Abstract:
A pass-through power take-off (PTO) mechanism for use with renewable energy systems is described to extract power from a linearly moving tether under high tension and to convert it to rotary power such as for driving an electric generator. Three such embodiments are described. The first uses two adjacent timing belts and transfers power from tether to PTO via friction. The second embodiment uses two adjacent roller chain loops and a mechanical engagement method to transfer power from tether to PTO. The third embodiment uses two adjacent double-sided timing belts and either a synchronous or an asynchronous method to transfer power from the tether to the PTO.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     The invention described and claimed herein below is described in substance within U.S. Provisional Patent Application No. 61/277,852, filed on Sep. 30, 2009, which provides a claim of priority of invention under 35 U.S.C. 119(e). This application is incorporated by reference herein. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a power take-off (PTO) mechanism for extracting rotary power from a linearly moving tether passing therethrough in renewable energy systems. 
     BACKGROUND OF THE INVENTION 
     My U.S. Pat. No. 6,555,931 describes renewable energy systems of a non-turbine variety using long-stroke reciprocating motion of one or more tethers each attached to an element extracting useful energy from naturally occurring fluid flow of air (wind) or water (currents or tides). U.S. Pat. No. 6,555,931 is incorporated by reference herein. 
     Wind turbines are being deployed at a rapid pace both on land and off-shore. Land use, push-back by local populace, land cost, and site-specific avian mortality problems have limited terrestrial development of wind farms. This has spurred interest in developing large off-shore wind farms. In shallow areas, turbine towers are attached to the seabed, but the interest in less congested and more remote deep-water areas increases as close off-shore shallow venues have also come under attack. 
     Regarding very large deep-water off-shore wind energy development, economies of scale point to ever increasing turbine size making the installation and very logistics of transporting tower and blade sections problematic. With turbine-tip speed limits and even taller structures to contend with, it is interesting that using oil platform technology or counter-weighted ocean floor tethered floating platforms are considered (by some) to be both cost-effective and practical. 
     Actually, large reciprocating wind energy systems may be more compatible with the task at hand. The main attraction for deep-water use is the elimination of the tower structure with its attendant turning moment transmitted to the supporting structure. The installation would be at sea-level since only airfoils would be aloft. A floating platform can be totally fitted at dockside and just towed to its deployed area; it can also be moved to shore for any major repairs (or they can be easily and safely performed at sea). Since all components of a reciprocating wind system are modular and relatively small (airfoils can be “folded”), there is no transportation problem. No special vessels with cranes are required for erection, deployment, or maintenance/repairs. There are no known size limitations comparable to those imposed by turbine blade root stress or blade tip speed, so that size can be more easily dictated by economic as opposed to technology considerations. 
     However, there are some problems in scaling up power drums, capstan, or windlass type tether handling devices for long-stroke systems that would be handling tethers of several inches diameter and under extremely high tension. These devices are used to convert the linear tether motion into more useful rotary motion. If very large diameters are used, rotary speed will be slow thereby increasing the cost of transmission components. If strokes are limited to mitigate this problem, system efficiency suffers. 
     OBJECTS OF THE INVENTION 
     It is, therefore, an object of the present invention to provide a pass-through PTO arrangement handling tether under tension linearly thereby avoiding the need for winding the tether under tension. 
     It is a further object of this invention to provide a pass-through PTO arrangement compatible with non-turbine long-stroke reciprocating renewable energy systems. 
     It is also an object of the present invention therefore to provide a viable alternative to very large deep-water off shore wind turbines with life-cycle cost and safety advantages from deployment throughout service life. 
     Other objects which become apparent from the following description of the present invention. 
     SUMMARY OF THE INVENTION 
     This invention replaces power drum, capstan, or windlass devices with a pass-through PTO mechanism that can be scaled up to accommodate large diameter tether under high tension to convert linear motion of the tether to rotary motion at advantageous rotary speed as compared to the prior art devices. This invention can be used in large reciprocating renewable energy systems such as wind energy conversion systems or water current or tidal systems. While most of the discussion is involved with extracting power from a moving tether to the PTO during the power stroke, the pass-through PTO is also used to supply power to the tether during the low-power rewind phase in the opposite direction. 
     In some embodiments, a modified lower portion of tether slightly longer than the maximum stroke length is used as compatible with the pass-through PTO mechanism. In other embodiments, the standard tether as that used for the portion beyond the maximum stroke length can be used unmodified. Although tethers with circular crossection are described in this application, it can be appreciated that other crossectional shapes such as oval or flat ribbons can be used with very slight modifications of the pass-through PTO mechanisms for their accommodation without departing from the operation or concept described. Even in the case of modified tethers, the average density is close to that of the unmodified tether so as not to impede proper operation of the unmodified upper portion of tether. This can be achieved in a variety of manners including differences in crossectional shape and size, material, elasticity and compressibility from that of the upper tether even if at the penalty of increased unit cost for this short lower section. 
     In the first embodiment, a frictional approach is used to transfer the tether motion to the PTO mechanism. Two timing belts supported by timing belt pulleys at the top and bottom are placed side-by-side such that the outer surface of one belt is slightly less than the thickness of the tether from the outer surface of the adjacent belt. Either the outer smooth surfaces of both timing belts or outside of the lower portion of the tether (&gt;stroke length) has a surface enhanced to increase the coefficient of friction. Both the belts and tether can be friction enhanced if desired. If the tether is slightly deformed so that it can squeeze between the adjacent belts and be locked to them by friction, it will drive both belts if it moves linearly in either direction. The two lower timing belt pulleys (one engaged in each belt) are also coupled to each other by an attached gear so that the two belts will move synchronously and extract power from the moving tether which can be harvested as rotary motion of either one (or both) of the gear shafts. Actually, power extraction can be either at the top (high tension) end or the bottom (no tension) end as the power stroke commences upward, but the lower end is preferred as it automatically pulls the belt segments taut. Smaller idler timing belt pulleys are deployed along the surface adjacent to the tether on each belt to maintain some squeeze pressure against the tether. Power is thereby transferred from the tether to the output gears along approximately one half of each belt length. The limitation on the diameter of timing belt pulleys used is that the diameter has to be able to engage enough power transfer ridges of the belt to accommodate the forces on the belt. The smallest diameter pulley that exceeds this criteria without slippage (or “jumping” a ridge) would be used to achieve the highest possible rotary speed for a given tether velocity. Note also that a rewind motor can be selectively engaged with either gear shaft to pull the tether back down (as might be used during the parasitic portion of the stroke of returning a closed airfoil to a lower position in a wind energy application). 
     The second embodiment uses a mechanical engagement to transfer power from a moving tether to the PTO. Using a geometric configuration not unlike the first embodiment, two loops of roller chain replace the function of the timing belts. Sprockets replace the timing belt pulleys. The lower portion of the tether (&gt;stroke length) is enhanced with the attachment of chain engaging members at the appropriate pitch to mesh with nibs attached to the roller chain. By judicious selection of the pitch of the engaging members on the tether as compared with the constant pitch of the roller chain nibs, multiple engagement along the roller chain will be insured thereby limiting point source stress loading of both tether and chain. 
     The third embodiment of this invention uses a specially designed timing belt which can be used to engage tether in either a synchronous or asynchronous method. The two timing belts used are “double-sided” with the design of the outer engagement blocks with a concave contour designed to grasp an unmodified or a “sleeve modified” tether in an asynchronous method, or a tether with periodic engagement rings molded onto its periphery. The asynchronous method would slightly deform the tether outer contour of an unmodified tether or one that has been overmolded with a smooth sleeve (such as polyurethane) so that a combination of friction and mechanical deformation will engage the tether within the concave portion of the belt engagement blocks. In the alternate method, the same concave portion will engage synchronously (mechanically) engagement rings overmolded onto the tether. Since the elastic stretch of the tether and belts can be designed to be the same, the pitch of the engagement rings and the outer engagement blocks can also be the same. 
     The pass-through PTO divides the tether into a high tension section above the PTO and a no-tension section below. In between, as tether passes through, tension is transferred from tether to PTO where it is converted into torque at the power output. While the tether under high tension, is not easy to handle, the no-tension lower end of the tether can be easily handled in a number of ways. It can simple fall into a bin from which it can be pulled up, it can be wound onto and unwound from a light-weight drum, or it can be pushed into and pulled from any rigid hollow tubing structure with either no or gentle curvature. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention can best be understood in connection with the accompanying drawings. It is noted that the invention is not limited to the precise embodiments shown in drawings, in which: 
         FIG. 1  is a front elevation of the pass-through PTO of this invention according to the first embodiment using a frictional power transfer from tether to PTO. 
         FIG. 2  is a front elevation of a pass-through PTO using mechanical engagement and roller chain according to the second embodiment. 
         FIG. 3  is a perspective detail of the modified tether of the second embodiment. 
         FIG. 4  is a side elevation detail of the central region of the two roller chain central sections of pass-through PTO with modified outer side links. 
         FIG. 5  is a perspective view of one double-sided outer roller chain link of the second embodiment. 
         FIG. 6  is an end view of the link of  FIG. 5  showing the crossover member. 
         FIG. 7  is a schematic representation of the relative position of tether engagement elements and chain crossover members under low, medium, and high tether tension conditions at A, B, and C respectively. 
         FIG. 8  is a side elevation of a pass-through PTO of this invention according to the third embodiment using a specially designed timing belt. 
         FIG. 9  is a perspective close-up of a section of timing belt of the PTO of  FIG. 8 . 
         FIG. 10  is a side elevation close-up of tether over molded with mechanical engagement rings. 
         FIG. 11  is a crossection of the tether of  FIG. 10 . 
         FIG. 12  is a schematic representation of several methods of handling the no-tension end of tether: A. bin, B. drum, C. straight tube, D. flat serpentine, E. flat spiral, F. helix 
         FIG. 13  is a top view showing the pass-through PTO of  FIG. 2  integrated into a power conversion subsystem. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows pass-through PTO mechanism  1  using timing belts  3 , timing belt idler pulleys  5  at the top and timing belt pulleys with attached synchronizing gears  4  at the bottom. Tether  2  passes through PTO  1  in intimate contact with outer sides of both timing belts  3  along one side each. Motion of tether is upward (power stroke) with end  10  at high tension and lower end  11  at no tension. Tether  2  passes through two pairs of highly grooved idler pulleys  6  to locate it between belts  3 . Pulleys  4  and  5  are turned in the indicated directions by virtue of tether  2  motion and the effects of being squeezed between belt  3  sections with high friction at the tether/belt junction. This friction is caused by frictional coefficient enhancement of either the outer surfaces of both belts  3  or of the outer periphery of tether  2  or both. This can be achieved by material selection (eg.—high friction polyurethane material or coating) or the use of adhesively attached high friction grains of abrasive material that would embed in the opposite contact surface. Small timing belt idler pulley pairs  7  help keep tether  2  in intimate contact with belts  3 . Idler pulleys  7  should have flanges (not shown to enhance clarity) to help locate tether  2  centrally transversely between belts  3 . 
       FIG. 2  shows schematically pass-through PTO  15  using two roller chain loops  18  engaging modified tether  22  mechanically whereby attached tether disks  23  engage chain nibs  21 . Roller chain  18  is located by upper idler sprockets  17  and lower sprockets  19  attached to synchronizing gears  20 . Intermediary idler sprocket pairs  16  help keep tether  22  and chains  18  engaged. Roller chains are relatively easy to scale up to enormous sizes and power ratings since there is much experience in their use in very large construction, mining, and maritime equipment. For this reason, this second embodiment is preferred. The mechanical engagement between tether  22  and chains  18  results in higher transmission efficiency. Roller chains, if properly lubricated, are known to offer long trouble-free service life. 
       FIGS. 3-7  show practical details of the elements of PTO  15  of  FIG. 2 .  FIG. 3  shows the preferred embodiment of modified tether  60  with actual tether fiber  61  and short tubular members  62  replacing the tether disks  23  of  FIG. 2 . Depending on the materials selected for tubular members  62  and tether fiber  61 , elements  62  can be directly over-molded onto tether fiber  61  in a continuous fabrication method. In any case, the length L provides more internal surface area (than a disk shape) for bonding with the outer surface of fiber  61  even if adhesives are used. 
       FIG. 4  shows the central region of pass-through PTO  15  using roller chain with modified outer links of the preferred embodiment. Both the left chain loop  70  and the right chain loop  71  are identical. They are made up of standard inner links  75  and modified double outer links  76  which are attached via rivets or other coupling elements  78 . Links  76  are spaced at double the chain pitch lengths.  FIGS. 5 and 6  show details of a double link  76 . Two side flanges  80 , with one long straight edge and one curved edge each, have rivet holes  81 . They are attached together via crossover  85  with a circular arc recess to receive and locate continuous tether fiber  61  between engagement elements  62 . If crossover  85  is moved to the straight edge of flanges  80 , or if side notches are formed in the regions of crossover  85  toward the straight edge, either of these changes would make it possible to fabricate each double outer link  76  by a die punch process which punches the entire shape and then bends it into a finished double link. Another alternative for double link  76  is to substitute two single links with one half of crossover  85  attached (as cut at the apex of the curved section shown in  FIG. 6 ); the two halves would function identically as double link  76 . Note that straight edges of double link  76  capture and locate engagement elements  62  while tether fiber  61  is located within crossover  85  whenever tether  60  is within the central region of pass-through PTO  15  as defined by the two adjacent chain linear portions. Crossovers  85  serve the function of chain nibs  21  shown in  FIG. 2  transferring power from modified tether  60  to output gears  20 . 
     Since tether fiber  61  has some elastic stretch which is significantly greater than any exhibited by roller chains  70  and  71 , the pitch of engagement elements  60  in modified tether  62  is slightly shorter than that of twice the chain pitch length (2×PL). The no-load pitch of modified tether  60  will stretch to exceed that of the roller chains at maximum load, but it will be constrained to chain pitch length within the region of engagement. In this way, although single element loading between tether and chain occurs at low tension, multiple element loading prolonging element life is encountered as tension load increases. This is illustrated schematically in  FIG. 7  where one-sided engagement between elements  62  and crossovers  85  is shown at three levels of tether tension. Note single element loading at A with gaps G 1 , G 2 , and G 3  because of the shorter pitch of tether  60 . At B, two element loading is illustrated; at C, tether pitch is stretched to be equal to chain pitch within the entire engagement region. 
       FIG. 8  shows a third embodiment of pass-through PTO of this invention based on the use of two pairs of modified double-sided timing belts. Timing belts  29  have engagement elements  30  periodically molded onto the base reinforced belt section so that they protrude inwardly  32  to engage timing belt pulleys  27  and  28  and as outward protrusions  31  where they engage a tether such as  33  which has periodic engagement rings  34  attached at the same pitch. Since belts  29  are designed with the same stretch characteristics as tether  33 , the pitch of both can be identical. Lower timing belt pulleys  27  are attached to meshed synchronizing gears  26  with their shafts constituting output power connections (PTO). The location of pairs of idler timing belt pulleys  35  is shown schematically. These should be flanged to locate belts  29  laterally. 
       FIG. 9  is an enlarged view of a section of belt  29 . Engagement elements  30  with inward pulley-engaging protrusions  32  and outward protrusions  31  with concave features to engage with modified tether  33  are shown. While a loose fit of tether  33  within the pair of facing concave outward protrusions  31  is sufficient if the engagement is synchronous using engagement rings  34  (see  FIGS. 10 and 11 ), an asynchronous engagement method on an unmodified or modified smooth tether would require the concave surfaces to squeeze and elastically deform the tether slightly (ie. grasp the tether). In  FIGS. 10 and 11 , modified tether is revealed to include a high strength fiber core  36  overmolded with a thin tubing layer  33  and periodic engagement rings  34  that would engage concave protrusions  31  from the top or bottom side much as protrusions  32  are engaged in the grooves of a timing belt pulley. For asynchronous use, a modified tether with an overmolding of tubing  33  of polyurethane (but without engagement rings  34 ) would provide a high friction wear resistant surface with a desirable resilient reaction to squeezing in the transverse direction. 
       FIG. 12  illustrates six methods of handling the end of the tether that is below the pass-through PTO and therefore under no tension. In A, B, and C, a pass-through PTO  40  is shown schematically as two adjacent ovals with tether  41  running through it. A simply shows a bin  45  to catch the tether  41  end as it is rewound; it is withdrawn from bin  45  during the power stroke. In B, a light weight drum  46  is used to wind and unwind the tether  41  end as needed using a low power winding motor (not shown). If tether end  41  is modified and unmodified tether above does not engage PTO  40  (passes loosely through it), drum  46  can be sized to wind the entire length of tether under low tension as would be used with a closed airfoil during a reefing operation. 
     In  FIGS. 12C-F , rigid hollow tube structures are shown that can hold the short “stroke length” end of modified or unmodified tether. Since large crossection tether has some rigidity, it can be pushed into these hollow rigid tubes when being rewound by the pass-through PTO. Straight pipe  47  in shown at C, while flat serpentine  48  with gentle end curvatures is at D. A flat spiral  49  is shown at E and a helical structure  50  at F. Storage structures as hollow rigid tubes of other shapes conformable to the space constraints of the platform in use can also be configured as long as tether can be pushed into them and withdrawn without kinking or excessive friction. 
       FIG. 13  shows a possible system configured around the use of pass-through PTO  15 . Both shafts of synchronizing gears  20  are used to couple devices. Two one-way clutches (OWC) are used to isolate devices from shafts during different phases of operation to minimize parasitic losses. OWC  134  isolates optional flywheel/gear box (or transmission)  136  from the power output shaft during the rewind phase, but it permits attachment in the power stroke phase to turn electrical generator (AC or DC)  138 . A smaller output shaft on the other gear  20  is connected to OWC  142  which selectively attaches to shaft  140  on rewind motor  144  which turns PTO  15  in the reverse direction to pull down tether  22  in that phase of the operation. This is just one example of a method to use a pass-through PTO of this invention in an electrical power generating system. 
     In the foregoing description, certain terms and visual depictions are used to illustrate the preferred embodiments. However, no unnecessary limitations are to be construed by the terms used or illustrations depicted, beyond what is shown in the prior art, since the terms and illustrations are exemplary only, and are not meant to limit the scope of the present invention. 
     It is further known that other modifications may be made to the present invention, without departing the scope of the invention, as noted in the appended Claims.