WO2017056029A1

WO2017056029A1 - Optical device

Info

Publication number: WO2017056029A1
Application number: PCT/IB2016/055823
Authority: WO
Inventors: Paolo Maioli
Original assignee: Vici & C S.P.A.
Priority date: 2015-10-02
Filing date: 2016-09-29
Publication date: 2017-04-06
Also published as: EP3356764A1; ITUB20154085A1

Abstract

Described is an optical device for machines for the optical measurement of workpieces, comprising a central tubular body (2), an optical video camera (5) for detecting images of a workpiece to be measured, a telecentric optical unit (8) comprising a plurality of lenses (6), at least partly housed in the central tubular body (2) and designed to convey the images towards the video camera (2), lighting means configured to generate a light beam (F) directed towards the workpiece to be measured.

Description

DESCRIPTION

OPTICAL DEVICE

Technical field

This invention relates to an optical device.

More specifically, this invention relates to an optical device to be integrated in a machine for optical measurement.

Still more specifically, the present invention relates to an optical device to be integrated in a machine for the optical measurement of workpieces which are mainly planar in extension.

Background art

In the prior art, numerous optical (optoelectronic) measuring machines are known which comprise a workpiece supporting stage made of substantially transparent material and interposed between a light source and an image detector.

These machines typically comprise a fixed mount defining the (vitreous) supporting stage along which the optoelectronic measuring system is movable in the main X-Y directions.

Optical measuring machines are known which are equipped with a transparent measuring stage on which the workpiece to be measured is positioned, a fixed light source located under the measuring stage and facing upwards in order to illuminate the workpiece with a light beam, and a video capturing system equipped with a camera which is partly movable relative to the stage (along two main directions X-Y) in order to capture a plurality of frames which are then combined by means of specific software to produce a complete image of the measuring field and, therefore, of the workpiece.

Whilst the prior art measuring machines are effective they are not free from drawbacks.

More specifically, under some circumstances and with workpieces to be measured of particular shapes, illumination only coming from a position below the workpiece has not proved to be effective for capturing an optimum image for the purposes of measurement. In an attempt to overcome this problem machines have been made which are also equipped with lateral illumination of the workpiece. Even this solution, even though partly an improvement has not proved to be entirely satisfactory, for example in measuring pieces that are not perfectly flat in which, therefore, the inclination of the rays can result in the formation of shade or similar alterations.

Disclosure of the invention

The technical purpose of this invention is to provide an optical measuring machine and method which overcome the above mentioned drawbacks of the prior art.

More specifically, the aim of this invention is to provide an optical measuring device which is able to optimise the lighting of the workpiece to be measured.

These aims are fully achieved by an optical measuring device according to this invention.

The technical features of the invention, with reference to the above aims, can be easily inferred from the appended claims, in particular claim 1 , and preferably any of the claims that depend, either directly or indirectly, on that claim. Brief description of drawings

The advantages of the invention are more apparent from the detailed description which follows, with reference to the accompanying drawings which illustrate a preferred, non-limiting example embodiment of the invention and in which:

- Figure 1 is a schematic side elevation view, with some parts transparent and others in cross section, of a preferred embodiment of the optical measuring device made according to this invention;

- Figure 2 is a schematic perspective top view of the device of Figure 1 ,

- Figure 3 is a schematic cross section view through the line Ill-Ill of Figure 1 .

Detailed description of preferred embodiments of the invention

With reference to the accompanying drawings, the numeral 1 denotes in its entirety an optical device according to this invention.

The optical device 1 is designed to be installed in a machine, not illustrated, for the optical measurement of workpieces.

These measuring machines are of the optoelectronic type, configured to measure mostly workpieces which are mainly planar or which, at least, do not vary significantly in shape along their thickness.

These machines, not illustrated, also comprise a supporting frame, a supporting surface for the workpiece to be measured, extending preferably horizontal and made of substantially transparent material, a light source located below the supporting surface to illuminate the bottom of the workpiece and an optical device designed to allow the capturing of an optical image of the workpiece.

The machine also comprises, also not illustrated, a computerised unit for processing the image captured, as well as movement means configured to vary the relative position between the optical device and the supporting surface.

As illustrated in Figures 1 and 2, the optical device 1 comprises a tubular central body 2 having a partly cylindrical extension, with a respective central axis A1 .

In a relative upper portion 2a, the central tubular body 2, hereinafter also referred to merely as the central body 2, has an inclined wall 3, in a plane incident at 45° with the central axis A1 .

At the above-mentioned upper portion 2a, in the cylindrical part facing the inclined wall 3, a second cylindrical body 4 engages on the central body 2, having a respective central axis A2, at right angles to the above- mentioned central axis A1 of the central body 2.

At a relative end longitudinally opposite the one connected to the central body 2, the second cylindrical body 4 is connected to an optical video camera, schematically illustrated in Figures 1 and 2 with a cube 5.

The video camera 5 is designed for detecting images of a workpiece to be measured.

Inside the central body 2 and the second cylindrical body 4, the device 1 comprises a plurality of optical lenses 6, illustrated only schematically in the accompanying drawings, and a mirror 7.

The mirror 7, shown in transparency also in Figure 2, is located on the above-mentioned inclined wall 3 and is configured to direct towards the second cylindrical body 4 and the video camera 5, diverting them by 45°, the images coming from the central body 2.

The above-mentioned images, in the context of use of the optical device 1 inside a machine for the optical measurement of workpieces, are advantageously the images of the workpieces being measured.

The lenses 6, together with the mirror 7, define in their entirety, for the device 1 , a telecentric optical unit 8 designed to convey towards the video camera 5 the images of the workpiece being measured.

The term telecentric optical unit is used to mean an optical system which is able to convey images towards the video camera in a way which is substantially perpendicular to a relative sensor for capturing the images. The axes A1 , A2 define, for the respective sections of the optical unit 8, the optical axis.

In this case, in which the unit 8 comprises a succession of lenses 6, the optical axis passes through their centre of curvature and coincides with the rotational axis of symmetry.

The optical device 1 comprises a plurality of light sources 9 positioned inside the tubular central body 2 and interposed between lenses 6 of the optical unit 8. More specifically, in the preferred embodiment illustrated in Figures 1 and 2, the device 1 comprises four supporting elements 10, each carrying a respective light source 9, positioned alongside a cylindrical surface C inside the central body 2.

The supporting elements 10 have an outer wall cylindrical in shape in such a way as to be mounted closely adhering to the above-mentioned inner cylindrical surface.

The lighting sources 9 and, consequently, also the supporting elements 10 are positioned angularly equally distributed relative to the central axis A1 which, for the section of optical unit housed in the central body 2, defines a respective optical axis.

In the preferred embodiment illustrated in the accompanying drawings, there are four light sources 9 and they are therefore angularly spaced at 90° to each other.

Also thanks to the industrial standards already in use, the images captured by the video camera 5 have a quadrangular shape and, therefore, advantageously, there are four light sources 9 and they are positioned outside the sides of a rectangle inscribed within a circumference which is concentric relative to the central tubular body 2, as shown by way of example in Figure 3.

Advantageously, the above-mentioned lighting sources 9 are of the LED (Light Emitting Diode) type.

The above-mentioned light sources 9 together form, for the optical device 1 , the means for illuminating the workpiece to be measured.

Advantageously, the central tubular body 2 has the above-mentioned inner cylindrical surface C made with a high light absorption for limiting the reflection of the light rays emitted by the light sources 9.

For example, the inner cylindrical surface C is coated with suitable materials to absorb the visible light.

As illustrated in Figures 1 and 2, the light sources 9 are positioned, inside the optical unit 9, in a position such that the light beam F emitted from them strikes one or more optical lenses 6 of the unit 9.

In that way, the one or more lenses may be advantageously made for diffusing the light beam F emitted by the light sources 9 and achieve a substantially uniform illumination of the workpiece to be measured, not illustrated, but positioned below the light beam F with reference to Figures 1 and 2.

More specifically, the one or more lenses 6 struck by the light beam F are also advantageously configured to rectify the rays of light which make up the beam F with, at the outlet from the optical unit 8, a limited inclination relative to the optical axis A1 .

Experimental tests have shown that optimum results are obtained with an angle of the rays of between 0 and 7 degrees relative to the optical axis A1 .

Advantageously, also for this purpose, the supporting elements 10 have, at the light sources 9, an "eyelid", not visible in the accompanying drawings, designed to screen the rays of light directed towards the centre of the central body 2 that is, towards the optical axis A1 .

In use, the optical device 1 according to this invention allows optimum lighting of the workpieces, not illustrated, to be measured.

Thanks in effect to the positioning of the light sources 9 inside the optical unit 8, the light beam F produced by them which strikes the workpiece to be measured illuminates the latter at the top and eliminates the distortions in the image captured by the camera 5 caused by lateral lighting sources. Moreover, thanks to the straightening of the light rays of the light beam F obtained with the lenses 6 shaped for the purpose, the beam F which strikes the workpiece to be measured is substantially parallel to the optical axis A1 , thereby contributing to the capturing of an image which corresponds particularly to the real shape of the workpiece.

Owing to limited angle of the rays which make up the light beam F which strikes the workpiece to be measured, one may speak in this case of light collimated relative to the optical axis, that is, the optimum lighting condition for capturing the image by the video camera.

The invention achieves the preset aims and brings major advantages.

Claims

1 . An optical device for machines for the optical measurement of workpieces, comprising:

- a central tubular body (2),

- an optical video camera (5) for detecting images of a workpiece to be measured,

- a telecentric optical unit (8) comprising a plurality of lenses (6), at least partly housed in the central tubular body (2) and designed to convey the images towards the video camera (5),

- lighting means configured to generate a beam (F) of light directed towards the workpiece to be measured, characterised in that the lighting means comprise at least one light source (9) housed in the central tubular body (2) and interposed between successive lenses (6) of the optical unit (8).

2. The device according to claim 1 , characterised in that the lighting means comprise a plurality of light sources (9) positioned angularly equally distributed relative to an optical axis (A1 ) of the optical unit (8).

3. The device according to claim 2, wherein the images acquired by the video camera (5) have a quadrangular shape, characterised in that the light sources (9) are positioned close to an inner wall (C) of the central tubular body (2).

4. The device according to claim 3, wherein the central tubular body (2) extends cylindrically, characterised in that there are four light sources (9) and they are positioned outside the sides of a rectangle inscribed within a circumference which is concentric relative to the central tubular body (2).

5. The device according to any of the claims from 2 to 4, characterised in that the light sources (9) are of the LED type.

6. The device according to any one of the preceding claims, characterised in that the tubular central body (2) has an inner surface (C) with a high absorption of light to limit the reflection of the light rays emitted by the lighting means.

7. The device according to any one of the preceding claims, characterised in that the at least one lens (6) of the optical unit (8) struck by the light beam (F) emitted by the at least one source (9) is configured to rectify the rays of light of the light beam (F) with an inclination between 0 and 7 degrees relative to the optical axis (A1 ) of the lenses (6).

8. The device according to any one of the preceding claims, characterised in that the light beam (F) emitted by the light sources (9) crosses at least two lenses (6) of the optical unit (8), to increase an effective diffusion of the beam (F) itself.

9. A machine for the optical measurement of mainly planar workpieces, comprising a surface for supporting the workpiece, made of substantially transparent material, a light source located below the supporting surface, characterised in that it comprises, positioned on the side opposite to the supporting surface relative to the light source, an optical device according to any of the claims from 1 to 8.

10. The machine according to claim 9, characterised in that it comprises movement means which are configured to vary the relative position of the optical device and supporting surface.