STABILIZATION SYSTEM FOR SENSORS ON MOVING PLATFORMS

• US 20110175604A1
• Filed: 01/15/2010
• Published: 07/21/2011
• Est. Priority Date: 01/15/2010
• Status: Active Grant

• Current Assignee: Vale SA (Caixa de Previdência Dos Funcionários Do Banco Do Brasil)
• Original Assignee: Vale SA (Caixa de Previdência Dos Funcionários Do Banco Do Brasil)
• Inventors: Walker, Peter Whyte, West, Gordon Fox, POLZER, Benjamin David, Hurley, Peter Anthony, Hogg, Robert Leslie Scott
• Granted Patent: US 8,456,159 B2
• Time in Patent Office: Days
• US Class Current: 324/246
• CPC Class Codes: G01R 33/022 Measuring gradient
• CPC Class Codes: G01V 3/165 operating with magnetic or electric fields produced or modified by the object or by the detecting device with electromagnetic waves G01V3/17

Abstract

A stabilized field sensor apparatus collects field data, in particular magnetic field data, with reduced motion noise. The apparatus includes a tear drop shaped housing, a tow frame in the housing, a plurality of vibration isolating dampers spaced around the frame, a base assembly mounted to the dampers, a support pedestal having a bottom end fixed to the base assembly and an upper free end, a single spherical air bearing connected to the upper free end of the pedestal, an instrument platform with a lower hollow funnel having an upper inside apex supported on the air bearing for a one point support, principal and secondary gyro stabilizers for maintaining pivotal and rotational stability, and at least one field sensor mounted to the instrument platform for collecting the field data while being stabilized against motion noise including vibration, pivoting and rotation from the base assembly, from the tow frame and from the housing. Stabilization of the instrument platform is enhanced by preserving accurate balance through a dynamic balancing system whereby small masses are moved under computer control to maintain the center of mass of the instrument platform at the center of rotation of the spherical air bearing. The dynamic stabilization process is made more precise by actively vibrating the instrument platform by a set of linear vibrators.

Claims

1. A stabilized field sensor apparatus (10) for collecting field data with reduced motion noise, comprising:

a tear drop shaped housing (20) having a bulbous front portion, a pointed rear end, a first front-to-back horizontal axis (22) and a second side-to-side horizontal axis (24);

a tow frame (30) in the bulbous end of the housing, the tow frame having a base ring (32), two crossing arcuate bars (34a, 34b) each with opposite ends connected at spaced locations to and around the base ring, and two horizontal axles (36a, 36b) laying on the second horizontal axis (24) of the housing (20) and protruding from opposite ends of one of the bars (34a), the axles protruding from opposite sides of said base ring and out through opposite sides of the bulbous portion of the housing for attaching the apparatus to a vehicle for carrying the apparatus, the axles being pivotally connected to the housing and the frame being sized for free relative rotation of the frame in and to the housing about the second horizontal axis (24);

a plurality of vibration isolating dampers (40) connected to and spaced around the tow frame (30), the dampers being effective for dampening vertical and horizontal vibrations of the tow frame;

a base assembly (50) mounted to the plurality of vibration isolating dampers (40) and positioned at least partly in the tow frame (30) and entirely in the bulbous portion of the housing (20) for free movement of the base assembly in the housing when the tow frame pivots about the second horizontal axis (24) of the housing (20), vertical and horizontal vibrations of the housing and frame being dampened by the dampeners before reaching the base assembly (50);

a support pedestal (54) having a bottom end fixed to the base assembly (50) near a bottom of the base assembly, the support pedestal extending upwardly in the base assembly and into the tow frame (30) and having an upper free end spaced inwardly from the tow frame;

a single spherical air bearing (55) connected to the upper free end of the pedestal;

a structurally rigid instrument platform (70) having a lower hollow cone portion (72) with an upper inside apex engaged to and supported on the spherical air bearing (55) for a rotatable and pivotal support of the instrument platform on the support pedestal, the instrument platform having an upper stem (71) extending upwardly of the cone portion, above the apex and into the tow frame (30), the instrument platform (70) having a central axis (75) extending through the cone portion and the stem;

a dynamic balancing system (80) for dynamically balancing the platform on the air bearing; and

at least one field sensor (79) mounted to the instrument platform (70) for collecting field data while being balanced against motion noise including vibration, pivoting and rotation from the base assembly, from the tow frame and from the housing.

2. The apparatus of claim 1, including a principal gyro stabilizer (91) mounted to the stem (71) and positioned on the central axis for reducing rotational jitter in roll and pitch of the instrument platform on the support pedestal and at least one secondary gyro stabilizer (78) mounted to the instrument platform at a location spaced radially from the central axis (75) for reducing rotational jitter in yaw.

3. The apparatus of claim 1, wherein the base assembly (50) comprises a suspension ring (51) connected to the vibration isolating dampers (40), a base plate (53) spaced below the suspension ring and having a plurality of circumferential spaced radially extending slots (60), a plurality of base ribs (52) connected between the suspension ring and the base plate and spaced around the base plate and suspension ring, each base rib (52) having a lower radially outwardly extending arcuate portion (52a) extending through one of the slots (60) in the base plate (53) and an inwardly inclined portion (52b) connected between the arcuate portion of the base rib and the suspension ring, a plurality of lower diagonal braces (56a) each connected between a lower end of each base rib and an intermediate location of an adjacent base rib, and a plurality of upper diagonal brace (56b) each connected between an upper end on each base rib and the intermediate location on the adjacent base rib, the diagonal braces increasing torsional rigidity of the base assembly (50), the support pedestal (54) having an upper portion above the base plate (53) and a lower portion below the base plate, a lower end of each base rib (52) being connected the lower portion of the support pedestal (54).

4. The apparatus of claim 1, wherein the base assembly (50) comprises a suspension ring (51) connected to the vibration isolating dampers (40), a base plate (53) spaced below the suspension ring and having a plurality of circumferential spaced radially extending slots (60), the plurality of base ribs (52) connected between the suspension ring and the base plate and spaced around the base plate and suspension ring, each base rib (52) having a lower radially outwardly extending arcuate portion (52a) extending through one of the slots (60) in the base plate (53) and an inwardly inclined portion (52b) connected between the arcuate portion of the base rib and the suspension ring, a plurality of lower diagonal braces (56a) each connected between a lower end of each base rib and an intermediate location of an adjacent base rib, and a plurality of upper diagonal brace (56b) each connected between an upper end on each base rib and the intermediate location on the adjacent base rib, the diagonal braces increasing torsional rigidity of the base assembly (50), the support pedestal (54) having an upper portion above the base plate (53) and a lower portion below the base plate, a lower end of each base rib (52) being connected the lower portion of the support pedestal (54), and a pair of reinforcing plates (61) on opposite sides of each base rib at a location below the base plate (53), the suspension ring, the ribs and the base plate being made of sandwich cored carbon fiber composite.

5. The apparatus of claim 1, including a principal gyro stabilizer (91) mounted to the stem (71) and positioned on the central axis for reducing rotational jitter in roll and pitch of the instrument platform on the support pedestal and at least one secondary gyro stabilizer (78) mounted to the instrument platform at a location spaced radially from the central axis (75) for reducing rotational jitter in yaw, the stem portion (71) and the cone portion (72) of the instrument platform (70) each comprising a single piece of sandwich cored carbon composite material, the stem portion (71) containing a plurality of stacked instrument modules (77) including the principal gyro stabilizer (91), a data acquisition system (90) and a power module (98) comprising an inverter and battery (100a), the instrument platform (70) including a plurality of circumferentially spaced vertical stiffening platform ribs (74) extending along the cone portion (72) and the stem (71), and a plurality of horizontal reinforcing flanges (73) expending around the platform and past the platform ribs, the apparatus including a pair of weight-balanced secondary gyro stabilizers (78) mounted on opposite sides of the stem and on one of the horizontal reinforcing flanges (73).

6. The apparatus of claim 1, wherein the field sensor (79) comprises a feedback induction coil for collecting magnetic field data including low frequency magnetic measurements in a bandwidth of 1 Hz to 25 Hz.

7. The apparatus of claim 1, wherein the field sensor (79) comprises feedback induction coils for collecting magnetic field data including low frequency magnetic measurements in a bandwidth of 1 Hz to 25 Hz, the apparatus including three of said sensors mounted at equally spaced locations around the cone portion, each comprising a vector component sensor (79) situated adjacent the lower rim of the cone and each having a longitudinal axis parallel to the cone surface and coplanar with the axis of the cone.

8. The apparatus of claim 1, wherein each vibration isolating dampers (40) comprises a set of vertical dampers (42) which suspend the base assembly from the arcuate bars (34a, 34b) of the frame, and horizontal dampers (44) which laterally connect cone portion to the base assembly (50) to the base ring (32) of the frame (30).

9. The apparatus of claim 1, wherein the base ribs (52) of the base assembly (50) are angled to accommodate a 10 to 30 degree roll and pitch range of the instrument platform (70) on the spherical air bearing (55).

10. The apparatus of claim 1, including a principal gyro stabilizer (91) mounted to the stem (71) and positioned on the central axis for reducing rotational jitter in roll and pitch of the instrument platform on the support pedestal and at least one secondary gyro stabilizer (78) mounted to the instrument platform at a location spaced radially from the central axis (75) for reducing rotational jitter in yaw, the gyro stabilizers being mounted to the instrument platform (70) inside a metal of high magnetic permeability (99), along with an inverter and a battery (100b).

11. The apparatus of claim 1, further comprising a dynamic balancing system (80) comprising a PC separate from the apparatus, a set of linear mass-balance actuators (A) mounted on the instrument platform (70) and oriented at 90 degrees to each other, as well as an embedded computer mounted on the instrument platform (70) which receives instructions from the PC for controlling the set of mass-balance actuators (A).

12. The apparatus of claim 1, further comprising:

a dynamic balancing system (80) comprising an embedded computer mounted on the platform (70);

a PC separate from the apparatus;

a dynamic balancing algorithm executing on the PC;

a set of three mutually-perpendicular linear pneumatic vibrators (V) contained within the support pedestal (54) below the air bearing (55);

each of the three mutually-perpendicular linear pneumatic vibrators (V) vibrating at a different frequency allowing the dynamic balancing algorithm to create information on how to more accurately determine the required re-distribution of mass, the dynamic balancing system further comprising a means of wirelessly conveying the information created by the dynamic balancing algorithm executing on the PC to the embedded computer.

13. A sensor stabilization device (10) to facilitate continuous collection of magnetic field data including low frequency magnetic measurements in the bandwidth of 1 Hz to 25 Hz without being affected by motion noise, said device (10) comprising:

a tear drop shaped housing (20);

a tow frame (30) comprising a base ring (32), two raised, convex cross bars (34a, 34b) connected to said base ring (32), and two horizontal axles (36a, 36b) protruding out from one of the two cross bars (34a, 34b) and positioned on opposite sides of the base ring (32), each of said two horizontal axles (34a, 34b) being pivotally connected to said housing (20) by reciprocal bearings (32a, 32b) and each of said two horizontal axles (34a, 34b) penetrating the housing (20) through said reciprocal bearings (32a, 32b), the horizontal axles (36a, 36b) forming tow points which facilitate attachment to a vehicle;

a base assembly (50) connected to the frame but vibrationally isolated from the housing (20) and from the frame (30), the base assembly comprising a support pedestal (54) having a bottom end integral with a circular base plate (53) which has an underside (62), the support pedestal (54) having an opposite top end with a single spherical air bearing (55) comprising a center of rotation, the base assembly (50) further comprising a suspension ring (51), a plurality of vertical ribs (52) connected to the circular base plate (53), said ribs (52) being radially angled and extending through slots (60) in said circular base plate (53), said vertical ribs (52) being sandwiched between pairs of ribs (61) permanently attached to said underside (62) of said base plate (53), said base assembly (50) also comprising diagonal carbon fiber braces (56) for increasing torsional rigidity and which connect adjacent members of said plurality of vertical ribs (52) to each other;

a hollow funnel-shaped rotationally stabilized instrument platform (70) comprising a single piece of sandwich cored carbon composite material, said platform having a longitudinal axis (75), a center of mass and an outer surface, said platform (70) being supported in an inverted fashion on said single spherical air bearing (55) and on the support pedestal (54), the platform (70) comprising a stem portion (71) and a cone portion (72), said cone portion having a lower rim, the stem portion containing a series of stacked instrument modules (77) comprising a data acquisition system (90), followed by a principal gyro stabilizer (91), followed by a power module (98) comprising an inverter and battery (100a);

three vector component magnetometers (79) each having a longitudinal axis, the magnetometers (79) being mounted on said outer surface of said cone portion (72) adjacent said lower rim, the instrument platform (70) comprising longitudinal ribs (74) fixedly attached to the outer surface of said stem portion (71) and cone portion (72) for additional rigidity to said platform (70);

two secondary opposite gyro stabilizers (78) for resisting rotational jitter and rotational motion about the axis (75) of the platform (70), mounted on the platforms (76) and positioned radially outwardly of the axis (75) of the platform, on either side of said stem portion (71), said two secondary gyro stabilizers (78) being mounted inside a mu-metal shield (99) along with an inverter and a battery (100b),

a dynamic balancing system (80) for ensuring that the platforms (70) center of mass is located at the center of rotation of the air bearing, the dynamic balancing system (80) comprising a set of linear mutually-perpendicular actuators (A) each having a small mass located on a small linear carriage;

a set of linear pneumatic mutually-perpendicular vibrators (V) each vibrating at a different frequency;

a PC separate from the device;

a dynamic balancing algorithm executing on the PC;

an embedded computer mounted on the platform (70) for controlling the set actuators (A); and

a means of conveying information wirelessly from the PC to the embedded computer;

wherein the embedded computer on the platform receives position instructions wirelessly from the dynamic balancing algorithm executing on the PC;

a vibration isolating damper system (40) for isolating the base assembly (50) and the platform (70) from vibrations and rotations of the housing (20), said damper system (40) comprising vertically-oriented dampers (42) for suspending said base from said cross bars (34a, 34b) of the frame, and horizontal dampers (44), for laterally connecting said base assembly (50) to said base ring (32) of the frame (30);

said radial ribs (52) of said base assembly (50) being angled to accommodate a selected amount of roll and pitch range of said instrument platform (70).

14. A stabilized field sensor apparatus for collecting field data with reduced motion noise, comprising:

a housing (20);

a tow frame (30) in the housing (20);

a base assembly (50) mounted to the dampers (40);

a support pedestal (54) having a bottom end fixed to the base assembly (50) and an upper free end;

a single spherical air bearing (55) connected to the upper free end of the pedestal (54);

an instrument platform (70) with a lower hollow funnel having an upper inside apex supported on the air bearing (55) for a one point support and having a central axis (75);

a dynamic balancing system (80) for dynamically balancing the platform on the air bearing; and

at least one field sensor (79) mounted to the instrument platform (70) for collecting the field data while being stabilized against motion noise including vibration, pivoting and rotation from the base assembly (50), from the tow frame (30) and from the housing (20).

15. A stabilized field sensor apparatus for collecting field data with reduced motion noise as claimed in claim 14, further comprising a plurality of gyro stabilizers (91, 78) connected to the instrument platform (70) for maintaining pivotal and rotational stability.

16. A stabilized field sensor apparatus for collecting field data with reduced motion noise as claimed in claim 14, the spherical air bearing (55) comprising a concave supporting section and a supported hemisphere section, wherein both the concave supporting section and the supported hemisphere section comprise a cross section of milled grooves (G) to minimize eddy currents induced by the spherical air bearing.

17. A stabilized field sensor apparatus for collecting field data with reduced motion noise as claimed in claim 14, wherein the instrument platform (70) comprises an upper stem portion (71) having an outside surface and a lower cone (72) portion having also having an outside surface as well as a lower rim.

18. A stabilized field sensor apparatus for collecting field data with reduced motion noise as claimed in claim 14, wherein the spherical air bearing (55) comprises a source of compressed air or gas (57) connected to the concave supporting section for supplying air to the concave supporting section so that the supported hemisphere floats on a cushion of air.

19. A stabilized field sensor apparatus for collecting field data with reduced motion noise as claimed in claim 15, wherein the plurality of gyro stabilizers (91, 78) comprising one principal gyrostabilizer (91) contained within the stem portion (71) of the instrument platform (70), and two secondary gyro stabilizers (78) mounted to and equally spaced around the outside surface of the stem portion (71) of the instrument platform.

20. A stabilized field sensor apparatus for collecting field data with reduced motion noise as claimed in claim 19, wherein the gyro stabilizers are mounted inside a metal enclosure of high magnetic permeability (99).

21. A stabilized field sensor apparatus for collecting field data with reduced motion noise as claimed in claim 20, comprising three field sensors each of which having a longitudinal axis and being mounted and equally spaced apart on the outside surface of the cone portion (72) of the instrument platform (70), wherein the three field sensors (79) are positioned adjacent the lower rim of the cone portion (72) and so that their longitudinal axes are coplanar with the central axis (75) of the instrument platform (70).