Catadioptric lens

Abstract

A catadioptric lens comprises a primary mirror (10), a secondary mirror (20), an adaptive lens (30) arranged to the rear with respect to the primary mirror (10) such as to receive the optical rays reflected by the secondary mirror (20), and at least one rear optical unit (40) that contains the stop aperture and is suitable for conveying the optical rays from the secondary mirror (20) towards an image plane (50) of a sensor. The adaptive lens (30) may be controlled to adjust the focusing of the lens.

Description

CATADIOPTRIC LENSDESCRIPTION

[0001] The present invention relates to a catadioptric lens, in particular for an artificial vision device.

[0002] Lenses are known for inspection and measurement applications that are capable of ensuring high optical performance throughout the operating range.

[0003] In these applications, there is at times a need to inspect the outer walls of a three-dimensional object, viewed from above, using a single camera. With lenses according to the state of the art, in order to inspect different diameters of the outer wall of the object, or objects of different sizes, it is necessary to either significantly close the iris of the lens thereby losing light and resolution, or to provide for the use of a user-operated manual lens focusing system to change the focusing area, thereby increasing the structural complexity of the lens and the working time.

[0004] The object of the present invention is to provide a catadioptric lens capable of inspecting different diameters of the outer wall of an object, while at the same time overcoming the limitations of lenses of the known art.

[0005] This object is achieved with a catadioptric lens according to claim 1 and with an artificial visiondevice according to claim 17.

[0006] The dependent claims refer to preferred or advantageous embodiments of the catadioptric lens according to the invention.

[0007] Further features and the advantages of the catadioptric lens according to the invention shall be made readily apparent from the description provided hereinafter of preferred exemplary embodiments thereof, provided purely by way of non-limiting example, with reference to the accompanying figures, wherein:- Figure 1 is an optical diagram of a catadioptric lens according to the invention, in a first embodiment;- Figure 2 is an optical diagram of a catadioptric lens according to the invention, in a second embodiment;- Figure 3 is an optical diagram of a catadioptric lens according to the invention, in a third embodiment;- Figure 4 is an optical diagram of a catadioptric lens according to the invention, in a fourth embodiment;- Figure 5 is an optical diagram of the catadioptric lens from Figure 1, wherein the observed object is arranged beyond the entrance pupil of the lens;- Figure 6 shows an example of a practical implementation of a catadioptric lens according to the invention;- Figure 7 shows an example of an object to beinspected using the catadioptric lens in Figure 6;- Figure 8 depicts the image of the outer wall of the object in Figure 7 taken by the catadioptric lens in Figure 6, wherein a first point of focus has been set;- Figure 8a is an enlarged view of the detail in the box in Figure 8;- Figure 9 depicts the image of the outer wall of the object in Figure 7 taken by the catadioptric lens in Figure 6, wherein a second point of focus has been set; and- Figure 9a is an enlarged view of the detail in the box in Figure 9.

[0008] In the following description, elements common to the various embodiments of the invention shall be indicated with the same reference numbers.

[0009] In addition, the terms "front" and "rear" will be used with reference to an observed object arranged in front of the lens and a sensor arranged behind the lens.

[0010] In said drawings, 1 denotes, in the entirety thereof, a catadioptric lens according to the present invention.

[0011] The catadioptric lens extends along an optical axis (X), which is shown horizontally in the drawings.

[0012] In accordance with a general embodiment, the catadioptric lens 1 comprises a primary mirror 10, asecondary mirror 20, an adaptive lens 30, and at least one rear optical unit 40.

[0013] The primary mirror 10 has a concave reflective surface 12 that extends around the optical axis (X) and faces forward to receive optical rays from an observed object 2.

[0014] A primary mirror central aperture 14 coaxial to the optical axis X is obtained in the primary mirror 10.

[0015] The secondary mirror 20 is coaxial to the optical axis X and has a convex reflective surface 22 facing the concave reflective surface 12 of the primary mirror 10.

[0016] The secondary mirror 20 is arranged in such a way that the convex reflective surface 22 receives the optical rays reflected by the concave reflective surface 12 and directs such optical rays to the rear with respect to the primary mirror 10, passing through the central primary mirror aperture 14.

[0017] The adaptive lens 30 is arranged to the rear with respect to the primary mirror 10 in such a way as to receive the optical rays reflected by the secondary mirror 20. The adaptive lens 30 is controllable such as to adjust the focusing of the catadioptric lens 1.

[0018] The rear optical unit 40 contains the stop aperture and is suitable for conveying the optical raysfrom the secondary mirror 20 towards an image plane 50 of a sensor.

[0019] In one embodiment, the concave reflective surface 12 is a spherical surface.

[0020] In an alternative embodiment, the concave reflective surface 12 is an aspherical surface.

[0021] In an alternative embodiment, the concave reflective surface 12 is a conical surface.

[0022] In one embodiment, the convex reflective surface 22 is a spherical surface.

[0023] In an alternative embodiment, the convex reflective surface 22 is an aspherical surface.

[0024] In an alternative embodiment, the convex reflective surface 22 is a conical surface.

[0025] In an embodiment shown in Figure 1, a secondary mirror central aperture 24, coaxial to the optical axis X, is obtained in the secondary mirror.

[0026] In an embodiment shown in Figure 3, in the secondary mirror central aperture 24 or in proximity to said secondary mirror central aperture 24, a lens with negative optical power 60 is arranged that is suitable for causing optical rays from a central portion 2a of the observed object 2, such as a bottom wall or a top wall, to converge towards the primary mirror central aperture 14 such as to enlarge the view angle of such centralportion 2a of the observed object 2.

[0027] In the embodiment shown in Figure 4, the secondary mirror 20 lacks a central aperture. In this case, considering that the observed object forms a sidewall 2b, e.g., substantially parallel to the optical axis X, and at least one transverse wall 2a substantially perpendicular and coaxial to the optical axis X, only those optical rays from the sidewall 2b of the object 2 are sent to the image plane of the sensor. In fact, the optical rays from the transverse wall 2a are blocked by the continuous rear wall 20' of the secondary mirror 20.

[0028] In one embodiment, the adaptive lens 30 is arranged to the rear of the rear optical unit 40, i.e., between the rear optical unit 40 and the image plane 50 of the sensor when the sensor is coupled to the catadioptric lens 1.

[0029] In one embodiment variant, the adaptive lens 30 is arranged inside the rear optical unit 40, i.e., between the lenses that make up the rear optical unit 40.

[0030] In one embodiment, the adaptive lens 30 is a liquid lens.

[0031] In one embodiment, the rear optical unit 40 has positive power.

[0032] In one embodiment, the rear optical unit 40, which in the optical diagrams is represented by a genericoptical element, may consist of one or more lenses.

[0033] The stop aperture of the system, contained in the rear optical unit 40, may be fixed or variable.

[0034] In one embodiment, the rear optical unit 40 is a fixed-focus of appropriate focal length, with fixed or variable iris, with a mechanism for adjusting the focus, such as by means of a manual ring.

[0035] The focusing mechanism of the rear optical unit 40 may also be made with an integrated liquid lens. In this case, the liquid lens 30 described in the general embodiment may coincide with the integrated liquid lens.

[0036] In one variant embodiment, the rear optical unit 40 is a varifocal lens, with a fixed or variable iris, and a variable focal length, which allows the size of the image circle produced by the lens to be changed.

[0037] In an embodiment shown in Figure 2, the secondary mirror 20 is attached to a window 70 lying in a plane orthogonal to the optical axis X, transparent to visible and near-infrared light. For example, the window 70 is made of glass.

[0038] The window 70 may also be mechanically attached to the primary mirror 10.

[0039] In one embodiment variant, the secondary mirror 20 is mechanically attached to a support arranged at some distance from the primary mirror 10.

[0040] The operating principle of the catadioptric lens 1 will now be described.

[0041] The optical design of the lens is such that the entrance pupil is in front of said lens, for example, at a distance varying between 300 mm and 0 mm from the front of the lens.

[0042] If the observed object 1 is arranged between the entrance pupil of the lens and the lens 1 (Figure 1), the optical rays from the outer sidewall 2b of the object, i.e., from the wall substantially parallel to the optical axis X, are collected by the primary mirror 10 at a view angle a, reflected back towards the secondary mirror 20 and further reflected by the secondary mirror 20 towards the primary mirror central aperture 14.

[0043] In the embodiment shown in Figure 1, wherein a secondary mirror central aperture 24 passes through the secondary mirror 20, the optical rays from the transverse portion 2a of the object 2, substantially orthogonal to the optical axis, pass through the secondary mirror central aperture 24 at a view angle p and pass through the primary mirror central aperture 14 without undergoing any reflection.

[0044] If, on the other hand, the secondary mirror 20 lacks a central aperture, an image of the transverse portion 2a of the object 2 is not created (Figure 4).

[0045] In the embodiment shown in Figure 3, the optical rays from the transverse portion 2a of the object 2 are collected by the lens with negative optical power 60 at a view angle y, and are made to pass through the primary mirror central aperture 14 without undergoing any reflection. By means of suitably choosing this lens with negative optical power 60, it is possible to enlarge the view angle of the transverse portion 2a of the object 2.

[0046] The optical diagram in Figure 5 may be used to inspect the inner surface 2c of the sidewall of a hollow object 2, which in the example in Figure 5 is shown schematically in the form of a cup. In this case, in fact, the observed object 2 is arranged beyond the entrance pupil of the lens. The optical rays from the inner sidewall of the object pass through a single point P coincident with the entrance pupil of the lens 1.

[0047] Such optical rays are then collected by the primary mirror 10 at a view angle a, reflected towards the secondary mirror 20 and further reflected by the secondary mirror 20 towards the primary mirror central aperture 14.

[0048] The optical rays from the transverse portion 2a of the observed object (in the example, the bottom wall of the object) pass through the secondary mirror central aperture 24 at a view angle p and arrive directly at theprimary mirror central aperture 14 without undergoing reflections.

[0049] If the secondary mirror 20 lacks a central aperture then an image of the bottom 2a of the object is not created (Figure 4).

[0050] If the optical rays from the bottom 2a of the object pass through a lens with negative power 60 (Figure 3) arranged in proximity to the secondary mirror central aperture 24, with a view angle y / then the optical rays arrive at the primary mirror central aperture 14 without ever being reflected. By means of appropriately choosing this lens with negative power 60, it is possible to enlarge the view angle of the bottom of the object 2a.

[0051] All optical rays that have passed through the primary mirror central aperture 14 then pass through the adaptive lens 30 (or liquid lens) and the rear optical unit 40 (not necessarily in this order — see the various embodiments described above), and form an image on the image plane 50 coincident with a sensor.

[0052] The inspectable object 2 may be, for example, a cylindrical or truncated-cone shaped object, a planar object, a donut-shaped object, a hemisphere-shaped object, a cone-shaped object. More generally, an object of random shape.

[0053] Figure 6 shows an example of a practicalimplementation of a catadioptric lens 1. To be noted in particular are those portions relating to the adaptive lens 30, the front optical unit 10, 20 and the rear optical unit 40.

[0054] An example of an object 2 inspectable by means of the catadioptric lens 1 is shown in Figure 7. The object has a first cylindrical portion 202, such as a threaded portion, with a first diameter DI, and a second cylindrical portion 204 having a second diameter D2, larger than the first. The second cylindrical portion 204 is set back with respect to the first cylindrical portion 202, i.e., it is at a greater distance from the catadioptric lens 1.

[0055] Figure 8 and 8a show an image of the top and sidewalls of the two cylindrical surfaces 202, 204, wherein, by acting on the optical power of the adaptive lens 30, the wall with the first diameter DI has been put in focus.

[0056] Figure 9 and 9a show an image of the top and sidewalls of the two cylindrical surfaces 202, 204, wherein, by varying the optical power of the adaptive lens 30, the wall with the second diameter D2 has been put in focus.

[0057] Due to the catadioptric lens 1 described above, it is thus possible to focus simultaneously on atransverse portion 2a with respect to the optical axis, such as a top or bottom part of the object, and the outer sidewalls 2b or inner sidewalls 2c of the object 2.

[0058] Due to the adaptive lens, the focusing area of the system may be changed quickly and remotely by acting only on the power of said adaptive lens. This allows different diameters of the outer wall of the object, or objects of different sizes, to be inspected without manually acting on the lens but by simply changing the optical power of the adaptive lens.

[0059] It should be noted, however, that in some embodiments the adaptive lens 30 may not be necessary, for example when there is no need to change the focus area or it is possible to change the focus by manually acting on the lens.

[0060] In any case, the lens according to the invention is optimised for a hypercentric view, and its main use relates to imaging an object extremely close to the optic (in a practically macro configuration) to inspect the outer part of an object, for example of cylindrical shape.

[0061] In embodiments in which a hole is drilled in the secondary mirror, an upper view of the object is added in addition to the hypercentric view, allowing simultaneous inspection of the side wall and the upperwall of said cylindrical object.

[0062] It should also be noted that, in some advantageous embodiments, the catadioptric lens according to the invention employs a single, very large primary mirror which is cheaper, simpler, more compact and free of chromatic aberrations than an equivalent lens system, which would have to include more lenses to correct aberrations, of the same size as the primary mirror but much bulkier, more expensive and heavier.

[0063] Also constituting the subject matter of the present invention is an artificial vision device comprising a catadioptric lens 1 as described above and a sensor forming an image plane 50 that is suitable for receiving the optical rays from the rear optical unit 40 of the catadioptric lens 1.

[0064] Furthermore, in one embodiment, the artificial vision device comprises a controller operatively connected to the adaptive lens 30 and configured to control the optical power of such adaptive lens according to the desired lens focus.

[0065] A person skilled in the art, in order to meet incidental needs, may make changes, adaptations, and replacements of elements with others that are functionally equivalent to the embodiments of the catadioptric lens and the artificial vision deviceaccording to the invention without departing from the scope of the following claims. Each of the features described as belonging to a possible embodiment may be obtained independently of the other described embodiments.

Claims

CLAIMS1. Catadioptric lens, comprising:- a primary mirror (10) having a concave reflective surface (12) extending around an optical axis (X) and facing forward to receive optical rays from an observed object (2), in the primary mirror there being obtained a primary mirror central aperture (14) coaxial to the optical axis (X);- a secondary mirror (20) coaxial to the optical axis (X) and having a convex reflective surface (22) facing the concave reflective surface (12) of the primary mirror (10), the secondary mirror (20) being arranged such that the convex reflective surface (22) receives the optical rays reflected by the concave reflective surface (12) and directs said optical rays to the rear with respect to the primary mirror (10) by passing through the primary mirror central aperture (14);- at least one rear optical unit (40) that contains the stop aperture and is suitable for conveying the optical rays from the secondary mirror (20) towards an image plane (50) of a sensor.

2. Catadioptric lens according to claim 1, further comprising an adaptive lens (30) arranged to the rear of the primary mirror (10) such as to receive the optical rays reflected by the secondary mirror (20), the adaptivelens (30) being controllable to adjust the focus of the lens.

3. Catadioptric lens according to claim 1 or 2, wherein the concave reflective surface (12) is a spherical surface.

4. Catadioptric lens according to claim 1 or 2, wherein the concave reflective surface (12) is an aspherical surface, e.g., a conical surface.

5. Catadioptric lens according to any one of the preceding claims, wherein the convex reflective surface (22) is a spherical surface.

6. Catadioptric lens according to any one of the claims 1-4, wherein the convex reflective surface (22) is an aspherical surface, for example, conical.

7. Catadioptric lens according to any one of the preceding claims, wherein in the secondary mirror (20) a secondary mirror central aperture (24) coaxial to the optical axis (X) is obtained.

8. Catadioptric lens according to claim 7, wherein in the secondary mirror central aperture (24) or in proximity to said secondary mirror central aperture (24) a lens is arranged having negative optical power (60) that is suitable for causing optical rays from a central portion of the observed object, such as a bottom or top wall, to converge towards the primary mirror centralaperture (14) such as to enlarge the view angle of said central portion of the observed object.

9. Catadioptric lens according to any one of the preceding claims, wherein the adaptive lens (30) is arranged to the rear with respect to the rear optical unit (40).

10. Catadioptric lens according to any one of the claims 2-8, wherein the adaptive lens (30) is arranged inside the rear optical unit (40).

11. Catadioptric lens according to any one of the preceding claims, wherein the rear optical unit (40) is a fixed-focus of appropriate focal length, with fixed or variable iris, with focus adjustment mechanism.

12. Catadioptric lens according to any one of the claims 1-10, wherein the rear optical unit (40) is a varifocal objective, with fixed or variable iris, and variable focal length that allows the size of the image circle produced by the objective to be changed.

13. Catadioptric lens according to any one of the preceding claims, wherein the secondary mirror (20) is attached to a window (70) lying in a plane orthogonal to the optical axis (X), transparent to visible and nearinfrared light.

14. Catadioptric lens according to the preceding claim, wherein the window (70) is mechanically integral to theprimary mirror (10).

15. Catadioptric lens according to any of the preceding claims, in which the entrance pupil (P) is located beyond the secondary mirror (20), on the side of the observed object.

16. Catadioptric lens according to claim 15, wherein the entrance pupil (P) is located in front of the lens itself, for example at a distance varying between 300 mm and 0 mm from the front of the lens.

17. Artificial vision device, comprising a catadioptric lens (1) according to any of the preceding claims and a sensor forming an image plane (50) that is suitable for receiving the optical rays from the rear optical unit (40) of the catadioptric lens.

18. Device according to claim 17, wherein the catadioptric lens comprises and adaptive lens (30), the device further comprising a controller operatively connected to the adaptive lens (30) and configured to control the optical power of such adaptive lens according to the desired focus of the lens.

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