Patent Application
20070201704
This Nonprovisional application claims priority under 35 U.S.C. §119(a) on Patent Application No. 2006-25155 filed in Japan on Feb. 1, 2006, the entire contents of which are hereby incorporated by reference.
The present invention relates to an analysis method and an analyzing apparatus for identifying which of a plurality of sound sources or vibration sources located in a target space or its periphery causes noise or vibration at an evaluation point within the target space.
Identification of a generation source of noise or vibration that appears at an evaluation point within a space is an important issue in various fields of industry. For example, reduction in the internal noise of a car cabin, especially in the noise heard by passengers in a car cabin, is important in the improvement of the passengers' comfortableness. For this purpose, a sound source or a vibration source of the target noise need be identified, and then an effective countermeasure need be taken against this sound source or vibration source.
A large number of analysis methods for sound or vibration for identifying such a sound source or a vibration source have been proposed in the prior art. A widely adopted analysis method for sound or vibration is a method based on the FFT (Fast Fourier Transform). In this method, a detection result of sound or vibration acquired as a waveform signal is processed by Fourier transformation, so that spectral intensity is obtained for each frequency component. Each of a detection signal of sound or vibration at an evaluation point set up in a target space and detection signals of sound or vibration at a plurality of candidate points expected to be a sound source or a vibration source is processed by Fourier transformation. Then, the spectrum distribution at each candidate point is compared with the spectrum distribution at the evaluation point, so that a sound source or a vibration source is identified.
Further, analysis methods for noise in a car cabin have been proposed in which noise is detected at an evaluation point inside a car cabin while sound or vibration is detected at a plurality of candidate points in the inside or the periphery of the car cabin, and in which the detection signal at each candidate point is filtered through an adaptive filter the filter coefficient of which is changed in accordance with the residual from the detection signal at the evaluation point, so that the degree of contribution of each candidate point is obtained on the basis of this result (see, for example, Japanese Patent Application Laid-Open No. H7-243906 and Japanese Patent Application Laid-Open No. H11-94642).
Nevertheless, these conventional analysis methods do not utilize time information, and hence have a problem that when sound or vibration in the same or near frequency range is detected at a plurality of candidate points, a generation source of the sound or vibration that appears at the evaluation point is difficult to be identified correctly. Thus, even when a countermeasure is taken at any one of the plurality of candidate points, the taken countermeasure could be at a candidate point other than the actual sound source or vibration source, so that the reduction effect for sound or vibration could be insufficient at the evaluation point. In contrast, if countermeasures were taken at all of the plurality of candidate points, this would disadvantageously cause excessive countermeasures even at unnecessary candidate points.
The present invention has been devised in view of this situation. An object of the present invention is to provide an analysis method and an analyzing apparatus for sound or vibration in which an analysis method utilizing time information is adopted, so that a generation source of sound or vibration that appears at an evaluation point is identified correctly. This permits countermeasure against sound or vibration without excess or deficiency, and hence realizes reliable reduction in the sound or vibration at the evaluation point.
The analysis method for sound or vibration according to the present invention is an analysis method for sound or vibration for identifying a generation source of sound or vibration that appears at an evaluation point in a target space from among a plurality of candidate points located in the target space and a periphery thereof, characterized by comprising: a first step of extracting an evaluation waveform signal from a detection result of sound or vibration at the evaluation point; a second step of extracting a plurality of candidate waveform signals having the same time axis as the evaluation waveform signal from respective detection results of sound or vibration at the plurality of candidate points; a third step of deriving a mother wavelet from the evaluation waveform signal extracted at the first step; and a fourth step of performing wavelet transformation on each of the plurality of candidate waveform signals extracted at the second step by using the mother wavelet derived at the third step so as to obtain instantaneous correlation between each candidate waveform signal and the mother wavelet.
The analyzing apparatus for sound or vibration according to the present invention is an analyzing apparatus for sound or vibration for identifying a generation source of sound or vibration that appears at an evaluation point in a target space from among a plurality of candidate points located in the target space and a periphery thereof, comprising: detecting means for sound or vibration arranged at each of the evaluation point and the plurality of candidate points; first extracting means for extracting an evaluation waveform signal from the detection result of the detecting means arranged at the evaluation point; second extracting means for extracting a plurality of candidate waveform signals having the same time axis as the evaluation waveform signal from the respective detection results of the detecting means arranged at the plurality of candidate points; deriving means for deriving a mother wavelet from the evaluation waveform signal extracted by the first extracting means; correlation calculating means for performing wavelet transformation on each of the plurality of candidate waveform signals extracted by the second extracting means by using the mother wavelet derived by the deriving means so as to calculate instantaneous correlation between each candidate waveform signal and the mother wavelet; and output means for outputting the degree of contribution of each of the plurality of candidate points for sound or vibration of the evaluation point on the basis of mutual comparison of the calculation results of the correlation calculating means.
In the analysis method and the analyzing apparatus for sound or vibration according to the present invention, a mother wavelet is derived from the evaluation waveform signal acquired at the evaluation point. Then, the candidate waveform signal acquired at each candidate point is processed by wavelet transformation using the mother wavelet, so that instantaneous correlation of each candidate waveform signal is calculated. Thus, an analysis result including time information is obtained, so that a generation source of sound or vibration that appears at the evaluation point can correctly be identified among the plurality of candidate points. Thus, when a countermeasure against the sound or vibration is taken at the identified candidate point, the sound or vibration can reliably be reduced at the evaluation point.
The above and further objects and features of the invention will more fully be apparent from the following detailed description with accompanying drawings.
The present invention is described below in detail with reference to the drawings showing an embodiment.
The electric power steering device shown in
The two ends of the rack shaft 1 that protrude outward from both sides of the rack housing 10 are linked through tie rods 11 and 11 respectively to right and left front wheels 12 and 12 serving as steerable wheel. The upper end of the pinion shaft 2 that protrudes to the outside of the pinion housing 20 is linked through a steering shaft 3 to a steering wheel 30 serving as a steering member. Further, a pinion (not shown) is formed in the lower part of the pinion shaft 2 that extends inside the pinion housing 20. In a part intersecting with the rack housing 10, the pinion engages with the rack teeth formed over an appropriate length on the external surface of the rack shaft 1.
The steering shaft 3 is supported in a rotatable manner inside a column housing 31 having a cylinder shape, and then fixed inside the car cabin via the column housing 31 in an inclined arrangement with the front side down. A protruding end of the steering shaft 3 toward the lower side of the column housing 31 is linked to the pinion shaft 2, while a protruding end toward the upper side is fixed to the steering wheel 30.
According to this configuration, when the steering wheel 30 is operated and rotated for steering, the rotation is transmitted to the pinion shaft 2 via the steering shaft 3. Then, the rotation of the pinion shaft 2 is converted into movement in the axial length direction of the rack shaft 1 in the engagement part between the pinion and the rack teeth. According to this movement of the rack shaft 1, the right and the left front wheels 12 and 12 are pushed and pulled respectively by the individual tie rods 11 and 11, so that steering is achieved.
In the middle of the column housing 31 that supports the steering shaft 3, a torque sensor 4 is provided for detecting a steering torque applied to the steering shaft 3 by the rotatory operation of the steering wheel 30. Further, a steering assistance motor 5 is attached at a position lower than the torque sensor 4.
The torque sensor 4 has a publicly known configuration in which the steering shaft 3 serving as the target for detection is divided into two up and down shafts while these two shafts are linked together on the same axis with a torsion bar having known torsion characteristics, and in which relative angular displacement generated by the operation of a steering torque between the two shafts that associates with a torsion in the torsion bar is detected by appropriate means. Further, the steering assistance motor 5 is attached outside the column housing 31 in a manner that its shaft axes intersect with each other approximately at rectangles. For example, in a transmission configuration, a worm fixed to the output end that extends inside the column housing 31 engages with the worm wheel fit and fixed to the outside of the steering shaft 3, so that the rotation of the motor 5 is transmitted to the steering shaft 3 with predetermined speed reduction via a transmission mechanism provided with a worm and a worm wheel.
The steering assistance motor 5 attached in this manner is driven in accordance with the direction and the magnitude of the steering torque detected by the torque sensor 4. At that time, the rotating force generated by the motor 5 is applied to the pinion shaft 2 linked to the lower end of the steering shaft 3, so that the rotating force assists the steering performed as described above.
In the electric power steering device having this configuration, when the above-mentioned steering is performed in accordance with a rotatory operation of the steering wheel 30, vibration occurs in the periphery of a part in which relative displacement is generated between the members, like in the periphery of the transmission mechanism that transmits the rotation of the steering assistance motor 5 to the steering shaft 3 with speed reduction, the periphery of the engagement part between the pinion shaft 2 and the rack shaft 1, and the periphery of the support part for supporting the rack shaft 1 in a slidable manner at one side-end part of the rack housing 10. This vibration propagates to the car cabin, and is then heard as noise by a driver who operates the steering wheel 30.
The analysis method for sound or vibration according to the present invention is implemented in order to identify a generation source of the noise generated as described above. An evaluation point is defined at an appropriate position inside the car cabin, preferably, in the periphery of the driver who operates the steering wheel 30. Then, a microphone 6 for noise detection is arranged at this evaluation point, while detectors 7, 7, . . . for detecting sound or vibration are arranged respectively at candidate points expected to be a generation source of this noise. Further, an analyzing apparatus 8 receives the detection signals from the microphone 6 and the detectors 7, 7, . . . .
In the embodiment shown in the drawings, candidate points are in the periphery of the transmission mechanism from the steering assistance motor 5 to the steering shaft 3, the periphery of the engagement part between the pinion shaft 2 and the rack shaft 1, and the periphery of the support part of the rack shaft 1 of one side-end part of the rack housing 10. Then, the vibration at each candidate point is detected by each of the individual detectors 7, 7, . . . . However, the number and the positions of the candidate points may be set up appropriately.
A noise detection signal at the evaluation point acquired by the microphone 6 is filtered by the low pass filter 80. Vibration detection signals at individual candidate points acquired by the detectors 7, 7, . . . are filtered by the individual low pass filters 81, 81, . . . As a result, waveform signals in which high frequency noise is removed are extracted. In the following description, the waveform signal extracted by filtering the detection signal acquired by the microphone 6 arranged at the evaluation point is denoted by the evaluation waveform signal S. Each of the waveform signals extracted by filtering the detection signals acquired by the detectors 7, 7, . . . arranged at the candidate points is denoted by the candidate waveform signal V.
Here, in
In the following description, for simplicity, it is assumed that vibration detection in one direction is performed at each candidate point. After the filtering by the low pass filter 80, one evaluation waveform signal S corresponding to the noise at the evaluation point is extracted. Further, after the filtering by the low pass filters 81, 81, and 81, three candidate waveform signals V1, V2, and V3 respectively corresponding to the vibration at the three candidate points are extracted. The evaluation waveform signal S is provided to the mother wavelet deriving section 82. The candidate waveform signals V1, V2, and V3 are respectively provided through the wavelet transformation sections 83, 83, and 83 to the correlation calculation sections 84, 84, and 84.
The analyzing apparatus 8 monitors a noise detection signal at the evaluation point acquired by the microphone 6. Then, when a detection signal serving as the target for detection is generated, the analyzing apparatus 8 acquires the noise detection signal together with the vibration detection signals at individual candidate points acquired by the detectors 7, 7, . . . (Step 1). Then, the analyzing apparatus 8 filters these detection signals, and thereby extracts an evaluation waveform signal and candidate waveform signals (Step 2). Here, the acquisition of the detection signal by the microphone 6 and the acquisition of the detection signals by the detectors 7, 7, . . . are performed simultaneously. However, since the processing of the following procedure is performed within the CPU, the result can be outputted in real time and displayed on the display section 9. Alternatively, the microphone 6 may serve as a vibration sensor, while the detector 7 may serve as a microphone.
Then, the analyzing apparatus 8 derives a real signal mother wavelet from the evaluation waveform signal S extracted at step 2 (Step 3). In the derivation of the real signal mother wavelet performed in the following procedure, a waveform is used that is within a range satisfying a predetermined magnitude condition among the evaluation waveform signal S. In the selection of the use range, for example, the evaluation waveform signal S may be displayed on the display section 9 in a manner shown in
A real signal mother wavelet Ψ(t) is a function given by the following Eq. (1). Quantity a in this Eq. (1) is a scale parameter corresponding to the inverse of the frequency, while b is a time parameter. In the following description, the adjunctive phrase “real signal” is omitted, so that the function is simply referred to as a mother wavelet Ψ(t).
The mother wavelet Ψ(t) need satisfy an admissible condition given by Eq. (2) in order that reconstruction of the signal should be possible. Here, Ψ(ω) hat denotes the Fourier transform of the mother wavelet Ψ(t).
Next, the analyzing apparatus 8 performs normalization on the derived mother wavelet Ψ(t) in such a manner that the norm should be unity as given by Eq. (3) (Step 13). In order that the feature should easily be recognized in the analysis of sound or vibration, it is preferable that a mother wavelet of complex type is used in place of that of real type. Thus, the analyzing apparatus 8 performs Hilbert transformation on the real type mother wavelet obtained by the normalization at Step 13 (Step 14), thereby constructs a complex type mother wavelet (Step 15), and then completes a series of derivation procedure of the mother wavelet Ψ(t). Here, obviously, the real type mother wavelet ΨR(t) obtained at Step 13 may be used.
The complex type mother wavelet Ψ(t) is given by Eq. (4). The real type mother wavelet ΨR(t) is processed by Fourier transformation, so that the frequency spectrum ΨR(f) hat is obtained. The inverse Fourier transformation is performed in a state that ΨR(f) hat is replaced to zero in the negative frequency domain while ΨR(f) hat is replaced by 2ΨR(f) hat in the positive frequency domain.
[Equation 4]
ψ(t)=ψR(t)+jψI(t) (4)
On completion of derivation of the mother wavelet Ψ(t) in accordance with the above-mentioned procedure, the analyzing apparatus 8 performs wavelet transformation respectively on the candidate waveform signals V1, V2, and V3 given as shown in
In the wavelet transformation at Step 4, the wavelet transformation formula expressed by Eq. (5) is used, which contains the mother wavelet Ψ(t) derived from the evaluation waveform signal S at Step 3. Then, each of the candidate waveform signals V1, V2, and V3 is applied to the transform function f(t) in this equation, so that the transformation is performed. Here, Ψ*(t) in Eq. (5) denotes the complex conjugate of the mother wavelet Ψ(t).
[Equation 5]
W(a,b)=∫−∞∞f(t)ψa,b*(t)dt (5)
The wavelet transformation performed as described above is the processing of obtaining the inner product between the transform function f(t) to which each of the candidate waveform signals V1, V2, and V3 is applied and the mother wavelet Ψ(t). When the transform function f(t) agrees with the mother wavelet Ψ(t), the inner product is unity, while when disagrees, the inner product is zero. In a state that the scale parameter a=1 in Eq. (1) is set up to be the center frequency, when the time parameter b is changed variously, correlation between the evaluation waveform signal S and each of the candidate waveform signals V1, V2, and V3 becomes clear on the time axis.
The mother wavelet Ψ(t) is normalized. Thus, when the candidate waveform signals V1, V2, and V3 applied to the transform function f(t) are larger than the mother wavelet Ψ(t), the correlation values become larger than unity in accordance with the ratio. Further, correlation can be obtained also for a frequency component of the mother wavelet Ψ(t). As such, for each of the three candidate waveform signals V1, V2, and V3 sequentially applied to the transform function f(t), instantaneous correlation can be obtained that indicates the degree of correlation including the component and the magnitude with respect to the evaluation waveform signal S used in the derivation of the mother wavelet Ψ(t).
The mother wavelet Ψ(t) is derived on the basis of the detection result of the noise acquired actually at the evaluation point. Thus, the instantaneous correlation calculated at Step 5 for each of the plurality of candidate waveform signals V1, V2, and V3 processed by wavelet transformation at Step 4 expresses correctly the correlation relation of the sound or vibration (vibration in this embodiment) detected at each candidate point with the noise at the evaluation point. Further, the result of the wavelet transformation contains time information, and hence the generation time can also be determined. Thus, even when the plurality of candidate waveform signals V1, V2, and V3 contain the same frequency component, the difference becomes clear in the degree of correlation of each signal with the evaluation waveform signal S.
On completion of the wavelet transformation at Step 4, the analyzing apparatus 8 compares with each other the instantaneous correlation values calculated respectively for the three candidate waveform signals V1, V2, and V3 (Step 6), then outputs the degree of contribution of vibration detected at the plurality of candidate points relative to the noise detected at the evaluation point (Step 7), and then completes the analysis operation.
Here, when the target noise or vibration is known in advance, or alternatively with the mother wavelet has already been derived, Steps 1 and 3 may be skipped, while the derived mother wavelet may be stored in a mother wavelet storage section 85 (see
Output of the degree of contribution may be performed by appropriate means. For example, the instantaneous correlation values calculated for the plurality of candidate waveform signals may be expressed into the form of graphs and then displayed on the display section 9. Then, an operator who recognizes visually this display may determine the degree of contribution.
Further, in general, the instantaneous correlation value of the candidate waveform signal V2 shown in
The above-mentioned embodiment has been described for an example of analysis performed for identifying a generation source of the noise caused in a car cabin by vibration generated in various sections of an electric power steering device. However, the analysis method and the analyzing apparatus according to the present invention is applicable to a general use for identifying a generation source of sound or vibration that appears at an evaluation point in a target space from among a plurality of candidate points. Thus, obviously, the present invention can be used widely in various fields of industry.
As this invention may be embodied in several forms without departing from the spirit of essential characteristics thereof, the present embodiment is therefore illustrative and not restrictive, since the scope of the invention is defined by the appended claims rather than by the description preceding them, and all changes that fall within metes and bounds of the claims, or equivalence of such metes and bounds thereof are therefore intended to be embraced by the claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2006-025155 | Feb 2006 | JP | national |
