Classifications

• • G—PHYSICS
  • G10—MUSICAL INSTRUMENTS; ACOUSTICS
  • G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
  • G10K11/00—Methods or devices for transmitting, conducting or directing sound in general; Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
  • G10K11/16—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
  • G10K11/175—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound
  • G10K11/178—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound by electro-acoustically regenerating the original acoustic waves in anti-phase
  • G10K11/1781—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound by electro-acoustically regenerating the original acoustic waves in anti-phase characterised by the analysis of input or output signals, e.g. frequency range, modes, transfer functions
  • G10K11/17821—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound by electro-acoustically regenerating the original acoustic waves in anti-phase characterised by the analysis of input or output signals, e.g. frequency range, modes, transfer functions characterised by the analysis of the input signals only
  • G10K11/17823—Reference signals, e.g. ambient acoustic environment
• • G—PHYSICS
  • G10—MUSICAL INSTRUMENTS; ACOUSTICS
  • G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
  • G10K11/00—Methods or devices for transmitting, conducting or directing sound in general; Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
  • G10K11/16—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
  • G10K11/175—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound
  • G10K11/178—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound by electro-acoustically regenerating the original acoustic waves in anti-phase
  • G10K11/1785—Methods, e.g. algorithms; Devices
  • G10K11/17853—Methods, e.g. algorithms; Devices of the filter
• • G—PHYSICS
  • G10—MUSICAL INSTRUMENTS; ACOUSTICS
  • G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
  • G10K11/00—Methods or devices for transmitting, conducting or directing sound in general; Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
  • G10K11/16—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
  • G10K11/175—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound
  • G10K11/178—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound by electro-acoustically regenerating the original acoustic waves in anti-phase
  • G10K11/1785—Methods, e.g. algorithms; Devices
  • G10K11/17853—Methods, e.g. algorithms; Devices of the filter
  • G10K11/17854—Methods, e.g. algorithms; Devices of the filter the filter being an adaptive filter
• • G—PHYSICS
  • G10—MUSICAL INSTRUMENTS; ACOUSTICS
  • G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
  • G10K11/00—Methods or devices for transmitting, conducting or directing sound in general; Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
  • G10K11/16—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
  • G10K11/175—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound
  • G10K11/178—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound by electro-acoustically regenerating the original acoustic waves in anti-phase
  • G10K11/1787—General system configurations
  • G10K11/17875—General system configurations using an error signal without a reference signal, e.g. pure feedback
• • G—PHYSICS
  • G10—MUSICAL INSTRUMENTS; ACOUSTICS
  • G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
  • G10K11/00—Methods or devices for transmitting, conducting or directing sound in general; Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
  • G10K11/16—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
  • G10K11/175—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound
  • G10K11/178—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound by electro-acoustically regenerating the original acoustic waves in anti-phase
  • G10K11/1787—General system configurations
  • G10K11/17879—General system configurations using both a reference signal and an error signal
  • G10K11/17883—General system configurations using both a reference signal and an error signal the reference signal being derived from a machine operating condition, e.g. engine RPM or vehicle speed
• • G—PHYSICS
  • G10—MUSICAL INSTRUMENTS; ACOUSTICS
  • G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
  • G10K2210/00—Details of active noise control [ANC] covered by G10K11/178 but not provided for in any of its subgroups
  • G10K2210/10—Applications
  • G10K2210/121—Rotating machines, e.g. engines, turbines, motors; Periodic or quasi-periodic signals in general
• • G—PHYSICS
  • G10—MUSICAL INSTRUMENTS; ACOUSTICS
  • G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
  • G10K2210/00—Details of active noise control [ANC] covered by G10K11/178 but not provided for in any of its subgroups
  • G10K2210/30—Means
  • G10K2210/301—Computational
  • G10K2210/3028—Filtering, e.g. Kalman filters or special analogue or digital filters
• • G—PHYSICS
  • G10—MUSICAL INSTRUMENTS; ACOUSTICS
  • G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
  • G10K2210/00—Details of active noise control [ANC] covered by G10K11/178 but not provided for in any of its subgroups
  • G10K2210/30—Means
  • G10K2210/301—Computational
  • G10K2210/3032—Harmonics or sub-harmonics
• • G—PHYSICS
  • G10—MUSICAL INSTRUMENTS; ACOUSTICS
  • G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
  • G10K2210/00—Details of active noise control [ANC] covered by G10K11/178 but not provided for in any of its subgroups
  • G10K2210/30—Means
  • G10K2210/301—Computational
  • G10K2210/3045—Multiple acoustic inputs, single acoustic output

Definitions

• This invention relates to a control system for canceling periodic or nearly periodic disturbances.
• This control system include a delayed inverse filter, a variable delay and, optionally, a comb filter. 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.
• the control system has many applications including the active control of sound and vibration and the selective removal of periodic noise in communications signals.
• 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.
• 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.
• Another object of this invention is to provide a control system based in the time domain for canceling periodic disturbances.
• 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.
• 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 adaption 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 system 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
• Fig. 12 is a time analysis of a sampled signal.
• This invention relates to a new type of control system for periodic disturbances.
• This control system has the following major advantages:
• the filter is determined by the system to be controlled and so does not have to be adapted to cope with changing disturbances.
• 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.
• the filter F is the inverse of A, which in digital form is defined by
• Equation (6) can then be written more compactly as
• the control system utilizes this property of the disturbance.
• the filter is obtained by combining the filter B and a filter D( ⁇ -mT) in series.
• the actuator drive signal is obtained by passing the signal y(t), obtained using equation (3), through this combined filter.
• the basic control system shown in Figure 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 ⁇ -mT, digital-to analog converter (DAC) (7) (only required if digital filters are to be used), signal conditioning (8), and actuator (9).
• ADC analog-to-digital converter
• DAC digital-to analog converter
• 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, ⁇ , 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.
• the part of the system from the controller output to the controller input is referred to as the plant. This includes the elements 6,7,8,9,1,2,3 in Figure 1 as well as the response of the physical system.
• the modeling delay is determined by the system to be controlled, and typically must be greater than the delay through the plant.
• the additional delay is determined by the modeling delay and the fundamental period of the noise (disturbance). Unlike previous control systems, the filter does not need to vary with the noise.
• the compensation filter can be avoided.
• the actuator drive signal is obtained by passing the error signal e(t) through the delayed inverse filter B and the delay line D( ⁇ -mT) and then through an additional gain K. (Note that the order of these elements can be interchanged).
• Disturbances with other periods 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 ⁇ .
• a 'comb filter' which can be positioned at any point in the feedback loop.
• a comb filter is a positive feedback loop with a one cycle delay around the loop and a loop gain, a, of less than unity. This is shown in Figure 2.
• a feedforward loop with a delay of 1/2 cycle in one of the paths as shown in Figure 3.
• Other ways of implementing the required delays include analog and digital delay lines and full digital filters.
• a comb filter avoids amplification of the disturbance at non- harmonic frequencies, and also makes the control system selective.
• 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.
• the filter can be a combination of finite impulse response filter and a recursive filter.
• the forward filter, A is also required. Again, there are well known techniques for identifying a model of A.
• 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.
• 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.
• the filter B can be calculated using Wiener Filtering
• the system response may change slowly over time. In these applications it is necessary to change the filters A and B.
• One way of doing this is to turn off the control system and remeasure the responses.
• 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 sensor 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.
• the filter B may then be updated 'off-line' using the model of A, as in Figure 8.
• the filter B can itself be treated as an adaptive filter.
• the filter B can itself be treated as an adaptive filter.
• the adaption as described in the Widrow publication, for example, one way is the 'filtered-input LMS' algorithm.
• 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.
• 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.
• the disturbance is in an electrical signal, such as a communication signal.
• 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.
• 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, Bjj 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.
• the input to the i-th comb filter is
• the output from the i-th channel is
• the filters Ajj 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.
• the filters A j have been identified, there are a variety of ways in which the filters Bjj can be obtained. These include time domain approaches, such as Weiner filtering, and frequency domain approaches.
• the filters Bjj can be obtained directly by adaptive filtering using the multichannel Least Mean Square algorithm, for example.
• the other single channel systems described above can also be implemented as multichannel systems.
• the effectiveness of the control system has been demonstrated on the selective filtering of a periodic noise from a communications signal.
• the communications microphone is in the vicinity of a loud periodic noise source and, untreated, the speech cannot be heard above the noise.
• the time trace of the untreated signal is shown in the upper plot in Figure 12.
• 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.

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• Physics & Mathematics (AREA)
• Engineering & Computer Science (AREA)
• Acoustics & Sound (AREA)
• Multimedia (AREA)
• Feedback Control In General (AREA)
• Soundproofing, Sound Blocking, And Sound Damping (AREA)
• Radar Systems Or Details Thereof (AREA)
• Separation Using Semi-Permeable Membranes (AREA)
• Electrical Control Of Air Or Fuel Supplied To Internal-Combustion Engine (AREA)
• Combined Controls Of Internal Combustion Engines (AREA)

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• 1992
  • 1992-06-25 EP EP92914496A patent/EP0694234B1/de not_active Expired - Lifetime
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  • 1992-06-25 DE DE69230867T patent/DE69230867T2/de not_active Expired - Fee Related
  • 1992-06-25 WO PCT/US1992/005229 patent/WO1994000930A1/en active IP Right Grant

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