Method for feeding back an artificial dry-friction torque during the movement of an aircraft trim control stick, and associated system

Abstract

This method for feeding back an artificial friction torque comprises the following steps: Calculating the difference between the position of the control stick at a given instant (Xm(t)) and the position of the anchor point at the preceding instant (Xc(t-1)) in the form of a positional difference (DIFF); Limiting the positional difference (DIFF) to a minimum value (MIN) or to a maximum value (MAX) using a saturation block (15); Calculating the position of the anchor point at the given instant (Xc(t)) by subtracting between the position of the control stick at the given instant (Xm(t)) and the limited positional difference (DIFFLIM); Obtaining a torque setpoint (Cm) as being the product of the limited positional difference (DIFFLIM) multiplied by a closed-loop control stiffness value (k).

Description

[0001] DESCRIPTION

[0002] TITLE: Method for restoring an artificial dry friction torque during the movement of an aircraft trim control stick, system and associated compensation method

[0003] technical field

[0004] The present invention relates to a method for simulating dry friction in the context of a control of a flight trim system of an aircraft, in particular a helicopter.

[0005] In particular, the present invention can be implemented within the framework of active stick control laws for trim control, for example in order to generate or compensate for a force resisting the movement of said stick, otherwise manipulated by a user.

[0006] In general, the invention applies to the restoration of an artificial dry friction torque in a system not comprising any physical device other than an electric motor to generate said dry friction torque.

[0007] Previous techniques

[0008] Flight trims, or trim systems, are designed to compensate for drifts caused by disturbances that may affect the aircraft's flight parameters, without the pilot having to act on the flight controls.

[0009] In addition, flight trims typically provide the aircraft pilot with resistance to the flight controls in the form of feedback. This resistance is generally passive, either linear (spring trims) or constant (friction trims), and can also be active. This resistance is also called restoring force or feedback. This resistance allows the pilot to better control the movement applied to the control stick.

[0010] Regarding flight trimmers that provide a passive friction or spring-based force, these are configured to provide a linear or even constant force once a release force is applied to the flight controls, for example, to a control element such as a control stick. These flight trimmers have specific settings for each flight control axis, particularly for collective pitch control.

[0011] When you want to modify the restoring force, in other words, the effort law of the control system, it is necessary to reconfigure the equipment settings, for example by changing components. Indeed, passive force feedback cannot be configured.

[0012] Flight trimmers that provide active force include controllable equipment such as an electric motor and possibly a physical device such as a brake, allowing for variable force feedback adapted to flight conditions. The term "controllable" for equipment means that its operating state, whether binary or with multiple discretization levels, can be modified through associated electronics.

[0013] A hybrid architecture of such an active-force flight trimmer allows, for example, the unanchoring force and the force return gradient to be modified in a more precise and complex way than passive systems.

[0014] Among the solutions of the prior art, one technology includes a hysteresis magnetic brake allowing to simulate dry friction using said magnetic brake.

[0015] However, these solutions involve a dedicated physical device, which increases the implementation cost, the onboard mass, and the complexity of the aircraft architecture.

[0016] Description of the invention

[0017] The present invention therefore aims to overcome the aforementioned drawbacks and to provide a means of artificially restoring a dry friction torque without the use of a physical device other than an electric motor.

[0018] The present invention relates to a method for restoring an artificial dry friction torque during the movement of an aircraft trim control stick whose position is centered around an anchor point of said stick, the method comprising the following steps implemented for different successive instants:

[0019] - Calculation of the difference between the position of the handle at a given instant and the position of the anchor point at the previous instant in the form of a position difference;

[0020] - Limitation by a saturation block of the position gap to a minimum value or to a maximum value if said position gap is outside the range between said minimum value and said maximum value;

[0021] - Calculation of the position of the anchor point at the given moment by subtracting the position of the handle at the given moment with the position deviation, or with the limited position deviation if applicable;

[0022] - Obtaining a torque setpoint by multiplying the position error, or the limited position error if applicable, by a servo stiffness value; and

[0023] - Application of the torque setting to an electric motor mechanically connected to the handle.

[0024] Thus, we obtain both a tracking of the position of the handle by the anchor point as well as a torque command artificially simulating dry friction and allowing us to compensate for friction, or conversely to add some.

[0025] Advantageously, before the step of applying the torque setpoint to the electric motor, the process includes a step of multiplying the torque setpoint by -1 or by 1 in order to simulate friction or to compensate for friction.

[0026] In one implementation mode, the maximum value is the quotient of an artificial dry friction value over the servo stiffness value, the minimum value being the opposite of the maximum value.

[0027] Advantageously, the value of artificial dry friction is expressed in Newton meters, the value of servo stiffness is expressed in Newton meters per radian, and the position of the handle and the position of the anchor point are expressed in radians. The present invention also relates to a method for compensating dry friction in a mechanical chain, the method comprising the steps defined above and further comprising the following steps:

[0028] - Adding or subtracting the torque setpoint from a force-law setpoint to obtain a total torque setpoint; and

[0029] - Application of the total torque setpoint to an aircraft trim actuation mechanism.

[0030] The present invention further relates to a system for restoring an artificial dry friction torque during the movement of an aircraft trim control stick, comprising an electric motor, an aircraft trim control stick, a mechanical chain connecting said electric motor to said stick, a position sensor for said stick, and an electronic data processing board comprising means for implementing the steps of the method as defined above.

[0031] The invention also relates to a computer program comprising instructions which, when the program is executed by a computer, lead the computer to implement the steps of the process as defined above.

[0032] The invention also relates to a computer-readable recording medium comprising instructions which, when executed by a computer, lead the computer to carry out the steps of the process as defined above.

[0033] Brief description of the drawings

[0034] Other objects, features and advantages of the invention will become apparent from the following description, given solely by way of non-limiting example, and made with reference to the accompanying drawings in which:

[0035] [Fig 1] is a schematic representation of the steps in the process of restoring an artificial dry friction torque according to the invention; [Fig 2] is a schematic representation of a system for restoring an artificial dry friction torque according to the invention;

[0036] [Fig 3] is a schematic representation of different algorithmic blocks involved in the process according to figure 1;

[0037] [Fig 4a] and

[0038] [Fig 4b] are a schematic representation of the effort to be applied to handle 1 as a function of displacement along a displacement axis;

[0039] [Fig 5] is a schematic representation of different algorithmic blocks for adding or subtracting a torque setpoint from a force-law setpoint in order to obtain a total torque setpoint; and

[0040] [Fig 6] is a schematic representation of curves of a force law setpoint, an actual force law subjected to disturbances and friction and a total torque setpoint Ct.

[0041] Detailed description of at least one embodiment

[0042] Figure 1 schematically represents the different stages of a process for restoring an artificial dry friction torque during the movement of an aircraft trim control stick 1 whose position is centered around an anchor point of said stick 1.

[0043] Figure 2 also schematically represents system 3 for the restitution of the artificial dry friction torque during the movement of said aircraft trim control stick 1.

[0044] The system 3 includes an electric motor 5, an aircraft trim control stick 1, a mechanical chain 7 linking said electric motor 5 to said stick 1, a position sensor 9 of said stick 1 and an electronic data processing card 1 1 comprising means for implementing the steps of the process described below and sending a torque command Cm to the electric motor 5.

[0045] The term restitution refers to a simulation or compensation of torque, applied to the trim control stick 1 or directly to a mechanism for actuation of said trim.

[0046] The process includes a series of steps implemented at different successive times.

[0047] The process according to the invention is implemented so as to repeat the steps of said process in the form of a loop whose frequency is adapted to the characteristics of system 3 to guarantee its stability.

[0048] For greater clarity, the different algorithmic blocks involved in the process according to the invention have been schematically represented in Figure 3.

[0049] To implement the process, a first step E1 is performed to calculate the difference between the position of handle 1 at a given time t, denoted Xm(t), and the position of the anchor point of handle 1 at the previous time t-1, denoted Xc(t-1). This difference is called the positional deviation, denoted DIFF(t) = Xm(t) - Xc(t-1). This calculation is performed by a first subtraction block 13.

[0050] Fa position Xm of stick 1 is the actual position of stick 1: it is modified as soon as the pilot moves, slightly or not, said stick 1.

[0051] The position Xc of the control stick 1 anchor point is a reference movable position. This is the position of control stick 1 when the pilot is not touching said control stick 1. The position of the anchor point is movable so as to be positioned in a so-called neutral position desired by the pilot.

[0052] These positions are previously measured or estimated by the position sensor 9 and have, for example, the radian as their unit.

[0053] Then, the positional deviation DIFF passes into a saturation block 15 and a step E2 is performed of limiting by said saturation block 15 the positional deviation DIFF to a minimum value MIN or to a maximum value MAX if said positional deviation DIFF is outside the range between said minimum value MIN and said maximum value MAX.

[0054] Thus, if the position deviation DIFF is in the interval [MIN:MAX], then the position deviation DIFF is not limited.

[0055] On the other hand, if the position difference DIFF is outside the interval [MIN : MAX], then we obtain a limited position difference noted DIFFLIM = MIN for values ​​of DIFF less than MIN, or DIFFLIM = MAX for values ​​of DIFF greater than MAX.

[0056] Advantageously, the maximum value MAX is the quotient of an artificial dry friction value Cf over a servo stiffness value k, the minimum value MIN being the opposite of the maximum value MAX. Thus, MAX = Cf / k and MIN = -Cf / k.

[0057] These values ​​of artificial dry friction Cf and servo stiffness k are defined beforehand by an operator or by the pilot according to the friction force he wishes to reproduce.

[0058] The value of artificial dry friction Cf is expressed for example in Newton meter (Nm) and the value of servo stiffness k is expressed in Newton meter per radian (Nm / rad).

[0059] The servo stiffness value k is directly related to the acquisition bandwidth of the position Xm of the joystick 1 and therefore to the implementation frequency of the process. Thus, for a chosen servo stiffness value k for a given system 3, said chosen value k determines the bandwidth and the implementation frequency of the process.

[0060] Then, step E3 calculates the position of the anchor point at a given time t, denoted Xc(t), by subtracting the position of handle 1 at a given time t, denoted Xm(t), from the position deviation DIEE, or from the limited position deviation DIFFLIM if applicable. This step is performed by a second subtraction block 17.

[0061] Thus, if the position difference DIFF is in the interval [MIN:MAX], then:

[0062] Xc(t) = Xm(t) - DIFF = Xm(t) - (Xm(t) - Xc(t- l)) = Xc(t- l)

[0063] In this situation, the Xc position of the anchor point does not change, as the Xm position of handle 1 has not changed sufficiently. Conversely, if the DIFF position difference is outside the [MIN:MAX] range, then:

[0064] Xc(t) = Xm(t) - DIFFLIM = Xm(t) - (MAX or MIN)

[0065] Here, the effective Xc position of the anchor point is modified: the anchor point shifts to follow the movement of the Xm position of handle 1 while maintaining a constant Xm(t) - Xc(t) gap equal to Cf / k.

[0066] The position of the anchor point Xc(t) can thus be used to reimplement the steps of the process at the next time t+ 1, via the return block 19.

[0067] Next, we carry out a step E4 to obtain a torque setpoint Cm by calculating the product of the position deviation DIFF, or the limited position deviation DIFFLIM if applicable, with the value of the servo stiffness k. This step is carried out by a multiplier block 21.

[0068] Finally, we carry out step E5 of applying the torque setpoint Cm to the electric motor 5 mechanically connected to the handle 1 in order to apply a force equivalent to artificial dry friction.

[0069] The implementation of these different steps therefore causes the pilot to feel an effort on the control stick 1 equivalent to a frictional effort.

[0070] Optionally, the process includes implementing, before step E5 of applying the torque setpoint Cm to the electric motor 5, a step E45 of multiplying the torque setpoint Cm by a factor - 1 or by a factor + 1 in order to simulate friction or to compensate for friction.

[0071] Figures 4a and 4b schematically illustrate the effort to be applied to handle 1 as a function of displacement along a displacement axis.

[0072] Figure 4a illustrates the rightward shift of the graph while Figure 4b illustrates a leftward shift.

[0073] It is shown that for a displacement less than Xm - Xc, the force follows a slope with a coefficient equal to the servo stiffness value k. Beyond this value, a constant force equal to the value of artificial dry friction Cf must be applied. Advantageously, the method described above can serve as the basis for a method of compensating dry friction in a mechanical chain.

[0074] In addition to the steps illustrated in Figure 1, a step E6 is performed involving the addition or subtraction of the torque setpoint Cm from a force law setpoint Cl in order to obtain a total torque setpoint Ct. An algorithmic diagram of this step E6 is shown in Figure 5, where block 23 represents the preceding steps E1 to E5.

[0075] The force law setpoint Cl is a predetermined setpoint that defines a specific force law profile to be applied to the aircraft's trim mechanical chain in order to actuate the trim. For example, the force law setpoint Cl is determined by a force law block 25 as a function of the value of Xm-Xc.

[0076] The total torque setpoint Ct is thus the combination of the force law setpoint Cl with the torque setpoint Cm allowing to compensate for dry friction applied to the trim.

[0077] Finally, step E7 is performed, applying the total torque setpoint Ct to an aircraft trim actuation mechanism, thus allowing the addition or subtraction of dry friction.

[0078] Figure 6 illustrates a force law setpoint Cl, an actual force law 31 subjected to disturbances and friction giving it a form of hysteresis according to the direction of movement of the trim, as well as the total torque setpoint Ct taking into account the torque setpoint Cm in order to compensate for friction and to bring the total torque setpoint Ct closer to the force law setpoint Cl.

[0079] As an example, during a positive displacement, the trim output axis remains in its anchor position Xc as long as the torque exerted on said trim does not exceed the total dry friction, namely the actual force law 31. As soon as the position of the trim begins to evolve, the compensation torque, namely the torque setpoint Cm, is activated and gradually stabilizes at its value -Cf.

Claims

DEMANDS 1. A method for restoring an artificial dry friction torque during the movement of an aircraft trim control stick (1) whose position is centered around an anchor point of said stick (1), characterized in that it comprises the following steps implemented for different successive instants: Calculation of the difference between the position of the handle ( 1 ) at a given instant (Xm(t)) and the position of the anchor point at the previous instant (Xc(t- l )) in the form of a position difference (DIFF) (step E l ) ; Limitation by a saturation block (15) of the position deviation (DIFF) to a minimum value (MIN) or to a maximum value (MAX) if said position deviation (DIFF) is outside the range between said minimum value (MIN) and said maximum value (MAX) (step E2); Calculation of the position of the anchor point at the given time (Xc(t)) by subtracting the position of the handle ( 1 ) at the given time (Xm(t)) with the position deviation (DIFF), or with the limited position deviation (DIFFLIM) if applicable (step E3); Obtaining a torque setpoint (Cm) by multiplying the position error (DIFF), or the limited position error (DIFFLIM) if applicable, by a servo stiffness value (k) (step E4); and - Application of the torque setpoint (Cm) to an electric motor (5) mechanically connected to the handle (1) (step E5).

2. Method according to claim 1, comprising, before the step (E5) of applying the torque setpoint (Cm) to the electric motor (5), a step (E45) of multiplying the torque setpoint (Cm) by -1 or by 1 so as to simulate friction or to compensate for friction.

3. A method according to any one of claims 1 and 2, wherein the maximum value (MAX) is the quotient of a dry friction value artificial (Cf) on the control stiffness value (k), the minimum value (MIN) being the opposite of the maximum value.

4. A method according to any one of claims 1 to 3, wherein the value of artificial dry friction (Cf) is expressed in Newton meters, the value of servo stiffness (k) is expressed in Newton meters per radian, the position of the handle (1) and the position of the anchor point are expressed in radians.

5. A method for compensating for dry friction in a mechanical chain, characterized in that it comprises the steps of the method according to any one of claims 1 to 4, the method further comprising the following steps: Adding or subtracting the torque setpoint from a force-law setpoint to obtain a total torque setpoint; and Application of the total torque setpoint to an aircraft trim actuation mechanism.

6. System (3) for restoring an artificial dry friction torque during the movement of an aircraft trim control stick (1) comprising an electric motor (5), an aircraft trim control stick (1), a mechanical chain (7) connecting said electric motor (5) to said stick (1), a position sensor (9) of said stick (1) and an electronic data processing card (11) comprising means for implementing the steps of the method according to any one of claims 1 to 5.

7. Computer program comprising instructions which, when the program is executed by a computer, cause the computer to carry out the steps of the process according to any one of claims 1 to 5.

8. Computer-readable recording medium comprising instructions which, when executed by a computer, cause the computer to carry out the steps of the process according to any one of claims 1 to 5.

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