Abstract:
An apparatus for conducting remote subsurface inspections from above is disclosed. The apparatus comprises a support structure, a telescoping mast held by a coupling and born by the support structure, an imaging system held by an extendable portion of the telescoping mast and an offsetting mechanism. The apparatus may further comprise an articulating radial arm with pivots for locating the telescoping mast. The support structure of the apparatus may also include an adaptor section for fitting to a receiver of a hitch of a vehicle. A method for conducting remote subsurface inspections from above is also disclosed. The method of inspection comprises the steps of locating an access point on a working surface, positioning an apparatus for conducting remote subsurface inspections from above, manipulating the telescoping mast above the access point, lowering it and reviewing images from the imaging system.

Description:
FIELD OF THE INVENTION 
     The present invention generally relates to the remote inspection of areas that are difficult to reach. More specifically, the invention relates to inspection of underground sewers, railroad bridge support structures and other facilities that may be examined remotely from a location above, using a video camera or other imaging system. 
     BACKGROUND OF THE INVENTION 
     It is sometimes necessary to inspect certain areas that are inconvenient and/or time-consuming to access. For illustrative purposes, the inspection of storm and sewer pipes will be described, although the scope of the present invention is by no means limited to this application. Most municipalities contain a vast network of storm and sewer pipes. Periodically, these pipes must be inspected for problems such as cracks, blockage, build-up, and root infiltration. If a problem is detected, detailed images must be obtained to facilitate planning to remedy the situation. To this end, it is common for an invasive device such as a pipe crawler or push camera to be introduced into the pipe to perform the inspection and, at the same time, to obtain details of any problem encountered. 
     Although effective in obtaining detailed images, using a pipe crawler is inconvenient and requires a great deal of time to set up and operate, even if no problems are discovered. Setting up a pipe crawler involves first interrupting the water flow ahead of the pipes to be inspected and diverting it with a pump system, then cleaning all the pipes and finally introducing the pipe crawler in the pipe, which in itself requires the entering of a man through a manhole. In other words, much work is needed to obtain detailed information regardless of whether a problem exists. 
     Other methods for routine inspection involve using a camera with a powerful zoom fitted to the lower end of a mast. The camera and mast are lowered into a manhole until the camera reaches one of the sewer pipes. There, the camera is made to zoom in and out to obtain images of the interior of the pipe. Suspending the camera and mast by hand requires much manipulation and becomes rapidly tiring. Mounting the camera and mast to a vehicle is far more convenient. The operator can drive up to the area to be inspected, position his vehicle over a manhole, lower the camera into the manhole until it reaches the pipe to be inspected, and start collecting data. 
     Known vehicle mounted inspection cameras have a major drawback however. Since the camera and mast are lowered vertically from the vehicle, they are not capable of adequately reaching lateral sewer pipes that are offset from the manhole. Although most manholes are positioned squarely above the lateral conduits that they access, some manholes are substantially offset, generally because of an obstacle being in the way. In many municipalities, approximately 10% of the underground piping network does not receive proper routine inspection with known equipment because the pipes are offset from the manholes that access them. 
     Therefore, there is a need for a routine inspection system that is both convenient for the operator, cost effective, and that allows reaching substantially all conduits radiating from a manhole, including those that are offset. 
     SUMMARY OF THE INVENTION 
     In accordance with a first broad aspect of the present invention, there is provided an apparatus for conducting remote subsurface inspection from above. The apparatus comprises a support structure, a mast, an imaging system and an offsetting mechanism. The support structure has an articulating radial arm and is adapted to be positioned above a working surface. The articulated radial arm has a pivot at one end and a coupling at the other end. The pivot has a rotation axis substantially normal to the working surface. Preferably, the support structure further comprises a retractable ground contacting leg to aid in stabilizing the mast when the apparatus is in use. The mast is held by the coupling and is born generally upright in use by the support structure. The mast has a portion that is downwardly extendable below the working surface and has a mounting on that extending portion to hold an imaging system. An actuating mechanism is preferably used to extend and retract the extending portion of the mast. More preferably, the mast comprises telescoping cylindrical sections. Advantageously, the imaging system comprises a video camera having a zoom lens of at least 20 times magnification. The imaging system preferably further comprises at least one light. More preferably, a plurality of lights is arranged around the video camera. The offsetting mechanism is operative to displace the imaging system laterally from a vertical reference axis beneath the coupling when the extending portion of the mast has been extended below the working surface. 
     The coupling preferably comprises a mast pivot having a mast rotation axis substantially perpendicular to the extension axis of the mast. The mast is maneuverable to allow its rotation with respect to the support structure around the mast rotation axis. 
     Optionally, the mounting comprises an adjustable interconnection between the imaging system and the extending portion of the mast. The interconnection is remotely maneuverable from a first position in which the imaging system is proximal to the extending portion of the mast, to a second position in which the imaging system is displaced from the extending portion of the mast. 
     Preferably, the articulating radial arm comprises a plurality of sections joined by swivels. More preferably, the swivels and the mast pivot have locking mechanism to prevent their free rotation. Even more preferably, the support structure comprises an adaptor section adapted to fit to a hitch installed on a vehicle. 
     A display may optionally be provided to display images from the imaging system. Preferably, the display is mounted on a portion of the mast that is not downwardly extendable below the working surface. 
     In accordance with a second broad aspect of the present invention, there is provided a method for conducting remote subsurface inspections from above. The method comprises the steps of (a) locating an access point on a working surface above a subsurface area, (b) positioning an apparatus for conducting remote subsurface inspections from above as here above disclosed proximal to the access point, (c) manipulating the mast of the apparatus in vertical alignment with the access point, (d) lowering the extending portion of the mast downwardly into such subsurface area until the imaging system of the apparatus is at the level to be inspected and (e) reviewing images of such subsurface area from the imaging system. Preferably, in step (d), the mast is lowered vertically, or substantially vertically, in the subsurface area. 
     Preferably, the method further comprises the step of displacing the imaging system laterally from a vertical reference axis beneath the coupling of the support structure of the apparatus when the extending portion of the mast has been extended below the working surface. More preferably, the coupling comprises a mast pivot, and the step of displacing the imaging system laterally comprises maneuvering the mast pivot to rotate the mast with respect to the support structure. 
     Optionally, the mounting of the extending portion of the mast comprises an adjustable interconnection between the imaging system and the extending portion of the mast. The step of displacing the imaging system laterally comprises remotely maneuvering the adjustable interconnection from a first position in which the imaging system is proximal to the extending portion of the mast, to a second position in which the imaging system is displaced from the extending portion of the mast. 
     In accordance with a third broad aspect of the invention, there is provided an apparatus for conducting remote subsurface inspections from above which comprises a support structure, a mast and an imaging system. The support structure has an articulated radial arm and a coupling and is adapted to be positioned above a working surface. The articulated radial arm is connected to the coupling. The mast is held by the coupling and is born generally upright in use by the support structure. Preferably, the mast comprises telescoping cylindrical sections. The mast has an extending portion that is downwardly extendable below the working surface. The extending portion has a mounting thereon. The imaging system is held by the mounting on the extending portion of the mast. Preferably, the imaging system comprises a video camera. 
     The apparatus preferably comprises an offsetting mechanism that is operative to displace the imaging system laterally from a vertical reference axis beneath the coupling when the extending portion of the mast has been extended below the working surface. More preferably, the coupling comprises a mast pivot having a mast rotation axis that is substantially perpendicular to the extension axis of the mast. The mast pivot is maneuverable to allow rotation of the mast with respect to the support structure around the mast rotation axis. 
     Optionally, the mounting comprises an adjustable interconnection between the imaging system and the extending portion of the mast. The interconnection is remotely maneuverable from a first position in which the imaging system is proximal to the extending portion of the mast, to a second position in which the imaging system is displaced from the extending portion of the mast. 
     Preferably, the articulating radial arm comprises a plurality of sections joined by swivels. More preferably, the support structure further comprises a retractable ground contacting leg to aid in stabilizing the mast when the apparatus is in use. Even more preferably, the support structure comprises an adaptor section adapted to fit to a hitch installed on a vehicle. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       These and other features of the present invention will become more apparent from the following description in which reference is made to the appended drawings wherein: 
         FIG. 1  shows a cross-sectional side view of prior art inspection assembly reaching an underground conduit. 
         FIG. 2  shows a cross-sectional side view of prior art inspection assembly trying to reach an offset underground conduit. 
         FIG. 3  shows a cross sectional front view of an embodiment of the present invention reaching an offset underground conduit. 
         FIG. 4  shows a perspective view of an embodiment of the present invention. 
         FIG. 5  shows a perspective view of another embodiment of the present invention in action. 
         FIG. 6  shows a perspective view of a further embodiment of the present invention. 
         FIG. 7  shows a partial cross-section perspective view of an embodiment of the invention in use. 
         FIG. 8  shows an exploded perspective view of a vehicle having a hitch as per another embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  depicts an example of prior art. In this example, an inspection system  10   a  is mounted to a vehicle  20   a  having a telescoping mast  50   a  deployed through a manhole  94   a  such that a video imaging system  60   a  is able to reach the lateral conduit  96   a.    
       FIG. 2  depicts the same example of prior art inspection system as in  FIG. 1  trying to reach an offset lateral conduit  98   a  this time. It is apparent that even by positioning the vehicle  20   a  as close as possible to the side of the manhole  94   a , it is not possible for the imaging system  60   a  to reach the center of the offset lateral conduit  98   a.    
       FIG. 3  shows an embodiment of the present invention reaching a similarly offset lateral conduit  98  as the offset lateral conduit  98   a  depicted in the prior art system of  FIG. 2 . It is possible to see that by using the features of the present invention, it is now possible for the video imaging system  60  to reach an offset lateral conduit  98 , even when not locating vehicle  20  precisely over the area to be inspected  90 . 
     As best seen in  FIG. 4 , the inspection system  10  is installed on a vehicle  20 . In the present case, the adaptor section  32  of support structure  30  is inserted in the receiver  22  of the hitch  24 . A locking pin  26  is used to hold the inspection system solidly connected to the hitch. Furthermore, a device using a set-screw (not shown) to press the support structure  30  against the receiver  22  may be used to remove any play in the assembly. To provide stability to the inspection system  10  such that the images sent by the video imaging system  60  are of good quality, a stabilizing mechanism  34  is used. When not in use, a leg  38  of the stabilizing mechanism  34  is retracted within the support structure  30 . When in use, the leg  38  is lowered until it contacts the ground. Whether in the up or the down position, the leg  38  needs to be locked in place using the locking mechanism  36 . In this embodiment of the invention, the inspection system  10  is depicted having an articulating radial arm  40  and a first, second and third pivots  42 ,  44 ,  46  having their respective first, second and third rotation axis  42   a ,  44   a  and  46   a.    
     In the embodiment of the present invention shown in  FIG. 4 , the articulating radial arm  40  is interrupted at two places by a second pivot  44  and third pivot  46 , defining three arm sections  45   a ,  45   b ,  45   c . When the inspection system  10  is installed at the back of a road vehicle  20 , the articulating radial arm  40 , when folded, does not extend beyond the sides of the vehicle  20 . 
     The telescoping mast  50  comprises multiple sections: a fixed outer section  52  and internally nested extending sections  54 . The outer section  52  is connected to the articulating radial arm  40 . The purpose of the telescoping mast  50  is to lower the video imaging system  60  into the manhole  94  closely to the centerline of lateral conduit. Typically, the telescoping mast  50  will be capable of reaching at least 20 feet underground. Sometimes, however, the lateral conduit is so offset from the manhole  94  that it is not possible for the video imaging system  60  to reach an offset lateral conduit  98  sufficiently well for it to be within field of view of the imaging system  60 . Hence, the present invention uses an offsetting mechanism to offset the video imaging system  60  and thereby reach such an offset lateral conduits  98 .  FIG. 4  shows an embodiment of such an offsetting mechanism in the form of a mast pivot  58 , connecting the outer section  52  to the articulating radial arm  40 . Once the extending section  54  of the telescoping mast  50  has been extended underground, the mast pivot  58  allows the operator to tilt the telescoping mast  50  such that the video imaging system  60  is displaced from its original position, where it was more or less in line with a vertical reference axis  51  located beneath the mast pivot  58 , to align with the offset lateral conduit  98 . Hence, the video imaging system  60  has the inside of the offset lateral conduit  98  in its field of view and is capable of zooming in and out permitting the inspection to proceed. Once in position, the operator uses the locking mechanisms  70  to lock the telescoping mast  50  at the desired angle. 
     A winch  80 , of which cable  82  is connected to the last extending section of the telescoping mast  50 , operates its extension or retraction. When the winch  80  unwinds its cable  82 , gravity pulls the video imaging system  60  and the extending sections  54  down. To pull the video imaging system  60  back up, the operator rewinds the cable  82 . The winch  80  is preferably installed on the telescoping mast  50 , but may be fixed to another part of the inspection system  10  that is convenient. 
     Although other materials may be used for the fabrication of the telescoping mast  50 , the use of composite materials is preferred. Two major reasons justify this choice. Firstly, in many instances, inspections are performed in harsh environments with corrosive elements. Secondly, when the articulating radial arm  40  is deployed, the weight of telescoping mast  50  plus video imaging system  60  generates a considerable torque on the first pivot  42 . Glass-fiber is a lightweight composite material meeting all design criteria while still keeping the cost reasonable. 
     A video imaging system  60  is installed at the lower extremity of the extending section  54  of the telescoping mast  50 . The video imaging system  60  may be fixed in many ways to the extremity of extending section  54 : it may be rigidly fixed, it may be rotatably fixed such as to provide rotation of the video imaging system  60  around the extending axis  56 , or it may use an articulation  112  such as to provide any angular movement of the video imaging system  60  with respect to the extending axis  56 . Installed in this manner, the video imaging system  60  is the lowest point of the inspection system  10  and can best reach the inside of underground conduits. The video imaging system  60  uses a camera  62  equipped with a relatively high magnification ratio to be capable to perform inspections both from close up and from a distance. Preferably, the camera uses a 26× optical zoom combined with a 12× numerical zoom. Furthermore, although the camera  62  is of a model tolerant to low-light conditions, the video imaging system  60  is equipped with an array of light projectors  64  to provide necessary lighting. The camera  62  and light projectors  64  are mounted in a lightweight housing having fins to dissipate heat generated by the light projectors  64 . Preferably, the camera  62  is mounted near the center of the housing  66  with the array of light projectors  64  surrounding it. This design provides the advantage of minimizing shadows captured by camera  62 . A further advantage is that this design is very compact. The housing  66  of the video imaging system  60  should be lightweight, resistant to corrosion and watertight. Aluminum is preferably used. 
     Images obtained by the camera  62  are relayed through wiring, or wirelessly, to the video equipment inside the vehicle for analysis. Alternatively, they could be recorded on a medium (CD, DVD, hard disk, etc) or sent remotely for analysis. Images obtained may be analyzed to determine whether problems such as cracks, blockage, and root infiltration exist. If no problem is detected, then the inspection system  10  may be moved quickly to another area to perform another inspection. On the other hand, if a problem is detected, a pipe crawler or other invasive type of inspection may be performed to obtain the details necessary to remedy the situation. This way, the time of setting up and operating a pipe crawler or similar device is not wasted on areas that are in acceptable condition. 
     A display  100  is mounted on the outer section  52  of the telescoping mast  50  to allow the operator to visualize where the video imaging system  60  is located. Images from the camera  62  are relayed to the display  100 . The display  100  may alternatively be mounted on another part of the inspection system  10 . For convenience, the display  100  is preferably mounted at eye level either on the telescoping mast  50  or on a section of the inspection system  10  close to it. 
     The inspection system  10  is installed on a vehicle  20  having a hitch  24 . The adaptor section  32  of support structure  30  is inserted in the receiver  22  of the hitch  24 . A locking pin  26  is used to hold the inspection system  10  solidly connected to the hitch  24 . Preferably, a standard commercially available hitch having a square cross section receiver is used. However, different models may be used, including non-standard ones, provided that the adaptor section  32  matches the receiver  22 . The fact that the inspection system  10  may be adapted to fit a hitch  24  having a standard receiver provides many benefits. For example, the inspection system  10  may be easily installed on, or removed from, in a matter of minutes, various vehicles equipped with a standard hitch having the right receiver. This yields large cost savings, as the owner, often a municipality, does not have to invest in a fleet of special vehicles equipped with a dedicated inspection system  10 . Furthermore, when the vehicle is not available (due to maintenance, repair or just plain too old to circulate), the inspection system  10  may be transferred to another vehicle equipped with a similar hitch, hence not jeopardizing the inspections to be conducted. Another advantage is that the considerable weight of a vehicle provides a stable platform for the inspection system  10 . Images coming from the video imaging system  60  are therefore of higher quality, in particular when the camera  62  zooms in. This is especially true when the present invention is compared with the hand-held inspection systems of prior art. The installation of the inspection system in the receiver of the hitch is performed in the conventional manner, such that it is not necessary to be described here. 
     The articulating radial arm  40  and first pivot  42  allow the lateral displacement of telescoping mast  50  and video imaging system  60 . Indeed, the operator no longer has to move his vehicle as close to the area to be inspected  90 . This feature is extremely useful when the area to be inspected  90  is, for instance, displaced away from the road. The operator may just park his vehicle  20  by the side of the road and extend the articulating radial arm  40  until the telescoping mast  50  is located above the manhole  94 . Furthermore, the more arm sections the articulating radial arm  40  has, the more easily the telescoping mast  50  may be deployed around obstacles and the farther from the vehicle  20  it can reach. On the other hand, more pivots add weight, play in the articulating radial arm  40 , and cost to the inspection system  10 . Hence, the number of arm sections of the articulating radial arm  40  is dictated by these practical considerations. It has been found that an articulating radial arm  40  split in two or three arm sections provides an optimum solution in most cases. In the specific example of  FIG. 4 , the second rotation axis  44   a  and third rotation axis  46   a  of second pivot  44  and third pivot  46  respectively are parallel and oriented vertically. These pivots do not necessarily have to be oriented parallel to each other or vertically. Each of them could well be oriented in any other way. However, it is considered to be preferable to orient them as described. The first arm section  45   a  of the articulating radial arm  40  is connected at one end to the support structure  30  through first pivot  42  and at the other end to the second arm section  45   b  of articulating radial arm  40  through second pivot  44 . The third arm section  45   c  of articulating radial arm  40  is connected at one end to the other end of the second arm section  45   b  through third pivot  46  and at its other end to the telescoping mast  50  through both forth pivot  48  and mast pivot  58 . In this specific example, forth pivot  48  is used to provide added maneuverability of the telescoping mast  50  by allowing both the telescoping mast  50  and its mast pivot  58  to rotate around the forth rotation axis  48   a . The rotation axis of pivot  48  is preferably oriented coaxially with the third arm section  45   c  of the articulating radial arm  40  and perpendicularly to the mast pivot  58 . The mast rotation axis  58   a  of mast pivot  58  is preferably oriented horizontally. Although the operator appreciates the added flexibility provided by the use of forth pivot  48 , the use of this element is not necessary to perform the invention, as it is possible to do without forth pivot  48 . 
     To simplify the manufacturing process, it is preferable to use the same pivot construction everywhere. Pivots, such as first pivot  42 , may use different types of elements to provide rotation: ball bearings, taper bearings and bushings, to name a few. Since the construction of pivots is well know in the art, it will not be covered in further detail here. One or many locking mechanisms  70  may be use to prevent the pivots from rotating. Preferably, a locking mechanism  70  is used at each pivot location to prevent it from rotating both when the inspection system  10  is stored or when the video imaging system  60  is in use. In the latter case, it is important to provide a stable platform for the video imaging system  60 , especially when the camera  62  zooms in with its powerful zoom. Each locking mechanism  70  is provided with a handle  72  such that they are easily operated by the operator. 
     The articulating radial arm  40  may fold on itself, allowing for a very compact storage position. In the present configuration, all arm sections  45   a ,  45   b ,  45   c  of the articulating radial arm  40  fold on the same vertical plane, one section above each other. Once deployed, the articulating radial arm  40  becomes approximately as long as the sum its three arm sections  45 , a ,  45 , b ,  45   c , providing added range to reach the area to be inspected  90 . 
       FIG. 5  depicts an alternative embodiment of the invention that includes a second offsetting mechanism. Similar components are given like reference numbers and their description will not be repeated. The second offsetting mechanism of the inspection system  10  takes the form of a locating arm  110  pivotally connected at the tip of the extending section  54  of the telescoping mast  50 . This locating arm  110  is provided with articulations  112  and  114  at each end such that it is possible to laterally offset the video imaging system  60  from the mast reference axis  51  such that the video imaging system  60  is located at the desired location for viewing the interior of the offset lateral conduit  98 . Both offsetting mechanisms, namely, the mast pivot  58  and the locating arm  110  may be jointly present on the inspection system. This embodiment provides the maximum flexibility in being able to reach offset lateral conduits. Alternatively, for cost considerations for example, only one of the two offsetting mechanisms may be present on the inspection system  10 .  FIG. 6  depicts an embodiment where only the locating arm  110  is present. Different offsetting mechanisms could also be used as an alternative to the locating arm  110 . For instance, the video imaging system  60  could be mounted on a mechanism that slides perpendicularly to the mast extension axis  56 , or a scissor type of mechanism could also be used to laterally project the video imaging system  60  in an offset lateral conduit  98 . Many different dispositions and mechanisms to project the video imaging system  60  laterally from the extending mast  50  would be apparent to one skilled in the art, and are all intended to be covered by the present invention. 
       FIG. 7  highlights the advantages of the invention in use. To work the invention, the operator drives to the area to be inspected  90  and parks his vehicle  20  nearby. If the inspection system  10  is not readily installed, the operator would install it in one of the receivers  22  of the hitches  24  on the vehicle  20 . The operator then connects a power supply to the video imaging system  60 , to the winch  80  and connects the wiring  68  between the camera  62  and the imaging processing equipment  120 . The manhole cover  92  is removed to gain access to the manhole  94 . He then lowers the video imaging system  60  in the manhole  94  using the winch  80 . Monitoring the images sent back from the camera  62  to the display  100 , the operator uses the winch  80 , and all adjustments provided by the different pivots  42 ,  44 ,  46 ,  48  and  58  to adequately position the camera  62  at the center of the offset lateral conduit  98  to be inspected. Alternatively, the operator could adjust articulations  112  and  114  to adequately position locating arm  110  and video imaging system  60 . If the lateral conduit  98  were not offset from the manhole  94 , the operator may not have to use mast pivot  58 . The camera  62  is then zoomed to obtain an image at the desired magnification. Once the inspection is finished, the video imaging system  60  is pulled back up, the articulating radial arm  40  is folded back into storage position and the manhole cover  92  put back in place. The operator may then drive to the next inspection area. 
     Optionally, for further convenience to the operator, or when it is better indicated for him to stay inside his vehicle, because of safety concerns for example, the inspection system  10  is remotely controllable. All moveable parts and joints of the system are motorized such that the operator may remotely manipulate the inspection system  10  from within his vehicle  20 . The imaging system  60  continuously sends an image to the operator such that he sees where the camera  62  is going. To get a better view of the environment and where the telescoping mast  50  or the articulating radial arm  40  are continuously located, additional cameras may be added at various locations on the inspection system  10 . 
     To further improve the reach of the inspection system, it is possible to use a specially designed hitch  24  as shown in  FIG. 8 . Such a hitch has one receiver  22   a  facing towards the back and one facing towards each side of the vehicle,  22   b  and  22   c , for a total of three receivers. This design is convenient as it allows the operator to install the inspection system  10  either at the back or at the left or the right of the vehicle  20 . This proves to be useful when all manholes to be inspected are located on the same side of the street, or if the operator needs to reach farther away on one side of the vehicle. The hitch  24  shown in  FIG. 8  shows a receiver normally located towards the back of a vehicle and a square tube placed perpendicularly to the back receiver  22   a , defining both lateral receivers  22   b  and  22   c  at each of its extremities. The inspection system  10  is connected in the same manner whether it is at the back or on the sides of the vehicle  20 . Alternatively, the hitch may have more or less than three receivers and they may be placed at any position, any angle and any height with respect to one another. 
     The person skilled in the art will recognize that many variations could be made to the present invention. For instance, the inspection system  10  could be equipped with a non-standard adaptor section  32  and fit into a corresponding non-standard receiver  22 . Furthermore, the inspection system  10  does not have to be installed on a hitch: indeed, it could be connected to a vehicle  20  either permanently, or through the use of fasteners. Also, the inspection system could be permanently installed on the back, or at the side, of a vehicle. The vehicle used with the invention is a land vehicle such as, without limitation, a car, a truck, a sport utility vehicle, an all-terrain vehicle, a trailer, or even a set of wheels, mounted or not on their own frame, fixed to the support structure  30 . 
     The present invention has been described with regards to preferred embodiments. In will be obvious to one skilled in the art that several modifications or variations may be brought to the invention without departing from the scope of the invention as described herein and are intended to be covered by the present description.