Title:
Lifting pump for manganese nodules
Kind Code:
A1


Abstract:
A lifting pump for manganese nodules includes: a cylindrical body that is sealed at upper and lower portions thereof by a semi-spherical upper cap having a fluid outflow port and a cable insertion tube, and by a semi-spherical lower cap to which an inflow case of a pump unit is coupled; a pumping motor that has a fluid passage formed between an inner surface of the body and an outer surface thereof, is vertically fixed in the body, and drives the pump unit using electric power supplied through a cable; a cover that provides a seal around a shaft of the pumping motor; the pump unit that is installed between the shaft of the pumping motor and the semi-spherical lower cap, is driven by the rotation of the pumping motor, and lifts seawater together with the manganese nodules; a sealing means that provides a seal between the pumping motor and the pump unit; and a reducer that is coupled to the bottom of the pump unit and guides the seawater including the manganese nodules to the pump unit.



Inventors:
Yoon, Chi-ho (Yuseong-Gu, KR)
Kim, Young-ju (Yuseong-Gu, KR)
Park, Yong-chan (Yuseong-Gu, KR)
Kwon, Seok-ki (Yuseong-Gu, KR)
Yang, Tae-yual (Seongnam-Si, KR)
Application Number:
11/730497
Publication Date:
11/22/2007
Filing Date:
04/02/2007
Assignee:
KOREA INSTITUTE OF GEOSCIENCE
MINERAL RESOURCES
Primary Class:
International Classes:
E02F3/88
View Patent Images:
Related US Applications:
20060038437Electrohydraulic boulder breakerFebruary, 2006Moeny
20060002770Lite mine roof support crib and methodJanuary, 2006Paton-ash et al.
20030111892Method of mining and an improved mining machine with a shovel moveable relative to a vehicle chassisJune, 2003Neilson et al.
20090051210Construction Machine, in Particular Road Milling Machine, Recycler or Stabilizer, and Drive Train for Construction Machines of This TypeFebruary, 2009Busley et al.
20100018515Green Concrete SawJanuary, 2010Marsic et al.
20070145810Gas hydrate material recovery apparatusJune, 2007Wendland
20080296959Cutter head for a ground cutter machine having rotary cuttersDecember, 2008Chagnot et al.
20080036277Pick Shank in Axial TensionFebruary, 2008Hall
20060105695Anchored mine ventilation structureMay, 2006Kennedy et al.
20090236898Ice Grooving Device and MethodSeptember, 2009Szukiewicz
20080290718Waste Disposal During Pit MiningNovember, 2008Zukerberg et al.



Primary Examiner:
BOBISH, CHRISTOPHER S
Attorney, Agent or Firm:
ARENT FOX LLP (WASHINGTON, DC, US)
Claims:
What is claimed is:

1. A lifting pump for manganese nodules, comprising: a cylindrical body that is sealed at upper and lower portions thereof by a semi-spherical upper cap having a fluid outflow port and a cable insertion tube and by a semi-spherical lower cap to which an inflow case of a pump unit is coupled; a pumping motor that has a fluid passage formed between an inner surface of the body and an outer surface thereof, is vertically fixed in the body, and drives the pump unit by electric power supplied through a cable; a cover that provides a seal around a shaft of the pumping motor; the pump unit that is installed between the shaft of the pumping motor and the semi-spherical lower cap, is driven by the rotation of the pumping motor, and lifts seawater together with the manganese nodules; a sealing means that provides a seal between the pumping motor and the pump unit; and a reducer that is coupled to a bottom of the pump unit, and guides the seawater, including the manganese nodules, to the pump unit.

2. The lifting pump as set forth in claim 1, wherein the pump unit includes: at least two impellers fixed to the shaft of the pumping motor in sequence; the inflow case fixed to the semi-spherical lower cap with outer surfaces of the impellers enclosed thereby; and an inflow cover installed in one opening of the inflow case with the reducer coupled thereto.

3. The lifting pump as set forth in claim 1 or 2, wherein the pump unit is installed in multiple stages.

4. The lifting pump as set forth in claim 1, wherein the sealing means installs a mechanical seal around the shaft of the pumping motor, which is exposed between a motor case and an inside of the cover, fills the inside of the cover with oil, and installs an upper ball bearing at an upper end of the shaft of the pumping motor supported in the motor case.

5. The lifting pump as set forth in claim 1, further comprising a stand that is vertically installed on a bottom of the lower cap so as to maintain the lifting pump itself in a vertically installed state.

Description:

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates, in general, to a lifting pump for manganese nodules, and more particularly, to a lifting pump for manganese nodules, in which a motor is installed in an upper portion of the lifting pump, a pump unit is installed at a lower end of the motor, and an inflow port for free suction is installed at a lower end of the lifting pump, thereby allowing suction under any adverse situation; in which the manganese nodules pumped by the pump unit pass through a separate fluid passage, thereby pre-emptively preventing a shaft of the pump unit from being restricted; in which a low lifting pump is produced for the sake of user's convenience of installing the lifting pump, thereby securing the stability of position fixture in the installed state; and in which the pumping motor is waterproofed by a combination of an O-ring and a mechanical seal, thereby increasing durability, reducing energy consumption and the number of parts due to high efficiency compared to a liquid ring motor.

2. Description of the Related Art

Generally, deep-seabed manganese nodules are flat or nodular, dark brown amorphous concretions, which are soft when mined, but are hard and brittle when dried.

These manganese nodules have major constituents that include manganese, iron, silicic acid, and moisture, and trace constituents that vary regionally. With regard to the creation of the manganese nodules, there are two theories: one based on the sedimentation of colloidal hydroxides and the other based on the formation by the catalysis of iron oxide. The manganese nodules have a growth rate that is known to be in the range from 0.01 mm to 1 mm per 1000 years.

The system for mining these deep-seabed manganese nodules includes a seabed collector, a lifting pipe, a lifting pump system, a buffer, and a marine mining ship.

When separated and collected from the seabed by the collector, the manganese nodules are continuously transferred up to sea level through the lifting pipe, after the lifting rate thereof is optimally adjusted at the buffer, that is, the intermediate reservoir, which is located at the bottom of the lifting pipe.

Further, the manganese nodules are transferred through a flexible hose between the collector and the buffer. Thereby, the collector can smoothly travel on the seabed.

In addition, when connected between the collector and the buffer, the flexible hose is connected with the collector in a vertical direction and with the buffer in a large arch shape, in order to guarantee maximum travel performance of the collector. At this time, the buffer is located at the front of the collector such that the flexible hose maintains the arch shape.

To maintain an optimal position of the buffer relative to the collector is almost impossible using only a dynamic positioning system (DPS) of the marine mining ship in spite of the exact consideration of a dynamic behavior of the lifting pipe.

In order to solve this problem, consideration is given to a plan of controlling the buffer to complement a function of the DPS of the marine mining ship as well as maintain the optimal relative position thereof by installing a self-propelled system on the buffer.

As described above, when the relative position of the buffer and the collector is optimally maintained by controlling the position of the buffer, the travel performance of the collector on the seabed is guaranteed. The excellent travel performance of a nodule collection travel vehicle in a mining system acts as the most important factor for determining the quantity of the manganese nodules yielded on a commercial scale.

Meanwhile, some of the deep-seabed manganese nodule mining systems employ a liquid ring pump. As illustrated in FIG. 1, such a liquid ring pump is constructed such that a body 101 is provided with a pump at an upper portion thereof, a motor at a lower portion thereof, and an inflow port 102 in the middle thereof. The intake port 102 is provided with a strainer 104.

The method of mining these deep-seabed manganese nodules covering the seabed using the pump having this construction is as follows.

Seawater is ejected through another ejection pipe, thereby floating sludge and manganese nodules. The floated sludge and manganese nodules are introduced into the inflow port 102, which is located in the middle of the body 101, together with seawater. The introduced mixture of the sludge and the manganese nodules is discharged to and collected at the surface by means of the kinetic energy of the seawater.

However, the liquid ring pump having this construction has the following problems. First, because the body is provided with the pump at the upper portion thereof, the motor at the lower portion thereof, and the inflow port in the middle thereof, the lower portion of the pump is spaced apart from the seabed by a predetermined distance. Due to the distance between the lower portion of the pump and the seabed, if the sludge and the manganese nodules are not floated even though the seawater is ejected through the ejection pipe, a lot of unnecessary seawater must be additionally sucked in. Hence, the quantity of the manganese nodules per unit volume of the seawater is low, which results in increasing the mining cost.

Second, because the inflow port is installed in the middle of the pump body, the strainer frequently blocks the inflow port, thus degrading inflow conditions, so that the motor fails to perform its normal function.

Third, the manganese nodules that have been sucked in have a high possibility of being jammed between the impeller and the shaft of the motor while passing through the motor. This entails a high possibility of damage to the motor.

Fourth, because the pump is long, there remains difficulty installing the motor. Fifth, because the motor is in contact with the seawater, the motor has a high possibility of being corroded by the seawater.

SUMMARY OF THE INVENTION

Accordingly, the present invention has been made keeping in mind the above problems occurring in the related art, and a first object of the present invention is to provide a lifting pump for manganese nodules, in which an inflow port can be precisely positioned at the seabed covered with the manganese nodules, so that a lot of manganese nodules can be mined using a small quantity of inflowing seawater, and thus the mining time and cost can be reduced.

A second object of the present invention is to provide a lifting pump for manganese nodules, in which the manganese nodules pumped pass through a fluid passage surrounding the motor, so that a fluid passage structure becomes simple, to thus eliminate the fear that the sludge or manganese nodules will become stuck, and thus stable operation is possible to not only increase the operational stability of the product but also considerably decrease the likelihood of damage to the pump.

A third object of the present invention is to provide a lifting pump for manganese nodules, in which a mechanical seal is used as a shaft sealing device, so that the sludge does not penetrate into the shaft sealing device, and thus maintenance expenses are very small.

A fourth object of the present invention is to provide a lifting pump for manganese nodules, in which a flexible hose is installed at the lower end of the pump, so that the manganese nodules can be easily pumped up under any situation.

A fifth object of the present invention is to provide a lifting pump for manganese nodules, in which a pump unit can be installed in multiple stages, such as two or three stages, so as to respond to changes in the installed depth in the seawater.

A sixth object of the present invention is to provide a lifting pump for manganese nodules, in which a pump unit is integrally formed with a pumping motor, so that the installation is easy, and a separate shaft joint is not required.

A seventh object of the present invention is to provide a lifting pump for manganese nodules, in which the center of gravity is located in the middle of the pump, so that the pump is easily installed, and the stable operation is possible without being influenced by ocean current.

In order to achieve the above objects, according to an aspect of the present invention, there is provided a lifting pump for manganese nodules, which includes: a cylindrical body that is sealed at upper and lower portions thereof by a semi-spherical upper cap having a fluid outflow port and a cable insertion tube and by a semi-spherical lower cap to which an inflow case of a pump unit is coupled; a pumping motor that has a fluid passage formed between an inner surface of the body and an outer surface thereof, is vertically fixed in the body, and drives the pump unit by electric power supplied through a cable; a cover that provides a seal around a shaft of the pumping motor; the pump unit that is installed between the shaft of the pumping motor and the semi-spherical lower cap, is driven by the rotation of the pumping motor, and lifts seawater together with the manganese nodules; a sealing means that provides a seal between the pumping motor and the pump unit; a stand that is vertically installed on the bottom of the lower cap so as to maintain the lifting pump itself in a vertically installed state; and a reducer that is coupled to the bottom of the pump unit, and guides the seawater including the manganese nodules to the pump unit.

Here, the pump unit may include at least two impellers fixed to the shaft of the pumping motor in sequence, the inflow case fixed to the semi-spherical lower cap, with outer surfaces of the impellers enclosed thereby, and an inflow cover installed in one opening of the inflow case with the reducer coupled thereto.

Further, the pump unit may be installed in multiple stages. Here, two impellers are basically installed. However, a greater number of impellers, such as three or four impellers, may be installed in a multiple stage mode. In this case, the shaft of the pumping motor is extended to be suitable for the number of impellers, and the impellers are fitted in respective inflow cases. In this state, the inflow cases are coupled to each other.

In addition, the sealing means may be realized by installing a mechanical seal around the shaft of the pumping motor, which is exposed between the motor case and the inside of the cover, filling the inside of the cover with oil, and installing an upper ball bearing at the upper end of the shaft of the pumping motor supported in the motor case.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description when taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a schematic view illustrating a conventional liquid ring pump used for mining manganese nodules;

FIG. 2 is a sectional view illustrating a lifting pump according to an embodiment of the present invention;

FIG. 3 is an enlarged sectional view illustrating the important part of a lifting pump according to an embodiment of the present invention; and

FIG. 4 is a sectional view illustrating a lifting pump according to another embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made in greater detail to an exemplary embodiment of the invention, an example of which is illustrated in the accompanying drawings. Wherever possible, the same reference numerals will be used throughout the drawings and the description to refer to the same or like parts.

FIG. 2 is a sectional view illustrating a lifting pump according to an embodiment of the present invention. FIG. 3 is an enlarged sectional view illustrating the important part of a lifting pump according to an embodiment of the present invention. FIG. 4 is a sectional view illustrating a lifting pump according to another embodiment of the present invention.

As illustrated, a lifting pump of the present invention includes:

a cylindrical body 1 that is sealed at upper and lower portions thereof by a semi-spherical upper cap 11 having a fluid outflow port 111, which is connected with a marine mining ship through a lifting pipe, and a cable insertion tube 112, and by a semi-spherical lower cap 12 to which the inflow case 42 of a pump unit 4 is coupled;

a pumping motor 2 that has a fluid passage 27 formed between an inner surface of the body 1 and an outer surface thereof, is fixedly installed in the body 1 in a vertical direction, and drives the pump unit 4 by electric power supplied through a cable 13;

a cover 3 that provides a seal around a shaft 21 of the pumping motor 2;

the pump unit 4 that is installed between the shaft 21 of the pumping motor 2 and the semi-spherical lower cap 12, is driven by the rotation of the pumping motor 2, lifts seawater into the body 1 together with manganese nodules, and transfers the lifted mixture to the marine mining ship through the fluid outflow port 111;

a sealing means 5 that provides a seal between the pumping motor 2 and the pump unit 4;

a stand 6 that is vertically installed on a bottom of the semi-spherical lower cap 12 so as to maintain the lifting pump itself in a vertically installed state; and

a reducer 7 that is coupled to a bottom of the pump unit 4, and guides the seawater including the manganese nodules to the pump unit 4.

Here, the pump unit 4 includes:

at least two impellers 41 fixedly installed on the shaft 21 of the pumping motor 2 in sequence;

the inflow case 42 fixedly installed on the semi-spherical lower cap 12 with outer surfaces of the impellers 41 enclosed thereby; and

an inflow cover 43 installed in one opening of the inflow case 42, with the reducer 7 coupled thereto.

As in FIGS. 2 and 3, two impellers 41 are basically installed. However, as in FIG. 4, a greater number of impellers, such as three or four impellers, may be installed in a multiple stage mode. In the case of such multiple stage installation, the shaft 21 of the pumping motor 2 is extended to be suitable for the number of impellers 41, and the impellers 41 are fitted in respective inflow cases 42. In this state, the inflow cases 42 are coupled to each other.

Further, the sealing means 5 is realized by installing a mechanical seal 51 around the shaft 21 of the pumping motor 2, which is exposed between a motor case 22 and the inside of the cover 3, such that the inside of the cover 3 is filled with oil 52, and an upper ball bearing 23 is installed at an upper end of the shaft 21 of the pumping motor 2 supported in the motor case 22.

Here, among the reference numbers that have not yet been described, 24 denotes a rotor, 25 denotes a stator, and 26 denotes a thrust bearing.

The operation and effects of the lifting pump of the present invention, which is constructed in this way, will be described below.

First, the lifting pump of the present invention includes main components of the cylindrical body 1 provided with the semi-spherical upper and lower caps 11 and 12 in the upper and lower openings thereof, the pumping motor 2, the cover 3, the pump unit 4, the sealing means 5, the stand 6, and the reducer 7.

At this time, the semi-spherical upper cap 11, installed in the upper opening of the cylindrical body 1, is provided with both the fluid outflow port 111, which is connected with the marine mining ship through the lifting pipe (not shown), and the cable insertion tube 112, in which the cable 13 for supplying electric power to the pumping motor 2 is hermetically installed so as not to be in contact with the seawater.

Further, the pumping motor 2 having the rotor 24, the stator 25, the shaft 21, and the motor case 22, is fixedly installed in the body 1 in a vertical direction. At this time, the pumping motor 2 is relatively smaller than the internal space of the body 1. Thereby, the fluid passage 27, which has a space through which the seawater including the manganese nodules can pass when sucked in by suction operation of the pump unit 4, is formed between the outer surface of the case 22 of the motor 2 and the inner surface of the cylindrical body 1.

In this manner, all parts of the lifting pump are assembled in the case 22 of the motor 2. In the lifting pump of the present invention, an important feature is that a heat dissipation structure for dissipating the heat generated from the pumping motor 2 is interconnected with a fluid passage structure for passing the seawater flowing out of the pump unit 4.

The seawater flowing out of the pump unit 4, which will be described below, flows out along the outer surface of the motor case 22. The heat generated from the pumping motor 2 is transmitted to the motor case 22, and is then conducted to the outer surface of the motor case 22. Thus, when the outer surface of the motor case 22 is in contact with the seawater, the heat undergoes convection in the seawater. As a result, the heat transfer takes place.

Therefore, the heat generated from the pumping motor 2 is automatically cooled by the seawater, so that the motor case 22 can be always maintained below a given temperature. For this reason, the pumping motor 2 is prevented from being overheated, and thus the stability of the pump can be increased.

Meanwhile, the lifting pump must thoroughly prevent penetration of the seawater because it is operated while the pumping motor 2 is submerged in the sea in an air-tight state.

Thus, the cover 3 is installed around the shaft 21 of the pumping motor 2, thereby preventing the seawater sucked in by the pump unit 4 from flowing into the pumping motor 2. At this time, the mechanical seal 51, as the sealing means 5, is installed around the shaft 21 of the motor 2, exposed between the motor case 22 and the inside of the cover 3, and the inside of the cover 3 is filled with the oil 52.

As a result, the seawater, which can penetrate through a shaft hole of the cover 3 through which the shaft 21 of the pumping motor 2 passes, is blocked by the mechanical seal 51, serving as the sealing means 5, and a shaft sealing device. Further, when the shaft 21 is rotated by the driving of the pumping motor 2, the mechanical seal 51 is also rotated, and the oil 52 in the cover 3 is splashed. Thereby, the heat generated by the friction between the shaft 21 of the motor 2 and the mechanical seal 51 can be cooled by the oil, so that damage to the mechanical seal 51 caused by frictional heat can be prevented in advance.

In addition, the shaft 21 of the motor 2, which is supported in the motor case 22, is provided with the upper ball bearing 23 at the upper end thereof and the thrust bearing 26 at the lower end thereof. Thereby, when the pumping motor 2 is powered through the cable 13, the shaft 21 and the rotor 24 of the pumping motor 2 can be smoothly rotated in the motor case 22.

Meanwhile, the pump unit 4 is driven by the pumping motor 2, thereby pulling up the seawater into the body 1 together with the manganese nodules, and transferring the seawater including the manganese nodules to the marine mining ship through the fluid outflow port 111. Here, the pump unit 4 is installed between the shaft 21 of the pumping motor 2 and the semi-spherical lower cap 12, and is rotated by the rotation of the pumping motor 2. At this time, the pump unit 4 includes at least two impellers 41, the inflow case 42, and the inflow cover 43.

Here, the impellers 41 are fixed around the shaft 21 of the pumping motor 2 in sequence. In the state in which one of the impellers 41, which is located at the bottom of the semi-spherical lower cap 12, is enclosed by the inflow case 42, the inflow case 42 is fixed to the semi-spherical lower cap 12. In the state in which the reducer 7 is coupled at the bottom of the inflow cover 43, the inflow cover 43 is installed in the opening of the inflow case 42.

At this time, among the impellers 41, the first-stage impeller 41, which is located at the lowermost stage, applies rotational force to the seawater flowing into the inflow cover 43 through the reducer 7, and thus converts the seawater to which the rotational force is applied into seawater to which centrifugal force is applied. Thereby, the first-stage impeller 41 serves to increase the flow rate of the seawater. The inflow case 42 causes the seawater flowing through the first-stage impeller 41 at a rapid flow rate to be changed in cross section, thereby serving to convert dynamic pressure (speed energy) into high static pressure (pressure energy) (as per Bernoulli's equation). Thus, the seawater flowing through the inflow case 42 has high static pressure after passing through the first-stage impeller.

As described above, the seawater flowing out of the inflow case 42 is imparted with high static pressure, i.e. the high lift, by the first-stage impeller. However, because the lifting pump must operate on the seabed, the seawater must be lifted higher.

For this reason, the present invention is designed such that at least two impellers 41 are installed, and such that the function of the first-stage impeller 41 is repeated by the second-stage impeller 41 located in the semi-spherical lower cap 12.

In this manner, the second-stage impeller 41 applies rotational force to the seawater having the high static pressure by means of the first-stage impeller 41, and thus converts the seawater to which the rotational force is applied into seawater to which centrifugal force is applied. Thereby, the second-stage impeller 41 can further increase the flow rate of the seawater.

As described above, the flow rate of the seawater flowing through the second-stage impeller 41 located in the semi-spherical lower cap 12 is again increased (i.e. the dynamic pressure is increased), and then flows out of the semi-spherical lower cap 12. However, the seawater may flow into another inflow case 42 depending on the number of impellers 41 of the pump unit 4.

Specifically, when the pump unit 4 is constructed in the present invention, two impellers 41 can be installed, as in FIGS. 2 and 3. Further, three impellers 41 can be installed as in FIG. 4. Although not illustrated, a greater number of impellers, such as four or five impellers, may be installed in a multiple stage mode, so that the flow rate of the seawater flowing through the second-stage impeller 41 is again increased depending on the number of impeller stages of the pump unit 4, and then flows out of the semi-spherical lower cap 12 or flows into another inflow case 42.

At this time, the number of impeller stages of the pump unit 4 can be modified according to capacity, the quantity of seawater to be pumped, etc. of the pumping motor 2. Therefore, the number of impeller stages is not limited to two or three, as illustrated in the figures, but includes any number greater than that number.

In this manner, in the case of installing the pump unit 4 in multiple stages, the shaft 21 of the pumping motor 2 is extended to be suitable for the number of impellers 41, and the impellers 41 are fitted in respective inflow cases 42. In this state, the inflow cases 42 are coupled to each other.

Meanwhile, as described above, the lower cap 12 functions to convert the reduction in flow rate (speed energy) caused by the change in the cross section of the high-pressure and high-speed seawater, which flows in from the impeller 41 of the immediately preceding stage, into static pressure (pressure energy).

Further, in the present invention, the stand 6 is vertically installed on the bottom of the semi-spherical lower cap 12. Thereby, in the state in which the lifting pump itself is vertically installed perpendicular to the seabed, the seawater including the manganese nodules can be continuously pumped up to the mining ship.

Of course, the reducer 7 having the shape of a pipe is coupled on the bottom of the pump unit 4, so that the manganese nodules covering the seabed and the surrounding seawater can be precisely guided to the pump unit 4. Thus, a lot of manganese nodules can be mined using the inflow of a small quantity of seawater, so that the mining time and cost can be reduced.

As is apparent from the above description, according to the present invention, first, the inflow port can be exactly positioned at the seabed covered with the manganese nodules. Thus, a lot of manganese nodules can be mined by the inflow of a small quantity of seawater, so that the mining time and cost can be reduced. Second, the pumped manganese nodules pass through the fluid passage surrounding the motor. A fluid passage structure is simple, and thus there is no fear of the sludge or manganese nodules becoming stuck. Thus, stable operation is possible, so that the operational stability of the product can be increased, and damage to the pump can be considerably decreased.

Third, because the mechanical seal is used as the shaft sealing device, the sludge does not penetrate into the shaft sealing device, so that maintenance expenses are very low. Fourth, the flexible hose is installed at the lower end of the pump, so that the manganese nodules can be easily pumped up under any situation. Fifth, multiple stage installation is possible, so as to enable response to changes in the installed depth in seawater, in multiple stages such as two or three stages.

Sixth, the pump unit is integrally formed with the motor, so that the installation is easy, and a separate shaft joint is not required. Seventh, the center of gravity is located in the middle of the pump, so that the pump is easily installed, and stable operation is possible without being influenced by ocean current.

Although an exemplary embodiment of the present invention has been described for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.