Abstract:
An extendable ramp apparatus is provided for automatically extending a ramp. The apparatus comprises a generally rectangular frame with a track for movement of a carriage pivotally connected to a ramp along the track. The ramp pivots downwardly as it is extends from the frame until it encounters a surface. A bidirectional motor is provided with a cabling arrangement to reciprocate the carriage and ramp along the track. Shock absorbers may slow the carriage movement as the ramp is extended so that hard contact of the ramp with a surface is minimized. An innovative capstan arrangement provides more rapid movement of the ramp as it retracts but provides more power during ramp extension, so that vertical movement of the ramp is slowed as the ramp is extended. The apparatus may find application in vehicles such as trucks, vans, and boats whenever it is desired to move goods or people between surfaces of different heights, such as a truck bed and the ground.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
   This patent application claims the benefit of U.S. Provisional Application No. 60/580,547, entitled “Improved Gangplank”, filed Jun. 17, 2004. 

   BACKGROUND OF THE INVENTION 
   The invention relates generally to extendable surfaces for supporting people and material for movement between two structures at a height. More specifically, the invention relates to extendable platforms or ramps to assist loading and unloading boats and vehicles, and, more particularly, but not by way of limitation, it relates to an improved extendable gangplank for use in combination with a pontoon-type barge or boat. 
   Ramps are in common use for loading and unloading vehicles, by providing a smooth transition from vehicle to the loading area. Examples of ramp use are, for example, ramps used by furniture movers to enable them to easily move a piece of furniture from the ground to the truck body, which is usually several feet above the ground. Ramps are also used as gangplanks in the boating industry to allow personnel to move from the shore or dock to a boat without getting wet. The ramp is usually stored in the body of the vehicle or underneath its floor when it is no longer required. Such ramps are usually heavy and cumbersome, and several persons are usually called upon to manhandle the ramp into its storage position. 
   The prior art includes numerous ways in which the use of ramps, platforms, or gangplanks has been automated to allow a single person to position and store such a device. U.S. Pat. No. 4,011,615, issued to Maxson et al., discloses a bow gangplank that is intended for use on an offshore oil rig platform when violent wave action is present. It has a springloaded body that will elongate and shorten in accordance with wave inducements. The gangplank itself is not controllable from the boat but must be manipulated and maintained in position between the rig platform and docking vessel. However, it does feature a self adjusting feature that accommodates rough seas by extending and shortening the gangway to allow for movement of the ship during heavy seas. U.S. Pat. No. 4,293,967, issued to Ord, discloses a boat with a flip-over bow gangplank, wherein the gangplank in the stowed position is compactly maintained in trim against the bow form of the vessel. In docking, the gangplank is simply swung up and over to extend forward of the vessel onto a docking structure. 
   Other prior art stores the ramp or gangplank under the floor of the vehicle or boat. For example, U.S. Pat. No. 4,993,341, issued to Merkel, discloses an extendable gangplank for a pontoon boat, the gangplank being carried beneath the deck of the boat and extending outwardly under control of a DC motor. The extension mechanism consists of a combination of cables and pulleys which may be prone to jamming and interference by debris and other foreign matter in the water under the boat. The gangplank consists of a short portion and a long portion held together by hinges, so that when the long portion extends outwardly from the pontoon boat, the hinges will allow the long portion to drop from a horizontally extending position when the hinges extend over an outer supporting roller. No provision is made to slow the descent of the gangplank as it extends from the boat and this may present a danger to personnel on the shore. 
   U.S. Pat. No. 5,085,165, issued to Reed, also discloses another gangplank for a pontoon boat. The gangplank is pivotally connected to a guide section and is suspended from rollers below a deck of the boat between the pontoons. A central rib is provided along the underside of the gangplank, where the rib has two inclined portions joined at an apex with the portions riding on a fixed roller also mounted below the deck. When the gangplank is extended, the inclined portions function like a cam to lower the gangplank to a surface after the apex traverses the fixed roller, and when the gangplank is retracted, the gangplank is raised from the surface by cam action of the rollers. The gangplank is actuated by a cable having two ends connected to the guide section and powered by a winch. 
   U.S. Pat. No. 6,868,799, issued to Wright, discloses a ramp for a pontoon boat, where the ramp consists of a platform and a supporting structure for suspending the platform under a pontoon boat. The platform is supported on its distal end by a float and has a proximal end that is slidingly attached by blocks to a pair of parallel rails in the support structure. The apparatus has no rollers or a winching arrangement. 
   Each of these inventions provides an apparatus for extending and stowing a ramp or gangplank for a marine vehicle. Each becomes more complicated when an automated means for extending or retracting the gangplank is used. Furthermore, the clearance and space requirements of the apparatus, or its profile, is not particularly addressed in the prior art. Clearance is particularly important for land based vehicles such as trucks or vans, in order to maintain road clearance above the road surface. If the apparatus is mounted below the vehicle frame so that it extends toward the road surface, then it is prone to damage from road objects. Alternatively, if the apparatus is mounted above the vehicle frame, then the vehicle body may have to be raised to accommodate the apparatus. If this amount of elevation is excessive, then the center of gravity of the vehicle might change, resulting in a top heavy vehicle, which would therefore be less stable. 
   Thus as can be seen, there is a need for an improved extendable ramp apparatus that is simple, easily maintained, resistant to interference by debris or obstructions, and exhibits smooth operation. The apparatus should be lightweight so that it may be employed on a variety of vehicular platforms and corrosion resistant, particularly in a marine environment. It is desirable that the apparatus be as thin as possible in order to increase its utility for different vehicles. Finally, it is also desirable to prevent the ramp from rapidly dropping when it is extended so that people are not hurt and equipment is not damaged. 
   SUMMARY OF THE INVENTION 
   In one aspect of the invention, an extendable ramp apparatus is provided, where the apparatus comprises a generally rectangular frame with a front end, a back end, and two tracks each extending between the front end and the back end, the frame having a roller aligned with each track and positioned at the back end; a ramp with a first ramp end and a second ramp end; a carriage with a plurality of wheels engaging the tracks for reciprocal movement thereon, the carriage being pivotally attached to the first ramp end, the carriage oriented proximate the front end, the ramp oriented proximate the back end, so that the ramp is supported by the carriage and the rollers; and a motor attached to the frame, the motor arranged to move the carriage in a first direction towards the back end and in a second direction towards the front end, the motor controlled by a switch having a first position causing the carriage to move in the first direction and a second position causing the carriage to move in the second direction. 
   In another aspect of the invention, an extendable ramp apparatus for use beneath a horizontal surface is provided where the apparatus comprises a rectangular frame having a front member, a back member, and two side members extending between the front member and the back member, each side member with a track, the frame having a roller aligned with each track proximate the back member, the frame having a profile; a motor mounted on the front member within the profile of the frame; a carriage within the profile of the frame, the carriage having two opposed carriage side members aligned with the tracks, each carriage side member with a first end proximate the back member of the frame and a second end proximate the front member of the frame, the carriage side members held in spaced relationship by a carriage back member fixedly attached to the opposed first ends and by one or more carriage cross members proximate the carriage back member, each carriage side member with a plurality of wheels supporting the carriage side member within each track for reciprocal movement of the carriage along the tracks, wherein the motor does not come into contact with the carriage when the second ends of the carriage side members contact the front member; and a ramp within the profile of the frame, the ramp having a first ramp end and a second ramp end, the first ramp end pivotally connected with the carriage back member, and the second ramp end supported by the rollers, so that the motor is disposed to selectively move the carriage and ramp in a first direction and a second direction along the tracks. 
   In still another aspect of the invention, an extendable ramp system is provide, the system comprising a frame having a track; a carriage mounted on the track for reciprocal motion along the track; a ramp pivotally attached to the carriage; an actuating apparatus that comprises a reversible motor mounted on the frame, a capstan having a barrel driven by the motor, and a cable wrapped around the barrel with two ends connected to the carriage and arranged to extend the ramp when the motor is operating in a first direction and retract the ramp when the motor is operating in a second direction; and a shock absorber disposed to oppose without preventing downward motion of the ramp as it is extended beyond the frame by the carriage. 
   These and other features, aspects and advantages of the present invention will become better understood with reference to the following drawings, pictures, description and claims. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view of an extendable ramp within its supporting frame, according to an embodiment of the invention; 
       FIG. 2  is a top view of a frame designed to support the ramp and carriage, according to an embodiment of the invention; 
       FIG. 3  is a side view of the frame, according to an embodiment of the invention; 
       FIG. 4  is an end view of the frame, according to an embodiment of the invention; 
       FIG. 5  is a top view of an extendable ramp attached to its carriage, according to an embodiment of the invention; 
       FIG. 6  is a top detailed view of the carriage and a portion of the ramp, according to an embodiment of the invention; 
       FIG. 7  is a side, detail view of a tensioning mechanism for maintaining tension on a drive wire, according to an embodiment of the invention; 
       FIG. 8  is a perspective view of an attachment means for attachment of the cable to a tensioning mechanism, according to an embodiment of the invention; 
       FIG. 9A  is a perspective view of a tapered capstan turning in a counterclockwise direction, according to an embodiment of the invention; 
       FIG. 9B  is a perspective view of a tapered capstan turning in a clockwise direction, according to an embodiment of the invention; and 
       FIG. 10  is a side view of an alternative placement of a shock absorber, according to an embodiment of the invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   The following detailed description is of the best currently contemplated modes of carrying out the invention. The description is not to be taken in a limiting sense, but is made merely for the purpose of illustrating the general principles of the invention, since the scope of the invention is best defined by the appended claims. 
   The invention may be used for applications in which an extendable ramp is required to move materials or personnel between a vehicle and a more stable surface. The invention may find use in the transportation industry, where ramps are used to move goods between the elevated bed of a truck to the ground or a loading dock. It may also find use in the boating industry, where a ramp may be required to extend between a floating vehicle, such as a boat, to the shore or dock, so that people and material can be moved thereon without becoming wet. The invention may also find use for handicapped persons, by providing a handicapped person riding a scooter or personal motorized device a means for entering and exiting a van without requiring manual labor to position a ramp. The invention may also be installed between the bed and the frame of a pickup truck to provide a ramp capability for general utility, commercial, or agricultural use, to allow a user to easily move bulky objects to and from the bed of the pickup truck. 
   The prior art is replete with different examples of automated, extendable ramps. These devices are generally integrated with the host equipment, e.g. a boat or a truck, so that they are not easily installed or removed. In order to provide structural rigidity and durability, they may be heavy and cumbersome. Furthermore, some of these devices have specialized features to extend the ramp horizontally and then to gently allow the ramp to drop until it encounters a stable surface, with the intent being to prevent abrupt, noisy, or dangerous contact. The extension mechanism may require an involved system of rollers, cables, belts, gears, and pulleys to provide these extension and lowering functions for the ramp. 
   The inventive extendable ramp system provides a lightweight, uncomplicated device that, because of its thin profile, can be installed in numerous vehicles without undue modification to the vehicle. The apparatus provided by the invention may be structurally rigid and corrosion resistant; its length may be adjusted to the particular application where it is used, while its overall thickness may be kept to a minimum, nominally about 3″ to 5″. Parts of the ramp that extend beyond this profile may be kept to a minimum. The construction of the extendable ramp apparatus may be simplified by using standard off-the-shelf parts, reducing the number of parts used for the device, and forming the structural parts in such a way as to provide rigidity, light weight, and structural strength. The extension mechanism may comprise a cabling system that provides both shock absorbing functions as well as rapid and simple replacement. It may be powered by a constant speed DC motor that drives an innovative, tapering capstan that allows rapid speed with low power at the beginning of a ramp extension and slower speed and higher power at the end of a ramp extension. Furthermore, at the end of a ramp extension, one or more shock absorbers may be provided to resist the vertical drop of the ramp so that it may gently encounter the solid surface. 
   Referring now to  FIG. 1 , an extendable ramp system  100  is shown, where the system  100  comprises a frame  110  that supports a ramp  101  and a carriage  102  arranged for joint, reciprocal movement along the frame  110  provided by a drive mechanism  103 . The drive mechanism  103  communicates the reciprocal movement to the carriage  102  and ramp  101  by a cable  104 . 
   A frame  110  is shown in  FIGS. 2 ,  3 , and  4 , according to one embodiment of the invention, as a basic rectangular structure having a front end  115  and a back end  120 . A pair of side members  135  may extend between the front and back ends  115 ,  120  to provide rigidity of the frame  110  and to define a track along which the carriage  102  and ramp  101  travel, as will be seen presently. The front end  115  may be defined by a front member  125  and the back end  120  may be defined by a back member  130 , so that the front and back members  125 ,  130  may rigidly maintain the side members  135  a spaced distance apart. One or more intermediate members  140  may be affixed to the lower surface of the side members  135  to provide additional structural rigidity to the frame  110 . 
   The side members  135  may be seen in cross-section more clearly in  FIG. 4 . They may be fabricated in the form of opposing C-shaped channels  145  with an extending flange  141  along the upper surface of the channel  145 . Since the cross-sectional area may be constant throughout the length of the side members  135 , they may be advantageously fabricated by means of extrusion. They may be comprised of any lightweight material that is amenable to extrusion, such as aluminum, stainless steel, plastics, or graphite fiber material. In the case of aluminum, aircraft grade  1060  aluminum has been found to be extremely resistant to corrosion and is advantageously used in wet environments. In the case of stainless steel, it has been found that further weight reduction can be achieved by providing longitudinal fluting along the vertical portions of the side member, the fluting achieved by removing material from the vertical portions to form oblong holes. In the case of graphite fiber material, the fabrication process may consist of pulling the fibers through a mold in the presence of a binder, or resin matrix; such a process may be termed pultrusion instead of extrusion. However, any process whereby a malleable material is forced through a shaped die, whether that process is termed pultrusion or extrusion, may be used to fabricate the side members  135  without departing from the scope of the invention. Furthermore, the side members  135  may also be fabricated by affixing individual longitudinal portions to one another, as by welding, gluing, braising, and other similar methods. 
   At the back end  120 , a pair of downwardly extending roller members  150  may be affixed to an outer surface  146  of the side members  135  and flush with the underside of the flange  141 . The roller members  150  may each provide support for a roller  155  positioned to vertically extend slightly higher than a lower surface of the track  145 . Thus any object that may slide along the track  145  may be kept out of contact with the lower surface  147  of the track  145  in the vicinity of the back end  120 . Each roller  155  may be supported for rotational movement by an axle  156  extending horizontally from the roller member  150  and positioned horizontally from the roller member  150  by a bushing  157 . The axle  156  may be held in place by a pair of nuts  158 , although any similar retaining means may be used without departing from the scope of the invention. The back member  130  may support a horizontally-oriented pulley  160  that may be approximately, centrally positioned along the back member  130 . The pulley  160  may receive the cable  104  along its circumference, as will presently be seen. 
   At the front end  115 , a rearwardly-extending bracket  116  may be affixed to and supported along a central portion of the front member  125 . The bracket  116  may provide support a horizontally-mounted capstan  117  for rotational movement. The capstan  117  may be driven by a motor  119  through a gear reduction means  118 . The cable  104  may be wrapped one or more times about the capstan  117  as needed to provide frictional contact thereto, so that the cable  104  may be actuated for reciprocal motion by the motor  119 . The motor  119  may be made to operate in two different directions by use of a control switch (not shown). One or more stops  245  may be positioned along the front member  125  to cushion the approach of the carriage  102 . Each stop  245  may be configured with a first limit switch (not shown) that may cut power to the motor  119  whenever the carriage  102  encounters the stop  245 . A second limit switch (not shown) may be configured with an arbitrary position along the back end  120  to similarly cut power to the motor  119  whenever the ramp  101  extends a desired distance beyond the back end  120 . The location of the second limit switch may be selected depending upon the configuration of the ramp and carriage  101 ,  102  and may be considered to be a design choice to be selected after reasonable experimentation. 
   Because of the unitary nature of the side members  135 , the overall frame  110  may be constructed to provide an exceedingly thin profile for the overall apparatus. The term “profile” means the general volume defined by planes along the upper and lower surfaces of the side members  135 . Profiles in the range of from 3″ to 5″ have been found to be attainable without undue loss of structural strength. Profiles within this range have been found in practice to be advantageous to the configuration of the frame in vehicles where available space is limited. Such profiles do not take into account individual components which may protrude beyond this envelope, such as the motor  119  or the roller members  150 . 
   Referring now to  FIGS. 5 ,  6 , and  7 , the carriage  102  and ramp  101  are shown as being pivotally connected by hinges  210 . The ramp  101  may be a lightweight structure comprised of a pair of longitudinally-extending ramp rails  215  that are interconnected by two or more ramp members  220  to form a simple rectangular form. An upper surface  225  of the ramp  101  may be comprised of any material to provide a continuous or semi-continuous surface upon which materials and people may be moved. The material may comprise wood, solid or stamped sheet metal, quilted sheet metal, expanded metal, or closely spaced rails, or any combination thereof. The upper surface  225  may also be coated as by anodizing, powder coating, or sprayed material so as to resist corrosion, to provide a non-slip surface, provide a pleasing appearance, or any combination thereof. The ramp  101  may lack any projections that may bind, catch, or otherwise prevent the smooth movement of the ramp as it is extended or retracted; notably, the ramp  101  does not contain rollers or pulleys. 
   The ramp  101  may be reciprocally moved along the tracks  145  by the carriage  102 , which may further be actuated by the cable  104 . The carriage  102  may be constructed in the shape of a rectangle with one side removed, or a C shape, with two carriage side members  231  aligned along the tracks  145  and held in spaced relationship along one end by a carriage back member  232 . Each carriage side member  231  may have a plurality of wheels  235  extending laterally therefrom, with the wheels  235  sized for movable insertion within track  145 . The carriage frame defined by the two carriage side members  231  and the carriage back member  232  may be rigidly supported by one or more carriage cross members  233  and one or more carriage brace members  234  in such a way that the cross members and associated shock absorbers  230  are confined to a back portion of the carriage frame, leaving a front portion  236  of the carriage frame unobstructed between the two carriage side members  231 . 
   Referring now to  FIGS. 6 and 7 , a more detailed view of the carriage  102  and its relationship with the frame  110  may be seen. The shock absorber  230  may be comprised of a strut  250  surrounded by a spring  255  that is held in place by a strut cap  260 . One or more shock absorbers  230  may be configured to the carriage  102 . Each shock absorber  230  may be supported in a position below the carriage  102  by one or more downwardly extending brackets  261 , so that the strut  250  extends through aligned holes in each of the brackets  261  and held in place by standard means well known in the art. The spring  255  is disposed so that, when the strut cap  260  encounters an obstacle, the strut  250  is forced through the holes in brackets  261 , thereby compressing the spring  255  between the strut cap  260  and a bracket  261  so as to resist the obstacle. Each shock absorber  230  may be positioned below the carriage  102  so that the strut cap  260  will encounter the back member  130  of the frame  110  at approximately the same time as the carriage  102  travels towards the back end  120 , thus preventing further movement in that direction. 
   In another embodiment of the invention, the shock absorbers  230  may be mounted on the frame  110 , and in particular, on the back member  130 . This embodiment may be employed if it is desired to further reduce clearance beneath the carriage  102  or if intermediate members  135  are required but found to interfere with the traversal of the shock absorber  230  thereover. In this embodiment, a forward facing shock absorber  230  may be positioned to encounter a horizontal surface of the carriage  102  as it approaches the back end  120  in a manner similar to that depicted in  FIG. 10 . One of the carriage cross members  233  may have a surface that extends slightly below the plane of the bottom surface of the carriage, so that it may encounter the strut cap  260  of a shock absorber  230 . The precise positioning of the shock absorber  230 , the carriage cross member  233 , and the bracket  261  supporting the shock absorber  230  and the tension of the shock absorber  230  may be adjusted through simple experimentation to determine the proper spacing and placement that would allow the ramp  101  to slowly descend when extended from the back end  120  of the frame  110 . 
   The ramp and carriage  101 ,  102  may be configured to the frame  110  by inserting the carriage  102  through the back end  120  of the frame  110 , so that the wheels  240  are closely contained within the tracks  145 . The ramp  101  may be sized in length so that, when the carriage  102  is positioned at the back end  120  of the frame  110  with the carriage side members  231  abutting the stops  245 , the ramp  101  may be supported at its free end by the rollers  155 . The ramp rails  215  may thus be confined within the tracks  145  and suspended above the lower surface  147  of the tracks  145 . 
   A tensioning mechanism  265 , shown in  FIG. 7 , may be provided to maintain the cable  104  in a taunt position. The tensioning mechanism  265  may comprise a plunger  267  with surrounding coil spring  266  that is prevented from removal from the plunger  267  by an end plate  269  fixedly attached to a forward end of the plunger  267  and supporting one end of the spring  266 . A downwardly extending bracket  270  may have a hole through which the back end of plunger  267  is inserted, thus capturing the spring  266  between the end plate  269  and the bracket  270 . Connected to the back end of plunger  267  may be an attachment means  268  that may provide an attachment point for an end of the cable  104 . An embodiment of an attachment means  268  may be seen in  FIG. 8 . Here, the end of the cable  104  may have a button, or some protuberance larger in diameter than the diameter of the cable  104 , permanently attached thereto as by swaging. The end having the button may then be inserted into a slot  275  that is wide enough to accept the cable  104  but prevents the button from being pulled through. In this way, the cable  104  can easily be replaced without trouble. The tensioning mechanism  265  may maintain a variable tension on the cable  104  so that no undue stress is placed upon the cable  104  when the carriage  102  approaches either end of the frame and experiences resistance to further movement. 
   The cable  104  may be arranged to communicate rotary motion of the capstan  117  to provide reciprocal motion to the ramp and carriage  101 ,  102 . The cable  104  may be connected at one end to the tensioning mechanism  265 . Thence, it may extend towards the back end  120 , around the pulley  160 , back towards the front end  115 , around the capstan  117  several turns, and then terminated at a carriage cross member  233  by an attachment means  275 . The capstan  117  ( FIG. 9 ) may have a tapered barrel  302  between its hubs  301 , so that a cable  104  wrapped several turns about the barrel  302  may be observed to travel towards the large end  303  of the barrel  302  when the barrel rotates in a clockwise direction  307  and towards the small end  304  when the barrel  302  rotates in a counterclockwise direction  308 . When the cable  104  is wound towards the large end  303  of the barrel  302 , then more of the cable  104  comes in contact with the barrel  302  for each revolution, resulting in more rapid movement of the ramp and carriage  101 ,  102  but less power exerted on the cable  104  due to the increased moment arm. Conversely, when the cable  104  is wound towards the small end  304  of the barrel  302 , then more less cable of cable  104  comes in contact with the barrel  302  for each turn, resulting in less rapid movement of the ramp and carriage  101 ,  102  but more power being exerted on the cable  104  due to the decreased moment arm of the capstan  117 . Thus, when a capstan  117  with a tapered barrel  302  is employed within the invention, the choice of orientation of the tapered barrel  302 , direction of rotation of the barrel  302 , position of the cable  104  on the barrel  302 , and number of turns of the cable  104  about the barrel  102  may be advantageously chosen so that the cable moves in a direction  305  towards the large end  303  when the ramp and carriage  101 ,  102  are being retracted, and the cable moves in a direction  306  towards the small end  304  when the ramp and carriage  101 ,  102  are being extended. 
   In operation, the motor  119  may be energized by a control means having a three switch position that may direct the motor to either turn off, turn in a clockwise direction, or turn in a counterclockwise direction. If the ramp and carriage  101 ,  102  are at the front end  115 , then one of the clockwise or counterclockwise switch positions, but not both, will result in no movement of the ramp and carriage  101 ,  102 , since the carriage would be forced against the limit switch at the front end  115  which would immediately deenergize the motor. The other switch position, either counterclockwise or clockwise switch position, would result in movement of the ramp and carriage  101 ,  102  towards the back end  120  of the frame  110 . The choice of which switch position results in rearward motion may be a design choice and dependent upon the orientation of the motor  119  and the capstan  117 . 
   As the ramp  101  horizontally extends beyond the back end  120 , with the rollers  155  serving as a fulcrum and the extended portion of the ramp  101  serving as a lever, the downward force exerted on the extended end of the ramp  101  by the force of gravity increases, resulting in an increasing, horizontally directed component of force being exerted against the cable  104 . As the carriage  102  approaches the back end  120 , the strut caps  260  of the shock absorbers  230  may encounter the back member  130  of the frame  110 , resulting in an opposing force against this horizontally directed component of force. This opposing force exerted by the shock absorbers  230  may allow the carriage movement to slow down as it approaches the back end  120 , so that the extended portion of the ramp  101  may pivot downwardly about the rollers  155  and allow the end of the extended ramp  101  to encounter the solid surface without undue shock. Use of a tapered barrel  302  working in cooperation with the shock absorbers  230  may also provide additional power to resist the downward movement of the extended ramp  101 . The second limit switch may be encountered before the wheels  240  of the carriage  101  encounter the rollers  155 , the ramp  101  is extended an unacceptable distance beyond the frame  110 , or both. 
   Retraction of the ramp and carriage  101 ,  102  may be performed in a manner similar to that of extension of the ramp  101 . The motor  119  may be energized through the control means by selecting the switch position that was not selected for extension of the ramp  101 . As the cable  104  pulls the carriage  102  back towards the front end  115 , the ramp  101  may be levered over the rollers  155  serving as a fulcrum and pulled back into the tracks  145  of the frame  110 . The carriage  102  may encounter the first limit switch as it approaches the front end  115 , which would deenergize the motor  119 . 
   An innovative extendable ramp has thus been presented. This invention may also find application in a number of areas that require a ramp to easily traverse the distance between a vehicle and a solid surface. Such applications may be the use on trailer trucks for extending a ramp to allow small machinery and/or goods to be loaded therein. It may also be used in the aircraft industry for servicing vehicles that must move supplies and provisions to and from the aircraft. Other uses may suggest themselves without departing from the scope of this invention. 
   While the invention has been illustrated by disclosing a number of embodiments herein and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character. It should be understood that only the preferred embodiments have been shown and described and that all changes and modifications that come within the spirit of the invention are desired to be protected. With respect to the above description, it should be further understood that the optimum dimensional relationships for the parts of the invention, to include variations in size, materials, shape, form, function and manner of operation, assembly and use, are deemed readily apparent and obvious to one skilled in the art, and all equivalent relationships to those illustrated in the drawings and described in the specification are intended to be encompassed by the present invention.