Abstract:
A machining tool for machining a panel is arranged in a working area of a machining surface of the panel. A holding element is arranged in a support area located on a holding surface of the panel, opposing the machining surface and on an opposite side in relation to the panel to the working area. The operating machining tool and the holding element are displaced on the panel in a co-coordinated manner according to movement presenting at least one component tangentially to the surface of the panel in such a way as to maintain the opposition of the support area and the working area during the displacement of the tool in order to machine at least a part of the machining surface.

Description:
FIELD OF THE INVENTION 
     The invention concerns the technical area of devices and processes used for the machining of pre-shaped blanks or of panels, such as, for example, the panels used to manufacture aircraft cabins or fuselages. 
     BACKGROUND OF THE INVENTION 
     In the aforementioned area, we are familiar with the process of machining pre-shaped panels by electro-erosion to non-developable shapes. Such machining involves masking of the zones that are not to be treated, and then immersion in baths of electrolytic solutions. Thus, effectively, this process allows a localised machining of panels of general non-developable shape, but nevertheless has two major drawbacks. 
     To begin with, machining by electro-erosion constitutes a significant source of discharges to be processed, to the extent that firstly it is necessary at the end of the machining process to clean the panels by removal of the masking elements and then rinsing followed by recycling of the cleaning solutions as well as of the different electrolytic baths used. 
     Another disadvantage of machining by electro-erosion concerns the impossibility, with this process, of effecting a machining process involving different areas of depth in a single operation. 
     In the light of the above disadvantages, and in particular of the cost of processing the polluting discharges from the installations used for machining by electro-erosion, a proposal was put forward for machining by the removal of material from panels of concave or convex or indeed complex shape. 
     To this end, patent U.S. Pat. No. 5,163,793 proposed the creation of a machining installation that includes a sort of mattress of hydraulic jacks, fitted at their top ends with gripping device mounted on a swivel. The device also includes, on top of the mattress of jacks, a portico which is mobile in horizontal translation and which carries a machining head. 
     To the extent that each jack is individually adjustable in height, it is thus possible to achieve the securing of panels that are of warped or complex shapes. 
     It appears however that although such a device actually allowed one to effect machining by the removal of materials from panels with non-developable warped or complex shapes, it could not be used to perform high-precision machining, particularly because of its inability to guarantee adequately rigid securing of the panel to be machined. 
     Thus, the need has arisen for a new machining process, and for a device for the implementation of this machining process that allows one to perform a variety of machining operations and, in particular, machining by the removal of material, while still providing better working accuracy than the processes and devices of previous designs, and also allowing a significant reduction in the polluting discharges. 
     BRIEF SUMMARY OF THE INVENTION 
     In order to attain these objectives, the invention concerns a machining process for a panel, that includes:
         the positioning of at least one machining tool at the working area of a face, called the machining face, of the panel,   the positioning of at least one retention element at a support area located, firstly, at a face, known as the retention face, of the panel, opposite to the machining face and, secondly, opposite to the working area in relation to the panel,   a coordinated movement, at the level of the panel and with a movement of the machining tool in operation and of the retention element, that has at least one component which is tangential to the surface of the panel, so as to preserve the opposition of the working and support areas during the movement, in order to machine at least part of the machining face.       

     Advantageously, the coordinated movement of the machining tool in operation and of the retention element, allows one to achieve continuous machining of the panel over an extended area greater than the working area of the tool, with considerable precision. 
     According to the invention, the retention element can act in different ways on the support area at the retention face of the panel. Thus, according to the invention, the retention element can direct a stream of fluid under pressure, such as water for example or indeed of compressed air, at the support area, in order to balance the force of the machining tool at the working area. The use of such a fluid under pressure also enables one to achieve cooling of the machined panel. 
     According to one characteristic of the invention, the coordinated movements of the tool and of the retention element are performed automatically using an automated process. 
     According to a preferred but not exclusive form of implementation of the machining process of the invention, the retention element is placed in contact with the panel during the coordinated guidance movement. In a preferred manner, the retention element then applies a support force to the panel in a direction that is perpendicular to the surface of the support area. Furthermore, the retention element will preferably have a punctual or quasi-punctual action on the retention face. This punctual character, in particular but not exclusively in the case of direct contact, then provides very broad freedom of action on complex surfaces. 
     According to another characteristic of the invention, and in order to avoid a drag on the panel by the machining tool, arrangements can be made for the application of at least one counter-support element at the working face. 
     According to the invention, the machining tool can be designed to effect different types of machining. Thus, the machining tool can, for example, be designed to effect machining by the projection of material or of particles, allowing one to perform a modification of the surface state of the panel to be machined or, again, a modification of the constraints or stresses on the latter, such as by means of the technique known as “peen-forming” for example, or “forming” by the projection of particles or shot. 
     In a preferred form for implementation of the machining process of the invention, the machining tool is designed to effect a machining process by the stripping or removal of material, and is provided with a rotation movement on itself, on axis Δ. Such a machining tool can, for example, be designed to what is normally referred to as high-speed machining or “HSM”. 
     According to one characteristic of the invention, the retention element applies to the support area a force in direction Δ′ and, while machining, during the coordinated movement of the machining tool and the support element, axes Δ and Δ′ are more or less coincident. 
     According to yet another characteristic of the invention, arrangements are made to provide damping of the machining vibrations at least at the location of the retention element. 
     According to the invention, the relative movement of the machining tool in operation and of the retention element can be achieved in different ways, such as by using a combination of a movement of the panel associated with movements of the machining tool and of the retention element for example. 
     According to a preferred form of implementation, the retention element and the machining tool are each moved with at least five degrees of freedom. In such a configuration, it is then possible to assign a fixed position to the panel throughout all of the machining process. 
     According to one preferred but not necessary characteristic of the invention, the machining tool and the retention element are each moved with three degrees of freedom of movement in translation on axes X, Y, Z and X′, Y′, Z′ respectively, and two degrees of movement in rotation on axes R 1 , R 2 , and R′ 1 , R′ 2  respectively, where R 1 , R′ 1  are parallel to axes Y, Y′ respectively and R 2 , R′ 2  are parallel to planes X, Z, and X′, Z′ respectively. 
     According to yet another characteristic of the invention, the panel to be machined is placed on a orientation that is more or less vertical. This placement of the invention then allows one to perform the removal, by gravity, of the particles stripped or removed from the panel during the machining process or, again, to perform easy recovery of any particles projected onto this same panel during the machining process. 
     Again, according to another characteristic of the invention, the process performs a determination of the actual geometry of the retention face before machining, as well as machining of the panel to a pre-determined machining depth by placing the retention element and the machining tool at a distance corresponding to the predetermined thickness, during the coordinated machining movement. 
     According to the invention, it is possible to envisage organising the retention of the panel in different ways. Thus, it is possible to envisage that the retention element also contributes to the machining of the panel and, to this end also includes a machining tool. 
     However, in a preferred form of implementation of the machining process of the invention, the retention element achieves the holding of the retention face of the panel without machining this retention face. 
     The invention also concerns a device to enable one to implement the machining process of the invention. Thus, the invention concerns a device for the machining of at least one panel, and that includes:
         resources to support the panel, designed to allow simultaneous access to two opposite faces of the panel, known as the working and retention faces,   resources for the movement of at least one machining tool,   resources for the movement of at least the retention element,   a unit to control the resources for movement of the machining tool and of the retention element, this unit being designed to control the movement resources, so as to position the machining tool at a working area of the machining face of the panel, during a machining operation on the panel:   to position the machining tool at a working area of the machining face of the panel.   to position the retention element at a contact area located on the retention face and opposite to the working area,   and to perform a coordinated movement at the panel, and with a movement that has at least one component which is tangential to the surface of the panel of the machining tool in operation and of the retention element, so as to preserve the opposition of the working and support areas during the movement, in order to machine at least part of the machining face of the panel.       

     According to one characteristic of the invention, the movement resources of the tool and of the retention element each have at least five axes of movement, so as to provide the tool and the retention element with at least five degrees of freedom. 
     Within the meaning of the invention, such an ability to move the tool and the retention element in relation to the panel to be machined can be provided in different ways, such as by means of two automated arms with six degrees of freedom for example, three degrees of freedom in rotation and three degrees of freedom in translation, where one of the arms carries the machining tool at its extremity, while the other arm carries the retention element. 
     It is also possible to envisage performing the movement of the tool and of the retention element by means of so-called parallel automated structures. 
     According to a preferred form of implementation, providing greater simplicity of automation and control, the movement resources of the tool and of the retention element each include three degrees of movement in translation on axes X, Y, Z, and X′, Y′, Z′ respectively, and two degrees of movement in rotation on axes R 1 , R 2  and R′ 1 , R′ 2  respectively, where R 1  and R′ 1  are parallel to axes Y, Y′ respectively, and R 2 , R′ 2  are parallel to the planes defined by axes X, Z and X′, Z′. 
     In a preferred form of implementation of the machining device of the invention, the movement resources of the tool then include:
         a beam that is mobile in translation along at least one guidance track on axi X , supported by a chassis and associated with motor resources commanded by the control unit,   a chariot that is mobile in translation along a guidance track on axis Z, carried by the beam and associated with motor resources that are commanded by the control unit, where axis Z is more or less perpendicular to axis X,   an arm that is telescopic in translation on axis Y, carried by the chariot and associated with motor resources that are commanded by the control unit, axis Y being more or less perpendicular to the plane defined by axes X, Z,   a head support designed to fit onto one end of the telescopic arms, and mobile in rotation in relation to the arms on axis R 1 , parallel to axis Y, and associated with motor resources that are commanded by the control unit,   a tool-bearing head, designed to fit onto the head support, mobile in rotation in relation to the support on axis R 2 , perpendicular to axis Y, and associated with motor resources that are commanded by the control unit.       

     For their part, the movement resources of the retention element include:
         a beam that is mobile in translation along at least one guidance track on axis X′, supported by a chassis and associated with motor resources that are commanded by the control unit,   a chariot that is mobile in translation along a guidance track on axis Z′, carried by the beam and associated with motor resources that are commanded by the control unit, with axis Z′ being more or less perpendicular to axis X′,   an arm that is telescopic in translation on axis Y′, carried by the chariot and associated with motor resources that are commanded by the control unit, axis Y′ being more or less perpendicular to the plane defined by axes X′, Z′,   a head support designed to fit onto one end of the telescopic arm and mobile in rotation in relation to the arm on axis R′ 1 , parallel to axis Y′, and associated with motor resources that are commanded by the control unit,   a retention-element-carrying head, designed to fit onto the head support and mobile in rotation in relation to the support on axis R′ 2 , perpendicular to axis Y′, and associated with motor resources that are commanded by the control unit.       

     The support resources are then fitted onto the chassis, so as to be interposed between the movement resources of the tool and the movement resources of the retention element. 
     According to another characteristic of the invention, and in order to provide a solution any control problems:
         the support of the tool-bearing head is firstly fitted on a cradle equipping the end of the telescopic arm, and mobile in rotation around axis R 1  and, secondly, is mobile in rotation around axis R 3 , perpendicular to axis R 1 , in relation to the cradle.   the support of the tool-bearing head is first fitted on a cradle equipping the end of the telescopic arm and mobile in rotation around axis R′ 1  and, secondly, mobile in rotation around axis R′ 3 , perpendicular to axis R′ 1 , in relation to the cradle.       

     In a preferred manner, axes X, Z and X′, Z′ define vertical planes that are more or less parallel, so that the panel has a more or less vertical orientation during the machining process. 
     According to the invention, the tool-bearing head can be designed so as to receive different types of tools, such as tools for the projection of particles for example, or tools for the removal or stripping of materials. Thus, in a preferred form, the tool-bearing head includes resources for driving the tool in rotation around an axis Δ that is more or less perpendicular to axis R 2 . 
     According to another characteristic of the invention, in order to avoid a phenomenon of attraction of the panel by the machining tool, otherwise known as drag, the movement resources include at least one counter-support element on the working face of the panel. 
     According to yet another characteristic of the invention, in order to perform high-precision machining, the device also includes resources for damping of the machining vibrations. 
     In a preferred manner, in order to achieve absorption of the machining vibrations as close as possible to their points of production, the damping resources are fitted onto the movement resources of the retention element. Such damping resources can then be composed of systems of hydraulic or hydro-pneumatic dampers for example, supporting the head of the movement resources of the retention element. 
     According to the invention, the retention element can be achieved in different ways. Thus, the retention element can be composed of a nozzle for the projection of a fluid under pressure for example, or in the form of a slide, made from a material with a low friction coefficient, intended to press against the retention face of the panel and to slide on the latter during the coordinated movement. In a preferred manner, the retention element will act punctually or quasi-punctually on the retention face, this action then, preferably, being more or less perpendicular to the retention face at its point of application. 
     According to a preferred implementation characteristic, the retention element includes at least one bearing sphere designed to roll on the retention face of the panel during the machining process. In one particularly advantageous method of implementation, the bearing sphere is composed of elastically deformable material, so as to damp the machining vibrations. 
     According to the invention, the support resources of the panel can be provided in any appropriate manner. 
     In a preferred form of implementation, the support resources of the panel are removable, so as to allow operation of the machining device concurrently with other operations for example. In fact, during the installation of a panel on the support resources, the device can machine another panel supported by other support resources for example, and thus in an alternating manner. 
     According to a preferred form of implementation, the support resources include a removable frame that is fitted with resources for the securing of a panel to be machined. 
     Thus, it is possible to envisage a certain number of such removable frames, allowing optimal use of the device. Likewise, it is possible to envisage different types of frames to match the different forms of panels that are liable to be machined on the device of the invention. 
     In a preferred form of implementation, the removable frame includes at least one mobile cross-member allowing adjustment of the dimensions of the frame to the dimensions of the panel to be machined. 
     Diverse other characteristics of the invention emerge from the following description provided with reference to the drawings, which illustrate preferred but not limiting forms of implementation of a machining device for executing the process of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a general schematic perspective view of a preferred form of implementation of a machining device of the invention. 
         FIG. 2  is a schematic cross section along plane II-II of  FIG. 1 . 
         FIG. 3  is an elevation showing a preferred mounting configuration for a machining tool and a retention element during the machining of a panel according to the process of the invention. 
         FIG. 4  is a perspective view, on a larger scale, of a preferred but not exclusive form of implementation of support resources for a panel to be machined according to the invention. 
         FIG. 5  is a view similar to that of  FIG. 3 , showing an implementation variant of the machining device of the invention. 
         FIG. 6  is an elevation from the side of another form of implementation of the machining device of the invention. 
         FIG. 7  is a view similar to that of  FIG. 5 , showing another implementation variant of the machining device. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A machining device of the invention, as illustrated in  FIG. 1  and designated as a whole by reference  1 , allows the machining of a panel  2  that is liable to have a generally complex and non-developable shape, such as, convex or concave for example, or again locally convex and locally concave. 
     In order to perform this machining process, the device  1  includes a chassis  3  which, according to the illustrated example, is made in the form of a sort of portico that is more or less vertical, defining a window  4  inside which the panel to be machined is positioned, being held there by support resources  5 . According to the illustrated example, the support resources  5  are made in the form of a removable frame that is capable of being immobilised in the window  4  on the chassis  3  by means of locking resources  6  that can be provided in any appropriate manner. 
     According to an essential characteristic of the invention, the machining device  1  also includes movement resources  10  for at least one tool and, according to the illustrated example, exactly one machining tool  11 , as well as movement resources  12  for at least one, and according to the illustrated example exactly one retention element  13 . As shown in particular in  FIG. 2 , the movement resources  10  and  11  are fitted on either side of the chassis  3 , so that the panel  2  is interposed between the machining tool  11  and the retention element  13 . 
     According to the illustrated example, the movement resources  10  for the tool include a beam  20 , that is mobile in translation along at least one, and according to the example two guidance tracks  21  on axis X, supported by the chassis  3 . Axis X of the guidance tracks  21  than has an orientation that is more or less horizontal. 
     In a manner that is familiar, as such, to the professional engineer who is a specialist in the design and construction of machines-tools, the beam  20  is associated with motor resources (not shown) and commanded by a control unit  22 , whose different functions will be described later, it being understood that the control unit  22  is designed so as to allow automated operation of the machining device  1 . 
     The movement resources  10  of the tool  11  also include a chariot  23  that is mobile in translation along a guidance track  24  on axis Z, carried by the beam  20 . According to the illustrated example, axis Z has an orientation that is more or less vertical and perpendicular to axis X, so that axes X and Z define a plane that is also vertical. The chariot  23  is also associated with motor resources (not shown) that provide for its movement along the track  24 , being commanded by the control unit  22 . 
     The movement resources  10  also include an arm  25  which is telescopic in translation on axis Y, and which is carried by the chariot  23 . According to the illustrated example, translation axis Y is more or less perpendicular to the plane defined by crossed translation axes X and Z of the chariot  23 . The telescopic arm is also associated with motor resources (not shown) commanded by the control unit  22 . 
     According to the illustrated example, the telescopic arm  25  is equipped at its end oriented toward the chassis  3  with a head support  26  that is mobile in rotation in relation to the arm  25  along an axis of rotation R 1  parallel to axis Y and, according to the example, coincident with this axe Y like the other mobile devices  20 ,  23  and  25  constituting the movement resources  10 , the head support  26  is associated with motor resources (not shown) commanded by the control unit  22 . 
     Finally, the movement resources  10  include a tool-bearing head  27  that is designed to fit onto the head support  26  so as to be mobile in rotation in relation to the support  26  along axis of rotation R 2 , more or less perpendicular to axis R 1 . Of course the rotation movement of the head  27  around axis R 2  is associated with motor resources (not shown) commanded by the control unit  22 . 
     The configuration, as described above, therefore provides the tool  11 , attached to the tool-bearing head  27 , with five degrees of freedom, namely three degrees of freedom in translation on axes X, Y, and Z, and two degrees of freedom in rotation on axes R 1  and R 2 . 
     Finally, according to the illustrated example, the tool-bearing head  27  is equipped with motor resources (not shown) used to drive the tool  11  in rotation while machining along axis Δ which, according to the example illustrated in  FIG. 2 , is more or less coincident with axis Y, to the extent that this figure corresponds to a wait or rest position. Of course in the light of the different degrees of freedom of the head  27 , axis Δ can have different orientations while still remaining more or less perpendicular to axis R 2 . The motor resources for rotation of the tool  11  equipping the head  27  are also commanded by the control unit  22 . 
     According to the invention, the machining tool  11  can be created in different ways and, according to the illustrated example, as shown more particularly by  FIG. 3 , the tool  11  is made in the form of a milling cutter that is driven in rotation on axis Δ by the motor resources equipping the tool-bearing head  27 . 
     The movement resources  12  of the retention element  13  have a structure that is more or less similar to that of the movement resources  10  of the tool  11 . 
     Thus the movement resources  12  of the retention tool  13  include:
         a beam  30  which is mobile in translation along at least one, and according to the example two guidance tracks  31  on axis X, supported by the chassis  3 , and which is associated with motor resources (not shown) commanded by the control unit, where axis X′ is horizontal,   a chariot  33  which is mobile in translation along a guidance track  34  on axis Z′, carried by the beam  30  and associated with motor resources (not shown) commanded by the control unit  2 , where axis Z′ is more or less perpendicular to axis X′,   an arm  35  that is telescopic in translation on axis Y′, carried by the chariot  33  and associated with motor resources (not shown) commanded by the control unit  22 , where axis Y′ is more or less perpendicular to the plane defined by axes X′, Z′,   a head support  36  designed to fit onto one end of the telescopic arm  35  and mobile in rotation in relation to the arm  35  along axis R 1  parallel to axis Y and associated with motor resources (not shown) commanded by the control unit  22 ,   and a retention-element-carrying head  37 , designed to fit onto the head support  36  and mobile in rotation in relation to the support  36  along axis R 2 , perpendicular to axis R′ 1  and associated with motor resources (not shown) commanded by the control unit  22 .       

     According to the invention, the retention element  13  can be implemented in any appropriate manner and, according to the illustrated example, the retention element  13  has a sphere  41  at one end  40  opposite to the support head  37 ,intended to exert a more or less intermittent pressure on the panel  2 , as will become apparent in what follows. In a preferred manner, the sphere  41  is made from an elastically deformable material, such as a synthetic polymer material or a plastic material for example. The elastic deformation quality of the sphere is then used with advantage to damp the machining vibrations. Of course the sphere could also be made from other materials, such as a metal like steel or other suitable metal alloys for example. According to the illustrated example, the sphere  41  is positioned more or less at the end of a body  42  of tapered shape on axis Δ′, more or less perpendicular to axis R′ 2  for rotation of the support head  37 . The sphere  41  is then fitted to the body  42  so as to be able to roll on the panel  2 , as will become evident in what follows. In addition, in a preferred manner, the retention element  13  is fitted in a removable manner to the head support  37 , so that it can be changed rapidly or, again, replaced by a tool. To this end, in a preferred manner, like head support  27 , the head  37  is equipped with resources for rotation of a tool around axe Δ′, where these drive resources are commanded by the control resources  22 . 
     The machining device thus constituted is then implemented in the following way. Firstly, a panel  2  is installed in the window  4 . To this end, according to the illustrated example, the chassis  3  has a lateral window  501  by which the support resources, composed of the mobile frame  5 , are engaged to position the plate  2  between the tool  11  and the retention element  13 , as illustrated in  FIG. 2 . In this state, the frame  5  is then locked onto the chassis  3 , so that the panel  2  is totally immobile in relation to the chassis. 
     Once this arrangement has been completed, and according to an essential characteristic of the invention, the control unit  22  commands the operation of the resources  10  for movement of the tool  11  and the movement resources  12  of the retention element  13 , so as to position the tool  11 , in operation, in contact with a face  2   T , called the machining face, of the panel  2  in an area  50  called the working area, as illustrated in  FIG. 3 . In a more or less similar manner, the control unit  22  commands the operation of the movement resources  12  so as to position the retention element  13 , and more particularly the sphere  41 , in contact with a face  2   M , known as the retention face of the panel  2 , at a retention area  52  located on the retention face  2   M  opposite to the machining face  2   T , this retention area  52  being located opposite to the working area  50  in relation to the panel  2 . 
     Once this positioning has been completed, the unit  22  commands a coordinated movement of the machining tool  11  in operation, and of the retention element  13  in contact with the panel  2 , so as to machine, in part at least, the machining face  2   T  of the panel  2 . 
     According to an essential characteristic of the invention, the control unit performs the coordinated movement of the tool  11  and of the retention element  13  so as to preserve the opposition of the contact area  52  and the working area  50  during this joint movement. During this movement, the sphere  41  then rolls on the retention face  2   M  of the panel  2 . This means that the movement of the tool  11  and of the retention element  13 , in relation to the panel, can be broken into components in a plane tangential to, and the plane normal to the surface of the panel in the machining area, and where at least the tangential component is non-zero. The coordinated movement therefore has at least one component that is tangential to the surface of the panel and, at least in certain phases of the machining process, also has a component normal to the surface of the panel, as is the case for the tools during adjustment of the depth of cut in particular. 
     In a preferred manner, during all of the machining stage on the panel  2 , the unit  22  controls these movements so as to preserve firstly the perpendicularity of bearing axis Δ′ of the retention element  13  with the surface of the support area  52  and, secondly, the conjugation of axis Δ′ and of rotation axis Δ of the tool  11 , so that, during the whole period of machining and coordinated movement, axes Δ and Δ′ are coincident. 
     Thus, it is possible, by association of the retention elements and of the machining tool  11 , to achieve machining of great precision on the panel  2  without deformation of the latter. The association of the retention element  13  and the machining tool  11 , together with the precision capabilities of the numerical-control resources equipping the control unit  22 , thus allows one to achieve machining with different depths of pass or different machining at different points of the panel  2 , according to the strength sought for the latter. This very high level of precision is rendered possible in particular by the balance of machining and retention forces applied by the tool  11  and the retention element  13  on either side of the panel  2 . 
     In a preferred but not strictly necessary form of implementation, with a view to obtaining perfect precision, it is possible to envisage implementing telemetry resources  55 , such as laser telemetry resources, to enable one to create a particularly precise cartography of the retention face  2   M  of the panel  2  before machining the latter. This telemetry thus allows one to obtain a perfect reference, allowing one to know, with great accuracy, the depth of the panel  2  at all points of the latter after machining. In fact, the residual depth will then be determined by the distance between the end of the tool  11  and the retention element  13  and, more particularly the sphere  41 , during the machining process, since this distance then corresponds to the residual depth of the panel  2  after machining. 
     According to another characteristic of the invention, it is also possible to envisage implementing telemetry resources  56  that enable one to measure the coordinates of the working face  2   T  of the panel with precision. Thus, the combined use of telemetry resources  55  and  56  allows one to have total knowledge of the geometry of the panel  2  before and after machining. 
     Once the machining of the panel  2  has been completed, the frame  5  is unlocked to be removed and to allow the fitting of another frame. 
     The invention, thus constituted, therefore allows simultaneous working, and it is possible to perform the machining of different types of panel  2  by the use of different frames. 
     It should be noted that according to the illustrated example, the frame  5  is fitted with a cross-member  57  which is mobile in translation and allows one to adjust the effective dimensions of the frame  5 , so as to allow the accommodation of panels of different dimensions with a single type of frame. 
     According to the invention, it is also possible to include, in the working area  50 , at least one counter-support element  58 , as illustrated in  FIG. 5 . According to this example, the counter-support element  58  includes three telescopic, isostatic fingers  59 , in continuous contact with the working face  2   T  of the panel  2 . The fingers  59  are preferably arranged in a triangle, though any other configuration can also be envisaged 
     The fingers  59  constituting the counter-support element are used to prevent any drag phenomenon on the panel by the tool  11 , and can also perform damping of machining vibrations. 
     In addition, according to another implementation variant of the invention, use is also made, at the tool-bearing head  27 , of resources for the movement of the tool in translation along direction Δ perpendicular to axis of rotation R 2 . Likewise, use is also made, at the element-carrying retention head  37 , of resources for the movement in translation of the retention element along direction Δ′, perpendicular to axis of rotation R′ 2 . Of course these movement resources in translation are associated with motor resources that are commanded by the control unit. 
     Such a configuration is particularly suitable to effect machining of the panel, so as to render it perfectly in accordance with the theoretical model sought. 
     In this case, the control unit performs control of the installation on the basis of the theoretical three-dimensional description file of the panel to be created, and then controls the operation of the different parts of the machining device to this end. 
     Of course the machining device of the invention can also be controlled in the context of a machining method which could be described as corrective, to the extent that, after a telemetry stage to enable one to detect the actual shape of the panel, the control unit will command the operation of the device so as to produce the shape sought from the actual shape. 
     Such machining operations on a panel in three dimensions are particularly favoured by the kinetics of the ends of arms  25  and  26 , and of supports of tools  26  and the retention element, as illustrated in  FIG. 3 . 
     However, in certain combinations of movement, the control unit encounters difficulties in calculating the rotations along axes R 1 , R 2  and R′ 1 , R′ 2  to attain the machining and support areas. 
     In order to provide a solution to these difficulties of calculation and the associated control, the invention proposes, in one form of implementation, particularly such as that illustrated in  FIG. 6 , elimination of the rotation movements around axes R, and R′ 1  of the head supports  26  and  36 . According to this variant, the rotation movements along R 1  and R′ 1  are replaced by rotation of the head supports  26 ,  36  around axes, R 3  and R′ 3  respectively, which are more or less vertical or contained within a vertical plane. In this configuration, axes of rotation R 2  and R′ 2  are placed so as to be perpendicular to axes R 3  and R′ 3  respectively. Of course the machining device includes motor resources that are commanded by the control unit and associated in rotation around axes R 3  and R′ 3 . 
       FIG. 7  illustrates an implementation variant of the machining device, as illustrated in  FIG. 6 . According to this implementation variant, the rotation movements along axes R 1  and R′ 1  are combined with the rotation movements along axes R 2 , R 3  and R′ 2 , R′ 3    
     To this end, the end of the arm  25  includes a cradle  60  which is mobile in rotation around horizontal axis R 1  parallel to axis Y. The head support  26  is then fitted on the cradle  60 , being mobile in relation to the latter in rotation around axis R 3  perpendicular to axis R 1 , while the tool-bearing head  27  is mobile in rotation in relation to the support  26  along axis R 2 , perpendicular both to axis R 1  and axis R 3 . The assembly that includes the end of the arm  35  to which the cradle  60  is fitted, the head support  26 , and the tool-bearing head  27 , forms what can be describes as a head assembly. 
     Likewise, the end of the arm  35  includes a cradle  61  which is mobile in rotation around horizontal axis R′ 1 . 
     The head support  36  is fitted on the cradle  61 , being mobile in relation to the said cradle in rotation around axis R′ 3 , perpendicular to axis R′ 1 . Finally, the retention element-carrying head  37  is mobile in rotation in relation to the support  37  along axis R′ 2 , perpendicular to axes of rotation R′ 1  and R′ 3 . 
     In this configuration, there is redundancy between axes R 1 , R 2 , and R 3  on the one hand and axes R′ 1 , R′ 2 , R′ 3  on the other. The control unit  22  then effects control of the machining device, giving priority to the movement combinations along R 2 , R 3  and R′ 2 , R′ 3  respectively, in relation to the rotations along R 1 , and R′ 1  respectively. 
     Of course it is also possible, for the forms of implementation of  FIG. 6 and 7 , to provide translation movements of the tool along axis Δ and of the retention element along axis Δ′.