阅读说明：本技术 一种光纤复合海底电缆及其制备方法 (Optical fiber composite submarine cable and preparation method thereof ) 是由 陈凯 宋光辉 宋晓涵 潘文林 袁振钦 孙达威 许谢君 于 2021-09-15 设计创作，主要内容包括：本发明涉及一种光纤复合海底电缆及其制备方法,包括缆芯和依次包覆在缆芯外的包带层、内衬层、铠装层和外护层,所述缆芯包括多根绞合设置的电单元、填充在任意相邻两个电单元之间空隙的填充条和穿设在所述填充条内的光单元,所述填充条为扇形结构,所述填充条包括扇形弧面和对称设置在扇形弧面两侧的两个扇形侧面,所述扇形弧面与电单元依次拼接形成圆周面,所述扇形侧面与所述电单元贴合匹配,在所述扇形弧面侧壁上还开设有凹槽,所述光单元嵌设在所述凹槽中,在所述填充条内还开设有镂空通孔。本发明结构设计合理,光电复合互不影响、且互相起到保护作用,能够降低风电企业初级建设成本及之后的运维成本。(The invention relates to an optical fiber composite submarine cable and a preparation method thereof, wherein the optical fiber composite submarine cable comprises a cable core, and a belting layer, an inner liner layer, an armor layer and an outer protective layer which are sequentially coated outside the cable core, the cable core comprises a plurality of electric units which are twisted, a filling strip for filling a gap between any two adjacent electric units and an optical unit which is arranged in the filling strip in a penetrating way, the filling strip is of a fan-shaped structure, the filling strip comprises a fan-shaped arc surface and two fan-shaped side surfaces which are symmetrically arranged at two sides of the fan-shaped arc surface, the fan-shaped arc surface and the electric units are sequentially spliced to form a circumferential surface, the fan-shaped side surfaces are matched with the electric units in a fitting way, the side walls of the fan-shaped arc surface are also provided with grooves, the optical unit is embedded in the grooves, and the filling strip is also provided with hollowed-out through holes. The invention has reasonable structural design, does not influence each other in photoelectric recombination and plays a protection role mutually, and can reduce the primary construction cost and the later operation and maintenance cost of wind power enterprises.)

1. The utility model provides an optical fiber composite submarine cable, its characterized in that includes the cable core and wraps belting layer, inner liner, armor and the outer jacket outside the cable core in proper order, the cable core includes the electric unit that many transposition set up, fills the packing in space between arbitrary two adjacent electric units and wears to establish optical unit in the packing, the packing is fan-shaped structure, the packing includes two fan-shaped sides that fan-shaped cambered surface and symmetry set up in fan-shaped cambered surface both sides, fan-shaped cambered surface splices in proper order with electric unit and forms the periphery, fan-shaped side with the laminating of electric unit matches still set up flutedly on the fan-shaped cambered surface lateral wall, optical unit inlays to be established in the recess fretwork through-hole has still been seted up in the packing.

2. The fiber optic composite submarine cable according to claim 1, wherein: the electric unit comprises a water-blocking conductor, a conductor shielding layer, an insulating shielding layer, a water-blocking buffer layer, a metal shielding layer, a semi-conductive water-blocking layer and an aluminum-plastic sheath layer which are sequentially arranged from inside to outside.

3. The fiber optic composite submarine cable according to claim 2, wherein: the water blocking conductor is made by pressing any one of copper, aluminum and aluminum alloy composite water blocking material.

4. The fiber optic composite submarine cable according to claim 2, wherein: conductor shielding layer, insulating layer, the common extrusion molding cladding of insulating shielding layer are in the conductor periphery blocks water, conductor shielding layer, insulating shielding layer and the concentric setting of conductor that blocks water.

5. The fiber optic composite submarine cable according to claim 2, wherein: the aluminum-plastic sheath layer is composed of a semi-conductive film-coated aluminum tape and semi-conductive polyethylene.

6. The fiber optic composite submarine cable according to claim 1, wherein: the optical unit comprises a loose tube, and optical fibers and water-blocking fiber paste filled between the optical fibers are arranged in the loose tube.

7. The fiber optic composite submarine cable according to claim 1, wherein: the armor layer comprises galvanized steel wires and PE strips, the shapes and the sizes of the sections of the galvanized steel wires and the PE strips are the same, and the galvanized steel wires and the PE strips are spirally wound on the periphery of the lining layer at staggered intervals.

8. A preparation method of an optical fiber composite submarine cable is characterized by comprising the following steps: the method comprises the following steps:

s1, preparing an electric unit: preparing a water-blocking conductor, preparing a conductor shielding layer, an insulating layer and an insulating shielding layer outside the water-blocking conductor by adopting a three-layer co-extrusion technology, after stress is eliminated, sequentially wrapping a water-blocking buffer layer, a metal shielding layer and a semi-conductive water-blocking layer, and finally performing extrusion molding to form an aluminum-plastic sheath layer to obtain an electric unit;

s2, preparing a filling strip: the filling strip comprises a fan-shaped cambered surface, two fan-shaped side surfaces symmetrically arranged at two sides of the fan-shaped cambered surface, a groove for embedding the light unit and a hollowed-out through hole;

s3, preparing a cable core: twisting a plurality of electric units formed in the step S1 together, enabling the sections of any two adjacent electric units to be contacted in a pairwise tangent manner, simultaneously twisting the fan-shaped filling strips formed in the step S2, sequentially splicing the fan-shaped cambered surfaces and the electric units to form a circumferential surface, and attaching and matching the fan-shaped side surfaces and the electric units;

s4, fill light unit: preparing an optical unit structure, and filling the optical unit structure in the groove in the filling strip;

s5, cabling: and sequentially wrapping a belting layer, an inner liner layer, an armor layer and an outer protective layer around the cable core to obtain the submarine optical cable, wherein the armor layer is spirally wrapped on the periphery of the inner liner layer at intervals by galvanized steel wires and PE strips in a staggered manner.

9. The method for preparing an optical fiber composite submarine cable according to claim 8, wherein: in step S1, the preparation method of the water blocking conductor includes: firstly, drawing a wire by using a wire drawing machine to obtain a monofilament, then penetrating the monofilament into a wire coiling machine and placing the wire coiling machine into a round nano die, adding a water-blocking material into the round nano die, and twisting to obtain the compact round water-blocking conductor.

10. The method for preparing an optical fiber composite submarine cable according to claim 8, wherein: in the step S1, the three-layer co-extrusion preparation of the conductor shielding layer, the insulating layer and the insulation shielding layer adopts a catenary crosslinking production line and is obtained by extrusion through a conical head, the thickness value of the three-layer co-extrusion preparation is 8.5-13 mm, and the maximum eccentricity is not more than 5%.

Technical Field

The invention relates to the technical field of submarine cable structures and preparation, in particular to an optical fiber composite submarine cable and a preparation method thereof.

Background

The installed capacity of offshore wind power is rapidly increased year by year, the voltage grade of the current collecting cables in the field of all the operated offshore wind power plants is 35kV, but along with the trend of competitive surfing, a 66kV current collecting scheme is generated in order to reduce investment and operation and maintenance cost, and the scheme can reduce the number of loops of the fan, thereby reducing the wiring complexity of the offshore booster station and even reducing the number of the offshore booster stations; meanwhile, the amount of submarine cables and laying time can be reduced, and the line loss is reduced.

In order to match with a 66kV current collection scheme, a 66kV crosslinked polyethylene insulated optical fiber composite submarine cable needs to be prepared, compared with a 35kV optical fiber composite submarine cable, the transmission voltage is higher, and relatively speaking, the requirements on the water resistance and the insulation performance are further improved, so that the number of waterproof protection layers and the insulation protection thickness are further improved, the manufacturing cost of a vehicle-making optical cable is improved, and the transportation and laying cost of the optical cable is correspondingly improved due to the improvement of the quality of the optical cable.

In addition, the optical unit of the existing 66kV crosslinked polyethylene insulated optical fiber composite submarine cable is directly and compositely arranged in the gap of the electrical unit inside the cable core, on one hand, the electrical unit is easy to interfere with the signal transmission of the optical unit from the performance, on the other hand, the size of the conventional optical unit is far smaller than that of the electrical unit from the structure, the optical unit is directly and compositely arranged in the gap of the electrical unit, the roundness of the cable core is not high, the cable core is easy to deform under the high pressure of the seabed, the performance of the optical unit and the electrical unit is affected, and meanwhile, the optical unit is exposed, lacks protection, and is easy to damage the optical fiber inside the optical unit.

Disclosure of Invention

Therefore, the technical problem to be solved by the invention is to overcome the problem of unreasonable design of the 66kV crosslinked polyethylene insulated optical fiber composite submarine cable in the prior art, and provide an optical fiber composite submarine cable and a preparation method thereof, wherein the optical fiber composite submarine cable is reasonable in structural design, does not influence photoelectric recombination mutually, plays a protection role mutually, and can reduce the primary construction cost and the later operation and maintenance cost of wind power enterprises.

In order to solve the technical problem, the invention provides an optical fiber composite submarine cable which comprises a cable core, and a belting layer, an inner liner layer, an armor layer and an outer protective layer which are sequentially coated outside the cable core, wherein the cable core comprises a plurality of electric units which are arranged in a twisted mode, a filling strip which is used for filling a gap between any two adjacent electric units and an optical unit which is arranged in the filling strip in a penetrating mode, the filling strip is of a fan-shaped structure and comprises a fan-shaped arc surface and two fan-shaped side surfaces which are symmetrically arranged on two sides of the fan-shaped arc surface, the fan-shaped arc surface and the electric units are sequentially spliced to form a circumferential surface, the fan-shaped side surfaces are matched with the electric units in a fit mode, grooves are further formed in the side walls of the fan-shaped arc surface, the optical unit is embedded in the grooves, and hollow through holes are further formed in the filling strip.

In one embodiment of the invention, the electric unit comprises a water-blocking conductor, a conductor shielding layer, an insulating shielding layer, a water-blocking buffer layer, a metal shielding layer, a semi-conductive water-blocking layer and an aluminum-plastic sheath layer which are arranged in sequence from inside to outside.

In one embodiment of the present invention, the water blocking conductor is made by compressing a water blocking material compounded with any one of copper, aluminum and aluminum alloy.

In one embodiment of the invention, the conductor shielding layer, the insulating layer and the insulating shielding layer are jointly extruded and coated on the periphery of the water-blocking conductor, and the conductor shielding layer, the insulating layer and the insulating shielding layer are concentrically arranged with the water-blocking conductor.

In one embodiment of the invention, the aluminum-plastic sheath layer is composed of a semi-conductive film-coated aluminum tape and semi-conductive polyethylene.

In one embodiment of the present invention, the light unit includes a loose tube in which optical fibers and water-blocking fiber paste filled between the optical fibers are disposed.

In one embodiment of the invention, the armor layer comprises galvanized steel wires and PE strips, the sections of the galvanized steel wires and the PE strips are the same in shape and size, and the galvanized steel wires and the PE strips are spirally wound on the periphery of the lining layer at staggered intervals.

In order to solve the technical problem, the invention also provides a preparation method of the optical fiber composite submarine cable, which comprises the following steps:

s1, preparing an electric unit: preparing a water-blocking conductor, preparing a conductor shielding layer, an insulating layer and an insulating shielding layer outside the water-blocking conductor by adopting a three-layer co-extrusion technology, after stress is eliminated, sequentially wrapping a water-blocking buffer layer, a metal shielding layer and a semi-conductive water-blocking layer, and finally performing extrusion molding to form an aluminum-plastic sheath layer to obtain an electric unit;

s2, preparing a filling strip: the filling strip comprises a fan-shaped cambered surface, two fan-shaped side surfaces symmetrically arranged at two sides of the fan-shaped cambered surface, a groove for embedding the light unit and a hollowed-out through hole;

s3, preparing a cable core: twisting a plurality of electric units formed in the step S1 together, enabling the sections of any two adjacent electric units to be contacted in a pairwise tangent manner, simultaneously twisting the fan-shaped filling strips formed in the step S2, sequentially splicing the fan-shaped cambered surfaces and the electric units to form a circumferential surface, and attaching and matching the fan-shaped side surfaces and the electric units;

s4, fill light unit: preparing an optical unit structure, and filling the optical unit structure in the groove in the filling strip;

s5, cabling: and sequentially wrapping a belting layer, an inner liner layer, an armor layer and an outer protective layer around the cable core to obtain the submarine optical cable, wherein the armor layer is spirally wrapped on the periphery of the inner liner layer at intervals by galvanized steel wires and PE strips in a staggered manner.

In an embodiment of the invention, in step S1, the water blocking conductor is prepared by: firstly, drawing a wire by using a wire drawing machine to obtain a monofilament, then penetrating the monofilament into a wire coiling machine and placing the wire coiling machine into a round nano die, adding a water-blocking material into the round nano die, and twisting to obtain the compact round water-blocking conductor.

In an embodiment of the invention, in the step S1, the three-layer co-extrusion preparation of the conductor shielding layer, the insulating layer and the insulation shielding layer adopts a catenary crosslinking production line, and is obtained by extrusion through a conical head, the thickness value of the conductor shielding layer, the insulating layer and the insulation shielding layer is 8.5mm-13mm, and the maximum eccentricity is not greater than 5%.

Compared with the prior art, the technical scheme of the invention has the following advantages:

the cable core of the optical fiber composite submarine cable is formed by twisting a plurality of electric units, the gaps among the electric units are provided with filling strips with fan-shaped structures, the fan-shaped cambered surfaces and the electric units are sequentially spliced to form a circumferential surface, so that the roundness of the outer part of the cable core is ensured, the fan-shaped side surfaces are attached and matched with the electric units, and the compactness in the cable core is ensured;

and, be provided with the recess that can hold the light unit in the packing strip, with the light unit embedding recess in, on the one hand keep apart the light unit with electric unit through the packing strip, prevent electromagnetic interference, on the other hand can play certain protection effect to the light unit through the packing strip, simultaneously, still seted up the fretwork through-hole in the packing strip, further alleviateed the overall quality of optical cable.

Drawings

In order that the present disclosure may be more readily and clearly understood, reference is now made to the following detailed description of the present disclosure taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a schematic cross-sectional structural view of a fiber optic composite undersea cable of the present invention;

FIG. 2 is a schematic cross-sectional view of the filler strip of the present invention;

FIG. 3 is a schematic cross-sectional configuration of an electrical unit of the present invention;

fig. 4 is a flow chart of a method of making the fiber optic composite undersea cable of the present invention.

The specification reference numbers indicate: 1. an electrical unit; 11. a water blocking conductor; 12. a conductor shield layer; 13. an insulating layer; 14. an insulating shield layer; 15. a water-blocking buffer layer; 16. a metal shielding layer; 17. a semiconductive water barrier layer; 18. an aluminum-plastic sheath layer; 2. filling the strip; 21. a fan-shaped cambered surface; 22. a fan-shaped side surface; 23. a groove; 24. hollowing out the through hole; 3. a light unit; 4. a belting layer; 5. an inner liner layer; 6. an armor layer; 7. an outer jacket.

Detailed Description

The present invention is further described below in conjunction with the following figures and specific examples so that those skilled in the art may better understand the present invention and practice it, but the examples are not intended to limit the present invention.

Referring to fig. 1, the optical fiber composite submarine cable of the present invention comprises a cable core, and a belting layer 4, an inner liner layer 5, an armor layer 6 and an outer protective layer 7 which are sequentially coated outside the cable core, wherein the cable core comprises a plurality of twisted electric units 1, a filler strip 2 filled in a gap between any two adjacent electric units 1, and an optical unit 3 penetrating through the filler strip 2;

referring to fig. 2, the filler strip 2 is of a fan-shaped structure, the filler strip 2 comprises a fan-shaped arc surface 21 and two fan-shaped side surfaces 22 symmetrically arranged on two sides of the fan-shaped arc surface 21, the fan-shaped arc surface 21 and the electric unit 1 are sequentially spliced to form a circumferential surface, so that the roundness of the outer part of the cable core is ensured, the fan-shaped side surfaces 22 are attached and matched with the electric unit 1, so that the compactness of the cable core is ensured, on one hand, the roundness of the cable core is improved, a tape, armor and a sheath in subsequent processes are facilitated, the bulge or collapse is prevented, on the other hand, the self-filling degree of the cable core is also improved, and the cable core is prevented from being deformed when the cable core is used in a submarine environment for a long time; a groove 23 is further formed in the side wall of the fan-shaped arc surface 21, the optical unit 3 is embedded in the groove 23, on one hand, the optical unit 3 is isolated from the electrical unit 1 through the filling strip 2 to prevent electromagnetic interference, on the other hand, the optical unit 3 can be protected to a certain extent through the filling strip 2, and the optical unit 3 is guaranteed not to be stressed completely in the production and laying processes of the submarine cable; meanwhile, the hollow through holes 24 are formed in the filling strips 2, so that the overall quality of the optical cable is further reduced.

Referring to fig. 3, the electrical unit 1 includes a water-blocking conductor 11, a conductor shielding layer 12, an insulating layer 13, an insulating shielding layer 14, a water-blocking buffer layer 15, a metal shielding layer 16, a semi-conductive water-blocking layer 17, and an aluminum-plastic sheath layer 18, which are sequentially arranged from inside to outside, and the cable laid on the seabed has two indexes which are important: the water-blocking performance and the shielding performance are good, the electric unit 1 is made of the water-blocking conductor 11 and has a radial water-blocking function, and meanwhile, the water-blocking buffer layer 15 and the semi-conductive water-blocking layer 17 are used for layered coating to play a role of double radial water blocking, so that the requirement of 500-meter water depth of offshore wind power is met; the shielding performance of the shielding layer is ensured by adopting four layers of shielding insulation, namely a conductor shielding layer 12, an insulating layer 13, an insulating shielding layer 14 and a metal shielding layer 16.

Specifically, the water blocking conductor 11 is formed by compressing any one material of copper, aluminum and aluminum alloy composite water blocking material to form a compressed round structure, and is compressed by twisting a plurality of single wires, so that the specification is larger, the coverage range is wider, and the compression coefficient is higher; specifically, the maximum cross-sectional area of the twisted monofilament reaches 20mm²The maximum cross section area after compaction reaches 1600mm²The compaction factor is up to 92%.

Specifically, conductor shielding layer 12, insulating layer 13, the common extrusion coating of insulating shielding layer 14 are in the conductor 11 periphery blocks water, conductor shielding layer 12, insulating layer 13, insulating shielding layer 14 and the concentric setting of conductor 11 blocks water, conductor shielding layer 12, insulating layer 13, insulating shielding layer 14's maximum eccentricity is not more than 5%, its highest withstand voltage 96 kV.

Specifically, the aluminum-plastic sheath layer 18 is formed by covering a semi-conductive film aluminum tape and semi-conductive polyethylene, and a traditional lead sheath is not used, so that the weight and the cost of the submarine cable are reduced, and the pollution to the environment is reduced; in addition, in this embodiment, the filling bar 2 is also made of a semiconductor material, the semiconductor film-coated aluminum tape in the aluminum-plastic sheath layer 18 is a single surface, and is connected with the short-circuit wires of the metal shielding layer 16, the filling bar 2 and the armor layer 6 to form an equipotential, and the equipotential is formed among the metal shielding layer 16, the aluminum-plastic sheath layer 18, the filling bar 2 and the armor layer 6, so that the loss of thermal resistance in the transmission process can be reduced, that is, the line loss is reduced, and the global energy crisis can be effectively alleviated; in addition, the induced potential can be eliminated, and the harm to equipment and people caused by the superposition of the induced potential is reduced.

Specifically, light unit 3 includes the pine sleeve pipe, be provided with optic fibre in the pine sleeve pipe and fill the fine cream of blocking water between optic fibre, optic fibre can set up different structural style such as bulk optical fibre, ribbon optical fibre, bundle form optic fibre according to actual demand, fills the fine cream of blocking water and further improves the inside water blocking performance of light unit 3.

In this embodiment, the armor layer 6 includes galvanized steel wire and PE strip, the cross-sectional shape size of galvanized steel wire and PE strip is the same, the periphery of lining layer 5 is wrapped around alternately the spiral of galvanized steel wire and PE strip, replaces the galvanized steel wire with the PE strip, satisfies under the overall strength and lays the tensile condition, further reduces manufacturing cost and the whole quality of optical cable, can reduce wind power enterprise elementary construction cost and later fortune dimension cost.

Referring to fig. 4, the invention also discloses a preparation method of the optical fiber composite submarine cable, which comprises the following steps:

s1, preparing an electric cell 1: preparing a water-blocking conductor 11, preparing a conductor shielding layer 12, an insulating layer 13 and an insulating shielding layer 14 outside the water-blocking conductor 11 by adopting a three-layer co-extrusion technology, after stress is eliminated, sequentially wrapping a water-blocking buffer layer 15, a metal shielding layer 16 and a semi-conductive water-blocking layer 17, and finally performing extrusion molding to form an aluminum-plastic sheath layer 18 to obtain an electric unit 1;

s2, preparing a fan-shaped filling strip 2: the fan-shaped filling strip 2 comprises a fan-shaped cambered surface 21, two fan-shaped side surfaces 22 symmetrically arranged at two sides of the fan-shaped cambered surface 21, a groove 23 for embedding the light unit 3 and a hollowed-out through hole 24;

s3, preparing a cable core: twisting a plurality of electric units 1 prepared in the step S1 together, wherein two phases of the cross sections of any two adjacent electric units 1 are in tangential contact, simultaneously twisting the fan-shaped filling strips 2 prepared in the step S2, the fan-shaped cambered surfaces 21 and the electric units 1 are sequentially spliced to form a circumferential surface, and the fan-shaped side surfaces 22 are attached and matched with the electric units 1;

s4, fill light unit 3: preparing a light unit 3 structure, and filling the light unit 3 structure in the groove 23 in the fan-shaped filling strip 2;

s5, cabling: and sequentially wrapping a belting layer 4, an inner liner layer 5, an armor layer 6 and an outer protective layer 7 on the periphery of the cable core to obtain the submarine optical cable, wherein the armor layer 6 is spirally wrapped on the periphery of the inner liner layer 5 by galvanized steel wires and PE strips at staggered intervals.

Specifically, the preparation method of the water blocking conductor 11 in step S1 includes: firstly, drawing wires by using a giant drawing machine, annealing to obtain monofilaments, then penetrating the monofilaments into a disc stranding machine, placing the monofilaments into a round nano die, adding a water-blocking glue into the disc stranding machine, completely filling the water-blocking glue into gaps of conductors, and stranding to obtain a tightly pressed round water-blocking conductor 11;

the waterproof conductor 11 prepared by the method has larger specification, wider coverage area and higher compression coefficient, and particularly, the sectional area of the maximum twisted monofilament reaches 20mm²The maximum sectional area reaches 1600mm²The compaction coefficient reaches 92 percent.

Specifically, the method for preparing the conductor shielding layer 12, the insulating layer 13 and the insulating shielding layer 14 by adopting a three-layer co-extrusion technology comprises the following steps: a catenary crosslinking production line is adopted, the conductor shielding layer 12, the insulating layer 13 and the insulation shielding layer 14 are respectively extruded by three extruders, and then the conductor shielding layer 12, the insulating layer 13 and the insulation shielding layer 14 are extruded by a conical machine head to obtain a three-layer co-extrusion structure of the conductor shielding layer 12, the insulating layer 13 and the insulation shielding layer 14;

the method and the equipment are adopted to finish the three-layer co-extrusion, so that the eccentricity and the insulation purity of the insulating layer 13 are ensured, specifically, the maximum voltage of the obtained insulating layer 13 reaches 72.5kV, and the maximum eccentricity is not more than 5%.

Specifically, a closed tray is adopted to eliminate stress; and sequentially wrapping the water blocking buffer layer 15, the metal shielding layer 16 and the semi-conductive water blocking layer 17 by using a wrapping machine, and finally extruding and coating the aluminum-plastic sheath layer 18 by using an extruding machine to obtain the electric unit 1.

Specifically, the fan-shaped filling strip 2 is extruded by an extruding machine and a special-shaped injection molding machine head.

Specifically, three electric units 1 are twisted together by adopting vertical cabling equipment, so that the sections of the electric units 1 are contacted in a pairwise tangent manner, and simultaneously, fan-shaped filling strips 2 are twisted to round cable cores;

specifically, the grooves 23 of the filling strips 2 are filled with the light units 3, then the lining layer 5 is wrapped, and a brass band can be wrapped as a belting layer 4 if necessary, so that the cable is prevented from being gnawed by marine organisms; and meanwhile, spirally winding galvanized steel wires and PE strips by using armor equipment to form an armor layer 6, and finally wrapping an outer protective layer 7 to obtain the submarine cable.

It should be understood that the above examples are only for clarity of illustration and are not intended to limit the embodiments. Other variations and modifications will be apparent to persons skilled in the art in light of the above description. And are neither required nor exhaustive of all embodiments. And obvious variations or modifications therefrom are within the scope of the invention.