Body motion compensation filter with pitch and roll correction
First Claim
1. For use in generating a signal indicative of the vertical displacement of a body travelling through water relative to a datum, the body containing an accelerometer that produces an acceleration signal comprising a vertical acceleration signal and an accelerometer noise signal, the body containing a pressure transducer that produces a pressure signal comprising a position signal indicative of the vertical displacement of the body relative to the datum and a pressure transducer noise signal, a filter comprising:
- differentiation means connectable to the pressure transducer for producing a differentiated signal proportional to the second derivative of the pressure signal;
first summing means, connected to the differentiation means and connectable to the accelerometer, for producing a first summation signal proportional to a weighted sum of the differentiated signal and the acceleration signal, the weighting being such that components of the first summation signal corresponding to the second derivative of the position signal and to the vertical acceleration signal cancel one another, whereby the first summation signal consists essentially of signal components proportional to the accelerometer noise signal and to the second derivative of the pressure transducer noise signal;
integration means connected to the first summing means for producing an integrated signal proportional to the double integral of the first summation signal, the integration means including attenuating means for attenuating zero frequency components of the integrated signal; and
,second summing means, connected to the integration means and connectable to the pressure transducer, for producing a second summation signal proportional to a weighted sum of the integrated signal and the pressure signal, the weighting being such that components of the second summation signal corresponding to the pressure transducer noise signal cancel, whereby the second summation signal is substantially proportional to the position signal.
0 Assignments
0 Petitions
Accused Products
Abstract
An electronic filter for use in determining the position of a body travelling through water relative to a datum such as mean sea level, and having specific application to underwater seismic systems that produce profiles of the terrain beneath bodies of water. The filter is connected to an accelerometer and a pressure transducer, physically located within the body, that respectively produce an acceleration signal indicative of the body'"'"'s vertical acceleration and a pressure signal indicative of the body'"'"'s vertical displacement with respect to the datum. The filter combines the acceleration and pressure signals to effectively isolate a signal proportional to noise generated by the pressure transducer. The filter then combines the signal so isolated with the pressure transducer signal to produce a vertical displacement signal relatively free from noise. The filter is used in association with apparatus that produces a correction signal that approximates accelerometer signal components corresponding to the effect of gravity on the accelerometer. The filter combines the correction signal with the acceleration signal to attenuate noise components in the filter output signal that correspond to the gravity effects.
20 Citations
7 Claims
-
1. For use in generating a signal indicative of the vertical displacement of a body travelling through water relative to a datum, the body containing an accelerometer that produces an acceleration signal comprising a vertical acceleration signal and an accelerometer noise signal, the body containing a pressure transducer that produces a pressure signal comprising a position signal indicative of the vertical displacement of the body relative to the datum and a pressure transducer noise signal, a filter comprising:
-
differentiation means connectable to the pressure transducer for producing a differentiated signal proportional to the second derivative of the pressure signal; first summing means, connected to the differentiation means and connectable to the accelerometer, for producing a first summation signal proportional to a weighted sum of the differentiated signal and the acceleration signal, the weighting being such that components of the first summation signal corresponding to the second derivative of the position signal and to the vertical acceleration signal cancel one another, whereby the first summation signal consists essentially of signal components proportional to the accelerometer noise signal and to the second derivative of the pressure transducer noise signal; integration means connected to the first summing means for producing an integrated signal proportional to the double integral of the first summation signal, the integration means including attenuating means for attenuating zero frequency components of the integrated signal; and
,second summing means, connected to the integration means and connectable to the pressure transducer, for producing a second summation signal proportional to a weighted sum of the integrated signal and the pressure signal, the weighting being such that components of the second summation signal corresponding to the pressure transducer noise signal cancel, whereby the second summation signal is substantially proportional to the position signal. - View Dependent Claims (2, 3)
-
-
4. For use in association with a body travelling through water, the body having an accelerometer which produces a signal indicative of the body'"'"'s acceleration along an axis whose orientation with respect to a vertical position varies with pitching and rolling of the body, a projection of the axis on a first vertical plane being inclined at any instant from a vertical position by an angle θ
-
1, a projection of the axis on a second vertical plane perpendicular to the first plane being inclined at any instant from a vertical position by an angle θ
2, apparatus for reproducing the accelerometer signal with signal components corresponding to the effect of gravity on the accelerometer attenuated, the apparatus comprising;correction signal generating means connectable to the body for generating a correction signal substantially proportional to at least the time varying portion of the product of the cosine of θ
1 and the cosine of θ
2 ; and
,summing means connectable to the accelerometer and to the correction signal generating means for producing a summation signal proportional to a weighted sum of the accelerometer signal and the correction signal, the weighting being such that components of the summation signal corresponding to the correction signal cancel portions of the summation signal corresponding to the effect of gravity on the accelerometer. - View Dependent Claims (5, 6, 7)
-
1, a projection of the axis on a second vertical plane perpendicular to the first plane being inclined at any instant from a vertical position by an angle θ
Specification