Patent Publication Number: US-8533932-B2

Title: Device and process for assembly of panels using riveting

Description:
TECHNICAL FIELD 
     The present invention relates in a general manner to the field of assembly of panels or thin metallic structures using riveting, with this technique being widespread in aeronautical construction activities. 
     The invention in effect finds a preferential application in but is not restricted to the field of robotic assembly using riveting of aircraft panels which exhibit highly curved drilling/riveting surfaces such as, for example, the leading edge of wings, or of those with lesser curvature, such as aircraft fuselage panels. 
     PRIOR ART 
     The devices used to assemble panels using riveting have already been widely developed in existing activities. 
     In the aeronautical industry these devices usually incorporate a chassis which, holds a drilling system, a riveting system, as well as a hold-down system. The hold-down system is usually operated first so as to establish contact with the panels to be assembled, then the drilling system in its turn drills the panels to produce a hole into which a rivet is then inserted, delivered by the riveting system. For indication purposes it should be noted that the hold-down system may be duplicated by a second hold-down system in order to apply pressure on both sides of the panel assembly. Moreover, depending on the options for access to this structure, the rivets are put in place from one side of the panels to be assembled, or from both sides of the latter. 
     The assembly formed by the chassis holding the various systems mentioned above is usually placed at the end of a robotic arm of the device, thus allowing this assembly to be brought to the desired location in relation to the panels to be assembled. 
     The drilling and riveting systems on existing devices, as described in document EP 1 329 270, are in general operated so that the riveting head and drilling head are alternately brought into the working axis of the device, in order to carry out one or more of the operations which are specific to them and involving the initiation of other movements. 
     This method of operation, which therefore requires that drilling and riveting systems are set in motion sequentially, requires that a relatively complex kinematic drive chain be present which combines many devices for carrying out rotation and translation movements and which results not only in an increased mass and greater overall volume, but above all in a loss of drilling precision. 
     In effect, an obvious loss of rigidity of the drilling head is observed which results not only from, the significant number of movement devices with which it is associated, but also due in particular to the fact that this multiplicity of movement devices encourages internal kinematic variations associated with the tooling to develop over time, which favours the development of play. These variations, combined with the flexibility of the robot arm carrying systems, naturally means that the drilling system does not exhibit sufficient rigidity in the drilling axis to be able to guarantee the formation of completely circular holes and/or regular countersinking. 
     OBJECT OF THE INVENTION 
     The purpose of the invention is therefore to propose a device and process for the assembly of panels using riveting which remedies, at least in part, the above mentioned problems associated with manufacturing using existing practices. 
     To this end the subject of the invention is a device for the assembly of panels using riveting, where the device includes a riveting system together with a drilling system, where the drilling system includes a first carriage, as well as a drilling head mounted on the first carriage, and defines an axis of the drilling head, and the riveting system which includes a second carriage as well as a riveting system head mounted on the second carriage and which defines an axis of the riveting head. According to the invention, the device additionally includes means for setting the riveting head in motion relative to the second carriage, designed to be capable of moving this same riveting head between an at-rest position where the drilling head axis is distinct from that of the riveting head, and a working position in which the drilling head axis and the riveting head axis coincide. 
     Advantageously, the device according to the invention provides improved precision of drilling, given that the kinematic drive mechanism associated with the drilling system may be simplified relative to those encountered in existing practice. In effect it is no longer necessary to set the drilling system in motion in order to ensure that the drilling and riveting systems are alternately put in position in the working axis. 
     This is explained by the fact that the solution that is proposed involves the drilling head remaining permanently in the device&#39;s drilling axis, whether during the drilling operation or during the riveting operation, since it is the riveting system itself which is designed so that its riveting head is alternately released from the working axis, and aligned along it by moving to a forward location in relation to the drilling head with which this riveting head is then also aligned. 
     Consequently the arrangement that is proposed provides a high degree of rigidity in the drilling axis, capable of ensuring that perfectly circular holes and regular countersinking are farmed. 
     Furthermore, it should be noted that the simplification of the kinematic drive chain associated with the drilling system is aimed not only at reducing the risk of internal kinematic variation associated with the tooling and which promotes the appearance of play, appearing over time, but also advantageously leads to a reduction in the mass of the device, as well as of its overall volume. 
     According to one preferred option for construction, the means for setting the riveting head in motion relative to the second carriage are means for initiating rotation, where the rotation movement sought is then produced along a second axis parallel to the drilling axis, and which is distinct from the drilling head axis. 
     In such a configuration which is not, it should be emphasised, intended to be restrictive in any way, the aforementioned axis of rotation, the drilling head axis and the riveting head axis are therefore permanently parallel to each other, and sometimes even coincide as far as the drilling head and riveting head are concerned. 
     The device may also include a chassis on which are mounted both the riveting system and the drilling system, with the first and second carriages each being arranged so as to be capable of sliding in a rectilinear manner relative to the chassis, along the same slide direction. With this arrangement it is preferable if the device is designed to include in addition some means of coupling which, when they are in an activated state, allow the first and second carriage to be coupled to each other in translation along the slide direction, and when they are in a deactivated state, allow these first and second carriages to slide relative to one another along this same slide direction. 
     This specific feature advantageously allows the same drive means to be used to produce movement in the slide direction of both the drilling system carriage, and also of the riveting system carriage at the same time. This naturally leads to a simplified design as well as to a reduction in mass and volume. 
     To do this the means of coupling include, for example, a guide rail which is arranged along the slide direction and which is firmly fixed to the first carriage, and at least one pad in the form of a brake calliper which can be actuated, fixed firmly to the second carriage, where the brake calliper which can be actuated fits against the guide rail. 
     It would be possible, however, to envisage movement of each of the first and second carriages being initiated by means for initiation of movement which are not common, but distinct, without going beyond the scope of the invention. 
     According to another mode of construction of the present invention which is even more preferable, the means for setting the riveting head in motion relative to the second carriage include a parallelogram whose shape can change, which in general allows the design of the device to be simplified even further and which therefore no longer requires the aforementioned means for initiating rotation to be present. The use of a parallelogram whose shape can change, similar to pantograph, in general terms ensures simplified sequencing of the riveting operation which follows the drilling operation, and therefore provides improved efficiency of the device. In effect, as will be described in more detail below, it should be noted that the parallelogram is designed to change shape so that brings the riveting head into its working position in which the drilling head axis and the riveting head axis coincide, where this change in shape may advantageously be effected automatically during a single movement of the second carriage, preferably in parallel with the drilling head axis. 
     More specifically, the means for setting the riveting head in motion relative to the second carriage include:
         two parallel arms which form the parallelogram which can change shape, each articulated at one of its two ends with the second carriage and articulated at the other of its ends with the riveting head;   a mechanical system for changing the shape of the parallelogram designed so as to produce, when the second carriage is sat in motion along a slide direction, a change in shape of the parallelogram from a first configuration which places the riveting head in its at rest position, to a second configuration which places the riveting head in its working position, and vice versa.       

     Consequently it should be understood that the second carriage and the riveting head respectively form two parallel sides of the parallelogram whose shape can be changed, with the other two parallel sides being formed, of course, by the aforementioned arms. 
     Furthermore, as stated previously, it is preferably envisaged that the parallelogram changes shape in a predetermined manner during a single initiation of movement of the second carriage along a slide direction which is preferably the same as the direction of movement of the riveting head at the end of the riveting operation, that is, along the direction of the working axis of the device, itself parallel to the direction of the drilling head axis. Consequently this preferred mode of construction is noteworthy in that the sequencing of the riveting operation is simplified in the extreme, given that it only involves setting the second carriage in motion along the slide direction. 
     The mechanical system for changing shape is preferably a guide system which includes a pin which is firmly attached to one of the parallel arms, with the pin sliding in a guide slot when the second carriage is set in motion along the slide direction. The slot, similar to a switching track or rail, has a shape which is suitable for ensuring that the desired change of shape of the parallelogram is achieved. 
     It should therefore be noted that the guide slot preferably successively exhibits a first portion which allows the parallelogram to be maintained in its initial configuration placing the riveting head in its at rest position, a second portion which gradually allows the parallelogram shape to change until it takes up its second configuration, placing the riveting head in its working position, and a third portion which allows the parallelogram to be maintained in its second configuration in order to allow riveting operations to take place. Each of the three contiguous portions is preferably rectilinear, respectively aligned in three distinct directions. In this respect it is preferably envisaged that the first and third parts are parallel to one another and parallel to the working axis, whereas the second part is inclined relative to these in order to ensure that the riveting head is gradually brought towards the working axis. Finally, it is indicated that the guide slot, which is preferably located in one plane, may not include the first aforementioned portion, but the other two portions only which respectively ensure firstly a change in shape of the parallelogram in order to bring the riveting head into its working position, then maintains the parallelogram in this modified shape in order to set this head in translation motion to carry out the riveting operation along the working axis. 
     The device preferably includes a chassis carrying the guide slot and on which are mounted both the riveting system and the drilling system, with the first and second carriages each being arranged so as to be capable of sliding in a rectilinear manner relative to the chassis, along the same slide direction, with the drilling system including means for setting the first carriage in motion in the slide direction, and the riveting system also including means for setting the second carriage in motion in the slide direction. 
     Alternatively, it could be envisaged that the first and second carriages respectively slide in two different directions, that is, not parallel to each other. Furthermore, another possibility would be to use same means for setting the first and second carriages in motion in a manner which is the same as or similar to that described above which includes means of coupling. 
     In order to restrict the overall volume of the device as much as possible, the means for setting the second carriage in motion in the slide direction include a rodless cylinder of conventional design and familiar to those working in the field. An alternative solution would, for example, involve the use of a linear motor, as is preferably used to construct the means for setting the first carriage in motion. In such a case, the linear motor employed is of the type widely available on the market. 
     Preferably again, irrespective of the preferred mode of construction involved, the first carriage is also preferably mounted on two guide rails firmly attached to the chassis, using multiple pads in the form of callipers which fit against the two guide rails and which are firmly fixed to the first carriage. It may then be envisaged that each of these guide rails for the first carriage are fitted with a core, arranged respectively in two inclined planes which together form a V in a section taken orthogonally the drilling head axis. 
     Thus activation of the solenoid of a primary component of the linear motor creates electromagnetic forces which cause movement of the first carriage on the rails and also attraction of the carriage to a secondary component which usually takes the form of a track of permanent magnets. The effect of this attraction is to cause the first carriage to be pressed onto the guide rails which, because of their V arrangement assist greatly keeping the drilling head centred in the working axis. Effectively, in operation these support forces continually maintain the first carriage on the rails arranged as a V, thus preventing play occurring which generates vibration and which would be extremely prejudicial to drilling precision. 
     For indication purposes, each of the two guide rails of the first carriage preferably has an I-shaped transverse section. 
     Furthermore, it could be preferentially envisaged that the first carriage be equipped with a first reading head designed to fit against an optical rule placed on the chassis. This allows the first carriage to undergo controlled micrometric movements on the device chassis, and therefore allows the creation of holes/countersinking with very precise dimensions to be envisaged. 
     The second carriage of the riveting system is in turn preferably mounted on a guide rail firmly attached to the chassis, and also aligned in the slide direction using at least one pad in the form of a calliper which fits against the guide rail and which is firmly fixed to the second carriage. Preferentially it is envisaged that this rail be distinct from the two guide rails on which the first drilling system carriage is secured. As an indication, the said rail is used both for the case where the riveting head is fitted on the means for initiating rotation and for the case where it is carried by a parallelogram which can change shape. 
     The device also preferably includes a hold-down system arranged in such a way as to be capable of sliding in a rectilinear manner relative to the chassis, along the slide direction. The hold-down system preferably includes a third carriage mounted on the chassis, together with means for setting this third carriage in motion in the slide direction. 
     In this respect it is preferably envisaged that the means for setting the third carriage in motion take the form of a linear motor, which may be such that it has a fixed secondary element in common with the linear motor of the first carriage, namely a track of permanent magnets placed between the two guide rails of the first carriage. This specific feature also allows the number of kinematic linkage elements in the device to be reduced, the consequence of which is a further reduction in the mass and overall volume of the device. 
     It could therefore also be envisaged that the third carriage be mounted on the two guide rails which guide the first carriage, using multiple pads in the form of a calliper which fit against these two guide rails and which are firmly fixed to the third carriage. 
     Here again the third carriage is equipped with a second reader head designed to fit against an optical rule placed on the chassis, which is of course preferably identical to that which fits against the first reader head with which the drilling system carriage is equipped. As stated above, this advantageously allows micrometric movements of the third carriage on the chassis to be envisaged. 
     Furthermore, it is indicated that the hold-down system has a hold-down head fitted on the third carriage and which defines a hold-down head axis which coincides with the drilling head axis. 
     It is envisaged that the chassis be preferably mounted on a robot arm of the device, for example by means of a five-axis head. 
     In addition, the device also preferably includes a control system provided with means for delivering advance speed settings for a drilling tool for the device, along the drilling axis together with rotation speed settings for this tool, where these settings depend on information on the local stiffness of panels at a hole to be drilled in order to receive a rivet. 
     Thus by using information on the local stiffness of the panels to control the hole drilling operation, which in a conventional but non-restrictive manner involves the creation of this hole as well as, preferably, countersinking designed for the rivet head housing, it is advantageously possible to guarantee that a perfectly circular hole is formed without delamination when drilling composites, together with regular countersinking at the end of this hole. 
     Finally one objective of the invention is a process for assembly of panels using riveting carried out using a device such as that which has just been described. 
     Other advantages and characteristics of the invention will appear in the detailed non-restrictive description below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       This description will be made in relation to the appended drawings, in which: 
         FIG. 1  represents a perspective view of a part of the device for assembling panels using riveting which is in accordance with one preferred mode of construction of the present invention; 
         FIG. 2  shows an exploded perspective view of the device shown in  FIG. 1 ; 
         FIG. 3  shows a section view taken through plane P of  FIG. 1 ; 
         FIGS. 4 to 6  represent schematic views of various parts of a control system fitted to the device shown in  FIGS. 1 to 3 ; 
         FIGS. 7   a  to  7   i  show the device in  FIGS. 1 to 3  at different stages during the operation of a process for assembling panels using riveting in accordance with one preferred mode of construction of the present invention; 
         FIG. 8  represents a perspective view of a part of a device for assembling panels using riveting which is in accordance with another preferred mode of construction of the present invention; 
         FIG. 9  shows a front view of the device shown in  FIG. 8 ; 
         FIG. 10  represents a perspective exploded view of a pert of the device shown in  FIGS. 8 and 9 , detailing more specifically the design of the second carriage carrying the riveting head; 
         FIG. 11  represents a schematic view from above illustrating the guide slot used to change the shape of the parallelogram whose shape can be changed which is fitted to the device shown in  FIGS. 8 to 10 ; and 
         FIGS. 12   a  and  12   b  show the device in  FIGS. 8 to 11  at different stages during the operation of a process for assembling panels using riveting in accordance with one preferred mode of construction of the present invention; 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     With reference first of all to  FIGS. 1 to 3  taken together, a part of the device  1  for assembling panels using riveting in accordance with a preferred mode of construction of the present invention can be seen, where the panels are of a metallic type or made from any other material such as from composite materials. 
     This device  1  according to the invention, which finds a particular application in the field of aeronautical construction, may be adapted to allow any type of rivet to be fitted automatically, such as pop rivets and/or staked rivets, and/or flattened rivets without exceeding the limits of the invention. It should nevertheless be noted that the device  1  is preferably designed for working blind using pop rivets. 
     The part of the device  1  represented in  FIGS. 1 to 3  only relate to an end portion of this device, and is preferably made up of a tool which can be removed/fitted which is designed to be assembled to the end of a robotic arm (not shown) preferably forming en integral part of this device. As an indication, should be noted that the junction between the end of this robot arm and the tool part which will now be described may be made up of a five-axis head familiar to those working in the field and which allows this tool to be aligned very precisely in space. 
     For reasons of clarity, the description of the device  1  will be made with reference to a system of axes for this device, which is specifically attached to a chassis  2  of the latter, also known as the tool chassis. Thus the longitudinal direction of the device is called X; Y is the direction aligned transversely relative to this device, and Z is the vertical direction or height, where these three directions are orthogonal to each other. It is understood, naturally, that the aforementioned system of axes moves accordance with the same movement as that of chassis  2 , operated by the robot arm. 
     The device  1  therefore includes overall, attached to the chassis  2 , three systems designed to ensure different functions, namely a drilling system  4 , a riveting system  6 , together with a hold-down system  8 . For information, it is indicated here that these systems are also known as actuators or effectors. 
     As far as the drilling system  4  is concerned, the latter has a first carriage  10  which holds the drilling spindle  12 , which on its front part has a drilling head  14  equipped with a drilling tool  17  and which defines a drilling head axis  16 , also known as the drilling tool axis, along which this tool is arranged. More specifically, the spindle  12  is fixed firmly to the carriage  10 , so that the relative positions between the axis of the drilling head  16  aligned along direction X and this carriage  10  is designed to remain unchanged throughout an assembly cycle using riveting. As an indication, the drilling head  14  is conventionally made up of the drilling tool  27 , together with the support for this tool, of a mandrel or similar type. 
     The first carriage  10  is fitted on the chassis  2  in such a way that it can slide in a rectilinear manner relative to the latter in a slide direction  18  parallel to direction X. To do this the carriage  10  is mounted so that it slides on two guide rails  20  aligned in direction X, and consequently also aligned in the slide direction  18 , where these two rails are spaced apart from each other in direction Y. 
     More precisely with reference to  FIG. 3  which shows a transverse section in a plane P aligned along directions Y and Z and which passes through the drilling system  4 , it may be seen that the two rails  20  which have, for example, an I-shaped transverse section, are arranged so that the two cores of these I&#39;s are respectively located in two inclined planes P 1 , P 2  which together form a V. In addition, the upper tracks of these two rails  20  are therefore also respectively located in two inclined planes P 3 , P 4  which together form a V, with the point of this last V being aligned downward in the direction Z. It should be noted that these two Vs each have two symmetric branches between them relative to a vertical plane XZ passing through the axis  16 , and which together form an angle of about 90°. 
     The V-shaped arrangement of the upper tracks of the rails  20  allow easy and Precise adjustment of the carriages arranged on these rails, and overall allows any unwanted movement of these carriages to be locked when they are in translation movement on the rails. 
     In order to allow it to be secured onto the rails  20 , the carriage  10  is fitted with multiple bearing pads  22  in the form of a calliper, designed, for example, so that there are four in number, with two of these associated with one of the rails  20 , and the remaining two associated with the other of these rails. Each of these pads  22  therefore grips the upper branch of the ‘I’ of one of the two rails  20 , as can be seen more easily in  FIG. 3 . 
     In order to allow movement for the first carriage  10  in the slide direction  18  relative to the chassis  2 , the drilling system  4  incorporates means for initiating movement  24 , which preferably takes the form of a linear motor which includes a primary mobile element  26  on board the first carriage  10 , together with a secondary fixed element  28  mounted on the chassis  2 . 
     As can clearly be seen in the figures, chassis  2  has an overall U-shape in section along a plane YZ, at the two ends of which are fixed the two rails  20 . Between the two arms of this U is a magnetic path made up of rare-earth permanent magnets, whose North and South polarities alternate along this path. This path, placed underneath the first carriage  10 , therefore forms the secondary fixed component  28  of the linear motor  24 . 
     Thus activation of the solenoid fitted to the primary mobile component  26  of the linear motor  24  creates electromagnetic forces which provide, on the one hand movement of the first carriage  10  on the rails  20  in direction X and on the other hand an attraction along direction Z between this carriage  10  towards the fixed secondary component  28 . 
     In order to achieve micrometric precision in the movement of the carriage  10 , it is envisaged that the latter be equipped with a reader head  30  which fits against an optic rule  32  placed on the chassis  2  along direction X. This rule is preferably made up of a glass bar which bears graduations of very high precision. Thus the reader head  30  converts markings on the rule  32 , which are read as the carriage  10  passes them, into electronic signals, in order to give its exact position on the guide rails  20 . 
     The description of the drilling system  4  which has just been given shows one of the specific features of the present invention, namely, that the axis of the drilling head  16  is designed to remain permanently in the working axis of the device, and is therefore not in any case intended to be given any movement relative to the chassis  2  during operation of the device. 
     Still with reference to  FIGS. 1 to 3 , for its part the riveting system  6  includes a second carriage  34  which supports the entire riveting tool  36  or riveter, the front part of which includes a riveting head  38 , which in turn defines a riveting head axis  40  which is parallel to directions X and  18 . More precisely, the riveting head  38 , and more generally the riveting tool assembly  36 , is mounted so that it is firmly fixed to the front of an offset arm  42  which overall extends in direction X, and whose rear part is mechanically connected to the carriage  34 . 
     The aforementioned mechanical connection is constructed using means for initiation of movement (hidden in the figures) designed to cause the arm  42  and the head  38  which is firmly fixed to it to rotate in relation to the carriage  34  around an axis of rotation  44 , with the aim of moving this same riveting head  38  between an at-rest position in which the drilling head axis  16  and the riveting head axis  40  are distinct and parallel as shown in  FIGS. 1 and 3 , and a working position in which these axes  16 ,  40  coincide, as will be explained later. The means for initiating movement therefore preferably take the form of a conventional rotary motor, whose axis of rotation  44  is preferably parallel to directions X and  18 , and naturally distinct from the axes of the drilling head and of the riveting head  16 ,  40 . This means that starting the rotary motor causes a movement of the head relative to the carriage  34 , with this movement describing a trajectory which corresponds to a part of a circle located in a plane YZ. 
     The second carriage  34  is fitted to the chassis  2  so that it may slide in a rectilinear manner relative to it in the slide direction  18 . To do this the second carriage  34  is mounted so that it slides on a guide rail  46 , preferably distinct from the two guide rails  20  of the carriage  10 , but also aligned along directions X and  18 . As shown in  FIG. 2 , the rail  46  with a transverse section in the form of an H is firmly fixed to a lateral external surface of one of the arms of the U formed by the chassis  2 . 
     In order for it to be secured on the rail  46 , the carriage  34  is equipped with one or more bearing pads  48  in the form of a calliper, for example as a set of two, spaced out along direction X. Each of these pads  48  therefore presses against the free side arm of the N which is opposite the other side arm which is firmly fixed to the chassis  2 . 
     The carriage  34  for the riveting system  6  preferably contains no means of its own for initiating translation movement, but is envisaged as being able to couple to the carriage of the drilling system  4 , and may consequently be made to move along the direction  18  by the operation of the first linear motor  24  described above. 
     In effect means of coupling  50  are envisaged which, when they are in an activated state, allow the first and second carriage  10 ,  34  to be coupled in translation along direction  18 , and when they are in the deactivated state, allow these same carriages to slide relative to one another. 
     To do this it is envisaged, for example, that these means  50  include a guide rail  52  firmly fixed to the first carriage and arranged along directions X and  18 , as well as at least one pad  54  in the form of a brake calliper which may be actuated, firmly fixed to the second carriage  34 , and more specifically with one upper inclined part of the latter which tends to move towards the spindle  12  in order to minimise the overall volume. Thus, depending on whether or not it is wished to couple these two carriages in translation along direction  18 , the brake callipers  54  secured permanently to the free upper part of the rail  52  with a transverse I-shaped section are consequently actuated, for example electromagnetically. In this respect it should be noted that in the case envisaged where the riveting system  6  is equipped with its own means of initiating translation movement, the latter may then take any form familiar to those working in the field, such as, for example, by incorporating a hydraulic actuator. 
     The direct coupling above also allows, of course, micrometric precision to be achieved in movements of the carriage  34 , thanks to the reading head  30  fitted to the carriage  10  and to the optical rule  32  placed on the chassis  2 . 
     As far as the hold-down system  8  is concerned, the latter has a third carriage  60  which holds a hold-down head  62 , also known as pressurisation gun, and which defines a hold-down head axis  64  aligned along directions X and  18 . In a manner which is familiar to those working in the field, the head  62 , designed to bring the panels to be assembled during drilling and riveting operations into contact with each other, is provided with a through hole  66  arranged along the hold-down head axis  64  and designed so that the drilling head  17  and the riveting head  38  alternately pass through it. More precisely this head  62  or gun is fitted firmly to the carriage  60 , so that the relative position between the hold-down head axis aligned along direction X and this carriage  60  is designed to remain unchanged throughout a cycle in which assembly is carried out using riveting. 
     Furthermore, one of the specific features of this preferred mode of construction relies on the fact that the axes  64  and  16  permanently coincide during the cycle in which assembly is carried out using riveting. 
     The third carriage  60  is fitted on the chassis  2  in such a way that it can slide in a rectilinear manner relative to the latter along a slide direction  18 . To do this the carriage  60  is mounted so that it slides on two guide rails  20  arranged in a V as described earlier, in a forwards direction relative to the first carriage  10  of the drilling system, it being understood, naturally, that forwards and backwards are here determined as a function of the orientation of the drilling tool used by the system  4 . 
     In order to allow it to be secured onto the rails  20 , the carriage  60  is fitted with multiple bearing pads  68  in the form of a calliper, envisaged, for example, as a set of 4 in number, with each of these associated with one of the two rails. Each of these pads  68  therefore grips the upper arm of the I of one of the two rails  20 . 
     In order to allow the third carriage  60  to move in the slide direction  18  relative to the chassis  2 , the hold-down system  8  incorporates means for initiating movement  70 , which preferably take, the form of a linear motor which includes a primary mobile element  72  on board the third carriage  60 , together with a secondary fixed element  28  mounted on the chassis  2 , and which is preferably the same as that used for the first linear motor, with the aim of minimising as much as possible the number of kinematic components required for operation of the device  1 . 
     Thus, here also, activation of the solenoid fitted to the primary mobile component  72  of the linear motor  70  creates electromagnetic forces which provide, on the one hand, movement of the third carriage  60  in direction X on the rails  20  and on the other hand an attraction along direction Z between this same carriage towards a fixed secondary component  28  of the permanent magnet type track. 
     In order to also achieve micrometric precision in the movement of the carriage  60 , it is envisaged that the latter be equipped with a reading head  74 , which fits onto the aforementioned optical rule  32  placed on the chassis  2 . This means that it is therefore possible to achieve complete control over the relative separation of the two carriages  10  and  60 , which offers the advantage of giving better control over the depth of the holes and countersinking made using the drilling tool. 
     In order to operate this device  1  in the desired manner, it is also equipped with a control system  83  shown schematically in  FIGS. 4 to 6 . Overall this system  83  includes a first means of control  84  associated with the hold-down system  8 , together with a second means of control  86  which is associated with the drilling system  4 , with these means  84 ,  86  naturally being capable of being combined within the same item of equipment. 
     As far as the first means  84  shown in  FIG. 4  are concerned, these include a first digital control unit  88  connected to a control board  90  for the linear motor  70  for the hold down system  8 . The unit  88  is therefore capable of delivering instructions for position, speed of advance and power to the board  90 , which then carries out a servo-control of position, speed of advance and power, by supplying an appropriate level of power to the motor  70  to which this board  90  is connected. 
     In return the servo-control board  90  receives information from the reading head  74  on the actual position of the carriage  60 , with this information being sent to the unit  88 . In addition this servo-control board  90  is also capable of sending measurements to the unit  88  which relate to the speed of advance of the carriage  60  and the effective power, where this effective power allows the unit  88  to determine the motor power passing through the system  8  during the approach and clamping operations. 
     As far as the second means  86  shown in  FIG. 6  are concerned, these include a second digital control unit  92  connected to a servo-control board  94  for the linear motor  24  for the hold down system  4 . The unit  92  is therefore capable of delivering instructions for position, speed of advance and power to the board  94 , which then carries out a servo-control of position, speed of advance and power, by supplying an appropriate current to the motor  24  to which this board  94  is connected. In return the servo-control board  94  receives information from the reading head  30  on the actual position of the carriage  10 , with this information being sent to the unit  92 . In addition this servo-control board  94  is also capable of sending measurements relating to the speed of advance of the carriage  10  and if necessary the effective power to the unit  92 . 
     Furthermore, the digital control unit  92  is also connected to a servo-control board  96  for the rotary motor for the spindle  12 . The  92  is therefore capable sending rotation speed and power settings to the board  96 , which then carries out a servo-control of rotation speed and power, by supplying an appropriate current to the rotary motor to which this board  96  is connected. In return, it could if necessary be envisaged that this servo-control board  96  sends the unit  92  measurements relating to the rotation speed of the tool  17  and effective power. 
     In this respect it should be indicated that the unit  92  includes means  82  which enable the delivery, to boards  94  and  96  respectively, of advance speed settings for the tool and speed of rotation settings of the tool which are a function of the information on the local stiffness of the panels at the hole which is destined to receive a rivet, with this information being given the name Info_stiffness. 
     More specifically with reference to  FIG. 5 , it can be seen that these means  82  take the form, for example, of a correction matrix for the two aforementioned settings, this matrix therefore taking into consideration not only the Info_stiffness information determined earlier, but also as appropriate the nature of the material and the type of drilling tool, data for which is pre-recorded in a specific programme. Naturally this correction matrix is designed so that the advance and rotation speed settings that is issues to boards  94  and  96  allow drilling to be carried out with as high a level of quality as possible. 
     The process for assembling using riveting which uses the device  1  described above will now be described with reference to  FIGS. 7   a  to  7   f , where this process overall includes a step for determining information on the local stiffness of panels at a hole to be drilled, followed by a drilling step whose purpose is to create the hole, together with the countersinking associated with it, mien finally a step for fitting a rivet in the aforementioned drilled hole, with these three steps being repeated for each rivet to be fitted in the panels to be assembled. 
     As shown in  FIG. 7   a , the chassis is first of all positioned in relation to the panels  80  to be assembled depending on the point in these where the rivet is to be placed, with all three systems  4 ,  6  and  8  being in their at-rest position. 
     More precisely, with reference to  FIG. 7   b , it can be seen that the chassis  2  is first of all brought by the robot arm close to the panels  80  to be assembled, so that the front end of the hold-down head  62  is located at a standard distance D_stand from the panels  80  along the slide direction  18  and the direction of the axis  64 , where this distance may be of the order of 15 mm. At this stage the carriage  60  is in a position such that its central point C is located at a set point R on the optical rule  32 . 
     Then the approach operation is initiated by commanding linear movement of the carriage  60  using the unit  88 , in order to achieve contact between the head  62  and the panels  80 . It should be noted that as soon as the aforementioned contact is established, the control unit  88  periodically determines the motor power value P 1 _absorbed passing through the system  8 , where this value P 1 _absorbed is then converted by a converter incorporated in the unit  88  in order to obtain a value of the resistance force of the panels at approach F 1 . As an indication, it should be noted that this force F 1 , updated every 5 ms, also corresponds in value to a depression force exerted by the hold-down system  8  against the panels  80 . 
     The control of this approach operation is envisaged to be such that movement of the system  8 , and more specifically that of its carriage  60 , occurs when the determined force F 1  reaches a target value F 1 _target, which may be for example set to a low value of the order of 1N. As shown in  FIG. 7   c , at the end of the approach operation, the carriage  60  has therefore covered a distance D 1 _final between the point R and a point C 1  on the rule  32 , where point C of carriage  60  is located, with the value of this distance F 1 _final measured using the rule  32  being sent to the unit  88 . In addition, at this moment, the resistance force of the panels at the end of the approach, referred to as F 1 _final is known and recorded using the unit  88  and this is, of course, effectively the same as force F 1 _target. 
     Furthermore, an error can also be detected using the value of the distance D 1 _final that is recorded. In effect, if this value is not within a predetermined range, one may then conclude that the device is incorrectly positioned in relation to the panel, or that the panel shape is outside tolerances. 
     The clamping operation is then initiated and this is started as soon as the approach operation is complete, possibly with a stoppage time between these two operations. In a matter which is identical to that which encountered in the context of the previous operation, clamping is carried out by sending a command for linear movement of carriage  60  using unit  88  in order to obtain enhanced adhesion in contact between the head  62  and the panels  80 . It should be noted that during this operation the control unit  88  periodically determines, on the one hand the value of the motor power P 2 _absorbed passing through the system  8 , where this value P 2 _absorbed is then converted by the converter in order to obtain a value of the force of resistance of the panels at clamping F 2 , and on the other hand the clamping distance D_clamping which corresponds to the actual distance travelled by point C of the carriage between the point on the optical rule  32  where it is at the moment t in question, and point C 1  on this rule. Here once again it should be stated that the force F 2 , updated every 5 ms, as is the value C_clamping, also corresponds in value to a depression force for the hold-down system  8  against the panels  80 . 
     The control of this clamping operation is envisaged such that the movement of the carriage  60  occurs when the determined force F 2  reaches a target value F 2 _target, or once the clamping distance D_camping has reached a target value D_clamping_target, with the clamping operation therefore taking place when either of these two target values is reached. 
     As an indication, the target value F 2 _target may be fixed, for example, at a value of the order of 150 N, and the target value D_camping_target may be fixed, for example, at a value of the order of 500 μm. As shown in  FIG. 7   d , at the end of the clamping operation, the carriage  60  has therefore travelled a distance of D 2 _final between point R and a point C 2  on the rule  32  where point C of carriage  60  is located, with the value of the distance D 2 _final as measured using the rule  32  being sent to unit  88 . This then allows the final clamping distance D_clamping_final actually travelled by the system  8  to be obtained by subtracting D 1 -finale from D 2 _final. Furthermore knowledge on the one hand of the dimensions of the system  8  and on the other hand of the actual position of the latter on chassis  2  at the end of the clamping operation allows the exact position of the constrained panels  80  to be determined relative to the chassis  2 . In this respect, the unit  88  may then determine and store the distance T_panels_final which corresponds to the distance along direction  18  between the point R of rule  32  and the forward end of the hold-down head  62  at the end of the clamping operation. 
     This specific feature is advantageous since it allows the linear movement of the drilling system  4  during the next drilling step to be optimised as much as possible, insofar as this system  4  may be operated at high speed over a precise fixed distance as a function of the distance T_panels_final, before being slowed to the advance speed for the tool determined beforehand. In addition, knowledge of this distance T_panels_final, of the order of 200 mm, is used to precisely fix the distance for the change of rotation speed of the drilling tool for the countersinking approach, when a staged drill-countersink tool is used. Finally another advantage rests in the fact that the depth of the countersink can be in full compliance with requirements. In this respect it should be indicated that the subsequent countersinking travel may also be corrected as a function of the Info_stiffness information determined as described below, and also if necessary as a function of the various characteristics of the rivets employed. In this respect it should be noted that the lower the local stiffness of the panels, the more these are deformed by the thrust of the hold-down head, and therefore the further the centre of this hold-down head is away from these same deformed panels. Thus, the lower the local stiffness of the panels, the greater the countersink travel relative to the hold-down system that is required to obtain a determined countersinking depth. 
     Furthermore, errors can also be detected using the value of the distance D 1 _clamping_final that is recorded. In effect, if this value is not within a predetermined range, one may then conclude that the device is incorrectly positioned in relation to the panel, or that the panel shape is outside tolerances. Furthermore, at the end of the clamping operation which is stopped when the target value D_clamping_target has been reached, the value of the resistance force of the panels at the end of clamping, known as F 2 _final is known and recorded. If this value is too low, the structure formed by the panels may be considered not to be present. 
     Using the panel resistance force value at the end of clamping F 2 _final it is then possible to determine, again using the unit  88 , the Info_stiffness information by establishing the following ratio:
 
Info_stiffness=( F 2_final− F 1_final)/ D _clamping_final
 
     This information on the local stiffness of the panels, the value of which is, for example, of the order of 30 kg/mm, is then sent to the second means of control  86 , associated with the drilling system  4 , and more specifically to the correction matrix  82  with which the unit  92  is equipped. As indicated previously, this info_stiffness information is envisaged as pre-assigning the advance speed and rotation speed settings of tool  17  used during the control of the drilling step which will now be described. 
     First of all it should be stated that this drilling step is initiated with system  8  in the position as shown in  FIG. 7   d , and systems  4  and  6  in their positions as shown in  FIG. 7   a , as shown overall in  FIG. 7   e.    
     This drilling operation involves setting carriage  10  of the drilling system  4  in motion, so that it passes through the hold-down system  8 , and also passes through the two panels to be assembled. 
     The required advance in the slide direction  18  is achieved using the first motor  24 . On this point it should be noted that this operation preferably aims not only to make a hole through the two superimposed panels  80 , but also to make a countersink which is designed to house the head of the rivet which will be later put in place. As shown in  FIG. 7   f , it should be noted that setting carriage  10  of the drilling system in motion along direction  18  does not result in any movement of the carriage  34  of the riveting system  6 , given that this operation has been carried out with the brake callipers  54  in a deactivated state, that is, without the brake callipers  54  being firmly fixed to the rail  52 . Consequently it should be noted that during the movement of the first carriage  10 , the second carriage  34  remains immobile relative to the chassis  2 . 
     More precisely, drilling is carried out by ordering the linear movement of the carriage  8  using the tool advance speed setting as determined beforehand and issued from the matrix  82 , and by simultaneously commanding rotation of the spindle  12  using the tool rotation speed setting also coming from the matrix  82 , with these settings being issued respectively to servo-control boards  94  and  96 . 
     During this drilling step the value of the pane: resistance force F 3  which results from the hold-down system  8  pressing on the panels  80  is periodically determined. This determination of F 3  is preferably carried out in the same manner as that used for the determination of F 1  and F 2 . In this respect it should be indicated that the motor associated with the carriage  60  of the hold-down system continues to be supplied during drilling, and that it is servo-controlled in position so that carriage  60  retains its position at C 2  on the chassis  2 . 
     As an indication, F 3  is updated every 5 ms and its value corresponds to a depression force for the hold-down system head  62  against the panels  80  during drilling. 
     This then allows the value of this force F 3  to be periodically compared during drilling by unit  92  with a minimum value F 3 _min, where the minimum value F 3 _min may be, for example, set at 5 N. 
     When F 3  is detected as being less than F 3 _min, a reduction in the drilling tool advance speed setting is made via matrix  82 , so that the value of the force F 3  returns above the minimum value F 3 _min. This method of operation thus advantageously means that the hold-down head  62  does not lose contact with the panels during the drilling operation, following the drilling tool  17  exerting excessive thrust on these panels. 
     At the end of this drilling step, as shown in  FIG. 7   g , the carriage  10  is one again operated in such a manner that it reverses along the rails  20  until it reaches a position which is further away than the start position shown in  FIG. 7   a . In effect, a relative separation is sought in direction  18  between the carriage  34  and the carriage  10  so that the riveting head  38  may pass in front of the drilling head without any difficulty in clearance, as will be described later. 
     The process is then continued by a step in which a rivet is placed in the hole that has been made, where this step starts with a movement of the riveting head  38  along the drilling head axis  14 , in front of the latter. 
     In order to align these two axes  16 ,  40  and therefore ensure that the riveting head  38  is in the working axle, the means for initiation rotation of this head  38  and of the arm  42  are activated until the desired position is achieved, as shown in  FIG. 7   h . Parallel to this the means of coupling  50  of the two carriages  10  and  34  are operated so as enter the activated state, allowing them to be coupled in a translation movement in direction  18 . 
     Then a movement of the assembly of the two carriages  10 ,  34  is undertaken using the first linear motor  24 , as can be seen in  FIG. 7   i . During this movement, the riveting head  38  located in front of the drilling head  14  penetrates inside the hold-down head  62  and therefore moves into a position which is very close to the two panels  80  to be assembled and on which the operation for putting the rivets in place is carried out in a conventional manner, familiar to those working in the field. 
     Once the rivet is in place, the three carriages  10 ,  34 ,  60  are operated so that they return to their at-rest positions as shown in  FIG. 7   a.    
     With reference now to  FIGS. 8 to 11 , one can see a part of the device  1  for assembling panels using riveting which is in accordance with one even more preferred mode of construction of the present invention. Certain parts of this have the same or similar design to that of device  1  described previously, and in this respect, it should be noted that on the diagrams those elements which have the same numerical references correspond to identical or similar elements. Consequently, it can be perceived that the notable difference between the two devices  1  is due to the design of the riveting system  6 , and more specifically to the design of the means for setting the riveting head  38  in motion relative to the second carriage, again designed so that it can move the same riveting head between the at-rest position in which the drilling head axis and the riveting head axis  16 ,  40  are distinct, and a working position in which the drilling head axis and the riveting axis  16 ,  40  coincide. However, the chassis  2 , the drilling system  4  and the hold-down system  8  are identical or similar to those described earlier. 
     More particularly, with reference to  FIGS. 8 and 9 , the riveting system  6  includes the second carriage  34  which supports entire riveting tool or riveter assembly, the front part of which includes a riveting head  38 , which in turn defines a riveting head axis  40  which is parallel to directions X and  18 . The riveting head  38 , and more generally the riveting tool assembly  36 , is mechanically mounted at its rear part onto the carriage  34  through a parallelogram  102  whose shape can be changed and which will be described below. 
     The second carriage  34  is, for its part, fitted to the chassis  2  so that it may slide in a rectilinear manner relative to the latter in the slide direction  18 . To do this the second carriage  34  is mounted so that it slides on a guide rail  46 , preferably distinct from the two guide rails  20  of the carriage  10 , but also aligned along directions X and  18 . As shown in  FIG. 9 , the rail  46  with a transverse section in the form of an H is firmly fixed to a lateral external surface of one of the arms of the U formed by the chassis  2 . 
     In order for it to be secured on the rail  46 , the carriage  34  is equipped with one or more bearing pads  48  in the form of a calliper, for example in a set of two, spaced out along direction X. Each of these pads  48  therefore presses against the free side arm of the H which is opposite the other side arm which is firmly fixed to the chassis  2 . 
     The riveting system  6  preferably also includes means for setting the second carriage  34  in motion along the slide direction  18 , with these means therefore preferably being distinct from the means  24  for setting the second carriage  10  in motion, although the latter could be different without the limits of the invention being exceeded. The means for setting the second carriage  34  in motion preferably takes the form of a rodless cylinder  104 , of a type readily available on the market, arranged along direction  18 . Overall, this is fitted with a hollow body  106 , fixed in relation to the chassis  2 , and a moving sliding contact  108 , which is able to move along direction  18  relative to the hollow body  106  in which it is partly housed. 
     As mentioned earlier, one of the noteworthy special features of this preferred mode of construction is due to the presence of the parallelogram whose shape can be changed  102  creating the mechanical junction between the rear part of the riveting tool  36  and the carriage  34 . This parallelogram  102  therefore forms an integral part of the means for setting the riveting head  38  in motion relative to the second carriage, given that the latter is easily capable of causing this same riveting head  38  to move between the at-rest position and the working position. 
     To do this the parallelogram  102  is made up of two parallel arms  110 , each of which is articulated at its rear end to the second carriage  34  along an axis  112 , and is articulated at its front end on the rear portion of the riveting tool  36  along an axis  114 , and more precisely articulated on a support block of the riveting head  38 . In this respect, the axes  122 ,  114  are arranged in parallel to direction Z, so that the parallelogram  102  changes its shape in a plane XY parallel to the slide direction  18 . Furthermore, it should be noted that the other two sides of the parallelogram  102  are in material terms formed by the second carriage  34  and the riveting tool. 
     To supplement the means for setting the riveting head  38  in motion, a mechanical system for changing the shape of the parallelogram is envisaged. This system is designed overall so that when the second carriage  34  is set in motion along a slide direction  10  by means of the cylinder  104 , a change in shape of the parallelogram  102  is automatically produced, from a first configuration shown in  FIGS. 8 and 9  which places the riveting head  38  in its at-rest position away from the working axis, to a second configuration which will be described later and which places this head  38  its working position. 
     To do this the mechanical system for changing shape  116  takes the form of a guide system which includes a pin or roller  118  firmly attached to one of the two parallel arms  110 , preferably the arm located furthest towards the exterior as shown, where the pin  118  slides in a guide slot  120  when the second carriage  34  is set in motion in the direction  18 . The fixed slot  120  on the chassis  2  is preferably located in a plane which is parallel to that in which it is envisaged that the parallelogram is to change shape. 
     Thus the slot  120 , details of which will be given later, has an appropriate shape which ensures that the desired change of shape of the parallelogram takes place, namely which enables a controlled approach of the riveting head  38  towards the device&#39;s working head, and which in addition ensures that the riveting head axis  40  is always parallel to direction  18  during movement of this head  38 . 
     With reference to  FIG. 10 , it can be seen that the carriage  34  may be made up of several components which may quickly be dismantled from each other. In effect the carriage part  122  which firmly holds the pad  48  which is in the form of a calliper in position and which fits against the guide rail  46 , is designed to remain permanently on this rail whilst another part of the carriage  124  which holds the parallelogram  102  is designed to be mounted using quick attachments to the aforementioned part  122 . In other terms, the part  124  is a key interface component whose function is rapid fitting and removal of the parallelogram  102 . Overall it is made up of two axes or shafts  125 ,  128  located one above the other and parallel to the direction X. These two axes  126 ,  128  are respectively designed to rest in a V-shaped slot  130  and a U-shaped slot  132  made in the component  122  directly fixed to the pad  48 . 
     On the other hand, the carriage  34  is also equipped with a component  134  which forms a mechanical junction between the component  124  and the sliding contact  108 , where this component  134  in reality has two distinct functions. The first function involves securing the component  124  onto component  122 , namely to ensure that each of the two shafts  126 ,  128  fit into their respective slots  130 ,  132 . This is simply achieved by rotating the lower shaft  128  carrying the junction component  134 , where the said shaft has an eccentric shape designed for this purpose. More precisely, the shaft  128  is introduced in the first instance fully into the U-shaped slot  132 , then shaft  126  is tipped to the vertical for the V-shaped slot, and finally the component  134  is thrust by pivoting against a component  138  which will be described below. Locking is simultaneously achieved by the eccentric support of the junction component  134  against the slot  132 . 
     The second function is due to mechanical coupling with the cylinder slide contact  108 . In effect, the H-shaped component  134  couples quickly at the two lower arms of the H between the forks of a receiving U-shaped component  138  bolted onto the sliding contact  108 . To do this, the U-shaped component  138  holds spring ball screws  140  for retaining the two lower arms of the H in a closed/locked position, thus ensuring that there is an end-stop for the H-shaped component  134  which plays a part in the mechanical coupling of the carriage  34  onto the rodless cylinder  104 . 
       FIG. 11  shows a view from above of the guide slot  120  in which the pin  118  is designed to slide when the carriage  34  is set in motion in direction  18 . First of all it can be seen that in the first direction  144  of the slide direction  18 , oriented towards the front of the device  1 , this slot  120  is made up of three distinct portions which are connected to one another. There is a first portion  148  which extends along an axis  149  parallel to direction  18 , where, overall, this first portion  148  allows the riveting head  36  to be moved whilst keeping it away from the working axis of the device. In this respect, it should be noted that whilst the pin  118  remains in the first portion  148 , the riveting head  38  moves in direction  18  without the position of its axis being changed. Thus it should be understood that the shape of the parallelogram  102  does not change during this part of the movement of the riveting tool  36 . The slot  120  then includes a second portion  150  whose function is to produce a gradual change in the shape of the parallelogram  102  until it adopts the configuration which allows the riveting head to be placed in its working position, namely, alignment of the riveting head axis  40  with the drilling head axis  16 . 
     To do this, in the mode of construction that is described, this second portion  150  extends along an axis  151  located in the horizontal plane of the slot  120 , and which is inclined in relation to the direction  18  and the axis  149  of the first portion. The slot  120  is then terminated by a third portion  152  which is similar in terms of shape to the first portion  148 , giver that it is aligned along an axis  153  which is parallel to direction  18 . This third portion is used to maintain the changed shape of the parallelogram and to allow the riveting head  38  to move along the working axis, with the riveting axis  40  parallel to the drilling head axis  16 . 
     In the light of the above it should be noted that the profile of the slot  120  has certain similarities to that of a car driver changing lane, insofar as it changes from a straight path to a gradual displacement to rejoin a new path once more which is offset from the first. Naturally, in order to prevent sudden jerks and to ensure fluid movement of the pin  118 , junctions  154  and  156  between the three portions  148 ,  150  and  152  are designed with a shape that is effectively rounded. 
     It should be noted that the position of the pin  118  near to the rear end of the exterior arm  110 , namely close to the axis of rotation  112 , amplifies the offset traced by the second portion  150  of the slot. Typically, since the between-centre distance for the articulations  112 ,  114  measures 240 mm, and since the distance of the pin  118  to axis  112  is about 30 mm, an amplification ratio of 240/30 is achieved for the offset, that is, eight times the offset made in the slot. Thus with an offset of 24 mm made in the slot, an offset of 192 mm is achieved between the disengagement axis and the work axis. 
     The process for assembly using riveting that is achieved using the device  1  presented above will now be described. 
     First of all, it should be stated that this process in overall terms includes the same steps as those indicated in the preceding mode of construction, namely a step for determining information on the local stiffness of the panels at the location of the hole to be drilled, followed by a drilling step whose purpose is to create the hole and the countersink associated with it, then finally a step in which a rivet is fitted in the drilled hole. Since the first two steps are identical to those mentioned earlier, they will not be described in any further detail. However, since the riveting step is effectively different, in particular in the manner in which the riveting tool  38  is brought into the working axis, details of this will now be given. 
     With reference to  FIG. 8 , can be seen that at the end of the drilling operation, the riveting carriage  34  is set in translation movement along direction  18 , which means that the pin  118  is set in motion along the first portion  148  of the slot. During this movement, the riveting head  38  is moved forwards in direction  144  of direction  18 , with its axis  40  not undergoing any movement because of the parallelogram  102  being maintained in the first configuration. Thus this first part of the movement of the riveting head  38  means that it is maintained in its at-rest position, whilst it moves forwards towards the front of the device. Then whilst the rodless cylinder  104  continues its movement, the pin  118  enters the second portion  150  of the slot, leading to a gradual change of shape of the parallelogram  102  until it achieves the second configuration, in which it places the riveting head  38  in the work axis in order that it may carry out the desired riveting operation. Consequently, as has already been stated above, the riveting head is aligned in the working axis by the change in shape of the parallelogram  102 , with this kinematic solution ensuring quick and accurate engagement in the hold-down system designed for this purpose.  FIG. 12   a  thus shows the riveting system during the movement of the pin  218  within the second portion  150 . 
     This solely mechanical solution has the benefit of no longer being dependent on a motorised system in order to gradually engage the riveting system, nor on position and control sensors for the automatic control systems associated with the drive. It thus ensures improved engagement of the riveting system within the working axis, since this engagement using a pantograph-type mechanical process is non-conditional, fast, simple and reliable. 
     The final part of the advance of the carriage  34 , carried out with the pin  118  in the third portion  152 , causes the riveting head  38  to move in direction  18 , parallel to the working axis, until the rivet is introduced into the drilled hole shown schematically in  FIG. 12   b    
     Furthermore, at the end of the introduction of the riveting head  38  into the gun  62  of the hold-down system  8 , a precise re-centring is carried out, thanks to the tolerancing of the through-hole  66  with the riveting head  38 , preferably of diameter 18 H7 g6. Furthermore a tapered lead in to the gun  62  of the hold-down is preferably envisaged. 
     Once this is achieved, the slide contact  108  of the cylinder  104  may be moved in the opposite direction  246  towards the rear, in order to return the device to the configuration shown in  FIG. 8 . 
     Naturally, various modifications can be made by professionals working in this field to the devices  1  and to the processes which have just been described as non-restrictive examples only.