FR2707388A1 - Method and device for measuring the profile of a plane section of a surface and, in particular, profiled sheet metal - Google Patents

Abstract

A straight line AA' is defined in the section plane and an origin O is defined on the straight line AA'. Successive points M on the straight line AA' are chosen. For each point M, the distance OM and the distance MK from M to a point K on the surface (1), in a direction MK making an angle alpha with AA', are measured. The coordinates of K in a reference frame (@, @) are calculated. The absolute value of the derivative of MK with respect to OM is calculated. If the value of the derivative is less than a predetermined value a, the point having the coordinates of K is plotted on a graph. The points on the graph are joined.

Description

The present invention relates to the reading of the

  profile of a plane section of a surface.

  To realize, for example, the cladding of buildings

  In this case, profiled plates are used which have large ribs whose geometry must be controlled. To do these checks, we use conventional dimensional metrology instruments such as brackets, truss and calipers. But these means are difficult to use and the measures are very long to perform. Metrology machines with mechanical feelers could be used, but they are very slow and not always well adapted to the control of

  shapes of profiled sheets for cladding.

  The object of the present invention is to provide a fast, accurate and economical means of measuring the

  geometry of a surface and in particular of a plate

  EEA. To this end, the subject of the invention is a method of reading the profile of a section of a surface by a plane, characterized in that: a line AA 'is defined in the plane of section and a point of origin fixed O on the line AA ', -on choose successive points M on the line AA', so as to perform a scan of the line AA ', and - for each of the points M chosen: measure the distance from the point M to point of origin O and the distance from the point M to at least one point K of the surface, in at least one direction MK making an angle α with the line AA ', and the coordinates x and y of the point K are calculated in a orthonormal landmark originating from point 0,

  an axis Ox along the line AA 'and an axis Oy perpendicular

  to Ox, using the equations: x = OM - MK cos ay = MK sin a OM and MK being the algebraic values of the segments OM and MK, - for each of the selected points M, we calculate from a set of values of OM and MK, the absolute value of the derivative of MK with respect to OM dMK

  z = - and this value is compared to a predefined value

  dOM ended a, - If z is smaller than a, we have a point k of x and y coordinates on a graph, in an orthonormal coordinate system, and we draw the curve (C) passing through the points k. Preferably, the distance from the point M to the surface is measured along three directions MK, MI and ML making with the line AA 'respective angles a, P and y, the angle a of MK with AA' and the angles 3 and being such that: a <90, = 90 and y> 900, - for each of the directions MK, MI and ML, the coordinates of the points K, I and L are calculated as well as the uncertainties r, ri and r1 on the positions of the points K, I and L and the derivatives of MK, MI and ML with respect to OM, - is determined by interpollation between two successive measurements, three profiles (x, Yk), (x, yi), (x, Y1 ) each characterized by an uncertainty rk, ri and r1 and a dMK dMI dML derived ---, ---, ---, dOM dOM dOM

  - for each value of, we eliminate the

  dMK jdMK dMIL son for which or is greater than the base dOM d O d6M a value set in advance a and keep the point for

  where the uncertainty rk, ri or r, is the lowest.

  To find the distances from the point M to the surface, we can either move the point M at the same time above the surface and simultaneously measure the distances from the point M to the surface along the different directions, or move the point M to above the

  surface as many times as there are measurement directions.

  The invention also relates to a device for measuring the profile of a plane section of a surface which comprises an incremental rule provided with a motor, a carriage, a position sensor of the carriage, at least one means for measuring the distance from the carriage to a surface, and electronic calculation, recording and control means connected to the motor, to the position sensor of the carriage and to the at least one means for measuring the distance

from the trolley to a surface.

  Preferably, the at least one means for measuring the distance of the carriage to a surface is mounted steerably

on the cart.

  The carriage can carry three means for measuring the distance to a surface, oriented in three different directions. Preferably, the at least one means for measuring the distance of the carriage to a surface is a laser range finder. The invention will now be described so

  more precise with reference to the appended figures.

  Figure 1 is an explanatory block diagram

  of the method of raising the profile of a profiled plate.

  FIG. 2 is a schematic representation of a device for raising the profile of a

cutting of a surface.

  - A section 1 of a profile portion made by a plane perpendicular to the profile surface and its longitudinal axis comprises ribs 2 separated by a range 3. The souls 4 of the ribs 2 and the range 3

have stiffeners 5.

  To raise the shape of the profile, a straight line AA 'is defined in the plane of section above the profile and parallel to the general surface of the profile constituted by the areas 3 and the top of the ribs 2 and a point O d fixed origin on this line. Successive points M are chosen on the line AA 'so as to scan this line and measure the distances of M at the origin O and at the surface of the section. Preferably, the point M is moved continuously along the line AA ', the distance OM of which is measured at the origin point O situated on the line AA' and

  the distance MK on the surface of the profile according to a direc-

  MK that makes an angle with the line AA '.

  The coordinates x and y of the point K are calculated in an orthonormal coordinate system (o oy) whose axis ox is directed along AA 'and the axis oy perpendicular to AA' using the relations: x = OK '= OM - MK cos ay = K'K = MK sin a We thus obtain a set of values of OM, MK, x and y corresponding to the successive points M

  for which measurements and calculations have been made.

  As long as the surface of the profile is at a relatively large angle with the direction MK, the measurement is relatively accurate, however, when the surface of the profile makes a small angle with the direction MK, the measurement is very imprecise; indeed, a small error on the position of M results in a significant error

on the measure of MK.

  To obtain a faithful representation of the profile 1, for each of the chosen points M, the absolute dMpK value of the derivative --- from a set of dOMs is calculated.

  values of OM and MK giving the variation of MK

  of OM and we eliminate the values of x and y when the absolute value of this derivative is greater than a threshold

set in advance.

  We plot on a graph all the points k of coordinates x and y corresponding to a point M for which dMK

  _ <a and draw the curve C passing through the points k.

  dOM But by doing so, you only get one

  partial representation of the shape of the profile.

  To obtain a complete representation, we make three readings with three observation directions MK, MI, ML; MK making an angle α with line AA ', less than 90, MI making an angle p with line AA', equal to 90, ML making an angle y with line AA ',

greater than 90.

  The three surveys make it possible to draw three distinct profiles from among which one chooses point by point the profile closest to reality. For this, we eliminate the points such that the absolute values derived from MK, MI and ML with respect to OM are greater than a predetermined value a, then for each value of x we retain the value y corresponding to the observation which leads to the lowest measurement error. If X is the abscissa of the point M x, the abscissa of the point K y, the ordinate of the point K p = MK 6 = the angle of incidence of MK with respect to the surface to be observed, measured with respect to the normal to this surface, We have: x = x -p Cos ay = p Sin has 1 dp tge = ---- - - Cotga Sina dX The uncertainty on x and y is written: Ax = AX + Ap cosa + p Sina Aa Ay = Ap Sina + p Cosa Aa and the characteristic uncertainty of the measuring point: r2 = Ax2 + Ay2 AX and Aa are characteristic quantities of the device

  measurement used; they can be known by calibration.

  Ap comprises two terms that add up: b: corresponds to the intrinsic measurement uncertainty of the device used, ctgE: corresponds to the uncertainty related to the angle of incidence on the surface of the beam used to make the measurement. Indeed, the beam of circular cross section

  radius c forms an elliptical spot on the surface

  whose projection of the major axis on the axis of the

  has a length 2c x tge and this length is a good

  indicator of measurement uncertainty.

  For each series of measurements, for example in the observation direction MK, there are N measuring points, corresponding to the successive abscissae Xk1, Xk2, ..., Xkn

  from point M to which the measurements were made.

  For each value of XkI we associate with the dFK-

  calculates the quadruplet of values (Xki, Y ki, rki, ----

  dOMi By interpollations between two values of xki, we can, for any value of x compute a quadruplet (x, Yk, dMK

rk, ---

  dOM Similarly for the observation directions MI and ML compute: dMI dMI (x, yi, ri, -) and (x, y1l rj, ---) dOM dOM To determine the profile we start with dMK dMMI dML eliminate the points M such that __, --- or - is dOM dOM dOMI greater than a magnitude fixed in advance, then, for each value of x the uncertainties rk, ri, r1 are compared and the smallest value is retained; we consider then that the profile has at the point of abscissa x, an ordinate y corresponding to the value yk; yi or Y1 for which rk, ri

where r1 is the smallest.

  Couples (x, y) are thus obtained which

  try to draw the profile by referring them to a graphi-

  than. This procedure can be generalized to any number of readings made from all different angles.

  To carry out these surveys a device is used

  tif consists of an incremental rule 10 provided with a motor 11 driving a carriage 12 carried and guided by the incremental rule 10. On the carriage 12 is mounted in a steerable manner a laser rangefinder 13 for measuring the distance d a fixed point of the carriage 12 to the surface 14 whose profile is to be determined. A captor

  continuously measures the position of the carriage 12.

  The motor 11, the telemeter 13 and the position sensor 15 are connected to a computer 16 equipped with a

printer 17.

  The computer 16 controls the rotation of the motor 11 which causes the carriage 12 to move. During the movement of the carriage 12, the computer 16 continuously receives from the sensor 15, the position of the carriage 12 and from the telemeter 13, the distance from the carriage 12 to the surface 14. From this information, the computer 16

  reconstructs the (at least partial) profile of the surface.

  To obtain a complete profile, three surveys are made with three different orientations of the rangefinder 13, the orientation of which can be read using a

  vernier whose measurement can be transmitted to the computer.

  The computer 16 makes it possible to choose the acceptable measurements and to determine the coordinates of the representative points of the profile. By plotting the representation points on a graph, we obtain an image of the profile 1 by superposition of three plots made with the three inclinations a, p and y. The representative points and the curve C joining these points are printed using

the printer 17.

  To measure in a single pass, it is possible to use a device comprising three laser rangefinders mounted on the carriage 12 and oriented in three different directions. The computer 16 can consist of any

  electronic control, computing and recording device

  tration. The incremental rule 10 can be mounted mobile parallel to itself and perpendicularly to its axis so as to make several readings according to several

cuts parallel to each other.

Claims (8)

  1. A method for reading the profile of a section of a surface by a plane, characterized in that: a line AA 'is defined in the plane of section and a fixed point of origin 0 is on the line AA', - we choose successive points M on the line AA ', so as to perform a scan of the line AA', and - for each of the points M selected: 10. we measure the distance from the point M to the point of origin O and the distance from the point M to at least one point K of the surface, in at least one direction MK making an angle α with the line AA ', and the coordinates x and y of the point K are calculated in an orthonormal frame originating from the point O,   an axis Ox along the line AA "and a perpendicular axis Oy   to Ox, using the equations: x = OM - MK cos ay = MKsin a OM and MK being the algebraic values of the segments OM and MK, - for each of the selected points M, one calculates from a set of values of OM and MK, the absolute value of the derivative of MK with respect to OM d = K   z .... and we compare this value to a predefined value   dOM ended a, - If z is smaller than a, we have a point k of x and y coordinates on a graph, in an orthonormal coordinate system, and we draw the curve (C) passing through the points k.   2. A process according to claim 1, characterized   in that, for each of the points M selected: - the distance from the point M to the surface is measured along three directions MK, MI and ML making with the line AA 'respective angles a, 1 and y, the angle a of MK with AA 'and the angles p and y being such that: a <90, p = 90 and y> 90, - for each of the directions MK, MI and ML, the coordinates of the points K, I and L are calculated, that the uncertainties rk, ri and r, on the positions of the points K, I and L and the derivatives of MK, MI and ML with respect to OM, - is determined by interpollation between two successive measurements, three profiles (x, Yk) , (x, yj), (x, yl) each characterized by an uncertainty rk, ri and r, and a dMK dMI dML derived ---, ---, ---, dOM dOM dOM   - for each value of x, we eliminate the   dMI iK diol son for which --- or --- or --- is greater than ddOM- dOM dôM 'a value set in advance a and keep the point for   where the uncertainty rk, ri or r is the lowest.   3. A process according to claim 2, characterized   in that, to record the distances from the point M to the surface, the point M is moved at one time above the surface and the distances of the   point M on the surface according to the different directions.   4. Process according to any one of the   cations 1 and 2, characterized in that, to record the distances from the point M to the surface in the different directions, the point M is moved over the surface   as many times as there are directions of measurement.   5.- Device for the profiling of a plane section of a surface (14) characterized in that it comprises an incremental ruler (10) provided with a motor (11), a carriage (12), a carriage position sensor (15), at least one means (13) for measuring the distance of the carriage (12) from a surface and an electronic means (16) for recording and control calculation connected to the motor (11) , to the position sensor (15) of the carriage (12) and to the at least one measuring means (13) of the distance of the trolley (12) on the surface (14).   6. Device according to claim 5, characterized in that the at least one measuring means (13) of the distance of the carriage (12) to a surface (14) is mounted orientable on the carriage (12).   7.- Device according to claim 5, characterized   characterized in that it comprises three measuring means (13) for the distance of the carriage (12) from a surface (14) oriented in three different directions.   8.- Device according to any one of   Claims 5 to 7, characterized in that the at least one   measuring means (13) of the distance of the carriage (12) to a surface is a laser range finder.