Telecentric lens

Abstract

The application relates to a telecentric lens comprising a lens body extending along an optical axis (X). Such a lens body supports: a front optical group, a rear optical group, an aperture, a sensor plane, and a liquid lens. The front optical group is configured to receive incident light rays (Ri) originating from an object. The rear optical group is configured to receive light rays (Rj) from the front optical group. An aperture is disposed between the front optical group and the rear optical group. The sensor plane is configured to collect outgoing light rays (Rz) projected by the rear optical group. The aperture is substantially disposed at a focal point of the front optical group. Further, a liquid lens is disposed between the front optical group and the rear optical group. The curvature of the liquid lens can be modified in such a way that the focal plane of the object is translated along the optical axis (X). The telecentric lens can overcome those limitations caused by the depth of field of the lens, thus enabling it to move to different focal planes.

Description

Technical Field

[0001] The present application relates to a telecentric lens; specifically, a telecentric lens including a liquid lens integrated therein. Background Art

[0002] A telecentric lens can be used, for example, to perform dimensional measurements of an object. In this case, the telecentric lens as object of the present application is configured to capture images within the visible field (also close to the near infrared field).

[0003] Telecentric lenses are optical systems widely used in the field of artificial vision for performing contactless measurements of objects by virtue of their particular property of collecting a cone of rays originating from the illuminated object, whose axis or chief ray is parallel to the axis of the optical system itself. In this way, in fact, the size of the image created by the lens is independent of the distance at which the observed object is arranged and this makes the measurements much more accurate in terms of their lack of perspective effects characteristic of all other types of optics.

[0004] This property, called telecentricity, is achieved using a lens, the entrance pupil of which is optically arranged at infinity with respect to the object being observed. This peculiarity makes it possible to ensure that those optical elements arranged between the aperture (i.e. the aperture of the lens) and the object being observed create as a whole a front optical group with a positive focal length, in which the position of its focus coincides with that of the aperture. The configuration in which the aperture is arranged at the focus of the front optical group is called "object-side telecentricity", and the telecentric lens can therefore select only those incident rays originating from the object that are parallel to the optical axis.

[0005] Object-side telecentric lenses are known in the prior art, but such lenses have a defined depth of field (DoF) and thus a single focal plane for the object. Utility Model Content

[0006] The object of the present application is to propose a telecentric lens capable of at least partially overcoming the above-mentioned drawbacks. Specifically, the object of the present application is to propose a telecentric lens capable of overcoming those limitations caused by the depth of field of the lens, thus enabling it to be moved to different focal planes.

[0007] According to one aspect of the present application, a telecentric lens includes: a lens body extending along an optical axis, the lens body supporting: - a front optical group, configured to receive incident light originating from an object and parallel to the optical axis; - a rear optical group, configured to receive light from the front optical group; - an aperture, arranged between the front optical group and the rear optical group; - a sensor plane, configured to collect outgoing light projected by the rear optical group, wherein the aperture is arranged at the focus of the front optical group, and wherein the telecentric lens also includes a liquid lens arranged between the front optical group and the rear optical group, and the curvature of the liquid lens can be modified in a manner that allows the focal plane of the object to be translated along the optical axis.

[0008] In an exemplary embodiment, the liquid lens is arranged close to the aperture.

[0009] In an exemplary embodiment, the liquid lens is disposed between the front optical group and the aperture.

[0010] In an exemplary embodiment, the liquid lens is disposed between the aperture and the rear optical group.

[0011] In an exemplary embodiment, the front optical group is converging, provided with positive optical power, and comprises at least one optical element comprising a converging lens and a doublet lens.

[0012] In an exemplary embodiment, the front optical group includes a converging lens having a convex surface facing the object.

[0013] In exemplary embodiments, the converging lens is biconvex or plano-convex or convex-concave.

[0014] In an exemplary embodiment, the front optical group includes a doublet lens, wherein the doublet lens convex surface is distal with respect to the aperture.

[0015] In exemplary embodiments, the doublet lens is either concave-convex or plano-convex.

[0016] In an exemplary embodiment, the front optical group consists of a biconvex converging lens and a concave-convex doublet lens, wherein the doublet lens convex surface faces the converging lens and the concave doublet surface is close to the aperture.

[0017] In an exemplary embodiment, the aperture is arranged at the focal point of the rear optical group.

[0018] In an exemplary embodiment, the aperture is adjustable.

[0019] In an exemplary embodiment, the aperture is fixed.

[0020] In an exemplary embodiment, the rear optical group is converging, provided with positive optical power, and comprises at least one lens and / or a positive doublet.

[0021] In an exemplary embodiment, a telecentric lens includes i) a light source arranged orthogonally to an optical axis; and ii) a light separation device configured to receive light from the light source and illuminate an object.

[0022] In an exemplary embodiment, the light source is an LED source.

[0023] In an exemplary embodiment, the light separating device is arranged between the front optical group and the aperture.

[0024] In an exemplary embodiment, the light separating device is arranged at an intermediate position between the front optical group and the aperture.

[0025] In an exemplary embodiment, the front optical group includes a light separating device.

[0026] This object is achieved by using the telecentric lens described in the technical solution. The following technical solution describes the preferred implementation of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The features and advantages of the telecentric lens according to the present application will become readily apparent from the following description of a preferred embodiment example thereof, provided purely by way of non-limiting example, with reference to the accompanying drawings, in which:

[0028] - Figure 1 shows a stereogram of a telecentric lens according to the present application;

[0029] - Figure 2 is an optical diagram of a telecentric lens according to the present application in a first embodiment;

[0030] - Figure 3 is an optical diagram of a telecentric lens in a second embodiment;

[0031] - Figure 4 is an optical diagram of a telecentric lens in a third embodiment;

[0032] - Figure 5 is an optical diagram of a telecentric lens in a fourth embodiment; and

[0033] - Figure 6a to Figure 6b These are two images of the same object in which details located on two different focal planes, i.e., on two different focal planes, are in focus. DETAILED DESCRIPTION

[0034] In this design—in its entirety—the telecentric lens according to the present application is indicated by 100 in its possible exemplary embodiment.

[0035] In the following description, elements common to the various embodiments shown in the drawings are denoted by the same reference numerals.

[0036] According to one aspect of the present application, the telecentric lens 100 includes a lens body 20 extending along an optical axis X.

[0037] Such a lens body 20 supports: a front optical group 2 , a rear optical group 5 , an aperture 4 , a sensor plane 6 and a liquid lens 3 .

[0038] Therefore, in addition to the lens body 20 , the telecentric lens further comprises a front optical group 2 , a rear optical group 5 , an aperture 4 , a sensor plane 6 and a liquid lens 3 .

[0039] The front optical group 2 is configured to receive an incident ray Ri originating from the object 1 and parallel to the optical axis X. Such an incident ray Ri passes through an entrance pupil which is ideally arranged at infinity.

[0040] The rear optical group 5 is configured to receive the light Rj from the front optical group 2 .

[0041] The aperture 4 is arranged between the front optical group 2 and the rear optical group 5 .

[0042] The sensor plane 6 is configured to collect the outgoing light rays Rz projected by the rear optical group 5 .

[0043] The aperture 4 is arranged substantially at the focal point of the upstream optical group 2 .

[0044] The liquid lens 3 is arranged between the front optical group 2 and the rear optical group 5; the curvature of the liquid lens 3 can be modified in such a way that the focal plane of the object 1 can be translated along the optical axis X. In other words, when changing the optical power of the adaptive lens, the focusing distance of the entire telecentric lens can be modified.

[0045] Preferably, the curvature of the liquid lens 3 can be modified by means of application of an electric field.

[0046] In one embodiment, the liquid lens 3 is arranged visibly near the aperture 4 .

[0047] According to the attached Figure 2 , Figure 4 and Figure 5 In the embodiment shown in , the liquid lens 3 is arranged between the front optical group 2 and the aperture 4. For example, the liquid lens 3 is located near the aperture 4 at a distance less than 1 / 3 (preferably, less than 1 / 6) of the distance between the front optical group 2 and the aperture 4.

[0048] according to Figure 3 In the embodiment of the present invention, the liquid lens 3 is arranged between the aperture 4 and the rear optical group 5. For example, the liquid lens 3 is located near the aperture 4 at a distance less than 1 / 3 (preferably, less than 1 / 6) of the distance between the aperture 4 and the rear optical group 5.

[0049] Preferably, the liquid lens 3 is able to continuously change its optical power from negative to zero, and even to positive. The incident light ray Ri originating from the front optical group 2 passes through the liquid lens 3, whereby the focusing distance of the entire telecentric lens can be modified.

[0050] According to one embodiment, the front optical group 2 is converging, ie has an overall positive optical power. In particular, such a front optical group 2 comprises at least one optical element comprising a converging lens 21 and a doublet lens 22 .

[0051] For the purposes of this discussion and unless otherwise specified, the term "optical element" means a singlet or a doublet.

[0052] The front optical group 2 sends the incident light ray Ri originating from the object 1 first toward the aperture 4 and then toward the rear optical group 5 .

[0053] In one embodiment, the front optical group 2 comprises a converging lens 21 having a convex surface 2 ′ facing the object 1 , which is preferably biconvex or plano-convex or convexo-concave.

[0054] Preferably, the front optical group 2 consists exclusively of refractive and converging optical elements, including a converging lens 21 and a doublet lens 22 .

[0055] According to one embodiment, the front optical group 2 comprises a doublet lens 22 , preferably concave-convex or plano-convex, wherein the doublet lens convex surface 2 ″ is distal with respect to the aperture 4 .

[0056] Preferably, the doublet lens convex surface 2 ″ faces the converging lens 21 .

[0057] According to one embodiment, the front optical group 2 is composed of a converging biconvex lens 21 and a concave-convex doublet lens 22 .

[0058] In this case, the doublet 22 is bounded by a doublet convex surface 2'" and a doublet concave surface 2'".

[0059] The doublet lens convex surface 2 ″ faces the converging lens 21 , while the doublet lens concave surface 2 ″′ is close to the aperture 4 .

[0060] According to one embodiment, the aperture 4 is arranged substantially at the focal point of the rear optical group 5 .

[0061] When the exit pupil is arranged at infinity (i.e. the aperture 4 of the telecentric lens is arranged substantially at the focus of the rear optical group 5), the lens is telecentric from the image side. Specifically, the configuration in which the aperture is arranged at the focus of the rear optical group is "image side telecentric".

[0062] Furthermore, when both the entrance pupil and the exit pupil are located at infinity, the aperture 4 is substantially arranged at the focal point of both the front optical group 2 and the rear optical group 5, in which particular configuration the lens is referred to as doubly telecentric, i.e. both object-side telecentric and image-side telecentric.

[0063] The main peculiarity of the object-side telecentric lens and the bi-telecentric lens is to receive only a beam of incident rays Ri originating from the object 1 and having a chief ray parallel to the optical axis X in such a way as to produce an image in which its viewing angle is eliminated.

[0064] Preferably, for purposes of the present application, the telecentric lens is bi-telecentric or object-side telecentric.

[0065] In one embodiment, the aperture 4 is adjustable, ie, its diameter is variable. Alternatively, the aperture 4 is fixed, ie, not adjustable.

[0066] According to one embodiment, the rear optical group 5 is convergent, ie has an overall positive optical power. Such a rear optical group 5 comprises at least one lens 51 and / or a positive doublet.

[0067] Preferably, the lens 51 is biconvex or plano-convex or convexo-concave.

[0068] According to one embodiment, at least one lens 51 is a single lens; the rear optical group 5 therefore consists of only one lens 51 .

[0069] In another embodiment, not shown in the figures, the rear optical group 5 consists of only one positive doublet lens.

[0070] In yet another embodiment, not shown in the figure, the rear optical group 5 is composed of a single lens 51 and a positive doublet lens.

[0071] The light rays Rj originating from the front optical group 2 pass through the aperture 4 and reach the rear optical group 5 , which then focuses the outgoing light rays Rj onto the sensor plane 6 .

[0072] In the attached Figure 4 and Figure 5 In one embodiment shown in , the telecentric lens 100 includes a light source 8 and a light separation device 7 .

[0073] The light source 8 is, for example, an LED source and is arranged orthogonally to the optical axis X.

[0074] The light separating device 7 is also referred to as a beam splitter and is configured to receive light from the light source 8 and illuminate the object 1 .

[0075] In particular, the light separation device 7 is configured to illuminate the object 1 in a manner substantially coaxial to the optical axis X through the front optical group 2 .

[0076] Preferably, the lens body 20 is provided with a side aperture through which the light emitted by the light source 8 passes. Specifically, such a light source 8 is arranged on the outer side surface of the lens body 20.

[0077] In accordance with Figure 4 In the embodiment of the present invention, the light separation device 7 is arranged between the front optical group 2 and the aperture 4. Preferably, the light separation device 7 is located approximately in the middle between the front optical group 2 and the aperture 4; more preferably, approximately in the middle between the doublet lens 22 and the aperture 4.

[0078] According to the attached Figure 5 In the embodiment shown in FIG. 2 , the front optical group 2 includes a light separation device 7 . In other words, the light separation device 7 is arranged in the front optical group 2 .

[0079] Preferably, the light separation device 7 is arranged between the biconvex converging lens 21 and the concave-convex doublet lens 22. In one embodiment, therefore, the front optical group 2 consists of the biconvex converging lens 21, the light separation device 7 and the concave-convex doublet lens 22, wherein the convex surface 2" of the doublet lens faces the light separation device 7 and the concave surface 2"' of the doublet lens is close to the aperture 4.

[0080] Attached Figure 6a and Figure 6b Different details of the same object are shown lying in two different focal planes (ie lying in two different focus planes). Such different focal planes are obtained simply by modifying the optical power of the liquid lens 3 integrated into the telecentric lens.

[0081] Innovatively, the telecentric lens of the present application fully achieves its intended purpose.

[0082] Advantageously, by means of a liquid lens, the focal plane of the entire telecentric lens can be changed. In other words, the focal plane can be displaced along the optical axis. The integration of a liquid lens is therefore particularly useful for overcoming those limitations related to the depth of field, insofar as it enables the focal plane to be translated.

[0083] According to one advantageous aspect, object-side telecentric or bi-telecentric lenses naturally tend to have very low distortion, which when added to perspective cancellation makes them particularly suitable for measurement and inspection of objects.

[0084] According to yet another advantageous aspect, as long as the liquid lens is located near the aperture, the impact of its distortion values ​​is greatly reduced. Keeping such values ​​very low, the liquid lens makes telecentric lenses (object of the present application) compatible with applications requiring low distortion and good telecentricity.

[0085] Advantageously, when using a liquid lens, it is possible to focus on objects located at different working distances. Thus, limitations imposed by the depth of field of a telecentric lens can be overcome while improving the ability to focus on different object planes.

[0086] For the implementation of the telecentric lens according to the present application, those skilled in the art may modify, adapt and replace the elements with functionally equivalent elements in order to meet possible needs without departing from the scope of protection of the attached claims. Each of the features described as belonging to possible implementations can be obtained independently of the other described implementations.

Claims

1. A telecentric lens (100), characterized in that: include: A lens body (20) extending along an optical axis (X), the lens body (20) supporting: - a front optical group (2) configured to receive an incident light ray (Ri) originating from the object (1) and parallel to said optical axis (X); - a rear optical group (5) configured to receive light (Rj) from the front optical group (2); - an aperture (4) arranged between the front optical group (2) and the rear optical group (5); - a sensor plane (6) configured to collect the outgoing light rays (Rz) projected by the rear optical group (5), wherein the aperture (4) is arranged at the focus of the front optical group (2), and wherein the telecentric lens further comprises a liquid lens (3) arranged between the front optical group (2) and the rear optical group (5), the curvature of the liquid lens (3) being modifiable in such a way that the focal plane of the object (1) can be translated along the optical axis (X).

2. The telecentric lens (100) according to claim 1, characterized in that: The liquid lens (3) is arranged close to the aperture (4).

3. The telecentric lens (100) according to any one of the preceding claims, characterized in that The liquid lens (3) is arranged between the front optical group (2) and the aperture (4).

4. The telecentric lens (100) according to claim 1 or 2, characterized in that: The liquid lens (3) is arranged between the aperture (4) and the rear optical group (5).

5. The telecentric lens (100) according to any one of the preceding claims, characterized in that The front optical group (2) is converging and provided with positive optical power, and comprises at least one optical element, wherein the optical element comprises a converging lens (21) and a doublet lens (22).

6. The telecentric lens (100) according to any one of the preceding claims, characterized in that The front optical group (2) comprises a converging lens (21) having a convex surface (2') facing the object (1).

7. The telecentric lens (100) according to claim 6, characterized in that: The converging lens (21) is biconvex or plano-convex or convex-concave.

8. The telecentric lens (100) according to any one of the preceding claims, characterized in that The front optical group (2) comprises a doublet lens (22), wherein the doublet lens convex surface (2") is distal with respect to the aperture (4).

9. The telecentric lens (100) according to claim 8, characterized in that: The doublet lens (22) is concave-convex or plano-convex.

10. The telecentric lens (100) according to claim 7 or 9, characterized in that: The front optical group (2) consists of a biconvex converging lens (21) and a concave-convex doublet lens (22), wherein the convex surface (2") of the doublet lens faces the converging lens (21) and the concave doublet surface (2'") is close to the aperture (4).

11. The telecentric lens (100) according to any one of the preceding claims, characterized in that The aperture (4) is arranged at the focus of the rear optical group (5).

12. The telecentric lens (100) according to any one of the preceding claims, characterized in that The aperture (4) is adjustable.

13. The telecentric lens (100) according to any one of claims 1 to 11, characterized in that: The aperture (4) is fixed.

14. The telecentric lens (100) according to any one of the preceding claims, characterized in that The rear optical group (5) is convergent and provided with positive optical power, and comprises at least one lens (51) and / or a positive doublet lens.

15. The telecentric lens (100) according to any one of the preceding claims, characterized in that include i) a light source (8), arranged orthogonally to the optical axis (X); ii) A light separation device (7) configured to receive light from the light source (8) and illuminate the object (1).

16. The telecentric lens (100) according to claim 15, characterized in that: The light source (8) is an LED source.

17. The telecentric lens (100) according to claim 15, characterized in that: in, The light separation device (7) is arranged between the front optical group (2) and the aperture (4).

18. The telecentric lens (100) according to claim 17, characterized in that: The light separation device (7) is arranged at an intermediate position between the front optical group (2) and the aperture (4).

19. The telecentric lens (100) according to claim 15, characterized in that: The front optical group (2) comprises the light separation device (7).

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