US 3552053 A
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Jan. 5, 1971 K. W. JARVIS MEANS FOR COUNTING SHOTS FIRED FROM A GUN Filed Feb. 24, 1969 REGISTER 1-vNTOR KENNETH HJanws United States Patent 3,552,053 MEANS FOR COUNTING SHOTS FIRED FROM A GUN Kenneth W. Jarvis, Old Lyme, Conn., assignor to General Time Corporation, Stamford, Conn., a corporation of Delaware Filed Feb. 24, 1969, Ser. No. 801,421 Int. Cl. F41c 27/00 US. Cl. 42-1 11 Claims ABSTRACT OF THE DISCLOSURE A device for counting shots fired by a gun consisting of a frame clamped to the gun barrel including a piezoelectric crystal which is stressed by reason of the transient radial expansion of the barrel to produce electrical output pulses which are sensed by a threshold detector and counted in a register.
Users of ordnance often desire to keep track of the number of shots fired from a particular gun. This need may be experienced during laboratory testing, range firing or actual field maneuvers. While each of these situations has its own operational requirements, the desirability of providing a single counter operable under all conditions is apparent.
In the past, efforts to provide such a device have for the most part employed switches, typically a switch with a plunger contacted by some movable portion of the firing mechanism. Such switches are not only bulky and may interfere with the firing mechanism but have the disadvantage of registering misfires as well as live rounds. Installation and adjustment are difficult. Others have utilized the change in gas pressure on a plunger mounted in a hole specially bored in the gun barrel. This not only affects the integrity of the gun but is unreliable due to corrosion problems. Still others have employed the fact of ionization in the gas ejected at the mouth of the barrel but such ionization is not easy to detect electrically.
It is accordingly a principal object of the present invention to provide a shot counter which may be easily attached and removed from the barrel of a gun without modification of, or damage to, the gun. It is a related object to provide a shot counter capable of universal usage with guns having a range of barrel diameter. It is another object of the invention to provide a shot counting device which is perfectly reliable, responding only to live shots, which may be employed either on a laboratory basis or under difficult field conditions, and which cannot be caused to miscount when the gun is subjected to a mechanical shock, Additionally, the counting device is not affected by moisture or dirt, is completely independent of the firing mechanism, and is so compact and light as to be susceptible of mounting in a hidden and protected position with no effect upon the balance or utility of the gun.
Other objects and advantages of the present invention will become apparent upon reading the following detailed description and upon reference to the drawings in which:
FIG. 1 is an elevational view of the well-known Ml6 rifie with a portion of the front end grip broken away to reveal the counter in place on the barrel;
FIG. 2 is a side elevation of the counter assembly and a portion of the barrel to which it is mounted;
FIG. 3 is a sectional view looking along the line 33 in FIG. 2;
FIG. 4 is a bottom View of the device shown in FIG. 3;
FIG. 5 is an elevational view similar to FIG. 2 but Showing a modified construction;
FIG. 6 is a view looking along the line 66 in FIG. 5; and
FIG. 7 is a wiring diagram showing the interposition of a threshold detector between the crystal and the registering portion of the counter.
While the invention will be described in connection with certain preferred embodiments, it will be understood that I do not intend to limit the invention to the particular embodiments shown but instead intend to cover all of the various alternative and equivalent constructions included within the spirit and scope of the appended claims.
Turning now to FIG. 1, there is shown the profile of a typical M-l6 rifle having a body 10, a barrel 11, and a stock 12. Located on the body is a rear hand grip 13 while surrounding the barrel is a front hand grip 14. The front hand grip 14 is of hollow construction and serves to accommodate the counter assembly 20 which is made up of the frame 21 and a threshold detector-register 22 arranged closely adjacent.
In accordance with the present invention, the frame 21 is clamped onto the gun barrel so as to be subjected to the transient radial expansion during firing with provision for transmitting such expansion to a transducer in the form of a piezoelectric crystal so that the latter produces a sharp electrical output pulse, with each pulse being registered in the detector-register 22. In the particular embodiment shown, the frame includes a pair of levers 31, 32. Such levers are preferably machined out of channel stock as shown in FIG. 4 to provide a high degree of rigidity. Thus each lever has a face portion 33 with integral side walls 34 defining a central space 35. The opposed upper ends of the levers are scalloped out as indicated at 41, 42 for conforming to, and gripping, the opposite sides of the gun barrel 11, Mounted between the opposed lower ends of the levers is a piezoelectric crystal 50 having mounts 51, 52 of insulating material which are seated upon the levers and which extend through openings 53, 54, for the purpose of bringing out electrical terminals 55, 56.
In order to draw the two members 31, 32 together at the center, and to provide a fulcrum for the transmission of radial expansion of the gun barrel to the crystal, a fulcrum screw 69 is used which extends through alined openings 61, 62 in the faces of the levers and which is fitted with a pair of pivot blocks 63, 64. The pivot block 64 has a clearance opening while the pivot block 63 is threaded so that upon turning of the screw both the gun barrel and crystal are firmly clamped to eliminate lost motion between them and to apply a certain amount of preload. Since the screw permits a wide range of take-up, the same device may be secured to gun barrels having a range of diameter. The pivot blocks are preferably oriented to provide sharp fulcruming edges indicated at 65, 66. Due to the channeled construction of the levers, the screw 60, the pivot blocks, and crystal terminals are all protectively nested, making a device which is not only compact but durable in the face of mistreatment or heavy usage. And, because of the inherent rigidity, the free pivoting around friction-free points of fulcruming, and absolute freedom from lost motion, it is found that the abruptness of the change in the diameter of the gun barrel is efiiciently transmitted to the crystal element to produce an output wave having an extremely abrupt wave front. Moreover, while the levers 31, 32 both are extremely rigid, they are, because of the channeled construction, of relatively low mass so that conversion from dimensional change to electrical output is not appreciably slowed or attenuated by inertial effects.
In accordance with one of the aspects of the present invention, a spring is incorporated into the mechanical system for the purpose of limiting the peak pressure applied to the crystal. More specifically, in accordance with the invention, a tension spring is substituted for the central fulcrum screw 60 which not only limits the peak pressure but which insures a reliably high clamping force and complete elimination of play automatically upon installation and without any need for care or adjustment on the part of the installer.
Thus turning to FIGS. and 6, which show the alternate embodiment, corresponding parts are indicated by the corresponding reference numerals with the additional subscript a. Briefly stated, thet levers 31a, 32a, are scalloped at their opposed upper ends as indicated at 41a, 42a, for clamping reception of the gun barrel 11a, while a crystal a on mounts 51a, 52a, is clamped between the levers at the lower ends. To draw the two levers together tension springs a are provided. For the purpose of transmitting the force of the springs to the levers 31a, 32a and to provide fulcrum for rocking movement, a yoke of C configuration is used made up of pairs of arms 71, 72
and articulated at a central pivot 73. The arms of each pair are spaced so that the levers 31a, 320 are protectively sandwiched inbetween. The pairs of arms mount fulcrum pins 63a, 6401 which project through the levers. The springs 60a bridge the lower ends of the yoke, being secured to suitable mounting pins 61a, 62a.
In contact with the crystal are terminals 55a, 56a for the bringing out of electrical connections. The scalloped or relieved portions 410, 42a, at the upper end of the levers preferably have a radius R which is equal to or less than the radius of the smallest gun barrel with which the device is to be used, thus providing either continuous or spaced point contact between the levers and the sides of the barrel. The springs 60a are dimensioned to have a length in natural state which is less than that which exists when the device is in working position. In use. the shot counter frame is snapped over the gun barrel with the resulting extension of the spring providing a reliably high level of clamping force and with prestress applied to the crystal. Any possibility of play in the system is thus eliminated by the single act of installation and without need for any screw adjustment and without risk of overstressing the crystal. The springs 60a preferably have a high spring constant so that the elongation which accompanies the normal transient change in diameter of the gun barrel upon firing is accompanied by a force change sufficiently high as to produce a well-defined output pulse from the crystal.
It is one of the features of the counting system disclosed herein that an electronic threshold detector is interposed between the crystal and the register so that impulses are transmitted to the register which are above a threshold level resulting from actual firings, but impulses resulting from casual mechanical shock due, for example, to dropping the gun or striking the gun barrel, are held back. Moreover, means are provided for insuring that impulses above the threshold level, and which are to be counted, are reduced to a safe reference level, thereby preventing any possible damage to, or malfunction of, the registering device or circuitry. Thus, referring to FIG. 7, which shows the threshold detector-register 2.2, the threshold detector portion of the device, indicated at 80, has an input terminal 81, and output terminals 82, 83. Included in series with the input terminal is a first diode 84 which insures that only negative impulses are utilized and appear at terminal 85 at one end of an input resistor 86. For passing those negative impulses which exceed a threshold level, corresponding to actual firing of the gun, a Zener diode 87 is provided polarized so that the Zener voltage must be overcome by the input signal, Any input signals aTa lesser level simply do not get through. For the purpose of limiting the magnitude of those impulses which do get through, a diode stack 90 is connected across the circuit in shunting relation. presenting a terminal 91 and having an associated resistor 92. It will be apparent that the maximum voltage which can appear across the diode stack is the summation of the forward voltage drop of the individual diodes. Thus where silicon diodes are employed having a forward drop on the order of 0.65 volt, clamping of the signal occurs at the level of approximately two volts. Such signal is fed to the input terminal of a transistor 93 having load resistors 94, 95, the latter being connected to the output terminal 82 which feeds a suitable register 100. The latter may be any device, preferably of miniaturized construction, which provides a direct read-out, or count, of the electrical impulses applied to the terminal 82.
It is one of the further features of the invention that the frame 21 of the counter and the capsule which contains the threshold detector-register are both highly compact, are mounted adjacent one another on the gun barrel and preferably are included within the front hand grip of the gun in an enclosed and protected position. The device, being out of sight, and so light as to not affect balance or usage, may be included on guns intended for the field without any modification or without any effect upon the efiiciency of operation. The total number of shots registered over a given period of time may be used in various ways, either in the evaluation of the gun or in the evaluation of the man carrying it.
While use of a piezoelectric crystal is preferred as an electromechanical transducer, it will be understood that the invention in its broader aspects is not limited to use with a piezoelectric crystal and that other types of pressure-sensitive transducers may be employed, as, for example, magnetrostrictive transducers, without departing from the invention. Consequently, the term piezoelectric crystal as used herein shall be understood to mean a piezoelectric transducer or its pressure-sensitive equivalent.
I claim as my invention:
1. In a counting device for counting the shots fired by a gun, the combination comprising a frame having two members spaced from one another, a piezoelectric crystal having electrical terminals, said members being shaped at one end to clampingly embrace a gun barrel and having provision at the other end for clampingly engaging the piezoelectric crystal, means for mechanically linking the center portions of the members so that relative movement of the members resulting from transient radial expansion of the barrel when a shot is fired results in stress being applied to the crystal, and means including an electrical impulse register connected to the terminals for registering impulses resulting from successive shots.
2. The combination as set forth in claim 1 in which the linking means is in the form of a threaded member r0- tatable to achieve takeup of lost motion and to establish a steady state clamping pressure.
3. The combination as set forth in claim 1 in which the linking means is in the form of a spring which is yieldable for installation or removal of the frame and which is dimensioned to achieve takeup of lost motion and to establish a steady state clamping pressure.
4. In a counting device for counting the shots fired by a gun, the combination of a frame including a pair of levers pivoted together to define pairs of jaws opposed to one another, means for gripping a barrel between one pair of jaws, a piezoelectric crystal having electrical terminals and mounted between the other pair of jaws so as to be stressed upon transient radial expansion of the barrel when a shot is fired, and means including an electrical impulse register connected to the crystal terminals for registering successive impulses therefrom.
5. The combination set forth in claim 4 in which the levers have a common central fulcrum.
6. In a counting device for counting the shots fired by a gun, the combination of a frame having means for gripping opposite sides of a gun barrel, a piezoelectric crystal having electrical terminals and mounted in the frame so as to be subjected to stress by reason of the transient radial expansion of the barrel when a shot is fired, and means including an electrical impulse register connected to the crystal terminals for registering successive impulses therefrom.
7. The combination as claimed in claim 6 including a threshold detector interposed between the crystal and the register for permitting response of the register to peak values of voltage accompanying firing but precluding response to voltage impulses created by casual mechanical shock.
8. In a counting device for counting the shots fired by a gun, the combination of a frame having means for gripping the opposite sides of a gun barrel, a piezoelectric crystal having electrical terminals and mounted in the frame so as to be subjected to stress by reason of the transient radial expansion of the gun barrel when a shot is fired, an electrically actuated register means for registering of input pulses, and a threshold detector having input and output terminals interposed between the crystal and the register means, said threshold detector including means effectively in series with an input terminal and having the characteristics of a Zener diode so that impulses are transmitted which are above the effective Zener voltage while impulses less than the Zener voltage and resulting from casual mechanical shock are held back.
9. The combination as claimed in claim 8 in which the threshold detector further includes a voltage limiter in a shunting circuit for limiting the voltage applied to the register means to a predetermined reference value.
10. In a counting device for counting the shots fired by a gun, the combination of a frame having means for gripping the opposite sides of a gun barrel, a piezoelectric crystal having electrical terminals and mounted in the frame so as to be subjected to stress by reason of the transient radial expansion of the barrel when a shot is fired, and means including an electrical impulse register connected to the crystal terminals for registering successive impulses therefrom, said impulse register means being mounted on the barrel closely adjacent the frame.
11. The combination as claimed in claim 10 in which the gun has a hollow front hand grip and in which the frame and impulse register means are included within the hollow of the hand grip for concealment and protection.
References Cited UNITED STATES PATENTS 2,306,747 12/ 1942 Ojalvo 421(E) 3,453,882 7/1969 Kirkendall et al. 42,1 (E) BENJAMIN A. BORCHELT, Primary Examiner C. T. JORDAN, Assistant Examiner