Classifications

• • G—PHYSICS
  • G05—CONTROLLING; REGULATING
  • G05D—SYSTEMS FOR CONTROLLING OR REGULATING NON-ELECTRIC VARIABLES
  • G05D1/00—Control of position, course, altitude or attitude of land, water, air or space vehicles, e.g. using automatic pilots
  • G05D1/0055—Control of position, course, altitude or attitude of land, water, air or space vehicles, e.g. using automatic pilots with safety arrangements
  • G05D1/0077—Control of position, course, altitude or attitude of land, water, air or space vehicles, e.g. using automatic pilots with safety arrangements using redundant signals or controls
• • G—PHYSICS
  • G06—COMPUTING OR CALCULATING; COUNTING
  • G06F—ELECTRIC DIGITAL DATA PROCESSING
  • G06F11/00—Error detection; Error correction; Monitoring
  • G06F11/07—Responding to the occurrence of a fault, e.g. fault tolerance
  • G06F11/16—Error detection or correction of the data by redundancy in hardware
  • G06F11/18—Error detection or correction of the data by redundancy in hardware using passive fault-masking of the redundant circuits
  • G06F11/187—Voting techniques
  • G06F11/188—Voting techniques where exact match is not required

Definitions

• the present invention relates to the processing of signals supplied to a flight control system by primary flight equipment doubled or tripled for safety. It relates more particularly to the processing operations intended to avoid untimely disconnections of an automatic control system of the flight control not justified by a real failure of an equipment delivering or processing the signals used by the automatic control.
• a certain number of flight information items including the attitude of the aircraft, the module and the orientation of the aircraft speed vector, and the altitude of the aircraft are essential for piloting an aircraft.
• This information is provided by sensors belonging to on-board equipment called “primary flight equipment”.
• primary flight equipment there are the static and dynamic pressure sensors and their associated computer (“Air Data System” in English) making it possible to know the air speed of the aircraft and the inertial unit or units delivering the accelerations and angular speeds of the aircraft which can be combined within the same equipment designated by the acronym ADIRS (acronym of the Anglo-Saxon expression "Air Data Inertial Reference System”).
• the essential information for piloting is exploited in a raw form or preprocessed by one or more flight control systems bringing together automatisms which facilitate piloting by ensuring either attitude stabilizations or follow-up of attitude, heading, slope instructions , route, altitude, speed, etc.
• automatisms which facilitate piloting by ensuring either attitude stabilizations or follow-up of attitude, heading, slope instructions , route, altitude, speed, etc.
• the best known of these automations is the autopilot and / or flight director.
• Primary flight equipment such as flight control systems, must have an extremely low failure rate which is often achieved only by redundancy, the same equipment being doubled or tripled as well as a flight control system, each copy of the same flight control system being linked to the various copies of the primary flight equipment by processing chains whose function is to choose the most credible version, from the different versions available of the same information, and to detect any discrepancy between the different versions available of the same information being able to make suspect an unreported failure of one of the copies of the primary flight equipment at the origin of the information.
• each processing chain operates independently of the others and includes a voting device whose function is to choose at all times the copy of the flight equipment which provides the information taken into account by the flight system or systems.
• This voting device makes its choice by applying a proximity criterion with respect to a value corresponding to the median value of the available versions of the same item of information offset by an arbitrary threshold.
• the voting device tends to switch randomly from one copy to another, which introduces a spurious switching noise which can disturb the operation of flight control systems. It is known to limit this random switching by introducing a certain threshold in the operation of the voting device.
• the flight information is delivered by the primary flight equipment at rates, for example of the order of 20 milliseconds, compatible with the speed of variation of the flight parameters that they measure, this in an asynchronous manner, two copies of the same equipment operating in completely independent ways with separate clocks.
• Flight control systems use the flight information delivered by the primary flight equipment at a lower rate adapted to their needs, for example of the order of 50 milliseconds, based on the reaction speed of the aircraft to their instructions.
• Information from primary flight equipment is preprocessed in flight control systems at the lowest rate, to minimize their computational load. Asynchronisms between the different copies of the same equipment connected to their inputs and between their inputs and their output are taken into account at the start of the chain by the use of buffer memories.
• monitoring the proper functioning of the processing chains and the equipment placed upstream is done by detecting discrepancies between the versions of the same information available at the output of the two processing chains.
• This discrepancy becomes too great, one suspects an unreported malfunction of one of the elements of the processing chains or of one of the equipment placed upstream of the processing chains and we prefer to stop the automations depending on the processing chains. treatment.
• This is obtained using a subtractor circuit placed at the outputs of the chains and followed by a threshold comparator.
• the threshold comparator generates, in the event of its threshold being exceeded by the difference existing between the versions of the same information available at the output of the two processing chains, an alarm leading to the stopping or disconnection of the automations in operation flight control systems using the channel exit information.
• the object of the present invention is to reduce the frequency of untimely disconnections of automatic systems of a flight control system due to artefacts from processing chains of primary flight information doubled or tripled to reinforce safety. It relates to a method for processing information originating from primary flight equipment mounted on board an aircraft, in a form sampled at a first rate, with a view to being delivered to a flight control system of the aircraft, at a second rate lower than the first rate, this method being remarkable in that it consists in subjecting the information samples to digital noise reduction filtering carried out at the first sampling rate.
• the digital noise reduction filtering is an anti-aliasing filtering blocking the undesirable components having frequencies lower than half of the first sampling rate and higher than half of the second sampling rate
• digital noise reduction filtering is first order low pass filtering.
• the digital noise filtering is a second order low-pass filtering.
• the digital noise reduction filtering is a low-pass or notch filtering of the Butterworth type.
• the noise reduction filtering is a cut-band filtering corresponding to the energy peaks of the noise.
• the digital filtering implements a transfer function depending on the flight configuration of the aircraft.
• the noise reduction filter is a sliding average filter operating on several samples.
• the invention also relates to a device for implementing the above method.
• figure 1 represents a redundant architecture used, in the prior art, for a lateral acceleration information processing chain provided by a inertial unit in order to make it available to a yaw stabilizing automation
• FIGS. 2a to 2d are diagrams of curves illustrating the evolution of the differences between the operating drifts of the two processing chains of the redundant architecture of FIG. 1 in the presence of highly noisy sensor signals and the untimely disconnections resulting therefrom for the yaw stabilizing automation,
• FIG. 3 represents a redundant architecture according to the invention for a chain for processing lateral acceleration information supplied by an inertial unit with a view to making it available to a yaw stabilizing automation
• Figures 4a to 4d are diagrams of curves illustrating the controlled operating drifts of the two processing chains of the redundant architecture of Figure 3 and the very infrequent blockages resulting therefrom for the yaw stabilizing automation.
• FIG. 1 shows a known type of redundant architecture used for the generation of integrated lateral acceleration information YD intended for a yaw stabilizing automation forming part of a flight control system and having the function of dampen the yaw oscillations of the aircraft and cancel the skid angle of the aircraft.
• This redundant architecture takes advantage of lateral acceleration information ⁇ l delivered in parallel and independently by two copies 10, 1 1 of INS inertial unit to also independently generate two versions of YD anti-skid control information all two intended for yaw stabilizing automation. Constant monitoring of the difference between the two supplied versions YDa and YDb of the control information is used as a test of the correct functioning of the elements of the redundant architecture of the yaw stabilizing automation.
• This type of redundant architecture contains two functionally identical parallel chains FGMa and FGMb, installed on separate hardware modules.
• the two copies 10, 11 of inertial unit INS deliver, in digital form, and at a repetition rate of 50 Hz (periodicity of 20 ms), two versions ⁇ l1 and ⁇ l2 of the lateral acceleration information.
• Their data flows are neither completely identical nor synchronized because they are subjected to different vibrational atmospheres due to their installations in different places of the aircraft cell and operate independently of each other with independent clocks .
• the two parallel processing chains FGMa, FGMb use the two versions ⁇ l1 and ⁇ l2 of the lateral acceleration information delivered asynchronously and at a repetition rate of 50 Hz (periodicity of 20 ms) by the two central units 10, 11 inertial INS to generate by integration, with a repetition rate of 20 Hz (periodicity of 50 ms), two versions of the anti-skid control information YDa, YDb.
• Each processing chain FG a, FGMb comprises at input a double buffer memory 20, 21, followed by a voting circuit 30, 31, an amplifier 40, 41 and an integrator 50, 51.
• the double buffers 20, 21 are loaded at a rate of 20 Hz with pairs of samples of the lateral acceleration information, the two samples of the same pair coming from one of copy 10 and the other from copy 11 of inertial unit INS and corresponding to the lateral acceleration information ⁇ l1 and ⁇ l2 delivered by the two copies 10, 11 of inertial unit for the same time slot.
• the voting circuits 30, 31 select, whenever necessary, that is to say every 20 ms, in the double buffer memory 20, 21 placed upstream, one of the samples of the last pair d 'lateral acceleration information samples entered. For this selection, they implement an arbitrary choice criterion consisting of a voting mechanism such as that described in the preamble.
• the amplifier circuits 40, 41 followed by the integrator circuits 50, 51 make it possible to extract, by integration, samples retained by the voting circuits 30, 31, two sampled versions YDa and YDb of anti-skid control information. intended for a yaw damping automation of a flight control system.
• a subtractor circuit 60 supplying a threshold comparator 61 which receives its threshold from a register 62 and which issues a blocking order for the automations supplied by the two processing chains FGMa and FGMb in the event of detection of an overstepping of the threshold by the difference existing between samples of the same rank coming from the two chains.
• a threshold comparator 61 which receives its threshold from a register 62 and which issues a blocking order for the automations supplied by the two processing chains FGMa and FGMb in the event of detection of an overstepping of the threshold by the difference existing between samples of the same rank coming from the two chains.
• FIGS. 2a to 2d This can be seen by studying the diagrams in FIGS. 2a to 2d relating to the operation over the same period of time of the two processing chains FGMa and FGMb, in the absence of a fault, with strongly input signals noise from inertial units in good working condition but subject to parasitic vibrations from the aircraft cell.
• the diagram in FIG. 2a represents a highly noisy signal ⁇ l1 originating from one of the two examples of inertial unit INS affected by parasitic vibrations of the aircraft cell.
• the diagram in FIG. 2b represents the highly noisy signal ⁇ l2 coming from the other 11 of the two examples of inertial unit INS also subjected to parasitic vibrations from the cell of the aircraft.
• the diagram in FIG. 2c represents the two versions YDa and YDb of the anti-skid control information delivered by the two chains FGMa and FGMb in response to the signals ⁇ l1 and ⁇ l2.
• the relative evolution of the difference between the two versions YDa and YDb due to the slow drift of the integrator circuits 50 and 51 is aggravated by the effects, on the hardware and software asymmetries of the two processing chains FGMa and FGMb, of vibrational noises affecting the ⁇ l1 and ⁇ l2 signals.
• the diagram in FIG. 2d shows the state resulting from the blocking order B generated by the threshold comparator 61 intended for automations depending on the processing chains. We notice, in the middle of the diagram, untimely automatic blocking orders.
• the redundant architecture of FIG. 3 differs from that of FIG. 1 by the presence in the two processing chains FGM'a and FGM'b, of two double noise filters 70, 71 interposed between the voting circuits 30 , 31 and the double buffers 20 ', 21' and by the fact that the double buffers 20 'and 21' operate at a rate of 50 Hz which is that of the data transmitted by the two copies 10, 11 of inertial unit and not at the 20 Hz rate of the output signals from the processing chains.
• Each double noise filter 70 or 71 filters in parallel, the two series of samples delivered by the two copies 10, 11 of the inertial unit INS, at the rate of these suites, without subsampling but under the control of its own clock not synchronized with one or the other of the clocks of copies 10, 11 of inertial unit.
• the double buffer memories 20 ′ and 21 ′ passing at the higher rate of the data transmitted by the two copies 10, 11 of INS inertial unit, are no longer used for sub-sampling but only for taking into account the absence of synchronism between the clocks at the same frequency two copies 10, 11 of INS inertial unit and double noise filters 70, 71.
• the double noise filters 70, 71 are digital filters operating at the rate of 50 Hz from the data sequences from the two copies 10, 11 of the INS inertial unit, therefore before subsampling, in order to avoid at their level , possible problems posed by the folding of the tape accompanying a sub-sampling.
• the sub-sampling enabling the output samples of the two processing chains FGM'a and FGM'b to be passed at the rate of 20 Hz is done at the outputs of the double noise filters 70, 71 whose registers also serve as buffer memories .
• the transfer functions of the double noise filters 70, 71 are chosen so as to block as best as possible the noises affecting the signals of the two copies 10, 11 of inertial unit INS1, INS2, while minimizing the useful signals. They are chosen after studying the vibrational environment of each exemplary inertial unit as a function of the flight configurations of the aircraft more particularly conducive to the appearance of vibrations on the airframe, such as outgoing landing gear configurations, flaps out, airbrakes out, open cargo door, carrying of external load, etc. They can even be changed depending on the current flight configuration. They are advantageously of the low-pass or band-cut type and of any order depending on the stiffness of the desired cut. (1 st , 2 nd order, Butterworth, etc.). They can also be obtained by sliding average over any number of samples.
• the transfer function chosen for the double anti-noise filters is that of an anti-aliasing filter.
• This anti-aliasing filter can be adjusted to block the components of frequency lower than half of the first sampling frequency of 50 Hz and of frequency higher than half of the second sampling frequency of 20 Hz.
• the transfer function adopted for the double noise filters can be of the notch or plug type , with one or more stop frequencies placed at the frequencies of the resonance vibrations developing in the airframe of the aircraft at the locations of copies 10, 11 of inertial unit.
• a double noise filter 70 or 71 as well as the control of the double buffer memory 20 'or 21' which precedes it and carries out the acquisitions of the samples of the lateral acceleration information delivered by the two copies 10, 11 of the inertial unit INS can be the subject in each FGM chain of the same software task executed at the same rate.
• the diagrams in FIGS. 4a to 4d illustrate the improvement brought by the noise filters. They are plotted over the same period of time and with the same highly noisy input signals as those of FIGS. 2a to 2d, always in the absence of failure of the inertial units and of the measurement chains.
• FIG. 4a represents the signal ⁇ i'1 coming after noise reduction filtering from one of the two examples of inertial unit INS affected by parasitic vibratory phenomena of the aircraft cell.
• the diagram in FIG. 4b represents the signal ⁇ l'2 coming, after anti-noise filtering, from the other 1 1 of the two examples of INS inertial unit also affected by parasitic vibrational phenomena of the aircraft cell.
• the effects of anti-noise filtering make the general evolutions of the signals ⁇ l'1 and ⁇ l'2 more apparent and their resemblance.
• FIG. 4c represents the two versions YDa and YDb of the anti-skid control information delivered by the two chains FGMa and FGMb in response to the signals ⁇ l1 and ⁇ l2.
• L redundant architecture with double noise filters which has just been described can be used with any flight control system receiving primary flight information, redundant processing chains having, by nature, a significant drift capacity due to terms of precision including integrators, such as those dealing with information coming from an inertial unit 1RS, AHRS or accelerometer block and this in any aircraft, whether it be an airplane, a helicopter, a drone, a missile, etc.

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• Engineering & Computer Science (AREA)
• Aviation & Aerospace Engineering (AREA)
• Radar, Positioning & Navigation (AREA)
• Remote Sensing (AREA)
• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Automation & Control Theory (AREA)
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• 2003
  • 2003-06-06 FR FR0306884A patent/FR2855922B1/fr not_active Expired - Fee Related
• 2004
  • 2004-05-24 WO PCT/EP2004/050902 patent/WO2004109516A1/fr not_active Ceased
  • 2004-05-24 EP EP04741640A patent/EP1631907A1/de not_active Withdrawn
  • 2004-05-24 US US10/559,689 patent/US20060287809A1/en not_active Abandoned

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