MX2008004245A - Digital image acquisition vision sensor - Google Patents

Abstract

A digital image acquisition vision sensor, wherein a television camera (2) defines a pickup axis (T), and a lighting device (4) associated with the television camera has a Fresnel lens (17) connected to the television camera so that the television camera is integrated with the lighting device, and the energy released by the lighting device is substantially coaxial with the pickup axis (T).

Description

VISION DETECTOR FOR THE COLLECTION OF DIGITAL IMAGES FIELD OF THE INVENTION The present invention relates to a vision detector for capturing digital images.

BACKGROUND OF THE INVENTION It is known that vision detectors constitute the detector element of artificial vision systems used for various purposes, such as, for example, to capture the number of license plates of vehicles, in video monitoring and security systems. , etc. The vision detectors generally include a television camera and a lighting device associated with the television camera to illuminate the area of the space that the television camera covers. The lighting device includes, in general, discrete LEDs or halogen spotlights with a filter. Known lighting devices have several disadvantages, including: • normally low efficiency; 52-498 normally, a considerable size.

SUMMARY OF THE INVENTION An object of the present invention is to offer a very efficient vision detector that allows to effectively illuminate the area of the space that the television camera covers. In accordance with the present invention, a detector is provided as described in claim 1.

BRIEF DESCRIPTION OF THE DRAWING The invention will be described below with particular reference to the attached drawing, which shows a detector in accordance with the teachings of the present invention.

DETAILED DESCRIPTION OF THE INVENTION The number 1 in the attached drawing denotes, as a whole, a vision detector for capturing a digital image. The detector 1 includes a commercial television camera 2 (in particular, a monochromatic camera) and a high intensity lighting device 4 integrated in the television camera 2.

The detector 1 also includes a protective cover 6 housing the television camera 2, the high intensity lighting device 4 and the electronic circuits 7 (shown schematically) that control the operation of the high intensity lighting device 4 and of the television camera 2. The power supply (not shown) of the detector 1 can be located both outside (as shown) and inside the detector 1. In the embodiment of the example shown, the television camera 2 has a cylindrical body 9 and a standard cylindrical objective lens 11 (for example, 25 mm) which is coaxial to the pick-up axis T. However, it is understood that the television camera 2 can take any form and include other objectives than the one shown. The high intensity lighting device 4 is located on one side of the cylindrical body 9 of the television camera 2 and includes: a light source 13 operating in the infrared range; a reflector device 15 having essentially a truncated cone shape adjusted to the light source 13 and having an axis S parallel to the axis T of the television camera 2, and a Fresnel lens 17 located opposite the reflector device 15 and to the obj et ivo 11. A Fresnel lens, as is known, is a flat convex lens that has several concentric rings staggered in the form of sections of convex surface that provide the same curvature of the light rays as that of a much thicker lens. The reflector device 15 is conveniently formed by depositing a metal (e.g., silver or gold) on the inner surface of a truncated or cup-shaped element 15t. More specifically, the light source 13 is defined by a matrix (e.g., a square or round matrix) of LED 19 operating in the infrared range and which is placed on a flat base 20 (e.g., a printed circuit ) perpendicular to the axis S. The LEDs 19 are arranged adjacent to each other so as to form, as a whole, a flat light source 13 located adjacent to a first end of the cup-shaped element 15t. In the illustrative mode shown, the lens Fresnel 17 has a flat circular perimeter, is perpendicular to the axes T and S and has an axis that coincides with the axis S of the light source 13. More specifically, the circular Fresnel lens 17 has a radius R; a free circular edge 22 extending beyond the points of intersection of the T and S axes with the lens 17 and a circular through hole 24 facing the objective lens 11, which is coaxial to the T axis and having a radius r, where r < R. The radius r of the opening 24 depends on the outside radius of the objective lens 11 used and its value is less than that. The cover 6 includes a cylindrical tubular body 26 having a Y axis parallel to the axes T and S and includes a first end portion 26a closed by a wall 27 transverse to the Y axis. The wall 27 is conveniently provided with various electrical connectors 28 communicating with the electronic circuits 7. The cylindrical tubular body 26 has a second end portion 26b closed by the Fresnel lens 17, whose free edge 22 rests on an edge of the tubular body 26, between which is interposed a ring of retention (arosello) 29. There is an infrared filter 31 located in front of the Fresnel lens 17, on the side opposite the light source 13, which is placed in an annular nut 33 screwed to the tubular body 26.

Already in use, when the LEDs 19 are energized, some of the rays emitted by the light source 13 directly reach the Fresnel lens 17, while others are directed towards the Fresnel lens 17 by the reflector 15. In fact, the flat light source 13 emits light at a solid angle whose magnitude is much greater than that of the angle subtended by the Fresnel lens 17 ( with respect to the light source 13). The reflector device 15 having a truncated cone shape recovers the rays emitted by the light source 13 that would otherwise be lost and reflects them again near the source, thus increasing its virtual dimension (the source plus the reflected image), but, above all, increasing the flow of energy to the lens. The flat light source 13 has only one point at the focus of the reflector device 15, so that, for known optical reasons, the rays strike the Fresnel lens at different angles of incidence. The Fresnel lens 17 allows to "straighten" the incident beam, in such a way that the rays coming out of the lens 17 travel essentially parallel to the axis S and, therefore, to the T axis of the television camera.

The television camera 2 is thus integrated into the lighting device 4 and the energy emitted by the lighting device 4 is essentially coaxial to the pick-up axis T. In fact, the spacing of the T and S axes is very small , normally 35 mm, but the infrared rays closest to the pick-up axis T are not more than 15 mm apart. The acquisition axis T of the television camera is thus placed closer to the flow of infrared energy emitted by the lighting device. The television camera 2 can also "see" through the opening 24 which is coaxial to the T-axis and which faces the objective lens 11, i.e., the light rays of the scene are seen by the sensitive element of the camera 2 through the opening 24 in the Fresnel lens. The flat light source 13 (i.e., the LED array) has a much smaller area A than the AF area defined by the perimeter of the Fresnel lens 17. In fact, the efficiency of the lighting device 4 increases as a function of the ratio AF / AL, where AL is the active area of the lighting device (ie, the area that includes the area of the flat light source 13 and the area of the reflected image). The vision detector 1 may also include an adjustment device 34 whose function is to adjust the distance (measured along the axis S) between the Fresnel lens 17 and the lighting device 4. The adjustment device 34 may allow, for example , the reversible linear movement of the light source 13 and the reflector device 15 with respect to the Fresnel lens 17, which remains fixed. The distance between the Fresnel lens 17 and the active area of the illumination device (the flat light source 13 plus the reflected image) defines the output angle of the energy flow. By increasing the distance between the lens Fresnel 17 and the active area reduces the beam's exit angle (the "collimated" beam) and by reducing the distance between the Fresnel lens 17 and the active area increases the beam's exit angle. In this regard, it should be noted that, in known devices using LEDs, the emission angle of the lighting device depends on the type of LED used and, therefore, can only be modified if a different type of LED is used. In a preferred embodiment, the filter 31 is of the high-pass type, the television camera 2 also has an internal low-pass filter (not shown) and the two filters act in combination to form a band-pass filter (band intern) whose central frequency is the frequency of the radiation emitted by the lighting device 4. The device according to the present invention has several advantages, among whare: maximum coupling of the capture axis T of the television camera 2 with the energy flow of the lighting device; the vision detector itself is extremely compact so that its visual impact is minimal; adjustment (by means of the adjusting device 34) of the angle of emission of the energy of the lighting device and • the possibility of supplying (within the cover 6) two or four lighting devices and their corresponding Fresnel lenses in order to obtain improved performance over very long distances (over 30 m).

Claims (9)

1. CLAIMS: 1. A vision detector that includes: a television camera (2) that defines a capture axis (T) and at least one lighting device (4) associated with the television camera; characterized in that the lighting device (4) includes a Fresnel lens (17) coupled to the television camera, such that the television camera is integrated to the lighting device and the energy emitted by the lighting device is essentially coaxial to the capture axis (T); the Fresnel lens has at least one through opening (24) which is essentially coaxial to the pick-up axis (T) and which is adjacent to the objective lens (11) of the television camera (2).
2. 2. A system according to claim 1, wherein the lighting device (4) includes a flat light source.
3. 3. A detector according to claim 2, wherein the flat light source is defined by an LED array.
4. A detector according to claim 2, wherein the flat light source (13) has an area (A) much smaller than the area (AF) defined by the perimeter of the Fresnel lens (17).
5. 5. A detector according to claim 2, wherein the lighting device (4) also includes a reflector device (15) which is interposed between the flat light source and the Fresnel lens.
6. 6. A detector according to claim 5, wherein the truncated cone-shaped reflective surface of the reflector device has a first free end facing the flat light source and a second free end facing the Fresnel lens (17).
7. 7. A detector according to claim 2, wherein the Fresnel lens (17) has an axis that coincides with the axis (S) of the light source. A detector according to claim 1, wherein the adjustment means (34) is provided to adjust the distance between the Fresnel lens (17) and the lighting device (4). A detector according to claim 1, wherein in front of the Fresnel lens (17) a first external filter (31) is provided, where the television camera (2) has a second internal filter and where the two filters act in a combined manner for forming a bandpass filter whose center frequency is the frequency of the radiation emitted by the lighting device (4).