US 3470818 A
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Oct. 7, 1969 HANS-DIETER HARNAU 70,
DETONATOR GENERATOR FOR A SPIN-STABILIZED PROJECTILE Filed Oct. 24, 1967 2 C) O O C) PIE'ZO- sucm 0 a [news Inventor- United States Patent Int. (:1. F4zc 11/02 US. Cl. 102-701 Claims ABSTRACT OF THE DISCLOSURE A detonator generator for a spin-stabilized projectile which comprises a piezoelectric element and means for mechanically loading the piezoelectric element by the centrifugal forces produced by rotation of the projectile.
The present invention relates to a detonator generator for a spin-stabilized projectile, in which in use at least one piezoelectric body is loaded by compressive forces during the entire flight of the projectile and the resultant electric charge effects firing of the detonator.
Due to the piezoelectric effect it is possible to generate electric charges on the surfaces of a piezoelectrical body in response to mechanical stress. The magnitude of the charge is dependent on the stress itself, whereby the dependence is quantitatively expressed by the piezoelectrical modulus as the proportionality factor between the charge unit and the stress unit. In the case of quartz, this dependence is strictly linear, but for the present application, materials such as barium, titanate, yet still better lead zirconate or mixtures thereof are used, where the piezoelectrical modulus is considerably greater however, so that higher charges can be produced with the same compressive forces, but the relationships are considerably more complicated; and in particular, considerable sensitivity to temperature exists.
Piezo-electrical systems as detonation generators for missiles are known, but numerous problems arise.
A promising proposal was that of utilizing the kinetic energy of the missile upon impact for pressure-loading the piezoelectric body, but if the surface coated electrodes of the piezoelectric body were to be directly connected with the detonator, it was necessary to employ a detonator of high electrical resistance, so as to be certain that detonation took place. Such detonators are, however, extremely delicate things to manufacture and to handle. It was therefore known to provide a spark gap and/or matching transformer, so as to be able to use detonators of low electrical resistance. The main disadvantage of this method was, however, not eliminated, namely that the forces occurring upon impact are not reproducible and depend upon the angle of impact, the target material, etc., so that no definite detonating energy is available.
A further disadvantage of this method resides in the fact, that the piezoelectric body is frequently destroyed upon impact before detonation takes place. It was therefore proposed to provide resilient cushioning members, and use was additionally made of a ball-and-socket joint, to reduce the effect of varying angle of impact. Despite this, detonation reliability was only slightly increased.
In other systems inertia weight was provided to apply pressure to the piezoelectric body under the action of the acceleration occuring on firing of the projectile. The electric charge so obtained had then to be stored in some way, since when acceleration of the projectile ceases, no further forces are applied and therefore the charge on the piezoelectric body disappears again.
To avoid this difficulty, a diode is connected in parallel with the piezoelectric body to short-circuit the electric charge produced during acceleration. The electric charge liberated upon the subsequent cessation of acceleration was stored in a condenser, the maximum degree of efiiciency being 25%. This arrangement is unsuitable in the case of missiles which accelerate up to the time of impact. For example, a rocket fitted with such a device would have to burn out completely before it could detonate.
Another known system for storing the electric charge employs the hysteresis properties of certain piezoelectrical materials. These possess the property of being able to retain an electric charge even after removal of stress; this retained charge is known as the remanent charge and is analogous to the remanent magnetism in ferromagnetism. This remanent charge however is not only considerably smaller than the saturation charge" developed under stress, but it is also very much dependent upon temperature, particularly in that temperature range in which the above-mentioned materials of high piezoelectric modulus are used. Also, with such so-called electrets, surface currents occur which counteract the remanent electric charge. Thus, with this arrangement too, no definite detonating energy is available.
A considerably better result can be obtained if the piezoelectric body remains under pressure during the whole of the time in which the projectile is in flight; the piezoelectric body itself then serves to store the electric charge. Such an arrangement is known, and again the compressive force is supplied by an inertia weight which presses upon the piezoelectric body under the action of the firing acceleration of the projectile. A spring member is interposed to store the pressure and, upon cessation of the acceleration, the spring is prevented from becoming detensioned, since the spring member itself plastically deforms a clamping member. A severe disadvantage of this system consists in the fact that a prior examination of the efiiciency of the generator is not possible. Furthermore, a number of parts must be produced to fit together rather accurately.
It is therefore one object of the present invention to provide a detonator generator for spin-stabilized projectiles which includes a system also based upon the piezoelectric body itself acting as the energy storing means. The compressive forces are not, however, transmitted to it under the action of the firing acceleration or impact retardation of the projectile.
It is another object of the present invention to provide a detonator generator for a spin-stabilized projectile which includes a piezoelectric element arranged to be mechanically loaded by the centrifugal forces produced by rotation of the projectile. Conveniently the piezoelectric element is acted upon by an inertia Weight which produces the relevant loading.
This arrangement offers many advantages. At first the course of the rotation of the projectile over the length of the flight path is exactly known, so that the produced stress is available in reproducible size. Furthermore an examination of the detonator generator is possible very easily, by subjecting the same and measuring of the produced load. Also the mechanical structure is very easy and economical, whereby finally the not to be neglected advantage of lesser space enters.
To effect maximum utilization of the forces occurring, the component of force acting on the piezoelectric element is preferably directed at right angles to the axis of rotation of the projectile, the inertia mass preferably consists of a dense metal, and is preferably located as far as possible from the axis of rotation of the projectile.
In the interest of simplicity, the mechanical loading may be applied directly to the piezoelectric element and elements, respectively, and for optimum balance, a number of piezoelectric elements according to the present invention may be distributed symmertically around the axis of rotation of the projectile.
Since suitably a great axial distance. is to be chosen for the stress masses and since the piezoelectric elements must be disposed radially behind the masses, a free space results about the projectileand rotation-axis, respectively, which can receive suitably the detonator and/or its fuse.
Conveniently, more than one piezoelectric element may be mechanically loaded by a given inertia weight. This is conveniently arranged by providing two piezoelectric elements, superposed along a radius and connected electrically in parallel, to be acted upon by the corresponding inertia weight. In this way, the two electrodes of the piezoelectric elements can be electrically connected, while only the center tapping needs to be insulated, The connection of the individual middle tappings is then only possible in a parallel connection for the same polarity of the piezoelectric elements. If required, however, another arrangement can be used wherein part of the surfaces cannot of course be grounded. It is then possible to adapt to the detonator cap in a more advantageous way. When a plurality of piezoelectric elements is employed, their outputs should be connected to match the impedance of the detonator.
Care must be taken to insulate the surfaces of the piezoelectric element during the flight of the projectile in order to prevent the loss of the electric charge. If the detonator does not function after the projectile has been fired then, as a result of insulation losses and losses within the piezoelectric element, the electric charge will be dissipated. Thus, the detonator is not only primed at the time of firing of the projectile, but also has the feature that it automatically becomes unprimed after a given time.
With these and other objects in view which will become apparent in the following detailed description, the present invention will be clearly understood in connection with the accompanying drawing, in which the single figure is a diagrammatic, transverse cross-section through a spin stabilized projectile fitted with a detonator generator according to the present invention.
Referring now to the drawing, the detonator for spinstabilized projectiles comprises four generators in accordance with the present invention arranged symmetrically around the axis of rotation 6 of the projectile 5. Each of the generators comprises an inertia weight 1, which in use mechanically loads two piezoelectric elements 3 under the effect of the centrifugal forces produced by rotation of the projectile 5. Each element 3 bears upon a corresponding seating 4, while the inertia weights are displaceable in radial direction, at right angles to the axis 6. Electrical connection to the two surface coated electrodes of each piezoelectric element 3 is achieved by means of strips or small plates of conductive foil 2. The four center tappings can be connected up in any selected manner, care being taken to see that the polarity of the individual piezoelectric elements 3 is correct. The inertia weights are made from a heavy metal having a density of about 18 grams/cm It will be seen from the drawing that there is a considerable space available around the axis of rotation of the projectile 5. The detonator 7, indicated by legend, is located in this available space.
Also, insulation (not shown) is provided, to prevent dissipation of the charges developed by the piezoelectric elements. It will be readily understood that the discharge time constant of the insulation system is to be made a multiple of the flight time of the projectile.
It will be seen from the above description that the illustrated embodiment offers several advantages over prior detonator generators. Firstly, the pattern of rotation of the projectile is precisely known throughout the length of the path of the flight so that the centrifugal force generated is reproducible from one projectile of a given type to another of the same type. Also, the detonator gen- 'erator can be readily tested by rotating it and measuring the charge produced. Furthermore, the mechanical construction of the detonator generator is simple and therefore cheap, and additionally the generator occupies a relatively small space.
. Although not illustrated in the drawing, the inertia weight may act indirectly, rather than directly, on the piezoelectric elements 3. Thus it is within the scope of the present invention for the mechanical loading of the or each piezoelectric element 3 to be fitted by a lever system. Also, several inertia weights may be provided to act upon any one piezoelectric element.
Preferably, the or each piezoelectric element is made from a material of high piezoelectric modulus, for example barium titanate, lead zirconate, lead titanate, or mixtures thereof.
1. A detonator generator for a spin-stabilized projectile, comprising a cylindrical projectile housing,
a plurality of piezoelectric means symmetrically disposed about the axis of rotation of said projectile at radial distances Within said housing substantially furthest from said axis, each piezoelectric means symmetrically located about a radial axis,
inertia mass means symmetrically disposed along the radial axis inwardly adjacent each of said plurality of piezoelectric means, said inertia mass means symmetrically disposed about said axis of rotation,
electrode plates on said piezoelectric means,
a projectile detonator located at least near said axis inwardly of said inertia mass means and electrically connected to said electrode plates of said piezoelectric means, and
said piezoelectric means being pressed by said inertia mass means during spinning of said projectile about said axis, said inertia mass means thereby sliding outwardly by centrifugal forces operatively pressing said piezoelectric means so as to transmit said forces to said piezoelectric means, said inertia mass means being operatively supported by said adjacent piezoelectric means, and thereby generating ignition charges for said projectile detonator on said electrode plates.
2. The detonator generator, as set forth in claim 1, wherein a component of the forces acting on said piezoelectric means is directed at right angles to the axis of ro tation of the projectile.
3. The detonator generator, as set forth in claim 1, wherein said inertia mass means comprises a dense metal.
4. The detonator generator, as set forth in claim 1, wherein said inertia mass means is located contiguous to said piezoelectric means.
5. The detonator generator, as set forth in claim 1, wherein said inertia mass means is applied directly to said piezoelectric means.
6. A detonator generator, as set forth in claim 1, wherein said inertia mass means produces mechanical loading for more than one of said piezoelectric means.
7. The detonator generator, as set forth in claim 1, wherein the outputs from said piezoelectric element are connected to match the impedance of the detonator.
'8. The detonator generator, as set forth in claim 1, wherein a plurality of said inertia masses are provided acting upon said plurality of piezoelectric elements.
9. The detonator generator, as set forth in claim 1, wherein each of said piezoelectric means is made of a material of high piezoelectric modulus, selected from the group consisting of barium titanate, lead zirconate, lead titanate, and mixtures thereof.
10. The detonator generator, as set forth in claim 1,
which includes means for providing a discharge time constant which is a multiple of the flight time of the projectile, constituting a charge insulation for said piezoelectric means.
References Cited UNITED STATES PATENTS Alexander et a1. 102-70.2 Bliss 10270.2 X Wallbaum et a1 102-70.2
Lohnert 102-702 Giattino et a1. 1()2 -70.2
VERLIN R. PENDEGRASS, Primary Examiner