Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01C—MEASURING DISTANCES, LEVELS OR BEARINGS; SURVEYING; NAVIGATION; GYROSCOPIC INSTRUMENTS; PHOTOGRAMMETRY OR VIDEOGRAMMETRY
  • G01C25/00—Manufacturing, calibrating, cleaning, or repairing instruments or devices referred to in the other groups of this subclass
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
  • G01D3/00—Indicating or recording apparatus with provision for the special purposes referred to in the subgroups
  • G01D3/02—Indicating or recording apparatus with provision for the special purposes referred to in the subgroups with provision for altering or correcting the law of variation
  • G01D3/022—Indicating or recording apparatus with provision for the special purposes referred to in the subgroups with provision for altering or correcting the law of variation having an ideal characteristic, map or correction data stored in a digital memory

Definitions

• the invention relates to a method for correcting the effects of measuring sensor aging. It also relates to a device delivering corrected measures of the effects of aging of the device.
• the invention finds particular utility in the field of navigational aids and steering instruments, and in particular the instruments which are intended for air navigation in which the constraints of accuracy on position and speed are high and which are autonomous, that is to say they operate without any external resources to the aircraft with the exception of the gravitational field and the Earth's magnetic field.
• inertial navigation systems in aircraft is very conventional today. These units use accelerometers to determine accelerations along axes defined with respect to the aircraft, gyrometers for determining angular rotation speeds with respect to axes that are also defined with respect to the aircraft, and possibly other sensors such as than a baro-altimeter. By integrating the gyro measurements, the orientation of the aircraft is determined at a given moment; by integrating the accelerometric measurements, which can be related to a terrestrial reference mark outside the aircraft thanks to the knowledge of the orientation of the aircraft, the speed components of the aircraft are determined in this terrestrial reference frame. By integrating speeds, geographical positions are determined.
• the short-term errors of the sensors are corrected by means of a registration as for example in the patent FR2830320 where an inertial navigation unit is hybridized with at least one satellite positioning receiver.
• the correction can also be carried out by means of a numerical model using a primary measurement often "real time" of a quantity, whose disruptive effect on the measurement is known, for example the internal temperature of the sensors.
• Long-term errors can not be reduced by these methods because they are related to the stability of the sensor over time over a fairly long period of up to several decades.
• the long-term errors are related to the stability of the bias (or offset) and the stability of the sensitivity (or scale factor) of the sensor.
• One way to reduce long-term sensor error is to build the sensor from extremely stable components. Indeed, the stability of the component or material on which the measurement is based, for example a mechanical component, an electrical component or a gas, ensures the stability of the measurement over time. This method, very natural, can be extremely expensive because it requires the use of high-end components.
• the present invention overcomes the disadvantages of the solution presented above. Its purpose is to correct the long-term errors of a measuring sensor only from the age of the sensor at the moment of measurement, that is to say from the time between the date of manufacture of the sensor and that of the sensor. measurement. This method requires to know the law of degradation of the measurement with the age of the sensor and to have permanently a clock delivering an absolute time. This last condition is very restrictive if the invention is to fit on existing aircraft.
• the subject of the invention is a method for correcting the effects of aging of a measurement sensor on a carrier, the sensor delivering measurements whose accuracy deteriorates with the age of the sensor, a law describing the degradation of the accuracy of the measurements according to the age of the sensor being known, the wearer being equipped with a unit processor processing measurements of the sensor, and a satellite positioning system receiver having absolute time information for ephemeris reading to establish satellite positions and to provide a positional measurement receiver, characterized in that it comprises the following steps:
• Another subject of the invention is a device delivering measurements, comprising a measurement sensor, the sensor supplying a processing unit with measurements whose accuracy deteriorates with the age of the sensor, the processing unit processing the measurements, a receiver of a satellite positioning system having absolute time information for ephemeris reading to establish satellite positions and providing a position measurement of the receiver and a means of storing a law describing the degradation of the accuracy of the sensor measurements as a function of the age of the sensor, characterized in that it comprises: - means for transmitting the absolute time information to the processing unit, to the powering up of the sensor, treatment unit;
• FIG. 1 shows schematically the principle of an inertial unit hybridized with a satellite positioning receiver, constituting the state of the art
• FIG. 2 diagrammatically represents the principle of an inertial unit hybridized with a satellite positioning receiver, comprising a device according to the invention
• FIG. 3 represents a flowchart for a method of correcting the effects of aging of a device, according to the invention
• the invention has a number of advantages detailed below:
• the effects of the aging of a sensor are corrected by means of absolute time information from a receiver of a satellite positioning system whose operation is independent of that of the sensor. This independence is motivated in general by the interest of maintaining access to sensor measurements in the event of a receiver failure and conversely to maintain access to position measurements delivered by the receiver in the event of a failure. of the sensor. Moreover, the likelihood of the absolute time information is examined before it is taken into account for the development of the correction. The correction of the effects of the aging of the sensor therefore does not question the independent nature of the operation of the sensor and the receiver or their individual interchangeability. It does not degrade the safety of the onboard equipment either.
• the accuracy of the absolute time information required for the correction of the effects of aging is small, it does not need to be less than one week. This allows the use of absolute time information from an absolute clock of the receiver operating continuously. This absolute time information has the advantage of being available almost instantly which makes it possible the development of the correction of the effects of aging of the sensor during a self-test sequence, for example when powering up a processing unit processing sensor measurements. In this case, the correction of the measurements does not require any modification of the software functioning during the movement of the carrier and does not degrade its speed of execution. Corrections are only taken into account once, when the power is turned on and does not affect subsequent real-time calculations.
• the device comprises an inertial unit UMI which comprises at least one sensor, for example an accelerometer or a gyrometer and a processing unit and a receiver of a satellite positioning system.
• the processing unit processes measurements delivered by the sensor. The measurement accuracy changes with the age of the sensor.
• a hybridized inertial unit comprises an UMI inertial unit, a satellite positioning receiver, which will subsequently be called a GPS receiver with reference to the most common positioning system known as the "Global Positioning System", and an electronic hybridization computer.
• CALC_HYB CALC_HYB.
• the UMI inertial unit is most often composed of:
• accelerometers typically three
• gyrometers typically three, each having a fixed axis with respect to the aircraft and providing values angular rotation speed around these axes
• a processing unit which is a calculator which determines numerical data of velocity deviation ( ⁇ Vn, ⁇ Ve, ⁇ Vv), attitude deviation in roll and pitch heading ( ⁇ , ⁇ , ⁇ ), geographical position ( Lat, Lon, Ait), geographical velocity (Vn, Ve, Vv), attitudes in roll and pitch heading ( ⁇ , ⁇ , ⁇ ), etc. from the indications provided by the accelerometers and gyrometers; the computer also provides a time marking pulse defining the time at which these data are valid and constituting a time base of the receiver.
• the data Numbers present errors, caused by the aging of the sensors, which are not corrected.
• raw INERT data D_INERT All of these data, hereinafter referred to as raw INERT data D_INERT, are provided by the UMI inertial unit to the hybridisation calculator.
• a barometric altimeter ALT-BARO
• the calculator of the UMI unit uses the information of this or these additional sensors together with the information of the gyrometers and accelerometers.
• the GPS receiver conventionally provides a geographical position in longitude, latitude and altitude, also called resolute position, also including an absolute date or time of position measurement. In principle, the receiver also provides travel speeds in relation to the earth. The whole of this position, this absolute time and this speed is called PVT point. A time marking pulse defining the validity time of the PVT point is also provided.
• the GPS receiver uses for its operation a measurement of distances between the receiver and each satellite in view of the receiver. These distances are actually pseudo-distances PDi (i denoting a satellite number) obtained in the form of signal propagation times between the satellite of rank i and the receiver along the axis (satellite axis) joining the satellite and the receiver. It is the combination of the pseudo-distances on several satellite axes with the knowledge of the positions of the satellites at a given moment which makes it possible to calculate the resolved position PVT.
• the position of the satellites is either loaded and stored in the receiver or sent periodically to the receiver in the form of ephemeris as well as an absolute time by the satellites themselves.
• GPS GPS and they will be used for hybridization between the inertial unit and the GPS receiver.
• the GPS receiver further establishes other data, including ephemeris representing the position of the satellites at any time, a signal-to-noise ratio (S / N) i for each satellite, and one or more values of protection radius Rp1 (in horizontal distance), Rp2 (in vertical distance) which represent a measurement accuracy.
• the GPS receiver provides the hybridisation calculator CALC_HYB all these data, hereinafter called D_GPS (GPS data).
• D_INERT raw inertial data and GPS data are processed in the hybridisation calculator to provide hybrid inertial data D_HYB which is a hybrid attitude, a hybrid speed and a hybrid position.
• the hybridization calculator also provides one or more RPH protection radius values representing the accuracy of the data from the hybridization.
• the computer can provide satellite identification data at fault and of course possibly alarm signals when the calculation of the protection radii demonstrates insufficient reliability of the information provided.
• the GPS receiver also provides the hybridisation calculator an indication, for each satellite observed, of the phase ⁇ j of the carrier of the satellite signal of rank i at the instant of observation.
• Hybridization is carried out by filtering algorithms of
• Kalman to obtain both the qualities of stability and lack of short-term noise of the inertial unit and the very high accuracy but highly noisy short-term GPS receiver. Kalman filtering makes it possible to take into account the short-term intrinsic behavior errors of the UMI inertial unit, and to correct these errors.
• the measurement error of the UMI inertial unit is determined during the filtering; it is added to the measurement provided by the UMI inertial unit to give a hybrid measurement in which errors due to the behavior of the UMI unit are minimized.
• the realization of the filtering algorithm using the pseudo-distances from the GPS receiver and the phases of the carrier of the satellite signals, is such that the faulty satellites can be determined, excluded, and calculated.
• Hybrid position protection both in the absence of a satellite fault and in the presence of a fault is therefore designed both to correct the short-term errors inherent to the sensors of the inertial unit and to take into account the defects of the space segment of the reception of the satellite signals.
• Additional means may also be provided for detecting (but not necessarily correcting) hardware defects of the inertial unit (non-modeled defects, ie faults) and hardware defects of the GPS receiver. These means consist in practice to provide redundant channels, with another inertial unit, another GPS receiver and another hybridization calculator. This type of redundancy is not the subject of the present invention and will not be described, but the invention can be incorporated in redundant systems as in non-redundant systems.
• the hybridization can be done in open loop, that is to say that the inertial unit is not slaved to the data resulting from the hybridization, it can also be done in closed loop, in this case the Inertial unit is corrected for sensor bias (short term) estimated by a hybridization calculator filter.
• initial values in the inertial unit and in the hybridisation calculator are given the first time with reference to an absolute reference point: for example, starting from a plane on the ground, immobile, in a known attitude and at a known position, this attitude and this position are introduced as initial values in the filtered. Subsequently, during flight, the measurements provided by the inertial unit may be readjusted from time to time depending on the measurements provided by the GPS receiver.
• FIG. 2 represents an exemplary device according to the invention, a hybridized inertial unit delivering a measurement of components of an acceleration vector.
• a receiver failure does not cause a sensor failure and conversely, a sensor failure does not cause a receiver failure
• the IMU inertial unit includes a law describing the degradation of the measurements of a sensor, for example a gyrometer, a date of manufacture of the sensor and means for recovering, when powering up the inertial unit, absolute time information from the GPS receiver.
• the GPS receiver has an absolute clock to pre-load ephemeris from the satellites and thus quickly provide position information of the receiver. It is preferentially this absolute time information, rather than that transmitted by the satellites to the GPS receiver, which is transmitted to the processing unit during power-up because it is immediately available.
• the absolute time information is transmitted to the UMI inertial unit by means of a digital channel.
• the UMI inertial unit uses the absolute time information to determine the age of the sensor.
• the absolute time information may be a universal time also called Greenwich time or any other time datation having the property of defining an instant unambiguously and uniquely.
• the calculator CALCJHYB of the hybridised inertial unit determines numerical data: geographical velocity (Vn C ⁇ rr , Ve C ⁇ rr , Vv C ⁇ rr ), attitudes in roll and pitch heading ( ⁇ corr, ⁇ corr, ⁇ corr) including corrections of aging effects of the sensors used to measure these data.
• the receiver comprises an absolute clock and a supply of energy supplying the clock continuously and the clock can deliver the absolute time information permanently.
• the positioning system receiver uses a time base reference from satellites to measure pseudo-distances.
• a hybridised inertial unit comprises a device according to the invention and a time base for measuring with the device
• the hybridised inertial unit may also comprise means for recovering the time base reference, which is transmitted to it by the receiver. by means of an analog electrical signal representing a duration between two transitions.
• the accuracy of the reference time base is very high, of the order of pico-second over a period of one second.
• the hybridised inertial unit uses the time base reference from the GPS receiver to re-calibrate its own time base, which is less stable in the long term than that of GPS, and thus correct the effects of the aging of its time base.
• the transmission to the calculator CALCJHYB of the absolute time information and time base reference is performed each time the calculator CALCJHYB is powered up.
• the calculator CALCJHYB determines corrections for measurements made by a sensor of the UMI inertial unit from the law of degradation of the measurements of the sensor.
• the degradation law is determined from a collective or individual sensor characterization performed in the factory. For example, for an accelerometer, it can be established that the long-term drift of the sensor follows a time-dependent law and has either an exponential or a linear form or a combination of several mathematical functions.
• the inertial unit includes means for verifying, for example, that the absolute time information transmitted to it is actually chronologically subsequent to an absolute time information transmitted to it during a previous power-up, or even better is chronologically posterior to the date of the previous power off.
• the sensor measurement processing unit comprises means for verifying the relevance of the absolute time information upon receipt of the information.
• the UMI inertial unit calibrates its own time base and determines temporal measurement corrections to be applied to all time or frequency measurements internal to the unit, either directly on the measurements or on the resulting size.
• the method used for the calibration of the time base of the inertial unit is any known method, for example a count of one number of periods of the time base during a time interval between two pulses from a time base of a GPS receiver.
• the processing unit includes a time base for processing the measurements
• the receiver has a time base reference information to define a moment of validity of the position measurements characterized in that it comprises the steps following:
• the time base reference information has a very high precision.
• the sensor is an accelerometer.
• the senor is a gyrometer.
• the sensor is a baro-altimeter.
• the device on board a carrier for example an aircraft, comprises a measurement sensor delivering to a processing unit a measurement which is tainted by errors caused by aging of the sensor, the processing unit processing the measurements, and a receiver a satellite positioning system.
• the sensor and the receiver are two distinct instruments that can be arranged at different positions on the carrier and have independent operation: a receiver failure does not cause a sensor failure and conversely a sensor failure does not result in receiver failure.
• the receiver comprises an absolute clock and a supply of energy supplying the clock continuously and the clock delivers an absolute time information continuously.
• a sequence comprising a succession of steps executes to implement a correction of the effects of aging of the sensor.
• a first step 100, of energizing the power supply of the processing unit and the sensor, is followed by a second step 101 of transmitting to the processing unit an absolute time information from the receiver. .
• a third step 102 is to determine the age of the sensor from the absolute time and the date of manufacture of the sensor, by comparing the absolute time information and the date of manufacture of the sensor.
• a fourth step 103 corrections are made to the measurement of the sensor as a function of the age of the sensor and a degradation law of the sensor.
• the corrections are applied systematically by the processing unit to the measurements delivered by the sensor to correct the effects of its aging.
• the processing unit comprises a time base for processing the measurements of the sensor
• the receiver of the satellite positioning system has a time base reference information
• the device comprises:
• the receiver comprises an absolute clock and a supply of energy which continuously supplies the clock, and the clock delivers the time base reference information.

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• Engineering & Computer Science (AREA)
• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Manufacturing & Machinery (AREA)
• Radar, Positioning & Navigation (AREA)
• Remote Sensing (AREA)
• Technology Law (AREA)
• Position Fixing By Use Of Radio Waves (AREA)

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• 2005
  • 2005-10-14 FR FR0510514A patent/FR2892193B1/fr not_active Expired - Fee Related
• 2006
  • 2006-10-03 EP EP06793955A patent/EP1934558A1/de not_active Withdrawn
  • 2006-10-03 WO PCT/EP2006/066998 patent/WO2007042427A1/fr active Application Filing
  • 2006-10-03 US US12/089,471 patent/US7584069B2/en not_active Expired - Fee Related

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