Methods for using a nuclear magnetic resonance gyroscope as a gyrocompass and gyrocompass

Abstract

To realize a gyrocompass using a nuclear magnetic resonance gyroscope, a method (100) for using a nuclear magnetic resonance gyroscope (10) as a gyrocompass (200) is proposed, wherein the nuclear magnetic resonance gyroscope (10) comprises at least one measuring unit (11) wherein at least one first rotation rate ω R,1 and a second rotation rate ω R,2 are determined using the nuclear magnetic resonance gyroscope (10), where the first rotation rate ω R,1 is determined along a first direction (27) parallel to the Earth's surface (24), and where the second rotation rate ω R,2 along a second direction (28) parallel to the Earth's surface (24), further provided that the first direction (27) is different from the second direction (28), and that at least the first rotation rate ω R,1 and the second rotation rate ω R,2 a north-south direction (26) is determined

Description

[0001] The present invention relates to a method for using a nuclear magnetic resonance gyroscope as a gyrocompass. Furthermore, the present invention relates to a gyrocompass comprising a nuclear magnetic resonance gyroscope. State of the art

[0002] The needle of a magnetic compass points towards the Earth's magnetic north pole. Magnetic north differs from true north, which is defined by the Earth's rotational axis. A gyrocompass, on the other hand, points towards true north.

[0003] A mechanical gyrocompass consists of a rapidly rotating gyroscope suspended in a gimbal. The gyroscope is also positioned so that it experiences a torque as long as its rotation is not pointing north. When the rotation is north, and thus the gyroscope's axis of rotation aligns with the Earth's rotational direction, the torque disappears. Damping causes the gyroscope to come to rest when the applied force is eliminated.

[0004] Gyrocompasses are used particularly in shipping and aviation. A particular advantage of gyrocompasses over magnetic compasses is that gyrocompasses are not susceptible to interference from ferromagnetic materials, such as ship steel.

[0005] However, mechanical gyrocompasses and their gimbal suspension are mechanically complex, large, and also expensive.

[0006] Furthermore, fiber optic gyrocompasses and gyrocompasses based on laser ring resonators are known. These are also large, expensive, and complex, and additionally require mechanical and temperature stabilization. Moreover, fiber optic gyrocompasses and laser ring resonator gyrocompasses are difficult to miniaturize.

[0007] Atomic nuclear magnetic resonance gyroscopes, also known as NMR rotation rate sensors, are known in the state of the art. These have the advantage of excellent sensitivity and drift stability, as well as a high miniaturization potential.

[0008] To determine rotation rates, nuclear magnetic resonance (NMR) gyroscopes analyze the NMR signals of atomic nuclei with non-zero magnetic moments. State-of-the-art technology includes optically pumped NMR gyroscopes based on a vapor cell. These gyroscopes measure the spin precession ω. messRead out in a steam cell. The spin precession is caused by a superposition of the Larmor precession ω. larmor and an external rotation ω R Given. The external rotation ω R represents an additional rotation, which can be derived from the equation ω mess = ω larmor ± ω R can be determined.

[0009] From CN 111060089 A a method for detecting nuclear spin precession based on a magnetic electron spin resonance difference is known. Disclosure of the invention

[0010] The present invention is based on the objective of realizing a gyrocompass using a nuclear magnetic resonance gyroscope.

[0011] To solve the problem underlying the invention, a method for using a nuclear magnetic resonance gyroscope as a gyrocompass is proposed, wherein the nuclear magnetic resonance gyroscope comprises at least one measuring unit, wherein at least one first rotation rate ω R,1 and a second rotation rate ω R,2 can be determined using the nuclear magnetic resonance gyroscope, where the first rotation rate ω R,1 is determined along a first direction parallel to the Earth's surface, and where the second rotation rate ω R,2 is determined along a second direction parallel to the Earth's surface, further provided that the first direction is different from the second direction, and that at least the first rotation rate ω R,1 and the second rotation rate ω R,2 a north-south direction is determined.

[0012] The basic structure and operating principle of a nuclear magnetic resonance gyroscope are known to the expert.

[0013] The nuclear magnetic resonance gyroscope comprises at least one measuring unit, which in turn includes a vapor cell, a pump laser, a probe laser, and magnetic field coils for generating a bias magnetic field and an alternating magnetic field. Furthermore, the measuring unit may include shielding against external magnetic fields. The nuclear magnetic resonance gyroscope comprises at least one measuring unit, but may also include a second measuring unit or additional measuring units.

[0014] If the magnetic resonance gyroscope comprises exactly one measuring unit, then the magnetic resonance gyroscope can be formed by exactly one measuring unit, and the terms "magnetic resonance gyroscope" and "measuring unit" can be used synonymously.

[0015] By procedure, at least one first rotation rate ω is used. R,1 and a second rotation rate ω R,2 Determined using a nuclear magnetic resonance gyroscope. At the first rotation rate ω R,1and the second rotation rate ω R,2 These are external rotation rates, which are each derived from the measured spin precession ω when the Larmor frequency of the nuclear spin isotopes used is known. mess according to the equation ω mess = ω larmor ± ω R = γB0 ± ω R The factor y represents the gyromagnetic ratio of the nuclear spin isotope used. B0 is the bias magnetic field generated by the magnetic field coil at the location of the steam cell.

[0016] The first rotation rate ω R,1 is determined along a first direction parallel to the Earth's surface, and the second rotation rate ω R,2The position is determined along a second direction parallel to the Earth's surface. The first and second directions are defined by the sensitive axis of the nuclear magnetic resonance gyroscope, or by at least one measuring unit of the nuclear magnetic resonance gyroscope. The sensitive axis is defined by the pump beam of the pump laser parallel to the bias magnetic field.

[0017] The rotation rates ω determined using the nuclear magnetic resonance gyroscope R,1 and ω R,2 The rotation rates ω are determined along a first direction and a second direction parallel to the Earth's surface, respectively. This means that the determined rotation rates ω R,1 and ω R,2 the projection of the Earth's rotation Ω E correspond to the Earth's surface along the respective direction. The following applies: ωR=ωEh cos α=ΩE cos φ cos α.

[0018] This is ωEh=ΩE cos φ the horizontal component of the Earth's rotation ΩE along the true north-south direction. The horizontal component ωEh The Earth's rotation depends on the geographical latitude φ. Furthermore, the measured rotation rates ω depend on R,1 and ω R,2 of the azimuth angle α between the horizontal component ωEh the Earth's rotation and the direction used for the measurement, i.e., the first direction and the second direction.

[0019] The horizontal component of the Earth's rotation ωEh Given knowledge of the geographical latitude φ, and using the known Earth's rotation Ω, it is possible to calculate E = 15.041° / h can be determined.

[0020] By procedure, the first rotation rate ω is used. R,1 and the second rotation rate ω R,2A north-south direction is determined. This means, in particular, that the azimuth angle α, preferably the azimuth angle α between the first direction and the north-south direction, is determined. Knowing the azimuth angle α between the first direction and the north-south direction, the north-south direction can be determined from the first direction by taking the azimuth angle α into account.

[0021] Preferably, a sensitive axis of the nuclear magnetic resonance gyroscope is aligned along the determined north-south direction.

[0022] Preferably, the nuclear magnetic resonance gyroscope, in particular the at least one measuring unit, and further in particular the vapor cell of the at least one measuring unit, may comprise or contain at least one nuclear spin isotope, preferably two nuclear spin isotopes.

[0023] If two nuclear spin isotopes are used, magnetic field inhomogeneities of the bias magnetic field can be factored out. Preferably, the two nuclear spin isotopes have different gyromagnetic ratios γ1 and γ2, respectively. In particular, the gyromagnetic ratios γ1 and γ2 can have different signs and magnitudes.

[0024] If two nuclear spin isotopes are used, the rotation rates ω are determined. R,1 and ω R,2 two spin precessions ω each mess,1 = γ1B0 - ω R and ω mess,2 = γ2B0 - ω R measured, with the first spin precession ω mess,1 the spin precession of the first nuclear spin isotope, and where the second spin precession ω mess,2 The spin precession of the second nuclear spin isotope is ω. R stands for ω R,1 and ω R,2 .

[0025] The outer rotation rates ω R,1 and ωR,2 can then be derived from the equation ωR=(γ1ωmess,2−γ2ωmess,1) / (γ2−γ1) be determined.

[0026] Preferably, an azimuth angle α is determined between the first direction and the north-south direction, and the north-south direction is obtained by applying the azimuth angle α to the first direction.

[0027] The knowledge of the north-south direction obtained in this way allows the nuclear magnetic resonance gyroscope to be used as a gyrocompass.

[0028] Preferably, the second direction has an angle of 90° to the first direction, with the azimuth angle α preferably being given by α = tan -1 (-ω R,2 / ω R,1 ) is determined.

[0029] Due to the 90° angle between the second direction and the first direction, because cos(α + 90°) = - sin(α), it follows that ωR,1=ωEh cos α and that ωR,2=−ωEh sin α.

[0030] By applying the azimuth angle α to the first direction, the north-south direction can then be determined.

[0031] Preferably, the nuclear magnetic resonance gyroscope is provided that, after determining the first rotation rate ω, R,1 in the first direction by an angle of 90°, preferably by means of a rotary table, and that subsequently the second rotation rate ω R,2 in the second direction, or that the nuclear magnetic resonance gyroscope comprises a first measuring unit oriented along the first direction and a second measuring unit oriented along the second direction, wherein preferably the first rotation rate ω R,1 and the second rotation rate ω R,2 be determined simultaneously.

[0032] If the nuclear magnetic resonance gyroscope has exactly one unit of measurement, the rotation rates ω are R,1 and ω R,2The rotation rate ω is determined sequentially. The sensitive axis of the nuclear magnetic resonance gyroscope is first aligned along the first direction parallel to the Earth's surface, and the rotation rate ω is measured. R,1 The rotation rate ω is determined. The magnetic resonance gyroscope is then rotated by an angle of 90°. A turntable can be used for this purpose, on which the magnetic resonance gyroscope is mounted. The axis of rotation of the turntable is preferably oriented perpendicular to the Earth's surface. After the rotation of the magnetic resonance gyroscope, the second rotation rate ω is determined. R,2 determined along the second direction.

[0033] Alternatively, the nuclear magnetic resonance gyroscope can be configured to comprise two measuring units, each of which includes a vapor cell, a pump laser, a probe laser, and magnetic field coils for generating a bias magnetic field and an alternating magnetic field. The sensitive axes of the two measuring units, which are parallel to the respective statically applied bias magnetic field due to the pump laser, are aligned at a 90° angle to each other. With such a configuration, the first rotation rate ω R,1 and the second rotation rate ω R,2 simultaneously determined, with the first rotation rate ω R,1 using the first measuring unit and the second rotation rate ω R,2 is determined using the second measuring unit.

[0034] Furthermore, it can be provided that the second direction has an angle of 180° to the first direction, wherein preferably the azimuth angle α is determined by α=cos−1((ωR,1−ωR,2) / 2ωEh) is determined, whereby a zero offset b of the nuclear magnetic resonance gyroscope is preferably determined by b = (ω R,1 + ω R,2 ) / 2 is determined.

[0035] In this case, it may be preferably provided that the nuclear magnetic resonance gyroscope, if it has exactly one measuring unit, is first aligned along the first direction, and that the first rotation rate ω is determined along the first direction. R,1 The first rotation rate is determined. The nuclear magnetic resonance gyroscope is then rotated 180° parallel to the Earth's surface, for example using a turntable, and the second rotation rate ω is measured. R,2 determined.

[0036] The nuclear magnetic resonance gyroscope can have a zero offset b, such that: ωR,1=ωEh cos α+bωR,2=−ωEh cos α+b

[0037] The zero offset b can be determined and compensated in the manner described above.

[0038] In a further embodiment of the method, it may be provided that a third rotation rate ω R,3 and a fourth rotation rate ω R,4 can be determined using the nuclear magnetic resonance gyroscope, where the third rotation rate ω R,3 is determined along a third direction parallel to the Earth's surface, and where the fourth rotation rate ω R,4 is determined along a fourth direction parallel to the Earth's surface, wherein the third direction has an angle of 90° to the first direction, wherein the fourth direction has an angle of 270° to the first direction, wherein the azimuth angle α is preferably determined by α = tan -1 ((ω R,3 - ω R,4 ) / (ω R,1 - ω R,2 )) is determined.

[0039] The second direction still has an angle of 180° to the first direction.

[0040] In contrast to the 2-point azimuth measurement described above, in which the rotation rates are measured along two directions offset by 180°, in the further embodiment four rotation rates can be determined at angles of 0°, 90°, 180° and 270°.

[0041] The advantage of evaluating rotation rates measured in four directions lies in the elimination of scaling factor errors. Furthermore, this method also compensates for gravity errors that could arise from incorrect gyroscope orientation. In addition, it mitigates the effects of cross-axis sensitivity.

[0042] In a further preferred embodiment, it can be provided that the nuclear magnetic resonance gyroscope is continuously rotated, preferably by means of a rotary table, more preferably about an axis of rotation vertical to the Earth's surface, with an angular frequency Ω, and that by measuring a plurality of rotation rates, comprising at least the first rotation rate ω R,1 and the second rotation rate ω R,2 , a time course of the rotation rate ω R (t) is determined, where the time course of the rotation rate ω R (t) through ωR(t)=ωEh cos(Ω t + α) + b is given, where the azimuth angle α is determined from the time course of the rotation rate ω R (t) is determined.

[0043] The continuous rotation of the nuclear magnetic resonance gyroscope results in a continuous modulation of the Earth's constant rotation. This is used to generate the temporal profile of the rotation rate ω. R (t) a multitude of rotation rates ω are used. Rmeasured values, which can then be plotted against time. From the temporal evolution of the rotation rate ω R (t) The azimuth angle α can then be determined. In particular, the azimuth angle α can be calculated for each 360° rotation of the turntable or the magnetic resonance gyroscope by subtracting the adjustment phase from the current position of the turntable.

[0044] Another variant of the method according to the invention consists in rotating the nuclear magnetic resonance gyroscope, preferably by means of a rotary table, whereby a direction is determined in which the rotation rate is zero, wherein the north-south direction is determined as being at an angle of 90° to the determined direction.

[0045] This variant of the method is based on the fact that if the sensitive axis of the magnetic resonance gyroscope is oriented in a north-south direction, the azimuth angle α = 0 or 180°. In this case, the measured rotation rate ωR=ωEh=ΩE cos φ. If the sensitive axis of the nuclear magnetic resonance gyroscope is oriented in an east-west direction, then the measured rotation rate ω R Zero. Thus, a direction is determined in which the measured rotation rate ω R If zero, then the north-south direction is at an angle of 90° to the direction thus determined.

[0046] Another solution to the problem underlying the invention consists in providing a gyrocompass comprising a nuclear magnetic resonance gyroscope with at least one measuring unit set up to carry out a previously described method.

[0047] All the functions, designs and features explained above regarding the procedure can also be applied analogously to the gyrocompass.

[0048] It is therefore particularly preferred that the gyroscope comprises a rotary table, wherein the rotary table more preferably comprises a stepper motor, wherein the nuclear magnetic resonance gyroscope is arranged on or at the rotary table, wherein the rotary table is designed to rotate the nuclear magnetic resonance gyroscope about an axis of rotation vertical to the Earth's surface.

[0049] The invention is explained in more detail below with reference to the accompanying figures. These show Fig. 1 a schematic representation of a nuclear magnetic resonance gyroscope, Fig. 2 a gyrocompass comprising a nuclear magnetic resonance gyroscope and a rotary table, Fig. 3a a view of the Earth, Fig. 3b a section of a side view of the Earth, Fig. 3c a view of the Earth's surface, Fig. 4 a magnetic resonance gyroscope, and Fig. 5 a flowchart for a procedure for using a nuclear magnetic resonance gyroscope as a gyrocompass.

[0050] With reference to the Fig. In sections 1 to 5, a method 100 for using a nuclear magnetic resonance gyroscope 10 as a gyrocompass 200 is explained.

[0051] Fig. Figure 1 schematically shows a nuclear magnetic resonance gyroscope 10. The nuclear magnetic resonance gyroscope 10 comprises a measuring unit 11 with a vapor cell 12, a pump laser 13, a probe laser 14, and magnetic coils 15 for generating a bias magnetic field and an alternating magnetic field at the location of the vapor cell 12. The vapor cell 12 and the magnetic coils 15 are arranged within a shield 16. A polarizing beam splitter cube 17 is provided outside the shield 16. Photodetectors 18 are provided for reading out the spin precession signal. The nuclear magnetic resonance gyroscope 10 has a sensitive axis 19, which is defined by the pump beam of the pump laser 13 parallel to the bias magnetic field. The operating principle of a nuclear magnetic resonance gyroscope is known to those skilled in the art. From the measured spin precession ω mess can an external rotation rate ω R to be determined.

[0052] Fig. Figure 2 shows a Gyrocompass 200. The Gyrocompass 200 includes a nuclear magnetic resonance gyroscope 10 according to Fig. 1. The magnetic resonance gyroscope 10 is arranged on a rotary table 20. The rotary table 20 has a stepper motor 21 and a control unit mounted on a circuit board 22. The rotary table 20 can be rotated about a vertical axis by means of the stepper motor 21. The magnetic resonance gyroscope 10 is arranged on the rotary table 20 such that its sensitive axis 19 is aligned parallel to the rotary table 20 and thus also parallel to the Earth's surface 24.

[0053] Fig. Figure 3a shows a schematic view of the Earth 23. Fig. Figure 3b shows a side view, and Fig. Figure 3c shows a top view of the Earth's surface 24. The Earth 23 rotates with a known rotation frequency Ω. Eabout its axis of rotation 25. A previously described nuclear magnetic resonance gyroscope 10 is arranged on the Earth's surface 24 at a geographical latitude φ. If the sensitive axis 19 of the nuclear magnetic resonance gyroscope 10 is aligned parallel to the north-south direction 26, then the determined external rotation rate ω R given by ωR=ωEh=ΩE cos φ, where ωEh=ΩE cos φ the horizontal component of the Earth's rotation Ω E along the north-south direction is 26.

[0054] At the beginning of the procedure, the north-south direction 26 is not known exactly. The sensitive axis 19 of the nuclear magnetic resonance gyroscope 10 is therefore generally not aligned exactly along the north-south direction 26, but along a first direction 27 ( Fig. 3c). In this case, as in Fig. Figure 4 shows schematically the nuclear magnetic resonance gyroscope 10 arranged on the Earth's surface 24, and the determined external rotation rate ω.R additionally dependent on the azimuth angle α, which is determined by the angle α between the horizontal component ωEh the Earth's rotation and the first direction 27 is given.

[0055] To determine the north-south direction 26, a first external rotation rate ω is first calculated. R,1 The first direction 27 is determined using the magnetic resonance gyroscope 10. The magnetic resonance gyroscope 10 is then rotated 180° by means of the turntable 20, so that the sensitive axis 19 is aligned in a second direction 28 that differs from the first direction 27 by 180°. A second external rotation rate ω is then determined. R,2 along the second direction 28 was determined using the nuclear magnetic resonance gyroscope 10. From the rotation rates ω R,1 and ω R,2 The azimuth angle α can then be calculated according to α = tan -1 (-ω R,2 / ω R,1) can be determined. With knowledge of the azimuth angle α, the sensitive axis 19 of the nuclear gyroscope 10 can then be aligned along the north-south direction 26.

[0056] Fig. Figure 5 shows a flowchart for a procedure 100 for using a nuclear magnetic resonance gyroscope 10 as a gyrocompass 200. In a first procedure step S1, a first rotation rate ω is determined. R,1 along a first direction 27 parallel to the Earth's surface 24. In a second process step S2, a second rotation rate ω is determined. R,2 The rotation rate ω is determined using the nuclear magnetic resonance gyroscope 10 along a second direction 28 parallel to the Earth's surface 24. In a third process step S3, at least the first rotation rate ω is used. R,1 and the second rotation rate ω R,2 a north-south direction 26 is determined. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] CN 111060089 A

[0009]

Claims

[1] Method (100) for using a nuclear magnetic resonance gyroscope (10) as a gyrocompass (200), wherein the nuclear magnetic resonance gyroscope (10) comprises at least one measuring unit (11), wherein at least one first rotation rate ω R,1 and a second rotation rate ω R,2 are determined using the nuclear magnetic resonance gyroscope (10), where the first rotation rate ω R,1 is determined along a first direction (27) parallel to the Earth's surface (24), and where the second rotation rate ω R,2 is determined along a second direction (28) parallel to the Earth's surface (24), characterized by , that the first direction (27) is different from the second direction (28), and that at least from the first rotation rate ω R,1 and the second rotation rate ω R,2 a north-south direction (26) is determined. [2] Method (100) according to claim 1, characterized by, that an azimuth angle α is determined between the first direction (27) and the north-south direction (26), and that the north-south direction (26) is obtained by applying the azimuth angle α to the first direction (27). [3] Method (100) according to claim 1 or 2, characterized by , that the second direction (28) has an angle of 90° to the first direction (27), wherein the azimuth angle α is preferably given by α = tan -1 (-ω R,2 / ω R,1 ) is determined. [4] Method (100) according to claim 3, characterized by , that the nuclear magnetic resonance gyroscope (10) after determining the first rotation rate ω R,1 in the first direction (27) is rotated by an angle of 90°, preferably by means of a rotary table (20), and that subsequently the second rotation rate ω R,2in the second direction (28), or that the nuclear magnetic resonance gyroscope (10) comprises a first measuring unit (11) oriented along the first direction (27) and a second measuring unit (11) oriented along the second direction (28), wherein preferably the first rotation rate ω R,1 and the second rotation rate ω R,2 be determined simultaneously. [5] Method (100) according to claim 1 or 2, characterized by , that the second direction (28) has an angle of 180° to the first direction (27), wherein preferably the azimuth angle α is determined by α=cos−1((ωR,1−ωR,2) / 2ωEh) is determined, further preferably a zero offset b of the nuclear magnetic resonance gyroscope (10) by b = (ω R,1 + ω R,2 ) / 2 is determined. [6] Method (100) according to claim 5, characterized by , that a third rotation rate ω R,3 and a fourth rotation rate ω R,4are determined using the nuclear magnetic resonance gyroscope (10), where the third rotation rate ω R,3 is determined along a third direction parallel to the Earth's surface (24) and where the fourth rotation rate ω R,4 along a fourth direction parallel to the Earth's surface (24), wherein the third direction has an angle of 90° to the first direction (27), wherein the fourth direction has an angle of 270° to the first direction (27), wherein the azimuth angle α is preferably determined by α = tan -1 ((ω R,3 - ω R,4 ) / (ω R,1 - ω R,2 )) is determined. [7] Method (100) according to any of the aforementioned claims, characterized by, that the nuclear magnetic resonance gyroscope (10) is continuously rotated, preferably by means of a rotating table (20), further preferably about a rotation axis vertical to the Earth's surface (24), with an angular frequency Ω, and that by measuring a plurality of rotation rates, comprising at least the first rotation rate ω R,1 and the second rotation rate ω R,2 , a time course of the rotation rate ω R (t) is determined, where the time course of the rotation rate ω R (t) through ωR(t)=ωEh cos(Ω t + α) + b is given, where the azimuth angle α is determined from the time course of the rotation rate ω R (t) is determined. [8] Method (100) according to any of the aforementioned claims, characterized by, that the nuclear magnetic resonance gyroscope (10) is rotated, preferably by means of a rotary table (20), whereby a direction is determined in which the rotation rate is zero, wherein the north-south direction (26) is determined as being at an angle of 90° to the determined direction. [9] Gyrocompass (200) comprising a nuclear magnetic resonance gyroscope (10) with at least one measuring unit (11) configured for carrying out a method (100) according to any one of claims 1 to 8. [10] Gyrocompass (200) according to claim 9, comprising a rotary table (20), wherein the rotary table (20) preferably comprises a stepper motor (21), wherein the nuclear magnetic resonance gyroscope (10) is arranged on or at the rotary table (20), wherein the rotary table (20) is configured to rotate the nuclear magnetic resonance gyroscope (10) about an axis of rotation perpendicular to the Earth's surface (24).

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