FR2648555A1 - Delay for pyrotechnic appliance - Google Patents

Abstract

Device forming a delay for pyrotechnic appliances characterised in that it comprises a piezo-electric sensor 10 designed to generate an electrical initiation pulse under the effect of a pressure wave which it receives, an electronic circuit 20 able to measure the passage of a predetermined time from the emission of the electrical initiation pulse by the piezo-electric sensor 10, and an output initiator 30 designed to invoke a downstream pyrotechnic chain at the end of the predetermined time monitored by the electronic circuit 20.

Description

 The present invention relates to the field of delays for pyrotechnic devices.

 We know that it is necessary to have, in many pyrotechnic devices, elements capable of delaying the transmission of fire for a predetermined and known time.

 The duration of the delay to be introduced depends on each application and can vary over a wide range, for example between 10 msec and several minutes.

 The delays hitherto proposed, for pyrotechnic devices, generally consist of sticks or pellets of materials having precisely known fire transmission characteristics, the geometry of which is adapted to the desired delay.

 The delays so far proposed, however, are not entirely satisfactory.

 It will be understood that in practice it has hitherto been necessary to design new delays as a function of each new application, in order to have the desired delay time.

 Furthermore, the precision of the delays hitherto proposed leaves something to be desired.

 The present invention now aims to provide a new device forming delay which is more precise than existing devices, compatible with pyrotechnic chains, and which is almost universal, that is to say that it allows, without modification of its basic structure, a choice of time delay in a wide range.

 An auxiliary object of the present invention is to propose a new delay-forming device which has a volume and a geometry of the same order as the existing delays, in order to be compatible with current pyrotechnic devices.

 These objects are achieved according to the present invention by means of a device forming a delay for pyrotechnic devices, characterized in that it coinprend - a piezoelectric sensor designed to generate an electrical initiation pulse under the effect of a pressure wave. that it receives, - an electronic circuit able to measure the flow of a predetermined time from the emission of the electric initiation pulse by the piezoelectric sensor, and - an output initiator designed to solicit a downstream pyrotechnic chain at the end of the predetermined time controlled by the electronic circuit.

 Other characteristics, objects and advantages of the present invention will become apparent on reading the detailed description which follows, and with reference to the single appended drawing which schematically represents, in the form of functional blocks, a delay in accordance with the present invention .

 A piezoelectric sensor 10, an electronic circuit 20, and an output initiator 30 can be seen in the appended figure.

 As previously indicated, the piezoelectric sensor 10 is designed to generate an electrical initiation pulse at its output II under the effect of a pressure wave which it receives. Such a pressure wave can be generated for example by a primer or a pyrotechnic composition placed in the chain upstream of the piezoelectric sensor 10.

 The function of the electronic circuit 20 is to measure the flow of a predetermined time from the emission of the electric initiation pulse from the output 11 of the piezoelectric sensor 10.

 Specialists in the field can easily design a large number of electronic circuits capable of fulfilling this timer function. For this reason, the electronic circuit 20 will not be described in detail. However, the essential means making up the electronic circuit shown by way of nonlimiting example in FIG. 1 will be discussed below.

 Finally, it is recalled that the function of the initiator 30 is to request the pyrotechnic chain located downstream at the end of the predetermined time controlled by the electronic circuit 20.

 For the most part the electronic circuit 20 shown in FIG. I comprises a door 22, a clock 23 and an element 24 forming an up or down counter.

 The constant frequency signal from the clock 23 is applied to the input of the up / down element 24 via the door 22. More specifically, the door 22 is designed not to be switched to the passing state only after emission of the initialization pulse on the output 11 of the piezoelectric sensor 10.

 Thus, before the transmission of this initialization pulse by the piezoelectric sensor 10, the door 22 being closed, the up / down counter element 24 receives no signal from the clock 23. No time count n is then operated.

 On the other hand, the time delay is initiated as soon as the door 22 is switched to the state passing through the initialization pulse coming from the piezoelectric sensor 10. In fact from this instant, the door 22 being on, the element 24 counts or counts the pulses from the clock signal 23.

 When a predetermined count or count is reached, the output of the up / down counter 24 requests the output initiator 30.

 It will be noted that preferably a signal shaping stage 21 is inserted between the piezoelectric sensor 10 and the validation input of the door 22.

 Likewise, preferably a power circuit 25 is interposed between the up or down counter element 24 and the initiator 30.

 Furthermore, the entire electronic circuit 20 is preferably supplied by an autonomous electrical energy source 40, such as an electric battery, by means of a mechanical safety switch 50.

 The element 24 is advantageously formed by a programmable up / down element, so that the delay time imposed by the device according to the present invention is easily programmable in the factory. Many existing systems fulfilling the function of a programmable up / down counter can thus be used in the context of the present invention.

 Preferably the up / down counter element 24 is designed to define a porgrammable delay of I to 2 steps of Xms, X being able to be chosen between several values. By way of example, element 24 can be designed to define a programmable delay from I to 212 steps of names, 100 ms or Is.

 Element 24 thus makes it possible to program delays of 10 ms to 40.96 s by step of names, or of 100 ms to 409.6 s in steps of 100 ms or again from Is to 4096 s by step of Is.

 It will be noted that all of the components forming the electronic circuit 20 can be combined in a single programmable integrated circuit box.

 The delay forming device according to the present invention has, among others, the following advantages - low volume compatible with existing devices, - very high precision, - perfect compatibility with pyrotechnic chains, - large varieties of time delay possible, by simple programming.

- availability of boxes with standard geometry and dimensions, but offering a wide variety of delay time choices, - possibility of standard mass production, whatever the desired delay value, and subsequent customization of each box , for example by programming in the manner of a PROM system, - low cost resulting therefrom.

 Of course the present invention is not limited to the particular embodiment which laughs at being described but extends to any variant in accordance with its spirit.

 As an example, note the possibility of inserting programmable dividers between the output of the clock 23 and the corresponding input of the gate 22, in order to selectively modify the period of the pulses applied to the element 24 and select thus the delay programming step.

Claims (10)

 1. Device forming a delay for pyrotechnic devices, characterized in that it comprises a piezoelectric sensor (10) designed to generate an electrical initiation pulse under the effect of a pressure wave which it receives, - a electronic circuit (20) capable of measuring the flow of a predetermined time from the emission of the electric initiation pulse by the piezoelectric sensor (10), and - an output initiator (30) designed to request a downstream pyrotechnic chain at the end of the predetermined time controlled by the electronic circuit (25).  2. Device forming delay according to claim 1, characterized in that the piezoelectric sensor (10), the electronic circuit (20) and the initiator (30) are housed in a common housing.  3. Device forming delay according to one of claims I or 2, characterized in that the electronic circuit (20) comprises a clock (23) and an element forming an up or down counter (24).  4. device forming delay according to claim 3, characterized in that the electronic circuit (20) further comprises a door (22) validated by the initialization pulse from the piezoelectric sensor (10) so that the door (20) authorizes the passage of signals from the clock (23), towards the element (24) forming an up or down counter only after emission of this initialization pulse by the piezoelectric sensor (10) .  5. Device forming delay according to claim 4, characterized in that a shaping stage (21) is interposed between the output of the piezoelectric sensor (10) and the door (22).  6. Device forming delay according to one of claims 3 to 5, characterized in that a power stage is interposed between the output of the element forming an up or down counter (24) and the output initiator (30) .  7. Device forming delay according to one of claims I to 6, characterized in that the electronic circuit (20) is supplied by an autonomous electrical energy source (40).  8. Device forming delay according to claim 7, characterized in that the electronic circuit (20) is supplied by the source of electrical energy (40) via a mechanical safety contact (50).  9. Device forming a delay according to one of claims 3 to 8, characterized in that the element forming an up or down counter (24) is programmable.  10. Device forming delay according to one of claims 4 to 9, characterized in that the electronic circuit (20) further comprises programmable dividers between the clock output (23) and the corresponding input of the door (22).