阅读说明：本技术 钻孔与锚杆装置 (Drilling and bolting arrangement ) 是由 P·R·维拉曼 于 2019-06-05 设计创作，主要内容包括：一种钻孔装置,包括：基架；馈送框架,所述馈送框架被支撑用于相对于所述基架移动；以及馈送装置,所述馈送装置用于将钻孔元件插入岩石表面中。所述基架包括一对液压缸。所述馈送框架沿馈送轴线延伸并包括平行于所述馈送轴线对齐的多个引导杆。所述馈送装置被支撑用于相对于所述馈送框架沿平行于所述馈送轴线的方向移动。所述馈送装置包括第一引导构件和第二引导构件。所述第一引导构件接合至少一个所述引导杆的一个表面,所述第二引导构件接合至少一个所述引导杆的另一表面。(A drilling apparatus comprising: a base frame; a feed frame supported for movement relative to the base frame; and a feeding device for inserting the drilling element into the rock surface. The base frame includes a pair of hydraulic cylinders. The feed frame extends along a feed axis and includes a plurality of guide rods aligned parallel to the feed axis. The feed device is supported for movement relative to the feed frame in a direction parallel to the feed axis. The feeding device includes a first guide member and a second guide member. The first guide member engages one surface of at least one of the guide bars and the second guide member engages another surface of at least one of the guide bars.)

1. A drilling apparatus, characterized in that the drilling apparatus comprises:

A base frame including a pair of hydraulic cylinders;

A feed frame supported for movement relative to the base frame, the feed frame extending along a feed axis and including a plurality of guide rods aligned parallel to the feed axis; and

A feed device for inserting drilling elements into a rock surface, the feed device being supported for movement relative to the feed frame in a direction parallel to the feed axis, the feed device comprising a first guide member engaging one surface of at least one of the guide rods and a second guide member engaging another surface of at least one of the guide rods.

2. Drilling device according to claim 1, wherein the feeding device comprises a yoke movable relative to the feeding frame and a carriage movable relative to the yoke and supporting a rotary unit, wherein the guiding rod engages and guides the yoke and the carriage.

3. The drilling apparatus of claim 2, wherein the feed frame includes an upper feed block and a lower feed block, the plurality of guide rods extending between the upper feed block and the lower feed block.

4. The drilling apparatus of claim 3, wherein the plurality of guide rods includes a first pair of guide rods disposed on one side of the feed frame and a second pair of guide rods disposed on the other side of the feed frame.

5. The drilling apparatus of claim 3, wherein the yoke comprises an upper plate and a yoke actuator coupled between the upper plate and the lower feed block.

6. The drilling apparatus of claim 1, wherein each of the guide rods has a polygonal cross-sectional profile.

7. The drilling apparatus of claim 1, wherein each of the guide rods has a hexagonal cross-sectional profile.

8. The drilling device of claim 1, wherein the first guide member is an inner guide member having a convex shape and including a tip disposed in a root formed by at least one of the guide rods, and the second guide member is an outer guide member having a concave shape and including a root that receives an edge of at least one of the guide rods.

9. Drilling device according to claim 1, wherein the first guide member and the second guide member are arranged on opposite sides of the feed axis with respect to each other, the first guide member having a convex shape and comprising a first apex end arranged in a first root formed by at least one of the guide rods, the second guide member having a convex shape and comprising a second apex end arranged in a second root formed by at least one of the guide rods.

10. Drilling device according to claim 1, wherein the first guide member and the second guide member are arranged on opposite sides of the feed axis with respect to each other, the first guide member having a concave shape and comprising a first root receiving a first edge of at least one of the guide rods, the second guide member having a concave shape and comprising a second root receiving a second edge of at least one of the guide rods.

11. The drilling apparatus of claim 1, wherein:

The first guide member comprises a pair of inner guide members arranged on opposite sides of the feed axis with respect to each other, each of the inner guide members having a convex shape and comprising a tip arranged in a root formed by at least one of the guide bars;

The second guide member comprises a pair of outer guide members arranged on opposite sides of the feed axis with respect to each other, each of the outer guide members having a concave shape and comprising a root portion that receives an edge of at least one associated guide rod;

The tip of the inner guide member is disposed in a first plane and the root of the outer guide member is disposed in a second plane, the second plane being offset from the first plane.

12. A drilling apparatus, characterized in that the drilling apparatus comprises:

A base frame including a pair of hydraulic cylinders;

A feed frame supported for movement relative to the base frame; and

A feed device supported on the feed frame and including a yoke, a main shaft supported on the yoke, and a flexible drive member engaged with the main shaft, the main shaft being releasably coupled to the yoke to allow at least one shim to be disposed between the main shaft and the yoke to adjust a tension of the flexible drive member.

13. The drilling device of claim 12, wherein the feed device further comprises a carriage, wherein a first end of the flexible drive member is coupled to a block connected to the feed frame and an opposite end of the flexible drive member is coupled to the carriage.

14. The drilling apparatus of claim 13, wherein the yoke includes a body supporting a drive member, the spindle including a non-rotating portion coupled to the body of the yoke.

15. A drilling apparatus, characterized in that the drilling apparatus comprises:

A base frame including a pair of hydraulic cylinders;

a feed frame supported for movement relative to the base frame; and

A feed actuator including a first end coupled to the base frame and a second end coupled to the feed frame, the feed actuator being extendable and retractable to move the feed frame relative to the base frame, the feed actuator having the same height and width as the hydraulic cylinder of the base frame, the feed actuator being positioned in an opposite orientation relative to the hydraulic cylinder of the base frame.

16. the drilling apparatus of claim 15, wherein at least one of the feed actuator and the hydraulic cylinder includes a first passage for providing pressurized fluid to one side of a piston, a second passage for providing pressurized fluid to an opposite side of the piston, and a manifold receiving pressurized fluid from a fluid source, the manifold providing fluid to each of the first and second passages.

17. the drilling apparatus of claim 15, wherein at least one of the feed actuator and the hydraulic cylinder includes a first passage for providing pressurized fluid to one side of a piston, a second passage for providing pressurized fluid to an opposite side of the piston, and a manifold providing fluid communication between a first portion of the first passage and a second portion of the first passage.

18. the drilling apparatus of claim 15, wherein the base frame includes a lower plate and a connecting plate, the hydraulic cylinder extending between the lower plate and the connecting plate.

19. The drilling apparatus of claim 18, wherein each of the hydraulic cylinders comprises a rod and a barrel, the rod comprising a proximal end and a distal end, the proximal end coupled to a piston, the piston slidably positioned within the barrel, the distal end secured to the connecting plate, the barrel secured to the lower block.

Technical Field

The present application relates to drilling apparatus, and in particular to drilling and bolting apparatus for forming an aperture or inserting a bolt (bolt) into an aperture in a rock surface.

Background

Conventional roof bolters may include an extendable support frame and a drive unit movable along the frame. The drive unit drives a drill bit or rock bolt into the rock surface. Actuation of the jumbolter may be achieved using fluid power (e.g., hydraulic power).

Disclosure of Invention

In a separate aspect, a drilling apparatus comprises: a base frame; a feed frame supported for movement relative to the base frame; and a feeding device for inserting the drilling element into the rock surface. The base frame includes a pair of hydraulic cylinders. The feed frame extends along a feed axis and includes a plurality of guide rods aligned parallel to the feed axis. The feed device is supported for movement relative to the feed frame in a direction parallel to the feed axis. The feeding device includes a first guide member and a second guide member. The first guide member engages one surface of at least one of the guide bars and the second guide member engages another surface of at least one of the guide bars.

In some aspects, the feeding device includes a yoke movable relative to the feeding frame and a carriage movable relative to the yoke and supporting a rotary unit, wherein the guide bar engages and guides the yoke and the carriage.

In some aspects, the feed frame includes an upper feed block and a lower feed block, the plurality of guide rods extending between the upper feed block and the lower feed block.

in some aspects, the plurality of guide bars includes a first pair of guide bars disposed on one side of the feed frame and a second pair of guide bars disposed on the other side of the feed frame.

In some aspects, the yoke includes an upper plate and a yoke actuator coupled between the upper plate and the lower feed block.

In some aspects, each of the guide rods has a polygonal cross-sectional profile.

In some aspects, each of the guide rods has a hexagonal cross-sectional profile.

In some aspects, the first guide member is an inner guide member having a convex shape and including a tip disposed in a root formed by at least one of the guide rods, and the second guide member is an outer guide member having a concave shape and including a root that receives an edge of at least one of the guide rods.

In some aspects, the first guide member and the second guide member are arranged on opposite sides of the feed axis with respect to each other, the first guide member having a convex shape and comprising a first apex end arranged in a first root formed by at least one of the guide rods, the second guide member having a convex shape and comprising a second apex end arranged in a second root formed by at least one of the guide rods.

In some aspects, the first guide member and the second guide member are arranged on opposite sides of the feed axis with respect to each other, the first guide member having a concave shape and including a first root portion that receives a first edge of at least one of the guide bars, the second guide member having a concave shape and including a second root portion that receives a second edge of at least one of the guide bars.

In some aspects, the first guide member comprises a pair of inner guide members disposed on opposite sides of the feed axis relative to each other, each of the inner guide members having a convex shape and including a tip disposed in a root formed by at least one of the guide rods. The second guide member comprises a pair of outer guide members arranged on opposite sides of the feed axis with respect to each other, each outer guide member having a concave shape and comprising a root portion which receives an edge of at least one associated guide rod. The tip of the inner guide member is disposed in a first plane and the root of the outer guide member is disposed in a second plane, the second plane being offset from the first plane.

In another independent aspect, a drilling apparatus comprises: a base frame including a pair of hydraulic cylinders; a feed frame supported for movement relative to the base frame; and a feed device supported on the feed frame and including a yoke, a main shaft supported on the yoke, and a flexible drive member engaged with the main shaft, the main shaft being releasably coupled to the yoke to allow at least one shim to be disposed between the main shaft and the yoke to adjust a tension of the flexible drive member.

In some aspects, the feeding device further comprises a carriage, wherein a first end of the flexible transmission member is coupled to a block connected with the feeding frame and an opposite end of the flexible transmission member is coupled to the carriage.

In some aspects, the yoke includes a body supporting a drive member, and the spindle includes a non-rotating portion coupled to the body of the yoke.

In yet another independent aspect, a drilling apparatus comprises: a base frame including a pair of hydraulic cylinders; a feed frame supported for movement relative to the base frame; and a feed actuator including a first end coupled to the base frame and a second end coupled to the feed frame, the feed actuator being retractable to move the feed frame relative to the base frame, the feed actuator having the same height and width as the hydraulic cylinder of the base frame, the feed actuator being disposed in an opposite direction relative to the hydraulic cylinder of the base frame.

In some aspects, at least one component of the feed actuator and the hydraulic cylinder includes a first passage for providing pressurized fluid to one side of a piston, a second passage for providing pressurized fluid to an opposite side of the piston, and a manifold receiving pressurized fluid from a fluid source, the manifold providing fluid to each of the first and second passages.

In some aspects, at least one component of the feed actuator and the hydraulic cylinder includes a first passage for providing pressurized fluid to one side of a piston, a second passage for providing pressurized fluid to an opposite side of the piston, and a manifold providing fluid communication between a first portion of the first passage and a second portion of the first passage.

in some aspects, the base frame includes a lower plate and a connecting plate, the hydraulic cylinder extending between the lower plate and the connecting plate.

in some aspects, each of the hydraulic cylinders includes a rod including a proximal end coupled to a piston slidably positioned within the barrel and a barrel fixed to the lower block, the proximal end being slidably positioned within the barrel, the distal end being fixed to the connecting plate.

other aspects will become apparent by consideration of the detailed description and accompanying drawings.

Drawings

Fig. 1 is a plan view of a mobile machine including a drilling apparatus.

Fig. 2 is a side view of the mobile machine of fig. 1.

Fig. 3 is a perspective view of the drilling apparatus.

Fig. 4 is a cross-sectional view of the drilling apparatus of fig. 3 taken along section 4-4.

Fig. 5 is a cross-sectional view of the drilling apparatus of fig. 3 taken along section 5-5.

fig. 6 is a side view of the feed frame.

Fig. 7 is a cross-sectional view of the drilling apparatus of fig. 3 taken along section 7-7.

Fig. 8 is a perspective view of the feeding device.

Fig. 9 is a cross-sectional view of the feeding device of fig. 8 taken along section 9-9.

Fig. 10 is a cross-sectional view of the drilling apparatus of fig. 3 taken along section 10-10.

fig. 11 is an enlarged cross-sectional view of a portion of the drilling apparatus of fig. 3 taken along section 5-5.

FIG. 12 is an enlarged side cross-sectional view of a portion of the drilling apparatus of FIG. 3 taken along section 5-5.

Detailed Description

Before any embodiments are explained in detail, it is to be understood that the application is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The application is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of "including" and "comprising" and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. As used herein, "consisting of and variants thereof is meant to include only the items listed thereafter and equivalents thereof. Unless specified or limited otherwise, the terms "mounted," "connected," "supported," and "coupled" and variations thereof are used broadly and encompass both direct and indirect mountings, connections, supports, and couplings.

Fig. 1 and 2 show a mobile mining machine, such as a bolting jumbo or a bolting machine 4. In the illustrated embodiment, machine 4 includes a traction device 6 (e.g., wheels — fig. 2) and a boom 8. The boom 8 supports a bolting and boring rig 10 for forming openings in a mine surface (e.g. mine roof, mine floor or mine wall or side wall-not shown) and/or installing a drilling element (e.g. drill bit or rock bolt-not shown). In the illustrated embodiment, the drilling apparatus 10 performs drilling and bolting operations. In some embodiments, the cantilever arm 8 is extendable and includes a pivot portion for supporting the drilling apparatus 10. The installed bolts may, among other elements, anchor or support a safety net (not shown) to protect personnel from rocks that may fall or fall off the surface of the mine. In some embodiments, the drilling apparatus 10 may be mounted on another type of mining machine, such as a continuous miner (not shown).

As shown in fig. 3, the drilling apparatus 10 includes a first stage or stand (timeber jack) or base frame 22, and a second stage or feed frame 26 supported on the base frame 22 for movement along a feed axis 30. The feed assembly 34 is supported on the feed frame 26 for movement parallel to the feed axis 30. The feed device 34 supports a drive unit or rotation unit (not shown) for rotating the drill bit or rock bolt to drive the drill bit/rock bolt into the rock surface as the feed device 34 moves along the feed frame 26.

The pedestal 22 includes a lower plate or block 42 and a pair of elongated pedestal members 46, wherein the lower block 42 is proximate a first end of the drilling apparatus 10 and the pair of elongated pedestal members 46 are oriented parallel to each other and extend away from the lower block 42. In other embodiments, the base frame 22 may include fewer or more base members. A connecting plate 50 is secured to the distal end of each base member 46. In some embodiments, the distal end of the base member 46 may be secured to an upper plate or block (not shown), wherein the upper plate or block may include an opening through which the anchor rod passes and/or a fastening/clamping device (for aligning and/or clamping the anchor rod).

As shown in fig. 4, in the illustrated embodiment, the base member 46 is a hydraulic cylinder and is extendable and retractable for moving the distal end of the base member 46 toward and away from the lower block 42. Each base member 46 includes a rod 54, the rod 54 being slidably received within a sleeve or bushing 58, the sleeve 58 being secured to the lower block 42. The proximal end of each rod 54 is coupled to a piston 62, the piston 62 being located within the sleeve 58, while the distal end of each rod 54 is secured to the connecting plate 50. First fluid passage 66 is in fluid communication with a portion of sleeve 58 adjacent the cap side of piston 62, and second fluid passage 68 is in fluid communication with a portion of sleeve 58 adjacent the rod side of piston 62. In the illustrated embodiment, the first and second fluid passages 66, 68 receive pressurized fluid through a manifold 64, the manifold 64 being in fluid communication with a fluid source (e.g., a pump — not shown). First fluid passage 66 includes a first portion 66a extending between manifold 64 and lower block 42, and a second portion 66b providing communication between lower block 42 and sleeve 58. In some embodiments, the manifold 64 provides fluid communication between a first fluid passage 66 and a second fluid passage 68.

Referring again to fig. 3, the feed frame 26 includes an upper feed block 70, a lower feed block 74, and a guide rod 78 extending between the upper feed block 70 and the lower feed block 74. In the illustrated embodiment, the rod 54 of the base member 46 passes through the upper feed block 70. In some embodiments, the upper feed block may include an opening (not shown) through which the anchor rod passes and a fastening/clamping device (not shown) for aligning and/or clamping the anchor rod during insertion into the rock surface.

As shown in fig. 5, the feed frame actuator 82 is coupled between the base frame 22 and the feed frame 26 to move the feed frame 26 along the feed axis 30. The feed frame actuator 82 is a hydraulic cylinder, and extension and retraction of the feed frame actuator 82 causes the feed frame 26 to move along the base member 46 (fig. 3). The feed frame actuator 82 includes a rod 86, the rod 86 being slidably received within a sleeve or bushing 90, the bushing 90 being secured to the upper feed block 70. The proximal end of the rod 86 is coupled to a piston 94, the piston 94 being disposed within the sleeve 90, while the distal end of the rod 86 is secured to the lower block 42 of the pedestal 22. In the illustrated embodiment, the rod 86 of the feed frame actuator 82 passes through the lower feed block 74. The feed frame actuator 82 is oriented anti-parallel with respect to the base member 46 (i.e., the rod 86 of the feed frame actuator 82 extends in an opposite direction from the sleeve 90 with respect to the rod 54 of the base member 46). Extension and retraction of the feed frame actuator 82 causes the feed frame to move in a direction parallel to the feed axis 30. When the base member 46 is fully extended, full extension of the feed frame actuator 82 positions the upper feed block 70 proximate the distal end of the base member 46.

In the illustrated embodiment, the feed frame actuator 82 is identical to the base member 46, but is positioned in the opposite direction. The feed frame actuator 82 includes a first fluid passage 96 and a second fluid passage 98, wherein the first fluid passage 96 is in fluid communication with a portion of the sleeve 90 adjacent the cap side of the piston 94 and the second fluid passage 98 is in fluid communication with a portion of the sleeve 90 adjacent the rod side of the piston 94. In the illustrated embodiment, a first fluid passage 96 of the actuator is in fluid communication with the sleeve 90 adjacent the upper feed block 70, and a second fluid passage 98 extends along the length of the sleeve 90 and is in fluid communication with an opposite end of the sleeve 90. The second fluid passageway 98 passes through a manifold 100 that includes ports 104a, 104b, the ports 104a, 104b being in continuous fluid connection with one another to allow fluid flow through the manifold 100. Both the first fluid passage 96 and the second fluid passage 98 of the feed frame actuator 82 receive pressurized fluid through the upper feed block 70. In other embodiments, the first and second fluid channels 96, 98 of the feed frame actuator 82 may receive pressurized fluid through a manifold 100, and the manifold may additionally provide fluid communication between the first and second fluid channels 96, 98.

Referring now to fig. 6 and 7, each guide rod 78 is oriented parallel to the feed axis 30 and has a polygonal cross-sectional profile. In the illustrated embodiment, the polygonal cross-sectional profile is hexagonal; in other embodiments, the profile may have another shape. In the illustrated embodiment, the guide rods 78 are positioned in pairs on each side of the feed frame 26, extending between the lower feed block 74 and the upper feed block 70. As shown in fig. 7, the surface of each guide bar 78 faces parallel sides of the pair of associated guide bars 78. Thus, each pair of guide rods 78 forms an inner slot 102a, 102b, the inner slots 102a, 102b opening toward the feed shaft 30, and each pair of guide rods 78 forms an outer slot 106a, 106b, the outer slots 106a, 106b opening away from the feed shaft 30.

As shown in fig. 8, the feeding device 34 supports a rotating unit (not shown). The feeding device 34 includes a yoke (yoke)114, a pair of yoke actuators 118, a driving member 122, and a carriage (carriage)126 that supports a rotating unit (not shown). The yoke 114 includes an upper plate 130 and a main body 134 that supports the drive member 122. Yoke actuator 118 is coupled between upper plate 130 and lower feed block 74 (fig. 6). In the illustrated embodiment, each yoke actuator 118 is a hydraulic cylinder, and extension and retraction of the yoke actuators 118 causes the upper plate 130 to move relative to the lower feed block 74.

as shown in fig. 9, each yoke actuator 118 includes a rod 126, with the rod 126 slidably received within a sleeve or bushing 132, with the bushing 132 secured to the lower feed block 74. The proximal end of each rod 126 is coupled to a piston 124, the piston 124 is located within a sleeve 132, and the distal end of each rod 126 is secured to an upper plate 130 of the yoke 114. In the illustrated embodiment, the yoke actuator 118 is oriented parallel to the base member 46 (i.e., the rod 126 extends from the sleeve 132 in the same direction as compared to the rod 54 of the base member 46; the rod 126 extends from the sleeve 132 in an opposite direction as compared to the rod 86 of the feed carriage actuator 82).

Each yoke actuator 118 includes a first fluid passage 136 and a second fluid passage 138, wherein the first fluid passage 136 is in fluid communication with a portion of the cap side of the sleeve 132 adjacent the piston 124, and the second fluid passage 138 is in fluid communication with a portion of the rod side of the sleeve 130 adjacent the piston 124. In the illustrated embodiment, a first fluid passage 136 of yoke actuator 118 is in fluid communication with sleeve 132 adjacent lower feed block 74 (fig. 6), and a second fluid passage 138 extends along the length of sleeve 132 and is in fluid communication with an opposite end of sleeve 132. In the illustrated embodiment, first and second fluid passages 136, 138 of yoke actuator 118 receive pressurized fluid through lower feed block 74 (fig. 6). Also, the connecting tube 128 may communicate pressurized fluid between the upper feed block 70 and the lower feed block 74.

Extension and retraction of the yoke actuator 118 moves the yoke 114, the drive member 122, the carriage 126, and the rotary unit in a direction parallel to the feed axis 30 (fig. 3). The full extension of the yoke actuator 118 positions the upper plate 130 adjacent the upper feed block 70. As shown in fig. 8, in the illustrated embodiment, the drive member 122 includes a pair of flexible transmission members (e.g., chains 140) oriented parallel to each other and supported on the body 134. The chain 140 extends between a pair of spindles 142. In one embodiment, the main shaft 142 is freely rotatable.

As shown in fig. 10, one end 140a of each chain 140 is coupled to a block 144 connected to the frame 26, and an opposite end 140b of each chain 140 is coupled to the carriage 126. As the yoke actuator 118 moves the yoke 114 along the feed axis 30, the chain 140, which is secured to the frame 26 by the block 144, moves the carriage 126 along the feed axis 30. When the yoke actuator 118 is extended, the carriage 126 moves toward the upper feed block 70 (fig. 3); when the yoke actuator 118 retracts, the carriage 126 moves away from the upper feed block 70. In some embodiments, the speed of movement of the carriage 126 is twice the speed of movement of the actuator 118 (i.e., the ratio of the amount of movement of the carriage 126 to the length of extension or retraction of the yoke actuator 118 is 2: 1).

Referring again to fig. 7, the body 134 includes a pair of inner guide members or guide shoes (guide shoes)148a, 148b that engage the inner grooves 102a, 102b of the guide rod 78; the carriage 126 includes a pair of outer guide members or outer guide blocks 152a, 152b that engage the outer slots 106a, 106b of the guide bar 78. In the illustrated embodiment, each inner guide block 148a, 148b has a convex wedge or conical shape with an apex 158a, 158b, respectively, the apex 158a, 158b being located in the root of the associated inner slot 102a, 102 b. Also, in the illustrated embodiment, each outer guide block 152a, 152b forms a concave wedge or conical shape that engages the outer surface of one of the guide rods 78. Each outer guide block 152a, 152b includes a root 160a, 160b, respectively, that receives an edge of the guide rod 78. In other embodiments, the outer guide blocks 152a, 152b may be formed to engage the outer surfaces of both guide rods 78 in each pair. The apexes 158a, 158b of the inner guide blocks 148a, 148b are aligned in a first plane 170 and the roots 160a, 160b of the outer guide blocks 152a, 152b are aligned in a second plane 174.

Referring now to fig. 11 and 12, one or more shims 182 may be disposed about one of the spindles 142. Specifically, in the illustrated embodiment, the non-rotating portion or body 186 of the main shaft 142 is coupled to an end of the body 134 of the yoke 114 (e.g., via a fastener 190). As the chain 140 wears and/or stretches, slack may be created in the chain 140. A shim 182 may be disposed between the main shaft 142 and the yoke 114 to increase the length between the main shaft 142 to eliminate slack. In some embodiments, shims 182 may be added alongside one or both of the spindles 142.

Although the various aspects have been described in detail with reference to certain preferred embodiments, variations and modifications exist within the scope and spirit of one or more of the individual aspects described. Various features and advantages are set forth in the following claims.