FR2710361A1 - Self-lifting platform - Google Patents

Abstract

The invention relates to self-lifting platforms used for the construction, renovation, or upkeep of façades of buildings. Essentially described is a structure with two masts (12 and 14) supporting a platform (10). Each mast has a rack and the platform has two motors each one interacting with one of the masts. Means are provided for improving safety, and especially for preventing any risk of tipping of the platform which might be due to a breakdown in one of the holding motors. These means include, in particular, a shaft for synchronising the two motors, and detectors making it possible to detect exaggerated loading of one of the motors, in order to cut off the power supply to the two motors if just one motor is not enough to keep the platform horizontal.

Description

SELF-LIFTING PLATFORM
The invention relates to self-elevating platforms or cabins used for the construction, renovation and exterior maintenance of buildings of significant height (typically several tens of meters in height). The term platform here also means elevation machines, in particular modular machines, which also includes passenger elevators.

 By building is meant here residential or administrative or industrial constructions, etc., but also, by extension, other structures in which self-elevating platforms may be necessary, for example ships in dry dock for construction, maintenance or repair.

 The object of the invention is to propose improvements to the structures of existing jack-up platforms, in order to bring there improvements in particular in terms of safety, solidity, and ease of use.

 It will of course be understood that safety is an extremely important factor, construction sites for tall buildings being unfortunately very often still the scene of serious industrial accidents.

 Accidents related to jack-up machines can be due either to faults in their construction, or to improper use which makes them dangerous.

 This is the reason why the invention proposes improvements aimed at limiting the risks as much as possible on these two planes.

 According to a first aspect of the invention, a self-elevating platform structure is proposed which comprises two vertical masts spaced from one another, each provided with a rack, with a movable carriage mounted on each mast and sliding in rolling along this mast; each carriage carries a respective motor cooperating with the rack; a platform connects the two carriages to constitute a work or transport surface for materials or people (elevators); each carriage comprises a housing for a vertical movable plate which carries the motor and which can move vertically and laterally in this housing; springs are provided between the plate and the housing to allow a damped transmission of the force exerted by the plate on the carriage when the motor which cooperates with the rack tends to drive the plate and therefore the carriage; mounted on each carriage, there is a free toothed pinion (that is to say not driven directly by the motor) which cooperates with the rack and which is rotated when the carriage moves; a transmission shaft extending between the two masts connects the free toothed pinions of the two carriages so that they rotate in synchronism; finally, at least one detector is provided in each carriage to detect the compression of the transmission springs; it is connected to a control of the two motors to cut the power to the two motors in the event of excessive compression of the springs. The device can be replaced or supplemented by strain gauges.

 This structure, which will be explained in more detail below, is intended to prevent an engine failure causing a tilting of the platform (driven on one mast but not on the other).

 According to another aspect of the invention, when a self-elevating platform is used to mount people and materials along an exterior facade of a building, in order to be able to enter this building through an overhead window, a block is provided. door protecting access to this window, this block being fixed to the two hoisting masts of the platform and not to the building; a floor plate fixed to the door block (and therefore integral with the mast) covers the gap that may exist between the lifting platform and the building facade, eliminating the risks inherent in this gap (sprains, falling objects, etc. ), and this even when the flexibility of the mast results in the existence of a significant clearance between platform and facade.

 According to yet another aspect of the invention, there is provided, accompanying the self-elevating structure for the transport of people and materials, a door block placed at the bottom of the hoisting masts to protect from access below the platform , the peculiarity being that this door block is mounted movably in height along the mast to allow the level at which the platform reaches the bottom of the stroke to be adjusted.

This allows in particular to make the platform arrive at different heights depending on the type of loading and unloading that we want to do from the bottom loads of people at the bottom, at ground level, loading materials directly from the bucket d 'a truck, etc.

 According to yet another aspect of the invention, provision is made for adding platform extensions on either side and all around the masts, which makes it possible to significantly increase the length of the platform for uses at low height. not requiring anchoring or possibly only at the top of the mast. The advantage of this solution is that the work floor is continuous along the facade.

Other characteristics and advantages of the invention will appear on reading the detailed description which follows and which is given with reference to the appended drawings in which
- Figure 1 shows a general view of a twin mast self-elevating platform placed in front of a building;
- Figure 2 shows the cooperation of a pinion and a rack for driving the platform along the hoisting masts;
- Figure 3 shows a top view of a carriage integral with the platform, this carriage carrying a drive motor;
- Figure 4 shows a drive with double toothed pinion on the rack;
- Figure 5 shows the floating mounting of the carriage drive plate, with the damping springs;
- Figure 6 shows the auxiliary gear used for mutual coupling of the motors of the two masts;
- Figure 7 shows the synchronization shaft of the two motors;
- Figure 8 and Figure 9 show, in side view and in top view, a door unit mounted fixed relative to the mast instead of being mounted fixed relative to the building;
- Figure 10 and Figure 11 show, in side view and in top view, a lower mast door block, mounted fixed relative to the mast but movable in height along the masts;
- Figures 12, 13 and 14 show, in side view, in top view and in section, the self-elevating platform in the case of a single attachment to the top of the masts;
- Figure 15 shows an improvement of the invention with which the dangers for people working at height are limited;
- Figures 16 and 17 show an improvement of a lowering brake of the platform.

 In Figure 1, to understand the context of the invention, there is shown a general view of a lifting structure of a self-elevating platform with two masts, placed along the facade of a building under construction or in renovation. This structure makes it possible to mount a work platform along this facade at any desired height, as and when required.

 The working platform is designated by the reference 10. It extends between two masts 12 and 14 and even partly cantilevered beyond the masts. The platform is of course fitted with all the safety barriers necessary to protect the people working on the platform and those below it (protection against falling objects).

 The masts are supported at their base on the ground, in principle by means of supports, 16 and 18 respectively, in the form of plates kept horizontal by adjustable jacks 20 resting on the ground.

 The masts are fixed from place to place (for example every 5 meters) to the facade of the building, by anchors 22 strong enough to withstand the tensile and torsional forces exerted on the masts by the weight and movements of the platform 10 .

 The movement of the platform is ensured by electric motors carried by the platform itself, motors which cooperate with rack and pinion carried by the masts.

 This is why we see in Figure 1 below the platform and against each of the masts of the drive blocks 24 and 26 which constitute forklifts integral with the platform and driving the latter in their movements along the mast.

 A rack 28 is visible on the right mast 14. That of the mast 12 is not shown in FIG. 1.

 Each carriage carries at least one electric motor coupled to a reduction gear, with at least one toothed pinion cooperating with the corresponding rack to ensure, during the rotation of the motor, movement of the carriage.

 The motors are connected by electric power cables 30 to a power source 32. The motor control is preferably located on the platform, so that the occupants can maneuver it themselves; but it is also possible to provide a command from below or a double command, both from below and by the occupants.

 It will be understood that the two motors must operate simultaneously, otherwise the platform will tilt and exert considerable lifting forces on the masts and anchors, leading to the destruction of the structure and to fatal accidents.

 We will describe below the provisions that are adopted to avoid these risks.

 First of all, FIG. 2 represents the cooperation of a motor and the rack. The gear pinion output from the reducer, designated by the reference 40, has teeth 42 which mesh with the teeth 44 of the rack 28; the teeth 44 of the rack are machined in a first face of a metal bar which is welded or bolted all along the hoist mast. A pressing roller 48 comes to bear against an opposite face 46 of this bar to keep the teeth of the pinion 40 nested in the teeth of the rack.

 For this, the roller 48 and the pinion 40 are both mounted in rotation on a common metal plate 50. The motor and the reduction gear (not visible because placed behind the plate) are fixed on the plate 50.

There is no play or practically no play between the roller 48 and the pinion 40 so that there is no risk of disengagement of the gear.

 The plate 50 will therefore be the main drive member of the platform on the hoist mast.

The arrangement is identical on the two masts.

 However, this plate 50 is not directly integral with the carriage (or drive unit) 24 or 26 of FIG. 1. The structure which makes it possible to drive the carriage 26 from the plate 50 is shown in FIG. 3 Unlike Figure 2 which is a horizontal view, the view of Figure 3 is a top view.

 The carriage 26, which is integral with the platform 10, comprises for example metal plates 52 or a profile constituting its main framework. The platform is secured by any conventional means (welding, bolts, rivets, etc.) to this frame.

 The rack 28 is welded or bolted to the mast 14, the framework of which is also seen in FIG. 3.

 In the carriage 26, a housing 54 has been provided for the drive plate 50, housing in which the latter can slide vertically over a certain distance (a few centimeters or tens of centimeters at most) and horizontally (of the order of a centimeter ). The housing 54 is defined for example by metal plates or profiles 56 welded or bolted to the frame 52 of the carriage.

 Horizontally, there is no or almost no clearance of the plate 50 in its housing in the direction perpendicular to the plate but there is a clearance (2 cm for example) parallel to the plate, as shown.

 In Figure 3, we see a geared motor 58 rigidly fixed to the plate 50, the axis of the geared motor passing through the plate to drive the pinion 40 placed on the other side thereof opposite the rack.

 The pressure roller 48 is also rigidly fixed to the plate in a position such that it comes to bear against the non-toothed face of the rack. This roller turns freely around an axis which crosses the plate.

 It should be noted that other means could be provided to keep the pinion 40 meshed on the rack, for example means which bear not on the rear face of the rack but on other parts of the mast. The rotating roller fixed to the plate is however the preferred means. Furthermore, the lateral escape of the pinion 40 from the rack is prevented by a profile (not shown) integral with the carriage 26 and bearing in reaction and sliding along the mast (14).

 Although a single drive pinion 40 has been shown coupled to the rack, it will be understood that it is also possible to provide a structure with two pinions, as shown in FIG. 4: the motor drives a first toothed pinion 41 which n is not coupled to the rack, this first pinion driving two identical satellite pinions 43 and 45 rotating in the same direction; the latter are coupled to the rack and two pressure rollers 47 and 49 are placed on the other side of the rack, opposite the pinions 43 and 45 respectively. The transmission of effort is better distributed. The radial force exerted on the gear motor is eliminated. The invention, with floating plate and double satellite pinion, aims to distribute the force equally on the two pinions. Indeed, in the case of rigid mounting, (without floating plate), the torques generated at the level of the guide carriages are much greater than those generated by the recoil or the advancement of the teeth meshing in the rack.

Also the force transmitted between a satellite pinion and the rack varies from zero to 100% depending on whether this pinion is more buried than the other or at the junction of two racks, the pitch changes. In this case one of the pinions works more than the other.

 With the floating plate, the pinions are automatically adjusted by entering or leaving more or less the rack, as the boogies distribute the effort equally (50% -50%) on two rollers or wheels.

 FIG. 5 represents a horizontal view, perpendicular to the plate 50, showing the plate in its housing 54, and especially showing the connection by springs between the plate and this housing.

 At the upper part of the plate 50, horizontal walls 60 close the upper part of the housing 54; springs, for example two springs 62 and 64, are placed between the plate 50 and these upper horizontal walls. The plate can exert an action on the walls 60 and more generally on the carriage 26 or the platform 10 only by means of these movement transmission springs. The transmission is therefore damped and there is no shock when the engines are started. The springs can be replaced by silent blocks or even gas shock absorbers.

 Likewise, at its lower part, the plate is separated from the lower horizontal walls 66 of the housing 54 by means of springs 68 and 70.

 The plate can slide vertically in its housing, but it must then exert a compressive force on the springs. The state of compression of the springs can be measured either by deformation detectors, such as strain gauges, or by detectors of displacement of the plate relative to the housing. Such detectors are provided, and are designated by the reference 72. They serve according to the invention to provide security. They can be simple so-called limit switches, but are preferably strain gauges.

 With twin mast machines, either with independent motors not linked by a synchronization order, or with central motors, the movement is distributed symmetrically. But in the first case, it is not possible to guarantee mechanical synchronization between the two motor elements (synchronization does not offer any guarantee in the event of failure of the latter or in the event of manual descent intervention with no electricity).

 In the second case, it is not possible to detect an overload, load imbalance or damage to a transmission member.

 The invention makes it possible to remedy all known risks of damage.

 Also shown in Figure 4 side shoes 74 limiting the horizontal clearance parallel to the plate and made of a material facilitating the sliding of the plate without friction.

 When the motor 58 rotates and drives the toothed pinion 40, the plate rises along the rack. The upper springs 62 and 64 compress proportionally to the resistance opposed by the weight of the platform 10; when the balance is reached between this resistance and the compression force of the spring, the carriage 26 is driven in height as well as the whole of the platform (the motors of the two carriages 24 and 26 being of course actuated simultaneously). The detectors 72 can precisely serve to detect an exaggerated compression of the springs, sign of an exaggerated resistance opposed by the platform to the movement that one seeks to impart to it.

 The springs allow in any case to start and stop smoothly: they dampen the acceleration of the engine.

 In the event of a motor failure on one of the masts, the platform continues to rise on one side only, the other being stopped or even tending to descend. The effort exerted on the rising side will be much greater; the detector 72 can be used to urgently interrupt the supply of the engine which continues to run.

 However, this is not enough. This is why a direct mechanical coupling is provided between the drive systems of the two masts, associated with a detection of excessive compression of the damping springs. By direct coupling, it is ensured that in the event of an engine failure, the two carriages continue to be driven by the engine which is not broken down; there is therefore no imbalance of the platform; it remains substantially horizontal and exerts no lifting forces on the masts; but then the motor which continues to work becomes overloaded. The springs 62 and 64 tend to compress more; the detectors 72 detect the deformation or shortening of the length of the springs, and trigger the engine to stop if a threshold is exceeded. This means that as soon as an engine is overloaded (overload or poor distribution of the load, or damage in a geared motor unit), the two motors are then stopped, which is much less dangerous than a single motor inefficient without anyone noticing.

 Thus, in the event of an overload, the platform cannot start. You have to either unload a part, or better distribute the load to be able to start. It should be noted that an audible and / or luminous alarm can be provided to warn of an overload, even when static.

 In the event of damage to a geared motor assembly, each geared motor being calculated to hold the total load, and the synchronization shaft being calculated to also transmit all the load, the platform is stopped instantly and only a manual descent is possible to descend and remedy the damage safely.

 In general, the motors are provided with centrifugal brakes which limit the descent speed of the platform to an acceptable value. It is also possible to provide automatic blocking systems released in the event of a power interruption, for example cam cleats, self-locking cams, brake pads integral with the carriage and applied strongly against the rack to slow down the descent.

 The invention is particularly advantageous in combination with eddy current brakes (comprising a metal disc, generally of copper, rotating in the air gap of a magnet).

These brakes can be mounted either on the motor pinion or on the synchronization shaft itself.

 FIGS. 16 and 17 show such a device where a motor 58 has a metal disc 145 rotating at the end of the shaft in the air gap of a magnet 146.

When the engine is to start, an electric actuator 147 moves the permanent magnet away from the copper disc and then, after control by a position contact, the engine starts. In the event of an interruption in the power supply, the permanent magnet is replaced by the push of a spring 148. The descent is regulated by the electromotive forces generated in the copper disc secured to the motor shaft. This technique makes it easy to periodically perform functional tests of the parachute brake. Indeed, with the old techniques with irreversibly movable weights, after a test, you have to disassemble the whole brake to put it back on hold (at the risk of badly reassembling it).

 To obtain a mechanical coupling of the drive systems of the two masts, the procedure is preferably as explained below with reference to FIGS. 6 and 7.

 On each mast, an auxiliary pinion is provided, carried by the carriage, cooperating with the rack.

But under normal operating conditions, this pinion does not drive the carriage. On the contrary, it is rotated by the movement of the carriage. Going up, the carriage moves relative to the rack, and this movement therefore rotates the auxiliary pinion.

 In Figure 6, we see the plate 50, the pinion 40 which causes the plate to rise, and the pressure roller 48, all coupled to the frame 52 of the carriage by springs. And we also see the auxiliary pinion 80 meshed on the rack 28, also with a pressure roller similar to the roller 48.

 In the example shown, the auxiliary pinion 80 is mounted on a second plate 90. This plate 90 is preferably secured to the carriage. But it can be similar to the plate 50, sliding in a housing 94 similar to the housing 54, this housing being integral with the carriage. damping springs are also provided between the plate 90 and the housing 94.

In this case, its state is also monitored by a detector 72 bis of the same type as the detector 72.

 But it can also be provided that the auxiliary pinion and its roller are mounted on the same plate 50 as the main drive pinion if it is possible from the point of view of space. In the case where they are mounted on different plates, the plate 90 carrying the auxiliary pinion is not necessarily mounted in a floating manner (that is to say by means of springs) like the plate 50. It is moreover possible while the auxiliary pinion is directly mounted on the carriage and not on a movable plate.

 Instead of the auxiliary pinion 80 being coupled to a motor, it is directly coupled to a drive shaft which extends between the two masts 12 and 14 and which is connected on the other side to the corresponding auxiliary pinion. The two auxiliary gears are therefore directly coupled in rotation.

 This is what we see in Figure 7 which shows in a simplified way (so as not to burden the diagram) only the coupling between the auxiliary pinions.

 The references are the same as in the previous figures for the mast 14. For the mast 12 the references are the same with the index "prime"; thus, the rack for the mast 12 is designated by 28 '. The carriages 26 and 24 are not shown; but they are connected to the auxiliary plates 90 and 90 'by springs, as has been explained.

 The transmission shaft, which can also be called synchronization shaft, is designated by 100. It extends over the entire length separating the masts 12 and 14 in FIG. 1.

 Under normal conditions, the auxiliary pinions rotate in synchronism, each driven by the movement of the corresponding carriage, since the two motors operate and rotate at the same speed. The platform rises or falls horizontally.

 In the event of a failure of the two motors (power failure), centrifugal braking plays its role of "parachute". With the invention, however, a parachute brake can also be mounted directly on the shaft 100 (in case the two motors are down).

 In the event of weakness or failure of a single motor, or more generally of imbalance between the motors, one of the carriages will tend to climb faster than the other; the drive shaft will tend to make up for the difference, but by making the engine work more on the side that goes up faster.

 The spring compression detectors 72 will be able to quickly detect an excessive compression threshold and control the interruption of the current in the overloaded motor or in the two motors. The detectors can be simple limit switches. They indeed detect the state of compression of the springs either directly (they are then for example strain gauges) or indirectly, for example by detection of the position of the plate 50 in its housing 54.

This has solved a serious safety problem inherent in structures with two masts. We can therefore safely use this type of structure which has the advantage, compared to structures with a single mast
- to be much more stable
- not to exert a twist on the mast during the movements of the platform,
- to authorize longer platform lengths.

 Another safety problem resolved here is the risk caused by the mismatch between the position of the jack-up platform and the facade of the building at the places where a passage must be provided between the platform and the building.

 This is the case when accessing the interior of the building through a high window, accessible only by the platform. The platform, which is normally surrounded by protective barriers against falling people or objects, then has a passage opening facing the building. In general, the building is also provided with a protective barrier which can be opened at the access point, in the same way as a modern elevator door: the door is integral with the building in which one accesses, even if there is also a door in the mobile part of the lift.

 A problem which results from this arrangement in the case of jack-up platforms is the fact that the flexibility of the hoisting mast or masts can cause a gap to appear between the facade of the building and the platform; this interval can be several tens of centimeters; it is dangerous, in particular by the risk of falling objects that it can cause.

 It is proposed according to the invention that a fixed door unit, placed at the location of the access opening in the building, be mounted integral with the mast or masts, and not integral with the building.

 This structure is particularly advantageous in the case of constructions with two masts, the door unit being fixed on a cross member secured to the two masts. Since the platform is integral with the masts, and the fixed door unit is also integral with the masts, there is no significant risk of play between the two.

 Figure 8 and Figure 9 show, respectively in side view and in top view, the corresponding construction.

 The masts are designated by the references 12 and 14, the platform by 10, the facade by 110 and the access window by 112; the structure of the fixed door unit, designated by 113, comprises a frame 114 integral with the two masts and therefore extending horizontally between them, and a horizontal plate 116. This plate extends from the platform 10 (when it is at the correct height) to the interior of the building through the window 112. The clearance between the platform 10 and the plate 116 can be very reduced (a few centimeters at most). The tray 116 is surrounded by protective barriers 118, and passage doors 120 are provided on the door block; doors 122 are in principle also provided on the platform 10.

This arrangement is particularly advantageous for structures with two masts where there is room to place a door between the masts and the facade (in the interval separating the masts)
According to yet another improvement to the lifting platform structures, described with reference to FIGS. 10 and 11, a door block is proposed at the very bottom (for access to the platform at ground level), this door block being fixed to the mast and being movable in height along this mast.

 For example, the door unit is mounted in the same way as the platform on a carriage driven by a motor cooperating with the rack of the mast. The assembly can be the same as described previously; however, it is simpler to provide a direct drive (without transmission springs) between the engine and the rack.

Figures 10 and 11 show this construction, applied to a lifting platform structure with a single mast to simplify the representation.
motor or the gear system cooperates with the rack 28 to ensure the positioning of the entire block at a desired height.

 Depending on whether you want to work practically at ground level or for example at the height of an unloading skip from a truck, you will place the bottom block at a corresponding height. In this case, the access ramp is removed.

 On the door unit are usually fixed the electrical limit switches which are actuated by the platform when it comes to the low position and which trigger its stopping.

 Consequently, by changing the height of the low door unit, nothing changes during operation: the platform will stop automatically at the unit regardless of its height.

 According to an additional characteristic of the invention, it will be noted that the structure can be easily transported over a short distance without dismantling it (for example a movement along a building facade). Rolling carriages are placed under the platform, for example one at each end, and the platform is lowered along the masts until it rests on the carriages. At the end of the descent, the platform rests on the rolling carts. The lifting motors of the platform are then actuated, in a direction tending to lower it along the masts. As the platform is already resting on the rolling carts, it cannot lower itself any more, and therefore the masts rise slightly. The carriages can then be rolled without having to dismantle the masts.

 Finally, it will be noted that one of the important advantages of the invention is the possibility of working suspended from a facade, or as on the side of a ship for example (Figure 14). In this case, the masts are mounted, but with only one anchor point at the top of the mast. This is possible with a twin-mast structure, whereas this would not be possible, given the torsional forces, with a single-mast structure. One can then use long platforms, because they are more resistant because they do not have a greatly reduced width at the location of the masts, unlike the usual platforms which are indented for the passage in front of the anchors. This possibility is not reserved for flared facades.

 Figures 12, 13 and 14 show the use of such a structure with attachment only at the top of the masts. The single anchor point of the mast 12 on the facade 110 is designated by the reference 140 in FIG. 12. It can be seen in FIG. 13 that the platform 10 has only two openings with closed outline for the passage of the masts 12 and 14, but no notches (openings with open outline) for the passage of the platform at the level of anchoring points.

 In order to improve the system and meet the needs for transporting materials with an on-board conductor, particularly for scaffolding and supplying scaffolding already in place in front of the platform, and for supplying buildings (including ships), there is a retractable airlock system as shown in Figure 15. The platform then rises at least 50 cm from the front. Thus, it avoids the risk of shearing for people leaning from the front or from the floor 140 of the scaffolding.

When the platform stops, and only when it is stopped, an airlock system deploys, creating a protected passage between the platform and the facade. A barrier system can prevent the operator from entering the unloading area without deploying the system.

 The airlock door comprises a door bottom 141 and a roof 142 which are two long plates opening by tilting around horizontal axes. Once tilted, they release the opening of leaves 143 and 144 of the cabin door. These leaves 143 and 144 are preferably of the deployable type like the wings of a fabric fan. When the leaves are folded over each other, the airlock door is extended: these leaves prevent operators from tipping sideways into the void. When folded, the platform is closed. Plate 141 is approximately 50 cm wide.

Claims (9)

 1. A lifting platform structure intended to mount people and materials along scaffolding or an exterior facade of a building, and to enter this scaffolding or this building by an opening in height, this structure comprising at minus a mast for hoisting the platform, the platform, and a platform door (141-144) to allow access out of the platform, characterized in that this door has a retractable part intended for deploy in an interval which may exist between the platform and the scaffolding or the facade of the building at the location of the opening.  2. Structure according to claim 1, characterized in that the retractable part comprises a door bottom (141) in the form of a long plate opening by tilting about a horizontal axis.  3. Structure according to one of claims 1 to 2, characterized in that the retractable part comprises side leaves (143,144) to prevent people from tilting laterally into the void.  4. Structure according to claim 3, characterized in that the side leaves (143,144) are of the deployable type like the wings of a fabric fan.  5. Structure according to one of claims 1 to 4, characterized in that the retractable part comprises a barrier system to prevent a person from entering the building without having deployed the retractable system.  6. Structure according to one of claims 1 to 5, characterized in that it comprises a door block (113) protecting access to this opening and fixed to the hoisting mast of the platform.  7. Structure according to claim 6, characterized in that a floor plate (116) fixed to the door block, and therefore integral with the mast, covers the gap which may exist between the platform and the facade of the building.  8. Structure according to one of claims 6 or 7, characterized in that the door unit is movably mounted in height along the mast to allow to adjust the level at which the platform arrives, especially at the bottom of the stroke.  9. Structure according to one of claims 1 to 8, characterized in that it comprises two masts, in that its only attachment to the building is at the upper end of the masts, and in that it comprises a platform shape extending between the masts.