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RELATED APPLICATIONS 
       [0001]    This application claims the benefit of a related U.S. Provisional Application Ser. No. 62/242,505 filed Oct. 16, 2015, entitled PASSIVE LATCH MECHANISM FOR A DRILLING RIG MAST, to Mark W. Trevithick, the disclosure of which is incorporated by reference herein in its entirety. 
     
    
     BACKGROUND 
       [0002]    In the exploration of oil, gas and geothermal energy, drilling operations are used to create boreholes, or wells, in the earth. Drilling rigs used in subterranean exploration are transported to the locations where drilling activity is to be commenced. These locations are often remotely located in rough terrain. The transportation of such rigs on state highways is performed in compliance with highway safety laws and clearance underneath bridges or inside tunnels. Once transported to the desired location, large rig components are moved from a transport trailer into engagement with the other components located on the drilling pad. 
         [0003]    Moving a full-size drilling rig includes disassembly and reassembly of the substructure and mast. Safety is of paramount importance. Speed of disassembly and reassembly impact profitability. Complete disassembly leads to errors and delay in reassembly. Modern drilling rigs may have two, three, or even four mast sections for sequential connection and raising above a substructure. 
         [0004]    The lower mast section is delivered and positioned by truck into proximity and alignment with the substructure. The front pair of lower mast section legs is aligned and pin connected to front shoes on the drill floor. The lower mast section truck then departs. The lower mast section is connected to the mast raising cylinders to enable height adjustment of the lower mast section. This is done, in part, because variations in the terrain surrounding the drilling rig render alignment difficult. The center mast section is then delivered and positioned by truck into proximity and alignment with the upper end of the lower mast section. At this stage, the four corners of the lower mast and center mast sections are aligned to permit connection. 
         [0005]    Connection of the front side of the lower mast section to the center mast section can be accomplished from ground level. However, connection of the rear side of the lower mast section to the center mast section involves placing rig personnel in a lift and raising them over the suspended and unconnected mast sections. From a position above the unconnected lower and center mast sections, the rig personnel can help direct their alignment to the truck driver and operator of the mast raising cylinders to permit placement of pins into the rear leg connectors. 
         [0006]    There are well-recognized inherent risks associated with raising personnel above ground and above unconnected structures. Additional risks are realized when one of the unconnected structure components is located on a vehicle. Additional risks are realized when the terrain is uneven and unpaved. It is desirable to reduce these risks. 
         [0007]    After connection of the center mast section to the lower mast section, the center mast section truck departs, and the upper mast section truck arrives. At this stage, the four corners of the center mast section and upper mast section are aligned to permit connection. With the mast section now extended further off of the substructure, mast section alignment may be more difficult. Rig personnel is again positioned in a lift suspended above the two unconnected mast sections to complete connection of the rear side of the center mast section to the upper mast section. 
         [0008]    When the upper mast section is securely connected to the center mast section, the upper mast truck departs. If the mast is a three section mast, it is now fully assembled and the assembled mast is raised vertically above the drill floor. If the mast is a four section mast, the crown mast section will now arrive on a crown section truck. 
         [0009]    At this stage, the four corners of the upper mast section and crown mast section are aligned to permit connection. With the partially assembled mast section now extended further off of the substructure, alignment will be even more difficult for the reasons stated above. Once again, rig personnel is positioned into a lift suspended above the two unconnected mast sections to complete connection of the rear side of the upper mast section to the crown mast section. When connected, the crown section truck departs. 
         [0010]    The fully assembled mast is then raised by pivoting it on the pin connection to the drill floor with lifting force supplied by the mast raising cylinders. When fully erect, the rear mast legs of the lower mast section are pin connected to the rear shoes on the drill floor. 
         [0011]    It is desirable to have a connection system that reduces rig-up and rig-down time. It is desirable to have a system that provides improved alignment and connectivity between sequential mast sections during rig-up. It is highly desirable to have a system with a lower risk of accidents. 
         [0012]    In particular, it is desirable to provide a mast latching system that enables connection of sequential mast sections without the need to expose personnel to the safety hazards associated with working from a lift device above large, unconnected sections of a drilling rig mast. 
         [0013]    The disclosed embodiments provide a novel solution to the engineering constraints and challenges of providing a rapid, safe, and reliable connection between mast sections of a drilling rig. 
       SUMMARY 
       [0014]    A drilling rig mast system is provided, having a first mast section and a series connectable second mast section. A slot flange extends beyond an end of the first mast section. A pin flange extends beyond an end of the second mast section for engagement with the slot flange. A first pin extends outward from the pin flange. A second pin also extends outward from the pin flange. 
         [0015]    A slot is formed on the slot flange and is configured to receive the first pin. A ramp is formed on the end of the slot flange and is configured to engage the second pin. A seat is formed on the ramp of the slot flange. The seat is configured to receive the second pin when the first pin is located in the slot. 
         [0016]    The first mast section is connectable to the second mast section by location of the first pin in the slot and location of the second pin in the pin seat. When the pins are located in the slot and seat, respectively, the first and second mast sections are sufficiently connected at the rear side of the mast such that pins may then be connected by rig personnel on the ground. This method can then be repeated for each successive section of mast added. 
         [0017]    As will be understood by one of ordinary skill in the art, the assembly disclosed may be modified and the same advantageous result obtained. In particular, one of ordinary skill in the art will recognize that the pin flange and slot flange may be reversed in orientation as between sequential sections of the mast or other large truss system. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]      FIG. 1  is a side view of a drilling rig with the lower mast section pinned to the drill floor and the center mast section being attached to the lower mast section and illustrating one embodiment of the passive mast latch mechanism. 
           [0019]      FIG. 2  is a side view of an embodiment of the slot flange of the passive mast latch mechanism. 
           [0020]      FIG. 3  is a side view of an embodiment of the pin flange of the passive mast latch mechanism. 
           [0021]      FIG. 4  is a side view of the pin flange of  FIG. 3  engaged with the slot flange of  FIG. 2 , and illustrating certain properties of the engagement of this embodiment. 
           [0022]      FIG. 5  is a side view of a step of the connection method of an embodiment, illustrating a first mast section having a slot flange on its upper end. The first mast section is in the proper angular position for approach by a second mast section having a pin flange on its lower end. 
           [0023]      FIG. 6  is a side view of another step of the connection method of an embodiment, illustrating the ramp of the slot flange impacted by the second pin of the pin flange, and illustrating the first pin positioned above the slot of the slot flange. 
           [0024]      FIG. 7  is a side view of another step of the connection method of an embodiment, illustrating the first mast section raised sufficiently to permit the first pin to engage in the slot. 
           [0025]      FIG. 8  is a side view of another step of the connection method of an embodiment, illustrating the first mast section raised sufficiently further to engage the second pin in the seat below the ramp, and to align the front side of the first and second mast sections to permit them to be manually pinned together. 
           [0026]      FIG. 9  is a side view of an optional step of the connection method of an embodiment, illustrating the second mast section having a slot flange on its upper end. The second mast section is in the proper angular position for approach by a third mast section having a pin flange on its lower end. 
           [0027]      FIG. 10  is a side view illustrating an optional step of the connection method, which is substantially a repeat of the second method step, illustrated as performed as between the second and third mast sections. 
           [0028]      FIG. 11  is a side view of an optional step of the connection method of an embodiment, which is substantially a repeat of the third method step, illustrated as performed as between the second and third mast sections. 
           [0029]      FIG. 12  is a side view of an optional step of the connection method of an embodiment, which is substantially a repeat of the fourth method step, illustrated as performed as between the second and third mast sections. 
           [0030]      FIG. 13  is a side view illustrating the first mast section positioned for connection to the second mast section with the passive latch system. 
           [0031]      FIG. 14  is a side view illustrating the first and second mast sections positioned for approach by the third mast section. 
           [0032]      FIG. 15  is a side view illustrating the first and second mast sections positioned for connection to the third mast section with the passive latch system. 
           [0033]      FIG. 16  is a side view illustrating the first, second, and third mast sections positioned for approach by the fourth mast section. 
           [0034]      FIG. 17  is a side view illustrating each of the first, second, third, and fourth mast sections connected in series with an embodiment of the passive latch system of the present invention. 
       
    
    
       [0035]    The steps listed above are not inclusive or exclusive of the numerous other procedures related to the rig-up or rig-down of a drilling rig. The features and benefits of the disclosed embodiments will become more readily understood from the following detailed description and appended claims when read in conjunction with the accompanying drawings in which like numerals represent like elements. 
         [0036]    The drawings constitute a part of this specification and include embodiments that may be embodied in various forms. It is to be understood that in some instances various aspects of the embodiments described may be shown exaggerated or enlarged to facilitate an understanding of the embodiments. 
       DETAILED DESCRIPTION 
       [0037]    The following description is presented to enable any person skilled in the art to make and use the disclosed embodiments, and is provided in the context of a particular application and its requirements. Various modifications to the disclosed embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be applied to other embodiments and applications without departing from the spirit and scope of the present invention. In particular, it will be recognized the relative positions of the slot flanges and pin flanges can be reversed to provide the equivalent structure, function, method, and result of the embodiments disclosed. 
         [0038]      FIG. 1  is a side view of one embodiment of a drilling rig  1 . Drilling rig  1  has an expandable substructure  10 . Substructure  10  has a drill floor  12  generally spanning across its top. A pair of front shoes  14  extends above drill floor  12 . A pair of rear shoes  16  extends above drill floor  12 . A pair of mast raising cylinders  20  is connected to substructure  10 . 
         [0039]    A first (“lower”) mast section  100  is provided. First mast section  100  may be generally rectilinear, having a front side  102  and an opposite rear side  104 , as well as a conventionally known Driller&#39;s side (shown) and an opposite Off-Driller&#39;s side (not visible, but opposite to the Driller&#39;s side). First mast section  100  has a pair of front legs  106  and a pair of rear legs  108  at its lower end. First mast section  100  has an opposite upper end  110 . 
         [0040]    Front legs  106  of a first mast section  100  are pivotally pin connected to front shoes  14 . Rear legs  108  are pin connectable to rear shoes  16  upon pivoted erection of first mast section  100  into a vertical orientation above drill floor  12 . 
         [0041]    First mast section  100  is raised into the vertical position above drill floor  12  by a pair of raising cylinders  20 . Raising cylinders  20  are capable of controlling the angular disposition of first mast section  100 , however, as a person of ordinary skill in the art of drilling rig design will appreciate, drilling masts are conventionally raised by one or more pairs of hydraulic cylinders arranged in various configurations depending upon the rig size, weight, and design configuration. For example, a pair of boost cylinders is commonly incorporated. Therefore, as used herein, “mast raising cylinders”  20  is intended to include any such combination or configuration of expandable cylinders used to control the angularity of the individual, partially assembled, and assembled mast sections relative to the drill floor during assembly and erection of the mast. 
         [0042]    Referring again to  FIG. 1 , a pair of conventional pin connections  120  is provided on front side  102  of first mast section  100 , proximate to upper end  110 . A pair of slot flanges  500  is provided on each side (Driller&#39;s side and Off-Driller&#39;s side) of upper end  110  of rear side  104  of first mast section  100 . 
         [0043]    A second (“center”) mast section  200  is provided for series connection to upper end  110  of first mast section  100 . Second mast section  200  may be generally rectilinear. It has a front side  202  and an opposite rear side  204 . Front side  202  and rear side  204  are separated by a conventionally known Driller&#39;s side (shown facing the page) and an opposite Off-Driller&#39;s side (not visible, opposite to the Driller&#39;s side). Second mast section  200  has a lower end  208  and an opposite upper end  210 . A pair of pin flanges  600  is provided on each side (Driller&#39;s side and Off-Driller&#39;s side) of lower end  208  of rear side  204  of second mast section  200 . A pair of conventional pin connections  220  is provided on front side  202  of lower end  208  of second mast section  200  for connection to pin connections  120  on front side  102  of upper end  110  of first mast section  100 . A pair of conventional pin connections  230  may be provided on front side  202  of upper end  210  of second mast section  200  for connection to another mast section. 
         [0044]      FIG. 2  is a side view of an embodiment of slot flange  500  of the passive mast latch mechanism. As seen in this view, slot flange  500  has a slot  510 , comprising a slide  512 , a cup  514 , and an edge  516 . Cup  514  connects slide  512  to edge  516 . In the embodiment illustrated in  FIG. 2 , cup  514  is non-tangent to edge  516  at slide inflection  518 . From a center  520 , cup  514  has a radius  522  that extends over an included arc  524 . A tension arc  526  is within included arc  524 , terminating at slide inflection  518 . 
         [0045]    Also formed on slot flange  500  is an impact ramp  532 . A seat  534  is formed at the bottom of impact ramp  532 . From a center  540 , seat  534  has a radius  542  that extends over an included arc  544 , terminating at ramp inflection  538 . In the embodiment illustrated in  FIG. 2 , seat  534  is non-tangent to impact ramp  532  at ramp inflection  538 . 
         [0046]    Also in the embodiment illustrated, impact ramp  532  is non-parallel to slide  512 . In particular, angle  528  of slide  512  is slightly greater than angle  548  of impact ramp  532 . Also in the embodiment illustrated, center  520  of cup  514  and center  540  of seat  534  are separated by a distance  550 , with center  520  of cup  514  disposed closer to rear surface  104  of first mast section  100  than is center  540  of seat  534 . 
         [0047]      FIG. 3  is a side view of one embodiment of a pin flange  600  of the passive mast latch mechanism. In the embodiment illustrated, pin flange  600  is attached to each side (Driller&#39;s side and Off-Driller&#39;s side) of lower end  208  of rear side  204  of a second mast section  200 . These two pin flanges  600  are thus positioned for engagement with two opposing slot flanges  500  located on the upper end  110  of rear side  104  of first mast section  100  (See  FIG. 1 ). 
         [0048]    Each pin flange  600  has a first pin  610  and a second pin  620 . Pin  610  has a diameter that renders it receivable in cup  514  of slot  510 . Pin  620  has a diameter that renders it receivable in seat  534  at the end of impact ramp  532 . 
         [0049]      FIG. 4  is a side view of pin flange  600  of  FIG. 3  engaged with slot flange  500  of  FIG. 2 , and illustrating certain properties of the engagement of this embodiment. As represented in  FIG. 4 , a tensile force T is present and acting on first pin  610  when assembled mast sections  100  and  200  are rotated about front shoe  14  connections by lifting cylinders  20  into a vertical position above drill floor  12 . When erect, wind loads create tensile force T at first pin  610 . To tolerate tensile force T without the urge to disengage, a tension bearing zone is provided along tension arc  526 . Tension arc  526  extends to within included arc  524 , and terminates at slide inflection  518 . For safety, the included angle of tension arc  526  should be at least about 35-45 degrees. 
         [0050]    In addition to providing a tension bearing zone, the location of slide inflection  518  provides resistance to disengagement of first pin  610  from slot  510  when first pin  610  experiences tensile load T. 
         [0051]    The remainder of included arc  524  resists shear forces S resulting from the extension of raising cylinders  20  when using the passive latch mechanism, such as will be described in the third and fourth method steps below. 
         [0052]    Still referring to  FIG. 4 , a compressive force C is present and acting on second pin  620  when the assembled mast sections  100  and  200  are rotated about front shoe  14  connections by lifting cylinders  20  into a vertical position above drill floor  12 . When erect, the weight of the fully assembled mast and drill string create compressive force C at second pin  620 . To tolerate compressive force C without the urge to disengage, a compressive bearing zone is provided along compression arc  546 . Compression arc  546  is within included arc  544 , and terminates at ramp inflection  538 . For safety, the minimum including angle of compression arc  546  is about 35 to 45 degrees. 
         [0053]    In addition to providing a compressive bearing zone, the location of ramp inflection  538  provides resistance to disengagement of second pin  620  from cup  534  when second pin  620  experiences compressive force C. 
         [0054]    The remainder of included arc  544  resists shear forces S resulting from the extension of raising cylinders  20  when using the passive latch mechanism, such as will be described in the third and fourth method steps below. 
         [0055]      FIG. 5  is a side view of the first step of the connection method of an embodiment, illustrating first mast section  100  angularly positioned by manipulation of raising cylinders  20  to permit approach by a second mast section truck (not shown) supporting second mast section  200  having pin flange  600  on its lower end  208 . 
         [0056]      FIG. 6  is a side view of the second step of the connection method of an embodiment, illustrating second mast section  200  moved into contact with first mast section  100 . In this view, second pin  620  has come in contact with impact ramp  532 , positioning first pin  610  above slot  510 , and preventing further movement of second mast section  200  in the direction of first mast section  100 . 
         [0057]      FIG. 7  is a side view of the third step of the connection method of an embodiment, illustrating first mast section  100  raised slightly by raising cylinders  20  in relation to second mast section  200  sufficiently such that first pin  610  moves into slot  510 , such as by sliding along slide  512  or edge  516  or other means, until first pin  610  has come to rest in cup  514 . 
         [0058]      FIG. 8  is a side view of the fourth step of the connection method of an embodiment, illustrating first mast section  100  raised slightly further by raising cylinders  20  in relation to second mast section  200  sufficiently such that second pin  620  is moved into a position of complementary fit in seat  534 . In moving into the illustrated position, second pin  620  departs from impact ramp  532  as it passes ramp inflection  538 . In this position, engagement of first pin  610  in cup  514  and engagement of second pin  620  in seat  534  aligns pin connection  120  of first mast section  100  with pin connection  220  of second mast section  200  such that they may be pin connected by rig personnel. Pinning a connection between front side  102  of first mast section  100  and front side  202  of second mast section  200  may be performed from the ground, without placing personnel in an elevated lift basket. 
         [0059]      FIG. 9  is a side view of an optional fifth step of the connection method of an embodiment. Connected first and second mast sections  100  and  200  are raised slightly further by raising cylinders  20  to permit the second mast section truck to be removed from its position of support of second mast section  200 . Connected first and second mast sections  100  and  200  are then angularly positioned by manipulation of raising cylinders  20  to permit approach by a third mast section truck (not shown) supporting a third (“upper”) mast section  300  having pin connection  330  on its lower end  308 . 
         [0060]      FIG. 10  is a side view illustrating an optional sixth step of the connection method, which is substantially a repeat of the second method step. In this sixth step, third mast section  300  is moved into contact with second mast section  200 . In this view, second pin  620  has come in contact with impact ramp  532 , positioning first pin  610  above slot  510 , and preventing further movement of third mast section  300  in the direction of second mast section  200 . 
         [0061]      FIG. 11  is a side view of an optional seventh step of the connection method of an embodiment, which is substantially a repeat of the third method step. In this seventh step, connected first and second mast sections  100  and  200  are raised slightly by raising cylinders  20  in relation to third mast section  300  sufficiently such that first pin  610  moves into slot  510 , such as by sliding along slide  512  or edge  516  or other means, until first pin  610  has come to rest in cup  514 . 
         [0062]      FIG. 12  is a side view of an optional eighth step of the connection method, which is substantially a repeat of the fourth method step. In this eighth step, connected first and second mast sections  100  and  200  are raised slightly further by raising cylinders  20  in relation to third mast section  300  sufficiently such that second pin  620  is moved into a position of complementary fit in seat  534 . In moving into the illustrated position, second pin  620  departs from impact ramp  532  as it passes ramp inflection  538  (See  FIG. 2 ). In this position, engagement of first pin  610  in cup  514  and engagement of second pin  620  in seat  534  aligns pin connection  230  of second mast section  200  with pin connection  330  of third mast section  300  such that they may be pin connected by rig personnel. Pinning a connection between front side  202  of second mast section  200  and front side  302  of third mast section  300  may be performed from the ground, without placing personnel in an elevated lift basket. 
         [0063]      FIG. 13  is a side view illustrating first mast section  100  positioned for connection to second mast section  200  with an embodiment of the passive latch system. 
         [0064]      FIG. 14  is a side view illustrating first and second mast sections ( 100 ,  200 ) positioned for approach by third mast section  300 . 
         [0065]      FIG. 15  is a side view illustrating first and second mast sections ( 100 ,  200 ) positioned for connection to third mast section ( 300 ) with an embodiment of the passive latch system. 
         [0066]      FIG. 16  is a side view illustrating first, second, and third mast sections ( 100 ,  200 ,  300 ) positioned for approach by a fourth (“crown”) mast section  400 . 
         [0067]      FIG. 17  is a side view illustrating each of first, second, third, and fourth mast sections ( 100 ,  200 ,  300 ,  400 ) connected in series with an embodiment of the passive latch system between each successive mast section. 
         [0068]    It has thus been illustrated that the presently disclosed passive latch mechanism provides a mast connection system that is automated to reduce rig-up and rig-down time. It provides for fast and automatic alignment and connection of sequential mast sections without positioning personnel in a lift above disconnected mast sections for the purposes of directing alignment and installing or removing pins. 
         [0069]    If used herein, the term “substantially” is intended for construction as meaning “more so than not.” 
         [0070]    It is noted that the embodiments disclosed are illustrative rather than limiting in nature and that a wide range of variations, modifications, changes, and substitutions are contemplated in the foregoing disclosure and, in some instances, some features may be employed without a corresponding use of the other features. Many such variations and modifications may be considered desirable by those skilled in the art based upon a review of the foregoing detailed description. Accordingly, it is appropriate that the appended claims be construed broadly and in a manner consistent with the scope of the disclosed embodiments.

Summary:
An automatic mast section latching system is disclosed that provides rapid and safe connection of sequential mast sections without placing an employee in a lift to complete the task. A slot flange extends above each mast section for connecting to a pin section extending below a mast section above it. A first pin and a second pin extend perpendicularly from each pin flange. A slot is formed on the slot flange for receiving the first pin. A ramp is formed on the top of the slot flange. A seat is formed on the ramp for receiving the second pin.