Patent Publication Number: US-8113299-B2

Title: Drill mast articulation assembly

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of prior U.S. patent application Ser. No. 12/233,363, filed Sep. 18, 2008, and entitled “ARTICULATION ASSEMBLY FOR MOVING A DRILL MAST.” The contents of the above-referenced patent application are hereby incorporated by reference in their entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     1. The Field of the Invention 
     The present invention relates to drilling equipment and to articulation assemblies for positioning a drill mast in particular. 
     2. The Relevant Technology 
     Drilling rigs are often used for drilling holes into various substrates. Such drill rigs include a drill head or drifter or both together as a double head system mounted to a mast assembly that is oriented at a desired drilling angle. The rig often includes mechanisms and devices that are capable of moving the drill head along at least a portion of the mast. The drill head often further includes mechanisms that receive and engage the upper end of a drill rod. The drill rod may be a single rod or a casing and rod combination as an overburden system or may be part of a drill string that includes a cutting bit or other device on the opposing end, which may be referred to as a bit end. In the case of a drill string, the drill string may include multiple rods, each of which has a length that is shorter than the usable length of the mast. 
     The drill head also applies one or more forces to the drill rod which is transmitted to the drill to string. If the applied force is a rotational force, the drill head may thereby cause the drill string rotate within the bore hole. The rotation of the drill string may include the corresponding rotation of the cutting bit, which in turn may result in a cutting action by the drill bit. The forces applied by the drill head can also include axial thrust forces, which may be transmitted to the drill string to facilitate penetration into the formation at the desired drilling angle. 
     Articulation assemblies are often provided on the drill rig to orient the drill mast at the desired angle. Such articulation assemblies often include a jib assembly that is configured to raise, lower, and tilt the mast assembly. In particular, jib assemblies often include a jib boom that supports the mast assembly. The jib boom is often raised and lowered by a lifting cylinder. A tilting cylinder is also often mounted directly to the jib boom on one end and coupled to the mast assembly on the other end. The tilting cylinder is extended and retracted in order to orient the mast assembly at a desired angle. 
     While such articulation assemblies are able to orient the mast assembly, the configuration of the articulation assemblies are often such that raising and lowering the mast assembly changes the drilling angle. Accordingly, in drilling operations where multiple holes are drilled at the same drilling angle, after one hole has been drilled the lifting cylinder is deployed to raise the mast assembly, the rig is moved to a new drilling location, the mast assembly is lowered, and the tilting cylinder is deployed to return the mast assembly to the appropriate drilling angle. Resetting the drilling angle each time can increase down time, thereby increasing the cost of the drilling operation. 
     The subject matter claimed herein is not limited to embodiments that solve any disadvantages or that operate only in environments such as those described above. Rather, this background is only provided to illustrate one exemplary technology area where some embodiments described herein may be practiced. 
     BRIEF SUMMARY OF THE INVENTION 
     In at least one example, a jib assembly for use with a drill rig includes a jib boom having a first end and a second end. The jib boom is configured to rotate about the first end and the second end is configured to be coupled to a mast assembly mount. The jib assembly also includes an articulation assembly having at least one variable length link having a first end and a second end. The first end of the variable length link is offset from the jib boom and the second end is configured to be pivotingly coupled to the mast assembly mount. 
     A jib assembly can also include a jib boom having a first end configured to be coupled to a mount and a second end configured to be coupled to a mast assembly mount. The jib assembly can also include an articulation assembly having at least one variable length link that is maintained parallel to a line between the first end and the second end of the jib boom. 
     Further, an assembly for positioning a drill mast is provided that can include a mast assembly mount, a jib boom having a first end coupled to a mount and a second end coupled to the mast assembly mount. A jib lifter is configured to rotate the jib boom about the first end. A jib articulation assembly can include a variable length link having a first end offset from the jib boom and a second end coupled to the mast assembly mount such that the variable length link is parallel to a line between the first end and the second end of the jib boom as the jib lifter rotates said jib boom about the first end of the jib boom. 
     A drilling system can include a mast and a jib assembly coupled to the rig. The jib assembly can include a mast assembly mount, a jib boom having a first end coupled to a mount and a second end coupled to the mast assembly mount. A jib lifter is configured to rotate the jib boom about the first end. A jib articulation assembly can include a variable length link having a first end offset from the jib boom and a second end coupled to the mast assembly mount such that the variable length link is parallel to a line between the first end and the second end of the jib boom as the jib lifter rotates said jib boom about the first end of the jib boom. The drilling system can further include a mast coupled to the mast assembly mount and a drill head coupled to the mast. 
     This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential characteristics of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       To further clarify the above and other advantages and features of the present invention, a more particular description of the invention will be rendered by reference to specific embodiments thereof which are illustrated in the appended drawings. It is appreciated that these drawings depict only typical embodiments of the invention and are therefore not to be considered limiting of its scope. The invention will be described and explained with additional specificity and detail through the use of the accompanying drawings in which: 
         FIG. 1A  illustrates a drilling system in which the mast assembly is oriented in a transport position; 
         FIG. 1B  illustrates the drilling system of  FIG. 1A  in which the mast assembly is positioned and oriented at a drilling angle during a drilling operation; 
         FIG. 1C  illustrates the drilling system of  FIGS. 1A and 1B  in which the mast assembly is raised while maintaining the mast assembly at the drilling angle; 
         FIG. 2A  illustrates a jib assembly and portions of a mast assembly in which the mast assembly is oriented in a transport position; 
         FIG. 2B  illustrates the jib assembly and mast assembly of  FIG. 2A  in which the mast assembly is positioned and oriented at a drilling angle; 
         FIG. 2C  illustrates the articulation assembly and mast assembly of  FIGS. 2A and 2B  in which the mast assembly is raised relative to the position shown in  FIG. 2B ; and 
         FIG. 3  illustrates a plan view of an articulation assembly and a mast assembly according to one example. 
     
    
    
     Together with the following description, the figures demonstrate non-limiting features of exemplary devices and methods. The thickness and configuration of components can be exaggerated in the Figures for clarity. The same reference numerals in different drawings represent similar, though necessarily identical, elements. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Articulation assemblies, jib assemblies, and drilling systems are provided herein that are configured to maintain a mast assembly at a drilling angle as the mast is raised and lowered. The mast may be raised and lowered to allow the drilling rig or drilling system to be moved. Accordingly, the drilling angle may be maintained as the drilling system or rig is moved between drilling locations on a job site where the same drilling angles are being used. The articulation assembly can provide a relatively high pull-back torque, which may allow the articulation assembly to readily move the mast assembly to a transport position out of an extreme position in the front. Further, the configuration of the articulation assembly may reduce the possibility that the drill mast will be over-rotated, thereby increasing the stability of the drilling system. 
     For ease of reference, the term “link” shall be broadly understood to mean a kinematic link, such as a line between points about which the link moves, such as the points about which the link rotates, regardless of the perimeter shape or other configuration of the link. The following description supplies specific details in order to provide a thorough understanding. Nevertheless, the skilled artisan would understand that assemblies and associated systems can be implemented and used without employing these specific details. 
       FIG. 1A  illustrates a drilling system  100  that includes a rig  105 , a jib assembly  110  and a mast assembly  115  in which the mast assembly  115  is positioned and oriented for transport. The jib assembly  110  can be coupled to a support structure, such as the rig  105 . For example, the jib assembly  110  can be coupled to a rig  105  or the jib assembly  110  may be provided as an integral part of the rig  105 . 
     The mast assembly  115  is coupled to and supported by the jib assembly  110 . The mast assembly  115  is further positioned and oriented by the jib assembly  110 . The jib assembly  110  generally includes a jib boom  125  that is raised and lowered by a jib lifter  130 , such as a lift hydraulic cylinder. The jib assembly  110  also includes a jib articulation assembly  135  that is configured to control the orientation of the mast assembly  115 . The orientation of the mast assembly  115  may be described relative to a generally vertical axis  140 . 
     The jib assembly  110  can include a jib slewing assembly  145  configured to move the jib boom  125  in a plane that is generally perpendicular to the vertical axis  140 . Such plane may be generally referred to as a horizontal plane. Accordingly, the jib boom  125  can be positioned by the jib lifter  130  and the jib slewing assembly  145 . The orientation of the mast assembly  115  can be controlled by the jib articulation assembly  135 . As illustrated in  FIG. 1 , the jib articulation assembly  135  includes at least one variable length link that is offset from the jib boom  125 . Such a configuration can allow the jib lifter  130  and the jib slewing assembly  145  to vary the position of the jib boom  125  while the jib articulation assembly  135  controls the orientation of the mast assembly  115  relative to the jib assembly  110 . In at least one example, the variable link can be generally parallel to the jib boom  125  in a kinematic sense. 
     The jib articulation assembly  135  can also maintain the orientation of the mast assembly  115  relative to the vertical axis  140  as the mast assembly  115  is moved as described above. Maintaining the orientation of the mast assembly  115  relative to the vertical axis  140  can describe the orientation of the entire mast assembly  115  or of specific components. In at least one example, the orientation of various components of the mast assembly  115  can be varied within the mast assembly  115 . In other examples, the orientation of components within the mast assembly  115  can be relatively fixed. For ease of reference, an example in which the components within the mast assembly  115  can be varied will be discussed below. 
     As illustrated in  FIG. 1A , the mast assembly  115  can include a mast assembly mount  150  that is coupled to the jib assembly  110 . In the illustrated example, the jib articulation assembly  135  is coupled to the mast assembly mount  150  in such a manner that one or more of the links of the jib articulation assembly  135  can be varied to control the orientation of the mast assembly mount  150 . For ease of reference, movement of the mast assembly  115  will be described relative to the jib assembly  110  while movement of other components within the mast assembly  115  will be described relative to the mast assembly mount  150 . 
     The mast assembly mount  150  is configured to support a mast carrier  152 , which in turn can be configured to support a mast  155 . A mast tilt cylinder  160  can also be coupled to the mast carrier  152  to lift the mast  155 . The mast assembly  115  can further include a mast slewing assembly  165 . The mast slewing assembly  165  can be supported by the mast assembly mount  150  and coupled to the mast carrier  152 . Such a configuration can allow the mast slewing assembly  165  to rotate the mast carrier  152  relative to the mast assembly mount  150 . In at least one example, the mast  155  can be configured to translate relative to the mast carrier  152 . In particular, a translation cylinder (not shown) can be coupled to both the mast carrier  152  and the mast  155  such that extension and retraction of the mast carrier  152  causes the mast  155  to translate relative to the mast carrier  152 . Such a configuration can allow the translation cylinder to selectively press the mast  155  to the ground to provide additional stability for the drilling system, and the jib assembly  110  and jib articulation assembly  135  in particular, during the drilling process. 
     As will be described in more detail below, the jib assembly  110  and the mast assembly  115  are configured to orient and position the mast  155 . The jib articulation assembly  135  is configured to maintain the orientation of the mast  155  as the mast  155  is raised and lowered. 
     A drill head  170  can be operatively associated with the mast  155 . As illustrated in  FIG. 1B , the jib assembly  110  and the mast assembly  115  can cooperate to move the mast carrier  152 , and the mast  155  in particular, into a drilling position. As further illustrated in  FIG. 1B , the drill head  170  is configured to have a drill rod  175  coupled thereto. The drill rod  175  can in turn be coupled to additional drill rods to form a drill string  180 . In turn, the drill string  180  can be coupled to a drill bit  185  configured to interface with the material to be drilled, such as a formation  190 . 
     In at least one example, the drill head  170  illustrated in  FIG. 1  is configured to rotate the drill string  180  during a drilling operation. In particular, the rotational rate of the drill string  180  can be varied as desired during the drilling operation. Further, the drill head  170  can be configured to translate relative to the mast  155  to apply an axial force to the drill head  170  to urge the drill bit  185  into the formation  190  during a drilling process. 
     The orientation of the mast  155  relative to the vertical axis  140  helps determine the direction the drill string  180  takes as it travels through the formation  190 . The orientation of the mast  155 , and consequently the orientation of the drill string  180  as it enters the formation  190  may be described as a drilling angle and may be referenced relative to any arbitrary axis, such as the vertical axis  140 . In the illustrated example, the mast  155  can be moved to a drilling angle θ d  (theta sub-d) by varying the lengths of one or more links of the jib articulation assembly  135  and/or varying the length of the mast tilt cylinder  160 . 
     In  FIG. 1B , the mast assembly  115  is shown positioned in proximity with the formation  190  and the mast  155  is oriented at a drilling angle θ d . As previously introduced, the jib articulation assembly  135  is configured to raise and lower the mast assembly  115  while maintaining the mast assembly  115  at the drilling angle θ d . Such a configuration is illustrated in  FIG. 1C , in which the jib lifter  130  has been operated to raise the mast assembly  115  away from the formation  190  while the jib articulation assembly  135  maintains the mast assembly  115  at the desired drilling angle θ d . Accordingly, the jib articulation assembly  135  is configured to maintain the mast assembly  115  in a desired orientation as the mast assembly  115  moves. Accordingly, using the jib boom articulation  135  to the mast assembly  115  to the desired angle θ d , the drilling can be maintained constant without changing the length of the links of the jib boom articulation assembly, such as changing the stroke of the tilt cylinder  230  ( FIG. 2A ). Such a configuration can allow the drilling system  100  to adjust a higher drilling position while maintaining the same drilling angle. This phenomenon is creating by the link  225  and  235  ( FIG. 2A ). 
     The rig  105  illustrated is provided for ease of reference only. It will be appreciated that the rig  105  can have any configuration, such as a wheeled rig, a tracked rig, some combination thereof, or any other type of rig. Further, in the illustrated example, the mast  155  can be positioned/or oriented with the mast tilt cylinder  160  and mast slewing assembly  165 . In other examples, the mast  155  can be fixedly mounted to the mast mount  150  such that the jib articulation assembly  135  controls the position and orientation of the mast  155 . In still other examples, the mast assembly  115  can include more or less positioning and/or orienting components than those described above. Further, while a rotary type drill head is illustrated, it will be appreciated that any type of drill head can be coupled to any type of mast, including percussive, sonic, or any other type of drill head. Further, any number of drill heads can be operatively associated with the drill mast. 
       FIGS. 2A-2C  illustrate elevation views of the jib assembly  110  and part of a mast assembly including the mast mount  150 , the mast carrier  152 , and the mast slewing assembly  165  in more detail. In particular,  FIGS. 2A-2C  illustrate these components in analogous positions as those illustrated with respect to the drilling system  100  in  FIGS. 1A-1C  respectively. 
       FIG. 3  illustrates a plan view of the jib boom assembly  110 , mast carrier  152 , mast tilt cylinder  160 , and mast slewing assembly  165  in more detail. In at least one example, the jib assembly  110  and mast carrier  152  may include two halves  300 A and  300 B that are generally symmetric about a plane represented by line  305 . For ease of reference, the components of half  300 A will be described with reference to  FIGS. 2A-2C . It will be appreciated that the same discussion may also be applicable to the components of half  300 B. A discussion of the operation of the jib assembly  110  and the mast tilt cylinder  160  to orient the mast carrier  152  relative to the vertical axis  140  will first be discussed followed by a discussion of the operation of the jib slewing assembly  145  and the mast slewing assembly  165  to position the mast carrier  152  relative to a horizontal plane. 
     Turning again to  FIG. 2A , the jib assembly  110  includes a jib mount  200  that is configured to be coupled to a base structure, such as the drill rig  105  ( FIGS. 1A-1C ). The jib boom  125  is configured to be coupled to the jib mount  200 . In particular, the jib boom  125  includes a first end  125 A that is coupled to the jib mount  200  by a pivot  205 . A second end  125 B of the jib boom  125  can be coupled to the mast assembly mount  150 , as will be described in more detail later. The jib lifter  130  can also be coupled to the jib mount  200  as well as the jib boom  125  such that a first end  130 A of the jib lifter  130  is coupled to the jib mount  200  by a pivot  210 . 
     The second end  130 B of the jib lifter  130  is coupled to the jib boom  125  such that as the jib lifter  130  is extended and retracted, the jib lifter  130  raises and lowers the jib boom  125 . For example, a pivot  215  can couple the second end  130 B of the jib lifter  130  to the jib boom  125  near the second end  125 B. In the example shown, the pivot  215  is coupled to an offset mount  220  such that the second end  130 B of the jib lifter  130  is offset from the jib boom  125 . 
     The jib articulation assembly  135  illustrated includes a lower link  225  and an upper link  230  that are coupled by a pivoting link  235 . A first end  225 A is pivotingly coupled to the jib mount  200  by a pivot  240  while a second end  225 B is pivotingly coupled to a first end  235 A of the pivoting link  235  by pivot  245 . 
     The pivoting link  235  can also be coupled to the jib boom  125 , such as by pivot  250 . The second end  235 B of the pivoting link  235  can be further coupled to a first end  230 A of the upper link  230 , such as by a pivot  255 . The second end  230 B of the upper link  230  can be coupled to the mast assembly mount  150 . In particular, the mast assembly mount  150  can include a plurality of arms  150 A and  150 B. 
     In the illustrated example, a second end  125 B of the jib boom  125  is coupled to arm  150 A by pivot  260  while the second end  230 B of the upper link  230  is coupled to arm  150 B by pivot  265 . The orientation of the mast assembly mount  150  depends, at least in part, on the relative positions of the arms  150 A and  150 B. In at least one example, the mast assembly mount  150  may be rigid, such that movement of arm  150 A results in a proportionate movement of the other arm  150 B and vice versa. Accordingly, orientation of the mast assembly mount  150  depends on the relative positions of the arms  150 A and  150 B, which in turn depends, at least in part, on movement of the jib boom  125  and the jib articulation assembly  135 . 
     As will be discussed in more detail below, the orientation of the arms  150 A and  150 B can be maintained relatively constant as the jib boom  125  is raised and lowered. Operation of the mast tilt cylinder  160  will first be discussed in the context of moving the mast assembly  115  from the transport position. Thereafter, operation of the jib articulation assembly  135  and the mast tilt cylinder  160  will be discussed in the context of establishing an orientation of the mast carrier  152 , followed by a discussion on the interaction of the jib articulation assembly  135 , the jib boom  125 , and the mast assembly mount  150  as the jib boom  125  is raised. 
     As illustrated in  FIG. 2A , the mast slewing assembly  165  can be mounted to the mast assembly mount  150 . The mast carrier  152  in turn can be coupled to the mast slewing assembly  165 . Operation of the mast slewing assembly  165  will be described in more detail with reference to  FIG. 3 . Continuing with reference to  FIG. 2A , the mast carrier  152  generally includes a base portion  270  coupled to the mast slewing assembly  165 . A platform  275  is pivotingly coupled to the base  270  by pivot  277 . 
     The mast tilt cylinder  160  is coupled to the base portion  270  and the platform  275  in such a manner that as the mast tilt cylinder  160  is extended and retracted, the platform  275  is raised and lowered. In at least one example, the mast tilt cylinder  160  is a hydraulic cylinder that includes a first end  160 A pivotingly coupled to the base  270  by a pivot  280  and a second end  160 B pivotingly coupled to the platform  275  by pivot  285 . Accordingly, the platform  275  can be raised by extending the mast tilt cylinder  160  to rotate the platform  275  as well as any components coupled thereto about the pivot  277  to the transport position illustrated in  FIG. 2A  toward a drilling position. In at least one example, the translation cylinder previously discussed (but not shown) can be coupled to one or more mounts  295 . The mast  155  ( FIGS. 1A-1C ) can be in turn coupled to the mounts  295  such that extension or refraction causes the mounts  295 , and thus the mast  155  ( FIGS. 1A-1B ) to translate relative to the platform  275 . 
       FIG. 2B  illustrates the mast carrier  152  in a raised position to orient the platform  275  at a desired angle relative to the vertical axis  140 . The orientation of the platform  275  can be further varied by further operation of the mast tilt cylinder  160  or by operation of the jib articulation assembly  135 . Operation of the jib articulation assembly  135  changes the orientation of the entire mast assembly  115  and thus the orientation of the mast tilt cylinder  160  as well. As previously introduced, the jib articulation assembly  135  includes at least one link having a variable length. In the example illustrated, the upper link  230  is the variable length link. It will be appreciated that the lower link  225  can have a variable length or a fixed length. Accordingly, either or both of the lower link  225  and the upper link  230  can have a variable length. Other links may also have variable lengths as desired. 
     The upper link  230  can have any configuration desired to provide a variable length. In the illustrated example, the upper link  230  is a hydraulic cylinder that is configured to extend and retract to vary the length of the upper link  230 . As previously introduced, arm  150 A is coupled to the second end  125 B of the jib boom by pivot  260 . Accordingly, extending the upper link  230  causes arm  150 B to rotate relative to arm  150 A about pivot  260 , thereby varying the orientation of the mast assembly  115  relative to the vertical axis  140 . 
     As previously introduced, the jib boom  125  can be raised and lowered by the jib lifter  130 . In particular, the jib lifter  130  extends and retracts to rotate the jib boom  125  about pivot  205 . Movement of the jib boom  125  due to rotation about pivot  205  includes both vertical and horizontal components. Accordingly, as the jib boom  125  rotates to the position illustrated in  FIG. 2C , movement of the second end  125 B includes both an upward component and a horizontal component. The horizontal component of rotating the jib boom  125  from the position in  FIG. 2B  to the position in  FIG. 2C  is directed toward the jib mount  200 . 
     The jib articulation assembly  135  is operatively associated with the jib boom  125  such that the jib articulation assembly  135  follows the jib boom  125 . Further the interaction between the jib boom  125  and the jib articulation assembly  135  is such that the jib articulation assembly  135  maintains the orientation of arm  150 B relative to arm  150 A. The articulation assembly may include any number of links and pivots to maintain the orientation between the arms  150 A and  150 B. Further, links may be positioned and oriented in any manner to maintain the alignment between the arms  150 A and  150 B. One exemplary configuration for the articulation will now be discussed in more detail. 
     As illustrated in  FIGS. 2B and 2C , the lower link  225  and the upper link  230  are coupled to each other and to the jib boom  125  by pivoting link  235 . Pivoting link  235  can be configured such that the lower link  225  and the upper link  230  are generally parallel to each other. In at least one example, the pivoting link  235  can position and maintain the lower link  225  and the upper link  230  parallel relative to each other and/or to maintain the lower link  225  and/or the upper link  230  parallel to the jib boom  125 . 
     Accordingly, movement of the jib articulation assembly  135  can be coupled to movement of the jib boom  125 . For example, as the jib boom  125  is raised, the jib boom  125  carries the pivoting link  235 . As the pivoting link  235  moves with the rotation of the jib boom  125 , the coupling of the lower link  225  to both the pivoting link  235  and the jib mount  200  causes the lower link  225  to rotate about pivot  210 . As the lower link  225  thus rotates, the second end  225 B moves both vertically and horizontally due to the rotation. The coupling between the jib boom  125  and the lower link  225  by the pivoting link  235  causes the vertical and horizontal movement of the lower link  225  to be proportional to the vertical and horizontal movement of the jib boom  125 . 
     Movement of the upper link  230  is coupled to movement of the lower link  225  by the pivoting link  235 . Accordingly, proportional movement of the lower link  225  is transmitted through the pivoting link  235  to the upper link  230 . Transmitting proportional movement of the lower link  225  to the upper link  230  causes the horizontal and vertical movement of the upper link  230  to be proportional to the horizontal and vertical movement of the jib boom  125 . As previously discussed, the upper link  230  is coupled to arm  150 B while the jib boom  125  is coupled to the arm  150 A. Accordingly, proportional movement of the upper link  230  relative to the lower link  225  results in proportional movement of the arms  150 A and  150 B. Proportional movement of the arms  150 A and  150 B can maintain the orientation of the arms  150 A and  150 B relative to each other. Maintaining the arms  150 A and  150 B at the same relative orientation maintains the orientation of the mast assembly mount  150  and thus the attached mast assembly  115  ( FIGS. 1A-1C ). 
     Accordingly, one configuration has been provided in which the lower link  225  and the upper link  230  are generally parallel to each other. In at least one example, the lower link  225  and the upper link  230  can also be generally parallel to the jib boom  125 . In at least one example, the lower link  225  and upper link  230  may be generally offset from each other as well as being offset from the jib boom  125 . The upper link  230  can also be a variable length link that is offset from the jib boom  125 . In other examples, links may be provided on a single side of the jib boom  125  that includes at least one variable length link. In such examples, the variable length link can be offset from the jib boom  125 . Further, in such examples, the link or links can move generally parallel to the jib boom  125  as the jib boom  125  rotates to raise and lower the mast assembly  115  ( FIG. 1A-1C ). 
     In yet another example, a single link may be provided that is generally parallel with the jib boom. Such a single link can be pivotingly coupled to a mount offset from the jib boom on one end and to the mast assembly mount on another end. Accordingly, various configurations can be provided by which a variable length link can be positioned at an offset relative to the jib boom while maintaining the variable length link generally parallel to the jib boom to maintain the orientation of a mast assembly mount while the jib boom is raised and lowered. 
       FIG. 3  illustrates a plan view of the jib assembly  110 , the mast assembly mount  150 , the mast slewing assembly  165 , and the mast tilt cylinder  160 . As previously introduced, the jib assembly  110  includes a jib slewing assembly  145 . In the illustrated example, the jib slewing assembly  145  can include slewing cylinders  305 A and  305 B. The slewing cylinders  305 A and  305 B can be coupled to a stationary structure, such as the jib mount  200 . Extension of slewing cylinder  305 A can be complimented by retraction of slewing cylinder  305 B to cause the rest of the jib assembly  110  to rotate about pivot  310  and thereby position the jib assembly  110  relative to the stationary structure. Slewing cylinder  305 B can be similarly extended while slewing cylinder  305 A is retracted to rotate the jib assembly  110  in the opposite direction. 
     In a similar manner, the mast slewing assembly  165  can be configured to pivot the mast carrier  152  relative to the jib assembly  110 . In particular, the mast carrier  152  can be coupled to a mast slewing head  315  by way of pivot  290 , illustrated in  FIGS. 2A-2C . Referring again to  FIG. 3 , the mast slewing assembly  165  can further include a mast slewing cylinder  320 . The mast slewing cylinder  320  can be secured to the mast slewing head  315  by a mount  325 . The mount  325  can provide a relatively stationary base from which the mast slewing cylinder  320  can be extended and retracted to rotate the mast carrier  152 . 
     The mast slewing cylinder  320  can be coupled to the mast carrier  152  by pivot  330 . The pivot  330  allows the mast slewing cylinder  320  to rotate as they expand and retract. Rotating the mast carrier  152  relative to the mast slewing head  315  can allow the mast slewing assembly  165  to further position the mast carrier  152  relative to the jib assembly  110 . 
     Relative extension of the jib lifter  130  ( FIGS. 2A-2C ) is maintained as the jib slewing assembly  145  rotates the jib boom  125 . Accordingly, the jib assembly  110  can be configured such that rotation of the jib boom  125  does not change the orientation of the jib boom  125 . Similarly, the mast assembly  115  ( FIGS. 2A-2B ) can be configured such that rotation of the mast carrier  152  by the mast slewing assembly  165  also does not change the orientation of the mast carrier  152 . Accordingly, the orientation of the jib boom  125  and/or the mast carrier  152  can be maintained as the jib boom  125  and mast carrier  152  are raised and lowered as well as rotated. 
     As previously introduced, the jib articulation assembly  135  ( FIGS. 2A-2C ) can be configured to provide relatively high-pull back torque as well as to help minimize the potential for over-rotation of the mast assembly  115  as the mast assembly  115  is moved from a drilling position to a transport position. A drilling position is illustrated in  FIG. 2B  while a transport position is illustrated in  FIG. 2A . 
     As previously introduced, the upper link  230  is offset from the jib boom  125 . As illustrated in  FIGS. 2A and 2B , a relatively short change in length of the upper link  230  may be used to move the mast assembly  115  from the drilling position to the transport position. A relatively short variance in length may increase the torque the upper link  230  exerts on the mast assembly mount  150  compared to configurations in which a lifting cylinder is mounted directly to a jib boom. Further, a relatively short variance in the upper link  230  may reduce the possibility that extension of the upper link  230  can cause the upper link  230  to over-rotate the mast assembly  115  past the vertical axis  140 . Accordingly, such a configuration can allow an operator to rotate the mast assembly  115  both toward and away from the rig ( 105 ,  FIGS. 1A-1B ) to a desired drilling angle. 
     Accordingly, articulation assemblies, jib assemblies, and drilling systems have been discussed herein that are configured to maintain a mast assembly at a drilling angle as the mast is raised and lowered. The mast may be raised and lowered to allow the drilling rig or drilling system to be moved. Accordingly, the drilling angle may be maintained as the drilling system or rig is moved between drilling locations on a job site where the same drilling angles are being used. The articulation assembly can provide a relatively high pull-back torque, which may allow the articulation assembly to readily move the mast assembly to a transport position. Further, the configuration of the articulation assembly may reduce the possibility that the drill mast will be over-rotated, thereby increasing the stability of the drilling system. 
     The present invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.