Method for managing optically pumped rotational speed sensors

Abstract

TITLE: Method for Managing Optically Pumped Rotational Speed ​​Sensors. Method for managing a sensor device (10) having a vapor cell (20) containing an alkali vapor and a noble gas. The alkali vapor and the noble gas are excited by a pulsed laser (13), and a static magnetic field (B0), oriented in the z direction, and an oscillating magnetic field (Bx), oriented in the x direction, are applied to the vapor cell (20). Measurement beams from a source (30), installed with a detector (31) in a transparent device, are applied. Using the intensity variation determined by the detector (30), a measurement frequency, for example, a Larmor frequency, is determined. The intensity of the static magnetic field (B0) is varied by a control loop (41). Figure 2b

Description

Title of the invention: Method for managing optically pumped rotation speed sensors FIELD OF THE INVENTION

[0001] The present invention relates to a method for managing a sensor device, in particular a rotation speed sensor having at least one vapor cell, containing an alkaline vapor and at least one rare gas,

[0002] according to which

[0003] - the atoms of the alkaline vapor and the atoms of the rare gas are optically excited in the vapor cell by a pulsed laser,

[0004] - a static magnetic field (Bo) is applied to the steam cell, oriented in the direction (z) and an oscillating magnetic field (Bx), oriented in the direction (x),

[0005] - measuring beams from a beam source are applied to the vapor cell measuring device, installed with a detector in a transparent device,

[0006] - using a variation in intensity determined by the detector, a measurement frequency, for example, a Larmor frequency (fiarmor),

[0007] - the initial intensity of the measuring beams being reduced by passing through the steam cell. STATE OF THE ART

[0008] The demand for increasingly precise sensors, particularly in the field of navigation systems, is constantly increasing. For example, gyroscopes are needed to precisely measure rotational speeds. In aircraft, extremely precise rotational speed sensors based on optical resonators are already used because the size and high price are not obstacles in this field. For autonomous driving and autonomous flight as well as for applications that have a poor connection to a GPS system, radar sensors or similar navigation means, such as, for example, underwater navigation, extremely precise on-board sensors are required. In particular, in the case of autonomous vehicles, compact and cost-effective rotational speed sensors are required.

[0009] Ensuring a guaranteed stop based on an inertial sensor, for example, in the event of failure of redundant sensors, is an essential condition for the operation of autonomous vehicles. The rotational speed sensors currently available for the field of automotive applications do not meet the imposed specifications regarding accuracy. It would be desirable in this field to significantly increase the drift stability and significantly reduce the noise of the rotational speed sensors to enable vehicles to function autonomous operation, to apply purely inertial navigation on extended journeys such as, for example, in tunnels or on traffic lanes embedded between buildings.

[0010] Optically pumped rotational speed sensors based on a vapor cell are already known. These sensors determine the optical spin-Larmor fiamor precession in the vapor cell. An external rotation frot represents an additional rotation of the rotational speed sensor which is determined by reading the rotation frequency fmess as follows:

[0011] fmess=fiarmor ± frot

[0012] Document US 2012 / 191396 A1 describes a method of illuminating a vapor cell with a measuring beam source to determine the Larmor precession based on the intensity of the transmitted measuring beams. The transmitted measuring beams are detected upstream of a detector. The detector signal contains different frequency components that are filtered with an electronic filter (e.g. a low-pass filter, a high-pass filter or a band-pass filter) to separate the components relating to the rare gases of the vapor cell from the component originating from the alkaline vapor. However, the bandwidth of the rotational speed sensor using the vapor cell is reduced because the electronic filter needs a long integration time for low frequencies.Additionally, higher order filters are required to have very sharp edges and to be able to use them in isotope resonance ranges, ideally in the ranges between 3 Hz and 11 Hz.

[0013] PURPOSE OF THE INVENTION

[0014] The present invention aims to develop a method for managing an optically pumped rotational speed sensor which imposes fewer requirements on the filter for exploiting the electronic signal detected in the transmitted measurement beams.

[0015] DISCLOSURE AND ADVANTAGES OF THE INVENTION

[0016] To this end, the invention relates to a method of the type defined above, characterized in that the intensity of the static magnetic field is varied by a control loop. The method makes it possible to determine a Larmor frequency or a Larmor precession with at least one vapor cell which depends on the rotation speed of the vapor cell.

[0017] The method may preferably be applied by a sensor device controlled or regulated by the control unit.

[0018] The rotation speed sensor has at least one vapor cell. The vapor cell is filled with an alkaline vapor and at least one rare gas. To convert the alkali metal into a gaseous or vaporous state, heating devices have been proposed. in the form of an electrical or optical heating device, based on radiation to heat the steam cell.

[0019] Then, the atoms of the alkaline vapor and those of the noble gas are excited in the vapor cell by a pump laser. The vapor cell is exposed to a static magnetic field oriented in the Z direction and to an oscillating magnetic field in the X direction. The lines of the oscillating magnetic field are preferably perpendicular to the lines of the static magnetic field.

[0020] The vapor cell receives the measuring beams from a measuring beam source. The measuring beam source is installed with a detector in the device traversed by the beams and using an intensity variation determined by the detector, a measuring frequency is determined, for example, the Larmor frequency. The measuring beam source is, for example, an infrared laser or an LED diode operating in the infrared spectral range.

[0021] The method provides a measurement frequency. In the absence of a signal, the measurement frequency corresponds to the Larmor frequency. On the other hand, if there is a signal, the measurement frequency differs from the Larmor frequency because the method is applied by a closed-loop system.

[0022] According to the invention, the intensity of the static magnetic field is varied using a control loop. In particular, the intensity of the static magnetic field is modified by a control loop to keep the frequency and / or amplitude of the oscillating magnetic field constant. This corresponds to a regulation mechanism and not to a correction mechanism.

[0023] Since the oscillating magnetic field has a constant amplitude and / or frequency, the sensor device may use static filters or fixed frequency filters or a frequency band to read the measurement signals, especially transmitted measurement signals.

[0024] This allows reducing requirements on the filters required by a closed-loop reaction of the static magnetic field or an electromagnet. In particular, instead of a second electromagnet to generate the oscillating or driving magnetic field. The first electromagnet is regulated to generate a static magnetic field by a control unit, to manage the sensor device and maintain the atoms of the vapor cell in the resonant state.

[0025] According to another development, the invention relates to a control unit for applying the method according to the invention.

[0026] The method allows the use of sensor devices, in particular NMR gyroscopes, to achieve high measurement accuracy at low rotational speeds. In addition, at the same time, high rotational speeds can be recorded with decreasing sensitivity, which allows, for example, the detection of accidents with high safety. In addition, the operating electronics will be technically simpler and more economical. The possibility of using fixed, i.e. narrowband, filters allows precise extraction of the respective measurement signals from the individual atoms in the measuring cell.

[0027] According to an exemplary embodiment, the intensity of the static magnetic field is varied by a control loop so as to keep the frequency and / or the amplitude of the oscillating magnetic field constant. The magnetic field is thus corrected instead of correcting the resonant alternating field or the oscillating magnetic field. Thus the atoms of the vapor cell are always in a sufficiently narrow range to reach the target frequencies and thus have better measurement results.

[0028] The respective fractions of the frequencies from the measuring signals which are assigned to different chemical materials in the vapor cell can be optimally extracted by filtering with at least one filter the detected electronic signal of the measuring beams transmitted by the vapor cell.

[0029] According to a development, the electronic signal generated by the detector and which represents the measuring beams transmitted through the vapor cell is filtered with at least one filter. Measuring beams from a measuring beam source are thus applied to the vapor cell. The measuring beam source may be, for example, an infrared laser or an LED diode operating in the infrared spectrum.

[0030] The measuring beam cell is installed with a detector in the device through which the beams pass. The measuring beams have their intensity attenuated in the infrared spectrum by the vapor cell and the chemical material of the vapor cell. This variation in intensity can be determined by knowing the initial intensity of the measuring beams.

[0031] The initial intensity of the measuring beams is determined, for example, by calibration or setting.

[0032] According to another embodiment, the detected electronic signal is filtered by a first filter and then by a second filter. This procedure makes it possible to first extract the frequency components corresponding to a first chemical material, for example, Xel29 and then the frequency components of a second chemical material, for example, Xel31 to allow an accurate calculation of the rotation speed linked to the Larmor frequency.

[0033] The measurement signals resulting from the measurement beams arriving at the detector can be used in different ways if the measurement beams transmitted by the vapor cell are filtered by at least one filter which is a bandpass filter and / or a combination of a lowpass filter and a highpass filter. The filter can be a theoretical filter and / or an optical filter and / or a program filter.

[0034] According to another exemplary embodiment, regulation is carried out actively by a loop regulation, the intensity of the static magnetic field based on the difference between a constant frequency of the oscillating magnetic field and a rotational speed of the steam cell which is divided by the gyromagnetic ratio, by actively regulating with a control loop. This allows precise control and regulation of the static magnetic field by the sensor device. In particular, the intensity of the static magnetic field corresponds to the values ​​of the set or varied parameters of the gyromagnetic ratio and the rotational speed of the steam cell.

[0035] According to a further development, the invention relates to a sensor device, in particular an optically pumped rotational speed sensor. The sensor device has a vapor cell. The sensor device has a first magnetic field source for generating and adjusting a static magnetic field and a second magnetic field source for generating an oscillating magnetic field, oriented perpendicular to the static magnetic field and a pump laser for optically pumping atoms in the vapor cell.

[0036] A measuring device is also provided for measuring the intensity of the lighting device. Preferably, to maintain the frequency and / or amplitude of the oscillating magnetic field, the magnetic field intensity of the first magnetic field is adjusted with a control unit.

[0037] A corresponding sensor device can be realized as a gyroscope exploiting the spin resonance signals of atomic nuclei with a non-vanishing magnetic moment of the atomic nuclei (i.e. the spin of the atomic nucleus is exploited with an odd multiple of 1 / 2).

[0038] Regulation of the static magnetic field or of the first magnetic field source instead of the oscillating magnetic field makes it possible to vary the measurement signals at essentially constant frequencies which can be used by technically simple or static filters.

[0039] A closed control loop can be applied in a technically simple manner if the control unit is designed to use the measurement data of at least one detector of the measuring device to receive and for regulation of the first magnetic field source. Brief description of the drawings

[0040] The present invention will be described below in more detail with the aid of exemplary embodiments of a device according to the invention shown in the appended drawings in which:

[0041] [Fig. 1a] schematic representation of a sensor device according to one embodiment of the invention,

[0042] [Fig.lb] schematic representation of a sensor device according to one embodiment of the invention,

[0043] [Fig.2a] schematic representation to explain the process according to a form of realization of the invention,

[0044] [Fig.2b], schematic representation to explain a process according to another embodiment of the invention.

[0045] DESCRIPTION OF EMBODIMENTS OF THE INVENTION

[0046] [Fig. 1a] is a schematic representation of a sensor device 10 according to one embodiment of the invention. The sensor device 10 is, for example, an optically pumped rotational speed sensor.

[0047] The sensor device 10 has a filled vapor cell 20 containing an alkali metal and at least one rare gas such as, for example, xenon. In the example shown, the vapor cell 20 contains isotopes Xel29 and Xel31 in addition to the alkali metal. To convert the alkali metal to a gaseous state, the vapor cell 20 is heated. The heating of the vapor cell 20 can be carried out using unreferenced electric heating installations or by the heat of a radiation source.

[0048] A first magnetic field source 11 is provided for generating and adjusting a static magnetic field Bo which is, for example, in the form of an electromagnet. A second magnetic field source 12 is also provided for generating an oscillating magnetic field Bx.

[0049] The lines of the oscillating magnetic field Bx generated by the second magnetic field source 12 are perpendicular to the field lines of the static magnetic field Bo generated by the first magnetic field source 11. Such a constellation of magnetic field lines makes it possible to put the atoms of the vapor cell 20 in a state of precession and to remove them from the presence of external facts.

[0050] The sensor device 10 comprises a pumped laser 13 for optically pumping the atoms in the vapor cell 20. The pumped laser 13 is, for example, an infrared laser tuned to an emission wavelength of the atoms of the vapor cell 20.

[0051] The sensor device 10 also comprises a measuring device consisting of a measuring beam or radiation source 30 and a detector 31. The vapor cell 20 is exposed to the measuring beams of the measuring beam source 30. The measuring beam source 30 is mounted with a detector 31 in a transparent device; by the variation in intensity emitted by the detector 31 of the measuring beams transmitted through the pump cell 20, the Larmor frequency is determined. Alternatively, using polarization optics (not shown), installed in front of the detector 31, the variation in polarization of the measuring beams transmitted through the vapor cell 20 is determined and thus the Larmor frequency. The measuring beam source 30 is, for example, an infrared laser or an LED diode with an emission spectrum in the infrared range.

[0052] To maintain a suitable frequency for the precession step and / or an amplitude of the oscillating magnetic field Bx generated by the second magnetic field source 12, the intensity of the static magnetic field Bo of the first magnetic field source 11 is regulated with a control unit 40.

[0053] The control unit 40 is preferably connected to the detector 31 by data transmission and can receive the measurement data received by the detector 31 and use them in a control loop 4L. From the received measurement data, the first magnetic field source 11 is suitably controlled to change the static magnetic field Bo. The purpose of the control loop 41 is to maintain the operating state in which the oscillating magnetic field Bx does not change frequency. The detector signal of the transmitted measurement beams of the measuring device 30, 31 thus has an essentially constant frequency component, which is filtered by a narrowband filter or a fixed filter 32. This avoids expensive and complicated filters. In the exemplary embodiment shown, the fixed filter 32 is an optical filter installed with the detector 31.To apply a control loop between the control unit 40 and the first magnetic field source 11, other data can be received and used, for example, from the second magnetic field source 12 and the pumped laser 13.

[0054] [Fig. lb] is a schematic representation of a sensor device 10 according to another embodiment of the invention. Unlike the sensor devices 10 in [Fig. la], this comprises a filter 32 implemented as an electronic filter. The signals from the detector 31, thus received, are thus filtered as part of a processing or pre-processing.

[0055] [Fig.2a] and [Fig.2b] schematically show a method according to a form of realization of the invention.

[0056] [Fig.2a] shows a control loop according to the state of the art used for the comparison with the method of the invention for managing a rotation speed sensor 10 comprising at least one vapor cell 20, as shown in [Fig.2b].

[0057] [Fig.2a] shows a sensor device 50 without representing the vapor cell acted upon by an oscillating magnetic field Bx alongside optical pumping and a constant static magnetic field Bo. Since the static magnetic field Bo is constant, permanent magnets can be used here.

[0058] A measuring device with a measuring beam source and a detector generates a measuring signal. The measuring signal is based on variations intensity and corresponds, for example, to a Larmor frequency because the intensity variation of the measuring device is modulated by the Larmor frequency. To extract static components and external influences, such as, for example, the rotational speed of the sensor device 50, the measuring signal is filtered during processing. The filtering of the measuring signal is done by a synchronous amplifier which also limits the measuring range for the rotational speed RR. The rotational speed RR obtained in the form of a frequency is used as input to a control loop. Using the constant static magnetic field Bo of the gyroscopic ratio y and the rotational speed RR obtained, controls the frequency f of the oscillating magnetic field Bx according to the following formula:

[0059] f(Bx)=yB0 + RR

[0060] The operating frequency of the sensor device 50 is thus modified continuously according to this formula.

[0061] In contrast to the control concept shown in [Fig.2a], [Fig.2b] shows a control concept that regulates the static magnetic field B0 instead of the frequency f of the oscillating magnetic field Bx. Thus, the sensor device 10 oscillates in a narrow frequency range around a fixed frequency regardless of the applied rotational speed. This allows reading with fixed filters 32 without limiting the dynamic range and bandwidth of the sensor device 10.

[0062] The method serves, for example, to manage the sensor device 10 of [Fig. 1a].

[0063] The process consists of optically exciting the atoms of the alkaline vapor and the atoms of the rare gas in the vapor cell 20 with a pumped laser 13. The vapor cell 20 is then acted upon by the static magnetic field Bo, oriented in the z direction and the oscillating magnetic field Bx, oriented in the x direction.

[0064] The vapor cell 20 is exposed to the measurement beams of a measurement beam source 30; this measurement beam source 30 is installed with the detector 31 in a device exposed to the beams.

[0065] Using a variation in intensity determined by the detector 31 and which serves as a measurement signal, the Larmor frequency and thus the rotation speed RR are determined.

[0066] The control loop 41 of the sensor device 10 does not vary the frequency of the oscillating magnetic field Bx but the intensity of the static magnetic field Bo. The adaptation of the static magnetic field Bo is done based on the following formula applied by the control unit 40:

[0067] B0=(f(Bx)-RR) / y

[0068] The sensor device 10 thus operates in an essentially constant frequency range which imposes less constraints on the filters used 32. Furthermore, such a sensor device 10 has better accuracy, in particular, at low rotation speeds.

[0069] NOMENCLATURE OF MAIN ELEMENTS

[0070] 10 Sensor device

[0071] 11 First source of static magnetic field

[0072] 12 Second source of oscillating magnetic field

[0073] 13 Optically pumped laser

[0074] 20 Steam cell

[0075] 30 Source of measuring beams

[0076] 31 Measuring beam source / detector

[0077] 32 Filter

[0078] 40 Control unit

[0079] 41 Control loop

[0080] 50 Sensor device

[0081] Bo Static magnetic field

[0082] Bx Oscillating magnetic field

[0083] F Frequency

[0084] RR Rotation speed

Claims

Claims

1. Method for managing a sensor device (10), in particular a rotational speed sensor having at least one vapor cell (20), containing an alkaline vapor and at least one rare gas, according to which - the atoms of the alkaline vapor and the atoms of the rare gas in the vapor cell (20) are optically excited by a pulsed laser (13), - a static magnetic field (Bo ), oriented in the (z) direction and an oscillating magnetic field (Bx), oriented in the (x) direction are applied to the vapor cell (20), - measuring beams from a measuring beam source (30), installed with a detector (31) in a transparent device are applied to the vapor cell (20), - using an intensity variation determined by the detector (30), a measuring frequency is determined, for example, a Larmor frequency (f^J, - the initial intensity of the measuring beams being reduced by passing through the steam cell (20),method characterized in that the intensity of the static magnetic field (Bo) is varied by a control loop (41).,

2. Method according to claim 1, according to which the intensity of the static magnetic field (Bo) is varied by the control loop (41) so that the frequency and / or the amplitude of the oscillating magnetic field (Bx) are practically constant.

3. Method according to claim 1 or 2, according to which an electronic signal generated by the detector (31) and which represents the measuring beams transmitted through the vapor cell (20) is filtered with at least one filter (32).

4. Method according to claim 3, according to which the detected electronic signal is filtered by a first filter and then by a second filter.

5. A method according to claim 3 or 4, wherein the detected electronic signal is filtered by at least one filter (32) in the form of a band-pass filter and / or a combination of a low-pass filter and a high-pass filter.

6. Method according to one of claims 1 to 5, according to which the intensity of the static magnetic field (Bo) is varied by the control loop (41), this intensity of the static magnetic field (Bo) being regulated according to the difference between a constant frequency (f(Bx)) of the oscillating magnetic field (Bx) and the rotation speed (RR) of the steam cell (20) divided by a gyromagnetic ratio (y), by active regulation by the control loop (41).

7. Control unit (40) adapted to carry out a method according to one of the preceding claims.

8. Sensor device (10), in particular an optically pumped rotational speed sensor, comprising a vapor cell (20), a first magnetic field source (11) for exciting and adjusting a static magnetic field (Bo), a second magnetic field source (12) for generating an oscillating magnetic field (Bx) oriented perpendicular to the static magnetic field (Bo), comprising a pumped laser (13) for optically pumping atoms in the vapor cell (20), comprising a measuring device (30, 31) for measuring the intensity in a transparent device, - to maintain a magnetic field frequency and / or amplitude of the oscillating magnetic field (Bx), the magnetic field intensity of the first magnetic field source (11) is adjusted by a control unit (40).

9. Sensor device according to claim 8, wherein the control unit (40) is adapted to receive measurement data from at least one detector (31) of the measuring device and to serve for regulating the first magnetic field source (11).

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