Abstract:
An installation formed of several independent groups is proposed to demolish structures such as buildings, bridges, materials, etc., in particular eliminating any risk of accidental firing. Each group comprises a control unit ( 10 ) with several outputs ( 18 ) including at least one laser source ( 16 ), pyrotechnic initiators ( 12 ) with optical control, and optical fibers ( 14 ) connecting the outputs ( 18 ) of the control unit ( 10 ) to the initiators ( 12 ). Laser sources ( 16 ) may be either laser diodes, or sources with a pumped solid rod operating in relaxed mode.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention concerns an installation designed for demolition or destruction of constructions, such as buildings, industrial buildings, bridges, rock and in general, any natural structure or constructed structure (buildings, public works, underground works, quarries, etc.) wherein the demolition of destruction of the constructions is accomplished using explosives. 
     2. Discussion of Background 
     When constructions, bridges, materials, etc., are destroyed using explosives, a large number of small explosive charges are placed in holes drilled in the structures of the works to be demolished. 
     At the present time, these small charges are primed by medium or high intensity electrical detonators that are electrically fired by means of firing apparatus. 
     More precisely, in order to limit nuisances such as vibrations, blast, noise, etc., the global explosion is broken down into a multitude of small explosions which occur at specific time intervals. 
     Electric detonators with micro-delays are usually used for this purpose and are grouped in series (for example twenty units). A time interval (for example 25 thousandths of a second) is provided between each detonator in the same series. 
     Sequential type exploders are also usually used, in which several lines of detonators are fired at time intervals. Several sequential firing apparatuses may then be coupled. 
     When designed to demolish a residential building, existing installations operating according to the above stated principle comprise 1500 to 2000 detonators for each firing. Firing may last for 3 to 4 seconds, due to the spacing of explosion initiated by the installation. This firing takes place after preliminary work to install charges and primers which may last for 3 to 4 days, or even a week. 
     With current installations, accidental priming or failures may occur throughout the duration of the prior work to install charges and primers. 
     The main risk of accidental ignition is due to stray currents that may occur around primed charges. These stray currents may originate from a number of causes, such as lightning, currents originating from overhead or underground electrical networks, currents originating from nearby electrical installations in operation (electrical transformers, e.g., railway or tramway catenary lines, lights, etc.), and natural currents circulating underground when boring tunnels. 
     Charges may also be fired accidentally due to the use of electronic devices, such as radios, walkie-talkies, portable telephones, etc., in the vicinity of these charges. 
     Accidental firing of the detonators may also occur during transport or during storage, for example, due to stray currents or accidents of various types. 
     Since the drilling work may last for 3 or 4 days or even a week, there is also a risk that the previously installed charges may be fired mischievously by means of a simple electric battery. 
     Furthermore, when the construction to be demolished concerns the nuclear industry, as is particularly the case for demolition of a nuclear power station, existing demolition installations cannot be used at the time of firing due to disturbances that exist in an intense radioactive environment. 
     Existing electrically fired demolition installations are also affected by failures that can affect the demolition work. One particular cause of these failures is broken electric wires or wires in contact with metal structures, such as protective grills, metal equipment in buildings to be demolished, etc. When the construction to be demolished is a large metal structure, such as a thermal power station, failures may also be caused by electric fields produced by the enormous mass of steel in the building. 
     Furthermore, electric detonators used in existing demolition installations may be stolen and easily reused, both during their transport or storage, and after being installed in the construction to be demolished. 
     Finally, note that when there are any problems in the circuits of this type of demolition installation, these problems are frequently very long and dangerous to detect. It is easy to find out which line is defective, but it is impossible to know the exact location of the break in the circuit. 
     SUMMARY OF THE INVENTION 
     The purpose of the present invention is a demolition installation, the original design of which enables it to eliminate all disadvantages of existing electrically controlled installations, and in particular, eliminates all risks of accidental or mischievous firing both during work to install charges and priming operations, and during prior storage and transport of components of the installation. 
     According to the present invention, this result is obtained by means of a demolition installation characterized by the fact that it comprises at least two independent groups, each including: 
     a control unit with several outputs, each comprising at least one laser source and at least one control switch for the said laser source, in which closure will cause the laser source to emit a laser beam at one or more of the said outputs; 
     optically controlled pyrotechnic initiators placed at determined locations in the structure to be demolished; and 
     optical fibers connecting each of the pyrotechnic initiators to one of the outputs of the control unit. 
     In an installation designed in this way, pyrotechnic initiators are only fired optically through the optical fibers. Therefore, firing is absolutely independent of stray currents. This procures optimum safety, particularly when the construction to be demolished is located in or close to electrical substations or under catenary lines. Furthermore, stormy weather has no influence on the work progress or safety. 
     The characteristic mentioned above also means that constructions located in large urban centers can be demolished at no risk, despite the large amount of electronic equipment present in these centers. 
     Furthermore, firing triggered by mischievous persons is impossible, since these persons would need a laser and the laser will have to be compatible with the precise frequency of the laser used in the installation. 
     Since firing is controlled optically, ignition cannot be disturbed by any metal mass. Safety during transport and during storage of components is also guaranteed. 
     Furthermore, optically controlled detonators cannot be used if they are stolen. 
     Finally, a computer can easily be used to determine the location of a break in the optical fibers. 
     In a first embodiment of the present invention, the laser sources are sources with a pumped solid rod operating in relaxed mode. Each control unit then comprises a single laser source and an optical divider coupler with an input that can receive the laser beam emitted by the laser source and several outputs forming control unit outputs. 
     Some or all of the optical fibers in each group then connect several pyrotechnic initiators to one of the outputs of the control unit through at least one second optical divider coupler. 
     Advantageously, each control unit comprises a secondary input and feedback means capable of aiming an additional laser beam penetrating into the control unit through its secondary input, towards the input of the optical divider coupler. A supplementary laser source common to all groups is then provided, so that the supplementary laser beam can be emitted whenever necessary following a failure of the laser source in one of the control units. 
     Each control unit may thus include an auxiliary control input and second feedback means capable of setting up a bypass optical path between the auxiliary input of the control and the input of the optical divider coupler for this control unit. In particular, this arrangement means that the integrity of optical fibers can be checked using a visible light source placed in front of the auxiliary control input. 
     Each control unit preferably comprises a retractable shutter that may be placed between the laser source and the input of the optical divider coupler. 
     The second feedback means are formed on this retractable shutter when it occupies an active shutter position. 
     Each control unit may also include a safety switch mounted in series with the laser source control switch. 
     In a second embodiment of the present invention, the laser sources are laser diodes. Each control unit then includes one laser diode for each output, and each laser diode is optically connected to one of these outputs. 
     In this second embodiment of the present invention, each laser diode may be installed in series with a distinct control switch in each of the control units. In this case, a common safety switch is installed in series with all laser diodes in each control unit. 
     As a variant, laser diodes in each of the control units form a matrix containing n rows and m columns, the laser diodes in each row being installed in series with a first control switch and the laser diode outputs in each column being connected to a second control switch. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING FIGURES 
     We will now describe various embodiments of the present invention using non-restrictive examples, with reference to the attached drawings in which: 
     FIG. 1 diagrammatically shows an installation for demolition of constructions, illustrating a first embodiment of the present invention; 
     FIG. 2 diagrammatically shows the constituents of one of the control blocks of the installation in FIG. 1; 
     FIG. 3 is a diagrammatic view comparable to FIG. 1, illustrating a second embodiment of the present invention; 
     FIG. 4 is a view that diagrammatically shows a first possible construction of the control unit in the installation in FIG. 3; and 
     FIG. 5 is a view comparable to FIG. 4, diagrammatically illustrating a variant of the second embodiment of the control unit used in the installation in FIG.  3 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the first embodiment of the present invention illustrated in FIGS. 1 and 2, the demolition installation comprises several completely independent groups. However, each of the several independent groups includes a control unit  10 , a number of pyrotechnic initiators  12  with optical control, and optical fibers  14  each connecting pyrotechnic initiators  12  to one of the outputs  18  from the control unit  10  of the corresponding unit. 
     FIG. 1 only shows two independent groups in a demolition installation according to the present invention. In practice, the number of independent groups in the installation is not limited and may be any number greater than or equal to 2. By convention, the number of independent groups in the installation will be denoted K. 
     Each control unit  10  in this case comprises a single laser source  16 , composed of a laser source with a pumped solid rod operating in a relaxed mode. In other words, without triggering using, Pockets cells or any other similar means. The characteristics of this type of laser source are such that a relatively long pulse stream (about 150 μs) is capable of outputting an instantaneous power on the order of several tens of optical kilowatts. 
     This power level of laser sources  16  makes it possible to divide the laser beam, successively inside each control unit  10 , and then possibly beyond this control unit. 
     Inside each of the control units  10  as illustrated more precisely in FIG. 2, the laser beam is divided by a first optical divider coupler  22 . This first optical divider coupler  22  has a single input located on the optical path of the laser source  16 , which receives the laser beam sent by this source. The optical divider coupler  22  also includes N outputs forming the outputs  18  from control unit  10 . 
     In practice, the number of outputs  18  in each control unit  10  is between, for example, four and twelve. Note that the number of outputs  18  from control units  10  in each group may be identical or different in different groups, without going outside the scope of the invention. 
     As shown diagrammatically but only partially in FIG. 1, the optical fibers  14  are used to connect each output  18  from control unit  10  depending on the case, with one or several pyrotechnic initiators  12  for the group considered. 
     Thus, the top of FIG. 1 shows the case of a pyrotechnic initiator  12  in which the optical input is directly connected to one of the outputs  18  of the corresponding control unit  10  through an optical fiber  14 , without any device having been placed on the path of the optical fiber. 
     On the other hand, all other links shown between the outputs of the control unit  10  and the optical inputs of the pyrotechnic initiators  12  are designed to connect several pyrotechnic initiators  12  to the same output  18 . Consequently, second optical divider couplers  20  are placed between the outputs  18  concerned and the initiators  12  that will be connected to these outputs. 
     More precisely, each of the second optical divider couplers  20  has a single input which is connected to one of the outputs  18  from the corresponding control unit  10  through a first optical fiber  14  and several outputs, each of which is connected to one of the pyrotechnic initiators  12  through a corresponding optical fiber  14 . 
     The second optical divider couplers  20  used in the installation may all be identical or may be of different types. Their number of outputs may be, for example, between 4 and 12. 
     When choosing the number of outputs in the divider couplers  22  and  20 , care must be taken to ensure that the power and the energy transferred to each pyrotechnic initiator  12  is sufficient for firing. The power and energy transferred depend on the characteristics of the laser source  16  contained in the control unit  10  and the total attenuation resulting from putting several divider couplers in cascade on the channel(s) considered. 
     This observation is confirmed by the approximate expression of the power PD (in dB ω ) available for any initiator  12 , which is given by the following formula in the case of a group comprising a control unit with N outputs  18  and a second optical divider coupler  20  with M outputs inserted between one of the outputs of the control unit  10  and the pyrotechnic initiator  12  considered          PD   =     PS   +     10                 log                   1   N       +     10                 log                   1   M       +   ∑       ,                          
     where 
     PS is the power output by the laser source (in dB ω ) and 
     Σ is the sum of losses due to the optical link and optical couplers. 
     The pyrotechnic initiators  12  are optically controlled detonators, capable of controlling priming of explosive charges placed in holes drilled in the structure to be demolished. Detonators with optical control may be made, depending on the case, either using detonators with conventional delays to which an optical input is adapted, or by using existent opto-detonators designed for the space industry, like those, for example, that are described in documents FR-A-2 615 609 and FR-A-2 646 901. 
     In the architecture of the demolition installation designed in this way, all initiators in the same group are fired simultaneously. On the other hand, independence between groups means that each can be controlled separately with programmed delays. Similarly, it is thus possible to make pyrotechnic initiators redundant by placing initiators belonging to different groups in nearby locations. 
     As illustrated more precisely in FIG. 2, each control unit  10  comprises an electric power supply circuit for the laser source  16 . This electric power supply circuit comprises a safety switch  24 , a low voltage/high voltage converter  26 , and a control switch  28  for the laser source  16 , in series between an input connector that may be connected to an external source (not shown) and the laser source  16 . When this power supply circuit is connected to the external electric power supply source, each of the switches  24  and  28  must be closed before the laser source  16  can be used. 
     The laser beam emitted by the laser source  16 , when used, is transmitted to the input of the optical divider coupler  22  through an adapter lens  30 . 
     On the input side of the adapter lens  30 , a retractable shutter  32  is placed on the optical path between laser source  16  at the input of the optical divider coupler  22 . This retractable shutter  32  is controlled by a motor  34  that moves it between a passive retracted position in which the shutter  32  is not placed on the optical path mentioned above, and an active shutter position shown in FIG. 2, in which the shutter is placed on this optical path. 
     The retractable shutter  32  and the safety switch  24  form two safety devices eliminating any risk of accidental firing following accidental closure of the control switch  28 . 
     As diagrammatically illustrated in FIG. 2, the retractable shutter  32  has an inclined reflecting face  32   a  facing the adapter lens  30  when the shutter occupies its active closing position. This inclined reflecting face  32   a  of the retractable shutter  32  is one means of feedback that can direct a light beam penetrating into the control unit  10  to the input of the optical divider coupler  22 , through an auxiliary control input (not shown) or on the other hand, by directing a light beam from one or several lines formed by optical fibers  14 , to this auxiliary control unit. 
     This arrangement makes it possible to check the integrity of the installation in different manners. Thus a known limited power may be injected through the auxiliary control input. The measurement of the fraction restored on each of the optical outputs can then be compared with the predicted calculation in order to carry out a first check. 
     Conversely, the measurement may be made by injecting a known power starting from the supposedly defective end of the line, possibly using conventional reflectrometry equipment facing the auxiliary input. A fault can then be located since each line is independent in the direction working from its end towards the control unit  10 . 
     The auxiliary control input may also be used by the operator connecting the pyrotechnic initiators  12 , to check that he is using the right line, simply by displaying a light source  36  (FIG. 2) placed facing the auxiliary control input and chosen in the visible range. 
     Furthermore, each control unit  10  is provided with a secondary optical input  40 , and feedback means for directing an additional laser beam towards the input of the optical divider coupler  22  through the adapter lens  30 , in the case in which the laser source  16  in this control unit is defective. 
     As shown diagrammatically in FIG. 2, the secondary optical input  40  is provided with an appropriate adapter lens and feedback means comprising a fixed feedback device such as a mirror  42 , and a mobile feedback device such as a mirror  44 . 
     The mobile feedback device  44  is controlled by a motor  46  that moves it between a retracted passive position (FIG. 2) and an active position. In the active position, the mobile feedback device  44  directs the supplementary laser beam which enters the control unit  10  through its secondary input  40 , towards the input of the optical divider coupler  22 . More precisely, the supplementary laser beam entering into the control unit  10  through the secondary input  40  is returned by the fixed feedback device  42  to the mobile feedback device  44  and the mobile feedback device is inserted between the output from laser source  16  and the retractable shutter  32  when it is placed in its active position. 
     The entire installation also comprises an additional source  48  (FIG. 1) common to all groups, and which may be used during firing if the laser source  16  of one of the control unit  10  is defective. Consequently, an additional laser source  48  is placed facing the secondary optical input  40  of the corresponding control unit  10 . 
     We will now describe a second embodiment of the present invention with reference to FIGS. 3 to  5 . 
     This second embodiment is distinguished from the first embodiment mainly by the nature of the laser sources, which are composed of laser diodes  16 . Since the power and energy output by a laser diode are significantly lower than the power and energy output by a laser source with a pumped solid rod as used in the first embodiment described above, in this case a distinct laser source is used for each pyrotechnic initiator  12 , and there is no need for optical divider couplers. 
     As illustrated in FIG. 3, the general architecture of the installation remains very similar to that described previously with reference to FIG.  1 . Thus, the installation consists of a number of independent groups each including a control unit  10  with several outputs  18 , pyrotechnic initiators  12 , and optical fibers  14  connecting the outputs  18  of each control unit to pyrotechnic initiators  12 . More precisely, in this case the number of outputs  18  is equal to the number of pyrotechnic initiators  12 , and an optical fiber  14  individually connects each output  18  to one of the pyrotechnic initiators  12 . 
     In the basic solution used in the second embodiment of the present invention illustrated in FIG. 4, each control unit  10  comprises one laser diode  16  for each output  18 , the laser beam output from each diode being directed towards the corresponding output. Furthermore, all these diodes  16  are installed to be electrically in parallel in an electric power supply circuit designed to be connected to an external low voltage electric power supply source  49  illustrated in in FIG.  3 . 
     More precisely, a control switch  28  is installed in series on each of the laser diodes  16 , on the input side of these diodes. In other words, if the number of outputs  18  of the control unit  10  is denoted N, the electric circuit comprises N parallel arms including a control switch  28  and a laser diode  16  in sequence. All these arms inside each control unit  10  are connected to a common power supply line that comprises a safety switch  24 . On the output side, the various parallel arms are connected to return line  25  that loops the circuit to the low voltage electric power supply source  49 . 
     For each laser diode  16  considered individually, the safety switch  24 , the control switch  28  corresponding to this diode and the laser diode itself are installed in series. 
     In the architecture illustrated in FIG. 4, each laser diode  16  can be controlled independently by a separate control switch  28 . Therefore, there is one control switch for each pyrotechnic initiator  12  to be controlled. This has the advantage of enabling the control of firings without any restrictions. 
     FIG. 5 shows a variant of the second embodiment of the present invention, by which the number of the control switches  28  may be reduced. In this case, each control unit  10  then includes one laser diode  16  for each output  18 . However, instead of being installed on separate parallel arms in the electric circuit, the laser diodes  16  are electrically connected to each other to form a matrix consisting of n rows and m columns. 
     More precisely, the laser diodes  16  on each line are installed in series with a first control switch  28   a  and the outputs of the laser diodes  16  in each column are connected together and are connected to a return line  25  in which a second control switch  28   b  is installed. 
     In this arrangement, the laser diodes  16  in the leftmost column can be controlled individually by closing the switch  28   a  on the corresponding line and the switch  28   b  connected to the output from this column. On the other hand, it is impossible to individually control laser diodes  16  located in the other columns. Thus, the only way to control any laser diode in the matrix is to simultaneously control all laser diodes located on the same row and before it. In other words, to the left of the laser diode considered in FIG.  5 . 
     The arrangement that has been described above with reference to FIG. 5 may significantly reduce the number of control switches, since instead of being equal to the total number of diodes (for example about 100 for each group), it is equal to the sum of the number of rows and the number of columns in the laser diode matrix (for example about 20). 
     In the second embodiment that has just been described with reference to FIGS. 3 to  5 , a failure in any of the lines may be detected from the end of the line, by means of conventional inspection devices (reflectrometry, echometry).