Body motion compensation filter with pitch and roll correction

• US 4,222,266 A
• Filed: 08/13/1979
• Issued: 09/16/1980
• Est. Priority Date: 08/17/1978
• Status: Expired due to Term

• Current Assignee: Samuel M. Theodoulou
• Original Assignee: Samuel M. Theodoulou
• Inventors: Theodoulou, Samuel M.
• Primary Examiner(s): Gill, James J.
• Application Number:
  US06/065,782
• Time in Patent Office: 400 Days
• Field of Search: 73/178 R, 73/179, 73/509, 367/130, 367/129, 367/100, 367/106, 367/124, 367/126
• US Class Current: 73/179
• CPC Class Codes: G01C 13/00 Surveying specially adapted to open water, e.g. sea, lake, river or canal liquid level metering G01F
• CPC Class Codes: G01C 21/185 for gravity
• CPC Class Codes: G01V 1/3835 measuring position, e.g. by GPS or acoustically
• CPC Class Codes: Y10S 367/901 Noise or unwanted signal reduction in nonseismic receiving system

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.

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.

2. A filter as claimed in claim 1 in which the attenuating means comprises a high pass filter whose pass band includes at least a substantial portion of the frequency range of the pressure transducer noise signal.

3. A filter as claimed in claim 2 in which the high pass filter completely blocks zero frequency signals.

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.

5. Apparatus as claimed in claim 4 in which the correction signal generating means comprise:

first signal generating means connectable to the body for generating a first signal, substantially proportional to the cosine of θ

₁ ;

second signal generating means connectable to the body for generating a second signal, substantially proportional to the cosine of θ

₂ ;

multiplication means connected to the first and the second signal generating means for producing a correction signal, the correction signal being proportional to the product of the first and second signals.

6. Apparatus as claimed in claim 5 in which the first signal generating means comprise:

a first transducer connectable to the body for producing a first transducer signal proportional to θ

₁ ; and

,

first cosine function generating means connected to the first transducer for producing a first cosine signal proportional to the cosine of the first transducer signal.

7. Apparatus as claimed in claim 6 in which the second signal generating means comprise:

a second transducer connectable to the body for producing a second transducer signal proportional to θ

₂ ; and

,

second cosine function generating means for producing a second cosine signal proportional to the cosine of the second transducer signal.