METHOD FOR CONTROLLING A CYLINDER

Description

Domaine Technique

[0001] The present invention relates to the field of cylinder control, and in particular cylinders for actuating moving parts of a variable geometry turbomachine.

[0002] In the field of aeronautics, aircraft turbomachines include components called "variable geometries". A variable geometry of a turbomachine such as a turbojet is a moving component whose position can be controlled to act on the circulation of a fluid in the turbojet, for example on the gas flow in the primary flow vein of a bypass turbojet, in order to control the behavior of the turbojet. Variable geometries can be, for example, moving valves or blades, such as air discharge valves also commonly referred to as VBV (for Variable Bleed Valve) or blades of a variable-pitch stator blade. The valves can also be valves for adjusting the cooling air flow of turbine casings, in a system for adjusting the clearances at the tips of the turbine blades by thermal shrinkage of the casings, in order to optimize fuel consumption. Technique antérieure

[0003] Cylinders traditionally comprise a piston that moves in translation in a cylinder body. Cylinders are known that are equipped with position sensors and controlled by servovalves, in order to control the position of the piston in the body of said cylinder. Such an assembly formed by a cylinder, a servovalve and a plurality of position sensors is also called a servocylinder. The servovalve forms a control member of the cylinder, for example configured to regulate the pressure or the flow rate of fluid supplying said cylinder, in order to regulate the position of the piston in the body of the cylinder.

[0004] It is known to use measuring devices to measure the position of the piston in the cylinder body. Said measuring devices traditionally comprise, for safety reasons, two redundant position sensors configured to measure the position of said piston simultaneously and independently of each other. The position of the piston in the cylinder body is then generally regulated from an average of the piston position measurements provided by the two position sensors.

[0005] A disadvantage of this type of process is that in the event of a failure or malfunction of one of the two position sensors causing drifts or amplitude biases, the control of the position of the piston in the cylinder body is disturbed, even in cases where the said average is only slightly impacted. As a result, the position of the piston in the cylinder body is not precisely regulated. Thus, when the cylinder is used to actuate variable geometries of a turbomachine such as, for example, VSVs (for Variable Stator Valves) which are variable-pitch blades in a stator vane (called a rectifier) ​​of a high-pressure compressor, this causes disturbances in the control of said blades which have the shape of fins, risking damaging them, in particular because the compressor risks initiating surge.The control of the turbomachine itself is also disturbed by the control deficit of the VSV or even the VBV, risking causing loss of power control (Loss of Thrust Control in English), which is not desirable.

[0006] Document EP 2 228 545 A2 describes a method for controlling a cylinder by measuring two values ​​representative of the position or movement of a valve and then selecting one of the two values ​​to generate a valve control signal. Document DE 103 18 171 A1 describes a method for determining a measured quantity using two sensors. Exposé de l'invention

[0007] An aim of the present invention is to propose a method for controlling a jack which overcomes the aforementioned problems.

[0008] To do this, the invention relates to a method for controlling a jack, according to claim 1.

[0009] Without limitation, the cylinder may be a pneumatic or hydraulic cylinder and is preferably a double-acting cylinder. Still without limitation, the cylinder may be used to actuate variable-pitch vanes in a stator vane of a high-pressure compressor of a turbomachine.

[0010] The servovalve controls the supply of fluid to the cylinder, for example, from an electronic control signal that it receives as input, in order to control the movement of the piston in the cylinder body and to regulate the position of said piston.

[0011] Each position sensor forms a separate measuring device. These sensors can be inductive or magnetic position sensors, but are not limited to these. These position sensors can be passive electronic linear displacement sensors (or LVDTs, for Linear Variable Differential Transformer).

[0012] The assembly formed by the cylinder, the servo and the measuring device forms a servo-cylinder allowing the position of the cylinder to be controlled in the cylinder body. In other words, the position of the cylinder is corrected from the position measurements provided by the sensors and a piston position setpoint.

[0013] The first and second position sensors are identical and placed under similar measurement conditions in order to perform the piston position measurements. These measurements are performed at the same time. Also, during normal operation of the two position sensors, the position measurements they provide are substantially identical.

[0014] The modeled or predetermined speed serves as a reference and is considered to be the actual and exact speed of the piston, which would be measured by a perfect position sensor.

[0015] The most reliable position sensor is the position sensor whose position measurements are the most accurate and most consistent with the actual position of the piston in the cylinder body. The most reliable position sensor is the one that provides position measurements that allow the determination of a piston displacement speed that is closest to the modeled or predetermined displacement speed.

[0016] In order to compare them, the first and second displacement speeds and the modeled or predetermined displacement speed of the piston are advantageously considered under similar operating conditions, for example in response to a given servovalve control signal.

[0017] The method according to the invention makes it possible to identify the most reliable position sensor quickly, precisely and with a minimum of measurements to be carried out. It is then possible to regulate the position of the piston from the position measurements provided by said position sensor identified as being the most reliable. The control of the position of the piston is therefore improved compared to the methods of the prior art in which the position of the piston is regulated from an average of the position measurements of the two position sensors.

[0018] The position of the piston is controlled more precisely so that the method according to the invention reduces the risk of damage to at least one variable geometry actuated by the cylinder in the turbomachine. The method according to the invention also makes it possible to avoid power control losses.

[0019] An advantage of the method according to the invention is also to target a defective position sensor among the two position sensors, so as not to regulate the position of the piston from the position measurements provided by this defective sensor and possibly to replace it.

[0020] Identifying the faulty position sensor also helps with maintenance and saves substantial time, as there is no longer any need to search for the fault by other means.

[0021] In the variant where the first and second piston displacement speeds are compared with a modeled piston displacement speed, said modeled piston displacement speed is preferably determined from a pre-established model of operation of the assembly formed by the servovalve and the cylinder. This model is considered to reflect the normal, incident-free operation of this assembly. This piston speed model has the particular advantage of being very precise and easy to implement, and in particular much more precise and easy to implement than the cylinder piston position models.

[0022] Indeed, the assembly formed by the servovalve and the cylinder behaves like an integrator. Therefore, it is difficult to estimate the position of the piston from a position model and to compare measured positions to such a modeled position. Comparing the displacement speeds of the piston, obtained from position measurements, with a modeled displacement speed is easier.

[0023] Using a modeled speed therefore makes it possible to identify the most reliable position sensor more quickly and efficiently.

[0024] In the variant where the first and second piston displacement speeds are compared with a predetermined piston displacement speed, said predetermined displacement speed can be extracted from a table of characteristic values ​​of piston displacement speeds, for example under normal operating conditions. This predetermined displacement speed can be stored in an internal memory of the measuring device.

[0025] Preferably, the steps of determining the first and second piston displacement speeds are repeated over a selected period of time so as to determine a plurality of first and second piston displacement speeds. All of the first and second piston displacement speeds thus determined are then compared with a plurality of modeled or predetermined piston displacement speeds.

[0026] Preferably, comparing said first and second determined piston displacement speeds with said predetermined or modeled piston displacement speed comprises a step of calculating a comparison factor. R and determining the sign of said comparison factor. Without limitation, a positive comparison factor indicates that the first position sensor is the most reliable and a negative comparison factor indicates that the second position sensor is the most reliable or vice versa.

[0027] Preferably, the comparison factor R is calculated according to the following equation: R = ∫ v 1 − v mod − ∫ v 2 − v mod

[0028] Where v 1 and v 2 are the first and second determined speeds of displacement of the piston in the cylinder body and v mod is the predetermined or modeled displacement speed of the piston.

[0029] The integration is preferably carried out over a chosen period of time, so that the comparison factor reflects a comparison of the first and second piston displacement speeds with the modeled piston displacement speed over said chosen period of time. The use of the integral makes it possible to overcome measurement aberrations and noise that may appear when determining said first and second piston displacement speeds. The accuracy of the comparison and therefore the identification of the most reliable position sensor are therefore improved.

[0030] The comparison factor is preferably kept in memory.

[0031] Advantageously, the piston is configured to define a first chamber and a second chamber within the piston body and the modeled displacement speed of the piston is a function of a modeled pressure difference between said first and second chambers.

[0032] In the case where the cylinder is used as an actuator within a turbomachine comprising an injection chamber, the modeled pressure difference can be a function of a modeled flow rate of fuel injected into the combustion chamber of the turbomachine as well as the pressure upstream of the combustion chamber.

[0033] Preferably, the modeled displacement speed of the piston is a function of a servovalve supply current. This current is also called the wrap current.

[0034] Advantageously, the modeled displacement speed of the piston is a function of an equilibrium current determined by applying a first-order filtering function to said servovalve supply current. The use of said equilibrium current makes it possible to obtain a particularly accurate piston displacement speed model.

[0035] The modeled displacement speed of the piston is preferably determined from the following relationship: v mod = K Δ P i − i eq where i is the servovalve supply current, i eq is the equilibrium current, ΔP is the modeled pressure difference between said first and second chambers. K is a gain that can be determined by linear regression from the modeled piston displacement speed, the servovalve supply current and said pressure difference.

[0036] Preferably, a preliminary step of detecting the presence of at least one defective position sensor is carried out and the step of comparing the first and second determined speeds of movement of the piston with the modeled or predetermined speed of movement of the piston is carried out when the presence of a defective position sensor is detected.

[0037] A defective position sensor is defined as a position sensor whose cylinder piston position measurements are particularly aberrant compared to the actual position of the piston in the cylinder body and are therefore unsatisfactory. This could be a faulty, misadjusted or poorly calibrated position sensor. A faulty position sensor generally results in a drift in the position measurements it provides.

[0038] The comparison step identifies the position sensor providing the most accurate piston position measurements and the most consistent with the actual piston position in the cylinder body, among the two position sensors. If one position sensor is faulty while the other is working properly, the properly functioning position sensor will be identified as the more reliable one. In the case where both position sensors are faulty, the least faulty position sensor will be identified as the more reliable one.

[0039] The detection step allows the comparison step to be performed only when a failure of one of the position sensors is detected. This makes it possible to not perform the comparison step permanently and to identify the most reliable position sensor only when necessary. One advantage is to save computing resources. In addition, the comparison step is only performed over a limited time interval, facilitating the identification of the failure, from a reduced number of piston position measurements. The identification of the most reliable position sensor is improved.

[0040] In a non-limiting manner, the presence of a defective position sensor can be detected by observing particularly aberrant position measurements provided by one of the position sensors or by observing a failure or incident in the control of the position of the piston of the cylinder. The detection step advantageously makes it possible to detect a failure or a very slight malfunction of one of the sensors, for example small amplitude biases or slow drifts.

[0041] Preferably, the presence of a defective position sensor is detected from the piston position measurements obtained respectively with the first position sensor and with the second position sensor. The presence of a defective position sensor is advantageously detected by observing a divergence between said piston position measurements provided by the two position sensors.

[0042] More preferably, the step of detecting the presence of a defective position sensor comprises a step according to which the difference between the piston position measurements obtained with the first position sensor and the piston position measurements obtained with the second position sensor is determined.

[0043] Advantageously, the step of detecting the presence of a defective position sensor further comprises steps according to which the variance of said deviation is calculated and said variance is compared to a predetermined detection threshold. In the presence of a defective position sensor, for example one that is faulty, the position measurements that it provides drift, just like said deviation, more or less strongly. The variance of said deviation evolves much more quickly and strongly and therefore makes it possible to detect a defective position sensor more quickly and therefore even a slight failure of the sensor.

[0044] The predetermined detection threshold is preferably chosen very low, so as to detect the presence of a defective position sensor very quickly. This also makes it possible to detect even a slight failure of a position sensor, for example the presence of a slightly misadjusted position sensor. One advantage is that it allows the identification of the most reliable position sensor as soon as one of the position sensors is slightly defective. Detection is therefore precise, which improves control of the cylinder.

[0045] Preferably, the counter value increments periodically from its initial value, for example every second. The counter threshold is set arbitrarily, for example to 30 seconds.

[0046] The use of the counter allows the comparison step to be carried out over a limited period of time, starting from the detection of a defective position sensor. This further facilitates the identification of the most reliable position sensor and reduces the resources mobilized to carry out the step of comparing the first and second determined piston displacement speeds with the modeled or predetermined piston displacement speed.

[0047] Advantageously, the position sensor identified as being the most reliable is selected and the position of the piston is regulated using the piston position measurements provided by said selected position sensor. One advantage is to control the position of the piston precisely, from the most precise position measurements of the piston in the cylinder body and consistent with the actual position of the piston. The regulation of the position of the piston is improved compared to the methods of the prior art providing regulation from the average of the position measurements provided by all the position sensors. The regulation of the position of the piston is not impacted in the event of failure of one of the position sensors.

[0048] Preferably, an additional step of detecting the presence of a defective position sensor is carried out and the step of selecting the most reliable position sensor is carried out if a defective position sensor has been detected during the additional detection step. One advantage is to ensure the presence of a defective position sensor and not to select a position sensor if all the position sensors are functioning correctly. If no defective position sensor is detected during the additional detection step, the position of the piston in the cylinder body will be regulated from the position measurements provided by all the position sensors.

[0049] In the embodiment where the method comprises a preliminary detection step, prior to the comparison step and conditioning the triggering of said comparison step, the additional detection step makes it possible to confirm the presence of a defective position sensor. Indeed, the preliminary detection step, conditioning the triggering of the comparison step, is preferably strict and may lead to the erroneous detection of a defective position sensor. The additional detection step is preferably less strict and makes it possible to detect only a significant failure of the position sensors and therefore to take into account only the position sensors that are actually defective. One advantage is to ensure the presence of a defective position sensor and to only carry out the step of selecting the most reliable position sensor when this proves necessary.

[0050] Preferably, the additional step of detecting the presence of a defective position sensor comprises a step of calculating the difference between the piston position measurements obtained respectively with the first position sensor and with the second position sensor and the step of selecting the most reliable position sensor is carried out if the absolute value of said difference is greater than a predetermined additional detection threshold. The presence of a defective position sensor is therefore detected when the piston position measurements provided by the two position sensors diverge significantly.

[0051] The predetermined additional detection threshold is preferably set at a value large enough for the selection step to be performed only when the difference between the position measurements obtained with the two position sensors is particularly large, indicating a failure or significant measurement inaccuracy of one of the position sensors. Below the predetermined additional detection threshold, it is considered that no position sensor is defective and the step of selecting the most reliable position sensor is not performed.

[0052] The invention also relates to a device for controlling a jack according to claim 13.

[0053] The processing module advantageously comprises a piston speed determination module configured to determine said first and second piston movement speeds and a comparison module configured to compare said first and second determined piston movement speeds with the modeled or predetermined piston movement speed. Brief description of the drawings

[0054] The invention will be better understood on reading the following description of an embodiment of the invention given by way of non-limiting example, with reference to the appended drawings, in which: [ Fig. 1 ]there figure 1 illustrates a control device according to the invention; [ Fig. 2 ]there figure 2 illustrates a processing module of the control device figure 1 ; [ Fig. 3 ]there figure 3 is a detailed view of the processing module of the figure 2 ; And [ Fig. 4 ]there figure 4 illustrates the steps of the method for controlling a jack according to the invention. Description of the embodiments

[0055] The invention relates to a method for controlling a cylinder and to a device for controlling a cylinder, making it possible to implement the method. This control method makes it possible to identify the most reliable position sensor among a set of position sensors and to control the position of the piston of the cylinder using the position measurements of the piston provided by this position sensor.

[0056] With the help of the figures 1à 3 , we will describe a device for controlling a jack, in accordance with the present invention, making it possible to implement a method for controlling a jack according to the invention.

[0057] In this non-limiting example, the cylinder makes it possible to actuate variable-pitch blades in a compressor, forming moving parts of a turbomachine. The turbomachine traditionally comprises a combustion chamber.

[0058] There figure 1 illustrates a control device 10 of a jack 12 in accordance with the present invention. The control device 10 includes a servovalve 14, a measuring device 16 and a processing module 18.

[0059] The jack 12 includes a cylinder body 20 and a piston 22 mobile in translation in the body of the cylinder. The piston delimits a first chamber 24 and a second bedroom 26 inside the cylinder body 20. Without limitation, the cylinder is a double-acting cylinder, so that it moves within the cylinder body 20depending on the fluid pressure present in the first and second chambers 24,26.

[0060] The servovalve 14 is a distributor for regulating the flow of fluid supplying the first and second chambers of the cylinder, according to an electronic control signal that it receives as an input. The servovalve 14 therefore allows the position of the piston to be adjusted 22 in the cylinder body 20, depending on a set position.

[0061] The measuring device 16 includes a first position sensor 28 and a second position sensor 30, each configured to measure the position and provide position measurements of the piston in the cylinder body.

[0062] As illustrated in the figure 2 , the processing device 18 includes a detection module 32configured to detect the presence of a faulty position sensor, an identification module 34 configured to identify the most reliable position sensor and a selection module 36 configured to select the most reliable position sensor and control the regulation of the piston position from the position measurements obtained by said selected position sensor. The processing device also comprises a reset module 37.

[0063] It is noted that the processing device 18 also includes a module for determining a modeled speed 38 configured to determine a modeled displacement speed v mod of the piston in the body 20 of the jack 12. The module for determining a modeled speed 38 includes a module for estimating a pressure difference 40, a module for determining a balance current42 and a calculator 44. The pressure difference estimation module 40 is configured to determine a pressure difference ΔP between the first and second chambers 24,26 of the jack 20.

[0064] As illustrated in the figure 3 , the detection module 32 includes an alert module 46, configured to generate a detection signal Y 0 , as well as a counter 48.

[0065] The identification module 34 includes a comparison module 50 and a piston speed determination module 52 configured to determine a first displacement speed v 1 of the piston from the position measurements provided by the first position sensor 28 and a second displacement speed v 2 of the piston in the cylinder body from the position measurements provided by the second position sensor30.

[0066] The selection module 36 the most reliable position sensor includes an additional detection module 54 and a control module 56.

[0067] We will now describe the steps of the control method, in accordance with the present invention, implemented by the control device 10.

[0068] The control device 10 of the jack 12 allows the piston position to be controlled in real time 22 in the cylinder body 20. In particular, the first and second position sensors 28,30 are configured to each provide measurements of the piston position. The servovalve 14 then controls the fluid supply to bring the piston to a set position, depending on the position measured by the position sensors.

[0069] In normal operation, the first and second position sensors continuously and simultaneously measure the position of the piston in the cylinder body. The first position sensor 28 allows to obtain a plurality of first measurements X 1 of the piston position and the second position sensor 30 allows to obtain second measurements X 2 of the piston position. The measurements X 1 ,X 2 position obtained by each of the first and second position sensors 28,30 are provided to the detection module 32 and more specifically to the alert module 46 of the detection module.

[0070] The alert module 46 is configured to determine in real time the gap between the first X 1 and second X 2 position measurements obtained simultaneously by the first and second position sensors and to calculate the variance of said deviation. The alert module 46then compares said variance to a predetermined detection threshold.

[0071] As long as said variance remains below said predetermined detection threshold, which indicates the absence of a defective position sensor, the alert module 46 does not transmit any detection signal and cylinder control is not affected.

[0072] We will now consider that the first position sensor 28 is broken and therefore defective, so the first position measurements X 1 that it provides are imprecise and divergent and are therefore far from the actual position of the piston and the second position measurements X 2 provided by the second position sensor 30. Also, the gap between the first and second measurements X 1 ,X 2 position varies rapidly and with a large amplitude.

[0073] The variance of said deviation, calculated by the alert module 46,then exceeds the predetermined detection threshold. This indicates the presence of a faulty position sensor and the alert module then transmits a detection signal Y 0 on the meter 48 set to an initial value.

[0074] The detection threshold is advantageously chosen low, in order to quickly detect a failure, even a slight one, of one of the position sensors. For example, a small divergence of the measurements X 1 ,X 2 position obtained by one of the position sensors 28,30 will be detected.

[0075] Upon receipt of the detection signal Y 0 , the counter 48 triggers a count, during which the counter value is incremented periodically, and transmits a trigger signal Y 1 to the identification module 34 and more precisely to the comparison module 50.

[0076] In parallel, the module for determining a modeled speed38 determines in real time a modeled speed v mod of the piston 22 in the cylinder body 20, that it provides to the comparison module 50.

[0077] To do this, the pressure difference estimation module 40 calculates a pressure difference ΔP between the first chamber 24 and the second bedroom 26 of the piston. This pressure difference is, without limitation, determined from the fuel injection flow rate D in the combustion chamber of the turbomachine, pressure P 0 upstream of said combustion chamber and the rotation speed a of the high pressure body of the turbomachine.

[0078] The pressure difference estimation module 40 provides the said determined pressure difference ΔP to the calculator 44.

[0079] The module for determining a balance current42 is configured to determine a balance current i eq from a current i servovalve supply 14, also called "current of" wrap ". When the position of the cylinder is constant or varies slightly, the equilibrium current i eq is determined by applying a first-order filter to said current i servovalve power supply In a non-limiting manner, the module for determining a balance current 42 is configured to determine the sliding variance of the cylinder piston position measured by one of the two position sensors. The module for determining an equilibrium current 42 is configured to maintain the equilibrium current value i eq constant when said sliding variance is greater than a sliding variance threshold, which reflects a sudden variation in the position of the jack.

[0080] The supply current of the servovalve i and the equilibrium current i eq are transmitted to the calculator 44. The calculator is configured to calculate the modeled displacement velocity v mod of the piston in the body 20 of the jack 12. Without limitation, this modeled movement speed is calculated according to the following equation: v mod = K Δ P i − i eq K is a gain that can be determined by linear regression from said modeled speed v mod , from the servovalve supply current i and the pressure difference ΔP between the first chamber 24 and the second bedroom 26 of the piston. The said modeled speed v mod is transmitted to the comparison module 50.

[0081] In parallel, the piston speed determination module 52 of the identification module 34determines a first displacement speed v 1 of the piston from the first position measurements X 1 provided by the first position sensor 28. It is understood that said first displacement speed v 1 of the piston is determined from a plurality of first position measurements X 1 of the piston 22 provided by the first position sensor 28. The piston speed determination module 52 also determines a second displacement speed v 2 of the piston from the second position measurements X 2 provided by the second position sensor 30.

[0082] The values ​​of the first and second displacement speeds v 1 , v 2 of the piston are transmitted to the comparison module 50 of the identification module 34.

[0083] In the absence of a trigger signal Y 1 received by the comparison module 50,the latter remains inactive.

[0084] On the other hand, as soon as a trigger signal Y 1 is received by the comparison module 50, the latter performs a comparison of the first and second displacement speeds v 1 ,v 2 of the piston with the modeled speed v mod used as a reference value. To do this, the comparison module 50 calculates a comparison factor R and determines the sign of said comparison factor R. The comparison factor R is calculated using the following equation: R = ∫ v 1 − v mod − ∫ v 2 − v mod

[0085] Integrations are performed over a chosen time period, for example 0.3 seconds, in order to reduce measurement noise. When the comparison factor R is positive, the first displacement speed v 1 of the piston, determined from the first position measurements X 1 obtained with the first position sensor 28,is further from the modeled speed v mod than the second displacement speed v 2 of the piston, determined from the second position measurements obtained with the second position sensor 30, over the chosen time period. This reflects the fact that the first piston displacement speed is less satisfactory than the second piston displacement speed, and that the second position measurements X 2 of the piston obtained with the second position sensor 30 are more accurate than the first position measurements X 1 of the piston obtained with the first position sensor 28.

[0086] A comparison factor R positive therefore indicates that the second position sensor 30 is more reliable than the first position sensor 28. Conversely, a comparison factor Rnegative indicates that the position measurements obtained with the first position sensor are more accurate than those obtained with the second position sensor. The first position sensor is then considered the most reliable.

[0087] In this example, we consider that the first sensor is defective, and that the comparison factor R calculated is therefore positive.

[0088] The comparison module 50 calculates, updates in real time and stores the comparison factor R, as long as the counter value remains below a predetermined counter threshold, e.g. 30 seconds. The comparison module passes the comparison factor R, positive in this example, to the selection module 36 and more precisely to the control module 56.

[0089] When the counter value 48reaches the predetermined counter threshold, the counter transmits an end of comparison signal Y 2 to the comparison module 50 and to the reset module 37. Upon receipt of the end of comparison signal Y 2 , the comparison module 50 interrupts the calculation of the comparison factor R.

[0090] The comparison module 50 is therefore only active after receiving the trigger signal Y 1 and before receiving the end of comparison signal Y 2 .

[0091] In parallel with the detection of the presence of at least one defective position sensor carried out by the detection module 32, and the identification of the most reliable position sensor carried out by the identification module 34, the additional identification module 54 of the selection module 36is configured to check and confirm the presence of a faulty position sensor. To do this, the additional detection module 54 calculates in real time the absolute value of the difference between the first piston position measurements X 1 obtained with the first position sensor 28 and the second position measurements X 2 obtained with the second position sensor 30 and compares this absolute value to an additional detection threshold.

[0092] When said absolute value of the difference between the first and second position measurements is greater than said additional detection threshold, the additional detection module 54 transmits an additional detection signal Y 3 to the control module 56 as well as the reset module 37.The additional detection threshold is preferably set at a value high enough so that the transmission of the additional detection signal Y 3 only occurs when the position measurements obtained with the two position sensors are particularly different and inconsistent, reflecting significant measurement inaccuracy of one of the position sensors.

[0093] Transmission of the additional detection signal Y 3 allows to confirm the presence of a faulty position sensor and to ensure that the presence of a faulty position sensor has not been mistakenly detected by the detection module 32.

[0094] In the absence of an additional detection signal Y 3 received by the control module 56, the presence of a faulty position sensor is not confirmed and the control module 56 remains inactive.

[0095] On the other hand, when the control module 56 receives an additional detection signal Y 3 , the presence of a faulty position sensor is confirmed.

[0096] In this example, the first position measurements X 1 provided by the first sensor 28 are particularly aberrant and far from the second position measurements X 2 provided by the second position sensor 30. Also, the additional detection module 54 transmits the additional detection signal Y 3 .

[0097] The control module 56 then selects the most reliable position sensor from the first and second position sensors 28,30, from the comparison factor R. In this example, the comparison factor R is positive so that the second sensor 30 is selected as the most reliable. The control module56 then transmits a control signal Z, especially to the servovalve, in order to select the most reliable position sensor, in this case the second sensor 30, and to control the regulation of the piston position 22 in the body 20 of the jack 12 only from position measurements obtained with the selected position sensor.

[0098] The step of selecting the most reliable position sensor is therefore carried out only when the presence of a defective position sensor is confirmed by the additional detection module 54.

[0099] If an end of comparison signal Y 2 is transmitted to the reset module 37 but no additional detection signal Y 3 is not transmitted to him, the reset module 37 transmits a reset signal Y 4 to the comparison module 50.This reflects the erroneous detection of a faulty position sensor by the detection module 32. Upon receipt of the reset signal Y 4 The comparison module 50 sets the value of the comparison factor R to a chosen initial value, for example 0. On the other hand, if it receives an additional detection signal Y 3 , the reset module 37 remains inactive.

[0100] There figure 4 illustrates the steps of an embodiment of the method for controlling a jack according to the invention. This method can be implemented by the control device illustrated in figures 1 à 3 . First of all, in a first step S1, piston position measurements are carried out in the cylinder body simultaneously with the first position sensor and the second position sensor. In a second step S2, a first speed of movement of the piston is determined from the position measurements of the piston obtained with the first position sensor and a second speed of movement of the piston is determined from the position measurements of the piston obtained with the second position sensor.

[0101] We then carry out a third step S3 detecting the presence of at least one defective position sensor from the piston position measurements obtained respectively with the first position sensor and with the second position sensor. In a non-limiting manner, this third step S3 detection comprises the steps of determining the deviation between the piston position measurements obtained with the first position sensor and the piston position measurements obtained with the second position sensor, calculating the variance of said deviation and comparing said variance to a predetermined detection threshold.

[0102] If a faulty position sensor is detected, a fourth step is performed S4 comparing each of the first and second determined piston displacement speeds with a modeled or predetermined piston displacement speed, so as to identify the most reliable position sensor.

[0103] In parallel with the fourth stage S4 a fifth step is carried out for comparison S5 triggering a counter. The fourth step S4 comparison is performed until the counter value exceeds a counter threshold.

[0104] We then carry out a sixth step S6additional detection of the presence of a defective position sensor. This step comprises a step of calculating the difference between the piston position measurements obtained respectively with the first position sensor and with the second position sensor and comparing the absolute value of said difference with a predetermined additional detection threshold.

[0105] If the absolute value of said deviation is greater than the predetermined additional detection threshold, the presence of a defective position sensor is confirmed and a seventh step is then carried out. S7 selection of the position sensor identified as the most reliable.

[0106] We then carry out an eighth step S8 regulating the piston position using the piston position measurements provided by said selected position sensor.

Claims

1. A method for controlling a cylinder (12), comprising steps in which: - a cylinder is provided comprising a cylinder body (20) and a piston (22) translationally movable inside the cylinder body; - a servo valve (14) is provided, configured to regulate the power supplied to said cylinder, in such a way as to control the position of the piston in the cylinder body; - a measuring device (16) is provided comprising at least one first position sensor (28) and one second position sensor (30); - measurements (X1,X2) are taken of the position of the piston in the cylinder body simultaneously with the first position sensor and the second position sensor; - at least one first displacement speed (v1) of the piston is determined on the basis of the piston position measurements obtained with the first position sensor; - at least one second displacement speed (v2) of the piston is determined on the basis of the piston position measurements obtained with the second position sensor; - the presence of at least one malfunctioning position sensor is detected; then - when the presence of a malfunctioning position sensor is detected, each of the first and second determined displacement speeds of the piston are compared with a modelled (vmod) or predetermined displacement speed of the piston, in such a way as to identify the most reliable position sensor, characterized in that a counter is initiated as soon as the presence of a malfunctioning position sensor is detected and the step of comparing the first and second determined displacement speeds (v1, v2) of the piston with a modeled (vmod) or predetermined displacement speed of the piston is stopped when the value of the counter is greater than a threshold of the counter.

2. The controlling method as claimed in claim 1, wherein the comparison of said first and second determined displacement speeds (v1,v2) of the piston with said modeled displacement speed (vmod) of the piston comprises a step of computing a comparison factor R and determining the sign of said comparison factor.

3. The controlling method as claimed in claim 2, wherein the comparison factor R is computed according to the following equation: R = ∫ v 1 − v mod − ∫ v 2 − v mod where v1 and v2 are the first and second determined displacement speeds of the piston and vmod is the modeled displacement speed of the piston.

4. The controlling method as claimed in any one of claims 1 to 3, wherein the piston is configured to delimit a first chamber (24) and a second chamber (26) inside the piston body (20) and wherein the modeled displacement speed (vmod) of the piston is a function of a modeled pressure difference between said first and second chambers.

5. The controlling method as claimed in any one of claims 1 to 4, wherein the modeled displacement speed of the piston is a function of a supply current (i) of the servo valve (14).

6. The controlling method as claimed in claim 5, wherein the modeled displacement speed (vmod) of the piston is a function of an equilibrium current (ieq) determined by applying a first-order filtering function to said supply current (i) of the servo valve (14).

7. The controlling method as claimed in any one of claims 1 to 6, wherein the presence of a malfunctioning position sensor is detected on the basis of the piston position measurements (X1,X2) obtained with the first position sensor (28) and with the second position sensor (30) respectively.

8. The controlling method as claimed in claim 7, wherein the step of detecting the presence of a malfunctioning position sensor comprises a step in which is determined the separation between the piston position measurements obtained with the first position sensor and the piston position measurements obtained with the second position sensor.

9. The controlling method as claimed in claim 8, characterized in that the step of detecting the presence of a malfunctioning position sensor further comprises steps in which the variance of said separation is computed and said variance is compared with a predetermined detection threshold.

10. The controlling method as claimed in any one of claims 1 to 9, wherein the position sensor identified as being the most reliable is selected and the piston position is regulated using the piston position measurements supplied by said selected position sensor.

11. The controlling method as claimed in claim 10, wherein a step is performed of additionally detecting the presence of a malfunctioning position sensor and the step of selecting the most reliable position sensor is performed if a malfunctioning position sensor has been detected during the step of additional detection.

12. The controlling method as claimed in claim 11, wherein the step of additionally detecting the presence of a malfunctioning position sensor comprises a step of computing the separation between the position measurement positions (X1,X2) obtained with the first position sensor (28) and with the second position sensor (30) respectively and wherein a step of selecting the most reliable position sensor is performed if the absolute value of said separation is greater than a predetermined additional detection threshold.

13. A device (10) for controlling a cylinder (12) comprising a cylinder body (20) and a piston (22) translationally movable inside the cylinder body, the control device comprising: - a servo valve (14) configured to regulate the power supplied to the cylinder, in such way as to control the position of the piston in the cylinder body; - a measuring device (16) comprising at least one first position sensor (28) and one second position sensor (30), the position sensor being configured to simultaneously take measurements of the piston position in the cylinder body; and - a processing module (18) configured to determine at least one first displacement speed (v1) of the piston on the basis of the piston position measurements obtained with the first position sensor and configured to determine at least one second displacement speed (v2) of the piston on the basis of the piston position measurements obtained with the second position sensor, the processing module being configured to compare said first and second determined displacement speeds of the piston with a modeled (vmod) or predetermined displacement speed of the piston, when the presence of a malfunctioning position sensor is detected, the device (10) being characterized in that the processing module (18) comprises a detecting module (32) configured to detect the presence of a malfunctioning position sensor, the detecting module (32) comprising a counter (48) configured to be initiated as soon as the presence of a malfunctioning position sensor is detected and configured to transmit an end-of-comparison signal (Y2) when the value of the counter is greater than a threshold of the counter in order to stop the step of comparing the first and second determined displacement speeds (v1, v2) of the piston with a modeled (vmod) or predetermined displacement speed of the piston.