Patent Publication Number: US-9845646-B2

Title: Pipe handler

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit under 35 USC 119(e) of provisional application No. 61/683,709 filed Aug. 15, 2012 herewith of like title and inventorship, and also claims the benefit under 35 USC 119(e) of provisional application No. 61/814,266 filed Apr. 20, 2013 herewith of like title and inventorship, the entire contents of each which are incorporated herein by reference in entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention pertains generally to material or article handling, and more particularly to a pipe handler such as might commonly be used in the oil drilling and rigging industry to assist with the handling of very large and heavy pipes that are regularly raised to and lowered from an elevated drilling platform. 
     2. Description of the Related Art 
     In the oil drilling and rigging industry, drilling platforms commonly referred to as derricks are assembled above the earth. These derricks facilitate the drilling and installation of wells. The platform or work floor typically may be elevated many feet above the ground. 
     Drill strings of very large and heavy pipes are assembled or disassembled on the derrick. For exemplary and non-limiting purposes, these pipes may be stored horizontally on or near the ground adjacent to the derrick. This means that these very large and heavy pipes must be re-oriented from horizontal to more nearly vertical orientation, and raised from near ground level to several tens of feet into the air. Consequently, the handling of these large and heavy pipes is not suited to manual labor, and instead requires mechanical assistance. 
     Pipe handlers are commonly be used to assist with the handling of these very large and heavy pipes that are regularly raised and lowered from an elevated drilling platform. A large number of patents are exemplary of this technology, and provide the background for the basic features, while also contrasting with the novel features of the present invention. These U.S. patents, the contents and teachings which are incorporated herein by reference, include: U.S. Pat. No. 2,643,006 by King, entitled “Automatic pipe handler,” that illustrates an early automatic pipe handler, and describes a bumper or stop having a resilient portion in the form of a rubber or spring against which the drill pipe may abut, that prevents a pipe section from sliding down the dolly. U.S. Pat. No. 3,792,783, entitled “Pipe Handling System” and U.S. Pat. No. 3,916,500 entitled “Pipe handling apparatus”, each by Cicero C. Brown, the contents and teachings which are incorporated herein by reference, describe another early automatic pipe handler having an endless cable or chain driving a lug to elevate a pipe in a trough to push the pipe toward the derrick. This same lug is also used to control the rate of descent of the pipe. U.S. Pat. No. 4,386,883 by Hogan et al, entitled “Materials lifting apparatus” and U.S. Pat. No. 4,494,899 by Hoang et al, entitled “Pipe trough for transporting pipe between upper and lower positions”, the contents and teachings which are incorporated herein by reference, each describe automatic pipe handlers with kickers to assist with the loading and unloading of pipes. Hogan refers to these kickers as pipe ejecting assemblies that eject the pipe from the carriage using an arm and a ram, and Hoang et al refers to these as unloading arms for ejecting the pipe from the trough. Hoang et al also describe pipe loading arms to assist with loading pipe into the trough. U.S. Pat. No. 4,235,566 by Beeman et al, entitled “Pipe-conveying catwalk” and U.S. Pat. No. 4,439,091 by Frias, entitled “Pipe feeding system”, the contents and teachings which are incorporated herein by reference, each illustrate carriages that move along a trough. The teachings and content of U.S. Pat. No. 3,559,821 by James, entitled “Drill Pipe Handling Apparatus” and which illustrates another drill pipe handling apparatus, is additionally incorporated herein by reference. 
     Additional U.S. patents illustrating various kicker constructions, the teachings and contents which are incorporated herein by reference, include: U.S. Pat. No. 4,140,227 by Beck, entitled “Cable way apparatus for transporting pipe”; and U.S. Pat. No. 4,403,898 by Thompson, entitled “Pipe pick-up and laydown machine”. Additional patents showing rigid pipe handler structures, the teachings and contents which are incorporated herein by reference, include: U.S. Pat. No. 2,880,881 by Robishaw, entitled “Unitized pipe rack”; U.S. Pat. No. 2,958,430 by Robishaw, entitled “Pipe rack and lay-down trough”; U.S. Pat. No. 4,684,314 by Luth, entitled “Pipe handling apparatus”; U.S. Pat. No. 6,079,925 by Morgan et al, entitled “Method and apparatus for lifting oilfield goods to a derrick floor”; U.S. Pat. No. 7,635,249 by Guidroz, entitled “Pipe pick-up and laydown apparatus”; U.S. Pat. No. 7,665,944 by Guidroz, entitled “Pipe pick-up and laydown apparatus and method”; U.S. Pat. No. 7,992,646 by Wright et al, entitled “Horizontal offline stand building system”; and U.S. Pat. No. 8,052,368 by Littlewood et al, entitled “Catwalk for a drilling rig”. Other relevant patents and published applications, the teachings and contents which are incorporated herein by reference, include: U.S. Pat. No. 6,899,510 by Morelli et al, entitled “Pipe handling system for presenting sections of pipe to a derrick work floor having a pipe ejection assembly”; U.S. Pat. No. 7,021,880 by Morelli et al, entitled “Pipe handling apparatus for presenting sections of pipe to a derrick work floor having a high-speed carriage assembly”; U.S. Pat. No. 7,163,367 by Handley, entitled “Multi-position height adjustment system for a pipe handling apparatus”; and 2008/0263990 by Morelli et al, entitled “Skidding system for a catwalk”. The Handley patent illustrates one technique for adjusting the height of the boom on an automatic pipe handler. In Handley, a plurality of boom ports and arm ports are provided, and one boom port is linked to one arm port through a hinge pin. Thee particular selection made by the hinge pin determines the height of the boom. 
     From these foregoing patents, the basic structure of a pipe handler and the function thereof will be well understood. In addition to the foregoing patents, Webster&#39;s New Universal Unabridged Dictionary, Second Edition copyright 1983, is incorporated herein by reference in entirety for the definitions of words and terms used herein. 
     SUMMARY OF THE INVENTION 
     The present invention provides a novel height adjustment assembly to set the maximum height that the skidway or trough, also sometimes referred to as the boom, will reach when the hydraulic lift cylinder is fully extended. 
     In a first manifestation, the invention is a pipe handler having a height adjustment assembly to set an adjustable maximum height that a skidway will reach above a deck when a hydraulic lift cylinder is extended. A supporting carriage supports at least a first end of the skidway. A lift arm is pivotally coupled to the supporting carriage adjacent a first terminus and is pivotal with respect to the supporting carriage about an axis transverse to a longitudinal axis of the skidway. An internal rack is fixed within the lift arm. An adjustment block couples the internal rack to the skidway. A locking block is coupled to the adjustment block and is operative to rigidly engage with the internal rack when the skidway is displaced from the deck, and thereby prevent relative movement of the adjustment block relative to the internal rack. A drive is operative to reposition the adjustment block longitudinally along the skidway and thereby alter the maximum height that the skidway will reach when the hydraulic lift cylinder is extended. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The objects, advantages, and novel features of the present invention can be understood and appreciated by reference to the following detailed description of the invention, taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  illustrates a preferred embodiment pipe handler designed in accord with the teachings of the present invention from a projected view; 
         FIG. 2  illustrates the preferred skidway and lift arms incorporated in the preferred embodiment pipe handler of  FIG. 1  from an enlarged, projected view with extraneous components hidden from view; 
         FIG. 3  illustrates selected interior components incorporated in the preferred skidway and lift arms of  FIG. 2  from a similar enlarged, projected view; 
         FIG. 4  illustrates selected interior components incorporated in the preferred skidway and lift arms of  FIG. 2  from a rotated, enlarged, projected view better illustrating the internal racks; 
         FIG. 5  illustrates a preferred plate and slide coupling the preferred skidway and lift arms of  FIG. 2  from underneath, by enlarged and projected view; 
         FIG. 6  illustrates an alternative embodiment pipe handler with the exterior components of the skidway and lift arms removed from view to illustrate the internal components therein, taken from a perspective view approximately midway on and slightly elevated above the trailer and viewing from the passenger side thereof; 
         FIG. 7  illustrates the alternative embodiment pipe handler of  FIG. 6  from a slightly more enlarged view and rotated about a vertical axis by approximately 180 degrees with respect to the view of  FIG. 6 , viewing from the driver&#39;s side and rear of the trailer, elevated substantially above the trailer; and 
         FIG. 8  illustrates the alternative embodiment pipe handler of  FIG. 6  from an enlarged perspective view, viewing from the driver&#39;s side and center of the trailer, elevated substantially above the trailer and looking upwards under the adjustment block and towards the passenger side rear of the trailer. 
         FIG. 9  illustrates the preferred embodiment pipe handler of  FIG. 1  illustrating the hydraulic lift cylinder and secondary hydraulic boom unlock cylinder in association with a lift arm, by a vertical and longitudinal section view taken along section line  9 ′ of  FIG. 1 . 
         FIG. 10  illustrates a preferred lift arm used in the preferred embodiment pipe handler of  FIG. 1  with a cam lock in a locked position, by a section view taken adjacent to a locking block along section line  10 ′ of  FIG. 5 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Manifested in the preferred embodiment, the present invention provides a pipe handler trailer  100  for use in the oil drilling and rigging industry and other appropriate industries to assist with the handling of very large and heavy pipes that are regularly raised to and lowered from an elevated surface such as a drilling platform. While a trailer is not critical to the operation of the invention, and so the pipe handler apparatus could conceivably be provided on a self-propelled vehicle such as a truck, or alternatively provided on a fixed structure without wheels, the provision of various trailer components such as a tongue assembly  110  with hitch  112 , wheels  114 , support legs  116 , and trailer undercarriage  118  illustrated in  FIG. 1  allow the preferred embodiment pipe handler trailer  100  to be transported conveniently to more than one drilling derrick. If a self-propelled vehicle such as truck were used, then the capital investment in the drive train and cab is tied up in the apparatus, and, since the pipe handler may be left at a single platform for extended periods, the drive train and cab are unavailable for use. Instead, the preferred embodiment pipe handler trailer  100  may be quickly anchored by dropping support legs  116 , which will preferably be independently adjustable to accommodate uneven surfaces, and then quickly disconnecting hitch  112  from a towing vehicle. The towing vehicle is then free for other productive use. 
     Trailer top  120  includes a deck  122  which in the preferred embodiment may be provided with one or more small gaps within which are provided pick-up and indexing arms  124  that facilitate the loading of pipes onto deck  122 . A motor, hydraulic pump and associated controls and components may be provided in power box  126 , though any suitable source of energy and motive power may be provided within the constraints of the present invention. 
     In accord with the teachings of the present invention, a novel height adjustment assembly is used to set the maximum height that the skidway or trough  130 , also sometimes referred to as the boom, will reach when a hydraulic lift cylinder  143  is fully extended. When stored, such as during periods of non-use or during transport, skidway  130  will preferably nest within deck  122 . Likewise, when a pipe is being loaded from deck  122  into trough  131 , skidway  130  will also be lowered and nested within deck  122 . 
     In the preferred embodiment pipe handler trailer  100  illustrated in  FIGS. 1-5 , the elevation of the skidway, whether nested within deck  122  or angled upward and rearward therefrom, is controlled by boom lift  140 . Boom lift  140  incorporates a pair of lift arms  141 ,  142  that are pivotally mounted onto the trailer undercarriage  118  adjacent the back end or rear of pipe handler trailer  100 . Lift arms  141 ,  142  pivot about an axis transverse to the longitudinal axis of the trailer, and the amount of pivot is controlled by hydraulic lift cylinder  143 . As lift arms  141 ,  142  raise in a clockwise direction as seen in  FIGS. 1 and 2  from a stored or lowermost position parallel to the trailer longitudinal axis, they carry skidway  130  both rearwardly along the trailer longitudinal axis, and also raise the rearward most point of skidway  130  significantly above deck  122 . Note that the forward most point of skidway  130  stays much closer to deck  122 , regardless of the pivotal orientation of lift arms  141 ,  142 . 
     Skidway  130  includes a trough  131  for receiving and holding a pipe during conveyance. This trough may be sized for a single pipe diameter, but will more typically be dimensioned to support the largest pipe for which the pipe handler trailer  100  is designed to accommodate. Various apparatus known in the art may optionally be provided to better secure, retain or hold pipes, whether the maximum size or smaller, safely in the trough, including various hoops, covers or the like. 
     In preferred embodiment pipe handler trailer  100 , and most visible in  FIG. 2 , located intermediate along skidway  130  are a plurality of flippers or kickers  132 - 135  that are operative to kick a pipe out of trough  131 . Kickers may preferably be provided in pairs, such as  132 ,  133 . In such case, kicker  132  may preferably be used to flip the pipe to a first side of the trailer herein identified as the passenger side, which corresponds to the side of the towing vehicle a passenger in the front seat would be seated. In this case, kicker  133  for exemplary purposes will flip the pipe to the opposite or driver&#39;s side of the trailer. While the exact number and placement of kickers is not critical to the invention, providing at least two pairs of kickers at distal locations along trough  131  helps to ensure smooth discharge of pipes from the trough. 
     Adjacent to the forward end of the trailer and positioned to roll along the top surface of trough  131  is skate  136 . Skate  136  may preferably be provided with a cradle  137  which holds one end of a pipe, and also with a backstop  138  which preferably rises above cradle  137  to engage the end of a pipe along a transverse plane. This allows skate  136  to cradle and move a pipe along trough  131 , to raise or lower the pipe relative to trailer deck  122 . 
     Skate  136  is driven longitudinally along trough  131  by a drive  150 , which in the preferred embodiment pipe handler trailer  100  is an endless chain  153  wrapping at distal ends of trough  131  about sprockets  151 ,  152 . At least one of sprockets  151 ,  152  will be connected to a source of motive power, such as through a hydraulic coupling back to power box  126 , though once again, any suitable source of motive power may be used. Furthermore, other methods and apparatus may be used to move skate  136  longitudinally along trough  131 . 
       FIG. 3  illustrates selected interior components incorporated in the preferred skidway and lift arms of  FIG. 2 , with the size and viewing angle maintained to be similar to  FIG. 2  to allow inspection and comparison there between. Skate underbody  139  is illustrated therein, to give perspective on component location. Further towards lift arms  141 ,  142  is a single kicker  133 , once again to maintain perspective. Surrounding kicker  133  is structure which operates through a plunging motion to activate kickers  132 - 135 , though the structure used for such activation is not important to the present invention, and prior art methods and apparatus incorporated herein above by reference may also be used. 
     Located within lift arms  141 ,  142  are toothed racks  144 ,  145 , respectively. The arrangement of lift arm  141  within rack  144  is visible in  FIG. 5 , with it understood that each rack will be rigidly fastened or affixed to the associated lift arm. This may be through removable or permanent fastening techniques, as will be determined by one skilled in the art of fabrication. 
     Coupling skidway  131  to lift arms  141 ,  142  through racks  144 ,  145  is adjustment block  160 . Again as best illustrated in  FIG. 5 , plate  164  and slide  162  sandwich about slide members  163 ,  165  that are supported and affixed within skidway  130 . This arrangement ensures that adjustment block  160  tracks and follows slide members  163 ,  165 . Plate  164  and slide  162  are rigidly coupled to a shaft  166  as best illustrated in  FIG. 4 . Shaft  166  pivotally passes through toothed locking blocks  168  that have teeth  169  complementary to the teeth on toothed racks  144 ,  145 . Shaft  166  then terminates through rigid coupling with cam lock  167 . 
     Because of the rigid couplings to shaft  166 , cam locks  167  are also rigidly coupled with plate  164  and slide  162 . This means that as lift arms  141 ,  142  rotate relative to skidway  130 , the surface of cam locks  167  most nearly adjacent to lift arms  141 ,  142  changes. By shaping the outer perimeter geometry of cam locks  167  to vary in radial distance from shaft  166 , and thereby define a cam surface which changes in radial distance with angular rotation, cam locks  167  will vary from firm contact with the inner wall of lift arms  141 ,  142  to having a gap there between, depending upon the angular orientation of skidway  130  relative to racks  144 ,  145 .  FIG. 10  illustrates a sectional view of lift arm  142  adjacent to locking block  168 , with cam lock  167  protruding above locking block  168  (in the orientation of the drawing figure) and thereby engaging the inner wall of lift arm  142 . This contact in turn forces locking block  168  downward (again, in the orientation of the drawing figure), which then drives complementary teeth  169  into secure engagement with the teeth of rack  145 . Consequently, when in firm contact with the inner wall of lift arms  141 ,  142 , this also means that locking blocks  168  will be forced into locking engagement with racks  144 ,  145 , ensuring that the locking blocks  168  are rigidly coupled to the respective racks  144 ,  145  by the complementary teeth  169 , and can support great strength without inducing relative motion there between. Most preferably, cam locks  167  will be shaped such that at some relatively small angular difference between skidway  130  and racks  144 ,  145 , cam locks  167  will securely engage the inner wall of lift arms  141 ,  142  and will also lock racks  144 ,  145  together to locking blocks  168 . However, when skidway  130  and racks  144 ,  145  are parallel, most preferably there will be a gap between cam locks  167  and the inner wall of lift arms  141 ,  142 . 
     The relative position of locking blocks  168  along racks  144 ,  145  is adjusted in preferred embodiment pipe handler trailer  100  only when skidway  130  is fully lowered into deck  122 , which results in skidway  130  and racks  144 ,  145  being parallel. Once lowered, then it will be apparent that locking blocks  168  are positioned directly vertically above racks  144 ,  145 . In this position, cam locks  167  are spaced from the inner wall of lift arms  141 ,  142 , allowing locking blocks  168  to be moved vertically away from racks  144 ,  145 . This vertical movement of locking blocks  168  relative to racks  144 ,  145  is achieved through a secondary unlock actuator  180 , visible in  FIG. 9 . Secondary unlock actuator  180  may as in the preferred embodiment include hydraulic boom unlock cylinder  182  as a source of motive power, and may be located adjacent to lift cylinder  143 . A pivotal coupling  186  couples undercarriage  118  to a lifter arm  184  located underneath but in contact with skidway  130  when skidway  130  is fully lowered. Skidway  130  will only be lifted slightly by actuation of hydraulic boom unlock cylinder  182 , but sufficiently to lift complementary teeth  169  on adjustment block  160  away and fully separated from racks  144 ,  145 . Next, hydraulic height adjustment cylinder  170 , which couples on a first end to skidway  130  and on a second end distal thereto to slide  162  as visible in  FIG. 4 , may be activated to move adjustment block  160  longitudinally along racks  144 ,  145  to a new position. When cylinder  170 , located within skidway  130  and visible in  FIG. 4 , is fully retracted, this positions adjustment block  160  closest to the tops of racks  144 ,  145  in  FIG. 4 , meaning skidway  130  will be raised to the greatest elevation using boom lift  140 . Alternatively, when cylinder  170  is fully extended, this will drive adjustment block  160  towards the bottom of racks  144 ,  145 , which will then result in a lower maximum elevation. Optionally, marks or other appropriate structure corresponding to various platform heights may be provided along one or more of lift arms  141 ,  142  and skidway  130 , so an operator can determine even when skidway  130  and boom lift  140  are fully lowered where to position adjustment block  160  relative to lift arms  141 ,  142 . 
     In an alternative embodiment to preferred embodiment pipe handler trailer  100  contemplated herein, hydraulically controlled locking blocks such as blocks  268  described herein below are used instead of locking blocks  168 . To change the height that skidway  130  reaches, or in other words to adjust pipe handler trailer  100  to a particular derrick platform elevation, lift arms  141 ,  142  and skidway  130  are fully lowered. This will then trigger a safety switch, detector or the like. When the safety switch is triggered, this in turn allows an operator to release locking blocks  168  from racks  144 ,  145  through hydraulic or other control Once locking blocks  168  are released, the operator may then activate hydraulic height adjustment cylinder  170  to move adjustment block  160  longitudinally along lift arms  141 ,  142 , simply by retracting or extending hydraulic height adjustment cylinder  170 . 
     Retracting the cylinder will cause adjustment block  160  to be drawn to the end of travel on lift arms  141 ,  142  and racks  144 ,  145 . When in this position, and when lift arms  141 ,  142  are subsequently raised by action of hydraulic lift cylinder  143 , skidway  130  will reach to the maximum height. To set pipe handler trailer  100  to raise skidway  130  to the minimum height, the operator will lower lift arms  141 ,  142  and skidway  130 , if they are not already lowered, which triggers the safety switch. Then the operator will release locking blocks  168 , and next extend hydraulic height adjustment cylinder  170 . 
     The limits of travel of adjustment block  160  along lift arms  141 ,  142  may be set by travel limit detectors, switches or the like. In addition to, or alternatively, the limits may be set by limits built or incorporated into hydraulic height adjustment cylinder  143 . 
     An alternative embodiment pipe handler trailer  200  is illustrated in  FIGS. 6-8  that has very similar construction to the preferred embodiment pipe handler trailer  100  illustrated in  FIGS. 1-5 , performs the same function, and includes the same basic structures, such as a wheel set  214 , deck  222 , supporting framework, skidway  230 , and lift arms  241 ,  242  with racks  244 ,  245 . The two different embodiment pipe handler trailers  100 ,  200  are distinguished by the hundreds digit, and various components within each embodiment pipe handler are designated by the ones and tens digits. However, many of the components are alike or similar between the two illustrated pipe handler embodiments, so numbering of the ones and tens digits have been maintained wherever possible, such that identical, like or similar components and functions will share the same tens and ones digits between the embodiments, and may more readily be identified and recognized between the embodiments. If not otherwise expressed, those skilled in the art will readily recognize the similarities and understand that in many cases like numbered ones and tens digit components may be substituted from one embodiment to another in accord with the present teachings, except where such substitution would otherwise destroy operation of the embodiment. Consequently, those skilled in the art will readily determine the function and operation of many of the components illustrated herein without unnecessary additional description. Furthermore, where a component is referenced by a particular reference numeral in one embodiment but not explicitly illustrated, it will be understood herein that the reference numeral of the corresponding other embodiment is being referenced. So, for exemplary purposes, since the exterior view of  FIG. 1  showing preferred embodiment pipe handler trailer  100  illustrates wheel set  114 , and since there is no reference numeral  214  explicitly shown, it will be understood that wheel set  214  is referring to a wheel set identical to wheel set  114 , but found on the alternative embodiment pipe handler trailer  200  rather than on the preferred embodiment pipe handler trailer  100 . 
     While many components are identical, as illustrated in  FIGS. 6-8  screw adjustment  270  in alternative embodiment pipe handler  200  uses acme screws  271 ,  272  that are rotated through a hydraulic motor  273  and reversing gear  274  to counter-rotate the screws and thereby to move adjustment block  260 , instead of using hydraulic height adjustment cylinder  170 . In this alternative embodiment, the acme screws  271 ,  272  are rotated to extend or retract adjustment block  260  when skidway  230  is fully lowered, similar to but instead of hydraulic cylinder  170  found in preferred embodiment pipe handler  100  of  FIGS. 1-5 . 
     Adjustment block  260  has internal threads where acme screws  271 ,  272  pass through. These internal threads mate with threads on the acme screws  271 ,  272 , and the ends of acme screws  271 ,  272  are fixed within and relative to skidway  230 . Since internal racks  244 ,  245  are fixed within lift arms  241 ,  242 , rotation of acme screws  271 ,  272  will apply forces that will cause adjustment block  260  to move relative to the racks. 
     Before the lift arms  241 ,  242  are rotated by the hydraulic lift cylinder  243 , and while they are fully lowered to a location nearly or fully parallel with deck  222 , a switch or the like is triggered that then, and only then, will allow motor  273  coupled to the end of the acme screws  271 ,  272  to turn. In this embodiment, motor  273  is a hydraulic motor, but other types of motors will be understood to reasonably be substituted therefore. Additional safety and strength in the adjustment assembly may be provided by a pinion gear within locking blocks  268  that rolls on associated racks  244 ,  245 . Locking blocks  268  may also preferably include locking cylinders  267  that otherwise prevent relative movement between adjustment block  260  and internal racks  244 ,  245 . In this alternative embodiment pipe handler trailer  200 , locking cylinders  267  perform the function of cam lock  167 , but instead of being a cam activated by rotary motion, cylinders may be provided that are hydraulically or otherwise actuated to engage with arms  241 ,  242 , creating the same pressure from that engagement that is generated by cam lock  167 . The locking cylinders, for exemplary purpose only and not limiting thereto, may comprise features  269  such as complementary teeth that engage with the teeth on the internal racks  244 ,  245 . These features  269  are ordinarily biased such as through spring, hydraulic, magnetic, gravitational or other force to engage securely with internal racks  244 ,  245  and prevent relative motion between features  269  and the racks. Only when motive forces are applied or removed to neutralize locking cylinders  267 , such as through a hydraulic cylinder, electrical solenoid or other suitable motive power source will the locking cylinders  267  release features  269  from the rack teeth. When the switch is triggered, signifying that skidway  230  has been lowered, then these locking cylinders  267  may also be released to permit this relative movement. 
     While  FIG. 6  solely illustrates locking cylinders  267  in association with locking blocks  268 ,  FIGS. 7 and 8  illustrate a further alternative embodiment comprising both locking cylinders  267  and cam locks  367 , either or both which may be utilized to lock locking blocks  268  to racks  244 ,  245 . 
     When acme screws  271 ,  272  are rotated, the point at which skidway  230  couples to lift arms  241 ,  242  through adjustment block  260  will change, and may preferably be adjustable from a lowermost point on the lift arms that is relatively close to deck  222  to a highest point on the lift arms relatively distal to deck  222 . The length of the internal racks  244 ,  245  and the length of acme screws  271 ,  272  will limit the extent of adjustment available. Since this relative movement changes the height of the skidway  230  end adjacent the rear of the trailer when lift arms  241 ,  242  are raised, rotating acme screws  271 ,  272  will adjust the height to a desired target height. Since the height of the drilling platform will vary between different drilling rigs, this permits both the maximum height (perpendicular to the trailer longitudinal axis) that skidway  230  can reach, and the stroke that skidway  230  travels parallel to the trailer  200  longitudinal axis as it is raised and lowered, to be changed through a very large number of positions and settings. By incorporating adequate locking cylinders and safety switches, these height and stroke settings can only be changed when skidway  230  is fully lowered, so that there is no risk of the skidway suddenly dropping during use. Where desired, markings may be provided on skidway  230  that correlate a relative position between the skidway and lift arms  241 ,  242  to a predetermined maximum height. 
     While the foregoing details what is felt to be the preferred and alternative embodiments of the invention, no material limitations to the scope of the claimed invention are intended. Further, features and design alternatives that would be obvious to one of ordinary skill in the art are considered to be incorporated herein. The scope of the invention is set forth and particularly described in the claims hereinbelow.