CA1112297A - Motor control system - Google Patents
Motor control systemInfo
- Publication number
- CA1112297A CA1112297A CA309,694A CA309694A CA1112297A CA 1112297 A CA1112297 A CA 1112297A CA 309694 A CA309694 A CA 309694A CA 1112297 A CA1112297 A CA 1112297A
- Authority
- CA
- Canada
- Prior art keywords
- motor
- wiper
- terminal
- potentiometer
- drive
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- 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
- H02P7/288—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 variable impedance
- H02P7/2885—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 variable impedance whereby the speed is regulated by measuring the motor speed and comparing it with a given physical value
-
- 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
- H02P7/03—Arrangements for regulating or controlling the speed or torque of electric DC motors for controlling the direction of rotation of DC motors
- H02P7/04—Arrangements for regulating or controlling the speed or torque of electric DC motors for controlling the direction of rotation of DC motors by means of a H-bridge circuit
-
- 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
Abstract
MOTOR CONTROL SYSTEM
ABSTRACT OF THE DISCLOSURE
A motor control system for controlling the speed and direction at which a motor operates. A drive circuit is provided for supplying a drive current to the motor, the magnitude of the drive current being determinative of the speed at which the motor operates. A direction-determining circuit determines the direction at which the motor operates and, for example, may comprise a steer-ing circuit for steering the drive current to the motor in first and second current paths. A potentiometer having a resistance connected between first and second terminals and an adjustable wiper which is settable along the resistance is used to determine the desired speed and direction of operation of the motor. The setting of the wiper includes a predetermined zero speed setting which, preferably, is at some intermediate point along the resistance.
A power supply having a power terminal and a reference terminal pro-duces an operating potential across these terminals. The power terminal is coupled to the potentiometer wiper and the reference terminal is coupled to one of the potentiometer terminals. A
resistor couples the other potentiometer terminal to the power supply reference terminal. The potentiometer wiper is coupled to the drive circuit and the potentiometer terminal which is coupled to the resistor also is coupled to the direction-determining circuit.
The setting of the wiper determines the magnitude of the voltage supplied to the drive circuit so as to determine the motor speed, and the setting of the wiper also determines the magnitude of the voltage supplied to the direction-determining circuit by the poten-tiometer terminal so as to determine the direction at which the motor operates. Advantageously, only a single source of operating -i-potential need be used with the potentiometer to determine motor direction.
-ii-
ABSTRACT OF THE DISCLOSURE
A motor control system for controlling the speed and direction at which a motor operates. A drive circuit is provided for supplying a drive current to the motor, the magnitude of the drive current being determinative of the speed at which the motor operates. A direction-determining circuit determines the direction at which the motor operates and, for example, may comprise a steer-ing circuit for steering the drive current to the motor in first and second current paths. A potentiometer having a resistance connected between first and second terminals and an adjustable wiper which is settable along the resistance is used to determine the desired speed and direction of operation of the motor. The setting of the wiper includes a predetermined zero speed setting which, preferably, is at some intermediate point along the resistance.
A power supply having a power terminal and a reference terminal pro-duces an operating potential across these terminals. The power terminal is coupled to the potentiometer wiper and the reference terminal is coupled to one of the potentiometer terminals. A
resistor couples the other potentiometer terminal to the power supply reference terminal. The potentiometer wiper is coupled to the drive circuit and the potentiometer terminal which is coupled to the resistor also is coupled to the direction-determining circuit.
The setting of the wiper determines the magnitude of the voltage supplied to the drive circuit so as to determine the motor speed, and the setting of the wiper also determines the magnitude of the voltage supplied to the direction-determining circuit by the poten-tiometer terminal so as to determine the direction at which the motor operates. Advantageously, only a single source of operating -i-potential need be used with the potentiometer to determine motor direction.
-ii-
Description
BACKGROUND OF TE~E INVENTION
This invention relates to a motor control system and, more particularly, to such a system wherein a potentiome~er is used to control the speed an~ direction at which a motor oper~tes, and wherein an operating potential of only a single polarity need be used with the potentiometer in determining the direction a~
which the motor operates.
Bidirectional motors admi~ of various and divers appli-cations. In a typical application thereo~, ~he motor should be capable of operating at a desirable speed and either in a forwaxd or reverse direction. Fur~hermore, if th~ motor is control~ed by a manually adjustable device, such as a potentiometer, there are certain circumstances wherein the motor should exhibit zero speed when the adj~stable element, or potentiometer, is at or very close to a zero speed setting. For example, when the motor is used to drive an article to a particular location, it is advan-tageous to be able .o operate the motor at a relatively high speed until the article approaches the predetermined location, and then to drive the motor at a progressively decreasing speed so as to be able to stop the motor abruptly when the article reaches its predetermined location. In the event of an over-shoot, it also is advantageous to drive the motor in a reverse direction so as to return the article to its predetermined location.
One type of motor control system which uses a potentiometer to determine the speed and direction of the motor is described in U.S. Pat. No. 3,950,683, issued to W. P. Lamson. In this system, the potentiometer is provided with ~oth positive and negative operating potentials. The wiper of the potentiometer i~ adjustable so as to ~e set either at a zero speed setting, which may corre-spond to the mid-point v~ the potenkiometer resistance, or ak any . .
z~
location between the zero speed setting and either terminal of the potentiometer. Thus, when the wiper is set at a location between the zero speed setting and the potentiometer terminal to which the positive operating potential is supplied, the magnitude of the voltage at the wiper determines the speed at which the motor operates, and the positive polarity of this voltage is used to drive the motor in, for example, the forward direction. Similarly, if the wiper is set at a location between the zero speed setting and the potentiometer terminal at which the operating potential ~f negative polarity is supplied, then the magnitude of the voltage at the wiper determines the motor speed, and the negative polarity of this voltage is used to drive the motor in, for example, the reverse direction. The motor control system described in this patent also includes a dead-band circuit which prevents undesired slow motor speed, such as motor creeping, when the wiper is set to, or very close to, its zero speed setting.
A significant disadvantage of the motor control system described in the aforementioned patent is the requirement that, in order to control the motor direction, operating potentials of positive and negative polarities must be applied to the potentiometer terminals. By requiring such positive and negative polarity operat-ing potentials, the power supply circuit which is needed to derive these operating potentials is relatively complex.
OBJECTS OF THE INVENTION
-Therefore, it is an object of the present invention to provide an improved motor control system which avoids the afore-noted disadvantages of the prior art.
Another o~ject of this invention is to provide a motor control system for controlling the speed and direction at which a motor operates in accordance with the setting of a potentiometer.
_ A further object of this invention is to provide a motor control system which uses a potentiometer for controlling the speed and direction of a motor, and wherein the potentiome~er is supplied with an operating potential of only a single polarity.
An additional object o~ this invention is to provide a motor control system which uses a potentiometer for controlling the speed and direction of the motor, which potentiometer is supplied with an operating potential of only one polarity, and wherein the setting of the wiper of the potentiometer determines both the speed and direction at which the motor operates.
Various other o~jects, advantages and features o~ the present invention will become readily apparent from the following detailed description, and the novel features will be particularly pointed out in the appended claims.
. . SUMM~RY OF THE INVENT ION
-In accordance with this invention, a motor control system is provided for controlling the speed and direction at which a motor operates. A drive circuit supplies a drive current to the motor, the magnitude of this drive current being determinative o~
the motor speed. A direction-determining circui~ is provided to determine the direction at which the motor operates. In a preferred embodiment, this direction-determ~ning circuit is a steering circuit or steering the drive current to the motor either in a first or in a se~ond current path. A potentiometer comprised of a resistance connected between first and second terminals has a wiper which is adjustably se~table along the res;stance to determine the desired speed and direction o operation of the motor. A power source has a power terminal and a reerence terminal for providing an operating potential across such terminals. The power terminal is coupled to the potentiometer wiper and the xe~erence terminal is coupled to Z~'7 one of the potentiometer terminals. A resistor couples the other potentiometer te~ninal to the reference terminal. The potentiometer wiper is coupled to the drive circuit and the potentiometer terminal, which is coupled to the reference terminal by the resistor, is coupled to the direction-determining circuit;
whereby the setting of the wiper determines the magnitude of the voltage ~upplied thereby to the drive circuit so as to determi~e the motor speed, and the setting of the wiper also determines the Jnagnitude of the voltage supplied to the direction-determining circult from the potentiometer terminal to determine the direction at which the motor operates.
BRIE~ DESCRIPTICN OF THE DRAWINGS
_ _ The following detailed description, given by way of example, will best be understood in conjunction with the accom-~5 panying drawings in which:
FIG. 1 is a schematic diagram of a prior art technique for controlling the speed and direction at which a motor operates;
FIG. ~ is a schematic diaaram of a preferred embodiment of the present invention;
.,.. ~ ., ~\ -FIG. 3, appearing with Fig. 1, is a graphical represen- ¦
tation showing the manner in which the circuit of FIG. 2 is used to control the operation of a motor; and FIG~. 4A-4E and 5A-5E are waveform diagrams which are useful in understanding the operation of the circuit sho~m-in FIG. 2 !5 DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT
Before describing an embodiment of the present invention reference i5 maae to FIG. 1 which is a schematic representation of a prior art technique or using a potentiometer to control the speed and direction o a motor. A negative opera-ting potential, repre-~0 sented as the DC power supply El, is coupled to one te:cminal of ~ !~
. . _ _ _ . . . _ .
the potentiometer, and a posi~ive operating potential, represented as the DC power supply E2, is coupled ~o the other terminal o~ the potentiometer. The positive and negative operating potentials are referenced to ground, as represen~ed by the ground potential applied to the junction of the positive and negative DC power supplies. The wiper of the potentiometer is coupled to a motor drive circuit which, in turn, drives a motor, the combination of the motor drive circuit and motor being represented at M.
Assuming that the operating potentials are equal (El=E2), then if the wiper of the potentiome~er is set at ~he mid-point o the potentiometer resistance, then a zero voltage is supplied to the motor dxive circuit, thereby esta~lishing a zero motor speed.
I~ the wiper of the potentiometer is adjusted in the upward dixec-tion, that is, toward the negative DC power supply El, then a 15 ne~ative voltage is supplied to the motor drive circuit so as to determine a corresponding direction at which the motor operates.
Furthermore, depending upon the particular setting of the wiper of the potentiometer, the magnitude of the negative voltage which is supplied to the motor drive circuit determines a corresponding motor speed. Converse~y, if the wiper of the potentiometer is adjusted in the downward direction, that is, toward the positive DC power supply E2~ then a positive voltage is supplied to the motor drive circuit, thereby determining an opposite direction for the motor. Also, the particular setting of the wiper estab-lishes a corresponding magnitude of this positive voltage so asto correspondingly determine the motor speed.
It is appreciated that, in khe prior art technique shown in FIG. 1, two separate power supplies El and E2, o~ opposite polarities, must be provided in order to determine the direction in which the motor is driven. The use of two power supplies E
~ . ............. ~ ..
., .
and E2 results in a relatively complex construc~ion of the power supply circuitry. It is a principal obj ect of the pxesent inven-tion to provide a motor control system wherein the setting o~ a potentiometer determines the speed and direction at which a motor operates, yet relies upon only a single po~er supply, that i~, a power supply which provides an operating voltage of only one polarity. Stated otherwise, the motor control system o the present invention achieves su~stan~ially the same result as the system shown in FIG. 1, while eliminating either power supply El or powex supply E2.
Turning now to FIG. 2, a prefexred embodimen~ o~ the motor control system in accordance with the present invention is schematically illustrated. This motor control system is adapted to control the speed and direction of a motor 10 which~ ~or example, - is a DC motor. The illustrated DC motor control system includes a speed control circuit 12, a direction control circuit 18, a potentiometer circuit 14 which is used in conjunction with speed control circuit 12 and dirPction control circuit 18 for determining the speed and direction of operation of motor lO, and a dead-band ~0 control circuit 16. Speed control circuit 12 is comprised of a frequency generator FG which is adapted to produce periodic signals, such as pulses, having a frequency determined by the speed at which motor lO operates. For exampie, motor 10 may be mechanically coupled to a tachometer device, such as a wheel having one or more magnetic elements mounted thereon. A magn~tic pickup is positioned adjacent the wheel so as to produce a pulse whenever a magnetic el~ment rotates therepast. Thus, depending upon the angular velocity of the wheel, and thus the speed of motor lO, a corresponding pulse train is produced ~ frequency generator FG.
Speed control clrcuit 12 additionally includes a sawtooth waveform generatox 20, monos~able multivibrators 25 and 27, a sample-and-hold circui~ comprised o~ a transistor Q4 and a capacitor C2~ and a reset circuit including a transis~or Ql Monostable multivibxator 25 is coupled to frequency generator FG by an amplifier 21 so as to produce pulses of a predetermined duration in response to, for example, the posi~ive ~ransition in the pulses which are generated by the freguency generator. The output of monostable mul~ivibrator 25 is coupled to sampling transis~or Q4 and, additionally, to mono-stable multivibrator 21. The lattex monostable multivibrator isadapted to generate pulses of predetermined duration in response to, for example, the negatîve transition in each pulse produced by monostable multivibrator 24. The outpu~ of monostable multi-vibrator 27 is coupled to reset transistor Ql whose collector-lS emitter circuit is connected in shunt relation across a capacitorCl, the latter being included in sawtooth waveform gener~tor 20.
The sawtooth waveform generator is comprised of the collector-emitter circuit of a transistor Q2 connect~d in series with capacitor C~. Depending upon the conductivity of transistor Q2' a current flows from a source o~ operating potential +~cc through the collector-emitter circuit thereof to charge capacitor C~ Thus, this capacitor charges at a relatively fast rate when transistor Q2 is more conductive; and, conv~rsely, the capacitor is charged at a relatively slow rate when transistor Q2 is less conductive. The voltage across capacitor Cl is coupled through an emitter-follower buffer transistor Q3 to samplir1g transistor Q~. Storage capacitor C2 is coupled to the emitter electrode of ~amplin~ -transistor Q~, and this capacitor is further coupled to the gate electrode of a ~ield effect transistor (FE~) Q5. It may be appreciated that, because of th~ high input impedance of FET Q5r capacitor C2 is subject to negligible leakage.
The base el~ectrode o~ transistor Q~ is coupled to the wiper of a potentiometer VR included in potentiometer circuit 14, and is adapted to receive a control voltage therefrom such that its conductivity is aetermined accordingly. Potentiometer VR~ is of conventional construction and mav be formed of typical thin film or integrated circuit techniques, or may be of other conventional construction. The resistance o~ this poten~iometer is provided with a pair of terminals a and b at opposite ends thereof, with terminal b co~nected to ground by a ~ixed resistor R2, and with terminal a connected to ground by a fixed resistor R3. Tha resistance of potentiometer VRl may be khought of as being cons~ituted by a resistance arm extending between the wiper and terminal b, and having a variable resistance r3, and another resistance arm extending be-tween the wiper and terminal a and having a resistance r4. It is appreciated that the sum of resistances X3 and r4 is constant, but the i~dividual resistance values thereof are dependent upon the positioning or setting of the wiper of the potentiometer. Operating potential Vcc is supplied to the wiper via a resistor Rl.
In addition to being coupled to the base electrode of transistor Q2' the wiper of potentiometer VRl also is coupled to the inverting input of an operational amplifier 17 included in dead-band control circuit 16. The non-invertin~ input o~ amplifier 17 is coupled to a resistor bias circuit so as to be supplied with a predetermined bias potential. ~or a purpose soon to be understood, this bias potential is equal to the voltage derived at the wiper of potentiometer VRl when this wiper is within a predetermined range of its zero speed setting. Ampli~ier 17 functions a a threshold detector wherein the bias voltage supplied to its non~inverting input consitutes the threshold voltage and the vol-tage derived at the wiper of potentiometer VRl, and supplied to the inverting input '"'7 of the amplifier, is compared to this threshold vol~age. The output of ampliier 17, which is a unction of the dif~erence between the voltage derived at the potentiometer wiper and the threshold voltage, is supplied to a transistor Q8~ which functions as an inverting amplifier, and the collector electrode o this transistor is connected to a shunt transistor Q6.
The output electrode of FET Q5, which may be the source electrode thereof, is coupled to the non-inverting input of an ampli~ier`13 which, for example, may comprise an operational amplifier having a feedback circuit connected to its inverting input and a bias circuit also connected to its inverting input.
The collec~or-emi~ter circui~ of shunting transistor Q6 is connected in series betw~een the non-inverting input of amplifier 13 and ground.
The output of amPliier 13 is amplified bv a current amplifying transistor Q7 whose collectox-emitter circuit is, connected between the source of operating potential Vcc and motor 10.
Direction control circuit 18 is comprised. of an amplifier 19, such as an operational amplifier, having its inverting input coupled to terminal a of potentiometer VRl, and its non-inverting input coupled to a bias circuit for receiving a predetermined bias voltage derived from operating potential Vcc. Amplifier 19 functions as a threshold detector; and the bias voltage supplied thereto con-stitutes a threshold voltage. This threshold voltaye is equal to the volta,ge derived at terminal a of potentiometer VRl when the wiper is set to the zero speed setting of the potentiometer. The voltage provided at terminal a for all settings of potentiometer VRl is compared to this threshold voltage. '' The output of amplifier 19 is coupled -to the base electrode of a transistor Qlo whose collector electrode i5 connected -to the base electrode of a similar transi~tor Qll These transistors are : .
_9_ adapted to be mutually exclusively conductive. That is, when transistor Qlo conducts, transistor Qll is non-conductive.
Conversely, when transistor Qll conducts, transistor Ql~ is non-conductive. The cvllector electrodes of transistors Qlo and Qll are connected to a current steering circuit formed of transistors Q12-Q15 The current steering circuit ~unctions to selectively establish two current paths from current amplifier transistor ~7 through motor 10. The direction in which ~he motor operates is directly dependent upon th~ current path therethrough. As will be explained below, transis~ors Q12-Q15 may be switching transistors wherein transistors Q12 and Q13 are PNP and NPN transistors, respec-tively, with their collector ele~trodes connected in common to one terminal of motor 10. Transistors Q14 and Q15 are PNP and NPN
transistors, respectively, with their collector electrodes conne~ted in common to the other terminal of the motor. Tra~sistors Q12 and Q15 are adapted to be conductive concurrently so as to establish the first current path through motor 10; and transistors Q13 and Q14 are adapted to be conductive concurrently to establish the other current path through the motor.
Operation of the Speed ~ontrol Circuit As mentioned above, frequency generatGr FG is adapted to generated pulse signals, such as the xectangular waveform shown in -FIG. 4A, having a frequency determined by the speed of motor 10.
Hence, as the motor speed increases, the frequency of the pulses generated by frequency generator FG increases and, conversely, as the speed of motor 10 decreases, the frequency of these pulses likewise decreases. The pulses produced by the ~requency generator are amplified by amplifier 21 and used to trigger monostable multi-vibrator 25. The pulses generated by this monostable multivibrator in response to the positive transition of the pulses generated by the ., .
'7 frequency generator are illustrated in FIG. 4B. These pulses proauced by the monostable multivibrator turn ON sampling tran-sistor Q4 and, additionally, trigger monostable multivibrator 27 to produce the pulses shown in FIG. 4C. As is apparent, mono stable multivibrator ~7 is triggered in response to the negative transitions of the pulses produced by monostable multivibrator 25~
Let it be assumed ~hat the wiper of potentiometer VRl is set at some desired speed set~ing. It may be appreciated that if the setting o the potentiometer is such that r3+R2=r4~R3, then a maximum voltage is derived at the wiper of the potentiometer.
This voltage decreases as the setting of the po entiometer changes.
If, for example, R2-R3~ then the maximum voltage is dexived at the wiper of the potentiometer when r3=r4, that is, a~ the mid-point setting of the potentiometer. When the wiper is adjusted from lS this mid-point setting, the voltage derived thereat is reduced.
As will be explained, this setting which results in the maximum wiper voltage, for example, the mid-point setting o~ potentiometer VRl, is equal to the zero speed setting. It is assumed, for the present discussion, that the potentiometer is set to some desired setting other than this zero speed setting. Accordingly, the voltage supplied to transistor Q2 by the wiper of potentiometer VRl is sufficient to establish a desired conductivity of the transistor. The collector-emitter impedance of txansistor Q2' taken in conjunction with the capacitance of capacitor Cl, estab-lishes a charging time constant, whereby capacitor Cl is chargedat a corresponding rate.
Transistor Ql is rendered conductive periodicially in response to the pulses produced by monostable multivibrator 27 (FIG. 4C). Consequently, capacltor Cl i5 periodically discharged through the low impedance collector-emitter circuit o~ transistor Ql ... . , . . __ ,_ _. , , _ .. . ... _ . . . . . , . . . ..... . . ... _ . . .. .. .. _ . _ Accordingly, the voltage across capacitor Cl exhibits the sawtooth wavefo~n shown in FIG. 4D. It is appreciated that the slope of this sawtooth wavefo~n is equal to the charging rate o~ the capacitor and, therefore, is determined by the conductivity of transistor Q2 Since the conductivity of this transistor is a function o~ the volt-age derived at the wiper o~ potentiometer VRl~ it is seen that the slope of the sawtooth waveform (FIG. 4D) is determined by the setting of the potentiometer. Emit~er-follower transistor Q3 supplias the sawtooth waveform shown in FIG. 4D to sampling transistor Q4.
The pulses produced by monostable multi~ibrator 25 (FIG. 4B) occur just prior to the rese~ting of the sawtooth wave~orm ~FIG. 4D).
Thus, transistor Q4, which is turned ON by the pulses supplied thereto from monostable multivibrator 25 samples the a~plitude of the sawtooth waveforrn, as shown by the horizontal broken lines in FIG. 4D. This lS sampled amplLtude is stored across capacitor C2 and is supplied through FET Q5 to amplifier 13 as the DC level illustrated in FIG. 4E.
A corresponding current, determined by the DC level sho~n in FIG. 4~, is supplied from transistor Q7 to motor 10. Depending upon the desired direction of operation of the motor, this current is supplied either from transistor Q7 via transistor Q12' motor 10 and transistor Q15 or, alternatively, from transistor Q7 via tran-sistor Q14 through motor 10 to transistor Ql3 Further discussïon of the direction-determining current path is set out hereinbelow.
Ass~ning that the setting of potentiometer VRl does not change, the speed of motor 10 is controlled so as to be equal to that speed corresponding to the potentiometer setting. Ass~ing that the speed of motor 10 increases above the desired speed thereof, the frequency o~ the pulses generated by frequency gen-erator FG (FIG. 4A) correspondingly increases. This increases the frequency of the pulses produced by rnonostable multivibrators 25 and 27 (FIGS. 4B and 4C, respectively~. Thus, since the slope of the sawtooth waveform generated by sawtooth wave.form generator 20 remains constant (because the setting of potentiometer VRl has not changed), it is appreciated tha~ the sawtooth waveorm is reset at a time that is earlier in its cycle than shown in FIG. 4D. Con-. sequently, the amplitude of the sawtooth waveform which is sampledby sampling transistor Q4 in response to the pulses produced by monosta~le multivibrator 25 (FIG. 4~) is less than that shown in FIG. 4D. There~ore, the DC voltage supplied to amplifier 13 is less ~han ~hat shown in FIG. 4E. ~ence, ~he magnitude o~ the drive current supplied to motor 10 is reduced. As a result thereof, the speed of motor 10 is reduced to be equal to the le~el established . by the setting of potentiometer VRl.
Conversely, if it is assumed that the motor undergoes an undesired reduction in speed, the frequency of the pulses produced lS by frequency generator FG, and thus the frequency of the puls~s pxoduced by monostable multivibrators 25 and 27, is reduced. This means that, since the slope of the sawtooth waveform remains con-stant, the sawtooth waveform is reset at a time which occurs much later in its cycle than shown in FIG. 4D. Accordingly, the ampli-tude of the sawtooth wave~orm which is sampled by sampling transistorQ4 is greater than the sampled amplitude shown in FIG. 4D. This means that the DC voltage supplied to ampliier 13 is greater than that shown in FIG. 4E. As a consequence thereo, the magnitude o~
the drive current supplied to motor 10 by transistor Q7 increases so as to correspondingly increase the speed of the motor, whereby the motor speed is restored to its proper, desired lev~l correspond-ing to the setting o~ potentiometer VRl.
Let it be assumed that po~entiometer VRl is adjusted to a setting corresponding to a slower desired motor speed. TKis is achieved by adjusting the wiper o~ the potentiometer in the direction ~.~.3 iZ~
toward the zero speed setting thereoE (i.e., the setting ~herein r3~R2=r4~R3~. It is apprecia~ed that, as the wiper of the pote~-tiometer is moved toward ~he zero speed setting, the voltage derived thereat increases. An increase in the wiper voltage results in an S increase in the base voltage of transistor Q2 Since this transistor -is a PNP transistor, its conductivity is reduced, there~y increasing its collector-emitter impedance. This, in turn, increases -~he charg-ing time constant of capacitor Cl, thereby reducing ~he slope of the sawtooth waveform. This reduced slope is shown in FIG. 5D.
The operation of speed control circuit 12 functions in the same manner as be~ore. ~ence, the pulses produced by mono-stable multivibrator 27 (FIG. 5C) serve ~o reset the sawtooth waveform; and the pulses produced by monostable multivibrator 25 tFIG. 5B) are used to sample the amplitude of the sawtooth waveform just prior to the resetting thereof. Since the slope of the sawtooth waveform is reduced, it is appreciated that the sampled amplitude thereof likewise is reduced~ Conse~uently, the sampled amplitude, represented by the broken horizontal lines in FIG. 5D, is less than the sampled amplitude sh~wn in FIG. 4D. Accordingly, the DC voltage supplied from capacitor C2 to amplifier 13, as shown in FIG. 5E, is o a lower level than the DC voltage shown in FIG. 4E. Hence, the magn;tude of the drive current supplied to motor 10 is reduced whereby the motor is driven at a slower speed determined by th~
setting of potentiometer VR1. Of course, any undesired change in the motor speed is detected and corrected in the manner described in detail hereinabove.
Operation of the Dead-band Control Circuit The purpose of dead-band control circuit 16 is to detexmine when the settin~ of potentiometer VRl is within a predetermined range ; 30 of the zero speed setting and then ;nhibit the drive current ~rom being supplied to motor 10. As may be appreciated, in the absence of a dead-band, drive current would be inhibited from motor 10 only when the potentiometer is set precisely to its zero speed setting.
It is preferred to proviae some tolerance ~or an operator in setting the potentiometer to a point whereat the motor is stopped.
The bias voltage supplied ~o the non-inverting input of amplifier 17 is equal to the voltage which is derived at the wiper of potentîometer VRl when this wiper is set at some predetermined location on either side of the zero speed setting. Since ~he 1~ wiper voltage is a maximum for the zero speed set~ing, it is appreciated that this bias, or threshold, voltage supplied to the non-inverting input of ampliEier 17 is a predetermined voltage which is less than this maximum voltage level. Accordingly, when the setting of potentiometer VRl is such that motor 10 is operated at some desired speed, it is recognized that the voltage derived at the wiper of the potentiometer for this setting is less than the threshold voltage. Consequently, since the threshola voltage exceeds the voltage which is supplied to the inverting input of amplifier 17 rom the wiper of potentiometer VRl, a positive potential is supplied to the base electrode o~ transistor Q8 by amplifier 17. Hence, transistor Q8 is rendered conductive so a~
to reduce its collector voltage to a relatively low level. This low level collectar voltage is supplied to shunting transistor Q6' thereby rendering this transistor non-conductive. In this condition, the sampled DC level across capacitor C2 i9 supplied via FET Q$ to amplifier 13. Hence, a drive current i5 supplied to motor 10 by drive transistor Q7.
As the wiper o~ potentiometer VRl is adjusted in a direction toward its zero speed setting, it is recalled that the drive current supplied to motor 10 is reduced so as to correspondingly '7 reduce the motor sneed. When the wiper is within the aforementioned predetermined range of its zero speed setting, ~he ~oltage supplied therefrom to the i~verting input of amplifier 17 exceeds the threshold voltage supplied to the non-inverting input of the amplifier. This is because the volta~e now derived at the wiper of the pot~ntiometer is greater than the voltage derived therea~ when the wiper is set to the outer limit of its pre~etermined range, i.e., ~he thxeshold voltage. Consequently, a low, or negative, potential is supplied to the base electrode of ~ransistor ~8. This renders transistor Q8 non-conductive, so as to raise the collector voltage thereof to a relatively high level. This high level collector voltage i5 supplied to shunting transistor Q6' thereby turning thi5 shunting transistor ON. Accordingly, the DC level which is stored ac~oss capacitor C2 and which is supplied to amplifier 13 via FET Q5 now is shunted to ground through transis~or Q6 Hence, the output of amplifier 13 is of a sufficiently low level so as to turn drive transistor Q7 OFF. This interrupts the drive current supplied to motar 10, thereby stopping the motor. So long as the wiper o potentiometer VRl is within the aforementioned predetermined range ` 20 about its zero speed setting, the voltage supplied to the inverting input o~ amplifier 17 by ~he potentiometer wiper exceeds the threshold voltage supplied to the non-inverting input o~ this ampli-fier. Hence, current is inhib ted from bein~ supplied to motor 10 so long as potentiometer VRl is adjusted to a setting within the aforementioned range, i.e., to a setting within the dead-ba~d range.
~ he manner in which the dead-band range is related to the setti~g of potentiometer VRl is diagramaticall~ represented in FIG. 3. Let it be assumed that the abscissa represen-ts the direc-tion in which the wiper o~ the potentiometer is adjusted, and the ordinate represents the direction in which the motor operates.
_ . . . ,, _ _ . .. ..
The deaa-band range is shown at 22, with re~erence numeral 23 identifying the zero speed setting of the potentiometer. That is, at the zero speed setting 2~, r3+R2=r4+R3 and the voltage at the wiper of the potentiometer is at a maximum level. If the wiper is moved in the ~irection 24, for example, the voltage thereat is reduced. However, no current is supplied to motor 10 until the wiper is moved ~eyond the dead-band range. When t~e outer limit of this dead-band range is reached, the speed of motor 10 increases abruptly to a level corresponding to the setting of the potentiometer, and in a negative direction. Alternatively, if the wiper is adjusted in the opposite direction, as represented by~arrow 26, then motor 10 abruptly starts with a speed correspond-ing to the setting of the potentiometer, and in a forward direction.
It may be appreciated from FIG. 3 that the speed of the motor is the same on either side of the zero setting 23, depending upon the corresponding setting of potentiometer VRl. That is, if the wiper of the potentiometer is adjusted by the same amount to either side of the zero setting, then the speed of the motor will be the same in both the orward and reverse directions. Of course, the direc-tion in which the motor operates depends upon the direction in which the potentiometer is ad~usted. Arrows 30 and 32 in FIG. 3 represent forward and reverse motor direction, respectively.
Hence, it is appreciated that i~ the setting o~ poten-tiometer VRl is within the dead-band range, as represented by the range 22 shown in FIG. 3, then motor 10 remains at rest, regardless of the precise setting of the potentiometer within this rangeO
Operation of the Direction Control Circuit It may be appreciated that the combina-tion of resistor Rl, resistance r4 and resistor R3 functions as a voltage divider to produce a voltage at terminal a depending upon the particular ~ $ ~c~ Ji~
settîng of the wiper of potentiometer VRl. Similarly, resistor Rl, resistance r3 and resistor R2 function as a voltage divider.
When the wiper of potentiometer VRl is set to its zero speed set-ting, then the voltage provided at terminal a is of a predetermined value. For example, if R2=R3, then the zero speed setting o~ poten-tiome~er VRl is the mid-point settiny wherein r3=r4. The bias circuit coupled to the non-inverting input of amplifier 19 supplies a bias voltage thereto which is equal to the voltage at terminal a when potentiometer VRl is set to the zero speed setting.
If the wiper of the potentiometer is moved toward the right, as viewed in FIG. 2, then resistance r4 decreases~ This increases the voltage divider ratio R ~R3+r Since resistance r4 decreas~s, the voltage supplied to terminal a increases. That is, this voltage now exceeds the ~ias voltage supplied to the non-inverting input of amplifier 19. Consequently, the outpu~ voltage ; produced by amplifier 19 renders transistor Qlo non-conductive.
`~ The coIlector voltage of this transistor now is sufficiently high to render transistor Qll conductive, whereby the collector voltage of this latter transistor is at a relatively low level. The high ~0 collector voltage o transistor Qlo turns transistor Q13 ON; and the low collector voltage of transistor Qll tuxns transistor Q14 ON.
Transistors Q12 and Q15 now are non-conductive. Thus, drive current is supplied from transistor Q7 to motor 10 via transistors Q14 and Q13 This current path drives motor 10 in a corresponding direction, for example, in the foxward direction. It is appreciated that the magnitude of the drive current is a function of the setting of potentiometer VRl, as described above, so as to correspondingly establish the desired motor speed.
If the wiper of potentiometer VRl is moved toward the 3G left (as viewed in FIG. 2) rom its zero speed setting, resistance r~
increases. Thus, the voltaye diviaer ratio R ~R3+r decreases so as to reduce the voltage supplied to terminal a. since this voltage now is less than the voltage ~hereat which is produced when potentiometer VRl is at its zero speed set~ing, it is appre-ciated that amplifier 19 supplies a voltage to transistor Qlo sufficient to render this transistor conductive. .Consequently, the collector vol~age of this transistor is at a rela~ively low level~ whereby transistor Qll is rendered non conductive. ~hus, the low collector voltage o txansistor Qlo turns transistor Q12 O~; and the high collector voltage of transistor Qll turns ~ran-sistor Q15 ON. Drive current now flows from transistor.Q7 tomotor 10 through transistors Q12 and Q15 This current path drives the motor in the opposite direction~ ~or example, in the reverse direction. of course, the magnitude of.the motor speed is determined by the magnitude of the drive current supplied thereto which, in turn, is a function of the setting of potentiometer VRl. -Therefore, it is seen that the adjus~ment of the wiper of potentiometer VRl to one or the o~her side of its zero speed setting is detected ~y amplifier 19. Depending upon whether the adjustment of this potentiometer is in a direction to determine -20 forward or reverse operation of motor 10, either transistor Qll or transistor Qlo is rendered conductive so as to correspondingly control the conductivities of the respective switching transistors included in the current steering circuit.
Thus, it is seen that the direction in which a motor operates is determined in accordance with the setting o~ a speed control potentiometer without requiring the use of two separate pow ~ supplies, or a power supply capable o~ producing both a positive and a negative operating potential, as was required in the prior art system shown in FIG. 1. Furthermore, the setting of a single potentiometer is used to control both motor speed and direction.
In the embodiment shown in ~I~. 2, if it is desired that motor 10 should be capable of operating at the same speeds in both the orward and reverse directions, then R2=R3. Alternati~ely, i~
it is preferred that motor 10 be capable of operating at higher speeds in one dixection t~an in ~he other direction, then resistors R2 and R3 should not ~e equal to each other.
: . While the present invention has been particu~arly shown and described with reference to a preferrea embodiment thereof, it should ~e readily apparent to those of ordinary skill in the art that various changes and modifications in form and details can be made without departing ~rom the spirit and scope of the invention. For example, resisto~s Rl, R2 and R3 may be replaced by transistors. Still further, resistors R~, R2 and R3 may be selected such that the slope of the sawtooth waveform generated : by sawtooth waveform generator 2Q is e~ual to zero at the zero ~::
speed setting of potentiometer V~l~ It is, therefore, intended that the appended claims be interpreted as including the foregoing 20 as well as various other modifications and changes.
'
This invention relates to a motor control system and, more particularly, to such a system wherein a potentiome~er is used to control the speed an~ direction at which a motor oper~tes, and wherein an operating potential of only a single polarity need be used with the potentiometer in determining the direction a~
which the motor operates.
Bidirectional motors admi~ of various and divers appli-cations. In a typical application thereo~, ~he motor should be capable of operating at a desirable speed and either in a forwaxd or reverse direction. Fur~hermore, if th~ motor is control~ed by a manually adjustable device, such as a potentiometer, there are certain circumstances wherein the motor should exhibit zero speed when the adj~stable element, or potentiometer, is at or very close to a zero speed setting. For example, when the motor is used to drive an article to a particular location, it is advan-tageous to be able .o operate the motor at a relatively high speed until the article approaches the predetermined location, and then to drive the motor at a progressively decreasing speed so as to be able to stop the motor abruptly when the article reaches its predetermined location. In the event of an over-shoot, it also is advantageous to drive the motor in a reverse direction so as to return the article to its predetermined location.
One type of motor control system which uses a potentiometer to determine the speed and direction of the motor is described in U.S. Pat. No. 3,950,683, issued to W. P. Lamson. In this system, the potentiometer is provided with ~oth positive and negative operating potentials. The wiper of the potentiometer i~ adjustable so as to ~e set either at a zero speed setting, which may corre-spond to the mid-point v~ the potenkiometer resistance, or ak any . .
z~
location between the zero speed setting and either terminal of the potentiometer. Thus, when the wiper is set at a location between the zero speed setting and the potentiometer terminal to which the positive operating potential is supplied, the magnitude of the voltage at the wiper determines the speed at which the motor operates, and the positive polarity of this voltage is used to drive the motor in, for example, the forward direction. Similarly, if the wiper is set at a location between the zero speed setting and the potentiometer terminal at which the operating potential ~f negative polarity is supplied, then the magnitude of the voltage at the wiper determines the motor speed, and the negative polarity of this voltage is used to drive the motor in, for example, the reverse direction. The motor control system described in this patent also includes a dead-band circuit which prevents undesired slow motor speed, such as motor creeping, when the wiper is set to, or very close to, its zero speed setting.
A significant disadvantage of the motor control system described in the aforementioned patent is the requirement that, in order to control the motor direction, operating potentials of positive and negative polarities must be applied to the potentiometer terminals. By requiring such positive and negative polarity operat-ing potentials, the power supply circuit which is needed to derive these operating potentials is relatively complex.
OBJECTS OF THE INVENTION
-Therefore, it is an object of the present invention to provide an improved motor control system which avoids the afore-noted disadvantages of the prior art.
Another o~ject of this invention is to provide a motor control system for controlling the speed and direction at which a motor operates in accordance with the setting of a potentiometer.
_ A further object of this invention is to provide a motor control system which uses a potentiometer for controlling the speed and direction of a motor, and wherein the potentiome~er is supplied with an operating potential of only a single polarity.
An additional object o~ this invention is to provide a motor control system which uses a potentiometer for controlling the speed and direction of the motor, which potentiometer is supplied with an operating potential of only one polarity, and wherein the setting of the wiper of the potentiometer determines both the speed and direction at which the motor operates.
Various other o~jects, advantages and features o~ the present invention will become readily apparent from the following detailed description, and the novel features will be particularly pointed out in the appended claims.
. . SUMM~RY OF THE INVENT ION
-In accordance with this invention, a motor control system is provided for controlling the speed and direction at which a motor operates. A drive circuit supplies a drive current to the motor, the magnitude of this drive current being determinative o~
the motor speed. A direction-determining circui~ is provided to determine the direction at which the motor operates. In a preferred embodiment, this direction-determ~ning circuit is a steering circuit or steering the drive current to the motor either in a first or in a se~ond current path. A potentiometer comprised of a resistance connected between first and second terminals has a wiper which is adjustably se~table along the res;stance to determine the desired speed and direction o operation of the motor. A power source has a power terminal and a reerence terminal for providing an operating potential across such terminals. The power terminal is coupled to the potentiometer wiper and the xe~erence terminal is coupled to Z~'7 one of the potentiometer terminals. A resistor couples the other potentiometer te~ninal to the reference terminal. The potentiometer wiper is coupled to the drive circuit and the potentiometer terminal, which is coupled to the reference terminal by the resistor, is coupled to the direction-determining circuit;
whereby the setting of the wiper determines the magnitude of the voltage ~upplied thereby to the drive circuit so as to determi~e the motor speed, and the setting of the wiper also determines the Jnagnitude of the voltage supplied to the direction-determining circult from the potentiometer terminal to determine the direction at which the motor operates.
BRIE~ DESCRIPTICN OF THE DRAWINGS
_ _ The following detailed description, given by way of example, will best be understood in conjunction with the accom-~5 panying drawings in which:
FIG. 1 is a schematic diagram of a prior art technique for controlling the speed and direction at which a motor operates;
FIG. ~ is a schematic diaaram of a preferred embodiment of the present invention;
.,.. ~ ., ~\ -FIG. 3, appearing with Fig. 1, is a graphical represen- ¦
tation showing the manner in which the circuit of FIG. 2 is used to control the operation of a motor; and FIG~. 4A-4E and 5A-5E are waveform diagrams which are useful in understanding the operation of the circuit sho~m-in FIG. 2 !5 DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT
Before describing an embodiment of the present invention reference i5 maae to FIG. 1 which is a schematic representation of a prior art technique or using a potentiometer to control the speed and direction o a motor. A negative opera-ting potential, repre-~0 sented as the DC power supply El, is coupled to one te:cminal of ~ !~
. . _ _ _ . . . _ .
the potentiometer, and a posi~ive operating potential, represented as the DC power supply E2, is coupled ~o the other terminal o~ the potentiometer. The positive and negative operating potentials are referenced to ground, as represen~ed by the ground potential applied to the junction of the positive and negative DC power supplies. The wiper of the potentiometer is coupled to a motor drive circuit which, in turn, drives a motor, the combination of the motor drive circuit and motor being represented at M.
Assuming that the operating potentials are equal (El=E2), then if the wiper of the potentiome~er is set at ~he mid-point o the potentiometer resistance, then a zero voltage is supplied to the motor dxive circuit, thereby esta~lishing a zero motor speed.
I~ the wiper of the potentiometer is adjusted in the upward dixec-tion, that is, toward the negative DC power supply El, then a 15 ne~ative voltage is supplied to the motor drive circuit so as to determine a corresponding direction at which the motor operates.
Furthermore, depending upon the particular setting of the wiper of the potentiometer, the magnitude of the negative voltage which is supplied to the motor drive circuit determines a corresponding motor speed. Converse~y, if the wiper of the potentiometer is adjusted in the downward direction, that is, toward the positive DC power supply E2~ then a positive voltage is supplied to the motor drive circuit, thereby determining an opposite direction for the motor. Also, the particular setting of the wiper estab-lishes a corresponding magnitude of this positive voltage so asto correspondingly determine the motor speed.
It is appreciated that, in khe prior art technique shown in FIG. 1, two separate power supplies El and E2, o~ opposite polarities, must be provided in order to determine the direction in which the motor is driven. The use of two power supplies E
~ . ............. ~ ..
., .
and E2 results in a relatively complex construc~ion of the power supply circuitry. It is a principal obj ect of the pxesent inven-tion to provide a motor control system wherein the setting o~ a potentiometer determines the speed and direction at which a motor operates, yet relies upon only a single po~er supply, that i~, a power supply which provides an operating voltage of only one polarity. Stated otherwise, the motor control system o the present invention achieves su~stan~ially the same result as the system shown in FIG. 1, while eliminating either power supply El or powex supply E2.
Turning now to FIG. 2, a prefexred embodimen~ o~ the motor control system in accordance with the present invention is schematically illustrated. This motor control system is adapted to control the speed and direction of a motor 10 which~ ~or example, - is a DC motor. The illustrated DC motor control system includes a speed control circuit 12, a direction control circuit 18, a potentiometer circuit 14 which is used in conjunction with speed control circuit 12 and dirPction control circuit 18 for determining the speed and direction of operation of motor lO, and a dead-band ~0 control circuit 16. Speed control circuit 12 is comprised of a frequency generator FG which is adapted to produce periodic signals, such as pulses, having a frequency determined by the speed at which motor lO operates. For exampie, motor 10 may be mechanically coupled to a tachometer device, such as a wheel having one or more magnetic elements mounted thereon. A magn~tic pickup is positioned adjacent the wheel so as to produce a pulse whenever a magnetic el~ment rotates therepast. Thus, depending upon the angular velocity of the wheel, and thus the speed of motor lO, a corresponding pulse train is produced ~ frequency generator FG.
Speed control clrcuit 12 additionally includes a sawtooth waveform generatox 20, monos~able multivibrators 25 and 27, a sample-and-hold circui~ comprised o~ a transistor Q4 and a capacitor C2~ and a reset circuit including a transis~or Ql Monostable multivibxator 25 is coupled to frequency generator FG by an amplifier 21 so as to produce pulses of a predetermined duration in response to, for example, the posi~ive ~ransition in the pulses which are generated by the freguency generator. The output of monostable mul~ivibrator 25 is coupled to sampling transis~or Q4 and, additionally, to mono-stable multivibrator 21. The lattex monostable multivibrator isadapted to generate pulses of predetermined duration in response to, for example, the negatîve transition in each pulse produced by monostable multivibrator 24. The outpu~ of monostable multi-vibrator 27 is coupled to reset transistor Ql whose collector-lS emitter circuit is connected in shunt relation across a capacitorCl, the latter being included in sawtooth waveform gener~tor 20.
The sawtooth waveform generator is comprised of the collector-emitter circuit of a transistor Q2 connect~d in series with capacitor C~. Depending upon the conductivity of transistor Q2' a current flows from a source o~ operating potential +~cc through the collector-emitter circuit thereof to charge capacitor C~ Thus, this capacitor charges at a relatively fast rate when transistor Q2 is more conductive; and, conv~rsely, the capacitor is charged at a relatively slow rate when transistor Q2 is less conductive. The voltage across capacitor Cl is coupled through an emitter-follower buffer transistor Q3 to samplir1g transistor Q~. Storage capacitor C2 is coupled to the emitter electrode of ~amplin~ -transistor Q~, and this capacitor is further coupled to the gate electrode of a ~ield effect transistor (FE~) Q5. It may be appreciated that, because of th~ high input impedance of FET Q5r capacitor C2 is subject to negligible leakage.
The base el~ectrode o~ transistor Q~ is coupled to the wiper of a potentiometer VR included in potentiometer circuit 14, and is adapted to receive a control voltage therefrom such that its conductivity is aetermined accordingly. Potentiometer VR~ is of conventional construction and mav be formed of typical thin film or integrated circuit techniques, or may be of other conventional construction. The resistance o~ this poten~iometer is provided with a pair of terminals a and b at opposite ends thereof, with terminal b co~nected to ground by a ~ixed resistor R2, and with terminal a connected to ground by a fixed resistor R3. Tha resistance of potentiometer VRl may be khought of as being cons~ituted by a resistance arm extending between the wiper and terminal b, and having a variable resistance r3, and another resistance arm extending be-tween the wiper and terminal a and having a resistance r4. It is appreciated that the sum of resistances X3 and r4 is constant, but the i~dividual resistance values thereof are dependent upon the positioning or setting of the wiper of the potentiometer. Operating potential Vcc is supplied to the wiper via a resistor Rl.
In addition to being coupled to the base electrode of transistor Q2' the wiper of potentiometer VRl also is coupled to the inverting input of an operational amplifier 17 included in dead-band control circuit 16. The non-invertin~ input o~ amplifier 17 is coupled to a resistor bias circuit so as to be supplied with a predetermined bias potential. ~or a purpose soon to be understood, this bias potential is equal to the voltage derived at the wiper of potentiometer VRl when this wiper is within a predetermined range of its zero speed setting. Ampli~ier 17 functions a a threshold detector wherein the bias voltage supplied to its non~inverting input consitutes the threshold voltage and the vol-tage derived at the wiper of potentiometer VRl, and supplied to the inverting input '"'7 of the amplifier, is compared to this threshold vol~age. The output of ampliier 17, which is a unction of the dif~erence between the voltage derived at the potentiometer wiper and the threshold voltage, is supplied to a transistor Q8~ which functions as an inverting amplifier, and the collector electrode o this transistor is connected to a shunt transistor Q6.
The output electrode of FET Q5, which may be the source electrode thereof, is coupled to the non-inverting input of an ampli~ier`13 which, for example, may comprise an operational amplifier having a feedback circuit connected to its inverting input and a bias circuit also connected to its inverting input.
The collec~or-emi~ter circui~ of shunting transistor Q6 is connected in series betw~een the non-inverting input of amplifier 13 and ground.
The output of amPliier 13 is amplified bv a current amplifying transistor Q7 whose collectox-emitter circuit is, connected between the source of operating potential Vcc and motor 10.
Direction control circuit 18 is comprised. of an amplifier 19, such as an operational amplifier, having its inverting input coupled to terminal a of potentiometer VRl, and its non-inverting input coupled to a bias circuit for receiving a predetermined bias voltage derived from operating potential Vcc. Amplifier 19 functions as a threshold detector; and the bias voltage supplied thereto con-stitutes a threshold voltage. This threshold voltaye is equal to the volta,ge derived at terminal a of potentiometer VRl when the wiper is set to the zero speed setting of the potentiometer. The voltage provided at terminal a for all settings of potentiometer VRl is compared to this threshold voltage. '' The output of amplifier 19 is coupled -to the base electrode of a transistor Qlo whose collector electrode i5 connected -to the base electrode of a similar transi~tor Qll These transistors are : .
_9_ adapted to be mutually exclusively conductive. That is, when transistor Qlo conducts, transistor Qll is non-conductive.
Conversely, when transistor Qll conducts, transistor Ql~ is non-conductive. The cvllector electrodes of transistors Qlo and Qll are connected to a current steering circuit formed of transistors Q12-Q15 The current steering circuit ~unctions to selectively establish two current paths from current amplifier transistor ~7 through motor 10. The direction in which ~he motor operates is directly dependent upon th~ current path therethrough. As will be explained below, transis~ors Q12-Q15 may be switching transistors wherein transistors Q12 and Q13 are PNP and NPN transistors, respec-tively, with their collector ele~trodes connected in common to one terminal of motor 10. Transistors Q14 and Q15 are PNP and NPN
transistors, respectively, with their collector electrodes conne~ted in common to the other terminal of the motor. Tra~sistors Q12 and Q15 are adapted to be conductive concurrently so as to establish the first current path through motor 10; and transistors Q13 and Q14 are adapted to be conductive concurrently to establish the other current path through the motor.
Operation of the Speed ~ontrol Circuit As mentioned above, frequency generatGr FG is adapted to generated pulse signals, such as the xectangular waveform shown in -FIG. 4A, having a frequency determined by the speed of motor 10.
Hence, as the motor speed increases, the frequency of the pulses generated by frequency generator FG increases and, conversely, as the speed of motor 10 decreases, the frequency of these pulses likewise decreases. The pulses produced by the ~requency generator are amplified by amplifier 21 and used to trigger monostable multi-vibrator 25. The pulses generated by this monostable multivibrator in response to the positive transition of the pulses generated by the ., .
'7 frequency generator are illustrated in FIG. 4B. These pulses proauced by the monostable multivibrator turn ON sampling tran-sistor Q4 and, additionally, trigger monostable multivibrator 27 to produce the pulses shown in FIG. 4C. As is apparent, mono stable multivibrator ~7 is triggered in response to the negative transitions of the pulses produced by monostable multivibrator 25~
Let it be assumed ~hat the wiper of potentiometer VRl is set at some desired speed set~ing. It may be appreciated that if the setting o the potentiometer is such that r3+R2=r4~R3, then a maximum voltage is derived at the wiper of the potentiometer.
This voltage decreases as the setting of the po entiometer changes.
If, for example, R2-R3~ then the maximum voltage is dexived at the wiper of the potentiometer when r3=r4, that is, a~ the mid-point setting of the potentiometer. When the wiper is adjusted from lS this mid-point setting, the voltage derived thereat is reduced.
As will be explained, this setting which results in the maximum wiper voltage, for example, the mid-point setting o~ potentiometer VRl, is equal to the zero speed setting. It is assumed, for the present discussion, that the potentiometer is set to some desired setting other than this zero speed setting. Accordingly, the voltage supplied to transistor Q2 by the wiper of potentiometer VRl is sufficient to establish a desired conductivity of the transistor. The collector-emitter impedance of txansistor Q2' taken in conjunction with the capacitance of capacitor Cl, estab-lishes a charging time constant, whereby capacitor Cl is chargedat a corresponding rate.
Transistor Ql is rendered conductive periodicially in response to the pulses produced by monostable multivibrator 27 (FIG. 4C). Consequently, capacltor Cl i5 periodically discharged through the low impedance collector-emitter circuit o~ transistor Ql ... . , . . __ ,_ _. , , _ .. . ... _ . . . . . , . . . ..... . . ... _ . . .. .. .. _ . _ Accordingly, the voltage across capacitor Cl exhibits the sawtooth wavefo~n shown in FIG. 4D. It is appreciated that the slope of this sawtooth wavefo~n is equal to the charging rate o~ the capacitor and, therefore, is determined by the conductivity of transistor Q2 Since the conductivity of this transistor is a function o~ the volt-age derived at the wiper o~ potentiometer VRl~ it is seen that the slope of the sawtooth waveform (FIG. 4D) is determined by the setting of the potentiometer. Emit~er-follower transistor Q3 supplias the sawtooth waveform shown in FIG. 4D to sampling transistor Q4.
The pulses produced by monostable multi~ibrator 25 (FIG. 4B) occur just prior to the rese~ting of the sawtooth wave~orm ~FIG. 4D).
Thus, transistor Q4, which is turned ON by the pulses supplied thereto from monostable multivibrator 25 samples the a~plitude of the sawtooth waveforrn, as shown by the horizontal broken lines in FIG. 4D. This lS sampled amplLtude is stored across capacitor C2 and is supplied through FET Q5 to amplifier 13 as the DC level illustrated in FIG. 4E.
A corresponding current, determined by the DC level sho~n in FIG. 4~, is supplied from transistor Q7 to motor 10. Depending upon the desired direction of operation of the motor, this current is supplied either from transistor Q7 via transistor Q12' motor 10 and transistor Q15 or, alternatively, from transistor Q7 via tran-sistor Q14 through motor 10 to transistor Ql3 Further discussïon of the direction-determining current path is set out hereinbelow.
Ass~ning that the setting of potentiometer VRl does not change, the speed of motor 10 is controlled so as to be equal to that speed corresponding to the potentiometer setting. Ass~ing that the speed of motor 10 increases above the desired speed thereof, the frequency o~ the pulses generated by frequency gen-erator FG (FIG. 4A) correspondingly increases. This increases the frequency of the pulses produced by rnonostable multivibrators 25 and 27 (FIGS. 4B and 4C, respectively~. Thus, since the slope of the sawtooth waveform generated by sawtooth wave.form generator 20 remains constant (because the setting of potentiometer VRl has not changed), it is appreciated tha~ the sawtooth waveorm is reset at a time that is earlier in its cycle than shown in FIG. 4D. Con-. sequently, the amplitude of the sawtooth waveform which is sampledby sampling transistor Q4 in response to the pulses produced by monosta~le multivibrator 25 (FIG. 4~) is less than that shown in FIG. 4D. There~ore, the DC voltage supplied to amplifier 13 is less ~han ~hat shown in FIG. 4E. ~ence, ~he magnitude o~ the drive current supplied to motor 10 is reduced. As a result thereof, the speed of motor 10 is reduced to be equal to the le~el established . by the setting of potentiometer VRl.
Conversely, if it is assumed that the motor undergoes an undesired reduction in speed, the frequency of the pulses produced lS by frequency generator FG, and thus the frequency of the puls~s pxoduced by monostable multivibrators 25 and 27, is reduced. This means that, since the slope of the sawtooth waveform remains con-stant, the sawtooth waveform is reset at a time which occurs much later in its cycle than shown in FIG. 4D. Accordingly, the ampli-tude of the sawtooth wave~orm which is sampled by sampling transistorQ4 is greater than the sampled amplitude shown in FIG. 4D. This means that the DC voltage supplied to ampliier 13 is greater than that shown in FIG. 4E. As a consequence thereo, the magnitude o~
the drive current supplied to motor 10 by transistor Q7 increases so as to correspondingly increase the speed of the motor, whereby the motor speed is restored to its proper, desired lev~l correspond-ing to the setting o~ potentiometer VRl.
Let it be assumed that po~entiometer VRl is adjusted to a setting corresponding to a slower desired motor speed. TKis is achieved by adjusting the wiper o~ the potentiometer in the direction ~.~.3 iZ~
toward the zero speed setting thereoE (i.e., the setting ~herein r3~R2=r4~R3~. It is apprecia~ed that, as the wiper of the pote~-tiometer is moved toward ~he zero speed setting, the voltage derived thereat increases. An increase in the wiper voltage results in an S increase in the base voltage of transistor Q2 Since this transistor -is a PNP transistor, its conductivity is reduced, there~y increasing its collector-emitter impedance. This, in turn, increases -~he charg-ing time constant of capacitor Cl, thereby reducing ~he slope of the sawtooth waveform. This reduced slope is shown in FIG. 5D.
The operation of speed control circuit 12 functions in the same manner as be~ore. ~ence, the pulses produced by mono-stable multivibrator 27 (FIG. 5C) serve ~o reset the sawtooth waveform; and the pulses produced by monostable multivibrator 25 tFIG. 5B) are used to sample the amplitude of the sawtooth waveform just prior to the resetting thereof. Since the slope of the sawtooth waveform is reduced, it is appreciated that the sampled amplitude thereof likewise is reduced~ Conse~uently, the sampled amplitude, represented by the broken horizontal lines in FIG. 5D, is less than the sampled amplitude sh~wn in FIG. 4D. Accordingly, the DC voltage supplied from capacitor C2 to amplifier 13, as shown in FIG. 5E, is o a lower level than the DC voltage shown in FIG. 4E. Hence, the magn;tude of the drive current supplied to motor 10 is reduced whereby the motor is driven at a slower speed determined by th~
setting of potentiometer VR1. Of course, any undesired change in the motor speed is detected and corrected in the manner described in detail hereinabove.
Operation of the Dead-band Control Circuit The purpose of dead-band control circuit 16 is to detexmine when the settin~ of potentiometer VRl is within a predetermined range ; 30 of the zero speed setting and then ;nhibit the drive current ~rom being supplied to motor 10. As may be appreciated, in the absence of a dead-band, drive current would be inhibited from motor 10 only when the potentiometer is set precisely to its zero speed setting.
It is preferred to proviae some tolerance ~or an operator in setting the potentiometer to a point whereat the motor is stopped.
The bias voltage supplied ~o the non-inverting input of amplifier 17 is equal to the voltage which is derived at the wiper of potentîometer VRl when this wiper is set at some predetermined location on either side of the zero speed setting. Since ~he 1~ wiper voltage is a maximum for the zero speed set~ing, it is appreciated that this bias, or threshold, voltage supplied to the non-inverting input of ampliEier 17 is a predetermined voltage which is less than this maximum voltage level. Accordingly, when the setting of potentiometer VRl is such that motor 10 is operated at some desired speed, it is recognized that the voltage derived at the wiper of the potentiometer for this setting is less than the threshold voltage. Consequently, since the threshola voltage exceeds the voltage which is supplied to the inverting input of amplifier 17 rom the wiper of potentiometer VRl, a positive potential is supplied to the base electrode o~ transistor Q8 by amplifier 17. Hence, transistor Q8 is rendered conductive so a~
to reduce its collector voltage to a relatively low level. This low level collectar voltage is supplied to shunting transistor Q6' thereby rendering this transistor non-conductive. In this condition, the sampled DC level across capacitor C2 i9 supplied via FET Q$ to amplifier 13. Hence, a drive current i5 supplied to motor 10 by drive transistor Q7.
As the wiper o~ potentiometer VRl is adjusted in a direction toward its zero speed setting, it is recalled that the drive current supplied to motor 10 is reduced so as to correspondingly '7 reduce the motor sneed. When the wiper is within the aforementioned predetermined range of its zero speed setting, ~he ~oltage supplied therefrom to the i~verting input of amplifier 17 exceeds the threshold voltage supplied to the non-inverting input of the amplifier. This is because the volta~e now derived at the wiper of the pot~ntiometer is greater than the voltage derived therea~ when the wiper is set to the outer limit of its pre~etermined range, i.e., ~he thxeshold voltage. Consequently, a low, or negative, potential is supplied to the base electrode of ~ransistor ~8. This renders transistor Q8 non-conductive, so as to raise the collector voltage thereof to a relatively high level. This high level collector voltage i5 supplied to shunting transistor Q6' thereby turning thi5 shunting transistor ON. Accordingly, the DC level which is stored ac~oss capacitor C2 and which is supplied to amplifier 13 via FET Q5 now is shunted to ground through transis~or Q6 Hence, the output of amplifier 13 is of a sufficiently low level so as to turn drive transistor Q7 OFF. This interrupts the drive current supplied to motar 10, thereby stopping the motor. So long as the wiper o potentiometer VRl is within the aforementioned predetermined range ` 20 about its zero speed setting, the voltage supplied to the inverting input o~ amplifier 17 by ~he potentiometer wiper exceeds the threshold voltage supplied to the non-inverting input o~ this ampli-fier. Hence, current is inhib ted from bein~ supplied to motor 10 so long as potentiometer VRl is adjusted to a setting within the aforementioned range, i.e., to a setting within the dead-ba~d range.
~ he manner in which the dead-band range is related to the setti~g of potentiometer VRl is diagramaticall~ represented in FIG. 3. Let it be assumed that the abscissa represen-ts the direc-tion in which the wiper o~ the potentiometer is adjusted, and the ordinate represents the direction in which the motor operates.
_ . . . ,, _ _ . .. ..
The deaa-band range is shown at 22, with re~erence numeral 23 identifying the zero speed setting of the potentiometer. That is, at the zero speed setting 2~, r3+R2=r4+R3 and the voltage at the wiper of the potentiometer is at a maximum level. If the wiper is moved in the ~irection 24, for example, the voltage thereat is reduced. However, no current is supplied to motor 10 until the wiper is moved ~eyond the dead-band range. When t~e outer limit of this dead-band range is reached, the speed of motor 10 increases abruptly to a level corresponding to the setting of the potentiometer, and in a negative direction. Alternatively, if the wiper is adjusted in the opposite direction, as represented by~arrow 26, then motor 10 abruptly starts with a speed correspond-ing to the setting of the potentiometer, and in a forward direction.
It may be appreciated from FIG. 3 that the speed of the motor is the same on either side of the zero setting 23, depending upon the corresponding setting of potentiometer VRl. That is, if the wiper of the potentiometer is adjusted by the same amount to either side of the zero setting, then the speed of the motor will be the same in both the orward and reverse directions. Of course, the direc-tion in which the motor operates depends upon the direction in which the potentiometer is ad~usted. Arrows 30 and 32 in FIG. 3 represent forward and reverse motor direction, respectively.
Hence, it is appreciated that i~ the setting o~ poten-tiometer VRl is within the dead-band range, as represented by the range 22 shown in FIG. 3, then motor 10 remains at rest, regardless of the precise setting of the potentiometer within this rangeO
Operation of the Direction Control Circuit It may be appreciated that the combina-tion of resistor Rl, resistance r4 and resistor R3 functions as a voltage divider to produce a voltage at terminal a depending upon the particular ~ $ ~c~ Ji~
settîng of the wiper of potentiometer VRl. Similarly, resistor Rl, resistance r3 and resistor R2 function as a voltage divider.
When the wiper of potentiometer VRl is set to its zero speed set-ting, then the voltage provided at terminal a is of a predetermined value. For example, if R2=R3, then the zero speed setting o~ poten-tiome~er VRl is the mid-point settiny wherein r3=r4. The bias circuit coupled to the non-inverting input of amplifier 19 supplies a bias voltage thereto which is equal to the voltage at terminal a when potentiometer VRl is set to the zero speed setting.
If the wiper of the potentiometer is moved toward the right, as viewed in FIG. 2, then resistance r4 decreases~ This increases the voltage divider ratio R ~R3+r Since resistance r4 decreas~s, the voltage supplied to terminal a increases. That is, this voltage now exceeds the ~ias voltage supplied to the non-inverting input of amplifier 19. Consequently, the outpu~ voltage ; produced by amplifier 19 renders transistor Qlo non-conductive.
`~ The coIlector voltage of this transistor now is sufficiently high to render transistor Qll conductive, whereby the collector voltage of this latter transistor is at a relatively low level. The high ~0 collector voltage o transistor Qlo turns transistor Q13 ON; and the low collector voltage of transistor Qll tuxns transistor Q14 ON.
Transistors Q12 and Q15 now are non-conductive. Thus, drive current is supplied from transistor Q7 to motor 10 via transistors Q14 and Q13 This current path drives motor 10 in a corresponding direction, for example, in the foxward direction. It is appreciated that the magnitude of the drive current is a function of the setting of potentiometer VRl, as described above, so as to correspondingly establish the desired motor speed.
If the wiper of potentiometer VRl is moved toward the 3G left (as viewed in FIG. 2) rom its zero speed setting, resistance r~
increases. Thus, the voltaye diviaer ratio R ~R3+r decreases so as to reduce the voltage supplied to terminal a. since this voltage now is less than the voltage ~hereat which is produced when potentiometer VRl is at its zero speed set~ing, it is appre-ciated that amplifier 19 supplies a voltage to transistor Qlo sufficient to render this transistor conductive. .Consequently, the collector vol~age of this transistor is at a rela~ively low level~ whereby transistor Qll is rendered non conductive. ~hus, the low collector voltage o txansistor Qlo turns transistor Q12 O~; and the high collector voltage of transistor Qll turns ~ran-sistor Q15 ON. Drive current now flows from transistor.Q7 tomotor 10 through transistors Q12 and Q15 This current path drives the motor in the opposite direction~ ~or example, in the reverse direction. of course, the magnitude of.the motor speed is determined by the magnitude of the drive current supplied thereto which, in turn, is a function of the setting of potentiometer VRl. -Therefore, it is seen that the adjus~ment of the wiper of potentiometer VRl to one or the o~her side of its zero speed setting is detected ~y amplifier 19. Depending upon whether the adjustment of this potentiometer is in a direction to determine -20 forward or reverse operation of motor 10, either transistor Qll or transistor Qlo is rendered conductive so as to correspondingly control the conductivities of the respective switching transistors included in the current steering circuit.
Thus, it is seen that the direction in which a motor operates is determined in accordance with the setting o~ a speed control potentiometer without requiring the use of two separate pow ~ supplies, or a power supply capable o~ producing both a positive and a negative operating potential, as was required in the prior art system shown in FIG. 1. Furthermore, the setting of a single potentiometer is used to control both motor speed and direction.
In the embodiment shown in ~I~. 2, if it is desired that motor 10 should be capable of operating at the same speeds in both the orward and reverse directions, then R2=R3. Alternati~ely, i~
it is preferred that motor 10 be capable of operating at higher speeds in one dixection t~an in ~he other direction, then resistors R2 and R3 should not ~e equal to each other.
: . While the present invention has been particu~arly shown and described with reference to a preferrea embodiment thereof, it should ~e readily apparent to those of ordinary skill in the art that various changes and modifications in form and details can be made without departing ~rom the spirit and scope of the invention. For example, resisto~s Rl, R2 and R3 may be replaced by transistors. Still further, resistors R~, R2 and R3 may be selected such that the slope of the sawtooth waveform generated : by sawtooth waveform generator 2Q is e~ual to zero at the zero ~::
speed setting of potentiometer V~l~ It is, therefore, intended that the appended claims be interpreted as including the foregoing 20 as well as various other modifications and changes.
'
Claims (12)
WHAT IS CLAIMED IS:
1. A motor control system for controlling the speed and direction at which a motor operates, comprising:
drive means for supplying a drive current to said motor, the magnitude of said drive current being determinative of the speed at which said motor operates;
steering means for steering said drive current to said motor in first and second current paths to determine the direction at which said motor operates;
potentiometer means having first and second terminals, a resistance connected between said first and second terminals, and an adjustable wiper settable along said resistance to determine a desired speed and a desired direction of operation of said motor, the setting of said wiper including a predetermined zero speed setting;
power supply means having a power terminal and a reference terminal for providing an operating potential thereacross, said power terminal being coupled to said wiper and said reference terminal being coupled to said second terminal of said potentiometer means; and first resistor means for coupling said first terminal of said potentiometer means to said reference terminal;
said wiper being coupled to said drive means and said first terminal being coupled to said steering means, whereby the setting of said wiper determines the magnitude of the voltage supplied thereby to said drive means so as to determine the speed at which said motor operates, and the setting of said wiper also determines the magnitude of the voltage supplied to said steering means by said first terminal to determine the direction at which said motor operates.
drive means for supplying a drive current to said motor, the magnitude of said drive current being determinative of the speed at which said motor operates;
steering means for steering said drive current to said motor in first and second current paths to determine the direction at which said motor operates;
potentiometer means having first and second terminals, a resistance connected between said first and second terminals, and an adjustable wiper settable along said resistance to determine a desired speed and a desired direction of operation of said motor, the setting of said wiper including a predetermined zero speed setting;
power supply means having a power terminal and a reference terminal for providing an operating potential thereacross, said power terminal being coupled to said wiper and said reference terminal being coupled to said second terminal of said potentiometer means; and first resistor means for coupling said first terminal of said potentiometer means to said reference terminal;
said wiper being coupled to said drive means and said first terminal being coupled to said steering means, whereby the setting of said wiper determines the magnitude of the voltage supplied thereby to said drive means so as to determine the speed at which said motor operates, and the setting of said wiper also determines the magnitude of the voltage supplied to said steering means by said first terminal to determine the direction at which said motor operates.
2. The motor control system of Claim 1 wherein said steering means includes threshold detecting means provided with a threshold voltage substantially equal to the voltage supplied by said first terminal when said wiper is set to said zero speed setting, said threshold detecting means detecting when said volt-age supplied by said first terminal exceeds said threshold voltage so as to cause said motor to be driven in a first direction and said threshold detecting means detecting when said voltage supplied by said first terminal is less than said threshold voltage so as to cause said motor to be driven in a second direction.
3. The motor control system of Claim 2 wherein said threshold detecting means comprises a bias circuit coupled between said power and reference terminals to produce said threshold voltage; and comparator means having one input coupled to said first terminal and another input coupled to said bias circuit for comparing said voltage supplied by said first terminal to said threshold voltage.
4. The motor control system of Claim 3 wherein said steering means further comprises first and second switching circuits for coupling said motor to said drive means, said first switching circuit being energized to establish said first current path when said voltage supplied by said first terminal exceeds said threshold voltage, and said second switching circuit being energized to estab-lish said second current path when said voltage supplied by said first terminal is less than said threshold voltage.
5. The motor control system of Claim 1, further comprising a dead-band circuit coupled to said wiper for inhibiting said drive means from supplying a drive current to said motor when the setting of said wiper is within a predetermined range of said zero speed setting thereof.
6. The motor control system of Claim 5 wherein said dead-band circuit comprises second threshold detecting means provided with a second threshold voltage substantially equal to the voltage supplied by said wiper when said wiper is set to the outer limit of said predetermined range, said second threshold detecting means detecting when said voltage supplied by said wiper exceeds said second threshold voltage to inhibit said drive means from supplying said drive current to said motor.
7. The motor control system of Claim 6 wherein said dead-band circuit further comprises a shunt circuit coupled to said drive means and operative when said second threshold detect-ing means detects that said voltage supplied by said wiper exceeds said second threshold voltage to prevent drive current from being supplied to said motor.
8. The motor control system of Claim 7 wherein said second threshold detecting means comprises a second bias circuit coupled between said power and reference terminals to produce said second threshold voltage; and second comparator means having one input coupled to said wiper and another input coupled to said second bias circuit for comparing said voltage supplied by said wiper to said second threshold voltage.
9. The motor control system of Claim 7 wherein said drive means comprises a drive control circuit for generating a drive control signal as a function of the voltage supplied by said wiper; and a current amplifier coupled to said drive control circuit for producing a motor drive current in accordance with said drive control signal, said shunt circuit being connected be-tween said drive control circuit and said current amplifier for shunting said drive control signal when operative.
10. The motor control system of Claim 9 wherein said drive control circuit comprises sawtooth generating means for generating a sawtooth signal, the slope of said sawtooth signal being a function of the voltage supplied by said wiper; pulse generating means for generating periodic pulses of a frequency determined by the speed of said motor; means for using said pulses to reset said sawtooth signal; and means for using said pulses to sample the level of said sawtooth signal, said sampled level constituting said drive control signal.
11. The motor control system of Claim 1 further comprising second resistor means for coupling said second ter-minal of said potentiometer means to said reference terminal.
12. The motor control system of Claim 11 further comprising third resistor means for coupling said power terminal to said wiper of said potentiometer means.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP101123/77 | 1977-08-25 | ||
| JP10112377A JPS5435314A (en) | 1977-08-25 | 1977-08-25 | Motor control system |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1112297A true CA1112297A (en) | 1981-11-10 |
Family
ID=14292287
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA309,694A Expired CA1112297A (en) | 1977-08-25 | 1978-08-21 | Motor control system |
Country Status (7)
| Country | Link |
|---|---|
| US (1) | US4210851A (en) |
| JP (1) | JPS5435314A (en) |
| CA (1) | CA1112297A (en) |
| DE (1) | DE2837051A1 (en) |
| FR (1) | FR2401546A1 (en) |
| GB (1) | GB2003338B (en) |
| NL (1) | NL7808705A (en) |
Families Citing this family (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS56133998A (en) * | 1980-03-22 | 1981-10-20 | Sharp Corp | Speed control circuit for motor |
| JPS57175597U (en) * | 1981-04-28 | 1982-11-06 | ||
| JPS602088A (en) * | 1983-06-15 | 1985-01-08 | Ricoh Co Ltd | Servo motor drive system |
| US5406183A (en) * | 1993-09-15 | 1995-04-11 | Tomovic; Joseph F. | Integrated reversible load controller |
| US5929577A (en) * | 1995-10-13 | 1999-07-27 | Unitrode Corporation | Brushless DC motor controller |
Family Cites Families (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US2519339A (en) * | 1948-03-31 | 1950-08-22 | Westinghouse Electric Corp | Dynamo field control by unsaturated reactors |
| US2675512A (en) * | 1953-02-24 | 1954-04-13 | Honeywell Regulator Co | Motor control apparatus |
| US2846632A (en) * | 1953-07-17 | 1958-08-05 | Intavex Inc | Control system |
| US3450973A (en) * | 1963-09-06 | 1969-06-17 | Ampex | Tape transport system including deadband amplifier means |
| US3678354A (en) * | 1968-10-16 | 1972-07-18 | Canon Kk | A dc motor control apparatus |
| US3753065A (en) * | 1971-10-29 | 1973-08-14 | Chiles Patents And Systems Ltd | Method of regulating and controlling speed and direction of electric motors and appliance |
| US3950683A (en) * | 1974-06-05 | 1976-04-13 | Cleveland Machine Controls, Inc. | Motor control system having dead band control |
-
1977
- 1977-08-25 JP JP10112377A patent/JPS5435314A/en active Pending
-
1978
- 1978-08-21 CA CA309,694A patent/CA1112297A/en not_active Expired
- 1978-08-22 US US05/935,967 patent/US4210851A/en not_active Expired - Lifetime
- 1978-08-23 NL NL7808705A patent/NL7808705A/en not_active Application Discontinuation
- 1978-08-24 GB GB7834485A patent/GB2003338B/en not_active Expired
- 1978-08-24 DE DE19782837051 patent/DE2837051A1/en not_active Withdrawn
- 1978-08-25 FR FR7824740A patent/FR2401546A1/en active Granted
Also Published As
| Publication number | Publication date |
|---|---|
| FR2401546B1 (en) | 1981-10-02 |
| GB2003338B (en) | 1982-01-27 |
| US4210851A (en) | 1980-07-01 |
| GB2003338A (en) | 1979-03-07 |
| JPS5435314A (en) | 1979-03-15 |
| DE2837051A1 (en) | 1979-03-01 |
| NL7808705A (en) | 1979-02-27 |
| FR2401546A1 (en) | 1979-03-23 |
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