smaller voltage on the base of the transistor 58~ Therefore, the transistor 58 would begin conducting later in the cycle causing the capacitor 54 to charge to the firing voltage oP the SCR 30 earlier in the cycle. With the earlier ~iring o~ the SCR
more power would be delivered to th~ motor 20.
~ n considering the ~unction o~ the transistor 58, lt. should bs noted that one o~ the proble~s ~rsquently 15 encountered in the less complex type ~eed bac~ circuits is the lack Or stability and the sensitivity o~ th~ circuits to varlations in lin~ voltage. Through the u~o Or the zener 68 to provide a rixed voltage re~erence o~ about 5.1 volts and the resistance 66 to vary the re~erence in a predetermined manner, we have ach~eved the ob~ect of increa~ed stability and lack o~ voltags sensitivity. I~
tha resistance 6~ were made largar, the regulation o~ the speed ~or v~rious chanqes in the load would in theory be more precise. However, it has been ~ound that the precise regulation produces an undesirable instability which is eliminated by the use Or a 3k ohm resistance 66 to provide slope to the speed torque curve to achievQ greater stabili-ty. While this r-~ults in some speed changa~ with varia-tions in load, thi~ relatlvely sm~ll chango i5 acceptabl~
; 30 to achieve the desired stability.
Th~ capacitor 72 in parallel with the zener 68 and~ resistor 66 ~ilters t~e commutation no~s~ and any :suddsn changes in the re~erence voltage to again add to the stab~lity o~ the cirCuit in controlling thQ ~peed Or the motor 20. The capacitor ~6 i8 similar in runctlon in that it redu~e~ the gain Or high ~requency tran~ient and keeps ::
. ~
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.., - , .
^ 203~2~7 g ,. .. .
noise ~rom de-stabilzing the control 22 and serves to bypass the transients ~rom the colle~tor to the base circuit. Capacitor 72 IS 1.0 micro~arad and capacitor 76 is .01 micro~arad.
S The capacitor 54 $8 a .22 micro~arad capacitor, and along with thQ 22K ohm re~istor 42, Porms the RC
network which controls the ~iring o~ the SCR 30. The resistor 42 not only controls the rate at which the'capaci-tor 54 is charged but also serves tc limit th~ current from lo t~e motor ~0 through the transistor 58 after the SC~ 30 has fired.
The diode 80 limits the negative voltage on the capacitor 54 to 1 volt when the cathode o the SCR is at a higher voltage than the collector on the transistor 58 The diode 82 is for the purpose o~ commutating the induc-tive energy in the motor 20 such that it is used as motor output power rather than as destructive high voltage energy.
Turn~ng now to the curves shown in Figs. 2 through 7, we are better able to understand the manner in which the control circuit 22 functions. $he curves o~
Figs. 2a and 2b show the voltage-across the output o~ the ~ull-wave rect~ier during condition~ of light load and heavy load. T~is voltage has been shown as Vs on the schematic diagram o~ Fig. 1 and in the diagram~ o~ Figs 2a and 2b~ Under both load c,onditions ths voltage is approxi-mately the same w~th the arc shaped curves ~eing spaced by periods o~ sub~tantially constant voltage which represents the result o~ the bac~ EMF of the motor 20. ~n the curves o~ Fig. 3 we note the change~ in the firing o~ the SCR as the load is increased from the li~ht load to the heavy load. Figs. 3a and 3b represent the voltaqe across the motor as the load is varied. Under the light load condi-tion, the SC~ fires past the peak of the input voltaqe curYe~ wherea~, in the heavy load ~ondition, the SCR 30 fires as the rising voltaqe approaches about 150 volt~.
: .
2~3~257 - 10 ~
The curves o~ Fig~. 4a and 4b represent t~e gate to cathode voltage on t~e SCR 30, or the voltage across the terminals 3 Oa to 3 Oc . To best understand the manner in which the back EMF affects the charging of the cap~citor 54 and the firing o~ the SCR 30, reference should be made to the curves o~ Figs. 6 and 7. Fig. 6 shows the voltage on the base o~ the transistor 58 which is principally a result o~ the bac~ EMF of the motor 20 attenuated through the re~istance network 44, 50 and 52. Under light load condi-lo tions the back EMF i8 greatest and decreas~s slightly as the load i8 increased ~rom Fig. 6a to 6b. Figs. Sa and 5bshow the voltage to the collector terminal S8b which is essentially the charging voltage ~or the ~C network, including the resistor 42 and the condenser S4. AB thi~
charging voltage, as shown in Figs. 5a and 5b, lncreases with lo~d, the SCR 30 fires earlier and earlier in each hal~ cycle o~ power, the firing point being shown by the curves o~ Figs. 3a and 3b. Fiq~. 4a and 4b show the voltage across the gate 30c and cathode 30a oP the SCR 30 which voltage determines when firing occurs. Th~ firinq point is a~ected by the charge on the capacitor 54 a~ well a~ the back EMF which, as shown by Figs, 3a and 3b is reduced as load increases.
:In considering the change in the voltage at the b~se o~ 58a o~ the transistor 58 in going ~rom ~ light load to a heavy load, we note that the higher voltage in Fig. 6a : as compared to Fig. 6b re~ult3 in conduction in the tran~istor 58 that lower~ the charging voltag~ at the collector terminal 58b thereby delaying the point as shown in F~g~ 4 when the gate to cathode voltago ~or SC~ 30 reache~ a level required ~or ~iring.In Fig. 4b, the charq~
ing complete~ rapidly and the SCR 30 rires early in the hal~ cycle.
: In claiming the speed control circuit 22, re~er-ence is made to the charging circuit which i9 connected to the RC network that controls the ~iring o~ tho S~R in 2~3~2~7 series with the motor across the full wave power supply.
This charging circuit includes the transistor 58, and the voltage divider comprised o~ the resistances 44, So and 52.
The speed control circuit 22 described above 5provides excellent speed control for motors in dome~t~c appliances, particularly mixers, giving good control under varying loads at ~peeds ~rom 500 to 1000 revolution~ per minute ~or mixinq element~ driven through g~ar reduction~ , o~ on the order o~ 20 to l.
' ' ',`.' , ~, ..
. :' .:' . .
: ; '.
~ . 20 ~, : . .
; -:
Claims (7)
1. A speed control circuit for a motor operated appliance of the type utilizing a permanent magnet motor comprising an SCR connected in series with said motor, rectifier means for supplying unfiltered full wave recti-fied power to said motor and SCR, a voltage divider con-nected across said motor, said SCR having a gate, said voltage divider including a selectively variable resistance and an output terminal to provide a voltage which is a selected portion of the back EMF produced by said motor, an RC network including a resistor and a capacitor connected to said gate to supply a signal for firing said SCR, a charging circuit connected across said motor and SCR and to said RC network, said charging circuit including amplifier means controlled by said voltage divider and a reference voltage to vary the rate of charging said RC network in an inverse relation to said back EMF produced by said motor.
2. The speed control circuit of claim 1 wherein said amplifier comprises a transistor connected to the output terminal of said voltage divider and said reference voltage being provided by a zener diods.
3. The speed control circuit of claim 2 wherein said transistor has a base and emitter connected between said output terminal and said zener diode.
4. The speed control circuit of claim 2 wherein said variable resistance is manually adjustable to a plurality of motor speed settings, and a resistance in series with said transistor and said zener diode to reduce the sensitivity of said control circuit by causing said circuit to vary motor speed inversely with load at each said speed setting.
5. The speed control circuit of claim 3 wherein said transistor includes a collector connected to said RC
network.
network.
6. The speed control circuit of claim 5 includ-ing a diode connect between the cathode and gate terminals of said SCR to conduct said back EMF to said collector to maintain conduction of said transistor when the power supply voltage applied to said transistor falls below said back EMF
7. The speed control circuit of claim 2 wherein said amplifier is connected across the output of said rectifier means, said transistor including a collector connected to the anode of said SCR and having an emitter connected through a resistor and a zener diode to said output of said rectifier means, said transistor having a base connected to said voltage divider output terminal.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US61341390A | 1990-11-15 | 1990-11-15 | |
| US07/613,413 | 1990-11-15 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2038257A1 true CA2038257A1 (en) | 1992-05-16 |
Family
ID=24457218
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2038257 Abandoned CA2038257A1 (en) | 1990-11-15 | 1991-03-14 | Full-wave feedback speed control for hand mixer |
Country Status (3)
| Country | Link |
|---|---|
| CA (1) | CA2038257A1 (en) |
| DE (1) | DE4114168A1 (en) |
| GB (1) | GB2249849A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US20210387865A1 (en) * | 2020-06-16 | 2021-12-16 | Yehonatan MORE | Water dispenser with means for refreshing and improving water quality |
Families Citing this family (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN109347401B (en) * | 2018-11-08 | 2023-11-28 | 深圳和而泰智能控制股份有限公司 | Motor rotation speed control device, motor and food processing equipment |
| CN114405384B (en) * | 2021-02-02 | 2024-03-26 | 上海品致测控技术有限公司 | Magnetic stirring controller |
| ES2948457A1 (en) * | 2022-02-16 | 2023-09-12 | Cecotec Res And Development S L | ADAPTIVE Kneading SYSTEM AND ASSOCIATED METHOD (Machine-translation by Google Translate, not legally binding) |
Family Cites Families (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR1591033A (en) * | 1968-11-12 | 1970-04-20 | ||
| AT315968B (en) * | 1972-03-07 | 1974-06-25 | Elin Union Ag | Speed control circuit for a universal or direct current motor, which is fed with pulsating voltage via a thyristor |
| JPS57153583A (en) * | 1981-03-18 | 1982-09-22 | Matsushita Electric Ind Co Ltd | Speed controller for dc motor |
| DE3444513C2 (en) * | 1984-12-06 | 1987-03-05 | Klöckner-Werke AG, 4100 Duisburg | Injection stone with a closure stone covering the injection channel of the injection stone for metallurgical vessels, in particular steel ladles, for injecting gases or solid/gas mixtures into metallic melts in the metallurgical vessels |
| DE3501727A1 (en) * | 1985-01-19 | 1986-07-24 | Telefunken electronic GmbH, 7100 Heilbronn | CIRCUIT ARRANGEMENT FOR SPEED CONTROL OF A SERIAL MOTOR |
-
1991
- 1991-03-14 CA CA 2038257 patent/CA2038257A1/en not_active Abandoned
- 1991-03-18 GB GB9105704A patent/GB2249849A/en not_active Withdrawn
- 1991-04-30 DE DE19914114168 patent/DE4114168A1/en not_active Ceased
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US20210387865A1 (en) * | 2020-06-16 | 2021-12-16 | Yehonatan MORE | Water dispenser with means for refreshing and improving water quality |
Also Published As
| Publication number | Publication date |
|---|---|
| GB9105704D0 (en) | 1991-05-01 |
| DE4114168A1 (en) | 1992-05-21 |
| GB2249849A (en) | 1992-05-20 |
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