CA2058832C - Piezoelectric ignition device for actuating an electric ignitor with a resistant wire - Google Patents

Abstract

To control the actuation of an electric igniter with a resistant wire, a piezoelectric firing device is proposed which comprises, inside a housing (10), a control mechanism (14) , a piezoelectric generator (16) and an electric transformer (18). The depressing of a push button (24) of the control mechanism (14) propels a mass (36) against the cap (52) of the piezoelectric generator. The high-voltage and very short-lived electrical signal thus produced is transformed, in the transformer (18), into a low-voltage signal, the intensity and duration of which allow the igniter to be actuated. As soon as the push button (24) is released, a return spring (46) returns the control mechanism to its initial state, so that the device can be actuated several thousand times without maintenance.

Description

PIEZOELECTRIC FIRE DEVICE FOR ACTION-NEMENT OF A RESISTANT WIRE ELECTRIC IGNITER.
DESCRIPTION
The invention relates to a setting device piezoelectric light designed for actuation an electric igniter with a resistant wire of a set pyrotechnic.
Such a device can in particular be used on shooting stations of different natures, for aces to secure the ignition of any pyrotechnic assembly powered by a heavy duty wire igniter low or medium energy.
Piezoelectric generators are often used in armament for the firing of active heads (anti-tank, flash, etc.), fitted with rockets, placed artillery sites or projectiles. In this case, the general The piezoelectric generator is consumable. He works shock on impact on the target and puts fire a very low or low detonator or igniter spark or breakdown type energy. The mode of operation of this type of component is as follows.
The high voltage produced by the generator creates a . spark between two electrodes, which initiates a pyrotechnic composition. The primary component initiates in turn the entire pyrotechnic chain and leads to the operation of the main load. As illustrated in document US-A-3 '106 161, it has also been consider $ to interpose a transformer between the genera-piezoelectric sensor and detonator) The invention relates to a setting device non-consumable fire that can be operated very large number of times and capable of re igniting an igniter electric with low or medium resistance wire, energy (1.5 to 5 mJ) and operating by Joule effect. Setting of such a resistant wire igniter ignites SP 6732.69 6P

2 performed in a conventional manner by means of devices linear electromagnetic devices, generators this rotating or battery or battery devices.
- Linear electromagnetic devices, constituted for example by a coil with plunger core or by a gap gap system, are based on a sudden variation of the flow inside a circuit magnetic. They have the advantage of being able to produce quite significant energy. However, they are quite heavy and relatively expensive, as they often require wind a cocking lever, in order to deliver, by action on a trigger, the mechanical energy required to activate the electromagnetic system.
Rotating generator devices such as that dynamos and alternators have the advantage of louse see produce, in a small footprint, ener relatively large lives. However, these devices are relatively complex and expensive, especially in rai sound of the generator's fast drive mechanism.
Battery or battery-powered devices can be sorted into three categories.
In the first category, a battery is used directly to produce the ignition. Such device must include a protective resistor to protect against a short circuit of the meur. This resistance, which adds to the resistance internal of the battery and that of the igniter, wax that the intensity provided by the device can sometimes be insufficient.
In the second category of this type a battery charges a working capacitor before firing. This device provides the impetus necessary for firing, but there is response time determined by the charge time of the capacitor is by times too long.
SP 6732.b9 GP

~~~~ ~~ 8

3 Improvements to battery devices and capacitor is to add a milking circuit electronic signal, allowing to calibrate this last according to the conditions of use. This per-s fectionement, which does not solve the problems mentioned previously, has the further disadvantage of adding to these electronic circuit devices which can be complex and expensive.
A major drawback of these devices battery or battery is that they ask for a check of the condition of the parts before each use and a rem periodic placement of batteries. In addition, an energy permanently stored requires great rigor in the development of security systems.
In document FR-A-2 123 924, he also was considered to ensure the ignition of an igniter electric through a transformer whose the primary is connected to a piezoelectric element.
However, this item is activated by decompression this which results in a gap between the production of electric current and its use.
The object of the invention is precisely: a provision particularly piezoelectric ignition simple and reusable a very large number of times (a few thousand), suitable for being operated manually and providing a high intensified electrical signal and of sufficient duration to order an electric igniter low to medium resistant wire fake.
sufficient safety margin.
According to the invention, this result is obtained at by means of a piezoelectric firing device for actuation of an electric igniter with resistant wire, comprising a piezoelectric generator capable of supplying electrical energy when subjected to constraint, and a control mechanism, characterized by SP 6732.69 6P

4 the fact that the control mechanism includes a member control whose actuation has the effect of propelling be a mass with a predetermined force against the piezoelectric generator, the device comprising in association with a transformer including a winding primary is electrically connected to the piezo generator zoelectric and of which a secondary winding is suitable with hearth connected to the igniter.
In such a device, manual actuation of the control unit triggers the control mechanism which propels the mass against the piezoelectric generator cudgel. The perfectly controlled energy of the shock as well product generates at the output of the piezoelectric generator than a high voltage electrical signal (for example, 10 at 15 kV) of very short duration (around 200 Vis). The trans-trainer transforms this electrical signal into a signal low voltage (around 30 V), but with a high high sity (about 15 A) sufficient for the action-The resistant wire igniter can take place.
In addition, this device provides electrical energy, up to about 17 mJ, which has a sufficient safety margin to ensure the implementation of a low or medium resistant wire initiator energy (1.5 mJ to about S mJ).
In a preferred embodiment of the invention tion, the control mechanism includes - a body fixed to the piezoelectric generator and in which is formed a bore, one end of which opens out in front of this generator - a push button mounted sliding in said bore, and constituting the control member;
- means for controlling a rotation of said mass in a first direction to an angular position predetermined When a push button is pressed itself r;
SP b732.69 GP

5 - means for immobilizing the mass in translation in said body when it is not in said predetermined angular position; and - elastic actuation means compressed between the earth and the push button When pressed of the latter, so as to store said pr.é force d. which propels the mass against the generator piezoelectric when said mass reaches the posi angular pr, ~ d. determined.
In order for the device to be reusable a many times without the operator having to inter come, it also includes means of auto reset control of the return of the control unit and mass in rest positions as soon as it stops actuation of the control member.
Advantageously, these self-resetting means matic include means, elastic return of the push button to its rest position and means to control a reverse and a reverse rotation of said mass to its rest position When the pushbutton.
Advantageously, the means for controlling a rotation of the mass, the means to immobilize the mass in translation in the body and the means to request a recoil and a reverse rotation of said mass include a radial pin integral with said mas-se; this pin passes through at least one cut formed in a tubular part, of the push button and which has two opposite ramps, and protrudes into at least one L-shaped groove formed in said bore and whose two branches are oriented respectively in a circumferential direction and in a direction axial tion; means are provided to prevent a relative rotation between the push button and the body.
The actuating means can then include SP 6732.69 GP

6 take a compression spring housed in the part push button tubular, between ground and a button of push button shooting.
Furthermore, the elastic return means may include a second compression spring housed in the bore between one end of the push button evening and the piezoelectric generator.
The preferred embodiment of the invention tion, the pi, ezo-.electric generator includes an .element.
piezoelectric prestressed in the direction of displacement of said mass between two electrical parts.
conductive, electrically isolated from one another tre, a first of these parts constituting a cap able to be struck by said mass.
A preferred embodiment of the invention will now be described, by way of non-limiting example tif, with reference to the accompanying drawings, in which.
Figure 1 is a longitudinal sectional view The representative a firing device pi.ézo-, élec stick according to the invention;
- Figure 2 is a perspective view and in section representing on a larger scale the interior, of the bore formed in the body of the control mechanism and in which are received the push button and the mass able to strike the pi.ézo- generator: electric;
- Figure 3 is a longitudi sectional view partial report representing part of the command in the position it normally occupies at rest; and - Figure 4 is a view comparable to the fig-re 3 representing the same part of the control mechanism in its depressed actuation position.
As illustrated in Figure 1, The device of piezoelectric ignition according to the invention includes, é L ° interior of a bore 12 formed in a SP 6732.69 GP

7 housing 10, a control mechanism 14, a generator piezoelectric 16 and a transformer 18 mounted end to the end and in that order.
The control mechanism 14 comprises a body cylindrical 20 traversed along its axis by a bore 22.
A push button 24 is slidably mounted in this random sage 22 and protrudes outside through a opening formed in a removable part 10a of the housing 10. The push button 24 mainly consists of a tubular part 26, the end of which is outside of the housing 10 carries a fire button 28, for example by through a pin 30.
The push button 24 is immobilized in rotation tion inside the body 20 of the control mechanism 14, for example by a finger 32 which projects radially lies outside the cylindrical part 26 and penetrates in a longitudinal groove 34 machined in the wall of bore 22.
A metallic mass 36, of cylindrical shape, is mounted in the tubular part 26 of the push button 24 so you can get around it by rotation and translation. This mass 36 is crossed radially by a pin 38 whose ends do not feels in two cutouts 40, symmetrical with respect to the axis of the push button 24, formed in the tubular part area 26 of push button 24 and enter two grooves 42, symmetrical about the same axis, machined in the wall of bore 22.
As best shown in Figures 3 and 4, each of the two cutouts 40 formed in the tubular part Glistening 26 of the push button 24 presents substantially the shape of a parallelogram with two opposite paral edges lines 40a and 40b are oriented parallel to the axis com equipped with bore 22 and with push button 24 and whose two other parallel opposite edges 40c and 40d form SP 6732.b9 GP

ramps. More precisely, the edge 40c is inclined towards the outer end of the push button 24 bearing the fire button 28, from the edge 40a, and the edge 40d is inclined towards the opposite inner end of the push button r 24, starting from edge 40b. By linkers, the edge 40b of each of the cutouts 4U is offset angularly counterclockwise relative to edge 40a, looking from the right towards the left in the figures.
As illustrated in Figure 2, each of the two grooves 42 has the shape of an L, one of the branches ches 42a is oriented in an axial direction, that is that is to say parallel to the axis of the bore 22, and of which the other branch 42b is oriented in a circular direction conference, i.e. located in a radial plane relative to the axis of the bore 22. The branch 42b of each of the L-shaped grooves 42 is connected to branch 42a at the end of this last tour towards the removable part 10a of the housing 10, and turns in clockwise when looking at the right to left in the figures.
Referring to Figure 1, we observe that a compression spring 44 constituting elastic means that actuation of the control mechanism 14 is housed in the tubular part 26 of the push button 24, way to be compressed between the end of this part tubular carrying the fire button 28 and the end in vis-à-vis ground 36.
To complete the description of the control 14, another compression spring 46 constitutes killing elastic means of recall for the button pusher 24 and mass 36, is housed in bore 22 between the end of the push button 24 located inside the body 20 and the piezoelectric generator 16.
Under the action of the return spring 46, the SP 6732.69 GP

205 ~~~~

your push button 24 and the metallic mass 26 occupy normally At rest, the positions illustrated in the figure 1. The push button 24 then projects to the maximum outside the removable part 10a of the 1U housing.
The pin 38 mounted in the mass 36 is then in support in the acute angle closest to the generator piezoelectric 16, formed between edges 40a and 40d of each of the cutouts 40. eg more, The ends of pin 40 can be found in the circumferential branches tials 42b of each of the L-shaped grooves 42, in the ends of these most distant branches 42b longitudinal branches 42a.
When an operator presses the push button 24 by acting on the fire button 28, it does not occur no rotation of the mass 36 as long as the ends of pin 38 do not arrive in obtuse angles formed between the edges 40a and 40c of each of the cutouts 40 (Figure 3). Therefore, the ends of the pins the 38 remain blocked in the branches 42b of the grooves 42 L-shaped and the mass 36 remains stationary. It is therefore produces compression of the spring 44.
If the operator continues to press the button pusher 24, pin 38 runs along the inclined edges 40c of the cutouts 40, so that the mass 36 turns-do counterclockwise in looking from right to left in the figures.
During this rotation, the ends of the pin 38 run through the circumferential branches 42b of the L-shaped grooves 42, 'gradually approaching-longitudinal branches 42a. The mass 36 is therefore always immobilized in translation in the bore 22 by the cooperation of the ends of the pin 38 with branches 42b. During this phase of the action of the device, the compression of the spring 44 is continues.
SP 6732.69 GP

When the push button 24 is pressed brings pin 38 near the defined angles between the edges 40c and 40d of the cutouts 40 (position il-glossy in phantom in Figure 4), the ends of pin 38 arrive in front of the branches longitu-dinals 42a of grooves 42 in the shape of L. The energy takes gasinated by the compression of the spring 44 is then suddenly released and propels mass 36 towards the general piezoelectric rectifier 16, so that the mass 36 strikes this generator. Since the con spring 44 for which the displacement of earth 3b to the piezoelectric generator is pro duit is determined by construction, the energy transmitted to the piezoelectric generator is known and reproduced corn.
When the operator releases his action on the fire button 28, the spring 4b recalls the push button evening 24 towards its rest position illustrated in the figure 1. From the start of this movement, the pin 38 comes pressing against the inclined edges 40d of the cutouts 40, near the longitudinal edges 40b. However, being since the ends' of pin 38 are then in the axial parts 42a of the grooves 42 in L shape, mass 3b cannot rotate and move therefore together with the push button 24 away from it °
ment of the piezoelectric generator 16.
Towards the end of this: joint displacement, the ends of pin 38 arrive opposite the branches ches 42b of kids 42, so that mass 36 is 3p rotated counter-clockwise of a watch looking towards the outer end opening of bore 22 under the effect of cooperation of pin 38 with inclined edges 40d of cut-outs pes 40. The mass 3b is thus found automatically in its rest position illustrated in Figure 1.
SP 6732.69 GP

Referring again to Figure 1, we sees that the piezoelectric generator 16 includes a piezoelectric element 48 consisting of a small bar-piezoelectric ceramic array with dimensions are determined based on the characteristics that we wish to obtain. This piezoelectric element 48 is arranged along the axis of the bore 12 of the housing 10, in the extension of the bore 22 formed in the body 20 of the control mechanism 14.
The piezoelectric element 48 is surrounded by a insulating element 50 and compressed axially between two feet these electrically conductive formed by a coif-fe 52 and by a positive pad 54.
The support planes between the axial ends of the piezoelectric element 48 and, on the one hand, the coif fe 52, and, on the other hand, the positive pad 5b have very good geometric correction to guarantee good transmission of electrical signals delivered by the generator.
The cap 52 has a part in the form of disc that enters the adjacent end of the bore ge 22, one side of which is in contact with the ground element zoelectric 48 and whose side faces inward of this bore carries a convex protuberance 52a (figures 3 and 4) that is struck by the mass 36 during the action control mechanism 14. Outside of The bore 22 is around the insulating element 50, .this disc-shaped part of the cap 52 is extended by a frustoconical part of thin thickness 52b termi born by a tubular end portion 52c.
The post posi ti f 54 has the form of a di sque whose one side is in contact with the end of the element piezoelectric opposite the cap 52 and the face of which opposite carries in its center a cylindrical part 54a electrical connection.
SP 6732.69 GP

The part of the positive stud 54 adjacent to the element electric piezo ° 48 is surrounded by a second insulating element 56 which also partly surrounds the element insulating 50 and the end of which penetrates inside of the tubular end portion 52c of the cap 52.
The insulating material constituting Element 56 is chosen so as to have good mechanical hardness and a high dielectric strength.
the piezoelectric generator 16 includes plus a metal carcass consisting of a body 58 and by an annular nut b0. The body 58 placed around of the insulating element 56, is supported on one face of this element facing the electrical transformer 18 and is in electrical contact with the tubular part of end 52c of the cap 52. The annular nut 60 is screwed on the end of the body 58 facing the mechanism control nism 14 and it has a part which makes protruding radially inwards, so as to be resting on the frustoconical part of small thickness 52b of The headdress 52.
This arrangement makes it possible to apply to mounting axial prestress on the piezoelectric element 48 between the cap 52 and the positive stud 54. This pre-stress, which can be measured during assembly by serving as piezoelectric element 48 as sensor effort, or by any other means, ensures the transmission to the piezoelectric element of energy resulting from the impact of mass 3b on the 52 "cap whatever the temperature in a range of functions predetermined operation (for example between about -50 ° C
and + 60 ° C). The particular structure of the cap 52 described above guarantees that a pre-acceptable bust despite differential expansions that occur in this temperature range.
The nut b0 further comprises, in its part SP 6732.69 GP

facing the control mechanism 14, a second threaded part capable of being screwed on one end adjja-threaded center of the body 20 of the mechanism 14, in order to put the assembly of these two parts.
For a shock of given mechanical energy, the e electrical energy delivered to the igniter is maximum for a given value of the transformation ratio (for example ple, around 450>, which can be determined as a function characteristics of the circuits. We can then reach dre a high yield, for example around 8%.
However, one of the advantages of the invention is that the transformation ratio is not critical, the yield remaining close to its maximum value even if the value of the transformation ratio is modified (by example, between about 280 and about 500).
We can thus, to facilitate the realization of the transformer, slightly lower the ratio of transformation by reducing the number of turns mayor. The transformation ratio can even be reduced More clearly if you want to lower the cost of the device, but this is done at the expense efficiency and therefore reliability of ac-ignition.
In the example of embodiment described, the-trans electric trainer 18 includes a primary winding which has a large number of turns C for example in won 3000) of fine pre-insulated wire which is connected directly ment to the piezoelectric generator by deGx conductors electric 62 and 64 connected respectively on the body 58 and on the cylindrical part 54a of the positive stud 54. The secondary winding of the transformer 18 instead includes a small number of wire turns (of the order of 8) and it is connected to an electric igniter only with resistant wire (not shown) outside the available two electrical conductors 66 running between SP 6732.69 GP

the wall of bore 12, the piezoelectric generator 16 and the control mechanism 14.
The primary and secondary windings of transformer 18 are placed on a ferrite pot 68 supported by a rod 70 arranged coaxially inside laughing hole 12. Using a transformer with ferrite core core, improves performance of the device and avoids any risk of overvoltage in the event of a load fault on the transformer secondary speaker. The rod 70 is integral with a skirt 72 which rem folds the annular space formed between the piezo generator electric 16, the control mechanism 14 and the bore 12. The end of this skirt 70 is fixed to the body of the control mechanism 14 for example by means of 15 screws 72.
The assembly formed by the electric transformer that 18, the piezoelectric generator 1ta and the mechanism thus constitutes a whole which can be taken sleeved in the bore 12 of the housing 10 when fitting 20 in place of the removable part 10a of this housing. In this effect, the end of the body 20 turned outwards is advantageously provided with a thread which is screwed in a tapped hole formed in this removable part 10a as illustrated in FIG. 1.
In the piezoelectric ignition device that which has just been described, 1st insertion by an operation tor of the push button 24 of the control mechanism 14 has the effect, as previously described, of 'pro-pulsating the metallic mass 3b with a predetermined force born against the cap 52 of the piezoelectric generator 16. Under the effect of impact, an electrical signal of high voltage (10 to 15 kV) of very, short duration (approximately 200 ~ s> is generated by the piezoelectric generator 16.
In transformer 18, this electrical signal SP 6732.69 GP

~ A58 ~~~
is transformed into a low voltage signal (approximately 30 V). A firing pulse whose maximum intensity male reaches around 15 A and lasts around 0.2 ms can thus obtained, which makes it possible to control an allu-5 strong wire killer with an inherent resistance of approx.
ron 2 ohms, using all of the piezo energy electric supplied by generator 16. In addition, electrical energy at the output of the setting device piezoelectric fire according to the invention can reach 10 to 17 mJ, which safely ensures the action-resistor of a resistant wire whose energy operation generally varies between 1.5 and 5 mJ.
Given the very high signal voltage delivered by the piezoelectric generator, the conduc 15 electric teurs 62 and 64 connecting the latter to the trans formator 18 are coated with an insulating product 74 to high dielectric strength. We can, as reported above, decrease the number of primary turns, this which has the effect of reducing high voltage and thereby 2p read the insulation of the wires.
The piezoelectric firing device according to the invention allows, in a completely original way, to order a heavy duty wire igniter particularly simple and inexpensive way, for very small footprint and extreme reliability guaranteeing the actuation of the device several thousand proud of successive times without maintenance. Furthermore, being given that the energy n ° is delivered only at the time of the shot, any energy storage problem is eliminated, which significantly improves security. Finally, the impulse of firing is delivered in a particularly short time short (less than 1 ms>, which can be an advantage appreciable compared to battery or bat-existing dried up.
Of course, the invention is not limited SP 6732.69 GP

not\
1 E ~
to the embodiment which has just been described as example, but covers all variants. In part-culier, we can easily understand that the request 14 can be modified according to the form given in the order 9 control handle (push button, lever, trigger, pedal, etc.) without departing from the scope of the invention. he the same goes for the generator mounting structure piezoelectric 16, and the transformation ratio which is not criticize as we said.
SP 6732: 69 GP

Claims (9)

1. Piezoelectric firing device for actuating a electric igniter with resistant wire, comprising a piezoelectric generator able to supply electrical energy when subjected to stress, and one control mechanism, wherein the control mechanism comprises a control member whose actuation has the effect of propelling a mass with a predetermined force against the piezoelectric generator, the device comprising in association a transformer including a winding primary is electrically connected to the piezoelectric generator and one of which secondary winding is suitable for connection to the igniter as well as automatic reset means controlling the return of the control and mass in rest positions as soon as ceases actuation of the control member. 2. Device according to claim 1, wherein the mechanism of order includes:
- a body fixed to the piezoelectric generator and in which is formed a bore one end of which opens out opposite this generator;
- a push button mounted sliding in said bore, and constituting the control unit;
- Means for controlling a rotation of said mass in a first direction to a predetermined angular position during a pressing the push button;
- Means for immobilizing the mass in translation in said body when it is not in said predetermined angular position; and - elastic actuation means compressed between the mass and the push button when it is pressed, so that storing said predetermined force which propels the mass against the piezoelectric generator when said mass reaches the position predetermined angle. 3. Device according to claim 2, wherein the means for automatic resetting include elastic means of recalling the push button to its rest position and means for controlling a recoil and reverse rotation of said mass to its rest position then a push button retreat. 4. Device according to claim 3, wherein the means for controlling a rotation of said mass, the means for immobilizing the mass in translation in the body and the means for controlling a recoil and a reverse rotation of said ruasse include a radial pin secured of said mass; this pin passing through at least one cut formed in a tubular part of the push button and which has two opposite ramps, and protruding into at least one L-shaped groove formed in said bore and whose two branches are oriented respectively in a direction circumferential and in an axial direction; means being provided for prevent relative rotation between the push button and the body. 5. Device according to claim 4, wherein the means actuating elastics include a compression spring housed in said tubular part of the push button, between said mass and a button shoot of the push button. 6. Device according to claim 3, wherein the means return elastics include a second compression spring housed in said bore between one end of the push button and the generator piezo electric. 7. Device according to claim 1, in which the generator piezoelectric includes a piezoelectric element prestressed according to the direction of movement of said mass between two parts electrically conductive, electrically isolated from each other, a first of said parts constituting a cap capable of being struck by said mass. 8. Device according to claim 1, wherein the mechanism of control, the piezoelectric generator and the transformer are placed in this order inside a case. 9. Device according to claim 1, in which the transformer includes a ferrite core pot.