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(11) | EP 0 126 829 A1 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Roof drill shock absorbing coupling |
| (57) A shock absorbing rotary drive coupling assembly for drivingly connecting a drive
shaft (19) to an axially aligned driven shaft (21). The coupling assembly has an inner
sleeve (17) axially aligned with the drive shaft (19), and in driving engagement with
the driven shaft. Bonded to the outer circumference of the inner sleeve (17) is a
resilient element (15) which is also axially aligned with the drive shaft (19). Bonded
to the outer circumference of the resilient element (15) is an outer sleeve (13).
This outer sleeve (13) is connected to a drive plate (11), which is further connected
to the drive chuck (21) of the roof drilling machine. During drilling operations,
the resilient element absorbs the axial and radial shocks of the drilling. The resilient
element (15) also allows for a limited amount of misalignment between the drill steel
and the drill chuck. |
[0001] This invention relates in general to flexible shock absorbing couplings and in particular to shock absorbing couplings for roof drilling machines.
[0002] For many years, anchor bolting systems have been used to shore up the roofs of coal mines to prevent chunks of coal from falling on miners. Metal plates are bolted to the roof with long bolts which extend through the coal roof into the rock strata above. During installation, an operator first drills a hole in the mine roof. A bolt is then passed through a plate and inserted into the hole to secure the plate to the roof. The bolt may be an expansion-type bolt, or a fast curing resin may be used to secure the bolt in the hole.
[0003] Many machines have been developed to drill holes in mine roofs. U.S. Patent No. 3,842,610 (Willis et al.) shows one such roof drilling machine. These machines typically have a rotating drill chuck onto which is mounted a hollow drill rod or drill steel. A cutter bit is attached to the opposite end of the drill steel. The drill chuck then rotates the drill steel and the cutter bit at high speeds, usually about 500 rpm. As the cutter bit drills into the coal and the rock above the mine, the drill chuck is raised until a hole of the required depth has been drilled. Holes of five feet or more are common.
[0004] Roof drilling machines are capable of exerting an upward force of 10.000 pounds and a torque of 3.600 inch pounds on the cutter bit. As the bit cuts into the coal and the hard rock strata above, the drill chuck receives a great number of both axial and radial shocks. These shocks shorten the useful life of the drilling machine and may result in breakage of the drill steel.
[0005] Breakage of the drill steel may also be caused by vertical misalignment of the drill steel. Additional stresses are placed on the drill steel when the top of the drill steel is misaligned while the drill chuck holds the bottom of the drill steel in a vertical orientation.
[0006] Rotary drills used in drilling blast holes experience axial and radial shocks which are similar to the shocks of drilling in a mine roof. Resilient elements have been used in rotary blast hole drills to absorb the shocks of drilling. U.S. Patent No. 4,109,488 (Work) shows a resilient element sandwiched between two plates, one connected to the drive shaft and the other connected to the driven shaft. This element absorbs the shocks of drilling and also provides some flexibility to allow slight misalignment between the drive shaft and the driven shaft.
[0007] The general object of this invention is to absorb the axial and radial shocks on the drill steel and drill chuck of a roof drilling machine during drilling operations.
[0008] The above object is accomplished by a coupling assembly which has an inner sleeve and an outer sleeve separated by a resilient element. The inner sleeve is axially aligned with the drive shaft and is in driving engagement with the driven shaft. The resilient element is also axially aligned with the drive shaft, and is secured to the periphery of the inner sleeve. The outer sleeve is secured to the periphery of the resilient element and is also axially aligned with the drive shaft. Connection means is provided for drivingly connecting the outer sleeve to the drive shaft. In the preferred embodiment, this connection means is a drive plate which is connected between the outer sleeve and the drive shaft.
[0009] In operation, the drive shaft and the drive plate rotate the outer sleeve, which in turn rotates the resilient element and the inner sleeve. The inner sleeve, which is in driving engagement with the driven shaft, rotates the driven shaft or the drill steel. During drilling, the axial and radial shocks are absorbed by the resilient element, rather than being passed on to the drive shaft, which is connected to the drill chuck. The resilient element also allows for some misalignment between the inner and outer sleeves, and thus allows some measure of misalignment between the drill steel and the drill chuck.
[0010] The above, as well as additional objects, features, and advantages of the invention, will become apparent in the following detailed description.
Figure 1 is a side view, partially in section, of a coupling assembly of the invention.
Figure 2 is a top view of the coupling assembly of the invention.
Figure 3 is a sectional view along lines III-III in figure 1.
[0011] Figures 1 and 2 depict the preferred embodiment of the shock absorbing rotary drive coupling assembly. The assembly has four basic parts: a drive plate 11, an outer sleeve 13, a resilient element 15, and an inner sleeve 17. The drive plate 11 is connected to a hollow, hexagonal drive shaft 19, which extends downward from the center of the drive plate 11 into a drill chuck 21. The drive plate 11 has a hold down shoulder 23, so that the coupling assembly can be secured in the drill chuck 21 with a retainer ring 25. Four evenly spaced bolts 27 attach the retainer ring 25 to a flinger 29, which is a plate for flinging debris away from the drill chuck 21.
[0012] Four projections 31 extend upward from the drive plate 11 for connection to the outer sleeve 13. The height of these projections 31 is approximately equal to the width of the drive plate 11, and the projections 31 are evenly spaced around the edge of the drive plate 11, as shown in figure 3. The inner and outer edges of the projections 31 are arcuate and correspond to the inner and outer circumferences of the outer sleeve 13 respectively. A circular hole 33 is located in the center of each projection 31. The sides of each projection 31 are parallel to each other and parallel to a line between the hole 33 and the center 35 of the drive shaft 19.
[0013] The outer sleeve 13 is a cylinder whose outer circumference is equal to the outer circumference of the projections 31, and whose thickness is equal to the width of the projections 31. The outer sleeve 13 is connected to the drive plate 11 with four bolts 37 which extend through the circular holes 33 in the projections 31. The projections 31 fit within indentations 39 in the lower end of the outer sleeve 13. The drive plate 11 is thus the connection means for drivingly connecting the outer sleeve 13 to the drive shaft 19.
[0014] The resilient element 15 is a cylinder of resilient, elastomeric material, such as natural rubber. The thickness of the resilient element 15 is approximately one to one and one-half times the thickness of the outer sleeve 13. The outer circumference of the resilient element 15 is bonded to the inner circumference of the outer sleeve 13 in a position so that the upper end of the resilient element 15 is flush with the upper end of the outer sleeve 13. The length of the resilient element 15, however, is less than the length of the outer sleeve 13, so the lower end of the resilient element 15 does not reach the drive plate 11, leaving a space 41 between the resilient element 15 and the drive plate 11.
[0015] The inner sleeve 17 is a cylinder whose outer circumference is bonded to the inner circumference of the resilient element 15. The lower end of the inner sleeve 17 is spaced away from the drive plate 11, to further define the space 41 between the resilient element 15 and the drive plate 11. The top edge of the inner sleeve 17 extends slightly above the top edge of the outer sleeve 13. A hexagonal bore 43 extends from the top of the inner sleeve 17 to near the bottom of the inner sleeve 17. A circular passage 45 extends from the bottom of the hexagonal bore to the space within the assembly. A square socket 47 is formed in the upper end of the hexagonal bore 43. A passageway is thus formed, so that during drilling dust may be drawn through the drill steel, through the bore 43 of the inner sleeve 17 into the space 41, and out through the hollow drill shaft 19.
[0016] In operation, the shock absorbing coupling assembly is connected between the driven shaft or drill steel and the drill chuck 21 of the roof drilling machine. The shaft 19 of the drive plate 11 is mounted in the drill chuck 21. The drill steel is then inserted into the inner sleeve 17. As the drill chuck 21 rotates the drive plate 11, the drive plate rotates the remainder of the coupling assembly, which in turn rotates the drill steel. During drilling, any radial or axial shocks are absorbed by the resilient element 15, rather than by the drill chuck 21 of the drilling machine. The resilient element 15 also allows for up to 15 degrees misalignment between the inner sleeve 17 and the outer sleeve 13. This allows the drill steel to be misaligned from the drill chuck, up to 15%, without breaking the drill steel.
[0017] The invention has significant advantages. The resilient element 15 of the invention is under a shear load, rather than compression. Thus, the coupling of the invention takes up less space than prior art couplings, and results in an improved distribution of the load. An additional advantage of the invention is that the coupling assembly may also be used to drive the roof bolts. This avoids the use of the heavy and dangerous bolt wrenches which are used in the prior art.
1. A shock absorbing rotary drive coupling assembly for drivingly connecting a drive
shaft (19) to an axially aligned driven shaft, characterized by
an inner sleeve (17), axially aligned with the drive shaft, and in driving engagement with the driven shaft;
a resilient element (15), axially aligned with the drive shaft, and secured to the periphery of the inner sleeve;
an outer sleeve (13), axially aligned with the drive shaft, and secured to the periphery of the resilient element; and
connection means (11) for drivingly connecting the outer sleeve (13) to the drive shaft (19).
2. The shock absorbing rotary drive coupling assembly of claim 1, characterized in
that said connection means (11) comprising a drive plate connected to the outer sleeve
(13) and to the drive shaft (19).
3. The shock absorbing rotary drive coupling assembly of claim 2, characterized in
that the inner sleeve (17) and the drive shaft (11) each have an axial bore therethrough.
4. The shock absorbing rotary drive coupling assembly of claim 2 or 3 characterized
in that the drive plate (11) is releasably connected to the outer sleeve (13), and
that the outer sleeve (13), the resilient element (15), and the inner sleeve (17)
may be removed and replaced as a unit.
5. The shock absorbing rotary drive coupling assembly of anyone of the claims 2 to
4, characterized in that
the inner sleeve (17) is cylindrical,
the resilient element (15) is cylindrical, and concentric with the inner sleeve,
and the outer sleeve (13) is cylindrical and concentric with the resilient element (15) and the inner sleeve (17), and bonded to the outer surface of the resilient element (15).