FR2496872A1 - Laser system for measurement of angular position - uses separator to generate beams in two incident planes for reflection by target mirror having half-mirrored perpendicular blade - Google Patents

Abstract

A plane mirror acting, as a target, is fixed to a solid whose angular position varies. A semi reflecting blade is mounted perpendicularly on the mirror. A beam from a laser mounted firmly on a reference is directed onto separators to direct two beams onto the target in two parallel incident planes. Each beam divides into two further beams by reflectionat the blade and mirror to produce parallel reflected beams. The four reflected beams are subjected to variations which are a function of the angular variation of the solid. Four detectors each comprising four quadrant photocells are servo controlled to remain centred on the beams to provide a differential measurement w.r.t. a zero position, and thus indicate angular position change.

Description

 The invention relates to measuring changes in the angular position of a solid relative to a reference solid.

 In order to measure the variations of the angular position of a structure such as a measuring machine, it is known to use a device comprising a laser beam divided into two rigorously parallel beams and to send these two beams on two detectors. placed on the structure whose deformation is to be measured. As axes ple, one can refer to the French patent application No. 77-21099 in the name of the applicant, which in Figure 6, describes a device for measuring the torsion of a tower 71 by means of two parallel laser beams xx 'and aa' sent on two cells 90 and 91. However, it is noted that this method is all the more precise as the distance between the two cells 90 and 91 in the example given is greater. Such a device is therefore cumbersome and can be difficult to implement on certain structures: for structures that do not allow cells to be placed at a sufficiently large distance from each other, measurement results can be obtained specific.

 The invention attempts to remedy this drawback. It allows the measurement of variations of the angular position of any structure, even compact, simply and accurately.

More particularly, the invention relates to a device for measuring changes in the angular position of a solid S1 around three orthogonal axes Ox, Oy, Oz linked to a reference solid.
According to the invention, this device comprises solid-solid S1, a target axis parallel to Ox may par.

mapping any incident beam into two reflected beams, one of which is parallel to the incident beam and the other symmetrical of the first with respect to the axis of the target, - integral with the SO solid, a laser beam transmitter from which at least a beam L1 parallel to the xOy plane and falling on the target, and detectors for measuring the deviations at each instant of the reflected beams, firstly in a direction parallel to the axis Oz on the other hand in a direction parallel to the plane xOy.

 According to a feature of the invention, the target consists of a plane mirror and a semi-reflective plate perpendicular to this mirror.

 In a preferred embodiment of the invention, the detectors are constituted by photoelectric cells which are slaved to remain centered on the beams, the measurements being made in a differential manner with respect to an arbitrary zero.

 The invention also relates to a method for measuring variations c <, p and ff of the angular position of a solid S1 around the Ox, Oy and Oz axes of an Oxyz reference linked to a reference solid S0, ut using a device according to the invention. The values of the angles a, ss ss and g can be deduced very easily from the values measured on the detectors.

We are going to determine the relations allowing to obtain the values C (,
ss and r with reference to a preferred embodiment in which two beams L1 and L2 are derived from the laser beam emitter and fall symmetrically onto the target, in two planes of incidence parallel to each other.

 Figure 1 shows a top view of this embodiment.

 FIG. 2 is a perspective view of the embodiment of FIG.

 FIGS. 1 and 2 show a device for measuring variations in the angular position of a solid Sd around three orthogonal axes Ox, Oy and Oz bonded to a reference solid S0. This target 1 is constituted, in this embodiment, by a plane mirror 2 on which is fixed a semi-reflecting plate 3 perpendicular to the mirror 2. As can be seen, the Target 1 has the characteristic of sharing any incident beam into two reflected beams, one of which is parallel to the incident beam and the other symmetrical of the first relative to the axis of the target 1.

In particular, the laser beam transmitter 4 integral with the solid SO sends two beams L1 and L2 shifted in s by means of separations 5 and 6. These beams L1 and L2 fall symmetrically on the target 1, but in two parallel incidence planes. between them. The beam L1 is divided into two beams which will be called L1 C1 and L1 C'20 The beam L1 C1 is obtained by a first reflection on the semi-reflecting plate 3 followed by a second reflection on the mirror 2. The beam L1 C 2 is obtained by a single reflection on the mirror 2 after the beam L1 has passed through the semi-reflective plate 3.The beam L1 C1 is parallel to the beam
L1 and the beam L1 C 'is symmetrical of the beam L1 C1 with respect to
2 the axis of the target 1.

In the same way, the beam L2 is divided into two reflected beams, a beam L2 C2 obtained by a first reflection on the semi-reflective lai 3 followed by a second reflection on the mirror 2 and a beam L2 C'1 obtained by a single reflection on the mirror 2 after crossing the semi-reflective plate 3. The beam L2 C2 is parallel to the beam L2 while the beam / L2 C2 relative to the axis of li
L2 C'1 is symmetrical of the target beam.

Since the beams L1 and L2 are sent symmetrically on one target, two groups of beams are obtained which parallel the beams L1, L1 C1 and L2 C'1 on the one hand and the beams L2, L2C2 and
L1C'2 on the other hand, the two groups of beams being symmetrical by ra port to the plane of symmetry of the target.

When the solid S1, therefore the target 1, undergoes variations in its angular position, the four reflected beams undergo, they also have variations that can be easily expressed according to the variatio experienced by
In order to measure the variations undergone by the reference beams, four detectors C1, C'1, C2 and C'2 have been fixed on the solid Sg. The detectors C1 and C'2 are intended to receive the reflected beams L1 C1 and
L1 Ct2 from the incident beam L1. These two detectors are placed symmetrically with respect to the plane of symmetry of the target and in the plane of the beam L1.

In a plane shifted at e, the detectors C2 and C'1 are placed for receiving the reflected beams L2 C2 and L2 C'1 coming from the incid beam L2. the
The four detectors measure / deviate at each moment from the four reflected beams, firstly in a direction parallel to lta)
Oz and on the other hand in a direction parallel to the plane x0y.

 These detectors may for example be constituted by photoelectric cells with four quadrants controlled to remain centered on the beams, the measurements being made in a differential manner with respect to an arbitrary zero.

We will now study the effects due to the movements of the target. On the detectors, the translations in the xoy plane will be positive counts towards the half-space B and negative towards the half-space
A, if we share the space of the two figures in two half spaces A and B delimited by the plane of symmetry of the target 1.

The movements of the solid S1 can be first of all movements of rotation around OxS axes Oy and 02: we will examine the effects due to these rotations, d being the distance separating the target 1 from the detectors: - Effects of a slight rotation of S1 around the Ox axis
It results in - a deviation alpha of the beam L1 C1 along the axis Oz - a deviation - &alpha;#d of the beam L2 C2 along the axis Oz - the beams L1 C'2 and L2 C'1 remain fixed.

-Effects of a weak rotation ss of S2 around the axis Oy
It results in - a deviation 2ss # d on the four paths along the Oz axis.

- Effects of low rotation &gamma; of S1 around the Oz axis.

It results in: - a deviation of 2 &gamma; d on the beams L1 C'2 and L2 C'1 in the plane
xoy (the two deviations in the same direction).

a translation T on the beams L1 C1 and LC along the y axis
(both translations are in the same direction).

The movements of the solid S1 can also be translations along the axes Ox, Oy and Oz. We will study below the effects due to these movements - Effects of a weak translation of S1 according to x
It results in - a translation T1 of L1 C1, in the plane xOy - a translation -T1 of L2 C2, in the plane xOy - a translation -T2 of L1 C'2 in the plane xOy - a translation T2 of L2 C '1 in the xOy plane.

- Effects of a weak translation of S1 according to y
It results in - a translation T3 of L1 C along y - a translation T3 of L2 C2 along y - no movement on L1 C'2 and L2 C'1 - Effects of a weak translation of S1 according to z
It results in - no movement on L1 C1, L1 C'2, L2 C2, L2 C'1.

 The deflections of the reflected beams may also be due to fluctuations of the beams L1 and L2 from fluctuations of the laser beam emitter itself or to the movements of the beams L1 and L2.

 We study below the effects of these fluctuations, which can be angular or transversal.

- Effects of angular fluctuations of the beams in the plane xoy
A fluctuation of the L1 beam results in: - a bd fluctuation on L1 C'2 in the xoy plane - a fluctuation - # d on L1 C1 in the xoy plane
A fluctuation of the L2 beam results in - a fluctuation .d on L2 C'1 in the xoy plane - a fluctuation -6.d on L2 C2 in the xoy plane.

- Effects of angular fluctuations of the beams according to z
They result in: - a fluctuation dld on L1 C1 and L1 C'2 according to z - a fluctuation # 'd on L2 C2 and L2 C'1 according to z - Effects of transversal fluctuations of the beams in the plane xoy
They result in - a displacement w on L1 C1 in the plane xOy - a displacement -w on L1 C'2 in the plane xOy - a displacement z on L2 C2 in the plane xOy - a displacement -z on L2 C'1 in the x0y plane.

- Effects of transverse fluctuations of beams according to z
They result in - a displacement u on L1 C1 and L1 C'2 - a displacement v on L2 G2 and L2 C'1.

 A and b will be called the very weak movements in translation of the part of the marble Sg carrying the detectors C1 and C'1 with respect to the part carrying the detectors C2 and C'2, a being the following movement z and b the movement in the x0y plane.

 We can deduce on the one hand the effects along the z axis and on the other hand the effects in the xOy plane of the various movements of the target and the beams or deformations of the marble, on the reflected beams.

The following table shows the effects along the oz axis: each line corresponds to one of the beams, each column corresponds to a cause of deflection of the reflected beams. The deviation which is read on one of the detectors, for example C1, ie the deflection of the beam L1 C1 is equal to the sum of the values indicated on the line L1 C1, that is to say

rot <SEP> T <SEP> T
<tb> bundles <SEP> rot <SEP> x <SEP> rot <SEP> y <SEP> rot <SEP> z <SEP> Tx <SEP> Ty <SEP> Tz <SEP> sender <SEP> sender <SEP > S0
<tb> 4 <SEP> 4
<tb> L1 <SEP> C1 <SEP> + <SEP>&alpha;<SEP> d <SEP> 2 <SEP> ssd <SEP> 0 <SEP> 0 <SEP> 0 <SEP> 0 <SEP>#' d <SEP> u <SEP> a
<tb> L1 <SEP>C'2<SEP> 0 <SEP> 2 <SEP> ssd <SEP> 0 <SEP> 0 <SEP> 0 <SEP> 0 <SEP>#'d<SEP> u <SEP > 0
<tb> L2 <SEP>C'1<SEP> 0 <SEP> 2 <SEP> ssd <SEP> 0 <SEP> 0 <SEP> 0 <SEP> 0 <SEP>#'d<SEP> v <SEP > a
<tb> L2 <SEP> C2 <SEP> - <SEP>&alpha;<SEP> d <SEP> 2 <SEP> ssd <SEP> 0 <SEP> 0 <SEP> 0 <SEP> 0 <SEP>#, d <SEP> v <SEP> 0
<Tb>
The table below is similar to the first table but indicates the effects in the xoy plane.

rot <SEP> T <SEP> T
<tb> bundles <SEP> rot <SEP> x <SEP> rot <SEP> y <SEP> rot <SEP> z <SEP> Tx <SEP> Ty <SEP> Tz <SEP> sender <SEP> sender <SEP > marble
<tb> 4 <SEP> 4 <SEP> So
<tb> L1 <SEP> C1 <SEP> 0 <SEP> 0 <SEP> T <SEP> T1 <SEP> T3 <SEP> 0 <SEP>#<SEP> d <SEP> w <SEP> b
<tb> L1 <SEP>C'2<SEP> 0 <SEP> 0 <SEP> 2 &gamma; d <SEP> -T2 <SEP> 0 <SEP> 0 <SEP> - # d <SEP> -w <SEP > 0
<tb> L2 <SEP>C'1<SEP> 0 <SEP> 0 <SEP> 2 &gamma;; d <SEP> T2 <SEP> 0 <SEP> 0 <SEP>#<SEP> d <SEP> z <SEP> b
<tb> L2 <SEP> C2 <SEP> 0 <SEP> 0 <SEP> T <SEP> -T1 <SEP> T3 <SEP> 0 <SEP> - # d <SEP> -z <SEP> 0
<Tb>
To measure the rotation around the x axis, it suffices to note that the difference between the sum of the deviations measured on the.

detectors C1 and C'1 and the sum of the deviations measured on the cells
C2 and C'2, in the first table, is equal to 2 that d + 2a.

 If we assume that the marble So is indeformable according to z, we obtain the rotation d around the Ox axis by dividing by 2d the difference entre between the sum of the information on the detectors C1 and C'1 and the sum of the information on detectors C2 and C'2.

 The method of measuring the rotation &alpha; the solid S1 around the axis Ox therefore consists in measuring, in a device according to the invention, the deviations along Oz on all the detectors C1, C'1, C2 and 5'2 and in deducing &alpha; the difference between the sum of the deviations measured on the detectors C1 and C'1 placed in the same half-space A with respect to the target 1 and the sum of the deviations measured on the detectors C2 and C'2 placed in the other half-space B, this difference being divided by twice the distance d separating the target 1 from the detectors.

 If we now carry out, always referring to the first table, the sum of the information read on the cells C1 and C2, we see that this sum is equal to: d (4 ss + '+ # #') + (u + v + a).

 If we consider that the various fluctuations due to the laser beam emitter 4 or to the movements of the beams L1 and L2 as well as the deformation of the So marble according to z are negligible, we deduce that 4dss is equal to the sum of information read on C1 and C2.

 The method for measuring the rotation ss of the solid S1 around the axis Oy thus consists in measuring, in a device according to the invention, the following deviations Oz on the two detectors C1 and C2 each associated with a beam L1 C1 or L2C2 which is reflected parallel to the incident ray L1 or L2 from which it is derived, and to deduce the angle ss of the sum of the deviations measured on these two detectors C1 and C2 divided by the quadruple of the distance d between the target 1 of the detectors.

 To measure P, one can also perform the sum of the information read on cells C'1 and C'2. This sum is equal to d (4ss + # '+') + (u + v + a). Assuming, as before, that the values # ', ft, u, v and a are negligible, we deduce that 4 d is equal to the sum of the information read on C'1 and C'2.

The method for measuring the rotation ss of the solid S1 around the axis Oy may therefore also consist in measuring the deviations along Oz on the detectors C'1 and C'2 each associated with a beam LC 'or LC' re
21 bent in a direction symmetrical to that of the incident beam L or L which it is derived, p @ r relative to the target 1, and to deduce the angle ss of the sum of the deviations measured on these two detectors C'1 and C'2 divided by the quadruple of the distance d separating the target from the cells.

 Referring now to the second table, it can be seen that the sum of the information read on the four cells is equal to 4 dz + gamma + 2T + 2T3 + 2b.

 If T, T3 and b are small, we can deduce g, that is to say the rotation angle of the solid S1 around the Oz axis.

 The method of measuring the rotation &gamma; the solid S1 around the axis Oz is therefore to use a device according to the invention and to measure the deviations in the xOy plane on all the detectors and to deduce the angle &gamma; the sum of these deviations divided by the quadruple of the distance d separating the target from the detectors.

 The calculation of the angles 9, (3 and g can be done either manually or by a computer placed at the exit of the four cells.

 The invention that has just been described therefore makes it possible to accurately measure the evolution of an SX solid over time. It has the big advantage that the part of the device that must be placed on the solid S1, that is to say for example on the radar or on the arm of a measuring machine which we want to study the deformations during time, is very compact, the main part of the device, ie the laser transmitter and the detectors being located on the fixed marble So.

 Of course, the invention is not limited to the embodiment which has just been described by way of example, but it also covers the embodiments which differ only in details, variants of execution or the use of equivalent means.

 In particular, the described device could be simplified by using only an incident beam, L1 for example, and thus limiting the number of detectors to two, C1 and C12. Such a device would have the advantage of being simpler and more compact but its accuracy would be divided by 2.

 Referring to the same tables as above, we see that we obtain, by an identical reasoning 1) ol d + a = information read on C1 - information read on C'2.

 By neglecting always a, we see that we get &alpha; by the same method as above but dividing by a factor d and no longer by a factor 2d. To generalize, we can say that we divide by a factor nd, n being the number of beams falling on the target.

2) 2 ss dd + u = information read on C'2.

 By neglecting always g and u, it is seen that one obtains by a method identical to one of those described in the preferred embodiment but dividing by a factor 2d instead of 4d. To generalize, we say that we divide by a factor nd.

 Note that the first method described in the preferred embodiment for measuring ss is not suitable in the case where only an incident beam is used.

3) 2 &gamma; d + (T + R1 - T2 + T3 + b) = information read on C1 + information read on C'2.

 By neglecting the same terms as above, we see that we obtain X by the same method as above but by dividing by a factor 2d and not 4d. To generalize, we say that we divide by nd.

Claims (8)

RESUME ICAT IONS  1.- Device for measuring the variations of the angular position of a solid S1 about three orthogonal axes Ox, Oy, Oz bonded to a reference solid SO, characterized in that it comprises - integral with the solid S1, a target 1 of axis Ox capable of sharing any incident beam (L1 or L in two reflected beams (L1 C1, L1 C'2 or L2 C2, L2 C'1) of which one (L1 C1 or L2 C2) / is parallel to the incide beam @ (L1 or L2) and the other, (L1 C'2 or L2 C '), symmetrical to the first, (L1 C1 or L2 with respect to the axis of the target 1, - integral with the solid SO, a laser beam emitter 4 from which at least one beam L1 or L2 is drawn which is parallel to the xOy plane and falls on the target j and measurement detectors (ç1, C'2 or C2, C'1) deviations at each inc both reflected beams (L1 C1, L1 C'2 or L2 C2, L2 C ', firstly in a direction parallel to the Oz axis, and secondly in a direction parallel to the xOy plane.  2. Measuring device according to claim 1, characterized in that the target 1 consists of a plane mirror 2 and a semi-reflecting plate 3 perpendicular to the mirror 2.  3.- Device according to one of claims 1 or 2, characterized in that the detectors (C1, C'2, C2, C11) are constituted by photoelectric cells, servocontrolled to remain centered on the beams (L1 C1 , L1 C'2, L2 C2, L2 C'1), the measurements being made in a differential manner with respect to an arbitrary zero.  4. Measuring device according to one of the preceding claims, characterized in that the laser beam emitter 4 is derived from two beams L1 and L2 falling symmetrically on the target 1 but in two parallel plane of incidence between them.  5. A method for measuring the rotation of a solid S1 around the Ox axis of an Oxyz reference linked to a reference solid SO, characterized in that a device according to one of the preceding claims, that the deviations along Oz on all the detectors (1 C'1 and / or C2, C'1) are measured and the angles & alpha are deduced; the difference between the sum of the deviations measured on the detectors (C1 and / or C'1) placed in the same half-space A relative to the target 1 and the sum of the deviations measured on the detectors (C2 and / or C 2) placed in the other half space B, this difference being divided by a factor nd, where n is the number of beams falling on the target 1 and the distance separating the cell 1 from the detectors.  6.- Method for measuring the rotation 2 of a solid S1 around  of the Oy axis of an Oxyz reference linked to a solid fé @ erence Sg, characterized in that one uses a device according to one of the preceding claims, that one measures the deviations following Oz on the detectors (C'1 and / or C'2) each associated with a reflected beam (L2 C'1 and / or L1 C'2) in a direction symmetrical to that of the incident beam (L2, L1) of which  it comes from the target 1, and we deduce the Angless of the  sum of the deviations measured on these two detectors (c'1, C'2), this sum being divided by a factor 2 n. d, where n is the number of beams  falling on target 1 and the distance separating the target from the detectors.  7.- Method for measuring the rotation ss of a solid S1 around the axis Oy of an Oxyz reference linked to a solid of reference SO, characterized  in that a device according to claim 4 is used, that the deviations along Oz are measured on the two detectors (C1, C2) each associated with a beam (L1 C1, L2 C2) reflected parallel to the radius  incident (L1, L2) from which it is derived and which is deduced 11 angle (3 of the sum of the deviations measured on these two detectors (C1, C2) divided by the quadruple of the distance d separating the target 1 from the detectors.  8.- Method for measuring the rotation &gamma; of a solid S1 around  the Oz axis of an Oxyz reference linked to a reference solid S0, characterized in that a device according to one of the preceding claims is used, that the deviations in the xOy plane are measured on all the detectors (C1> C'2 and / or C2, C'1) and deduce the angle T from the sum of these deviations divided by a factor 2 nd, where n is the number of beams falling on the target 1 and the distance separating the target from the detectors.