EP1780496A1 - Pyrotechnical safety device with micromachined barrier. - Google Patents

Abstract

A security device, comprising a screen (13.1) blocking a transmission channel (7a, 7b) between an initiator and a pyrotechnic charge, has the screen made in the form of at least one micro-machined or micro-engraved element mounted on or forming part of a substrate plate. The plate is positioned so that it is parallel to the transmission channel, with the initiator and pyrotechnic charge on opposite sides of its thickest section. The transmission channel itself has a cross-section of 1 mm 2>or less while being greater that the pyrotechnic charge's primer surface. The screen is moved, e.g. by a micro-spring (15.1) or micro-electric vibration motor.

Description

The technical field of the invention is that of firing safety devices for pyrotechnic apparatus.

Security devices (or DSAs) are well known. They generally comprise a screen closing a transmission channel which connects an initiator and a pyrotechnic charge.

The screen is thus interposed on the flame passage between the initiator and the load and it prevents the ignition or firing of the latter.

Licences FR2650662 and FR2801099 thus describe known safety devices.

One of the problems encountered with these devices is their size. The pieces are relatively massive to ensure the interruption of the pyrotechnic chain. The motor means for moving the screen must be powerful. In most cases, springs are used which remain bandaged during the storage phases, which can lead to a degradation of their mechanical characteristics and to a loss of reliability of the armament.

It is also possible to use small electric motors, but these remain bulky and require a significant source of energy.

In recent years it has been proposed to carry out all or part of the safety devices using chips incorporating electromechanical elements micro machined or etched either in an element deposited on a substrate or directly on the substrate itself. This technology known under the name of MEMS (Micro Electro Mechanical System) makes it possible today to achieve micro mechanisms by implementing a technique similar to that for producing electronic integrated circuits.

Licences EP1559986 and US6173650 describe such safety devices.

However, this technique is used today only to make electrical contacts or screens for interrupting an optical firing signal, or projectable elements for initiators ("slapper" type detonators).

Such screens are not directly interposed between the pyrotechnic initiator and the load, and the interruption of the pyrotechnic chain is not ensured.

The patent EP1189012 discloses a miniature security device in which a transmission channel receives an initiator. This channel is closed, firstly by a first screen held by a lock, and secondly by a second screen, transverse to the first, and which can slide by the action of an actuator.

The dimensions of such a device are relatively important since the initiator has substantially the same diameter as the transmission channel. In addition, the pyrotechnic charge which is initiated by this device is arranged in a direction which is perpendicular to the plane of the screen and it can be initiated only through a transverse light of the second screen and after displacement of the two screens.

Such a device is complex and relatively bulky. The energy provided by the initiator is partly used to unlock and move a screen. Only the residual energy is used to initiate a pyrotechnic composition. Such a principle is dysfunctional and unreliable.

The object of the invention is to provide a safety device for firing mass reduced and yet reliable and effective.

The invention thus proposes a security device implementing the MEMS technologies but also making it possible to ensure the interruption of the pyrotechnic initiation chain between an initiator and a load.

Thus, the subject of the invention is a firing safety device for a pyrotechnic device, a device comprising at least one screen closing a transmission channel connecting an initiator and a pyrotechnic charge, a device characterized in that the screen is produced under the at least one micro-machined or micro-engraved element, reported or made on at least one plate of a substrate, the wafer being oriented so that it is substantially parallel to the transmission channel which thus opens facing the screen at the thickness thereof, the load pyrotechnic (5,5a) and the initiator (6) are thus on both sides of the screen (13.1,13.2) and opposite the thickness of the screen.

Advantageously, the transmission channel will have a section whose surface will be less than or equal to 1 mm ² while being chosen greater than the ignition surface of the pyrotechnic charge.

The screen can be moved by the action of motor means between a safety position in which it closes the transmission channel and an armed position in which it releases at least partially a portion of the transmission channel, the motor means being made under the shape of micro-machined parts or micro engraved on the or platelets.

The device may comprise at least two micro-machined or micro-etched platelets stacked one on top of the other, control means ensuring a synchronized movement of the screens or screen elements of the various platelets.

The screen may comprise at least two elements that can move relative to each other to clear the transmission channel.

The elements of the screens may comprise, at their contact zone, shape-concordant profiles whose juxtaposition will constitute at least one baffle ensuring a seal against the gases generated by the initiator.

The motor means may be designed to ensure reversibility of movement of the screen or screens.

Each screen or screen element can be held in the safety position by a micromachined latch or micro engraved on the wafer considered.

• la figure 1 représente en coupe schématique un dispositif de sécurité selon l'invention,
• les figures 2 et 3 montrent en position de sécurité une partie du dispositif selon un premier mode de réalisation de l'invention, la figure 2 étant une coupe réalisée suivant le plan BB repéré à la figure 3 et la figure 3 une coupe suivant le plan AA repéré sur la figure 2,
• la figure 4 est analogue à la figure 2 mais montre le dispositif dans sa position armée,
• les figures 5 et 6 montrent en position de sécurité une partie du dispositif selon un deuxième mode de réalisation de l'invention, la figure 5 étant une coupe réalisée suivant le plan DD repéré à la figure 6 et la figure 6 une coupe suivant le plan CC repéré sur la figure 5,
• la figure 7 est analogue à la figure 5 mais montre le dispositif dans sa position armée.

The invention will be better understood on reading the following description of various embodiments, a description given with reference to the appended drawings and in which:

• FIG. 1 represents in schematic section a safety device according to the invention,
• FIGS. 2 and 3 show in the safety position a portion of the device according to a first embodiment of the invention, FIG. 2 being a section taken along the plane BB marked in FIG. 3 and FIG. AA identified in Figure 2,
• FIG. 4 is similar to FIG. 2 but shows the device in its armed position,
• FIGS. 5 and 6 show in the safety position a portion of the device according to a second embodiment of the invention, FIG. 5 being a section taken along the plane DD indicated in FIG. 6 and FIG. CC identified in Figure 5,
• Figure 7 is similar to Figure 5 but shows the device in its armed position.

Referring to FIG. 1, a firing safety device 1 for a pyrotechnic device 2 according to the invention comprises an envelope 3 which is fixed by means (not shown) on the holster 4 of the pyrotechnic device 2.

The case 4 contains a pyrotechnic charge 5 (for example an explosive on which a priming relay 5a is placed) and the safety device 1 carries an initiator 6. The initiator 6 is connected directly to the explosive charge 5 by a transmission channel 7. This channel is linear and it contains no pyrotechnic composition. It serves as a guide to the gases generated by the initiator 6 and directs them to the explosive charge 5.

The envelope 3 encloses a cavity 8 inside which is disposed a housing 9 which incorporates the means ensuring the interruption of the pyrotechnic chain (means not shown in this figure).

The housing 9 and the initiator 6 are connected by electrical connection means 10a, 10b, 16 to an electronic control means 11.

The arming of the device intervenes only as a result of the detection of a certain number of associated events obligatory shooting (for example the acceleration of firing for a projectile). This is the means 11 that manages these events. It is therefore connected to sensors (not shown) and incorporates event management software.

With the device according to the invention, the means ensuring the interruption of the pyrotechnic chain will include micro-machined or micro-engraved elements (MEMS).

The dimensions of these elements being reduced, it is necessary to define the entire pyrotechnic chain (6,5a, 5) so as to reduce the effects of priming.

It is thus necessary to optimize the entire pyrotechnic chain and to implement an initiator 6 having the minimum size to ensure operation, initiator coupled to a suitable pyrotechnic relay 5a which is disposed on the side of the pyrotechnic charge 5.

It has been verified that by using an initiator comprising an output stage of 10 milligrams of Hexogen coupled to a very insensitive relay, for example in HNS (hexanotrostilbene), it was possible to make a transmission channel 7 of less than 1 mm ² section (channel diameter of the order of mm) while ensuring the desired initiation transmission. It should be noted that conventional initiators have an output stage of about 30 milligrams of Hexogen. The initiator 6 chosen therefore has a reduced power.

Indeed, the critical diameter of the HNS is 0.5 mm and this explosive therefore requires to be initiated a priming surface of substantially 0.2 mm ² which is much lower than the section of the transmission channel.

It was then verified that it was possible to ensure an interruption of the pyrotechnic effect with a silicon screen of the order of 3 mm thick which is achievable with MEMS technology.

It is therefore possible to implement a micro-machined technology (MEMS) provided that it can interpose a length of silicon of the order of 3 mm between the initiator and the pyrotechnic charge. This length is indeed sufficient to stop the pyrotechnic effects due to inadvertent initiation of the chosen initiator. Figures 2 and 3 show a first embodiment of a case 9 MEMS technology according to the invention.

Generally the thickness of the micro-machined elements does not exceed half a millimeter. To ensure the closure of a channel 7 with a diameter of 1 mm, it is therefore necessary to stack at least two micro-mechanisms on one another and thus to associate two identical screens arranged one over the other. .

The housing 9 thus encloses two plates of a substrate 12.1 and 12.2, for example an insulating substrate such as silicon, each bonded to a glass plate 19.1, 19.2 which closes the housing.

Each substrate carries a screen 13.1, 13.2 made in the form of a micromachined part (or micro etched) in the silicon substrate. It will be provided a slight set of editing (a few micrometers) to allow the joint movement of the screens 13 carried by the two plates.

Gas tightness is not absolute. It will be possible to reduce the diameter of the exit hole Z - see FIG. 1 (while maintaining it greater than or equal to the diameter of the channel 7) in order to reduce the effects on the relay 5a of an initiation into the safety state of the device.

Alternatively it would be possible to make the screen on another plate (thicker) and then report it on the substrate 13.1, 13.2 considered.

The housing 9 carries two cylindrical holes 7a and 7b of the same axis 17 and which extend the transmission channel 7.

In FIG. 2 the device is shown in a safety position in which the screens 13.1, 13.2 interpose between the holes 7a and 7b and thus block the transmission channel 7.

Each screen is kept locked by a latch 14.1, 14.2 micromachined which may for example be constituted by a thermal fuse or an electrothermal or electromagnetic actuator.

Each screen 13.1, 13.2 once unlocked is moved by the action of a motor means 15.1, 15.2 which will be for example a micro-machined spring or a micro electric motor vibrating or friction or thermal.

The locks and the motors will preferably be designed so as to ensure the reversibility of the control of the screen from the security state to the armed state and vice versa.

Also shown in the figures a connector 16 which allows the connection of the housing 9 to the electronic control means 11. This control means is furthermore designed so as to ensure the synchronized displacement of the screens 13.1, 13.2 of the plates 12.1, 12.2.

Also shown schematically in the figures by bold lines some conductive tracks carried by the pads 12.1, 12.2 and connecting the micro-machined locks and actuators to the connector 16.

Each screen 13.1, 13.2 has a substantially parallelepipedal geometry and moves on the plane of its substrate 12.1, 12.2 in the direction D (Figure 2) to adopt its armed position (Figure 4).

In conventional mechanical safety devices, the transmission channel has an axis that passes through the screen according to the thickness of the latter. The transmission channel is usually perpendicular to the plane on which the screen slides.

With a screen made using micro-machined technology (MEMS) the thickness of silicon is too small to ensure the arrest of a pyrotechnic effect (a thickness of a micro-machined element is usually a few hundred micrometers).

According to the invention, the screens 13.1, 13.2 thus receive the pyrotechnic effect in a direction 17 parallel to their plane of displacement 12.1, 12.2.

The pads 12.1, 12.2 are therefore integrated on their edge so that they are substantially parallel to the transmission channel 7.

The transmission channel has its axis 17 which thus passes through each screen along a dimension L much greater than its thickness. It is thus possible to produce in MEMS technology screens 13.1, 13.2 having an L dimension of the order of a few millimeters.

Thanks to the invention, it is therefore possible to define a safety device in which the screen is micro-machined and arranged in such a way that both the pyrotechnic charge and the initiator itself are on either side of the screen. the screen.

The pyrotechnic elements are thus placed opposite the thickness of the screen. They exert their effect in a direction that is in the plane of movement of the screen and not perpendicular to this plane of movement as in conventional solutions. The interposed screen thickness can therefore be maximum with a screen which is nevertheless of minimal thickness as can be obtained with micro-machining technologies.

The skilled person will easily determine the structure of the various micro machined elements. Electrothermal or electromagnetic actuators are well known in the field of MEMS. The same applies to fuses and micro-machined springs. For example, we can refer to patents EP1573782 , US2005139577 , US6691513 and US2004027029 which describe possible solutions.

FIGS. 5 to 7 show a second embodiment of a MEMS technology package 9 according to the invention.

This mode differs from the previous one in that each screen 13.1 or 13.2 is divided into two elements that are movable relative to each other.

Thus the substrate 12.1 carries two screen elements 13a.1 and 13b.1 and the substrate 12.2 carries two screen elements 13a.2 and 13b.2.

Each screen element is displaceable by motor means 15a.1, 15b.1; 15a.2, 15b.2.

Lock means 14a.1, 14b.1 or 14a.2, 14b.2 ensures at each pad the immobilization of each element of the screen considered.

It will be provided a slight assembly game (a few microns) to allow the joint movement of the elements 13 carried by the two plates.

Each plate 12.1, 12.2 is connected to the electronic control means 11 which are designed to ensure the synchronized movement of the elements 13a.1, 13b.1, 13a.2, 13b.2 of the various plates.

There is shown in the figures a connector 16 which provides the interface between the wafers and the cable from the control means 11. Diagrammatically represented in the figures by bold lines certain conductive tracks carried by the wafers 12.1, 12.2 and connecting micro machined locks and actuators to connector 16.

When the device is in its safety position (FIG. 5), the two elements constituting each screen are in contact with each other substantially at the level of the axis 17 of the priming channel. The contact surfaces preferably have shape matching profiles 18a, 18b.

According to the embodiment represented here, the profiles consist of a succession of teeth defined by inclined planes with respect to the axis 17 of the channel 7.

The juxtaposition of the teeth thus constitutes baffles which make it possible to improve the tightness to the gases generated by the initiator 6.

Figure 7 shows the device in its armed position. Each motor means has moved an element in a direction Da or Db. The channel 7 is then released and the initiation of the load 5,5a is allowed.

Each element 13a, 13b of each screen has thus moved by a distance substantially equal to one half-diameter of the channel. The movements are therefore of reduced amplitude which allows a faster arming.

Of course, Figures 1 to 7 are diagrammatic and do not prejudge the dimensions and proportions of the various components that are represented.

Various variants are possible without departing from the scope of the invention.

It is thus possible (for one or other of the previous embodiments) to provide more than two plates 12 of substrate carrying moving elements.

Of course each plate will be connected to the electronic control means that will ensure the synchronized movement of micro machined elements forming the screens carried by the various plates.

Such a solution will make it possible to adapt the device to a larger diameter of the transmission channel.

Conversely, it would be possible to produce a device according to the invention in which there would be only one plate carrying a mobile screen formed of one or more elements. This solution will be considered if it is possible to sufficiently reduce the diameter of the transmission channel so that it remains substantially equal to the thickness of the mobile screen.

It may be possible to make a screen of sufficient thickness on a first wafer then bring this screen on another wafer carrying micro machined or micro engraved motor means.

Claims (8)

Fire safety device for a pyrotechnic device, device comprising at least one screen (13.1, 13.2) closing a transmission channel (7, 7a, 7b) connecting an initiator (6) and a pyrotechnic charge (5, 5a), characterized in that the screen is made in the form of at least one micro-machined or micro-engraved element (13.1, 13.2), attached to or formed on at least one plate (12.1, 12.2) of a substrate, the plate being oriented so that it is substantially parallel to the transmission channel (7, 7a, 7b) which thus opens facing the screen (13.1, 13.2) at the thickness thereof, the load pyrotechnic (5,5a) and the initiator (6) are thus on both sides of the screen (13.1, 13.2) and opposite the thickness of the screen. Safety device according to claim 1, characterized in that the transmission channel (7, 7a, 7b) has a section whose area is less than or equal to 1 mm ² while being chosen greater than the starting surface of the pyrotechnic charge (5, 5a). Safety device according to one of claims 1 or 2, characterized in that the screen (13.1, 13.2) is movable by the action of motor means (15.1, 15.2) between a safety position in which it closes the transmission channel (7, 7a, 7b) and an armed position in which it releases at least partially a portion of the transmission channel, the drive means being made in the form of micro-machined parts or micro etched on the or platelets. Safety device according to one of Claims 1 to 3, characterized in that it comprises at least two micro-machined or micro-engraved plates (12.1, 12.2) stacked one on top of the other, control means (11) providing a synchronized movement of the screens or screen elements of the different plates. Safety device according to one of claims 1 to 3, characterized in that the screen (13.1, 13.2) comprises at least two moving elements (13a.1, 13b.1, 13a.2, 13b.2) relative to each other to disengage the transmission channel (7, 7a, 7b). Safety device according to claim 5, characterized in that the elements (13a.1, 13b.1, 13a.2, 13b.2) of the screens comprise at their contact zone profiles (18a.1, 18b. 1) with a shape matching whose juxtaposition constitutes at least one baffle sealing the gases generated by the initiator. Safety device according to one of Claims 3 to 6, characterized in that the motor means (15.1, 15.2, 15a.1, 15a.2, 15b.1, 15b.2) are designed to ensure reversibility of the displacements of the or screens. Safety device according to one of claims 1 to 7, characterized in that each screen or screen element is held in the safety position by a latch (14.1, 14.2; 14a.1, 14a.2; 14b.1, 14b. 2) micromachined or micro engraved on the wafer (12.1, 12.2) considered.

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