Method for evaluating the installation of blind rivets, method and system for installing blind rivets, method and system for obtaining a pattern, and aircraft

Abstract

A method for evaluating installation of blind rivets including measuring the “cycle time” represented “y.sub.0”, transmitting sound waves through the blind rivet installed in the structure, measuring the “travel time” represented “x.sub.0”, relating “travel time” and “cycle time”, and obtaining a pair of times (x.sub.0,y.sub.0), providing a time relation pattern establishing a borderline between an area of suitable rivets and an area of unsuitable rivets, the border represented y=f(x), so for cycle time values greater than y=f(x), it is considered a “suitable area”, for cycle time values less than y=f(x), it is considered an “unsuitable area”, representing pair (x.sub.0,y.sub.0) in the graphic representation and verifying if the value of y.sub.0 is greater or less than the value of y=f(x0), classifying installation of the rivet as suitable or unsuitable according to the verification.

Claims

1. A non-invasive method for evaluating an installed blind rivet used in attaching structures, where the installed blind rivet comprises a stem, an installation nut, a break notch, cut-off points and a bushing, wherein the method comprises: a) measuring “cycle time” defined as installation time of the rivet which is installed and represented as “y.sub.0”; b) transmitting sound waves through the blind rivet installed in the structure; c) measuring “travel time” defined as propagation time of transmitted and reflected sound waves of the installed blind rivet, and represented as “x.sub.0”; d) relating the “travel time” and the “cycle time”, and obtaining a pair of times (x.sub.0,y.sub.0); e) providing a time relation pattern establishing a border in a graphic representation the coordinates of which are (travel time, cycle time) or (x, y) between an area of suitable rivets and an area of unsuitable rivets, where the border is represented as y=f(x), such that for cycle time values greater than y=f(x), it is considered a “suitable area”, for cycle time values less than y=f(x), it is considered an “unsuitable area”; f) representing the pair (x.sub.0,y.sub.0) in the graphic representation and verifying if the value of y.sub.0 is greater or less than the value of y=f(x.sub.0); and g) classifying the installation of the rivet as suitable or unsuitable according to the verification, such that if y.sub.0>f(x.sub.0) then it is considered a suitable installation if y.sub.0<f(x.sub.0) then it is considered an unsuitable installation.

2. The method according to claim 1, wherein the sound waves are ultrasounds.

3. The method according to claim 2, wherein the frequency of the sound waves is 20 MHZ.

4. The method according to claim 1, where the “cycle time” is obtained as the time elapsed between the opening of pneumatic valves of a machine used to install the rivet and an instant a stem of the rivet breaks.

5. The method according to claim 1, where the “cycle time” is provided by a numerical control of a machine used to install the rivet.

6. The method according to claim 1, wherein the “travel time” is measured by a pulse-echo method in which a receiver is the same generator-transmitter generating and transmitting the sound waves.

7. A system for creating a time relation pattern, wherein the system comprises: a set of blind rivets; a structure in which to verify quality of an installed rivet; a system for installing blind rivets comprising: a riveting machine for measuring installation “cycle time”, defined as installation time of the rivet which is installed; a transmitter which transmits sound waves into installed rivets and measures “travel time”, defined as propagation time of transmitted and reflected sounds waves in the installed rivet; a device for viewing quality of an installed rivet; a process or configured for data capture suitable for receiving and representing “cycle time” and “travel time” of each installation of each rivet in a graph and for marking each installation as “suitable” or “unsuitable” according to the quality of the installation of each rivet; wherein the processor is further configured to generate a “cycle time”=f(“travel time”) relation which defines a border in the graph between “suitable” installations of the installed rivets and “unsuitable” installations of the installed rivets; and an output for providing result, this result being the “cycle time”=f(“travel time”) relation.

8. The system of claim 7, further comprising a non-transitory computer readable medium containing instructions thereon which cause the processor to: generate a first data set of two-dimensional points which contains “cycle time”, represented as “y.sub.0”, and measured “travel time”, represented as “x.sub.0”, for each one of a second set of installed rivets; and analyze the first data set using the “cycle time”=f(“travel time”) relation, represented as y=f(x), wherein the analysis comprises: for each measured cycle time of each of the second set of installed rivets, classifying a rivet installation as “suitable” if the cycle time value is greater than y=f(x) and “unsuitable” if the cycle time value is less than y=f(x).

9. An aircraft comprising at least one structure installed by a system according to claim 8.

10. The system according to claim 7, wherein the sound waves are ultrasound waves at 20 MHz.

11. The system according to claim 8, wherein the sound waves are ultrasound waves at 20 MHz.

12. An aircraft comprising at least one structure installed by a system according to claim 10.

13. An aircraft comprising at least one structure Installed by a system according to claim11.

Description

DETAILED DESCRIPTION

(1) These and other features and advantages of the invention will become more evident from the following detailed description of preferred embodiments, given only by way of illustrative and non-limiting example, in reference to the attached figures.

(2) FIG. 1 shows a pull-through blind rivet with a countersunk head.

(3) FIG. 2 shows an installed pull-through blind rivet with a countersunk head.

(4) FIG. 3 shows a sound wave transmitter on the countersunk head of a rivet.

(5) FIG. 4 shows an example of the characterisation result of the “travel time—cycle time” plan.

(6) FIG. 5 shows the division of the “travel time—cycle time” plan by the border determining the area of suitable and unsuitable installations.

(7) FIG. 6 shows the “travel time—cycle time” plan already characterised, and the method for evaluating a rivet to be evaluated.

(8) FIG. 7 shows a graph of a first actual experiment where the cycle time is represented on the y-axis in seconds and the travel time on the x-axis in microseconds.

(9) FIG. 8 shows a graph of a second actual experiment where the cycle time is represented on the y-axis in seconds and the travel time on the x-axis in microseconds.

DETAILED DESCRIPTION

(10) The present invention relates to a method for evaluating the installation of a blind rivet used in attaching closed structures or structures for which it is complicated or costly to access the “unexposed face” for verifying whether or not the rivets have been correctly installed. An example of a blind rivet is depicted in FIG. 1. A pull-through blind rivet with a countersunk head can be seen in this figure. It shows the different parts of a rivet: stem (1), installation nut (2), break notch (3), cut-off points (4) and bushing (5). FIG. 2 shows the rivet of FIG. 1 installed in a structure where the bushing (5) is folded and can be seen abutting with the structure to prevent the rivet from coming out. The length of the rivet is represented as less than in FIG. 1 due to the breaking of the stem (1).

(11) Non-Invasive Method for Evaluating the Installation of a Rivet

(12) In one embodiment, the non-invasive method for evaluating the installation of a blind rivet used in attaching structures, where the blind rivet comprises a stem (1), an installation nut (2), a break notch (3), cut-off points (4) and a bushing (5), comprises the steps of: a) measuring the “cycle time” (8) defined as the installation time of the rivet which is installed and represented as “y.sub.0”, b) transmitting sound waves through the blind rivet installed in the structure, c) measuring the “travel time” (7) defined as the propagation time of the transmitted and reflected sound wave, and represented as “x.sub.0”, d) relating the “travel time” and the “cycle time”, and obtaining a pair of times (x.sub.0,y.sub.0), e) providing a time relation pattern establishing a borderline in a graphic representation the coordinates of which are (travel time, cycle time) or (x, y) between an area of suitable rivets and an area of unsuitable rivets, where the border is represented as y=f(x), such that for cycle time values greater than y=f(x), it is considered a “suitable area”, for cycle time values less than y=f(x), it is considered an “unsuitable area”, f) representing the pair (x.sub.0,y.sub.0) in the graphic representation and verifying if the value of y.sub.0 is greater or less than the value of y=f(x0), g) classifying the installation of the rivet as suitable or unsuitable according to the verification, such that if y.sub.0>f(x.sub.0) then it is considered a suitable installation if y.sub.0<f(x.sub.0) then it is considered an unsuitable installation.

(13) In one embodiment, the sound waves transmitted in step b) of the method for evaluating the installation of the rivet are ultrasounds, i.e., frequency thereof exceeds 20 KHz. This feature provides the method with discretion since the human ear is not capable of perceiving sounds at this frequency. In a particular embodiment, the frequency of the sound waves used is 20 MHz.

(14) For measuring the “travel time” correctly a suitable frequency must be used, and to that end the precision of such measurement is greater with high frequencies. However, the attenuation of the sound wave is greater when the frequency is high, and in turn, if the frequency is too high the wave can completely attenuate and it would not be possible to measure the travel time. Therefore, a compromise between precision and attenuation is necessary. Ultrasound waves in the 20 MHz frequency are advantageously used, thereby measuring the “travel time” with sufficient precision.

System for Installing Blind Rivets

(15) In one embodiment, the system for installing blind rivets comprises: a riveting machine with means for measuring the “cycle time” of the installation, and a sound wave transmitter (6) comprising: means for transmitting sound waves, means of injecting the waves into a rivet and means for measuring the “travel time”.

(16) In one embodiment of the system, ultrasound waves at 20 MHz are used and a 20 MHz ultrasound wave generator-transmitter (6) is used. As can be seen in FIG. 3, the same sound wave generator-transmitter (6) is used as emitter-transmitter and receiver generating ultrasound waves and receiving the reflected waves, placing it on the installed rivet for injecting the ultrasound wave at 20 MHz into the rivet and thus being able to measure the “travel time”.

(17) In one embodiment of the system, the machine which installs the rivet incorporates a numerical control suitable for measuring the “cycle time”.

Method for Creating a Time Relation Pattern

(18) In one embodiment, the method for creating a time relation pattern relating “cycle time” with “travel time” comprises the steps of: providing a set of rivets to install and a structure in which it is possible to verify the quality of the installed rivet, installing each rivet in the structure and measuring for each one the “cycle time” represented as y.sub.p, with p=A . . . B, where y.sub.A is the minimum “cycle time” that can be implemented for installing a rivet, and y.sub.3 is the maximum “cycle time” that can be implemented, once each rivet is installed, measuring the “travel time” and representing it as x.sub.p, with p=A . . . B, where x.sub.A is the minimum “travel time” that can be implemented for installing a rivet, and x.sub.B is the maximum “travel time” that can be implemented, verifying the quality of the installation of each rivet, representing “travel time” and “cycle time” for each installation of each rivet in a graph with coordinates (x, y) and marking each installation as “suitable” or “unsuitable” according to the quality of the installation of each rivet, plotting a border y=f(x), x ε [x.sub.A, x.sub.B], and ε [y.sub.A, y.sub.D], representing values of “y.sub.p=f(x.sub.p)” above which the installations are considered “suitable” and below which the installations are considered “unsuitable”, therefore, there are two areas, “suitable area” and “unsuitable area”, separated by the border y=f(x).

(19) The method for creating a pattern generates a graphic representation of “suitable” and “unsuitable” installations based on the “travel time” and the “cycle time” as well as a border y=f(x) determining two regions: “suitable area” and “unsuitable area”.

(20) FIG. 4 is an example of the characterisation result of the “travel time” (7)—“cycle time” (8) plan as a result of a group of rivets used to create the pattern. The group of rivets is installed in a structure in which accessing the “unexposed” face is possible to evaluate the quality. For each indicated rivet, its “travel time” (7) and its “cycle time” (8) is obtained, and the “unexposed face” is accessed to evaluate the quality of the installation of the rivet. A technician decides which quality level is acceptable inspecting the installed rivets and represents the rivets in the plan of FIG. 4, circles (O) correspond to the positions in the “travel time” (7)—“cycle time” (8) plan of rivets the quality of which is considered “suitable”, and exes (X) correspond to the positions in the plan of rivets the quality of which is considered “unsuitable”.

(21) FIG. 5 shows the division of the “travel time” (7)—“cycle time” (8) plan depending on the two regions defined by the suitable and the unsuitable rivets. The two regions are referred to as “suitable area” (11) and “unsuitable area” (9) and are separated by the border (10). The border corresponds to the relation y=f(x) and represents values of “y.sub.p=f(x.sub.p)” above which the installations are considered “suitable” and below which the installations are considered “unsuitable”, therefore, there are two areas, “suitable area” and “unsuitable area”, separated by the border y=f(x).

(22) FIG. 6 shows the “travel time” (7)—“cycle time” (8) plan of an already installed rivet, and the method for evaluating the rivet to be evaluated (14). Given the “travel time of the rivet to be evaluated” (12), or x.sub.0, and the “cycle time of the rivet to be evaluated” (13), or y.sub.0, the position (14) of the rivet to be evaluated corresponds to the “unsuitable area” (9) since it is seen that y=f(x0)>y0, and the installation of the rivet is therefore classified as “unsuitable”.

(23) FIG. 7 shows the results of a first experiment with real time values used in the installation of each represented rivet. Circles (O) represent suitable rivets and exes (X) represent rivets which are considered unsuitable. In the graph, the x-axis represents “travel time” in microseconds (μs) and the y-axis represents “cycle time” in seconds (s). Some of the values of the following table (Table 1) are represented in the graph of FIG. 7. “M” represents unsuitable installations and “B” represents suitable installations:

(24) TABLE-US-00001 TABLE 1 Installation Travel time (μs) Cycle time (s) M 3.92 2.76 M 3.98 2.61 M 3.95 2.82 M 3.92 2.72 M 3.96 2.84 M 3.92 2.73 M 3.81 2.99 M 3.93 2.66 M 3.98 2.87 M 3.92 2.67 M 3.91 2.81 M 3.86 2.86 M 3.94 2.99 M 4.08 2.57 M 3.94 2.73 M 3.94 2.78 M 3.85 2.84 B 4.37 2.94 B 4.29 2.82 B 4.34 2.76 B 4.33 2.80 B 4.31 2.70 B 4.35 2.79 B 4.43 2.85 B 4.36 2.75 B 0.03 1.27 B 4.30 2.89 B 4.33 2.80 B 4.33 2.77 B 4.43 2.92 B 4.42 2.84 B 4.40 3.01 B 4.32 2.93 B 4.28 2.87 B 4.39 2.80 M 3.90 2.87 M 3.94 2.77 M 3.96 2.68 M 3.92 2.73 M 3.91 2.80 M 3.87 2.73 M 4.38 2.24 M 3.97 2.60 M 3.95 2.67 B 4.32 2.83 B 4.31 2.80 M 3.98 2.68 M 3.92 2.83 M 3.90 2.71 M 3.90 2.68 M 3.95 2.66 B 4.41 2.98 B 4.30 3.06 B 4.47 2.92 B 4.30 2.94 B 4.27 2.85 B 4.32 2.88 B 4.32 2.92 B 4.40 2.92 B 4.29 2.90 B 4.24 2.98 B 4.36 2.91 B 4.36 2.70

(25) FIG. 8 shows the results of a second experiment with real time values used in the installation of each represented rivet. Circles (O) represent suitable rivets and exes (X) represent rivets which are considered unsuitable. In the graph, the x-axis represents the “travel time” in microseconds (μs) and the y-axis represents “cycle time” in seconds (s). Some of the values of the following table (Table 2) are represented in the graph of FIG. 8. “M” represents unsuitable installations and “B” represents suitable installations:

(26) TABLE-US-00002 TABLE 2 Installation Travel time (μs) Cycle time (s) M 3.49 2.86 M 3.53 2.97 M 3.48 2.86 B 3.91 3.01 B 3.79 3.23 B 3.82 2.96 M 3.64 2.79 M 3.68 2.62 M 3.79 2.50 M 3.90 2.50 M 3.67 2.74 M 3.59 2.75 M 3.63 2.74 M 3.67 2.73 M 3.88 2.52 M 3.52 2.79 M 3.69 2.74 B 3.90 2.93 B 3.76 3.31 B 3.81 2.87 B 3.77 2.94 B 3.81 2.85 B 3.72 2.99 B 3.88 2.88 B 3.77 3.02 B 3.80 2.83 B 3.84 2.84 B 3.89 2.75 M 3.64 2.74 M 3.75 2.82 M 3.75 2.54 M 3.71 2.72 M 3.80 2.46 M 3.91 2.41 M 3.67 2.71 M 3.80 2.51 M 3.72 2.79 M 3.41 3.00 M 3.64 2.77 M 3.45 2.70 M 3.65 2.71 M 3.92 2.35 M 3.81 2.63 M 3.42 2.74 M 3.42 2.93 M 3.40 2.75 M 3.45 2.86 M 3.47 2.69 M 3.45 2.70 B 3.75 3.00 B 3.71 3.05 B 3.76 2.92 B 3.67 3.03 B 3.74 3.02 B 3.66 3.15 B 3.82 2.82 B 3.74 3.12 B 3.69 3.09 B 3.75 3.06 B 3.74 2.93 B 3.64 3.07 B 3.73 3.04 B 3.86 3.05

(27) In one embodiment of the method, the “cycle time” is defined as the time elapsed between the opening of pneumatic valves of the machine used to perform the riveting and the instant the stem (1) of the rivet breaks. This data is obtained by means of external sensors or other similar means.

(28) In one embodiment of the method, the “cycle time” is provided by a numerical control which the machine installing the rivet incorporates.

(29) In one embodiment of the method for creating a time relation pattern, the “travel time” is measured by the pulse-echo method where the receiver is the same sound wave generator.

System for Creating a Time Relation Pattern

(30) In one embodiment, the system for creating a time relation pattern comprises: a set of blind rivets, a structure in which it is possible to verify the quality of an installed rivet, a system for installing blind rivets according to the second inventive aspect or any of the embodiments thereof described above, means of viewing the quality of an installed rivet, processing means comprising data capture means suitable for receiving and representing “cycle time” and “travel time” of each installation of each rivet in a graph and for marking each installation as “suitable” or “unsuitable” according to the quality of the installation of each rivet, processing means suitable for generating a “cycle time”=f(“travel time”) relation determining a “suitable area” comprising the “suitable” installations in a graphic representation of “cycle time”-“travel time” and an “unsuitable area”, output means for providing the result, this result being the “cycle time”=f(“travel time”) relation,
wherein the system for creating a time relation pattern it implements the steps of the non-invasive method for evaluating the installation of a blind rivet according to the first inventive aspect or any of the embodiments thereof described above.

System for Installing and Evaluating Blind Rivets

(31) In one embodiment, the system for installing and evaluating blind rivets comprises a system for installing blind rivets according to the first inventive aspect or any of the embodiments thereof described above, a system for creating a pattern according to the fourth inventive aspect or any of the embodiments thereof described above, means of viewing the result of the quality of a blind rivet, this quality being “suitable” or “unsuitable”,
wherein the system implements the steps of a method according to the first inventive aspect or any of the embodiments thereof described above.