WO2004099714A1

WO2004099714A1 - Laser alignment device with sets of reflectors

Info

Publication number: WO2004099714A1
Application number: PCT/FR2004/050175
Authority: WO
Inventors: François GAULT; Eric Journot; Vincent Denis
Original assignee: Commissariat A L'energie Atomique
Priority date: 2003-04-30
Filing date: 2004-04-28
Publication date: 2004-11-18
Also published as: FR2854454A1; FR2854454B1

Abstract

A laser alignment device, comprising sets of reflectors, and a method for using said device. According to the invention, at least two rectilinear, aligned and interspaced sets (26,28) of reflectors are used, enabling a laser beam (30) to be centred by comparing the images obtained from the light reflected by said sets.

Description

LASER ALIGNMENT DEVICE WITH CATADIOPT _R ES ASSEMBLIES

5 DESCRIPTION

TECHNICAL AREA

The present invention relates to a laser alignment device.

The invention also relates to a method 10 of using this device.

It applies in particular to the alignment of a laser beam whose size is large and / or whose environment is complex.

15 STATE OF THE PRIOR ART

In order to place elements with great precision, use is often made of the use of a laser 2 (FIG. 1). To align the beam 4 emitted by this laser, it is necessary to be able to quantify the position of this beam with respect to a target 6.

Generally, the laser 2 and the target 6 are respectively mounted on two sets A and B and a sensor 8 is provided for detecting the laser light

25 from the target which is illuminated by the laser beam 4.

Several techniques are known for aligning a collimated laser beam in the near field. They are mentioned below. In the technique using a laser tracker, the sets A and B

(Figure 2) are equipped with targets 10 and 12 and the laser source is external to these assemblies. This source is associated with the laser light sensor and constitutes with the latter the assembly 14.

This technique leads to an important accuracy for alignment, because it uses two targets. In addition, these targets are passive. However, the size of the device allowing its implementation is important.

In the so-called “four quadrant” technique (FIG. 3), the laser is mounted on the assembly A and the target is mounted on the assembly B and consists of a sensor 16 which is cut into four segments making it possible to detect the position of the laser beam 4.

This technique leads to a small footprint but it leads to a multiplication of sensors when it is necessary to install several elements.

In the technique known as “of the diffusing target” (FIG. 4), the laser is associated with the laser light sensor and constitutes with the latter a set 18 which is mounted on the set A. The target is mounted on the set B and made up of a diffusing element 20, in frosted glass for example, making it possible to form the image of the trace of the laser beam 4.

This technique leads to a small footprint and uses passive targets but it causes a loss of light flux. In the so-called “cube corner” technique (FIG. 5), the target is mounted on the assembly B and consists of a single cube corner 22 making it possible to form the image of the trace of the laser beam 4.

This technique still leads to a small footprint and still uses passive targets. However, it can only be implemented with a laser beam whose size is at most equal to that of the cube corner.

STATEMENT OF THE INVENTION

The object of the present invention is to remedy the drawbacks of the known laser alignment techniques mentioned above. The subject of the invention is a laser alignment device which uses sets of retro-reflectors.

This device is precise and compact, has a good photometric yield and makes it possible to align large laser beams.

Specifically, the subject of the present invention is a laser alignment device, in particular in the near field, characterized in that it comprises at least two identical straight sets of retro-reflectors, these two straight sets being aligned and spaced one from the other. the other and allowing the centering of an incident laser beam with respect to the two sets of retro-reflectors, by comparison of images obtained from the lights respectively reflected by these sets of retro-reflectors. According to a particular embodiment, the device which is the subject of the invention comprises two identical groups of retro-reflectors, each group comprising a plurality of identical rectilinear sets of retro-reflectors, these sets being offset in translation with respect to each other, the two groups being spaced from each other and symmetrical to each other with respect to a plane, constituting a plane of symmetry. According to a preferred embodiment, the straight sets of each group are placed side by side and offset to form an arrow oriented opposite the plane of symmetry, the number N of sets of each group being at least equal to 2D / dl, where d is the desired alignment accuracy and D is the minimum size of the retro-reflectors.

The size of the reflectors is for example less than 10mm.

The reflectors can be cube corners.

Alternatively, the reflectors may be converging lenses whose optical axes are parallel and which have a common focal plane, this focal plane being made specular or diffuse reflector.

The invention also relates to a method of using the device that is the subject of the invention, in which the two sets of retro-reflectors are illuminated with the laser beam, images are formed from the lights respectively reflected by the sets of retro-reflectors and the we move the beam laser with respect to the sets of retro-reflectors, or vice versa, until the images are symmetrical with each other with respect to the plane with respect to which the sets of retro-reflectors are symmetrical with each other.

According to a particular implementation of this method, in the case where the device comprises the two groups of retro-reflectors, these two groups are illuminated with the laser beam, images are formed from the lights respectively reflected by these two groups and the laser beam is displaced with respect to the two groups, or vice versa, until the images are symmetrical with each other with respect to the plane with respect to which the two groups are symmetrical with one another other.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be better understood on reading the description of exemplary embodiments given below, by way of purely indicative and in no way limiting, with reference to the appended drawings in which: FIGS. 1 to 5 schematically illustrate known techniques of alignment and have already been described,

- Figure 6 is a schematic view of a particular embodiment of the device object of the invention, using two arrays of reflectors, Figures 7 to 9 schematically illustrate the alignment of a laser beam by means of the device of the figure 6, - Figure 10 is a schematic view of another particular embodiment of the device object of the invention, using groups of retro-reflector arrays, - Figure 11 schematically illustrates the alignment of a laser beam by means of the device in Figure 10, and

- Figure 12 schematically illustrates the possibility of using, in the invention, lenses instead of reflectors.

DETAILED PRESENTATION OF PARTICULAR EMBODIMENTS

For a laser beam of large transverse dimensions, the known techniques mentioned above make it difficult to obtain good accuracy, in a small footprint and with an interesting photometric ratio, without multiplying the sensors.

To overcome these drawbacks, two straight sets or bars ("arrays") of cube corners are used, in accordance with the invention.

Each cube corner preferably has a size close to a millimeter, for example 1 mm, and each bar preferably has a length of a few centimeters, for example 5 cm.

Each bar is put in place in order to have the expected precision.

These bars are placed on the edges of the laser beam that we want to align and we center the beam by comparing the portion of cube corners "Lit" by the laser beam, on the different edges of the beam.

In an example of the invention (FIG. 6), a laser is associated with a sensor and constitutes with the latter a transmission-detection assembly 24. This assembly 24 is mounted on an assembly A.

Two bars 26 and 28 of cube corners are aligned, spaced from one another and made rigidly integral with one another by a suitable support 29 which is mounted on an assembly B so that all of the two bars either opposite the transmission-reception assembly 24.

We want to center, or align, the beam 30 emitted by the laser with respect to the two bars, that is to say to make the plane of symmetry P of the set of two bars coincide with the plane of symmetry

Q of the laser beam 30.

This beam emitted by the laser is picked up by a certain number of cube corners of the bars and re-emitted by these cube corners in the opposite direction to the assembly 24. The light 31 thus re-emitted is picked up by the sensor that comprises the set 24.

The latter forms the respective images of the cube corner arrays and these images are compared in appropriate image processing means 32, associated with the assembly 24.

One seeks to obtain two images symmetrical with respect to the plane P. To do this, means of displacement are provided along three orthogonal axes, symbolized by the arrows 34. These means 34 are provided for moving the sensor-laser assembly 24 relative to all of the bars 26 and 28 or vice versa.

The device according to the invention of Figure 6 has a small footprint, the targets used are passive and this device is capable of aligning a laser beam of large dimensions (transverse).

Let us return to the physical principle of the device in Figure 6. The property of the cube corner is to return the light in the direction of the incident beam. This optimizes the photometric balance.

The use of bars of “cube micro-corners” allows to have as many returns as of illuminated cube corners, as shown in Figure 7. It will be noted that if the left part of a cube micro-corner is illuminated, it is its right part which is "reflected" towards the sensor. In Figure 7, we see the strip 26 of cube corners, lit by the beam 30, and the image 36 obtained in return.

By positioning the system of arrays of cube micro-wedges on either side of the laser beam and comparing the images obtained, the laser can be centered on the arrays.

FIG. 8 illustrates the case where the laser beam 30 is misaligned with respect to all of the bars 26 and 28. The planes P and Q do not coincide. In the image 38 obtained in return, the images respective 36 and 40 of the bars 26 and 28 are not symmetrical with respect to the plane P.

On the contrary, FIG. 9 illustrates the case where the beam 30 has been aligned with respect to the bars. The P and Q planes coincide. In the image 38 obtained in return, the respective images of the bars are symmetrical with respect to the plane P.

The relative position of the laser beam relative to the retro-reflector arrays has been adjusted, by means of displacement means 34, until these symmetrical images are obtained.

As can be seen, the precision of the device is linked to the pitch ("pitch") p of the retro-reflectors in the bars. Depending on the opening of the device, which is equal to nsin α, where α is the opening angle of the medium, generally the air, in which the device is immersed, and n the optical index of this medium , there is a minimum size of a cube micro-corner (limitation by diffraction).

For a simple bar, the precision is therefore limited by the physical size of the cube micro-corner. The smaller the size of the cube micro-corner, the greater the precision. Consider below an example of the invention for improving the alignment accuracy.

As we have seen previously, for a strip of cube micro-corners, this precision is limited by the physical size of the cube micro-corners.

If you want to improve accuracy, you have to use several arrays of cube micro-wedges offset between them (instead of the two arrays).

If we want precision d while the minimum size of the cube micro-corners is D, we put N bars side by side, arranged as shown in Figure 10, with:

N> 2xD / d-l.

Note that the example in Figure 10 corresponds to the case where D is equal to 4xd. We see there two identical groups 42 and 44 of cube micro-corners 46. These groups are spaced from each other and symmetrical with respect to the plane P. Only group 42 is completely represented.

Each group, or matrix, comprises several arrays 48 of cube micro-corners. These bars are adjacent but offset from each other. They form an arrow whose tip is turned away from the plane of symmetry P.

We have seen that if a cube micro-corner was partially illuminated, it was the part opposite to the beam that lit up first on the return image. If the cube micro-corner is of minimum size, it will appear completely illuminated as soon as a part is lit. In FIG. 11, only the interaction of the laser beam 30 with one of the two groups of cube micro-corners, namely group 42, has been shown. The corresponding image obtained is also seen.

We see in fact four different relative positions 1a, 2a, 3a and 4a of the laser beam with respect to group 42 and the four images corresponding 1b, 2b, 3b and 4b, obtained from the light reflected by this group.

For each displacement of the beam by a distance d, these images of FIG. 11 are obtained. We see that it is therefore possible to obtain any resolution.

We consider below another example of the invention in which micro-lenses are used instead of cube micro-corners. It is indeed possible to simulate arrays or arrays of cube micro-wedges by arrays or arrays of microlenses associated with a plane diffuser or a plane mirror, placed in the focal plane of these microlenses. This is schematically illustrated by FIG. 12 which is a side view of a matrix 50 of convergent microlenses 52.

The optical axes X of these micro-lenses are parallel. These micro-lenses have a common focal plane 54. This focal plane is made able to reflect the incident laser light in a specular or diffuse manner thanks to a layer 56 of suitable material, which is placed at the level of this focal plane.

To obtain a specular reflection, it is possible to use a polished, flat and reflecting surface of the mirror type and, to obtain a diffuse reflection, a flat and rough surface, for example a frosted glass.

We see the incident laser beam 30 and the light 58 which is reflected at the focal plane, by the reflecting surface thus obtained, ie from specular (mirror) or diffuse (diffuser).

The matrix 50 thus re-forms a laser beam 60 which has the same path as the beam 30 but an opposite direction.

The use of arrays of retro-reflectors (for example arrays of cube micro-corners or arrays of microlenses with reflective focal plane thus leads to a new technique of alignment in the near field which is space-saving, is precise and present. photometric advantages.

This technique allows simple alignment of large laser beams. In addition, it is well suited to harsh environments because it allows the active detection part of a laser beam to be offset.

Claims

1. A laser alignment device, in particular in the near field, characterized in that it comprises at least two identical rectilinear sets of retro-reflectors (26-28, 42-44, 50), these two rectilinear assemblies being aligned and spaced apart. one from the other and allowing the centering of an incident laser beam (30) with respect to the two sets of retro-reflectors, by comparison of images obtained from the lights respectively reflected by these sets of retro-reflectors.

2. Device according to claim 1, comprising two identical groups (42, 44) of retro-reflectors, each group comprising a plurality of identical rectilinear sets (48) of retro-reflectors, these sets being offset in translation relative to one another, the two groups being spaced from each other and symmetrical to each other with respect to - a plane (P), constituting a plane of symmetry.

3. Device according to claim 2, in which the rectilinear assemblies (48) of each group (42, 44) are placed side by side and offset to form an arrow oriented opposite the plane of symmetry (P), the number N of sets of each group being at least equal to 2D / dl, where d is the desired alignment precision and D is the minimum size of the retro-reflectors.

4. Device according to any one of claims 1 to 3, wherein the size of the reflectors is less than 10mm.

5. Device according to any one of claims 1 to 4, wherein the reflectors are cube corners (26-28, 42-44).

6. Device according to any one of claims 1 to 4, in which the reflectors are converging lenses (50) whose optical axes (X) are parallel and which have a common focal plane (54), this focal plane being rendered specular or diffuse reflector.

7. A method of using the device according to claim 1, in which the two sets of retro-reflectors (26, 28) are illuminated with the laser beam (30), images are formed from the lights respectively reflected by the sets of retro-reflectors and the laser beam is displaced with respect to the sets of retro-reflectors, or vice versa, until the images are symmetrical with respect to each other with respect to the plane P with respect to which the sets of retro-reflectors are symmetrical l ' one of the other.

8. A method of using the device according to claim 2, in which the two groups (42, 44) of illuminators are illuminated with the laser beam (30), images (lb, 2b, 3b, 4b) are formed from lights respectively reflected by these two groups and the laser beam is moved relative to the two groups, or vice versa, until the images are symmetrical to each other with respect to the plane (P) with respect to to which the two groups are symmetrical to each other.