SELF-CENTERING LENS ENCLOSURE AND OBJECTIVE FOR A METROLOGICAL CAMERA

Abstract

A lens enclosure and objective for a metrological camera, the lens enclosure comprising a first support area for support of the first optical element and a second support area for support of the second optical element, spaced apart from each other. The first and second support area are shaped as a segment of a surface of at least one right cone each such that the support of the first and second optical element each is self-centering with respect to translation in all directions as well as tilt in relation to the optical axis.

Claims

1. A lens enclosure for enclosure of at least a glass lens as a first optical element and of a second optical element of a metrological camera, the lens enclosure comprising: a first support area for support of the first optical element and a second support area for support of the second optical element, wherein the first and second support area are spaced apart from each other in direction of the optical axis of the lens enclosure, wherein the first and second support area are shaped as a segment of a surface of at least one right cone each, referred to as inner cone, the central axis of which is coaxial to/extends along the optical axis, such that the support of the first and second optical element each is self-centering with respect to translation in all directions as well as tilt in relation to the optical axis.

2. The lens enclosure according to any one claim 1, wherein the support of a respective optical element is non-self-locking.

3. The lens enclosure according to claim 1 or 2, wherein the enclosure of a respective optical element is locally defined, virtually punctiform or linear.

4. The lens enclosure according to claim 1, wherein the draft angle of a respective support area is between 60° and 120°, in particular between 70° and 110°.

5. The lens enclosure according to claim 1, wherein the draft angle of a respective support area is between 70° and 110°.

6. The lens enclosure according to claim 1, wherein the maximum diameter of the respective support area is 30 mm at most.

7. The lens enclosure according to claim 1, wherein the maximum diameter of the respective support area is 14 mm at most.

8. The lens enclosure according to claim 1, wherein the first and second support area are arranged in such a way that they are accessible for a turning tool of a turning machine in one and the same clamping.

9. An imaging objective for a metrological camera, comprising a first lens enclosure and a first optical element embodied as a glass lens and at least a second optical element, wherein: the lens enclosure comprises a first support area for support of the first optical element and a second support area for support of the second optical element, the first and second support area are spaced apart from each other in direction of the optical axis of the objective, wherein a respective support area and/or a respective contact area of the first or second optical element for contacting the respective support area is shaped as a segment of a surface of at least one right cone each, referred to as inner cone, the central axis of which extends along the optical axis, such that the support of the first and second optical element each is self-centering with respect to translation in all directions as well as tilt in relation to the optical axis.

10. The objective according to claim 9, wherein the optical axis of a respective optical element is aligned coaxially to the optical axis of the objective solely due to the self-centering support.

11. The objective according to claim 9, wherein the lens enclosure is supported self-centered due to the lens enclosure having an outer support area shaped as a segment of a surface of another right cone, referred to as outer cone, wherein the central axes of the at least one inner cone and the outer cone are coaxial.

12. The objective according to claim 9, wherein the objective comprises fixation means for fixation of the lens enclosure and/or the optical elements, whereby: a respective fixation is free of play in direction of the optical axis and/or at least one of the fixation means serves for fixation of at least two optical elements.

13. The objective according to claim 9, wherein the first and second optical element are preloaded, by a spring element, by a force which is at least a hundred times the weight of a respective optical element, in particular whereby the force is maximal 100N.

14. The objective according to claim 9, wherein the surface of a respective support area and/or contact area is coated with a hardened and/or low-friction coating.

15. The objective according to claim 9, wherein the length of the objective is between 4 mm and 40 mm.

16. The objective according to claim 9, wherein the length of the objective is between 5 mm and 30 mm.

17. The objective according to claim 9, wherein the length of the objective is between 10 mm and 25 mm.

18. The objective according to claim 9, wherein the objective comprises materials with different coefficients of thermal expansion, wherein at least the coefficients of thermal expansion of the lens enclosure and first and second optical element are different to each other.

19. A metrological camera for industrial and/or geodetic measuring, comprising the objective according to claim 9.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The lens enclosure and objective and the method will be described in greater detail hereinafter, purely by way of example, with reference to example embodiments depicted schematically in the drawings.

[0025] More specifically, in the drawings:

[0026] FIG. 1 shows a schematical 3D-view of an embodiment of a lens enclosure for mounting of at least two optical elements, therein at least one glass lens;

[0027] FIG. 2 schematically shows an objective for a metrological camera in a cross sectional view; and

[0028] FIG. 3a,b schematically depict a cross-sectional view of a part of an objective.

DETAILED DESCRIPTION

[0029] FIG. 1 shows a 3D-view of an embodiment of a lens enclosure 3 for a metrological camera. Such a metrological camera is for example part of an industrial or geodetic metrology system such as a vision inspection system, 3D scanner, photogrammetric systems, machine vision apparatus, 3D-microscope or surveying system.

[0030] In the example, the lens enclosure is formed as a barrel with a circular entry area 7 and a circular exit area 8 with a smaller diameter than the entry area 7. The lens enclosure 3 comprises two support areas 1, 2 (marked grey in the figure), namely a first support area 1, in the example situated at the front, and a second support area 2, in the example situated in a middle section of the barrel. In the example, the second support area 2 is smaller than the first support area 1, however, they can also be both of same size or diameter or the second one can be greater than the first one. Preferably, the maximum diameter of a support area 1, 2 is 30 millimeter at most, in particular 14 mm at most.

[0031] The support areas 1, 2 are designed for support of an optical element each, whereby at least one of the optical elements is a glass lens. The optical axis 5 of the lens enclosure is defined by the midpoints C1, C2 of the support areas 1, 2, in the example the center of the circle or ring which can be inscribed in a respective support area 1, 2. In the example, the optical axis 5 is identical or coaxial to the central axis of the cylinder defined by the barrel 3, in particular within a tolerance of 20 or 10 micrometers. The two support areas 1, 2 are spaced apart from each other in direction of the optical axis 5.

[0032] A respective support area 1, 2 are each lying on the surface of an “imaginary” right cone 4. In the example, the two areas 1, 2 are part of one and the same cone 4, however, each support area 1, 2 can be a segment of a separate or different cone envelope, whereby the central axis 6 of each cone is coaxial to the optical axis (the apex and center of the cone's bottom surface are lying on the optical axis 5). In any case, each support area 1, 2 is narrowing along the optical axis 5 in the sense that the diameter of the enclosed area decreases in direction of the optical axis 5.

[0033] Each support area 1, 2 has a uniform angle of inclination towards the optical axis 5 which is half the draft angle α of the cone 4. Preferably, the draft angle α or angle of inclination is the same for both support areas 1, 2; however, the respective angles of different support areas 1, 2 can be different, too. Preferably, the draft angle is between 60° and 120°, most preferably between 70° and 110°, meaning that the inclination angle is between 30° and 60° resp. 35° and 55°. A most preferred inclination angle is 45°.

[0034] Such an inclination angle is particularly advantageous for self-centering support of a respective optical element which is enabled by the tapered support areas 1, 2 of the lens enclosure 3. The particular, conical shape of the receiving sections 1, 2 allow for an enclosing support of an optical element, in particular a glass lens, which is locally defined or limited. The present lens mount 3 provides advantageously self-centering stops for of at least two optical elements with respect to translation in all directions as well as tilt (yaw and pitch) in relation to the optical axis 5.

[0035] When an optical element (lens, filter, aperture etc.) is inserted into the lens enclosure 3, it is centered “by itself”, e.g. using gravitational force and activation by vibration, in particular ultrasound, without the need of active or “external” positioning or aligning of the optical element as is the case in lens enclosures known in the art. Proper alignment of the optical elements with respect to the optical axis (and with respect to each other) is “automatically” achieved, without need of force application or additional spacing components or the like. As the support of a respective optical element is non-self-locking, it cannot become locked, even in case of dimensional change e.g. induced by temperature changes.

[0036] The lens assembly 3 can be a single piece as indicated in the figure, however, it can also be an assembly of multiple modules or segments. For instance, a first piece or first lens spacer comprising the first stop 1 is mounted in succession to a separate second piece or second lens spacer comprising the second stop 2 in a common frame/housing/objective (barrel). An objective in turn can comprise multiple lens enclosures 3.

[0037] In particular, in case of a single piece-lens enclosure 3, the geometry is chosen such that first and second support area 1, 2 are accessible for a turning tool of a turning machine in one and the same clamping as is the case in the example shown which face the same direction (to the front) and whereby the inner support area 2 is smaller in diameter than the outer support area 1. In other words, both (all) stops are arranged in such a way that they can be produced in one manufacturing step.

[0038] However, a respective support area 1, 2 needs not to be shaped like a complete, closed or continuous (narrowing) ring as shown in the figure but can be a, preferably axially symmetrical, arrangement of discrete or separate points or sections spaced from another distributed on a segment of a cone surface around the central axis 6. Said otherwise, the support area 1, 2 is not necessarily a continuous 360°-section or strip of a cone envelope but can also be a number of points or sections lying on such a cone envelope line or strip, preferably with equal distance to each other.

[0039] Preferably, the lens enclosure 3 is made from metal, preferably anodized aluminum, glass and/or ceramics. Or at least the support areas 1, 2 are made therefrom; e.g. in case of a modular lens enclosure 3 as described above, the lens enclosure 3 can be a combination of different materials. These materials combine endurance with low friction or seen the other way round comparatively high sliding properties, which is advantageous for the self-centering.

[0040] FIG. 2 shows an objective 10 for a metrological camera in a cross sectional view (with the optical axis 5 lying in the image layer, i.e. a section along the optical axis 5). A preferred size of such an imaging measuring objective 10 is between 5 mm and 30 mm Thereby, the form factor of the objective 10 is comparatively small due to the combined arrangement of several stops in one lens enclosure as shown in FIG. 1 or FIG. 2.

[0041] In the example, the objective 10 comprises a first lens enclosure 3, a second lens enclosure 3′ and a third lens enclosure 3″ with conical support areas, each lens enclosure 3, 3′, 3″ enclosing multiple optical elements 11-12′ such as lenses, filters, aperture, diffractive optical elements (DOE). At least one of the optical parts is glass lens; plastic lenses in general do not fulfill the high demands of a metrological camera for industrial and/or geodetic measuring. Besides the conically enclosed optical elements, the measuring objective 10 may comprise additional optical elements with conventional enclosure/mount.

[0042] For mounting of the optical elements 11-12′, each lens enclosure 3, 3′ comprises multiple enclosing stops, wherein for better clearance only three of them are indicated in the figure (numbered 1, 2, 2a, inside the dotted frame). As can be seen, the first and second lens enclosures 3, 3′ are embodied as separate pieces, inserted in the objective's housing, whereas the third lens enclosure 3″, supporting optical elements 12a, 12b is an integral part of the housing or objective 10. That is, for instance support area 2a, supporting the optics 12a, is part of or in direct contact to the objective's main body.

[0043] As in principle described with respect to FIG. 1, the support areas 1, 2, 2a provided by the lens enclosures 3, 3′, 3″ are narrowing along the optical axis 5 according to the surface or envelope of a cone each. Two of these virtual cones 4, 4′ are indicated in the figure (cone 4 for the first enclosure 3, cone 4′ for the second enclosure 3′). Each cone 4, 4′ is a right cone with its central axis lying on the optical axis of the objective 10, whereby in the example, the cones 4 of the first lens spacer 3 are oriented opposite to the cones 4′ of the second lens spacer 3′.

[0044] Due to the design with tapered support areas 1, 2, 2a, the optical axis of respective optical element 11, 12, 12a, 11′, 12′ is aligned coaxially to the optical axis 5 of the objective 10 solely due to the provided self-centering support. That is, there is a self-centering of a respective optical element 1, 2, 2a such as a glass lens regarding shift (translation with respect to the optical axis 5) as well as tilt (inclination with respect the optical axis 5). Thus, the optical elements 1, 2, 2a are auto-aligned.

[0045] In the example, the objective 10 comprises fixation means 9 such as flexures, o-rings or spring elements with which a respective optical element 1, 2, 2a is fixed in its self-centered position/alignment. As shown, a fixation means 9 thereby is preferably embodied as a single, e.g. ring-shaped, element. Each optical element 1, 2, 2a may be fixed by its own fixation means 9 as shown or alternatively a fixation means 9 may fix more than one optical element 1, 2, 2a.

[0046] As another option, the fixation is free of play with direction of the optical axis and/or exactly adapted to the optical element/support area in such a way that a respective optical element is pressed onto the points of support in such a way that a lifting of the optical element 11-12′ is prevented, even in case of geometrical fluctuations or instabilities e.g. because of temperature change.

[0047] For instance, the fixation means 9 preloads a respective optical element 11-12′ with a force which is at least a hundred times the weight (gravitational force) of the respective optical element, typically in the range of 10N-20N, thereby preferably not exceeding a maximal force of 100N. As another option, the preload is lower than the maximum force occurring by temperature change induced deformation, e.g. dilation, of a respective optical element 11-12′ and/or a respective lens spacer 3-3″, thus avoiding any stress caused by different length/dimensional changes due to different CTEs of optical elements and lens enclosure/objective.

[0048] In the example, the two separate lens enclosures 3, 3′ are themselves supported self-centered by the objective 10. Here, they have an outer support area —one of which is marked in the figure by the dotted enclosing mark with reference number 13—which is narrowing along the optical axis 5, too. As indicated in the figure with “imaginary” cone 14, there are in addition to the inner cones 4, 4′ describing the support areas 1, 2, 2a for the optical elements outer cones 14 describing the support areas 13 for support of the lens enclosures 3, 3′ themselves.

[0049] Like the inner cones 4, 4′, the central axis of an outer cone 14 is coaxial to the optical axis 5 of the objective 10. Seen otherwise, the central axes of inner cones 4, 4′ and outer cones 14 are identical (however, their draft angles as well as the position of their apex and length can be different). Hence, the embodiment shown in FIG. 2 can be denoted or described as double-conical, providing a two-fold self-centering objective assembly, having a concentric (concentric at least within a tolerance of maximal 20 μm or in particular maximal 10 μm) inner and outer support area. Such an arrangement can be further extended e.g. by stacking multiple of such self-centering lens enclosures into each other.

[0050] FIGS. 3a, 3b show a cross-sectional view (with the optical axis 5 lying in the image layer) of a section of an objective for a metrological camera wherein only part of the lens enclosure 3 and of an optical element 11 is depicted.

[0051] FIG. 3a illustrates an arrangement as in principle described above. The support area 1 is narrowing along the optical axis 5, following the surface of a cone 4 with the cone's axis 6 being identical to the optical axis 5. Hence, there are points of support provided which—in the plain comprising the optical axis 5—are inclined towards the optical axis with an inclination angle being half the cone's draft angle α.

[0052] The counterpart, the optical element 11 in the example has a rectangular edge or contact area facing the support area 1. The resulting geometry between the lens enclosure 3 and the optical element 11 resp. between the support area 1 and the element's contact area provides a locally defined, in the example namely virtually punctiform or linear enclosure 16 of the optical element 11.

[0053] In the embodiment according to FIG. 3b, the arrangement is so to say the other way round. In this example, the lens enclosure 3 shows an edge whereas the contact area 15 of the optical element 11 is tapered. That is, the outer, circular surface of e.g. the glass lens 11 is—in parallel to the optical axis 5—shaped according to a cone 4, the cone's axis 6 again being identical to the optical axis 5. Hence, in this case, it is the optical element 11 where the area 15 to be supported is conically shaped.

[0054] Spoken generally, at least one side, either the support area 1 or the contact area 15, shows a cone (segment) 4. The other side facing the conical side needs not to be shaped conically but can have a different geometry. For instance, the side or area facing the conical side can be designed as a straight ring or three or more circumferential points of support.

[0055] Thus, in all cases the zone of contact between optical element 11 and lens enclosure 3 is reduced to limited area or even minimized to virtually a line (circle) or circumferential succession of points. Such a small or even minimal contact zone is particularly advantageous for self-centering support.

[0056] Optionally, there is an intermediate medium such as a coating, lubricant or bearing means in between lens enclosure 3 and optical element 11 whereby the medium is adapted in such a way that it does not disrupt or disturb the conical shape/geometry as such. An advantageous medium is for example hardening a respective contact area and/or makes the surface more flat/even/polished, therewith supporting self-centering. A roughness as low as 1.6 μm or 0.8 μm (Ra) or better of the contact or support surfaces, either with or without coating, is desirable.

[0057] Although aspects are illustrated above, partly with reference to some preferred embodiments, it must be understood that numerous modifications and combinations of different features of the embodiments can be made. All of these modifications lie within the scope of the appended claims.