Abstract:
A deflector ( 10 ) for collecting and guiding harvested tree-fruit is implemented for resilient recovery from collisions with obstacles in the field. The deflector is coupled in cantilever to a boom harvester ( 4 ) mounted on a vehicle ( 2 ). The harvester has a telescopic boom ( 8 ) with a mobile portion ( 14 ) terminated by a clamp ( 6 ) able to move in horizontal and in vertical translation towards and along a tree trunk (T). The deflector is coupled to the mobile portion for slaved translation with the clamp. Implemented as an array of separate ribs ( 32 ) flexibly coupled together and made of flexible elastic plastic material such as fiberglass, the deflector is lightweight and flexes upon collision to resiliently recover shape after the collision. Being lightweight, the cantilever does not destabilize the vehicle. The structure and the materials of construction of the deflector prevent transmission of vibrations generated by the vibrator ( 12 ) used to shake the trunk when harvesting.

Description:
[0001]     This application is a U.S. National Phase Application under 35 U.S.C. 371 of International Application PCT/IL02/00353 (published in English) filed 06 May 2002. 
     
    
     BACKGROUND  
       [0002]     1. Technical Field  
         [0003]     The present invention relates in general to harvesting performed by a tree-fruit harvester carried by a vehicle and in particular, to equipment for deflecting harvested fruit away from the vehicle.  
         [0004]     2. Prior Art  
         [0005]     U.S. Pat. No. 5,469,695 granted to Zehavi et al., hereafter &#39;695, for a tree shaking and harvesting apparatus is hereby incorporated by reference in whole. In the disclosure, Zehavi et al. present a tilted-plane face  18  for collecting and for guiding the harvested fruit, with an extension of steel rods  22 . When in field use, the steel rods  22  vibrated severely and broke in collision with obstacles. Collisions of rods  22  with low-hanging branches and other obstacles currently occur. Sometimes, rather small twigs give way to the forces moving the rods  22  and the shaker  10 , which forces are applied by a powerful hydraulic jack. Most of the time, a rigid obstacle, such as a tree-trunk, roots protruding out of the ground, or a big low-hanging branch, will resist the motion of the rods  22  that are then irreparably damaged.  
         [0006]     Obviously, the equipment made of steel, is reinforced for better collision survival, but then, inevitably, becomes heavier. Being mounted in overhang alongside the vehicle, as are the oscillation units  15   a  and  15   b , the vehicle becomes heavily destabilized, which is a second problem. Furthermore, the sturdily reinforced equipment suffers from the rather violent vibrations of the oscillation units, and tends to develop cracks that propagate quickly until total failure.  
         [0007]     In U.S. Pat. No. 4,986,065 to Compton, the same problem is solved by adding extensions to fruit catch platforms  38  provided to collect harvested fruit. For example, seal panel  54 , is operated by rams  58  that are lowered for harvesting and raised afterwards. Such a solution copes with collisions in a rather complex and expensive manner. Furthermore, it is left to the operator to remember to operate the seal panels in the proper sequence so as to avoid mutual collision.  
         [0008]     There are thus many problems to overcome before the introduction in the field of a practical harvested fruit collector for use with tree-harvesting equipment.  
       SUMMARY  
       [0009]     In accordance with the invention, there is provided a deflector for collecting fruit when harvesting trees, the deflector being able to elastically deform upon collision with an obstacle and to recover original shape after the collision.  
         [0010]     In further accordance with the invention, the deflector consists of an array of independent ribs coupled to deflect individually as separate elements.  
         [0011]     Moreover, in accordance with the invention, there is provided a deflector with rib structures made of flexible elastic and lightweight plastic material, to prevent destabilization of the vehicle on which the harvester is mounted in cantilever.  
         [0012]     Still further, in accordance with the invention, there is provided a deflector with a structure and materials of construction designed for dampening the vibrations generated by the vibration unit of the harvester.  
         [0013]     In addition, in accordance with the invention, there is provided a deflector with releasable joints to permit replacement in situ of a rib.  
         [0014]     It is an object of the present invention to provide a deflector for collecting and guiding harvested tree-fruit, the deflector being coupled to a boom harvester mounted on a vehicle, the harvester comprising:  
         [0015]     a telescopic boom extending away from the vehicle, and comprising a mobile portion with a free end terminated by a clamp configured for movement in longitudinal and in vertical translation towards and along a trunk of a tree with foliage, and the deflector comprising:  
         [0016]     a deflector structure for extending under the tree foliage, characterized in that:  
         [0017]     the deflector is coupled away from the vehicle in cantilever to and above the free end of the mobile portion, in slaved longitudinal and vertical translation with the clamp, for extension on opposite sides and proximate the trunk,  
         [0018]     the deflector structure is coupled in overhang alongside the vehicle and configured to extend to proximate the tree trunk and longitudinally sideways from opposite sides of the trunk, and  
         [0019]     the deflector structure is configured to sustain flexible elastic deformation in collision with an obstacle, and for resilient elastic recovery of deflector structure shape after collision.  
         [0020]     The deflector consists of an array of ribs coupled in equally spaced-apart aligned parallel distribution as a grid, forming a slanted deflector surface, wherein each rib is flexibly coupled to permit separate deflection in elastic deformation.  
         [0021]     The deflector structure is of rectangular top elevation and has a backbone and at least one longeron running in parallel along the length of the deflector. These are coupled to each rib crossing the width of the deflector. Each rib has a rib structure built as a truss supporting elastic deformation. The longeron and the rib structure are constructed out of elastically flexible plastic material for elastic deformation during collision with an obstacle, and for elastic recovery of rib structure and longeron shape after collision. If desired, the array of ribs is mutually coupled to more than one longeron parallel to the backbone.  
         [0022]     It is another object of the present invention to provide a deflector with a backbone having a longitudinal rigid unitary beam with a lateral cross-section featuring a height with a top portion, a middle and a bottom portion. The rib structure comprises an upper member and a lower member in perpendicular to the backbone and to the at least one longeron. The lower member is in alignment below the upper member. The upper member comprises a lower portion, an intermediate bend and an upper portion. The upper member is joined at the intermediate bend, in perpendicular to the unitary beam, at the middle and top portion so that the upper portion is cantilevered to extend upwards off the vertical and away from the backbone to comprises a free hanging upper extremity. The lower portion is cantilevered to extend slantingly downwards and away from the backbone towards the trunk and comprises a free hanging lower extremity. The upper member is configured for resilient elastic recovery of shape after either any of both the free hanging upper extremity and the free hanging lower extremity collides with an obstacle.  
         [0023]     It is a further object of the present invention to provide a deflector with a lower member having a first back extremity joined from below to the bottom portion of the lateral cross-section, and a second front extremity joined from below to the upper member, about midways between the backbone and the free hanging lower extremity to form a truss tip. The longeron is joined transversally to and between the upper and the lower member about midways between the backbone and the truss tip. There are thus defined in the rib structure a plurality of sections with each one section out of the plurality of sections extending between each adjacent two joints in the upper member and in the lower member. When the deflector collides with an obstacle, at least one section of the rib structure deflects in flexible deformation selected alone and in combination from the group consisting of bending, buckling, and torsion, and the backbone is accommodated to flexibly deform in torsion. It is noted that the deflector is made from a combination of non-metallic materials with metallic materials and of non-metallic materials. Reinforced plastic materials, such as fiberglass, are suitable for the task. The backbone is configured as an open beam profile, thus an open shape as opposed to a closed beam profile, such as a closed polygon, if desired, of metal or of fiberglass.  
         [0024]     In accordance with the invention, the rib structure is made from materials selected from reinforced plastic materials, synthetic materials, and composite materials, but such as fiberglass, joined releasably to permit replacement in situ. It is preferable to use material lighter than aluminum and to provide a lightweight structure design in addition to the lightweight materials, to prevent destabilization of the vehicle. The weight of the platform, when extended away from the vehicle towards the trunk creates a destabilizing moment on the vehicle.  
         [0025]     It is yet an object of the present invention to provide a method for implementing a deflector resistant to collision, the deflector being coupled to a boom harvester mounted on a vehicle for collection and guidance of harvested tree-fruit. The harvester has a telescopic boom extending away from the vehicle, and a mobile portion with a free end terminated by a clamp configured for movement in longitudinal and in vertical translation towards and along a trunk of a tree with foliage:  
         [0026]     a deflector structure for extending under the tree foliage,  
         [0027]     The steps of the method call for coupling the deflector away from the vehicle in cantilever to and above the free end of the mobile portion, in slaved longitudinal and vertical translation with the clamp. The deflector extends under the tree foliage and to opposite sides of the trunk and proximate thereto. By the method, the deflector structure is configured to sustain flexible elastic deformation in collision with an obstacle, and for resilient elastic recovery of deflector structure shape after collision.  
         [0028]     It is yet an object of the present invention to provide a harvesting system comprising a deflector coupled to a boom harvester mounted on a vehicle, the deflector for collecting and guiding the harvested tree-fruit. In this case to, the harvester has a telescopic boom extending away from the vehicle, and comprising a mobile portion with a free end terminated by a clamp configured for movement in longitudinal and in vertical translation towards and along a trunk of a tree with foliage. The deflector comprises a deflector structure in overhang alongside the vehicle, the deflector being configured to extend under the tree foliage to proximate the trunk and longitudinally sideways from opposite sides of the trunk. The deflector is coupled to and above the mobile portion of the telescopic boom and slaved to the longitudinal and vertical translation of the mobile portion. Furthermore, the deflector structure is configured to sustain elastic deformation upon collision with an obstacle encountered during translation, to prevent mechanical damage of the deflector, and for elastic recovery of deflector shape after the collision. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0029]     In order to understand the invention and to see how it may be carried out in practice, a preferred embodiment will now be described, by way on non-limiting example only, with reference to the accompanying drawings, in which:  
         [0030]      FIG. 1   a  and  FIG. 1   b  are respectively a side elevation and a top elevation of a flexible deflector mounted on a boom harvester,  
         [0031]      FIG. 2  is an isometric elevation of the flexible deflector illustrated in  FIG. 1 , and  
         [0032]      FIG. 3  is a side view of the flexible deflector shown in  FIG. 1 .  
     
    
     DISCLOSURE OF THE INVENTION  
       [0033]     The problem to be solved consists of providing a deflector, or a collection and guiding deflection platform that will receive and guide harvested fruit. First comes the need to prevent gathering of fruit under or close to the harvesting vehicle. Second, the fruit is guided towards a conveyor or to a loading site.  
         [0034]     The solution of the problem is presented as a flexible and elastic deflector, or platform surface, built as a single unitary construction made mainly or entirely from lightweight reinforced plastic material, for use with a tree-fruit boom harvester, briefly described below.  
         [0035]     In a copending PCT Patent Application No. PCT/IL02/00147, by Zehavi et al., referred to hereafter as &#39;147, there is described a boom harvester for use with the flexible deflector.  FIG. 2  in &#39;147 offers an isometric view of the disclosed harvester showing a structure portion IV for mounting the harvester to a carrying vehicle, and for supporting a bi-directional telescopic boom  16 . A clamp with clamping jaws  2  is attached to the extremity of the extensible member  20  of the telescopic boom  16 . One of the jaws of the clamp  2  contains a vibrator whereby a tree trunk is shaken when both jaws are clamped on diametrically opposite sides of a tree-trunk, as shown in  FIG. 1  of &#39;147. In operation, the boom harvester stops opposite a tree to be harvested, extends the clamp  2  attached at the extremity of the extensible member  20  towards and along the trunk, that is then clamped for shaking.  
         [0036]     In the present inventions, the flexible deflector is intended for mounting to and above the extensible member of the boom harvester for translation together with the clamp wherein the vibrator is integrated inside one of the jaws.  
         [0037]     With reference to  FIGS. 1   a  and  1   b , of the present disclosure, there is shown a vehicle  2 , carrying a boom harvester  4  with a clamp  6  attached to the telescopic boom  8 , and the flexible deflector  10 . A vibrator  12  is integrated inside one of two jaws  6 J of the clamp  6 , as disclosed in a further copending application No. PCT/IL 00/00716. The telescopic boom  8  has a mobile portion  14  with a free end  16  to which the clamp  6  is attached and above which the deflector  10  is coupled in cantilevered at an attachment place  18 . There is shown a tree  20  with tree foliage  22  above the trunk T, that protrudes from the ground  24 .  
         [0038]     The mobile portion  14  is controllable, by means not shown in the FIGS., for translation of the open jaws  6 J of the clamp  6 , horizontally towards and vertically along the trunk T, which jaws are then clamped, as shown in the  FIGS. 1   a  and  1   b , on diametrically opposite sides of the trunk.  
         [0039]     Evidently, since both the clamp  6  and the flexible deflector, or deflector  10 , are attached above the free end  16  of the mobile portion  14 , they are also slaved to translate together. However, as the deflector  10  is mounted above but somewhat backwards over the jaws  6 J, the extremity of deflector will not hit the trunk T when this last one is clamped.  
         [0040]     With reference to  FIG. 1   b , the deflector  10  is shown to practically fill the gap between the vehicle  2  and the trunk T, and to extend on both sides of the tree  20  further outwardly than the outer dimensions of the tree foliage  22 , and underneath thereof.  
         [0041]     Many impediments confront the implementation of a practical flexible deflector  10 . Basically, the functional demands require a large deflector surface, of reasonable weight, but a deflector structure sturdy enough to successfully survive the harsh work conditions encountered during operation of the equipment.  
         [0042]     Traditionally, the conventional approach employed for agricultural gear operating in heavy-duty field conditions is to strengthen and ruggedize, by adding structural steel mass to the equipment. However strongly built, the heavy weight of added metal is ill suited for the implementation of a practical deflector as this added load imposes unacceptable penalties. Hence, departing from standard procedures, a new approach is embraced and instead of steel for strength, engineering plastic materials are considered, for elastic flexibility, high strength, resiliency, and light weight. Advantage is taken from the properties of the material, in combination with superior structural design.  
         [0043]     A flexible deflector made from fiberglass for example, will easily assume the required dimensions and the functional demands to be met, while featuring reduced weight.  
         [0044]     An illustration of the problems encountered in operation will better explain the descriptions that follow. For example, before shaking of the trunk T for harvesting, the clamp  6  is translated towards and along the tree trunk T, and clamped thereon. It is during this horizontal translation and vertical positioning stage that the flexible deflector  10 , moving in slaved association with the clamp  6 , very often inevitably collides with obstacles, not shown in the schematic  FIGS. 1   a  and  1   b . Since the clamp  6  is translated by a powerful hydraulic jack, not shown in the FIGS., that also moves the flexible deflector  10 , huge forces develop on the deflector  10  upon collision, and it is either the obstacle or the deflector  10  that give way. The obstacles which may collide with and break the deflector  10  are manifold. Sometimes, the operator misses the trunk T, thereby crashing the deflector  10  into that trunk, whereafter the deflector  10  is retrieved from service, and so is the boom harvester  4 . Other obstacles counting as potential danger to the flexible deflector  10 , are low hanging branches, stumps from broken trees, outgrowths of roots extending above the ground  24 , rocks and other protrusions found in the field but not shown in the FIGS. It is described below how a flexible deflector structure combined with flexible elastic elements allows the deflector  10  to deform elastically in bending, buckling and torsion, and to regain original shape after collision.  
         [0045]     Furthermore, when the mobile portion  14  of the telescopic boom  8  is translated outwards, the extended elements, namely, the clamp  6 , the deflector  10  and the mobile portion itself, all extend out of the footprint  26  of the vehicle  2 . The footprint  26  of the vehicle  2  is defined as the top elevation surface delimited by the area between the wheels W, or of the caterpillars, not shown in the FIGS. The weight of the extended elements, all cantilevered and hanging outside of the footprint  26 , exerts a destabilizing moment on the vehicle  2 . To this end also, an enhanced deflector structure and the use of reinforced plastic material allow the implementation of a lightweight deflector  10 , as described below.  
         [0046]     Another hurdle to overcome is the destructive effect of the vibrations transmitted by the vibrator  12 . With standard prior art solid metal-mass deflectors, the violent vibration regime induced by the vibrator, initiates cracks that propagate and finally destroy the equipment. The combination of plastic material and deflector structure dampen the vibrations and resolve the problem, as described below.  
         [0047]     Moreover, should replacement of an element be required, it is important to ensure repair of the deflector in situ, fast and at low cost. This request is fulfilled by the lightweight plastic material array of separate rib elements and by the releasable joints use to assemble the structure of the deflector  10 .  
         [0048]     In short, the solution provided by the present invention is a flexible and elastic single-piece collection and guiding platform  10 , made of lightweight plastic material. In practice, the flexible deflector  10  weighs between one fourth to one-third in comparison with equivalent existing implements, due to both the choice of materials and to the method of construction selected. Upon collision with an obstacle, parts especially designed to flex, return to their original shape after the collision. The combination of platform structure with plastic material permits the realization of a lightweight platform  10  that does not destabilize the vehicle  2 . Moreover, the inherent dampening properties of plastic material reduce the vibrations generated by the vibrator  12 . Furthermore, releasable joints allow replacement of members in situ.  
       DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0049]     With reference to the FIGS.  1  to  3 , the structure of the deflector  10  is now described.  
         [0050]     The schematic  FIGS. 1   a  and  1   b  present the flexible deflector  10 , or deflector  10 , which appears in top elevation as a rectangular skeleton with a longitudinal backbone  30 , a longeron  40  spaced apart and parallel thereto, and an array of lateral ribs  32 , in perpendicular to the backbone. The backbone  30  and the longeron  40  span the entire length of the deflector  10  and each rib  32  traverses the whole width thereof.  
         [0051]      FIGS. 1   a  and  1   b  illustrate the various elements of the system cooperating for tree-fruit harvesting. A vehicle  2  supports a laterally mounted telescopic boom  8  extending outwards and away from the vehicle, ending in a mobile portion  14  terminated by a clamp  6 . The mobile portion  14  is the extensible and retractable portion of the telescopic boom  8 . A vibrator  12  is integrated in one of the two jaws  6 J constituting the clamp  6 , seen to firmly grab diametrically opposite side of the tree trunk T. The deflector  10  is fixedly coupled in cantilever to and above the free end  16  of the mobile portion  14 , at attachment place  18 , and covers the telescopic boom  8 , the mobile portion  14  and most of the clamp  6 . Mounted in parallel to the vehicle  2 , the deflector penetrates from the side and under the foliage  22  of the tree  20 . Sideways, the width of the deflector  10  reaches out to cover a surface between the vehicle  2  up to proximate and almost abutting the tree-trunk T, and in lateral extension, the length of the deflector spreads away from the diametrically opposite sides of the trunk to well beyond the plan view of the foliage  22 . As the deflector  10  slopes downwards from the side of the vehicle  2  towards the trunk T, fruit dropping thereon is collected and guided away from the vehicle.  
         [0052]     The array of aligned parallel ribs  32 , forming the fruit receiving surface of the deflector  10 , is spaced apart in equal distribution to cover a rectangular surface as long as the backbone  30  and as wide as the length of the top elevation of a rib  32 .  
         [0053]     The parallel interstices between consecutively aligned ribs  32  are as wide a possible to alighten the structure of the deflector  10  and to dispose of fruit of unwanted small dimensions, but narrow enough to collect and guide the harvested fruit as desired.  
         [0054]     The structure of the flexible deflector  10  is better seen in the isometric view of  FIG. 2  that illustrates the assembled array of aligned, equidistant, closely separated parallel rib (truss) structures  34 , which form the ribs  32 . The horizontal backbone  30 , crossing the length of the deflector  10 , which is the largest single element, is designed as a hollow closed profile to which are coupled an upper member  36 , a lower member  38  and the longeron  40  to these last two. The array of upper members  36  and lower members  38  form the fruit collection and guiding platform surface of the deflector  10 . Similar reference numerals refer to similar elements in the various FIGS.  
         [0055]     Referring to the side elevation of the rib structure  34  of  FIG. 3 , the upper member  36  is configured in the shape of an elbow featuring an upper portion  36 U and an intermediate bend, or bend  36 B, both coupled to the backbone  30 . A lower portion  36 L, is coupled to the longeron  40  and to the lower member  38 .  
         [0056]     The upper portion  36 U of the upper member  36  is directed upwards, somewhat off the vertical, towards the supporting vehicle  2 , seen in  FIGS. 1 , while the lower portion  36 L slopes downwards, towards the trunk T, seen in  FIGS. 1 , in inclination to the horizon. Both the upper member  36 U and the lower member  36 L are cantilevered to the horizontal backbone  30  and have their extremities  36 LE and  36 UE hanging freely away from the backbone.  
         [0057]     According to  FIGS. 1 , the side of the deflector  10  close to trunk T is called front, or forward, and the opposite side, near to the vehicle  2 , is referred to as back, or rear.  
         [0058]     The backbone  30  has a lateral hollow cross-section  42  implemented of bent sheet metal, to form a rigid unitary beam of constant cross-section. If desired, the backbone is made of plastic material, synthetic material or composite material, with fiberglass being an example. The transverse cross-section  42  of the backbone  30  may consist of a custom made profile or of a stock item profile. When made of sheet metal, it is easy to bend the backbone  30  to a cross-section  42  in the general shape of a polygon. As desired, the backbone  30  is designed either as a closed cross-section  42 , or as an open beam cross-section, not shown in the FIGS. Direction-wise the cross-section  42  has a front  42 F oriented towards the trunk T, a top portion  42 T, a middle portion  42 M, and a bottom portion  42 B.  
         [0059]     Together, the backbone cross-section  42 , the upper member  36 , the lower member  38  and the longeron  40  define the rib truss structure  34 , where the intermediate bend  36 B of the upper member  36  is attached to the top portion  42 T and to the middle portion  42 M of the front of the cross-section  42 F. More accurately, the bend  36 B is rigidly joined to a top projection  44  extending upwards from the top portion  42 T of the cross-section  42 .  
         [0060]     The lower member  38  is rigidly joined at the back extremity  38 B to a bottom projection  46  at the front of the cross-section  42 F and has a front extremity  38 F that is fixedly joined to the front portion  36 F of the upper member  36 . If desired, the rigid and fixed joints of the elements of the rib structure  34  are releasable, to allow easy and fast replacement in situ.  
         [0061]     The rib truss structure  34  is now seen to consist of five different sections, designed from I to V, as follows. I: in the upper member  36 , from the lower extremity  36 LE to the attachment point  50  that forms a truss tip where front extremities of the upper and of the lower members, namely  36 F and  38 F are joined; II: from the attachment point  50  or joint  50 , to the fixation point  52  where the lower portion  36 L forms joint with the longeron  40 ; and III: from the longeron  40  to the joint  54  on the middle portion  42 M on the front  42 F of the cross-section  42 . On the lower member  38  section IV: from the attachment point  50  or joint  50  to the joint with the longeron  40  at joint point  56 ; and section V: from joint point  56  to the attachment point  58  or joint  58 , on the front  42 F of the bottom portion  42 B of the cross-section  42 .  
         [0062]     The longeron  40  is joined in perpendicular to both the upper and the lower member, respectively  36  and  38 , at about half the distance between the bend  36 B and the lower portion extremity  36 LE. The front extremity  38 F of the lower member  38  is fixedly joined to the lower portion  36 L at about half distance between the longeron  40  and the lower portion extremity  36 LE.  
         [0063]     In the middle of the length of the backbone  30 , as seen in  FIGS. 1 , at an attachment place  18 , the flexible deflector  10  is secured to the mobile extensible member  14  of the telescopic boom  8  mounted on the vehicle  2 , in conventional manner, known to the art, and therefore not described.  
         [0064]     The truss components, defined above as the cross-section  42 , the upper member  36 , the lower member  38  and the longeron  40  are made from reinforced plastic material, or composite materials, or of other engineering synthetic materials, such as fiberglass. The term fiberglass is used as generic term. These materials are elastically flexible, thus with shape-recovery capabilities, and also lightweight and vibration dampening.  
         [0065]     Both the upper and the lower member, respectively  36  and  38 , are made from thin slats of fiberglass of the same width, or of different width, mutually aligned one above the other. When fruit such as say oranges, drop from the tree  20 , thus from above on the upper member  36  of the deflector  10 , the rib (truss) structure  34  flexes and absorbs the impact to prevent damage to the skin of the fruit. It is not only the upper member  36  that deflects, but also the lower member  38  together with the longeron  46  that deform, the latter supporting the neighboring rib truss structures  34 , which also participate in the shock absorbing process. Therefore, the shock of the fall of fruit just above the longeron  40  will also be absorbed not only by the deflection of the rib (truss) structure  34 , but also by the participation of the whole structure of the deflector  10 .  
         [0066]     Fruit falling on the deflector  10  are received on the array of flexible ribs  32 , which are aligned to form a surface that is concave towards the tree  20 , but sloping downwards to guide the fruit away from rolling under and close to the vehicle  2 .  
         [0067]     It was explained above under what circumstances the platform  10  may collide with obstacles, and the results from such collisions will now be described.  
         [0068]     When the lower extremity  36 LE which is part or section I of the upper member  36 , crashes into an obstacle, such as a tree trunk, a stump, roots or low hanging branches, that extremity flexes elastically and deforms. The original shape of the lower extremity  36  LE and of section I are resiliently recovered after the collision. The deformation of the fiberglass slat forming the upper member  36  is elastic, regardless whether the deformation resulting from the collision is either one of, or a combination of bending, buckling, and torsion. Considering a single rib (truss) structure  34 , a load on the lower extremity  36 LE, stresses not only the sections I to II of the upper member  36 , but also the sections IV and V of the lower member  38 , the longeron  40  and the backbone  30 . Therefore, when section I collides flexes in a deformation mode, such as bending, buckling, torsion or a combination thereof, one or more of the other sections from II to V included, may respond in a single or combination of deformation modes, as cited above. It is the whole rib (truss) structure  34  that participates in reaction to the collision, to resiliently recover original shape after the collision.  
         [0069]     Each one of the sections I to V may flex independently in any simple, combined or complex mode of bending, buckling, or torsion in one or more deflection mode curves ranging from a half sine wave to a multiple of half sine waves. The pair of endpoints of each section I to V, thus the joints of those sections, are in fact a pair of nodes. Various modes of deflection may develop between each pair of nodes. Depending on the stress developed during a collision, each section I to V, in simple or complex mode of deformation, performs as an elastic energy absorbing section, with torsion possibly superimposed on top of bending and buckling. Original shape is recovered after the collision.  
         [0070]     Since the cantilevered upper portion  36 U may get entangled with the foliage  22  or hit low hanging branches, the same afore-cited modes of deformation may apply. Evidently, the upper portion  36 U, also made from fiberglass, will elastically recover to regain its original shape.  
         [0071]     The deflector  10  also participates as a unitary structure upon collision. In addition to the deflection of each single rib  32  and of a plurality of ribs  32 , the whole structure is linked by the backbone  30  and by the longeron  40 . Deformations are transmitted lengthwise, and although the backbone  30  is a rigid unitary beam, it is nevertheless hollow and deforms in elastic torsion that will recover from the deformation after the collision. The backbone  30  thus also supports and is actively involved in backing-up and recovery of original shape after the collision.  
         [0072]     Together, the plastic materials from which the deflector  10  is built and the structure of separated ribs  32  and hollow backbone  40 , collaborate to achieve a lightweight deflector to prevent destabilization of the vehicle  2 , since the deflector is coupled in overhang out the footprint  26  of the vehicle. The more the mobile portion  14  is extended, the larger the destabilization moment imposed on the vehicle  2 . It is therefore beneficial that by the method of the present invention, both the structure of the deflector  10  and the plastic materials of construction thereof reduce the weight to about 25% of that of conventional prior art deflectors.  
         [0073]     The inherent flexibility and dampening properties of plastic materials, such as fiberglass, in combination with a backbone  30 , made from sheet metal or of plastic material, and of the joints of the sections I to V of the rib structures  34 , all participate to effectively dampen the vibrations generated by the vibrator  12  located in the clamp  6 . Furthermore, should it be necessary, shock-absorbing elements or dampeners are easily added at the attachment place  18  of the deflector  10  to the mobile portion  14  and to joints of the sections I to V.  
         [0074]     The flexible deflector  10  benefits from an additional advantage stemming from its mode of construction, which is the plurality of identical separate and lightweight elements attached to each other at only but very few joints of the sections I to V. Should it be desired to replace an upper member  36 , or a lower member  38 , they are easily removed, quickly replaced, and the longeron  40  is easily repaired by affixing a splint extending on both sides of the failure point. It will be appreciated by persons skilled in the art, that the present invention is not limited to what has been particularly shown and described hereinabove. For example, the truss rib structure may be designed differently and there may be added more than one longeron. Rather, the scope of the present invention is defined by the appended claims and includes both combinations and subcombinations of the various features described hereinabove as well as variations and modifications thereof which would occur to persons skilled in the art upon reading the foregoing description.