GB2257601A

GB2257601A - Active vibration control system

Info

Publication number: GB2257601A
Application number: GB9211661A
Authority: GB
Inventors: Hisashi Sano; Hideshi Sawada; Mitsuo Nakamura; Tsuyoshi Yamashita
Original assignee: Honda Motor Co Ltd
Current assignee: Honda Motor Co Ltd
Priority date: 1991-07-09
Filing date: 1992-06-02
Publication date: 1993-01-13
Also published as: GB9211661D0; DE4221290A1; JPH0519776A

Description

01 31 ACTIVE VIBRATION CONTROL SYSTEM This invention relates to an active

vibration control system, and more particularly to an active vibration control system for suppressing vibrations in a compartment or a cabin in which an occupant or occupants stay, of traffic facilities such as automotive vehicles, aircraft, and ships or boats.

The term "vibration" used throughout the present specification includes not only vibration in its proper or literal meaning but also noise and sound.

Conventional active vibration control systems of this kind include a system which has been proposed by Japanese Provisional Patent Publication (Kohyo) No. I501344. The proposed system comprises a vibration source, a vibration sensor for sensing vibration emitted from the vibration source, an adaptive control circuit which receives an output from the vibration sensor as a reference signal and generates, based upon the reference signal, a signal having a transfer characteristic inverse to a transfer characteristic of vibration from the vibration source to a human body, cancelling vibration-generating means (secondary vibration source) responsive to an output from the adaptive control circuit for generating cancelling vibration, and an error sensor for sensing an error between the vibration from the vibration source and the cancelling vibration from the cancelling vibrationgenerating means. The adaptive control circuit varies - 2 the above-mentioned inverse transfer characteristic so as to minimize the above-mentioned error, based upon a transfer characteristic of the cancelling vibration from the cancelling vibration-generating means to the error sensor and an error signal from the error sensor.

An active vibration control system of this kind can be applied to a road noise control system for a vehicle, which reduces so-called road noise caused by uneveness of the road surface on which the vehicle runs. In such a road noise control system, advantageously, a plurality of vibration sensors are provided, respectively, for a plurality of wheels of the vehicle as vibration sources, for sensing vibrations from the respective wheels. An adaptive control circuit, cancelling vibration- generating means such as a loudspeaker, and an error sensor such as a microphone are provided for each of the vibration sensors.

An example of the road noise control system is shown in Fig. 1. The illustrated system is comprised of two circuit systems formed of two noise sensors (vibration sensors) provided, respectively, for two wheels of a vehicle, two loud speakers (cancelling vibration-generating means) arranged at suitable locations in a compartment of the vehicle, and two microphones (error sensors) arranged at locations close to the occupant's ears.

As shown in Fig. 1, the noise sensors 21.2 2' which may be formed, e.g., of acceleration pick-ups, are mounted, respectively, on knuckles of vehicle body suspensions, not shown, which are arranged close to the respective wheels 11. 1 2 of the vehicle as noise or vibration sources. Signals from the noise sensors r 211 2 2' which are indicative of noise from the wheels ill 1 2' i.e. road noise pulses, are supplied via antialiasing filters 121, 12 2 to respective A/D converters 41# 4 2 of an adaptive control circuit 3 as control means. The A/D converters 41, 4 2 sample the input signals and supply the resulting pulse trains as reference signals x(n) to control blocks 3 1 3 4 The control blocks 3 1 3 4 operate based on the input reference signals x(n) to create cancelling signals having transfer characteristics H' 1 - H' 4 (pseudo inverse transfer characteristics) which have the same amplitude as and are inverse in phase to respective transfer characteristics H 1 - H 4 of noise from the corresponding wheels 11. 1 2 to the occupant (corresponding microphones 91, 9 2). The pseudo inverse transfer characteristics are previously set for the respective control blocks 3 1 - 3 4 The control blocks 31. 3 2 are each formed of two FIR (finite impulse response) filters FIRi (i = 1-8) each having a transfer characteristic Cmj2 (m = 1, 2, Q = 1, 2) including various characteristics such as a sound transfer characteristic between the corresponding loud speaker 8 and the corresponding microphone 9, an adaptive digital filter ADFi (i= 1 - 4) for providing a pseudo inverse transfer characteristic H1i (i = 1 4) which is inverse to the corresponding transfer characteristic Hj (j = 1 - 4), and a processor LMS having an LMS-algorithm. Eight FIR filters FIRI - FIR8 are provided as the FIR filter FIRi,which have different transfer characteristics C ill C 21; C ill C 21; C 121 C 22; C 12' C 22 corresponding, respectively, ta four combinations of the two loudspeakers 81, 8 2 and the two microphones 91, 9 2' including sound transfer delay between the loudspeakers 81. 8 2 and the microphones 91, 9 2 As the algorithm of the processor LMS of each control block 3 1 34,, a Multiple Error Filtered-X LMS algorithm may be used, for example, which is disclosed by a paper entitled "A Multiple Error LMS Algorithm and Its Application to the Active Control of Sound and Vibration" in "ASSP 35" No. 10 issued in October, 1987. The transfer characteristics Cm.Q stored in the FIR filters FIR 1 - FIR 8 contain all necessary characteristics of components of the control circuit, e.g. characteristics of the speakers 8, microphones 9, D/A converters 6, analog filters 12, 13, and A/D converters 4, 10, including a sound transfer time lag between the speakers 8 and the microphones 9. All these characteristics of the components including the sound transfer delay are previously measured, and then the transfer characteristics CmR are calculated from the results of the measurements.

The cancelling signals from the control blocks 3.1, 3 2 are added together by an adder 5,,, while the cancelling signals from the control blocks 3 3' 3 4 are added together by an adder 5 2' The resulting sums are converted into analog signals at respective D/A converters 6:L. 6 2' and the analog signals are amplified by respective amplifiers 7,, 7 2 to drive the loudspeakers- 8:L, 8 2 to generate secondary noise, i.e. cancelling noise.

The microphones 9,J 9 2 pick up the secondary noise from the respective loudspeakers 81, 8 2 and noise directly transmitted from the wheels 1.1, 1 2 as noise sources, and the picked up noise signals are-fed through anti-aliasing filters 13,, 13 2 to A/D converters 10,. 10 2 which sample the respective input noise signals and output the resulting pulse trains as 0 error signals -' 1 cl/ E 2 are suppl 1 2' respectively. The error signals ied to the processors LMS of the control blocks 3 1 - 3 4 The error signals c 1, a 2 show errors between noise directly-transmitted from the wheels 11, 1 2 and secondary noise from the loud speakers 81. 8 2 Each processor LMS operates in response to the input error signals E,, 4,2 and transfer characteristics CT2 between the corresponding loudspeaker 8 1 or 8 2 and the corresponding microphone 9 1 or 9 2 to vary a corresponding one of the inverse transfer characteristics H' 1 - H' 4 of the filters ADFl - ADF4 so as to minimize the values of the error signals El.E, 2 by the use of the following equation:

a = Hi Qx + Cm.QH 1 ix... (1) In a conventional multi-channel control system as described above, which uses a plurality of vibration sensors (noise sensors 21. 2 2), a plurality of cancelling vibration-generating means (loudspeakers 81. 8 2), a plurality of error sensors (microphones 91. 9 2), etc., a great amount of calculation of the transfer characteristics Cmj2 is required, which necessitates a long calculation time. In the above described example, in order to shorten the calculation time, the adaptive control circuit 3 employs high-speed digital signal processors (DSP1s),and large-capacity memories, which are expensive. Further, an active vibration control system, which detects vibrations from a plurality of vibration sources, requires the use of many such DSPIs and memories, which results in a very high manufacturing cost, as well as in the system having a large size and a complicated structure. Therefore, the system is not 6 - suitable for mass production.

It is, therefore, the object of the invention to provide an active vibration control system which dispenses with the use of transfer characteristics Cm and hence the use of memories storing the transfer characteristics, allowing omission of complicated calculations, and is therefore simple in structure and low in cost.

To attain the above object, the present invention provides an active vibration control system comprising:

at least one vibration source; first sensor means for sensing vibration from the vibration source; control means disposed to receive an output from the first sensor means as a reference signal, the control means being responsive to the reference signal for generating a cancelling signal having a transfer characteristic inverse to a transfer characteristic of vibration from the vibration source to a human body; cancelling vibration-generating means responsive to an output from the control means for generating cancelling vibration; and second sensor means for sensing an error between the vibration from the vibration source and the cancelling vibration from the cancelling vibration generating means and generating an error signal indicative of the sensed error, wherein the control means varies the inverse transfer characteristic by an amount corresponding to the error signal as well as by delaying the reference 7 9 1 A is signal by a predetermined delay time period, so as to minimize the error.

Preferably, the predetermined delay time period includes a transfer time lag between the cancelling vibration-generating means and the second sensor means, and a time lag of the active vibration control system.

The above and other objects, features, and advantages of the invention will be more apparent from the following detailed description of an embodiment given by way of example only and taken in conjunction with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a block diagram showing the arrangement of a conventional road noise control system; and Fig. 2 is a block diagram showing the arrangement of an active vibration control system according to an embodiment of the invention, which is embodied as a road noise control system.

Fig. 2 shows an embodiment of the invention, in which the active vibration control system according to the invention is applied to a road noise control system for automotive vehicles. The road noise control system according to the embodiment comprises two noise sensors, and two sets of loudspeakers as cancelling vibration-generating means and microphones as error sensors, the two sets being arranged at left - 8 and right sides of the-vehicle. In Fig. 2, elements corresponding to those in Fig. 1 are designated by identical reference numerals.

According to the present embodiment, the FIR filters FIR1 - FIR8 of the adaptive control circuit 3 in the conventional system of Fig. 1 are omitted, and accordingly A/D converters 41.. 4 2 are directly connected to respective processors LMS1. More specifically, the present invention dispenses with the use of transfer characteristics Cmj2 stored in the FIR filters FIRI - FIR8 in Fig. 1, and uses a delay factor contained in the transfer characteristics CmQ (a predetermined delay time period), instead of the transfer characteristics CmQ. The algorithm of each processor LMS' of the adaptive control circuit 3 contains the delay factor imie (m = 1, 2, Q = 1, 2).

The delay factors AmJ2 mainly include a signal transfer time lag between a corresponding combination of the loudspeakers 81. 8 2' and the microphones 91, 9 2' and a time lag of a corresponding one of the analog systems formed by anti-aliasing filters 121.. 12 2' 1311 13 2 which are analog filters, etc. Each processor LMS' operates according to its algorithm such that based upon an error signalt ("E 11 E 2) showing an error fi.e between noise from a noise source 1 (lli 1 2) and secondary noise (cancelling noise) from loudspeakers.8 (81r 8 2), and the delay factor omQ of the circuit system including a correspondi.ng one of four combinations of the loudspeakers 81, 8 2 and the microphones 91. 9 2 it calculates the inverse transfer characteristic H1i according to the following equations so as to minimize the error- E Q = H1j2x + H' ix ..... (2) Q R 9 W! = H1i + dH'i BASE X dm.Q... (3) is where AH'i BASE is a basic. variation value by which the inverse transfer characteristic is to be varied. The value jHli BASE is determined in accordance with the error& j2.

The other components in Fig. 2 than those described above are substantially identical in structure and function with corresponding ones of the conventional system of Fig. 1 described hereinbefore, and description thereof is ttlerefore omitted.

The operation of the present embodiment will now be described.

Signals from the noise sensors 21. 2 2' which are indicative of noise from the wheels 11. 1 2 are supplied via the anti-aliasing filters 121. 12 2 to the respective A/D converters 41, 4 2 of the adaptive control circuit 3. The A/D converters 41, 4 2 in turn sample the input signals and supply the resulting pulse trains as reference signals x(n) to control blocks 3 1 3 4 The control blocks 3 1 - 3 4 operate based on the input reference signals x(n) to create cancelling signals having transfer characteristics H' 1 - H' 4 (pseudo inverse transfer characteristics) which have the same amplitude and are inverse in phase to respective transfer characteristic H 1 - H 4 of noise from the corresponding wheels 11, 1 2 to the occupant. The cancelling signal from the control blocks 31. 3 2 are added together by an adder 51. while the cancelling signals from the control blocks 3 3 3 4 hre added together by an adder 5 2 The resulting sums are converted into analog signals at respective D/A converters 61. 6 2' and the analog signals are - is 2 5 amplified by respective amplifiers 7.,,, 7 2 to drive the respective loudspeakers 8.1 8 2 to generate secondary noise, i.e. cancelling noise.

The microphones 9,,,_9 2 pick up the secondary noise from the loudspeakers 8:Lr 8 2 and the noise directly trans mitteu rrom tue wheels 1,, 1 2 as noise sources, and the picked up noise signals are fed through anti-aliasing filters 13,,, 13 2 to A/D converters 10,, 10 2 which sample the respective input noise signals and supply the resulting pulse trains as error signals C I' E 2 to the processors LMS' of the control blocks 3 1 - 3 4 Each processor LMS' determines the basic variation value zH'i BASE by which is to be varied the inverse transfer characteristic Hi of the circuit system to which a corresponding combination of the loudspeakers 811 8 2 and the microphones 9,.. 9 2 belongs, in accordance with the error signals EjE 2' and corrects the determined basic variation value AH'i BASE (specifically, a time component in the value AH'i BASE) by the delay factor jmP- of the same circuit system, in other words, delays the input reference signal x(n) by a predetermined delay time period corresponding to the delay factor,jmj2. Thus, the inverse transfer characteristic H'i is varied so as to minimize the error Ej, 5 2' The delay factor zme is previously determined based upon the transfer time lag between the loud speaker 8m, and the corresponding microphone 9. e, the time lag of the corresponding analog system (filters 12, 13, etc.), etc., and incorporated in the algorithm of the corresponding processor LMS' of the adaptive control circuit 3.

Although in the above described embodiment the active vibration control system according to the t 1.

11 - p 9 invention is applied to a so-called two-input/two output/two-point control type comprising two noise sensors as first sensor means, two loudspeakers as cancelling vibration-generating means, and two microphones as second sensor means, the invention is not limited to this type, but may be applied to any other possible types such as a onelnput/multioutput/multi-point control type and a multi-Input/multioutput/multi-point control type. Further, the invention is not limited to a road noise control system as applied in the above described embodiment, but may be applied to all possible kinds of active vibration control systems including an engine noise control system.

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Claims

1. An active vibration control system comprising:

at least one vibration source; first sensor means for sensing vibration from said vibration source; control means disposed to receive an output from said first sensor means as a reference signal, said control means being responsive to said reference signal for generating a cancelling signal having a transfer characteristic inverse to a transfer characteristic of vibration from said vibration source to a human body; cancelling vibration-generating means responsive to an output from said control means for generating cancelling vibration; and second sensor means for sensing an error between said vibration from said vibration source and said cancelling vibration from said cancelling vibrationgenerating means and generating an error signal indicative of the sensed error, wherein said control means varies said inverse transfer characteristic by an amount corresponding to said error signal as well as by delaying said reference signal by a predetermined delay time period, so as to minimize said error.

2. An active vibration control system as claimed in claim 1, wherein said predetermined delay time period includes a transfer time lag between said cancelling vibration-generating means and said second sensor means, and a time lag of said active vibration control system.

3. An active vibration control system as -X 1 1 13 - 1 claimed in claim 1 or 2, wherein said control means determines a basic variation value by which said inverse transfer characteristic of said cancelling signal is to be varied, in accordance with said error signal, and corrects the determined basic variation value by said predetermined delay time period.

4. An active vibration control system as claimed in claim 1, 2 or 3, wherein said control means comprises A/D converter means for sampling output pulses from said first sensor means and creating a pulse train as said reference signal, adaptive digital filter means for providing a pseudo inverse transfer characteristic which is inverse to said transfer characteristic of said vibration; and processor means having a predetermined algorithm, said processor means being disposed to receive said error signal from said second sensor means, and said A/D converter means and said processor means being directly connected with each other.