[0001] This invention relates to a method and to a control system for attenuating by means
of a counter disturbance an initial periodic disturbance in a physical system according
to the introductory parts of claims 1 and 9.
[0002] The principle of reducing unwanted disturbance by generating a disturbance with the
opposite phase is well documented. The technique is often referred to as active control
to distinguish from passiv control where the elements of the system are incapable
of generating disturbances.
[0003] EP-A 0 465 174 discloses an adpative active noise cancelation apparatus in which
the signal of a first sensor element for picking up vibrations on a noise source is
passed through a signal processor to a speaker means for generating a counter-disturbance.
This counter-disturbance cancels an original disturbance at a second sensing means
used for detecting a residual disturbance. The output of the second sensing means
is connected to a delay means and an inverse filter means for feeding an adaptive
controller used to adapt the signal processor. In case of successfull adaptation thereof,
the signal of the first sensor element is processed in a way that effectively no residual
disturbance is detected by this second sensing means.
[0004] Nelson and Elliot review some of the work done to date in: "
Active Control of Sound", Academic Press (1992).
[0005] The earliest technique in this field was done by P. Lueg who described an actuator
and sensor coupled by a simple negative feedback loop in U.S. Patent 2.034.416.
[0006] The main shortcoming of this system is that the disturbance can only be reduced over
a limited range of low frequencies. This is because of the finite response time of
the control system (the time taken for a signal sent to the actuator to cause a response
of the sensor). The control loop cannot compensate for the phase shifts associated
with this delay, and so only operates at low frequencies where the phase shifts are
small. The gain of the feedback loop must be low at other frequencies to maintain
the stability of the system. This is achieved by incorporating a low pass filter into
the loop - which introduces additional delay.
[0007] The range of applicability of active control systems has been extended by the use
of more modern adaptive control techniques such as those described by B. Widrow and
S.D. Stearns in "
Adaptive Signal Processing", Prentice Hall (1985). In U.S. Patent No. 5,105,377, Ziegler achieves feedback system
stability by use of a compensation filter but the digital filter must still try to
compensate for the phase characteristics of the system. This is not possible in general,
but when the disturbance has a limited frequency bandwidth the digital filter can
be adapted to have approximately the right phase characteristic at the frequencies
of interest. The filter characteristic therefore depends on the disturbance as well
as the system to be controlled and must be changed as the noise changes.
[0008] One class of disturbances for which this approach can be successful is periodic disturbances.
These are characterized by a fundamental period, a time over which the disturbance
repeats itself. Disturbances are not often exactly periodic, but any disturbance where
the period changes over a timescale longer than that over which the disturbance itself
changes can be included in this class.
[0009] Several approaches have been put forth for controlling periodic disturbances including
that described by C. Ross in U.S. Patent No. 4,480,333. The patent describes a feedforward
control system in which a tachometer signal is fed through an adaptive digital filter.
There is no description of the form of the tachometer signal but it contains no information
on the amplitude of the disturbance to be controlled and thus the filter must again
be adapted in response to the disturbance. Chaplin et al, in U.S. Patent 4,153,815,
describe the method of wave form synthesis, where a model of one cycle of the desired
control signal is stored and then sent repetitively to the actuator. Nelson and Elliot,
infra, describe the equivalence of these two approaches in the special case where
the period remains constant.
[0010] In U.S. Patent 4,490,841, Chaplin et al recognize the benefit of splitting the stored
waveform into its frequency components. The advantage of this step is that each frequency
component can be adapted independently. This can improve the ability of the system
to adapt to rapidly changing disturbances and can reduce the computational requirements
associated with this adaption. Others have recognized this technique such as Swinbanks
in U.S. Patent No. 4.423.289 which describes the use of Frequency Sampling Filters
and the equivalence of time or frequency domain weights.
[0011] In all of the above systems the filters have to be adjusted to cope with changing
disturbances. This requires processing power and so adds costs to the control system.
In addition, all of the systems above become increasingly complicated as the number
of harmonics in the disturbance increase. This is a problem for disturbances which
are impulsive in nature - such as the sound from the exhaust or inlet of an internal
combustion engine.
[0012] Accordingly it is an object of this invention to provide a control system for periodic
disturbances that requires little or no adaption.
[0013] Another object of this invention is to provide a control system based in the time
domain for canceling periodic disturbances.
[0014] A further object of this invention is to provide a unique system for controlling
the cancellation of periodic disturbances wherein the amount of computation required
does not increase with the number of harmonics to be controlled.
[0015] These objects are achieved as a method by claim 1 and as a control system by claim
9 where use is made of a delayed inverse filter, a variable delay and, optionally,
a comb filter.
[0016] Unlike previous systems, little or no adaption is required and, since the system
is based in the time domain rather than the frequency domain, the computation required
does not increase with the number of harmonics to be controlled.
[0017] The control system has many applications including the active control of sound and
vibration and the selective removal of periodic noise in communications signals.
[0018] The invention will become apparent when reference is had to the drawings in which
- Fig. 1
- is a diagrammatic view of the basic control system,
- Fig. 2
- is a diagrammatic view of a recursive comb filter,
- Fig. 3
- is a diagrammatic view of a comb filter configuration,
- Fig. 4
- is a diagrammatic view of a control system,
- Fig. 5
- is a diagrammatic view of a combined system,
- Fig. 6
- is a diagrammatic view of the adaptation of a delayed inverse filter,
- Fig. 7
- is a diagrammatic view of the identification of model filter A,
- Fig. 8
- is a view of an off-line adaption of delayed inverse,
- Fig. 9
- is a diagrammatic view of a system with on-line identification,
- Fig. 10
- is a diagrammatic view of an in-wire noise cancellation system,
- Fig. 11
- is a diagrammatic view of a multi-channel system, and
- Fig. 12
- is a time analysis of a sampled signal.
[0019] The invention allows for cancellation of periodic disturbances and has the following
major advantages:
1) The filter is determined by the system to be controlled and so does not have to
be adapted to cope with changing disturbances.
2) The filter operates in the time domain, relying only on the periodicity of the
noise, and so the computational requirements are independent of the number of harmonic
components in the disturbance.
[0020] By way of explanation a single channel digital control system will be described first.
[0021] The basic control system shown in Fig. 1 consists of feedback loop comprising an
error sensor (1), signal conditioning (2), analog to digital converter (ADC) (3) (only
required if digital filters are to be used), compensation filter (4), a 'delayed inverse'
filter (5), a delay line (6) with delay τ -mT, digital - to analog converter (DAC)(7)
(only required if digital filters are to be used), signal conditioning (8), and actuator
(9).
[0022] The additional delay is chosen so that the modeling delay and the additional delay
is a whole number of noise cycles. If the cycle length τ is not known in advance,
or it is subject to variations, the delay must be varied as the period of the noise
varies. The period can be measured from the noise itself or from a sensor, such as
an accelerometer or tachometer, responsive to the frequency of the source of the noise.
[0023] The part of the system from the controller output to the controller input is referred
to as the plant. It includes the elements 6, 7, 8, 9, 1, 2, 3 in figure 1 as well
as the response of the physical system.
[0024] The modeling delay is determined by the
system to be controlled, and typically must be greater than the delay through the plant.
It is implemented by the delayed inverse filter 5.
[0025] The additional delay is determined by the modeling delay and the funtamental period of the
noise (disturbance). It is implemented by the delay line 6.
[0026] Unlike previous control systems, the filter does not need to vary with the noise.
[0027] For a sampling period T, the sampled error signal e(nT) is given by
where * denotes a convolution defined by
and where y(nT) is the signal due to the uncanceled disturbance, A(kT) is the response
at error sensor at time
due to a unit impulse sent to the actuator at time t=0, and x is the controller output.
[0028] For electrical disturbances the signal y is available, for other applications the
signal y can be estimated by subtracting the predicted effect of the controller from
the error signal,
provided that the response, A, is known.
[0029] The ideal output, x, can be obtained by passing the signal y through a filter F,
and inverting, so that
The filter F is the inverse of A, which in digital form is defined by
Unfortunately, the filter F cannot be realized since it must compensate for the delay
in the response A.
However, it is often possible to realize a filter B which is the
delayed inverse of A with a phase inversion. B is defined by
where mT is referred to as the modeling delay.
We can define a filter D(t) which corresponds to a pure delay of time t. Equation
(6) can then be written more compactly as
A periodic disturbance is changed very little by delaying it by one noise cycle,
so, for a disturbance with period τ, we have
or, equivalently,
The control system utilizes this property of the disturbance.
[0030] In one form of the control system, the filter is obtained by combining the filter
B and a filter D(τ-mT) in series. The actuator drive signal is obtained by passing
the signal y(t), obtained using equation (3), through this combined filter. The response
at the sensor is
Using the definition (7), it can be seen that the combination A*B*D is equivalent
of a pure delay of time τ, hence the residual disturbance is
For periodic signals, which satisfy (9), this residual disturbance is small.
[0031] If the modeling delay is greater than one period, τ in equation 10 and the systems
described below must be replaced by an integer multiple of the period, Nτ, such that
Nτ > mT.
[0032] Fig.4 shows a control system in which the compensation filter can be avoided. In
this form, the actuator drive signal is obtained by passing the error signal e(t)
through the delayed inverse filter B and the delay line D(τ-mT) and then through an
additional gain K. (Note that the order of these elements can be interchanged). The
response at the sensor is
The combination A*B*D is equivalent to a pure delay τ, hence
If the error signal is periodic with period τ, (13) can be rearranged to give
Hence the disturbance is reduced by a factor 1+K.
[0033] Disturbances with other periods (other frequencies) may not be reduced and could
cause the system to become unstable. This can be avoided by filtering out disturbances
which do not have a fundamental period τ.
[0034] One way of doing this is to use a 'comb filter, which can be positioned at any point
in the feedback loop. One example of a comb filter is a positive feedback loop with
a one cycle delay around the loop and a loop gain, α, of less than unity. This is
shown in Figure 2. Another example is a feedforward loop with a delay of 1/2 cycle
in one of the paths as shown in Figure 3.
[0035] The full control system is shown in Figure 4. The delay and the comb filter have
been combined in this example, so that only a single variable delay is required. The
output from the controller is
[0036] In the first form of the control system, shown in Figure 1, the estimate of the uncanceled
signal, y, is obtained using equation (3). This signal is then passed through the
filter B to give a signal B*y. This requires the calculation of two convolutions.
However, using the relation
it can be seen that the signal B*y can be calculated via a single convolution and
a delay. This require less computation.
[0037] The output from the controller is
which is very similar to equation (15), since the compensation filter appears as
a comb filter. Formally, the two equations are the same in the limit as
a tends to one with
[0038] If an additional comb filter is added to the controller in equation (17), the comb
filter and the feedback compensation can be combined. The controller output is then
[0039] The resulting control system is shown in Figure 5. In this form of the control system
the parameter
a determines the degree of selectivity of the controller,
a=0 being the least selective and the selectivity increasing as
a increases.
[0040] There are many known ways of implementing the required delays. One example, which
can be used when the sampling frequency is high compared to highest frequency of the
disturbance, is to use a digital filter with only two non-zero coefficients. For a
delay
which is not a whole number of sampling periods, this is equivalent to writing
This can be implemented as digital filter with n-th coefficient 1-δ and (n+1)-th
coefficient δ.
[0041] Other ways of implementing the required delays include analog and digital delay lines
and full digital filters.
[0042] The inclusion of a comb filter avoids amplification of the disturbance at non-harmonic
frequencies, and also makes the control system selective.
[0043] A comb filter can be included in either form of the control system. In the first
form it is only required when selectivity is required, since stability is obtained
by use of the compensation filter. In the second form, the filter is necessary to
stabilize the feedback loop.
[0044] There are well known methods for obtaining the delayed inverse filter. Some of these
are described by Widrow and Stearns. An example is shown in Figure 6. A test signal
is passed through an adaptive filter and then sent to the actuator. The response from
the sensor is added to a delayed version of the test signal and any difference is
used to adapt the filter. When the filter adaption is complete, the filter will be
an approximation to the required filter B, which is a delayed inverse of the system
with a phase inversion. The filter can be a combination of finite impulse response
filter and a recursive filter.
[0045] It is not always possible to obtain a delayed inverse of the system. This happens,
for example, when the system cannot be modeled as minimum phase system plus a delay.
There are ways of overcoming this problem, one way is to use an extra filter and actuator.
This technique is well known in the field of audio processing, where compensation
for room acoustics is required, see Miyoshi et al in "Inverse Filtering of Room Acoustics",
IEEE Trans Acoustics Speech and Signal Processing, ASSP-36, 145-152 (1988). For application
of active control in aircraft and automobile cabins for example, where the reverberation
of the cabin make a single channel system difficult to implement, it is likely that
multichannel versions of the control system will be used.
[0046] For the first form of the control system, shown in Figure 1, the forward filter,
A, is also required. Again, there are well known techniques for identifying a model
of A which are e.g. disclosed in "adaptive signal processing" by Bernard Widrow and
Samuel D. Stearns Prentice-Hall Inc., chapter 9. One example is shown in Figure 7.
A test signal is sent to the actuator and through an adaptive filter. The response
at the sensor is compared to the output of the adaptive filter and any difference
is used to adapt the filter.
[0047] Once the filter A is known, the filter B can be determined as in Figure 8. This is
equivalent to Figure 6 except that the actual system has been replaced by the model
of the system. Alternatively, the filter B can be calculated using Wiener Filtering
Theory. This approach is useful when the frequency bandwidth of the noise is limited,
or when an exact inverse is not achievable (because of finite filter length or non-minimum
phase effects).
[0048] In some applications, the system response may change slowly over time. In these applications
it is necessary to change the filters A and B.
[0049] One way of doing this is to turn off the control system and remeasure the responses.
Alternatively, there are some well known techniques for identifying A 'on-line', i.e.
while the control system is still in operation. For example, a low-level test signal
can be added to the controller output. The difference between the actual response
and the predicted response can be used to adapt the model of A, provided that the
test signal is uncorrelated with the original noise.
[0050] The filter B may then be updated 'off-line' using the model of A, as in Figure 8.
[0051] An example of a complete control system, including on-line system identification,
is shown in Figure 9.
[0052] Alternatively, the filter B can itself be treated as an adaptive filter. There are
many methods for performing the adaption as described in the Widrow publication, for
example, one way is the 'filtered-input LMS' algorithm. In this approach the input
to the filter is passed through a model of the response of the rest of the system
(including the variable delay and comb filter if present) and then correlated with
the error signal to determine the required change to the filter. This will only provide
information at frequencies which are harmonic multiples of the fundamental frequency
of the noise. However, in some applications, there are more harmonics in the noise
than there are coefficients in the filter. In these cases there is sufficient information
to update all of the coefficients.
[0053] In some applications, the disturbance is in an electrical signal, such as a communication
signal. In this case the system response is typically a pure delay (plus some gain
factor). The delayed inverse filter, B, is then also a pure delay, and the whole system
consists just of a fixed delay and a variable delay as shown in Figure 10.
[0054] The extension of the system to multiple interacting channels will be obvious to those
skilled in the art. An example of a multichannel system with three inputs and two
outputs is shown in Figure 11. One inverse filter, B
ij, is required for each pair of interacting sensor and actuator, whereas only one comb
filter (or variable delay unit) is required for each output channel (CF1 and CF2 in
the figure). The comb filters could be applied to the input channels instead, but
often there are more inputs than outputs in which case this would result in a more
complex control system.
[0055] The input to the i-th comb filter is
where
ej is the signal from the j-th sensor and
Bij is the appropriate inverse filter.
[0056] The output from the i-th channel is
The filters A
ij which model the system response can be found in the same way as the single channel
filters by driving the output channels in turn with a test signal. Alternatively,
all of the channels can be driven simultaneously with independent (uncorrelated) signals.
[0057] Once the filters A
ij have been identified, there are a variety of ways in which the filters B
ij can be obtained. These include time domain approaches, such as Weiner filtering,
and frequency domain approaches.
[0058] Alternatively, the filters B
ij can be obtained directly by adaptive filtering using the multichannel Least Mean
Square algorithm, for example.
[0059] The other single channel systems described above can also be implemented as multichannel
systems.
Reduction to practice
[0060] The effectiveness of the control system has been demonstrated on the selective filtering
of a periodic noise from a communications signal. In this example the communications
microphone is in the vicinity of a loud periodic noise source and, untreated, the
speech cannot be herd above the noise. The time trace of the untreated signal is shown
in the upper plot in Figure 12.
[0061] The treated signal is shown in the lower plot, and the speech signal can be clearly
seen (and heard) above the reduced noise level. The noise level decays exponentially
when the system is first turned on since the canceling signal must pass around the
control loop several times for the response to build up.
1. Method for attenuating by means of a counter disturbance an initial periodic disturbance
in a physical system utilizing a control system comprising the steps of:
- generating the counter disturbance by one or more actuator means (9) in response
to a control signal (x(t)) produced by a control circuit,
- sensing a residual disturbance within said physical system by one or more sensor
means (1) whereas the residual disturbance is defined as being a combination of the
initial disturbance and the counter disturbance to produce an error signal (e(t))
related to the residual disturbance,
- passing the error signal (e(t)) or a first signal (y(t)) derived from the error
signal (e(t)) through an inverse filter means (5) and a first delay means (6) coupled
together in a series arrangement,
characterized in that
- the inverse filter means (5) outputs a signal having a fixed modeling delay representative
of an inverse modeling delay of the physical system and
- the first delay means (6) outputs a signal with a delay time which is adjusted to
the period of the initial periodic disturbance and the fixed modeling delay such that
the sum of the fixed modeling delay and the delay time is equal to a whole number
multiple of the period of said initial periodic disturbance.
2. A method as in claim 1, characterized in that
it comprises passing the error signal (e(t)) or the first signal (y(t)) derived from
the error signal (e(t)) first through the inverse filter means (5) and then subsequently
through the first delay means (6).
3. A method as in claim 1 or 2, characterized in that
an additional step of measuring a fundamental period of the initial periodic disturbance
and of varying the delay time of the first delay means (6) based on the fundamental
period of the initial periodic disturbance is included.
4. A method as in claim 3, characterized in that
said measuring is done on the error signal (e(t)) or the first signal y(t)) derived
from the error signal (e(t)).
5. A method as in claim 3, characterized in that
said measuring is done from an additional frequency signal.
6. A method as in one the claims 1 to 5, characterized in that said method comprises
passing the control signal (x(t)) through a feedback compensation filter means (4)
and subracting its output from the error signal (e(t)) to provide said first signal
(y(t)) derived from the error signal (e(t)) said first signal (y(t)) being representative
of the initial disturbance.
7. A method as in one of the claims 1 to 5, characterized in that
said method comprises passing the error signal (e(t)) through a comb filter means
located before or after the inverse filter means (5) to only control those disturbances
with a chosen fundamental period.
8. A method as in claim 7, characterized in that
the step of signal filtering in the comb filter is combined with a step of amplifying
or attenuating by a gain means (12).
9. Control system for attenuating by means of a counter disturbance an inital periodic
disturbance in a physical system comprising:
- means for generating the counter disturbance by one or more actuator means (9) in
response to a control signal (x(t)) produced by a control circuit,
- means (1) for sensing a residual disturbance within said physical system whereas
the residual disturbance is defined as being a combination of the initial disturbance
and the counter disturbance and for producing an error signal (e(t)) related to the
residual disturbance,
- a control circuit whose input is fed by the error signal comprising an inverse filter
means (5) and a first delay means (6) coupled together in a series arrangement through
which the error signal (e(t)) or a first signal (y(t)) derived from the error signal
(e(t)) is passed,
characterized in that
- the inverse filter means (5) includes means for outputting a signal having a fixed
modeling delay representative of an inverse modeling delay of the physical system
and
- the first delay means (6) includes means for outputting a signal with a delay time
which is adjusted to the period of the initial periodic disturbance and the fixed
modeling delay such that the sum of the fixed modeling delay and the delay time is
equal to a whole number multiple of the period of said initial periodic disturbance.
10. A system as in claim 9,
characterized in that it includes adjustment means for said first delay means (6)
so as to vary the delay time thereof to make the sum of the fixed modeling delay of
the inverse filter means (5) and the delay time of the first delay means (6) equal
to a whole number multiple of said initial periodic disturbance.
11. A system as in claim 9 or 10, characterized in that
it includes means for measuring a fundamental period of the initial periodic disturbance
for varying the delay time of the first delay means (6) based on said fundamental
period.
12. A system as in claim 11, characterized in that
said measuring means for measuring a fundamental period of the initial periodic disturbance
is adapted to use the error signal (e(t)) or the first signal (y(t)) derived from
the error signal (e(t)).
13. A system as in claim 11,
characterized in that said measuring means is adapted to use an additional frequency
signal.
14. A system as in one of the claims 9 to 13, characterized in that
a feedback compensation filter means (4) is provided through which a feedback signal
is passed and subtracting means are provided for subtracting the output of the feedback
compensation filter means (4) from the error signal (e(t)) to provide said first signal
(y(t)) being representative of the initial disturbance.
15. A system as in one of the claims 9 to 13, characterized in that
a comb filter means located before or after the inverse filter means (5) is provided
through which the error signal (e(t)) is passed for controlling only those disturbances
with a chosen fundamental period.
16. A system as in claim 15, characterized in that
an adjustable gain means (12) adapted to amplify or attenuate is provided whereby
the comb filter means is combined with said adjustable gain means (12).
1. Verfahren zur Reduktion einer periodischen Anfangs-Störung in einem physikalischen
System mittels einer Gegen-Störung unter Einstatz eines Steuer- und Regelsystems mit
den Schritten des:
- Erzeugens der Gegen-Störung durch ein oder mehrere Geber-Mittel (9) aufgrund eines
Steuer-Signals (x(t)), das mittels eines Schaltkreises erzeugt wird,
- Erfassens einer Rest-Störung in dem physikalischen System durch ein oder mehrere
Sensor-Mittel (1), wobei die Rest-Störung als Überlagerung der Anfangs-Störung und
der Gegen-Störung definiert ist, um ein Fehler-Signal (e(t)) zu erzeugen, das mit
der Rest-Störung verknüpft ist,
- Führens des Fehler-Signals (e(t)) oder eines ersten Signales (y(t)), welches von
dem Fehler-Signal (e(t)) abgeleitet ist, durch ein inverses Filter-Mittel (5) und
ein erstes Verzögerungs-Mittel (6), die in serieller Anordnung aneinander gekoppelt
sind,
dadurch gekennzeichnet, daß
- das inverse Filter-Mittel (5) ein Signal mit einer festen Modellverzögerung ausgibt,
die für eine inverse Modellverzögerung des physikalischen Systems repräsentativ ist,
und
- das erste Verzögerungsmittel (6) ein Signal mit einer Verzögerungszeit ausgibt,
das an die Periode der ursprünglichen periodischen Führung und die feste Modellverzögerung
angepaßt ist, so daß die Summe der festen Modellverzögerung und der Verzögerungszeit
gleich einem ganzzahligen Vielfachen der Periode der ursprünglichen periodischen Störung
ist.
2. Verfahren nach Anspruch 1, dadurch gekennzeichnet, daß es das Führen des Fehler-Signales
(e(t)) oder des ersten Signales (y(t)), das von dem Fehler-Signal (e(t)) abgeleitet
ist, durch zunächst das inverse Filter-Mittel (5) und dann darauffolgend durch das
erste Verzögerungs-Mittel (6) umfaßt.
3. Verfahren nach Anspruch 1 oder 2, dadurch gekennzeichnet, daß ein zusätzlicher Schritt
des Messens einer Fundamentalperiode der ursprünglichen periodischen Störung und,
basierend auf der Fundamentalperiode der ursprünglichen periodischen Störung, des
Variierens der Verzögerungszeit des ersten Verzögerungs-Mittels (6) enthalten ist.
4. Verfahren nach Anspruch 3, dadurch gekennzeichnet, daß das Messen an dem Fehler-Signal
(e(t)) oder dem ersten Signal (y(t)) durchgeführt wird, das von dem Fehler-Signal
(e(t)) abgeleitet ist.
5. Verfahren nach Anspruch 3, dadurch gekennzeichnet, daß das Messen an einem zusätzlichen
Frequenz-Signal durchgeführt wird.
6. Verfahren nach einem der Ansprüche 1 bis 5, dadurch gekennzeichnet, daß das Verfahren
das Führen des Steuer-Signales (x(t)) durch ein Rückkopplungskompensation-Filter-Mittel
(4) und das Subtrahieren seines Ausgangs von dem Fehler-Signal (e(t)) umfaßt, um das
erste Signal (y(t)) bereitzustellen, das von dem Fehler-Signal (e(t)) abgeleitet ist,
wobei das erste Signal (y(t)) für die ursprüngliche Störung repräsentativ ist.
7. Verfahren nach einem der Ansprüche 1 bis 5, dadurch gekennzeichnet, daß das Verfahren
das Führen des Fehler-Signales (e(t)) durch ein Kamm-Filter-Mittel umfaßt, welches
vor oder nach dem inversen Filter-Mittel (5) angeordnet ist, um lediglich die Störungen
mit einer ausgewählten Fundamentalperiode zu regeln.
8. Verfahren nach Anspruch 7, dadurch gekennzeichnet, daß der Schritt des Signal-Filterns
in dem Kamm-Filter mit einem Schritt des Verstärkens oder Abschwächens über ein Verstärker-Mittel
(12) kombiniert ist.
9. Steuer- und Regelsystem zur Reduktion einer ursprünglichen periodischen Störung in
einem physikalischen System mittels einer Gegen-Störung mit:
- Mitteln zum Erzeugen der Gegen-Störung auf ein Steuer-Signal (x(t)) hin, das mit
einem Schaltkreis erzeugt ist, durch ein oder mehrere Geber-Mittel (9),
- Mitteln (1) zum Erfassen einer Rest-Störung in dem physikalischen System, wobei
die Rest-Störung als eine Kombination der ursprünglichen Störung und der Gegen-Störung
definiert ist und zum Zwecke des Erzeugens eines Fehler-Signales (e(t)) mit der Rest-Störung
verknüpft ist,
- einem Schaltkreis, dessen Eingang mit dem Fehler-Signal gespeist ist, der ein inverses
Filter-Mittel (5) und ein erstes Verzögerungs-Mittel (6) enthält, die in serieller
Anordnung zusammengekoppelt sind, durch die das Fehler-Signal (e(t)) oder ein erstes
Signal (y(t)), das von dem Fehler-Signal (e(t)) abgeleitet ist, geführt ist,
dadurch gekennzeichnet, daß
- das inverse Filter-Mittel (5) Mittel zum Ausgeben eines Signales enthält, die eine
feste Modellverzögerung haben, die für eine inverse Modellverzögerung des physikalischen
Systems repräsentativ ist, und
- das erste Verzögerungs-Mittel (6) Mittel zum Ausgeben eines Signales mit einer Verzögerungszeit
enthält, die an die Periode der ursprünglichen periodischen Störung und die feste
Modellverzögerung angepaßt ist, so daß die Summe aus der festen Modellverzögerung
und der Verzögerungszeit gleich einem ganzzahligen Vielfachen der Periode der ursprünglichen
periodischen Störung ist.
10. System nach Anspruch 9, dadurch gekennzeichnet, daß es Einstell-Mittel für das erste
Verzögerungs-Mittel (6) aufweist, um dessen Verzögerungszeit zu variieren, um die
Summe der festen Modellverzögerung des inversen Filter-Mittels (5) und der Verzögerungszeit
des ersten Verzögerungs-Mittels (6) einem ganzzahligen Vielfachen dieser ursprünglichen
periodischen Störung gleichzusetzen.
11. System nach Anspruch 9 oder 10, dadurch gekennzeichnet, daß es Mittel zum Messen einer
Fundamentalperiode der ursprünglichen periodischen Störung enthält, um die Verzögerungszeit
des ersten Verzögerungs-Mittels (6) entsprechend dieser Fundamentalperiode zu variieren.
12. System nach Anspruch 11, dadurch gekennzeichnet, daß das Meß-Mittel zum Messen einer
Fundamentalperiode der ursprünglichen periodischen Störung so ausgelegt ist, daß es
das Fehler-Signal (e(t)) oder das erste Signal (y(t)), das von dem Fehler-Signal (e(t))
abgeleitet ist, verwenden kann.
13. System nach Anspruch 11, dadurch gekennzeichnet, daß das Meß-Mittel für das Verwenden
eines zusätzlichen Frequenz-Signales ausgelegt ist.
14. System nach einem der Ansprüche 9 bis 13, dadurch gekennzeichnet, daß ein Rückkopplungskompensation-Filter-Mittel
(4) vorgesehen ist, durch das ein Rückkopplungs-Signal geführt ist, und Subtrahier-Mittel
vorgesehen sind, um das Ausgangs-Signal des Rückkopplungskompensation-Filter-Mittels
(4) von dem Fehler-Signal (e(t)) zu subtrahieren, um das erste Signal (y(t)) bereitzustellen,
das für die ursprüngliche Störung repräsentativ ist.
15. System nach einem der Ansprüche 9 bis 13, dadurch gekennzeichnet, daß ein Kamm-Filter-Mittel
vorgesehen ist, das vor oder nach dem inversen Filter-Mittel (5) angeordnet ist, durch
das das Fehler-Signal (e(t)) geführt ist, um lediglich die Störungen mit einer ausgewählten
Fundamentalperiode zu regeln.
16. System nach Anspruch 15, dadurch gekennzeichnet, daß ein einstellbares Verstärker-Mittel
(12) vorgesehen ist, das sich zum Verstärken oder Bedämpfen eignet, wobei das Kamm-Filter-Mittel
mit diesem einstellbaren Verstärker-Mittel (12) kombiniert ist.
1. Procédé d'atténuation au moyen d'une contre-perturbation d'une perturbation périodique
initiale dans un système physique utilisant un système de commande, comprenant les
étapes consistant à :
- générer la contre-perturbation grâce à un ou plusieurs moyens d'actionneurs (9)
en réponse à un signal de commande (x(t)) produit par un circuit de commande,
- détecter une perturbation résiduelle à l'intérieur dudit système physique grâce
à un ou plusieurs moyens de capteurs (1) alors que la perturbation résiduelle est
définie comme étant une combinaison de la perturbation initiale et de la contre-perturbation
afin de produire un signal d'erreur (e(t)) associé à la perturbation résiduelle,
- transmettre le signal d'erreur (e(t)) ou bien un premier signal (y(t)) obtenu à
partir du signal d'erreur (e(t)) par l'intermédiaire d'un moyen de filtre inverse
(5) et d'un premier moyen de retard (6) reliés ensemble suivant un agencement en série,
caractérisé en ce que
- le moyen de filtre inverse (5) fournit en sortie un signal présentant un retard
de modélisation fixe représentatif d'un retard de modélisation inverse du système
physique et
- le premier moyen de retard (6) fournit en sortie un signal avec un temps de retard
qui est ajusté sur la période de la perturbation périodique initiale et le retard
de modélisation fixe
de sorte que la somme du retard de modélisation fixe et du temps de retard est égale
à un nombre entier multiple de la période de ladite perturbation périodique initiale.
2. Procédé selon la revendication 1, caractérisé en ce qu'il comprend la transmission
du signal d'erreur (e(t)) ou bien du premier signal (y(t)) obtenu à partir du signal
d'erreur (e(t)), tout d'abord par l'intermédiaire du moyen de filtre inverse (5) et
puis ensuite par l'intermédiaire du premier moyen de retard (6).
3. Procédé selon la revendication 1 ou 2, caractérisé en ce qu'une étape supplémentaire
consistant à mesurer une période fondamentale de la perturbation périodique initiale
et à faire varier le temps de retard du premier moyen de retard (6) sur la base de
la période fondamentale de la perturbation périodique initiale, est incluse.
4. Procédé selon la revendication 3, caractérisé en ce que ladite mesure est effectuée
sur le signal d'erreur (e(t)) ou bien sur le premier signal (y(t)) obtenu à partir
du signal d'erreur (e(t)).
5. Procédé selon la revendication 3, caractérisé en ce que ladite mesure est effectuée
à partir d'un signal de fréquence supplémentaire.
6. Procédé selon l'une des revendications 1 à 5, caractérisé en ce que ledit procédé
comprend la transmission du signal de commande (x(t)) par l'intermédiaire d'un moyen
de filtre de compensation de contre-réaction (4) et la soustraction de sa sortie du
signal d'erreur (e(t)) afin de fournir ledit premier signal (y(t)) obtenu à partir
du signal d'erreur (e(t)), ledit premier signal (y(t)) étant représentatif de la perturbation
initiale.
7. Procédé selon l'une des revendications 1 à 5, caractérisé en ce que
ledit procédé comprend la transmission du signal d'erreur (e(t)) par l'intermédiaire
d'un moyen de filtre en peigne situé avant ou après le moyen de filtre inverse (5)
afin de commander uniquement ces perturbations qui présentent une période fondamentale
choisie.
8. Procédé selon la revendication 7, caractérisé en ce que l'étape de filtrage du signal
dans le filtre en peigne est combinée à une étape d'amplification ou d'atténuation
par un moyen de gain (12).
9. Système de commande destiné à atténuer au moyen d'une contre-perturbation, une perturbation
périodique initiale dans un système physique comprenant :
- un moyen destiné à générer la contre-perturbation grâce à un ou plusieurs moyens
d'actionneurs (9) en réponse à un signal de commande (x(t)) produit par un circuit
de commande,
- un moyen (1) destiné à détecter une perturbation résiduelle à l'intérieur dudit
système physique, alors que la perturbation résiduelle est définie comme étant une
combinaison de la perturbation initiale et de la contre-perturbation et destiné à
produire un signal d'erreur (e(t)) associé à la perturbation résiduelle,
- un circuit de commande dont l'entrée reçoit le signal d'erreur comprenant un moyen
de filtre inverse (5) et un premier moyen de retard (6) reliés ensemble suivant un
agencement en série par l'intermédiaire duquel le signal d'erreur (e(t)) ou bien un
premier signal (y(t)) obtenu à partir du signal d'erreur (e(t)), est transmis,
caractérisé en ce que
- le moyen de filtre inverse (5) comprend un moyen destiné à fournir en sortie un
signal présentant un retard de modélisation fixe représentatif d'un retard de modélisation
inverse du système physique et
- le premier moyen de retard (6) comprend un moyen destiné à fournir en sortie un
signal avec un temps de retard qui est ajusté sur la période de la perturbation périodique
initiale et le retard de modélisation fixe de sorte que la somme du retard de modélisation
fixe et du temps de retard est égale à un nombre entier multiple de la période de
ladite perturbation périodique initiale.
10. Système selon la revendication 9,
caractérisé en ce qu'il comprend un moyen d'ajustement destiné audit premier moyen
de retard (6) de façon à faire varier le temps de retard de celui-ci en vue de rendre
la somme du retard de modélisation fixe du moyen de filtre inverse (5) et du temps
de retard du premier moyen de retard (6), égale à un nombre entier multiple de ladite
perturbation périodique initiale.
11. Système selon la revendication 9 ou 10, caractérisé en ce qu'il comprend un moyen
destiné à mesurer une période fondamentale de la perturbation périodique initiale
afin de faire varier le temps de retard du premier moyen de retard (6) sur la base
de ladite période fondamentale.
12. Système selon la revendication 11, caractérisé en ce que ledit moyen de mesure destiné
à mesurer une période fondamentale de la perturbation périodique initiale est conçu
pour utiliser le signal d'erreur (e(t)) ou bien le premier signal (y(t)) obtenu à
partir du signal d'erreur (e(t)).
13. Système selon la revendication 11,
caractérisé en ce que ledit moyen de mesure est conçu pour utiliser un signal de fréquence
supplémentaire.
14. Système selon l'une des revendications 9 à 13, caractérisé en ce que
un moyen de filtre de compensation de contre-réaction (4) est prévu, au travers duquel
un signal de contre-réaction est transmis et un moyen de soustraction est prévu afin
de soustraire la sortie du moyen de filtre de compensation de contre-réaction (4)
du signal d'erreur (e(t)) afin de fournir ledit premier signal (y(t)) qui est représentatif
de la perturbation initiale.
15. Système selon l'une des revendications 9 à 13, caractérisé en ce que
un moyen de filtre en peigne situé avant ou après le moyen de filtre inverse (5) est
prévu, au travers duquel le signal d'erreur (e(t)) est transmis afin de commander
uniquement ces perturbations qui présentent une période fondamentale choisie.
16. Système selon la revendication 15, caractérisé en ce que
un moyen de gain ajustable (12) conçu pour amplifier ou atténuer, est prévu, d'où
il résulte que le moyen de filtre en peigne est combiné audit moyen de gain ajustable
(12).