More specifically, the invention relates to a platform assembly comprising at least one tower along which a platform may be moved up or down by means of a lifting mechanism incorporating at least one caterpillar belt that is mounted on the platform and operatively engages a rack mounted on the tower. b) Brief description of the prior art Platform assemblies made of modular elements that can be erected close to a building so that workman can work on the same, are well known and commonly used in the construction areas.

As non-restrictive examples of such assemblies, reference can be made to United States patent Nos. 3,323,616 (BEST), and 4,809,814 (ST- GERMAIN) which disclose platform assemblies wherein the platform are moved by a cable hoist mechanism and a set of hydraulic rams, respectively.

Reference can also be made to U. S. patent No. 4,293,054 (PIERI) which discloses a scaffolding comprising two posts along which a working platform called"bridge"may be moved up and down by means of toothed wheels that are driven by an electric motor through a suitable transmission.

The toothed wheels are meshed with corresponding gear racks mounted on bars forming part of both posts.

Reference can further be made to U. S. patent No. 4,294,332 (READY) which discloses a scaffold unit comprising a pair of towers, each having a pair of rails held together by cross-ties. Each rail has a gear rack, which extends all over its length on its front face. A self-elevating platform supporting carriage is mounted onto each tower. Each carriage comprises a frame supporting a pair of upright shoes that fit over and guide the carriage on the rails when the carriage is in motion. Each carriage also comprises a shaft that carries a pair of gears, which mesh with the gear racks of the adjacent rails through slots provided in the shoes. A controllable motor is connected to the shaft of each carriage so as to rotate the gears and thus move the carriage and the platform supported by the same up or down along the towers.

If the known platform assemblies are efficient, their lifting mechanisms are rather complicated and/or expensive. This is particularly true in the case of assemblies making use of gears (or toothed wheels) meshed with racks, since the gears and racks must be made of very strong material and they must be shaped, mounted and held in such a manner as to perfectly and permanently mesh.

OBJECT AND SUMMARY OF THE INVENTION The object of the present invention is to provide a platform assembly of the above mentioned type, wherein the lifting mechanism incorporates at least one and preferably two symmetrically positioned caterpillar belts mounted onto the platform and each engaging a corresponding rack mounted onto the tower.

The fact that use is made of caterpillar belts and corresponding racks instead of conventional gears and racks is essential, since, by nature, caterpillar belts have a large number of teeth that engage a corresponding number of grooves of the adjacent racks. As a result, much more contact is achieved and the strength of the whole assembly is improved.

More specifically, the platform assembly according to the invention comprises at least one tower made of a plurality of tower sections devised to be connected to each other in end-to-end relationship.

It also comprises a platform that is slidably mounted onto each tower.

The platform comprises an elongated, sleeve-shaped frame surrounding the tower.

A lifting mechanism is provided to move the platform up and down long the tower. This lifting mechanism inclues plates that are provided with embossed grooves and are connected to at least one side of the tower sections so as to form at least one continuous rack vertically extending on one side of the tower when the same is assemble. The lifting mechanism also includes at least one caterpillar belt that is provided with outwardly projecting teeth and is held onto a pair of spaced away shafts mounted onto the frame of the platform. The shafts extend horizontally one above the other in a direction parallel to the one side of the tower where the rack is located the rack, and they are positioned in such a manner that the outwardly projecting teeth of the caterpillar belt fit into the grooves embossed in the plates forming the rack. The lifting mechanism further comprises driving means that is mounted onto the frame and operatively connected to the caterpillar belt (s) so as to drive the same and thus cause the platform to move up or down along the tower.

In one preferred embodiment, the caterpillar belt comprises inwardly projecting teeth and the driving means include toothed wheels that are mounted onto one of the shafts on which the caterpillar belt is mounted, so as to engage the inwardly projecting teeth of the belt. In another preferred embodiment, the caterpillar belt is caused to make an inwards winding and the driving means include toothed wheels that are mounted onto a driving shaft positioned into the winding so as to engage the outwardly projecting teeth.

In practice, the caterpillar belt (s) can be made of reinforced rubber or any similar material (belts of this kind are very strong and some of them

already used as caterpillar belts in military tanks). The toothed wheels can be made of plastic material. The embossed plates forming the rack (s) can be made of stamped or cast aluminium eventhough they are preferably made of plastic material also.

Thus, one may appreciate that the platform assembly according to the invention can be manufactured at much lower costs than the existing assemblies while having the same strength and efficiency. Its maintenance is also much simpler and less expensive, especially in the case of damages to the rack (s). Moreover, its operation is smooth.

As aforesaid, use is preferably made of two symmetrically positioned caterpillar belts, which engage corresponding racks positioned on two opposite sides of the tower. In such a case, the driving shafts of both caterpillar belts are connected to a same driving source to make it sure that they rotate in unison.

Preferably, the driving source consists of hydraulic motors each connected to one of the driving shaft, which are connected to a same hydraulic pump driven by a motor, preferably a diesel motor, or otherwise, a synchronized dual driving source.

The invention will be better understood upon reading the following non- restrictive description of a preferred embodiment thereof, made with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a front perspective view of a platform assembly according to a preferred embodiment of the invention; Figure 2 is a perspective view of the basic components of the lifting mechanism of the platform assembly shown in Figure 1; Figure 3 is a partial, front elevational view of the platform of the assembly shown in the preceding figures, this view showing the frame and the caterpillar belts mounted onto it; Figure 4 is a top plan view of the platform shown in Figure 3; Figure 5 is a side elevational view of the platform shown in Figures 3 and 4; and

Figure 6 is a side elevational view of a caterpillar belt with no inwardly projecting teeth, said view showing the way such a belt can be driven to achieve the same result as with the belts shown in the preceding figures.

DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION The platform assembly 1 according to the preferred embodiment of the invention shown in Figure 1, comprises at least one tower 3 supporting a platform 23. When use is made of only one tower, the platform 23 may be used as an elevator and may thus support a cabin (not shown). When use is made of more than one towers 3, the platform 23 of the adjacent towers may be connected by horizontal structural members 23'to form a bridge. Such is well known in this field and needs not be further described.

Each tower 3 is made of a plurality of modular tower sections 5 that are stackable on top of each other to achieve the requested tower height. Each tower section 5 is made of a set of vertical tubular rods 7 held together by cross- ties 9. Preferably, each tower section 5 has a square or rectangular, horizontal cross-section with a pair of opposite sides 11,13 that extend perpendicular to the wall"W"close to which the tower 3 is built up.

The platform 23 is slidably mounted onto the tower 3. The platform comprises an elongated, sleeve-shaped frame 25 of rectangular, horizontal cross-section surrounding the tower 3. It also comprises a floor 27 and a sub- floor structure 29 integral to the frame. The floor 27 is intended to be used by the workmen and may include a protective fence opposite to the wall W.

Alternatively, the floor may be used as a supporting structure for a cabin when the platform 23 is designed to be used as an elevator.

The way the platform 23 can be operatively mounted for sliding motion onto the tower 3 is conventional and needs not be described.

As is shown in Figure 4, the platform 23 is preferably shaped to permanently leave a structural"gap"24 between the tower 3 and the adjacent wall W. This allows the installation of permanent anchors (not shown) between the tower and wall, as is often required for safety reasons.

A lifting mechanism is provided to move the platform 23 up and down

along the corresponding 3.

This lifting mechanism includes plates 15,17 that are provided with embossed grooves 19. These plates are rigidly connected to the opposite sides 11,13 of the tower sections 5 so as to form a pair of continuous racks vertically extending on both sides 11,13 of the tower 3 when the same is erected. The plates can be made of plastic material. However, they are preferably made of a cast or stamped aluminium. Preferably also, they are sized to extend over the full width of the tower 3 as is shown in the drawings and thus to be directly connected to the tubes 7. They each may be 14 inches long and include 4 grooves. The advantage of such a"restricted"size is that it makes it possible to easily remove and replace at low cost every plate that could be damaged during transportation or assembly of the tower sections.

As is better shown in Figure 2, the lifting mechanism also includes a pair of caterpillar belts 31,33 that is provided with outwardly projecting teeth 35 and are each held by a pair of spaced away shafts 37,39 mounted onto the upper and lower parts of the frame 25 of the platform. The shafts 37,39 extend horizontally one above the other in a direction parallel to the opposite side 11, 13 of the tower 3 where is located the rack, and they are positioned in such a manner that the outwardly projecting teeth 35 of the caterpillar belts fit into the grooves 19 embossed in the adjacent plates 15,17 forming the racks.

The lifting mechanism further comprises driving means that is mounted onto the frame 25 and sub-floor structure 29, and is operatively connected to the caterpillar belts 31,33 so as to drive the same and thus causes the platform 23 to be moved up or down along the tower 3.

In the preferred embodiment illustrated in Figures 1 to 5, the caterpillar belts 31,33 comprise inwardly projecting teeth 41 and the driving means include toothed wheels 43 that are mounted onto the lower shafts 39 so as to engage the inwardly projecting teeth 41 of the belts.

In another preferred embodiment illustrated in Figure 6, each caterpillar belt 31 (or 33) is caused to make a"inwards winding"45 and the driving means include toothed wheels 45 that are mounted onto a driving shaft 47 positioned into the"bottom"of the winding so as to engage the outwardly projecting teeth

35, thereby making the structure of the belt much simpler than the one of the embodiment previously disclosed.

In practice, the caterpillar belt (s) 31,33 can be made of reinforced rubber or any similar material (belts of this kind are very strong and some of them already used as caterpillar belts in military tanks). The toothed wheels used to drive the same can be made of plastic material.

Of course, suitable tensioning means 49 of conventional structure (see Figure 3) can be connected to at least one 33 of the shafts to make it sure that the caterpillar belts 31,33 are kept tight. Rollers 51 (see Figure 3) may also be provided to make it sure that all the teeth 35 of the caterpillar belts 31,33 remain engaged within the corresponding grooves 19 of the rack over the full height of the belts.

As better shown in Figures 4 and 5, the driving mans of the caterpillar belts preferably comprises a pair of hydraulic motors 53 each connected to one of the shafts 39. Both motors 53 are connected to one or two hydraulic pump (s) 55 mounted onto the sub-floor structure 29, thereby making it sure that they work in unison at the same speed. The pump 55 is operated by a motor 57, which is preferably a diesel-operated

motor eventhough any other kind of motor such as an electric motor, could alternatively be used.

As aforesaid, the fact that use is made of caterpillar belts 31,33 and corresponding racks 15,17 instead of conventional bears and racks is essential, since, by nature, caterpillar belts have a large number of teeth 35 that engage a corresponding large number of grooves 19 of the adjacent racks. As a result, much more contact is achieved and the strength of the whole assembly is improved. Moreover, this makes the sliding motion smoother.

Of course, numerous modifications could be made to the platform assembly 1 disclosed hereinabove without departing from the scope of the invention as defined in the appended claims. By way of example, only one caterpillar belt could be used instead of two. The driving means could also be different (mechanical or electrical) and use could be made of transmission gears. Safety devices such as locking pins or bars could also be provided to lock the platform at a given height once it has reached this height, as is of common practice in scaffolding.