IMAGE-ACQUIRING EQUIPMENT EQUIPPED WITH TELECENTRIC OPTICAL OBJECTIVE WITH PRIMARY CYLINDRICAL LENS

Abstract

An image-acquiring equipment with camera with linear sensor is described, having a telecentric optical objective whose main lens 23 is of the cylindrical type, placed in the same way as of the main lens of a known telecentric optics; the lens 23 can be of an a-cylindrical type, with profile computed for removing the cylindrical aberration; the optical assembly 13 for forming a real image 16 on the sensor 26 of the linear camera can be replaced with an optics of the photographic type, obtaining the best possible exploitation of the opening A of the main lens 23, greatly simplifying the construction of the telecentric optics; the image-acquiring equipment comprises a telecentric optics 27, a lamp 34 and a camera 24 of the linear or array type, and is pertaining to a viewing system for dimensional, geometric, or metrological checks.

Claims

1. Image-acquiring equipment adapted to acquire an image of an object (15, 37) lacking perspective parallax, said equipment comprising: a lighting apparatus (34); a handling system (38) of the object (15, 37); characterized in that it further comprises: a linear camera (24) equipped with a linear image sensor (26); a telecentric optical objective (27) composed of: an optical assembly (13) for forming a real image (16) of the object (15, 37) placed between the linear camera (24) and the object (15, 37); a diaphragm (20) placed between the optical assembly (13) and the object (15, 37), said diaphragm (20) having an opening (21); and a main lens composed of a cylindrical lens (23), placed between the diaphragm (20) and the object (15, 37) so that: an optical axis (AO) of the cylindrical lens (23), passing through the opening (21) of the diaphragm (20) and the optical assembly (13), orthogonally intersects a plane of the image sensor (26) in its central point; a cylindrical axis (AC) of the cylindrical lens (23) is orthogonal to the optical axis (AO) which is also the main axis of the image sensor (26).

2. The equipment according to claim 1, characterized in that said cylindrical lens (23) has at least one optical separating surface with an a-cylindrical shape, namely a shape different from the shape of a cylindrical surface with constant radius, computed in order to remove a cylindrical aberration of said lens (23).

3. The equipment of claim 1, further capable of generating the telecentric optical objective being composed of: a photographic objective for forming a real image of the object placed between the lighting source and the object, the photographic objective having a diaphragm with an opening; and the main lens composed of a cylindrical lens, placed between the photographic objective and the object, the cylindrical lens being of a bi-convex profile, wherein the internal profile of the cylindrical lens has an a-cylindrical shape, namely a shape different from the shape of a cylindrical surface with constant radius, while the external profile of the cylindrical lens is cylindrical, with such a radius as to maximize the distortion of the telecentric objective, so that: an optical axis of the cylindrical lens, passing through the photographic assembly, coincides with an axis of the lighting source; a cylindrical axis of the cylindrical lens is orthogonal to the optical axis.

4. The equipment according to claim 3, characterized in that said external profile (41) has also an a-cylindrical shape, and is computed so that the cylindrical lens (23) has a geometric distortion equal and contrary to the geometric distortion of the photographic assembly (33) for forming the real image.

5. The equipment according to claim 1, characterized in that said cylindrical lens (23) is composed of two or more cylindrical lenses to form an achromatic or apochromatic assembly.

6. The according to claim 1, characterized in that the optical assembly (13) for forming the real image (16) is composed of a photographic objective with fixed focus (33), which is applied to the body (25) of the camera (24) through a fitting (32), whose focus is chosen so that the resulting viewing angle (Phi) for the format of the sensor (26) covers at least 80% of the opening (A) of the main lens (23).

7. The equipment according to claim 1, characterized in that the optical assembly (13) for forming the real image (16) is composed of a photographic objective with variable focus (zoom), which is applied to the body (25) of the camera (24) through a fitting (32), wherein the range of focal lengths is chosen so that a viewing angle (Phi) which covers 100% of the opening (A) of the main lens is obtained.

8. The equipment according to claim 1, characterized in that the lighting apparatus (34) is made with luminous sources with narrow spectrum band.

9. The equipment according to claim 8, characterized in that the lighting apparatus (34) is made with LED sources with single color.

10. The equipment according to claim 1, characterized in that it has a viewing field greater than 300 mm.

11. The equipment according to claim 1, characterized in that it comprises at least one mirror (39) adapted to reduce the overall sizes of the equipment by a factor approximately equal to the number of used mirrors plus 1.

12. The equipment according to claim 11, characterized in that the mirrors (39) are of the type with first surface.

Description

[0038] These and other features of the present invention will clearly appear form the following description of some embodiments thereof, provided as a non-limiting example, with reference to the enclosed drawings, in which:

[0039] FIG. 1 is a schematic representation of a prior art telecentric objective;

[0040] FIG. 2 shows the main lens 23 of a cylindrical type according to the present invention in compliance with a first embodiment. Such embodiment provides that the cylindrical lens has an a-cylindrical profile for removing the cylindrical aberration; moreover, the lens 23 is composed of many elements adapted to reduce other forms of aberration, for example the chromatic aberration;

[0041] FIGS. 3, 4 and 5 show the operation of the invention as previously described;

[0042] FIG. 6 shows a further embodiment of the invention, comprising a photographic optics 33 of a known type as assembly for forming the real image 16 on the sensor 26 of the camera 24. The diagram comprises an adaptor fitting between connection of the optics 33 and the body of the camera 25;

[0043] FIG. 7 shows, as a non-limiting example, a generic apparatus for acquiring and processing images, known in the art as “viewing system”, which includes the invention, exploiting the property of producing images which are almost lacking a perspective parallax, to perform geometric, dimensional and metrological checks;

[0044] FIG. 8 shows, as a non-limiting example, a generic image acquiring and processing apparatus with wide viewed field. In such diagram, due mirrors with first surface have been inserted to fold the optical path in three sections and widely contain the size of the equipment comprising the invention; and

[0045] FIG. 9 shows, as a non-limiting example, an application of the optics of the invention as system for generating unidimensional collimated beams, suitable to be used in a 3D image-acquiring solution, with better performance with respect to known systems of this type.

[0046] The terms “mirrors with first surface” mean mirrors with a reflecting surface placed frontally, so that incident and reflected rays do not cross the glass which composes the mirror body.

[0047] It must be noted that in all Figures elements for supporting and bearing the drawn components have been omitted, both for more clarity of the drawings, and because the containing and supporting elements are not innovations with respect to the invention. It is anyway intended that supporting and containing elements are necessary for making the invention in practice, and that any skilled person in this field, with the benefit of all information included in the present description, would be able to practice the invention.

[0048] It is clear that, to the telecentric optics 27 with cylindrical lens 23 described here, modifications and/or additions of parts could be made, without thereby departing from the scope of the present invention.

[0049] It is also clear that, though the present invention has been described with reference to a specific example, a skilled person in this field will surely be able to make many other equivalent embodiments of telecentric optics having the features expressed in the claims and therefore all falling within the scope defined thereby.

[0050] FIG. 7 schematically shows a piece of equipment 35 for acquiring images of various types of pieces, placed in an industrial mass production environment. The equipment comprises the telecentric optics 27 of the invention, a lighting system 34, a belt-type transporting system 38, and a camera 24. Should the cylindrical lens 23 be of the simple type, the lighting 23 could be monochromatic of with narrow spectrum band, for example 40 nm, to obtain images lacking chromaticism and therefore sharper. Therefore, it will be advantageous to use illuminators with LED sources and with the emission of a single color, or based on fluorescent tubes with almost monochromatic emission (sodium, argon, neon, etc.). The belt brings the pieces 37 to move. Next to a certain advancement pitch of the belt 38, an encoder coupled therewith through a pulley (not shown) generates a train of pulses which drives the acquisition of as many image lines to the camera 24. The camera signal, containing the image lines shaped as a string of binary words (Byte), is taken to the RAM memory of a processor, through a communication port. The set of lines forms the digital image of the object 27. In such image the object appears lacking a parallax: therefore, by processing the image itself, it is possible to extract a series of measures of the piece 37, such as for example: number and position of the holes, diameter of each hole, piece sizes.

[0051] The use of the cylindrical lens 23 in making the invention is advantageous with respect to the prior art also in terms of reduction of the volume of the resulting telecentric optics, in particular along direction Y. The relative easiness with which it is possible to make a big-format cylindrical lens, for example with opening A equal to 1 meter, anyway makes the invention very big along axis Z, parallel to the optical axis in the diagram of FIG. 5.

[0052] In order to reduce the size along axis Z, plane mirrors can be used to fold the optical path a certain number of times, as shown in FIG. 8. For example, by using two mirrors, it can be possible to divide the optical path into three sections, strongly reducing the overall space size of the invention. Depending on the Applicant's experience, it is advisable to use first surface mirrors, to avoid forming halos and double images; moreover, it is advisable not to introduce more than three mirrors to prevent the degrading/attenuation of the image quality of the object which has to be acquired.

[0053] With reference to FIG. 9, the new optics shown therein can be used to generate perfectly collimated luminous lines, namely lines which are composed of a propagation of parallel light rays.

[0054] A known technique for 3D mapping images is based on the use of a generator of a luminous line, typically laser, and a camera which shoots, from a certain angle, the luminous line projected on the object to be 3D-mapped. Typically, the optical axis of the luminous line is normally incident on the object plane, while the optical axis of the 3D profile-acquiring camera is slanted by 20-40 degrees with respect to the normal line to such plane. In this case, an important prior art limit is the divergence of the luminous rays which form the luminous line. Due to such divergence, light is not able to reach the bottom of blind recesses 46 placed outside the optical axis; when moving away from the optical axis of the luminous line, luminous rays can reach the bottom of recesses (for example holes) less and less deep. FIG. 9 shows how the use of the optics of the invention allows obtaining the collimation of the luminous line in rays 45 parallel to the optical axis. Such rays can reach the bottom of a blind hole 46, forming the luminous line 47, independently from the hole depth and independently from its distance from the optical axis. On the other hand, it can be seen how, without the lens 23 of the invention, the divergent rays 44 produced by the luminous line generator 43 (composed of a light source 42 and of the optical assembly 33) are not able to reach the bottom of a similar blind hole.

[0055] If, in order to shoot the luminous line projected by the object to be 3D-mapped, an array camera is used, coupled with a further telecentric optics of the invention, blind recesses can also be mapped which have a high depth with respect to their diameter, for example holes with a diameter of 3 mm and a depth of 15 mm, which cannot be generally mapped with traditional 3D scanners. Therefore, the invention is capable of greatly improving known 3D scanning systems.