WO2017090069A1

WO2017090069A1 - Movement system for machines used for additive manufacturing

Info

Publication number: WO2017090069A1
Application number: PCT/IT2016/000280
Authority: WO
Inventors: Davide MARIN
Original assignee: Lumi Industries S.R.L.
Priority date: 2015-11-27
Filing date: 2016-11-25
Publication date: 2017-06-01
Also published as: ITUB20159588A1

Abstract

A movement system for machines used for additive manufacturing (3D printers), which uses two scissor jack systems (110, 112) capable of working combined or independently, permits to obtain 3D printers of very small thickness and even portable. The scissor jack system (110, 112) allows vertical movement of an upper mobile platform (102), in addition to significantly make easier the removal of a printed object (105) made of photosensitive resin from the bottom (600) of a tank (106) containing resin, with respect to a building platform (700), by combining specific movements of said scissor jack systems (110, 112) one relative to the other. Said mechanical lifting mechanism, which can be implemented in more types of 3D printers, allows to obtain 3D printers whose main feature is their compactness, with a very reduced overall dimensions in height, so that the 3D printer is able to print three-dimensional objects (105) having a greater height with respect to the height of the 3D printer when said 3D printer is closed.

Description

MOVEMENT SYSTEM FOR MACHINES USED FOR ADDITIVE

MANUFACTURING

The present invention relates to an electronic and mechanical structure which can be implemented in a machine used for additive manufacturing (hereinafter defined as a "3D printer") and which uses two scissor jack systems configured to work independently or combined together in order to make 3D printers.

One of the advantages derived from this system is the possibility to obtain compact and portable 3D printers, which have therefore reduced thickness with respect to the 3D printers based on different techniques.

The 3D printing, also known as additive manufacturing, is a technique used to create physical copies of a three-dimensional object, which is stored as a series of data on a digital support. The scissor jack system of the invention allows a vertical movement of a movable upper platform and makes significantly easier the detachment of a printed object made of photosensitive resin from the bottom of a resin bath, by combining specific movements of the scissor jacks between them.

More particularly, the invention relates to a mechanical and electronic structure formed by a mechanical lifting mechanism, which is used for making many types of 3D printers, in order to obtain a 3D printer whose main feature is its extreme compactness, with a very reduced overall dimensions in height, for which the same printer can print portions which are higher than the height measure of the printer when closed.

According to the present invention, a system using scissor jacks is provided to move a top portion of the 3D printer with respect to a lower portion.

A 3D printer based on a photosensitive resin technology, according to the present invention, comprises a lower fixed base build platform, which is integral with a reservoir containing resin, and an upper build platform integral with a mobile platform.

The two parts are connected by means of a system based on scissor- shaped lifting jacks, whereby the upper mobile platform can be moved relative to the lower base build platform to provide an internal building volume/space for building of the desired three-dimensional object that is printed layer by layer onto the lower part of the upper mobile building platform and ultimately, when finished, detached from the base build platform.

The use of two scissor jack systems permits the mobile platform to be vertically moved and, moreover, the two sides of the mobile platform, being capable of moving in different degrees, permits the tilting of the mobile platform along a vertical "Z" axis.

Currently available on the market there are different types of 3D printers and the main categories are the following:

- Filament Deposit 3D printers (hereinafter "FFM" or Fused Filament Modeling);

- Powder 3D printers (hereinafter "PLS" or Powder Laser Sintering);

- 3D printers based on photosensitive liquid resin (hereinafter "DLC" or Digital Light Curing).

Each type of 3D printers can use a wide variety of printing materials.

A FFM 3D printer typically includes a base, a 3-axis handling system and a printhead through which the print material is extruded.

A plastic filament is melted and placed by the extruder on the base surface, in which a heated plate makes easier the adhesion of the fused plastic material to the base. The extruder is moved on three axes and therefore the plastic material can be placed, layer by layer, to create 3D parts.

The FFM printing generally involves the use of a wire of ABS or PLA plastic material, which is melted and extruded by a head, which can be moved vertically ("Z" axis) and onto a plane (according to both axes "X" and "Y"), thus placing the plastic material on the printing base.

This technology has the advantage of being versatile, as there are many types of filaments which can be used and is generally the more economical technology than the others mentioned above.

A drawback is constituted by the fact that the resolution of the parts and/or of the printed 3D objects is generally not very high. The PLS Selective Laser Sintering 3D printers typically comprise a "bed" where is deposited, layer by layer, a very fine plastic or metallic powder and a laser unit which is moved on the horizontal axis "X" and Ύ". The laser melts the powder in a selective manner and this step is repeated by applying new powder onto the previous layer, until the part and/or the 3D object is built.

The PLS printing generally involves the use of one or more high-power laser beams for melting the plastic or metal particles. The advantage of this system is that it provides high print quality, good printing sizes in a wide range of materials, including metals, but it has very high costs and risks for the operator's health, because of the very fine powder which it is not easy to block even with suitable filters.

A DLC technology 3D printer based on laser generally involves the use of a tank containing a special liquid resin capable of solidifying when exposed to light (photo-polymerization).

A plate which is capable to vertically move and which serves as a printing base is typically placed in a starting position, just below the liquid level. A laser beam is deflected by a mirror system for reconstructing an image corresponding to a first section of the object to be built.

Then, after a first scan, the plate rises slightly and a subsequent laser scanning produces a second section.

The process is repeated several times until the entire 3D object is printed. An advantage of this system is that it provides a very high printing resolution with respect to the other 3D printing techniques.

The drawbacks generally include the rather high costs of the 3D printer and a relatively slow printing speed.

The DLC printing technology based on a DLP projector always uses a tank containing a photosensitive liquid polymer that is exposed to the light of a DLP projector.

The liquid resin hardens in correspondence of the horizontal sections of a three-dimensional object, which are projected from the projector in the form of images, and the building plate then moves upwards for small steps and the liquid polymer is again exposed to the light. The process is repeated until the part and/or the 3D object is built. The polymer is then drained from the tank, leaving the printed 3D object which is ready to be removed.

An advantage of this system is that it provides a better printing speed with a resolution comparable to the laser-based DLC technology; moreover, it is generally more economic with respect to said DLC technology.

Currently available 3D printers are generally of medium or large size and are too large to be truly portable by a user.

There is therefore a need for a compact, portable and cost-effective 3D printer capable of printing a variety of materials and sizes, which would also be extremely useful and practical when there is a need to perform a 3D printing job during a workshop or a course about 3D printing, during a visit to a customer for showing him/her a physical prototype, or in places where a portable 3D printer is easier to use and sharing, as in developing countries.

The object of the present invention is therefore to obviate the technical drawbacks mentioned above and, in particular, to provide a lifting mechanism implemented in different types of 3D printers, in order to obtain a 3D printer whose main feature is the high compactness, with a very reduced overall dimensions in height, so that said 3D printer is truly portable and is able to print parts higher than the height of the same printer when closed.

Another object of the present invention is to provide a lifting mechanism implemented in different types of 3D printers, which allows a high printing resolution that is comparable with the resolution obtainable with currently employed mechanical systems.

These and other objects, which will become clear hereafter in the description, are achieved by means of a movement system for machines used for additive manufacturing (3D printers using the DLC technology), according to the appended claim 1; more detailed features are contained in the subsequent dependent claims.

Advantageously, a system equipped with scissor lifting jacks is provided to move an upper portion of the 3D printer with respect to a lower portion. A 3D printer based on DLC technology according to the present invention comprises a fixed lower base, integral with a tank containing a liquid resin, and an upper build platform integral with a mobile platform.

The two parts are connected together by means of a system based on two scissor lifting jacks, whereby the upper movable platform can be moved with respect to the lower base to provide an internal building space/volume for building the desired three-dimensional object, which is printed layer by layer on the bottom of the building platform and finally, once finished, detached from said platform.

The use of two combined scissor jacks allows the mobile platform to move vertically and, moreover, the two sides of the mobile platform, being able to move independently, permit tilting of the mobile platform along the vertical "Z" axis.

Further characteristics and advantages of the movement system for machines used for additive manufacturing will become clear from the following description of preferred embodiments of the invention and from the enclosed drawings, in which:

- FIG. 1 is a schematic view of the system according to the invention;

- FIG. 2 is a perspective view of the system of the present invention, in which the two scissor jacks are highlighted;

- FIG. 2A is a perspective view of a single scissor jack;

- FIG. 2B is a side view of a single scissor bridge;

- FIG. 3A and 3B show, respectively, a front view and a schematic side view of a vertical movement system of the printing platform in a 3D printer according to the technical prior art;

- FIG. 4 is a perspective view of a single scissor jack;

- FIG. 5 is a view of a single scissor jack bridge according to the present invention in the fully open position;

- FIG. 6 is a view of a single scissor jack according to the present invention in the fully closed position;

- FIG. 7 is a perspective view of a resin 3D printer, according to the present invention, in the fully closed position;

- FIG. 8 is a perspective view of a resin 3D printer, according to the present invention, in the fully open position;

- FIG. 9A, 9B, 9C and 9D show schematically a printing procedure step- by-step or layer-by-layer of a 3D object, with the movement of the platforms used in a 3D photosensitive resin printer, according to the present invention;

- FIG. 10A and 10B show two schematic views of possible methods for filling a tank with resin in a 3D photosensitive resin printer, according to the present invention;

- FIG. 11A and 11 B show a schematic view of a scissor double jacks system, according to the present invention, in a FDM filament printer;

- FIG. 12A and 12B show a 3D photosensitive resin printer having a scissor jack system, according to the present invention, in which a flexible bellows made of semi-transparent material is provided for shielding the resin from the external light, according to the present invention;

- Fig.13 is a schematic block diagram of the control unit of a 3D photosensitive resin printer, according to the present invention.

The detailed description set forth below is intended as a description of the presently exemplary system provided in accordance with aspects of the present invention and is not intended to represent the only forms in which the present invention may be prepared or utilized.

It is to be understood, rather, that the same or equivalent functions and components may be accomplished by different embodiments that are also intended to be encompassed within the spirit and scope of the invention. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood to one of ordinary skill in the art to which this invention belongs.

Although any methods, devices and materials similar or equivalent to those described can be used in the practice or testing of the invention, the exemplary methods, devices and materials are now described.

With reference to the above mentioned drawings, two scissor jack systems 110, 112 connect an upper platform 102 to a lower fixed base or platform 600; said scissor jack systems can be used in different types of machines used for additive manufacturing (3D printers), including FFM filament 3D printers, DLC resin 3D printers and other possible types.

As schematically shown in figure 1 , the mechanical movement system of a

3D printer based on liquid resins, according to the present invention, comprises a building platform 700 suitably secured onto the upper movable platform 102 so that said building platform 700 can be moved.

A building space/volume or chamber 104 is thus provided between the building platform 700 and the fixed base 600 on which the reservoir or tank 106 containing the photosensitive resin is placed.

The 3D object 105, which will be printed, will be formed on the bottom of the building platform 700.

The bottom of the tank 106 containing photosensitive resins is made from glass or other transparent material to allow the passage of light from the image generation system 108, which is located under the tank 106 and whose function is to project the sections of the 3D object 105 starting from the data relating to the shape of said object which are stored on a digital media.

The movement of the upper mobile platform 102 allows the formation of many layers of solidified resin on the building platform 700 so as to form the object to be printed 105, according to a layer-by-layer process.

The tank 106 may contain many types of photo-hardening resin, depending on the specific application related to the 3D printer used.

In a possible configuration, the tank 106 containing photosensitive resins may contain a liquid resin, which is solidified by exposure to a particular frequency of light, such as UV light.

Among the various available resins current on the market and usable according to the present invention, liquid resins can be used, that, once made solid, have similar properties to the PLA and to the ABS, as well as resins with fillers and castable resins.

The last type of resins can be used for printing 3D objects 105 that, through the so-called "lost wax" casting process, are used to obtain a final piece made of metal.

Possible applications are mainly in the dental and jewelery industry.

The tank 106 of the photosensitive resin, as shown in fig. 10A and 10B, can be manually filled, by lifting and/or by removing the mobile upper platform 102 to provide access to the tank 106 or can be filled automatically through a pumping mechanism 121 associated with a resin reservoir 122, which is outside or integrated in the printer.

The building platform 700 and the upper mobile platform 102 are configured to move with respect to the tank 106 containing the photosensitive resins and with respect to the fixed base 600 by means of a two scissor jack systems 110, 112, in which the scissor jacks are able to move independently and are placed on the two opposite sides of the platforms 102, 600, as shown in fig. 1 and 2.

As best shown in fig. 2A and 2B, each single scissor jack system 110, 112 comprises two pairs of crossed support bars 114 and a horizontal threaded rod 116 that mechanically cooperates, by means of a nut 119, with the support bars 114, such that, turning of the horizontal threaded rod 116 causes, respectively, opening and closing of each scissor jack system 110, 112 and lifting or lower of the upper mobile platform 102 relative to the tank 106 containing the photosensitive resins.

The presence of two opposing scissor jack systems 110, 112 that can be independently operated and which are located at the opposite sides of the upper mobile platform 102 permits the upper mobile platform 102 to be moved vertically (in the "Z" axis) and, if operated at different rates, thereby permits tilting of the upper mobile platform 102 in controlled degrees as desired for building of the printed object 105.

The building platform 700 is suitably fixed so as to be removable with respect to the upper mobile platform 102.

During the printing process, the 3D object 105 adheres to the underside of the building platform 700.

The tank 106 containing the photosensitive resins is placed on the fixed base 600 and comprises a transparent bottom through which passes the light of the image generating system 108, which allows a thin layer of resin to solidify and adhere to the lower surface of the building platform 700; then, every layer hardens over the previous one. In this way, each single layer of resin is solidified on a previous hardened layer. Therefore, the 3D object 105 is printed layer by layer.

The image generation system 108 projects each layer as the image of a horizontal section of the object and a possible implementation provides that said image generation system 108 is driven by a digital video input provided by a computer.

As shown in fig. 3A and 3B, some prior art devices utilize a vertical threaded rod 132 to move a mobile platform 131 by means of a stepper motor or a DC motor with encoder 133 in the vertical "Z" axis and by means of a nut 134, integral with the platform 131 , which slides along one or more guides or vertical rails 135, 136 through respective bearings 139. However, the 3D printers that use the above system suffer from two main problems; first, the minimum height of the 3D printer cannot be less than the maximum printable height (and therefore it is not possible to obtain a real compact and portable 3D printer), second, since the vertical threaded rod 132 only permits uniform vertical movement of the mobile platform 131 , an additional mechanical system is required to allow removal of the 3D printed object 137, during the printing process, from the bottom of the tank 138, in order to overcome a resulting "suction effect".

This problem is overcome in some cases by applying a force in one direction or versus which is different with respect to the vertical axis or by applying a combination of movements.

The present invention, on the other hand, utilizes the two scissor jack systems described above both to move the upper mobile platform 102 in the vertical "Z" axis and to help the removal of the 3D printed object 105, through independent movements of the two scissor jack systems.

In fact, as shown in fig. 4, each single scissor jack system 110, 112 comprises two sets of two cross rods 114 and a horizontal threaded rod 116 that mechanically cooperates, through a nut 119, with the cross rods 114, such that rotation of the threaded rod 116 causes vertical movement of the upper mobile platform 102.

According to a possible embodiment of the invention, rotation of the threaded rod 116 is controlled by a stepper or DC motor with reduction and position feedback control. Each motor 118, which is coupled to each single scissor jack system 110, 112, is controlled by an integrated electronic board of the 3D printer.

As schematically shown in fig. 1 and 13, the control system 109 manages both the movement of the two scissor jack systems 110, 112 and the image generation system 108.

A possible embodiment of the invention, shown in fig. 13, provides for using an integrated electronic board 101, which receives input data relating to the shape of a three-dimensional object which are stored as data structure 103 on a physical support, such as a USB stick or an internal memory, or which are stored in the memory of a PC connected to the electronic board 101.

As already described, a digital representation of the desired 3D object, which is usually stored in a standard file format widely adopted as ".STL" or similar (data structure 103), is contained in a memory card, USB memory, hard drive or other digital storage media.

These data are communicated to the control system 109, which in turn controls the image generation system 108, in order to make a photo- polymerisation of the resin contained in the tank 106, and the motors 118, which drive the scissor jack systems 110, 112.

Therefore, the digital input, through the integrated electronic board 101, drives the 3D printing process by controlling the movement of the building platform 700 and by controlling, through the image generation system 108, the hardening of the resin layers during the printing phase.

The control of each of said objects allows an accurate printing of the 3D object 105.

Fig. 5 is a schematic side view showing the scissor jack system 110, 112 in the completely open position.

Fig. 6 is a schematic side view showing the scissor jack system 110, 112 in the completely closed position.

Similarly, fig. 7 shows the fixed base 600 and the upper mobile platform 102 in the closed position, while fig. 8 shows the fixed base 600 and the upper mobile platform 102 in the fully open position.

In the fully open position, the distance between the fixed base 600 and the upper mobile platform 102 is generally about 15 cm (including the thicknesses of the fixed base 600 and of the upper mobile platform 102), while the total height of the device (base and upper platform together) in the closed position is about 6 cm.

To provide the desired full range of motion for the mobile platform 102, the present invention provides two scissor jack systems 110, 112 on opposite sides of the base 600 and of the platform 102.

For a better understanding of the 3D printing process carried out by means of a DLC technology 3D printer, according to the present invention, fig. 9A, 9B, 9C and 9D show a step-by-step representation of the printing process of a three-dimensional object 105 and, specifically, of a simple pyramid made up of three layers with a circular base (the deposition of the first layer is shown in fig. 9A, the deposition of the second layer is shown in fig. 9B, the deposition of the third layer is shown in fig. 9C, while in fig. 9D is shown a phase of removal of said three-dimensional object 105 from the mobile platform 102).

Please note that the synchronized and simultaneous driving of the two scissor jack systems 110, 112 allows to adjust the height of the building platform 102 with respect to the bottom of the tank 106, so as to form the desired 3D object 105, by building said 3D object 105 layer by layer, starting from a thin layer of resin 107, which is transformed into solidified resin 1 1 due to the light projected from the image generation system 108. It is also shown how the use of the two scissor jack systems 110, 112 permits one side of the upper mobile platform 102 to be moved higher or lower along the vertical "Z" axis as compared to the other side of the platform 102, so as to permit tilting of the mobile platform 102 relative to its horizontal position.

Said tilting system of the platform 102, according to the invention, permits, alone or in combination with other systems, the removal of the 3D printed object 105 from the bottom of the tank 106.

Fig. 11A and 11B show the scissor jack system so far described, which is implemented in a different type of 3D printer and specifically in a filament deposition or FFM printer. In this case, a base or printing plate 200 is positioned above a filament coil 220 and an upper mobile platform 202 comprises a filament extruder 206, which can be moved using a movement system 230 in the horizontal axis "X" and "Y", so as to perform the 3D printing of a desired object 225, starting from the upper surface of the plate 200.

Similarly to what described for a DLC 3D printer according to the present invention, each scissor jack system 210, 212 includes two sets of a pair of cross rods 214 and a horizontal threaded rod 216 which mechanically cooperates, by means of a nut 219, with the cross rods 214, so that the rotation of the threaded rod 216 causes the vertical movement of the upper mobile platform 202.

During the printing process, the rotation of the threaded rod 216 is controlled by a stepper or DC motor with reduction and encoding 218.

Said motors that are coupled to each of the scissor jack systems 210, 212 are driven by the control system 209.

An embodiment of said control system 209 includes an integrated electronic board, which drives the scissor jack systems 210, 212 and the movement of the head 206 equipped with an extruder in the "X" and Ύ" axis, through the movement system 230.

Information for controlling the movement of the 3D printing system and for controlling the filament extrusion may be contained in the internal memory of the electronic board or stored in an external memory or transferred from an external computer.

Moreover, said control system can be quite similar to the control system previously described for a DLC-resin printer.

Fig. 12A and 12B show a DLC resin 3D printer, which is provided with the scissor jack systems according to the present invention and which includes a bellows system 300 configured to surround the molding chamber 104, in order to shield the resin contained in the printing tank 106 from unwanted external light.

This system avoids the possibility that the external light, in case in which the frequency and the intensity of the light are enough to trigger the polymerization process, causes a solidification of the resin in unwanted points, thus compromising the proper formation of the 3D object 105 to be printed.

As shown in fig. 12A and 12B, a bellows system 300 is provided between the upper mobile platform 102 and the base 600 and surrounds the molding chamber 104, in order to limit the amount and type of light that reaches the building chamber from outside.

In this way, the photosensitive resin that builds the 3D printed object 105 can be shielded from the external light such that said light does not interfere with the accurate and proper polymerization of the resin managed by the image generation system 108.

The bellows system 300 may be made of any material configured to block the specific frequency of light that solidifies the resin (which can be comprised in the visible light or in the ultraviolet light range). The use of a material which is partially transparent to visible light is useful for performing a visual inspection of the printing process from outside. The material must also be sufficiently flexible so that it can be deformed through zig-zag folds, thus forming an expandable surface whose ends are integral with the mobile platform 102 and the base 600.

Therefore, the bellows system 300 may expand or contract following the movement of the scissor jack systems 110, 112 in the vertical displacement of the mobile platform 102 with respect to the base 600.

The invention thus conceived and illustrated herein is susceptible to numerous modifications and variations, all falling within the inventive concept as claimed in the appended claims.

Moreover, all the details may be replaced with other technically equivalent elements. Finally, the components used, so long as compatible with the specific use, as well as the dimensions, may be any according to requirements and the state of the art.

Claims

1. A movement system for machines used for additive manufacturing or 3D printing devices comprising

- a fixed base (600),

- an upper mobile platform (102) positioned above said fixed base (600) so that said mobile platform (102) and said fixed base (600) define a building chamber (104) of a three-dimensional object (105),

- a first scissor jack system (110) attached to a first side of said fixed base (600) and to a first side, corresponding to said first side of said fixed base (600), of said upper mobile platform (102),

- a control unit (109), which handles the processing of the printing material according to the type of the 3D printing device in which said movement system is implemented,

characterised in that said movement system also includes

- a second scissor jack system (112) attached to said first side of said upper mobile platform (102) and to a second side of said fixed base (600), which is opposite to said first side of said fixed base (600),

- a first threaded rod (116) mechanically engaged with said first scissor jack system (110), whereby rotation of said first threaded rod (116) causes opening and closing of said first scissor jack system (110) and permits said upper mobile platform (102) to move relative to said fixed base (600),

- a second threaded rod (116) mechanically connected with said second scissor jack system (112), so that the rotation of said second threaded rod (116) causes opening and closing of said second scissor jack system (112) and permits said upper mobile platform (102) to move relative to said fixed base (600),

and wherein said control unit (109) manages the rotation of said first and second threaded rods (116) by means of respective motors (118), so as to control the movement of said upper mobile platform (102) relative to said fixed base (600).

2. A movement system as claimed in claim 1 , characterised in that said system comprises a first linear guide (117), connected to the first scissor jack system (110), and a second linear guide (117), connected to the second scissor jack system (112), whereby the linear motion of said upper mobile platform (102) are kept straight by said linear guides (117).

3. A movement system as claimed in claim 1, characterised in that said motors (118) are stepper motors (118A) or DC feedback controlled motors with reduction and encoder.

4. A movement system as claimed in at least one of the previous claims, characterised in that said control unit (109) includes an electronic board (101), which receives input data to control the printing material so as to build said three-dimensional object (105).

5. A movement system as claimed in at least one of the previous claims, characterised in that said upper mobile platform (102, 202) comprises a two axis moving system (230), an extrusor (206) and additional control systems for placing a molded filament (225) onto a printing plate.

6. A movement system as claimed in at least one of the previous claims, characterised in that said fixed base (600) comprises a reservoir or tank (106) containing phot-sensible resin for printing said three-dimensional object (105) and said upper mobile platform (102) is fixed to a building platform (700), so that said three-dimensional object (105) is formed onto a lower part of said building platform (700).

7. A movement system as claimed in at least one of the previous claims, characterised in that an image generation system (108), managed by said control unit (109) and placed below said tank (106), is provided to emit control light so as to start the photo-polimerization of said resin, said light having intensity and frequency such as to start a reaction of said resin.

8. A movement system as claimed in cliam 7, characterised in that said tank comprises a transparent base which permits the passage of light emitted from said image generation system (108).

9. A movement system as claimed in claim 7, characterised in that said image generation system (108) is configured to provide UV light and said resin is a UV curable resin.

10. A movement system as claimed in claim 7, characterised in that said image generation system (108) is configured to provide visible light and said resin is a visible light curable resin.

11. A movement system as claimed in at least one of the previous claims, characterised in that a bellows system (300) is coupled to said fixed base (600) and to said upper mobile platform (102) and surrounds said building chamber (104), so as to protect said resin from the outside light, said bellows system (300) being flexible in order to follow the movement of said fixed base (600) and of said upper mobile platform (102).