WO1996003002A1

WO1996003002A1 - Device for viewing a field located within a hostile area subjected to strong nuclear radiation

Info

Publication number: WO1996003002A1
Application number: PCT/FR1995/000970
Authority: WO
Inventors: Jean-Claude Thevenin
Original assignee: Commissariat A L'energie Atomique
Priority date: 1994-07-20
Filing date: 1995-07-19
Publication date: 1996-02-01
Also published as: EP0771503A1; CA2193662A1; FR2722932B1; FR2722932A1; JPH10503334A

Abstract

Device for viewing a field (1) located within a hostile area (H) subjected to strong nuclear radiation from a radiation-protected accessible area (A). The device includes image-capturing means (5-9-13) for forming, within a hostile area, successive images of a plurality of field locations to be observed; at least one transmitting optical fiber (3) with an input side (3a) in the hostile area and an output side (3b) in the accessible area, for carrying the image of each field location from the hostile area to the accessible area; and field image processing means (15) located within the accessible area. The device of the invention is designed for viewing inside hostile environments.

Description

DEVICE FOR VIEWING A FIELD LOCATED

IN A HOSTILE AREA

SUBJECT TO STRONG NUCLEAR RADIATION

DESCRIPTION

Technical area

The invention relates to a device for viewing a scene located in an area subjected to intense nuclear radiation. It finds an application in the field of vision in a hostile environment and, in particular, in the nuclear field. It can also be used for observations in inaccessible and / or remote areas and, especially, when access to these areas leads to maintenance difficulties.

State of the art

In the nuclear field, notably for the reprocessing and dismantling of nuclear material, man cannot intervene directly in the hostile zone because of the intense nuclear radiation which reigns in this zone. Also, to visualize scenes in such an area, it is known to use, in general, devices provided with electronic tubes for taking pictures (for example tubes of the Vidicon type) because, under intense nuclear radiation, the systems of Current electronic vision is too disturbed to provide usable images. Indeed, the radiation undergone by the devices used can reach an energy dose of the order of 10 to 100 kGy. Electronic systems, such as consumer cameras comprising detectors on silicon of the charge transfer detector (CCD) type, do not support more than about 100 Gy.

However, although resistant to strong radiation, when subjected to such doses of energy the Vidicon electronic picture tubes must be changed very frequently. It is therefore usual to choose very good quality tubes to allow the longest possible duration of use, but which cannot however exceed a few tens of hours. However, such Vidicon tubes have a high cost; the system using these Vidicon tubes therefore has the disadvantage of being very expensive.

Another method is to use Vidicon tubes of lower quality, and therefore lower cost, and to change them even more frequently. The disadvantage of this method is that it is also expensive, due to the high maintenance costs.

In addition, today, the development of Charge Coupled Divice (CCD) devices, made up of a detector mosaic on silicon and used in camcorders and in current electronic cameras, is increasing considerably. Also, electronic tubes for taking pictures are more and more competed by these devices in silicon technology, whose performance in spatial resolution and speed are constantly improving. This strong competition leads to the disappearance of certain types of electronic shooting tubes and to higher and higher tube manufacturing costs due to the decrease in demand. Their manufacture may even, in the medium term, cease. Statement of the invention

The object of the present invention is precisely to remedy these drawbacks. To this end, it offers a display device for a field located in a hostile area; this device is arranged partly in a hostile zone and partly in an accessible zone, the elements located in a hostile zone being chosen so as to be able to withstand intense nuclear radiation. These elements are essentially optical elements and mechanical elements controlled from the accessible area.

More specifically, the invention relates to a display device for observing a field located inside a hostile area subjected to strong nuclear radiation, from an accessible area protected from this radiation. This device is characterized by the fact that it comprises: - image taking means capable of forming, in a hostile area, successive images of a plurality of points of the field to be observed; at least one optical transmission fiber having an entry face in a hostile area and an exit face in an accessible area and which ensures the transport of the image of each point of the field from the hostile area to the accessible area; and

- means for processing field images, located in an accessible area. Advantageously, the image-taking means comprise, in the hostile zone, deflection means able to deflect successively each point of the field to be observed, as well as focusing means capable of focusing each of these points, deflected by the deflection means, on the entry face of the optical transmission fiber.

According to the invention, the deflection means comprise at least first and second mirrors for deflecting each image, respectively, along the X axis and along the Y axis. These mirrors are mobile, each actuated by a galvanometric system.

According to one embodiment of the invention, the image taking means comprise at least one position detector associated with each mirror to control the position and the mobility of this mirror.

The position detectors associated with each mirror can be connected to their respective mirror by at least one optical fiber; in this case, the detectors are then placed in the accessible area.

According to the invention, the focusing means comprise at least one converging lens, capable of directing the deflected image in X and in Y, towards the entry face of the optical transmission fiber.

According to one embodiment of the invention, the optical fibers are fibers with a silica core that can withstand a dose of radiation greater than 10- "Gy.

According to one embodiment of the invention, the device can comprise a plurality of optical fibers whose input faces are close to each other in the plane of the image and filtered in wavelength at their outputs to ensure a reconstruction of a color image of the field to be observed. Brief description of the drawings

The single figure schematically represents the preferred embodiment of the display device under intense nuclear radiation, according to the invention.

Detailed description of embodiments

There is shown in the figure, a device for viewing remotely a field 1 located in a hostile zone H subjected to strong nuclear radiation. According to the invention, the field 1 to be observed can be viewed from the accessible zone A, that is to say the zone which is not subjected to nuclear radiation.

The invention consists of a device comprising image taking means which are capable of scanning the field 1 to be observed in order to successively form the image of each point of the field 1 on the input face of an optical fiber. 3. This optical fiber 3 transports each of these images from the hostile zone H where the images were formed to the accessible zone A where these images will be processed. Deflection means therefore make it possible to successively project the points of the field 1 to be observed on the input face of the optical fiber 3. By synchronization of two mirrors 9 and 5 in X and Y, one of which performs rapid scanning and the other a slow scan, we obtain a video type scan. The modulation of the light, leaving the fiber in the accessible area, is therefore directly transposable into a video signal which can be synchronized with the frequency of oscillation of the mirrors and the information supplied by detectors (12 and 8) for position of the mirrors.

More precisely, the image taking means comprise, in the hostile zone H, deflection mirrors 5 and 9. According to the embodiment shown in the figure, the deflection mirrors are two in number:

- the mirror 5 which deflects the images of the field 1 along the Y axis; and

- the mirror 9 which deflects the images of the field 1 along the X axis.

These mirrors 5 and 9 consist of a polished metal plate or a glass plate covered with a reflective metal deposit. Such mirrors therefore do not have any particular sensitivity to radiation and can therefore be used without risk in hostile zones H. Each of these mirrors 5 and 9 is associated with a galvanometric oscillator, respectively 7 and 11, by the intermediate of a support rod, respectively 6 and 10.

Each galvanometric oscillator 7 or 11 comprises a coil, a permanent magnet and a soft iron for closing the field lines, these elements not being shown in the figure by way of simplification of this figure. They are also described in the commercial notices entitled "M3 Series Optical Scanner with Driver" and "Moving Magnet Optical Galvanometer Scanners, A New Génération" from GENERAL SCANNING INC.

The galvanometric oscillators 7 and 11 therefore make it possible to subject the support rods 6 and 10 to rotations which each have one end fixed in said galvanometric oscillators 7 and 11 and another end fixed to the mirrors 5 and 7. These mirrors 5 and 7 are thus actuated by the galvanometric oscillators, respectively, 7 and 11.

The mobility of the mirror 5 in the direction of the arrow shown around the rod 6 therefore allows a deflection in the Y direction of the images of the field 1 captured by said mirror 5.

At the same time, the mobility of the mirror 9, in the direction of the arrow shown around the rod 10, therefore allows a deflection in the X direction of the images deflected at Y by the mirror 5 and captured by said mirror 9.

Dashed dashed lines have been represented in the figure to indicate the trajectory of the light signals representative of the images of the field

I to the mirror 5, then to the mirror 9 and finally to the input face 3a of the optical fiber 3.

The galvanometric oscillators comprising only mechanical parts or electrically conductive parts (namely the winding), they do not have any particular susceptibility to nuclear radiation. However, in order to ensure that the coils retain, despite time and radiation, all their properties, inorganic materials will preferably be used as the coating insulator for the coils, and especially as the support cores for the wires of the winding. such as silica and alumina. It is however possible to choose a winding wire coated with an organic resin; in this case, a coil with non-contiguous turns is used, which makes it possible to compensate for any deterioration in the insulation properties of the coating material.

Such galvanometric oscillators 7 and

They can therefore be safely placed in a hostile H zone. The image-taking means furthermore comprise position detectors 8 and 12 associated, respectively, with the mirrors 5 and 9. These position detectors 8 and 12 make it possible to precisely control the movements of the mirrors 5 and 9 and, more precisely, the position of each mirror at each oscillation, as well as the scanning frequency of these mirrors. A control of the scanning frequency is, in fact, necessary since it can vary as a function of the temperature variations which may take place in the hostile zone H.

More precisely, for the synchronization of the mirrors and for the precision of localization of the points of the object field, it is important to have a reference for the position of the mirror. To do this, a light source and a detector are used which are designed so that there is only one position of the mirror for which the light coming from the source is reflected towards the detector. The corresponding received signal gives temporal information of the position of the mirror. For example, if the frequency of oscillation of the mirror varies with temperature, the time between two signals varies. We can then carry out an electronic correction to restore the frequency to its initial value.

According to an embodiment of the invention, not shown in the figure, the position detectors 8 and 12 are of the optical type. They each include a light emitting diode, a receiver (for example a PIN diode) and a control system. Certain types of light-emitting diodes and receivers and their associated electronic control can thus have a good resistance to radiation. They can indeed withstand a radiation dose of around 10 ^ Gy and therefore be placed in a hostile H zone. According to a variant of the invention, the display device may further comprise lighting means located in accessible area A. According to a first embodiment of this variant, the light is introduced through the exit face of the optical fiber 3 used for image transport which sends it to the hostile zone H. This solution is elegant and simple to operate; however, it can impose significant constraints on stray light.

According to a second embodiment of this variant, two identical and synchronized assemblies are used; one of them ensures the lighting of the field to be observed, while the other allows the observation of the field thus lit. In this latter embodiment, additional mirrors are placed in hostile zone H to direct the light beams emitted by the lighting systems to illuminate the field to be observed.

In accordance with the invention, the image taking means comprise a focusing system 13 making it possible to focus the light signals picked up by the mirror 9 (and which correspond to deflected images in X and in Y) on the input face 3a of optical fiber 3.

According to the embodiment shown in the figure, the focusing system 13 consists of a converging lens made of silica and having a fairly good resistance to nuclear radiation.

According to another embodiment, the focusing system 13 consists of a doublet corrected for longitudinal chromatic aberrations. In any case, since the lens glass can be very thin, the possible influence of radiation on the behavior of the lens 13 could only be negligible since the effects of yellowing of the glass on the images passing through the lens 13 , correspond to a small thickness crossed.

According to one embodiment of the invention, the focusing system 13 can be mounted on a support mechanism which provides this focusing system with a certain mobility by which the system can be brought into focus. The movable part of the support mechanism is controlled by a motor which can either be fixed to this mechanism, or arranged in accessible area A and connected to the support mechanism by a flexible system resistant to radiation.

Following the scanning of the field 1 to be observed, carried out line by line by the mirrors 5 and 9, there is obtained, at the output of the focusing means 13, a modulated time signal representative of the image of this field 1. It is this signal modulated time which is transported from the focusing means 13 to the accessible area A via the optical fiber 3.

According to one embodiment of the invention, several optical fibers are used, of the same type as optical fiber 3 and associated with this optical fiber 3 in the image plane of the focusing system 13 to allow a trichromatic vision of the field 1 to be observed .

According to the invention, image processing means 15 are placed in accessible area A, at the end of the optical fiber (s) 3. These processing means 15 acquire the modulated time signals transmitted by the optical fiber (s) 3, then their processing to transform them into images.

Being arranged in accessible zone A, these processing means 15 may comprise conventional elements having a resistance to nuclear radiation quite ordinary. These elements are therefore, advantageously, electronic or optoelectronic elements such as those found in commerce.

More precisely, the processing means 15 comprise a fast and highly sensitive detector 15a. This detector 15a can be a photodiode or else a photomultiplier such as 1OPT08® sold by the company HAMAMATSU.

These processing means 15 further comprise a mixer capable of homogenizing the distribution of the photons on the detector 15a.

In accessible area A, there are also means for controlling the mobile elements located in hostile area H. These control means include the position detectors 8 and 12 described above when these are connected to the mirrors 5 and 7 by fibers optics 8a and 12a. They further comprise a system for controlling the focusing of the focusing system 13, in the embodiment where this focusing system is mobile.

We will now describe an example of application of the device of the invention. In this example, the optical fiber 3 for transmitting image information is an optical fiber with a core diameter of 50 μm. The focusing system 13 is a lens having a focal length of 50 mm, which makes it possible to obtain, in the field space, a resolution of 1 mm to 1 m. A scan making it possible to obtain approximately 720 points per line corresponds to an equivalent quality, if not better than that of the image coming from a CCD camera. We can notice that this scanning corresponds to a field angle of + _ 20 ° and to the large dimension of a shooting in 24 x 36 mm format

(classic format in photography) with a lens of

50 mm focal length. The object field corresponding to one meter, is 720 mm in its dimension corresponding to the lines. This line scanning, which is the fastest, and therefore the most difficult to carry out (compared to the column scanning), is carried out by means of a synchronous galvanometric mirror (reference 9 in the figure), operating at 5 kHz for an angle of deviation of + 30 °. The sinusoidal variation of the speed of rotation of this mirror in the field to be observed by + _ 20 ° causes a variation in brightness of the signal of 50% between the center and the edge of the image. This variation in brightness can be compensated by electronic means and, in particular, by varying the polarization voltage of the detector.

The light signals corresponding to the images of field 1 deflected in Y and in X by the respective mirrors 5 and 9 are therefore focused by the lens 13 on the input 3a of the optical fiber 3 whose role is to transport these light signals from the hostile zone H towards the processing means 15 located in accessible zone A. Thus, only these elements located in hostile zone H must be chosen so as to have good resistance to radiation. In particular, the optical fibers 3, 8a and 12a are chosen from types of optical fibers capable of supporting a radiation dose of at least 10 ⁶ Gy. All the elements located in accessible zone A are, on the contrary, entirely conventional. Such a device therefore does not require significant maintenance, in particular for equipment located in hostile zones. This design allows for greatly reduced maintenance costs, which results in particularly advantageous overall operating costs.

Claims

1. Display device for observing a field (1), located inside a hostile area (H) subjected to strong nuclear radiation, from an accessible area (A) protected from this radiation, characterized in that it comprises :

- means (5-9-13) for taking images capable of forming, in a hostile zone, successive images of a plurality of points of the field to be observed; at least one optical fiber (3) for transmission having an entry face (3a) in a hostile zone, and an exit face (3b) in an accessible zone and which ensures the transport of the image of each point of the field (1 ) from the hostile zone to the accessible zone; and

- processing means (15) of the field images, located in an accessible area.

2. Display device according to claim 1, characterized in that the image taking means comprise, in the hostile zone, deflection means (5-7, 9-11) capable of deflecting successively each point of the field to observe, as well as focusing means (13) capable of focusing each of these points deflected by the deflection means on the input face of the optical transmission fiber.

3. Display device according to claim 2, characterized in that the deflection means comprise at least first and second mirrors (9, 5) for deflecting each image, respectively, along the X axis and along the Y axis .

4. Display device according to claim 3, characterized in that the mirrors are mobile, each actuated by a galvanometric system (11, 7).

5. Display device according to claim 3 or 4, characterized in that the image taking means comprise at least one position detector (12, 8) associated with each mirror to control the position and the mobility of this mirror.

6. Display device according to claim 5, characterized in that each position detector is connected to a mirror by at least one optical fiber (12a, 8a), said detector then being placed in the accessible area.

7. Display device according to any one of claims 3 to 6, characterized in that the focusing means comprise at least one converging lens capable of directing the deflected image in X and in Y towards the entry face of the optical fiber transmission.

8. Display device according to any one of claims 1 to 7, characterized in that the optical fibers are fibers with a silica core which can withstand a dose of radiation greater than 10 ° Gy.

9. Display device according to any one of claims 1 to 8, characterized in that it comprises a plurality of optical fibers having neighboring input faces, and outputs filtered in wavelength to ensure a reconstruction of 'a color image of the field to be observed.