Patent Application
20080282595
1. Field of Invention
This invention relates generally to the field of usage monitors for small-arms and more specifically to a device for determining the amount of ammunition usage in small-arms through data collection and statistical analysis and real time visual display.
2. Description of Related Art
Prior art discloses many devices have that claim to monitor the number of rounds fired by an automatic or semi-automatic firearm. Generally speaking, these devices are either used to record the number of rounds fired for later study or meant to warn the user before the magazine of the firearm becomes empty. Some of these devices count the number of rounds in a magazine; others assume that a full magazine has been inserted and count the number of rounds fired using a shot detector. A few devices have been proposed that record the time and date when a weapon was fired, particularly for use in criminal investigations. Yet other devices are currently in use on paint-ball guns for scoring, timekeeping and billing purposes. Although all of these devices are able to impart useful information about small-arms use over short periods, none can provide information that can be related to wear of the barrel or internal mechanisms of the firearm that are an essential part of any preventative maintenance program or recommended servicing schedule.
The maintenance of firearms is of particular concern to the military, to law enforcement, to competitive users and to a lesser extent, shooters in general. Wear from use gradually degrades the reliability and accuracy of a firearm and in extreme cases can lead to the failure of the firearm and or potential injury to the operator. Wear can also lead to jamming, particularly in automatic and semi-automatic firearms. Maintenance schedules that are generally based on time in service completely ignore the firing schedule of a firearm. For example, when used in training, thousands of rounds can be fired in a period of several months while in other periods a firearm may remain completely unused. A monitor that can be used to relate the firing history to barrel wear would allow maintenance to be based on usage, thereby benefiting all users of small-arms.
Some attempts have been made to record such data. In patents by Davis et al, (1975, U.S. Pat. No. 3,914,996) and by Gartz (1999, U.S. Pat. No. 5,918,304) an electronic apparatus is disclosed for determining the wear of the gun tube of an artillery weapon. Wear in an artillery gun tube is governed not only by the number of rounds fired but also by the charge, which may be varied with each round. Davis et al used a strain transducer to detect that a shot had been fired and applied a weighting function, proportional to the strain level, to determine the charge. The weighted number of shots fired was then stored in memory so that barrel wear could be estimated. Rates of wear on artillery barrels are greater than those of small arms due to factors such as propellant make-up and projectile type.
The approach of Davis et al fails to take into account the effects of temperature on barrel wear. If a series of rounds are fired the gun tube is heated and wear, which results from the abrasive properties of the propellant, corrosion by the expanding gases and thermal gradients through the tube wall, is greatly accelerated. It is also of limited applicability to small-arms where the shock and vibration of ordinary handling could produce many false counts.
In U.S. Pat. No. 4,001,961 (Johnson et al, 1977) a shot counter is attached to a firearm for use in a weapon maintenance program. As an example, they cite the replacement of the extractor after 15,000 rounds have been fired. Firing is detected by a micro-switch on the trigger, an inductance or piezoelectric transducer in the buffer, or an inertial switch that responds to the recoil of the weapon. The switches complete an electric circuit containing a battery that allows an electrochemical plating process to proceed while the transducers are used in a passive system, providing the electric potential that drives the plating. Usage is monitored by comparing the thickness of the plated layer at one end of a transparent tube to a color-coded scale on or adjacent to the tube. As in the previous citation there has been no thought given to avoiding false counts through handling.
Avoiding false counts is addressed in a patent by Hudson et al (1979, U.S. Pat. No. 4,146,987). An inertial switch comprising a pivoting, eccentric mass, a mechanical counter and a spring that allows a threshold acceleration to be set. This purely mechanical system is relatively large and difficult to implement on small-arms. It is also likely to undergo a change in threshold as the contact surface between the spring and the shaft wear during use. Clearly an electronic device is preferable for use with small-arms where size and weight are important concerns. Electronic devices generally provide more reliability than mechanical devices in adverse environments and weather conditions.
An example of an electronic shot counter for small-arms is that patented by Home and Wolf (1991, U.S. Pat. No. 5,005,307). Two micro-switches are used to provide input to a micro-controller that counts the rounds remaining in a magazine. An LCD display is used to indicate this count. Insertion of a new magazine is sensed by the first switch and the count is reset. Firing is detected by a second switch on the gun's slide. Doubtless this device could be modified to count the cumulative number of shots fired, however, slide movement while unloaded or when chambering the first round from a new magazine will result in false round counts being applied by the device to the cumulative total displayed.
A number of other patents add desirable features to the teaching of Home and Wolf. The aforementioned device cannot differentiate whether a round is in the chamber when a new magazine is inserted; Herold et al (1997, U.S. Pat. No. 5,642,581) resolve this ambiguity by allowing the user to increment the count indicated by the counting device; Villani (2000, U.S. Pat. No. 6,094,850) teaches the use of an additional switch within the chamber to automatically adjust the count. Neither device can differentiate between a round that has been fired and one that has been ejected without firing as required when a weapon is to be made safe and the round in the chamber must be removed by the operator.
Other inventors have sought to eliminate micro-switches in order to reduce cost and complexity while improving accuracy, reliability and sensor life. U.S. Pat. No. 5,406,730 (1995, Sayre) describes the use of an inertial switch in combination with an acoustic sensor to detect firing. Handling shocks cannot cause false counts because an acoustic signal must occur simultaneously before the count is incremented. Similarly, an acoustic signal from a weapon fired nearby cannot increment the count unless a simultaneous recoil impulse is detected. Brinkley, in U.S. Pat. No. 5,566,486 (1996), discloses an inertial switch that is adjustable; this makes it possible to set the acceleration level that will trigger a count so that recoil can be differentiated from handling shock. An additional benefit of this device is it ability to be adjusted to work on weapons with different recoil characteristics. A stated use of Brinkley's shot counter is to record the number of shots fired during a firearm's lifetime for use in its preventative maintenance schedule.
The patent of Harthcock (1994, U.S. Pat. No. 5,303,495) teaches the use of a Hall-effect device for counting shots fired from small-arms. A micro-processor records in non-volatile memory, the time and date of each shot fired along with the direction, from a Hall-effect compass, for crime lab analysis. In common with many of the previously described devices, this counter cannot distinguish between the firing of a live round, the chambering of the first new round after the last shot in a magazine has been fired, or the deliberate or accidental ejection from the host weapon of an unfired round.
The most technologically advanced devices for monitoring the firing of a projectile have been developed for use in paintball guns. When used in commercial applications it is important to record the number of rounds fired and the amount of time that a gun has been used. It is also desirable to provide information such as firing rate, maximum firing rate and battery condition to the user and to communicate these data, along with the gun's identification number, back to a control center. These features are all taught in U.S. Pat. Nos. 6,590,386 (2003, Williams) and 6,615,814 (2003, Rice and Marks). Both patents teach the use of a temperature sensor that is used to monitor the pneumatic canister that powers the projectiles. Williams differs from Rice et al in the use of a detachable device that fits onto the muzzle end of the barrel and additionally measures projectile velocity.
The main shortcomings of the aforementioned devices are their inability to be easily adapted for use on different weapons. With the exception of Williams's device all are difficult to retrofit to a variety of firearms. Furthermore, those devices that utilize inertial switches, thereby avoiding the potential miscounts that are inherent in other sensing systems, cannot easily be altered to accommodate the fitment of various accessories such as night-vision sights or sound suppressors that are common additions to firearms and that can substantially change the mass of the host weapon to which the device is fitted.
The invention provides a system and method for collecting data on firearms usage in the form of a device which is mounted to the firearm so as to be able to sense at least an impulse in the firearm due to firing. The device has a means to mount the electronics onto or within a gun so that it is protected from the environment; an impulse sensor; a processor and memory. The processor accepts impulse signals from the detector, and uses vector analysis to discriminate a true shot by comparing the signal from said impulse detector to a stored representation of a true shot in amplitude and direction, where prior art teaches the use of a scalar threshold. The stored information may comprise any combination of temperature, firing rate, firing intervals and time data for immediate display or subsequent analysis, and, optionally, information identifying the weapon to which the device is attached. In addition to a visual display screen, the device preferably has an interface to transfer data from the device to a computer or other data collection device.
The invention is an incrementally variable cost, electronic data capture system that records, stores and gives a real-time visual read-out of each shot discharged by a firearm allowing the user to instantly know how many rounds they have fired, when the firearm requires reloading and the lifetime usage of the firearm, all of which can be downloaded to a personal computer or data collection device via a USB port or similar interface.
The software also allows the system to be upgraded to support additional data retrieval functions as well as alert the operator to any anomalies or variations between the rounds fired.
The device is capable of distinguishing between dry-firing, rough-handling and actual ammunition discharge and is also capable of recognizing magazine changes, automatically resetting itself to the default round capacity preset by the weapon's operator. The device can be mounted on any existing firearm from a pistol to a crew-served weapon or alternatively, can be integrated into the electronics suite of a future weapons platform.
The electronic shot counter is a device mounted on a weapon system that measures the number of times that weapon is fired. In the desired embodiment, the shot counter detects shots using a three axis accelerometer and increments a visual display for each shot, however additional accelerometers either single or multi axis may be incorporated to isolate additional parameters of detection. The counter can be reset on a button press. Additional types of sensors may be used for different applications provided they allow vector detection.
In the desired embodiment, the device polls the accelerometer for “handling” accelerations and will “go to sleep” after some period of non-handling which is programmable and turns off the display and powers off most of the system. The display brightness responds to ambient light such that as ambient light gets darker, the display brightness should get dimmer.
In the desired embodiment, the device runs a system voltage of 6V nominal using 2×½AA 3.6V 1200 mAh Lithium cylindrical cells. Integrated battery holders mounted to the “bottom” (accessible side) of the board (20 mm wide, 28.6 mm long, 5 mm high) although various internal or remote battery casings may be utilized. The system provides power for a minimum of 36 hours “wake” state i.e. it is ready to detect a shot and 250 minutes of visual display on-time on a single set of batteries. Other power sources can be used.
In the desired embodiment, the device has a comprehensive digital and/or graphical display. The device has a three axis accelerometer to measure the shot events. It has a detection range within a 1<3000 g envelope in X, Y, and Z directions.
In the desired embodiment, the counter shall have two or three navigation buttons to allow the user to operate the device. The main board has a board width of 35 mm max with 1×½ AA battery or 2×½ AA batteries and a board length of <50 mm; ideally less than 40 mm. The display board width is up to 32 mm max as above. With a height up to 18 mm although it may be larger to accommodate interconnect and pads for the LED's which are variable height packages. The maximum allowable total package height is 23 mm excluding shielding; the front board may mount buttons for navigation and the front board maximum height is approx 18 mm. The three buttons are ideally Alps SKRCAA or equivalent IP water resistant rated or mounted in an IP rated structure for dust and water proofing. The buttons must be mounted to prevent water and dust ingress into the case to IP-60 or greater. The 3 axis accelerometer, has >1 G minimum range.
The following features require host access to the device's memory. Such access may be accomplished by USB or by IR-DA. IR-DA may be preferred as this does not require opening the device or access to an external connector, especially if the battery life of the device is “permanent” (>1 year).
In one embodiment, the device has a bit serial asynchronous interface and supports transmission of data stored in the EEPROM of the device upon a particular button command sequence.
In another embodiment, the device has a USB interface. The interface connector is protected behind the battery door. The interface provides operating power to the device when connected. The device uses three buttons for operation, although more or less may be utilized in alternative embodiments, which allow the following operations at a minimum: The default magazine capacity to be entered; switching between the magazine read-out and total rounds fired readout plus additional modes; resetting the default number; waking the shot counter. The overall shot count and other archive information is not resettable without recourse to computer reset software.
In the preferred embodiment, the physical size of the device is approximately 35 mm wide; 23 mm high maximum from top of picatinny rail and no longer than 50 mm. In another embodiment for use on pistols for example, the device can be smaller.
The device detects shots and increments the visual display counter. The counter shows the shot count and can be reset on a button press. The display operates at a minimum visible level during handling. The display brightens to an easily visible level on detected shot. The display will then fade or drop back to a barely visible level 1-5 seconds after a shot is detected.
In an alternative embodiment, after a shot is detected, the display shows the current shot count at maximum brightness for 10 seconds and then dims to a value based on the ambient light sensor. The brightness stays at the dimmed level for another 30 seconds and then shut off.
The device will detect shots and decrement the visual display counter from a “full magazine count”.
In the desired embodiment, the device will reset on a brief button press. A long button press will cause the display to flash indicating “set magazine count mode,” brief button presses increment through a table of counts, nominally 1-30, 50, 100 . . . 1). A longer button press will restore solid display mode at the chosen magazine capacity. The device stores every shot recorded with a time stamp in non-volatile memory. The device will store every shot's “signature” parameters—the acceleration vector and peak acceleration, along with the time stamp in non-volatile memory. The device will record the actual detected acceleration profile in non-volatile memory at the sampling frequency of the system.
The device will record the ambient temperature along with other shot data. It is preferable that the device does a vector sum of the accelerometer data and look for peak values in this data. The device carries out vector detection of the acceleration profile, discriminating a “true shot” from handling by bounds checking of a detected acceleration vector to acceptance volume. For example, the tail fitting inside a box defined by X-Y or XYZ bounds, head fitting in a second box defined by XY or XYZ bounds, any vector falling outside the head and tail bounds being discarded. The 3d profile of the recoil rise and fall is vector detected against the stored profile, which may be comprised of 100 (0.1 msec sampling interval over 10 msec) XYZ points, or can be stored as coefficients of a matching equation (e.g. a rise vector and a fall vector, 3 sets of 3 data points).
There is an option to detect the slide return time and close force and detect and record jams. The device should poll the accelerometer for “handling” accelerations and “go to sleep” after some period of non-handling (programmable, up to 10 min) which turns off the display.
Testing has suggested a peak recoil acceleration of approximately 3,000 gravities over about 0.35 msec or recoil of 2.2 mm. It appears from the data that there are mechanical resonances at a frequency 3-10× higher than the recoil acceleration (10-20 kHz), and that the return acceleration is on the order of 8 msec. This suggests an analog filter with a fall-off around 2.5 kHz would reduce the system's sensitivity to mechanical resonance and minimize aliasing of the signal, and that the accelerometer's typical 3 db roll off at 5 kHz is well suited to the application.
The accelerometers have an analog interface circuit that will trigger a digital signal when they detect a small amount of movement. This signal can be used to wake the CPU up from Sleep mode so that it can sample the data at a high rate to allow detection of shot data. In the desired embodiment, the signal from the accelerometer circuitry is AC coupled to reject any DC values such as gravity.
