PADDLE BUTTON

Description

[0001] The invention relates to a paddle switch and a method of operating the paddle switch.

[0002] Paddle buttons generate a signal based on the position of a paddle along a path. The paddle is manually moved along this path by a user.

[0003] Paddle switches are part of human-machine interfaces used to control electrical equipment. When such a paddle switch is integrated into the instrument panel of a controllable device such as an airplane or helicopter, it is particularly important to ensure robust operation of this switch. Indeed, a failure of the switch can have serious consequences. By robust, we mean robust mechanically and in the information it produces.

[0004] To increase the robustness of this button against failures, different solutions are known. According to a first solution, the position of the paddle is measured by a first and a second position sensors independent of each other. Thus, if one of these sensors fails, the other sensor can compensate for this failure. On the other hand, if the movement of the paddle is blocked, the two sensors are inoperative, so the button is no longer usable.

[0005] To overcome this drawback of the first solution, a second solution has been proposed. This second solution is identical to the first solution except that the button has a first and a second paddle that can be moved independently of each other along the path. The position of the first paddle is measured by the first sensor and the position of the second paddle is measured by the second sensor. The first and second paddles are close enough to each other to be simultaneously moved by the user using a single finger. If the movement of one of these paddles is blocked, the user can continue to use the button by moving only the other paddle.

[0006] However, when using such a two-paddle button, it may happen that the user accidentally hooks only one of the two paddles. In this case, one of the paddles is moved and not the other. This results in an inconsistency between the measurements of the first and second sensors. The electronic computer that acquires the measurements of the first and second sensors does not know, in such a case, which measurement represents the true intention of the user. This can lead to the generation of an unexpected command, and therefore to unforeseen behavior of the controlled equipment. The computer can also conclude that there is a fault and initiate an appropriate procedure.

[0007] Prior art is also known from WO2012 / 154188A1 and EP2258577A1.

[0008] The invention aims to remedy at least one of these drawbacks. It therefore relates to a paddle button according to claim 1.

[0009] The invention also relates to a method of operating the paddle button according to claim 10.

[0010] The invention will be better understood upon reading the following description, given solely as a non-limiting example and with reference to the drawings in which: there Figure 1 is a schematic illustration of a device equipped with a paddle switch; the Figure 2 is a schematic illustration of a first embodiment of the paddle button of the Figure 1 ; there Figure 3 is a flowchart of a method of operating the paddle switch of the Figure 1 ; THE Figures 4 and 5 are schematic illustrations, in horizontal and partial section, of, respectively, a second and a third embodiment of the paddle button of the Figure 1 ; there Figure 6 is a front and partial view of a fourth embodiment of the paddle button of the Figure 1 ; there Figure 7 is a schematic and top view illustration of the button of the Figure 6 .

[0011] In the remainder of this description, the features and functions well known to those skilled in the art are not described in detail. In this description, detailed examples of embodiments are first described in a chapter I with reference to the figures. Then, in a chapter II, variants of these embodiments are presented. Finally, the advantages of the different embodiments are presented in a chapter III. Chapter I: Examples of embodiments

[0012] There Figure 1represents a device 2 that can be controlled by a user via a human-machine interface 4. The device 2 is, for example, a vehicle piloted by a human being. The device 2 may be an airplane, a helicopter, a motor vehicle, a train, a boat or other. In this context, the human-machine interface must be robust against failures.

[0013] The human-machine interface 4 is, for example, that of an airplane or helicopter cockpit. To simplify the Figure 1 , only one button 8 with palette of this interface 4 is represented.

[0014] The button 8 comprises a fixed frame 10 and a lever 12 movable by hand by a user relative to the frame 10. The frame 10 is, for example, fixed to a dashboard.

[0015] The lever 12 is reversibly movable between a retracted position and a pushed position. In this embodiment, the lever 12 is movable using a single finger of the user's hand. On the Figure 1 , the lever 12 is shown in an intermediate position, in which it extends mainly vertically. Between the retracted position and the pushed position, the paddle moves along a path 14. In this embodiment, the path 14 is an arc of a circle.

[0016] The lever 12 comprises two pallets 16 and 18 mechanically connected to each other by a dissociable zone 20. In this embodiment, the pallets 16 and 18 are symmetrical to each other with respect to a vertical plane P1 containing the trajectory 14 and passing through the dissociable zone 20. Consequently, subsequently, only the pallet 16 is described in more detail.

[0017] The palette 16 comprises a front support face 22 which extends mainly in a plane perpendicular to the trajectory 14. The surface of the front face 22 is shaped to come to bear on a part of the user's finger. For this purpose, its surface is generally greater than 1 cm 2< . To limit its size, the surface of the front face 22 is also generally less than 10 cm 2< or 5 cm 2< .

[0018] On the side opposite the front face 22, the pallet 16 has a rear face 24. For example, the rear face 24 is symmetrical to the front face 22 with respect to a plane perpendicular to the trajectory 14.

[0019] The pallet 16 also comprises a lateral face 26 facing the pallet 18. The lateral face 26 extends, between the front 22 and rear 24 faces, mainly in a plane parallel to the plane P1. The lateral face 26 is therefore opposite a corresponding lateral face of the pallet 18 and separated from this pallet 18 by a vertical lateral limit 28. The limit 28 extends mainly vertically in the plane P1.

[0020] The pallet 16 also has a foot 30 which mechanically connects it to a mechanism 32 ( Figure 2 ) guiding. The mechanism 32 guides the movement of the pallet 16 along the path 14. Here, the mechanism 32 is located inside the chassis 10.

[0021] In order to be systematically and simultaneously moved together in a normal operating mode, the pallets 16 and 18 are mechanically connected to each other by means of the separable zone 20. This zone 20 is called " separable ", because if the movement of one of the paddles 16, 18 is blocked, then by pushing with his finger only on the other paddle, the separable zone gives way and the paddles 16 and 18 are then no longer mechanically connected to each other. When the paddles 16 and 18 are no longer mechanically connected to each other, the operating mode of the button 8 is said to be " degraded » .

[0022] The separable zone 20 is designed to remain intact, that is to say not to give way, as long as the difference between the support forces exerted by the user on the front faces of the paddles 16 and 18 does not exceed a predetermined threshold S 1 . Here, this threshold S 1 is greater than or equal to 2F min or 3F min , where F min is equal to the minimum force that the user must exert on the front faces of the paddles 16, 18 to move the lever 12 from its retracted position to its pushed position in the normal operating mode. Typically, in the case of paddles moved using a single finger, the force F min is between 0.5 N and 10 N, and most often between 1 N and 7 N or between 3 N and 7 N.

[0023] The threshold S 1 is also usually less than 10F min or 5F min , and preferably less than 4F rmin . Thus, the force required by the user to switch from normal operating mode to degraded operating mode is not too high.

[0024] In this first embodiment, the pallets 16 and 18 and the separable zone 20 form a single block of material. In this case, the zone 20 is a breakable zone. Thus, the pallets 16 and 18 and the separable zone 20 can be manufactured by molding using a single mold comprising the hollow impression of these pallets 16 and 18, and of the zone 20. For this, the zone 20 is formed in a single piece with the pallets. More precisely, it is formed by recesses made in the block of material along the boundary 28. By way of illustration, on the Figure 1 , zone 20 includes: an upper recess 40; a lower recess 42; a horizontal arm 44 which mechanically connects the pallets 16 and 18 together.

[0025] Here, the recesses 40 and 42 are delimited on each side by the lateral faces of the pallets 16 and 18. In this embodiment, the recesses 40 and 42 completely pass through the thickness of the block of material from which the pallets 16 and 18 are made. These recesses 40 and 42 therefore form slots.

[0026] Preferably, the horizontal width of the recess 40 is small so that the user's finger can simultaneously come to bear on the front faces of the paddles 16 and 18. Typically, the width of the recess 40 is less than 5 mm and, preferably, less than 1 mm or 0.5 mm.

[0027] The recesses 40 and 42 are separated from each other in the vertical direction by the material arm 44. Here, this arm 44 forms a beam which extends horizontally from the lateral face of the pallet 16 to the lateral face of the pallet 18. The cross-section of the arm 44 is dimensioned to break when the difference between the bearing forces exerted on the front faces of the pallets 16 and 18 reaches the threshold S 1 . For this purpose, the material used to produce the pallets 16, 18 and the zone 20 is a brittle material, that is to say it breaks suddenly as soon as the shear stress in the arm 44 reaches the value S 1 / SU , where: SU is the cross-sectional area of arm 44, and S 1 is the threshold, in newtons, at which zone 20 yields.

[0028] For example, the material used is hard plastic or ceramic.

[0029] The angular position of the pallets 16 and 18 along the trajectory 14 is measured by sensors 50, 52 ( Figure 2 ) position. These sensors 50 and 52 are fixed in the chassis 10.

[0030] The button 8 also includes an interface 54 which connects the button 8 to an information transmission network 56. More precisely, the button 8 transmits on this network 56 the measurements of the angular positions of the pallets 16 and 18. In this embodiment, the button 8 is also capable of transmitting on this network 56 information which indicates whether the separable zone 20 has failed or not. For this purpose, the button 8 includes two electrical terminals 60 and 62.

[0031] An electronic calculator 70 is connected to the network 56 to process the measurements and information delivered by the button 8. For this purpose, it typically comprises: a microprocessor 72; a non-volatile memory 74 containing the instructions executed by the microprocessor 72; an information transmission bus 73 which connects the memory 74 to the microprocessor 72.

[0032] Memory 74 contains the instructions here: of a module 76 for controlling equipment depending on the position of the paddles 16 and 18, and of a module 78 for diagnosing the failure of the button 8.

[0033] Here, the device 2 comprises controllable equipment 80. The module 76 controls the equipment 80 as a function of the angular position of the pallets 16 and 18. The module 78 is capable of communicating to a maintenance agent, via a human-machine interface, a possible failure of the button 8.

[0034] There Figure 2schematically represents the internal architecture of the button 8. Here, the guide mechanism 32 is a pivot link which only allows the rotational movement of the pallet 16 around a horizontal axis 82.

[0035] The pallet 18 is mechanically connected to the chassis 10 by its own guide mechanism 84. Thus, in the degraded operating mode, the pallet 18 can be moved along the path 14 independently of the pallet 16. Here, the mechanism 84 is structurally identical to the mechanism 32. It therefore allows the rotation of the pallet 18 around the axis 82.

[0036] As illustrated on the Figure 2, the sensor 50 measures the angular position of the pallet 16, while the sensor 52 measures the angular position of the pallet 18. The sensor 50 is able to operate independently of the sensor 52 and vice versa. Thus, in the degraded operating mode, the sensor 50 measures the angular position of the pallet 16 independently of the angular position of the pallet 18. Conversely, in the degraded operating mode, the sensor 52 measures the angular position of the pallet 18 independently of the angular position of the pallet 16. In the normal operating mode, the sensors 50 and 52 measure the same angular position, with the operating clearance ready. Thus, in the normal operating mode, they are redundant. Therefore, even if one of these sensors fails, the other sensor makes it possible to continue to measure and transmit the position of the lever 12.For this purpose, the pallet 16 is mechanically connected only to the sensor 50, while the pallet 18 is mechanically connected only to the sensor 52.

[0037] The sensors 50 and 52 deliver their respective measurements on terminals 86, 88 of the interface 54 ( Figure 2 ).

[0038] In this embodiment, the button 8 also comprises an electrical connection 90 which electrically connects the terminals 60 and 62 together. A portion 92 of this connection 90 is mechanically attached to the separable zone 20 so that, when this zone breaks, this also causes the part 92 to break. When the part 92 is broken, the terminals 60 and 62 are electrically isolated from each other. Thus, the electrical conductivity between the terminals 60 and 62 has a first value in the normal operating mode and switches to a second, lower value in the degraded operating mode.

[0039] For example, portion 92 is a strip of electrically conductive material attached to arm 44. This strip extends from one end of this arm to the other. Thus, when arm 44 is broken, this tears this strip and severs electrical connection 90.

[0040] The operation of button 8 will now be described with reference to the method of the Figure 3 .

[0041] The method begins with a phase 100 during which the button is in its normal operating mode. In this normal operating mode, the paddles 16 and 18 are mechanically connected to each other by the zone 20. When the user presses with his finger simultaneously on the two front faces of the paddles 16 and 18 or on only one of its front faces, the paddles 16 and 18 systematically move together along the trajectory 14. Thus, the angular positions of the paddles 16 and 18 along the trajectory 14 are systematically equal. In other words, the difference between the angular positions of the paddles 16 and 18 is here systematically equal to zero. In addition, in the normal operating mode, the terminals 60 and 62 are electrically connected to each other.

[0042] During a step 102, the sensors 50 and 52 measure the angular positions, respectively, of the pallets 16 and 18 and transmit these measurements, via the network 56, to the computer 70.

[0043] During this step 102, the electrical conductivity between terminals 60 and 62 is also transmitted to the computer 70.

[0044] In response, during a step 104, the module 76 processes these measurements and transmits a command established based on these measurements to the equipment 80.

[0045] During a step 106, the equipment 80 executes the received command.

[0046] In parallel, during a step 108, in the event of a failure of one of the sensors 50, 52, the module 76 detects this failure and triggers the execution of a corrective step 110. Here, the module 78 detects a failure when one of the sensors no longer transmits a measurement. It also detects a failure if the difference between the measurements of the sensors 50 and 52 crosses a predetermined threshold S 2 while the electrical conductivity acquired for the connection 90 remains equal to its first value.

[0047] When the faulty sensor can be identified, the corrective step 110 consists, for example, of using only the measurements of the non-faulty sensor during step 104. A sensor is identified as faulty when it no longer transmits measurements or when it transmits measurements that are outside a plausible measurement range. If the faulty sensor cannot be identified, the step 110 then consists, for example, of inhibiting step 104 and triggering an alarm to signal this malfunction.

[0048] Buttons such as button 8 are also subject to mechanical failures such as the blocking, for example by a foreign body, of the movement of one of the paddles 16 or 18.

[0049] In this case, in response, the user pushes harder than usual on the paddle that is not blocked. Subsequently, it is assumed that it is paddle 18 that is the only paddle to be blocked. When the pressing force exerted on paddle 16 exceeds threshold S 1 , in response, zone 20 gives way during a step 118. The operating mode of button 8 then switches from the normal operating mode to its degraded operating mode.

[0050] During phase 120, the button is used in this degraded operating mode. During this phase 120, the user can continue to use button 8, but only by moving paddle 16.

[0051] More precisely, during a step 122, the sensors 50 and 52 measure the angular position of the pallets 16 and 18. This step 122 is, for example, identical to step 102. During step 122, the electrical conductivity between the terminals 60 and 62 transmitted to the computer 70, takes the second value smaller than the first value.

[0052] In parallel, during a step 124, the module 78 detects that the electrical conductivity between the terminals 60 and 62 is equal to the second value. In response, it identifies the pallet that is blocked. For example, for this, the pallet that is identified as being blocked is the one whose angular position remains constant, while at the same time, the angular position of the other pallet varies.

[0053] Then, during a step 126, the module 76 processes the measurements only of the unblocked pallet, that is to say here of the pallet 16, and transmits a command to the equipment 80 established only from the measured angular position of the pallet 16.

[0054] Then, throughout the duration of the degraded operating mode, steps 122 and 126 are repeated in a loop for each new measurement acquired from the sensor 50, in order to control the equipment 80 from only the angular position of the pallet 16. During these reiterations of steps 122 and 126, step 124 is no longer executed since the blocked pallet has already been identified.

[0055] The phase 126 of operation in degraded mode is here followed by a maintenance phase 130. During this phase 130, the module 78 transmits, via a human-machine interface, the information that the paddle 18 of the button 8 is blocked. The human-machine interface then displays this information to communicate it to the maintenance agent. From then on, this maintenance agent is able to repair the fault in the button 8.

[0056] There Figure 4 represents a 150 paddle button. This 150 button is identical to button 8 except that: pallets 16 and 18 are replaced by pallets, respectively, 156 and 158, and the separable zone 20 is replaced by a separable zone 160.

[0057] Here, to simplify the Figure 4, only a partial horizontal section of the button 150 is shown. This section is made along a horizontal cutting plane which is perpendicular to the front faces of the pallets 156 and 158 and which passes through these front faces.

[0058] The pallets 156 and 158 are identical to the pallets 16 and 18, except that they are mechanically separated from each other. For this purpose, they each have a lateral face, respectively 162 and 164, facing each other and which extends over the entire height of the pallet. These lateral faces 162, 164 extend mainly in a plane perpendicular to the plane containing the front face of these pallets. The hollow space between the lateral faces 162 and 164 forms a through slot 166.

[0059] The separable zone 160 includes: a blind hole 170 dug in the pallet 156 and which opens into the lateral face 162, a housing 172 dug in the lateral face 164 opposite the blind hole 170, a pin 174 or a ball received inside the blind hole 170, a spring 176 which permanently urges the pin 174 outside the blind hole 170.

[0060] The pin 174 is movable, by sliding inside the blind hole 170, between a protruding position, shown in the Figure 4 , and a retracted position. In the protruding position, the distal end of the pin 174 is received inside the housing 172. In this protruding position, the pin 174 only allows simultaneous movement of the pallets 156 and 158.

[0061] In the retracted position, the distal end of the pin 174 is no longer received inside the housing 172. In this retracted position, the pin 174 allows the movement of one pallet independently of the other pallet.

[0062] At least one of the housing 172 and the distal end of the pin 174 comprises an inclined face capable of transforming the difference between the bearing forces exerted by the user on the front faces of the paddles 156, 158, into a horizontal force which pushes the pin 174 towards the inside of the blind hole 170 against the return force of the spring 176. The stiffness of the spring 176 is chosen so that the pin 174 reaches its retracted position only when the difference between the bearing forces exerted by the user on the front faces of the paddles 156, 158 exceeds the threshold S 1 .

[0063] Preferably, in this embodiment, the pin 174 is made of a material that does not break when the area 160 yields. In addition, the separable area 160 comprises a mechanism for retaining the pin 174 inside the hole 170. This mechanism retains the pin 174 inside the hole 170 even when the side face 164 is no longer opposite the side face 162.

[0064] The operation of the button 150 is deduced from the explanations given for the button 8. In addition, the operation of the button 150 has the following particularity. This particularity appears, for example, in the case where the blocking of the pallet 158 is a blocking which prevents it from reaching the pushed position but which does not prevent it from reaching the retracted position. In this case, when the pallet 156 returns from the pushed position to the retracted position, it crosses the pallet 158. At this moment, the pin 174 returns to the housing 172. Thus, on the remainder of the trajectory towards the retracted position, the pallets 156, 158 are again moved simultaneously.

[0065] There Figure 5 represents a button 178 identical to button 150, except that area 160 is replaced by a separable area 180. Separable area 180 is identical to separable area 160 except that: housing 172 is replaced by a blind hole 182; pin 174 is replaced by a pin 184; spring 176 is omitted.

[0066] In this embodiment, the blind holes 170, 182 are configured to generate a shear stress in the pin 184 when the user presses one of the paddles while the other paddle is blocked. For example, unlike the embodiment of the Figure 4 , the blind hole 182 is devoid of an inclined face capable of generating a horizontal force which moves the pin 184 in translation inside these blind holes 170, 182.

[0067] In this embodiment, the pin 184 is made of a brittle material. More specifically, the pin 184 is capable of breaking as soon as the difference between the bearing forces exerted by the user on the front faces of the paddles 156, 158 exceeds the threshold S 1 . For example, the pin 184 is made of ceramic or hard plastic. Here, the pin 184 is mechanically distinct from the paddles 156 and 158.

[0068] THE Figures 6 and 7represent a button 198 identical to the button 8, except that the separable zone 20 is replaced by a separable zone 200. The zone 200 is identical to the zone 20, except that the recess 40 and the arm 44 are replaced by a non-through recess 202. The recess 202 here forms a groove which extends along the boundary 28 and forms a thinning of materials in the block of material from which the pallets 16 and 18 are made. Here, the depth of the recess 202 is adjusted so that the zone 200 gives way as soon as the difference between the support forces exerted by the user on the front faces of the pallets 16 and 18 exceeds the threshold S 1 . Chapter II: Variants:

[0069] Other embodiments of the dissociable zone are possible. For example, the dissociable zone 160 is replaced by a dissociable zone produced using a first and a second permanent magnet. The first and second permanent magnets are fixed, without any degree of freedom, on, respectively, the first and second pallets 156 and 158. In the normal operating mode, the South pole of the first magnet is glued to the North pole of the second permanent magnet so as to ensure a rigid connection between the pallets 156, 158 as long as the difference between the support forces exerted by the user on the front faces of these pallets does not exceed the threshold S 1 . When the difference between the support forces exerted by the user on the front faces of the first and second pallets exceeds this threshold S 1 , then the shear force is sufficient to detach the first magnet from the second permanent magnet. The dissociable zone then yields.Thus, if for example, it is the first pallet that is blocked and can no longer be moved, the second pallet can be moved from its retracted position to its pushed position. When the second pallet returns from the pushed position to the retracted position, it crosses the first pallet. At this moment, the first and second permanent magnets stick together again. Thus, on the remainder of the trajectory towards the retracted position, the first and second pallets are again moved simultaneously. In this embodiment, the switching between the normal operating mode and the degraded operating mode is reversible as in the embodiment of the . Figure 4 .

[0070] The recess 202 can also be made on the rear face of the pallets 16 and 18.

[0071] Alternatively, in the normal operating mode, the gap between the positions of the first and second pallets along the path 14 is not zero. In this case, there is a constant gap between these positions.

[0072] Alternatively, the paddle switch has a return mechanism that automatically returns the switch to its retracted position as soon as the user no longer touches the lever 12.

[0073] In a simplified embodiment, the electrical connection 90 is omitted. In this case, the terminals 60 and 62 can also be omitted.

[0074] In a simplified embodiment, the electrical connection 90 is present and the information that its part 92 is cut is sent back via the bus 56. For this, for example, the module 76 is implemented in the button 8 and not in the computer 70. In this case, the terminals 60 and 62 can also be omitted.

[0075] The trajectory 14 along which the paddles move may be other than an arc of a circle. For example, as a variant, this trajectory is a rectilinear trajectory or having any other suitable shape. For example, in a particular embodiment, the paddles are movable, by the user, along a rectilinear trajectory coincident with the axis 28 and not along the trajectory 14. In this case, the paddle button functions as a push button. In the normal operating mode, both paddles are pressed simultaneously. In the degraded operating mode, it is possible to continue to use the button by pressing only one of the two paddles.

[0076] Other shapes and dimensions are possible for the pallets. For example, in a particular embodiment, the pallets are intended to be moved, not using a single finger, but using several fingers or using one or both hands of the user or using the user's foot. In each of these cases, the dimensions of the pallets must be adapted to the intended use. When a pallet is intended to be pushed by the user's hand, the force F min can be between 30 N and 150 N and, most often, between 30 N and 100 N.

[0077] Alternatively, sensors 50 and 52 are replaced by all-or-nothing sensors which only indicate whether or not the pallet has reached its pushed position. Chapter III: Advantages of the embodiments described:

[0078] The separable zone ensures that during normal operation, the two pallets are systematically moved in parallel. This therefore prevents an accidental gap from appearing between the positions of the first and second pallets. Thus, any unexpected operation of the controlled equipment 80 is avoided.

[0079] Furthermore, since the difference between the measurements of the two sensors is systematically constant during the normal operating phase, a variation in the difference between the positions measured by these sensors is a reliable indicator of a button failure.

[0080] The button described here also has the advantage of being able to be used in a degraded operating mode in which only one of the paddles is used. This is made possible by the fact that each paddle can be moved independently of the other and by the fact that the user can easily cause the separable zone to give way and thus release the movement of one of the paddles relative to the other.

[0081] This increases the robustness of the button against failures such as accidentally blocking the movement of one of the paddles. Indeed, in this case, the button remains usable, by moving only the paddle that is not blocked.

[0082] In addition, this button is also tolerant of a malfunction of one of the sensors, because in this case the position is measured by the other sensor.

[0083] The break in the electrical connection 90 when the separable zone fails makes it possible to simply and reliably indicate to the computer 70 that a failure has occurred. The module 78 can then simply identify the part to be replaced.

[0084] Forming the two paddles 16, 18 and the separable area 20 from the same block of material simplifies the manufacture of the button 8. For example, the two paddles and the separable area can then be produced using a single mold and a single molding operation.

[0085] The creation of the separable zone using a breakable pin 184, separate from the pallets 156 and 158, makes it possible to replace the broken pin with a new, intact pin without having to systematically replace these two pallets 156, 158.

[0086] The creation of the separable zone using the pin 174 also makes it possible to restore the mechanical connection between the two pallets 156 and 158 without necessarily replacing at least one of these pallets.

Claims

1. User-operated paddle button with : - a first pallet (16; 156) and a second pallet (18; 158), each able to move parallel to a common trajectory (14), between a retracted position and a pushed position when the user presses on at least one of these pallets, - a first sensor (50) capable of measuring the position of the first pallet along the common path independently of the position of the second pallet along this common path, - a second sensor (52) capable of measuring the position of the second pallet along the common path independently of the position of the first pallet along this common path, characterised in that : - the first and second pallets (16, 18; 156, 158) are mechanically attached to each other solely by means of a detachable zone (20; 160; 180; 200) to allow only simultaneous movement of the first and second pallets as long as one of the pallets is not locked relative to the other, - this dissociable zone is capable of giving way as soon as the difference between the bearing forces exerted on the first and second pallets, respectively, exceeds a predetermined threshold, this predetermined threshold being adjusted so as to be crossed by the user bearing on one of the pallets while the movement of the other of the pallets is blocked, and - when the dissociable zone has given way, the first pallet (16; 156) and the second pallet (18; 158) are dissociated from each other, i.e. the dissociable zone no longer mechanically connects the first and second pallets together so that the second pallet can be moved, by the user, between its retracted and pushed positions independently of the first pallet parallel to the common path .

2. A button according to claim 1, wherein the button comprises : - two electrical terminals (60, 62) suitable for connection to a fault diagnosis module (78), and - an electrical link (90) which electrically connects the electrical terminals together, a part (92) of this electrical link being attached to the dissociable zone so as to be cut when the dissociable zone gives way.

3. A button according to any one of the preceding claims, wherein : - the button comprises a single block of material from which the first and second pallets (16, 18) are formed, - the first and second pallets each have a bearing face (22), the bearing faces of each of the pallets extending, side by side, mainly in a plane perpendicular to the common path and each being located on a respective side of a lateral boundary (28), - the separable zone (20; 200) comprises one or more recesses (40, 42; 202) made in the block of material along the lateral boundary to cause the block of material to break along this lateral boundary as soon as the difference between the bearing forces exerted on the first and second pallets respectively exceeds a predetermined threshold.

4. A button according to any one of claims 1 to 2, wherein : - the first and second pallets (156, 158) each comprise : - a bearing face, the bearing faces of each of the pallets extending side by side mainly in a plane perpendicular to the trajectory, - a side face (162, 164) which extends substantially perpendicular to the support face, the side faces of each of the pallets facing each other and separated from each other by a through slot (166), and - the dissociable zone (180) comprises : - a first hole (170) made in the side face (162) of the first pallet and a second hole (182) made in the side face (164) of the second pallet opposite the first hole, - a pin (184), mechanically distinct from the first and second pallets, this pin having one end received in the first hole and an opposite end received in the second hole to mechanically connect the first and second pallets together and only allow simultaneous movement of the first and second pallets as long as one of the pallets is not locked relative to the other, this pin being made of a brittle material capable of breaking as soon as the difference between the bearing forces exerted on the first and second pallets respectively exceeds a predetermined threshold.

5. A button according to any one of claims 1 to 2, wherein : - the first and second pallets (156, 158) each comprise : - a bearing face, the bearing faces of each of the pallets extending side by side mainly in a plane perpendicular to the trajectory, - a side face (162, 164) which extends substantially perpendicular to the support face, the side faces of each of the pallets facing each other and separated from each other by a through slot (166), and - the dissociable zone (160) comprises : - a blind hole (170) opening out in the side face (162) of the first pallet and a housing (172) hollowed out, opposite, in the side face (164) of the second pallet, - a pin (174) having a distal end turned towards the side face of the second pallet, this pin being able to slide inside the blind hole between : - a protruding position in which its distal end is received inside the housing to mechanically connect the first and second pallets together and allow only simultaneous movement of the first and second pallets as long as one of the pallets is not locked relative to the other, and - a retracted position inside the blind hole in which the pin allows the user to move one of the pallets independently of the other, - a spring (176) which permanently biases the pin towards its protruding position and which allows the pin to move towards its retracted position only when the difference between the bearing forces exerted on the first and second vanes respectively exceeds a predetermined threshold.

6. Button according to any one of the preceding claims, in which the dissociable zone (20; 160; 180; 200) is capable of resisting, and therefore of not giving way, as long as the bearing force exerted by the user on one of the pallets while the movement of the other of the pallets is blocked, does not exceed 2Fmin, where Fminis the minimum force that the user must exert on the pallets to move them simultaneously from their retracted positions to their pushed positions.

7. Button according to any one of the preceding claims, in which the dissociable zone (20; 160; 180; 200) is capable of giving way as soon as the bearing force exerted by the user on one of the pallets while the movement of the other of the pallets is blocked, exceeds 5Fmin, where Fminis the minimum force that the user must exert on the pallets to move them simultaneously from their retracted positions to their pushed positions.

8. Button according to claim 6 or 7, wherein the force Fminis between 0.5N and 10N.

9. Button according to claim 6 or 7, wherein the force Fminis between 30N and 150N.

10. A method of operating a button in accordance with any one of the preceding claims, wherein : - during a normal operating phase (100), the separable zone mechanically connects the two pallets together so that, when the user presses on at least one of the two pallets, the two pallets systematically move simultaneously between their retracted positions and their pushed positions s, - if the movement of the first pallet is blocked and in response to a pressure exerted by the user solely on the second pallet, the separable zone gives way (20; 160; 180; 200) and the button switches to a degraded operating phase, - during the degraded operating phase (120), the separable zone no longer mechanically connects the two pallets together so that the second pallet can be moved by the user between its retracted and pushed positions independently of the first pallet.