OFF-LEVELING COMPUTER

• US 3,633,003 A
• Filed: 02/11/1970
• Issued: 01/04/1972
• Est. Priority Date: 02/11/1970
• Status: Expired due to Term

• Current Assignee: Manik Talwani
• Original Assignee: Manik Talwani
• Inventors: Talwani, Manik
• Primary Examiner(s): Botz, Eugene G.
• Assistant Examiner(s): Dildine, Jr., R. Stephen
• Application Number:
  US05/010,327
• Time in Patent Office: 692 Days
• Field of Search: 33/226Z 73/382,504 74/5,5.4,5.41,5.6,5.8,5.9 235/150.25,151.3
• US Class Current: 702/94
• CPC Class Codes: G01V 7/16 specially adapted for use on moving platforms, e.g. ship, aircraft
• CPC Class Codes: G06G 7/78 for direction-finding, locating, distance or velocity measuring, or navigation systems
• CPC Class Codes: Y10T 74/12 Gyroscopes
• CPC Class Codes: Y10T 74/1229 Gyroscope control
• CPC Class Codes: Y10T 74/1232 Erecting

Abstract

This invention describes an off-leveling computer which continuously corrects for the error induced in sea gravimetry measurements because the gravimeter measuring axis is not aligned with the local vertical at all times. The apparatus computes the error in the measurement of the local gravitational acceleration due to off-leveling of a stable platform on which the gravimeter is mounted by first determining the sum of the angular positioning errors induced by the servo loop and the gyro erection system. It then computes the component of the horizontal acceleration which, by virtue of this error in verticality, is along the gravimeter measuring axis. This computed signal is then subtracted from the gravimeter signal to eliminate errors in the measurement of gravitational acceleration due to the misalignment of the gravimeter with the local vertical.

Claims

1. Apparatus for computing error in the measurement of gravity due to off-leveling of a gravimeter mounted on a platform which employs a gyroscope mounted thereon and a servosystem linked to said gyroscope for maintaining the horizontality of said platform, comprising:

means for computing the angular error in the alignment of the measuring axis of said gravimeter in a predetermined direction with respect to the local vertical and for generating a first signal having an amplitude corresponding to the magnitude of said angular error;

means for sensing accelerations to which said gravimeter is subjected, occurring in a plane perpendicular to the measuring axis of said gravimeter in said predetermined direction and for producing a second signal having an amplitude proportional to the acceleration sensed; and

means for multiplying said first signal by said second signal to produce a third signal whose amplitude is the product of the angular off-leveling error and the acceleration sensed, whereby said third signal represents the error in acceleration detected by said gravimeter due to off-leveling in said predetermined direction.

2. The apparatus as recited in claim 1 wherein an error signal whose amplitude is equal to the instantaneous angular error introduced by said servosystem is available as an output thereof and wherein said means for computing and generating a signal whose amplitude is proportional to the angular error in alignment between said measuring axis and said local vertical includes:

means for producing a fourth signal whose amplitude is equal to the instantaneous angular deviation of the spin axis of said gyroscope from the local vertical in said predetermined direction; and

means for adding said fourth signal to the error signal available at the output of said servosytem.

3. The apparatus as recited in claim 2 wherein said predetermined direction is in the direction of maximum off-leveling of said platform.

4. The apparatus as recited in claim 2 wherein said predetermined direction is one of two orthogonally oriented directions used in combination in determining the total off-leveling of said platform in the direction of maximum off-leveling.

5. Apparatus for computing error in the measurement of gravity due to off-leveling of a gravimeter which is subjected to horizontal accelerations and which is mounted on a gyrostabilized platform and for removing this error from the gravity measurement, compriSing:

means for computing the angular off-leveling of said gravimeter in a predetermined direction and for generating a first signal having an amplitude equal to the angular magnitude of said off-leveling;

means for sensing accelerations to which said gravimeter is subjected in said predetermined direction and for providing a second signal having an amplitude proportional to the acceleration sensed;

means for multiplying said first signal with said second signal to produce a third signal whose amplitude is the product of the angle of said off-leveling and the acceleration sensed; and

means for subtracting said third signal from the output signal generated by said gravimeter, whereby whenever said gravimeter is off-leveled and subjected to horizontal accelerations in said predetermined direction, errors in acceleration induced along the measuring axis of said gravimeter are removed from the gravity measurement.

6. Apparatus for eliminating off-leveling error introduced into the measurement of gravity at sea by the motion of a seagoing vessel comprising:

a gyrostabilized platform mounted within said vessel having a gyroscope mounted on said platform, initially oriented with its spin axis perpendicular to the plane of said platform when said platform is horizontal, whereby said spin axis is colinear with the local vertical, and having a servosystem linked to said gyroscope for maintaining the horizontality of said platform when said vessel is subjected to sea motions and which produces a servo loop error signal whose amplitude is proportional to the instantaneous positioning error introduced by said servosystem in returning said platform to a horizontal position, said gyroscope having an orthogonally oriented pair of accelerometers carried on one of its gimbals such that said pair of accelerometers defines a primary horizontal reference plane and including both motor means for changing the orientation of the inner and outer gimbals which support the rotating member of said gyroscope, and gyroerection circuitry coupled to the outputs of said accelerometers and said motor means for producing two signals, one of which controlling the outer gimbal of said gyroscope in response to the output of one of said accelerometers, and the other of which controlling the inner gimbal of said gyroscope in response to the output of the other of said accelerometers, thereby controlling the position of said spin axis in two orthogonal directions such that when said spin axis is made to deviate from the local vertical by horizontal accelerations, it is restored to said local vertical by said gyroerection circuitry and said motor means operating in response to the sensing of horizontal accelerations by said accelerometers;

a gravimeter mounted on said platform and oriented so that its measuring axis is perpendicular to the plane of said platform for producing an output signal whose amplitude is proportional to accelerations having components along its measuring axis;

a second pair of accelerometers, identical to those carried by said gyroscope, mounted on said platform in the same orthogonal directions as those accelerometers carried by said gyroscope whereby this second pair of accelerometers duplicates the accelerometers carried by said gyroscope;

circuit means identical to said gyroerection circuitry and coupled to the outputs of said second pair of accelerometers for producing two additional signals respectively corresponding to the two signals generated by said gyroerection circuitry for controlling the movement of the inner and outer gimbals of said gyroscope;

means for integrating each of these two additional signals over time so as to analog the response of the gyroscope to the two signals from said gyroerection circuitry;

means for adding said servo loop error signal to each of said integrated signals so as to produce two off-leveling error signals corresponding respectively to the angular off-leveling error in each of said orthogonaL directions;

means for multiplying the off-leveling error signal representing the off-leveling error in one of said orthogonal directions by the output of the accelerometer of the second pair oriented in this orthogonal direction and for multiplying the other off-leveling error signal by the output of the accelerometer of the second pair oriented in the other orthogonal direction; and

means for subtracting both of said multiplied signals from the output of said gravimeter so as to provide a corrected signal corresponding to the local gravitational field whereby accelerations due to off-leveling of said platform are removed from the output of said gravimeter.