Patent Description:
A smoke and heat exhaust ventilation system, which here below will be simply referred to as "ventilation system" for the sake of description simplicity, substantially comprises a cover, perimetrically delimited by a frame and made of a metallic or non-metallic material, which is connected to a counter frame by means of hinges, wherein said counter frame perimetrically delimits a base.

The base, which is also preferably made of a metallic material, delimits the perimeter of a through opening made in the structure of a building and communicating with the external environment.

The installation of ventilation systems in buildings is required by the safety regulations in force, according to which, furthermore, in case of fire the cover must open automatically and within a predetermined lapse of time.

According to the known art, the cover is usually arranged in the closed position with the frame facing and resting against the counter frame of the base and is mechanically connected to moving means comprising one or more connecting mechanisms and a gas-operated actuator which, in case of fire, is fed with pressurized carbon dioxide (CO<NUM>) to open the cover almost instantaneously.

More specifically, carbon dioxide is contained in a small cylinder whose dispenser mouth is connected to the feeding way of the pneumatic actuator and sealed by means of a breakable membrane.

When special sensors installed in the room detect the presence of smoke or a temperature increase exceeding a pre-established threshold, a suitable actuator perforates the membrane so that the carbon dioxide flows out of the small cylinder towards the gas-operated actuator, causing the cover to open.

According to an embodiment known in the art, the membrane is perforated by an actuator that is activated by an explosive micro charge which is primed by the Joule effect of a remotely powered electric resistor.

According to another embodiment, also belonging to the known art, the membrane is perforated by an actuator that is activated by preloaded elastic means when the latter are released following the breakage of a heat sensitive vial.

Both of the known embodiments mentioned above, however, have some recognized drawbacks that are briefly listed here below.

The embodiment using an explosive micro charge has the drawback that in some cases the opening of the cover of the ventilation system can take place in a completely accidental manner.

In fact, the electric device that triggers the explosive micro charge is highly sensitive to atmospheric discharges, induced currents and radio frequency interference present in the environment, and in some circumstances this may cause the ignition of the explosive micro charge and thus the undesired opening of the cover of the ventilation system.

Another drawback is constituted by the fact that in order to periodically check the efficiency of the cover opening device of each ventilation system it is necessary to detonate an explosive micro charge or to intentionally destroy a heat sensitive vial.

Since the cost of the maintenance technician entrusted with this task must be added to the cost of the explosive micro charges and of the heat sensitive vials, it can be understood that each periodic efficiency check is expensive, especially if a large number of ventilation systems is installed in the building.

A further drawback is due to the fact that, after each periodic efficiency check, the operators must reach each ventilation system, usually installed on the roof of the building and thus in a position which is uncomfortable to reach, to replace the explosive micro charges or the heat sensitive vials.

Another and yet not the least drawback also lies in that, every time the user needs to open the cover intentionally, he has to proceed manually or through an automatic activation, which involves the destruction of an explosive micro charge or of a heat sensitive vial with the respective CO<NUM> or nitrogen cylinders. In the case of opening devices using heat sensitive vials, in order to avoid the need to make the explosive micro charge explode whenever the cover of the ventilation system is opened intentionally, suitable electromechanical solenoid means have been devised which are installed in each ventilation system and allow the operator to rearm it after the opening of the cover of the ventilation system.

The devices of this type have high costs for the implementation of the system, to which the cost for the work of the maintenance technician must in any case be added.

Notwithstanding the limitations and the drawbacks listed above, all the opening devices of the ventilation systems described above have, however, the advantage of being extremely reliable as they guarantee with almost absolute certainty that the cover of the skylights will open in case of fire.

However, according to the present state of the art in the sector, most manufacturers tend to replace the gas-operated actuators fed with pressurized CO<NUM> or nitrogen with linear electric actuators, wherein each actuator comprises an extendable stem that is set moving by kinematic mechanisms associated with an electric motor.

<CIT> and <CIT> show examples of such smoke and heat exhaust ventilation systems.

<CIT> discloses a smoke and heat exhaust ventilation system according to the preamble of claim <NUM>.

The use of linear electric actuators instead of gas-operated actuators fed with CO<NUM> or nitrogen requires that the electric motors that activate the actuators be powered at a low voltage with batteries connected to the electric power supply line in buffer mode.

It can be understood that the manufacturers of ventilation systems prefer to use linear electric actuators of the type mentioned above, considering that using them instead of gas-operated actuators fed with pressurized CO<NUM> allows the ventilation systems to be constructed in a simpler manner as wells as a simplification of the entire system, since it is only necessary to provide an electric power supply line for the electric motors that set the stems of the actuators in motion.

In the known embodiments of ventilation systems using linear electric actuators, the end of the stem is directly connected to the frame of the cover, and this leads to the drawback that the manufacturer needs to use actuators where the stroke of the stem is longer, which means having stems whose length and cost increase as the size of the cover, measured according to the thrust direction of the actuator, increases.

Furthermore, the need to use actuators with stems having increasing lengths means that the manufacturer cannot standardize the electric actuators to be used, limiting the number of the latter.

The present invention intends to overcome all the drawbacks mentioned above by providing a ventilation system that uses a single linear electric actuator whose stem has just one length and one stroke, independently of the size of the cover measured according to the thrust direction of the actuator.

The object is achieved through the provision of the improved smoke and heat exhaust ventilation system carried out according to the main claim, to which reference is made.

Other characteristics of the invention are described in the dependent claims.

Advantageously, the ventilation system with electric actuator that is the subject of the invention makes it possible to use linear electric actuators having shorter and thus less expensive stems compared to the linear electric actuators that are applied to ventilation systems of the known art having the same size.

Still advantageously, the invention makes it possible to standardize the device designed to move the cover of the ventilation systems by using a single electric actuator whose stem has just one length and one stroke for all the sizes of covers.

This also results in the further advantage that it is possible to unify all the types and sizes of the steelwork elements connecting the electric actuator and the lever mechanisms that open and close the cover and the other elements making up the ventilation system.

The objects and advantages listed above are highlighted in greater detail in the description of a preferred embodiment of the invention, which is provided here below, by way of non-limiting example, making reference to the attached drawings, wherein:.

An overview of the smoke and heat exhaust ventilation system of the invention is shown in Figures from <NUM> to <NUM>, where it is indicated as a whole by <NUM>.

Furthermore, <FIG>, <FIG>, <FIG> represent enlarged details of the ventilation system shown in the overall views of Figures from <NUM> to <NUM>.

With particular reference to <FIG>, it can be observed that the smoke and heat exhaust ventilation system <NUM>, which here below is referred to just with the term "ventilation system <NUM>" for the sake of description simplicity, comprises a base <NUM> delimited by a counter frame <NUM> and arranged on the periphery of a through opening <NUM> made in the structure of a building and a cover <NUM> delimited by a frame <NUM> associated with the counter frame <NUM> of the base <NUM> by means of hinges <NUM>.

The through opening <NUM> places one or more rooms of the building in communication with the external environment and in case of fire the hinges <NUM> allow the cover <NUM> to rotate and open so that smoke and heat can be let out.

For this purpose, the ventilation system <NUM> is provided with rotation means <NUM> suited to rotate the cover <NUM>, which can be observed in particular in <FIG> and in the successive Figures from <NUM> to <NUM>, and which comprise a linear electric actuator <NUM>, here below referred to just with the term "actuator <NUM>" for the sake of description simplicity, having a power unit 11a which sets a stem <NUM> moving linearly inside a cylinder <NUM>.

The rotation means <NUM> comprise also an articulation unit <NUM> operatively connected to the actuator <NUM> and comprising at least one first rod <NUM> visible in particular in Figures from <NUM> to <NUM> and connecting the head <NUM> of the stem <NUM> of the actuator <NUM> to the counter frame <NUM> of the base <NUM> and at least one second rod <NUM> connecting the cylinder <NUM> to the counter frame <NUM> of the base <NUM>.

Preferably but not necessarily, in order to guarantee good stability during the movement, in the embodiment of the articulation unit <NUM> described herein there are two first rods <NUM> placed side by side and parallel to each other and two second rods <NUM> also placed side by side and parallel to each other.

According to the invention, the articulation unit <NUM> comprises also at least one connecting rod <NUM> that connects the head <NUM> of the stem <NUM> to the frame <NUM> of the cover <NUM>.

In order to guarantee good stability during movement two connecting rods <NUM> are provided, placed side by side and parallel to each other.

More specifically, it can be observed that each connecting rod <NUM> has the first end 18a hinged to the head <NUM> of the stem <NUM> of the actuator <NUM> and the second end 18b hinged to the crosspiece <NUM> of the cover <NUM>, which is included and fixed between two opposite sides 6a, 6b of the frame <NUM> that delimits the cover <NUM> peripherally.

Regarding the first rods <NUM> and the second rods <NUM>, it can be observed that each first rod <NUM> has the first end 15a hinged to the head <NUM> of the stem <NUM> of the actuator <NUM>, while each second rod <NUM> has the first end 17a hinged to the cylinder <NUM>.

Furthermore, the second end 15b of each first rod <NUM> and the second end 17b of each second rod <NUM> are both connected to the counter frame <NUM> as they are hinged to a supporting bracket <NUM> that belongs to the crosspiece <NUM> of the counter frame <NUM>, which is included between and fixed to the ends of two opposite sides 3a, 3b of the counter frame <NUM> of the base <NUM>.

It can also be observed that the second end 15b of each first rod <NUM> and the second end 17b of each second rod <NUM> are hinged to distinct points of the supporting bracket <NUM>.

More specifically, the second end 17b of each second rod <NUM> is arranged within the area perimetrically delimited by the base <NUM> and located below the plane X defined by the upper surface 3c of the counter frame <NUM> and the second end 15b of each first rod <NUM> is located above said plane X defined by the upper surface 3c of the counter frame <NUM>.

Furthermore, the second end 15b of each first rod <NUM> and the second end 17b of each second rod <NUM> are aligned according to a direction Z that is inclined with respect to a vertical direction and incident on the plane X defined by the upper surface 3c of the counter frame <NUM>.

Finally, it can be observed that the articulation unit <NUM> also comprises at least one third rod <NUM>, in the embodiment described herein two third rods <NUM> placed sided by side and parallel to each other, each of which connects a first rod <NUM> and a second rod <NUM> corresponding to it, and in each third rod <NUM> it is possible to identify a first end 21a hinged to an intermediate area of the first rod <NUM> and a second end 21b hinged to an intermediate area of the second rod <NUM>.

In this way, the actuator <NUM> and the articulation unit <NUM> are kinematically connected to each other, and when the actuator <NUM> is operated they cooperate with each other to rotate the cover <NUM>, as illustrated below with reference to the figures.

The ventilation system <NUM> comprises also coupling means <NUM> which are configured in such a way as to lock the cover <NUM> onto the counter frame <NUM> when the linear electric actuator <NUM> is in the rest condition and the frame <NUM>, which delimits the cover <NUM>, is arranged so that it faces and is in contact with the counter frame <NUM> of the base <NUM>, as shown in <FIG>.

Furthermore, the coupling means <NUM> are configured to be also able to open the cover <NUM> after it has been released from the counter frame <NUM>, which takes place automatically when the actuator <NUM> is activated, as described in greater detail below.

It can be observed that the coupling means <NUM> comprise a revolving rod <NUM>, visible also in the detail <FIG>, associated with the cover <NUM> through supporting means, not indicated in the figures and supported by the frame <NUM>, to which rod one or more hook-shaped coupling elements <NUM> are fixed and thus rotate rigidly with the revolving rod <NUM> when it is set rotating according to its longitudinal axis.

In the particular embodiment described herein, and as shown in <FIG> and <FIG>, the hook-shaped coupling elements <NUM> are three and two of them are arranged at the ends of the revolving rod <NUM>, while one of them, instead, is arranged in an intermediate position on the revolving rod <NUM> itself, as shown in <FIG>.

In another embodiment, the hook-shaped coupling elements <NUM> can be present in any number and be arranged in any position along the revolving rod <NUM>.

Hook-shaped coupling counter elements <NUM> are also provided, which belong to the counter frame <NUM> of the base <NUM> and are configured to cooperate with the hook-shaped coupling elements <NUM>.

Finally, there is a tie rod <NUM> which connects the rod <NUM> to a manoeuvring lever <NUM> associated with the cover <NUM> and visible in <FIG>, which is configured to activate the tie rod <NUM> and release the hook-shaped coupling elements <NUM> from the hook-shaped coupling counter elements <NUM> when the thrusting action of the head <NUM> of the stem <NUM> of the actuator <NUM> acts on the manoeuvring lever <NUM> and makes it rotate, as can be observed in <FIG>.

In fact, as clearly shown in <FIG>, the manoeuvring lever <NUM> is revolvingly associated with the cover <NUM> through a rotation pin 39a which constrains it to a fixed support <NUM> fixed to the crosspiece <NUM> of the cover <NUM> itself.

Furthermore, the manoeuvring lever <NUM> is provided with a reference plane <NUM> suited to come into contact with the head <NUM> of the stem <NUM> of the actuator <NUM>, as can be observed in particular in <FIG>.

It can also be observed, in particular in Figures from <NUM> to <NUM> and in the detail <FIG>, that the tie rod <NUM> has the first end 35a fixed to a projecting coupling element <NUM> belonging to the revolving rod <NUM> and the second end 35b fixed to the manoeuvring lever <NUM> through a fork <NUM> and a pin <NUM> passing therethrough. The ends of the tie rod <NUM> can be connected to the revolving rod <NUM> and to the manoeuvring lever <NUM> even through means that are different from those described.

When the cover <NUM> is in the closed position, as shown in <FIG>, if the head <NUM> of the stem <NUM> of the actuator <NUM> counteracts the reference plane <NUM> of the manoeuvring lever <NUM>, the thrusting action produced by the actuator <NUM> generates, with respect to the rotation pin 39a, a torque which causes the rotation of the manoeuvring lever <NUM> around the rotation pin 39a and places the tie rod <NUM> under traction.

The traction of the tie rod <NUM> in turn causes the rotation of the rod <NUM> around its longitudinal axis and of the hook-shaped coupling elements <NUM> connected to it, which release the respective hook-shaped coupling counter elements <NUM>, thus allowing the opening of the cover <NUM> to start, as shown in <FIG>.

The revolving rod <NUM> is also associated with elastic means <NUM> visible in particular in <FIG>, which are configured to make the rotation of the revolving rod <NUM> elastic, so that the hook-shaped coupling elements <NUM> spontaneously snap on the hook-shaped coupling counter elements <NUM> when the manoeuvring lever <NUM> is free from contact with the head <NUM> of the stem <NUM> of the actuator <NUM> and the frame <NUM> of the cover <NUM> is lowered so that it faces and rests against the counter frame <NUM> of the base <NUM>, in the position which can be observed in <FIG>.

Preferably but not necessarily, the elastic means <NUM> comprise a cylindrical spring 41a wound externally on the revolving rod <NUM> and having one end fixed to the same revolving rod <NUM> and the opposite end in contact with the crosspiece <NUM> of the cover <NUM>.

It can be observed, in particular in <FIG> and <FIG>, that the elastic means <NUM>, the tie rod <NUM> and the manoeuvring lever <NUM> are associated with the cover <NUM>, being arranged on and connected to the crosspiece <NUM> included between two opposite sides 6a, 6b of the frame <NUM> which delimits the cover <NUM> peripherally.

From an operational point of view, with reference to <FIG> showing the side sectional view of the ventilation system <NUM> with the cover <NUM> arranged in the closed position, it can be observed that the head <NUM> of the stem <NUM> of the actuator <NUM> is spaced from the reference plane <NUM> of the manoeuvring lever <NUM> and the hook-shaped coupling elements <NUM> are coupled with the respective hook-shaped coupling counter elements <NUM>, as shown in <FIG>, and are maintained in the coupled position by the elastic torsion exerted by the cylindrical spring 41a on the revolving rod <NUM>.

In this configuration the cover <NUM> is and remains permanently closed.

If the actuator <NUM> is activated, when the head <NUM> of its stem <NUM> comes into contact with the reference plane <NUM> of the manoeuvring lever <NUM>, the latter rotates around the rotation pin 39a and places the tie rod <NUM> under traction.

The traction applied to the tie rod <NUM> overcomes the elastic force of the cylindrical spring 41a and causes the rotation of the revolving rod <NUM>, which separates the hook-shaped coupling elements <NUM> from the corresponding hook-shaped coupling counter elements <NUM> and causes the cover <NUM> to start opening.

From this moment, the cover <NUM>, which is not coupled with the counter frame <NUM> any longer, can be opened through the movement of the stem <NUM> of the actuator <NUM>, passing through all the configurations shown in Figures from <NUM> to <NUM> until reaching the configuration of maximum opening, which corresponds to an angle of approximately <NUM>° and is shown in <FIG>.

It should be noticed that when the stem <NUM> is withdrawn from the cylinder <NUM>, the length of the actuator <NUM> increases and the articulation unit <NUM> makes the actuator <NUM> rotate clockwise so that it progressively assumes all the different positions shown in Figures from <NUM> to <NUM>.

During these movements, the head <NUM> of the stem <NUM> of the actuator <NUM> axially compresses the connecting rod <NUM> which, being rigid and indeformable and forming an angle α, always smaller than a straight angle, with the crosspiece <NUM> of the cover <NUM>, starting from the configuration represented in <FIG> is forced to rotate rigidly counter clockwise, thus moving its second end 18b upwards until reaching the configuration shown in <FIG>, in which the cover <NUM> is open in a position that is substantially orthogonal to the base <NUM>.

In this way, the second end 18b of the connecting rod <NUM>, being connected to the crosspiece <NUM>, exerts a thrusting action on the cover <NUM>, lifting it due to the rotation around the hinges <NUM>.

In addition to the operational description provided above, in order to illustrate the invention correctly and to show that the set objects of the invention have been achieved, reference is made to Figures from <NUM> to <NUM>, which illustrate how the stem <NUM> of the actuator <NUM> is lengthened as a result of different opening angles of the cover <NUM>.

In particular, Figures from <NUM> to <NUM> compare, for some identical opening angles of the cover <NUM>, the lengthening C of the stem <NUM> in the case of the invention, in which its head <NUM> is connected to the crosspiece <NUM> through the connecting rod <NUM>, with the lengthening C' that would result if the stem of the actuator, schematically represented with a thick broken line, had the head <NUM>' directly connected to the crosspiece <NUM>, as is the case in the ventilation systems known in the art.

Substantially, in Figures from <NUM> to <NUM> it is shown a comparison between the values of the lenghtening C and C', respectively in the case of the invention, in which the head <NUM> of the stem <NUM> is connected to the crosspiece <NUM> through the connecting rod <NUM>, and in the case of the known art, indicated with a thick broken line, in which the head <NUM> of the stem <NUM> is directly connected to the crosspiece <NUM>.

Switching from the configuration represented in <FIG>, which corresponds to an opening angle of the cover <NUM> of approximately <NUM>° and in which the lenghtening C and C' of the stems are substantially equal to each other, to the configuration shown in <FIG> and to the final configuration of maximum opening, equal to approximately <NUM>°, it can be observed that the lengthening C' continues to increase considerably with respect to the lengthening C.

This proves that if the head <NUM>' of the stem of the actuator were directly connected to the crosspiece <NUM> of the cover <NUM>, it would be necessary to use an actuator with a longer stem and thus a larger size, and consequently more expensive than that used in the ventilation system <NUM> of the invention.

However, it is essential to take into consideration also the presence of the third rod <NUM> which connects the first rod <NUM> and the second rod <NUM> together.

In fact, it can be observed in the figures that the lengthening of the stem <NUM> of the actuator <NUM> causes the first rod <NUM> and the second rod <NUM> to rotate clockwise, as the third rod <NUM> that connects them makes both of them rotate clockwise with respect to the respective second end 15b and second end 17b.

In this way, the rotation of the second rod <NUM> causes the progressive lifting of the actuator <NUM>, which on the contrary in the absence of the third rod <NUM> would not be lifted, with respect to the initial position of <FIG> when the cover <NUM> is closed.

Therefore, to obtain the openings shown in Figures from <NUM> to <NUM> it would be necessary to use an actuator having an extremely longer and thus more cumbersome and above all more expensive stem compared to that which, instead, can be used in the ventilation system <NUM> of the invention thanks to the presence of the third rod <NUM>.

Thus, in the ventilation system <NUM> of the invention the connecting rod <NUM> and the third rod <NUM> operatively interact during the stroke of the stem <NUM> of the actuator <NUM> and produce a synergy which, in comparison with the known art and given the same opening angles of the covers, makes it possible to considerably reduce the stroke of the stem of the actuator being used.

Consequently, it is possible to use smaller, less cumbersome, and also less expensive actuators, thus achieving the object of the invention.

It is also important to note that the articulation unit <NUM> is sized in such a way that when the cover <NUM> is opened by an angle of approximately <NUM>°, as shown in <FIG>, the second rod <NUM> is arranged in a substantially horizontal direction and the actuator <NUM>, instead, is arranged in a substantially vertical direction.

In this configuration, the head <NUM> of the stem <NUM> is arranged in the limit condition in which it is in contact with the manoeuvring lever <NUM> and directly exerts on the crosspiece <NUM> the maximum thrust to lift the cover <NUM>.

Once the opening angle of approximately <NUM>° has been exceeded, the head <NUM> of the stem <NUM> is not in contact with the manoeuvring lever <NUM> any longer, as can be observed for example in <FIG>, and the connecting rod <NUM> transmits to the crosspiece <NUM> the thrust force required to lift the cover <NUM> which is produced by the lengthening of the stem <NUM> of the actuator <NUM>.

It should also be observed that, starting from the geometric and functional configuration of the articulation unit <NUM> shown in <FIG>, the angle α formed by the connecting rod <NUM> and the crosspiece <NUM> during the progressive opening of the cover <NUM> keeps decreasing.

Experimental tests have made it possible to verify that as the amplitude of the angle α decreases the opening of the cover <NUM> is accelerated continuously until reaching the position of maximum opening shown in <FIG>.

The advantage represented by a higher opening speed of the cover <NUM> compared to the known art is thus achieved.

Finally, it can be observed that the rotation means <NUM> suited to rotate the cover <NUM>, comprising the articulation unit <NUM> and the actuator <NUM> cooperating with each other, in the position shown in Figures from <NUM> to <NUM> are capable of moving a cover <NUM> of any size and can therefore be applied to any ventilation system of any size.

It may be necessary to vary the power of the power unit 11a so as to adapt it to the weight of the cover <NUM> to be lifted.

It is thus possible to standardize the construction of the ventilation systems <NUM> using always the same rotation means <NUM> for rotating the cover <NUM> and modifying only the dimensions of the base <NUM> and of the cover <NUM> according to the user's needs.

There are, therefore, evident economic advantages deriving, for the manufacturer, from the smaller number of components to be managed in the warehouse, and, for the user, from an increased availability of spare parts for maintenance activities.

Obviously, the ventilation system <NUM> of the invention will be electrically connected to batteries fed by the electrical network in buffer mode and will be managed by a special control unit comprising sensors suited to detect smoke, heat, or other exceptional conditions so as to activate the opening of one or more ventilation systems <NUM> of the invention in case of fire or other anomalous conditions.

The cover <NUM> can be of any type and shape, and can be made from any opaque, translucent, or transparent material.

Furthermore, the ventilation system <NUM> of the invention can also serve as a skylight and be opened and closed as desired by the user to ventilate rooms. According to the above, it can be understood that the ventilation system <NUM> of the invention achieves all the set objects.

Claim 1:
Smoke and heat exhaust ventilation system (<NUM>) comprising:
- a base (<NUM>) delimited by a counter frame (<NUM>) and arranged peripherally with respect to a through opening (<NUM>) made in the structure of a building, said through opening (<NUM>) being configured to place the inside of one or more rooms of said building in communication with the external environment;
- a cover (<NUM>) delimited by a frame (<NUM>) associated with the counter frame (<NUM>) of said base (<NUM>) by means of hinges (<NUM>) that allow said cover (<NUM>) to rotate to open and close said through opening (<NUM>);
- rotation means (<NUM>) suited to rotate said cover (<NUM>), comprising:
- a linear electric actuator (<NUM>) comprising a power unit (11a) which sets a stem (<NUM>) moving linearly inside a cylinder (<NUM>);
- an articulation unit (<NUM>) operatively connected to said linear electric actuator (<NUM>) and comprising at least one first rod (<NUM>) connecting the head (<NUM>) of said stem (<NUM>) to said counter frame (<NUM>) and at least one second rod (<NUM>) connecting said cylinder (<NUM>) to said counter frame (<NUM>);
said articulation unit (<NUM>) also comprising at least one connecting rod (<NUM>) which connects said head (<NUM>) of said stem (<NUM>) to said frame (<NUM>),
wherein said articulation unit (<NUM>) also comprises at least one third rod (<NUM>) which connects said first rod (<NUM>) and said second rod (<NUM>) together, wherein in said third rod (<NUM>) it is possible to identify a first end (21a) hinged to an intermediate area of said first rod (<NUM>) and a second end (21b) hinged to an intermediate area of said second rod (<NUM>);
characterized in that said connecting rod (<NUM>) comprises a first end (18a) hinged to said head (<NUM>) of said stem (<NUM>) and a second end (18b) hinged to a crosspiece (<NUM>) fixed between two opposite sides (6a, 6b) of said frame (<NUM>).