Patent Grant
7100437
Not Applicable
Not Applicable
Not Applicable
This invention relates generally to the field of usage monitors for small-arms and more specifically to a device for determining wear in small-arms through data collection and statistical analysis.
Many devices have been proposed to monitor the number of rounds fired an automatic or semi-automatic weapon. In general these devices are meant to warn the shooter before the magazine 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 that are an essential part of any maintenance program.
Maintenance of small-arms is of particular concern to law enforcement, the military and to competitive shooters. Wear gradually degrades the accuracy of a firearm and in extreme cases can lead to the bursting of a barrel and injury to the shooter. Wear can also lead to jamming, particularly in automatic and semi-automatic firearms. Maintenance schedules based on time in service completely ignore the firing schedule of a firearm. 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 barrel 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.
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 barrel is heated and wear, which results from the abrasive properties of the propellant, corrosion by the expanding gases and thermal gradients through the barrel 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 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 recoil. 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.
An example of an electronic shot counter for small-arms is that patented by Horne 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 counts.
A number of other patents add desirable features to the teaching of Horne 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.
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 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 maintenance.
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 round, the chambering of the first round after the last shot in a magazine has been fired or the ejection 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. No. 6,590,386 (2003, Williams) and U.S. Pat. No. 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.
Since barrel temperature is known to be a critical factor in determining the rate of wear it must be monitored during firing if an accurate assessment of a weapon's condition is to be made. None of the patents cited have means to measure this temperature nor do they have a way to determine the number of rounds fired at a particular temperature. None address data storage and its presentation so that it can be easily interpreted by the user or by an armorer. Further shortcomings of the aforementioned devices is 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 small-arms. Furthermore, those devices that utilize inertial switches, thereby avoiding the miscounts that are inherent in other sensing systems, cannot easily be altered to accommodate accessories such as night-vision scopes or noise suppressors that substantially change the mass of a weapon.
It is, therefore, the primary object of this invention to monitor the firing of small-arms so that service actions may be taken to maintain the weapon in serviceable condition.
Another object of the invention is to record information regarding the number of shots fired, the firing interval between shots and the temperature of the barrel as each shot was fired so that wear can be accurately assessed.
Still another object of the invention is to monitor the firing rate so that the weapon may be serviced before an excessive rate, that could lead to jamming, occurs.
A further object of the invention is to record and present firing data statistically so that it may be easily interpreted by the user or an armorer.
A yet further object of the invention is to record firing rate data that can be used to monitor and certify a user's training.
Yet another object of the invention is to record times and dates that a weapon has been fired for use in criminal investigations.
Still yet another object of the invention is to package the electronics of this data collection system so that it can withstand temperatures of up to at least 1100° F. on the barrel's surface.
An additional object of the invention is to provide a complete Faraday cage surrounding the electronics so that radio frequency emissions are minimized.
A further object of the invention is to provide a simple, easy-to-use, man-machine interface for data collection in the field.
Other objects and advantages of the present invention will become apparent from the following descriptions, taken in conjunction with the accompanying drawings, wherein, by way of illustration and example, an embodiment of the present invention is disclosed.
In accordance with a preferred embodiment of the invention there is disclosed a device for collecting data on small-arms usage comprising: A means to mount the electronics onto or within a gun so that it is protected from the heat of the barrel; a means to sense that a shot has been fired from a gun using acceleration, acoustic noise, magnetic field or RF emissions; a means to measure the interval between shots so that the firing rate may be determined; a means to measure the time at which each shot has been fired; a means to measure the temperature of the barrel when each shot is fired; means to store any combination of temperature, firing rate, firing intervals and time data for subsequent analysis, and a means to transfer data from the device to a computer or other data collection device.
The drawings constitute a part of this specification and include exemplary embodiments to the invention, which may be embodied in various forms. It is to be understood that in some instances various aspects of the invention may be shown exaggerated or enlarged to facilitate an understanding of the invention. Like numbers are used to represent like parts of the invention throughout the drawings.
a and 8b are sample histograms of data collected by the invention.
Detailed descriptions of the preferred embodiment are provided herein. It is to be understood, however, that the present invention may be embodied in various forms. Therefore, specific details disclosed herein are not to be interpreted as limiting, but rather as a basis for the claims and as a representative basis for teaching one skilled in the art to employ the present invention in virtually any appropriately detailed system, structure or manner.
Before describing the function and uses of the shot counter its mounting to a weapon will be described. Since an object of the invention is to measure the barrel temperature during firing the shot counter must be in thermal communication with the barrel. During heavy firing of an automatic weapon the gun barrel can reach temperatures of 400° C. or higher. Most commercial electronics are designed to operate at temperatures no higher than 125° C. and eutectic tin-lead solders melt at 183° C. Consequently, the shot counter must be thermally isolated from the barrel. This may be accomplished by separating the device from the barrel and using a remote temperature sensor or by insulating the device from the barrel and providing sufficient surface area for free convection cooling to be effective.
One of many possible mounting schemes is shown in figure one. In this embodiment the shot counter's case 12 is attached to the barrel 11 by clips 16 via insulators 13 and adhesive layer 14. The clips 16 may be threaded into nipples (not shown) that are retained within insulator 13 or they may be designed to simply clip into place; these and other mounting schemes are widely practiced. It is advantageous to use a material such as stainless steel for clips 16 since this may be easily formed, has a high yield strength and a low thermal conductivity, however, many other materials may be used.
Insulator 13 may be made from any material that has sufficient strength and a low thermal conductivity. Ceramic materials meet these requirements, particularly glass ceramics which have a conductivity of less than 1 W/m° C. Stainless steel may also be used if its higher conductivity, typically 10 to 20 W/m° C., is countered by the addition of cooling fins on the insulator.
Case 12 may be attached to insulator 13 by any means that does not form an efficient thermal conduction path. A high-temperature silicone adhesive 14 is preferred as this class of material can withstand temperatures of over 400° C., has excellent adhesion to most materials and is resistant to attack by most common solvents. Useful alternate adhesives include cyano-acrylates and high-temperature epoxies. Mechanical fasteners with low thermal conductivity, for example ceramic or stainless steel machine screws, can also be used.
A thermocouple can be used as the temperature sensor. This may be embedded within the contact surface of insulator 13 with the bead 18 positioned so that it will contact the barrel 11. Alternatively a spring or compliant material can be used to maintain the thermocouple bead in contact with the barrel. If an infrared device 19 is used it is sufficient to provide a path for thermal radiation to reach the detector.
The shot counter case 12 is provided with a plurality of contacts 15a–c for communication to an external device such as a laptop or hand-held computer. These contacts must be electrically isolated from case 12 by an insulating material 17. It is important to minimize the size of the electrical connection in order to prevent the escape of electro-magnetic radiation and to minimize radio-frequency interference. This is of great concern in military applications where an enemy combatant could use RF emissions to target a shooter. A display, such as an LCD, is a common source of RF emissions—for this reason a display is an optional part of the shot counter depending on its intended use.
A second mounting scheme for the shot counter is shown in figure two. In this embodiment a segmented insulating material 23a–d is clamped around the barrel 11 by a strap 26. This clamp may be tightened by any well-known means such as an eccentric lever, cam, thermal expansion, stretching, etc. It may also mechanically retain case 22 against insulator segment 23a although mechanical fasteners and adhesives can equally well be used. The insulating segments 23a–d accommodate small variations in the diameter of the barrel 11 and simplify installation.
Insulating material 23a–d must be able to withstand contact with barrel 11 as temperatures rise to 400° C. and above. There is, however, a significant thermal gradient radially outwards from the barrel 11 through the insulators 23a–d to the strap 26. Another insulating layer, 28, that has lower conductivity than material 23a–d but is less able to survive the high temperatures adjacent to barrel 11, may optionally be used to further reduce heat-transfer to the strap 26. Similarly, a layer of low conductivity material 29 may be disposed between insulator 23a and case 22. Materials that may be used for layers 28 and 29 include silicones and Muscovite mica. Insulation of any insulating layer may be further improved by surface roughening, the creation of air pockets, sintering with minimal densification and other processes known to those versed in the art.
The temperature sensor (not visible) projects from the case 22 through insulators 29 and 23a to barrel 11. If a thermocouple is used as a sensor a spring or compliant material can be used to maintain it in contact with the barrel. If an infrared device is used it is sufficient to provide an opening for thermal radiation to reach the detector.
As in the first embodiment contacts 25a–c are provided for communication. A display may optionally be provided.
The shot counter may be incorporated within a weapon or adapted to be mounted on an attachment rail as illustrated in
Many other mounting methods may be envisaged for the shot counter. It may be embedded within a hand grip or stock, clipped or strapped onto the weapon or inserted within the space between the barrel heat-shield and the hand-grip or rail interface system.
The operation of the shot counter will next be explained with reference to the block diagram of figure four. Power is supplied by one or more batteries 42. Since it is desirable to minimize the size and weight of the shot counter while maximizing the intervals between battery replacement zinc-air batteries are preferred. These have the highest charge density that is currently available.
Since power consumption is of critical importance a low-power microprocessor 40 that has a sleep mode has been used. In this embodiment at least three A/D inputs and at least two timers are required although these requirements can be reduced if different sensors and timing schemes are employed. It is also advantageous to have on-board non-volatile memory for data storage. An example of a processor that meets these requirements is the PIC18LF2320 by MicroChip Inc. This is a RISC processor with 256 bytes of onboard EEPROM and 8192 bytes of program memory. In sleep mode its power consumption can be as low as 0.2 μA while in operation it is less than 600 μA when operating at a clock speed of 4 MHz. This clock speed represents a good compromise between processing speed and power consumption within this device.
Three inputs are provided to the microprocessor 40 that make it possible to sense that a shot has been fired and to measure the temperature of the barrel. In one embodiment a piezo-electric accelerometer 43 is used to detect firing. This accelerometer is most effectively mounted with its base attached to the case of the shot counter (not shown) and oriented along the axis of the barrel so that the recoil of the gun, which occurs whenever a shot has been fired, produces a measurable charge. This charge may be measured as a voltage at one of the A/D inputs 41a of the microprocessor 40. An accelerometer is especially useful in this application since it consumes no power. In addition, it can be tuned to provide peak response in the frequency range of interest.
Referring now to figure five the details of the accelerometer mounting will be described. An accelerometer typically consists of a piezo-electric ceramic slab 51 that is loaded by a mass 52 and mounted within a case 53. Tuning may be accomplished by mounting the accelerometer 56 on a thick layer of a soft material such as silicone rubber 54. The relationship between the stiffness of the mounting layer 54 and the mass of the accelerometer 56 determines the system's frequency response.
From
The remaining inputs to the shot counter will now be described with reference to figure four. Elevated barrel temperature has been shown to increase the rate of barrel wear which leads to inaccuracy of the weapon. Thus it is important to know the temperature of the barrel as each shot is fired. Temperature may be measured with a thermocouple 45 and a thermistor 46 using well-known techniques. The thermocouple consists of two wires of different materials joined to form a measurement junction 45a that produces a voltage proportional to the junction temperature. Measurement junction 45a is held against the gun barrel when the shot counter is mounted so that its temperature may be measured. A leaf-spring (not shown) is easily adapted for this purpose.
The opposite end of the thermocouple leads are typically mounted on copper pads to form reference junctions 45b and 45c. These reference junctions 45a and 45b also produce a voltage that is proportional to their temperature and, as a result, it is necessary to know their temperature if the temperature at the measurement junction 45a is to be determined. This is accomplished by providing an isothermal block 44 that is electrically, but not thermally, isolated from the reference junctions 45b, 45c by a very thin electrically insulating layer. In printed circuit cards block 44 is usually a large copper feature such as a buried ground plane. In addition thermistor 46 is also electrically, but not thermally, isolated from the isothermal block 44. By using the resistance of the thermistor 46 the temperature of the isothermal block 44 can be determined and the voltage produced at the reference junctions 45b and 45c can be compensated for.
Compensation can be accomplished with the addition of discrete components within the device or, preferably, using logic within the microprocessor 40. Discrete devices are not favored because they consume power unnecessarily. The voltage produced by the thermocouple 44 is conditioned using an op-amp 47 and input to one of the A/D converters 41b of the microprocessor 40. The voltage from the thermistor 46 is conditioned by a second op-amp 48 and input to a second A/D converter 41c. Look-up tables within the microprocessor are then used to compensate for the reference junction temperature and accurately determine the temperature at the measurement junction 45a.
Power consumption by the op-amps 47 and 48 is limited by making use of a remote enable line 49 to turn them on and off. It has been found that a period of less than 10 milli-seconds is sufficient to make temperature measurements. When a shot has been detected the microprocessor output 41d drives the enable line 49 high so that the temperature can be read. After a period of less than 10 milli-seconds the enable line 49 is driven low and no further power is consumed by the op-amps 47 and 48.
The data collection and storage scheme will now be described with reference to
a and 8b show two histograms that each have 20 intervals or bins. The choice of the number of bins that are used is arbitrary and limited only by the available on-chip memory. Whenever a shot has been fired the interval from the previous shot is calculated, compared to the limits of the interval histogram in
The logic used by the shot counter in response to a signal similar to that of
INT0 is generated by the onboard comparator. This comparator uses the internal, programmable, reference voltage as one input and the signal from the piezo-electric accelerometer as the other. This allows the user to alter the threshold level so that shocks produced by normal handling are not registered as shots. It also allows the shot counter to be adjusted to work on a wide variety of small-arms.
When an interrupt is received the interrupt handler routine 100 is initiated as shown in
The sequence of operations of the MSSP service routine 300 is shown in
Further operation of the interrupt handler routine 100 will now be described with reference to
The sequence of operations of the TMR0 interrupt service routine 400 is shown ill
Referring once again to
Referring next to
Referring yet again to
Referring next to
Referring to
The general operation of the shot counter will now be described with reference to
Once initialization is complete and interrupts are enabled, the processor loops through the main routine beginning at step 206. If the shot active tracker is found to be true when evaluated at 208 this indicates that there has been an INT0 interrupt and the update shot information subroutine 700 is executed.
Referring next to
In step 712 the bin tracker is used to retrieve the count for the appropriate shot interval, which is incremented and saved. If the bin tracker retains its initial value it is the wake-up bin that is incremented. The interval in this case is indeterminate.
Next, in step 714, the temperature of the barrel is calculated and stored. The op-amps are enabled, the voltages from the thermistor and thermocouple are read, and the op-amps are disabled. Control of power to the op-amps is necessary if battery life is to be maximized. These voltages are then converted to temperatures using look-up tables. The temperature at the reference junction, determined from the thermistor, is then used to calculate the correct temperature at the measurement junction.
Flowchart 15a is continued on flowchart 15b by matching point “A” on flowchart 15a to point “A” on flowchart 15b.
The bin tracker is then re-initialized in step 718 and the first bin's upper limit is retrieved in 720. If the bin's upper limit is less than the temperature when tested in step 722 the bin tracker is incremented in 724 and the routine loops back to step 720. Steps 720, 722 and 724 are repeated until the value of the upper limit for some bin is greater than the temperature and the routine progresses to 726. In this step the bin tracker is used to retrieve the count for the appropriate shot temperature, which is incremented and saved. Note that program flow can go from step 722 directly to step 726 the first time that the temperature is tested. Subroutine 700 returns to the main program after clearing the shot active tracker in step 728.
Referring once again to the main program 200, as shown in
The operation of the shot counter can be most easily understood by following the events that occur beginning with the processor in its sleep mode at step 212 in
The holdoff tracker has not yet been set true so step 504 is executed. Since this is the first shot detected after waking, the value saved for the TMR0 tracker value is irrelevant. The shot active tracker is set true, TMR1 is started (initiating the hold-off period) and TMR0 is reset. It should be noted, however, that TMR0 is not restarted and cannot produce interrupts at this step—timing during the hold-off period is controlled by TMR1.
Control returns to the interrupt handler routine 100 at step 112 and from there to the main program 200 at step 216 as shown in
At step 702 the bin tracker is initialized and the TMR0 tracker is read and added to the hold-off period to get the interval between shots. Since the shot counter has just awakened from its sleep mode the interval is indeterminate and when the value of the first shot tracker is tested in step 704 the program braches to step 712. The initial value of the bin tracker, which was assigned in step 702, points to the wake-up bin within the shot interval histogram. The value in this bin is read, incremented and returned to memory.
With the shot interval histogram updated the temperature is next read in step 714. Power is supplied to the op-amps 47 and 48 in
The sequence used to update the temperature histogram varies slightly from that used for the shot interval because all temperatures are determinate. The bin tracker is initialized in step 718 and the upper limit of each bin is tested sequentially until one is found to be greater than the calculated temperature in steps 720, 722 and 724. The subroutine then branches out of this loop to step 726 where the count in the appropriate bin is read, incremented and returned to memory. The shot active tracker is then set false and control returns to the main program 200 at step 210.
The TMR0 tracker has not yet been updated so when tested at step 210 the program loops back to 206 and continues to loop through steps 208 and 210 until an INT0 interrupt occurs. Referring now to
This time through subroutine 500, the holdoff tracker has been set true so step 504 is not executed. TMR1, which controls the hold-off, continues to increment and the shot active tracker is not turned on. As a result, when control returns to main program 200 it continues to loop through steps 206–210.
A final impulse 73, shown in
This time through subroutine 500 the holdoff tracker has been set true so step 504 is not executed. TMR1, which controls the hold-off, continues to increment and the shot active tracker is not turned on. As a result, when control returns to main program 200 in
The next event to occur is the interrupt generated when TMR1 reaches its time-out state. The interrupt handler routine 100 in
It must be emphasized that the number of impulses that occur during the firing of a shot may vary from the three shown in
If no other shot is detected before the TMR0 tracker exceeds the sleep value, which is evaluated each time the main program passes through step 210, then step 212 will be executed. The timers will then be stopped, all interrupts except INT0 or MSSP disabled, and the processor will enter sleep-mode. If, however, a shot is detected before step 212 is executed then INT0 is activated and the program enters the interrupt handler routine 100 shown in
The holdoff tracker has not yet been set true so step 504 is executed. The value of the TMR0 tracker is saved so that the interval between shots may later be calculated. The shot active tracker is set true, TMR1 is started (initiating the hold-off period) and TMR0 is reset. As noted previously TMR0 is not restarted.
Control returns to the interrupt handler routine 100 at step 112 and from there to the main program 200 within the loop through steps 206–210 as shown in
At step 702 the bin tracker is initialized and the TMR0 tracker is read and added to the hold-off period to get the interval between shots. As this is not the first shot detected since the processor awoke the first shot tracker is found to be false at step 704 and the bin tracker is incremented from its initial value. The upper limit of each bin is tested sequentially until one is found to be greater than the interval between shots in steps 708 and 710. The subroutine then branches out of this loop to step 712 where the count in the appropriate bin is read, incremented and returned to memory. The temperature data is then read and stored in the appropriate bin in steps 714 through 726. The shot active tracker is cleared in step 728 and control returns to the main program 200 at step 210.
The TMR0 tracker has not yet been updated so when tested at step 210 the program loops back to 206 and continues to loop through steps 208 and 210 until an INT0 interrupt occurs. From this point onwards program flow is identical to that already described for the first shot detected from waking.
For the shot counter to be used in a program of small-arms maintenance it must be possible to easily access and interpret the collected data. This has been accomplished by providing histograms that can be displayed on a hand-held computer or down-loaded into another computing device. Subsequent analysis can apply weighting functions to predict wear-out where, for example, shots fired at high barrel temperature are weighted more heavily. Sample histograms for firing rate and temperature are shown in
In another embodiment of the invention the time and date of firing is stored for subsequent analysis. This is of particular importance in law-enforcement where reconstruction of events may be required. Time can be kept within the microprocessor, however, less power is consumed by using a stand-alone time and date chip. Time and date can be stored as each shot is fired up to the limit of available memory.
While the invention has been described in connection with a particular embodiment, it is not intended to limit the scope of the invention to the particular form set forth, but on the contrary, it is intended to cover such alternatives, modifications, and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims.
Primary Elements:
| Number | Name | Date | Kind |
|---|---|---|---|
| 2306747 | Edmond | Dec 1942 | A |
| 2984104 | Levine | May 1961 | A |
| 3127768 | Mason | Apr 1964 | A |
| 3453882 | Deas et al. | Jul 1969 | A |
| 3792638 | Cox et al. | Feb 1974 | A |
| 3902368 | Hasenbein et al. | Sep 1975 | A |
| 3914996 | Davis et al. | Oct 1975 | A |
| 4001961 | Johnson et al. | Jan 1977 | A |
| 4146987 | Hudson et al. | Apr 1979 | A |
| 4379405 | Engeler et al. | Apr 1983 | A |
| 4486710 | Schmidt | Dec 1984 | A |
| 4541191 | Morris et al. | Sep 1985 | A |
| 4928523 | Muhrer et al. | May 1990 | A |
| 5005307 | Horne et al. | Apr 1991 | A |
| 5303495 | Harthcock | Apr 1994 | A |
| 5402678 | Fritz et al. | Apr 1995 | A |
| 5406730 | Sayre | Apr 1995 | A |
| 5566486 | Brinkley | Oct 1996 | A |
| 5642581 | Herold et al. | Jul 1997 | A |
| 5659148 | Isgen | Aug 1997 | A |
| 5918304 | Gartz | Jun 1999 | A |
| 6094850 | Villani | Aug 2000 | A |
| 6311682 | Rice et al. | Nov 2001 | B1 |
| 6590386 | Williams | Jul 2003 | B1 |
| 6615814 | Rice et al. | Sep 2003 | B1 |
| 6643968 | Glock | Nov 2003 | B1 |
| 20030167909 | Matter | Sep 2003 | A1 |
| Number | Date | Country |
|---|---|---|
| 3911804 | Jul 1990 | DE |
| 4022038 | Jan 1992 | DE |
| 4417545 | Nov 1995 | DE |
| 283524 | Sep 1988 | EP |
| 10089894 | Apr 1998 | JP |
| 11051785 | Feb 1999 | JP |
| Number | Date | Country | |
|---|---|---|---|
| 20050155420 A1 | Jul 2005 | US |
