CA1297544C - Method of and apparatus for digitally setting a control frequency - Google Patents
Method of and apparatus for digitally setting a control frequencyInfo
- Publication number
- CA1297544C CA1297544C CA000564227A CA564227A CA1297544C CA 1297544 C CA1297544 C CA 1297544C CA 000564227 A CA000564227 A CA 000564227A CA 564227 A CA564227 A CA 564227A CA 1297544 C CA1297544 C CA 1297544C
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- Prior art keywords
- frequency
- periods
- period
- control
- control frequency
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03B—GENERATION OF OSCILLATIONS, DIRECTLY OR BY FREQUENCY-CHANGING, BY CIRCUITS EMPLOYING ACTIVE ELEMENTS WHICH OPERATE IN A NON-SWITCHING MANNER; GENERATION OF NOISE BY SUCH CIRCUITS
- H03B21/00—Generation of oscillations by combining unmodulated signals of different frequencies
Abstract
ABSTRACT OF THE DISCLOSURE
A method of and an apparatus for generating a control frequency in which two submultiples of a frequency standard are obtained which differ by unity in the respective frequency division and are mixed so that the contribution of a prior control frequency is reduced form period group to period group while the contribution of the new control frequency is increased from period group to period group. The system provides fine control of frequencies for, for example, driving synchronous motors without requiring excessively high frequency standard oscillators.
A method of and an apparatus for generating a control frequency in which two submultiples of a frequency standard are obtained which differ by unity in the respective frequency division and are mixed so that the contribution of a prior control frequency is reduced form period group to period group while the contribution of the new control frequency is increased from period group to period group. The system provides fine control of frequencies for, for example, driving synchronous motors without requiring excessively high frequency standard oscillators.
Description
1297'$4~4 METHOD OF AND APPARATUS FOR DIGITALLY SETTI~G A
CONTROL FREQUENCY
SPECIFICATION
Field of the Invention My present invention relates to a method of digitally setting a control frequency and to an apparatus for that purpose, e.g. for the gener-ation of a reference frequency for any particular electronic-control fur.ction.
Background of the Invention In order to generate with precision a particular control frequency, systems have been developed which utilize divider-type integrated circuits based upon microprocessor technology and whose limiting frequencies for many applications may not be sufficiently high. Divider ICs use as a frequency standard quartz oscillators with a quartz frequency of 9 MHz.
While such frequencies suffice in many cases, they are not satisfac-tory in other situations in which a large number of intermediate frequencies must be generated from the quartz oscillator frequency. This is the case, for example, for very fine or precise control of speed--setting in synchronous motor operation.
,`~
1Z~7S~4 For example, when the standard frequency of 9MHz serves as a prima-ry frequency and an integral divisor of 1500 is selected, a variation in the divisor by unity in the digital setting of the divisor can result in a control frequency change jump Qf of 4 HZ.
Such a frequency jump in the control of a synchronous motor can result in loss of synchronous characteristics to significant phase-current fluctuations.
The problem can be avoided by the use of a converter to shift the frequency range which is employed in the 100 MHz ultrahigh frequency range by, for example, increasing the frequency standard used as the primary frequency by a power of 10. This, however, requires expensive microelec-tronic modules for frequency transformation.
It is also possible to provide fine-step control of a frequency or a finely selectable control frequency with the aid of a synthesizer. With a synthesizer, it is possible to mix two frequencies which can be obtained by an integral deviation of a frequency standard to generate respective subharmonics or submultiples of the frequency standard. The mixing may involve addition or subtraction of the two submultiple frequencies.
Synthesizers of conventional design utilizing these techniques are, however, relatively expensive and to use synthesizers of such cost to generate precisely controllable frequency ou~puts for the operations of synchronous motors is especially uneconomical because many of the charac-teristics of the high-quality synthesizer units thereby are unutilized.
It is also not possible with this system to drive a synchronous motor together with other motors of a drive cascade, (for example in a system for feeding a web material in paper manufacture, for driving pres-sure rolls, or for driving spinning machines) since it is not possible to generate special phase differences as may be required for such systems.
For the simultaneous drive of the motors of such cascade, additional devices are required for phase control of the respective motors.
~ 2 g 7 S 4 4 70577_54 Objects of the I m ention It is the principal object of the present invention to provide an improved process for digitally generating a control frequency which allows very fine variation in the control frequency (i.e. digital-frequency con-trol in very small space Qf) while avoiding the use of ultrahighfrequencies.
Another object is to provide an improved apparatus for carrying out this method.
A further object is to obviate drawbacks of earlier systems for generating and controlling a variable frequency with high precision.
Slnnm~ry of the Invention These objects are attained, in accordance with the invention, in a method or process for the digital setting of a control frequency fst which comprises the steps of:
(a~ dividing a standard frequency by an integer to form a first control frequency fo as a first submultiple of said standard frequency;
(b) dividing said standard frequency by another integer to form a second control frequency fn as a second submultiple of said standard frequency; and (c) mixing said first control frequency fo and said second control frequency fn so that within each period group xO
of x periods of a resulting mixed signal constituting an output control frequency fst a fraction of the periods nfO is driven by the control frequency fo while a remaining fraction nfn of the periods is driven with the control frequency fn so that in each period group xO for the x periods:
x - nfn + nfo ~z97S44 70577_54 Advantageously, the method further comprises the steps of:
inducing a change in the control frequency within a period count of x ;
dividing the x periods into period groups xl to XX each of x periods so that the period groups xl to x follow one another in succession; and increasing the fraction of the periods nf by at least one period and decreasing the fraction of the periods nf by at least one period from period group to period group in said succession of xl to x period groups so that after the lapse Of x2 periods, all periods have the frequency fn.
Advantageously, the period count x2 is selected as a funct-ion of the desired control frequency fst.
The period count x is selected so that:
x2 = k~ f t3' wherein k is a proportionality constant.
The method can also comprise the step of generating said standard frequency by exciting a quartz crystal controlled oscillator.
From the foregoing, it will be apparent that for the setting of the control frequency, initially two control frequencies f and f are generated by the division of a standard frequency by respective integers, i.e. as submultiples.
~297544 70577-54 The two control frequencies are then mixed together within successive periods x in the following way:
each of the periods x is subdivided into periods nfO and nfn, whereby x = nfO + nfn-During the period nfO, the control frequency fO is suppliedwhile during the period nf , the control frequency fn is supplied so that over the period x, a mean control frequency fst f f = l/x (nfO fO + nfn n is obtained.
The mean control frequency f t is then determined by a corresponding selection of the number of periods nfO and nfn which are used in the mixing step.
The frequencies fO and fn are submultiples which differ from one another in that the divisor integers differ by at least one, i.e. the dividers forming these frequencies have divisors differing by at least one and such that:
o fst fn-It will be apparent that the invention therefore allows selection of a control frequency over a wide range but with high precision because 129~5~4 of the fine setting which is possible within the range indicated. Any intermediate frequency between fO and fn may therefore be obtained with ease.
The process of the invention is therefore most advantageous when a variable control frequency is to be obtained.
It has been found to be advantageous to complete a control frequency change ~f within an integral number of periods x2 which can be subdivided into successive period groups, xl to X2 which can be subdivided into successive period groups, x 10 to xx1 for example in period groups xl, x2 x10. Each period group thus contains x periods of the aforedescribed type, whereby in each period group x a portion of the periods nfO of a prior frequency, for example the starting frequency fO, will appear while the other part of the periods nfn are driven with the new frequency fn (fn fo _ ~f).
This means that:
X(from xl to *) - nfO + nfn-The number of periods, respectively, with the new and old frequencies can be so altered from period group to period group that the number of periods nfn with the new frequency increases by at least one period from xl to xx, while the number of periods nfO with the old or original frequency decreases by at least one period from xl to xx.
Thus by passing through a period number x2 in each period group xl to * fro~ period group to period group with an increase of the new frequency drive fn by at least one period and a reduction of the old frequency fn by at least one period, after each x2 periods, the newly set control frequency, say the frequency fnt will be achieved.
lZ97544 For example, in the control of synchronous motors utilizing the control frequency which is outputted by the system of the invention, within the first period group xl, the motor is energized only for a single period of that group with the new rotary field frequency fn For all other periods of the period group xl, the original driving frequency fo applies.
In the next period group, x2, the number of periods nfn with a new frequency fn is increased by unity (1) so that the synchronous motor is energized for two periods with the new control frequency fn and for the remainder of the period group Z2 by the original frequency fO.
With each further period group z, the number of periods nfn (at which the frequency fn applies) is increased by 1 so that the lapse of x2 periods the new driving frequency fn is the exclusive driving frequency for the motor.
The process of the invention, therefore, provides a stepwise approximation to the new frequency fn by control frequency incre~ents which are changed by a factor x which can correspond in essence to the increase in a standard frequency by corresponding factors x.
According to another feature of the invention, the number of periods x2 is selected in dependence upon the required control frequency. Most advantageously a relationship x2 ~ k.fSt3 will apply. In this relationship, k is a proportionality factor which depends upon the technological conditions of use. For example, if the control irequency is to be used as a driving frequency for an electric motor, k will be proportional to the output speed. The period count x2 is thus greater as the control frequency fst is greater.
12~S~4 It increases with increasing control frequency change ~f and a quasilinearization can be obtained by changing the divisor. A change in the standard frequency is not required.
Brief Description o the Drawing The above and other objects, features and advantages of the present invention will become more readily apparent from the following description, reference being made to the accompanying drawing in which:
FIG. l is a block diagram of a circuit in accordance with the invention for carrying out the claimed process; and FIG. 2 is a graphic illustration of the change in the control frequency by ~f.
S~ecific Description FIG. 1 is a block diagram which shows frequency converters 13 and l_ which can be connected to a standard frequency source 2, i.e. a quartz oscillator having a primary frequency fq. The outputs of the frequency converters la and l_ can be applied to the calculator units 3a and 3_ which are frequency controllers so set that the output from the frequency converters represented at 4 has the control frequency fst. In the embodiment illustrated, the output port 4 of the frequency controller is applied to a frequency changer 5 connected to synchronous motors 6.
The frequency converters l_ and l_ are programmable counters or divider integrated circuits and the calculator units can be controlled via a corresponding bus by a central processor unit or CPU, not shown.
From the calculator unit 3_ the frequency starting frequency fO is obtained as a submultiple of the standard frequency fq and from this starting frequency, a period count x is obtained in lZ975~
165~8 accordance with the relationship:
X2 _ k.fSt3 where fst - fO. The new control frequency which is to be imparted to the motor can be another submultiple of the standard frequency fq derived by the frequency converter or divider 1_ and representcd as fn The frequency fn is thus set at the frequency converter l_ and is tapped from the calculator unit 3k.
To apply the new control frequency fn to the output elements 5 and 6, there is applied to the frequency output element 4, in accordance with calculator generated periods within a period count:
x - nfO + nfn ei~her the starting frequency fO or the new control frequency fn.
Thus in each period group xl to XX the number of periods nfn with the new frequency fn will be increased by 1 from period group to period group and the number nfO of the periods with the original frequency fO will be reduced by 1 from period group to period group.
Switching over between old and new frequencies is effected by ganged electronic switches represented at 7 and 8.
Thus during the interval when the starting frequency fO is to be tapped, the frequency standard 2 is connected by the switch 7 with the frequencyconverter la and the calculator unit 3a while switch 8 connects the frequency converter la with the frequency output element 4.
In FIG. 1 the switch 7 is connected to the frequency converter 1_ and via the switch 8, the control frequency is delivered at the frequency output 4. The calculator units 3a and 3_ step a counter9for resetting the switches 7 and 8 at the end of each period group for the increase in the output of one divider and the decrease in the output of the other divider for the ne~t period group as described.
lZ9~5~4 The completion of a frequency change within a period count x2 for a frequency change of af is seen in FIG. 2.
In the practical embodiment illustrated, the divider ICs are connected to a frequency standard which can be a quartz oscillator or quartz standard with a primary frequency fq of 9 MHz. The submultiples of the dividers are set so that the starting frequency fO provides a control frequency fst of 1200 Hz for a drive frequency at the motor of 100 Hz. For determining the period count x2 within which a complete frequency change is to be effected with an integral alteration of the divisor of 1, a constant ka is selected where ~a - 10-10-5. This corresponds to:
x2 _ k.f5t3 _ ka . fa3 ~ 100 for x - 10.
The new control frequency fn will thus be reached after 100 periods and each period group x will correspond to 10 periods so that for the control frequency change ~f 10 period groups are required. Thus, the number of periods carrying the new frequency fn will increase from the first period group xl to the last period group x10 from nfn ~ 1 to nfn ~ 10, an increment of 1 in each case from period group to period group. Concomitantly the number nfO at which the starting frequency fO appears decreases in each of the period groups xl to x10 from 9 to 0 in increments of 1 from group to group.
FIG. 2 shows a frequency change for 3 control frequency increments ~f which is achieved by submultiple division of the frequency standard and a change in the divisor by 1 in each case.
In all three cases the change in the control frequency ~f is completed after 100 periods have passed whereby:
x ~ nfn + nfO - 10.
~Z~754~
1659~
If one starts with a frequency standard of 9 MHz as described, Eor the required control frequency fsr of 1200 Hz, a divisor of 7500 is required. If this divisor is varied by 1, the control frequency change ~f will be about 0.16 Hz.
According to the invention, however, this control frequency change is spread over the 10 periods of each period group and the 10 period groups so that the control frequency is adjusted in steps with 10 times more precision than could be obtained with a jump of ~f.
In earlier techniques such high precision could be obtained only by a 10-fold increase in the standard frequency with the drawbacks enumerated above.
By altering the factor k, in accordance with the invention, it is possible to change the period count within whi~h the change in control frequency ~f is competed to suit the technological requirements of the system. Of course, with a change in the proportionality factor k, there is also a change in the time within which the control frequency change will be completed. In practice this permits an inversely proportional adjustment of the rotary field frequency to the required speed of the synchronous motor.
The applications of the system of the invention are not limited to the control of synchronous motors.
The method and apparatus can be used with advantage wherever large jumps in a control frequency is disadvantageous or where perfect linearity in a response is required.
Of course, instead of a linear response, the control frequency change can be nonlinear, if desired. It is, therefore, possible to increase the number of nfn periods with the new frequency from period group to period group by increments other than unity or in a nonlinear manner.
129~S~4 The number nfn of period groups can be varied advantageously in many cases in the succession 1, 3, 6, 10 in successive period groups. The control frequency change ~f i5 then completed after only four period groups xl to x4.
The circuit shown in FIG. 1 can be used to generate intermediate frequencies over long time intervals. For example, it is possible to set the calculator units so that they will not affect changes in the numbers of the frequency packets fO and fn in each period group for l~ng periods of time and thus so that the values nfO and nfn will remain constant. The intermediate frequency at the frequency output thus has the mean control frequency value -~-st ~ l/x (nfO fO + nfn fn) For example, for a frequency standard fq 9 MHz, if it is required instead of a control frequency of 6000 Hz to have a control frequency of 5998.8 Hz, the divisor of the frequency converter la can be selected at 1500 Hz, the divisor of the frequency converter lk at 1501 and the frequency converters l_ and lb so switched that the frequency output within 10 periods will contain 7 periods (nfO _ 7) with the control frequency fO -6000 Hz and 3 periods (nfn _ 3) with a control frequency fn - 5996 Hz. In this case, an intermediate frequency of:
fst - 1/10 (7 . 6000 + 3 . 5996) - 5998.8 Hz is obtained as the desired frequency.
CONTROL FREQUENCY
SPECIFICATION
Field of the Invention My present invention relates to a method of digitally setting a control frequency and to an apparatus for that purpose, e.g. for the gener-ation of a reference frequency for any particular electronic-control fur.ction.
Background of the Invention In order to generate with precision a particular control frequency, systems have been developed which utilize divider-type integrated circuits based upon microprocessor technology and whose limiting frequencies for many applications may not be sufficiently high. Divider ICs use as a frequency standard quartz oscillators with a quartz frequency of 9 MHz.
While such frequencies suffice in many cases, they are not satisfac-tory in other situations in which a large number of intermediate frequencies must be generated from the quartz oscillator frequency. This is the case, for example, for very fine or precise control of speed--setting in synchronous motor operation.
,`~
1Z~7S~4 For example, when the standard frequency of 9MHz serves as a prima-ry frequency and an integral divisor of 1500 is selected, a variation in the divisor by unity in the digital setting of the divisor can result in a control frequency change jump Qf of 4 HZ.
Such a frequency jump in the control of a synchronous motor can result in loss of synchronous characteristics to significant phase-current fluctuations.
The problem can be avoided by the use of a converter to shift the frequency range which is employed in the 100 MHz ultrahigh frequency range by, for example, increasing the frequency standard used as the primary frequency by a power of 10. This, however, requires expensive microelec-tronic modules for frequency transformation.
It is also possible to provide fine-step control of a frequency or a finely selectable control frequency with the aid of a synthesizer. With a synthesizer, it is possible to mix two frequencies which can be obtained by an integral deviation of a frequency standard to generate respective subharmonics or submultiples of the frequency standard. The mixing may involve addition or subtraction of the two submultiple frequencies.
Synthesizers of conventional design utilizing these techniques are, however, relatively expensive and to use synthesizers of such cost to generate precisely controllable frequency ou~puts for the operations of synchronous motors is especially uneconomical because many of the charac-teristics of the high-quality synthesizer units thereby are unutilized.
It is also not possible with this system to drive a synchronous motor together with other motors of a drive cascade, (for example in a system for feeding a web material in paper manufacture, for driving pres-sure rolls, or for driving spinning machines) since it is not possible to generate special phase differences as may be required for such systems.
For the simultaneous drive of the motors of such cascade, additional devices are required for phase control of the respective motors.
~ 2 g 7 S 4 4 70577_54 Objects of the I m ention It is the principal object of the present invention to provide an improved process for digitally generating a control frequency which allows very fine variation in the control frequency (i.e. digital-frequency con-trol in very small space Qf) while avoiding the use of ultrahighfrequencies.
Another object is to provide an improved apparatus for carrying out this method.
A further object is to obviate drawbacks of earlier systems for generating and controlling a variable frequency with high precision.
Slnnm~ry of the Invention These objects are attained, in accordance with the invention, in a method or process for the digital setting of a control frequency fst which comprises the steps of:
(a~ dividing a standard frequency by an integer to form a first control frequency fo as a first submultiple of said standard frequency;
(b) dividing said standard frequency by another integer to form a second control frequency fn as a second submultiple of said standard frequency; and (c) mixing said first control frequency fo and said second control frequency fn so that within each period group xO
of x periods of a resulting mixed signal constituting an output control frequency fst a fraction of the periods nfO is driven by the control frequency fo while a remaining fraction nfn of the periods is driven with the control frequency fn so that in each period group xO for the x periods:
x - nfn + nfo ~z97S44 70577_54 Advantageously, the method further comprises the steps of:
inducing a change in the control frequency within a period count of x ;
dividing the x periods into period groups xl to XX each of x periods so that the period groups xl to x follow one another in succession; and increasing the fraction of the periods nf by at least one period and decreasing the fraction of the periods nf by at least one period from period group to period group in said succession of xl to x period groups so that after the lapse Of x2 periods, all periods have the frequency fn.
Advantageously, the period count x2 is selected as a funct-ion of the desired control frequency fst.
The period count x is selected so that:
x2 = k~ f t3' wherein k is a proportionality constant.
The method can also comprise the step of generating said standard frequency by exciting a quartz crystal controlled oscillator.
From the foregoing, it will be apparent that for the setting of the control frequency, initially two control frequencies f and f are generated by the division of a standard frequency by respective integers, i.e. as submultiples.
~297544 70577-54 The two control frequencies are then mixed together within successive periods x in the following way:
each of the periods x is subdivided into periods nfO and nfn, whereby x = nfO + nfn-During the period nfO, the control frequency fO is suppliedwhile during the period nf , the control frequency fn is supplied so that over the period x, a mean control frequency fst f f = l/x (nfO fO + nfn n is obtained.
The mean control frequency f t is then determined by a corresponding selection of the number of periods nfO and nfn which are used in the mixing step.
The frequencies fO and fn are submultiples which differ from one another in that the divisor integers differ by at least one, i.e. the dividers forming these frequencies have divisors differing by at least one and such that:
o fst fn-It will be apparent that the invention therefore allows selection of a control frequency over a wide range but with high precision because 129~5~4 of the fine setting which is possible within the range indicated. Any intermediate frequency between fO and fn may therefore be obtained with ease.
The process of the invention is therefore most advantageous when a variable control frequency is to be obtained.
It has been found to be advantageous to complete a control frequency change ~f within an integral number of periods x2 which can be subdivided into successive period groups, xl to X2 which can be subdivided into successive period groups, x 10 to xx1 for example in period groups xl, x2 x10. Each period group thus contains x periods of the aforedescribed type, whereby in each period group x a portion of the periods nfO of a prior frequency, for example the starting frequency fO, will appear while the other part of the periods nfn are driven with the new frequency fn (fn fo _ ~f).
This means that:
X(from xl to *) - nfO + nfn-The number of periods, respectively, with the new and old frequencies can be so altered from period group to period group that the number of periods nfn with the new frequency increases by at least one period from xl to xx, while the number of periods nfO with the old or original frequency decreases by at least one period from xl to xx.
Thus by passing through a period number x2 in each period group xl to * fro~ period group to period group with an increase of the new frequency drive fn by at least one period and a reduction of the old frequency fn by at least one period, after each x2 periods, the newly set control frequency, say the frequency fnt will be achieved.
lZ97544 For example, in the control of synchronous motors utilizing the control frequency which is outputted by the system of the invention, within the first period group xl, the motor is energized only for a single period of that group with the new rotary field frequency fn For all other periods of the period group xl, the original driving frequency fo applies.
In the next period group, x2, the number of periods nfn with a new frequency fn is increased by unity (1) so that the synchronous motor is energized for two periods with the new control frequency fn and for the remainder of the period group Z2 by the original frequency fO.
With each further period group z, the number of periods nfn (at which the frequency fn applies) is increased by 1 so that the lapse of x2 periods the new driving frequency fn is the exclusive driving frequency for the motor.
The process of the invention, therefore, provides a stepwise approximation to the new frequency fn by control frequency incre~ents which are changed by a factor x which can correspond in essence to the increase in a standard frequency by corresponding factors x.
According to another feature of the invention, the number of periods x2 is selected in dependence upon the required control frequency. Most advantageously a relationship x2 ~ k.fSt3 will apply. In this relationship, k is a proportionality factor which depends upon the technological conditions of use. For example, if the control irequency is to be used as a driving frequency for an electric motor, k will be proportional to the output speed. The period count x2 is thus greater as the control frequency fst is greater.
12~S~4 It increases with increasing control frequency change ~f and a quasilinearization can be obtained by changing the divisor. A change in the standard frequency is not required.
Brief Description o the Drawing The above and other objects, features and advantages of the present invention will become more readily apparent from the following description, reference being made to the accompanying drawing in which:
FIG. l is a block diagram of a circuit in accordance with the invention for carrying out the claimed process; and FIG. 2 is a graphic illustration of the change in the control frequency by ~f.
S~ecific Description FIG. 1 is a block diagram which shows frequency converters 13 and l_ which can be connected to a standard frequency source 2, i.e. a quartz oscillator having a primary frequency fq. The outputs of the frequency converters la and l_ can be applied to the calculator units 3a and 3_ which are frequency controllers so set that the output from the frequency converters represented at 4 has the control frequency fst. In the embodiment illustrated, the output port 4 of the frequency controller is applied to a frequency changer 5 connected to synchronous motors 6.
The frequency converters l_ and l_ are programmable counters or divider integrated circuits and the calculator units can be controlled via a corresponding bus by a central processor unit or CPU, not shown.
From the calculator unit 3_ the frequency starting frequency fO is obtained as a submultiple of the standard frequency fq and from this starting frequency, a period count x is obtained in lZ975~
165~8 accordance with the relationship:
X2 _ k.fSt3 where fst - fO. The new control frequency which is to be imparted to the motor can be another submultiple of the standard frequency fq derived by the frequency converter or divider 1_ and representcd as fn The frequency fn is thus set at the frequency converter l_ and is tapped from the calculator unit 3k.
To apply the new control frequency fn to the output elements 5 and 6, there is applied to the frequency output element 4, in accordance with calculator generated periods within a period count:
x - nfO + nfn ei~her the starting frequency fO or the new control frequency fn.
Thus in each period group xl to XX the number of periods nfn with the new frequency fn will be increased by 1 from period group to period group and the number nfO of the periods with the original frequency fO will be reduced by 1 from period group to period group.
Switching over between old and new frequencies is effected by ganged electronic switches represented at 7 and 8.
Thus during the interval when the starting frequency fO is to be tapped, the frequency standard 2 is connected by the switch 7 with the frequencyconverter la and the calculator unit 3a while switch 8 connects the frequency converter la with the frequency output element 4.
In FIG. 1 the switch 7 is connected to the frequency converter 1_ and via the switch 8, the control frequency is delivered at the frequency output 4. The calculator units 3a and 3_ step a counter9for resetting the switches 7 and 8 at the end of each period group for the increase in the output of one divider and the decrease in the output of the other divider for the ne~t period group as described.
lZ9~5~4 The completion of a frequency change within a period count x2 for a frequency change of af is seen in FIG. 2.
In the practical embodiment illustrated, the divider ICs are connected to a frequency standard which can be a quartz oscillator or quartz standard with a primary frequency fq of 9 MHz. The submultiples of the dividers are set so that the starting frequency fO provides a control frequency fst of 1200 Hz for a drive frequency at the motor of 100 Hz. For determining the period count x2 within which a complete frequency change is to be effected with an integral alteration of the divisor of 1, a constant ka is selected where ~a - 10-10-5. This corresponds to:
x2 _ k.f5t3 _ ka . fa3 ~ 100 for x - 10.
The new control frequency fn will thus be reached after 100 periods and each period group x will correspond to 10 periods so that for the control frequency change ~f 10 period groups are required. Thus, the number of periods carrying the new frequency fn will increase from the first period group xl to the last period group x10 from nfn ~ 1 to nfn ~ 10, an increment of 1 in each case from period group to period group. Concomitantly the number nfO at which the starting frequency fO appears decreases in each of the period groups xl to x10 from 9 to 0 in increments of 1 from group to group.
FIG. 2 shows a frequency change for 3 control frequency increments ~f which is achieved by submultiple division of the frequency standard and a change in the divisor by 1 in each case.
In all three cases the change in the control frequency ~f is completed after 100 periods have passed whereby:
x ~ nfn + nfO - 10.
~Z~754~
1659~
If one starts with a frequency standard of 9 MHz as described, Eor the required control frequency fsr of 1200 Hz, a divisor of 7500 is required. If this divisor is varied by 1, the control frequency change ~f will be about 0.16 Hz.
According to the invention, however, this control frequency change is spread over the 10 periods of each period group and the 10 period groups so that the control frequency is adjusted in steps with 10 times more precision than could be obtained with a jump of ~f.
In earlier techniques such high precision could be obtained only by a 10-fold increase in the standard frequency with the drawbacks enumerated above.
By altering the factor k, in accordance with the invention, it is possible to change the period count within whi~h the change in control frequency ~f is competed to suit the technological requirements of the system. Of course, with a change in the proportionality factor k, there is also a change in the time within which the control frequency change will be completed. In practice this permits an inversely proportional adjustment of the rotary field frequency to the required speed of the synchronous motor.
The applications of the system of the invention are not limited to the control of synchronous motors.
The method and apparatus can be used with advantage wherever large jumps in a control frequency is disadvantageous or where perfect linearity in a response is required.
Of course, instead of a linear response, the control frequency change can be nonlinear, if desired. It is, therefore, possible to increase the number of nfn periods with the new frequency from period group to period group by increments other than unity or in a nonlinear manner.
129~S~4 The number nfn of period groups can be varied advantageously in many cases in the succession 1, 3, 6, 10 in successive period groups. The control frequency change ~f i5 then completed after only four period groups xl to x4.
The circuit shown in FIG. 1 can be used to generate intermediate frequencies over long time intervals. For example, it is possible to set the calculator units so that they will not affect changes in the numbers of the frequency packets fO and fn in each period group for l~ng periods of time and thus so that the values nfO and nfn will remain constant. The intermediate frequency at the frequency output thus has the mean control frequency value -~-st ~ l/x (nfO fO + nfn fn) For example, for a frequency standard fq 9 MHz, if it is required instead of a control frequency of 6000 Hz to have a control frequency of 5998.8 Hz, the divisor of the frequency converter la can be selected at 1500 Hz, the divisor of the frequency converter lk at 1501 and the frequency converters l_ and lb so switched that the frequency output within 10 periods will contain 7 periods (nfO _ 7) with the control frequency fO -6000 Hz and 3 periods (nfn _ 3) with a control frequency fn - 5996 Hz. In this case, an intermediate frequency of:
fst - 1/10 (7 . 6000 + 3 . 5996) - 5998.8 Hz is obtained as the desired frequency.
Claims (6)
1. A method of digital setting of a control frequency fst, comprising the steps of:
(a) dividing a standard frequency by an integer to form a first control frequency fo as a first submultiple of said standard frequency;
(b) dividing said standard frequency by another integer to form a second control frequency fn as a second submultiple of said standard frequency; and (c) mixing said first control frequency fo and said second control frequency fn so that within each period group xo of x periods of a resulting mixed signal constituting an output control frequency fst a fraction of the periods nfo is driven by the control frequency fo while a remaining fraction nfn of the periods is driven with the control frequency fn so that in each period group xo for the x periods:
x - nfn + nfo?
(a) dividing a standard frequency by an integer to form a first control frequency fo as a first submultiple of said standard frequency;
(b) dividing said standard frequency by another integer to form a second control frequency fn as a second submultiple of said standard frequency; and (c) mixing said first control frequency fo and said second control frequency fn so that within each period group xo of x periods of a resulting mixed signal constituting an output control frequency fst a fraction of the periods nfo is driven by the control frequency fo while a remaining fraction nfn of the periods is driven with the control frequency fn so that in each period group xo for the x periods:
x - nfn + nfo?
2. The method defined in claim 1, further comprising the steps of:
inducing a change in the control frequency within a period count of x2;
dividing the x2 periods into period groups x1 to xx each of x periods so that the period groups x1 to xx follow one another in succession; and increasing the fraction of the periods nfn by at least one period and decreasing the fraction of the periods nfo by at least one period from period grout to period group in said succession of x1 to xx period groups so that after the lapse of x2 peri-ods, all periods have the frequency fn.
inducing a change in the control frequency within a period count of x2;
dividing the x2 periods into period groups x1 to xx each of x periods so that the period groups x1 to xx follow one another in succession; and increasing the fraction of the periods nfn by at least one period and decreasing the fraction of the periods nfo by at least one period from period grout to period group in said succession of x1 to xx period groups so that after the lapse of x2 peri-ods, all periods have the frequency fn.
3. The method defined in claim 2 wherein the period count x2 is selected as a function of the desired control frequency fst?
4. The method defined in claim 3 wherein the period count x2 is selected so that:
x2 - k ? fst3?
wherein k is a proportionality constant.
x2 - k ? fst3?
wherein k is a proportionality constant.
5. The method defined in claim 1, further comprising the step of:
generating said standard frequency by exciting a quartz crys-tal controlled oscillator.
generating said standard frequency by exciting a quartz crys-tal controlled oscillator.
6. An apparatus for digitally generating a control frequency fst? comprising a quartz crystal controlled oscillator for generating a stan-dard frequency;
first divider means connected to said oscillator for dividing said standard frequency by an integer to form a first control frequency fo as a first submultiple of said standard frequency;
second divider means connected to said oscillator for dividing said standard frequency by another integer to form a second control fre-quency fn as a second submultiple of said standard frequency; and frequency converter means connected to said divider means for mixing said first control frequency fo and said second control frequen-cy fn so that within each period group xo of x periods of a resulting mixed signal constituting an output control frequency fst a fraction of the periods nfo is driven by the control frequency fo while a remaining fraction nfn of the periods is driven with the control frequency fn so that in each period group xo for the x periods:
x - nfn + nfo?
first divider means connected to said oscillator for dividing said standard frequency by an integer to form a first control frequency fo as a first submultiple of said standard frequency;
second divider means connected to said oscillator for dividing said standard frequency by another integer to form a second control fre-quency fn as a second submultiple of said standard frequency; and frequency converter means connected to said divider means for mixing said first control frequency fo and said second control frequen-cy fn so that within each period group xo of x periods of a resulting mixed signal constituting an output control frequency fst a fraction of the periods nfo is driven by the control frequency fo while a remaining fraction nfn of the periods is driven with the control frequency fn so that in each period group xo for the x periods:
x - nfn + nfo?
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE19873712975 DE3712975A1 (en) | 1987-04-16 | 1987-04-16 | METHOD AND CIRCUIT FOR THE DIGITAL SETTING OF A CONTROL FREQUENCY |
| DEP3712975.9 | 1987-04-16 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1297544C true CA1297544C (en) | 1992-03-17 |
Family
ID=6325791
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000564227A Expired - Lifetime CA1297544C (en) | 1987-04-16 | 1988-04-15 | Method of and apparatus for digitally setting a control frequency |
Country Status (8)
| Country | Link |
|---|---|
| US (1) | US4851783A (en) |
| EP (1) | EP0287053B1 (en) |
| JP (1) | JP2598078B2 (en) |
| AT (1) | ATE74697T1 (en) |
| AU (1) | AU606675B2 (en) |
| CA (1) | CA1297544C (en) |
| DE (2) | DE3712975A1 (en) |
| RU (1) | RU1838875C (en) |
Families Citing this family (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| NL8800697A (en) * | 1988-03-21 | 1989-10-16 | Philips Nv | TRACTOR SYSTEM AND OSCILLOSCOPE FITTED WITH A TRACTOR SYSTEM. |
| DE3939974A1 (en) * | 1989-12-02 | 1991-06-06 | Alexander Wunsch | DEVICE FOR BRAINWAVE STIMULATION |
| US5048065A (en) * | 1990-03-12 | 1991-09-10 | Westinghouse Electric Corp. | Method and circuit for controlling the frequency of an electronic inverter |
| US5065408A (en) * | 1990-04-26 | 1991-11-12 | Motorola, Inc. | Fractional-division synthesizer for a voice/data communications systems |
| US5422584A (en) * | 1992-09-30 | 1995-06-06 | The United States Of America As Represented By The Secretary Of The Navy | Variable phase sine wave generator for active phased arrays |
| US5425074A (en) * | 1993-12-17 | 1995-06-13 | Intel Corporation | Fast programmable/resettable CMOS Johnson counters |
Family Cites Families (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR2286564A1 (en) * | 1974-09-30 | 1976-04-23 | Roche Bernard | MULTIFREQUENCY SIGNAL SYNTHESIZER DEVICE |
| DE2539692C2 (en) * | 1975-09-06 | 1983-07-21 | Robert Bosch Gmbh, 7000 Stuttgart | Digital process for generating signal voltages and arrangement for carrying out the process |
| US4075544A (en) * | 1976-10-27 | 1978-02-21 | The Superior Electric Company | Linear velocity change stepping motor circuit |
| US4325031A (en) * | 1980-02-13 | 1982-04-13 | Motorola, Inc. | Divider with dual modulus prescaler for phase locked loop frequency synthesizer |
| US4516085A (en) * | 1982-08-02 | 1985-05-07 | Hughes Aircraft Company | Microwave frequency synthesizer using plural switchable low noise oscillators |
| US4658406A (en) * | 1985-08-12 | 1987-04-14 | Andreas Pappas | Digital frequency divider or synthesizer and applications thereof |
-
1987
- 1987-04-16 DE DE19873712975 patent/DE3712975A1/en active Granted
-
1988
- 1988-04-08 RU SU884355497A patent/RU1838875C/en active
- 1988-04-13 EP EP88105864A patent/EP0287053B1/en not_active Expired - Lifetime
- 1988-04-13 DE DE8888105864T patent/DE3869816D1/en not_active Expired - Lifetime
- 1988-04-13 AT AT88105864T patent/ATE74697T1/en not_active IP Right Cessation
- 1988-04-14 AU AU14614/88A patent/AU606675B2/en not_active Ceased
- 1988-04-15 US US07/181,974 patent/US4851783A/en not_active Expired - Lifetime
- 1988-04-15 CA CA000564227A patent/CA1297544C/en not_active Expired - Lifetime
- 1988-04-15 JP JP63091870A patent/JP2598078B2/en not_active Expired - Lifetime
Also Published As
| Publication number | Publication date |
|---|---|
| AU606675B2 (en) | 1991-02-14 |
| DE3869816D1 (en) | 1992-05-14 |
| EP0287053A2 (en) | 1988-10-19 |
| RU1838875C (en) | 1993-08-30 |
| DE3712975C2 (en) | 1990-09-27 |
| ATE74697T1 (en) | 1992-04-15 |
| DE3712975A1 (en) | 1988-11-03 |
| US4851783A (en) | 1989-07-25 |
| AU1461488A (en) | 1988-10-20 |
| EP0287053B1 (en) | 1992-04-08 |
| JPS63280510A (en) | 1988-11-17 |
| EP0287053A3 (en) | 1990-05-09 |
| JP2598078B2 (en) | 1997-04-09 |
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