The present invention relates to a tapered ground auger, and more particularly to a spiral auger having fixed-position auger teeth. The invention further relates to a spiral auger screw and to a method of forming a tapered ground auger. Ground augers are used to drill bores into the ground, typically through rock formations, and therefore are required to be very durable. A typical auger is formed having an elongate shaft which has a helical or constant radius auger screw attached to it. Rotation of the auger via a rotary drive unit attached to one end of the auger shaft will cause the auger to rotate, with hard-wearing teeth being positioned at an opposing, ground-contacting end of the auger shaft so as to cut into the ground material.

The most common variety of auger has a helical auger screw of uniform width, which at its cutting end has auger teeth positioned in a linear arrangement across the bottom of the auger screw, also known as an auger flight. This allows the auger to cut into the ground material using the full diameter of the auger screw immediately. However, the efficiency of the drilling process is limited, as the sheer volume of material to be cut initially limits the rotational velocity of the auger. It therefore takes a reasonable amount of time to drill a given depth.

To circumvent this issue, there is an alternative type of ground auger available, in which the auger screw or flight tapers at least at its ground-contacting end in a spiral, thereby bringing the auger to or substantially to a point or head portion which facilitates more rapid drilling into the ground. However, since the cutting end of the auger screw is now arcuate and spiral in form, it has not been possible to affix planar fixed auger teeth to the auger screw as would be used in the auger of uniform width.

Instead, the cutting surface is provided by cutting picks which are rotatably supported in pick holders attached at an angle to the auger screw. The picks can cut through rock on any part of the full circumferential extent of the external surface of their cutting heads, and can rotate within their holders to thereby reduce wear on any single portion of the cutting head. However, one problem associated with such rotatable picks is that during a drilling procedure, the rapid rotation can cause frictional heating of an interface between the pick and its holder, resulting in the two thermally fusing to one another in certain circumstances. This prevents rotation of the pick, leading to over-wear of one surface of the cutting head of the pick, resulting in an uneven bore.

It is an object of the present invention to provide a tapered ground auger which is capable of utilising traditional fixed auger teeth so as to obviate or avoid the above-mentioned problems.

According to a first aspect of the invention there is provided a tapered ground auger comprising: an auger shaft having an auger screw with an at least in part spiral flight; and a plurality of auger teeth, each auger tooth including a tooth body and a cutter defining an elongate cutting edge; each said auger tooth being engagable with the auger screw such that the elongate leading cutting edge of the cutter is or substantially is aligned with a radius of the spiral. By providing a tapered ground auger which has fixed angle teeth, having cutters which are aligned to the radius of the spiral of the auger screw, it is possible to overcome many of the deficiencies associated with standard augers having uniform radius and with spiral augers which utilise rotating picks.

Tests using the a tapered ground auger to drill a bore through rocky material have shown that it is possible to achieve close to a tenfold increase in the speed of drilling when compared with standard ground augers, whilst the fixed angle of the cutters ensures that wear is uniform across the full radial extent of their cutting surfaces.

Preferably, the auger teeth may be engagable with the auger screw so as to be perpendicular to the said radius of the spiral. By positioning the auger teeth themselves tangentially to a circle defined by the radius of the spiral of the auger screw, shear forces on the auger teeth during a drilling process are reduced, substantially decreasing the probability of dislocation of the teeth during use. Optionally, at least one of the plurality of auger teeth may be releasably engagable with the auger screw.

By providing releasably engagable auger teeth, it becomes relatively straightforward to replace damaged or broken auger teeth during a drilling process, substantially reducing the amount of time and cost required to fix or replace a damaged auger.

There may further be provided a plurality of auger tooth mounts engagable with the auger screw, each auger tooth mount receiving an auger tooth for mounting to the auger screw. Each of the plurality of auger tooth mounts may be releasably engagable with the auger screw, and/or each of the plurality of auger tooth mounts may be releasably engagable with its respective auger tooth. Each of the plurality of auger tooth mounts may be engagable with the auger screw so as to be perpendicular to the said radius of the spiral.

By providing auger tooth mounts which can receive auger teeth, it may be possible to provide a common interface with the auger screw which is capable of receiving a plurality of different types of auger tooth, which can substantially broaden the functional operation of a single auger.

Preferably, each auger tooth may include at least one alignment element for aligning the auger tooth with its respective auger tooth mount.

The relative angular configuration of the auger teeth within their auger tooth mounts may be critical when optimising the cutting efficiency of the auger as a whole. As such, it is important to have some means of aligning an auger tooth within its auger tooth mount; this is particularly important for releasably mountable auger teeth, since rapid dis- and re-engagement of auger teeth within their mounts is paramount to the smooth functioning of the auger. In one optional embodiment, a radial extent of the cutter of each auger tooth may at least in part overlap the radial extent of a cutter of an adjacent auger tooth along the flight. Overlapping radial extents of cutters can advantageously ensure that an auger can continue to operate at full capacity, that is, cutting across its entire diameter, even if its auger teeth are partially worn or damaged in use.

A cutting surface of the cutter may preferably be fluted to facilitate dispersal of cut material.

The ability to disperse cut material is a critical factor in the cutting efficiency of an auger. If cut material is stuck at or adjacent the cutting surface, the rotation of the auger may be inhibited, slowing the cutting process. Fluted cutting surfaces advantageously direct cut material up into the auger screw for rapid dispersal. In one embodiment, a plurality of auger screw portions may be provided in a helical arrangement on the auger shaft to form the auger screw. The arrangement of auger teeth on each auger screw portion may be identical, or alternatively the auger teeth may be engagable with adjacent auger screw portions in an alternating arrangement, in which case a radial extent of the cutter of each auger tooth may at least in part overlap the radial extent of a cutter on an adjacent auger tooth on an adjacent auger screw portion.

By providing multiple auger screw portions on a single auger shaft to form the auger screw having identical sets of auger teeth, the available cutting surface to the auger can be advantageously increased, which may result in a faster and more efficient drill. However, it has been found that the provision of an alternating arrangement of auger teeth across multiple auger screw portions can result in a more well-balanced drilling process, which may in turn result in a smoother bore.

The auger may further comprise at least one further auger tooth which is engagable with the auger screw such that an elongate leading cutting edge of a cutter of the or each further auger tooth is not aligned to a radius of the spiral. It may not be possible to provide all auger teeth so as to be aligned with the radius of the spiral, in particular at the tapered end. From a manufacturing perspective, it may therefore be advantageous to only provide a majority of the auger teeth in radial alignment. Preferably, a plane of a cutting surface of the cutter of each auger tooth may be angularly offset relative to an axial direction of the auger shaft. The elongate leading cutting edge of the cutter may be positioned at a bottom edge of the angularly offset cutting surface in such an arrangement. Optionally, the elongate leading cutting edge of the cutter may be tilted in a plane perpendicular to an axial direction of the auger shaft. If so, a radially outermost point of the elongate leading cutting edge of the cutter may be elevated relative to a radially innermost point of the elongate leading cutting edge.

The alignment of the plane of the cutting surface can be of great benefit to the cutting efficiency of the auger. Tilting the cutting surface out of alignment with the vertical axis of the auger shaft beneficially facilitates upward dispersal of cut material away from the elongate leading cutting edge of the cutter. Tilting the elongate leading cutting edge of the cutter so as to lean in toward the shaft also provides a superior angle of approach for the auger teeth into the material to be cut, and by providing the tilt so as to generally match a slope of the spiral, tangential forces on the auger tooth or auger tooth mount can be kept to a minimum.

According to a second aspect of the invention, there is provided an auger screw for a tapered ground auger, preferably in accordance with the first aspect of the invention, the auger screw comprising: a spiral screw body having an inner edge and an outer edge, the inner edge being engagable with a shaft of a tapered ground auger; and a plurality of auger tooth mounting portions positioned at or adjacent to the outer edge of the screw body; each auger tooth mounting portion having an alignment ridge which is at least in part perpendicular to a radius of the screw body at or adjacent the auger tooth mounting portion. By providing such an auger screw, it is possible to readily align fixed auger teeth to the radius of the spiral of the auger screw. This provides for a superior ground auger capable of cutting through rocky material at a much greater rate than existing ground augers, whilst ensuring even wear on the cutting surfaces of the auger teeth. According to a third aspect of the invention, there is provided a method of forming a tapered ground auger, the method comprising the steps of: providing a ground auger having an auger screw which is at least in part spiral; and engaging a plurality of auger teeth to the auger screw such that an elongate leading cutting edge of a cutting surface of each auger tooth is aligned or substantially aligned to a radius of the spiral.

According to a fourth aspect of the invention, there is provided a tapered ground auger comprising: an auger shaft having an auger screw with an at least in part spiral flight; and a plurality of auger teeth, each auger tooth including a tooth body and a cutter having a cutting surface having an elongate leading cutting edge; each said auger tooth being engagable with the auger screw such that the cutting surface of the cutter is angularly offset relative to an axial direction of the auger shaft.

Preferably, the elongate leading cutting edge of the cutter may be positioned at a bottom edge of the angularly offset cutting surface. The angular offset may be in the range 0 to 45 degrees, 0 to 25 degrees, or preferably in the range 0 to 10 degrees. Providing a spiral auger in which the cutting surfaces are planar and angled with respect to a vertical axis of the auger shaft, the auger can cut through rocky material far more readily, since cut material is directed up and away from the elongate leading cutting edge of the cutter more rapidly.

According to a fifth aspect of the invention, there is provided a tapered ground auger comprising: an auger shaft having an auger screw with an at least in part spiral flight; and a plurality of auger teeth, each auger tooth including a tooth body and a cutter having a cutting surface with an elongate leading cutting edge; each said auger tooth being engagable with the auger screw such that the elongate leading cutting edge of the cutter is tilted out of a plane perpendicular to an axial direction of the auger shaft. Preferably, a radially outermost point of the elongate leading cutting edge may be elevated relative to a radially innermost point of the elongate leading cutting edge. The angular offset may then be in the range -45 to 45 degrees, the range -25 to 25 degrees, or most preferably in the range -10 to 10 degrees. Providing a spiral auger in which an elongate leading cutting edge of the auger teeth is inclined out of a plane perpendicular to the axis of the auger shaft advantageously provides for a more efficient approach angle of the auger teeth towards the material to be cut, improving the cutting efficiency of the auger.

The invention will now be more particularly described, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 shows a perspective view of a first embodiment of a tapered ground auger, in accordance with the first aspect of the invention;

Figure 2 shows a perspective view of the tapered ground auger of Figure 1 with the auger teeth removed;

Figure 3a shows an enlarged perspective view of the auger teeth of the tapered ground auger of Figure 1;

Figure 3b shows an enlarged perspective view of the auger teeth of the tapered ground auger of Figure 1, from an angle orthogonal to that of Figure 3 a;

Figure 4 shows a bottom plan view of the tapered ground auger of Figure 1;

Figure 5 shows a bottom plan view of a second embodiment of a tapered ground auger in accordance with the first aspect of the invention;

Figure 6 shows a perspective view of one embodiment of an auger screw, in accordance with the second aspect of the invention, for use in assembling a tapered ground auger in accordance with the first aspect of the invention;

Figure 7 shows a perspective view of the auger screw of Figure 6, inclusive of the auger teeth; and

Figure 8 shows a bottom plan view of the auger screw of Figure 7, showing concentric circles to illustrate the paths taken by the auger teeth upon rotation of the auger screw.

Referring firstly to Figure 1, there is provided a tapered ground auger, indicated globally at 10 which is attachable to a rotary drive unit for cutting or drilling into rock formations. The rotary drive unit may be formed as part of a wheeled or tracked vehicle, such as an excavator or digger, may be detachably attached to such a wheeled or tracked vehicle, or may be a standalone portable or mobile hand-holdable device. The tapered ground auger 10 comprises an auger shaft 12 having first and second ends 14, 16 with an auger screw or auger flight 18 which extends along at least part of the auger shaft 12 to terminate at the first end 14. The first end 14 of the auger shaft 12 forms the ground-contacting end of the ground auger 10, whereas the second end 16 is engagable with an output shaft of a rotary drive unit (not shown). In the depicted embodiment, the auger screw 18 extends partway along, and preferably around half way along, the auger shaft 12 from its first end 14 and may be formed, for the most part, as a helix having constant radius. However, towards the first end 14 of the auger shaft 12, the auger screw 18 tapers into a spiral helix, the radius of an outer edge 20 of the auger screw 18 decreasing towards its first end 14. Where the term radius of the spiral is used, this is deemed to mean the distance from the centre of the spiral to the outer edge 20 of the auger screw 18 at that particular point of the spiral.

As shown, the flight of the auger screw 18 is formed as a double helix having first and second screw portions 22, 24, but it will be appreciated that a single helix, triple helix or higher multiple of helices are equally plausible for use as part of a ground auger.

At a tip 26 of the first end 14 of the auger screw 12, there is mounted a feed point 28 which is formed as a toothed cone and is capable of centring the ground auger 10 in use.

Attached to the outer edge 20 of the auger screw 18 is a plurality of auger tooth mounts or holders 30, each auger tooth mount 30 being spaced-apart from one another along the spiral portion of the auger screw 18. This can be readily seen in Figure 2. Each auger tooth mount 30 in the depicted embodiment is preferably formed as a hollow cylinder having recesses 32 into which auger teeth 34 may be receivable, and the auger tooth mounts 30 are welded to the outer edge 20 of the auger screw 18 to secure them in place. It will however be appreciated that the auger tooth mounts 30 could be integrally formed with the auger screw 18, or be releasably attachable thereto so as to permit the auger tooth mounts 30 to be easily replaced should they become damaged in use.

The auger teeth 34 of the tapered ground auger 10 are formed having an elongate tooth body 36, shaped to be receivable in the recesses 32 of the auger tooth mounts 30 so as to be perpendicular to a radius of the spiral portion of the auger screw 18 at the point of mounting, and a cutter 38 fixed at one end of the tooth body 36. In the depicted embodiment, the recesses 32 are formed having a female taper, with the tooth body 36 of the auger tooth 34 having a male taper which engages with the female taper in a press fit friction lock, wedging engagement or Morse taper lock. Whilst the tooth body 36 and recess 32 of the auger tooth mount 30 are formed as mutually engagable cylindrical portions, it will be apparent that any complementarily shaped components could be mutually interengaged to connect the auger teeth 34 to their auger tooth mounts 30. Furthermore, whilst the auger teeth 34 are here described as being releasably engagable with their auger tooth mounts 30, the auger teeth 34 could be fixedly secured in place, for example, using welding, should this result in a more robust ground auger 10. Preferably, the auger tooth mounts 30 may be directly mountable to the auger screw 18, rather than utilising a separate adapter plate.

The cutter 38 of each auger tooth 34 has a cutting surface 40 which lies substantially within a plane P, illustrated in Figure 3a, having an elongate leading cutting edge, illustrated by line L in Figure 3b which is perpendicular or substantially perpendicular to a primary axis of the tooth body 36. It will be understood that the cutting surface 40 need not necessarily itself be planar in order for there to be a linear elongate leading cutting edge L, as can be seen in Figure 3b.

In order to improve the cutting ability of the cutter 38, the plane P of the cutting surface 40 may be titled at an angle with respect to the vertical, that is, relative to the rotational axis of the auger shaft 12, such that the elongate leading cutting edge L is at a lowermost edge of the cutter 38; this facilitates upward removal of cut material. This can be best seen in Figure 3a.

The tilt angle may be in the range 0 to 45 degrees with respect to the vertical axis, may be more preferably in the range 0 to 25 degrees, but will most preferably be in the range 0 to 10 degrees; this gives a reasonably shallow angle to allow upward removal of the cut material without significantly compromising the robustness of the auger tooth 34.

Furthermore, the plane P or elongate leading cutting edge L may also be tilted at an angle with respect to a plane perpendicular to the axis of the auger shaft 12 so as to lean in a direction towards the auger shaft 12. This means that a radially outermost point of the elongate leading cutting edge L is elevated relative to a radially innermost point of the elongate leading cutting edge L. This further improves the cutting ability of the cutter 38 of each auger tooth 34 placed around the auger screw 18. This is illustrated in Figure 3b.

The tilt of the elongate leading cutting edge L may be in the range -45 to 45 degrees with respect to the perpendicular plane, may be more preferably in the more narrow range of -25 to 25 degrees, but would most preferably be in the range -10 to 10 degrees, which in this instance would relatively closely match the spiral angle. By matching the tilt of the auger tooth 34 closely to the angle of the auger screw 18, perpendicular forces which could dislocate the auger tooth mount 30 from the auger screw 18 can be minimized. As such, it is preferable to provide an elongate leading cutting edge L wherein a radially outermost point of the elongate leading cutting edge L is elevated with respect to a radially innermost point of the elongate leading cutting edge L, that is, positive tilt angles, since this would most closely match the angle of the spiral of the auger screw 18 as it tapers towards the first end 14 of the auger shaft 12.

The cutting surface 40 of the cutter 38 preferably has three fluted portions 42 which thereby cause the cutting surface 40 itself to be fluted. This advantageously enables cut material or chaff to be urged away from the cutting surface 40 in use. However, the cutting surface 38 is still therefore substantially planar, that is, not curved, and perpendicular to the primary axis of the tooth body 36. It will be noted, however, that the auger tooth 34 could readily be curved, and therefore may not necessarily have a primary axis, in which case the position of the cutter 38 will define the front of the auger tooth 34 and therefore the position of the elongate leading cutting edge L and plane P of the cutting surface 38. The auger tooth 34 as depicted also includes two alignment elements 44, here positioned either side of the cutter 38, which rest against complementarily-shaped lips 46 positioned on the exterior portion of each auger tooth mount 30. The alignment elements 44 help to locate the auger tooth 34 within its respective auger tooth mount 30 before being locked into place. It will be appreciated however that a different number or form of alignment element could be provided, or could in fact be dispensed with altogether.

The auger teeth 34 are mounted to the auger screw 18 using the auger tooth mounts 34 at regular intervals along the spiral outer edge 20 of the auger screw 18, as can be seen in Figure 4.

It can be seen that the majority of the auger tooth mounts 30 are positioned such that when the respective auger tooth 34 is engaged with the auger tooth mount 30, the auger tooth 34 is tangentially positioned to the concentric circle having a radius which is equal to the radius of the spiral outer edge 20 of the auger screw 18 at the point at which the auger tooth 34 is positioned. It may, however, not be physically possible to position the auger teeth 34 which are closest to the first end 14 of the auger shaft 12 in such a tangential configuration, and therefore only a majority of the auger teeth 34 may adopt this positioning, with further auger teeth 48 being provided at or adjacent the first end 14 of the auger shaft 12. However, it is preferred that the auger teeth 34 higher up the spiral outer edge 20 of the auger screw 18 all be aligned to the radius. In any event, it is preferred that the auger teeth 34 extend over a large extent of the spiral outer edge 20, preferably over a span of at least 180 degrees about the auger shaft 12 of the flight of the auger screw 18, and preferably with the auger teeth 34 being spaced apart along the spiral outer edge 20 of the auger screw 18 at regular intervals. If the auger teeth 34 are positioned so as to be at a tangent to the circle defined at a radius of the radius of the spiral outer edge 20, then the elongate leading cutting edge L of the cutter 38 will necessarily be positioned so as to be aligned with the radius. As such, as the ground auger 10 rotates in use, the full cutting surface 40 of the cutter 38 is presented to the material being cut. This advantageously spreads the wear across the entirety of the cutting surface 40, rather than to a corner or side thereof. The cutters 38 of the auger teeth 34 are arranged on the spiral outer edge 20 of the auger screw 18 such that a radial extent of the cutting surface 40 at least abuts the radial extent of adjacent auger teeth 34, thereby ensuring that when the ground auger 10 rotates, the full radial extent of the auger screw 18 is excavated. However, the cutters 38 may be arranged such that the radial extents of adjacent auger teeth 34 overlap slightly to allow for any manufacturing tolerance in the positioning of adjacent auger teeth 34.

The spiral outer edge 20 is formed so as to spiral inwardly substantially as a constant spiral, that is, a spiral in which the decrease in the spiral radius towards the tapered end is constant. This optimises the cutting efficiency of the ground auger 10 in use. A second embodiment of the ground auger, indicated globally at 110 is illustrated in Figure 5. Identical or similar features to those of the first embodiment are referred to using identical or similar reference numerals, and further detailed description is omitted for brevity. In this second embodiment, the auger screw 118 is largely identical to that of the first embodiment, the outer edge 120 of which spiralling toward the first end 114 of the auger shaft 112. Again, the auger screw 118 is formed having first and second screw portions 122, 124 in a double helix.

However, in this ground auger 110, the auger teeth 134 are positioned along the outer edge 120 at their auger tooth mounting portions 150 of each of the first and second screw portions 122, 124 in an alternating manner, such that if an auger tooth 134 is mounted at a particular vertical position on the auger screw 118 on the first screw portion 122, a subsequent nominal auger tooth mounting portion of the auger screw 118 on the first screw portion 122, at which point an auger tooth mount 130 would ordinarily be positioned, is left vacant. Instead, the next auger tooth 134 in the vertical sequence is position at the equivalent position on the second screw portion 124. In this manner, the full radial extent of the auger screw 118 can be covered with cutting surfaces whilst utilising fewer auger teeth 134 to form the ground auger 110.

By providing such a ground auger 110, the number of auger teeth 134 and auger tooth mounts 130 is reduced, meaning that the manufacture of such grounds augers 1 10 becomes more cost-effective. The spacing of the auger teeth 134 in this arrangement also produces the most efficient cut, covering the radial extent of the spiral with the fewest possible number of auger teeth 134, whilst also balancing the ground auger 110 in use, as the auger teeth 134 are evenly spread over the first and second screw portions 122, 124.

The common component across the two embodiments of the ground auger 10, 110 is therefore the spiral portion of the auger screw, an example of which is illustrated in Figures 6 and 7, and indicated globally as 200.

Spiral auger screws are known in the prior art, but are always formed having rotating picks which define the cutting surface of the ground auger. Such rotating picks are provided so as to project slightly outwardly of the radial extent of the auger screw, and therefore the actual cutting radius of such devices can be greater than that of the auger screw itself. Using the present invention, it is now possible to provide a spiral ground auger with cutting faces which are aligned with the radius of the spiral, which improves the wear properties of the auger teeth.

The spiral portion of the auger screw 200 has a spiral screw body 218 having an inner edge 252 which engages a shaft of a ground auger in use, and an outer edge 220 into which is formed a plurality of auger tooth mounting portions 250. Each auger tooth mounting portion 250 is here formed as a rounded recess into which an auger tooth mount 30 could be mounted. In a down-spiral direction from each auger tooth mounting portion 250 is formed an alignment ridge 254, which here is formed as a flat portion of the outer edge 220 of the screw body 218 adjacent to the recess of the auger tooth mounting portion 250.

This alignment ridge 254 is preferably formed so as to be at least in part perpendicular to a radius of the screw body 218. As such, when an auger tooth 34 is affixed to the screw body 218, it can be positioned so as to abut the alignment ridge 254 thereby being tangential to the radius of the spiral, and thus the elongate leading cutting edge of the cutter 38 is aligned with the radius of the spiral. This can be best seen in Figure 8, in which the paths of the cutters 38 of the auger teeth 34 are overlaid as imaginary or phantom concentric circles onto the bottom plan of the auger screw 200.

The illustrated auger screw 200 highlights the difficulty of forming all auger tooth mounting portions 250 so as to be perpendicular to the radius of the spiral; towards the tapered end 256 of the spiral screw body 218, the amount of usable material in the screw body 218 is substantially reduced, and therefore it may not be possible to position the auger teeth 34 nearest the tapered end 256 so as to be perpendicular to the radius, and therefore only the auger teeth 34 nearest the wide end 258 may be perpendicular to the radius in the assembled ground auger.

It will be appreciated that the provision of auger tooth mounts is not limited to the form of auger tooth mounts described above, that is, those utilising a taper interference fit. Auger tooth mounts could, of course, be formed so as to be compatible with existing engagement means for auger teeth, and these could be provided as part of a spiral auger in accordance with the present invention.

It is therefore possible to provide a ground auger having an at least in part spiral auger screw, in which there are provided auger teeth having a cutting edge with a fixed position, that fixed position being in alignment with a radius of the spiral. This improves the uniformity of the wear on the cutting edges of the auger teeth, whilst avoiding many of the issues associated with rotating pick auger cutters, such as frictional fusing and non-uniform wear across the circumference of the pick.

The words 'comprises/comprising' and the words 'having/including' when used herein with reference to the present invention are used to specify the presence of stated features, integers, steps or components, but do not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.

It is appreciated that certain features of the invention, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable sub-combination.

The embodiments described above are provided by way of examples only, and various other modifications will be apparent to persons skilled in the field without departing from the scope of the invention herein described and defined.