FR2506953A1 - Infrared beam barrier surveillance system - comprises conical reflector collecting radiation from wide angle for IR sensitive diode - Google Patents

Abstract

The infra-red detector is intended for use with an infrared beam forming a barrier, the interruption of which indicates the presence of a person or object. The IR sensitive element - a diode (4) -is placed at the apex of a conical reflector (2). The inside surfaces of the reflector are highly polished, and shaped so that any radiation incident on the mouth of the cone reaches the detector after a few reflections. The cone may be folded, so that is mouth opens in a direction at right angles to that in which the detecting element faces. In this case the inside surface of the outside of the elbow (13) is also highly reflecting. The detector is not as sensitive to atmospheric variations as other radiation focussingdetectors.

Description

Optical receiving system for infrared barrier.

 The present invention relates to protection and monitoring devices of the infrared barrier type and relates to an optical reception system for such a device.

 The infrared barriers include a transmitting system and a receiving system. The emission comprises an infrared emitter, generally a diode, and an optic to form a parallel or slightly divergent and rectilinear beam oriented towards the receiving system. The latter generally comprises a lens at the focus of which is placed a receiver, generally a diode or a phototransistor.

 The position and orientation of the receiver system must be made with great precision, the greater the greater the distance between the transmitter and the receiver. With a slight defect in orientation, the infrared rays incident on the input lens converge in the focal plane, but at a point outside the focal point, the receiving element is not touched and the system does not work. It can also occur that the rays have a non-rectilinear path due to atmospheric diffraction, and that the angle of incidence on the receiving lens is not normal, even if this lens is correctly oriented. In this case too, the rays converge at a point distinct from the focal point, and the reception is poor. Finally the orientation of the transmitting beam can be incorrect, or the receiver badly placed, and the rays strike the receiving lens on marginal areas, and the rays, due to the aberrations can be concentrated at a point distinct from the focal point, where the intensity of the radiation reaching the focal point may be insufficient, and in this case again, the device does not work.

 The object of the invention is to propose an optical reception system which eliminates the above drawbacks, and which allows reliable reception with simple adjustment, even with poor atmospheric conditions.

 According to the present invention, the optical reception system for infrared barrier comprises an element sensitive to infrared radiation, such as a diode, arranged at the top and inside a horn-shaped sensor, having a generally conical shape. lined with a reflective coating on its interior surface.

 Any incident ray entering the opening of the conical surface will therefore reach the element sensitive to infrared rays by one or more reflections, whatever the angle of the incident ray. The device thus produced has been shown to be more sensitive and more effective than the conventional lens device.

 Other characteristics of the invention will appear during the description which follows, given by way of nonlimiting example, with reference to the attached drawing and which will make it very clear how the invention can be implemented.

In the drawings:
FIG. 1 is a sectional view of a receiver according to the invention and,
FIG. 2 is a view along arrow F in FIG. 1.

 The device of the invention, the main part of which (in the sense of the novelty) can be designated "concentration cone" is part of an assembly comprising an infrared transmitter, an appropriate receiver, means for processing received signals, and means for triggering an alarm or other signals.

 According to the invention, the receiver consists of a horn or the like, of generally conical or pyramidal shape, the internal surface of which is reflective, and the element sensitive to infrared rays is placed at the top inside.

It is thus conceivable that any ray passing inside the opening perimeter of the horn will reach if necessary after one or more reflections to the sensitive element. The internal reflecting surface can thus be a cone or a pyramid, but can also deviate from such a surface and present a curvature or angles (dihedrons) provided that the section of the horn narrows down to the sensitive element in concentrating the rays towards the top of the horn.

 To reduce the size, for a given collection surface, the horn can be folded or bent, like a prismatic binocular.

 In the figures, an infrared receiving diode is placed at the top inside a folded horn 2 (it could be curved like a trumpet horn). The horn has an opening section 3, delimited by the edges of four walls 4, 5, 6 and forming a trunk of a pyramid. The walls 6 and 7 can be parallel or flared like the other walls 4 and 5. The horn ends with four walls 9, 10, 11 and 12 forming a pyramid whose apex is occupied by the receiving diode 1. An intermediate face make 13 can be inserted to encourage reflections by limiting the number and avoiding the exit of an incoming ray. All of the faces 4, 13, 10 could for example be replaced by a continuous curved surface.

 It is obvious that the number of faces, or curved surfaces is not limiting, the principle being that the device operates in the manner of a horn, straight, bent and curved.

 The internal surfaces are treated to be reflective, which does not require any particular comment.

Claims (3)

1 / Optical reception system for infrared radiation barrier comprising an element (1) sensitive to infrared rays, in particular of the diode type, characterized in that the sensitive element is placed internally at the top of a horn-shaped sensor (2) whose interior surface is treated to be reflective. 2 / System according to claim 1, characterized in that the sensor (1) in the shape of a cone, the sensitive element (1) being placed internally at the top, the outline of the base of the cone can be polygonal, circular , oval or other. 3 / System according to one of claims 1 or 2, characterized in that the horn (1) has at least one curvature, a fold, an elbow or an angle, in order to reduce the size for the same opening section.