Lens

Abstract

The object of the present invention is a lens, in particular for artificial vision, comprising, along an optical axis (X) : - a front optical unit with positive optical power; - an intermediate focal plane whereupon optical rays from the front optical unit are focused; - an intermediate optical unit with positive optical power, arranged behind the intermediate focal plane; - a rear optical unit with positive optical power that contains the stop aperture of the lens and receives optical rays from the intermediate optical unit. The entrance pupil of the lens is arranged in the front optical unit.

Description

LENSDESCRIPTION

[0001] The present invention relates to a lens, in particular for a visible and near infrared artificial vision device.

[0002] Lenses are known for inspection and measurement applications that are capable of ensuring elevated optical performance over the entire functional range.

[0003] In such applications there is a strong need to be able to also inspect, rapidly and precisely, the inner walls of a hollow object, and in particular the inner surfaces of a bottom wall and the sidewalls that delimit the cavity of the object.

[0004] Such applications carry a further degree of criticality when the hollow object has an end constriction, i.e., wherein the diameter thereof is smaller compared to the inner diameter defined by the sidewall, or sidewalls, of the object.

[0005] A fixed focal length lens is normally used for these applications with an entrance pupil that is as far forward as possible - but nonetheless within the lens - placing the object to be inspected as close as possible, nearly in contact therefore with the opening of the constriction. Fixed focal lenses are however optimized for elevated working distances on planar fields of viewand have certain mechanical dimensions that impede the possibility of seeing through a constriction therefore narrowing the field of view.

[0006] Furthermore, in having to position the fixed focal length lens extremely close to the constriction, there is the risk of the lens colliding with the inspected object, and finally there is no way to add any illumination between the lens and the inspected object.

[0007] In the case wherein there is no constriction it is nonetheless required to utilize a fixed focal length lens with an extremely elevated F-number (closed iris) in order to contemporaneously have the bottom and the wall in focus. This however results in a reduction in light and therefore in resolution.

[0008] The object of the present invention is providing a lens that, in a rapid and precise manner, is capable of satisfying the aforementioned inspection requirements including inspecting the inner walls of a hollow object, in particular in the presence of an end constriction, whilst at the same time avoiding the prior art limitations and inconveniences complained of above.

[0009] Such object is achieved with a lens according to claim 1, with an artificial vision device according to claim 9 and with an inspection method according to claim

[0010] The dependent claims refer to preferred or advantageous embodiments of the lens according to the invention.

[0011] Further features and the advantages of the lens according to the invention shall be made readily apparent from the following description of preferred exemplary embodiments thereof, provided purely by way of nonlimiting example, with reference to the accompanying figures, wherein:- Figure 1 shows a optical diagram of a lens according to the invention, in a first embodiment and engaged in inspecting the inner walls of a hollow cylindrical object;- Figure 2 shows the optical diagram of the lens of Figure 1 but engaged in inspecting a flat object;- Figure 3 shows the optical diagram of the lens of Figure 1 but engaged in inspecting a hollow object with a truncated cone shape;- Figure 4 shows the optical diagram of the lens of Figure 1 but engaged in inspecting a hollow object with an irregular shape;- Figure 5 shows an optical diagram of a lens according to the invention, in a second embodiment;- Figure 6 shows the optical diagram of a catadioptric lens according to the invention, in a third embodiment;Figure 7 shows an artificial vision device that employs a lens according to the optical diagram of Figure 1, engaged in inspecting the inner surfaces of the walls of a bottle;- Figure 7a shows the image obtained from the inspection represented in Figure 7;- Figure 8 shows an artificial vision device that employs a lens according to the optical diagram of Figure 1, engaged in inspecting the inner surfaces of the walls of a can;- Figure 8a shows the image obtained from the inspection represented in Figure 8;- Figure 9 shows an artificial vision device that employs a lens according to the optical diagram of Figure 1, engaged in inspecting the inner surfaces of the walls of a screw-cap;- Figure 9a shows the image obtained from the inspection represented in Figure 9.

[0012] In the remainder of the present disclosure those elements that are common to the various embodiments of the invention shall be indicated with the same reference numbers.

[0013] Furthermore, the terms "front" and "rear" shall be used with reference to an observed object that is arranged in front of the object and a sensor that isarranged behind the lens.

[0014] In said drawings a lens according to the present invention is indicated in the entirety thereof with 100.

[0015] The lens 100 extends along an optical axis X which in the optical diagrams of figures 1-6 is represented horizontally, whilst in the exemplary real applications is oriented vertically.

[0016] According to one general embodiment the lens 100 comprises, along the optical axis X, a front optical unit 3, an intermediate focal plane 4, an intermediate optical unit 5 and a rear optical unit 6.

[0017] The front optical unit 3 has positive optical power and may be formed from one or more lenses.

[0018] Optical rays from the front optical unit 3 are focused onto the intermediate focal plane 4.

[0019] The intermediate optical unit 5 also has positive optical power and is arranged behind the intermediate focal plane 4.

[0020] The rear optical unit 6 also has positive optical power and comprises the stop aperture of the lens. The rear optical unit 6 is adapted to receive light rays from the intermediate optical unit 5 and to convey them towards an image plane 7 of a sensor.

[0021] The lens 100 is configured in such a way thatthe entrance pupil 2 is arranged in front of the front optical unit 3.

[0022] The entrance pupil 2 is the image of the stop aperture produced by those lenses in front of such stop aperture.

[0023] In other words, the entrance pupil 2 is within the space between an observed object 1 and the lens 100 itself.

[0024] All of the light rays from an object 1 arranged in front of the entrance pupil 2 therefore pass through a single point that is coincident with the entrance pupil 2 of the lens 100.

[0025] For example, the entrance pupil 2 is located at a distance of between 0 mm and 200 mm from the front lens 3a of the front optical unit 3.

[0026] It should be noted that the presence of the intermediate focal plane 4 is owing to the imaging geometry. In fact, insofar as the physical stop of the system is arranged to the rear, beyond the total focal length of those lenses that are in front of it (hypercentricity condition) any object arranged in front of the entrance pupil of the lens must necessarily produce the image - the intermediate image - before the physical stop of the system present within the optical unit 6.

[0027] It is also important that the intermediate plane 4 falls within an area that is free of lenses, for if light rays were to be focused near or within a lens then the final image would be disturbed / altered due to the imperfections of the lenses themselves which would be visible due to the focusing of the optical rays thereupon.

[0028] In one embodiment the rear optical unit 6 is a fixed focal length lens with a fixed or variable iris (or diaphragm) . The choice of the fixed length of the focal length of the lens determines the dimensions of the image circle produced by the lens, where the term image circle signifies the maximum focused circular image that the lens may produce, independently from the sensor that is then used to collect the image. For example, a sensor is used with a diagonal length that is equal to, or less than, the diameter of the image circle of the lens, in such a way as to not see black areas (vignettes) within the sensor.

[0029] In one embodiment, the rear optical unit 6 is provided with a focusing mechanism.

[0030] In one embodiment the focusing mechanism comprises a manual bezel.

[0031] In one embodiment variant the focusing mechanism comprises an adaptive lens, for example aliquid lens that is integrated into the rear optical unit6.

[0032] In one embodiment the rear optical unit 6 is a varifocal lens with a fixed or variable iris and a variable focal length. The variable focal length makes it possible to modify the dimensions of the image circle produced by the lens.

[0033] Also in this case the variable focal length makes it possible to modify the dimensions of the image circle produced by the lens.

[0034] In one embodiment shown in Figure 5 a beamsplitter 11, 12 is inserted between the front optical unit 3 and the intermediate optical unit 5 that is capable of allowing coaxial illumination to be introduced into the lens suitable for illuminating the object 1 through the front optical unit 3.

[0035] To this end a lateral opening 102 is obtained within the body 100' of the lens 100, in proximity whereto the source of illumination 12 of the beamsplitter 11 is arranged. The source of illumination 12, of the LED type for example, is configured so as to emit a luminous beam that is oriented perpendicularly to the optical axis X. The luminous beam passes through the lateral opening 102 and is reflected by a beamsplitter 11 so as to be directed towards the front optical unit 3, coaxially tothe optical axis X.

[0036] A further object of the present invention is an artificial vision device 200 that comprises, other than the lens 100 described above, a sensor arranged within the image plane 7 that is suitable for receiving optical rays from the rear optical unit 6.

[0037] The artificial vision device 200 may advantageously be used, as will be described below, to inspect the inner surfaces of a hollow object 1.

[0038] In the embodiment wherein the rear optical unit 6 is provided with an adaptive lens, the artificial vision device 200 furthermore comprises a controller - not shown - that is operatively connected to the adaptive lens and configured to control the optical power of such adaptive lens as a function of the desired focusing of the lens.

[0039] The embodiment of the optical diagram shown in Figure 6 is functionally similar to that of Figures 1-5 but is more compact and has an entrance pupil 2 that is closer to the lens.

[0040] A further object of the present invention is an inspection method for contemporaneously inspecting the inner surfaces of a bottom wall la and the sidewalls lb of a hollow object 1.

[0041] The method includes the use of theaforementioned artificial vision device 200 and the arrangement of the hollow object 1 in front of the entrance pupil of the lens 2 with the bottom wall la substantially orthogonal to the optical axis X.

[0042] By adjusting the focusing of the lens 100 it is possible to contemporaneously inspect such inner surfaces of the hollow object 1.

[0043] In particular, it is possible to focus on the inner surfaces of a hollow object 1, also when the latter has an end obstruction (for example the neck 300' of a bottle 300, as in Figure 7, or the upper hole of a can), insofar as such obstruction may have a diameter that is equal to or greater than the diameter of the entrance pupil 2. The hollow object 1 is arranged so that the obstruction is located in front of, and in proximity to, the pupil entrance 2.

[0044] The path of the optical rays that is obtained with the lens 100 according to the invention therefore makes it possible to see the object 1, also through a constriction arranged in proximity to the entrance pupil 2.

[0045] Thus created is a first image of the object in proximity to the intermediate plane 4 and subsequently upon the image plane 7.

[0046] For example, with reference to the attachedfigures, the lens 100 may collect optical rays from:- a hollow object 1 of a cylindrical shape (Figures 1 and 6), with an angle of view a;- a hollow object 9 of a truncated cone shape (Figure 3), with an angle of view a;- a flat object 8 (Figure 2), with an angle of view a;- a hollow object 10 of an irregular shape (Figure 4), with an angle of view a;- an object with a donut shape, hemisphere shape or conical shape etc., with an angle of view a.

[0047] Figure 7 shows the vision device 200 used to inspect the inner surfaces of a bottle 300 through the constriction 302 created by the neck of the bottle.

[0048] Figure 7a shows the obtained image. Notice centrally the circle 304 corresponding to the bottom of the bottle and the circular crown 306 that corresponds to the inner surface of the sidewall of the bottle 300.

[0049] Figure 8 shows the vision device 200 used to inspect the inner surfaces of a 33 cl can 400.

[0050] Figure 8a shows the obtained image. Notice centrally the circle 402 corresponding to the bottom of the can 400 and the circular crown 404 that corresponds to the inner surface of the cylindrical sidewall of the bottle 400.

[0051] Figure 9 shows the vision device 200 used toinspect the inner surfaces of a screw-cap 500.

[0052] Figure 9a shows the obtained image. Notice centrally the circle 502 corresponding to the bottom of the bottle and the circular crown 504 that corresponds to the inner surface of the sidewall of the cap. In particular it is possible to appreciate the clarity of the markings seen on the surface of the bottom wall of the cap and the thread formed in the sidewall.

[0053] It should be noted that, advantageously, the proposed lens makes it possible to collocate the observable object at a certain working distance from the lens itself, for example so as to be able to possibly insert, between the lens and the object, additional illumination or other elements such as protective glass.

[0054] Furthermore, it is possible to see the sidewall of the objects at a relatively high angle. It is consequently possible to inspect such areas over a wide sensor region with more information regarding the details of the sample, details that would otherwise be undetectable.

[0055] It should be noted that the proposed lens is not limited to creating images of objects located in an object plane, but is designed to also inspect hollow objects by simultaneously focusing on the bottom and walls of such objects.

[0056] Unlike lenses according to the prior art, which have the stop aperture between the front optical group and a rear optical group, the stop aperture of the lens according to the invention is located within a rear optical group.

[0057] In contrast to lenses according to the prior art, which create a distorted image of microscopic objects in order to see the top and the outer side walls, the lens according to the invention is optimised to see macroscopic objects on the inside, thus to see the bottom and the inner side walls.

[0058] The presence of the intermediate optical group 5 makes the proposed lens particularly suitable for hypercentric viewing of hollow objects; without this intermediate optical group, the resulting image would not have a quality comparable to that which can be produced with the lens according to the invention and can that be appreciated from the images of Figures 7, 8 and 9.

[0059] A person skilled in the art may make several changes, adjustments, adaptations, and replacements of elements with others that are functionally equivalent to the embodiments of the lens and artificial vision device according to the invention in order to meet incidental needs without departing from the scope of the following claims. Each of the features described as belonging to apossible embodiment may be obtained independently of the other described embodiments.

Claims

CLAIMS1. Lens, comprising, along an optical axis (X):- a front optical unit with positive optical power;- an intermediate focal plane whereupon optical rays from the front optical unit are focused;- an intermediate optical unit with positive optical power, arranged behind the intermediate focal plane;- a rear optical unit with positive optical power that contains the stop aperture of the lens and that receives optical rays from the intermediate optical unit, wherein the entrance pupil of the lens is arranged in front of the front optical unit.

2. Lens according to claim 1, wherein the rear optical unit is a fixed focal length lens with a fixed or variable iris, and is provided with a focusing mechanism.

3. Lens according to claim 2, wherein the focusing mechanism comprises a manual bezel.

4. Lens according to claim 2, wherein the focusing mechanism comprises an adaptive lens, for example an integrated liquid lens.

5. Lens according to claim 1, wherein the rear optical unit is a varifocal lens with a fixed or variable iris and a variable focal length that makes it possible to modify the dimensions of the image circle produced by the lens.

6. Lens according to any one of the preceding claims, wherein a beamsplitter is inserted between the front optical unit and the intermediate optical unit that is capable of allowing coaxial illumination to be introduced into the lens that is suitable for illuminating the object through the front optical unit.

7. Lens according to claim 6, wherein the beamsplitter is arranged in proximity to the side aperture obtained in the body of the lens and extends perpendicularly to the optical axis of the lens.

8. Lens according to any one of the preceding claims, wherein the entrance pupil is located at a distance of between 0 mm and 200 mm from the rear lens of the front optical unit.

9. Artificial vision device comprising a lens according to any one of the preceding claims and a sensor that forms an image plane that is suitable for receiving optical rays from the rear optical unit.

10. Device according to claims 4 and 9, further comprising a controller that is operatively connected to the adaptive lens of the rear optical unit and configured so as to control the optical power of such adaptive lens as a function of the desired focusing of the lens.

11. Inspection method for contemporaneously inspecting the inner surfaces of a bottom wall and the sidewalls ofa hollow object comprising the steps of:- providing an artificial vision device according to claims 9 or 10;- positioning the hollow object in front of the entrance pupil of the lens, with the bottom wall substantially orthogonal to the optical axis;- adjusting the focusing of the lens so as to contemporaneously focus said inner surfaces of the hollow object.

12. Inspection method according to claim 11, wherein the hollow object has an end obstruction having a diameter equal to, or greater than, the diameter of the entrance pupil, wherein said obstruction is arranged in proximity to the entrance pupil.

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