Ammunition and explosives – Igniting devices and systems – Electrical primer or ignitor
Reexamination Certificate
2002-05-13
2004-11-09
Keith, Jack (Department: 3641)
Ammunition and explosives
Igniting devices and systems
Electrical primer or ignitor
C102S275110
Reexamination Certificate
active
06814005
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an electronic detonator adapted for civil use of the type which comprises an ignition charge, a battery unit for emitting igniter current for initiating the ignition charge and an electronic circuit for controlling said emission of igniter current.
TECHNICAL AREA
Electronic detonators which have been proposed up to the present are generally adapted to use, as an igniter current emitting means, a current storing means, such as a capacitor, which before initiating the ignition charge is charged by means of current that is supplied via the control lines (often a two-wire bus) to which the detonator is connected and by which detonator set-up signals and detonator firing signals are communicated. If the detonator has a built-in battery, for instance, to drive the electronics of the detonator, it has been deemed to be most essential that the capacity or energy content of the battery does not allow emission of current which could initiate the ignition charge even if, for unknown reasons, current paths required therefor would be provided.
A “nonelectrical” detonator has been suggested (see WO 96/04522) which is activated via a so-called ignition or shock tube and which comprises a battery for emitting igniter current for initiating an ignition charge, the battery either being active and connected by means of a switch which is acted upon by the pressure generated by the burning ignition tube in the detonator, or alternatively being connected but will be activated, for instance thermally, by action from the burning ignition tube.
However, those skilled in the art would realise that using a switch or activating a battery as stated above generally means uncertainty in the present context and can easily result in an undesirable current supply with the ensuing uncontrollable detonation.
SUMMARY OF THE INVENTION
The object of the present invention is to provide an electronic detonator which is provided with a battery, whereby the risks of uncontrollable initiation of the ignition charge of the detonator as a result of non-intended battery current supply are, in practice, completely eliminated.
The above-mentioned object is achieved by means of an electronic detonator which exhibits features according to the invention which are evident from the appended claims.
The invention is thus based on the understanding that primarily battery connection must not take place by switch-controlled connection or externally provided activation of a battery, but by an active battery unit (consisting of one or more active cells), in the following referred to as “battery”, being caused to move inside the detonator to a position where igniter current can be emitted. Suitably, it is a matter of the battery being caused to move between a resting position, in which igniter current cannot be taken out of the battery, to an activated position, in which the battery is prepared to emit igniter current. The motion of the battery is conditioned by the action of mechanical forces exerted on the battery, which has to be of a predetermined magnitude and has a predetermined direction in order to overcome a strong inertia of motion of the battery. These parameters of action may be chosen so that only desirable, expected action of forces causes motion of the battery while overcoming said inertia of motion of the battery, while other sorts of uncontrolled action owing to shock, acceleration and similar rough treatment, as well as action caused by static electricity and electric and magnetic fields do not cause any motion of the battery and, consequently, any risk of undesirable battery connection.
Suitably, the detonator according to the invention comprises battery activating means which are adapted to provide, in response to external activation, such as by means of an ignition tube or electric control signals, the required application of forces on the battery. Said activating means preferably operate pyrotechnically. Advantageously, use is made of a drive or propellant charge which is arranged in the detonator and is releasable in a controlled manner and which in connection with combustion generates such a pressure that the desired application of forces is obtained. The drive charge can be released electrically or by means of an ignition tube. It is also possible to work without a drive charge, in which case the pressure of the gases which are generated in connection with the combustion of the ignition tube charge is used to generate the required driving pressure inside the detonator.
When using a drive charge, it is advantageously arranged in a drive chamber, to which an actuation part of the battery is exposed to be acted upon so as to cause movement by means of a driving pressure which is generated in the drive chamber by the drive charge. When an ignition tube is used, it is suitable to arrange a non-return valve at the connection of the ignition tube to the drive chamber in order to prevent the driving pressure generated in the drive chamber from being discharged via the ignition tube.
The battery is advantageously given the shape of a plunger or piston which is arranged in a corresponding bore in the detonator. In this connection, it is preferred for the bore to be arranged in a tubular element which is dimensionally stable and resistant to mechanical action and which has a longitudinal extension at least corresponding to the longitudinal extension of the battery and the distance of motion of the battery between a resting position and an activated position as well as a preferred free space in front of the front end of the battery (seen in the direction of motion), when the battery has moved to the activated position.
Since detonators conventionally are elongated and have an ignition charge in one end, it is suitable that the axial direction of said tubular element is parallel to and preferably coincides with the longitudinal axial direction of the detonator.
When using a drive chamber, it is suitably aligned with the bore in a tubular element according to the above, preferably constituting an extension thereof.
Constructively, the tubular element and the drive chamber are advantageously formed as a pressure vessel in order to be able to resist a predetermined pressure which in any case exceeds the driving pressure required to cause the battery to move from a resting position to an activated position. At the same time, a very stable and resistant construction is obtained, as is appreciated, the construction having a great capacity of resisting rough treatment, especially in the transverse direction, which otherwise could possibly involve a risk of uncontrolled change as regards motion of the battery.
The motion of the battery from a resting position to the activated position preferably occurs towards the ignition charge. Thus, improved safety is obtained in connection with uncontrolled axial action due to acceleration (transverses action due to acceleration constitutes, as those skilled in the art realise, no risk). Action due to acceleration which should be able to cause “forward” motion of the battery towards the ignition charge must in principle mean an impact in the longitudinal direction of the detonator on the end of the ignition charge of the detonator or, alternatively, “backward” jerks in the opposite end of the detonator. In the first case, the ignition charge will detonate due to the impact itself a long time before the battery starts moving towards the activated position. In other words, here it is not a matter of any additional risks. In the second case, with “backward” jerks, it is in practice almost impossible to bring about such a powerful longitudinal acceleration of the detonator that the battery will be caused to move forwards to the activated position. If an ignition tube or the like is connected to the associated end of the detonator, it may also be advantageous to make the connection to the detonator in such a manner that in connection with jerks, for instance, in the ignition tube, the ignition tube or its fixing in the detonator breaks well before th
Burns Doane Swecker & Mathis L.L.P.
Dyno Nobel Sweden AB
Keith Jack
Sukman Gabriel S.
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