Patent Application
20130206480
1. Field of the Invention
The present invention relates to borehole drills, and more particularly to a manual or human-powered borehole drill
2. Background and Related Art
Tanzania is one of the many countries in the world that suffers from extreme poverty.
Many of the hardships in Tanzania can be attributed to the lack of clean water. Despite the facts that the country is surrounded by three major lakes and an ocean, and 7% of its area is covered by fresh water, it is difficult to find clean water because the water is contaminated and not suitable for human consumption.
Potable, or drinkable, water is the basis for a better life. It is estimated that Tanzanian women and children spend an average of 2 hours a day just collecting water, and it is common to find people who walk 6 hours just to find water. Other than the time concerns, 80% of all disease in developing countries is caused by bad water. Many of these people die because of the lack of medicine and health care. Since these people are collecting contaminated water, they spend their time being sick, visiting doctors, and paying for medicine they cannot afford. Although the people know the water makes them sick, they have no alternative.
Installing a village water well dramatically reduces all of these concerns and provides clean water for up to 1,500 families. Not only can the children go to school and the people have more time to help themselves financially, but they also have more opportunities to start businesses and in turn help the village progress.
Unfortunately, many villages lack clean water wells because the current methods of drilling in Tanzania are limited by opposite extremes. One option for drilling a well is a professional drilling rig, which is too expensive (from $15,000 to $20,000), while the other option is a homemade drilling system, which is too primitive and therefore unsuccessful drilling beyond 100 feet, where potable water is reached.
Of course, a professional drilling rig can drill to depths sufficient to access clean drinking water, but it costs upwards of $20,000 to hire the rig for the few days required to drill the borehole. The villages that need these wells cannot afford to spend this extreme amount of money. As a result, they turn to homemade drilling systems, which often are insufficient. The primitive, manual methods with which they dig or drill simply cannot penetrate deep enough to access clean water. The two main manual methods in most developing countries are hand augering and Rota-sludge. Hand augering simply uses an auger to dig the earth away and is effective only in soft soil formations, reaching depths of no more than 30 m (about 100 ft). Rotasludge is a less effective method because it reaches the same depths but has success in much less diverse formations. In all manual techniques, due to limited mechanical advantage and strength of tools, these methods generally are not sufficient to reach the depths required to access clean water.
A human-powered borehole drill bridges the gap between the large drilling rigs and the other less effective manual methods. A human-powered borehole drill will enable the people to drill their own wells for roughly $1,500, or even less. Intended mainly for developing countries such as Tanzania, the design is affordable and also extremely simple, as very little product support or spare parts will be needed. The drill uses conventional drill pipe and drill bits allowing the drill system to mimic more conventional methods of drilling and existing hardware to maintain uniformity in drilling and easier access to more drilling products.
The human-powered borehole drill will provide clean drinking water to almost any location having an aquifer at a reasonable depth, including remote locations such as villages in Tanzania at an affordable cost. The drill is capable of drilling a six-inch borehole reaching 250 feet through various soil formations to reach potable water. In an effort to bridge the gap between expensive professional rigs and less effective homemade systems, the drill uses existing drill pipe and bits, operates strictly on human power and is portable to move from village to village.
The design consists of three major components: the structure, the wheel support, and the wheel. The structure is designed to withstand loads of over three times the weight of 250 feet of drill pipe before yielding. Additionally, the structure is designed with a low center of gravity to prevent tipping and to add stability to the drilling process. The lifting of the pipe is accomplished through the use of a winch and pulley system, which also allows the operators to control the penetration rate of the drill bit. The wheel support is able to stabilize and support the weight of the wheel and allows ready access to the borehole and the drill pipe beneath the wheel. The innovative design of the wheel consists of a hub that is permanently attached to the wheel support via a bearing and eight removable spokes. Each of the spokes is pinned in place on the hub, and additional strength is gained from cross braces that are placed between the spokes. This design also allows for easy transportation.
In addition to meeting the quantitative specifications for drilling a borehole, the final design also meets the economic specifications. It can be manufactured for less than $5,000 and because the design consists mostly of welded steel, the majority of manufacturing can be performed in local regions. The entire drilling rig can also be easily disassembled and transported in the bed of a regular-sized truck or on a small trailer and can even be manually transported for transportation to remote areas.
The design has been tested in both theory and reality. Many tests were conducted, culminating in a final test with a fully functional steel prototype in which a six-inch-diameter borehole, 27 feet deep, was drilled in a sandy soil condition. Including setup, drilling, and cleanup, the entire test was completed in a five-hour period. More than a dozen boreholes fitted with working hand pumps have been completed.
The objects and features of the present invention will become more fully apparent from the following description and appended claims, taken in conjunction with the accompanying drawings. Understanding that these drawings depict only typical embodiments of the invention and are, therefore, not to be considered limiting of its scope, the invention will be described and explained with additional specificity and detail through the use of the accompanying drawings in which:
A description of embodiments of the present invention will now be given with reference to the Figures. It is expected that the present invention may take many other forms and shapes, hence the following disclosure is intended to be illustrative and not limiting, and the scope of the invention should be determined by reference to the appended claims. In addition, headings are provided to guide the discussion, but such headings are not intended to in any way be limiting of the scope of the invention.
Exemplary Functional Specifications:
Based on anticipated plans, goals, and research, various functional specifications to which the human-powered borehole drill would conform were originally defined. Of those, the ones that were deemed most influential on the design of the drill are set forth below in Table 1. The specific embodiments and examples set forth herein have been based on meeting or exceeding the functional specifications contained in Table 1. It should be understood that the illustrated embodiments and examples are merely examples of one potential design and configuration intended to meet one set of functional characteristics. It should also be understood that the embodiments and examples might be varied while still satisfying or exceeding the functional characteristics shown in Table 1, or that the embodiments and examples might also be varied to satisfy or exceed other functional characteristics depending on the specific needs. Therefore, the illustrated examples and embodiments are intended to be instructional and are not to be deemed limiting of the invention in its various forms.
Description of Exemplary Drill:
The components and assembly of the supporting structure 12 are shown in
The first vertical column 22 and the second vertical column 24 are three-inch square tubes, ¼ of an inch thick. This allows enough clearance to slide into a first sleeve 32 and a second sleeve 34 of the base 20, while remaining strong enough to withstand the applied loads. A series of rectangular steel tubing sections are welded between the legs of the base over the borehole for additional support. They also provide a rest for a slip plate 38 (see
The cantilevered beam 26 is a five-inch square steel tube that is seven feet long with a thickness of 3/16 of an inch. The beam 26 has two sleeves 40 of three-and-one-half-inch steel tubing welded at a 45-degree angle that allow the beam 26 to be slid securely on top of the first and second vertical columns 22, 24. The beam 26 will be pinned to the columns 24, 26 by four four-inch-long clevis pins. The high end of the beam 26 is nine feet above the ground, directly above the borehole. Both ends of the beam 26 have a pulley 42 inside, and a winch 44 is attached to the low end of the beam 26. The wire rope or cable from the winch 44 goes through the beam 26 and can then hook onto the pipe 28 or a Kelly bar 46 (see below) for lifting.
The functional specification for the lifting system is to be able to support and lift the weight of 250 feet of drill pipe. Based on the density of steel (490.6 pounds per cubic foot), a pipe wall thickness of 0.25 inches, and an outer diameter of 2.875 inches, the weight of 250 feet of pipe is 1725 pounds. While drilling, the borehole may cave in on top of the pipe; thus necessitating the ability to lift more than the just the weight of the drill pipe.
The three major components of the lifting system are the hoist structure, the winch 44, and the pulleys 42. The hoist structure was designed to never yield, even under extreme lifting conditions. Because of the length of the cantilevered beam 26, the highest stresses occur in the beam 26 at the junction with the first vertical column 22. This stress is due to a combined bending load and axial load. Therefore, to select the appropriate beam size of the beam 26, the von Mises stresses were calculated at this point. A simple optimization program was created in Excel to optimize the beam dimensions given a load, a safety factor, and a beam wall thickness. From this optimization routine a five-inch square steel beam was chosen with the yield strength of steel as 50,000 psi, a safety factor of 1.5, a wall thickness of 0.188 inches and a vertical load of 4,500 pounds. If other design considerations are applicable, a similar optimization could be used to create a satisfactory design for those conditions.
The winch 44 and pulleys 42 were then chosen to be able to lift the weight of the pipe 28 and more, but both of these components have a lower capacity than the beam 26. The goal was to ensure that there would never be any failure of the lifting structure. A hand winch with a 3,500 pound first layer capacity (and an 1849 pound full drum capacity) was selected as the winch 44. The selected winch has an enclosed gear for protection from the harsh environments of drilling, and it has an automatic brake, which means that it cannot move unless an operator is rotating the handle even with tension in the wire rope. Furthermore, at its maximum capacity the operator only has to apply 19.4 pounds of force to the end of the winch handle to move the load.
The pulleys 42 were selected to match the lifting capabilities of the winch 44 as closely as possible; however, the pulleys 42 were also constrained in size by the inside dimension of the beam 26. Stainless steel pulleys with a 4.25-inch diameter and plain bronze bearings were selected. These pulleys have an operating capacity of 3,000 pounds.
One major advantage that the structure shown in
Assembly of the wheel support 14 to the structure 12 is shown in
The platform 50 end is approximately forty-five inches from the ground, which will make it ergonomically ideal for an average height operator to turn the wheel. The platform 50 is twelve inches wide with ample space in the middle for the Kelly bar 46 and pipe 28 to slide through. Essentially, the only load that will be seen by the wheel support 14 is the weight of the wheel 16 itself.
This wheel support 14 is advantageous in that it allows unimpeded access to the drill pipe 28 that is beneath the wheel 16. In other designs, cross braces that provided structural stability to the table or platform that supported the wheel restricted access to the pipe 28 and made adding or removing pipe sections difficult. Also, this wheel support 14 offers more strength and stability because it is attached to a rigid structure 12 with a wide base 20.
The spokes 62 are three-foot long 1.5 inch by 2.5 inch rectangular tubing sections. One end of each spoke 62 fits into one of the sleeves 64 of the hub 60 and is pinned in place. The other end of each spoke 62 has an 11.5 inch long and 1.25-inch diameter solid steel rod 70 going through the middle perpendicular to the main axis of the spoke 62. A 1.25-inch diameter is ergonomically optimal for a power grip. Each rod 70 serves as a handle and is centered on the spoke 62 with five inches protruding both above and below the spoke 62. This accommodates people of different heights working on the drill 10. The outside end of the spoke 62 is closed and deburred for safety. For additional support of the wheel spokes 62, a 2 foot piece of one inch by one inch angle iron is pinned as a cross brace 72 between all adjacent spokes 62.
The six-foot diameter of the wheel 16 provides enough torque to drill efficiently in all soil types while still maintaining its portability. The spokes 62 are not permanently attached to the hub 60 so that the wheel 16 may easily be assembled and taken apart for transportation. Additionally, the weight of the wheel 16, especially the solid steel rods 70 serving as handles at the end of the spokes 62, provides enough inertia for the wheel 16 to maintain a continuous motion and act as a flywheel.
With the wheel 16 applying a constant torque to the drill pipe 28, it is possible that some angle of twist will develop through the length of the drill pipe 28 (within the borehole). This can cause unwanted wind-up that could potentially be dangerous if the wheel 16 were suddenly released. Therefore, calculations were performed to determine the twist angle with 250 feet of pipe 28 and a maximum torque of 1,000 foot-pounds, which corresponds to three operators exerting 111 pounds of force at the edge of the wheel. In the limiting case where the drill bit is held stationary, forty-nine degrees of twist will develop in the pipe. This would result in the wheel unwinding approximately ⅛ of a turn, which means that at most one spoke 62 will pass by the operator. In addition, with use of the winch 44 and the subsequent upward force that can be applied to the pipe 28, the situation in which the drill bit is held stationary can be avoided.
This wheel design holds many advantages over other possible designs. While testing with a wooden wheel prototype, it became apparent that moving six-foot diameter wheel was cumbersome and problematic. In order to begin the drilling process, the heavy wheel had to be slid over the top of the Kelly bar. Adjustment and placement of the wheel was also difficult because the operators had to work from three feet away. With the illustrated design of the wheel 16, the Kelly bar 46 is slid through the permanent hub 60. There are no awkward or heavy pieces to lift overhead and transport. Additionally the wheel 16 is able to be disassembled for transport and it can easily fit with in the required space (six feet by ten feet) with all of the other components.
The change-over process is facilitated by using three-foot sections of the pipe 28. The Kelly bar 46 has a square cross section slightly smaller than the diameter of the square hole 68 of the hub 60 and has a length of approximately 3 and ⅔ feet. Of course, the Kelly bar 46 and the hole 68 can be formed of any appropriate cross-section and corresponding shape that permits the transfer of torque from the wheel 16 to the Kelly bar 46 and thence to the pipe string. Regardless, this length of the Kelley bar 46 allows a quicker changeover and more manageable parts for manual labor.
When drilling starts, the Kelly bar 46 is almost completely above the wheel 16. As the drill cuts, the Kelly bar 46 and pipe 28 will lower until the top of the Kelly bar 46 is level with the top of the wheel hub 60. Then the winch operator lifts the pipe 28 until the slip plate 38 can fit under a coupler 80 between sections of pipe 28 and over the legs 36 of the base 20 (see
The major advantage of the change-over process came with the decision to use pipe segments that are three feet long instead of pipe segments that are longer, thus allowing the Kelly bar 46 to never be removed completely. Likewise a pump hose 90 and a swivel 92 never need to be removed. The pump hose 90 rests on hose hooks 94 attached to the beam 26. The small pipe sections are also easy to lift and handle, and there is plenty of space to comfortably work on the changeover under the wheel 16. Since there is no need to completely remove the Kelly bar 46 and raise and lower the pipe string, this process is much faster and easier than if longer pipe sections were used.
The final design of the drilling rig may optionally include a human powered pump. For example, a treadle pump system may be used. Regardless, in order to operate an effective mud rotary drill, a drilling fluid must be utilized that can remove the cuttings from the borehole. This process occurs by pumping a viscous slurry down the hole through the center of the drill pipe. The slurry then returns through the annulus between the borehole wall and the pipe with the cuttings created by the drill bit. This process can remove any type of cuttings by adjusting the viscosity of the slurry. As one example, a slurry additive called bentonite may be mixed with water to change the viscosity of the slurry. Since the cuttings are typically denser than the slurry, a combination of fluid pressure and shear stress act on the cuttings to propel them to the surface.
This results in pump requirements that can provide the necessary flow rate and fluid pressure, as is known in the art. A flow rate of fifty to one hundred gallons per minute is sufficient to create the necessary shear stresses on the cuttings and remove the cuttings at a quick enough rate. In order to provide adequate pressure, the pump needs to provide one foot of pressure head for every foot of depth of the borehole. This equates to a pressure of approximately 100 psi at a depth of 250 feet. Using these pump specifications, a table of pump power requirements can be calculated to determine pump needs, including the feasibility of operating a pump or pumps with human power.
Prototype Testing Results:
The final design was generated by proving many different concepts in preliminary prototypes. The first concept that was proved through testing was the ability to turn the pipe by walking in circles around the pipe. The test was very simple. A drill bit was spot welded to a pipe, and using pipe wrenches, the pipe was gripped and turned. During this test, one inch of depth was drilled in ten minutes. Originally, a system that would have the workers walk around the pipe twisting it as they walked in circles was envisioned. However, while testing this primitive prototype the idea that it would be much easier to be stationary and pass the wrench around was developed. This idea was selected as a part of the first fully functional prototype.
The first fully functional prototype was made of wood. This was done to reduce cost and decrease manufacturing time. A six-foot wooden wheel was used to harness human power to turn the pipe. This wheel had vertical handles and was pushed along by up to six workers that could stand around it in a circle. This design could be both operated with minimal effort and apply large amounts of torque to the drill pipe. This prototype was first tested in a small hole to ensure its feasibility. It met all expectations. The inertia of the wheel was able to keep the drill spinning in between pushes. This made for a smooth operation. The diameter of the wheel was a good size to operate and it would easily enable operators to apply enough torque.
After the two proof of concept tests, the fully functional wooden prototype was finished. The next test location was selected because of ease of access to water and clay soil conditions. Parts of the design that were being proved were the pumping system, the wheel, and the amount of downward pressure needed to drill. Through twenty-four minutes of continuous drilling a hole twenty-nine inches deep was drilled. This corresponded to an average drilling rate of one inch per minute. From this test, it was evident that one human-powered treadle pump as then being tested could not provide enough flow to lift all of the cuttings out of the hole. This caused the drill to get stuck easily and increased the effort required by the operators to turn the wheel. When extra downward pressure was added the drill dug a little faster at first but then the bit became stuck. It was determined that the ability to remove the cuttings needed to be improved by adding a second treadle pump before the next test.
The next two tests were located where the soil contained rocks varying in diameter from one-half inch to four inches. This condition is known as cobblestone. These tests were performed on two separate days using the wooden prototype. In these tests a second pump was added and bentonite was used to thicken the drilling mud. This was done in hopes that the cuttings would be removed more effectively. However, during the second test both treadle pumps broke because they could not generate the pressure needed to move the thick slurry. During the second test a mud pump was rented to enable the rest of the prototype to be tested.
The first four feet went just as the test in clay, but then the cobblestones were encountered. The cobblestones made the drilling slow and arduous and it became difficult to measure progress. Since there was no way to lift the drill bit off of the bottom of the borehole, the cobblestones were simply moved around instead of being cut through. Despite the slow progress the prototype was able to drill through rock and pull up the cuttings with a mud pump. From the borehole a rock was pulled that had the profile of the drill bit carved in, and the settling pond had shovels full gravel as proof that the drill had drilled through and removed rock. During these tests it became apparent that the design made it hard to access under and around the table to add and remove pipe. This resulted in modifications to the design.
The final design needed to include a way to remove the wheel to provide greater access in and around the pipe interchange area. Also, a hoist that would always be in place so that the pipe could be lifted and lowered while drilling. At this point it was decided that the initial implementation of the drilling rig would use a gas-powered pump to pump the drilling slurry. Although this uses a consumable fuel, it will use drastically less fuel than a conventional rig.
The final test with the final steel prototype was performed in sandy soil conditions. In all, twenty-seven feet were drilled in one and one-half hours. The actual time the drill was spinning was twenty-one minutes. The average time for adding a new pipe was two and one-half minutes. Extrapolating from this data it is calculated that it would take approximately eleven hours to drill 250 feet. This number may be optimistic because it assumes that no problems will be encountered with increased depth that have not already been encountered; however, a professional driller present at the test stated that there is no reason to believe that it becomes harder to dig with increased depth. This makes the 11 hour estimate more feasible.
The ability to raise and lower the pipe while drilling was an important part of this success. When the drill's full weight was resting in the hole the drill would dig too fast and the wheel would become very hard to turn. The winch was used to control the rate of penetration. This made the drill easy to keep at an approximately constant thirty rotations per minute. Being able to keep a constant rhythm while spinning the wheel greatly increases its sustainability.
Before this test, the process of adding new pipe had only been tested once. The procedure was very difficult, dangerous and took an entire team to perform. One of the main purposes of the final test was to test the modified pipe changing procedure. In the final design, the pipe sections were made smaller, for easy handling, and cleared out space to work underneath the wheel. During the testing it was very easy to change the pipe with only two people. Overall the results were very pleasing. More than a dozen boreholes fitted with functioning hand pumps have been completed using embodiments of the drill 10.
Through testing, it was determined that the illustrated design is capable of drilling in several soil types including clay, sand and cobblestones. Although at times the progress may be slow, the drill 10 remains effective. The drill 10 is also easily transportable and robust.
Although not specifically illustrated in the drawings, several possible modifications to the design have been contemplated as a result of the testing process. As a whole the manufacturing of the device is accomplished with simple operations; however, there are a few components that are manufactured using mills. Ways to eliminate the need for these more complex operations could be sought. The drill 10 also contains many exposed moving parts, which might be better shielded to prevent the possible pinching of operators' body parts. Finally, ways to reduce the overall cost of the device could be sought. Any such changes are embraced by the various embodiments of the invention.
In addition, tool joints might be used at every pipe connection to improve change-over and prevent over-tightening of joints. Also, a second slip plate 38 could be added to introduce redundancy to better prevent the pipe 28 from falling down the borehole during the removal of pipe sections. A sealed thrust bearing could be used between the wheel hub 60 and the wheel support 14 to protect against corrosion and to improve the performance of the wheel 16. Finally, the wheel 16 could be provided with a unidirectional mechanism that can prevent the wheel 16 from being spun in the wrong direction and employing a method of stopping the wheel 16 while it is turning. Any of these changes are also embraced by the various embodiments of the invention.
Instructions for Use:
To further assist in understanding the illustrated embodiment of the invention, the following paragraphs provide instructions for using the drill 10. First, an appropriate location to drill, directly above an aquifer, is located. An appropriate water source is also located to be used to pump down the drill pipe 28 while drilling. A flat, level location of appropriate size is then selected.
As is illustrated in
The structure 12, wheel support 14 and wheel 16 may be assembled at the same time as the slurry pump is set up. The slurry pump (not shown) is set up by placing the pump near the second basin 104 (that most distant from the pilot hole 100) and by feeding the pump inlet hose (also not shown) into the second basin 104. It should be ensured that a filter is in place to avoid clogging the pump with small pebbles. At the beginning, the outlet hose (not shown) is placed inside the pilot hole 100.
The trenches 102 and basin holes 104 are lined with Bentonite and all holes are filled with water until about three inches from ground level. The Bentonite will seal the trench and borehole walls reducing seepage and lowering the risk of down-the-hole cave-in. While the pump is running, cycling the water through the trench and basins, Bentonite is mixed in near the pump inlet hose, with vigorous stirring with a shovel. This is continued until the slurry is almost as thick as runny yogurt. Additional water or Bentonite may need to be added throughout the process to keep a proper slurry mixture.
Meanwhile, as shown in
As shown in
Next, as illustrated in
As is shown in
The first segment 110 of the pipe string is placed down into the pilot hole and is aligned underneath the Kelly bar as shown in
The slurry pump should always be running before beginning to spin the wheel 12 to drill.
Thus, the pump is run and the worker ensures that slurry comes out the bottom of the drill bit 112. At later stages, the worker ensures that slurry is rising in the borehole. Any leaks in the hose connections are fixed, then the wheel 16 is spun clockwise at a comfortable rate, such as thirty rotations per minute. Safety is ensured by keeping hands and arms out of the path of the spokes 52 and rods 70. Meanwhile, the operator of the winch 44 uses it to slowly lower the pipe string at a rate that allows the wheel 16 to continue to spin freely from the inertia of the wheel 16.
Controlling the descent of the pipe string helps ensure efficient drilling: if the wheel 16 stops immediately after being released, the pipe string should be pulled up using the winch 44 until the wheel 16 spins freely again. When the descent rate is too quick, the drill bit 112 becomes buried in the bottom of the borehole and will become difficult to turn, while a proper slow rate allows the slurry to flush excavated material away so the drill bit 112 does not become buried at the bottom of the borehole. If rock or harder soil is encountered, it may be necessary to allow the drill bit 112 to fully rest on the bottom to grind away the rock or harder soil, and the wheel 16 will become harder to turn.
Drilling continues until the top of the Kelly bar 46 is approximately flush with the top of the wheel hub 60 as shown in
After the cuttings are flushed, the slurry pump is stopped, and the pipe wrench 82 is snugged around the coupler 80 as shown in
A new segment of pipe 28 is prepared by attaching a coupler 80 to one end and by generously spreading thread grease on the open threads of the pipe 28 and inside the coupler 80 as indicated in
When the desired borehole depth is reached (measured by the number of segments of pipe 28 that have been added to the pipe string multiplied by the segment length), the pump is left running for ten to fifteen minutes to flush all cuttings from the borehole. Then, the slurry pump is no longer needed, and the pipe string can be removed from the borehole as will be illustrated in
The pipe string removal process occurs first by using the winch 44 to lift the pipe string until the slip plate 38 and wrench 82 can be positioned as shown in
A hook 114 is then threaded into the remaining top coupler 80 by hand, securing the pipe string with the pipe wrench 82, as shown in
Once the entire pipe string has been removed, the slurry is removed from around the borehole, such as by using a bailer or other method, and a plastic or metal casing is inserted the length of the borehole. Gravel is then packed around the outside of the casing, and the pump and connecting pipe is lowered to the bottom of the hole. The Bentonite slurry used to drill the hole is flushed out, and the ground surface around the casing is sealed with cement or with another method. Then a water wheel or pump is installed at ground level to draw up the water.
The present invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims, rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.
This application claims the benefit of U.S. Provisional Application No. 61/587,409, filed Jan. 17, 2012.
| Number | Date | Country | |
|---|---|---|---|
| 61587409 | Jan 2012 | US |
