Abstract:
A method for blocking a pocket of a multi-pocket feed structure used to feed rods to and from a magazine of a directional drilling machine. The method includes providing a blocker at a non-blocking position, engaging the blocker with the feed structure, and extending the feed structure from beneath the magazine while the blocker engages and moves in concert with the feed structure. The method also includes disengaging the blocker from the feed structure after the feed structure has been extended, retracting the feed structure relative to the blocker until the blocker is positioned in a first blocking position in which at least one of the pockets of the feed structure is blocked, and re-engaging the blocker with the feed structure once the blocker is oriented in the first blocking position.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to underground drilling machines. More particularly, the present invention relates to rod loaders for feeding rods to and from horizontal directional drilling machines. 
     BACKGROUND OF THE INVENTION 
     Utility lines for water, electricity, gas, telephone and cable television are often run underground for reasons of safety and aesthetics. Sometimes, the underground utilities can be buried in a trench that is later back filled. However, trenching can be time consuming and can cause substantial damage to existing structures or roadways. Consequently, alternative techniques such as horizontal directional drilling (HDD) are becoming increasingly more popular. 
     A typical horizontal directional drilling machine includes a frame on which is mounted a drive mechanism that can be slidably moved along the longitudinal axis of the frame. The drive mechanism is adapted to rotate a drill string (i.e., a length of interconnected rods) about its longitudinal axis. Sliding movement of the drive mechanism along the frame, in concert with the rotation of the drill string, causes the drill string to be longitudinally advanced into or withdrawn from the ground. 
     In a typical horizontal directional drilling sequence, the horizontal directional drilling machine drills a hole into the ground at an oblique angle with respect to the ground surface. During drilling, drilling fluid can be pumped through the drill string, over a drill head (e.g., a cutting or boring tool) at the end of the drill string, and back up through the hole to remove cuttings and dirt. After the drill head reaches a desired depth, the drill head is then directed along a substantially horizontal path to create a horizontal hole. After the desired length of hole has been drilled, the drill head is then directed upwards to break through the ground surface. A pull-back sequence is then initiated. During the pull-back sequence, a reamer is attached to the drill string, and the drill string is pulled back through the hole. As the drill string is pulled back, the reamer enlarges the hole. It is common to attach a utility line or other conduit to the drill string so that it is dragged through the hole along with the reamer. 
     A typical horizontal directional drilling machine includes a rod box (i.e., a rack or magazine) for storing rods (i.e., pipes or other elongated members) used to make the drill strings. A rod transfer mechanism is used to transport rods between the drive mechanism of the directional drilling machine and the rod box. During a drilling sequence, the rod transfer mechanism transports rods from the rod box to the drive mechanism. During a pull-back sequence, the rod transfer mechanism transports rods from the drive mechanism back to the rod box. 
     U.S. Pat. No. 5,607,280 discloses a prior art rod handling device adapted for use with a horizontal directional drilling machine. As shown in FIG. 1, the rod handling device includes a rod box  24  having five vertical columns  41 - 45 . Bottom ends of the columns  41 - 45  are open so as to define five separate discharge openings  41   a - 45   a  through which rods can be fed. A selection member  50  is mounted beneath the discharge openings  41   a - 45   a . The selection member  50  has five pockets  41   b - 45   b , and functions to index or feed rods  20  to and from the rod box  24 . For example, during a drilling sequence, the selection member  50  indexes rods  20  from the rod box  24  to a pickup location where the rods are individually picked up and carried to a rotational drive head  16  of the drilling machine by a transfer arm  51 . During a pull-back sequence, the transfer arm  51  carries rods  20  from the rotational drive head  16  back to the pickup location, and the selection member  50  indexes the rods from the pickup location back beneath the rod box  24 . To move the rods from the selection member  50  back into the rod box, a lift is used to push pipes upwardly into the columns  51 - 54  of the rod box  24 . 
     During a typical drilling sequence, the rod box is unloaded starting with column  45 . After column  45  has been unloaded, column  44  is unloaded. Thereafter, column  43 , column  42  and column  41  are sequentially unloaded. During a pull-back sequence (i.e., a sequence in which rods are transferred from the drive head  16  back to the rod box  24 ), the columns are typically sequentially loaded starting with column  45  and finishing with column  41 . Once column  45  has been loaded, a block or plug is manually inserted into pocket  45   b  of the selection member  50  to prevent additional rods from being loaded into column  45 . Thereafter, column  44  is loaded. Once column  44  has been filled, a plug or block is manually inserted into pocket  44   b  of the selection member  50  to prevent additional rods from being loaded into column  44 . Column  43  is then loaded. After column  43  has been loaded, a block or plug is inserted into pocket  43   b  of the selection member to prevent additional rods from being loaded into column  43 , and column  42  is loaded. Once column  42  has been fully loaded, a block or a plug is manually inserted into pocket  42   b  of the selection member  50  to prevent additional rods from being loaded into column  42 , and column  41  is loaded. 
     SUMMARY OF THE INVENTION 
     One aspect of the present invention relates to a method for blocking a pocket of a multi-pocket feed structure used to feed rods to and from a magazine of a directional drilling machine. The method includes providing a blocker at a non-blocking position, engaging the blocker with the feed structure, and extending the feed structure from beneath the magazine while the blocker engages and moves in concert with the feed structure. The method also includes disengaging the blocker from the feed structure after the feed structure has been extended, retracting the feed structure relative to the blocker until the blocker is positioned in a first blocking position in which at least one of the pockets of the feed structure is blocked, and re-engaging the blocker with the feed structure once the blocker is oriented in the first blocking position. 
     A further aspect of the present invention relates to a horizontal directional drilling machine including a magazine, a feed structure for indexing rods to and from the magazine, a rotational drive head for propelling rods into the ground, and a transfer mechanism for moving the rods between the rotational drive head and the feed structure. The transfer mechanism includes a rod holder for holding the rods, and a drive cylinder for moving the holder between the rotational drive head and the feed structure. The transfer mechanism of this embodiment also includes a camming structure for causing the holder to move along an arcuate path as the drive cylinder moves the holder between the rotational drive head and the feed structure. 
     A variety of advantages of the invention will be set forth in part in the description that follows, and in part will be apparent from the description, or may be learned by practicing the invention. It is to be understood that both the foregoing general description and the following detailed description are explanatory only and are not restrictive of the invention as claimed. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate several aspects of the invention and together with the description, serve to explain the principles of the invention. A brief description of the drawings is as follows: 
     FIG. 1 illustrates a prior art rod handling apparatus; 
     FIG. 2 is an elevational view of a horizontal directional drilling machine constructed in accordance with the principles of the present invention; 
     FIG. 3 is a perspective view of the horizontal directional drilling machine of FIG. 2; 
     FIG. 4 is a perspective view of the horizontal directional drilling machine of FIG. 2 with the rod box removed; 
     FIGS. 5 a - 5   g  illustrate a rod transfer sequence for moving a rod from the magazine to the rotational drive head of the horizontal directional drilling machine of FIG. 2; 
     FIGS. 6 a - 6   g  illustrate a rod transfer sequence for moving a rod from the rotational drive head to the magazine of the horizontal directional drilling machine of FIG. 2; 
     FIG. 7 illustrates a rod lift used by the horizontal directional drilling machine of FIG. 2; 
     FIG. 8 is a perspective view of a rod transfer mechanism used by the horizontal directional drilling machine of FIG. 2; 
     FIG. 9 is a top plan view of the rod transfer mechanism of FIG. 8; 
     FIGS. 10 a - 10   d  illustrate how the rod transfer mechanism of FIGS. 8 and 9 moves a rod along a curved path as the rod is transferred between the magazine and the rotational drive head; 
     FIG. 11 a  illustrates one side of a rod indexing arrangement used by the horizontal directional drilling machine of FIG. 2; 
     FIG. 11 b  illustrates the other side of the rod indexing arrangement of the FIG. 11 a ; and 
     FIGS. 12 a - 12   f  illustrate a blocker sequence for the rod indexing arrangement of FIGS. 11 a  and  11   b , portions of the rod indexing assembly have been broken away for clarity. 
    
    
     DETAILED DESCRIPTION 
     With reference now to the various drawings in which identical elements are numbered identically throughout, a description of various exemplary aspects of the present invention will now be provided. 
     I. Overview of Directional Drilling Machine 
     FIGS. 2-4 illustrate a horizontal directional drilling machine  120  constructed in accordance with the principles of the present invention. The directional drilling machine  120  includes an elongated guide or track  122  that can be positioned by an operator at any number of different oblique angles relative to the ground. A rotational driver  124  (i.e., a drive head) is mounted on the track  122 . The rotational driver  124  is adapted for rotating a drill string (i.e., a string of interconnected rods) in forward and reverse directions about a longitudinal axis of the drill string. The rotational driver  124  includes a drive chuck  123  for connecting the rotational driver to the drill string. Gripping units  150  (e.g., vice grips or wrenches) are provided adjacent the track  122  for use in coupling and uncoupling rods to the drive chuck  123 . A thrust mechanism (not shown) is provided for: 1) pushing the rotational driver  124  down the track  122  to push a drill string into the ground during drilling operations; and 2) pulling the rotational driver  124  up the track  122  to pull a drill string from the ground during reaming/pull-back operations. 
     It will be appreciated that the above-described components are well known in the art and can have any number of different configurations. Exemplary prior art machines including such components are manufactured by Vermeer Manufacturing Company of Pella, Iowa. 
     Referring again to FIGS. 2 and 3, the horizontal directional drilling machine  120  also includes a removable rod box  128  (i.e., a magazine or rack) for storing the drilling rods. As best shown in FIG. 3, the rod box  128  defines four separate vertical rod storage columns  130   a - 133   a . Each of the columns  130   a - 133   a  has an open lower end for allowing rods to be discharged from the rod box  128  and/or for allowing rods to be loaded back into the rod box  128 . While four columns have been shown, it will be appreciated that the number of columns can be varied without departing from the principles of the present invention. 
     As best shown in FIG. 4, the directional drilling machine  120  also includes a cycling apparatus for feeding rods to and from the rod box  128 . The cycling apparatus includes two indexing assemblies  140 . A shown in FIG. 3, the indexing assembles  140  are positioned so as to be located beneath opposite ends of the rod box  128  when the rod box  128  is mounted on the directional drilling machine  120 . Alignment structures  142  are provided on the directional drilling machine  120  for aligning the rod box  128  relative to the indexing assemblies  140 . 
     The indexing assemblies  140  each include a feed structure  144  (i.e., an indexing member or a feed member) and a blocking structure  146 . Each of the feed structures  144  includes a plurality of upwardly opening pockets. Preferably, the number of pockets provided on each feed structure  144  is equal to the number of columns provided in the rod box  128 . For example, as shown in FIG. 4, each feed structure  144  includes four pockets  130   b - 133   b  corresponding to the four columns  130   a - 133   a  of the rod box  128 . The pockets  130   b - 133   b  are sized for receiving and holding rods. Each of the feed structures  144  also includes a blocking element  134  positioned adjacent to the pocket  133   b  or within the feed structure  144 . 
     The feed structures  144  are used to feed rods out from beneath the rod box  128  during drilling operations, and also used to feed rods back under the rod box  128  during pull-back operations. A pair of transfer mechanisms  136  are provided for transferring rods between the feed structures  144  and the gripping units  150  of the directional drilling machine  120 . The directional drilling machine  120  further includes a pair of lifts  138  for lowering rods from the rod box  128  to the feed structures  144 , and also for lifting rods from the feed structure  144  to the rod box  128 . 
     II. Sequence for Transferring Rods from Rod Box to Rotational Driver 
     FIGS. 5 a - 5   g  illustrate a transfer sequence for moving rod  160  from the rod box  128  to the gripping units  150  during a drilling operation. In FIG. 5 a , rod  160  is located within pockets  130   b  of the feed structures  144 , and the feed structures  144  are oriented in a retracted position in which pockets  130   b - 133   b  are positioned directly beneath respective columns  130   a - 133   a . Also, the lifts  138  are lowered, and the rod transfer mechanisms  136  are retracted. 
     To initiate the transfer sequence, the feed structures  144  are moved from the retracted position of FIG. 5 a  to an extended position as shown in FIG. 5 b . The distance between the retracted position and the extended position is preferably about one column width. In the extended position, the pockets  130   b  are no longer positioned beneath the rod box  128 . With the feed structures  144  extended, the lifts  138  are raised as shown in FIG. 5 c . By raising the lifts  138 , the rods of the rod box  128  are lifted from the pockets  130   b - 133   b . With the lifts  138  raised, the feed structures  144  are the retracted as shown in FIG. 5 d . Next, the lifts  138  are lowered such that the lowermost rods within the rod box  128  are placed in the pockets  130   b - 133   b , and rod  160  is placed into engagement with the transfer mechanisms  136  (see FIG. 5 e ). Thereafter, the transfer mechanisms  136  are extended to place rod  160  in the gripping units  150  as shown in FIG. 5 f . With rod  160  so positioned, the gripping units  150  hold rod  160  in axial alignment with the drive chuck  123  of the rotational driver  124 . Rod  160  is also held in axial alignment with a drill string that may have already been drilled into the ground. As so aligned, rod  160  can be coupled to both the rotational driver  124  and the drill string thereby enabling rod  160  to be propelled into the ground. Finally, the transfer mechanisms  136  are retracted as (shown in FIG. 5 g ), and the cycle can be repeated to transfer the next rod (i.e., the rod held within pocket  130   b ) to the drill string. 
     III. Sequence for Transferring Rods from Rotational Driver to Rod Box 
     FIGS. 6 a - 6   g  illustrate a transfer sequence for transferring rod  160  from the drill string back to the rod box  128  during a pull-back sequence. As shown in FIG. 6 a , rod  160  is located at the gripping units  150 , the feed structures  144  and the transfer mechanisms  136  are retracted, and the lifts  138  are lowered. To initiate the sequence, the transfer mechanisms  136  are extended to engage rod  160  as shown in FIG. 6 b . Next, the transfer mechanisms  136  are retracted as shown in FIG. 6 c . Subsequently, the lifts  138  are raised thereby clearing the rods from the feed structures  144  as shown in FIG. 6 d . With the rods raised, the feed structures  144  are moved from the retracted orientation to the extended orientation as shown in FIG. 6 e . Thereafter, the lifts  138  are lowered thereby lowering the rods into the pockets  130   b - 133   b  of the feed structures  144  (see FIG. 6 f ). After the lifts  138  have been lowered, the feed structures  144  are retracted such that the pockets  130   b - 133   b  align beneath the columns  130   a - 133   a  as shown in FIG. 6 g . Finally, the lifts  138  can again be raised to lift all of the rods into the rod box  128 . The sequence is repeated to load additional rods into the rod box  128 . 
     IV. Lift Apparatus 
     FIG. 7 shows one of the lifts  138  in isolation from the horizontal directional drilling machine  120 . The depicted lift  138  can be raised and lowered by any number of conventional structures. For example, one or more hydraulic cylinders can be used to raise and lower the lift  138 . The lift  138  includes a top piece  162  having a first portion  164  and a second portion  166 . The first portion  164  is adapted to align beneath the rod box  128 , and the second portion  166  is adapted to extend laterally outward beyond the bottom of the rod box  128 . The first portion  164  defines four rod cradling recesses  130   c - 133   c , and the second portion  166  also defines a rod cradling recess  134   c . When the rod box  128  is mounted on the directional drilling machine  120 , as shown in FIG. 5 c , the pipe cradling recesses  130   c - 133   c  respectively align with the columns  130   a - 133   a  of the rod box  128 , and the recess  134   c  is laterally offset from the rod box  128 . The location of the rod holding recess structure  134   c  facilitates its use as a rod staging location for temporarily holding rods as they are transferred between the feed structures  144  and the transfer mechanisms  136 . 
     While recesses has been shown for holding or cradling rods on the top piece  162  of the lift  138 , it will be appreciated that other structures for retaining rods (e.g., lips, mechanical grippers, flanges, fingers, etc.) can also be used. For example, optional stops  139  can be used. Additionally, a fixed stop (e.g., a wall or barrier) attached to the frame at a location adjacent to the end of the second portion  166  could also be used. 
     V. Rod Transfer Mechanism 
     FIGS. 8 and 9 illustrate one of the transfer mechanisms  136  in isolation from the horizontal directional drilling machine  120 . The depicted transfer mechanism  136  includes a frame including two spaced-apart, substantially parallel plates  168 . The plates  168  are interconnected by spacers  170 . The plates  160  define arcuate camming slots  172  that are aligned with one another. A drive cylinder  174  is mounted between the plates  168 . The drive cylinder  174  includes a cylinder portion  176  and a piston rod portion  178 . A base end  180  of the cylinder portion  176  is pivotally connected to the plates  168 , and a free end  182  of the piston rod portion  178  is connected to a rod holder  184 . As shown, the rod holder  184  comprises a magnet (e.g., an electromagnet or a permanent magnet) having a rod cradling recess  186 . Alternatively, the rod holder can include any number of different configurations such as mechanical grippers, suction type holders, or full pockets. It will be appreciated that the drive cylinder  174  is preferably powered by hydraulic pressure. 
     The transfer mechanism  136  also includes a linkage  190  that extends along the drive cylinder  174 . The linkage includes elongated members  192  positioned on opposite sides of the drive cylinder  174 . The elongated members  192  are connected to the rod holder  184  and are parallel to the piston rod portion  178 . Extensions  193  project transversely outward from the elongated members  192 . The extensions  193  include rollers  194  that fit within the arcuate slots  172  of the plates  168 . 
     To move the rod holder  184  from the rod box  128  to the drill string, the drive cylinder  174  is extended. By contrast, to return the rod holder  184  from the drill string to the rod box  128 , the drive cylinder  174  is retracted. As the drive cylinder  174  is extended or retracted, the rollers  194  ride along the camming slots  172  thereby causing the base end  180  of the cylinder portion  176  to pivot such that the rod holder  184  moves along an arcuate path. 
     FIGS. 10 a - 10   d  illustrate a sequence in which the transfer mechanisms  136  move rod  160  from the rod cradling recesses  134   c  of the lifts  138  to the gripping units  150 . As the drive cylinder  174  is extended, the base end  180  pivots about pivot point  191 . Also, as the drive cylinder  174  is extended, rollers  194  ride in the arcuate slots  172  causing the rod holder  194  to move along an arcuate path. The arcuate path traversed by the rod holder  184  facilitates loading rods into side loading style gripping units. Concurrently, the transfer mechanisms  136  allow the bottom of the rod box  128  to be positioned below the gripping units  150  thereby lowering the center of gravity of the rod box  128 . 
     VI. Indexing Assembly 
     FIGS. 11 a  and  11   b  illustrate one of the indexing assemblies  140  in isolation from the horizontal directional drilling machine  120 . The depicted indexing assembly  140  includes one of the feed structures  144  and one of the blocking structures  146 . As shown in FIGS. 11 a  and  11   b , a hydraulic cylinder  195  is provided for moving the feed structure  144  between the retracted position (shown in FIG. 5 a ) and the extended position (shown in FIG. 5 b ). However, it will be appreciated that other types of drives (e.g., rack and pinion drives, chain drives, etc.) could also be used. 
     For certain applications, it is desirable to block one or more of the pockets  131   b - 133   b  of the feed structure  144  so as to prevent rods from entering the pocket structures  131   b - 133   b . This function is provided by the blocking structure  146 . The blocking structure  146  is mounted between the feed structure  144  and a guide member  197 . The guide member  197  is substantially parallel to the feed structure  144 . The blocking structure  146  includes a top blocking surface  199  preferably positioned at the top of the feed structure  144 . Preferably, the blocking surface  199  is sufficiently long or otherwise sized/shaped to be capable of concurrently blocking all but one of the pockets (e.g., pockets  131   b - 133   b ). 
     The blocking structure  146  also includes a pin  200  adapted to fit within openings  201 - 204  defined by the feed structure  144 . The pin is preferably mechanically actuated (e.g., by a solenoid or drive cylinder). When the pin  200  is inserted within opening  201 , the blocking structure  46  is oriented in a non-blocking position (shown in FIGS. 11 a  and  11   b ) in which the blocking surface  199  is positioned generally adjacent to the blocking element  134  of the feed structure  144 . In the non-blocking position, the blocking surface  199  does not block any of the pockets  131   b - 133   b . Because the pin  200  is inserted within the opening  201 , the blocking structure  146  moves in concert with the feed structure  144  as the feed structure  144  is retracted and extended. 
     A The blocking structure  146  is particularly useful for loading rods into the rod box  128 . For example, when rods are loaded into the rod box  128  with none of the pockets  131   b - 133   b  blocked, the rods will continuously be fed into the last column  133   a  of the rod box  128 . When the column  133   a  becomes full of rods, it is desirable to block the pocket  133   b  to prevent further rods from being fed into the last column  133   a . This is accomplished by disengaging the pin  200  from the opening  201 , generating relative movement between the blocking structure  146  and the feed structure  144  until the pin  200  aligns with the opening  202 , and then inserting the pin  200  within the opening  202 . With the pin  200  inserted within the opening  202 , the blocking structure  146  is oriented in a first blocking position in which the blocking surface  199  blocks the pocket  133   b . With the pocket  133   b  blocked, rods fed into the rod box  128  are loaded into the column  132   a . Because the pin  200  is inserted within the opening  202 , the blocking structure  146  once again moves in concert with the feed structure  144  as the column  132   a  is loaded. 
     After the column  132   a  has been filled with rods, it is desirable to block the pocket  142   b  to prevent additional rods from being loaded into the column  132   a . Thus, the blocking structure  146  is moved to a second blocking position by: 1) removing the pin  200  from the opening  202 ; 2) generating relative movement between the blocking structure  146  and the feed structure  144  until the pin  200  aligns with the opening  203 ; and 3) inserting the pin  200  into the opening  203 . With the pin  200  inserted into the opening  203 , the blocking structure  146  moves in concert with the feed structure  144  and functions to block both of the pockets  132   b  and  133   b.    
     With the blocking structure  146  in the second blocking position, rods fed into the rod box  128  are loaded into the column  131   a . Once the column  131   a  is filled, the blocking structure  146  is moved to a third blocking position by: 1) removing the pin  200  from the opening  203 ; 2) generating relative movement between the blocking structure  146  and the feed structure  144  until the pin  200  is brought into alignment with the opening  204 ; and 3) inserting the pin  201  into the opening  204 . With the pin  200  inserted into the opening  204 , the blocking structure  146  moves in concert with the feed structure  144  and functions to concurrently block each of the pockets  131   b - 133   b . Thus, rods fed into the rod box  128  are loaded into the first column  130   a.    
     FIGS. 12 a - 12   f  illustrate a sequence for moving the blocking structure  146  from the non-blocking position to the first blocking position in which the blocking structure  146  blocks the pocket  133   b . As shown in FIG. 12 a , the blocking structure  146  is positioned in the non-blocking position with the pin  200  inserted in the opening  201  of the feed structure  144 . The feed structure  144  is shown in a retracted position. To initiate the sequence, the feed structure  144  is first extended as shown in FIG. 12 b . With the feed structure  144  extended, the pin  200  is disengaged from the opening  201  and inserted into an opening  205  defined by the guide member  197  (see FIG. 12 c ). Movement of the pin  200  is preferably done automatically/mechanically (e.g., by a solenoid), but could also be done manually. The feed structure  144  is then retracted, while the blocking structure  146  remains stationary, to generate relative movement between the feed structure  144  and the blocking structure  146 . After retraction, the blocking structure  146  is located at the position in which pocket structure  133   b  is blocked (see FIG. 12 d ). To retain the blocking structure  146  in this position, the pin  200  is removed from the opening  205  in the guide member  197 , and inserted into the opening  202  defined by the feed structure  144  (see FIG. 12 e ). Thereafter, the blocking structure  146  will move in concert with the feed structure  144  as the feed structure  144  is retracted and extended to load additional rods into the magazine (see FIG. 12 f ). 
     As described above, FIGS. 12 a - 12   f  illustrate a sequence for moving the blocking structure  146  from the non-blocking position to the first blocking position in which the pocket  133   b  is blocked. It will be appreciated that similar sequences can be used to move the blocking structure  146  to the second blocking position corresponding to the opening  203  (i.e., position in which both of the pockets  132   b  and  133   b  are blocked), and the third blocking position corresponding to the opening  204  (i.e., the blocking position in which all three of the pockets  131   b - 133   b  are blocked). For example, to move the blocking structure  146  from the first blocking position to the second blocking position, the feed structure  144  is extended, and the pin  200  is inserted into opening  206  defined by the guide member  197 . The feed structure  144  is then retracted while the blocking structure  146  remains stationary. The feed structure  144  is preferably retracted until the opening  203  is brought into alignment with the pin  200 . Once alignment is achieved, the pin  200  is removed from the opening  206  of the guide member  197 , and inserted into the opening  203  of the feed structure  144  such that the blocking structure  146  is locked in the second blocking position. 
     To move the blocking structure  146  from the second blocking position to the third blocking position, the feed structure  144  is again extended. Once extended, the pin  200  is inserted into opening  207  defined by the guide member  197  to prevent the blocking structure  146  from moving with the feed structure  144 . The feed structure  144  is then retracted until the pin  200  is brought into alignment with the opening  204  of the feed structure  144 . Finally, pin  200  is removed from the opening  207  in the guide member  197 , and inserted into the opening  204  of the feed structure  144  to lock the blocking structure  146  in the third blocking position. 
     In addition to performing blocking functions when rods are being loaded into the rod box  128 , the blocking structures  146  can also be used to control which column of the rod box  128  from which rods are unloaded. For example, during a typical unloading operation, rods are first unloaded from column  133   a , next unloaded from column  132   a , subsequently unloaded from column  131   a  and finally unloaded from  130   a . However, this can be varied by using the blocking structures  146 . For example, with the rod box  128  full, the blocking structures  146  can be placed in the third blocking location thereby causing rods to initially be unloaded from the column  130   a . After column  130   a  has been emptied, the blocking structures  146  can be moved to the second blocking position thereby allowing rods to be unloaded from column  131   a . Once column  131   a  has been unloaded, the blocking structures  146  can be moved to the first blocking position thereby allowing rods to be unloaded from column  132   a . After column  132   a  has been unloaded, the blocking structures  146  can be moved to the non-blocking position such that rods can be unloaded from column  133   a.    
     In certain embodiments, a controller can be used to automatically sequence the blockers  146  through the above-described steps. The controller can interface with sensors (e.g., proximity sensors) at the columns to determine when the columns are full. 
     The above specification and examples provide a complete description of the manufacture and use of the composition of the invention. Since many embodiments of the invention can be made without departing from the spirit and scope of the invention, the invention resides in the claims hereinafter appended.