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CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation application of application Ser. No. 13/466,911 filed May 8, 2012, which is a continuation-in-part of and claims the benefit of priority to application Ser. No. 12/418,302 filed Apr. 3, 2009, now U.S. Pat. No. 8,172,497. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to the delivery of tubulars from a horizontal orientation to a vertical orientation at a well head. Particularly, the present invention relates to a pipe handling apparatus that positions tubulars at a wellhead. More particularly, the present invention relates to a device for assisting pivotal movement of a boom relative to a base of a pipe handling apparatus. 
       BACKGROUND OF THE INVENTION 
       [0003]    Drill rigs have utilized several methods for transferring tubular members from a pipe rack adjacent to the drill floor to a mousehole in the drill floor or the well bore for connection to a previously transferred tubular or tubular string. The term “tubular” as used herein includes all forms of pipe, drill pipe, drill collars, casing, liner, bottom hole assemblies (BHA), and other types of tubulars known in the art. 
         [0004]    Conventionally, drill rigs have utilized a combination of the rig cranes and the traveling system for transferring a tubular from the pipe rack to a vertical position above the center of the well. The obvious disadvantage with the prior art systems is that there is a significant manual involvement in attaching the pipe elevators to the tubular and moving the pipe from the drill rack to the rotary table at the wellhead. This manual transfer operation in the vicinity of workers is potentially dangerous and has caused numerous injuries in drilling operations. Further, the hoisting system may allow the tubular to come into contact with the catwalk or other portions of the rig as the tubular is transferred from the pipe rack to the drill floor. This can damage the tubular and may affect the integrity of the connections between successive tubulars in the well. 
         [0005]    In the past, various devices have been created which mechanically move a pipe from a horizontal orientation to a vertical orientation such that the vertically-oriented pipe can be installed into the well bore. Typically, these devices have utilized several interconnected arms that are associated with a boom. In order to move the pipe, a succession of individual movements of the levers, arms, and other components of the boom must be performed in a coordinated manner in order to achieve the desired result. Typically, a wide variety of hydraulic actuators are connected to each of the components so as to carry out the prescribed movement. A complex control mechanism is connected to each of these actuators so as to achieve the desired movement. Advanced programming is required of the controller in order to properly coordinate the movements in order to achieve this desired result. 
         [0006]    Unfortunately, with such systems, the hydraulic actuators, along with other components, can become worn with time. Furthermore, the hydraulic integrity of each of the actuators can become compromised over time. As such, small variations in each of the actuators can occur. These variations, as they occur, can make the complex mechanism rather inaccurate. The failure of one hydraulic component can exacerbate the problems associated with the alignment of the pipe in a vertical orientation. Adjustments of the programming are often necessary so as to continue to achieve the desired results. Fundamentally, the more hydraulic actuators that are incorporated into such a system, the more likely it is to have errors, inaccuracies and deviations in the desired delivery profile of the tubular. Typically, very experienced and knowledgeable operators are required to carry out this pipe movement operation. This adds significantly to the cost associated with pipe delivery. 
         [0007]    To address these problems and needs, U.S. application Ser. No. 11/923,451, filed on Oct. 24, 2007 by the present applicant, discloses a pipe handling apparatus that has a boom pivotally movable between a first position and a second position, a lever assembly pivotally connected to the boom, an arm pivotally connected at one end to the first portion of the lever assembly and extending outwardly therefrom, a gripper affixed to an opposite end of the arm suitable for gripping a diameter of the pipe, a link pivotally connected to the lever assembly and pivotable so as to move relative to the movement of the boom between the first and second positions, and a brace having one end pivotally connected to the boom and an opposite end pivotally connected to the arm between the ends of the arm. The lever assembly has a first portion extending outwardly at an obtuse angle with respect to the second portion. 
         [0008]    The pipe handling apparatus delivers a pipe to a wellhead when in the second position. The boom of the above pipe handling apparatus is pivotally connected to a skid so as to pivot between the first and second positions. Pipes can be of extraordinary lengths and weights; therefore, the pivotal connection between the boom and skid must be strong so as to withstand the forces created by the movement of the boom between the first and second positions. Typically, hydraulic cylinders are placed between the boom and skid so as to raise and lower the boom between the first and second positions. The hydraulic cylinders are connected to a hydraulic power system so as to raise and lower the boom between the first and second positions. Through use of the above-discussed pipe handling apparatus, it was found that large amounts of power are needed for certain portions of the power band of the stroke of the hydraulic cylinders. That is, the power requirements for extending the hydraulic cylinders so as to move the boom between the first and second positions is not uniform for the entire movement of the hydraulic cylinders. Thus, there is a need to make the power band of the hydraulic cylinders more uniform across the entire length of travel of the hydraulic cylinders. Moreover, there is a need to reduce the total energy required to move the boom between the first and second positions. 
         [0009]    Various patents have issued relating to the movement of a boom of a pipe handling apparatus with hydraulic cylinders or other similar means. For example, U.S. Pat. No. 7,077,209, issued on Jul. 18, 2006 to McCulloch et al., discloses a mast for lifting and suspending a coiled tubing injector and blowout preventer over a wellhead that is pivotally mounted on a rear portion of a truck. The mast has two side-by-side telescoping legs that extend and retract synchronously. Hydraulic cylinders pivotally move the mast between a lower position and an upper position. 
         [0010]    U.S. Pat. No. 4,336,840, issued on Jun. 29, 1982 to Bailey, discloses a suspension system for use with a mast. The system has two or more fluid pressure piston-and-cylinder assemblies. The cylinders are linked in pairs so that retraction of both piston rods reduces the length of the pair of assemblies to the length of a single assembly. Operation of both pistons in a pair provides an effective stroke twice the length of a single assembly stroke. In a particular embodiment, a double cylinder system is used as a pickup system for elevating equipment along a mast in a well work over rig. 
         [0011]    U.S. Pat. No. 7,289,871, issued on Oct. 30, 2007 to Williams, discloses a drilling apparatus that has a base from which a drilling arm is pivotally mounted. The drilling arm has an inner arm and an outer arm. The inner arm has a first end and a second end. The first end is pivotally connected by a first pivot joint to the base. The outer arm has a first end and a second end. The second end of the inner arm is pivotally connected via a second pivot joint to the first end of the outer arm. A drill-mounting assembly is positioned at the second end of the outer arm. Actuation of the inner and outer arms is achieved by hydraulic cylinders. Proper operation of the cylinders causes the second end of the outer arm to follow a substantially linear path. 
         [0012]    U.S. Pat. No. 6,003,598, issued on Dec. 21, 1999 to Andreychuk, discloses a mobile hybrid rig adapted to run coiled tubing and wireline equipment for oil and gas wells. The rig has a chassis and power unit for transporting the rig. An adjustable platform with a number of hydraulically-operated stabilizers aligns the tubing at the wellhead. A mast is pivotable into slanted or vertical positions for coil tubing operation with a blowout preventer and an injector. A cradle supports and aligns an injector to the wellhead. A coil-tubing reel cartridge assembly is adapted to run coil-tubing reels. A winching facility is used to manipulate wireline equipment. A control cabin is used to manage rig activities. 
         [0013]    U.S. Pat. No. 6,234,253, issued on May 22, 2001 to Dallas, discloses a method and apparatus for servicing a well. The apparatus has a pair of hydraulic cylinders pivotally mounted to a pair of base beams. The cylinders are movable from a horizontal position for transportation to a vertical position for operation. In the vertical position, the cylinders flank a wellhead and are adapted to lift the wellhead and attached production tubing using a workover beam and a lifting sub. The wellhead and production tubing can be rotated during or after elevation. A motor can be mounted to the workover beam to rotate the wellhead and the tubing. A calibrated pressure gauge can be used to indicate the weight being lifted. The apparatus can be connected to a crane truck. 
         [0014]    U.S. Pat. No. 6,264,128, issued on Jul. 24, 2001 to Shampine et al., discloses a levelwind system for a coiled-tubing reel that has an arcuate guide arm extending over the upper surface of the reel, a universal joint mounted to the lower end of the arm, a guide member supported on the free end of the guide arm, a lift cylinder for raising and lowering the guide arm, a balancing cylinder for moving the guide arm laterally, and a hydraulic fluid circuit that is responsive to a position sensor and a microprocessor. 
         [0015]    U.S. Pat. No. 6,431,286, issued on Aug. 13, 2002 to Andreychuk, discloses an injector arrangement for use in a rig that has a movable carrier, a derrick tiltably mounted to the carrier, and a trolley capable of sliding along the derrick. An injector cradle is movable along the trolley in at least a plane perpendicular to the derrick and is pivotally mountable beneath the trolley. An injector is supported at its upper end from the cradle. At least two hydraulic cylinders are supported at one end by the derrick. The cylinders are engaged at an opposed end to a lower end of the injector. 
         [0016]    U.S. Pat. No. 6,502,641, issued on Jan. 7, 2003 to Carriere et al., discloses a hybrid apparatus for operation with both coiled tubing and sectional tubing that has a coiled-tubing rig. The rig has a frame, a mast normally aligned over a wellhead, an injector located on the mast, and a tubing straightener positioned between the injector and the wellhead. A rotary table is affixed to the wellhead for rotationally supporting tubing passing through the wellhead. A jib crane is mounted atop the mast. A mechanism pivots the mast between a first position and a second position. 
         [0017]    It is an object of the present invention to reduce operating pressures of hydraulic cylinders connected to the boom of a pipe handling apparatus. 
         [0018]    It is another object of the present invention to decrease the duty of hydraulic cylinders of a pipe handling apparatus. 
         [0019]    It is another object of the present invention to reduce the peak and average horsepower requirements for pivoting a boom of a pipe handling apparatus. 
         [0020]    It is still another object of the present invention to reduce peak cooling requirements while lowering the boom of a pipe handling apparatus. 
         [0021]    It is another object of the present invention to reduce fuel consumption due to pivoting a boom of a pipe handling apparatus by up to seventy-five percent. 
         [0022]    It is another object of the present invention to create negative gravity accelerations while lowering the boom of a pipe handling apparatus so as to almost “float” the boom. 
         [0023]    It is another object of the present invention to provide extra capacity or speed in horse power of a pipe handling apparatus. 
         [0024]    It is still another object of the present invention to increase the useful life and reliability of a pipe handling apparatus. 
         [0025]    It is another object of the present invention to create lifting mechanisms for a boom of a pipe handling apparatus that are completely separate sub systems that have no significant impact on raising the boom or controlling the boom. 
         [0026]    These and other objects and advantages of the present invention will become apparent from a reading of the attached specification and appended claims. 
       BRIEF SUMMARY OF THE INVENTION 
       [0027]    The present invention is an apparatus for pivoting a boom relative to a frame of a pipe handling system between a first position and a second position. The apparatus includes the frame, a boom pivotally interconnected to the frame so as to be movable between the first position and the second position, a hydraulic actuating assembly having one end affixed to the frame and an opposite end connected to the boom so as to move the boom between the first and second positions, and a pneumatic spring assembly having one end affixed to the frame and an opposite end connected to the boom. The pneumatic spring assembly serves to urge the boom from the first position to the second position while resisting movement of the boom from the second position to the first position. 
         [0028]    The hydraulic actuating assembly comprises a cylinder having one end pivotally coupled to the frame, a piston slidably received in the cylinder and extending outwardly therefrom so as to have an end pivotally coupled to the boom, and a hydraulic fluid pumping assembly fluidically connected to the cylinder. The hydraulic fluid pumping assembly serves to deliver hydraulic fluid to the cylinder so as to urge against the piston so as to move the boom from the first position to the second position. 
         [0029]    The pneumatic spring assembly comprises a cylinder having one end pivotally coupled to the boom and a piston slidably received in the cylinder and extending outwardly therefrom. The piston is pivotally coupled to the frame. The piston defines a gas-containing space within the cylinder. This gas-containing space is filled with a compressible fluid. In the preferred embodiment of the present invention, the compressible fluid is a nitrogen gas. A gas-charging assembly is fluidically coupled to the gas-containing space so as to pass the compressible fluid into the gas-containing space. The gas-charging assembly may be connected to a reservoir for containing compressible fluid. The reservoir may be used to increase or decrease the amount of compressible gas within the cylinder of the pneumatic spring, which in turn increases or decreases the stiffness of the pneumatic spring. This results in increased or decreased pushing and braking forces that the pneumatic spring may exert on the boom. 
         [0030]    In a preferred embodiment of the present invention, the gas-charging assembly may further comprise a feedback mechanism for monitoring the pressure in the gas-containing space, as well as the current load upon the boom as the boom travels between the first and second positions. The feedback mechanism may also operate in real-time for actively monitoring the pressure in the gas-containing space. As the load upon the boom, and therefore the pressure within the gas-containing space changes, the feedback mechanism senses these pressure changes and the gas-charging assembly accordingly adjusts the volume of compressible fluid within the gas-containing space in order to provide greater pneumatic resistance for heavier loads and lesser pneumatic resistance for lighter loads. 
         [0031]    Specifically, the hydraulic actuating assembly comprises a first piston-and-cylinder assembly connected adjacent one side of the frame and adjacent one side of the boom, and a second piston-and-cylinder assembly connected adjacent an opposite side of the frame and adjacent an opposite side of the boom. The pneumatic spring assembly is positioned between the first and second piston-and-cylinder assemblies of the hydraulic actuating means. In the preferred embodiment of the present invention, the pneumatic spring assembly comprises a pair of piston-and-cylinder assemblies extending in generally parallel relation to each other. 
         [0032]    The piston defines a liquid-containing space within the cylinder. This liquid-containing space has a corrosion-resistant liquid therein. 
         [0033]    In the present invention, the pipe handling system further includes a lever assembly pivotally coupled to the boom, an arm pivotally connected at one end to the first portion of the lever assembly and extending outwardly therefrom, a link pivotally connected to the second portion of the lever assembly so as to pivot at an end of the second portion opposite of the first portion so as to move relative to the movement of the boom between the first and second positions, a brace having an end pivotally connected to the boom and an opposite end pivotally connected to the arm, and a gripper attached to an opposite end of the arm for gripping a surface of a tubular. The gripper includes a stab frame fixedly attached to the opposite end of the arm and at least one gripper attached to a side of the stab frame opposite the arm. 
         [0034]    In the preferred embodiment of the present invention, the frame is a skid that extends in a generally horizontal plane. The boom extends in generally parallel relation to the skid in the first position. The boom extends angularly upwardly of the skid in the second position. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0035]      FIG. 1  shows a side elevational view of the apparatus of the present invention as used on a pipe handling system. 
           [0036]      FIG. 2  shows a side elevational view of the apparatus of the present invention as used on a pipe handling system, with the system in a first position. 
           [0037]      FIG. 3  shows a side elevational view of the apparatus of the present invention as used on the pipe handling system, with the pipe handling system moving from the first position toward a second position. 
           [0038]      FIG. 4  shows a side elevational view of the apparatus of the present invention as used on a pipe handling system, with the pipe handling system moving further towards the second position. 
           [0039]      FIG. 5  shows a side elevational view of the apparatus of the present invention as used on a pipe handling system, with the pipe handling system in the second position. 
           [0040]      FIG. 6  shows an isolated plan perspective view of the preferred embodiment of the apparatus of the present invention. 
           [0041]      FIG. 6A  shows an isolated plan perspective of the pneumatic spring assembly and pneumatic reservoirs of the preferred embodiment of the apparatus of the present invention. 
           [0042]      FIG. 7  shows a side perspective view of the preferred embodiment of the apparatus of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0043]    Referring to  FIG. 1 , there is shown a side elevational view of the preferred embodiment of the apparatus  100  of the present invention as used with a pipe handling system  10 . The pipe handling system  10  is mounted on a frame  12  (such as a skid) that is supported upon the bed  14  of a vehicle, such as a truck. The pipe handling system  10  includes a boom  16  that is pivotally movable between a first position and a second position relative to a frame  12 . In  FIG. 1 , an intermediate position of the pipe handling system  10  is particularly shown. In this position, the pipe  18  is illustrated in its position prior to installation on the drill rig  20 . A lever assembly  22  is pivotally connected to the boom  16 . An arm  24  is pivotally connected to an end of the lever assembly  22  opposite the boom  16 . A gripper  26  is fixedly connected to an opposite end of the arm  24  opposite the lever assembly  22 . The gripper  26  includes a stab frame  28  and grippers  30  and  32 . A link  34  has one end pivotally connected to the frame  12  and an opposite end pivotally connected to the end of the lever assembly  22  opposite the arm  24 . A brace  36  is pivotally connected to a small frame member  46  of the boom  16  and also pivotally connected to the arm  24  between the lever assembly  22  and the stab frame  28  of gripper  26 . 
         [0044]    The apparatus  100  of the present invention extends between the boom  16  and the frame  12  of the pipe handling system  10 . The second hydraulic piston-and-cylinder assembly  124  can be seen from side  146  of the frame  12 . The system  10  is in an intermediate position between the first and second positions; thus the piston  156  can be seen as extending outwardly from an interior of the cylinder  148  of the second hydraulic piston-and-cylinder assembly  124 . The other piston-and-cylinder assemblies and pneumatic springs are in extended positions similar to that of the second hydraulic piston-and-cylinder assembly  124 . These pneumatic springs are illustrated in greater detail in  FIGS. 6 and 7 . 
         [0045]    The boom  16  is a structural framework of struts, cross members and beams. In particular, the boom  16  is configured so as to have an open interior such that the pipe  18  will be able to be lifted in a manner so as to pass through the interior of the boom  16 . As such, the end  38  of the boom  16  should be strongly reinforced so as to provide the necessary structural integrity to the boom  16 . A lug  40  extends outwardly from one side of the boom  16 . This lug  40  is suitable for pivotable connection to the lever assembly  22 . The boom  16  is pivotally connected at the opposite end  42  to a location on the frame  12 . The pivotable connection at end  42  of the boom  16  is located in offset relationship and above the pivotable connection  44  of the link  34  with the frame  12 . A small frame member  46  extends outwardly from the side of the boom  16  opposite the link  34 . This frame assembly  46  has a pivotable connection with the brace  36 . 
         [0046]    The lever assembly  22  includes a first portion  48  and a second portion  50 . The first portion  48  extends at an obtuse angle with respect to the second portion  50 . The link  34  is pivotally connected to the end of the second portion  50  opposite the first portion  48 . The arm  24  is pivotally connected to the end of the first portion  48  opposite the second portion  50 . The lug  40  of the boom  16  is pivotally connected in an area generally between the first portion  48  and the second portion  50 . This unique arrangement of the lever assembly  22  facilitates the ability of the present invention to carry out the movement of the pipe  18  between the horizontal orientation and the vertical orientation. 
         [0047]    The arm  24  has an end pivotally connected to the end of the first portion  48  of the lever assembly  22 . The opposite end of the arm  24  is connected to the gripper  26 . In particular, a pair of pin connections engages a surface of the stab frame  28  of the gripper  26  so as to fixedly position the gripper  26  with respect to the end of the arm  24 . The pin connections  52  and  54  can be in the nature of bolts, or other fasteners, so as to strongly connect the stab frame  28  of the gripper  26  with the arm  24 . The bolts associated with pin connections  52  and  54  can be removed such that other gripper  26  can be affixed to the end of the arm  24 . As such, the pipe handling system  10  is adaptable to various sizes of pipe  18  and various heights of drilling rigs  20 . 
         [0048]    The gripper  26  includes the stab frame  28  with the grippers  30  and  32  translatable along the length of the stab frame  28 . This vertical translation of the grippers  30  and  32  allows the pipe  18  to be properly moved upwardly and downwardly once the vertical orientation of the pipe  18  is achieved. The grippers  30  and  32  are in the nature of conventional grippers which can open and close so as to engage the outer diameter of the pipe  18 , as desired. 
         [0049]    The link  34  is an elongate member that extends from the pivotable connection  44  with the frame  12  to the pivotable connection  68  of the second portion  50  of the lever assembly  22 . The link  34  is non-extensible and extends generally adjacent to the opposite side from the boom  16  from that of the arm  24 . The link  34  will generally move relative to the movement of the boom  16 . The brace  36  is pivotally connected to the small framework  46  associated with boom  16  and also pivotally connected at a location along the arm  24  between the ends thereof. Brace  36  provides structural support to the arm  24  and also facilitates the desired movement of the arm  24  during the movement of the pipe  18  between the horizontal orientation and the vertical orientation. 
         [0050]    The drilling rig  20  is illustrated as having drill pipes  60  and  62  extending upwardly so as to have an end above the drill floor  64 . When the pipe  18  is in its vertical orientation, the translatable movement of the grippers  30  and  32  can be utilized so as to cause the end of the pipe  18  to engage with the box of one of the drill pipes  60  and  62 . 
         [0051]    Referring still to  FIG. 1 , the general movement of the bottom end of the pipe  18  is illustrated by line  66 . The movement of the pivot point  68  of the connection between the lever assembly  22  and the link  34  is illustrated by line  70 . Curved line  71  illustrates the movement of the pivotable connection  40  between the boom  16  and the lever assembly  22 . 
         [0052]    The coordinated movement of each of the non-extensible members of the system  10  is achieved with proper sizing and angular relationships. In essence, the system  10  provides a four-bar link between the various components. As a result, the movement of the drill pipe  18  between a horizontal orientation and a vertical orientation can be achieved purely through the mechanics associated with the various components. As can be seen, only a single hydraulic actuator may be necessary so as to achieve this desired movement. There does not need to be coordinated movement of hydraulic actuators. The hydraulic actuators are only used for the pivoting of the boom. Since the frame  12  is a skid located on the bed of a vehicle  14 , the vehicle  14  can be maneuvered into place so as to properly align with the centerline of the drill pipe  60  and  62  of the drilling rig  20 . Once the proper alignment is achieved by the vehicle  14 , the system  10  can be operated so as to effectively move the drill pipe to its desired position. The gripper assemblies allow the drill pipe  18  to be moved upwardly and downwardly for the proper stabbing of the drill pipes  60  and  62 . 
         [0053]    Referring to  FIG. 2 , there is shown a side elevational view of the apparatus  100  of the present invention as used on a pipe handling system  10 , with the pipe handling system  10  in the first position. The drill pipe  18  is in a generally horizontal orientation. The drill pipe can be delivered to the system  10  in a position below the boom  16 . In particular, the drill pipe can be loaded upon the frame  12  in a location generally adjacent to the grippers  30  and  32  associated with the gripper  26 . As such, the present invention facilitates the easy delivery of the drill pipe to the desired location. The grippers  30  and  32  grip the outer diameter of the pipe  18  in this horizontal orientation. The boom  16  resides above the drill pipe  18  and in generally parallel relationship to the top surface of the frame  12 . The lever assembly  22  is suitably pivoted so that the arm  24  extends through the interior of the framework of the boom  16  and such that the gripper  26  engages the pipe  18 . The brace  36  resides in connection with the small frame member  46  of the boom  16  and also is pivotally connected to the arm  24 . The link  34  resides below the boom  16  generally adjacent to the upper surface of the frame  12  and is connected to the second portion  50  of the lever assembly  22  below the boom  16 . 
         [0054]    Because the system  10  is in the first position, the piston of the second hydraulic piston-and-cylinder assembly  124  of the apparatus  100  is shown as in the retracted position, i.e. retracted within the cylinder  148  of the second hydraulic piston-and-cylinder assembly  124 . The other hydraulic piston-and-cylinder assemblies and pneumatic springs (not shown) of the apparatus  100  are in similar retracted positions. 
         [0055]    Referring to  FIG. 3 , there is shown a side elevational view of the apparatus  10  of the present invention as used on a pipe handling system  10  moving from the first position to a second position. Particularly, the system  10  is shown in an intermediate position while moving the drill pipe  18  from the horizontal orientation to the vertical orientation. As can be seen, the gripper  26  has engaged with the pipe  18 . The lever assembly  22  has pivoted so that the end  79  of pipe  18  passes through the interior of the framework of the boom  16 . Also, the arm  24  associated with the gripper  26  serves to move the stab frame  28  of the gripper  26  through the interior of the framework of the boom  16 . The brace  36  pulls on the first portion  48  of lever assembly  22 . The link  34  pulls on the end of the second portion  50  of the lever assembly  22  so as to draw the first portion  48  upwardly and to cause the movement of the stab frame  28  of the gripper  26 . The apparatus  100  has operated so as to urge the boom  16  pivotally upwardly. The second piston-and-cylinder assembly  124  can be seen as extending between the frame  12  and the boom  16 . The piston  156  extends slightly outwardly of the cylinder  148  of the second piston-and-cylinder assembly  124  when the system  10  is in this intermediate position. The other hydraulic piston-and-cylinder assemblies and pneumatic springs of the apparatus  100  have similar extensions to that of the second piston-and-cylinder assembly  124 . 
         [0056]    Referring to  FIG. 4 , there is shown a side elevational view of the apparatus  10  of the present invention as used with a pipe handling system  10 , with the system  10  moving further from the first position to the second position. The apparatus  100  urges the boom  16  angularly upwardly away from the top surface of the frame  12 . This causes the link  34  to have a pulling force on the pivotal connection  68  of the second portion  50  of the lever assembly  22 . This causes the first portion  48  of the lever assembly  22  to move upwardly thereby causing the arm  24 , in combination with the brace  36 , to lift the gripper  26  further upwardly and draw the pipe  18  completely through the interior of the boom  16 . The second hydraulic piston-and-cylinder assembly  124  can be seen in another intermediate position as the system  10  extends further toward the second position from the first position. The piston  156  extends even further outwardly of the cylinder  148  in  FIG. 4  than in the position shown in  FIG. 3 . The other hydraulic piston-and-cylinder assemblies and pneumatic springs of the apparatus  100  have similar extensions to that of the second hydraulic piston-and-cylinder assembly  124 . 
         [0057]    Referring to  FIG. 5 , there is shown a side elevational view of the preferred embodiment of the present invention as used on a pipe handling system  10 , with the system  10  in the second position. The drill pipe  18  is in the vertical orientation. As can be seen, the drill pipe  18  is positioned directly above the underlying pipe  62  on the drilling rig  20 . The further upward pivotal movement of the boom  16  is caused by extension of the apparatus  100 . This causes the link  34  to rotate and draw the end of the second portion  50  of the lever assembly  22  downwardly. The lever assembly  22  rotates about the pivot point  40  such that the first portion  48  of the lever assembly  22  has a pivot  72  at its upper end. The brace  36  is now rotated in a position so as to provide support for the arm  24  in this upper position. The gripper  26  has grippers  30  and  32  aligned vertically and in spaced parallel relationship to each other. If any further precise movement is required between the bottom end  80  of the pipe  18  and the upper end  82  of pipe  62 , then the vehicle  14  can be moved slightly so as to achieve further precise movement. In the manner described hereinbefore, the drill pipe  18  has achieved a completely vertical orientation by virtue of the interrelationship of the various components of the system  10  and apparatus  100  without the need for complex control mechanisms and hydraulics. In order to install the drill pipe  18  upon the pipe  62 , it is only necessary to vertically translate the grippers  30  and  32  along the stab frame  28  of the gripper  26 . As such, the end  80  can be stabbed into the box connection  82  of pipe  62 . Suitable tongs, spinners, or other mechanisms can be utilized so as to rotate the pipe  18  in order to achieve a desired connection. The grippers  30  and  32  can then be released from the exterior of the pipe  18  and returned back to the original position such that another length of drill pipe can be installed. 
         [0058]    The second hydraulic piston-and-cylinder assembly  124  of the apparatus  100  has a piston  156  and a cylinder  148 . An end  150  of the cylinder  148  is connected to the frame  12 . An end  158  of the piston  156  is connected to the boom  16 . When the apparatus  100  is activated, the apparatus  100  pivots the boom  16  relative to the frame  12  upwardly from the first position to the second position so as to cause the pipe  18  to achieve a vertical orientation. The first hydraulic piston-and-cylinder assembly of the hydraulic actuator  128  has a similar connection to the frame  12  and boom  16 . The pneumatic springs are inverted relative to the hydraulic piston-and-cylinder assemblies  128  so that an end of the cylinder is connected to the boom  16  and an end of the piston is connected to the frame  12 . The piston  156  of the second hydraulic piston-and-cylinder assembly  124  is shown in  FIG. 5  as fully extended from the cylinder  148  so that the opposite end  160  of the piston  156  is adjacent the opposite end  152  of the cylinder  148 . The other hydraulic piston-and-cylinder assemblies and gas springs of the apparatus  100  have similar extensions to that of the second hydraulic piston-and-cylinder assembly  124 . 
         [0059]    Referring to  FIG. 6 , there is shown an isolated plan perspective view of the preferred embodiment of the apparatus  100  of the present invention as used on a pipe handling system  10 . The system  10  is shown in the second position, with the apparatus  100  in an extended position. The apparatus  100  pivots the boom  16  of the system  10  between the first and second positions. The apparatus  100  has hydraulic piston-and-cylinder assemblies  128  connected to the boom  16  and frame  12 , and pneumatic springs  102  connected to the boom  16  and frame  12 . 
         [0060]    Each of the pneumatic springs  102  has a piston and a cylinder. The first pneumatic spring  118  has a cylinder  104  that has an end  106  pivotally connected to the boom  16 , and a piston  110  movably positioned within an interior of the cylinder  104 . The piston  110  has an end  112  pivotally connected to the frame  12 . The second pneumatic spring  120  has a cylinder  162  that has an end  164  pivotally connected to the boom  16 , and a piston  168  movably positioned within an interior of the cylinder  162 . The piston  168  has an end  170  pivotally connected to the skid  12 . The interior of the cylinders  104  and  162  may be filled with nitrogen gas. An opposite end  114  of the piston  110  of the first pneumatic spring  118  extends within the interior of the cylinder  104  of the first pneumatic spring  118  adjacent the boom  16  when the boom  16  is in the first position. An opposite end  172  of the piston  168  of the second pneumatic spring  120  extends within the interior of the cylinder  162  of the second pneumatic spring  120  adjacent the boom  16  when the boom  16  is in the first position. An opposite end  114  of the piston  110  of the first pneumatic spring  118  extends within the interior of the cylinder  104  of the first pneumatic spring  118  adjacent an opposite end  108  of the cylinder  104  when the boom  16  is in the second position. An opposite end  172  of the piston  168  of the second pneumatic spring  120  extends within the interior of the cylinder  162  of the second pneumatic spring  120  adjacent an opposite end  166  of the cylinder  162  when the boom  16  is in the second position. 
         [0061]    Each of the hydraulic piston-and-cylinder assemblies  128  has a piston and a cylinder. The first hydraulic piston-and-cylinder assembly  122  has a cylinder  130  having an end  132  pivotally connected to the frame  12 , and a piston  138  movably positioned within an interior of the cylinder  130 . The piston  138  has an end  140  pivotally connected to the boom  16 . The second hydraulic piston-and-cylinder assembly  124  has a cylinder  148  having an end  150  pivotally connected to the frame  12 , and a piston  156  movably positioned within an interior of the cylinder  148 . The piston  156  has an end  158  pivotally connected to the boom  16 . 
         [0062]    An opposite end  142  of the piston  138  of the first hydraulic piston-and-cylinder assembly  122  extends within an interior of the cylinder  130  of the first hydraulic piston-and-cylinder assembly  122  adjacent the frame  12  when the boom  16  is in the first position. An opposite end  160  of the piston  156  of the second hydraulic piston-and-cylinder assembly  124  extends within an interior of the cylinder  148  of the second hydraulic piston-and-cylinder assembly  124  adjacent the frame  12  when the boom  16  is in the first position. The opposite end  142  of the piston  138  of the first hydraulic piston-and-cylinder assembly  122  extends within the interior of the cylinder  130  adjacent an opposite end  134  of the cylinder  130  when the boom  16  is in the second position. The opposite end  160  of the piston  156  of the second hydraulic piston-and-cylinder assembly  124  extends within the interior of the cylinder  148  adjacent an opposite end  152  of the cylinder  148  when the boom  16  is in the second position. 
         [0063]    The hydraulic powering assembly  126  is operatively connected to the first and second hydraulic piston-and-cylinder assemblies  122  and  124 . The hydraulic powering assembly  126  pumps hydraulic fluid into and out of the interiors of the cylinders  130  and  148  of the hydraulic piston-and cylinder assemblies  122  and  124  so as to cause the pistons  138  and  156  to extend and retract from the interiors of the cylinders  130  and  148 . The extension and retraction of the pistons  138  and  156  pivots the boom  16  relative to the skid  12  between the first and second positions. Suitable lines are connected between the hydraulic powering assembly  126  and cylinders  130  and  148  to allow fluid to travel therebetween. 
         [0064]    Referring still to  FIG. 6 , it can be seen that the first and second pneumatic springs  118  and  120  are inverted so that the cylinders  104  and  162  are connected to the boom  16  while the pistons  110  and  168  are connected to the frame  12 . Having the pneumatic springs  118  and  120  in this orientation gives extra pushing force when moving the boom  16  from the first position to the second position, and gives extra braking force when moving the boom  16  from the second position to the first position. Thus, the power band requirements of the first and second hydraulic piston-and-cylinder assemblies  122  and  124  are reduced by the addition of pneumatic springs  118  and  120  in the apparatus  100 . The peak and total operating pressures of the hydraulic fluid in the cylinders  130  and  148  of the hydraulic piston-and-cylinder assemblies  122  and  124  are thus reduced by the use of pneumatic springs  118  and  120 . Because less hydraulic pressure is required for the hydraulic piston-and-cylinder assemblies  122  and  124 , the horsepower requirements of a pump of the hydraulic powering assembly  126  are reduced. The consumption of fuel of hydraulic powering assembly  126  may be reduced by up to 75%. Because lower pressures are used on the hydraulic piston-and-cylinder assemblies  122  and  124 , there is less wear and tear and thus prolonged operative life of the assemblies  122  and  124 . The apparatus  100  with pneumatic springs  118  and  120  allows the energy saved to be used on other components of the pipe handling system  10 , if desired. Thus, additional power supplies do not have to be purchased with use of the apparatus  100  of the present invention. 
         [0065]    The pneumatic springs  118  and  120  are separate from the hydraulic system of the piston-and-cylinder assemblies  122  and  124 . Thus, a failure in the hydraulic piston-and-cylinder assemblies  122  and  124  does not cause a failure in the pneumatic springs  118  and  120 , and vice versa. The pneumatic springs  118  and  120  provide upward forces on the boom  16  as the boom  16  moves from the second position to the first position (and vice versa) so as to counter the acceleration of the boom  16  by gravity, thus “floating” the boom  16  downwardly from the second position to the first position. This “floating” makes the movement of the boom  16  safer for personnel in the vicinity of the boom and helps prevent the boom from moving too quickly and/or colliding with the frame  12  when reaching the first position. 
         [0066]    Turning now to  FIG. 6A , in a preferred embodiment of the apparatus  100 , a pair of pneumatic reservoirs  180  may be located adjacent to the pneumatic springs  102  in order to provide even greater control over the pushing and braking forces provided for by the pneumatic springs  102 . The pneumatic reservoirs may be directly attached to the pneumatic springs  102 , and may be oriented parallel to the pneumatic springs  102 . The pneumatic reservoirs  180  may each include a cylinder and piston. In a preferred embodiment of the apparatus  100 , the pneumatic reservoirs  180  may be replaced with other accumulator devices, such as variable displacement accumulators, that may variably change the pneumatic pressure within the pneumatic springs  102 . 
         [0067]    A first pneumatic reservoir  182  is adjacent the first pneumatic spring  118 . A second pneumatic reservoir  192  is adjacent the second pneumatic spring  120 . The first pneumatic reservoir  182  has a cylinder  184  that has an end  186  adjacent to the end  106  of the first pneumatic spring  118 . The first pneumatic reservoir  182  additionally has a piston  188  that has a rod end  190  of the piston  188  adjacent to the opposite end  108  of first pneumatic spring  118 . The piston  188  of the first reservoir cylinder  182  is slidably positioned within an interior of the cylinder  184 . The piston  188  additionally defines a liquid-containing space within the cylinder  184 . This liquid-containing space has a hydraulic liquid present therein. 
         [0068]    A second reservoir cylinder  192  is adjacent the second pneumatic spring  120 . The second reservoir cylinder  192  has a cylinder  194  that has an end  196  adjacent to the end  164  of the second pneumatic spring  118 . Second reservoir cylinder  192  has a piston  198  that has a rod end  200  of the piston  198  adjacent to the opposite end  108  of second pneumatic spring  120 . The piston  198  of the second reservoir cylinder  192  is slidably positioned within an interior of the cylinder  194 . The piston  198  additionally defines a liquid-containing space within the cylinder  194 . This liquid-containing space has a hydraulic liquid present therein. 
         [0069]    The first pneumatic reservoir  182  is fluidically connected to the first cylinder  104  via a first pneumatic valve  202 . In the preferred embodiment of the apparatus  100 , the first pneumatic valve  202  is fluidically connected to the first pneumatic reservoir  182  and cylinder  104  at ends  186  and  106 , respectively. The second pneumatic reservoir  192  is fluidically connected to the second cylinder  162  via a second pneumatic valve  204 . In the preferred embodiment of the apparatus  100 , the second pneumatic valve  204  is fluidically connected to the second pneumatic reservoir  192  and cylinder  162  at ends  196  and  164 , respectively. 
         [0070]    A first hydraulic line  206  is fluidically connected to an opposite end of the first pneumatic reservoir cylinder  182 . The first hydraulic line  206  fluidically connects the liquid receiving space of the first pneumatic reservoir cylinder  182  with a hydraulic fluid source  210 . A second hydraulic line  208  is fluidically connected to an opposite end of the second pneumatic reservoir cylinder  192 . The second hydraulic line  208  fluidically connects the liquid receiving space of the second pneumatic reservoir cylinder  192  with the hydraulic fluid source  210 . 
         [0071]    The hydraulic fluid source  210  may supply a quantity of hydraulic fluid to the liquid receiving space within the pneumatic reservoirs  180  via the first and second hydraulic lines  206  and  208 . In a preferred embodiment of the apparatus  100 , the hydraulic fluid is a hydraulic oil. The hydraulic fluid thus may increase or decrease the pressure within the first and second liquid receiving space located within pneumatic reservoir cylinders  184  and  194 . As the hydraulic fluid fills the liquid receiving space located within pneumatic reservoir cylinders  184  and  194 , it causes pneumatic reservoir pistons  188  and  198  to retract in the direction of the reservoir cylinder ends  186  and  196 . This causes the pneumatic pressure within the reservoir cylinders  184  and  194  to increase, which, in a preferred embodiment, is a nitrogen gas. The increase in nitrogen gas pressure causes the nitrogen gas to travel from the first and second pneumatic reservoirs  182  and  192  into the respective first and second pneumatic springs  118  and  120  via the respective first and second pneumatic valves  202  and  204 . The resulting increase in nitrogen gas pressure within the pneumatic springs  102  serves to increase the stiffness and resiliency provided for by the pneumatic springs  102 . Likewise, to decrease the stiffness and resiliency in pneumatic springs  102 , the hydraulic fluid source  210  may simply reverse the flow of the hydraulic fluid back from the pneumatic reservoirs  180  to the hydraulic fluid source  210  through the first and second hydraulic lines  206  and  208 . This in turn decreases the fluid pressure inside the pneumatic reservoirs, and as fluid flows from the pneumatic springs  102  back into the pneumatic reservoirs  180 , will decrease the pressure and stiffness of the pneumatic springs  102 . 
         [0072]    During operation of the apparatus  100 , it is desirable for the pneumatic springs  102  to provide sufficient stiffness and resistance to the load being encountered in order to reduce the amount of force required for the hydraulic assemblies to raise or lower the boom. However, due to the different loads that may be encountered by the apparatus  100 , as well as different forces at a particular stroke during the travel of the boom  10  between the first and second positions, a real-time variable pneumatic spring resistance is desired to most efficiently and effectively provide pushing and braking forces to the hydraulic assemblies  128 . More specifically, various factors may affect the optimal amount of pneumatic pressure within the pneumatic spring assembly, including the type of pipe or tubular currently being moved, the weight of the load currently being moved, the speed at which the operation is being conducted, the amount of energy conservation desired for a given operation, as well as other possible factors. These factors may accordingly affect the optimal level of pneumatic pressure that should be present within the pneumatic spring assemblies. 
         [0073]    Thus, in the preferred embodiment of the apparatus  100 , positional sensors may be located on apparatus  100  to provide feedback information on the real-time position of various elements of the apparatus  100 . More specifically, positional sensors may be located on the boom  16 , the hydraulic assemblies  128 , the pneumatic springs  102 , the pneumatic reservoirs  180 , or any combination of the aforementioned elements. These positional sensors may collectively provide positional feedback information for the apparatus  100 , and the positional feedback information may then be used either alone or in combination with other feedback information to adjust hydraulic pressure in the hydraulic assemblies  128  or pneumatic pressure in the pneumatic springs  102 . 
         [0074]    In another embodiment, pressure sensors may be present in apparatus  100  to provide information on the current hydraulic pressure of the hydraulic assemblies  128 . Preferably, the pressure sensors may be located on the hydraulic assemblies  128  to provide feedback information of the current pressure of the hydraulic fluid. Pressure sensors may also be located on the pneumatic springs  102  or on the pneumatic reservoirs  180  to provide feedback information on the current pneumatic pressure within those respective devices. As with the positional feedback information, the pressure feedback information obtained by the pressure sensors may be used either alone or in combination with other feedback information to adjust hydraulic pressure in the hydraulic assemblies  128  or pneumatic pressure in the pneumatic springs  102 . 
         [0075]    In still another embodiment, flow meters may be located on the apparatus  100  to measure the flow rate of hydraulic or pneumatic fluid. In this manner, the apparatus  100  may determine, based upon the measured hydraulic or pneumatic flow rate, what the optimal hydraulic pressure for the hydraulic assemblies  128  should be at a given location or stroke of boom  128 . The apparatus  100  may accordingly adjust the hydraulic fluid pressure in the hydraulic assemblies  128  or the pneumatic fluid pressure in the pneumatic springs  102 . Additionally, hydraulic or pneumatic flow rate may alternatively be calculated based upon feedback data provided by the positional sensors, without the use of flow meters. 
         [0076]    In a preferred embodiment, the apparatus  100  may adjust the stiffness of the pneumatic springs  102  to support the hydraulic assemblies in a fully automatic mode. In this mode, a controller, or computer receives feedback information received from any combination of the positional sensors, pressure sensors, and flow meters to perform geometric calculations to determine the optimal pneumatic pressure for the pneumatic springs  102 . In this fully automatic mode, the computer automatically and continuously adjusts the pressure inside the pneumatic springs  102  in real-time to optimize the amount of energy necessary for the raising and lowering of boom  16  as the boom  16  moves between the first and second positions, 
         [0077]    In another embodiment, the apparatus  100  may adjust the stiffness of the pneumatic springs  102  to support the hydraulic assemblies in a fully manual mode. In this mode, a rig operator may manually control the flow of hydraulic oil between the hydraulic fluid source  210  and the pneumatic reservoirs  180  in order to control the pneumatic pressure present inside pneumatic springs  102 . 
         [0078]    In still another embodiment, the apparatus  100  may adjust the stiffness of the pneumatic springs  102  to support the hydraulic assemblies in a semi-automatic mode. In this mode, the computer receives feedback information received from any combination of the positional sensors, pressure sensors, and flow meters and performs geometric calculations to determine a number of pneumatic pressure settings for the pneumatic springs  102 . The settings may be based upon different needs of the rig operator, and may allow for the pneumatic springs  102  to provide minimal or significant assistance to the hydraulic assemblies  128 . The rig operator may then select a setting to be applied to the pneumatic reservoirs  180 , which, in turn, affects the pneumatic pressure present in the pneumatic springs  102 . 
         [0079]    Referring to  FIG. 7 , there is shown a side perspective view of the apparatus  100  of the present invention as used on a pipe handling system  10 . The end  158  of the piston  156  of the second hydraulic piston-and-cylinder assembly  124  can be seen pivotally connected to the boom  16 . The end  164  of the cylinder  162  of the second pneumatic spring  120  can be seen pivotally connected to the boom  16 . The end  106  of the cylinder  104  of the first pneumatic spring  118  can be seen pivotally connected to the boom  16 . The end  140  of the piston  138  of the first piston-and-cylinder assembly  122  can be seen pivotally connected to the boom  16 . The first hydraulic piston-and-cylinder assembly  122  is positioned adjacent the side  144  of the frame  12 . The second hydraulic piston-and-cylinder assembly  124  is positioned adjacent the opposite side  146  of the frame  12 . The first pneumatic spring  118  is positioned between the first and second hydraulic piston-and-cylinder assemblies  122  and  124  adjacent the side  144  of the frame  12 . The second pneumatic spring  120  is positioned adjacent the opposite side  146  of the frame  12  between the first and second hydraulic piston-and-cylinder assemblies  122  and  124 . The frame  12  is shown with sides  144  and  146 , which is a structural framework suitable for housing the rest of the pipe handling system  10 . 
         [0080]    The foregoing disclosure and description of the invention is illustrative and explanatory thereof. Various changes in the details of the illustrated construction can be made within the scope of the appended claims without departing from the true spirit of the invention. The present invention should be limited only by the following claims and their legal equivalents.

Summary:
The invention relates to a pipe handling apparatus that delivers and positions tubulars at a wellhead and a device for assisting pivotal movement of a boom relative to a base of the apparatus. A pneumatic spring assembly is pivotally connected between the boom and base. During operation, the pneumatic spring assembly urges the boom from a first position to a second position and resists movement of the boom from the second position to the first position. A pneumatic reservoir may be attached to the pipe handling apparatus. A gas-charging assembly fluidically connects the pneumatic spring assembly and pneumatic reservoir and allows the pneumatic reservoir to vary the pneumatic pressure within the pneumatic spring assembly. Sensors mounted in the pipe handling apparatus may provide feedback to a controller which may automatically adjust the amount of pneumatic pressure within the pneumatic springs for ideal performance of the springs.