Abstract:
A tracked climbing vehicle containing a compliant suspension apparatus to prescribe the distribution of forces on the adhering members in the tracked climbing machine capable of negotiating irregular surfaces. The compliant suspension apparatus is configured to negotiate irregularities in a climbing-surface without its tracks losing full surface contact and adhesion. It does this by distributing the loads from the climbing machine chassis to the adhering traction members in a specific prescribed fashion to avoid exceeding the allowable force in any adhering traction member and thus significantly improve the performance of the climbing machine.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
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     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
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     DESCRIPTION OF ATTACHED APPENDIX 
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     BACKGROUND OF THE INVENTION 
     This invention relates generally to the field of robotics and more specifically to a self-propelled climbing machine having endless-tracks. Such vehicles may be employed to perform remote operations in locations that are difficult for, or incompatible with, human presence or access. One example is a vehicle that can travel over a steel surface in a vertical, horizontal or upside-down configuration, such as on tanks, pipes, boiler walls or ship hulls, and also carry equipment to perform manufacture, maintenance or inspection functions. 
     There are many structures which require maintenance, repair, inspection or manufacturing operations that could be performed by a remote machine in a tele-operated or autonomous fashion. Numerous vehicles have been proposed to travel over inclined surfaces, and even operate upside down. These vehicles generally employ legs, wheels, or endless-tracks. Vehicles using endless-tracks provide several advantages, in particular the potential for a large area of contact between the vehicle and contact surface. Endless-tracks provide exceptional potential for large-area surface contact between the track-members (for example magnets) and the climbing-surface. 
     This invention concerns vehicles of the endless-track type with magnetic track-members incorporated in the endless-tracks. These vehicles are intended to operate on significant inclines, or upside down and/or on surfaces having, alone or in combination, concave, convex or irregular contours. 
     The endless-track type climbing vehicles available in previous technologies, may have, adhering track-members attached to the tracks and employ an endless-track of specific properties, to include very high tensile stiffness of the endless-track itself, in the axial direction of the track, but negligible stiffness in all transverse directions and negligible stiffness with respect to in bending. This creates a technological disadvantage in that the track in such cases is capable of supporting tensile forces, but, has only minimal stiffness in bending or in torsion for small angles it. Accordingly, it can support only negligible loads in any other direction, cannot support shear side-loads, and cannot support compressive loads. 
     To more closely examine circumstances under which this disadvantage becomes apparent, we note that for such a climbing vehicle to remain in equilibrium in any given position and orientation on a climbing-surface, forces affecting that equilibrium must be transferred from the climbing-surface to the vehicle. For a simple track type climbing vehicle, these forces are transferred from the track-members to the vehicle chassis through tensions in the endless-track. This would, ideally, allow the endless-track to accommodate irregular climbing-surface, but would concurrently result in localizing, on the outer adhering track-members, all of, or a majority of, the forces necessary to affect and maintain positional and orientational equilibrium with the climbing-surface. 
     The surface normal forces are a subset of the total forces that are required to maintain vehicle equilibrium on the climbing-surface. The surface normal forces are perpendicular to the climbing-surface and are required for equilibrium. To distribute this subset of forces in a manner intended to maintain equilibrium between the climbing vehicle and the climbing-CS, one might envision employment of a rigid guide section that slidably connects to the endless-track. But, this approach creates its own set of disadvantages in that it causes the surface normal forces to be localized on individual adhering track-members whenever and wherever climbing-surface irregularities are encountered. 
     The performance of an endless-track type climbing vehicle depends directly on the effective ability of the track, and accordingly, the track-members, to adhere to the climbing-surface. Numerous patents exist for climbing vehicles containing endless-tracks with adhering track-members incorporated into the tracks. One shortcoming of these previous technologies is their universal lack of a means to distribute the load among these adhering track-members in a manner that can accommodate a wide variety of surface geometries. Creation of such a load distribution means would significantly improve the performance of these climbing vehicles, and is, therefore, a desirable advancement in the art. 
     As is detailed below, previous technologies do not provide effective means to distribute the load among a plurality of adhering track-members. 
     Thus, an invention such as described herein, that distributes the forces required to maintain equilibrium between the vehicle and climbing-surface during operation among a plurality of adhering track-members, is novel to the state of art and is usefully and directly applicable to climbing vehicles having, or requiring, adhering track-members incorporated in endless-tracks. The herein taught art comprises a compliant suspension apparatus that distributes stiffness (and correspondingly the forces of equilibrium) relative to the plurality of adhering track-members. 
     The following discussion details and contrasts the instant art with illustrative examples of previous technologies and their associated shortcomings that the instant art overcomes. 
     U.S. Pat. No. 5,894,901, by Awamura, presents a traditional suspension system consisting of a plurality of press wheels equipped with elastic members (springs). These are capable of providing adjustment to the adhering members directed in to the climbing-surface only. The device provides, in contrast to the instant art, no means to compensate for, or to integrate, any other forces or balance adjustments. Although, as does the instant art, the Awamura et al. device includes magnets, an endless-track, and a suspension system, as designed, it only makes provision to adjustments necessary to push the magnets into contact with the climbing-surface. The device is equipped with auxiliary wheels, each wheel having a suspension supported by the vehicle body, pressing the wheel against the endless-track. These wheels are each supported by an elastic member in communication with the vehicle chassis. This is in contrast to the instant applicant&#39;s use of a compliant beam guide and support which automatically adjusts to balance the load carried and to maximize traction U.S. Pat. No. 5,435,405 by Schempf, et at teaches a reconfigurable mobile robot with magnetic tracks. 
     In contrast to the instant art, which uses permanently active magnets in the tracks, U.S. Pat. No. 5,435,405 by Schempf, et al teaches a magnetic system that can be activated and deactivated in the propulsion tracks. In further contrast, no guide, rigid or otherwise is mentioned with respect to the endless-track. Finally, unlike the instant art, the track appears to have no track-guide. 
     U.S. Pat. No. 4,789,037 by Kneebone uses two or more endless-tracks with plurality of permanent magnetic adhering members. Each adhering member comprises a permanent magnet sandwiched between magnetic metal plates. The magnet does not, itself, contact the climbing-surface, but contacts only these metal plates. As taught, it does allow pivotal rocking motion of track assemblies relative to the vehicle body, for negotiating uneven or curved surfaces, the track assemblies comprising, for each track unit, two laterally spaced chains, each forming an endless member. The device also uses a pump in the center of the body to apply additional upward or downward pressure to press the tracks onto the climbing-surface, and does teach a fan to create suction force normal to the climbing-surface. But the patent mentions no sort of trackguide, rigid or otherwise. 
     U.S. Pat. No. 5,884,642 by Broadbent teaches endless-tracks with plurality of magnetic sections, each tread using four rare earth magnetic segments, adjacent treads being oriented in opposing polarities. It does not, however, discuss any type of guide for the tracks, nor automatic balance control or adjustment. 
     U.S. Pat. No. 4,828,059, by Naito, et al. employs a track guide that is used only to engage and disengage track magnets from climbing-surfaces. Locations of loads carried by the Naito device are limited to remaining within the upper and lower planes of the endless propulsion tracks. It employs a plurality of permanent magnets on outer surface of crawler tracks and has a guidance device on crawler tracks for restraining and releasing crawler track from moving relative to crawler body in direction normal to traveling plane of magnets. It also includes a track control mechanism so designed such that the guidance device can restrain or release motion of the track to the main body in a direction normal to the surface. When this guide load is released, the load is essentially transferred in its entirety, to only the end magnets of the tracks. 
     U.S. Pat. No. 5,487,440, by Seemann presents a rigid guide, and a pair of parallel, endless-tracks equipped with suction cup feet These tracks slide along a grooved structure that allows for communication between a vacuum pump and those suction cups which are positioned for contact with the climbing-surface. It makes little or no provision for significant surface irregularities. 
     U.S. Pat. No. 6,672,413 B2 by Moore, et al. describes a remote controlled inspection vehicle utilizing magnetic adhesion to traverse non-horizontal, non-flat, ferromagnetic surfaces. Although this device employs magnets to adhere to the climbing-surface, no magnets are attached to, or guided by a track. The magnets are, rather, attached directly to the vehicle. The track comprises modules each of which contains a permanent magnet that the endless-track surrounds. These modules are so constructed as to pivot about longitudinal axes in an attempt to conform to pipes or other irregularities. 
     BRIEF SUMMARY OF THE INVENTION 
     In accordance with a preferred embodiment of the invention, there is disclosed a tracked climbing machine having one or more revolving or cyclical gripping devices with adhering track-members. The revolving or cyclical gripping device is preferably in the form of one or more closed or endless, tracks, chains, belts, or cables upon the exterior of which the previously mentioned adhering track-members are mounted. 
     This tracked vehicle can climb vertical surfaces and overhangs, and negotiate surface irregularities, and in doing so, prevent its tracks from losing full surface contact and adhesion. 
     Its innovations are particularly useful in transiting, ascending and otherwise negotiating unprepared boiler sides, submarine hulls, ships sides, towers and other ferrous structures to perform automated or remotely controlled inspection, maintenance, and cleaning tasks that could not otherwise be accomplished. The device is notably adept at climbing vertical surfaces and overhangs and it is able to negotiate surface irregularities without its tracks losing full surface contact and adhesion. 
     It moves and climbs in a manner employing multiple feet, preferably aligned in two or more columns, by applying, adjusting, and releasing each individually gripping foot in response to whatever surface contour may be encountered by that particular foot. 
     A significant advance introduced by this technology is the bias devices installed along the compliant beam. These devices exert forces on the beam, in such as way as to distribute the pressure of the track in a uniform manner, even when the transited surface is non-planar. This particularly improves overall track performance when transiting small bumps or hummocks on the surface. 
     Further objects and advantages of the present invention will become apparent from the following descriptions, taken in connection with the accompanying drawings, wherein, by way of illustration and example, an embodiment of the present invention is disclosed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The drawings constitute a part of this specification and include exemplary embodiments to the invention, which may be embodied in various forms. It is to be understood that in some instances various aspects of the invention may be shown exaggerated or enlarged to facilitate an understanding of the invention. 
         FIG. 1  is an isometric view of the climbing vehicle composed of the vehicle chassis, two track-modules, and endless-track. 
         FIG. 2  is a front view of the climbing vehicle showing a front view of the vehicle chassis, track-modules, and endless-track. 
         FIG. 3  is an isometric view of a single track-module showing the endless-track and adhering track-members. 
         FIG. 4  gives an isometric view of a single track-module with the exterior cover cut away showing the compliant suspension apparatus consisting of compliant beam member, fore tangential guide link, aft tangential guide link, contour-following bias-devices, fore, mid and aft bias adjuster and tensioning mechanism. Also shown in  FIG. 4  are the track drive components; drive-sprocket, track-sprocket, drive-motor, and transmission. 
         FIG. 5  shows the primary components of the compliant suspension apparatus isolated from the track-module. 
         FIG. 6  shows a cross-sectional end-view of the slidable connection between the compliant beam member, the endless-track, and the sliding track-member, guided through guide-slot and also of the support block, magnetic adhering track member, and the connection between the adhering track-member, and the endless-track. 
         FIGS. 7 ,  8 , and  9  are side views of the device moving in direction D 1 , encountering an irregularity CI in a climbing-surface, CS, also showing operation of the compliant suspension apparatus. 
         FIG. 10  shows a diagram of the climbing-surface CS, with compliant beam. A basis set of directions are defined at a point along the compliant beam, as u 1 , a unit axis normal to the climbing-surface CS, u 2  along the axis of the endless-track at this point, and u 3  the right-hand axis of the frame. 
     
    
    
     LIST OF NUMBERED ELEMENTS 
     
         
           101  vehicle chassis 
           101   a  chassis payload-rack 
           102   a  port side track-module 
           102   b  starboard side track-module 
           103  endless track 
           103   a  track sliding-members 
           104  adhering track-members 
           105  compliant beam 
           106  fore tangential guide-linkage 
           107  aft tangential guide-linkage 
           108  contour-following bias-device 
           108   a  fore contour-following bias-device 
           108   b  midship&#39;s contour-following bias-device 
           108   c  aft contour-following bias-device 
           109  drive-sprocket 
           110  track-sprocket 
           111  drive-motor 
           112  transmission 
           113  guide-slot 
           114  drive-sprocket axle 
           115  track-sprocket axle 
           116  compliant suspension apparatus 
           118  tensioning mechanism 
           119  magnet 
           120  support-block 
           121   a  fore bias-adjuster 
           121   b  mid bias-adjuster 
           121   c  aft bias-adjuster 
         D 1  direction of motion 
         CS climbing-surface 
         CI contour or irregularity 
         u 1  axis u 1  normal to the climbing-surface CS 
         u 2  axis u 2 , in the plane of the climbing-surface CS and normal to the axis of the 
         direction of movement endless-track 
         u 3  axis along track direction of motion D 1   
         R 1  first independent track-module axes of limited rotational freedom about an axis in the plane of the climbing-surface CS 
         R 2  second independent track-module axes of limited rotational freedom about an axis in the plane normal to that of the climbing-surface CS 
       
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Detailed descriptions of the preferred embodiment are provided herein. It is to be understood, however, that the present invention may be embodied in various forms. Therefore, specific details disclosed herein are not to be interpreted as limiting, but rather as a basis for the claims and as a representative basis for teaching one skilled in the art to employ the present invention in virtually any appropriately detailed system, structure or manner. 
     Referring to  FIGS. 1 and 2 , we see illustrated a self-propelled vehicle for traversing a surface, comprised of a vehicle chassis  101 , to which a payload may be attached. The vehicle is equipped with one or more track-modules  102   a ,  102   b  that support the vehicle chassis  101 , and which support endless-tracks  103 , these tracks  103  incorporating a plurality of magnetic track-members  104  spaced along each endless-track  103 . The chassis  101  may be adapted to carry a multiplicity of payloads, tools or equipments. 
     Referring to  FIGS. 3 ,  4 , and  7 - 9 , this endless-track  103  with track-members  104 , cyclically moves in such a way as to provide locomotive force. When the vehicle is in motion, portions of the track are constantly cycling through a traction-portion of its cycle, wherein they make contact with the climbing-surface CS. Referring to  FIGS. 4 ,  5 , and  7 - 9 , a compliant suspension apparatus  116  incorporates a compliant beam member  105  to which the revolving or cyclical track  103  is slidably connected. 
     In short summary of the device and its operation, the climbing vehicle and chassis  101  are subject to a variety of forces, including gravitational and dynamic loads associated with the vehicle and payload motion, as well as to forces generated by the operation of the tooling or equipment attached to the vehicle. These forces are to be transferred to the climbing-surface CS through the endless-track  103  and adhering track-members  104  preferably permanent magnets  119 . The forces are compensated for by the compliant suspension apparatus, and bias devices, adjusted according to Hooke&#39;s law which relates force, displacement and stiffness. This adjustment may be applied automatically or manually. 
     The suspension and compliant beam apparatus of this device dictate how the above forces are transmitted from the vehicle chassis  101  to the adhering track-members  104  over a wide range of surface irregularities or contours CI of the climbing-surface CS. This apparatus, a combination mechanism of a compliant beam  105  slidably connected to the track  103 , rigid-body members, and bias-devices or springs  108 , maximizes track contact with the climbing-surface CS in a manner different from and superior to previous technologies and permits the flexible endless-track to propel and support a rigid vehicle chassis in a more continuous, and therefore more effective manner. 
     The apparatus which achieves the above prescribed stiffness or compliance consists of three primary components. These components are shown in  FIG. 5  as: the one or more compliant beams  105 , the rigid-body tangential guide-linkages,  106 ,  107  and the contour-following bias-device elements,  108 . A compliant beam  105  is slidably attached to the endless-track  103 . The compliant beam  105  geometric and material properties are established to be compatible with the geometry of a climbing-surface CS having a wide range of contours or irregularities. 
     The compliant beam  105  of  FIG. 10  is conjugate and slidably connected to the endless-track (not shown) and prescribes five specific stiffness (or compliance) components between the climbing-surface CS and the climbing machine body. These include all axis cardinal directions in three-dimensional space except the direction of movement D 1  of the endless-track. Since the compliant apparatus is slidably connected to the endless-track, no stiffness is prescribed on that axis of the endless-track. 
     Listing the components addressed, they are, as shown in  FIG. 10 . 
     1) translational stiffness along unit axis u 1  normal to the climbing-surface CS 
     2) translational stiffness along unit axis u 2 , in the plane of the climbing-surface CS and normal to the axis of the endless-track 
     3) rotational stiffness about u 1  normal to the climbing-surface CS 
     4) rotational stiffness about u 2 , an axis in the plane of the climbing-surface CS and normal to the axis of the endless-track, and 
     5) rotational stiffness about u 3 , the axis of the endless-track. 
     The linear stiffness along u 1  is prescribed along the entire track to uniformly distribute the forces on the adhering track-members. The linear stiffness along u 2  is prescribed to limit transverse deflection of the endless-track (high stiffness) The rotational stiffness about u 1  is prescribed to limit rotation of the endless-track (high stiffness) about an axis normal to the climbing-surface CS. The rotational stiffness about u 2  is prescribed to allow low stiffness along the center portion of the endless track to accommodate contours or irregularities in the climbing-surface CS, and high stiffness where the endless-track engages the track-sprockets. 
     The rotational stiffness, about u 3  is prescribed to allow low stiffness along the center portion of the endless-track to accommodate contours or irregularities in the climbing-surface CS, and high stiffness where the endless-track engages the track-sprockets. 
     As noted above, the compliant beam  105  provides a surface conjugate to the endless-track  103  in a slidable connection. The fore tangential guide-linkage  106  enforces the stiffness and geometry of the compliant beam  105  conjugate to the endless-track  103  at the point where the endless-track  103  engages the drive-sprocket  109 . The aft tangential guide-linkage  107  enforces the stiffness and geometry of the compliant beam  105  conjugate to the endless-track  103  at the point where the endless-track  103  engages the track-sprocket  110 . The contour-following bias-device members to  108   a ,  108   b ,  108   c  prescribe the stiffness of the compliant beam  105  in the u 1  direction to more uniformly distribute the forces in the adhering track-members  104 . 
     This compliant beam member  105  is so contrived and adjusted, by means of contour following bias devices  108 ,  108   a ,  108   b ,  108   c  and adjustors,  121   a ,  121   b , and  121   c , (See  FIG. 4 .) These bias-devices  108  are located at points along the compliant is beam  105 , such that each bias-device  108  exerts force upon the compliant beam  105  at its particular point on the beam  105 . This changes the force of the track  103  against the transited surface CS at that particular tension point. The change of force at this point creates a force to pull portions of the track,  103  more firmly against the transited surface CS by promoting deformation of the compliant beam  105  to conform with the topography of the surface CS being transited. 
     This causes track  103  force against the transited surface CS, to be more equally distributed, promoting increased surface contact of all adhering members along the rest of the track, thereby maximizing the area over which the adhering members of the endless track contact the transited surface and distributing the force along the track. The benefits of these effects are particularly notable when and where the track encounters small bumps, hummocks or other irregularities CI in the climbing surface CS. 
     A useful way of understanding this innovation is to imagine this climbing machine, inverted, transiting an overhead surface CS, essentially clinging magnetically to, and hanging from, the ceiling. In such a position, one can see the benefit of distributing the load along the track  103  through the bias devices and simultaneously ensuring positive pressure between the track  103  and the overhead surface CS at each end of the track. In the same way, referring to  FIGS. 8 ,  9 , and  10 , one can see that as the device passes over an irregularity CI, the portion of track  103  not in contact with the irregularity Cl would tend to be pushed out of contact with the climbing surface CS, were it not for the bias devices  108 . But, because of the tension exerted by the bias device  108  on the track  103  in the vicinity of the irregularity CI, the rest of the track  103  tends to be pulled more firmly into contact with the climbing surface CS. 
     Thus the track  103 , and the compliant beam  105 , tend to better adapt to contours CI of climbing-surfaces CS in such as way as to allow the magnetically adhering track-members  104  to maintain traction on the surface CS. The system is powered by the drive-motor  111  and transmission  112  that propels the track via one or more drive-sprockets  109   
     Referring to  FIG. 2 , the chassis  101  is attached to the track-modules  102   a  and  102   b  in a manner that allows two degrees of rotary movement between each track-module  102   a ,  102   b  and the chassis  101 . As shown in  FIG. 1 , this movement is about two independent axes R 1  being an axis in the plane of the climbing surface, and R 2  being an axis normal to the climbing-surface CS. 
     Referring to  FIGS. 6 and 7 , the adhering track-members  104  each are preferably comprised of a magnet  119  located in a support-block  120 . Referring to  FIGS. 3 and 4 , the support-block  120  is connected to respective sections of the endless-track  103 , and sliding member  103   a  in the guide-slot  113 , so that necessary relative motion is available to allow the assembly of endless-track  103  and adhering track-members  104  to pass along and around the path described by the location of the drive and track-sprockets,  109  and  110 , the track tensioning mechanism  118 , and the guide-slots  113 , in the compliant beam member  105 . 
     Referring to  FIGS. 3 and 4 , a compliant suspension apparatus  116  is contained within the track-module  102   a  and  102   b . The compliant suspension apparatus  116  consists of compliant beam member  105 , fore tangential guide-linkage  106 , aft tangential guide-linkage  107 , and a plurality of contour-following bias-devices  108   a ,  108   b , and  108   c.    
     The compliant beam member  105  is slidably connected to the endless-track  103  through guide-slots  113 . The fore tangential guide-linkage  106  is rigidly attached to the compliant beam member  105  and pivotally connected to the track-module  102   a  at the drive-sprocket axle  114 . The aft tangential guide-linkage  107  is slidably connected to the compliant beam member  105  and pivotally connected to the track-module  102   a  at the track-sprocket axle  115 . 
     The endless-track  103  engages drive-sprocket  109  and track-sprocket  110 . The drive-sprocket  109  and track-sprocket  110  are pivotally connected at the drive-sprocket axle  114  and track-sprocket axle  115  respectively to the track-module  102   a  to permit pivotal movement of the drive and track-sprockets,  109  and  110 . The drive-sprocket  109  is driven by a drive-motor  111  through a transmission  112 . Each track-module  102   a ,  102   b  is independently driven, allowing the vehicle to by propelled and steered by judicious control of speed and direction of the drive-motor(s)  111 . 
     The endless-track  103  engages the track tensioning mechanism  118 . The track tensioning mechanism  118  is pivotally connected to the track-module  102   a  and is biased with a track-tension bias-device  118  to provide tension in the endless-track  103 , as the length of endless-track  103  in contact with the climbing-surface CS varies according to the surface irregularities or contours encountered CI. 
     The forward external contour-following bias-device  108   a  is pivotally connected to the compliant beam member  105  and pivotally connected to the track-module  102   b . The aft contour-following bias-device  108   c  is pivotally connected to the fore tangential guide-linkage  106  pivotally connected to the track-module  102   b . The aft contour-following bias-device  108  is pivotally connected to the aft tangential guide-linkage  107  and pivotally connected to the track-module  102   b  as shown in  FIG. 4 . 
     In operation, the vehicle chassis  101  is positioned with track adhering members  104  in contact with a climbing-surface CS. Then, the drive-motor(s)  111  are activated. Proceeding along the climbing-surface CS, the adhering track-members  104  make sequential contact, each in its turn, with the climbing-surface CS, while the endless-track  103  slides along the compliant beam member  105 , thereby propelling the vehicle. 
     Referring to  FIGS. 7-9 , when a track adhering member  104  encounters an irregularity CI in the climbing-surface CS, the vehicle and suspension system ingeniously compensate for this surface irregularity CI with a high level of precision. Here an irregularity CI of the climbing-surface CS is defined as any spatial departure of the climbing-surface CS from a planar surface. Such surface irregularities may be concave or convex, sharply defined protrusions or rifts, or a, combination thereof. 
     The means of this notably effective compensation are employed as follows. The compliant beam portion  105  of the suspension deforms to match the contour of the climbing-surface CS irregularity Cl. While deformed, the compliant beam  105  portion maintains its slidable connection  103   a  to the endless-track  120 . The contour-following bias-devices  108   a , and  108   b , maintain tension or compression between the deformed compliant beam  105  and the rigid vehicle chassis  101 , creating forces directed from the rigid vehicle chassis  101  toward the climbing-surface CS. These forces keep the chassis  101  in positive contact with the climbing-surface CS. 
     This in turn forces the fore track-sprocket  109  toward with the climbing-surface CS. The fore tangential guide linkage  106  then maintains contact of the compliant beam portion of the suspension and the leading adhering tractive members  104 , guiding the compliant beam  105  to deform to match irregularities in the climbing-surface CS. 
     To better understand the device in negotiation of a climbing-surface CS, we refer to  FIG. 7 , a side view of the device climbing a surface CS prior to the surface irregularity CI, and compare it to  FIG. 8 .  FIG. 9 , a similar view of the device on a climbing-surface CS that has a significant contour or irregularity CI to be negotiated. The function of the compliant beam member  105  as it adapts to the climbing-surface CS contours and irregularities CI is demonstrated. 
     Also illustrated are the adaptive functions of the contour-following bias-devices  108   a ,  108   b , and  108   c  in supporting the compliant beam member  105  while linking the compliant beam member  105  to the chassis  101 , and the adaptive function of the tangential guide-linkages  106  and  107  and of the tensioning mechanism  118 . Note particularly how the tensioning mechanism  118  adjusts to allow a greater total area of contact for the endless-track  103  to conform to brief climbing-surface CS contours and irregularities CI. 
     While the preceding description has described a preferred embodiment for the present invention, it should be understood by those skilled in the art that alternative configurations of the elements of the invention can be formed without departing from the primary scope of the present invention. 
     Thus, while the invention has been described in connection with a preferred embodiment, it is not intended to limit the scope of the invention to the particular form set forth, but on the contrary, it is intended to cover such alternatives, modifications, and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims.