Abstract:
The invention relates to the field of electrical firing mechanisms and particularly to a device for firing a primer of the type having, in particular, an electrical power supply for a circuit including a detector, a switch and an igniting device for igniting the primer, such as an electrical resistor or a striker and a device able to move the striker. The detector and switch may include a network of contacts able to open or close the circuit under the influence of a contact or a force and to close or open the circuit when the contact or the force has disappeared.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of Invention 
     The invention relates to the field of electrical firing mechanisms for miniature bombs, mines, missiles, and projectiles, and particularly to a device for firing a primer of the type having, in particular, an electrical power supply for a circuit including in particular, a switch, an ignition device for igniting the primer, such as an electrical resistor, or a striker and an actuation device to actuate the striker. 
     2. Description of Related Art 
     A certain number of devices for firing a primer are already known. Patent Application No. FR2742859, for example, describes a time-settable priming device including a primer, an electrical power supply for a circuit, including principally a priming resistor, a switch for switching the supply circuit of the priming resistor, a timer for setting a time delay, and a control switch for controlling switching, including a microcontroller, a code wheel, and a trapping device connected to the microcontroller. 
     As an example, the trapping device can be of the contact-opening type and includes a closed circuit supplied by a supply device. The trapping device may have a certain number of contacts opened by remote control, inertia, or a tripwire. 
     These types of contacts may have drawbacks when implemented in an antitank land mine. In certain cases, it is not possible to provide remote-controlled or inertial tripping and moreover, the tripwire does not discriminate between a soldier and a vehicle when firing the primer. 
     To overcome this problem and to actuate firing only in the presence of a vehicle, Patent FR2653824 states that, for recognition of a vehicle, use may be made, for example, of a detector sensitive to contact by the vehicle or to pressure, a detector sensitive to the vehicle&#39;s magnetic field, or to the change in the magnetic field of the ground caused by the vehicle, or a vibration detector. The use of double detection with an influence detector and a contact or pressure detector is also described. 
     Detectors sensitive to contact with, or the pressure of, a vehicle include those described in patents FR2504254 and FR2507307. FR2504254 describes an antitank mine, including a detector at its upper part that includes, in particular, a pressure plate designed to actuate firing by igniting a pyrotechnic chain composed of a striker, a primer, an ignition relay, and an ignition block for firing the true pyrotechnic charge contained in the mine. 
     FR2507307 describes an antitank mine having a release charge and a true charge as well as double detection of the tank with a detector for firing the release charge followed by the true charge, and a contact or pressure detector causing direct firing of the true charge. 
     All the devices described in the aforesaid patents have drawbacks. Thus, the plate mine described in patent FR2504254 requires the vehicle to be destroyed to pass right over the mine, which considerably reduces the probability that the mine will act on the vehicle. 
     Patents FR2654824 and FR2507307 teach the possibility of considerably increasing the range of a mine by using influence detection in addition to contact or pressure detection. 
     However, this double detection requires the presence of two separate electronic assemblies, thus, increasing the number of components and hence the cost of the primer firing device, and reducing the overall reliability of the device. 
     Moreover, the devices described in these latter patents do not optimize the effects of the mine explosion on the tank. 
     SUMMARY OF THE INVENTION 
     The invention provides a firing device for firing a primer, requiring a minimum of electronic components and, although using only one type of detector having a greater range than that of a device as described in Patent FR2504254, for example, enabling the effects of the explosive device associated with the firing device to be optimized. 
     The firing device may include at least one electrical power supply, a detector, a switch, and an ignition device, such as an electrical resistor, or a striker and device able to move the striker and ignite the primer. The detector and switch may include a network of contacts able to open or close a circuit including at least the electrical power supply, under the influence of a contact or a force, to close or open the circuit when the contact or the force disappears. 
     According to one particular feature, the network includes of a strip of contacts. According to another feature, the contacts include membrane switches. 
     According to another feature, the membrane switches include a first plate having a hole, a second plate itself having a hole, and sloping edges inscribed in the hole in the first plate, a spherical membrane shaped like an upwardly directed spherical segment attached to the ends of the sloping edges, and an electrically conducting strip attached to the lower surface of the membrane. 
     According to one preferred feature for introducing a detection threshold, specifically a pressure threshold, the network is disposed inside a deformable sheath made of a material whose hardness is preferably greater than 40° Shore. The choice of the shape of the sheath, the material or materials of which it is made, and the composition of the membrane switches, allows introduction of a minimum pressure threshold above which the membrane switch can close and below which it cannot do so. 
     According to one particular feature, this sheath is made of an extruded silicone shape whose hardness can be 60° Shore. According to one preferred feature, the sheath has several segments delimited by a change in its structure in order to facilitate its bending. According to an additional feature, this change in structure of the sheath includes reducing its thickness over all or part of its circumference and can, for example, be a recess. The switches are preferably positioned outside the straight section of the change in structure of the sheath. 
     According to another feature that, for example, enables a primer-tripping threshold to be introduced, the membrane switches are connected to a processor for processing electrical signals coming from the detector. The processor is able, in particular, to filter the targets and control the tripping of the primer. 
     According to one additional feature, the processor may include a counting module. According to another particular feature, the processor may be a microcontroller. According to another feature, the processor may be connected to the electrical power supply, to the detector, and to the primer-firing resistor. 
     According to an additional feature, the switch controlled by the processor is disposed between the processor and the primer-firing resistor. According to an additional feature, the timer is associated with the processor and/or the switch controlled by the processor. 
     The invention also relates to an explosive device of the type having an explosive charge, a primer, and a firing device for firing this explosive charge. The firing device may be a firing device according to one of the aforesaid features. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other advantages and characteristics will emerge from the description of particular embodiments of the invention with reference to the attached figures, wherein: 
     FIG. 1 shows an embodiment of the detector according to the invention; 
     FIG. 2 is a diagram of a cross section of the detector according to this embodiment of the invention; 
     FIG. 3 illustrates a membrane switch used in the framework of this embodiment of the invention; 
     FIG. 4 is a diagram of a firing device according to a first embodiment; 
     FIGS. 5 and 6 show a firing device according to a second embodiment; 
     FIGS. 7 a  and  7   b  show an example of actuating a membrane switch; 
     FIG. 8 shows a firing device according to a third embodiment; and 
     FIG. 9 shows a particular arrangement of explosive devices using a firing device according to the invention. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     FIGS. 1 and 2 show a detector  10  according to the invention designed to be integrated into a firing device for firing a primer with a view to its combination with an explosive device, such as a mine. 
     The detector  10  includes a strip  11  of membrane switches  12  that are inserted into a sheath  13  in the shape of a tube with a rectangular cross section. 
     This sheath  13  is made of extruded silicone with Shore hardness 60° and obtained by extrusion. In addition, the sheath  13  has structural modifications  25  regularly distributed over its length so that it can be folded accordion-wise. These structural modifications consist in a lengthwise indentation of several millimeters in its cross section, or in other words, a recess going around the entire external periphery of sheath  13 . 
     The outside dimensions of this sheath are, for example, width 65 mm and height 10 mm while the free internal space is 30 mm wide and 6 mm high. Its total length is 4 m and it has four structural modifications enabling it to be bent into 5 segments. 
     Strip  11  of switches  12  is, for example, 24 mm wide and is centered on the lower internal face  14  of sheath  13 . Switches  12  are of the type described in Patent EP202711. As shown in FIG. 3, they have a first plate  15  having a circular hole  16 , a second plate  17  having a circular hole  18  and sloping edges  19  inscribed in hole  16  in first plate  15 . A spherical membrane  21  in the shape of an upwardly directed spherical segment is attached to ends  20  of sloping edges  19 . An electrically conducting strip  22  is attached to the lower face of membrane  21 . 
     Second plate  17  is glued onto first plate  15 . A conducting strip  23  disposed lengthwise is centered on flexible strip  11  and each of the assemblies constituted by plates  15  and  17  of membrane  21  is attached to strip  11  and centered thereon. Thus, for each assembly, part of conducting strip  22  is vertically above part of conducting strip  23 . 
     As shown in FIG. 4, the detector  10  is connected to a processor  30  that processes electrical signals (0 or 5 V) generated by the detector  10 . The processor  30  is additionally connected to either side of electrical power supply  40  and to a priming resistor  31  used for firing a primer  32 . 
     As shown in FIG.  5  and in order to improve priming reliability, the processor  30  can be a microcontroller and may be connected to a timer  38  for setting a time delay, including, for example, code wheels, and a switch  34  for switching the power supply circuit of priming resistor  31  and a capacitor  36  supplying an intensity  12  when discharged. The intensity I 2  is necessary because the I 1  of the charging current of capacitor  36  is insufficient to cause the primer  32  to fire. Processor  30  controls the opening and/or closing of switch  34 . 
     As shown schematically in FIG. 6, an electromechanical safety device  41  that includes a mechanical clock associated with a mechanical toggle switch normally in the open position that closes the circuit after this clock has run for a preset time. This switch is connected to a capacitor  36  able to supply an intensity  12  when it discharges, since the intensity I 1  of the charging current supplied by the power supply  40  of this capacitor  36  is insufficient to cause the primer  32  to fire. 
     A transistor  50  of which the source is connected to power supply  40 , the gate to processor  30 , and the drain to the input of the switch of electromechanical safety device  41 , and a transistor  55  of which the source is connected to priming resistor  31 , the gate to processor  30  via a resistor  72 , and the drain to the output of capacitor  36 . 
     Moreover, the drain  53  of transistor  50  is connected to a short-circuit transistor  60 , itself connected to the processor  30  and ground. 
     In addition, resistors  70 ,  71 ,  72  that limit current intensity are disposed in the circuit upstream of the electromechanical safety device and between processor  30  and transistor  55  so that, if the transistor  55  and electromechanical safety device  41  means should fail, priming resistor  31  is traversed by a current of insufficient intensity to cause the detonator to be primed. 
     Moreover, signaling devices  81  and  80  are disposed downstream of the electrical power supply and in parallel with priming resistor  31 , respectively. 
     Finally, a two-position mechanical bolt  21  at the output of the power supply in a first position is able to ground all the electronic devices, while in the second position all of the electronic devices are powered but capacitor  36  is, in all cases, not connected to the power supply  40  until a safety delay generated by electromechanical safety device  41  has elapsed. 
     The primer firing device according to the invention operates as follows. All the membrane switches in the network are initially open. As shown in FIGS. 7 a  and  7   b , application of a tank wheel  90  to one of switches  12  brings conducting elements  22 ,  23  into contact then breaks this contact as soon as the wheel has passed as the switch  12  is reversed and returns to its initial position. A voltage pulse is thus generated and counted by processor  30 . 
     The processor  30  can either immediately cause current to flow to the priming resistor  31  at an intensity sufficient to fire primer  32 , or trigger this firing only once a certain number of pulses has been detected. For example, the processor  30  can be programmed to trip firing of the primer only when three pulses separated by a minimum time interval are detected, hence only after three wheels have passed, so that the explosion takes place at the most vulnerable spot in the tank, namely the ammunition magazine. 
     These devices can also be programmed not to fire the primer until four or five pulses separated by a minimum time interval and occurring in a limited space of time are detected in order to destroy only the track mechanism. The processor  30  can thus filter the targets. 
     In the example of FIGS. 5 and 6, the operation is substantially the same as described above but additional safety devices are provided to maximize safety to the individuals laying the mines. Operation is then as follows: Mechanical bolt  21  is initially in its first position and electronic devices  10 ,  30 ,  34 ,  36  are not energized. Using code wheels, the user sets a time delay D 1  then, using a special key, turns the bolt  21  to the position in which all the electronic devices  10 ,  30 ,  34 ,  36  are electrically powered and the code wheels are locked. The firing device is then positioned on a mine, and this mine is buried in the ground while the detector  10  is either placed on the ground or buried. 
     In this position, the countdown of time delay D 1 , started by turning bolt  21 , continues while the mechanical clock for timing the electromechanical safety device  41  is triggered. At the end of a preset clock operation time Tp 1 , the clock throws mechanical switch and hence closes the part of the circuit located between transistor  50  and capacitor  36 . 
     Thus, in all cases where the time delay D 1  set by the user is less than preset Tp 1  or if processor  30  or transistors  50 ,  55 ,  60  should fail, firing can in all cases occur only after this time Tp 1  has elapsed. 
     After the countdown of value D 1 , processor  30  deactivates short-circuit transistor  60  and activates transistor  50  which then becomes conducting. Capacitor  36  is then charged and, after a preset time Tp 2 , activation of transistor  55  by processor  30  causes capacitor  36  to discharge through this transistor  55  and priming resistor  31 , as the intensity I 2  in the latter is then sufficient to trigger the detonator and explode the mine. 
     Activation of transistor  55  is operated as described above, namely as soon as a voltage pulse is detected by detector  10  or after a certain number of pulses have been detected, three for example, to reach a sensitive part of the tank or four or even five to destroy only the track mechanism. This pulse number is preferably combined with the time between, and including, these pulses. 
     It should also be noted that, for safety reasons, it is preferable for the capacitor charging time Tp 2  to be long relative to its discharging time. Hence, dysfunctions resulting in simultaneous operation of all the transducers (in the case of EMP and nuclear effects) would have no consequences. 
     According to one embodiment of the invention, the delay device can be simplified as shown in FIG.  6 . The priming device then has detector  10 , an electrical power supply  40 , in this case batteries, a time-delay opening relay  33 , a time-delay closing relay  35 , a capacitor  36 , and a priming resistor  31  of primer  32 . 
     As soon as the batteries are installed, the two relays are energized. Since relay  33  is closes first, capacitor  36  is charged. This relay  33  opens after a time Tp 4  then relay  35  closes and, as soon as one of the membrane switches  12  of the detector  10  closes the circuit, capacitor  36  discharges through resistor  31 , causing primer  32  to fire. 
     In the case of priming by displacement of a mechanical part, discharging the capacitor  36  energizes a solenoid, activation of which unlocks the electromechanical device  41  which primes the detonator. 
     Due to the reversibility of the detector  10  according to the invention, it is possible to adapt the firing modalities according to the nature of the target. Thus, if the target is a tank column as shown in FIG. 9, it is possible to program processor  30  so that the primer  32  is not fired until a certain number of tanks has passed. 
     The explosive devices  91 - 95  shown in FIG. 9 are disposed every 30 meters over a distance of 150 meters. According to a possible embodiment of the invention, each of these five explosive devices  91 - 95  has its own detector  10  connected to for processor  30 . 
     However, the firing device of explosive devices  91 ,  92 ,  94 , and  95  may be deactivated while the firing explosive device  93  is activated. This deactivation consists of preventing the primer  32  from firing even if a tank is detected. Thus, tanks can drive over the detector  10  and be detected without the primer  32  being fired. Firing can be accomplished, for example, by software in the microcontroller of processor  30  or by hardware with a switch, etc. 
     Also, the processor  30  associated with explosive devices  91 ,  92 ,  94  and  95  may be programmed to trigger firing, after activation, when a tank is first detected by the associated detector  10 . 
     Processor  30  associated with explosive device  93  may be programmed to trigger firing of explosive device  93  when passage of a third tank is detected, for example, and to activate the processor  30  of the other explosive devices after this third passage has been detected. This activation can be effected by wire or by radio with a transceiver assembly. 
     Thus, detection of the passage of tanks  100  and  101  over the detector  10  associated with explosive device  93  (i.e., the only explosive device whose firing device is activated) has no effect. On the other hand, passage of a third tank, in this case tank  102 , causes explosive device  93  to explode and activates the firing device associated with explosive devices  91 ,  92 ,  94 , and  95 . Thus, detection of a tank by one of the detectors  10  associated with these explosive devices causes the primer  32  to fire and hence the corresponding explosive device to explode. 
     Such operation of the firing device has a trapping effect. The tanks located between the detector  10  of explosive device  91  and those of explosive device  95  are destroyed in their turn when explosive device  93  explodes, as soon as they are detected by the detector  10  of an explosive device that has not yet exploded, continuing until all the explosive devices  91 - 95  have exploded. Thus, in the example of the tank column in FIG. 9, at least five tanks are destroyed thanks to the utilization of the firing device according to the invention. 
     Numerous modifications may be made to the embodiment described without thereby departing from the framework of the invention. Thus, the network can have a star shape or a square shape, etc., and in the case of a strip  11  of contacts, the network can be approximately one meter or one decameter long, and be connected to several explosive devices. 
     Moreover, by adding a receiver associated with the firing device, it is possible, using a transmitter, to cause, for example, a switch in the firing circuit of the primer  32  to close, in which case firing can occur at the proper time after detection of a tank by the detector  10 . Thus, it is possible to select the target.