Patent Application
20090260534
The invention described herein may be manufactured and used by or for the government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.
Ships may be vulnerable to attack from underwater swimmers. In order to defend from this threat anti-swimmer weapons such as the MK3A2 concussion grenade, small arms, .50 caliber machine guns, and ship sonar is used. Unfortunately conventional grenades have fixed time delay fuses (approx. 4 to 5 seconds) and will detonate at various depths depending on how long the grenade is held after activation, the height above the water the grenade is dropped from and how far the grenade is thrown. The MK3A2 has a limited lethal radius and is no longer in production. Although fragmentation hand grenades may be used, they are less effective in water than grenades that release pressure. Guns may be used to engage an attacker at long ranges in air but their projectiles only penetrate water to a depth of a few feet. Ship sonar powerful enough to disrupt a swimmer also affects underwater work in a large radius around the ship. Conventional grenades have inherent safety risk as well. Grenades may be dropped in the ship before thrown, harming personnel. There is a need for a safe, accurate grenade for defense from underwater attack.
Before explaining the disclosed embodiments of the present invention in detail it is to be understood that the invention is not limited in its application to the details of the particular arrangement shown since the invention is capable of other embodiments. Also, the terminology used herein is for the purpose of description and not of limitation. In the figures, the same reference numbers are used to identify the same components.
Embodiments of the invention include an underwater grenade and a method for using an underwater grenade. Embodiments of the invention include a depth activated, hand emplaced ordnance utilizing safe and arm technology to address underwater threats (such as enemy swimmers) while providing a safe interface with personnel. The grenade is armed after a sequence of events have occurred including reaching a desired depth and a desired passage of time. Failure of any of the events to occur will cause the grenade to be rendered safe (a dud). Embodiments of the invention meet a need for safer, hand emplaced, underwater ordnance.
An interface section 112, within the casing and coupled to the other sections, is utilized to interface with personnel operating the grenade 100. The interface section 112 includes a means for tamper protection, such as having a sealed pop-top lid 170, pull tabs or grab loops. The interface section 112 includes a means for selecting a detonation depth wherein personnel may adjust a depth select switch (dial) 120 so as to set a depth (underwater) for the grenade 100 to explode. A means to effect the operation of the grenade includes a pull pin ring 110 to be removed by personnel. The pull top seal 170 shall be removed and the depth select switch 120 shall be set prior to pulling the pin 110. When the pin is pulled, a pair of switches interrupting both the positive and negative side of the battery 132 are closed in a power supply section 130 and power is applied to the electronics, thereby powering up the grenade, (interior electronics not shown) A pair of voltage regulators supply power for the arming logic circuitry and the high voltage convertor. The energy for the high voltage convertor is interrupted by the pressure switch and the two electrical switches (The electrical switches are referred to as ‘static switch’ and ‘dynamic switch’ in the block diagram. The dynamic switch must be cycled on and off continuously to enable the high voltage conversion process).
A safe and arm logic section 114 includes means for sensing initial environmental conditions, means for sensing subsequent environmental conditions, and means for determining whether a plurality of conditions are met for arming of the grenade 100. Upon removal of the pull pin ring 110 and powering up, the initial existing environmental conditions are inputted to the section such as the atmospheric pressure, the desired depth setting, and whether the system clock is working.
For arming and detonation to occur a plurality of conditions or sequence of events must be met. Failure to meet the conditions and sequence of events (such as dropping the grenade in the boat) will cause the grenade 100 to be rendered safe. Once these conditions are met, the safe and arm logic section 114 enables the high voltage converter and provides energy to the initiating section 140. Once armed, an output/power is provided to the initiating section 140 at the preselected depth. In one embodiment the grenade 100 may be set to detonate at depths between 10 and 100 feet. Depth is determined by use of a commercially available pressure transducer (such as Honeywell's stainless steel isolated pressure sensors) as known in the art. In the event of a failure of the pressure transducer, a backup delay timer controls initiation. The backup delay time is determined individually for each depth setting.
In one embodiment, an initiating section 140 includes a fireset including a high voltage capacitor, high voltage switch, and initiator. By using a low energy exploding foil initiator (EFT) the explosive train can be made ‘in-line’, thus eliminating moving parts. In one embodiment, when the desired depth is reached the fireset is electrically charged. This allows the fireset to be self-triggering (through the use of a breakdown switch), thus reducing the number of parts and the cost while increasing reliability. Once the voltage on the firing capacitor exceeds the breakdown voltage on the breakdown tubes, the energy stored in the capacitor is discharged into the detonator, thus detonating the explosive charge.
An explosive section 160 contains a secondary explosive compound optimized for underwater use, where the creation of expanding gases is a key characteristic (such as PBXN-109). This explosive is contained within a liner 150 for materials compatibility and mechanical properties. In another embodiment a liner 150 may be omitted if the casing material is suitable for the explosive.
The pull ring and pin is pulled 206 and allows power to flow 208 from the power supply section 130 and is applied to the grenade electronics. During power up, the arming logic is initialized and the switch setting of the depth dial is latched. The latched value is decoded into a maximum and a minimum fire time as well as a pressure sensor threshold value for the selected depth. As part of a power up test the initial existing environmental conditions are sensed 210, such as a valid depth selected, clocks and pressure sensors being operational, and the position of switches. In an embodiment of the invention, upon power up the grenade safe and arm logic section:
a) Verifies proper operation of system clock.
b) Latches depth setting and verifies setting is valid.
c) Verifies pressure sensor is within expected range (for example at sea level). If reading is within expected range depth is zeroed (measured pressure is treated as zero depth). If reading is out of range the unit is rendered safe (placed in a condition in which arming is no longer possible).
d) Verifies static switch drive is inactive.
e) Verifies pressure switch open assuring that grenade has reached a minimum depth such as 7 ft.
f) Starts timers.
A first timer 212 begins a countdown to a desired number of seconds. When the grenade is still not thrown into water by the end of the time period the grenade is rendered safe. After grenade emplacement into the water, current conditions are continually sensed and compared to required conditions and required sequence of events 214 so as to determine whether or not to continue towards arming the grenade. For example, in an embodiment of the invention the safe and arm logic section monitors the pressure switch and sensor via a digital circuit. At the same time, a separate analog circuit in the safe and arm logic section is performing similar checks. The analog circuit is composed of discrete components; resistors, capacitors, and comparators. This circuit is looking for the closure of the pressure switch prior to the sensing of 10 feet. If this sequence is detected, the electrical static switch is closed.
In one embodiment, the first timer (timer 1) is started 212 and sequence checking circuit 1 and 2 monitor the output of the pressure switch, the pressure sensor, and timer 1 to determine if the pressure switch and the pressure sensor detect water pressure in the proper sequence and in the proper time window (between 1 and 15 seconds after power-up). The pressure switch is designed to close at approximately 7 ft of water. The grenade is placed in the safe position if: 7 ft depth (pressure switch output) is sensed before 1 second or if 10 ft depth (pressure sensor output) is not reached within 15 seconds. Otherwise, the unit commits towards arming if it is determined that the fall rate is less that a predetermined value during the 7 ft to 10 ft range. When the required conditions are not met 214 the grenade is rendered SAFE 224.
When the required conditions are met 214 an additional test is made to ensure there is a safe separation 216 distance from the emplacement location (such as a ship). In one embodiment, the pressure sensor reading is compared to the expected value for 10 feet of water. Therefore, the logic expects to see the switch close prior to the sensor indicating 10 feet. If both sequence checks pass, timer 2 is started and the output for driving the dynamic switch is enabled (but not activated). The second timer begins to count 218 and the time to reach the desired depth is continuously sensed. If the grenade is within its proper fall rate, it will function on depth. If the unit falls either too fast or too slow it will function on time. In one embodiment, if the desired depth is reached OR the max time to reach the desired depth, AND the minimum time to reach desired depth 220 has passed then power will be supplied to the detonator and the grenade shall FIRE 230. This ensures the grenade shall not fire too early. In addition, if for some reason the grenade has risen above the safe separation depth 222 the grenade will be rendered SAFE 224. When the proper environmental conditions have been sensed, energy is supplied to arm and fire the explosive charge 230.
Another embodiment of the invention includes a method for defending against underwater attackers including: providing a grenade for underwater application with a plurality of sections enclosed within a casing; at least one interface section within the casing, coupled to the plurality of sections, having means for tamper prevention, means for selecting a detonation depth, and means to effect the operation of the grenade; at least one power supply section within the casing, coupled to the plurality of sections; at least one safe and arm logic section within the casing, coupled to the plurality of sections, having means for sensing initial environmental conditions, means for sensing subsequent environmental conditions, and means for determining whether a plurality of conditions are met for arming of the grenade; at least one initiating section within the casing, coupled to the plurality of sections, including a safe and arm device, and at least one explosive section within the casing, coupled to the plurality of sections, containing an explosive compound. The method further includes setting a plurality of desired detonation conditions to be met prior to detonation of the grenade on the grenade and dropping the grenade amongst the underwater attackers.
It is to be understood that the foregoing detailed description is exemplary and explanatory only and is not to be viewed as being restrictive of embodiments of the invention, as claimed. The invention is capable of other and different embodiments, and its several details are capable of modifications in various obvious respects, all without departing from the invention. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not as restrictive. Thus the scope of this invention should be determined by the appended claims, drawings and their legal equivalents.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 11193695 | Jul 2005 | US |
| Child | 12043659 | US |
