US3926054A
Expired / Lapsed
US
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Gravity gradiometer
Assignee: Charles Stark Draper Laboratory Inc
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Filing: 1974-11-11
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Granted: 1975-12-16
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Expires: 1994-11-11
Abstract
Abstract An apparatus for continuously measuring the gravity gradient. Two dynamically balanced pendulums (DBP''s) are configured with their respective sensitive axes being parallel to a common gradiometer sensitive axis. The DBP''s each include a pendulous sensor, with the sensors being separated by a predetermined distance along the gradiometer sensitive axis. A coupling means rotationally couples the sensors about their sensitive axes. According to one embodiment, the first DBP (DBP-1) is configured as an accelerometer having associated servo electronics and a torque motor. DBP-1 nulls the angular displacement of the DBP-1 sensor input axis from its sensitive axis (induced by the gravitational field at the DBP-1 sensor axis) by rotating the coupled sensors about their respective sensitive axes at an angular rate proportional to the gravitational acceleration sensed by the DBP-1 sensor. The second DBP (DBP-2) is arranged in a torque-to-balance loop configuration having associated servo electronics and a torquer. DBP-2 nulls the angular displacement of the DBP-2 sensor input axis from its sensitive axis (induced by both the gravitational field at the DBP-2 sensor and rotation of the coupled sensors) by generating a torque-to-null signal, to which the torquer is responsive to balance DPB-2. The torque-tonull for this loop is proportional to the difference in gravitational forces sensed by the DBP-1 and DBP-2 sensors. When the sensitive axis is vertically aligned, the torque-to-null is directly proportional to the vertical gravity gradient along the length of the coupling shaft.
Inventors
- 👤 Sheldon W Buck
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-03 22:58
CPC Classifications
G; G01; G01V; G01V7/00; G01V7/12
Claims Analysis
Total Claims: 24
Claim 1
Independent Claim
111 words
A gravity gradiometer comprising: A. first and second dynamically balanced pendulum (DBP), each including a sensor having perpendicular DBP input and output axes and a DBP sensitive axis, said DBP sensitive axis being perpendicular to said output axis and having a common intersection point with said input and output axes, wherein the sensitive axis of each sensor is parallel to a common gradiometer sensitive axis, and B. a means for coupling said first and second sensors to rotate at related angular rates about their respective sensitive axes, said angular rates being related to physical characteristics of said sensors, said sensors being separated by a predetermined distance along said gradiometer sensitive axis.
Claim 2
Dependent Claim
111 words
A gravity gradiometer comprising: A. first and second dynamically balanced pendulum (DBP), each including a sensor having perpendicular DBP input and output axes and a DBP sensitive axis, said DBP sensitive axis being perpendicular to said output axis and having a common intersection point with said input and output axes, wherein the sensitive axis of each sensor is parallel to a common gradiometer sensitive axis, and B. a means for coupling said first and second sensors to rotate at related angular rates about their respective sensitive axes, said angular rates being related to physical characteristics of said sensors, said sensors being separated by a predetermined distance along said gradiometer sensitive axis.
Claim 3
Dependent Claim
15 words
A gravity gradiometer according to claim 1 wherein said coupling means mechanically couples said sensors.
Claim 4
Dependent Claim
27 words
A gravity gradiometer according to claim 2 wherein said coupling means comprises a shaft rigidly coNnecting said sensors, said shaft being coaxial with said gradiometer sensitive axis.
Claim 5
Dependent Claim
15 words
A gravity gradiometer according to claim 1 wherein said coupling means electrically couples said sensors.
Claim 6
Dependent Claim
79 words
A gravity gradiometer according to claim 4 wherein said coupling means comprises a synchro resolver having an angle encoder associated with one of said sensors for generating an angle signal representative of the angular displacement of that sensor about its sensitive axis, and a driving means associated with the other of said sensors, said driving means being responsive to said angle signal for angularly displacing said other sensor about its sensitive axis by an angle related to said signal.
Claim 7
Dependent Claim
57 words
A gravity gradiometer according to claim 1 wherein said first DBP (DBP-1) comprises an accelerometer servo loop, said loop being configured to null gravity-induced displacements of the DBP-1 input axis from the DBP-1 sensitive axis and to rotate said first sensor about said DBP-1 sensitive axis at an angular rate proportional to the gravitational force applied thereto.
Claim 8
Dependent Claim
64 words
A gravity gradiometer according to claim 6 wherein said second DBP (DBP-2) comprises a torque-to-balance loop (TBL), said TBL being configured to null displacements of the DBP-2 input axis from the DBP-2 sensitive axis, said displacements being due to both the gravitational force applied to said second sensor and any torque applied to said second sensor about its sensitive axis via said coupling means.
Claim 9
Dependent Claim
38 words
A gravity gradiometer according to claim 7 wherein the ratio of said angular rates of said first and second sensors is proportional to the square root of the ratio of the pendulosities of said first and second sensors.
Claim 10
Dependent Claim
100 words
A gravity gradiometer according to claim 6 wherein said accelerometer servo loop comprises a pendulous integrating gyro accelerometer (PIGA) including said first sensor, said first sensor being: a pendulous integrating gyro (PIG-1) having its sensitive axis aligned with and being free to rotate about said DBP-1 sensitive axis, and said PIGA further including: A. servo electronics including a signal generator for generating a control signal representative of the angular displacement of said PIG-1 about said DBP-1 output axis, and B. a torque motor responsive to said control signal to apply a torque to said PIG-1 about said DBP-1 sensitive axis.
Claim 11
Dependent Claim
149 words
A gravity gradiometer according to claim 9 wherein said PIG-1 comprises: A. a gyro float, said float being free to rotate about said DBP-1 output axis, said float being characterized by a primary mass having its center of gravity located at the point of intersection of said DBP-1 input and output axes and an unbalance mass having its center of gravity located at a predetermined distance from said intersection point along a PIG-1 spin axis, said PIG-1 spin axis passing through said intersection point and being perpendicular to both said DBP-1 input and output axis, and B. a gyro wheel and wheel driving means, said wheel being driven by said driving means to rotate at a predetermined angular rate about said PIG-1 spin axis, said wheel being coupled to said float so that the angular displacements of said input axis and said float about said output axis are identical.
Claim 12
Dependent Claim
64 words
A gravity gradiometer according to claim 10 wherein said second DBP (DBP-2) comprises a torque-to-balance loop (TBL), said TBL being configured to null displacements of the DBP-2 input axis from the DBP-2 sensitive axis, said displacements being due to both the gravitational force applied to said second sensor and any torque applied to said second sensor about its sensitive axis via said coupling means.
Claim 13
Dependent Claim
87 words
A gravity gradiometer according to claim 11 wherein said TBL includes said second sensor, said second sensor being: a pendulous integrating gyro (PIG-2), said PIG-2 having its sensitive axis aligned with said DBP-2 sensitive axis, and said TBL further Includes: A. servo electronics including a signal generator for generating a control signal representative of the angular displacement of said PIG-2 about said DBP-2 output axis, and B. a PIG torquer responsive to said control signal to apply a torque to said PIG-2 about said DBP-2 output axis.
Claim 14
Dependent Claim
149 words
A gravity gradiometer according to claim 12 wherein said PIG-2 comprises: A. a gyro float, said float being free to rotate about said DBP-2 output axis, said float being characterized by a primary mass having its center of gravity located at the point of intersection of said DBP-2 input and output axes and an unbalance mass having its center of gravity located at a predetermined distance from said intersection point along a PIG-2 spin axis, said PIG-2 spin axis passing through said intersection point and being perpendicular to both said DBP-2 input and output axes, and B. a gyro wheel and wheel driving means, said wheel being driven by said driving means to rotate at a predetermined angular rate about said PIG-2 spin axis, said wheel being coupled to said float so that the angular displacements of said input axis and said float about said output axis are identical.
Claim 15
Dependent Claim
57 words
A gravity gradiometer according to claim 13 wherein the ratio of said angular rates of said first and second sensor is proportional to the product of the ratio of the gyro wheel angular momentum to the pendulosity of said first sensor and the ratio of the pendulosity to the gyro wheel angular momentum of said second sensor.
Claim 16
Dependent Claim
65 words
A gravity gradiometer according to claim 10 wherein said second DBP (DBP-2) comprises a wheel speed control loop (WSCL), said WSCL being configured to null displacements of the DBP-2 input axis from the DBP-2 sensitive axis, said displacements being due to both gravitational force applied to said second sensor and any torque applied to said second sensor about its sensitive axis via said coupling means.
Claim 17
Dependent Claim
69 words
A gravity gradiometer according to claim 15 wherein said WSCL includes said second sensor, said second sensor being: a pendulous integrating gyro (PIG-2), said PIG-2 having its sensitive axis aligned with said DBP-2 sensitive axis, and said WSCL further includes: a signal generator for generating a wheel speed control signal, said wheel speed control signal being representative of the angular displacement of said PIG-2 about said DBP-2 output axis.
Claim 18
Dependent Claim
171 words
A gravity gradiometer according to claim 16 wherein said PIG-2 comprises: A. a gyro float, said float being free to rotate about said DBP-2 output axis, said float being characterized by a primary mass having its center of gravity located at the point of intersection of said DBP-2 input and output axes and an unbalance mass having its center of gravity located at a predetermined distance from said intersection point along a PIG-2 spin axis, said PIG-2 spin axis passing through said intersection point and being perpendicular to both said DBP-2 input and output axes, and B. a gyro wheel and wheel driving means, said wheel driving means being responsive to said wheel speed control signal to rotate said wheel at an angular rate about said PIG-2 spin axis, said rate being proportional to the angular displacement of said PIG-2 about said DBP-2 output axis, and said wheel being coupled to said float so that the angular displacements of said input axis and said float about said output axis are identical.
Claim 19
Dependent Claim
57 words
A gravity gradiometer according to claim 17 wherein the ratio of said angular rates of said first and second sensor is proportional to the product of the ratio of the gyro wheel angular momentum to the pendulosity of said first sensor and the ratio of the pendulosity to the gyro wheel angular momentum of said second sensor.
Claim 20
Dependent Claim
112 words
A gravity gradiometer according to claim 1 wherein said first and second DBP''s (DBP-1 and DBP-2) comprise an average acceleration loop, said loop being configured to null Angular displacements of DBP-1 and DBP-2 input axes from the respective DBP sensitive axes, said displacements being due to both gravitational force applied to said first and second sensors and any torque applied to said first and second sensors about their respective sensitive axes via said coupling means, and said loop being further configured to rotate first and second sensors about their respective DBP sensitive axes at an angular rate, said rate being proportional to the sum of the gravitational forces applied to each sensor.
Claim 21
Dependent Claim
148 words
A gravity gradiometer according to claim 19 wherein said average acceleration loop comprises: A. said first and second sensors, B. a signal generator associated with each sensor for generating an error control signal representative of the angular displacement of its associated sensor about its DBP output axis, C. a torquer associated with each sensor responsive to said error control signal to apply a torque to its associated sensor about its DBP output axis, D. a sum network for generating said sum control signal representative of the sum of the error control signal generated by said signal generators, E. a torque motor responsive to said sum control signal to apply a torque to said first and second sensors about their respective DBP sensitive axes, and F. a difference network for generating a difference control signal representative of the difference between the error control signals generated by said signal generators.
Claim 22
Dependent Claim
178 words
A gravity gradiometer according to claim 20 wherein each of said first and second sensors comprises a pendulous integrating gyro (PIG), each PIG having its sensitive axis aligned with the associated DBP sensitive axis, and each PIG including: A. a gyro float, said float being free to rotate about its associated DBP output axis, said float being characterized by a primary mass having its center of gravity located at the point of intersection of the associated DBP input and output axes and an unbalance mass having its center of gravity located at a predetermined distance from said intersection point along a PIG spin axis, said PIG spin axis passing through said intersection point and being perpendicular to both associated DBP input and output axes, and B. a gyro wheel and wheel driving means, said wheel being driven by said driving means to rotate at a predetermined angular rate about said PIG spin axis, said wheel being coupled to said float so that the angular displacements of said input axis and said float about said output axis are identical.
Claim 23
Dependent Claim
139 words
A gravity gradiometer according to claim 19 wherein said average acceleration loop comprises: A. said first and second sensors, B. a signal generator associated with each sensor for generating an error control signal representative of the angular displacement of its associated sensor about its DBP output axis, C. a wheel speed control means associated with each sensor responsive to said error control signal to generate a wheel drive signal, D. a sum network for generating a sum control signal representative of the sum of said error control signals applied from each of said signal generators, E. a torque motor responsive to said sum control signal to apply a torque to both of said sensors about their respective DBP sensitive axes, and F. a difference network for generating a difference signal representative of the difference between said error control signals.
Claim 24
Dependent Claim
205 words
A gravity gradiometer according to claim 22 wherein each of said first and second sensors comprises a pendulous integrating gyro (PIG), each PIG having its sensitive axis aligned with the associated DBP sensitive axis, and each PIG including: A. a gyro float, said float being free to rotate about its associated DBP output axis, said float being characterized by a primary mass having its center of gravity located at the point of intersection of the assoCiated DBP input and output axes and an unbalance mass having its center of gravity located at a predetermined distance from said intersection point along a PIG spin axis, said PIG spin axis passing through said intersection point and being perpendicular to both associated DBP input and output axes, and B. a gyro wheel and wheel driving means, said wheel driving means being responsive to the associated one of said wheel speed drive signals to rotate said wheel at an angular rate about said PIG spin axis, said rate being proportional to the angular displacement of said PIG about its associated DBP output axis, and said wheel being coupled to said float so that the angular displacements of said input axis and said float about said output axis are identical.
References Cited (Backward Citations)
US3073165A
Cited
US3180151A
Cited
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1978-12-15 | 1979-06-16 | 1979-12-16 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1982-12-15 | 1983-06-16 | 1983-12-16 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1986-12-15 | 1987-06-16 | 1987-12-16 | $7700.00 | Window Closed / Lapsed |