WO2014000774A1

WO2014000774A1 - Flexible facility for assembling different sheet metal elements

Info

Publication number: WO2014000774A1
Application number: PCT/EP2012/062377
Authority: WO
Inventors: Bernard Negre
Original assignee: Abb Technology Ag
Priority date: 2012-06-26
Filing date: 2012-06-26
Publication date: 2014-01-03

Abstract

The invention concerns a flexible facility for assembling pieces of sheet metal in order to constitute a plurality of types of sheet metal elements, comprising: • - a series of assembly stations (41-43) aligned longitudinally to carry out the succession of assembly operations, each station (41-43) comprising one or a plurality of assembly robots (50-53) to assemble pieces of sheet metal presented in a tool (68-71); • - one or more handling robots (46, 47) to move each assembly of sheet metal pieces from one station (41-43) to another; • - a plurality of transverse structures (56-58) each associated with an assembly station (41-43), each transverse structure (56-58) carrying a plurality of tools (68-71) each suitable for assembling one type of element and means for moving each tool at least transversely between a service location (67) in the assembly station (41-43) and a waiting location (61-66) laterally offset relative to the station (41-43). It is possible to provide rails and at least one carriage on each structure, laterally loading and unloading the tools at the waiting locations, and/or taking them to the assembly station.

Description

Flexible assembly installation of various sheet metal components

The invention relates to a flexible robotized assembly line of sheet metal elements, for example by welding, different sheet metal parts to each other. It fits into the context of automated lines where handling and assembly are provided by robots in the form of articulated arms whose operations and movements are coordinated and controlled by a centralized unit.

The invention relates to the assembly of motor vehicle sheet metal elements such as body sides, openings such as hoods, side doors or rags, or subsets of floors, which typically require to assemble, for example by welding, a skin and a lining to form a rigid assembly.

Such an installation is expected to be fully flexible: it must be able to produce different types of elements in any order, for rates of up to 90 vehicles per hour.

The different types of the same element correspond for example to different versions of the same vehicle such as coupe, sedan or estate. Specifically, the ragged type coupe, sedan type or break type is not the same for the same model of vehicle. Since vehicle controls are not predictable, the production line is designed to be completely flexible to accommodate demand throughout the life of the vehicle production line. Such a line can also be used to assemble the doors of different vehicle models, so as to adapt to the demand for the vehicles in question which is also not predictable.

The object of the invention is to provide a standard sheet metal assembly line arrangement which has a reduced cost and is fully flexible for any type of vehicle subassemblies. SUMMARY OF THE INVENTION

For this purpose, the object of the invention is a flexible installation for assembling sheet metal parts in order to constitute sheet metal elements of several types, each sheet metal element resulting from a succession of separate assembly operations performed on this installation. , this installation comprising:

a series of assembly stations longitudinally aligned to carry out the succession of assembly operations necessary for the constitution of each sheet metal element, each station comprising one or more assembly robots for assembling sheet metal parts installed in a tool ;

one or more handling robots for moving each assembly of sheet metal parts from one station to another;

several transverse structures each associated with an assembly station, each transverse structure bearing several tools each adapted to the assembly of a type of element, and means for moving each tool at least transversely between a remote waiting position. laterally to the station, and a service location located in the assembly station.

The invention also relates to an installation as defined above, comprising at least one transverse structure integrating at least one loading station positioned to allow the loading of pieces of sheet metal to be assembled in a tool immobilized at at least one waiting location .

The invention also relates to an installation as defined above, comprising at least one transverse structure provided with waiting places located on either side of the alignment of the assembly stations and integrating at least two positions of loading located on either side of the alignment of the assembly stations. The invention also relates to an installation as defined above, further comprising a loading station equipped with robotic means for loading pieces of sheet metal to be assembled in each tool immobilized in a waiting location. The invention also relates to an installation as defined above, wherein each transverse structure comprises a tool change rail and waiting locations along the tool change rail, and wherein the means for moving each The tool between the service location and each standby location includes a carriage carried by the tool change rail, which carriage is provided with means for laterally loading and unloading a tool at a standby location.

The invention also relates to an installation as defined above, wherein the waiting locations along the tool change rail are located on either side of the tool change rail.

The invention also relates to an installation as defined above, in which the carriage comprises at least one element movable transversely with respect to the direction of movement of this carriage, each movable element carrying a gripping member adapted to mate with a complementary member of a tool edge, so as to move a tool transversely between a waiting location along the tool change rail and the upper face of the carriage, or vice versa.

The invention also relates to an installation as defined above, wherein the tool change rail carries a second carriage controlled to place the next tool to be used at a waiting location near the service location while the other carriage is immobilized at the service location during an assembly operation

The invention also relates to an installation as defined above, comprising waiting locations located on either side of the assembly station and on both sides of the tool change rail, and in wherein the tool change rail carries two trolleys each suitable for performing tool change operations.

BRIEF DESCRIPTION OF THE FIGURES

Figure 1 is a top view schematically showing a first embodiment of an installation according to the invention;

Figure 2 is a top view of a transverse structure associated with an assembly station shown in isolation;

Figure 3 is a top view schematically showing a second embodiment of an installation according to the invention; Figure 4 is a top view of the carriage of the second embodiment rolling on the rail carrying it while carrying a tool to be unloaded on a waiting location;

Figure 5 is a top view showing the carriage of the second embodiment carrying the tool to be unloaded and when it is approaching another tool to be loaded;

Figure 6 is a top view of the carriage of the second embodiment carrying the tool to be discharged while being accosted to the tool to be loaded;

Figure 7 is a top view of the carriage when it jointly finishes placing the tool to be unloaded on its standby and load the tool to use;

Figure 8 is a side view showing the gripping member of the carriage;

Figure 9 is a front view of the gripping member of the carriage;

Figure 10 is a top view of a transverse structure according to a third embodiment of the invention. DETAILED DESCRIPTION OF THE INVENTION

The idea underlying the invention is an installation in which the sheet metal parts are assembled step by step while being moved from one assembly station to another, these stations being aligned in a longitudinal direction, but in which transverse structures have been provided at each station to use different tools so as to benefit from flexibility to manufacture different types of sheet metal on the same installation.

According to the first embodiment of the invention shown in FIG. 1, the assembly line comprises a head station 1 followed by four other stations 2-5, for assembling sheet metal parts in order to constitute a sheet metal element such that a front of a motor vehicle body, during various successive assembly operations performed on each station.

These different stations are aligned in a longitudinal direction, and longitudinal rails carrying handling robots are interposed between each pair of adjacent posts along the longitudinal direction, being marked respectively by 6 to 9.

Each of the stations 1 to 5 is provided with four robot assemblies in the form of robotic articulated arms, these arms carrying here at their ends welding tongs, or any other means of assembly, so as to assemble with each other sheet metal parts by making welding points.

These robots which are identified by 1 1 to 14 at the assembly station 2 which is shown alone in Figure 2, surround a service location of the station where these robots jointly access to assemble the sheet metal parts. The configuration of the assembly robots on each of the other stations of FIG. 1 is identical to that of station 2.

In operation, the sheet metal parts to be assembled are presented in a tool which is brought to the service location of the station, so that these robotic arms perform the assembly while the parts are held in position in the tool.

In order to provide the line with considerable flexibility, a transverse tool change structure is associated with each of the stations 2 to 5, these structures respectively indicated by 16 to 19 in FIG. 1 being oriented perpendicularly to the longitudinal direction.

Each tool corresponds to a type of sheet metal element to be manufactured, so that the line of Figure 1 allows to flexibly manufacture three types of sheet metal elements, in this case three types of central floors. The transverse structure of the station 2 comprises three motorized trucks that are movable individually between six locations marked 21 to 26, these locations being distributed transversely and contiguous. The locations 21 and 22 are so-called waiting locations to the left of the location 23 which is the service location. Locations 24 to 26 are also waiting locations, but are located to the right of service location 23.

The transverse structure 16 comprises three tools, marked by 27,

28 and 29 which are respectively at the locations 22, 23 and 26, in the situation of Figure 2, being carried by their respective motorized carriages. Complementarily, the transverse structure also includes a loading station 31 which is located opposite the three waiting locations 24-26. This loading station 31 is here occupied by an operator to install sheet metal parts on a tool immobilized on a waiting location. In the situation of FIG. 2, the operator is thus able to load the tool 29 with sheet metal parts with a view to the subsequent assembly of these parts by the robotic arms of the assembly station 2.

Each motorized carriage, that is to say each tool 27, 28, 29 is movable transversely from one location to another, having its movements controlled by a central unit not shown. As can be understood, in the situation corresponding to that illustrated in FIG. 2, welding operations at station 2 make it possible to weld sheet metal parts installed in tool 28, these sheet metal parts having been put in place beforehand. by the operator when the tool 28 was immobilized at its waiting location 25.

Once the welding operations of the sheet metal parts presented in the tool 28 are completed, the handling system constituted by the robot 7 and its rail grasps the assembly of parts to place it on a corresponding tool located at the location service station of the following assembly station, namely substation 3.

The tool station 3 in which the robot 7 installs the assembly of parts from the station 2, already includes additional sheet metal parts previously installed in this tool by the operator of the transverse structure associated with station 3. These pieces of Additional sheet metal was installed in the tool of the station 3, during a previous step where the tool in question was immobilized at its waiting position vis-à-vis the loading station.

Returning again to the station 2 and its associated transverse structure, it is understood that the tool 28, now emptied of the pieces of plate it was carrying, is then moved to the left in the figure, together with the tool

27 for these two tools respectively occupy the waiting locations 21 and 22. This movement then allows the tool 29 which has just been loaded with sheet metal by the operator, to be moved by the motorized carriage which the door, to the service location 23 which is now free. To increase flexibility, another loading station may be provided on the left side of the transverse structure, namely a loading station located opposite the waiting locations 21 and 22, so as to allow the loading of Sheet metal parts in the tools waiting at these locations. The transverse structures 17-19 which are associated with the positions 3-5 are identical to the transverse structure 16 which has just been described.

Moreover, in the example of FIGS. 1 and 2, each supply station is a tool supply station that is manual: it requires a loading operator to manually grab the sheet metal elements to load them into the machine. immobilized tool at its location of waiting. But it is also possible to provide a supply robot or a mechanism that loads each tool at its waiting location with pieces of sheet metal to be welded. To save time and increase value, the assembly of several parts on a station can be provided in accordance with the method described in patent FR2874190. A first step of producing several welding points is then provided when the parts are installed in the tool, after which the partially assembled parts are lifted by the robotic arms of the station to carry out the other points of welding in height. During this time, the tool is removed transversely from the service location to be returned to its standby position, while a new coin loaded tool is returned to the service location.

Furthermore, in the example of Figures 1 and 2, the tools are motorized in isolation, but it may also be envisaged that these tools are coupled to each other to be moved together during operation of the installation.

With regard to the head station which is identified by 1, the associated structure ensures the supply of major bulk metal parts, so that this structure is substantially different from the transverse structures associated with the stations 2 to 5, both functionally as structurally.

In the second embodiment of the invention, which is shown in Figure 3, the tools are not worn and linked to individual motorized carts. Each transverse structure comprises a central rail carrying a mobile cart which serves a store with up to six waiting positions, but these waiting locations are located on either side of the central rail.

This other installation comprises here three assembly stations, marked 41, 42, and 43, aligned in a longitudinal direction, and rails carrying handling robots, marked by 45, 46, 47, 48 and 49, respectively are placed upstream of 41, between 41 and 42, between 42 and 43, and downstream from 43.

Each assembly station 41 -43 is equipped with five robotic arms, provided for example with welding tongs for welding sheet metal parts presented in a tool immobilized at the service location corresponding to the central region of the station extending between the robotic arms. The robotic arms of the station 41 which surround the service location of this station are marked 50, 51, 52, 53 and 54. A transverse tool change structure is associated with each assembly station 41, 42 and 43. these three transverse structures being identified by 56, 57 and 58.

The transverse structure associated with the station 41 comprises a tool-changing rail 59 oriented transversely, that is to say perpendicular to the alignment axis of the stations 41, 42 and 43, being entirely situated on the same axis. side of station 41. This transverse structure comprises three waiting positions arranged on one side of the central rail, marked 61 to 63, and three other waiting locations 64 to 66 disposed on the other side of this tool change rail 59 This tool change rail 59 carries a movable motorized carriage along the rail between the service location, and opposite each of the standby locations 61 to 66. This carriage can on the one hand unload the tool it carries on a free waiting slot and secondly load a tool resting on another waiting slot to bring it to the service location. This carriage is thus arranged to grasp a tool among the tools that can rest on one or other of the six waiting locations 61 to 66, to load it, and come to be positioned at the service location. Once the tool is installed at the service location between the robotic arms, it is possible to perform assembly operations of sheet metal parts by the arms, these sheet metal parts having been previously installed in the tool in question at the service location, by a handling arm.

The transverse structure of this second embodiment is a tool change structure incorporating a magazine with six waiting locations. In the configuration of FIG. 3, this transverse structure automatically manages four tools, marked 68 to 71, the tool 68 being at the service location 67 in the configuration of FIG.

3. The loading of each tool with the sheet metal parts to be assembled is here carried out when the tool is at the service location, but the structure could also be provided for installing the sheet metal parts in the tools when they are at a waiting location as in the first embodiment of the invention.

The transverse structure 57 associated with the station 42 is generally identical to the transverse structure 56 which has just been described with reference to the station 41. And the transverse structure 58 associated with the station 43 is of the same type as the structure 56, but it comprises only four waiting places instead of six: its central rail is therefore substantially shorter, as can be seen in FIG.

In practice, the sheet metal parts are put in place at a supply station identified by 69 which is upstream of the first assembly station 41. These sheet metal parts are then entered by the manipulator robot 45 to be installed in the tool 68 which corresponds to these parts, that is to say to one of the various types of elements that can be assembled on the installation. .

When the parts have been installed in the tool 68, the robotic arms assemble these parts together, for example by welding. Once this assembly is completed, the manipulator robots 46 located between the station 41 and the station 42 seize the assembly, by means of appropriate grippers, to come and install it on the tool which is immobilized at the service location. of the next assembly station, namely the station 42. Additionally, another welding parts supply station is located between the posts 41 and 42 being offset laterally with respect to the alignment of these positions, so that the manipulator robots carried by the rail 46 enter parts present on this supply station to install them in the immobilized tool at the service location of the station 41 as well as in the immobilized tool at the service location the assembly station 42.

Similarly, once assembly has been completed at station 42, manipulator robot 47 grasps this assembly for installation in the immobilized tool at the service location of the next assembly station, namely the post 43.

During operation, the plant is also commissioned to carry out tool changes on each station, using transverse structures and their motorized trucks, in order to ensure a completely flexible production. The motorized carriage which moves on the tool change rail 59, and which is shown in more detail in FIG. 4 and following, where it is marked at 72, has a motorized base 73 for rolling on the rail 59. It further comprises two motorized pulleys 74 and 75 spaced along the direction of travel of the carriage on the rail 59 and which are oriented perpendicular to this direction of travel.

These two pulleys are motorized and synchronized by a drive bar 76 extending parallel to the direction of movement of the carriage, and which is driven by an independent motor 77 carried by the base 73, so that the movement of these two pulleys is identical when the motor 77 which actuates them is controlled. Complementarily, the base 73 still carries two systems of pads 78 and 79 located on the upper face of the carriage, and which respectively follow the belt 74 and the belt 75.

The belts 74 and 75 each carry a gripping member, these gripping members being respectively identified by 81 and 82. In the configuration of FIG. 4, the carriage 72 is located at the service location 67 of the station 41, and carries the tool 68. The tool 69 is located at the standby slot 61, and the standby slot 66 which is located opposite the slot 61, is empty, these two locations being each materialized by two systems of pads of the same type as the systems 78 and 79 carried by the carriage.

In practice, the tool 68 is supported on the pads 78 and 79, it is held precisely in position on the carriage by additional elements, daggers type or the like, not visible in the figure and carried by the carriage. Complementarily, the gripping members 81 and 82 are engaged in complementary members situated at a longitudinal edge of the lower face of the tool 68.

To unload the tool 68 on the standby slot 66, and load the tool 69 from the standby slot 61, the carriage is first moved from the service location 67 to position it on the rail 59 at the standby locations 61 and 66 located on either side of the rail 59, as shown in Figure 5.

During the last phase of this movement, which corresponds to the transition between the situation of FIG. 5 and that of FIG. 6, the gripping members 81 and 82 which are already taken in the complementary members of the tool 68, are complementary to the complementary members located on the underside of the longitudinal edge of the tool 69 to be loaded.

In general, the gripping members 81 and 82 are in the form of baffles, and the complementary members of the tools are in the form of ribs protruding from the underside of the longitudinal edge of each tool. When a baffle arrives at a rib of a tool immobilized at its waiting location, the rib engages in this baffle, so that a motor control 77 to rotate the pulleys 74 and 75 is sufficient to move transversely the tool in question.

Thus, in the situation of FIG. 6, the carriage 72 which is at the standby locations 61 and 66 carries the tool 68, and its hooking members 81 and 82 are engaged in the complementary members of the tool 68 that it carries, but also in those of the tool 69 that it accosts.

As can be seen in FIG. 6, in this situation, one of the longitudinal edges of the tool 68 runs along a corresponding longitudinal edge of the tool 69, and the gripping members 81 and 82 are engaged in the complementary members of the tool. tool 68 and tool 69 which are located on the lower faces of the contiguous edges of these tools.

At this stage, the control of the motor 77 makes it possible to turn the pulleys 74 and 75 to move the gripping members towards the waiting position 66. During this synchronized movement of these two pulleys, the tool 68 is placed on the standby slot 66, at the same time as the tool 69 is placed on the carriage 72, in the place previously occupied by the tool

68.

Once the transverse movement of the pulleys is completed, which corresponds to the situation of FIG. 7, the carriage can be controlled to roll again towards the service location 67. As will have been understood, during the beginning of the movement of the carriage 72 along the rail, the complementary attachment members located on the lower face of the edge of the tool 68 leave the baffles of the gripping members 81 and 82, so that the tool 68 which has just to be unloaded at its waiting location 66 becomes completely detached from the carriage 72.

Once the carriage 72 has reached the service location, the loading operations of parts into this tool, and / or assembly of these parts to each other can begin. The succession of situations shown in FIGS. 4 to 7 corresponds to a tool change operation in which the same operation of the carriage 72 jointly ensures the unloading of the tool 68 on the location 66 and the loading of the tool 69. Furthermore, when the carriage 72 is at the service location, it is held in position by additional elements forming part of the service element, so that it is possible to actuate the belts of this carriage for change the side of its gripping members 81 and 82 when the future tool change requires such an inversion. The gripping member 81 which is shown in section in FIG. 8 may simply comprise a base 83, rectangular in plan view as in FIG. 9, which is rigidly secured to the belt 74, and this base may simply be provided with two studs or fingers 84, 85 protruding from its upper face being situated at the opposite vertices of the rectangular contour of this base 83.

In this case, the complementary members located on the underside of the edge of each tool are in the form of ribs 86, 87 having a length substantially shorter than that of the base, and a height sufficient to bear against the studs or fingers 84, 85. In the example illustrated in Figures 8 and 9, the rib 86 of the tool 68 further carries a roller 88 rotating about a vertical axis and bearing on the rib 87 of the tool 69 when these two ribs are taken in the baffle delimited by the studs 84, 85.

The transverse structure 56 associated with the station 41 manages four different tools 68-71 by using a motorized carriage 72 cooperating with a service location and six waiting locations.

But such a transverse structure may advantageously be equipped with a second carriage 80, of the same type as the carriage 72 and which is also moved on the tool change rail 59, but being operated for a tool storage function during the phases when the carriage 72 is immobilized at the service location.

This sorting carriage 80 shown in dashed lines has the same operation as the carriage 72, and it is actuated when the carriage 72 is stationary at the service location, to place the next tool to be used at one or other of the waiting locations closest to the service station 67, namely locations 61 and 66.

Such sorting trolley 80 and / or storage on the one hand saves time because when the carriage 72 comes for the next tool, it was previously placed closer to the service station 67, this which reduces its distance of movement. And it allows on the other hand, as illustrated in the figure

3, to operate not four but five different tools on the same transverse structure with six waiting places and a service location, because this sorting carriage continually carries an additional tool 90. In another embodiment of the invention illustrated in Figure 10 is used two carriages of the same type as that of Figures 4 to 9, but which play the same roles instead of having a dedicated dolly for tool change operations and another dedicated to their storage.

This other transverse structure which is marked by 56 'includes a tool change rail 59' which is also oriented transversely to the longitudinal direction of the installation, but which extends on either side of its assembly station 41 'which comprises, as in the embodiment of Figure 3, a service location surrounded by a plurality of assembly robots 51' -53 '. The transverse structure 56 'here comprises, on the one hand two holding locations 61' and 62 'located on the same side of the tool change rail 59' but being on either side of the station of assembly 41 ', and two other waiting locations 65' and 66 'which are located on the other side of the tool change rail 59' while being on either side of the assembly station 41 '. The locations 61 'and 66' are opposite one another by being separated by the rail 59 ', and the positions 62' and 65 'are also vis-à-vis one another also being separated by the rail 59'.

The tool change rail 59 'here carries two motorized carriages 72' and 80 'each carry a tool, which may for example be coupled to one another. When the carriage 72 'is at the service location 67' of the station 41 ', the carriage 80' is vis-à-vis the waiting locations 62 'and 65'.

As will be understood, a transverse structure is then obtained at four holding locations 61 ', 62', 65 ', 66' and a service location 67 'which makes it possible to manage four different tools. These various tools which are identified by 68 ', 69', 70 'and 90' are carried respectively by the carriage 72 ', the location 61', the location 62 ', and the carriage 80' in the situation of FIG. 10.

In operation, when one of the trolleys, for example the trolley 72 ', is at the service location and assembly operations are in progress, the other trolley 80' can carry out a tool change by view of the next assembly operation, which offers an additional gain with respect to the cycle time of the installation.

Claims

1. Flexible installation for assembling sheet metal parts to form sheet metal elements of several types, each sheet metal element resulting from a succession of separate assembly operations performed on this installation, this installation comprising:

a series of assembly stations (2-5; 41 -43; 41 ') aligned longitudinally to carry out the succession of assembly operations necessary for the constitution of each sheet metal element, each station (2-5;

41-43; 41 ') having one or more assembly robots (1 1 -13; 50-53; 51' -53 ') for assembling sheet metal parts installed in a tool (27-29;

71, 90; 68'-70 ', 90');

one or more handling robots (6-9; 46,47) for moving each sheet metal assembly of one station (2-5; 41 -43; 41 ') to another;

several transverse structures (16-19, 56-58, 56 ') each associated with an assembly station (2-5; 41 -43; 41'), each transverse structure (16-19; 56-58; ') carrying a plurality of tools (27-29; 68-71, 90; 68'-70', 90 ') each adapted to the assembly of one type of element and means for moving each tool at least transversely between a waiting position (21, 22, 24-26; 61-66; 61 ', 62', 65 ', 66') offset laterally with respect to the station (2-5; 41 -43; 41 '), and a service location (23; 67; 67 ') located in the assembly station (2-5; 41 -43; 41').

2. Installation according to claim 1, comprising at least one transverse structure (16-19) incorporating at least one loading station (31) positioned to allow the loading of sheet metal parts to be assembled in a tool (28) immobilized at least a waiting area (24-26).

3. Installation according to claim 2, comprising at least one transverse structure (16-19) provided with waiting locations located from and other of the alignment of the assembly stations (2-5) and incorporating at least two loading stations located on either side of the alignment of the assembly stations (2-5).

4. Installation according to claim 2 or 3, further comprising a loading station (31) equipped with robotic means for loading sheet metal parts to be assembled in each tool (28) immobilized in a holding position.

An installation according to claim 1, wherein each transverse structure comprises a tool change rail (59; 59 ') and holding locations (61-66; 61', 62 ', 65', 66 '). along the tool change rail (59; 59 '), and wherein the means for moving each tool between the service location (67; 67') and each standby location (61-66; 61 '); 62 ', 65', 66 ') comprise a carriage (72; 72') carried by the tool change rail (59; 59 '), which carriage (72; 72') is provided with means for loading and unloading laterally a tool at a waiting location.

An installation according to claim 5, wherein the waiting locations (61-66; 61 ', 62', 65 ', 66') which run along the tool change rail (59; 59 ') are located both sides of this tool change rail (59; 59 ').

7. Installation according to claim 5 or 6, wherein the carriage (72) comprises at least one element (74, 75) movable transversely relative to the direction of movement of the carriage (72) each element (74, 75) movable carrying a gripping member (81, 82) adapted to mate with a complementary member (86, 87) of a tool edge, so as to transversely move a tool between a waiting location along the change rail tool (59) and the upper face of the carriage (72), or vice versa.

8. Installation according to one of claims 5 to 7, wherein the tool change rail (59) carries a second carriage (80) controlled to place the next tool to use at a waiting location close to the service location (67) while the other carriage (72) is stationary at the service location (67) during an assembly operation

9. Installation according to one of claims 5 to 7, comprising holding locations (61 ', 62', 65 ', 66') located on either side of the assembly station (41 ') and of on both sides of the tool change rail (59 '), and in which the tool change rail (59') carries two carriages (72 ', 80') each adapted to perform tool change operations.