Patent Grant
7878041
The present invention belongs to the field of riveting technology for blind rivets and is particularly applicable to the sector of automatic riveting stations which requires great precision and reliability in the riveting finishings, such as for example the aeronautical industry.
The problem associated with the manufacture of structures closed with pieces joined by riveting, for example torsion boxes introduced in the structure, is well known, since it is not possible to use hi-lock type (nut and bolt) rivets due to the fact that the rear parts of the riveted pieces are not accessible. Therefore, in order to rivet this type of structure one usually uses blind rivets which only need access from one side in order to be applied.
A blind rivet consists of a body with an interior passage, a deformable free end part and an end part with a rivet head in the form of a collar, together with a stem displaceable in said interior passage by application of a traction force. The stem comprises a stem body with a free end that projects from the rivet head and an end with a stem head which has a dimension greater than said interior passage but no greater than the contour of the first free part of the rivet body and which, prior to application of the rivet, projects from the free end part of the rivet body.
In order to attach pieces by means of blind rivets, first the rivet body is inserted via its free end part in a drill-hole passing through the internal piece and the external piece which have to be joined in such a way that the end part projects from the interior piece and the collar of the rivet head remains resting on the external piece. A traction force, known as a “pull”, is then applied to the free end of the stem of the blind rivet by means of a riveting apparatus which simultaneously presses the collar against the exterior piece so that the head of the stem enters into the interior passage of the free end part of the body of the rivet deforming the free end part until it becomes widened beyond the contour of the free end part of the body of the rivet found in the drill-hole and until that free end part wraps and press the head of the stem. After that, at least part of the body of the stem is then separated from the head of the stem.
The problem existing in the use of blind rivets lies in, among other things, the fact that once the rivet has been attached, there is no possibility of gaining access in order to inspect whether the free end part of the rivet has really trapped the head of the stem correctly or not, and therefore of not knowing whether the rivet has been placed correctly or not. In order to solve this problem systems have been developed such as traction rivets with a threaded stem and traction nut that breaks at a calibrated stress and, in so doing, determines the quality of the join. Nevertheless, these rivets are relatively costly and their reliability in terms of the possibility of detecting the incorrect placing of a rivet is less than desirable. These drawbacks have a special effect on the aeronautical industry since a very large number of rivets is used in the manufacture of aircraft and their correct placing is crucial for guaranteeing the safety of the aircraft.
It was therefore desirable to have a technology that would solve the problems inherent in the verification of the quality of the placing of blind rivets and which would permit a verification that would provide a certainty of the quality of it instantly after each riveting.
The aim of the present invention is to solve the problems inherent in the verification of the quality of the placing of blind rivets by means of a verification method and a verifying device for carrying out the method whose characteristics are going to be described below.
In accordance with the invention, the verification method comprises successively carrying out, during the application of the traction force to the stem, some initial measurements in an initial stage of the application of the traction force, some intermediate measurements in an intermediate stage of the application of the traction force and some terminal measurements in a terminal stage of the application of the traction force.
The initial measurements consist of an initial measurement of the traction force in order to obtain an initial value of traction force, and simultaneously an initial measurement of the displacement of the stem with respect to the body of the rivet in order to obtain an initial value of displacement, while the intermediate measurements consist of at least one intermediate measurement of the traction force in order to obtain an initial value of traction force, and simultaneously an initial measurement of the displacement of the stem with respect to the body of the rivet in order to obtain an intermediate value of displacement. In turn, the final measurements consist of a terminal measurement of the traction force in order to obtain a terminal value of traction force, and simultaneously a terminal measurement of the displacement of the stem with respect to the body of the rivet in order to obtain a terminal value of displacement. The measurements of the traction forces are done by means of a traction force meter connected to the riveting apparatus and the displacement measurements are made by means of a displacement meter connected to the riveting apparatus. Each traction value measured and each displacement value measured are transmitted to data processing means.
The data processing means are provided with a memory in which is stored a type assignment table. The type assignment table consists of type values referring to a type rivet corresponding to the riveting being carried out with a standard blind rivet corresponding to the blind rivet being applied, by means of a standard riveting apparatus corresponding to the riveting apparatus being used. Those type values in the assignment table include at least one initial type value of displacement assigned to at least one initial type value of traction force applied in an initial type stage, at least one intermediate type value of displacement assigned to at least one intermediate initial type value of traction force applied in an intermediate type stage, along with at least one terminal type value of displacement assigned to at least one terminal type value of traction force. The assignment table can, with respect to each initial type value of displacement, include an initial type value of minimum displacement and an initial type value of maximum displacement which between them define the acceptable initial interval of initial type values of displacement, and an initial type value of minimum traction force and also, with respect to each initial type value of traction force, a type value of maximum initial traction force which between them define the acceptable initial interval of initial type values of traction force. Moreover, and with respect to each intermediate type value of displacement, the assignment table can include an intermediate type value of minimum displacement and an intermediate type value of maximum displacement which define an acceptable intermediate interval of intermediate type values of displacement, and an intermediate type value of minimum traction force and also, with respect to each intermediate type value of traction force, an type value of maximum intermediate traction force which define the acceptable intermediate interval of intermediate type values of traction force. Finally, and with respect to terminal type value of displacement, the assignment table can include a terminal type value of minimum displacement and a terminal type value of maximum displacement which define an acceptable terminal interval of terminal type values of displacement, and a terminal type value of minimum traction force and also, with respect to each terminal type value of traction force, a type value of maximum terminal traction force which define the acceptable terminal interval of terminal type values of traction force.
By means of the data processing means, a comparison is then respectively made of the measured initial values, the measured intermediate values and the measured terminal values with the initial type values, the intermediate type values and the terminal type values contained in the assignment table, with a signal being given of each measured value which does not coincide with at least one corresponding type value or when the measured initial values, the measured intermediate values and the measured terminal values are respectively compared with the acceptable initial values, the acceptable intermediate values and the acceptable terminal values contained in the assignment table, and a signal is given of at least each measured value which does not coincide with at least one type value covered by those acceptable intervals in the assignment table.
The assignment table can furthermore contain a plurality of consecutive intermediate type values of displacement assigned to respective consecutive intermediate type values of traction force consecutively applied in the intermediate type stage. In this embodiment, in the intermediate stage of application of the traction force, a plurality of successive intermediate measurements of displacement are taken in order to obtain a plurality of successive intermediate values of displacement, and simultaneously with each of the intermediate measurements of displacement, each intermediate measurements of traction force are made in order to obtain each intermediate values of traction force. The successive intermediate values that are measured are compared with the consecutive intermediate type values of the assignment table, and a signal is given if at least one intermediate value that is measured which does not coincide with at least one corresponding intermediate type value.
Moreover, the verifying device of the present invention which can be used for embodying the method of this invention consists of a traction force sensor connected to the riveting apparatus in order to measure successive values of a traction force applied to a stem of a blind rivet, a displacement sensor connected to the riveting apparatus for measuring successive values of the displacement of the stem of the blind rivet to which the traction force is applied with respect to the body of the blind rivet, and transmitter means for transmitting the values measured by the sensors to data processing means which consist of a memory in which is stored at least one type assignment table like the one described above with respect to the verification method of the present invention. The device furthermore includes controlling means for ordering the displacement sensors and the traction force sensors to simultaneously carry out the successive initial, intermediate and terminal measurements during the application of the traction force to the stem, comparing means for respectively comparing the initial measured values, the intermediate measured values and the terminal measured values with the initial type values, the intermediate type values and the terminal type values contained in the assignment table, and means of signalling in order to signal at least each measured value that does not coincide with at least one corresponding type value.
In addition, the device can include generating means for graphic representations in order to generate a graphic representation of the values measured in the riveting of each blind rivet in a system of coordinates that includes a first coordinate of displacement values and a second coordinate of traction force values, along with means of generation of an alert signal, for example, in the form of acoustic signals, visual signals and combinations of them, which generate an alert signal when a measured values does not coincide with at least one corresponding type value. The generating means for graphic representations can furthermore be adapted to generate in the said system of coordinates a graphic representation of the type values contained in the type assignment table.
The graphic representations generated by the generating means for graphic representations can be curves, both in terms of the measured values and in terms of the type values. When the graphic representation of the values measured during the riveting and of the measured values consists of curves, these curves can be discerned visually and a determination can be made of when the curve of the measured values corresponds to the curve of the type values or lies between the curve of the minimum and maximum type values, in which case the riveting has been carried out correctly.
The present invention can be implemented in various different environments, such as for example in systems habitually used in the aeronautical industry based on a robot or numerical control system with sufficient precision, repetitiveness and rigidity, duly programmed for locating itself in front of the unit to rivet, which already has the drill-holes previously made under the required conditions and which incorporates the mechanism (independent of the above) which couples the rivet, introduces it and perpendicularly adjusts it to the surface and fires the traction mechanism for the stem, provided with a positioning device based on a PC plus PLC, which contains the positioning control software with analogue and logic inputs and outputs, normally linked to the actual control of the robot or similar. The verifying device of the present invention can be incorporated into the already existing system by means of connection of the displacement meter to be included in the traction system, and of the stress meter likewise applied to that mechanism, to an additional data acquisition card, and compatible with the computing tools already existing in the system and commercial software for analysis of the inputs corresponding to the measurements which will classify the results and store data.
From the foregoing it is revealed that the present invention permits the effective checking in real time and in situ of the state of the blind rivets applied, and permits the generation of either a results report at the end of a programmed task or signals and/or actions during and/or after each riveting. To achieve this, each of the results will be able to be associated with a reference code for each rivet, corresponding to the code of the rivet used to position each of them.
Explained below are aspects of the invention on the basis of some attached drawings in which
Appearing in these figures are reference numbers having the following meanings:
As can be seen in
In the embodiment of the verifying device 8 for the dynamic verification of the state of riveting of blind rivets carried out with an automatic riveting apparatus shown in
In accordance with this embodiment of the invention, the signalling means 10 includes generator means of graphic representations 11 for generating a graphic representation of the values measured in the riveting of each blind rivet in a system of coordinates with a first coordinate of measured values of displacement and a second coordinate of measured values of traction force. To achieve this, the generator means of graphic representations 11 are adapted for generating, in the system of coordinates, a graphic representation of, the type values contained in the type assignment table. The system of coordinates and the graphic representation are shown on the screen 13a of a monitor 13 in which are also incorporated a loudspeaker 13b, an indicator light for confirmation of correct location 13c of the rivet and an indicator light alert for incorrect location 13d of the rivet which are connected to means for generation of alert signals 12 incorporated into the signalling means 10 which generate alert signals when a measured value does not coincide with at least one corresponding type value. These signals result in an acoustic alert signal emitted by the loudspeaker 13b and/or a light alert signal emitted by the indicator light for incorrect location 13d.
The type values (aa1, ab1, ba1-ban, bb1-bbn, ca1, cb1) correspond to a type riveting corresponding to the riveting carried out with a standard blind rivet corresponding to the blind rivet 3 which is applied by means of a standard riveting apparatus corresponding to the riveting apparatus 1 that is used.
The processing means include controlling means 6b, for example in the form of a control programme, which, via the electrical connection means 9, order the meters 4, 5 to carry out successive and respective measurements of the traction force applied and of the displacement achieved in the initial stage A, the intermediate stage B and the terminal stage C of the application of the traction force. In the embodiment with the assignment table shown in
The comparing means (6c) respectively compare the initial measured values (AA1, AB1), the successive intermediate measured values (BA1-BAn, BB1-BBn) and the terminal measured values (CA1, CB1) with the initial type values (aa1, ab1), with the consecutive intermediate type values of the assignment table (ba1-ban, bb1-bbn) and with the terminal type values (ca1, cb1) included in the assignment table 7. In turn, the signalling means 10 are adapted for detecting and signalling at least each measured value which does not coincide with at least one corresponding type value.
In this embodiment, the comparing means (6c) respectively compare the initial measured values (AA, AB), the intermediate measured values (BA1-BAn, BB1-BBn) and the terminal measured values (CA, CB) with the acceptable initial intervals (ac, ad), the acceptable intermediate intervals (bc1-bcn, bd1-bdn) and the acceptable terminal intervals (cc, cd), and the signalling means 10 are adapted to signal at least each measured value that does not lie in its corresponding acceptable interval.
It can be seen that in the case that is represented, the curve of the measured values lies between the maximum and minimum type values, and is therefore representative of the correct application of the rivet.
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