Device for quantitatively measuring the relative position and orientation of two bodies in the presence of metals utilizing direct current magnetic fields

• US 4,945,305 A
• Filed: 04/11/1989
• Issued: 07/31/1990
• Est. Priority Date: 10/09/1986
• Status: Expired due to Term

• Current Assignee: BAE Systems Plc
• Original Assignee: Ascension Technology Corporation (Roper Technologies, Inc.)
• Inventors: Blood, Ernest B.
• Primary Examiner(s): Eisenzopf, Reinhard J.
• Assistant Examiner(s): Snow, Walter E.
• Application Number:
  US07/336,342
• Time in Patent Office: 476 Days
• Field of Search: 324/207, 324/208, 324/235, 324/247, 342/450, 342/451, 342/452, 342/453, 348/870.31
• US Class Current: 324/207.17
• CPC Class Codes: F41G 3/225 Helmet sighting systems
• CPC Class Codes: G01B 7/004 for measuring coordinates of points
• CPC Class Codes: G01B 7/14 for measuring distance or clearance between spaced objects or spaced apertures G01B7/30 takes precedence
• CPC Class Codes: H04B 5/00 Near-field transmission systems, e.g. inductive or capacitive transmission systems
• CPC Class Codes: H04B 5/26 using coils
• CPC Class Codes: H04B 5/73 for taking measurements, e.g. using sensing coils

Abstract

A device for measuring the position (location and orientation), in the six degrees of freedom of receiving antennae (3) with respect to transmitting antennae (2) utilizing pulsed DC magnetic signals. The transmitting and receiving components consist of two or more transmitting antennae of known location and orientation with respect to each other. The transmitting antenna (2) are driven one at a time (or in the case of three or more antennae one or two at a time) by a pulsed, direct current signal. The receiving antennae (3) measure the transmitted direct current magnetic fields and the earth'"'"'s magnetic field. A computer (5) is used to control the transmitting and receiving elements and to convert the received signals into location and orientation outputs.

Claims

1. A device for quantitatively measuring the position of receiver antennae relative to transmitter antennae comprising:

transmitter antennae consisting of at least two aparallel antennae to generate at least two DC magnetic vectors;

drive means for sequentially supplying said aparallel antennae with DC pulses to generate said DC magnetic vectors;

receiver antennae consisting of at least two aparallel antennae to detect said DC magnetic vectors;

the number of transmitter antennae times the number of receiver antennae being at least equal to the number of degrees of freedom of the desired quantitative measurement of the position of the receiver antennae relative to the transmitter antennae;

means for compensating for the effects of the earth'"'"'s magnetic field on the operation of the device; and

signal processing means to ascertain the magnitude of the detected DC magnetic vectors and to quantitatively compute said relative position from said received DC magnetic vectors.

2. A device according to claim 1 wherein the number of transmitter antennae times the number of receiver antennae is at least six.

3. A device according to claim 2 wherein there are three transmitter antennae arranged to generate three orthogonal DC magnetic vectors.

4. A device according to claim 2 wherein there are three receiver antennae arranged to detect said generated DC magnetic vectors on three orthogonal axes.

5. A device according to claim 4 wherein there are three transmitter antennae arranged to generate three orthogonal DC magnetic vectors.

6. A device according to claim 5 wherein said transmitter antennae consist of three orthogonal wire windings.

7. A device according to claim 3 wherein said drive means sequentially supplies each transmitter antennae one at a time with a DC pulse.

8. A device according to claim 3 wherein said drive means sequentially supplies transmitter antennae in pairs with a DC pulse.

9. A device according to claim 6 wherein said receiver simultaneously detects three orthogonal components of said DC magnetic vectors.

10. A device according to claim 1 wherein said means for compensating for the earth'"'"'s magnetic field comprises using said receiver antennae to detect components of the earth'"'"'s magnetic field while the transmitter antennae are not transmitting, causing said signal processing means to ascertain the magnitude of said components of the detected earth'"'"'s magnetic field and using the information so ascertained to compensate for the detection of the earth'"'"'s magnetic field by the receiver antennae when the transmitter antennae are transmitting DC magnetic vectors.

11. A device according to claim 1 wherein said DC pulses are of square waveform.

15. A device according to claim 1, wherein said receiving means for receiving said transmitted direct current magnetic fields consists of three orthogonal antennae axes that are sensitive to transmitted direct current magnetic fields to earth'"'"'s magnetic fields.

16. A device according to claim 1 wherein low frequency AC noise interference superimposed on the detected DC magnetic vectors is cancelled by said signal processing means by first measuring the desired signal (S) with the interference (N) to provide a first measurement M(t) which is S+N, then measuring the desired signal with the interference (N) an odd number of half periods of the low frequency noise interference after the first measurement to provide a second measurement M(t+n/f) which is S-N when n is the odd number and f is the frequency of the noise, and adding the first and second measurements together to obtain the desired signals free from the interference N.

17. A device according to claim 10 wherein AC noise interference superimposed on the detected DC magnetic vectors is cancelled by using said receiver antennae to sequentially measure each transmitter vector and the earth'"'"'s magnetic field while the transmitter antennae are not transmitting, at a rate equal to the frequency of the noise, whereby the noise is treated as if it were a part of the earth'"'"'s magnetic field, said signal processing means being caused to ascertain the magnitude of components of the detected earth'"'"'s magnetic field and noise and to use the information so ascertained to compensate for the detection of the earth'"'"'s magnetic field and the noise by the receiver antennae when the transmitter antennae are transmitting DC magnetic vectors.

18. A device according to claim 1 wherein low frequency AC noise interference superimposed on the detected DC magnetic vectors is minimized by the signal processing means by ascertaining the zero crossing points of the AC noise and ascertaining the magnitude of the detected magnetic vectors at said zero crossing points.

19. A device according to claim 18 wherein successive measurements of said magnitude are made at zero crossing points an odd number of half periods, of the low frequency AC noise interference, apart, these measurements are added together to cancel remaining interference from the desired signals.

20. A device according to claim 10 wherein said signal processing means computes the components of the earth'"'"'s magnetic field between successive detections thereof while the transmitter antennae are not transmitting and uses these computed components to compensate for the earth'"'"'s magnetic field detected by the receiver antennae while the transmitter antennae were transmitting between said successive detections.

21. A device according to claim 10 wherein said signal processing means projects the components of the earth'"'"'s magnetic field between successive detections thereof while the transmitter antennae are not transmitting and uses these projected components to compensate for the detection of the earth'"'"'s magnetic field by the receiver antennae while the transmitter antennae are transmitting between following successive said detections.

22. A device according to claim 1 wherein, in order to increase usable rate of supply of said DC pulses in the presence of metals, said signal processing means makes multiple measurements of the detected DC magnetic vectors during the decay of interfering eddy currents induced by the wavefront of each DC pulse, fits these measurements to an appropriate exponential function, projects the steady state measurement of the detected DC magnetic vectors after said decay is complete and uses these projected steady state measurements to compute said position.

23. A device according to claim 1 wherein, in order to increase the usable rate of supply of said DC pulses in the presence of metals stationary relative to the transmitting antennae, the signal processing means measures the detected DC magnetic vectors during a DC pulse after decay of eddy currents induced by the wavefront of that DC pulse for a known location of the receiver antennae relative to the transmitter antennae, measures the detected DC magnetic vectors at a desired rate of supply of said, DC pulses in the same said known location, computes the eddy current induced distortion in the measurement made at the desired rate, stores the computed distortion information and uses this stored information to correct subsequent measurements of detected DC magnetic vectors at said desired rate at said known location to compute attitude data free from eddy current induced distortion.

25. A device according to claim 1 wherein said means for compensating for the effects of the earth'"'"'s magnetic field comprises alternating the polarity of transmitted DC magnetic vectors to discriminate against the earth'"'"'s magnetic field.

12. A device for quantitatively measuring the relative location and orientation of receiving antennae with respect to transmitting antennae in the presence of metals utilizing direct current magnetic fields, comprising:

(a) Transmitting means for transmitting direct current magnetic fields sequentially on three orthogonal axes no more than two at a time;

(b) Receiving means for receiving said transmitted direct current magnetic fields;

(c) Means for supplying direct current electrical signal pulses to said transmitting means for creating said transmitted direct current magnetic fields;

(d) Means for controlling circuit elements of said transmitting and receiving means, measuring received signals, and converting output signals from said receiving means into location in three coordinate directions and orientation about three coordinate axes measurements.

13. A device according to claim 12 comprising said transmitting means consists of a core and three orthogonal antenna axis wire windings.

14. A device according to claim 12 wherein said means for controlling, measures the earth'"'"'s magnetic field while the said transmitting means is shut off, and produces a signal representing the earth'"'"'s magnetic field and subtracts said earth'"'"'s field signal from said received signal to cancel the effect of the earth'"'"'s magnetic field when the transmitting means is transmitting.

24. A system for quantitatively measuring the position of magnetic field sensor means with respect to magnetic field transmitter means, comprising:

transmitter means consisting of at least two magnetic field transmitter elements to generate a corresponding number of aparallel DC magnetic field vectors;

drive means for sequentially supplying said transmitter elements with DC pulses to generate said aparallel DC magnetic field vectors;

magnetic field sensor means consisting of at least two magnetic field sensor elements differentially responsive to said magnetic field vectors generated by the said transmitter elements;

the arithmetic product of the number of transmitter elements and the number of sensor elements being not less than the number of degrees of freedom to be measured;

means for compensating for the effects of the earth'"'"'s magnetic field;

means operable to effect executive control of the said drive means and of the said compensating means and to compute from signals derived as a result of such executive control the relative position of the magnetic field sensor means with respect to the said magnetic field transmitter means.