Patent Publication Number: US-6698529-B2

Title: Translating turret rock bolter

Description:
FIELD OF THE INVENTION 
     The present invention is for a rock bolter which drills holes and sets bolts for stabilizing the roof and walls of mines, and more particularly for a rock bolter which can set bolts into rough rock surfaces while remaining compact in overall size. 
     BACKGROUND OF THE INVENTION 
     Rock bolters have been developed to drill holes and set bolts to stabilize rock walls in mines and similar excavations. One type of rock bolter is the turret rock bolter, which typically has two feed tracks. One feed track directs a rock drill as it advances toward a rock surface to bore a hole into which a bolt is to be set, while a second feed track directs a bolt driver as it is advanced toward the rock surface to set the bolt into the hole. The feed tracks are sequentially rotated into a work position where the drill or the rock bolter residing thereon is in alignment with a particular location on the rock surface, and the rock drill or bolt driver is then advanced along its feed track to the rock surface. First, the drill is placed in the work position and advanced to drill a hole in the rock surface at the desired location. The drill is then withdrawn from the hole, and the turret is rotated to place the bolt driver in the work position, aligned with the hole. The bolt driver is then advanced to set the bolt into the hole. A stinger assembly is usually employed to engage the rock surface to stabilize the turret during the bolt setting process, in which case the turret typically rotates about an axis extending through the stinger assembly. 
     In many instances, the rock surface into which bolts are to be set is uneven, which limits the ability to rotate the feed tracks when they are positioned in close proximity to the rock surface. In an attempt to overcome this problem, U.S. Pat. No. 4,497,378 teaches a turret rock bolter where the feed tracks are translated away from the rock surface before rotating to allow the turret to rotate when the feed tracks are spaced further from the rock surface. 
     FIG. 1 is a schematic representation of the basic elements of the turret rock bolter taught in the &#39;378 patent. The rock bolter has a turret  10  having a support base  12  which is connected to a boom  14  for positioning the turret  10 . A first cylindrical member  16  is fixed to the support base  12  and has an anchoring point  18  on one end. When the boom  14  is moved to position the anchoring point  18  against a rock surface (not shown), the anchoring point  18  engages the rock surface to act as a stinger. 
     A pair of spaced-apart bearing brackets  20  are rotatably and slidably mounted on the first cylindrical member  16 , and a feed track support  22  is fixed to the bearing brackets  20  so as to extend parallel to the first cylindrical member  16 . A drill track  24  and a bolt driver track  26  are provided on the feed track support  22 . A rock drill  28  is longitudinally movable along the drill feed track  24 , while a bolt driver  30  is longitudinally movable along the bolt driver track  26 . An advancing mechanism  32  is employed to selectively move the rock drill  28  and the bolt driver  30  along their respective feed tracks ( 24 ,  26 ). In the rock bolter of the &#39;378 patent, the advancing mechanism  32  employs a system of pulleys  34  to allow a single advancing piston  36  to move either the drill  28  or the bolt driver  30  when the other of the two is immobilized. 
     To translate the feed track support  22  away from the rock surface, providing greater space for rotation, a translating piston  38  is mounted to the first cylindrical member  16  and is rotatably mounted to the feed track support  22 . When the translating piston  38  is extended, the feed track support  22  is moved such that the separation of the drill feed track  24  and the bolt driver feed track  26  from the rock surface is increased. 
     To pivot the feed track support  22  to position either the drill  28  or the rock bolter  30  in alignment with a work axis  40 , a second cylindrical member  42  is fixed to the bearing brackets  20 . A pivot link  44  is rotatably mounted on the first cylindrical member  16  and both slidably and rotatably engages the second cylindrical member  42 . A pivot piston  46  is connected at one end to the support  12 , and at the other end to the pivot link  44 . By extending and retracting the pivot piston  46 , the pivot link  44  is rotated with respect to the first cylindrical member  16 . The second cylindrical member  42 , the bearing brackets  20 , and the feed track support  22  rotate with the pivot link  44 , and thus the feed track support  22  is rotated to position either the drill  28  or the rock bolter  30  in alignment with the work axis  40 . 
     While the rock bolter of the &#39;378 patent allows translating the feed tracks away from the rock surface to facilitate rotation, it requires a complex structure to accomplish such action. The rock bolter has multiple, widely spaced bearings, which complicates the task of keeping the bearings protected from dirt and adequately lubricated. Furthermore, the use of the translating piston  38  to translate the feed track support  22  toward and away from the rock surface can result in binding. Because the translating piston  38  is mounted to one end of the first cylindrical member  16 , forces on the various bearings are unbalanced, and must be transmitted long distances through other elements of the structure. The slidable bearing between the pivot link  44  and the second cylindrical member  42  can be particularly problematic, since it is not only axially spaced apart from the translating piston  38 , but is also positioned on a different axis and thus is highly subject to torque. Because the feed track support  22  must rotate with respect to the translating piston  38 , all translation forces must be transmitted through the pivotable connection between these two elements, placing great strain on this connection. 
     Thus, there is a need for a turret rock bolter which allows translation of the feed track support while overcoming the deficiencies of the device discussed above. 
     SUMMARY OF THE INVENTION 
     The rock bolter of the present invention employs a turret assembly where a boom is employed to position the turret assembly at a desired location with respect to a rock surface. The turret assembly has a base which is connectable to the boom. The connection of the base to the boom may include one or more knuckles, roll actuators, or similar devices known in the art for further adjusting the position and orientation of the turret assembly. The base may also serve to support other elements of the rock bolter, such as a bolt magazine for supplying a number of bolts and bolt plates sequentially to the bolt driver, such as taught in U.S. Pat. No. 5,597,267. 
     The base has at least one base bearing, and preferably a pair of spaced-apart base bearings. The at least one base bearing slidably and rotatably engages a cylindrical member having a cylinder axis. The cylindrical member terminates in a cylinder first end region and a cylinder second end region. A pair of spaced-apart brackets are fixably connected to the cylindrical member, with the base residing therebetween. One of the brackets is fixed to the cylinder first end region, while the other is fixed to the cylinder second end region. 
     Attached to the brackets is a feed track support which extends parallel to the cylindrical member. The feed track support has a drill feed track and a rock bolter feed track mounted thereon, and the feed tracks can be formed as integral parts of the feed track support. A rock drill is longitudinally movable along the drill feed track, and typically is mounted to the drill feed track via a drill carriage. The drill has a drill steel for drilling a hole in the rock surface as the drill is advanced along the drill feed track. A bolt driver is longitudinally movable along the bolt driver feed track support, and typically is mounted to the bolt driver feed track by a bolt driver carriage. The bolt driver, when advanced along the bolt driver feed track, advances a bolt into a hole bored by the drill. 
     Preferably, the base is configured such that the feed track support faces the operator of the rock bolter to provide the operator clear visibility of the drill and the rock bolter during the bolt setting process. 
     An advancement mechanism is provided for selectively moving the drill and the bolt driver along their respective feed tracks. Such advancement mechanisms are known in the art, such as the mechanism taught in U.S. Pat. No. 4,497,378 and discussed above, which employs single actuator for advancing both the drill and the bolt driver. 
     A jack is provided, having a jack body with at least one jack bearing which is rotatably mounted on the cylindrical member between the pair of brackets, and thus is rotatable relative to the base about the cylinder axis. The at least one jack bearing is also slidably engaged with the cylindrical member. The jack has at least one extendable piston which can be extended from the jack body and is connected to one of the brackets attached to the cylindrical member. 
     Means are provided for limiting translation between the at least one jack bearing and the at least one base bearing of the base such that the jack is allowed only very limited or, more preferably, no translational motion with respect to the base. Thus, when the cylinder translates relative to the base, it also translates relative to the jack body as well. The means for limiting translation of the at least one jack bearing with respect to the at least one base bearing can be provided by various means, such as by employing paired bearings positioned on either side of another bearing and constrainably engaging it either directly or via spacers, or by providing a bracket on either the base or the jack positioned to constrain the translational motion of a bearing. Preferably, a pair of base bearings are employed with a single jack bearing positioned therebetween and constrained thereby. In addition to providing a simple structure for constraining translational motion of the jack with respect to the base, the pair of base bearings and the jack bearing can be positioned adjacent to each other to provide reduced exposure of the individual bearings to dirt and debris. 
     Since translation of the jack body with respect to the base is limited, extending or retracting the at least one piston of the jack relative to the jack body provides a motivating force to translate the cylindrical member relative to the base and the jack. Preferably, the jack is a dual-action jack, having a pair of opposed pistons extending from either end of the jack body and moving in coordination, the opposed pistons each being attached to one of the pair of brackets. The use of opposed pistons provides more balanced forces on the translating elements to minimize binding. In all cases, when the at least one piston of the jack is activated, it moves the brackets relative to the one or more jack bearings, and the cylindrical member which is affixed to the brackets is moved longitudinally relative to the base. The feed tracks, which are fixed relative to the cylindrical member, are thus moved toward and away from the rock surface. 
     Since the at least one piston of the jack is attached to the brackets which are in turn affixed to the cylindrical member, the jack rotates with respect to the base about the cylinder axis in coordination with the cylindrical member. 
     A stinger assembly is provided, which is brought into engagement with the rock surface to stabilize the base during the drilling and bolt setting process. The stinger assembly is connected to the base either by attaching it thereto or by linking the stinger assembly to the base so as to avoid translational motion of the base in a direction parallel to the cylinder axis of the cylindrical member. The stinger assembly preferably has a stinger fixed portion which includes a stinger support structure that is affixed to either the base or the jack. It is further preferred for the stinger support structure to be configured to provide engagement with the rock surface at a point which lies along the cylinder axis. 
     Preferably, the stinger assembly has a stinger extendable portion which is extendably attached to the stinger fixed portion and terminates in a rock-engaging pad which is advanced toward the rock surface when the stinger extendable portion is extended. Preferably, the extension of the stinger extendable portion is provided by a linear actuator operating between the rock-engaging pad and the stinger support structure to eliminate the need to position the rock-engaging pad against the rock surface solely by motion of the boom. When the stinger support structure is mounted to the jack, it is preferred for the rock-engaging pad to be rotatable with respect to the stinger fixed portion. 
     A pivot actuator is operably connected between the base and the jack. When activated, the pivot actuator rotates the jack relative to the base about the cylinder axis. Since the feed track support is fixed to the brackets which in turn are affixed to the at least one piston of the jack, the feed track support rotates with the jack. Thus, the pivot actuator serves to rotate the feed track support to selectively place either the drill or the bolt driver in alignment with a desired location on the rock surface where the rock bolt is to be placed. When the drill has been positioned, it can be advanced along the drill feed track to bore a hole in the rock surface at the desired location. After the drill is withdrawn, the pivot actuator is activated to rotate the feed track support to place the bolt driver in alignment with the hole, and the bolt driver can thereafter be advanced to insert a bolt into the hole. 
     In one preferred embodiment, the pivot actuator is provided by a pivot linear actuator which is pivotably connected at one end to the base and at the other end to the jack. The pivot linear actuator is offset from the cylinder axis, and rotates the jack relative to the base as the pivot linear actuator is extended and retracted. 
     In use, the boom of the rock bolter is employed to position the turret assembly in a desired location and orientation relative to the rock surface, and the stinger assembly is engaged with the rock surface. When the stinger assembly includes a stinger extendable portion, the boom need only position the stinger assembly in close proximity to the rock surface, and the stinger extendable portion is then extended to engage the stinger assembly with the rock surface. At this time, the drill is positioned by the pivot actuator in alignment with the desired location for placement of the bolt if it is not already so aligned. If the jack is positioned so as to place the feed tracks at a substantial separation from the rock surface, the jack is activated to move the feed tracks in closer proximity to the rock surface. 
     The drill is then advanced along the drill feed track to bore a hole into the rock surface at the desired location. The drill is then withdrawn from the rock surface along the drill feed track and, if necessary, the jack is activated to move the feed track support away from the rock surface. If the rock surface is relatively flat, and there is sufficient space in close proximity to the rock surface to rotate the feed track support, withdrawal of the feed track support away from the rock surface is not required. 
     To move the bolt driver into alignment with the bolt hole, the pivot actuator is activated to rotate the jack and feed track support about the cylinder axis. The jack is then activated, if necessary, to bring the bolt driver feed track into close proximity to the rock surface, and the bolt driver is advanced to insert the bolt into the hole bored by the drill. 
    
    
     BRIEF DESCRIPTION OF THE FIGURES 
     FIG. 1 is an isometric view of a prior art turret rock bolter where a pair of feed tracks can be translated with respect to a base. 
     FIG. 2 is an isometric view illustrating a turret rock bolter which forms one embodiment of the present invention. A base of the rock bolter has a pair of base bearings which slidably and rotatably engage a cylindrical member which in turn is affixed to a pair of brackets. A feed track support is mounted to the brackets, and can be translated with respect to the base by a dual-action jack which is rotatably engaged with the cylindrical member. In FIG. 2, the feed track support is positioned to align a rock drill with a desired location on a rock surface and is advanced towards the rock surface to facilitate drilling a bolt hole thereinto. A stinger assembly mounted to the base engages the rock surface to stabilize the rock bolter. 
     FIG. 3 illustrates the embodiment shown in FIG. 2 where the dual-action jack has been activated to move the feed track support to a position of increased separation from the rock surface prior to pivoting the feed track support. 
     FIG. 4 illustrates the embodiment shown in FIGS. 2 and 3 where a pivot actuator has been activated to move the feed track support to place a bolt driver into alignment with the bolt hole. Since the feed track support is withdrawn from the rock surface, the pivoting of the feed track support is not impeded by unevenness of the rock surface. 
     FIG. 5 illustrates the embodiment shown in FIGS. 2-4 where the dual-action jack has again been activated, to move the feed track support into closer proximity to the rock surface to facilitate insertion of a bolt into the bolt hole by the bolt driver. 
     FIG. 6 is an isometric view which illustrates an embodiment similar to that shown in FIGS. 2-5, but where the jack has a pair of bearings which engage the cylindrical element and bracket a single base bearing, and where a stinger assembly of the rock bolter is mounted to the jack, rather than to the base. 
     FIG. 7 is an isometric view which illustrates an embodiment that has many features in common with the embodiment shown in FIGS. 2-5, but where a stinger assembly is again mounted to the jack, and where the base is a curved structure to position the feed track support for better visibility by an operator. 
    
    
     BEST MODE OF CARRYING THE INVENTION INTO PRACTICE 
     FIGS. 2 through 5 illustrate a turret assembly  100  which forms one embodiment of the present invention. The turret assembly  100  has a base  102  which is connected to a boom  104  of a rock bolter (not shown). The boom  104  serves to position the turret assembly  100  in a desired location to install a rock bolt  106  (shown in FIGS. 4 and 5) into a rock surface  108 . 
     In this embodiment, the base  102  has a pair of base bearings  110  which are spaced apart and are fixably positioned on the base  102  opposite the point of attachment to the boom  104 . A cylindrical member  112  is slidably and rotatably mounted to the base bearings  110  such that it can both translate with respect to the base  102  along a longitudinal cylinder axis  114  and pivot with respect to the base  102  about the cylinder axis  114 . The cylindrical member  112  terminates in a cylinder first end region  116  and a cylinder second end region  118 . A pair of brackets  120  are fixed onto the cylindrical member  112 , one positioned at each of the cylinder first end region  116  and the cylinder second end region  118 , such that the base bearings  110  reside between the pair of brackets  120 . 
     A feed track support  122  is affixed onto the pair of brackets  120  and extends parallel to the cylinder axis  114 . The feed track support  122  supports a drill  124  and a bolt driver  126 . The drill  124  can be advanced along the feed track support  122  to drill a bolt hole  128  into the rock surface  108 , as shown in FIG.  2 . When the drill  124  is advanced, it is preferred for the feed track support  122  to be located in close proximity to the rock surface  108  to maximize the depth of the bolt hole  128  which can be drilled. Similarly, when aligned with the bolt hole  128 , the bolt driver  126  can be advanced to insert the rock bolt  106  into the bolt hole  128 , as shown in FIG.  5 . An advancing mechanism  130  is employed to selectively advance either the drill  124  or the bolt driver  126  along the feed track support  122 . In this embodiment, the advancing mechanism  130  employs a pulley and piston system mounted to the feed track support  122 , such as the advancing system described in U.S. Pat. No. 4,497,378, incorporated herein by reference. 
     The slidable engagement between the cylindrical member  112  and the base bearings  110  allows the feed track support  122 , which is affixed to the cylindrical member  112  by the pair of brackets  120 , to translate toward or away from the rock surface  108 , while the rotatable engagement between the cylindrical member  112  and the base bearings  110  allows the feed track support  122  to be pivoted to move the bolt driver  126  into alignment with the bolt hole  128  after it is has been bored by the drill  124 . As the feed track support  122  is pivoted, it sweeps out a region in space. When the rock surface  108  is uneven with a high degree of relief, there is frequently insufficient space in close proximity to the rock surface  108  to pivot the feed track support  122 . For this reason, it is often necessary to move the feed track support  122  to increase its separation from the rock surface  108  to provide room for the feed track support  122  to pivot. 
     In this embodiment, a dual-action jack  132  is provided to control the translation of the feed track support  122 . The dual-action jack  132  of this embodiment has a jack body  134  with a single jack bearing  136  affixed thereto. The jack bearing  136  rotatably and slidably engages the cylindrical member  112 . 
     The dual-action jack  132  has a first piston  138  and a second piston  140 , which move in coordination and extend from opposite sides of the jack body  134 . The first piston  138  and the second piston  140  are each attached to one of the pair of brackets  120 , and the use of the dual-action jack  132  connected to both of the pair of brackets  120  provides increased stability for the feed track support  122 . The dual-action jack  132  can be selectively activated to extend the first piston  138  while retracting the second piston  140 , or to extend the second piston  140  while retracting the first piston  138 . 
     In this embodiment, means for limiting translation of the jack bearing  136  with respect to the base bearings  110  is provided by having the jack bearing  136  engage the base bearings  110  such that the base bearings  110  bracket the jack bearing  136  to prevent translation. Thus, while the jack body  134  is slidably engaged with respect to the cylindrical member  112  via the jack bearing  136 , the jack body  134  is effectively limited from translating with respect to the base  102 . When the cylindrical member  112  slides, it translates with respect to both the base  102  and the dual-action jack  132 . While the dual-action jack  132  is not effectively translatable with respect to the base  102 , the rotatable engagement between the base bearings  110  and the cylindrical member  112  allows the dual-action jack  132  to pivot with respect to the base  102  about the cylinder axis  114 . It should be noted that the dual-action jack  132  would be able to rotate with respect to the cylindrical member  112 , but is prevented from such rotation by the connection of first piston  138  and the second piston  140  to the pair of brackets  120 . Thus, the dual-action jack  132 , the feed track support  122 , and the cylindrical member  112  pivot together about the cylinder axis  114 . 
     When the bolt hole  128  is to be drilled, the dual-action jack  132  is activated to extend the first piston  138  and retract the second piston  140 , placing the feed track support  122  in close proximity to the rock surface  108 , as shown in FIG.  2 . The drill  124  is then advanced to drill the bolt hole  128 . After the bolt hole  128  is completed, the drill  124  is moved along the feed track support  122  to withdraw the drill  124  from the bolt hole  128 . To provide space to pivot the bolt driver  126  into alignment with the bolt hole  128 , the dual-action jack  132  is activated to extend the second piston  140  and retract the first piston  138 , thus moving the feed track support  122  away from the rock surface  108  to the position shown in FIG.  3 . In this position, the feed track support  122  is sufficiently spaced apart from the rock surface  108  to allow the dual-action jack  132  and the feed track support  122  to be pivoted to bring the bolt driver  126  into alignment with the bolt hole  128 , as shown in FIG.  4 . 
     During the drilling and bolting process, the turret assembly  100  is stabilized by a stinger assembly  142  which forcibly engages the rock surface  108 . The stinger assembly  142  of this embodiment has a stinger fixed portion  144 , which includes a stinger support structure  146  that is affixed to the base  102 . Preferably, the stinger assembly  142  also has a stinger extendable portion  148 , which can be extended from the stinger fixed portion  144  towards the rock surface  108 . In this embodiment, a portion of the stinger assembly  142  is formed by a hydraulic cylinder having a body and an extendable piston, with the piston of the cylinder serving as part of the stinger fixed portion  144  and the body of the cylinder serving as part of the stinger extendable portion  148 . When the piston is extended, the stinger extendable portion  148  is forced toward the rock surface  108 . Thus, the stinger assembly  142  can be brought into contact with the rock surface  108  without requiring movement of the boom  104 . 
     Preferably, the stinger assembly  142  also includes a rock-engaging pad  150  formed of a resilient material such as urethane. The rock-engaging pad  150  is mounted to the stinger extendable portion  148 , when such is employed, and forcibly engages the rock surface  108  when the stinger extendable portion  148  is extended relative to the stinger fixed portion  144 . The forcible engagement of the rock-engaging pad  150  with the rock surface  108  stabilizes the base  102  with respect to the rock surface  108  during the drilling and bolt setting operations, as well as providing a fixed reference point for the turret assembly  100  so that the bolt driver  126  can be brought into alignment with the bolt hole  128 . It is preferred for the stinger assembly  142  to be positioned on the cylinder axis  114  to provide a fixed pivot axis for the feed track support  122 . To provide further stability, the stinger fixed portion  144  can be configured to slidably engage the cylindrical member  112 . In this embodiment, since the stinger support structure  146  is affixed to the base  102 , the stinger fixed portion  144  must also be rotatable with respect to the cylindrical member  112  to allow the cylindrical member  112  and the attached feed track support  122  to pivot with respect to the base  102 . 
     A pivot actuator  152  is operably connected between the base  102  and the dual-action jack  132  to provide motivating force to pivot the dual-action jack  132  about the cylinder axis  114 . Since the feed track support  122  pivots with the dual-action jack  132  as noted above, the pivot actuator  152  serves to pivot the feed track support  122 . In this embodiment, the pivot actuator  152  is provided by a linear actuator, such as a hydraulic cylinder, pivotably connected to both the base  102  and the jack body  134  of the dual-action jack  132 , and offset from the cylinder axis  114 . The throw of the pivot actuator  152  is adjusted such that, after the bolt hole  128  has been bored by the drill  124  while the pivot actuator  152  is extended, as shown in FIGS. 2 and 3, the pivot actuator  152  can be retracted to rotate the feed track support  122  to a position where the bolt driver  126  is aligned with the bolt hole  128 , as shown in FIGS. 4 and 5. As noted above, it may be necessary for the dual-action jack  132  to be activated to move the feed track support  122  away from the rock surface  108  (as shown in FIGS. 3 and 4) before pivoting the feed track support  122 . After the pivot actuator  152  rotates the feed track support  122  to place the bolt driver  126  into alignment with the bolt hole  128  (as shown in FIG.  4 ), the dual-action jack  132  is activated to move the feed track support  122  towards the rock surface  108  (as shown in FIG. 5) to allow the bolt driver  126  to insert the rock bolt  106  fully into the bolt hole  128 . 
     After the rock bolt  106  has been installed into the bolt hole  128 , the bolt driver  126  is retracted along the feed track support  122  away from the rock surface  108 , and the boom  104  can be moved to remove the turret assembly  100  from the vicinity of the rock surface  108 . The pivot actuator  152  can then be extended to return the feed track support  122  to its initial position in preparation for drilling a bolt hole at a new location. Since the entire turret assembly  100  is moved away from the rock surface  108 , there is no need in this case to activate the dual-action jack  132  before pivoting the feed track support  122 . Typically, the stinger extendable portion  148  is retracted before the boom  104  is employed to position the turret assembly  100  in close proximity to a new location for placement of a rock bolt. The stinger extendable portion  148  is then extended to place the rock-engaging pad  150  into forcible engagement with the rock surface at the new location, and the sequence illustrated in FIGS. 2 through 5 is repeated to drill a new bolt hole and install a rock bolt therein. 
     FIG. 6 illustrates a turret assembly  200  which forms another embodiment of the present invention, which shares many features in common with the turret assembly  100  shown in FIGS. 2-5. The turret assembly  200  again has a base  202  which is attached at one end to a boom  204  of a rock bolter (not shown). In this embodiment, the base  202  has a single base bearing  206  which is fixably positioned on the base  202  opposite the end which attaches to the boom  204 . A cylindrical member  208  is slidably and rotatably mounted to the base bearing  206 , and has a longitudinal cylinder axis  210 . A feed track support  212  is affixed to the cylindrical member  208  by a pair of brackets  214 . 
     Again, a dual-action jack  216  is employed to provide translational motion for the feed track support  212 . The dual-action jack  216  in this embodiment has a jack body  218  having a pair of jack bearings  220  affixed thereto which slidably engage the cylindrical member  208 . The jack bearings  220  are positioned to bracket the base bearing  206 , and preferably engage the base bearing  206  such that, while the jack body  218  is slidably engaged with respect to the cylindrical member  208 , it cannot effectively translate with respect to the base  202 . The rotatable engagement between the base bearing  206  and the cylindrical member  208  allows the dual-action jack  216  to pivot with respect to the base  202  about the cylinder axis  210 . It should be noted that the use of the pair of jack bearings  220  which engage the base bearing  206  does decrease the stability of the turret assembly  200 , since the overall contact region between the base  202  and the cylindrical member  208  is shortened. 
     The turret assembly  200  is again stabilized during use by a stinger assembly  222  which forcibly engages a rock surface (not shown). In this embodiment, the stinger assembly  222  is mounted to the jack body  218  rather than to the base  202 . The stinger assembly  222  has a stinger fixed portion  224 , which is affixed to the jack body  218  via a stinger support structure  226 , and a stinger extendable portion  228 , which can be extended from the stinger fixed portion  224  towards the rock surface. It is again preferred for the stinger assembly  222  to include a rock-engaging pad  230 , which in this embodiment is rotatably mounted to the stinger extendable portion  228 . The rotational mounting between the rock-engaging pad  230  and the stinger extendable portion  228  allows the stinger extendable portion  228 , which is connected to the jack body  218 , to rotate freely when the rock-engaging pad  230  is forcibly engaged with the rock surface. 
     In this embodiment, placing the stinger assembly  222  on the cylinder axis  210  such that the rotational motion between the rock-engaging pad  230  and the stinger extendable portion  228  is about the cylinder axis  210  prevents binding as the feed track support  212  and the dual-action jack  216  are pivoted. It is again preferred for the stinger fixed portion  224  to slidably engage the cylindrical member  208 . Since the stinger support structure  226  in this embodiment is affixed to the jack body  218  and pivots with the cylindrical member  208 , the stinger fixed portion  224  does not need to be rotatable with respect to the cylindrical member  208 . 
     A pivot actuator  232  is provided, which is pivotably connected between the base  202  and the jack body  218 , and which operates in a manner similar to that of the pivot actuator  152  discussed above. 
     FIG. 7 illustrates a turret assembly  300  which forms another embodiment of the present invention, which provides improved visibility for an operator. The turret assembly  300  again has a base  302  which mounts to a boom  304  of a rock bolter (not shown) for positioning the turret assembly  300 . The base  302  has a pair of base bearings  306  (only one of which is shown), similar to the base bearings  110  of the embodiment shown in FIGS. 2-5. A cylindrical member  308  is slidably and rotatably mounted to the base bearings  306 , and a feed track support  310  is affixed to the cylindrical member  308  by a pair of brackets  312 . In this embodiment, the base  302  is curved such that the feed track support  310  faces the boom  304 , and thus an operator situated in the direction of the boom  304  can readily view the feed track support  310 , as well as the actions of a drill  314  and a bolt driver (not shown) which are movably mounted thereto. 
     A dual-action jack  316  is provided, having a jack body  318  with a single jack bearing  320  affixed thereto. The jack bearing  320  engages the cylindrical member  308  and the base bearings  306  in a manner similar to the jack bearing  136 , the cylindrical member  112 , and the base bearings  110  discussed earlier. 
     A stinger assembly  322  is again provided to stabilize the turret assembly  300  with respect to a rock surface (not shown) during the drilling and bolting operations. In this embodiment, the stinger assembly  322  is mounted to the jack body  318  via a stinger support structure  324 , and is essentially similar to the stinger assembly  222  discussed in detail above. 
     A pivot actuator  326  is provided, which is pivotably connected to the base  302  and to the jack body  318 . The pivot actuator  326  can be extended to position the drill  314  for drilling a bolt hole (not shown) into a desired location in the rock surface, and can be retracted to the position illustrated to position the bolt driver into alignment with the bolt hole. 
     While the novel features of the present invention have been described in terms of particular embodiments and preferred applications, it should be appreciated by one skilled in the art that substitution of materials and modification of details obviously can be made without departing from the spirit of the invention.