Telecentric lens with integrated liquid lens

Abstract

The present invention relates to a telecentric lens (100; 100a; 100b; 100c) comprising a lens body (20) that extends along an optical axis (X). Such lens body (20) supports: a front optical group (2), a rear optical group (5), a stop aperture (4), a sensor plane (6) and a liquid lens (3). The front optical group (2) is configured to receive entrance rays (Ri) originating from an object (1). The rear optical group (5) is configured to receive the rays (Rj) coming from the front optical group (2). The stop aperture (4) is arranged between the front optical group (2) and the rear optical group (5). The sensor plane (6) is configured to collect the exiting rays (Rz) projected by the rear optical group (5). The stop aperture (4) is substantially arranged at the point of focus of the front optical group (2). Furthermore, 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) may be modified in such a way as to translate the plane of focus of the object (1) along the optical axis (X).

Description

[0001] TELECENTRIC LENS WITH INTEGRATED LIQUID LENS DESCRIPTION

[0002] The present invention relates to a telecentric lens; in particular, a telecentric lens comprising a liquid lens integrated therewithin.

[0003] A telecentric lens may for example be used to perform dimensional measurements of objects. In this case, the telecentric lens, object of the present invention, is configured to capture images within the visible field (also in proximity to the infrared field).

[0004] Telecentric lenses are optical systems that are widely used in the field of artificial vision for performing non-contact measurements of objects by virtue of the specific property thereof of collecting cones of light rays originating from an illuminated object wherein the axis, or main ray, thereof 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 from the distance at which the observed object is arranged and this allows the measurement to be more accurate insofar as it lacks the characteristic perspective effects of every other type of optics.

[0005] This property, called telecentricity, is implemented using a lens wherein the entrance pupil of the lens is optically arranged at infinity, with respect to the object observed. This peculiarity is made possible by ensuring that those optical elements that are arranged between the stop aperture, namely the aperture of the lens, and the observed object create, as a whole, a front optical group with a positive focal length, wherein the position of its focus coincides with the position of the stop aperture. The configuration wherein the stop aperture is arranged at the point of focus of the front optical group is called "object side telecentric" and the telecentric lens may therefore select only those entrance rays originating from the object that are parallel to the optical axis.

[0006] Already known in the state of the art are object side telecentric lenses, such lenses nonetheless have a defined Depth of Field (DoF) and therefore a single plane of focus for the object.

[0007] The object of the present invention is that of proposing a telecentric lens that is capable of at least partially overcoming the drawbacks mentioned above. In particular, the object of the present invention is that of proposing a telecentric lens that is capable of overcoming those limitations deriving from the depth of field of the lens therefore making it possible to move between differing planes of focus.

[0008] Said object is achieved with a telecentric lens according to claim 1. The dependent claims describe preferred embodiments of the invention.

[0009] The features and the advantages of the telecentric lens according to the invention shall be made readily apparent from the following description of preferred embodiment examples thereof, provided purely by way of a nonlimiting example, with reference to the accompanying figures, wherein:

[0010] - Figure 1 shows a perspective view of a telecentric lens in accordance with the present invention;

[0011] - Figure 2 is an optical diagram of a telecentric lens according to the invention, in a first embodiment;

[0012] - Figure 3 is an optical diagram of a telecentric lens in a second embodiment;

[0013] - Figure 4 is an optical diagram of a telecentric lens in a third embodiment;

[0014] - Figure 5 is an optical diagram of a telecentric lens in a fourth embodiment; and

[0015] - Figures 6a-6b are two images of the same object, where details lying on two different focal planes were brought into focus, i.e., on two different planes of focus.

[0016] In said designs - in the entirety thereof - a telecentric lens according to the invention has been indicated in its possible exemplary embodiments with 100; 100a; 100b; 100c. In the following description, elements common to the various embodiments represented in the drawings are indicated with the same reference numerals.

[0017] According to one aspect of the invention, the telecentric lens 100; 100a; 100b; 100c comprises a lens body 20 that develops along an optical axis X.

[0018] Such lens body 20 supports: a front optical group 2, a rear optical group 5, a stop aperture 4, a sensor plane 6 and a liquid lens 3.

[0019] The telecentric lens therefore comprises - other than the lens body 20 - the front optical group 2, the rear optical group 5, the stop aperture 4, the sensor plane 6 and the liquid lens 3.

[0020] The front optical group 2 is configured to receive entrance rays Ri originating from an object 1 and parallel to the optical axis X. Such entrance rays Ri pass through an entrance pupil that is ideally arranged at infinity.

[0021] The rear optical group 5 is configured to receive the rays Rj coming from the front optical group 2.

[0022] The stop aperture 4 is arranged between the front optical group 2 and the rear optical group 5.

[0023] The sensor plane 6 is configured to collect the exiting rays Rz projected by the rear optical group 5.

[0024] The stop aperture 4 is substantially arranged at the point of focus of the front optical group 2.

[0025] 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 may be modified in such a way as to render the plane of focus of the object 1 translatable along the optical axis X. In other words, in varying the optical power of the adaptive lens it is possible to modify the focusing distance of the entire telecentric lens.

[0026] Preferably, the curvature of the liquid lens 3 may be modified by means of the application of an electric field.

[0027] In one embodiment, the liquid lens 3 is significantly arranged in proximity to the stop aperture 4.

[0028] According to the embodiment shown in the attached Figures 2, 4 and 5, the liquid lens 3 is arranged between the front optical group 2 and the stop aperture 4. For example, the liquid lens 3 is located in proximity to the stop aperture 4 at less than 1 / 3 of the distance between the front optical group 2 and the stop aperture 4, preferably at less than 1 / 6.

[0029] According to the embodiment in Figure 3, the liquid lens 3 is arranged between the stop aperture 4 and the rear optical group 5. For example, the liquid lens 3 is located in proximity to the stop aperture 4 at less than 1 / 3 of the distance between the stop aperture 4 and the rear optical group 5, preferably at less than 1 / 6.

[0030] Preferably, the liquid lens 3 is capable of continuously changing the optical power thereof from negative to null and even to positive. The entrance rays Ri originating from the front optical group 2 pass through the liquid lens 3, by virtue thereof it is possible to modify the focusing distance of the entire telecentric lens.

[0031] According to one embodiment, the front optical group 2 is convergent, i.e., having overall positive optical power. In particular, such front optical group 2 comprises at least one optical element 21; 22.

[0032] For the purposes of this discussion and unless otherwise specified, the term "optical element" signifies a single lens or else a doublet.

[0033] The front optical group 2 sends the entrance rays Ri originating from the object 1 towards the stop aperture 4 and then towards the rear optical group 5.

[0034] In one embodiment, the front optical group 2 comprises a convergent lens 21, preferably biconvex or planoconvex or else convex-concave, having a convex surface 2' facing the object 1.

[0035] Preferably, the front optical group 2 consists exclusively of refractive and convergent optical elements 21, 22. According to one embodiment, the front optical group 2 comprises a doublet 22, preferably concave-convex or plano-convex, wherein a doublet convex surface 2" is distal with respect to the stop aperture 4.

[0036] Preferably, the doublet convex surface 2" faces the convergent lens 21.

[0037] According to one embodiment, the front optical group 2 consists of the convergent biconvex lens 21 and the concave-convex doublet 22.

[0038] In this case, the doublet 22 is delimited by the doublet convex surface 2" and by a concave doublet surface 2"'. The doublet convex surface 2" faces the convergent lens 21, whilst the concave doublet surface 2''' is proximal to the stop aperture 4.

[0039] In one embodiment, the front optical group 2 has overall positive optical power and comprises at least two optical elements; preferably, the front optical group 2 comprises exclusively two converging optical elements. According to one embodiment, the front optical group 2 comprises at least three optical elements-preferably, it consists exclusively of three optical elements-wherein two optical elements of said three optical elements are convergent and the remaining optical element of said three optical elements is divergent. Specifically, the three optical elements include a first optical element, a second optical element and a third optical element. The first optical element faces object 1, that is, it receives Ri input rays coming directly from object 1; such first optical element is a convergent first lens. The second optical element can be a second lens or a second doublet. Finally, the third optical element, which is distal to object 1, may be a third lens or a third doublet.

[0040] In an embodiment, the front optical group 2 has between two and four optical elements (extremes included). In other words, the front optical group 2 may comprise a minimum of two optical elements and a maximum of four optical elements.

[0041] Preferably, the front optical group 2 consists exclusively of four optical elements, where at least two optical elements of said four optical elements are convergent and at least one optical element of said four optical elements is divergent. Specifically, the four optical elements include a first optical element, a second optical element, a third optical element, and a fourth optical element. The first optical element faces object 1, that is, it receives Ri input rays coming directly from object 1; such first optical element is the first converging lens. The second optical element is positioned behind the first optical element moving away from the object 1 along the optical X axis and can be a second lens or a second doublet. The third optical element is positioned behind the second optical element moving away from the object 1 along the optical X axis and can be a third lens or a third doublet. Finally, the fourth optical element, which is distal to object 1, can be a fourth lens or a fourth doublet.

[0042] According to one embodiment, the stop aperture 4 is substantially arranged at the point of focus of the rear optical group 5.

[0043] In the case wherein the exit pupil is arranged at infinity, i.e., the stop aperture 4 of the telecentric lens is substantially arranged at the point of focus of the rear optical group 5, the lens is telecentric from the image side. In particular, the configuration wherein the stop aperture is arranged at the point of focus of the rear optical group is called "image side telecentric" .

[0044] Furthermore, when both the entrance pupil and the exit pupil are located at infinity, the stop aperture 4 is substantially arranged at the point of focus of both the front optical group 2 and the rear optical group 5; then, in this particular configuration the lens is said to be double-telecentric, i.e., both object side and image side telecentric. The main peculiarity of object side telecentric and double-telecentric lenses is that of accepting only beams of entrance rays Ri originating from the object 1 with a main ray of light that is parallel to the optical axis X, in such a way as to produce an image wherein the perspective thereof is nullified.

[0045] Preferably, the telecentric lens, object of the present invention, is bi-telecentric or else object side telecentric .

[0046] In one embodiment, the stop aperture 4 is adjustable, i.e., the diameter thereof is variable. Alternatively, the stop aperture 4 is fixed, i.e., not adjustable. According to one embodiment, the rear optical group 5 is convergent, i.e., having overall positive optical power. Such rear optical group 5 comprises at least one lens 51 and / or a positive doublet.

[0047] Preferably, the lens 51 is biconvex or plano-convex or else convex-concave.

[0048] According to one embodiment, the at least one lens 51 is singular; the rear optical group 5 therefore consists of only one lens 51.

[0049] In a further embodiment, not shown in the figures, the rear optical group 5 consists of only one positive doublet.

[0050] In a still further embodiment, not shown in the figures, the rear optical group 5 consists of one single lens 51 and one positive doublet.

[0051] Rays Rj originating from the front optical group 2 pass through the stop aperture 4 and arrive at the rear optical group 5 which then focuses the exiting rays Rz onto the sensor plane 6.

[0052] In a form of embodiment, the rear optical group 5 comprises (preferably consists exclusively of) a rear optical element, wherein said rear optical element is a converging lens.

[0053] In an embodiment, the rear optical group 5 comprises (preferably consists exclusively of) a first rear optical element proximal to the object 1 and a second rear optical element. At least one of the first and second rear optical elements is convergent. In particular, the first rear optical element may be a first rear lens or a first rear doublet. The second rear optical element may be a second rear lens or a second rear doublet.

[0054] In an embodiment, the rear optical group 5 comprises (preferably consists exclusively of) a first rear optical element proximal to object 1, a second rear optical element positioned behind the first rear optical element moving away from the object 1 along the optical axis X, and a third rear optical element distal to object 1. In the rear optical group 5, at least one rear optical element is convergent and at least one rear optical element is divergent. In particular, the first rear optical element may be a first rear lens or a first rear doublet. The second rear optical element may be a second rear lens or a second rear doublet. The third rear optical element may be a third rear lens or a third rear doublet.

[0055] In an embodiment, the rear optical group 5 comprises (preferably consists exclusively of) a first rear optical element proximal to object 1, a second rear optical element positioned behind the first rear optical element moving away from the object 1 along the optical axis X, a third rear optical element positioned behind the second rear optical element moving away from the object 1 along the optical axis X, and a fourth rear optical element distal to object 1. In the rear optical group 5, at least two rear optical elements are convergent and at least one rear optical element is divergent. In particular, the first rear optical element may be a first rear lens or a first rear doublet. The second rear optical element may be a second rear lens or a second rear doublet. The third rear optical element may be a third rear lens or a third rear doublet. Finally, the fourth rear optical element can be a fourth rear lens or a fourth rear doublet.

[0056] In an embodiment, the rear optical group 5 has between two and four rear optical elements (extremes included). In other words, the rear optical group 5 can include a minimum of two rear optical elements and a maximum of four rear optical elements.

[0057] In one embodiment shown in the attached Figures 4 and 5, the telecentric lens 100b; 100c comprises a light source 8 and a ray separating device 7.

[0058] The light source 8 is for example an LED source and is arranged orthogonally to the optical axis X.

[0059] The ray separating device 7 is otherwise known as a beamsplitter and is configured to receive light rays originating from the light source 8 and to illuminate the object 1.

[0060] In particular, the ray separating device 7 is configured to illuminate the object 1 through the front optical group 2 in a way that is substantially coaxial to the optical axis X.

[0061] Preferably, the lens body 20 is provided with a side aperture wherethrough the light that is emitted by the light source 8 passes. In particular, such light source 8 is arranged upon an external lateral surface of the lens body 20.

[0062] In an embodiment according to Figure 4, the ray separating device 7 is arranged between the front optical group 2 and the stop aperture 4. Preferably, the ray separating device 7 is located about halfway between the front optical group 2 and the stop aperture 4; even more preferably, about halfway between the doublet 22 and the stop aperture 4.

[0063] According to the embodiment illustrated in the attached Figure 5, the front optical group 2 comprises the ray separating device 7. In other words, the ray separating device 7 is arranged within the front optical group 2. Preferably, the ray separating device 7 is arranged between the biconvex converging lens 21 and the concave- convex doublet 22. In one embodiment therefore the front optical group 2 consists of the biconvex converging lens 21, the ray separating device 7 and the concave-convex doublet 22, where the doublet convex surface 2" faces the ray separating device 7 and the concave doublet surface 2''' is proximal to the stop aperture 4.

[0064] The attached Figures 6a and 6b show different details of the same object that lie on two different focal planes, i.e., on two different planes of focus. Such different focal planes were obtained only by modifying the optical power of the liquid lens 3 which is integrated into the telecentric lens.

[0065] Innovatively, the telecentric lens of the present invention fully fulfills the intended object thereof. Advantageously, by virtue of the liquid lens it is possible to change the plane of focus of the entire telecentric lens. In other words, it is possible to shift the plane of focus along the optical axis. Hence, the integration of the liquid lens is particularly useful in overcoming those limitations that relate to depth of field insofar as it makes it possible to translate the plane of focus.

[0066] According to one advantageous aspect, the object side telecentric or double-telecentric lens is naturally inclined to have very low distortion which, when added to the perspective cancellation, makes it particularly suitable for the measurement and inspection of objects. According to one still further advantageous aspect, insofar as the liquid lens is located in proximity to the stop aperture, the effect thereof distortion values is extremely reduced. In maintaining such values extremely low the liquid lens renders the telecentric lens, object of the present invention, compatible with applications wherein low distortion and good telecentricity are required.

[0067] Advantageously, in using the liquid lens it is possible to focus on objects at differing working distances. In increasing the ability to focus on different object planes it is therefore possible to overcome those limitations deriving from the depth of field of the telecentric lens.

[0068] To the embodiments of the telecentric lens according to the invention, a person skilled in the art, in order to meet contingent needs, may make modifications, adaptations and replacements of elements with functionally equivalent ones, without leaving the scope of protection 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. Telecentric lens (100; 100a; 100b; 100c) comprising a lens body (20) extending along an optical axis (X), said lens body (20) supporting:- a front optical group (2) configured to receive entrance rays (Ri) originating from an object (1) and parallel to the optical axis (X);- a rear optical group (5) configured to receive the rays (Rj) coming from the front optical group (2);- a stop aperture (4) arranged between the front optical group (2) and the rear optical group (5);- a sensor plane (6) that is configured to collect the exiting rays (Rz) projected by the rear optical group (5), wherein the stop aperture (4) is substantially arranged at the point of focus of the front optical group (2), and wherein the telecentric lens furthermore 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) may be modified in such a way as to render the plane of focus of the object (1) translatable along the optical axis (X).

2. Telecentric lens (100; 100a; 100b; 100c) according to any one of the preceding claims, wherein the liquid lens (3) is arranged significantly in proximity to thestop aperture (4).

3. Telecentric lens (100; 100b; 100c) according to anyone of the preceding claims, wherein the liquid lens (3) is arranged between the front optical group (2) and the stop aperture (4).

4. Telecentric lens (100a) according to claims 1 or 2, wherein the liquid lens (3) is arranged between the stop aperture (4) and the rear optical group (5).

5. Telecentric lens (100; 100a; 100b; 100c) according to any one of the preceding claims, wherein the front optical group (2) is convergent, that is provided with positive optical power, said front optical group (2) comprising at least one optical element (21; 22).

6. Telecentric lens (100; 100a; 100b; 100c) according to any one of the preceding claims, wherein the front optical group (2) comprises one convergent lens (21), preferably biconvex or plano-convex or else convex- concave, having a convex surface (2') facing the object (1)•7. Telecentric lens (100; 100a; 100b; 100c) according to any one of the preceding claims, wherein the front optical group (2) comprises a doublet (22), preferably concave-convex or plano-convex, wherein a doublet convex surface (2") is distal with respect to the stop aperture (4).

8. Telecentric lens (100; 100a; 100b; 100c) according to claims 6 and 7, wherein the front optical group (2) consists of the biconvex convergent lens (21) and the concave-convex doublet (22), wherein the doublet convex surface (2") faces the convergent lens (21) and a concave doublet surface (2''') is proximal to the stop aperture (4).

9. Telecentric lens (100; 100a; 100b; 100c) according to any one of the preceding claims, wherein the stop aperture (4) is significantly arranged at the point of focus of the rear optical group (5).

10. Telecentric lens (100; 100a; 100b; 100c) according to any one of the preceding claims, wherein the stop aperture (4) is adjustable.

11. Telecentric lens (100; 100a; 100b; 100c) according to any one of the claims from 1 to 9, wherein the stop aperture (4) is fixed.

12. Telecentric lens (100; 100a; 100b; 100c) according to any one of the preceding claims, wherein the rear optical group (5) is convergent, that is provided with positive optical power, said rear optical group (5) comprising at least one optical element (51) and / or a positive doublet.

13. Telecentric lens (100b; 100c) according to any one of the preceding claims, comprisingi) a light source (8), for example an LED source, arranged orthogonally to the optical axis (X); ii) a ray separating device (7) configured to receive light rays originating from the light source (8) and to illuminate the object (1).

14. Telecentric lens (100b) according to the preceding claim, wherein the ray separating device (7) is arranged between the front optical group (2) and the stop aperture (4), preferably about halfway between the front optical group (2) and the stop aperture (4).

15. Telecentric lens (100c) according to claim 13, wherein the front optical group (2) comprises the ray separating device (7).

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