Abstract:
A method and a device for assembling an air-craft wing incorporating at least two of the operations drilling, riveting and fitting of anchor nuts ( 20 ), where a robot ( 7 ) is mobile relative to the wing in a plane parallel to the wing and where the robot ( 7 ) is equipped with an arm ( 9 ) designed to accommodate a tool holder ( 15 ), where the tool holder ( 15 ) is primarily equipped with tools for performing a single work operation, whereby the robot is moved so that the robot arm ( 9 ) is positioned at the first work position on the aircraft wing unit, where the robot ( 7 ) carries out the first work operation at the said first work position, where the robot arm ( 9 ) is manoeuvred in the correct order to new work positions on the wing unit within a work area ( 10 ) reachable by the robot arm ( 9 ), and carries out the first work operation at these new work positions.

Description:
TECHNICAL FIELD 
     The invention presented below concerns a method for the assembly of a wing according to the introduction to claim  1 . Additionally, the invention involves a device for the assembly of a wing used in the implementation of the said method according to the introduction to the independent claim for the device. 
     STATE OF THE ART 
     A wing of an aircraft is normally constructed as a structure of spars and ribs, which is covered by a wing skin. The term stay is used below to include both the terms spars and ribs. The wing skin is generally fixed to the stays by means of screws. The stays underlying the wing skin have been formed in order to give the wing its profile and thus the final profile of the wing is formed when the wing skin is fixed to the underlying stay. 
     The stays supporting the wing skin are constructed of, for example, light metal such as aluminium, or, as is now common, composite. These stays consist of U-shaped sections with both upper and lower flanges against the upper and lower wing skin respectively. The flanges follow, as mentioned above, the surface profile of the wing in the stay&#39;s vertical plane through the wing. 
     Since the wing skin is fastened by a large number of screws to the said flanges of the stays this assembly requires some type of nut or fixed thread in the dolly underlying the wing skin, that is in the flanges of the stays. With present-day technology this is performed by so called anchor nuts being fixed to the flanges of the stays on the side which faces away from the wing skin of the wing. Furthermore, the current technique is such that the anchor nuts have holed lugs which are suitably riveted to the inside of the flange. Supplying the frame, i.e. the stay, in this way with a thread in each position where a screw is to fix the wing skin to the frame makes fitting of the wing skin a simple procedure. 
     Assembly of the wing involves a number of steps. In the initial steps the frame is built using a jig, i.e. all of the wing&#39;s stays are fixed together to produce the said frame. The skin of the wing is applied temporarily to the frame, after which, in the third step, the wing skin and frame are drilled jointly. This drilling means that holes for the wing skin&#39;s mounting screws are drilled through the wing skin and the flanges of the stays in the frame during one and the same operation. In this way the exact positions are determined for the anchor nuts which in the subsequent assembly stage are to be fixed to the frame. In this stage of the assembly the wing skin has been removed, so that the operation of fixing the anchor nuts can be performed. 
     The work involving the fixing of the anchor nuts in position is very time-consuming when carried out manually. The nuts vary in type, so that holes for riveting of the lugs of the nuts have to be made and adjusted to the type of nut. Then the lugs of the nuts are riveted to the frame, that is to the flange of the stay. Drilling of the rivet holes must be done in the correct position so that the nut hole is aligned with the previously drilled screw hole in the frame. The holes for the rivets are of different diameters. The rivets vary in type according to the type of nut. All of this work requires a lot of time since thousands of anchor nuts must be fixed in position. 
     There are, on the market, solutions for the automatization of the drilling and riveting of anchor nuts. In large-scale production of aircraft wing units as described above there is one solution used whereby a clamp for handling tools has a range such that the tool at the end of both arms of the clamp can be extended in over the wing unit and reach every point of the same and is thereby capable of performing work operations on the top side and underside of the wing simultaneously. This process is automated, the operations being carried out according to a program. Such a solution, however, is expensive and requires large series for it to be profitable. 
     According to another method, a robot, which is able to move along the wing on a carriage, operates by looking for work positions using its robot hand, on which a automatic tool machine is mounted. The automatic tool machine grips the flange and holds the piece to be machined to the automatic tool machine. The automatic tool machine is constructed in such a way that, in a revolving fashion, it can select the tools in the correct order so as to carry out all the stages in the operation necessary for fixing an anchor nut in position. In this case the turret contains tools for making rivet holes, a device for transporting anchor nuts and placing them in the correct position, and a riveting tool for selecting the correct type of rivet and performing the riveting operation. An automatic tool machine of the said type designed for executing all steps in the operation is sophisticated and very expensive. Furthermore, having the tool holder secured in a turret means that the equipment is heavy and clumsy, thereby reducing the accessibility of the tool. 
     Another method which has been employed uses ordinary floor or carriage mounted six axle robots with a large range of movement which allows the robot to reach large areas of a wing. According to this method the robot, in accordance with a program, chooses a tool holder, supplies the tool holder with the correct tools, searches for the next work position, performs the first work operation, searches for a new work position, performs the first work operation again, and so on within a specified work area. When the first work operation is completed at all programmed positions the robot fetches and attaches to itself the next tool holder with the requisite tools, and performs all the elements of a second work operation. In trials using this method it has, however, proved difficult to achieve the exactness demanded in positioning the tool to the wing stays. Furthermore, neither does this type of robot with long arms and large manoeuvre area have the stability that is necessary, since there are large forces present between the mounted tool and the wing profile during certain work operations. 
     In order to find a solution to the above difficulties and, furthermore, to achieve an economically viable level of automatization for the assembly of a wing according to the description a new method and a new device for the assembly of a wing are presented here. 
     DESCRIPTION OF THE INVENTION 
     The invention constitutes a method and a device for the assembly of a wing of an aircraft. In the said assembly the wing skin is fixed to the wing frame using fasteners. The wing frame is built up of an number of stays with flanges to which the wing skin is secured. The fasteners are generally in the form of screws, although other types of fasteners are also possible. Fitting of the wing skin using fasteners involves various operations which have to be performed on the frame. Examples of such operations, in the case where the fasteners are composed of screws that are threaded into anchor nuts in the frame, are drilling of rivet holes, fitting of anchor nuts and riveting. Simultaneous drilling of the wing skin and frame to make screw holes is another example of an operation that can be performed according to the aspect of the invention. 
     According to an aspect of the invention in question a method for the assembly of a wing as specified in the independent method claims is presented. 
     According to a further aspect of the invention in question a device for the assembly of a wing as specified in the independent device claims is presented. 
     An advantage of using the method or the device according to the invention is that a robot with a relatively limited range of movement can be used. Thus, for example, a robot with an arm moved by ball screws can be used. This type of robot has a high degree of precision in locating work positions and can, in addition, withstand large tool forces, which produces stability when the various operations are being performed. 
     An additional advantage is that different tool holders are used for different operations. Such tool holders are relatively inexpensive and uncomplicated. 
    
    
     BRIEF DESCRIPTION OF FIGURES. 
     FIG. 1 illustrates a section of a frame of a wing with stays according to the description. 
     FIG. 2 shows schematically a view of the automatic assembly machine from above. 
     FIG. 3 shows schematically a lateral view of the automatic assembly machine according to the description, where a robot is shown laterally mounted on a moveable column. 
     FIG. 4 shows a robot with a ball screw mechanism, which, according to an embodiment of the invention, is employed in the automatic assembly machine. 
     FIG. 5 depicts the division into a number of work areas for the robot, where the work areas are arranged to cover virtually the complete wing. 
     FIG. 6 illustrates an example of a tool holder for the robot in the automatic assembly machine, in this case a tool holder for fitting the actual anchor nuts. 
     FIG. 7 shows schematically an example of an anchor nut riveted to a flange of a wing stay. 
     FIG. 8 shows a part of a wing stay, where some anchor nuts of various types are shown fitted. 
    
    
     EMBODIMENTS OF THE INVENTION 
     A number of preferred embodiments are described below with the aid of the figures. 
     As mentioned above the invention is intended for the automatization of certain operations in the assembly of a wing  1 , where the assembly of the stays  3  which makes up the wing frame  2  has already been completed. The wing frame is, in this example, mounted in a moveable jig, allowing the jig to be moved between different work stations where various steps of the assembly are performed. The wing is mounted vertically in the jig, which means that the plane of the wing is positioned more or less vertically. Close to the wing  1  and essentially parallel to the wing there is a rail  4 . On the rail  4  a carriage  5  can be moved mechanically to and fro along the wing  1 . The carriage  5  is equipped with a column  6 . On one side of the column a vertically mobile robot  7  is mounted. The robot  7  runs vertically on a second rail  8  fitted on the side of the column  6 . By moving the carriage  5  along the wing  1  on the first rail  4  and moving the robot  7  vertically on the second rail it is thus possible for the robot arm  9  to reach every point on the wing surface. Normally, however, the robot  7  is moved in steps, so that after being moved it can reach all positions within a work area  10 , which fully or partly covers a subset of the aircraft wing unit. The robot  7  which is used according to an embodiment of the invention has a relatively limited range of movement. This does not constitute a disadvantage, since the robot  7  described above can be moved between the different work areas  10 . On the contrary, this makes it possible to choose a very stable type of robot. According to the example a robot  7  has been chosen in which the robot arm  9  is manoeuvred with three ball screws  11 ,  12 ,  13 . This affords very good stability and the capacity to handle large tool forces when using different tools, while allowing the robot arm to move to new work positions with sufficient speed. 
     The end of the robot arm  9  is equipped with a changing plate  14 , which can accommodate different types of tool holder  15 . 
     The operations which are most suited for the robot  7  to perform are simultaneous drilling of the wing skin  16  and frame, making of holes intended for screws which fix the wing skin  16  to the frame  2 , measuring of positions of already drilled holes  17  where the anchor nuts are to be fixed exactly in front of the said holes  17 , drilling of rivet holes  18  in the flanges of the stays for the lugs  21  of the anchor nuts  20 , fitting and riveting of the anchor nuts  20  with rivets which fasten the lugs  21  with the flanges of the stays at the rivet holes  18 , screwing of mounting screws for fixing of the wing skin  16  to the frame. For at least one of the above operations a separate tool holder  15  is needed. The tool holder is meant to be changed after execution of the operations for which the tool holder is tailored and can be changed automatically by the robot itself by having the tool holders  15  stored in a magazine for tool holders close to the wing. The tool holders  15  are fitted on the robots  7  changing plate  14 . An obvious advantage of the above arrangement is that the tool holders are uncomplicated and are intended primarily for one task, which means that they are simple and inexpensive, making the complete automated process attractive from a production point of view. 
     Below is a description of the process for the automatic execution of successive operations in the assembly of the wing according to the example of the embodiment of the invention. 
     In a memory in the central unit  24  there is matrix stored data on every anchor nut of the entire wing unit, their positions, the dimensions of the centre holes, type of anchor nut, rivet hole position in relation to the centre hole, rivet type, the dimension of the holes for the rivets, the thickness of the material at the respective holes, the wing skin&#39;s thickness at each anchor nut and so on. The wing unit is divided into work areas  10 . In the said memory the stored data is divided into one matrix for each side of the wing. 
     The operation involving drilling centre holes  17  for anchor nuts is not dealt with here, which, however, does not mean that this operation cannot be performed by means of the automatic assembly machine according to the invention. It is assumed here that these centre holes  17  are already drilled in the frame  2 . 
     According to a program in the central unit  24  of the automatic assembly machine a new operation is initiated when the carriage  5  and the robot  7  are moved along the tracks  4  and  8  to the magazine that stores the tool holder  15 . There, the robot  7  exchanges the tool holder, by removing the existing tool holder  15  from the shunting plate  14 , placing the previous tool holder in the magazine and attaching a tool holder  15  for the new operation to the changing plate  14 . After that, the program commands the robot to position itself within the first work area  10 . 
     For the operation involving drilling of rivets  18  at the position for the first anchor nut within the work area, the tool holder  15  is equipped with a drill the dimension of which is in accordance with the information in the memory on the first anchor nut position. Using a sensor in the tool holder in question, the robot arm searches for the exact position of the centre hole  17  for the first anchor nut  20 . By reading the information in the memory matrix a drill is centred in position for drilling of each rivet hole  18  associated with the first type of anchor nut. The rivet holes  18  are drilled. Likewise, the drilling of rivet holes  18  proceeds according to the program for all rivet holes within the first work area  10 . 
     At this stage there are two alternatives to choose between. Either the same operation  10  is performed, that is to say drilling of rivet holes  18  for all work areas, or all operations within a work area are completed before the robot is given the command to move to a new work area  10 . Which method is chosen is immaterial. A third alternative involves a combination of these two methods. In other words, it is possible to program the automatic assembly machine to carry out the work in the sequence of one&#39;s choice. 
     It is assumed here that the robot  7  continues the work within the work area and is followed by the next operation. The robot  7  is then commanded to move to the magazine so as to deposit the tool holder  15  for drilling and fit the tool holder for carrying out the subsequent stage of the operation, which in this example involves fitting of the actual anchor nut  20 . The tool holder  15  is now equipped with a tool in the form of a gripping appliance for positioning and holding an anchor nut in the correct position during the riveting operation, as well as tools for riveting of the anchor nut to the rivet holes  18  made in the previous operation. By reading in the memory matrix the automatic machine obtains information on the type of anchor nuts  20  and type of rivets for these. The robot  7  has access to and can reach a pick-up point where the tool holder  15  collects anchor nuts  20  and matching rivets. The tool holder centres the anchor nut  20  to the centre hole  17  on the inside of the stay&#39;s  3  flange and rotates the anchor nut, if necessary, to the angle read from the data in the memory in order to position the anchor nut lugs exactly in front of the respective associated rivet holes  18 . At this stage a rivet is moved forward with a tool for riveting in the tool holder. The riveting operation is executed. The robot arm  9  is moved to the position, read from the memory, of the second rivet hole  18  of the same anchor nut  20 , so that riveting of the anchor nut&#39;s other rivet can be executed. The fitting of anchor nuts to the other positions within the work area continues in a similar way. When all anchor nuts  20  within a work area  10  are fitted the procedure is repeated following this example for the remaining work areas  10  until all anchor nuts have been fitted to the side of the wing where the work is being performed according to the description. The wing can then be turned so that the same assembly work can be performed on the other side of the wing. An alternative would be to use two automatic assembly machines simultaneously, one on either side of the wing. 
     After completion of the operations presented above the work continues by fixing the wing skin to the frame by means of screws which fasten the wing skin to the frame, the screws being threaded into the accompanying nuts. This operation can also be done by the automatic assembly machine according to the invention. Operations other than those mentioned can be incorporated into the schedule of the automatic machine, such as, for example, flat face milling, as well as trimming of any edges present.