FR2678298A1 - Device for actuating a barrier or an automatic safety gate - Google Patents

Abstract

Actuation device for a barrier arm (13) which is articulated and movable between two locked positions, including control logic (LC) and motorisation driving a crank pin (17) in rotation, one end (16) of the crank pin, away from the axis of rotation of the crank pin, sliding along a lever, this lever being linked in rotation with a shaft (12) on which the arm is mounted, the whole being arranged so that, when the arm (13) is in the locked position, the crank pin is perpendicular to the lever (14).

Description

 The present invention relates to an actuating device for barrier or automatic gate comprising an arm.

More specifically, the present invention relates to an improvement to the automatic barrier or gate described in French patent 76.06755 filed by one of the inventors of the present invention and assigned to the company ERO
AUTOMATION.

 The actuation mechanism described in this patent is a mechanism known under the name "three-quarter movement - one quarter".

 The device operates as follows: the lifting barrier constituted, in a simple embodiment, by an arm, is mounted on an axis itself integral in rotation with a slide lever comprising a slot. In the slot slides a roller arranged at one end of a crank pin driven in rotation at its other end by a motorization.

 When the arm is in a first of these two positions, for example in the low position, the roller is in abutment with the end of the slot of the sliding lever close to the axis of articulation of the arm and of the lever. To move the arm to the second position, in this example the raised position, the motor rotates the crankpin; this rotation causes the roller to slide in the slot of the lever, while the latter is rotated.

When the crankpin has made three quarters of a turn (2700), the roller again comes into abutment against the end of the slot close to the axis of rotation. The lever and, therefore, the arm then traveled a quarter turn (900).

 The assembly is locked in the two extreme positions. Indeed, if a force is exerted on the arm upwards, when the latter is in the low position, as the crankpin is arranged perpendicular to the lever while the roller is in abutment on the end of the slot, the force is taken up by the axis of rotation of the crankpin and oriented perpendicular to this axis: the assembly is in quadrature and there is locking.

 It is the same when the arm is in the raised position, in the event that we try to exert a force tending to lower the arm.

 In the two extreme positions of the crankpin, micro-contacts make it possible to cut off the power supply to the motor, so that the crankpin cannot go beyond 2700, which, in any event, would be impossible to achieve mechanically, because of the quadrature mentioned above. However, the micro-contacts make it possible to avoid mechanical deterioration of the motor.

This device, developed by the applicant, has many advantages, among which
the assembly is locked in the high or low position of the barrier for the reasons mentioned above,
- when the crankpin is rotated, it almost instantly reaches its maximum rotational speed, but the arm is gradually rotated. Indeed, the speed of rotation of the barrier passing from zero speed to a maximum speed until it is at 450, the speed of rotation of the barrier being decelerated between the position at 450 and the other position extreme. There is therefore a gradual acceleration and decelaration of the barrier.

- at the start of the movement of the arm, the load on the gear motor is zero and becomes progressively maximum, when the barrier is at 450, then decreases when the arm approaches the other extreme position, which is particularly favorable on the engine load plan,
- one can use a friction drive coupled to the motor. This friction is effective as long as the arm is between these two extreme positions and thus makes it possible either to absorb shocks, or even to stop the arm in the presence of an obstacle (for example a car), without blocking the motor, while friction is ineffective in the extreme positions due to the quadrature mounting.

The friction however contributes to absorbing the possible inertia of the crank pin 17 if the speed of rotation of the latter is high, thus limiting the wear of the reduction gear possibly associated with the motor.

 However, the Applicant has found in use various imperfections in this system that it wished to remedy with the present invention.

 First of all, the specifications for such a safety barrier, particularly in car parks, provides for an automatic lifting of the arm in the event of a power failure. In the actuation device mentioned above, such automatic lifting is not possible.

 In addition, the safety barriers are more and more subject to acts of vandalism Indeed, on this occasion, efforts are exerted on the arm, these efforts being either directed upwards when the barrier is closed (this is the case of a fraudster who wants to leave the parking lot without paying), or exercised downwards (for example a child who hangs on his arm). In both cases, to avoid a final deterioration of the barrier or the mechanism, the applicant has provided a safety pin which breaks when the force on the barrier is greater than a predetermined force. This solution is not satisfactory in terms of economical and practical for the user of such barriers: in fact, when the pin is released, the barrier is still in the raised position and vehicles can enter or leave the parking lot freely: the barrier is no longer operational. We must then consider changing the pin, which requires time and, in any case, costs money.

 The applicant has sought a means of obtaining the automatic lifting of the barrier both in the event of a power failure and when an abnormal force is applied to the arm.

 Furthermore, as has been specified above, the locking of the system is obtained by good squaring of the main elements of the actuating device (crank pin and slide lever), which freezes the geometry of the device. However, during the operations of mounting the barrier in situ, it often turns out that the arm is not really horizontal or parallel to the ground. This problem is solved in the prior art by providing a system for adjusting the attachment of the arm to its axis of rotation. The Applicant has sought to improve these provisions to allow adjustment of the horizontality of the barrier, which has no effect on the squaring of the drive mechanism, while making it possible to avoid the addition of an adjustment means during the mounting the arm on its axis.

 The present invention achieves all of these objectives.

 To this end, the present invention relates to an actuating device for an articulated and movable barrier arm between two locked positions comprising a control logic and a motorization driving a crankpin in rotation, one end of the crankpin, distant from the axis of rotation. of the crankpin, sliding along a lever, this lever being integral in rotation with a shaft on which the arm is mounted, the assembly being arranged so that, when the arm is in the locked positions, the crankpin is perpendicular to the slide lever, characterized in that the motorization is arranged in a frame movable in rotation around said shaft, between a position called "normal" and a position called "safety", this frame being associated with one of the first suitable means on its return to a safety position of the stop means preventing its rotation beyond the safety position, and to a presence sensor detecting the casing is in its normal working position, while blocking means, implemented by the control unit when the device is powered, to lock said support in the normal position, the control unit being further arranged to control the neutralization blocking means, when the power supply to the device is cut off, the support then being driven towards its safety position under the action of said first return means then, when the device is again supplied to engage the motorization means for driving , via the crankpin and the lever, the chassis in rotation against the return means until the locking means are engaged.

 Thanks to these provisions, all of the objectives set out above are achieved.

 Indeed, the blocking means, which advantageously consist of an articulated ratchet, associated with an electromagnet, allow effective blocking of the motorized chassis, under normal conditions of use.

 On the other hand, when the conditions of use deteriorate, for example when a force is exerted on the lowered barrier, force oriented either upwards or downwards, and when, at the level of the axis of the barrier, a torque of predetermined amplitude is reached, the ratchet detaches from the electromagnet and no longer performs its blocking function, the barrier then rising automatically (case where the force is exerted upwards) or, at on the contrary, lowering itself until it touches the ground (case where the effort is exerted downwards). The barrier then automatically returns to the closed position.

 In addition, when a power failure occurs, the electromagnet is no longer supplied and the barrier is raised automatically.

The characteristics and advantages will moreover emerge from the description which will follow with reference to the appended drawings in which
FIG. 1 is a simplified perspective view of the main elements of a preferred embodiment of the actuating device according to the present invention,
FIG. 2 is an elevation view of the device of FIG. 1,
FIG. 3 is an elevation view of part of the device in FIGS. 1 and 2,
- Figure 4 is a side view along the arrow
IV of Figure 3,
FIG. 5 is an elevation view of the device, barrier raised, after a power failure,
FIGS. 6a and 6b are similar views but illustrate the return of the chassis of the device illustrated in the figures, to its normal position,
- Figure 7 is an electrical block diagram of the device according to the present invention.

Figure 1 shows in simplified and schematic perspective, an embodiment of a device according to the present invention
According to the embodiment shown, the actuating device 10 comprises a motorization assembly constituted, here, by a motor and a reduction gear arranged in a frame. This is a "SNT" brand gear motor with incorporated friction; the engine is the model reference M 63 a 4; the reduction gear is the model referenced CBF50 (speed of rotation of the output shaft 6.9 rpm). In Figure 1, only has been shown, very schematically, the frame 11. This frame is, in accordance with a characteristic of the invention, articulated around a shaft 12 called "main". At a first end of the shaft 12, an arm 13 is mounted, acting here as a barrier. The arm 13 is rotatably integral with the shaft 12.

 At a second end, a lever 14 is mounted on the main shaft 12. The latter is also integral in rotation with the shaft 12. The lever 14 here has a slot 15 in which slides a roller 16 arranged at one end of a crank pin 17 and integral in rotation with the output shaft 18 of the motorization arranged in the chassis 11.

 A stop 19 is arranged on a rod 20 fixed on the slide lever 14, as illustrated in FIGS. 1 and 2.

 When the support has the position illustrated in solid lines in FIGS. 1 and 2, the stop 19, or more precisely, the stop surface 21 comes into contact with a fixed stop piece: in the embodiment chosen and shown, the fixed abutment piece is constituted by a wall 22 of the housing containing the entire device 10.

In Figure 2, the housing has been shown in section and is generally referenced at 23. In Figure 1, for clarity, the housing 23 and the wall 22 have only been partially shown .

 In accordance with the invention, the actuation device 10 also includes blocking means generally referenced at 25 in FIG. 1.

 In the embodiment chosen and shown, the locking means comprise a ratchet 26 and an electromagnet 34. The ratchet 26 is articulated around a shaft 27 secured to the housing 23, while the chassis 11 is secured to an arm of retainer 28 adapted to cooperate with the ratchet 26, as will be described later in support of FIGS. 3 and 4.

 The arm 28 has an orientation at 450 relative to the horizontal, the ratchet 26, or more precisely its long branch 47, having a substantially vertical orientation in the position illustrated in FIG. 1.

It is observed that the retaining arm 28 cooperates, in this embodiment, with the upper end of the ratchet 26
At its lower end, the ratchet 26 comprises a magnetization piece 30 which, in this embodiment, is fixed to the ratchet by means of a screw 31, nut 32 assembly making it possible to adjust its spacing relative to the end bottom of the ratchet. The magnetization part 30 comprises a magnetization surface 33 adapted to cooperate with the electromagnet 34 which is integral, in this embodiment, with the wall 22 and the housing 23. The electromagnet 34 is a particular mode "second return means adapted to hold the ratchet in a position where the latter blocks the chassis in its normal position" (that illustrated in FIG. 1).

 At its upper end, the ratchet 26 has a horizontal support surface 36 and a vertical support surface 37 able to cooperate with a cylindrical support piece or support roller 38 that comprises the arm 28. It can be seen that the point of contact between the cylindrical part 38 and the horizontal bearing surface 36 is at a distance "d7" from an axis 40 parallel to the large branch of the ratchet 26, while the bearing point of the roller 38 on the surface 37 is distant by a distance "d2, 'relative to an axis 39 perpendicular to the axis 40, the intersection of the axes 39 and 40 correspond to the axis of the shaft 27. In this embodiment, the distances dl and d2 are 55mm, the distance between the axis 39 and the axis of the screw 31 is 300mm.

 According to one aspect of the present invention, the position of the roller 38 at the end of the retaining arm 28 is adjustable radially relative to this arm. To this end, the part 38 is integral with a threaded retaining rod 41 cooperating with a nut 42, the threaded rod 41 passing through an oblong hole 43 oriented in an arc centered on the axis of the shaft 12.

 The upper part of the ratchet 26 carries a presence sensor 44 resting on the roller 38. This presence sensor which is constituted here by two sensor switches 44i '442 (FIG. 7) is connected to the electrical circuit shown diagrammatically by the wires 45 of FIG. 4. It is suitable for transmitting a signal to an LC control logic (FIG. 7), when there is contact between the presence sensor 44 and the roller 38.

In the block diagram of Figure 7, it is illustrated
- LC control logic,
- the M engine (model M63a4 of SNT brand),
- Ph limit switch switches
Pb.

These sensor switches are arranged on the crank pin 14 (not shown in FIG. 1 for the sake of clarity). These sensor switches are branded here
CROUZET, model 83106 (5A, 250V). They are closed when the crankpin reaches the end of its travel and the barrier is in the high position (Ph probe closed) or low (Pb switch closed).

 Ph Pb probes are connected to the LC control unit.

 - the electromagnet 34. In this embodiment, it is a BINDER electromagnet (model 10 320 03 C). Its holding force is 27 kg.

 - the presence sensor 44. In this embodiment, the presence sensor 44 is here constituted by two sensor switches 441 and 442 The sensor switches 441 442 are of the same model as the sensor switches Ph and Pb. probe 441 is connected on the one hand, to the electromagnet 34 and, on the other hand, to the control logic LC. It therefore allows the supply of the electromagnet 34. The sensor switch 442 is connected to the control unit.

 - the power supply of the assembly, ie 220 V AC.

 The LC control logic is adapted to manage the information coming from the various feeler switches, while allowing the supply of the motor M and of the electromagnet 34 in the various cycles described below.

 We will now describe the operation of the device.

 In Figure 1, there is shown in solid lines the position of certain elements when the arm 13 is raised and in phantom, the position of these same elements when the arm 13 is lowered.

 In the presence of supply voltage, the operation is as follows.

 The electromagnet 34 is supplied and therefore attracts the magnetization surface 33. The ratchet 26 is then in the position where it is shown in FIGS. 1 and 3. In this position, the ratchet 26 acts in cooperation with the retaining arm 28 and, more precisely, the roller 38, as a means of blocking the chassis II in the so-called "normal" position where the latter is shown in FIG. 1. In fact, the part 38 comes to bear on the horizontal support surface 36 which prevents the frame II from tilting down.

Furthermore, the cooperation of the cylindrical part 38 with the vertical bearing surface 37 prevents any rotation of the arm in the clockwise direction (arrow A, FIG. 3).

 It turns out that in the presence of electric current, the chassis It is blocked by the ratchet 26 in the so-called "normal" position where it is illustrated in FIG. 1.

The operation of the drive mechanism of the arm is then conventional. When the LC logic commands the closing of the arm (passage from the position of the arm 13 illustrated in solid lines to its position illustrated in dashed lines), the motorization M arranged in the frame 11 rotates the shaft 18, which drives in rotation the crank pin 17. The roller 16 then slides in the slot 15 and drives the main shaft 12 in rotation. When the crankpin has made three quarters of a turn (in the direction of the arrow
B), the sliding lever 14 is found in the position illustrated in phantom, after having made a quarter turn.

 In the two extreme positions of the arm 13 or of the lever 14, the assembly is locked. Indeed, in the first position, that illustrated in solid lines, the crank pin 17 arranged perpendicular to the sliding lever 14, and it is the same in the position illustrated in phantom: therefore, if a force such as one forces F1, F2 is exerted on the arm 13, the assembly remains locked due to this squaring because the slide lever 14 then exerts a force oriented along the crankpin, which ensures the blocking of the device.

 If the barrier 13 encounters an obstacle during its movement, the friction associated with the motor M starts to slip and the safety of the users is thus ensured (see patent 76.06755).

 We will now describe the operation of the device in the event of a power failure.

 If the power failure occurs while the barrier is raised (solid lines in Figure 1), as the stop 19 is supported on the wall 22, the barrier remains raised, all of the mechanics remain in place.

 On the other hand, if the power failure occurs while the barrier is in the low position, the geometry of the assembly changes.

Indeed, as the magnetization surface 33 is no longer attracted by the electromagnet 34, the force of attraction
C exerted by the electromagnet (Figure 3) is canceled. Consequently, the weight of the frame 11 and of all the elements carried by this frame (in particular the motor) exert on the bearing surface 36, by means of the cylindrical part 38, a force oriented upwards. This force generates a torque in the clockwise direction, due to the offset of the fulcrum relative to the articulation 27 of the ratchet 26 (distance d1). Consequently, the ratchet rocks in the direction of arrow D, while the frame 11 is driven by its weight and rocks in the direction of arrow E (Figure 1). In doing so, the crank pin 17 (illustrated in phantom lines on Figure 1) exerts traction on the sliding lever 14 via the roller 16, which drives the shaft 12 in rotation and causes that of the arm 13 to its high position. The assembly then takes the so-called "safety" position illustrated in FIG. 5.

 It therefore appears that the present invention allows the barrier arm 13 to return automatically to the high position in the event of a power failure, that is to say as soon as the ratchet 25 no longer blocks the retaining arm 28.

 In the embodiment described here, this automatic return is caused by the balancing of the assembly constituted by the motorization chassis there (and the elements carried by the latter) and the arm 13, so that in the absence of any restraint, there is tilting as illustrated in Figure 5, so that the arm of the barrier 13 takes its high position. This balancing constitutes a particular embodiment of "first means" of recall.

 In other embodiments, for example in the case where it would not be possible to produce a balanced assembly so that there is automatic tilting, other means may be provided for returning the assembly to the position illustrated in FIG. 5. These return means could consist, for example, of a spring arranged in such a way that when the ratchet 26 is no longer blocked by the second return means constituted here by the electromagnet 34, as illustrated in Figure 1, the motorized frame tips under the effect of the spring in the safety position illustrated in Figure 5, causing the opening of the barrier.

 Figures 6a and 6b illustrate the operation of the device when the current returns.

When the current returns, the control unit
LC detects through the presence sensor (feeler) 44, the fact that the ratchet 25 is not engaged on the roller 38. Indeed, the feeler switch 442 is open. Under these conditions, the control logic LC controls the starting of the motor M, so that the crankpin is driven anticlockwise (that is to say in the direction in which it turns to proceed when the barrier is opened in normal operation). However, as the stop 19 is then in contact with the wall 22, when the crankpin is rotated counterclockwise, but it cannot rotate the slide lever 14 due to the cooperation in abutment of the part 19 with the wall 22. Also, by reaction, the whole of the frame 11 is rotated in a clockwise direction (see arrow G in FIG. 6a, then FIG. 6b) , until the crankpin has completed three quarters of a turn, the assembly then returning to the position illustrated in solid lines in FIG. 1, that is to say the case where the barrier is open in normal operation.

 During this time, the roller 38 of the retaining arm 28 is received in the upper part of the ratchet 26 in the same position as that illustrated in FIGS. 1 and 3.

However, during the movement illustrated in FIGS. 6a and 6b, the probe 44 cannot come into contact with the roller 38, and, therefore, the control unit, which does not receive a presence signal (switch 442 open), cannot power the electromagnet 34 because the probe switch 44i is also open; the ratchet 26 remains free to rotate around the shaft 27 and can be erased to allow the positioning of the retaining arm 28 (FIG. 6b). Then, the roller 38 takes the position illustrated in FIGS. 1 and 3 and there is contact recorded by the closing of the sensor switches 441 '442 of the presence sensor 44: the control logic allows the supply, which allows the blocking of the frame which can no longer tilt in the direction of arrow E (Figure 1).

 The LC control logic then controls the closing of the barrier, which takes place in accordance with what has been described in support of FIG. 1.

 It therefore appears that in the event of a power failure, the excitation of the electromagnet 34 allows the barrier to rise automatically, under the action of the restoring force, produced here by the appropriate unbalance of the assembly , while when the current returns, firstly the frame returns to its normal position and secondly the barrier is lowered without external intervention.

 The invention therefore achieves the first of its objectives which is to allow an automatic opening of the barrier in the event of a power failure and the automatic return of the barrier to a low position when the voltage is again present at the terminals of the device. .

 The present invention also makes it possible to prevent significant forces caused in the direction of the arrows F1, F2 in FIG. 1, from causing damage.

It has been described above that when efforts
F1, F2 remain below a predetermined value, the arrangement in quadrature of the lever 14 and the crank pin 17 causes a blockage of the system
However, when the forces F1, F2 are excessive (greater than a predetermined value), the present invention allows easy implementation of a security intended to preserve the material.

Thus, when the force in the direction of the arrow F1 is greater than a predetermined value, the force exerted by the roller 38 on the bearing surface 36 and directed upwards is also greater than a predetermined value: it the same goes for the torque generated by this force on the ratchet and a force in the opposite direction to the arrow
C is then exerted by the lower end of the ratchet 26.

This results in detachment from the magnetization surface 33.

Consequently, by providing an electromagnet whose attraction force is chosen in an appropriate manner, it is possible to provide for a stalling of the electromagnet without mechanical deterioration, the frame 11 tilting as has been explained in support of Figures 1 and 5, which causes the barrier to be raised.

 The probe 44 then records the absence of the roller 38. The control unit, which receives the electrical signal from the probe 44, also records a signal showing that the electrical supply current is present. The control unit then cuts the power supply to the electromagnet 34, so that the ratchet 26 is released, and then controls the operations described above with the support of FIGS. 6a and 6b.

 If during the lowering of the barrier, a force is exerted on the latter to prevent its closing, the friction of the motor, if the latter has one, comes into play, to prevent excessive heating of the latter.

In the event of effort exerted in the direction of the arrow
F2 (for example if a child hangs on the barrier), this effort generates, at the level of the support surface 37, of the ratchet 26, a force oriented perpendicular to this support surface, which generates on the ratchet a torque in the direction of arrow D. When this torque reaches a predetermined value, there is separation of the magnetization surface 33, so that the ratchet 25 swings in the direction of arrow D. The barrier is then free to continue its race down until it contacts the ground: the material is still preserved.

 When the cause of the force F2 disappears, the barrier returns to its equilibrium position under the effect of the abovementioned restoring force (in the embodiment described here, the imbalance between the masses of the barrier and of the elements carried by chassis 11). At the same time, the magnetization surface 33 is returned by the electromagnet 34, so that the roller 38 of the retaining arm 28 is again housed in the upper part of the ratchet, as illustrated in FIG. 3.

 We will now describe another advantage provided by one of the characteristics of the present invention.

 It is possible that during the installation of the barrier at the entrance of a parking lot, the barrel carrying the box 23, is not arranged in a manner strictly perpendicular to the ground plane. Under these conditions, as the arm of the barrier 13, when it is in the low position, is arranged pendulumally to the barrel, it is not found parallel to the ground. The present invention allows, thanks to a feature illustrated in Figure 3, to adjust the horizontality of the barrier.

 The position of the cylindrical support piece 38 can be adjusted inside the oblong hole 43 arranged at the end of the retaining arm 28. This arrangement makes it possible to adjust the position of the barrier 13 relative to the arm 26 and, therefore, relative to the entire frame 11. It will be observed that the quadrature geometry of the crank pin 17 and of the slide lever 14 is preserved.

 Of course, the present invention encompasses any variant within the reach of ordinary skill in the art and is in no way limited by the limiting example described above.

 In particular, in this embodiment, the safety position is a raised position of the barrier.

In other cases (for example in a level crossing case), the safety position of the barrier is the lowered position. In these cases, the person skilled in the art will be able, on the basis of the teachings of the present invention, to find an arrangement making it possible to automatically obtain this safety position. Similarly, any other intermediate position can be chosen between horizontal and vertical as the safety position.

Claims (9)

 1. Actuation device for barrier arm (13) articulated and movable between two locked positions comprising a control logic (LC) and a motorization driving a crank pin (17) in rotation, one end (16) of the crank pin, distant from the axis of rotation of the crankpin, sliding along a lever, this lever being integral in rotation with a shaft (12) on which the arm is mounted, the assembly being arranged so that, when the arm ( 13) is in the locked positions the crankpin is perpendicular to the lever (14), characterized in that the motorization is arranged in a frame (11) movable in rotation around said shaft (12) between a position called "normal" and a position called "safety, this chassis being associated with first means adapted to return it to a safety position, stop means (19, 21, 22) preventing its rotation beyond the safety position, and with a sensor presence (44) detecting the ch frame in its normal working position, the device comprising blocking means (25, 34) implemented by the control unit (LC) when the device is supplied, to block said support (11) in the normal position, the control logic being further arranged to control the neutralization of the blocking means, when the power supply to the device is cut, the support (11) then being driven towards its safety position under the action of said first return means then, when the device is again supplied to engage the motorization means to drive, by means of the crankpin and the lever, the chassis in rotation against the return means until the locking means are engaged.  2. Device according to claim 1, characterized in that said locking means comprise a ratchet (26) cooperating with a retaining arm (28) secured to the frame (11), associated with second return means adapted to hold the ratchet in a position where the latter blocks the chassis in its normal position  3. Device according to claim 2, characterized in that the ratchet (26) has an inverted L shape, and has respectively horizontal and vertical abutment surfaces being arranged at its upper end and adapted to cooperate in abutment with a roller stop (38) arranged at the end of the retaining arm (28).  4. Device according to any one of claims 2 and 3, characterized in that the second return means comprise an electromagnet (34).  5. Device according to claims 3 and 4, characterized in that the ratchet (26) has at its lower end a magnetization surface (33) adapted to cooperate with the electromagnet (34).  6. Device according to any one of claims 1 to 5, characterized in that said first return means consist of an imbalance of the arm - elements carried by the frame assembly, such that, when said blocking means are neutralized, the chassis tilts under the effect of this imbalance towards its safety position.  7. Device according to any one of claims 1 to 6, characterized in that it further comprises means making it possible to adjust the position relative to the chassis relative to the locking means, when the chassis is in its normal position.  8. Device according to claim 7, characterized in that these means consist of an adjustment of the radial position of the support roller (38) formed at the end of the retaining arm (28).  9. Device according to any one of claims 1 to 8, characterized in that said second return means exert a return force of predetermined intensity, so that if an intensity force is exerted on the barrier arm (13), said second return means release said blocking means.