Active noise and vibration control system accounting for time varying plant, using residual signal to create probe signal

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The general layout of the active noise and vibration control system according to the present invention is shown in FIG.
3.
Again, only system elements differing from the basic structure of FIGS.
1 and 2 will be explained.
Like FIG.
2, the system of Fig.
3 injects a probe signal n into the output of the control filter 351 by means of an addition circuit 355.
However, the origin of the probe signal n is quite different.
The output of residual sensor 12 is fed back into the controller 35 and into a probe generation circuit 353, whose details will be explained below.
The probe generation circuit also receives as input the weights of filter circuit 357 which corresponds to the filter 257 of FIG.
2, so that the transfer function characteristics of filter 357 can be transferred to the probe generation circuit 353.
The output of probe generation circuit 353 is probe signal n, which is fed to filter 357, LMS circuit 358, and addition circuit 355.
Another modification of the FIG.
2 system is that the output of the residual sensor is fed into another electrical addition circuit 359a, which receives as input the output of residual sensor 12, and also receives, through an inverted input, the output of filter 357 along line 356.
The output of addition circuit 359a is then fed as an input to LMS circuit 352.
FIG.
3 presents an approach for deriving the probe signal n from on-line measurements of the residual signal e.
According to the invention, the spectral shape of the probe signal is optimized to result in nominally a constant signal-to-noise ratio (SNR) for the purpose of adapting the plant filter P 357 throughout the frequency range of concern.
In addition, this SNR is maximized consistent with limiting noise amplification to a specified level.
Finally, since injection of the probe signal n will degrade the effective convergence rate for the control filter, a procedure for minimizing this degradation is included.
The theory embodied in Applicant's embodiments adapted to attain the above goals will now be derived