DEVICE FOR VERIFYING THE POSITION OF MIRRORS IN AN OPTICAL ENCODER

Abstract

The invention relates to a device for verifying the position of the mirrors (13) of an optical encoder (7), characterized in that it comprises at least one receiving surface of the optical encoder (7), a visible light source (11) positioned opposite said receiving surface and emitting a light beam (12) of a width adapted to simultaneously illuminate all the mirrors (13) of the optical encoder (7), a reflecting surface (9) for the light (120) reflected by the mirrors (13) of the optical encoder (7) when they are illuminated by the light beam (12), the reflecting surface (9) being placed parallel to the receiving surface of the optical encoder (7) and behind the light source (11), and a reading target (10). Figure to be published with the abstract: Fig. 3

Description

Description Title of the invention: DEVICE FOR VERIFYING THE POSITION OF THE MIRRORS OF AN OPTICAL ENCODER

[0001] | The invention relates to a device for checking the position of the mirrors of an optical encoder. An optical encoder, in particular a so-called high-re- solution, is a device for determining the angular position of an object in movement relative to another. For this, according to a type of optical encoder described in EP-B-964 226, an optical beam is emitted towards reflecting means ensuring the deflection of the light beam towards means of reception of the beam. A rotating disk whose angular position is to be determined being placed between the means of emission and reception of the light beam and the reflecting means of the light beam. The disc consists of tracks defined by zones opaque and translucent areas, characteristic of each disc. It includes also diffraction means formed by a reticle. Apertures form the reflective means for diffracting the light beam between the emission means and receiving. These openings comprise at least two surfaces arranged angularly clearly in relation to the plane in which the means of emission and reception of the light beam. The light beam passes successively over the two surfaces between emission and reception, the optical path of the beam passing through also at least once the rotating disk and at least once the reticle ensuring diffraction. It should be noted that the light beam is emitted in the range waves corresponding to Infrared, therefore not directly visible to the human eye.

[0002] The reflective surfaces of the encoder are arranged angularly, for example at 45° from the vertical. If such an encoder allows, in a reduced footprint, to perform a measurement of the angular position of a rotating object, it is essential to ensure optimal reflection of the light beam between surfaces. In other words terms, there must not be a change in the coefficient of reflection between the surfaces, for the wavelength concerned, knowing that the co- reflection efficiency must be as high as possible to avoid any light loss during the path of the optical beam. However, here, the reflective surfaces are obtained, according to a preferred embodiment, by machining openings of given shapes in a block of material and polishing the surfaces, the latter then being covered each by a mirror. If machining techniques allow to obtain surfaces identical, regular and presenting few or no defects likely to affect measurement, it is not the same with mirrors placed on inclined surfaces. In fact, these mirrors being hot glued to the machined surface, there may be a defect in position of the mirror, excess glue causing a mirror flatness defect, a mirror plating defect on the surface, burrs between the mirror and the surface or other defects that affect the measurement. It turns out that such defects are not only not reproducible and identical between encoders but are only detectable when using the encoder, i.e. when the latter is either calibrated or already delivered to the customer. In the case of a position defect, heating is necessary to liquefy the glue and reposition the mirror. There is therefore a need for a reliable solution to quickly detect any fault in the position of the mirrors in order to be able to remedy them as early as possible and in any case before the encoder is delivered to the customer. The invention aims to meet these needs by offering a quick, reliable and low-cost solution for verifying the position of mirrors. To this end, the invention relates to a device for verifying the position of the mirrors of an optical encoder, characterized in that it comprises at least one receiving surface of an optical encoder, a visible light source positioned opposite said receiving surface and emitting a light beam of a width suitable for simultaneously illuminating all the mirrors of the optical encoder, a surface for reflecting the light returned by the mirrors of the optical encoder when they are illuminated by the light beam, the reflection surface being placed parallel to the receiving surface of the optical encoder and behind the light source, and a reading target. Thus, thanks to the invention, we have a solution which makes it possible to visualize and follow the path of the visible light beam returned by the optical encoder and to verify, using a reading target, that the position of the beam reflected by the encoder mirrors is correct, and therefore to verify that the position of the mirrors is correct. According to advantageous but not mandatory aspects of the invention, such a device may comprise one or more of the following characteristics: The light source is a laser emitting a beam of visible light. The light source is inclined relative to the normal to the principal plane of the receiving surface so that the light beam returned by the mirrors of the optical encoder when illuminated by the beam arrives on the reflecting surface and not on the light source. The tilt angle of the light source is between 0.1° and 30° relative to the normal to the principal plane of the receiving surface of the optical encoder. The tilt angle of the light source is between 0.1° and 4° relative to the normal to the principal plane of the receiving surface of the optical encoder. The reading target is placed coplanar with the receiving surface of the optical encoder. The positions of the reading target and the reflection surface are reversed, the reflection surface being coplanar with the receiving surface of the optical encoder. The invention will be better understood and other advantages thereof will appear more clearly on reading the description which follows, given solely by way of non-limiting example and made with reference to the appended drawings in which: [Fig.1] is a perspective view of a device for verifying the position of mirrors of an optical encoder according to an embodiment of the invention, the light beam emitted by the light source being shown diagrammatically, [Fig.2] is a partial view, in perspective and on another scale, of an encoder in place on the receiving surface and of the target, the light beams being schematically illustrated, [Fig.3] is a simplified diagram illustrating the path of the light beam between the different elements of the device, [Fig.4] is a simplified side view, on a larger scale, of an optical encoder and [Fig.5] is a simplified diagram illustrating a device for verifying the position of the mirrors of an optical encoder known from the state of the art. [Fig. 1] is an illustration of a device 1 according to one embodiment of the invention. The device 1 comprises a frame 2 made of a rigid, inert, stable and easily machinable material, for example metal. The frame 2 comprises a generally H-shaped lower part defining a foot 3 for the frame 2. From the crossbar 4 of the H constituting the foot 3, a frame 5 extends perpendicular to the main plane of the foot 3 and above the latter when looking at [Fig. 1]. Here, the frame 5 is rectangular, alternatively it can be square. Thus, when the frame 2 is in place on a stable and flat structure, for example a work surface such as a marble, a table or a laboratory bench, the foot 3 rests on the work surface and the vertical frame 5 extends above the latter. In the lower part of the chassis 2, at the front of the crossbar 4 of the foot 3 looking at [Fig. 1], therefore forward relative to the frame 5, there is a receiving surface 6 for at least one optical encoder 7. This receiving surface 6 is here rectangular, alternatively it can be square or circular. In all cases, it has dimensions adapted to the device 1 and to the measurements to be carried out. In particular, the dimensions of the receiving surface 6 allow it to receive at least one optical encoder 7 in the middle position. This receiving surface 6 is strictly flat and non-deformable. It is, for example, made of marble. In the upper part, on one of the sides 8 of the frame 5 constituting an upper terminal end of the chassis 2, a reflection surface 9 is positioned. The reflection surface 9 consists of a plane mirror whose dimensions are close to those of the receiving surface 6 of the encoder 7. Advantageously, the two surfaces, receiving 6 and reflecting 9, have identical dimensions and shapes. Alternatively, they do not have the same shape but in all cases the area of ​​the reflecting surface 9 is substantially equal to the area of ​​the receiving surface 6. The reflecting surface or mirror 9 is fixed on the chassis 2 and positioned parallel to the receiving surface 6 of the optical encoder 7. The distance between the two surfaces 6 and 9 corresponds to the height of the frame 5. Here, this distance is fixed, alternatively the vertical uprights of the frame 5 are telescopic, which makes it possible to adjust the distance between the surfaces. Alternatively, at least one of the two surfaces, receiving 6 and reflecting 9, is formed of several elements, identical or not, coplanar and individually adjustable. A reading target 10, also called an abacus, is advantageously arranged on the receiving surface 6 of the optical encoder 7, slightly behind it as shown in Figures 1 and 2. Alternatively, as can be seen in [Fig. 3], the target 10 is offset relative to the receiving surface 6 of the optical encoder 7. In all cases, the target 10 is arranged in a location such that when a light beam is returned by the mirror 9, it illuminates the target 10 or a part of it. Here the target 10 comprises a rectangular grid defined for the type of optical encoder 7 to be checked. Alternatively, the target is adapted to be usable with several types of optical encoders. In another embodiment, the target is formed by a removable grid element placed on a part of the receiving surface 6, which makes it possible to easily change the grid, therefore the target 10, depending on the optical encoder to be checked. A visible light source 11 emitting a beam in visible light, for example between 400 nm and 700 nm, is positioned above the receiving surface 6 of the optical encoder 7. This light source 11 is fixed to the chassis 2 in the upper part of the frame 5, for example on the bar 8 like the reflection surface 9. In all cases, the reflection surface 9 is located behind, and here above, the light source 11. The light source 11 is chosen to emit a focused, non-conical and narrow light beam 12 in the form of a visible band. Advantageously, the light source 11 is a laser. The distance between the light source 11 and the receiving surface 6 is chosen so that the two mirrors 13 of the optical encoder 7 are simultaneously and identically illuminated by the beam 12. In this case, the width of the beam 12 is such that it extends beyond the optical encoder 7 on either side, as shown in Figures 1 and 2.It is understood that it is possible to easily modify the length of the light beam 12 by modifying the distance between the light source 11 and the receiving surface 6. For this, in addition to an adjustable frame 5, it is possible to have a fixing member 14 of the laser 11 on the bar 8 which is also adjustable. The light source !1 is arranged so that the main optical axis A12 of the light beam 12 is not oriented perpendicular to the receiving surfaces 6 and reflection 9, so that it is not coincident or parallel with the normal N to the main plane P of the receiving surface 6 but slightly inclined. This inclination is illustrated in [Fig.1] by the angle λ between the optical axis A12 of the laser and the normal N, it being understood that the normal to the reflection surface 9 is coincident, or at least parallel, with the normal N to the receiving surface 6. The angle λ is between 0.1° and 30° and preferably between 0.1° and 4°. The angle λ is preferably adjustable. For this, the support 14 comprises an articulated part 15, known per se. The operation of the device 1 is now described with reference to Figures 2 to 4. First of all, the optical encoder 7 is placed on the receiving surface 6, at a defined location corresponding substantially to a median position on the surface 6. Such an encoder 7 is schematically illustrated in [Fig.4]. It comprises a flat base 70 intended to rest on the surface 6. The mirrors 13 face each other and are each inclined at 45° relative to the vertical, illustrated by the edges 71, 72 of the encoder 7. When the laser beam 12 illuminates the optical encoder 7, as illustrated in [Fig. 3], the two mirrors 13 are illuminated simultaneously due to the width of the beam 12. Thus the beam 12, which is not a point, is not returned orthogonally from one mirror 13 to the other mirror 13 but in the direction of the reflection surface 9, this due to the inclination λ of the laser 11 relative to the normal.The light 120 reflected by the mirrors 13 arrives directly, without obstacle, on the reflection surface 9, that is to say the mirror placed above and parallel to the reception surface 6, without the reflected light being partially absorbed by the laser 11 since the return is carried out behind the laser 11. The mirror 9 will thus return a reflected beam 121 angularly in the direction of the target 10 which is placed substantially at the same level as the reception surface 6 of the optical encoder 7. The reflected beam 121 is materialized on the target 10 by two light points 150 materialized in [Fig. 2]. The points 150 are then visible in an area of ​​the target 10 which has been previously positioned and calibrated, for example by a grid as a function of the optical encoder 7, of the optical distances between the surfaces 6 and 9.It is possible to define zones, for example circles or rectangles in which the points 150 must be located and which correspond to an acceptable position of the mirrors 13 of the optical encoder 7 when these are well positioned, both with respect to the inclined planes and their respective positions. Such a solution therefore makes it possible to easily visualize mechanically and optically for each encoder 7 the positions of the mirrors 13. Not only is each mirror 13 thus well positioned on its inclined plane but it is also ensured that the mirrors 13 are opposite each other. Indeed, in another known solution illustrated in [Fig.5], if we illuminate a mirror 13 with a point beam of visible light 16, it will return the beam light on the other mirror 13 which will return it to a target 17. This solution effectively makes it possible to simply check the position of each of the mirrors 13 but the distance of the mirrors being variable depending on the size of the encoder 7 and the optical path this solution makes it possible to check that each mirror 13 is correctly positioned on its plane inclined at 45° but it is not possible to check that the mirrors 13 are correctly opposite each other since they are tested independently of each other. In another embodiment of the invention not illustrated, the target 10 is arranged not at the same level as the receiving surface 6 of the encoder 7 but in the upper part in place of the mirror 9. The positioning of the encoder 7 can be mechanically and / or visually identified on the receiving surface 6. Similarly, it is possible to have several test charts 10 that are changed depending on the encoder to be tested. Alternatively, several charts are available that are positioned in a removable manner on the same chart depending on the encoders. Advantageously, spirit levels make it possible to check the levels and flatness of the receiving surface 6 of the encoder 7, of the reflection surface 9 and to precisely adjust the angle of inclination λ of the laser light source 11. Alternatively, other light sources having other wavelengths can be used provided that they are in visible light and that the emitted beams are sufficiently wide. Alternatively, the receiving surfaces 6 of the encoders 7 and mirrors 9 can be arranged on either side of the vertical frame with two light sources 11, which makes it possible to carry out two measurements on two different encoders 7 simultaneously. Such a device is intended to equip a control laboratory, but it is easy to see that it can be mobile and moved as required.

Claims

Claims

1. Device (1) for checking the position of the mirrors (13) of an encoder optical (7), characterized in that it comprises at least one surface of reception (6) of the optical encoder (7), a visible light source (11) positioned opposite (8) said receiving surface (6) and emitting a light beam (12) of a width suitable for simultaneously illuminating simultaneously all the mirrors (13) of the optical encoder (7), a surface of reflection (9) of the light (120) returned by the mirrors (13) of the encoder optics (7) when illuminated by the light beam (12), the reflection surface (9) being placed parallel to the surface of reception (6) of the optical encoder (7) and behind the light source (11), and a reading target (10).

2. Device according to claim 1, characterized in that the source light source (11) is a laser emitting a beam (12) of visible light.

3. Device according to claim 1, characterized in that the source light (11) is inclined (A) with respect to the normal (N) to the plane main (P) of the receiving surface (6) so that the beam light (120) returned by the mirrors (13) of the optical encoder (7) when they are illuminated by the beam (12) arrives on the surface of reflection (9) and not on the light source (11).

4. Device according to claim 3, characterized in that the angle (A) tilt of the light source (11) is between 0.1° and 30° relative to the normal (N) to the principal plane (P) of the surface of reception (6) of the optical encoder (7).

5. Device according to claim 4, characterized in that the angle (A) tilt of the light source (11) is between 0.1° and 4° relative to the normal (N) to the principal plane (P) of the surface of reception (6) of the optical encoder (7).

6. Device according to claim 1, characterized in that the target of reading (10) is placed coplanar with the receiving surface (6) of the optical encoder (7).

7. Device according to claim 1, characterized in that the positions of the reading target (10) and the reflection surface (9) are reversed, the reflection surface (9) being coplanar with the receiving surface (6) of the optical encoder (7).