This invention relates to support system carrying a utility platform, wherein the platform is spatially manipulable. The support system is useful for example, as a tracking system or as a support structure for various construction purposes, etc.
Tracking systems for flat and concentrating panels are used to focus/direct solar energy and other forms of radiation onto a receiver which collects the radiation or signal for use. The tracker must keep the collecting surface pointing at the sun or energy source so that maximum energy will be absorbed by the receiver. For that purpose it is required that a tracking system be capable of accurate incremental angular displacement.
The prior art contains a number of examples of methods for azimuth and elevation tracking of energy concentrating antennas and solar collectors. Most conventional heliostat and dish trackers use pedestal mounted gear box drives to provide azimuth and elevation control. Wind loads on large area collectors place very large torques and moments on these gear boxes. Most of these devices simply resist wind and gravity loadings with increased structural weight.
An example of a prior art tracking system is disclosed in GB Patent Application 2114376 disclosing an antenna apparatus having a support device to be fixed to a given installing body, an antenna body e.g. a parabolic reflector having a given directivity, and a ball joint mechanically coupling the support device to the antenna body. Two different positions of the antenna body are coupled via a wire or rope so that the direction of the antenna body with respect to a given axis is changed by the push-pull movement of the rope. Similarly other pairs of positions connected by wires provide orientation about other axes. Once the apparatus has been installed and the direction adjusted, the wires are fixed so that the reflector cannot move. Details of fixings, pulleys, ball joints and clamps are disclosed. The arrangement is useful for domestic reception of Super High Frequency signals from a geostationary satellite.
Japan Patent Publication JP2004-64195 discloses a drive comprising a 1st circular slide rail that rotates to one shaft orientations, a 2nd circular slide rail that rotates to shaft orientations which have a slot into which said 1st slide rail fits, and are different from said 1st slide rail and a mount table with a slot into which said 2nd slide rail fits.
Other prior art systems relating to tracking systems are disclosed, for example, in U.S. Pat. Nos. 4,363,354, 4,608,964, 4,870,949 and 5,325,844.
Hereinafter in the specification and claims, reference is made to several particular designs. However, it is by no means intended to restrict the system according to the present invention to an equatorially oriented system. Thus, the structure may be oriented otherwise, such as for example, azimuth/altitude, or the like, where a plane defined by a utility platform can be either parallel to the horizon or disposed at some other angle.
Herein after, the invention will be described without reference to a particular application, however without being limited to any. The term utility platform as used herein in the specification and claims denotes any such collector or other construction mounted directly or indirectly on a manipulable platform.
The terms front side and rear side as used herein in the specification and claims define location along the longitudinal, X-X axis, wherein the rear side direction is related to a side at which the cords are pulled. Said platform is manipulable to roll about said X-X axis (i.e. left/right tilting).
The terms left side and right side as used herein in the specification and claims define respective location along the lateral, Y-Y axis, wherein said platform is manipulable to pitch about said Y-Y axis (i.e. up/down, or as often referred to also as front/rear tilting). Accordingly, the terms front and rear, respectively refer to those sides of the system extending along the X-X axis
The X-Y plane is considered to be horizontal when the plane of the utility platform is transverse at right angles to the vertical axis (Z-Z) of the support post, regardless if the post is vertical.
The term cord connection element (CCE) is defined as one of:
i) a Static Cord Connection Elements (SCCE); wherein there is substantially no displacement of the cord with respect to the connection element (i.e. fixed thereto); and,
ii) a Dynamic Cord Connection Elements (DCCE); wherein the cord is displaceable with respect to the connection element (i.e. rolling/sliding); the term DCCE is used in s broad sense and also denotes a pulley or a motor, as defined herein.
The Cord Connection Elements are either articulated to the utility platform (in which case they are indexed P; e.g. PDCCE designates a utility platform mounted dynamic cord connection element), or to the ground (in which case they are indexed G; e.g. GSCCE designates a ground mounted static cord connection element).
The term pulley as used herein in the specification and claims is used in its broad sense and is used to denote any sort of hook through which a cord/cable extends and is free to slide/roll (change its point of application) and changes its direction. A pulley may be a simple hook or eye structure fixed to the utility platform or to the ground, or it may be a multiplication wheel-type pulley wherein force is traded for distance (i.e. a load is pulled over a longer distance, however at reduced force), etc.
In a system according to the present invention it is assumed that the tension cords are substantially non-stretchable (i.e. non-elongatable).
A motor as used herein in the specification and claims denotes any type of motor including, but not limited to linear retraction/expansion motors, rotary (winding) motors, winch, manipulators of various types, etc.
The present invention is directed to a structural support and tracking system which provides substantially accurate displacement/tracking, also upon displaced at substantially small increments. The manipulating construction is light weight and nevertheless provides rigidity and durability also at the event of strong wind. Even more so, the system may be tilted with respect to the horizon at significant degrees, optionally exceeding 90°.
The present invention is applicable to a wide range of radiation collector systems and to other systems which require precise one or two-axis tracking of a body. Examples for tracking systems are solar radiation collectors (in any form, e.g. flat panels, dish or trough-like), electromagnetic radiation collectors and the like. Another example of utility platforms is a vehicle simulator, motion simulator (e.g. ski simulator), aiming platform (e.g. for a weaponry system), double-deck car park or storage facility, etc.
According to the present invention there is provided a structural support and tracking system comprising a utility platform defining an X-Y plane and supported over a central support post defining a longitudinal axis Z being normal to the plane X-Y; said utility platform comprises at least three platform cord connection elements (PCCEs); at least three left ground cord connection elements (GCCEs) associated with two left platform cord connection elements (PCCEl), and at least one right ground cord connection element (GCCEr) associated with at least one right platform cord connection element (PCCE); a tension cord system (TCS) wherein a cord extends from each platform cord connection element (PCCE) towards at least one corresponding ground cord connection element (GCCE); and a manipulating system for tilting the utility platform by tension adjustment of the cords.
Where only one cord extends between a ground cord connection element (GCCE) and a platform cord connection element (PCCE), thus said GCCE is provided at a right side of the system, and at least one of said PCCE and said GCCE is dynamic.
The structural support and tracking system is a dynamic tensegrity system, integrating balanced tension of the tension cords and compression of the support post. The system is such that the utility platform may acquire a tilt/angular displacement over its support post, at any increment and also at a continuous manner.
According to one particular design there is provided a structural support and tracking system comprising a utility platform defining an X-Y plane and supported over at least one support post defining a longitudinal axis Z being normal to the plane X-Y; said utility platform comprises at least four platform cord connection elements (PCCEs) extending on the circumcircle of said utility platform and being equiangularly disposed thereabout; two rear ground cord connection elements (GCCEs) disposed below said utility platform such that at a horizontal position of the X-Y plane said rear GCCEs extend below rear PCCEs, respectively, and at least one front ground fixed CCE (GSCCE) extends on a radius of at least an inscribed circle but not more than the radius of circumcircle of said utility platform; a tension cord system (TCS) wherein a cord extends from each platform CCE towards a rear ground CCE at an X-Z plane, and a cord extending from each platform CCE towards said at least one front ground GCCE; and a manipulating system for at least roll tilting of the utility platform by tension adjustment of four cords extending from the two rear GCCEs.
In the particular example above, where a static cord connection element is provided, the cord is split into a first cord segment and a second cord segment, each of said segments extending from the SCCE, towards a DCCE. Likewise, a static cord connection element may consist of two adjoining static cord connection elements, each associated with a cord extending towards a DCCE.
Any one or more of the following features of the invention may be incorporated with a system according to the invention:
In order to understand the invention and to see how it may be carried out in practice, embodiments will now be described, by way of non-limiting examples only, with reference to the accompanying drawings, in which:
Turning first to
The utility platform 12 is defined over a longitudinal axis X and a lateral axis Y. The utility platform 12 further defines a front side and a rear side extending along the longitudinal X-X axis. A manipulating system generally designated 24 comprises three motors M1, M2 and M3 and a controller assembly C, to be discussed hereinafter in further detail. The longitudinal axis X-X is the axis about which the utility platform 12 rolls. The utility platform further has defined a left side and right side extending along the lateral Y-Y axis about which the utility platform is designed to pitch.
Accordingly, the vertical axis Z is the direction about which the utility platform 12 yaws.
A right tension cord system (TCS) 17r extending between a dynamic rear right ground cord connection element (GDCCErr), a dynamic right platform cord connection element (PDCCEr) and a dynamic front right ground cord connection element (GDCCEfr), said cord having two ends 17fr and 17rr coupled to a respective manipulating motor assembly (i.e. each end is articulated to a respective spool of a motor M1 and M1′, or to oppositely directed spools of the single motor M1).
A left tension cord system (TCS) 171 is composed of two cooperating sub-tension cord systems 1711 and 1712 which together have an ∞ resembling pattern. Tension cord systems 1711 and 1712 are substantially coplanar and parallel to the right tension cord system 17r.
The left tension cord system 1711 comprises cord section extending from a rear left dynamic ground cord connection element GDCCEr1 (coupled to a respective manipulating motor assembly M2) towards a rear left dynamic platform cord connection element PDCCEr1 and then through a front left dynamic cord connection element GDCCEfl. From there the cord continues (as part of the second left tension cord system 1712) towards the rear left dynamic platform cord connection element (PDCCEr1) from where it extends down through an other GDCCElr and extends towards a manipulating motor assembly M3.
The arrangement is such that tensioning one or more of the cords 17r1, 17r2 1711 or 1712, while simultaneous loosening the tension in the other of the one or more cords, will result in corresponding tilt of the utility platform 12 about the post 14, however maintaining the cords substantially under constant tension. Such tilting is gradual and continuous (as opposed to incremental), may be at substantially small increments, and the utility platform 12 may acquire practically any desired orientation. Even more so, the provision of the controller assembly C provides real-time information regarding a plurality of parameters such as position of the utility platform 12, tension in the cords, external forces acting on the system (e.g. wind, payload mounted thereon, etc.), and the controller also provides the required signals for operation of the motors so as to obtain the desired position of the utility platform 12.
Turning now to
In
A right cord system has a cord 47r fixedly articulated at one end to the ground surface 46 at a static cord connection element GSCCEfr, said cord 47r extending through a platform dynamic cord connection elements PDCCEr substantially centrally disposed about a right edge of the utility platform 42, with an other end of the cord extending through a ground dynamic cord connection elements GDCCErr in the form of a pulley, said cord further coupled to a motor M1.
Likewise, a first left cord assembly comprises a cord 4711 extending from a ground static cord connection element GSCCEfl disposed at the front left side of the ground surface 46 towards a platform front right dynamic cord connection elements PDCCEfl, and then extends through a ground dynamic cord connection elements GDCCErl1 in the form of a pulley, said cord further coupled to a motor M3.
A second left cord assembly comprises a cord 4712 extending from the common ground static cord connection element GSCCEfl, extending towards a rear left dynamic cord connection elements PDCCErl, and then extends through a ground dynamic cord connection elements GDCCErl2 in the form of a pulley, said cord further coupled to a motor M2.
In
A right cord assembly comprises a cord 57r extends from a motor M1 towards a platform dynamic cord connection element PDCCEr (substantially centrally positioned at a right edge of the utility platform 50) and further the cord 57r extends towards a front right dynamic ground cord connection elements GDCCEfr and back towards the motor M1 serving as a right dynamic ground cord connection elements GDCCErr.
A first left cord system comprises a cord 5711 fixedly articulated at one end to the ground surface 51 at a static cord connection element GSCCEfl, said cord 5711 extending through a platform dynamic cord connection element PDCCErl fitted at a rear left corner of the utility platform 50, said cord 57r1 further extending through a ground dynamic cord connection elements GDCCErl1 in the form of a motorized pickup pulley.
A second rear cord system comprises a cord 5712 commonly fixedly articulated at one end to the ground surface 51 at said static cord connection element GSCCEfl, said cord 5712 extending through a platform dynamic cord connection element PDCCErl fitted at a front left corner of the utility platform 50, said cord 5712 further extending through a ground dynamic cord connection elements GDCCErl2 in the form of a motorized pickup pulley.
It is noted that in the particular example, the static cord connection element GSCCEfl is common to both cord systems 5711 and 5712, though according to a modification, each cord may extend from a separate CCE.
The example illustrated in
A right cord assembly comprises a cord 69r is fixedly articulated at a platform static cord connection element PSCCEr (substantially centrally positioned at a front edge of the utility platform 62) with one segment of the cord 69r1 extending towards a front right dynamic ground cord connection elements GDCCEfr in the form of a pulley, and an other segment of the cord 69r2 extending towards a rear right dynamic ground cord connection elements GDCCErr, wherein both said ends extend towards a central, common motor Mr, wherein rotating the motor in one direction entails tensioning one cord 69r1 and simultaneous releasing the other end of cord 69r2 and vise versa. Whilst cord 69f is illustrated as having two segments (69r1 and 69r2), both extending from the common PSCCEr, it is appreciated that separate cords may extend form a single or adjoining SCCE.
The right and rear cord systems 7111 and 7112 of the embodiment of
Turning now to the example illustrated in
The left tension cord system (TCSl) is identical with that disclosed in connection with the previous examples of
A right cord assembly comprises a cord 90r is fixedly articulated at a platform static cord connection element PSCCEr (substantially centrally positioned at a right edge of the utility platform 80) with one cord segment 90r1 extends towards a front right dynamic ground cord connection elements GDCCEfr in the form of a pulley, and an other cord segment 90r2 extends towards a rear right dynamic ground cord connection elements GDCCErr, wherein both said cord segment 90r1 and 90r2 extend towards a central, common motor Mr, coupled to a spool GDCEEr wherein rotating the motor Mr entails simultaneous tensioning one of the segments of the cord and releasing the other segment, and vise versa.
A first left cord system comprises a cord 9011 fixedly articulated at one end to the ground surface 86 at a static cord connection element GSCCErl, said cord 90l1 extending through a platform dynamic cord connection element PDCCErl fitted at a rear left corner of the utility platform 80, and further extending through a ground dynamic cord connection elements GDCCErl in the form of a pickup pulley articulated to a front left motor Mlr.
A second left cord system comprises a cord 9012 is fixedly articulated at one end to the ground surface 86 at a static cord connection element GSCCErl, said cord 9012 extending through a platform dynamic cord connection element PDCCEfl fitted at a front left corner of the utility platform 80, and further extending through a ground dynamic cord connection elements GDCCEfl in the form of a pickup pulley articulated to a rear left motor Mlf.
Whilst the system illustrated in
Furthermore, whilst in
Considering the substantial horizontal position illustrated in
Manipulating the utility platform 80 into the position of
Whilst not mentioned, each of the disclosed examples is associated with a controller unit (designated C in
In the embodiments and examples hereinafter, the utility platform is always fitted with four Platform Dynamic Cord Connection Elements (PDCCEs), whilst there are provided three or four Ground Cord Connection Elements (GCCEs), depending on the case.
Turning now to
The utility platform 112 is defined over a longitudinal axis X and a lateral axis Y. The utility platform 112 defines a front side and a rear side extending along the longitudinal X-X axis. A manipulating system generally designated 124 comprises three motors M and a controller assembly C, to be discussed hereinafter in further detail. The longitudinal axis X-X is the axis about which the utility platform 112 rolls. The utility platform further has defined a left side and right side extending along the lateral Y-Y axis about which the utility platform is designed to pitch. Accordingly, the vertical axis Z is the direction about which the utility platform 112 yaws.
The utility platform is fitted at its respective corners with four platform cord connection elements, in the form of pulleys and designated a follows:
Front right platform pulley—PCCEfr;
Rear right platform pulley—PCCErr;
Front left platform anchor—PCEEfl; and Rear left platform pulley—PCEErl.
The term pulley is used in its broad sense, however, fitted for a cord to extend therethrough and change its direction, as will become apparent hereinafter. A pulley may be provided with one or more friction reducing wheels or it may be devoid of any wheels.
As can further be noted in
Front right ground platform—GCCEfr;
Rear right ground platform—GCCErr;
Front left ground platform—GCCEfl; and
Rear left ground platform—GCCErl.
The four Platform Cord Connection Elements (PCCEs) are schematically illustrated in the following drawings as circles, as opposed to the Ground Cord Connection Elements (GCCEs), represented by squares.
Noting that two cord ends extend rearwards, the rear ground pulleys GCCErl and GCCErr are each configured as double pulleys, or as two separate pulleys each receiving a cord's free end. As mentioned hereinabove, the one or two front ground cord connecting elements may either be a pulley facilitating rolling of the respective cord therethrough, i.e. a dynamic CCE designated DCCE, or a fixture wherein the respective cord is fixedly anchored with respect to the ground, i.e. a static CCE designated SCCE.
The four ground cord connecting elements GCCEs are disposed substantially below the utility platform PCCEs, respectively. However, as will become apparent in connection with the embodiment of
A tension cord system is provided, wherein a first continuous, non elongatable cord 130 extends at the right side of the system, and a similar cord 132 extends at the left side of the system, both tension cord systems 130 and 132 extending substantially at an X-Z plane of the system. As can be seen in
Likewise, the left tension cord system 132 has a first end 142 engaged with a third motor M3 of the manipulating system 124 from which the cord 132 extends through the GDCCErl, then through the PDCCEfl, down to the GDCCEfl, then through the PDCCrl and back through the GDCCErl where the second end 144 of the cord 132 is secured to a force motor M4 of the manipulating system 124.
As already mentioned hereinabove, the motors M1 to M4 may be of any one or more type such as, for example, rotary (winding) motors, linear retraction/expansion motors (i.e. piston-type motors), etc. Furthermore, in the embodiment disclosed in
It is further noticed that the manipulating system 124 comprises a controller C associated with each of the motors M1 to M4 for tensioning/dispensing the respective cords. Thus, there is provided a computerized processor receiving an input data from a sensor S (positioned on the utility platform 112 and transmitting data to the controller C) correlating with the desired tilt angle of the utility platform 112 and responsive thereto emitting a control signal to each of the associated motors M1 to M4 to thereby activate the appropriate direction in order to attain the required tilt of the utility platform 112. The manipulating system 124 further comprises cord tension sensors and respective cord tension mechanism for maintaining the cords tense.
In order to maintain tension of the cords, a cord tensioning mechanism may be introduced, e.g. within or adjacent the motor units, or at other locations along the cords. Such a tensioning mechanism may be, for example, a mechanical spring, a pneumatic spring, magnetic spring, etc.
With further reference to
Turning now to
For sake of clarity, elements similar to those disclosed in connection with
The significant difference between the embodiment of
As noticed, two tension cord systems are provided namely tension cord 230 associated with the right side of the system, and tension cord 232 associated with the left side of the system.
However, it is noticed that instead of the front right ground CCE and the front left CCE each extending below a respective corner of the utility platform 212, in the embodiment of
It is thus seen that the first free end 236 of the tension cord 230 extends from a first motor M1 through the rear right DGCCErr, up through the PDCCErr, then down towards the single ground cord connector GDCCEf wherefrom it extends through the PDCCEfr, then back through the DGCCErr from which the second free end 238 extends to a second tension motor M2.
Likewise, the left tension cord 232 has its first free end 242 articulated to a tension motor M3 from which it extends through a right left ground cord connector GDCCErl, from which it extends up towards the rear left cord connector PDCCErl then down to the common single front ground connector GDCCEf (which in this particular case is common with the tension cord 230, however, each of the cords 230 and 232 is free to independently, substantially frictionless roll through said GDCCEf. From the GDCCEf the cord 232 extends up to the front left cord connector PDCCEfl, then back to the rear left ground cord connector GDCCErl from which the second free end 244 extends and is linked to the fourth motor M4 of the manipulating system 224
In the embodiment of
Turning now to
Turning now to the embodiment illustrated in
The radiation collector system 370 may be for example a tracking solar radiation collector dish or an electromagnetic radiation collector dish, etc.
In the present example, the utility platform is in the form of a collector dish 372 which for sake of clarity is imposed over a rectangular utility platform 312 It is however, noted that the collector dish 372 is mounted on a rigid truss comprising rigid lateral projecting arms 374 each of which extending towards the corners of the rectangle platform designated 312
The collector dish 372 is mounted on a support post generally designated 314 composed of a bottom portion 314a fixedly secured to the ground surface 316 and a top post component 314b wherein the top post component 314b is telescopically displaceable with respect to the bottom post component 314a to thereby change the overall height of the support post 314 Extending at the top of the top support post 314b there is a link arm 319 pivotally coupled via a ball-type, universal or other type joint 320 to a bottom surface 373 of the collector dish 372.
Similar to the arrangement disclosed in connection with
Two tension cord systems are provided namely 330 and 332 one extending on the right side of the system and the other extending on the left side of the system as explained in connection with the previous embodiments. The free ends 336; 338 and 342, 344 and of the left and right tension cord systems 330 and 332 respectively, extend towards the manipulating system 324 which in turn comprises four motors M1, M2, M3 and M4 each articulated for tensioning-dispensing the respective free ends of the cords. The manipulating system 324 further comprises a computerized controller generally designated C designed for receiving an input signal Sin corresponding with the azimuth of the collector dish 372 which in turn is fitted with a heliostat sensor mechanism for determining the azimuth towards the source of radiation (e.g. sun, satellite, etc.). in this example the signal Sin is transmitted e.g. in a wireless fashion, or otherwise transferred, to the controller C. The computerized controller C then calculates the respective direction at which the dish 372 is to be tilted and generates a series of responsive signals S1, S2, S3 and S4 to each of the respective motors M1, M2, M3 and M4 to either tension or dispense the respective cords, until the radiation dish 372 acquires its desired position. The computerized controller C also can control the height of the post by axial displacement of the top post component 314b with respect to the bottom post component 314a, to thereby change the height of the support post 314
With further reference to
It is appreciated that the tension cords 130 and 132 maintain tension at all times for stability of the system and its accuracy. In
Obtaining the position of the utility platform as illustrated in
Acquiring the position illustrated in
In
The position of
In
The position of
Whilst several significant positions have been illustrated and exemplified, it is appreciated that angular/tilt position beyond 90° degrees of the utility platform 112 is possible by appropriate manipulation of the tension cords. However, for that purpose an appropriate pivot joint is required between the top of the support post and the utility platform, e.g. as illustrated in
It is further appreciated that the platform cord connecting elements PCCEs may be fitted at other locations about the utility platform in a substantially symmetrically disposed manner, for example, the platform cord connecting elements PCCEs may be fitted at the middle of each of the respective edges of the utility platform, however, in this case, the entire platform will be angularly shifted by 45° (about the vertical Z axis). Turning now to
Turning now to
Turning now to
It is appreciated that in the examples disclosed in connection with the previous embodiments, the front ground cord connecting elements GCCEfr (two as in of
Further embodiments are illustrated with reference to
In the embodiment of
It is noticed that the utility platform 712is mounted over a single support post 714. However, this embodiment differs from previous embodiments in that the front ground cord connecting elements are static (GSCCEs) namely front left ground cord connecting element GSCCEfr and front right ground cord connecting element GSCCEfl fixedly secure the respective cord portions 730 and 732 to the ground surface 716(at locations extending below the front left platform cord connecting element PDCCEfl and front right platform cord connecting element PDCCEfr.
According to this configuration, each of the cords 730and 732 is split into a first cord segment 730A; 732B, and a second cord segment 730A; 732B. Cord segment 730A is fixed to the front right ground cord connecting element GSCCEfr, and from there it extends towards the front right platform cord connecting element PDCCEfr and then down towards the rear right ground cord connecting element GDCCErr and towards a manipulator M. The second cord segment 730B is also fixed to the front right ground cord connecting element GSCCEfr, and from there it extends towards the rear right platform cord connecting element PDCCErr and down towards the rear right ground cord connecting element GDCCErr and towards a manipulator M.
Likewise, Cord segment 532A is fixed to the front left ground cord connecting element GSCCEfl, and from there it extends towards the front left platform cord connecting element PDCCEfl and then down towards the rear left ground cord connecting element GDCCEr1 and towards the manipulator M. The second cord segment 532B is also fixed to the front left ground cord connecting element GSCCEfl, and from there it extends towards the rear left platform cord connecting element PDCCErl and down towards the rear left ground cord connecting element GDCCErl and towards a manipulator (motor) M.
The arrangement is such that the four platform cord connecting element s namely PDCCEfr, PDCEErr, PDCCEfr and PDCCfl, and the two rear ground cord connecting elements namely GDCCEri and GDCCErr are cord connecting elements (pulleys) of the type disclosed hereinbefore facilitating rolling of the respective cords therethrough, said cords 730 and 732eventually extending to a cord tensioning motor M. The arrangement is such that tensioning the cords by means of motor M yields corresponding tilting of the utility platform 712 about the X and Y axes, namely in roll and pitch directions.
It is noted that in the embodiment of
For example,
With further reference to
In the embodiment of
The arrangement in accordance with the embodiment of
It is appreciated that the examples of
In order to maintain tension of the cords, a cord tensioning mechanism 859 is introduced on each of the cords 830 and 832, adjacent the front left ground static cord connecting element GSCCEfl and the front right ground static cord connecting element GSCCEfr, respectively (or at other locations along the cords). Such a tensioning mechanism may be, for example, a mechanical spring, a pneumatic spring, magnetic spring, etc.
In the example illustrated in
Those skilled in the art to which this invention pertains will readily appreciate that numerous changes, variations, and modifications can be made without departing from the scope of the invention, Mutatis Mutandis.
Number | Date | Country | Kind |
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61129980 | Aug 2008 | US | national |
61/136513 | Sep 2008 | US | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/IL09/00759 | 8/4/2009 | WO | 00 | 2/1/2011 |