Benchmark device for a plane face, and a machining system implementing it

A benchmark device for a plane face comprises at least three benchmark elements which together define a reference plane parallel to said plane face, together with a system of rectangular axes enabling any point of said plane face to be located.

DETAILED DESCRIPTION 
FIGS. 1 to 3 show a device 1, e.g. a drilling template (in which the guide 
holes are not shown) that is provided with a plane face 2. 
The following are fixed on said plane face: 
a first benchmark element 3 in the form of a one-fourth of a cylinder, 
comprising two axial facets 3.1 and 3.2 that are mutually orthogonal, and 
that are orthogonal to said plane face 2, together with an end face 3.3 
that is orthogonal to said axial facets 3.1 and 3.2 and parallel to said 
plane face 2. The three facets 3.1, 3.2, and 3.3 form a rectangular 
trihedron defining three edges, two of which 3.4 and 3.5 are mutually 
perpendicular but parallel to the plane face 2, while the third edge 3.6 
is perpendicular to said plane face 2; 
a second benchmark element 4 which is semi-cylindrical in shape, having a 
diametral facet 4.1 orthogonal to the plane face 2, and an end facet 4.2 
orthogonal to the diametral facet 4.1 and parallel to said plane face 2. 
The two facets 4.1 and 4.2 form a rectangular dihedron whose edge 4.3 is 
parallel to said plane face 2; 
a third benchmark element 5 which is cylindrical in shape, having an end 
facet 5.1 parallel to the plane face 2; and 
a fourth benchmark element 6 which is semi-cylindrical in shape like the 
second benchmark element 4, comprising a diametral facet 6.1 orthogonal to 
the plane face 2 and an end facet 6.2 orthogonal to the diametral facet 
6.1 and parallel to said plane face 2. The two facets 6.1 and 6.2 form a 
rectangular dihedron whose edge 6.3 is parallel to said plane face 2. 
The end facets 3.3, 4.2, 5.1, and 6.2 of the elements 3, 4, 5, and 6 are 
coplanar, thereby defining a reference plane P. In addition, the edges 
3.4, 4.3, and 6.3 of the elements 3, 4, and 6 are colinear, thereby 
defining an axis X--X, the elements 4 and 6 being disposed on opposite 
sides of the element 3. The element 5 is at least approximately disposed 
in line with the edge 3.5 of the element 3, with said edge 3.5 defining an 
axis Y--Y perpendicular to the axis X--X. 
The benchmark elements 3 to 5 are disposed in the vicinity of the periphery 
of the plane face 2. 
It can thus be seen that the benchmark elements 3 to 5 determine: 
a reference plane P parallel to said plane face 2 and enabling the 
orientation thereof to be located; and 
a system of rectangular axes X--X, Y--Y having its origin situated at the 
intersection between the edges 3.4, 3.5, and 3.6 of the element 3 and 
which enables any point of said face 2 to be located. 
FIG. 4 is a diagram showing an application of the device shown in FIGS. 1 
to 3. 
The device 1 is a drilling template, i.e. a plate pierced by a plurality of 
guide holes 7 for a drill bit or for a reamer 8. The drilling template 1 
is fixed on a workpiece 9 in which holes are to be drilled corresponding 
to guide holes 7. For example, the workpiece 9 is the wing of an aircraft 
in the vicinity of its connection to the fuselage, with the holes to be 
drilled serving to receive fixing means for connecting said wing to said 
fuselage. 
The tool 8 is mounted on the "hand" 10 of a robot (not shown) under the 
control of a computer 11. The "hand" 10 can be displaced in translation 
parallel to the three axes Ox, Oy, and Oz of a reference axis system, and 
it may be pivoted about two perpendicular axes u--u and v--v. 
After being fixed on the workpiece 9, the drilling template 1 occupies an 
accurate position relative thereto. However, because of possible tolerance 
in the positioning of the workpiece 9 relative to its support (not shown), 
the position of the template 1 does not coincide in the robot's axis 
system Ox, Oy, and Oz with the nominal reference position that it ought to 
occupy. 
Thus, in order to correct the resulting positioning and orientation errors 
of the guide holes 7 relative to the axis system Ox, Oy, and Oz, the 
above-described benchmark elements 3 to 6 are provided on the plane face 2 
of said template 1. In addition, a distance measuring device 12, e.g. of 
the laser type is mounted on the "hand" 10. The distance measuring device 
12 emits a signal when it is at a predetermined distance from an obstacle. 
Naturally, the positioning of the distance measuring device 12 relative to 
the axis of the tool 8 is fixed and known, thereby making it easy to 
deduce the position of the tool 8 once the position of the detector 12 is 
known. 
Thus, with the drilling template 1 fixed on the workpiece 9, the robot 
"hand" 10 is displaced in translation parallel to the plane Ox,Oy until it 
comes over the position that ought to be occupied by one of the studs 3 to 
6, e.g. the stud 3, assuming that the drilling template 1 is in its 
nominal reference position which is known to the robot. Given that the 
positioning tolerances of the drilling template 1 relative to said nominal 
reference position are such that the real position of said stud 3 overlaps 
the nominal position thereof, at least in part, the detector 12 always 
finds itself over said stud 3. The robot "hand" 10 is then displaced 
parallel to the axis Oz to move closer to said stud 3. When the detector 
12 is at a predetermined distance from the face 3.3 of the stud 3, it 
sends a detection signal to the computer 11. The computer then knows the 
exact position of said face 3.3 relative to the plane Ox,Oy. 
By performing similar operations with the other studs 4, 5, and 6, the 
computer 11 measures the distances between each of the faces 4.2, 5.1, and 
6.2 and said plane Ox,Oy. It thus knows the orientation of the plane face 
2 relative to the plane Ox,Oy, and it deduces therefrom the value of the 
angle or of the angles through which it needs to rotate the "hand" 10 
about the axes u--u and v--v so as to bring the tool 8 perpendicular to 
said plane face 2. 
Thereafter, the "hand" 10 is displaced successively parallel to the axis Oy 
to discover the distances between said faces 3.1, 4.1, and 6.1 and the 
plane Ox,Oz. The computer 11 then knows the position of the axis X--X in 
the reference axis system Ox, Oy, and Oz. 
Similar distance measuring operations are then performed to determine the 
distance of the face 3.2 of stud 3 from the plane Oy,Oz and thus the 
position of the axis Y--Y in the reference axis system Ox, Oy, Oz. 
Once the orientation of the face 2 and then the position of the axis system 
X--X, Y--Y have been located relative to the axis system Ox, Oy, and Oz, 
it will readily be understood that the computer 11 can insert the tool 8 
into any of the holes 7 (defined by its coordinates relative to the axes 
X--X and Y--Y) in the plane face 2. 
The studs 3 to 6 thus make it possible for the computer 11 to know the 
position and the orientation of each hole accurately by means of an axis 
transformation. 
It may be observed that in FIGS. 1 to 4, the plane face 2 is physically 
embodied. However this need not be the case and it could be determined 
solely by the faces of the studs 3, 4, 5, and 6 opposite to the faces 3.3, 
4.2, 5.1, and 6.2, with said studs being fixed to an object (not shown) by 
columns carrying said studs at their free ends. Naturally, the benchmark 
of said non-physically embodied plane face 2 can still be used to locate 
any point of said object which is fixed relative thereto.