Abstract:
A ring derrick includes a carriage which moves on a fixed circular track around a stationary counterweight. A tension and compression column assembled from transportable tubular segments is affixed to the counterweight by a universal swivel joint. The back mast of the derrick is secured at its upper end to the tension column, while the main boom of the derrick extends radially away from the tension column. The main boom and back mast are hinged directly together at the carriage by massive hinge pins which pass through spherical bearings mounted on the carriage. The carriage&#39;s suspension distributes the load from the boom and mast to an array of trucks and has an automatic stabilizing system that compensates for uneven track.

Description:
This application claims benefit of provisional U.S. patent application 61/170,441, filed Apr. 17, 2009. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates to a ring derrick having a stationary counterweight. 
     Cranes and derricks lift heavy loads at varying radii from the base of the lifting boom. The value of the load times radius—load moment—is an important measure of lifting capacity. The world&#39;s largest crawler cranes have maximum load moments of about 32,000 metric tonne-meters (Manitowoc 31000), 44,000 tonne-meters (Terex Demag CC8800 Twin), 50,000 tonne-meter range (new Liebherr XXL not yet released), and 80,000 tonne-meters (Lampson LTL2600). These maximum load moments typically occur at minimum operating radius with the heaviest lifted load. 
     It would be desirable to achieve substantially greater load moment capacity, at much greater operating radii. 
     Typical mobile crawler cranes may produce ground bearing pressures of 20,000 psi. Such pressures normally require a pile-supported foundation system. It would be better to substantially reduce bearing pressures and thus avoid the need for a pile supported foundation. 
     Maximum operating wind speeds for cranes identified above are in the 18 mph range. Low wind tolerance can cause considerable down time, which leads to schedule problems for a major construction project. Substantial improvements in wind tolerance would substantially improve productivity in windy locations. 
     All existing construction crawler cranes carry their counterweights. That arrangement increases ground bearing pressure, which adversely affects the machine&#39;s stability and ultimately its safety. Eliminating this problem is a primary goal of the present invention. 
     SUMMARY OF THE INVENTION 
     An object of the invention is to provide a derrick capable of lifting very heavy loads, in which the counterweight is not carried by the derrick structure, but instead is stationary, either above ground or below grade. 
     These and other objects are attained by a ring derrick as described below. 
     The derrick includes a boom and a back mast, both of which have an A-frame construction which stiffens the structure and in particular provides improved performance in strong winds. 
     An advantage of the invention is that the derrick does not have to support any of the counterweight, so its carriage can be designed solely to support the boom and ultimately any load lifted by the derrick. 
     Another advantage is that a buried counterweight does not obstruct movement of the derrick or other vehicles, which can drive over the counterweight. 
     A further advantage is that, despite its great lifting capacity, the derrick is constructed of modules which can be legally and safely transported over highways. 
     By reducing the construction schedule, improving safety, and eliminating the need for very large and mid-sized crawler cranes, the present invention provides a cost-effective tool for large construction projects. 
     Other objects and advantage of the invention will be apparent from the attached drawings and the following description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the accompanying drawings: 
         FIG. 1  is a perspective view of a ring derrick embodying the invention; 
         FIG. 2  side elevation thereof; 
         FIG. 3  is side view of the derrick, with its main boom shown in alternative positions; 
         FIG. 4  is a top plan view of the derrick; 
         FIG. 5  is a perspective view of the derrick&#39;s carriage, from the front and one side; 
         FIG. 6  is a perspective view thereof, from the rear, with the booms removed; 
         FIG. 7  is a sectional view of the cast-in-place slew ring for the derrick, taken on a vertical plane, 
         FIG. 8  is a front elevation of a tension column and the counterweight; 
         FIG. 9  is a perspective view of the swivel joint at the bottom of the tension column; 
         FIG. 10  is an exploded perspective view of the swivel joint; 
         FIG. 11  is a perspective view of the head of the tension column; 
         FIG. 12  is a close-up perspective view of a foot of the boom, a foot of the mast and their shared supporting structure; 
         FIG. 13  is a detail of the bearing shown in  FIG. 12 ; 
         FIG. 14  is a detail of the hinge pin shown in  FIG. 12 ; 
         FIG. 15  is a sectional view, taken on a vertical diametral plane of the hinge pin, of the structure shown in  FIG. 12 ; 
         FIG. 16  is a view of the structure of  FIG. 13 , with the boom and mast laid out horizontal, and with the addition of a pin cradle; 
         FIG. 17  is a view of a portion of the carriage showing an alternative leveling suspension arrangement; 
         FIG. 18  is a perspective view of one truck of the carriage, from above; and 
         FIG. 19  is a perspective view of the truck, from below. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     An A-frame ring derrick embodying the invention includes a slew carriage  10  ( FIGS. 1-6 ) which rides on a circular track railway or “slewing ring”  12  centered around a geographically fixed vertical axis of revolution “C”. The derrick&#39;s counter-weight  14 , which is situated on the axis of revolution, is supported not by the slew carriage but rather entirely by the ground. The counterweight remains stationary while the slew carriage moves in an arc around it. 
     The counterweight  14  is preferably buried in the ground, with its top approximately flush with the grade of the site. This provides several advantages: other vehicles can drive over it; mobile offices and other items can be stored on it when the derrick is not in use; and after the derrick is removed, the counterweight can be left in place. Preferably the counterweight is cast of concrete in situ, around reinforcing structure (not shown). As an example, approximately 2700 cubic yards of concrete form a counterweight of sufficient mass to counterbalance a lifting moment of 110,000 tonne-meters. 
     As shown in  FIG. 1 , a tension column  16  extends vertically upward from the counterweight. The tension column is described in detail below. 
     The circular track  12  or slewing ring preferably is formed by a pair of concentric rails  20 ,  22  which have broad, horizontal, flat (uncrowned) heads, as shown in the detail of  FIG. 7 . The rails are supported by a concrete or steel pad  24  at or below grade level; preferably the rails are embedded in the pad or backfilled with crushed stone or the like so that the rail heads  26  ( FIG. 7 ) are nearly flush with the grade whereby cars and trucks can cross the track. 
       FIG. 2  shows the carriage  10  on the track  12  which encircles the tension column  16 . A main boom  30  extends from the carriage to the right and a smaller boom, called a “mast”  50  extends to the left, from the carriage to the top of the column  16 . The mast head  64  and the tension tie column head  104  ( FIG. 1 ) are interconnected by a pin and eye system (see  FIGS. 8 ,  11 ) capable of handling the compression and tension loads imposed by the derrick. 
       FIG. 3  shows the derrick with its main boom at various elevations. Normally the column is in tension to counterbalance the load being lifted. However, at high boom elevations with low load, or when the boom  30  (described below) is removed or resting on the ground, the column may be loaded in compression. High winds may also contribute to the creation of a compression force. Therefore, the tension column cannot be a flaccid or flexible member, and must be constructed to withstand substantial compression force without buckling, as well as high tension. 
     Preferably, the tension column  16  is assembled from a series of column segments  75 , as shown in  FIG. 8  (where several segments are omitted). Each segment is made of steel pipe, and has end flanges  76 . Each end flange comprises two rings  77  with gussets  78  ( FIG. 11 ) between the rings; both rings have a circumferential array of holes to receive bolts whereby the segments can be joined in series. 
     Because the tension column  16  is rigid and torsionally stiff and the counterweight is stationary, a universal swivel base  80  is placed between it and the counterweight  14  to minimize or eliminate torques and bending moments on the column. As shown in the details of  FIGS. 9 and 10 , the universal swivel base contains a Hookes-type universal joint  82  that permits the tension column to deviate slightly from vertical without bending. The universal joint has a cross journal  84  having four trunnions  86 , which are received in—and are supported by—plain trunnion bearings  88 . These bearings are retained by respective bearing caps  90 , two of which face bearing seats on a bottom yoke  92  and two of which face bearing seats on a top yoke  94 . The items  96  are O-rings. The top yoke  94  is bolted to the bottommost column segment  75 , while the bottom yoke  92  is free to turn about a vertical axis, which is coincident with the derrick&#39;s axis of revolution “C”. A flange  97  on the bottom yoke bears upward against a triple roller thrust bearing  98 , which is sandwiched between that flange and a bearing retainer ring  100 . The retainer ring is bolted through the sole plate  102  to the counterweight&#39;s reinforcing rod structure (not shown). 
     A column head  104  ( FIG. 11 ) is bolted to the top of the uppermost column segment. The head comprises a body portion  105  with a bolting flange  106  at its bottom and an arrangement of parallel plates  107  at its top. The plates have aligned holes forming eyes through which a pair of shafts  108  are passed to interconnect the column head  104  and the mast head  64  (see  FIG. 1 ). Bushings  109  maintain the spacing between the plates. 
     The derrick&#39;s boom  30  can be raised or lowered to various inclination angles, away from the counterweight. The boom (see  FIG. 1 ) is an A-frame structure, comprising two non-prismatic lattice mast sections  34 ,  36 . Non-prismatic lattice masts are well known, and their design is a matter of ordinary skill in this field. The boom sections  34 ,  36  are braced near their bottom ends by a tension tie frame  38  which interconnects transition frames  40 . Each transition frame connects one of the boom sections  34 ,  36  to a respective boom foot  42 . 
     The top ends of the boom sections meet at a boom head  46 , which contains sheave packs that carry the hoisting cables  47  over the end of the boom to the load block  48 . 
     The back mast  50  also has an A-frame design, and is composed of two lattice mast sections  52 ,  54  separated by a tie frame  56  near their bottom ends. Mast feet  58  extends downward from the tie frame, to a hinge connection described below. The upper ends of the masts meet at a mast head  64 , which supports a sheave pack assembly that carries the boom hoist cables over the end of the back mast. The mast head has a series of eyes, like those shown in  FIG. 11 , which interleave with the eyes on the mast head  104 . The shafts  108  are inserted through the interleaved eyes to secure the top of the mast  50  to the top of the column  16 . The hinge mounting of the back mast—even though the mast is not raised and lowered in operation—allows for minor variations in mast inclination, yawing of the carriage as it moves on the track, and dynamic deformation of the carriage. 
     The boom feet  42  and the feet  58  of the mast are hinged to each other and to the slew carriage. The hinges  32  are formed by a pair of massive hinge pins  60 , which support the boom and the mast on the carriage and connect the boom and mast to one another. 
     Each hinge pin  60  passes through a spherical plain bearing  61  mounted on the carriage. The bearing is best seen in  FIGS. 13 and 15 . Each bearing is mounted on the carriage above and on the center plane of one of the articulating girders  150 ′, described below. The combined weight of the boom, the mast, the lifted load and the reaction force from the tension column is distributed directly and evenly to the carriage&#39;s trucks so that the bearing force on the tracks is spread over the entire length of the carriage. 
     The hinge pin  60  ( FIG. 14 ) is stepped, having a big end  62  and a small end  63 . The pin passes through the spherical bearing and both the boom foot and the mast foot, which straddle the bearing. Retainer plates  64  are bolted to the ends of the hinge pin to keep it in position. Each outer retainer plate has a pair of ears  65  which sit in recesses in a retaining collar  71  that is bolted to the boom foot  42 . 
     The bearing  61  ( FIG. 13 ) comprises a body having a foot  66  which is connected to the carriage, and a hoop portion  67  which contains a split spherical race  68  ( FIG. 15 ). The halves of the race are kept within the hoop by race retainers  69  that are bolted to either side of the hoop. The inside surface of the spherical race bears against a barrel-shaped bushing  70  sized to receive the small end of the hinge pin. 
       FIG. 12  shows a retaining collar  71  disposed around the pin retainer plate. The collar may have reliefs formed on its periphery, as shown in  FIG. 15 , so that it can serve as a mount for a pin cradle  72 , shown in  FIG. 16 . The cradle supports the pin when the joint is being assembled or disassembled. 
     As seen in  FIGS. 5 and 6 , the slew carriage has a chassis or frame  120  which is connected to eight swing arms  150 , four at either end of the frame. The swing arms are connected to the frame by pins  152  which permit the swing arms to pivot on a horizontal axis. Horizontally extending hydraulic cylinders (linear motors)  154 , best seen in  FIG. 5 , dynamically and independently control the position of the respective swing arms. Extension of one of the cylinders pushes its respective swing arm down, as necessary to keep the carriage level, when a track irregularity such as a depression is encountered. 
     The swing arms have the primary purpose of leveling the slew carriage to compensate for settlement of the slew ring. It is critical that the slew carriage be kept level to avoid side loading the boom and mast. The presently preferred leveling arrangement is shown in  FIGS. 5 and 6 ; an alternative is shown in  FIG. 17 . described below. Many modifications to, and variations of the disclosed arrangements are possible. 
     Each end of each swing arm is supported by an equalizer saddle  122  (see  FIGS. 5 ,  6  and  17 ), each of which has a bearing or gudgeon connection to the articulating girder. Each equalizer saddle is, in turn, connected by gudgeons  123  to a pair of trucks  124 , one of which is shown in  FIGS. 18 and 19 . All connections below the articulating girder have swivel bearings to allow for out-of-parallel conditions between the interior and exterior rails. The truck has two wheels  126  which ride on one of the rails  20 ,  22 . Four pairs of equalizer beams and eight pairs of trucks—thus thirty-two wheels in all—are illustrated in the drawings, but many other arrangements are possible. One can determine the best arrangement by conducting an analysis of cost versus allowable ground bearing capacity in a particular situation. 
     Some or all of the trucks have driving wheels which may be activated to move the carriage on the track. We presently prefer that the innermost trucks be driving trucks, and that the outermost trucks be idlers. Power is applied to driving truck&#39;s wheels by hydraulic or electric motors, not shown. Hydraulic power is generated at units  142  ( FIG. 5 ) mounted on the carriage deck; fluid flow to the truck motors is regulated by an operator in the cab  140 . 
     An alternative arranged for compensative for track irregularities is shown in  FIG. 17 . Here, an articulating girder  150 ′ has replaced each pair of swing arms, and instead of the horizontal cylinders  154  shown in  FIG. 5 , a hydraulic jack  128  is disposed between each wheel truck and its equalizer beam. The jacks are raised or lowered dynamically by an automatic leveling system (not shown) to keep the carriage steady despite height variations in the rails. The jacks  128  are shown extended different distances in  FIG. 17 , compensating for track variations. The jacks draw power from the same units that drive the wheels. 
     Each of the wheels  126  has a peripheral bearing surface  130  ( FIG. 19 ) that runs on one of the concentric rails  20 ,  22 . The wheels have no flanges: they are kept on the tracks by opposed rollers  127  that rotate on vertical axes and are supported by the truck. The wheel&#39;s peripheral surface is not cylindrical, but rather is frustoconical (the apex of the cone being a spot on the axis of revolution at the base of the swivel). The wheels&#39; axles are all aligned toward that spot. This geometry avoids scuffing which would otherwise occur between the wheels and the rails, especially considering their width of about 20 cm. Consequently, the wheel axles are not parallel to one another: they converge on the axis of revolution mentioned previously. Other details of the trucks are matters of ordinary design skill, and therefore they are not elaborated on. 
     The wheels of this preferred embodiment of the invention ride on the concentric circular rails  20 ,  22 . Alternatively, however, the invention could be practiced by replacing the wheels and rails with crawler tracks, which are well known in the art, or some other arrangement which constrains the slewing carriage to movement about the axis of revolution. 
     As shown in  FIGS. 5 and 6 , the frame  120  of the slewing carriage supports a prime mover  142  such as a diesel engine and hydraulic pump set, or a diesel-generator set. The primer mover provides power (in mechanical, hydraulic or electrical form) to at least some of the trucks when it is desired to move the derrick along the rails. The prime mover also supplies power to the cable drums which reel in cable to raise the boom, or to lift a load at the end of the boom. The drums are independently controllable by the derrick operator. Design details of the prime mover, the motors for operating the drums and the wheels, the operator controls, the hydraulic/electrical circuitry and the leveling system are matters of ordinary design choice and therefore are not described in detail. The leveling is essential for a derrick which moves around a static counterweight. 
     The inclination angle of the main boom is controlled by boom cables  110  ( FIG. 1 ) which are reeled onto the innermost reels or drums  111  (see  FIGS. 5 and 6 ) on the slew carriage. The cables are reeved on a sheave assembly or bridle  112  ( FIG. 1 ) which is connected to the tip of the main boom by a pair of steel pendants  114 . 
     The load line hoisting cables  47  are wound onto the outermost reels  115  in  FIG. 6 . Both sets of reels are driven by power units  116  mounted on the carriage deck. Preferably, sufficient wire rope friction at the torque drum  118  is developed by using a double capstan traction hoist, however, a standard single drum hoist is also capable of fulfilling the requirement. 
     It should be understood that the foregoing is a description of the presently preferred form of the invention, and that many modifications are possible. For example, a monorail version could be implemented, booms other than A-frame types could be used, and details of the running gear could be altered, without departing from the inventive concepts. 
     Since the invention is subject to modifications and variations, it is intended that the foregoing description and the accompanying drawings shall be interpreted as only illustrative of the invention defined by the following claims.